1 /*
   2  * Copyright (c) 2001, 2013, 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/classLoaderData.hpp"
  27 #include "classfile/symbolTable.hpp"
  28 #include "classfile/systemDictionary.hpp"
  29 #include "code/codeCache.hpp"
  30 #include "gc_implementation/concurrentMarkSweep/cmsAdaptiveSizePolicy.hpp"
  31 #include "gc_implementation/concurrentMarkSweep/cmsCollectorPolicy.hpp"
  32 #include "gc_implementation/concurrentMarkSweep/cmsGCAdaptivePolicyCounters.hpp"
  33 #include "gc_implementation/concurrentMarkSweep/cmsOopClosures.inline.hpp"
  34 #include "gc_implementation/concurrentMarkSweep/compactibleFreeListSpace.hpp"
  35 #include "gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.inline.hpp"
  36 #include "gc_implementation/concurrentMarkSweep/concurrentMarkSweepThread.hpp"
  37 #include "gc_implementation/concurrentMarkSweep/vmCMSOperations.hpp"
  38 #include "gc_implementation/parNew/parNewGeneration.hpp"
  39 #include "gc_implementation/shared/collectorCounters.hpp"
  40 #include "gc_implementation/shared/isGCActiveMark.hpp"
  41 #include "gc_interface/collectedHeap.inline.hpp"
  42 #include "memory/cardTableRS.hpp"
  43 #include "memory/collectorPolicy.hpp"
  44 #include "memory/gcLocker.inline.hpp"
  45 #include "memory/genCollectedHeap.hpp"
  46 #include "memory/genMarkSweep.hpp"
  47 #include "memory/genOopClosures.inline.hpp"
  48 #include "memory/iterator.hpp"
  49 #include "memory/referencePolicy.hpp"
  50 #include "memory/resourceArea.hpp"
  51 #include "oops/oop.inline.hpp"
  52 #include "prims/jvmtiExport.hpp"
  53 #include "runtime/globals_extension.hpp"
  54 #include "runtime/handles.inline.hpp"
  55 #include "runtime/java.hpp"
  56 #include "runtime/vmThread.hpp"
  57 #include "services/memoryService.hpp"
  58 #include "services/runtimeService.hpp"
  59 
  60 // statics
  61 CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL;
  62 bool          CMSCollector::_full_gc_requested          = false;
  63 
  64 //////////////////////////////////////////////////////////////////
  65 // In support of CMS/VM thread synchronization
  66 //////////////////////////////////////////////////////////////////
  67 // We split use of the CGC_lock into 2 "levels".
  68 // The low-level locking is of the usual CGC_lock monitor. We introduce
  69 // a higher level "token" (hereafter "CMS token") built on top of the
  70 // low level monitor (hereafter "CGC lock").
  71 // The token-passing protocol gives priority to the VM thread. The
  72 // CMS-lock doesn't provide any fairness guarantees, but clients
  73 // should ensure that it is only held for very short, bounded
  74 // durations.
  75 //
  76 // When either of the CMS thread or the VM thread is involved in
  77 // collection operations during which it does not want the other
  78 // thread to interfere, it obtains the CMS token.
  79 //
  80 // If either thread tries to get the token while the other has
  81 // it, that thread waits. However, if the VM thread and CMS thread
  82 // both want the token, then the VM thread gets priority while the
  83 // CMS thread waits. This ensures, for instance, that the "concurrent"
  84 // phases of the CMS thread's work do not block out the VM thread
  85 // for long periods of time as the CMS thread continues to hog
  86 // the token. (See bug 4616232).
  87 //
  88 // The baton-passing functions are, however, controlled by the
  89 // flags _foregroundGCShouldWait and _foregroundGCIsActive,
  90 // and here the low-level CMS lock, not the high level token,
  91 // ensures mutual exclusion.
  92 //
  93 // Two important conditions that we have to satisfy:
  94 // 1. if a thread does a low-level wait on the CMS lock, then it
  95 //    relinquishes the CMS token if it were holding that token
  96 //    when it acquired the low-level CMS lock.
  97 // 2. any low-level notifications on the low-level lock
  98 //    should only be sent when a thread has relinquished the token.
  99 //
 100 // In the absence of either property, we'd have potential deadlock.
 101 //
 102 // We protect each of the CMS (concurrent and sequential) phases
 103 // with the CMS _token_, not the CMS _lock_.
 104 //
 105 // The only code protected by CMS lock is the token acquisition code
 106 // itself, see ConcurrentMarkSweepThread::[de]synchronize(), and the
 107 // baton-passing code.
 108 //
 109 // Unfortunately, i couldn't come up with a good abstraction to factor and
 110 // hide the naked CGC_lock manipulation in the baton-passing code
 111 // further below. That's something we should try to do. Also, the proof
 112 // of correctness of this 2-level locking scheme is far from obvious,
 113 // and potentially quite slippery. We have an uneasy supsicion, for instance,
 114 // that there may be a theoretical possibility of delay/starvation in the
 115 // low-level lock/wait/notify scheme used for the baton-passing because of
 116 // potential intereference with the priority scheme embodied in the
 117 // CMS-token-passing protocol. See related comments at a CGC_lock->wait()
 118 // invocation further below and marked with "XXX 20011219YSR".
 119 // Indeed, as we note elsewhere, this may become yet more slippery
 120 // in the presence of multiple CMS and/or multiple VM threads. XXX
 121 
 122 class CMSTokenSync: public StackObj {
 123  private:
 124   bool _is_cms_thread;
 125  public:
 126   CMSTokenSync(bool is_cms_thread):
 127     _is_cms_thread(is_cms_thread) {
 128     assert(is_cms_thread == Thread::current()->is_ConcurrentGC_thread(),
 129            "Incorrect argument to constructor");
 130     ConcurrentMarkSweepThread::synchronize(_is_cms_thread);
 131   }
 132 
 133   ~CMSTokenSync() {
 134     assert(_is_cms_thread ?
 135              ConcurrentMarkSweepThread::cms_thread_has_cms_token() :
 136              ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
 137           "Incorrect state");
 138     ConcurrentMarkSweepThread::desynchronize(_is_cms_thread);
 139   }
 140 };
 141 
 142 // Convenience class that does a CMSTokenSync, and then acquires
 143 // upto three locks.
 144 class CMSTokenSyncWithLocks: public CMSTokenSync {
 145  private:
 146   // Note: locks are acquired in textual declaration order
 147   // and released in the opposite order
 148   MutexLockerEx _locker1, _locker2, _locker3;
 149  public:
 150   CMSTokenSyncWithLocks(bool is_cms_thread, Mutex* mutex1,
 151                         Mutex* mutex2 = NULL, Mutex* mutex3 = NULL):
 152     CMSTokenSync(is_cms_thread),
 153     _locker1(mutex1, Mutex::_no_safepoint_check_flag),
 154     _locker2(mutex2, Mutex::_no_safepoint_check_flag),
 155     _locker3(mutex3, Mutex::_no_safepoint_check_flag)
 156   { }
 157 };
 158 
 159 
 160 // Wrapper class to temporarily disable icms during a foreground cms collection.
 161 class ICMSDisabler: public StackObj {
 162  public:
 163   // The ctor disables icms and wakes up the thread so it notices the change;
 164   // the dtor re-enables icms.  Note that the CMSCollector methods will check
 165   // CMSIncrementalMode.
 166   ICMSDisabler()  { CMSCollector::disable_icms(); CMSCollector::start_icms(); }
 167   ~ICMSDisabler() { CMSCollector::enable_icms(); }
 168 };
 169 
 170 //////////////////////////////////////////////////////////////////
 171 //  Concurrent Mark-Sweep Generation /////////////////////////////
 172 //////////////////////////////////////////////////////////////////
 173 
 174 NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;)
 175 
 176 // This struct contains per-thread things necessary to support parallel
 177 // young-gen collection.
 178 class CMSParGCThreadState: public CHeapObj<mtGC> {
 179  public:
 180   CFLS_LAB lab;
 181   PromotionInfo promo;
 182 
 183   // Constructor.
 184   CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) {
 185     promo.setSpace(cfls);
 186   }
 187 };
 188 
 189 ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration(
 190      ReservedSpace rs, size_t initial_byte_size, int level,
 191      CardTableRS* ct, bool use_adaptive_freelists,
 192      FreeBlockDictionary<FreeChunk>::DictionaryChoice dictionaryChoice) :
 193   CardGeneration(rs, initial_byte_size, level, ct),
 194   _dilatation_factor(((double)MinChunkSize)/((double)(CollectedHeap::min_fill_size()))),
 195   _debug_collection_type(Concurrent_collection_type)
 196 {
 197   HeapWord* bottom = (HeapWord*) _virtual_space.low();
 198   HeapWord* end    = (HeapWord*) _virtual_space.high();
 199 
 200   _direct_allocated_words = 0;
 201   NOT_PRODUCT(
 202     _numObjectsPromoted = 0;
 203     _numWordsPromoted = 0;
 204     _numObjectsAllocated = 0;
 205     _numWordsAllocated = 0;
 206   )
 207 
 208   _cmsSpace = new CompactibleFreeListSpace(_bts, MemRegion(bottom, end),
 209                                            use_adaptive_freelists,
 210                                            dictionaryChoice);
 211   NOT_PRODUCT(debug_cms_space = _cmsSpace;)
 212   if (_cmsSpace == NULL) {
 213     vm_exit_during_initialization(
 214       "CompactibleFreeListSpace allocation failure");
 215   }
 216   _cmsSpace->_gen = this;
 217 
 218   _gc_stats = new CMSGCStats();
 219 
 220   // Verify the assumption that FreeChunk::_prev and OopDesc::_klass
 221   // offsets match. The ability to tell free chunks from objects
 222   // depends on this property.
 223   debug_only(
 224     FreeChunk* junk = NULL;
 225     assert(UseCompressedKlassPointers ||
 226            junk->prev_addr() == (void*)(oop(junk)->klass_addr()),
 227            "Offset of FreeChunk::_prev within FreeChunk must match"
 228            "  that of OopDesc::_klass within OopDesc");
 229   )
 230   if (CollectedHeap::use_parallel_gc_threads()) {
 231     typedef CMSParGCThreadState* CMSParGCThreadStatePtr;
 232     _par_gc_thread_states =
 233       NEW_C_HEAP_ARRAY(CMSParGCThreadStatePtr, ParallelGCThreads, mtGC);
 234     if (_par_gc_thread_states == NULL) {
 235       vm_exit_during_initialization("Could not allocate par gc structs");
 236     }
 237     for (uint i = 0; i < ParallelGCThreads; i++) {
 238       _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace());
 239       if (_par_gc_thread_states[i] == NULL) {
 240         vm_exit_during_initialization("Could not allocate par gc structs");
 241       }
 242     }
 243   } else {
 244     _par_gc_thread_states = NULL;
 245   }
 246   _incremental_collection_failed = false;
 247   // The "dilatation_factor" is the expansion that can occur on
 248   // account of the fact that the minimum object size in the CMS
 249   // generation may be larger than that in, say, a contiguous young
 250   //  generation.
 251   // Ideally, in the calculation below, we'd compute the dilatation
 252   // factor as: MinChunkSize/(promoting_gen's min object size)
 253   // Since we do not have such a general query interface for the
 254   // promoting generation, we'll instead just use the mimimum
 255   // object size (which today is a header's worth of space);
 256   // note that all arithmetic is in units of HeapWords.
 257   assert(MinChunkSize >= CollectedHeap::min_fill_size(), "just checking");
 258   assert(_dilatation_factor >= 1.0, "from previous assert");
 259 }
 260 
 261 
 262 // The field "_initiating_occupancy" represents the occupancy percentage
 263 // at which we trigger a new collection cycle.  Unless explicitly specified
 264 // via CMSInitiatingOccupancyFraction (argument "io" below), it
 265 // is calculated by:
 266 //
 267 //   Let "f" be MinHeapFreeRatio in
 268 //
 269 //    _intiating_occupancy = 100-f +
 270 //                           f * (CMSTriggerRatio/100)
 271 //   where CMSTriggerRatio is the argument "tr" below.
 272 //
 273 // That is, if we assume the heap is at its desired maximum occupancy at the
 274 // end of a collection, we let CMSTriggerRatio of the (purported) free
 275 // space be allocated before initiating a new collection cycle.
 276 //
 277 void ConcurrentMarkSweepGeneration::init_initiating_occupancy(intx io, uintx tr) {
 278   assert(io <= 100 && tr <= 100, "Check the arguments");
 279   if (io >= 0) {
 280     _initiating_occupancy = (double)io / 100.0;
 281   } else {
 282     _initiating_occupancy = ((100 - MinHeapFreeRatio) +
 283                              (double)(tr * MinHeapFreeRatio) / 100.0)
 284                             / 100.0;
 285   }
 286 }
 287 
 288 void ConcurrentMarkSweepGeneration::ref_processor_init() {
 289   assert(collector() != NULL, "no collector");
 290   collector()->ref_processor_init();
 291 }
 292 
 293 void CMSCollector::ref_processor_init() {
 294   if (_ref_processor == NULL) {
 295     // Allocate and initialize a reference processor
 296     _ref_processor =
 297       new ReferenceProcessor(_span,                               // span
 298                              (ParallelGCThreads > 1) && ParallelRefProcEnabled, // mt processing
 299                              (int) ParallelGCThreads,             // mt processing degree
 300                              _cmsGen->refs_discovery_is_mt(),     // mt discovery
 301                              (int) MAX2(ConcGCThreads, ParallelGCThreads), // mt discovery degree
 302                              _cmsGen->refs_discovery_is_atomic(), // discovery is not atomic
 303                              &_is_alive_closure,                  // closure for liveness info
 304                              false);                              // next field updates do not need write barrier
 305     // Initialize the _ref_processor field of CMSGen
 306     _cmsGen->set_ref_processor(_ref_processor);
 307 
 308   }
 309 }
 310 
 311 CMSAdaptiveSizePolicy* CMSCollector::size_policy() {
 312   GenCollectedHeap* gch = GenCollectedHeap::heap();
 313   assert(gch->kind() == CollectedHeap::GenCollectedHeap,
 314     "Wrong type of heap");
 315   CMSAdaptiveSizePolicy* sp = (CMSAdaptiveSizePolicy*)
 316     gch->gen_policy()->size_policy();
 317   assert(sp->is_gc_cms_adaptive_size_policy(),
 318     "Wrong type of size policy");
 319   return sp;
 320 }
 321 
 322 CMSGCAdaptivePolicyCounters* CMSCollector::gc_adaptive_policy_counters() {
 323   CMSGCAdaptivePolicyCounters* results =
 324     (CMSGCAdaptivePolicyCounters*) collector_policy()->counters();
 325   assert(
 326     results->kind() == GCPolicyCounters::CMSGCAdaptivePolicyCountersKind,
 327     "Wrong gc policy counter kind");
 328   return results;
 329 }
 330 
 331 
 332 void ConcurrentMarkSweepGeneration::initialize_performance_counters() {
 333 
 334   const char* gen_name = "old";
 335 
 336   // Generation Counters - generation 1, 1 subspace
 337   _gen_counters = new GenerationCounters(gen_name, 1, 1, &_virtual_space);
 338 
 339   _space_counters = new GSpaceCounters(gen_name, 0,
 340                                        _virtual_space.reserved_size(),
 341                                        this, _gen_counters);
 342 }
 343 
 344 CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha):
 345   _cms_gen(cms_gen)
 346 {
 347   assert(alpha <= 100, "bad value");
 348   _saved_alpha = alpha;
 349 
 350   // Initialize the alphas to the bootstrap value of 100.
 351   _gc0_alpha = _cms_alpha = 100;
 352 
 353   _cms_begin_time.update();
 354   _cms_end_time.update();
 355 
 356   _gc0_duration = 0.0;
 357   _gc0_period = 0.0;
 358   _gc0_promoted = 0;
 359 
 360   _cms_duration = 0.0;
 361   _cms_period = 0.0;
 362   _cms_allocated = 0;
 363 
 364   _cms_used_at_gc0_begin = 0;
 365   _cms_used_at_gc0_end = 0;
 366   _allow_duty_cycle_reduction = false;
 367   _valid_bits = 0;
 368   _icms_duty_cycle = CMSIncrementalDutyCycle;
 369 }
 370 
 371 double CMSStats::cms_free_adjustment_factor(size_t free) const {
 372   // TBD: CR 6909490
 373   return 1.0;
 374 }
 375 
 376 void CMSStats::adjust_cms_free_adjustment_factor(bool fail, size_t free) {
 377 }
 378 
 379 // If promotion failure handling is on use
 380 // the padded average size of the promotion for each
 381 // young generation collection.
 382 double CMSStats::time_until_cms_gen_full() const {
 383   size_t cms_free = _cms_gen->cmsSpace()->free();
 384   GenCollectedHeap* gch = GenCollectedHeap::heap();
 385   size_t expected_promotion = MIN2(gch->get_gen(0)->capacity(),
 386                                    (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average());
 387   if (cms_free > expected_promotion) {
 388     // Start a cms collection if there isn't enough space to promote
 389     // for the next minor collection.  Use the padded average as
 390     // a safety factor.
 391     cms_free -= expected_promotion;
 392 
 393     // Adjust by the safety factor.
 394     double cms_free_dbl = (double)cms_free;
 395     double cms_adjustment = (100.0 - CMSIncrementalSafetyFactor)/100.0;
 396     // Apply a further correction factor which tries to adjust
 397     // for recent occurance of concurrent mode failures.
 398     cms_adjustment = cms_adjustment * cms_free_adjustment_factor(cms_free);
 399     cms_free_dbl = cms_free_dbl * cms_adjustment;
 400 
 401     if (PrintGCDetails && Verbose) {
 402       gclog_or_tty->print_cr("CMSStats::time_until_cms_gen_full: cms_free "
 403         SIZE_FORMAT " expected_promotion " SIZE_FORMAT,
 404         cms_free, expected_promotion);
 405       gclog_or_tty->print_cr("  cms_free_dbl %f cms_consumption_rate %f",
 406         cms_free_dbl, cms_consumption_rate() + 1.0);
 407     }
 408     // Add 1 in case the consumption rate goes to zero.
 409     return cms_free_dbl / (cms_consumption_rate() + 1.0);
 410   }
 411   return 0.0;
 412 }
 413 
 414 // Compare the duration of the cms collection to the
 415 // time remaining before the cms generation is empty.
 416 // Note that the time from the start of the cms collection
 417 // to the start of the cms sweep (less than the total
 418 // duration of the cms collection) can be used.  This
 419 // has been tried and some applications experienced
 420 // promotion failures early in execution.  This was
 421 // possibly because the averages were not accurate
 422 // enough at the beginning.
 423 double CMSStats::time_until_cms_start() const {
 424   // We add "gc0_period" to the "work" calculation
 425   // below because this query is done (mostly) at the
 426   // end of a scavenge, so we need to conservatively
 427   // account for that much possible delay
 428   // in the query so as to avoid concurrent mode failures
 429   // due to starting the collection just a wee bit too
 430   // late.
 431   double work = cms_duration() + gc0_period();
 432   double deadline = time_until_cms_gen_full();
 433   // If a concurrent mode failure occurred recently, we want to be
 434   // more conservative and halve our expected time_until_cms_gen_full()
 435   if (work > deadline) {
 436     if (Verbose && PrintGCDetails) {
 437       gclog_or_tty->print(
 438         " CMSCollector: collect because of anticipated promotion "
 439         "before full %3.7f + %3.7f > %3.7f ", cms_duration(),
 440         gc0_period(), time_until_cms_gen_full());
 441     }
 442     return 0.0;
 443   }
 444   return work - deadline;
 445 }
 446 
 447 // Return a duty cycle based on old_duty_cycle and new_duty_cycle, limiting the
 448 // amount of change to prevent wild oscillation.
 449 unsigned int CMSStats::icms_damped_duty_cycle(unsigned int old_duty_cycle,
 450                                               unsigned int new_duty_cycle) {
 451   assert(old_duty_cycle <= 100, "bad input value");
 452   assert(new_duty_cycle <= 100, "bad input value");
 453 
 454   // Note:  use subtraction with caution since it may underflow (values are
 455   // unsigned).  Addition is safe since we're in the range 0-100.
 456   unsigned int damped_duty_cycle = new_duty_cycle;
 457   if (new_duty_cycle < old_duty_cycle) {
 458     const unsigned int largest_delta = MAX2(old_duty_cycle / 4, 5U);
 459     if (new_duty_cycle + largest_delta < old_duty_cycle) {
 460       damped_duty_cycle = old_duty_cycle - largest_delta;
 461     }
 462   } else if (new_duty_cycle > old_duty_cycle) {
 463     const unsigned int largest_delta = MAX2(old_duty_cycle / 4, 15U);
 464     if (new_duty_cycle > old_duty_cycle + largest_delta) {
 465       damped_duty_cycle = MIN2(old_duty_cycle + largest_delta, 100U);
 466     }
 467   }
 468   assert(damped_duty_cycle <= 100, "invalid duty cycle computed");
 469 
 470   if (CMSTraceIncrementalPacing) {
 471     gclog_or_tty->print(" [icms_damped_duty_cycle(%d,%d) = %d] ",
 472                            old_duty_cycle, new_duty_cycle, damped_duty_cycle);
 473   }
 474   return damped_duty_cycle;
 475 }
 476 
 477 unsigned int CMSStats::icms_update_duty_cycle_impl() {
 478   assert(CMSIncrementalPacing && valid(),
 479          "should be handled in icms_update_duty_cycle()");
 480 
 481   double cms_time_so_far = cms_timer().seconds();
 482   double scaled_duration = cms_duration_per_mb() * _cms_used_at_gc0_end / M;
 483   double scaled_duration_remaining = fabsd(scaled_duration - cms_time_so_far);
 484 
 485   // Avoid division by 0.
 486   double time_until_full = MAX2(time_until_cms_gen_full(), 0.01);
 487   double duty_cycle_dbl = 100.0 * scaled_duration_remaining / time_until_full;
 488 
 489   unsigned int new_duty_cycle = MIN2((unsigned int)duty_cycle_dbl, 100U);
 490   if (new_duty_cycle > _icms_duty_cycle) {
 491     // Avoid very small duty cycles (1 or 2); 0 is allowed.
 492     if (new_duty_cycle > 2) {
 493       _icms_duty_cycle = icms_damped_duty_cycle(_icms_duty_cycle,
 494                                                 new_duty_cycle);
 495     }
 496   } else if (_allow_duty_cycle_reduction) {
 497     // The duty cycle is reduced only once per cms cycle (see record_cms_end()).
 498     new_duty_cycle = icms_damped_duty_cycle(_icms_duty_cycle, new_duty_cycle);
 499     // Respect the minimum duty cycle.
 500     unsigned int min_duty_cycle = (unsigned int)CMSIncrementalDutyCycleMin;
 501     _icms_duty_cycle = MAX2(new_duty_cycle, min_duty_cycle);
 502   }
 503 
 504   if (PrintGCDetails || CMSTraceIncrementalPacing) {
 505     gclog_or_tty->print(" icms_dc=%d ", _icms_duty_cycle);
 506   }
 507 
 508   _allow_duty_cycle_reduction = false;
 509   return _icms_duty_cycle;
 510 }
 511 
 512 #ifndef PRODUCT
 513 void CMSStats::print_on(outputStream *st) const {
 514   st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha);
 515   st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo=" SIZE_FORMAT,
 516                gc0_duration(), gc0_period(), gc0_promoted());
 517   st->print(",cms_dur=%g,cms_dur_per_mb=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT,
 518             cms_duration(), cms_duration_per_mb(),
 519             cms_period(), cms_allocated());
 520   st->print(",cms_since_beg=%g,cms_since_end=%g",
 521             cms_time_since_begin(), cms_time_since_end());
 522   st->print(",cms_used_beg=" SIZE_FORMAT ",cms_used_end=" SIZE_FORMAT,
 523             _cms_used_at_gc0_begin, _cms_used_at_gc0_end);
 524   if (CMSIncrementalMode) {
 525     st->print(",dc=%d", icms_duty_cycle());
 526   }
 527 
 528   if (valid()) {
 529     st->print(",promo_rate=%g,cms_alloc_rate=%g",
 530               promotion_rate(), cms_allocation_rate());
 531     st->print(",cms_consumption_rate=%g,time_until_full=%g",
 532               cms_consumption_rate(), time_until_cms_gen_full());
 533   }
 534   st->print(" ");
 535 }
 536 #endif // #ifndef PRODUCT
 537 
 538 CMSCollector::CollectorState CMSCollector::_collectorState =
 539                              CMSCollector::Idling;
 540 bool CMSCollector::_foregroundGCIsActive = false;
 541 bool CMSCollector::_foregroundGCShouldWait = false;
 542 
 543 CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
 544                            CardTableRS*                   ct,
 545                            ConcurrentMarkSweepPolicy*     cp):
 546   _cmsGen(cmsGen),
 547   _ct(ct),
 548   _ref_processor(NULL),    // will be set later
 549   _conc_workers(NULL),     // may be set later
 550   _abort_preclean(false),
 551   _start_sampling(false),
 552   _between_prologue_and_epilogue(false),
 553   _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"),
 554   _modUnionTable((CardTableModRefBS::card_shift - LogHeapWordSize),
 555                  -1 /* lock-free */, "No_lock" /* dummy */),
 556   _modUnionClosure(&_modUnionTable),
 557   _modUnionClosurePar(&_modUnionTable),
 558   // Adjust my span to cover old (cms) gen
 559   _span(cmsGen->reserved()),
 560   // Construct the is_alive_closure with _span & markBitMap
 561   _is_alive_closure(_span, &_markBitMap),
 562   _restart_addr(NULL),
 563   _overflow_list(NULL),
 564   _stats(cmsGen),
 565   _eden_chunk_array(NULL),     // may be set in ctor body
 566   _eden_chunk_capacity(0),     // -- ditto --
 567   _eden_chunk_index(0),        // -- ditto --
 568   _survivor_plab_array(NULL),  // -- ditto --
 569   _survivor_chunk_array(NULL), // -- ditto --
 570   _survivor_chunk_capacity(0), // -- ditto --
 571   _survivor_chunk_index(0),    // -- ditto --
 572   _ser_pmc_preclean_ovflw(0),
 573   _ser_kac_preclean_ovflw(0),
 574   _ser_pmc_remark_ovflw(0),
 575   _par_pmc_remark_ovflw(0),
 576   _ser_kac_ovflw(0),
 577   _par_kac_ovflw(0),
 578 #ifndef PRODUCT
 579   _num_par_pushes(0),
 580 #endif
 581   _collection_count_start(0),
 582   _verifying(false),
 583   _icms_start_limit(NULL),
 584   _icms_stop_limit(NULL),
 585   _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"),
 586   _completed_initialization(false),
 587   _collector_policy(cp),
 588   _should_unload_classes(false),
 589   _concurrent_cycles_since_last_unload(0),
 590   _roots_scanning_options(0),
 591   _inter_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
 592   _intra_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding)
 593 {
 594   if (ExplicitGCInvokesConcurrentAndUnloadsClasses) {
 595     ExplicitGCInvokesConcurrent = true;
 596   }
 597   // Now expand the span and allocate the collection support structures
 598   // (MUT, marking bit map etc.) to cover both generations subject to
 599   // collection.
 600 
 601   // For use by dirty card to oop closures.
 602   _cmsGen->cmsSpace()->set_collector(this);
 603 
 604   // Allocate MUT and marking bit map
 605   {
 606     MutexLockerEx x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag);
 607     if (!_markBitMap.allocate(_span)) {
 608       warning("Failed to allocate CMS Bit Map");
 609       return;
 610     }
 611     assert(_markBitMap.covers(_span), "_markBitMap inconsistency?");
 612   }
 613   {
 614     _modUnionTable.allocate(_span);
 615     assert(_modUnionTable.covers(_span), "_modUnionTable inconsistency?");
 616   }
 617 
 618   if (!_markStack.allocate(MarkStackSize)) {
 619     warning("Failed to allocate CMS Marking Stack");
 620     return;
 621   }
 622 
 623   // Support for multi-threaded concurrent phases
 624   if (CMSConcurrentMTEnabled) {
 625     if (FLAG_IS_DEFAULT(ConcGCThreads)) {
 626       // just for now
 627       FLAG_SET_DEFAULT(ConcGCThreads, (ParallelGCThreads + 3)/4);
 628     }
 629     if (ConcGCThreads > 1) {
 630       _conc_workers = new YieldingFlexibleWorkGang("Parallel CMS Threads",
 631                                  ConcGCThreads, true);
 632       if (_conc_workers == NULL) {
 633         warning("GC/CMS: _conc_workers allocation failure: "
 634               "forcing -CMSConcurrentMTEnabled");
 635         CMSConcurrentMTEnabled = false;
 636       } else {
 637         _conc_workers->initialize_workers();
 638       }
 639     } else {
 640       CMSConcurrentMTEnabled = false;
 641     }
 642   }
 643   if (!CMSConcurrentMTEnabled) {
 644     ConcGCThreads = 0;
 645   } else {
 646     // Turn off CMSCleanOnEnter optimization temporarily for
 647     // the MT case where it's not fixed yet; see 6178663.
 648     CMSCleanOnEnter = false;
 649   }
 650   assert((_conc_workers != NULL) == (ConcGCThreads > 1),
 651          "Inconsistency");
 652 
 653   // Parallel task queues; these are shared for the
 654   // concurrent and stop-world phases of CMS, but
 655   // are not shared with parallel scavenge (ParNew).
 656   {
 657     uint i;
 658     uint num_queues = (uint) MAX2(ParallelGCThreads, ConcGCThreads);
 659 
 660     if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled
 661          || ParallelRefProcEnabled)
 662         && num_queues > 0) {
 663       _task_queues = new OopTaskQueueSet(num_queues);
 664       if (_task_queues == NULL) {
 665         warning("task_queues allocation failure.");
 666         return;
 667       }
 668       _hash_seed = NEW_C_HEAP_ARRAY(int, num_queues, mtGC);
 669       if (_hash_seed == NULL) {
 670         warning("_hash_seed array allocation failure");
 671         return;
 672       }
 673 
 674       typedef Padded<OopTaskQueue> PaddedOopTaskQueue;
 675       for (i = 0; i < num_queues; i++) {
 676         PaddedOopTaskQueue *q = new PaddedOopTaskQueue();
 677         if (q == NULL) {
 678           warning("work_queue allocation failure.");
 679           return;
 680         }
 681         _task_queues->register_queue(i, q);
 682       }
 683       for (i = 0; i < num_queues; i++) {
 684         _task_queues->queue(i)->initialize();
 685         _hash_seed[i] = 17;  // copied from ParNew
 686       }
 687     }
 688   }
 689 
 690   _cmsGen ->init_initiating_occupancy(CMSInitiatingOccupancyFraction, CMSTriggerRatio);
 691 
 692   // Clip CMSBootstrapOccupancy between 0 and 100.
 693   _bootstrap_occupancy = ((double)MIN2((uintx)100, MAX2((uintx)0, CMSBootstrapOccupancy)))
 694                          /(double)100;
 695 
 696   _full_gcs_since_conc_gc = 0;
 697 
 698   // Now tell CMS generations the identity of their collector
 699   ConcurrentMarkSweepGeneration::set_collector(this);
 700 
 701   // Create & start a CMS thread for this CMS collector
 702   _cmsThread = ConcurrentMarkSweepThread::start(this);
 703   assert(cmsThread() != NULL, "CMS Thread should have been created");
 704   assert(cmsThread()->collector() == this,
 705          "CMS Thread should refer to this gen");
 706   assert(CGC_lock != NULL, "Where's the CGC_lock?");
 707 
 708   // Support for parallelizing young gen rescan
 709   GenCollectedHeap* gch = GenCollectedHeap::heap();
 710   _young_gen = gch->prev_gen(_cmsGen);
 711   if (gch->supports_inline_contig_alloc()) {
 712     _top_addr = gch->top_addr();
 713     _end_addr = gch->end_addr();
 714     assert(_young_gen != NULL, "no _young_gen");
 715     _eden_chunk_index = 0;
 716     _eden_chunk_capacity = (_young_gen->max_capacity()+CMSSamplingGrain)/CMSSamplingGrain;
 717     _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity, mtGC);
 718     if (_eden_chunk_array == NULL) {
 719       _eden_chunk_capacity = 0;
 720       warning("GC/CMS: _eden_chunk_array allocation failure");
 721     }
 722   }
 723   assert(_eden_chunk_array != NULL || _eden_chunk_capacity == 0, "Error");
 724 
 725   // Support for parallelizing survivor space rescan
 726   if (CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) {
 727     const size_t max_plab_samples =
 728       ((DefNewGeneration*)_young_gen)->max_survivor_size()/MinTLABSize;
 729 
 730     _survivor_plab_array  = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads, mtGC);
 731     _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, 2*max_plab_samples, mtGC);
 732     _cursor               = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads, mtGC);
 733     if (_survivor_plab_array == NULL || _survivor_chunk_array == NULL
 734         || _cursor == NULL) {
 735       warning("Failed to allocate survivor plab/chunk array");
 736       if (_survivor_plab_array  != NULL) {
 737         FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array, mtGC);
 738         _survivor_plab_array = NULL;
 739       }
 740       if (_survivor_chunk_array != NULL) {
 741         FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array, mtGC);
 742         _survivor_chunk_array = NULL;
 743       }
 744       if (_cursor != NULL) {
 745         FREE_C_HEAP_ARRAY(size_t, _cursor, mtGC);
 746         _cursor = NULL;
 747       }
 748     } else {
 749       _survivor_chunk_capacity = 2*max_plab_samples;
 750       for (uint i = 0; i < ParallelGCThreads; i++) {
 751         HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
 752         if (vec == NULL) {
 753           warning("Failed to allocate survivor plab array");
 754           for (int j = i; j > 0; j--) {
 755             FREE_C_HEAP_ARRAY(HeapWord*, _survivor_plab_array[j-1].array(), mtGC);
 756           }
 757           FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array, mtGC);
 758           FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array, mtGC);
 759           _survivor_plab_array = NULL;
 760           _survivor_chunk_array = NULL;
 761           _survivor_chunk_capacity = 0;
 762           break;
 763         } else {
 764           ChunkArray* cur =
 765             ::new (&_survivor_plab_array[i]) ChunkArray(vec,
 766                                                         max_plab_samples);
 767           assert(cur->end() == 0, "Should be 0");
 768           assert(cur->array() == vec, "Should be vec");
 769           assert(cur->capacity() == max_plab_samples, "Error");
 770         }
 771       }
 772     }
 773   }
 774   assert(   (   _survivor_plab_array  != NULL
 775              && _survivor_chunk_array != NULL)
 776          || (   _survivor_chunk_capacity == 0
 777              && _survivor_chunk_index == 0),
 778          "Error");
 779 
 780   // Choose what strong roots should be scanned depending on verification options
 781   if (!CMSClassUnloadingEnabled) {
 782     // If class unloading is disabled we want to include all classes into the root set.
 783     add_root_scanning_option(SharedHeap::SO_AllClasses);
 784   } else {
 785     add_root_scanning_option(SharedHeap::SO_SystemClasses);
 786   }
 787 
 788   NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;)
 789   _gc_counters = new CollectorCounters("CMS", 1);
 790   _completed_initialization = true;
 791   _inter_sweep_timer.start();  // start of time
 792 }
 793 
 794 const char* ConcurrentMarkSweepGeneration::name() const {
 795   return "concurrent mark-sweep generation";
 796 }
 797 void ConcurrentMarkSweepGeneration::update_counters() {
 798   if (UsePerfData) {
 799     _space_counters->update_all();
 800     _gen_counters->update_all();
 801   }
 802 }
 803 
 804 // this is an optimized version of update_counters(). it takes the
 805 // used value as a parameter rather than computing it.
 806 //
 807 void ConcurrentMarkSweepGeneration::update_counters(size_t used) {
 808   if (UsePerfData) {
 809     _space_counters->update_used(used);
 810     _space_counters->update_capacity();
 811     _gen_counters->update_all();
 812   }
 813 }
 814 
 815 void ConcurrentMarkSweepGeneration::print() const {
 816   Generation::print();
 817   cmsSpace()->print();
 818 }
 819 
 820 #ifndef PRODUCT
 821 void ConcurrentMarkSweepGeneration::print_statistics() {
 822   cmsSpace()->printFLCensus(0);
 823 }
 824 #endif
 825 
 826 void ConcurrentMarkSweepGeneration::printOccupancy(const char *s) {
 827   GenCollectedHeap* gch = GenCollectedHeap::heap();
 828   if (PrintGCDetails) {
 829     if (Verbose) {
 830       gclog_or_tty->print("[%d %s-%s: "SIZE_FORMAT"("SIZE_FORMAT")]",
 831         level(), short_name(), s, used(), capacity());
 832     } else {
 833       gclog_or_tty->print("[%d %s-%s: "SIZE_FORMAT"K("SIZE_FORMAT"K)]",
 834         level(), short_name(), s, used() / K, capacity() / K);
 835     }
 836   }
 837   if (Verbose) {
 838     gclog_or_tty->print(" "SIZE_FORMAT"("SIZE_FORMAT")",
 839               gch->used(), gch->capacity());
 840   } else {
 841     gclog_or_tty->print(" "SIZE_FORMAT"K("SIZE_FORMAT"K)",
 842               gch->used() / K, gch->capacity() / K);
 843   }
 844 }
 845 
 846 size_t
 847 ConcurrentMarkSweepGeneration::contiguous_available() const {
 848   // dld proposes an improvement in precision here. If the committed
 849   // part of the space ends in a free block we should add that to
 850   // uncommitted size in the calculation below. Will make this
 851   // change later, staying with the approximation below for the
 852   // time being. -- ysr.
 853   return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc());
 854 }
 855 
 856 size_t
 857 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const {
 858   return _cmsSpace->max_alloc_in_words() * HeapWordSize;
 859 }
 860 
 861 size_t ConcurrentMarkSweepGeneration::max_available() const {
 862   return free() + _virtual_space.uncommitted_size();
 863 }
 864 
 865 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(size_t max_promotion_in_bytes) const {
 866   size_t available = max_available();
 867   size_t av_promo  = (size_t)gc_stats()->avg_promoted()->padded_average();
 868   bool   res = (available >= av_promo) || (available >= max_promotion_in_bytes);
 869   if (Verbose && PrintGCDetails) {
 870     gclog_or_tty->print_cr(
 871       "CMS: promo attempt is%s safe: available("SIZE_FORMAT") %s av_promo("SIZE_FORMAT"),"
 872       "max_promo("SIZE_FORMAT")",
 873       res? "":" not", available, res? ">=":"<",
 874       av_promo, max_promotion_in_bytes);
 875   }
 876   return res;
 877 }
 878 
 879 // At a promotion failure dump information on block layout in heap
 880 // (cms old generation).
 881 void ConcurrentMarkSweepGeneration::promotion_failure_occurred() {
 882   if (CMSDumpAtPromotionFailure) {
 883     cmsSpace()->dump_at_safepoint_with_locks(collector(), gclog_or_tty);
 884   }
 885 }
 886 
 887 CompactibleSpace*
 888 ConcurrentMarkSweepGeneration::first_compaction_space() const {
 889   return _cmsSpace;
 890 }
 891 
 892 void ConcurrentMarkSweepGeneration::reset_after_compaction() {
 893   // Clear the promotion information.  These pointers can be adjusted
 894   // along with all the other pointers into the heap but
 895   // compaction is expected to be a rare event with
 896   // a heap using cms so don't do it without seeing the need.
 897   if (CollectedHeap::use_parallel_gc_threads()) {
 898     for (uint i = 0; i < ParallelGCThreads; i++) {
 899       _par_gc_thread_states[i]->promo.reset();
 900     }
 901   }
 902 }
 903 
 904 void ConcurrentMarkSweepGeneration::space_iterate(SpaceClosure* blk, bool usedOnly) {
 905   blk->do_space(_cmsSpace);
 906 }
 907 
 908 void ConcurrentMarkSweepGeneration::compute_new_size() {
 909   assert_locked_or_safepoint(Heap_lock);
 910 
 911   // If incremental collection failed, we just want to expand
 912   // to the limit.
 913   if (incremental_collection_failed()) {
 914     clear_incremental_collection_failed();
 915     grow_to_reserved();
 916     return;
 917   }
 918 
 919   size_t expand_bytes = 0;
 920   double free_percentage = ((double) free()) / capacity();
 921   double desired_free_percentage = (double) MinHeapFreeRatio / 100;
 922   double maximum_free_percentage = (double) MaxHeapFreeRatio / 100;
 923 
 924   // compute expansion delta needed for reaching desired free percentage
 925   if (free_percentage < desired_free_percentage) {
 926     size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
 927     assert(desired_capacity >= capacity(), "invalid expansion size");
 928     expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes);
 929   }
 930   if (expand_bytes > 0) {
 931     if (PrintGCDetails && Verbose) {
 932       size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
 933       gclog_or_tty->print_cr("\nFrom compute_new_size: ");
 934       gclog_or_tty->print_cr("  Free fraction %f", free_percentage);
 935       gclog_or_tty->print_cr("  Desired free fraction %f",
 936         desired_free_percentage);
 937       gclog_or_tty->print_cr("  Maximum free fraction %f",
 938         maximum_free_percentage);
 939       gclog_or_tty->print_cr("  Capactiy "SIZE_FORMAT, capacity()/1000);
 940       gclog_or_tty->print_cr("  Desired capacity "SIZE_FORMAT,
 941         desired_capacity/1000);
 942       int prev_level = level() - 1;
 943       if (prev_level >= 0) {
 944         size_t prev_size = 0;
 945         GenCollectedHeap* gch = GenCollectedHeap::heap();
 946         Generation* prev_gen = gch->_gens[prev_level];
 947         prev_size = prev_gen->capacity();
 948           gclog_or_tty->print_cr("  Younger gen size "SIZE_FORMAT,
 949                                  prev_size/1000);
 950       }
 951       gclog_or_tty->print_cr("  unsafe_max_alloc_nogc "SIZE_FORMAT,
 952         unsafe_max_alloc_nogc()/1000);
 953       gclog_or_tty->print_cr("  contiguous available "SIZE_FORMAT,
 954         contiguous_available()/1000);
 955       gclog_or_tty->print_cr("  Expand by "SIZE_FORMAT" (bytes)",
 956         expand_bytes);
 957     }
 958     // safe if expansion fails
 959     expand(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio);
 960     if (PrintGCDetails && Verbose) {
 961       gclog_or_tty->print_cr("  Expanded free fraction %f",
 962         ((double) free()) / capacity());
 963     }
 964   }
 965 }
 966 
 967 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const {
 968   return cmsSpace()->freelistLock();
 969 }
 970 
 971 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size,
 972                                                   bool   tlab) {
 973   CMSSynchronousYieldRequest yr;
 974   MutexLockerEx x(freelistLock(),
 975                   Mutex::_no_safepoint_check_flag);
 976   return have_lock_and_allocate(size, tlab);
 977 }
 978 
 979 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size,
 980                                                   bool   tlab /* ignored */) {
 981   assert_lock_strong(freelistLock());
 982   size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size);
 983   HeapWord* res = cmsSpace()->allocate(adjustedSize);
 984   // Allocate the object live (grey) if the background collector has
 985   // started marking. This is necessary because the marker may
 986   // have passed this address and consequently this object will
 987   // not otherwise be greyed and would be incorrectly swept up.
 988   // Note that if this object contains references, the writing
 989   // of those references will dirty the card containing this object
 990   // allowing the object to be blackened (and its references scanned)
 991   // either during a preclean phase or at the final checkpoint.
 992   if (res != NULL) {
 993     // We may block here with an uninitialized object with
 994     // its mark-bit or P-bits not yet set. Such objects need
 995     // to be safely navigable by block_start().
 996     assert(oop(res)->klass_or_null() == NULL, "Object should be uninitialized here.");
 997     assert(!((FreeChunk*)res)->is_free(), "Error, block will look free but show wrong size");
 998     collector()->direct_allocated(res, adjustedSize);
 999     _direct_allocated_words += adjustedSize;
1000     // allocation counters
1001     NOT_PRODUCT(
1002       _numObjectsAllocated++;
1003       _numWordsAllocated += (int)adjustedSize;
1004     )
1005   }
1006   return res;
1007 }
1008 
1009 // In the case of direct allocation by mutators in a generation that
1010 // is being concurrently collected, the object must be allocated
1011 // live (grey) if the background collector has started marking.
1012 // This is necessary because the marker may
1013 // have passed this address and consequently this object will
1014 // not otherwise be greyed and would be incorrectly swept up.
1015 // Note that if this object contains references, the writing
1016 // of those references will dirty the card containing this object
1017 // allowing the object to be blackened (and its references scanned)
1018 // either during a preclean phase or at the final checkpoint.
1019 void CMSCollector::direct_allocated(HeapWord* start, size_t size) {
1020   assert(_markBitMap.covers(start, size), "Out of bounds");
1021   if (_collectorState >= Marking) {
1022     MutexLockerEx y(_markBitMap.lock(),
1023                     Mutex::_no_safepoint_check_flag);
1024     // [see comments preceding SweepClosure::do_blk() below for details]
1025     //
1026     // Can the P-bits be deleted now?  JJJ
1027     //
1028     // 1. need to mark the object as live so it isn't collected
1029     // 2. need to mark the 2nd bit to indicate the object may be uninitialized
1030     // 3. need to mark the end of the object so marking, precleaning or sweeping
1031     //    can skip over uninitialized or unparsable objects. An allocated
1032     //    object is considered uninitialized for our purposes as long as
1033     //    its klass word is NULL.  All old gen objects are parsable
1034     //    as soon as they are initialized.)
1035     _markBitMap.mark(start);          // object is live
1036     _markBitMap.mark(start + 1);      // object is potentially uninitialized?
1037     _markBitMap.mark(start + size - 1);
1038                                       // mark end of object
1039   }
1040   // check that oop looks uninitialized
1041   assert(oop(start)->klass_or_null() == NULL, "_klass should be NULL");
1042 }
1043 
1044 void CMSCollector::promoted(bool par, HeapWord* start,
1045                             bool is_obj_array, size_t obj_size) {
1046   assert(_markBitMap.covers(start), "Out of bounds");
1047   // See comment in direct_allocated() about when objects should
1048   // be allocated live.
1049   if (_collectorState >= Marking) {
1050     // we already hold the marking bit map lock, taken in
1051     // the prologue
1052     if (par) {
1053       _markBitMap.par_mark(start);
1054     } else {
1055       _markBitMap.mark(start);
1056     }
1057     // We don't need to mark the object as uninitialized (as
1058     // in direct_allocated above) because this is being done with the
1059     // world stopped and the object will be initialized by the
1060     // time the marking, precleaning or sweeping get to look at it.
1061     // But see the code for copying objects into the CMS generation,
1062     // where we need to ensure that concurrent readers of the
1063     // block offset table are able to safely navigate a block that
1064     // is in flux from being free to being allocated (and in
1065     // transition while being copied into) and subsequently
1066     // becoming a bona-fide object when the copy/promotion is complete.
1067     assert(SafepointSynchronize::is_at_safepoint(),
1068            "expect promotion only at safepoints");
1069 
1070     if (_collectorState < Sweeping) {
1071       // Mark the appropriate cards in the modUnionTable, so that
1072       // this object gets scanned before the sweep. If this is
1073       // not done, CMS generation references in the object might
1074       // not get marked.
1075       // For the case of arrays, which are otherwise precisely
1076       // marked, we need to dirty the entire array, not just its head.
1077       if (is_obj_array) {
1078         // The [par_]mark_range() method expects mr.end() below to
1079         // be aligned to the granularity of a bit's representation
1080         // in the heap. In the case of the MUT below, that's a
1081         // card size.
1082         MemRegion mr(start,
1083                      (HeapWord*)round_to((intptr_t)(start + obj_size),
1084                         CardTableModRefBS::card_size /* bytes */));
1085         if (par) {
1086           _modUnionTable.par_mark_range(mr);
1087         } else {
1088           _modUnionTable.mark_range(mr);
1089         }
1090       } else {  // not an obj array; we can just mark the head
1091         if (par) {
1092           _modUnionTable.par_mark(start);
1093         } else {
1094           _modUnionTable.mark(start);
1095         }
1096       }
1097     }
1098   }
1099 }
1100 
1101 static inline size_t percent_of_space(Space* space, HeapWord* addr)
1102 {
1103   size_t delta = pointer_delta(addr, space->bottom());
1104   return (size_t)(delta * 100.0 / (space->capacity() / HeapWordSize));
1105 }
1106 
1107 void CMSCollector::icms_update_allocation_limits()
1108 {
1109   Generation* gen0 = GenCollectedHeap::heap()->get_gen(0);
1110   EdenSpace* eden = gen0->as_DefNewGeneration()->eden();
1111 
1112   const unsigned int duty_cycle = stats().icms_update_duty_cycle();
1113   if (CMSTraceIncrementalPacing) {
1114     stats().print();
1115   }
1116 
1117   assert(duty_cycle <= 100, "invalid duty cycle");
1118   if (duty_cycle != 0) {
1119     // The duty_cycle is a percentage between 0 and 100; convert to words and
1120     // then compute the offset from the endpoints of the space.
1121     size_t free_words = eden->free() / HeapWordSize;
1122     double free_words_dbl = (double)free_words;
1123     size_t duty_cycle_words = (size_t)(free_words_dbl * duty_cycle / 100.0);
1124     size_t offset_words = (free_words - duty_cycle_words) / 2;
1125 
1126     _icms_start_limit = eden->top() + offset_words;
1127     _icms_stop_limit = eden->end() - offset_words;
1128 
1129     // The limits may be adjusted (shifted to the right) by
1130     // CMSIncrementalOffset, to allow the application more mutator time after a
1131     // young gen gc (when all mutators were stopped) and before CMS starts and
1132     // takes away one or more cpus.
1133     if (CMSIncrementalOffset != 0) {
1134       double adjustment_dbl = free_words_dbl * CMSIncrementalOffset / 100.0;
1135       size_t adjustment = (size_t)adjustment_dbl;
1136       HeapWord* tmp_stop = _icms_stop_limit + adjustment;
1137       if (tmp_stop > _icms_stop_limit && tmp_stop < eden->end()) {
1138         _icms_start_limit += adjustment;
1139         _icms_stop_limit = tmp_stop;
1140       }
1141     }
1142   }
1143   if (duty_cycle == 0 || (_icms_start_limit == _icms_stop_limit)) {
1144     _icms_start_limit = _icms_stop_limit = eden->end();
1145   }
1146 
1147   // Install the new start limit.
1148   eden->set_soft_end(_icms_start_limit);
1149 
1150   if (CMSTraceIncrementalMode) {
1151     gclog_or_tty->print(" icms alloc limits:  "
1152                            PTR_FORMAT "," PTR_FORMAT
1153                            " (" SIZE_FORMAT "%%," SIZE_FORMAT "%%) ",
1154                            _icms_start_limit, _icms_stop_limit,
1155                            percent_of_space(eden, _icms_start_limit),
1156                            percent_of_space(eden, _icms_stop_limit));
1157     if (Verbose) {
1158       gclog_or_tty->print("eden:  ");
1159       eden->print_on(gclog_or_tty);
1160     }
1161   }
1162 }
1163 
1164 // Any changes here should try to maintain the invariant
1165 // that if this method is called with _icms_start_limit
1166 // and _icms_stop_limit both NULL, then it should return NULL
1167 // and not notify the icms thread.
1168 HeapWord*
1169 CMSCollector::allocation_limit_reached(Space* space, HeapWord* top,
1170                                        size_t word_size)
1171 {
1172   // A start_limit equal to end() means the duty cycle is 0, so treat that as a
1173   // nop.
1174   if (CMSIncrementalMode && _icms_start_limit != space->end()) {
1175     if (top <= _icms_start_limit) {
1176       if (CMSTraceIncrementalMode) {
1177         space->print_on(gclog_or_tty);
1178         gclog_or_tty->stamp();
1179         gclog_or_tty->print_cr(" start limit top=" PTR_FORMAT
1180                                ", new limit=" PTR_FORMAT
1181                                " (" SIZE_FORMAT "%%)",
1182                                top, _icms_stop_limit,
1183                                percent_of_space(space, _icms_stop_limit));
1184       }
1185       ConcurrentMarkSweepThread::start_icms();
1186       assert(top < _icms_stop_limit, "Tautology");
1187       if (word_size < pointer_delta(_icms_stop_limit, top)) {
1188         return _icms_stop_limit;
1189       }
1190 
1191       // The allocation will cross both the _start and _stop limits, so do the
1192       // stop notification also and return end().
1193       if (CMSTraceIncrementalMode) {
1194         space->print_on(gclog_or_tty);
1195         gclog_or_tty->stamp();
1196         gclog_or_tty->print_cr(" +stop limit top=" PTR_FORMAT
1197                                ", new limit=" PTR_FORMAT
1198                                " (" SIZE_FORMAT "%%)",
1199                                top, space->end(),
1200                                percent_of_space(space, space->end()));
1201       }
1202       ConcurrentMarkSweepThread::stop_icms();
1203       return space->end();
1204     }
1205 
1206     if (top <= _icms_stop_limit) {
1207       if (CMSTraceIncrementalMode) {
1208         space->print_on(gclog_or_tty);
1209         gclog_or_tty->stamp();
1210         gclog_or_tty->print_cr(" stop limit top=" PTR_FORMAT
1211                                ", new limit=" PTR_FORMAT
1212                                " (" SIZE_FORMAT "%%)",
1213                                top, space->end(),
1214                                percent_of_space(space, space->end()));
1215       }
1216       ConcurrentMarkSweepThread::stop_icms();
1217       return space->end();
1218     }
1219 
1220     if (CMSTraceIncrementalMode) {
1221       space->print_on(gclog_or_tty);
1222       gclog_or_tty->stamp();
1223       gclog_or_tty->print_cr(" end limit top=" PTR_FORMAT
1224                              ", new limit=" PTR_FORMAT,
1225                              top, NULL);
1226     }
1227   }
1228 
1229   return NULL;
1230 }
1231 
1232 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size) {
1233   assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
1234   // allocate, copy and if necessary update promoinfo --
1235   // delegate to underlying space.
1236   assert_lock_strong(freelistLock());
1237 
1238 #ifndef PRODUCT
1239   if (Universe::heap()->promotion_should_fail()) {
1240     return NULL;
1241   }
1242 #endif  // #ifndef PRODUCT
1243 
1244   oop res = _cmsSpace->promote(obj, obj_size);
1245   if (res == NULL) {
1246     // expand and retry
1247     size_t s = _cmsSpace->expansionSpaceRequired(obj_size);  // HeapWords
1248     expand(s*HeapWordSize, MinHeapDeltaBytes,
1249       CMSExpansionCause::_satisfy_promotion);
1250     // Since there's currently no next generation, we don't try to promote
1251     // into a more senior generation.
1252     assert(next_gen() == NULL, "assumption, based upon which no attempt "
1253                                "is made to pass on a possibly failing "
1254                                "promotion to next generation");
1255     res = _cmsSpace->promote(obj, obj_size);
1256   }
1257   if (res != NULL) {
1258     // See comment in allocate() about when objects should
1259     // be allocated live.
1260     assert(obj->is_oop(), "Will dereference klass pointer below");
1261     collector()->promoted(false,           // Not parallel
1262                           (HeapWord*)res, obj->is_objArray(), obj_size);
1263     // promotion counters
1264     NOT_PRODUCT(
1265       _numObjectsPromoted++;
1266       _numWordsPromoted +=
1267         (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size()));
1268     )
1269   }
1270   return res;
1271 }
1272 
1273 
1274 HeapWord*
1275 ConcurrentMarkSweepGeneration::allocation_limit_reached(Space* space,
1276                                              HeapWord* top,
1277                                              size_t word_sz)
1278 {
1279   return collector()->allocation_limit_reached(space, top, word_sz);
1280 }
1281 
1282 // IMPORTANT: Notes on object size recognition in CMS.
1283 // ---------------------------------------------------
1284 // A block of storage in the CMS generation is always in
1285 // one of three states. A free block (FREE), an allocated
1286 // object (OBJECT) whose size() method reports the correct size,
1287 // and an intermediate state (TRANSIENT) in which its size cannot
1288 // be accurately determined.
1289 // STATE IDENTIFICATION:   (32 bit and 64 bit w/o COOPS)
1290 // -----------------------------------------------------
1291 // FREE:      klass_word & 1 == 1; mark_word holds block size
1292 //
1293 // OBJECT:    klass_word installed; klass_word != 0 && klass_word & 1 == 0;
1294 //            obj->size() computes correct size
1295 //
1296 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1297 //
1298 // STATE IDENTIFICATION: (64 bit+COOPS)
1299 // ------------------------------------
1300 // FREE:      mark_word & CMS_FREE_BIT == 1; mark_word & ~CMS_FREE_BIT gives block_size
1301 //
1302 // OBJECT:    klass_word installed; klass_word != 0;
1303 //            obj->size() computes correct size
1304 //
1305 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1306 //
1307 //
1308 // STATE TRANSITION DIAGRAM
1309 //
1310 //        mut / parnew                     mut  /  parnew
1311 // FREE --------------------> TRANSIENT ---------------------> OBJECT --|
1312 //  ^                                                                   |
1313 //  |------------------------ DEAD <------------------------------------|
1314 //         sweep                            mut
1315 //
1316 // While a block is in TRANSIENT state its size cannot be determined
1317 // so readers will either need to come back later or stall until
1318 // the size can be determined. Note that for the case of direct
1319 // allocation, P-bits, when available, may be used to determine the
1320 // size of an object that may not yet have been initialized.
1321 
1322 // Things to support parallel young-gen collection.
1323 oop
1324 ConcurrentMarkSweepGeneration::par_promote(int thread_num,
1325                                            oop old, markOop m,
1326                                            size_t word_sz) {
1327 #ifndef PRODUCT
1328   if (Universe::heap()->promotion_should_fail()) {
1329     return NULL;
1330   }
1331 #endif  // #ifndef PRODUCT
1332 
1333   CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1334   PromotionInfo* promoInfo = &ps->promo;
1335   // if we are tracking promotions, then first ensure space for
1336   // promotion (including spooling space for saving header if necessary).
1337   // then allocate and copy, then track promoted info if needed.
1338   // When tracking (see PromotionInfo::track()), the mark word may
1339   // be displaced and in this case restoration of the mark word
1340   // occurs in the (oop_since_save_marks_)iterate phase.
1341   if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) {
1342     // Out of space for allocating spooling buffers;
1343     // try expanding and allocating spooling buffers.
1344     if (!expand_and_ensure_spooling_space(promoInfo)) {
1345       return NULL;
1346     }
1347   }
1348   assert(promoInfo->has_spooling_space(), "Control point invariant");
1349   const size_t alloc_sz = CompactibleFreeListSpace::adjustObjectSize(word_sz);
1350   HeapWord* obj_ptr = ps->lab.alloc(alloc_sz);
1351   if (obj_ptr == NULL) {
1352      obj_ptr = expand_and_par_lab_allocate(ps, alloc_sz);
1353      if (obj_ptr == NULL) {
1354        return NULL;
1355      }
1356   }
1357   oop obj = oop(obj_ptr);
1358   OrderAccess::storestore();
1359   assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1360   assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1361   // IMPORTANT: See note on object initialization for CMS above.
1362   // Otherwise, copy the object.  Here we must be careful to insert the
1363   // klass pointer last, since this marks the block as an allocated object.
1364   // Except with compressed oops it's the mark word.
1365   HeapWord* old_ptr = (HeapWord*)old;
1366   // Restore the mark word copied above.
1367   obj->set_mark(m);
1368   assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1369   assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1370   OrderAccess::storestore();
1371 
1372   if (UseCompressedKlassPointers) {
1373     // Copy gap missed by (aligned) header size calculation below
1374     obj->set_klass_gap(old->klass_gap());
1375   }
1376   if (word_sz > (size_t)oopDesc::header_size()) {
1377     Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1378                                  obj_ptr + oopDesc::header_size(),
1379                                  word_sz - oopDesc::header_size());
1380   }
1381 
1382   // Now we can track the promoted object, if necessary.  We take care
1383   // to delay the transition from uninitialized to full object
1384   // (i.e., insertion of klass pointer) until after, so that it
1385   // atomically becomes a promoted object.
1386   if (promoInfo->tracking()) {
1387     promoInfo->track((PromotedObject*)obj, old->klass());
1388   }
1389   assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1390   assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1391   assert(old->is_oop(), "Will use and dereference old klass ptr below");
1392 
1393   // Finally, install the klass pointer (this should be volatile).
1394   OrderAccess::storestore();
1395   obj->set_klass(old->klass());
1396   // We should now be able to calculate the right size for this object
1397   assert(obj->is_oop() && obj->size() == (int)word_sz, "Error, incorrect size computed for promoted object");
1398 
1399   collector()->promoted(true,          // parallel
1400                         obj_ptr, old->is_objArray(), word_sz);
1401 
1402   NOT_PRODUCT(
1403     Atomic::inc_ptr(&_numObjectsPromoted);
1404     Atomic::add_ptr(alloc_sz, &_numWordsPromoted);
1405   )
1406 
1407   return obj;
1408 }
1409 
1410 void
1411 ConcurrentMarkSweepGeneration::
1412 par_promote_alloc_undo(int thread_num,
1413                        HeapWord* obj, size_t word_sz) {
1414   // CMS does not support promotion undo.
1415   ShouldNotReachHere();
1416 }
1417 
1418 void
1419 ConcurrentMarkSweepGeneration::
1420 par_promote_alloc_done(int thread_num) {
1421   CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1422   ps->lab.retire(thread_num);
1423 }
1424 
1425 void
1426 ConcurrentMarkSweepGeneration::
1427 par_oop_since_save_marks_iterate_done(int thread_num) {
1428   CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1429   ParScanWithoutBarrierClosure* dummy_cl = NULL;
1430   ps->promo.promoted_oops_iterate_nv(dummy_cl);
1431 }
1432 
1433 bool ConcurrentMarkSweepGeneration::should_collect(bool   full,
1434                                                    size_t size,
1435                                                    bool   tlab)
1436 {
1437   // We allow a STW collection only if a full
1438   // collection was requested.
1439   return full || should_allocate(size, tlab); // FIX ME !!!
1440   // This and promotion failure handling are connected at the
1441   // hip and should be fixed by untying them.
1442 }
1443 
1444 bool CMSCollector::shouldConcurrentCollect() {
1445   if (_full_gc_requested) {
1446     if (Verbose && PrintGCDetails) {
1447       gclog_or_tty->print_cr("CMSCollector: collect because of explicit "
1448                              " gc request (or gc_locker)");
1449     }
1450     return true;
1451   }
1452 
1453   // For debugging purposes, change the type of collection.
1454   // If the rotation is not on the concurrent collection
1455   // type, don't start a concurrent collection.
1456   NOT_PRODUCT(
1457     if (RotateCMSCollectionTypes &&
1458         (_cmsGen->debug_collection_type() !=
1459           ConcurrentMarkSweepGeneration::Concurrent_collection_type)) {
1460       assert(_cmsGen->debug_collection_type() !=
1461         ConcurrentMarkSweepGeneration::Unknown_collection_type,
1462         "Bad cms collection type");
1463       return false;
1464     }
1465   )
1466 
1467   FreelistLocker x(this);
1468   // ------------------------------------------------------------------
1469   // Print out lots of information which affects the initiation of
1470   // a collection.
1471   if (PrintCMSInitiationStatistics && stats().valid()) {
1472     gclog_or_tty->print("CMSCollector shouldConcurrentCollect: ");
1473     gclog_or_tty->stamp();
1474     gclog_or_tty->print_cr("");
1475     stats().print_on(gclog_or_tty);
1476     gclog_or_tty->print_cr("time_until_cms_gen_full %3.7f",
1477       stats().time_until_cms_gen_full());
1478     gclog_or_tty->print_cr("free="SIZE_FORMAT, _cmsGen->free());
1479     gclog_or_tty->print_cr("contiguous_available="SIZE_FORMAT,
1480                            _cmsGen->contiguous_available());
1481     gclog_or_tty->print_cr("promotion_rate=%g", stats().promotion_rate());
1482     gclog_or_tty->print_cr("cms_allocation_rate=%g", stats().cms_allocation_rate());
1483     gclog_or_tty->print_cr("occupancy=%3.7f", _cmsGen->occupancy());
1484     gclog_or_tty->print_cr("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy());
1485     gclog_or_tty->print_cr("metadata initialized %d",
1486       MetaspaceGC::should_concurrent_collect());
1487   }
1488   // ------------------------------------------------------------------
1489 
1490   // If the estimated time to complete a cms collection (cms_duration())
1491   // is less than the estimated time remaining until the cms generation
1492   // is full, start a collection.
1493   if (!UseCMSInitiatingOccupancyOnly) {
1494     if (stats().valid()) {
1495       if (stats().time_until_cms_start() == 0.0) {
1496         return true;
1497       }
1498     } else {
1499       // We want to conservatively collect somewhat early in order
1500       // to try and "bootstrap" our CMS/promotion statistics;
1501       // this branch will not fire after the first successful CMS
1502       // collection because the stats should then be valid.
1503       if (_cmsGen->occupancy() >= _bootstrap_occupancy) {
1504         if (Verbose && PrintGCDetails) {
1505           gclog_or_tty->print_cr(
1506             " CMSCollector: collect for bootstrapping statistics:"
1507             " occupancy = %f, boot occupancy = %f", _cmsGen->occupancy(),
1508             _bootstrap_occupancy);
1509         }
1510         return true;
1511       }
1512     }
1513   }
1514 
1515   // Otherwise, we start a collection cycle if
1516   // old gen want a collection cycle started. Each may use
1517   // an appropriate criterion for making this decision.
1518   // XXX We need to make sure that the gen expansion
1519   // criterion dovetails well with this. XXX NEED TO FIX THIS
1520   if (_cmsGen->should_concurrent_collect()) {
1521     if (Verbose && PrintGCDetails) {
1522       gclog_or_tty->print_cr("CMS old gen initiated");
1523     }
1524     return true;
1525   }
1526 
1527   // We start a collection if we believe an incremental collection may fail;
1528   // this is not likely to be productive in practice because it's probably too
1529   // late anyway.
1530   GenCollectedHeap* gch = GenCollectedHeap::heap();
1531   assert(gch->collector_policy()->is_two_generation_policy(),
1532          "You may want to check the correctness of the following");
1533   if (gch->incremental_collection_will_fail(true /* consult_young */)) {
1534     if (Verbose && PrintGCDetails) {
1535       gclog_or_tty->print("CMSCollector: collect because incremental collection will fail ");
1536     }
1537     return true;
1538   }
1539 
1540   if (MetaspaceGC::should_concurrent_collect()) {
1541       if (Verbose && PrintGCDetails) {
1542       gclog_or_tty->print("CMSCollector: collect for metadata allocation ");
1543       }
1544       return true;
1545     }
1546 
1547   return false;
1548 }
1549 
1550 // Clear _expansion_cause fields of constituent generations
1551 void CMSCollector::clear_expansion_cause() {
1552   _cmsGen->clear_expansion_cause();
1553 }
1554 
1555 // We should be conservative in starting a collection cycle.  To
1556 // start too eagerly runs the risk of collecting too often in the
1557 // extreme.  To collect too rarely falls back on full collections,
1558 // which works, even if not optimum in terms of concurrent work.
1559 // As a work around for too eagerly collecting, use the flag
1560 // UseCMSInitiatingOccupancyOnly.  This also has the advantage of
1561 // giving the user an easily understandable way of controlling the
1562 // collections.
1563 // We want to start a new collection cycle if any of the following
1564 // conditions hold:
1565 // . our current occupancy exceeds the configured initiating occupancy
1566 //   for this generation, or
1567 // . we recently needed to expand this space and have not, since that
1568 //   expansion, done a collection of this generation, or
1569 // . the underlying space believes that it may be a good idea to initiate
1570 //   a concurrent collection (this may be based on criteria such as the
1571 //   following: the space uses linear allocation and linear allocation is
1572 //   going to fail, or there is believed to be excessive fragmentation in
1573 //   the generation, etc... or ...
1574 // [.(currently done by CMSCollector::shouldConcurrentCollect() only for
1575 //   the case of the old generation; see CR 6543076):
1576 //   we may be approaching a point at which allocation requests may fail because
1577 //   we will be out of sufficient free space given allocation rate estimates.]
1578 bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const {
1579 
1580   assert_lock_strong(freelistLock());
1581   if (occupancy() > initiating_occupancy()) {
1582     if (PrintGCDetails && Verbose) {
1583       gclog_or_tty->print(" %s: collect because of occupancy %f / %f  ",
1584         short_name(), occupancy(), initiating_occupancy());
1585     }
1586     return true;
1587   }
1588   if (UseCMSInitiatingOccupancyOnly) {
1589     return false;
1590   }
1591   if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) {
1592     if (PrintGCDetails && Verbose) {
1593       gclog_or_tty->print(" %s: collect because expanded for allocation ",
1594         short_name());
1595     }
1596     return true;
1597   }
1598   if (_cmsSpace->should_concurrent_collect()) {
1599     if (PrintGCDetails && Verbose) {
1600       gclog_or_tty->print(" %s: collect because cmsSpace says so ",
1601         short_name());
1602     }
1603     return true;
1604   }
1605   return false;
1606 }
1607 
1608 void ConcurrentMarkSweepGeneration::collect(bool   full,
1609                                             bool   clear_all_soft_refs,
1610                                             size_t size,
1611                                             bool   tlab)
1612 {
1613   collector()->collect(full, clear_all_soft_refs, size, tlab);
1614 }
1615 
1616 void CMSCollector::collect(bool   full,
1617                            bool   clear_all_soft_refs,
1618                            size_t size,
1619                            bool   tlab)
1620 {
1621   if (!UseCMSCollectionPassing && _collectorState > Idling) {
1622     // For debugging purposes skip the collection if the state
1623     // is not currently idle
1624     if (TraceCMSState) {
1625       gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " skipped full:%d CMS state %d",
1626         Thread::current(), full, _collectorState);
1627     }
1628     return;
1629   }
1630 
1631   // The following "if" branch is present for defensive reasons.
1632   // In the current uses of this interface, it can be replaced with:
1633   // assert(!GC_locker.is_active(), "Can't be called otherwise");
1634   // But I am not placing that assert here to allow future
1635   // generality in invoking this interface.
1636   if (GC_locker::is_active()) {
1637     // A consistency test for GC_locker
1638     assert(GC_locker::needs_gc(), "Should have been set already");
1639     // Skip this foreground collection, instead
1640     // expanding the heap if necessary.
1641     // Need the free list locks for the call to free() in compute_new_size()
1642     compute_new_size();
1643     return;
1644   }
1645   acquire_control_and_collect(full, clear_all_soft_refs);
1646   _full_gcs_since_conc_gc++;
1647 
1648 }
1649 
1650 void CMSCollector::request_full_gc(unsigned int full_gc_count) {
1651   GenCollectedHeap* gch = GenCollectedHeap::heap();
1652   unsigned int gc_count = gch->total_full_collections();
1653   if (gc_count == full_gc_count) {
1654     MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag);
1655     _full_gc_requested = true;
1656     CGC_lock->notify();   // nudge CMS thread
1657   } else {
1658     assert(gc_count > full_gc_count, "Error: causal loop");
1659   }
1660 }
1661 
1662 
1663 // The foreground and background collectors need to coordinate in order
1664 // to make sure that they do not mutually interfere with CMS collections.
1665 // When a background collection is active,
1666 // the foreground collector may need to take over (preempt) and
1667 // synchronously complete an ongoing collection. Depending on the
1668 // frequency of the background collections and the heap usage
1669 // of the application, this preemption can be seldom or frequent.
1670 // There are only certain
1671 // points in the background collection that the "collection-baton"
1672 // can be passed to the foreground collector.
1673 //
1674 // The foreground collector will wait for the baton before
1675 // starting any part of the collection.  The foreground collector
1676 // will only wait at one location.
1677 //
1678 // The background collector will yield the baton before starting a new
1679 // phase of the collection (e.g., before initial marking, marking from roots,
1680 // precleaning, final re-mark, sweep etc.)  This is normally done at the head
1681 // of the loop which switches the phases. The background collector does some
1682 // of the phases (initial mark, final re-mark) with the world stopped.
1683 // Because of locking involved in stopping the world,
1684 // the foreground collector should not block waiting for the background
1685 // collector when it is doing a stop-the-world phase.  The background
1686 // collector will yield the baton at an additional point just before
1687 // it enters a stop-the-world phase.  Once the world is stopped, the
1688 // background collector checks the phase of the collection.  If the
1689 // phase has not changed, it proceeds with the collection.  If the
1690 // phase has changed, it skips that phase of the collection.  See
1691 // the comments on the use of the Heap_lock in collect_in_background().
1692 //
1693 // Variable used in baton passing.
1694 //   _foregroundGCIsActive - Set to true by the foreground collector when
1695 //      it wants the baton.  The foreground clears it when it has finished
1696 //      the collection.
1697 //   _foregroundGCShouldWait - Set to true by the background collector
1698 //        when it is running.  The foreground collector waits while
1699 //      _foregroundGCShouldWait is true.
1700 //  CGC_lock - monitor used to protect access to the above variables
1701 //      and to notify the foreground and background collectors.
1702 //  _collectorState - current state of the CMS collection.
1703 //
1704 // The foreground collector
1705 //   acquires the CGC_lock
1706 //   sets _foregroundGCIsActive
1707 //   waits on the CGC_lock for _foregroundGCShouldWait to be false
1708 //     various locks acquired in preparation for the collection
1709 //     are released so as not to block the background collector
1710 //     that is in the midst of a collection
1711 //   proceeds with the collection
1712 //   clears _foregroundGCIsActive
1713 //   returns
1714 //
1715 // The background collector in a loop iterating on the phases of the
1716 //      collection
1717 //   acquires the CGC_lock
1718 //   sets _foregroundGCShouldWait
1719 //   if _foregroundGCIsActive is set
1720 //     clears _foregroundGCShouldWait, notifies _CGC_lock
1721 //     waits on _CGC_lock for _foregroundGCIsActive to become false
1722 //     and exits the loop.
1723 //   otherwise
1724 //     proceed with that phase of the collection
1725 //     if the phase is a stop-the-world phase,
1726 //       yield the baton once more just before enqueueing
1727 //       the stop-world CMS operation (executed by the VM thread).
1728 //   returns after all phases of the collection are done
1729 //
1730 
1731 void CMSCollector::acquire_control_and_collect(bool full,
1732         bool clear_all_soft_refs) {
1733   assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
1734   assert(!Thread::current()->is_ConcurrentGC_thread(),
1735          "shouldn't try to acquire control from self!");
1736 
1737   // Start the protocol for acquiring control of the
1738   // collection from the background collector (aka CMS thread).
1739   assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1740          "VM thread should have CMS token");
1741   // Remember the possibly interrupted state of an ongoing
1742   // concurrent collection
1743   CollectorState first_state = _collectorState;
1744 
1745   // Signal to a possibly ongoing concurrent collection that
1746   // we want to do a foreground collection.
1747   _foregroundGCIsActive = true;
1748 
1749   // Disable incremental mode during a foreground collection.
1750   ICMSDisabler icms_disabler;
1751 
1752   // release locks and wait for a notify from the background collector
1753   // releasing the locks in only necessary for phases which
1754   // do yields to improve the granularity of the collection.
1755   assert_lock_strong(bitMapLock());
1756   // We need to lock the Free list lock for the space that we are
1757   // currently collecting.
1758   assert(haveFreelistLocks(), "Must be holding free list locks");
1759   bitMapLock()->unlock();
1760   releaseFreelistLocks();
1761   {
1762     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1763     if (_foregroundGCShouldWait) {
1764       // We are going to be waiting for action for the CMS thread;
1765       // it had better not be gone (for instance at shutdown)!
1766       assert(ConcurrentMarkSweepThread::cmst() != NULL,
1767              "CMS thread must be running");
1768       // Wait here until the background collector gives us the go-ahead
1769       ConcurrentMarkSweepThread::clear_CMS_flag(
1770         ConcurrentMarkSweepThread::CMS_vm_has_token);  // release token
1771       // Get a possibly blocked CMS thread going:
1772       //   Note that we set _foregroundGCIsActive true above,
1773       //   without protection of the CGC_lock.
1774       CGC_lock->notify();
1775       assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(),
1776              "Possible deadlock");
1777       while (_foregroundGCShouldWait) {
1778         // wait for notification
1779         CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1780         // Possibility of delay/starvation here, since CMS token does
1781         // not know to give priority to VM thread? Actually, i think
1782         // there wouldn't be any delay/starvation, but the proof of
1783         // that "fact" (?) appears non-trivial. XXX 20011219YSR
1784       }
1785       ConcurrentMarkSweepThread::set_CMS_flag(
1786         ConcurrentMarkSweepThread::CMS_vm_has_token);
1787     }
1788   }
1789   // The CMS_token is already held.  Get back the other locks.
1790   assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1791          "VM thread should have CMS token");
1792   getFreelistLocks();
1793   bitMapLock()->lock_without_safepoint_check();
1794   if (TraceCMSState) {
1795     gclog_or_tty->print_cr("CMS foreground collector has asked for control "
1796       INTPTR_FORMAT " with first state %d", Thread::current(), first_state);
1797     gclog_or_tty->print_cr("    gets control with state %d", _collectorState);
1798   }
1799 
1800   // Check if we need to do a compaction, or if not, whether
1801   // we need to start the mark-sweep from scratch.
1802   bool should_compact    = false;
1803   bool should_start_over = false;
1804   decide_foreground_collection_type(clear_all_soft_refs,
1805     &should_compact, &should_start_over);
1806 
1807 NOT_PRODUCT(
1808   if (RotateCMSCollectionTypes) {
1809     if (_cmsGen->debug_collection_type() ==
1810         ConcurrentMarkSweepGeneration::MSC_foreground_collection_type) {
1811       should_compact = true;
1812     } else if (_cmsGen->debug_collection_type() ==
1813                ConcurrentMarkSweepGeneration::MS_foreground_collection_type) {
1814       should_compact = false;
1815     }
1816   }
1817 )
1818 
1819   if (PrintGCDetails && first_state > Idling) {
1820     GCCause::Cause cause = GenCollectedHeap::heap()->gc_cause();
1821     if (GCCause::is_user_requested_gc(cause) ||
1822         GCCause::is_serviceability_requested_gc(cause)) {
1823       gclog_or_tty->print(" (concurrent mode interrupted)");
1824     } else {
1825       gclog_or_tty->print(" (concurrent mode failure)");
1826     }
1827   }
1828 
1829   if (should_compact) {
1830     // If the collection is being acquired from the background
1831     // collector, there may be references on the discovered
1832     // references lists that have NULL referents (being those
1833     // that were concurrently cleared by a mutator) or
1834     // that are no longer active (having been enqueued concurrently
1835     // by the mutator).
1836     // Scrub the list of those references because Mark-Sweep-Compact
1837     // code assumes referents are not NULL and that all discovered
1838     // Reference objects are active.
1839     ref_processor()->clean_up_discovered_references();
1840 
1841     do_compaction_work(clear_all_soft_refs);
1842 
1843     // Has the GC time limit been exceeded?
1844     DefNewGeneration* young_gen = _young_gen->as_DefNewGeneration();
1845     size_t max_eden_size = young_gen->max_capacity() -
1846                            young_gen->to()->capacity() -
1847                            young_gen->from()->capacity();
1848     GenCollectedHeap* gch = GenCollectedHeap::heap();
1849     GCCause::Cause gc_cause = gch->gc_cause();
1850     size_policy()->check_gc_overhead_limit(_young_gen->used(),
1851                                            young_gen->eden()->used(),
1852                                            _cmsGen->max_capacity(),
1853                                            max_eden_size,
1854                                            full,
1855                                            gc_cause,
1856                                            gch->collector_policy());
1857   } else {
1858     do_mark_sweep_work(clear_all_soft_refs, first_state,
1859       should_start_over);
1860   }
1861   // Reset the expansion cause, now that we just completed
1862   // a collection cycle.
1863   clear_expansion_cause();
1864   _foregroundGCIsActive = false;
1865   return;
1866 }
1867 
1868 // Resize the tenured generation
1869 // after obtaining the free list locks for the
1870 // two generations.
1871 void CMSCollector::compute_new_size() {
1872   assert_locked_or_safepoint(Heap_lock);
1873   FreelistLocker z(this);
1874   MetaspaceGC::compute_new_size();
1875   _cmsGen->compute_new_size();
1876 }
1877 
1878 // A work method used by foreground collection to determine
1879 // what type of collection (compacting or not, continuing or fresh)
1880 // it should do.
1881 // NOTE: the intent is to make UseCMSCompactAtFullCollection
1882 // and CMSCompactWhenClearAllSoftRefs the default in the future
1883 // and do away with the flags after a suitable period.
1884 void CMSCollector::decide_foreground_collection_type(
1885   bool clear_all_soft_refs, bool* should_compact,
1886   bool* should_start_over) {
1887   // Normally, we'll compact only if the UseCMSCompactAtFullCollection
1888   // flag is set, and we have either requested a System.gc() or
1889   // the number of full gc's since the last concurrent cycle
1890   // has exceeded the threshold set by CMSFullGCsBeforeCompaction,
1891   // or if an incremental collection has failed
1892   GenCollectedHeap* gch = GenCollectedHeap::heap();
1893   assert(gch->collector_policy()->is_two_generation_policy(),
1894          "You may want to check the correctness of the following");
1895   // Inform cms gen if this was due to partial collection failing.
1896   // The CMS gen may use this fact to determine its expansion policy.
1897   if (gch->incremental_collection_will_fail(false /* don't consult_young */)) {
1898     assert(!_cmsGen->incremental_collection_failed(),
1899            "Should have been noticed, reacted to and cleared");
1900     _cmsGen->set_incremental_collection_failed();
1901   }
1902   *should_compact =
1903     UseCMSCompactAtFullCollection &&
1904     ((_full_gcs_since_conc_gc >= CMSFullGCsBeforeCompaction) ||
1905      GCCause::is_user_requested_gc(gch->gc_cause()) ||
1906      gch->incremental_collection_will_fail(true /* consult_young */));
1907   *should_start_over = false;
1908   if (clear_all_soft_refs && !*should_compact) {
1909     // We are about to do a last ditch collection attempt
1910     // so it would normally make sense to do a compaction
1911     // to reclaim as much space as possible.
1912     if (CMSCompactWhenClearAllSoftRefs) {
1913       // Default: The rationale is that in this case either
1914       // we are past the final marking phase, in which case
1915       // we'd have to start over, or so little has been done
1916       // that there's little point in saving that work. Compaction
1917       // appears to be the sensible choice in either case.
1918       *should_compact = true;
1919     } else {
1920       // We have been asked to clear all soft refs, but not to
1921       // compact. Make sure that we aren't past the final checkpoint
1922       // phase, for that is where we process soft refs. If we are already
1923       // past that phase, we'll need to redo the refs discovery phase and
1924       // if necessary clear soft refs that weren't previously
1925       // cleared. We do so by remembering the phase in which
1926       // we came in, and if we are past the refs processing
1927       // phase, we'll choose to just redo the mark-sweep
1928       // collection from scratch.
1929       if (_collectorState > FinalMarking) {
1930         // We are past the refs processing phase;
1931         // start over and do a fresh synchronous CMS cycle
1932         _collectorState = Resetting; // skip to reset to start new cycle
1933         reset(false /* == !asynch */);
1934         *should_start_over = true;
1935       } // else we can continue a possibly ongoing current cycle
1936     }
1937   }
1938 }
1939 
1940 // A work method used by the foreground collector to do
1941 // a mark-sweep-compact.
1942 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) {
1943   GenCollectedHeap* gch = GenCollectedHeap::heap();
1944   TraceTime t("CMS:MSC ", PrintGCDetails && Verbose, true, gclog_or_tty);
1945   if (PrintGC && Verbose && !(GCCause::is_user_requested_gc(gch->gc_cause()))) {
1946     gclog_or_tty->print_cr("Compact ConcurrentMarkSweepGeneration after %d "
1947       "collections passed to foreground collector", _full_gcs_since_conc_gc);
1948   }
1949 
1950   // Sample collection interval time and reset for collection pause.
1951   if (UseAdaptiveSizePolicy) {
1952     size_policy()->msc_collection_begin();
1953   }
1954 
1955   // Temporarily widen the span of the weak reference processing to
1956   // the entire heap.
1957   MemRegion new_span(GenCollectedHeap::heap()->reserved_region());
1958   ReferenceProcessorSpanMutator rp_mut_span(ref_processor(), new_span);
1959   // Temporarily, clear the "is_alive_non_header" field of the
1960   // reference processor.
1961   ReferenceProcessorIsAliveMutator rp_mut_closure(ref_processor(), NULL);
1962   // Temporarily make reference _processing_ single threaded (non-MT).
1963   ReferenceProcessorMTProcMutator rp_mut_mt_processing(ref_processor(), false);
1964   // Temporarily make refs discovery atomic
1965   ReferenceProcessorAtomicMutator rp_mut_atomic(ref_processor(), true);
1966   // Temporarily make reference _discovery_ single threaded (non-MT)
1967   ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
1968 
1969   ref_processor()->set_enqueuing_is_done(false);
1970   ref_processor()->enable_discovery(false /*verify_disabled*/, false /*check_no_refs*/);
1971   ref_processor()->setup_policy(clear_all_soft_refs);
1972   // If an asynchronous collection finishes, the _modUnionTable is
1973   // all clear.  If we are assuming the collection from an asynchronous
1974   // collection, clear the _modUnionTable.
1975   assert(_collectorState != Idling || _modUnionTable.isAllClear(),
1976     "_modUnionTable should be clear if the baton was not passed");
1977   _modUnionTable.clear_all();
1978   assert(_collectorState != Idling || _ct->klass_rem_set()->mod_union_is_clear(),
1979     "mod union for klasses should be clear if the baton was passed");
1980   _ct->klass_rem_set()->clear_mod_union();
1981 
1982   // We must adjust the allocation statistics being maintained
1983   // in the free list space. We do so by reading and clearing
1984   // the sweep timer and updating the block flux rate estimates below.
1985   assert(!_intra_sweep_timer.is_active(), "_intra_sweep_timer should be inactive");
1986   if (_inter_sweep_timer.is_active()) {
1987     _inter_sweep_timer.stop();
1988     // Note that we do not use this sample to update the _inter_sweep_estimate.
1989     _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
1990                                             _inter_sweep_estimate.padded_average(),
1991                                             _intra_sweep_estimate.padded_average());
1992   }
1993 
1994   GenMarkSweep::invoke_at_safepoint(_cmsGen->level(),
1995     ref_processor(), clear_all_soft_refs);
1996   #ifdef ASSERT
1997     CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
1998     size_t free_size = cms_space->free();
1999     assert(free_size ==
2000            pointer_delta(cms_space->end(), cms_space->compaction_top())
2001            * HeapWordSize,
2002       "All the free space should be compacted into one chunk at top");
2003     assert(cms_space->dictionary()->total_chunk_size(
2004                                       debug_only(cms_space->freelistLock())) == 0 ||
2005            cms_space->totalSizeInIndexedFreeLists() == 0,
2006       "All the free space should be in a single chunk");
2007     size_t num = cms_space->totalCount();
2008     assert((free_size == 0 && num == 0) ||
2009            (free_size > 0  && (num == 1 || num == 2)),
2010          "There should be at most 2 free chunks after compaction");
2011   #endif // ASSERT
2012   _collectorState = Resetting;
2013   assert(_restart_addr == NULL,
2014          "Should have been NULL'd before baton was passed");
2015   reset(false /* == !asynch */);
2016   _cmsGen->reset_after_compaction();
2017   _concurrent_cycles_since_last_unload = 0;
2018 
2019   // Clear any data recorded in the PLAB chunk arrays.
2020   if (_survivor_plab_array != NULL) {
2021     reset_survivor_plab_arrays();
2022   }
2023 
2024   // Adjust the per-size allocation stats for the next epoch.
2025   _cmsGen->cmsSpace()->endSweepFLCensus(sweep_count() /* fake */);
2026   // Restart the "inter sweep timer" for the next epoch.
2027   _inter_sweep_timer.reset();
2028   _inter_sweep_timer.start();
2029 
2030   // Sample collection pause time and reset for collection interval.
2031   if (UseAdaptiveSizePolicy) {
2032     size_policy()->msc_collection_end(gch->gc_cause());
2033   }
2034 
2035   // For a mark-sweep-compact, compute_new_size() will be called
2036   // in the heap's do_collection() method.
2037 }
2038 
2039 // A work method used by the foreground collector to do
2040 // a mark-sweep, after taking over from a possibly on-going
2041 // concurrent mark-sweep collection.
2042 void CMSCollector::do_mark_sweep_work(bool clear_all_soft_refs,
2043   CollectorState first_state, bool should_start_over) {
2044   if (PrintGC && Verbose) {
2045     gclog_or_tty->print_cr("Pass concurrent collection to foreground "
2046       "collector with count %d",
2047       _full_gcs_since_conc_gc);
2048   }
2049   switch (_collectorState) {
2050     case Idling:
2051       if (first_state == Idling || should_start_over) {
2052         // The background GC was not active, or should
2053         // restarted from scratch;  start the cycle.
2054         _collectorState = InitialMarking;
2055       }
2056       // If first_state was not Idling, then a background GC
2057       // was in progress and has now finished.  No need to do it
2058       // again.  Leave the state as Idling.
2059       break;
2060     case Precleaning:
2061       // In the foreground case don't do the precleaning since
2062       // it is not done concurrently and there is extra work
2063       // required.
2064       _collectorState = FinalMarking;
2065   }
2066   collect_in_foreground(clear_all_soft_refs);
2067 
2068   // For a mark-sweep, compute_new_size() will be called
2069   // in the heap's do_collection() method.
2070 }
2071 
2072 
2073 void CMSCollector::getFreelistLocks() const {
2074   // Get locks for all free lists in all generations that this
2075   // collector is responsible for
2076   _cmsGen->freelistLock()->lock_without_safepoint_check();
2077 }
2078 
2079 void CMSCollector::releaseFreelistLocks() const {
2080   // Release locks for all free lists in all generations that this
2081   // collector is responsible for
2082   _cmsGen->freelistLock()->unlock();
2083 }
2084 
2085 bool CMSCollector::haveFreelistLocks() const {
2086   // Check locks for all free lists in all generations that this
2087   // collector is responsible for
2088   assert_lock_strong(_cmsGen->freelistLock());
2089   PRODUCT_ONLY(ShouldNotReachHere());
2090   return true;
2091 }
2092 
2093 // A utility class that is used by the CMS collector to
2094 // temporarily "release" the foreground collector from its
2095 // usual obligation to wait for the background collector to
2096 // complete an ongoing phase before proceeding.
2097 class ReleaseForegroundGC: public StackObj {
2098  private:
2099   CMSCollector* _c;
2100  public:
2101   ReleaseForegroundGC(CMSCollector* c) : _c(c) {
2102     assert(_c->_foregroundGCShouldWait, "Else should not need to call");
2103     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2104     // allow a potentially blocked foreground collector to proceed
2105     _c->_foregroundGCShouldWait = false;
2106     if (_c->_foregroundGCIsActive) {
2107       CGC_lock->notify();
2108     }
2109     assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2110            "Possible deadlock");
2111   }
2112 
2113   ~ReleaseForegroundGC() {
2114     assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?");
2115     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2116     _c->_foregroundGCShouldWait = true;
2117   }
2118 };
2119 
2120 // There are separate collect_in_background and collect_in_foreground because of
2121 // the different locking requirements of the background collector and the
2122 // foreground collector.  There was originally an attempt to share
2123 // one "collect" method between the background collector and the foreground
2124 // collector but the if-then-else required made it cleaner to have
2125 // separate methods.
2126 void CMSCollector::collect_in_background(bool clear_all_soft_refs) {
2127   assert(Thread::current()->is_ConcurrentGC_thread(),
2128     "A CMS asynchronous collection is only allowed on a CMS thread.");
2129 
2130   GenCollectedHeap* gch = GenCollectedHeap::heap();
2131   {
2132     bool safepoint_check = Mutex::_no_safepoint_check_flag;
2133     MutexLockerEx hl(Heap_lock, safepoint_check);
2134     FreelistLocker fll(this);
2135     MutexLockerEx x(CGC_lock, safepoint_check);
2136     if (_foregroundGCIsActive || !UseAsyncConcMarkSweepGC) {
2137       // The foreground collector is active or we're
2138       // not using asynchronous collections.  Skip this
2139       // background collection.
2140       assert(!_foregroundGCShouldWait, "Should be clear");
2141       return;
2142     } else {
2143       assert(_collectorState == Idling, "Should be idling before start.");
2144       _collectorState = InitialMarking;
2145       // Reset the expansion cause, now that we are about to begin
2146       // a new cycle.
2147       clear_expansion_cause();
2148 
2149       // Clear the MetaspaceGC flag since a concurrent collection
2150       // is starting but also clear it after the collection.
2151       MetaspaceGC::set_should_concurrent_collect(false);
2152     }
2153     // Decide if we want to enable class unloading as part of the
2154     // ensuing concurrent GC cycle.
2155     update_should_unload_classes();
2156     _full_gc_requested = false;           // acks all outstanding full gc requests
2157     // Signal that we are about to start a collection
2158     gch->increment_total_full_collections();  // ... starting a collection cycle
2159     _collection_count_start = gch->total_full_collections();
2160   }
2161 
2162   // Used for PrintGC
2163   size_t prev_used;
2164   if (PrintGC && Verbose) {
2165     prev_used = _cmsGen->used(); // XXXPERM
2166   }
2167 
2168   // The change of the collection state is normally done at this level;
2169   // the exceptions are phases that are executed while the world is
2170   // stopped.  For those phases the change of state is done while the
2171   // world is stopped.  For baton passing purposes this allows the
2172   // background collector to finish the phase and change state atomically.
2173   // The foreground collector cannot wait on a phase that is done
2174   // while the world is stopped because the foreground collector already
2175   // has the world stopped and would deadlock.
2176   while (_collectorState != Idling) {
2177     if (TraceCMSState) {
2178       gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
2179         Thread::current(), _collectorState);
2180     }
2181     // The foreground collector
2182     //   holds the Heap_lock throughout its collection.
2183     //   holds the CMS token (but not the lock)
2184     //     except while it is waiting for the background collector to yield.
2185     //
2186     // The foreground collector should be blocked (not for long)
2187     //   if the background collector is about to start a phase
2188     //   executed with world stopped.  If the background
2189     //   collector has already started such a phase, the
2190     //   foreground collector is blocked waiting for the
2191     //   Heap_lock.  The stop-world phases (InitialMarking and FinalMarking)
2192     //   are executed in the VM thread.
2193     //
2194     // The locking order is
2195     //   PendingListLock (PLL)  -- if applicable (FinalMarking)
2196     //   Heap_lock  (both this & PLL locked in VM_CMS_Operation::prologue())
2197     //   CMS token  (claimed in
2198     //                stop_world_and_do() -->
2199     //                  safepoint_synchronize() -->
2200     //                    CMSThread::synchronize())
2201 
2202     {
2203       // Check if the FG collector wants us to yield.
2204       CMSTokenSync x(true); // is cms thread
2205       if (waitForForegroundGC()) {
2206         // We yielded to a foreground GC, nothing more to be
2207         // done this round.
2208         assert(_foregroundGCShouldWait == false, "We set it to false in "
2209                "waitForForegroundGC()");
2210         if (TraceCMSState) {
2211           gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2212             " exiting collection CMS state %d",
2213             Thread::current(), _collectorState);
2214         }
2215         return;
2216       } else {
2217         // The background collector can run but check to see if the
2218         // foreground collector has done a collection while the
2219         // background collector was waiting to get the CGC_lock
2220         // above.  If yes, break so that _foregroundGCShouldWait
2221         // is cleared before returning.
2222         if (_collectorState == Idling) {
2223           break;
2224         }
2225       }
2226     }
2227 
2228     assert(_foregroundGCShouldWait, "Foreground collector, if active, "
2229       "should be waiting");
2230 
2231     switch (_collectorState) {
2232       case InitialMarking:
2233         {
2234           ReleaseForegroundGC x(this);
2235           stats().record_cms_begin();
2236 
2237           VM_CMS_Initial_Mark initial_mark_op(this);
2238           VMThread::execute(&initial_mark_op);
2239         }
2240         // The collector state may be any legal state at this point
2241         // since the background collector may have yielded to the
2242         // foreground collector.
2243         break;
2244       case Marking:
2245         // initial marking in checkpointRootsInitialWork has been completed
2246         if (markFromRoots(true)) { // we were successful
2247           assert(_collectorState == Precleaning, "Collector state should "
2248             "have changed");
2249         } else {
2250           assert(_foregroundGCIsActive, "Internal state inconsistency");
2251         }
2252         break;
2253       case Precleaning:
2254         if (UseAdaptiveSizePolicy) {
2255           size_policy()->concurrent_precleaning_begin();
2256         }
2257         // marking from roots in markFromRoots has been completed
2258         preclean();
2259         if (UseAdaptiveSizePolicy) {
2260           size_policy()->concurrent_precleaning_end();
2261         }
2262         assert(_collectorState == AbortablePreclean ||
2263                _collectorState == FinalMarking,
2264                "Collector state should have changed");
2265         break;
2266       case AbortablePreclean:
2267         if (UseAdaptiveSizePolicy) {
2268         size_policy()->concurrent_phases_resume();
2269         }
2270         abortable_preclean();
2271         if (UseAdaptiveSizePolicy) {
2272           size_policy()->concurrent_precleaning_end();
2273         }
2274         assert(_collectorState == FinalMarking, "Collector state should "
2275           "have changed");
2276         break;
2277       case FinalMarking:
2278         {
2279           ReleaseForegroundGC x(this);
2280 
2281           VM_CMS_Final_Remark final_remark_op(this);
2282           VMThread::execute(&final_remark_op);
2283         }
2284         assert(_foregroundGCShouldWait, "block post-condition");
2285         break;
2286       case Sweeping:
2287         if (UseAdaptiveSizePolicy) {
2288           size_policy()->concurrent_sweeping_begin();
2289         }
2290         // final marking in checkpointRootsFinal has been completed
2291         sweep(true);
2292         assert(_collectorState == Resizing, "Collector state change "
2293           "to Resizing must be done under the free_list_lock");
2294         _full_gcs_since_conc_gc = 0;
2295 
2296         // Stop the timers for adaptive size policy for the concurrent phases
2297         if (UseAdaptiveSizePolicy) {
2298           size_policy()->concurrent_sweeping_end();
2299           size_policy()->concurrent_phases_end(gch->gc_cause(),
2300                                              gch->prev_gen(_cmsGen)->capacity(),
2301                                              _cmsGen->free());
2302         }
2303 
2304       case Resizing: {
2305         // Sweeping has been completed...
2306         // At this point the background collection has completed.
2307         // Don't move the call to compute_new_size() down
2308         // into code that might be executed if the background
2309         // collection was preempted.
2310         {
2311           ReleaseForegroundGC x(this);   // unblock FG collection
2312           MutexLockerEx       y(Heap_lock, Mutex::_no_safepoint_check_flag);
2313           CMSTokenSync        z(true);   // not strictly needed.
2314           if (_collectorState == Resizing) {
2315             compute_new_size();
2316             _collectorState = Resetting;
2317           } else {
2318             assert(_collectorState == Idling, "The state should only change"
2319                    " because the foreground collector has finished the collection");
2320           }
2321         }
2322         break;
2323       }
2324       case Resetting:
2325         // CMS heap resizing has been completed
2326         reset(true);
2327         assert(_collectorState == Idling, "Collector state should "
2328           "have changed");
2329 
2330         MetaspaceGC::set_should_concurrent_collect(false);
2331 
2332         stats().record_cms_end();
2333         // Don't move the concurrent_phases_end() and compute_new_size()
2334         // calls to here because a preempted background collection
2335         // has it's state set to "Resetting".
2336         break;
2337       case Idling:
2338       default:
2339         ShouldNotReachHere();
2340         break;
2341     }
2342     if (TraceCMSState) {
2343       gclog_or_tty->print_cr("  Thread " INTPTR_FORMAT " done - next CMS state %d",
2344         Thread::current(), _collectorState);
2345     }
2346     assert(_foregroundGCShouldWait, "block post-condition");
2347   }
2348 
2349   // Should this be in gc_epilogue?
2350   collector_policy()->counters()->update_counters();
2351 
2352   {
2353     // Clear _foregroundGCShouldWait and, in the event that the
2354     // foreground collector is waiting, notify it, before
2355     // returning.
2356     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2357     _foregroundGCShouldWait = false;
2358     if (_foregroundGCIsActive) {
2359       CGC_lock->notify();
2360     }
2361     assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2362            "Possible deadlock");
2363   }
2364   if (TraceCMSState) {
2365     gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2366       " exiting collection CMS state %d",
2367       Thread::current(), _collectorState);
2368   }
2369   if (PrintGC && Verbose) {
2370     _cmsGen->print_heap_change(prev_used);
2371   }
2372 }
2373 
2374 void CMSCollector::collect_in_foreground(bool clear_all_soft_refs) {
2375   assert(_foregroundGCIsActive && !_foregroundGCShouldWait,
2376          "Foreground collector should be waiting, not executing");
2377   assert(Thread::current()->is_VM_thread(), "A foreground collection"
2378     "may only be done by the VM Thread with the world stopped");
2379   assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
2380          "VM thread should have CMS token");
2381 
2382   NOT_PRODUCT(TraceTime t("CMS:MS (foreground) ", PrintGCDetails && Verbose,
2383     true, gclog_or_tty);)
2384   if (UseAdaptiveSizePolicy) {
2385     size_policy()->ms_collection_begin();
2386   }
2387   COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact);
2388 
2389   HandleMark hm;  // Discard invalid handles created during verification
2390 
2391   if (VerifyBeforeGC &&
2392       GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2393     Universe::verify();
2394   }
2395 
2396   // Snapshot the soft reference policy to be used in this collection cycle.
2397   ref_processor()->setup_policy(clear_all_soft_refs);
2398 
2399   bool init_mark_was_synchronous = false; // until proven otherwise
2400   while (_collectorState != Idling) {
2401     if (TraceCMSState) {
2402       gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
2403         Thread::current(), _collectorState);
2404     }
2405     switch (_collectorState) {
2406       case InitialMarking:
2407         init_mark_was_synchronous = true;  // fact to be exploited in re-mark
2408         checkpointRootsInitial(false);
2409         assert(_collectorState == Marking, "Collector state should have changed"
2410           " within checkpointRootsInitial()");
2411         break;
2412       case Marking:
2413         // initial marking in checkpointRootsInitialWork has been completed
2414         if (VerifyDuringGC &&
2415             GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2416           gclog_or_tty->print("Verify before initial mark: ");
2417           Universe::verify();
2418         }
2419         {
2420           bool res = markFromRoots(false);
2421           assert(res && _collectorState == FinalMarking, "Collector state should "
2422             "have changed");
2423           break;
2424         }
2425       case FinalMarking:
2426         if (VerifyDuringGC &&
2427             GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2428           gclog_or_tty->print("Verify before re-mark: ");
2429           Universe::verify();
2430         }
2431         checkpointRootsFinal(false, clear_all_soft_refs,
2432                              init_mark_was_synchronous);
2433         assert(_collectorState == Sweeping, "Collector state should not "
2434           "have changed within checkpointRootsFinal()");
2435         break;
2436       case Sweeping:
2437         // final marking in checkpointRootsFinal has been completed
2438         if (VerifyDuringGC &&
2439             GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2440           gclog_or_tty->print("Verify before sweep: ");
2441           Universe::verify();
2442         }
2443         sweep(false);
2444         assert(_collectorState == Resizing, "Incorrect state");
2445         break;
2446       case Resizing: {
2447         // Sweeping has been completed; the actual resize in this case
2448         // is done separately; nothing to be done in this state.
2449         _collectorState = Resetting;
2450         break;
2451       }
2452       case Resetting:
2453         // The heap has been resized.
2454         if (VerifyDuringGC &&
2455             GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2456           gclog_or_tty->print("Verify before reset: ");
2457           Universe::verify();
2458         }
2459         reset(false);
2460         assert(_collectorState == Idling, "Collector state should "
2461           "have changed");
2462         break;
2463       case Precleaning:
2464       case AbortablePreclean:
2465         // Elide the preclean phase
2466         _collectorState = FinalMarking;
2467         break;
2468       default:
2469         ShouldNotReachHere();
2470     }
2471     if (TraceCMSState) {
2472       gclog_or_tty->print_cr("  Thread " INTPTR_FORMAT " done - next CMS state %d",
2473         Thread::current(), _collectorState);
2474     }
2475   }
2476 
2477   if (UseAdaptiveSizePolicy) {
2478     GenCollectedHeap* gch = GenCollectedHeap::heap();
2479     size_policy()->ms_collection_end(gch->gc_cause());
2480   }
2481 
2482   if (VerifyAfterGC &&
2483       GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2484     Universe::verify();
2485   }
2486   if (TraceCMSState) {
2487     gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2488       " exiting collection CMS state %d",
2489       Thread::current(), _collectorState);
2490   }
2491 }
2492 
2493 bool CMSCollector::waitForForegroundGC() {
2494   bool res = false;
2495   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2496          "CMS thread should have CMS token");
2497   // Block the foreground collector until the
2498   // background collectors decides whether to
2499   // yield.
2500   MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2501   _foregroundGCShouldWait = true;
2502   if (_foregroundGCIsActive) {
2503     // The background collector yields to the
2504     // foreground collector and returns a value
2505     // indicating that it has yielded.  The foreground
2506     // collector can proceed.
2507     res = true;
2508     _foregroundGCShouldWait = false;
2509     ConcurrentMarkSweepThread::clear_CMS_flag(
2510       ConcurrentMarkSweepThread::CMS_cms_has_token);
2511     ConcurrentMarkSweepThread::set_CMS_flag(
2512       ConcurrentMarkSweepThread::CMS_cms_wants_token);
2513     // Get a possibly blocked foreground thread going
2514     CGC_lock->notify();
2515     if (TraceCMSState) {
2516       gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d",
2517         Thread::current(), _collectorState);
2518     }
2519     while (_foregroundGCIsActive) {
2520       CGC_lock->wait(Mutex::_no_safepoint_check_flag);
2521     }
2522     ConcurrentMarkSweepThread::set_CMS_flag(
2523       ConcurrentMarkSweepThread::CMS_cms_has_token);
2524     ConcurrentMarkSweepThread::clear_CMS_flag(
2525       ConcurrentMarkSweepThread::CMS_cms_wants_token);
2526   }
2527   if (TraceCMSState) {
2528     gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d",
2529       Thread::current(), _collectorState);
2530   }
2531   return res;
2532 }
2533 
2534 // Because of the need to lock the free lists and other structures in
2535 // the collector, common to all the generations that the collector is
2536 // collecting, we need the gc_prologues of individual CMS generations
2537 // delegate to their collector. It may have been simpler had the
2538 // current infrastructure allowed one to call a prologue on a
2539 // collector. In the absence of that we have the generation's
2540 // prologue delegate to the collector, which delegates back
2541 // some "local" work to a worker method in the individual generations
2542 // that it's responsible for collecting, while itself doing any
2543 // work common to all generations it's responsible for. A similar
2544 // comment applies to the  gc_epilogue()'s.
2545 // The role of the varaible _between_prologue_and_epilogue is to
2546 // enforce the invocation protocol.
2547 void CMSCollector::gc_prologue(bool full) {
2548   // Call gc_prologue_work() for the CMSGen
2549   // we are responsible for.
2550 
2551   // The following locking discipline assumes that we are only called
2552   // when the world is stopped.
2553   assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption");
2554 
2555   // The CMSCollector prologue must call the gc_prologues for the
2556   // "generations" that it's responsible
2557   // for.
2558 
2559   assert(   Thread::current()->is_VM_thread()
2560          || (   CMSScavengeBeforeRemark
2561              && Thread::current()->is_ConcurrentGC_thread()),
2562          "Incorrect thread type for prologue execution");
2563 
2564   if (_between_prologue_and_epilogue) {
2565     // We have already been invoked; this is a gc_prologue delegation
2566     // from yet another CMS generation that we are responsible for, just
2567     // ignore it since all relevant work has already been done.
2568     return;
2569   }
2570 
2571   // set a bit saying prologue has been called; cleared in epilogue
2572   _between_prologue_and_epilogue = true;
2573   // Claim locks for common data structures, then call gc_prologue_work()
2574   // for each CMSGen.
2575 
2576   getFreelistLocks();   // gets free list locks on constituent spaces
2577   bitMapLock()->lock_without_safepoint_check();
2578 
2579   // Should call gc_prologue_work() for all cms gens we are responsible for
2580   bool duringMarking =    _collectorState >= Marking
2581                          && _collectorState < Sweeping;
2582 
2583   // The young collections clear the modified oops state, which tells if
2584   // there are any modified oops in the class. The remark phase also needs
2585   // that information. Tell the young collection to save the union of all
2586   // modified klasses.
2587   if (duringMarking) {
2588     _ct->klass_rem_set()->set_accumulate_modified_oops(true);
2589   }
2590 
2591   bool registerClosure = duringMarking;
2592 
2593   ModUnionClosure* muc = CollectedHeap::use_parallel_gc_threads() ?
2594                                                &_modUnionClosurePar
2595                                                : &_modUnionClosure;
2596   _cmsGen->gc_prologue_work(full, registerClosure, muc);
2597 
2598   if (!full) {
2599     stats().record_gc0_begin();
2600   }
2601 }
2602 
2603 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) {
2604   // Delegate to CMScollector which knows how to coordinate between
2605   // this and any other CMS generations that it is responsible for
2606   // collecting.
2607   collector()->gc_prologue(full);
2608 }
2609 
2610 // This is a "private" interface for use by this generation's CMSCollector.
2611 // Not to be called directly by any other entity (for instance,
2612 // GenCollectedHeap, which calls the "public" gc_prologue method above).
2613 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full,
2614   bool registerClosure, ModUnionClosure* modUnionClosure) {
2615   assert(!incremental_collection_failed(), "Shouldn't be set yet");
2616   assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL,
2617     "Should be NULL");
2618   if (registerClosure) {
2619     cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure);
2620   }
2621   cmsSpace()->gc_prologue();
2622   // Clear stat counters
2623   NOT_PRODUCT(
2624     assert(_numObjectsPromoted == 0, "check");
2625     assert(_numWordsPromoted   == 0, "check");
2626     if (Verbose && PrintGC) {
2627       gclog_or_tty->print("Allocated "SIZE_FORMAT" objects, "
2628                           SIZE_FORMAT" bytes concurrently",
2629       _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord));
2630     }
2631     _numObjectsAllocated = 0;
2632     _numWordsAllocated   = 0;
2633   )
2634 }
2635 
2636 void CMSCollector::gc_epilogue(bool full) {
2637   // The following locking discipline assumes that we are only called
2638   // when the world is stopped.
2639   assert(SafepointSynchronize::is_at_safepoint(),
2640          "world is stopped assumption");
2641 
2642   // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks
2643   // if linear allocation blocks need to be appropriately marked to allow the
2644   // the blocks to be parsable. We also check here whether we need to nudge the
2645   // CMS collector thread to start a new cycle (if it's not already active).
2646   assert(   Thread::current()->is_VM_thread()
2647          || (   CMSScavengeBeforeRemark
2648              && Thread::current()->is_ConcurrentGC_thread()),
2649          "Incorrect thread type for epilogue execution");
2650 
2651   if (!_between_prologue_and_epilogue) {
2652     // We have already been invoked; this is a gc_epilogue delegation
2653     // from yet another CMS generation that we are responsible for, just
2654     // ignore it since all relevant work has already been done.
2655     return;
2656   }
2657   assert(haveFreelistLocks(), "must have freelist locks");
2658   assert_lock_strong(bitMapLock());
2659 
2660   _ct->klass_rem_set()->set_accumulate_modified_oops(false);
2661 
2662   _cmsGen->gc_epilogue_work(full);
2663 
2664   if (_collectorState == AbortablePreclean || _collectorState == Precleaning) {
2665     // in case sampling was not already enabled, enable it
2666     _start_sampling = true;
2667   }
2668   // reset _eden_chunk_array so sampling starts afresh
2669   _eden_chunk_index = 0;
2670 
2671   size_t cms_used   = _cmsGen->cmsSpace()->used();
2672 
2673   // update performance counters - this uses a special version of
2674   // update_counters() that allows the utilization to be passed as a
2675   // parameter, avoiding multiple calls to used().
2676   //
2677   _cmsGen->update_counters(cms_used);
2678 
2679   if (CMSIncrementalMode) {
2680     icms_update_allocation_limits();
2681   }
2682 
2683   bitMapLock()->unlock();
2684   releaseFreelistLocks();
2685 
2686   if (!CleanChunkPoolAsync) {
2687     Chunk::clean_chunk_pool();
2688   }
2689 
2690   _between_prologue_and_epilogue = false;  // ready for next cycle
2691 }
2692 
2693 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) {
2694   collector()->gc_epilogue(full);
2695 
2696   // Also reset promotion tracking in par gc thread states.
2697   if (CollectedHeap::use_parallel_gc_threads()) {
2698     for (uint i = 0; i < ParallelGCThreads; i++) {
2699       _par_gc_thread_states[i]->promo.stopTrackingPromotions(i);
2700     }
2701   }
2702 }
2703 
2704 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2705   assert(!incremental_collection_failed(), "Should have been cleared");
2706   cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2707   cmsSpace()->gc_epilogue();
2708     // Print stat counters
2709   NOT_PRODUCT(
2710     assert(_numObjectsAllocated == 0, "check");
2711     assert(_numWordsAllocated == 0, "check");
2712     if (Verbose && PrintGC) {
2713       gclog_or_tty->print("Promoted "SIZE_FORMAT" objects, "
2714                           SIZE_FORMAT" bytes",
2715                  _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2716     }
2717     _numObjectsPromoted = 0;
2718     _numWordsPromoted   = 0;
2719   )
2720 
2721   if (PrintGC && Verbose) {
2722     // Call down the chain in contiguous_available needs the freelistLock
2723     // so print this out before releasing the freeListLock.
2724     gclog_or_tty->print(" Contiguous available "SIZE_FORMAT" bytes ",
2725                         contiguous_available());
2726   }
2727 }
2728 
2729 #ifndef PRODUCT
2730 bool CMSCollector::have_cms_token() {
2731   Thread* thr = Thread::current();
2732   if (thr->is_VM_thread()) {
2733     return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2734   } else if (thr->is_ConcurrentGC_thread()) {
2735     return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2736   } else if (thr->is_GC_task_thread()) {
2737     return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2738            ParGCRareEvent_lock->owned_by_self();
2739   }
2740   return false;
2741 }
2742 #endif
2743 
2744 // Check reachability of the given heap address in CMS generation,
2745 // treating all other generations as roots.
2746 bool CMSCollector::is_cms_reachable(HeapWord* addr) {
2747   // We could "guarantee" below, rather than assert, but i'll
2748   // leave these as "asserts" so that an adventurous debugger
2749   // could try this in the product build provided some subset of
2750   // the conditions were met, provided they were intersted in the
2751   // results and knew that the computation below wouldn't interfere
2752   // with other concurrent computations mutating the structures
2753   // being read or written.
2754   assert(SafepointSynchronize::is_at_safepoint(),
2755          "Else mutations in object graph will make answer suspect");
2756   assert(have_cms_token(), "Should hold cms token");
2757   assert(haveFreelistLocks(), "must hold free list locks");
2758   assert_lock_strong(bitMapLock());
2759 
2760   // Clear the marking bit map array before starting, but, just
2761   // for kicks, first report if the given address is already marked
2762   gclog_or_tty->print_cr("Start: Address 0x%x is%s marked", addr,
2763                 _markBitMap.isMarked(addr) ? "" : " not");
2764 
2765   if (verify_after_remark()) {
2766     MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2767     bool result = verification_mark_bm()->isMarked(addr);
2768     gclog_or_tty->print_cr("TransitiveMark: Address 0x%x %s marked", addr,
2769                            result ? "IS" : "is NOT");
2770     return result;
2771   } else {
2772     gclog_or_tty->print_cr("Could not compute result");
2773     return false;
2774   }
2775 }
2776 
2777 ////////////////////////////////////////////////////////
2778 // CMS Verification Support
2779 ////////////////////////////////////////////////////////
2780 // Following the remark phase, the following invariant
2781 // should hold -- each object in the CMS heap which is
2782 // marked in markBitMap() should be marked in the verification_mark_bm().
2783 
2784 class VerifyMarkedClosure: public BitMapClosure {
2785   CMSBitMap* _marks;
2786   bool       _failed;
2787 
2788  public:
2789   VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2790 
2791   bool do_bit(size_t offset) {
2792     HeapWord* addr = _marks->offsetToHeapWord(offset);
2793     if (!_marks->isMarked(addr)) {
2794       oop(addr)->print_on(gclog_or_tty);
2795       gclog_or_tty->print_cr(" ("INTPTR_FORMAT" should have been marked)", addr);
2796       _failed = true;
2797     }
2798     return true;
2799   }
2800 
2801   bool failed() { return _failed; }
2802 };
2803 
2804 bool CMSCollector::verify_after_remark() {
2805   gclog_or_tty->print(" [Verifying CMS Marking... ");
2806   MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2807   static bool init = false;
2808 
2809   assert(SafepointSynchronize::is_at_safepoint(),
2810          "Else mutations in object graph will make answer suspect");
2811   assert(have_cms_token(),
2812          "Else there may be mutual interference in use of "
2813          " verification data structures");
2814   assert(_collectorState > Marking && _collectorState <= Sweeping,
2815          "Else marking info checked here may be obsolete");
2816   assert(haveFreelistLocks(), "must hold free list locks");
2817   assert_lock_strong(bitMapLock());
2818 
2819 
2820   // Allocate marking bit map if not already allocated
2821   if (!init) { // first time
2822     if (!verification_mark_bm()->allocate(_span)) {
2823       return false;
2824     }
2825     init = true;
2826   }
2827 
2828   assert(verification_mark_stack()->isEmpty(), "Should be empty");
2829 
2830   // Turn off refs discovery -- so we will be tracing through refs.
2831   // This is as intended, because by this time
2832   // GC must already have cleared any refs that need to be cleared,
2833   // and traced those that need to be marked; moreover,
2834   // the marking done here is not going to intefere in any
2835   // way with the marking information used by GC.
2836   NoRefDiscovery no_discovery(ref_processor());
2837 
2838   COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
2839 
2840   // Clear any marks from a previous round
2841   verification_mark_bm()->clear_all();
2842   assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
2843   verify_work_stacks_empty();
2844 
2845   GenCollectedHeap* gch = GenCollectedHeap::heap();
2846   gch->ensure_parsability(false);  // fill TLABs, but no need to retire them
2847   // Update the saved marks which may affect the root scans.
2848   gch->save_marks();
2849 
2850   if (CMSRemarkVerifyVariant == 1) {
2851     // In this first variant of verification, we complete
2852     // all marking, then check if the new marks-verctor is
2853     // a subset of the CMS marks-vector.
2854     verify_after_remark_work_1();
2855   } else if (CMSRemarkVerifyVariant == 2) {
2856     // In this second variant of verification, we flag an error
2857     // (i.e. an object reachable in the new marks-vector not reachable
2858     // in the CMS marks-vector) immediately, also indicating the
2859     // identify of an object (A) that references the unmarked object (B) --
2860     // presumably, a mutation to A failed to be picked up by preclean/remark?
2861     verify_after_remark_work_2();
2862   } else {
2863     warning("Unrecognized value %d for CMSRemarkVerifyVariant",
2864             CMSRemarkVerifyVariant);
2865   }
2866   gclog_or_tty->print(" done] ");
2867   return true;
2868 }
2869 
2870 void CMSCollector::verify_after_remark_work_1() {
2871   ResourceMark rm;
2872   HandleMark  hm;
2873   GenCollectedHeap* gch = GenCollectedHeap::heap();
2874 
2875   // Get a clear set of claim bits for the strong roots processing to work with.
2876   ClassLoaderDataGraph::clear_claimed_marks();
2877 
2878   // Mark from roots one level into CMS
2879   MarkRefsIntoClosure notOlder(_span, verification_mark_bm());
2880   gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2881 
2882   gch->gen_process_strong_roots(_cmsGen->level(),
2883                                 true,   // younger gens are roots
2884                                 true,   // activate StrongRootsScope
2885                                 false,  // not scavenging
2886                                 SharedHeap::ScanningOption(roots_scanning_options()),
2887                                 &notOlder,
2888                                 true,   // walk code active on stacks
2889                                 NULL,
2890                                 NULL); // SSS: Provide correct closure
2891 
2892   // Now mark from the roots
2893   MarkFromRootsClosure markFromRootsClosure(this, _span,
2894     verification_mark_bm(), verification_mark_stack(),
2895     false /* don't yield */, true /* verifying */);
2896   assert(_restart_addr == NULL, "Expected pre-condition");
2897   verification_mark_bm()->iterate(&markFromRootsClosure);
2898   while (_restart_addr != NULL) {
2899     // Deal with stack overflow: by restarting at the indicated
2900     // address.
2901     HeapWord* ra = _restart_addr;
2902     markFromRootsClosure.reset(ra);
2903     _restart_addr = NULL;
2904     verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2905   }
2906   assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2907   verify_work_stacks_empty();
2908 
2909   // Marking completed -- now verify that each bit marked in
2910   // verification_mark_bm() is also marked in markBitMap(); flag all
2911   // errors by printing corresponding objects.
2912   VerifyMarkedClosure vcl(markBitMap());
2913   verification_mark_bm()->iterate(&vcl);
2914   if (vcl.failed()) {
2915     gclog_or_tty->print("Verification failed");
2916     Universe::heap()->print_on(gclog_or_tty);
2917     fatal("CMS: failed marking verification after remark");
2918   }
2919 }
2920 
2921 class VerifyKlassOopsKlassClosure : public KlassClosure {
2922   class VerifyKlassOopsClosure : public OopClosure {
2923     CMSBitMap* _bitmap;
2924    public:
2925     VerifyKlassOopsClosure(CMSBitMap* bitmap) : _bitmap(bitmap) { }
2926     void do_oop(oop* p)       { guarantee(*p == NULL || _bitmap->isMarked((HeapWord*) *p), "Should be marked"); }
2927     void do_oop(narrowOop* p) { ShouldNotReachHere(); }
2928   } _oop_closure;
2929  public:
2930   VerifyKlassOopsKlassClosure(CMSBitMap* bitmap) : _oop_closure(bitmap) {}
2931   void do_klass(Klass* k) {
2932     k->oops_do(&_oop_closure);
2933   }
2934 };
2935 
2936 void CMSCollector::verify_after_remark_work_2() {
2937   ResourceMark rm;
2938   HandleMark  hm;
2939   GenCollectedHeap* gch = GenCollectedHeap::heap();
2940 
2941   // Get a clear set of claim bits for the strong roots processing to work with.
2942   ClassLoaderDataGraph::clear_claimed_marks();
2943 
2944   // Mark from roots one level into CMS
2945   MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
2946                                      markBitMap());
2947   CMKlassClosure klass_closure(&notOlder);
2948 
2949   gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2950   gch->gen_process_strong_roots(_cmsGen->level(),
2951                                 true,   // younger gens are roots
2952                                 true,   // activate StrongRootsScope
2953                                 false,  // not scavenging
2954                                 SharedHeap::ScanningOption(roots_scanning_options()),
2955                                 &notOlder,
2956                                 true,   // walk code active on stacks
2957                                 NULL,
2958                                 &klass_closure);
2959 
2960   // Now mark from the roots
2961   MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
2962     verification_mark_bm(), markBitMap(), verification_mark_stack());
2963   assert(_restart_addr == NULL, "Expected pre-condition");
2964   verification_mark_bm()->iterate(&markFromRootsClosure);
2965   while (_restart_addr != NULL) {
2966     // Deal with stack overflow: by restarting at the indicated
2967     // address.
2968     HeapWord* ra = _restart_addr;
2969     markFromRootsClosure.reset(ra);
2970     _restart_addr = NULL;
2971     verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2972   }
2973   assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2974   verify_work_stacks_empty();
2975 
2976   VerifyKlassOopsKlassClosure verify_klass_oops(verification_mark_bm());
2977   ClassLoaderDataGraph::classes_do(&verify_klass_oops);
2978 
2979   // Marking completed -- now verify that each bit marked in
2980   // verification_mark_bm() is also marked in markBitMap(); flag all
2981   // errors by printing corresponding objects.
2982   VerifyMarkedClosure vcl(markBitMap());
2983   verification_mark_bm()->iterate(&vcl);
2984   assert(!vcl.failed(), "Else verification above should not have succeeded");
2985 }
2986 
2987 void ConcurrentMarkSweepGeneration::save_marks() {
2988   // delegate to CMS space
2989   cmsSpace()->save_marks();
2990   for (uint i = 0; i < ParallelGCThreads; i++) {
2991     _par_gc_thread_states[i]->promo.startTrackingPromotions();
2992   }
2993 }
2994 
2995 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
2996   return cmsSpace()->no_allocs_since_save_marks();
2997 }
2998 
2999 #define CMS_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix)    \
3000                                                                 \
3001 void ConcurrentMarkSweepGeneration::                            \
3002 oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) {   \
3003   cl->set_generation(this);                                     \
3004   cmsSpace()->oop_since_save_marks_iterate##nv_suffix(cl);      \
3005   cl->reset_generation();                                       \
3006   save_marks();                                                 \
3007 }
3008 
3009 ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DEFN)
3010 
3011 void
3012 ConcurrentMarkSweepGeneration::object_iterate_since_last_GC(ObjectClosure* blk)
3013 {
3014   // Not currently implemented; need to do the following. -- ysr.
3015   // dld -- I think that is used for some sort of allocation profiler.  So it
3016   // really means the objects allocated by the mutator since the last
3017   // GC.  We could potentially implement this cheaply by recording only
3018   // the direct allocations in a side data structure.
3019   //
3020   // I think we probably ought not to be required to support these
3021   // iterations at any arbitrary point; I think there ought to be some
3022   // call to enable/disable allocation profiling in a generation/space,
3023   // and the iterator ought to return the objects allocated in the
3024   // gen/space since the enable call, or the last iterator call (which
3025   // will probably be at a GC.)  That way, for gens like CM&S that would
3026   // require some extra data structure to support this, we only pay the
3027   // cost when it's in use...
3028   cmsSpace()->object_iterate_since_last_GC(blk);
3029 }
3030 
3031 void
3032 ConcurrentMarkSweepGeneration::younger_refs_iterate(OopsInGenClosure* cl) {
3033   cl->set_generation(this);
3034   younger_refs_in_space_iterate(_cmsSpace, cl);
3035   cl->reset_generation();
3036 }
3037 
3038 void
3039 ConcurrentMarkSweepGeneration::oop_iterate(MemRegion mr, ExtendedOopClosure* cl) {
3040   if (freelistLock()->owned_by_self()) {
3041     Generation::oop_iterate(mr, cl);
3042   } else {
3043     MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3044     Generation::oop_iterate(mr, cl);
3045   }
3046 }
3047 
3048 void
3049 ConcurrentMarkSweepGeneration::oop_iterate(ExtendedOopClosure* cl) {
3050   if (freelistLock()->owned_by_self()) {
3051     Generation::oop_iterate(cl);
3052   } else {
3053     MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3054     Generation::oop_iterate(cl);
3055   }
3056 }
3057 
3058 void
3059 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
3060   if (freelistLock()->owned_by_self()) {
3061     Generation::object_iterate(cl);
3062   } else {
3063     MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3064     Generation::object_iterate(cl);
3065   }
3066 }
3067 
3068 void
3069 ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) {
3070   if (freelistLock()->owned_by_self()) {
3071     Generation::safe_object_iterate(cl);
3072   } else {
3073     MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3074     Generation::safe_object_iterate(cl);
3075   }
3076 }
3077 
3078 void
3079 ConcurrentMarkSweepGeneration::post_compact() {
3080 }
3081 
3082 void
3083 ConcurrentMarkSweepGeneration::prepare_for_verify() {
3084   // Fix the linear allocation blocks to look like free blocks.
3085 
3086   // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
3087   // are not called when the heap is verified during universe initialization and
3088   // at vm shutdown.
3089   if (freelistLock()->owned_by_self()) {
3090     cmsSpace()->prepare_for_verify();
3091   } else {
3092     MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
3093     cmsSpace()->prepare_for_verify();
3094   }
3095 }
3096 
3097 void
3098 ConcurrentMarkSweepGeneration::verify() {
3099   // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
3100   // are not called when the heap is verified during universe initialization and
3101   // at vm shutdown.
3102   if (freelistLock()->owned_by_self()) {
3103     cmsSpace()->verify();
3104   } else {
3105     MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
3106     cmsSpace()->verify();
3107   }
3108 }
3109 
3110 void CMSCollector::verify() {
3111   _cmsGen->verify();
3112 }
3113 
3114 #ifndef PRODUCT
3115 bool CMSCollector::overflow_list_is_empty() const {
3116   assert(_num_par_pushes >= 0, "Inconsistency");
3117   if (_overflow_list == NULL) {
3118     assert(_num_par_pushes == 0, "Inconsistency");
3119   }
3120   return _overflow_list == NULL;
3121 }
3122 
3123 // The methods verify_work_stacks_empty() and verify_overflow_empty()
3124 // merely consolidate assertion checks that appear to occur together frequently.
3125 void CMSCollector::verify_work_stacks_empty() const {
3126   assert(_markStack.isEmpty(), "Marking stack should be empty");
3127   assert(overflow_list_is_empty(), "Overflow list should be empty");
3128 }
3129 
3130 void CMSCollector::verify_overflow_empty() const {
3131   assert(overflow_list_is_empty(), "Overflow list should be empty");
3132   assert(no_preserved_marks(), "No preserved marks");
3133 }
3134 #endif // PRODUCT
3135 
3136 // Decide if we want to enable class unloading as part of the
3137 // ensuing concurrent GC cycle. We will collect and
3138 // unload classes if it's the case that:
3139 // (1) an explicit gc request has been made and the flag
3140 //     ExplicitGCInvokesConcurrentAndUnloadsClasses is set, OR
3141 // (2) (a) class unloading is enabled at the command line, and
3142 //     (b) old gen is getting really full
3143 // NOTE: Provided there is no change in the state of the heap between
3144 // calls to this method, it should have idempotent results. Moreover,
3145 // its results should be monotonically increasing (i.e. going from 0 to 1,
3146 // but not 1 to 0) between successive calls between which the heap was
3147 // not collected. For the implementation below, it must thus rely on
3148 // the property that concurrent_cycles_since_last_unload()
3149 // will not decrease unless a collection cycle happened and that
3150 // _cmsGen->is_too_full() are
3151 // themselves also monotonic in that sense. See check_monotonicity()
3152 // below.
3153 void CMSCollector::update_should_unload_classes() {
3154   _should_unload_classes = false;
3155   // Condition 1 above
3156   if (_full_gc_requested && ExplicitGCInvokesConcurrentAndUnloadsClasses) {
3157     _should_unload_classes = true;
3158   } else if (CMSClassUnloadingEnabled) { // Condition 2.a above
3159     // Disjuncts 2.b.(i,ii,iii) above
3160     _should_unload_classes = (concurrent_cycles_since_last_unload() >=
3161                               CMSClassUnloadingMaxInterval)
3162                            || _cmsGen->is_too_full();
3163   }
3164 }
3165 
3166 bool ConcurrentMarkSweepGeneration::is_too_full() const {
3167   bool res = should_concurrent_collect();
3168   res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
3169   return res;
3170 }
3171 
3172 void CMSCollector::setup_cms_unloading_and_verification_state() {
3173   const  bool should_verify =   VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
3174                              || VerifyBeforeExit;
3175   const  int  rso           =   SharedHeap::SO_Strings | SharedHeap::SO_CodeCache;
3176 
3177   if (should_unload_classes()) {   // Should unload classes this cycle
3178     remove_root_scanning_option(rso);  // Shrink the root set appropriately
3179     set_verifying(should_verify);    // Set verification state for this cycle
3180     return;                            // Nothing else needs to be done at this time
3181   }
3182 
3183   // Not unloading classes this cycle
3184   assert(!should_unload_classes(), "Inconsitency!");
3185   if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
3186     // Include symbols, strings and code cache elements to prevent their resurrection.
3187     add_root_scanning_option(rso);
3188     set_verifying(true);
3189   } else if (verifying() && !should_verify) {
3190     // We were verifying, but some verification flags got disabled.
3191     set_verifying(false);
3192     // Exclude symbols, strings and code cache elements from root scanning to
3193     // reduce IM and RM pauses.
3194     remove_root_scanning_option(rso);
3195   }
3196 }
3197 
3198 
3199 #ifndef PRODUCT
3200 HeapWord* CMSCollector::block_start(const void* p) const {
3201   const HeapWord* addr = (HeapWord*)p;
3202   if (_span.contains(p)) {
3203     if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
3204       return _cmsGen->cmsSpace()->block_start(p);
3205     }
3206   }
3207   return NULL;
3208 }
3209 #endif
3210 
3211 HeapWord*
3212 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
3213                                                    bool   tlab,
3214                                                    bool   parallel) {
3215   CMSSynchronousYieldRequest yr;
3216   assert(!tlab, "Can't deal with TLAB allocation");
3217   MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3218   expand(word_size*HeapWordSize, MinHeapDeltaBytes,
3219     CMSExpansionCause::_satisfy_allocation);
3220   if (GCExpandToAllocateDelayMillis > 0) {
3221     os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3222   }
3223   return have_lock_and_allocate(word_size, tlab);
3224 }
3225 
3226 // YSR: All of this generation expansion/shrinking stuff is an exact copy of
3227 // OneContigSpaceCardGeneration, which makes me wonder if we should move this
3228 // to CardGeneration and share it...
3229 bool ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes) {
3230   return CardGeneration::expand(bytes, expand_bytes);
3231 }
3232 
3233 void ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes,
3234   CMSExpansionCause::Cause cause)
3235 {
3236 
3237   bool success = expand(bytes, expand_bytes);
3238 
3239   // remember why we expanded; this information is used
3240   // by shouldConcurrentCollect() when making decisions on whether to start
3241   // a new CMS cycle.
3242   if (success) {
3243     set_expansion_cause(cause);
3244     if (PrintGCDetails && Verbose) {
3245       gclog_or_tty->print_cr("Expanded CMS gen for %s",
3246         CMSExpansionCause::to_string(cause));
3247     }
3248   }
3249 }
3250 
3251 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
3252   HeapWord* res = NULL;
3253   MutexLocker x(ParGCRareEvent_lock);
3254   while (true) {
3255     // Expansion by some other thread might make alloc OK now:
3256     res = ps->lab.alloc(word_sz);
3257     if (res != NULL) return res;
3258     // If there's not enough expansion space available, give up.
3259     if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
3260       return NULL;
3261     }
3262     // Otherwise, we try expansion.
3263     expand(word_sz*HeapWordSize, MinHeapDeltaBytes,
3264       CMSExpansionCause::_allocate_par_lab);
3265     // Now go around the loop and try alloc again;
3266     // A competing par_promote might beat us to the expansion space,
3267     // so we may go around the loop again if promotion fails agaion.
3268     if (GCExpandToAllocateDelayMillis > 0) {
3269       os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3270     }
3271   }
3272 }
3273 
3274 
3275 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
3276   PromotionInfo* promo) {
3277   MutexLocker x(ParGCRareEvent_lock);
3278   size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
3279   while (true) {
3280     // Expansion by some other thread might make alloc OK now:
3281     if (promo->ensure_spooling_space()) {
3282       assert(promo->has_spooling_space(),
3283              "Post-condition of successful ensure_spooling_space()");
3284       return true;
3285     }
3286     // If there's not enough expansion space available, give up.
3287     if (_virtual_space.uncommitted_size() < refill_size_bytes) {
3288       return false;
3289     }
3290     // Otherwise, we try expansion.
3291     expand(refill_size_bytes, MinHeapDeltaBytes,
3292       CMSExpansionCause::_allocate_par_spooling_space);
3293     // Now go around the loop and try alloc again;
3294     // A competing allocation might beat us to the expansion space,
3295     // so we may go around the loop again if allocation fails again.
3296     if (GCExpandToAllocateDelayMillis > 0) {
3297       os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3298     }
3299   }
3300 }
3301 
3302 
3303 
3304 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
3305   assert_locked_or_safepoint(Heap_lock);
3306   size_t size = ReservedSpace::page_align_size_down(bytes);
3307   if (size > 0) {
3308     shrink_by(size);
3309   }
3310 }
3311 
3312 bool ConcurrentMarkSweepGeneration::grow_by(size_t bytes) {
3313   assert_locked_or_safepoint(Heap_lock);
3314   bool result = _virtual_space.expand_by(bytes);
3315   if (result) {
3316     HeapWord* old_end = _cmsSpace->end();
3317     size_t new_word_size =
3318       heap_word_size(_virtual_space.committed_size());
3319     MemRegion mr(_cmsSpace->bottom(), new_word_size);
3320     _bts->resize(new_word_size);  // resize the block offset shared array
3321     Universe::heap()->barrier_set()->resize_covered_region(mr);
3322     // Hmmmm... why doesn't CFLS::set_end verify locking?
3323     // This is quite ugly; FIX ME XXX
3324     _cmsSpace->assert_locked(freelistLock());
3325     _cmsSpace->set_end((HeapWord*)_virtual_space.high());
3326 
3327     // update the space and generation capacity counters
3328     if (UsePerfData) {
3329       _space_counters->update_capacity();
3330       _gen_counters->update_all();
3331     }
3332 
3333     if (Verbose && PrintGC) {
3334       size_t new_mem_size = _virtual_space.committed_size();
3335       size_t old_mem_size = new_mem_size - bytes;
3336       gclog_or_tty->print_cr("Expanding %s from " SIZE_FORMAT "K by " SIZE_FORMAT "K to " SIZE_FORMAT "K",
3337                     name(), old_mem_size/K, bytes/K, new_mem_size/K);
3338     }
3339   }
3340   return result;
3341 }
3342 
3343 bool ConcurrentMarkSweepGeneration::grow_to_reserved() {
3344   assert_locked_or_safepoint(Heap_lock);
3345   bool success = true;
3346   const size_t remaining_bytes = _virtual_space.uncommitted_size();
3347   if (remaining_bytes > 0) {
3348     success = grow_by(remaining_bytes);
3349     DEBUG_ONLY(if (!success) warning("grow to reserved failed");)
3350   }
3351   return success;
3352 }
3353 
3354 void ConcurrentMarkSweepGeneration::shrink_by(size_t bytes) {
3355   assert_locked_or_safepoint(Heap_lock);
3356   assert_lock_strong(freelistLock());
3357   // XXX Fix when compaction is implemented.
3358   warning("Shrinking of CMS not yet implemented");
3359   return;
3360 }
3361 
3362 
3363 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
3364 // phases.
3365 class CMSPhaseAccounting: public StackObj {
3366  public:
3367   CMSPhaseAccounting(CMSCollector *collector,
3368                      const char *phase,
3369                      bool print_cr = true);
3370   ~CMSPhaseAccounting();
3371 
3372  private:
3373   CMSCollector *_collector;
3374   const char *_phase;
3375   elapsedTimer _wallclock;
3376   bool _print_cr;
3377 
3378  public:
3379   // Not MT-safe; so do not pass around these StackObj's
3380   // where they may be accessed by other threads.
3381   jlong wallclock_millis() {
3382     assert(_wallclock.is_active(), "Wall clock should not stop");
3383     _wallclock.stop();  // to record time
3384     jlong ret = _wallclock.milliseconds();
3385     _wallclock.start(); // restart
3386     return ret;
3387   }
3388 };
3389 
3390 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
3391                                        const char *phase,
3392                                        bool print_cr) :
3393   _collector(collector), _phase(phase), _print_cr(print_cr) {
3394 
3395   if (PrintCMSStatistics != 0) {
3396     _collector->resetYields();
3397   }
3398   if (PrintGCDetails) {
3399     gclog_or_tty->date_stamp(PrintGCDateStamps);
3400     gclog_or_tty->stamp(PrintGCTimeStamps);
3401     gclog_or_tty->print_cr("[%s-concurrent-%s-start]",
3402       _collector->cmsGen()->short_name(), _phase);
3403   }
3404   _collector->resetTimer();
3405   _wallclock.start();
3406   _collector->startTimer();
3407 }
3408 
3409 CMSPhaseAccounting::~CMSPhaseAccounting() {
3410   assert(_wallclock.is_active(), "Wall clock should not have stopped");
3411   _collector->stopTimer();
3412   _wallclock.stop();
3413   if (PrintGCDetails) {
3414     gclog_or_tty->date_stamp(PrintGCDateStamps);
3415     gclog_or_tty->stamp(PrintGCTimeStamps);
3416     gclog_or_tty->print("[%s-concurrent-%s: %3.3f/%3.3f secs]",
3417                  _collector->cmsGen()->short_name(),
3418                  _phase, _collector->timerValue(), _wallclock.seconds());
3419     if (_print_cr) {
3420       gclog_or_tty->print_cr("");
3421     }
3422     if (PrintCMSStatistics != 0) {
3423       gclog_or_tty->print_cr(" (CMS-concurrent-%s yielded %d times)", _phase,
3424                     _collector->yields());
3425     }
3426   }
3427 }
3428 
3429 // CMS work
3430 
3431 // Checkpoint the roots into this generation from outside
3432 // this generation. [Note this initial checkpoint need only
3433 // be approximate -- we'll do a catch up phase subsequently.]
3434 void CMSCollector::checkpointRootsInitial(bool asynch) {
3435   assert(_collectorState == InitialMarking, "Wrong collector state");
3436   check_correct_thread_executing();
3437   TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
3438 
3439   ReferenceProcessor* rp = ref_processor();
3440   SpecializationStats::clear();
3441   assert(_restart_addr == NULL, "Control point invariant");
3442   if (asynch) {
3443     // acquire locks for subsequent manipulations
3444     MutexLockerEx x(bitMapLock(),
3445                     Mutex::_no_safepoint_check_flag);
3446     checkpointRootsInitialWork(asynch);
3447     // enable ("weak") refs discovery
3448     rp->enable_discovery(true /*verify_disabled*/, true /*check_no_refs*/);
3449     _collectorState = Marking;
3450   } else {
3451     // (Weak) Refs discovery: this is controlled from genCollectedHeap::do_collection
3452     // which recognizes if we are a CMS generation, and doesn't try to turn on
3453     // discovery; verify that they aren't meddling.
3454     assert(!rp->discovery_is_atomic(),
3455            "incorrect setting of discovery predicate");
3456     assert(!rp->discovery_enabled(), "genCollectedHeap shouldn't control "
3457            "ref discovery for this generation kind");
3458     // already have locks
3459     checkpointRootsInitialWork(asynch);
3460     // now enable ("weak") refs discovery
3461     rp->enable_discovery(true /*verify_disabled*/, false /*verify_no_refs*/);
3462     _collectorState = Marking;
3463   }
3464   SpecializationStats::print();
3465 }
3466 
3467 void CMSCollector::checkpointRootsInitialWork(bool asynch) {
3468   assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
3469   assert(_collectorState == InitialMarking, "just checking");
3470 
3471   // If there has not been a GC[n-1] since last GC[n] cycle completed,
3472   // precede our marking with a collection of all
3473   // younger generations to keep floating garbage to a minimum.
3474   // XXX: we won't do this for now -- it's an optimization to be done later.
3475 
3476   // already have locks
3477   assert_lock_strong(bitMapLock());
3478   assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
3479 
3480   // Setup the verification and class unloading state for this
3481   // CMS collection cycle.
3482   setup_cms_unloading_and_verification_state();
3483 
3484   NOT_PRODUCT(TraceTime t("\ncheckpointRootsInitialWork",
3485     PrintGCDetails && Verbose, true, gclog_or_tty);)
3486   if (UseAdaptiveSizePolicy) {
3487     size_policy()->checkpoint_roots_initial_begin();
3488   }
3489 
3490   // Reset all the PLAB chunk arrays if necessary.
3491   if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
3492     reset_survivor_plab_arrays();
3493   }
3494 
3495   ResourceMark rm;
3496   HandleMark  hm;
3497 
3498   FalseClosure falseClosure;
3499   // In the case of a synchronous collection, we will elide the
3500   // remark step, so it's important to catch all the nmethod oops
3501   // in this step.
3502   // The final 'true' flag to gen_process_strong_roots will ensure this.
3503   // If 'async' is true, we can relax the nmethod tracing.
3504   MarkRefsIntoClosure notOlder(_span, &_markBitMap);
3505   GenCollectedHeap* gch = GenCollectedHeap::heap();
3506 
3507   verify_work_stacks_empty();
3508   verify_overflow_empty();
3509 
3510   gch->ensure_parsability(false);  // fill TLABs, but no need to retire them
3511   // Update the saved marks which may affect the root scans.
3512   gch->save_marks();
3513 
3514   // weak reference processing has not started yet.
3515   ref_processor()->set_enqueuing_is_done(false);
3516 
3517   // Need to remember all newly created CLDs,
3518   // so that we can guarantee that the remark finds them.
3519   ClassLoaderDataGraph::remember_new_clds(true);
3520 
3521   // Whenever a CLD is found, it will be claimed before proceeding to mark
3522   // the klasses. The claimed marks need to be cleared before marking starts.
3523   ClassLoaderDataGraph::clear_claimed_marks();
3524 
3525   CMKlassClosure klass_closure(&notOlder);
3526   {
3527     COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
3528     gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3529     gch->gen_process_strong_roots(_cmsGen->level(),
3530                                   true,   // younger gens are roots
3531                                   true,   // activate StrongRootsScope
3532                                   false,  // not scavenging
3533                                   SharedHeap::ScanningOption(roots_scanning_options()),
3534                                   &notOlder,
3535                                   true,   // walk all of code cache if (so & SO_CodeCache)
3536                                   NULL,
3537                                   &klass_closure);
3538   }
3539 
3540   // Clear mod-union table; it will be dirtied in the prologue of
3541   // CMS generation per each younger generation collection.
3542 
3543   assert(_modUnionTable.isAllClear(),
3544        "Was cleared in most recent final checkpoint phase"
3545        " or no bits are set in the gc_prologue before the start of the next "
3546        "subsequent marking phase.");
3547 
3548   assert(_ct->klass_rem_set()->mod_union_is_clear(), "Must be");
3549 
3550   // Save the end of the used_region of the constituent generations
3551   // to be used to limit the extent of sweep in each generation.
3552   save_sweep_limits();
3553   if (UseAdaptiveSizePolicy) {
3554     size_policy()->checkpoint_roots_initial_end(gch->gc_cause());
3555   }
3556   verify_overflow_empty();
3557 }
3558 
3559 bool CMSCollector::markFromRoots(bool asynch) {
3560   // we might be tempted to assert that:
3561   // assert(asynch == !SafepointSynchronize::is_at_safepoint(),
3562   //        "inconsistent argument?");
3563   // However that wouldn't be right, because it's possible that
3564   // a safepoint is indeed in progress as a younger generation
3565   // stop-the-world GC happens even as we mark in this generation.
3566   assert(_collectorState == Marking, "inconsistent state?");
3567   check_correct_thread_executing();
3568   verify_overflow_empty();
3569 
3570   bool res;
3571   if (asynch) {
3572 
3573     // Start the timers for adaptive size policy for the concurrent phases
3574     // Do it here so that the foreground MS can use the concurrent
3575     // timer since a foreground MS might has the sweep done concurrently
3576     // or STW.
3577     if (UseAdaptiveSizePolicy) {
3578       size_policy()->concurrent_marking_begin();
3579     }
3580 
3581     // Weak ref discovery note: We may be discovering weak
3582     // refs in this generation concurrent (but interleaved) with
3583     // weak ref discovery by a younger generation collector.
3584 
3585     CMSTokenSyncWithLocks ts(true, bitMapLock());
3586     TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3587     CMSPhaseAccounting pa(this, "mark", !PrintGCDetails);
3588     res = markFromRootsWork(asynch);
3589     if (res) {
3590       _collectorState = Precleaning;
3591     } else { // We failed and a foreground collection wants to take over
3592       assert(_foregroundGCIsActive, "internal state inconsistency");
3593       assert(_restart_addr == NULL,  "foreground will restart from scratch");
3594       if (PrintGCDetails) {
3595         gclog_or_tty->print_cr("bailing out to foreground collection");
3596       }
3597     }
3598     if (UseAdaptiveSizePolicy) {
3599       size_policy()->concurrent_marking_end();
3600     }
3601   } else {
3602     assert(SafepointSynchronize::is_at_safepoint(),
3603            "inconsistent with asynch == false");
3604     if (UseAdaptiveSizePolicy) {
3605       size_policy()->ms_collection_marking_begin();
3606     }
3607     // already have locks
3608     res = markFromRootsWork(asynch);
3609     _collectorState = FinalMarking;
3610     if (UseAdaptiveSizePolicy) {
3611       GenCollectedHeap* gch = GenCollectedHeap::heap();
3612       size_policy()->ms_collection_marking_end(gch->gc_cause());
3613     }
3614   }
3615   verify_overflow_empty();
3616   return res;
3617 }
3618 
3619 bool CMSCollector::markFromRootsWork(bool asynch) {
3620   // iterate over marked bits in bit map, doing a full scan and mark
3621   // from these roots using the following algorithm:
3622   // . if oop is to the right of the current scan pointer,
3623   //   mark corresponding bit (we'll process it later)
3624   // . else (oop is to left of current scan pointer)
3625   //   push oop on marking stack
3626   // . drain the marking stack
3627 
3628   // Note that when we do a marking step we need to hold the
3629   // bit map lock -- recall that direct allocation (by mutators)
3630   // and promotion (by younger generation collectors) is also
3631   // marking the bit map. [the so-called allocate live policy.]
3632   // Because the implementation of bit map marking is not
3633   // robust wrt simultaneous marking of bits in the same word,
3634   // we need to make sure that there is no such interference
3635   // between concurrent such updates.
3636 
3637   // already have locks
3638   assert_lock_strong(bitMapLock());
3639 
3640   verify_work_stacks_empty();
3641   verify_overflow_empty();
3642   bool result = false;
3643   if (CMSConcurrentMTEnabled && ConcGCThreads > 0) {
3644     result = do_marking_mt(asynch);
3645   } else {
3646     result = do_marking_st(asynch);
3647   }
3648   return result;
3649 }
3650 
3651 // Forward decl
3652 class CMSConcMarkingTask;
3653 
3654 class CMSConcMarkingTerminator: public ParallelTaskTerminator {
3655   CMSCollector*       _collector;
3656   CMSConcMarkingTask* _task;
3657  public:
3658   virtual void yield();
3659 
3660   // "n_threads" is the number of threads to be terminated.
3661   // "queue_set" is a set of work queues of other threads.
3662   // "collector" is the CMS collector associated with this task terminator.
3663   // "yield" indicates whether we need the gang as a whole to yield.
3664   CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
3665     ParallelTaskTerminator(n_threads, queue_set),
3666     _collector(collector) { }
3667 
3668   void set_task(CMSConcMarkingTask* task) {
3669     _task = task;
3670   }
3671 };
3672 
3673 class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator {
3674   CMSConcMarkingTask* _task;
3675  public:
3676   bool should_exit_termination();
3677   void set_task(CMSConcMarkingTask* task) {
3678     _task = task;
3679   }
3680 };
3681 
3682 // MT Concurrent Marking Task
3683 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3684   CMSCollector* _collector;
3685   int           _n_workers;                  // requested/desired # workers
3686   bool          _asynch;
3687   bool          _result;
3688   CompactibleFreeListSpace*  _cms_space;
3689   char          _pad_front[64];   // padding to ...
3690   HeapWord*     _global_finger;   // ... avoid sharing cache line
3691   char          _pad_back[64];
3692   HeapWord*     _restart_addr;
3693 
3694   //  Exposed here for yielding support
3695   Mutex* const _bit_map_lock;
3696 
3697   // The per thread work queues, available here for stealing
3698   OopTaskQueueSet*  _task_queues;
3699 
3700   // Termination (and yielding) support
3701   CMSConcMarkingTerminator _term;
3702   CMSConcMarkingTerminatorTerminator _term_term;
3703 
3704  public:
3705   CMSConcMarkingTask(CMSCollector* collector,
3706                  CompactibleFreeListSpace* cms_space,
3707                  bool asynch,
3708                  YieldingFlexibleWorkGang* workers,
3709                  OopTaskQueueSet* task_queues):
3710     YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3711     _collector(collector),
3712     _cms_space(cms_space),
3713     _asynch(asynch), _n_workers(0), _result(true),
3714     _task_queues(task_queues),
3715     _term(_n_workers, task_queues, _collector),
3716     _bit_map_lock(collector->bitMapLock())
3717   {
3718     _requested_size = _n_workers;
3719     _term.set_task(this);
3720     _term_term.set_task(this);
3721     _restart_addr = _global_finger = _cms_space->bottom();
3722   }
3723 
3724 
3725   OopTaskQueueSet* task_queues()  { return _task_queues; }
3726 
3727   OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3728 
3729   HeapWord** global_finger_addr() { return &_global_finger; }
3730 
3731   CMSConcMarkingTerminator* terminator() { return &_term; }
3732 
3733   virtual void set_for_termination(int active_workers) {
3734     terminator()->reset_for_reuse(active_workers);
3735   }
3736 
3737   void work(uint worker_id);
3738   bool should_yield() {
3739     return    ConcurrentMarkSweepThread::should_yield()
3740            && !_collector->foregroundGCIsActive()
3741            && _asynch;
3742   }
3743 
3744   virtual void coordinator_yield();  // stuff done by coordinator
3745   bool result() { return _result; }
3746 
3747   void reset(HeapWord* ra) {
3748     assert(_global_finger >= _cms_space->end(),  "Postcondition of ::work(i)");
3749     _restart_addr = _global_finger = ra;
3750     _term.reset_for_reuse();
3751   }
3752 
3753   static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3754                                            OopTaskQueue* work_q);
3755 
3756  private:
3757   void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3758   void do_work_steal(int i);
3759   void bump_global_finger(HeapWord* f);
3760 };
3761 
3762 bool CMSConcMarkingTerminatorTerminator::should_exit_termination() {
3763   assert(_task != NULL, "Error");
3764   return _task->yielding();
3765   // Note that we do not need the disjunct || _task->should_yield() above
3766   // because we want terminating threads to yield only if the task
3767   // is already in the midst of yielding, which happens only after at least one
3768   // thread has yielded.
3769 }
3770 
3771 void CMSConcMarkingTerminator::yield() {
3772   if (_task->should_yield()) {
3773     _task->yield();
3774   } else {
3775     ParallelTaskTerminator::yield();
3776   }
3777 }
3778 
3779 ////////////////////////////////////////////////////////////////
3780 // Concurrent Marking Algorithm Sketch
3781 ////////////////////////////////////////////////////////////////
3782 // Until all tasks exhausted (both spaces):
3783 // -- claim next available chunk
3784 // -- bump global finger via CAS
3785 // -- find first object that starts in this chunk
3786 //    and start scanning bitmap from that position
3787 // -- scan marked objects for oops
3788 // -- CAS-mark target, and if successful:
3789 //    . if target oop is above global finger (volatile read)
3790 //      nothing to do
3791 //    . if target oop is in chunk and above local finger
3792 //        then nothing to do
3793 //    . else push on work-queue
3794 // -- Deal with possible overflow issues:
3795 //    . local work-queue overflow causes stuff to be pushed on
3796 //      global (common) overflow queue
3797 //    . always first empty local work queue
3798 //    . then get a batch of oops from global work queue if any
3799 //    . then do work stealing
3800 // -- When all tasks claimed (both spaces)
3801 //    and local work queue empty,
3802 //    then in a loop do:
3803 //    . check global overflow stack; steal a batch of oops and trace
3804 //    . try to steal from other threads oif GOS is empty
3805 //    . if neither is available, offer termination
3806 // -- Terminate and return result
3807 //
3808 void CMSConcMarkingTask::work(uint worker_id) {
3809   elapsedTimer _timer;
3810   ResourceMark rm;
3811   HandleMark hm;
3812 
3813   DEBUG_ONLY(_collector->verify_overflow_empty();)
3814 
3815   // Before we begin work, our work queue should be empty
3816   assert(work_queue(worker_id)->size() == 0, "Expected to be empty");
3817   // Scan the bitmap covering _cms_space, tracing through grey objects.
3818   _timer.start();
3819   do_scan_and_mark(worker_id, _cms_space);
3820   _timer.stop();
3821   if (PrintCMSStatistics != 0) {
3822     gclog_or_tty->print_cr("Finished cms space scanning in %dth thread: %3.3f sec",
3823       worker_id, _timer.seconds());
3824       // XXX: need xxx/xxx type of notation, two timers
3825   }
3826 
3827   // ... do work stealing
3828   _timer.reset();
3829   _timer.start();
3830   do_work_steal(worker_id);
3831   _timer.stop();
3832   if (PrintCMSStatistics != 0) {
3833     gclog_or_tty->print_cr("Finished work stealing in %dth thread: %3.3f sec",
3834       worker_id, _timer.seconds());
3835       // XXX: need xxx/xxx type of notation, two timers
3836   }
3837   assert(_collector->_markStack.isEmpty(), "Should have been emptied");
3838   assert(work_queue(worker_id)->size() == 0, "Should have been emptied");
3839   // Note that under the current task protocol, the
3840   // following assertion is true even of the spaces
3841   // expanded since the completion of the concurrent
3842   // marking. XXX This will likely change under a strict
3843   // ABORT semantics.
3844   // After perm removal the comparison was changed to
3845   // greater than or equal to from strictly greater than.
3846   // Before perm removal the highest address sweep would
3847   // have been at the end of perm gen but now is at the
3848   // end of the tenured gen.
3849   assert(_global_finger >=  _cms_space->end(),
3850          "All tasks have been completed");
3851   DEBUG_ONLY(_collector->verify_overflow_empty();)
3852 }
3853 
3854 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
3855   HeapWord* read = _global_finger;
3856   HeapWord* cur  = read;
3857   while (f > read) {
3858     cur = read;
3859     read = (HeapWord*) Atomic::cmpxchg_ptr(f, &_global_finger, cur);
3860     if (cur == read) {
3861       // our cas succeeded
3862       assert(_global_finger >= f, "protocol consistency");
3863       break;
3864     }
3865   }
3866 }
3867 
3868 // This is really inefficient, and should be redone by
3869 // using (not yet available) block-read and -write interfaces to the
3870 // stack and the work_queue. XXX FIX ME !!!
3871 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3872                                                       OopTaskQueue* work_q) {
3873   // Fast lock-free check
3874   if (ovflw_stk->length() == 0) {
3875     return false;
3876   }
3877   assert(work_q->size() == 0, "Shouldn't steal");
3878   MutexLockerEx ml(ovflw_stk->par_lock(),
3879                    Mutex::_no_safepoint_check_flag);
3880   // Grab up to 1/4 the size of the work queue
3881   size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
3882                     (size_t)ParGCDesiredObjsFromOverflowList);
3883   num = MIN2(num, ovflw_stk->length());
3884   for (int i = (int) num; i > 0; i--) {
3885     oop cur = ovflw_stk->pop();
3886     assert(cur != NULL, "Counted wrong?");
3887     work_q->push(cur);
3888   }
3889   return num > 0;
3890 }
3891 
3892 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
3893   SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
3894   int n_tasks = pst->n_tasks();
3895   // We allow that there may be no tasks to do here because
3896   // we are restarting after a stack overflow.
3897   assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
3898   uint nth_task = 0;
3899 
3900   HeapWord* aligned_start = sp->bottom();
3901   if (sp->used_region().contains(_restart_addr)) {
3902     // Align down to a card boundary for the start of 0th task
3903     // for this space.
3904     aligned_start =
3905       (HeapWord*)align_size_down((uintptr_t)_restart_addr,
3906                                  CardTableModRefBS::card_size);
3907   }
3908 
3909   size_t chunk_size = sp->marking_task_size();
3910   while (!pst->is_task_claimed(/* reference */ nth_task)) {
3911     // Having claimed the nth task in this space,
3912     // compute the chunk that it corresponds to:
3913     MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
3914                                aligned_start + (nth_task+1)*chunk_size);
3915     // Try and bump the global finger via a CAS;
3916     // note that we need to do the global finger bump
3917     // _before_ taking the intersection below, because
3918     // the task corresponding to that region will be
3919     // deemed done even if the used_region() expands
3920     // because of allocation -- as it almost certainly will
3921     // during start-up while the threads yield in the
3922     // closure below.
3923     HeapWord* finger = span.end();
3924     bump_global_finger(finger);   // atomically
3925     // There are null tasks here corresponding to chunks
3926     // beyond the "top" address of the space.
3927     span = span.intersection(sp->used_region());
3928     if (!span.is_empty()) {  // Non-null task
3929       HeapWord* prev_obj;
3930       assert(!span.contains(_restart_addr) || nth_task == 0,
3931              "Inconsistency");
3932       if (nth_task == 0) {
3933         // For the 0th task, we'll not need to compute a block_start.
3934         if (span.contains(_restart_addr)) {
3935           // In the case of a restart because of stack overflow,
3936           // we might additionally skip a chunk prefix.
3937           prev_obj = _restart_addr;
3938         } else {
3939           prev_obj = span.start();
3940         }
3941       } else {
3942         // We want to skip the first object because
3943         // the protocol is to scan any object in its entirety
3944         // that _starts_ in this span; a fortiori, any
3945         // object starting in an earlier span is scanned
3946         // as part of an earlier claimed task.
3947         // Below we use the "careful" version of block_start
3948         // so we do not try to navigate uninitialized objects.
3949         prev_obj = sp->block_start_careful(span.start());
3950         // Below we use a variant of block_size that uses the
3951         // Printezis bits to avoid waiting for allocated
3952         // objects to become initialized/parsable.
3953         while (prev_obj < span.start()) {
3954           size_t sz = sp->block_size_no_stall(prev_obj, _collector);
3955           if (sz > 0) {
3956             prev_obj += sz;
3957           } else {
3958             // In this case we may end up doing a bit of redundant
3959             // scanning, but that appears unavoidable, short of
3960             // locking the free list locks; see bug 6324141.
3961             break;
3962           }
3963         }
3964       }
3965       if (prev_obj < span.end()) {
3966         MemRegion my_span = MemRegion(prev_obj, span.end());
3967         // Do the marking work within a non-empty span --
3968         // the last argument to the constructor indicates whether the
3969         // iteration should be incremental with periodic yields.
3970         Par_MarkFromRootsClosure cl(this, _collector, my_span,
3971                                     &_collector->_markBitMap,
3972                                     work_queue(i),
3973                                     &_collector->_markStack,
3974                                     _asynch);
3975         _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
3976       } // else nothing to do for this task
3977     }   // else nothing to do for this task
3978   }
3979   // We'd be tempted to assert here that since there are no
3980   // more tasks left to claim in this space, the global_finger
3981   // must exceed space->top() and a fortiori space->end(). However,
3982   // that would not quite be correct because the bumping of
3983   // global_finger occurs strictly after the claiming of a task,
3984   // so by the time we reach here the global finger may not yet
3985   // have been bumped up by the thread that claimed the last
3986   // task.
3987   pst->all_tasks_completed();
3988 }
3989 
3990 class Par_ConcMarkingClosure: public CMSOopClosure {
3991  private:
3992   CMSCollector* _collector;
3993   CMSConcMarkingTask* _task;
3994   MemRegion     _span;
3995   CMSBitMap*    _bit_map;
3996   CMSMarkStack* _overflow_stack;
3997   OopTaskQueue* _work_queue;
3998  protected:
3999   DO_OOP_WORK_DEFN
4000  public:
4001   Par_ConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue,
4002                          CMSBitMap* bit_map, CMSMarkStack* overflow_stack):
4003     CMSOopClosure(collector->ref_processor()),
4004     _collector(collector),
4005     _task(task),
4006     _span(collector->_span),
4007     _work_queue(work_queue),
4008     _bit_map(bit_map),
4009     _overflow_stack(overflow_stack)
4010   { }
4011   virtual void do_oop(oop* p);
4012   virtual void do_oop(narrowOop* p);
4013 
4014   void trim_queue(size_t max);
4015   void handle_stack_overflow(HeapWord* lost);
4016   void do_yield_check() {
4017     if (_task->should_yield()) {
4018       _task->yield();
4019     }
4020   }
4021 };
4022 
4023 // Grey object scanning during work stealing phase --
4024 // the salient assumption here is that any references
4025 // that are in these stolen objects being scanned must
4026 // already have been initialized (else they would not have
4027 // been published), so we do not need to check for
4028 // uninitialized objects before pushing here.
4029 void Par_ConcMarkingClosure::do_oop(oop obj) {
4030   assert(obj->is_oop_or_null(true), "expected an oop or NULL");
4031   HeapWord* addr = (HeapWord*)obj;
4032   // Check if oop points into the CMS generation
4033   // and is not marked
4034   if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
4035     // a white object ...
4036     // If we manage to "claim" the object, by being the
4037     // first thread to mark it, then we push it on our
4038     // marking stack
4039     if (_bit_map->par_mark(addr)) {     // ... now grey
4040       // push on work queue (grey set)
4041       bool simulate_overflow = false;
4042       NOT_PRODUCT(
4043         if (CMSMarkStackOverflowALot &&
4044             _collector->simulate_overflow()) {
4045           // simulate a stack overflow
4046           simulate_overflow = true;
4047         }
4048       )
4049       if (simulate_overflow ||
4050           !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
4051         // stack overflow
4052         if (PrintCMSStatistics != 0) {
4053           gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
4054                                  SIZE_FORMAT, _overflow_stack->capacity());
4055         }
4056         // We cannot assert that the overflow stack is full because
4057         // it may have been emptied since.
4058         assert(simulate_overflow ||
4059                _work_queue->size() == _work_queue->max_elems(),
4060               "Else push should have succeeded");
4061         handle_stack_overflow(addr);
4062       }
4063     } // Else, some other thread got there first
4064     do_yield_check();
4065   }
4066 }
4067 
4068 void Par_ConcMarkingClosure::do_oop(oop* p)       { Par_ConcMarkingClosure::do_oop_work(p); }
4069 void Par_ConcMarkingClosure::do_oop(narrowOop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
4070 
4071 void Par_ConcMarkingClosure::trim_queue(size_t max) {
4072   while (_work_queue->size() > max) {
4073     oop new_oop;
4074     if (_work_queue->pop_local(new_oop)) {
4075       assert(new_oop->is_oop(), "Should be an oop");
4076       assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
4077       assert(_span.contains((HeapWord*)new_oop), "Not in span");
4078       new_oop->oop_iterate(this);  // do_oop() above
4079       do_yield_check();
4080     }
4081   }
4082 }
4083 
4084 // Upon stack overflow, we discard (part of) the stack,
4085 // remembering the least address amongst those discarded
4086 // in CMSCollector's _restart_address.
4087 void Par_ConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
4088   // We need to do this under a mutex to prevent other
4089   // workers from interfering with the work done below.
4090   MutexLockerEx ml(_overflow_stack->par_lock(),
4091                    Mutex::_no_safepoint_check_flag);
4092   // Remember the least grey address discarded
4093   HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
4094   _collector->lower_restart_addr(ra);
4095   _overflow_stack->reset();  // discard stack contents
4096   _overflow_stack->expand(); // expand the stack if possible
4097 }
4098 
4099 
4100 void CMSConcMarkingTask::do_work_steal(int i) {
4101   OopTaskQueue* work_q = work_queue(i);
4102   oop obj_to_scan;
4103   CMSBitMap* bm = &(_collector->_markBitMap);
4104   CMSMarkStack* ovflw = &(_collector->_markStack);
4105   int* seed = _collector->hash_seed(i);
4106   Par_ConcMarkingClosure cl(_collector, this, work_q, bm, ovflw);
4107   while (true) {
4108     cl.trim_queue(0);
4109     assert(work_q->size() == 0, "Should have been emptied above");
4110     if (get_work_from_overflow_stack(ovflw, work_q)) {
4111       // Can't assert below because the work obtained from the
4112       // overflow stack may already have been stolen from us.
4113       // assert(work_q->size() > 0, "Work from overflow stack");
4114       continue;
4115     } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
4116       assert(obj_to_scan->is_oop(), "Should be an oop");
4117       assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
4118       obj_to_scan->oop_iterate(&cl);
4119     } else if (terminator()->offer_termination(&_term_term)) {
4120       assert(work_q->size() == 0, "Impossible!");
4121       break;
4122     } else if (yielding() || should_yield()) {
4123       yield();
4124     }
4125   }
4126 }
4127 
4128 // This is run by the CMS (coordinator) thread.
4129 void CMSConcMarkingTask::coordinator_yield() {
4130   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
4131          "CMS thread should hold CMS token");
4132   // First give up the locks, then yield, then re-lock
4133   // We should probably use a constructor/destructor idiom to
4134   // do this unlock/lock or modify the MutexUnlocker class to
4135   // serve our purpose. XXX
4136   assert_lock_strong(_bit_map_lock);
4137   _bit_map_lock->unlock();
4138   ConcurrentMarkSweepThread::desynchronize(true);
4139   ConcurrentMarkSweepThread::acknowledge_yield_request();
4140   _collector->stopTimer();
4141   if (PrintCMSStatistics != 0) {
4142     _collector->incrementYields();
4143   }
4144   _collector->icms_wait();
4145 
4146   // It is possible for whichever thread initiated the yield request
4147   // not to get a chance to wake up and take the bitmap lock between
4148   // this thread releasing it and reacquiring it. So, while the
4149   // should_yield() flag is on, let's sleep for a bit to give the
4150   // other thread a chance to wake up. The limit imposed on the number
4151   // of iterations is defensive, to avoid any unforseen circumstances
4152   // putting us into an infinite loop. Since it's always been this
4153   // (coordinator_yield()) method that was observed to cause the
4154   // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
4155   // which is by default non-zero. For the other seven methods that
4156   // also perform the yield operation, as are using a different
4157   // parameter (CMSYieldSleepCount) which is by default zero. This way we
4158   // can enable the sleeping for those methods too, if necessary.
4159   // See 6442774.
4160   //
4161   // We really need to reconsider the synchronization between the GC
4162   // thread and the yield-requesting threads in the future and we
4163   // should really use wait/notify, which is the recommended
4164   // way of doing this type of interaction. Additionally, we should
4165   // consolidate the eight methods that do the yield operation and they
4166   // are almost identical into one for better maintenability and
4167   // readability. See 6445193.
4168   //
4169   // Tony 2006.06.29
4170   for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
4171                    ConcurrentMarkSweepThread::should_yield() &&
4172                    !CMSCollector::foregroundGCIsActive(); ++i) {
4173     os::sleep(Thread::current(), 1, false);
4174     ConcurrentMarkSweepThread::acknowledge_yield_request();
4175   }
4176 
4177   ConcurrentMarkSweepThread::synchronize(true);
4178   _bit_map_lock->lock_without_safepoint_check();
4179   _collector->startTimer();
4180 }
4181 
4182 bool CMSCollector::do_marking_mt(bool asynch) {
4183   assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition");
4184   int num_workers = AdaptiveSizePolicy::calc_active_conc_workers(
4185                                        conc_workers()->total_workers(),
4186                                        conc_workers()->active_workers(),
4187                                        Threads::number_of_non_daemon_threads());
4188   conc_workers()->set_active_workers(num_workers);
4189 
4190   CompactibleFreeListSpace* cms_space  = _cmsGen->cmsSpace();
4191 
4192   CMSConcMarkingTask tsk(this,
4193                          cms_space,
4194                          asynch,
4195                          conc_workers(),
4196                          task_queues());
4197 
4198   // Since the actual number of workers we get may be different
4199   // from the number we requested above, do we need to do anything different
4200   // below? In particular, may be we need to subclass the SequantialSubTasksDone
4201   // class?? XXX
4202   cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
4203 
4204   // Refs discovery is already non-atomic.
4205   assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
4206   assert(ref_processor()->discovery_is_mt(), "Discovery should be MT");
4207   conc_workers()->start_task(&tsk);
4208   while (tsk.yielded()) {
4209     tsk.coordinator_yield();
4210     conc_workers()->continue_task(&tsk);
4211   }
4212   // If the task was aborted, _restart_addr will be non-NULL
4213   assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
4214   while (_restart_addr != NULL) {
4215     // XXX For now we do not make use of ABORTED state and have not
4216     // yet implemented the right abort semantics (even in the original
4217     // single-threaded CMS case). That needs some more investigation
4218     // and is deferred for now; see CR# TBF. 07252005YSR. XXX
4219     assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
4220     // If _restart_addr is non-NULL, a marking stack overflow
4221     // occurred; we need to do a fresh marking iteration from the
4222     // indicated restart address.
4223     if (_foregroundGCIsActive && asynch) {
4224       // We may be running into repeated stack overflows, having
4225       // reached the limit of the stack size, while making very
4226       // slow forward progress. It may be best to bail out and
4227       // let the foreground collector do its job.
4228       // Clear _restart_addr, so that foreground GC
4229       // works from scratch. This avoids the headache of
4230       // a "rescan" which would otherwise be needed because
4231       // of the dirty mod union table & card table.
4232       _restart_addr = NULL;
4233       return false;
4234     }
4235     // Adjust the task to restart from _restart_addr
4236     tsk.reset(_restart_addr);
4237     cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
4238                   _restart_addr);
4239     _restart_addr = NULL;
4240     // Get the workers going again
4241     conc_workers()->start_task(&tsk);
4242     while (tsk.yielded()) {
4243       tsk.coordinator_yield();
4244       conc_workers()->continue_task(&tsk);
4245     }
4246   }
4247   assert(tsk.completed(), "Inconsistency");
4248   assert(tsk.result() == true, "Inconsistency");
4249   return true;
4250 }
4251 
4252 bool CMSCollector::do_marking_st(bool asynch) {
4253   ResourceMark rm;
4254   HandleMark   hm;
4255 
4256   // Temporarily make refs discovery single threaded (non-MT)
4257   ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
4258   MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
4259     &_markStack, CMSYield && asynch);
4260   // the last argument to iterate indicates whether the iteration
4261   // should be incremental with periodic yields.
4262   _markBitMap.iterate(&markFromRootsClosure);
4263   // If _restart_addr is non-NULL, a marking stack overflow
4264   // occurred; we need to do a fresh iteration from the
4265   // indicated restart address.
4266   while (_restart_addr != NULL) {
4267     if (_foregroundGCIsActive && asynch) {
4268       // We may be running into repeated stack overflows, having
4269       // reached the limit of the stack size, while making very
4270       // slow forward progress. It may be best to bail out and
4271       // let the foreground collector do its job.
4272       // Clear _restart_addr, so that foreground GC
4273       // works from scratch. This avoids the headache of
4274       // a "rescan" which would otherwise be needed because
4275       // of the dirty mod union table & card table.
4276       _restart_addr = NULL;
4277       return false;  // indicating failure to complete marking
4278     }
4279     // Deal with stack overflow:
4280     // we restart marking from _restart_addr
4281     HeapWord* ra = _restart_addr;
4282     markFromRootsClosure.reset(ra);
4283     _restart_addr = NULL;
4284     _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
4285   }
4286   return true;
4287 }
4288 
4289 void CMSCollector::preclean() {
4290   check_correct_thread_executing();
4291   assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
4292   verify_work_stacks_empty();
4293   verify_overflow_empty();
4294   _abort_preclean = false;
4295   if (CMSPrecleaningEnabled) {
4296     _eden_chunk_index = 0;
4297     size_t used = get_eden_used();
4298     size_t capacity = get_eden_capacity();
4299     // Don't start sampling unless we will get sufficiently
4300     // many samples.
4301     if (used < (capacity/(CMSScheduleRemarkSamplingRatio * 100)
4302                 * CMSScheduleRemarkEdenPenetration)) {
4303       _start_sampling = true;
4304     } else {
4305       _start_sampling = false;
4306     }
4307     TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
4308     CMSPhaseAccounting pa(this, "preclean", !PrintGCDetails);
4309     preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
4310   }
4311   CMSTokenSync x(true); // is cms thread
4312   if (CMSPrecleaningEnabled) {
4313     sample_eden();
4314     _collectorState = AbortablePreclean;
4315   } else {
4316     _collectorState = FinalMarking;
4317   }
4318   verify_work_stacks_empty();
4319   verify_overflow_empty();
4320 }
4321 
4322 // Try and schedule the remark such that young gen
4323 // occupancy is CMSScheduleRemarkEdenPenetration %.
4324 void CMSCollector::abortable_preclean() {
4325   check_correct_thread_executing();
4326   assert(CMSPrecleaningEnabled,  "Inconsistent control state");
4327   assert(_collectorState == AbortablePreclean, "Inconsistent control state");
4328 
4329   // If Eden's current occupancy is below this threshold,
4330   // immediately schedule the remark; else preclean
4331   // past the next scavenge in an effort to
4332   // schedule the pause as described avove. By choosing
4333   // CMSScheduleRemarkEdenSizeThreshold >= max eden size
4334   // we will never do an actual abortable preclean cycle.
4335   if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
4336     TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
4337     CMSPhaseAccounting pa(this, "abortable-preclean", !PrintGCDetails);
4338     // We need more smarts in the abortable preclean
4339     // loop below to deal with cases where allocation
4340     // in young gen is very very slow, and our precleaning
4341     // is running a losing race against a horde of
4342     // mutators intent on flooding us with CMS updates
4343     // (dirty cards).
4344     // One, admittedly dumb, strategy is to give up
4345     // after a certain number of abortable precleaning loops
4346     // or after a certain maximum time. We want to make
4347     // this smarter in the next iteration.
4348     // XXX FIX ME!!! YSR
4349     size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
4350     while (!(should_abort_preclean() ||
4351              ConcurrentMarkSweepThread::should_terminate())) {
4352       workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
4353       cumworkdone += workdone;
4354       loops++;
4355       // Voluntarily terminate abortable preclean phase if we have
4356       // been at it for too long.
4357       if ((CMSMaxAbortablePrecleanLoops != 0) &&
4358           loops >= CMSMaxAbortablePrecleanLoops) {
4359         if (PrintGCDetails) {
4360           gclog_or_tty->print(" CMS: abort preclean due to loops ");
4361         }
4362         break;
4363       }
4364       if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
4365         if (PrintGCDetails) {
4366           gclog_or_tty->print(" CMS: abort preclean due to time ");
4367         }
4368         break;
4369       }
4370       // If we are doing little work each iteration, we should
4371       // take a short break.
4372       if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
4373         // Sleep for some time, waiting for work to accumulate
4374         stopTimer();
4375         cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
4376         startTimer();
4377         waited++;
4378       }
4379     }
4380     if (PrintCMSStatistics > 0) {
4381       gclog_or_tty->print(" [%d iterations, %d waits, %d cards)] ",
4382                           loops, waited, cumworkdone);
4383     }
4384   }
4385   CMSTokenSync x(true); // is cms thread
4386   if (_collectorState != Idling) {
4387     assert(_collectorState == AbortablePreclean,
4388            "Spontaneous state transition?");
4389     _collectorState = FinalMarking;
4390   } // Else, a foreground collection completed this CMS cycle.
4391   return;
4392 }
4393 
4394 // Respond to an Eden sampling opportunity
4395 void CMSCollector::sample_eden() {
4396   // Make sure a young gc cannot sneak in between our
4397   // reading and recording of a sample.
4398   assert(Thread::current()->is_ConcurrentGC_thread(),
4399          "Only the cms thread may collect Eden samples");
4400   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
4401          "Should collect samples while holding CMS token");
4402   if (!_start_sampling) {
4403     return;
4404   }
4405   if (_eden_chunk_array) {
4406     if (_eden_chunk_index < _eden_chunk_capacity) {
4407       _eden_chunk_array[_eden_chunk_index] = *_top_addr;   // take sample
4408       assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4409              "Unexpected state of Eden");
4410       // We'd like to check that what we just sampled is an oop-start address;
4411       // however, we cannot do that here since the object may not yet have been
4412       // initialized. So we'll instead do the check when we _use_ this sample
4413       // later.
4414       if (_eden_chunk_index == 0 ||
4415           (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4416                          _eden_chunk_array[_eden_chunk_index-1])
4417            >= CMSSamplingGrain)) {
4418         _eden_chunk_index++;  // commit sample
4419       }
4420     }
4421   }
4422   if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
4423     size_t used = get_eden_used();
4424     size_t capacity = get_eden_capacity();
4425     assert(used <= capacity, "Unexpected state of Eden");
4426     if (used >  (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
4427       _abort_preclean = true;
4428     }
4429   }
4430 }
4431 
4432 
4433 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
4434   assert(_collectorState == Precleaning ||
4435          _collectorState == AbortablePreclean, "incorrect state");
4436   ResourceMark rm;
4437   HandleMark   hm;
4438 
4439   // Precleaning is currently not MT but the reference processor
4440   // may be set for MT.  Disable it temporarily here.
4441   ReferenceProcessor* rp = ref_processor();
4442   ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false);
4443 
4444   // Do one pass of scrubbing the discovered reference lists
4445   // to remove any reference objects with strongly-reachable
4446   // referents.
4447   if (clean_refs) {
4448     CMSPrecleanRefsYieldClosure yield_cl(this);
4449     assert(rp->span().equals(_span), "Spans should be equal");
4450     CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
4451                                    &_markStack, true /* preclean */);
4452     CMSDrainMarkingStackClosure complete_trace(this,
4453                                    _span, &_markBitMap, &_markStack,
4454                                    &keep_alive, true /* preclean */);
4455 
4456     // We don't want this step to interfere with a young
4457     // collection because we don't want to take CPU
4458     // or memory bandwidth away from the young GC threads
4459     // (which may be as many as there are CPUs).
4460     // Note that we don't need to protect ourselves from
4461     // interference with mutators because they can't
4462     // manipulate the discovered reference lists nor affect
4463     // the computed reachability of the referents, the
4464     // only properties manipulated by the precleaning
4465     // of these reference lists.
4466     stopTimer();
4467     CMSTokenSyncWithLocks x(true /* is cms thread */,
4468                             bitMapLock());
4469     startTimer();
4470     sample_eden();
4471 
4472     // The following will yield to allow foreground
4473     // collection to proceed promptly. XXX YSR:
4474     // The code in this method may need further
4475     // tweaking for better performance and some restructuring
4476     // for cleaner interfaces.
4477     rp->preclean_discovered_references(
4478           rp->is_alive_non_header(), &keep_alive, &complete_trace, &yield_cl);
4479   }
4480 
4481   if (clean_survivor) {  // preclean the active survivor space(s)
4482     assert(_young_gen->kind() == Generation::DefNew ||
4483            _young_gen->kind() == Generation::ParNew ||
4484            _young_gen->kind() == Generation::ASParNew,
4485          "incorrect type for cast");
4486     DefNewGeneration* dng = (DefNewGeneration*)_young_gen;
4487     PushAndMarkClosure pam_cl(this, _span, ref_processor(),
4488                              &_markBitMap, &_modUnionTable,
4489                              &_markStack, true /* precleaning phase */);
4490     stopTimer();
4491     CMSTokenSyncWithLocks ts(true /* is cms thread */,
4492                              bitMapLock());
4493     startTimer();
4494     unsigned int before_count =
4495       GenCollectedHeap::heap()->total_collections();
4496     SurvivorSpacePrecleanClosure
4497       sss_cl(this, _span, &_markBitMap, &_markStack,
4498              &pam_cl, before_count, CMSYield);
4499     dng->from()->object_iterate_careful(&sss_cl);
4500     dng->to()->object_iterate_careful(&sss_cl);
4501   }
4502   MarkRefsIntoAndScanClosure
4503     mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
4504              &_markStack, this, CMSYield,
4505              true /* precleaning phase */);
4506   // CAUTION: The following closure has persistent state that may need to
4507   // be reset upon a decrease in the sequence of addresses it
4508   // processes.
4509   ScanMarkedObjectsAgainCarefullyClosure
4510     smoac_cl(this, _span,
4511       &_markBitMap, &_markStack, &mrias_cl, CMSYield);
4512 
4513   // Preclean dirty cards in ModUnionTable and CardTable using
4514   // appropriate convergence criterion;
4515   // repeat CMSPrecleanIter times unless we find that
4516   // we are losing.
4517   assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
4518   assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
4519          "Bad convergence multiplier");
4520   assert(CMSPrecleanThreshold >= 100,
4521          "Unreasonably low CMSPrecleanThreshold");
4522 
4523   size_t numIter, cumNumCards, lastNumCards, curNumCards;
4524   for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
4525        numIter < CMSPrecleanIter;
4526        numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
4527     curNumCards  = preclean_mod_union_table(_cmsGen, &smoac_cl);
4528     if (Verbose && PrintGCDetails) {
4529       gclog_or_tty->print(" (modUnionTable: %d cards)", curNumCards);
4530     }
4531     // Either there are very few dirty cards, so re-mark
4532     // pause will be small anyway, or our pre-cleaning isn't
4533     // that much faster than the rate at which cards are being
4534     // dirtied, so we might as well stop and re-mark since
4535     // precleaning won't improve our re-mark time by much.
4536     if (curNumCards <= CMSPrecleanThreshold ||
4537         (numIter > 0 &&
4538          (curNumCards * CMSPrecleanDenominator >
4539          lastNumCards * CMSPrecleanNumerator))) {
4540       numIter++;
4541       cumNumCards += curNumCards;
4542       break;
4543     }
4544   }
4545 
4546   preclean_klasses(&mrias_cl, _cmsGen->freelistLock());
4547 
4548   curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
4549   cumNumCards += curNumCards;
4550   if (PrintGCDetails && PrintCMSStatistics != 0) {
4551     gclog_or_tty->print_cr(" (cardTable: %d cards, re-scanned %d cards, %d iterations)",
4552                   curNumCards, cumNumCards, numIter);
4553   }
4554   return cumNumCards;   // as a measure of useful work done
4555 }
4556 
4557 // PRECLEANING NOTES:
4558 // Precleaning involves:
4559 // . reading the bits of the modUnionTable and clearing the set bits.
4560 // . For the cards corresponding to the set bits, we scan the
4561 //   objects on those cards. This means we need the free_list_lock
4562 //   so that we can safely iterate over the CMS space when scanning
4563 //   for oops.
4564 // . When we scan the objects, we'll be both reading and setting
4565 //   marks in the marking bit map, so we'll need the marking bit map.
4566 // . For protecting _collector_state transitions, we take the CGC_lock.
4567 //   Note that any races in the reading of of card table entries by the
4568 //   CMS thread on the one hand and the clearing of those entries by the
4569 //   VM thread or the setting of those entries by the mutator threads on the
4570 //   other are quite benign. However, for efficiency it makes sense to keep
4571 //   the VM thread from racing with the CMS thread while the latter is
4572 //   dirty card info to the modUnionTable. We therefore also use the
4573 //   CGC_lock to protect the reading of the card table and the mod union
4574 //   table by the CM thread.
4575 // . We run concurrently with mutator updates, so scanning
4576 //   needs to be done carefully  -- we should not try to scan
4577 //   potentially uninitialized objects.
4578 //
4579 // Locking strategy: While holding the CGC_lock, we scan over and
4580 // reset a maximal dirty range of the mod union / card tables, then lock
4581 // the free_list_lock and bitmap lock to do a full marking, then
4582 // release these locks; and repeat the cycle. This allows for a
4583 // certain amount of fairness in the sharing of these locks between
4584 // the CMS collector on the one hand, and the VM thread and the
4585 // mutators on the other.
4586 
4587 // NOTE: preclean_mod_union_table() and preclean_card_table()
4588 // further below are largely identical; if you need to modify
4589 // one of these methods, please check the other method too.
4590 
4591 size_t CMSCollector::preclean_mod_union_table(
4592   ConcurrentMarkSweepGeneration* gen,
4593   ScanMarkedObjectsAgainCarefullyClosure* cl) {
4594   verify_work_stacks_empty();
4595   verify_overflow_empty();
4596 
4597   // strategy: starting with the first card, accumulate contiguous
4598   // ranges of dirty cards; clear these cards, then scan the region
4599   // covered by these cards.
4600 
4601   // Since all of the MUT is committed ahead, we can just use
4602   // that, in case the generations expand while we are precleaning.
4603   // It might also be fine to just use the committed part of the
4604   // generation, but we might potentially miss cards when the
4605   // generation is rapidly expanding while we are in the midst
4606   // of precleaning.
4607   HeapWord* startAddr = gen->reserved().start();
4608   HeapWord* endAddr   = gen->reserved().end();
4609 
4610   cl->setFreelistLock(gen->freelistLock());   // needed for yielding
4611 
4612   size_t numDirtyCards, cumNumDirtyCards;
4613   HeapWord *nextAddr, *lastAddr;
4614   for (cumNumDirtyCards = numDirtyCards = 0,
4615        nextAddr = lastAddr = startAddr;
4616        nextAddr < endAddr;
4617        nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4618 
4619     ResourceMark rm;
4620     HandleMark   hm;
4621 
4622     MemRegion dirtyRegion;
4623     {
4624       stopTimer();
4625       // Potential yield point
4626       CMSTokenSync ts(true);
4627       startTimer();
4628       sample_eden();
4629       // Get dirty region starting at nextOffset (inclusive),
4630       // simultaneously clearing it.
4631       dirtyRegion =
4632         _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
4633       assert(dirtyRegion.start() >= nextAddr,
4634              "returned region inconsistent?");
4635     }
4636     // Remember where the next search should begin.
4637     // The returned region (if non-empty) is a right open interval,
4638     // so lastOffset is obtained from the right end of that
4639     // interval.
4640     lastAddr = dirtyRegion.end();
4641     // Should do something more transparent and less hacky XXX
4642     numDirtyCards =
4643       _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
4644 
4645     // We'll scan the cards in the dirty region (with periodic
4646     // yields for foreground GC as needed).
4647     if (!dirtyRegion.is_empty()) {
4648       assert(numDirtyCards > 0, "consistency check");
4649       HeapWord* stop_point = NULL;
4650       stopTimer();
4651       // Potential yield point
4652       CMSTokenSyncWithLocks ts(true, gen->freelistLock(),
4653                                bitMapLock());
4654       startTimer();
4655       {
4656         verify_work_stacks_empty();
4657         verify_overflow_empty();
4658         sample_eden();
4659         stop_point =
4660           gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4661       }
4662       if (stop_point != NULL) {
4663         // The careful iteration stopped early either because it found an
4664         // uninitialized object, or because we were in the midst of an
4665         // "abortable preclean", which should now be aborted. Redirty
4666         // the bits corresponding to the partially-scanned or unscanned
4667         // cards. We'll either restart at the next block boundary or
4668         // abort the preclean.
4669         assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4670                "Should only be AbortablePreclean.");
4671         _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
4672         if (should_abort_preclean()) {
4673           break; // out of preclean loop
4674         } else {
4675           // Compute the next address at which preclean should pick up;
4676           // might need bitMapLock in order to read P-bits.
4677           lastAddr = next_card_start_after_block(stop_point);
4678         }
4679       }
4680     } else {
4681       assert(lastAddr == endAddr, "consistency check");
4682       assert(numDirtyCards == 0, "consistency check");
4683       break;
4684     }
4685   }
4686   verify_work_stacks_empty();
4687   verify_overflow_empty();
4688   return cumNumDirtyCards;
4689 }
4690 
4691 // NOTE: preclean_mod_union_table() above and preclean_card_table()
4692 // below are largely identical; if you need to modify
4693 // one of these methods, please check the other method too.
4694 
4695 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* gen,
4696   ScanMarkedObjectsAgainCarefullyClosure* cl) {
4697   // strategy: it's similar to precleamModUnionTable above, in that
4698   // we accumulate contiguous ranges of dirty cards, mark these cards
4699   // precleaned, then scan the region covered by these cards.
4700   HeapWord* endAddr   = (HeapWord*)(gen->_virtual_space.high());
4701   HeapWord* startAddr = (HeapWord*)(gen->_virtual_space.low());
4702 
4703   cl->setFreelistLock(gen->freelistLock());   // needed for yielding
4704 
4705   size_t numDirtyCards, cumNumDirtyCards;
4706   HeapWord *lastAddr, *nextAddr;
4707 
4708   for (cumNumDirtyCards = numDirtyCards = 0,
4709        nextAddr = lastAddr = startAddr;
4710        nextAddr < endAddr;
4711        nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4712 
4713     ResourceMark rm;
4714     HandleMark   hm;
4715 
4716     MemRegion dirtyRegion;
4717     {
4718       // See comments in "Precleaning notes" above on why we
4719       // do this locking. XXX Could the locking overheads be
4720       // too high when dirty cards are sparse? [I don't think so.]
4721       stopTimer();
4722       CMSTokenSync x(true); // is cms thread
4723       startTimer();
4724       sample_eden();
4725       // Get and clear dirty region from card table
4726       dirtyRegion = _ct->ct_bs()->dirty_card_range_after_reset(
4727                                     MemRegion(nextAddr, endAddr),
4728                                     true,
4729                                     CardTableModRefBS::precleaned_card_val());
4730 
4731       assert(dirtyRegion.start() >= nextAddr,
4732              "returned region inconsistent?");
4733     }
4734     lastAddr = dirtyRegion.end();
4735     numDirtyCards =
4736       dirtyRegion.word_size()/CardTableModRefBS::card_size_in_words;
4737 
4738     if (!dirtyRegion.is_empty()) {
4739       stopTimer();
4740       CMSTokenSyncWithLocks ts(true, gen->freelistLock(), bitMapLock());
4741       startTimer();
4742       sample_eden();
4743       verify_work_stacks_empty();
4744       verify_overflow_empty();
4745       HeapWord* stop_point =
4746         gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4747       if (stop_point != NULL) {
4748         assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4749                "Should only be AbortablePreclean.");
4750         _ct->ct_bs()->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4751         if (should_abort_preclean()) {
4752           break; // out of preclean loop
4753         } else {
4754           // Compute the next address at which preclean should pick up.
4755           lastAddr = next_card_start_after_block(stop_point);
4756         }
4757       }
4758     } else {
4759       break;
4760     }
4761   }
4762   verify_work_stacks_empty();
4763   verify_overflow_empty();
4764   return cumNumDirtyCards;
4765 }
4766 
4767 class PrecleanKlassClosure : public KlassClosure {
4768   CMKlassClosure _cm_klass_closure;
4769  public:
4770   PrecleanKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4771   void do_klass(Klass* k) {
4772     if (k->has_accumulated_modified_oops()) {
4773       k->clear_accumulated_modified_oops();
4774 
4775       _cm_klass_closure.do_klass(k);
4776     }
4777   }
4778 };
4779 
4780 // The freelist lock is needed to prevent asserts, is it really needed?
4781 void CMSCollector::preclean_klasses(MarkRefsIntoAndScanClosure* cl, Mutex* freelistLock) {
4782 
4783   cl->set_freelistLock(freelistLock);
4784 
4785   CMSTokenSyncWithLocks ts(true, freelistLock, bitMapLock());
4786 
4787   // SSS: Add equivalent to ScanMarkedObjectsAgainCarefullyClosure::do_yield_check and should_abort_preclean?
4788   // SSS: We should probably check if precleaning should be aborted, at suitable intervals?
4789   PrecleanKlassClosure preclean_klass_closure(cl);
4790   ClassLoaderDataGraph::classes_do(&preclean_klass_closure);
4791 
4792   verify_work_stacks_empty();
4793   verify_overflow_empty();
4794 }
4795 
4796 void CMSCollector::checkpointRootsFinal(bool asynch,
4797   bool clear_all_soft_refs, bool init_mark_was_synchronous) {
4798   assert(_collectorState == FinalMarking, "incorrect state transition?");
4799   check_correct_thread_executing();
4800   // world is stopped at this checkpoint
4801   assert(SafepointSynchronize::is_at_safepoint(),
4802          "world should be stopped");
4803   TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
4804 
4805   verify_work_stacks_empty();
4806   verify_overflow_empty();
4807 
4808   SpecializationStats::clear();
4809   if (PrintGCDetails) {
4810     gclog_or_tty->print("[YG occupancy: "SIZE_FORMAT" K ("SIZE_FORMAT" K)]",
4811                         _young_gen->used() / K,
4812                         _young_gen->capacity() / K);
4813   }
4814   if (asynch) {
4815     if (CMSScavengeBeforeRemark) {
4816       GenCollectedHeap* gch = GenCollectedHeap::heap();
4817       // Temporarily set flag to false, GCH->do_collection will
4818       // expect it to be false and set to true
4819       FlagSetting fl(gch->_is_gc_active, false);
4820       NOT_PRODUCT(TraceTime t("Scavenge-Before-Remark",
4821         PrintGCDetails && Verbose, true, gclog_or_tty);)
4822       int level = _cmsGen->level() - 1;
4823       if (level >= 0) {
4824         gch->do_collection(true,        // full (i.e. force, see below)
4825                            false,       // !clear_all_soft_refs
4826                            0,           // size
4827                            false,       // is_tlab
4828                            level        // max_level
4829                           );
4830       }
4831     }
4832     FreelistLocker x(this);
4833     MutexLockerEx y(bitMapLock(),
4834                     Mutex::_no_safepoint_check_flag);
4835     assert(!init_mark_was_synchronous, "but that's impossible!");
4836     checkpointRootsFinalWork(asynch, clear_all_soft_refs, false);
4837   } else {
4838     // already have all the locks
4839     checkpointRootsFinalWork(asynch, clear_all_soft_refs,
4840                              init_mark_was_synchronous);
4841   }
4842   verify_work_stacks_empty();
4843   verify_overflow_empty();
4844   SpecializationStats::print();
4845 }
4846 
4847 void CMSCollector::checkpointRootsFinalWork(bool asynch,
4848   bool clear_all_soft_refs, bool init_mark_was_synchronous) {
4849 
4850   NOT_PRODUCT(TraceTime tr("checkpointRootsFinalWork", PrintGCDetails, false, gclog_or_tty);)
4851 
4852   assert(haveFreelistLocks(), "must have free list locks");
4853   assert_lock_strong(bitMapLock());
4854 
4855   if (UseAdaptiveSizePolicy) {
4856     size_policy()->checkpoint_roots_final_begin();
4857   }
4858 
4859   ResourceMark rm;
4860   HandleMark   hm;
4861 
4862   GenCollectedHeap* gch = GenCollectedHeap::heap();
4863 
4864   if (should_unload_classes()) {
4865     CodeCache::gc_prologue();
4866   }
4867   assert(haveFreelistLocks(), "must have free list locks");
4868   assert_lock_strong(bitMapLock());
4869 
4870   if (!init_mark_was_synchronous) {
4871     // We might assume that we need not fill TLAB's when
4872     // CMSScavengeBeforeRemark is set, because we may have just done
4873     // a scavenge which would have filled all TLAB's -- and besides
4874     // Eden would be empty. This however may not always be the case --
4875     // for instance although we asked for a scavenge, it may not have
4876     // happened because of a JNI critical section. We probably need
4877     // a policy for deciding whether we can in that case wait until
4878     // the critical section releases and then do the remark following
4879     // the scavenge, and skip it here. In the absence of that policy,
4880     // or of an indication of whether the scavenge did indeed occur,
4881     // we cannot rely on TLAB's having been filled and must do
4882     // so here just in case a scavenge did not happen.
4883     gch->ensure_parsability(false);  // fill TLAB's, but no need to retire them
4884     // Update the saved marks which may affect the root scans.
4885     gch->save_marks();
4886 
4887     {
4888       COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
4889 
4890       // Note on the role of the mod union table:
4891       // Since the marker in "markFromRoots" marks concurrently with
4892       // mutators, it is possible for some reachable objects not to have been
4893       // scanned. For instance, an only reference to an object A was
4894       // placed in object B after the marker scanned B. Unless B is rescanned,
4895       // A would be collected. Such updates to references in marked objects
4896       // are detected via the mod union table which is the set of all cards
4897       // dirtied since the first checkpoint in this GC cycle and prior to
4898       // the most recent young generation GC, minus those cleaned up by the
4899       // concurrent precleaning.
4900       if (CMSParallelRemarkEnabled && CollectedHeap::use_parallel_gc_threads()) {
4901         TraceTime t("Rescan (parallel) ", PrintGCDetails, false, gclog_or_tty);
4902         do_remark_parallel();
4903       } else {
4904         TraceTime t("Rescan (non-parallel) ", PrintGCDetails, false,
4905                     gclog_or_tty);
4906         do_remark_non_parallel();
4907       }
4908     }
4909   } else {
4910     assert(!asynch, "Can't have init_mark_was_synchronous in asynch mode");
4911     // The initial mark was stop-world, so there's no rescanning to
4912     // do; go straight on to the next step below.
4913   }
4914   verify_work_stacks_empty();
4915   verify_overflow_empty();
4916 
4917   {
4918     NOT_PRODUCT(TraceTime ts("refProcessingWork", PrintGCDetails, false, gclog_or_tty);)
4919     refProcessingWork(asynch, clear_all_soft_refs);
4920   }
4921   verify_work_stacks_empty();
4922   verify_overflow_empty();
4923 
4924   if (should_unload_classes()) {
4925     CodeCache::gc_epilogue();
4926   }
4927   JvmtiExport::gc_epilogue();
4928 
4929   // If we encountered any (marking stack / work queue) overflow
4930   // events during the current CMS cycle, take appropriate
4931   // remedial measures, where possible, so as to try and avoid
4932   // recurrence of that condition.
4933   assert(_markStack.isEmpty(), "No grey objects");
4934   size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
4935                      _ser_kac_ovflw        + _ser_kac_preclean_ovflw;
4936   if (ser_ovflw > 0) {
4937     if (PrintCMSStatistics != 0) {
4938       gclog_or_tty->print_cr("Marking stack overflow (benign) "
4939         "(pmc_pc="SIZE_FORMAT", pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT
4940         ", kac_preclean="SIZE_FORMAT")",
4941         _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw,
4942         _ser_kac_ovflw, _ser_kac_preclean_ovflw);
4943     }
4944     _markStack.expand();
4945     _ser_pmc_remark_ovflw = 0;
4946     _ser_pmc_preclean_ovflw = 0;
4947     _ser_kac_preclean_ovflw = 0;
4948     _ser_kac_ovflw = 0;
4949   }
4950   if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
4951     if (PrintCMSStatistics != 0) {
4952       gclog_or_tty->print_cr("Work queue overflow (benign) "
4953         "(pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT")",
4954         _par_pmc_remark_ovflw, _par_kac_ovflw);
4955     }
4956     _par_pmc_remark_ovflw = 0;
4957     _par_kac_ovflw = 0;
4958   }
4959   if (PrintCMSStatistics != 0) {
4960      if (_markStack._hit_limit > 0) {
4961        gclog_or_tty->print_cr(" (benign) Hit max stack size limit ("SIZE_FORMAT")",
4962                               _markStack._hit_limit);
4963      }
4964      if (_markStack._failed_double > 0) {
4965        gclog_or_tty->print_cr(" (benign) Failed stack doubling ("SIZE_FORMAT"),"
4966                               " current capacity "SIZE_FORMAT,
4967                               _markStack._failed_double,
4968                               _markStack.capacity());
4969      }
4970   }
4971   _markStack._hit_limit = 0;
4972   _markStack._failed_double = 0;
4973 
4974   if ((VerifyAfterGC || VerifyDuringGC) &&
4975       GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
4976     verify_after_remark();
4977   }
4978 
4979   // Change under the freelistLocks.
4980   _collectorState = Sweeping;
4981   // Call isAllClear() under bitMapLock
4982   assert(_modUnionTable.isAllClear(),
4983       "Should be clear by end of the final marking");
4984   assert(_ct->klass_rem_set()->mod_union_is_clear(),
4985       "Should be clear by end of the final marking");
4986   if (UseAdaptiveSizePolicy) {
4987     size_policy()->checkpoint_roots_final_end(gch->gc_cause());
4988   }
4989 }
4990 
4991 // Parallel remark task
4992 class CMSParRemarkTask: public AbstractGangTask {
4993   CMSCollector* _collector;
4994   int           _n_workers;
4995   CompactibleFreeListSpace* _cms_space;
4996 
4997   // The per-thread work queues, available here for stealing.
4998   OopTaskQueueSet*       _task_queues;
4999   ParallelTaskTerminator _term;
5000 
5001  public:
5002   // A value of 0 passed to n_workers will cause the number of
5003   // workers to be taken from the active workers in the work gang.
5004   CMSParRemarkTask(CMSCollector* collector,
5005                    CompactibleFreeListSpace* cms_space,
5006                    int n_workers, FlexibleWorkGang* workers,
5007                    OopTaskQueueSet* task_queues):
5008     AbstractGangTask("Rescan roots and grey objects in parallel"),
5009     _collector(collector),
5010     _cms_space(cms_space),
5011     _n_workers(n_workers),
5012     _task_queues(task_queues),
5013     _term(n_workers, task_queues) { }
5014 
5015   OopTaskQueueSet* task_queues() { return _task_queues; }
5016 
5017   OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5018 
5019   ParallelTaskTerminator* terminator() { return &_term; }
5020   int n_workers() { return _n_workers; }
5021 
5022   void work(uint worker_id);
5023 
5024  private:
5025   // Work method in support of parallel rescan ... of young gen spaces
5026   void do_young_space_rescan(int i, Par_MarkRefsIntoAndScanClosure* cl,
5027                              ContiguousSpace* space,
5028                              HeapWord** chunk_array, size_t chunk_top);
5029 
5030   // ... of  dirty cards in old space
5031   void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
5032                                   Par_MarkRefsIntoAndScanClosure* cl);
5033 
5034   // ... work stealing for the above
5035   void do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl, int* seed);
5036 };
5037 
5038 class RemarkKlassClosure : public KlassClosure {
5039   CMKlassClosure _cm_klass_closure;
5040  public:
5041   RemarkKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
5042   void do_klass(Klass* k) {
5043     // Check if we have modified any oops in the Klass during the concurrent marking.
5044     if (k->has_accumulated_modified_oops()) {
5045       k->clear_accumulated_modified_oops();
5046 
5047       // We could have transfered the current modified marks to the accumulated marks,
5048       // like we do with the Card Table to Mod Union Table. But it's not really necessary.
5049     } else if (k->has_modified_oops()) {
5050       // Don't clear anything, this info is needed by the next young collection.
5051     } else {
5052       // No modified oops in the Klass.
5053       return;
5054     }
5055 
5056     // The klass has modified fields, need to scan the klass.
5057     _cm_klass_closure.do_klass(k);
5058   }
5059 };
5060 
5061 // work_queue(i) is passed to the closure
5062 // Par_MarkRefsIntoAndScanClosure.  The "i" parameter
5063 // also is passed to do_dirty_card_rescan_tasks() and to
5064 // do_work_steal() to select the i-th task_queue.
5065 
5066 void CMSParRemarkTask::work(uint worker_id) {
5067   elapsedTimer _timer;
5068   ResourceMark rm;
5069   HandleMark   hm;
5070 
5071   // ---------- rescan from roots --------------
5072   _timer.start();
5073   GenCollectedHeap* gch = GenCollectedHeap::heap();
5074   Par_MarkRefsIntoAndScanClosure par_mrias_cl(_collector,
5075     _collector->_span, _collector->ref_processor(),
5076     &(_collector->_markBitMap),
5077     work_queue(worker_id));
5078 
5079   // Rescan young gen roots first since these are likely
5080   // coarsely partitioned and may, on that account, constitute
5081   // the critical path; thus, it's best to start off that
5082   // work first.
5083   // ---------- young gen roots --------------
5084   {
5085     DefNewGeneration* dng = _collector->_young_gen->as_DefNewGeneration();
5086     EdenSpace* eden_space = dng->eden();
5087     ContiguousSpace* from_space = dng->from();
5088     ContiguousSpace* to_space   = dng->to();
5089 
5090     HeapWord** eca = _collector->_eden_chunk_array;
5091     size_t     ect = _collector->_eden_chunk_index;
5092     HeapWord** sca = _collector->_survivor_chunk_array;
5093     size_t     sct = _collector->_survivor_chunk_index;
5094 
5095     assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
5096     assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
5097 
5098     do_young_space_rescan(worker_id, &par_mrias_cl, to_space, NULL, 0);
5099     do_young_space_rescan(worker_id, &par_mrias_cl, from_space, sca, sct);
5100     do_young_space_rescan(worker_id, &par_mrias_cl, eden_space, eca, ect);
5101 
5102     _timer.stop();
5103     if (PrintCMSStatistics != 0) {
5104       gclog_or_tty->print_cr(
5105         "Finished young gen rescan work in %dth thread: %3.3f sec",
5106         worker_id, _timer.seconds());
5107     }
5108   }
5109 
5110   // ---------- remaining roots --------------
5111   _timer.reset();
5112   _timer.start();
5113   gch->gen_process_strong_roots(_collector->_cmsGen->level(),
5114                                 false,     // yg was scanned above
5115                                 false,     // this is parallel code
5116                                 false,     // not scavenging
5117                                 SharedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
5118                                 &par_mrias_cl,
5119                                 true,   // walk all of code cache if (so & SO_CodeCache)
5120                                 NULL,
5121                                 NULL);     // The dirty klasses will be handled below
5122   assert(_collector->should_unload_classes()
5123          || (_collector->CMSCollector::roots_scanning_options() & SharedHeap::SO_CodeCache),
5124          "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5125   _timer.stop();
5126   if (PrintCMSStatistics != 0) {
5127     gclog_or_tty->print_cr(
5128       "Finished remaining root rescan work in %dth thread: %3.3f sec",
5129       worker_id, _timer.seconds());
5130   }
5131 
5132   // ---------- unhandled CLD scanning ----------
5133   if (worker_id == 0) { // Single threaded at the moment.
5134     _timer.reset();
5135     _timer.start();
5136 
5137     // Scan all new class loader data objects and new dependencies that were
5138     // introduced during concurrent marking.
5139     ResourceMark rm;
5140     GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
5141     for (int i = 0; i < array->length(); i++) {
5142       par_mrias_cl.do_class_loader_data(array->at(i));
5143     }
5144 
5145     // We don't need to keep track of new CLDs anymore.
5146     ClassLoaderDataGraph::remember_new_clds(false);
5147 
5148     _timer.stop();
5149     if (PrintCMSStatistics != 0) {
5150       gclog_or_tty->print_cr(
5151           "Finished unhandled CLD scanning work in %dth thread: %3.3f sec",
5152           worker_id, _timer.seconds());
5153     }
5154   }
5155 
5156   // ---------- dirty klass scanning ----------
5157   if (worker_id == 0) { // Single threaded at the moment.
5158     _timer.reset();
5159     _timer.start();
5160 
5161     // Scan all classes that was dirtied during the concurrent marking phase.
5162     RemarkKlassClosure remark_klass_closure(&par_mrias_cl);
5163     ClassLoaderDataGraph::classes_do(&remark_klass_closure);
5164 
5165     _timer.stop();
5166     if (PrintCMSStatistics != 0) {
5167       gclog_or_tty->print_cr(
5168           "Finished dirty klass scanning work in %dth thread: %3.3f sec",
5169           worker_id, _timer.seconds());
5170     }
5171   }
5172 
5173   // We might have added oops to ClassLoaderData::_handles during the
5174   // concurrent marking phase. These oops point to newly allocated objects
5175   // that are guaranteed to be kept alive. Either by the direct allocation
5176   // code, or when the young collector processes the strong roots. Hence,
5177   // we don't have to revisit the _handles block during the remark phase.
5178 
5179   // ---------- rescan dirty cards ------------
5180   _timer.reset();
5181   _timer.start();
5182 
5183   // Do the rescan tasks for each of the two spaces
5184   // (cms_space) in turn.
5185   // "worker_id" is passed to select the task_queue for "worker_id"
5186   do_dirty_card_rescan_tasks(_cms_space, worker_id, &par_mrias_cl);
5187   _timer.stop();
5188   if (PrintCMSStatistics != 0) {
5189     gclog_or_tty->print_cr(
5190       "Finished dirty card rescan work in %dth thread: %3.3f sec",
5191       worker_id, _timer.seconds());
5192   }
5193 
5194   // ---------- steal work from other threads ...
5195   // ---------- ... and drain overflow list.
5196   _timer.reset();
5197   _timer.start();
5198   do_work_steal(worker_id, &par_mrias_cl, _collector->hash_seed(worker_id));
5199   _timer.stop();
5200   if (PrintCMSStatistics != 0) {
5201     gclog_or_tty->print_cr(
5202       "Finished work stealing in %dth thread: %3.3f sec",
5203       worker_id, _timer.seconds());
5204   }
5205 }
5206 
5207 // Note that parameter "i" is not used.
5208 void
5209 CMSParRemarkTask::do_young_space_rescan(int i,
5210   Par_MarkRefsIntoAndScanClosure* cl, ContiguousSpace* space,
5211   HeapWord** chunk_array, size_t chunk_top) {
5212   // Until all tasks completed:
5213   // . claim an unclaimed task
5214   // . compute region boundaries corresponding to task claimed
5215   //   using chunk_array
5216   // . par_oop_iterate(cl) over that region
5217 
5218   ResourceMark rm;
5219   HandleMark   hm;
5220 
5221   SequentialSubTasksDone* pst = space->par_seq_tasks();
5222   assert(pst->valid(), "Uninitialized use?");
5223 
5224   uint nth_task = 0;
5225   uint n_tasks  = pst->n_tasks();
5226 
5227   HeapWord *start, *end;
5228   while (!pst->is_task_claimed(/* reference */ nth_task)) {
5229     // We claimed task # nth_task; compute its boundaries.
5230     if (chunk_top == 0) {  // no samples were taken
5231       assert(nth_task == 0 && n_tasks == 1, "Can have only 1 EdenSpace task");
5232       start = space->bottom();
5233       end   = space->top();
5234     } else if (nth_task == 0) {
5235       start = space->bottom();
5236       end   = chunk_array[nth_task];
5237     } else if (nth_task < (uint)chunk_top) {
5238       assert(nth_task >= 1, "Control point invariant");
5239       start = chunk_array[nth_task - 1];
5240       end   = chunk_array[nth_task];
5241     } else {
5242       assert(nth_task == (uint)chunk_top, "Control point invariant");
5243       start = chunk_array[chunk_top - 1];
5244       end   = space->top();
5245     }
5246     MemRegion mr(start, end);
5247     // Verify that mr is in space
5248     assert(mr.is_empty() || space->used_region().contains(mr),
5249            "Should be in space");
5250     // Verify that "start" is an object boundary
5251     assert(mr.is_empty() || oop(mr.start())->is_oop(),
5252            "Should be an oop");
5253     space->par_oop_iterate(mr, cl);
5254   }
5255   pst->all_tasks_completed();
5256 }
5257 
5258 void
5259 CMSParRemarkTask::do_dirty_card_rescan_tasks(
5260   CompactibleFreeListSpace* sp, int i,
5261   Par_MarkRefsIntoAndScanClosure* cl) {
5262   // Until all tasks completed:
5263   // . claim an unclaimed task
5264   // . compute region boundaries corresponding to task claimed
5265   // . transfer dirty bits ct->mut for that region
5266   // . apply rescanclosure to dirty mut bits for that region
5267 
5268   ResourceMark rm;
5269   HandleMark   hm;
5270 
5271   OopTaskQueue* work_q = work_queue(i);
5272   ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
5273   // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
5274   // CAUTION: This closure has state that persists across calls to
5275   // the work method dirty_range_iterate_clear() in that it has
5276   // imbedded in it a (subtype of) UpwardsObjectClosure. The
5277   // use of that state in the imbedded UpwardsObjectClosure instance
5278   // assumes that the cards are always iterated (even if in parallel
5279   // by several threads) in monotonically increasing order per each
5280   // thread. This is true of the implementation below which picks
5281   // card ranges (chunks) in monotonically increasing order globally
5282   // and, a-fortiori, in monotonically increasing order per thread
5283   // (the latter order being a subsequence of the former).
5284   // If the work code below is ever reorganized into a more chaotic
5285   // work-partitioning form than the current "sequential tasks"
5286   // paradigm, the use of that persistent state will have to be
5287   // revisited and modified appropriately. See also related
5288   // bug 4756801 work on which should examine this code to make
5289   // sure that the changes there do not run counter to the
5290   // assumptions made here and necessary for correctness and
5291   // efficiency. Note also that this code might yield inefficient
5292   // behaviour in the case of very large objects that span one or
5293   // more work chunks. Such objects would potentially be scanned
5294   // several times redundantly. Work on 4756801 should try and
5295   // address that performance anomaly if at all possible. XXX
5296   MemRegion  full_span  = _collector->_span;
5297   CMSBitMap* bm    = &(_collector->_markBitMap);     // shared
5298   MarkFromDirtyCardsClosure
5299     greyRescanClosure(_collector, full_span, // entire span of interest
5300                       sp, bm, work_q, cl);
5301 
5302   SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
5303   assert(pst->valid(), "Uninitialized use?");
5304   uint nth_task = 0;
5305   const int alignment = CardTableModRefBS::card_size * BitsPerWord;
5306   MemRegion span = sp->used_region();
5307   HeapWord* start_addr = span.start();
5308   HeapWord* end_addr = (HeapWord*)round_to((intptr_t)span.end(),
5309                                            alignment);
5310   const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
5311   assert((HeapWord*)round_to((intptr_t)start_addr, alignment) ==
5312          start_addr, "Check alignment");
5313   assert((size_t)round_to((intptr_t)chunk_size, alignment) ==
5314          chunk_size, "Check alignment");
5315 
5316   while (!pst->is_task_claimed(/* reference */ nth_task)) {
5317     // Having claimed the nth_task, compute corresponding mem-region,
5318     // which is a-fortiori aligned correctly (i.e. at a MUT bopundary).
5319     // The alignment restriction ensures that we do not need any
5320     // synchronization with other gang-workers while setting or
5321     // clearing bits in thus chunk of the MUT.
5322     MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
5323                                     start_addr + (nth_task+1)*chunk_size);
5324     // The last chunk's end might be way beyond end of the
5325     // used region. In that case pull back appropriately.
5326     if (this_span.end() > end_addr) {
5327       this_span.set_end(end_addr);
5328       assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
5329     }
5330     // Iterate over the dirty cards covering this chunk, marking them
5331     // precleaned, and setting the corresponding bits in the mod union
5332     // table. Since we have been careful to partition at Card and MUT-word
5333     // boundaries no synchronization is needed between parallel threads.
5334     _collector->_ct->ct_bs()->dirty_card_iterate(this_span,
5335                                                  &modUnionClosure);
5336 
5337     // Having transferred these marks into the modUnionTable,
5338     // rescan the marked objects on the dirty cards in the modUnionTable.
5339     // Even if this is at a synchronous collection, the initial marking
5340     // may have been done during an asynchronous collection so there
5341     // may be dirty bits in the mod-union table.
5342     _collector->_modUnionTable.dirty_range_iterate_clear(
5343                   this_span, &greyRescanClosure);
5344     _collector->_modUnionTable.verifyNoOneBitsInRange(
5345                                  this_span.start(),
5346                                  this_span.end());
5347   }
5348   pst->all_tasks_completed();  // declare that i am done
5349 }
5350 
5351 // . see if we can share work_queues with ParNew? XXX
5352 void
5353 CMSParRemarkTask::do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl,
5354                                 int* seed) {
5355   OopTaskQueue* work_q = work_queue(i);
5356   NOT_PRODUCT(int num_steals = 0;)
5357   oop obj_to_scan;
5358   CMSBitMap* bm = &(_collector->_markBitMap);
5359 
5360   while (true) {
5361     // Completely finish any left over work from (an) earlier round(s)
5362     cl->trim_queue(0);
5363     size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5364                                          (size_t)ParGCDesiredObjsFromOverflowList);
5365     // Now check if there's any work in the overflow list
5366     // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5367     // only affects the number of attempts made to get work from the
5368     // overflow list and does not affect the number of workers.  Just
5369     // pass ParallelGCThreads so this behavior is unchanged.
5370     if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5371                                                 work_q,
5372                                                 ParallelGCThreads)) {
5373       // found something in global overflow list;
5374       // not yet ready to go stealing work from others.
5375       // We'd like to assert(work_q->size() != 0, ...)
5376       // because we just took work from the overflow list,
5377       // but of course we can't since all of that could have
5378       // been already stolen from us.
5379       // "He giveth and He taketh away."
5380       continue;
5381     }
5382     // Verify that we have no work before we resort to stealing
5383     assert(work_q->size() == 0, "Have work, shouldn't steal");
5384     // Try to steal from other queues that have work
5385     if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5386       NOT_PRODUCT(num_steals++;)
5387       assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5388       assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5389       // Do scanning work
5390       obj_to_scan->oop_iterate(cl);
5391       // Loop around, finish this work, and try to steal some more
5392     } else if (terminator()->offer_termination()) {
5393         break;  // nirvana from the infinite cycle
5394     }
5395   }
5396   NOT_PRODUCT(
5397     if (PrintCMSStatistics != 0) {
5398       gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5399     }
5400   )
5401   assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
5402          "Else our work is not yet done");
5403 }
5404 
5405 // Return a thread-local PLAB recording array, as appropriate.
5406 void* CMSCollector::get_data_recorder(int thr_num) {
5407   if (_survivor_plab_array != NULL &&
5408       (CMSPLABRecordAlways ||
5409        (_collectorState > Marking && _collectorState < FinalMarking))) {
5410     assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
5411     ChunkArray* ca = &_survivor_plab_array[thr_num];
5412     ca->reset();   // clear it so that fresh data is recorded
5413     return (void*) ca;
5414   } else {
5415     return NULL;
5416   }
5417 }
5418 
5419 // Reset all the thread-local PLAB recording arrays
5420 void CMSCollector::reset_survivor_plab_arrays() {
5421   for (uint i = 0; i < ParallelGCThreads; i++) {
5422     _survivor_plab_array[i].reset();
5423   }
5424 }
5425 
5426 // Merge the per-thread plab arrays into the global survivor chunk
5427 // array which will provide the partitioning of the survivor space
5428 // for CMS rescan.
5429 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv,
5430                                               int no_of_gc_threads) {
5431   assert(_survivor_plab_array  != NULL, "Error");
5432   assert(_survivor_chunk_array != NULL, "Error");
5433   assert(_collectorState == FinalMarking, "Error");
5434   for (int j = 0; j < no_of_gc_threads; j++) {
5435     _cursor[j] = 0;
5436   }
5437   HeapWord* top = surv->top();
5438   size_t i;
5439   for (i = 0; i < _survivor_chunk_capacity; i++) {  // all sca entries
5440     HeapWord* min_val = top;          // Higher than any PLAB address
5441     uint      min_tid = 0;            // position of min_val this round
5442     for (int j = 0; j < no_of_gc_threads; j++) {
5443       ChunkArray* cur_sca = &_survivor_plab_array[j];
5444       if (_cursor[j] == cur_sca->end()) {
5445         continue;
5446       }
5447       assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
5448       HeapWord* cur_val = cur_sca->nth(_cursor[j]);
5449       assert(surv->used_region().contains(cur_val), "Out of bounds value");
5450       if (cur_val < min_val) {
5451         min_tid = j;
5452         min_val = cur_val;
5453       } else {
5454         assert(cur_val < top, "All recorded addresses should be less");
5455       }
5456     }
5457     // At this point min_val and min_tid are respectively
5458     // the least address in _survivor_plab_array[j]->nth(_cursor[j])
5459     // and the thread (j) that witnesses that address.
5460     // We record this address in the _survivor_chunk_array[i]
5461     // and increment _cursor[min_tid] prior to the next round i.
5462     if (min_val == top) {
5463       break;
5464     }
5465     _survivor_chunk_array[i] = min_val;
5466     _cursor[min_tid]++;
5467   }
5468   // We are all done; record the size of the _survivor_chunk_array
5469   _survivor_chunk_index = i; // exclusive: [0, i)
5470   if (PrintCMSStatistics > 0) {
5471     gclog_or_tty->print(" (Survivor:" SIZE_FORMAT "chunks) ", i);
5472   }
5473   // Verify that we used up all the recorded entries
5474   #ifdef ASSERT
5475     size_t total = 0;
5476     for (int j = 0; j < no_of_gc_threads; j++) {
5477       assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
5478       total += _cursor[j];
5479     }
5480     assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
5481     // Check that the merged array is in sorted order
5482     if (total > 0) {
5483       for (size_t i = 0; i < total - 1; i++) {
5484         if (PrintCMSStatistics > 0) {
5485           gclog_or_tty->print(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
5486                               i, _survivor_chunk_array[i]);
5487         }
5488         assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
5489                "Not sorted");
5490       }
5491     }
5492   #endif // ASSERT
5493 }
5494 
5495 // Set up the space's par_seq_tasks structure for work claiming
5496 // for parallel rescan of young gen.
5497 // See ParRescanTask where this is currently used.
5498 void
5499 CMSCollector::
5500 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
5501   assert(n_threads > 0, "Unexpected n_threads argument");
5502   DefNewGeneration* dng = (DefNewGeneration*)_young_gen;
5503 
5504   // Eden space
5505   {
5506     SequentialSubTasksDone* pst = dng->eden()->par_seq_tasks();
5507     assert(!pst->valid(), "Clobbering existing data?");
5508     // Each valid entry in [0, _eden_chunk_index) represents a task.
5509     size_t n_tasks = _eden_chunk_index + 1;
5510     assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
5511     // Sets the condition for completion of the subtask (how many threads
5512     // need to finish in order to be done).
5513     pst->set_n_threads(n_threads);
5514     pst->set_n_tasks((int)n_tasks);
5515   }
5516 
5517   // Merge the survivor plab arrays into _survivor_chunk_array
5518   if (_survivor_plab_array != NULL) {
5519     merge_survivor_plab_arrays(dng->from(), n_threads);
5520   } else {
5521     assert(_survivor_chunk_index == 0, "Error");
5522   }
5523 
5524   // To space
5525   {
5526     SequentialSubTasksDone* pst = dng->to()->par_seq_tasks();
5527     assert(!pst->valid(), "Clobbering existing data?");
5528     // Sets the condition for completion of the subtask (how many threads
5529     // need to finish in order to be done).
5530     pst->set_n_threads(n_threads);
5531     pst->set_n_tasks(1);
5532     assert(pst->valid(), "Error");
5533   }
5534 
5535   // From space
5536   {
5537     SequentialSubTasksDone* pst = dng->from()->par_seq_tasks();
5538     assert(!pst->valid(), "Clobbering existing data?");
5539     size_t n_tasks = _survivor_chunk_index + 1;
5540     assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
5541     // Sets the condition for completion of the subtask (how many threads
5542     // need to finish in order to be done).
5543     pst->set_n_threads(n_threads);
5544     pst->set_n_tasks((int)n_tasks);
5545     assert(pst->valid(), "Error");
5546   }
5547 }
5548 
5549 // Parallel version of remark
5550 void CMSCollector::do_remark_parallel() {
5551   GenCollectedHeap* gch = GenCollectedHeap::heap();
5552   FlexibleWorkGang* workers = gch->workers();
5553   assert(workers != NULL, "Need parallel worker threads.");
5554   // Choose to use the number of GC workers most recently set
5555   // into "active_workers".  If active_workers is not set, set it
5556   // to ParallelGCThreads.
5557   int n_workers = workers->active_workers();
5558   if (n_workers == 0) {
5559     assert(n_workers > 0, "Should have been set during scavenge");
5560     n_workers = ParallelGCThreads;
5561     workers->set_active_workers(n_workers);
5562   }
5563   CompactibleFreeListSpace* cms_space  = _cmsGen->cmsSpace();
5564 
5565   CMSParRemarkTask tsk(this,
5566     cms_space,
5567     n_workers, workers, task_queues());
5568 
5569   // Set up for parallel process_strong_roots work.
5570   gch->set_par_threads(n_workers);
5571   // We won't be iterating over the cards in the card table updating
5572   // the younger_gen cards, so we shouldn't call the following else
5573   // the verification code as well as subsequent younger_refs_iterate
5574   // code would get confused. XXX
5575   // gch->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
5576 
5577   // The young gen rescan work will not be done as part of
5578   // process_strong_roots (which currently doesn't knw how to
5579   // parallelize such a scan), but rather will be broken up into
5580   // a set of parallel tasks (via the sampling that the [abortable]
5581   // preclean phase did of EdenSpace, plus the [two] tasks of
5582   // scanning the [two] survivor spaces. Further fine-grain
5583   // parallelization of the scanning of the survivor spaces
5584   // themselves, and of precleaning of the younger gen itself
5585   // is deferred to the future.
5586   initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
5587 
5588   // The dirty card rescan work is broken up into a "sequence"
5589   // of parallel tasks (per constituent space) that are dynamically
5590   // claimed by the parallel threads.
5591   cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
5592 
5593   // It turns out that even when we're using 1 thread, doing the work in a
5594   // separate thread causes wide variance in run times.  We can't help this
5595   // in the multi-threaded case, but we special-case n=1 here to get
5596   // repeatable measurements of the 1-thread overhead of the parallel code.
5597   if (n_workers > 1) {
5598     // Make refs discovery MT-safe, if it isn't already: it may not
5599     // necessarily be so, since it's possible that we are doing
5600     // ST marking.
5601     ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), true);
5602     GenCollectedHeap::StrongRootsScope srs(gch);
5603     workers->run_task(&tsk);
5604   } else {
5605     ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5606     GenCollectedHeap::StrongRootsScope srs(gch);
5607     tsk.work(0);
5608   }
5609 
5610   gch->set_par_threads(0);  // 0 ==> non-parallel.
5611   // restore, single-threaded for now, any preserved marks
5612   // as a result of work_q overflow
5613   restore_preserved_marks_if_any();
5614 }
5615 
5616 // Non-parallel version of remark
5617 void CMSCollector::do_remark_non_parallel() {
5618   ResourceMark rm;
5619   HandleMark   hm;
5620   GenCollectedHeap* gch = GenCollectedHeap::heap();
5621   ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5622 
5623   MarkRefsIntoAndScanClosure
5624     mrias_cl(_span, ref_processor(), &_markBitMap, NULL /* not precleaning */,
5625              &_markStack, this,
5626              false /* should_yield */, false /* not precleaning */);
5627   MarkFromDirtyCardsClosure
5628     markFromDirtyCardsClosure(this, _span,
5629                               NULL,  // space is set further below
5630                               &_markBitMap, &_markStack, &mrias_cl);
5631   {
5632     TraceTime t("grey object rescan", PrintGCDetails, false, gclog_or_tty);
5633     // Iterate over the dirty cards, setting the corresponding bits in the
5634     // mod union table.
5635     {
5636       ModUnionClosure modUnionClosure(&_modUnionTable);
5637       _ct->ct_bs()->dirty_card_iterate(
5638                       _cmsGen->used_region(),
5639                       &modUnionClosure);
5640     }
5641     // Having transferred these marks into the modUnionTable, we just need
5642     // to rescan the marked objects on the dirty cards in the modUnionTable.
5643     // The initial marking may have been done during an asynchronous
5644     // collection so there may be dirty bits in the mod-union table.
5645     const int alignment =
5646       CardTableModRefBS::card_size * BitsPerWord;
5647     {
5648       // ... First handle dirty cards in CMS gen
5649       markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
5650       MemRegion ur = _cmsGen->used_region();
5651       HeapWord* lb = ur.start();
5652       HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
5653       MemRegion cms_span(lb, ub);
5654       _modUnionTable.dirty_range_iterate_clear(cms_span,
5655                                                &markFromDirtyCardsClosure);
5656       verify_work_stacks_empty();
5657       if (PrintCMSStatistics != 0) {
5658         gclog_or_tty->print(" (re-scanned "SIZE_FORMAT" dirty cards in cms gen) ",
5659           markFromDirtyCardsClosure.num_dirty_cards());
5660       }
5661     }
5662   }
5663   if (VerifyDuringGC &&
5664       GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5665     HandleMark hm;  // Discard invalid handles created during verification
5666     Universe::verify();
5667   }
5668   {
5669     TraceTime t("root rescan", PrintGCDetails, false, gclog_or_tty);
5670 
5671     verify_work_stacks_empty();
5672 
5673     gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
5674     GenCollectedHeap::StrongRootsScope srs(gch);
5675     gch->gen_process_strong_roots(_cmsGen->level(),
5676                                   true,  // younger gens as roots
5677                                   false, // use the local StrongRootsScope
5678                                   false, // not scavenging
5679                                   SharedHeap::ScanningOption(roots_scanning_options()),
5680                                   &mrias_cl,
5681                                   true,   // walk code active on stacks
5682                                   NULL,
5683                                   NULL);  // The dirty klasses will be handled below
5684 
5685     assert(should_unload_classes()
5686            || (roots_scanning_options() & SharedHeap::SO_CodeCache),
5687            "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5688   }
5689 
5690   {
5691     TraceTime t("visit unhandled CLDs", PrintGCDetails, false, gclog_or_tty);
5692 
5693     verify_work_stacks_empty();
5694 
5695     // Scan all class loader data objects that might have been introduced
5696     // during concurrent marking.
5697     ResourceMark rm;
5698     GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
5699     for (int i = 0; i < array->length(); i++) {
5700       mrias_cl.do_class_loader_data(array->at(i));
5701     }
5702 
5703     // We don't need to keep track of new CLDs anymore.
5704     ClassLoaderDataGraph::remember_new_clds(false);
5705 
5706     verify_work_stacks_empty();
5707   }
5708 
5709   {
5710     TraceTime t("dirty klass scan", PrintGCDetails, false, gclog_or_tty);
5711 
5712     verify_work_stacks_empty();
5713 
5714     RemarkKlassClosure remark_klass_closure(&mrias_cl);
5715     ClassLoaderDataGraph::classes_do(&remark_klass_closure);
5716 
5717     verify_work_stacks_empty();
5718   }
5719 
5720   // We might have added oops to ClassLoaderData::_handles during the
5721   // concurrent marking phase. These oops point to newly allocated objects
5722   // that are guaranteed to be kept alive. Either by the direct allocation
5723   // code, or when the young collector processes the strong roots. Hence,
5724   // we don't have to revisit the _handles block during the remark phase.
5725 
5726   verify_work_stacks_empty();
5727   // Restore evacuated mark words, if any, used for overflow list links
5728   if (!CMSOverflowEarlyRestoration) {
5729     restore_preserved_marks_if_any();
5730   }
5731   verify_overflow_empty();
5732 }
5733 
5734 ////////////////////////////////////////////////////////
5735 // Parallel Reference Processing Task Proxy Class
5736 ////////////////////////////////////////////////////////
5737 class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues {
5738   typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
5739   CMSCollector*          _collector;
5740   CMSBitMap*             _mark_bit_map;
5741   const MemRegion        _span;
5742   ProcessTask&           _task;
5743 
5744 public:
5745   CMSRefProcTaskProxy(ProcessTask&     task,
5746                       CMSCollector*    collector,
5747                       const MemRegion& span,
5748                       CMSBitMap*       mark_bit_map,
5749                       AbstractWorkGang* workers,
5750                       OopTaskQueueSet* task_queues):
5751     // XXX Should superclass AGTWOQ also know about AWG since it knows
5752     // about the task_queues used by the AWG? Then it could initialize
5753     // the terminator() object. See 6984287. The set_for_termination()
5754     // below is a temporary band-aid for the regression in 6984287.
5755     AbstractGangTaskWOopQueues("Process referents by policy in parallel",
5756       task_queues),
5757     _task(task),
5758     _collector(collector), _span(span), _mark_bit_map(mark_bit_map)
5759   {
5760     assert(_collector->_span.equals(_span) && !_span.is_empty(),
5761            "Inconsistency in _span");
5762     set_for_termination(workers->active_workers());
5763   }
5764 
5765   OopTaskQueueSet* task_queues() { return queues(); }
5766 
5767   OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5768 
5769   void do_work_steal(int i,
5770                      CMSParDrainMarkingStackClosure* drain,
5771                      CMSParKeepAliveClosure* keep_alive,
5772                      int* seed);
5773 
5774   virtual void work(uint worker_id);
5775 };
5776 
5777 void CMSRefProcTaskProxy::work(uint worker_id) {
5778   assert(_collector->_span.equals(_span), "Inconsistency in _span");
5779   CMSParKeepAliveClosure par_keep_alive(_collector, _span,
5780                                         _mark_bit_map,
5781                                         work_queue(worker_id));
5782   CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
5783                                                  _mark_bit_map,
5784                                                  work_queue(worker_id));
5785   CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
5786   _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack);
5787   if (_task.marks_oops_alive()) {
5788     do_work_steal(worker_id, &par_drain_stack, &par_keep_alive,
5789                   _collector->hash_seed(worker_id));
5790   }
5791   assert(work_queue(worker_id)->size() == 0, "work_queue should be empty");
5792   assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
5793 }
5794 
5795 class CMSRefEnqueueTaskProxy: public AbstractGangTask {
5796   typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
5797   EnqueueTask& _task;
5798 
5799 public:
5800   CMSRefEnqueueTaskProxy(EnqueueTask& task)
5801     : AbstractGangTask("Enqueue reference objects in parallel"),
5802       _task(task)
5803   { }
5804 
5805   virtual void work(uint worker_id)
5806   {
5807     _task.work(worker_id);
5808   }
5809 };
5810 
5811 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
5812   MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue):
5813    _span(span),
5814    _bit_map(bit_map),
5815    _work_queue(work_queue),
5816    _mark_and_push(collector, span, bit_map, work_queue),
5817    _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
5818                         (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads)))
5819 { }
5820 
5821 // . see if we can share work_queues with ParNew? XXX
5822 void CMSRefProcTaskProxy::do_work_steal(int i,
5823   CMSParDrainMarkingStackClosure* drain,
5824   CMSParKeepAliveClosure* keep_alive,
5825   int* seed) {
5826   OopTaskQueue* work_q = work_queue(i);
5827   NOT_PRODUCT(int num_steals = 0;)
5828   oop obj_to_scan;
5829 
5830   while (true) {
5831     // Completely finish any left over work from (an) earlier round(s)
5832     drain->trim_queue(0);
5833     size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5834                                          (size_t)ParGCDesiredObjsFromOverflowList);
5835     // Now check if there's any work in the overflow list
5836     // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5837     // only affects the number of attempts made to get work from the
5838     // overflow list and does not affect the number of workers.  Just
5839     // pass ParallelGCThreads so this behavior is unchanged.
5840     if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5841                                                 work_q,
5842                                                 ParallelGCThreads)) {
5843       // Found something in global overflow list;
5844       // not yet ready to go stealing work from others.
5845       // We'd like to assert(work_q->size() != 0, ...)
5846       // because we just took work from the overflow list,
5847       // but of course we can't, since all of that might have
5848       // been already stolen from us.
5849       continue;
5850     }
5851     // Verify that we have no work before we resort to stealing
5852     assert(work_q->size() == 0, "Have work, shouldn't steal");
5853     // Try to steal from other queues that have work
5854     if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5855       NOT_PRODUCT(num_steals++;)
5856       assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5857       assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5858       // Do scanning work
5859       obj_to_scan->oop_iterate(keep_alive);
5860       // Loop around, finish this work, and try to steal some more
5861     } else if (terminator()->offer_termination()) {
5862       break;  // nirvana from the infinite cycle
5863     }
5864   }
5865   NOT_PRODUCT(
5866     if (PrintCMSStatistics != 0) {
5867       gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5868     }
5869   )
5870 }
5871 
5872 void CMSRefProcTaskExecutor::execute(ProcessTask& task)
5873 {
5874   GenCollectedHeap* gch = GenCollectedHeap::heap();
5875   FlexibleWorkGang* workers = gch->workers();
5876   assert(workers != NULL, "Need parallel worker threads.");
5877   CMSRefProcTaskProxy rp_task(task, &_collector,
5878                               _collector.ref_processor()->span(),
5879                               _collector.markBitMap(),
5880                               workers, _collector.task_queues());
5881   workers->run_task(&rp_task);
5882 }
5883 
5884 void CMSRefProcTaskExecutor::execute(EnqueueTask& task)
5885 {
5886 
5887   GenCollectedHeap* gch = GenCollectedHeap::heap();
5888   FlexibleWorkGang* workers = gch->workers();
5889   assert(workers != NULL, "Need parallel worker threads.");
5890   CMSRefEnqueueTaskProxy enq_task(task);
5891   workers->run_task(&enq_task);
5892 }
5893 
5894 void CMSCollector::refProcessingWork(bool asynch, bool clear_all_soft_refs) {
5895 
5896   ResourceMark rm;
5897   HandleMark   hm;
5898 
5899   ReferenceProcessor* rp = ref_processor();
5900   assert(rp->span().equals(_span), "Spans should be equal");
5901   assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
5902   // Process weak references.
5903   rp->setup_policy(clear_all_soft_refs);
5904   verify_work_stacks_empty();
5905 
5906   CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
5907                                           &_markStack, false /* !preclean */);
5908   CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
5909                                 _span, &_markBitMap, &_markStack,
5910                                 &cmsKeepAliveClosure, false /* !preclean */);
5911   {
5912     TraceTime t("weak refs processing", PrintGCDetails, false, gclog_or_tty);
5913     if (rp->processing_is_mt()) {
5914       // Set the degree of MT here.  If the discovery is done MT, there
5915       // may have been a different number of threads doing the discovery
5916       // and a different number of discovered lists may have Ref objects.
5917       // That is OK as long as the Reference lists are balanced (see
5918       // balance_all_queues() and balance_queues()).
5919       GenCollectedHeap* gch = GenCollectedHeap::heap();
5920       int active_workers = ParallelGCThreads;
5921       FlexibleWorkGang* workers = gch->workers();
5922       if (workers != NULL) {
5923         active_workers = workers->active_workers();
5924         // The expectation is that active_workers will have already
5925         // been set to a reasonable value.  If it has not been set,
5926         // investigate.
5927         assert(active_workers > 0, "Should have been set during scavenge");
5928       }
5929       rp->set_active_mt_degree(active_workers);
5930       CMSRefProcTaskExecutor task_executor(*this);
5931       rp->process_discovered_references(&_is_alive_closure,
5932                                         &cmsKeepAliveClosure,
5933                                         &cmsDrainMarkingStackClosure,
5934                                         &task_executor);
5935     } else {
5936       rp->process_discovered_references(&_is_alive_closure,
5937                                         &cmsKeepAliveClosure,
5938                                         &cmsDrainMarkingStackClosure,
5939                                         NULL);
5940     }
5941     verify_work_stacks_empty();
5942   }
5943 
5944   if (should_unload_classes()) {
5945     {
5946       TraceTime t("class unloading", PrintGCDetails, false, gclog_or_tty);
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, purged_class);
5953 
5954       cmsDrainMarkingStackClosure.do_void();
5955       verify_work_stacks_empty();
5956 
5957       // Update subklass/sibling/implementor links in KlassKlass descendants
5958       Klass::clean_weak_klass_links(&_is_alive_closure);
5959       // Nothing should have been pushed onto the working stacks.
5960       verify_work_stacks_empty();
5961     }
5962 
5963     {
5964       TraceTime t("scrub symbol table", PrintGCDetails, false, gclog_or_tty);
5965       // Clean up unreferenced symbols in symbol table.
5966       SymbolTable::unlink();
5967     }
5968   }
5969 
5970   // CMS doesn't use the StringTable as hard roots when class unloading is turned off.
5971   // Need to check if we really scanned the StringTable.
5972   if ((roots_scanning_options() & SharedHeap::SO_Strings) == 0) {
5973     TraceTime t("scrub string table", PrintGCDetails, false, gclog_or_tty);
5974     // Now clean up stale oops in StringTable
5975     StringTable::unlink(&_is_alive_closure);
5976   }
5977 
5978   verify_work_stacks_empty();
5979   // Restore any preserved marks as a result of mark stack or
5980   // work queue overflow
5981   restore_preserved_marks_if_any();  // done single-threaded for now
5982 
5983   rp->set_enqueuing_is_done(true);
5984   if (rp->processing_is_mt()) {
5985     rp->balance_all_queues();
5986     CMSRefProcTaskExecutor task_executor(*this);
5987     rp->enqueue_discovered_references(&task_executor);
5988   } else {
5989     rp->enqueue_discovered_references(NULL);
5990   }
5991   rp->verify_no_references_recorded();
5992   assert(!rp->discovery_enabled(), "should have been disabled");
5993 }
5994 
5995 #ifndef PRODUCT
5996 void CMSCollector::check_correct_thread_executing() {
5997   Thread* t = Thread::current();
5998   // Only the VM thread or the CMS thread should be here.
5999   assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
6000          "Unexpected thread type");
6001   // If this is the vm thread, the foreground process
6002   // should not be waiting.  Note that _foregroundGCIsActive is
6003   // true while the foreground collector is waiting.
6004   if (_foregroundGCShouldWait) {
6005     // We cannot be the VM thread
6006     assert(t->is_ConcurrentGC_thread(),
6007            "Should be CMS thread");
6008   } else {
6009     // We can be the CMS thread only if we are in a stop-world
6010     // phase of CMS collection.
6011     if (t->is_ConcurrentGC_thread()) {
6012       assert(_collectorState == InitialMarking ||
6013              _collectorState == FinalMarking,
6014              "Should be a stop-world phase");
6015       // The CMS thread should be holding the CMS_token.
6016       assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6017              "Potential interference with concurrently "
6018              "executing VM thread");
6019     }
6020   }
6021 }
6022 #endif
6023 
6024 void CMSCollector::sweep(bool asynch) {
6025   assert(_collectorState == Sweeping, "just checking");
6026   check_correct_thread_executing();
6027   verify_work_stacks_empty();
6028   verify_overflow_empty();
6029   increment_sweep_count();
6030   TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
6031 
6032   _inter_sweep_timer.stop();
6033   _inter_sweep_estimate.sample(_inter_sweep_timer.seconds());
6034   size_policy()->avg_cms_free_at_sweep()->sample(_cmsGen->free());
6035 
6036   assert(!_intra_sweep_timer.is_active(), "Should not be active");
6037   _intra_sweep_timer.reset();
6038   _intra_sweep_timer.start();
6039   if (asynch) {
6040     TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6041     CMSPhaseAccounting pa(this, "sweep", !PrintGCDetails);
6042     // First sweep the old gen
6043     {
6044       CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
6045                                bitMapLock());
6046       sweepWork(_cmsGen, asynch);
6047     }
6048 
6049     // Update Universe::_heap_*_at_gc figures.
6050     // We need all the free list locks to make the abstract state
6051     // transition from Sweeping to Resetting. See detailed note
6052     // further below.
6053     {
6054       CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock());
6055       // Update heap occupancy information which is used as
6056       // input to soft ref clearing policy at the next gc.
6057       Universe::update_heap_info_at_gc();
6058       _collectorState = Resizing;
6059     }
6060   } else {
6061     // already have needed locks
6062     sweepWork(_cmsGen,  asynch);
6063     // Update heap occupancy information which is used as
6064     // input to soft ref clearing policy at the next gc.
6065     Universe::update_heap_info_at_gc();
6066     _collectorState = Resizing;
6067   }
6068   verify_work_stacks_empty();
6069   verify_overflow_empty();
6070 
6071   if (should_unload_classes()) {
6072     ClassLoaderDataGraph::purge();
6073   }
6074 
6075   _intra_sweep_timer.stop();
6076   _intra_sweep_estimate.sample(_intra_sweep_timer.seconds());
6077 
6078   _inter_sweep_timer.reset();
6079   _inter_sweep_timer.start();
6080 
6081   // We need to use a monotonically non-deccreasing time in ms
6082   // or we will see time-warp warnings and os::javaTimeMillis()
6083   // does not guarantee monotonicity.
6084   jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
6085   update_time_of_last_gc(now);
6086 
6087   // NOTE on abstract state transitions:
6088   // Mutators allocate-live and/or mark the mod-union table dirty
6089   // based on the state of the collection.  The former is done in
6090   // the interval [Marking, Sweeping] and the latter in the interval
6091   // [Marking, Sweeping).  Thus the transitions into the Marking state
6092   // and out of the Sweeping state must be synchronously visible
6093   // globally to the mutators.
6094   // The transition into the Marking state happens with the world
6095   // stopped so the mutators will globally see it.  Sweeping is
6096   // done asynchronously by the background collector so the transition
6097   // from the Sweeping state to the Resizing state must be done
6098   // under the freelistLock (as is the check for whether to
6099   // allocate-live and whether to dirty the mod-union table).
6100   assert(_collectorState == Resizing, "Change of collector state to"
6101     " Resizing must be done under the freelistLocks (plural)");
6102 
6103   // Now that sweeping has been completed, we clear
6104   // the incremental_collection_failed flag,
6105   // thus inviting a younger gen collection to promote into
6106   // this generation. If such a promotion may still fail,
6107   // the flag will be set again when a young collection is
6108   // attempted.
6109   GenCollectedHeap* gch = GenCollectedHeap::heap();
6110   gch->clear_incremental_collection_failed();  // Worth retrying as fresh space may have been freed up
6111   gch->update_full_collections_completed(_collection_count_start);
6112 }
6113 
6114 // FIX ME!!! Looks like this belongs in CFLSpace, with
6115 // CMSGen merely delegating to it.
6116 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
6117   double nearLargestPercent = FLSLargestBlockCoalesceProximity;
6118   HeapWord*  minAddr        = _cmsSpace->bottom();
6119   HeapWord*  largestAddr    =
6120     (HeapWord*) _cmsSpace->dictionary()->find_largest_dict();
6121   if (largestAddr == NULL) {
6122     // The dictionary appears to be empty.  In this case
6123     // try to coalesce at the end of the heap.
6124     largestAddr = _cmsSpace->end();
6125   }
6126   size_t largestOffset     = pointer_delta(largestAddr, minAddr);
6127   size_t nearLargestOffset =
6128     (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
6129   if (PrintFLSStatistics != 0) {
6130     gclog_or_tty->print_cr(
6131       "CMS: Large Block: " PTR_FORMAT ";"
6132       " Proximity: " PTR_FORMAT " -> " PTR_FORMAT,
6133       largestAddr,
6134       _cmsSpace->nearLargestChunk(), minAddr + nearLargestOffset);
6135   }
6136   _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
6137 }
6138 
6139 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
6140   return addr >= _cmsSpace->nearLargestChunk();
6141 }
6142 
6143 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
6144   return _cmsSpace->find_chunk_at_end();
6145 }
6146 
6147 void ConcurrentMarkSweepGeneration::update_gc_stats(int current_level,
6148                                                     bool full) {
6149   // The next lower level has been collected.  Gather any statistics
6150   // that are of interest at this point.
6151   if (!full && (current_level + 1) == level()) {
6152     // Gather statistics on the young generation collection.
6153     collector()->stats().record_gc0_end(used());
6154   }
6155 }
6156 
6157 CMSAdaptiveSizePolicy* ConcurrentMarkSweepGeneration::size_policy() {
6158   GenCollectedHeap* gch = GenCollectedHeap::heap();
6159   assert(gch->kind() == CollectedHeap::GenCollectedHeap,
6160     "Wrong type of heap");
6161   CMSAdaptiveSizePolicy* sp = (CMSAdaptiveSizePolicy*)
6162     gch->gen_policy()->size_policy();
6163   assert(sp->is_gc_cms_adaptive_size_policy(),
6164     "Wrong type of size policy");
6165   return sp;
6166 }
6167 
6168 void ConcurrentMarkSweepGeneration::rotate_debug_collection_type() {
6169   if (PrintGCDetails && Verbose) {
6170     gclog_or_tty->print("Rotate from %d ", _debug_collection_type);
6171   }
6172   _debug_collection_type = (CollectionTypes) (_debug_collection_type + 1);
6173   _debug_collection_type =
6174     (CollectionTypes) (_debug_collection_type % Unknown_collection_type);
6175   if (PrintGCDetails && Verbose) {
6176     gclog_or_tty->print_cr("to %d ", _debug_collection_type);
6177   }
6178 }
6179 
6180 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* gen,
6181   bool asynch) {
6182   // We iterate over the space(s) underlying this generation,
6183   // checking the mark bit map to see if the bits corresponding
6184   // to specific blocks are marked or not. Blocks that are
6185   // marked are live and are not swept up. All remaining blocks
6186   // are swept up, with coalescing on-the-fly as we sweep up
6187   // contiguous free and/or garbage blocks:
6188   // We need to ensure that the sweeper synchronizes with allocators
6189   // and stop-the-world collectors. In particular, the following
6190   // locks are used:
6191   // . CMS token: if this is held, a stop the world collection cannot occur
6192   // . freelistLock: if this is held no allocation can occur from this
6193   //                 generation by another thread
6194   // . bitMapLock: if this is held, no other thread can access or update
6195   //
6196 
6197   // Note that we need to hold the freelistLock if we use
6198   // block iterate below; else the iterator might go awry if
6199   // a mutator (or promotion) causes block contents to change
6200   // (for instance if the allocator divvies up a block).
6201   // If we hold the free list lock, for all practical purposes
6202   // young generation GC's can't occur (they'll usually need to
6203   // promote), so we might as well prevent all young generation
6204   // GC's while we do a sweeping step. For the same reason, we might
6205   // as well take the bit map lock for the entire duration
6206 
6207   // check that we hold the requisite locks
6208   assert(have_cms_token(), "Should hold cms token");
6209   assert(   (asynch && ConcurrentMarkSweepThread::cms_thread_has_cms_token())
6210          || (!asynch && ConcurrentMarkSweepThread::vm_thread_has_cms_token()),
6211         "Should possess CMS token to sweep");
6212   assert_lock_strong(gen->freelistLock());
6213   assert_lock_strong(bitMapLock());
6214 
6215   assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context");
6216   assert(_intra_sweep_timer.is_active(),  "Was switched on  in an outer context");
6217   gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
6218                                       _inter_sweep_estimate.padded_average(),
6219                                       _intra_sweep_estimate.padded_average());
6220   gen->setNearLargestChunk();
6221 
6222   {
6223     SweepClosure sweepClosure(this, gen, &_markBitMap,
6224                             CMSYield && asynch);
6225     gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
6226     // We need to free-up/coalesce garbage/blocks from a
6227     // co-terminal free run. This is done in the SweepClosure
6228     // destructor; so, do not remove this scope, else the
6229     // end-of-sweep-census below will be off by a little bit.
6230   }
6231   gen->cmsSpace()->sweep_completed();
6232   gen->cmsSpace()->endSweepFLCensus(sweep_count());
6233   if (should_unload_classes()) {                // unloaded classes this cycle,
6234     _concurrent_cycles_since_last_unload = 0;   // ... reset count
6235   } else {                                      // did not unload classes,
6236     _concurrent_cycles_since_last_unload++;     // ... increment count
6237   }
6238 }
6239 
6240 // Reset CMS data structures (for now just the marking bit map)
6241 // preparatory for the next cycle.
6242 void CMSCollector::reset(bool asynch) {
6243   GenCollectedHeap* gch = GenCollectedHeap::heap();
6244   CMSAdaptiveSizePolicy* sp = size_policy();
6245   AdaptiveSizePolicyOutput(sp, gch->total_collections());
6246   if (asynch) {
6247     CMSTokenSyncWithLocks ts(true, bitMapLock());
6248 
6249     // If the state is not "Resetting", the foreground  thread
6250     // has done a collection and the resetting.
6251     if (_collectorState != Resetting) {
6252       assert(_collectorState == Idling, "The state should only change"
6253         " because the foreground collector has finished the collection");
6254       return;
6255     }
6256 
6257     // Clear the mark bitmap (no grey objects to start with)
6258     // for the next cycle.
6259     TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6260     CMSPhaseAccounting cmspa(this, "reset", !PrintGCDetails);
6261 
6262     HeapWord* curAddr = _markBitMap.startWord();
6263     while (curAddr < _markBitMap.endWord()) {
6264       size_t remaining  = pointer_delta(_markBitMap.endWord(), curAddr);
6265       MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
6266       _markBitMap.clear_large_range(chunk);
6267       if (ConcurrentMarkSweepThread::should_yield() &&
6268           !foregroundGCIsActive() &&
6269           CMSYield) {
6270         assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6271                "CMS thread should hold CMS token");
6272         assert_lock_strong(bitMapLock());
6273         bitMapLock()->unlock();
6274         ConcurrentMarkSweepThread::desynchronize(true);
6275         ConcurrentMarkSweepThread::acknowledge_yield_request();
6276         stopTimer();
6277         if (PrintCMSStatistics != 0) {
6278           incrementYields();
6279         }
6280         icms_wait();
6281 
6282         // See the comment in coordinator_yield()
6283         for (unsigned i = 0; i < CMSYieldSleepCount &&
6284                          ConcurrentMarkSweepThread::should_yield() &&
6285                          !CMSCollector::foregroundGCIsActive(); ++i) {
6286           os::sleep(Thread::current(), 1, false);
6287           ConcurrentMarkSweepThread::acknowledge_yield_request();
6288         }
6289 
6290         ConcurrentMarkSweepThread::synchronize(true);
6291         bitMapLock()->lock_without_safepoint_check();
6292         startTimer();
6293       }
6294       curAddr = chunk.end();
6295     }
6296     // A successful mostly concurrent collection has been done.
6297     // Because only the full (i.e., concurrent mode failure) collections
6298     // are being measured for gc overhead limits, clean the "near" flag
6299     // and count.
6300     sp->reset_gc_overhead_limit_count();
6301     _collectorState = Idling;
6302   } else {
6303     // already have the lock
6304     assert(_collectorState == Resetting, "just checking");
6305     assert_lock_strong(bitMapLock());
6306     _markBitMap.clear_all();
6307     _collectorState = Idling;
6308   }
6309 
6310   // Stop incremental mode after a cycle completes, so that any future cycles
6311   // are triggered by allocation.
6312   stop_icms();
6313 
6314   NOT_PRODUCT(
6315     if (RotateCMSCollectionTypes) {
6316       _cmsGen->rotate_debug_collection_type();
6317     }
6318   )
6319 }
6320 
6321 void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) {
6322   gclog_or_tty->date_stamp(PrintGC && PrintGCDateStamps);
6323   TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6324   TraceTime t(GCCauseString("GC", gc_cause), PrintGC, !PrintGCDetails, gclog_or_tty);
6325   TraceCollectorStats tcs(counters());
6326 
6327   switch (op) {
6328     case CMS_op_checkpointRootsInitial: {
6329       SvcGCMarker sgcm(SvcGCMarker::OTHER);
6330       checkpointRootsInitial(true);       // asynch
6331       if (PrintGC) {
6332         _cmsGen->printOccupancy("initial-mark");
6333       }
6334       break;
6335     }
6336     case CMS_op_checkpointRootsFinal: {
6337       SvcGCMarker sgcm(SvcGCMarker::OTHER);
6338       checkpointRootsFinal(true,    // asynch
6339                            false,   // !clear_all_soft_refs
6340                            false);  // !init_mark_was_synchronous
6341       if (PrintGC) {
6342         _cmsGen->printOccupancy("remark");
6343       }
6344       break;
6345     }
6346     default:
6347       fatal("No such CMS_op");
6348   }
6349 }
6350 
6351 #ifndef PRODUCT
6352 size_t const CMSCollector::skip_header_HeapWords() {
6353   return FreeChunk::header_size();
6354 }
6355 
6356 // Try and collect here conditions that should hold when
6357 // CMS thread is exiting. The idea is that the foreground GC
6358 // thread should not be blocked if it wants to terminate
6359 // the CMS thread and yet continue to run the VM for a while
6360 // after that.
6361 void CMSCollector::verify_ok_to_terminate() const {
6362   assert(Thread::current()->is_ConcurrentGC_thread(),
6363          "should be called by CMS thread");
6364   assert(!_foregroundGCShouldWait, "should be false");
6365   // We could check here that all the various low-level locks
6366   // are not held by the CMS thread, but that is overkill; see
6367   // also CMSThread::verify_ok_to_terminate() where the CGC_lock
6368   // is checked.
6369 }
6370 #endif
6371 
6372 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
6373    assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
6374           "missing Printezis mark?");
6375   HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
6376   size_t size = pointer_delta(nextOneAddr + 1, addr);
6377   assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6378          "alignment problem");
6379   assert(size >= 3, "Necessary for Printezis marks to work");
6380   return size;
6381 }
6382 
6383 // A variant of the above (block_size_using_printezis_bits()) except
6384 // that we return 0 if the P-bits are not yet set.
6385 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
6386   if (_markBitMap.isMarked(addr + 1)) {
6387     assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects");
6388     HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
6389     size_t size = pointer_delta(nextOneAddr + 1, addr);
6390     assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6391            "alignment problem");
6392     assert(size >= 3, "Necessary for Printezis marks to work");
6393     return size;
6394   }
6395   return 0;
6396 }
6397 
6398 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
6399   size_t sz = 0;
6400   oop p = (oop)addr;
6401   if (p->klass_or_null() != NULL) {
6402     sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
6403   } else {
6404     sz = block_size_using_printezis_bits(addr);
6405   }
6406   assert(sz > 0, "size must be nonzero");
6407   HeapWord* next_block = addr + sz;
6408   HeapWord* next_card  = (HeapWord*)round_to((uintptr_t)next_block,
6409                                              CardTableModRefBS::card_size);
6410   assert(round_down((uintptr_t)addr,      CardTableModRefBS::card_size) <
6411          round_down((uintptr_t)next_card, CardTableModRefBS::card_size),
6412          "must be different cards");
6413   return next_card;
6414 }
6415 
6416 
6417 // CMS Bit Map Wrapper /////////////////////////////////////////
6418 
6419 // Construct a CMS bit map infrastructure, but don't create the
6420 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
6421 // further below.
6422 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
6423   _bm(),
6424   _shifter(shifter),
6425   _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true) : NULL)
6426 {
6427   _bmStartWord = 0;
6428   _bmWordSize  = 0;
6429 }
6430 
6431 bool CMSBitMap::allocate(MemRegion mr) {
6432   _bmStartWord = mr.start();
6433   _bmWordSize  = mr.word_size();
6434   ReservedSpace brs(ReservedSpace::allocation_align_size_up(
6435                      (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
6436   if (!brs.is_reserved()) {
6437     warning("CMS bit map allocation failure");
6438     return false;
6439   }
6440   // For now we'll just commit all of the bit map up fromt.
6441   // Later on we'll try to be more parsimonious with swap.
6442   if (!_virtual_space.initialize(brs, brs.size())) {
6443     warning("CMS bit map backing store failure");
6444     return false;
6445   }
6446   assert(_virtual_space.committed_size() == brs.size(),
6447          "didn't reserve backing store for all of CMS bit map?");
6448   _bm.set_map((BitMap::bm_word_t*)_virtual_space.low());
6449   assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
6450          _bmWordSize, "inconsistency in bit map sizing");
6451   _bm.set_size(_bmWordSize >> _shifter);
6452 
6453   // bm.clear(); // can we rely on getting zero'd memory? verify below
6454   assert(isAllClear(),
6455          "Expected zero'd memory from ReservedSpace constructor");
6456   assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
6457          "consistency check");
6458   return true;
6459 }
6460 
6461 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
6462   HeapWord *next_addr, *end_addr, *last_addr;
6463   assert_locked();
6464   assert(covers(mr), "out-of-range error");
6465   // XXX assert that start and end are appropriately aligned
6466   for (next_addr = mr.start(), end_addr = mr.end();
6467        next_addr < end_addr; next_addr = last_addr) {
6468     MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
6469     last_addr = dirty_region.end();
6470     if (!dirty_region.is_empty()) {
6471       cl->do_MemRegion(dirty_region);
6472     } else {
6473       assert(last_addr == end_addr, "program logic");
6474       return;
6475     }
6476   }
6477 }
6478 
6479 #ifndef PRODUCT
6480 void CMSBitMap::assert_locked() const {
6481   CMSLockVerifier::assert_locked(lock());
6482 }
6483 
6484 bool CMSBitMap::covers(MemRegion mr) const {
6485   // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
6486   assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
6487          "size inconsistency");
6488   return (mr.start() >= _bmStartWord) &&
6489          (mr.end()   <= endWord());
6490 }
6491 
6492 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
6493     return (start >= _bmStartWord && (start + size) <= endWord());
6494 }
6495 
6496 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
6497   // verify that there are no 1 bits in the interval [left, right)
6498   FalseBitMapClosure falseBitMapClosure;
6499   iterate(&falseBitMapClosure, left, right);
6500 }
6501 
6502 void CMSBitMap::region_invariant(MemRegion mr)
6503 {
6504   assert_locked();
6505   // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
6506   assert(!mr.is_empty(), "unexpected empty region");
6507   assert(covers(mr), "mr should be covered by bit map");
6508   // convert address range into offset range
6509   size_t start_ofs = heapWordToOffset(mr.start());
6510   // Make sure that end() is appropriately aligned
6511   assert(mr.end() == (HeapWord*)round_to((intptr_t)mr.end(),
6512                         (1 << (_shifter+LogHeapWordSize))),
6513          "Misaligned mr.end()");
6514   size_t end_ofs   = heapWordToOffset(mr.end());
6515   assert(end_ofs > start_ofs, "Should mark at least one bit");
6516 }
6517 
6518 #endif
6519 
6520 bool CMSMarkStack::allocate(size_t size) {
6521   // allocate a stack of the requisite depth
6522   ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6523                    size * sizeof(oop)));
6524   if (!rs.is_reserved()) {
6525     warning("CMSMarkStack allocation failure");
6526     return false;
6527   }
6528   if (!_virtual_space.initialize(rs, rs.size())) {
6529     warning("CMSMarkStack backing store failure");
6530     return false;
6531   }
6532   assert(_virtual_space.committed_size() == rs.size(),
6533          "didn't reserve backing store for all of CMS stack?");
6534   _base = (oop*)(_virtual_space.low());
6535   _index = 0;
6536   _capacity = size;
6537   NOT_PRODUCT(_max_depth = 0);
6538   return true;
6539 }
6540 
6541 // XXX FIX ME !!! In the MT case we come in here holding a
6542 // leaf lock. For printing we need to take a further lock
6543 // which has lower rank. We need to recallibrate the two
6544 // lock-ranks involved in order to be able to rpint the
6545 // messages below. (Or defer the printing to the caller.
6546 // For now we take the expedient path of just disabling the
6547 // messages for the problematic case.)
6548 void CMSMarkStack::expand() {
6549   assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted");
6550   if (_capacity == MarkStackSizeMax) {
6551     if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6552       // We print a warning message only once per CMS cycle.
6553       gclog_or_tty->print_cr(" (benign) Hit CMSMarkStack max size limit");
6554     }
6555     return;
6556   }
6557   // Double capacity if possible
6558   size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax);
6559   // Do not give up existing stack until we have managed to
6560   // get the double capacity that we desired.
6561   ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6562                    new_capacity * sizeof(oop)));
6563   if (rs.is_reserved()) {
6564     // Release the backing store associated with old stack
6565     _virtual_space.release();
6566     // Reinitialize virtual space for new stack
6567     if (!_virtual_space.initialize(rs, rs.size())) {
6568       fatal("Not enough swap for expanded marking stack");
6569     }
6570     _base = (oop*)(_virtual_space.low());
6571     _index = 0;
6572     _capacity = new_capacity;
6573   } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6574     // Failed to double capacity, continue;
6575     // we print a detail message only once per CMS cycle.
6576     gclog_or_tty->print(" (benign) Failed to expand marking stack from "SIZE_FORMAT"K to "
6577             SIZE_FORMAT"K",
6578             _capacity / K, new_capacity / K);
6579   }
6580 }
6581 
6582 
6583 // Closures
6584 // XXX: there seems to be a lot of code  duplication here;
6585 // should refactor and consolidate common code.
6586 
6587 // This closure is used to mark refs into the CMS generation in
6588 // the CMS bit map. Called at the first checkpoint. This closure
6589 // assumes that we do not need to re-mark dirty cards; if the CMS
6590 // generation on which this is used is not an oldest
6591 // generation then this will lose younger_gen cards!
6592 
6593 MarkRefsIntoClosure::MarkRefsIntoClosure(
6594   MemRegion span, CMSBitMap* bitMap):
6595     _span(span),
6596     _bitMap(bitMap)
6597 {
6598     assert(_ref_processor == NULL, "deliberately left NULL");
6599     assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6600 }
6601 
6602 void MarkRefsIntoClosure::do_oop(oop obj) {
6603   // if p points into _span, then mark corresponding bit in _markBitMap
6604   assert(obj->is_oop(), "expected an oop");
6605   HeapWord* addr = (HeapWord*)obj;
6606   if (_span.contains(addr)) {
6607     // this should be made more efficient
6608     _bitMap->mark(addr);
6609   }
6610 }
6611 
6612 void MarkRefsIntoClosure::do_oop(oop* p)       { MarkRefsIntoClosure::do_oop_work(p); }
6613 void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6614 
6615 // A variant of the above, used for CMS marking verification.
6616 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
6617   MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm):
6618     _span(span),
6619     _verification_bm(verification_bm),
6620     _cms_bm(cms_bm)
6621 {
6622     assert(_ref_processor == NULL, "deliberately left NULL");
6623     assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
6624 }
6625 
6626 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
6627   // if p points into _span, then mark corresponding bit in _markBitMap
6628   assert(obj->is_oop(), "expected an oop");
6629   HeapWord* addr = (HeapWord*)obj;
6630   if (_span.contains(addr)) {
6631     _verification_bm->mark(addr);
6632     if (!_cms_bm->isMarked(addr)) {
6633       oop(addr)->print();
6634       gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)", addr);
6635       fatal("... aborting");
6636     }
6637   }
6638 }
6639 
6640 void MarkRefsIntoVerifyClosure::do_oop(oop* p)       { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6641 void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6642 
6643 //////////////////////////////////////////////////
6644 // MarkRefsIntoAndScanClosure
6645 //////////////////////////////////////////////////
6646 
6647 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
6648                                                        ReferenceProcessor* rp,
6649                                                        CMSBitMap* bit_map,
6650                                                        CMSBitMap* mod_union_table,
6651                                                        CMSMarkStack*  mark_stack,
6652                                                        CMSCollector* collector,
6653                                                        bool should_yield,
6654                                                        bool concurrent_precleaning):
6655   _collector(collector),
6656   _span(span),
6657   _bit_map(bit_map),
6658   _mark_stack(mark_stack),
6659   _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table,
6660                       mark_stack, concurrent_precleaning),
6661   _yield(should_yield),
6662   _concurrent_precleaning(concurrent_precleaning),
6663   _freelistLock(NULL)
6664 {
6665   _ref_processor = rp;
6666   assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6667 }
6668 
6669 // This closure is used to mark refs into the CMS generation at the
6670 // second (final) checkpoint, and to scan and transitively follow
6671 // the unmarked oops. It is also used during the concurrent precleaning
6672 // phase while scanning objects on dirty cards in the CMS generation.
6673 // The marks are made in the marking bit map and the marking stack is
6674 // used for keeping the (newly) grey objects during the scan.
6675 // The parallel version (Par_...) appears further below.
6676 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6677   if (obj != NULL) {
6678     assert(obj->is_oop(), "expected an oop");
6679     HeapWord* addr = (HeapWord*)obj;
6680     assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6681     assert(_collector->overflow_list_is_empty(),
6682            "overflow list should be empty");
6683     if (_span.contains(addr) &&
6684         !_bit_map->isMarked(addr)) {
6685       // mark bit map (object is now grey)
6686       _bit_map->mark(addr);
6687       // push on marking stack (stack should be empty), and drain the
6688       // stack by applying this closure to the oops in the oops popped
6689       // from the stack (i.e. blacken the grey objects)
6690       bool res = _mark_stack->push(obj);
6691       assert(res, "Should have space to push on empty stack");
6692       do {
6693         oop new_oop = _mark_stack->pop();
6694         assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6695         assert(_bit_map->isMarked((HeapWord*)new_oop),
6696                "only grey objects on this stack");
6697         // iterate over the oops in this oop, marking and pushing
6698         // the ones in CMS heap (i.e. in _span).
6699         new_oop->oop_iterate(&_pushAndMarkClosure);
6700         // check if it's time to yield
6701         do_yield_check();
6702       } while (!_mark_stack->isEmpty() ||
6703                (!_concurrent_precleaning && take_from_overflow_list()));
6704         // if marking stack is empty, and we are not doing this
6705         // during precleaning, then check the overflow list
6706     }
6707     assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6708     assert(_collector->overflow_list_is_empty(),
6709            "overflow list was drained above");
6710     // We could restore evacuated mark words, if any, used for
6711     // overflow list links here because the overflow list is
6712     // provably empty here. That would reduce the maximum
6713     // size requirements for preserved_{oop,mark}_stack.
6714     // But we'll just postpone it until we are all done
6715     // so we can just stream through.
6716     if (!_concurrent_precleaning && CMSOverflowEarlyRestoration) {
6717       _collector->restore_preserved_marks_if_any();
6718       assert(_collector->no_preserved_marks(), "No preserved marks");
6719     }
6720     assert(!CMSOverflowEarlyRestoration || _collector->no_preserved_marks(),
6721            "All preserved marks should have been restored above");
6722   }
6723 }
6724 
6725 void MarkRefsIntoAndScanClosure::do_oop(oop* p)       { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6726 void MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6727 
6728 void MarkRefsIntoAndScanClosure::do_yield_work() {
6729   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6730          "CMS thread should hold CMS token");
6731   assert_lock_strong(_freelistLock);
6732   assert_lock_strong(_bit_map->lock());
6733   // relinquish the free_list_lock and bitMaplock()
6734   _bit_map->lock()->unlock();
6735   _freelistLock->unlock();
6736   ConcurrentMarkSweepThread::desynchronize(true);
6737   ConcurrentMarkSweepThread::acknowledge_yield_request();
6738   _collector->stopTimer();
6739   GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
6740   if (PrintCMSStatistics != 0) {
6741     _collector->incrementYields();
6742   }
6743   _collector->icms_wait();
6744 
6745   // See the comment in coordinator_yield()
6746   for (unsigned i = 0;
6747        i < CMSYieldSleepCount &&
6748        ConcurrentMarkSweepThread::should_yield() &&
6749        !CMSCollector::foregroundGCIsActive();
6750        ++i) {
6751     os::sleep(Thread::current(), 1, false);
6752     ConcurrentMarkSweepThread::acknowledge_yield_request();
6753   }
6754 
6755   ConcurrentMarkSweepThread::synchronize(true);
6756   _freelistLock->lock_without_safepoint_check();
6757   _bit_map->lock()->lock_without_safepoint_check();
6758   _collector->startTimer();
6759 }
6760 
6761 ///////////////////////////////////////////////////////////
6762 // Par_MarkRefsIntoAndScanClosure: a parallel version of
6763 //                                 MarkRefsIntoAndScanClosure
6764 ///////////////////////////////////////////////////////////
6765 Par_MarkRefsIntoAndScanClosure::Par_MarkRefsIntoAndScanClosure(
6766   CMSCollector* collector, MemRegion span, ReferenceProcessor* rp,
6767   CMSBitMap* bit_map, OopTaskQueue* work_queue):
6768   _span(span),
6769   _bit_map(bit_map),
6770   _work_queue(work_queue),
6771   _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
6772                        (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads))),
6773   _par_pushAndMarkClosure(collector, span, rp, bit_map, work_queue)
6774 {
6775   _ref_processor = rp;
6776   assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6777 }
6778 
6779 // This closure is used to mark refs into the CMS generation at the
6780 // second (final) checkpoint, and to scan and transitively follow
6781 // the unmarked oops. The marks are made in the marking bit map and
6782 // the work_queue is used for keeping the (newly) grey objects during
6783 // the scan phase whence they are also available for stealing by parallel
6784 // threads. Since the marking bit map is shared, updates are
6785 // synchronized (via CAS).
6786 void Par_MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6787   if (obj != NULL) {
6788     // Ignore mark word because this could be an already marked oop
6789     // that may be chained at the end of the overflow list.
6790     assert(obj->is_oop(true), "expected an oop");
6791     HeapWord* addr = (HeapWord*)obj;
6792     if (_span.contains(addr) &&
6793         !_bit_map->isMarked(addr)) {
6794       // mark bit map (object will become grey):
6795       // It is possible for several threads to be
6796       // trying to "claim" this object concurrently;
6797       // the unique thread that succeeds in marking the
6798       // object first will do the subsequent push on
6799       // to the work queue (or overflow list).
6800       if (_bit_map->par_mark(addr)) {
6801         // push on work_queue (which may not be empty), and trim the
6802         // queue to an appropriate length by applying this closure to
6803         // the oops in the oops popped from the stack (i.e. blacken the
6804         // grey objects)
6805         bool res = _work_queue->push(obj);
6806         assert(res, "Low water mark should be less than capacity?");
6807         trim_queue(_low_water_mark);
6808       } // Else, another thread claimed the object
6809     }
6810   }
6811 }
6812 
6813 void Par_MarkRefsIntoAndScanClosure::do_oop(oop* p)       { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6814 void Par_MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6815 
6816 // This closure is used to rescan the marked objects on the dirty cards
6817 // in the mod union table and the card table proper.
6818 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
6819   oop p, MemRegion mr) {
6820 
6821   size_t size = 0;
6822   HeapWord* addr = (HeapWord*)p;
6823   DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6824   assert(_span.contains(addr), "we are scanning the CMS generation");
6825   // check if it's time to yield
6826   if (do_yield_check()) {
6827     // We yielded for some foreground stop-world work,
6828     // and we have been asked to abort this ongoing preclean cycle.
6829     return 0;
6830   }
6831   if (_bitMap->isMarked(addr)) {
6832     // it's marked; is it potentially uninitialized?
6833     if (p->klass_or_null() != NULL) {
6834         // an initialized object; ignore mark word in verification below
6835         // since we are running concurrent with mutators
6836         assert(p->is_oop(true), "should be an oop");
6837         if (p->is_objArray()) {
6838           // objArrays are precisely marked; restrict scanning
6839           // to dirty cards only.
6840           size = CompactibleFreeListSpace::adjustObjectSize(
6841                    p->oop_iterate(_scanningClosure, mr));
6842         } else {
6843           // A non-array may have been imprecisely marked; we need
6844           // to scan object in its entirety.
6845           size = CompactibleFreeListSpace::adjustObjectSize(
6846                    p->oop_iterate(_scanningClosure));
6847         }
6848         #ifdef DEBUG
6849           size_t direct_size =
6850             CompactibleFreeListSpace::adjustObjectSize(p->size());
6851           assert(size == direct_size, "Inconsistency in size");
6852           assert(size >= 3, "Necessary for Printezis marks to work");
6853           if (!_bitMap->isMarked(addr+1)) {
6854             _bitMap->verifyNoOneBitsInRange(addr+2, addr+size);
6855           } else {
6856             _bitMap->verifyNoOneBitsInRange(addr+2, addr+size-1);
6857             assert(_bitMap->isMarked(addr+size-1),
6858                    "inconsistent Printezis mark");
6859           }
6860         #endif // DEBUG
6861     } else {
6862       // an unitialized object
6863       assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
6864       HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
6865       size = pointer_delta(nextOneAddr + 1, addr);
6866       assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6867              "alignment problem");
6868       // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
6869       // will dirty the card when the klass pointer is installed in the
6870       // object (signalling the completion of initialization).
6871     }
6872   } else {
6873     // Either a not yet marked object or an uninitialized object
6874     if (p->klass_or_null() == NULL) {
6875       // An uninitialized object, skip to the next card, since
6876       // we may not be able to read its P-bits yet.
6877       assert(size == 0, "Initial value");
6878     } else {
6879       // An object not (yet) reached by marking: we merely need to
6880       // compute its size so as to go look at the next block.
6881       assert(p->is_oop(true), "should be an oop");
6882       size = CompactibleFreeListSpace::adjustObjectSize(p->size());
6883     }
6884   }
6885   DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6886   return size;
6887 }
6888 
6889 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
6890   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6891          "CMS thread should hold CMS token");
6892   assert_lock_strong(_freelistLock);
6893   assert_lock_strong(_bitMap->lock());
6894   // relinquish the free_list_lock and bitMaplock()
6895   _bitMap->lock()->unlock();
6896   _freelistLock->unlock();
6897   ConcurrentMarkSweepThread::desynchronize(true);
6898   ConcurrentMarkSweepThread::acknowledge_yield_request();
6899   _collector->stopTimer();
6900   GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
6901   if (PrintCMSStatistics != 0) {
6902     _collector->incrementYields();
6903   }
6904   _collector->icms_wait();
6905 
6906   // See the comment in coordinator_yield()
6907   for (unsigned i = 0; i < CMSYieldSleepCount &&
6908                    ConcurrentMarkSweepThread::should_yield() &&
6909                    !CMSCollector::foregroundGCIsActive(); ++i) {
6910     os::sleep(Thread::current(), 1, false);
6911     ConcurrentMarkSweepThread::acknowledge_yield_request();
6912   }
6913 
6914   ConcurrentMarkSweepThread::synchronize(true);
6915   _freelistLock->lock_without_safepoint_check();
6916   _bitMap->lock()->lock_without_safepoint_check();
6917   _collector->startTimer();
6918 }
6919 
6920 
6921 //////////////////////////////////////////////////////////////////
6922 // SurvivorSpacePrecleanClosure
6923 //////////////////////////////////////////////////////////////////
6924 // This (single-threaded) closure is used to preclean the oops in
6925 // the survivor spaces.
6926 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
6927 
6928   HeapWord* addr = (HeapWord*)p;
6929   DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6930   assert(!_span.contains(addr), "we are scanning the survivor spaces");
6931   assert(p->klass_or_null() != NULL, "object should be initializd");
6932   // an initialized object; ignore mark word in verification below
6933   // since we are running concurrent with mutators
6934   assert(p->is_oop(true), "should be an oop");
6935   // Note that we do not yield while we iterate over
6936   // the interior oops of p, pushing the relevant ones
6937   // on our marking stack.
6938   size_t size = p->oop_iterate(_scanning_closure);
6939   do_yield_check();
6940   // Observe that below, we do not abandon the preclean
6941   // phase as soon as we should; rather we empty the
6942   // marking stack before returning. This is to satisfy
6943   // some existing assertions. In general, it may be a
6944   // good idea to abort immediately and complete the marking
6945   // from the grey objects at a later time.
6946   while (!_mark_stack->isEmpty()) {
6947     oop new_oop = _mark_stack->pop();
6948     assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6949     assert(_bit_map->isMarked((HeapWord*)new_oop),
6950            "only grey objects on this stack");
6951     // iterate over the oops in this oop, marking and pushing
6952     // the ones in CMS heap (i.e. in _span).
6953     new_oop->oop_iterate(_scanning_closure);
6954     // check if it's time to yield
6955     do_yield_check();
6956   }
6957   unsigned int after_count =
6958     GenCollectedHeap::heap()->total_collections();
6959   bool abort = (_before_count != after_count) ||
6960                _collector->should_abort_preclean();
6961   return abort ? 0 : size;
6962 }
6963 
6964 void SurvivorSpacePrecleanClosure::do_yield_work() {
6965   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6966          "CMS thread should hold CMS token");
6967   assert_lock_strong(_bit_map->lock());
6968   // Relinquish the bit map lock
6969   _bit_map->lock()->unlock();
6970   ConcurrentMarkSweepThread::desynchronize(true);
6971   ConcurrentMarkSweepThread::acknowledge_yield_request();
6972   _collector->stopTimer();
6973   GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
6974   if (PrintCMSStatistics != 0) {
6975     _collector->incrementYields();
6976   }
6977   _collector->icms_wait();
6978 
6979   // See the comment in coordinator_yield()
6980   for (unsigned i = 0; i < CMSYieldSleepCount &&
6981                        ConcurrentMarkSweepThread::should_yield() &&
6982                        !CMSCollector::foregroundGCIsActive(); ++i) {
6983     os::sleep(Thread::current(), 1, false);
6984     ConcurrentMarkSweepThread::acknowledge_yield_request();
6985   }
6986 
6987   ConcurrentMarkSweepThread::synchronize(true);
6988   _bit_map->lock()->lock_without_safepoint_check();
6989   _collector->startTimer();
6990 }
6991 
6992 // This closure is used to rescan the marked objects on the dirty cards
6993 // in the mod union table and the card table proper. In the parallel
6994 // case, although the bitMap is shared, we do a single read so the
6995 // isMarked() query is "safe".
6996 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
6997   // Ignore mark word because we are running concurrent with mutators
6998   assert(p->is_oop_or_null(true), "expected an oop or null");
6999   HeapWord* addr = (HeapWord*)p;
7000   assert(_span.contains(addr), "we are scanning the CMS generation");
7001   bool is_obj_array = false;
7002   #ifdef DEBUG
7003     if (!_parallel) {
7004       assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
7005       assert(_collector->overflow_list_is_empty(),
7006              "overflow list should be empty");
7007 
7008     }
7009   #endif // DEBUG
7010   if (_bit_map->isMarked(addr)) {
7011     // Obj arrays are precisely marked, non-arrays are not;
7012     // so we scan objArrays precisely and non-arrays in their
7013     // entirety.
7014     if (p->is_objArray()) {
7015       is_obj_array = true;
7016       if (_parallel) {
7017         p->oop_iterate(_par_scan_closure, mr);
7018       } else {
7019         p->oop_iterate(_scan_closure, mr);
7020       }
7021     } else {
7022       if (_parallel) {
7023         p->oop_iterate(_par_scan_closure);
7024       } else {
7025         p->oop_iterate(_scan_closure);
7026       }
7027     }
7028   }
7029   #ifdef DEBUG
7030     if (!_parallel) {
7031       assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
7032       assert(_collector->overflow_list_is_empty(),
7033              "overflow list should be empty");
7034 
7035     }
7036   #endif // DEBUG
7037   return is_obj_array;
7038 }
7039 
7040 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
7041                         MemRegion span,
7042                         CMSBitMap* bitMap, CMSMarkStack*  markStack,
7043                         bool should_yield, bool verifying):
7044   _collector(collector),
7045   _span(span),
7046   _bitMap(bitMap),
7047   _mut(&collector->_modUnionTable),
7048   _markStack(markStack),
7049   _yield(should_yield),
7050   _skipBits(0)
7051 {
7052   assert(_markStack->isEmpty(), "stack should be empty");
7053   _finger = _bitMap->startWord();
7054   _threshold = _finger;
7055   assert(_collector->_restart_addr == NULL, "Sanity check");
7056   assert(_span.contains(_finger), "Out of bounds _finger?");
7057   DEBUG_ONLY(_verifying = verifying;)
7058 }
7059 
7060 void MarkFromRootsClosure::reset(HeapWord* addr) {
7061   assert(_markStack->isEmpty(), "would cause duplicates on stack");
7062   assert(_span.contains(addr), "Out of bounds _finger?");
7063   _finger = addr;
7064   _threshold = (HeapWord*)round_to(
7065                  (intptr_t)_finger, CardTableModRefBS::card_size);
7066 }
7067 
7068 // Should revisit to see if this should be restructured for
7069 // greater efficiency.
7070 bool MarkFromRootsClosure::do_bit(size_t offset) {
7071   if (_skipBits > 0) {
7072     _skipBits--;
7073     return true;
7074   }
7075   // convert offset into a HeapWord*
7076   HeapWord* addr = _bitMap->startWord() + offset;
7077   assert(_bitMap->endWord() && addr < _bitMap->endWord(),
7078          "address out of range");
7079   assert(_bitMap->isMarked(addr), "tautology");
7080   if (_bitMap->isMarked(addr+1)) {
7081     // this is an allocated but not yet initialized object
7082     assert(_skipBits == 0, "tautology");
7083     _skipBits = 2;  // skip next two marked bits ("Printezis-marks")
7084     oop p = oop(addr);
7085     if (p->klass_or_null() == NULL) {
7086       DEBUG_ONLY(if (!_verifying) {)
7087         // We re-dirty the cards on which this object lies and increase
7088         // the _threshold so that we'll come back to scan this object
7089         // during the preclean or remark phase. (CMSCleanOnEnter)
7090         if (CMSCleanOnEnter) {
7091           size_t sz = _collector->block_size_using_printezis_bits(addr);
7092           HeapWord* end_card_addr   = (HeapWord*)round_to(
7093                                          (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7094           MemRegion redirty_range = MemRegion(addr, end_card_addr);
7095           assert(!redirty_range.is_empty(), "Arithmetical tautology");
7096           // Bump _threshold to end_card_addr; note that
7097           // _threshold cannot possibly exceed end_card_addr, anyhow.
7098           // This prevents future clearing of the card as the scan proceeds
7099           // to the right.
7100           assert(_threshold <= end_card_addr,
7101                  "Because we are just scanning into this object");
7102           if (_threshold < end_card_addr) {
7103             _threshold = end_card_addr;
7104           }
7105           if (p->klass_or_null() != NULL) {
7106             // Redirty the range of cards...
7107             _mut->mark_range(redirty_range);
7108           } // ...else the setting of klass will dirty the card anyway.
7109         }
7110       DEBUG_ONLY(})
7111       return true;
7112     }
7113   }
7114   scanOopsInOop(addr);
7115   return true;
7116 }
7117 
7118 // We take a break if we've been at this for a while,
7119 // so as to avoid monopolizing the locks involved.
7120 void MarkFromRootsClosure::do_yield_work() {
7121   // First give up the locks, then yield, then re-lock
7122   // We should probably use a constructor/destructor idiom to
7123   // do this unlock/lock or modify the MutexUnlocker class to
7124   // serve our purpose. XXX
7125   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7126          "CMS thread should hold CMS token");
7127   assert_lock_strong(_bitMap->lock());
7128   _bitMap->lock()->unlock();
7129   ConcurrentMarkSweepThread::desynchronize(true);
7130   ConcurrentMarkSweepThread::acknowledge_yield_request();
7131   _collector->stopTimer();
7132   GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7133   if (PrintCMSStatistics != 0) {
7134     _collector->incrementYields();
7135   }
7136   _collector->icms_wait();
7137 
7138   // See the comment in coordinator_yield()
7139   for (unsigned i = 0; i < CMSYieldSleepCount &&
7140                        ConcurrentMarkSweepThread::should_yield() &&
7141                        !CMSCollector::foregroundGCIsActive(); ++i) {
7142     os::sleep(Thread::current(), 1, false);
7143     ConcurrentMarkSweepThread::acknowledge_yield_request();
7144   }
7145 
7146   ConcurrentMarkSweepThread::synchronize(true);
7147   _bitMap->lock()->lock_without_safepoint_check();
7148   _collector->startTimer();
7149 }
7150 
7151 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
7152   assert(_bitMap->isMarked(ptr), "expected bit to be set");
7153   assert(_markStack->isEmpty(),
7154          "should drain stack to limit stack usage");
7155   // convert ptr to an oop preparatory to scanning
7156   oop obj = oop(ptr);
7157   // Ignore mark word in verification below, since we
7158   // may be running concurrent with mutators.
7159   assert(obj->is_oop(true), "should be an oop");
7160   assert(_finger <= ptr, "_finger runneth ahead");
7161   // advance the finger to right end of this object
7162   _finger = ptr + obj->size();
7163   assert(_finger > ptr, "we just incremented it above");
7164   // On large heaps, it may take us some time to get through
7165   // the marking phase (especially if running iCMS). During
7166   // this time it's possible that a lot of mutations have
7167   // accumulated in the card table and the mod union table --
7168   // these mutation records are redundant until we have
7169   // actually traced into the corresponding card.
7170   // Here, we check whether advancing the finger would make
7171   // us cross into a new card, and if so clear corresponding
7172   // cards in the MUT (preclean them in the card-table in the
7173   // future).
7174 
7175   DEBUG_ONLY(if (!_verifying) {)
7176     // The clean-on-enter optimization is disabled by default,
7177     // until we fix 6178663.
7178     if (CMSCleanOnEnter && (_finger > _threshold)) {
7179       // [_threshold, _finger) represents the interval
7180       // of cards to be cleared  in MUT (or precleaned in card table).
7181       // The set of cards to be cleared is all those that overlap
7182       // with the interval [_threshold, _finger); note that
7183       // _threshold is always kept card-aligned but _finger isn't
7184       // always card-aligned.
7185       HeapWord* old_threshold = _threshold;
7186       assert(old_threshold == (HeapWord*)round_to(
7187               (intptr_t)old_threshold, CardTableModRefBS::card_size),
7188              "_threshold should always be card-aligned");
7189       _threshold = (HeapWord*)round_to(
7190                      (intptr_t)_finger, CardTableModRefBS::card_size);
7191       MemRegion mr(old_threshold, _threshold);
7192       assert(!mr.is_empty(), "Control point invariant");
7193       assert(_span.contains(mr), "Should clear within span");
7194       _mut->clear_range(mr);
7195     }
7196   DEBUG_ONLY(})
7197   // Note: the finger doesn't advance while we drain
7198   // the stack below.
7199   PushOrMarkClosure pushOrMarkClosure(_collector,
7200                                       _span, _bitMap, _markStack,
7201                                       _finger, this);
7202   bool res = _markStack->push(obj);
7203   assert(res, "Empty non-zero size stack should have space for single push");
7204   while (!_markStack->isEmpty()) {
7205     oop new_oop = _markStack->pop();
7206     // Skip verifying header mark word below because we are
7207     // running concurrent with mutators.
7208     assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
7209     // now scan this oop's oops
7210     new_oop->oop_iterate(&pushOrMarkClosure);
7211     do_yield_check();
7212   }
7213   assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
7214 }
7215 
7216 Par_MarkFromRootsClosure::Par_MarkFromRootsClosure(CMSConcMarkingTask* task,
7217                        CMSCollector* collector, MemRegion span,
7218                        CMSBitMap* bit_map,
7219                        OopTaskQueue* work_queue,
7220                        CMSMarkStack*  overflow_stack,
7221                        bool should_yield):
7222   _collector(collector),
7223   _whole_span(collector->_span),
7224   _span(span),
7225   _bit_map(bit_map),
7226   _mut(&collector->_modUnionTable),
7227   _work_queue(work_queue),
7228   _overflow_stack(overflow_stack),
7229   _yield(should_yield),
7230   _skip_bits(0),
7231   _task(task)
7232 {
7233   assert(_work_queue->size() == 0, "work_queue should be empty");
7234   _finger = span.start();
7235   _threshold = _finger;     // XXX Defer clear-on-enter optimization for now
7236   assert(_span.contains(_finger), "Out of bounds _finger?");
7237 }
7238 
7239 // Should revisit to see if this should be restructured for
7240 // greater efficiency.
7241 bool Par_MarkFromRootsClosure::do_bit(size_t offset) {
7242   if (_skip_bits > 0) {
7243     _skip_bits--;
7244     return true;
7245   }
7246   // convert offset into a HeapWord*
7247   HeapWord* addr = _bit_map->startWord() + offset;
7248   assert(_bit_map->endWord() && addr < _bit_map->endWord(),
7249          "address out of range");
7250   assert(_bit_map->isMarked(addr), "tautology");
7251   if (_bit_map->isMarked(addr+1)) {
7252     // this is an allocated object that might not yet be initialized
7253     assert(_skip_bits == 0, "tautology");
7254     _skip_bits = 2;  // skip next two marked bits ("Printezis-marks")
7255     oop p = oop(addr);
7256     if (p->klass_or_null() == NULL) {
7257       // in the case of Clean-on-Enter optimization, redirty card
7258       // and avoid clearing card by increasing  the threshold.
7259       return true;
7260     }
7261   }
7262   scan_oops_in_oop(addr);
7263   return true;
7264 }
7265 
7266 void Par_MarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
7267   assert(_bit_map->isMarked(ptr), "expected bit to be set");
7268   // Should we assert that our work queue is empty or
7269   // below some drain limit?
7270   assert(_work_queue->size() == 0,
7271          "should drain stack to limit stack usage");
7272   // convert ptr to an oop preparatory to scanning
7273   oop obj = oop(ptr);
7274   // Ignore mark word in verification below, since we
7275   // may be running concurrent with mutators.
7276   assert(obj->is_oop(true), "should be an oop");
7277   assert(_finger <= ptr, "_finger runneth ahead");
7278   // advance the finger to right end of this object
7279   _finger = ptr + obj->size();
7280   assert(_finger > ptr, "we just incremented it above");
7281   // On large heaps, it may take us some time to get through
7282   // the marking phase (especially if running iCMS). During
7283   // this time it's possible that a lot of mutations have
7284   // accumulated in the card table and the mod union table --
7285   // these mutation records are redundant until we have
7286   // actually traced into the corresponding card.
7287   // Here, we check whether advancing the finger would make
7288   // us cross into a new card, and if so clear corresponding
7289   // cards in the MUT (preclean them in the card-table in the
7290   // future).
7291 
7292   // The clean-on-enter optimization is disabled by default,
7293   // until we fix 6178663.
7294   if (CMSCleanOnEnter && (_finger > _threshold)) {
7295     // [_threshold, _finger) represents the interval
7296     // of cards to be cleared  in MUT (or precleaned in card table).
7297     // The set of cards to be cleared is all those that overlap
7298     // with the interval [_threshold, _finger); note that
7299     // _threshold is always kept card-aligned but _finger isn't
7300     // always card-aligned.
7301     HeapWord* old_threshold = _threshold;
7302     assert(old_threshold == (HeapWord*)round_to(
7303             (intptr_t)old_threshold, CardTableModRefBS::card_size),
7304            "_threshold should always be card-aligned");
7305     _threshold = (HeapWord*)round_to(
7306                    (intptr_t)_finger, CardTableModRefBS::card_size);
7307     MemRegion mr(old_threshold, _threshold);
7308     assert(!mr.is_empty(), "Control point invariant");
7309     assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
7310     _mut->clear_range(mr);
7311   }
7312 
7313   // Note: the local finger doesn't advance while we drain
7314   // the stack below, but the global finger sure can and will.
7315   HeapWord** gfa = _task->global_finger_addr();
7316   Par_PushOrMarkClosure pushOrMarkClosure(_collector,
7317                                       _span, _bit_map,
7318                                       _work_queue,
7319                                       _overflow_stack,
7320                                       _finger,
7321                                       gfa, this);
7322   bool res = _work_queue->push(obj);   // overflow could occur here
7323   assert(res, "Will hold once we use workqueues");
7324   while (true) {
7325     oop new_oop;
7326     if (!_work_queue->pop_local(new_oop)) {
7327       // We emptied our work_queue; check if there's stuff that can
7328       // be gotten from the overflow stack.
7329       if (CMSConcMarkingTask::get_work_from_overflow_stack(
7330             _overflow_stack, _work_queue)) {
7331         do_yield_check();
7332         continue;
7333       } else {  // done
7334         break;
7335       }
7336     }
7337     // Skip verifying header mark word below because we are
7338     // running concurrent with mutators.
7339     assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
7340     // now scan this oop's oops
7341     new_oop->oop_iterate(&pushOrMarkClosure);
7342     do_yield_check();
7343   }
7344   assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
7345 }
7346 
7347 // Yield in response to a request from VM Thread or
7348 // from mutators.
7349 void Par_MarkFromRootsClosure::do_yield_work() {
7350   assert(_task != NULL, "sanity");
7351   _task->yield();
7352 }
7353 
7354 // A variant of the above used for verifying CMS marking work.
7355 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
7356                         MemRegion span,
7357                         CMSBitMap* verification_bm, CMSBitMap* cms_bm,
7358                         CMSMarkStack*  mark_stack):
7359   _collector(collector),
7360   _span(span),
7361   _verification_bm(verification_bm),
7362   _cms_bm(cms_bm),
7363   _mark_stack(mark_stack),
7364   _pam_verify_closure(collector, span, verification_bm, cms_bm,
7365                       mark_stack)
7366 {
7367   assert(_mark_stack->isEmpty(), "stack should be empty");
7368   _finger = _verification_bm->startWord();
7369   assert(_collector->_restart_addr == NULL, "Sanity check");
7370   assert(_span.contains(_finger), "Out of bounds _finger?");
7371 }
7372 
7373 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
7374   assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
7375   assert(_span.contains(addr), "Out of bounds _finger?");
7376   _finger = addr;
7377 }
7378 
7379 // Should revisit to see if this should be restructured for
7380 // greater efficiency.
7381 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
7382   // convert offset into a HeapWord*
7383   HeapWord* addr = _verification_bm->startWord() + offset;
7384   assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
7385          "address out of range");
7386   assert(_verification_bm->isMarked(addr), "tautology");
7387   assert(_cms_bm->isMarked(addr), "tautology");
7388 
7389   assert(_mark_stack->isEmpty(),
7390          "should drain stack to limit stack usage");
7391   // convert addr to an oop preparatory to scanning
7392   oop obj = oop(addr);
7393   assert(obj->is_oop(), "should be an oop");
7394   assert(_finger <= addr, "_finger runneth ahead");
7395   // advance the finger to right end of this object
7396   _finger = addr + obj->size();
7397   assert(_finger > addr, "we just incremented it above");
7398   // Note: the finger doesn't advance while we drain
7399   // the stack below.
7400   bool res = _mark_stack->push(obj);
7401   assert(res, "Empty non-zero size stack should have space for single push");
7402   while (!_mark_stack->isEmpty()) {
7403     oop new_oop = _mark_stack->pop();
7404     assert(new_oop->is_oop(), "Oops! expected to pop an oop");
7405     // now scan this oop's oops
7406     new_oop->oop_iterate(&_pam_verify_closure);
7407   }
7408   assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
7409   return true;
7410 }
7411 
7412 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
7413   CMSCollector* collector, MemRegion span,
7414   CMSBitMap* verification_bm, CMSBitMap* cms_bm,
7415   CMSMarkStack*  mark_stack):
7416   CMSOopClosure(collector->ref_processor()),
7417   _collector(collector),
7418   _span(span),
7419   _verification_bm(verification_bm),
7420   _cms_bm(cms_bm),
7421   _mark_stack(mark_stack)
7422 { }
7423 
7424 void PushAndMarkVerifyClosure::do_oop(oop* p)       { PushAndMarkVerifyClosure::do_oop_work(p); }
7425 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
7426 
7427 // Upon stack overflow, we discard (part of) the stack,
7428 // remembering the least address amongst those discarded
7429 // in CMSCollector's _restart_address.
7430 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
7431   // Remember the least grey address discarded
7432   HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
7433   _collector->lower_restart_addr(ra);
7434   _mark_stack->reset();  // discard stack contents
7435   _mark_stack->expand(); // expand the stack if possible
7436 }
7437 
7438 void PushAndMarkVerifyClosure::do_oop(oop obj) {
7439   assert(obj->is_oop_or_null(), "expected an oop or NULL");
7440   HeapWord* addr = (HeapWord*)obj;
7441   if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
7442     // Oop lies in _span and isn't yet grey or black
7443     _verification_bm->mark(addr);            // now grey
7444     if (!_cms_bm->isMarked(addr)) {
7445       oop(addr)->print();
7446       gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)",
7447                              addr);
7448       fatal("... aborting");
7449     }
7450 
7451     if (!_mark_stack->push(obj)) { // stack overflow
7452       if (PrintCMSStatistics != 0) {
7453         gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7454                                SIZE_FORMAT, _mark_stack->capacity());
7455       }
7456       assert(_mark_stack->isFull(), "Else push should have succeeded");
7457       handle_stack_overflow(addr);
7458     }
7459     // anything including and to the right of _finger
7460     // will be scanned as we iterate over the remainder of the
7461     // bit map
7462   }
7463 }
7464 
7465 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
7466                      MemRegion span,
7467                      CMSBitMap* bitMap, CMSMarkStack*  markStack,
7468                      HeapWord* finger, MarkFromRootsClosure* parent) :
7469   CMSOopClosure(collector->ref_processor()),
7470   _collector(collector),
7471   _span(span),
7472   _bitMap(bitMap),
7473   _markStack(markStack),
7474   _finger(finger),
7475   _parent(parent)
7476 { }
7477 
7478 Par_PushOrMarkClosure::Par_PushOrMarkClosure(CMSCollector* collector,
7479                      MemRegion span,
7480                      CMSBitMap* bit_map,
7481                      OopTaskQueue* work_queue,
7482                      CMSMarkStack*  overflow_stack,
7483                      HeapWord* finger,
7484                      HeapWord** global_finger_addr,
7485                      Par_MarkFromRootsClosure* parent) :
7486   CMSOopClosure(collector->ref_processor()),
7487   _collector(collector),
7488   _whole_span(collector->_span),
7489   _span(span),
7490   _bit_map(bit_map),
7491   _work_queue(work_queue),
7492   _overflow_stack(overflow_stack),
7493   _finger(finger),
7494   _global_finger_addr(global_finger_addr),
7495   _parent(parent)
7496 { }
7497 
7498 // Assumes thread-safe access by callers, who are
7499 // responsible for mutual exclusion.
7500 void CMSCollector::lower_restart_addr(HeapWord* low) {
7501   assert(_span.contains(low), "Out of bounds addr");
7502   if (_restart_addr == NULL) {
7503     _restart_addr = low;
7504   } else {
7505     _restart_addr = MIN2(_restart_addr, low);
7506   }
7507 }
7508 
7509 // Upon stack overflow, we discard (part of) the stack,
7510 // remembering the least address amongst those discarded
7511 // in CMSCollector's _restart_address.
7512 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7513   // Remember the least grey address discarded
7514   HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
7515   _collector->lower_restart_addr(ra);
7516   _markStack->reset();  // discard stack contents
7517   _markStack->expand(); // expand the stack if possible
7518 }
7519 
7520 // Upon stack overflow, we discard (part of) the stack,
7521 // remembering the least address amongst those discarded
7522 // in CMSCollector's _restart_address.
7523 void Par_PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7524   // We need to do this under a mutex to prevent other
7525   // workers from interfering with the work done below.
7526   MutexLockerEx ml(_overflow_stack->par_lock(),
7527                    Mutex::_no_safepoint_check_flag);
7528   // Remember the least grey address discarded
7529   HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
7530   _collector->lower_restart_addr(ra);
7531   _overflow_stack->reset();  // discard stack contents
7532   _overflow_stack->expand(); // expand the stack if possible
7533 }
7534 
7535 void CMKlassClosure::do_klass(Klass* k) {
7536   assert(_oop_closure != NULL, "Not initialized?");
7537   k->oops_do(_oop_closure);
7538 }
7539 
7540 void PushOrMarkClosure::do_oop(oop obj) {
7541   // Ignore mark word because we are running concurrent with mutators.
7542   assert(obj->is_oop_or_null(true), "expected an oop or NULL");
7543   HeapWord* addr = (HeapWord*)obj;
7544   if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
7545     // Oop lies in _span and isn't yet grey or black
7546     _bitMap->mark(addr);            // now grey
7547     if (addr < _finger) {
7548       // the bit map iteration has already either passed, or
7549       // sampled, this bit in the bit map; we'll need to
7550       // use the marking stack to scan this oop's oops.
7551       bool simulate_overflow = false;
7552       NOT_PRODUCT(
7553         if (CMSMarkStackOverflowALot &&
7554             _collector->simulate_overflow()) {
7555           // simulate a stack overflow
7556           simulate_overflow = true;
7557         }
7558       )
7559       if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
7560         if (PrintCMSStatistics != 0) {
7561           gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7562                                  SIZE_FORMAT, _markStack->capacity());
7563         }
7564         assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
7565         handle_stack_overflow(addr);
7566       }
7567     }
7568     // anything including and to the right of _finger
7569     // will be scanned as we iterate over the remainder of the
7570     // bit map
7571     do_yield_check();
7572   }
7573 }
7574 
7575 void PushOrMarkClosure::do_oop(oop* p)       { PushOrMarkClosure::do_oop_work(p); }
7576 void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); }
7577 
7578 void Par_PushOrMarkClosure::do_oop(oop obj) {
7579   // Ignore mark word because we are running concurrent with mutators.
7580   assert(obj->is_oop_or_null(true), "expected an oop or NULL");
7581   HeapWord* addr = (HeapWord*)obj;
7582   if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
7583     // Oop lies in _span and isn't yet grey or black
7584     // We read the global_finger (volatile read) strictly after marking oop
7585     bool res = _bit_map->par_mark(addr);    // now grey
7586     volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
7587     // Should we push this marked oop on our stack?
7588     // -- if someone else marked it, nothing to do
7589     // -- if target oop is above global finger nothing to do
7590     // -- if target oop is in chunk and above local finger
7591     //      then nothing to do
7592     // -- else push on work queue
7593     if (   !res       // someone else marked it, they will deal with it
7594         || (addr >= *gfa)  // will be scanned in a later task
7595         || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
7596       return;
7597     }
7598     // the bit map iteration has already either passed, or
7599     // sampled, this bit in the bit map; we'll need to
7600     // use the marking stack to scan this oop's oops.
7601     bool simulate_overflow = false;
7602     NOT_PRODUCT(
7603       if (CMSMarkStackOverflowALot &&
7604           _collector->simulate_overflow()) {
7605         // simulate a stack overflow
7606         simulate_overflow = true;
7607       }
7608     )
7609     if (simulate_overflow ||
7610         !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
7611       // stack overflow
7612       if (PrintCMSStatistics != 0) {
7613         gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7614                                SIZE_FORMAT, _overflow_stack->capacity());
7615       }
7616       // We cannot assert that the overflow stack is full because
7617       // it may have been emptied since.
7618       assert(simulate_overflow ||
7619              _work_queue->size() == _work_queue->max_elems(),
7620             "Else push should have succeeded");
7621       handle_stack_overflow(addr);
7622     }
7623     do_yield_check();
7624   }
7625 }
7626 
7627 void Par_PushOrMarkClosure::do_oop(oop* p)       { Par_PushOrMarkClosure::do_oop_work(p); }
7628 void Par_PushOrMarkClosure::do_oop(narrowOop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7629 
7630 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
7631                                        MemRegion span,
7632                                        ReferenceProcessor* rp,
7633                                        CMSBitMap* bit_map,
7634                                        CMSBitMap* mod_union_table,
7635                                        CMSMarkStack*  mark_stack,
7636                                        bool           concurrent_precleaning):
7637   CMSOopClosure(rp),
7638   _collector(collector),
7639   _span(span),
7640   _bit_map(bit_map),
7641   _mod_union_table(mod_union_table),
7642   _mark_stack(mark_stack),
7643   _concurrent_precleaning(concurrent_precleaning)
7644 {
7645   assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7646 }
7647 
7648 // Grey object rescan during pre-cleaning and second checkpoint phases --
7649 // the non-parallel version (the parallel version appears further below.)
7650 void PushAndMarkClosure::do_oop(oop obj) {
7651   // Ignore mark word verification. If during concurrent precleaning,
7652   // the object monitor may be locked. If during the checkpoint
7653   // phases, the object may already have been reached by a  different
7654   // path and may be at the end of the global overflow list (so
7655   // the mark word may be NULL).
7656   assert(obj->is_oop_or_null(true /* ignore mark word */),
7657          "expected an oop or NULL");
7658   HeapWord* addr = (HeapWord*)obj;
7659   // Check if oop points into the CMS generation
7660   // and is not marked
7661   if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7662     // a white object ...
7663     _bit_map->mark(addr);         // ... now grey
7664     // push on the marking stack (grey set)
7665     bool simulate_overflow = false;
7666     NOT_PRODUCT(
7667       if (CMSMarkStackOverflowALot &&
7668           _collector->simulate_overflow()) {
7669         // simulate a stack overflow
7670         simulate_overflow = true;
7671       }
7672     )
7673     if (simulate_overflow || !_mark_stack->push(obj)) {
7674       if (_concurrent_precleaning) {
7675          // During precleaning we can just dirty the appropriate card(s)
7676          // in the mod union table, thus ensuring that the object remains
7677          // in the grey set  and continue. In the case of object arrays
7678          // we need to dirty all of the cards that the object spans,
7679          // since the rescan of object arrays will be limited to the
7680          // dirty cards.
7681          // Note that no one can be intefering with us in this action
7682          // of dirtying the mod union table, so no locking or atomics
7683          // are required.
7684          if (obj->is_objArray()) {
7685            size_t sz = obj->size();
7686            HeapWord* end_card_addr = (HeapWord*)round_to(
7687                                         (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7688            MemRegion redirty_range = MemRegion(addr, end_card_addr);
7689            assert(!redirty_range.is_empty(), "Arithmetical tautology");
7690            _mod_union_table->mark_range(redirty_range);
7691          } else {
7692            _mod_union_table->mark(addr);
7693          }
7694          _collector->_ser_pmc_preclean_ovflw++;
7695       } else {
7696          // During the remark phase, we need to remember this oop
7697          // in the overflow list.
7698          _collector->push_on_overflow_list(obj);
7699          _collector->_ser_pmc_remark_ovflw++;
7700       }
7701     }
7702   }
7703 }
7704 
7705 Par_PushAndMarkClosure::Par_PushAndMarkClosure(CMSCollector* collector,
7706                                                MemRegion span,
7707                                                ReferenceProcessor* rp,
7708                                                CMSBitMap* bit_map,
7709                                                OopTaskQueue* work_queue):
7710   CMSOopClosure(rp),
7711   _collector(collector),
7712   _span(span),
7713   _bit_map(bit_map),
7714   _work_queue(work_queue)
7715 {
7716   assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7717 }
7718 
7719 void PushAndMarkClosure::do_oop(oop* p)       { PushAndMarkClosure::do_oop_work(p); }
7720 void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); }
7721 
7722 // Grey object rescan during second checkpoint phase --
7723 // the parallel version.
7724 void Par_PushAndMarkClosure::do_oop(oop obj) {
7725   // In the assert below, we ignore the mark word because
7726   // this oop may point to an already visited object that is
7727   // on the overflow stack (in which case the mark word has
7728   // been hijacked for chaining into the overflow stack --
7729   // if this is the last object in the overflow stack then
7730   // its mark word will be NULL). Because this object may
7731   // have been subsequently popped off the global overflow
7732   // stack, and the mark word possibly restored to the prototypical
7733   // value, by the time we get to examined this failing assert in
7734   // the debugger, is_oop_or_null(false) may subsequently start
7735   // to hold.
7736   assert(obj->is_oop_or_null(true),
7737          "expected an oop or NULL");
7738   HeapWord* addr = (HeapWord*)obj;
7739   // Check if oop points into the CMS generation
7740   // and is not marked
7741   if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7742     // a white object ...
7743     // If we manage to "claim" the object, by being the
7744     // first thread to mark it, then we push it on our
7745     // marking stack
7746     if (_bit_map->par_mark(addr)) {     // ... now grey
7747       // push on work queue (grey set)
7748       bool simulate_overflow = false;
7749       NOT_PRODUCT(
7750         if (CMSMarkStackOverflowALot &&
7751             _collector->par_simulate_overflow()) {
7752           // simulate a stack overflow
7753           simulate_overflow = true;
7754         }
7755       )
7756       if (simulate_overflow || !_work_queue->push(obj)) {
7757         _collector->par_push_on_overflow_list(obj);
7758         _collector->_par_pmc_remark_ovflw++; //  imprecise OK: no need to CAS
7759       }
7760     } // Else, some other thread got there first
7761   }
7762 }
7763 
7764 void Par_PushAndMarkClosure::do_oop(oop* p)       { Par_PushAndMarkClosure::do_oop_work(p); }
7765 void Par_PushAndMarkClosure::do_oop(narrowOop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7766 
7767 void CMSPrecleanRefsYieldClosure::do_yield_work() {
7768   Mutex* bml = _collector->bitMapLock();
7769   assert_lock_strong(bml);
7770   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7771          "CMS thread should hold CMS token");
7772 
7773   bml->unlock();
7774   ConcurrentMarkSweepThread::desynchronize(true);
7775 
7776   ConcurrentMarkSweepThread::acknowledge_yield_request();
7777 
7778   _collector->stopTimer();
7779   GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7780   if (PrintCMSStatistics != 0) {
7781     _collector->incrementYields();
7782   }
7783   _collector->icms_wait();
7784 
7785   // See the comment in coordinator_yield()
7786   for (unsigned i = 0; i < CMSYieldSleepCount &&
7787                        ConcurrentMarkSweepThread::should_yield() &&
7788                        !CMSCollector::foregroundGCIsActive(); ++i) {
7789     os::sleep(Thread::current(), 1, false);
7790     ConcurrentMarkSweepThread::acknowledge_yield_request();
7791   }
7792 
7793   ConcurrentMarkSweepThread::synchronize(true);
7794   bml->lock();
7795 
7796   _collector->startTimer();
7797 }
7798 
7799 bool CMSPrecleanRefsYieldClosure::should_return() {
7800   if (ConcurrentMarkSweepThread::should_yield()) {
7801     do_yield_work();
7802   }
7803   return _collector->foregroundGCIsActive();
7804 }
7805 
7806 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
7807   assert(((size_t)mr.start())%CardTableModRefBS::card_size_in_words == 0,
7808          "mr should be aligned to start at a card boundary");
7809   // We'd like to assert:
7810   // assert(mr.word_size()%CardTableModRefBS::card_size_in_words == 0,
7811   //        "mr should be a range of cards");
7812   // However, that would be too strong in one case -- the last
7813   // partition ends at _unallocated_block which, in general, can be
7814   // an arbitrary boundary, not necessarily card aligned.
7815   if (PrintCMSStatistics != 0) {
7816     _num_dirty_cards +=
7817          mr.word_size()/CardTableModRefBS::card_size_in_words;
7818   }
7819   _space->object_iterate_mem(mr, &_scan_cl);
7820 }
7821 
7822 SweepClosure::SweepClosure(CMSCollector* collector,
7823                            ConcurrentMarkSweepGeneration* g,
7824                            CMSBitMap* bitMap, bool should_yield) :
7825   _collector(collector),
7826   _g(g),
7827   _sp(g->cmsSpace()),
7828   _limit(_sp->sweep_limit()),
7829   _freelistLock(_sp->freelistLock()),
7830   _bitMap(bitMap),
7831   _yield(should_yield),
7832   _inFreeRange(false),           // No free range at beginning of sweep
7833   _freeRangeInFreeLists(false),  // No free range at beginning of sweep
7834   _lastFreeRangeCoalesced(false),
7835   _freeFinger(g->used_region().start())
7836 {
7837   NOT_PRODUCT(
7838     _numObjectsFreed = 0;
7839     _numWordsFreed   = 0;
7840     _numObjectsLive = 0;
7841     _numWordsLive = 0;
7842     _numObjectsAlreadyFree = 0;
7843     _numWordsAlreadyFree = 0;
7844     _last_fc = NULL;
7845 
7846     _sp->initializeIndexedFreeListArrayReturnedBytes();
7847     _sp->dictionary()->initialize_dict_returned_bytes();
7848   )
7849   assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7850          "sweep _limit out of bounds");
7851   if (CMSTraceSweeper) {
7852     gclog_or_tty->print_cr("\n====================\nStarting new sweep with limit " PTR_FORMAT,
7853                         _limit);
7854   }
7855 }
7856 
7857 void SweepClosure::print_on(outputStream* st) const {
7858   tty->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")",
7859                 _sp->bottom(), _sp->end());
7860   tty->print_cr("_limit = " PTR_FORMAT, _limit);
7861   tty->print_cr("_freeFinger = " PTR_FORMAT, _freeFinger);
7862   NOT_PRODUCT(tty->print_cr("_last_fc = " PTR_FORMAT, _last_fc);)
7863   tty->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d",
7864                 _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced);
7865 }
7866 
7867 #ifndef PRODUCT
7868 // Assertion checking only:  no useful work in product mode --
7869 // however, if any of the flags below become product flags,
7870 // you may need to review this code to see if it needs to be
7871 // enabled in product mode.
7872 SweepClosure::~SweepClosure() {
7873   assert_lock_strong(_freelistLock);
7874   assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7875          "sweep _limit out of bounds");
7876   if (inFreeRange()) {
7877     warning("inFreeRange() should have been reset; dumping state of SweepClosure");
7878     print();
7879     ShouldNotReachHere();
7880   }
7881   if (Verbose && PrintGC) {
7882     gclog_or_tty->print("Collected "SIZE_FORMAT" objects, " SIZE_FORMAT " bytes",
7883                         _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
7884     gclog_or_tty->print_cr("\nLive "SIZE_FORMAT" objects,  "
7885                            SIZE_FORMAT" bytes  "
7886       "Already free "SIZE_FORMAT" objects, "SIZE_FORMAT" bytes",
7887       _numObjectsLive, _numWordsLive*sizeof(HeapWord),
7888       _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
7889     size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree)
7890                         * sizeof(HeapWord);
7891     gclog_or_tty->print_cr("Total sweep: "SIZE_FORMAT" bytes", totalBytes);
7892 
7893     if (PrintCMSStatistics && CMSVerifyReturnedBytes) {
7894       size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
7895       size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes();
7896       size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes;
7897       gclog_or_tty->print("Returned "SIZE_FORMAT" bytes", returned_bytes);
7898       gclog_or_tty->print("   Indexed List Returned "SIZE_FORMAT" bytes",
7899         indexListReturnedBytes);
7900       gclog_or_tty->print_cr("        Dictionary Returned "SIZE_FORMAT" bytes",
7901         dict_returned_bytes);
7902     }
7903   }
7904   if (CMSTraceSweeper) {
7905     gclog_or_tty->print_cr("end of sweep with _limit = " PTR_FORMAT "\n================",
7906                            _limit);
7907   }
7908 }
7909 #endif  // PRODUCT
7910 
7911 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
7912     bool freeRangeInFreeLists) {
7913   if (CMSTraceSweeper) {
7914     gclog_or_tty->print("---- Start free range at 0x%x with free block (%d)\n",
7915                freeFinger, freeRangeInFreeLists);
7916   }
7917   assert(!inFreeRange(), "Trampling existing free range");
7918   set_inFreeRange(true);
7919   set_lastFreeRangeCoalesced(false);
7920 
7921   set_freeFinger(freeFinger);
7922   set_freeRangeInFreeLists(freeRangeInFreeLists);
7923   if (CMSTestInFreeList) {
7924     if (freeRangeInFreeLists) {
7925       FreeChunk* fc = (FreeChunk*) freeFinger;
7926       assert(fc->is_free(), "A chunk on the free list should be free.");
7927       assert(fc->size() > 0, "Free range should have a size");
7928       assert(_sp->verify_chunk_in_free_list(fc), "Chunk is not in free lists");
7929     }
7930   }
7931 }
7932 
7933 // Note that the sweeper runs concurrently with mutators. Thus,
7934 // it is possible for direct allocation in this generation to happen
7935 // in the middle of the sweep. Note that the sweeper also coalesces
7936 // contiguous free blocks. Thus, unless the sweeper and the allocator
7937 // synchronize appropriately freshly allocated blocks may get swept up.
7938 // This is accomplished by the sweeper locking the free lists while
7939 // it is sweeping. Thus blocks that are determined to be free are
7940 // indeed free. There is however one additional complication:
7941 // blocks that have been allocated since the final checkpoint and
7942 // mark, will not have been marked and so would be treated as
7943 // unreachable and swept up. To prevent this, the allocator marks
7944 // the bit map when allocating during the sweep phase. This leads,
7945 // however, to a further complication -- objects may have been allocated
7946 // but not yet initialized -- in the sense that the header isn't yet
7947 // installed. The sweeper can not then determine the size of the block
7948 // in order to skip over it. To deal with this case, we use a technique
7949 // (due to Printezis) to encode such uninitialized block sizes in the
7950 // bit map. Since the bit map uses a bit per every HeapWord, but the
7951 // CMS generation has a minimum object size of 3 HeapWords, it follows
7952 // that "normal marks" won't be adjacent in the bit map (there will
7953 // always be at least two 0 bits between successive 1 bits). We make use
7954 // of these "unused" bits to represent uninitialized blocks -- the bit
7955 // corresponding to the start of the uninitialized object and the next
7956 // bit are both set. Finally, a 1 bit marks the end of the object that
7957 // started with the two consecutive 1 bits to indicate its potentially
7958 // uninitialized state.
7959 
7960 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
7961   FreeChunk* fc = (FreeChunk*)addr;
7962   size_t res;
7963 
7964   // Check if we are done sweeping. Below we check "addr >= _limit" rather
7965   // than "addr == _limit" because although _limit was a block boundary when
7966   // we started the sweep, it may no longer be one because heap expansion
7967   // may have caused us to coalesce the block ending at the address _limit
7968   // with a newly expanded chunk (this happens when _limit was set to the
7969   // previous _end of the space), so we may have stepped past _limit:
7970   // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740.
7971   if (addr >= _limit) { // we have swept up to or past the limit: finish up
7972     assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7973            "sweep _limit out of bounds");
7974     assert(addr < _sp->end(), "addr out of bounds");
7975     // Flush any free range we might be holding as a single
7976     // coalesced chunk to the appropriate free list.
7977     if (inFreeRange()) {
7978       assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit,
7979              err_msg("freeFinger() " PTR_FORMAT" is out-of-bounds", freeFinger()));
7980       flush_cur_free_chunk(freeFinger(),
7981                            pointer_delta(addr, freeFinger()));
7982       if (CMSTraceSweeper) {
7983         gclog_or_tty->print("Sweep: last chunk: ");
7984         gclog_or_tty->print("put_free_blk 0x%x ("SIZE_FORMAT") "
7985                    "[coalesced:"SIZE_FORMAT"]\n",
7986                    freeFinger(), pointer_delta(addr, freeFinger()),
7987                    lastFreeRangeCoalesced());
7988       }
7989     }
7990 
7991     // help the iterator loop finish
7992     return pointer_delta(_sp->end(), addr);
7993   }
7994 
7995   assert(addr < _limit, "sweep invariant");
7996   // check if we should yield
7997   do_yield_check(addr);
7998   if (fc->is_free()) {
7999     // Chunk that is already free
8000     res = fc->size();
8001     do_already_free_chunk(fc);
8002     debug_only(_sp->verifyFreeLists());
8003     // If we flush the chunk at hand in lookahead_and_flush()
8004     // and it's coalesced with a preceding chunk, then the
8005     // process of "mangling" the payload of the coalesced block
8006     // will cause erasure of the size information from the
8007     // (erstwhile) header of all the coalesced blocks but the
8008     // first, so the first disjunct in the assert will not hold
8009     // in that specific case (in which case the second disjunct
8010     // will hold).
8011     assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit,
8012            "Otherwise the size info doesn't change at this step");
8013     NOT_PRODUCT(
8014       _numObjectsAlreadyFree++;
8015       _numWordsAlreadyFree += res;
8016     )
8017     NOT_PRODUCT(_last_fc = fc;)
8018   } else if (!_bitMap->isMarked(addr)) {
8019     // Chunk is fresh garbage
8020     res = do_garbage_chunk(fc);
8021     debug_only(_sp->verifyFreeLists());
8022     NOT_PRODUCT(
8023       _numObjectsFreed++;
8024       _numWordsFreed += res;
8025     )
8026   } else {
8027     // Chunk that is alive.
8028     res = do_live_chunk(fc);
8029     debug_only(_sp->verifyFreeLists());
8030     NOT_PRODUCT(
8031         _numObjectsLive++;
8032         _numWordsLive += res;
8033     )
8034   }
8035   return res;
8036 }
8037 
8038 // For the smart allocation, record following
8039 //  split deaths - a free chunk is removed from its free list because
8040 //      it is being split into two or more chunks.
8041 //  split birth - a free chunk is being added to its free list because
8042 //      a larger free chunk has been split and resulted in this free chunk.
8043 //  coal death - a free chunk is being removed from its free list because
8044 //      it is being coalesced into a large free chunk.
8045 //  coal birth - a free chunk is being added to its free list because
8046 //      it was created when two or more free chunks where coalesced into
8047 //      this free chunk.
8048 //
8049 // These statistics are used to determine the desired number of free
8050 // chunks of a given size.  The desired number is chosen to be relative
8051 // to the end of a CMS sweep.  The desired number at the end of a sweep
8052 // is the
8053 //      count-at-end-of-previous-sweep (an amount that was enough)
8054 //              - count-at-beginning-of-current-sweep  (the excess)
8055 //              + split-births  (gains in this size during interval)
8056 //              - split-deaths  (demands on this size during interval)
8057 // where the interval is from the end of one sweep to the end of the
8058 // next.
8059 //
8060 // When sweeping the sweeper maintains an accumulated chunk which is
8061 // the chunk that is made up of chunks that have been coalesced.  That
8062 // will be termed the left-hand chunk.  A new chunk of garbage that
8063 // is being considered for coalescing will be referred to as the
8064 // right-hand chunk.
8065 //
8066 // When making a decision on whether to coalesce a right-hand chunk with
8067 // the current left-hand chunk, the current count vs. the desired count
8068 // of the left-hand chunk is considered.  Also if the right-hand chunk
8069 // is near the large chunk at the end of the heap (see
8070 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
8071 // left-hand chunk is coalesced.
8072 //
8073 // When making a decision about whether to split a chunk, the desired count
8074 // vs. the current count of the candidate to be split is also considered.
8075 // If the candidate is underpopulated (currently fewer chunks than desired)
8076 // a chunk of an overpopulated (currently more chunks than desired) size may
8077 // be chosen.  The "hint" associated with a free list, if non-null, points
8078 // to a free list which may be overpopulated.
8079 //
8080 
8081 void SweepClosure::do_already_free_chunk(FreeChunk* fc) {
8082   const size_t size = fc->size();
8083   // Chunks that cannot be coalesced are not in the
8084   // free lists.
8085   if (CMSTestInFreeList && !fc->cantCoalesce()) {
8086     assert(_sp->verify_chunk_in_free_list(fc),
8087       "free chunk should be in free lists");
8088   }
8089   // a chunk that is already free, should not have been
8090   // marked in the bit map
8091   HeapWord* const addr = (HeapWord*) fc;
8092   assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
8093   // Verify that the bit map has no bits marked between
8094   // addr and purported end of this block.
8095   _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8096 
8097   // Some chunks cannot be coalesced under any circumstances.
8098   // See the definition of cantCoalesce().
8099   if (!fc->cantCoalesce()) {
8100     // This chunk can potentially be coalesced.
8101     if (_sp->adaptive_freelists()) {
8102       // All the work is done in
8103       do_post_free_or_garbage_chunk(fc, size);
8104     } else {  // Not adaptive free lists
8105       // this is a free chunk that can potentially be coalesced by the sweeper;
8106       if (!inFreeRange()) {
8107         // if the next chunk is a free block that can't be coalesced
8108         // it doesn't make sense to remove this chunk from the free lists
8109         FreeChunk* nextChunk = (FreeChunk*)(addr + size);
8110         assert((HeapWord*)nextChunk <= _sp->end(), "Chunk size out of bounds?");
8111         if ((HeapWord*)nextChunk < _sp->end() &&     // There is another free chunk to the right ...
8112             nextChunk->is_free()               &&     // ... which is free...
8113             nextChunk->cantCoalesce()) {             // ... but can't be coalesced
8114           // nothing to do
8115         } else {
8116           // Potentially the start of a new free range:
8117           // Don't eagerly remove it from the free lists.
8118           // No need to remove it if it will just be put
8119           // back again.  (Also from a pragmatic point of view
8120           // if it is a free block in a region that is beyond
8121           // any allocated blocks, an assertion will fail)
8122           // Remember the start of a free run.
8123           initialize_free_range(addr, true);
8124           // end - can coalesce with next chunk
8125         }
8126       } else {
8127         // the midst of a free range, we are coalescing
8128         print_free_block_coalesced(fc);
8129         if (CMSTraceSweeper) {
8130           gclog_or_tty->print("  -- pick up free block 0x%x (%d)\n", fc, size);
8131         }
8132         // remove it from the free lists
8133         _sp->removeFreeChunkFromFreeLists(fc);
8134         set_lastFreeRangeCoalesced(true);
8135         // If the chunk is being coalesced and the current free range is
8136         // in the free lists, remove the current free range so that it
8137         // will be returned to the free lists in its entirety - all
8138         // the coalesced pieces included.
8139         if (freeRangeInFreeLists()) {
8140           FreeChunk* ffc = (FreeChunk*) freeFinger();
8141           assert(ffc->size() == pointer_delta(addr, freeFinger()),
8142             "Size of free range is inconsistent with chunk size.");
8143           if (CMSTestInFreeList) {
8144             assert(_sp->verify_chunk_in_free_list(ffc),
8145               "free range is not in free lists");
8146           }
8147           _sp->removeFreeChunkFromFreeLists(ffc);
8148           set_freeRangeInFreeLists(false);
8149         }
8150       }
8151     }
8152     // Note that if the chunk is not coalescable (the else arm
8153     // below), we unconditionally flush, without needing to do
8154     // a "lookahead," as we do below.
8155     if (inFreeRange()) lookahead_and_flush(fc, size);
8156   } else {
8157     // Code path common to both original and adaptive free lists.
8158 
8159     // cant coalesce with previous block; this should be treated
8160     // as the end of a free run if any
8161     if (inFreeRange()) {
8162       // we kicked some butt; time to pick up the garbage
8163       assert(freeFinger() < addr, "freeFinger points too high");
8164       flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8165     }
8166     // else, nothing to do, just continue
8167   }
8168 }
8169 
8170 size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) {
8171   // This is a chunk of garbage.  It is not in any free list.
8172   // Add it to a free list or let it possibly be coalesced into
8173   // a larger chunk.
8174   HeapWord* const addr = (HeapWord*) fc;
8175   const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
8176 
8177   if (_sp->adaptive_freelists()) {
8178     // Verify that the bit map has no bits marked between
8179     // addr and purported end of just dead object.
8180     _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8181 
8182     do_post_free_or_garbage_chunk(fc, size);
8183   } else {
8184     if (!inFreeRange()) {
8185       // start of a new free range
8186       assert(size > 0, "A free range should have a size");
8187       initialize_free_range(addr, false);
8188     } else {
8189       // this will be swept up when we hit the end of the
8190       // free range
8191       if (CMSTraceSweeper) {
8192         gclog_or_tty->print("  -- pick up garbage 0x%x (%d) \n", fc, size);
8193       }
8194       // If the chunk is being coalesced and the current free range is
8195       // in the free lists, remove the current free range so that it
8196       // will be returned to the free lists in its entirety - all
8197       // the coalesced pieces included.
8198       if (freeRangeInFreeLists()) {
8199         FreeChunk* ffc = (FreeChunk*)freeFinger();
8200         assert(ffc->size() == pointer_delta(addr, freeFinger()),
8201           "Size of free range is inconsistent with chunk size.");
8202         if (CMSTestInFreeList) {
8203           assert(_sp->verify_chunk_in_free_list(ffc),
8204             "free range is not in free lists");
8205         }
8206         _sp->removeFreeChunkFromFreeLists(ffc);
8207         set_freeRangeInFreeLists(false);
8208       }
8209       set_lastFreeRangeCoalesced(true);
8210     }
8211     // this will be swept up when we hit the end of the free range
8212 
8213     // Verify that the bit map has no bits marked between
8214     // addr and purported end of just dead object.
8215     _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8216   }
8217   assert(_limit >= addr + size,
8218          "A freshly garbage chunk can't possibly straddle over _limit");
8219   if (inFreeRange()) lookahead_and_flush(fc, size);
8220   return size;
8221 }
8222 
8223 size_t SweepClosure::do_live_chunk(FreeChunk* fc) {
8224   HeapWord* addr = (HeapWord*) fc;
8225   // The sweeper has just found a live object. Return any accumulated
8226   // left hand chunk to the free lists.
8227   if (inFreeRange()) {
8228     assert(freeFinger() < addr, "freeFinger points too high");
8229     flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8230   }
8231 
8232   // This object is live: we'd normally expect this to be
8233   // an oop, and like to assert the following:
8234   // assert(oop(addr)->is_oop(), "live block should be an oop");
8235   // However, as we commented above, this may be an object whose
8236   // header hasn't yet been initialized.
8237   size_t size;
8238   assert(_bitMap->isMarked(addr), "Tautology for this control point");
8239   if (_bitMap->isMarked(addr + 1)) {
8240     // Determine the size from the bit map, rather than trying to
8241     // compute it from the object header.
8242     HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
8243     size = pointer_delta(nextOneAddr + 1, addr);
8244     assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
8245            "alignment problem");
8246 
8247 #ifdef DEBUG
8248       if (oop(addr)->klass_or_null() != NULL) {
8249         // Ignore mark word because we are running concurrent with mutators
8250         assert(oop(addr)->is_oop(true), "live block should be an oop");
8251         assert(size ==
8252                CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
8253                "P-mark and computed size do not agree");
8254       }
8255 #endif
8256 
8257   } else {
8258     // This should be an initialized object that's alive.
8259     assert(oop(addr)->klass_or_null() != NULL,
8260            "Should be an initialized object");
8261     // Ignore mark word because we are running concurrent with mutators
8262     assert(oop(addr)->is_oop(true), "live block should be an oop");
8263     // Verify that the bit map has no bits marked between
8264     // addr and purported end of this block.
8265     size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
8266     assert(size >= 3, "Necessary for Printezis marks to work");
8267     assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
8268     DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
8269   }
8270   return size;
8271 }
8272 
8273 void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc,
8274                                                  size_t chunkSize) {
8275   // do_post_free_or_garbage_chunk() should only be called in the case
8276   // of the adaptive free list allocator.
8277   const bool fcInFreeLists = fc->is_free();
8278   assert(_sp->adaptive_freelists(), "Should only be used in this case.");
8279   assert((HeapWord*)fc <= _limit, "sweep invariant");
8280   if (CMSTestInFreeList && fcInFreeLists) {
8281     assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists");
8282   }
8283 
8284   if (CMSTraceSweeper) {
8285     gclog_or_tty->print_cr("  -- pick up another chunk at 0x%x (%d)", fc, chunkSize);
8286   }
8287 
8288   HeapWord* const fc_addr = (HeapWord*) fc;
8289 
8290   bool coalesce;
8291   const size_t left  = pointer_delta(fc_addr, freeFinger());
8292   const size_t right = chunkSize;
8293   switch (FLSCoalescePolicy) {
8294     // numeric value forms a coalition aggressiveness metric
8295     case 0:  { // never coalesce
8296       coalesce = false;
8297       break;
8298     }
8299     case 1: { // coalesce if left & right chunks on overpopulated lists
8300       coalesce = _sp->coalOverPopulated(left) &&
8301                  _sp->coalOverPopulated(right);
8302       break;
8303     }
8304     case 2: { // coalesce if left chunk on overpopulated list (default)
8305       coalesce = _sp->coalOverPopulated(left);
8306       break;
8307     }
8308     case 3: { // coalesce if left OR right chunk on overpopulated list
8309       coalesce = _sp->coalOverPopulated(left) ||
8310                  _sp->coalOverPopulated(right);
8311       break;
8312     }
8313     case 4: { // always coalesce
8314       coalesce = true;
8315       break;
8316     }
8317     default:
8318      ShouldNotReachHere();
8319   }
8320 
8321   // Should the current free range be coalesced?
8322   // If the chunk is in a free range and either we decided to coalesce above
8323   // or the chunk is near the large block at the end of the heap
8324   // (isNearLargestChunk() returns true), then coalesce this chunk.
8325   const bool doCoalesce = inFreeRange()
8326                           && (coalesce || _g->isNearLargestChunk(fc_addr));
8327   if (doCoalesce) {
8328     // Coalesce the current free range on the left with the new
8329     // chunk on the right.  If either is on a free list,
8330     // it must be removed from the list and stashed in the closure.
8331     if (freeRangeInFreeLists()) {
8332       FreeChunk* const ffc = (FreeChunk*)freeFinger();
8333       assert(ffc->size() == pointer_delta(fc_addr, freeFinger()),
8334         "Size of free range is inconsistent with chunk size.");
8335       if (CMSTestInFreeList) {
8336         assert(_sp->verify_chunk_in_free_list(ffc),
8337           "Chunk is not in free lists");
8338       }
8339       _sp->coalDeath(ffc->size());
8340       _sp->removeFreeChunkFromFreeLists(ffc);
8341       set_freeRangeInFreeLists(false);
8342     }
8343     if (fcInFreeLists) {
8344       _sp->coalDeath(chunkSize);
8345       assert(fc->size() == chunkSize,
8346         "The chunk has the wrong size or is not in the free lists");
8347       _sp->removeFreeChunkFromFreeLists(fc);
8348     }
8349     set_lastFreeRangeCoalesced(true);
8350     print_free_block_coalesced(fc);
8351   } else {  // not in a free range and/or should not coalesce
8352     // Return the current free range and start a new one.
8353     if (inFreeRange()) {
8354       // In a free range but cannot coalesce with the right hand chunk.
8355       // Put the current free range into the free lists.
8356       flush_cur_free_chunk(freeFinger(),
8357                            pointer_delta(fc_addr, freeFinger()));
8358     }
8359     // Set up for new free range.  Pass along whether the right hand
8360     // chunk is in the free lists.
8361     initialize_free_range((HeapWord*)fc, fcInFreeLists);
8362   }
8363 }
8364 
8365 // Lookahead flush:
8366 // If we are tracking a free range, and this is the last chunk that
8367 // we'll look at because its end crosses past _limit, we'll preemptively
8368 // flush it along with any free range we may be holding on to. Note that
8369 // this can be the case only for an already free or freshly garbage
8370 // chunk. If this block is an object, it can never straddle
8371 // over _limit. The "straddling" occurs when _limit is set at
8372 // the previous end of the space when this cycle started, and
8373 // a subsequent heap expansion caused the previously co-terminal
8374 // free block to be coalesced with the newly expanded portion,
8375 // thus rendering _limit a non-block-boundary making it dangerous
8376 // for the sweeper to step over and examine.
8377 void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) {
8378   assert(inFreeRange(), "Should only be called if currently in a free range.");
8379   HeapWord* const eob = ((HeapWord*)fc) + chunk_size;
8380   assert(_sp->used_region().contains(eob - 1),
8381          err_msg("eob = " PTR_FORMAT " out of bounds wrt _sp = [" PTR_FORMAT "," PTR_FORMAT ")"
8382                  " when examining fc = " PTR_FORMAT "(" SIZE_FORMAT ")",
8383                  _limit, _sp->bottom(), _sp->end(), fc, chunk_size));
8384   if (eob >= _limit) {
8385     assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit");
8386     if (CMSTraceSweeper) {
8387       gclog_or_tty->print_cr("_limit " PTR_FORMAT " reached or crossed by block "
8388                              "[" PTR_FORMAT "," PTR_FORMAT ") in space "
8389                              "[" PTR_FORMAT "," PTR_FORMAT ")",
8390                              _limit, fc, eob, _sp->bottom(), _sp->end());
8391     }
8392     // Return the storage we are tracking back into the free lists.
8393     if (CMSTraceSweeper) {
8394       gclog_or_tty->print_cr("Flushing ... ");
8395     }
8396     assert(freeFinger() < eob, "Error");
8397     flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger()));
8398   }
8399 }
8400 
8401 void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) {
8402   assert(inFreeRange(), "Should only be called if currently in a free range.");
8403   assert(size > 0,
8404     "A zero sized chunk cannot be added to the free lists.");
8405   if (!freeRangeInFreeLists()) {
8406     if (CMSTestInFreeList) {
8407       FreeChunk* fc = (FreeChunk*) chunk;
8408       fc->set_size(size);
8409       assert(!_sp->verify_chunk_in_free_list(fc),
8410         "chunk should not be in free lists yet");
8411     }
8412     if (CMSTraceSweeper) {
8413       gclog_or_tty->print_cr(" -- add free block 0x%x (%d) to free lists",
8414                     chunk, size);
8415     }
8416     // A new free range is going to be starting.  The current
8417     // free range has not been added to the free lists yet or
8418     // was removed so add it back.
8419     // If the current free range was coalesced, then the death
8420     // of the free range was recorded.  Record a birth now.
8421     if (lastFreeRangeCoalesced()) {
8422       _sp->coalBirth(size);
8423     }
8424     _sp->addChunkAndRepairOffsetTable(chunk, size,
8425             lastFreeRangeCoalesced());
8426   } else if (CMSTraceSweeper) {
8427     gclog_or_tty->print_cr("Already in free list: nothing to flush");
8428   }
8429   set_inFreeRange(false);
8430   set_freeRangeInFreeLists(false);
8431 }
8432 
8433 // We take a break if we've been at this for a while,
8434 // so as to avoid monopolizing the locks involved.
8435 void SweepClosure::do_yield_work(HeapWord* addr) {
8436   // Return current free chunk being used for coalescing (if any)
8437   // to the appropriate freelist.  After yielding, the next
8438   // free block encountered will start a coalescing range of
8439   // free blocks.  If the next free block is adjacent to the
8440   // chunk just flushed, they will need to wait for the next
8441   // sweep to be coalesced.
8442   if (inFreeRange()) {
8443     flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8444   }
8445 
8446   // First give up the locks, then yield, then re-lock.
8447   // We should probably use a constructor/destructor idiom to
8448   // do this unlock/lock or modify the MutexUnlocker class to
8449   // serve our purpose. XXX
8450   assert_lock_strong(_bitMap->lock());
8451   assert_lock_strong(_freelistLock);
8452   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
8453          "CMS thread should hold CMS token");
8454   _bitMap->lock()->unlock();
8455   _freelistLock->unlock();
8456   ConcurrentMarkSweepThread::desynchronize(true);
8457   ConcurrentMarkSweepThread::acknowledge_yield_request();
8458   _collector->stopTimer();
8459   GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
8460   if (PrintCMSStatistics != 0) {
8461     _collector->incrementYields();
8462   }
8463   _collector->icms_wait();
8464 
8465   // See the comment in coordinator_yield()
8466   for (unsigned i = 0; i < CMSYieldSleepCount &&
8467                        ConcurrentMarkSweepThread::should_yield() &&
8468                        !CMSCollector::foregroundGCIsActive(); ++i) {
8469     os::sleep(Thread::current(), 1, false);
8470     ConcurrentMarkSweepThread::acknowledge_yield_request();
8471   }
8472 
8473   ConcurrentMarkSweepThread::synchronize(true);
8474   _freelistLock->lock();
8475   _bitMap->lock()->lock_without_safepoint_check();
8476   _collector->startTimer();
8477 }
8478 
8479 #ifndef PRODUCT
8480 // This is actually very useful in a product build if it can
8481 // be called from the debugger.  Compile it into the product
8482 // as needed.
8483 bool debug_verify_chunk_in_free_list(FreeChunk* fc) {
8484   return debug_cms_space->verify_chunk_in_free_list(fc);
8485 }
8486 #endif
8487 
8488 void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const {
8489   if (CMSTraceSweeper) {
8490     gclog_or_tty->print_cr("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")",
8491                            fc, fc->size());
8492   }
8493 }
8494 
8495 // CMSIsAliveClosure
8496 bool CMSIsAliveClosure::do_object_b(oop obj) {
8497   HeapWord* addr = (HeapWord*)obj;
8498   return addr != NULL &&
8499          (!_span.contains(addr) || _bit_map->isMarked(addr));
8500 }
8501 
8502 
8503 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector,
8504                       MemRegion span,
8505                       CMSBitMap* bit_map, CMSMarkStack* mark_stack,
8506                       bool cpc):
8507   _collector(collector),
8508   _span(span),
8509   _bit_map(bit_map),
8510   _mark_stack(mark_stack),
8511   _concurrent_precleaning(cpc) {
8512   assert(!_span.is_empty(), "Empty span could spell trouble");
8513 }
8514 
8515 
8516 // CMSKeepAliveClosure: the serial version
8517 void CMSKeepAliveClosure::do_oop(oop obj) {
8518   HeapWord* addr = (HeapWord*)obj;
8519   if (_span.contains(addr) &&
8520       !_bit_map->isMarked(addr)) {
8521     _bit_map->mark(addr);
8522     bool simulate_overflow = false;
8523     NOT_PRODUCT(
8524       if (CMSMarkStackOverflowALot &&
8525           _collector->simulate_overflow()) {
8526         // simulate a stack overflow
8527         simulate_overflow = true;
8528       }
8529     )
8530     if (simulate_overflow || !_mark_stack->push(obj)) {
8531       if (_concurrent_precleaning) {
8532         // We dirty the overflown object and let the remark
8533         // phase deal with it.
8534         assert(_collector->overflow_list_is_empty(), "Error");
8535         // In the case of object arrays, we need to dirty all of
8536         // the cards that the object spans. No locking or atomics
8537         // are needed since no one else can be mutating the mod union
8538         // table.
8539         if (obj->is_objArray()) {
8540           size_t sz = obj->size();
8541           HeapWord* end_card_addr =
8542             (HeapWord*)round_to((intptr_t)(addr+sz), CardTableModRefBS::card_size);
8543           MemRegion redirty_range = MemRegion(addr, end_card_addr);
8544           assert(!redirty_range.is_empty(), "Arithmetical tautology");
8545           _collector->_modUnionTable.mark_range(redirty_range);
8546         } else {
8547           _collector->_modUnionTable.mark(addr);
8548         }
8549         _collector->_ser_kac_preclean_ovflw++;
8550       } else {
8551         _collector->push_on_overflow_list(obj);
8552         _collector->_ser_kac_ovflw++;
8553       }
8554     }
8555   }
8556 }
8557 
8558 void CMSKeepAliveClosure::do_oop(oop* p)       { CMSKeepAliveClosure::do_oop_work(p); }
8559 void CMSKeepAliveClosure::do_oop(narrowOop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8560 
8561 // CMSParKeepAliveClosure: a parallel version of the above.
8562 // The work queues are private to each closure (thread),
8563 // but (may be) available for stealing by other threads.
8564 void CMSParKeepAliveClosure::do_oop(oop obj) {
8565   HeapWord* addr = (HeapWord*)obj;
8566   if (_span.contains(addr) &&
8567       !_bit_map->isMarked(addr)) {
8568     // In general, during recursive tracing, several threads
8569     // may be concurrently getting here; the first one to
8570     // "tag" it, claims it.
8571     if (_bit_map->par_mark(addr)) {
8572       bool res = _work_queue->push(obj);
8573       assert(res, "Low water mark should be much less than capacity");
8574       // Do a recursive trim in the hope that this will keep
8575       // stack usage lower, but leave some oops for potential stealers
8576       trim_queue(_low_water_mark);
8577     } // Else, another thread got there first
8578   }
8579 }
8580 
8581 void CMSParKeepAliveClosure::do_oop(oop* p)       { CMSParKeepAliveClosure::do_oop_work(p); }
8582 void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8583 
8584 void CMSParKeepAliveClosure::trim_queue(uint max) {
8585   while (_work_queue->size() > max) {
8586     oop new_oop;
8587     if (_work_queue->pop_local(new_oop)) {
8588       assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
8589       assert(_bit_map->isMarked((HeapWord*)new_oop),
8590              "no white objects on this stack!");
8591       assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8592       // iterate over the oops in this oop, marking and pushing
8593       // the ones in CMS heap (i.e. in _span).
8594       new_oop->oop_iterate(&_mark_and_push);
8595     }
8596   }
8597 }
8598 
8599 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
8600                                 CMSCollector* collector,
8601                                 MemRegion span, CMSBitMap* bit_map,
8602                                 OopTaskQueue* work_queue):
8603   _collector(collector),
8604   _span(span),
8605   _bit_map(bit_map),
8606   _work_queue(work_queue) { }
8607 
8608 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
8609   HeapWord* addr = (HeapWord*)obj;
8610   if (_span.contains(addr) &&
8611       !_bit_map->isMarked(addr)) {
8612     if (_bit_map->par_mark(addr)) {
8613       bool simulate_overflow = false;
8614       NOT_PRODUCT(
8615         if (CMSMarkStackOverflowALot &&
8616             _collector->par_simulate_overflow()) {
8617           // simulate a stack overflow
8618           simulate_overflow = true;
8619         }
8620       )
8621       if (simulate_overflow || !_work_queue->push(obj)) {
8622         _collector->par_push_on_overflow_list(obj);
8623         _collector->_par_kac_ovflw++;
8624       }
8625     } // Else another thread got there already
8626   }
8627 }
8628 
8629 void CMSInnerParMarkAndPushClosure::do_oop(oop* p)       { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8630 void CMSInnerParMarkAndPushClosure::do_oop(narrowOop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8631 
8632 //////////////////////////////////////////////////////////////////
8633 //  CMSExpansionCause                /////////////////////////////
8634 //////////////////////////////////////////////////////////////////
8635 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
8636   switch (cause) {
8637     case _no_expansion:
8638       return "No expansion";
8639     case _satisfy_free_ratio:
8640       return "Free ratio";
8641     case _satisfy_promotion:
8642       return "Satisfy promotion";
8643     case _satisfy_allocation:
8644       return "allocation";
8645     case _allocate_par_lab:
8646       return "Par LAB";
8647     case _allocate_par_spooling_space:
8648       return "Par Spooling Space";
8649     case _adaptive_size_policy:
8650       return "Ergonomics";
8651     default:
8652       return "unknown";
8653   }
8654 }
8655 
8656 void CMSDrainMarkingStackClosure::do_void() {
8657   // the max number to take from overflow list at a time
8658   const size_t num = _mark_stack->capacity()/4;
8659   assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
8660          "Overflow list should be NULL during concurrent phases");
8661   while (!_mark_stack->isEmpty() ||
8662          // if stack is empty, check the overflow list
8663          _collector->take_from_overflow_list(num, _mark_stack)) {
8664     oop obj = _mark_stack->pop();
8665     HeapWord* addr = (HeapWord*)obj;
8666     assert(_span.contains(addr), "Should be within span");
8667     assert(_bit_map->isMarked(addr), "Should be marked");
8668     assert(obj->is_oop(), "Should be an oop");
8669     obj->oop_iterate(_keep_alive);
8670   }
8671 }
8672 
8673 void CMSParDrainMarkingStackClosure::do_void() {
8674   // drain queue
8675   trim_queue(0);
8676 }
8677 
8678 // Trim our work_queue so its length is below max at return
8679 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
8680   while (_work_queue->size() > max) {
8681     oop new_oop;
8682     if (_work_queue->pop_local(new_oop)) {
8683       assert(new_oop->is_oop(), "Expected an oop");
8684       assert(_bit_map->isMarked((HeapWord*)new_oop),
8685              "no white objects on this stack!");
8686       assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8687       // iterate over the oops in this oop, marking and pushing
8688       // the ones in CMS heap (i.e. in _span).
8689       new_oop->oop_iterate(&_mark_and_push);
8690     }
8691   }
8692 }
8693 
8694 ////////////////////////////////////////////////////////////////////
8695 // Support for Marking Stack Overflow list handling and related code
8696 ////////////////////////////////////////////////////////////////////
8697 // Much of the following code is similar in shape and spirit to the
8698 // code used in ParNewGC. We should try and share that code
8699 // as much as possible in the future.
8700 
8701 #ifndef PRODUCT
8702 // Debugging support for CMSStackOverflowALot
8703 
8704 // It's OK to call this multi-threaded;  the worst thing
8705 // that can happen is that we'll get a bunch of closely
8706 // spaced simulated oveflows, but that's OK, in fact
8707 // probably good as it would exercise the overflow code
8708 // under contention.
8709 bool CMSCollector::simulate_overflow() {
8710   if (_overflow_counter-- <= 0) { // just being defensive
8711     _overflow_counter = CMSMarkStackOverflowInterval;
8712     return true;
8713   } else {
8714     return false;
8715   }
8716 }
8717 
8718 bool CMSCollector::par_simulate_overflow() {
8719   return simulate_overflow();
8720 }
8721 #endif
8722 
8723 // Single-threaded
8724 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
8725   assert(stack->isEmpty(), "Expected precondition");
8726   assert(stack->capacity() > num, "Shouldn't bite more than can chew");
8727   size_t i = num;
8728   oop  cur = _overflow_list;
8729   const markOop proto = markOopDesc::prototype();
8730   NOT_PRODUCT(ssize_t n = 0;)
8731   for (oop next; i > 0 && cur != NULL; cur = next, i--) {
8732     next = oop(cur->mark());
8733     cur->set_mark(proto);   // until proven otherwise
8734     assert(cur->is_oop(), "Should be an oop");
8735     bool res = stack->push(cur);
8736     assert(res, "Bit off more than can chew?");
8737     NOT_PRODUCT(n++;)
8738   }
8739   _overflow_list = cur;
8740 #ifndef PRODUCT
8741   assert(_num_par_pushes >= n, "Too many pops?");
8742   _num_par_pushes -=n;
8743 #endif
8744   return !stack->isEmpty();
8745 }
8746 
8747 #define BUSY  (oop(0x1aff1aff))
8748 // (MT-safe) Get a prefix of at most "num" from the list.
8749 // The overflow list is chained through the mark word of
8750 // each object in the list. We fetch the entire list,
8751 // break off a prefix of the right size and return the
8752 // remainder. If other threads try to take objects from
8753 // the overflow list at that time, they will wait for
8754 // some time to see if data becomes available. If (and
8755 // only if) another thread places one or more object(s)
8756 // on the global list before we have returned the suffix
8757 // to the global list, we will walk down our local list
8758 // to find its end and append the global list to
8759 // our suffix before returning it. This suffix walk can
8760 // prove to be expensive (quadratic in the amount of traffic)
8761 // when there are many objects in the overflow list and
8762 // there is much producer-consumer contention on the list.
8763 // *NOTE*: The overflow list manipulation code here and
8764 // in ParNewGeneration:: are very similar in shape,
8765 // except that in the ParNew case we use the old (from/eden)
8766 // copy of the object to thread the list via its klass word.
8767 // Because of the common code, if you make any changes in
8768 // the code below, please check the ParNew version to see if
8769 // similar changes might be needed.
8770 // CR 6797058 has been filed to consolidate the common code.
8771 bool CMSCollector::par_take_from_overflow_list(size_t num,
8772                                                OopTaskQueue* work_q,
8773                                                int no_of_gc_threads) {
8774   assert(work_q->size() == 0, "First empty local work queue");
8775   assert(num < work_q->max_elems(), "Can't bite more than we can chew");
8776   if (_overflow_list == NULL) {
8777     return false;
8778   }
8779   // Grab the entire list; we'll put back a suffix
8780   oop prefix = (oop)Atomic::xchg_ptr(BUSY, &_overflow_list);
8781   Thread* tid = Thread::current();
8782   // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was
8783   // set to ParallelGCThreads.
8784   size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads;
8785   size_t sleep_time_millis = MAX2((size_t)1, num/100);
8786   // If the list is busy, we spin for a short while,
8787   // sleeping between attempts to get the list.
8788   for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) {
8789     os::sleep(tid, sleep_time_millis, false);
8790     if (_overflow_list == NULL) {
8791       // Nothing left to take
8792       return false;
8793     } else if (_overflow_list != BUSY) {
8794       // Try and grab the prefix
8795       prefix = (oop)Atomic::xchg_ptr(BUSY, &_overflow_list);
8796     }
8797   }
8798   // If the list was found to be empty, or we spun long
8799   // enough, we give up and return empty-handed. If we leave
8800   // the list in the BUSY state below, it must be the case that
8801   // some other thread holds the overflow list and will set it
8802   // to a non-BUSY state in the future.
8803   if (prefix == NULL || prefix == BUSY) {
8804      // Nothing to take or waited long enough
8805      if (prefix == NULL) {
8806        // Write back the NULL in case we overwrote it with BUSY above
8807        // and it is still the same value.
8808        (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8809      }
8810      return false;
8811   }
8812   assert(prefix != NULL && prefix != BUSY, "Error");
8813   size_t i = num;
8814   oop cur = prefix;
8815   // Walk down the first "num" objects, unless we reach the end.
8816   for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--);
8817   if (cur->mark() == NULL) {
8818     // We have "num" or fewer elements in the list, so there
8819     // is nothing to return to the global list.
8820     // Write back the NULL in lieu of the BUSY we wrote
8821     // above, if it is still the same value.
8822     if (_overflow_list == BUSY) {
8823       (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8824     }
8825   } else {
8826     // Chop off the suffix and rerturn it to the global list.
8827     assert(cur->mark() != BUSY, "Error");
8828     oop suffix_head = cur->mark(); // suffix will be put back on global list
8829     cur->set_mark(NULL);           // break off suffix
8830     // It's possible that the list is still in the empty(busy) state
8831     // we left it in a short while ago; in that case we may be
8832     // able to place back the suffix without incurring the cost
8833     // of a walk down the list.
8834     oop observed_overflow_list = _overflow_list;
8835     oop cur_overflow_list = observed_overflow_list;
8836     bool attached = false;
8837     while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
8838       observed_overflow_list =
8839         (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
8840       if (cur_overflow_list == observed_overflow_list) {
8841         attached = true;
8842         break;
8843       } else cur_overflow_list = observed_overflow_list;
8844     }
8845     if (!attached) {
8846       // Too bad, someone else sneaked in (at least) an element; we'll need
8847       // to do a splice. Find tail of suffix so we can prepend suffix to global
8848       // list.
8849       for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark()));
8850       oop suffix_tail = cur;
8851       assert(suffix_tail != NULL && suffix_tail->mark() == NULL,
8852              "Tautology");
8853       observed_overflow_list = _overflow_list;
8854       do {
8855         cur_overflow_list = observed_overflow_list;
8856         if (cur_overflow_list != BUSY) {
8857           // Do the splice ...
8858           suffix_tail->set_mark(markOop(cur_overflow_list));
8859         } else { // cur_overflow_list == BUSY
8860           suffix_tail->set_mark(NULL);
8861         }
8862         // ... and try to place spliced list back on overflow_list ...
8863         observed_overflow_list =
8864           (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
8865       } while (cur_overflow_list != observed_overflow_list);
8866       // ... until we have succeeded in doing so.
8867     }
8868   }
8869 
8870   // Push the prefix elements on work_q
8871   assert(prefix != NULL, "control point invariant");
8872   const markOop proto = markOopDesc::prototype();
8873   oop next;
8874   NOT_PRODUCT(ssize_t n = 0;)
8875   for (cur = prefix; cur != NULL; cur = next) {
8876     next = oop(cur->mark());
8877     cur->set_mark(proto);   // until proven otherwise
8878     assert(cur->is_oop(), "Should be an oop");
8879     bool res = work_q->push(cur);
8880     assert(res, "Bit off more than we can chew?");
8881     NOT_PRODUCT(n++;)
8882   }
8883 #ifndef PRODUCT
8884   assert(_num_par_pushes >= n, "Too many pops?");
8885   Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
8886 #endif
8887   return true;
8888 }
8889 
8890 // Single-threaded
8891 void CMSCollector::push_on_overflow_list(oop p) {
8892   NOT_PRODUCT(_num_par_pushes++;)
8893   assert(p->is_oop(), "Not an oop");
8894   preserve_mark_if_necessary(p);
8895   p->set_mark((markOop)_overflow_list);
8896   _overflow_list = p;
8897 }
8898 
8899 // Multi-threaded; use CAS to prepend to overflow list
8900 void CMSCollector::par_push_on_overflow_list(oop p) {
8901   NOT_PRODUCT(Atomic::inc_ptr(&_num_par_pushes);)
8902   assert(p->is_oop(), "Not an oop");
8903   par_preserve_mark_if_necessary(p);
8904   oop observed_overflow_list = _overflow_list;
8905   oop cur_overflow_list;
8906   do {
8907     cur_overflow_list = observed_overflow_list;
8908     if (cur_overflow_list != BUSY) {
8909       p->set_mark(markOop(cur_overflow_list));
8910     } else {
8911       p->set_mark(NULL);
8912     }
8913     observed_overflow_list =
8914       (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list);
8915   } while (cur_overflow_list != observed_overflow_list);
8916 }
8917 #undef BUSY
8918 
8919 // Single threaded
8920 // General Note on GrowableArray: pushes may silently fail
8921 // because we are (temporarily) out of C-heap for expanding
8922 // the stack. The problem is quite ubiquitous and affects
8923 // a lot of code in the JVM. The prudent thing for GrowableArray
8924 // to do (for now) is to exit with an error. However, that may
8925 // be too draconian in some cases because the caller may be
8926 // able to recover without much harm. For such cases, we
8927 // should probably introduce a "soft_push" method which returns
8928 // an indication of success or failure with the assumption that
8929 // the caller may be able to recover from a failure; code in
8930 // the VM can then be changed, incrementally, to deal with such
8931 // failures where possible, thus, incrementally hardening the VM
8932 // in such low resource situations.
8933 void CMSCollector::preserve_mark_work(oop p, markOop m) {
8934   _preserved_oop_stack.push(p);
8935   _preserved_mark_stack.push(m);
8936   assert(m == p->mark(), "Mark word changed");
8937   assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8938          "bijection");
8939 }
8940 
8941 // Single threaded
8942 void CMSCollector::preserve_mark_if_necessary(oop p) {
8943   markOop m = p->mark();
8944   if (m->must_be_preserved(p)) {
8945     preserve_mark_work(p, m);
8946   }
8947 }
8948 
8949 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
8950   markOop m = p->mark();
8951   if (m->must_be_preserved(p)) {
8952     MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
8953     // Even though we read the mark word without holding
8954     // the lock, we are assured that it will not change
8955     // because we "own" this oop, so no other thread can
8956     // be trying to push it on the overflow list; see
8957     // the assertion in preserve_mark_work() that checks
8958     // that m == p->mark().
8959     preserve_mark_work(p, m);
8960   }
8961 }
8962 
8963 // We should be able to do this multi-threaded,
8964 // a chunk of stack being a task (this is
8965 // correct because each oop only ever appears
8966 // once in the overflow list. However, it's
8967 // not very easy to completely overlap this with
8968 // other operations, so will generally not be done
8969 // until all work's been completed. Because we
8970 // expect the preserved oop stack (set) to be small,
8971 // it's probably fine to do this single-threaded.
8972 // We can explore cleverer concurrent/overlapped/parallel
8973 // processing of preserved marks if we feel the
8974 // need for this in the future. Stack overflow should
8975 // be so rare in practice and, when it happens, its
8976 // effect on performance so great that this will
8977 // likely just be in the noise anyway.
8978 void CMSCollector::restore_preserved_marks_if_any() {
8979   assert(SafepointSynchronize::is_at_safepoint(),
8980          "world should be stopped");
8981   assert(Thread::current()->is_ConcurrentGC_thread() ||
8982          Thread::current()->is_VM_thread(),
8983          "should be single-threaded");
8984   assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8985          "bijection");
8986 
8987   while (!_preserved_oop_stack.is_empty()) {
8988     oop p = _preserved_oop_stack.pop();
8989     assert(p->is_oop(), "Should be an oop");
8990     assert(_span.contains(p), "oop should be in _span");
8991     assert(p->mark() == markOopDesc::prototype(),
8992            "Set when taken from overflow list");
8993     markOop m = _preserved_mark_stack.pop();
8994     p->set_mark(m);
8995   }
8996   assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(),
8997          "stacks were cleared above");
8998 }
8999 
9000 #ifndef PRODUCT
9001 bool CMSCollector::no_preserved_marks() const {
9002   return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty();
9003 }
9004 #endif
9005 
9006 CMSAdaptiveSizePolicy* ASConcurrentMarkSweepGeneration::cms_size_policy() const
9007 {
9008   GenCollectedHeap* gch = (GenCollectedHeap*) GenCollectedHeap::heap();
9009   CMSAdaptiveSizePolicy* size_policy =
9010     (CMSAdaptiveSizePolicy*) gch->gen_policy()->size_policy();
9011   assert(size_policy->is_gc_cms_adaptive_size_policy(),
9012     "Wrong type for size policy");
9013   return size_policy;
9014 }
9015 
9016 void ASConcurrentMarkSweepGeneration::resize(size_t cur_promo_size,
9017                                            size_t desired_promo_size) {
9018   if (cur_promo_size < desired_promo_size) {
9019     size_t expand_bytes = desired_promo_size - cur_promo_size;
9020     if (PrintAdaptiveSizePolicy && Verbose) {
9021       gclog_or_tty->print_cr(" ASConcurrentMarkSweepGeneration::resize "
9022         "Expanding tenured generation by " SIZE_FORMAT " (bytes)",
9023         expand_bytes);
9024     }
9025     expand(expand_bytes,
9026            MinHeapDeltaBytes,
9027            CMSExpansionCause::_adaptive_size_policy);
9028   } else if (desired_promo_size < cur_promo_size) {
9029     size_t shrink_bytes = cur_promo_size - desired_promo_size;
9030     if (PrintAdaptiveSizePolicy && Verbose) {
9031       gclog_or_tty->print_cr(" ASConcurrentMarkSweepGeneration::resize "
9032         "Shrinking tenured generation by " SIZE_FORMAT " (bytes)",
9033         shrink_bytes);
9034     }
9035     shrink(shrink_bytes);
9036   }
9037 }
9038 
9039 CMSGCAdaptivePolicyCounters* ASConcurrentMarkSweepGeneration::gc_adaptive_policy_counters() {
9040   GenCollectedHeap* gch = GenCollectedHeap::heap();
9041   CMSGCAdaptivePolicyCounters* counters =
9042     (CMSGCAdaptivePolicyCounters*) gch->collector_policy()->counters();
9043   assert(counters->kind() == GCPolicyCounters::CMSGCAdaptivePolicyCountersKind,
9044     "Wrong kind of counters");
9045   return counters;
9046 }
9047 
9048 
9049 void ASConcurrentMarkSweepGeneration::update_counters() {
9050   if (UsePerfData) {
9051     _space_counters->update_all();
9052     _gen_counters->update_all();
9053     CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
9054     GenCollectedHeap* gch = GenCollectedHeap::heap();
9055     CMSGCStats* gc_stats_l = (CMSGCStats*) gc_stats();
9056     assert(gc_stats_l->kind() == GCStats::CMSGCStatsKind,
9057       "Wrong gc statistics type");
9058     counters->update_counters(gc_stats_l);
9059   }
9060 }
9061 
9062 void ASConcurrentMarkSweepGeneration::update_counters(size_t used) {
9063   if (UsePerfData) {
9064     _space_counters->update_used(used);
9065     _space_counters->update_capacity();
9066     _gen_counters->update_all();
9067 
9068     CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
9069     GenCollectedHeap* gch = GenCollectedHeap::heap();
9070     CMSGCStats* gc_stats_l = (CMSGCStats*) gc_stats();
9071     assert(gc_stats_l->kind() == GCStats::CMSGCStatsKind,
9072       "Wrong gc statistics type");
9073     counters->update_counters(gc_stats_l);
9074   }
9075 }
9076 
9077 // The desired expansion delta is computed so that:
9078 // . desired free percentage or greater is used
9079 void ASConcurrentMarkSweepGeneration::compute_new_size() {
9080   assert_locked_or_safepoint(Heap_lock);
9081 
9082   GenCollectedHeap* gch = (GenCollectedHeap*) GenCollectedHeap::heap();
9083 
9084   // If incremental collection failed, we just want to expand
9085   // to the limit.
9086   if (incremental_collection_failed()) {
9087     clear_incremental_collection_failed();
9088     grow_to_reserved();
9089     return;
9090   }
9091 
9092   assert(UseAdaptiveSizePolicy, "Should be using adaptive sizing");
9093 
9094   assert(gch->kind() == CollectedHeap::GenCollectedHeap,
9095     "Wrong type of heap");
9096   int prev_level = level() - 1;
9097   assert(prev_level >= 0, "The cms generation is the lowest generation");
9098   Generation* prev_gen = gch->get_gen(prev_level);
9099   assert(prev_gen->kind() == Generation::ASParNew,
9100     "Wrong type of young generation");
9101   ParNewGeneration* younger_gen = (ParNewGeneration*) prev_gen;
9102   size_t cur_eden = younger_gen->eden()->capacity();
9103   CMSAdaptiveSizePolicy* size_policy = cms_size_policy();
9104   size_t cur_promo = free();
9105   size_policy->compute_tenured_generation_free_space(cur_promo,
9106                                                        max_available(),
9107                                                        cur_eden);
9108   resize(cur_promo, size_policy->promo_size());
9109 
9110   // Record the new size of the space in the cms generation
9111   // that is available for promotions.  This is temporary.
9112   // It should be the desired promo size.
9113   size_policy->avg_cms_promo()->sample(free());
9114   size_policy->avg_old_live()->sample(used());
9115 
9116   if (UsePerfData) {
9117     CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
9118     counters->update_cms_capacity_counter(capacity());
9119   }
9120 }
9121 
9122 void ASConcurrentMarkSweepGeneration::shrink_by(size_t desired_bytes) {
9123   assert_locked_or_safepoint(Heap_lock);
9124   assert_lock_strong(freelistLock());
9125   HeapWord* old_end = _cmsSpace->end();
9126   HeapWord* unallocated_start = _cmsSpace->unallocated_block();
9127   assert(old_end >= unallocated_start, "Miscalculation of unallocated_start");
9128   FreeChunk* chunk_at_end = find_chunk_at_end();
9129   if (chunk_at_end == NULL) {
9130     // No room to shrink
9131     if (PrintGCDetails && Verbose) {
9132       gclog_or_tty->print_cr("No room to shrink: old_end  "
9133         PTR_FORMAT "  unallocated_start  " PTR_FORMAT
9134         " chunk_at_end  " PTR_FORMAT,
9135         old_end, unallocated_start, chunk_at_end);
9136     }
9137     return;
9138   } else {
9139 
9140     // Find the chunk at the end of the space and determine
9141     // how much it can be shrunk.
9142     size_t shrinkable_size_in_bytes = chunk_at_end->size();
9143     size_t aligned_shrinkable_size_in_bytes =
9144       align_size_down(shrinkable_size_in_bytes, os::vm_page_size());
9145     assert(unallocated_start <= (HeapWord*) chunk_at_end->end(),
9146       "Inconsistent chunk at end of space");
9147     size_t bytes = MIN2(desired_bytes, aligned_shrinkable_size_in_bytes);
9148     size_t word_size_before = heap_word_size(_virtual_space.committed_size());
9149 
9150     // Shrink the underlying space
9151     _virtual_space.shrink_by(bytes);
9152     if (PrintGCDetails && Verbose) {
9153       gclog_or_tty->print_cr("ConcurrentMarkSweepGeneration::shrink_by:"
9154         " desired_bytes " SIZE_FORMAT
9155         " shrinkable_size_in_bytes " SIZE_FORMAT
9156         " aligned_shrinkable_size_in_bytes " SIZE_FORMAT
9157         "  bytes  " SIZE_FORMAT,
9158         desired_bytes, shrinkable_size_in_bytes,
9159         aligned_shrinkable_size_in_bytes, bytes);
9160       gclog_or_tty->print_cr("          old_end  " SIZE_FORMAT
9161         "  unallocated_start  " SIZE_FORMAT,
9162         old_end, unallocated_start);
9163     }
9164 
9165     // If the space did shrink (shrinking is not guaranteed),
9166     // shrink the chunk at the end by the appropriate amount.
9167     if (((HeapWord*)_virtual_space.high()) < old_end) {
9168       size_t new_word_size =
9169         heap_word_size(_virtual_space.committed_size());
9170 
9171       // Have to remove the chunk from the dictionary because it is changing
9172       // size and might be someplace elsewhere in the dictionary.
9173 
9174       // Get the chunk at end, shrink it, and put it
9175       // back.
9176       _cmsSpace->removeChunkFromDictionary(chunk_at_end);
9177       size_t word_size_change = word_size_before - new_word_size;
9178       size_t chunk_at_end_old_size = chunk_at_end->size();
9179       assert(chunk_at_end_old_size >= word_size_change,
9180         "Shrink is too large");
9181       chunk_at_end->set_size(chunk_at_end_old_size -
9182                           word_size_change);
9183       _cmsSpace->freed((HeapWord*) chunk_at_end->end(),
9184         word_size_change);
9185 
9186       _cmsSpace->returnChunkToDictionary(chunk_at_end);
9187 
9188       MemRegion mr(_cmsSpace->bottom(), new_word_size);
9189       _bts->resize(new_word_size);  // resize the block offset shared array
9190       Universe::heap()->barrier_set()->resize_covered_region(mr);
9191       _cmsSpace->assert_locked();
9192       _cmsSpace->set_end((HeapWord*)_virtual_space.high());
9193 
9194       NOT_PRODUCT(_cmsSpace->dictionary()->verify());
9195 
9196       // update the space and generation capacity counters
9197       if (UsePerfData) {
9198         _space_counters->update_capacity();
9199         _gen_counters->update_all();
9200       }
9201 
9202       if (Verbose && PrintGCDetails) {
9203         size_t new_mem_size = _virtual_space.committed_size();
9204         size_t old_mem_size = new_mem_size + bytes;
9205         gclog_or_tty->print_cr("Shrinking %s from " SIZE_FORMAT "K by " SIZE_FORMAT "K to " SIZE_FORMAT "K",
9206                       name(), old_mem_size/K, bytes/K, new_mem_size/K);
9207       }
9208     }
9209 
9210     assert(_cmsSpace->unallocated_block() <= _cmsSpace->end(),
9211       "Inconsistency at end of space");
9212     assert(chunk_at_end->end() == (uintptr_t*) _cmsSpace->end(),
9213       "Shrinking is inconsistent");
9214     return;
9215   }
9216 }
9217 
9218 // Transfer some number of overflown objects to usual marking
9219 // stack. Return true if some objects were transferred.
9220 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
9221   size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,
9222                     (size_t)ParGCDesiredObjsFromOverflowList);
9223 
9224   bool res = _collector->take_from_overflow_list(num, _mark_stack);
9225   assert(_collector->overflow_list_is_empty() || res,
9226          "If list is not empty, we should have taken something");
9227   assert(!res || !_mark_stack->isEmpty(),
9228          "If we took something, it should now be on our stack");
9229   return res;
9230 }
9231 
9232 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
9233   size_t res = _sp->block_size_no_stall(addr, _collector);
9234   if (_sp->block_is_obj(addr)) {
9235     if (_live_bit_map->isMarked(addr)) {
9236       // It can't have been dead in a previous cycle
9237       guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
9238     } else {
9239       _dead_bit_map->mark(addr);      // mark the dead object
9240     }
9241   }
9242   // Could be 0, if the block size could not be computed without stalling.
9243   return res;
9244 }
9245 
9246 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() {
9247 
9248   switch (phase) {
9249     case CMSCollector::InitialMarking:
9250       initialize(true  /* fullGC */ ,
9251                  cause /* cause of the GC */,
9252                  true  /* recordGCBeginTime */,
9253                  true  /* recordPreGCUsage */,
9254                  false /* recordPeakUsage */,
9255                  false /* recordPostGCusage */,
9256                  true  /* recordAccumulatedGCTime */,
9257                  false /* recordGCEndTime */,
9258                  false /* countCollection */  );
9259       break;
9260 
9261     case CMSCollector::FinalMarking:
9262       initialize(true  /* fullGC */ ,
9263                  cause /* cause of the GC */,
9264                  false /* recordGCBeginTime */,
9265                  false /* recordPreGCUsage */,
9266                  false /* recordPeakUsage */,
9267                  false /* recordPostGCusage */,
9268                  true  /* recordAccumulatedGCTime */,
9269                  false /* recordGCEndTime */,
9270                  false /* countCollection */  );
9271       break;
9272 
9273     case CMSCollector::Sweeping:
9274       initialize(true  /* fullGC */ ,
9275                  cause /* cause of the GC */,
9276                  false /* recordGCBeginTime */,
9277                  false /* recordPreGCUsage */,
9278                  true  /* recordPeakUsage */,
9279                  true  /* recordPostGCusage */,
9280                  false /* recordAccumulatedGCTime */,
9281                  true  /* recordGCEndTime */,
9282                  true  /* countCollection */  );
9283       break;
9284 
9285     default:
9286       ShouldNotReachHere();
9287   }
9288 }
9289 
--- EOF ---