rev 4213 : 8008382: Remove redundant use of Atomic::add(jlong, jlong *) in create_new_gc_id()
Summary: There is no need to use atomics in create_new_gc_id() since it is not called by multiple threads in parallel. Also, Atomic::add(jlong, jlong *) is broken for ARM.
Reviewed-by:

   1 /*
   2  * Copyright (c) 2001, 2012, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
  21  * questions.
  22  *
  23  */
  24 
  25 #include "precompiled.hpp"
  26 #include "classfile/symbolTable.hpp"
  27 #include "classfile/systemDictionary.hpp"
  28 #include "code/codeCache.hpp"
  29 #include "gc_implementation/concurrentMarkSweep/cmsAdaptiveSizePolicy.hpp"
  30 #include "gc_implementation/concurrentMarkSweep/cmsCollectorPolicy.hpp"
  31 #include "gc_implementation/concurrentMarkSweep/cmsGCAdaptivePolicyCounters.hpp"
  32 #include "gc_implementation/concurrentMarkSweep/cmsOopClosures.inline.hpp"
  33 #include "gc_implementation/concurrentMarkSweep/compactibleFreeListSpace.hpp"
  34 #include "gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.inline.hpp"
  35 #include "gc_implementation/concurrentMarkSweep/concurrentMarkSweepThread.hpp"
  36 #include "gc_implementation/concurrentMarkSweep/vmCMSOperations.hpp"
  37 #include "gc_implementation/parNew/parNewGeneration.hpp"
  38 #include "gc_implementation/shared/collectorCounters.hpp"
  39 #include "gc_implementation/shared/gcTimer.hpp"
  40 #include "gc_implementation/shared/gcTrace.hpp"
  41 #include "gc_implementation/shared/gcTraceTime.hpp"
  42 #include "gc_implementation/shared/isGCActiveMark.hpp"
  43 #include "gc_interface/collectedHeap.inline.hpp"
  44 #include "memory/allocation.hpp"
  45 #include "memory/cardTableRS.hpp"
  46 #include "memory/collectorPolicy.hpp"
  47 #include "memory/gcLocker.inline.hpp"
  48 #include "memory/genCollectedHeap.hpp"
  49 #include "memory/genMarkSweep.hpp"
  50 #include "memory/genOopClosures.inline.hpp"
  51 #include "memory/iterator.hpp"
  52 #include "memory/referencePolicy.hpp"
  53 #include "memory/resourceArea.hpp"
  54 #include "oops/oop.inline.hpp"
  55 #include "prims/jvmtiExport.hpp"
  56 #include "runtime/globals_extension.hpp"
  57 #include "runtime/handles.inline.hpp"
  58 #include "runtime/java.hpp"
  59 #include "runtime/vmThread.hpp"
  60 #include "services/memoryService.hpp"
  61 #include "services/runtimeService.hpp"
  62 
  63 // statics
  64 CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL;
  65 bool          CMSCollector::_full_gc_requested          = false;
  66 
  67 //////////////////////////////////////////////////////////////////
  68 // In support of CMS/VM thread synchronization
  69 //////////////////////////////////////////////////////////////////
  70 // We split use of the CGC_lock into 2 "levels".
  71 // The low-level locking is of the usual CGC_lock monitor. We introduce
  72 // a higher level "token" (hereafter "CMS token") built on top of the
  73 // low level monitor (hereafter "CGC lock").
  74 // The token-passing protocol gives priority to the VM thread. The
  75 // CMS-lock doesn't provide any fairness guarantees, but clients
  76 // should ensure that it is only held for very short, bounded
  77 // durations.
  78 //
  79 // When either of the CMS thread or the VM thread is involved in
  80 // collection operations during which it does not want the other
  81 // thread to interfere, it obtains the CMS token.
  82 //
  83 // If either thread tries to get the token while the other has
  84 // it, that thread waits. However, if the VM thread and CMS thread
  85 // both want the token, then the VM thread gets priority while the
  86 // CMS thread waits. This ensures, for instance, that the "concurrent"
  87 // phases of the CMS thread's work do not block out the VM thread
  88 // for long periods of time as the CMS thread continues to hog
  89 // the token. (See bug 4616232).
  90 //
  91 // The baton-passing functions are, however, controlled by the
  92 // flags _foregroundGCShouldWait and _foregroundGCIsActive,
  93 // and here the low-level CMS lock, not the high level token,
  94 // ensures mutual exclusion.
  95 //
  96 // Two important conditions that we have to satisfy:
  97 // 1. if a thread does a low-level wait on the CMS lock, then it
  98 //    relinquishes the CMS token if it were holding that token
  99 //    when it acquired the low-level CMS lock.
 100 // 2. any low-level notifications on the low-level lock
 101 //    should only be sent when a thread has relinquished the token.
 102 //
 103 // In the absence of either property, we'd have potential deadlock.
 104 //
 105 // We protect each of the CMS (concurrent and sequential) phases
 106 // with the CMS _token_, not the CMS _lock_.
 107 //
 108 // The only code protected by CMS lock is the token acquisition code
 109 // itself, see ConcurrentMarkSweepThread::[de]synchronize(), and the
 110 // baton-passing code.
 111 //
 112 // Unfortunately, i couldn't come up with a good abstraction to factor and
 113 // hide the naked CGC_lock manipulation in the baton-passing code
 114 // further below. That's something we should try to do. Also, the proof
 115 // of correctness of this 2-level locking scheme is far from obvious,
 116 // and potentially quite slippery. We have an uneasy supsicion, for instance,
 117 // that there may be a theoretical possibility of delay/starvation in the
 118 // low-level lock/wait/notify scheme used for the baton-passing because of
 119 // potential intereference with the priority scheme embodied in the
 120 // CMS-token-passing protocol. See related comments at a CGC_lock->wait()
 121 // invocation further below and marked with "XXX 20011219YSR".
 122 // Indeed, as we note elsewhere, this may become yet more slippery
 123 // in the presence of multiple CMS and/or multiple VM threads. XXX
 124 
 125 class CMSTokenSync: public StackObj {
 126  private:
 127   bool _is_cms_thread;
 128  public:
 129   CMSTokenSync(bool is_cms_thread):
 130     _is_cms_thread(is_cms_thread) {
 131     assert(is_cms_thread == Thread::current()->is_ConcurrentGC_thread(),
 132            "Incorrect argument to constructor");
 133     ConcurrentMarkSweepThread::synchronize(_is_cms_thread);
 134   }
 135 
 136   ~CMSTokenSync() {
 137     assert(_is_cms_thread ?
 138              ConcurrentMarkSweepThread::cms_thread_has_cms_token() :
 139              ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
 140           "Incorrect state");
 141     ConcurrentMarkSweepThread::desynchronize(_is_cms_thread);
 142   }
 143 };
 144 
 145 // Convenience class that does a CMSTokenSync, and then acquires
 146 // upto three locks.
 147 class CMSTokenSyncWithLocks: public CMSTokenSync {
 148  private:
 149   // Note: locks are acquired in textual declaration order
 150   // and released in the opposite order
 151   MutexLockerEx _locker1, _locker2, _locker3;
 152  public:
 153   CMSTokenSyncWithLocks(bool is_cms_thread, Mutex* mutex1,
 154                         Mutex* mutex2 = NULL, Mutex* mutex3 = NULL):
 155     CMSTokenSync(is_cms_thread),
 156     _locker1(mutex1, Mutex::_no_safepoint_check_flag),
 157     _locker2(mutex2, Mutex::_no_safepoint_check_flag),
 158     _locker3(mutex3, Mutex::_no_safepoint_check_flag)
 159   { }
 160 };
 161 
 162 
 163 // Wrapper class to temporarily disable icms during a foreground cms collection.
 164 class ICMSDisabler: public StackObj {
 165  public:
 166   // The ctor disables icms and wakes up the thread so it notices the change;
 167   // the dtor re-enables icms.  Note that the CMSCollector methods will check
 168   // CMSIncrementalMode.
 169   ICMSDisabler()  { CMSCollector::disable_icms(); CMSCollector::start_icms(); }
 170   ~ICMSDisabler() { CMSCollector::enable_icms(); }
 171 };
 172 
 173 //////////////////////////////////////////////////////////////////
 174 //  Concurrent Mark-Sweep Generation /////////////////////////////
 175 //////////////////////////////////////////////////////////////////
 176 
 177 NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;)
 178 
 179 // This struct contains per-thread things necessary to support parallel
 180 // young-gen collection.
 181 class CMSParGCThreadState: public CHeapObj<mtGC> {
 182  public:
 183   CFLS_LAB lab;
 184   PromotionInfo promo;
 185 
 186   // Constructor.
 187   CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) {
 188     promo.setSpace(cfls);
 189   }
 190 };
 191 
 192 ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration(
 193      ReservedSpace rs, size_t initial_byte_size, int level,
 194      CardTableRS* ct, bool use_adaptive_freelists,
 195      FreeBlockDictionary<FreeChunk>::DictionaryChoice dictionaryChoice) :
 196   CardGeneration(rs, initial_byte_size, level, ct),
 197   _dilatation_factor(((double)MinChunkSize)/((double)(CollectedHeap::min_fill_size()))),
 198   _debug_collection_type(Concurrent_collection_type)
 199 {
 200   HeapWord* bottom = (HeapWord*) _virtual_space.low();
 201   HeapWord* end    = (HeapWord*) _virtual_space.high();
 202 
 203   _direct_allocated_words = 0;
 204   NOT_PRODUCT(
 205     _numObjectsPromoted = 0;
 206     _numWordsPromoted = 0;
 207     _numObjectsAllocated = 0;
 208     _numWordsAllocated = 0;
 209   )
 210 
 211   _cmsSpace = new CompactibleFreeListSpace(_bts, MemRegion(bottom, end),
 212                                            use_adaptive_freelists,
 213                                            dictionaryChoice);
 214   NOT_PRODUCT(debug_cms_space = _cmsSpace;)
 215   if (_cmsSpace == NULL) {
 216     vm_exit_during_initialization(
 217       "CompactibleFreeListSpace allocation failure");
 218   }
 219   _cmsSpace->_gen = this;
 220 
 221   _gc_stats = new CMSGCStats();
 222 
 223   // Verify the assumption that FreeChunk::_prev and OopDesc::_klass
 224   // offsets match. The ability to tell free chunks from objects
 225   // depends on this property.
 226   debug_only(
 227     FreeChunk* junk = NULL;
 228     assert(UseCompressedOops ||
 229            junk->prev_addr() == (void*)(oop(junk)->klass_addr()),
 230            "Offset of FreeChunk::_prev within FreeChunk must match"
 231            "  that of OopDesc::_klass within OopDesc");
 232   )
 233   if (CollectedHeap::use_parallel_gc_threads()) {
 234     typedef CMSParGCThreadState* CMSParGCThreadStatePtr;
 235     _par_gc_thread_states =
 236       NEW_C_HEAP_ARRAY(CMSParGCThreadStatePtr, ParallelGCThreads, mtGC);
 237     if (_par_gc_thread_states == NULL) {
 238       vm_exit_during_initialization("Could not allocate par gc structs");
 239     }
 240     for (uint i = 0; i < ParallelGCThreads; i++) {
 241       _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace());
 242       if (_par_gc_thread_states[i] == NULL) {
 243         vm_exit_during_initialization("Could not allocate par gc structs");
 244       }
 245     }
 246   } else {
 247     _par_gc_thread_states = NULL;
 248   }
 249   _incremental_collection_failed = false;
 250   // The "dilatation_factor" is the expansion that can occur on
 251   // account of the fact that the minimum object size in the CMS
 252   // generation may be larger than that in, say, a contiguous young
 253   //  generation.
 254   // Ideally, in the calculation below, we'd compute the dilatation
 255   // factor as: MinChunkSize/(promoting_gen's min object size)
 256   // Since we do not have such a general query interface for the
 257   // promoting generation, we'll instead just use the mimimum
 258   // object size (which today is a header's worth of space);
 259   // note that all arithmetic is in units of HeapWords.
 260   assert(MinChunkSize >= CollectedHeap::min_fill_size(), "just checking");
 261   assert(_dilatation_factor >= 1.0, "from previous assert");
 262 }
 263 
 264 
 265 // The field "_initiating_occupancy" represents the occupancy percentage
 266 // at which we trigger a new collection cycle.  Unless explicitly specified
 267 // via CMSInitiating[Perm]OccupancyFraction (argument "io" below), it
 268 // is calculated by:
 269 //
 270 //   Let "f" be MinHeapFreeRatio in
 271 //
 272 //    _intiating_occupancy = 100-f +
 273 //                           f * (CMSTrigger[Perm]Ratio/100)
 274 //   where CMSTrigger[Perm]Ratio is the argument "tr" below.
 275 //
 276 // That is, if we assume the heap is at its desired maximum occupancy at the
 277 // end of a collection, we let CMSTrigger[Perm]Ratio of the (purported) free
 278 // space be allocated before initiating a new collection cycle.
 279 //
 280 void ConcurrentMarkSweepGeneration::init_initiating_occupancy(intx io, intx tr) {
 281   assert(io <= 100 && tr >= 0 && tr <= 100, "Check the arguments");
 282   if (io >= 0) {
 283     _initiating_occupancy = (double)io / 100.0;
 284   } else {
 285     _initiating_occupancy = ((100 - MinHeapFreeRatio) +
 286                              (double)(tr * MinHeapFreeRatio) / 100.0)
 287                             / 100.0;
 288   }
 289 }
 290 
 291 void ConcurrentMarkSweepGeneration::ref_processor_init() {
 292   assert(collector() != NULL, "no collector");
 293   collector()->ref_processor_init();
 294 }
 295 
 296 void CMSCollector::ref_processor_init() {
 297   if (_ref_processor == NULL) {
 298     // Allocate and initialize a reference processor
 299     _ref_processor =
 300       new ReferenceProcessor(_span,                               // span
 301                              (ParallelGCThreads > 1) && ParallelRefProcEnabled, // mt processing
 302                              (int) ParallelGCThreads,             // mt processing degree
 303                              _cmsGen->refs_discovery_is_mt(),     // mt discovery
 304                              (int) MAX2(ConcGCThreads, ParallelGCThreads), // mt discovery degree
 305                              _cmsGen->refs_discovery_is_atomic(), // discovery is not atomic
 306                              &_is_alive_closure,                  // closure for liveness info
 307                              false);                              // next field updates do not need write barrier
 308     // Initialize the _ref_processor field of CMSGen
 309     _cmsGen->set_ref_processor(_ref_processor);
 310 
 311     // Allocate a dummy ref processor for perm gen.
 312     ReferenceProcessor* rp2 = new ReferenceProcessor();
 313     if (rp2 == NULL) {
 314       vm_exit_during_initialization("Could not allocate ReferenceProcessor object");
 315     }
 316     _permGen->set_ref_processor(rp2);
 317   }
 318 }
 319 
 320 CMSAdaptiveSizePolicy* CMSCollector::size_policy() {
 321   GenCollectedHeap* gch = GenCollectedHeap::heap();
 322   assert(gch->kind() == CollectedHeap::GenCollectedHeap,
 323     "Wrong type of heap");
 324   CMSAdaptiveSizePolicy* sp = (CMSAdaptiveSizePolicy*)
 325     gch->gen_policy()->size_policy();
 326   assert(sp->is_gc_cms_adaptive_size_policy(),
 327     "Wrong type of size policy");
 328   return sp;
 329 }
 330 
 331 CMSGCAdaptivePolicyCounters* CMSCollector::gc_adaptive_policy_counters() {
 332   CMSGCAdaptivePolicyCounters* results =
 333     (CMSGCAdaptivePolicyCounters*) collector_policy()->counters();
 334   assert(
 335     results->kind() == GCPolicyCounters::CMSGCAdaptivePolicyCountersKind,
 336     "Wrong gc policy counter kind");
 337   return results;
 338 }
 339 
 340 
 341 void ConcurrentMarkSweepGeneration::initialize_performance_counters() {
 342 
 343   const char* gen_name = "old";
 344 
 345   // Generation Counters - generation 1, 1 subspace
 346   _gen_counters = new GenerationCounters(gen_name, 1, 1, &_virtual_space);
 347 
 348   _space_counters = new GSpaceCounters(gen_name, 0,
 349                                        _virtual_space.reserved_size(),
 350                                        this, _gen_counters);
 351 }
 352 
 353 CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha):
 354   _cms_gen(cms_gen)
 355 {
 356   assert(alpha <= 100, "bad value");
 357   _saved_alpha = alpha;
 358 
 359   // Initialize the alphas to the bootstrap value of 100.
 360   _gc0_alpha = _cms_alpha = 100;
 361 
 362   _cms_begin_time.update();
 363   _cms_end_time.update();
 364 
 365   _gc0_duration = 0.0;
 366   _gc0_period = 0.0;
 367   _gc0_promoted = 0;
 368 
 369   _cms_duration = 0.0;
 370   _cms_period = 0.0;
 371   _cms_allocated = 0;
 372 
 373   _cms_used_at_gc0_begin = 0;
 374   _cms_used_at_gc0_end = 0;
 375   _allow_duty_cycle_reduction = false;
 376   _valid_bits = 0;
 377   _icms_duty_cycle = CMSIncrementalDutyCycle;
 378 }
 379 
 380 double CMSStats::cms_free_adjustment_factor(size_t free) const {
 381   // TBD: CR 6909490
 382   return 1.0;
 383 }
 384 
 385 void CMSStats::adjust_cms_free_adjustment_factor(bool fail, size_t free) {
 386 }
 387 
 388 // If promotion failure handling is on use
 389 // the padded average size of the promotion for each
 390 // young generation collection.
 391 double CMSStats::time_until_cms_gen_full() const {
 392   size_t cms_free = _cms_gen->cmsSpace()->free();
 393   GenCollectedHeap* gch = GenCollectedHeap::heap();
 394   size_t expected_promotion = MIN2(gch->get_gen(0)->capacity(),
 395                                    (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average());
 396   if (cms_free > expected_promotion) {
 397     // Start a cms collection if there isn't enough space to promote
 398     // for the next minor collection.  Use the padded average as
 399     // a safety factor.
 400     cms_free -= expected_promotion;
 401 
 402     // Adjust by the safety factor.
 403     double cms_free_dbl = (double)cms_free;
 404     double cms_adjustment = (100.0 - CMSIncrementalSafetyFactor)/100.0;
 405     // Apply a further correction factor which tries to adjust
 406     // for recent occurance of concurrent mode failures.
 407     cms_adjustment = cms_adjustment * cms_free_adjustment_factor(cms_free);
 408     cms_free_dbl = cms_free_dbl * cms_adjustment;
 409 
 410     if (PrintGCDetails && Verbose) {
 411       gclog_or_tty->print_cr("CMSStats::time_until_cms_gen_full: cms_free "
 412         SIZE_FORMAT " expected_promotion " SIZE_FORMAT,
 413         cms_free, expected_promotion);
 414       gclog_or_tty->print_cr("  cms_free_dbl %f cms_consumption_rate %f",
 415         cms_free_dbl, cms_consumption_rate() + 1.0);
 416     }
 417     // Add 1 in case the consumption rate goes to zero.
 418     return cms_free_dbl / (cms_consumption_rate() + 1.0);
 419   }
 420   return 0.0;
 421 }
 422 
 423 // Compare the duration of the cms collection to the
 424 // time remaining before the cms generation is empty.
 425 // Note that the time from the start of the cms collection
 426 // to the start of the cms sweep (less than the total
 427 // duration of the cms collection) can be used.  This
 428 // has been tried and some applications experienced
 429 // promotion failures early in execution.  This was
 430 // possibly because the averages were not accurate
 431 // enough at the beginning.
 432 double CMSStats::time_until_cms_start() const {
 433   // We add "gc0_period" to the "work" calculation
 434   // below because this query is done (mostly) at the
 435   // end of a scavenge, so we need to conservatively
 436   // account for that much possible delay
 437   // in the query so as to avoid concurrent mode failures
 438   // due to starting the collection just a wee bit too
 439   // late.
 440   double work = cms_duration() + gc0_period();
 441   double deadline = time_until_cms_gen_full();
 442   // If a concurrent mode failure occurred recently, we want to be
 443   // more conservative and halve our expected time_until_cms_gen_full()
 444   if (work > deadline) {
 445     if (Verbose && PrintGCDetails) {
 446       gclog_or_tty->print(
 447         " CMSCollector: collect because of anticipated promotion "
 448         "before full %3.7f + %3.7f > %3.7f ", cms_duration(),
 449         gc0_period(), time_until_cms_gen_full());
 450     }
 451     return 0.0;
 452   }
 453   return work - deadline;
 454 }
 455 
 456 // Return a duty cycle based on old_duty_cycle and new_duty_cycle, limiting the
 457 // amount of change to prevent wild oscillation.
 458 unsigned int CMSStats::icms_damped_duty_cycle(unsigned int old_duty_cycle,
 459                                               unsigned int new_duty_cycle) {
 460   assert(old_duty_cycle <= 100, "bad input value");
 461   assert(new_duty_cycle <= 100, "bad input value");
 462 
 463   // Note:  use subtraction with caution since it may underflow (values are
 464   // unsigned).  Addition is safe since we're in the range 0-100.
 465   unsigned int damped_duty_cycle = new_duty_cycle;
 466   if (new_duty_cycle < old_duty_cycle) {
 467     const unsigned int largest_delta = MAX2(old_duty_cycle / 4, 5U);
 468     if (new_duty_cycle + largest_delta < old_duty_cycle) {
 469       damped_duty_cycle = old_duty_cycle - largest_delta;
 470     }
 471   } else if (new_duty_cycle > old_duty_cycle) {
 472     const unsigned int largest_delta = MAX2(old_duty_cycle / 4, 15U);
 473     if (new_duty_cycle > old_duty_cycle + largest_delta) {
 474       damped_duty_cycle = MIN2(old_duty_cycle + largest_delta, 100U);
 475     }
 476   }
 477   assert(damped_duty_cycle <= 100, "invalid duty cycle computed");
 478 
 479   if (CMSTraceIncrementalPacing) {
 480     gclog_or_tty->print(" [icms_damped_duty_cycle(%d,%d) = %d] ",
 481                            old_duty_cycle, new_duty_cycle, damped_duty_cycle);
 482   }
 483   return damped_duty_cycle;
 484 }
 485 
 486 unsigned int CMSStats::icms_update_duty_cycle_impl() {
 487   assert(CMSIncrementalPacing && valid(),
 488          "should be handled in icms_update_duty_cycle()");
 489 
 490   double cms_time_so_far = cms_timer().seconds();
 491   double scaled_duration = cms_duration_per_mb() * _cms_used_at_gc0_end / M;
 492   double scaled_duration_remaining = fabsd(scaled_duration - cms_time_so_far);
 493 
 494   // Avoid division by 0.
 495   double time_until_full = MAX2(time_until_cms_gen_full(), 0.01);
 496   double duty_cycle_dbl = 100.0 * scaled_duration_remaining / time_until_full;
 497 
 498   unsigned int new_duty_cycle = MIN2((unsigned int)duty_cycle_dbl, 100U);
 499   if (new_duty_cycle > _icms_duty_cycle) {
 500     // Avoid very small duty cycles (1 or 2); 0 is allowed.
 501     if (new_duty_cycle > 2) {
 502       _icms_duty_cycle = icms_damped_duty_cycle(_icms_duty_cycle,
 503                                                 new_duty_cycle);
 504     }
 505   } else if (_allow_duty_cycle_reduction) {
 506     // The duty cycle is reduced only once per cms cycle (see record_cms_end()).
 507     new_duty_cycle = icms_damped_duty_cycle(_icms_duty_cycle, new_duty_cycle);
 508     // Respect the minimum duty cycle.
 509     unsigned int min_duty_cycle = (unsigned int)CMSIncrementalDutyCycleMin;
 510     _icms_duty_cycle = MAX2(new_duty_cycle, min_duty_cycle);
 511   }
 512 
 513   if (PrintGCDetails || CMSTraceIncrementalPacing) {
 514     gclog_or_tty->print(" icms_dc=%d ", _icms_duty_cycle);
 515   }
 516 
 517   _allow_duty_cycle_reduction = false;
 518   return _icms_duty_cycle;
 519 }
 520 
 521 #ifndef PRODUCT
 522 void CMSStats::print_on(outputStream *st) const {
 523   st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha);
 524   st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo=" SIZE_FORMAT,
 525                gc0_duration(), gc0_period(), gc0_promoted());
 526   st->print(",cms_dur=%g,cms_dur_per_mb=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT,
 527             cms_duration(), cms_duration_per_mb(),
 528             cms_period(), cms_allocated());
 529   st->print(",cms_since_beg=%g,cms_since_end=%g",
 530             cms_time_since_begin(), cms_time_since_end());
 531   st->print(",cms_used_beg=" SIZE_FORMAT ",cms_used_end=" SIZE_FORMAT,
 532             _cms_used_at_gc0_begin, _cms_used_at_gc0_end);
 533   if (CMSIncrementalMode) {
 534     st->print(",dc=%d", icms_duty_cycle());
 535   }
 536 
 537   if (valid()) {
 538     st->print(",promo_rate=%g,cms_alloc_rate=%g",
 539               promotion_rate(), cms_allocation_rate());
 540     st->print(",cms_consumption_rate=%g,time_until_full=%g",
 541               cms_consumption_rate(), time_until_cms_gen_full());
 542   }
 543   st->print(" ");
 544 }
 545 #endif // #ifndef PRODUCT
 546 
 547 CMSCollector::CollectorState CMSCollector::_collectorState =
 548                              CMSCollector::Idling;
 549 bool CMSCollector::_foregroundGCIsActive = false;
 550 bool CMSCollector::_foregroundGCShouldWait = false;
 551 
 552 CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
 553                            ConcurrentMarkSweepGeneration* permGen,
 554                            CardTableRS*                   ct,
 555                            ConcurrentMarkSweepPolicy*     cp):
 556   _cmsGen(cmsGen),
 557   _permGen(permGen),
 558   _ct(ct),
 559   _ref_processor(NULL),    // will be set later
 560   _conc_workers(NULL),     // may be set later
 561   _abort_preclean(false),
 562   _start_sampling(false),
 563   _between_prologue_and_epilogue(false),
 564   _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"),
 565   _perm_gen_verify_bit_map(0, -1 /* no mutex */, "No_lock"),
 566   _modUnionTable((CardTableModRefBS::card_shift - LogHeapWordSize),
 567                  -1 /* lock-free */, "No_lock" /* dummy */),
 568   _modUnionClosure(&_modUnionTable),
 569   _modUnionClosurePar(&_modUnionTable),
 570   // Adjust my span to cover old (cms) gen and perm gen
 571   _span(cmsGen->reserved()._union(permGen->reserved())),
 572   // Construct the is_alive_closure with _span & markBitMap
 573   _is_alive_closure(_span, &_markBitMap),
 574   _restart_addr(NULL),
 575   _overflow_list(NULL),
 576   _stats(cmsGen),
 577   _eden_chunk_array(NULL),     // may be set in ctor body
 578   _eden_chunk_capacity(0),     // -- ditto --
 579   _eden_chunk_index(0),        // -- ditto --
 580   _survivor_plab_array(NULL),  // -- ditto --
 581   _survivor_chunk_array(NULL), // -- ditto --
 582   _survivor_chunk_capacity(0), // -- ditto --
 583   _survivor_chunk_index(0),    // -- ditto --
 584   _ser_pmc_preclean_ovflw(0),
 585   _ser_kac_preclean_ovflw(0),
 586   _ser_pmc_remark_ovflw(0),
 587   _par_pmc_remark_ovflw(0),
 588   _ser_kac_ovflw(0),
 589   _par_kac_ovflw(0),
 590 #ifndef PRODUCT
 591   _num_par_pushes(0),
 592 #endif
 593   _collection_count_start(0),
 594   _verifying(false),
 595   _icms_start_limit(NULL),
 596   _icms_stop_limit(NULL),
 597   _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"),
 598   _completed_initialization(false),
 599   _collector_policy(cp),
 600   _should_unload_classes(false),
 601   _concurrent_cycles_since_last_unload(0),
 602   _roots_scanning_options(0),
 603   _inter_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
 604   _intra_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
 605   _gc_tracer_cm(new (ResourceObj::C_HEAP, mtGC) CMSTracer()),
 606   _gc_timer_cm(new (ResourceObj::C_HEAP, mtGC) ConcurrentGCTimer()),
 607   _cms_start_registered(false)
 608 {
 609   if (ExplicitGCInvokesConcurrentAndUnloadsClasses) {
 610     ExplicitGCInvokesConcurrent = true;
 611   }
 612   // Now expand the span and allocate the collection support structures
 613   // (MUT, marking bit map etc.) to cover both generations subject to
 614   // collection.
 615 
 616   // First check that _permGen is adjacent to _cmsGen and above it.
 617   assert(   _cmsGen->reserved().word_size()  > 0
 618          && _permGen->reserved().word_size() > 0,
 619          "generations should not be of zero size");
 620   assert(_cmsGen->reserved().intersection(_permGen->reserved()).is_empty(),
 621          "_cmsGen and _permGen should not overlap");
 622   assert(_cmsGen->reserved().end() == _permGen->reserved().start(),
 623          "_cmsGen->end() different from _permGen->start()");
 624 
 625   // For use by dirty card to oop closures.
 626   _cmsGen->cmsSpace()->set_collector(this);
 627   _permGen->cmsSpace()->set_collector(this);
 628 
 629   // Allocate MUT and marking bit map
 630   {
 631     MutexLockerEx x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag);
 632     if (!_markBitMap.allocate(_span)) {
 633       warning("Failed to allocate CMS Bit Map");
 634       return;
 635     }
 636     assert(_markBitMap.covers(_span), "_markBitMap inconsistency?");
 637   }
 638   {
 639     _modUnionTable.allocate(_span);
 640     assert(_modUnionTable.covers(_span), "_modUnionTable inconsistency?");
 641   }
 642 
 643   if (!_markStack.allocate(MarkStackSize)) {
 644     warning("Failed to allocate CMS Marking Stack");
 645     return;
 646   }
 647   if (!_revisitStack.allocate(CMSRevisitStackSize)) {
 648     warning("Failed to allocate CMS Revisit Stack");
 649     return;
 650   }
 651 
 652   // Support for multi-threaded concurrent phases
 653   if (CMSConcurrentMTEnabled) {
 654     if (FLAG_IS_DEFAULT(ConcGCThreads)) {
 655       // just for now
 656       FLAG_SET_DEFAULT(ConcGCThreads, (ParallelGCThreads + 3)/4);
 657     }
 658     if (ConcGCThreads > 1) {
 659       _conc_workers = new YieldingFlexibleWorkGang("Parallel CMS Threads",
 660                                  ConcGCThreads, true);
 661       if (_conc_workers == NULL) {
 662         warning("GC/CMS: _conc_workers allocation failure: "
 663               "forcing -CMSConcurrentMTEnabled");
 664         CMSConcurrentMTEnabled = false;
 665       } else {
 666         _conc_workers->initialize_workers();
 667       }
 668     } else {
 669       CMSConcurrentMTEnabled = false;
 670     }
 671   }
 672   if (!CMSConcurrentMTEnabled) {
 673     ConcGCThreads = 0;
 674   } else {
 675     // Turn off CMSCleanOnEnter optimization temporarily for
 676     // the MT case where it's not fixed yet; see 6178663.
 677     CMSCleanOnEnter = false;
 678   }
 679   assert((_conc_workers != NULL) == (ConcGCThreads > 1),
 680          "Inconsistency");
 681 
 682   // Parallel task queues; these are shared for the
 683   // concurrent and stop-world phases of CMS, but
 684   // are not shared with parallel scavenge (ParNew).
 685   {
 686     uint i;
 687     uint num_queues = (uint) MAX2(ParallelGCThreads, ConcGCThreads);
 688 
 689     if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled
 690          || ParallelRefProcEnabled)
 691         && num_queues > 0) {
 692       _task_queues = new OopTaskQueueSet(num_queues);
 693       if (_task_queues == NULL) {
 694         warning("task_queues allocation failure.");
 695         return;
 696       }
 697       _hash_seed = NEW_C_HEAP_ARRAY(int, num_queues, mtGC);
 698       if (_hash_seed == NULL) {
 699         warning("_hash_seed array allocation failure");
 700         return;
 701       }
 702 
 703       typedef Padded<OopTaskQueue> PaddedOopTaskQueue;
 704       for (i = 0; i < num_queues; i++) {
 705         PaddedOopTaskQueue *q = new PaddedOopTaskQueue();
 706         if (q == NULL) {
 707           warning("work_queue allocation failure.");
 708           return;
 709         }
 710         _task_queues->register_queue(i, q);
 711       }
 712       for (i = 0; i < num_queues; i++) {
 713         _task_queues->queue(i)->initialize();
 714         _hash_seed[i] = 17;  // copied from ParNew
 715       }
 716     }
 717   }
 718 
 719   _cmsGen ->init_initiating_occupancy(CMSInitiatingOccupancyFraction, CMSTriggerRatio);
 720   _permGen->init_initiating_occupancy(CMSInitiatingPermOccupancyFraction, CMSTriggerPermRatio);
 721 
 722   // Clip CMSBootstrapOccupancy between 0 and 100.
 723   _bootstrap_occupancy = ((double)MIN2((uintx)100, MAX2((uintx)0, CMSBootstrapOccupancy)))
 724                          /(double)100;
 725 
 726   _full_gcs_since_conc_gc = 0;
 727 
 728   // Now tell CMS generations the identity of their collector
 729   ConcurrentMarkSweepGeneration::set_collector(this);
 730 
 731   // Create & start a CMS thread for this CMS collector
 732   _cmsThread = ConcurrentMarkSweepThread::start(this);
 733   assert(cmsThread() != NULL, "CMS Thread should have been created");
 734   assert(cmsThread()->collector() == this,
 735          "CMS Thread should refer to this gen");
 736   assert(CGC_lock != NULL, "Where's the CGC_lock?");
 737 
 738   // Support for parallelizing young gen rescan
 739   GenCollectedHeap* gch = GenCollectedHeap::heap();
 740   _young_gen = gch->prev_gen(_cmsGen);
 741   if (gch->supports_inline_contig_alloc()) {
 742     _top_addr = gch->top_addr();
 743     _end_addr = gch->end_addr();
 744     assert(_young_gen != NULL, "no _young_gen");
 745     _eden_chunk_index = 0;
 746     _eden_chunk_capacity = (_young_gen->max_capacity()+CMSSamplingGrain)/CMSSamplingGrain;
 747     _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity, mtGC);
 748     if (_eden_chunk_array == NULL) {
 749       _eden_chunk_capacity = 0;
 750       warning("GC/CMS: _eden_chunk_array allocation failure");
 751     }
 752   }
 753   assert(_eden_chunk_array != NULL || _eden_chunk_capacity == 0, "Error");
 754 
 755   // Support for parallelizing survivor space rescan
 756   if (CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) {
 757     const size_t max_plab_samples =
 758       ((DefNewGeneration*)_young_gen)->max_survivor_size()/MinTLABSize;
 759 
 760     _survivor_plab_array  = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads, mtGC);
 761     _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, 2*max_plab_samples, mtGC);
 762     _cursor               = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads, mtGC);
 763     if (_survivor_plab_array == NULL || _survivor_chunk_array == NULL
 764         || _cursor == NULL) {
 765       warning("Failed to allocate survivor plab/chunk array");
 766       if (_survivor_plab_array  != NULL) {
 767         FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array, mtGC);
 768         _survivor_plab_array = NULL;
 769       }
 770       if (_survivor_chunk_array != NULL) {
 771         FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array, mtGC);
 772         _survivor_chunk_array = NULL;
 773       }
 774       if (_cursor != NULL) {
 775         FREE_C_HEAP_ARRAY(size_t, _cursor, mtGC);
 776         _cursor = NULL;
 777       }
 778     } else {
 779       _survivor_chunk_capacity = 2*max_plab_samples;
 780       for (uint i = 0; i < ParallelGCThreads; i++) {
 781         HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
 782         if (vec == NULL) {
 783           warning("Failed to allocate survivor plab array");
 784           for (int j = i; j > 0; j--) {
 785             FREE_C_HEAP_ARRAY(HeapWord*, _survivor_plab_array[j-1].array(), mtGC);
 786           }
 787           FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array, mtGC);
 788           FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array, mtGC);
 789           _survivor_plab_array = NULL;
 790           _survivor_chunk_array = NULL;
 791           _survivor_chunk_capacity = 0;
 792           break;
 793         } else {
 794           ChunkArray* cur =
 795             ::new (&_survivor_plab_array[i]) ChunkArray(vec,
 796                                                         max_plab_samples);
 797           assert(cur->end() == 0, "Should be 0");
 798           assert(cur->array() == vec, "Should be vec");
 799           assert(cur->capacity() == max_plab_samples, "Error");
 800         }
 801       }
 802     }
 803   }
 804   assert(   (   _survivor_plab_array  != NULL
 805              && _survivor_chunk_array != NULL)
 806          || (   _survivor_chunk_capacity == 0
 807              && _survivor_chunk_index == 0),
 808          "Error");
 809 
 810   // Choose what strong roots should be scanned depending on verification options
 811   // and perm gen collection mode.
 812   if (!CMSClassUnloadingEnabled) {
 813     // If class unloading is disabled we want to include all classes into the root set.
 814     add_root_scanning_option(SharedHeap::SO_AllClasses);
 815   } else {
 816     add_root_scanning_option(SharedHeap::SO_SystemClasses);
 817   }
 818 
 819   NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;)
 820   _gc_counters = new CollectorCounters("CMS", 1);
 821   _completed_initialization = true;
 822   _inter_sweep_timer.start();  // start of time
 823 }
 824 
 825 const char* ConcurrentMarkSweepGeneration::name() const {
 826   return "concurrent mark-sweep generation";
 827 }
 828 void ConcurrentMarkSweepGeneration::update_counters() {
 829   if (UsePerfData) {
 830     _space_counters->update_all();
 831     _gen_counters->update_all();
 832   }
 833 }
 834 
 835 // this is an optimized version of update_counters(). it takes the
 836 // used value as a parameter rather than computing it.
 837 //
 838 void ConcurrentMarkSweepGeneration::update_counters(size_t used) {
 839   if (UsePerfData) {
 840     _space_counters->update_used(used);
 841     _space_counters->update_capacity();
 842     _gen_counters->update_all();
 843   }
 844 }
 845 
 846 void ConcurrentMarkSweepGeneration::print() const {
 847   Generation::print();
 848   cmsSpace()->print();
 849 }
 850 
 851 #ifndef PRODUCT
 852 void ConcurrentMarkSweepGeneration::print_statistics() {
 853   cmsSpace()->printFLCensus(0);
 854 }
 855 #endif
 856 
 857 void ConcurrentMarkSweepGeneration::printOccupancy(const char *s) {
 858   GenCollectedHeap* gch = GenCollectedHeap::heap();
 859   if (PrintGCDetails) {
 860     if (Verbose) {
 861       gclog_or_tty->print(" [%d %s-%s: "SIZE_FORMAT"("SIZE_FORMAT")]",
 862         level(), short_name(), s, used(), capacity());
 863     } else {
 864       gclog_or_tty->print(" [%d %s-%s: "SIZE_FORMAT"K("SIZE_FORMAT"K)]",
 865         level(), short_name(), s, used() / K, capacity() / K);
 866     }
 867   }
 868   if (Verbose) {
 869     gclog_or_tty->print(" "SIZE_FORMAT"("SIZE_FORMAT")",
 870               gch->used(), gch->capacity());
 871   } else {
 872     gclog_or_tty->print(" "SIZE_FORMAT"K("SIZE_FORMAT"K)",
 873               gch->used() / K, gch->capacity() / K);
 874   }
 875 }
 876 
 877 size_t
 878 ConcurrentMarkSweepGeneration::contiguous_available() const {
 879   // dld proposes an improvement in precision here. If the committed
 880   // part of the space ends in a free block we should add that to
 881   // uncommitted size in the calculation below. Will make this
 882   // change later, staying with the approximation below for the
 883   // time being. -- ysr.
 884   return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc());
 885 }
 886 
 887 size_t
 888 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const {
 889   return _cmsSpace->max_alloc_in_words() * HeapWordSize;
 890 }
 891 
 892 size_t ConcurrentMarkSweepGeneration::max_available() const {
 893   return free() + _virtual_space.uncommitted_size();
 894 }
 895 
 896 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(size_t max_promotion_in_bytes) const {
 897   size_t available = max_available();
 898   size_t av_promo  = (size_t)gc_stats()->avg_promoted()->padded_average();
 899   bool   res = (available >= av_promo) || (available >= max_promotion_in_bytes);
 900   if (Verbose && PrintGCDetails) {
 901     gclog_or_tty->print_cr(
 902       "CMS: promo attempt is%s safe: available("SIZE_FORMAT") %s av_promo("SIZE_FORMAT"),"
 903       "max_promo("SIZE_FORMAT")",
 904       res? "":" not", available, res? ">=":"<",
 905       av_promo, max_promotion_in_bytes);
 906   }
 907   return res;
 908 }
 909 
 910 // At a promotion failure dump information on block layout in heap
 911 // (cms old generation).
 912 void ConcurrentMarkSweepGeneration::promotion_failure_occurred() {
 913   if (CMSDumpAtPromotionFailure) {
 914     cmsSpace()->dump_at_safepoint_with_locks(collector(), gclog_or_tty);
 915   }
 916 }
 917 
 918 CompactibleSpace*
 919 ConcurrentMarkSweepGeneration::first_compaction_space() const {
 920   return _cmsSpace;
 921 }
 922 
 923 void ConcurrentMarkSweepGeneration::reset_after_compaction() {
 924   // Clear the promotion information.  These pointers can be adjusted
 925   // along with all the other pointers into the heap but
 926   // compaction is expected to be a rare event with
 927   // a heap using cms so don't do it without seeing the need.
 928   if (CollectedHeap::use_parallel_gc_threads()) {
 929     for (uint i = 0; i < ParallelGCThreads; i++) {
 930       _par_gc_thread_states[i]->promo.reset();
 931     }
 932   }
 933 }
 934 
 935 void ConcurrentMarkSweepGeneration::space_iterate(SpaceClosure* blk, bool usedOnly) {
 936   blk->do_space(_cmsSpace);
 937 }
 938 
 939 void ConcurrentMarkSweepGeneration::compute_new_size() {
 940   assert_locked_or_safepoint(Heap_lock);
 941 
 942   // If incremental collection failed, we just want to expand
 943   // to the limit.
 944   if (incremental_collection_failed()) {
 945     clear_incremental_collection_failed();
 946     grow_to_reserved();
 947     return;
 948   }
 949 
 950   size_t expand_bytes = 0;
 951   double free_percentage = ((double) free()) / capacity();
 952   double desired_free_percentage = (double) MinHeapFreeRatio / 100;
 953   double maximum_free_percentage = (double) MaxHeapFreeRatio / 100;
 954 
 955   // compute expansion delta needed for reaching desired free percentage
 956   if (free_percentage < desired_free_percentage) {
 957     size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
 958     assert(desired_capacity >= capacity(), "invalid expansion size");
 959     expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes);
 960   }
 961   if (expand_bytes > 0) {
 962     if (PrintGCDetails && Verbose) {
 963       size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
 964       gclog_or_tty->print_cr("\nFrom compute_new_size: ");
 965       gclog_or_tty->print_cr("  Free fraction %f", free_percentage);
 966       gclog_or_tty->print_cr("  Desired free fraction %f",
 967         desired_free_percentage);
 968       gclog_or_tty->print_cr("  Maximum free fraction %f",
 969         maximum_free_percentage);
 970       gclog_or_tty->print_cr("  Capactiy "SIZE_FORMAT, capacity()/1000);
 971       gclog_or_tty->print_cr("  Desired capacity "SIZE_FORMAT,
 972         desired_capacity/1000);
 973       int prev_level = level() - 1;
 974       if (prev_level >= 0) {
 975         size_t prev_size = 0;
 976         GenCollectedHeap* gch = GenCollectedHeap::heap();
 977         Generation* prev_gen = gch->_gens[prev_level];
 978         prev_size = prev_gen->capacity();
 979           gclog_or_tty->print_cr("  Younger gen size "SIZE_FORMAT,
 980                                  prev_size/1000);
 981       }
 982       gclog_or_tty->print_cr("  unsafe_max_alloc_nogc "SIZE_FORMAT,
 983         unsafe_max_alloc_nogc()/1000);
 984       gclog_or_tty->print_cr("  contiguous available "SIZE_FORMAT,
 985         contiguous_available()/1000);
 986       gclog_or_tty->print_cr("  Expand by "SIZE_FORMAT" (bytes)",
 987         expand_bytes);
 988     }
 989     // safe if expansion fails
 990     expand(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio);
 991     if (PrintGCDetails && Verbose) {
 992       gclog_or_tty->print_cr("  Expanded free fraction %f",
 993         ((double) free()) / capacity());
 994     }
 995   }
 996 }
 997 
 998 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const {
 999   return cmsSpace()->freelistLock();
1000 }
1001 
1002 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size,
1003                                                   bool   tlab) {
1004   CMSSynchronousYieldRequest yr;
1005   MutexLockerEx x(freelistLock(),
1006                   Mutex::_no_safepoint_check_flag);
1007   return have_lock_and_allocate(size, tlab);
1008 }
1009 
1010 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size,
1011                                                   bool   tlab /* ignored */) {
1012   assert_lock_strong(freelistLock());
1013   size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size);
1014   HeapWord* res = cmsSpace()->allocate(adjustedSize);
1015   // Allocate the object live (grey) if the background collector has
1016   // started marking. This is necessary because the marker may
1017   // have passed this address and consequently this object will
1018   // not otherwise be greyed and would be incorrectly swept up.
1019   // Note that if this object contains references, the writing
1020   // of those references will dirty the card containing this object
1021   // allowing the object to be blackened (and its references scanned)
1022   // either during a preclean phase or at the final checkpoint.
1023   if (res != NULL) {
1024     // We may block here with an uninitialized object with
1025     // its mark-bit or P-bits not yet set. Such objects need
1026     // to be safely navigable by block_start().
1027     assert(oop(res)->klass_or_null() == NULL, "Object should be uninitialized here.");
1028     assert(!((FreeChunk*)res)->is_free(), "Error, block will look free but show wrong size");
1029     collector()->direct_allocated(res, adjustedSize);
1030     _direct_allocated_words += adjustedSize;
1031     // allocation counters
1032     NOT_PRODUCT(
1033       _numObjectsAllocated++;
1034       _numWordsAllocated += (int)adjustedSize;
1035     )
1036   }
1037   return res;
1038 }
1039 
1040 // In the case of direct allocation by mutators in a generation that
1041 // is being concurrently collected, the object must be allocated
1042 // live (grey) if the background collector has started marking.
1043 // This is necessary because the marker may
1044 // have passed this address and consequently this object will
1045 // not otherwise be greyed and would be incorrectly swept up.
1046 // Note that if this object contains references, the writing
1047 // of those references will dirty the card containing this object
1048 // allowing the object to be blackened (and its references scanned)
1049 // either during a preclean phase or at the final checkpoint.
1050 void CMSCollector::direct_allocated(HeapWord* start, size_t size) {
1051   assert(_markBitMap.covers(start, size), "Out of bounds");
1052   if (_collectorState >= Marking) {
1053     MutexLockerEx y(_markBitMap.lock(),
1054                     Mutex::_no_safepoint_check_flag);
1055     // [see comments preceding SweepClosure::do_blk() below for details]
1056     // 1. need to mark the object as live so it isn't collected
1057     // 2. need to mark the 2nd bit to indicate the object may be uninitialized
1058     // 3. need to mark the end of the object so marking, precleaning or sweeping
1059     //    can skip over uninitialized or unparsable objects. An allocated
1060     //    object is considered uninitialized for our purposes as long as
1061     //    its klass word is NULL. (Unparsable objects are those which are
1062     //    initialized in the sense just described, but whose sizes can still
1063     //    not be correctly determined. Note that the class of unparsable objects
1064     //    can only occur in the perm gen. All old gen objects are parsable
1065     //    as soon as they are initialized.)
1066     _markBitMap.mark(start);          // object is live
1067     _markBitMap.mark(start + 1);      // object is potentially uninitialized?
1068     _markBitMap.mark(start + size - 1);
1069                                       // mark end of object
1070   }
1071   // check that oop looks uninitialized
1072   assert(oop(start)->klass_or_null() == NULL, "_klass should be NULL");
1073 }
1074 
1075 void CMSCollector::promoted(bool par, HeapWord* start,
1076                             bool is_obj_array, size_t obj_size) {
1077   assert(_markBitMap.covers(start), "Out of bounds");
1078   // See comment in direct_allocated() about when objects should
1079   // be allocated live.
1080   if (_collectorState >= Marking) {
1081     // we already hold the marking bit map lock, taken in
1082     // the prologue
1083     if (par) {
1084       _markBitMap.par_mark(start);
1085     } else {
1086       _markBitMap.mark(start);
1087     }
1088     // We don't need to mark the object as uninitialized (as
1089     // in direct_allocated above) because this is being done with the
1090     // world stopped and the object will be initialized by the
1091     // time the marking, precleaning or sweeping get to look at it.
1092     // But see the code for copying objects into the CMS generation,
1093     // where we need to ensure that concurrent readers of the
1094     // block offset table are able to safely navigate a block that
1095     // is in flux from being free to being allocated (and in
1096     // transition while being copied into) and subsequently
1097     // becoming a bona-fide object when the copy/promotion is complete.
1098     assert(SafepointSynchronize::is_at_safepoint(),
1099            "expect promotion only at safepoints");
1100 
1101     if (_collectorState < Sweeping) {
1102       // Mark the appropriate cards in the modUnionTable, so that
1103       // this object gets scanned before the sweep. If this is
1104       // not done, CMS generation references in the object might
1105       // not get marked.
1106       // For the case of arrays, which are otherwise precisely
1107       // marked, we need to dirty the entire array, not just its head.
1108       if (is_obj_array) {
1109         // The [par_]mark_range() method expects mr.end() below to
1110         // be aligned to the granularity of a bit's representation
1111         // in the heap. In the case of the MUT below, that's a
1112         // card size.
1113         MemRegion mr(start,
1114                      (HeapWord*)round_to((intptr_t)(start + obj_size),
1115                         CardTableModRefBS::card_size /* bytes */));
1116         if (par) {
1117           _modUnionTable.par_mark_range(mr);
1118         } else {
1119           _modUnionTable.mark_range(mr);
1120         }
1121       } else {  // not an obj array; we can just mark the head
1122         if (par) {
1123           _modUnionTable.par_mark(start);
1124         } else {
1125           _modUnionTable.mark(start);
1126         }
1127       }
1128     }
1129   }
1130 }
1131 
1132 static inline size_t percent_of_space(Space* space, HeapWord* addr)
1133 {
1134   size_t delta = pointer_delta(addr, space->bottom());
1135   return (size_t)(delta * 100.0 / (space->capacity() / HeapWordSize));
1136 }
1137 
1138 void CMSCollector::icms_update_allocation_limits()
1139 {
1140   Generation* gen0 = GenCollectedHeap::heap()->get_gen(0);
1141   EdenSpace* eden = gen0->as_DefNewGeneration()->eden();
1142 
1143   const unsigned int duty_cycle = stats().icms_update_duty_cycle();
1144   if (CMSTraceIncrementalPacing) {
1145     stats().print();
1146   }
1147 
1148   assert(duty_cycle <= 100, "invalid duty cycle");
1149   if (duty_cycle != 0) {
1150     // The duty_cycle is a percentage between 0 and 100; convert to words and
1151     // then compute the offset from the endpoints of the space.
1152     size_t free_words = eden->free() / HeapWordSize;
1153     double free_words_dbl = (double)free_words;
1154     size_t duty_cycle_words = (size_t)(free_words_dbl * duty_cycle / 100.0);
1155     size_t offset_words = (free_words - duty_cycle_words) / 2;
1156 
1157     _icms_start_limit = eden->top() + offset_words;
1158     _icms_stop_limit = eden->end() - offset_words;
1159 
1160     // The limits may be adjusted (shifted to the right) by
1161     // CMSIncrementalOffset, to allow the application more mutator time after a
1162     // young gen gc (when all mutators were stopped) and before CMS starts and
1163     // takes away one or more cpus.
1164     if (CMSIncrementalOffset != 0) {
1165       double adjustment_dbl = free_words_dbl * CMSIncrementalOffset / 100.0;
1166       size_t adjustment = (size_t)adjustment_dbl;
1167       HeapWord* tmp_stop = _icms_stop_limit + adjustment;
1168       if (tmp_stop > _icms_stop_limit && tmp_stop < eden->end()) {
1169         _icms_start_limit += adjustment;
1170         _icms_stop_limit = tmp_stop;
1171       }
1172     }
1173   }
1174   if (duty_cycle == 0 || (_icms_start_limit == _icms_stop_limit)) {
1175     _icms_start_limit = _icms_stop_limit = eden->end();
1176   }
1177 
1178   // Install the new start limit.
1179   eden->set_soft_end(_icms_start_limit);
1180 
1181   if (CMSTraceIncrementalMode) {
1182     gclog_or_tty->print(" icms alloc limits:  "
1183                            PTR_FORMAT "," PTR_FORMAT
1184                            " (" SIZE_FORMAT "%%," SIZE_FORMAT "%%) ",
1185                            _icms_start_limit, _icms_stop_limit,
1186                            percent_of_space(eden, _icms_start_limit),
1187                            percent_of_space(eden, _icms_stop_limit));
1188     if (Verbose) {
1189       gclog_or_tty->print("eden:  ");
1190       eden->print_on(gclog_or_tty);
1191     }
1192   }
1193 }
1194 
1195 // Any changes here should try to maintain the invariant
1196 // that if this method is called with _icms_start_limit
1197 // and _icms_stop_limit both NULL, then it should return NULL
1198 // and not notify the icms thread.
1199 HeapWord*
1200 CMSCollector::allocation_limit_reached(Space* space, HeapWord* top,
1201                                        size_t word_size)
1202 {
1203   // A start_limit equal to end() means the duty cycle is 0, so treat that as a
1204   // nop.
1205   if (CMSIncrementalMode && _icms_start_limit != space->end()) {
1206     if (top <= _icms_start_limit) {
1207       if (CMSTraceIncrementalMode) {
1208         space->print_on(gclog_or_tty);
1209         gclog_or_tty->stamp();
1210         gclog_or_tty->print_cr(" start limit top=" PTR_FORMAT
1211                                ", new limit=" PTR_FORMAT
1212                                " (" SIZE_FORMAT "%%)",
1213                                top, _icms_stop_limit,
1214                                percent_of_space(space, _icms_stop_limit));
1215       }
1216       ConcurrentMarkSweepThread::start_icms();
1217       assert(top < _icms_stop_limit, "Tautology");
1218       if (word_size < pointer_delta(_icms_stop_limit, top)) {
1219         return _icms_stop_limit;
1220       }
1221 
1222       // The allocation will cross both the _start and _stop limits, so do the
1223       // stop notification also and return end().
1224       if (CMSTraceIncrementalMode) {
1225         space->print_on(gclog_or_tty);
1226         gclog_or_tty->stamp();
1227         gclog_or_tty->print_cr(" +stop limit top=" PTR_FORMAT
1228                                ", new limit=" PTR_FORMAT
1229                                " (" SIZE_FORMAT "%%)",
1230                                top, space->end(),
1231                                percent_of_space(space, space->end()));
1232       }
1233       ConcurrentMarkSweepThread::stop_icms();
1234       return space->end();
1235     }
1236 
1237     if (top <= _icms_stop_limit) {
1238       if (CMSTraceIncrementalMode) {
1239         space->print_on(gclog_or_tty);
1240         gclog_or_tty->stamp();
1241         gclog_or_tty->print_cr(" stop limit top=" PTR_FORMAT
1242                                ", new limit=" PTR_FORMAT
1243                                " (" SIZE_FORMAT "%%)",
1244                                top, space->end(),
1245                                percent_of_space(space, space->end()));
1246       }
1247       ConcurrentMarkSweepThread::stop_icms();
1248       return space->end();
1249     }
1250 
1251     if (CMSTraceIncrementalMode) {
1252       space->print_on(gclog_or_tty);
1253       gclog_or_tty->stamp();
1254       gclog_or_tty->print_cr(" end limit top=" PTR_FORMAT
1255                              ", new limit=" PTR_FORMAT,
1256                              top, NULL);
1257     }
1258   }
1259 
1260   return NULL;
1261 }
1262 
1263 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size) {
1264   assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
1265   // allocate, copy and if necessary update promoinfo --
1266   // delegate to underlying space.
1267   assert_lock_strong(freelistLock());
1268 
1269 #ifndef PRODUCT
1270   if (Universe::heap()->promotion_should_fail()) {
1271     return NULL;
1272   }
1273 #endif  // #ifndef PRODUCT
1274 
1275   oop res = _cmsSpace->promote(obj, obj_size);
1276   if (res == NULL) {
1277     // expand and retry
1278     size_t s = _cmsSpace->expansionSpaceRequired(obj_size);  // HeapWords
1279     expand(s*HeapWordSize, MinHeapDeltaBytes,
1280       CMSExpansionCause::_satisfy_promotion);
1281     // Since there's currently no next generation, we don't try to promote
1282     // into a more senior generation.
1283     assert(next_gen() == NULL, "assumption, based upon which no attempt "
1284                                "is made to pass on a possibly failing "
1285                                "promotion to next generation");
1286     res = _cmsSpace->promote(obj, obj_size);
1287   }
1288   if (res != NULL) {
1289     // See comment in allocate() about when objects should
1290     // be allocated live.
1291     assert(obj->is_oop(), "Will dereference klass pointer below");
1292     collector()->promoted(false,           // Not parallel
1293                           (HeapWord*)res, obj->is_objArray(), obj_size);
1294     // promotion counters
1295     NOT_PRODUCT(
1296       _numObjectsPromoted++;
1297       _numWordsPromoted +=
1298         (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size()));
1299     )
1300   }
1301   return res;
1302 }
1303 
1304 
1305 HeapWord*
1306 ConcurrentMarkSweepGeneration::allocation_limit_reached(Space* space,
1307                                              HeapWord* top,
1308                                              size_t word_sz)
1309 {
1310   return collector()->allocation_limit_reached(space, top, word_sz);
1311 }
1312 
1313 // IMPORTANT: Notes on object size recognition in CMS.
1314 // ---------------------------------------------------
1315 // A block of storage in the CMS generation is always in
1316 // one of three states. A free block (FREE), an allocated
1317 // object (OBJECT) whose size() method reports the correct size,
1318 // and an intermediate state (TRANSIENT) in which its size cannot
1319 // be accurately determined.
1320 // STATE IDENTIFICATION:   (32 bit and 64 bit w/o COOPS)
1321 // -----------------------------------------------------
1322 // FREE:      klass_word & 1 == 1; mark_word holds block size
1323 //
1324 // OBJECT:    klass_word installed; klass_word != 0 && klass_word & 1 == 0;
1325 //            obj->size() computes correct size
1326 //            [Perm Gen objects needs to be "parsable" before they can be navigated]
1327 //
1328 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1329 //
1330 // STATE IDENTIFICATION: (64 bit+COOPS)
1331 // ------------------------------------
1332 // FREE:      mark_word & CMS_FREE_BIT == 1; mark_word & ~CMS_FREE_BIT gives block_size
1333 //
1334 // OBJECT:    klass_word installed; klass_word != 0;
1335 //            obj->size() computes correct size
1336 //            [Perm Gen comment above continues to hold]
1337 //
1338 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1339 //
1340 //
1341 // STATE TRANSITION DIAGRAM
1342 //
1343 //        mut / parnew                     mut  /  parnew
1344 // FREE --------------------> TRANSIENT ---------------------> OBJECT --|
1345 //  ^                                                                   |
1346 //  |------------------------ DEAD <------------------------------------|
1347 //         sweep                            mut
1348 //
1349 // While a block is in TRANSIENT state its size cannot be determined
1350 // so readers will either need to come back later or stall until
1351 // the size can be determined. Note that for the case of direct
1352 // allocation, P-bits, when available, may be used to determine the
1353 // size of an object that may not yet have been initialized.
1354 
1355 // Things to support parallel young-gen collection.
1356 oop
1357 ConcurrentMarkSweepGeneration::par_promote(int thread_num,
1358                                            oop old, markOop m,
1359                                            size_t word_sz) {
1360 #ifndef PRODUCT
1361   if (Universe::heap()->promotion_should_fail()) {
1362     return NULL;
1363   }
1364 #endif  // #ifndef PRODUCT
1365 
1366   CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1367   PromotionInfo* promoInfo = &ps->promo;
1368   // if we are tracking promotions, then first ensure space for
1369   // promotion (including spooling space for saving header if necessary).
1370   // then allocate and copy, then track promoted info if needed.
1371   // When tracking (see PromotionInfo::track()), the mark word may
1372   // be displaced and in this case restoration of the mark word
1373   // occurs in the (oop_since_save_marks_)iterate phase.
1374   if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) {
1375     // Out of space for allocating spooling buffers;
1376     // try expanding and allocating spooling buffers.
1377     if (!expand_and_ensure_spooling_space(promoInfo)) {
1378       return NULL;
1379     }
1380   }
1381   assert(promoInfo->has_spooling_space(), "Control point invariant");
1382   const size_t alloc_sz = CompactibleFreeListSpace::adjustObjectSize(word_sz);
1383   HeapWord* obj_ptr = ps->lab.alloc(alloc_sz);
1384   if (obj_ptr == NULL) {
1385      obj_ptr = expand_and_par_lab_allocate(ps, alloc_sz);
1386      if (obj_ptr == NULL) {
1387        return NULL;
1388      }
1389   }
1390   oop obj = oop(obj_ptr);
1391   OrderAccess::storestore();
1392   assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1393   assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1394   // IMPORTANT: See note on object initialization for CMS above.
1395   // Otherwise, copy the object.  Here we must be careful to insert the
1396   // klass pointer last, since this marks the block as an allocated object.
1397   // Except with compressed oops it's the mark word.
1398   HeapWord* old_ptr = (HeapWord*)old;
1399   // Restore the mark word copied above.
1400   obj->set_mark(m);
1401   assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1402   assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1403   OrderAccess::storestore();
1404 
1405   if (UseCompressedOops) {
1406     // Copy gap missed by (aligned) header size calculation below
1407     obj->set_klass_gap(old->klass_gap());
1408   }
1409   if (word_sz > (size_t)oopDesc::header_size()) {
1410     Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1411                                  obj_ptr + oopDesc::header_size(),
1412                                  word_sz - oopDesc::header_size());
1413   }
1414 
1415   // Now we can track the promoted object, if necessary.  We take care
1416   // to delay the transition from uninitialized to full object
1417   // (i.e., insertion of klass pointer) until after, so that it
1418   // atomically becomes a promoted object.
1419   if (promoInfo->tracking()) {
1420     promoInfo->track((PromotedObject*)obj, old->klass());
1421   }
1422   assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1423   assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1424   assert(old->is_oop(), "Will use and dereference old klass ptr below");
1425 
1426   // Finally, install the klass pointer (this should be volatile).
1427   OrderAccess::storestore();
1428   obj->set_klass(old->klass());
1429   // We should now be able to calculate the right size for this object
1430   assert(obj->is_oop() && obj->size() == (int)word_sz, "Error, incorrect size computed for promoted object");
1431 
1432   collector()->promoted(true,          // parallel
1433                         obj_ptr, old->is_objArray(), word_sz);
1434 
1435   NOT_PRODUCT(
1436     Atomic::inc_ptr(&_numObjectsPromoted);
1437     Atomic::add_ptr(alloc_sz, &_numWordsPromoted);
1438   )
1439 
1440   return obj;
1441 }
1442 
1443 void
1444 ConcurrentMarkSweepGeneration::
1445 par_promote_alloc_undo(int thread_num,
1446                        HeapWord* obj, size_t word_sz) {
1447   // CMS does not support promotion undo.
1448   ShouldNotReachHere();
1449 }
1450 
1451 void
1452 ConcurrentMarkSweepGeneration::
1453 par_promote_alloc_done(int thread_num) {
1454   CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1455   ps->lab.retire(thread_num);
1456 }
1457 
1458 void
1459 ConcurrentMarkSweepGeneration::
1460 par_oop_since_save_marks_iterate_done(int thread_num) {
1461   CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1462   ParScanWithoutBarrierClosure* dummy_cl = NULL;
1463   ps->promo.promoted_oops_iterate_nv(dummy_cl);
1464 }
1465 
1466 // XXXPERM
1467 bool ConcurrentMarkSweepGeneration::should_collect(bool   full,
1468                                                    size_t size,
1469                                                    bool   tlab)
1470 {
1471   // We allow a STW collection only if a full
1472   // collection was requested.
1473   return full || should_allocate(size, tlab); // FIX ME !!!
1474   // This and promotion failure handling are connected at the
1475   // hip and should be fixed by untying them.
1476 }
1477 
1478 bool CMSCollector::shouldConcurrentCollect() {
1479   if (_full_gc_requested) {
1480     if (Verbose && PrintGCDetails) {
1481       gclog_or_tty->print_cr("CMSCollector: collect because of explicit "
1482                              " gc request (or gc_locker)");
1483     }
1484     return true;
1485   }
1486 
1487   // For debugging purposes, change the type of collection.
1488   // If the rotation is not on the concurrent collection
1489   // type, don't start a concurrent collection.
1490   NOT_PRODUCT(
1491     if (RotateCMSCollectionTypes &&
1492         (_cmsGen->debug_collection_type() !=
1493           ConcurrentMarkSweepGeneration::Concurrent_collection_type)) {
1494       assert(_cmsGen->debug_collection_type() !=
1495         ConcurrentMarkSweepGeneration::Unknown_collection_type,
1496         "Bad cms collection type");
1497       return false;
1498     }
1499   )
1500 
1501   FreelistLocker x(this);
1502   // ------------------------------------------------------------------
1503   // Print out lots of information which affects the initiation of
1504   // a collection.
1505   if (PrintCMSInitiationStatistics && stats().valid()) {
1506     gclog_or_tty->print("CMSCollector shouldConcurrentCollect: ");
1507     gclog_or_tty->stamp();
1508     gclog_or_tty->print_cr("");
1509     stats().print_on(gclog_or_tty);
1510     gclog_or_tty->print_cr("time_until_cms_gen_full %3.7f",
1511       stats().time_until_cms_gen_full());
1512     gclog_or_tty->print_cr("free="SIZE_FORMAT, _cmsGen->free());
1513     gclog_or_tty->print_cr("contiguous_available="SIZE_FORMAT,
1514                            _cmsGen->contiguous_available());
1515     gclog_or_tty->print_cr("promotion_rate=%g", stats().promotion_rate());
1516     gclog_or_tty->print_cr("cms_allocation_rate=%g", stats().cms_allocation_rate());
1517     gclog_or_tty->print_cr("occupancy=%3.7f", _cmsGen->occupancy());
1518     gclog_or_tty->print_cr("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy());
1519     gclog_or_tty->print_cr("initiatingPermOccupancy=%3.7f", _permGen->initiating_occupancy());
1520   }
1521   // ------------------------------------------------------------------
1522 
1523   // If the estimated time to complete a cms collection (cms_duration())
1524   // is less than the estimated time remaining until the cms generation
1525   // is full, start a collection.
1526   if (!UseCMSInitiatingOccupancyOnly) {
1527     if (stats().valid()) {
1528       if (stats().time_until_cms_start() == 0.0) {
1529         return true;
1530       }
1531     } else {
1532       // We want to conservatively collect somewhat early in order
1533       // to try and "bootstrap" our CMS/promotion statistics;
1534       // this branch will not fire after the first successful CMS
1535       // collection because the stats should then be valid.
1536       if (_cmsGen->occupancy() >= _bootstrap_occupancy) {
1537         if (Verbose && PrintGCDetails) {
1538           gclog_or_tty->print_cr(
1539             " CMSCollector: collect for bootstrapping statistics:"
1540             " occupancy = %f, boot occupancy = %f", _cmsGen->occupancy(),
1541             _bootstrap_occupancy);
1542         }
1543         return true;
1544       }
1545     }
1546   }
1547 
1548   // Otherwise, we start a collection cycle if either the perm gen or
1549   // old gen want a collection cycle started. Each may use
1550   // an appropriate criterion for making this decision.
1551   // XXX We need to make sure that the gen expansion
1552   // criterion dovetails well with this. XXX NEED TO FIX THIS
1553   if (_cmsGen->should_concurrent_collect()) {
1554     if (Verbose && PrintGCDetails) {
1555       gclog_or_tty->print_cr("CMS old gen initiated");
1556     }
1557     return true;
1558   }
1559 
1560   // We start a collection if we believe an incremental collection may fail;
1561   // this is not likely to be productive in practice because it's probably too
1562   // late anyway.
1563   GenCollectedHeap* gch = GenCollectedHeap::heap();
1564   assert(gch->collector_policy()->is_two_generation_policy(),
1565          "You may want to check the correctness of the following");
1566   if (gch->incremental_collection_will_fail(true /* consult_young */)) {
1567     if (Verbose && PrintGCDetails) {
1568       gclog_or_tty->print("CMSCollector: collect because incremental collection will fail ");
1569     }
1570     return true;
1571   }
1572 
1573   if (CMSClassUnloadingEnabled && _permGen->should_concurrent_collect()) {
1574     bool res = update_should_unload_classes();
1575     if (res) {
1576       if (Verbose && PrintGCDetails) {
1577         gclog_or_tty->print_cr("CMS perm gen initiated");
1578       }
1579       return true;
1580     }
1581   }
1582   return false;
1583 }
1584 
1585 // Clear _expansion_cause fields of constituent generations
1586 void CMSCollector::clear_expansion_cause() {
1587   _cmsGen->clear_expansion_cause();
1588   _permGen->clear_expansion_cause();
1589 }
1590 
1591 // We should be conservative in starting a collection cycle.  To
1592 // start too eagerly runs the risk of collecting too often in the
1593 // extreme.  To collect too rarely falls back on full collections,
1594 // which works, even if not optimum in terms of concurrent work.
1595 // As a work around for too eagerly collecting, use the flag
1596 // UseCMSInitiatingOccupancyOnly.  This also has the advantage of
1597 // giving the user an easily understandable way of controlling the
1598 // collections.
1599 // We want to start a new collection cycle if any of the following
1600 // conditions hold:
1601 // . our current occupancy exceeds the configured initiating occupancy
1602 //   for this generation, or
1603 // . we recently needed to expand this space and have not, since that
1604 //   expansion, done a collection of this generation, or
1605 // . the underlying space believes that it may be a good idea to initiate
1606 //   a concurrent collection (this may be based on criteria such as the
1607 //   following: the space uses linear allocation and linear allocation is
1608 //   going to fail, or there is believed to be excessive fragmentation in
1609 //   the generation, etc... or ...
1610 // [.(currently done by CMSCollector::shouldConcurrentCollect() only for
1611 //   the case of the old generation, not the perm generation; see CR 6543076):
1612 //   we may be approaching a point at which allocation requests may fail because
1613 //   we will be out of sufficient free space given allocation rate estimates.]
1614 bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const {
1615 
1616   assert_lock_strong(freelistLock());
1617   if (occupancy() > initiating_occupancy()) {
1618     if (PrintGCDetails && Verbose) {
1619       gclog_or_tty->print(" %s: collect because of occupancy %f / %f  ",
1620         short_name(), occupancy(), initiating_occupancy());
1621     }
1622     return true;
1623   }
1624   if (UseCMSInitiatingOccupancyOnly) {
1625     return false;
1626   }
1627   if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) {
1628     if (PrintGCDetails && Verbose) {
1629       gclog_or_tty->print(" %s: collect because expanded for allocation ",
1630         short_name());
1631     }
1632     return true;
1633   }
1634   if (_cmsSpace->should_concurrent_collect()) {
1635     if (PrintGCDetails && Verbose) {
1636       gclog_or_tty->print(" %s: collect because cmsSpace says so ",
1637         short_name());
1638     }
1639     return true;
1640   }
1641   return false;
1642 }
1643 
1644 void ConcurrentMarkSweepGeneration::collect(bool   full,
1645                                             bool   clear_all_soft_refs,
1646                                             size_t size,
1647                                             bool   tlab)
1648 {
1649   collector()->collect(full, clear_all_soft_refs, size, tlab);
1650 }
1651 
1652 void CMSCollector::collect(bool   full,
1653                            bool   clear_all_soft_refs,
1654                            size_t size,
1655                            bool   tlab)
1656 {
1657   if (!UseCMSCollectionPassing && _collectorState > Idling) {
1658     // For debugging purposes skip the collection if the state
1659     // is not currently idle
1660     if (TraceCMSState) {
1661       gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " skipped full:%d CMS state %d",
1662         Thread::current(), full, _collectorState);
1663     }
1664     return;
1665   }
1666 
1667   // The following "if" branch is present for defensive reasons.
1668   // In the current uses of this interface, it can be replaced with:
1669   // assert(!GC_locker.is_active(), "Can't be called otherwise");
1670   // But I am not placing that assert here to allow future
1671   // generality in invoking this interface.
1672   if (GC_locker::is_active()) {
1673     // A consistency test for GC_locker
1674     assert(GC_locker::needs_gc(), "Should have been set already");
1675     // Skip this foreground collection, instead
1676     // expanding the heap if necessary.
1677     // Need the free list locks for the call to free() in compute_new_size()
1678     compute_new_size();
1679     return;
1680   }
1681   acquire_control_and_collect(full, clear_all_soft_refs);
1682   _full_gcs_since_conc_gc++;
1683 
1684 }
1685 
1686 void CMSCollector::request_full_gc(unsigned int full_gc_count) {
1687   GenCollectedHeap* gch = GenCollectedHeap::heap();
1688   unsigned int gc_count = gch->total_full_collections();
1689   if (gc_count == full_gc_count) {
1690     MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag);
1691     _full_gc_requested = true;
1692     CGC_lock->notify();   // nudge CMS thread
1693   } else {
1694     assert(gc_count > full_gc_count, "Error: causal loop");
1695   }
1696 }
1697 
1698 
1699 // The foreground and background collectors need to coordinate in order
1700 // to make sure that they do not mutually interfere with CMS collections.
1701 // When a background collection is active,
1702 // the foreground collector may need to take over (preempt) and
1703 // synchronously complete an ongoing collection. Depending on the
1704 // frequency of the background collections and the heap usage
1705 // of the application, this preemption can be seldom or frequent.
1706 // There are only certain
1707 // points in the background collection that the "collection-baton"
1708 // can be passed to the foreground collector.
1709 //
1710 // The foreground collector will wait for the baton before
1711 // starting any part of the collection.  The foreground collector
1712 // will only wait at one location.
1713 //
1714 // The background collector will yield the baton before starting a new
1715 // phase of the collection (e.g., before initial marking, marking from roots,
1716 // precleaning, final re-mark, sweep etc.)  This is normally done at the head
1717 // of the loop which switches the phases. The background collector does some
1718 // of the phases (initial mark, final re-mark) with the world stopped.
1719 // Because of locking involved in stopping the world,
1720 // the foreground collector should not block waiting for the background
1721 // collector when it is doing a stop-the-world phase.  The background
1722 // collector will yield the baton at an additional point just before
1723 // it enters a stop-the-world phase.  Once the world is stopped, the
1724 // background collector checks the phase of the collection.  If the
1725 // phase has not changed, it proceeds with the collection.  If the
1726 // phase has changed, it skips that phase of the collection.  See
1727 // the comments on the use of the Heap_lock in collect_in_background().
1728 //
1729 // Variable used in baton passing.
1730 //   _foregroundGCIsActive - Set to true by the foreground collector when
1731 //      it wants the baton.  The foreground clears it when it has finished
1732 //      the collection.
1733 //   _foregroundGCShouldWait - Set to true by the background collector
1734 //        when it is running.  The foreground collector waits while
1735 //      _foregroundGCShouldWait is true.
1736 //  CGC_lock - monitor used to protect access to the above variables
1737 //      and to notify the foreground and background collectors.
1738 //  _collectorState - current state of the CMS collection.
1739 //
1740 // The foreground collector
1741 //   acquires the CGC_lock
1742 //   sets _foregroundGCIsActive
1743 //   waits on the CGC_lock for _foregroundGCShouldWait to be false
1744 //     various locks acquired in preparation for the collection
1745 //     are released so as not to block the background collector
1746 //     that is in the midst of a collection
1747 //   proceeds with the collection
1748 //   clears _foregroundGCIsActive
1749 //   returns
1750 //
1751 // The background collector in a loop iterating on the phases of the
1752 //      collection
1753 //   acquires the CGC_lock
1754 //   sets _foregroundGCShouldWait
1755 //   if _foregroundGCIsActive is set
1756 //     clears _foregroundGCShouldWait, notifies _CGC_lock
1757 //     waits on _CGC_lock for _foregroundGCIsActive to become false
1758 //     and exits the loop.
1759 //   otherwise
1760 //     proceed with that phase of the collection
1761 //     if the phase is a stop-the-world phase,
1762 //       yield the baton once more just before enqueueing
1763 //       the stop-world CMS operation (executed by the VM thread).
1764 //   returns after all phases of the collection are done
1765 //
1766 
1767 void CMSCollector::acquire_control_and_collect(bool full,
1768         bool clear_all_soft_refs) {
1769   assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
1770   assert(!Thread::current()->is_ConcurrentGC_thread(),
1771          "shouldn't try to acquire control from self!");
1772 
1773   // Start the protocol for acquiring control of the
1774   // collection from the background collector (aka CMS thread).
1775   assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1776          "VM thread should have CMS token");
1777   // Remember the possibly interrupted state of an ongoing
1778   // concurrent collection
1779   CollectorState first_state = _collectorState;
1780 
1781   // Signal to a possibly ongoing concurrent collection that
1782   // we want to do a foreground collection.
1783   _foregroundGCIsActive = true;
1784 
1785   // Disable incremental mode during a foreground collection.
1786   ICMSDisabler icms_disabler;
1787 
1788   // release locks and wait for a notify from the background collector
1789   // releasing the locks in only necessary for phases which
1790   // do yields to improve the granularity of the collection.
1791   assert_lock_strong(bitMapLock());
1792   // We need to lock the Free list lock for the space that we are
1793   // currently collecting.
1794   assert(haveFreelistLocks(), "Must be holding free list locks");
1795   bitMapLock()->unlock();
1796   releaseFreelistLocks();
1797   {
1798     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1799     if (_foregroundGCShouldWait) {
1800       // We are going to be waiting for action for the CMS thread;
1801       // it had better not be gone (for instance at shutdown)!
1802       assert(ConcurrentMarkSweepThread::cmst() != NULL,
1803              "CMS thread must be running");
1804       // Wait here until the background collector gives us the go-ahead
1805       ConcurrentMarkSweepThread::clear_CMS_flag(
1806         ConcurrentMarkSweepThread::CMS_vm_has_token);  // release token
1807       // Get a possibly blocked CMS thread going:
1808       //   Note that we set _foregroundGCIsActive true above,
1809       //   without protection of the CGC_lock.
1810       CGC_lock->notify();
1811       assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(),
1812              "Possible deadlock");
1813       while (_foregroundGCShouldWait) {
1814         // wait for notification
1815         CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1816         // Possibility of delay/starvation here, since CMS token does
1817         // not know to give priority to VM thread? Actually, i think
1818         // there wouldn't be any delay/starvation, but the proof of
1819         // that "fact" (?) appears non-trivial. XXX 20011219YSR
1820       }
1821       ConcurrentMarkSweepThread::set_CMS_flag(
1822         ConcurrentMarkSweepThread::CMS_vm_has_token);
1823     }
1824   }
1825   // The CMS_token is already held.  Get back the other locks.
1826   assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1827          "VM thread should have CMS token");
1828   getFreelistLocks();
1829   bitMapLock()->lock_without_safepoint_check();
1830   if (TraceCMSState) {
1831     gclog_or_tty->print_cr("CMS foreground collector has asked for control "
1832       INTPTR_FORMAT " with first state %d", Thread::current(), first_state);
1833     gclog_or_tty->print_cr("    gets control with state %d", _collectorState);
1834   }
1835 
1836   // Check if we need to do a compaction, or if not, whether
1837   // we need to start the mark-sweep from scratch.
1838   bool should_compact    = false;
1839   bool should_start_over = false;
1840   decide_foreground_collection_type(clear_all_soft_refs,
1841     &should_compact, &should_start_over);
1842 
1843 NOT_PRODUCT(
1844   if (RotateCMSCollectionTypes) {
1845     if (_cmsGen->debug_collection_type() ==
1846         ConcurrentMarkSweepGeneration::MSC_foreground_collection_type) {
1847       should_compact = true;
1848     } else if (_cmsGen->debug_collection_type() ==
1849                ConcurrentMarkSweepGeneration::MS_foreground_collection_type) {
1850       should_compact = false;
1851     }
1852   }
1853 )
1854 
1855   if (PrintGCDetails && first_state > Idling) {
1856     GCCause::Cause cause = GenCollectedHeap::heap()->gc_cause();
1857     if (GCCause::is_user_requested_gc(cause) ||
1858         GCCause::is_serviceability_requested_gc(cause)) {
1859       gclog_or_tty->print(" (concurrent mode interrupted)");
1860     } else {
1861       gclog_or_tty->print(" (concurrent mode failure)");
1862     }
1863   }
1864 
1865   if (should_compact) {
1866     // If the collection is being acquired from the background
1867     // collector, there may be references on the discovered
1868     // references lists that have NULL referents (being those
1869     // that were concurrently cleared by a mutator) or
1870     // that are no longer active (having been enqueued concurrently
1871     // by the mutator).
1872     // Scrub the list of those references because Mark-Sweep-Compact
1873     // code assumes referents are not NULL and that all discovered
1874     // Reference objects are active.
1875     ref_processor()->clean_up_discovered_references();
1876 
1877     do_compaction_work(clear_all_soft_refs);
1878 
1879     // Has the GC time limit been exceeded?
1880     DefNewGeneration* young_gen = _young_gen->as_DefNewGeneration();
1881     size_t max_eden_size = young_gen->max_capacity() -
1882                            young_gen->to()->capacity() -
1883                            young_gen->from()->capacity();
1884     GenCollectedHeap* gch = GenCollectedHeap::heap();
1885     GCCause::Cause gc_cause = gch->gc_cause();
1886     size_policy()->check_gc_overhead_limit(_young_gen->used(),
1887                                            young_gen->eden()->used(),
1888                                            _cmsGen->max_capacity(),
1889                                            max_eden_size,
1890                                            full,
1891                                            gc_cause,
1892                                            gch->collector_policy());
1893   } else {
1894     do_mark_sweep_work(clear_all_soft_refs, first_state,
1895       should_start_over);
1896   }
1897   // Reset the expansion cause, now that we just completed
1898   // a collection cycle.
1899   clear_expansion_cause();
1900   _foregroundGCIsActive = false;
1901   return;
1902 }
1903 
1904 // Resize the perm generation and the tenured generation
1905 // after obtaining the free list locks for the
1906 // two generations.
1907 void CMSCollector::compute_new_size() {
1908   assert_locked_or_safepoint(Heap_lock);
1909   FreelistLocker z(this);
1910   _permGen->compute_new_size();
1911   _cmsGen->compute_new_size();
1912 }
1913 
1914 // A work method used by foreground collection to determine
1915 // what type of collection (compacting or not, continuing or fresh)
1916 // it should do.
1917 // NOTE: the intent is to make UseCMSCompactAtFullCollection
1918 // and CMSCompactWhenClearAllSoftRefs the default in the future
1919 // and do away with the flags after a suitable period.
1920 void CMSCollector::decide_foreground_collection_type(
1921   bool clear_all_soft_refs, bool* should_compact,
1922   bool* should_start_over) {
1923   // Normally, we'll compact only if the UseCMSCompactAtFullCollection
1924   // flag is set, and we have either requested a System.gc() or
1925   // the number of full gc's since the last concurrent cycle
1926   // has exceeded the threshold set by CMSFullGCsBeforeCompaction,
1927   // or if an incremental collection has failed
1928   GenCollectedHeap* gch = GenCollectedHeap::heap();
1929   assert(gch->collector_policy()->is_two_generation_policy(),
1930          "You may want to check the correctness of the following");
1931   // Inform cms gen if this was due to partial collection failing.
1932   // The CMS gen may use this fact to determine its expansion policy.
1933   if (gch->incremental_collection_will_fail(false /* don't consult_young */)) {
1934     assert(!_cmsGen->incremental_collection_failed(),
1935            "Should have been noticed, reacted to and cleared");
1936     _cmsGen->set_incremental_collection_failed();
1937   }
1938   *should_compact =
1939     UseCMSCompactAtFullCollection &&
1940     ((_full_gcs_since_conc_gc >= CMSFullGCsBeforeCompaction) ||
1941      GCCause::is_user_requested_gc(gch->gc_cause()) ||
1942      gch->incremental_collection_will_fail(true /* consult_young */));
1943   *should_start_over = false;
1944   if (clear_all_soft_refs && !*should_compact) {
1945     // We are about to do a last ditch collection attempt
1946     // so it would normally make sense to do a compaction
1947     // to reclaim as much space as possible.
1948     if (CMSCompactWhenClearAllSoftRefs) {
1949       // Default: The rationale is that in this case either
1950       // we are past the final marking phase, in which case
1951       // we'd have to start over, or so little has been done
1952       // that there's little point in saving that work. Compaction
1953       // appears to be the sensible choice in either case.
1954       *should_compact = true;
1955     } else {
1956       // We have been asked to clear all soft refs, but not to
1957       // compact. Make sure that we aren't past the final checkpoint
1958       // phase, for that is where we process soft refs. If we are already
1959       // past that phase, we'll need to redo the refs discovery phase and
1960       // if necessary clear soft refs that weren't previously
1961       // cleared. We do so by remembering the phase in which
1962       // we came in, and if we are past the refs processing
1963       // phase, we'll choose to just redo the mark-sweep
1964       // collection from scratch.
1965       if (_collectorState > FinalMarking) {
1966         // We are past the refs processing phase;
1967         // start over and do a fresh synchronous CMS cycle
1968         _collectorState = Resetting; // skip to reset to start new cycle
1969         reset(false /* == !asynch */);
1970         *should_start_over = true;
1971       } // else we can continue a possibly ongoing current cycle
1972     }
1973   }
1974 }
1975 
1976 // A work method used by the foreground collector to do
1977 // a mark-sweep-compact.
1978 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) {
1979   GenCollectedHeap* gch = GenCollectedHeap::heap();
1980 
1981   STWGCTimer* gc_timer = GenMarkSweep::gc_timer();
1982   gc_timer->register_gc_start(os::elapsed_counter());
1983 
1984   SerialOldTracer* gc_tracer = GenMarkSweep::gc_tracer();
1985   gc_tracer->report_gc_start(gch->gc_cause(), gc_timer->gc_start());
1986 
1987   GCTraceTime t("CMS:MSC ", PrintGCDetails && Verbose, true, NULL);
1988   if (PrintGC && Verbose && !(GCCause::is_user_requested_gc(gch->gc_cause()))) {
1989     gclog_or_tty->print_cr("Compact ConcurrentMarkSweepGeneration after %d "
1990       "collections passed to foreground collector", _full_gcs_since_conc_gc);
1991   }
1992 
1993   // Sample collection interval time and reset for collection pause.
1994   if (UseAdaptiveSizePolicy) {
1995     size_policy()->msc_collection_begin();
1996   }
1997 
1998   // Temporarily widen the span of the weak reference processing to
1999   // the entire heap.
2000   MemRegion new_span(GenCollectedHeap::heap()->reserved_region());
2001   ReferenceProcessorSpanMutator rp_mut_span(ref_processor(), new_span);
2002   // Temporarily, clear the "is_alive_non_header" field of the
2003   // reference processor.
2004   ReferenceProcessorIsAliveMutator rp_mut_closure(ref_processor(), NULL);
2005   // Temporarily make reference _processing_ single threaded (non-MT).
2006   ReferenceProcessorMTProcMutator rp_mut_mt_processing(ref_processor(), false);
2007   // Temporarily make refs discovery atomic
2008   ReferenceProcessorAtomicMutator rp_mut_atomic(ref_processor(), true);
2009   // Temporarily make reference _discovery_ single threaded (non-MT)
2010   ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
2011 
2012   ref_processor()->set_enqueuing_is_done(false);
2013   ref_processor()->enable_discovery(false /*verify_disabled*/, false /*check_no_refs*/);
2014   ref_processor()->setup_policy(clear_all_soft_refs);
2015   // If an asynchronous collection finishes, the _modUnionTable is
2016   // all clear.  If we are assuming the collection from an asynchronous
2017   // collection, clear the _modUnionTable.
2018   assert(_collectorState != Idling || _modUnionTable.isAllClear(),
2019     "_modUnionTable should be clear if the baton was not passed");
2020   _modUnionTable.clear_all();
2021 
2022   // We must adjust the allocation statistics being maintained
2023   // in the free list space. We do so by reading and clearing
2024   // the sweep timer and updating the block flux rate estimates below.
2025   assert(!_intra_sweep_timer.is_active(), "_intra_sweep_timer should be inactive");
2026   if (_inter_sweep_timer.is_active()) {
2027     _inter_sweep_timer.stop();
2028     // Note that we do not use this sample to update the _inter_sweep_estimate.
2029     _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
2030                                             _inter_sweep_estimate.padded_average(),
2031                                             _intra_sweep_estimate.padded_average());
2032   }
2033 
2034   GenMarkSweep::invoke_at_safepoint(_cmsGen->level(),
2035     ref_processor(), clear_all_soft_refs);
2036   #ifdef ASSERT
2037     CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
2038     size_t free_size = cms_space->free();
2039     assert(free_size ==
2040            pointer_delta(cms_space->end(), cms_space->compaction_top())
2041            * HeapWordSize,
2042       "All the free space should be compacted into one chunk at top");
2043     assert(cms_space->dictionary()->total_chunk_size(
2044                                       debug_only(cms_space->freelistLock())) == 0 ||
2045            cms_space->totalSizeInIndexedFreeLists() == 0,
2046       "All the free space should be in a single chunk");
2047     size_t num = cms_space->totalCount();
2048     assert((free_size == 0 && num == 0) ||
2049            (free_size > 0  && (num == 1 || num == 2)),
2050          "There should be at most 2 free chunks after compaction");
2051   #endif // ASSERT
2052   _collectorState = Resetting;
2053   assert(_restart_addr == NULL,
2054          "Should have been NULL'd before baton was passed");
2055   reset(false /* == !asynch */);
2056   _cmsGen->reset_after_compaction();
2057   _concurrent_cycles_since_last_unload = 0;
2058 
2059   if (verifying() && !should_unload_classes()) {
2060     perm_gen_verify_bit_map()->clear_all();
2061   }
2062 
2063   // Clear any data recorded in the PLAB chunk arrays.
2064   if (_survivor_plab_array != NULL) {
2065     reset_survivor_plab_arrays();
2066   }
2067 
2068   // Adjust the per-size allocation stats for the next epoch.
2069   _cmsGen->cmsSpace()->endSweepFLCensus(sweep_count() /* fake */);
2070   // Restart the "inter sweep timer" for the next epoch.
2071   _inter_sweep_timer.reset();
2072   _inter_sweep_timer.start();
2073 
2074   // Sample collection pause time and reset for collection interval.
2075   if (UseAdaptiveSizePolicy) {
2076     size_policy()->msc_collection_end(gch->gc_cause());
2077   }
2078 
2079   gc_timer->register_gc_end(os::elapsed_counter());
2080 
2081   gc_tracer->report_gc_end(gc_timer->gc_end(), gc_timer->time_partitions());
2082 
2083   // For a mark-sweep-compact, compute_new_size() will be called
2084   // in the heap's do_collection() method.
2085 }
2086 
2087 // A work method used by the foreground collector to do
2088 // a mark-sweep, after taking over from a possibly on-going
2089 // concurrent mark-sweep collection.
2090 void CMSCollector::do_mark_sweep_work(bool clear_all_soft_refs,
2091   CollectorState first_state, bool should_start_over) {
2092   if (PrintGC && Verbose) {
2093     gclog_or_tty->print_cr("Pass concurrent collection to foreground "
2094       "collector with count %d",
2095       _full_gcs_since_conc_gc);
2096   }
2097   switch (_collectorState) {
2098     case Idling:
2099       if (first_state == Idling || should_start_over) {
2100         // The background GC was not active, or should
2101         // restarted from scratch;  start the cycle.
2102         _collectorState = InitialMarking;
2103       }
2104       // If first_state was not Idling, then a background GC
2105       // was in progress and has now finished.  No need to do it
2106       // again.  Leave the state as Idling.
2107       break;
2108     case Precleaning:
2109       // In the foreground case don't do the precleaning since
2110       // it is not done concurrently and there is extra work
2111       // required.
2112       _collectorState = FinalMarking;
2113   }
2114   if (PrintGCDetails &&
2115       (_collectorState > Idling ||
2116        !GCCause::is_user_requested_gc(GenCollectedHeap::heap()->gc_cause()))) {
2117     gclog_or_tty->print(" (concurrent mode failure)");
2118   }
2119   collect_in_foreground(clear_all_soft_refs);
2120 
2121   // For a mark-sweep, compute_new_size() will be called
2122   // in the heap's do_collection() method.
2123 }
2124 
2125 
2126 void CMSCollector::getFreelistLocks() const {
2127   // Get locks for all free lists in all generations that this
2128   // collector is responsible for
2129   _cmsGen->freelistLock()->lock_without_safepoint_check();
2130   _permGen->freelistLock()->lock_without_safepoint_check();
2131 }
2132 
2133 void CMSCollector::releaseFreelistLocks() const {
2134   // Release locks for all free lists in all generations that this
2135   // collector is responsible for
2136   _cmsGen->freelistLock()->unlock();
2137   _permGen->freelistLock()->unlock();
2138 }
2139 
2140 bool CMSCollector::haveFreelistLocks() const {
2141   // Check locks for all free lists in all generations that this
2142   // collector is responsible for
2143   assert_lock_strong(_cmsGen->freelistLock());
2144   assert_lock_strong(_permGen->freelistLock());
2145   PRODUCT_ONLY(ShouldNotReachHere());
2146   return true;
2147 }
2148 
2149 // A utility class that is used by the CMS collector to
2150 // temporarily "release" the foreground collector from its
2151 // usual obligation to wait for the background collector to
2152 // complete an ongoing phase before proceeding.
2153 class ReleaseForegroundGC: public StackObj {
2154  private:
2155   CMSCollector* _c;
2156  public:
2157   ReleaseForegroundGC(CMSCollector* c) : _c(c) {
2158     assert(_c->_foregroundGCShouldWait, "Else should not need to call");
2159     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2160     // allow a potentially blocked foreground collector to proceed
2161     _c->_foregroundGCShouldWait = false;
2162     if (_c->_foregroundGCIsActive) {
2163       CGC_lock->notify();
2164     }
2165     assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2166            "Possible deadlock");
2167   }
2168 
2169   ~ReleaseForegroundGC() {
2170     assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?");
2171     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2172     _c->_foregroundGCShouldWait = true;
2173   }
2174 };
2175 
2176 // There are separate collect_in_background and collect_in_foreground because of
2177 // the different locking requirements of the background collector and the
2178 // foreground collector.  There was originally an attempt to share
2179 // one "collect" method between the background collector and the foreground
2180 // collector but the if-then-else required made it cleaner to have
2181 // separate methods.
2182 void CMSCollector::collect_in_background(bool clear_all_soft_refs) {
2183   assert(Thread::current()->is_ConcurrentGC_thread(),
2184     "A CMS asynchronous collection is only allowed on a CMS thread.");
2185 
2186   GenCollectedHeap* gch = GenCollectedHeap::heap();
2187   {
2188     bool safepoint_check = Mutex::_no_safepoint_check_flag;
2189     MutexLockerEx hl(Heap_lock, safepoint_check);
2190     FreelistLocker fll(this);
2191     MutexLockerEx x(CGC_lock, safepoint_check);
2192     if (_foregroundGCIsActive || !UseAsyncConcMarkSweepGC) {
2193       // The foreground collector is active or we're
2194       // not using asynchronous collections.  Skip this
2195       // background collection.
2196       assert(!_foregroundGCShouldWait, "Should be clear");
2197       return;
2198     } else {
2199       assert(_collectorState == Idling, "Should be idling before start.");
2200       _collectorState = InitialMarking;
2201       // Reset the expansion cause, now that we are about to begin
2202       // a new cycle.
2203       clear_expansion_cause();
2204     }
2205     // Decide if we want to enable class unloading as part of the
2206     // ensuing concurrent GC cycle.
2207     update_should_unload_classes();
2208     _full_gc_requested = false;           // acks all outstanding full gc requests
2209     // Signal that we are about to start a collection
2210     gch->increment_total_full_collections();  // ... starting a collection cycle
2211     _collection_count_start = gch->total_full_collections();
2212   }
2213 
2214   // Used for PrintGC
2215   size_t prev_used;
2216   if (PrintGC && Verbose) {
2217     prev_used = _cmsGen->used(); // XXXPERM
2218   }
2219 
2220   // The change of the collection state is normally done at this level;
2221   // the exceptions are phases that are executed while the world is
2222   // stopped.  For those phases the change of state is done while the
2223   // world is stopped.  For baton passing purposes this allows the
2224   // background collector to finish the phase and change state atomically.
2225   // The foreground collector cannot wait on a phase that is done
2226   // while the world is stopped because the foreground collector already
2227   // has the world stopped and would deadlock.
2228   while (_collectorState != Idling) {
2229     if (TraceCMSState) {
2230       gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
2231         Thread::current(), _collectorState);
2232     }
2233     // The foreground collector
2234     //   holds the Heap_lock throughout its collection.
2235     //   holds the CMS token (but not the lock)
2236     //     except while it is waiting for the background collector to yield.
2237     //
2238     // The foreground collector should be blocked (not for long)
2239     //   if the background collector is about to start a phase
2240     //   executed with world stopped.  If the background
2241     //   collector has already started such a phase, the
2242     //   foreground collector is blocked waiting for the
2243     //   Heap_lock.  The stop-world phases (InitialMarking and FinalMarking)
2244     //   are executed in the VM thread.
2245     //
2246     // The locking order is
2247     //   PendingListLock (PLL)  -- if applicable (FinalMarking)
2248     //   Heap_lock  (both this & PLL locked in VM_CMS_Operation::prologue())
2249     //   CMS token  (claimed in
2250     //                stop_world_and_do() -->
2251     //                  safepoint_synchronize() -->
2252     //                    CMSThread::synchronize())
2253 
2254     {
2255       // Check if the FG collector wants us to yield.
2256       CMSTokenSync x(true); // is cms thread
2257       if (waitForForegroundGC()) {
2258         // We yielded to a foreground GC, nothing more to be
2259         // done this round.
2260         assert(_foregroundGCShouldWait == false, "We set it to false in "
2261                "waitForForegroundGC()");
2262         if (TraceCMSState) {
2263           gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2264             " exiting collection CMS state %d",
2265             Thread::current(), _collectorState);
2266         }
2267         return;
2268       } else {
2269         // The background collector can run but check to see if the
2270         // foreground collector has done a collection while the
2271         // background collector was waiting to get the CGC_lock
2272         // above.  If yes, break so that _foregroundGCShouldWait
2273         // is cleared before returning.
2274         if (_collectorState == Idling) {
2275           break;
2276         }
2277       }
2278     }
2279 
2280     assert(_foregroundGCShouldWait, "Foreground collector, if active, "
2281       "should be waiting");
2282 
2283     switch (_collectorState) {
2284       case InitialMarking:
2285         {
2286           ReleaseForegroundGC x(this);
2287           stats().record_cms_begin();


2288           VM_CMS_Initial_Mark initial_mark_op(this);
2289           VMThread::execute(&initial_mark_op);
2290         }
2291         // The collector state may be any legal state at this point
2292         // since the background collector may have yielded to the
2293         // foreground collector.
2294         break;
2295       case Marking:
2296         // initial marking in checkpointRootsInitialWork has been completed
2297         if (markFromRoots(true)) { // we were successful
2298           assert(_collectorState == Precleaning, "Collector state should "
2299             "have changed");
2300         } else {
2301           assert(_foregroundGCIsActive, "Internal state inconsistency");
2302         }
2303         break;
2304       case Precleaning:
2305         if (UseAdaptiveSizePolicy) {
2306           size_policy()->concurrent_precleaning_begin();
2307         }
2308         // marking from roots in markFromRoots has been completed
2309         preclean();
2310         if (UseAdaptiveSizePolicy) {
2311           size_policy()->concurrent_precleaning_end();
2312         }
2313         assert(_collectorState == AbortablePreclean ||
2314                _collectorState == FinalMarking,
2315                "Collector state should have changed");
2316         break;
2317       case AbortablePreclean:
2318         if (UseAdaptiveSizePolicy) {
2319         size_policy()->concurrent_phases_resume();
2320         }
2321         abortable_preclean();
2322         if (UseAdaptiveSizePolicy) {
2323           size_policy()->concurrent_precleaning_end();
2324         }
2325         assert(_collectorState == FinalMarking, "Collector state should "
2326           "have changed");
2327         break;
2328       case FinalMarking:
2329         {
2330           ReleaseForegroundGC x(this);
2331 
2332           VM_CMS_Final_Remark final_remark_op(this);
2333           VMThread::execute(&final_remark_op);
2334         }
2335         assert(_foregroundGCShouldWait, "block post-condition");
2336         break;
2337       case Sweeping:
2338         if (UseAdaptiveSizePolicy) {
2339           size_policy()->concurrent_sweeping_begin();
2340         }
2341         // final marking in checkpointRootsFinal has been completed
2342         sweep(true);
2343         assert(_collectorState == Resizing, "Collector state change "
2344           "to Resizing must be done under the free_list_lock");
2345         _full_gcs_since_conc_gc = 0;
2346 
2347         // Stop the timers for adaptive size policy for the concurrent phases
2348         if (UseAdaptiveSizePolicy) {
2349           size_policy()->concurrent_sweeping_end();
2350           size_policy()->concurrent_phases_end(gch->gc_cause(),
2351                                              gch->prev_gen(_cmsGen)->capacity(),
2352                                              _cmsGen->free());
2353         }
2354 
2355       case Resizing: {
2356         // Sweeping has been completed...
2357         // At this point the background collection has completed.
2358         // Don't move the call to compute_new_size() down
2359         // into code that might be executed if the background
2360         // collection was preempted.
2361         {
2362           ReleaseForegroundGC x(this);   // unblock FG collection
2363           MutexLockerEx       y(Heap_lock, Mutex::_no_safepoint_check_flag);
2364           CMSTokenSync        z(true);   // not strictly needed.
2365           if (_collectorState == Resizing) {
2366             compute_new_size();
2367             _collectorState = Resetting;
2368           } else {
2369             assert(_collectorState == Idling, "The state should only change"
2370                    " because the foreground collector has finished the collection");
2371           }
2372         }
2373         break;
2374       }
2375       case Resetting:
2376         // CMS heap resizing has been completed
2377         reset(true);
2378         assert(_collectorState == Idling, "Collector state should "
2379           "have changed");
2380         stats().record_cms_end();
2381         // Don't move the concurrent_phases_end() and compute_new_size()
2382         // calls to here because a preempted background collection
2383         // has it's state set to "Resetting".
2384         break;
2385       case Idling:
2386       default:
2387         ShouldNotReachHere();
2388         break;
2389     }
2390     if (TraceCMSState) {
2391       gclog_or_tty->print_cr("  Thread " INTPTR_FORMAT " done - next CMS state %d",
2392         Thread::current(), _collectorState);
2393     }
2394     assert(_foregroundGCShouldWait, "block post-condition");
2395   }
2396 
2397   // Should this be in gc_epilogue?
2398   collector_policy()->counters()->update_counters();
2399 
2400   {
2401     // Clear _foregroundGCShouldWait and, in the event that the
2402     // foreground collector is waiting, notify it, before
2403     // returning.
2404     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2405     _foregroundGCShouldWait = false;
2406     if (_foregroundGCIsActive) {
2407       CGC_lock->notify();
2408     }
2409     assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2410            "Possible deadlock");
2411   }
2412   if (TraceCMSState) {
2413     gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2414       " exiting collection CMS state %d",
2415       Thread::current(), _collectorState);
2416   }
2417   if (PrintGC && Verbose) {
2418     _cmsGen->print_heap_change(prev_used);
2419   }
2420 }
2421 
2422 void CMSCollector::register_gc_start(GCCause::Cause cause) {
2423   _cms_start_registered = true;

2424   _gc_timer_cm->register_gc_start(os::elapsed_counter());
2425   _gc_tracer_cm->report_gc_start(cause, _gc_timer_cm->gc_start());
2426 }
2427 
2428 void CMSCollector::register_gc_end() {
2429   if (_cms_start_registered) {
2430     _gc_timer_cm->register_gc_end(os::elapsed_counter());
2431     _gc_tracer_cm->report_gc_end(_gc_timer_cm->gc_end(), _gc_timer_cm->time_partitions());
2432     _cms_start_registered = false;
2433   }
2434 }
2435 
2436 void CMSCollector::collect_in_foreground(bool clear_all_soft_refs) {
2437   assert(_foregroundGCIsActive && !_foregroundGCShouldWait,
2438          "Foreground collector should be waiting, not executing");
2439   assert(Thread::current()->is_VM_thread(), "A foreground collection"
2440     "may only be done by the VM Thread with the world stopped");
2441   assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
2442          "VM thread should have CMS token");
2443 
2444   NOT_PRODUCT(GCTraceTime t("CMS:MS (foreground) ", PrintGCDetails && Verbose,
2445     true, NULL);)
2446   if (UseAdaptiveSizePolicy) {
2447     size_policy()->ms_collection_begin();
2448   }
2449   COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact);
2450 
2451   HandleMark hm;  // Discard invalid handles created during verification
2452 
2453   if (VerifyBeforeGC &&
2454       GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2455     Universe::verify();
2456   }
2457 
2458   // Snapshot the soft reference policy to be used in this collection cycle.
2459   ref_processor()->setup_policy(clear_all_soft_refs);
2460 
2461   bool init_mark_was_synchronous = false; // until proven otherwise
2462   while (_collectorState != Idling) {
2463     if (TraceCMSState) {
2464       gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
2465         Thread::current(), _collectorState);
2466     }
2467     switch (_collectorState) {
2468       case InitialMarking:
2469         register_gc_start(GenCollectedHeap::heap()->gc_cause());
2470         init_mark_was_synchronous = true;  // fact to be exploited in re-mark
2471         checkpointRootsInitial(false);
2472         assert(_collectorState == Marking, "Collector state should have changed"
2473           " within checkpointRootsInitial()");
2474         break;
2475       case Marking:
2476         // initial marking in checkpointRootsInitialWork has been completed
2477         if (VerifyDuringGC &&
2478             GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2479           gclog_or_tty->print("Verify before initial mark: ");
2480           Universe::verify();
2481         }
2482         {
2483           bool res = markFromRoots(false);
2484           assert(res && _collectorState == FinalMarking, "Collector state should "
2485             "have changed");
2486           break;
2487         }
2488       case FinalMarking:
2489         if (VerifyDuringGC &&
2490             GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2491           gclog_or_tty->print("Verify before re-mark: ");
2492           Universe::verify();
2493         }
2494         checkpointRootsFinal(false, clear_all_soft_refs,
2495                              init_mark_was_synchronous);
2496         assert(_collectorState == Sweeping, "Collector state should not "
2497           "have changed within checkpointRootsFinal()");
2498         break;
2499       case Sweeping:
2500         // final marking in checkpointRootsFinal has been completed
2501         if (VerifyDuringGC &&
2502             GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2503           gclog_or_tty->print("Verify before sweep: ");
2504           Universe::verify();
2505         }
2506         sweep(false);
2507         assert(_collectorState == Resizing, "Incorrect state");
2508         break;
2509       case Resizing: {
2510         // Sweeping has been completed; the actual resize in this case
2511         // is done separately; nothing to be done in this state.
2512         _collectorState = Resetting;
2513         break;
2514       }
2515       case Resetting:
2516         // The heap has been resized.
2517         if (VerifyDuringGC &&
2518             GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2519           gclog_or_tty->print("Verify before reset: ");
2520           Universe::verify();
2521         }
2522         reset(false);
2523         assert(_collectorState == Idling, "Collector state should "
2524           "have changed");
2525         break;
2526       case Precleaning:
2527       case AbortablePreclean:
2528         // Elide the preclean phase
2529         _collectorState = FinalMarking;
2530         break;
2531       default:
2532         ShouldNotReachHere();
2533     }
2534     if (TraceCMSState) {
2535       gclog_or_tty->print_cr("  Thread " INTPTR_FORMAT " done - next CMS state %d",
2536         Thread::current(), _collectorState);
2537     }
2538   }
2539 
2540   if (UseAdaptiveSizePolicy) {
2541     GenCollectedHeap* gch = GenCollectedHeap::heap();
2542     size_policy()->ms_collection_end(gch->gc_cause());
2543   }
2544 
2545   if (VerifyAfterGC &&
2546       GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2547     Universe::verify();
2548   }
2549   if (TraceCMSState) {
2550     gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2551       " exiting collection CMS state %d",
2552       Thread::current(), _collectorState);
2553   }
2554 }
2555 
2556 bool CMSCollector::waitForForegroundGC() {
2557   bool res = false;
2558   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2559          "CMS thread should have CMS token");
2560   // Block the foreground collector until the
2561   // background collectors decides whether to
2562   // yield.
2563   MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2564   _foregroundGCShouldWait = true;
2565   if (_foregroundGCIsActive) {
2566     // The background collector yields to the
2567     // foreground collector and returns a value
2568     // indicating that it has yielded.  The foreground
2569     // collector can proceed.
2570     res = true;
2571     _foregroundGCShouldWait = false;
2572     ConcurrentMarkSweepThread::clear_CMS_flag(
2573       ConcurrentMarkSweepThread::CMS_cms_has_token);
2574     ConcurrentMarkSweepThread::set_CMS_flag(
2575       ConcurrentMarkSweepThread::CMS_cms_wants_token);
2576     // Get a possibly blocked foreground thread going
2577     CGC_lock->notify();
2578     if (TraceCMSState) {
2579       gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d",
2580         Thread::current(), _collectorState);
2581     }
2582     while (_foregroundGCIsActive) {
2583       CGC_lock->wait(Mutex::_no_safepoint_check_flag);
2584     }
2585     ConcurrentMarkSweepThread::set_CMS_flag(
2586       ConcurrentMarkSweepThread::CMS_cms_has_token);
2587     ConcurrentMarkSweepThread::clear_CMS_flag(
2588       ConcurrentMarkSweepThread::CMS_cms_wants_token);
2589   }
2590   if (TraceCMSState) {
2591     gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d",
2592       Thread::current(), _collectorState);
2593   }
2594   return res;
2595 }
2596 
2597 // Because of the need to lock the free lists and other structures in
2598 // the collector, common to all the generations that the collector is
2599 // collecting, we need the gc_prologues of individual CMS generations
2600 // delegate to their collector. It may have been simpler had the
2601 // current infrastructure allowed one to call a prologue on a
2602 // collector. In the absence of that we have the generation's
2603 // prologue delegate to the collector, which delegates back
2604 // some "local" work to a worker method in the individual generations
2605 // that it's responsible for collecting, while itself doing any
2606 // work common to all generations it's responsible for. A similar
2607 // comment applies to the  gc_epilogue()'s.
2608 // The role of the varaible _between_prologue_and_epilogue is to
2609 // enforce the invocation protocol.
2610 void CMSCollector::gc_prologue(bool full) {
2611   // Call gc_prologue_work() for each CMSGen and PermGen that
2612   // we are responsible for.
2613 
2614   // The following locking discipline assumes that we are only called
2615   // when the world is stopped.
2616   assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption");
2617 
2618   // The CMSCollector prologue must call the gc_prologues for the
2619   // "generations" (including PermGen if any) that it's responsible
2620   // for.
2621 
2622   assert(   Thread::current()->is_VM_thread()
2623          || (   CMSScavengeBeforeRemark
2624              && Thread::current()->is_ConcurrentGC_thread()),
2625          "Incorrect thread type for prologue execution");
2626 
2627   if (_between_prologue_and_epilogue) {
2628     // We have already been invoked; this is a gc_prologue delegation
2629     // from yet another CMS generation that we are responsible for, just
2630     // ignore it since all relevant work has already been done.
2631     return;
2632   }
2633 
2634   // set a bit saying prologue has been called; cleared in epilogue
2635   _between_prologue_and_epilogue = true;
2636   // Claim locks for common data structures, then call gc_prologue_work()
2637   // for each CMSGen and PermGen that we are responsible for.
2638 
2639   getFreelistLocks();   // gets free list locks on constituent spaces
2640   bitMapLock()->lock_without_safepoint_check();
2641 
2642   // Should call gc_prologue_work() for all cms gens we are responsible for
2643   bool registerClosure =    _collectorState >= Marking
2644                          && _collectorState < Sweeping;
2645   ModUnionClosure* muc = CollectedHeap::use_parallel_gc_threads() ?
2646                                                &_modUnionClosurePar
2647                                                : &_modUnionClosure;
2648   _cmsGen->gc_prologue_work(full, registerClosure, muc);
2649   _permGen->gc_prologue_work(full, registerClosure, muc);
2650 
2651   if (!full) {
2652     stats().record_gc0_begin();
2653   }
2654 }
2655 
2656 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) {
2657   // Delegate to CMScollector which knows how to coordinate between
2658   // this and any other CMS generations that it is responsible for
2659   // collecting.
2660   collector()->gc_prologue(full);
2661 }
2662 
2663 // This is a "private" interface for use by this generation's CMSCollector.
2664 // Not to be called directly by any other entity (for instance,
2665 // GenCollectedHeap, which calls the "public" gc_prologue method above).
2666 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full,
2667   bool registerClosure, ModUnionClosure* modUnionClosure) {
2668   assert(!incremental_collection_failed(), "Shouldn't be set yet");
2669   assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL,
2670     "Should be NULL");
2671   if (registerClosure) {
2672     cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure);
2673   }
2674   cmsSpace()->gc_prologue();
2675   // Clear stat counters
2676   NOT_PRODUCT(
2677     assert(_numObjectsPromoted == 0, "check");
2678     assert(_numWordsPromoted   == 0, "check");
2679     if (Verbose && PrintGC) {
2680       gclog_or_tty->print("Allocated "SIZE_FORMAT" objects, "
2681                           SIZE_FORMAT" bytes concurrently",
2682       _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord));
2683     }
2684     _numObjectsAllocated = 0;
2685     _numWordsAllocated   = 0;
2686   )
2687 }
2688 
2689 void CMSCollector::gc_epilogue(bool full) {
2690   // The following locking discipline assumes that we are only called
2691   // when the world is stopped.
2692   assert(SafepointSynchronize::is_at_safepoint(),
2693          "world is stopped assumption");
2694 
2695   // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks
2696   // if linear allocation blocks need to be appropriately marked to allow the
2697   // the blocks to be parsable. We also check here whether we need to nudge the
2698   // CMS collector thread to start a new cycle (if it's not already active).
2699   assert(   Thread::current()->is_VM_thread()
2700          || (   CMSScavengeBeforeRemark
2701              && Thread::current()->is_ConcurrentGC_thread()),
2702          "Incorrect thread type for epilogue execution");
2703 
2704   if (!_between_prologue_and_epilogue) {
2705     // We have already been invoked; this is a gc_epilogue delegation
2706     // from yet another CMS generation that we are responsible for, just
2707     // ignore it since all relevant work has already been done.
2708     return;
2709   }
2710   assert(haveFreelistLocks(), "must have freelist locks");
2711   assert_lock_strong(bitMapLock());
2712 
2713   _cmsGen->gc_epilogue_work(full);
2714   _permGen->gc_epilogue_work(full);
2715 
2716   if (_collectorState == AbortablePreclean || _collectorState == Precleaning) {
2717     // in case sampling was not already enabled, enable it
2718     _start_sampling = true;
2719   }
2720   // reset _eden_chunk_array so sampling starts afresh
2721   _eden_chunk_index = 0;
2722 
2723   size_t cms_used   = _cmsGen->cmsSpace()->used();
2724   size_t perm_used  = _permGen->cmsSpace()->used();
2725 
2726   // update performance counters - this uses a special version of
2727   // update_counters() that allows the utilization to be passed as a
2728   // parameter, avoiding multiple calls to used().
2729   //
2730   _cmsGen->update_counters(cms_used);
2731   _permGen->update_counters(perm_used);
2732 
2733   if (CMSIncrementalMode) {
2734     icms_update_allocation_limits();
2735   }
2736 
2737   bitMapLock()->unlock();
2738   releaseFreelistLocks();
2739 
2740   if (!CleanChunkPoolAsync) {
2741     Chunk::clean_chunk_pool();
2742   }
2743 
2744   _between_prologue_and_epilogue = false;  // ready for next cycle
2745 }
2746 
2747 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) {
2748   collector()->gc_epilogue(full);
2749 
2750   // Also reset promotion tracking in par gc thread states.
2751   if (CollectedHeap::use_parallel_gc_threads()) {
2752     for (uint i = 0; i < ParallelGCThreads; i++) {
2753       _par_gc_thread_states[i]->promo.stopTrackingPromotions(i);
2754     }
2755   }
2756 }
2757 
2758 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2759   assert(!incremental_collection_failed(), "Should have been cleared");
2760   cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2761   cmsSpace()->gc_epilogue();
2762     // Print stat counters
2763   NOT_PRODUCT(
2764     assert(_numObjectsAllocated == 0, "check");
2765     assert(_numWordsAllocated == 0, "check");
2766     if (Verbose && PrintGC) {
2767       gclog_or_tty->print("Promoted "SIZE_FORMAT" objects, "
2768                           SIZE_FORMAT" bytes",
2769                  _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2770     }
2771     _numObjectsPromoted = 0;
2772     _numWordsPromoted   = 0;
2773   )
2774 
2775   if (PrintGC && Verbose) {
2776     // Call down the chain in contiguous_available needs the freelistLock
2777     // so print this out before releasing the freeListLock.
2778     gclog_or_tty->print(" Contiguous available "SIZE_FORMAT" bytes ",
2779                         contiguous_available());
2780   }
2781 }
2782 
2783 #ifndef PRODUCT
2784 bool CMSCollector::have_cms_token() {
2785   Thread* thr = Thread::current();
2786   if (thr->is_VM_thread()) {
2787     return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2788   } else if (thr->is_ConcurrentGC_thread()) {
2789     return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2790   } else if (thr->is_GC_task_thread()) {
2791     return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2792            ParGCRareEvent_lock->owned_by_self();
2793   }
2794   return false;
2795 }
2796 #endif
2797 
2798 // Check reachability of the given heap address in CMS generation,
2799 // treating all other generations as roots.
2800 bool CMSCollector::is_cms_reachable(HeapWord* addr) {
2801   // We could "guarantee" below, rather than assert, but i'll
2802   // leave these as "asserts" so that an adventurous debugger
2803   // could try this in the product build provided some subset of
2804   // the conditions were met, provided they were intersted in the
2805   // results and knew that the computation below wouldn't interfere
2806   // with other concurrent computations mutating the structures
2807   // being read or written.
2808   assert(SafepointSynchronize::is_at_safepoint(),
2809          "Else mutations in object graph will make answer suspect");
2810   assert(have_cms_token(), "Should hold cms token");
2811   assert(haveFreelistLocks(), "must hold free list locks");
2812   assert_lock_strong(bitMapLock());
2813 
2814   // Clear the marking bit map array before starting, but, just
2815   // for kicks, first report if the given address is already marked
2816   gclog_or_tty->print_cr("Start: Address 0x%x is%s marked", addr,
2817                 _markBitMap.isMarked(addr) ? "" : " not");
2818 
2819   if (verify_after_remark()) {
2820     MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2821     bool result = verification_mark_bm()->isMarked(addr);
2822     gclog_or_tty->print_cr("TransitiveMark: Address 0x%x %s marked", addr,
2823                            result ? "IS" : "is NOT");
2824     return result;
2825   } else {
2826     gclog_or_tty->print_cr("Could not compute result");
2827     return false;
2828   }
2829 }
2830 
2831 ////////////////////////////////////////////////////////
2832 // CMS Verification Support
2833 ////////////////////////////////////////////////////////
2834 // Following the remark phase, the following invariant
2835 // should hold -- each object in the CMS heap which is
2836 // marked in markBitMap() should be marked in the verification_mark_bm().
2837 
2838 class VerifyMarkedClosure: public BitMapClosure {
2839   CMSBitMap* _marks;
2840   bool       _failed;
2841 
2842  public:
2843   VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2844 
2845   bool do_bit(size_t offset) {
2846     HeapWord* addr = _marks->offsetToHeapWord(offset);
2847     if (!_marks->isMarked(addr)) {
2848       oop(addr)->print_on(gclog_or_tty);
2849       gclog_or_tty->print_cr(" ("INTPTR_FORMAT" should have been marked)", addr);
2850       _failed = true;
2851     }
2852     return true;
2853   }
2854 
2855   bool failed() { return _failed; }
2856 };
2857 
2858 bool CMSCollector::verify_after_remark() {
2859   gclog_or_tty->print(" [Verifying CMS Marking... ");
2860   MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2861   static bool init = false;
2862 
2863   assert(SafepointSynchronize::is_at_safepoint(),
2864          "Else mutations in object graph will make answer suspect");
2865   assert(have_cms_token(),
2866          "Else there may be mutual interference in use of "
2867          " verification data structures");
2868   assert(_collectorState > Marking && _collectorState <= Sweeping,
2869          "Else marking info checked here may be obsolete");
2870   assert(haveFreelistLocks(), "must hold free list locks");
2871   assert_lock_strong(bitMapLock());
2872 
2873 
2874   // Allocate marking bit map if not already allocated
2875   if (!init) { // first time
2876     if (!verification_mark_bm()->allocate(_span)) {
2877       return false;
2878     }
2879     init = true;
2880   }
2881 
2882   assert(verification_mark_stack()->isEmpty(), "Should be empty");
2883 
2884   // Turn off refs discovery -- so we will be tracing through refs.
2885   // This is as intended, because by this time
2886   // GC must already have cleared any refs that need to be cleared,
2887   // and traced those that need to be marked; moreover,
2888   // the marking done here is not going to intefere in any
2889   // way with the marking information used by GC.
2890   NoRefDiscovery no_discovery(ref_processor());
2891 
2892   COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
2893 
2894   // Clear any marks from a previous round
2895   verification_mark_bm()->clear_all();
2896   assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
2897   verify_work_stacks_empty();
2898 
2899   GenCollectedHeap* gch = GenCollectedHeap::heap();
2900   gch->ensure_parsability(false);  // fill TLABs, but no need to retire them
2901   // Update the saved marks which may affect the root scans.
2902   gch->save_marks();
2903 
2904   if (CMSRemarkVerifyVariant == 1) {
2905     // In this first variant of verification, we complete
2906     // all marking, then check if the new marks-verctor is
2907     // a subset of the CMS marks-vector.
2908     verify_after_remark_work_1();
2909   } else if (CMSRemarkVerifyVariant == 2) {
2910     // In this second variant of verification, we flag an error
2911     // (i.e. an object reachable in the new marks-vector not reachable
2912     // in the CMS marks-vector) immediately, also indicating the
2913     // identify of an object (A) that references the unmarked object (B) --
2914     // presumably, a mutation to A failed to be picked up by preclean/remark?
2915     verify_after_remark_work_2();
2916   } else {
2917     warning("Unrecognized value %d for CMSRemarkVerifyVariant",
2918             CMSRemarkVerifyVariant);
2919   }
2920   gclog_or_tty->print(" done] ");
2921   return true;
2922 }
2923 
2924 void CMSCollector::verify_after_remark_work_1() {
2925   ResourceMark rm;
2926   HandleMark  hm;
2927   GenCollectedHeap* gch = GenCollectedHeap::heap();
2928 
2929   // Mark from roots one level into CMS
2930   MarkRefsIntoClosure notOlder(_span, verification_mark_bm());
2931   gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2932 
2933   gch->gen_process_strong_roots(_cmsGen->level(),
2934                                 true,   // younger gens are roots
2935                                 true,   // activate StrongRootsScope
2936                                 true,   // collecting perm gen
2937                                 SharedHeap::ScanningOption(roots_scanning_options()),
2938                                 &notOlder,
2939                                 true,   // walk code active on stacks
2940                                 NULL);
2941 
2942   // Now mark from the roots
2943   assert(_revisitStack.isEmpty(), "Should be empty");
2944   MarkFromRootsClosure markFromRootsClosure(this, _span,
2945     verification_mark_bm(), verification_mark_stack(), &_revisitStack,
2946     false /* don't yield */, true /* verifying */);
2947   assert(_restart_addr == NULL, "Expected pre-condition");
2948   verification_mark_bm()->iterate(&markFromRootsClosure);
2949   while (_restart_addr != NULL) {
2950     // Deal with stack overflow: by restarting at the indicated
2951     // address.
2952     HeapWord* ra = _restart_addr;
2953     markFromRootsClosure.reset(ra);
2954     _restart_addr = NULL;
2955     verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2956   }
2957   assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2958   verify_work_stacks_empty();
2959   // Should reset the revisit stack above, since no class tree
2960   // surgery is forthcoming.
2961   _revisitStack.reset(); // throwing away all contents
2962 
2963   // Marking completed -- now verify that each bit marked in
2964   // verification_mark_bm() is also marked in markBitMap(); flag all
2965   // errors by printing corresponding objects.
2966   VerifyMarkedClosure vcl(markBitMap());
2967   verification_mark_bm()->iterate(&vcl);
2968   if (vcl.failed()) {
2969     gclog_or_tty->print("Verification failed");
2970     Universe::heap()->print_on(gclog_or_tty);
2971     fatal("CMS: failed marking verification after remark");
2972   }
2973 }
2974 
2975 void CMSCollector::verify_after_remark_work_2() {
2976   ResourceMark rm;
2977   HandleMark  hm;
2978   GenCollectedHeap* gch = GenCollectedHeap::heap();
2979 
2980   // Mark from roots one level into CMS
2981   MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
2982                                      markBitMap());
2983   gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2984   gch->gen_process_strong_roots(_cmsGen->level(),
2985                                 true,   // younger gens are roots
2986                                 true,   // activate StrongRootsScope
2987                                 true,   // collecting perm gen
2988                                 SharedHeap::ScanningOption(roots_scanning_options()),
2989                                 &notOlder,
2990                                 true,   // walk code active on stacks
2991                                 NULL);
2992 
2993   // Now mark from the roots
2994   assert(_revisitStack.isEmpty(), "Should be empty");
2995   MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
2996     verification_mark_bm(), markBitMap(), verification_mark_stack());
2997   assert(_restart_addr == NULL, "Expected pre-condition");
2998   verification_mark_bm()->iterate(&markFromRootsClosure);
2999   while (_restart_addr != NULL) {
3000     // Deal with stack overflow: by restarting at the indicated
3001     // address.
3002     HeapWord* ra = _restart_addr;
3003     markFromRootsClosure.reset(ra);
3004     _restart_addr = NULL;
3005     verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
3006   }
3007   assert(verification_mark_stack()->isEmpty(), "Should have been drained");
3008   verify_work_stacks_empty();
3009   // Should reset the revisit stack above, since no class tree
3010   // surgery is forthcoming.
3011   _revisitStack.reset(); // throwing away all contents
3012 
3013   // Marking completed -- now verify that each bit marked in
3014   // verification_mark_bm() is also marked in markBitMap(); flag all
3015   // errors by printing corresponding objects.
3016   VerifyMarkedClosure vcl(markBitMap());
3017   verification_mark_bm()->iterate(&vcl);
3018   assert(!vcl.failed(), "Else verification above should not have succeeded");
3019 }
3020 
3021 void ConcurrentMarkSweepGeneration::save_marks() {
3022   // delegate to CMS space
3023   cmsSpace()->save_marks();
3024   for (uint i = 0; i < ParallelGCThreads; i++) {
3025     _par_gc_thread_states[i]->promo.startTrackingPromotions();
3026   }
3027 }
3028 
3029 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
3030   return cmsSpace()->no_allocs_since_save_marks();
3031 }
3032 
3033 #define CMS_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix)    \
3034                                                                 \
3035 void ConcurrentMarkSweepGeneration::                            \
3036 oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) {   \
3037   cl->set_generation(this);                                     \
3038   cmsSpace()->oop_since_save_marks_iterate##nv_suffix(cl);      \
3039   cl->reset_generation();                                       \
3040   save_marks();                                                 \
3041 }
3042 
3043 ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DEFN)
3044 
3045 void
3046 ConcurrentMarkSweepGeneration::object_iterate_since_last_GC(ObjectClosure* blk)
3047 {
3048   // Not currently implemented; need to do the following. -- ysr.
3049   // dld -- I think that is used for some sort of allocation profiler.  So it
3050   // really means the objects allocated by the mutator since the last
3051   // GC.  We could potentially implement this cheaply by recording only
3052   // the direct allocations in a side data structure.
3053   //
3054   // I think we probably ought not to be required to support these
3055   // iterations at any arbitrary point; I think there ought to be some
3056   // call to enable/disable allocation profiling in a generation/space,
3057   // and the iterator ought to return the objects allocated in the
3058   // gen/space since the enable call, or the last iterator call (which
3059   // will probably be at a GC.)  That way, for gens like CM&S that would
3060   // require some extra data structure to support this, we only pay the
3061   // cost when it's in use...
3062   cmsSpace()->object_iterate_since_last_GC(blk);
3063 }
3064 
3065 void
3066 ConcurrentMarkSweepGeneration::younger_refs_iterate(OopsInGenClosure* cl) {
3067   cl->set_generation(this);
3068   younger_refs_in_space_iterate(_cmsSpace, cl);
3069   cl->reset_generation();
3070 }
3071 
3072 void
3073 ConcurrentMarkSweepGeneration::oop_iterate(MemRegion mr, OopClosure* cl) {
3074   if (freelistLock()->owned_by_self()) {
3075     Generation::oop_iterate(mr, cl);
3076   } else {
3077     MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3078     Generation::oop_iterate(mr, cl);
3079   }
3080 }
3081 
3082 void
3083 ConcurrentMarkSweepGeneration::oop_iterate(OopClosure* cl) {
3084   if (freelistLock()->owned_by_self()) {
3085     Generation::oop_iterate(cl);
3086   } else {
3087     MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3088     Generation::oop_iterate(cl);
3089   }
3090 }
3091 
3092 void
3093 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
3094   if (freelistLock()->owned_by_self()) {
3095     Generation::object_iterate(cl);
3096   } else {
3097     MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3098     Generation::object_iterate(cl);
3099   }
3100 }
3101 
3102 void
3103 ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) {
3104   if (freelistLock()->owned_by_self()) {
3105     Generation::safe_object_iterate(cl);
3106   } else {
3107     MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3108     Generation::safe_object_iterate(cl);
3109   }
3110 }
3111 
3112 void
3113 ConcurrentMarkSweepGeneration::pre_adjust_pointers() {
3114 }
3115 
3116 void
3117 ConcurrentMarkSweepGeneration::post_compact() {
3118 }
3119 
3120 void
3121 ConcurrentMarkSweepGeneration::prepare_for_verify() {
3122   // Fix the linear allocation blocks to look like free blocks.
3123 
3124   // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
3125   // are not called when the heap is verified during universe initialization and
3126   // at vm shutdown.
3127   if (freelistLock()->owned_by_self()) {
3128     cmsSpace()->prepare_for_verify();
3129   } else {
3130     MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
3131     cmsSpace()->prepare_for_verify();
3132   }
3133 }
3134 
3135 void
3136 ConcurrentMarkSweepGeneration::verify() {
3137   // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
3138   // are not called when the heap is verified during universe initialization and
3139   // at vm shutdown.
3140   if (freelistLock()->owned_by_self()) {
3141     cmsSpace()->verify();
3142   } else {
3143     MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
3144     cmsSpace()->verify();
3145   }
3146 }
3147 
3148 void CMSCollector::verify() {
3149   _cmsGen->verify();
3150   _permGen->verify();
3151 }
3152 
3153 #ifndef PRODUCT
3154 bool CMSCollector::overflow_list_is_empty() const {
3155   assert(_num_par_pushes >= 0, "Inconsistency");
3156   if (_overflow_list == NULL) {
3157     assert(_num_par_pushes == 0, "Inconsistency");
3158   }
3159   return _overflow_list == NULL;
3160 }
3161 
3162 // The methods verify_work_stacks_empty() and verify_overflow_empty()
3163 // merely consolidate assertion checks that appear to occur together frequently.
3164 void CMSCollector::verify_work_stacks_empty() const {
3165   assert(_markStack.isEmpty(), "Marking stack should be empty");
3166   assert(overflow_list_is_empty(), "Overflow list should be empty");
3167 }
3168 
3169 void CMSCollector::verify_overflow_empty() const {
3170   assert(overflow_list_is_empty(), "Overflow list should be empty");
3171   assert(no_preserved_marks(), "No preserved marks");
3172 }
3173 #endif // PRODUCT
3174 
3175 // Decide if we want to enable class unloading as part of the
3176 // ensuing concurrent GC cycle. We will collect the perm gen and
3177 // unload classes if it's the case that:
3178 // (1) an explicit gc request has been made and the flag
3179 //     ExplicitGCInvokesConcurrentAndUnloadsClasses is set, OR
3180 // (2) (a) class unloading is enabled at the command line, and
3181 //     (b) (i)   perm gen threshold has been crossed, or
3182 //         (ii)  old gen is getting really full, or
3183 //         (iii) the previous N CMS collections did not collect the
3184 //               perm gen
3185 // NOTE: Provided there is no change in the state of the heap between
3186 // calls to this method, it should have idempotent results. Moreover,
3187 // its results should be monotonically increasing (i.e. going from 0 to 1,
3188 // but not 1 to 0) between successive calls between which the heap was
3189 // not collected. For the implementation below, it must thus rely on
3190 // the property that concurrent_cycles_since_last_unload()
3191 // will not decrease unless a collection cycle happened and that
3192 // _permGen->should_concurrent_collect() and _cmsGen->is_too_full() are
3193 // themselves also monotonic in that sense. See check_monotonicity()
3194 // below.
3195 bool CMSCollector::update_should_unload_classes() {
3196   _should_unload_classes = false;
3197   // Condition 1 above
3198   if (_full_gc_requested && ExplicitGCInvokesConcurrentAndUnloadsClasses) {
3199     _should_unload_classes = true;
3200   } else if (CMSClassUnloadingEnabled) { // Condition 2.a above
3201     // Disjuncts 2.b.(i,ii,iii) above
3202     _should_unload_classes = (concurrent_cycles_since_last_unload() >=
3203                               CMSClassUnloadingMaxInterval)
3204                            || _permGen->should_concurrent_collect()
3205                            || _cmsGen->is_too_full();
3206   }
3207   return _should_unload_classes;
3208 }
3209 
3210 bool ConcurrentMarkSweepGeneration::is_too_full() const {
3211   bool res = should_concurrent_collect();
3212   res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
3213   return res;
3214 }
3215 
3216 void CMSCollector::setup_cms_unloading_and_verification_state() {
3217   const  bool should_verify =   VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
3218                              || VerifyBeforeExit;
3219   const  int  rso           =   SharedHeap::SO_Strings | SharedHeap::SO_CodeCache;
3220 
3221   if (should_unload_classes()) {   // Should unload classes this cycle
3222     remove_root_scanning_option(rso);  // Shrink the root set appropriately
3223     set_verifying(should_verify);    // Set verification state for this cycle
3224     return;                            // Nothing else needs to be done at this time
3225   }
3226 
3227   // Not unloading classes this cycle
3228   assert(!should_unload_classes(), "Inconsitency!");
3229   if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
3230     // We were not verifying, or we _were_ unloading classes in the last cycle,
3231     // AND some verification options are enabled this cycle; in this case,
3232     // we must make sure that the deadness map is allocated if not already so,
3233     // and cleared (if already allocated previously --
3234     // CMSBitMap::sizeInBits() is used to determine if it's allocated).
3235     if (perm_gen_verify_bit_map()->sizeInBits() == 0) {
3236       if (!perm_gen_verify_bit_map()->allocate(_permGen->reserved())) {
3237         warning("Failed to allocate permanent generation verification CMS Bit Map;\n"
3238                 "permanent generation verification disabled");
3239         return;  // Note that we leave verification disabled, so we'll retry this
3240                  // allocation next cycle. We _could_ remember this failure
3241                  // and skip further attempts and permanently disable verification
3242                  // attempts if that is considered more desirable.
3243       }
3244       assert(perm_gen_verify_bit_map()->covers(_permGen->reserved()),
3245               "_perm_gen_ver_bit_map inconsistency?");
3246     } else {
3247       perm_gen_verify_bit_map()->clear_all();
3248     }
3249     // Include symbols, strings and code cache elements to prevent their resurrection.
3250     add_root_scanning_option(rso);
3251     set_verifying(true);
3252   } else if (verifying() && !should_verify) {
3253     // We were verifying, but some verification flags got disabled.
3254     set_verifying(false);
3255     // Exclude symbols, strings and code cache elements from root scanning to
3256     // reduce IM and RM pauses.
3257     remove_root_scanning_option(rso);
3258   }
3259 }
3260 
3261 
3262 #ifndef PRODUCT
3263 HeapWord* CMSCollector::block_start(const void* p) const {
3264   const HeapWord* addr = (HeapWord*)p;
3265   if (_span.contains(p)) {
3266     if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
3267       return _cmsGen->cmsSpace()->block_start(p);
3268     } else {
3269       assert(_permGen->cmsSpace()->is_in_reserved(addr),
3270              "Inconsistent _span?");
3271       return _permGen->cmsSpace()->block_start(p);
3272     }
3273   }
3274   return NULL;
3275 }
3276 #endif
3277 
3278 HeapWord*
3279 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
3280                                                    bool   tlab,
3281                                                    bool   parallel) {
3282   CMSSynchronousYieldRequest yr;
3283   assert(!tlab, "Can't deal with TLAB allocation");
3284   MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3285   expand(word_size*HeapWordSize, MinHeapDeltaBytes,
3286     CMSExpansionCause::_satisfy_allocation);
3287   if (GCExpandToAllocateDelayMillis > 0) {
3288     os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3289   }
3290   return have_lock_and_allocate(word_size, tlab);
3291 }
3292 
3293 // YSR: All of this generation expansion/shrinking stuff is an exact copy of
3294 // OneContigSpaceCardGeneration, which makes me wonder if we should move this
3295 // to CardGeneration and share it...
3296 bool ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes) {
3297   return CardGeneration::expand(bytes, expand_bytes);
3298 }
3299 
3300 void ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes,
3301   CMSExpansionCause::Cause cause)
3302 {
3303 
3304   bool success = expand(bytes, expand_bytes);
3305 
3306   // remember why we expanded; this information is used
3307   // by shouldConcurrentCollect() when making decisions on whether to start
3308   // a new CMS cycle.
3309   if (success) {
3310     set_expansion_cause(cause);
3311     if (PrintGCDetails && Verbose) {
3312       gclog_or_tty->print_cr("Expanded CMS gen for %s",
3313         CMSExpansionCause::to_string(cause));
3314     }
3315   }
3316 }
3317 
3318 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
3319   HeapWord* res = NULL;
3320   MutexLocker x(ParGCRareEvent_lock);
3321   while (true) {
3322     // Expansion by some other thread might make alloc OK now:
3323     res = ps->lab.alloc(word_sz);
3324     if (res != NULL) return res;
3325     // If there's not enough expansion space available, give up.
3326     if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
3327       return NULL;
3328     }
3329     // Otherwise, we try expansion.
3330     expand(word_sz*HeapWordSize, MinHeapDeltaBytes,
3331       CMSExpansionCause::_allocate_par_lab);
3332     // Now go around the loop and try alloc again;
3333     // A competing par_promote might beat us to the expansion space,
3334     // so we may go around the loop again if promotion fails agaion.
3335     if (GCExpandToAllocateDelayMillis > 0) {
3336       os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3337     }
3338   }
3339 }
3340 
3341 
3342 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
3343   PromotionInfo* promo) {
3344   MutexLocker x(ParGCRareEvent_lock);
3345   size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
3346   while (true) {
3347     // Expansion by some other thread might make alloc OK now:
3348     if (promo->ensure_spooling_space()) {
3349       assert(promo->has_spooling_space(),
3350              "Post-condition of successful ensure_spooling_space()");
3351       return true;
3352     }
3353     // If there's not enough expansion space available, give up.
3354     if (_virtual_space.uncommitted_size() < refill_size_bytes) {
3355       return false;
3356     }
3357     // Otherwise, we try expansion.
3358     expand(refill_size_bytes, MinHeapDeltaBytes,
3359       CMSExpansionCause::_allocate_par_spooling_space);
3360     // Now go around the loop and try alloc again;
3361     // A competing allocation might beat us to the expansion space,
3362     // so we may go around the loop again if allocation fails again.
3363     if (GCExpandToAllocateDelayMillis > 0) {
3364       os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3365     }
3366   }
3367 }
3368 
3369 
3370 
3371 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
3372   assert_locked_or_safepoint(Heap_lock);
3373   size_t size = ReservedSpace::page_align_size_down(bytes);
3374   if (size > 0) {
3375     shrink_by(size);
3376   }
3377 }
3378 
3379 bool ConcurrentMarkSweepGeneration::grow_by(size_t bytes) {
3380   assert_locked_or_safepoint(Heap_lock);
3381   bool result = _virtual_space.expand_by(bytes);
3382   if (result) {
3383     HeapWord* old_end = _cmsSpace->end();
3384     size_t new_word_size =
3385       heap_word_size(_virtual_space.committed_size());
3386     MemRegion mr(_cmsSpace->bottom(), new_word_size);
3387     _bts->resize(new_word_size);  // resize the block offset shared array
3388     Universe::heap()->barrier_set()->resize_covered_region(mr);
3389     // Hmmmm... why doesn't CFLS::set_end verify locking?
3390     // This is quite ugly; FIX ME XXX
3391     _cmsSpace->assert_locked(freelistLock());
3392     _cmsSpace->set_end((HeapWord*)_virtual_space.high());
3393 
3394     // update the space and generation capacity counters
3395     if (UsePerfData) {
3396       _space_counters->update_capacity();
3397       _gen_counters->update_all();
3398     }
3399 
3400     if (Verbose && PrintGC) {
3401       size_t new_mem_size = _virtual_space.committed_size();
3402       size_t old_mem_size = new_mem_size - bytes;
3403       gclog_or_tty->print_cr("Expanding %s from %ldK by %ldK to %ldK",
3404                     name(), old_mem_size/K, bytes/K, new_mem_size/K);
3405     }
3406   }
3407   return result;
3408 }
3409 
3410 bool ConcurrentMarkSweepGeneration::grow_to_reserved() {
3411   assert_locked_or_safepoint(Heap_lock);
3412   bool success = true;
3413   const size_t remaining_bytes = _virtual_space.uncommitted_size();
3414   if (remaining_bytes > 0) {
3415     success = grow_by(remaining_bytes);
3416     DEBUG_ONLY(if (!success) warning("grow to reserved failed");)
3417   }
3418   return success;
3419 }
3420 
3421 void ConcurrentMarkSweepGeneration::shrink_by(size_t bytes) {
3422   assert_locked_or_safepoint(Heap_lock);
3423   assert_lock_strong(freelistLock());
3424   // XXX Fix when compaction is implemented.
3425   warning("Shrinking of CMS not yet implemented");
3426   return;
3427 }
3428 
3429 
3430 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
3431 // phases.
3432 class CMSPhaseAccounting: public StackObj {
3433  public:
3434   CMSPhaseAccounting(CMSCollector *collector,
3435                      const char *phase,
3436                      bool print_cr = true);
3437   ~CMSPhaseAccounting();
3438 
3439  private:
3440   CMSCollector *_collector;
3441   const char *_phase;
3442   elapsedTimer _wallclock;
3443   bool _print_cr;
3444 
3445  public:
3446   // Not MT-safe; so do not pass around these StackObj's
3447   // where they may be accessed by other threads.
3448   jlong wallclock_millis() {
3449     assert(_wallclock.is_active(), "Wall clock should not stop");
3450     _wallclock.stop();  // to record time
3451     jlong ret = _wallclock.milliseconds();
3452     _wallclock.start(); // restart
3453     return ret;
3454   }
3455 };
3456 
3457 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
3458                                        const char *phase,
3459                                        bool print_cr) :
3460   _collector(collector), _phase(phase), _print_cr(print_cr) {
3461 
3462   if (PrintCMSStatistics != 0) {
3463     _collector->resetYields();
3464   }
3465   if (PrintGCDetails && PrintGCTimeStamps) {
3466     gclog_or_tty->date_stamp(PrintGCDateStamps);
3467     gclog_or_tty->stamp();
3468     gclog_or_tty->print_cr(": [%s-concurrent-%s-start]",
3469       _collector->cmsGen()->short_name(), _phase);
3470   }
3471   _collector->resetTimer();
3472   _wallclock.start();
3473   _collector->startTimer();
3474 }
3475 
3476 CMSPhaseAccounting::~CMSPhaseAccounting() {
3477   assert(_wallclock.is_active(), "Wall clock should not have stopped");
3478   _collector->stopTimer();
3479   _wallclock.stop();
3480   if (PrintGCDetails) {
3481     gclog_or_tty->date_stamp(PrintGCDateStamps);
3482     gclog_or_tty->stamp(PrintGCTimeStamps);
3483     gclog_or_tty->print("[%s-concurrent-%s: %3.3f/%3.3f secs]",
3484                  _collector->cmsGen()->short_name(),
3485                  _phase, _collector->timerValue(), _wallclock.seconds());
3486     if (_print_cr) {
3487       gclog_or_tty->print_cr("");
3488     }
3489     if (PrintCMSStatistics != 0) {
3490       gclog_or_tty->print_cr(" (CMS-concurrent-%s yielded %d times)", _phase,
3491                     _collector->yields());
3492     }
3493   }
3494 }
3495 
3496 // CMS work
3497 
3498 // Checkpoint the roots into this generation from outside
3499 // this generation. [Note this initial checkpoint need only
3500 // be approximate -- we'll do a catch up phase subsequently.]
3501 void CMSCollector::checkpointRootsInitial(bool asynch) {
3502   assert(_collectorState == InitialMarking, "Wrong collector state");
3503   check_correct_thread_executing();
3504   TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
3505 
3506   ReferenceProcessor* rp = ref_processor();
3507   SpecializationStats::clear();
3508   assert(_restart_addr == NULL, "Control point invariant");
3509   if (asynch) {
3510     // acquire locks for subsequent manipulations
3511     MutexLockerEx x(bitMapLock(),
3512                     Mutex::_no_safepoint_check_flag);
3513     checkpointRootsInitialWork(asynch);
3514     // enable ("weak") refs discovery
3515     rp->enable_discovery(true /*verify_disabled*/, true /*check_no_refs*/);
3516     _collectorState = Marking;
3517   } else {
3518     // (Weak) Refs discovery: this is controlled from genCollectedHeap::do_collection
3519     // which recognizes if we are a CMS generation, and doesn't try to turn on
3520     // discovery; verify that they aren't meddling.
3521     assert(!rp->discovery_is_atomic(),
3522            "incorrect setting of discovery predicate");
3523     assert(!rp->discovery_enabled(), "genCollectedHeap shouldn't control "
3524            "ref discovery for this generation kind");
3525     // already have locks
3526     checkpointRootsInitialWork(asynch);
3527     // now enable ("weak") refs discovery
3528     rp->enable_discovery(true /*verify_disabled*/, false /*verify_no_refs*/);
3529     _collectorState = Marking;
3530   }
3531   SpecializationStats::print();
3532 }
3533 
3534 void CMSCollector::checkpointRootsInitialWork(bool asynch) {
3535   assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
3536   assert(_collectorState == InitialMarking, "just checking");
3537 
3538   // If there has not been a GC[n-1] since last GC[n] cycle completed,
3539   // precede our marking with a collection of all
3540   // younger generations to keep floating garbage to a minimum.
3541   // XXX: we won't do this for now -- it's an optimization to be done later.
3542 
3543   // already have locks
3544   assert_lock_strong(bitMapLock());
3545   assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
3546 
3547   // Setup the verification and class unloading state for this
3548   // CMS collection cycle.
3549   setup_cms_unloading_and_verification_state();
3550 
3551   NOT_PRODUCT(GCTraceTime t("\ncheckpointRootsInitialWork",
3552     PrintGCDetails && Verbose, true, _gc_timer_cm);)
3553   if (UseAdaptiveSizePolicy) {
3554     size_policy()->checkpoint_roots_initial_begin();
3555   }
3556 
3557   // Reset all the PLAB chunk arrays if necessary.
3558   if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
3559     reset_survivor_plab_arrays();
3560   }
3561 
3562   ResourceMark rm;
3563   HandleMark  hm;
3564 
3565   FalseClosure falseClosure;
3566   // In the case of a synchronous collection, we will elide the
3567   // remark step, so it's important to catch all the nmethod oops
3568   // in this step.
3569   // The final 'true' flag to gen_process_strong_roots will ensure this.
3570   // If 'async' is true, we can relax the nmethod tracing.
3571   MarkRefsIntoClosure notOlder(_span, &_markBitMap);
3572   GenCollectedHeap* gch = GenCollectedHeap::heap();
3573 
3574   verify_work_stacks_empty();
3575   verify_overflow_empty();
3576 
3577   gch->ensure_parsability(false);  // fill TLABs, but no need to retire them
3578   // Update the saved marks which may affect the root scans.
3579   gch->save_marks();
3580 
3581   // weak reference processing has not started yet.
3582   ref_processor()->set_enqueuing_is_done(false);
3583 
3584   {
3585     // This is not needed. DEBUG_ONLY(RememberKlassesChecker imx(true);)
3586     COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
3587     gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3588     gch->gen_process_strong_roots(_cmsGen->level(),
3589                                   true,   // younger gens are roots
3590                                   true,   // activate StrongRootsScope
3591                                   true,   // collecting perm gen
3592                                   SharedHeap::ScanningOption(roots_scanning_options()),
3593                                   &notOlder,
3594                                   true,   // walk all of code cache if (so & SO_CodeCache)
3595                                   NULL);
3596   }
3597 
3598   // Clear mod-union table; it will be dirtied in the prologue of
3599   // CMS generation per each younger generation collection.
3600 
3601   assert(_modUnionTable.isAllClear(),
3602        "Was cleared in most recent final checkpoint phase"
3603        " or no bits are set in the gc_prologue before the start of the next "
3604        "subsequent marking phase.");
3605 
3606   // Save the end of the used_region of the constituent generations
3607   // to be used to limit the extent of sweep in each generation.
3608   save_sweep_limits();
3609   if (UseAdaptiveSizePolicy) {
3610     size_policy()->checkpoint_roots_initial_end(gch->gc_cause());
3611   }
3612   verify_overflow_empty();
3613 }
3614 
3615 bool CMSCollector::markFromRoots(bool asynch) {
3616   // we might be tempted to assert that:
3617   // assert(asynch == !SafepointSynchronize::is_at_safepoint(),
3618   //        "inconsistent argument?");
3619   // However that wouldn't be right, because it's possible that
3620   // a safepoint is indeed in progress as a younger generation
3621   // stop-the-world GC happens even as we mark in this generation.
3622   assert(_collectorState == Marking, "inconsistent state?");
3623   check_correct_thread_executing();
3624   verify_overflow_empty();
3625 
3626   bool res;
3627   if (asynch) {
3628 
3629     // Start the timers for adaptive size policy for the concurrent phases
3630     // Do it here so that the foreground MS can use the concurrent
3631     // timer since a foreground MS might has the sweep done concurrently
3632     // or STW.
3633     if (UseAdaptiveSizePolicy) {
3634       size_policy()->concurrent_marking_begin();
3635     }
3636 
3637     // Weak ref discovery note: We may be discovering weak
3638     // refs in this generation concurrent (but interleaved) with
3639     // weak ref discovery by a younger generation collector.
3640 
3641     CMSTokenSyncWithLocks ts(true, bitMapLock());
3642     TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3643     CMSPhaseAccounting pa(this, "mark", !PrintGCDetails);
3644     res = markFromRootsWork(asynch);
3645     if (res) {
3646       _collectorState = Precleaning;
3647     } else { // We failed and a foreground collection wants to take over
3648       assert(_foregroundGCIsActive, "internal state inconsistency");
3649       assert(_restart_addr == NULL,  "foreground will restart from scratch");
3650       if (PrintGCDetails) {
3651         gclog_or_tty->print_cr("bailing out to foreground collection");
3652       }
3653     }
3654     if (UseAdaptiveSizePolicy) {
3655       size_policy()->concurrent_marking_end();
3656     }
3657   } else {
3658     assert(SafepointSynchronize::is_at_safepoint(),
3659            "inconsistent with asynch == false");
3660     if (UseAdaptiveSizePolicy) {
3661       size_policy()->ms_collection_marking_begin();
3662     }
3663     // already have locks
3664     res = markFromRootsWork(asynch);
3665     _collectorState = FinalMarking;
3666     if (UseAdaptiveSizePolicy) {
3667       GenCollectedHeap* gch = GenCollectedHeap::heap();
3668       size_policy()->ms_collection_marking_end(gch->gc_cause());
3669     }
3670   }
3671   verify_overflow_empty();
3672   return res;
3673 }
3674 
3675 bool CMSCollector::markFromRootsWork(bool asynch) {
3676   // iterate over marked bits in bit map, doing a full scan and mark
3677   // from these roots using the following algorithm:
3678   // . if oop is to the right of the current scan pointer,
3679   //   mark corresponding bit (we'll process it later)
3680   // . else (oop is to left of current scan pointer)
3681   //   push oop on marking stack
3682   // . drain the marking stack
3683 
3684   // Note that when we do a marking step we need to hold the
3685   // bit map lock -- recall that direct allocation (by mutators)
3686   // and promotion (by younger generation collectors) is also
3687   // marking the bit map. [the so-called allocate live policy.]
3688   // Because the implementation of bit map marking is not
3689   // robust wrt simultaneous marking of bits in the same word,
3690   // we need to make sure that there is no such interference
3691   // between concurrent such updates.
3692 
3693   // already have locks
3694   assert_lock_strong(bitMapLock());
3695 
3696   // Clear the revisit stack, just in case there are any
3697   // obsolete contents from a short-circuited previous CMS cycle.
3698   _revisitStack.reset();
3699   verify_work_stacks_empty();
3700   verify_overflow_empty();
3701   assert(_revisitStack.isEmpty(), "tabula rasa");
3702   DEBUG_ONLY(RememberKlassesChecker cmx(should_unload_classes());)
3703   bool result = false;
3704   if (CMSConcurrentMTEnabled && ConcGCThreads > 0) {
3705     result = do_marking_mt(asynch);
3706   } else {
3707     result = do_marking_st(asynch);
3708   }
3709   return result;
3710 }
3711 
3712 // Forward decl
3713 class CMSConcMarkingTask;
3714 
3715 class CMSConcMarkingTerminator: public ParallelTaskTerminator {
3716   CMSCollector*       _collector;
3717   CMSConcMarkingTask* _task;
3718  public:
3719   virtual void yield();
3720 
3721   // "n_threads" is the number of threads to be terminated.
3722   // "queue_set" is a set of work queues of other threads.
3723   // "collector" is the CMS collector associated with this task terminator.
3724   // "yield" indicates whether we need the gang as a whole to yield.
3725   CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
3726     ParallelTaskTerminator(n_threads, queue_set),
3727     _collector(collector) { }
3728 
3729   void set_task(CMSConcMarkingTask* task) {
3730     _task = task;
3731   }
3732 };
3733 
3734 class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator {
3735   CMSConcMarkingTask* _task;
3736  public:
3737   bool should_exit_termination();
3738   void set_task(CMSConcMarkingTask* task) {
3739     _task = task;
3740   }
3741 };
3742 
3743 // MT Concurrent Marking Task
3744 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3745   CMSCollector* _collector;
3746   int           _n_workers;                  // requested/desired # workers
3747   bool          _asynch;
3748   bool          _result;
3749   CompactibleFreeListSpace*  _cms_space;
3750   CompactibleFreeListSpace* _perm_space;
3751   char          _pad_front[64];   // padding to ...
3752   HeapWord*     _global_finger;   // ... avoid sharing cache line
3753   char          _pad_back[64];
3754   HeapWord*     _restart_addr;
3755 
3756   //  Exposed here for yielding support
3757   Mutex* const _bit_map_lock;
3758 
3759   // The per thread work queues, available here for stealing
3760   OopTaskQueueSet*  _task_queues;
3761 
3762   // Termination (and yielding) support
3763   CMSConcMarkingTerminator _term;
3764   CMSConcMarkingTerminatorTerminator _term_term;
3765 
3766  public:
3767   CMSConcMarkingTask(CMSCollector* collector,
3768                  CompactibleFreeListSpace* cms_space,
3769                  CompactibleFreeListSpace* perm_space,
3770                  bool asynch,
3771                  YieldingFlexibleWorkGang* workers,
3772                  OopTaskQueueSet* task_queues):
3773     YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3774     _collector(collector),
3775     _cms_space(cms_space),
3776     _perm_space(perm_space),
3777     _asynch(asynch), _n_workers(0), _result(true),
3778     _task_queues(task_queues),
3779     _term(_n_workers, task_queues, _collector),
3780     _bit_map_lock(collector->bitMapLock())
3781   {
3782     _requested_size = _n_workers;
3783     _term.set_task(this);
3784     _term_term.set_task(this);
3785     assert(_cms_space->bottom() < _perm_space->bottom(),
3786            "Finger incorrectly initialized below");
3787     _restart_addr = _global_finger = _cms_space->bottom();
3788   }
3789 
3790 
3791   OopTaskQueueSet* task_queues()  { return _task_queues; }
3792 
3793   OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3794 
3795   HeapWord** global_finger_addr() { return &_global_finger; }
3796 
3797   CMSConcMarkingTerminator* terminator() { return &_term; }
3798 
3799   virtual void set_for_termination(int active_workers) {
3800     terminator()->reset_for_reuse(active_workers);
3801   }
3802 
3803   void work(uint worker_id);
3804   bool should_yield() {
3805     return    ConcurrentMarkSweepThread::should_yield()
3806            && !_collector->foregroundGCIsActive()
3807            && _asynch;
3808   }
3809 
3810   virtual void coordinator_yield();  // stuff done by coordinator
3811   bool result() { return _result; }
3812 
3813   void reset(HeapWord* ra) {
3814     assert(_global_finger >= _cms_space->end(),  "Postcondition of ::work(i)");
3815     assert(_global_finger >= _perm_space->end(), "Postcondition of ::work(i)");
3816     assert(ra             <  _perm_space->end(), "ra too large");
3817     _restart_addr = _global_finger = ra;
3818     _term.reset_for_reuse();
3819   }
3820 
3821   static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3822                                            OopTaskQueue* work_q);
3823 
3824  private:
3825   void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3826   void do_work_steal(int i);
3827   void bump_global_finger(HeapWord* f);
3828 };
3829 
3830 bool CMSConcMarkingTerminatorTerminator::should_exit_termination() {
3831   assert(_task != NULL, "Error");
3832   return _task->yielding();
3833   // Note that we do not need the disjunct || _task->should_yield() above
3834   // because we want terminating threads to yield only if the task
3835   // is already in the midst of yielding, which happens only after at least one
3836   // thread has yielded.
3837 }
3838 
3839 void CMSConcMarkingTerminator::yield() {
3840   if (_task->should_yield()) {
3841     _task->yield();
3842   } else {
3843     ParallelTaskTerminator::yield();
3844   }
3845 }
3846 
3847 ////////////////////////////////////////////////////////////////
3848 // Concurrent Marking Algorithm Sketch
3849 ////////////////////////////////////////////////////////////////
3850 // Until all tasks exhausted (both spaces):
3851 // -- claim next available chunk
3852 // -- bump global finger via CAS
3853 // -- find first object that starts in this chunk
3854 //    and start scanning bitmap from that position
3855 // -- scan marked objects for oops
3856 // -- CAS-mark target, and if successful:
3857 //    . if target oop is above global finger (volatile read)
3858 //      nothing to do
3859 //    . if target oop is in chunk and above local finger
3860 //        then nothing to do
3861 //    . else push on work-queue
3862 // -- Deal with possible overflow issues:
3863 //    . local work-queue overflow causes stuff to be pushed on
3864 //      global (common) overflow queue
3865 //    . always first empty local work queue
3866 //    . then get a batch of oops from global work queue if any
3867 //    . then do work stealing
3868 // -- When all tasks claimed (both spaces)
3869 //    and local work queue empty,
3870 //    then in a loop do:
3871 //    . check global overflow stack; steal a batch of oops and trace
3872 //    . try to steal from other threads oif GOS is empty
3873 //    . if neither is available, offer termination
3874 // -- Terminate and return result
3875 //
3876 void CMSConcMarkingTask::work(uint worker_id) {
3877   elapsedTimer _timer;
3878   ResourceMark rm;
3879   HandleMark hm;
3880 
3881   DEBUG_ONLY(_collector->verify_overflow_empty();)
3882 
3883   // Before we begin work, our work queue should be empty
3884   assert(work_queue(worker_id)->size() == 0, "Expected to be empty");
3885   // Scan the bitmap covering _cms_space, tracing through grey objects.
3886   _timer.start();
3887   do_scan_and_mark(worker_id, _cms_space);
3888   _timer.stop();
3889   if (PrintCMSStatistics != 0) {
3890     gclog_or_tty->print_cr("Finished cms space scanning in %dth thread: %3.3f sec",
3891       worker_id, _timer.seconds());
3892       // XXX: need xxx/xxx type of notation, two timers
3893   }
3894 
3895   // ... do the same for the _perm_space
3896   _timer.reset();
3897   _timer.start();
3898   do_scan_and_mark(worker_id, _perm_space);
3899   _timer.stop();
3900   if (PrintCMSStatistics != 0) {
3901     gclog_or_tty->print_cr("Finished perm space scanning in %dth thread: %3.3f sec",
3902       worker_id, _timer.seconds());
3903       // XXX: need xxx/xxx type of notation, two timers
3904   }
3905 
3906   // ... do work stealing
3907   _timer.reset();
3908   _timer.start();
3909   do_work_steal(worker_id);
3910   _timer.stop();
3911   if (PrintCMSStatistics != 0) {
3912     gclog_or_tty->print_cr("Finished work stealing in %dth thread: %3.3f sec",
3913       worker_id, _timer.seconds());
3914       // XXX: need xxx/xxx type of notation, two timers
3915   }
3916   assert(_collector->_markStack.isEmpty(), "Should have been emptied");
3917   assert(work_queue(worker_id)->size() == 0, "Should have been emptied");
3918   // Note that under the current task protocol, the
3919   // following assertion is true even of the spaces
3920   // expanded since the completion of the concurrent
3921   // marking. XXX This will likely change under a strict
3922   // ABORT semantics.
3923   assert(_global_finger >  _cms_space->end() &&
3924          _global_finger >= _perm_space->end(),
3925          "All tasks have been completed");
3926   DEBUG_ONLY(_collector->verify_overflow_empty();)
3927 }
3928 
3929 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
3930   HeapWord* read = _global_finger;
3931   HeapWord* cur  = read;
3932   while (f > read) {
3933     cur = read;
3934     read = (HeapWord*) Atomic::cmpxchg_ptr(f, &_global_finger, cur);
3935     if (cur == read) {
3936       // our cas succeeded
3937       assert(_global_finger >= f, "protocol consistency");
3938       break;
3939     }
3940   }
3941 }
3942 
3943 // This is really inefficient, and should be redone by
3944 // using (not yet available) block-read and -write interfaces to the
3945 // stack and the work_queue. XXX FIX ME !!!
3946 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3947                                                       OopTaskQueue* work_q) {
3948   // Fast lock-free check
3949   if (ovflw_stk->length() == 0) {
3950     return false;
3951   }
3952   assert(work_q->size() == 0, "Shouldn't steal");
3953   MutexLockerEx ml(ovflw_stk->par_lock(),
3954                    Mutex::_no_safepoint_check_flag);
3955   // Grab up to 1/4 the size of the work queue
3956   size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
3957                     (size_t)ParGCDesiredObjsFromOverflowList);
3958   num = MIN2(num, ovflw_stk->length());
3959   for (int i = (int) num; i > 0; i--) {
3960     oop cur = ovflw_stk->pop();
3961     assert(cur != NULL, "Counted wrong?");
3962     work_q->push(cur);
3963   }
3964   return num > 0;
3965 }
3966 
3967 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
3968   SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
3969   int n_tasks = pst->n_tasks();
3970   // We allow that there may be no tasks to do here because
3971   // we are restarting after a stack overflow.
3972   assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
3973   uint nth_task = 0;
3974 
3975   HeapWord* aligned_start = sp->bottom();
3976   if (sp->used_region().contains(_restart_addr)) {
3977     // Align down to a card boundary for the start of 0th task
3978     // for this space.
3979     aligned_start =
3980       (HeapWord*)align_size_down((uintptr_t)_restart_addr,
3981                                  CardTableModRefBS::card_size);
3982   }
3983 
3984   size_t chunk_size = sp->marking_task_size();
3985   while (!pst->is_task_claimed(/* reference */ nth_task)) {
3986     // Having claimed the nth task in this space,
3987     // compute the chunk that it corresponds to:
3988     MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
3989                                aligned_start + (nth_task+1)*chunk_size);
3990     // Try and bump the global finger via a CAS;
3991     // note that we need to do the global finger bump
3992     // _before_ taking the intersection below, because
3993     // the task corresponding to that region will be
3994     // deemed done even if the used_region() expands
3995     // because of allocation -- as it almost certainly will
3996     // during start-up while the threads yield in the
3997     // closure below.
3998     HeapWord* finger = span.end();
3999     bump_global_finger(finger);   // atomically
4000     // There are null tasks here corresponding to chunks
4001     // beyond the "top" address of the space.
4002     span = span.intersection(sp->used_region());
4003     if (!span.is_empty()) {  // Non-null task
4004       HeapWord* prev_obj;
4005       assert(!span.contains(_restart_addr) || nth_task == 0,
4006              "Inconsistency");
4007       if (nth_task == 0) {
4008         // For the 0th task, we'll not need to compute a block_start.
4009         if (span.contains(_restart_addr)) {
4010           // In the case of a restart because of stack overflow,
4011           // we might additionally skip a chunk prefix.
4012           prev_obj = _restart_addr;
4013         } else {
4014           prev_obj = span.start();
4015         }
4016       } else {
4017         // We want to skip the first object because
4018         // the protocol is to scan any object in its entirety
4019         // that _starts_ in this span; a fortiori, any
4020         // object starting in an earlier span is scanned
4021         // as part of an earlier claimed task.
4022         // Below we use the "careful" version of block_start
4023         // so we do not try to navigate uninitialized objects.
4024         prev_obj = sp->block_start_careful(span.start());
4025         // Below we use a variant of block_size that uses the
4026         // Printezis bits to avoid waiting for allocated
4027         // objects to become initialized/parsable.
4028         while (prev_obj < span.start()) {
4029           size_t sz = sp->block_size_no_stall(prev_obj, _collector);
4030           if (sz > 0) {
4031             prev_obj += sz;
4032           } else {
4033             // In this case we may end up doing a bit of redundant
4034             // scanning, but that appears unavoidable, short of
4035             // locking the free list locks; see bug 6324141.
4036             break;
4037           }
4038         }
4039       }
4040       if (prev_obj < span.end()) {
4041         MemRegion my_span = MemRegion(prev_obj, span.end());
4042         // Do the marking work within a non-empty span --
4043         // the last argument to the constructor indicates whether the
4044         // iteration should be incremental with periodic yields.
4045         Par_MarkFromRootsClosure cl(this, _collector, my_span,
4046                                     &_collector->_markBitMap,
4047                                     work_queue(i),
4048                                     &_collector->_markStack,
4049                                     &_collector->_revisitStack,
4050                                     _asynch);
4051         _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
4052       } // else nothing to do for this task
4053     }   // else nothing to do for this task
4054   }
4055   // We'd be tempted to assert here that since there are no
4056   // more tasks left to claim in this space, the global_finger
4057   // must exceed space->top() and a fortiori space->end(). However,
4058   // that would not quite be correct because the bumping of
4059   // global_finger occurs strictly after the claiming of a task,
4060   // so by the time we reach here the global finger may not yet
4061   // have been bumped up by the thread that claimed the last
4062   // task.
4063   pst->all_tasks_completed();
4064 }
4065 
4066 class Par_ConcMarkingClosure: public Par_KlassRememberingOopClosure {
4067  private:
4068   CMSConcMarkingTask* _task;
4069   MemRegion     _span;
4070   CMSBitMap*    _bit_map;
4071   CMSMarkStack* _overflow_stack;
4072   OopTaskQueue* _work_queue;
4073  protected:
4074   DO_OOP_WORK_DEFN
4075  public:
4076   Par_ConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue,
4077                          CMSBitMap* bit_map, CMSMarkStack* overflow_stack,
4078                          CMSMarkStack* revisit_stack):
4079     Par_KlassRememberingOopClosure(collector, collector->ref_processor(), revisit_stack),
4080     _task(task),
4081     _span(collector->_span),
4082     _work_queue(work_queue),
4083     _bit_map(bit_map),
4084     _overflow_stack(overflow_stack)
4085   { }
4086   virtual void do_oop(oop* p);
4087   virtual void do_oop(narrowOop* p);
4088   void trim_queue(size_t max);
4089   void handle_stack_overflow(HeapWord* lost);
4090   void do_yield_check() {
4091     if (_task->should_yield()) {
4092       _task->yield();
4093     }
4094   }
4095 };
4096 
4097 // Grey object scanning during work stealing phase --
4098 // the salient assumption here is that any references
4099 // that are in these stolen objects being scanned must
4100 // already have been initialized (else they would not have
4101 // been published), so we do not need to check for
4102 // uninitialized objects before pushing here.
4103 void Par_ConcMarkingClosure::do_oop(oop obj) {
4104   assert(obj->is_oop_or_null(true), "expected an oop or NULL");
4105   HeapWord* addr = (HeapWord*)obj;
4106   // Check if oop points into the CMS generation
4107   // and is not marked
4108   if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
4109     // a white object ...
4110     // If we manage to "claim" the object, by being the
4111     // first thread to mark it, then we push it on our
4112     // marking stack
4113     if (_bit_map->par_mark(addr)) {     // ... now grey
4114       // push on work queue (grey set)
4115       bool simulate_overflow = false;
4116       NOT_PRODUCT(
4117         if (CMSMarkStackOverflowALot &&
4118             _collector->simulate_overflow()) {
4119           // simulate a stack overflow
4120           simulate_overflow = true;
4121         }
4122       )
4123       if (simulate_overflow ||
4124           !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
4125         // stack overflow
4126         if (PrintCMSStatistics != 0) {
4127           gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
4128                                  SIZE_FORMAT, _overflow_stack->capacity());
4129         }
4130         // We cannot assert that the overflow stack is full because
4131         // it may have been emptied since.
4132         assert(simulate_overflow ||
4133                _work_queue->size() == _work_queue->max_elems(),
4134               "Else push should have succeeded");
4135         handle_stack_overflow(addr);
4136       }
4137     } // Else, some other thread got there first
4138     do_yield_check();
4139   }
4140 }
4141 
4142 void Par_ConcMarkingClosure::do_oop(oop* p)       { Par_ConcMarkingClosure::do_oop_work(p); }
4143 void Par_ConcMarkingClosure::do_oop(narrowOop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
4144 
4145 void Par_ConcMarkingClosure::trim_queue(size_t max) {
4146   while (_work_queue->size() > max) {
4147     oop new_oop;
4148     if (_work_queue->pop_local(new_oop)) {
4149       assert(new_oop->is_oop(), "Should be an oop");
4150       assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
4151       assert(_span.contains((HeapWord*)new_oop), "Not in span");
4152       assert(new_oop->is_parsable(), "Should be parsable");
4153       new_oop->oop_iterate(this);  // do_oop() above
4154       do_yield_check();
4155     }
4156   }
4157 }
4158 
4159 // Upon stack overflow, we discard (part of) the stack,
4160 // remembering the least address amongst those discarded
4161 // in CMSCollector's _restart_address.
4162 void Par_ConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
4163   // We need to do this under a mutex to prevent other
4164   // workers from interfering with the work done below.
4165   MutexLockerEx ml(_overflow_stack->par_lock(),
4166                    Mutex::_no_safepoint_check_flag);
4167   // Remember the least grey address discarded
4168   HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
4169   _collector->lower_restart_addr(ra);
4170   _overflow_stack->reset();  // discard stack contents
4171   _overflow_stack->expand(); // expand the stack if possible
4172 }
4173 
4174 
4175 void CMSConcMarkingTask::do_work_steal(int i) {
4176   OopTaskQueue* work_q = work_queue(i);
4177   oop obj_to_scan;
4178   CMSBitMap* bm = &(_collector->_markBitMap);
4179   CMSMarkStack* ovflw = &(_collector->_markStack);
4180   CMSMarkStack* revisit = &(_collector->_revisitStack);
4181   int* seed = _collector->hash_seed(i);
4182   Par_ConcMarkingClosure cl(_collector, this, work_q, bm, ovflw, revisit);
4183   while (true) {
4184     cl.trim_queue(0);
4185     assert(work_q->size() == 0, "Should have been emptied above");
4186     if (get_work_from_overflow_stack(ovflw, work_q)) {
4187       // Can't assert below because the work obtained from the
4188       // overflow stack may already have been stolen from us.
4189       // assert(work_q->size() > 0, "Work from overflow stack");
4190       continue;
4191     } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
4192       assert(obj_to_scan->is_oop(), "Should be an oop");
4193       assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
4194       obj_to_scan->oop_iterate(&cl);
4195     } else if (terminator()->offer_termination(&_term_term)) {
4196       assert(work_q->size() == 0, "Impossible!");
4197       break;
4198     } else if (yielding() || should_yield()) {
4199       yield();
4200     }
4201   }
4202 }
4203 
4204 // This is run by the CMS (coordinator) thread.
4205 void CMSConcMarkingTask::coordinator_yield() {
4206   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
4207          "CMS thread should hold CMS token");
4208   DEBUG_ONLY(RememberKlassesChecker mux(false);)
4209   // First give up the locks, then yield, then re-lock
4210   // We should probably use a constructor/destructor idiom to
4211   // do this unlock/lock or modify the MutexUnlocker class to
4212   // serve our purpose. XXX
4213   assert_lock_strong(_bit_map_lock);
4214   _bit_map_lock->unlock();
4215   ConcurrentMarkSweepThread::desynchronize(true);
4216   ConcurrentMarkSweepThread::acknowledge_yield_request();
4217   _collector->stopTimer();
4218   if (PrintCMSStatistics != 0) {
4219     _collector->incrementYields();
4220   }
4221   _collector->icms_wait();
4222 
4223   // It is possible for whichever thread initiated the yield request
4224   // not to get a chance to wake up and take the bitmap lock between
4225   // this thread releasing it and reacquiring it. So, while the
4226   // should_yield() flag is on, let's sleep for a bit to give the
4227   // other thread a chance to wake up. The limit imposed on the number
4228   // of iterations is defensive, to avoid any unforseen circumstances
4229   // putting us into an infinite loop. Since it's always been this
4230   // (coordinator_yield()) method that was observed to cause the
4231   // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
4232   // which is by default non-zero. For the other seven methods that
4233   // also perform the yield operation, as are using a different
4234   // parameter (CMSYieldSleepCount) which is by default zero. This way we
4235   // can enable the sleeping for those methods too, if necessary.
4236   // See 6442774.
4237   //
4238   // We really need to reconsider the synchronization between the GC
4239   // thread and the yield-requesting threads in the future and we
4240   // should really use wait/notify, which is the recommended
4241   // way of doing this type of interaction. Additionally, we should
4242   // consolidate the eight methods that do the yield operation and they
4243   // are almost identical into one for better maintenability and
4244   // readability. See 6445193.
4245   //
4246   // Tony 2006.06.29
4247   for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
4248                    ConcurrentMarkSweepThread::should_yield() &&
4249                    !CMSCollector::foregroundGCIsActive(); ++i) {
4250     os::sleep(Thread::current(), 1, false);
4251     ConcurrentMarkSweepThread::acknowledge_yield_request();
4252   }
4253 
4254   ConcurrentMarkSweepThread::synchronize(true);
4255   _bit_map_lock->lock_without_safepoint_check();
4256   _collector->startTimer();
4257 }
4258 
4259 bool CMSCollector::do_marking_mt(bool asynch) {
4260   assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition");
4261   int num_workers = AdaptiveSizePolicy::calc_active_conc_workers(
4262                                        conc_workers()->total_workers(),
4263                                        conc_workers()->active_workers(),
4264                                        Threads::number_of_non_daemon_threads());
4265   conc_workers()->set_active_workers(num_workers);
4266 
4267   CompactibleFreeListSpace* cms_space  = _cmsGen->cmsSpace();
4268   CompactibleFreeListSpace* perm_space = _permGen->cmsSpace();
4269 
4270   CMSConcMarkingTask tsk(this,
4271                          cms_space,
4272                          perm_space,
4273                          asynch,
4274                          conc_workers(),
4275                          task_queues());
4276 
4277   // Since the actual number of workers we get may be different
4278   // from the number we requested above, do we need to do anything different
4279   // below? In particular, may be we need to subclass the SequantialSubTasksDone
4280   // class?? XXX
4281   cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
4282   perm_space->initialize_sequential_subtasks_for_marking(num_workers);
4283 
4284   // Refs discovery is already non-atomic.
4285   assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
4286   assert(ref_processor()->discovery_is_mt(), "Discovery should be MT");
4287   DEBUG_ONLY(RememberKlassesChecker cmx(should_unload_classes());)
4288   conc_workers()->start_task(&tsk);
4289   while (tsk.yielded()) {
4290     tsk.coordinator_yield();
4291     conc_workers()->continue_task(&tsk);
4292   }
4293   // If the task was aborted, _restart_addr will be non-NULL
4294   assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
4295   while (_restart_addr != NULL) {
4296     // XXX For now we do not make use of ABORTED state and have not
4297     // yet implemented the right abort semantics (even in the original
4298     // single-threaded CMS case). That needs some more investigation
4299     // and is deferred for now; see CR# TBF. 07252005YSR. XXX
4300     assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
4301     // If _restart_addr is non-NULL, a marking stack overflow
4302     // occurred; we need to do a fresh marking iteration from the
4303     // indicated restart address.
4304     if (_foregroundGCIsActive && asynch) {
4305       // We may be running into repeated stack overflows, having
4306       // reached the limit of the stack size, while making very
4307       // slow forward progress. It may be best to bail out and
4308       // let the foreground collector do its job.
4309       // Clear _restart_addr, so that foreground GC
4310       // works from scratch. This avoids the headache of
4311       // a "rescan" which would otherwise be needed because
4312       // of the dirty mod union table & card table.
4313       _restart_addr = NULL;
4314       return false;
4315     }
4316     // Adjust the task to restart from _restart_addr
4317     tsk.reset(_restart_addr);
4318     cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
4319                   _restart_addr);
4320     perm_space->initialize_sequential_subtasks_for_marking(num_workers,
4321                   _restart_addr);
4322     _restart_addr = NULL;
4323     // Get the workers going again
4324     conc_workers()->start_task(&tsk);
4325     while (tsk.yielded()) {
4326       tsk.coordinator_yield();
4327       conc_workers()->continue_task(&tsk);
4328     }
4329   }
4330   assert(tsk.completed(), "Inconsistency");
4331   assert(tsk.result() == true, "Inconsistency");
4332   return true;
4333 }
4334 
4335 bool CMSCollector::do_marking_st(bool asynch) {
4336   ResourceMark rm;
4337   HandleMark   hm;
4338 
4339   // Temporarily make refs discovery single threaded (non-MT)
4340   ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
4341   MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
4342     &_markStack, &_revisitStack, CMSYield && asynch);
4343   // the last argument to iterate indicates whether the iteration
4344   // should be incremental with periodic yields.
4345   _markBitMap.iterate(&markFromRootsClosure);
4346   // If _restart_addr is non-NULL, a marking stack overflow
4347   // occurred; we need to do a fresh iteration from the
4348   // indicated restart address.
4349   while (_restart_addr != NULL) {
4350     if (_foregroundGCIsActive && asynch) {
4351       // We may be running into repeated stack overflows, having
4352       // reached the limit of the stack size, while making very
4353       // slow forward progress. It may be best to bail out and
4354       // let the foreground collector do its job.
4355       // Clear _restart_addr, so that foreground GC
4356       // works from scratch. This avoids the headache of
4357       // a "rescan" which would otherwise be needed because
4358       // of the dirty mod union table & card table.
4359       _restart_addr = NULL;
4360       return false;  // indicating failure to complete marking
4361     }
4362     // Deal with stack overflow:
4363     // we restart marking from _restart_addr
4364     HeapWord* ra = _restart_addr;
4365     markFromRootsClosure.reset(ra);
4366     _restart_addr = NULL;
4367     _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
4368   }
4369   return true;
4370 }
4371 
4372 void CMSCollector::preclean() {
4373   check_correct_thread_executing();
4374   assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
4375   verify_work_stacks_empty();
4376   verify_overflow_empty();
4377   _abort_preclean = false;
4378   if (CMSPrecleaningEnabled) {
4379     _eden_chunk_index = 0;
4380     size_t used = get_eden_used();
4381     size_t capacity = get_eden_capacity();
4382     // Don't start sampling unless we will get sufficiently
4383     // many samples.
4384     if (used < (capacity/(CMSScheduleRemarkSamplingRatio * 100)
4385                 * CMSScheduleRemarkEdenPenetration)) {
4386       _start_sampling = true;
4387     } else {
4388       _start_sampling = false;
4389     }
4390     TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
4391     CMSPhaseAccounting pa(this, "preclean", !PrintGCDetails);
4392     preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
4393   }
4394   CMSTokenSync x(true); // is cms thread
4395   if (CMSPrecleaningEnabled) {
4396     sample_eden();
4397     _collectorState = AbortablePreclean;
4398   } else {
4399     _collectorState = FinalMarking;
4400   }
4401   verify_work_stacks_empty();
4402   verify_overflow_empty();
4403 }
4404 
4405 // Try and schedule the remark such that young gen
4406 // occupancy is CMSScheduleRemarkEdenPenetration %.
4407 void CMSCollector::abortable_preclean() {
4408   check_correct_thread_executing();
4409   assert(CMSPrecleaningEnabled,  "Inconsistent control state");
4410   assert(_collectorState == AbortablePreclean, "Inconsistent control state");
4411 
4412   // If Eden's current occupancy is below this threshold,
4413   // immediately schedule the remark; else preclean
4414   // past the next scavenge in an effort to
4415   // schedule the pause as described avove. By choosing
4416   // CMSScheduleRemarkEdenSizeThreshold >= max eden size
4417   // we will never do an actual abortable preclean cycle.
4418   if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
4419     TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
4420     CMSPhaseAccounting pa(this, "abortable-preclean", !PrintGCDetails);
4421     // We need more smarts in the abortable preclean
4422     // loop below to deal with cases where allocation
4423     // in young gen is very very slow, and our precleaning
4424     // is running a losing race against a horde of
4425     // mutators intent on flooding us with CMS updates
4426     // (dirty cards).
4427     // One, admittedly dumb, strategy is to give up
4428     // after a certain number of abortable precleaning loops
4429     // or after a certain maximum time. We want to make
4430     // this smarter in the next iteration.
4431     // XXX FIX ME!!! YSR
4432     size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
4433     while (!(should_abort_preclean() ||
4434              ConcurrentMarkSweepThread::should_terminate())) {
4435       workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
4436       cumworkdone += workdone;
4437       loops++;
4438       // Voluntarily terminate abortable preclean phase if we have
4439       // been at it for too long.
4440       if ((CMSMaxAbortablePrecleanLoops != 0) &&
4441           loops >= CMSMaxAbortablePrecleanLoops) {
4442         if (PrintGCDetails) {
4443           gclog_or_tty->print(" CMS: abort preclean due to loops ");
4444         }
4445         break;
4446       }
4447       if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
4448         if (PrintGCDetails) {
4449           gclog_or_tty->print(" CMS: abort preclean due to time ");
4450         }
4451         break;
4452       }
4453       // If we are doing little work each iteration, we should
4454       // take a short break.
4455       if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
4456         // Sleep for some time, waiting for work to accumulate
4457         stopTimer();
4458         cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
4459         startTimer();
4460         waited++;
4461       }
4462     }
4463     if (PrintCMSStatistics > 0) {
4464       gclog_or_tty->print(" [%d iterations, %d waits, %d cards)] ",
4465                           loops, waited, cumworkdone);
4466     }
4467   }
4468   CMSTokenSync x(true); // is cms thread
4469   if (_collectorState != Idling) {
4470     assert(_collectorState == AbortablePreclean,
4471            "Spontaneous state transition?");
4472     _collectorState = FinalMarking;
4473   } // Else, a foreground collection completed this CMS cycle.
4474   return;
4475 }
4476 
4477 // Respond to an Eden sampling opportunity
4478 void CMSCollector::sample_eden() {
4479   // Make sure a young gc cannot sneak in between our
4480   // reading and recording of a sample.
4481   assert(Thread::current()->is_ConcurrentGC_thread(),
4482          "Only the cms thread may collect Eden samples");
4483   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
4484          "Should collect samples while holding CMS token");
4485   if (!_start_sampling) {
4486     return;
4487   }
4488   if (_eden_chunk_array) {
4489     if (_eden_chunk_index < _eden_chunk_capacity) {
4490       _eden_chunk_array[_eden_chunk_index] = *_top_addr;   // take sample
4491       assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4492              "Unexpected state of Eden");
4493       // We'd like to check that what we just sampled is an oop-start address;
4494       // however, we cannot do that here since the object may not yet have been
4495       // initialized. So we'll instead do the check when we _use_ this sample
4496       // later.
4497       if (_eden_chunk_index == 0 ||
4498           (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4499                          _eden_chunk_array[_eden_chunk_index-1])
4500            >= CMSSamplingGrain)) {
4501         _eden_chunk_index++;  // commit sample
4502       }
4503     }
4504   }
4505   if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
4506     size_t used = get_eden_used();
4507     size_t capacity = get_eden_capacity();
4508     assert(used <= capacity, "Unexpected state of Eden");
4509     if (used >  (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
4510       _abort_preclean = true;
4511     }
4512   }
4513 }
4514 
4515 
4516 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
4517   assert(_collectorState == Precleaning ||
4518          _collectorState == AbortablePreclean, "incorrect state");
4519   ResourceMark rm;
4520   HandleMark   hm;
4521 
4522   // Precleaning is currently not MT but the reference processor
4523   // may be set for MT.  Disable it temporarily here.
4524   ReferenceProcessor* rp = ref_processor();
4525   ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false);
4526 
4527   // Do one pass of scrubbing the discovered reference lists
4528   // to remove any reference objects with strongly-reachable
4529   // referents.
4530   if (clean_refs) {
4531     CMSPrecleanRefsYieldClosure yield_cl(this);
4532     assert(rp->span().equals(_span), "Spans should be equal");
4533     CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
4534                                    &_markStack, &_revisitStack,
4535                                    true /* preclean */);
4536     CMSDrainMarkingStackClosure complete_trace(this,
4537                                    _span, &_markBitMap, &_markStack,
4538                                    &keep_alive, true /* preclean */);
4539 
4540     // We don't want this step to interfere with a young
4541     // collection because we don't want to take CPU
4542     // or memory bandwidth away from the young GC threads
4543     // (which may be as many as there are CPUs).
4544     // Note that we don't need to protect ourselves from
4545     // interference with mutators because they can't
4546     // manipulate the discovered reference lists nor affect
4547     // the computed reachability of the referents, the
4548     // only properties manipulated by the precleaning
4549     // of these reference lists.
4550     stopTimer();
4551     CMSTokenSyncWithLocks x(true /* is cms thread */,
4552                             bitMapLock());
4553     startTimer();
4554     sample_eden();
4555 
4556     // The following will yield to allow foreground
4557     // collection to proceed promptly. XXX YSR:
4558     // The code in this method may need further
4559     // tweaking for better performance and some restructuring
4560     // for cleaner interfaces.
4561     GCTimer *gc_timer = NULL; // Currently not tracing concurrent phases
4562     rp->preclean_discovered_references(
4563           rp->is_alive_non_header(), &keep_alive, &complete_trace,
4564           &yield_cl, should_unload_classes(), gc_timer);
4565   }
4566 
4567   if (clean_survivor) {  // preclean the active survivor space(s)
4568     assert(_young_gen->kind() == Generation::DefNew ||
4569            _young_gen->kind() == Generation::ParNew ||
4570            _young_gen->kind() == Generation::ASParNew,
4571          "incorrect type for cast");
4572     DefNewGeneration* dng = (DefNewGeneration*)_young_gen;
4573     PushAndMarkClosure pam_cl(this, _span, ref_processor(),
4574                              &_markBitMap, &_modUnionTable,
4575                              &_markStack, &_revisitStack,
4576                              true /* precleaning phase */);
4577     stopTimer();
4578     CMSTokenSyncWithLocks ts(true /* is cms thread */,
4579                              bitMapLock());
4580     startTimer();
4581     unsigned int before_count =
4582       GenCollectedHeap::heap()->total_collections();
4583     SurvivorSpacePrecleanClosure
4584       sss_cl(this, _span, &_markBitMap, &_markStack,
4585              &pam_cl, before_count, CMSYield);
4586     DEBUG_ONLY(RememberKlassesChecker mx(should_unload_classes());)
4587     dng->from()->object_iterate_careful(&sss_cl);
4588     dng->to()->object_iterate_careful(&sss_cl);
4589   }
4590   MarkRefsIntoAndScanClosure
4591     mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
4592              &_markStack, &_revisitStack, this, CMSYield,
4593              true /* precleaning phase */);
4594   // CAUTION: The following closure has persistent state that may need to
4595   // be reset upon a decrease in the sequence of addresses it
4596   // processes.
4597   ScanMarkedObjectsAgainCarefullyClosure
4598     smoac_cl(this, _span,
4599       &_markBitMap, &_markStack, &_revisitStack, &mrias_cl, CMSYield);
4600 
4601   // Preclean dirty cards in ModUnionTable and CardTable using
4602   // appropriate convergence criterion;
4603   // repeat CMSPrecleanIter times unless we find that
4604   // we are losing.
4605   assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
4606   assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
4607          "Bad convergence multiplier");
4608   assert(CMSPrecleanThreshold >= 100,
4609          "Unreasonably low CMSPrecleanThreshold");
4610 
4611   size_t numIter, cumNumCards, lastNumCards, curNumCards;
4612   for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
4613        numIter < CMSPrecleanIter;
4614        numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
4615     curNumCards  = preclean_mod_union_table(_cmsGen, &smoac_cl);
4616     if (CMSPermGenPrecleaningEnabled) {
4617       curNumCards  += preclean_mod_union_table(_permGen, &smoac_cl);
4618     }
4619     if (Verbose && PrintGCDetails) {
4620       gclog_or_tty->print(" (modUnionTable: %d cards)", curNumCards);
4621     }
4622     // Either there are very few dirty cards, so re-mark
4623     // pause will be small anyway, or our pre-cleaning isn't
4624     // that much faster than the rate at which cards are being
4625     // dirtied, so we might as well stop and re-mark since
4626     // precleaning won't improve our re-mark time by much.
4627     if (curNumCards <= CMSPrecleanThreshold ||
4628         (numIter > 0 &&
4629          (curNumCards * CMSPrecleanDenominator >
4630          lastNumCards * CMSPrecleanNumerator))) {
4631       numIter++;
4632       cumNumCards += curNumCards;
4633       break;
4634     }
4635   }
4636   curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
4637   if (CMSPermGenPrecleaningEnabled) {
4638     curNumCards += preclean_card_table(_permGen, &smoac_cl);
4639   }
4640   cumNumCards += curNumCards;
4641   if (PrintGCDetails && PrintCMSStatistics != 0) {
4642     gclog_or_tty->print_cr(" (cardTable: %d cards, re-scanned %d cards, %d iterations)",
4643                   curNumCards, cumNumCards, numIter);
4644   }
4645   return cumNumCards;   // as a measure of useful work done
4646 }
4647 
4648 // PRECLEANING NOTES:
4649 // Precleaning involves:
4650 // . reading the bits of the modUnionTable and clearing the set bits.
4651 // . For the cards corresponding to the set bits, we scan the
4652 //   objects on those cards. This means we need the free_list_lock
4653 //   so that we can safely iterate over the CMS space when scanning
4654 //   for oops.
4655 // . When we scan the objects, we'll be both reading and setting
4656 //   marks in the marking bit map, so we'll need the marking bit map.
4657 // . For protecting _collector_state transitions, we take the CGC_lock.
4658 //   Note that any races in the reading of of card table entries by the
4659 //   CMS thread on the one hand and the clearing of those entries by the
4660 //   VM thread or the setting of those entries by the mutator threads on the
4661 //   other are quite benign. However, for efficiency it makes sense to keep
4662 //   the VM thread from racing with the CMS thread while the latter is
4663 //   dirty card info to the modUnionTable. We therefore also use the
4664 //   CGC_lock to protect the reading of the card table and the mod union
4665 //   table by the CM thread.
4666 // . We run concurrently with mutator updates, so scanning
4667 //   needs to be done carefully  -- we should not try to scan
4668 //   potentially uninitialized objects.
4669 //
4670 // Locking strategy: While holding the CGC_lock, we scan over and
4671 // reset a maximal dirty range of the mod union / card tables, then lock
4672 // the free_list_lock and bitmap lock to do a full marking, then
4673 // release these locks; and repeat the cycle. This allows for a
4674 // certain amount of fairness in the sharing of these locks between
4675 // the CMS collector on the one hand, and the VM thread and the
4676 // mutators on the other.
4677 
4678 // NOTE: preclean_mod_union_table() and preclean_card_table()
4679 // further below are largely identical; if you need to modify
4680 // one of these methods, please check the other method too.
4681 
4682 size_t CMSCollector::preclean_mod_union_table(
4683   ConcurrentMarkSweepGeneration* gen,
4684   ScanMarkedObjectsAgainCarefullyClosure* cl) {
4685   verify_work_stacks_empty();
4686   verify_overflow_empty();
4687 
4688   // Turn off checking for this method but turn it back on
4689   // selectively.  There are yield points in this method
4690   // but it is difficult to turn the checking off just around
4691   // the yield points.  It is simpler to selectively turn
4692   // it on.
4693   DEBUG_ONLY(RememberKlassesChecker mux(false);)
4694 
4695   // strategy: starting with the first card, accumulate contiguous
4696   // ranges of dirty cards; clear these cards, then scan the region
4697   // covered by these cards.
4698 
4699   // Since all of the MUT is committed ahead, we can just use
4700   // that, in case the generations expand while we are precleaning.
4701   // It might also be fine to just use the committed part of the
4702   // generation, but we might potentially miss cards when the
4703   // generation is rapidly expanding while we are in the midst
4704   // of precleaning.
4705   HeapWord* startAddr = gen->reserved().start();
4706   HeapWord* endAddr   = gen->reserved().end();
4707 
4708   cl->setFreelistLock(gen->freelistLock());   // needed for yielding
4709 
4710   size_t numDirtyCards, cumNumDirtyCards;
4711   HeapWord *nextAddr, *lastAddr;
4712   for (cumNumDirtyCards = numDirtyCards = 0,
4713        nextAddr = lastAddr = startAddr;
4714        nextAddr < endAddr;
4715        nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4716 
4717     ResourceMark rm;
4718     HandleMark   hm;
4719 
4720     MemRegion dirtyRegion;
4721     {
4722       stopTimer();
4723       // Potential yield point
4724       CMSTokenSync ts(true);
4725       startTimer();
4726       sample_eden();
4727       // Get dirty region starting at nextOffset (inclusive),
4728       // simultaneously clearing it.
4729       dirtyRegion =
4730         _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
4731       assert(dirtyRegion.start() >= nextAddr,
4732              "returned region inconsistent?");
4733     }
4734     // Remember where the next search should begin.
4735     // The returned region (if non-empty) is a right open interval,
4736     // so lastOffset is obtained from the right end of that
4737     // interval.
4738     lastAddr = dirtyRegion.end();
4739     // Should do something more transparent and less hacky XXX
4740     numDirtyCards =
4741       _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
4742 
4743     // We'll scan the cards in the dirty region (with periodic
4744     // yields for foreground GC as needed).
4745     if (!dirtyRegion.is_empty()) {
4746       assert(numDirtyCards > 0, "consistency check");
4747       HeapWord* stop_point = NULL;
4748       stopTimer();
4749       // Potential yield point
4750       CMSTokenSyncWithLocks ts(true, gen->freelistLock(),
4751                                bitMapLock());
4752       startTimer();
4753       {
4754         verify_work_stacks_empty();
4755         verify_overflow_empty();
4756         sample_eden();
4757         DEBUG_ONLY(RememberKlassesChecker mx(should_unload_classes());)
4758         stop_point =
4759           gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4760       }
4761       if (stop_point != NULL) {
4762         // The careful iteration stopped early either because it found an
4763         // uninitialized object, or because we were in the midst of an
4764         // "abortable preclean", which should now be aborted. Redirty
4765         // the bits corresponding to the partially-scanned or unscanned
4766         // cards. We'll either restart at the next block boundary or
4767         // abort the preclean.
4768         assert((CMSPermGenPrecleaningEnabled && (gen == _permGen)) ||
4769                (_collectorState == AbortablePreclean && should_abort_preclean()),
4770                "Unparsable objects should only be in perm gen.");
4771         _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
4772         if (should_abort_preclean()) {
4773           break; // out of preclean loop
4774         } else {
4775           // Compute the next address at which preclean should pick up;
4776           // might need bitMapLock in order to read P-bits.
4777           lastAddr = next_card_start_after_block(stop_point);
4778         }
4779       }
4780     } else {
4781       assert(lastAddr == endAddr, "consistency check");
4782       assert(numDirtyCards == 0, "consistency check");
4783       break;
4784     }
4785   }
4786   verify_work_stacks_empty();
4787   verify_overflow_empty();
4788   return cumNumDirtyCards;
4789 }
4790 
4791 // NOTE: preclean_mod_union_table() above and preclean_card_table()
4792 // below are largely identical; if you need to modify
4793 // one of these methods, please check the other method too.
4794 
4795 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* gen,
4796   ScanMarkedObjectsAgainCarefullyClosure* cl) {
4797   // strategy: it's similar to precleamModUnionTable above, in that
4798   // we accumulate contiguous ranges of dirty cards, mark these cards
4799   // precleaned, then scan the region covered by these cards.
4800   HeapWord* endAddr   = (HeapWord*)(gen->_virtual_space.high());
4801   HeapWord* startAddr = (HeapWord*)(gen->_virtual_space.low());
4802 
4803   cl->setFreelistLock(gen->freelistLock());   // needed for yielding
4804 
4805   size_t numDirtyCards, cumNumDirtyCards;
4806   HeapWord *lastAddr, *nextAddr;
4807 
4808   for (cumNumDirtyCards = numDirtyCards = 0,
4809        nextAddr = lastAddr = startAddr;
4810        nextAddr < endAddr;
4811        nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4812 
4813     ResourceMark rm;
4814     HandleMark   hm;
4815 
4816     MemRegion dirtyRegion;
4817     {
4818       // See comments in "Precleaning notes" above on why we
4819       // do this locking. XXX Could the locking overheads be
4820       // too high when dirty cards are sparse? [I don't think so.]
4821       stopTimer();
4822       CMSTokenSync x(true); // is cms thread
4823       startTimer();
4824       sample_eden();
4825       // Get and clear dirty region from card table
4826       dirtyRegion = _ct->ct_bs()->dirty_card_range_after_reset(
4827                                     MemRegion(nextAddr, endAddr),
4828                                     true,
4829                                     CardTableModRefBS::precleaned_card_val());
4830 
4831       assert(dirtyRegion.start() >= nextAddr,
4832              "returned region inconsistent?");
4833     }
4834     lastAddr = dirtyRegion.end();
4835     numDirtyCards =
4836       dirtyRegion.word_size()/CardTableModRefBS::card_size_in_words;
4837 
4838     if (!dirtyRegion.is_empty()) {
4839       stopTimer();
4840       CMSTokenSyncWithLocks ts(true, gen->freelistLock(), bitMapLock());
4841       startTimer();
4842       sample_eden();
4843       verify_work_stacks_empty();
4844       verify_overflow_empty();
4845       DEBUG_ONLY(RememberKlassesChecker mx(should_unload_classes());)
4846       HeapWord* stop_point =
4847         gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4848       if (stop_point != NULL) {
4849         // The careful iteration stopped early because it found an
4850         // uninitialized object.  Redirty the bits corresponding to the
4851         // partially-scanned or unscanned cards, and start again at the
4852         // next block boundary.
4853         assert(CMSPermGenPrecleaningEnabled ||
4854                (_collectorState == AbortablePreclean && should_abort_preclean()),
4855                "Unparsable objects should only be in perm gen.");
4856         _ct->ct_bs()->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4857         if (should_abort_preclean()) {
4858           break; // out of preclean loop
4859         } else {
4860           // Compute the next address at which preclean should pick up.
4861           lastAddr = next_card_start_after_block(stop_point);
4862         }
4863       }
4864     } else {
4865       break;
4866     }
4867   }
4868   verify_work_stacks_empty();
4869   verify_overflow_empty();
4870   return cumNumDirtyCards;
4871 }
4872 
4873 void CMSCollector::checkpointRootsFinal(bool asynch,
4874   bool clear_all_soft_refs, bool init_mark_was_synchronous) {
4875   assert(_collectorState == FinalMarking, "incorrect state transition?");
4876   check_correct_thread_executing();
4877   // world is stopped at this checkpoint
4878   assert(SafepointSynchronize::is_at_safepoint(),
4879          "world should be stopped");
4880   TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
4881 
4882   verify_work_stacks_empty();
4883   verify_overflow_empty();
4884 
4885   SpecializationStats::clear();
4886   if (PrintGCDetails) {
4887     gclog_or_tty->print("[YG occupancy: "SIZE_FORMAT" K ("SIZE_FORMAT" K)]",
4888                         _young_gen->used() / K,
4889                         _young_gen->capacity() / K);
4890   }
4891   if (asynch) {
4892     if (CMSScavengeBeforeRemark) {
4893       GenCollectedHeap* gch = GenCollectedHeap::heap();
4894       // Temporarily set flag to false, GCH->do_collection will
4895       // expect it to be false and set to true
4896       FlagSetting fl(gch->_is_gc_active, false);
4897       NOT_PRODUCT(GCTraceTime t("Scavenge-Before-Remark",
4898         PrintGCDetails && Verbose, true, _gc_timer_cm);)
4899       int level = _cmsGen->level() - 1;
4900       if (level >= 0) {
4901         gch->do_collection(true,        // full (i.e. force, see below)
4902                            false,       // !clear_all_soft_refs
4903                            0,           // size
4904                            false,       // is_tlab
4905                            level        // max_level
4906                           );
4907       }
4908     }
4909     FreelistLocker x(this);
4910     MutexLockerEx y(bitMapLock(),
4911                     Mutex::_no_safepoint_check_flag);
4912     assert(!init_mark_was_synchronous, "but that's impossible!");
4913     checkpointRootsFinalWork(asynch, clear_all_soft_refs, false);
4914   } else {
4915     // already have all the locks
4916     checkpointRootsFinalWork(asynch, clear_all_soft_refs,
4917                              init_mark_was_synchronous);
4918   }
4919   verify_work_stacks_empty();
4920   verify_overflow_empty();
4921   SpecializationStats::print();
4922 }
4923 
4924 void CMSCollector::checkpointRootsFinalWork(bool asynch,
4925   bool clear_all_soft_refs, bool init_mark_was_synchronous) {
4926 
4927   NOT_PRODUCT(GCTraceTime tr("checkpointRootsFinalWork", PrintGCDetails, false, _gc_timer_cm);)
4928 
4929   assert(haveFreelistLocks(), "must have free list locks");
4930   assert_lock_strong(bitMapLock());
4931 
4932   if (UseAdaptiveSizePolicy) {
4933     size_policy()->checkpoint_roots_final_begin();
4934   }
4935 
4936   ResourceMark rm;
4937   HandleMark   hm;
4938 
4939   GenCollectedHeap* gch = GenCollectedHeap::heap();
4940 
4941   if (should_unload_classes()) {
4942     CodeCache::gc_prologue();
4943   }
4944   assert(haveFreelistLocks(), "must have free list locks");
4945   assert_lock_strong(bitMapLock());
4946 
4947   DEBUG_ONLY(RememberKlassesChecker fmx(should_unload_classes());)
4948   if (!init_mark_was_synchronous) {
4949     // We might assume that we need not fill TLAB's when
4950     // CMSScavengeBeforeRemark is set, because we may have just done
4951     // a scavenge which would have filled all TLAB's -- and besides
4952     // Eden would be empty. This however may not always be the case --
4953     // for instance although we asked for a scavenge, it may not have
4954     // happened because of a JNI critical section. We probably need
4955     // a policy for deciding whether we can in that case wait until
4956     // the critical section releases and then do the remark following
4957     // the scavenge, and skip it here. In the absence of that policy,
4958     // or of an indication of whether the scavenge did indeed occur,
4959     // we cannot rely on TLAB's having been filled and must do
4960     // so here just in case a scavenge did not happen.
4961     gch->ensure_parsability(false);  // fill TLAB's, but no need to retire them
4962     // Update the saved marks which may affect the root scans.
4963     gch->save_marks();
4964 
4965     {
4966       COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
4967 
4968       // Note on the role of the mod union table:
4969       // Since the marker in "markFromRoots" marks concurrently with
4970       // mutators, it is possible for some reachable objects not to have been
4971       // scanned. For instance, an only reference to an object A was
4972       // placed in object B after the marker scanned B. Unless B is rescanned,
4973       // A would be collected. Such updates to references in marked objects
4974       // are detected via the mod union table which is the set of all cards
4975       // dirtied since the first checkpoint in this GC cycle and prior to
4976       // the most recent young generation GC, minus those cleaned up by the
4977       // concurrent precleaning.
4978       if (CMSParallelRemarkEnabled && CollectedHeap::use_parallel_gc_threads()) {
4979         GCTraceTime t("Rescan (parallel) ", PrintGCDetails, false, _gc_timer_cm);
4980         do_remark_parallel();
4981       } else {
4982         GCTraceTime t("Rescan (non-parallel) ", PrintGCDetails, false,
4983                     _gc_timer_cm);
4984         do_remark_non_parallel();
4985       }
4986     }
4987   } else {
4988     assert(!asynch, "Can't have init_mark_was_synchronous in asynch mode");
4989     // The initial mark was stop-world, so there's no rescanning to
4990     // do; go straight on to the next step below.
4991   }
4992   verify_work_stacks_empty();
4993   verify_overflow_empty();
4994 
4995   {
4996     NOT_PRODUCT(GCTraceTime ts("refProcessingWork", PrintGCDetails, false, _gc_timer_cm);)
4997     refProcessingWork(asynch, clear_all_soft_refs);
4998   }
4999   verify_work_stacks_empty();
5000   verify_overflow_empty();
5001 
5002   if (should_unload_classes()) {
5003     CodeCache::gc_epilogue();
5004   }
5005   JvmtiExport::gc_epilogue();
5006 
5007   // If we encountered any (marking stack / work queue) overflow
5008   // events during the current CMS cycle, take appropriate
5009   // remedial measures, where possible, so as to try and avoid
5010   // recurrence of that condition.
5011   assert(_markStack.isEmpty(), "No grey objects");
5012   size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
5013                      _ser_kac_ovflw        + _ser_kac_preclean_ovflw;
5014   if (ser_ovflw > 0) {
5015     if (PrintCMSStatistics != 0) {
5016       gclog_or_tty->print_cr("Marking stack overflow (benign) "
5017         "(pmc_pc="SIZE_FORMAT", pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT
5018         ", kac_preclean="SIZE_FORMAT")",
5019         _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw,
5020         _ser_kac_ovflw, _ser_kac_preclean_ovflw);
5021     }
5022     _markStack.expand();
5023     _ser_pmc_remark_ovflw = 0;
5024     _ser_pmc_preclean_ovflw = 0;
5025     _ser_kac_preclean_ovflw = 0;
5026     _ser_kac_ovflw = 0;
5027   }
5028   if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
5029     if (PrintCMSStatistics != 0) {
5030       gclog_or_tty->print_cr("Work queue overflow (benign) "
5031         "(pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT")",
5032         _par_pmc_remark_ovflw, _par_kac_ovflw);
5033     }
5034     _par_pmc_remark_ovflw = 0;
5035     _par_kac_ovflw = 0;
5036   }
5037   if (PrintCMSStatistics != 0) {
5038      if (_markStack._hit_limit > 0) {
5039        gclog_or_tty->print_cr(" (benign) Hit max stack size limit ("SIZE_FORMAT")",
5040                               _markStack._hit_limit);
5041      }
5042      if (_markStack._failed_double > 0) {
5043        gclog_or_tty->print_cr(" (benign) Failed stack doubling ("SIZE_FORMAT"),"
5044                               " current capacity "SIZE_FORMAT,
5045                               _markStack._failed_double,
5046                               _markStack.capacity());
5047      }
5048   }
5049   _markStack._hit_limit = 0;
5050   _markStack._failed_double = 0;
5051 
5052   // Check that all the klasses have been checked
5053   assert(_revisitStack.isEmpty(), "Not all klasses revisited");
5054 
5055   if ((VerifyAfterGC || VerifyDuringGC) &&
5056       GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5057     verify_after_remark();
5058   }
5059 
5060   // Change under the freelistLocks.
5061   _collectorState = Sweeping;
5062   // Call isAllClear() under bitMapLock
5063   assert(_modUnionTable.isAllClear(), "Should be clear by end of the"
5064     " final marking");
5065   if (UseAdaptiveSizePolicy) {
5066     size_policy()->checkpoint_roots_final_end(gch->gc_cause());
5067   }
5068 }
5069 
5070 // Parallel remark task
5071 class CMSParRemarkTask: public AbstractGangTask {
5072   CMSCollector* _collector;
5073   int           _n_workers;
5074   CompactibleFreeListSpace* _cms_space;
5075   CompactibleFreeListSpace* _perm_space;
5076 
5077   // The per-thread work queues, available here for stealing.
5078   OopTaskQueueSet*       _task_queues;
5079   ParallelTaskTerminator _term;
5080 
5081  public:
5082   // A value of 0 passed to n_workers will cause the number of
5083   // workers to be taken from the active workers in the work gang.
5084   CMSParRemarkTask(CMSCollector* collector,
5085                    CompactibleFreeListSpace* cms_space,
5086                    CompactibleFreeListSpace* perm_space,
5087                    int n_workers, FlexibleWorkGang* workers,
5088                    OopTaskQueueSet* task_queues):
5089     AbstractGangTask("Rescan roots and grey objects in parallel"),
5090     _collector(collector),
5091     _cms_space(cms_space), _perm_space(perm_space),
5092     _n_workers(n_workers),
5093     _task_queues(task_queues),
5094     _term(n_workers, task_queues) { }
5095 
5096   OopTaskQueueSet* task_queues() { return _task_queues; }
5097 
5098   OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5099 
5100   ParallelTaskTerminator* terminator() { return &_term; }
5101   int n_workers() { return _n_workers; }
5102 
5103   void work(uint worker_id);
5104 
5105  private:
5106   // Work method in support of parallel rescan ... of young gen spaces
5107   void do_young_space_rescan(int i, Par_MarkRefsIntoAndScanClosure* cl,
5108                              ContiguousSpace* space,
5109                              HeapWord** chunk_array, size_t chunk_top);
5110 
5111   // ... of  dirty cards in old space
5112   void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
5113                                   Par_MarkRefsIntoAndScanClosure* cl);
5114 
5115   // ... work stealing for the above
5116   void do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl, int* seed);
5117 };
5118 
5119 // work_queue(i) is passed to the closure
5120 // Par_MarkRefsIntoAndScanClosure.  The "i" parameter
5121 // also is passed to do_dirty_card_rescan_tasks() and to
5122 // do_work_steal() to select the i-th task_queue.
5123 
5124 void CMSParRemarkTask::work(uint worker_id) {
5125   elapsedTimer _timer;
5126   ResourceMark rm;
5127   HandleMark   hm;
5128 
5129   // ---------- rescan from roots --------------
5130   _timer.start();
5131   GenCollectedHeap* gch = GenCollectedHeap::heap();
5132   Par_MarkRefsIntoAndScanClosure par_mrias_cl(_collector,
5133     _collector->_span, _collector->ref_processor(),
5134     &(_collector->_markBitMap),
5135     work_queue(worker_id), &(_collector->_revisitStack));
5136 
5137   // Rescan young gen roots first since these are likely
5138   // coarsely partitioned and may, on that account, constitute
5139   // the critical path; thus, it's best to start off that
5140   // work first.
5141   // ---------- young gen roots --------------
5142   {
5143     DefNewGeneration* dng = _collector->_young_gen->as_DefNewGeneration();
5144     EdenSpace* eden_space = dng->eden();
5145     ContiguousSpace* from_space = dng->from();
5146     ContiguousSpace* to_space   = dng->to();
5147 
5148     HeapWord** eca = _collector->_eden_chunk_array;
5149     size_t     ect = _collector->_eden_chunk_index;
5150     HeapWord** sca = _collector->_survivor_chunk_array;
5151     size_t     sct = _collector->_survivor_chunk_index;
5152 
5153     assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
5154     assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
5155 
5156     do_young_space_rescan(worker_id, &par_mrias_cl, to_space, NULL, 0);
5157     do_young_space_rescan(worker_id, &par_mrias_cl, from_space, sca, sct);
5158     do_young_space_rescan(worker_id, &par_mrias_cl, eden_space, eca, ect);
5159 
5160     _timer.stop();
5161     if (PrintCMSStatistics != 0) {
5162       gclog_or_tty->print_cr(
5163         "Finished young gen rescan work in %dth thread: %3.3f sec",
5164         worker_id, _timer.seconds());
5165     }
5166   }
5167 
5168   // ---------- remaining roots --------------
5169   _timer.reset();
5170   _timer.start();
5171   gch->gen_process_strong_roots(_collector->_cmsGen->level(),
5172                                 false,     // yg was scanned above
5173                                 false,     // this is parallel code
5174                                 true,      // collecting perm gen
5175                                 SharedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
5176                                 &par_mrias_cl,
5177                                 true,   // walk all of code cache if (so & SO_CodeCache)
5178                                 NULL);
5179   assert(_collector->should_unload_classes()
5180          || (_collector->CMSCollector::roots_scanning_options() & SharedHeap::SO_CodeCache),
5181          "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5182   _timer.stop();
5183   if (PrintCMSStatistics != 0) {
5184     gclog_or_tty->print_cr(
5185       "Finished remaining root rescan work in %dth thread: %3.3f sec",
5186       worker_id, _timer.seconds());
5187   }
5188 
5189   // ---------- rescan dirty cards ------------
5190   _timer.reset();
5191   _timer.start();
5192 
5193   // Do the rescan tasks for each of the two spaces
5194   // (cms_space and perm_space) in turn.
5195   // "worker_id" is passed to select the task_queue for "worker_id"
5196   do_dirty_card_rescan_tasks(_cms_space, worker_id, &par_mrias_cl);
5197   do_dirty_card_rescan_tasks(_perm_space, worker_id, &par_mrias_cl);
5198   _timer.stop();
5199   if (PrintCMSStatistics != 0) {
5200     gclog_or_tty->print_cr(
5201       "Finished dirty card rescan work in %dth thread: %3.3f sec",
5202       worker_id, _timer.seconds());
5203   }
5204 
5205   // ---------- steal work from other threads ...
5206   // ---------- ... and drain overflow list.
5207   _timer.reset();
5208   _timer.start();
5209   do_work_steal(worker_id, &par_mrias_cl, _collector->hash_seed(worker_id));
5210   _timer.stop();
5211   if (PrintCMSStatistics != 0) {
5212     gclog_or_tty->print_cr(
5213       "Finished work stealing in %dth thread: %3.3f sec",
5214       worker_id, _timer.seconds());
5215   }
5216 }
5217 
5218 // Note that parameter "i" is not used.
5219 void
5220 CMSParRemarkTask::do_young_space_rescan(int i,
5221   Par_MarkRefsIntoAndScanClosure* cl, ContiguousSpace* space,
5222   HeapWord** chunk_array, size_t chunk_top) {
5223   // Until all tasks completed:
5224   // . claim an unclaimed task
5225   // . compute region boundaries corresponding to task claimed
5226   //   using chunk_array
5227   // . par_oop_iterate(cl) over that region
5228 
5229   ResourceMark rm;
5230   HandleMark   hm;
5231 
5232   SequentialSubTasksDone* pst = space->par_seq_tasks();
5233   assert(pst->valid(), "Uninitialized use?");
5234 
5235   uint nth_task = 0;
5236   uint n_tasks  = pst->n_tasks();
5237 
5238   HeapWord *start, *end;
5239   while (!pst->is_task_claimed(/* reference */ nth_task)) {
5240     // We claimed task # nth_task; compute its boundaries.
5241     if (chunk_top == 0) {  // no samples were taken
5242       assert(nth_task == 0 && n_tasks == 1, "Can have only 1 EdenSpace task");
5243       start = space->bottom();
5244       end   = space->top();
5245     } else if (nth_task == 0) {
5246       start = space->bottom();
5247       end   = chunk_array[nth_task];
5248     } else if (nth_task < (uint)chunk_top) {
5249       assert(nth_task >= 1, "Control point invariant");
5250       start = chunk_array[nth_task - 1];
5251       end   = chunk_array[nth_task];
5252     } else {
5253       assert(nth_task == (uint)chunk_top, "Control point invariant");
5254       start = chunk_array[chunk_top - 1];
5255       end   = space->top();
5256     }
5257     MemRegion mr(start, end);
5258     // Verify that mr is in space
5259     assert(mr.is_empty() || space->used_region().contains(mr),
5260            "Should be in space");
5261     // Verify that "start" is an object boundary
5262     assert(mr.is_empty() || oop(mr.start())->is_oop(),
5263            "Should be an oop");
5264     space->par_oop_iterate(mr, cl);
5265   }
5266   pst->all_tasks_completed();
5267 }
5268 
5269 void
5270 CMSParRemarkTask::do_dirty_card_rescan_tasks(
5271   CompactibleFreeListSpace* sp, int i,
5272   Par_MarkRefsIntoAndScanClosure* cl) {
5273   // Until all tasks completed:
5274   // . claim an unclaimed task
5275   // . compute region boundaries corresponding to task claimed
5276   // . transfer dirty bits ct->mut for that region
5277   // . apply rescanclosure to dirty mut bits for that region
5278 
5279   ResourceMark rm;
5280   HandleMark   hm;
5281 
5282   OopTaskQueue* work_q = work_queue(i);
5283   ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
5284   // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
5285   // CAUTION: This closure has state that persists across calls to
5286   // the work method dirty_range_iterate_clear() in that it has
5287   // imbedded in it a (subtype of) UpwardsObjectClosure. The
5288   // use of that state in the imbedded UpwardsObjectClosure instance
5289   // assumes that the cards are always iterated (even if in parallel
5290   // by several threads) in monotonically increasing order per each
5291   // thread. This is true of the implementation below which picks
5292   // card ranges (chunks) in monotonically increasing order globally
5293   // and, a-fortiori, in monotonically increasing order per thread
5294   // (the latter order being a subsequence of the former).
5295   // If the work code below is ever reorganized into a more chaotic
5296   // work-partitioning form than the current "sequential tasks"
5297   // paradigm, the use of that persistent state will have to be
5298   // revisited and modified appropriately. See also related
5299   // bug 4756801 work on which should examine this code to make
5300   // sure that the changes there do not run counter to the
5301   // assumptions made here and necessary for correctness and
5302   // efficiency. Note also that this code might yield inefficient
5303   // behaviour in the case of very large objects that span one or
5304   // more work chunks. Such objects would potentially be scanned
5305   // several times redundantly. Work on 4756801 should try and
5306   // address that performance anomaly if at all possible. XXX
5307   MemRegion  full_span  = _collector->_span;
5308   CMSBitMap* bm    = &(_collector->_markBitMap);     // shared
5309   CMSMarkStack* rs = &(_collector->_revisitStack);   // shared
5310   MarkFromDirtyCardsClosure
5311     greyRescanClosure(_collector, full_span, // entire span of interest
5312                       sp, bm, work_q, rs, cl);
5313 
5314   SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
5315   assert(pst->valid(), "Uninitialized use?");
5316   uint nth_task = 0;
5317   const int alignment = CardTableModRefBS::card_size * BitsPerWord;
5318   MemRegion span = sp->used_region();
5319   HeapWord* start_addr = span.start();
5320   HeapWord* end_addr = (HeapWord*)round_to((intptr_t)span.end(),
5321                                            alignment);
5322   const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
5323   assert((HeapWord*)round_to((intptr_t)start_addr, alignment) ==
5324          start_addr, "Check alignment");
5325   assert((size_t)round_to((intptr_t)chunk_size, alignment) ==
5326          chunk_size, "Check alignment");
5327 
5328   while (!pst->is_task_claimed(/* reference */ nth_task)) {
5329     // Having claimed the nth_task, compute corresponding mem-region,
5330     // which is a-fortiori aligned correctly (i.e. at a MUT bopundary).
5331     // The alignment restriction ensures that we do not need any
5332     // synchronization with other gang-workers while setting or
5333     // clearing bits in thus chunk of the MUT.
5334     MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
5335                                     start_addr + (nth_task+1)*chunk_size);
5336     // The last chunk's end might be way beyond end of the
5337     // used region. In that case pull back appropriately.
5338     if (this_span.end() > end_addr) {
5339       this_span.set_end(end_addr);
5340       assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
5341     }
5342     // Iterate over the dirty cards covering this chunk, marking them
5343     // precleaned, and setting the corresponding bits in the mod union
5344     // table. Since we have been careful to partition at Card and MUT-word
5345     // boundaries no synchronization is needed between parallel threads.
5346     _collector->_ct->ct_bs()->dirty_card_iterate(this_span,
5347                                                  &modUnionClosure);
5348 
5349     // Having transferred these marks into the modUnionTable,
5350     // rescan the marked objects on the dirty cards in the modUnionTable.
5351     // Even if this is at a synchronous collection, the initial marking
5352     // may have been done during an asynchronous collection so there
5353     // may be dirty bits in the mod-union table.
5354     _collector->_modUnionTable.dirty_range_iterate_clear(
5355                   this_span, &greyRescanClosure);
5356     _collector->_modUnionTable.verifyNoOneBitsInRange(
5357                                  this_span.start(),
5358                                  this_span.end());
5359   }
5360   pst->all_tasks_completed();  // declare that i am done
5361 }
5362 
5363 // . see if we can share work_queues with ParNew? XXX
5364 void
5365 CMSParRemarkTask::do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl,
5366                                 int* seed) {
5367   OopTaskQueue* work_q = work_queue(i);
5368   NOT_PRODUCT(int num_steals = 0;)
5369   oop obj_to_scan;
5370   CMSBitMap* bm = &(_collector->_markBitMap);
5371 
5372   while (true) {
5373     // Completely finish any left over work from (an) earlier round(s)
5374     cl->trim_queue(0);
5375     size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5376                                          (size_t)ParGCDesiredObjsFromOverflowList);
5377     // Now check if there's any work in the overflow list
5378     // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5379     // only affects the number of attempts made to get work from the
5380     // overflow list and does not affect the number of workers.  Just
5381     // pass ParallelGCThreads so this behavior is unchanged.
5382     if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5383                                                 work_q,
5384                                                 ParallelGCThreads)) {
5385       // found something in global overflow list;
5386       // not yet ready to go stealing work from others.
5387       // We'd like to assert(work_q->size() != 0, ...)
5388       // because we just took work from the overflow list,
5389       // but of course we can't since all of that could have
5390       // been already stolen from us.
5391       // "He giveth and He taketh away."
5392       continue;
5393     }
5394     // Verify that we have no work before we resort to stealing
5395     assert(work_q->size() == 0, "Have work, shouldn't steal");
5396     // Try to steal from other queues that have work
5397     if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5398       NOT_PRODUCT(num_steals++;)
5399       assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5400       assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5401       // Do scanning work
5402       obj_to_scan->oop_iterate(cl);
5403       // Loop around, finish this work, and try to steal some more
5404     } else if (terminator()->offer_termination()) {
5405         break;  // nirvana from the infinite cycle
5406     }
5407   }
5408   NOT_PRODUCT(
5409     if (PrintCMSStatistics != 0) {
5410       gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5411     }
5412   )
5413   assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
5414          "Else our work is not yet done");
5415 }
5416 
5417 // Return a thread-local PLAB recording array, as appropriate.
5418 void* CMSCollector::get_data_recorder(int thr_num) {
5419   if (_survivor_plab_array != NULL &&
5420       (CMSPLABRecordAlways ||
5421        (_collectorState > Marking && _collectorState < FinalMarking))) {
5422     assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
5423     ChunkArray* ca = &_survivor_plab_array[thr_num];
5424     ca->reset();   // clear it so that fresh data is recorded
5425     return (void*) ca;
5426   } else {
5427     return NULL;
5428   }
5429 }
5430 
5431 // Reset all the thread-local PLAB recording arrays
5432 void CMSCollector::reset_survivor_plab_arrays() {
5433   for (uint i = 0; i < ParallelGCThreads; i++) {
5434     _survivor_plab_array[i].reset();
5435   }
5436 }
5437 
5438 // Merge the per-thread plab arrays into the global survivor chunk
5439 // array which will provide the partitioning of the survivor space
5440 // for CMS rescan.
5441 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv,
5442                                               int no_of_gc_threads) {
5443   assert(_survivor_plab_array  != NULL, "Error");
5444   assert(_survivor_chunk_array != NULL, "Error");
5445   assert(_collectorState == FinalMarking, "Error");
5446   for (int j = 0; j < no_of_gc_threads; j++) {
5447     _cursor[j] = 0;
5448   }
5449   HeapWord* top = surv->top();
5450   size_t i;
5451   for (i = 0; i < _survivor_chunk_capacity; i++) {  // all sca entries
5452     HeapWord* min_val = top;          // Higher than any PLAB address
5453     uint      min_tid = 0;            // position of min_val this round
5454     for (int j = 0; j < no_of_gc_threads; j++) {
5455       ChunkArray* cur_sca = &_survivor_plab_array[j];
5456       if (_cursor[j] == cur_sca->end()) {
5457         continue;
5458       }
5459       assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
5460       HeapWord* cur_val = cur_sca->nth(_cursor[j]);
5461       assert(surv->used_region().contains(cur_val), "Out of bounds value");
5462       if (cur_val < min_val) {
5463         min_tid = j;
5464         min_val = cur_val;
5465       } else {
5466         assert(cur_val < top, "All recorded addresses should be less");
5467       }
5468     }
5469     // At this point min_val and min_tid are respectively
5470     // the least address in _survivor_plab_array[j]->nth(_cursor[j])
5471     // and the thread (j) that witnesses that address.
5472     // We record this address in the _survivor_chunk_array[i]
5473     // and increment _cursor[min_tid] prior to the next round i.
5474     if (min_val == top) {
5475       break;
5476     }
5477     _survivor_chunk_array[i] = min_val;
5478     _cursor[min_tid]++;
5479   }
5480   // We are all done; record the size of the _survivor_chunk_array
5481   _survivor_chunk_index = i; // exclusive: [0, i)
5482   if (PrintCMSStatistics > 0) {
5483     gclog_or_tty->print(" (Survivor:" SIZE_FORMAT "chunks) ", i);
5484   }
5485   // Verify that we used up all the recorded entries
5486   #ifdef ASSERT
5487     size_t total = 0;
5488     for (int j = 0; j < no_of_gc_threads; j++) {
5489       assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
5490       total += _cursor[j];
5491     }
5492     assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
5493     // Check that the merged array is in sorted order
5494     if (total > 0) {
5495       for (size_t i = 0; i < total - 1; i++) {
5496         if (PrintCMSStatistics > 0) {
5497           gclog_or_tty->print(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
5498                               i, _survivor_chunk_array[i]);
5499         }
5500         assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
5501                "Not sorted");
5502       }
5503     }
5504   #endif // ASSERT
5505 }
5506 
5507 // Set up the space's par_seq_tasks structure for work claiming
5508 // for parallel rescan of young gen.
5509 // See ParRescanTask where this is currently used.
5510 void
5511 CMSCollector::
5512 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
5513   assert(n_threads > 0, "Unexpected n_threads argument");
5514   DefNewGeneration* dng = (DefNewGeneration*)_young_gen;
5515 
5516   // Eden space
5517   {
5518     SequentialSubTasksDone* pst = dng->eden()->par_seq_tasks();
5519     assert(!pst->valid(), "Clobbering existing data?");
5520     // Each valid entry in [0, _eden_chunk_index) represents a task.
5521     size_t n_tasks = _eden_chunk_index + 1;
5522     assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
5523     // Sets the condition for completion of the subtask (how many threads
5524     // need to finish in order to be done).
5525     pst->set_n_threads(n_threads);
5526     pst->set_n_tasks((int)n_tasks);
5527   }
5528 
5529   // Merge the survivor plab arrays into _survivor_chunk_array
5530   if (_survivor_plab_array != NULL) {
5531     merge_survivor_plab_arrays(dng->from(), n_threads);
5532   } else {
5533     assert(_survivor_chunk_index == 0, "Error");
5534   }
5535 
5536   // To space
5537   {
5538     SequentialSubTasksDone* pst = dng->to()->par_seq_tasks();
5539     assert(!pst->valid(), "Clobbering existing data?");
5540     // Sets the condition for completion of the subtask (how many threads
5541     // need to finish in order to be done).
5542     pst->set_n_threads(n_threads);
5543     pst->set_n_tasks(1);
5544     assert(pst->valid(), "Error");
5545   }
5546 
5547   // From space
5548   {
5549     SequentialSubTasksDone* pst = dng->from()->par_seq_tasks();
5550     assert(!pst->valid(), "Clobbering existing data?");
5551     size_t n_tasks = _survivor_chunk_index + 1;
5552     assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
5553     // Sets the condition for completion of the subtask (how many threads
5554     // need to finish in order to be done).
5555     pst->set_n_threads(n_threads);
5556     pst->set_n_tasks((int)n_tasks);
5557     assert(pst->valid(), "Error");
5558   }
5559 }
5560 
5561 // Parallel version of remark
5562 void CMSCollector::do_remark_parallel() {
5563   GenCollectedHeap* gch = GenCollectedHeap::heap();
5564   FlexibleWorkGang* workers = gch->workers();
5565   assert(workers != NULL, "Need parallel worker threads.");
5566   // Choose to use the number of GC workers most recently set
5567   // into "active_workers".  If active_workers is not set, set it
5568   // to ParallelGCThreads.
5569   int n_workers = workers->active_workers();
5570   if (n_workers == 0) {
5571     assert(n_workers > 0, "Should have been set during scavenge");
5572     n_workers = ParallelGCThreads;
5573     workers->set_active_workers(n_workers);
5574   }
5575   CompactibleFreeListSpace* cms_space  = _cmsGen->cmsSpace();
5576   CompactibleFreeListSpace* perm_space = _permGen->cmsSpace();
5577 
5578   CMSParRemarkTask tsk(this,
5579     cms_space, perm_space,
5580     n_workers, workers, task_queues());
5581 
5582   // Set up for parallel process_strong_roots work.
5583   gch->set_par_threads(n_workers);
5584   // We won't be iterating over the cards in the card table updating
5585   // the younger_gen cards, so we shouldn't call the following else
5586   // the verification code as well as subsequent younger_refs_iterate
5587   // code would get confused. XXX
5588   // gch->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
5589 
5590   // The young gen rescan work will not be done as part of
5591   // process_strong_roots (which currently doesn't knw how to
5592   // parallelize such a scan), but rather will be broken up into
5593   // a set of parallel tasks (via the sampling that the [abortable]
5594   // preclean phase did of EdenSpace, plus the [two] tasks of
5595   // scanning the [two] survivor spaces. Further fine-grain
5596   // parallelization of the scanning of the survivor spaces
5597   // themselves, and of precleaning of the younger gen itself
5598   // is deferred to the future.
5599   initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
5600 
5601   // The dirty card rescan work is broken up into a "sequence"
5602   // of parallel tasks (per constituent space) that are dynamically
5603   // claimed by the parallel threads.
5604   cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
5605   perm_space->initialize_sequential_subtasks_for_rescan(n_workers);
5606 
5607   // It turns out that even when we're using 1 thread, doing the work in a
5608   // separate thread causes wide variance in run times.  We can't help this
5609   // in the multi-threaded case, but we special-case n=1 here to get
5610   // repeatable measurements of the 1-thread overhead of the parallel code.
5611   if (n_workers > 1) {
5612     // Make refs discovery MT-safe, if it isn't already: it may not
5613     // necessarily be so, since it's possible that we are doing
5614     // ST marking.
5615     ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), true);
5616     GenCollectedHeap::StrongRootsScope srs(gch);
5617     workers->run_task(&tsk);
5618   } else {
5619     ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5620     GenCollectedHeap::StrongRootsScope srs(gch);
5621     tsk.work(0);
5622   }
5623   gch->set_par_threads(0);  // 0 ==> non-parallel.
5624   // restore, single-threaded for now, any preserved marks
5625   // as a result of work_q overflow
5626   restore_preserved_marks_if_any();
5627 }
5628 
5629 // Non-parallel version of remark
5630 void CMSCollector::do_remark_non_parallel() {
5631   ResourceMark rm;
5632   HandleMark   hm;
5633   GenCollectedHeap* gch = GenCollectedHeap::heap();
5634   ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5635 
5636   MarkRefsIntoAndScanClosure
5637     mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
5638              &_markStack, &_revisitStack, this,
5639              false /* should_yield */, false /* not precleaning */);
5640   MarkFromDirtyCardsClosure
5641     markFromDirtyCardsClosure(this, _span,
5642                               NULL,  // space is set further below
5643                               &_markBitMap, &_markStack, &_revisitStack,
5644                               &mrias_cl);
5645   {
5646     GCTraceTime t("grey object rescan", PrintGCDetails, false, _gc_timer_cm);
5647     // Iterate over the dirty cards, setting the corresponding bits in the
5648     // mod union table.
5649     {
5650       ModUnionClosure modUnionClosure(&_modUnionTable);
5651       _ct->ct_bs()->dirty_card_iterate(
5652                       _cmsGen->used_region(),
5653                       &modUnionClosure);
5654       _ct->ct_bs()->dirty_card_iterate(
5655                       _permGen->used_region(),
5656                       &modUnionClosure);
5657     }
5658     // Having transferred these marks into the modUnionTable, we just need
5659     // to rescan the marked objects on the dirty cards in the modUnionTable.
5660     // The initial marking may have been done during an asynchronous
5661     // collection so there may be dirty bits in the mod-union table.
5662     const int alignment =
5663       CardTableModRefBS::card_size * BitsPerWord;
5664     {
5665       // ... First handle dirty cards in CMS gen
5666       markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
5667       MemRegion ur = _cmsGen->used_region();
5668       HeapWord* lb = ur.start();
5669       HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
5670       MemRegion cms_span(lb, ub);
5671       _modUnionTable.dirty_range_iterate_clear(cms_span,
5672                                                &markFromDirtyCardsClosure);
5673       verify_work_stacks_empty();
5674       if (PrintCMSStatistics != 0) {
5675         gclog_or_tty->print(" (re-scanned "SIZE_FORMAT" dirty cards in cms gen) ",
5676           markFromDirtyCardsClosure.num_dirty_cards());
5677       }
5678     }
5679     {
5680       // .. and then repeat for dirty cards in perm gen
5681       markFromDirtyCardsClosure.set_space(_permGen->cmsSpace());
5682       MemRegion ur = _permGen->used_region();
5683       HeapWord* lb = ur.start();
5684       HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
5685       MemRegion perm_span(lb, ub);
5686       _modUnionTable.dirty_range_iterate_clear(perm_span,
5687                                                &markFromDirtyCardsClosure);
5688       verify_work_stacks_empty();
5689       if (PrintCMSStatistics != 0) {
5690         gclog_or_tty->print(" (re-scanned "SIZE_FORMAT" dirty cards in perm gen) ",
5691           markFromDirtyCardsClosure.num_dirty_cards());
5692       }
5693     }
5694   }
5695   if (VerifyDuringGC &&
5696       GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5697     HandleMark hm;  // Discard invalid handles created during verification
5698     Universe::verify();
5699   }
5700   {
5701     GCTraceTime t("root rescan", PrintGCDetails, false, _gc_timer_cm);
5702 
5703     verify_work_stacks_empty();
5704 
5705     gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
5706     GenCollectedHeap::StrongRootsScope srs(gch);
5707     gch->gen_process_strong_roots(_cmsGen->level(),
5708                                   true,  // younger gens as roots
5709                                   false, // use the local StrongRootsScope
5710                                   true,  // collecting perm gen
5711                                   SharedHeap::ScanningOption(roots_scanning_options()),
5712                                   &mrias_cl,
5713                                   true,   // walk code active on stacks
5714                                   NULL);
5715     assert(should_unload_classes()
5716            || (roots_scanning_options() & SharedHeap::SO_CodeCache),
5717            "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5718   }
5719   verify_work_stacks_empty();
5720   // Restore evacuated mark words, if any, used for overflow list links
5721   if (!CMSOverflowEarlyRestoration) {
5722     restore_preserved_marks_if_any();
5723   }
5724   verify_overflow_empty();
5725 }
5726 
5727 ////////////////////////////////////////////////////////
5728 // Parallel Reference Processing Task Proxy Class
5729 ////////////////////////////////////////////////////////
5730 class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues {
5731   typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
5732   CMSCollector*          _collector;
5733   CMSBitMap*             _mark_bit_map;
5734   const MemRegion        _span;
5735   ProcessTask&           _task;
5736 
5737 public:
5738   CMSRefProcTaskProxy(ProcessTask&     task,
5739                       CMSCollector*    collector,
5740                       const MemRegion& span,
5741                       CMSBitMap*       mark_bit_map,
5742                       AbstractWorkGang* workers,
5743                       OopTaskQueueSet* task_queues):
5744     // XXX Should superclass AGTWOQ also know about AWG since it knows
5745     // about the task_queues used by the AWG? Then it could initialize
5746     // the terminator() object. See 6984287. The set_for_termination()
5747     // below is a temporary band-aid for the regression in 6984287.
5748     AbstractGangTaskWOopQueues("Process referents by policy in parallel",
5749       task_queues),
5750     _task(task),
5751     _collector(collector), _span(span), _mark_bit_map(mark_bit_map)
5752   {
5753     assert(_collector->_span.equals(_span) && !_span.is_empty(),
5754            "Inconsistency in _span");
5755     set_for_termination(workers->active_workers());
5756   }
5757 
5758   OopTaskQueueSet* task_queues() { return queues(); }
5759 
5760   OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5761 
5762   void do_work_steal(int i,
5763                      CMSParDrainMarkingStackClosure* drain,
5764                      CMSParKeepAliveClosure* keep_alive,
5765                      int* seed);
5766 
5767   virtual void work(uint worker_id);
5768 };
5769 
5770 void CMSRefProcTaskProxy::work(uint worker_id) {
5771   assert(_collector->_span.equals(_span), "Inconsistency in _span");
5772   CMSParKeepAliveClosure par_keep_alive(_collector, _span,
5773                                         _mark_bit_map,
5774                                         &_collector->_revisitStack,
5775                                         work_queue(worker_id));
5776   CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
5777                                                  _mark_bit_map,
5778                                                  &_collector->_revisitStack,
5779                                                  work_queue(worker_id));
5780   CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
5781   _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack);
5782   if (_task.marks_oops_alive()) {
5783     do_work_steal(worker_id, &par_drain_stack, &par_keep_alive,
5784                   _collector->hash_seed(worker_id));
5785   }
5786   assert(work_queue(worker_id)->size() == 0, "work_queue should be empty");
5787   assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
5788 }
5789 
5790 class CMSRefEnqueueTaskProxy: public AbstractGangTask {
5791   typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
5792   EnqueueTask& _task;
5793 
5794 public:
5795   CMSRefEnqueueTaskProxy(EnqueueTask& task)
5796     : AbstractGangTask("Enqueue reference objects in parallel"),
5797       _task(task)
5798   { }
5799 
5800   virtual void work(uint worker_id)
5801   {
5802     _task.work(worker_id);
5803   }
5804 };
5805 
5806 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
5807   MemRegion span, CMSBitMap* bit_map, CMSMarkStack* revisit_stack,
5808   OopTaskQueue* work_queue):
5809    Par_KlassRememberingOopClosure(collector, NULL, revisit_stack),
5810    _span(span),
5811    _bit_map(bit_map),
5812    _work_queue(work_queue),
5813    _mark_and_push(collector, span, bit_map, revisit_stack, work_queue),
5814    _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
5815                         (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads)))
5816 { }
5817 
5818 // . see if we can share work_queues with ParNew? XXX
5819 void CMSRefProcTaskProxy::do_work_steal(int i,
5820   CMSParDrainMarkingStackClosure* drain,
5821   CMSParKeepAliveClosure* keep_alive,
5822   int* seed) {
5823   OopTaskQueue* work_q = work_queue(i);
5824   NOT_PRODUCT(int num_steals = 0;)
5825   oop obj_to_scan;
5826 
5827   while (true) {
5828     // Completely finish any left over work from (an) earlier round(s)
5829     drain->trim_queue(0);
5830     size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5831                                          (size_t)ParGCDesiredObjsFromOverflowList);
5832     // Now check if there's any work in the overflow list
5833     // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5834     // only affects the number of attempts made to get work from the
5835     // overflow list and does not affect the number of workers.  Just
5836     // pass ParallelGCThreads so this behavior is unchanged.
5837     if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5838                                                 work_q,
5839                                                 ParallelGCThreads)) {
5840       // Found something in global overflow list;
5841       // not yet ready to go stealing work from others.
5842       // We'd like to assert(work_q->size() != 0, ...)
5843       // because we just took work from the overflow list,
5844       // but of course we can't, since all of that might have
5845       // been already stolen from us.
5846       continue;
5847     }
5848     // Verify that we have no work before we resort to stealing
5849     assert(work_q->size() == 0, "Have work, shouldn't steal");
5850     // Try to steal from other queues that have work
5851     if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5852       NOT_PRODUCT(num_steals++;)
5853       assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5854       assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5855       // Do scanning work
5856       obj_to_scan->oop_iterate(keep_alive);
5857       // Loop around, finish this work, and try to steal some more
5858     } else if (terminator()->offer_termination()) {
5859       break;  // nirvana from the infinite cycle
5860     }
5861   }
5862   NOT_PRODUCT(
5863     if (PrintCMSStatistics != 0) {
5864       gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5865     }
5866   )
5867 }
5868 
5869 void CMSRefProcTaskExecutor::execute(ProcessTask& task)
5870 {
5871   GenCollectedHeap* gch = GenCollectedHeap::heap();
5872   FlexibleWorkGang* workers = gch->workers();
5873   assert(workers != NULL, "Need parallel worker threads.");
5874   CMSRefProcTaskProxy rp_task(task, &_collector,
5875                               _collector.ref_processor()->span(),
5876                               _collector.markBitMap(),
5877                               workers, _collector.task_queues());
5878   workers->run_task(&rp_task);
5879 }
5880 
5881 void CMSRefProcTaskExecutor::execute(EnqueueTask& task)
5882 {
5883 
5884   GenCollectedHeap* gch = GenCollectedHeap::heap();
5885   FlexibleWorkGang* workers = gch->workers();
5886   assert(workers != NULL, "Need parallel worker threads.");
5887   CMSRefEnqueueTaskProxy enq_task(task);
5888   workers->run_task(&enq_task);
5889 }
5890 
5891 void CMSCollector::refProcessingWork(bool asynch, bool clear_all_soft_refs) {
5892 
5893   ResourceMark rm;
5894   HandleMark   hm;
5895 
5896   ReferenceProcessor* rp = ref_processor();
5897   assert(rp->span().equals(_span), "Spans should be equal");
5898   assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
5899   // Process weak references.
5900   rp->setup_policy(clear_all_soft_refs);
5901   verify_work_stacks_empty();
5902 
5903   CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
5904                                           &_markStack, &_revisitStack,
5905                                           false /* !preclean */);
5906   CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
5907                                 _span, &_markBitMap, &_markStack,
5908                                 &cmsKeepAliveClosure, false /* !preclean */);
5909   {
5910     GCTraceTime t("weak refs processing", PrintGCDetails, false, _gc_timer_cm);
5911     if (rp->processing_is_mt()) {
5912       // Set the degree of MT here.  If the discovery is done MT, there
5913       // may have been a different number of threads doing the discovery
5914       // and a different number of discovered lists may have Ref objects.
5915       // That is OK as long as the Reference lists are balanced (see
5916       // balance_all_queues() and balance_queues()).
5917       GenCollectedHeap* gch = GenCollectedHeap::heap();
5918       int active_workers = ParallelGCThreads;
5919       FlexibleWorkGang* workers = gch->workers();
5920       if (workers != NULL) {
5921         active_workers = workers->active_workers();
5922         // The expectation is that active_workers will have already
5923         // been set to a reasonable value.  If it has not been set,
5924         // investigate.
5925         assert(active_workers > 0, "Should have been set during scavenge");
5926       }
5927       rp->set_active_mt_degree(active_workers);
5928       CMSRefProcTaskExecutor task_executor(*this);
5929       rp->process_discovered_references(&_is_alive_closure,
5930                                         &cmsKeepAliveClosure,
5931                                         &cmsDrainMarkingStackClosure,
5932                                         &task_executor,
5933                                         _gc_timer_cm);
5934     } else {
5935       rp->process_discovered_references(&_is_alive_closure,
5936                                         &cmsKeepAliveClosure,
5937                                         &cmsDrainMarkingStackClosure,
5938                                         NULL,
5939                                         _gc_timer_cm);
5940     }
5941     verify_work_stacks_empty();
5942   }
5943 
5944   if (should_unload_classes()) {
5945     {
5946       GCTraceTime t("class unloading", PrintGCDetails, false, _gc_timer_cm);
5947 
5948       // Follow SystemDictionary roots and unload classes
5949       bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure);
5950 
5951       // Follow CodeCache roots and unload any methods marked for unloading
5952       CodeCache::do_unloading(&_is_alive_closure,
5953                               &cmsKeepAliveClosure,
5954                               purged_class);
5955 
5956       cmsDrainMarkingStackClosure.do_void();
5957       verify_work_stacks_empty();
5958 
5959       // Update subklass/sibling/implementor links in KlassKlass descendants
5960       assert(!_revisitStack.isEmpty(), "revisit stack should not be empty");
5961       oop k;
5962       while ((k = _revisitStack.pop()) != NULL) {
5963         ((Klass*)(oopDesc*)k)->follow_weak_klass_links(
5964                        &_is_alive_closure,
5965                        &cmsKeepAliveClosure);
5966       }
5967       assert(!ClassUnloading ||
5968              (_markStack.isEmpty() && overflow_list_is_empty()),
5969              "Should not have found new reachable objects");
5970       assert(_revisitStack.isEmpty(), "revisit stack should have been drained");
5971       cmsDrainMarkingStackClosure.do_void();
5972       verify_work_stacks_empty();
5973     }
5974 
5975     {
5976       GCTraceTime t("scrub symbol table", PrintGCDetails, false, _gc_timer_cm);
5977       // Clean up unreferenced symbols in symbol table.
5978       SymbolTable::unlink();
5979     }
5980   }
5981 
5982   if (should_unload_classes() || !JavaObjectsInPerm) {
5983     GCTraceTime t("scrub string table", PrintGCDetails, false, _gc_timer_cm);
5984     // Now clean up stale oops in StringTable
5985     StringTable::unlink(&_is_alive_closure);
5986   }
5987 
5988   verify_work_stacks_empty();
5989   // Restore any preserved marks as a result of mark stack or
5990   // work queue overflow
5991   restore_preserved_marks_if_any();  // done single-threaded for now
5992 
5993   rp->set_enqueuing_is_done(true);
5994   if (rp->processing_is_mt()) {
5995     rp->balance_all_queues();
5996     CMSRefProcTaskExecutor task_executor(*this);
5997     rp->enqueue_discovered_references(&task_executor);
5998   } else {
5999     rp->enqueue_discovered_references(NULL);
6000   }
6001   rp->verify_no_references_recorded();
6002   assert(!rp->discovery_enabled(), "should have been disabled");
6003 }
6004 
6005 #ifndef PRODUCT
6006 void CMSCollector::check_correct_thread_executing() {
6007   Thread* t = Thread::current();
6008   // Only the VM thread or the CMS thread should be here.
6009   assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
6010          "Unexpected thread type");
6011   // If this is the vm thread, the foreground process
6012   // should not be waiting.  Note that _foregroundGCIsActive is
6013   // true while the foreground collector is waiting.
6014   if (_foregroundGCShouldWait) {
6015     // We cannot be the VM thread
6016     assert(t->is_ConcurrentGC_thread(),
6017            "Should be CMS thread");
6018   } else {
6019     // We can be the CMS thread only if we are in a stop-world
6020     // phase of CMS collection.
6021     if (t->is_ConcurrentGC_thread()) {
6022       assert(_collectorState == InitialMarking ||
6023              _collectorState == FinalMarking,
6024              "Should be a stop-world phase");
6025       // The CMS thread should be holding the CMS_token.
6026       assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6027              "Potential interference with concurrently "
6028              "executing VM thread");
6029     }
6030   }
6031 }
6032 #endif
6033 
6034 void CMSCollector::sweep(bool asynch) {
6035   assert(_collectorState == Sweeping, "just checking");
6036   check_correct_thread_executing();
6037   verify_work_stacks_empty();
6038   verify_overflow_empty();
6039   increment_sweep_count();
6040   TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
6041 
6042   _inter_sweep_timer.stop();
6043   _inter_sweep_estimate.sample(_inter_sweep_timer.seconds());
6044   size_policy()->avg_cms_free_at_sweep()->sample(_cmsGen->free());
6045 
6046   // PermGen verification support: If perm gen sweeping is disabled in
6047   // this cycle, we preserve the perm gen object "deadness" information
6048   // in the perm_gen_verify_bit_map. In order to do that we traverse
6049   // all blocks in perm gen and mark all dead objects.
6050   if (verifying() && !should_unload_classes()) {
6051     assert(perm_gen_verify_bit_map()->sizeInBits() != 0,
6052            "Should have already been allocated");
6053     MarkDeadObjectsClosure mdo(this, _permGen->cmsSpace(),
6054                                markBitMap(), perm_gen_verify_bit_map());
6055     if (asynch) {
6056       CMSTokenSyncWithLocks ts(true, _permGen->freelistLock(),
6057                                bitMapLock());
6058       _permGen->cmsSpace()->blk_iterate(&mdo);
6059     } else {
6060       // In the case of synchronous sweep, we already have
6061       // the requisite locks/tokens.
6062       _permGen->cmsSpace()->blk_iterate(&mdo);
6063     }
6064   }
6065 
6066   assert(!_intra_sweep_timer.is_active(), "Should not be active");
6067   _intra_sweep_timer.reset();
6068   _intra_sweep_timer.start();
6069   if (asynch) {
6070     TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6071     CMSPhaseAccounting pa(this, "sweep", !PrintGCDetails);
6072     // First sweep the old gen then the perm gen
6073     {
6074       CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
6075                                bitMapLock());
6076       sweepWork(_cmsGen, asynch);
6077     }
6078 
6079     // Now repeat for perm gen
6080     if (should_unload_classes()) {
6081       CMSTokenSyncWithLocks ts(true, _permGen->freelistLock(),
6082                              bitMapLock());
6083       sweepWork(_permGen, asynch);
6084     }
6085 
6086     // Update Universe::_heap_*_at_gc figures.
6087     // We need all the free list locks to make the abstract state
6088     // transition from Sweeping to Resetting. See detailed note
6089     // further below.
6090     {
6091       CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
6092                                _permGen->freelistLock());
6093       // Update heap occupancy information which is used as
6094       // input to soft ref clearing policy at the next gc.
6095       Universe::update_heap_info_at_gc();
6096       _collectorState = Resizing;
6097     }
6098   } else {
6099     // already have needed locks
6100     sweepWork(_cmsGen,  asynch);
6101 
6102     if (should_unload_classes()) {
6103       sweepWork(_permGen, asynch);
6104     }
6105     // Update heap occupancy information which is used as
6106     // input to soft ref clearing policy at the next gc.
6107     Universe::update_heap_info_at_gc();
6108     _collectorState = Resizing;
6109   }
6110   verify_work_stacks_empty();
6111   verify_overflow_empty();
6112 
6113   _intra_sweep_timer.stop();
6114   _intra_sweep_estimate.sample(_intra_sweep_timer.seconds());
6115 
6116   _inter_sweep_timer.reset();
6117   _inter_sweep_timer.start();
6118 
6119   // We need to use a monotonically non-deccreasing time in ms
6120   // or we will see time-warp warnings and os::javaTimeMillis()
6121   // does not guarantee monotonicity.
6122   jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
6123   update_time_of_last_gc(now);
6124 
6125   // NOTE on abstract state transitions:
6126   // Mutators allocate-live and/or mark the mod-union table dirty
6127   // based on the state of the collection.  The former is done in
6128   // the interval [Marking, Sweeping] and the latter in the interval
6129   // [Marking, Sweeping).  Thus the transitions into the Marking state
6130   // and out of the Sweeping state must be synchronously visible
6131   // globally to the mutators.
6132   // The transition into the Marking state happens with the world
6133   // stopped so the mutators will globally see it.  Sweeping is
6134   // done asynchronously by the background collector so the transition
6135   // from the Sweeping state to the Resizing state must be done
6136   // under the freelistLock (as is the check for whether to
6137   // allocate-live and whether to dirty the mod-union table).
6138   assert(_collectorState == Resizing, "Change of collector state to"
6139     " Resizing must be done under the freelistLocks (plural)");
6140 
6141   // Now that sweeping has been completed, we clear
6142   // the incremental_collection_failed flag,
6143   // thus inviting a younger gen collection to promote into
6144   // this generation. If such a promotion may still fail,
6145   // the flag will be set again when a young collection is
6146   // attempted.
6147   GenCollectedHeap* gch = GenCollectedHeap::heap();
6148   gch->clear_incremental_collection_failed();  // Worth retrying as fresh space may have been freed up
6149   gch->update_full_collections_completed(_collection_count_start);
6150 }
6151 
6152 // FIX ME!!! Looks like this belongs in CFLSpace, with
6153 // CMSGen merely delegating to it.
6154 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
6155   double nearLargestPercent = FLSLargestBlockCoalesceProximity;
6156   HeapWord*  minAddr        = _cmsSpace->bottom();
6157   HeapWord*  largestAddr    =
6158     (HeapWord*) _cmsSpace->dictionary()->find_largest_dict();
6159   if (largestAddr == NULL) {
6160     // The dictionary appears to be empty.  In this case
6161     // try to coalesce at the end of the heap.
6162     largestAddr = _cmsSpace->end();
6163   }
6164   size_t largestOffset     = pointer_delta(largestAddr, minAddr);
6165   size_t nearLargestOffset =
6166     (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
6167   if (PrintFLSStatistics != 0) {
6168     gclog_or_tty->print_cr(
6169       "CMS: Large Block: " PTR_FORMAT ";"
6170       " Proximity: " PTR_FORMAT " -> " PTR_FORMAT,
6171       largestAddr,
6172       _cmsSpace->nearLargestChunk(), minAddr + nearLargestOffset);
6173   }
6174   _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
6175 }
6176 
6177 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
6178   return addr >= _cmsSpace->nearLargestChunk();
6179 }
6180 
6181 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
6182   return _cmsSpace->find_chunk_at_end();
6183 }
6184 
6185 void ConcurrentMarkSweepGeneration::update_gc_stats(int current_level,
6186                                                     bool full) {
6187   // The next lower level has been collected.  Gather any statistics
6188   // that are of interest at this point.
6189   if (!full && (current_level + 1) == level()) {
6190     // Gather statistics on the young generation collection.
6191     collector()->stats().record_gc0_end(used());
6192   }
6193 }
6194 
6195 CMSAdaptiveSizePolicy* ConcurrentMarkSweepGeneration::size_policy() {
6196   GenCollectedHeap* gch = GenCollectedHeap::heap();
6197   assert(gch->kind() == CollectedHeap::GenCollectedHeap,
6198     "Wrong type of heap");
6199   CMSAdaptiveSizePolicy* sp = (CMSAdaptiveSizePolicy*)
6200     gch->gen_policy()->size_policy();
6201   assert(sp->is_gc_cms_adaptive_size_policy(),
6202     "Wrong type of size policy");
6203   return sp;
6204 }
6205 
6206 void ConcurrentMarkSweepGeneration::rotate_debug_collection_type() {
6207   if (PrintGCDetails && Verbose) {
6208     gclog_or_tty->print("Rotate from %d ", _debug_collection_type);
6209   }
6210   _debug_collection_type = (CollectionTypes) (_debug_collection_type + 1);
6211   _debug_collection_type =
6212     (CollectionTypes) (_debug_collection_type % Unknown_collection_type);
6213   if (PrintGCDetails && Verbose) {
6214     gclog_or_tty->print_cr("to %d ", _debug_collection_type);
6215   }
6216 }
6217 
6218 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* gen,
6219   bool asynch) {
6220   // We iterate over the space(s) underlying this generation,
6221   // checking the mark bit map to see if the bits corresponding
6222   // to specific blocks are marked or not. Blocks that are
6223   // marked are live and are not swept up. All remaining blocks
6224   // are swept up, with coalescing on-the-fly as we sweep up
6225   // contiguous free and/or garbage blocks:
6226   // We need to ensure that the sweeper synchronizes with allocators
6227   // and stop-the-world collectors. In particular, the following
6228   // locks are used:
6229   // . CMS token: if this is held, a stop the world collection cannot occur
6230   // . freelistLock: if this is held no allocation can occur from this
6231   //                 generation by another thread
6232   // . bitMapLock: if this is held, no other thread can access or update
6233   //
6234 
6235   // Note that we need to hold the freelistLock if we use
6236   // block iterate below; else the iterator might go awry if
6237   // a mutator (or promotion) causes block contents to change
6238   // (for instance if the allocator divvies up a block).
6239   // If we hold the free list lock, for all practical purposes
6240   // young generation GC's can't occur (they'll usually need to
6241   // promote), so we might as well prevent all young generation
6242   // GC's while we do a sweeping step. For the same reason, we might
6243   // as well take the bit map lock for the entire duration
6244 
6245   // check that we hold the requisite locks
6246   assert(have_cms_token(), "Should hold cms token");
6247   assert(   (asynch && ConcurrentMarkSweepThread::cms_thread_has_cms_token())
6248          || (!asynch && ConcurrentMarkSweepThread::vm_thread_has_cms_token()),
6249         "Should possess CMS token to sweep");
6250   assert_lock_strong(gen->freelistLock());
6251   assert_lock_strong(bitMapLock());
6252 
6253   assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context");
6254   assert(_intra_sweep_timer.is_active(),  "Was switched on  in an outer context");
6255   gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
6256                                       _inter_sweep_estimate.padded_average(),
6257                                       _intra_sweep_estimate.padded_average());
6258   gen->setNearLargestChunk();
6259 
6260   {
6261     SweepClosure sweepClosure(this, gen, &_markBitMap,
6262                             CMSYield && asynch);
6263     gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
6264     // We need to free-up/coalesce garbage/blocks from a
6265     // co-terminal free run. This is done in the SweepClosure
6266     // destructor; so, do not remove this scope, else the
6267     // end-of-sweep-census below will be off by a little bit.
6268   }
6269   gen->cmsSpace()->sweep_completed();
6270   gen->cmsSpace()->endSweepFLCensus(sweep_count());
6271   if (should_unload_classes()) {                // unloaded classes this cycle,
6272     _concurrent_cycles_since_last_unload = 0;   // ... reset count
6273   } else {                                      // did not unload classes,
6274     _concurrent_cycles_since_last_unload++;     // ... increment count
6275   }
6276 }
6277 
6278 // Reset CMS data structures (for now just the marking bit map)
6279 // preparatory for the next cycle.
6280 void CMSCollector::reset(bool asynch) {
6281   GenCollectedHeap* gch = GenCollectedHeap::heap();
6282   CMSAdaptiveSizePolicy* sp = size_policy();
6283   AdaptiveSizePolicyOutput(sp, gch->total_collections());
6284   if (asynch) {
6285     CMSTokenSyncWithLocks ts(true, bitMapLock());
6286 
6287     // If the state is not "Resetting", the foreground  thread
6288     // has done a collection and the resetting.
6289     if (_collectorState != Resetting) {
6290       assert(_collectorState == Idling, "The state should only change"
6291         " because the foreground collector has finished the collection");
6292       return;
6293     }
6294 
6295     // Clear the mark bitmap (no grey objects to start with)
6296     // for the next cycle.
6297     TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6298     CMSPhaseAccounting cmspa(this, "reset", !PrintGCDetails);
6299 
6300     HeapWord* curAddr = _markBitMap.startWord();
6301     while (curAddr < _markBitMap.endWord()) {
6302       size_t remaining  = pointer_delta(_markBitMap.endWord(), curAddr);
6303       MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
6304       _markBitMap.clear_large_range(chunk);
6305       if (ConcurrentMarkSweepThread::should_yield() &&
6306           !foregroundGCIsActive() &&
6307           CMSYield) {
6308         assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6309                "CMS thread should hold CMS token");
6310         assert_lock_strong(bitMapLock());
6311         bitMapLock()->unlock();
6312         ConcurrentMarkSweepThread::desynchronize(true);
6313         ConcurrentMarkSweepThread::acknowledge_yield_request();
6314         stopTimer();
6315         if (PrintCMSStatistics != 0) {
6316           incrementYields();
6317         }
6318         icms_wait();
6319 
6320         // See the comment in coordinator_yield()
6321         for (unsigned i = 0; i < CMSYieldSleepCount &&
6322                          ConcurrentMarkSweepThread::should_yield() &&
6323                          !CMSCollector::foregroundGCIsActive(); ++i) {
6324           os::sleep(Thread::current(), 1, false);
6325           ConcurrentMarkSweepThread::acknowledge_yield_request();
6326         }
6327 
6328         ConcurrentMarkSweepThread::synchronize(true);
6329         bitMapLock()->lock_without_safepoint_check();
6330         startTimer();
6331       }
6332       curAddr = chunk.end();
6333     }
6334     // A successful mostly concurrent collection has been done.
6335     // Because only the full (i.e., concurrent mode failure) collections
6336     // are being measured for gc overhead limits, clean the "near" flag
6337     // and count.
6338     sp->reset_gc_overhead_limit_count();
6339     _collectorState = Idling;
6340   } else {
6341     // already have the lock
6342     assert(_collectorState == Resetting, "just checking");
6343     assert_lock_strong(bitMapLock());
6344     _markBitMap.clear_all();
6345     _collectorState = Idling;
6346   }
6347 
6348   // Stop incremental mode after a cycle completes, so that any future cycles
6349   // are triggered by allocation.
6350   stop_icms();
6351 
6352   NOT_PRODUCT(
6353     if (RotateCMSCollectionTypes) {
6354       _cmsGen->rotate_debug_collection_type();
6355     }
6356   )
6357 
6358   register_gc_end();
6359 }
6360 
6361 void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) {
6362   gclog_or_tty->date_stamp(PrintGC && PrintGCDateStamps);
6363   TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6364   GCTraceTime t(GCCauseString("GC", gc_cause), PrintGC, !PrintGCDetails, NULL);
6365   TraceCollectorStats tcs(counters());
6366 
6367   switch (op) {
6368     case CMS_op_checkpointRootsInitial: {
6369       SvcGCMarker sgcm(SvcGCMarker::OTHER);
6370       checkpointRootsInitial(true);       // asynch
6371       if (PrintGC) {
6372         _cmsGen->printOccupancy("initial-mark");
6373       }
6374       break;
6375     }
6376     case CMS_op_checkpointRootsFinal: {
6377       SvcGCMarker sgcm(SvcGCMarker::OTHER);
6378       checkpointRootsFinal(true,    // asynch
6379                            false,   // !clear_all_soft_refs
6380                            false);  // !init_mark_was_synchronous
6381       if (PrintGC) {
6382         _cmsGen->printOccupancy("remark");
6383       }
6384       break;
6385     }
6386     default:
6387       fatal("No such CMS_op");
6388   }
6389 }
6390 
6391 #ifndef PRODUCT
6392 size_t const CMSCollector::skip_header_HeapWords() {
6393   return FreeChunk::header_size();
6394 }
6395 
6396 // Try and collect here conditions that should hold when
6397 // CMS thread is exiting. The idea is that the foreground GC
6398 // thread should not be blocked if it wants to terminate
6399 // the CMS thread and yet continue to run the VM for a while
6400 // after that.
6401 void CMSCollector::verify_ok_to_terminate() const {
6402   assert(Thread::current()->is_ConcurrentGC_thread(),
6403          "should be called by CMS thread");
6404   assert(!_foregroundGCShouldWait, "should be false");
6405   // We could check here that all the various low-level locks
6406   // are not held by the CMS thread, but that is overkill; see
6407   // also CMSThread::verify_ok_to_terminate() where the CGC_lock
6408   // is checked.
6409 }
6410 #endif
6411 
6412 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
6413    assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
6414           "missing Printezis mark?");
6415   HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
6416   size_t size = pointer_delta(nextOneAddr + 1, addr);
6417   assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6418          "alignment problem");
6419   assert(size >= 3, "Necessary for Printezis marks to work");
6420   return size;
6421 }
6422 
6423 // A variant of the above (block_size_using_printezis_bits()) except
6424 // that we return 0 if the P-bits are not yet set.
6425 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
6426   if (_markBitMap.isMarked(addr + 1)) {
6427     assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects");
6428     HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
6429     size_t size = pointer_delta(nextOneAddr + 1, addr);
6430     assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6431            "alignment problem");
6432     assert(size >= 3, "Necessary for Printezis marks to work");
6433     return size;
6434   }
6435   return 0;
6436 }
6437 
6438 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
6439   size_t sz = 0;
6440   oop p = (oop)addr;
6441   if (p->klass_or_null() != NULL && p->is_parsable()) {
6442     sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
6443   } else {
6444     sz = block_size_using_printezis_bits(addr);
6445   }
6446   assert(sz > 0, "size must be nonzero");
6447   HeapWord* next_block = addr + sz;
6448   HeapWord* next_card  = (HeapWord*)round_to((uintptr_t)next_block,
6449                                              CardTableModRefBS::card_size);
6450   assert(round_down((uintptr_t)addr,      CardTableModRefBS::card_size) <
6451          round_down((uintptr_t)next_card, CardTableModRefBS::card_size),
6452          "must be different cards");
6453   return next_card;
6454 }
6455 
6456 
6457 // CMS Bit Map Wrapper /////////////////////////////////////////
6458 
6459 // Construct a CMS bit map infrastructure, but don't create the
6460 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
6461 // further below.
6462 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
6463   _bm(),
6464   _shifter(shifter),
6465   _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true) : NULL)
6466 {
6467   _bmStartWord = 0;
6468   _bmWordSize  = 0;
6469 }
6470 
6471 bool CMSBitMap::allocate(MemRegion mr) {
6472   _bmStartWord = mr.start();
6473   _bmWordSize  = mr.word_size();
6474   ReservedSpace brs(ReservedSpace::allocation_align_size_up(
6475                      (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
6476   if (!brs.is_reserved()) {
6477     warning("CMS bit map allocation failure");
6478     return false;
6479   }
6480   // For now we'll just commit all of the bit map up fromt.
6481   // Later on we'll try to be more parsimonious with swap.
6482   if (!_virtual_space.initialize(brs, brs.size())) {
6483     warning("CMS bit map backing store failure");
6484     return false;
6485   }
6486   assert(_virtual_space.committed_size() == brs.size(),
6487          "didn't reserve backing store for all of CMS bit map?");
6488   _bm.set_map((BitMap::bm_word_t*)_virtual_space.low());
6489   assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
6490          _bmWordSize, "inconsistency in bit map sizing");
6491   _bm.set_size(_bmWordSize >> _shifter);
6492 
6493   // bm.clear(); // can we rely on getting zero'd memory? verify below
6494   assert(isAllClear(),
6495          "Expected zero'd memory from ReservedSpace constructor");
6496   assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
6497          "consistency check");
6498   return true;
6499 }
6500 
6501 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
6502   HeapWord *next_addr, *end_addr, *last_addr;
6503   assert_locked();
6504   assert(covers(mr), "out-of-range error");
6505   // XXX assert that start and end are appropriately aligned
6506   for (next_addr = mr.start(), end_addr = mr.end();
6507        next_addr < end_addr; next_addr = last_addr) {
6508     MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
6509     last_addr = dirty_region.end();
6510     if (!dirty_region.is_empty()) {
6511       cl->do_MemRegion(dirty_region);
6512     } else {
6513       assert(last_addr == end_addr, "program logic");
6514       return;
6515     }
6516   }
6517 }
6518 
6519 #ifndef PRODUCT
6520 void CMSBitMap::assert_locked() const {
6521   CMSLockVerifier::assert_locked(lock());
6522 }
6523 
6524 bool CMSBitMap::covers(MemRegion mr) const {
6525   // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
6526   assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
6527          "size inconsistency");
6528   return (mr.start() >= _bmStartWord) &&
6529          (mr.end()   <= endWord());
6530 }
6531 
6532 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
6533     return (start >= _bmStartWord && (start + size) <= endWord());
6534 }
6535 
6536 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
6537   // verify that there are no 1 bits in the interval [left, right)
6538   FalseBitMapClosure falseBitMapClosure;
6539   iterate(&falseBitMapClosure, left, right);
6540 }
6541 
6542 void CMSBitMap::region_invariant(MemRegion mr)
6543 {
6544   assert_locked();
6545   // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
6546   assert(!mr.is_empty(), "unexpected empty region");
6547   assert(covers(mr), "mr should be covered by bit map");
6548   // convert address range into offset range
6549   size_t start_ofs = heapWordToOffset(mr.start());
6550   // Make sure that end() is appropriately aligned
6551   assert(mr.end() == (HeapWord*)round_to((intptr_t)mr.end(),
6552                         (1 << (_shifter+LogHeapWordSize))),
6553          "Misaligned mr.end()");
6554   size_t end_ofs   = heapWordToOffset(mr.end());
6555   assert(end_ofs > start_ofs, "Should mark at least one bit");
6556 }
6557 
6558 #endif
6559 
6560 bool CMSMarkStack::allocate(size_t size) {
6561   // allocate a stack of the requisite depth
6562   ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6563                    size * sizeof(oop)));
6564   if (!rs.is_reserved()) {
6565     warning("CMSMarkStack allocation failure");
6566     return false;
6567   }
6568   if (!_virtual_space.initialize(rs, rs.size())) {
6569     warning("CMSMarkStack backing store failure");
6570     return false;
6571   }
6572   assert(_virtual_space.committed_size() == rs.size(),
6573          "didn't reserve backing store for all of CMS stack?");
6574   _base = (oop*)(_virtual_space.low());
6575   _index = 0;
6576   _capacity = size;
6577   NOT_PRODUCT(_max_depth = 0);
6578   return true;
6579 }
6580 
6581 // XXX FIX ME !!! In the MT case we come in here holding a
6582 // leaf lock. For printing we need to take a further lock
6583 // which has lower rank. We need to recallibrate the two
6584 // lock-ranks involved in order to be able to rpint the
6585 // messages below. (Or defer the printing to the caller.
6586 // For now we take the expedient path of just disabling the
6587 // messages for the problematic case.)
6588 void CMSMarkStack::expand() {
6589   assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted");
6590   if (_capacity == MarkStackSizeMax) {
6591     if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6592       // We print a warning message only once per CMS cycle.
6593       gclog_or_tty->print_cr(" (benign) Hit CMSMarkStack max size limit");
6594     }
6595     return;
6596   }
6597   // Double capacity if possible
6598   size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax);
6599   // Do not give up existing stack until we have managed to
6600   // get the double capacity that we desired.
6601   ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6602                    new_capacity * sizeof(oop)));
6603   if (rs.is_reserved()) {
6604     // Release the backing store associated with old stack
6605     _virtual_space.release();
6606     // Reinitialize virtual space for new stack
6607     if (!_virtual_space.initialize(rs, rs.size())) {
6608       fatal("Not enough swap for expanded marking stack");
6609     }
6610     _base = (oop*)(_virtual_space.low());
6611     _index = 0;
6612     _capacity = new_capacity;
6613   } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6614     // Failed to double capacity, continue;
6615     // we print a detail message only once per CMS cycle.
6616     gclog_or_tty->print(" (benign) Failed to expand marking stack from "SIZE_FORMAT"K to "
6617             SIZE_FORMAT"K",
6618             _capacity / K, new_capacity / K);
6619   }
6620 }
6621 
6622 
6623 // Closures
6624 // XXX: there seems to be a lot of code  duplication here;
6625 // should refactor and consolidate common code.
6626 
6627 // This closure is used to mark refs into the CMS generation in
6628 // the CMS bit map. Called at the first checkpoint. This closure
6629 // assumes that we do not need to re-mark dirty cards; if the CMS
6630 // generation on which this is used is not an oldest (modulo perm gen)
6631 // generation then this will lose younger_gen cards!
6632 
6633 MarkRefsIntoClosure::MarkRefsIntoClosure(
6634   MemRegion span, CMSBitMap* bitMap):
6635     _span(span),
6636     _bitMap(bitMap)
6637 {
6638     assert(_ref_processor == NULL, "deliberately left NULL");
6639     assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6640 }
6641 
6642 void MarkRefsIntoClosure::do_oop(oop obj) {
6643   // if p points into _span, then mark corresponding bit in _markBitMap
6644   assert(obj->is_oop(), "expected an oop");
6645   HeapWord* addr = (HeapWord*)obj;
6646   if (_span.contains(addr)) {
6647     // this should be made more efficient
6648     _bitMap->mark(addr);
6649   }
6650 }
6651 
6652 void MarkRefsIntoClosure::do_oop(oop* p)       { MarkRefsIntoClosure::do_oop_work(p); }
6653 void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6654 
6655 // A variant of the above, used for CMS marking verification.
6656 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
6657   MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm):
6658     _span(span),
6659     _verification_bm(verification_bm),
6660     _cms_bm(cms_bm)
6661 {
6662     assert(_ref_processor == NULL, "deliberately left NULL");
6663     assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
6664 }
6665 
6666 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
6667   // if p points into _span, then mark corresponding bit in _markBitMap
6668   assert(obj->is_oop(), "expected an oop");
6669   HeapWord* addr = (HeapWord*)obj;
6670   if (_span.contains(addr)) {
6671     _verification_bm->mark(addr);
6672     if (!_cms_bm->isMarked(addr)) {
6673       oop(addr)->print();
6674       gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)", addr);
6675       fatal("... aborting");
6676     }
6677   }
6678 }
6679 
6680 void MarkRefsIntoVerifyClosure::do_oop(oop* p)       { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6681 void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6682 
6683 //////////////////////////////////////////////////
6684 // MarkRefsIntoAndScanClosure
6685 //////////////////////////////////////////////////
6686 
6687 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
6688                                                        ReferenceProcessor* rp,
6689                                                        CMSBitMap* bit_map,
6690                                                        CMSBitMap* mod_union_table,
6691                                                        CMSMarkStack*  mark_stack,
6692                                                        CMSMarkStack*  revisit_stack,
6693                                                        CMSCollector* collector,
6694                                                        bool should_yield,
6695                                                        bool concurrent_precleaning):
6696   _collector(collector),
6697   _span(span),
6698   _bit_map(bit_map),
6699   _mark_stack(mark_stack),
6700   _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table,
6701                       mark_stack, revisit_stack, concurrent_precleaning),
6702   _yield(should_yield),
6703   _concurrent_precleaning(concurrent_precleaning),
6704   _freelistLock(NULL)
6705 {
6706   _ref_processor = rp;
6707   assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6708 }
6709 
6710 // This closure is used to mark refs into the CMS generation at the
6711 // second (final) checkpoint, and to scan and transitively follow
6712 // the unmarked oops. It is also used during the concurrent precleaning
6713 // phase while scanning objects on dirty cards in the CMS generation.
6714 // The marks are made in the marking bit map and the marking stack is
6715 // used for keeping the (newly) grey objects during the scan.
6716 // The parallel version (Par_...) appears further below.
6717 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6718   if (obj != NULL) {
6719     assert(obj->is_oop(), "expected an oop");
6720     HeapWord* addr = (HeapWord*)obj;
6721     assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6722     assert(_collector->overflow_list_is_empty(),
6723            "overflow list should be empty");
6724     if (_span.contains(addr) &&
6725         !_bit_map->isMarked(addr)) {
6726       // mark bit map (object is now grey)
6727       _bit_map->mark(addr);
6728       // push on marking stack (stack should be empty), and drain the
6729       // stack by applying this closure to the oops in the oops popped
6730       // from the stack (i.e. blacken the grey objects)
6731       bool res = _mark_stack->push(obj);
6732       assert(res, "Should have space to push on empty stack");
6733       do {
6734         oop new_oop = _mark_stack->pop();
6735         assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6736         assert(new_oop->is_parsable(), "Found unparsable oop");
6737         assert(_bit_map->isMarked((HeapWord*)new_oop),
6738                "only grey objects on this stack");
6739         // iterate over the oops in this oop, marking and pushing
6740         // the ones in CMS heap (i.e. in _span).
6741         new_oop->oop_iterate(&_pushAndMarkClosure);
6742         // check if it's time to yield
6743         do_yield_check();
6744       } while (!_mark_stack->isEmpty() ||
6745                (!_concurrent_precleaning && take_from_overflow_list()));
6746         // if marking stack is empty, and we are not doing this
6747         // during precleaning, then check the overflow list
6748     }
6749     assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6750     assert(_collector->overflow_list_is_empty(),
6751            "overflow list was drained above");
6752     // We could restore evacuated mark words, if any, used for
6753     // overflow list links here because the overflow list is
6754     // provably empty here. That would reduce the maximum
6755     // size requirements for preserved_{oop,mark}_stack.
6756     // But we'll just postpone it until we are all done
6757     // so we can just stream through.
6758     if (!_concurrent_precleaning && CMSOverflowEarlyRestoration) {
6759       _collector->restore_preserved_marks_if_any();
6760       assert(_collector->no_preserved_marks(), "No preserved marks");
6761     }
6762     assert(!CMSOverflowEarlyRestoration || _collector->no_preserved_marks(),
6763            "All preserved marks should have been restored above");
6764   }
6765 }
6766 
6767 void MarkRefsIntoAndScanClosure::do_oop(oop* p)       { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6768 void MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6769 
6770 void MarkRefsIntoAndScanClosure::do_yield_work() {
6771   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6772          "CMS thread should hold CMS token");
6773   assert_lock_strong(_freelistLock);
6774   assert_lock_strong(_bit_map->lock());
6775   // relinquish the free_list_lock and bitMaplock()
6776   DEBUG_ONLY(RememberKlassesChecker mux(false);)
6777   _bit_map->lock()->unlock();
6778   _freelistLock->unlock();
6779   ConcurrentMarkSweepThread::desynchronize(true);
6780   ConcurrentMarkSweepThread::acknowledge_yield_request();
6781   _collector->stopTimer();
6782   GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
6783   if (PrintCMSStatistics != 0) {
6784     _collector->incrementYields();
6785   }
6786   _collector->icms_wait();
6787 
6788   // See the comment in coordinator_yield()
6789   for (unsigned i = 0;
6790        i < CMSYieldSleepCount &&
6791        ConcurrentMarkSweepThread::should_yield() &&
6792        !CMSCollector::foregroundGCIsActive();
6793        ++i) {
6794     os::sleep(Thread::current(), 1, false);
6795     ConcurrentMarkSweepThread::acknowledge_yield_request();
6796   }
6797 
6798   ConcurrentMarkSweepThread::synchronize(true);
6799   _freelistLock->lock_without_safepoint_check();
6800   _bit_map->lock()->lock_without_safepoint_check();
6801   _collector->startTimer();
6802 }
6803 
6804 ///////////////////////////////////////////////////////////
6805 // Par_MarkRefsIntoAndScanClosure: a parallel version of
6806 //                                 MarkRefsIntoAndScanClosure
6807 ///////////////////////////////////////////////////////////
6808 Par_MarkRefsIntoAndScanClosure::Par_MarkRefsIntoAndScanClosure(
6809   CMSCollector* collector, MemRegion span, ReferenceProcessor* rp,
6810   CMSBitMap* bit_map, OopTaskQueue* work_queue, CMSMarkStack*  revisit_stack):
6811   _span(span),
6812   _bit_map(bit_map),
6813   _work_queue(work_queue),
6814   _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
6815                        (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads))),
6816   _par_pushAndMarkClosure(collector, span, rp, bit_map, work_queue,
6817                           revisit_stack)
6818 {
6819   _ref_processor = rp;
6820   assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6821 }
6822 
6823 // This closure is used to mark refs into the CMS generation at the
6824 // second (final) checkpoint, and to scan and transitively follow
6825 // the unmarked oops. The marks are made in the marking bit map and
6826 // the work_queue is used for keeping the (newly) grey objects during
6827 // the scan phase whence they are also available for stealing by parallel
6828 // threads. Since the marking bit map is shared, updates are
6829 // synchronized (via CAS).
6830 void Par_MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6831   if (obj != NULL) {
6832     // Ignore mark word because this could be an already marked oop
6833     // that may be chained at the end of the overflow list.
6834     assert(obj->is_oop(true), "expected an oop");
6835     HeapWord* addr = (HeapWord*)obj;
6836     if (_span.contains(addr) &&
6837         !_bit_map->isMarked(addr)) {
6838       // mark bit map (object will become grey):
6839       // It is possible for several threads to be
6840       // trying to "claim" this object concurrently;
6841       // the unique thread that succeeds in marking the
6842       // object first will do the subsequent push on
6843       // to the work queue (or overflow list).
6844       if (_bit_map->par_mark(addr)) {
6845         // push on work_queue (which may not be empty), and trim the
6846         // queue to an appropriate length by applying this closure to
6847         // the oops in the oops popped from the stack (i.e. blacken the
6848         // grey objects)
6849         bool res = _work_queue->push(obj);
6850         assert(res, "Low water mark should be less than capacity?");
6851         trim_queue(_low_water_mark);
6852       } // Else, another thread claimed the object
6853     }
6854   }
6855 }
6856 
6857 void Par_MarkRefsIntoAndScanClosure::do_oop(oop* p)       { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6858 void Par_MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6859 
6860 // This closure is used to rescan the marked objects on the dirty cards
6861 // in the mod union table and the card table proper.
6862 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
6863   oop p, MemRegion mr) {
6864 
6865   size_t size = 0;
6866   HeapWord* addr = (HeapWord*)p;
6867   DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6868   assert(_span.contains(addr), "we are scanning the CMS generation");
6869   // check if it's time to yield
6870   if (do_yield_check()) {
6871     // We yielded for some foreground stop-world work,
6872     // and we have been asked to abort this ongoing preclean cycle.
6873     return 0;
6874   }
6875   if (_bitMap->isMarked(addr)) {
6876     // it's marked; is it potentially uninitialized?
6877     if (p->klass_or_null() != NULL) {
6878       // If is_conc_safe is false, the object may be undergoing
6879       // change by the VM outside a safepoint.  Don't try to
6880       // scan it, but rather leave it for the remark phase.
6881       if (CMSPermGenPrecleaningEnabled &&
6882           (!p->is_conc_safe() || !p->is_parsable())) {
6883         // Signal precleaning to redirty the card since
6884         // the klass pointer is already installed.
6885         assert(size == 0, "Initial value");
6886       } else {
6887         assert(p->is_parsable(), "must be parsable.");
6888         // an initialized object; ignore mark word in verification below
6889         // since we are running concurrent with mutators
6890         assert(p->is_oop(true), "should be an oop");
6891         if (p->is_objArray()) {
6892           // objArrays are precisely marked; restrict scanning
6893           // to dirty cards only.
6894           size = CompactibleFreeListSpace::adjustObjectSize(
6895                    p->oop_iterate(_scanningClosure, mr));
6896         } else {
6897           // A non-array may have been imprecisely marked; we need
6898           // to scan object in its entirety.
6899           size = CompactibleFreeListSpace::adjustObjectSize(
6900                    p->oop_iterate(_scanningClosure));
6901         }
6902         #ifdef DEBUG
6903           size_t direct_size =
6904             CompactibleFreeListSpace::adjustObjectSize(p->size());
6905           assert(size == direct_size, "Inconsistency in size");
6906           assert(size >= 3, "Necessary for Printezis marks to work");
6907           if (!_bitMap->isMarked(addr+1)) {
6908             _bitMap->verifyNoOneBitsInRange(addr+2, addr+size);
6909           } else {
6910             _bitMap->verifyNoOneBitsInRange(addr+2, addr+size-1);
6911             assert(_bitMap->isMarked(addr+size-1),
6912                    "inconsistent Printezis mark");
6913           }
6914         #endif // DEBUG
6915       }
6916     } else {
6917       // an unitialized object
6918       assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
6919       HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
6920       size = pointer_delta(nextOneAddr + 1, addr);
6921       assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6922              "alignment problem");
6923       // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
6924       // will dirty the card when the klass pointer is installed in the
6925       // object (signalling the completion of initialization).
6926     }
6927   } else {
6928     // Either a not yet marked object or an uninitialized object
6929     if (p->klass_or_null() == NULL || !p->is_parsable()) {
6930       // An uninitialized object, skip to the next card, since
6931       // we may not be able to read its P-bits yet.
6932       assert(size == 0, "Initial value");
6933     } else {
6934       // An object not (yet) reached by marking: we merely need to
6935       // compute its size so as to go look at the next block.
6936       assert(p->is_oop(true), "should be an oop");
6937       size = CompactibleFreeListSpace::adjustObjectSize(p->size());
6938     }
6939   }
6940   DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6941   return size;
6942 }
6943 
6944 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
6945   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6946          "CMS thread should hold CMS token");
6947   assert_lock_strong(_freelistLock);
6948   assert_lock_strong(_bitMap->lock());
6949   DEBUG_ONLY(RememberKlassesChecker mux(false);)
6950   // relinquish the free_list_lock and bitMaplock()
6951   _bitMap->lock()->unlock();
6952   _freelistLock->unlock();
6953   ConcurrentMarkSweepThread::desynchronize(true);
6954   ConcurrentMarkSweepThread::acknowledge_yield_request();
6955   _collector->stopTimer();
6956   GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
6957   if (PrintCMSStatistics != 0) {
6958     _collector->incrementYields();
6959   }
6960   _collector->icms_wait();
6961 
6962   // See the comment in coordinator_yield()
6963   for (unsigned i = 0; i < CMSYieldSleepCount &&
6964                    ConcurrentMarkSweepThread::should_yield() &&
6965                    !CMSCollector::foregroundGCIsActive(); ++i) {
6966     os::sleep(Thread::current(), 1, false);
6967     ConcurrentMarkSweepThread::acknowledge_yield_request();
6968   }
6969 
6970   ConcurrentMarkSweepThread::synchronize(true);
6971   _freelistLock->lock_without_safepoint_check();
6972   _bitMap->lock()->lock_without_safepoint_check();
6973   _collector->startTimer();
6974 }
6975 
6976 
6977 //////////////////////////////////////////////////////////////////
6978 // SurvivorSpacePrecleanClosure
6979 //////////////////////////////////////////////////////////////////
6980 // This (single-threaded) closure is used to preclean the oops in
6981 // the survivor spaces.
6982 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
6983 
6984   HeapWord* addr = (HeapWord*)p;
6985   DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6986   assert(!_span.contains(addr), "we are scanning the survivor spaces");
6987   assert(p->klass_or_null() != NULL, "object should be initializd");
6988   assert(p->is_parsable(), "must be parsable.");
6989   // an initialized object; ignore mark word in verification below
6990   // since we are running concurrent with mutators
6991   assert(p->is_oop(true), "should be an oop");
6992   // Note that we do not yield while we iterate over
6993   // the interior oops of p, pushing the relevant ones
6994   // on our marking stack.
6995   size_t size = p->oop_iterate(_scanning_closure);
6996   do_yield_check();
6997   // Observe that below, we do not abandon the preclean
6998   // phase as soon as we should; rather we empty the
6999   // marking stack before returning. This is to satisfy
7000   // some existing assertions. In general, it may be a
7001   // good idea to abort immediately and complete the marking
7002   // from the grey objects at a later time.
7003   while (!_mark_stack->isEmpty()) {
7004     oop new_oop = _mark_stack->pop();
7005     assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
7006     assert(new_oop->is_parsable(), "Found unparsable oop");
7007     assert(_bit_map->isMarked((HeapWord*)new_oop),
7008            "only grey objects on this stack");
7009     // iterate over the oops in this oop, marking and pushing
7010     // the ones in CMS heap (i.e. in _span).
7011     new_oop->oop_iterate(_scanning_closure);
7012     // check if it's time to yield
7013     do_yield_check();
7014   }
7015   unsigned int after_count =
7016     GenCollectedHeap::heap()->total_collections();
7017   bool abort = (_before_count != after_count) ||
7018                _collector->should_abort_preclean();
7019   return abort ? 0 : size;
7020 }
7021 
7022 void SurvivorSpacePrecleanClosure::do_yield_work() {
7023   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7024          "CMS thread should hold CMS token");
7025   assert_lock_strong(_bit_map->lock());
7026   DEBUG_ONLY(RememberKlassesChecker smx(false);)
7027   // Relinquish the bit map lock
7028   _bit_map->lock()->unlock();
7029   ConcurrentMarkSweepThread::desynchronize(true);
7030   ConcurrentMarkSweepThread::acknowledge_yield_request();
7031   _collector->stopTimer();
7032   GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7033   if (PrintCMSStatistics != 0) {
7034     _collector->incrementYields();
7035   }
7036   _collector->icms_wait();
7037 
7038   // See the comment in coordinator_yield()
7039   for (unsigned i = 0; i < CMSYieldSleepCount &&
7040                        ConcurrentMarkSweepThread::should_yield() &&
7041                        !CMSCollector::foregroundGCIsActive(); ++i) {
7042     os::sleep(Thread::current(), 1, false);
7043     ConcurrentMarkSweepThread::acknowledge_yield_request();
7044   }
7045 
7046   ConcurrentMarkSweepThread::synchronize(true);
7047   _bit_map->lock()->lock_without_safepoint_check();
7048   _collector->startTimer();
7049 }
7050 
7051 // This closure is used to rescan the marked objects on the dirty cards
7052 // in the mod union table and the card table proper. In the parallel
7053 // case, although the bitMap is shared, we do a single read so the
7054 // isMarked() query is "safe".
7055 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
7056   // Ignore mark word because we are running concurrent with mutators
7057   assert(p->is_oop_or_null(true), "expected an oop or null");
7058   HeapWord* addr = (HeapWord*)p;
7059   assert(_span.contains(addr), "we are scanning the CMS generation");
7060   bool is_obj_array = false;
7061   #ifdef DEBUG
7062     if (!_parallel) {
7063       assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
7064       assert(_collector->overflow_list_is_empty(),
7065              "overflow list should be empty");
7066 
7067     }
7068   #endif // DEBUG
7069   if (_bit_map->isMarked(addr)) {
7070     // Obj arrays are precisely marked, non-arrays are not;
7071     // so we scan objArrays precisely and non-arrays in their
7072     // entirety.
7073     if (p->is_objArray()) {
7074       is_obj_array = true;
7075       if (_parallel) {
7076         p->oop_iterate(_par_scan_closure, mr);
7077       } else {
7078         p->oop_iterate(_scan_closure, mr);
7079       }
7080     } else {
7081       if (_parallel) {
7082         p->oop_iterate(_par_scan_closure);
7083       } else {
7084         p->oop_iterate(_scan_closure);
7085       }
7086     }
7087   }
7088   #ifdef DEBUG
7089     if (!_parallel) {
7090       assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
7091       assert(_collector->overflow_list_is_empty(),
7092              "overflow list should be empty");
7093 
7094     }
7095   #endif // DEBUG
7096   return is_obj_array;
7097 }
7098 
7099 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
7100                         MemRegion span,
7101                         CMSBitMap* bitMap, CMSMarkStack*  markStack,
7102                         CMSMarkStack*  revisitStack,
7103                         bool should_yield, bool verifying):
7104   _collector(collector),
7105   _span(span),
7106   _bitMap(bitMap),
7107   _mut(&collector->_modUnionTable),
7108   _markStack(markStack),
7109   _revisitStack(revisitStack),
7110   _yield(should_yield),
7111   _skipBits(0)
7112 {
7113   assert(_markStack->isEmpty(), "stack should be empty");
7114   _finger = _bitMap->startWord();
7115   _threshold = _finger;
7116   assert(_collector->_restart_addr == NULL, "Sanity check");
7117   assert(_span.contains(_finger), "Out of bounds _finger?");
7118   DEBUG_ONLY(_verifying = verifying;)
7119 }
7120 
7121 void MarkFromRootsClosure::reset(HeapWord* addr) {
7122   assert(_markStack->isEmpty(), "would cause duplicates on stack");
7123   assert(_span.contains(addr), "Out of bounds _finger?");
7124   _finger = addr;
7125   _threshold = (HeapWord*)round_to(
7126                  (intptr_t)_finger, CardTableModRefBS::card_size);
7127 }
7128 
7129 // Should revisit to see if this should be restructured for
7130 // greater efficiency.
7131 bool MarkFromRootsClosure::do_bit(size_t offset) {
7132   if (_skipBits > 0) {
7133     _skipBits--;
7134     return true;
7135   }
7136   // convert offset into a HeapWord*
7137   HeapWord* addr = _bitMap->startWord() + offset;
7138   assert(_bitMap->endWord() && addr < _bitMap->endWord(),
7139          "address out of range");
7140   assert(_bitMap->isMarked(addr), "tautology");
7141   if (_bitMap->isMarked(addr+1)) {
7142     // this is an allocated but not yet initialized object
7143     assert(_skipBits == 0, "tautology");
7144     _skipBits = 2;  // skip next two marked bits ("Printezis-marks")
7145     oop p = oop(addr);
7146     if (p->klass_or_null() == NULL || !p->is_parsable()) {
7147       DEBUG_ONLY(if (!_verifying) {)
7148         // We re-dirty the cards on which this object lies and increase
7149         // the _threshold so that we'll come back to scan this object
7150         // during the preclean or remark phase. (CMSCleanOnEnter)
7151         if (CMSCleanOnEnter) {
7152           size_t sz = _collector->block_size_using_printezis_bits(addr);
7153           HeapWord* end_card_addr   = (HeapWord*)round_to(
7154                                          (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7155           MemRegion redirty_range = MemRegion(addr, end_card_addr);
7156           assert(!redirty_range.is_empty(), "Arithmetical tautology");
7157           // Bump _threshold to end_card_addr; note that
7158           // _threshold cannot possibly exceed end_card_addr, anyhow.
7159           // This prevents future clearing of the card as the scan proceeds
7160           // to the right.
7161           assert(_threshold <= end_card_addr,
7162                  "Because we are just scanning into this object");
7163           if (_threshold < end_card_addr) {
7164             _threshold = end_card_addr;
7165           }
7166           if (p->klass_or_null() != NULL) {
7167             // Redirty the range of cards...
7168             _mut->mark_range(redirty_range);
7169           } // ...else the setting of klass will dirty the card anyway.
7170         }
7171       DEBUG_ONLY(})
7172       return true;
7173     }
7174   }
7175   scanOopsInOop(addr);
7176   return true;
7177 }
7178 
7179 // We take a break if we've been at this for a while,
7180 // so as to avoid monopolizing the locks involved.
7181 void MarkFromRootsClosure::do_yield_work() {
7182   // First give up the locks, then yield, then re-lock
7183   // We should probably use a constructor/destructor idiom to
7184   // do this unlock/lock or modify the MutexUnlocker class to
7185   // serve our purpose. XXX
7186   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7187          "CMS thread should hold CMS token");
7188   assert_lock_strong(_bitMap->lock());
7189   DEBUG_ONLY(RememberKlassesChecker mux(false);)
7190   _bitMap->lock()->unlock();
7191   ConcurrentMarkSweepThread::desynchronize(true);
7192   ConcurrentMarkSweepThread::acknowledge_yield_request();
7193   _collector->stopTimer();
7194   GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7195   if (PrintCMSStatistics != 0) {
7196     _collector->incrementYields();
7197   }
7198   _collector->icms_wait();
7199 
7200   // See the comment in coordinator_yield()
7201   for (unsigned i = 0; i < CMSYieldSleepCount &&
7202                        ConcurrentMarkSweepThread::should_yield() &&
7203                        !CMSCollector::foregroundGCIsActive(); ++i) {
7204     os::sleep(Thread::current(), 1, false);
7205     ConcurrentMarkSweepThread::acknowledge_yield_request();
7206   }
7207 
7208   ConcurrentMarkSweepThread::synchronize(true);
7209   _bitMap->lock()->lock_without_safepoint_check();
7210   _collector->startTimer();
7211 }
7212 
7213 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
7214   assert(_bitMap->isMarked(ptr), "expected bit to be set");
7215   assert(_markStack->isEmpty(),
7216          "should drain stack to limit stack usage");
7217   // convert ptr to an oop preparatory to scanning
7218   oop obj = oop(ptr);
7219   // Ignore mark word in verification below, since we
7220   // may be running concurrent with mutators.
7221   assert(obj->is_oop(true), "should be an oop");
7222   assert(_finger <= ptr, "_finger runneth ahead");
7223   // advance the finger to right end of this object
7224   _finger = ptr + obj->size();
7225   assert(_finger > ptr, "we just incremented it above");
7226   // On large heaps, it may take us some time to get through
7227   // the marking phase (especially if running iCMS). During
7228   // this time it's possible that a lot of mutations have
7229   // accumulated in the card table and the mod union table --
7230   // these mutation records are redundant until we have
7231   // actually traced into the corresponding card.
7232   // Here, we check whether advancing the finger would make
7233   // us cross into a new card, and if so clear corresponding
7234   // cards in the MUT (preclean them in the card-table in the
7235   // future).
7236 
7237   DEBUG_ONLY(if (!_verifying) {)
7238     // The clean-on-enter optimization is disabled by default,
7239     // until we fix 6178663.
7240     if (CMSCleanOnEnter && (_finger > _threshold)) {
7241       // [_threshold, _finger) represents the interval
7242       // of cards to be cleared  in MUT (or precleaned in card table).
7243       // The set of cards to be cleared is all those that overlap
7244       // with the interval [_threshold, _finger); note that
7245       // _threshold is always kept card-aligned but _finger isn't
7246       // always card-aligned.
7247       HeapWord* old_threshold = _threshold;
7248       assert(old_threshold == (HeapWord*)round_to(
7249               (intptr_t)old_threshold, CardTableModRefBS::card_size),
7250              "_threshold should always be card-aligned");
7251       _threshold = (HeapWord*)round_to(
7252                      (intptr_t)_finger, CardTableModRefBS::card_size);
7253       MemRegion mr(old_threshold, _threshold);
7254       assert(!mr.is_empty(), "Control point invariant");
7255       assert(_span.contains(mr), "Should clear within span");
7256       // XXX When _finger crosses from old gen into perm gen
7257       // we may be doing unnecessary cleaning; do better in the
7258       // future by detecting that condition and clearing fewer
7259       // MUT/CT entries.
7260       _mut->clear_range(mr);
7261     }
7262   DEBUG_ONLY(})
7263   // Note: the finger doesn't advance while we drain
7264   // the stack below.
7265   PushOrMarkClosure pushOrMarkClosure(_collector,
7266                                       _span, _bitMap, _markStack,
7267                                       _revisitStack,
7268                                       _finger, this);
7269   bool res = _markStack->push(obj);
7270   assert(res, "Empty non-zero size stack should have space for single push");
7271   while (!_markStack->isEmpty()) {
7272     oop new_oop = _markStack->pop();
7273     // Skip verifying header mark word below because we are
7274     // running concurrent with mutators.
7275     assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
7276     // now scan this oop's oops
7277     new_oop->oop_iterate(&pushOrMarkClosure);
7278     do_yield_check();
7279   }
7280   assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
7281 }
7282 
7283 Par_MarkFromRootsClosure::Par_MarkFromRootsClosure(CMSConcMarkingTask* task,
7284                        CMSCollector* collector, MemRegion span,
7285                        CMSBitMap* bit_map,
7286                        OopTaskQueue* work_queue,
7287                        CMSMarkStack*  overflow_stack,
7288                        CMSMarkStack*  revisit_stack,
7289                        bool should_yield):
7290   _collector(collector),
7291   _whole_span(collector->_span),
7292   _span(span),
7293   _bit_map(bit_map),
7294   _mut(&collector->_modUnionTable),
7295   _work_queue(work_queue),
7296   _overflow_stack(overflow_stack),
7297   _revisit_stack(revisit_stack),
7298   _yield(should_yield),
7299   _skip_bits(0),
7300   _task(task)
7301 {
7302   assert(_work_queue->size() == 0, "work_queue should be empty");
7303   _finger = span.start();
7304   _threshold = _finger;     // XXX Defer clear-on-enter optimization for now
7305   assert(_span.contains(_finger), "Out of bounds _finger?");
7306 }
7307 
7308 // Should revisit to see if this should be restructured for
7309 // greater efficiency.
7310 bool Par_MarkFromRootsClosure::do_bit(size_t offset) {
7311   if (_skip_bits > 0) {
7312     _skip_bits--;
7313     return true;
7314   }
7315   // convert offset into a HeapWord*
7316   HeapWord* addr = _bit_map->startWord() + offset;
7317   assert(_bit_map->endWord() && addr < _bit_map->endWord(),
7318          "address out of range");
7319   assert(_bit_map->isMarked(addr), "tautology");
7320   if (_bit_map->isMarked(addr+1)) {
7321     // this is an allocated object that might not yet be initialized
7322     assert(_skip_bits == 0, "tautology");
7323     _skip_bits = 2;  // skip next two marked bits ("Printezis-marks")
7324     oop p = oop(addr);
7325     if (p->klass_or_null() == NULL || !p->is_parsable()) {
7326       // in the case of Clean-on-Enter optimization, redirty card
7327       // and avoid clearing card by increasing  the threshold.
7328       return true;
7329     }
7330   }
7331   scan_oops_in_oop(addr);
7332   return true;
7333 }
7334 
7335 void Par_MarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
7336   assert(_bit_map->isMarked(ptr), "expected bit to be set");
7337   // Should we assert that our work queue is empty or
7338   // below some drain limit?
7339   assert(_work_queue->size() == 0,
7340          "should drain stack to limit stack usage");
7341   // convert ptr to an oop preparatory to scanning
7342   oop obj = oop(ptr);
7343   // Ignore mark word in verification below, since we
7344   // may be running concurrent with mutators.
7345   assert(obj->is_oop(true), "should be an oop");
7346   assert(_finger <= ptr, "_finger runneth ahead");
7347   // advance the finger to right end of this object
7348   _finger = ptr + obj->size();
7349   assert(_finger > ptr, "we just incremented it above");
7350   // On large heaps, it may take us some time to get through
7351   // the marking phase (especially if running iCMS). During
7352   // this time it's possible that a lot of mutations have
7353   // accumulated in the card table and the mod union table --
7354   // these mutation records are redundant until we have
7355   // actually traced into the corresponding card.
7356   // Here, we check whether advancing the finger would make
7357   // us cross into a new card, and if so clear corresponding
7358   // cards in the MUT (preclean them in the card-table in the
7359   // future).
7360 
7361   // The clean-on-enter optimization is disabled by default,
7362   // until we fix 6178663.
7363   if (CMSCleanOnEnter && (_finger > _threshold)) {
7364     // [_threshold, _finger) represents the interval
7365     // of cards to be cleared  in MUT (or precleaned in card table).
7366     // The set of cards to be cleared is all those that overlap
7367     // with the interval [_threshold, _finger); note that
7368     // _threshold is always kept card-aligned but _finger isn't
7369     // always card-aligned.
7370     HeapWord* old_threshold = _threshold;
7371     assert(old_threshold == (HeapWord*)round_to(
7372             (intptr_t)old_threshold, CardTableModRefBS::card_size),
7373            "_threshold should always be card-aligned");
7374     _threshold = (HeapWord*)round_to(
7375                    (intptr_t)_finger, CardTableModRefBS::card_size);
7376     MemRegion mr(old_threshold, _threshold);
7377     assert(!mr.is_empty(), "Control point invariant");
7378     assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
7379     // XXX When _finger crosses from old gen into perm gen
7380     // we may be doing unnecessary cleaning; do better in the
7381     // future by detecting that condition and clearing fewer
7382     // MUT/CT entries.
7383     _mut->clear_range(mr);
7384   }
7385 
7386   // Note: the local finger doesn't advance while we drain
7387   // the stack below, but the global finger sure can and will.
7388   HeapWord** gfa = _task->global_finger_addr();
7389   Par_PushOrMarkClosure pushOrMarkClosure(_collector,
7390                                       _span, _bit_map,
7391                                       _work_queue,
7392                                       _overflow_stack,
7393                                       _revisit_stack,
7394                                       _finger,
7395                                       gfa, this);
7396   bool res = _work_queue->push(obj);   // overflow could occur here
7397   assert(res, "Will hold once we use workqueues");
7398   while (true) {
7399     oop new_oop;
7400     if (!_work_queue->pop_local(new_oop)) {
7401       // We emptied our work_queue; check if there's stuff that can
7402       // be gotten from the overflow stack.
7403       if (CMSConcMarkingTask::get_work_from_overflow_stack(
7404             _overflow_stack, _work_queue)) {
7405         do_yield_check();
7406         continue;
7407       } else {  // done
7408         break;
7409       }
7410     }
7411     // Skip verifying header mark word below because we are
7412     // running concurrent with mutators.
7413     assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
7414     // now scan this oop's oops
7415     new_oop->oop_iterate(&pushOrMarkClosure);
7416     do_yield_check();
7417   }
7418   assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
7419 }
7420 
7421 // Yield in response to a request from VM Thread or
7422 // from mutators.
7423 void Par_MarkFromRootsClosure::do_yield_work() {
7424   assert(_task != NULL, "sanity");
7425   _task->yield();
7426 }
7427 
7428 // A variant of the above used for verifying CMS marking work.
7429 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
7430                         MemRegion span,
7431                         CMSBitMap* verification_bm, CMSBitMap* cms_bm,
7432                         CMSMarkStack*  mark_stack):
7433   _collector(collector),
7434   _span(span),
7435   _verification_bm(verification_bm),
7436   _cms_bm(cms_bm),
7437   _mark_stack(mark_stack),
7438   _pam_verify_closure(collector, span, verification_bm, cms_bm,
7439                       mark_stack)
7440 {
7441   assert(_mark_stack->isEmpty(), "stack should be empty");
7442   _finger = _verification_bm->startWord();
7443   assert(_collector->_restart_addr == NULL, "Sanity check");
7444   assert(_span.contains(_finger), "Out of bounds _finger?");
7445 }
7446 
7447 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
7448   assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
7449   assert(_span.contains(addr), "Out of bounds _finger?");
7450   _finger = addr;
7451 }
7452 
7453 // Should revisit to see if this should be restructured for
7454 // greater efficiency.
7455 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
7456   // convert offset into a HeapWord*
7457   HeapWord* addr = _verification_bm->startWord() + offset;
7458   assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
7459          "address out of range");
7460   assert(_verification_bm->isMarked(addr), "tautology");
7461   assert(_cms_bm->isMarked(addr), "tautology");
7462 
7463   assert(_mark_stack->isEmpty(),
7464          "should drain stack to limit stack usage");
7465   // convert addr to an oop preparatory to scanning
7466   oop obj = oop(addr);
7467   assert(obj->is_oop(), "should be an oop");
7468   assert(_finger <= addr, "_finger runneth ahead");
7469   // advance the finger to right end of this object
7470   _finger = addr + obj->size();
7471   assert(_finger > addr, "we just incremented it above");
7472   // Note: the finger doesn't advance while we drain
7473   // the stack below.
7474   bool res = _mark_stack->push(obj);
7475   assert(res, "Empty non-zero size stack should have space for single push");
7476   while (!_mark_stack->isEmpty()) {
7477     oop new_oop = _mark_stack->pop();
7478     assert(new_oop->is_oop(), "Oops! expected to pop an oop");
7479     // now scan this oop's oops
7480     new_oop->oop_iterate(&_pam_verify_closure);
7481   }
7482   assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
7483   return true;
7484 }
7485 
7486 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
7487   CMSCollector* collector, MemRegion span,
7488   CMSBitMap* verification_bm, CMSBitMap* cms_bm,
7489   CMSMarkStack*  mark_stack):
7490   OopClosure(collector->ref_processor()),
7491   _collector(collector),
7492   _span(span),
7493   _verification_bm(verification_bm),
7494   _cms_bm(cms_bm),
7495   _mark_stack(mark_stack)
7496 { }
7497 
7498 void PushAndMarkVerifyClosure::do_oop(oop* p)       { PushAndMarkVerifyClosure::do_oop_work(p); }
7499 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
7500 
7501 // Upon stack overflow, we discard (part of) the stack,
7502 // remembering the least address amongst those discarded
7503 // in CMSCollector's _restart_address.
7504 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
7505   // Remember the least grey address discarded
7506   HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
7507   _collector->lower_restart_addr(ra);
7508   _mark_stack->reset();  // discard stack contents
7509   _mark_stack->expand(); // expand the stack if possible
7510 }
7511 
7512 void PushAndMarkVerifyClosure::do_oop(oop obj) {
7513   assert(obj->is_oop_or_null(), "expected an oop or NULL");
7514   HeapWord* addr = (HeapWord*)obj;
7515   if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
7516     // Oop lies in _span and isn't yet grey or black
7517     _verification_bm->mark(addr);            // now grey
7518     if (!_cms_bm->isMarked(addr)) {
7519       oop(addr)->print();
7520       gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)",
7521                              addr);
7522       fatal("... aborting");
7523     }
7524 
7525     if (!_mark_stack->push(obj)) { // stack overflow
7526       if (PrintCMSStatistics != 0) {
7527         gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7528                                SIZE_FORMAT, _mark_stack->capacity());
7529       }
7530       assert(_mark_stack->isFull(), "Else push should have succeeded");
7531       handle_stack_overflow(addr);
7532     }
7533     // anything including and to the right of _finger
7534     // will be scanned as we iterate over the remainder of the
7535     // bit map
7536   }
7537 }
7538 
7539 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
7540                      MemRegion span,
7541                      CMSBitMap* bitMap, CMSMarkStack*  markStack,
7542                      CMSMarkStack*  revisitStack,
7543                      HeapWord* finger, MarkFromRootsClosure* parent) :
7544   KlassRememberingOopClosure(collector, collector->ref_processor(), revisitStack),
7545   _span(span),
7546   _bitMap(bitMap),
7547   _markStack(markStack),
7548   _finger(finger),
7549   _parent(parent)
7550 { }
7551 
7552 Par_PushOrMarkClosure::Par_PushOrMarkClosure(CMSCollector* collector,
7553                      MemRegion span,
7554                      CMSBitMap* bit_map,
7555                      OopTaskQueue* work_queue,
7556                      CMSMarkStack*  overflow_stack,
7557                      CMSMarkStack*  revisit_stack,
7558                      HeapWord* finger,
7559                      HeapWord** global_finger_addr,
7560                      Par_MarkFromRootsClosure* parent) :
7561   Par_KlassRememberingOopClosure(collector,
7562                             collector->ref_processor(),
7563                             revisit_stack),
7564   _whole_span(collector->_span),
7565   _span(span),
7566   _bit_map(bit_map),
7567   _work_queue(work_queue),
7568   _overflow_stack(overflow_stack),
7569   _finger(finger),
7570   _global_finger_addr(global_finger_addr),
7571   _parent(parent)
7572 { }
7573 
7574 // Assumes thread-safe access by callers, who are
7575 // responsible for mutual exclusion.
7576 void CMSCollector::lower_restart_addr(HeapWord* low) {
7577   assert(_span.contains(low), "Out of bounds addr");
7578   if (_restart_addr == NULL) {
7579     _restart_addr = low;
7580   } else {
7581     _restart_addr = MIN2(_restart_addr, low);
7582   }
7583 }
7584 
7585 // Upon stack overflow, we discard (part of) the stack,
7586 // remembering the least address amongst those discarded
7587 // in CMSCollector's _restart_address.
7588 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7589   // Remember the least grey address discarded
7590   HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
7591   _collector->lower_restart_addr(ra);
7592   _markStack->reset();  // discard stack contents
7593   _markStack->expand(); // expand the stack if possible
7594 }
7595 
7596 // Upon stack overflow, we discard (part of) the stack,
7597 // remembering the least address amongst those discarded
7598 // in CMSCollector's _restart_address.
7599 void Par_PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7600   // We need to do this under a mutex to prevent other
7601   // workers from interfering with the work done below.
7602   MutexLockerEx ml(_overflow_stack->par_lock(),
7603                    Mutex::_no_safepoint_check_flag);
7604   // Remember the least grey address discarded
7605   HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
7606   _collector->lower_restart_addr(ra);
7607   _overflow_stack->reset();  // discard stack contents
7608   _overflow_stack->expand(); // expand the stack if possible
7609 }
7610 
7611 void PushOrMarkClosure::do_oop(oop obj) {
7612   // Ignore mark word because we are running concurrent with mutators.
7613   assert(obj->is_oop_or_null(true), "expected an oop or NULL");
7614   HeapWord* addr = (HeapWord*)obj;
7615   if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
7616     // Oop lies in _span and isn't yet grey or black
7617     _bitMap->mark(addr);            // now grey
7618     if (addr < _finger) {
7619       // the bit map iteration has already either passed, or
7620       // sampled, this bit in the bit map; we'll need to
7621       // use the marking stack to scan this oop's oops.
7622       bool simulate_overflow = false;
7623       NOT_PRODUCT(
7624         if (CMSMarkStackOverflowALot &&
7625             _collector->simulate_overflow()) {
7626           // simulate a stack overflow
7627           simulate_overflow = true;
7628         }
7629       )
7630       if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
7631         if (PrintCMSStatistics != 0) {
7632           gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7633                                  SIZE_FORMAT, _markStack->capacity());
7634         }
7635         assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
7636         handle_stack_overflow(addr);
7637       }
7638     }
7639     // anything including and to the right of _finger
7640     // will be scanned as we iterate over the remainder of the
7641     // bit map
7642     do_yield_check();
7643   }
7644 }
7645 
7646 void PushOrMarkClosure::do_oop(oop* p)       { PushOrMarkClosure::do_oop_work(p); }
7647 void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); }
7648 
7649 void Par_PushOrMarkClosure::do_oop(oop obj) {
7650   // Ignore mark word because we are running concurrent with mutators.
7651   assert(obj->is_oop_or_null(true), "expected an oop or NULL");
7652   HeapWord* addr = (HeapWord*)obj;
7653   if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
7654     // Oop lies in _span and isn't yet grey or black
7655     // We read the global_finger (volatile read) strictly after marking oop
7656     bool res = _bit_map->par_mark(addr);    // now grey
7657     volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
7658     // Should we push this marked oop on our stack?
7659     // -- if someone else marked it, nothing to do
7660     // -- if target oop is above global finger nothing to do
7661     // -- if target oop is in chunk and above local finger
7662     //      then nothing to do
7663     // -- else push on work queue
7664     if (   !res       // someone else marked it, they will deal with it
7665         || (addr >= *gfa)  // will be scanned in a later task
7666         || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
7667       return;
7668     }
7669     // the bit map iteration has already either passed, or
7670     // sampled, this bit in the bit map; we'll need to
7671     // use the marking stack to scan this oop's oops.
7672     bool simulate_overflow = false;
7673     NOT_PRODUCT(
7674       if (CMSMarkStackOverflowALot &&
7675           _collector->simulate_overflow()) {
7676         // simulate a stack overflow
7677         simulate_overflow = true;
7678       }
7679     )
7680     if (simulate_overflow ||
7681         !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
7682       // stack overflow
7683       if (PrintCMSStatistics != 0) {
7684         gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7685                                SIZE_FORMAT, _overflow_stack->capacity());
7686       }
7687       // We cannot assert that the overflow stack is full because
7688       // it may have been emptied since.
7689       assert(simulate_overflow ||
7690              _work_queue->size() == _work_queue->max_elems(),
7691             "Else push should have succeeded");
7692       handle_stack_overflow(addr);
7693     }
7694     do_yield_check();
7695   }
7696 }
7697 
7698 void Par_PushOrMarkClosure::do_oop(oop* p)       { Par_PushOrMarkClosure::do_oop_work(p); }
7699 void Par_PushOrMarkClosure::do_oop(narrowOop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7700 
7701 KlassRememberingOopClosure::KlassRememberingOopClosure(CMSCollector* collector,
7702                                              ReferenceProcessor* rp,
7703                                              CMSMarkStack* revisit_stack) :
7704   OopClosure(rp),
7705   _collector(collector),
7706   _revisit_stack(revisit_stack),
7707   _should_remember_klasses(collector->should_unload_classes()) {}
7708 
7709 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
7710                                        MemRegion span,
7711                                        ReferenceProcessor* rp,
7712                                        CMSBitMap* bit_map,
7713                                        CMSBitMap* mod_union_table,
7714                                        CMSMarkStack*  mark_stack,
7715                                        CMSMarkStack*  revisit_stack,
7716                                        bool           concurrent_precleaning):
7717   KlassRememberingOopClosure(collector, rp, revisit_stack),
7718   _span(span),
7719   _bit_map(bit_map),
7720   _mod_union_table(mod_union_table),
7721   _mark_stack(mark_stack),
7722   _concurrent_precleaning(concurrent_precleaning)
7723 {
7724   assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7725 }
7726 
7727 // Grey object rescan during pre-cleaning and second checkpoint phases --
7728 // the non-parallel version (the parallel version appears further below.)
7729 void PushAndMarkClosure::do_oop(oop obj) {
7730   // Ignore mark word verification. If during concurrent precleaning,
7731   // the object monitor may be locked. If during the checkpoint
7732   // phases, the object may already have been reached by a  different
7733   // path and may be at the end of the global overflow list (so
7734   // the mark word may be NULL).
7735   assert(obj->is_oop_or_null(true /* ignore mark word */),
7736          "expected an oop or NULL");
7737   HeapWord* addr = (HeapWord*)obj;
7738   // Check if oop points into the CMS generation
7739   // and is not marked
7740   if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7741     // a white object ...
7742     _bit_map->mark(addr);         // ... now grey
7743     // push on the marking stack (grey set)
7744     bool simulate_overflow = false;
7745     NOT_PRODUCT(
7746       if (CMSMarkStackOverflowALot &&
7747           _collector->simulate_overflow()) {
7748         // simulate a stack overflow
7749         simulate_overflow = true;
7750       }
7751     )
7752     if (simulate_overflow || !_mark_stack->push(obj)) {
7753       if (_concurrent_precleaning) {
7754          // During precleaning we can just dirty the appropriate card(s)
7755          // in the mod union table, thus ensuring that the object remains
7756          // in the grey set  and continue. In the case of object arrays
7757          // we need to dirty all of the cards that the object spans,
7758          // since the rescan of object arrays will be limited to the
7759          // dirty cards.
7760          // Note that no one can be intefering with us in this action
7761          // of dirtying the mod union table, so no locking or atomics
7762          // are required.
7763          if (obj->is_objArray()) {
7764            size_t sz = obj->size();
7765            HeapWord* end_card_addr = (HeapWord*)round_to(
7766                                         (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7767            MemRegion redirty_range = MemRegion(addr, end_card_addr);
7768            assert(!redirty_range.is_empty(), "Arithmetical tautology");
7769            _mod_union_table->mark_range(redirty_range);
7770          } else {
7771            _mod_union_table->mark(addr);
7772          }
7773          _collector->_ser_pmc_preclean_ovflw++;
7774       } else {
7775          // During the remark phase, we need to remember this oop
7776          // in the overflow list.
7777          _collector->push_on_overflow_list(obj);
7778          _collector->_ser_pmc_remark_ovflw++;
7779       }
7780     }
7781   }
7782 }
7783 
7784 Par_PushAndMarkClosure::Par_PushAndMarkClosure(CMSCollector* collector,
7785                                                MemRegion span,
7786                                                ReferenceProcessor* rp,
7787                                                CMSBitMap* bit_map,
7788                                                OopTaskQueue* work_queue,
7789                                                CMSMarkStack* revisit_stack):
7790   Par_KlassRememberingOopClosure(collector, rp, revisit_stack),
7791   _span(span),
7792   _bit_map(bit_map),
7793   _work_queue(work_queue)
7794 {
7795   assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7796 }
7797 
7798 void PushAndMarkClosure::do_oop(oop* p)       { PushAndMarkClosure::do_oop_work(p); }
7799 void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); }
7800 
7801 // Grey object rescan during second checkpoint phase --
7802 // the parallel version.
7803 void Par_PushAndMarkClosure::do_oop(oop obj) {
7804   // In the assert below, we ignore the mark word because
7805   // this oop may point to an already visited object that is
7806   // on the overflow stack (in which case the mark word has
7807   // been hijacked for chaining into the overflow stack --
7808   // if this is the last object in the overflow stack then
7809   // its mark word will be NULL). Because this object may
7810   // have been subsequently popped off the global overflow
7811   // stack, and the mark word possibly restored to the prototypical
7812   // value, by the time we get to examined this failing assert in
7813   // the debugger, is_oop_or_null(false) may subsequently start
7814   // to hold.
7815   assert(obj->is_oop_or_null(true),
7816          "expected an oop or NULL");
7817   HeapWord* addr = (HeapWord*)obj;
7818   // Check if oop points into the CMS generation
7819   // and is not marked
7820   if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7821     // a white object ...
7822     // If we manage to "claim" the object, by being the
7823     // first thread to mark it, then we push it on our
7824     // marking stack
7825     if (_bit_map->par_mark(addr)) {     // ... now grey
7826       // push on work queue (grey set)
7827       bool simulate_overflow = false;
7828       NOT_PRODUCT(
7829         if (CMSMarkStackOverflowALot &&
7830             _collector->par_simulate_overflow()) {
7831           // simulate a stack overflow
7832           simulate_overflow = true;
7833         }
7834       )
7835       if (simulate_overflow || !_work_queue->push(obj)) {
7836         _collector->par_push_on_overflow_list(obj);
7837         _collector->_par_pmc_remark_ovflw++; //  imprecise OK: no need to CAS
7838       }
7839     } // Else, some other thread got there first
7840   }
7841 }
7842 
7843 void Par_PushAndMarkClosure::do_oop(oop* p)       { Par_PushAndMarkClosure::do_oop_work(p); }
7844 void Par_PushAndMarkClosure::do_oop(narrowOop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7845 
7846 void PushAndMarkClosure::remember_mdo(DataLayout* v) {
7847   // TBD
7848 }
7849 
7850 void Par_PushAndMarkClosure::remember_mdo(DataLayout* v) {
7851   // TBD
7852 }
7853 
7854 void CMSPrecleanRefsYieldClosure::do_yield_work() {
7855   DEBUG_ONLY(RememberKlassesChecker mux(false);)
7856   Mutex* bml = _collector->bitMapLock();
7857   assert_lock_strong(bml);
7858   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7859          "CMS thread should hold CMS token");
7860 
7861   bml->unlock();
7862   ConcurrentMarkSweepThread::desynchronize(true);
7863 
7864   ConcurrentMarkSweepThread::acknowledge_yield_request();
7865 
7866   _collector->stopTimer();
7867   GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7868   if (PrintCMSStatistics != 0) {
7869     _collector->incrementYields();
7870   }
7871   _collector->icms_wait();
7872 
7873   // See the comment in coordinator_yield()
7874   for (unsigned i = 0; i < CMSYieldSleepCount &&
7875                        ConcurrentMarkSweepThread::should_yield() &&
7876                        !CMSCollector::foregroundGCIsActive(); ++i) {
7877     os::sleep(Thread::current(), 1, false);
7878     ConcurrentMarkSweepThread::acknowledge_yield_request();
7879   }
7880 
7881   ConcurrentMarkSweepThread::synchronize(true);
7882   bml->lock();
7883 
7884   _collector->startTimer();
7885 }
7886 
7887 bool CMSPrecleanRefsYieldClosure::should_return() {
7888   if (ConcurrentMarkSweepThread::should_yield()) {
7889     do_yield_work();
7890   }
7891   return _collector->foregroundGCIsActive();
7892 }
7893 
7894 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
7895   assert(((size_t)mr.start())%CardTableModRefBS::card_size_in_words == 0,
7896          "mr should be aligned to start at a card boundary");
7897   // We'd like to assert:
7898   // assert(mr.word_size()%CardTableModRefBS::card_size_in_words == 0,
7899   //        "mr should be a range of cards");
7900   // However, that would be too strong in one case -- the last
7901   // partition ends at _unallocated_block which, in general, can be
7902   // an arbitrary boundary, not necessarily card aligned.
7903   if (PrintCMSStatistics != 0) {
7904     _num_dirty_cards +=
7905          mr.word_size()/CardTableModRefBS::card_size_in_words;
7906   }
7907   _space->object_iterate_mem(mr, &_scan_cl);
7908 }
7909 
7910 SweepClosure::SweepClosure(CMSCollector* collector,
7911                            ConcurrentMarkSweepGeneration* g,
7912                            CMSBitMap* bitMap, bool should_yield) :
7913   _collector(collector),
7914   _g(g),
7915   _sp(g->cmsSpace()),
7916   _limit(_sp->sweep_limit()),
7917   _freelistLock(_sp->freelistLock()),
7918   _bitMap(bitMap),
7919   _yield(should_yield),
7920   _inFreeRange(false),           // No free range at beginning of sweep
7921   _freeRangeInFreeLists(false),  // No free range at beginning of sweep
7922   _lastFreeRangeCoalesced(false),
7923   _freeFinger(g->used_region().start())
7924 {
7925   NOT_PRODUCT(
7926     _numObjectsFreed = 0;
7927     _numWordsFreed   = 0;
7928     _numObjectsLive = 0;
7929     _numWordsLive = 0;
7930     _numObjectsAlreadyFree = 0;
7931     _numWordsAlreadyFree = 0;
7932     _last_fc = NULL;
7933 
7934     _sp->initializeIndexedFreeListArrayReturnedBytes();
7935     _sp->dictionary()->initialize_dict_returned_bytes();
7936   )
7937   assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7938          "sweep _limit out of bounds");
7939   if (CMSTraceSweeper) {
7940     gclog_or_tty->print_cr("\n====================\nStarting new sweep with limit " PTR_FORMAT,
7941                         _limit);
7942   }
7943 }
7944 
7945 void SweepClosure::print_on(outputStream* st) const {
7946   tty->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")",
7947                 _sp->bottom(), _sp->end());
7948   tty->print_cr("_limit = " PTR_FORMAT, _limit);
7949   tty->print_cr("_freeFinger = " PTR_FORMAT, _freeFinger);
7950   NOT_PRODUCT(tty->print_cr("_last_fc = " PTR_FORMAT, _last_fc);)
7951   tty->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d",
7952                 _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced);
7953 }
7954 
7955 #ifndef PRODUCT
7956 // Assertion checking only:  no useful work in product mode --
7957 // however, if any of the flags below become product flags,
7958 // you may need to review this code to see if it needs to be
7959 // enabled in product mode.
7960 SweepClosure::~SweepClosure() {
7961   assert_lock_strong(_freelistLock);
7962   assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7963          "sweep _limit out of bounds");
7964   if (inFreeRange()) {
7965     warning("inFreeRange() should have been reset; dumping state of SweepClosure");
7966     print();
7967     ShouldNotReachHere();
7968   }
7969   if (Verbose && PrintGC) {
7970     gclog_or_tty->print("Collected "SIZE_FORMAT" objects, " SIZE_FORMAT " bytes",
7971                         _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
7972     gclog_or_tty->print_cr("\nLive "SIZE_FORMAT" objects,  "
7973                            SIZE_FORMAT" bytes  "
7974       "Already free "SIZE_FORMAT" objects, "SIZE_FORMAT" bytes",
7975       _numObjectsLive, _numWordsLive*sizeof(HeapWord),
7976       _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
7977     size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree)
7978                         * sizeof(HeapWord);
7979     gclog_or_tty->print_cr("Total sweep: "SIZE_FORMAT" bytes", totalBytes);
7980 
7981     if (PrintCMSStatistics && CMSVerifyReturnedBytes) {
7982       size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
7983       size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes();
7984       size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes;
7985       gclog_or_tty->print("Returned "SIZE_FORMAT" bytes", returned_bytes);
7986       gclog_or_tty->print("   Indexed List Returned "SIZE_FORMAT" bytes",
7987         indexListReturnedBytes);
7988       gclog_or_tty->print_cr("        Dictionary Returned "SIZE_FORMAT" bytes",
7989         dict_returned_bytes);
7990     }
7991   }
7992   if (CMSTraceSweeper) {
7993     gclog_or_tty->print_cr("end of sweep with _limit = " PTR_FORMAT "\n================",
7994                            _limit);
7995   }
7996 }
7997 #endif  // PRODUCT
7998 
7999 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
8000     bool freeRangeInFreeLists) {
8001   if (CMSTraceSweeper) {
8002     gclog_or_tty->print("---- Start free range at 0x%x with free block (%d)\n",
8003                freeFinger, freeRangeInFreeLists);
8004   }
8005   assert(!inFreeRange(), "Trampling existing free range");
8006   set_inFreeRange(true);
8007   set_lastFreeRangeCoalesced(false);
8008 
8009   set_freeFinger(freeFinger);
8010   set_freeRangeInFreeLists(freeRangeInFreeLists);
8011   if (CMSTestInFreeList) {
8012     if (freeRangeInFreeLists) {
8013       FreeChunk* fc = (FreeChunk*) freeFinger;
8014       assert(fc->is_free(), "A chunk on the free list should be free.");
8015       assert(fc->size() > 0, "Free range should have a size");
8016       assert(_sp->verify_chunk_in_free_list(fc), "Chunk is not in free lists");
8017     }
8018   }
8019 }
8020 
8021 // Note that the sweeper runs concurrently with mutators. Thus,
8022 // it is possible for direct allocation in this generation to happen
8023 // in the middle of the sweep. Note that the sweeper also coalesces
8024 // contiguous free blocks. Thus, unless the sweeper and the allocator
8025 // synchronize appropriately freshly allocated blocks may get swept up.
8026 // This is accomplished by the sweeper locking the free lists while
8027 // it is sweeping. Thus blocks that are determined to be free are
8028 // indeed free. There is however one additional complication:
8029 // blocks that have been allocated since the final checkpoint and
8030 // mark, will not have been marked and so would be treated as
8031 // unreachable and swept up. To prevent this, the allocator marks
8032 // the bit map when allocating during the sweep phase. This leads,
8033 // however, to a further complication -- objects may have been allocated
8034 // but not yet initialized -- in the sense that the header isn't yet
8035 // installed. The sweeper can not then determine the size of the block
8036 // in order to skip over it. To deal with this case, we use a technique
8037 // (due to Printezis) to encode such uninitialized block sizes in the
8038 // bit map. Since the bit map uses a bit per every HeapWord, but the
8039 // CMS generation has a minimum object size of 3 HeapWords, it follows
8040 // that "normal marks" won't be adjacent in the bit map (there will
8041 // always be at least two 0 bits between successive 1 bits). We make use
8042 // of these "unused" bits to represent uninitialized blocks -- the bit
8043 // corresponding to the start of the uninitialized object and the next
8044 // bit are both set. Finally, a 1 bit marks the end of the object that
8045 // started with the two consecutive 1 bits to indicate its potentially
8046 // uninitialized state.
8047 
8048 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
8049   FreeChunk* fc = (FreeChunk*)addr;
8050   size_t res;
8051 
8052   // Check if we are done sweeping. Below we check "addr >= _limit" rather
8053   // than "addr == _limit" because although _limit was a block boundary when
8054   // we started the sweep, it may no longer be one because heap expansion
8055   // may have caused us to coalesce the block ending at the address _limit
8056   // with a newly expanded chunk (this happens when _limit was set to the
8057   // previous _end of the space), so we may have stepped past _limit:
8058   // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740.
8059   if (addr >= _limit) { // we have swept up to or past the limit: finish up
8060     assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
8061            "sweep _limit out of bounds");
8062     assert(addr < _sp->end(), "addr out of bounds");
8063     // Flush any free range we might be holding as a single
8064     // coalesced chunk to the appropriate free list.
8065     if (inFreeRange()) {
8066       assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit,
8067              err_msg("freeFinger() " PTR_FORMAT" is out-of-bounds", freeFinger()));
8068       flush_cur_free_chunk(freeFinger(),
8069                            pointer_delta(addr, freeFinger()));
8070       if (CMSTraceSweeper) {
8071         gclog_or_tty->print("Sweep: last chunk: ");
8072         gclog_or_tty->print("put_free_blk 0x%x ("SIZE_FORMAT") "
8073                    "[coalesced:"SIZE_FORMAT"]\n",
8074                    freeFinger(), pointer_delta(addr, freeFinger()),
8075                    lastFreeRangeCoalesced());
8076       }
8077     }
8078 
8079     // help the iterator loop finish
8080     return pointer_delta(_sp->end(), addr);
8081   }
8082 
8083   assert(addr < _limit, "sweep invariant");
8084   // check if we should yield
8085   do_yield_check(addr);
8086   if (fc->is_free()) {
8087     // Chunk that is already free
8088     res = fc->size();
8089     do_already_free_chunk(fc);
8090     debug_only(_sp->verifyFreeLists());
8091     // If we flush the chunk at hand in lookahead_and_flush()
8092     // and it's coalesced with a preceding chunk, then the
8093     // process of "mangling" the payload of the coalesced block
8094     // will cause erasure of the size information from the
8095     // (erstwhile) header of all the coalesced blocks but the
8096     // first, so the first disjunct in the assert will not hold
8097     // in that specific case (in which case the second disjunct
8098     // will hold).
8099     assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit,
8100            "Otherwise the size info doesn't change at this step");
8101     NOT_PRODUCT(
8102       _numObjectsAlreadyFree++;
8103       _numWordsAlreadyFree += res;
8104     )
8105     NOT_PRODUCT(_last_fc = fc;)
8106   } else if (!_bitMap->isMarked(addr)) {
8107     // Chunk is fresh garbage
8108     res = do_garbage_chunk(fc);
8109     debug_only(_sp->verifyFreeLists());
8110     NOT_PRODUCT(
8111       _numObjectsFreed++;
8112       _numWordsFreed += res;
8113     )
8114   } else {
8115     // Chunk that is alive.
8116     res = do_live_chunk(fc);
8117     debug_only(_sp->verifyFreeLists());
8118     NOT_PRODUCT(
8119         _numObjectsLive++;
8120         _numWordsLive += res;
8121     )
8122   }
8123   return res;
8124 }
8125 
8126 // For the smart allocation, record following
8127 //  split deaths - a free chunk is removed from its free list because
8128 //      it is being split into two or more chunks.
8129 //  split birth - a free chunk is being added to its free list because
8130 //      a larger free chunk has been split and resulted in this free chunk.
8131 //  coal death - a free chunk is being removed from its free list because
8132 //      it is being coalesced into a large free chunk.
8133 //  coal birth - a free chunk is being added to its free list because
8134 //      it was created when two or more free chunks where coalesced into
8135 //      this free chunk.
8136 //
8137 // These statistics are used to determine the desired number of free
8138 // chunks of a given size.  The desired number is chosen to be relative
8139 // to the end of a CMS sweep.  The desired number at the end of a sweep
8140 // is the
8141 //      count-at-end-of-previous-sweep (an amount that was enough)
8142 //              - count-at-beginning-of-current-sweep  (the excess)
8143 //              + split-births  (gains in this size during interval)
8144 //              - split-deaths  (demands on this size during interval)
8145 // where the interval is from the end of one sweep to the end of the
8146 // next.
8147 //
8148 // When sweeping the sweeper maintains an accumulated chunk which is
8149 // the chunk that is made up of chunks that have been coalesced.  That
8150 // will be termed the left-hand chunk.  A new chunk of garbage that
8151 // is being considered for coalescing will be referred to as the
8152 // right-hand chunk.
8153 //
8154 // When making a decision on whether to coalesce a right-hand chunk with
8155 // the current left-hand chunk, the current count vs. the desired count
8156 // of the left-hand chunk is considered.  Also if the right-hand chunk
8157 // is near the large chunk at the end of the heap (see
8158 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
8159 // left-hand chunk is coalesced.
8160 //
8161 // When making a decision about whether to split a chunk, the desired count
8162 // vs. the current count of the candidate to be split is also considered.
8163 // If the candidate is underpopulated (currently fewer chunks than desired)
8164 // a chunk of an overpopulated (currently more chunks than desired) size may
8165 // be chosen.  The "hint" associated with a free list, if non-null, points
8166 // to a free list which may be overpopulated.
8167 //
8168 
8169 void SweepClosure::do_already_free_chunk(FreeChunk* fc) {
8170   const size_t size = fc->size();
8171   // Chunks that cannot be coalesced are not in the
8172   // free lists.
8173   if (CMSTestInFreeList && !fc->cantCoalesce()) {
8174     assert(_sp->verify_chunk_in_free_list(fc),
8175       "free chunk should be in free lists");
8176   }
8177   // a chunk that is already free, should not have been
8178   // marked in the bit map
8179   HeapWord* const addr = (HeapWord*) fc;
8180   assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
8181   // Verify that the bit map has no bits marked between
8182   // addr and purported end of this block.
8183   _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8184 
8185   // Some chunks cannot be coalesced under any circumstances.
8186   // See the definition of cantCoalesce().
8187   if (!fc->cantCoalesce()) {
8188     // This chunk can potentially be coalesced.
8189     if (_sp->adaptive_freelists()) {
8190       // All the work is done in
8191       do_post_free_or_garbage_chunk(fc, size);
8192     } else {  // Not adaptive free lists
8193       // this is a free chunk that can potentially be coalesced by the sweeper;
8194       if (!inFreeRange()) {
8195         // if the next chunk is a free block that can't be coalesced
8196         // it doesn't make sense to remove this chunk from the free lists
8197         FreeChunk* nextChunk = (FreeChunk*)(addr + size);
8198         assert((HeapWord*)nextChunk <= _sp->end(), "Chunk size out of bounds?");
8199         if ((HeapWord*)nextChunk < _sp->end() &&     // There is another free chunk to the right ...
8200             nextChunk->is_free()               &&     // ... which is free...
8201             nextChunk->cantCoalesce()) {             // ... but can't be coalesced
8202           // nothing to do
8203         } else {
8204           // Potentially the start of a new free range:
8205           // Don't eagerly remove it from the free lists.
8206           // No need to remove it if it will just be put
8207           // back again.  (Also from a pragmatic point of view
8208           // if it is a free block in a region that is beyond
8209           // any allocated blocks, an assertion will fail)
8210           // Remember the start of a free run.
8211           initialize_free_range(addr, true);
8212           // end - can coalesce with next chunk
8213         }
8214       } else {
8215         // the midst of a free range, we are coalescing
8216         print_free_block_coalesced(fc);
8217         if (CMSTraceSweeper) {
8218           gclog_or_tty->print("  -- pick up free block 0x%x (%d)\n", fc, size);
8219         }
8220         // remove it from the free lists
8221         _sp->removeFreeChunkFromFreeLists(fc);
8222         set_lastFreeRangeCoalesced(true);
8223         // If the chunk is being coalesced and the current free range is
8224         // in the free lists, remove the current free range so that it
8225         // will be returned to the free lists in its entirety - all
8226         // the coalesced pieces included.
8227         if (freeRangeInFreeLists()) {
8228           FreeChunk* ffc = (FreeChunk*) freeFinger();
8229           assert(ffc->size() == pointer_delta(addr, freeFinger()),
8230             "Size of free range is inconsistent with chunk size.");
8231           if (CMSTestInFreeList) {
8232             assert(_sp->verify_chunk_in_free_list(ffc),
8233               "free range is not in free lists");
8234           }
8235           _sp->removeFreeChunkFromFreeLists(ffc);
8236           set_freeRangeInFreeLists(false);
8237         }
8238       }
8239     }
8240     // Note that if the chunk is not coalescable (the else arm
8241     // below), we unconditionally flush, without needing to do
8242     // a "lookahead," as we do below.
8243     if (inFreeRange()) lookahead_and_flush(fc, size);
8244   } else {
8245     // Code path common to both original and adaptive free lists.
8246 
8247     // cant coalesce with previous block; this should be treated
8248     // as the end of a free run if any
8249     if (inFreeRange()) {
8250       // we kicked some butt; time to pick up the garbage
8251       assert(freeFinger() < addr, "freeFinger points too high");
8252       flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8253     }
8254     // else, nothing to do, just continue
8255   }
8256 }
8257 
8258 size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) {
8259   // This is a chunk of garbage.  It is not in any free list.
8260   // Add it to a free list or let it possibly be coalesced into
8261   // a larger chunk.
8262   HeapWord* const addr = (HeapWord*) fc;
8263   const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
8264 
8265   if (_sp->adaptive_freelists()) {
8266     // Verify that the bit map has no bits marked between
8267     // addr and purported end of just dead object.
8268     _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8269 
8270     do_post_free_or_garbage_chunk(fc, size);
8271   } else {
8272     if (!inFreeRange()) {
8273       // start of a new free range
8274       assert(size > 0, "A free range should have a size");
8275       initialize_free_range(addr, false);
8276     } else {
8277       // this will be swept up when we hit the end of the
8278       // free range
8279       if (CMSTraceSweeper) {
8280         gclog_or_tty->print("  -- pick up garbage 0x%x (%d) \n", fc, size);
8281       }
8282       // If the chunk is being coalesced and the current free range is
8283       // in the free lists, remove the current free range so that it
8284       // will be returned to the free lists in its entirety - all
8285       // the coalesced pieces included.
8286       if (freeRangeInFreeLists()) {
8287         FreeChunk* ffc = (FreeChunk*)freeFinger();
8288         assert(ffc->size() == pointer_delta(addr, freeFinger()),
8289           "Size of free range is inconsistent with chunk size.");
8290         if (CMSTestInFreeList) {
8291           assert(_sp->verify_chunk_in_free_list(ffc),
8292             "free range is not in free lists");
8293         }
8294         _sp->removeFreeChunkFromFreeLists(ffc);
8295         set_freeRangeInFreeLists(false);
8296       }
8297       set_lastFreeRangeCoalesced(true);
8298     }
8299     // this will be swept up when we hit the end of the free range
8300 
8301     // Verify that the bit map has no bits marked between
8302     // addr and purported end of just dead object.
8303     _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8304   }
8305   assert(_limit >= addr + size,
8306          "A freshly garbage chunk can't possibly straddle over _limit");
8307   if (inFreeRange()) lookahead_and_flush(fc, size);
8308   return size;
8309 }
8310 
8311 size_t SweepClosure::do_live_chunk(FreeChunk* fc) {
8312   HeapWord* addr = (HeapWord*) fc;
8313   // The sweeper has just found a live object. Return any accumulated
8314   // left hand chunk to the free lists.
8315   if (inFreeRange()) {
8316     assert(freeFinger() < addr, "freeFinger points too high");
8317     flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8318   }
8319 
8320   // This object is live: we'd normally expect this to be
8321   // an oop, and like to assert the following:
8322   // assert(oop(addr)->is_oop(), "live block should be an oop");
8323   // However, as we commented above, this may be an object whose
8324   // header hasn't yet been initialized.
8325   size_t size;
8326   assert(_bitMap->isMarked(addr), "Tautology for this control point");
8327   if (_bitMap->isMarked(addr + 1)) {
8328     // Determine the size from the bit map, rather than trying to
8329     // compute it from the object header.
8330     HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
8331     size = pointer_delta(nextOneAddr + 1, addr);
8332     assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
8333            "alignment problem");
8334 
8335 #ifdef DEBUG
8336       if (oop(addr)->klass_or_null() != NULL &&
8337           (   !_collector->should_unload_classes()
8338            || (oop(addr)->is_parsable()) &&
8339                oop(addr)->is_conc_safe())) {
8340         // Ignore mark word because we are running concurrent with mutators
8341         assert(oop(addr)->is_oop(true), "live block should be an oop");
8342         // is_conc_safe is checked before performing this assertion
8343         // because an object that is not is_conc_safe may yet have
8344         // the return from size() correct.
8345         assert(size ==
8346                CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
8347                "P-mark and computed size do not agree");
8348       }
8349 #endif
8350 
8351   } else {
8352     // This should be an initialized object that's alive.
8353     assert(oop(addr)->klass_or_null() != NULL &&
8354            (!_collector->should_unload_classes()
8355             || oop(addr)->is_parsable()),
8356            "Should be an initialized object");
8357     // Note that there are objects used during class redefinition,
8358     // e.g. merge_cp in VM_RedefineClasses::merge_cp_and_rewrite(),
8359     // which are discarded with their is_conc_safe state still
8360     // false.  These object may be floating garbage so may be
8361     // seen here.  If they are floating garbage their size
8362     // should be attainable from their klass.  Do not that
8363     // is_conc_safe() is true for oop(addr).
8364     // Ignore mark word because we are running concurrent with mutators
8365     assert(oop(addr)->is_oop(true), "live block should be an oop");
8366     // Verify that the bit map has no bits marked between
8367     // addr and purported end of this block.
8368     size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
8369     assert(size >= 3, "Necessary for Printezis marks to work");
8370     assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
8371     DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
8372   }
8373   return size;
8374 }
8375 
8376 void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc,
8377                                                  size_t chunkSize) {
8378   // do_post_free_or_garbage_chunk() should only be called in the case
8379   // of the adaptive free list allocator.
8380   const bool fcInFreeLists = fc->is_free();
8381   assert(_sp->adaptive_freelists(), "Should only be used in this case.");
8382   assert((HeapWord*)fc <= _limit, "sweep invariant");
8383   if (CMSTestInFreeList && fcInFreeLists) {
8384     assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists");
8385   }
8386 
8387   if (CMSTraceSweeper) {
8388     gclog_or_tty->print_cr("  -- pick up another chunk at 0x%x (%d)", fc, chunkSize);
8389   }
8390 
8391   HeapWord* const fc_addr = (HeapWord*) fc;
8392 
8393   bool coalesce;
8394   const size_t left  = pointer_delta(fc_addr, freeFinger());
8395   const size_t right = chunkSize;
8396   switch (FLSCoalescePolicy) {
8397     // numeric value forms a coalition aggressiveness metric
8398     case 0:  { // never coalesce
8399       coalesce = false;
8400       break;
8401     }
8402     case 1: { // coalesce if left & right chunks on overpopulated lists
8403       coalesce = _sp->coalOverPopulated(left) &&
8404                  _sp->coalOverPopulated(right);
8405       break;
8406     }
8407     case 2: { // coalesce if left chunk on overpopulated list (default)
8408       coalesce = _sp->coalOverPopulated(left);
8409       break;
8410     }
8411     case 3: { // coalesce if left OR right chunk on overpopulated list
8412       coalesce = _sp->coalOverPopulated(left) ||
8413                  _sp->coalOverPopulated(right);
8414       break;
8415     }
8416     case 4: { // always coalesce
8417       coalesce = true;
8418       break;
8419     }
8420     default:
8421      ShouldNotReachHere();
8422   }
8423 
8424   // Should the current free range be coalesced?
8425   // If the chunk is in a free range and either we decided to coalesce above
8426   // or the chunk is near the large block at the end of the heap
8427   // (isNearLargestChunk() returns true), then coalesce this chunk.
8428   const bool doCoalesce = inFreeRange()
8429                           && (coalesce || _g->isNearLargestChunk(fc_addr));
8430   if (doCoalesce) {
8431     // Coalesce the current free range on the left with the new
8432     // chunk on the right.  If either is on a free list,
8433     // it must be removed from the list and stashed in the closure.
8434     if (freeRangeInFreeLists()) {
8435       FreeChunk* const ffc = (FreeChunk*)freeFinger();
8436       assert(ffc->size() == pointer_delta(fc_addr, freeFinger()),
8437         "Size of free range is inconsistent with chunk size.");
8438       if (CMSTestInFreeList) {
8439         assert(_sp->verify_chunk_in_free_list(ffc),
8440           "Chunk is not in free lists");
8441       }
8442       _sp->coalDeath(ffc->size());
8443       _sp->removeFreeChunkFromFreeLists(ffc);
8444       set_freeRangeInFreeLists(false);
8445     }
8446     if (fcInFreeLists) {
8447       _sp->coalDeath(chunkSize);
8448       assert(fc->size() == chunkSize,
8449         "The chunk has the wrong size or is not in the free lists");
8450       _sp->removeFreeChunkFromFreeLists(fc);
8451     }
8452     set_lastFreeRangeCoalesced(true);
8453     print_free_block_coalesced(fc);
8454   } else {  // not in a free range and/or should not coalesce
8455     // Return the current free range and start a new one.
8456     if (inFreeRange()) {
8457       // In a free range but cannot coalesce with the right hand chunk.
8458       // Put the current free range into the free lists.
8459       flush_cur_free_chunk(freeFinger(),
8460                            pointer_delta(fc_addr, freeFinger()));
8461     }
8462     // Set up for new free range.  Pass along whether the right hand
8463     // chunk is in the free lists.
8464     initialize_free_range((HeapWord*)fc, fcInFreeLists);
8465   }
8466 }
8467 
8468 // Lookahead flush:
8469 // If we are tracking a free range, and this is the last chunk that
8470 // we'll look at because its end crosses past _limit, we'll preemptively
8471 // flush it along with any free range we may be holding on to. Note that
8472 // this can be the case only for an already free or freshly garbage
8473 // chunk. If this block is an object, it can never straddle
8474 // over _limit. The "straddling" occurs when _limit is set at
8475 // the previous end of the space when this cycle started, and
8476 // a subsequent heap expansion caused the previously co-terminal
8477 // free block to be coalesced with the newly expanded portion,
8478 // thus rendering _limit a non-block-boundary making it dangerous
8479 // for the sweeper to step over and examine.
8480 void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) {
8481   assert(inFreeRange(), "Should only be called if currently in a free range.");
8482   HeapWord* const eob = ((HeapWord*)fc) + chunk_size;
8483   assert(_sp->used_region().contains(eob - 1),
8484          err_msg("eob = " PTR_FORMAT " out of bounds wrt _sp = [" PTR_FORMAT "," PTR_FORMAT ")"
8485                  " when examining fc = " PTR_FORMAT "(" SIZE_FORMAT ")",
8486                  _limit, _sp->bottom(), _sp->end(), fc, chunk_size));
8487   if (eob >= _limit) {
8488     assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit");
8489     if (CMSTraceSweeper) {
8490       gclog_or_tty->print_cr("_limit " PTR_FORMAT " reached or crossed by block "
8491                              "[" PTR_FORMAT "," PTR_FORMAT ") in space "
8492                              "[" PTR_FORMAT "," PTR_FORMAT ")",
8493                              _limit, fc, eob, _sp->bottom(), _sp->end());
8494     }
8495     // Return the storage we are tracking back into the free lists.
8496     if (CMSTraceSweeper) {
8497       gclog_or_tty->print_cr("Flushing ... ");
8498     }
8499     assert(freeFinger() < eob, "Error");
8500     flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger()));
8501   }
8502 }
8503 
8504 void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) {
8505   assert(inFreeRange(), "Should only be called if currently in a free range.");
8506   assert(size > 0,
8507     "A zero sized chunk cannot be added to the free lists.");
8508   if (!freeRangeInFreeLists()) {
8509     if (CMSTestInFreeList) {
8510       FreeChunk* fc = (FreeChunk*) chunk;
8511       fc->set_size(size);
8512       assert(!_sp->verify_chunk_in_free_list(fc),
8513         "chunk should not be in free lists yet");
8514     }
8515     if (CMSTraceSweeper) {
8516       gclog_or_tty->print_cr(" -- add free block 0x%x (%d) to free lists",
8517                     chunk, size);
8518     }
8519     // A new free range is going to be starting.  The current
8520     // free range has not been added to the free lists yet or
8521     // was removed so add it back.
8522     // If the current free range was coalesced, then the death
8523     // of the free range was recorded.  Record a birth now.
8524     if (lastFreeRangeCoalesced()) {
8525       _sp->coalBirth(size);
8526     }
8527     _sp->addChunkAndRepairOffsetTable(chunk, size,
8528             lastFreeRangeCoalesced());
8529   } else if (CMSTraceSweeper) {
8530     gclog_or_tty->print_cr("Already in free list: nothing to flush");
8531   }
8532   set_inFreeRange(false);
8533   set_freeRangeInFreeLists(false);
8534 }
8535 
8536 // We take a break if we've been at this for a while,
8537 // so as to avoid monopolizing the locks involved.
8538 void SweepClosure::do_yield_work(HeapWord* addr) {
8539   // Return current free chunk being used for coalescing (if any)
8540   // to the appropriate freelist.  After yielding, the next
8541   // free block encountered will start a coalescing range of
8542   // free blocks.  If the next free block is adjacent to the
8543   // chunk just flushed, they will need to wait for the next
8544   // sweep to be coalesced.
8545   if (inFreeRange()) {
8546     flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8547   }
8548 
8549   // First give up the locks, then yield, then re-lock.
8550   // We should probably use a constructor/destructor idiom to
8551   // do this unlock/lock or modify the MutexUnlocker class to
8552   // serve our purpose. XXX
8553   assert_lock_strong(_bitMap->lock());
8554   assert_lock_strong(_freelistLock);
8555   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
8556          "CMS thread should hold CMS token");
8557   _bitMap->lock()->unlock();
8558   _freelistLock->unlock();
8559   ConcurrentMarkSweepThread::desynchronize(true);
8560   ConcurrentMarkSweepThread::acknowledge_yield_request();
8561   _collector->stopTimer();
8562   GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
8563   if (PrintCMSStatistics != 0) {
8564     _collector->incrementYields();
8565   }
8566   _collector->icms_wait();
8567 
8568   // See the comment in coordinator_yield()
8569   for (unsigned i = 0; i < CMSYieldSleepCount &&
8570                        ConcurrentMarkSweepThread::should_yield() &&
8571                        !CMSCollector::foregroundGCIsActive(); ++i) {
8572     os::sleep(Thread::current(), 1, false);
8573     ConcurrentMarkSweepThread::acknowledge_yield_request();
8574   }
8575 
8576   ConcurrentMarkSweepThread::synchronize(true);
8577   _freelistLock->lock();
8578   _bitMap->lock()->lock_without_safepoint_check();
8579   _collector->startTimer();
8580 }
8581 
8582 #ifndef PRODUCT
8583 // This is actually very useful in a product build if it can
8584 // be called from the debugger.  Compile it into the product
8585 // as needed.
8586 bool debug_verify_chunk_in_free_list(FreeChunk* fc) {
8587   return debug_cms_space->verify_chunk_in_free_list(fc);
8588 }
8589 #endif
8590 
8591 void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const {
8592   if (CMSTraceSweeper) {
8593     gclog_or_tty->print_cr("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")",
8594                            fc, fc->size());
8595   }
8596 }
8597 
8598 // CMSIsAliveClosure
8599 bool CMSIsAliveClosure::do_object_b(oop obj) {
8600   HeapWord* addr = (HeapWord*)obj;
8601   return addr != NULL &&
8602          (!_span.contains(addr) || _bit_map->isMarked(addr));
8603 }
8604 
8605 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector,
8606                       MemRegion span,
8607                       CMSBitMap* bit_map, CMSMarkStack* mark_stack,
8608                       CMSMarkStack* revisit_stack, bool cpc):
8609   KlassRememberingOopClosure(collector, NULL, revisit_stack),
8610   _span(span),
8611   _bit_map(bit_map),
8612   _mark_stack(mark_stack),
8613   _concurrent_precleaning(cpc) {
8614   assert(!_span.is_empty(), "Empty span could spell trouble");
8615 }
8616 
8617 
8618 // CMSKeepAliveClosure: the serial version
8619 void CMSKeepAliveClosure::do_oop(oop obj) {
8620   HeapWord* addr = (HeapWord*)obj;
8621   if (_span.contains(addr) &&
8622       !_bit_map->isMarked(addr)) {
8623     _bit_map->mark(addr);
8624     bool simulate_overflow = false;
8625     NOT_PRODUCT(
8626       if (CMSMarkStackOverflowALot &&
8627           _collector->simulate_overflow()) {
8628         // simulate a stack overflow
8629         simulate_overflow = true;
8630       }
8631     )
8632     if (simulate_overflow || !_mark_stack->push(obj)) {
8633       if (_concurrent_precleaning) {
8634         // We dirty the overflown object and let the remark
8635         // phase deal with it.
8636         assert(_collector->overflow_list_is_empty(), "Error");
8637         // In the case of object arrays, we need to dirty all of
8638         // the cards that the object spans. No locking or atomics
8639         // are needed since no one else can be mutating the mod union
8640         // table.
8641         if (obj->is_objArray()) {
8642           size_t sz = obj->size();
8643           HeapWord* end_card_addr =
8644             (HeapWord*)round_to((intptr_t)(addr+sz), CardTableModRefBS::card_size);
8645           MemRegion redirty_range = MemRegion(addr, end_card_addr);
8646           assert(!redirty_range.is_empty(), "Arithmetical tautology");
8647           _collector->_modUnionTable.mark_range(redirty_range);
8648         } else {
8649           _collector->_modUnionTable.mark(addr);
8650         }
8651         _collector->_ser_kac_preclean_ovflw++;
8652       } else {
8653         _collector->push_on_overflow_list(obj);
8654         _collector->_ser_kac_ovflw++;
8655       }
8656     }
8657   }
8658 }
8659 
8660 void CMSKeepAliveClosure::do_oop(oop* p)       { CMSKeepAliveClosure::do_oop_work(p); }
8661 void CMSKeepAliveClosure::do_oop(narrowOop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8662 
8663 // CMSParKeepAliveClosure: a parallel version of the above.
8664 // The work queues are private to each closure (thread),
8665 // but (may be) available for stealing by other threads.
8666 void CMSParKeepAliveClosure::do_oop(oop obj) {
8667   HeapWord* addr = (HeapWord*)obj;
8668   if (_span.contains(addr) &&
8669       !_bit_map->isMarked(addr)) {
8670     // In general, during recursive tracing, several threads
8671     // may be concurrently getting here; the first one to
8672     // "tag" it, claims it.
8673     if (_bit_map->par_mark(addr)) {
8674       bool res = _work_queue->push(obj);
8675       assert(res, "Low water mark should be much less than capacity");
8676       // Do a recursive trim in the hope that this will keep
8677       // stack usage lower, but leave some oops for potential stealers
8678       trim_queue(_low_water_mark);
8679     } // Else, another thread got there first
8680   }
8681 }
8682 
8683 void CMSParKeepAliveClosure::do_oop(oop* p)       { CMSParKeepAliveClosure::do_oop_work(p); }
8684 void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8685 
8686 void CMSParKeepAliveClosure::trim_queue(uint max) {
8687   while (_work_queue->size() > max) {
8688     oop new_oop;
8689     if (_work_queue->pop_local(new_oop)) {
8690       assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
8691       assert(_bit_map->isMarked((HeapWord*)new_oop),
8692              "no white objects on this stack!");
8693       assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8694       // iterate over the oops in this oop, marking and pushing
8695       // the ones in CMS heap (i.e. in _span).
8696       new_oop->oop_iterate(&_mark_and_push);
8697     }
8698   }
8699 }
8700 
8701 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
8702                                 CMSCollector* collector,
8703                                 MemRegion span, CMSBitMap* bit_map,
8704                                 CMSMarkStack* revisit_stack,
8705                                 OopTaskQueue* work_queue):
8706   Par_KlassRememberingOopClosure(collector, NULL, revisit_stack),
8707   _span(span),
8708   _bit_map(bit_map),
8709   _work_queue(work_queue) { }
8710 
8711 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
8712   HeapWord* addr = (HeapWord*)obj;
8713   if (_span.contains(addr) &&
8714       !_bit_map->isMarked(addr)) {
8715     if (_bit_map->par_mark(addr)) {
8716       bool simulate_overflow = false;
8717       NOT_PRODUCT(
8718         if (CMSMarkStackOverflowALot &&
8719             _collector->par_simulate_overflow()) {
8720           // simulate a stack overflow
8721           simulate_overflow = true;
8722         }
8723       )
8724       if (simulate_overflow || !_work_queue->push(obj)) {
8725         _collector->par_push_on_overflow_list(obj);
8726         _collector->_par_kac_ovflw++;
8727       }
8728     } // Else another thread got there already
8729   }
8730 }
8731 
8732 void CMSInnerParMarkAndPushClosure::do_oop(oop* p)       { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8733 void CMSInnerParMarkAndPushClosure::do_oop(narrowOop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8734 
8735 //////////////////////////////////////////////////////////////////
8736 //  CMSExpansionCause                /////////////////////////////
8737 //////////////////////////////////////////////////////////////////
8738 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
8739   switch (cause) {
8740     case _no_expansion:
8741       return "No expansion";
8742     case _satisfy_free_ratio:
8743       return "Free ratio";
8744     case _satisfy_promotion:
8745       return "Satisfy promotion";
8746     case _satisfy_allocation:
8747       return "allocation";
8748     case _allocate_par_lab:
8749       return "Par LAB";
8750     case _allocate_par_spooling_space:
8751       return "Par Spooling Space";
8752     case _adaptive_size_policy:
8753       return "Ergonomics";
8754     default:
8755       return "unknown";
8756   }
8757 }
8758 
8759 void CMSDrainMarkingStackClosure::do_void() {
8760   // the max number to take from overflow list at a time
8761   const size_t num = _mark_stack->capacity()/4;
8762   assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
8763          "Overflow list should be NULL during concurrent phases");
8764   while (!_mark_stack->isEmpty() ||
8765          // if stack is empty, check the overflow list
8766          _collector->take_from_overflow_list(num, _mark_stack)) {
8767     oop obj = _mark_stack->pop();
8768     HeapWord* addr = (HeapWord*)obj;
8769     assert(_span.contains(addr), "Should be within span");
8770     assert(_bit_map->isMarked(addr), "Should be marked");
8771     assert(obj->is_oop(), "Should be an oop");
8772     obj->oop_iterate(_keep_alive);
8773   }
8774 }
8775 
8776 void CMSParDrainMarkingStackClosure::do_void() {
8777   // drain queue
8778   trim_queue(0);
8779 }
8780 
8781 // Trim our work_queue so its length is below max at return
8782 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
8783   while (_work_queue->size() > max) {
8784     oop new_oop;
8785     if (_work_queue->pop_local(new_oop)) {
8786       assert(new_oop->is_oop(), "Expected an oop");
8787       assert(_bit_map->isMarked((HeapWord*)new_oop),
8788              "no white objects on this stack!");
8789       assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8790       // iterate over the oops in this oop, marking and pushing
8791       // the ones in CMS heap (i.e. in _span).
8792       new_oop->oop_iterate(&_mark_and_push);
8793     }
8794   }
8795 }
8796 
8797 ////////////////////////////////////////////////////////////////////
8798 // Support for Marking Stack Overflow list handling and related code
8799 ////////////////////////////////////////////////////////////////////
8800 // Much of the following code is similar in shape and spirit to the
8801 // code used in ParNewGC. We should try and share that code
8802 // as much as possible in the future.
8803 
8804 #ifndef PRODUCT
8805 // Debugging support for CMSStackOverflowALot
8806 
8807 // It's OK to call this multi-threaded;  the worst thing
8808 // that can happen is that we'll get a bunch of closely
8809 // spaced simulated oveflows, but that's OK, in fact
8810 // probably good as it would exercise the overflow code
8811 // under contention.
8812 bool CMSCollector::simulate_overflow() {
8813   if (_overflow_counter-- <= 0) { // just being defensive
8814     _overflow_counter = CMSMarkStackOverflowInterval;
8815     return true;
8816   } else {
8817     return false;
8818   }
8819 }
8820 
8821 bool CMSCollector::par_simulate_overflow() {
8822   return simulate_overflow();
8823 }
8824 #endif
8825 
8826 // Single-threaded
8827 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
8828   assert(stack->isEmpty(), "Expected precondition");
8829   assert(stack->capacity() > num, "Shouldn't bite more than can chew");
8830   size_t i = num;
8831   oop  cur = _overflow_list;
8832   const markOop proto = markOopDesc::prototype();
8833   NOT_PRODUCT(ssize_t n = 0;)
8834   for (oop next; i > 0 && cur != NULL; cur = next, i--) {
8835     next = oop(cur->mark());
8836     cur->set_mark(proto);   // until proven otherwise
8837     assert(cur->is_oop(), "Should be an oop");
8838     bool res = stack->push(cur);
8839     assert(res, "Bit off more than can chew?");
8840     NOT_PRODUCT(n++;)
8841   }
8842   _overflow_list = cur;
8843 #ifndef PRODUCT
8844   assert(_num_par_pushes >= n, "Too many pops?");
8845   _num_par_pushes -=n;
8846 #endif
8847   return !stack->isEmpty();
8848 }
8849 
8850 #define BUSY  (oop(0x1aff1aff))
8851 // (MT-safe) Get a prefix of at most "num" from the list.
8852 // The overflow list is chained through the mark word of
8853 // each object in the list. We fetch the entire list,
8854 // break off a prefix of the right size and return the
8855 // remainder. If other threads try to take objects from
8856 // the overflow list at that time, they will wait for
8857 // some time to see if data becomes available. If (and
8858 // only if) another thread places one or more object(s)
8859 // on the global list before we have returned the suffix
8860 // to the global list, we will walk down our local list
8861 // to find its end and append the global list to
8862 // our suffix before returning it. This suffix walk can
8863 // prove to be expensive (quadratic in the amount of traffic)
8864 // when there are many objects in the overflow list and
8865 // there is much producer-consumer contention on the list.
8866 // *NOTE*: The overflow list manipulation code here and
8867 // in ParNewGeneration:: are very similar in shape,
8868 // except that in the ParNew case we use the old (from/eden)
8869 // copy of the object to thread the list via its klass word.
8870 // Because of the common code, if you make any changes in
8871 // the code below, please check the ParNew version to see if
8872 // similar changes might be needed.
8873 // CR 6797058 has been filed to consolidate the common code.
8874 bool CMSCollector::par_take_from_overflow_list(size_t num,
8875                                                OopTaskQueue* work_q,
8876                                                int no_of_gc_threads) {
8877   assert(work_q->size() == 0, "First empty local work queue");
8878   assert(num < work_q->max_elems(), "Can't bite more than we can chew");
8879   if (_overflow_list == NULL) {
8880     return false;
8881   }
8882   // Grab the entire list; we'll put back a suffix
8883   oop prefix = (oop)Atomic::xchg_ptr(BUSY, &_overflow_list);
8884   Thread* tid = Thread::current();
8885   // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was
8886   // set to ParallelGCThreads.
8887   size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads;
8888   size_t sleep_time_millis = MAX2((size_t)1, num/100);
8889   // If the list is busy, we spin for a short while,
8890   // sleeping between attempts to get the list.
8891   for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) {
8892     os::sleep(tid, sleep_time_millis, false);
8893     if (_overflow_list == NULL) {
8894       // Nothing left to take
8895       return false;
8896     } else if (_overflow_list != BUSY) {
8897       // Try and grab the prefix
8898       prefix = (oop)Atomic::xchg_ptr(BUSY, &_overflow_list);
8899     }
8900   }
8901   // If the list was found to be empty, or we spun long
8902   // enough, we give up and return empty-handed. If we leave
8903   // the list in the BUSY state below, it must be the case that
8904   // some other thread holds the overflow list and will set it
8905   // to a non-BUSY state in the future.
8906   if (prefix == NULL || prefix == BUSY) {
8907      // Nothing to take or waited long enough
8908      if (prefix == NULL) {
8909        // Write back the NULL in case we overwrote it with BUSY above
8910        // and it is still the same value.
8911        (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8912      }
8913      return false;
8914   }
8915   assert(prefix != NULL && prefix != BUSY, "Error");
8916   size_t i = num;
8917   oop cur = prefix;
8918   // Walk down the first "num" objects, unless we reach the end.
8919   for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--);
8920   if (cur->mark() == NULL) {
8921     // We have "num" or fewer elements in the list, so there
8922     // is nothing to return to the global list.
8923     // Write back the NULL in lieu of the BUSY we wrote
8924     // above, if it is still the same value.
8925     if (_overflow_list == BUSY) {
8926       (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8927     }
8928   } else {
8929     // Chop off the suffix and rerturn it to the global list.
8930     assert(cur->mark() != BUSY, "Error");
8931     oop suffix_head = cur->mark(); // suffix will be put back on global list
8932     cur->set_mark(NULL);           // break off suffix
8933     // It's possible that the list is still in the empty(busy) state
8934     // we left it in a short while ago; in that case we may be
8935     // able to place back the suffix without incurring the cost
8936     // of a walk down the list.
8937     oop observed_overflow_list = _overflow_list;
8938     oop cur_overflow_list = observed_overflow_list;
8939     bool attached = false;
8940     while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
8941       observed_overflow_list =
8942         (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
8943       if (cur_overflow_list == observed_overflow_list) {
8944         attached = true;
8945         break;
8946       } else cur_overflow_list = observed_overflow_list;
8947     }
8948     if (!attached) {
8949       // Too bad, someone else sneaked in (at least) an element; we'll need
8950       // to do a splice. Find tail of suffix so we can prepend suffix to global
8951       // list.
8952       for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark()));
8953       oop suffix_tail = cur;
8954       assert(suffix_tail != NULL && suffix_tail->mark() == NULL,
8955              "Tautology");
8956       observed_overflow_list = _overflow_list;
8957       do {
8958         cur_overflow_list = observed_overflow_list;
8959         if (cur_overflow_list != BUSY) {
8960           // Do the splice ...
8961           suffix_tail->set_mark(markOop(cur_overflow_list));
8962         } else { // cur_overflow_list == BUSY
8963           suffix_tail->set_mark(NULL);
8964         }
8965         // ... and try to place spliced list back on overflow_list ...
8966         observed_overflow_list =
8967           (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
8968       } while (cur_overflow_list != observed_overflow_list);
8969       // ... until we have succeeded in doing so.
8970     }
8971   }
8972 
8973   // Push the prefix elements on work_q
8974   assert(prefix != NULL, "control point invariant");
8975   const markOop proto = markOopDesc::prototype();
8976   oop next;
8977   NOT_PRODUCT(ssize_t n = 0;)
8978   for (cur = prefix; cur != NULL; cur = next) {
8979     next = oop(cur->mark());
8980     cur->set_mark(proto);   // until proven otherwise
8981     assert(cur->is_oop(), "Should be an oop");
8982     bool res = work_q->push(cur);
8983     assert(res, "Bit off more than we can chew?");
8984     NOT_PRODUCT(n++;)
8985   }
8986 #ifndef PRODUCT
8987   assert(_num_par_pushes >= n, "Too many pops?");
8988   Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
8989 #endif
8990   return true;
8991 }
8992 
8993 // Single-threaded
8994 void CMSCollector::push_on_overflow_list(oop p) {
8995   NOT_PRODUCT(_num_par_pushes++;)
8996   assert(p->is_oop(), "Not an oop");
8997   preserve_mark_if_necessary(p);
8998   p->set_mark((markOop)_overflow_list);
8999   _overflow_list = p;
9000 }
9001 
9002 // Multi-threaded; use CAS to prepend to overflow list
9003 void CMSCollector::par_push_on_overflow_list(oop p) {
9004   NOT_PRODUCT(Atomic::inc_ptr(&_num_par_pushes);)
9005   assert(p->is_oop(), "Not an oop");
9006   par_preserve_mark_if_necessary(p);
9007   oop observed_overflow_list = _overflow_list;
9008   oop cur_overflow_list;
9009   do {
9010     cur_overflow_list = observed_overflow_list;
9011     if (cur_overflow_list != BUSY) {
9012       p->set_mark(markOop(cur_overflow_list));
9013     } else {
9014       p->set_mark(NULL);
9015     }
9016     observed_overflow_list =
9017       (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list);
9018   } while (cur_overflow_list != observed_overflow_list);
9019 }
9020 #undef BUSY
9021 
9022 // Single threaded
9023 // General Note on GrowableArray: pushes may silently fail
9024 // because we are (temporarily) out of C-heap for expanding
9025 // the stack. The problem is quite ubiquitous and affects
9026 // a lot of code in the JVM. The prudent thing for GrowableArray
9027 // to do (for now) is to exit with an error. However, that may
9028 // be too draconian in some cases because the caller may be
9029 // able to recover without much harm. For such cases, we
9030 // should probably introduce a "soft_push" method which returns
9031 // an indication of success or failure with the assumption that
9032 // the caller may be able to recover from a failure; code in
9033 // the VM can then be changed, incrementally, to deal with such
9034 // failures where possible, thus, incrementally hardening the VM
9035 // in such low resource situations.
9036 void CMSCollector::preserve_mark_work(oop p, markOop m) {
9037   _preserved_oop_stack.push(p);
9038   _preserved_mark_stack.push(m);
9039   assert(m == p->mark(), "Mark word changed");
9040   assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
9041          "bijection");
9042 }
9043 
9044 // Single threaded
9045 void CMSCollector::preserve_mark_if_necessary(oop p) {
9046   markOop m = p->mark();
9047   if (m->must_be_preserved(p)) {
9048     preserve_mark_work(p, m);
9049   }
9050 }
9051 
9052 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
9053   markOop m = p->mark();
9054   if (m->must_be_preserved(p)) {
9055     MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
9056     // Even though we read the mark word without holding
9057     // the lock, we are assured that it will not change
9058     // because we "own" this oop, so no other thread can
9059     // be trying to push it on the overflow list; see
9060     // the assertion in preserve_mark_work() that checks
9061     // that m == p->mark().
9062     preserve_mark_work(p, m);
9063   }
9064 }
9065 
9066 // We should be able to do this multi-threaded,
9067 // a chunk of stack being a task (this is
9068 // correct because each oop only ever appears
9069 // once in the overflow list. However, it's
9070 // not very easy to completely overlap this with
9071 // other operations, so will generally not be done
9072 // until all work's been completed. Because we
9073 // expect the preserved oop stack (set) to be small,
9074 // it's probably fine to do this single-threaded.
9075 // We can explore cleverer concurrent/overlapped/parallel
9076 // processing of preserved marks if we feel the
9077 // need for this in the future. Stack overflow should
9078 // be so rare in practice and, when it happens, its
9079 // effect on performance so great that this will
9080 // likely just be in the noise anyway.
9081 void CMSCollector::restore_preserved_marks_if_any() {
9082   assert(SafepointSynchronize::is_at_safepoint(),
9083          "world should be stopped");
9084   assert(Thread::current()->is_ConcurrentGC_thread() ||
9085          Thread::current()->is_VM_thread(),
9086          "should be single-threaded");
9087   assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
9088          "bijection");
9089 
9090   while (!_preserved_oop_stack.is_empty()) {
9091     oop p = _preserved_oop_stack.pop();
9092     assert(p->is_oop(), "Should be an oop");
9093     assert(_span.contains(p), "oop should be in _span");
9094     assert(p->mark() == markOopDesc::prototype(),
9095            "Set when taken from overflow list");
9096     markOop m = _preserved_mark_stack.pop();
9097     p->set_mark(m);
9098   }
9099   assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(),
9100          "stacks were cleared above");
9101 }
9102 
9103 #ifndef PRODUCT
9104 bool CMSCollector::no_preserved_marks() const {
9105   return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty();
9106 }
9107 #endif
9108 
9109 CMSAdaptiveSizePolicy* ASConcurrentMarkSweepGeneration::cms_size_policy() const
9110 {
9111   GenCollectedHeap* gch = (GenCollectedHeap*) GenCollectedHeap::heap();
9112   CMSAdaptiveSizePolicy* size_policy =
9113     (CMSAdaptiveSizePolicy*) gch->gen_policy()->size_policy();
9114   assert(size_policy->is_gc_cms_adaptive_size_policy(),
9115     "Wrong type for size policy");
9116   return size_policy;
9117 }
9118 
9119 void ASConcurrentMarkSweepGeneration::resize(size_t cur_promo_size,
9120                                            size_t desired_promo_size) {
9121   if (cur_promo_size < desired_promo_size) {
9122     size_t expand_bytes = desired_promo_size - cur_promo_size;
9123     if (PrintAdaptiveSizePolicy && Verbose) {
9124       gclog_or_tty->print_cr(" ASConcurrentMarkSweepGeneration::resize "
9125         "Expanding tenured generation by " SIZE_FORMAT " (bytes)",
9126         expand_bytes);
9127     }
9128     expand(expand_bytes,
9129            MinHeapDeltaBytes,
9130            CMSExpansionCause::_adaptive_size_policy);
9131   } else if (desired_promo_size < cur_promo_size) {
9132     size_t shrink_bytes = cur_promo_size - desired_promo_size;
9133     if (PrintAdaptiveSizePolicy && Verbose) {
9134       gclog_or_tty->print_cr(" ASConcurrentMarkSweepGeneration::resize "
9135         "Shrinking tenured generation by " SIZE_FORMAT " (bytes)",
9136         shrink_bytes);
9137     }
9138     shrink(shrink_bytes);
9139   }
9140 }
9141 
9142 CMSGCAdaptivePolicyCounters* ASConcurrentMarkSweepGeneration::gc_adaptive_policy_counters() {
9143   GenCollectedHeap* gch = GenCollectedHeap::heap();
9144   CMSGCAdaptivePolicyCounters* counters =
9145     (CMSGCAdaptivePolicyCounters*) gch->collector_policy()->counters();
9146   assert(counters->kind() == GCPolicyCounters::CMSGCAdaptivePolicyCountersKind,
9147     "Wrong kind of counters");
9148   return counters;
9149 }
9150 
9151 
9152 void ASConcurrentMarkSweepGeneration::update_counters() {
9153   if (UsePerfData) {
9154     _space_counters->update_all();
9155     _gen_counters->update_all();
9156     CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
9157     GenCollectedHeap* gch = GenCollectedHeap::heap();
9158     CMSGCStats* gc_stats_l = (CMSGCStats*) gc_stats();
9159     assert(gc_stats_l->kind() == GCStats::CMSGCStatsKind,
9160       "Wrong gc statistics type");
9161     counters->update_counters(gc_stats_l);
9162   }
9163 }
9164 
9165 void ASConcurrentMarkSweepGeneration::update_counters(size_t used) {
9166   if (UsePerfData) {
9167     _space_counters->update_used(used);
9168     _space_counters->update_capacity();
9169     _gen_counters->update_all();
9170 
9171     CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
9172     GenCollectedHeap* gch = GenCollectedHeap::heap();
9173     CMSGCStats* gc_stats_l = (CMSGCStats*) gc_stats();
9174     assert(gc_stats_l->kind() == GCStats::CMSGCStatsKind,
9175       "Wrong gc statistics type");
9176     counters->update_counters(gc_stats_l);
9177   }
9178 }
9179 
9180 // The desired expansion delta is computed so that:
9181 // . desired free percentage or greater is used
9182 void ASConcurrentMarkSweepGeneration::compute_new_size() {
9183   assert_locked_or_safepoint(Heap_lock);
9184 
9185   GenCollectedHeap* gch = (GenCollectedHeap*) GenCollectedHeap::heap();
9186 
9187   // If incremental collection failed, we just want to expand
9188   // to the limit.
9189   if (incremental_collection_failed()) {
9190     clear_incremental_collection_failed();
9191     grow_to_reserved();
9192     return;
9193   }
9194 
9195   assert(UseAdaptiveSizePolicy, "Should be using adaptive sizing");
9196 
9197   assert(gch->kind() == CollectedHeap::GenCollectedHeap,
9198     "Wrong type of heap");
9199   int prev_level = level() - 1;
9200   assert(prev_level >= 0, "The cms generation is the lowest generation");
9201   Generation* prev_gen = gch->get_gen(prev_level);
9202   assert(prev_gen->kind() == Generation::ASParNew,
9203     "Wrong type of young generation");
9204   ParNewGeneration* younger_gen = (ParNewGeneration*) prev_gen;
9205   size_t cur_eden = younger_gen->eden()->capacity();
9206   CMSAdaptiveSizePolicy* size_policy = cms_size_policy();
9207   size_t cur_promo = free();
9208   size_policy->compute_tenured_generation_free_space(cur_promo,
9209                                                        max_available(),
9210                                                        cur_eden);
9211   resize(cur_promo, size_policy->promo_size());
9212 
9213   // Record the new size of the space in the cms generation
9214   // that is available for promotions.  This is temporary.
9215   // It should be the desired promo size.
9216   size_policy->avg_cms_promo()->sample(free());
9217   size_policy->avg_old_live()->sample(used());
9218 
9219   if (UsePerfData) {
9220     CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
9221     counters->update_cms_capacity_counter(capacity());
9222   }
9223 }
9224 
9225 void ASConcurrentMarkSweepGeneration::shrink_by(size_t desired_bytes) {
9226   assert_locked_or_safepoint(Heap_lock);
9227   assert_lock_strong(freelistLock());
9228   HeapWord* old_end = _cmsSpace->end();
9229   HeapWord* unallocated_start = _cmsSpace->unallocated_block();
9230   assert(old_end >= unallocated_start, "Miscalculation of unallocated_start");
9231   FreeChunk* chunk_at_end = find_chunk_at_end();
9232   if (chunk_at_end == NULL) {
9233     // No room to shrink
9234     if (PrintGCDetails && Verbose) {
9235       gclog_or_tty->print_cr("No room to shrink: old_end  "
9236         PTR_FORMAT "  unallocated_start  " PTR_FORMAT
9237         " chunk_at_end  " PTR_FORMAT,
9238         old_end, unallocated_start, chunk_at_end);
9239     }
9240     return;
9241   } else {
9242 
9243     // Find the chunk at the end of the space and determine
9244     // how much it can be shrunk.
9245     size_t shrinkable_size_in_bytes = chunk_at_end->size();
9246     size_t aligned_shrinkable_size_in_bytes =
9247       align_size_down(shrinkable_size_in_bytes, os::vm_page_size());
9248     assert(unallocated_start <= chunk_at_end->end(),
9249       "Inconsistent chunk at end of space");
9250     size_t bytes = MIN2(desired_bytes, aligned_shrinkable_size_in_bytes);
9251     size_t word_size_before = heap_word_size(_virtual_space.committed_size());
9252 
9253     // Shrink the underlying space
9254     _virtual_space.shrink_by(bytes);
9255     if (PrintGCDetails && Verbose) {
9256       gclog_or_tty->print_cr("ConcurrentMarkSweepGeneration::shrink_by:"
9257         " desired_bytes " SIZE_FORMAT
9258         " shrinkable_size_in_bytes " SIZE_FORMAT
9259         " aligned_shrinkable_size_in_bytes " SIZE_FORMAT
9260         "  bytes  " SIZE_FORMAT,
9261         desired_bytes, shrinkable_size_in_bytes,
9262         aligned_shrinkable_size_in_bytes, bytes);
9263       gclog_or_tty->print_cr("          old_end  " SIZE_FORMAT
9264         "  unallocated_start  " SIZE_FORMAT,
9265         old_end, unallocated_start);
9266     }
9267 
9268     // If the space did shrink (shrinking is not guaranteed),
9269     // shrink the chunk at the end by the appropriate amount.
9270     if (((HeapWord*)_virtual_space.high()) < old_end) {
9271       size_t new_word_size =
9272         heap_word_size(_virtual_space.committed_size());
9273 
9274       // Have to remove the chunk from the dictionary because it is changing
9275       // size and might be someplace elsewhere in the dictionary.
9276 
9277       // Get the chunk at end, shrink it, and put it
9278       // back.
9279       _cmsSpace->removeChunkFromDictionary(chunk_at_end);
9280       size_t word_size_change = word_size_before - new_word_size;
9281       size_t chunk_at_end_old_size = chunk_at_end->size();
9282       assert(chunk_at_end_old_size >= word_size_change,
9283         "Shrink is too large");
9284       chunk_at_end->set_size(chunk_at_end_old_size -
9285                           word_size_change);
9286       _cmsSpace->freed((HeapWord*) chunk_at_end->end(),
9287         word_size_change);
9288 
9289       _cmsSpace->returnChunkToDictionary(chunk_at_end);
9290 
9291       MemRegion mr(_cmsSpace->bottom(), new_word_size);
9292       _bts->resize(new_word_size);  // resize the block offset shared array
9293       Universe::heap()->barrier_set()->resize_covered_region(mr);
9294       _cmsSpace->assert_locked();
9295       _cmsSpace->set_end((HeapWord*)_virtual_space.high());
9296 
9297       NOT_PRODUCT(_cmsSpace->dictionary()->verify());
9298 
9299       // update the space and generation capacity counters
9300       if (UsePerfData) {
9301         _space_counters->update_capacity();
9302         _gen_counters->update_all();
9303       }
9304 
9305       if (Verbose && PrintGCDetails) {
9306         size_t new_mem_size = _virtual_space.committed_size();
9307         size_t old_mem_size = new_mem_size + bytes;
9308         gclog_or_tty->print_cr("Shrinking %s from %ldK by %ldK to %ldK",
9309                       name(), old_mem_size/K, bytes/K, new_mem_size/K);
9310       }
9311     }
9312 
9313     assert(_cmsSpace->unallocated_block() <= _cmsSpace->end(),
9314       "Inconsistency at end of space");
9315     assert(chunk_at_end->end() == _cmsSpace->end(),
9316       "Shrinking is inconsistent");
9317     return;
9318   }
9319 }
9320 
9321 // Transfer some number of overflown objects to usual marking
9322 // stack. Return true if some objects were transferred.
9323 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
9324   size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,
9325                     (size_t)ParGCDesiredObjsFromOverflowList);
9326 
9327   bool res = _collector->take_from_overflow_list(num, _mark_stack);
9328   assert(_collector->overflow_list_is_empty() || res,
9329          "If list is not empty, we should have taken something");
9330   assert(!res || !_mark_stack->isEmpty(),
9331          "If we took something, it should now be on our stack");
9332   return res;
9333 }
9334 
9335 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
9336   size_t res = _sp->block_size_no_stall(addr, _collector);
9337   if (_sp->block_is_obj(addr)) {
9338     if (_live_bit_map->isMarked(addr)) {
9339       // It can't have been dead in a previous cycle
9340       guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
9341     } else {
9342       _dead_bit_map->mark(addr);      // mark the dead object
9343     }
9344   }
9345   // Could be 0, if the block size could not be computed without stalling.
9346   return res;
9347 }
9348 
9349 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() {
9350 
9351   switch (phase) {
9352     case CMSCollector::InitialMarking:
9353       initialize(true  /* fullGC */ ,
9354                  cause /* cause of the GC */,
9355                  true  /* recordGCBeginTime */,
9356                  true  /* recordPreGCUsage */,
9357                  false /* recordPeakUsage */,
9358                  false /* recordPostGCusage */,
9359                  true  /* recordAccumulatedGCTime */,
9360                  false /* recordGCEndTime */,
9361                  false /* countCollection */  );
9362       break;
9363 
9364     case CMSCollector::FinalMarking:
9365       initialize(true  /* fullGC */ ,
9366                  cause /* cause of the GC */,
9367                  false /* recordGCBeginTime */,
9368                  false /* recordPreGCUsage */,
9369                  false /* recordPeakUsage */,
9370                  false /* recordPostGCusage */,
9371                  true  /* recordAccumulatedGCTime */,
9372                  false /* recordGCEndTime */,
9373                  false /* countCollection */  );
9374       break;
9375 
9376     case CMSCollector::Sweeping:
9377       initialize(true  /* fullGC */ ,
9378                  cause /* cause of the GC */,
9379                  false /* recordGCBeginTime */,
9380                  false /* recordPreGCUsage */,
9381                  true  /* recordPeakUsage */,
9382                  true  /* recordPostGCusage */,
9383                  false /* recordAccumulatedGCTime */,
9384                  true  /* recordGCEndTime */,
9385                  true  /* countCollection */  );
9386       break;
9387 
9388     default:
9389       ShouldNotReachHere();
9390   }
9391 }
9392 
--- EOF ---