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 "memory/tenuredGeneration.hpp"
  52 #include "oops/oop.inline.hpp"
  53 #include "prims/jvmtiExport.hpp"
  54 #include "runtime/globals_extension.hpp"
  55 #include "runtime/handles.inline.hpp"
  56 #include "runtime/java.hpp"
  57 #include "runtime/vmThread.hpp"
  58 #include "services/memoryService.hpp"
  59 #include "services/runtimeService.hpp"
  60 
  61 // statics
  62 CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL;
  63 bool          CMSCollector::_full_gc_requested          = false;
  64 
  65 //////////////////////////////////////////////////////////////////
  66 // In support of CMS/VM thread synchronization
  67 //////////////////////////////////////////////////////////////////
  68 // We split use of the CGC_lock into 2 "levels".
  69 // The low-level locking is of the usual CGC_lock monitor. We introduce
  70 // a higher level "token" (hereafter "CMS token") built on top of the
  71 // low level monitor (hereafter "CGC lock").
  72 // The token-passing protocol gives priority to the VM thread. The
  73 // CMS-lock doesn't provide any fairness guarantees, but clients
  74 // should ensure that it is only held for very short, bounded
  75 // durations.
  76 //
  77 // When either of the CMS thread or the VM thread is involved in
  78 // collection operations during which it does not want the other
  79 // thread to interfere, it obtains the CMS token.
  80 //
  81 // If either thread tries to get the token while the other has
  82 // it, that thread waits. However, if the VM thread and CMS thread
  83 // both want the token, then the VM thread gets priority while the
  84 // CMS thread waits. This ensures, for instance, that the "concurrent"
  85 // phases of the CMS thread's work do not block out the VM thread
  86 // for long periods of time as the CMS thread continues to hog
  87 // the token. (See bug 4616232).
  88 //
  89 // The baton-passing functions are, however, controlled by the
  90 // flags _foregroundGCShouldWait and _foregroundGCIsActive,
  91 // and here the low-level CMS lock, not the high level token,
  92 // ensures mutual exclusion.
  93 //
  94 // Two important conditions that we have to satisfy:
  95 // 1. if a thread does a low-level wait on the CMS lock, then it
  96 //    relinquishes the CMS token if it were holding that token
  97 //    when it acquired the low-level CMS lock.
  98 // 2. any low-level notifications on the low-level lock
  99 //    should only be sent when a thread has relinquished the token.
 100 //
 101 // In the absence of either property, we'd have potential deadlock.
 102 //
 103 // We protect each of the CMS (concurrent and sequential) phases
 104 // with the CMS _token_, not the CMS _lock_.
 105 //
 106 // The only code protected by CMS lock is the token acquisition code
 107 // itself, see ConcurrentMarkSweepThread::[de]synchronize(), and the
 108 // baton-passing code.
 109 //
 110 // Unfortunately, i couldn't come up with a good abstraction to factor and
 111 // hide the naked CGC_lock manipulation in the baton-passing code
 112 // further below. That's something we should try to do. Also, the proof
 113 // of correctness of this 2-level locking scheme is far from obvious,
 114 // and potentially quite slippery. We have an uneasy supsicion, for instance,
 115 // that there may be a theoretical possibility of delay/starvation in the
 116 // low-level lock/wait/notify scheme used for the baton-passing because of
 117 // potential intereference with the priority scheme embodied in the
 118 // CMS-token-passing protocol. See related comments at a CGC_lock->wait()
 119 // invocation further below and marked with "XXX 20011219YSR".
 120 // Indeed, as we note elsewhere, this may become yet more slippery
 121 // in the presence of multiple CMS and/or multiple VM threads. XXX
 122 
 123 class CMSTokenSync: public StackObj {
 124  private:
 125   bool _is_cms_thread;
 126  public:
 127   CMSTokenSync(bool is_cms_thread):
 128     _is_cms_thread(is_cms_thread) {
 129     assert(is_cms_thread == Thread::current()->is_ConcurrentGC_thread(),
 130            "Incorrect argument to constructor");
 131     ConcurrentMarkSweepThread::synchronize(_is_cms_thread);
 132   }
 133 
 134   ~CMSTokenSync() {
 135     assert(_is_cms_thread ?
 136              ConcurrentMarkSweepThread::cms_thread_has_cms_token() :
 137              ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
 138           "Incorrect state");
 139     ConcurrentMarkSweepThread::desynchronize(_is_cms_thread);
 140   }
 141 };
 142 
 143 // Convenience class that does a CMSTokenSync, and then acquires
 144 // upto three locks.
 145 class CMSTokenSyncWithLocks: public CMSTokenSync {
 146  private:
 147   // Note: locks are acquired in textual declaration order
 148   // and released in the opposite order
 149   MutexLockerEx _locker1, _locker2, _locker3;
 150  public:
 151   CMSTokenSyncWithLocks(bool is_cms_thread, Mutex* mutex1,
 152                         Mutex* mutex2 = NULL, Mutex* mutex3 = NULL):
 153     CMSTokenSync(is_cms_thread),
 154     _locker1(mutex1, Mutex::_no_safepoint_check_flag),
 155     _locker2(mutex2, Mutex::_no_safepoint_check_flag),
 156     _locker3(mutex3, Mutex::_no_safepoint_check_flag)
 157   { }
 158 };
 159 
 160 
 161 // Wrapper class to temporarily disable icms during a foreground cms collection.
 162 class ICMSDisabler: public StackObj {
 163  public:
 164   // The ctor disables icms and wakes up the thread so it notices the change;
 165   // the dtor re-enables icms.  Note that the CMSCollector methods will check
 166   // CMSIncrementalMode.
 167   ICMSDisabler()  { CMSCollector::disable_icms(); CMSCollector::start_icms(); }
 168   ~ICMSDisabler() { CMSCollector::enable_icms(); }
 169 };
 170 
 171 //////////////////////////////////////////////////////////////////
 172 //  Concurrent Mark-Sweep Generation /////////////////////////////
 173 //////////////////////////////////////////////////////////////////
 174 
 175 NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;)
 176 
 177 // This struct contains per-thread things necessary to support parallel
 178 // young-gen collection.
 179 class CMSParGCThreadState: public CHeapObj<mtGC> {
 180  public:
 181   CFLS_LAB lab;
 182   PromotionInfo promo;
 183 
 184   // Constructor.
 185   CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) {
 186     promo.setSpace(cfls);
 187   }
 188 };
 189 
 190 ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration(
 191      ReservedSpace rs, size_t initial_byte_size, int level,
 192      CardTableRS* ct, bool use_adaptive_freelists,
 193      FreeBlockDictionary<FreeChunk>::DictionaryChoice dictionaryChoice) :
 194   CardGeneration(rs, initial_byte_size, level, ct),
 195   _dilatation_factor(((double)MinChunkSize)/((double)(CollectedHeap::min_fill_size()))),
 196   _debug_collection_type(Concurrent_collection_type),
 197   _did_compact(false)
 198 {
 199   HeapWord* bottom = (HeapWord*) _virtual_space.low();
 200   HeapWord* end    = (HeapWord*) _virtual_space.high();
 201 
 202   _direct_allocated_words = 0;
 203   NOT_PRODUCT(
 204     _numObjectsPromoted = 0;
 205     _numWordsPromoted = 0;
 206     _numObjectsAllocated = 0;
 207     _numWordsAllocated = 0;
 208   )
 209 
 210   _cmsSpace = new CompactibleFreeListSpace(_bts, MemRegion(bottom, end),
 211                                            use_adaptive_freelists,
 212                                            dictionaryChoice);
 213   NOT_PRODUCT(debug_cms_space = _cmsSpace;)
 214   if (_cmsSpace == NULL) {
 215     vm_exit_during_initialization(
 216       "CompactibleFreeListSpace allocation failure");
 217   }
 218   _cmsSpace->_gen = this;
 219 
 220   _gc_stats = new CMSGCStats();
 221 
 222   // Verify the assumption that FreeChunk::_prev and OopDesc::_klass
 223   // offsets match. The ability to tell free chunks from objects
 224   // depends on this property.
 225   debug_only(
 226     FreeChunk* junk = NULL;
 227     assert(UseCompressedKlassPointers ||
 228            junk->prev_addr() == (void*)(oop(junk)->klass_addr()),
 229            "Offset of FreeChunk::_prev within FreeChunk must match"
 230            "  that of OopDesc::_klass within OopDesc");
 231   )
 232   if (CollectedHeap::use_parallel_gc_threads()) {
 233     typedef CMSParGCThreadState* CMSParGCThreadStatePtr;
 234     _par_gc_thread_states =
 235       NEW_C_HEAP_ARRAY(CMSParGCThreadStatePtr, ParallelGCThreads, mtGC);
 236     if (_par_gc_thread_states == NULL) {
 237       vm_exit_during_initialization("Could not allocate par gc structs");
 238     }
 239     for (uint i = 0; i < ParallelGCThreads; i++) {
 240       _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace());
 241       if (_par_gc_thread_states[i] == NULL) {
 242         vm_exit_during_initialization("Could not allocate par gc structs");
 243       }
 244     }
 245   } else {
 246     _par_gc_thread_states = NULL;
 247   }
 248   _incremental_collection_failed = false;
 249   // The "dilatation_factor" is the expansion that can occur on
 250   // account of the fact that the minimum object size in the CMS
 251   // generation may be larger than that in, say, a contiguous young
 252   //  generation.
 253   // Ideally, in the calculation below, we'd compute the dilatation
 254   // factor as: MinChunkSize/(promoting_gen's min object size)
 255   // Since we do not have such a general query interface for the
 256   // promoting generation, we'll instead just use the mimimum
 257   // object size (which today is a header's worth of space);
 258   // note that all arithmetic is in units of HeapWords.
 259   assert(MinChunkSize >= CollectedHeap::min_fill_size(), "just checking");
 260   assert(_dilatation_factor >= 1.0, "from previous assert");
 261 }
 262 
 263 
 264 // The field "_initiating_occupancy" represents the occupancy percentage
 265 // at which we trigger a new collection cycle.  Unless explicitly specified
 266 // via CMSInitiatingOccupancyFraction (argument "io" below), it
 267 // is calculated by:
 268 //
 269 //   Let "f" be MinHeapFreeRatio in
 270 //
 271 //    _intiating_occupancy = 100-f +
 272 //                           f * (CMSTriggerRatio/100)
 273 //   where CMSTriggerRatio is the argument "tr" below.
 274 //
 275 // That is, if we assume the heap is at its desired maximum occupancy at the
 276 // end of a collection, we let CMSTriggerRatio of the (purported) free
 277 // space be allocated before initiating a new collection cycle.
 278 //
 279 void ConcurrentMarkSweepGeneration::init_initiating_occupancy(intx io, uintx tr) {
 280   assert(io <= 100 && tr <= 100, "Check the arguments");
 281   if (io >= 0) {
 282     _initiating_occupancy = (double)io / 100.0;
 283   } else {
 284     _initiating_occupancy = ((100 - MinHeapFreeRatio) +
 285                              (double)(tr * MinHeapFreeRatio) / 100.0)
 286                             / 100.0;
 287   }
 288 }
 289 
 290 void ConcurrentMarkSweepGeneration::ref_processor_init() {
 291   assert(collector() != NULL, "no collector");
 292   collector()->ref_processor_init();
 293 }
 294 
 295 void CMSCollector::ref_processor_init() {
 296   if (_ref_processor == NULL) {
 297     // Allocate and initialize a reference processor
 298     _ref_processor =
 299       new ReferenceProcessor(_span,                               // span
 300                              (ParallelGCThreads > 1) && ParallelRefProcEnabled, // mt processing
 301                              (int) ParallelGCThreads,             // mt processing degree
 302                              _cmsGen->refs_discovery_is_mt(),     // mt discovery
 303                              (int) MAX2(ConcGCThreads, ParallelGCThreads), // mt discovery degree
 304                              _cmsGen->refs_discovery_is_atomic(), // discovery is not atomic
 305                              &_is_alive_closure,                  // closure for liveness info
 306                              false);                              // next field updates do not need write barrier
 307     // Initialize the _ref_processor field of CMSGen
 308     _cmsGen->set_ref_processor(_ref_processor);
 309 
 310   }
 311 }
 312 
 313 CMSAdaptiveSizePolicy* CMSCollector::size_policy() {
 314   GenCollectedHeap* gch = GenCollectedHeap::heap();
 315   assert(gch->kind() == CollectedHeap::GenCollectedHeap,
 316     "Wrong type of heap");
 317   CMSAdaptiveSizePolicy* sp = (CMSAdaptiveSizePolicy*)
 318     gch->gen_policy()->size_policy();
 319   assert(sp->is_gc_cms_adaptive_size_policy(),
 320     "Wrong type of size policy");
 321   return sp;
 322 }
 323 
 324 CMSGCAdaptivePolicyCounters* CMSCollector::gc_adaptive_policy_counters() {
 325   CMSGCAdaptivePolicyCounters* results =
 326     (CMSGCAdaptivePolicyCounters*) collector_policy()->counters();
 327   assert(
 328     results->kind() == GCPolicyCounters::CMSGCAdaptivePolicyCountersKind,
 329     "Wrong gc policy counter kind");
 330   return results;
 331 }
 332 
 333 
 334 void ConcurrentMarkSweepGeneration::initialize_performance_counters() {
 335 
 336   const char* gen_name = "old";
 337 
 338   // Generation Counters - generation 1, 1 subspace
 339   _gen_counters = new GenerationCounters(gen_name, 1, 1, &_virtual_space);
 340 
 341   _space_counters = new GSpaceCounters(gen_name, 0,
 342                                        _virtual_space.reserved_size(),
 343                                        this, _gen_counters);
 344 }
 345 
 346 CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha):
 347   _cms_gen(cms_gen)
 348 {
 349   assert(alpha <= 100, "bad value");
 350   _saved_alpha = alpha;
 351 
 352   // Initialize the alphas to the bootstrap value of 100.
 353   _gc0_alpha = _cms_alpha = 100;
 354 
 355   _cms_begin_time.update();
 356   _cms_end_time.update();
 357 
 358   _gc0_duration = 0.0;
 359   _gc0_period = 0.0;
 360   _gc0_promoted = 0;
 361 
 362   _cms_duration = 0.0;
 363   _cms_period = 0.0;
 364   _cms_allocated = 0;
 365 
 366   _cms_used_at_gc0_begin = 0;
 367   _cms_used_at_gc0_end = 0;
 368   _allow_duty_cycle_reduction = false;
 369   _valid_bits = 0;
 370   _icms_duty_cycle = CMSIncrementalDutyCycle;
 371 }
 372 
 373 double CMSStats::cms_free_adjustment_factor(size_t free) const {
 374   // TBD: CR 6909490
 375   return 1.0;
 376 }
 377 
 378 void CMSStats::adjust_cms_free_adjustment_factor(bool fail, size_t free) {
 379 }
 380 
 381 // If promotion failure handling is on use
 382 // the padded average size of the promotion for each
 383 // young generation collection.
 384 double CMSStats::time_until_cms_gen_full() const {
 385   size_t cms_free = _cms_gen->cmsSpace()->free();
 386   GenCollectedHeap* gch = GenCollectedHeap::heap();
 387   size_t expected_promotion = MIN2(gch->get_gen(0)->capacity(),
 388                                    (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average());
 389   if (cms_free > expected_promotion) {
 390     // Start a cms collection if there isn't enough space to promote
 391     // for the next minor collection.  Use the padded average as
 392     // a safety factor.
 393     cms_free -= expected_promotion;
 394 
 395     // Adjust by the safety factor.
 396     double cms_free_dbl = (double)cms_free;
 397     double cms_adjustment = (100.0 - CMSIncrementalSafetyFactor)/100.0;
 398     // Apply a further correction factor which tries to adjust
 399     // for recent occurance of concurrent mode failures.
 400     cms_adjustment = cms_adjustment * cms_free_adjustment_factor(cms_free);
 401     cms_free_dbl = cms_free_dbl * cms_adjustment;
 402 
 403     if (PrintGCDetails && Verbose) {
 404       gclog_or_tty->print_cr("CMSStats::time_until_cms_gen_full: cms_free "
 405         SIZE_FORMAT " expected_promotion " SIZE_FORMAT,
 406         cms_free, expected_promotion);
 407       gclog_or_tty->print_cr("  cms_free_dbl %f cms_consumption_rate %f",
 408         cms_free_dbl, cms_consumption_rate() + 1.0);
 409     }
 410     // Add 1 in case the consumption rate goes to zero.
 411     return cms_free_dbl / (cms_consumption_rate() + 1.0);
 412   }
 413   return 0.0;
 414 }
 415 
 416 // Compare the duration of the cms collection to the
 417 // time remaining before the cms generation is empty.
 418 // Note that the time from the start of the cms collection
 419 // to the start of the cms sweep (less than the total
 420 // duration of the cms collection) can be used.  This
 421 // has been tried and some applications experienced
 422 // promotion failures early in execution.  This was
 423 // possibly because the averages were not accurate
 424 // enough at the beginning.
 425 double CMSStats::time_until_cms_start() const {
 426   // We add "gc0_period" to the "work" calculation
 427   // below because this query is done (mostly) at the
 428   // end of a scavenge, so we need to conservatively
 429   // account for that much possible delay
 430   // in the query so as to avoid concurrent mode failures
 431   // due to starting the collection just a wee bit too
 432   // late.
 433   double work = cms_duration() + gc0_period();
 434   double deadline = time_until_cms_gen_full();
 435   // If a concurrent mode failure occurred recently, we want to be
 436   // more conservative and halve our expected time_until_cms_gen_full()
 437   if (work > deadline) {
 438     if (Verbose && PrintGCDetails) {
 439       gclog_or_tty->print(
 440         " CMSCollector: collect because of anticipated promotion "
 441         "before full %3.7f + %3.7f > %3.7f ", cms_duration(),
 442         gc0_period(), time_until_cms_gen_full());
 443     }
 444     return 0.0;
 445   }
 446   return work - deadline;
 447 }
 448 
 449 // Return a duty cycle based on old_duty_cycle and new_duty_cycle, limiting the
 450 // amount of change to prevent wild oscillation.
 451 unsigned int CMSStats::icms_damped_duty_cycle(unsigned int old_duty_cycle,
 452                                               unsigned int new_duty_cycle) {
 453   assert(old_duty_cycle <= 100, "bad input value");
 454   assert(new_duty_cycle <= 100, "bad input value");
 455 
 456   // Note:  use subtraction with caution since it may underflow (values are
 457   // unsigned).  Addition is safe since we're in the range 0-100.
 458   unsigned int damped_duty_cycle = new_duty_cycle;
 459   if (new_duty_cycle < old_duty_cycle) {
 460     const unsigned int largest_delta = MAX2(old_duty_cycle / 4, 5U);
 461     if (new_duty_cycle + largest_delta < old_duty_cycle) {
 462       damped_duty_cycle = old_duty_cycle - largest_delta;
 463     }
 464   } else if (new_duty_cycle > old_duty_cycle) {
 465     const unsigned int largest_delta = MAX2(old_duty_cycle / 4, 15U);
 466     if (new_duty_cycle > old_duty_cycle + largest_delta) {
 467       damped_duty_cycle = MIN2(old_duty_cycle + largest_delta, 100U);
 468     }
 469   }
 470   assert(damped_duty_cycle <= 100, "invalid duty cycle computed");
 471 
 472   if (CMSTraceIncrementalPacing) {
 473     gclog_or_tty->print(" [icms_damped_duty_cycle(%d,%d) = %d] ",
 474                            old_duty_cycle, new_duty_cycle, damped_duty_cycle);
 475   }
 476   return damped_duty_cycle;
 477 }
 478 
 479 unsigned int CMSStats::icms_update_duty_cycle_impl() {
 480   assert(CMSIncrementalPacing && valid(),
 481          "should be handled in icms_update_duty_cycle()");
 482 
 483   double cms_time_so_far = cms_timer().seconds();
 484   double scaled_duration = cms_duration_per_mb() * _cms_used_at_gc0_end / M;
 485   double scaled_duration_remaining = fabsd(scaled_duration - cms_time_so_far);
 486 
 487   // Avoid division by 0.
 488   double time_until_full = MAX2(time_until_cms_gen_full(), 0.01);
 489   double duty_cycle_dbl = 100.0 * scaled_duration_remaining / time_until_full;
 490 
 491   unsigned int new_duty_cycle = MIN2((unsigned int)duty_cycle_dbl, 100U);
 492   if (new_duty_cycle > _icms_duty_cycle) {
 493     // Avoid very small duty cycles (1 or 2); 0 is allowed.
 494     if (new_duty_cycle > 2) {
 495       _icms_duty_cycle = icms_damped_duty_cycle(_icms_duty_cycle,
 496                                                 new_duty_cycle);
 497     }
 498   } else if (_allow_duty_cycle_reduction) {
 499     // The duty cycle is reduced only once per cms cycle (see record_cms_end()).
 500     new_duty_cycle = icms_damped_duty_cycle(_icms_duty_cycle, new_duty_cycle);
 501     // Respect the minimum duty cycle.
 502     unsigned int min_duty_cycle = (unsigned int)CMSIncrementalDutyCycleMin;
 503     _icms_duty_cycle = MAX2(new_duty_cycle, min_duty_cycle);
 504   }
 505 
 506   if (PrintGCDetails || CMSTraceIncrementalPacing) {
 507     gclog_or_tty->print(" icms_dc=%d ", _icms_duty_cycle);
 508   }
 509 
 510   _allow_duty_cycle_reduction = false;
 511   return _icms_duty_cycle;
 512 }
 513 
 514 #ifndef PRODUCT
 515 void CMSStats::print_on(outputStream *st) const {
 516   st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha);
 517   st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo=" SIZE_FORMAT,
 518                gc0_duration(), gc0_period(), gc0_promoted());
 519   st->print(",cms_dur=%g,cms_dur_per_mb=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT,
 520             cms_duration(), cms_duration_per_mb(),
 521             cms_period(), cms_allocated());
 522   st->print(",cms_since_beg=%g,cms_since_end=%g",
 523             cms_time_since_begin(), cms_time_since_end());
 524   st->print(",cms_used_beg=" SIZE_FORMAT ",cms_used_end=" SIZE_FORMAT,
 525             _cms_used_at_gc0_begin, _cms_used_at_gc0_end);
 526   if (CMSIncrementalMode) {
 527     st->print(",dc=%d", icms_duty_cycle());
 528   }
 529 
 530   if (valid()) {
 531     st->print(",promo_rate=%g,cms_alloc_rate=%g",
 532               promotion_rate(), cms_allocation_rate());
 533     st->print(",cms_consumption_rate=%g,time_until_full=%g",
 534               cms_consumption_rate(), time_until_cms_gen_full());
 535   }
 536   st->print(" ");
 537 }
 538 #endif // #ifndef PRODUCT
 539 
 540 CMSCollector::CollectorState CMSCollector::_collectorState =
 541                              CMSCollector::Idling;
 542 bool CMSCollector::_foregroundGCIsActive = false;
 543 bool CMSCollector::_foregroundGCShouldWait = false;
 544 
 545 CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
 546                            CardTableRS*                   ct,
 547                            ConcurrentMarkSweepPolicy*     cp):
 548   _cmsGen(cmsGen),
 549   _ct(ct),
 550   _ref_processor(NULL),    // will be set later
 551   _conc_workers(NULL),     // may be set later
 552   _abort_preclean(false),
 553   _start_sampling(false),
 554   _between_prologue_and_epilogue(false),
 555   _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"),
 556   _modUnionTable((CardTableModRefBS::card_shift - LogHeapWordSize),
 557                  -1 /* lock-free */, "No_lock" /* dummy */),
 558   _modUnionClosure(&_modUnionTable),
 559   _modUnionClosurePar(&_modUnionTable),
 560   // Adjust my span to cover old (cms) gen
 561   _span(cmsGen->reserved()),
 562   // Construct the is_alive_closure with _span & markBitMap
 563   _is_alive_closure(_span, &_markBitMap),
 564   _restart_addr(NULL),
 565   _overflow_list(NULL),
 566   _stats(cmsGen),
 567   _eden_chunk_array(NULL),     // may be set in ctor body
 568   _eden_chunk_capacity(0),     // -- ditto --
 569   _eden_chunk_index(0),        // -- ditto --
 570   _survivor_plab_array(NULL),  // -- ditto --
 571   _survivor_chunk_array(NULL), // -- ditto --
 572   _survivor_chunk_capacity(0), // -- ditto --
 573   _survivor_chunk_index(0),    // -- ditto --
 574   _ser_pmc_preclean_ovflw(0),
 575   _ser_kac_preclean_ovflw(0),
 576   _ser_pmc_remark_ovflw(0),
 577   _par_pmc_remark_ovflw(0),
 578   _ser_kac_ovflw(0),
 579   _par_kac_ovflw(0),
 580 #ifndef PRODUCT
 581   _num_par_pushes(0),
 582 #endif
 583   _collection_count_start(0),
 584   _verifying(false),
 585   _icms_start_limit(NULL),
 586   _icms_stop_limit(NULL),
 587   _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"),
 588   _completed_initialization(false),
 589   _collector_policy(cp),
 590   _should_unload_classes(false),
 591   _concurrent_cycles_since_last_unload(0),
 592   _roots_scanning_options(0),
 593   _inter_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
 594   _intra_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding)
 595 {
 596   if (ExplicitGCInvokesConcurrentAndUnloadsClasses) {
 597     ExplicitGCInvokesConcurrent = true;
 598   }
 599   // Now expand the span and allocate the collection support structures
 600   // (MUT, marking bit map etc.) to cover both generations subject to
 601   // collection.
 602 
 603   // For use by dirty card to oop closures.
 604   _cmsGen->cmsSpace()->set_collector(this);
 605 
 606   // Allocate MUT and marking bit map
 607   {
 608     MutexLockerEx x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag);
 609     if (!_markBitMap.allocate(_span)) {
 610       warning("Failed to allocate CMS Bit Map");
 611       return;
 612     }
 613     assert(_markBitMap.covers(_span), "_markBitMap inconsistency?");
 614   }
 615   {
 616     _modUnionTable.allocate(_span);
 617     assert(_modUnionTable.covers(_span), "_modUnionTable inconsistency?");
 618   }
 619 
 620   if (!_markStack.allocate(MarkStackSize)) {
 621     warning("Failed to allocate CMS Marking Stack");
 622     return;
 623   }
 624 
 625   // Support for multi-threaded concurrent phases
 626   if (CMSConcurrentMTEnabled) {
 627     if (FLAG_IS_DEFAULT(ConcGCThreads)) {
 628       // just for now
 629       FLAG_SET_DEFAULT(ConcGCThreads, (ParallelGCThreads + 3)/4);
 630     }
 631     if (ConcGCThreads > 1) {
 632       _conc_workers = new YieldingFlexibleWorkGang("Parallel CMS Threads",
 633                                  ConcGCThreads, true);
 634       if (_conc_workers == NULL) {
 635         warning("GC/CMS: _conc_workers allocation failure: "
 636               "forcing -CMSConcurrentMTEnabled");
 637         CMSConcurrentMTEnabled = false;
 638       } else {
 639         _conc_workers->initialize_workers();
 640       }
 641     } else {
 642       CMSConcurrentMTEnabled = false;
 643     }
 644   }
 645   if (!CMSConcurrentMTEnabled) {
 646     ConcGCThreads = 0;
 647   } else {
 648     // Turn off CMSCleanOnEnter optimization temporarily for
 649     // the MT case where it's not fixed yet; see 6178663.
 650     CMSCleanOnEnter = false;
 651   }
 652   assert((_conc_workers != NULL) == (ConcGCThreads > 1),
 653          "Inconsistency");
 654 
 655   // Parallel task queues; these are shared for the
 656   // concurrent and stop-world phases of CMS, but
 657   // are not shared with parallel scavenge (ParNew).
 658   {
 659     uint i;
 660     uint num_queues = (uint) MAX2(ParallelGCThreads, ConcGCThreads);
 661 
 662     if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled
 663          || ParallelRefProcEnabled)
 664         && num_queues > 0) {
 665       _task_queues = new OopTaskQueueSet(num_queues);
 666       if (_task_queues == NULL) {
 667         warning("task_queues allocation failure.");
 668         return;
 669       }
 670       _hash_seed = NEW_C_HEAP_ARRAY(int, num_queues, mtGC);
 671       if (_hash_seed == NULL) {
 672         warning("_hash_seed array allocation failure");
 673         return;
 674       }
 675 
 676       typedef Padded<OopTaskQueue> PaddedOopTaskQueue;
 677       for (i = 0; i < num_queues; i++) {
 678         PaddedOopTaskQueue *q = new PaddedOopTaskQueue();
 679         if (q == NULL) {
 680           warning("work_queue allocation failure.");
 681           return;
 682         }
 683         _task_queues->register_queue(i, q);
 684       }
 685       for (i = 0; i < num_queues; i++) {
 686         _task_queues->queue(i)->initialize();
 687         _hash_seed[i] = 17;  // copied from ParNew
 688       }
 689     }
 690   }
 691 
 692   _cmsGen ->init_initiating_occupancy(CMSInitiatingOccupancyFraction, CMSTriggerRatio);
 693 
 694   // Clip CMSBootstrapOccupancy between 0 and 100.
 695   _bootstrap_occupancy = ((double)CMSBootstrapOccupancy)/(double)100;
 696 
 697   _full_gcs_since_conc_gc = 0;
 698 
 699   // Now tell CMS generations the identity of their collector
 700   ConcurrentMarkSweepGeneration::set_collector(this);
 701 
 702   // Create & start a CMS thread for this CMS collector
 703   _cmsThread = ConcurrentMarkSweepThread::start(this);
 704   assert(cmsThread() != NULL, "CMS Thread should have been created");
 705   assert(cmsThread()->collector() == this,
 706          "CMS Thread should refer to this gen");
 707   assert(CGC_lock != NULL, "Where's the CGC_lock?");
 708 
 709   // Support for parallelizing young gen rescan
 710   GenCollectedHeap* gch = GenCollectedHeap::heap();
 711   _young_gen = gch->prev_gen(_cmsGen);
 712   if (gch->supports_inline_contig_alloc()) {
 713     _top_addr = gch->top_addr();
 714     _end_addr = gch->end_addr();
 715     assert(_young_gen != NULL, "no _young_gen");
 716     _eden_chunk_index = 0;
 717     _eden_chunk_capacity = (_young_gen->max_capacity()+CMSSamplingGrain)/CMSSamplingGrain;
 718     _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity, mtGC);
 719     if (_eden_chunk_array == NULL) {
 720       _eden_chunk_capacity = 0;
 721       warning("GC/CMS: _eden_chunk_array allocation failure");
 722     }
 723   }
 724   assert(_eden_chunk_array != NULL || _eden_chunk_capacity == 0, "Error");
 725 
 726   // Support for parallelizing survivor space rescan
 727   if (CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) {
 728     const size_t max_plab_samples =
 729       ((DefNewGeneration*)_young_gen)->max_survivor_size()/MinTLABSize;
 730 
 731     _survivor_plab_array  = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads, mtGC);
 732     _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, 2*max_plab_samples, mtGC);
 733     _cursor               = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads, mtGC);
 734     if (_survivor_plab_array == NULL || _survivor_chunk_array == NULL
 735         || _cursor == NULL) {
 736       warning("Failed to allocate survivor plab/chunk array");
 737       if (_survivor_plab_array  != NULL) {
 738         FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array, mtGC);
 739         _survivor_plab_array = NULL;
 740       }
 741       if (_survivor_chunk_array != NULL) {
 742         FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array, mtGC);
 743         _survivor_chunk_array = NULL;
 744       }
 745       if (_cursor != NULL) {
 746         FREE_C_HEAP_ARRAY(size_t, _cursor, mtGC);
 747         _cursor = NULL;
 748       }
 749     } else {
 750       _survivor_chunk_capacity = 2*max_plab_samples;
 751       for (uint i = 0; i < ParallelGCThreads; i++) {
 752         HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
 753         if (vec == NULL) {
 754           warning("Failed to allocate survivor plab array");
 755           for (int j = i; j > 0; j--) {
 756             FREE_C_HEAP_ARRAY(HeapWord*, _survivor_plab_array[j-1].array(), mtGC);
 757           }
 758           FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array, mtGC);
 759           FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array, mtGC);
 760           _survivor_plab_array = NULL;
 761           _survivor_chunk_array = NULL;
 762           _survivor_chunk_capacity = 0;
 763           break;
 764         } else {
 765           ChunkArray* cur =
 766             ::new (&_survivor_plab_array[i]) ChunkArray(vec,
 767                                                         max_plab_samples);
 768           assert(cur->end() == 0, "Should be 0");
 769           assert(cur->array() == vec, "Should be vec");
 770           assert(cur->capacity() == max_plab_samples, "Error");
 771         }
 772       }
 773     }
 774   }
 775   assert(   (   _survivor_plab_array  != NULL
 776              && _survivor_chunk_array != NULL)
 777          || (   _survivor_chunk_capacity == 0
 778              && _survivor_chunk_index == 0),
 779          "Error");
 780 
 781   // Choose what strong roots should be scanned depending on verification options
 782   if (!CMSClassUnloadingEnabled) {
 783     // If class unloading is disabled we want to include all classes into the root set.
 784     add_root_scanning_option(SharedHeap::SO_AllClasses);
 785   } else {
 786     add_root_scanning_option(SharedHeap::SO_SystemClasses);
 787   }
 788 
 789   NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;)
 790   _gc_counters = new CollectorCounters("CMS", 1);
 791   _completed_initialization = true;
 792   _inter_sweep_timer.start();  // start of time
 793 }
 794 
 795 const char* ConcurrentMarkSweepGeneration::name() const {
 796   return "concurrent mark-sweep generation";
 797 }
 798 void ConcurrentMarkSweepGeneration::update_counters() {
 799   if (UsePerfData) {
 800     _space_counters->update_all();
 801     _gen_counters->update_all();
 802   }
 803 }
 804 
 805 // this is an optimized version of update_counters(). it takes the
 806 // used value as a parameter rather than computing it.
 807 //
 808 void ConcurrentMarkSweepGeneration::update_counters(size_t used) {
 809   if (UsePerfData) {
 810     _space_counters->update_used(used);
 811     _space_counters->update_capacity();
 812     _gen_counters->update_all();
 813   }
 814 }
 815 
 816 void ConcurrentMarkSweepGeneration::print() const {
 817   Generation::print();
 818   cmsSpace()->print();
 819 }
 820 
 821 #ifndef PRODUCT
 822 void ConcurrentMarkSweepGeneration::print_statistics() {
 823   cmsSpace()->printFLCensus(0);
 824 }
 825 #endif
 826 
 827 void ConcurrentMarkSweepGeneration::printOccupancy(const char *s) {
 828   GenCollectedHeap* gch = GenCollectedHeap::heap();
 829   if (PrintGCDetails) {
 830     if (Verbose) {
 831       gclog_or_tty->print("[%d %s-%s: "SIZE_FORMAT"("SIZE_FORMAT")]",
 832         level(), short_name(), s, used(), capacity());
 833     } else {
 834       gclog_or_tty->print("[%d %s-%s: "SIZE_FORMAT"K("SIZE_FORMAT"K)]",
 835         level(), short_name(), s, used() / K, capacity() / K);
 836     }
 837   }
 838   if (Verbose) {
 839     gclog_or_tty->print(" "SIZE_FORMAT"("SIZE_FORMAT")",
 840               gch->used(), gch->capacity());
 841   } else {
 842     gclog_or_tty->print(" "SIZE_FORMAT"K("SIZE_FORMAT"K)",
 843               gch->used() / K, gch->capacity() / K);
 844   }
 845 }
 846 
 847 size_t
 848 ConcurrentMarkSweepGeneration::contiguous_available() const {
 849   // dld proposes an improvement in precision here. If the committed
 850   // part of the space ends in a free block we should add that to
 851   // uncommitted size in the calculation below. Will make this
 852   // change later, staying with the approximation below for the
 853   // time being. -- ysr.
 854   return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc());
 855 }
 856 
 857 size_t
 858 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const {
 859   return _cmsSpace->max_alloc_in_words() * HeapWordSize;
 860 }
 861 
 862 size_t ConcurrentMarkSweepGeneration::max_available() const {
 863   return free() + _virtual_space.uncommitted_size();
 864 }
 865 
 866 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(size_t max_promotion_in_bytes) const {
 867   size_t available = max_available();
 868   size_t av_promo  = (size_t)gc_stats()->avg_promoted()->padded_average();
 869   bool   res = (available >= av_promo) || (available >= max_promotion_in_bytes);
 870   if (Verbose && PrintGCDetails) {
 871     gclog_or_tty->print_cr(
 872       "CMS: promo attempt is%s safe: available("SIZE_FORMAT") %s av_promo("SIZE_FORMAT"),"
 873       "max_promo("SIZE_FORMAT")",
 874       res? "":" not", available, res? ">=":"<",
 875       av_promo, max_promotion_in_bytes);
 876   }
 877   return res;
 878 }
 879 
 880 // At a promotion failure dump information on block layout in heap
 881 // (cms old generation).
 882 void ConcurrentMarkSweepGeneration::promotion_failure_occurred() {
 883   if (CMSDumpAtPromotionFailure) {
 884     cmsSpace()->dump_at_safepoint_with_locks(collector(), gclog_or_tty);
 885   }
 886 }
 887 
 888 CompactibleSpace*
 889 ConcurrentMarkSweepGeneration::first_compaction_space() const {
 890   return _cmsSpace;
 891 }
 892 
 893 void ConcurrentMarkSweepGeneration::reset_after_compaction() {
 894   // Clear the promotion information.  These pointers can be adjusted
 895   // along with all the other pointers into the heap but
 896   // compaction is expected to be a rare event with
 897   // a heap using cms so don't do it without seeing the need.
 898   if (CollectedHeap::use_parallel_gc_threads()) {
 899     for (uint i = 0; i < ParallelGCThreads; i++) {
 900       _par_gc_thread_states[i]->promo.reset();
 901     }
 902   }
 903 }
 904 
 905 void ConcurrentMarkSweepGeneration::space_iterate(SpaceClosure* blk, bool usedOnly) {
 906   blk->do_space(_cmsSpace);
 907 }
 908 
 909 void ConcurrentMarkSweepGeneration::compute_new_size() {
 910   assert_locked_or_safepoint(Heap_lock);
 911 
 912   // If incremental collection failed, we just want to expand
 913   // to the limit.
 914   if (incremental_collection_failed()) {
 915     clear_incremental_collection_failed();
 916     grow_to_reserved();
 917     return;
 918   }
 919 
 920   // The heap has been compacted but not reset yet.
 921   // Any metric such as free() or used() will be incorrect.
 922 
 923   CardGeneration::compute_new_size();
 924 
 925   // Reset again after a possible resizing
 926   if (did_compact()) {
 927     cmsSpace()->reset_after_compaction();
 928   }
 929 }
 930 
 931 void ConcurrentMarkSweepGeneration::compute_new_size_free_list() {
 932   assert_locked_or_safepoint(Heap_lock);
 933 
 934   // If incremental collection failed, we just want to expand
 935   // to the limit.
 936   if (incremental_collection_failed()) {
 937     clear_incremental_collection_failed();
 938     grow_to_reserved();
 939     return;
 940   }
 941 
 942   double free_percentage = ((double) free()) / capacity();
 943   double desired_free_percentage = (double) MinHeapFreeRatio / 100;
 944   double maximum_free_percentage = (double) MaxHeapFreeRatio / 100;
 945 
 946   // compute expansion delta needed for reaching desired free percentage
 947   if (free_percentage < desired_free_percentage) {
 948     size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
 949     assert(desired_capacity >= capacity(), "invalid expansion size");
 950     size_t expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes);
 951     if (PrintGCDetails && Verbose) {
 952       size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
 953       gclog_or_tty->print_cr("\nFrom compute_new_size: ");
 954       gclog_or_tty->print_cr("  Free fraction %f", free_percentage);
 955       gclog_or_tty->print_cr("  Desired free fraction %f",
 956         desired_free_percentage);
 957       gclog_or_tty->print_cr("  Maximum free fraction %f",
 958         maximum_free_percentage);
 959       gclog_or_tty->print_cr("  Capactiy "SIZE_FORMAT, capacity()/1000);
 960       gclog_or_tty->print_cr("  Desired capacity "SIZE_FORMAT,
 961         desired_capacity/1000);
 962       int prev_level = level() - 1;
 963       if (prev_level >= 0) {
 964         size_t prev_size = 0;
 965         GenCollectedHeap* gch = GenCollectedHeap::heap();
 966         Generation* prev_gen = gch->_gens[prev_level];
 967         prev_size = prev_gen->capacity();
 968           gclog_or_tty->print_cr("  Younger gen size "SIZE_FORMAT,
 969                                  prev_size/1000);
 970       }
 971       gclog_or_tty->print_cr("  unsafe_max_alloc_nogc "SIZE_FORMAT,
 972         unsafe_max_alloc_nogc()/1000);
 973       gclog_or_tty->print_cr("  contiguous available "SIZE_FORMAT,
 974         contiguous_available()/1000);
 975       gclog_or_tty->print_cr("  Expand by "SIZE_FORMAT" (bytes)",
 976         expand_bytes);
 977     }
 978     // safe if expansion fails
 979     expand(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio);
 980     if (PrintGCDetails && Verbose) {
 981       gclog_or_tty->print_cr("  Expanded free fraction %f",
 982         ((double) free()) / capacity());
 983     }
 984   } else {
 985     size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
 986     assert(desired_capacity <= capacity(), "invalid expansion size");
 987     size_t shrink_bytes = capacity() - desired_capacity;
 988     // Don't shrink unless the delta is greater than the minimum shrink we want
 989     if (shrink_bytes >= MinHeapDeltaBytes) {
 990       shrink_free_list_by(shrink_bytes);
 991     }
 992   }
 993 }
 994 
 995 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const {
 996   return cmsSpace()->freelistLock();
 997 }
 998 
 999 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size,
1000                                                   bool   tlab) {
1001   CMSSynchronousYieldRequest yr;
1002   MutexLockerEx x(freelistLock(),
1003                   Mutex::_no_safepoint_check_flag);
1004   return have_lock_and_allocate(size, tlab);
1005 }
1006 
1007 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size,
1008                                                   bool   tlab /* ignored */) {
1009   assert_lock_strong(freelistLock());
1010   size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size);
1011   HeapWord* res = cmsSpace()->allocate(adjustedSize);
1012   // Allocate the object live (grey) if the background collector has
1013   // started marking. This is necessary because the marker may
1014   // have passed this address and consequently this object will
1015   // not otherwise be greyed and would be incorrectly swept up.
1016   // Note that if this object contains references, the writing
1017   // of those references will dirty the card containing this object
1018   // allowing the object to be blackened (and its references scanned)
1019   // either during a preclean phase or at the final checkpoint.
1020   if (res != NULL) {
1021     // We may block here with an uninitialized object with
1022     // its mark-bit or P-bits not yet set. Such objects need
1023     // to be safely navigable by block_start().
1024     assert(oop(res)->klass_or_null() == NULL, "Object should be uninitialized here.");
1025     assert(!((FreeChunk*)res)->is_free(), "Error, block will look free but show wrong size");
1026     collector()->direct_allocated(res, adjustedSize);
1027     _direct_allocated_words += adjustedSize;
1028     // allocation counters
1029     NOT_PRODUCT(
1030       _numObjectsAllocated++;
1031       _numWordsAllocated += (int)adjustedSize;
1032     )
1033   }
1034   return res;
1035 }
1036 
1037 // In the case of direct allocation by mutators in a generation that
1038 // is being concurrently collected, the object must be allocated
1039 // live (grey) if the background collector has started marking.
1040 // This is necessary because the marker may
1041 // have passed this address and consequently this object will
1042 // not otherwise be greyed and would be incorrectly swept up.
1043 // Note that if this object contains references, the writing
1044 // of those references will dirty the card containing this object
1045 // allowing the object to be blackened (and its references scanned)
1046 // either during a preclean phase or at the final checkpoint.
1047 void CMSCollector::direct_allocated(HeapWord* start, size_t size) {
1048   assert(_markBitMap.covers(start, size), "Out of bounds");
1049   if (_collectorState >= Marking) {
1050     MutexLockerEx y(_markBitMap.lock(),
1051                     Mutex::_no_safepoint_check_flag);
1052     // [see comments preceding SweepClosure::do_blk() below for details]
1053     //
1054     // Can the P-bits be deleted now?  JJJ
1055     //
1056     // 1. need to mark the object as live so it isn't collected
1057     // 2. need to mark the 2nd bit to indicate the object may be uninitialized
1058     // 3. need to mark the end of the object so marking, precleaning or sweeping
1059     //    can skip over uninitialized or unparsable objects. An allocated
1060     //    object is considered uninitialized for our purposes as long as
1061     //    its klass word is NULL.  All old gen objects are parsable
1062     //    as soon as they are initialized.)
1063     _markBitMap.mark(start);          // object is live
1064     _markBitMap.mark(start + 1);      // object is potentially uninitialized?
1065     _markBitMap.mark(start + size - 1);
1066                                       // mark end of object
1067   }
1068   // check that oop looks uninitialized
1069   assert(oop(start)->klass_or_null() == NULL, "_klass should be NULL");
1070 }
1071 
1072 void CMSCollector::promoted(bool par, HeapWord* start,
1073                             bool is_obj_array, size_t obj_size) {
1074   assert(_markBitMap.covers(start), "Out of bounds");
1075   // See comment in direct_allocated() about when objects should
1076   // be allocated live.
1077   if (_collectorState >= Marking) {
1078     // we already hold the marking bit map lock, taken in
1079     // the prologue
1080     if (par) {
1081       _markBitMap.par_mark(start);
1082     } else {
1083       _markBitMap.mark(start);
1084     }
1085     // We don't need to mark the object as uninitialized (as
1086     // in direct_allocated above) because this is being done with the
1087     // world stopped and the object will be initialized by the
1088     // time the marking, precleaning or sweeping get to look at it.
1089     // But see the code for copying objects into the CMS generation,
1090     // where we need to ensure that concurrent readers of the
1091     // block offset table are able to safely navigate a block that
1092     // is in flux from being free to being allocated (and in
1093     // transition while being copied into) and subsequently
1094     // becoming a bona-fide object when the copy/promotion is complete.
1095     assert(SafepointSynchronize::is_at_safepoint(),
1096            "expect promotion only at safepoints");
1097 
1098     if (_collectorState < Sweeping) {
1099       // Mark the appropriate cards in the modUnionTable, so that
1100       // this object gets scanned before the sweep. If this is
1101       // not done, CMS generation references in the object might
1102       // not get marked.
1103       // For the case of arrays, which are otherwise precisely
1104       // marked, we need to dirty the entire array, not just its head.
1105       if (is_obj_array) {
1106         // The [par_]mark_range() method expects mr.end() below to
1107         // be aligned to the granularity of a bit's representation
1108         // in the heap. In the case of the MUT below, that's a
1109         // card size.
1110         MemRegion mr(start,
1111                      (HeapWord*)round_to((intptr_t)(start + obj_size),
1112                         CardTableModRefBS::card_size /* bytes */));
1113         if (par) {
1114           _modUnionTable.par_mark_range(mr);
1115         } else {
1116           _modUnionTable.mark_range(mr);
1117         }
1118       } else {  // not an obj array; we can just mark the head
1119         if (par) {
1120           _modUnionTable.par_mark(start);
1121         } else {
1122           _modUnionTable.mark(start);
1123         }
1124       }
1125     }
1126   }
1127 }
1128 
1129 static inline size_t percent_of_space(Space* space, HeapWord* addr)
1130 {
1131   size_t delta = pointer_delta(addr, space->bottom());
1132   return (size_t)(delta * 100.0 / (space->capacity() / HeapWordSize));
1133 }
1134 
1135 void CMSCollector::icms_update_allocation_limits()
1136 {
1137   Generation* gen0 = GenCollectedHeap::heap()->get_gen(0);
1138   EdenSpace* eden = gen0->as_DefNewGeneration()->eden();
1139 
1140   const unsigned int duty_cycle = stats().icms_update_duty_cycle();
1141   if (CMSTraceIncrementalPacing) {
1142     stats().print();
1143   }
1144 
1145   assert(duty_cycle <= 100, "invalid duty cycle");
1146   if (duty_cycle != 0) {
1147     // The duty_cycle is a percentage between 0 and 100; convert to words and
1148     // then compute the offset from the endpoints of the space.
1149     size_t free_words = eden->free() / HeapWordSize;
1150     double free_words_dbl = (double)free_words;
1151     size_t duty_cycle_words = (size_t)(free_words_dbl * duty_cycle / 100.0);
1152     size_t offset_words = (free_words - duty_cycle_words) / 2;
1153 
1154     _icms_start_limit = eden->top() + offset_words;
1155     _icms_stop_limit = eden->end() - offset_words;
1156 
1157     // The limits may be adjusted (shifted to the right) by
1158     // CMSIncrementalOffset, to allow the application more mutator time after a
1159     // young gen gc (when all mutators were stopped) and before CMS starts and
1160     // takes away one or more cpus.
1161     if (CMSIncrementalOffset != 0) {
1162       double adjustment_dbl = free_words_dbl * CMSIncrementalOffset / 100.0;
1163       size_t adjustment = (size_t)adjustment_dbl;
1164       HeapWord* tmp_stop = _icms_stop_limit + adjustment;
1165       if (tmp_stop > _icms_stop_limit && tmp_stop < eden->end()) {
1166         _icms_start_limit += adjustment;
1167         _icms_stop_limit = tmp_stop;
1168       }
1169     }
1170   }
1171   if (duty_cycle == 0 || (_icms_start_limit == _icms_stop_limit)) {
1172     _icms_start_limit = _icms_stop_limit = eden->end();
1173   }
1174 
1175   // Install the new start limit.
1176   eden->set_soft_end(_icms_start_limit);
1177 
1178   if (CMSTraceIncrementalMode) {
1179     gclog_or_tty->print(" icms alloc limits:  "
1180                            PTR_FORMAT "," PTR_FORMAT
1181                            " (" SIZE_FORMAT "%%," SIZE_FORMAT "%%) ",
1182                            _icms_start_limit, _icms_stop_limit,
1183                            percent_of_space(eden, _icms_start_limit),
1184                            percent_of_space(eden, _icms_stop_limit));
1185     if (Verbose) {
1186       gclog_or_tty->print("eden:  ");
1187       eden->print_on(gclog_or_tty);
1188     }
1189   }
1190 }
1191 
1192 // Any changes here should try to maintain the invariant
1193 // that if this method is called with _icms_start_limit
1194 // and _icms_stop_limit both NULL, then it should return NULL
1195 // and not notify the icms thread.
1196 HeapWord*
1197 CMSCollector::allocation_limit_reached(Space* space, HeapWord* top,
1198                                        size_t word_size)
1199 {
1200   // A start_limit equal to end() means the duty cycle is 0, so treat that as a
1201   // nop.
1202   if (CMSIncrementalMode && _icms_start_limit != space->end()) {
1203     if (top <= _icms_start_limit) {
1204       if (CMSTraceIncrementalMode) {
1205         space->print_on(gclog_or_tty);
1206         gclog_or_tty->stamp();
1207         gclog_or_tty->print_cr(" start limit top=" PTR_FORMAT
1208                                ", new limit=" PTR_FORMAT
1209                                " (" SIZE_FORMAT "%%)",
1210                                top, _icms_stop_limit,
1211                                percent_of_space(space, _icms_stop_limit));
1212       }
1213       ConcurrentMarkSweepThread::start_icms();
1214       assert(top < _icms_stop_limit, "Tautology");
1215       if (word_size < pointer_delta(_icms_stop_limit, top)) {
1216         return _icms_stop_limit;
1217       }
1218 
1219       // The allocation will cross both the _start and _stop limits, so do the
1220       // stop notification also and return end().
1221       if (CMSTraceIncrementalMode) {
1222         space->print_on(gclog_or_tty);
1223         gclog_or_tty->stamp();
1224         gclog_or_tty->print_cr(" +stop limit top=" PTR_FORMAT
1225                                ", new limit=" PTR_FORMAT
1226                                " (" SIZE_FORMAT "%%)",
1227                                top, space->end(),
1228                                percent_of_space(space, space->end()));
1229       }
1230       ConcurrentMarkSweepThread::stop_icms();
1231       return space->end();
1232     }
1233 
1234     if (top <= _icms_stop_limit) {
1235       if (CMSTraceIncrementalMode) {
1236         space->print_on(gclog_or_tty);
1237         gclog_or_tty->stamp();
1238         gclog_or_tty->print_cr(" stop limit top=" PTR_FORMAT
1239                                ", new limit=" PTR_FORMAT
1240                                " (" SIZE_FORMAT "%%)",
1241                                top, space->end(),
1242                                percent_of_space(space, space->end()));
1243       }
1244       ConcurrentMarkSweepThread::stop_icms();
1245       return space->end();
1246     }
1247 
1248     if (CMSTraceIncrementalMode) {
1249       space->print_on(gclog_or_tty);
1250       gclog_or_tty->stamp();
1251       gclog_or_tty->print_cr(" end limit top=" PTR_FORMAT
1252                              ", new limit=" PTR_FORMAT,
1253                              top, NULL);
1254     }
1255   }
1256 
1257   return NULL;
1258 }
1259 
1260 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size) {
1261   assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
1262   // allocate, copy and if necessary update promoinfo --
1263   // delegate to underlying space.
1264   assert_lock_strong(freelistLock());
1265 
1266 #ifndef PRODUCT
1267   if (Universe::heap()->promotion_should_fail()) {
1268     return NULL;
1269   }
1270 #endif  // #ifndef PRODUCT
1271 
1272   oop res = _cmsSpace->promote(obj, obj_size);
1273   if (res == NULL) {
1274     // expand and retry
1275     size_t s = _cmsSpace->expansionSpaceRequired(obj_size);  // HeapWords
1276     expand(s*HeapWordSize, MinHeapDeltaBytes,
1277       CMSExpansionCause::_satisfy_promotion);
1278     // Since there's currently no next generation, we don't try to promote
1279     // into a more senior generation.
1280     assert(next_gen() == NULL, "assumption, based upon which no attempt "
1281                                "is made to pass on a possibly failing "
1282                                "promotion to next generation");
1283     res = _cmsSpace->promote(obj, obj_size);
1284   }
1285   if (res != NULL) {
1286     // See comment in allocate() about when objects should
1287     // be allocated live.
1288     assert(obj->is_oop(), "Will dereference klass pointer below");
1289     collector()->promoted(false,           // Not parallel
1290                           (HeapWord*)res, obj->is_objArray(), obj_size);
1291     // promotion counters
1292     NOT_PRODUCT(
1293       _numObjectsPromoted++;
1294       _numWordsPromoted +=
1295         (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size()));
1296     )
1297   }
1298   return res;
1299 }
1300 
1301 
1302 HeapWord*
1303 ConcurrentMarkSweepGeneration::allocation_limit_reached(Space* space,
1304                                              HeapWord* top,
1305                                              size_t word_sz)
1306 {
1307   return collector()->allocation_limit_reached(space, top, word_sz);
1308 }
1309 
1310 // IMPORTANT: Notes on object size recognition in CMS.
1311 // ---------------------------------------------------
1312 // A block of storage in the CMS generation is always in
1313 // one of three states. A free block (FREE), an allocated
1314 // object (OBJECT) whose size() method reports the correct size,
1315 // and an intermediate state (TRANSIENT) in which its size cannot
1316 // be accurately determined.
1317 // STATE IDENTIFICATION:   (32 bit and 64 bit w/o COOPS)
1318 // -----------------------------------------------------
1319 // FREE:      klass_word & 1 == 1; mark_word holds block size
1320 //
1321 // OBJECT:    klass_word installed; klass_word != 0 && klass_word & 1 == 0;
1322 //            obj->size() computes correct size
1323 //
1324 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1325 //
1326 // STATE IDENTIFICATION: (64 bit+COOPS)
1327 // ------------------------------------
1328 // FREE:      mark_word & CMS_FREE_BIT == 1; mark_word & ~CMS_FREE_BIT gives block_size
1329 //
1330 // OBJECT:    klass_word installed; klass_word != 0;
1331 //            obj->size() computes correct size
1332 //
1333 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1334 //
1335 //
1336 // STATE TRANSITION DIAGRAM
1337 //
1338 //        mut / parnew                     mut  /  parnew
1339 // FREE --------------------> TRANSIENT ---------------------> OBJECT --|
1340 //  ^                                                                   |
1341 //  |------------------------ DEAD <------------------------------------|
1342 //         sweep                            mut
1343 //
1344 // While a block is in TRANSIENT state its size cannot be determined
1345 // so readers will either need to come back later or stall until
1346 // the size can be determined. Note that for the case of direct
1347 // allocation, P-bits, when available, may be used to determine the
1348 // size of an object that may not yet have been initialized.
1349 
1350 // Things to support parallel young-gen collection.
1351 oop
1352 ConcurrentMarkSweepGeneration::par_promote(int thread_num,
1353                                            oop old, markOop m,
1354                                            size_t word_sz) {
1355 #ifndef PRODUCT
1356   if (Universe::heap()->promotion_should_fail()) {
1357     return NULL;
1358   }
1359 #endif  // #ifndef PRODUCT
1360 
1361   CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1362   PromotionInfo* promoInfo = &ps->promo;
1363   // if we are tracking promotions, then first ensure space for
1364   // promotion (including spooling space for saving header if necessary).
1365   // then allocate and copy, then track promoted info if needed.
1366   // When tracking (see PromotionInfo::track()), the mark word may
1367   // be displaced and in this case restoration of the mark word
1368   // occurs in the (oop_since_save_marks_)iterate phase.
1369   if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) {
1370     // Out of space for allocating spooling buffers;
1371     // try expanding and allocating spooling buffers.
1372     if (!expand_and_ensure_spooling_space(promoInfo)) {
1373       return NULL;
1374     }
1375   }
1376   assert(promoInfo->has_spooling_space(), "Control point invariant");
1377   const size_t alloc_sz = CompactibleFreeListSpace::adjustObjectSize(word_sz);
1378   HeapWord* obj_ptr = ps->lab.alloc(alloc_sz);
1379   if (obj_ptr == NULL) {
1380      obj_ptr = expand_and_par_lab_allocate(ps, alloc_sz);
1381      if (obj_ptr == NULL) {
1382        return NULL;
1383      }
1384   }
1385   oop obj = oop(obj_ptr);
1386   OrderAccess::storestore();
1387   assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1388   assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1389   // IMPORTANT: See note on object initialization for CMS above.
1390   // Otherwise, copy the object.  Here we must be careful to insert the
1391   // klass pointer last, since this marks the block as an allocated object.
1392   // Except with compressed oops it's the mark word.
1393   HeapWord* old_ptr = (HeapWord*)old;
1394   // Restore the mark word copied above.
1395   obj->set_mark(m);
1396   assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1397   assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1398   OrderAccess::storestore();
1399 
1400   if (UseCompressedKlassPointers) {
1401     // Copy gap missed by (aligned) header size calculation below
1402     obj->set_klass_gap(old->klass_gap());
1403   }
1404   if (word_sz > (size_t)oopDesc::header_size()) {
1405     Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1406                                  obj_ptr + oopDesc::header_size(),
1407                                  word_sz - oopDesc::header_size());
1408   }
1409 
1410   // Now we can track the promoted object, if necessary.  We take care
1411   // to delay the transition from uninitialized to full object
1412   // (i.e., insertion of klass pointer) until after, so that it
1413   // atomically becomes a promoted object.
1414   if (promoInfo->tracking()) {
1415     promoInfo->track((PromotedObject*)obj, old->klass());
1416   }
1417   assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1418   assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1419   assert(old->is_oop(), "Will use and dereference old klass ptr below");
1420 
1421   // Finally, install the klass pointer (this should be volatile).
1422   OrderAccess::storestore();
1423   obj->set_klass(old->klass());
1424   // We should now be able to calculate the right size for this object
1425   assert(obj->is_oop() && obj->size() == (int)word_sz, "Error, incorrect size computed for promoted object");
1426 
1427   collector()->promoted(true,          // parallel
1428                         obj_ptr, old->is_objArray(), word_sz);
1429 
1430   NOT_PRODUCT(
1431     Atomic::inc_ptr(&_numObjectsPromoted);
1432     Atomic::add_ptr(alloc_sz, &_numWordsPromoted);
1433   )
1434 
1435   return obj;
1436 }
1437 
1438 void
1439 ConcurrentMarkSweepGeneration::
1440 par_promote_alloc_undo(int thread_num,
1441                        HeapWord* obj, size_t word_sz) {
1442   // CMS does not support promotion undo.
1443   ShouldNotReachHere();
1444 }
1445 
1446 void
1447 ConcurrentMarkSweepGeneration::
1448 par_promote_alloc_done(int thread_num) {
1449   CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1450   ps->lab.retire(thread_num);
1451 }
1452 
1453 void
1454 ConcurrentMarkSweepGeneration::
1455 par_oop_since_save_marks_iterate_done(int thread_num) {
1456   CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1457   ParScanWithoutBarrierClosure* dummy_cl = NULL;
1458   ps->promo.promoted_oops_iterate_nv(dummy_cl);
1459 }
1460 
1461 bool ConcurrentMarkSweepGeneration::should_collect(bool   full,
1462                                                    size_t size,
1463                                                    bool   tlab)
1464 {
1465   // We allow a STW collection only if a full
1466   // collection was requested.
1467   return full || should_allocate(size, tlab); // FIX ME !!!
1468   // This and promotion failure handling are connected at the
1469   // hip and should be fixed by untying them.
1470 }
1471 
1472 bool CMSCollector::shouldConcurrentCollect() {
1473   if (_full_gc_requested) {
1474     if (Verbose && PrintGCDetails) {
1475       gclog_or_tty->print_cr("CMSCollector: collect because of explicit "
1476                              " gc request (or gc_locker)");
1477     }
1478     return true;
1479   }
1480 
1481   // For debugging purposes, change the type of collection.
1482   // If the rotation is not on the concurrent collection
1483   // type, don't start a concurrent collection.
1484   NOT_PRODUCT(
1485     if (RotateCMSCollectionTypes &&
1486         (_cmsGen->debug_collection_type() !=
1487           ConcurrentMarkSweepGeneration::Concurrent_collection_type)) {
1488       assert(_cmsGen->debug_collection_type() !=
1489         ConcurrentMarkSweepGeneration::Unknown_collection_type,
1490         "Bad cms collection type");
1491       return false;
1492     }
1493   )
1494 
1495   FreelistLocker x(this);
1496   // ------------------------------------------------------------------
1497   // Print out lots of information which affects the initiation of
1498   // a collection.
1499   if (PrintCMSInitiationStatistics && stats().valid()) {
1500     gclog_or_tty->print("CMSCollector shouldConcurrentCollect: ");
1501     gclog_or_tty->stamp();
1502     gclog_or_tty->print_cr("");
1503     stats().print_on(gclog_or_tty);
1504     gclog_or_tty->print_cr("time_until_cms_gen_full %3.7f",
1505       stats().time_until_cms_gen_full());
1506     gclog_or_tty->print_cr("free="SIZE_FORMAT, _cmsGen->free());
1507     gclog_or_tty->print_cr("contiguous_available="SIZE_FORMAT,
1508                            _cmsGen->contiguous_available());
1509     gclog_or_tty->print_cr("promotion_rate=%g", stats().promotion_rate());
1510     gclog_or_tty->print_cr("cms_allocation_rate=%g", stats().cms_allocation_rate());
1511     gclog_or_tty->print_cr("occupancy=%3.7f", _cmsGen->occupancy());
1512     gclog_or_tty->print_cr("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy());
1513     gclog_or_tty->print_cr("metadata initialized %d",
1514       MetaspaceGC::should_concurrent_collect());
1515   }
1516   // ------------------------------------------------------------------
1517 
1518   // If the estimated time to complete a cms collection (cms_duration())
1519   // is less than the estimated time remaining until the cms generation
1520   // is full, start a collection.
1521   if (!UseCMSInitiatingOccupancyOnly) {
1522     if (stats().valid()) {
1523       if (stats().time_until_cms_start() == 0.0) {
1524         return true;
1525       }
1526     } else {
1527       // We want to conservatively collect somewhat early in order
1528       // to try and "bootstrap" our CMS/promotion statistics;
1529       // this branch will not fire after the first successful CMS
1530       // collection because the stats should then be valid.
1531       if (_cmsGen->occupancy() >= _bootstrap_occupancy) {
1532         if (Verbose && PrintGCDetails) {
1533           gclog_or_tty->print_cr(
1534             " CMSCollector: collect for bootstrapping statistics:"
1535             " occupancy = %f, boot occupancy = %f", _cmsGen->occupancy(),
1536             _bootstrap_occupancy);
1537         }
1538         return true;
1539       }
1540     }
1541   }
1542 
1543   // Otherwise, we start a collection cycle if
1544   // old gen want a collection cycle started. Each may use
1545   // an appropriate criterion for making this decision.
1546   // XXX We need to make sure that the gen expansion
1547   // criterion dovetails well with this. XXX NEED TO FIX THIS
1548   if (_cmsGen->should_concurrent_collect()) {
1549     if (Verbose && PrintGCDetails) {
1550       gclog_or_tty->print_cr("CMS old gen initiated");
1551     }
1552     return true;
1553   }
1554 
1555   // We start a collection if we believe an incremental collection may fail;
1556   // this is not likely to be productive in practice because it's probably too
1557   // late anyway.
1558   GenCollectedHeap* gch = GenCollectedHeap::heap();
1559   assert(gch->collector_policy()->is_two_generation_policy(),
1560          "You may want to check the correctness of the following");
1561   if (gch->incremental_collection_will_fail(true /* consult_young */)) {
1562     if (Verbose && PrintGCDetails) {
1563       gclog_or_tty->print("CMSCollector: collect because incremental collection will fail ");
1564     }
1565     return true;
1566   }
1567 
1568   if (MetaspaceGC::should_concurrent_collect()) {
1569       if (Verbose && PrintGCDetails) {
1570       gclog_or_tty->print("CMSCollector: collect for metadata allocation ");
1571       }
1572       return true;
1573     }
1574 
1575   return false;
1576 }
1577 
1578 void CMSCollector::set_did_compact(bool v) { _cmsGen->set_did_compact(v); }
1579 
1580 // Clear _expansion_cause fields of constituent generations
1581 void CMSCollector::clear_expansion_cause() {
1582   _cmsGen->clear_expansion_cause();
1583 }
1584 
1585 // We should be conservative in starting a collection cycle.  To
1586 // start too eagerly runs the risk of collecting too often in the
1587 // extreme.  To collect too rarely falls back on full collections,
1588 // which works, even if not optimum in terms of concurrent work.
1589 // As a work around for too eagerly collecting, use the flag
1590 // UseCMSInitiatingOccupancyOnly.  This also has the advantage of
1591 // giving the user an easily understandable way of controlling the
1592 // collections.
1593 // We want to start a new collection cycle if any of the following
1594 // conditions hold:
1595 // . our current occupancy exceeds the configured initiating occupancy
1596 //   for this generation, or
1597 // . we recently needed to expand this space and have not, since that
1598 //   expansion, done a collection of this generation, or
1599 // . the underlying space believes that it may be a good idea to initiate
1600 //   a concurrent collection (this may be based on criteria such as the
1601 //   following: the space uses linear allocation and linear allocation is
1602 //   going to fail, or there is believed to be excessive fragmentation in
1603 //   the generation, etc... or ...
1604 // [.(currently done by CMSCollector::shouldConcurrentCollect() only for
1605 //   the case of the old generation; see CR 6543076):
1606 //   we may be approaching a point at which allocation requests may fail because
1607 //   we will be out of sufficient free space given allocation rate estimates.]
1608 bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const {
1609 
1610   assert_lock_strong(freelistLock());
1611   if (occupancy() > initiating_occupancy()) {
1612     if (PrintGCDetails && Verbose) {
1613       gclog_or_tty->print(" %s: collect because of occupancy %f / %f  ",
1614         short_name(), occupancy(), initiating_occupancy());
1615     }
1616     return true;
1617   }
1618   if (UseCMSInitiatingOccupancyOnly) {
1619     return false;
1620   }
1621   if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) {
1622     if (PrintGCDetails && Verbose) {
1623       gclog_or_tty->print(" %s: collect because expanded for allocation ",
1624         short_name());
1625     }
1626     return true;
1627   }
1628   if (_cmsSpace->should_concurrent_collect()) {
1629     if (PrintGCDetails && Verbose) {
1630       gclog_or_tty->print(" %s: collect because cmsSpace says so ",
1631         short_name());
1632     }
1633     return true;
1634   }
1635   return false;
1636 }
1637 
1638 void ConcurrentMarkSweepGeneration::collect(bool   full,
1639                                             bool   clear_all_soft_refs,
1640                                             size_t size,
1641                                             bool   tlab)
1642 {
1643   collector()->collect(full, clear_all_soft_refs, size, tlab);
1644 }
1645 
1646 void CMSCollector::collect(bool   full,
1647                            bool   clear_all_soft_refs,
1648                            size_t size,
1649                            bool   tlab)
1650 {
1651   if (!UseCMSCollectionPassing && _collectorState > Idling) {
1652     // For debugging purposes skip the collection if the state
1653     // is not currently idle
1654     if (TraceCMSState) {
1655       gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " skipped full:%d CMS state %d",
1656         Thread::current(), full, _collectorState);
1657     }
1658     return;
1659   }
1660 
1661   // The following "if" branch is present for defensive reasons.
1662   // In the current uses of this interface, it can be replaced with:
1663   // assert(!GC_locker.is_active(), "Can't be called otherwise");
1664   // But I am not placing that assert here to allow future
1665   // generality in invoking this interface.
1666   if (GC_locker::is_active()) {
1667     // A consistency test for GC_locker
1668     assert(GC_locker::needs_gc(), "Should have been set already");
1669     // Skip this foreground collection, instead
1670     // expanding the heap if necessary.
1671     // Need the free list locks for the call to free() in compute_new_size()
1672     compute_new_size();
1673     return;
1674   }
1675   acquire_control_and_collect(full, clear_all_soft_refs);
1676   _full_gcs_since_conc_gc++;
1677 }
1678 
1679 void CMSCollector::request_full_gc(unsigned int full_gc_count) {
1680   GenCollectedHeap* gch = GenCollectedHeap::heap();
1681   unsigned int gc_count = gch->total_full_collections();
1682   if (gc_count == full_gc_count) {
1683     MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag);
1684     _full_gc_requested = true;
1685     CGC_lock->notify();   // nudge CMS thread
1686   } else {
1687     assert(gc_count > full_gc_count, "Error: causal loop");
1688   }
1689 }
1690 
1691 
1692 // The foreground and background collectors need to coordinate in order
1693 // to make sure that they do not mutually interfere with CMS collections.
1694 // When a background collection is active,
1695 // the foreground collector may need to take over (preempt) and
1696 // synchronously complete an ongoing collection. Depending on the
1697 // frequency of the background collections and the heap usage
1698 // of the application, this preemption can be seldom or frequent.
1699 // There are only certain
1700 // points in the background collection that the "collection-baton"
1701 // can be passed to the foreground collector.
1702 //
1703 // The foreground collector will wait for the baton before
1704 // starting any part of the collection.  The foreground collector
1705 // will only wait at one location.
1706 //
1707 // The background collector will yield the baton before starting a new
1708 // phase of the collection (e.g., before initial marking, marking from roots,
1709 // precleaning, final re-mark, sweep etc.)  This is normally done at the head
1710 // of the loop which switches the phases. The background collector does some
1711 // of the phases (initial mark, final re-mark) with the world stopped.
1712 // Because of locking involved in stopping the world,
1713 // the foreground collector should not block waiting for the background
1714 // collector when it is doing a stop-the-world phase.  The background
1715 // collector will yield the baton at an additional point just before
1716 // it enters a stop-the-world phase.  Once the world is stopped, the
1717 // background collector checks the phase of the collection.  If the
1718 // phase has not changed, it proceeds with the collection.  If the
1719 // phase has changed, it skips that phase of the collection.  See
1720 // the comments on the use of the Heap_lock in collect_in_background().
1721 //
1722 // Variable used in baton passing.
1723 //   _foregroundGCIsActive - Set to true by the foreground collector when
1724 //      it wants the baton.  The foreground clears it when it has finished
1725 //      the collection.
1726 //   _foregroundGCShouldWait - Set to true by the background collector
1727 //        when it is running.  The foreground collector waits while
1728 //      _foregroundGCShouldWait is true.
1729 //  CGC_lock - monitor used to protect access to the above variables
1730 //      and to notify the foreground and background collectors.
1731 //  _collectorState - current state of the CMS collection.
1732 //
1733 // The foreground collector
1734 //   acquires the CGC_lock
1735 //   sets _foregroundGCIsActive
1736 //   waits on the CGC_lock for _foregroundGCShouldWait to be false
1737 //     various locks acquired in preparation for the collection
1738 //     are released so as not to block the background collector
1739 //     that is in the midst of a collection
1740 //   proceeds with the collection
1741 //   clears _foregroundGCIsActive
1742 //   returns
1743 //
1744 // The background collector in a loop iterating on the phases of the
1745 //      collection
1746 //   acquires the CGC_lock
1747 //   sets _foregroundGCShouldWait
1748 //   if _foregroundGCIsActive is set
1749 //     clears _foregroundGCShouldWait, notifies _CGC_lock
1750 //     waits on _CGC_lock for _foregroundGCIsActive to become false
1751 //     and exits the loop.
1752 //   otherwise
1753 //     proceed with that phase of the collection
1754 //     if the phase is a stop-the-world phase,
1755 //       yield the baton once more just before enqueueing
1756 //       the stop-world CMS operation (executed by the VM thread).
1757 //   returns after all phases of the collection are done
1758 //
1759 
1760 void CMSCollector::acquire_control_and_collect(bool full,
1761         bool clear_all_soft_refs) {
1762   assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
1763   assert(!Thread::current()->is_ConcurrentGC_thread(),
1764          "shouldn't try to acquire control from self!");
1765 
1766   // Start the protocol for acquiring control of the
1767   // collection from the background collector (aka CMS thread).
1768   assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1769          "VM thread should have CMS token");
1770   // Remember the possibly interrupted state of an ongoing
1771   // concurrent collection
1772   CollectorState first_state = _collectorState;
1773 
1774   // Signal to a possibly ongoing concurrent collection that
1775   // we want to do a foreground collection.
1776   _foregroundGCIsActive = true;
1777 
1778   // Disable incremental mode during a foreground collection.
1779   ICMSDisabler icms_disabler;
1780 
1781   // release locks and wait for a notify from the background collector
1782   // releasing the locks in only necessary for phases which
1783   // do yields to improve the granularity of the collection.
1784   assert_lock_strong(bitMapLock());
1785   // We need to lock the Free list lock for the space that we are
1786   // currently collecting.
1787   assert(haveFreelistLocks(), "Must be holding free list locks");
1788   bitMapLock()->unlock();
1789   releaseFreelistLocks();
1790   {
1791     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1792     if (_foregroundGCShouldWait) {
1793       // We are going to be waiting for action for the CMS thread;
1794       // it had better not be gone (for instance at shutdown)!
1795       assert(ConcurrentMarkSweepThread::cmst() != NULL,
1796              "CMS thread must be running");
1797       // Wait here until the background collector gives us the go-ahead
1798       ConcurrentMarkSweepThread::clear_CMS_flag(
1799         ConcurrentMarkSweepThread::CMS_vm_has_token);  // release token
1800       // Get a possibly blocked CMS thread going:
1801       //   Note that we set _foregroundGCIsActive true above,
1802       //   without protection of the CGC_lock.
1803       CGC_lock->notify();
1804       assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(),
1805              "Possible deadlock");
1806       while (_foregroundGCShouldWait) {
1807         // wait for notification
1808         CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1809         // Possibility of delay/starvation here, since CMS token does
1810         // not know to give priority to VM thread? Actually, i think
1811         // there wouldn't be any delay/starvation, but the proof of
1812         // that "fact" (?) appears non-trivial. XXX 20011219YSR
1813       }
1814       ConcurrentMarkSweepThread::set_CMS_flag(
1815         ConcurrentMarkSweepThread::CMS_vm_has_token);
1816     }
1817   }
1818   // The CMS_token is already held.  Get back the other locks.
1819   assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1820          "VM thread should have CMS token");
1821   getFreelistLocks();
1822   bitMapLock()->lock_without_safepoint_check();
1823   if (TraceCMSState) {
1824     gclog_or_tty->print_cr("CMS foreground collector has asked for control "
1825       INTPTR_FORMAT " with first state %d", Thread::current(), first_state);
1826     gclog_or_tty->print_cr("    gets control with state %d", _collectorState);
1827   }
1828 
1829   // Check if we need to do a compaction, or if not, whether
1830   // we need to start the mark-sweep from scratch.
1831   bool should_compact    = false;
1832   bool should_start_over = false;
1833   decide_foreground_collection_type(clear_all_soft_refs,
1834     &should_compact, &should_start_over);
1835 
1836 NOT_PRODUCT(
1837   if (RotateCMSCollectionTypes) {
1838     if (_cmsGen->debug_collection_type() ==
1839         ConcurrentMarkSweepGeneration::MSC_foreground_collection_type) {
1840       should_compact = true;
1841     } else if (_cmsGen->debug_collection_type() ==
1842                ConcurrentMarkSweepGeneration::MS_foreground_collection_type) {
1843       should_compact = false;
1844     }
1845   }
1846 )
1847 
1848   if (PrintGCDetails && first_state > Idling) {
1849     GCCause::Cause cause = GenCollectedHeap::heap()->gc_cause();
1850     if (GCCause::is_user_requested_gc(cause) ||
1851         GCCause::is_serviceability_requested_gc(cause)) {
1852       gclog_or_tty->print(" (concurrent mode interrupted)");
1853     } else {
1854       gclog_or_tty->print(" (concurrent mode failure)");
1855     }
1856   }
1857 
1858   set_did_compact(should_compact);
1859   if (should_compact) {
1860     // If the collection is being acquired from the background
1861     // collector, there may be references on the discovered
1862     // references lists that have NULL referents (being those
1863     // that were concurrently cleared by a mutator) or
1864     // that are no longer active (having been enqueued concurrently
1865     // by the mutator).
1866     // Scrub the list of those references because Mark-Sweep-Compact
1867     // code assumes referents are not NULL and that all discovered
1868     // Reference objects are active.
1869     ref_processor()->clean_up_discovered_references();
1870 
1871     do_compaction_work(clear_all_soft_refs);
1872 
1873     // Has the GC time limit been exceeded?
1874     DefNewGeneration* young_gen = _young_gen->as_DefNewGeneration();
1875     size_t max_eden_size = young_gen->max_capacity() -
1876                            young_gen->to()->capacity() -
1877                            young_gen->from()->capacity();
1878     GenCollectedHeap* gch = GenCollectedHeap::heap();
1879     GCCause::Cause gc_cause = gch->gc_cause();
1880     size_policy()->check_gc_overhead_limit(_young_gen->used(),
1881                                            young_gen->eden()->used(),
1882                                            _cmsGen->max_capacity(),
1883                                            max_eden_size,
1884                                            full,
1885                                            gc_cause,
1886                                            gch->collector_policy());
1887   } else {
1888     do_mark_sweep_work(clear_all_soft_refs, first_state,
1889       should_start_over);
1890   }
1891   // Reset the expansion cause, now that we just completed
1892   // a collection cycle.
1893   clear_expansion_cause();
1894   _foregroundGCIsActive = false;
1895   return;
1896 }
1897 
1898 // Resize the tenured generation
1899 // after obtaining the free list locks for the
1900 // two generations.
1901 void CMSCollector::compute_new_size() {
1902   assert_locked_or_safepoint(Heap_lock);
1903   FreelistLocker z(this);
1904   MetaspaceGC::compute_new_size();
1905   _cmsGen->compute_new_size_free_list();
1906 }
1907 
1908 // A work method used by foreground collection to determine
1909 // what type of collection (compacting or not, continuing or fresh)
1910 // it should do.
1911 // NOTE: the intent is to make UseCMSCompactAtFullCollection
1912 // and CMSCompactWhenClearAllSoftRefs the default in the future
1913 // and do away with the flags after a suitable period.
1914 void CMSCollector::decide_foreground_collection_type(
1915   bool clear_all_soft_refs, bool* should_compact,
1916   bool* should_start_over) {
1917   // Normally, we'll compact only if the UseCMSCompactAtFullCollection
1918   // flag is set, and we have either requested a System.gc() or
1919   // the number of full gc's since the last concurrent cycle
1920   // has exceeded the threshold set by CMSFullGCsBeforeCompaction,
1921   // or if an incremental collection has failed
1922   GenCollectedHeap* gch = GenCollectedHeap::heap();
1923   assert(gch->collector_policy()->is_two_generation_policy(),
1924          "You may want to check the correctness of the following");
1925   // Inform cms gen if this was due to partial collection failing.
1926   // The CMS gen may use this fact to determine its expansion policy.
1927   if (gch->incremental_collection_will_fail(false /* don't consult_young */)) {
1928     assert(!_cmsGen->incremental_collection_failed(),
1929            "Should have been noticed, reacted to and cleared");
1930     _cmsGen->set_incremental_collection_failed();
1931   }
1932   *should_compact =
1933     UseCMSCompactAtFullCollection &&
1934     ((_full_gcs_since_conc_gc >= CMSFullGCsBeforeCompaction) ||
1935      GCCause::is_user_requested_gc(gch->gc_cause()) ||
1936      gch->incremental_collection_will_fail(true /* consult_young */));
1937   *should_start_over = false;
1938   if (clear_all_soft_refs && !*should_compact) {
1939     // We are about to do a last ditch collection attempt
1940     // so it would normally make sense to do a compaction
1941     // to reclaim as much space as possible.
1942     if (CMSCompactWhenClearAllSoftRefs) {
1943       // Default: The rationale is that in this case either
1944       // we are past the final marking phase, in which case
1945       // we'd have to start over, or so little has been done
1946       // that there's little point in saving that work. Compaction
1947       // appears to be the sensible choice in either case.
1948       *should_compact = true;
1949     } else {
1950       // We have been asked to clear all soft refs, but not to
1951       // compact. Make sure that we aren't past the final checkpoint
1952       // phase, for that is where we process soft refs. If we are already
1953       // past that phase, we'll need to redo the refs discovery phase and
1954       // if necessary clear soft refs that weren't previously
1955       // cleared. We do so by remembering the phase in which
1956       // we came in, and if we are past the refs processing
1957       // phase, we'll choose to just redo the mark-sweep
1958       // collection from scratch.
1959       if (_collectorState > FinalMarking) {
1960         // We are past the refs processing phase;
1961         // start over and do a fresh synchronous CMS cycle
1962         _collectorState = Resetting; // skip to reset to start new cycle
1963         reset(false /* == !asynch */);
1964         *should_start_over = true;
1965       } // else we can continue a possibly ongoing current cycle
1966     }
1967   }
1968 }
1969 
1970 // A work method used by the foreground collector to do
1971 // a mark-sweep-compact.
1972 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) {
1973   GenCollectedHeap* gch = GenCollectedHeap::heap();
1974   TraceTime t("CMS:MSC ", PrintGCDetails && Verbose, true, gclog_or_tty);
1975   if (PrintGC && Verbose && !(GCCause::is_user_requested_gc(gch->gc_cause()))) {
1976     gclog_or_tty->print_cr("Compact ConcurrentMarkSweepGeneration after %d "
1977       "collections passed to foreground collector", _full_gcs_since_conc_gc);
1978   }
1979 
1980   // Sample collection interval time and reset for collection pause.
1981   if (UseAdaptiveSizePolicy) {
1982     size_policy()->msc_collection_begin();
1983   }
1984 
1985   // Temporarily widen the span of the weak reference processing to
1986   // the entire heap.
1987   MemRegion new_span(GenCollectedHeap::heap()->reserved_region());
1988   ReferenceProcessorSpanMutator rp_mut_span(ref_processor(), new_span);
1989   // Temporarily, clear the "is_alive_non_header" field of the
1990   // reference processor.
1991   ReferenceProcessorIsAliveMutator rp_mut_closure(ref_processor(), NULL);
1992   // Temporarily make reference _processing_ single threaded (non-MT).
1993   ReferenceProcessorMTProcMutator rp_mut_mt_processing(ref_processor(), false);
1994   // Temporarily make refs discovery atomic
1995   ReferenceProcessorAtomicMutator rp_mut_atomic(ref_processor(), true);
1996   // Temporarily make reference _discovery_ single threaded (non-MT)
1997   ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
1998 
1999   ref_processor()->set_enqueuing_is_done(false);
2000   ref_processor()->enable_discovery(false /*verify_disabled*/, false /*check_no_refs*/);
2001   ref_processor()->setup_policy(clear_all_soft_refs);
2002   // If an asynchronous collection finishes, the _modUnionTable is
2003   // all clear.  If we are assuming the collection from an asynchronous
2004   // collection, clear the _modUnionTable.
2005   assert(_collectorState != Idling || _modUnionTable.isAllClear(),
2006     "_modUnionTable should be clear if the baton was not passed");
2007   _modUnionTable.clear_all();
2008   assert(_collectorState != Idling || _ct->klass_rem_set()->mod_union_is_clear(),
2009     "mod union for klasses should be clear if the baton was passed");
2010   _ct->klass_rem_set()->clear_mod_union();
2011 
2012   // We must adjust the allocation statistics being maintained
2013   // in the free list space. We do so by reading and clearing
2014   // the sweep timer and updating the block flux rate estimates below.
2015   assert(!_intra_sweep_timer.is_active(), "_intra_sweep_timer should be inactive");
2016   if (_inter_sweep_timer.is_active()) {
2017     _inter_sweep_timer.stop();
2018     // Note that we do not use this sample to update the _inter_sweep_estimate.
2019     _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
2020                                             _inter_sweep_estimate.padded_average(),
2021                                             _intra_sweep_estimate.padded_average());
2022   }
2023 
2024   GenMarkSweep::invoke_at_safepoint(_cmsGen->level(),
2025     ref_processor(), clear_all_soft_refs);
2026   #ifdef ASSERT
2027     CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
2028     size_t free_size = cms_space->free();
2029     assert(free_size ==
2030            pointer_delta(cms_space->end(), cms_space->compaction_top())
2031            * HeapWordSize,
2032       "All the free space should be compacted into one chunk at top");
2033     assert(cms_space->dictionary()->total_chunk_size(
2034                                       debug_only(cms_space->freelistLock())) == 0 ||
2035            cms_space->totalSizeInIndexedFreeLists() == 0,
2036       "All the free space should be in a single chunk");
2037     size_t num = cms_space->totalCount();
2038     assert((free_size == 0 && num == 0) ||
2039            (free_size > 0  && (num == 1 || num == 2)),
2040          "There should be at most 2 free chunks after compaction");
2041   #endif // ASSERT
2042   _collectorState = Resetting;
2043   assert(_restart_addr == NULL,
2044          "Should have been NULL'd before baton was passed");
2045   reset(false /* == !asynch */);
2046   _cmsGen->reset_after_compaction();
2047   _concurrent_cycles_since_last_unload = 0;
2048 
2049   // Clear any data recorded in the PLAB chunk arrays.
2050   if (_survivor_plab_array != NULL) {
2051     reset_survivor_plab_arrays();
2052   }
2053 
2054   // Adjust the per-size allocation stats for the next epoch.
2055   _cmsGen->cmsSpace()->endSweepFLCensus(sweep_count() /* fake */);
2056   // Restart the "inter sweep timer" for the next epoch.
2057   _inter_sweep_timer.reset();
2058   _inter_sweep_timer.start();
2059 
2060   // Sample collection pause time and reset for collection interval.
2061   if (UseAdaptiveSizePolicy) {
2062     size_policy()->msc_collection_end(gch->gc_cause());
2063   }
2064 
2065   // For a mark-sweep-compact, compute_new_size() will be called
2066   // in the heap's do_collection() method.
2067 }
2068 
2069 // A work method used by the foreground collector to do
2070 // a mark-sweep, after taking over from a possibly on-going
2071 // concurrent mark-sweep collection.
2072 void CMSCollector::do_mark_sweep_work(bool clear_all_soft_refs,
2073   CollectorState first_state, bool should_start_over) {
2074   if (PrintGC && Verbose) {
2075     gclog_or_tty->print_cr("Pass concurrent collection to foreground "
2076       "collector with count %d",
2077       _full_gcs_since_conc_gc);
2078   }
2079   switch (_collectorState) {
2080     case Idling:
2081       if (first_state == Idling || should_start_over) {
2082         // The background GC was not active, or should
2083         // restarted from scratch;  start the cycle.
2084         _collectorState = InitialMarking;
2085       }
2086       // If first_state was not Idling, then a background GC
2087       // was in progress and has now finished.  No need to do it
2088       // again.  Leave the state as Idling.
2089       break;
2090     case Precleaning:
2091       // In the foreground case don't do the precleaning since
2092       // it is not done concurrently and there is extra work
2093       // required.
2094       _collectorState = FinalMarking;
2095   }
2096   collect_in_foreground(clear_all_soft_refs);
2097 
2098   // For a mark-sweep, compute_new_size() will be called
2099   // in the heap's do_collection() method.
2100 }
2101 
2102 
2103 void CMSCollector::getFreelistLocks() const {
2104   // Get locks for all free lists in all generations that this
2105   // collector is responsible for
2106   _cmsGen->freelistLock()->lock_without_safepoint_check();
2107 }
2108 
2109 void CMSCollector::releaseFreelistLocks() const {
2110   // Release locks for all free lists in all generations that this
2111   // collector is responsible for
2112   _cmsGen->freelistLock()->unlock();
2113 }
2114 
2115 bool CMSCollector::haveFreelistLocks() const {
2116   // Check locks for all free lists in all generations that this
2117   // collector is responsible for
2118   assert_lock_strong(_cmsGen->freelistLock());
2119   PRODUCT_ONLY(ShouldNotReachHere());
2120   return true;
2121 }
2122 
2123 // A utility class that is used by the CMS collector to
2124 // temporarily "release" the foreground collector from its
2125 // usual obligation to wait for the background collector to
2126 // complete an ongoing phase before proceeding.
2127 class ReleaseForegroundGC: public StackObj {
2128  private:
2129   CMSCollector* _c;
2130  public:
2131   ReleaseForegroundGC(CMSCollector* c) : _c(c) {
2132     assert(_c->_foregroundGCShouldWait, "Else should not need to call");
2133     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2134     // allow a potentially blocked foreground collector to proceed
2135     _c->_foregroundGCShouldWait = false;
2136     if (_c->_foregroundGCIsActive) {
2137       CGC_lock->notify();
2138     }
2139     assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2140            "Possible deadlock");
2141   }
2142 
2143   ~ReleaseForegroundGC() {
2144     assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?");
2145     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2146     _c->_foregroundGCShouldWait = true;
2147   }
2148 };
2149 
2150 // There are separate collect_in_background and collect_in_foreground because of
2151 // the different locking requirements of the background collector and the
2152 // foreground collector.  There was originally an attempt to share
2153 // one "collect" method between the background collector and the foreground
2154 // collector but the if-then-else required made it cleaner to have
2155 // separate methods.
2156 void CMSCollector::collect_in_background(bool clear_all_soft_refs) {
2157   assert(Thread::current()->is_ConcurrentGC_thread(),
2158     "A CMS asynchronous collection is only allowed on a CMS thread.");
2159 
2160   GenCollectedHeap* gch = GenCollectedHeap::heap();
2161   {
2162     bool safepoint_check = Mutex::_no_safepoint_check_flag;
2163     MutexLockerEx hl(Heap_lock, safepoint_check);
2164     FreelistLocker fll(this);
2165     MutexLockerEx x(CGC_lock, safepoint_check);
2166     if (_foregroundGCIsActive || !UseAsyncConcMarkSweepGC) {
2167       // The foreground collector is active or we're
2168       // not using asynchronous collections.  Skip this
2169       // background collection.
2170       assert(!_foregroundGCShouldWait, "Should be clear");
2171       return;
2172     } else {
2173       assert(_collectorState == Idling, "Should be idling before start.");
2174       _collectorState = InitialMarking;
2175       // Reset the expansion cause, now that we are about to begin
2176       // a new cycle.
2177       clear_expansion_cause();
2178 
2179       // Clear the MetaspaceGC flag since a concurrent collection
2180       // is starting but also clear it after the collection.
2181       MetaspaceGC::set_should_concurrent_collect(false);
2182     }
2183     // Decide if we want to enable class unloading as part of the
2184     // ensuing concurrent GC cycle.
2185     update_should_unload_classes();
2186     _full_gc_requested = false;           // acks all outstanding full gc requests
2187     // Signal that we are about to start a collection
2188     gch->increment_total_full_collections();  // ... starting a collection cycle
2189     _collection_count_start = gch->total_full_collections();
2190   }
2191 
2192   // Used for PrintGC
2193   size_t prev_used;
2194   if (PrintGC && Verbose) {
2195     prev_used = _cmsGen->used(); // XXXPERM
2196   }
2197 
2198   // The change of the collection state is normally done at this level;
2199   // the exceptions are phases that are executed while the world is
2200   // stopped.  For those phases the change of state is done while the
2201   // world is stopped.  For baton passing purposes this allows the
2202   // background collector to finish the phase and change state atomically.
2203   // The foreground collector cannot wait on a phase that is done
2204   // while the world is stopped because the foreground collector already
2205   // has the world stopped and would deadlock.
2206   while (_collectorState != Idling) {
2207     if (TraceCMSState) {
2208       gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
2209         Thread::current(), _collectorState);
2210     }
2211     // The foreground collector
2212     //   holds the Heap_lock throughout its collection.
2213     //   holds the CMS token (but not the lock)
2214     //     except while it is waiting for the background collector to yield.
2215     //
2216     // The foreground collector should be blocked (not for long)
2217     //   if the background collector is about to start a phase
2218     //   executed with world stopped.  If the background
2219     //   collector has already started such a phase, the
2220     //   foreground collector is blocked waiting for the
2221     //   Heap_lock.  The stop-world phases (InitialMarking and FinalMarking)
2222     //   are executed in the VM thread.
2223     //
2224     // The locking order is
2225     //   PendingListLock (PLL)  -- if applicable (FinalMarking)
2226     //   Heap_lock  (both this & PLL locked in VM_CMS_Operation::prologue())
2227     //   CMS token  (claimed in
2228     //                stop_world_and_do() -->
2229     //                  safepoint_synchronize() -->
2230     //                    CMSThread::synchronize())
2231 
2232     {
2233       // Check if the FG collector wants us to yield.
2234       CMSTokenSync x(true); // is cms thread
2235       if (waitForForegroundGC()) {
2236         // We yielded to a foreground GC, nothing more to be
2237         // done this round.
2238         assert(_foregroundGCShouldWait == false, "We set it to false in "
2239                "waitForForegroundGC()");
2240         if (TraceCMSState) {
2241           gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2242             " exiting collection CMS state %d",
2243             Thread::current(), _collectorState);
2244         }
2245         return;
2246       } else {
2247         // The background collector can run but check to see if the
2248         // foreground collector has done a collection while the
2249         // background collector was waiting to get the CGC_lock
2250         // above.  If yes, break so that _foregroundGCShouldWait
2251         // is cleared before returning.
2252         if (_collectorState == Idling) {
2253           break;
2254         }
2255       }
2256     }
2257 
2258     assert(_foregroundGCShouldWait, "Foreground collector, if active, "
2259       "should be waiting");
2260 
2261     switch (_collectorState) {
2262       case InitialMarking:
2263         {
2264           ReleaseForegroundGC x(this);
2265           stats().record_cms_begin();
2266 
2267           VM_CMS_Initial_Mark initial_mark_op(this);
2268           VMThread::execute(&initial_mark_op);
2269         }
2270         // The collector state may be any legal state at this point
2271         // since the background collector may have yielded to the
2272         // foreground collector.
2273         break;
2274       case Marking:
2275         // initial marking in checkpointRootsInitialWork has been completed
2276         if (markFromRoots(true)) { // we were successful
2277           assert(_collectorState == Precleaning, "Collector state should "
2278             "have changed");
2279         } else {
2280           assert(_foregroundGCIsActive, "Internal state inconsistency");
2281         }
2282         break;
2283       case Precleaning:
2284         if (UseAdaptiveSizePolicy) {
2285           size_policy()->concurrent_precleaning_begin();
2286         }
2287         // marking from roots in markFromRoots has been completed
2288         preclean();
2289         if (UseAdaptiveSizePolicy) {
2290           size_policy()->concurrent_precleaning_end();
2291         }
2292         assert(_collectorState == AbortablePreclean ||
2293                _collectorState == FinalMarking,
2294                "Collector state should have changed");
2295         break;
2296       case AbortablePreclean:
2297         if (UseAdaptiveSizePolicy) {
2298         size_policy()->concurrent_phases_resume();
2299         }
2300         abortable_preclean();
2301         if (UseAdaptiveSizePolicy) {
2302           size_policy()->concurrent_precleaning_end();
2303         }
2304         assert(_collectorState == FinalMarking, "Collector state should "
2305           "have changed");
2306         break;
2307       case FinalMarking:
2308         {
2309           ReleaseForegroundGC x(this);
2310 
2311           VM_CMS_Final_Remark final_remark_op(this);
2312           VMThread::execute(&final_remark_op);
2313         }
2314         assert(_foregroundGCShouldWait, "block post-condition");
2315         break;
2316       case Sweeping:
2317         if (UseAdaptiveSizePolicy) {
2318           size_policy()->concurrent_sweeping_begin();
2319         }
2320         // final marking in checkpointRootsFinal has been completed
2321         sweep(true);
2322         assert(_collectorState == Resizing, "Collector state change "
2323           "to Resizing must be done under the free_list_lock");
2324         _full_gcs_since_conc_gc = 0;
2325 
2326         // Stop the timers for adaptive size policy for the concurrent phases
2327         if (UseAdaptiveSizePolicy) {
2328           size_policy()->concurrent_sweeping_end();
2329           size_policy()->concurrent_phases_end(gch->gc_cause(),
2330                                              gch->prev_gen(_cmsGen)->capacity(),
2331                                              _cmsGen->free());
2332         }
2333 
2334       case Resizing: {
2335         // Sweeping has been completed...
2336         // At this point the background collection has completed.
2337         // Don't move the call to compute_new_size() down
2338         // into code that might be executed if the background
2339         // collection was preempted.
2340         {
2341           ReleaseForegroundGC x(this);   // unblock FG collection
2342           MutexLockerEx       y(Heap_lock, Mutex::_no_safepoint_check_flag);
2343           CMSTokenSync        z(true);   // not strictly needed.
2344           if (_collectorState == Resizing) {
2345             compute_new_size();
2346             _collectorState = Resetting;
2347           } else {
2348             assert(_collectorState == Idling, "The state should only change"
2349                    " because the foreground collector has finished the collection");
2350           }
2351         }
2352         break;
2353       }
2354       case Resetting:
2355         // CMS heap resizing has been completed
2356         reset(true);
2357         assert(_collectorState == Idling, "Collector state should "
2358           "have changed");
2359 
2360         MetaspaceGC::set_should_concurrent_collect(false);
2361 
2362         stats().record_cms_end();
2363         // Don't move the concurrent_phases_end() and compute_new_size()
2364         // calls to here because a preempted background collection
2365         // has it's state set to "Resetting".
2366         break;
2367       case Idling:
2368       default:
2369         ShouldNotReachHere();
2370         break;
2371     }
2372     if (TraceCMSState) {
2373       gclog_or_tty->print_cr("  Thread " INTPTR_FORMAT " done - next CMS state %d",
2374         Thread::current(), _collectorState);
2375     }
2376     assert(_foregroundGCShouldWait, "block post-condition");
2377   }
2378 
2379   // Should this be in gc_epilogue?
2380   collector_policy()->counters()->update_counters();
2381 
2382   {
2383     // Clear _foregroundGCShouldWait and, in the event that the
2384     // foreground collector is waiting, notify it, before
2385     // returning.
2386     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2387     _foregroundGCShouldWait = false;
2388     if (_foregroundGCIsActive) {
2389       CGC_lock->notify();
2390     }
2391     assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2392            "Possible deadlock");
2393   }
2394   if (TraceCMSState) {
2395     gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2396       " exiting collection CMS state %d",
2397       Thread::current(), _collectorState);
2398   }
2399   if (PrintGC && Verbose) {
2400     _cmsGen->print_heap_change(prev_used);
2401   }
2402 }
2403 
2404 void CMSCollector::collect_in_foreground(bool clear_all_soft_refs) {
2405   assert(_foregroundGCIsActive && !_foregroundGCShouldWait,
2406          "Foreground collector should be waiting, not executing");
2407   assert(Thread::current()->is_VM_thread(), "A foreground collection"
2408     "may only be done by the VM Thread with the world stopped");
2409   assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
2410          "VM thread should have CMS token");
2411 
2412   NOT_PRODUCT(TraceTime t("CMS:MS (foreground) ", PrintGCDetails && Verbose,
2413     true, gclog_or_tty);)
2414   if (UseAdaptiveSizePolicy) {
2415     size_policy()->ms_collection_begin();
2416   }
2417   COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact);
2418 
2419   HandleMark hm;  // Discard invalid handles created during verification
2420 
2421   if (VerifyBeforeGC &&
2422       GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2423     Universe::verify();
2424   }
2425 
2426   // Snapshot the soft reference policy to be used in this collection cycle.
2427   ref_processor()->setup_policy(clear_all_soft_refs);
2428 
2429   bool init_mark_was_synchronous = false; // until proven otherwise
2430   while (_collectorState != Idling) {
2431     if (TraceCMSState) {
2432       gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
2433         Thread::current(), _collectorState);
2434     }
2435     switch (_collectorState) {
2436       case InitialMarking:
2437         init_mark_was_synchronous = true;  // fact to be exploited in re-mark
2438         checkpointRootsInitial(false);
2439         assert(_collectorState == Marking, "Collector state should have changed"
2440           " within checkpointRootsInitial()");
2441         break;
2442       case Marking:
2443         // initial marking in checkpointRootsInitialWork has been completed
2444         if (VerifyDuringGC &&
2445             GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2446           Universe::verify("Verify before initial mark: ");
2447         }
2448         {
2449           bool res = markFromRoots(false);
2450           assert(res && _collectorState == FinalMarking, "Collector state should "
2451             "have changed");
2452           break;
2453         }
2454       case FinalMarking:
2455         if (VerifyDuringGC &&
2456             GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2457           Universe::verify("Verify before re-mark: ");
2458         }
2459         checkpointRootsFinal(false, clear_all_soft_refs,
2460                              init_mark_was_synchronous);
2461         assert(_collectorState == Sweeping, "Collector state should not "
2462           "have changed within checkpointRootsFinal()");
2463         break;
2464       case Sweeping:
2465         // final marking in checkpointRootsFinal has been completed
2466         if (VerifyDuringGC &&
2467             GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2468           Universe::verify("Verify before sweep: ");
2469         }
2470         sweep(false);
2471         assert(_collectorState == Resizing, "Incorrect state");
2472         break;
2473       case Resizing: {
2474         // Sweeping has been completed; the actual resize in this case
2475         // is done separately; nothing to be done in this state.
2476         _collectorState = Resetting;
2477         break;
2478       }
2479       case Resetting:
2480         // The heap has been resized.
2481         if (VerifyDuringGC &&
2482             GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2483           Universe::verify("Verify before reset: ");
2484         }
2485         reset(false);
2486         assert(_collectorState == Idling, "Collector state should "
2487           "have changed");
2488         break;
2489       case Precleaning:
2490       case AbortablePreclean:
2491         // Elide the preclean phase
2492         _collectorState = FinalMarking;
2493         break;
2494       default:
2495         ShouldNotReachHere();
2496     }
2497     if (TraceCMSState) {
2498       gclog_or_tty->print_cr("  Thread " INTPTR_FORMAT " done - next CMS state %d",
2499         Thread::current(), _collectorState);
2500     }
2501   }
2502 
2503   if (UseAdaptiveSizePolicy) {
2504     GenCollectedHeap* gch = GenCollectedHeap::heap();
2505     size_policy()->ms_collection_end(gch->gc_cause());
2506   }
2507 
2508   if (VerifyAfterGC &&
2509       GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2510     Universe::verify();
2511   }
2512   if (TraceCMSState) {
2513     gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2514       " exiting collection CMS state %d",
2515       Thread::current(), _collectorState);
2516   }
2517 }
2518 
2519 bool CMSCollector::waitForForegroundGC() {
2520   bool res = false;
2521   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2522          "CMS thread should have CMS token");
2523   // Block the foreground collector until the
2524   // background collectors decides whether to
2525   // yield.
2526   MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2527   _foregroundGCShouldWait = true;
2528   if (_foregroundGCIsActive) {
2529     // The background collector yields to the
2530     // foreground collector and returns a value
2531     // indicating that it has yielded.  The foreground
2532     // collector can proceed.
2533     res = true;
2534     _foregroundGCShouldWait = false;
2535     ConcurrentMarkSweepThread::clear_CMS_flag(
2536       ConcurrentMarkSweepThread::CMS_cms_has_token);
2537     ConcurrentMarkSweepThread::set_CMS_flag(
2538       ConcurrentMarkSweepThread::CMS_cms_wants_token);
2539     // Get a possibly blocked foreground thread going
2540     CGC_lock->notify();
2541     if (TraceCMSState) {
2542       gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d",
2543         Thread::current(), _collectorState);
2544     }
2545     while (_foregroundGCIsActive) {
2546       CGC_lock->wait(Mutex::_no_safepoint_check_flag);
2547     }
2548     ConcurrentMarkSweepThread::set_CMS_flag(
2549       ConcurrentMarkSweepThread::CMS_cms_has_token);
2550     ConcurrentMarkSweepThread::clear_CMS_flag(
2551       ConcurrentMarkSweepThread::CMS_cms_wants_token);
2552   }
2553   if (TraceCMSState) {
2554     gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d",
2555       Thread::current(), _collectorState);
2556   }
2557   return res;
2558 }
2559 
2560 // Because of the need to lock the free lists and other structures in
2561 // the collector, common to all the generations that the collector is
2562 // collecting, we need the gc_prologues of individual CMS generations
2563 // delegate to their collector. It may have been simpler had the
2564 // current infrastructure allowed one to call a prologue on a
2565 // collector. In the absence of that we have the generation's
2566 // prologue delegate to the collector, which delegates back
2567 // some "local" work to a worker method in the individual generations
2568 // that it's responsible for collecting, while itself doing any
2569 // work common to all generations it's responsible for. A similar
2570 // comment applies to the  gc_epilogue()'s.
2571 // The role of the varaible _between_prologue_and_epilogue is to
2572 // enforce the invocation protocol.
2573 void CMSCollector::gc_prologue(bool full) {
2574   // Call gc_prologue_work() for the CMSGen
2575   // we are responsible for.
2576 
2577   // The following locking discipline assumes that we are only called
2578   // when the world is stopped.
2579   assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption");
2580 
2581   // The CMSCollector prologue must call the gc_prologues for the
2582   // "generations" that it's responsible
2583   // for.
2584 
2585   assert(   Thread::current()->is_VM_thread()
2586          || (   CMSScavengeBeforeRemark
2587              && Thread::current()->is_ConcurrentGC_thread()),
2588          "Incorrect thread type for prologue execution");
2589 
2590   if (_between_prologue_and_epilogue) {
2591     // We have already been invoked; this is a gc_prologue delegation
2592     // from yet another CMS generation that we are responsible for, just
2593     // ignore it since all relevant work has already been done.
2594     return;
2595   }
2596 
2597   // set a bit saying prologue has been called; cleared in epilogue
2598   _between_prologue_and_epilogue = true;
2599   // Claim locks for common data structures, then call gc_prologue_work()
2600   // for each CMSGen.
2601 
2602   getFreelistLocks();   // gets free list locks on constituent spaces
2603   bitMapLock()->lock_without_safepoint_check();
2604 
2605   // Should call gc_prologue_work() for all cms gens we are responsible for
2606   bool duringMarking =    _collectorState >= Marking
2607                          && _collectorState < Sweeping;
2608 
2609   // The young collections clear the modified oops state, which tells if
2610   // there are any modified oops in the class. The remark phase also needs
2611   // that information. Tell the young collection to save the union of all
2612   // modified klasses.
2613   if (duringMarking) {
2614     _ct->klass_rem_set()->set_accumulate_modified_oops(true);
2615   }
2616 
2617   bool registerClosure = duringMarking;
2618 
2619   ModUnionClosure* muc = CollectedHeap::use_parallel_gc_threads() ?
2620                                                &_modUnionClosurePar
2621                                                : &_modUnionClosure;
2622   _cmsGen->gc_prologue_work(full, registerClosure, muc);
2623 
2624   if (!full) {
2625     stats().record_gc0_begin();
2626   }
2627 }
2628 
2629 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) {
2630 
2631   _capacity_at_prologue = capacity();
2632   _used_at_prologue = used();
2633 
2634   // Delegate to CMScollector which knows how to coordinate between
2635   // this and any other CMS generations that it is responsible for
2636   // collecting.
2637   collector()->gc_prologue(full);
2638 }
2639 
2640 // This is a "private" interface for use by this generation's CMSCollector.
2641 // Not to be called directly by any other entity (for instance,
2642 // GenCollectedHeap, which calls the "public" gc_prologue method above).
2643 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full,
2644   bool registerClosure, ModUnionClosure* modUnionClosure) {
2645   assert(!incremental_collection_failed(), "Shouldn't be set yet");
2646   assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL,
2647     "Should be NULL");
2648   if (registerClosure) {
2649     cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure);
2650   }
2651   cmsSpace()->gc_prologue();
2652   // Clear stat counters
2653   NOT_PRODUCT(
2654     assert(_numObjectsPromoted == 0, "check");
2655     assert(_numWordsPromoted   == 0, "check");
2656     if (Verbose && PrintGC) {
2657       gclog_or_tty->print("Allocated "SIZE_FORMAT" objects, "
2658                           SIZE_FORMAT" bytes concurrently",
2659       _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord));
2660     }
2661     _numObjectsAllocated = 0;
2662     _numWordsAllocated   = 0;
2663   )
2664 }
2665 
2666 void CMSCollector::gc_epilogue(bool full) {
2667   // The following locking discipline assumes that we are only called
2668   // when the world is stopped.
2669   assert(SafepointSynchronize::is_at_safepoint(),
2670          "world is stopped assumption");
2671 
2672   // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks
2673   // if linear allocation blocks need to be appropriately marked to allow the
2674   // the blocks to be parsable. We also check here whether we need to nudge the
2675   // CMS collector thread to start a new cycle (if it's not already active).
2676   assert(   Thread::current()->is_VM_thread()
2677          || (   CMSScavengeBeforeRemark
2678              && Thread::current()->is_ConcurrentGC_thread()),
2679          "Incorrect thread type for epilogue execution");
2680 
2681   if (!_between_prologue_and_epilogue) {
2682     // We have already been invoked; this is a gc_epilogue delegation
2683     // from yet another CMS generation that we are responsible for, just
2684     // ignore it since all relevant work has already been done.
2685     return;
2686   }
2687   assert(haveFreelistLocks(), "must have freelist locks");
2688   assert_lock_strong(bitMapLock());
2689 
2690   _ct->klass_rem_set()->set_accumulate_modified_oops(false);
2691 
2692   _cmsGen->gc_epilogue_work(full);
2693 
2694   if (_collectorState == AbortablePreclean || _collectorState == Precleaning) {
2695     // in case sampling was not already enabled, enable it
2696     _start_sampling = true;
2697   }
2698   // reset _eden_chunk_array so sampling starts afresh
2699   _eden_chunk_index = 0;
2700 
2701   size_t cms_used   = _cmsGen->cmsSpace()->used();
2702 
2703   // update performance counters - this uses a special version of
2704   // update_counters() that allows the utilization to be passed as a
2705   // parameter, avoiding multiple calls to used().
2706   //
2707   _cmsGen->update_counters(cms_used);
2708 
2709   if (CMSIncrementalMode) {
2710     icms_update_allocation_limits();
2711   }
2712 
2713   bitMapLock()->unlock();
2714   releaseFreelistLocks();
2715 
2716   if (!CleanChunkPoolAsync) {
2717     Chunk::clean_chunk_pool();
2718   }
2719 
2720   set_did_compact(false);
2721   _between_prologue_and_epilogue = false;  // ready for next cycle
2722 }
2723 
2724 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) {
2725   collector()->gc_epilogue(full);
2726 
2727   // Also reset promotion tracking in par gc thread states.
2728   if (CollectedHeap::use_parallel_gc_threads()) {
2729     for (uint i = 0; i < ParallelGCThreads; i++) {
2730       _par_gc_thread_states[i]->promo.stopTrackingPromotions(i);
2731     }
2732   }
2733 }
2734 
2735 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2736   assert(!incremental_collection_failed(), "Should have been cleared");
2737   cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2738   cmsSpace()->gc_epilogue();
2739     // Print stat counters
2740   NOT_PRODUCT(
2741     assert(_numObjectsAllocated == 0, "check");
2742     assert(_numWordsAllocated == 0, "check");
2743     if (Verbose && PrintGC) {
2744       gclog_or_tty->print("Promoted "SIZE_FORMAT" objects, "
2745                           SIZE_FORMAT" bytes",
2746                  _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2747     }
2748     _numObjectsPromoted = 0;
2749     _numWordsPromoted   = 0;
2750   )
2751 
2752   if (PrintGC && Verbose) {
2753     // Call down the chain in contiguous_available needs the freelistLock
2754     // so print this out before releasing the freeListLock.
2755     gclog_or_tty->print(" Contiguous available "SIZE_FORMAT" bytes ",
2756                         contiguous_available());
2757   }
2758 }
2759 
2760 #ifndef PRODUCT
2761 bool CMSCollector::have_cms_token() {
2762   Thread* thr = Thread::current();
2763   if (thr->is_VM_thread()) {
2764     return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2765   } else if (thr->is_ConcurrentGC_thread()) {
2766     return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2767   } else if (thr->is_GC_task_thread()) {
2768     return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2769            ParGCRareEvent_lock->owned_by_self();
2770   }
2771   return false;
2772 }
2773 #endif
2774 
2775 // Check reachability of the given heap address in CMS generation,
2776 // treating all other generations as roots.
2777 bool CMSCollector::is_cms_reachable(HeapWord* addr) {
2778   // We could "guarantee" below, rather than assert, but i'll
2779   // leave these as "asserts" so that an adventurous debugger
2780   // could try this in the product build provided some subset of
2781   // the conditions were met, provided they were intersted in the
2782   // results and knew that the computation below wouldn't interfere
2783   // with other concurrent computations mutating the structures
2784   // being read or written.
2785   assert(SafepointSynchronize::is_at_safepoint(),
2786          "Else mutations in object graph will make answer suspect");
2787   assert(have_cms_token(), "Should hold cms token");
2788   assert(haveFreelistLocks(), "must hold free list locks");
2789   assert_lock_strong(bitMapLock());
2790 
2791   // Clear the marking bit map array before starting, but, just
2792   // for kicks, first report if the given address is already marked
2793   gclog_or_tty->print_cr("Start: Address 0x%x is%s marked", addr,
2794                 _markBitMap.isMarked(addr) ? "" : " not");
2795 
2796   if (verify_after_remark()) {
2797     MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2798     bool result = verification_mark_bm()->isMarked(addr);
2799     gclog_or_tty->print_cr("TransitiveMark: Address 0x%x %s marked", addr,
2800                            result ? "IS" : "is NOT");
2801     return result;
2802   } else {
2803     gclog_or_tty->print_cr("Could not compute result");
2804     return false;
2805   }
2806 }
2807 
2808 
2809 void
2810 CMSCollector::print_on_error(outputStream* st) {
2811   CMSCollector* collector = ConcurrentMarkSweepGeneration::_collector;
2812   if (collector != NULL) {
2813     CMSBitMap* bitmap = &collector->_markBitMap;
2814     st->print_cr("Marking Bits: (CMSBitMap*) " PTR_FORMAT, bitmap);
2815     bitmap->print_on_error(st, " Bits: ");
2816 
2817     st->cr();
2818 
2819     CMSBitMap* mut_bitmap = &collector->_modUnionTable;
2820     st->print_cr("Mod Union Table: (CMSBitMap*) " PTR_FORMAT, mut_bitmap);
2821     mut_bitmap->print_on_error(st, " Bits: ");
2822   }
2823 }
2824 
2825 ////////////////////////////////////////////////////////
2826 // CMS Verification Support
2827 ////////////////////////////////////////////////////////
2828 // Following the remark phase, the following invariant
2829 // should hold -- each object in the CMS heap which is
2830 // marked in markBitMap() should be marked in the verification_mark_bm().
2831 
2832 class VerifyMarkedClosure: public BitMapClosure {
2833   CMSBitMap* _marks;
2834   bool       _failed;
2835 
2836  public:
2837   VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2838 
2839   bool do_bit(size_t offset) {
2840     HeapWord* addr = _marks->offsetToHeapWord(offset);
2841     if (!_marks->isMarked(addr)) {
2842       oop(addr)->print_on(gclog_or_tty);
2843       gclog_or_tty->print_cr(" ("INTPTR_FORMAT" should have been marked)", addr);
2844       _failed = true;
2845     }
2846     return true;
2847   }
2848 
2849   bool failed() { return _failed; }
2850 };
2851 
2852 bool CMSCollector::verify_after_remark(bool silent) {
2853   if (!silent) gclog_or_tty->print(" [Verifying CMS Marking... ");
2854   MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2855   static bool init = false;
2856 
2857   assert(SafepointSynchronize::is_at_safepoint(),
2858          "Else mutations in object graph will make answer suspect");
2859   assert(have_cms_token(),
2860          "Else there may be mutual interference in use of "
2861          " verification data structures");
2862   assert(_collectorState > Marking && _collectorState <= Sweeping,
2863          "Else marking info checked here may be obsolete");
2864   assert(haveFreelistLocks(), "must hold free list locks");
2865   assert_lock_strong(bitMapLock());
2866 
2867 
2868   // Allocate marking bit map if not already allocated
2869   if (!init) { // first time
2870     if (!verification_mark_bm()->allocate(_span)) {
2871       return false;
2872     }
2873     init = true;
2874   }
2875 
2876   assert(verification_mark_stack()->isEmpty(), "Should be empty");
2877 
2878   // Turn off refs discovery -- so we will be tracing through refs.
2879   // This is as intended, because by this time
2880   // GC must already have cleared any refs that need to be cleared,
2881   // and traced those that need to be marked; moreover,
2882   // the marking done here is not going to intefere in any
2883   // way with the marking information used by GC.
2884   NoRefDiscovery no_discovery(ref_processor());
2885 
2886   COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
2887 
2888   // Clear any marks from a previous round
2889   verification_mark_bm()->clear_all();
2890   assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
2891   verify_work_stacks_empty();
2892 
2893   GenCollectedHeap* gch = GenCollectedHeap::heap();
2894   gch->ensure_parsability(false);  // fill TLABs, but no need to retire them
2895   // Update the saved marks which may affect the root scans.
2896   gch->save_marks();
2897 
2898   if (CMSRemarkVerifyVariant == 1) {
2899     // In this first variant of verification, we complete
2900     // all marking, then check if the new marks-verctor is
2901     // a subset of the CMS marks-vector.
2902     verify_after_remark_work_1();
2903   } else if (CMSRemarkVerifyVariant == 2) {
2904     // In this second variant of verification, we flag an error
2905     // (i.e. an object reachable in the new marks-vector not reachable
2906     // in the CMS marks-vector) immediately, also indicating the
2907     // identify of an object (A) that references the unmarked object (B) --
2908     // presumably, a mutation to A failed to be picked up by preclean/remark?
2909     verify_after_remark_work_2();
2910   } else {
2911     warning("Unrecognized value %d for CMSRemarkVerifyVariant",
2912             CMSRemarkVerifyVariant);
2913   }
2914   if (!silent) gclog_or_tty->print(" done] ");
2915   return true;
2916 }
2917 
2918 void CMSCollector::verify_after_remark_work_1() {
2919   ResourceMark rm;
2920   HandleMark  hm;
2921   GenCollectedHeap* gch = GenCollectedHeap::heap();
2922 
2923   // Get a clear set of claim bits for the strong roots processing to work with.
2924   ClassLoaderDataGraph::clear_claimed_marks();
2925 
2926   // Mark from roots one level into CMS
2927   MarkRefsIntoClosure notOlder(_span, verification_mark_bm());
2928   gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2929 
2930   gch->gen_process_strong_roots(_cmsGen->level(),
2931                                 true,   // younger gens are roots
2932                                 true,   // activate StrongRootsScope
2933                                 false,  // not scavenging
2934                                 SharedHeap::ScanningOption(roots_scanning_options()),
2935                                 &notOlder,
2936                                 true,   // walk code active on stacks
2937                                 NULL,
2938                                 NULL); // SSS: Provide correct closure
2939 
2940   // Now mark from the roots
2941   MarkFromRootsClosure markFromRootsClosure(this, _span,
2942     verification_mark_bm(), verification_mark_stack(),
2943     false /* don't yield */, true /* verifying */);
2944   assert(_restart_addr == NULL, "Expected pre-condition");
2945   verification_mark_bm()->iterate(&markFromRootsClosure);
2946   while (_restart_addr != NULL) {
2947     // Deal with stack overflow: by restarting at the indicated
2948     // address.
2949     HeapWord* ra = _restart_addr;
2950     markFromRootsClosure.reset(ra);
2951     _restart_addr = NULL;
2952     verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2953   }
2954   assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2955   verify_work_stacks_empty();
2956 
2957   // Marking completed -- now verify that each bit marked in
2958   // verification_mark_bm() is also marked in markBitMap(); flag all
2959   // errors by printing corresponding objects.
2960   VerifyMarkedClosure vcl(markBitMap());
2961   verification_mark_bm()->iterate(&vcl);
2962   if (vcl.failed()) {
2963     gclog_or_tty->print("Verification failed");
2964     Universe::heap()->print_on(gclog_or_tty);
2965     fatal("CMS: failed marking verification after remark");
2966   }
2967 }
2968 
2969 class VerifyKlassOopsKlassClosure : public KlassClosure {
2970   class VerifyKlassOopsClosure : public OopClosure {
2971     CMSBitMap* _bitmap;
2972    public:
2973     VerifyKlassOopsClosure(CMSBitMap* bitmap) : _bitmap(bitmap) { }
2974     void do_oop(oop* p)       { guarantee(*p == NULL || _bitmap->isMarked((HeapWord*) *p), "Should be marked"); }
2975     void do_oop(narrowOop* p) { ShouldNotReachHere(); }
2976   } _oop_closure;
2977  public:
2978   VerifyKlassOopsKlassClosure(CMSBitMap* bitmap) : _oop_closure(bitmap) {}
2979   void do_klass(Klass* k) {
2980     k->oops_do(&_oop_closure);
2981   }
2982 };
2983 
2984 void CMSCollector::verify_after_remark_work_2() {
2985   ResourceMark rm;
2986   HandleMark  hm;
2987   GenCollectedHeap* gch = GenCollectedHeap::heap();
2988 
2989   // Get a clear set of claim bits for the strong roots processing to work with.
2990   ClassLoaderDataGraph::clear_claimed_marks();
2991 
2992   // Mark from roots one level into CMS
2993   MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
2994                                      markBitMap());
2995   CMKlassClosure klass_closure(&notOlder);
2996 
2997   gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2998   gch->gen_process_strong_roots(_cmsGen->level(),
2999                                 true,   // younger gens are roots
3000                                 true,   // activate StrongRootsScope
3001                                 false,  // not scavenging
3002                                 SharedHeap::ScanningOption(roots_scanning_options()),
3003                                 &notOlder,
3004                                 true,   // walk code active on stacks
3005                                 NULL,
3006                                 &klass_closure);
3007 
3008   // Now mark from the roots
3009   MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
3010     verification_mark_bm(), markBitMap(), verification_mark_stack());
3011   assert(_restart_addr == NULL, "Expected pre-condition");
3012   verification_mark_bm()->iterate(&markFromRootsClosure);
3013   while (_restart_addr != NULL) {
3014     // Deal with stack overflow: by restarting at the indicated
3015     // address.
3016     HeapWord* ra = _restart_addr;
3017     markFromRootsClosure.reset(ra);
3018     _restart_addr = NULL;
3019     verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
3020   }
3021   assert(verification_mark_stack()->isEmpty(), "Should have been drained");
3022   verify_work_stacks_empty();
3023 
3024   VerifyKlassOopsKlassClosure verify_klass_oops(verification_mark_bm());
3025   ClassLoaderDataGraph::classes_do(&verify_klass_oops);
3026 
3027   // Marking completed -- now verify that each bit marked in
3028   // verification_mark_bm() is also marked in markBitMap(); flag all
3029   // errors by printing corresponding objects.
3030   VerifyMarkedClosure vcl(markBitMap());
3031   verification_mark_bm()->iterate(&vcl);
3032   assert(!vcl.failed(), "Else verification above should not have succeeded");
3033 }
3034 
3035 void ConcurrentMarkSweepGeneration::save_marks() {
3036   // delegate to CMS space
3037   cmsSpace()->save_marks();
3038   for (uint i = 0; i < ParallelGCThreads; i++) {
3039     _par_gc_thread_states[i]->promo.startTrackingPromotions();
3040   }
3041 }
3042 
3043 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
3044   return cmsSpace()->no_allocs_since_save_marks();
3045 }
3046 
3047 #define CMS_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix)    \
3048                                                                 \
3049 void ConcurrentMarkSweepGeneration::                            \
3050 oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) {   \
3051   cl->set_generation(this);                                     \
3052   cmsSpace()->oop_since_save_marks_iterate##nv_suffix(cl);      \
3053   cl->reset_generation();                                       \
3054   save_marks();                                                 \
3055 }
3056 
3057 ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DEFN)
3058 
3059 void
3060 ConcurrentMarkSweepGeneration::object_iterate_since_last_GC(ObjectClosure* blk)
3061 {
3062   // Not currently implemented; need to do the following. -- ysr.
3063   // dld -- I think that is used for some sort of allocation profiler.  So it
3064   // really means the objects allocated by the mutator since the last
3065   // GC.  We could potentially implement this cheaply by recording only
3066   // the direct allocations in a side data structure.
3067   //
3068   // I think we probably ought not to be required to support these
3069   // iterations at any arbitrary point; I think there ought to be some
3070   // call to enable/disable allocation profiling in a generation/space,
3071   // and the iterator ought to return the objects allocated in the
3072   // gen/space since the enable call, or the last iterator call (which
3073   // will probably be at a GC.)  That way, for gens like CM&S that would
3074   // require some extra data structure to support this, we only pay the
3075   // cost when it's in use...
3076   cmsSpace()->object_iterate_since_last_GC(blk);
3077 }
3078 
3079 void
3080 ConcurrentMarkSweepGeneration::younger_refs_iterate(OopsInGenClosure* cl) {
3081   cl->set_generation(this);
3082   younger_refs_in_space_iterate(_cmsSpace, cl);
3083   cl->reset_generation();
3084 }
3085 
3086 void
3087 ConcurrentMarkSweepGeneration::oop_iterate(MemRegion mr, ExtendedOopClosure* cl) {
3088   if (freelistLock()->owned_by_self()) {
3089     Generation::oop_iterate(mr, cl);
3090   } else {
3091     MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3092     Generation::oop_iterate(mr, cl);
3093   }
3094 }
3095 
3096 void
3097 ConcurrentMarkSweepGeneration::oop_iterate(ExtendedOopClosure* cl) {
3098   if (freelistLock()->owned_by_self()) {
3099     Generation::oop_iterate(cl);
3100   } else {
3101     MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3102     Generation::oop_iterate(cl);
3103   }
3104 }
3105 
3106 void
3107 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
3108   if (freelistLock()->owned_by_self()) {
3109     Generation::object_iterate(cl);
3110   } else {
3111     MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3112     Generation::object_iterate(cl);
3113   }
3114 }
3115 
3116 void
3117 ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) {
3118   if (freelistLock()->owned_by_self()) {
3119     Generation::safe_object_iterate(cl);
3120   } else {
3121     MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3122     Generation::safe_object_iterate(cl);
3123   }
3124 }
3125 
3126 void
3127 ConcurrentMarkSweepGeneration::post_compact() {
3128 }
3129 
3130 void
3131 ConcurrentMarkSweepGeneration::prepare_for_verify() {
3132   // Fix the linear allocation blocks to look like free blocks.
3133 
3134   // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
3135   // are not called when the heap is verified during universe initialization and
3136   // at vm shutdown.
3137   if (freelistLock()->owned_by_self()) {
3138     cmsSpace()->prepare_for_verify();
3139   } else {
3140     MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
3141     cmsSpace()->prepare_for_verify();
3142   }
3143 }
3144 
3145 void
3146 ConcurrentMarkSweepGeneration::verify() {
3147   // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
3148   // are not called when the heap is verified during universe initialization and
3149   // at vm shutdown.
3150   if (freelistLock()->owned_by_self()) {
3151     cmsSpace()->verify();
3152   } else {
3153     MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
3154     cmsSpace()->verify();
3155   }
3156 }
3157 
3158 void CMSCollector::verify() {
3159   _cmsGen->verify();
3160 }
3161 
3162 #ifndef PRODUCT
3163 bool CMSCollector::overflow_list_is_empty() const {
3164   assert(_num_par_pushes >= 0, "Inconsistency");
3165   if (_overflow_list == NULL) {
3166     assert(_num_par_pushes == 0, "Inconsistency");
3167   }
3168   return _overflow_list == NULL;
3169 }
3170 
3171 // The methods verify_work_stacks_empty() and verify_overflow_empty()
3172 // merely consolidate assertion checks that appear to occur together frequently.
3173 void CMSCollector::verify_work_stacks_empty() const {
3174   assert(_markStack.isEmpty(), "Marking stack should be empty");
3175   assert(overflow_list_is_empty(), "Overflow list should be empty");
3176 }
3177 
3178 void CMSCollector::verify_overflow_empty() const {
3179   assert(overflow_list_is_empty(), "Overflow list should be empty");
3180   assert(no_preserved_marks(), "No preserved marks");
3181 }
3182 #endif // PRODUCT
3183 
3184 // Decide if we want to enable class unloading as part of the
3185 // ensuing concurrent GC cycle. We will collect and
3186 // unload classes if it's the case that:
3187 // (1) an explicit gc request has been made and the flag
3188 //     ExplicitGCInvokesConcurrentAndUnloadsClasses is set, OR
3189 // (2) (a) class unloading is enabled at the command line, and
3190 //     (b) old gen is getting really full
3191 // NOTE: Provided there is no change in the state of the heap between
3192 // calls to this method, it should have idempotent results. Moreover,
3193 // its results should be monotonically increasing (i.e. going from 0 to 1,
3194 // but not 1 to 0) between successive calls between which the heap was
3195 // not collected. For the implementation below, it must thus rely on
3196 // the property that concurrent_cycles_since_last_unload()
3197 // will not decrease unless a collection cycle happened and that
3198 // _cmsGen->is_too_full() are
3199 // themselves also monotonic in that sense. See check_monotonicity()
3200 // below.
3201 void CMSCollector::update_should_unload_classes() {
3202   _should_unload_classes = false;
3203   // Condition 1 above
3204   if (_full_gc_requested && ExplicitGCInvokesConcurrentAndUnloadsClasses) {
3205     _should_unload_classes = true;
3206   } else if (CMSClassUnloadingEnabled) { // Condition 2.a above
3207     // Disjuncts 2.b.(i,ii,iii) above
3208     _should_unload_classes = (concurrent_cycles_since_last_unload() >=
3209                               CMSClassUnloadingMaxInterval)
3210                            || _cmsGen->is_too_full();
3211   }
3212 }
3213 
3214 bool ConcurrentMarkSweepGeneration::is_too_full() const {
3215   bool res = should_concurrent_collect();
3216   res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
3217   return res;
3218 }
3219 
3220 void CMSCollector::setup_cms_unloading_and_verification_state() {
3221   const  bool should_verify =   VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
3222                              || VerifyBeforeExit;
3223   const  int  rso           =   SharedHeap::SO_Strings | SharedHeap::SO_CodeCache;
3224 
3225   if (should_unload_classes()) {   // Should unload classes this cycle
3226     remove_root_scanning_option(rso);  // Shrink the root set appropriately
3227     set_verifying(should_verify);    // Set verification state for this cycle
3228     return;                            // Nothing else needs to be done at this time
3229   }
3230 
3231   // Not unloading classes this cycle
3232   assert(!should_unload_classes(), "Inconsitency!");
3233   if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
3234     // Include symbols, strings and code cache elements to prevent their resurrection.
3235     add_root_scanning_option(rso);
3236     set_verifying(true);
3237   } else if (verifying() && !should_verify) {
3238     // We were verifying, but some verification flags got disabled.
3239     set_verifying(false);
3240     // Exclude symbols, strings and code cache elements from root scanning to
3241     // reduce IM and RM pauses.
3242     remove_root_scanning_option(rso);
3243   }
3244 }
3245 
3246 
3247 #ifndef PRODUCT
3248 HeapWord* CMSCollector::block_start(const void* p) const {
3249   const HeapWord* addr = (HeapWord*)p;
3250   if (_span.contains(p)) {
3251     if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
3252       return _cmsGen->cmsSpace()->block_start(p);
3253     }
3254   }
3255   return NULL;
3256 }
3257 #endif
3258 
3259 HeapWord*
3260 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
3261                                                    bool   tlab,
3262                                                    bool   parallel) {
3263   CMSSynchronousYieldRequest yr;
3264   assert(!tlab, "Can't deal with TLAB allocation");
3265   MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3266   expand(word_size*HeapWordSize, MinHeapDeltaBytes,
3267     CMSExpansionCause::_satisfy_allocation);
3268   if (GCExpandToAllocateDelayMillis > 0) {
3269     os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3270   }
3271   return have_lock_and_allocate(word_size, tlab);
3272 }
3273 
3274 // YSR: All of this generation expansion/shrinking stuff is an exact copy of
3275 // OneContigSpaceCardGeneration, which makes me wonder if we should move this
3276 // to CardGeneration and share it...
3277 bool ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes) {
3278   return CardGeneration::expand(bytes, expand_bytes);
3279 }
3280 
3281 void ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes,
3282   CMSExpansionCause::Cause cause)
3283 {
3284 
3285   bool success = expand(bytes, expand_bytes);
3286 
3287   // remember why we expanded; this information is used
3288   // by shouldConcurrentCollect() when making decisions on whether to start
3289   // a new CMS cycle.
3290   if (success) {
3291     set_expansion_cause(cause);
3292     if (PrintGCDetails && Verbose) {
3293       gclog_or_tty->print_cr("Expanded CMS gen for %s",
3294         CMSExpansionCause::to_string(cause));
3295     }
3296   }
3297 }
3298 
3299 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
3300   HeapWord* res = NULL;
3301   MutexLocker x(ParGCRareEvent_lock);
3302   while (true) {
3303     // Expansion by some other thread might make alloc OK now:
3304     res = ps->lab.alloc(word_sz);
3305     if (res != NULL) return res;
3306     // If there's not enough expansion space available, give up.
3307     if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
3308       return NULL;
3309     }
3310     // Otherwise, we try expansion.
3311     expand(word_sz*HeapWordSize, MinHeapDeltaBytes,
3312       CMSExpansionCause::_allocate_par_lab);
3313     // Now go around the loop and try alloc again;
3314     // A competing par_promote might beat us to the expansion space,
3315     // so we may go around the loop again if promotion fails agaion.
3316     if (GCExpandToAllocateDelayMillis > 0) {
3317       os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3318     }
3319   }
3320 }
3321 
3322 
3323 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
3324   PromotionInfo* promo) {
3325   MutexLocker x(ParGCRareEvent_lock);
3326   size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
3327   while (true) {
3328     // Expansion by some other thread might make alloc OK now:
3329     if (promo->ensure_spooling_space()) {
3330       assert(promo->has_spooling_space(),
3331              "Post-condition of successful ensure_spooling_space()");
3332       return true;
3333     }
3334     // If there's not enough expansion space available, give up.
3335     if (_virtual_space.uncommitted_size() < refill_size_bytes) {
3336       return false;
3337     }
3338     // Otherwise, we try expansion.
3339     expand(refill_size_bytes, MinHeapDeltaBytes,
3340       CMSExpansionCause::_allocate_par_spooling_space);
3341     // Now go around the loop and try alloc again;
3342     // A competing allocation might beat us to the expansion space,
3343     // so we may go around the loop again if allocation fails again.
3344     if (GCExpandToAllocateDelayMillis > 0) {
3345       os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3346     }
3347   }
3348 }
3349 
3350 
3351 void ConcurrentMarkSweepGeneration::shrink_by(size_t bytes) {
3352   assert_locked_or_safepoint(ExpandHeap_lock);
3353   // Shrink committed space
3354   _virtual_space.shrink_by(bytes);
3355   // Shrink space; this also shrinks the space's BOT
3356   _cmsSpace->set_end((HeapWord*) _virtual_space.high());
3357   size_t new_word_size = heap_word_size(_cmsSpace->capacity());
3358   // Shrink the shared block offset array
3359   _bts->resize(new_word_size);
3360   MemRegion mr(_cmsSpace->bottom(), new_word_size);
3361   // Shrink the card table
3362   Universe::heap()->barrier_set()->resize_covered_region(mr);
3363 
3364   if (Verbose && PrintGC) {
3365     size_t new_mem_size = _virtual_space.committed_size();
3366     size_t old_mem_size = new_mem_size + bytes;
3367     gclog_or_tty->print_cr("Shrinking %s from " SIZE_FORMAT "K to " SIZE_FORMAT "K",
3368                   name(), old_mem_size/K, new_mem_size/K);
3369   }
3370 }
3371 
3372 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
3373   assert_locked_or_safepoint(Heap_lock);
3374   size_t size = ReservedSpace::page_align_size_down(bytes);
3375   if (size > 0) {
3376     shrink_by(size);
3377   }
3378 }
3379 
3380 bool ConcurrentMarkSweepGeneration::grow_by(size_t bytes) {
3381   assert_locked_or_safepoint(Heap_lock);
3382   bool result = _virtual_space.expand_by(bytes);
3383   if (result) {
3384     HeapWord* old_end = _cmsSpace->end();
3385     size_t new_word_size =
3386       heap_word_size(_virtual_space.committed_size());
3387     MemRegion mr(_cmsSpace->bottom(), new_word_size);
3388     _bts->resize(new_word_size);  // resize the block offset shared array
3389     Universe::heap()->barrier_set()->resize_covered_region(mr);
3390     // Hmmmm... why doesn't CFLS::set_end verify locking?
3391     // This is quite ugly; FIX ME XXX
3392     _cmsSpace->assert_locked(freelistLock());
3393     _cmsSpace->set_end((HeapWord*)_virtual_space.high());
3394 
3395     // update the space and generation capacity counters
3396     if (UsePerfData) {
3397       _space_counters->update_capacity();
3398       _gen_counters->update_all();
3399     }
3400 
3401     if (Verbose && PrintGC) {
3402       size_t new_mem_size = _virtual_space.committed_size();
3403       size_t old_mem_size = new_mem_size - bytes;
3404       gclog_or_tty->print_cr("Expanding %s from " SIZE_FORMAT "K by " SIZE_FORMAT "K to " SIZE_FORMAT "K",
3405                     name(), old_mem_size/K, bytes/K, new_mem_size/K);
3406     }
3407   }
3408   return result;
3409 }
3410 
3411 bool ConcurrentMarkSweepGeneration::grow_to_reserved() {
3412   assert_locked_or_safepoint(Heap_lock);
3413   bool success = true;
3414   const size_t remaining_bytes = _virtual_space.uncommitted_size();
3415   if (remaining_bytes > 0) {
3416     success = grow_by(remaining_bytes);
3417     DEBUG_ONLY(if (!success) warning("grow to reserved failed");)
3418   }
3419   return success;
3420 }
3421 
3422 void ConcurrentMarkSweepGeneration::shrink_free_list_by(size_t bytes) {
3423   assert_locked_or_safepoint(Heap_lock);
3424   assert_lock_strong(freelistLock());
3425   if (PrintGCDetails && Verbose) {
3426     warning("Shrinking of CMS not yet implemented");
3427   }
3428   return;
3429 }
3430 
3431 
3432 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
3433 // phases.
3434 class CMSPhaseAccounting: public StackObj {
3435  public:
3436   CMSPhaseAccounting(CMSCollector *collector,
3437                      const char *phase,
3438                      bool print_cr = true);
3439   ~CMSPhaseAccounting();
3440 
3441  private:
3442   CMSCollector *_collector;
3443   const char *_phase;
3444   elapsedTimer _wallclock;
3445   bool _print_cr;
3446 
3447  public:
3448   // Not MT-safe; so do not pass around these StackObj's
3449   // where they may be accessed by other threads.
3450   jlong wallclock_millis() {
3451     assert(_wallclock.is_active(), "Wall clock should not stop");
3452     _wallclock.stop();  // to record time
3453     jlong ret = _wallclock.milliseconds();
3454     _wallclock.start(); // restart
3455     return ret;
3456   }
3457 };
3458 
3459 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
3460                                        const char *phase,
3461                                        bool print_cr) :
3462   _collector(collector), _phase(phase), _print_cr(print_cr) {
3463 
3464   if (PrintCMSStatistics != 0) {
3465     _collector->resetYields();
3466   }
3467   if (PrintGCDetails) {
3468     gclog_or_tty->date_stamp(PrintGCDateStamps);
3469     gclog_or_tty->stamp(PrintGCTimeStamps);
3470     gclog_or_tty->print_cr("[%s-concurrent-%s-start]",
3471       _collector->cmsGen()->short_name(), _phase);
3472   }
3473   _collector->resetTimer();
3474   _wallclock.start();
3475   _collector->startTimer();
3476 }
3477 
3478 CMSPhaseAccounting::~CMSPhaseAccounting() {
3479   assert(_wallclock.is_active(), "Wall clock should not have stopped");
3480   _collector->stopTimer();
3481   _wallclock.stop();
3482   if (PrintGCDetails) {
3483     gclog_or_tty->date_stamp(PrintGCDateStamps);
3484     gclog_or_tty->stamp(PrintGCTimeStamps);
3485     gclog_or_tty->print("[%s-concurrent-%s: %3.3f/%3.3f secs]",
3486                  _collector->cmsGen()->short_name(),
3487                  _phase, _collector->timerValue(), _wallclock.seconds());
3488     if (_print_cr) {
3489       gclog_or_tty->print_cr("");
3490     }
3491     if (PrintCMSStatistics != 0) {
3492       gclog_or_tty->print_cr(" (CMS-concurrent-%s yielded %d times)", _phase,
3493                     _collector->yields());
3494     }
3495   }
3496 }
3497 
3498 // CMS work
3499 


























3500 // Checkpoint the roots into this generation from outside
3501 // this generation. [Note this initial checkpoint need only
3502 // be approximate -- we'll do a catch up phase subsequently.]
3503 void CMSCollector::checkpointRootsInitial(bool asynch) {
3504   assert(_collectorState == InitialMarking, "Wrong collector state");
3505   check_correct_thread_executing();
3506   TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
3507 
3508   ReferenceProcessor* rp = ref_processor();
3509   SpecializationStats::clear();
3510   assert(_restart_addr == NULL, "Control point invariant");
3511   if (asynch) {
3512     // acquire locks for subsequent manipulations
3513     MutexLockerEx x(bitMapLock(),
3514                     Mutex::_no_safepoint_check_flag);
3515     checkpointRootsInitialWork(asynch);
3516     // enable ("weak") refs discovery
3517     rp->enable_discovery(true /*verify_disabled*/, true /*check_no_refs*/);
3518     _collectorState = Marking;
3519   } else {
3520     // (Weak) Refs discovery: this is controlled from genCollectedHeap::do_collection
3521     // which recognizes if we are a CMS generation, and doesn't try to turn on
3522     // discovery; verify that they aren't meddling.
3523     assert(!rp->discovery_is_atomic(),
3524            "incorrect setting of discovery predicate");
3525     assert(!rp->discovery_enabled(), "genCollectedHeap shouldn't control "
3526            "ref discovery for this generation kind");
3527     // already have locks
3528     checkpointRootsInitialWork(asynch);
3529     // now enable ("weak") refs discovery
3530     rp->enable_discovery(true /*verify_disabled*/, false /*verify_no_refs*/);
3531     _collectorState = Marking;
3532   }
3533   SpecializationStats::print();
3534 }
3535 
3536 void CMSCollector::checkpointRootsInitialWork(bool asynch) {
3537   assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
3538   assert(_collectorState == InitialMarking, "just checking");
3539 
3540   // If there has not been a GC[n-1] since last GC[n] cycle completed,
3541   // precede our marking with a collection of all
3542   // younger generations to keep floating garbage to a minimum.
3543   // XXX: we won't do this for now -- it's an optimization to be done later.
3544 
3545   // already have locks
3546   assert_lock_strong(bitMapLock());
3547   assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
3548 
3549   // Setup the verification and class unloading state for this
3550   // CMS collection cycle.
3551   setup_cms_unloading_and_verification_state();
3552 
3553   NOT_PRODUCT(TraceTime t("\ncheckpointRootsInitialWork",
3554     PrintGCDetails && Verbose, true, gclog_or_tty);)
3555   if (UseAdaptiveSizePolicy) {
3556     size_policy()->checkpoint_roots_initial_begin();
3557   }
3558 
3559   // Reset all the PLAB chunk arrays if necessary.
3560   if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
3561     reset_survivor_plab_arrays();
3562   }
3563 
3564   ResourceMark rm;
3565   HandleMark  hm;
3566 
3567   FalseClosure falseClosure;
3568   // In the case of a synchronous collection, we will elide the
3569   // remark step, so it's important to catch all the nmethod oops
3570   // in this step.
3571   // The final 'true' flag to gen_process_strong_roots will ensure this.
3572   // If 'async' is true, we can relax the nmethod tracing.
3573   MarkRefsIntoClosure notOlder(_span, &_markBitMap);
3574   GenCollectedHeap* gch = GenCollectedHeap::heap();
3575 
3576   verify_work_stacks_empty();
3577   verify_overflow_empty();
3578 
3579   gch->ensure_parsability(false);  // fill TLABs, but no need to retire them
3580   // Update the saved marks which may affect the root scans.
3581   gch->save_marks();
3582 
3583   // weak reference processing has not started yet.
3584   ref_processor()->set_enqueuing_is_done(false);
3585 
3586   // Need to remember all newly created CLDs,
3587   // so that we can guarantee that the remark finds them.
3588   ClassLoaderDataGraph::remember_new_clds(true);
3589 
3590   // Whenever a CLD is found, it will be claimed before proceeding to mark
3591   // the klasses. The claimed marks need to be cleared before marking starts.
3592   ClassLoaderDataGraph::clear_claimed_marks();
3593 
3594   CMKlassClosure klass_closure(&notOlder);
3595   {
3596     COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)



















3597     gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3598     gch->gen_process_strong_roots(_cmsGen->level(),
3599                                   true,   // younger gens are roots
3600                                   true,   // activate StrongRootsScope
3601                                   false,  // not scavenging
3602                                   SharedHeap::ScanningOption(roots_scanning_options()),
3603                                   &notOlder,
3604                                   true,   // walk all of code cache if (so & SO_CodeCache)
3605                                   NULL,
3606                                   &klass_closure);
3607   }

3608 
3609   // Clear mod-union table; it will be dirtied in the prologue of
3610   // CMS generation per each younger generation collection.
3611 
3612   assert(_modUnionTable.isAllClear(),
3613        "Was cleared in most recent final checkpoint phase"
3614        " or no bits are set in the gc_prologue before the start of the next "
3615        "subsequent marking phase.");
3616 
3617   assert(_ct->klass_rem_set()->mod_union_is_clear(), "Must be");
3618 
3619   // Save the end of the used_region of the constituent generations
3620   // to be used to limit the extent of sweep in each generation.
3621   save_sweep_limits();
3622   if (UseAdaptiveSizePolicy) {
3623     size_policy()->checkpoint_roots_initial_end(gch->gc_cause());
3624   }
3625   verify_overflow_empty();
3626 }
3627 
3628 bool CMSCollector::markFromRoots(bool asynch) {
3629   // we might be tempted to assert that:
3630   // assert(asynch == !SafepointSynchronize::is_at_safepoint(),
3631   //        "inconsistent argument?");
3632   // However that wouldn't be right, because it's possible that
3633   // a safepoint is indeed in progress as a younger generation
3634   // stop-the-world GC happens even as we mark in this generation.
3635   assert(_collectorState == Marking, "inconsistent state?");
3636   check_correct_thread_executing();
3637   verify_overflow_empty();
3638 
3639   bool res;
3640   if (asynch) {
3641 
3642     // Start the timers for adaptive size policy for the concurrent phases
3643     // Do it here so that the foreground MS can use the concurrent
3644     // timer since a foreground MS might has the sweep done concurrently
3645     // or STW.
3646     if (UseAdaptiveSizePolicy) {
3647       size_policy()->concurrent_marking_begin();
3648     }
3649 
3650     // Weak ref discovery note: We may be discovering weak
3651     // refs in this generation concurrent (but interleaved) with
3652     // weak ref discovery by a younger generation collector.
3653 
3654     CMSTokenSyncWithLocks ts(true, bitMapLock());
3655     TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3656     CMSPhaseAccounting pa(this, "mark", !PrintGCDetails);
3657     res = markFromRootsWork(asynch);
3658     if (res) {
3659       _collectorState = Precleaning;
3660     } else { // We failed and a foreground collection wants to take over
3661       assert(_foregroundGCIsActive, "internal state inconsistency");
3662       assert(_restart_addr == NULL,  "foreground will restart from scratch");
3663       if (PrintGCDetails) {
3664         gclog_or_tty->print_cr("bailing out to foreground collection");
3665       }
3666     }
3667     if (UseAdaptiveSizePolicy) {
3668       size_policy()->concurrent_marking_end();
3669     }
3670   } else {
3671     assert(SafepointSynchronize::is_at_safepoint(),
3672            "inconsistent with asynch == false");
3673     if (UseAdaptiveSizePolicy) {
3674       size_policy()->ms_collection_marking_begin();
3675     }
3676     // already have locks
3677     res = markFromRootsWork(asynch);
3678     _collectorState = FinalMarking;
3679     if (UseAdaptiveSizePolicy) {
3680       GenCollectedHeap* gch = GenCollectedHeap::heap();
3681       size_policy()->ms_collection_marking_end(gch->gc_cause());
3682     }
3683   }
3684   verify_overflow_empty();
3685   return res;
3686 }
3687 
3688 bool CMSCollector::markFromRootsWork(bool asynch) {
3689   // iterate over marked bits in bit map, doing a full scan and mark
3690   // from these roots using the following algorithm:
3691   // . if oop is to the right of the current scan pointer,
3692   //   mark corresponding bit (we'll process it later)
3693   // . else (oop is to left of current scan pointer)
3694   //   push oop on marking stack
3695   // . drain the marking stack
3696 
3697   // Note that when we do a marking step we need to hold the
3698   // bit map lock -- recall that direct allocation (by mutators)
3699   // and promotion (by younger generation collectors) is also
3700   // marking the bit map. [the so-called allocate live policy.]
3701   // Because the implementation of bit map marking is not
3702   // robust wrt simultaneous marking of bits in the same word,
3703   // we need to make sure that there is no such interference
3704   // between concurrent such updates.
3705 
3706   // already have locks
3707   assert_lock_strong(bitMapLock());
3708 
3709   verify_work_stacks_empty();
3710   verify_overflow_empty();
3711   bool result = false;
3712   if (CMSConcurrentMTEnabled && ConcGCThreads > 0) {
3713     result = do_marking_mt(asynch);
3714   } else {
3715     result = do_marking_st(asynch);
3716   }
3717   return result;
3718 }
3719 
3720 // Forward decl
3721 class CMSConcMarkingTask;
3722 
3723 class CMSConcMarkingTerminator: public ParallelTaskTerminator {
3724   CMSCollector*       _collector;
3725   CMSConcMarkingTask* _task;
3726  public:
3727   virtual void yield();
3728 
3729   // "n_threads" is the number of threads to be terminated.
3730   // "queue_set" is a set of work queues of other threads.
3731   // "collector" is the CMS collector associated with this task terminator.
3732   // "yield" indicates whether we need the gang as a whole to yield.
3733   CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
3734     ParallelTaskTerminator(n_threads, queue_set),
3735     _collector(collector) { }
3736 
3737   void set_task(CMSConcMarkingTask* task) {
3738     _task = task;
3739   }
3740 };
3741 
3742 class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator {
3743   CMSConcMarkingTask* _task;
3744  public:
3745   bool should_exit_termination();
3746   void set_task(CMSConcMarkingTask* task) {
3747     _task = task;
3748   }
3749 };
3750 
3751 // MT Concurrent Marking Task
3752 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3753   CMSCollector* _collector;
3754   int           _n_workers;                  // requested/desired # workers
3755   bool          _asynch;
3756   bool          _result;
3757   CompactibleFreeListSpace*  _cms_space;
3758   char          _pad_front[64];   // padding to ...
3759   HeapWord*     _global_finger;   // ... avoid sharing cache line
3760   char          _pad_back[64];
3761   HeapWord*     _restart_addr;
3762 
3763   //  Exposed here for yielding support
3764   Mutex* const _bit_map_lock;
3765 
3766   // The per thread work queues, available here for stealing
3767   OopTaskQueueSet*  _task_queues;
3768 
3769   // Termination (and yielding) support
3770   CMSConcMarkingTerminator _term;
3771   CMSConcMarkingTerminatorTerminator _term_term;
3772 
3773  public:
3774   CMSConcMarkingTask(CMSCollector* collector,
3775                  CompactibleFreeListSpace* cms_space,
3776                  bool asynch,
3777                  YieldingFlexibleWorkGang* workers,
3778                  OopTaskQueueSet* task_queues):
3779     YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3780     _collector(collector),
3781     _cms_space(cms_space),
3782     _asynch(asynch), _n_workers(0), _result(true),
3783     _task_queues(task_queues),
3784     _term(_n_workers, task_queues, _collector),
3785     _bit_map_lock(collector->bitMapLock())
3786   {
3787     _requested_size = _n_workers;
3788     _term.set_task(this);
3789     _term_term.set_task(this);
3790     _restart_addr = _global_finger = _cms_space->bottom();
3791   }
3792 
3793 
3794   OopTaskQueueSet* task_queues()  { return _task_queues; }
3795 
3796   OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3797 
3798   HeapWord** global_finger_addr() { return &_global_finger; }
3799 
3800   CMSConcMarkingTerminator* terminator() { return &_term; }
3801 
3802   virtual void set_for_termination(int active_workers) {
3803     terminator()->reset_for_reuse(active_workers);
3804   }
3805 
3806   void work(uint worker_id);
3807   bool should_yield() {
3808     return    ConcurrentMarkSweepThread::should_yield()
3809            && !_collector->foregroundGCIsActive()
3810            && _asynch;
3811   }
3812 
3813   virtual void coordinator_yield();  // stuff done by coordinator
3814   bool result() { return _result; }
3815 
3816   void reset(HeapWord* ra) {
3817     assert(_global_finger >= _cms_space->end(),  "Postcondition of ::work(i)");
3818     _restart_addr = _global_finger = ra;
3819     _term.reset_for_reuse();
3820   }
3821 
3822   static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3823                                            OopTaskQueue* work_q);
3824 
3825  private:
3826   void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3827   void do_work_steal(int i);
3828   void bump_global_finger(HeapWord* f);
3829 };
3830 
3831 bool CMSConcMarkingTerminatorTerminator::should_exit_termination() {
3832   assert(_task != NULL, "Error");
3833   return _task->yielding();
3834   // Note that we do not need the disjunct || _task->should_yield() above
3835   // because we want terminating threads to yield only if the task
3836   // is already in the midst of yielding, which happens only after at least one
3837   // thread has yielded.
3838 }
3839 
3840 void CMSConcMarkingTerminator::yield() {
3841   if (_task->should_yield()) {
3842     _task->yield();
3843   } else {
3844     ParallelTaskTerminator::yield();
3845   }
3846 }
3847 
3848 ////////////////////////////////////////////////////////////////
3849 // Concurrent Marking Algorithm Sketch
3850 ////////////////////////////////////////////////////////////////
3851 // Until all tasks exhausted (both spaces):
3852 // -- claim next available chunk
3853 // -- bump global finger via CAS
3854 // -- find first object that starts in this chunk
3855 //    and start scanning bitmap from that position
3856 // -- scan marked objects for oops
3857 // -- CAS-mark target, and if successful:
3858 //    . if target oop is above global finger (volatile read)
3859 //      nothing to do
3860 //    . if target oop is in chunk and above local finger
3861 //        then nothing to do
3862 //    . else push on work-queue
3863 // -- Deal with possible overflow issues:
3864 //    . local work-queue overflow causes stuff to be pushed on
3865 //      global (common) overflow queue
3866 //    . always first empty local work queue
3867 //    . then get a batch of oops from global work queue if any
3868 //    . then do work stealing
3869 // -- When all tasks claimed (both spaces)
3870 //    and local work queue empty,
3871 //    then in a loop do:
3872 //    . check global overflow stack; steal a batch of oops and trace
3873 //    . try to steal from other threads oif GOS is empty
3874 //    . if neither is available, offer termination
3875 // -- Terminate and return result
3876 //
3877 void CMSConcMarkingTask::work(uint worker_id) {
3878   elapsedTimer _timer;
3879   ResourceMark rm;
3880   HandleMark hm;
3881 
3882   DEBUG_ONLY(_collector->verify_overflow_empty();)
3883 
3884   // Before we begin work, our work queue should be empty
3885   assert(work_queue(worker_id)->size() == 0, "Expected to be empty");
3886   // Scan the bitmap covering _cms_space, tracing through grey objects.
3887   _timer.start();
3888   do_scan_and_mark(worker_id, _cms_space);
3889   _timer.stop();
3890   if (PrintCMSStatistics != 0) {
3891     gclog_or_tty->print_cr("Finished cms space scanning in %dth thread: %3.3f sec",
3892       worker_id, _timer.seconds());
3893       // XXX: need xxx/xxx type of notation, two timers
3894   }
3895 
3896   // ... do work stealing
3897   _timer.reset();
3898   _timer.start();
3899   do_work_steal(worker_id);
3900   _timer.stop();
3901   if (PrintCMSStatistics != 0) {
3902     gclog_or_tty->print_cr("Finished work stealing in %dth thread: %3.3f sec",
3903       worker_id, _timer.seconds());
3904       // XXX: need xxx/xxx type of notation, two timers
3905   }
3906   assert(_collector->_markStack.isEmpty(), "Should have been emptied");
3907   assert(work_queue(worker_id)->size() == 0, "Should have been emptied");
3908   // Note that under the current task protocol, the
3909   // following assertion is true even of the spaces
3910   // expanded since the completion of the concurrent
3911   // marking. XXX This will likely change under a strict
3912   // ABORT semantics.
3913   // After perm removal the comparison was changed to
3914   // greater than or equal to from strictly greater than.
3915   // Before perm removal the highest address sweep would
3916   // have been at the end of perm gen but now is at the
3917   // end of the tenured gen.
3918   assert(_global_finger >=  _cms_space->end(),
3919          "All tasks have been completed");
3920   DEBUG_ONLY(_collector->verify_overflow_empty();)
3921 }
3922 
3923 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
3924   HeapWord* read = _global_finger;
3925   HeapWord* cur  = read;
3926   while (f > read) {
3927     cur = read;
3928     read = (HeapWord*) Atomic::cmpxchg_ptr(f, &_global_finger, cur);
3929     if (cur == read) {
3930       // our cas succeeded
3931       assert(_global_finger >= f, "protocol consistency");
3932       break;
3933     }
3934   }
3935 }
3936 
3937 // This is really inefficient, and should be redone by
3938 // using (not yet available) block-read and -write interfaces to the
3939 // stack and the work_queue. XXX FIX ME !!!
3940 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3941                                                       OopTaskQueue* work_q) {
3942   // Fast lock-free check
3943   if (ovflw_stk->length() == 0) {
3944     return false;
3945   }
3946   assert(work_q->size() == 0, "Shouldn't steal");
3947   MutexLockerEx ml(ovflw_stk->par_lock(),
3948                    Mutex::_no_safepoint_check_flag);
3949   // Grab up to 1/4 the size of the work queue
3950   size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
3951                     (size_t)ParGCDesiredObjsFromOverflowList);
3952   num = MIN2(num, ovflw_stk->length());
3953   for (int i = (int) num; i > 0; i--) {
3954     oop cur = ovflw_stk->pop();
3955     assert(cur != NULL, "Counted wrong?");
3956     work_q->push(cur);
3957   }
3958   return num > 0;
3959 }
3960 
3961 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
3962   SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
3963   int n_tasks = pst->n_tasks();
3964   // We allow that there may be no tasks to do here because
3965   // we are restarting after a stack overflow.
3966   assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
3967   uint nth_task = 0;
3968 
3969   HeapWord* aligned_start = sp->bottom();
3970   if (sp->used_region().contains(_restart_addr)) {
3971     // Align down to a card boundary for the start of 0th task
3972     // for this space.
3973     aligned_start =
3974       (HeapWord*)align_size_down((uintptr_t)_restart_addr,
3975                                  CardTableModRefBS::card_size);
3976   }
3977 
3978   size_t chunk_size = sp->marking_task_size();
3979   while (!pst->is_task_claimed(/* reference */ nth_task)) {
3980     // Having claimed the nth task in this space,
3981     // compute the chunk that it corresponds to:
3982     MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
3983                                aligned_start + (nth_task+1)*chunk_size);
3984     // Try and bump the global finger via a CAS;
3985     // note that we need to do the global finger bump
3986     // _before_ taking the intersection below, because
3987     // the task corresponding to that region will be
3988     // deemed done even if the used_region() expands
3989     // because of allocation -- as it almost certainly will
3990     // during start-up while the threads yield in the
3991     // closure below.
3992     HeapWord* finger = span.end();
3993     bump_global_finger(finger);   // atomically
3994     // There are null tasks here corresponding to chunks
3995     // beyond the "top" address of the space.
3996     span = span.intersection(sp->used_region());
3997     if (!span.is_empty()) {  // Non-null task
3998       HeapWord* prev_obj;
3999       assert(!span.contains(_restart_addr) || nth_task == 0,
4000              "Inconsistency");
4001       if (nth_task == 0) {
4002         // For the 0th task, we'll not need to compute a block_start.
4003         if (span.contains(_restart_addr)) {
4004           // In the case of a restart because of stack overflow,
4005           // we might additionally skip a chunk prefix.
4006           prev_obj = _restart_addr;
4007         } else {
4008           prev_obj = span.start();
4009         }
4010       } else {
4011         // We want to skip the first object because
4012         // the protocol is to scan any object in its entirety
4013         // that _starts_ in this span; a fortiori, any
4014         // object starting in an earlier span is scanned
4015         // as part of an earlier claimed task.
4016         // Below we use the "careful" version of block_start
4017         // so we do not try to navigate uninitialized objects.
4018         prev_obj = sp->block_start_careful(span.start());
4019         // Below we use a variant of block_size that uses the
4020         // Printezis bits to avoid waiting for allocated
4021         // objects to become initialized/parsable.
4022         while (prev_obj < span.start()) {
4023           size_t sz = sp->block_size_no_stall(prev_obj, _collector);
4024           if (sz > 0) {
4025             prev_obj += sz;
4026           } else {
4027             // In this case we may end up doing a bit of redundant
4028             // scanning, but that appears unavoidable, short of
4029             // locking the free list locks; see bug 6324141.
4030             break;
4031           }
4032         }
4033       }
4034       if (prev_obj < span.end()) {
4035         MemRegion my_span = MemRegion(prev_obj, span.end());
4036         // Do the marking work within a non-empty span --
4037         // the last argument to the constructor indicates whether the
4038         // iteration should be incremental with periodic yields.
4039         Par_MarkFromRootsClosure cl(this, _collector, my_span,
4040                                     &_collector->_markBitMap,
4041                                     work_queue(i),
4042                                     &_collector->_markStack,
4043                                     _asynch);
4044         _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
4045       } // else nothing to do for this task
4046     }   // else nothing to do for this task
4047   }
4048   // We'd be tempted to assert here that since there are no
4049   // more tasks left to claim in this space, the global_finger
4050   // must exceed space->top() and a fortiori space->end(). However,
4051   // that would not quite be correct because the bumping of
4052   // global_finger occurs strictly after the claiming of a task,
4053   // so by the time we reach here the global finger may not yet
4054   // have been bumped up by the thread that claimed the last
4055   // task.
4056   pst->all_tasks_completed();
4057 }
4058 
4059 class Par_ConcMarkingClosure: public CMSOopClosure {
4060  private:
4061   CMSCollector* _collector;
4062   CMSConcMarkingTask* _task;
4063   MemRegion     _span;
4064   CMSBitMap*    _bit_map;
4065   CMSMarkStack* _overflow_stack;
4066   OopTaskQueue* _work_queue;
4067  protected:
4068   DO_OOP_WORK_DEFN
4069  public:
4070   Par_ConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue,
4071                          CMSBitMap* bit_map, CMSMarkStack* overflow_stack):
4072     CMSOopClosure(collector->ref_processor()),
4073     _collector(collector),
4074     _task(task),
4075     _span(collector->_span),
4076     _work_queue(work_queue),
4077     _bit_map(bit_map),
4078     _overflow_stack(overflow_stack)
4079   { }
4080   virtual void do_oop(oop* p);
4081   virtual void do_oop(narrowOop* p);
4082 
4083   void trim_queue(size_t max);
4084   void handle_stack_overflow(HeapWord* lost);
4085   void do_yield_check() {
4086     if (_task->should_yield()) {
4087       _task->yield();
4088     }
4089   }
4090 };
4091 
4092 // Grey object scanning during work stealing phase --
4093 // the salient assumption here is that any references
4094 // that are in these stolen objects being scanned must
4095 // already have been initialized (else they would not have
4096 // been published), so we do not need to check for
4097 // uninitialized objects before pushing here.
4098 void Par_ConcMarkingClosure::do_oop(oop obj) {
4099   assert(obj->is_oop_or_null(true), "expected an oop or NULL");
4100   HeapWord* addr = (HeapWord*)obj;
4101   // Check if oop points into the CMS generation
4102   // and is not marked
4103   if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
4104     // a white object ...
4105     // If we manage to "claim" the object, by being the
4106     // first thread to mark it, then we push it on our
4107     // marking stack
4108     if (_bit_map->par_mark(addr)) {     // ... now grey
4109       // push on work queue (grey set)
4110       bool simulate_overflow = false;
4111       NOT_PRODUCT(
4112         if (CMSMarkStackOverflowALot &&
4113             _collector->simulate_overflow()) {
4114           // simulate a stack overflow
4115           simulate_overflow = true;
4116         }
4117       )
4118       if (simulate_overflow ||
4119           !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
4120         // stack overflow
4121         if (PrintCMSStatistics != 0) {
4122           gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
4123                                  SIZE_FORMAT, _overflow_stack->capacity());
4124         }
4125         // We cannot assert that the overflow stack is full because
4126         // it may have been emptied since.
4127         assert(simulate_overflow ||
4128                _work_queue->size() == _work_queue->max_elems(),
4129               "Else push should have succeeded");
4130         handle_stack_overflow(addr);
4131       }
4132     } // Else, some other thread got there first
4133     do_yield_check();
4134   }
4135 }
4136 
4137 void Par_ConcMarkingClosure::do_oop(oop* p)       { Par_ConcMarkingClosure::do_oop_work(p); }
4138 void Par_ConcMarkingClosure::do_oop(narrowOop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
4139 
4140 void Par_ConcMarkingClosure::trim_queue(size_t max) {
4141   while (_work_queue->size() > max) {
4142     oop new_oop;
4143     if (_work_queue->pop_local(new_oop)) {
4144       assert(new_oop->is_oop(), "Should be an oop");
4145       assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
4146       assert(_span.contains((HeapWord*)new_oop), "Not in span");
4147       new_oop->oop_iterate(this);  // do_oop() above
4148       do_yield_check();
4149     }
4150   }
4151 }
4152 
4153 // Upon stack overflow, we discard (part of) the stack,
4154 // remembering the least address amongst those discarded
4155 // in CMSCollector's _restart_address.
4156 void Par_ConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
4157   // We need to do this under a mutex to prevent other
4158   // workers from interfering with the work done below.
4159   MutexLockerEx ml(_overflow_stack->par_lock(),
4160                    Mutex::_no_safepoint_check_flag);
4161   // Remember the least grey address discarded
4162   HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
4163   _collector->lower_restart_addr(ra);
4164   _overflow_stack->reset();  // discard stack contents
4165   _overflow_stack->expand(); // expand the stack if possible
4166 }
4167 
4168 
4169 void CMSConcMarkingTask::do_work_steal(int i) {
4170   OopTaskQueue* work_q = work_queue(i);
4171   oop obj_to_scan;
4172   CMSBitMap* bm = &(_collector->_markBitMap);
4173   CMSMarkStack* ovflw = &(_collector->_markStack);
4174   int* seed = _collector->hash_seed(i);
4175   Par_ConcMarkingClosure cl(_collector, this, work_q, bm, ovflw);
4176   while (true) {
4177     cl.trim_queue(0);
4178     assert(work_q->size() == 0, "Should have been emptied above");
4179     if (get_work_from_overflow_stack(ovflw, work_q)) {
4180       // Can't assert below because the work obtained from the
4181       // overflow stack may already have been stolen from us.
4182       // assert(work_q->size() > 0, "Work from overflow stack");
4183       continue;
4184     } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
4185       assert(obj_to_scan->is_oop(), "Should be an oop");
4186       assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
4187       obj_to_scan->oop_iterate(&cl);
4188     } else if (terminator()->offer_termination(&_term_term)) {
4189       assert(work_q->size() == 0, "Impossible!");
4190       break;
4191     } else if (yielding() || should_yield()) {
4192       yield();
4193     }
4194   }
4195 }
4196 
4197 // This is run by the CMS (coordinator) thread.
4198 void CMSConcMarkingTask::coordinator_yield() {
4199   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
4200          "CMS thread should hold CMS token");
4201   // First give up the locks, then yield, then re-lock
4202   // We should probably use a constructor/destructor idiom to
4203   // do this unlock/lock or modify the MutexUnlocker class to
4204   // serve our purpose. XXX
4205   assert_lock_strong(_bit_map_lock);
4206   _bit_map_lock->unlock();
4207   ConcurrentMarkSweepThread::desynchronize(true);
4208   ConcurrentMarkSweepThread::acknowledge_yield_request();
4209   _collector->stopTimer();
4210   if (PrintCMSStatistics != 0) {
4211     _collector->incrementYields();
4212   }
4213   _collector->icms_wait();
4214 
4215   // It is possible for whichever thread initiated the yield request
4216   // not to get a chance to wake up and take the bitmap lock between
4217   // this thread releasing it and reacquiring it. So, while the
4218   // should_yield() flag is on, let's sleep for a bit to give the
4219   // other thread a chance to wake up. The limit imposed on the number
4220   // of iterations is defensive, to avoid any unforseen circumstances
4221   // putting us into an infinite loop. Since it's always been this
4222   // (coordinator_yield()) method that was observed to cause the
4223   // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
4224   // which is by default non-zero. For the other seven methods that
4225   // also perform the yield operation, as are using a different
4226   // parameter (CMSYieldSleepCount) which is by default zero. This way we
4227   // can enable the sleeping for those methods too, if necessary.
4228   // See 6442774.
4229   //
4230   // We really need to reconsider the synchronization between the GC
4231   // thread and the yield-requesting threads in the future and we
4232   // should really use wait/notify, which is the recommended
4233   // way of doing this type of interaction. Additionally, we should
4234   // consolidate the eight methods that do the yield operation and they
4235   // are almost identical into one for better maintenability and
4236   // readability. See 6445193.
4237   //
4238   // Tony 2006.06.29
4239   for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
4240                    ConcurrentMarkSweepThread::should_yield() &&
4241                    !CMSCollector::foregroundGCIsActive(); ++i) {
4242     os::sleep(Thread::current(), 1, false);
4243     ConcurrentMarkSweepThread::acknowledge_yield_request();
4244   }
4245 
4246   ConcurrentMarkSweepThread::synchronize(true);
4247   _bit_map_lock->lock_without_safepoint_check();
4248   _collector->startTimer();
4249 }
4250 
4251 bool CMSCollector::do_marking_mt(bool asynch) {
4252   assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition");
4253   int num_workers = AdaptiveSizePolicy::calc_active_conc_workers(
4254                                        conc_workers()->total_workers(),
4255                                        conc_workers()->active_workers(),
4256                                        Threads::number_of_non_daemon_threads());
4257   conc_workers()->set_active_workers(num_workers);
4258 
4259   CompactibleFreeListSpace* cms_space  = _cmsGen->cmsSpace();
4260 
4261   CMSConcMarkingTask tsk(this,
4262                          cms_space,
4263                          asynch,
4264                          conc_workers(),
4265                          task_queues());
4266 
4267   // Since the actual number of workers we get may be different
4268   // from the number we requested above, do we need to do anything different
4269   // below? In particular, may be we need to subclass the SequantialSubTasksDone
4270   // class?? XXX
4271   cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
4272 
4273   // Refs discovery is already non-atomic.
4274   assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
4275   assert(ref_processor()->discovery_is_mt(), "Discovery should be MT");
4276   conc_workers()->start_task(&tsk);
4277   while (tsk.yielded()) {
4278     tsk.coordinator_yield();
4279     conc_workers()->continue_task(&tsk);
4280   }
4281   // If the task was aborted, _restart_addr will be non-NULL
4282   assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
4283   while (_restart_addr != NULL) {
4284     // XXX For now we do not make use of ABORTED state and have not
4285     // yet implemented the right abort semantics (even in the original
4286     // single-threaded CMS case). That needs some more investigation
4287     // and is deferred for now; see CR# TBF. 07252005YSR. XXX
4288     assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
4289     // If _restart_addr is non-NULL, a marking stack overflow
4290     // occurred; we need to do a fresh marking iteration from the
4291     // indicated restart address.
4292     if (_foregroundGCIsActive && asynch) {
4293       // We may be running into repeated stack overflows, having
4294       // reached the limit of the stack size, while making very
4295       // slow forward progress. It may be best to bail out and
4296       // let the foreground collector do its job.
4297       // Clear _restart_addr, so that foreground GC
4298       // works from scratch. This avoids the headache of
4299       // a "rescan" which would otherwise be needed because
4300       // of the dirty mod union table & card table.
4301       _restart_addr = NULL;
4302       return false;
4303     }
4304     // Adjust the task to restart from _restart_addr
4305     tsk.reset(_restart_addr);
4306     cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
4307                   _restart_addr);
4308     _restart_addr = NULL;
4309     // Get the workers going again
4310     conc_workers()->start_task(&tsk);
4311     while (tsk.yielded()) {
4312       tsk.coordinator_yield();
4313       conc_workers()->continue_task(&tsk);
4314     }
4315   }
4316   assert(tsk.completed(), "Inconsistency");
4317   assert(tsk.result() == true, "Inconsistency");
4318   return true;
4319 }
4320 
4321 bool CMSCollector::do_marking_st(bool asynch) {
4322   ResourceMark rm;
4323   HandleMark   hm;
4324 
4325   // Temporarily make refs discovery single threaded (non-MT)
4326   ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
4327   MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
4328     &_markStack, CMSYield && asynch);
4329   // the last argument to iterate indicates whether the iteration
4330   // should be incremental with periodic yields.
4331   _markBitMap.iterate(&markFromRootsClosure);
4332   // If _restart_addr is non-NULL, a marking stack overflow
4333   // occurred; we need to do a fresh iteration from the
4334   // indicated restart address.
4335   while (_restart_addr != NULL) {
4336     if (_foregroundGCIsActive && asynch) {
4337       // We may be running into repeated stack overflows, having
4338       // reached the limit of the stack size, while making very
4339       // slow forward progress. It may be best to bail out and
4340       // let the foreground collector do its job.
4341       // Clear _restart_addr, so that foreground GC
4342       // works from scratch. This avoids the headache of
4343       // a "rescan" which would otherwise be needed because
4344       // of the dirty mod union table & card table.
4345       _restart_addr = NULL;
4346       return false;  // indicating failure to complete marking
4347     }
4348     // Deal with stack overflow:
4349     // we restart marking from _restart_addr
4350     HeapWord* ra = _restart_addr;
4351     markFromRootsClosure.reset(ra);
4352     _restart_addr = NULL;
4353     _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
4354   }
4355   return true;
4356 }
4357 
4358 void CMSCollector::preclean() {
4359   check_correct_thread_executing();
4360   assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
4361   verify_work_stacks_empty();
4362   verify_overflow_empty();
4363   _abort_preclean = false;
4364   if (CMSPrecleaningEnabled) {
4365     _eden_chunk_index = 0;
4366     size_t used = get_eden_used();
4367     size_t capacity = get_eden_capacity();
4368     // Don't start sampling unless we will get sufficiently
4369     // many samples.
4370     if (used < (capacity/(CMSScheduleRemarkSamplingRatio * 100)
4371                 * CMSScheduleRemarkEdenPenetration)) {
4372       _start_sampling = true;
4373     } else {
4374       _start_sampling = false;
4375     }
4376     TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
4377     CMSPhaseAccounting pa(this, "preclean", !PrintGCDetails);
4378     preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
4379   }
4380   CMSTokenSync x(true); // is cms thread
4381   if (CMSPrecleaningEnabled) {
4382     sample_eden();
4383     _collectorState = AbortablePreclean;
4384   } else {
4385     _collectorState = FinalMarking;
4386   }
4387   verify_work_stacks_empty();
4388   verify_overflow_empty();
4389 }
4390 
4391 // Try and schedule the remark such that young gen
4392 // occupancy is CMSScheduleRemarkEdenPenetration %.
4393 void CMSCollector::abortable_preclean() {
4394   check_correct_thread_executing();
4395   assert(CMSPrecleaningEnabled,  "Inconsistent control state");
4396   assert(_collectorState == AbortablePreclean, "Inconsistent control state");
4397 
4398   // If Eden's current occupancy is below this threshold,
4399   // immediately schedule the remark; else preclean
4400   // past the next scavenge in an effort to
4401   // schedule the pause as described avove. By choosing
4402   // CMSScheduleRemarkEdenSizeThreshold >= max eden size
4403   // we will never do an actual abortable preclean cycle.
4404   if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
4405     TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
4406     CMSPhaseAccounting pa(this, "abortable-preclean", !PrintGCDetails);
4407     // We need more smarts in the abortable preclean
4408     // loop below to deal with cases where allocation
4409     // in young gen is very very slow, and our precleaning
4410     // is running a losing race against a horde of
4411     // mutators intent on flooding us with CMS updates
4412     // (dirty cards).
4413     // One, admittedly dumb, strategy is to give up
4414     // after a certain number of abortable precleaning loops
4415     // or after a certain maximum time. We want to make
4416     // this smarter in the next iteration.
4417     // XXX FIX ME!!! YSR
4418     size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
4419     while (!(should_abort_preclean() ||
4420              ConcurrentMarkSweepThread::should_terminate())) {
4421       workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
4422       cumworkdone += workdone;
4423       loops++;
4424       // Voluntarily terminate abortable preclean phase if we have
4425       // been at it for too long.
4426       if ((CMSMaxAbortablePrecleanLoops != 0) &&
4427           loops >= CMSMaxAbortablePrecleanLoops) {
4428         if (PrintGCDetails) {
4429           gclog_or_tty->print(" CMS: abort preclean due to loops ");
4430         }
4431         break;
4432       }
4433       if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
4434         if (PrintGCDetails) {
4435           gclog_or_tty->print(" CMS: abort preclean due to time ");
4436         }
4437         break;
4438       }
4439       // If we are doing little work each iteration, we should
4440       // take a short break.
4441       if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
4442         // Sleep for some time, waiting for work to accumulate
4443         stopTimer();
4444         cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
4445         startTimer();
4446         waited++;
4447       }
4448     }
4449     if (PrintCMSStatistics > 0) {
4450       gclog_or_tty->print(" [%d iterations, %d waits, %d cards)] ",
4451                           loops, waited, cumworkdone);
4452     }
4453   }
4454   CMSTokenSync x(true); // is cms thread
4455   if (_collectorState != Idling) {
4456     assert(_collectorState == AbortablePreclean,
4457            "Spontaneous state transition?");
4458     _collectorState = FinalMarking;
4459   } // Else, a foreground collection completed this CMS cycle.
4460   return;
4461 }
4462 
4463 // Respond to an Eden sampling opportunity
4464 void CMSCollector::sample_eden() {
4465   // Make sure a young gc cannot sneak in between our
4466   // reading and recording of a sample.
4467   assert(Thread::current()->is_ConcurrentGC_thread(),
4468          "Only the cms thread may collect Eden samples");
4469   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
4470          "Should collect samples while holding CMS token");
4471   if (!_start_sampling) {
4472     return;
4473   }
4474   if (_eden_chunk_array) {
4475     if (_eden_chunk_index < _eden_chunk_capacity) {
4476       _eden_chunk_array[_eden_chunk_index] = *_top_addr;   // take sample
4477       assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4478              "Unexpected state of Eden");
4479       // We'd like to check that what we just sampled is an oop-start address;
4480       // however, we cannot do that here since the object may not yet have been
4481       // initialized. So we'll instead do the check when we _use_ this sample
4482       // later.
4483       if (_eden_chunk_index == 0 ||
4484           (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4485                          _eden_chunk_array[_eden_chunk_index-1])
4486            >= CMSSamplingGrain)) {
4487         _eden_chunk_index++;  // commit sample
4488       }
4489     }
4490   }
4491   if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
4492     size_t used = get_eden_used();
4493     size_t capacity = get_eden_capacity();
4494     assert(used <= capacity, "Unexpected state of Eden");
4495     if (used >  (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
4496       _abort_preclean = true;
4497     }
4498   }
4499 }
4500 
4501 
4502 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
4503   assert(_collectorState == Precleaning ||
4504          _collectorState == AbortablePreclean, "incorrect state");
4505   ResourceMark rm;
4506   HandleMark   hm;
4507 
4508   // Precleaning is currently not MT but the reference processor
4509   // may be set for MT.  Disable it temporarily here.
4510   ReferenceProcessor* rp = ref_processor();
4511   ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false);
4512 
4513   // Do one pass of scrubbing the discovered reference lists
4514   // to remove any reference objects with strongly-reachable
4515   // referents.
4516   if (clean_refs) {
4517     CMSPrecleanRefsYieldClosure yield_cl(this);
4518     assert(rp->span().equals(_span), "Spans should be equal");
4519     CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
4520                                    &_markStack, true /* preclean */);
4521     CMSDrainMarkingStackClosure complete_trace(this,
4522                                    _span, &_markBitMap, &_markStack,
4523                                    &keep_alive, true /* preclean */);
4524 
4525     // We don't want this step to interfere with a young
4526     // collection because we don't want to take CPU
4527     // or memory bandwidth away from the young GC threads
4528     // (which may be as many as there are CPUs).
4529     // Note that we don't need to protect ourselves from
4530     // interference with mutators because they can't
4531     // manipulate the discovered reference lists nor affect
4532     // the computed reachability of the referents, the
4533     // only properties manipulated by the precleaning
4534     // of these reference lists.
4535     stopTimer();
4536     CMSTokenSyncWithLocks x(true /* is cms thread */,
4537                             bitMapLock());
4538     startTimer();
4539     sample_eden();
4540 
4541     // The following will yield to allow foreground
4542     // collection to proceed promptly. XXX YSR:
4543     // The code in this method may need further
4544     // tweaking for better performance and some restructuring
4545     // for cleaner interfaces.
4546     rp->preclean_discovered_references(
4547           rp->is_alive_non_header(), &keep_alive, &complete_trace, &yield_cl);
4548   }
4549 
4550   if (clean_survivor) {  // preclean the active survivor space(s)
4551     assert(_young_gen->kind() == Generation::DefNew ||
4552            _young_gen->kind() == Generation::ParNew ||
4553            _young_gen->kind() == Generation::ASParNew,
4554          "incorrect type for cast");
4555     DefNewGeneration* dng = (DefNewGeneration*)_young_gen;
4556     PushAndMarkClosure pam_cl(this, _span, ref_processor(),
4557                              &_markBitMap, &_modUnionTable,
4558                              &_markStack, true /* precleaning phase */);
4559     stopTimer();
4560     CMSTokenSyncWithLocks ts(true /* is cms thread */,
4561                              bitMapLock());
4562     startTimer();
4563     unsigned int before_count =
4564       GenCollectedHeap::heap()->total_collections();
4565     SurvivorSpacePrecleanClosure
4566       sss_cl(this, _span, &_markBitMap, &_markStack,
4567              &pam_cl, before_count, CMSYield);
4568     dng->from()->object_iterate_careful(&sss_cl);
4569     dng->to()->object_iterate_careful(&sss_cl);
4570   }
4571   MarkRefsIntoAndScanClosure
4572     mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
4573              &_markStack, this, CMSYield,
4574              true /* precleaning phase */);
4575   // CAUTION: The following closure has persistent state that may need to
4576   // be reset upon a decrease in the sequence of addresses it
4577   // processes.
4578   ScanMarkedObjectsAgainCarefullyClosure
4579     smoac_cl(this, _span,
4580       &_markBitMap, &_markStack, &mrias_cl, CMSYield);
4581 
4582   // Preclean dirty cards in ModUnionTable and CardTable using
4583   // appropriate convergence criterion;
4584   // repeat CMSPrecleanIter times unless we find that
4585   // we are losing.
4586   assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
4587   assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
4588          "Bad convergence multiplier");
4589   assert(CMSPrecleanThreshold >= 100,
4590          "Unreasonably low CMSPrecleanThreshold");
4591 
4592   size_t numIter, cumNumCards, lastNumCards, curNumCards;
4593   for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
4594        numIter < CMSPrecleanIter;
4595        numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
4596     curNumCards  = preclean_mod_union_table(_cmsGen, &smoac_cl);
4597     if (Verbose && PrintGCDetails) {
4598       gclog_or_tty->print(" (modUnionTable: %d cards)", curNumCards);
4599     }
4600     // Either there are very few dirty cards, so re-mark
4601     // pause will be small anyway, or our pre-cleaning isn't
4602     // that much faster than the rate at which cards are being
4603     // dirtied, so we might as well stop and re-mark since
4604     // precleaning won't improve our re-mark time by much.
4605     if (curNumCards <= CMSPrecleanThreshold ||
4606         (numIter > 0 &&
4607          (curNumCards * CMSPrecleanDenominator >
4608          lastNumCards * CMSPrecleanNumerator))) {
4609       numIter++;
4610       cumNumCards += curNumCards;
4611       break;
4612     }
4613   }
4614 
4615   preclean_klasses(&mrias_cl, _cmsGen->freelistLock());
4616 
4617   curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
4618   cumNumCards += curNumCards;
4619   if (PrintGCDetails && PrintCMSStatistics != 0) {
4620     gclog_or_tty->print_cr(" (cardTable: %d cards, re-scanned %d cards, %d iterations)",
4621                   curNumCards, cumNumCards, numIter);
4622   }
4623   return cumNumCards;   // as a measure of useful work done
4624 }
4625 
4626 // PRECLEANING NOTES:
4627 // Precleaning involves:
4628 // . reading the bits of the modUnionTable and clearing the set bits.
4629 // . For the cards corresponding to the set bits, we scan the
4630 //   objects on those cards. This means we need the free_list_lock
4631 //   so that we can safely iterate over the CMS space when scanning
4632 //   for oops.
4633 // . When we scan the objects, we'll be both reading and setting
4634 //   marks in the marking bit map, so we'll need the marking bit map.
4635 // . For protecting _collector_state transitions, we take the CGC_lock.
4636 //   Note that any races in the reading of of card table entries by the
4637 //   CMS thread on the one hand and the clearing of those entries by the
4638 //   VM thread or the setting of those entries by the mutator threads on the
4639 //   other are quite benign. However, for efficiency it makes sense to keep
4640 //   the VM thread from racing with the CMS thread while the latter is
4641 //   dirty card info to the modUnionTable. We therefore also use the
4642 //   CGC_lock to protect the reading of the card table and the mod union
4643 //   table by the CM thread.
4644 // . We run concurrently with mutator updates, so scanning
4645 //   needs to be done carefully  -- we should not try to scan
4646 //   potentially uninitialized objects.
4647 //
4648 // Locking strategy: While holding the CGC_lock, we scan over and
4649 // reset a maximal dirty range of the mod union / card tables, then lock
4650 // the free_list_lock and bitmap lock to do a full marking, then
4651 // release these locks; and repeat the cycle. This allows for a
4652 // certain amount of fairness in the sharing of these locks between
4653 // the CMS collector on the one hand, and the VM thread and the
4654 // mutators on the other.
4655 
4656 // NOTE: preclean_mod_union_table() and preclean_card_table()
4657 // further below are largely identical; if you need to modify
4658 // one of these methods, please check the other method too.
4659 
4660 size_t CMSCollector::preclean_mod_union_table(
4661   ConcurrentMarkSweepGeneration* gen,
4662   ScanMarkedObjectsAgainCarefullyClosure* cl) {
4663   verify_work_stacks_empty();
4664   verify_overflow_empty();
4665 
4666   // strategy: starting with the first card, accumulate contiguous
4667   // ranges of dirty cards; clear these cards, then scan the region
4668   // covered by these cards.
4669 
4670   // Since all of the MUT is committed ahead, we can just use
4671   // that, in case the generations expand while we are precleaning.
4672   // It might also be fine to just use the committed part of the
4673   // generation, but we might potentially miss cards when the
4674   // generation is rapidly expanding while we are in the midst
4675   // of precleaning.
4676   HeapWord* startAddr = gen->reserved().start();
4677   HeapWord* endAddr   = gen->reserved().end();
4678 
4679   cl->setFreelistLock(gen->freelistLock());   // needed for yielding
4680 
4681   size_t numDirtyCards, cumNumDirtyCards;
4682   HeapWord *nextAddr, *lastAddr;
4683   for (cumNumDirtyCards = numDirtyCards = 0,
4684        nextAddr = lastAddr = startAddr;
4685        nextAddr < endAddr;
4686        nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4687 
4688     ResourceMark rm;
4689     HandleMark   hm;
4690 
4691     MemRegion dirtyRegion;
4692     {
4693       stopTimer();
4694       // Potential yield point
4695       CMSTokenSync ts(true);
4696       startTimer();
4697       sample_eden();
4698       // Get dirty region starting at nextOffset (inclusive),
4699       // simultaneously clearing it.
4700       dirtyRegion =
4701         _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
4702       assert(dirtyRegion.start() >= nextAddr,
4703              "returned region inconsistent?");
4704     }
4705     // Remember where the next search should begin.
4706     // The returned region (if non-empty) is a right open interval,
4707     // so lastOffset is obtained from the right end of that
4708     // interval.
4709     lastAddr = dirtyRegion.end();
4710     // Should do something more transparent and less hacky XXX
4711     numDirtyCards =
4712       _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
4713 
4714     // We'll scan the cards in the dirty region (with periodic
4715     // yields for foreground GC as needed).
4716     if (!dirtyRegion.is_empty()) {
4717       assert(numDirtyCards > 0, "consistency check");
4718       HeapWord* stop_point = NULL;
4719       stopTimer();
4720       // Potential yield point
4721       CMSTokenSyncWithLocks ts(true, gen->freelistLock(),
4722                                bitMapLock());
4723       startTimer();
4724       {
4725         verify_work_stacks_empty();
4726         verify_overflow_empty();
4727         sample_eden();
4728         stop_point =
4729           gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4730       }
4731       if (stop_point != NULL) {
4732         // The careful iteration stopped early either because it found an
4733         // uninitialized object, or because we were in the midst of an
4734         // "abortable preclean", which should now be aborted. Redirty
4735         // the bits corresponding to the partially-scanned or unscanned
4736         // cards. We'll either restart at the next block boundary or
4737         // abort the preclean.
4738         assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4739                "Should only be AbortablePreclean.");
4740         _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
4741         if (should_abort_preclean()) {
4742           break; // out of preclean loop
4743         } else {
4744           // Compute the next address at which preclean should pick up;
4745           // might need bitMapLock in order to read P-bits.
4746           lastAddr = next_card_start_after_block(stop_point);
4747         }
4748       }
4749     } else {
4750       assert(lastAddr == endAddr, "consistency check");
4751       assert(numDirtyCards == 0, "consistency check");
4752       break;
4753     }
4754   }
4755   verify_work_stacks_empty();
4756   verify_overflow_empty();
4757   return cumNumDirtyCards;
4758 }
4759 
4760 // NOTE: preclean_mod_union_table() above and preclean_card_table()
4761 // below are largely identical; if you need to modify
4762 // one of these methods, please check the other method too.
4763 
4764 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* gen,
4765   ScanMarkedObjectsAgainCarefullyClosure* cl) {
4766   // strategy: it's similar to precleamModUnionTable above, in that
4767   // we accumulate contiguous ranges of dirty cards, mark these cards
4768   // precleaned, then scan the region covered by these cards.
4769   HeapWord* endAddr   = (HeapWord*)(gen->_virtual_space.high());
4770   HeapWord* startAddr = (HeapWord*)(gen->_virtual_space.low());
4771 
4772   cl->setFreelistLock(gen->freelistLock());   // needed for yielding
4773 
4774   size_t numDirtyCards, cumNumDirtyCards;
4775   HeapWord *lastAddr, *nextAddr;
4776 
4777   for (cumNumDirtyCards = numDirtyCards = 0,
4778        nextAddr = lastAddr = startAddr;
4779        nextAddr < endAddr;
4780        nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4781 
4782     ResourceMark rm;
4783     HandleMark   hm;
4784 
4785     MemRegion dirtyRegion;
4786     {
4787       // See comments in "Precleaning notes" above on why we
4788       // do this locking. XXX Could the locking overheads be
4789       // too high when dirty cards are sparse? [I don't think so.]
4790       stopTimer();
4791       CMSTokenSync x(true); // is cms thread
4792       startTimer();
4793       sample_eden();
4794       // Get and clear dirty region from card table
4795       dirtyRegion = _ct->ct_bs()->dirty_card_range_after_reset(
4796                                     MemRegion(nextAddr, endAddr),
4797                                     true,
4798                                     CardTableModRefBS::precleaned_card_val());
4799 
4800       assert(dirtyRegion.start() >= nextAddr,
4801              "returned region inconsistent?");
4802     }
4803     lastAddr = dirtyRegion.end();
4804     numDirtyCards =
4805       dirtyRegion.word_size()/CardTableModRefBS::card_size_in_words;
4806 
4807     if (!dirtyRegion.is_empty()) {
4808       stopTimer();
4809       CMSTokenSyncWithLocks ts(true, gen->freelistLock(), bitMapLock());
4810       startTimer();
4811       sample_eden();
4812       verify_work_stacks_empty();
4813       verify_overflow_empty();
4814       HeapWord* stop_point =
4815         gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4816       if (stop_point != NULL) {
4817         assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4818                "Should only be AbortablePreclean.");
4819         _ct->ct_bs()->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4820         if (should_abort_preclean()) {
4821           break; // out of preclean loop
4822         } else {
4823           // Compute the next address at which preclean should pick up.
4824           lastAddr = next_card_start_after_block(stop_point);
4825         }
4826       }
4827     } else {
4828       break;
4829     }
4830   }
4831   verify_work_stacks_empty();
4832   verify_overflow_empty();
4833   return cumNumDirtyCards;
4834 }
4835 
4836 class PrecleanKlassClosure : public KlassClosure {
4837   CMKlassClosure _cm_klass_closure;
4838  public:
4839   PrecleanKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4840   void do_klass(Klass* k) {
4841     if (k->has_accumulated_modified_oops()) {
4842       k->clear_accumulated_modified_oops();
4843 
4844       _cm_klass_closure.do_klass(k);
4845     }
4846   }
4847 };
4848 
4849 // The freelist lock is needed to prevent asserts, is it really needed?
4850 void CMSCollector::preclean_klasses(MarkRefsIntoAndScanClosure* cl, Mutex* freelistLock) {
4851 
4852   cl->set_freelistLock(freelistLock);
4853 
4854   CMSTokenSyncWithLocks ts(true, freelistLock, bitMapLock());
4855 
4856   // SSS: Add equivalent to ScanMarkedObjectsAgainCarefullyClosure::do_yield_check and should_abort_preclean?
4857   // SSS: We should probably check if precleaning should be aborted, at suitable intervals?
4858   PrecleanKlassClosure preclean_klass_closure(cl);
4859   ClassLoaderDataGraph::classes_do(&preclean_klass_closure);
4860 
4861   verify_work_stacks_empty();
4862   verify_overflow_empty();
4863 }
4864 
4865 void CMSCollector::checkpointRootsFinal(bool asynch,
4866   bool clear_all_soft_refs, bool init_mark_was_synchronous) {
4867   assert(_collectorState == FinalMarking, "incorrect state transition?");
4868   check_correct_thread_executing();
4869   // world is stopped at this checkpoint
4870   assert(SafepointSynchronize::is_at_safepoint(),
4871          "world should be stopped");
4872   TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
4873 
4874   verify_work_stacks_empty();
4875   verify_overflow_empty();
4876 
4877   SpecializationStats::clear();
4878   if (PrintGCDetails) {
4879     gclog_or_tty->print("[YG occupancy: "SIZE_FORMAT" K ("SIZE_FORMAT" K)]",
4880                         _young_gen->used() / K,
4881                         _young_gen->capacity() / K);
4882   }
4883   if (asynch) {
4884     if (CMSScavengeBeforeRemark) {
4885       GenCollectedHeap* gch = GenCollectedHeap::heap();
4886       // Temporarily set flag to false, GCH->do_collection will
4887       // expect it to be false and set to true
4888       FlagSetting fl(gch->_is_gc_active, false);
4889       NOT_PRODUCT(TraceTime t("Scavenge-Before-Remark",
4890         PrintGCDetails && Verbose, true, gclog_or_tty);)
4891       int level = _cmsGen->level() - 1;
4892       if (level >= 0) {
4893         gch->do_collection(true,        // full (i.e. force, see below)
4894                            false,       // !clear_all_soft_refs
4895                            0,           // size
4896                            false,       // is_tlab
4897                            level        // max_level
4898                           );
4899       }
4900     }
4901     FreelistLocker x(this);
4902     MutexLockerEx y(bitMapLock(),
4903                     Mutex::_no_safepoint_check_flag);
4904     assert(!init_mark_was_synchronous, "but that's impossible!");
4905     checkpointRootsFinalWork(asynch, clear_all_soft_refs, false);
4906   } else {
4907     // already have all the locks
4908     checkpointRootsFinalWork(asynch, clear_all_soft_refs,
4909                              init_mark_was_synchronous);
4910   }
4911   verify_work_stacks_empty();
4912   verify_overflow_empty();
4913   SpecializationStats::print();
4914 }
4915 
4916 void CMSCollector::checkpointRootsFinalWork(bool asynch,
4917   bool clear_all_soft_refs, bool init_mark_was_synchronous) {
4918 
4919   NOT_PRODUCT(TraceTime tr("checkpointRootsFinalWork", PrintGCDetails, false, gclog_or_tty);)
4920 
4921   assert(haveFreelistLocks(), "must have free list locks");
4922   assert_lock_strong(bitMapLock());
4923 
4924   if (UseAdaptiveSizePolicy) {
4925     size_policy()->checkpoint_roots_final_begin();
4926   }
4927 
4928   ResourceMark rm;
4929   HandleMark   hm;
4930 
4931   GenCollectedHeap* gch = GenCollectedHeap::heap();
4932 
4933   if (should_unload_classes()) {
4934     CodeCache::gc_prologue();
4935   }
4936   assert(haveFreelistLocks(), "must have free list locks");
4937   assert_lock_strong(bitMapLock());
4938 
4939   if (!init_mark_was_synchronous) {
4940     // We might assume that we need not fill TLAB's when
4941     // CMSScavengeBeforeRemark is set, because we may have just done
4942     // a scavenge which would have filled all TLAB's -- and besides
4943     // Eden would be empty. This however may not always be the case --
4944     // for instance although we asked for a scavenge, it may not have
4945     // happened because of a JNI critical section. We probably need
4946     // a policy for deciding whether we can in that case wait until
4947     // the critical section releases and then do the remark following
4948     // the scavenge, and skip it here. In the absence of that policy,
4949     // or of an indication of whether the scavenge did indeed occur,
4950     // we cannot rely on TLAB's having been filled and must do
4951     // so here just in case a scavenge did not happen.
4952     gch->ensure_parsability(false);  // fill TLAB's, but no need to retire them
4953     // Update the saved marks which may affect the root scans.
4954     gch->save_marks();
4955 
4956     {
4957       COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
4958 
4959       // Note on the role of the mod union table:
4960       // Since the marker in "markFromRoots" marks concurrently with
4961       // mutators, it is possible for some reachable objects not to have been
4962       // scanned. For instance, an only reference to an object A was
4963       // placed in object B after the marker scanned B. Unless B is rescanned,
4964       // A would be collected. Such updates to references in marked objects
4965       // are detected via the mod union table which is the set of all cards
4966       // dirtied since the first checkpoint in this GC cycle and prior to
4967       // the most recent young generation GC, minus those cleaned up by the
4968       // concurrent precleaning.
4969       if (CMSParallelRemarkEnabled && CollectedHeap::use_parallel_gc_threads()) {
4970         TraceTime t("Rescan (parallel) ", PrintGCDetails, false, gclog_or_tty);
4971         do_remark_parallel();
4972       } else {
4973         TraceTime t("Rescan (non-parallel) ", PrintGCDetails, false,
4974                     gclog_or_tty);
4975         do_remark_non_parallel();
4976       }
4977     }
4978   } else {
4979     assert(!asynch, "Can't have init_mark_was_synchronous in asynch mode");
4980     // The initial mark was stop-world, so there's no rescanning to
4981     // do; go straight on to the next step below.
4982   }
4983   verify_work_stacks_empty();
4984   verify_overflow_empty();
4985 
4986   {
4987     NOT_PRODUCT(TraceTime ts("refProcessingWork", PrintGCDetails, false, gclog_or_tty);)
4988     refProcessingWork(asynch, clear_all_soft_refs);
4989   }
4990   verify_work_stacks_empty();
4991   verify_overflow_empty();
4992 
4993   if (should_unload_classes()) {
4994     CodeCache::gc_epilogue();
4995   }
4996   JvmtiExport::gc_epilogue();
4997 
4998   // If we encountered any (marking stack / work queue) overflow
4999   // events during the current CMS cycle, take appropriate
5000   // remedial measures, where possible, so as to try and avoid
5001   // recurrence of that condition.
5002   assert(_markStack.isEmpty(), "No grey objects");
5003   size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
5004                      _ser_kac_ovflw        + _ser_kac_preclean_ovflw;
5005   if (ser_ovflw > 0) {
5006     if (PrintCMSStatistics != 0) {
5007       gclog_or_tty->print_cr("Marking stack overflow (benign) "
5008         "(pmc_pc="SIZE_FORMAT", pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT
5009         ", kac_preclean="SIZE_FORMAT")",
5010         _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw,
5011         _ser_kac_ovflw, _ser_kac_preclean_ovflw);
5012     }
5013     _markStack.expand();
5014     _ser_pmc_remark_ovflw = 0;
5015     _ser_pmc_preclean_ovflw = 0;
5016     _ser_kac_preclean_ovflw = 0;
5017     _ser_kac_ovflw = 0;
5018   }
5019   if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
5020     if (PrintCMSStatistics != 0) {
5021       gclog_or_tty->print_cr("Work queue overflow (benign) "
5022         "(pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT")",
5023         _par_pmc_remark_ovflw, _par_kac_ovflw);
5024     }
5025     _par_pmc_remark_ovflw = 0;
5026     _par_kac_ovflw = 0;
5027   }
5028   if (PrintCMSStatistics != 0) {
5029      if (_markStack._hit_limit > 0) {
5030        gclog_or_tty->print_cr(" (benign) Hit max stack size limit ("SIZE_FORMAT")",
5031                               _markStack._hit_limit);
5032      }
5033      if (_markStack._failed_double > 0) {
5034        gclog_or_tty->print_cr(" (benign) Failed stack doubling ("SIZE_FORMAT"),"
5035                               " current capacity "SIZE_FORMAT,
5036                               _markStack._failed_double,
5037                               _markStack.capacity());
5038      }
5039   }
5040   _markStack._hit_limit = 0;
5041   _markStack._failed_double = 0;
5042 
5043   if ((VerifyAfterGC || VerifyDuringGC) &&
5044       GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5045     verify_after_remark();
5046   }
5047 
5048   // Change under the freelistLocks.
5049   _collectorState = Sweeping;
5050   // Call isAllClear() under bitMapLock
5051   assert(_modUnionTable.isAllClear(),
5052       "Should be clear by end of the final marking");
5053   assert(_ct->klass_rem_set()->mod_union_is_clear(),
5054       "Should be clear by end of the final marking");
5055   if (UseAdaptiveSizePolicy) {
5056     size_policy()->checkpoint_roots_final_end(gch->gc_cause());
5057   }
5058 }
5059 













































5060 // Parallel remark task
5061 class CMSParRemarkTask: public AbstractGangTask {
5062   CMSCollector* _collector;
5063   int           _n_workers;
5064   CompactibleFreeListSpace* _cms_space;
5065 
5066   // The per-thread work queues, available here for stealing.
5067   OopTaskQueueSet*       _task_queues;
5068   ParallelTaskTerminator _term;
5069 
5070  public:
5071   // A value of 0 passed to n_workers will cause the number of
5072   // workers to be taken from the active workers in the work gang.
5073   CMSParRemarkTask(CMSCollector* collector,
5074                    CompactibleFreeListSpace* cms_space,
5075                    int n_workers, FlexibleWorkGang* workers,
5076                    OopTaskQueueSet* task_queues):
5077     AbstractGangTask("Rescan roots and grey objects in parallel"),
5078     _collector(collector),
5079     _cms_space(cms_space),
5080     _n_workers(n_workers),
5081     _task_queues(task_queues),
5082     _term(n_workers, task_queues) { }
5083 
5084   OopTaskQueueSet* task_queues() { return _task_queues; }
5085 
5086   OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5087 
5088   ParallelTaskTerminator* terminator() { return &_term; }
5089   int n_workers() { return _n_workers; }
5090 
5091   void work(uint worker_id);
5092 
5093  private:
5094   // Work method in support of parallel rescan ... of young gen spaces
5095   void do_young_space_rescan(int i, Par_MarkRefsIntoAndScanClosure* cl,
5096                              ContiguousSpace* space,
5097                              HeapWord** chunk_array, size_t chunk_top);
5098 
5099   // ... of  dirty cards in old space
5100   void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
5101                                   Par_MarkRefsIntoAndScanClosure* cl);
5102 
5103   // ... work stealing for the above
5104   void do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl, int* seed);
5105 };
5106 
5107 class RemarkKlassClosure : public KlassClosure {
5108   CMKlassClosure _cm_klass_closure;
5109  public:
5110   RemarkKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
5111   void do_klass(Klass* k) {
5112     // Check if we have modified any oops in the Klass during the concurrent marking.
5113     if (k->has_accumulated_modified_oops()) {
5114       k->clear_accumulated_modified_oops();
5115 
5116       // We could have transfered the current modified marks to the accumulated marks,
5117       // like we do with the Card Table to Mod Union Table. But it's not really necessary.
5118     } else if (k->has_modified_oops()) {
5119       // Don't clear anything, this info is needed by the next young collection.
5120     } else {
5121       // No modified oops in the Klass.
5122       return;
5123     }
5124 
5125     // The klass has modified fields, need to scan the klass.
5126     _cm_klass_closure.do_klass(k);
5127   }
5128 };
5129 



















5130 // work_queue(i) is passed to the closure
5131 // Par_MarkRefsIntoAndScanClosure.  The "i" parameter
5132 // also is passed to do_dirty_card_rescan_tasks() and to
5133 // do_work_steal() to select the i-th task_queue.
5134 
5135 void CMSParRemarkTask::work(uint worker_id) {
5136   elapsedTimer _timer;
5137   ResourceMark rm;
5138   HandleMark   hm;
5139 
5140   // ---------- rescan from roots --------------
5141   _timer.start();
5142   GenCollectedHeap* gch = GenCollectedHeap::heap();
5143   Par_MarkRefsIntoAndScanClosure par_mrias_cl(_collector,
5144     _collector->_span, _collector->ref_processor(),
5145     &(_collector->_markBitMap),
5146     work_queue(worker_id));
5147 
5148   // Rescan young gen roots first since these are likely
5149   // coarsely partitioned and may, on that account, constitute
5150   // the critical path; thus, it's best to start off that
5151   // work first.
5152   // ---------- young gen roots --------------
5153   {
5154     DefNewGeneration* dng = _collector->_young_gen->as_DefNewGeneration();
5155     EdenSpace* eden_space = dng->eden();
5156     ContiguousSpace* from_space = dng->from();
5157     ContiguousSpace* to_space   = dng->to();
5158 
5159     HeapWord** eca = _collector->_eden_chunk_array;
5160     size_t     ect = _collector->_eden_chunk_index;
5161     HeapWord** sca = _collector->_survivor_chunk_array;
5162     size_t     sct = _collector->_survivor_chunk_index;
5163 
5164     assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
5165     assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
5166 
5167     do_young_space_rescan(worker_id, &par_mrias_cl, to_space, NULL, 0);
5168     do_young_space_rescan(worker_id, &par_mrias_cl, from_space, sca, sct);
5169     do_young_space_rescan(worker_id, &par_mrias_cl, eden_space, eca, ect);
5170 
5171     _timer.stop();
5172     if (PrintCMSStatistics != 0) {
5173       gclog_or_tty->print_cr(
5174         "Finished young gen rescan work in %dth thread: %3.3f sec",
5175         worker_id, _timer.seconds());
5176     }
5177   }
5178 
5179   // ---------- remaining roots --------------
5180   _timer.reset();
5181   _timer.start();
5182   gch->gen_process_strong_roots(_collector->_cmsGen->level(),
5183                                 false,     // yg was scanned above
5184                                 false,     // this is parallel code
5185                                 false,     // not scavenging
5186                                 SharedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
5187                                 &par_mrias_cl,
5188                                 true,   // walk all of code cache if (so & SO_CodeCache)
5189                                 NULL,
5190                                 NULL);     // The dirty klasses will be handled below
5191   assert(_collector->should_unload_classes()
5192          || (_collector->CMSCollector::roots_scanning_options() & SharedHeap::SO_CodeCache),
5193          "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5194   _timer.stop();
5195   if (PrintCMSStatistics != 0) {
5196     gclog_or_tty->print_cr(
5197       "Finished remaining root rescan work in %dth thread: %3.3f sec",
5198       worker_id, _timer.seconds());
5199   }
5200 
5201   // ---------- unhandled CLD scanning ----------
5202   if (worker_id == 0) { // Single threaded at the moment.
5203     _timer.reset();
5204     _timer.start();
5205 
5206     // Scan all new class loader data objects and new dependencies that were
5207     // introduced during concurrent marking.
5208     ResourceMark rm;
5209     GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
5210     for (int i = 0; i < array->length(); i++) {
5211       par_mrias_cl.do_class_loader_data(array->at(i));
5212     }
5213 
5214     // We don't need to keep track of new CLDs anymore.
5215     ClassLoaderDataGraph::remember_new_clds(false);
5216 
5217     _timer.stop();
5218     if (PrintCMSStatistics != 0) {
5219       gclog_or_tty->print_cr(
5220           "Finished unhandled CLD scanning work in %dth thread: %3.3f sec",
5221           worker_id, _timer.seconds());
5222     }
5223   }
5224 
5225   // ---------- dirty klass scanning ----------
5226   if (worker_id == 0) { // Single threaded at the moment.
5227     _timer.reset();
5228     _timer.start();
5229 
5230     // Scan all classes that was dirtied during the concurrent marking phase.
5231     RemarkKlassClosure remark_klass_closure(&par_mrias_cl);
5232     ClassLoaderDataGraph::classes_do(&remark_klass_closure);
5233 
5234     _timer.stop();
5235     if (PrintCMSStatistics != 0) {
5236       gclog_or_tty->print_cr(
5237           "Finished dirty klass scanning work in %dth thread: %3.3f sec",
5238           worker_id, _timer.seconds());
5239     }
5240   }
5241 
5242   // We might have added oops to ClassLoaderData::_handles during the
5243   // concurrent marking phase. These oops point to newly allocated objects
5244   // that are guaranteed to be kept alive. Either by the direct allocation
5245   // code, or when the young collector processes the strong roots. Hence,
5246   // we don't have to revisit the _handles block during the remark phase.
5247 
5248   // ---------- rescan dirty cards ------------
5249   _timer.reset();
5250   _timer.start();
5251 
5252   // Do the rescan tasks for each of the two spaces
5253   // (cms_space) in turn.
5254   // "worker_id" is passed to select the task_queue for "worker_id"
5255   do_dirty_card_rescan_tasks(_cms_space, worker_id, &par_mrias_cl);
5256   _timer.stop();
5257   if (PrintCMSStatistics != 0) {
5258     gclog_or_tty->print_cr(
5259       "Finished dirty card rescan work in %dth thread: %3.3f sec",
5260       worker_id, _timer.seconds());
5261   }
5262 
5263   // ---------- steal work from other threads ...
5264   // ---------- ... and drain overflow list.
5265   _timer.reset();
5266   _timer.start();
5267   do_work_steal(worker_id, &par_mrias_cl, _collector->hash_seed(worker_id));
5268   _timer.stop();
5269   if (PrintCMSStatistics != 0) {
5270     gclog_or_tty->print_cr(
5271       "Finished work stealing in %dth thread: %3.3f sec",
5272       worker_id, _timer.seconds());
5273   }
5274 }
5275 
5276 // Note that parameter "i" is not used.
5277 void
5278 CMSParRemarkTask::do_young_space_rescan(int i,
5279   Par_MarkRefsIntoAndScanClosure* cl, ContiguousSpace* space,
5280   HeapWord** chunk_array, size_t chunk_top) {
5281   // Until all tasks completed:
5282   // . claim an unclaimed task
5283   // . compute region boundaries corresponding to task claimed
5284   //   using chunk_array
5285   // . par_oop_iterate(cl) over that region
5286 
5287   ResourceMark rm;
5288   HandleMark   hm;
5289 
5290   SequentialSubTasksDone* pst = space->par_seq_tasks();
5291   assert(pst->valid(), "Uninitialized use?");
5292 
5293   uint nth_task = 0;
5294   uint n_tasks  = pst->n_tasks();
5295 
5296   HeapWord *start, *end;
5297   while (!pst->is_task_claimed(/* reference */ nth_task)) {
5298     // We claimed task # nth_task; compute its boundaries.
5299     if (chunk_top == 0) {  // no samples were taken
5300       assert(nth_task == 0 && n_tasks == 1, "Can have only 1 EdenSpace task");
5301       start = space->bottom();
5302       end   = space->top();
5303     } else if (nth_task == 0) {
5304       start = space->bottom();
5305       end   = chunk_array[nth_task];
5306     } else if (nth_task < (uint)chunk_top) {
5307       assert(nth_task >= 1, "Control point invariant");
5308       start = chunk_array[nth_task - 1];
5309       end   = chunk_array[nth_task];
5310     } else {
5311       assert(nth_task == (uint)chunk_top, "Control point invariant");
5312       start = chunk_array[chunk_top - 1];
5313       end   = space->top();
5314     }
5315     MemRegion mr(start, end);
5316     // Verify that mr is in space
5317     assert(mr.is_empty() || space->used_region().contains(mr),
5318            "Should be in space");
5319     // Verify that "start" is an object boundary
5320     assert(mr.is_empty() || oop(mr.start())->is_oop(),
5321            "Should be an oop");
5322     space->par_oop_iterate(mr, cl);
5323   }
5324   pst->all_tasks_completed();
5325 }
5326 
5327 void
5328 CMSParRemarkTask::do_dirty_card_rescan_tasks(
5329   CompactibleFreeListSpace* sp, int i,
5330   Par_MarkRefsIntoAndScanClosure* cl) {
5331   // Until all tasks completed:
5332   // . claim an unclaimed task
5333   // . compute region boundaries corresponding to task claimed
5334   // . transfer dirty bits ct->mut for that region
5335   // . apply rescanclosure to dirty mut bits for that region
5336 
5337   ResourceMark rm;
5338   HandleMark   hm;
5339 
5340   OopTaskQueue* work_q = work_queue(i);
5341   ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
5342   // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
5343   // CAUTION: This closure has state that persists across calls to
5344   // the work method dirty_range_iterate_clear() in that it has
5345   // imbedded in it a (subtype of) UpwardsObjectClosure. The
5346   // use of that state in the imbedded UpwardsObjectClosure instance
5347   // assumes that the cards are always iterated (even if in parallel
5348   // by several threads) in monotonically increasing order per each
5349   // thread. This is true of the implementation below which picks
5350   // card ranges (chunks) in monotonically increasing order globally
5351   // and, a-fortiori, in monotonically increasing order per thread
5352   // (the latter order being a subsequence of the former).
5353   // If the work code below is ever reorganized into a more chaotic
5354   // work-partitioning form than the current "sequential tasks"
5355   // paradigm, the use of that persistent state will have to be
5356   // revisited and modified appropriately. See also related
5357   // bug 4756801 work on which should examine this code to make
5358   // sure that the changes there do not run counter to the
5359   // assumptions made here and necessary for correctness and
5360   // efficiency. Note also that this code might yield inefficient
5361   // behaviour in the case of very large objects that span one or
5362   // more work chunks. Such objects would potentially be scanned
5363   // several times redundantly. Work on 4756801 should try and
5364   // address that performance anomaly if at all possible. XXX
5365   MemRegion  full_span  = _collector->_span;
5366   CMSBitMap* bm    = &(_collector->_markBitMap);     // shared
5367   MarkFromDirtyCardsClosure
5368     greyRescanClosure(_collector, full_span, // entire span of interest
5369                       sp, bm, work_q, cl);
5370 
5371   SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
5372   assert(pst->valid(), "Uninitialized use?");
5373   uint nth_task = 0;
5374   const int alignment = CardTableModRefBS::card_size * BitsPerWord;
5375   MemRegion span = sp->used_region();
5376   HeapWord* start_addr = span.start();
5377   HeapWord* end_addr = (HeapWord*)round_to((intptr_t)span.end(),
5378                                            alignment);
5379   const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
5380   assert((HeapWord*)round_to((intptr_t)start_addr, alignment) ==
5381          start_addr, "Check alignment");
5382   assert((size_t)round_to((intptr_t)chunk_size, alignment) ==
5383          chunk_size, "Check alignment");
5384 
5385   while (!pst->is_task_claimed(/* reference */ nth_task)) {
5386     // Having claimed the nth_task, compute corresponding mem-region,
5387     // which is a-fortiori aligned correctly (i.e. at a MUT bopundary).
5388     // The alignment restriction ensures that we do not need any
5389     // synchronization with other gang-workers while setting or
5390     // clearing bits in thus chunk of the MUT.
5391     MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
5392                                     start_addr + (nth_task+1)*chunk_size);
5393     // The last chunk's end might be way beyond end of the
5394     // used region. In that case pull back appropriately.
5395     if (this_span.end() > end_addr) {
5396       this_span.set_end(end_addr);
5397       assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
5398     }
5399     // Iterate over the dirty cards covering this chunk, marking them
5400     // precleaned, and setting the corresponding bits in the mod union
5401     // table. Since we have been careful to partition at Card and MUT-word
5402     // boundaries no synchronization is needed between parallel threads.
5403     _collector->_ct->ct_bs()->dirty_card_iterate(this_span,
5404                                                  &modUnionClosure);
5405 
5406     // Having transferred these marks into the modUnionTable,
5407     // rescan the marked objects on the dirty cards in the modUnionTable.
5408     // Even if this is at a synchronous collection, the initial marking
5409     // may have been done during an asynchronous collection so there
5410     // may be dirty bits in the mod-union table.
5411     _collector->_modUnionTable.dirty_range_iterate_clear(
5412                   this_span, &greyRescanClosure);
5413     _collector->_modUnionTable.verifyNoOneBitsInRange(
5414                                  this_span.start(),
5415                                  this_span.end());
5416   }
5417   pst->all_tasks_completed();  // declare that i am done
5418 }
5419 
5420 // . see if we can share work_queues with ParNew? XXX
5421 void
5422 CMSParRemarkTask::do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl,
5423                                 int* seed) {
5424   OopTaskQueue* work_q = work_queue(i);
5425   NOT_PRODUCT(int num_steals = 0;)
5426   oop obj_to_scan;
5427   CMSBitMap* bm = &(_collector->_markBitMap);
5428 
5429   while (true) {
5430     // Completely finish any left over work from (an) earlier round(s)
5431     cl->trim_queue(0);
5432     size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5433                                          (size_t)ParGCDesiredObjsFromOverflowList);
5434     // Now check if there's any work in the overflow list
5435     // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5436     // only affects the number of attempts made to get work from the
5437     // overflow list and does not affect the number of workers.  Just
5438     // pass ParallelGCThreads so this behavior is unchanged.
5439     if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5440                                                 work_q,
5441                                                 ParallelGCThreads)) {
5442       // found something in global overflow list;
5443       // not yet ready to go stealing work from others.
5444       // We'd like to assert(work_q->size() != 0, ...)
5445       // because we just took work from the overflow list,
5446       // but of course we can't since all of that could have
5447       // been already stolen from us.
5448       // "He giveth and He taketh away."
5449       continue;
5450     }
5451     // Verify that we have no work before we resort to stealing
5452     assert(work_q->size() == 0, "Have work, shouldn't steal");
5453     // Try to steal from other queues that have work
5454     if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5455       NOT_PRODUCT(num_steals++;)
5456       assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5457       assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5458       // Do scanning work
5459       obj_to_scan->oop_iterate(cl);
5460       // Loop around, finish this work, and try to steal some more
5461     } else if (terminator()->offer_termination()) {
5462         break;  // nirvana from the infinite cycle
5463     }
5464   }
5465   NOT_PRODUCT(
5466     if (PrintCMSStatistics != 0) {
5467       gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5468     }
5469   )
5470   assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
5471          "Else our work is not yet done");
5472 }
5473 
5474 // Return a thread-local PLAB recording array, as appropriate.
5475 void* CMSCollector::get_data_recorder(int thr_num) {
5476   if (_survivor_plab_array != NULL &&
5477       (CMSPLABRecordAlways ||
5478        (_collectorState > Marking && _collectorState < FinalMarking))) {
5479     assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
5480     ChunkArray* ca = &_survivor_plab_array[thr_num];
5481     ca->reset();   // clear it so that fresh data is recorded
5482     return (void*) ca;
5483   } else {
5484     return NULL;
5485   }
5486 }
5487 
5488 // Reset all the thread-local PLAB recording arrays
5489 void CMSCollector::reset_survivor_plab_arrays() {
5490   for (uint i = 0; i < ParallelGCThreads; i++) {
5491     _survivor_plab_array[i].reset();
5492   }
5493 }
5494 
5495 // Merge the per-thread plab arrays into the global survivor chunk
5496 // array which will provide the partitioning of the survivor space
5497 // for CMS rescan.
5498 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv,
5499                                               int no_of_gc_threads) {
5500   assert(_survivor_plab_array  != NULL, "Error");
5501   assert(_survivor_chunk_array != NULL, "Error");
5502   assert(_collectorState == FinalMarking, "Error");

5503   for (int j = 0; j < no_of_gc_threads; j++) {
5504     _cursor[j] = 0;
5505   }
5506   HeapWord* top = surv->top();
5507   size_t i;
5508   for (i = 0; i < _survivor_chunk_capacity; i++) {  // all sca entries
5509     HeapWord* min_val = top;          // Higher than any PLAB address
5510     uint      min_tid = 0;            // position of min_val this round
5511     for (int j = 0; j < no_of_gc_threads; j++) {
5512       ChunkArray* cur_sca = &_survivor_plab_array[j];
5513       if (_cursor[j] == cur_sca->end()) {
5514         continue;
5515       }
5516       assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
5517       HeapWord* cur_val = cur_sca->nth(_cursor[j]);
5518       assert(surv->used_region().contains(cur_val), "Out of bounds value");
5519       if (cur_val < min_val) {
5520         min_tid = j;
5521         min_val = cur_val;
5522       } else {
5523         assert(cur_val < top, "All recorded addresses should be less");
5524       }
5525     }
5526     // At this point min_val and min_tid are respectively
5527     // the least address in _survivor_plab_array[j]->nth(_cursor[j])
5528     // and the thread (j) that witnesses that address.
5529     // We record this address in the _survivor_chunk_array[i]
5530     // and increment _cursor[min_tid] prior to the next round i.
5531     if (min_val == top) {
5532       break;
5533     }
5534     _survivor_chunk_array[i] = min_val;
5535     _cursor[min_tid]++;
5536   }
5537   // We are all done; record the size of the _survivor_chunk_array
5538   _survivor_chunk_index = i; // exclusive: [0, i)
5539   if (PrintCMSStatistics > 0) {
5540     gclog_or_tty->print(" (Survivor:" SIZE_FORMAT "chunks) ", i);
5541   }
5542   // Verify that we used up all the recorded entries
5543   #ifdef ASSERT
5544     size_t total = 0;
5545     for (int j = 0; j < no_of_gc_threads; j++) {
5546       assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
5547       total += _cursor[j];
5548     }
5549     assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
5550     // Check that the merged array is in sorted order
5551     if (total > 0) {
5552       for (size_t i = 0; i < total - 1; i++) {
5553         if (PrintCMSStatistics > 0) {
5554           gclog_or_tty->print(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
5555                               i, _survivor_chunk_array[i]);
5556         }
5557         assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
5558                "Not sorted");
5559       }
5560     }
5561   #endif // ASSERT
5562 }
5563 
5564 // Set up the space's par_seq_tasks structure for work claiming
5565 // for parallel rescan of young gen.
5566 // See ParRescanTask where this is currently used.
5567 void
5568 CMSCollector::
5569 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
5570   assert(n_threads > 0, "Unexpected n_threads argument");
5571   DefNewGeneration* dng = (DefNewGeneration*)_young_gen;
5572 
5573   // Eden space
5574   {
5575     SequentialSubTasksDone* pst = dng->eden()->par_seq_tasks();
5576     assert(!pst->valid(), "Clobbering existing data?");
5577     // Each valid entry in [0, _eden_chunk_index) represents a task.
5578     size_t n_tasks = _eden_chunk_index + 1;
5579     assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
5580     // Sets the condition for completion of the subtask (how many threads
5581     // need to finish in order to be done).
5582     pst->set_n_threads(n_threads);
5583     pst->set_n_tasks((int)n_tasks);
5584   }
5585 
5586   // Merge the survivor plab arrays into _survivor_chunk_array
5587   if (_survivor_plab_array != NULL) {
5588     merge_survivor_plab_arrays(dng->from(), n_threads);
5589   } else {
5590     assert(_survivor_chunk_index == 0, "Error");
5591   }
5592 
5593   // To space
5594   {
5595     SequentialSubTasksDone* pst = dng->to()->par_seq_tasks();
5596     assert(!pst->valid(), "Clobbering existing data?");
5597     // Sets the condition for completion of the subtask (how many threads
5598     // need to finish in order to be done).
5599     pst->set_n_threads(n_threads);
5600     pst->set_n_tasks(1);
5601     assert(pst->valid(), "Error");
5602   }
5603 
5604   // From space
5605   {
5606     SequentialSubTasksDone* pst = dng->from()->par_seq_tasks();
5607     assert(!pst->valid(), "Clobbering existing data?");
5608     size_t n_tasks = _survivor_chunk_index + 1;
5609     assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
5610     // Sets the condition for completion of the subtask (how many threads
5611     // need to finish in order to be done).
5612     pst->set_n_threads(n_threads);
5613     pst->set_n_tasks((int)n_tasks);
5614     assert(pst->valid(), "Error");
5615   }
5616 }
5617 
5618 // Parallel version of remark
5619 void CMSCollector::do_remark_parallel() {
5620   GenCollectedHeap* gch = GenCollectedHeap::heap();
5621   FlexibleWorkGang* workers = gch->workers();
5622   assert(workers != NULL, "Need parallel worker threads.");
5623   // Choose to use the number of GC workers most recently set
5624   // into "active_workers".  If active_workers is not set, set it
5625   // to ParallelGCThreads.
5626   int n_workers = workers->active_workers();
5627   if (n_workers == 0) {
5628     assert(n_workers > 0, "Should have been set during scavenge");
5629     n_workers = ParallelGCThreads;
5630     workers->set_active_workers(n_workers);
5631   }
5632   CompactibleFreeListSpace* cms_space  = _cmsGen->cmsSpace();
5633 
5634   CMSParRemarkTask tsk(this,
5635     cms_space,
5636     n_workers, workers, task_queues());
5637 
5638   // Set up for parallel process_strong_roots work.
5639   gch->set_par_threads(n_workers);
5640   // We won't be iterating over the cards in the card table updating
5641   // the younger_gen cards, so we shouldn't call the following else
5642   // the verification code as well as subsequent younger_refs_iterate
5643   // code would get confused. XXX
5644   // gch->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
5645 
5646   // The young gen rescan work will not be done as part of
5647   // process_strong_roots (which currently doesn't knw how to
5648   // parallelize such a scan), but rather will be broken up into
5649   // a set of parallel tasks (via the sampling that the [abortable]
5650   // preclean phase did of EdenSpace, plus the [two] tasks of
5651   // scanning the [two] survivor spaces. Further fine-grain
5652   // parallelization of the scanning of the survivor spaces
5653   // themselves, and of precleaning of the younger gen itself
5654   // is deferred to the future.
5655   initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
5656 
5657   // The dirty card rescan work is broken up into a "sequence"
5658   // of parallel tasks (per constituent space) that are dynamically
5659   // claimed by the parallel threads.
5660   cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
5661 
5662   // It turns out that even when we're using 1 thread, doing the work in a
5663   // separate thread causes wide variance in run times.  We can't help this
5664   // in the multi-threaded case, but we special-case n=1 here to get
5665   // repeatable measurements of the 1-thread overhead of the parallel code.
5666   if (n_workers > 1) {
5667     // Make refs discovery MT-safe, if it isn't already: it may not
5668     // necessarily be so, since it's possible that we are doing
5669     // ST marking.
5670     ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), true);
5671     GenCollectedHeap::StrongRootsScope srs(gch);
5672     workers->run_task(&tsk);
5673   } else {
5674     ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5675     GenCollectedHeap::StrongRootsScope srs(gch);
5676     tsk.work(0);
5677   }
5678 
5679   gch->set_par_threads(0);  // 0 ==> non-parallel.
5680   // restore, single-threaded for now, any preserved marks
5681   // as a result of work_q overflow
5682   restore_preserved_marks_if_any();
5683 }
5684 
5685 // Non-parallel version of remark
5686 void CMSCollector::do_remark_non_parallel() {
5687   ResourceMark rm;
5688   HandleMark   hm;
5689   GenCollectedHeap* gch = GenCollectedHeap::heap();
5690   ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5691 
5692   MarkRefsIntoAndScanClosure
5693     mrias_cl(_span, ref_processor(), &_markBitMap, NULL /* not precleaning */,
5694              &_markStack, this,
5695              false /* should_yield */, false /* not precleaning */);
5696   MarkFromDirtyCardsClosure
5697     markFromDirtyCardsClosure(this, _span,
5698                               NULL,  // space is set further below
5699                               &_markBitMap, &_markStack, &mrias_cl);
5700   {
5701     TraceTime t("grey object rescan", PrintGCDetails, false, gclog_or_tty);
5702     // Iterate over the dirty cards, setting the corresponding bits in the
5703     // mod union table.
5704     {
5705       ModUnionClosure modUnionClosure(&_modUnionTable);
5706       _ct->ct_bs()->dirty_card_iterate(
5707                       _cmsGen->used_region(),
5708                       &modUnionClosure);
5709     }
5710     // Having transferred these marks into the modUnionTable, we just need
5711     // to rescan the marked objects on the dirty cards in the modUnionTable.
5712     // The initial marking may have been done during an asynchronous
5713     // collection so there may be dirty bits in the mod-union table.
5714     const int alignment =
5715       CardTableModRefBS::card_size * BitsPerWord;
5716     {
5717       // ... First handle dirty cards in CMS gen
5718       markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
5719       MemRegion ur = _cmsGen->used_region();
5720       HeapWord* lb = ur.start();
5721       HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
5722       MemRegion cms_span(lb, ub);
5723       _modUnionTable.dirty_range_iterate_clear(cms_span,
5724                                                &markFromDirtyCardsClosure);
5725       verify_work_stacks_empty();
5726       if (PrintCMSStatistics != 0) {
5727         gclog_or_tty->print(" (re-scanned "SIZE_FORMAT" dirty cards in cms gen) ",
5728           markFromDirtyCardsClosure.num_dirty_cards());
5729       }
5730     }
5731   }
5732   if (VerifyDuringGC &&
5733       GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5734     HandleMark hm;  // Discard invalid handles created during verification
5735     Universe::verify();
5736   }
5737   {
5738     TraceTime t("root rescan", PrintGCDetails, false, gclog_or_tty);
5739 
5740     verify_work_stacks_empty();
5741 
5742     gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
5743     GenCollectedHeap::StrongRootsScope srs(gch);
5744     gch->gen_process_strong_roots(_cmsGen->level(),
5745                                   true,  // younger gens as roots
5746                                   false, // use the local StrongRootsScope
5747                                   false, // not scavenging
5748                                   SharedHeap::ScanningOption(roots_scanning_options()),
5749                                   &mrias_cl,
5750                                   true,   // walk code active on stacks
5751                                   NULL,
5752                                   NULL);  // The dirty klasses will be handled below
5753 
5754     assert(should_unload_classes()
5755            || (roots_scanning_options() & SharedHeap::SO_CodeCache),
5756            "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5757   }
5758 
5759   {
5760     TraceTime t("visit unhandled CLDs", PrintGCDetails, false, gclog_or_tty);
5761 
5762     verify_work_stacks_empty();
5763 
5764     // Scan all class loader data objects that might have been introduced
5765     // during concurrent marking.
5766     ResourceMark rm;
5767     GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
5768     for (int i = 0; i < array->length(); i++) {
5769       mrias_cl.do_class_loader_data(array->at(i));
5770     }
5771 
5772     // We don't need to keep track of new CLDs anymore.
5773     ClassLoaderDataGraph::remember_new_clds(false);
5774 
5775     verify_work_stacks_empty();
5776   }
5777 
5778   {
5779     TraceTime t("dirty klass scan", PrintGCDetails, false, gclog_or_tty);
5780 
5781     verify_work_stacks_empty();
5782 
5783     RemarkKlassClosure remark_klass_closure(&mrias_cl);
5784     ClassLoaderDataGraph::classes_do(&remark_klass_closure);
5785 
5786     verify_work_stacks_empty();
5787   }
5788 
5789   // We might have added oops to ClassLoaderData::_handles during the
5790   // concurrent marking phase. These oops point to newly allocated objects
5791   // that are guaranteed to be kept alive. Either by the direct allocation
5792   // code, or when the young collector processes the strong roots. Hence,
5793   // we don't have to revisit the _handles block during the remark phase.
5794 
5795   verify_work_stacks_empty();
5796   // Restore evacuated mark words, if any, used for overflow list links
5797   if (!CMSOverflowEarlyRestoration) {
5798     restore_preserved_marks_if_any();
5799   }
5800   verify_overflow_empty();
5801 }
5802 
5803 ////////////////////////////////////////////////////////
5804 // Parallel Reference Processing Task Proxy Class
5805 ////////////////////////////////////////////////////////
5806 class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues {
5807   typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
5808   CMSCollector*          _collector;
5809   CMSBitMap*             _mark_bit_map;
5810   const MemRegion        _span;
5811   ProcessTask&           _task;
5812 
5813 public:
5814   CMSRefProcTaskProxy(ProcessTask&     task,
5815                       CMSCollector*    collector,
5816                       const MemRegion& span,
5817                       CMSBitMap*       mark_bit_map,
5818                       AbstractWorkGang* workers,
5819                       OopTaskQueueSet* task_queues):
5820     // XXX Should superclass AGTWOQ also know about AWG since it knows
5821     // about the task_queues used by the AWG? Then it could initialize
5822     // the terminator() object. See 6984287. The set_for_termination()
5823     // below is a temporary band-aid for the regression in 6984287.
5824     AbstractGangTaskWOopQueues("Process referents by policy in parallel",
5825       task_queues),
5826     _task(task),
5827     _collector(collector), _span(span), _mark_bit_map(mark_bit_map)
5828   {
5829     assert(_collector->_span.equals(_span) && !_span.is_empty(),
5830            "Inconsistency in _span");
5831     set_for_termination(workers->active_workers());
5832   }
5833 
5834   OopTaskQueueSet* task_queues() { return queues(); }
5835 
5836   OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5837 
5838   void do_work_steal(int i,
5839                      CMSParDrainMarkingStackClosure* drain,
5840                      CMSParKeepAliveClosure* keep_alive,
5841                      int* seed);
5842 
5843   virtual void work(uint worker_id);
5844 };
5845 
5846 void CMSRefProcTaskProxy::work(uint worker_id) {
5847   assert(_collector->_span.equals(_span), "Inconsistency in _span");
5848   CMSParKeepAliveClosure par_keep_alive(_collector, _span,
5849                                         _mark_bit_map,
5850                                         work_queue(worker_id));
5851   CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
5852                                                  _mark_bit_map,
5853                                                  work_queue(worker_id));
5854   CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
5855   _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack);
5856   if (_task.marks_oops_alive()) {
5857     do_work_steal(worker_id, &par_drain_stack, &par_keep_alive,
5858                   _collector->hash_seed(worker_id));
5859   }
5860   assert(work_queue(worker_id)->size() == 0, "work_queue should be empty");
5861   assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
5862 }
5863 
5864 class CMSRefEnqueueTaskProxy: public AbstractGangTask {
5865   typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
5866   EnqueueTask& _task;
5867 
5868 public:
5869   CMSRefEnqueueTaskProxy(EnqueueTask& task)
5870     : AbstractGangTask("Enqueue reference objects in parallel"),
5871       _task(task)
5872   { }
5873 
5874   virtual void work(uint worker_id)
5875   {
5876     _task.work(worker_id);
5877   }
5878 };
5879 
5880 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
5881   MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue):
5882    _span(span),
5883    _bit_map(bit_map),
5884    _work_queue(work_queue),
5885    _mark_and_push(collector, span, bit_map, work_queue),
5886    _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
5887                         (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads)))
5888 { }
5889 
5890 // . see if we can share work_queues with ParNew? XXX
5891 void CMSRefProcTaskProxy::do_work_steal(int i,
5892   CMSParDrainMarkingStackClosure* drain,
5893   CMSParKeepAliveClosure* keep_alive,
5894   int* seed) {
5895   OopTaskQueue* work_q = work_queue(i);
5896   NOT_PRODUCT(int num_steals = 0;)
5897   oop obj_to_scan;
5898 
5899   while (true) {
5900     // Completely finish any left over work from (an) earlier round(s)
5901     drain->trim_queue(0);
5902     size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5903                                          (size_t)ParGCDesiredObjsFromOverflowList);
5904     // Now check if there's any work in the overflow list
5905     // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5906     // only affects the number of attempts made to get work from the
5907     // overflow list and does not affect the number of workers.  Just
5908     // pass ParallelGCThreads so this behavior is unchanged.
5909     if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5910                                                 work_q,
5911                                                 ParallelGCThreads)) {
5912       // Found something in global overflow list;
5913       // not yet ready to go stealing work from others.
5914       // We'd like to assert(work_q->size() != 0, ...)
5915       // because we just took work from the overflow list,
5916       // but of course we can't, since all of that might have
5917       // been already stolen from us.
5918       continue;
5919     }
5920     // Verify that we have no work before we resort to stealing
5921     assert(work_q->size() == 0, "Have work, shouldn't steal");
5922     // Try to steal from other queues that have work
5923     if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5924       NOT_PRODUCT(num_steals++;)
5925       assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5926       assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5927       // Do scanning work
5928       obj_to_scan->oop_iterate(keep_alive);
5929       // Loop around, finish this work, and try to steal some more
5930     } else if (terminator()->offer_termination()) {
5931       break;  // nirvana from the infinite cycle
5932     }
5933   }
5934   NOT_PRODUCT(
5935     if (PrintCMSStatistics != 0) {
5936       gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5937     }
5938   )
5939 }
5940 
5941 void CMSRefProcTaskExecutor::execute(ProcessTask& task)
5942 {
5943   GenCollectedHeap* gch = GenCollectedHeap::heap();
5944   FlexibleWorkGang* workers = gch->workers();
5945   assert(workers != NULL, "Need parallel worker threads.");
5946   CMSRefProcTaskProxy rp_task(task, &_collector,
5947                               _collector.ref_processor()->span(),
5948                               _collector.markBitMap(),
5949                               workers, _collector.task_queues());
5950   workers->run_task(&rp_task);
5951 }
5952 
5953 void CMSRefProcTaskExecutor::execute(EnqueueTask& task)
5954 {
5955 
5956   GenCollectedHeap* gch = GenCollectedHeap::heap();
5957   FlexibleWorkGang* workers = gch->workers();
5958   assert(workers != NULL, "Need parallel worker threads.");
5959   CMSRefEnqueueTaskProxy enq_task(task);
5960   workers->run_task(&enq_task);
5961 }
5962 
5963 void CMSCollector::refProcessingWork(bool asynch, bool clear_all_soft_refs) {
5964 
5965   ResourceMark rm;
5966   HandleMark   hm;
5967 
5968   ReferenceProcessor* rp = ref_processor();
5969   assert(rp->span().equals(_span), "Spans should be equal");
5970   assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
5971   // Process weak references.
5972   rp->setup_policy(clear_all_soft_refs);
5973   verify_work_stacks_empty();
5974 
5975   CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
5976                                           &_markStack, false /* !preclean */);
5977   CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
5978                                 _span, &_markBitMap, &_markStack,
5979                                 &cmsKeepAliveClosure, false /* !preclean */);
5980   {
5981     TraceTime t("weak refs processing", PrintGCDetails, false, gclog_or_tty);
5982     if (rp->processing_is_mt()) {
5983       // Set the degree of MT here.  If the discovery is done MT, there
5984       // may have been a different number of threads doing the discovery
5985       // and a different number of discovered lists may have Ref objects.
5986       // That is OK as long as the Reference lists are balanced (see
5987       // balance_all_queues() and balance_queues()).
5988       GenCollectedHeap* gch = GenCollectedHeap::heap();
5989       int active_workers = ParallelGCThreads;
5990       FlexibleWorkGang* workers = gch->workers();
5991       if (workers != NULL) {
5992         active_workers = workers->active_workers();
5993         // The expectation is that active_workers will have already
5994         // been set to a reasonable value.  If it has not been set,
5995         // investigate.
5996         assert(active_workers > 0, "Should have been set during scavenge");
5997       }
5998       rp->set_active_mt_degree(active_workers);
5999       CMSRefProcTaskExecutor task_executor(*this);
6000       rp->process_discovered_references(&_is_alive_closure,
6001                                         &cmsKeepAliveClosure,
6002                                         &cmsDrainMarkingStackClosure,
6003                                         &task_executor);
6004     } else {
6005       rp->process_discovered_references(&_is_alive_closure,
6006                                         &cmsKeepAliveClosure,
6007                                         &cmsDrainMarkingStackClosure,
6008                                         NULL);
6009     }
6010   }
6011 
6012   // This is the point where the entire marking should have completed.
6013   verify_work_stacks_empty();
6014 
6015   if (should_unload_classes()) {
6016     {
6017       TraceTime t("class unloading", PrintGCDetails, false, gclog_or_tty);
6018 
6019       // Unload classes and purge the SystemDictionary.
6020       bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure);
6021 
6022       // Unload nmethods.
6023       CodeCache::do_unloading(&_is_alive_closure, purged_class);
6024 
6025       // Prune dead klasses from subklass/sibling/implementor lists.
6026       Klass::clean_weak_klass_links(&_is_alive_closure);
6027     }
6028 
6029     {
6030       TraceTime t("scrub symbol table", PrintGCDetails, false, gclog_or_tty);
6031       // Clean up unreferenced symbols in symbol table.
6032       SymbolTable::unlink();
6033     }
6034   }
6035 
6036   // CMS doesn't use the StringTable as hard roots when class unloading is turned off.
6037   // Need to check if we really scanned the StringTable.
6038   if ((roots_scanning_options() & SharedHeap::SO_Strings) == 0) {
6039     TraceTime t("scrub string table", PrintGCDetails, false, gclog_or_tty);
6040     // Delete entries for dead interned strings.
6041     StringTable::unlink(&_is_alive_closure);
6042   }
6043 
6044   // Restore any preserved marks as a result of mark stack or
6045   // work queue overflow
6046   restore_preserved_marks_if_any();  // done single-threaded for now
6047 
6048   rp->set_enqueuing_is_done(true);
6049   if (rp->processing_is_mt()) {
6050     rp->balance_all_queues();
6051     CMSRefProcTaskExecutor task_executor(*this);
6052     rp->enqueue_discovered_references(&task_executor);
6053   } else {
6054     rp->enqueue_discovered_references(NULL);
6055   }
6056   rp->verify_no_references_recorded();
6057   assert(!rp->discovery_enabled(), "should have been disabled");
6058 }
6059 
6060 #ifndef PRODUCT
6061 void CMSCollector::check_correct_thread_executing() {
6062   Thread* t = Thread::current();
6063   // Only the VM thread or the CMS thread should be here.
6064   assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
6065          "Unexpected thread type");
6066   // If this is the vm thread, the foreground process
6067   // should not be waiting.  Note that _foregroundGCIsActive is
6068   // true while the foreground collector is waiting.
6069   if (_foregroundGCShouldWait) {
6070     // We cannot be the VM thread
6071     assert(t->is_ConcurrentGC_thread(),
6072            "Should be CMS thread");
6073   } else {
6074     // We can be the CMS thread only if we are in a stop-world
6075     // phase of CMS collection.
6076     if (t->is_ConcurrentGC_thread()) {
6077       assert(_collectorState == InitialMarking ||
6078              _collectorState == FinalMarking,
6079              "Should be a stop-world phase");
6080       // The CMS thread should be holding the CMS_token.
6081       assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6082              "Potential interference with concurrently "
6083              "executing VM thread");
6084     }
6085   }
6086 }
6087 #endif
6088 
6089 void CMSCollector::sweep(bool asynch) {
6090   assert(_collectorState == Sweeping, "just checking");
6091   check_correct_thread_executing();
6092   verify_work_stacks_empty();
6093   verify_overflow_empty();
6094   increment_sweep_count();
6095   TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
6096 
6097   _inter_sweep_timer.stop();
6098   _inter_sweep_estimate.sample(_inter_sweep_timer.seconds());
6099   size_policy()->avg_cms_free_at_sweep()->sample(_cmsGen->free());
6100 
6101   assert(!_intra_sweep_timer.is_active(), "Should not be active");
6102   _intra_sweep_timer.reset();
6103   _intra_sweep_timer.start();
6104   if (asynch) {
6105     TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6106     CMSPhaseAccounting pa(this, "sweep", !PrintGCDetails);
6107     // First sweep the old gen
6108     {
6109       CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
6110                                bitMapLock());
6111       sweepWork(_cmsGen, asynch);
6112     }
6113 
6114     // Update Universe::_heap_*_at_gc figures.
6115     // We need all the free list locks to make the abstract state
6116     // transition from Sweeping to Resetting. See detailed note
6117     // further below.
6118     {
6119       CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock());
6120       // Update heap occupancy information which is used as
6121       // input to soft ref clearing policy at the next gc.
6122       Universe::update_heap_info_at_gc();
6123       _collectorState = Resizing;
6124     }
6125   } else {
6126     // already have needed locks
6127     sweepWork(_cmsGen,  asynch);
6128     // Update heap occupancy information which is used as
6129     // input to soft ref clearing policy at the next gc.
6130     Universe::update_heap_info_at_gc();
6131     _collectorState = Resizing;
6132   }
6133   verify_work_stacks_empty();
6134   verify_overflow_empty();
6135 
6136   if (should_unload_classes()) {
6137     ClassLoaderDataGraph::purge();
6138   }
6139 
6140   _intra_sweep_timer.stop();
6141   _intra_sweep_estimate.sample(_intra_sweep_timer.seconds());
6142 
6143   _inter_sweep_timer.reset();
6144   _inter_sweep_timer.start();
6145 
6146   // We need to use a monotonically non-deccreasing time in ms
6147   // or we will see time-warp warnings and os::javaTimeMillis()
6148   // does not guarantee monotonicity.
6149   jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
6150   update_time_of_last_gc(now);
6151 
6152   // NOTE on abstract state transitions:
6153   // Mutators allocate-live and/or mark the mod-union table dirty
6154   // based on the state of the collection.  The former is done in
6155   // the interval [Marking, Sweeping] and the latter in the interval
6156   // [Marking, Sweeping).  Thus the transitions into the Marking state
6157   // and out of the Sweeping state must be synchronously visible
6158   // globally to the mutators.
6159   // The transition into the Marking state happens with the world
6160   // stopped so the mutators will globally see it.  Sweeping is
6161   // done asynchronously by the background collector so the transition
6162   // from the Sweeping state to the Resizing state must be done
6163   // under the freelistLock (as is the check for whether to
6164   // allocate-live and whether to dirty the mod-union table).
6165   assert(_collectorState == Resizing, "Change of collector state to"
6166     " Resizing must be done under the freelistLocks (plural)");
6167 
6168   // Now that sweeping has been completed, we clear
6169   // the incremental_collection_failed flag,
6170   // thus inviting a younger gen collection to promote into
6171   // this generation. If such a promotion may still fail,
6172   // the flag will be set again when a young collection is
6173   // attempted.
6174   GenCollectedHeap* gch = GenCollectedHeap::heap();
6175   gch->clear_incremental_collection_failed();  // Worth retrying as fresh space may have been freed up
6176   gch->update_full_collections_completed(_collection_count_start);
6177 }
6178 
6179 // FIX ME!!! Looks like this belongs in CFLSpace, with
6180 // CMSGen merely delegating to it.
6181 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
6182   double nearLargestPercent = FLSLargestBlockCoalesceProximity;
6183   HeapWord*  minAddr        = _cmsSpace->bottom();
6184   HeapWord*  largestAddr    =
6185     (HeapWord*) _cmsSpace->dictionary()->find_largest_dict();
6186   if (largestAddr == NULL) {
6187     // The dictionary appears to be empty.  In this case
6188     // try to coalesce at the end of the heap.
6189     largestAddr = _cmsSpace->end();
6190   }
6191   size_t largestOffset     = pointer_delta(largestAddr, minAddr);
6192   size_t nearLargestOffset =
6193     (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
6194   if (PrintFLSStatistics != 0) {
6195     gclog_or_tty->print_cr(
6196       "CMS: Large Block: " PTR_FORMAT ";"
6197       " Proximity: " PTR_FORMAT " -> " PTR_FORMAT,
6198       largestAddr,
6199       _cmsSpace->nearLargestChunk(), minAddr + nearLargestOffset);
6200   }
6201   _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
6202 }
6203 
6204 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
6205   return addr >= _cmsSpace->nearLargestChunk();
6206 }
6207 
6208 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
6209   return _cmsSpace->find_chunk_at_end();
6210 }
6211 
6212 void ConcurrentMarkSweepGeneration::update_gc_stats(int current_level,
6213                                                     bool full) {
6214   // The next lower level has been collected.  Gather any statistics
6215   // that are of interest at this point.
6216   if (!full && (current_level + 1) == level()) {
6217     // Gather statistics on the young generation collection.
6218     collector()->stats().record_gc0_end(used());
6219   }
6220 }
6221 
6222 CMSAdaptiveSizePolicy* ConcurrentMarkSweepGeneration::size_policy() {
6223   GenCollectedHeap* gch = GenCollectedHeap::heap();
6224   assert(gch->kind() == CollectedHeap::GenCollectedHeap,
6225     "Wrong type of heap");
6226   CMSAdaptiveSizePolicy* sp = (CMSAdaptiveSizePolicy*)
6227     gch->gen_policy()->size_policy();
6228   assert(sp->is_gc_cms_adaptive_size_policy(),
6229     "Wrong type of size policy");
6230   return sp;
6231 }
6232 
6233 void ConcurrentMarkSweepGeneration::rotate_debug_collection_type() {
6234   if (PrintGCDetails && Verbose) {
6235     gclog_or_tty->print("Rotate from %d ", _debug_collection_type);
6236   }
6237   _debug_collection_type = (CollectionTypes) (_debug_collection_type + 1);
6238   _debug_collection_type =
6239     (CollectionTypes) (_debug_collection_type % Unknown_collection_type);
6240   if (PrintGCDetails && Verbose) {
6241     gclog_or_tty->print_cr("to %d ", _debug_collection_type);
6242   }
6243 }
6244 
6245 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* gen,
6246   bool asynch) {
6247   // We iterate over the space(s) underlying this generation,
6248   // checking the mark bit map to see if the bits corresponding
6249   // to specific blocks are marked or not. Blocks that are
6250   // marked are live and are not swept up. All remaining blocks
6251   // are swept up, with coalescing on-the-fly as we sweep up
6252   // contiguous free and/or garbage blocks:
6253   // We need to ensure that the sweeper synchronizes with allocators
6254   // and stop-the-world collectors. In particular, the following
6255   // locks are used:
6256   // . CMS token: if this is held, a stop the world collection cannot occur
6257   // . freelistLock: if this is held no allocation can occur from this
6258   //                 generation by another thread
6259   // . bitMapLock: if this is held, no other thread can access or update
6260   //
6261 
6262   // Note that we need to hold the freelistLock if we use
6263   // block iterate below; else the iterator might go awry if
6264   // a mutator (or promotion) causes block contents to change
6265   // (for instance if the allocator divvies up a block).
6266   // If we hold the free list lock, for all practical purposes
6267   // young generation GC's can't occur (they'll usually need to
6268   // promote), so we might as well prevent all young generation
6269   // GC's while we do a sweeping step. For the same reason, we might
6270   // as well take the bit map lock for the entire duration
6271 
6272   // check that we hold the requisite locks
6273   assert(have_cms_token(), "Should hold cms token");
6274   assert(   (asynch && ConcurrentMarkSweepThread::cms_thread_has_cms_token())
6275          || (!asynch && ConcurrentMarkSweepThread::vm_thread_has_cms_token()),
6276         "Should possess CMS token to sweep");
6277   assert_lock_strong(gen->freelistLock());
6278   assert_lock_strong(bitMapLock());
6279 
6280   assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context");
6281   assert(_intra_sweep_timer.is_active(),  "Was switched on  in an outer context");
6282   gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
6283                                       _inter_sweep_estimate.padded_average(),
6284                                       _intra_sweep_estimate.padded_average());
6285   gen->setNearLargestChunk();
6286 
6287   {
6288     SweepClosure sweepClosure(this, gen, &_markBitMap,
6289                             CMSYield && asynch);
6290     gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
6291     // We need to free-up/coalesce garbage/blocks from a
6292     // co-terminal free run. This is done in the SweepClosure
6293     // destructor; so, do not remove this scope, else the
6294     // end-of-sweep-census below will be off by a little bit.
6295   }
6296   gen->cmsSpace()->sweep_completed();
6297   gen->cmsSpace()->endSweepFLCensus(sweep_count());
6298   if (should_unload_classes()) {                // unloaded classes this cycle,
6299     _concurrent_cycles_since_last_unload = 0;   // ... reset count
6300   } else {                                      // did not unload classes,
6301     _concurrent_cycles_since_last_unload++;     // ... increment count
6302   }
6303 }
6304 
6305 // Reset CMS data structures (for now just the marking bit map)
6306 // preparatory for the next cycle.
6307 void CMSCollector::reset(bool asynch) {
6308   GenCollectedHeap* gch = GenCollectedHeap::heap();
6309   CMSAdaptiveSizePolicy* sp = size_policy();
6310   AdaptiveSizePolicyOutput(sp, gch->total_collections());
6311   if (asynch) {
6312     CMSTokenSyncWithLocks ts(true, bitMapLock());
6313 
6314     // If the state is not "Resetting", the foreground  thread
6315     // has done a collection and the resetting.
6316     if (_collectorState != Resetting) {
6317       assert(_collectorState == Idling, "The state should only change"
6318         " because the foreground collector has finished the collection");
6319       return;
6320     }
6321 
6322     // Clear the mark bitmap (no grey objects to start with)
6323     // for the next cycle.
6324     TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6325     CMSPhaseAccounting cmspa(this, "reset", !PrintGCDetails);
6326 
6327     HeapWord* curAddr = _markBitMap.startWord();
6328     while (curAddr < _markBitMap.endWord()) {
6329       size_t remaining  = pointer_delta(_markBitMap.endWord(), curAddr);
6330       MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
6331       _markBitMap.clear_large_range(chunk);
6332       if (ConcurrentMarkSweepThread::should_yield() &&
6333           !foregroundGCIsActive() &&
6334           CMSYield) {
6335         assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6336                "CMS thread should hold CMS token");
6337         assert_lock_strong(bitMapLock());
6338         bitMapLock()->unlock();
6339         ConcurrentMarkSweepThread::desynchronize(true);
6340         ConcurrentMarkSweepThread::acknowledge_yield_request();
6341         stopTimer();
6342         if (PrintCMSStatistics != 0) {
6343           incrementYields();
6344         }
6345         icms_wait();
6346 
6347         // See the comment in coordinator_yield()
6348         for (unsigned i = 0; i < CMSYieldSleepCount &&
6349                          ConcurrentMarkSweepThread::should_yield() &&
6350                          !CMSCollector::foregroundGCIsActive(); ++i) {
6351           os::sleep(Thread::current(), 1, false);
6352           ConcurrentMarkSweepThread::acknowledge_yield_request();
6353         }
6354 
6355         ConcurrentMarkSweepThread::synchronize(true);
6356         bitMapLock()->lock_without_safepoint_check();
6357         startTimer();
6358       }
6359       curAddr = chunk.end();
6360     }
6361     // A successful mostly concurrent collection has been done.
6362     // Because only the full (i.e., concurrent mode failure) collections
6363     // are being measured for gc overhead limits, clean the "near" flag
6364     // and count.
6365     sp->reset_gc_overhead_limit_count();
6366     _collectorState = Idling;
6367   } else {
6368     // already have the lock
6369     assert(_collectorState == Resetting, "just checking");
6370     assert_lock_strong(bitMapLock());
6371     _markBitMap.clear_all();
6372     _collectorState = Idling;
6373   }
6374 
6375   // Stop incremental mode after a cycle completes, so that any future cycles
6376   // are triggered by allocation.
6377   stop_icms();
6378 
6379   NOT_PRODUCT(
6380     if (RotateCMSCollectionTypes) {
6381       _cmsGen->rotate_debug_collection_type();
6382     }
6383   )
6384 }
6385 
6386 void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) {
6387   gclog_or_tty->date_stamp(PrintGC && PrintGCDateStamps);
6388   TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6389   TraceTime t(GCCauseString("GC", gc_cause), PrintGC, !PrintGCDetails, gclog_or_tty);
6390   TraceCollectorStats tcs(counters());
6391 
6392   switch (op) {
6393     case CMS_op_checkpointRootsInitial: {
6394       SvcGCMarker sgcm(SvcGCMarker::OTHER);
6395       checkpointRootsInitial(true);       // asynch
6396       if (PrintGC) {
6397         _cmsGen->printOccupancy("initial-mark");
6398       }
6399       break;
6400     }
6401     case CMS_op_checkpointRootsFinal: {
6402       SvcGCMarker sgcm(SvcGCMarker::OTHER);
6403       checkpointRootsFinal(true,    // asynch
6404                            false,   // !clear_all_soft_refs
6405                            false);  // !init_mark_was_synchronous
6406       if (PrintGC) {
6407         _cmsGen->printOccupancy("remark");
6408       }
6409       break;
6410     }
6411     default:
6412       fatal("No such CMS_op");
6413   }
6414 }
6415 
6416 #ifndef PRODUCT
6417 size_t const CMSCollector::skip_header_HeapWords() {
6418   return FreeChunk::header_size();
6419 }
6420 
6421 // Try and collect here conditions that should hold when
6422 // CMS thread is exiting. The idea is that the foreground GC
6423 // thread should not be blocked if it wants to terminate
6424 // the CMS thread and yet continue to run the VM for a while
6425 // after that.
6426 void CMSCollector::verify_ok_to_terminate() const {
6427   assert(Thread::current()->is_ConcurrentGC_thread(),
6428          "should be called by CMS thread");
6429   assert(!_foregroundGCShouldWait, "should be false");
6430   // We could check here that all the various low-level locks
6431   // are not held by the CMS thread, but that is overkill; see
6432   // also CMSThread::verify_ok_to_terminate() where the CGC_lock
6433   // is checked.
6434 }
6435 #endif
6436 
6437 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
6438    assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
6439           "missing Printezis mark?");
6440   HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
6441   size_t size = pointer_delta(nextOneAddr + 1, addr);
6442   assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6443          "alignment problem");
6444   assert(size >= 3, "Necessary for Printezis marks to work");
6445   return size;
6446 }
6447 
6448 // A variant of the above (block_size_using_printezis_bits()) except
6449 // that we return 0 if the P-bits are not yet set.
6450 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
6451   if (_markBitMap.isMarked(addr + 1)) {
6452     assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects");
6453     HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
6454     size_t size = pointer_delta(nextOneAddr + 1, addr);
6455     assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6456            "alignment problem");
6457     assert(size >= 3, "Necessary for Printezis marks to work");
6458     return size;
6459   }
6460   return 0;
6461 }
6462 
6463 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
6464   size_t sz = 0;
6465   oop p = (oop)addr;
6466   if (p->klass_or_null() != NULL) {
6467     sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
6468   } else {
6469     sz = block_size_using_printezis_bits(addr);
6470   }
6471   assert(sz > 0, "size must be nonzero");
6472   HeapWord* next_block = addr + sz;
6473   HeapWord* next_card  = (HeapWord*)round_to((uintptr_t)next_block,
6474                                              CardTableModRefBS::card_size);
6475   assert(round_down((uintptr_t)addr,      CardTableModRefBS::card_size) <
6476          round_down((uintptr_t)next_card, CardTableModRefBS::card_size),
6477          "must be different cards");
6478   return next_card;
6479 }
6480 
6481 
6482 // CMS Bit Map Wrapper /////////////////////////////////////////
6483 
6484 // Construct a CMS bit map infrastructure, but don't create the
6485 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
6486 // further below.
6487 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
6488   _bm(),
6489   _shifter(shifter),
6490   _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true) : NULL)
6491 {
6492   _bmStartWord = 0;
6493   _bmWordSize  = 0;
6494 }
6495 
6496 bool CMSBitMap::allocate(MemRegion mr) {
6497   _bmStartWord = mr.start();
6498   _bmWordSize  = mr.word_size();
6499   ReservedSpace brs(ReservedSpace::allocation_align_size_up(
6500                      (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
6501   if (!brs.is_reserved()) {
6502     warning("CMS bit map allocation failure");
6503     return false;
6504   }
6505   // For now we'll just commit all of the bit map up fromt.
6506   // Later on we'll try to be more parsimonious with swap.
6507   if (!_virtual_space.initialize(brs, brs.size())) {
6508     warning("CMS bit map backing store failure");
6509     return false;
6510   }
6511   assert(_virtual_space.committed_size() == brs.size(),
6512          "didn't reserve backing store for all of CMS bit map?");
6513   _bm.set_map((BitMap::bm_word_t*)_virtual_space.low());
6514   assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
6515          _bmWordSize, "inconsistency in bit map sizing");
6516   _bm.set_size(_bmWordSize >> _shifter);
6517 
6518   // bm.clear(); // can we rely on getting zero'd memory? verify below
6519   assert(isAllClear(),
6520          "Expected zero'd memory from ReservedSpace constructor");
6521   assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
6522          "consistency check");
6523   return true;
6524 }
6525 
6526 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
6527   HeapWord *next_addr, *end_addr, *last_addr;
6528   assert_locked();
6529   assert(covers(mr), "out-of-range error");
6530   // XXX assert that start and end are appropriately aligned
6531   for (next_addr = mr.start(), end_addr = mr.end();
6532        next_addr < end_addr; next_addr = last_addr) {
6533     MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
6534     last_addr = dirty_region.end();
6535     if (!dirty_region.is_empty()) {
6536       cl->do_MemRegion(dirty_region);
6537     } else {
6538       assert(last_addr == end_addr, "program logic");
6539       return;
6540     }
6541   }
6542 }
6543 
6544 void CMSBitMap::print_on_error(outputStream* st, const char* prefix) const {
6545   _bm.print_on_error(st, prefix);
6546 }
6547 
6548 #ifndef PRODUCT
6549 void CMSBitMap::assert_locked() const {
6550   CMSLockVerifier::assert_locked(lock());
6551 }
6552 
6553 bool CMSBitMap::covers(MemRegion mr) const {
6554   // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
6555   assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
6556          "size inconsistency");
6557   return (mr.start() >= _bmStartWord) &&
6558          (mr.end()   <= endWord());
6559 }
6560 
6561 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
6562     return (start >= _bmStartWord && (start + size) <= endWord());
6563 }
6564 
6565 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
6566   // verify that there are no 1 bits in the interval [left, right)
6567   FalseBitMapClosure falseBitMapClosure;
6568   iterate(&falseBitMapClosure, left, right);
6569 }
6570 
6571 void CMSBitMap::region_invariant(MemRegion mr)
6572 {
6573   assert_locked();
6574   // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
6575   assert(!mr.is_empty(), "unexpected empty region");
6576   assert(covers(mr), "mr should be covered by bit map");
6577   // convert address range into offset range
6578   size_t start_ofs = heapWordToOffset(mr.start());
6579   // Make sure that end() is appropriately aligned
6580   assert(mr.end() == (HeapWord*)round_to((intptr_t)mr.end(),
6581                         (1 << (_shifter+LogHeapWordSize))),
6582          "Misaligned mr.end()");
6583   size_t end_ofs   = heapWordToOffset(mr.end());
6584   assert(end_ofs > start_ofs, "Should mark at least one bit");
6585 }
6586 
6587 #endif
6588 
6589 bool CMSMarkStack::allocate(size_t size) {
6590   // allocate a stack of the requisite depth
6591   ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6592                    size * sizeof(oop)));
6593   if (!rs.is_reserved()) {
6594     warning("CMSMarkStack allocation failure");
6595     return false;
6596   }
6597   if (!_virtual_space.initialize(rs, rs.size())) {
6598     warning("CMSMarkStack backing store failure");
6599     return false;
6600   }
6601   assert(_virtual_space.committed_size() == rs.size(),
6602          "didn't reserve backing store for all of CMS stack?");
6603   _base = (oop*)(_virtual_space.low());
6604   _index = 0;
6605   _capacity = size;
6606   NOT_PRODUCT(_max_depth = 0);
6607   return true;
6608 }
6609 
6610 // XXX FIX ME !!! In the MT case we come in here holding a
6611 // leaf lock. For printing we need to take a further lock
6612 // which has lower rank. We need to recallibrate the two
6613 // lock-ranks involved in order to be able to rpint the
6614 // messages below. (Or defer the printing to the caller.
6615 // For now we take the expedient path of just disabling the
6616 // messages for the problematic case.)
6617 void CMSMarkStack::expand() {
6618   assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted");
6619   if (_capacity == MarkStackSizeMax) {
6620     if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6621       // We print a warning message only once per CMS cycle.
6622       gclog_or_tty->print_cr(" (benign) Hit CMSMarkStack max size limit");
6623     }
6624     return;
6625   }
6626   // Double capacity if possible
6627   size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax);
6628   // Do not give up existing stack until we have managed to
6629   // get the double capacity that we desired.
6630   ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6631                    new_capacity * sizeof(oop)));
6632   if (rs.is_reserved()) {
6633     // Release the backing store associated with old stack
6634     _virtual_space.release();
6635     // Reinitialize virtual space for new stack
6636     if (!_virtual_space.initialize(rs, rs.size())) {
6637       fatal("Not enough swap for expanded marking stack");
6638     }
6639     _base = (oop*)(_virtual_space.low());
6640     _index = 0;
6641     _capacity = new_capacity;
6642   } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6643     // Failed to double capacity, continue;
6644     // we print a detail message only once per CMS cycle.
6645     gclog_or_tty->print(" (benign) Failed to expand marking stack from "SIZE_FORMAT"K to "
6646             SIZE_FORMAT"K",
6647             _capacity / K, new_capacity / K);
6648   }
6649 }
6650 
6651 
6652 // Closures
6653 // XXX: there seems to be a lot of code  duplication here;
6654 // should refactor and consolidate common code.
6655 
6656 // This closure is used to mark refs into the CMS generation in
6657 // the CMS bit map. Called at the first checkpoint. This closure
6658 // assumes that we do not need to re-mark dirty cards; if the CMS
6659 // generation on which this is used is not an oldest
6660 // generation then this will lose younger_gen cards!
6661 
6662 MarkRefsIntoClosure::MarkRefsIntoClosure(
6663   MemRegion span, CMSBitMap* bitMap):
6664     _span(span),
6665     _bitMap(bitMap)
6666 {
6667     assert(_ref_processor == NULL, "deliberately left NULL");
6668     assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6669 }
6670 
6671 void MarkRefsIntoClosure::do_oop(oop obj) {
6672   // if p points into _span, then mark corresponding bit in _markBitMap
6673   assert(obj->is_oop(), "expected an oop");
6674   HeapWord* addr = (HeapWord*)obj;
6675   if (_span.contains(addr)) {
6676     // this should be made more efficient
6677     _bitMap->mark(addr);
6678   }
6679 }
6680 
6681 void MarkRefsIntoClosure::do_oop(oop* p)       { MarkRefsIntoClosure::do_oop_work(p); }
6682 void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6683 






















6684 // A variant of the above, used for CMS marking verification.
6685 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
6686   MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm):
6687     _span(span),
6688     _verification_bm(verification_bm),
6689     _cms_bm(cms_bm)
6690 {
6691     assert(_ref_processor == NULL, "deliberately left NULL");
6692     assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
6693 }
6694 
6695 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
6696   // if p points into _span, then mark corresponding bit in _markBitMap
6697   assert(obj->is_oop(), "expected an oop");
6698   HeapWord* addr = (HeapWord*)obj;
6699   if (_span.contains(addr)) {
6700     _verification_bm->mark(addr);
6701     if (!_cms_bm->isMarked(addr)) {
6702       oop(addr)->print();
6703       gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)", addr);
6704       fatal("... aborting");
6705     }
6706   }
6707 }
6708 
6709 void MarkRefsIntoVerifyClosure::do_oop(oop* p)       { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6710 void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6711 
6712 //////////////////////////////////////////////////
6713 // MarkRefsIntoAndScanClosure
6714 //////////////////////////////////////////////////
6715 
6716 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
6717                                                        ReferenceProcessor* rp,
6718                                                        CMSBitMap* bit_map,
6719                                                        CMSBitMap* mod_union_table,
6720                                                        CMSMarkStack*  mark_stack,
6721                                                        CMSCollector* collector,
6722                                                        bool should_yield,
6723                                                        bool concurrent_precleaning):
6724   _collector(collector),
6725   _span(span),
6726   _bit_map(bit_map),
6727   _mark_stack(mark_stack),
6728   _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table,
6729                       mark_stack, concurrent_precleaning),
6730   _yield(should_yield),
6731   _concurrent_precleaning(concurrent_precleaning),
6732   _freelistLock(NULL)
6733 {
6734   _ref_processor = rp;
6735   assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6736 }
6737 
6738 // This closure is used to mark refs into the CMS generation at the
6739 // second (final) checkpoint, and to scan and transitively follow
6740 // the unmarked oops. It is also used during the concurrent precleaning
6741 // phase while scanning objects on dirty cards in the CMS generation.
6742 // The marks are made in the marking bit map and the marking stack is
6743 // used for keeping the (newly) grey objects during the scan.
6744 // The parallel version (Par_...) appears further below.
6745 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6746   if (obj != NULL) {
6747     assert(obj->is_oop(), "expected an oop");
6748     HeapWord* addr = (HeapWord*)obj;
6749     assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6750     assert(_collector->overflow_list_is_empty(),
6751            "overflow list should be empty");
6752     if (_span.contains(addr) &&
6753         !_bit_map->isMarked(addr)) {
6754       // mark bit map (object is now grey)
6755       _bit_map->mark(addr);
6756       // push on marking stack (stack should be empty), and drain the
6757       // stack by applying this closure to the oops in the oops popped
6758       // from the stack (i.e. blacken the grey objects)
6759       bool res = _mark_stack->push(obj);
6760       assert(res, "Should have space to push on empty stack");
6761       do {
6762         oop new_oop = _mark_stack->pop();
6763         assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6764         assert(_bit_map->isMarked((HeapWord*)new_oop),
6765                "only grey objects on this stack");
6766         // iterate over the oops in this oop, marking and pushing
6767         // the ones in CMS heap (i.e. in _span).
6768         new_oop->oop_iterate(&_pushAndMarkClosure);
6769         // check if it's time to yield
6770         do_yield_check();
6771       } while (!_mark_stack->isEmpty() ||
6772                (!_concurrent_precleaning && take_from_overflow_list()));
6773         // if marking stack is empty, and we are not doing this
6774         // during precleaning, then check the overflow list
6775     }
6776     assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6777     assert(_collector->overflow_list_is_empty(),
6778            "overflow list was drained above");
6779     // We could restore evacuated mark words, if any, used for
6780     // overflow list links here because the overflow list is
6781     // provably empty here. That would reduce the maximum
6782     // size requirements for preserved_{oop,mark}_stack.
6783     // But we'll just postpone it until we are all done
6784     // so we can just stream through.
6785     if (!_concurrent_precleaning && CMSOverflowEarlyRestoration) {
6786       _collector->restore_preserved_marks_if_any();
6787       assert(_collector->no_preserved_marks(), "No preserved marks");
6788     }
6789     assert(!CMSOverflowEarlyRestoration || _collector->no_preserved_marks(),
6790            "All preserved marks should have been restored above");
6791   }
6792 }
6793 
6794 void MarkRefsIntoAndScanClosure::do_oop(oop* p)       { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6795 void MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6796 
6797 void MarkRefsIntoAndScanClosure::do_yield_work() {
6798   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6799          "CMS thread should hold CMS token");
6800   assert_lock_strong(_freelistLock);
6801   assert_lock_strong(_bit_map->lock());
6802   // relinquish the free_list_lock and bitMaplock()
6803   _bit_map->lock()->unlock();
6804   _freelistLock->unlock();
6805   ConcurrentMarkSweepThread::desynchronize(true);
6806   ConcurrentMarkSweepThread::acknowledge_yield_request();
6807   _collector->stopTimer();
6808   GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
6809   if (PrintCMSStatistics != 0) {
6810     _collector->incrementYields();
6811   }
6812   _collector->icms_wait();
6813 
6814   // See the comment in coordinator_yield()
6815   for (unsigned i = 0;
6816        i < CMSYieldSleepCount &&
6817        ConcurrentMarkSweepThread::should_yield() &&
6818        !CMSCollector::foregroundGCIsActive();
6819        ++i) {
6820     os::sleep(Thread::current(), 1, false);
6821     ConcurrentMarkSweepThread::acknowledge_yield_request();
6822   }
6823 
6824   ConcurrentMarkSweepThread::synchronize(true);
6825   _freelistLock->lock_without_safepoint_check();
6826   _bit_map->lock()->lock_without_safepoint_check();
6827   _collector->startTimer();
6828 }
6829 
6830 ///////////////////////////////////////////////////////////
6831 // Par_MarkRefsIntoAndScanClosure: a parallel version of
6832 //                                 MarkRefsIntoAndScanClosure
6833 ///////////////////////////////////////////////////////////
6834 Par_MarkRefsIntoAndScanClosure::Par_MarkRefsIntoAndScanClosure(
6835   CMSCollector* collector, MemRegion span, ReferenceProcessor* rp,
6836   CMSBitMap* bit_map, OopTaskQueue* work_queue):
6837   _span(span),
6838   _bit_map(bit_map),
6839   _work_queue(work_queue),
6840   _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
6841                        (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads))),
6842   _par_pushAndMarkClosure(collector, span, rp, bit_map, work_queue)
6843 {
6844   _ref_processor = rp;
6845   assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6846 }
6847 
6848 // This closure is used to mark refs into the CMS generation at the
6849 // second (final) checkpoint, and to scan and transitively follow
6850 // the unmarked oops. The marks are made in the marking bit map and
6851 // the work_queue is used for keeping the (newly) grey objects during
6852 // the scan phase whence they are also available for stealing by parallel
6853 // threads. Since the marking bit map is shared, updates are
6854 // synchronized (via CAS).
6855 void Par_MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6856   if (obj != NULL) {
6857     // Ignore mark word because this could be an already marked oop
6858     // that may be chained at the end of the overflow list.
6859     assert(obj->is_oop(true), "expected an oop");
6860     HeapWord* addr = (HeapWord*)obj;
6861     if (_span.contains(addr) &&
6862         !_bit_map->isMarked(addr)) {
6863       // mark bit map (object will become grey):
6864       // It is possible for several threads to be
6865       // trying to "claim" this object concurrently;
6866       // the unique thread that succeeds in marking the
6867       // object first will do the subsequent push on
6868       // to the work queue (or overflow list).
6869       if (_bit_map->par_mark(addr)) {
6870         // push on work_queue (which may not be empty), and trim the
6871         // queue to an appropriate length by applying this closure to
6872         // the oops in the oops popped from the stack (i.e. blacken the
6873         // grey objects)
6874         bool res = _work_queue->push(obj);
6875         assert(res, "Low water mark should be less than capacity?");
6876         trim_queue(_low_water_mark);
6877       } // Else, another thread claimed the object
6878     }
6879   }
6880 }
6881 
6882 void Par_MarkRefsIntoAndScanClosure::do_oop(oop* p)       { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6883 void Par_MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6884 
6885 // This closure is used to rescan the marked objects on the dirty cards
6886 // in the mod union table and the card table proper.
6887 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
6888   oop p, MemRegion mr) {
6889 
6890   size_t size = 0;
6891   HeapWord* addr = (HeapWord*)p;
6892   DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6893   assert(_span.contains(addr), "we are scanning the CMS generation");
6894   // check if it's time to yield
6895   if (do_yield_check()) {
6896     // We yielded for some foreground stop-world work,
6897     // and we have been asked to abort this ongoing preclean cycle.
6898     return 0;
6899   }
6900   if (_bitMap->isMarked(addr)) {
6901     // it's marked; is it potentially uninitialized?
6902     if (p->klass_or_null() != NULL) {
6903         // an initialized object; ignore mark word in verification below
6904         // since we are running concurrent with mutators
6905         assert(p->is_oop(true), "should be an oop");
6906         if (p->is_objArray()) {
6907           // objArrays are precisely marked; restrict scanning
6908           // to dirty cards only.
6909           size = CompactibleFreeListSpace::adjustObjectSize(
6910                    p->oop_iterate(_scanningClosure, mr));
6911         } else {
6912           // A non-array may have been imprecisely marked; we need
6913           // to scan object in its entirety.
6914           size = CompactibleFreeListSpace::adjustObjectSize(
6915                    p->oop_iterate(_scanningClosure));
6916         }
6917         #ifdef ASSERT
6918           size_t direct_size =
6919             CompactibleFreeListSpace::adjustObjectSize(p->size());
6920           assert(size == direct_size, "Inconsistency in size");
6921           assert(size >= 3, "Necessary for Printezis marks to work");
6922           if (!_bitMap->isMarked(addr+1)) {
6923             _bitMap->verifyNoOneBitsInRange(addr+2, addr+size);
6924           } else {
6925             _bitMap->verifyNoOneBitsInRange(addr+2, addr+size-1);
6926             assert(_bitMap->isMarked(addr+size-1),
6927                    "inconsistent Printezis mark");
6928           }
6929         #endif // ASSERT
6930     } else {
6931       // an unitialized object
6932       assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
6933       HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
6934       size = pointer_delta(nextOneAddr + 1, addr);
6935       assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6936              "alignment problem");
6937       // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
6938       // will dirty the card when the klass pointer is installed in the
6939       // object (signalling the completion of initialization).
6940     }
6941   } else {
6942     // Either a not yet marked object or an uninitialized object
6943     if (p->klass_or_null() == NULL) {
6944       // An uninitialized object, skip to the next card, since
6945       // we may not be able to read its P-bits yet.
6946       assert(size == 0, "Initial value");
6947     } else {
6948       // An object not (yet) reached by marking: we merely need to
6949       // compute its size so as to go look at the next block.
6950       assert(p->is_oop(true), "should be an oop");
6951       size = CompactibleFreeListSpace::adjustObjectSize(p->size());
6952     }
6953   }
6954   DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6955   return size;
6956 }
6957 
6958 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
6959   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6960          "CMS thread should hold CMS token");
6961   assert_lock_strong(_freelistLock);
6962   assert_lock_strong(_bitMap->lock());
6963   // relinquish the free_list_lock and bitMaplock()
6964   _bitMap->lock()->unlock();
6965   _freelistLock->unlock();
6966   ConcurrentMarkSweepThread::desynchronize(true);
6967   ConcurrentMarkSweepThread::acknowledge_yield_request();
6968   _collector->stopTimer();
6969   GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
6970   if (PrintCMSStatistics != 0) {
6971     _collector->incrementYields();
6972   }
6973   _collector->icms_wait();
6974 
6975   // See the comment in coordinator_yield()
6976   for (unsigned i = 0; i < CMSYieldSleepCount &&
6977                    ConcurrentMarkSweepThread::should_yield() &&
6978                    !CMSCollector::foregroundGCIsActive(); ++i) {
6979     os::sleep(Thread::current(), 1, false);
6980     ConcurrentMarkSweepThread::acknowledge_yield_request();
6981   }
6982 
6983   ConcurrentMarkSweepThread::synchronize(true);
6984   _freelistLock->lock_without_safepoint_check();
6985   _bitMap->lock()->lock_without_safepoint_check();
6986   _collector->startTimer();
6987 }
6988 
6989 
6990 //////////////////////////////////////////////////////////////////
6991 // SurvivorSpacePrecleanClosure
6992 //////////////////////////////////////////////////////////////////
6993 // This (single-threaded) closure is used to preclean the oops in
6994 // the survivor spaces.
6995 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
6996 
6997   HeapWord* addr = (HeapWord*)p;
6998   DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6999   assert(!_span.contains(addr), "we are scanning the survivor spaces");
7000   assert(p->klass_or_null() != NULL, "object should be initializd");
7001   // an initialized object; ignore mark word in verification below
7002   // since we are running concurrent with mutators
7003   assert(p->is_oop(true), "should be an oop");
7004   // Note that we do not yield while we iterate over
7005   // the interior oops of p, pushing the relevant ones
7006   // on our marking stack.
7007   size_t size = p->oop_iterate(_scanning_closure);
7008   do_yield_check();
7009   // Observe that below, we do not abandon the preclean
7010   // phase as soon as we should; rather we empty the
7011   // marking stack before returning. This is to satisfy
7012   // some existing assertions. In general, it may be a
7013   // good idea to abort immediately and complete the marking
7014   // from the grey objects at a later time.
7015   while (!_mark_stack->isEmpty()) {
7016     oop new_oop = _mark_stack->pop();
7017     assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
7018     assert(_bit_map->isMarked((HeapWord*)new_oop),
7019            "only grey objects on this stack");
7020     // iterate over the oops in this oop, marking and pushing
7021     // the ones in CMS heap (i.e. in _span).
7022     new_oop->oop_iterate(_scanning_closure);
7023     // check if it's time to yield
7024     do_yield_check();
7025   }
7026   unsigned int after_count =
7027     GenCollectedHeap::heap()->total_collections();
7028   bool abort = (_before_count != after_count) ||
7029                _collector->should_abort_preclean();
7030   return abort ? 0 : size;
7031 }
7032 
7033 void SurvivorSpacePrecleanClosure::do_yield_work() {
7034   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7035          "CMS thread should hold CMS token");
7036   assert_lock_strong(_bit_map->lock());
7037   // Relinquish the bit map lock
7038   _bit_map->lock()->unlock();
7039   ConcurrentMarkSweepThread::desynchronize(true);
7040   ConcurrentMarkSweepThread::acknowledge_yield_request();
7041   _collector->stopTimer();
7042   GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7043   if (PrintCMSStatistics != 0) {
7044     _collector->incrementYields();
7045   }
7046   _collector->icms_wait();
7047 
7048   // See the comment in coordinator_yield()
7049   for (unsigned i = 0; i < CMSYieldSleepCount &&
7050                        ConcurrentMarkSweepThread::should_yield() &&
7051                        !CMSCollector::foregroundGCIsActive(); ++i) {
7052     os::sleep(Thread::current(), 1, false);
7053     ConcurrentMarkSweepThread::acknowledge_yield_request();
7054   }
7055 
7056   ConcurrentMarkSweepThread::synchronize(true);
7057   _bit_map->lock()->lock_without_safepoint_check();
7058   _collector->startTimer();
7059 }
7060 
7061 // This closure is used to rescan the marked objects on the dirty cards
7062 // in the mod union table and the card table proper. In the parallel
7063 // case, although the bitMap is shared, we do a single read so the
7064 // isMarked() query is "safe".
7065 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
7066   // Ignore mark word because we are running concurrent with mutators
7067   assert(p->is_oop_or_null(true), "expected an oop or null");
7068   HeapWord* addr = (HeapWord*)p;
7069   assert(_span.contains(addr), "we are scanning the CMS generation");
7070   bool is_obj_array = false;
7071   #ifdef ASSERT
7072     if (!_parallel) {
7073       assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
7074       assert(_collector->overflow_list_is_empty(),
7075              "overflow list should be empty");
7076 
7077     }
7078   #endif // ASSERT
7079   if (_bit_map->isMarked(addr)) {
7080     // Obj arrays are precisely marked, non-arrays are not;
7081     // so we scan objArrays precisely and non-arrays in their
7082     // entirety.
7083     if (p->is_objArray()) {
7084       is_obj_array = true;
7085       if (_parallel) {
7086         p->oop_iterate(_par_scan_closure, mr);
7087       } else {
7088         p->oop_iterate(_scan_closure, mr);
7089       }
7090     } else {
7091       if (_parallel) {
7092         p->oop_iterate(_par_scan_closure);
7093       } else {
7094         p->oop_iterate(_scan_closure);
7095       }
7096     }
7097   }
7098   #ifdef ASSERT
7099     if (!_parallel) {
7100       assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
7101       assert(_collector->overflow_list_is_empty(),
7102              "overflow list should be empty");
7103 
7104     }
7105   #endif // ASSERT
7106   return is_obj_array;
7107 }
7108 
7109 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
7110                         MemRegion span,
7111                         CMSBitMap* bitMap, CMSMarkStack*  markStack,
7112                         bool should_yield, bool verifying):
7113   _collector(collector),
7114   _span(span),
7115   _bitMap(bitMap),
7116   _mut(&collector->_modUnionTable),
7117   _markStack(markStack),
7118   _yield(should_yield),
7119   _skipBits(0)
7120 {
7121   assert(_markStack->isEmpty(), "stack should be empty");
7122   _finger = _bitMap->startWord();
7123   _threshold = _finger;
7124   assert(_collector->_restart_addr == NULL, "Sanity check");
7125   assert(_span.contains(_finger), "Out of bounds _finger?");
7126   DEBUG_ONLY(_verifying = verifying;)
7127 }
7128 
7129 void MarkFromRootsClosure::reset(HeapWord* addr) {
7130   assert(_markStack->isEmpty(), "would cause duplicates on stack");
7131   assert(_span.contains(addr), "Out of bounds _finger?");
7132   _finger = addr;
7133   _threshold = (HeapWord*)round_to(
7134                  (intptr_t)_finger, CardTableModRefBS::card_size);
7135 }
7136 
7137 // Should revisit to see if this should be restructured for
7138 // greater efficiency.
7139 bool MarkFromRootsClosure::do_bit(size_t offset) {
7140   if (_skipBits > 0) {
7141     _skipBits--;
7142     return true;
7143   }
7144   // convert offset into a HeapWord*
7145   HeapWord* addr = _bitMap->startWord() + offset;
7146   assert(_bitMap->endWord() && addr < _bitMap->endWord(),
7147          "address out of range");
7148   assert(_bitMap->isMarked(addr), "tautology");
7149   if (_bitMap->isMarked(addr+1)) {
7150     // this is an allocated but not yet initialized object
7151     assert(_skipBits == 0, "tautology");
7152     _skipBits = 2;  // skip next two marked bits ("Printezis-marks")
7153     oop p = oop(addr);
7154     if (p->klass_or_null() == NULL) {
7155       DEBUG_ONLY(if (!_verifying) {)
7156         // We re-dirty the cards on which this object lies and increase
7157         // the _threshold so that we'll come back to scan this object
7158         // during the preclean or remark phase. (CMSCleanOnEnter)
7159         if (CMSCleanOnEnter) {
7160           size_t sz = _collector->block_size_using_printezis_bits(addr);
7161           HeapWord* end_card_addr   = (HeapWord*)round_to(
7162                                          (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7163           MemRegion redirty_range = MemRegion(addr, end_card_addr);
7164           assert(!redirty_range.is_empty(), "Arithmetical tautology");
7165           // Bump _threshold to end_card_addr; note that
7166           // _threshold cannot possibly exceed end_card_addr, anyhow.
7167           // This prevents future clearing of the card as the scan proceeds
7168           // to the right.
7169           assert(_threshold <= end_card_addr,
7170                  "Because we are just scanning into this object");
7171           if (_threshold < end_card_addr) {
7172             _threshold = end_card_addr;
7173           }
7174           if (p->klass_or_null() != NULL) {
7175             // Redirty the range of cards...
7176             _mut->mark_range(redirty_range);
7177           } // ...else the setting of klass will dirty the card anyway.
7178         }
7179       DEBUG_ONLY(})
7180       return true;
7181     }
7182   }
7183   scanOopsInOop(addr);
7184   return true;
7185 }
7186 
7187 // We take a break if we've been at this for a while,
7188 // so as to avoid monopolizing the locks involved.
7189 void MarkFromRootsClosure::do_yield_work() {
7190   // First give up the locks, then yield, then re-lock
7191   // We should probably use a constructor/destructor idiom to
7192   // do this unlock/lock or modify the MutexUnlocker class to
7193   // serve our purpose. XXX
7194   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7195          "CMS thread should hold CMS token");
7196   assert_lock_strong(_bitMap->lock());
7197   _bitMap->lock()->unlock();
7198   ConcurrentMarkSweepThread::desynchronize(true);
7199   ConcurrentMarkSweepThread::acknowledge_yield_request();
7200   _collector->stopTimer();
7201   GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7202   if (PrintCMSStatistics != 0) {
7203     _collector->incrementYields();
7204   }
7205   _collector->icms_wait();
7206 
7207   // See the comment in coordinator_yield()
7208   for (unsigned i = 0; i < CMSYieldSleepCount &&
7209                        ConcurrentMarkSweepThread::should_yield() &&
7210                        !CMSCollector::foregroundGCIsActive(); ++i) {
7211     os::sleep(Thread::current(), 1, false);
7212     ConcurrentMarkSweepThread::acknowledge_yield_request();
7213   }
7214 
7215   ConcurrentMarkSweepThread::synchronize(true);
7216   _bitMap->lock()->lock_without_safepoint_check();
7217   _collector->startTimer();
7218 }
7219 
7220 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
7221   assert(_bitMap->isMarked(ptr), "expected bit to be set");
7222   assert(_markStack->isEmpty(),
7223          "should drain stack to limit stack usage");
7224   // convert ptr to an oop preparatory to scanning
7225   oop obj = oop(ptr);
7226   // Ignore mark word in verification below, since we
7227   // may be running concurrent with mutators.
7228   assert(obj->is_oop(true), "should be an oop");
7229   assert(_finger <= ptr, "_finger runneth ahead");
7230   // advance the finger to right end of this object
7231   _finger = ptr + obj->size();
7232   assert(_finger > ptr, "we just incremented it above");
7233   // On large heaps, it may take us some time to get through
7234   // the marking phase (especially if running iCMS). During
7235   // this time it's possible that a lot of mutations have
7236   // accumulated in the card table and the mod union table --
7237   // these mutation records are redundant until we have
7238   // actually traced into the corresponding card.
7239   // Here, we check whether advancing the finger would make
7240   // us cross into a new card, and if so clear corresponding
7241   // cards in the MUT (preclean them in the card-table in the
7242   // future).
7243 
7244   DEBUG_ONLY(if (!_verifying) {)
7245     // The clean-on-enter optimization is disabled by default,
7246     // until we fix 6178663.
7247     if (CMSCleanOnEnter && (_finger > _threshold)) {
7248       // [_threshold, _finger) represents the interval
7249       // of cards to be cleared  in MUT (or precleaned in card table).
7250       // The set of cards to be cleared is all those that overlap
7251       // with the interval [_threshold, _finger); note that
7252       // _threshold is always kept card-aligned but _finger isn't
7253       // always card-aligned.
7254       HeapWord* old_threshold = _threshold;
7255       assert(old_threshold == (HeapWord*)round_to(
7256               (intptr_t)old_threshold, CardTableModRefBS::card_size),
7257              "_threshold should always be card-aligned");
7258       _threshold = (HeapWord*)round_to(
7259                      (intptr_t)_finger, CardTableModRefBS::card_size);
7260       MemRegion mr(old_threshold, _threshold);
7261       assert(!mr.is_empty(), "Control point invariant");
7262       assert(_span.contains(mr), "Should clear within span");
7263       _mut->clear_range(mr);
7264     }
7265   DEBUG_ONLY(})
7266   // Note: the finger doesn't advance while we drain
7267   // the stack below.
7268   PushOrMarkClosure pushOrMarkClosure(_collector,
7269                                       _span, _bitMap, _markStack,
7270                                       _finger, this);
7271   bool res = _markStack->push(obj);
7272   assert(res, "Empty non-zero size stack should have space for single push");
7273   while (!_markStack->isEmpty()) {
7274     oop new_oop = _markStack->pop();
7275     // Skip verifying header mark word below because we are
7276     // running concurrent with mutators.
7277     assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
7278     // now scan this oop's oops
7279     new_oop->oop_iterate(&pushOrMarkClosure);
7280     do_yield_check();
7281   }
7282   assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
7283 }
7284 
7285 Par_MarkFromRootsClosure::Par_MarkFromRootsClosure(CMSConcMarkingTask* task,
7286                        CMSCollector* collector, MemRegion span,
7287                        CMSBitMap* bit_map,
7288                        OopTaskQueue* work_queue,
7289                        CMSMarkStack*  overflow_stack,
7290                        bool should_yield):
7291   _collector(collector),
7292   _whole_span(collector->_span),
7293   _span(span),
7294   _bit_map(bit_map),
7295   _mut(&collector->_modUnionTable),
7296   _work_queue(work_queue),
7297   _overflow_stack(overflow_stack),
7298   _yield(should_yield),
7299   _skip_bits(0),
7300   _task(task)
7301 {
7302   assert(_work_queue->size() == 0, "work_queue should be empty");
7303   _finger = span.start();
7304   _threshold = _finger;     // XXX Defer clear-on-enter optimization for now
7305   assert(_span.contains(_finger), "Out of bounds _finger?");
7306 }
7307 
7308 // Should revisit to see if this should be restructured for
7309 // greater efficiency.
7310 bool Par_MarkFromRootsClosure::do_bit(size_t offset) {
7311   if (_skip_bits > 0) {
7312     _skip_bits--;
7313     return true;
7314   }
7315   // convert offset into a HeapWord*
7316   HeapWord* addr = _bit_map->startWord() + offset;
7317   assert(_bit_map->endWord() && addr < _bit_map->endWord(),
7318          "address out of range");
7319   assert(_bit_map->isMarked(addr), "tautology");
7320   if (_bit_map->isMarked(addr+1)) {
7321     // this is an allocated object that might not yet be initialized
7322     assert(_skip_bits == 0, "tautology");
7323     _skip_bits = 2;  // skip next two marked bits ("Printezis-marks")
7324     oop p = oop(addr);
7325     if (p->klass_or_null() == NULL) {
7326       // in the case of Clean-on-Enter optimization, redirty card
7327       // and avoid clearing card by increasing  the threshold.
7328       return true;
7329     }
7330   }
7331   scan_oops_in_oop(addr);
7332   return true;
7333 }
7334 
7335 void Par_MarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
7336   assert(_bit_map->isMarked(ptr), "expected bit to be set");
7337   // Should we assert that our work queue is empty or
7338   // below some drain limit?
7339   assert(_work_queue->size() == 0,
7340          "should drain stack to limit stack usage");
7341   // convert ptr to an oop preparatory to scanning
7342   oop obj = oop(ptr);
7343   // Ignore mark word in verification below, since we
7344   // may be running concurrent with mutators.
7345   assert(obj->is_oop(true), "should be an oop");
7346   assert(_finger <= ptr, "_finger runneth ahead");
7347   // advance the finger to right end of this object
7348   _finger = ptr + obj->size();
7349   assert(_finger > ptr, "we just incremented it above");
7350   // On large heaps, it may take us some time to get through
7351   // the marking phase (especially if running iCMS). During
7352   // this time it's possible that a lot of mutations have
7353   // accumulated in the card table and the mod union table --
7354   // these mutation records are redundant until we have
7355   // actually traced into the corresponding card.
7356   // Here, we check whether advancing the finger would make
7357   // us cross into a new card, and if so clear corresponding
7358   // cards in the MUT (preclean them in the card-table in the
7359   // future).
7360 
7361   // The clean-on-enter optimization is disabled by default,
7362   // until we fix 6178663.
7363   if (CMSCleanOnEnter && (_finger > _threshold)) {
7364     // [_threshold, _finger) represents the interval
7365     // of cards to be cleared  in MUT (or precleaned in card table).
7366     // The set of cards to be cleared is all those that overlap
7367     // with the interval [_threshold, _finger); note that
7368     // _threshold is always kept card-aligned but _finger isn't
7369     // always card-aligned.
7370     HeapWord* old_threshold = _threshold;
7371     assert(old_threshold == (HeapWord*)round_to(
7372             (intptr_t)old_threshold, CardTableModRefBS::card_size),
7373            "_threshold should always be card-aligned");
7374     _threshold = (HeapWord*)round_to(
7375                    (intptr_t)_finger, CardTableModRefBS::card_size);
7376     MemRegion mr(old_threshold, _threshold);
7377     assert(!mr.is_empty(), "Control point invariant");
7378     assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
7379     _mut->clear_range(mr);
7380   }
7381 
7382   // Note: the local finger doesn't advance while we drain
7383   // the stack below, but the global finger sure can and will.
7384   HeapWord** gfa = _task->global_finger_addr();
7385   Par_PushOrMarkClosure pushOrMarkClosure(_collector,
7386                                       _span, _bit_map,
7387                                       _work_queue,
7388                                       _overflow_stack,
7389                                       _finger,
7390                                       gfa, this);
7391   bool res = _work_queue->push(obj);   // overflow could occur here
7392   assert(res, "Will hold once we use workqueues");
7393   while (true) {
7394     oop new_oop;
7395     if (!_work_queue->pop_local(new_oop)) {
7396       // We emptied our work_queue; check if there's stuff that can
7397       // be gotten from the overflow stack.
7398       if (CMSConcMarkingTask::get_work_from_overflow_stack(
7399             _overflow_stack, _work_queue)) {
7400         do_yield_check();
7401         continue;
7402       } else {  // done
7403         break;
7404       }
7405     }
7406     // Skip verifying header mark word below because we are
7407     // running concurrent with mutators.
7408     assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
7409     // now scan this oop's oops
7410     new_oop->oop_iterate(&pushOrMarkClosure);
7411     do_yield_check();
7412   }
7413   assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
7414 }
7415 
7416 // Yield in response to a request from VM Thread or
7417 // from mutators.
7418 void Par_MarkFromRootsClosure::do_yield_work() {
7419   assert(_task != NULL, "sanity");
7420   _task->yield();
7421 }
7422 
7423 // A variant of the above used for verifying CMS marking work.
7424 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
7425                         MemRegion span,
7426                         CMSBitMap* verification_bm, CMSBitMap* cms_bm,
7427                         CMSMarkStack*  mark_stack):
7428   _collector(collector),
7429   _span(span),
7430   _verification_bm(verification_bm),
7431   _cms_bm(cms_bm),
7432   _mark_stack(mark_stack),
7433   _pam_verify_closure(collector, span, verification_bm, cms_bm,
7434                       mark_stack)
7435 {
7436   assert(_mark_stack->isEmpty(), "stack should be empty");
7437   _finger = _verification_bm->startWord();
7438   assert(_collector->_restart_addr == NULL, "Sanity check");
7439   assert(_span.contains(_finger), "Out of bounds _finger?");
7440 }
7441 
7442 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
7443   assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
7444   assert(_span.contains(addr), "Out of bounds _finger?");
7445   _finger = addr;
7446 }
7447 
7448 // Should revisit to see if this should be restructured for
7449 // greater efficiency.
7450 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
7451   // convert offset into a HeapWord*
7452   HeapWord* addr = _verification_bm->startWord() + offset;
7453   assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
7454          "address out of range");
7455   assert(_verification_bm->isMarked(addr), "tautology");
7456   assert(_cms_bm->isMarked(addr), "tautology");
7457 
7458   assert(_mark_stack->isEmpty(),
7459          "should drain stack to limit stack usage");
7460   // convert addr to an oop preparatory to scanning
7461   oop obj = oop(addr);
7462   assert(obj->is_oop(), "should be an oop");
7463   assert(_finger <= addr, "_finger runneth ahead");
7464   // advance the finger to right end of this object
7465   _finger = addr + obj->size();
7466   assert(_finger > addr, "we just incremented it above");
7467   // Note: the finger doesn't advance while we drain
7468   // the stack below.
7469   bool res = _mark_stack->push(obj);
7470   assert(res, "Empty non-zero size stack should have space for single push");
7471   while (!_mark_stack->isEmpty()) {
7472     oop new_oop = _mark_stack->pop();
7473     assert(new_oop->is_oop(), "Oops! expected to pop an oop");
7474     // now scan this oop's oops
7475     new_oop->oop_iterate(&_pam_verify_closure);
7476   }
7477   assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
7478   return true;
7479 }
7480 
7481 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
7482   CMSCollector* collector, MemRegion span,
7483   CMSBitMap* verification_bm, CMSBitMap* cms_bm,
7484   CMSMarkStack*  mark_stack):
7485   CMSOopClosure(collector->ref_processor()),
7486   _collector(collector),
7487   _span(span),
7488   _verification_bm(verification_bm),
7489   _cms_bm(cms_bm),
7490   _mark_stack(mark_stack)
7491 { }
7492 
7493 void PushAndMarkVerifyClosure::do_oop(oop* p)       { PushAndMarkVerifyClosure::do_oop_work(p); }
7494 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
7495 
7496 // Upon stack overflow, we discard (part of) the stack,
7497 // remembering the least address amongst those discarded
7498 // in CMSCollector's _restart_address.
7499 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
7500   // Remember the least grey address discarded
7501   HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
7502   _collector->lower_restart_addr(ra);
7503   _mark_stack->reset();  // discard stack contents
7504   _mark_stack->expand(); // expand the stack if possible
7505 }
7506 
7507 void PushAndMarkVerifyClosure::do_oop(oop obj) {
7508   assert(obj->is_oop_or_null(), "expected an oop or NULL");
7509   HeapWord* addr = (HeapWord*)obj;
7510   if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
7511     // Oop lies in _span and isn't yet grey or black
7512     _verification_bm->mark(addr);            // now grey
7513     if (!_cms_bm->isMarked(addr)) {
7514       oop(addr)->print();
7515       gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)",
7516                              addr);
7517       fatal("... aborting");
7518     }
7519 
7520     if (!_mark_stack->push(obj)) { // stack overflow
7521       if (PrintCMSStatistics != 0) {
7522         gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7523                                SIZE_FORMAT, _mark_stack->capacity());
7524       }
7525       assert(_mark_stack->isFull(), "Else push should have succeeded");
7526       handle_stack_overflow(addr);
7527     }
7528     // anything including and to the right of _finger
7529     // will be scanned as we iterate over the remainder of the
7530     // bit map
7531   }
7532 }
7533 
7534 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
7535                      MemRegion span,
7536                      CMSBitMap* bitMap, CMSMarkStack*  markStack,
7537                      HeapWord* finger, MarkFromRootsClosure* parent) :
7538   CMSOopClosure(collector->ref_processor()),
7539   _collector(collector),
7540   _span(span),
7541   _bitMap(bitMap),
7542   _markStack(markStack),
7543   _finger(finger),
7544   _parent(parent)
7545 { }
7546 
7547 Par_PushOrMarkClosure::Par_PushOrMarkClosure(CMSCollector* collector,
7548                      MemRegion span,
7549                      CMSBitMap* bit_map,
7550                      OopTaskQueue* work_queue,
7551                      CMSMarkStack*  overflow_stack,
7552                      HeapWord* finger,
7553                      HeapWord** global_finger_addr,
7554                      Par_MarkFromRootsClosure* parent) :
7555   CMSOopClosure(collector->ref_processor()),
7556   _collector(collector),
7557   _whole_span(collector->_span),
7558   _span(span),
7559   _bit_map(bit_map),
7560   _work_queue(work_queue),
7561   _overflow_stack(overflow_stack),
7562   _finger(finger),
7563   _global_finger_addr(global_finger_addr),
7564   _parent(parent)
7565 { }
7566 
7567 // Assumes thread-safe access by callers, who are
7568 // responsible for mutual exclusion.
7569 void CMSCollector::lower_restart_addr(HeapWord* low) {
7570   assert(_span.contains(low), "Out of bounds addr");
7571   if (_restart_addr == NULL) {
7572     _restart_addr = low;
7573   } else {
7574     _restart_addr = MIN2(_restart_addr, low);
7575   }
7576 }
7577 
7578 // Upon stack overflow, we discard (part of) the stack,
7579 // remembering the least address amongst those discarded
7580 // in CMSCollector's _restart_address.
7581 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7582   // Remember the least grey address discarded
7583   HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
7584   _collector->lower_restart_addr(ra);
7585   _markStack->reset();  // discard stack contents
7586   _markStack->expand(); // expand the stack if possible
7587 }
7588 
7589 // Upon stack overflow, we discard (part of) the stack,
7590 // remembering the least address amongst those discarded
7591 // in CMSCollector's _restart_address.
7592 void Par_PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7593   // We need to do this under a mutex to prevent other
7594   // workers from interfering with the work done below.
7595   MutexLockerEx ml(_overflow_stack->par_lock(),
7596                    Mutex::_no_safepoint_check_flag);
7597   // Remember the least grey address discarded
7598   HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
7599   _collector->lower_restart_addr(ra);
7600   _overflow_stack->reset();  // discard stack contents
7601   _overflow_stack->expand(); // expand the stack if possible
7602 }
7603 
7604 void CMKlassClosure::do_klass(Klass* k) {
7605   assert(_oop_closure != NULL, "Not initialized?");
7606   k->oops_do(_oop_closure);
7607 }
7608 
7609 void PushOrMarkClosure::do_oop(oop obj) {
7610   // Ignore mark word because we are running concurrent with mutators.
7611   assert(obj->is_oop_or_null(true), "expected an oop or NULL");
7612   HeapWord* addr = (HeapWord*)obj;
7613   if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
7614     // Oop lies in _span and isn't yet grey or black
7615     _bitMap->mark(addr);            // now grey
7616     if (addr < _finger) {
7617       // the bit map iteration has already either passed, or
7618       // sampled, this bit in the bit map; we'll need to
7619       // use the marking stack to scan this oop's oops.
7620       bool simulate_overflow = false;
7621       NOT_PRODUCT(
7622         if (CMSMarkStackOverflowALot &&
7623             _collector->simulate_overflow()) {
7624           // simulate a stack overflow
7625           simulate_overflow = true;
7626         }
7627       )
7628       if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
7629         if (PrintCMSStatistics != 0) {
7630           gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7631                                  SIZE_FORMAT, _markStack->capacity());
7632         }
7633         assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
7634         handle_stack_overflow(addr);
7635       }
7636     }
7637     // anything including and to the right of _finger
7638     // will be scanned as we iterate over the remainder of the
7639     // bit map
7640     do_yield_check();
7641   }
7642 }
7643 
7644 void PushOrMarkClosure::do_oop(oop* p)       { PushOrMarkClosure::do_oop_work(p); }
7645 void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); }
7646 
7647 void Par_PushOrMarkClosure::do_oop(oop obj) {
7648   // Ignore mark word because we are running concurrent with mutators.
7649   assert(obj->is_oop_or_null(true), "expected an oop or NULL");
7650   HeapWord* addr = (HeapWord*)obj;
7651   if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
7652     // Oop lies in _span and isn't yet grey or black
7653     // We read the global_finger (volatile read) strictly after marking oop
7654     bool res = _bit_map->par_mark(addr);    // now grey
7655     volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
7656     // Should we push this marked oop on our stack?
7657     // -- if someone else marked it, nothing to do
7658     // -- if target oop is above global finger nothing to do
7659     // -- if target oop is in chunk and above local finger
7660     //      then nothing to do
7661     // -- else push on work queue
7662     if (   !res       // someone else marked it, they will deal with it
7663         || (addr >= *gfa)  // will be scanned in a later task
7664         || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
7665       return;
7666     }
7667     // the bit map iteration has already either passed, or
7668     // sampled, this bit in the bit map; we'll need to
7669     // use the marking stack to scan this oop's oops.
7670     bool simulate_overflow = false;
7671     NOT_PRODUCT(
7672       if (CMSMarkStackOverflowALot &&
7673           _collector->simulate_overflow()) {
7674         // simulate a stack overflow
7675         simulate_overflow = true;
7676       }
7677     )
7678     if (simulate_overflow ||
7679         !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
7680       // stack overflow
7681       if (PrintCMSStatistics != 0) {
7682         gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7683                                SIZE_FORMAT, _overflow_stack->capacity());
7684       }
7685       // We cannot assert that the overflow stack is full because
7686       // it may have been emptied since.
7687       assert(simulate_overflow ||
7688              _work_queue->size() == _work_queue->max_elems(),
7689             "Else push should have succeeded");
7690       handle_stack_overflow(addr);
7691     }
7692     do_yield_check();
7693   }
7694 }
7695 
7696 void Par_PushOrMarkClosure::do_oop(oop* p)       { Par_PushOrMarkClosure::do_oop_work(p); }
7697 void Par_PushOrMarkClosure::do_oop(narrowOop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7698 
7699 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
7700                                        MemRegion span,
7701                                        ReferenceProcessor* rp,
7702                                        CMSBitMap* bit_map,
7703                                        CMSBitMap* mod_union_table,
7704                                        CMSMarkStack*  mark_stack,
7705                                        bool           concurrent_precleaning):
7706   CMSOopClosure(rp),
7707   _collector(collector),
7708   _span(span),
7709   _bit_map(bit_map),
7710   _mod_union_table(mod_union_table),
7711   _mark_stack(mark_stack),
7712   _concurrent_precleaning(concurrent_precleaning)
7713 {
7714   assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7715 }
7716 
7717 // Grey object rescan during pre-cleaning and second checkpoint phases --
7718 // the non-parallel version (the parallel version appears further below.)
7719 void PushAndMarkClosure::do_oop(oop obj) {
7720   // Ignore mark word verification. If during concurrent precleaning,
7721   // the object monitor may be locked. If during the checkpoint
7722   // phases, the object may already have been reached by a  different
7723   // path and may be at the end of the global overflow list (so
7724   // the mark word may be NULL).
7725   assert(obj->is_oop_or_null(true /* ignore mark word */),
7726          "expected an oop or NULL");
7727   HeapWord* addr = (HeapWord*)obj;
7728   // Check if oop points into the CMS generation
7729   // and is not marked
7730   if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7731     // a white object ...
7732     _bit_map->mark(addr);         // ... now grey
7733     // push on the marking stack (grey set)
7734     bool simulate_overflow = false;
7735     NOT_PRODUCT(
7736       if (CMSMarkStackOverflowALot &&
7737           _collector->simulate_overflow()) {
7738         // simulate a stack overflow
7739         simulate_overflow = true;
7740       }
7741     )
7742     if (simulate_overflow || !_mark_stack->push(obj)) {
7743       if (_concurrent_precleaning) {
7744          // During precleaning we can just dirty the appropriate card(s)
7745          // in the mod union table, thus ensuring that the object remains
7746          // in the grey set  and continue. In the case of object arrays
7747          // we need to dirty all of the cards that the object spans,
7748          // since the rescan of object arrays will be limited to the
7749          // dirty cards.
7750          // Note that no one can be intefering with us in this action
7751          // of dirtying the mod union table, so no locking or atomics
7752          // are required.
7753          if (obj->is_objArray()) {
7754            size_t sz = obj->size();
7755            HeapWord* end_card_addr = (HeapWord*)round_to(
7756                                         (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7757            MemRegion redirty_range = MemRegion(addr, end_card_addr);
7758            assert(!redirty_range.is_empty(), "Arithmetical tautology");
7759            _mod_union_table->mark_range(redirty_range);
7760          } else {
7761            _mod_union_table->mark(addr);
7762          }
7763          _collector->_ser_pmc_preclean_ovflw++;
7764       } else {
7765          // During the remark phase, we need to remember this oop
7766          // in the overflow list.
7767          _collector->push_on_overflow_list(obj);
7768          _collector->_ser_pmc_remark_ovflw++;
7769       }
7770     }
7771   }
7772 }
7773 
7774 Par_PushAndMarkClosure::Par_PushAndMarkClosure(CMSCollector* collector,
7775                                                MemRegion span,
7776                                                ReferenceProcessor* rp,
7777                                                CMSBitMap* bit_map,
7778                                                OopTaskQueue* work_queue):
7779   CMSOopClosure(rp),
7780   _collector(collector),
7781   _span(span),
7782   _bit_map(bit_map),
7783   _work_queue(work_queue)
7784 {
7785   assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7786 }
7787 
7788 void PushAndMarkClosure::do_oop(oop* p)       { PushAndMarkClosure::do_oop_work(p); }
7789 void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); }
7790 
7791 // Grey object rescan during second checkpoint phase --
7792 // the parallel version.
7793 void Par_PushAndMarkClosure::do_oop(oop obj) {
7794   // In the assert below, we ignore the mark word because
7795   // this oop may point to an already visited object that is
7796   // on the overflow stack (in which case the mark word has
7797   // been hijacked for chaining into the overflow stack --
7798   // if this is the last object in the overflow stack then
7799   // its mark word will be NULL). Because this object may
7800   // have been subsequently popped off the global overflow
7801   // stack, and the mark word possibly restored to the prototypical
7802   // value, by the time we get to examined this failing assert in
7803   // the debugger, is_oop_or_null(false) may subsequently start
7804   // to hold.
7805   assert(obj->is_oop_or_null(true),
7806          "expected an oop or NULL");
7807   HeapWord* addr = (HeapWord*)obj;
7808   // Check if oop points into the CMS generation
7809   // and is not marked
7810   if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7811     // a white object ...
7812     // If we manage to "claim" the object, by being the
7813     // first thread to mark it, then we push it on our
7814     // marking stack
7815     if (_bit_map->par_mark(addr)) {     // ... now grey
7816       // push on work queue (grey set)
7817       bool simulate_overflow = false;
7818       NOT_PRODUCT(
7819         if (CMSMarkStackOverflowALot &&
7820             _collector->par_simulate_overflow()) {
7821           // simulate a stack overflow
7822           simulate_overflow = true;
7823         }
7824       )
7825       if (simulate_overflow || !_work_queue->push(obj)) {
7826         _collector->par_push_on_overflow_list(obj);
7827         _collector->_par_pmc_remark_ovflw++; //  imprecise OK: no need to CAS
7828       }
7829     } // Else, some other thread got there first
7830   }
7831 }
7832 
7833 void Par_PushAndMarkClosure::do_oop(oop* p)       { Par_PushAndMarkClosure::do_oop_work(p); }
7834 void Par_PushAndMarkClosure::do_oop(narrowOop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7835 
7836 void CMSPrecleanRefsYieldClosure::do_yield_work() {
7837   Mutex* bml = _collector->bitMapLock();
7838   assert_lock_strong(bml);
7839   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7840          "CMS thread should hold CMS token");
7841 
7842   bml->unlock();
7843   ConcurrentMarkSweepThread::desynchronize(true);
7844 
7845   ConcurrentMarkSweepThread::acknowledge_yield_request();
7846 
7847   _collector->stopTimer();
7848   GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7849   if (PrintCMSStatistics != 0) {
7850     _collector->incrementYields();
7851   }
7852   _collector->icms_wait();
7853 
7854   // See the comment in coordinator_yield()
7855   for (unsigned i = 0; i < CMSYieldSleepCount &&
7856                        ConcurrentMarkSweepThread::should_yield() &&
7857                        !CMSCollector::foregroundGCIsActive(); ++i) {
7858     os::sleep(Thread::current(), 1, false);
7859     ConcurrentMarkSweepThread::acknowledge_yield_request();
7860   }
7861 
7862   ConcurrentMarkSweepThread::synchronize(true);
7863   bml->lock();
7864 
7865   _collector->startTimer();
7866 }
7867 
7868 bool CMSPrecleanRefsYieldClosure::should_return() {
7869   if (ConcurrentMarkSweepThread::should_yield()) {
7870     do_yield_work();
7871   }
7872   return _collector->foregroundGCIsActive();
7873 }
7874 
7875 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
7876   assert(((size_t)mr.start())%CardTableModRefBS::card_size_in_words == 0,
7877          "mr should be aligned to start at a card boundary");
7878   // We'd like to assert:
7879   // assert(mr.word_size()%CardTableModRefBS::card_size_in_words == 0,
7880   //        "mr should be a range of cards");
7881   // However, that would be too strong in one case -- the last
7882   // partition ends at _unallocated_block which, in general, can be
7883   // an arbitrary boundary, not necessarily card aligned.
7884   if (PrintCMSStatistics != 0) {
7885     _num_dirty_cards +=
7886          mr.word_size()/CardTableModRefBS::card_size_in_words;
7887   }
7888   _space->object_iterate_mem(mr, &_scan_cl);
7889 }
7890 
7891 SweepClosure::SweepClosure(CMSCollector* collector,
7892                            ConcurrentMarkSweepGeneration* g,
7893                            CMSBitMap* bitMap, bool should_yield) :
7894   _collector(collector),
7895   _g(g),
7896   _sp(g->cmsSpace()),
7897   _limit(_sp->sweep_limit()),
7898   _freelistLock(_sp->freelistLock()),
7899   _bitMap(bitMap),
7900   _yield(should_yield),
7901   _inFreeRange(false),           // No free range at beginning of sweep
7902   _freeRangeInFreeLists(false),  // No free range at beginning of sweep
7903   _lastFreeRangeCoalesced(false),
7904   _freeFinger(g->used_region().start())
7905 {
7906   NOT_PRODUCT(
7907     _numObjectsFreed = 0;
7908     _numWordsFreed   = 0;
7909     _numObjectsLive = 0;
7910     _numWordsLive = 0;
7911     _numObjectsAlreadyFree = 0;
7912     _numWordsAlreadyFree = 0;
7913     _last_fc = NULL;
7914 
7915     _sp->initializeIndexedFreeListArrayReturnedBytes();
7916     _sp->dictionary()->initialize_dict_returned_bytes();
7917   )
7918   assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7919          "sweep _limit out of bounds");
7920   if (CMSTraceSweeper) {
7921     gclog_or_tty->print_cr("\n====================\nStarting new sweep with limit " PTR_FORMAT,
7922                         _limit);
7923   }
7924 }
7925 
7926 void SweepClosure::print_on(outputStream* st) const {
7927   tty->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")",
7928                 _sp->bottom(), _sp->end());
7929   tty->print_cr("_limit = " PTR_FORMAT, _limit);
7930   tty->print_cr("_freeFinger = " PTR_FORMAT, _freeFinger);
7931   NOT_PRODUCT(tty->print_cr("_last_fc = " PTR_FORMAT, _last_fc);)
7932   tty->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d",
7933                 _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced);
7934 }
7935 
7936 #ifndef PRODUCT
7937 // Assertion checking only:  no useful work in product mode --
7938 // however, if any of the flags below become product flags,
7939 // you may need to review this code to see if it needs to be
7940 // enabled in product mode.
7941 SweepClosure::~SweepClosure() {
7942   assert_lock_strong(_freelistLock);
7943   assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7944          "sweep _limit out of bounds");
7945   if (inFreeRange()) {
7946     warning("inFreeRange() should have been reset; dumping state of SweepClosure");
7947     print();
7948     ShouldNotReachHere();
7949   }
7950   if (Verbose && PrintGC) {
7951     gclog_or_tty->print("Collected "SIZE_FORMAT" objects, " SIZE_FORMAT " bytes",
7952                         _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
7953     gclog_or_tty->print_cr("\nLive "SIZE_FORMAT" objects,  "
7954                            SIZE_FORMAT" bytes  "
7955       "Already free "SIZE_FORMAT" objects, "SIZE_FORMAT" bytes",
7956       _numObjectsLive, _numWordsLive*sizeof(HeapWord),
7957       _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
7958     size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree)
7959                         * sizeof(HeapWord);
7960     gclog_or_tty->print_cr("Total sweep: "SIZE_FORMAT" bytes", totalBytes);
7961 
7962     if (PrintCMSStatistics && CMSVerifyReturnedBytes) {
7963       size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
7964       size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes();
7965       size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes;
7966       gclog_or_tty->print("Returned "SIZE_FORMAT" bytes", returned_bytes);
7967       gclog_or_tty->print("   Indexed List Returned "SIZE_FORMAT" bytes",
7968         indexListReturnedBytes);
7969       gclog_or_tty->print_cr("        Dictionary Returned "SIZE_FORMAT" bytes",
7970         dict_returned_bytes);
7971     }
7972   }
7973   if (CMSTraceSweeper) {
7974     gclog_or_tty->print_cr("end of sweep with _limit = " PTR_FORMAT "\n================",
7975                            _limit);
7976   }
7977 }
7978 #endif  // PRODUCT
7979 
7980 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
7981     bool freeRangeInFreeLists) {
7982   if (CMSTraceSweeper) {
7983     gclog_or_tty->print("---- Start free range at 0x%x with free block (%d)\n",
7984                freeFinger, freeRangeInFreeLists);
7985   }
7986   assert(!inFreeRange(), "Trampling existing free range");
7987   set_inFreeRange(true);
7988   set_lastFreeRangeCoalesced(false);
7989 
7990   set_freeFinger(freeFinger);
7991   set_freeRangeInFreeLists(freeRangeInFreeLists);
7992   if (CMSTestInFreeList) {
7993     if (freeRangeInFreeLists) {
7994       FreeChunk* fc = (FreeChunk*) freeFinger;
7995       assert(fc->is_free(), "A chunk on the free list should be free.");
7996       assert(fc->size() > 0, "Free range should have a size");
7997       assert(_sp->verify_chunk_in_free_list(fc), "Chunk is not in free lists");
7998     }
7999   }
8000 }
8001 
8002 // Note that the sweeper runs concurrently with mutators. Thus,
8003 // it is possible for direct allocation in this generation to happen
8004 // in the middle of the sweep. Note that the sweeper also coalesces
8005 // contiguous free blocks. Thus, unless the sweeper and the allocator
8006 // synchronize appropriately freshly allocated blocks may get swept up.
8007 // This is accomplished by the sweeper locking the free lists while
8008 // it is sweeping. Thus blocks that are determined to be free are
8009 // indeed free. There is however one additional complication:
8010 // blocks that have been allocated since the final checkpoint and
8011 // mark, will not have been marked and so would be treated as
8012 // unreachable and swept up. To prevent this, the allocator marks
8013 // the bit map when allocating during the sweep phase. This leads,
8014 // however, to a further complication -- objects may have been allocated
8015 // but not yet initialized -- in the sense that the header isn't yet
8016 // installed. The sweeper can not then determine the size of the block
8017 // in order to skip over it. To deal with this case, we use a technique
8018 // (due to Printezis) to encode such uninitialized block sizes in the
8019 // bit map. Since the bit map uses a bit per every HeapWord, but the
8020 // CMS generation has a minimum object size of 3 HeapWords, it follows
8021 // that "normal marks" won't be adjacent in the bit map (there will
8022 // always be at least two 0 bits between successive 1 bits). We make use
8023 // of these "unused" bits to represent uninitialized blocks -- the bit
8024 // corresponding to the start of the uninitialized object and the next
8025 // bit are both set. Finally, a 1 bit marks the end of the object that
8026 // started with the two consecutive 1 bits to indicate its potentially
8027 // uninitialized state.
8028 
8029 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
8030   FreeChunk* fc = (FreeChunk*)addr;
8031   size_t res;
8032 
8033   // Check if we are done sweeping. Below we check "addr >= _limit" rather
8034   // than "addr == _limit" because although _limit was a block boundary when
8035   // we started the sweep, it may no longer be one because heap expansion
8036   // may have caused us to coalesce the block ending at the address _limit
8037   // with a newly expanded chunk (this happens when _limit was set to the
8038   // previous _end of the space), so we may have stepped past _limit:
8039   // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740.
8040   if (addr >= _limit) { // we have swept up to or past the limit: finish up
8041     assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
8042            "sweep _limit out of bounds");
8043     assert(addr < _sp->end(), "addr out of bounds");
8044     // Flush any free range we might be holding as a single
8045     // coalesced chunk to the appropriate free list.
8046     if (inFreeRange()) {
8047       assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit,
8048              err_msg("freeFinger() " PTR_FORMAT" is out-of-bounds", freeFinger()));
8049       flush_cur_free_chunk(freeFinger(),
8050                            pointer_delta(addr, freeFinger()));
8051       if (CMSTraceSweeper) {
8052         gclog_or_tty->print("Sweep: last chunk: ");
8053         gclog_or_tty->print("put_free_blk 0x%x ("SIZE_FORMAT") "
8054                    "[coalesced:"SIZE_FORMAT"]\n",
8055                    freeFinger(), pointer_delta(addr, freeFinger()),
8056                    lastFreeRangeCoalesced());
8057       }
8058     }
8059 
8060     // help the iterator loop finish
8061     return pointer_delta(_sp->end(), addr);
8062   }
8063 
8064   assert(addr < _limit, "sweep invariant");
8065   // check if we should yield
8066   do_yield_check(addr);
8067   if (fc->is_free()) {
8068     // Chunk that is already free
8069     res = fc->size();
8070     do_already_free_chunk(fc);
8071     debug_only(_sp->verifyFreeLists());
8072     // If we flush the chunk at hand in lookahead_and_flush()
8073     // and it's coalesced with a preceding chunk, then the
8074     // process of "mangling" the payload of the coalesced block
8075     // will cause erasure of the size information from the
8076     // (erstwhile) header of all the coalesced blocks but the
8077     // first, so the first disjunct in the assert will not hold
8078     // in that specific case (in which case the second disjunct
8079     // will hold).
8080     assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit,
8081            "Otherwise the size info doesn't change at this step");
8082     NOT_PRODUCT(
8083       _numObjectsAlreadyFree++;
8084       _numWordsAlreadyFree += res;
8085     )
8086     NOT_PRODUCT(_last_fc = fc;)
8087   } else if (!_bitMap->isMarked(addr)) {
8088     // Chunk is fresh garbage
8089     res = do_garbage_chunk(fc);
8090     debug_only(_sp->verifyFreeLists());
8091     NOT_PRODUCT(
8092       _numObjectsFreed++;
8093       _numWordsFreed += res;
8094     )
8095   } else {
8096     // Chunk that is alive.
8097     res = do_live_chunk(fc);
8098     debug_only(_sp->verifyFreeLists());
8099     NOT_PRODUCT(
8100         _numObjectsLive++;
8101         _numWordsLive += res;
8102     )
8103   }
8104   return res;
8105 }
8106 
8107 // For the smart allocation, record following
8108 //  split deaths - a free chunk is removed from its free list because
8109 //      it is being split into two or more chunks.
8110 //  split birth - a free chunk is being added to its free list because
8111 //      a larger free chunk has been split and resulted in this free chunk.
8112 //  coal death - a free chunk is being removed from its free list because
8113 //      it is being coalesced into a large free chunk.
8114 //  coal birth - a free chunk is being added to its free list because
8115 //      it was created when two or more free chunks where coalesced into
8116 //      this free chunk.
8117 //
8118 // These statistics are used to determine the desired number of free
8119 // chunks of a given size.  The desired number is chosen to be relative
8120 // to the end of a CMS sweep.  The desired number at the end of a sweep
8121 // is the
8122 //      count-at-end-of-previous-sweep (an amount that was enough)
8123 //              - count-at-beginning-of-current-sweep  (the excess)
8124 //              + split-births  (gains in this size during interval)
8125 //              - split-deaths  (demands on this size during interval)
8126 // where the interval is from the end of one sweep to the end of the
8127 // next.
8128 //
8129 // When sweeping the sweeper maintains an accumulated chunk which is
8130 // the chunk that is made up of chunks that have been coalesced.  That
8131 // will be termed the left-hand chunk.  A new chunk of garbage that
8132 // is being considered for coalescing will be referred to as the
8133 // right-hand chunk.
8134 //
8135 // When making a decision on whether to coalesce a right-hand chunk with
8136 // the current left-hand chunk, the current count vs. the desired count
8137 // of the left-hand chunk is considered.  Also if the right-hand chunk
8138 // is near the large chunk at the end of the heap (see
8139 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
8140 // left-hand chunk is coalesced.
8141 //
8142 // When making a decision about whether to split a chunk, the desired count
8143 // vs. the current count of the candidate to be split is also considered.
8144 // If the candidate is underpopulated (currently fewer chunks than desired)
8145 // a chunk of an overpopulated (currently more chunks than desired) size may
8146 // be chosen.  The "hint" associated with a free list, if non-null, points
8147 // to a free list which may be overpopulated.
8148 //
8149 
8150 void SweepClosure::do_already_free_chunk(FreeChunk* fc) {
8151   const size_t size = fc->size();
8152   // Chunks that cannot be coalesced are not in the
8153   // free lists.
8154   if (CMSTestInFreeList && !fc->cantCoalesce()) {
8155     assert(_sp->verify_chunk_in_free_list(fc),
8156       "free chunk should be in free lists");
8157   }
8158   // a chunk that is already free, should not have been
8159   // marked in the bit map
8160   HeapWord* const addr = (HeapWord*) fc;
8161   assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
8162   // Verify that the bit map has no bits marked between
8163   // addr and purported end of this block.
8164   _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8165 
8166   // Some chunks cannot be coalesced under any circumstances.
8167   // See the definition of cantCoalesce().
8168   if (!fc->cantCoalesce()) {
8169     // This chunk can potentially be coalesced.
8170     if (_sp->adaptive_freelists()) {
8171       // All the work is done in
8172       do_post_free_or_garbage_chunk(fc, size);
8173     } else {  // Not adaptive free lists
8174       // this is a free chunk that can potentially be coalesced by the sweeper;
8175       if (!inFreeRange()) {
8176         // if the next chunk is a free block that can't be coalesced
8177         // it doesn't make sense to remove this chunk from the free lists
8178         FreeChunk* nextChunk = (FreeChunk*)(addr + size);
8179         assert((HeapWord*)nextChunk <= _sp->end(), "Chunk size out of bounds?");
8180         if ((HeapWord*)nextChunk < _sp->end() &&     // There is another free chunk to the right ...
8181             nextChunk->is_free()               &&     // ... which is free...
8182             nextChunk->cantCoalesce()) {             // ... but can't be coalesced
8183           // nothing to do
8184         } else {
8185           // Potentially the start of a new free range:
8186           // Don't eagerly remove it from the free lists.
8187           // No need to remove it if it will just be put
8188           // back again.  (Also from a pragmatic point of view
8189           // if it is a free block in a region that is beyond
8190           // any allocated blocks, an assertion will fail)
8191           // Remember the start of a free run.
8192           initialize_free_range(addr, true);
8193           // end - can coalesce with next chunk
8194         }
8195       } else {
8196         // the midst of a free range, we are coalescing
8197         print_free_block_coalesced(fc);
8198         if (CMSTraceSweeper) {
8199           gclog_or_tty->print("  -- pick up free block 0x%x (%d)\n", fc, size);
8200         }
8201         // remove it from the free lists
8202         _sp->removeFreeChunkFromFreeLists(fc);
8203         set_lastFreeRangeCoalesced(true);
8204         // If the chunk is being coalesced and the current free range is
8205         // in the free lists, remove the current free range so that it
8206         // will be returned to the free lists in its entirety - all
8207         // the coalesced pieces included.
8208         if (freeRangeInFreeLists()) {
8209           FreeChunk* ffc = (FreeChunk*) freeFinger();
8210           assert(ffc->size() == pointer_delta(addr, freeFinger()),
8211             "Size of free range is inconsistent with chunk size.");
8212           if (CMSTestInFreeList) {
8213             assert(_sp->verify_chunk_in_free_list(ffc),
8214               "free range is not in free lists");
8215           }
8216           _sp->removeFreeChunkFromFreeLists(ffc);
8217           set_freeRangeInFreeLists(false);
8218         }
8219       }
8220     }
8221     // Note that if the chunk is not coalescable (the else arm
8222     // below), we unconditionally flush, without needing to do
8223     // a "lookahead," as we do below.
8224     if (inFreeRange()) lookahead_and_flush(fc, size);
8225   } else {
8226     // Code path common to both original and adaptive free lists.
8227 
8228     // cant coalesce with previous block; this should be treated
8229     // as the end of a free run if any
8230     if (inFreeRange()) {
8231       // we kicked some butt; time to pick up the garbage
8232       assert(freeFinger() < addr, "freeFinger points too high");
8233       flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8234     }
8235     // else, nothing to do, just continue
8236   }
8237 }
8238 
8239 size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) {
8240   // This is a chunk of garbage.  It is not in any free list.
8241   // Add it to a free list or let it possibly be coalesced into
8242   // a larger chunk.
8243   HeapWord* const addr = (HeapWord*) fc;
8244   const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
8245 
8246   if (_sp->adaptive_freelists()) {
8247     // Verify that the bit map has no bits marked between
8248     // addr and purported end of just dead object.
8249     _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8250 
8251     do_post_free_or_garbage_chunk(fc, size);
8252   } else {
8253     if (!inFreeRange()) {
8254       // start of a new free range
8255       assert(size > 0, "A free range should have a size");
8256       initialize_free_range(addr, false);
8257     } else {
8258       // this will be swept up when we hit the end of the
8259       // free range
8260       if (CMSTraceSweeper) {
8261         gclog_or_tty->print("  -- pick up garbage 0x%x (%d) \n", fc, size);
8262       }
8263       // If the chunk is being coalesced and the current free range is
8264       // in the free lists, remove the current free range so that it
8265       // will be returned to the free lists in its entirety - all
8266       // the coalesced pieces included.
8267       if (freeRangeInFreeLists()) {
8268         FreeChunk* ffc = (FreeChunk*)freeFinger();
8269         assert(ffc->size() == pointer_delta(addr, freeFinger()),
8270           "Size of free range is inconsistent with chunk size.");
8271         if (CMSTestInFreeList) {
8272           assert(_sp->verify_chunk_in_free_list(ffc),
8273             "free range is not in free lists");
8274         }
8275         _sp->removeFreeChunkFromFreeLists(ffc);
8276         set_freeRangeInFreeLists(false);
8277       }
8278       set_lastFreeRangeCoalesced(true);
8279     }
8280     // this will be swept up when we hit the end of the free range
8281 
8282     // Verify that the bit map has no bits marked between
8283     // addr and purported end of just dead object.
8284     _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8285   }
8286   assert(_limit >= addr + size,
8287          "A freshly garbage chunk can't possibly straddle over _limit");
8288   if (inFreeRange()) lookahead_and_flush(fc, size);
8289   return size;
8290 }
8291 
8292 size_t SweepClosure::do_live_chunk(FreeChunk* fc) {
8293   HeapWord* addr = (HeapWord*) fc;
8294   // The sweeper has just found a live object. Return any accumulated
8295   // left hand chunk to the free lists.
8296   if (inFreeRange()) {
8297     assert(freeFinger() < addr, "freeFinger points too high");
8298     flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8299   }
8300 
8301   // This object is live: we'd normally expect this to be
8302   // an oop, and like to assert the following:
8303   // assert(oop(addr)->is_oop(), "live block should be an oop");
8304   // However, as we commented above, this may be an object whose
8305   // header hasn't yet been initialized.
8306   size_t size;
8307   assert(_bitMap->isMarked(addr), "Tautology for this control point");
8308   if (_bitMap->isMarked(addr + 1)) {
8309     // Determine the size from the bit map, rather than trying to
8310     // compute it from the object header.
8311     HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
8312     size = pointer_delta(nextOneAddr + 1, addr);
8313     assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
8314            "alignment problem");
8315 
8316 #ifdef ASSERT
8317       if (oop(addr)->klass_or_null() != NULL) {
8318         // Ignore mark word because we are running concurrent with mutators
8319         assert(oop(addr)->is_oop(true), "live block should be an oop");
8320         assert(size ==
8321                CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
8322                "P-mark and computed size do not agree");
8323       }
8324 #endif
8325 
8326   } else {
8327     // This should be an initialized object that's alive.
8328     assert(oop(addr)->klass_or_null() != NULL,
8329            "Should be an initialized object");
8330     // Ignore mark word because we are running concurrent with mutators
8331     assert(oop(addr)->is_oop(true), "live block should be an oop");
8332     // Verify that the bit map has no bits marked between
8333     // addr and purported end of this block.
8334     size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
8335     assert(size >= 3, "Necessary for Printezis marks to work");
8336     assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
8337     DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
8338   }
8339   return size;
8340 }
8341 
8342 void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc,
8343                                                  size_t chunkSize) {
8344   // do_post_free_or_garbage_chunk() should only be called in the case
8345   // of the adaptive free list allocator.
8346   const bool fcInFreeLists = fc->is_free();
8347   assert(_sp->adaptive_freelists(), "Should only be used in this case.");
8348   assert((HeapWord*)fc <= _limit, "sweep invariant");
8349   if (CMSTestInFreeList && fcInFreeLists) {
8350     assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists");
8351   }
8352 
8353   if (CMSTraceSweeper) {
8354     gclog_or_tty->print_cr("  -- pick up another chunk at 0x%x (%d)", fc, chunkSize);
8355   }
8356 
8357   HeapWord* const fc_addr = (HeapWord*) fc;
8358 
8359   bool coalesce;
8360   const size_t left  = pointer_delta(fc_addr, freeFinger());
8361   const size_t right = chunkSize;
8362   switch (FLSCoalescePolicy) {
8363     // numeric value forms a coalition aggressiveness metric
8364     case 0:  { // never coalesce
8365       coalesce = false;
8366       break;
8367     }
8368     case 1: { // coalesce if left & right chunks on overpopulated lists
8369       coalesce = _sp->coalOverPopulated(left) &&
8370                  _sp->coalOverPopulated(right);
8371       break;
8372     }
8373     case 2: { // coalesce if left chunk on overpopulated list (default)
8374       coalesce = _sp->coalOverPopulated(left);
8375       break;
8376     }
8377     case 3: { // coalesce if left OR right chunk on overpopulated list
8378       coalesce = _sp->coalOverPopulated(left) ||
8379                  _sp->coalOverPopulated(right);
8380       break;
8381     }
8382     case 4: { // always coalesce
8383       coalesce = true;
8384       break;
8385     }
8386     default:
8387      ShouldNotReachHere();
8388   }
8389 
8390   // Should the current free range be coalesced?
8391   // If the chunk is in a free range and either we decided to coalesce above
8392   // or the chunk is near the large block at the end of the heap
8393   // (isNearLargestChunk() returns true), then coalesce this chunk.
8394   const bool doCoalesce = inFreeRange()
8395                           && (coalesce || _g->isNearLargestChunk(fc_addr));
8396   if (doCoalesce) {
8397     // Coalesce the current free range on the left with the new
8398     // chunk on the right.  If either is on a free list,
8399     // it must be removed from the list and stashed in the closure.
8400     if (freeRangeInFreeLists()) {
8401       FreeChunk* const ffc = (FreeChunk*)freeFinger();
8402       assert(ffc->size() == pointer_delta(fc_addr, freeFinger()),
8403         "Size of free range is inconsistent with chunk size.");
8404       if (CMSTestInFreeList) {
8405         assert(_sp->verify_chunk_in_free_list(ffc),
8406           "Chunk is not in free lists");
8407       }
8408       _sp->coalDeath(ffc->size());
8409       _sp->removeFreeChunkFromFreeLists(ffc);
8410       set_freeRangeInFreeLists(false);
8411     }
8412     if (fcInFreeLists) {
8413       _sp->coalDeath(chunkSize);
8414       assert(fc->size() == chunkSize,
8415         "The chunk has the wrong size or is not in the free lists");
8416       _sp->removeFreeChunkFromFreeLists(fc);
8417     }
8418     set_lastFreeRangeCoalesced(true);
8419     print_free_block_coalesced(fc);
8420   } else {  // not in a free range and/or should not coalesce
8421     // Return the current free range and start a new one.
8422     if (inFreeRange()) {
8423       // In a free range but cannot coalesce with the right hand chunk.
8424       // Put the current free range into the free lists.
8425       flush_cur_free_chunk(freeFinger(),
8426                            pointer_delta(fc_addr, freeFinger()));
8427     }
8428     // Set up for new free range.  Pass along whether the right hand
8429     // chunk is in the free lists.
8430     initialize_free_range((HeapWord*)fc, fcInFreeLists);
8431   }
8432 }
8433 
8434 // Lookahead flush:
8435 // If we are tracking a free range, and this is the last chunk that
8436 // we'll look at because its end crosses past _limit, we'll preemptively
8437 // flush it along with any free range we may be holding on to. Note that
8438 // this can be the case only for an already free or freshly garbage
8439 // chunk. If this block is an object, it can never straddle
8440 // over _limit. The "straddling" occurs when _limit is set at
8441 // the previous end of the space when this cycle started, and
8442 // a subsequent heap expansion caused the previously co-terminal
8443 // free block to be coalesced with the newly expanded portion,
8444 // thus rendering _limit a non-block-boundary making it dangerous
8445 // for the sweeper to step over and examine.
8446 void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) {
8447   assert(inFreeRange(), "Should only be called if currently in a free range.");
8448   HeapWord* const eob = ((HeapWord*)fc) + chunk_size;
8449   assert(_sp->used_region().contains(eob - 1),
8450          err_msg("eob = " PTR_FORMAT " out of bounds wrt _sp = [" PTR_FORMAT "," PTR_FORMAT ")"
8451                  " when examining fc = " PTR_FORMAT "(" SIZE_FORMAT ")",
8452                  _limit, _sp->bottom(), _sp->end(), fc, chunk_size));
8453   if (eob >= _limit) {
8454     assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit");
8455     if (CMSTraceSweeper) {
8456       gclog_or_tty->print_cr("_limit " PTR_FORMAT " reached or crossed by block "
8457                              "[" PTR_FORMAT "," PTR_FORMAT ") in space "
8458                              "[" PTR_FORMAT "," PTR_FORMAT ")",
8459                              _limit, fc, eob, _sp->bottom(), _sp->end());
8460     }
8461     // Return the storage we are tracking back into the free lists.
8462     if (CMSTraceSweeper) {
8463       gclog_or_tty->print_cr("Flushing ... ");
8464     }
8465     assert(freeFinger() < eob, "Error");
8466     flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger()));
8467   }
8468 }
8469 
8470 void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) {
8471   assert(inFreeRange(), "Should only be called if currently in a free range.");
8472   assert(size > 0,
8473     "A zero sized chunk cannot be added to the free lists.");
8474   if (!freeRangeInFreeLists()) {
8475     if (CMSTestInFreeList) {
8476       FreeChunk* fc = (FreeChunk*) chunk;
8477       fc->set_size(size);
8478       assert(!_sp->verify_chunk_in_free_list(fc),
8479         "chunk should not be in free lists yet");
8480     }
8481     if (CMSTraceSweeper) {
8482       gclog_or_tty->print_cr(" -- add free block 0x%x (%d) to free lists",
8483                     chunk, size);
8484     }
8485     // A new free range is going to be starting.  The current
8486     // free range has not been added to the free lists yet or
8487     // was removed so add it back.
8488     // If the current free range was coalesced, then the death
8489     // of the free range was recorded.  Record a birth now.
8490     if (lastFreeRangeCoalesced()) {
8491       _sp->coalBirth(size);
8492     }
8493     _sp->addChunkAndRepairOffsetTable(chunk, size,
8494             lastFreeRangeCoalesced());
8495   } else if (CMSTraceSweeper) {
8496     gclog_or_tty->print_cr("Already in free list: nothing to flush");
8497   }
8498   set_inFreeRange(false);
8499   set_freeRangeInFreeLists(false);
8500 }
8501 
8502 // We take a break if we've been at this for a while,
8503 // so as to avoid monopolizing the locks involved.
8504 void SweepClosure::do_yield_work(HeapWord* addr) {
8505   // Return current free chunk being used for coalescing (if any)
8506   // to the appropriate freelist.  After yielding, the next
8507   // free block encountered will start a coalescing range of
8508   // free blocks.  If the next free block is adjacent to the
8509   // chunk just flushed, they will need to wait for the next
8510   // sweep to be coalesced.
8511   if (inFreeRange()) {
8512     flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8513   }
8514 
8515   // First give up the locks, then yield, then re-lock.
8516   // We should probably use a constructor/destructor idiom to
8517   // do this unlock/lock or modify the MutexUnlocker class to
8518   // serve our purpose. XXX
8519   assert_lock_strong(_bitMap->lock());
8520   assert_lock_strong(_freelistLock);
8521   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
8522          "CMS thread should hold CMS token");
8523   _bitMap->lock()->unlock();
8524   _freelistLock->unlock();
8525   ConcurrentMarkSweepThread::desynchronize(true);
8526   ConcurrentMarkSweepThread::acknowledge_yield_request();
8527   _collector->stopTimer();
8528   GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
8529   if (PrintCMSStatistics != 0) {
8530     _collector->incrementYields();
8531   }
8532   _collector->icms_wait();
8533 
8534   // See the comment in coordinator_yield()
8535   for (unsigned i = 0; i < CMSYieldSleepCount &&
8536                        ConcurrentMarkSweepThread::should_yield() &&
8537                        !CMSCollector::foregroundGCIsActive(); ++i) {
8538     os::sleep(Thread::current(), 1, false);
8539     ConcurrentMarkSweepThread::acknowledge_yield_request();
8540   }
8541 
8542   ConcurrentMarkSweepThread::synchronize(true);
8543   _freelistLock->lock();
8544   _bitMap->lock()->lock_without_safepoint_check();
8545   _collector->startTimer();
8546 }
8547 
8548 #ifndef PRODUCT
8549 // This is actually very useful in a product build if it can
8550 // be called from the debugger.  Compile it into the product
8551 // as needed.
8552 bool debug_verify_chunk_in_free_list(FreeChunk* fc) {
8553   return debug_cms_space->verify_chunk_in_free_list(fc);
8554 }
8555 #endif
8556 
8557 void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const {
8558   if (CMSTraceSweeper) {
8559     gclog_or_tty->print_cr("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")",
8560                            fc, fc->size());
8561   }
8562 }
8563 
8564 // CMSIsAliveClosure
8565 bool CMSIsAliveClosure::do_object_b(oop obj) {
8566   HeapWord* addr = (HeapWord*)obj;
8567   return addr != NULL &&
8568          (!_span.contains(addr) || _bit_map->isMarked(addr));
8569 }
8570 
8571 
8572 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector,
8573                       MemRegion span,
8574                       CMSBitMap* bit_map, CMSMarkStack* mark_stack,
8575                       bool cpc):
8576   _collector(collector),
8577   _span(span),
8578   _bit_map(bit_map),
8579   _mark_stack(mark_stack),
8580   _concurrent_precleaning(cpc) {
8581   assert(!_span.is_empty(), "Empty span could spell trouble");
8582 }
8583 
8584 
8585 // CMSKeepAliveClosure: the serial version
8586 void CMSKeepAliveClosure::do_oop(oop obj) {
8587   HeapWord* addr = (HeapWord*)obj;
8588   if (_span.contains(addr) &&
8589       !_bit_map->isMarked(addr)) {
8590     _bit_map->mark(addr);
8591     bool simulate_overflow = false;
8592     NOT_PRODUCT(
8593       if (CMSMarkStackOverflowALot &&
8594           _collector->simulate_overflow()) {
8595         // simulate a stack overflow
8596         simulate_overflow = true;
8597       }
8598     )
8599     if (simulate_overflow || !_mark_stack->push(obj)) {
8600       if (_concurrent_precleaning) {
8601         // We dirty the overflown object and let the remark
8602         // phase deal with it.
8603         assert(_collector->overflow_list_is_empty(), "Error");
8604         // In the case of object arrays, we need to dirty all of
8605         // the cards that the object spans. No locking or atomics
8606         // are needed since no one else can be mutating the mod union
8607         // table.
8608         if (obj->is_objArray()) {
8609           size_t sz = obj->size();
8610           HeapWord* end_card_addr =
8611             (HeapWord*)round_to((intptr_t)(addr+sz), CardTableModRefBS::card_size);
8612           MemRegion redirty_range = MemRegion(addr, end_card_addr);
8613           assert(!redirty_range.is_empty(), "Arithmetical tautology");
8614           _collector->_modUnionTable.mark_range(redirty_range);
8615         } else {
8616           _collector->_modUnionTable.mark(addr);
8617         }
8618         _collector->_ser_kac_preclean_ovflw++;
8619       } else {
8620         _collector->push_on_overflow_list(obj);
8621         _collector->_ser_kac_ovflw++;
8622       }
8623     }
8624   }
8625 }
8626 
8627 void CMSKeepAliveClosure::do_oop(oop* p)       { CMSKeepAliveClosure::do_oop_work(p); }
8628 void CMSKeepAliveClosure::do_oop(narrowOop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8629 
8630 // CMSParKeepAliveClosure: a parallel version of the above.
8631 // The work queues are private to each closure (thread),
8632 // but (may be) available for stealing by other threads.
8633 void CMSParKeepAliveClosure::do_oop(oop obj) {
8634   HeapWord* addr = (HeapWord*)obj;
8635   if (_span.contains(addr) &&
8636       !_bit_map->isMarked(addr)) {
8637     // In general, during recursive tracing, several threads
8638     // may be concurrently getting here; the first one to
8639     // "tag" it, claims it.
8640     if (_bit_map->par_mark(addr)) {
8641       bool res = _work_queue->push(obj);
8642       assert(res, "Low water mark should be much less than capacity");
8643       // Do a recursive trim in the hope that this will keep
8644       // stack usage lower, but leave some oops for potential stealers
8645       trim_queue(_low_water_mark);
8646     } // Else, another thread got there first
8647   }
8648 }
8649 
8650 void CMSParKeepAliveClosure::do_oop(oop* p)       { CMSParKeepAliveClosure::do_oop_work(p); }
8651 void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8652 
8653 void CMSParKeepAliveClosure::trim_queue(uint max) {
8654   while (_work_queue->size() > max) {
8655     oop new_oop;
8656     if (_work_queue->pop_local(new_oop)) {
8657       assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
8658       assert(_bit_map->isMarked((HeapWord*)new_oop),
8659              "no white objects on this stack!");
8660       assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8661       // iterate over the oops in this oop, marking and pushing
8662       // the ones in CMS heap (i.e. in _span).
8663       new_oop->oop_iterate(&_mark_and_push);
8664     }
8665   }
8666 }
8667 
8668 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
8669                                 CMSCollector* collector,
8670                                 MemRegion span, CMSBitMap* bit_map,
8671                                 OopTaskQueue* work_queue):
8672   _collector(collector),
8673   _span(span),
8674   _bit_map(bit_map),
8675   _work_queue(work_queue) { }
8676 
8677 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
8678   HeapWord* addr = (HeapWord*)obj;
8679   if (_span.contains(addr) &&
8680       !_bit_map->isMarked(addr)) {
8681     if (_bit_map->par_mark(addr)) {
8682       bool simulate_overflow = false;
8683       NOT_PRODUCT(
8684         if (CMSMarkStackOverflowALot &&
8685             _collector->par_simulate_overflow()) {
8686           // simulate a stack overflow
8687           simulate_overflow = true;
8688         }
8689       )
8690       if (simulate_overflow || !_work_queue->push(obj)) {
8691         _collector->par_push_on_overflow_list(obj);
8692         _collector->_par_kac_ovflw++;
8693       }
8694     } // Else another thread got there already
8695   }
8696 }
8697 
8698 void CMSInnerParMarkAndPushClosure::do_oop(oop* p)       { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8699 void CMSInnerParMarkAndPushClosure::do_oop(narrowOop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8700 
8701 //////////////////////////////////////////////////////////////////
8702 //  CMSExpansionCause                /////////////////////////////
8703 //////////////////////////////////////////////////////////////////
8704 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
8705   switch (cause) {
8706     case _no_expansion:
8707       return "No expansion";
8708     case _satisfy_free_ratio:
8709       return "Free ratio";
8710     case _satisfy_promotion:
8711       return "Satisfy promotion";
8712     case _satisfy_allocation:
8713       return "allocation";
8714     case _allocate_par_lab:
8715       return "Par LAB";
8716     case _allocate_par_spooling_space:
8717       return "Par Spooling Space";
8718     case _adaptive_size_policy:
8719       return "Ergonomics";
8720     default:
8721       return "unknown";
8722   }
8723 }
8724 
8725 void CMSDrainMarkingStackClosure::do_void() {
8726   // the max number to take from overflow list at a time
8727   const size_t num = _mark_stack->capacity()/4;
8728   assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
8729          "Overflow list should be NULL during concurrent phases");
8730   while (!_mark_stack->isEmpty() ||
8731          // if stack is empty, check the overflow list
8732          _collector->take_from_overflow_list(num, _mark_stack)) {
8733     oop obj = _mark_stack->pop();
8734     HeapWord* addr = (HeapWord*)obj;
8735     assert(_span.contains(addr), "Should be within span");
8736     assert(_bit_map->isMarked(addr), "Should be marked");
8737     assert(obj->is_oop(), "Should be an oop");
8738     obj->oop_iterate(_keep_alive);
8739   }
8740 }
8741 
8742 void CMSParDrainMarkingStackClosure::do_void() {
8743   // drain queue
8744   trim_queue(0);
8745 }
8746 
8747 // Trim our work_queue so its length is below max at return
8748 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
8749   while (_work_queue->size() > max) {
8750     oop new_oop;
8751     if (_work_queue->pop_local(new_oop)) {
8752       assert(new_oop->is_oop(), "Expected an oop");
8753       assert(_bit_map->isMarked((HeapWord*)new_oop),
8754              "no white objects on this stack!");
8755       assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8756       // iterate over the oops in this oop, marking and pushing
8757       // the ones in CMS heap (i.e. in _span).
8758       new_oop->oop_iterate(&_mark_and_push);
8759     }
8760   }
8761 }
8762 
8763 ////////////////////////////////////////////////////////////////////
8764 // Support for Marking Stack Overflow list handling and related code
8765 ////////////////////////////////////////////////////////////////////
8766 // Much of the following code is similar in shape and spirit to the
8767 // code used in ParNewGC. We should try and share that code
8768 // as much as possible in the future.
8769 
8770 #ifndef PRODUCT
8771 // Debugging support for CMSStackOverflowALot
8772 
8773 // It's OK to call this multi-threaded;  the worst thing
8774 // that can happen is that we'll get a bunch of closely
8775 // spaced simulated oveflows, but that's OK, in fact
8776 // probably good as it would exercise the overflow code
8777 // under contention.
8778 bool CMSCollector::simulate_overflow() {
8779   if (_overflow_counter-- <= 0) { // just being defensive
8780     _overflow_counter = CMSMarkStackOverflowInterval;
8781     return true;
8782   } else {
8783     return false;
8784   }
8785 }
8786 
8787 bool CMSCollector::par_simulate_overflow() {
8788   return simulate_overflow();
8789 }
8790 #endif
8791 
8792 // Single-threaded
8793 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
8794   assert(stack->isEmpty(), "Expected precondition");
8795   assert(stack->capacity() > num, "Shouldn't bite more than can chew");
8796   size_t i = num;
8797   oop  cur = _overflow_list;
8798   const markOop proto = markOopDesc::prototype();
8799   NOT_PRODUCT(ssize_t n = 0;)
8800   for (oop next; i > 0 && cur != NULL; cur = next, i--) {
8801     next = oop(cur->mark());
8802     cur->set_mark(proto);   // until proven otherwise
8803     assert(cur->is_oop(), "Should be an oop");
8804     bool res = stack->push(cur);
8805     assert(res, "Bit off more than can chew?");
8806     NOT_PRODUCT(n++;)
8807   }
8808   _overflow_list = cur;
8809 #ifndef PRODUCT
8810   assert(_num_par_pushes >= n, "Too many pops?");
8811   _num_par_pushes -=n;
8812 #endif
8813   return !stack->isEmpty();
8814 }
8815 
8816 #define BUSY  (oop(0x1aff1aff))
8817 // (MT-safe) Get a prefix of at most "num" from the list.
8818 // The overflow list is chained through the mark word of
8819 // each object in the list. We fetch the entire list,
8820 // break off a prefix of the right size and return the
8821 // remainder. If other threads try to take objects from
8822 // the overflow list at that time, they will wait for
8823 // some time to see if data becomes available. If (and
8824 // only if) another thread places one or more object(s)
8825 // on the global list before we have returned the suffix
8826 // to the global list, we will walk down our local list
8827 // to find its end and append the global list to
8828 // our suffix before returning it. This suffix walk can
8829 // prove to be expensive (quadratic in the amount of traffic)
8830 // when there are many objects in the overflow list and
8831 // there is much producer-consumer contention on the list.
8832 // *NOTE*: The overflow list manipulation code here and
8833 // in ParNewGeneration:: are very similar in shape,
8834 // except that in the ParNew case we use the old (from/eden)
8835 // copy of the object to thread the list via its klass word.
8836 // Because of the common code, if you make any changes in
8837 // the code below, please check the ParNew version to see if
8838 // similar changes might be needed.
8839 // CR 6797058 has been filed to consolidate the common code.
8840 bool CMSCollector::par_take_from_overflow_list(size_t num,
8841                                                OopTaskQueue* work_q,
8842                                                int no_of_gc_threads) {
8843   assert(work_q->size() == 0, "First empty local work queue");
8844   assert(num < work_q->max_elems(), "Can't bite more than we can chew");
8845   if (_overflow_list == NULL) {
8846     return false;
8847   }
8848   // Grab the entire list; we'll put back a suffix
8849   oop prefix = (oop)Atomic::xchg_ptr(BUSY, &_overflow_list);
8850   Thread* tid = Thread::current();
8851   // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was
8852   // set to ParallelGCThreads.
8853   size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads;
8854   size_t sleep_time_millis = MAX2((size_t)1, num/100);
8855   // If the list is busy, we spin for a short while,
8856   // sleeping between attempts to get the list.
8857   for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) {
8858     os::sleep(tid, sleep_time_millis, false);
8859     if (_overflow_list == NULL) {
8860       // Nothing left to take
8861       return false;
8862     } else if (_overflow_list != BUSY) {
8863       // Try and grab the prefix
8864       prefix = (oop)Atomic::xchg_ptr(BUSY, &_overflow_list);
8865     }
8866   }
8867   // If the list was found to be empty, or we spun long
8868   // enough, we give up and return empty-handed. If we leave
8869   // the list in the BUSY state below, it must be the case that
8870   // some other thread holds the overflow list and will set it
8871   // to a non-BUSY state in the future.
8872   if (prefix == NULL || prefix == BUSY) {
8873      // Nothing to take or waited long enough
8874      if (prefix == NULL) {
8875        // Write back the NULL in case we overwrote it with BUSY above
8876        // and it is still the same value.
8877        (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8878      }
8879      return false;
8880   }
8881   assert(prefix != NULL && prefix != BUSY, "Error");
8882   size_t i = num;
8883   oop cur = prefix;
8884   // Walk down the first "num" objects, unless we reach the end.
8885   for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--);
8886   if (cur->mark() == NULL) {
8887     // We have "num" or fewer elements in the list, so there
8888     // is nothing to return to the global list.
8889     // Write back the NULL in lieu of the BUSY we wrote
8890     // above, if it is still the same value.
8891     if (_overflow_list == BUSY) {
8892       (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8893     }
8894   } else {
8895     // Chop off the suffix and rerturn it to the global list.
8896     assert(cur->mark() != BUSY, "Error");
8897     oop suffix_head = cur->mark(); // suffix will be put back on global list
8898     cur->set_mark(NULL);           // break off suffix
8899     // It's possible that the list is still in the empty(busy) state
8900     // we left it in a short while ago; in that case we may be
8901     // able to place back the suffix without incurring the cost
8902     // of a walk down the list.
8903     oop observed_overflow_list = _overflow_list;
8904     oop cur_overflow_list = observed_overflow_list;
8905     bool attached = false;
8906     while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
8907       observed_overflow_list =
8908         (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
8909       if (cur_overflow_list == observed_overflow_list) {
8910         attached = true;
8911         break;
8912       } else cur_overflow_list = observed_overflow_list;
8913     }
8914     if (!attached) {
8915       // Too bad, someone else sneaked in (at least) an element; we'll need
8916       // to do a splice. Find tail of suffix so we can prepend suffix to global
8917       // list.
8918       for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark()));
8919       oop suffix_tail = cur;
8920       assert(suffix_tail != NULL && suffix_tail->mark() == NULL,
8921              "Tautology");
8922       observed_overflow_list = _overflow_list;
8923       do {
8924         cur_overflow_list = observed_overflow_list;
8925         if (cur_overflow_list != BUSY) {
8926           // Do the splice ...
8927           suffix_tail->set_mark(markOop(cur_overflow_list));
8928         } else { // cur_overflow_list == BUSY
8929           suffix_tail->set_mark(NULL);
8930         }
8931         // ... and try to place spliced list back on overflow_list ...
8932         observed_overflow_list =
8933           (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
8934       } while (cur_overflow_list != observed_overflow_list);
8935       // ... until we have succeeded in doing so.
8936     }
8937   }
8938 
8939   // Push the prefix elements on work_q
8940   assert(prefix != NULL, "control point invariant");
8941   const markOop proto = markOopDesc::prototype();
8942   oop next;
8943   NOT_PRODUCT(ssize_t n = 0;)
8944   for (cur = prefix; cur != NULL; cur = next) {
8945     next = oop(cur->mark());
8946     cur->set_mark(proto);   // until proven otherwise
8947     assert(cur->is_oop(), "Should be an oop");
8948     bool res = work_q->push(cur);
8949     assert(res, "Bit off more than we can chew?");
8950     NOT_PRODUCT(n++;)
8951   }
8952 #ifndef PRODUCT
8953   assert(_num_par_pushes >= n, "Too many pops?");
8954   Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
8955 #endif
8956   return true;
8957 }
8958 
8959 // Single-threaded
8960 void CMSCollector::push_on_overflow_list(oop p) {
8961   NOT_PRODUCT(_num_par_pushes++;)
8962   assert(p->is_oop(), "Not an oop");
8963   preserve_mark_if_necessary(p);
8964   p->set_mark((markOop)_overflow_list);
8965   _overflow_list = p;
8966 }
8967 
8968 // Multi-threaded; use CAS to prepend to overflow list
8969 void CMSCollector::par_push_on_overflow_list(oop p) {
8970   NOT_PRODUCT(Atomic::inc_ptr(&_num_par_pushes);)
8971   assert(p->is_oop(), "Not an oop");
8972   par_preserve_mark_if_necessary(p);
8973   oop observed_overflow_list = _overflow_list;
8974   oop cur_overflow_list;
8975   do {
8976     cur_overflow_list = observed_overflow_list;
8977     if (cur_overflow_list != BUSY) {
8978       p->set_mark(markOop(cur_overflow_list));
8979     } else {
8980       p->set_mark(NULL);
8981     }
8982     observed_overflow_list =
8983       (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list);
8984   } while (cur_overflow_list != observed_overflow_list);
8985 }
8986 #undef BUSY
8987 
8988 // Single threaded
8989 // General Note on GrowableArray: pushes may silently fail
8990 // because we are (temporarily) out of C-heap for expanding
8991 // the stack. The problem is quite ubiquitous and affects
8992 // a lot of code in the JVM. The prudent thing for GrowableArray
8993 // to do (for now) is to exit with an error. However, that may
8994 // be too draconian in some cases because the caller may be
8995 // able to recover without much harm. For such cases, we
8996 // should probably introduce a "soft_push" method which returns
8997 // an indication of success or failure with the assumption that
8998 // the caller may be able to recover from a failure; code in
8999 // the VM can then be changed, incrementally, to deal with such
9000 // failures where possible, thus, incrementally hardening the VM
9001 // in such low resource situations.
9002 void CMSCollector::preserve_mark_work(oop p, markOop m) {
9003   _preserved_oop_stack.push(p);
9004   _preserved_mark_stack.push(m);
9005   assert(m == p->mark(), "Mark word changed");
9006   assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
9007          "bijection");
9008 }
9009 
9010 // Single threaded
9011 void CMSCollector::preserve_mark_if_necessary(oop p) {
9012   markOop m = p->mark();
9013   if (m->must_be_preserved(p)) {
9014     preserve_mark_work(p, m);
9015   }
9016 }
9017 
9018 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
9019   markOop m = p->mark();
9020   if (m->must_be_preserved(p)) {
9021     MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
9022     // Even though we read the mark word without holding
9023     // the lock, we are assured that it will not change
9024     // because we "own" this oop, so no other thread can
9025     // be trying to push it on the overflow list; see
9026     // the assertion in preserve_mark_work() that checks
9027     // that m == p->mark().
9028     preserve_mark_work(p, m);
9029   }
9030 }
9031 
9032 // We should be able to do this multi-threaded,
9033 // a chunk of stack being a task (this is
9034 // correct because each oop only ever appears
9035 // once in the overflow list. However, it's
9036 // not very easy to completely overlap this with
9037 // other operations, so will generally not be done
9038 // until all work's been completed. Because we
9039 // expect the preserved oop stack (set) to be small,
9040 // it's probably fine to do this single-threaded.
9041 // We can explore cleverer concurrent/overlapped/parallel
9042 // processing of preserved marks if we feel the
9043 // need for this in the future. Stack overflow should
9044 // be so rare in practice and, when it happens, its
9045 // effect on performance so great that this will
9046 // likely just be in the noise anyway.
9047 void CMSCollector::restore_preserved_marks_if_any() {
9048   assert(SafepointSynchronize::is_at_safepoint(),
9049          "world should be stopped");
9050   assert(Thread::current()->is_ConcurrentGC_thread() ||
9051          Thread::current()->is_VM_thread(),
9052          "should be single-threaded");
9053   assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
9054          "bijection");
9055 
9056   while (!_preserved_oop_stack.is_empty()) {
9057     oop p = _preserved_oop_stack.pop();
9058     assert(p->is_oop(), "Should be an oop");
9059     assert(_span.contains(p), "oop should be in _span");
9060     assert(p->mark() == markOopDesc::prototype(),
9061            "Set when taken from overflow list");
9062     markOop m = _preserved_mark_stack.pop();
9063     p->set_mark(m);
9064   }
9065   assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(),
9066          "stacks were cleared above");
9067 }
9068 
9069 #ifndef PRODUCT
9070 bool CMSCollector::no_preserved_marks() const {
9071   return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty();
9072 }
9073 #endif
9074 
9075 CMSAdaptiveSizePolicy* ASConcurrentMarkSweepGeneration::cms_size_policy() const
9076 {
9077   GenCollectedHeap* gch = (GenCollectedHeap*) GenCollectedHeap::heap();
9078   CMSAdaptiveSizePolicy* size_policy =
9079     (CMSAdaptiveSizePolicy*) gch->gen_policy()->size_policy();
9080   assert(size_policy->is_gc_cms_adaptive_size_policy(),
9081     "Wrong type for size policy");
9082   return size_policy;
9083 }
9084 
9085 void ASConcurrentMarkSweepGeneration::resize(size_t cur_promo_size,
9086                                            size_t desired_promo_size) {
9087   if (cur_promo_size < desired_promo_size) {
9088     size_t expand_bytes = desired_promo_size - cur_promo_size;
9089     if (PrintAdaptiveSizePolicy && Verbose) {
9090       gclog_or_tty->print_cr(" ASConcurrentMarkSweepGeneration::resize "
9091         "Expanding tenured generation by " SIZE_FORMAT " (bytes)",
9092         expand_bytes);
9093     }
9094     expand(expand_bytes,
9095            MinHeapDeltaBytes,
9096            CMSExpansionCause::_adaptive_size_policy);
9097   } else if (desired_promo_size < cur_promo_size) {
9098     size_t shrink_bytes = cur_promo_size - desired_promo_size;
9099     if (PrintAdaptiveSizePolicy && Verbose) {
9100       gclog_or_tty->print_cr(" ASConcurrentMarkSweepGeneration::resize "
9101         "Shrinking tenured generation by " SIZE_FORMAT " (bytes)",
9102         shrink_bytes);
9103     }
9104     shrink(shrink_bytes);
9105   }
9106 }
9107 
9108 CMSGCAdaptivePolicyCounters* ASConcurrentMarkSweepGeneration::gc_adaptive_policy_counters() {
9109   GenCollectedHeap* gch = GenCollectedHeap::heap();
9110   CMSGCAdaptivePolicyCounters* counters =
9111     (CMSGCAdaptivePolicyCounters*) gch->collector_policy()->counters();
9112   assert(counters->kind() == GCPolicyCounters::CMSGCAdaptivePolicyCountersKind,
9113     "Wrong kind of counters");
9114   return counters;
9115 }
9116 
9117 
9118 void ASConcurrentMarkSweepGeneration::update_counters() {
9119   if (UsePerfData) {
9120     _space_counters->update_all();
9121     _gen_counters->update_all();
9122     CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
9123     GenCollectedHeap* gch = GenCollectedHeap::heap();
9124     CMSGCStats* gc_stats_l = (CMSGCStats*) gc_stats();
9125     assert(gc_stats_l->kind() == GCStats::CMSGCStatsKind,
9126       "Wrong gc statistics type");
9127     counters->update_counters(gc_stats_l);
9128   }
9129 }
9130 
9131 void ASConcurrentMarkSweepGeneration::update_counters(size_t used) {
9132   if (UsePerfData) {
9133     _space_counters->update_used(used);
9134     _space_counters->update_capacity();
9135     _gen_counters->update_all();
9136 
9137     CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
9138     GenCollectedHeap* gch = GenCollectedHeap::heap();
9139     CMSGCStats* gc_stats_l = (CMSGCStats*) gc_stats();
9140     assert(gc_stats_l->kind() == GCStats::CMSGCStatsKind,
9141       "Wrong gc statistics type");
9142     counters->update_counters(gc_stats_l);
9143   }
9144 }
9145 
9146 void ASConcurrentMarkSweepGeneration::shrink_by(size_t desired_bytes) {
9147   assert_locked_or_safepoint(Heap_lock);
9148   assert_lock_strong(freelistLock());
9149   HeapWord* old_end = _cmsSpace->end();
9150   HeapWord* unallocated_start = _cmsSpace->unallocated_block();
9151   assert(old_end >= unallocated_start, "Miscalculation of unallocated_start");
9152   FreeChunk* chunk_at_end = find_chunk_at_end();
9153   if (chunk_at_end == NULL) {
9154     // No room to shrink
9155     if (PrintGCDetails && Verbose) {
9156       gclog_or_tty->print_cr("No room to shrink: old_end  "
9157         PTR_FORMAT "  unallocated_start  " PTR_FORMAT
9158         " chunk_at_end  " PTR_FORMAT,
9159         old_end, unallocated_start, chunk_at_end);
9160     }
9161     return;
9162   } else {
9163 
9164     // Find the chunk at the end of the space and determine
9165     // how much it can be shrunk.
9166     size_t shrinkable_size_in_bytes = chunk_at_end->size();
9167     size_t aligned_shrinkable_size_in_bytes =
9168       align_size_down(shrinkable_size_in_bytes, os::vm_page_size());
9169     assert(unallocated_start <= (HeapWord*) chunk_at_end->end(),
9170       "Inconsistent chunk at end of space");
9171     size_t bytes = MIN2(desired_bytes, aligned_shrinkable_size_in_bytes);
9172     size_t word_size_before = heap_word_size(_virtual_space.committed_size());
9173 
9174     // Shrink the underlying space
9175     _virtual_space.shrink_by(bytes);
9176     if (PrintGCDetails && Verbose) {
9177       gclog_or_tty->print_cr("ConcurrentMarkSweepGeneration::shrink_by:"
9178         " desired_bytes " SIZE_FORMAT
9179         " shrinkable_size_in_bytes " SIZE_FORMAT
9180         " aligned_shrinkable_size_in_bytes " SIZE_FORMAT
9181         "  bytes  " SIZE_FORMAT,
9182         desired_bytes, shrinkable_size_in_bytes,
9183         aligned_shrinkable_size_in_bytes, bytes);
9184       gclog_or_tty->print_cr("          old_end  " SIZE_FORMAT
9185         "  unallocated_start  " SIZE_FORMAT,
9186         old_end, unallocated_start);
9187     }
9188 
9189     // If the space did shrink (shrinking is not guaranteed),
9190     // shrink the chunk at the end by the appropriate amount.
9191     if (((HeapWord*)_virtual_space.high()) < old_end) {
9192       size_t new_word_size =
9193         heap_word_size(_virtual_space.committed_size());
9194 
9195       // Have to remove the chunk from the dictionary because it is changing
9196       // size and might be someplace elsewhere in the dictionary.
9197 
9198       // Get the chunk at end, shrink it, and put it
9199       // back.
9200       _cmsSpace->removeChunkFromDictionary(chunk_at_end);
9201       size_t word_size_change = word_size_before - new_word_size;
9202       size_t chunk_at_end_old_size = chunk_at_end->size();
9203       assert(chunk_at_end_old_size >= word_size_change,
9204         "Shrink is too large");
9205       chunk_at_end->set_size(chunk_at_end_old_size -
9206                           word_size_change);
9207       _cmsSpace->freed((HeapWord*) chunk_at_end->end(),
9208         word_size_change);
9209 
9210       _cmsSpace->returnChunkToDictionary(chunk_at_end);
9211 
9212       MemRegion mr(_cmsSpace->bottom(), new_word_size);
9213       _bts->resize(new_word_size);  // resize the block offset shared array
9214       Universe::heap()->barrier_set()->resize_covered_region(mr);
9215       _cmsSpace->assert_locked();
9216       _cmsSpace->set_end((HeapWord*)_virtual_space.high());
9217 
9218       NOT_PRODUCT(_cmsSpace->dictionary()->verify());
9219 
9220       // update the space and generation capacity counters
9221       if (UsePerfData) {
9222         _space_counters->update_capacity();
9223         _gen_counters->update_all();
9224       }
9225 
9226       if (Verbose && PrintGCDetails) {
9227         size_t new_mem_size = _virtual_space.committed_size();
9228         size_t old_mem_size = new_mem_size + bytes;
9229         gclog_or_tty->print_cr("Shrinking %s from " SIZE_FORMAT "K by " SIZE_FORMAT "K to " SIZE_FORMAT "K",
9230                       name(), old_mem_size/K, bytes/K, new_mem_size/K);
9231       }
9232     }
9233 
9234     assert(_cmsSpace->unallocated_block() <= _cmsSpace->end(),
9235       "Inconsistency at end of space");
9236     assert(chunk_at_end->end() == (uintptr_t*) _cmsSpace->end(),
9237       "Shrinking is inconsistent");
9238     return;
9239   }
9240 }
9241 
9242 // Transfer some number of overflown objects to usual marking
9243 // stack. Return true if some objects were transferred.
9244 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
9245   size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,
9246                     (size_t)ParGCDesiredObjsFromOverflowList);
9247 
9248   bool res = _collector->take_from_overflow_list(num, _mark_stack);
9249   assert(_collector->overflow_list_is_empty() || res,
9250          "If list is not empty, we should have taken something");
9251   assert(!res || !_mark_stack->isEmpty(),
9252          "If we took something, it should now be on our stack");
9253   return res;
9254 }
9255 
9256 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
9257   size_t res = _sp->block_size_no_stall(addr, _collector);
9258   if (_sp->block_is_obj(addr)) {
9259     if (_live_bit_map->isMarked(addr)) {
9260       // It can't have been dead in a previous cycle
9261       guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
9262     } else {
9263       _dead_bit_map->mark(addr);      // mark the dead object
9264     }
9265   }
9266   // Could be 0, if the block size could not be computed without stalling.
9267   return res;
9268 }
9269 
9270 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() {
9271 
9272   switch (phase) {
9273     case CMSCollector::InitialMarking:
9274       initialize(true  /* fullGC */ ,
9275                  cause /* cause of the GC */,
9276                  true  /* recordGCBeginTime */,
9277                  true  /* recordPreGCUsage */,
9278                  false /* recordPeakUsage */,
9279                  false /* recordPostGCusage */,
9280                  true  /* recordAccumulatedGCTime */,
9281                  false /* recordGCEndTime */,
9282                  false /* countCollection */  );
9283       break;
9284 
9285     case CMSCollector::FinalMarking:
9286       initialize(true  /* fullGC */ ,
9287                  cause /* cause of the GC */,
9288                  false /* recordGCBeginTime */,
9289                  false /* recordPreGCUsage */,
9290                  false /* recordPeakUsage */,
9291                  false /* recordPostGCusage */,
9292                  true  /* recordAccumulatedGCTime */,
9293                  false /* recordGCEndTime */,
9294                  false /* countCollection */  );
9295       break;
9296 
9297     case CMSCollector::Sweeping:
9298       initialize(true  /* fullGC */ ,
9299                  cause /* cause of the GC */,
9300                  false /* recordGCBeginTime */,
9301                  false /* recordPreGCUsage */,
9302                  true  /* recordPeakUsage */,
9303                  true  /* recordPostGCusage */,
9304                  false /* recordAccumulatedGCTime */,
9305                  true  /* recordGCEndTime */,
9306                  true  /* countCollection */  );
9307       break;
9308 
9309     default:
9310       ShouldNotReachHere();
9311   }
9312 }
9313 
--- EOF ---