1 /*
   2  * Copyright (c) 2001, 2018, 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/stringTable.hpp"
  28 #include "classfile/symbolTable.hpp"
  29 #include "classfile/systemDictionary.hpp"
  30 #include "code/codeCache.hpp"
  31 #include "gc/cms/cmsCollectorPolicy.hpp"
  32 #include "gc/cms/cmsGCStats.hpp"
  33 #include "gc/cms/cmsHeap.hpp"
  34 #include "gc/cms/cmsOopClosures.inline.hpp"
  35 #include "gc/cms/compactibleFreeListSpace.hpp"
  36 #include "gc/cms/concurrentMarkSweepGeneration.inline.hpp"
  37 #include "gc/cms/concurrentMarkSweepThread.hpp"
  38 #include "gc/cms/parNewGeneration.hpp"
  39 #include "gc/cms/promotionInfo.inline.hpp"
  40 #include "gc/cms/vmCMSOperations.hpp"
  41 #include "gc/serial/genMarkSweep.hpp"
  42 #include "gc/serial/tenuredGeneration.hpp"
  43 #include "gc/shared/adaptiveSizePolicy.hpp"
  44 #include "gc/shared/cardGeneration.inline.hpp"
  45 #include "gc/shared/cardTableRS.hpp"
  46 #include "gc/shared/collectedHeap.inline.hpp"
  47 #include "gc/shared/collectorCounters.hpp"
  48 #include "gc/shared/collectorPolicy.hpp"
  49 #include "gc/shared/gcLocker.hpp"
  50 #include "gc/shared/gcPolicyCounters.hpp"
  51 #include "gc/shared/gcTimer.hpp"
  52 #include "gc/shared/gcTrace.hpp"
  53 #include "gc/shared/gcTraceTime.inline.hpp"
  54 #include "gc/shared/genCollectedHeap.hpp"
  55 #include "gc/shared/genOopClosures.inline.hpp"
  56 #include "gc/shared/isGCActiveMark.hpp"
  57 #include "gc/shared/oopStorageParState.hpp"
  58 #include "gc/shared/referencePolicy.hpp"
  59 #include "gc/shared/space.inline.hpp"
  60 #include "gc/shared/strongRootsScope.hpp"
  61 #include "gc/shared/taskqueue.inline.hpp"
  62 #include "gc/shared/weakProcessor.hpp"
  63 #include "logging/log.hpp"
  64 #include "logging/logStream.hpp"
  65 #include "memory/allocation.hpp"
  66 #include "memory/binaryTreeDictionary.inline.hpp"
  67 #include "memory/iterator.inline.hpp"
  68 #include "memory/padded.hpp"
  69 #include "memory/resourceArea.hpp"
  70 #include "oops/access.inline.hpp"
  71 #include "oops/oop.inline.hpp"
  72 #include "prims/jvmtiExport.hpp"
  73 #include "runtime/atomic.hpp"
  74 #include "runtime/flags/flagSetting.hpp"
  75 #include "runtime/globals_extension.hpp"
  76 #include "runtime/handles.inline.hpp"
  77 #include "runtime/java.hpp"
  78 #include "runtime/orderAccess.inline.hpp"
  79 #include "runtime/timer.hpp"
  80 #include "runtime/vmThread.hpp"
  81 #include "services/memoryService.hpp"
  82 #include "services/runtimeService.hpp"
  83 #include "utilities/align.hpp"
  84 #include "utilities/stack.inline.hpp"
  85 
  86 // statics
  87 CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL;
  88 bool CMSCollector::_full_gc_requested = false;
  89 GCCause::Cause CMSCollector::_full_gc_cause = GCCause::_no_gc;
  90 
  91 //////////////////////////////////////////////////////////////////
  92 // In support of CMS/VM thread synchronization
  93 //////////////////////////////////////////////////////////////////
  94 // We split use of the CGC_lock into 2 "levels".
  95 // The low-level locking is of the usual CGC_lock monitor. We introduce
  96 // a higher level "token" (hereafter "CMS token") built on top of the
  97 // low level monitor (hereafter "CGC lock").
  98 // The token-passing protocol gives priority to the VM thread. The
  99 // CMS-lock doesn't provide any fairness guarantees, but clients
 100 // should ensure that it is only held for very short, bounded
 101 // durations.
 102 //
 103 // When either of the CMS thread or the VM thread is involved in
 104 // collection operations during which it does not want the other
 105 // thread to interfere, it obtains the CMS token.
 106 //
 107 // If either thread tries to get the token while the other has
 108 // it, that thread waits. However, if the VM thread and CMS thread
 109 // both want the token, then the VM thread gets priority while the
 110 // CMS thread waits. This ensures, for instance, that the "concurrent"
 111 // phases of the CMS thread's work do not block out the VM thread
 112 // for long periods of time as the CMS thread continues to hog
 113 // the token. (See bug 4616232).
 114 //
 115 // The baton-passing functions are, however, controlled by the
 116 // flags _foregroundGCShouldWait and _foregroundGCIsActive,
 117 // and here the low-level CMS lock, not the high level token,
 118 // ensures mutual exclusion.
 119 //
 120 // Two important conditions that we have to satisfy:
 121 // 1. if a thread does a low-level wait on the CMS lock, then it
 122 //    relinquishes the CMS token if it were holding that token
 123 //    when it acquired the low-level CMS lock.
 124 // 2. any low-level notifications on the low-level lock
 125 //    should only be sent when a thread has relinquished the token.
 126 //
 127 // In the absence of either property, we'd have potential deadlock.
 128 //
 129 // We protect each of the CMS (concurrent and sequential) phases
 130 // with the CMS _token_, not the CMS _lock_.
 131 //
 132 // The only code protected by CMS lock is the token acquisition code
 133 // itself, see ConcurrentMarkSweepThread::[de]synchronize(), and the
 134 // baton-passing code.
 135 //
 136 // Unfortunately, i couldn't come up with a good abstraction to factor and
 137 // hide the naked CGC_lock manipulation in the baton-passing code
 138 // further below. That's something we should try to do. Also, the proof
 139 // of correctness of this 2-level locking scheme is far from obvious,
 140 // and potentially quite slippery. We have an uneasy suspicion, for instance,
 141 // that there may be a theoretical possibility of delay/starvation in the
 142 // low-level lock/wait/notify scheme used for the baton-passing because of
 143 // potential interference with the priority scheme embodied in the
 144 // CMS-token-passing protocol. See related comments at a CGC_lock->wait()
 145 // invocation further below and marked with "XXX 20011219YSR".
 146 // Indeed, as we note elsewhere, this may become yet more slippery
 147 // in the presence of multiple CMS and/or multiple VM threads. XXX
 148 
 149 class CMSTokenSync: public StackObj {
 150  private:
 151   bool _is_cms_thread;
 152  public:
 153   CMSTokenSync(bool is_cms_thread):
 154     _is_cms_thread(is_cms_thread) {
 155     assert(is_cms_thread == Thread::current()->is_ConcurrentGC_thread(),
 156            "Incorrect argument to constructor");
 157     ConcurrentMarkSweepThread::synchronize(_is_cms_thread);
 158   }
 159 
 160   ~CMSTokenSync() {
 161     assert(_is_cms_thread ?
 162              ConcurrentMarkSweepThread::cms_thread_has_cms_token() :
 163              ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
 164           "Incorrect state");
 165     ConcurrentMarkSweepThread::desynchronize(_is_cms_thread);
 166   }
 167 };
 168 
 169 // Convenience class that does a CMSTokenSync, and then acquires
 170 // upto three locks.
 171 class CMSTokenSyncWithLocks: public CMSTokenSync {
 172  private:
 173   // Note: locks are acquired in textual declaration order
 174   // and released in the opposite order
 175   MutexLockerEx _locker1, _locker2, _locker3;
 176  public:
 177   CMSTokenSyncWithLocks(bool is_cms_thread, Mutex* mutex1,
 178                         Mutex* mutex2 = NULL, Mutex* mutex3 = NULL):
 179     CMSTokenSync(is_cms_thread),
 180     _locker1(mutex1, Mutex::_no_safepoint_check_flag),
 181     _locker2(mutex2, Mutex::_no_safepoint_check_flag),
 182     _locker3(mutex3, Mutex::_no_safepoint_check_flag)
 183   { }
 184 };
 185 
 186 
 187 //////////////////////////////////////////////////////////////////
 188 //  Concurrent Mark-Sweep Generation /////////////////////////////
 189 //////////////////////////////////////////////////////////////////
 190 
 191 NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;)
 192 
 193 // This struct contains per-thread things necessary to support parallel
 194 // young-gen collection.
 195 class CMSParGCThreadState: public CHeapObj<mtGC> {
 196  public:
 197   CompactibleFreeListSpaceLAB lab;
 198   PromotionInfo promo;
 199 
 200   // Constructor.
 201   CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) {
 202     promo.setSpace(cfls);
 203   }
 204 };
 205 
 206 ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration(
 207      ReservedSpace rs, size_t initial_byte_size, CardTableRS* ct) :
 208   CardGeneration(rs, initial_byte_size, ct),
 209   _dilatation_factor(((double)MinChunkSize)/((double)(CollectedHeap::min_fill_size()))),
 210   _did_compact(false)
 211 {
 212   HeapWord* bottom = (HeapWord*) _virtual_space.low();
 213   HeapWord* end    = (HeapWord*) _virtual_space.high();
 214 
 215   _direct_allocated_words = 0;
 216   NOT_PRODUCT(
 217     _numObjectsPromoted = 0;
 218     _numWordsPromoted = 0;
 219     _numObjectsAllocated = 0;
 220     _numWordsAllocated = 0;
 221   )
 222 
 223   _cmsSpace = new CompactibleFreeListSpace(_bts, MemRegion(bottom, end));
 224   NOT_PRODUCT(debug_cms_space = _cmsSpace;)
 225   _cmsSpace->_old_gen = this;
 226 
 227   _gc_stats = new CMSGCStats();
 228 
 229   // Verify the assumption that FreeChunk::_prev and OopDesc::_klass
 230   // offsets match. The ability to tell free chunks from objects
 231   // depends on this property.
 232   debug_only(
 233     FreeChunk* junk = NULL;
 234     assert(UseCompressedClassPointers ||
 235            junk->prev_addr() == (void*)(oop(junk)->klass_addr()),
 236            "Offset of FreeChunk::_prev within FreeChunk must match"
 237            "  that of OopDesc::_klass within OopDesc");
 238   )
 239 
 240   _par_gc_thread_states = NEW_C_HEAP_ARRAY(CMSParGCThreadState*, ParallelGCThreads, mtGC);
 241   for (uint i = 0; i < ParallelGCThreads; i++) {
 242     _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace());
 243   }
 244 
 245   _incremental_collection_failed = false;
 246   // The "dilatation_factor" is the expansion that can occur on
 247   // account of the fact that the minimum object size in the CMS
 248   // generation may be larger than that in, say, a contiguous young
 249   //  generation.
 250   // Ideally, in the calculation below, we'd compute the dilatation
 251   // factor as: MinChunkSize/(promoting_gen's min object size)
 252   // Since we do not have such a general query interface for the
 253   // promoting generation, we'll instead just use the minimum
 254   // object size (which today is a header's worth of space);
 255   // note that all arithmetic is in units of HeapWords.
 256   assert(MinChunkSize >= CollectedHeap::min_fill_size(), "just checking");
 257   assert(_dilatation_factor >= 1.0, "from previous assert");
 258 }
 259 
 260 
 261 // The field "_initiating_occupancy" represents the occupancy percentage
 262 // at which we trigger a new collection cycle.  Unless explicitly specified
 263 // via CMSInitiatingOccupancyFraction (argument "io" below), it
 264 // is calculated by:
 265 //
 266 //   Let "f" be MinHeapFreeRatio in
 267 //
 268 //    _initiating_occupancy = 100-f +
 269 //                           f * (CMSTriggerRatio/100)
 270 //   where CMSTriggerRatio is the argument "tr" below.
 271 //
 272 // That is, if we assume the heap is at its desired maximum occupancy at the
 273 // end of a collection, we let CMSTriggerRatio of the (purported) free
 274 // space be allocated before initiating a new collection cycle.
 275 //
 276 void ConcurrentMarkSweepGeneration::init_initiating_occupancy(intx io, uintx tr) {
 277   assert(io <= 100 && tr <= 100, "Check the arguments");
 278   if (io >= 0) {
 279     _initiating_occupancy = (double)io / 100.0;
 280   } else {
 281     _initiating_occupancy = ((100 - MinHeapFreeRatio) +
 282                              (double)(tr * MinHeapFreeRatio) / 100.0)
 283                             / 100.0;
 284   }
 285 }
 286 
 287 void ConcurrentMarkSweepGeneration::ref_processor_init() {
 288   assert(collector() != NULL, "no collector");
 289   collector()->ref_processor_init();
 290 }
 291 
 292 void CMSCollector::ref_processor_init() {
 293   if (_ref_processor == NULL) {
 294     // Allocate and initialize a reference processor
 295     _ref_processor =
 296       new ReferenceProcessor(&_span_based_discoverer,
 297                              (ParallelGCThreads > 1) && ParallelRefProcEnabled, // mt processing
 298                              ParallelGCThreads,                      // mt processing degree
 299                              _cmsGen->refs_discovery_is_mt(),        // mt discovery
 300                              MAX2(ConcGCThreads, ParallelGCThreads), // mt discovery degree
 301                              _cmsGen->refs_discovery_is_atomic(),    // discovery is not atomic
 302                              &_is_alive_closure);                    // closure for liveness info
 303     // Initialize the _ref_processor field of CMSGen
 304     _cmsGen->set_ref_processor(_ref_processor);
 305 
 306   }
 307 }
 308 
 309 AdaptiveSizePolicy* CMSCollector::size_policy() {
 310   return CMSHeap::heap()->size_policy();
 311 }
 312 
 313 void ConcurrentMarkSweepGeneration::initialize_performance_counters() {
 314 
 315   const char* gen_name = "old";
 316   GenCollectorPolicy* gcp = CMSHeap::heap()->gen_policy();
 317   // Generation Counters - generation 1, 1 subspace
 318   _gen_counters = new GenerationCounters(gen_name, 1, 1,
 319       gcp->min_old_size(), gcp->max_old_size(), &_virtual_space);
 320 
 321   _space_counters = new GSpaceCounters(gen_name, 0,
 322                                        _virtual_space.reserved_size(),
 323                                        this, _gen_counters);
 324 }
 325 
 326 CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha):
 327   _cms_gen(cms_gen)
 328 {
 329   assert(alpha <= 100, "bad value");
 330   _saved_alpha = alpha;
 331 
 332   // Initialize the alphas to the bootstrap value of 100.
 333   _gc0_alpha = _cms_alpha = 100;
 334 
 335   _cms_begin_time.update();
 336   _cms_end_time.update();
 337 
 338   _gc0_duration = 0.0;
 339   _gc0_period = 0.0;
 340   _gc0_promoted = 0;
 341 
 342   _cms_duration = 0.0;
 343   _cms_period = 0.0;
 344   _cms_allocated = 0;
 345 
 346   _cms_used_at_gc0_begin = 0;
 347   _cms_used_at_gc0_end = 0;
 348   _allow_duty_cycle_reduction = false;
 349   _valid_bits = 0;
 350 }
 351 
 352 double CMSStats::cms_free_adjustment_factor(size_t free) const {
 353   // TBD: CR 6909490
 354   return 1.0;
 355 }
 356 
 357 void CMSStats::adjust_cms_free_adjustment_factor(bool fail, size_t free) {
 358 }
 359 
 360 // If promotion failure handling is on use
 361 // the padded average size of the promotion for each
 362 // young generation collection.
 363 double CMSStats::time_until_cms_gen_full() const {
 364   size_t cms_free = _cms_gen->cmsSpace()->free();
 365   CMSHeap* heap = CMSHeap::heap();
 366   size_t expected_promotion = MIN2(heap->young_gen()->capacity(),
 367                                    (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average());
 368   if (cms_free > expected_promotion) {
 369     // Start a cms collection if there isn't enough space to promote
 370     // for the next young collection.  Use the padded average as
 371     // a safety factor.
 372     cms_free -= expected_promotion;
 373 
 374     // Adjust by the safety factor.
 375     double cms_free_dbl = (double)cms_free;
 376     double cms_adjustment = (100.0 - CMSIncrementalSafetyFactor) / 100.0;
 377     // Apply a further correction factor which tries to adjust
 378     // for recent occurance of concurrent mode failures.
 379     cms_adjustment = cms_adjustment * cms_free_adjustment_factor(cms_free);
 380     cms_free_dbl = cms_free_dbl * cms_adjustment;
 381 
 382     log_trace(gc)("CMSStats::time_until_cms_gen_full: cms_free " SIZE_FORMAT " expected_promotion " SIZE_FORMAT,
 383                   cms_free, expected_promotion);
 384     log_trace(gc)("  cms_free_dbl %f cms_consumption_rate %f", cms_free_dbl, cms_consumption_rate() + 1.0);
 385     // Add 1 in case the consumption rate goes to zero.
 386     return cms_free_dbl / (cms_consumption_rate() + 1.0);
 387   }
 388   return 0.0;
 389 }
 390 
 391 // Compare the duration of the cms collection to the
 392 // time remaining before the cms generation is empty.
 393 // Note that the time from the start of the cms collection
 394 // to the start of the cms sweep (less than the total
 395 // duration of the cms collection) can be used.  This
 396 // has been tried and some applications experienced
 397 // promotion failures early in execution.  This was
 398 // possibly because the averages were not accurate
 399 // enough at the beginning.
 400 double CMSStats::time_until_cms_start() const {
 401   // We add "gc0_period" to the "work" calculation
 402   // below because this query is done (mostly) at the
 403   // end of a scavenge, so we need to conservatively
 404   // account for that much possible delay
 405   // in the query so as to avoid concurrent mode failures
 406   // due to starting the collection just a wee bit too
 407   // late.
 408   double work = cms_duration() + gc0_period();
 409   double deadline = time_until_cms_gen_full();
 410   // If a concurrent mode failure occurred recently, we want to be
 411   // more conservative and halve our expected time_until_cms_gen_full()
 412   if (work > deadline) {
 413     log_develop_trace(gc)("CMSCollector: collect because of anticipated promotion before full %3.7f + %3.7f > %3.7f ",
 414                           cms_duration(), gc0_period(), time_until_cms_gen_full());
 415     return 0.0;
 416   }
 417   return work - deadline;
 418 }
 419 
 420 #ifndef PRODUCT
 421 void CMSStats::print_on(outputStream *st) const {
 422   st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha);
 423   st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo=" SIZE_FORMAT,
 424                gc0_duration(), gc0_period(), gc0_promoted());
 425   st->print(",cms_dur=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT,
 426             cms_duration(), cms_period(), cms_allocated());
 427   st->print(",cms_since_beg=%g,cms_since_end=%g",
 428             cms_time_since_begin(), cms_time_since_end());
 429   st->print(",cms_used_beg=" SIZE_FORMAT ",cms_used_end=" SIZE_FORMAT,
 430             _cms_used_at_gc0_begin, _cms_used_at_gc0_end);
 431 
 432   if (valid()) {
 433     st->print(",promo_rate=%g,cms_alloc_rate=%g",
 434               promotion_rate(), cms_allocation_rate());
 435     st->print(",cms_consumption_rate=%g,time_until_full=%g",
 436               cms_consumption_rate(), time_until_cms_gen_full());
 437   }
 438   st->cr();
 439 }
 440 #endif // #ifndef PRODUCT
 441 
 442 CMSCollector::CollectorState CMSCollector::_collectorState =
 443                              CMSCollector::Idling;
 444 bool CMSCollector::_foregroundGCIsActive = false;
 445 bool CMSCollector::_foregroundGCShouldWait = false;
 446 
 447 CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
 448                            CardTableRS*                   ct,
 449                            ConcurrentMarkSweepPolicy*     cp):
 450   _cmsGen(cmsGen),
 451   // Adjust span to cover old (cms) gen
 452   _span(cmsGen->reserved()),
 453   _ct(ct),
 454   _span_based_discoverer(_span),
 455   _ref_processor(NULL),    // will be set later
 456   _conc_workers(NULL),     // may be set later
 457   _abort_preclean(false),
 458   _start_sampling(false),
 459   _between_prologue_and_epilogue(false),
 460   _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"),
 461   _modUnionTable((CardTable::card_shift - LogHeapWordSize),
 462                  -1 /* lock-free */, "No_lock" /* dummy */),
 463   _modUnionClosurePar(&_modUnionTable),
 464   // Construct the is_alive_closure with _span & markBitMap
 465   _is_alive_closure(_span, &_markBitMap),
 466   _restart_addr(NULL),
 467   _overflow_list(NULL),
 468   _stats(cmsGen),
 469   _eden_chunk_lock(new Mutex(Mutex::leaf + 1, "CMS_eden_chunk_lock", true,
 470                              //verify that this lock should be acquired with safepoint check.
 471                              Monitor::_safepoint_check_sometimes)),
 472   _eden_chunk_array(NULL),     // may be set in ctor body
 473   _eden_chunk_capacity(0),     // -- ditto --
 474   _eden_chunk_index(0),        // -- ditto --
 475   _survivor_plab_array(NULL),  // -- ditto --
 476   _survivor_chunk_array(NULL), // -- ditto --
 477   _survivor_chunk_capacity(0), // -- ditto --
 478   _survivor_chunk_index(0),    // -- ditto --
 479   _ser_pmc_preclean_ovflw(0),
 480   _ser_kac_preclean_ovflw(0),
 481   _ser_pmc_remark_ovflw(0),
 482   _par_pmc_remark_ovflw(0),
 483   _ser_kac_ovflw(0),
 484   _par_kac_ovflw(0),
 485 #ifndef PRODUCT
 486   _num_par_pushes(0),
 487 #endif
 488   _collection_count_start(0),
 489   _verifying(false),
 490   _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"),
 491   _completed_initialization(false),
 492   _collector_policy(cp),
 493   _should_unload_classes(CMSClassUnloadingEnabled),
 494   _concurrent_cycles_since_last_unload(0),
 495   _roots_scanning_options(GenCollectedHeap::SO_None),
 496   _inter_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
 497   _intra_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
 498   _gc_tracer_cm(new (ResourceObj::C_HEAP, mtGC) CMSTracer()),
 499   _gc_timer_cm(new (ResourceObj::C_HEAP, mtGC) ConcurrentGCTimer()),
 500   _cms_start_registered(false)
 501 {
 502   // Now expand the span and allocate the collection support structures
 503   // (MUT, marking bit map etc.) to cover both generations subject to
 504   // collection.
 505 
 506   // For use by dirty card to oop closures.
 507   _cmsGen->cmsSpace()->set_collector(this);
 508 
 509   // Allocate MUT and marking bit map
 510   {
 511     MutexLockerEx x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag);
 512     if (!_markBitMap.allocate(_span)) {
 513       log_warning(gc)("Failed to allocate CMS Bit Map");
 514       return;
 515     }
 516     assert(_markBitMap.covers(_span), "_markBitMap inconsistency?");
 517   }
 518   {
 519     _modUnionTable.allocate(_span);
 520     assert(_modUnionTable.covers(_span), "_modUnionTable inconsistency?");
 521   }
 522 
 523   if (!_markStack.allocate(MarkStackSize)) {
 524     log_warning(gc)("Failed to allocate CMS Marking Stack");
 525     return;
 526   }
 527 
 528   // Support for multi-threaded concurrent phases
 529   if (CMSConcurrentMTEnabled) {
 530     if (FLAG_IS_DEFAULT(ConcGCThreads)) {
 531       // just for now
 532       FLAG_SET_DEFAULT(ConcGCThreads, (ParallelGCThreads + 3) / 4);
 533     }
 534     if (ConcGCThreads > 1) {
 535       _conc_workers = new YieldingFlexibleWorkGang("CMS Thread",
 536                                  ConcGCThreads, true);
 537       if (_conc_workers == NULL) {
 538         log_warning(gc)("GC/CMS: _conc_workers allocation failure: forcing -CMSConcurrentMTEnabled");
 539         CMSConcurrentMTEnabled = false;
 540       } else {
 541         _conc_workers->initialize_workers();
 542       }
 543     } else {
 544       CMSConcurrentMTEnabled = false;
 545     }
 546   }
 547   if (!CMSConcurrentMTEnabled) {
 548     ConcGCThreads = 0;
 549   } else {
 550     // Turn off CMSCleanOnEnter optimization temporarily for
 551     // the MT case where it's not fixed yet; see 6178663.
 552     CMSCleanOnEnter = false;
 553   }
 554   assert((_conc_workers != NULL) == (ConcGCThreads > 1),
 555          "Inconsistency");
 556   log_debug(gc)("ConcGCThreads: %u", ConcGCThreads);
 557   log_debug(gc)("ParallelGCThreads: %u", ParallelGCThreads);
 558 
 559   // Parallel task queues; these are shared for the
 560   // concurrent and stop-world phases of CMS, but
 561   // are not shared with parallel scavenge (ParNew).
 562   {
 563     uint i;
 564     uint num_queues = MAX2(ParallelGCThreads, ConcGCThreads);
 565 
 566     if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled
 567          || ParallelRefProcEnabled)
 568         && num_queues > 0) {
 569       _task_queues = new OopTaskQueueSet(num_queues);
 570       if (_task_queues == NULL) {
 571         log_warning(gc)("task_queues allocation failure.");
 572         return;
 573       }
 574       _hash_seed = NEW_C_HEAP_ARRAY(int, num_queues, mtGC);
 575       typedef Padded<OopTaskQueue> PaddedOopTaskQueue;
 576       for (i = 0; i < num_queues; i++) {
 577         PaddedOopTaskQueue *q = new PaddedOopTaskQueue();
 578         if (q == NULL) {
 579           log_warning(gc)("work_queue allocation failure.");
 580           return;
 581         }
 582         _task_queues->register_queue(i, q);
 583       }
 584       for (i = 0; i < num_queues; i++) {
 585         _task_queues->queue(i)->initialize();
 586         _hash_seed[i] = 17;  // copied from ParNew
 587       }
 588     }
 589   }
 590 
 591   _cmsGen ->init_initiating_occupancy(CMSInitiatingOccupancyFraction, CMSTriggerRatio);
 592 
 593   // Clip CMSBootstrapOccupancy between 0 and 100.
 594   _bootstrap_occupancy = CMSBootstrapOccupancy / 100.0;
 595 
 596   // Now tell CMS generations the identity of their collector
 597   ConcurrentMarkSweepGeneration::set_collector(this);
 598 
 599   // Create & start a CMS thread for this CMS collector
 600   _cmsThread = ConcurrentMarkSweepThread::start(this);
 601   assert(cmsThread() != NULL, "CMS Thread should have been created");
 602   assert(cmsThread()->collector() == this,
 603          "CMS Thread should refer to this gen");
 604   assert(CGC_lock != NULL, "Where's the CGC_lock?");
 605 
 606   // Support for parallelizing young gen rescan
 607   CMSHeap* heap = CMSHeap::heap();
 608   _young_gen = heap->young_gen();
 609   if (heap->supports_inline_contig_alloc()) {
 610     _top_addr = heap->top_addr();
 611     _end_addr = heap->end_addr();
 612     assert(_young_gen != NULL, "no _young_gen");
 613     _eden_chunk_index = 0;
 614     _eden_chunk_capacity = (_young_gen->max_capacity() + CMSSamplingGrain) / CMSSamplingGrain;
 615     _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity, mtGC);
 616   }
 617 
 618   // Support for parallelizing survivor space rescan
 619   if ((CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) || CMSParallelInitialMarkEnabled) {
 620     const size_t max_plab_samples =
 621       _young_gen->max_survivor_size() / (PLAB::min_size() * HeapWordSize);
 622 
 623     _survivor_plab_array  = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads, mtGC);
 624     _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
 625     _cursor               = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads, mtGC);
 626     _survivor_chunk_capacity = max_plab_samples;
 627     for (uint i = 0; i < ParallelGCThreads; i++) {
 628       HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
 629       ChunkArray* cur = ::new (&_survivor_plab_array[i]) ChunkArray(vec, max_plab_samples);
 630       assert(cur->end() == 0, "Should be 0");
 631       assert(cur->array() == vec, "Should be vec");
 632       assert(cur->capacity() == max_plab_samples, "Error");
 633     }
 634   }
 635 
 636   NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;)
 637   _gc_counters = new CollectorCounters("CMS", 1);
 638   _cgc_counters = new CollectorCounters("CMS stop-the-world phases", 2);
 639   _completed_initialization = true;
 640   _inter_sweep_timer.start();  // start of time
 641 }
 642 
 643 const char* ConcurrentMarkSweepGeneration::name() const {
 644   return "concurrent mark-sweep generation";
 645 }
 646 void ConcurrentMarkSweepGeneration::update_counters() {
 647   if (UsePerfData) {
 648     _space_counters->update_all();
 649     _gen_counters->update_all();
 650   }
 651 }
 652 
 653 // this is an optimized version of update_counters(). it takes the
 654 // used value as a parameter rather than computing it.
 655 //
 656 void ConcurrentMarkSweepGeneration::update_counters(size_t used) {
 657   if (UsePerfData) {
 658     _space_counters->update_used(used);
 659     _space_counters->update_capacity();
 660     _gen_counters->update_all();
 661   }
 662 }
 663 
 664 void ConcurrentMarkSweepGeneration::print() const {
 665   Generation::print();
 666   cmsSpace()->print();
 667 }
 668 
 669 #ifndef PRODUCT
 670 void ConcurrentMarkSweepGeneration::print_statistics() {
 671   cmsSpace()->printFLCensus(0);
 672 }
 673 #endif
 674 
 675 size_t
 676 ConcurrentMarkSweepGeneration::contiguous_available() const {
 677   // dld proposes an improvement in precision here. If the committed
 678   // part of the space ends in a free block we should add that to
 679   // uncommitted size in the calculation below. Will make this
 680   // change later, staying with the approximation below for the
 681   // time being. -- ysr.
 682   return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc());
 683 }
 684 
 685 size_t
 686 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const {
 687   return _cmsSpace->max_alloc_in_words() * HeapWordSize;
 688 }
 689 
 690 size_t ConcurrentMarkSweepGeneration::max_available() const {
 691   return free() + _virtual_space.uncommitted_size();
 692 }
 693 
 694 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(size_t max_promotion_in_bytes) const {
 695   size_t available = max_available();
 696   size_t av_promo  = (size_t)gc_stats()->avg_promoted()->padded_average();
 697   bool   res = (available >= av_promo) || (available >= max_promotion_in_bytes);
 698   log_trace(gc, promotion)("CMS: promo attempt is%s safe: available(" SIZE_FORMAT ") %s av_promo(" SIZE_FORMAT "), max_promo(" SIZE_FORMAT ")",
 699                            res? "":" not", available, res? ">=":"<", av_promo, max_promotion_in_bytes);
 700   return res;
 701 }
 702 
 703 // At a promotion failure dump information on block layout in heap
 704 // (cms old generation).
 705 void ConcurrentMarkSweepGeneration::promotion_failure_occurred() {
 706   Log(gc, promotion) log;
 707   if (log.is_trace()) {
 708     LogStream ls(log.trace());
 709     cmsSpace()->dump_at_safepoint_with_locks(collector(), &ls);
 710   }
 711 }
 712 
 713 void ConcurrentMarkSweepGeneration::reset_after_compaction() {
 714   // Clear the promotion information.  These pointers can be adjusted
 715   // along with all the other pointers into the heap but
 716   // compaction is expected to be a rare event with
 717   // a heap using cms so don't do it without seeing the need.
 718   for (uint i = 0; i < ParallelGCThreads; i++) {
 719     _par_gc_thread_states[i]->promo.reset();
 720   }
 721 }
 722 
 723 void ConcurrentMarkSweepGeneration::compute_new_size() {
 724   assert_locked_or_safepoint(Heap_lock);
 725 
 726   // If incremental collection failed, we just want to expand
 727   // to the limit.
 728   if (incremental_collection_failed()) {
 729     clear_incremental_collection_failed();
 730     grow_to_reserved();
 731     return;
 732   }
 733 
 734   // The heap has been compacted but not reset yet.
 735   // Any metric such as free() or used() will be incorrect.
 736 
 737   CardGeneration::compute_new_size();
 738 
 739   // Reset again after a possible resizing
 740   if (did_compact()) {
 741     cmsSpace()->reset_after_compaction();
 742   }
 743 }
 744 
 745 void ConcurrentMarkSweepGeneration::compute_new_size_free_list() {
 746   assert_locked_or_safepoint(Heap_lock);
 747 
 748   // If incremental collection failed, we just want to expand
 749   // to the limit.
 750   if (incremental_collection_failed()) {
 751     clear_incremental_collection_failed();
 752     grow_to_reserved();
 753     return;
 754   }
 755 
 756   double free_percentage = ((double) free()) / capacity();
 757   double desired_free_percentage = (double) MinHeapFreeRatio / 100;
 758   double maximum_free_percentage = (double) MaxHeapFreeRatio / 100;
 759 
 760   // compute expansion delta needed for reaching desired free percentage
 761   if (free_percentage < desired_free_percentage) {
 762     size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
 763     assert(desired_capacity >= capacity(), "invalid expansion size");
 764     size_t expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes);
 765     Log(gc) log;
 766     if (log.is_trace()) {
 767       size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
 768       log.trace("From compute_new_size: ");
 769       log.trace("  Free fraction %f", free_percentage);
 770       log.trace("  Desired free fraction %f", desired_free_percentage);
 771       log.trace("  Maximum free fraction %f", maximum_free_percentage);
 772       log.trace("  Capacity " SIZE_FORMAT, capacity() / 1000);
 773       log.trace("  Desired capacity " SIZE_FORMAT, desired_capacity / 1000);
 774       CMSHeap* heap = CMSHeap::heap();
 775       size_t young_size = heap->young_gen()->capacity();
 776       log.trace("  Young gen size " SIZE_FORMAT, young_size / 1000);
 777       log.trace("  unsafe_max_alloc_nogc " SIZE_FORMAT, unsafe_max_alloc_nogc() / 1000);
 778       log.trace("  contiguous available " SIZE_FORMAT, contiguous_available() / 1000);
 779       log.trace("  Expand by " SIZE_FORMAT " (bytes)", expand_bytes);
 780     }
 781     // safe if expansion fails
 782     expand_for_gc_cause(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio);
 783     log.trace("  Expanded free fraction %f", ((double) free()) / capacity());
 784   } else {
 785     size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
 786     assert(desired_capacity <= capacity(), "invalid expansion size");
 787     size_t shrink_bytes = capacity() - desired_capacity;
 788     // Don't shrink unless the delta is greater than the minimum shrink we want
 789     if (shrink_bytes >= MinHeapDeltaBytes) {
 790       shrink_free_list_by(shrink_bytes);
 791     }
 792   }
 793 }
 794 
 795 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const {
 796   return cmsSpace()->freelistLock();
 797 }
 798 
 799 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size, bool tlab) {
 800   CMSSynchronousYieldRequest yr;
 801   MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
 802   return have_lock_and_allocate(size, tlab);
 803 }
 804 
 805 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size,
 806                                                                 bool   tlab /* ignored */) {
 807   assert_lock_strong(freelistLock());
 808   size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size);
 809   HeapWord* res = cmsSpace()->allocate(adjustedSize);
 810   // Allocate the object live (grey) if the background collector has
 811   // started marking. This is necessary because the marker may
 812   // have passed this address and consequently this object will
 813   // not otherwise be greyed and would be incorrectly swept up.
 814   // Note that if this object contains references, the writing
 815   // of those references will dirty the card containing this object
 816   // allowing the object to be blackened (and its references scanned)
 817   // either during a preclean phase or at the final checkpoint.
 818   if (res != NULL) {
 819     // We may block here with an uninitialized object with
 820     // its mark-bit or P-bits not yet set. Such objects need
 821     // to be safely navigable by block_start().
 822     assert(oop(res)->klass_or_null() == NULL, "Object should be uninitialized here.");
 823     assert(!((FreeChunk*)res)->is_free(), "Error, block will look free but show wrong size");
 824     collector()->direct_allocated(res, adjustedSize);
 825     _direct_allocated_words += adjustedSize;
 826     // allocation counters
 827     NOT_PRODUCT(
 828       _numObjectsAllocated++;
 829       _numWordsAllocated += (int)adjustedSize;
 830     )
 831   }
 832   return res;
 833 }
 834 
 835 // In the case of direct allocation by mutators in a generation that
 836 // is being concurrently collected, the object must be allocated
 837 // live (grey) if the background collector has started marking.
 838 // This is necessary because the marker may
 839 // have passed this address and consequently this object will
 840 // not otherwise be greyed and would be incorrectly swept up.
 841 // Note that if this object contains references, the writing
 842 // of those references will dirty the card containing this object
 843 // allowing the object to be blackened (and its references scanned)
 844 // either during a preclean phase or at the final checkpoint.
 845 void CMSCollector::direct_allocated(HeapWord* start, size_t size) {
 846   assert(_markBitMap.covers(start, size), "Out of bounds");
 847   if (_collectorState >= Marking) {
 848     MutexLockerEx y(_markBitMap.lock(),
 849                     Mutex::_no_safepoint_check_flag);
 850     // [see comments preceding SweepClosure::do_blk() below for details]
 851     //
 852     // Can the P-bits be deleted now?  JJJ
 853     //
 854     // 1. need to mark the object as live so it isn't collected
 855     // 2. need to mark the 2nd bit to indicate the object may be uninitialized
 856     // 3. need to mark the end of the object so marking, precleaning or sweeping
 857     //    can skip over uninitialized or unparsable objects. An allocated
 858     //    object is considered uninitialized for our purposes as long as
 859     //    its klass word is NULL.  All old gen objects are parsable
 860     //    as soon as they are initialized.)
 861     _markBitMap.mark(start);          // object is live
 862     _markBitMap.mark(start + 1);      // object is potentially uninitialized?
 863     _markBitMap.mark(start + size - 1);
 864                                       // mark end of object
 865   }
 866   // check that oop looks uninitialized
 867   assert(oop(start)->klass_or_null() == NULL, "_klass should be NULL");
 868 }
 869 
 870 void CMSCollector::promoted(bool par, HeapWord* start,
 871                             bool is_obj_array, size_t obj_size) {
 872   assert(_markBitMap.covers(start), "Out of bounds");
 873   // See comment in direct_allocated() about when objects should
 874   // be allocated live.
 875   if (_collectorState >= Marking) {
 876     // we already hold the marking bit map lock, taken in
 877     // the prologue
 878     if (par) {
 879       _markBitMap.par_mark(start);
 880     } else {
 881       _markBitMap.mark(start);
 882     }
 883     // We don't need to mark the object as uninitialized (as
 884     // in direct_allocated above) because this is being done with the
 885     // world stopped and the object will be initialized by the
 886     // time the marking, precleaning or sweeping get to look at it.
 887     // But see the code for copying objects into the CMS generation,
 888     // where we need to ensure that concurrent readers of the
 889     // block offset table are able to safely navigate a block that
 890     // is in flux from being free to being allocated (and in
 891     // transition while being copied into) and subsequently
 892     // becoming a bona-fide object when the copy/promotion is complete.
 893     assert(SafepointSynchronize::is_at_safepoint(),
 894            "expect promotion only at safepoints");
 895 
 896     if (_collectorState < Sweeping) {
 897       // Mark the appropriate cards in the modUnionTable, so that
 898       // this object gets scanned before the sweep. If this is
 899       // not done, CMS generation references in the object might
 900       // not get marked.
 901       // For the case of arrays, which are otherwise precisely
 902       // marked, we need to dirty the entire array, not just its head.
 903       if (is_obj_array) {
 904         // The [par_]mark_range() method expects mr.end() below to
 905         // be aligned to the granularity of a bit's representation
 906         // in the heap. In the case of the MUT below, that's a
 907         // card size.
 908         MemRegion mr(start,
 909                      align_up(start + obj_size,
 910                               CardTable::card_size /* bytes */));
 911         if (par) {
 912           _modUnionTable.par_mark_range(mr);
 913         } else {
 914           _modUnionTable.mark_range(mr);
 915         }
 916       } else {  // not an obj array; we can just mark the head
 917         if (par) {
 918           _modUnionTable.par_mark(start);
 919         } else {
 920           _modUnionTable.mark(start);
 921         }
 922       }
 923     }
 924   }
 925 }
 926 
 927 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size) {
 928   assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
 929   // allocate, copy and if necessary update promoinfo --
 930   // delegate to underlying space.
 931   assert_lock_strong(freelistLock());
 932 
 933 #ifndef PRODUCT
 934   if (CMSHeap::heap()->promotion_should_fail()) {
 935     return NULL;
 936   }
 937 #endif  // #ifndef PRODUCT
 938 
 939   oop res = _cmsSpace->promote(obj, obj_size);
 940   if (res == NULL) {
 941     // expand and retry
 942     size_t s = _cmsSpace->expansionSpaceRequired(obj_size);  // HeapWords
 943     expand_for_gc_cause(s*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_promotion);
 944     // Since this is the old generation, we don't try to promote
 945     // into a more senior generation.
 946     res = _cmsSpace->promote(obj, obj_size);
 947   }
 948   if (res != NULL) {
 949     // See comment in allocate() about when objects should
 950     // be allocated live.
 951     assert(oopDesc::is_oop(obj), "Will dereference klass pointer below");
 952     collector()->promoted(false,           // Not parallel
 953                           (HeapWord*)res, obj->is_objArray(), obj_size);
 954     // promotion counters
 955     NOT_PRODUCT(
 956       _numObjectsPromoted++;
 957       _numWordsPromoted +=
 958         (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size()));
 959     )
 960   }
 961   return res;
 962 }
 963 
 964 
 965 // IMPORTANT: Notes on object size recognition in CMS.
 966 // ---------------------------------------------------
 967 // A block of storage in the CMS generation is always in
 968 // one of three states. A free block (FREE), an allocated
 969 // object (OBJECT) whose size() method reports the correct size,
 970 // and an intermediate state (TRANSIENT) in which its size cannot
 971 // be accurately determined.
 972 // STATE IDENTIFICATION:   (32 bit and 64 bit w/o COOPS)
 973 // -----------------------------------------------------
 974 // FREE:      klass_word & 1 == 1; mark_word holds block size
 975 //
 976 // OBJECT:    klass_word installed; klass_word != 0 && klass_word & 1 == 0;
 977 //            obj->size() computes correct size
 978 //
 979 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
 980 //
 981 // STATE IDENTIFICATION: (64 bit+COOPS)
 982 // ------------------------------------
 983 // FREE:      mark_word & CMS_FREE_BIT == 1; mark_word & ~CMS_FREE_BIT gives block_size
 984 //
 985 // OBJECT:    klass_word installed; klass_word != 0;
 986 //            obj->size() computes correct size
 987 //
 988 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
 989 //
 990 //
 991 // STATE TRANSITION DIAGRAM
 992 //
 993 //        mut / parnew                     mut  /  parnew
 994 // FREE --------------------> TRANSIENT ---------------------> OBJECT --|
 995 //  ^                                                                   |
 996 //  |------------------------ DEAD <------------------------------------|
 997 //         sweep                            mut
 998 //
 999 // While a block is in TRANSIENT state its size cannot be determined
1000 // so readers will either need to come back later or stall until
1001 // the size can be determined. Note that for the case of direct
1002 // allocation, P-bits, when available, may be used to determine the
1003 // size of an object that may not yet have been initialized.
1004 
1005 // Things to support parallel young-gen collection.
1006 oop
1007 ConcurrentMarkSweepGeneration::par_promote(int thread_num,
1008                                            oop old, markOop m,
1009                                            size_t word_sz) {
1010 #ifndef PRODUCT
1011   if (CMSHeap::heap()->promotion_should_fail()) {
1012     return NULL;
1013   }
1014 #endif  // #ifndef PRODUCT
1015 
1016   CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1017   PromotionInfo* promoInfo = &ps->promo;
1018   // if we are tracking promotions, then first ensure space for
1019   // promotion (including spooling space for saving header if necessary).
1020   // then allocate and copy, then track promoted info if needed.
1021   // When tracking (see PromotionInfo::track()), the mark word may
1022   // be displaced and in this case restoration of the mark word
1023   // occurs in the (oop_since_save_marks_)iterate phase.
1024   if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) {
1025     // Out of space for allocating spooling buffers;
1026     // try expanding and allocating spooling buffers.
1027     if (!expand_and_ensure_spooling_space(promoInfo)) {
1028       return NULL;
1029     }
1030   }
1031   assert(!promoInfo->tracking() || promoInfo->has_spooling_space(), "Control point invariant");
1032   const size_t alloc_sz = CompactibleFreeListSpace::adjustObjectSize(word_sz);
1033   HeapWord* obj_ptr = ps->lab.alloc(alloc_sz);
1034   if (obj_ptr == NULL) {
1035      obj_ptr = expand_and_par_lab_allocate(ps, alloc_sz);
1036      if (obj_ptr == NULL) {
1037        return NULL;
1038      }
1039   }
1040   oop obj = oop(obj_ptr);
1041   OrderAccess::storestore();
1042   assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1043   assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1044   // IMPORTANT: See note on object initialization for CMS above.
1045   // Otherwise, copy the object.  Here we must be careful to insert the
1046   // klass pointer last, since this marks the block as an allocated object.
1047   // Except with compressed oops it's the mark word.
1048   HeapWord* old_ptr = (HeapWord*)old;
1049   // Restore the mark word copied above.
1050   obj->set_mark_raw(m);
1051   assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1052   assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1053   OrderAccess::storestore();
1054 
1055   if (UseCompressedClassPointers) {
1056     // Copy gap missed by (aligned) header size calculation below
1057     obj->set_klass_gap(old->klass_gap());
1058   }
1059   if (word_sz > (size_t)oopDesc::header_size()) {
1060     Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1061                                  obj_ptr + oopDesc::header_size(),
1062                                  word_sz - oopDesc::header_size());
1063   }
1064 
1065   // Now we can track the promoted object, if necessary.  We take care
1066   // to delay the transition from uninitialized to full object
1067   // (i.e., insertion of klass pointer) until after, so that it
1068   // atomically becomes a promoted object.
1069   if (promoInfo->tracking()) {
1070     promoInfo->track((PromotedObject*)obj, old->klass());
1071   }
1072   assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1073   assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1074   assert(oopDesc::is_oop(old), "Will use and dereference old klass ptr below");
1075 
1076   // Finally, install the klass pointer (this should be volatile).
1077   OrderAccess::storestore();
1078   obj->set_klass(old->klass());
1079   // We should now be able to calculate the right size for this object
1080   assert(oopDesc::is_oop(obj) && obj->size() == (int)word_sz, "Error, incorrect size computed for promoted object");
1081 
1082   collector()->promoted(true,          // parallel
1083                         obj_ptr, old->is_objArray(), word_sz);
1084 
1085   NOT_PRODUCT(
1086     Atomic::inc(&_numObjectsPromoted);
1087     Atomic::add(alloc_sz, &_numWordsPromoted);
1088   )
1089 
1090   return obj;
1091 }
1092 
1093 void
1094 ConcurrentMarkSweepGeneration::
1095 par_promote_alloc_done(int thread_num) {
1096   CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1097   ps->lab.retire(thread_num);
1098 }
1099 
1100 void
1101 ConcurrentMarkSweepGeneration::
1102 par_oop_since_save_marks_iterate_done(int thread_num) {
1103   CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1104   ParScanWithoutBarrierClosure* dummy_cl = NULL;
1105   ps->promo.promoted_oops_iterate(dummy_cl);
1106 
1107   // Because card-scanning has been completed, subsequent phases
1108   // (e.g., reference processing) will not need to recognize which
1109   // objects have been promoted during this GC. So, we can now disable
1110   // promotion tracking.
1111   ps->promo.stopTrackingPromotions();
1112 }
1113 
1114 bool ConcurrentMarkSweepGeneration::should_collect(bool   full,
1115                                                    size_t size,
1116                                                    bool   tlab)
1117 {
1118   // We allow a STW collection only if a full
1119   // collection was requested.
1120   return full || should_allocate(size, tlab); // FIX ME !!!
1121   // This and promotion failure handling are connected at the
1122   // hip and should be fixed by untying them.
1123 }
1124 
1125 bool CMSCollector::shouldConcurrentCollect() {
1126   LogTarget(Trace, gc) log;
1127 
1128   if (_full_gc_requested) {
1129     log.print("CMSCollector: collect because of explicit  gc request (or GCLocker)");
1130     return true;
1131   }
1132 
1133   FreelistLocker x(this);
1134   // ------------------------------------------------------------------
1135   // Print out lots of information which affects the initiation of
1136   // a collection.
1137   if (log.is_enabled() && stats().valid()) {
1138     log.print("CMSCollector shouldConcurrentCollect: ");
1139 
1140     LogStream out(log);
1141     stats().print_on(&out);
1142 
1143     log.print("time_until_cms_gen_full %3.7f", stats().time_until_cms_gen_full());
1144     log.print("free=" SIZE_FORMAT, _cmsGen->free());
1145     log.print("contiguous_available=" SIZE_FORMAT, _cmsGen->contiguous_available());
1146     log.print("promotion_rate=%g", stats().promotion_rate());
1147     log.print("cms_allocation_rate=%g", stats().cms_allocation_rate());
1148     log.print("occupancy=%3.7f", _cmsGen->occupancy());
1149     log.print("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy());
1150     log.print("cms_time_since_begin=%3.7f", stats().cms_time_since_begin());
1151     log.print("cms_time_since_end=%3.7f", stats().cms_time_since_end());
1152     log.print("metadata initialized %d", MetaspaceGC::should_concurrent_collect());
1153   }
1154   // ------------------------------------------------------------------
1155 
1156   // If the estimated time to complete a cms collection (cms_duration())
1157   // is less than the estimated time remaining until the cms generation
1158   // is full, start a collection.
1159   if (!UseCMSInitiatingOccupancyOnly) {
1160     if (stats().valid()) {
1161       if (stats().time_until_cms_start() == 0.0) {
1162         return true;
1163       }
1164     } else {
1165       // We want to conservatively collect somewhat early in order
1166       // to try and "bootstrap" our CMS/promotion statistics;
1167       // this branch will not fire after the first successful CMS
1168       // collection because the stats should then be valid.
1169       if (_cmsGen->occupancy() >= _bootstrap_occupancy) {
1170         log.print(" CMSCollector: collect for bootstrapping statistics: occupancy = %f, boot occupancy = %f",
1171                   _cmsGen->occupancy(), _bootstrap_occupancy);
1172         return true;
1173       }
1174     }
1175   }
1176 
1177   // Otherwise, we start a collection cycle if
1178   // old gen want a collection cycle started. Each may use
1179   // an appropriate criterion for making this decision.
1180   // XXX We need to make sure that the gen expansion
1181   // criterion dovetails well with this. XXX NEED TO FIX THIS
1182   if (_cmsGen->should_concurrent_collect()) {
1183     log.print("CMS old gen initiated");
1184     return true;
1185   }
1186 
1187   // We start a collection if we believe an incremental collection may fail;
1188   // this is not likely to be productive in practice because it's probably too
1189   // late anyway.
1190   CMSHeap* heap = CMSHeap::heap();
1191   if (heap->incremental_collection_will_fail(true /* consult_young */)) {
1192     log.print("CMSCollector: collect because incremental collection will fail ");
1193     return true;
1194   }
1195 
1196   if (MetaspaceGC::should_concurrent_collect()) {
1197     log.print("CMSCollector: collect for metadata allocation ");
1198     return true;
1199   }
1200 
1201   // CMSTriggerInterval starts a CMS cycle if enough time has passed.
1202   if (CMSTriggerInterval >= 0) {
1203     if (CMSTriggerInterval == 0) {
1204       // Trigger always
1205       return true;
1206     }
1207 
1208     // Check the CMS time since begin (we do not check the stats validity
1209     // as we want to be able to trigger the first CMS cycle as well)
1210     if (stats().cms_time_since_begin() >= (CMSTriggerInterval / ((double) MILLIUNITS))) {
1211       if (stats().valid()) {
1212         log.print("CMSCollector: collect because of trigger interval (time since last begin %3.7f secs)",
1213                   stats().cms_time_since_begin());
1214       } else {
1215         log.print("CMSCollector: collect because of trigger interval (first collection)");
1216       }
1217       return true;
1218     }
1219   }
1220 
1221   return false;
1222 }
1223 
1224 void CMSCollector::set_did_compact(bool v) { _cmsGen->set_did_compact(v); }
1225 
1226 // Clear _expansion_cause fields of constituent generations
1227 void CMSCollector::clear_expansion_cause() {
1228   _cmsGen->clear_expansion_cause();
1229 }
1230 
1231 // We should be conservative in starting a collection cycle.  To
1232 // start too eagerly runs the risk of collecting too often in the
1233 // extreme.  To collect too rarely falls back on full collections,
1234 // which works, even if not optimum in terms of concurrent work.
1235 // As a work around for too eagerly collecting, use the flag
1236 // UseCMSInitiatingOccupancyOnly.  This also has the advantage of
1237 // giving the user an easily understandable way of controlling the
1238 // collections.
1239 // We want to start a new collection cycle if any of the following
1240 // conditions hold:
1241 // . our current occupancy exceeds the configured initiating occupancy
1242 //   for this generation, or
1243 // . we recently needed to expand this space and have not, since that
1244 //   expansion, done a collection of this generation, or
1245 // . the underlying space believes that it may be a good idea to initiate
1246 //   a concurrent collection (this may be based on criteria such as the
1247 //   following: the space uses linear allocation and linear allocation is
1248 //   going to fail, or there is believed to be excessive fragmentation in
1249 //   the generation, etc... or ...
1250 // [.(currently done by CMSCollector::shouldConcurrentCollect() only for
1251 //   the case of the old generation; see CR 6543076):
1252 //   we may be approaching a point at which allocation requests may fail because
1253 //   we will be out of sufficient free space given allocation rate estimates.]
1254 bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const {
1255 
1256   assert_lock_strong(freelistLock());
1257   if (occupancy() > initiating_occupancy()) {
1258     log_trace(gc)(" %s: collect because of occupancy %f / %f  ",
1259                   short_name(), occupancy(), initiating_occupancy());
1260     return true;
1261   }
1262   if (UseCMSInitiatingOccupancyOnly) {
1263     return false;
1264   }
1265   if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) {
1266     log_trace(gc)(" %s: collect because expanded for allocation ", short_name());
1267     return true;
1268   }
1269   return false;
1270 }
1271 
1272 void ConcurrentMarkSweepGeneration::collect(bool   full,
1273                                             bool   clear_all_soft_refs,
1274                                             size_t size,
1275                                             bool   tlab)
1276 {
1277   collector()->collect(full, clear_all_soft_refs, size, tlab);
1278 }
1279 
1280 void CMSCollector::collect(bool   full,
1281                            bool   clear_all_soft_refs,
1282                            size_t size,
1283                            bool   tlab)
1284 {
1285   // The following "if" branch is present for defensive reasons.
1286   // In the current uses of this interface, it can be replaced with:
1287   // assert(!GCLocker.is_active(), "Can't be called otherwise");
1288   // But I am not placing that assert here to allow future
1289   // generality in invoking this interface.
1290   if (GCLocker::is_active()) {
1291     // A consistency test for GCLocker
1292     assert(GCLocker::needs_gc(), "Should have been set already");
1293     // Skip this foreground collection, instead
1294     // expanding the heap if necessary.
1295     // Need the free list locks for the call to free() in compute_new_size()
1296     compute_new_size();
1297     return;
1298   }
1299   acquire_control_and_collect(full, clear_all_soft_refs);
1300 }
1301 
1302 void CMSCollector::request_full_gc(unsigned int full_gc_count, GCCause::Cause cause) {
1303   CMSHeap* heap = CMSHeap::heap();
1304   unsigned int gc_count = heap->total_full_collections();
1305   if (gc_count == full_gc_count) {
1306     MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag);
1307     _full_gc_requested = true;
1308     _full_gc_cause = cause;
1309     CGC_lock->notify();   // nudge CMS thread
1310   } else {
1311     assert(gc_count > full_gc_count, "Error: causal loop");
1312   }
1313 }
1314 
1315 bool CMSCollector::is_external_interruption() {
1316   GCCause::Cause cause = CMSHeap::heap()->gc_cause();
1317   return GCCause::is_user_requested_gc(cause) ||
1318          GCCause::is_serviceability_requested_gc(cause);
1319 }
1320 
1321 void CMSCollector::report_concurrent_mode_interruption() {
1322   if (is_external_interruption()) {
1323     log_debug(gc)("Concurrent mode interrupted");
1324   } else {
1325     log_debug(gc)("Concurrent mode failure");
1326     _gc_tracer_cm->report_concurrent_mode_failure();
1327   }
1328 }
1329 
1330 
1331 // The foreground and background collectors need to coordinate in order
1332 // to make sure that they do not mutually interfere with CMS collections.
1333 // When a background collection is active,
1334 // the foreground collector may need to take over (preempt) and
1335 // synchronously complete an ongoing collection. Depending on the
1336 // frequency of the background collections and the heap usage
1337 // of the application, this preemption can be seldom or frequent.
1338 // There are only certain
1339 // points in the background collection that the "collection-baton"
1340 // can be passed to the foreground collector.
1341 //
1342 // The foreground collector will wait for the baton before
1343 // starting any part of the collection.  The foreground collector
1344 // will only wait at one location.
1345 //
1346 // The background collector will yield the baton before starting a new
1347 // phase of the collection (e.g., before initial marking, marking from roots,
1348 // precleaning, final re-mark, sweep etc.)  This is normally done at the head
1349 // of the loop which switches the phases. The background collector does some
1350 // of the phases (initial mark, final re-mark) with the world stopped.
1351 // Because of locking involved in stopping the world,
1352 // the foreground collector should not block waiting for the background
1353 // collector when it is doing a stop-the-world phase.  The background
1354 // collector will yield the baton at an additional point just before
1355 // it enters a stop-the-world phase.  Once the world is stopped, the
1356 // background collector checks the phase of the collection.  If the
1357 // phase has not changed, it proceeds with the collection.  If the
1358 // phase has changed, it skips that phase of the collection.  See
1359 // the comments on the use of the Heap_lock in collect_in_background().
1360 //
1361 // Variable used in baton passing.
1362 //   _foregroundGCIsActive - Set to true by the foreground collector when
1363 //      it wants the baton.  The foreground clears it when it has finished
1364 //      the collection.
1365 //   _foregroundGCShouldWait - Set to true by the background collector
1366 //        when it is running.  The foreground collector waits while
1367 //      _foregroundGCShouldWait is true.
1368 //  CGC_lock - monitor used to protect access to the above variables
1369 //      and to notify the foreground and background collectors.
1370 //  _collectorState - current state of the CMS collection.
1371 //
1372 // The foreground collector
1373 //   acquires the CGC_lock
1374 //   sets _foregroundGCIsActive
1375 //   waits on the CGC_lock for _foregroundGCShouldWait to be false
1376 //     various locks acquired in preparation for the collection
1377 //     are released so as not to block the background collector
1378 //     that is in the midst of a collection
1379 //   proceeds with the collection
1380 //   clears _foregroundGCIsActive
1381 //   returns
1382 //
1383 // The background collector in a loop iterating on the phases of the
1384 //      collection
1385 //   acquires the CGC_lock
1386 //   sets _foregroundGCShouldWait
1387 //   if _foregroundGCIsActive is set
1388 //     clears _foregroundGCShouldWait, notifies _CGC_lock
1389 //     waits on _CGC_lock for _foregroundGCIsActive to become false
1390 //     and exits the loop.
1391 //   otherwise
1392 //     proceed with that phase of the collection
1393 //     if the phase is a stop-the-world phase,
1394 //       yield the baton once more just before enqueueing
1395 //       the stop-world CMS operation (executed by the VM thread).
1396 //   returns after all phases of the collection are done
1397 //
1398 
1399 void CMSCollector::acquire_control_and_collect(bool full,
1400         bool clear_all_soft_refs) {
1401   assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
1402   assert(!Thread::current()->is_ConcurrentGC_thread(),
1403          "shouldn't try to acquire control from self!");
1404 
1405   // Start the protocol for acquiring control of the
1406   // collection from the background collector (aka CMS thread).
1407   assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1408          "VM thread should have CMS token");
1409   // Remember the possibly interrupted state of an ongoing
1410   // concurrent collection
1411   CollectorState first_state = _collectorState;
1412 
1413   // Signal to a possibly ongoing concurrent collection that
1414   // we want to do a foreground collection.
1415   _foregroundGCIsActive = true;
1416 
1417   // release locks and wait for a notify from the background collector
1418   // releasing the locks in only necessary for phases which
1419   // do yields to improve the granularity of the collection.
1420   assert_lock_strong(bitMapLock());
1421   // We need to lock the Free list lock for the space that we are
1422   // currently collecting.
1423   assert(haveFreelistLocks(), "Must be holding free list locks");
1424   bitMapLock()->unlock();
1425   releaseFreelistLocks();
1426   {
1427     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1428     if (_foregroundGCShouldWait) {
1429       // We are going to be waiting for action for the CMS thread;
1430       // it had better not be gone (for instance at shutdown)!
1431       assert(ConcurrentMarkSweepThread::cmst() != NULL && !ConcurrentMarkSweepThread::cmst()->has_terminated(),
1432              "CMS thread must be running");
1433       // Wait here until the background collector gives us the go-ahead
1434       ConcurrentMarkSweepThread::clear_CMS_flag(
1435         ConcurrentMarkSweepThread::CMS_vm_has_token);  // release token
1436       // Get a possibly blocked CMS thread going:
1437       //   Note that we set _foregroundGCIsActive true above,
1438       //   without protection of the CGC_lock.
1439       CGC_lock->notify();
1440       assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(),
1441              "Possible deadlock");
1442       while (_foregroundGCShouldWait) {
1443         // wait for notification
1444         CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1445         // Possibility of delay/starvation here, since CMS token does
1446         // not know to give priority to VM thread? Actually, i think
1447         // there wouldn't be any delay/starvation, but the proof of
1448         // that "fact" (?) appears non-trivial. XXX 20011219YSR
1449       }
1450       ConcurrentMarkSweepThread::set_CMS_flag(
1451         ConcurrentMarkSweepThread::CMS_vm_has_token);
1452     }
1453   }
1454   // The CMS_token is already held.  Get back the other locks.
1455   assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1456          "VM thread should have CMS token");
1457   getFreelistLocks();
1458   bitMapLock()->lock_without_safepoint_check();
1459   log_debug(gc, state)("CMS foreground collector has asked for control " INTPTR_FORMAT " with first state %d",
1460                        p2i(Thread::current()), first_state);
1461   log_debug(gc, state)("    gets control with state %d", _collectorState);
1462 
1463   // Inform cms gen if this was due to partial collection failing.
1464   // The CMS gen may use this fact to determine its expansion policy.
1465   CMSHeap* heap = CMSHeap::heap();
1466   if (heap->incremental_collection_will_fail(false /* don't consult_young */)) {
1467     assert(!_cmsGen->incremental_collection_failed(),
1468            "Should have been noticed, reacted to and cleared");
1469     _cmsGen->set_incremental_collection_failed();
1470   }
1471 
1472   if (first_state > Idling) {
1473     report_concurrent_mode_interruption();
1474   }
1475 
1476   set_did_compact(true);
1477 
1478   // If the collection is being acquired from the background
1479   // collector, there may be references on the discovered
1480   // references lists.  Abandon those references, since some
1481   // of them may have become unreachable after concurrent
1482   // discovery; the STW compacting collector will redo discovery
1483   // more precisely, without being subject to floating garbage.
1484   // Leaving otherwise unreachable references in the discovered
1485   // lists would require special handling.
1486   ref_processor()->disable_discovery();
1487   ref_processor()->abandon_partial_discovery();
1488   ref_processor()->verify_no_references_recorded();
1489 
1490   if (first_state > Idling) {
1491     save_heap_summary();
1492   }
1493 
1494   do_compaction_work(clear_all_soft_refs);
1495 
1496   // Has the GC time limit been exceeded?
1497   size_t max_eden_size = _young_gen->max_eden_size();
1498   GCCause::Cause gc_cause = heap->gc_cause();
1499   size_policy()->check_gc_overhead_limit(_young_gen->used(),
1500                                          _young_gen->eden()->used(),
1501                                          _cmsGen->max_capacity(),
1502                                          max_eden_size,
1503                                          full,
1504                                          gc_cause,
1505                                          heap->soft_ref_policy());
1506 
1507   // Reset the expansion cause, now that we just completed
1508   // a collection cycle.
1509   clear_expansion_cause();
1510   _foregroundGCIsActive = false;
1511   return;
1512 }
1513 
1514 // Resize the tenured generation
1515 // after obtaining the free list locks for the
1516 // two generations.
1517 void CMSCollector::compute_new_size() {
1518   assert_locked_or_safepoint(Heap_lock);
1519   FreelistLocker z(this);
1520   MetaspaceGC::compute_new_size();
1521   _cmsGen->compute_new_size_free_list();
1522 }
1523 
1524 // A work method used by the foreground collector to do
1525 // a mark-sweep-compact.
1526 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) {
1527   CMSHeap* heap = CMSHeap::heap();
1528 
1529   STWGCTimer* gc_timer = GenMarkSweep::gc_timer();
1530   gc_timer->register_gc_start();
1531 
1532   SerialOldTracer* gc_tracer = GenMarkSweep::gc_tracer();
1533   gc_tracer->report_gc_start(heap->gc_cause(), gc_timer->gc_start());
1534 
1535   heap->pre_full_gc_dump(gc_timer);
1536 
1537   GCTraceTime(Trace, gc, phases) t("CMS:MSC");
1538 
1539   // Temporarily widen the span of the weak reference processing to
1540   // the entire heap.
1541   MemRegion new_span(CMSHeap::heap()->reserved_region());
1542   ReferenceProcessorSpanMutator rp_mut_span(ref_processor(), new_span);
1543   // Temporarily, clear the "is_alive_non_header" field of the
1544   // reference processor.
1545   ReferenceProcessorIsAliveMutator rp_mut_closure(ref_processor(), NULL);
1546   // Temporarily make reference _processing_ single threaded (non-MT).
1547   ReferenceProcessorMTProcMutator rp_mut_mt_processing(ref_processor(), false);
1548   // Temporarily make refs discovery atomic
1549   ReferenceProcessorAtomicMutator rp_mut_atomic(ref_processor(), true);
1550   // Temporarily make reference _discovery_ single threaded (non-MT)
1551   ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
1552 
1553   ref_processor()->set_enqueuing_is_done(false);
1554   ref_processor()->enable_discovery();
1555   ref_processor()->setup_policy(clear_all_soft_refs);
1556   // If an asynchronous collection finishes, the _modUnionTable is
1557   // all clear.  If we are assuming the collection from an asynchronous
1558   // collection, clear the _modUnionTable.
1559   assert(_collectorState != Idling || _modUnionTable.isAllClear(),
1560     "_modUnionTable should be clear if the baton was not passed");
1561   _modUnionTable.clear_all();
1562   assert(_collectorState != Idling || _ct->cld_rem_set()->mod_union_is_clear(),
1563     "mod union for klasses should be clear if the baton was passed");
1564   _ct->cld_rem_set()->clear_mod_union();
1565 
1566 
1567   // We must adjust the allocation statistics being maintained
1568   // in the free list space. We do so by reading and clearing
1569   // the sweep timer and updating the block flux rate estimates below.
1570   assert(!_intra_sweep_timer.is_active(), "_intra_sweep_timer should be inactive");
1571   if (_inter_sweep_timer.is_active()) {
1572     _inter_sweep_timer.stop();
1573     // Note that we do not use this sample to update the _inter_sweep_estimate.
1574     _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
1575                                             _inter_sweep_estimate.padded_average(),
1576                                             _intra_sweep_estimate.padded_average());
1577   }
1578 
1579   GenMarkSweep::invoke_at_safepoint(ref_processor(), clear_all_soft_refs);
1580   #ifdef ASSERT
1581     CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
1582     size_t free_size = cms_space->free();
1583     assert(free_size ==
1584            pointer_delta(cms_space->end(), cms_space->compaction_top())
1585            * HeapWordSize,
1586       "All the free space should be compacted into one chunk at top");
1587     assert(cms_space->dictionary()->total_chunk_size(
1588                                       debug_only(cms_space->freelistLock())) == 0 ||
1589            cms_space->totalSizeInIndexedFreeLists() == 0,
1590       "All the free space should be in a single chunk");
1591     size_t num = cms_space->totalCount();
1592     assert((free_size == 0 && num == 0) ||
1593            (free_size > 0  && (num == 1 || num == 2)),
1594          "There should be at most 2 free chunks after compaction");
1595   #endif // ASSERT
1596   _collectorState = Resetting;
1597   assert(_restart_addr == NULL,
1598          "Should have been NULL'd before baton was passed");
1599   reset_stw();
1600   _cmsGen->reset_after_compaction();
1601   _concurrent_cycles_since_last_unload = 0;
1602 
1603   // Clear any data recorded in the PLAB chunk arrays.
1604   if (_survivor_plab_array != NULL) {
1605     reset_survivor_plab_arrays();
1606   }
1607 
1608   // Adjust the per-size allocation stats for the next epoch.
1609   _cmsGen->cmsSpace()->endSweepFLCensus(sweep_count() /* fake */);
1610   // Restart the "inter sweep timer" for the next epoch.
1611   _inter_sweep_timer.reset();
1612   _inter_sweep_timer.start();
1613 
1614   // No longer a need to do a concurrent collection for Metaspace.
1615   MetaspaceGC::set_should_concurrent_collect(false);
1616 
1617   heap->post_full_gc_dump(gc_timer);
1618 
1619   gc_timer->register_gc_end();
1620 
1621   gc_tracer->report_gc_end(gc_timer->gc_end(), gc_timer->time_partitions());
1622 
1623   // For a mark-sweep-compact, compute_new_size() will be called
1624   // in the heap's do_collection() method.
1625 }
1626 
1627 void CMSCollector::print_eden_and_survivor_chunk_arrays() {
1628   Log(gc, heap) log;
1629   if (!log.is_trace()) {
1630     return;
1631   }
1632 
1633   ContiguousSpace* eden_space = _young_gen->eden();
1634   ContiguousSpace* from_space = _young_gen->from();
1635   ContiguousSpace* to_space   = _young_gen->to();
1636   // Eden
1637   if (_eden_chunk_array != NULL) {
1638     log.trace("eden " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1639               p2i(eden_space->bottom()), p2i(eden_space->top()),
1640               p2i(eden_space->end()), eden_space->capacity());
1641     log.trace("_eden_chunk_index=" SIZE_FORMAT ", _eden_chunk_capacity=" SIZE_FORMAT,
1642               _eden_chunk_index, _eden_chunk_capacity);
1643     for (size_t i = 0; i < _eden_chunk_index; i++) {
1644       log.trace("_eden_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT, i, p2i(_eden_chunk_array[i]));
1645     }
1646   }
1647   // Survivor
1648   if (_survivor_chunk_array != NULL) {
1649     log.trace("survivor " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1650               p2i(from_space->bottom()), p2i(from_space->top()),
1651               p2i(from_space->end()), from_space->capacity());
1652     log.trace("_survivor_chunk_index=" SIZE_FORMAT ", _survivor_chunk_capacity=" SIZE_FORMAT,
1653               _survivor_chunk_index, _survivor_chunk_capacity);
1654     for (size_t i = 0; i < _survivor_chunk_index; i++) {
1655       log.trace("_survivor_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT, i, p2i(_survivor_chunk_array[i]));
1656     }
1657   }
1658 }
1659 
1660 void CMSCollector::getFreelistLocks() const {
1661   // Get locks for all free lists in all generations that this
1662   // collector is responsible for
1663   _cmsGen->freelistLock()->lock_without_safepoint_check();
1664 }
1665 
1666 void CMSCollector::releaseFreelistLocks() const {
1667   // Release locks for all free lists in all generations that this
1668   // collector is responsible for
1669   _cmsGen->freelistLock()->unlock();
1670 }
1671 
1672 bool CMSCollector::haveFreelistLocks() const {
1673   // Check locks for all free lists in all generations that this
1674   // collector is responsible for
1675   assert_lock_strong(_cmsGen->freelistLock());
1676   PRODUCT_ONLY(ShouldNotReachHere());
1677   return true;
1678 }
1679 
1680 // A utility class that is used by the CMS collector to
1681 // temporarily "release" the foreground collector from its
1682 // usual obligation to wait for the background collector to
1683 // complete an ongoing phase before proceeding.
1684 class ReleaseForegroundGC: public StackObj {
1685  private:
1686   CMSCollector* _c;
1687  public:
1688   ReleaseForegroundGC(CMSCollector* c) : _c(c) {
1689     assert(_c->_foregroundGCShouldWait, "Else should not need to call");
1690     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1691     // allow a potentially blocked foreground collector to proceed
1692     _c->_foregroundGCShouldWait = false;
1693     if (_c->_foregroundGCIsActive) {
1694       CGC_lock->notify();
1695     }
1696     assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1697            "Possible deadlock");
1698   }
1699 
1700   ~ReleaseForegroundGC() {
1701     assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?");
1702     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1703     _c->_foregroundGCShouldWait = true;
1704   }
1705 };
1706 
1707 void CMSCollector::collect_in_background(GCCause::Cause cause) {
1708   assert(Thread::current()->is_ConcurrentGC_thread(),
1709     "A CMS asynchronous collection is only allowed on a CMS thread.");
1710 
1711   CMSHeap* heap = CMSHeap::heap();
1712   {
1713     bool safepoint_check = Mutex::_no_safepoint_check_flag;
1714     MutexLockerEx hl(Heap_lock, safepoint_check);
1715     FreelistLocker fll(this);
1716     MutexLockerEx x(CGC_lock, safepoint_check);
1717     if (_foregroundGCIsActive) {
1718       // The foreground collector is. Skip this
1719       // background collection.
1720       assert(!_foregroundGCShouldWait, "Should be clear");
1721       return;
1722     } else {
1723       assert(_collectorState == Idling, "Should be idling before start.");
1724       _collectorState = InitialMarking;
1725       register_gc_start(cause);
1726       // Reset the expansion cause, now that we are about to begin
1727       // a new cycle.
1728       clear_expansion_cause();
1729 
1730       // Clear the MetaspaceGC flag since a concurrent collection
1731       // is starting but also clear it after the collection.
1732       MetaspaceGC::set_should_concurrent_collect(false);
1733     }
1734     // Decide if we want to enable class unloading as part of the
1735     // ensuing concurrent GC cycle.
1736     update_should_unload_classes();
1737     _full_gc_requested = false;           // acks all outstanding full gc requests
1738     _full_gc_cause = GCCause::_no_gc;
1739     // Signal that we are about to start a collection
1740     heap->increment_total_full_collections();  // ... starting a collection cycle
1741     _collection_count_start = heap->total_full_collections();
1742   }
1743 
1744   size_t prev_used = _cmsGen->used();
1745 
1746   // The change of the collection state is normally done at this level;
1747   // the exceptions are phases that are executed while the world is
1748   // stopped.  For those phases the change of state is done while the
1749   // world is stopped.  For baton passing purposes this allows the
1750   // background collector to finish the phase and change state atomically.
1751   // The foreground collector cannot wait on a phase that is done
1752   // while the world is stopped because the foreground collector already
1753   // has the world stopped and would deadlock.
1754   while (_collectorState != Idling) {
1755     log_debug(gc, state)("Thread " INTPTR_FORMAT " in CMS state %d",
1756                          p2i(Thread::current()), _collectorState);
1757     // The foreground collector
1758     //   holds the Heap_lock throughout its collection.
1759     //   holds the CMS token (but not the lock)
1760     //     except while it is waiting for the background collector to yield.
1761     //
1762     // The foreground collector should be blocked (not for long)
1763     //   if the background collector is about to start a phase
1764     //   executed with world stopped.  If the background
1765     //   collector has already started such a phase, the
1766     //   foreground collector is blocked waiting for the
1767     //   Heap_lock.  The stop-world phases (InitialMarking and FinalMarking)
1768     //   are executed in the VM thread.
1769     //
1770     // The locking order is
1771     //   PendingListLock (PLL)  -- if applicable (FinalMarking)
1772     //   Heap_lock  (both this & PLL locked in VM_CMS_Operation::prologue())
1773     //   CMS token  (claimed in
1774     //                stop_world_and_do() -->
1775     //                  safepoint_synchronize() -->
1776     //                    CMSThread::synchronize())
1777 
1778     {
1779       // Check if the FG collector wants us to yield.
1780       CMSTokenSync x(true); // is cms thread
1781       if (waitForForegroundGC()) {
1782         // We yielded to a foreground GC, nothing more to be
1783         // done this round.
1784         assert(_foregroundGCShouldWait == false, "We set it to false in "
1785                "waitForForegroundGC()");
1786         log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " exiting collection CMS state %d",
1787                              p2i(Thread::current()), _collectorState);
1788         return;
1789       } else {
1790         // The background collector can run but check to see if the
1791         // foreground collector has done a collection while the
1792         // background collector was waiting to get the CGC_lock
1793         // above.  If yes, break so that _foregroundGCShouldWait
1794         // is cleared before returning.
1795         if (_collectorState == Idling) {
1796           break;
1797         }
1798       }
1799     }
1800 
1801     assert(_foregroundGCShouldWait, "Foreground collector, if active, "
1802       "should be waiting");
1803 
1804     switch (_collectorState) {
1805       case InitialMarking:
1806         {
1807           ReleaseForegroundGC x(this);
1808           stats().record_cms_begin();
1809           VM_CMS_Initial_Mark initial_mark_op(this);
1810           VMThread::execute(&initial_mark_op);
1811         }
1812         // The collector state may be any legal state at this point
1813         // since the background collector may have yielded to the
1814         // foreground collector.
1815         break;
1816       case Marking:
1817         // initial marking in checkpointRootsInitialWork has been completed
1818         if (markFromRoots()) { // we were successful
1819           assert(_collectorState == Precleaning, "Collector state should "
1820             "have changed");
1821         } else {
1822           assert(_foregroundGCIsActive, "Internal state inconsistency");
1823         }
1824         break;
1825       case Precleaning:
1826         // marking from roots in markFromRoots has been completed
1827         preclean();
1828         assert(_collectorState == AbortablePreclean ||
1829                _collectorState == FinalMarking,
1830                "Collector state should have changed");
1831         break;
1832       case AbortablePreclean:
1833         abortable_preclean();
1834         assert(_collectorState == FinalMarking, "Collector state should "
1835           "have changed");
1836         break;
1837       case FinalMarking:
1838         {
1839           ReleaseForegroundGC x(this);
1840 
1841           VM_CMS_Final_Remark final_remark_op(this);
1842           VMThread::execute(&final_remark_op);
1843         }
1844         assert(_foregroundGCShouldWait, "block post-condition");
1845         break;
1846       case Sweeping:
1847         // final marking in checkpointRootsFinal has been completed
1848         sweep();
1849         assert(_collectorState == Resizing, "Collector state change "
1850           "to Resizing must be done under the free_list_lock");
1851 
1852       case Resizing: {
1853         // Sweeping has been completed...
1854         // At this point the background collection has completed.
1855         // Don't move the call to compute_new_size() down
1856         // into code that might be executed if the background
1857         // collection was preempted.
1858         {
1859           ReleaseForegroundGC x(this);   // unblock FG collection
1860           MutexLockerEx       y(Heap_lock, Mutex::_no_safepoint_check_flag);
1861           CMSTokenSync        z(true);   // not strictly needed.
1862           if (_collectorState == Resizing) {
1863             compute_new_size();
1864             save_heap_summary();
1865             _collectorState = Resetting;
1866           } else {
1867             assert(_collectorState == Idling, "The state should only change"
1868                    " because the foreground collector has finished the collection");
1869           }
1870         }
1871         break;
1872       }
1873       case Resetting:
1874         // CMS heap resizing has been completed
1875         reset_concurrent();
1876         assert(_collectorState == Idling, "Collector state should "
1877           "have changed");
1878 
1879         MetaspaceGC::set_should_concurrent_collect(false);
1880 
1881         stats().record_cms_end();
1882         // Don't move the concurrent_phases_end() and compute_new_size()
1883         // calls to here because a preempted background collection
1884         // has it's state set to "Resetting".
1885         break;
1886       case Idling:
1887       default:
1888         ShouldNotReachHere();
1889         break;
1890     }
1891     log_debug(gc, state)("  Thread " INTPTR_FORMAT " done - next CMS state %d",
1892                          p2i(Thread::current()), _collectorState);
1893     assert(_foregroundGCShouldWait, "block post-condition");
1894   }
1895 
1896   // Should this be in gc_epilogue?
1897   heap->counters()->update_counters();
1898 
1899   {
1900     // Clear _foregroundGCShouldWait and, in the event that the
1901     // foreground collector is waiting, notify it, before
1902     // returning.
1903     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1904     _foregroundGCShouldWait = false;
1905     if (_foregroundGCIsActive) {
1906       CGC_lock->notify();
1907     }
1908     assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1909            "Possible deadlock");
1910   }
1911   log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " exiting collection CMS state %d",
1912                        p2i(Thread::current()), _collectorState);
1913   log_info(gc, heap)("Old: " SIZE_FORMAT "K->" SIZE_FORMAT "K("  SIZE_FORMAT "K)",
1914                      prev_used / K, _cmsGen->used()/K, _cmsGen->capacity() /K);
1915 }
1916 
1917 void CMSCollector::register_gc_start(GCCause::Cause cause) {
1918   _cms_start_registered = true;
1919   _gc_timer_cm->register_gc_start();
1920   _gc_tracer_cm->report_gc_start(cause, _gc_timer_cm->gc_start());
1921 }
1922 
1923 void CMSCollector::register_gc_end() {
1924   if (_cms_start_registered) {
1925     report_heap_summary(GCWhen::AfterGC);
1926 
1927     _gc_timer_cm->register_gc_end();
1928     _gc_tracer_cm->report_gc_end(_gc_timer_cm->gc_end(), _gc_timer_cm->time_partitions());
1929     _cms_start_registered = false;
1930   }
1931 }
1932 
1933 void CMSCollector::save_heap_summary() {
1934   CMSHeap* heap = CMSHeap::heap();
1935   _last_heap_summary = heap->create_heap_summary();
1936   _last_metaspace_summary = heap->create_metaspace_summary();
1937 }
1938 
1939 void CMSCollector::report_heap_summary(GCWhen::Type when) {
1940   _gc_tracer_cm->report_gc_heap_summary(when, _last_heap_summary);
1941   _gc_tracer_cm->report_metaspace_summary(when, _last_metaspace_summary);
1942 }
1943 
1944 bool CMSCollector::waitForForegroundGC() {
1945   bool res = false;
1946   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1947          "CMS thread should have CMS token");
1948   // Block the foreground collector until the
1949   // background collectors decides whether to
1950   // yield.
1951   MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1952   _foregroundGCShouldWait = true;
1953   if (_foregroundGCIsActive) {
1954     // The background collector yields to the
1955     // foreground collector and returns a value
1956     // indicating that it has yielded.  The foreground
1957     // collector can proceed.
1958     res = true;
1959     _foregroundGCShouldWait = false;
1960     ConcurrentMarkSweepThread::clear_CMS_flag(
1961       ConcurrentMarkSweepThread::CMS_cms_has_token);
1962     ConcurrentMarkSweepThread::set_CMS_flag(
1963       ConcurrentMarkSweepThread::CMS_cms_wants_token);
1964     // Get a possibly blocked foreground thread going
1965     CGC_lock->notify();
1966     log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d",
1967                          p2i(Thread::current()), _collectorState);
1968     while (_foregroundGCIsActive) {
1969       CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1970     }
1971     ConcurrentMarkSweepThread::set_CMS_flag(
1972       ConcurrentMarkSweepThread::CMS_cms_has_token);
1973     ConcurrentMarkSweepThread::clear_CMS_flag(
1974       ConcurrentMarkSweepThread::CMS_cms_wants_token);
1975   }
1976   log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d",
1977                        p2i(Thread::current()), _collectorState);
1978   return res;
1979 }
1980 
1981 // Because of the need to lock the free lists and other structures in
1982 // the collector, common to all the generations that the collector is
1983 // collecting, we need the gc_prologues of individual CMS generations
1984 // delegate to their collector. It may have been simpler had the
1985 // current infrastructure allowed one to call a prologue on a
1986 // collector. In the absence of that we have the generation's
1987 // prologue delegate to the collector, which delegates back
1988 // some "local" work to a worker method in the individual generations
1989 // that it's responsible for collecting, while itself doing any
1990 // work common to all generations it's responsible for. A similar
1991 // comment applies to the  gc_epilogue()'s.
1992 // The role of the variable _between_prologue_and_epilogue is to
1993 // enforce the invocation protocol.
1994 void CMSCollector::gc_prologue(bool full) {
1995   // Call gc_prologue_work() for the CMSGen
1996   // we are responsible for.
1997 
1998   // The following locking discipline assumes that we are only called
1999   // when the world is stopped.
2000   assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption");
2001 
2002   // The CMSCollector prologue must call the gc_prologues for the
2003   // "generations" that it's responsible
2004   // for.
2005 
2006   assert(   Thread::current()->is_VM_thread()
2007          || (   CMSScavengeBeforeRemark
2008              && Thread::current()->is_ConcurrentGC_thread()),
2009          "Incorrect thread type for prologue execution");
2010 
2011   if (_between_prologue_and_epilogue) {
2012     // We have already been invoked; this is a gc_prologue delegation
2013     // from yet another CMS generation that we are responsible for, just
2014     // ignore it since all relevant work has already been done.
2015     return;
2016   }
2017 
2018   // set a bit saying prologue has been called; cleared in epilogue
2019   _between_prologue_and_epilogue = true;
2020   // Claim locks for common data structures, then call gc_prologue_work()
2021   // for each CMSGen.
2022 
2023   getFreelistLocks();   // gets free list locks on constituent spaces
2024   bitMapLock()->lock_without_safepoint_check();
2025 
2026   // Should call gc_prologue_work() for all cms gens we are responsible for
2027   bool duringMarking =    _collectorState >= Marking
2028                          && _collectorState < Sweeping;
2029 
2030   // The young collections clear the modified oops state, which tells if
2031   // there are any modified oops in the class. The remark phase also needs
2032   // that information. Tell the young collection to save the union of all
2033   // modified klasses.
2034   if (duringMarking) {
2035     _ct->cld_rem_set()->set_accumulate_modified_oops(true);
2036   }
2037 
2038   bool registerClosure = duringMarking;
2039 
2040   _cmsGen->gc_prologue_work(full, registerClosure, &_modUnionClosurePar);
2041 
2042   if (!full) {
2043     stats().record_gc0_begin();
2044   }
2045 }
2046 
2047 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) {
2048 
2049   _capacity_at_prologue = capacity();
2050   _used_at_prologue = used();
2051 
2052   // We enable promotion tracking so that card-scanning can recognize
2053   // which objects have been promoted during this GC and skip them.
2054   for (uint i = 0; i < ParallelGCThreads; i++) {
2055     _par_gc_thread_states[i]->promo.startTrackingPromotions();
2056   }
2057 
2058   // Delegate to CMScollector which knows how to coordinate between
2059   // this and any other CMS generations that it is responsible for
2060   // collecting.
2061   collector()->gc_prologue(full);
2062 }
2063 
2064 // This is a "private" interface for use by this generation's CMSCollector.
2065 // Not to be called directly by any other entity (for instance,
2066 // GenCollectedHeap, which calls the "public" gc_prologue method above).
2067 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full,
2068   bool registerClosure, ModUnionClosure* modUnionClosure) {
2069   assert(!incremental_collection_failed(), "Shouldn't be set yet");
2070   assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL,
2071     "Should be NULL");
2072   if (registerClosure) {
2073     cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure);
2074   }
2075   cmsSpace()->gc_prologue();
2076   // Clear stat counters
2077   NOT_PRODUCT(
2078     assert(_numObjectsPromoted == 0, "check");
2079     assert(_numWordsPromoted   == 0, "check");
2080     log_develop_trace(gc, alloc)("Allocated " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes concurrently",
2081                                  _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord));
2082     _numObjectsAllocated = 0;
2083     _numWordsAllocated   = 0;
2084   )
2085 }
2086 
2087 void CMSCollector::gc_epilogue(bool full) {
2088   // The following locking discipline assumes that we are only called
2089   // when the world is stopped.
2090   assert(SafepointSynchronize::is_at_safepoint(),
2091          "world is stopped assumption");
2092 
2093   // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks
2094   // if linear allocation blocks need to be appropriately marked to allow the
2095   // the blocks to be parsable. We also check here whether we need to nudge the
2096   // CMS collector thread to start a new cycle (if it's not already active).
2097   assert(   Thread::current()->is_VM_thread()
2098          || (   CMSScavengeBeforeRemark
2099              && Thread::current()->is_ConcurrentGC_thread()),
2100          "Incorrect thread type for epilogue execution");
2101 
2102   if (!_between_prologue_and_epilogue) {
2103     // We have already been invoked; this is a gc_epilogue delegation
2104     // from yet another CMS generation that we are responsible for, just
2105     // ignore it since all relevant work has already been done.
2106     return;
2107   }
2108   assert(haveFreelistLocks(), "must have freelist locks");
2109   assert_lock_strong(bitMapLock());
2110 
2111   _ct->cld_rem_set()->set_accumulate_modified_oops(false);
2112 
2113   _cmsGen->gc_epilogue_work(full);
2114 
2115   if (_collectorState == AbortablePreclean || _collectorState == Precleaning) {
2116     // in case sampling was not already enabled, enable it
2117     _start_sampling = true;
2118   }
2119   // reset _eden_chunk_array so sampling starts afresh
2120   _eden_chunk_index = 0;
2121 
2122   size_t cms_used   = _cmsGen->cmsSpace()->used();
2123 
2124   // update performance counters - this uses a special version of
2125   // update_counters() that allows the utilization to be passed as a
2126   // parameter, avoiding multiple calls to used().
2127   //
2128   _cmsGen->update_counters(cms_used);
2129 
2130   bitMapLock()->unlock();
2131   releaseFreelistLocks();
2132 
2133   if (!CleanChunkPoolAsync) {
2134     Chunk::clean_chunk_pool();
2135   }
2136 
2137   set_did_compact(false);
2138   _between_prologue_and_epilogue = false;  // ready for next cycle
2139 }
2140 
2141 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) {
2142   collector()->gc_epilogue(full);
2143 
2144   // When using ParNew, promotion tracking should have already been
2145   // disabled. However, the prologue (which enables promotion
2146   // tracking) and epilogue are called irrespective of the type of
2147   // GC. So they will also be called before and after Full GCs, during
2148   // which promotion tracking will not be explicitly disabled. So,
2149   // it's safer to also disable it here too (to be symmetric with
2150   // enabling it in the prologue).
2151   for (uint i = 0; i < ParallelGCThreads; i++) {
2152     _par_gc_thread_states[i]->promo.stopTrackingPromotions();
2153   }
2154 }
2155 
2156 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2157   assert(!incremental_collection_failed(), "Should have been cleared");
2158   cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2159   cmsSpace()->gc_epilogue();
2160     // Print stat counters
2161   NOT_PRODUCT(
2162     assert(_numObjectsAllocated == 0, "check");
2163     assert(_numWordsAllocated == 0, "check");
2164     log_develop_trace(gc, promotion)("Promoted " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
2165                                      _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2166     _numObjectsPromoted = 0;
2167     _numWordsPromoted   = 0;
2168   )
2169 
2170   // Call down the chain in contiguous_available needs the freelistLock
2171   // so print this out before releasing the freeListLock.
2172   log_develop_trace(gc)(" Contiguous available " SIZE_FORMAT " bytes ", contiguous_available());
2173 }
2174 
2175 #ifndef PRODUCT
2176 bool CMSCollector::have_cms_token() {
2177   Thread* thr = Thread::current();
2178   if (thr->is_VM_thread()) {
2179     return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2180   } else if (thr->is_ConcurrentGC_thread()) {
2181     return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2182   } else if (thr->is_GC_task_thread()) {
2183     return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2184            ParGCRareEvent_lock->owned_by_self();
2185   }
2186   return false;
2187 }
2188 
2189 // Check reachability of the given heap address in CMS generation,
2190 // treating all other generations as roots.
2191 bool CMSCollector::is_cms_reachable(HeapWord* addr) {
2192   // We could "guarantee" below, rather than assert, but I'll
2193   // leave these as "asserts" so that an adventurous debugger
2194   // could try this in the product build provided some subset of
2195   // the conditions were met, provided they were interested in the
2196   // results and knew that the computation below wouldn't interfere
2197   // with other concurrent computations mutating the structures
2198   // being read or written.
2199   assert(SafepointSynchronize::is_at_safepoint(),
2200          "Else mutations in object graph will make answer suspect");
2201   assert(have_cms_token(), "Should hold cms token");
2202   assert(haveFreelistLocks(), "must hold free list locks");
2203   assert_lock_strong(bitMapLock());
2204 
2205   // Clear the marking bit map array before starting, but, just
2206   // for kicks, first report if the given address is already marked
2207   tty->print_cr("Start: Address " PTR_FORMAT " is%s marked", p2i(addr),
2208                 _markBitMap.isMarked(addr) ? "" : " not");
2209 
2210   if (verify_after_remark()) {
2211     MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2212     bool result = verification_mark_bm()->isMarked(addr);
2213     tty->print_cr("TransitiveMark: Address " PTR_FORMAT " %s marked", p2i(addr),
2214                   result ? "IS" : "is NOT");
2215     return result;
2216   } else {
2217     tty->print_cr("Could not compute result");
2218     return false;
2219   }
2220 }
2221 #endif
2222 
2223 void
2224 CMSCollector::print_on_error(outputStream* st) {
2225   CMSCollector* collector = ConcurrentMarkSweepGeneration::_collector;
2226   if (collector != NULL) {
2227     CMSBitMap* bitmap = &collector->_markBitMap;
2228     st->print_cr("Marking Bits: (CMSBitMap*) " PTR_FORMAT, p2i(bitmap));
2229     bitmap->print_on_error(st, " Bits: ");
2230 
2231     st->cr();
2232 
2233     CMSBitMap* mut_bitmap = &collector->_modUnionTable;
2234     st->print_cr("Mod Union Table: (CMSBitMap*) " PTR_FORMAT, p2i(mut_bitmap));
2235     mut_bitmap->print_on_error(st, " Bits: ");
2236   }
2237 }
2238 
2239 ////////////////////////////////////////////////////////
2240 // CMS Verification Support
2241 ////////////////////////////////////////////////////////
2242 // Following the remark phase, the following invariant
2243 // should hold -- each object in the CMS heap which is
2244 // marked in markBitMap() should be marked in the verification_mark_bm().
2245 
2246 class VerifyMarkedClosure: public BitMapClosure {
2247   CMSBitMap* _marks;
2248   bool       _failed;
2249 
2250  public:
2251   VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2252 
2253   bool do_bit(size_t offset) {
2254     HeapWord* addr = _marks->offsetToHeapWord(offset);
2255     if (!_marks->isMarked(addr)) {
2256       Log(gc, verify) log;
2257       ResourceMark rm;
2258       LogStream ls(log.error());
2259       oop(addr)->print_on(&ls);
2260       log.error(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
2261       _failed = true;
2262     }
2263     return true;
2264   }
2265 
2266   bool failed() { return _failed; }
2267 };
2268 
2269 bool CMSCollector::verify_after_remark() {
2270   GCTraceTime(Info, gc, phases, verify) tm("Verifying CMS Marking.");
2271   MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2272   static bool init = false;
2273 
2274   assert(SafepointSynchronize::is_at_safepoint(),
2275          "Else mutations in object graph will make answer suspect");
2276   assert(have_cms_token(),
2277          "Else there may be mutual interference in use of "
2278          " verification data structures");
2279   assert(_collectorState > Marking && _collectorState <= Sweeping,
2280          "Else marking info checked here may be obsolete");
2281   assert(haveFreelistLocks(), "must hold free list locks");
2282   assert_lock_strong(bitMapLock());
2283 
2284 
2285   // Allocate marking bit map if not already allocated
2286   if (!init) { // first time
2287     if (!verification_mark_bm()->allocate(_span)) {
2288       return false;
2289     }
2290     init = true;
2291   }
2292 
2293   assert(verification_mark_stack()->isEmpty(), "Should be empty");
2294 
2295   // Turn off refs discovery -- so we will be tracing through refs.
2296   // This is as intended, because by this time
2297   // GC must already have cleared any refs that need to be cleared,
2298   // and traced those that need to be marked; moreover,
2299   // the marking done here is not going to interfere in any
2300   // way with the marking information used by GC.
2301   NoRefDiscovery no_discovery(ref_processor());
2302 
2303 #if COMPILER2_OR_JVMCI
2304   DerivedPointerTableDeactivate dpt_deact;
2305 #endif
2306 
2307   // Clear any marks from a previous round
2308   verification_mark_bm()->clear_all();
2309   assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
2310   verify_work_stacks_empty();
2311 
2312   CMSHeap* heap = CMSHeap::heap();
2313   heap->ensure_parsability(false);  // fill TLABs, but no need to retire them
2314   // Update the saved marks which may affect the root scans.
2315   heap->save_marks();
2316 
2317   if (CMSRemarkVerifyVariant == 1) {
2318     // In this first variant of verification, we complete
2319     // all marking, then check if the new marks-vector is
2320     // a subset of the CMS marks-vector.
2321     verify_after_remark_work_1();
2322   } else {
2323     guarantee(CMSRemarkVerifyVariant == 2, "Range checking for CMSRemarkVerifyVariant should guarantee 1 or 2");
2324     // In this second variant of verification, we flag an error
2325     // (i.e. an object reachable in the new marks-vector not reachable
2326     // in the CMS marks-vector) immediately, also indicating the
2327     // identify of an object (A) that references the unmarked object (B) --
2328     // presumably, a mutation to A failed to be picked up by preclean/remark?
2329     verify_after_remark_work_2();
2330   }
2331 
2332   return true;
2333 }
2334 
2335 void CMSCollector::verify_after_remark_work_1() {
2336   ResourceMark rm;
2337   HandleMark  hm;
2338   CMSHeap* heap = CMSHeap::heap();
2339 
2340   // Get a clear set of claim bits for the roots processing to work with.
2341   ClassLoaderDataGraph::clear_claimed_marks();
2342 
2343   // Mark from roots one level into CMS
2344   MarkRefsIntoClosure notOlder(_span, verification_mark_bm());
2345   heap->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2346 
2347   {
2348     StrongRootsScope srs(1);
2349 
2350     heap->cms_process_roots(&srs,
2351                            true,   // young gen as roots
2352                            GenCollectedHeap::ScanningOption(roots_scanning_options()),
2353                            should_unload_classes(),
2354                            &notOlder,
2355                            NULL);
2356   }
2357 
2358   // Now mark from the roots
2359   MarkFromRootsClosure markFromRootsClosure(this, _span,
2360     verification_mark_bm(), verification_mark_stack(),
2361     false /* don't yield */, true /* verifying */);
2362   assert(_restart_addr == NULL, "Expected pre-condition");
2363   verification_mark_bm()->iterate(&markFromRootsClosure);
2364   while (_restart_addr != NULL) {
2365     // Deal with stack overflow: by restarting at the indicated
2366     // address.
2367     HeapWord* ra = _restart_addr;
2368     markFromRootsClosure.reset(ra);
2369     _restart_addr = NULL;
2370     verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2371   }
2372   assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2373   verify_work_stacks_empty();
2374 
2375   // Marking completed -- now verify that each bit marked in
2376   // verification_mark_bm() is also marked in markBitMap(); flag all
2377   // errors by printing corresponding objects.
2378   VerifyMarkedClosure vcl(markBitMap());
2379   verification_mark_bm()->iterate(&vcl);
2380   if (vcl.failed()) {
2381     Log(gc, verify) log;
2382     log.error("Failed marking verification after remark");
2383     ResourceMark rm;
2384     LogStream ls(log.error());
2385     heap->print_on(&ls);
2386     fatal("CMS: failed marking verification after remark");
2387   }
2388 }
2389 
2390 class VerifyCLDOopsCLDClosure : public CLDClosure {
2391   class VerifyCLDOopsClosure : public OopClosure {
2392     CMSBitMap* _bitmap;
2393    public:
2394     VerifyCLDOopsClosure(CMSBitMap* bitmap) : _bitmap(bitmap) { }
2395     void do_oop(oop* p)       { guarantee(*p == NULL || _bitmap->isMarked((HeapWord*) *p), "Should be marked"); }
2396     void do_oop(narrowOop* p) { ShouldNotReachHere(); }
2397   } _oop_closure;
2398  public:
2399   VerifyCLDOopsCLDClosure(CMSBitMap* bitmap) : _oop_closure(bitmap) {}
2400   void do_cld(ClassLoaderData* cld) {
2401     cld->oops_do(&_oop_closure, false, false);
2402   }
2403 };
2404 
2405 void CMSCollector::verify_after_remark_work_2() {
2406   ResourceMark rm;
2407   HandleMark  hm;
2408   CMSHeap* heap = CMSHeap::heap();
2409 
2410   // Get a clear set of claim bits for the roots processing to work with.
2411   ClassLoaderDataGraph::clear_claimed_marks();
2412 
2413   // Mark from roots one level into CMS
2414   MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
2415                                      markBitMap());
2416   CLDToOopClosure cld_closure(&notOlder, true);
2417 
2418   heap->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2419 
2420   {
2421     StrongRootsScope srs(1);
2422 
2423     heap->cms_process_roots(&srs,
2424                            true,   // young gen as roots
2425                            GenCollectedHeap::ScanningOption(roots_scanning_options()),
2426                            should_unload_classes(),
2427                            &notOlder,
2428                            &cld_closure);
2429   }
2430 
2431   // Now mark from the roots
2432   MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
2433     verification_mark_bm(), markBitMap(), verification_mark_stack());
2434   assert(_restart_addr == NULL, "Expected pre-condition");
2435   verification_mark_bm()->iterate(&markFromRootsClosure);
2436   while (_restart_addr != NULL) {
2437     // Deal with stack overflow: by restarting at the indicated
2438     // address.
2439     HeapWord* ra = _restart_addr;
2440     markFromRootsClosure.reset(ra);
2441     _restart_addr = NULL;
2442     verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2443   }
2444   assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2445   verify_work_stacks_empty();
2446 
2447   VerifyCLDOopsCLDClosure verify_cld_oops(verification_mark_bm());
2448   ClassLoaderDataGraph::cld_do(&verify_cld_oops);
2449 
2450   // Marking completed -- now verify that each bit marked in
2451   // verification_mark_bm() is also marked in markBitMap(); flag all
2452   // errors by printing corresponding objects.
2453   VerifyMarkedClosure vcl(markBitMap());
2454   verification_mark_bm()->iterate(&vcl);
2455   assert(!vcl.failed(), "Else verification above should not have succeeded");
2456 }
2457 
2458 void ConcurrentMarkSweepGeneration::save_marks() {
2459   // delegate to CMS space
2460   cmsSpace()->save_marks();
2461 }
2462 
2463 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
2464   return cmsSpace()->no_allocs_since_save_marks();
2465 }
2466 
2467 void
2468 ConcurrentMarkSweepGeneration::oop_iterate(ExtendedOopClosure* cl) {
2469   if (freelistLock()->owned_by_self()) {
2470     Generation::oop_iterate(cl);
2471   } else {
2472     MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2473     Generation::oop_iterate(cl);
2474   }
2475 }
2476 
2477 void
2478 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
2479   if (freelistLock()->owned_by_self()) {
2480     Generation::object_iterate(cl);
2481   } else {
2482     MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2483     Generation::object_iterate(cl);
2484   }
2485 }
2486 
2487 void
2488 ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) {
2489   if (freelistLock()->owned_by_self()) {
2490     Generation::safe_object_iterate(cl);
2491   } else {
2492     MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2493     Generation::safe_object_iterate(cl);
2494   }
2495 }
2496 
2497 void
2498 ConcurrentMarkSweepGeneration::post_compact() {
2499 }
2500 
2501 void
2502 ConcurrentMarkSweepGeneration::prepare_for_verify() {
2503   // Fix the linear allocation blocks to look like free blocks.
2504 
2505   // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2506   // are not called when the heap is verified during universe initialization and
2507   // at vm shutdown.
2508   if (freelistLock()->owned_by_self()) {
2509     cmsSpace()->prepare_for_verify();
2510   } else {
2511     MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2512     cmsSpace()->prepare_for_verify();
2513   }
2514 }
2515 
2516 void
2517 ConcurrentMarkSweepGeneration::verify() {
2518   // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2519   // are not called when the heap is verified during universe initialization and
2520   // at vm shutdown.
2521   if (freelistLock()->owned_by_self()) {
2522     cmsSpace()->verify();
2523   } else {
2524     MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2525     cmsSpace()->verify();
2526   }
2527 }
2528 
2529 void CMSCollector::verify() {
2530   _cmsGen->verify();
2531 }
2532 
2533 #ifndef PRODUCT
2534 bool CMSCollector::overflow_list_is_empty() const {
2535   assert(_num_par_pushes >= 0, "Inconsistency");
2536   if (_overflow_list == NULL) {
2537     assert(_num_par_pushes == 0, "Inconsistency");
2538   }
2539   return _overflow_list == NULL;
2540 }
2541 
2542 // The methods verify_work_stacks_empty() and verify_overflow_empty()
2543 // merely consolidate assertion checks that appear to occur together frequently.
2544 void CMSCollector::verify_work_stacks_empty() const {
2545   assert(_markStack.isEmpty(), "Marking stack should be empty");
2546   assert(overflow_list_is_empty(), "Overflow list should be empty");
2547 }
2548 
2549 void CMSCollector::verify_overflow_empty() const {
2550   assert(overflow_list_is_empty(), "Overflow list should be empty");
2551   assert(no_preserved_marks(), "No preserved marks");
2552 }
2553 #endif // PRODUCT
2554 
2555 // Decide if we want to enable class unloading as part of the
2556 // ensuing concurrent GC cycle. We will collect and
2557 // unload classes if it's the case that:
2558 //  (a) class unloading is enabled at the command line, and
2559 //  (b) old gen is getting really full
2560 // NOTE: Provided there is no change in the state of the heap between
2561 // calls to this method, it should have idempotent results. Moreover,
2562 // its results should be monotonically increasing (i.e. going from 0 to 1,
2563 // but not 1 to 0) between successive calls between which the heap was
2564 // not collected. For the implementation below, it must thus rely on
2565 // the property that concurrent_cycles_since_last_unload()
2566 // will not decrease unless a collection cycle happened and that
2567 // _cmsGen->is_too_full() are
2568 // themselves also monotonic in that sense. See check_monotonicity()
2569 // below.
2570 void CMSCollector::update_should_unload_classes() {
2571   _should_unload_classes = false;
2572   if (CMSClassUnloadingEnabled) {
2573     _should_unload_classes = (concurrent_cycles_since_last_unload() >=
2574                               CMSClassUnloadingMaxInterval)
2575                            || _cmsGen->is_too_full();
2576   }
2577 }
2578 
2579 bool ConcurrentMarkSweepGeneration::is_too_full() const {
2580   bool res = should_concurrent_collect();
2581   res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
2582   return res;
2583 }
2584 
2585 void CMSCollector::setup_cms_unloading_and_verification_state() {
2586   const  bool should_verify =   VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
2587                              || VerifyBeforeExit;
2588   const  int  rso           =   GenCollectedHeap::SO_AllCodeCache;
2589 
2590   // We set the proper root for this CMS cycle here.
2591   if (should_unload_classes()) {   // Should unload classes this cycle
2592     remove_root_scanning_option(rso);  // Shrink the root set appropriately
2593     set_verifying(should_verify);    // Set verification state for this cycle
2594     return;                            // Nothing else needs to be done at this time
2595   }
2596 
2597   // Not unloading classes this cycle
2598   assert(!should_unload_classes(), "Inconsistency!");
2599 
2600   // If we are not unloading classes then add SO_AllCodeCache to root
2601   // scanning options.
2602   add_root_scanning_option(rso);
2603 
2604   if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
2605     set_verifying(true);
2606   } else if (verifying() && !should_verify) {
2607     // We were verifying, but some verification flags got disabled.
2608     set_verifying(false);
2609     // Exclude symbols, strings and code cache elements from root scanning to
2610     // reduce IM and RM pauses.
2611     remove_root_scanning_option(rso);
2612   }
2613 }
2614 
2615 
2616 #ifndef PRODUCT
2617 HeapWord* CMSCollector::block_start(const void* p) const {
2618   const HeapWord* addr = (HeapWord*)p;
2619   if (_span.contains(p)) {
2620     if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
2621       return _cmsGen->cmsSpace()->block_start(p);
2622     }
2623   }
2624   return NULL;
2625 }
2626 #endif
2627 
2628 HeapWord*
2629 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
2630                                                    bool   tlab,
2631                                                    bool   parallel) {
2632   CMSSynchronousYieldRequest yr;
2633   assert(!tlab, "Can't deal with TLAB allocation");
2634   MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2635   expand_for_gc_cause(word_size*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_allocation);
2636   if (GCExpandToAllocateDelayMillis > 0) {
2637     os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2638   }
2639   return have_lock_and_allocate(word_size, tlab);
2640 }
2641 
2642 void ConcurrentMarkSweepGeneration::expand_for_gc_cause(
2643     size_t bytes,
2644     size_t expand_bytes,
2645     CMSExpansionCause::Cause cause)
2646 {
2647 
2648   bool success = expand(bytes, expand_bytes);
2649 
2650   // remember why we expanded; this information is used
2651   // by shouldConcurrentCollect() when making decisions on whether to start
2652   // a new CMS cycle.
2653   if (success) {
2654     set_expansion_cause(cause);
2655     log_trace(gc)("Expanded CMS gen for %s",  CMSExpansionCause::to_string(cause));
2656   }
2657 }
2658 
2659 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
2660   HeapWord* res = NULL;
2661   MutexLocker x(ParGCRareEvent_lock);
2662   while (true) {
2663     // Expansion by some other thread might make alloc OK now:
2664     res = ps->lab.alloc(word_sz);
2665     if (res != NULL) return res;
2666     // If there's not enough expansion space available, give up.
2667     if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
2668       return NULL;
2669     }
2670     // Otherwise, we try expansion.
2671     expand_for_gc_cause(word_sz*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_lab);
2672     // Now go around the loop and try alloc again;
2673     // A competing par_promote might beat us to the expansion space,
2674     // so we may go around the loop again if promotion fails again.
2675     if (GCExpandToAllocateDelayMillis > 0) {
2676       os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2677     }
2678   }
2679 }
2680 
2681 
2682 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
2683   PromotionInfo* promo) {
2684   MutexLocker x(ParGCRareEvent_lock);
2685   size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
2686   while (true) {
2687     // Expansion by some other thread might make alloc OK now:
2688     if (promo->ensure_spooling_space()) {
2689       assert(promo->has_spooling_space(),
2690              "Post-condition of successful ensure_spooling_space()");
2691       return true;
2692     }
2693     // If there's not enough expansion space available, give up.
2694     if (_virtual_space.uncommitted_size() < refill_size_bytes) {
2695       return false;
2696     }
2697     // Otherwise, we try expansion.
2698     expand_for_gc_cause(refill_size_bytes, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_spooling_space);
2699     // Now go around the loop and try alloc again;
2700     // A competing allocation might beat us to the expansion space,
2701     // so we may go around the loop again if allocation fails again.
2702     if (GCExpandToAllocateDelayMillis > 0) {
2703       os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2704     }
2705   }
2706 }
2707 
2708 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
2709   // Only shrink if a compaction was done so that all the free space
2710   // in the generation is in a contiguous block at the end.
2711   if (did_compact()) {
2712     CardGeneration::shrink(bytes);
2713   }
2714 }
2715 
2716 void ConcurrentMarkSweepGeneration::assert_correct_size_change_locking() {
2717   assert_locked_or_safepoint(Heap_lock);
2718 }
2719 
2720 void ConcurrentMarkSweepGeneration::shrink_free_list_by(size_t bytes) {
2721   assert_locked_or_safepoint(Heap_lock);
2722   assert_lock_strong(freelistLock());
2723   log_trace(gc)("Shrinking of CMS not yet implemented");
2724   return;
2725 }
2726 
2727 
2728 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
2729 // phases.
2730 class CMSPhaseAccounting: public StackObj {
2731  public:
2732   CMSPhaseAccounting(CMSCollector *collector,
2733                      const char *title);
2734   ~CMSPhaseAccounting();
2735 
2736  private:
2737   CMSCollector *_collector;
2738   const char *_title;
2739   GCTraceConcTime(Info, gc) _trace_time;
2740 
2741  public:
2742   // Not MT-safe; so do not pass around these StackObj's
2743   // where they may be accessed by other threads.
2744   double wallclock_millis() {
2745     return TimeHelper::counter_to_millis(os::elapsed_counter() - _trace_time.start_time());
2746   }
2747 };
2748 
2749 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
2750                                        const char *title) :
2751   _collector(collector), _title(title), _trace_time(title) {
2752 
2753   _collector->resetYields();
2754   _collector->resetTimer();
2755   _collector->startTimer();
2756   _collector->gc_timer_cm()->register_gc_concurrent_start(title);
2757 }
2758 
2759 CMSPhaseAccounting::~CMSPhaseAccounting() {
2760   _collector->gc_timer_cm()->register_gc_concurrent_end();
2761   _collector->stopTimer();
2762   log_debug(gc)("Concurrent active time: %.3fms", TimeHelper::counter_to_seconds(_collector->timerTicks()));
2763   log_trace(gc)(" (CMS %s yielded %d times)", _title, _collector->yields());
2764 }
2765 
2766 // CMS work
2767 
2768 // The common parts of CMSParInitialMarkTask and CMSParRemarkTask.
2769 class CMSParMarkTask : public AbstractGangTask {
2770  protected:
2771   CMSCollector*     _collector;
2772   uint              _n_workers;
2773   OopStorage::ParState<false, false> _par_state_string;
2774   CMSParMarkTask(const char* name, CMSCollector* collector, uint n_workers) :
2775       AbstractGangTask(name),
2776       _collector(collector),
2777       _n_workers(n_workers),
2778       _par_state_string(StringTable::weak_storage()) {}
2779   // Work method in support of parallel rescan ... of young gen spaces
2780   void do_young_space_rescan(OopsInGenClosure* cl,
2781                              ContiguousSpace* space,
2782                              HeapWord** chunk_array, size_t chunk_top);
2783   void work_on_young_gen_roots(OopsInGenClosure* cl);
2784 };
2785 
2786 // Parallel initial mark task
2787 class CMSParInitialMarkTask: public CMSParMarkTask {
2788   StrongRootsScope* _strong_roots_scope;
2789  public:
2790   CMSParInitialMarkTask(CMSCollector* collector, StrongRootsScope* strong_roots_scope, uint n_workers) :
2791       CMSParMarkTask("Scan roots and young gen for initial mark in parallel", collector, n_workers),
2792       _strong_roots_scope(strong_roots_scope) {}
2793   void work(uint worker_id);
2794 };
2795 
2796 // Checkpoint the roots into this generation from outside
2797 // this generation. [Note this initial checkpoint need only
2798 // be approximate -- we'll do a catch up phase subsequently.]
2799 void CMSCollector::checkpointRootsInitial() {
2800   assert(_collectorState == InitialMarking, "Wrong collector state");
2801   check_correct_thread_executing();
2802   TraceCMSMemoryManagerStats tms(_collectorState, CMSHeap::heap()->gc_cause());
2803 
2804   save_heap_summary();
2805   report_heap_summary(GCWhen::BeforeGC);
2806 
2807   ReferenceProcessor* rp = ref_processor();
2808   assert(_restart_addr == NULL, "Control point invariant");
2809   {
2810     // acquire locks for subsequent manipulations
2811     MutexLockerEx x(bitMapLock(),
2812                     Mutex::_no_safepoint_check_flag);
2813     checkpointRootsInitialWork();
2814     // enable ("weak") refs discovery
2815     rp->enable_discovery();
2816     _collectorState = Marking;
2817   }
2818 }
2819 
2820 void CMSCollector::checkpointRootsInitialWork() {
2821   assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
2822   assert(_collectorState == InitialMarking, "just checking");
2823 
2824   // Already have locks.
2825   assert_lock_strong(bitMapLock());
2826   assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
2827 
2828   // Setup the verification and class unloading state for this
2829   // CMS collection cycle.
2830   setup_cms_unloading_and_verification_state();
2831 
2832   GCTraceTime(Trace, gc, phases) ts("checkpointRootsInitialWork", _gc_timer_cm);
2833 
2834   // Reset all the PLAB chunk arrays if necessary.
2835   if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
2836     reset_survivor_plab_arrays();
2837   }
2838 
2839   ResourceMark rm;
2840   HandleMark  hm;
2841 
2842   MarkRefsIntoClosure notOlder(_span, &_markBitMap);
2843   CMSHeap* heap = CMSHeap::heap();
2844 
2845   verify_work_stacks_empty();
2846   verify_overflow_empty();
2847 
2848   heap->ensure_parsability(false);  // fill TLABs, but no need to retire them
2849   // Update the saved marks which may affect the root scans.
2850   heap->save_marks();
2851 
2852   // weak reference processing has not started yet.
2853   ref_processor()->set_enqueuing_is_done(false);
2854 
2855   // Need to remember all newly created CLDs,
2856   // so that we can guarantee that the remark finds them.
2857   ClassLoaderDataGraph::remember_new_clds(true);
2858 
2859   // Whenever a CLD is found, it will be claimed before proceeding to mark
2860   // the klasses. The claimed marks need to be cleared before marking starts.
2861   ClassLoaderDataGraph::clear_claimed_marks();
2862 
2863   print_eden_and_survivor_chunk_arrays();
2864 
2865   {
2866 #if COMPILER2_OR_JVMCI
2867     DerivedPointerTableDeactivate dpt_deact;
2868 #endif
2869     if (CMSParallelInitialMarkEnabled) {
2870       // The parallel version.
2871       WorkGang* workers = heap->workers();
2872       assert(workers != NULL, "Need parallel worker threads.");
2873       uint n_workers = workers->active_workers();
2874 
2875       StrongRootsScope srs(n_workers);
2876 
2877       CMSParInitialMarkTask tsk(this, &srs, n_workers);
2878       initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
2879       // If the total workers is greater than 1, then multiple workers
2880       // may be used at some time and the initialization has been set
2881       // such that the single threaded path cannot be used.
2882       if (workers->total_workers() > 1) {
2883         workers->run_task(&tsk);
2884       } else {
2885         tsk.work(0);
2886       }
2887     } else {
2888       // The serial version.
2889       CLDToOopClosure cld_closure(&notOlder, true);
2890       heap->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2891 
2892       StrongRootsScope srs(1);
2893 
2894       heap->cms_process_roots(&srs,
2895                              true,   // young gen as roots
2896                              GenCollectedHeap::ScanningOption(roots_scanning_options()),
2897                              should_unload_classes(),
2898                              &notOlder,
2899                              &cld_closure);
2900     }
2901   }
2902 
2903   // Clear mod-union table; it will be dirtied in the prologue of
2904   // CMS generation per each young generation collection.
2905 
2906   assert(_modUnionTable.isAllClear(),
2907        "Was cleared in most recent final checkpoint phase"
2908        " or no bits are set in the gc_prologue before the start of the next "
2909        "subsequent marking phase.");
2910 
2911   assert(_ct->cld_rem_set()->mod_union_is_clear(), "Must be");
2912 
2913   // Save the end of the used_region of the constituent generations
2914   // to be used to limit the extent of sweep in each generation.
2915   save_sweep_limits();
2916   verify_overflow_empty();
2917 }
2918 
2919 bool CMSCollector::markFromRoots() {
2920   // we might be tempted to assert that:
2921   // assert(!SafepointSynchronize::is_at_safepoint(),
2922   //        "inconsistent argument?");
2923   // However that wouldn't be right, because it's possible that
2924   // a safepoint is indeed in progress as a young generation
2925   // stop-the-world GC happens even as we mark in this generation.
2926   assert(_collectorState == Marking, "inconsistent state?");
2927   check_correct_thread_executing();
2928   verify_overflow_empty();
2929 
2930   // Weak ref discovery note: We may be discovering weak
2931   // refs in this generation concurrent (but interleaved) with
2932   // weak ref discovery by the young generation collector.
2933 
2934   CMSTokenSyncWithLocks ts(true, bitMapLock());
2935   GCTraceCPUTime tcpu;
2936   CMSPhaseAccounting pa(this, "Concurrent Mark");
2937   bool res = markFromRootsWork();
2938   if (res) {
2939     _collectorState = Precleaning;
2940   } else { // We failed and a foreground collection wants to take over
2941     assert(_foregroundGCIsActive, "internal state inconsistency");
2942     assert(_restart_addr == NULL,  "foreground will restart from scratch");
2943     log_debug(gc)("bailing out to foreground collection");
2944   }
2945   verify_overflow_empty();
2946   return res;
2947 }
2948 
2949 bool CMSCollector::markFromRootsWork() {
2950   // iterate over marked bits in bit map, doing a full scan and mark
2951   // from these roots using the following algorithm:
2952   // . if oop is to the right of the current scan pointer,
2953   //   mark corresponding bit (we'll process it later)
2954   // . else (oop is to left of current scan pointer)
2955   //   push oop on marking stack
2956   // . drain the marking stack
2957 
2958   // Note that when we do a marking step we need to hold the
2959   // bit map lock -- recall that direct allocation (by mutators)
2960   // and promotion (by the young generation collector) is also
2961   // marking the bit map. [the so-called allocate live policy.]
2962   // Because the implementation of bit map marking is not
2963   // robust wrt simultaneous marking of bits in the same word,
2964   // we need to make sure that there is no such interference
2965   // between concurrent such updates.
2966 
2967   // already have locks
2968   assert_lock_strong(bitMapLock());
2969 
2970   verify_work_stacks_empty();
2971   verify_overflow_empty();
2972   bool result = false;
2973   if (CMSConcurrentMTEnabled && ConcGCThreads > 0) {
2974     result = do_marking_mt();
2975   } else {
2976     result = do_marking_st();
2977   }
2978   return result;
2979 }
2980 
2981 // Forward decl
2982 class CMSConcMarkingTask;
2983 
2984 class CMSConcMarkingTerminator: public ParallelTaskTerminator {
2985   CMSCollector*       _collector;
2986   CMSConcMarkingTask* _task;
2987  public:
2988   virtual void yield();
2989 
2990   // "n_threads" is the number of threads to be terminated.
2991   // "queue_set" is a set of work queues of other threads.
2992   // "collector" is the CMS collector associated with this task terminator.
2993   // "yield" indicates whether we need the gang as a whole to yield.
2994   CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
2995     ParallelTaskTerminator(n_threads, queue_set),
2996     _collector(collector) { }
2997 
2998   void set_task(CMSConcMarkingTask* task) {
2999     _task = task;
3000   }
3001 };
3002 
3003 class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator {
3004   CMSConcMarkingTask* _task;
3005  public:
3006   bool should_exit_termination();
3007   void set_task(CMSConcMarkingTask* task) {
3008     _task = task;
3009   }
3010 };
3011 
3012 // MT Concurrent Marking Task
3013 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3014   CMSCollector*             _collector;
3015   uint                      _n_workers;      // requested/desired # workers
3016   bool                      _result;
3017   CompactibleFreeListSpace* _cms_space;
3018   char                      _pad_front[64];   // padding to ...
3019   HeapWord* volatile        _global_finger;   // ... avoid sharing cache line
3020   char                      _pad_back[64];
3021   HeapWord*                 _restart_addr;
3022 
3023   //  Exposed here for yielding support
3024   Mutex* const _bit_map_lock;
3025 
3026   // The per thread work queues, available here for stealing
3027   OopTaskQueueSet*  _task_queues;
3028 
3029   // Termination (and yielding) support
3030   CMSConcMarkingTerminator _term;
3031   CMSConcMarkingTerminatorTerminator _term_term;
3032 
3033  public:
3034   CMSConcMarkingTask(CMSCollector* collector,
3035                  CompactibleFreeListSpace* cms_space,
3036                  YieldingFlexibleWorkGang* workers,
3037                  OopTaskQueueSet* task_queues):
3038     YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3039     _collector(collector),
3040     _cms_space(cms_space),
3041     _n_workers(0), _result(true),
3042     _task_queues(task_queues),
3043     _term(_n_workers, task_queues, _collector),
3044     _bit_map_lock(collector->bitMapLock())
3045   {
3046     _requested_size = _n_workers;
3047     _term.set_task(this);
3048     _term_term.set_task(this);
3049     _restart_addr = _global_finger = _cms_space->bottom();
3050   }
3051 
3052 
3053   OopTaskQueueSet* task_queues()  { return _task_queues; }
3054 
3055   OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3056 
3057   HeapWord* volatile* global_finger_addr() { return &_global_finger; }
3058 
3059   CMSConcMarkingTerminator* terminator() { return &_term; }
3060 
3061   virtual void set_for_termination(uint active_workers) {
3062     terminator()->reset_for_reuse(active_workers);
3063   }
3064 
3065   void work(uint worker_id);
3066   bool should_yield() {
3067     return    ConcurrentMarkSweepThread::should_yield()
3068            && !_collector->foregroundGCIsActive();
3069   }
3070 
3071   virtual void coordinator_yield();  // stuff done by coordinator
3072   bool result() { return _result; }
3073 
3074   void reset(HeapWord* ra) {
3075     assert(_global_finger >= _cms_space->end(),  "Postcondition of ::work(i)");
3076     _restart_addr = _global_finger = ra;
3077     _term.reset_for_reuse();
3078   }
3079 
3080   static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3081                                            OopTaskQueue* work_q);
3082 
3083  private:
3084   void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3085   void do_work_steal(int i);
3086   void bump_global_finger(HeapWord* f);
3087 };
3088 
3089 bool CMSConcMarkingTerminatorTerminator::should_exit_termination() {
3090   assert(_task != NULL, "Error");
3091   return _task->yielding();
3092   // Note that we do not need the disjunct || _task->should_yield() above
3093   // because we want terminating threads to yield only if the task
3094   // is already in the midst of yielding, which happens only after at least one
3095   // thread has yielded.
3096 }
3097 
3098 void CMSConcMarkingTerminator::yield() {
3099   if (_task->should_yield()) {
3100     _task->yield();
3101   } else {
3102     ParallelTaskTerminator::yield();
3103   }
3104 }
3105 
3106 ////////////////////////////////////////////////////////////////
3107 // Concurrent Marking Algorithm Sketch
3108 ////////////////////////////////////////////////////////////////
3109 // Until all tasks exhausted (both spaces):
3110 // -- claim next available chunk
3111 // -- bump global finger via CAS
3112 // -- find first object that starts in this chunk
3113 //    and start scanning bitmap from that position
3114 // -- scan marked objects for oops
3115 // -- CAS-mark target, and if successful:
3116 //    . if target oop is above global finger (volatile read)
3117 //      nothing to do
3118 //    . if target oop is in chunk and above local finger
3119 //        then nothing to do
3120 //    . else push on work-queue
3121 // -- Deal with possible overflow issues:
3122 //    . local work-queue overflow causes stuff to be pushed on
3123 //      global (common) overflow queue
3124 //    . always first empty local work queue
3125 //    . then get a batch of oops from global work queue if any
3126 //    . then do work stealing
3127 // -- When all tasks claimed (both spaces)
3128 //    and local work queue empty,
3129 //    then in a loop do:
3130 //    . check global overflow stack; steal a batch of oops and trace
3131 //    . try to steal from other threads oif GOS is empty
3132 //    . if neither is available, offer termination
3133 // -- Terminate and return result
3134 //
3135 void CMSConcMarkingTask::work(uint worker_id) {
3136   elapsedTimer _timer;
3137   ResourceMark rm;
3138   HandleMark hm;
3139 
3140   DEBUG_ONLY(_collector->verify_overflow_empty();)
3141 
3142   // Before we begin work, our work queue should be empty
3143   assert(work_queue(worker_id)->size() == 0, "Expected to be empty");
3144   // Scan the bitmap covering _cms_space, tracing through grey objects.
3145   _timer.start();
3146   do_scan_and_mark(worker_id, _cms_space);
3147   _timer.stop();
3148   log_trace(gc, task)("Finished cms space scanning in %dth thread: %3.3f sec", worker_id, _timer.seconds());
3149 
3150   // ... do work stealing
3151   _timer.reset();
3152   _timer.start();
3153   do_work_steal(worker_id);
3154   _timer.stop();
3155   log_trace(gc, task)("Finished work stealing in %dth thread: %3.3f sec", worker_id, _timer.seconds());
3156   assert(_collector->_markStack.isEmpty(), "Should have been emptied");
3157   assert(work_queue(worker_id)->size() == 0, "Should have been emptied");
3158   // Note that under the current task protocol, the
3159   // following assertion is true even of the spaces
3160   // expanded since the completion of the concurrent
3161   // marking. XXX This will likely change under a strict
3162   // ABORT semantics.
3163   // After perm removal the comparison was changed to
3164   // greater than or equal to from strictly greater than.
3165   // Before perm removal the highest address sweep would
3166   // have been at the end of perm gen but now is at the
3167   // end of the tenured gen.
3168   assert(_global_finger >=  _cms_space->end(),
3169          "All tasks have been completed");
3170   DEBUG_ONLY(_collector->verify_overflow_empty();)
3171 }
3172 
3173 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
3174   HeapWord* read = _global_finger;
3175   HeapWord* cur  = read;
3176   while (f > read) {
3177     cur = read;
3178     read = Atomic::cmpxchg(f, &_global_finger, cur);
3179     if (cur == read) {
3180       // our cas succeeded
3181       assert(_global_finger >= f, "protocol consistency");
3182       break;
3183     }
3184   }
3185 }
3186 
3187 // This is really inefficient, and should be redone by
3188 // using (not yet available) block-read and -write interfaces to the
3189 // stack and the work_queue. XXX FIX ME !!!
3190 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3191                                                       OopTaskQueue* work_q) {
3192   // Fast lock-free check
3193   if (ovflw_stk->length() == 0) {
3194     return false;
3195   }
3196   assert(work_q->size() == 0, "Shouldn't steal");
3197   MutexLockerEx ml(ovflw_stk->par_lock(),
3198                    Mutex::_no_safepoint_check_flag);
3199   // Grab up to 1/4 the size of the work queue
3200   size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
3201                     (size_t)ParGCDesiredObjsFromOverflowList);
3202   num = MIN2(num, ovflw_stk->length());
3203   for (int i = (int) num; i > 0; i--) {
3204     oop cur = ovflw_stk->pop();
3205     assert(cur != NULL, "Counted wrong?");
3206     work_q->push(cur);
3207   }
3208   return num > 0;
3209 }
3210 
3211 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
3212   SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
3213   int n_tasks = pst->n_tasks();
3214   // We allow that there may be no tasks to do here because
3215   // we are restarting after a stack overflow.
3216   assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
3217   uint nth_task = 0;
3218 
3219   HeapWord* aligned_start = sp->bottom();
3220   if (sp->used_region().contains(_restart_addr)) {
3221     // Align down to a card boundary for the start of 0th task
3222     // for this space.
3223     aligned_start = align_down(_restart_addr, CardTable::card_size);
3224   }
3225 
3226   size_t chunk_size = sp->marking_task_size();
3227   while (!pst->is_task_claimed(/* reference */ nth_task)) {
3228     // Having claimed the nth task in this space,
3229     // compute the chunk that it corresponds to:
3230     MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
3231                                aligned_start + (nth_task+1)*chunk_size);
3232     // Try and bump the global finger via a CAS;
3233     // note that we need to do the global finger bump
3234     // _before_ taking the intersection below, because
3235     // the task corresponding to that region will be
3236     // deemed done even if the used_region() expands
3237     // because of allocation -- as it almost certainly will
3238     // during start-up while the threads yield in the
3239     // closure below.
3240     HeapWord* finger = span.end();
3241     bump_global_finger(finger);   // atomically
3242     // There are null tasks here corresponding to chunks
3243     // beyond the "top" address of the space.
3244     span = span.intersection(sp->used_region());
3245     if (!span.is_empty()) {  // Non-null task
3246       HeapWord* prev_obj;
3247       assert(!span.contains(_restart_addr) || nth_task == 0,
3248              "Inconsistency");
3249       if (nth_task == 0) {
3250         // For the 0th task, we'll not need to compute a block_start.
3251         if (span.contains(_restart_addr)) {
3252           // In the case of a restart because of stack overflow,
3253           // we might additionally skip a chunk prefix.
3254           prev_obj = _restart_addr;
3255         } else {
3256           prev_obj = span.start();
3257         }
3258       } else {
3259         // We want to skip the first object because
3260         // the protocol is to scan any object in its entirety
3261         // that _starts_ in this span; a fortiori, any
3262         // object starting in an earlier span is scanned
3263         // as part of an earlier claimed task.
3264         // Below we use the "careful" version of block_start
3265         // so we do not try to navigate uninitialized objects.
3266         prev_obj = sp->block_start_careful(span.start());
3267         // Below we use a variant of block_size that uses the
3268         // Printezis bits to avoid waiting for allocated
3269         // objects to become initialized/parsable.
3270         while (prev_obj < span.start()) {
3271           size_t sz = sp->block_size_no_stall(prev_obj, _collector);
3272           if (sz > 0) {
3273             prev_obj += sz;
3274           } else {
3275             // In this case we may end up doing a bit of redundant
3276             // scanning, but that appears unavoidable, short of
3277             // locking the free list locks; see bug 6324141.
3278             break;
3279           }
3280         }
3281       }
3282       if (prev_obj < span.end()) {
3283         MemRegion my_span = MemRegion(prev_obj, span.end());
3284         // Do the marking work within a non-empty span --
3285         // the last argument to the constructor indicates whether the
3286         // iteration should be incremental with periodic yields.
3287         ParMarkFromRootsClosure cl(this, _collector, my_span,
3288                                    &_collector->_markBitMap,
3289                                    work_queue(i),
3290                                    &_collector->_markStack);
3291         _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
3292       } // else nothing to do for this task
3293     }   // else nothing to do for this task
3294   }
3295   // We'd be tempted to assert here that since there are no
3296   // more tasks left to claim in this space, the global_finger
3297   // must exceed space->top() and a fortiori space->end(). However,
3298   // that would not quite be correct because the bumping of
3299   // global_finger occurs strictly after the claiming of a task,
3300   // so by the time we reach here the global finger may not yet
3301   // have been bumped up by the thread that claimed the last
3302   // task.
3303   pst->all_tasks_completed();
3304 }
3305 
3306 class ParConcMarkingClosure: public MetadataAwareOopClosure {
3307  private:
3308   CMSCollector* _collector;
3309   CMSConcMarkingTask* _task;
3310   MemRegion     _span;
3311   CMSBitMap*    _bit_map;
3312   CMSMarkStack* _overflow_stack;
3313   OopTaskQueue* _work_queue;
3314  protected:
3315   DO_OOP_WORK_DEFN
3316  public:
3317   ParConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue,
3318                         CMSBitMap* bit_map, CMSMarkStack* overflow_stack):
3319     MetadataAwareOopClosure(collector->ref_processor()),
3320     _collector(collector),
3321     _task(task),
3322     _span(collector->_span),
3323     _work_queue(work_queue),
3324     _bit_map(bit_map),
3325     _overflow_stack(overflow_stack)
3326   { }
3327   virtual void do_oop(oop* p);
3328   virtual void do_oop(narrowOop* p);
3329 
3330   void trim_queue(size_t max);
3331   void handle_stack_overflow(HeapWord* lost);
3332   void do_yield_check() {
3333     if (_task->should_yield()) {
3334       _task->yield();
3335     }
3336   }
3337 };
3338 
3339 DO_OOP_WORK_IMPL(ParConcMarkingClosure)
3340 
3341 // Grey object scanning during work stealing phase --
3342 // the salient assumption here is that any references
3343 // that are in these stolen objects being scanned must
3344 // already have been initialized (else they would not have
3345 // been published), so we do not need to check for
3346 // uninitialized objects before pushing here.
3347 void ParConcMarkingClosure::do_oop(oop obj) {
3348   assert(oopDesc::is_oop_or_null(obj, true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
3349   HeapWord* addr = (HeapWord*)obj;
3350   // Check if oop points into the CMS generation
3351   // and is not marked
3352   if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
3353     // a white object ...
3354     // If we manage to "claim" the object, by being the
3355     // first thread to mark it, then we push it on our
3356     // marking stack
3357     if (_bit_map->par_mark(addr)) {     // ... now grey
3358       // push on work queue (grey set)
3359       bool simulate_overflow = false;
3360       NOT_PRODUCT(
3361         if (CMSMarkStackOverflowALot &&
3362             _collector->simulate_overflow()) {
3363           // simulate a stack overflow
3364           simulate_overflow = true;
3365         }
3366       )
3367       if (simulate_overflow ||
3368           !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
3369         // stack overflow
3370         log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _overflow_stack->capacity());
3371         // We cannot assert that the overflow stack is full because
3372         // it may have been emptied since.
3373         assert(simulate_overflow ||
3374                _work_queue->size() == _work_queue->max_elems(),
3375               "Else push should have succeeded");
3376         handle_stack_overflow(addr);
3377       }
3378     } // Else, some other thread got there first
3379     do_yield_check();
3380   }
3381 }
3382 
3383 void ParConcMarkingClosure::do_oop(oop* p)       { ParConcMarkingClosure::do_oop_work(p); }
3384 void ParConcMarkingClosure::do_oop(narrowOop* p) { ParConcMarkingClosure::do_oop_work(p); }
3385 
3386 void ParConcMarkingClosure::trim_queue(size_t max) {
3387   while (_work_queue->size() > max) {
3388     oop new_oop;
3389     if (_work_queue->pop_local(new_oop)) {
3390       assert(oopDesc::is_oop(new_oop), "Should be an oop");
3391       assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
3392       assert(_span.contains((HeapWord*)new_oop), "Not in span");
3393       new_oop->oop_iterate(this);  // do_oop() above
3394       do_yield_check();
3395     }
3396   }
3397 }
3398 
3399 // Upon stack overflow, we discard (part of) the stack,
3400 // remembering the least address amongst those discarded
3401 // in CMSCollector's _restart_address.
3402 void ParConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
3403   // We need to do this under a mutex to prevent other
3404   // workers from interfering with the work done below.
3405   MutexLockerEx ml(_overflow_stack->par_lock(),
3406                    Mutex::_no_safepoint_check_flag);
3407   // Remember the least grey address discarded
3408   HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
3409   _collector->lower_restart_addr(ra);
3410   _overflow_stack->reset();  // discard stack contents
3411   _overflow_stack->expand(); // expand the stack if possible
3412 }
3413 
3414 
3415 void CMSConcMarkingTask::do_work_steal(int i) {
3416   OopTaskQueue* work_q = work_queue(i);
3417   oop obj_to_scan;
3418   CMSBitMap* bm = &(_collector->_markBitMap);
3419   CMSMarkStack* ovflw = &(_collector->_markStack);
3420   int* seed = _collector->hash_seed(i);
3421   ParConcMarkingClosure cl(_collector, this, work_q, bm, ovflw);
3422   while (true) {
3423     cl.trim_queue(0);
3424     assert(work_q->size() == 0, "Should have been emptied above");
3425     if (get_work_from_overflow_stack(ovflw, work_q)) {
3426       // Can't assert below because the work obtained from the
3427       // overflow stack may already have been stolen from us.
3428       // assert(work_q->size() > 0, "Work from overflow stack");
3429       continue;
3430     } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
3431       assert(oopDesc::is_oop(obj_to_scan), "Should be an oop");
3432       assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
3433       obj_to_scan->oop_iterate(&cl);
3434     } else if (terminator()->offer_termination(&_term_term)) {
3435       assert(work_q->size() == 0, "Impossible!");
3436       break;
3437     } else if (yielding() || should_yield()) {
3438       yield();
3439     }
3440   }
3441 }
3442 
3443 // This is run by the CMS (coordinator) thread.
3444 void CMSConcMarkingTask::coordinator_yield() {
3445   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3446          "CMS thread should hold CMS token");
3447   // First give up the locks, then yield, then re-lock
3448   // We should probably use a constructor/destructor idiom to
3449   // do this unlock/lock or modify the MutexUnlocker class to
3450   // serve our purpose. XXX
3451   assert_lock_strong(_bit_map_lock);
3452   _bit_map_lock->unlock();
3453   ConcurrentMarkSweepThread::desynchronize(true);
3454   _collector->stopTimer();
3455   _collector->incrementYields();
3456 
3457   // It is possible for whichever thread initiated the yield request
3458   // not to get a chance to wake up and take the bitmap lock between
3459   // this thread releasing it and reacquiring it. So, while the
3460   // should_yield() flag is on, let's sleep for a bit to give the
3461   // other thread a chance to wake up. The limit imposed on the number
3462   // of iterations is defensive, to avoid any unforseen circumstances
3463   // putting us into an infinite loop. Since it's always been this
3464   // (coordinator_yield()) method that was observed to cause the
3465   // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
3466   // which is by default non-zero. For the other seven methods that
3467   // also perform the yield operation, as are using a different
3468   // parameter (CMSYieldSleepCount) which is by default zero. This way we
3469   // can enable the sleeping for those methods too, if necessary.
3470   // See 6442774.
3471   //
3472   // We really need to reconsider the synchronization between the GC
3473   // thread and the yield-requesting threads in the future and we
3474   // should really use wait/notify, which is the recommended
3475   // way of doing this type of interaction. Additionally, we should
3476   // consolidate the eight methods that do the yield operation and they
3477   // are almost identical into one for better maintainability and
3478   // readability. See 6445193.
3479   //
3480   // Tony 2006.06.29
3481   for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
3482                    ConcurrentMarkSweepThread::should_yield() &&
3483                    !CMSCollector::foregroundGCIsActive(); ++i) {
3484     os::sleep(Thread::current(), 1, false);
3485   }
3486 
3487   ConcurrentMarkSweepThread::synchronize(true);
3488   _bit_map_lock->lock_without_safepoint_check();
3489   _collector->startTimer();
3490 }
3491 
3492 bool CMSCollector::do_marking_mt() {
3493   assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition");
3494   uint num_workers = AdaptiveSizePolicy::calc_active_conc_workers(conc_workers()->total_workers(),
3495                                                                   conc_workers()->active_workers(),
3496                                                                   Threads::number_of_non_daemon_threads());
3497   num_workers = conc_workers()->update_active_workers(num_workers);
3498   log_info(gc,task)("Using %u workers of %u for marking", num_workers, conc_workers()->total_workers());
3499 
3500   CompactibleFreeListSpace* cms_space  = _cmsGen->cmsSpace();
3501 
3502   CMSConcMarkingTask tsk(this,
3503                          cms_space,
3504                          conc_workers(),
3505                          task_queues());
3506 
3507   // Since the actual number of workers we get may be different
3508   // from the number we requested above, do we need to do anything different
3509   // below? In particular, may be we need to subclass the SequantialSubTasksDone
3510   // class?? XXX
3511   cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
3512 
3513   // Refs discovery is already non-atomic.
3514   assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
3515   assert(ref_processor()->discovery_is_mt(), "Discovery should be MT");
3516   conc_workers()->start_task(&tsk);
3517   while (tsk.yielded()) {
3518     tsk.coordinator_yield();
3519     conc_workers()->continue_task(&tsk);
3520   }
3521   // If the task was aborted, _restart_addr will be non-NULL
3522   assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
3523   while (_restart_addr != NULL) {
3524     // XXX For now we do not make use of ABORTED state and have not
3525     // yet implemented the right abort semantics (even in the original
3526     // single-threaded CMS case). That needs some more investigation
3527     // and is deferred for now; see CR# TBF. 07252005YSR. XXX
3528     assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
3529     // If _restart_addr is non-NULL, a marking stack overflow
3530     // occurred; we need to do a fresh marking iteration from the
3531     // indicated restart address.
3532     if (_foregroundGCIsActive) {
3533       // We may be running into repeated stack overflows, having
3534       // reached the limit of the stack size, while making very
3535       // slow forward progress. It may be best to bail out and
3536       // let the foreground collector do its job.
3537       // Clear _restart_addr, so that foreground GC
3538       // works from scratch. This avoids the headache of
3539       // a "rescan" which would otherwise be needed because
3540       // of the dirty mod union table & card table.
3541       _restart_addr = NULL;
3542       return false;
3543     }
3544     // Adjust the task to restart from _restart_addr
3545     tsk.reset(_restart_addr);
3546     cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
3547                   _restart_addr);
3548     _restart_addr = NULL;
3549     // Get the workers going again
3550     conc_workers()->start_task(&tsk);
3551     while (tsk.yielded()) {
3552       tsk.coordinator_yield();
3553       conc_workers()->continue_task(&tsk);
3554     }
3555   }
3556   assert(tsk.completed(), "Inconsistency");
3557   assert(tsk.result() == true, "Inconsistency");
3558   return true;
3559 }
3560 
3561 bool CMSCollector::do_marking_st() {
3562   ResourceMark rm;
3563   HandleMark   hm;
3564 
3565   // Temporarily make refs discovery single threaded (non-MT)
3566   ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
3567   MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
3568     &_markStack, CMSYield);
3569   // the last argument to iterate indicates whether the iteration
3570   // should be incremental with periodic yields.
3571   _markBitMap.iterate(&markFromRootsClosure);
3572   // If _restart_addr is non-NULL, a marking stack overflow
3573   // occurred; we need to do a fresh iteration from the
3574   // indicated restart address.
3575   while (_restart_addr != NULL) {
3576     if (_foregroundGCIsActive) {
3577       // We may be running into repeated stack overflows, having
3578       // reached the limit of the stack size, while making very
3579       // slow forward progress. It may be best to bail out and
3580       // let the foreground collector do its job.
3581       // Clear _restart_addr, so that foreground GC
3582       // works from scratch. This avoids the headache of
3583       // a "rescan" which would otherwise be needed because
3584       // of the dirty mod union table & card table.
3585       _restart_addr = NULL;
3586       return false;  // indicating failure to complete marking
3587     }
3588     // Deal with stack overflow:
3589     // we restart marking from _restart_addr
3590     HeapWord* ra = _restart_addr;
3591     markFromRootsClosure.reset(ra);
3592     _restart_addr = NULL;
3593     _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
3594   }
3595   return true;
3596 }
3597 
3598 void CMSCollector::preclean() {
3599   check_correct_thread_executing();
3600   assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
3601   verify_work_stacks_empty();
3602   verify_overflow_empty();
3603   _abort_preclean = false;
3604   if (CMSPrecleaningEnabled) {
3605     if (!CMSEdenChunksRecordAlways) {
3606       _eden_chunk_index = 0;
3607     }
3608     size_t used = get_eden_used();
3609     size_t capacity = get_eden_capacity();
3610     // Don't start sampling unless we will get sufficiently
3611     // many samples.
3612     if (used < (((capacity / CMSScheduleRemarkSamplingRatio) / 100)
3613                 * CMSScheduleRemarkEdenPenetration)) {
3614       _start_sampling = true;
3615     } else {
3616       _start_sampling = false;
3617     }
3618     GCTraceCPUTime tcpu;
3619     CMSPhaseAccounting pa(this, "Concurrent Preclean");
3620     preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
3621   }
3622   CMSTokenSync x(true); // is cms thread
3623   if (CMSPrecleaningEnabled) {
3624     sample_eden();
3625     _collectorState = AbortablePreclean;
3626   } else {
3627     _collectorState = FinalMarking;
3628   }
3629   verify_work_stacks_empty();
3630   verify_overflow_empty();
3631 }
3632 
3633 // Try and schedule the remark such that young gen
3634 // occupancy is CMSScheduleRemarkEdenPenetration %.
3635 void CMSCollector::abortable_preclean() {
3636   check_correct_thread_executing();
3637   assert(CMSPrecleaningEnabled,  "Inconsistent control state");
3638   assert(_collectorState == AbortablePreclean, "Inconsistent control state");
3639 
3640   // If Eden's current occupancy is below this threshold,
3641   // immediately schedule the remark; else preclean
3642   // past the next scavenge in an effort to
3643   // schedule the pause as described above. By choosing
3644   // CMSScheduleRemarkEdenSizeThreshold >= max eden size
3645   // we will never do an actual abortable preclean cycle.
3646   if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
3647     GCTraceCPUTime tcpu;
3648     CMSPhaseAccounting pa(this, "Concurrent Abortable Preclean");
3649     // We need more smarts in the abortable preclean
3650     // loop below to deal with cases where allocation
3651     // in young gen is very very slow, and our precleaning
3652     // is running a losing race against a horde of
3653     // mutators intent on flooding us with CMS updates
3654     // (dirty cards).
3655     // One, admittedly dumb, strategy is to give up
3656     // after a certain number of abortable precleaning loops
3657     // or after a certain maximum time. We want to make
3658     // this smarter in the next iteration.
3659     // XXX FIX ME!!! YSR
3660     size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
3661     while (!(should_abort_preclean() ||
3662              ConcurrentMarkSweepThread::cmst()->should_terminate())) {
3663       workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
3664       cumworkdone += workdone;
3665       loops++;
3666       // Voluntarily terminate abortable preclean phase if we have
3667       // been at it for too long.
3668       if ((CMSMaxAbortablePrecleanLoops != 0) &&
3669           loops >= CMSMaxAbortablePrecleanLoops) {
3670         log_debug(gc)(" CMS: abort preclean due to loops ");
3671         break;
3672       }
3673       if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
3674         log_debug(gc)(" CMS: abort preclean due to time ");
3675         break;
3676       }
3677       // If we are doing little work each iteration, we should
3678       // take a short break.
3679       if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
3680         // Sleep for some time, waiting for work to accumulate
3681         stopTimer();
3682         cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
3683         startTimer();
3684         waited++;
3685       }
3686     }
3687     log_trace(gc)(" [" SIZE_FORMAT " iterations, " SIZE_FORMAT " waits, " SIZE_FORMAT " cards)] ",
3688                                loops, waited, cumworkdone);
3689   }
3690   CMSTokenSync x(true); // is cms thread
3691   if (_collectorState != Idling) {
3692     assert(_collectorState == AbortablePreclean,
3693            "Spontaneous state transition?");
3694     _collectorState = FinalMarking;
3695   } // Else, a foreground collection completed this CMS cycle.
3696   return;
3697 }
3698 
3699 // Respond to an Eden sampling opportunity
3700 void CMSCollector::sample_eden() {
3701   // Make sure a young gc cannot sneak in between our
3702   // reading and recording of a sample.
3703   assert(Thread::current()->is_ConcurrentGC_thread(),
3704          "Only the cms thread may collect Eden samples");
3705   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3706          "Should collect samples while holding CMS token");
3707   if (!_start_sampling) {
3708     return;
3709   }
3710   // When CMSEdenChunksRecordAlways is true, the eden chunk array
3711   // is populated by the young generation.
3712   if (_eden_chunk_array != NULL && !CMSEdenChunksRecordAlways) {
3713     if (_eden_chunk_index < _eden_chunk_capacity) {
3714       _eden_chunk_array[_eden_chunk_index] = *_top_addr;   // take sample
3715       assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
3716              "Unexpected state of Eden");
3717       // We'd like to check that what we just sampled is an oop-start address;
3718       // however, we cannot do that here since the object may not yet have been
3719       // initialized. So we'll instead do the check when we _use_ this sample
3720       // later.
3721       if (_eden_chunk_index == 0 ||
3722           (pointer_delta(_eden_chunk_array[_eden_chunk_index],
3723                          _eden_chunk_array[_eden_chunk_index-1])
3724            >= CMSSamplingGrain)) {
3725         _eden_chunk_index++;  // commit sample
3726       }
3727     }
3728   }
3729   if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
3730     size_t used = get_eden_used();
3731     size_t capacity = get_eden_capacity();
3732     assert(used <= capacity, "Unexpected state of Eden");
3733     if (used >  (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
3734       _abort_preclean = true;
3735     }
3736   }
3737 }
3738 
3739 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
3740   assert(_collectorState == Precleaning ||
3741          _collectorState == AbortablePreclean, "incorrect state");
3742   ResourceMark rm;
3743   HandleMark   hm;
3744 
3745   // Precleaning is currently not MT but the reference processor
3746   // may be set for MT.  Disable it temporarily here.
3747   ReferenceProcessor* rp = ref_processor();
3748   ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false);
3749 
3750   // Do one pass of scrubbing the discovered reference lists
3751   // to remove any reference objects with strongly-reachable
3752   // referents.
3753   if (clean_refs) {
3754     CMSPrecleanRefsYieldClosure yield_cl(this);
3755     assert(_span_based_discoverer.span().equals(_span), "Spans should be equal");
3756     CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
3757                                    &_markStack, true /* preclean */);
3758     CMSDrainMarkingStackClosure complete_trace(this,
3759                                    _span, &_markBitMap, &_markStack,
3760                                    &keep_alive, true /* preclean */);
3761 
3762     // We don't want this step to interfere with a young
3763     // collection because we don't want to take CPU
3764     // or memory bandwidth away from the young GC threads
3765     // (which may be as many as there are CPUs).
3766     // Note that we don't need to protect ourselves from
3767     // interference with mutators because they can't
3768     // manipulate the discovered reference lists nor affect
3769     // the computed reachability of the referents, the
3770     // only properties manipulated by the precleaning
3771     // of these reference lists.
3772     stopTimer();
3773     CMSTokenSyncWithLocks x(true /* is cms thread */,
3774                             bitMapLock());
3775     startTimer();
3776     sample_eden();
3777 
3778     // The following will yield to allow foreground
3779     // collection to proceed promptly. XXX YSR:
3780     // The code in this method may need further
3781     // tweaking for better performance and some restructuring
3782     // for cleaner interfaces.
3783     GCTimer *gc_timer = NULL; // Currently not tracing concurrent phases
3784     rp->preclean_discovered_references(
3785           rp->is_alive_non_header(), &keep_alive, &complete_trace, &yield_cl,
3786           gc_timer);
3787   }
3788 
3789   if (clean_survivor) {  // preclean the active survivor space(s)
3790     PushAndMarkClosure pam_cl(this, _span, ref_processor(),
3791                              &_markBitMap, &_modUnionTable,
3792                              &_markStack, true /* precleaning phase */);
3793     stopTimer();
3794     CMSTokenSyncWithLocks ts(true /* is cms thread */,
3795                              bitMapLock());
3796     startTimer();
3797     unsigned int before_count =
3798       CMSHeap::heap()->total_collections();
3799     SurvivorSpacePrecleanClosure
3800       sss_cl(this, _span, &_markBitMap, &_markStack,
3801              &pam_cl, before_count, CMSYield);
3802     _young_gen->from()->object_iterate_careful(&sss_cl);
3803     _young_gen->to()->object_iterate_careful(&sss_cl);
3804   }
3805   MarkRefsIntoAndScanClosure
3806     mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
3807              &_markStack, this, CMSYield,
3808              true /* precleaning phase */);
3809   // CAUTION: The following closure has persistent state that may need to
3810   // be reset upon a decrease in the sequence of addresses it
3811   // processes.
3812   ScanMarkedObjectsAgainCarefullyClosure
3813     smoac_cl(this, _span,
3814       &_markBitMap, &_markStack, &mrias_cl, CMSYield);
3815 
3816   // Preclean dirty cards in ModUnionTable and CardTable using
3817   // appropriate convergence criterion;
3818   // repeat CMSPrecleanIter times unless we find that
3819   // we are losing.
3820   assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
3821   assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
3822          "Bad convergence multiplier");
3823   assert(CMSPrecleanThreshold >= 100,
3824          "Unreasonably low CMSPrecleanThreshold");
3825 
3826   size_t numIter, cumNumCards, lastNumCards, curNumCards;
3827   for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
3828        numIter < CMSPrecleanIter;
3829        numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
3830     curNumCards  = preclean_mod_union_table(_cmsGen, &smoac_cl);
3831     log_trace(gc)(" (modUnionTable: " SIZE_FORMAT " cards)", curNumCards);
3832     // Either there are very few dirty cards, so re-mark
3833     // pause will be small anyway, or our pre-cleaning isn't
3834     // that much faster than the rate at which cards are being
3835     // dirtied, so we might as well stop and re-mark since
3836     // precleaning won't improve our re-mark time by much.
3837     if (curNumCards <= CMSPrecleanThreshold ||
3838         (numIter > 0 &&
3839          (curNumCards * CMSPrecleanDenominator >
3840          lastNumCards * CMSPrecleanNumerator))) {
3841       numIter++;
3842       cumNumCards += curNumCards;
3843       break;
3844     }
3845   }
3846 
3847   preclean_cld(&mrias_cl, _cmsGen->freelistLock());
3848 
3849   curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
3850   cumNumCards += curNumCards;
3851   log_trace(gc)(" (cardTable: " SIZE_FORMAT " cards, re-scanned " SIZE_FORMAT " cards, " SIZE_FORMAT " iterations)",
3852                              curNumCards, cumNumCards, numIter);
3853   return cumNumCards;   // as a measure of useful work done
3854 }
3855 
3856 // PRECLEANING NOTES:
3857 // Precleaning involves:
3858 // . reading the bits of the modUnionTable and clearing the set bits.
3859 // . For the cards corresponding to the set bits, we scan the
3860 //   objects on those cards. This means we need the free_list_lock
3861 //   so that we can safely iterate over the CMS space when scanning
3862 //   for oops.
3863 // . When we scan the objects, we'll be both reading and setting
3864 //   marks in the marking bit map, so we'll need the marking bit map.
3865 // . For protecting _collector_state transitions, we take the CGC_lock.
3866 //   Note that any races in the reading of of card table entries by the
3867 //   CMS thread on the one hand and the clearing of those entries by the
3868 //   VM thread or the setting of those entries by the mutator threads on the
3869 //   other are quite benign. However, for efficiency it makes sense to keep
3870 //   the VM thread from racing with the CMS thread while the latter is
3871 //   dirty card info to the modUnionTable. We therefore also use the
3872 //   CGC_lock to protect the reading of the card table and the mod union
3873 //   table by the CM thread.
3874 // . We run concurrently with mutator updates, so scanning
3875 //   needs to be done carefully  -- we should not try to scan
3876 //   potentially uninitialized objects.
3877 //
3878 // Locking strategy: While holding the CGC_lock, we scan over and
3879 // reset a maximal dirty range of the mod union / card tables, then lock
3880 // the free_list_lock and bitmap lock to do a full marking, then
3881 // release these locks; and repeat the cycle. This allows for a
3882 // certain amount of fairness in the sharing of these locks between
3883 // the CMS collector on the one hand, and the VM thread and the
3884 // mutators on the other.
3885 
3886 // NOTE: preclean_mod_union_table() and preclean_card_table()
3887 // further below are largely identical; if you need to modify
3888 // one of these methods, please check the other method too.
3889 
3890 size_t CMSCollector::preclean_mod_union_table(
3891   ConcurrentMarkSweepGeneration* old_gen,
3892   ScanMarkedObjectsAgainCarefullyClosure* cl) {
3893   verify_work_stacks_empty();
3894   verify_overflow_empty();
3895 
3896   // strategy: starting with the first card, accumulate contiguous
3897   // ranges of dirty cards; clear these cards, then scan the region
3898   // covered by these cards.
3899 
3900   // Since all of the MUT is committed ahead, we can just use
3901   // that, in case the generations expand while we are precleaning.
3902   // It might also be fine to just use the committed part of the
3903   // generation, but we might potentially miss cards when the
3904   // generation is rapidly expanding while we are in the midst
3905   // of precleaning.
3906   HeapWord* startAddr = old_gen->reserved().start();
3907   HeapWord* endAddr   = old_gen->reserved().end();
3908 
3909   cl->setFreelistLock(old_gen->freelistLock());   // needed for yielding
3910 
3911   size_t numDirtyCards, cumNumDirtyCards;
3912   HeapWord *nextAddr, *lastAddr;
3913   for (cumNumDirtyCards = numDirtyCards = 0,
3914        nextAddr = lastAddr = startAddr;
3915        nextAddr < endAddr;
3916        nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
3917 
3918     ResourceMark rm;
3919     HandleMark   hm;
3920 
3921     MemRegion dirtyRegion;
3922     {
3923       stopTimer();
3924       // Potential yield point
3925       CMSTokenSync ts(true);
3926       startTimer();
3927       sample_eden();
3928       // Get dirty region starting at nextOffset (inclusive),
3929       // simultaneously clearing it.
3930       dirtyRegion =
3931         _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
3932       assert(dirtyRegion.start() >= nextAddr,
3933              "returned region inconsistent?");
3934     }
3935     // Remember where the next search should begin.
3936     // The returned region (if non-empty) is a right open interval,
3937     // so lastOffset is obtained from the right end of that
3938     // interval.
3939     lastAddr = dirtyRegion.end();
3940     // Should do something more transparent and less hacky XXX
3941     numDirtyCards =
3942       _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
3943 
3944     // We'll scan the cards in the dirty region (with periodic
3945     // yields for foreground GC as needed).
3946     if (!dirtyRegion.is_empty()) {
3947       assert(numDirtyCards > 0, "consistency check");
3948       HeapWord* stop_point = NULL;
3949       stopTimer();
3950       // Potential yield point
3951       CMSTokenSyncWithLocks ts(true, old_gen->freelistLock(),
3952                                bitMapLock());
3953       startTimer();
3954       {
3955         verify_work_stacks_empty();
3956         verify_overflow_empty();
3957         sample_eden();
3958         stop_point =
3959           old_gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
3960       }
3961       if (stop_point != NULL) {
3962         // The careful iteration stopped early either because it found an
3963         // uninitialized object, or because we were in the midst of an
3964         // "abortable preclean", which should now be aborted. Redirty
3965         // the bits corresponding to the partially-scanned or unscanned
3966         // cards. We'll either restart at the next block boundary or
3967         // abort the preclean.
3968         assert((_collectorState == AbortablePreclean && should_abort_preclean()),
3969                "Should only be AbortablePreclean.");
3970         _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
3971         if (should_abort_preclean()) {
3972           break; // out of preclean loop
3973         } else {
3974           // Compute the next address at which preclean should pick up;
3975           // might need bitMapLock in order to read P-bits.
3976           lastAddr = next_card_start_after_block(stop_point);
3977         }
3978       }
3979     } else {
3980       assert(lastAddr == endAddr, "consistency check");
3981       assert(numDirtyCards == 0, "consistency check");
3982       break;
3983     }
3984   }
3985   verify_work_stacks_empty();
3986   verify_overflow_empty();
3987   return cumNumDirtyCards;
3988 }
3989 
3990 // NOTE: preclean_mod_union_table() above and preclean_card_table()
3991 // below are largely identical; if you need to modify
3992 // one of these methods, please check the other method too.
3993 
3994 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* old_gen,
3995   ScanMarkedObjectsAgainCarefullyClosure* cl) {
3996   // strategy: it's similar to precleamModUnionTable above, in that
3997   // we accumulate contiguous ranges of dirty cards, mark these cards
3998   // precleaned, then scan the region covered by these cards.
3999   HeapWord* endAddr   = (HeapWord*)(old_gen->_virtual_space.high());
4000   HeapWord* startAddr = (HeapWord*)(old_gen->_virtual_space.low());
4001 
4002   cl->setFreelistLock(old_gen->freelistLock());   // needed for yielding
4003 
4004   size_t numDirtyCards, cumNumDirtyCards;
4005   HeapWord *lastAddr, *nextAddr;
4006 
4007   for (cumNumDirtyCards = numDirtyCards = 0,
4008        nextAddr = lastAddr = startAddr;
4009        nextAddr < endAddr;
4010        nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4011 
4012     ResourceMark rm;
4013     HandleMark   hm;
4014 
4015     MemRegion dirtyRegion;
4016     {
4017       // See comments in "Precleaning notes" above on why we
4018       // do this locking. XXX Could the locking overheads be
4019       // too high when dirty cards are sparse? [I don't think so.]
4020       stopTimer();
4021       CMSTokenSync x(true); // is cms thread
4022       startTimer();
4023       sample_eden();
4024       // Get and clear dirty region from card table
4025       dirtyRegion = _ct->dirty_card_range_after_reset(MemRegion(nextAddr, endAddr),
4026                                                       true,
4027                                                       CardTable::precleaned_card_val());
4028 
4029       assert(dirtyRegion.start() >= nextAddr,
4030              "returned region inconsistent?");
4031     }
4032     lastAddr = dirtyRegion.end();
4033     numDirtyCards =
4034       dirtyRegion.word_size()/CardTable::card_size_in_words;
4035 
4036     if (!dirtyRegion.is_empty()) {
4037       stopTimer();
4038       CMSTokenSyncWithLocks ts(true, old_gen->freelistLock(), bitMapLock());
4039       startTimer();
4040       sample_eden();
4041       verify_work_stacks_empty();
4042       verify_overflow_empty();
4043       HeapWord* stop_point =
4044         old_gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4045       if (stop_point != NULL) {
4046         assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4047                "Should only be AbortablePreclean.");
4048         _ct->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4049         if (should_abort_preclean()) {
4050           break; // out of preclean loop
4051         } else {
4052           // Compute the next address at which preclean should pick up.
4053           lastAddr = next_card_start_after_block(stop_point);
4054         }
4055       }
4056     } else {
4057       break;
4058     }
4059   }
4060   verify_work_stacks_empty();
4061   verify_overflow_empty();
4062   return cumNumDirtyCards;
4063 }
4064 
4065 class PrecleanCLDClosure : public CLDClosure {
4066   MetadataAwareOopsInGenClosure* _cm_closure;
4067  public:
4068   PrecleanCLDClosure(MetadataAwareOopsInGenClosure* oop_closure) : _cm_closure(oop_closure) {}
4069   void do_cld(ClassLoaderData* cld) {
4070     if (cld->has_accumulated_modified_oops()) {
4071       cld->clear_accumulated_modified_oops();
4072 
4073       _cm_closure->do_cld(cld);
4074     }
4075   }
4076 };
4077 
4078 // The freelist lock is needed to prevent asserts, is it really needed?
4079 void CMSCollector::preclean_cld(MarkRefsIntoAndScanClosure* cl, Mutex* freelistLock) {
4080 
4081   cl->set_freelistLock(freelistLock);
4082 
4083   CMSTokenSyncWithLocks ts(true, freelistLock, bitMapLock());
4084 
4085   // SSS: Add equivalent to ScanMarkedObjectsAgainCarefullyClosure::do_yield_check and should_abort_preclean?
4086   // SSS: We should probably check if precleaning should be aborted, at suitable intervals?
4087   PrecleanCLDClosure preclean_closure(cl);
4088   ClassLoaderDataGraph::cld_do(&preclean_closure);
4089 
4090   verify_work_stacks_empty();
4091   verify_overflow_empty();
4092 }
4093 
4094 void CMSCollector::checkpointRootsFinal() {
4095   assert(_collectorState == FinalMarking, "incorrect state transition?");
4096   check_correct_thread_executing();
4097   // world is stopped at this checkpoint
4098   assert(SafepointSynchronize::is_at_safepoint(),
4099          "world should be stopped");
4100   TraceCMSMemoryManagerStats tms(_collectorState, CMSHeap::heap()->gc_cause());
4101 
4102   verify_work_stacks_empty();
4103   verify_overflow_empty();
4104 
4105   log_debug(gc)("YG occupancy: " SIZE_FORMAT " K (" SIZE_FORMAT " K)",
4106                 _young_gen->used() / K, _young_gen->capacity() / K);
4107   {
4108     if (CMSScavengeBeforeRemark) {
4109       CMSHeap* heap = CMSHeap::heap();
4110       // Temporarily set flag to false, GCH->do_collection will
4111       // expect it to be false and set to true
4112       FlagSetting fl(heap->_is_gc_active, false);
4113 
4114       heap->do_collection(true,                      // full (i.e. force, see below)
4115                           false,                     // !clear_all_soft_refs
4116                           0,                         // size
4117                           false,                     // is_tlab
4118                           GenCollectedHeap::YoungGen // type
4119         );
4120     }
4121     FreelistLocker x(this);
4122     MutexLockerEx y(bitMapLock(),
4123                     Mutex::_no_safepoint_check_flag);
4124     checkpointRootsFinalWork();
4125   }
4126   verify_work_stacks_empty();
4127   verify_overflow_empty();
4128 }
4129 
4130 void CMSCollector::checkpointRootsFinalWork() {
4131   GCTraceTime(Trace, gc, phases) tm("checkpointRootsFinalWork", _gc_timer_cm);
4132 
4133   assert(haveFreelistLocks(), "must have free list locks");
4134   assert_lock_strong(bitMapLock());
4135 
4136   ResourceMark rm;
4137   HandleMark   hm;
4138 
4139   CMSHeap* heap = CMSHeap::heap();
4140 
4141   if (should_unload_classes()) {
4142     CodeCache::gc_prologue();
4143   }
4144   assert(haveFreelistLocks(), "must have free list locks");
4145   assert_lock_strong(bitMapLock());
4146 
4147   // We might assume that we need not fill TLAB's when
4148   // CMSScavengeBeforeRemark is set, because we may have just done
4149   // a scavenge which would have filled all TLAB's -- and besides
4150   // Eden would be empty. This however may not always be the case --
4151   // for instance although we asked for a scavenge, it may not have
4152   // happened because of a JNI critical section. We probably need
4153   // a policy for deciding whether we can in that case wait until
4154   // the critical section releases and then do the remark following
4155   // the scavenge, and skip it here. In the absence of that policy,
4156   // or of an indication of whether the scavenge did indeed occur,
4157   // we cannot rely on TLAB's having been filled and must do
4158   // so here just in case a scavenge did not happen.
4159   heap->ensure_parsability(false);  // fill TLAB's, but no need to retire them
4160   // Update the saved marks which may affect the root scans.
4161   heap->save_marks();
4162 
4163   print_eden_and_survivor_chunk_arrays();
4164 
4165   {
4166 #if COMPILER2_OR_JVMCI
4167     DerivedPointerTableDeactivate dpt_deact;
4168 #endif
4169 
4170     // Note on the role of the mod union table:
4171     // Since the marker in "markFromRoots" marks concurrently with
4172     // mutators, it is possible for some reachable objects not to have been
4173     // scanned. For instance, an only reference to an object A was
4174     // placed in object B after the marker scanned B. Unless B is rescanned,
4175     // A would be collected. Such updates to references in marked objects
4176     // are detected via the mod union table which is the set of all cards
4177     // dirtied since the first checkpoint in this GC cycle and prior to
4178     // the most recent young generation GC, minus those cleaned up by the
4179     // concurrent precleaning.
4180     if (CMSParallelRemarkEnabled) {
4181       GCTraceTime(Debug, gc, phases) t("Rescan (parallel)", _gc_timer_cm);
4182       do_remark_parallel();
4183     } else {
4184       GCTraceTime(Debug, gc, phases) t("Rescan (non-parallel)", _gc_timer_cm);
4185       do_remark_non_parallel();
4186     }
4187   }
4188   verify_work_stacks_empty();
4189   verify_overflow_empty();
4190 
4191   {
4192     GCTraceTime(Trace, gc, phases) ts("refProcessingWork", _gc_timer_cm);
4193     refProcessingWork();
4194   }
4195   verify_work_stacks_empty();
4196   verify_overflow_empty();
4197 
4198   if (should_unload_classes()) {
4199     CodeCache::gc_epilogue();
4200   }
4201   JvmtiExport::gc_epilogue();
4202 
4203   // If we encountered any (marking stack / work queue) overflow
4204   // events during the current CMS cycle, take appropriate
4205   // remedial measures, where possible, so as to try and avoid
4206   // recurrence of that condition.
4207   assert(_markStack.isEmpty(), "No grey objects");
4208   size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
4209                      _ser_kac_ovflw        + _ser_kac_preclean_ovflw;
4210   if (ser_ovflw > 0) {
4211     log_trace(gc)("Marking stack overflow (benign) (pmc_pc=" SIZE_FORMAT ", pmc_rm=" SIZE_FORMAT ", kac=" SIZE_FORMAT ", kac_preclean=" SIZE_FORMAT ")",
4212                          _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw, _ser_kac_ovflw, _ser_kac_preclean_ovflw);
4213     _markStack.expand();
4214     _ser_pmc_remark_ovflw = 0;
4215     _ser_pmc_preclean_ovflw = 0;
4216     _ser_kac_preclean_ovflw = 0;
4217     _ser_kac_ovflw = 0;
4218   }
4219   if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
4220      log_trace(gc)("Work queue overflow (benign) (pmc_rm=" SIZE_FORMAT ", kac=" SIZE_FORMAT ")",
4221                           _par_pmc_remark_ovflw, _par_kac_ovflw);
4222      _par_pmc_remark_ovflw = 0;
4223     _par_kac_ovflw = 0;
4224   }
4225    if (_markStack._hit_limit > 0) {
4226      log_trace(gc)(" (benign) Hit max stack size limit (" SIZE_FORMAT ")",
4227                           _markStack._hit_limit);
4228    }
4229    if (_markStack._failed_double > 0) {
4230      log_trace(gc)(" (benign) Failed stack doubling (" SIZE_FORMAT "), current capacity " SIZE_FORMAT,
4231                           _markStack._failed_double, _markStack.capacity());
4232    }
4233   _markStack._hit_limit = 0;
4234   _markStack._failed_double = 0;
4235 
4236   if ((VerifyAfterGC || VerifyDuringGC) &&
4237       CMSHeap::heap()->total_collections() >= VerifyGCStartAt) {
4238     verify_after_remark();
4239   }
4240 
4241   _gc_tracer_cm->report_object_count_after_gc(&_is_alive_closure);
4242 
4243   // Change under the freelistLocks.
4244   _collectorState = Sweeping;
4245   // Call isAllClear() under bitMapLock
4246   assert(_modUnionTable.isAllClear(),
4247       "Should be clear by end of the final marking");
4248   assert(_ct->cld_rem_set()->mod_union_is_clear(),
4249       "Should be clear by end of the final marking");
4250 }
4251 
4252 void CMSParInitialMarkTask::work(uint worker_id) {
4253   elapsedTimer _timer;
4254   ResourceMark rm;
4255   HandleMark   hm;
4256 
4257   // ---------- scan from roots --------------
4258   _timer.start();
4259   CMSHeap* heap = CMSHeap::heap();
4260   ParMarkRefsIntoClosure par_mri_cl(_collector->_span, &(_collector->_markBitMap));
4261 
4262   // ---------- young gen roots --------------
4263   {
4264     work_on_young_gen_roots(&par_mri_cl);
4265     _timer.stop();
4266     log_trace(gc, task)("Finished young gen initial mark scan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4267   }
4268 
4269   // ---------- remaining roots --------------
4270   _timer.reset();
4271   _timer.start();
4272 
4273   CLDToOopClosure cld_closure(&par_mri_cl, true);
4274 
4275   heap->cms_process_roots(_strong_roots_scope,
4276                           false,     // yg was scanned above
4277                           GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4278                           _collector->should_unload_classes(),
4279                           &par_mri_cl,
4280                           &cld_closure,
4281                           &_par_state_string);
4282 
4283   assert(_collector->should_unload_classes()
4284          || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4285          "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4286   _timer.stop();
4287   log_trace(gc, task)("Finished remaining root initial mark scan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4288 }
4289 
4290 // Parallel remark task
4291 class CMSParRemarkTask: public CMSParMarkTask {
4292   CompactibleFreeListSpace* _cms_space;
4293 
4294   // The per-thread work queues, available here for stealing.
4295   OopTaskQueueSet*       _task_queues;
4296   ParallelTaskTerminator _term;
4297   StrongRootsScope*      _strong_roots_scope;
4298 
4299  public:
4300   // A value of 0 passed to n_workers will cause the number of
4301   // workers to be taken from the active workers in the work gang.
4302   CMSParRemarkTask(CMSCollector* collector,
4303                    CompactibleFreeListSpace* cms_space,
4304                    uint n_workers, WorkGang* workers,
4305                    OopTaskQueueSet* task_queues,
4306                    StrongRootsScope* strong_roots_scope):
4307     CMSParMarkTask("Rescan roots and grey objects in parallel",
4308                    collector, n_workers),
4309     _cms_space(cms_space),
4310     _task_queues(task_queues),
4311     _term(n_workers, task_queues),
4312     _strong_roots_scope(strong_roots_scope) { }
4313 
4314   OopTaskQueueSet* task_queues() { return _task_queues; }
4315 
4316   OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
4317 
4318   ParallelTaskTerminator* terminator() { return &_term; }
4319   uint n_workers() { return _n_workers; }
4320 
4321   void work(uint worker_id);
4322 
4323  private:
4324   // ... of  dirty cards in old space
4325   void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
4326                                   ParMarkRefsIntoAndScanClosure* cl);
4327 
4328   // ... work stealing for the above
4329   void do_work_steal(int i, ParMarkRefsIntoAndScanClosure* cl, int* seed);
4330 };
4331 
4332 class RemarkCLDClosure : public CLDClosure {
4333   CLDToOopClosure _cm_closure;
4334  public:
4335   RemarkCLDClosure(OopClosure* oop_closure) : _cm_closure(oop_closure) {}
4336   void do_cld(ClassLoaderData* cld) {
4337     // Check if we have modified any oops in the CLD during the concurrent marking.
4338     if (cld->has_accumulated_modified_oops()) {
4339       cld->clear_accumulated_modified_oops();
4340 
4341       // We could have transfered the current modified marks to the accumulated marks,
4342       // like we do with the Card Table to Mod Union Table. But it's not really necessary.
4343     } else if (cld->has_modified_oops()) {
4344       // Don't clear anything, this info is needed by the next young collection.
4345     } else {
4346       // No modified oops in the ClassLoaderData.
4347       return;
4348     }
4349 
4350     // The klass has modified fields, need to scan the klass.
4351     _cm_closure.do_cld(cld);
4352   }
4353 };
4354 
4355 void CMSParMarkTask::work_on_young_gen_roots(OopsInGenClosure* cl) {
4356   ParNewGeneration* young_gen = _collector->_young_gen;
4357   ContiguousSpace* eden_space = young_gen->eden();
4358   ContiguousSpace* from_space = young_gen->from();
4359   ContiguousSpace* to_space   = young_gen->to();
4360 
4361   HeapWord** eca = _collector->_eden_chunk_array;
4362   size_t     ect = _collector->_eden_chunk_index;
4363   HeapWord** sca = _collector->_survivor_chunk_array;
4364   size_t     sct = _collector->_survivor_chunk_index;
4365 
4366   assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
4367   assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
4368 
4369   do_young_space_rescan(cl, to_space, NULL, 0);
4370   do_young_space_rescan(cl, from_space, sca, sct);
4371   do_young_space_rescan(cl, eden_space, eca, ect);
4372 }
4373 
4374 // work_queue(i) is passed to the closure
4375 // ParMarkRefsIntoAndScanClosure.  The "i" parameter
4376 // also is passed to do_dirty_card_rescan_tasks() and to
4377 // do_work_steal() to select the i-th task_queue.
4378 
4379 void CMSParRemarkTask::work(uint worker_id) {
4380   elapsedTimer _timer;
4381   ResourceMark rm;
4382   HandleMark   hm;
4383 
4384   // ---------- rescan from roots --------------
4385   _timer.start();
4386   CMSHeap* heap = CMSHeap::heap();
4387   ParMarkRefsIntoAndScanClosure par_mrias_cl(_collector,
4388     _collector->_span, _collector->ref_processor(),
4389     &(_collector->_markBitMap),
4390     work_queue(worker_id));
4391 
4392   // Rescan young gen roots first since these are likely
4393   // coarsely partitioned and may, on that account, constitute
4394   // the critical path; thus, it's best to start off that
4395   // work first.
4396   // ---------- young gen roots --------------
4397   {
4398     work_on_young_gen_roots(&par_mrias_cl);
4399     _timer.stop();
4400     log_trace(gc, task)("Finished young gen rescan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4401   }
4402 
4403   // ---------- remaining roots --------------
4404   _timer.reset();
4405   _timer.start();
4406   heap->cms_process_roots(_strong_roots_scope,
4407                           false,     // yg was scanned above
4408                           GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4409                           _collector->should_unload_classes(),
4410                           &par_mrias_cl,
4411                           NULL,     // The dirty klasses will be handled below
4412                           &_par_state_string);
4413 
4414   assert(_collector->should_unload_classes()
4415          || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4416          "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4417   _timer.stop();
4418   log_trace(gc, task)("Finished remaining root rescan work in %dth thread: %3.3f sec",  worker_id, _timer.seconds());
4419 
4420   // ---------- unhandled CLD scanning ----------
4421   if (worker_id == 0) { // Single threaded at the moment.
4422     _timer.reset();
4423     _timer.start();
4424 
4425     // Scan all new class loader data objects and new dependencies that were
4426     // introduced during concurrent marking.
4427     ResourceMark rm;
4428     GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
4429     for (int i = 0; i < array->length(); i++) {
4430       par_mrias_cl.do_cld_nv(array->at(i));
4431     }
4432 
4433     // We don't need to keep track of new CLDs anymore.
4434     ClassLoaderDataGraph::remember_new_clds(false);
4435 
4436     _timer.stop();
4437     log_trace(gc, task)("Finished unhandled CLD scanning work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4438   }
4439 
4440   // We might have added oops to ClassLoaderData::_handles during the
4441   // concurrent marking phase. These oops do not always point to newly allocated objects
4442   // that are guaranteed to be kept alive.  Hence,
4443   // we do have to revisit the _handles block during the remark phase.
4444 
4445   // ---------- dirty CLD scanning ----------
4446   if (worker_id == 0) { // Single threaded at the moment.
4447     _timer.reset();
4448     _timer.start();
4449 
4450     // Scan all classes that was dirtied during the concurrent marking phase.
4451     RemarkCLDClosure remark_closure(&par_mrias_cl);
4452     ClassLoaderDataGraph::cld_do(&remark_closure);
4453 
4454     _timer.stop();
4455     log_trace(gc, task)("Finished dirty CLD scanning work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4456   }
4457 
4458 
4459   // ---------- rescan dirty cards ------------
4460   _timer.reset();
4461   _timer.start();
4462 
4463   // Do the rescan tasks for each of the two spaces
4464   // (cms_space) in turn.
4465   // "worker_id" is passed to select the task_queue for "worker_id"
4466   do_dirty_card_rescan_tasks(_cms_space, worker_id, &par_mrias_cl);
4467   _timer.stop();
4468   log_trace(gc, task)("Finished dirty card rescan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4469 
4470   // ---------- steal work from other threads ...
4471   // ---------- ... and drain overflow list.
4472   _timer.reset();
4473   _timer.start();
4474   do_work_steal(worker_id, &par_mrias_cl, _collector->hash_seed(worker_id));
4475   _timer.stop();
4476   log_trace(gc, task)("Finished work stealing in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4477 }
4478 
4479 void
4480 CMSParMarkTask::do_young_space_rescan(
4481   OopsInGenClosure* cl, ContiguousSpace* space,
4482   HeapWord** chunk_array, size_t chunk_top) {
4483   // Until all tasks completed:
4484   // . claim an unclaimed task
4485   // . compute region boundaries corresponding to task claimed
4486   //   using chunk_array
4487   // . par_oop_iterate(cl) over that region
4488 
4489   ResourceMark rm;
4490   HandleMark   hm;
4491 
4492   SequentialSubTasksDone* pst = space->par_seq_tasks();
4493 
4494   uint nth_task = 0;
4495   uint n_tasks  = pst->n_tasks();
4496 
4497   if (n_tasks > 0) {
4498     assert(pst->valid(), "Uninitialized use?");
4499     HeapWord *start, *end;
4500     while (!pst->is_task_claimed(/* reference */ nth_task)) {
4501       // We claimed task # nth_task; compute its boundaries.
4502       if (chunk_top == 0) {  // no samples were taken
4503         assert(nth_task == 0 && n_tasks == 1, "Can have only 1 eden task");
4504         start = space->bottom();
4505         end   = space->top();
4506       } else if (nth_task == 0) {
4507         start = space->bottom();
4508         end   = chunk_array[nth_task];
4509       } else if (nth_task < (uint)chunk_top) {
4510         assert(nth_task >= 1, "Control point invariant");
4511         start = chunk_array[nth_task - 1];
4512         end   = chunk_array[nth_task];
4513       } else {
4514         assert(nth_task == (uint)chunk_top, "Control point invariant");
4515         start = chunk_array[chunk_top - 1];
4516         end   = space->top();
4517       }
4518       MemRegion mr(start, end);
4519       // Verify that mr is in space
4520       assert(mr.is_empty() || space->used_region().contains(mr),
4521              "Should be in space");
4522       // Verify that "start" is an object boundary
4523       assert(mr.is_empty() || oopDesc::is_oop(oop(mr.start())),
4524              "Should be an oop");
4525       space->par_oop_iterate(mr, cl);
4526     }
4527     pst->all_tasks_completed();
4528   }
4529 }
4530 
4531 void
4532 CMSParRemarkTask::do_dirty_card_rescan_tasks(
4533   CompactibleFreeListSpace* sp, int i,
4534   ParMarkRefsIntoAndScanClosure* cl) {
4535   // Until all tasks completed:
4536   // . claim an unclaimed task
4537   // . compute region boundaries corresponding to task claimed
4538   // . transfer dirty bits ct->mut for that region
4539   // . apply rescanclosure to dirty mut bits for that region
4540 
4541   ResourceMark rm;
4542   HandleMark   hm;
4543 
4544   OopTaskQueue* work_q = work_queue(i);
4545   ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
4546   // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
4547   // CAUTION: This closure has state that persists across calls to
4548   // the work method dirty_range_iterate_clear() in that it has
4549   // embedded in it a (subtype of) UpwardsObjectClosure. The
4550   // use of that state in the embedded UpwardsObjectClosure instance
4551   // assumes that the cards are always iterated (even if in parallel
4552   // by several threads) in monotonically increasing order per each
4553   // thread. This is true of the implementation below which picks
4554   // card ranges (chunks) in monotonically increasing order globally
4555   // and, a-fortiori, in monotonically increasing order per thread
4556   // (the latter order being a subsequence of the former).
4557   // If the work code below is ever reorganized into a more chaotic
4558   // work-partitioning form than the current "sequential tasks"
4559   // paradigm, the use of that persistent state will have to be
4560   // revisited and modified appropriately. See also related
4561   // bug 4756801 work on which should examine this code to make
4562   // sure that the changes there do not run counter to the
4563   // assumptions made here and necessary for correctness and
4564   // efficiency. Note also that this code might yield inefficient
4565   // behavior in the case of very large objects that span one or
4566   // more work chunks. Such objects would potentially be scanned
4567   // several times redundantly. Work on 4756801 should try and
4568   // address that performance anomaly if at all possible. XXX
4569   MemRegion  full_span  = _collector->_span;
4570   CMSBitMap* bm    = &(_collector->_markBitMap);     // shared
4571   MarkFromDirtyCardsClosure
4572     greyRescanClosure(_collector, full_span, // entire span of interest
4573                       sp, bm, work_q, cl);
4574 
4575   SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
4576   assert(pst->valid(), "Uninitialized use?");
4577   uint nth_task = 0;
4578   const int alignment = CardTable::card_size * BitsPerWord;
4579   MemRegion span = sp->used_region();
4580   HeapWord* start_addr = span.start();
4581   HeapWord* end_addr = align_up(span.end(), alignment);
4582   const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
4583   assert(is_aligned(start_addr, alignment), "Check alignment");
4584   assert(is_aligned(chunk_size, alignment), "Check alignment");
4585 
4586   while (!pst->is_task_claimed(/* reference */ nth_task)) {
4587     // Having claimed the nth_task, compute corresponding mem-region,
4588     // which is a-fortiori aligned correctly (i.e. at a MUT boundary).
4589     // The alignment restriction ensures that we do not need any
4590     // synchronization with other gang-workers while setting or
4591     // clearing bits in thus chunk of the MUT.
4592     MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
4593                                     start_addr + (nth_task+1)*chunk_size);
4594     // The last chunk's end might be way beyond end of the
4595     // used region. In that case pull back appropriately.
4596     if (this_span.end() > end_addr) {
4597       this_span.set_end(end_addr);
4598       assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
4599     }
4600     // Iterate over the dirty cards covering this chunk, marking them
4601     // precleaned, and setting the corresponding bits in the mod union
4602     // table. Since we have been careful to partition at Card and MUT-word
4603     // boundaries no synchronization is needed between parallel threads.
4604     _collector->_ct->dirty_card_iterate(this_span,
4605                                                  &modUnionClosure);
4606 
4607     // Having transferred these marks into the modUnionTable,
4608     // rescan the marked objects on the dirty cards in the modUnionTable.
4609     // Even if this is at a synchronous collection, the initial marking
4610     // may have been done during an asynchronous collection so there
4611     // may be dirty bits in the mod-union table.
4612     _collector->_modUnionTable.dirty_range_iterate_clear(
4613                   this_span, &greyRescanClosure);
4614     _collector->_modUnionTable.verifyNoOneBitsInRange(
4615                                  this_span.start(),
4616                                  this_span.end());
4617   }
4618   pst->all_tasks_completed();  // declare that i am done
4619 }
4620 
4621 // . see if we can share work_queues with ParNew? XXX
4622 void
4623 CMSParRemarkTask::do_work_steal(int i, ParMarkRefsIntoAndScanClosure* cl,
4624                                 int* seed) {
4625   OopTaskQueue* work_q = work_queue(i);
4626   NOT_PRODUCT(int num_steals = 0;)
4627   oop obj_to_scan;
4628   CMSBitMap* bm = &(_collector->_markBitMap);
4629 
4630   while (true) {
4631     // Completely finish any left over work from (an) earlier round(s)
4632     cl->trim_queue(0);
4633     size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
4634                                          (size_t)ParGCDesiredObjsFromOverflowList);
4635     // Now check if there's any work in the overflow list
4636     // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
4637     // only affects the number of attempts made to get work from the
4638     // overflow list and does not affect the number of workers.  Just
4639     // pass ParallelGCThreads so this behavior is unchanged.
4640     if (_collector->par_take_from_overflow_list(num_from_overflow_list,
4641                                                 work_q,
4642                                                 ParallelGCThreads)) {
4643       // found something in global overflow list;
4644       // not yet ready to go stealing work from others.
4645       // We'd like to assert(work_q->size() != 0, ...)
4646       // because we just took work from the overflow list,
4647       // but of course we can't since all of that could have
4648       // been already stolen from us.
4649       // "He giveth and He taketh away."
4650       continue;
4651     }
4652     // Verify that we have no work before we resort to stealing
4653     assert(work_q->size() == 0, "Have work, shouldn't steal");
4654     // Try to steal from other queues that have work
4655     if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
4656       NOT_PRODUCT(num_steals++;)
4657       assert(oopDesc::is_oop(obj_to_scan), "Oops, not an oop!");
4658       assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
4659       // Do scanning work
4660       obj_to_scan->oop_iterate(cl);
4661       // Loop around, finish this work, and try to steal some more
4662     } else if (terminator()->offer_termination()) {
4663         break;  // nirvana from the infinite cycle
4664     }
4665   }
4666   log_develop_trace(gc, task)("\t(%d: stole %d oops)", i, num_steals);
4667   assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
4668          "Else our work is not yet done");
4669 }
4670 
4671 // Record object boundaries in _eden_chunk_array by sampling the eden
4672 // top in the slow-path eden object allocation code path and record
4673 // the boundaries, if CMSEdenChunksRecordAlways is true. If
4674 // CMSEdenChunksRecordAlways is false, we use the other asynchronous
4675 // sampling in sample_eden() that activates during the part of the
4676 // preclean phase.
4677 void CMSCollector::sample_eden_chunk() {
4678   if (CMSEdenChunksRecordAlways && _eden_chunk_array != NULL) {
4679     if (_eden_chunk_lock->try_lock()) {
4680       // Record a sample. This is the critical section. The contents
4681       // of the _eden_chunk_array have to be non-decreasing in the
4682       // address order.
4683       _eden_chunk_array[_eden_chunk_index] = *_top_addr;
4684       assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4685              "Unexpected state of Eden");
4686       if (_eden_chunk_index == 0 ||
4687           ((_eden_chunk_array[_eden_chunk_index] > _eden_chunk_array[_eden_chunk_index-1]) &&
4688            (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4689                           _eden_chunk_array[_eden_chunk_index-1]) >= CMSSamplingGrain))) {
4690         _eden_chunk_index++;  // commit sample
4691       }
4692       _eden_chunk_lock->unlock();
4693     }
4694   }
4695 }
4696 
4697 // Return a thread-local PLAB recording array, as appropriate.
4698 void* CMSCollector::get_data_recorder(int thr_num) {
4699   if (_survivor_plab_array != NULL &&
4700       (CMSPLABRecordAlways ||
4701        (_collectorState > Marking && _collectorState < FinalMarking))) {
4702     assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
4703     ChunkArray* ca = &_survivor_plab_array[thr_num];
4704     ca->reset();   // clear it so that fresh data is recorded
4705     return (void*) ca;
4706   } else {
4707     return NULL;
4708   }
4709 }
4710 
4711 // Reset all the thread-local PLAB recording arrays
4712 void CMSCollector::reset_survivor_plab_arrays() {
4713   for (uint i = 0; i < ParallelGCThreads; i++) {
4714     _survivor_plab_array[i].reset();
4715   }
4716 }
4717 
4718 // Merge the per-thread plab arrays into the global survivor chunk
4719 // array which will provide the partitioning of the survivor space
4720 // for CMS initial scan and rescan.
4721 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv,
4722                                               int no_of_gc_threads) {
4723   assert(_survivor_plab_array  != NULL, "Error");
4724   assert(_survivor_chunk_array != NULL, "Error");
4725   assert(_collectorState == FinalMarking ||
4726          (CMSParallelInitialMarkEnabled && _collectorState == InitialMarking), "Error");
4727   for (int j = 0; j < no_of_gc_threads; j++) {
4728     _cursor[j] = 0;
4729   }
4730   HeapWord* top = surv->top();
4731   size_t i;
4732   for (i = 0; i < _survivor_chunk_capacity; i++) {  // all sca entries
4733     HeapWord* min_val = top;          // Higher than any PLAB address
4734     uint      min_tid = 0;            // position of min_val this round
4735     for (int j = 0; j < no_of_gc_threads; j++) {
4736       ChunkArray* cur_sca = &_survivor_plab_array[j];
4737       if (_cursor[j] == cur_sca->end()) {
4738         continue;
4739       }
4740       assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
4741       HeapWord* cur_val = cur_sca->nth(_cursor[j]);
4742       assert(surv->used_region().contains(cur_val), "Out of bounds value");
4743       if (cur_val < min_val) {
4744         min_tid = j;
4745         min_val = cur_val;
4746       } else {
4747         assert(cur_val < top, "All recorded addresses should be less");
4748       }
4749     }
4750     // At this point min_val and min_tid are respectively
4751     // the least address in _survivor_plab_array[j]->nth(_cursor[j])
4752     // and the thread (j) that witnesses that address.
4753     // We record this address in the _survivor_chunk_array[i]
4754     // and increment _cursor[min_tid] prior to the next round i.
4755     if (min_val == top) {
4756       break;
4757     }
4758     _survivor_chunk_array[i] = min_val;
4759     _cursor[min_tid]++;
4760   }
4761   // We are all done; record the size of the _survivor_chunk_array
4762   _survivor_chunk_index = i; // exclusive: [0, i)
4763   log_trace(gc, survivor)(" (Survivor:" SIZE_FORMAT "chunks) ", i);
4764   // Verify that we used up all the recorded entries
4765   #ifdef ASSERT
4766     size_t total = 0;
4767     for (int j = 0; j < no_of_gc_threads; j++) {
4768       assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
4769       total += _cursor[j];
4770     }
4771     assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
4772     // Check that the merged array is in sorted order
4773     if (total > 0) {
4774       for (size_t i = 0; i < total - 1; i++) {
4775         log_develop_trace(gc, survivor)(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
4776                                      i, p2i(_survivor_chunk_array[i]));
4777         assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
4778                "Not sorted");
4779       }
4780     }
4781   #endif // ASSERT
4782 }
4783 
4784 // Set up the space's par_seq_tasks structure for work claiming
4785 // for parallel initial scan and rescan of young gen.
4786 // See ParRescanTask where this is currently used.
4787 void
4788 CMSCollector::
4789 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
4790   assert(n_threads > 0, "Unexpected n_threads argument");
4791 
4792   // Eden space
4793   if (!_young_gen->eden()->is_empty()) {
4794     SequentialSubTasksDone* pst = _young_gen->eden()->par_seq_tasks();
4795     assert(!pst->valid(), "Clobbering existing data?");
4796     // Each valid entry in [0, _eden_chunk_index) represents a task.
4797     size_t n_tasks = _eden_chunk_index + 1;
4798     assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
4799     // Sets the condition for completion of the subtask (how many threads
4800     // need to finish in order to be done).
4801     pst->set_n_threads(n_threads);
4802     pst->set_n_tasks((int)n_tasks);
4803   }
4804 
4805   // Merge the survivor plab arrays into _survivor_chunk_array
4806   if (_survivor_plab_array != NULL) {
4807     merge_survivor_plab_arrays(_young_gen->from(), n_threads);
4808   } else {
4809     assert(_survivor_chunk_index == 0, "Error");
4810   }
4811 
4812   // To space
4813   {
4814     SequentialSubTasksDone* pst = _young_gen->to()->par_seq_tasks();
4815     assert(!pst->valid(), "Clobbering existing data?");
4816     // Sets the condition for completion of the subtask (how many threads
4817     // need to finish in order to be done).
4818     pst->set_n_threads(n_threads);
4819     pst->set_n_tasks(1);
4820     assert(pst->valid(), "Error");
4821   }
4822 
4823   // From space
4824   {
4825     SequentialSubTasksDone* pst = _young_gen->from()->par_seq_tasks();
4826     assert(!pst->valid(), "Clobbering existing data?");
4827     size_t n_tasks = _survivor_chunk_index + 1;
4828     assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
4829     // Sets the condition for completion of the subtask (how many threads
4830     // need to finish in order to be done).
4831     pst->set_n_threads(n_threads);
4832     pst->set_n_tasks((int)n_tasks);
4833     assert(pst->valid(), "Error");
4834   }
4835 }
4836 
4837 // Parallel version of remark
4838 void CMSCollector::do_remark_parallel() {
4839   CMSHeap* heap = CMSHeap::heap();
4840   WorkGang* workers = heap->workers();
4841   assert(workers != NULL, "Need parallel worker threads.");
4842   // Choose to use the number of GC workers most recently set
4843   // into "active_workers".
4844   uint n_workers = workers->active_workers();
4845 
4846   CompactibleFreeListSpace* cms_space  = _cmsGen->cmsSpace();
4847 
4848   StrongRootsScope srs(n_workers);
4849 
4850   CMSParRemarkTask tsk(this, cms_space, n_workers, workers, task_queues(), &srs);
4851 
4852   // We won't be iterating over the cards in the card table updating
4853   // the younger_gen cards, so we shouldn't call the following else
4854   // the verification code as well as subsequent younger_refs_iterate
4855   // code would get confused. XXX
4856   // heap->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
4857 
4858   // The young gen rescan work will not be done as part of
4859   // process_roots (which currently doesn't know how to
4860   // parallelize such a scan), but rather will be broken up into
4861   // a set of parallel tasks (via the sampling that the [abortable]
4862   // preclean phase did of eden, plus the [two] tasks of
4863   // scanning the [two] survivor spaces. Further fine-grain
4864   // parallelization of the scanning of the survivor spaces
4865   // themselves, and of precleaning of the young gen itself
4866   // is deferred to the future.
4867   initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
4868 
4869   // The dirty card rescan work is broken up into a "sequence"
4870   // of parallel tasks (per constituent space) that are dynamically
4871   // claimed by the parallel threads.
4872   cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
4873 
4874   // It turns out that even when we're using 1 thread, doing the work in a
4875   // separate thread causes wide variance in run times.  We can't help this
4876   // in the multi-threaded case, but we special-case n=1 here to get
4877   // repeatable measurements of the 1-thread overhead of the parallel code.
4878   if (n_workers > 1) {
4879     // Make refs discovery MT-safe, if it isn't already: it may not
4880     // necessarily be so, since it's possible that we are doing
4881     // ST marking.
4882     ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), true);
4883     workers->run_task(&tsk);
4884   } else {
4885     ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
4886     tsk.work(0);
4887   }
4888 
4889   // restore, single-threaded for now, any preserved marks
4890   // as a result of work_q overflow
4891   restore_preserved_marks_if_any();
4892 }
4893 
4894 // Non-parallel version of remark
4895 void CMSCollector::do_remark_non_parallel() {
4896   ResourceMark rm;
4897   HandleMark   hm;
4898   CMSHeap* heap = CMSHeap::heap();
4899   ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
4900 
4901   MarkRefsIntoAndScanClosure
4902     mrias_cl(_span, ref_processor(), &_markBitMap, NULL /* not precleaning */,
4903              &_markStack, this,
4904              false /* should_yield */, false /* not precleaning */);
4905   MarkFromDirtyCardsClosure
4906     markFromDirtyCardsClosure(this, _span,
4907                               NULL,  // space is set further below
4908                               &_markBitMap, &_markStack, &mrias_cl);
4909   {
4910     GCTraceTime(Trace, gc, phases) t("Grey Object Rescan", _gc_timer_cm);
4911     // Iterate over the dirty cards, setting the corresponding bits in the
4912     // mod union table.
4913     {
4914       ModUnionClosure modUnionClosure(&_modUnionTable);
4915       _ct->dirty_card_iterate(_cmsGen->used_region(),
4916                               &modUnionClosure);
4917     }
4918     // Having transferred these marks into the modUnionTable, we just need
4919     // to rescan the marked objects on the dirty cards in the modUnionTable.
4920     // The initial marking may have been done during an asynchronous
4921     // collection so there may be dirty bits in the mod-union table.
4922     const int alignment = CardTable::card_size * BitsPerWord;
4923     {
4924       // ... First handle dirty cards in CMS gen
4925       markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
4926       MemRegion ur = _cmsGen->used_region();
4927       HeapWord* lb = ur.start();
4928       HeapWord* ub = align_up(ur.end(), alignment);
4929       MemRegion cms_span(lb, ub);
4930       _modUnionTable.dirty_range_iterate_clear(cms_span,
4931                                                &markFromDirtyCardsClosure);
4932       verify_work_stacks_empty();
4933       log_trace(gc)(" (re-scanned " SIZE_FORMAT " dirty cards in cms gen) ", markFromDirtyCardsClosure.num_dirty_cards());
4934     }
4935   }
4936   if (VerifyDuringGC &&
4937       CMSHeap::heap()->total_collections() >= VerifyGCStartAt) {
4938     HandleMark hm;  // Discard invalid handles created during verification
4939     Universe::verify();
4940   }
4941   {
4942     GCTraceTime(Trace, gc, phases) t("Root Rescan", _gc_timer_cm);
4943 
4944     verify_work_stacks_empty();
4945 
4946     heap->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
4947     StrongRootsScope srs(1);
4948 
4949     heap->cms_process_roots(&srs,
4950                             true,  // young gen as roots
4951                             GenCollectedHeap::ScanningOption(roots_scanning_options()),
4952                             should_unload_classes(),
4953                             &mrias_cl,
4954                             NULL); // The dirty klasses will be handled below
4955 
4956     assert(should_unload_classes()
4957            || (roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4958            "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4959   }
4960 
4961   {
4962     GCTraceTime(Trace, gc, phases) t("Visit Unhandled CLDs", _gc_timer_cm);
4963 
4964     verify_work_stacks_empty();
4965 
4966     // Scan all class loader data objects that might have been introduced
4967     // during concurrent marking.
4968     ResourceMark rm;
4969     GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
4970     for (int i = 0; i < array->length(); i++) {
4971       mrias_cl.do_cld_nv(array->at(i));
4972     }
4973 
4974     // We don't need to keep track of new CLDs anymore.
4975     ClassLoaderDataGraph::remember_new_clds(false);
4976 
4977     verify_work_stacks_empty();
4978   }
4979 
4980   // We might have added oops to ClassLoaderData::_handles during the
4981   // concurrent marking phase. These oops do not point to newly allocated objects
4982   // that are guaranteed to be kept alive.  Hence,
4983   // we do have to revisit the _handles block during the remark phase.
4984   {
4985     GCTraceTime(Trace, gc, phases) t("Dirty CLD Scan", _gc_timer_cm);
4986 
4987     verify_work_stacks_empty();
4988 
4989     RemarkCLDClosure remark_closure(&mrias_cl);
4990     ClassLoaderDataGraph::cld_do(&remark_closure);
4991 
4992     verify_work_stacks_empty();
4993   }
4994 
4995   verify_work_stacks_empty();
4996   // Restore evacuated mark words, if any, used for overflow list links
4997   restore_preserved_marks_if_any();
4998 
4999   verify_overflow_empty();
5000 }
5001 
5002 ////////////////////////////////////////////////////////
5003 // Parallel Reference Processing Task Proxy Class
5004 ////////////////////////////////////////////////////////
5005 class AbstractGangTaskWOopQueues : public AbstractGangTask {
5006   OopTaskQueueSet*       _queues;
5007   ParallelTaskTerminator _terminator;
5008  public:
5009   AbstractGangTaskWOopQueues(const char* name, OopTaskQueueSet* queues, uint n_threads) :
5010     AbstractGangTask(name), _queues(queues), _terminator(n_threads, _queues) {}
5011   ParallelTaskTerminator* terminator() { return &_terminator; }
5012   OopTaskQueueSet* queues() { return _queues; }
5013 };
5014 
5015 class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues {
5016   typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
5017   CMSCollector*          _collector;
5018   CMSBitMap*             _mark_bit_map;
5019   const MemRegion        _span;
5020   ProcessTask&           _task;
5021 
5022 public:
5023   CMSRefProcTaskProxy(ProcessTask&     task,
5024                       CMSCollector*    collector,
5025                       const MemRegion& span,
5026                       CMSBitMap*       mark_bit_map,
5027                       AbstractWorkGang* workers,
5028                       OopTaskQueueSet* task_queues):
5029     AbstractGangTaskWOopQueues("Process referents by policy in parallel",
5030       task_queues,
5031       workers->active_workers()),
5032     _task(task),
5033     _collector(collector), _span(span), _mark_bit_map(mark_bit_map)
5034   {
5035     assert(_collector->_span.equals(_span) && !_span.is_empty(),
5036            "Inconsistency in _span");
5037   }
5038 
5039   OopTaskQueueSet* task_queues() { return queues(); }
5040 
5041   OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5042 
5043   void do_work_steal(int i,
5044                      CMSParDrainMarkingStackClosure* drain,
5045                      CMSParKeepAliveClosure* keep_alive,
5046                      int* seed);
5047 
5048   virtual void work(uint worker_id);
5049 };
5050 
5051 void CMSRefProcTaskProxy::work(uint worker_id) {
5052   ResourceMark rm;
5053   HandleMark hm;
5054   assert(_collector->_span.equals(_span), "Inconsistency in _span");
5055   CMSParKeepAliveClosure par_keep_alive(_collector, _span,
5056                                         _mark_bit_map,
5057                                         work_queue(worker_id));
5058   CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
5059                                                  _mark_bit_map,
5060                                                  work_queue(worker_id));
5061   CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
5062   _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack);
5063   if (_task.marks_oops_alive()) {
5064     do_work_steal(worker_id, &par_drain_stack, &par_keep_alive,
5065                   _collector->hash_seed(worker_id));
5066   }
5067   assert(work_queue(worker_id)->size() == 0, "work_queue should be empty");
5068   assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
5069 }
5070 
5071 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
5072   MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue):
5073    _span(span),
5074    _bit_map(bit_map),
5075    _work_queue(work_queue),
5076    _mark_and_push(collector, span, bit_map, work_queue),
5077    _low_water_mark(MIN2((work_queue->max_elems()/4),
5078                         ((uint)CMSWorkQueueDrainThreshold * ParallelGCThreads)))
5079 { }
5080 
5081 // . see if we can share work_queues with ParNew? XXX
5082 void CMSRefProcTaskProxy::do_work_steal(int i,
5083   CMSParDrainMarkingStackClosure* drain,
5084   CMSParKeepAliveClosure* keep_alive,
5085   int* seed) {
5086   OopTaskQueue* work_q = work_queue(i);
5087   NOT_PRODUCT(int num_steals = 0;)
5088   oop obj_to_scan;
5089 
5090   while (true) {
5091     // Completely finish any left over work from (an) earlier round(s)
5092     drain->trim_queue(0);
5093     size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5094                                          (size_t)ParGCDesiredObjsFromOverflowList);
5095     // Now check if there's any work in the overflow list
5096     // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5097     // only affects the number of attempts made to get work from the
5098     // overflow list and does not affect the number of workers.  Just
5099     // pass ParallelGCThreads so this behavior is unchanged.
5100     if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5101                                                 work_q,
5102                                                 ParallelGCThreads)) {
5103       // Found something in global overflow list;
5104       // not yet ready to go stealing work from others.
5105       // We'd like to assert(work_q->size() != 0, ...)
5106       // because we just took work from the overflow list,
5107       // but of course we can't, since all of that might have
5108       // been already stolen from us.
5109       continue;
5110     }
5111     // Verify that we have no work before we resort to stealing
5112     assert(work_q->size() == 0, "Have work, shouldn't steal");
5113     // Try to steal from other queues that have work
5114     if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5115       NOT_PRODUCT(num_steals++;)
5116       assert(oopDesc::is_oop(obj_to_scan), "Oops, not an oop!");
5117       assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5118       // Do scanning work
5119       obj_to_scan->oop_iterate(keep_alive);
5120       // Loop around, finish this work, and try to steal some more
5121     } else if (terminator()->offer_termination()) {
5122       break;  // nirvana from the infinite cycle
5123     }
5124   }
5125   log_develop_trace(gc, task)("\t(%d: stole %d oops)", i, num_steals);
5126 }
5127 
5128 void CMSRefProcTaskExecutor::execute(ProcessTask& task)
5129 {
5130   CMSHeap* heap = CMSHeap::heap();
5131   WorkGang* workers = heap->workers();
5132   assert(workers != NULL, "Need parallel worker threads.");
5133   CMSRefProcTaskProxy rp_task(task, &_collector,
5134                               _collector.ref_processor_span(),
5135                               _collector.markBitMap(),
5136                               workers, _collector.task_queues());
5137   workers->run_task(&rp_task);
5138 }
5139 
5140 void CMSCollector::refProcessingWork() {
5141   ResourceMark rm;
5142   HandleMark   hm;
5143 
5144   ReferenceProcessor* rp = ref_processor();
5145   assert(_span_based_discoverer.span().equals(_span), "Spans should be equal");
5146   assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
5147   // Process weak references.
5148   rp->setup_policy(false);
5149   verify_work_stacks_empty();
5150 
5151   ReferenceProcessorPhaseTimes pt(_gc_timer_cm, rp->num_queues());
5152   {
5153     GCTraceTime(Debug, gc, phases) t("Reference Processing", _gc_timer_cm);
5154 
5155     // Setup keep_alive and complete closures.
5156     CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
5157                                             &_markStack, false /* !preclean */);
5158     CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
5159                                   _span, &_markBitMap, &_markStack,
5160                                   &cmsKeepAliveClosure, false /* !preclean */);
5161 
5162     ReferenceProcessorStats stats;
5163     if (rp->processing_is_mt()) {
5164       // Set the degree of MT here.  If the discovery is done MT, there
5165       // may have been a different number of threads doing the discovery
5166       // and a different number of discovered lists may have Ref objects.
5167       // That is OK as long as the Reference lists are balanced (see
5168       // balance_all_queues() and balance_queues()).
5169       CMSHeap* heap = CMSHeap::heap();
5170       uint active_workers = ParallelGCThreads;
5171       WorkGang* workers = heap->workers();
5172       if (workers != NULL) {
5173         active_workers = workers->active_workers();
5174         // The expectation is that active_workers will have already
5175         // been set to a reasonable value.  If it has not been set,
5176         // investigate.
5177         assert(active_workers > 0, "Should have been set during scavenge");
5178       }
5179       rp->set_active_mt_degree(active_workers);
5180       CMSRefProcTaskExecutor task_executor(*this);
5181       stats = rp->process_discovered_references(&_is_alive_closure,
5182                                         &cmsKeepAliveClosure,
5183                                         &cmsDrainMarkingStackClosure,
5184                                         &task_executor,
5185                                         &pt);
5186     } else {
5187       stats = rp->process_discovered_references(&_is_alive_closure,
5188                                         &cmsKeepAliveClosure,
5189                                         &cmsDrainMarkingStackClosure,
5190                                         NULL,
5191                                         &pt);
5192     }
5193     _gc_tracer_cm->report_gc_reference_stats(stats);
5194     pt.print_all_references();
5195   }
5196 
5197   // This is the point where the entire marking should have completed.
5198   verify_work_stacks_empty();
5199 
5200   {
5201     GCTraceTime(Debug, gc, phases) t("Weak Processing", _gc_timer_cm);
5202     WeakProcessor::weak_oops_do(&_is_alive_closure, &do_nothing_cl);
5203   }
5204 
5205   if (should_unload_classes()) {
5206     {
5207       GCTraceTime(Debug, gc, phases) t("Class Unloading", _gc_timer_cm);
5208 
5209       // Unload classes and purge the SystemDictionary.
5210       bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure, _gc_timer_cm);
5211 
5212       // Unload nmethods.
5213       CodeCache::do_unloading(&_is_alive_closure, purged_class);
5214 
5215       // Prune dead klasses from subklass/sibling/implementor lists.
5216       Klass::clean_weak_klass_links(purged_class);
5217     }
5218 
5219     {
5220       GCTraceTime(Debug, gc, phases) t("Scrub Symbol Table", _gc_timer_cm);
5221       // Clean up unreferenced symbols in symbol table.
5222       SymbolTable::unlink();
5223     }
5224 
5225     {
5226       GCTraceTime(Debug, gc, phases) t("Scrub String Table", _gc_timer_cm);
5227       // Delete entries for dead interned strings.
5228       StringTable::unlink(&_is_alive_closure);
5229     }
5230   }
5231 
5232   // Restore any preserved marks as a result of mark stack or
5233   // work queue overflow
5234   restore_preserved_marks_if_any();  // done single-threaded for now
5235 
5236   rp->set_enqueuing_is_done(true);
5237   rp->verify_no_references_recorded();
5238 }
5239 
5240 #ifndef PRODUCT
5241 void CMSCollector::check_correct_thread_executing() {
5242   Thread* t = Thread::current();
5243   // Only the VM thread or the CMS thread should be here.
5244   assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
5245          "Unexpected thread type");
5246   // If this is the vm thread, the foreground process
5247   // should not be waiting.  Note that _foregroundGCIsActive is
5248   // true while the foreground collector is waiting.
5249   if (_foregroundGCShouldWait) {
5250     // We cannot be the VM thread
5251     assert(t->is_ConcurrentGC_thread(),
5252            "Should be CMS thread");
5253   } else {
5254     // We can be the CMS thread only if we are in a stop-world
5255     // phase of CMS collection.
5256     if (t->is_ConcurrentGC_thread()) {
5257       assert(_collectorState == InitialMarking ||
5258              _collectorState == FinalMarking,
5259              "Should be a stop-world phase");
5260       // The CMS thread should be holding the CMS_token.
5261       assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5262              "Potential interference with concurrently "
5263              "executing VM thread");
5264     }
5265   }
5266 }
5267 #endif
5268 
5269 void CMSCollector::sweep() {
5270   assert(_collectorState == Sweeping, "just checking");
5271   check_correct_thread_executing();
5272   verify_work_stacks_empty();
5273   verify_overflow_empty();
5274   increment_sweep_count();
5275   TraceCMSMemoryManagerStats tms(_collectorState, CMSHeap::heap()->gc_cause());
5276 
5277   _inter_sweep_timer.stop();
5278   _inter_sweep_estimate.sample(_inter_sweep_timer.seconds());
5279 
5280   assert(!_intra_sweep_timer.is_active(), "Should not be active");
5281   _intra_sweep_timer.reset();
5282   _intra_sweep_timer.start();
5283   {
5284     GCTraceCPUTime tcpu;
5285     CMSPhaseAccounting pa(this, "Concurrent Sweep");
5286     // First sweep the old gen
5287     {
5288       CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
5289                                bitMapLock());
5290       sweepWork(_cmsGen);
5291     }
5292 
5293     // Update Universe::_heap_*_at_gc figures.
5294     // We need all the free list locks to make the abstract state
5295     // transition from Sweeping to Resetting. See detailed note
5296     // further below.
5297     {
5298       CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock());
5299       // Update heap occupancy information which is used as
5300       // input to soft ref clearing policy at the next gc.
5301       Universe::update_heap_info_at_gc();
5302       _collectorState = Resizing;
5303     }
5304   }
5305   verify_work_stacks_empty();
5306   verify_overflow_empty();
5307 
5308   if (should_unload_classes()) {
5309     // Delay purge to the beginning of the next safepoint.  Metaspace::contains
5310     // requires that the virtual spaces are stable and not deleted.
5311     ClassLoaderDataGraph::set_should_purge(true);
5312   }
5313 
5314   _intra_sweep_timer.stop();
5315   _intra_sweep_estimate.sample(_intra_sweep_timer.seconds());
5316 
5317   _inter_sweep_timer.reset();
5318   _inter_sweep_timer.start();
5319 
5320   // We need to use a monotonically non-decreasing time in ms
5321   // or we will see time-warp warnings and os::javaTimeMillis()
5322   // does not guarantee monotonicity.
5323   jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
5324   update_time_of_last_gc(now);
5325 
5326   // NOTE on abstract state transitions:
5327   // Mutators allocate-live and/or mark the mod-union table dirty
5328   // based on the state of the collection.  The former is done in
5329   // the interval [Marking, Sweeping] and the latter in the interval
5330   // [Marking, Sweeping).  Thus the transitions into the Marking state
5331   // and out of the Sweeping state must be synchronously visible
5332   // globally to the mutators.
5333   // The transition into the Marking state happens with the world
5334   // stopped so the mutators will globally see it.  Sweeping is
5335   // done asynchronously by the background collector so the transition
5336   // from the Sweeping state to the Resizing state must be done
5337   // under the freelistLock (as is the check for whether to
5338   // allocate-live and whether to dirty the mod-union table).
5339   assert(_collectorState == Resizing, "Change of collector state to"
5340     " Resizing must be done under the freelistLocks (plural)");
5341 
5342   // Now that sweeping has been completed, we clear
5343   // the incremental_collection_failed flag,
5344   // thus inviting a younger gen collection to promote into
5345   // this generation. If such a promotion may still fail,
5346   // the flag will be set again when a young collection is
5347   // attempted.
5348   CMSHeap* heap = CMSHeap::heap();
5349   heap->clear_incremental_collection_failed();  // Worth retrying as fresh space may have been freed up
5350   heap->update_full_collections_completed(_collection_count_start);
5351 }
5352 
5353 // FIX ME!!! Looks like this belongs in CFLSpace, with
5354 // CMSGen merely delegating to it.
5355 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
5356   double nearLargestPercent = FLSLargestBlockCoalesceProximity;
5357   HeapWord*  minAddr        = _cmsSpace->bottom();
5358   HeapWord*  largestAddr    =
5359     (HeapWord*) _cmsSpace->dictionary()->find_largest_dict();
5360   if (largestAddr == NULL) {
5361     // The dictionary appears to be empty.  In this case
5362     // try to coalesce at the end of the heap.
5363     largestAddr = _cmsSpace->end();
5364   }
5365   size_t largestOffset     = pointer_delta(largestAddr, minAddr);
5366   size_t nearLargestOffset =
5367     (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
5368   log_debug(gc, freelist)("CMS: Large Block: " PTR_FORMAT "; Proximity: " PTR_FORMAT " -> " PTR_FORMAT,
5369                           p2i(largestAddr), p2i(_cmsSpace->nearLargestChunk()), p2i(minAddr + nearLargestOffset));
5370   _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
5371 }
5372 
5373 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
5374   return addr >= _cmsSpace->nearLargestChunk();
5375 }
5376 
5377 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
5378   return _cmsSpace->find_chunk_at_end();
5379 }
5380 
5381 void ConcurrentMarkSweepGeneration::update_gc_stats(Generation* current_generation,
5382                                                     bool full) {
5383   // If the young generation has been collected, gather any statistics
5384   // that are of interest at this point.
5385   bool current_is_young = CMSHeap::heap()->is_young_gen(current_generation);
5386   if (!full && current_is_young) {
5387     // Gather statistics on the young generation collection.
5388     collector()->stats().record_gc0_end(used());
5389   }
5390 }
5391 
5392 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* old_gen) {
5393   // We iterate over the space(s) underlying this generation,
5394   // checking the mark bit map to see if the bits corresponding
5395   // to specific blocks are marked or not. Blocks that are
5396   // marked are live and are not swept up. All remaining blocks
5397   // are swept up, with coalescing on-the-fly as we sweep up
5398   // contiguous free and/or garbage blocks:
5399   // We need to ensure that the sweeper synchronizes with allocators
5400   // and stop-the-world collectors. In particular, the following
5401   // locks are used:
5402   // . CMS token: if this is held, a stop the world collection cannot occur
5403   // . freelistLock: if this is held no allocation can occur from this
5404   //                 generation by another thread
5405   // . bitMapLock: if this is held, no other thread can access or update
5406   //
5407 
5408   // Note that we need to hold the freelistLock if we use
5409   // block iterate below; else the iterator might go awry if
5410   // a mutator (or promotion) causes block contents to change
5411   // (for instance if the allocator divvies up a block).
5412   // If we hold the free list lock, for all practical purposes
5413   // young generation GC's can't occur (they'll usually need to
5414   // promote), so we might as well prevent all young generation
5415   // GC's while we do a sweeping step. For the same reason, we might
5416   // as well take the bit map lock for the entire duration
5417 
5418   // check that we hold the requisite locks
5419   assert(have_cms_token(), "Should hold cms token");
5420   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), "Should possess CMS token to sweep");
5421   assert_lock_strong(old_gen->freelistLock());
5422   assert_lock_strong(bitMapLock());
5423 
5424   assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context");
5425   assert(_intra_sweep_timer.is_active(),  "Was switched on  in an outer context");
5426   old_gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
5427                                           _inter_sweep_estimate.padded_average(),
5428                                           _intra_sweep_estimate.padded_average());
5429   old_gen->setNearLargestChunk();
5430 
5431   {
5432     SweepClosure sweepClosure(this, old_gen, &_markBitMap, CMSYield);
5433     old_gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
5434     // We need to free-up/coalesce garbage/blocks from a
5435     // co-terminal free run. This is done in the SweepClosure
5436     // destructor; so, do not remove this scope, else the
5437     // end-of-sweep-census below will be off by a little bit.
5438   }
5439   old_gen->cmsSpace()->sweep_completed();
5440   old_gen->cmsSpace()->endSweepFLCensus(sweep_count());
5441   if (should_unload_classes()) {                // unloaded classes this cycle,
5442     _concurrent_cycles_since_last_unload = 0;   // ... reset count
5443   } else {                                      // did not unload classes,
5444     _concurrent_cycles_since_last_unload++;     // ... increment count
5445   }
5446 }
5447 
5448 // Reset CMS data structures (for now just the marking bit map)
5449 // preparatory for the next cycle.
5450 void CMSCollector::reset_concurrent() {
5451   CMSTokenSyncWithLocks ts(true, bitMapLock());
5452 
5453   // If the state is not "Resetting", the foreground  thread
5454   // has done a collection and the resetting.
5455   if (_collectorState != Resetting) {
5456     assert(_collectorState == Idling, "The state should only change"
5457       " because the foreground collector has finished the collection");
5458     return;
5459   }
5460 
5461   {
5462     // Clear the mark bitmap (no grey objects to start with)
5463     // for the next cycle.
5464     GCTraceCPUTime tcpu;
5465     CMSPhaseAccounting cmspa(this, "Concurrent Reset");
5466 
5467     HeapWord* curAddr = _markBitMap.startWord();
5468     while (curAddr < _markBitMap.endWord()) {
5469       size_t remaining  = pointer_delta(_markBitMap.endWord(), curAddr);
5470       MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
5471       _markBitMap.clear_large_range(chunk);
5472       if (ConcurrentMarkSweepThread::should_yield() &&
5473           !foregroundGCIsActive() &&
5474           CMSYield) {
5475         assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5476                "CMS thread should hold CMS token");
5477         assert_lock_strong(bitMapLock());
5478         bitMapLock()->unlock();
5479         ConcurrentMarkSweepThread::desynchronize(true);
5480         stopTimer();
5481         incrementYields();
5482 
5483         // See the comment in coordinator_yield()
5484         for (unsigned i = 0; i < CMSYieldSleepCount &&
5485                          ConcurrentMarkSweepThread::should_yield() &&
5486                          !CMSCollector::foregroundGCIsActive(); ++i) {
5487           os::sleep(Thread::current(), 1, false);
5488         }
5489 
5490         ConcurrentMarkSweepThread::synchronize(true);
5491         bitMapLock()->lock_without_safepoint_check();
5492         startTimer();
5493       }
5494       curAddr = chunk.end();
5495     }
5496     // A successful mostly concurrent collection has been done.
5497     // Because only the full (i.e., concurrent mode failure) collections
5498     // are being measured for gc overhead limits, clean the "near" flag
5499     // and count.
5500     size_policy()->reset_gc_overhead_limit_count();
5501     _collectorState = Idling;
5502   }
5503 
5504   register_gc_end();
5505 }
5506 
5507 // Same as above but for STW paths
5508 void CMSCollector::reset_stw() {
5509   // already have the lock
5510   assert(_collectorState == Resetting, "just checking");
5511   assert_lock_strong(bitMapLock());
5512   GCIdMark gc_id_mark(_cmsThread->gc_id());
5513   _markBitMap.clear_all();
5514   _collectorState = Idling;
5515   register_gc_end();
5516 }
5517 
5518 void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) {
5519   GCTraceCPUTime tcpu;
5520   TraceCollectorStats tcs_cgc(cgc_counters());
5521 
5522   switch (op) {
5523     case CMS_op_checkpointRootsInitial: {
5524       GCTraceTime(Info, gc) t("Pause Initial Mark", NULL, GCCause::_no_gc, true);
5525       SvcGCMarker sgcm(SvcGCMarker::CONCURRENT);
5526       checkpointRootsInitial();
5527       break;
5528     }
5529     case CMS_op_checkpointRootsFinal: {
5530       GCTraceTime(Info, gc) t("Pause Remark", NULL, GCCause::_no_gc, true);
5531       SvcGCMarker sgcm(SvcGCMarker::CONCURRENT);
5532       checkpointRootsFinal();
5533       break;
5534     }
5535     default:
5536       fatal("No such CMS_op");
5537   }
5538 }
5539 
5540 #ifndef PRODUCT
5541 size_t const CMSCollector::skip_header_HeapWords() {
5542   return FreeChunk::header_size();
5543 }
5544 
5545 // Try and collect here conditions that should hold when
5546 // CMS thread is exiting. The idea is that the foreground GC
5547 // thread should not be blocked if it wants to terminate
5548 // the CMS thread and yet continue to run the VM for a while
5549 // after that.
5550 void CMSCollector::verify_ok_to_terminate() const {
5551   assert(Thread::current()->is_ConcurrentGC_thread(),
5552          "should be called by CMS thread");
5553   assert(!_foregroundGCShouldWait, "should be false");
5554   // We could check here that all the various low-level locks
5555   // are not held by the CMS thread, but that is overkill; see
5556   // also CMSThread::verify_ok_to_terminate() where the CGC_lock
5557   // is checked.
5558 }
5559 #endif
5560 
5561 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
5562    assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
5563           "missing Printezis mark?");
5564   HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5565   size_t size = pointer_delta(nextOneAddr + 1, addr);
5566   assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5567          "alignment problem");
5568   assert(size >= 3, "Necessary for Printezis marks to work");
5569   return size;
5570 }
5571 
5572 // A variant of the above (block_size_using_printezis_bits()) except
5573 // that we return 0 if the P-bits are not yet set.
5574 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
5575   if (_markBitMap.isMarked(addr + 1)) {
5576     assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects");
5577     HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5578     size_t size = pointer_delta(nextOneAddr + 1, addr);
5579     assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5580            "alignment problem");
5581     assert(size >= 3, "Necessary for Printezis marks to work");
5582     return size;
5583   }
5584   return 0;
5585 }
5586 
5587 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
5588   size_t sz = 0;
5589   oop p = (oop)addr;
5590   if (p->klass_or_null_acquire() != NULL) {
5591     sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
5592   } else {
5593     sz = block_size_using_printezis_bits(addr);
5594   }
5595   assert(sz > 0, "size must be nonzero");
5596   HeapWord* next_block = addr + sz;
5597   HeapWord* next_card  = align_up(next_block, CardTable::card_size);
5598   assert(align_down((uintptr_t)addr,      CardTable::card_size) <
5599          align_down((uintptr_t)next_card, CardTable::card_size),
5600          "must be different cards");
5601   return next_card;
5602 }
5603 
5604 
5605 // CMS Bit Map Wrapper /////////////////////////////////////////
5606 
5607 // Construct a CMS bit map infrastructure, but don't create the
5608 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
5609 // further below.
5610 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
5611   _bm(),
5612   _shifter(shifter),
5613   _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true,
5614                                     Monitor::_safepoint_check_sometimes) : NULL)
5615 {
5616   _bmStartWord = 0;
5617   _bmWordSize  = 0;
5618 }
5619 
5620 bool CMSBitMap::allocate(MemRegion mr) {
5621   _bmStartWord = mr.start();
5622   _bmWordSize  = mr.word_size();
5623   ReservedSpace brs(ReservedSpace::allocation_align_size_up(
5624                      (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
5625   if (!brs.is_reserved()) {
5626     log_warning(gc)("CMS bit map allocation failure");
5627     return false;
5628   }
5629   // For now we'll just commit all of the bit map up front.
5630   // Later on we'll try to be more parsimonious with swap.
5631   if (!_virtual_space.initialize(brs, brs.size())) {
5632     log_warning(gc)("CMS bit map backing store failure");
5633     return false;
5634   }
5635   assert(_virtual_space.committed_size() == brs.size(),
5636          "didn't reserve backing store for all of CMS bit map?");
5637   assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
5638          _bmWordSize, "inconsistency in bit map sizing");
5639   _bm = BitMapView((BitMap::bm_word_t*)_virtual_space.low(), _bmWordSize >> _shifter);
5640 
5641   // bm.clear(); // can we rely on getting zero'd memory? verify below
5642   assert(isAllClear(),
5643          "Expected zero'd memory from ReservedSpace constructor");
5644   assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
5645          "consistency check");
5646   return true;
5647 }
5648 
5649 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
5650   HeapWord *next_addr, *end_addr, *last_addr;
5651   assert_locked();
5652   assert(covers(mr), "out-of-range error");
5653   // XXX assert that start and end are appropriately aligned
5654   for (next_addr = mr.start(), end_addr = mr.end();
5655        next_addr < end_addr; next_addr = last_addr) {
5656     MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
5657     last_addr = dirty_region.end();
5658     if (!dirty_region.is_empty()) {
5659       cl->do_MemRegion(dirty_region);
5660     } else {
5661       assert(last_addr == end_addr, "program logic");
5662       return;
5663     }
5664   }
5665 }
5666 
5667 void CMSBitMap::print_on_error(outputStream* st, const char* prefix) const {
5668   _bm.print_on_error(st, prefix);
5669 }
5670 
5671 #ifndef PRODUCT
5672 void CMSBitMap::assert_locked() const {
5673   CMSLockVerifier::assert_locked(lock());
5674 }
5675 
5676 bool CMSBitMap::covers(MemRegion mr) const {
5677   // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
5678   assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
5679          "size inconsistency");
5680   return (mr.start() >= _bmStartWord) &&
5681          (mr.end()   <= endWord());
5682 }
5683 
5684 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
5685     return (start >= _bmStartWord && (start + size) <= endWord());
5686 }
5687 
5688 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
5689   // verify that there are no 1 bits in the interval [left, right)
5690   FalseBitMapClosure falseBitMapClosure;
5691   iterate(&falseBitMapClosure, left, right);
5692 }
5693 
5694 void CMSBitMap::region_invariant(MemRegion mr)
5695 {
5696   assert_locked();
5697   // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
5698   assert(!mr.is_empty(), "unexpected empty region");
5699   assert(covers(mr), "mr should be covered by bit map");
5700   // convert address range into offset range
5701   size_t start_ofs = heapWordToOffset(mr.start());
5702   // Make sure that end() is appropriately aligned
5703   assert(mr.end() == align_up(mr.end(), (1 << (_shifter+LogHeapWordSize))),
5704          "Misaligned mr.end()");
5705   size_t end_ofs   = heapWordToOffset(mr.end());
5706   assert(end_ofs > start_ofs, "Should mark at least one bit");
5707 }
5708 
5709 #endif
5710 
5711 bool CMSMarkStack::allocate(size_t size) {
5712   // allocate a stack of the requisite depth
5713   ReservedSpace rs(ReservedSpace::allocation_align_size_up(
5714                    size * sizeof(oop)));
5715   if (!rs.is_reserved()) {
5716     log_warning(gc)("CMSMarkStack allocation failure");
5717     return false;
5718   }
5719   if (!_virtual_space.initialize(rs, rs.size())) {
5720     log_warning(gc)("CMSMarkStack backing store failure");
5721     return false;
5722   }
5723   assert(_virtual_space.committed_size() == rs.size(),
5724          "didn't reserve backing store for all of CMS stack?");
5725   _base = (oop*)(_virtual_space.low());
5726   _index = 0;
5727   _capacity = size;
5728   NOT_PRODUCT(_max_depth = 0);
5729   return true;
5730 }
5731 
5732 // XXX FIX ME !!! In the MT case we come in here holding a
5733 // leaf lock. For printing we need to take a further lock
5734 // which has lower rank. We need to recalibrate the two
5735 // lock-ranks involved in order to be able to print the
5736 // messages below. (Or defer the printing to the caller.
5737 // For now we take the expedient path of just disabling the
5738 // messages for the problematic case.)
5739 void CMSMarkStack::expand() {
5740   assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted");
5741   if (_capacity == MarkStackSizeMax) {
5742     if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled) {
5743       // We print a warning message only once per CMS cycle.
5744       log_debug(gc)(" (benign) Hit CMSMarkStack max size limit");
5745     }
5746     return;
5747   }
5748   // Double capacity if possible
5749   size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax);
5750   // Do not give up existing stack until we have managed to
5751   // get the double capacity that we desired.
5752   ReservedSpace rs(ReservedSpace::allocation_align_size_up(
5753                    new_capacity * sizeof(oop)));
5754   if (rs.is_reserved()) {
5755     // Release the backing store associated with old stack
5756     _virtual_space.release();
5757     // Reinitialize virtual space for new stack
5758     if (!_virtual_space.initialize(rs, rs.size())) {
5759       fatal("Not enough swap for expanded marking stack");
5760     }
5761     _base = (oop*)(_virtual_space.low());
5762     _index = 0;
5763     _capacity = new_capacity;
5764   } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled) {
5765     // Failed to double capacity, continue;
5766     // we print a detail message only once per CMS cycle.
5767     log_debug(gc)(" (benign) Failed to expand marking stack from " SIZE_FORMAT "K to " SIZE_FORMAT "K",
5768                         _capacity / K, new_capacity / K);
5769   }
5770 }
5771 
5772 
5773 // Closures
5774 // XXX: there seems to be a lot of code  duplication here;
5775 // should refactor and consolidate common code.
5776 
5777 // This closure is used to mark refs into the CMS generation in
5778 // the CMS bit map. Called at the first checkpoint. This closure
5779 // assumes that we do not need to re-mark dirty cards; if the CMS
5780 // generation on which this is used is not an oldest
5781 // generation then this will lose younger_gen cards!
5782 
5783 MarkRefsIntoClosure::MarkRefsIntoClosure(
5784   MemRegion span, CMSBitMap* bitMap):
5785     _span(span),
5786     _bitMap(bitMap)
5787 {
5788   assert(ref_discoverer() == NULL, "deliberately left NULL");
5789   assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
5790 }
5791 
5792 void MarkRefsIntoClosure::do_oop(oop obj) {
5793   // if p points into _span, then mark corresponding bit in _markBitMap
5794   assert(oopDesc::is_oop(obj), "expected an oop");
5795   HeapWord* addr = (HeapWord*)obj;
5796   if (_span.contains(addr)) {
5797     // this should be made more efficient
5798     _bitMap->mark(addr);
5799   }
5800 }
5801 
5802 void MarkRefsIntoClosure::do_oop(oop* p)       { MarkRefsIntoClosure::do_oop_work(p); }
5803 void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); }
5804 
5805 ParMarkRefsIntoClosure::ParMarkRefsIntoClosure(
5806   MemRegion span, CMSBitMap* bitMap):
5807     _span(span),
5808     _bitMap(bitMap)
5809 {
5810   assert(ref_discoverer() == NULL, "deliberately left NULL");
5811   assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
5812 }
5813 
5814 void ParMarkRefsIntoClosure::do_oop(oop obj) {
5815   // if p points into _span, then mark corresponding bit in _markBitMap
5816   assert(oopDesc::is_oop(obj), "expected an oop");
5817   HeapWord* addr = (HeapWord*)obj;
5818   if (_span.contains(addr)) {
5819     // this should be made more efficient
5820     _bitMap->par_mark(addr);
5821   }
5822 }
5823 
5824 void ParMarkRefsIntoClosure::do_oop(oop* p)       { ParMarkRefsIntoClosure::do_oop_work(p); }
5825 void ParMarkRefsIntoClosure::do_oop(narrowOop* p) { ParMarkRefsIntoClosure::do_oop_work(p); }
5826 
5827 // A variant of the above, used for CMS marking verification.
5828 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
5829   MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm):
5830     _span(span),
5831     _verification_bm(verification_bm),
5832     _cms_bm(cms_bm)
5833 {
5834   assert(ref_discoverer() == NULL, "deliberately left NULL");
5835   assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
5836 }
5837 
5838 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
5839   // if p points into _span, then mark corresponding bit in _markBitMap
5840   assert(oopDesc::is_oop(obj), "expected an oop");
5841   HeapWord* addr = (HeapWord*)obj;
5842   if (_span.contains(addr)) {
5843     _verification_bm->mark(addr);
5844     if (!_cms_bm->isMarked(addr)) {
5845       Log(gc, verify) log;
5846       ResourceMark rm;
5847       LogStream ls(log.error());
5848       oop(addr)->print_on(&ls);
5849       log.error(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
5850       fatal("... aborting");
5851     }
5852   }
5853 }
5854 
5855 void MarkRefsIntoVerifyClosure::do_oop(oop* p)       { MarkRefsIntoVerifyClosure::do_oop_work(p); }
5856 void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
5857 
5858 //////////////////////////////////////////////////
5859 // MarkRefsIntoAndScanClosure
5860 //////////////////////////////////////////////////
5861 
5862 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
5863                                                        ReferenceDiscoverer* rd,
5864                                                        CMSBitMap* bit_map,
5865                                                        CMSBitMap* mod_union_table,
5866                                                        CMSMarkStack*  mark_stack,
5867                                                        CMSCollector* collector,
5868                                                        bool should_yield,
5869                                                        bool concurrent_precleaning):
5870   _collector(collector),
5871   _span(span),
5872   _bit_map(bit_map),
5873   _mark_stack(mark_stack),
5874   _pushAndMarkClosure(collector, span, rd, bit_map, mod_union_table,
5875                       mark_stack, concurrent_precleaning),
5876   _yield(should_yield),
5877   _concurrent_precleaning(concurrent_precleaning),
5878   _freelistLock(NULL)
5879 {
5880   // FIXME: Should initialize in base class constructor.
5881   assert(rd != NULL, "ref_discoverer shouldn't be NULL");
5882   set_ref_discoverer_internal(rd);
5883 }
5884 
5885 // This closure is used to mark refs into the CMS generation at the
5886 // second (final) checkpoint, and to scan and transitively follow
5887 // the unmarked oops. It is also used during the concurrent precleaning
5888 // phase while scanning objects on dirty cards in the CMS generation.
5889 // The marks are made in the marking bit map and the marking stack is
5890 // used for keeping the (newly) grey objects during the scan.
5891 // The parallel version (Par_...) appears further below.
5892 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
5893   if (obj != NULL) {
5894     assert(oopDesc::is_oop(obj), "expected an oop");
5895     HeapWord* addr = (HeapWord*)obj;
5896     assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
5897     assert(_collector->overflow_list_is_empty(),
5898            "overflow list should be empty");
5899     if (_span.contains(addr) &&
5900         !_bit_map->isMarked(addr)) {
5901       // mark bit map (object is now grey)
5902       _bit_map->mark(addr);
5903       // push on marking stack (stack should be empty), and drain the
5904       // stack by applying this closure to the oops in the oops popped
5905       // from the stack (i.e. blacken the grey objects)
5906       bool res = _mark_stack->push(obj);
5907       assert(res, "Should have space to push on empty stack");
5908       do {
5909         oop new_oop = _mark_stack->pop();
5910         assert(new_oop != NULL && oopDesc::is_oop(new_oop), "Expected an oop");
5911         assert(_bit_map->isMarked((HeapWord*)new_oop),
5912                "only grey objects on this stack");
5913         // iterate over the oops in this oop, marking and pushing
5914         // the ones in CMS heap (i.e. in _span).
5915         new_oop->oop_iterate(&_pushAndMarkClosure);
5916         // check if it's time to yield
5917         do_yield_check();
5918       } while (!_mark_stack->isEmpty() ||
5919                (!_concurrent_precleaning && take_from_overflow_list()));
5920         // if marking stack is empty, and we are not doing this
5921         // during precleaning, then check the overflow list
5922     }
5923     assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
5924     assert(_collector->overflow_list_is_empty(),
5925            "overflow list was drained above");
5926 
5927     assert(_collector->no_preserved_marks(),
5928            "All preserved marks should have been restored above");
5929   }
5930 }
5931 
5932 void MarkRefsIntoAndScanClosure::do_oop(oop* p)       { MarkRefsIntoAndScanClosure::do_oop_work(p); }
5933 void MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
5934 
5935 void MarkRefsIntoAndScanClosure::do_yield_work() {
5936   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5937          "CMS thread should hold CMS token");
5938   assert_lock_strong(_freelistLock);
5939   assert_lock_strong(_bit_map->lock());
5940   // relinquish the free_list_lock and bitMaplock()
5941   _bit_map->lock()->unlock();
5942   _freelistLock->unlock();
5943   ConcurrentMarkSweepThread::desynchronize(true);
5944   _collector->stopTimer();
5945   _collector->incrementYields();
5946 
5947   // See the comment in coordinator_yield()
5948   for (unsigned i = 0;
5949        i < CMSYieldSleepCount &&
5950        ConcurrentMarkSweepThread::should_yield() &&
5951        !CMSCollector::foregroundGCIsActive();
5952        ++i) {
5953     os::sleep(Thread::current(), 1, false);
5954   }
5955 
5956   ConcurrentMarkSweepThread::synchronize(true);
5957   _freelistLock->lock_without_safepoint_check();
5958   _bit_map->lock()->lock_without_safepoint_check();
5959   _collector->startTimer();
5960 }
5961 
5962 ///////////////////////////////////////////////////////////
5963 // ParMarkRefsIntoAndScanClosure: a parallel version of
5964 //                                MarkRefsIntoAndScanClosure
5965 ///////////////////////////////////////////////////////////
5966 ParMarkRefsIntoAndScanClosure::ParMarkRefsIntoAndScanClosure(
5967   CMSCollector* collector, MemRegion span, ReferenceDiscoverer* rd,
5968   CMSBitMap* bit_map, OopTaskQueue* work_queue):
5969   _span(span),
5970   _bit_map(bit_map),
5971   _work_queue(work_queue),
5972   _low_water_mark(MIN2((work_queue->max_elems()/4),
5973                        ((uint)CMSWorkQueueDrainThreshold * ParallelGCThreads))),
5974   _parPushAndMarkClosure(collector, span, rd, bit_map, work_queue)
5975 {
5976   // FIXME: Should initialize in base class constructor.
5977   assert(rd != NULL, "ref_discoverer shouldn't be NULL");
5978   set_ref_discoverer_internal(rd);
5979 }
5980 
5981 // This closure is used to mark refs into the CMS generation at the
5982 // second (final) checkpoint, and to scan and transitively follow
5983 // the unmarked oops. The marks are made in the marking bit map and
5984 // the work_queue is used for keeping the (newly) grey objects during
5985 // the scan phase whence they are also available for stealing by parallel
5986 // threads. Since the marking bit map is shared, updates are
5987 // synchronized (via CAS).
5988 void ParMarkRefsIntoAndScanClosure::do_oop(oop obj) {
5989   if (obj != NULL) {
5990     // Ignore mark word because this could be an already marked oop
5991     // that may be chained at the end of the overflow list.
5992     assert(oopDesc::is_oop(obj, true), "expected an oop");
5993     HeapWord* addr = (HeapWord*)obj;
5994     if (_span.contains(addr) &&
5995         !_bit_map->isMarked(addr)) {
5996       // mark bit map (object will become grey):
5997       // It is possible for several threads to be
5998       // trying to "claim" this object concurrently;
5999       // the unique thread that succeeds in marking the
6000       // object first will do the subsequent push on
6001       // to the work queue (or overflow list).
6002       if (_bit_map->par_mark(addr)) {
6003         // push on work_queue (which may not be empty), and trim the
6004         // queue to an appropriate length by applying this closure to
6005         // the oops in the oops popped from the stack (i.e. blacken the
6006         // grey objects)
6007         bool res = _work_queue->push(obj);
6008         assert(res, "Low water mark should be less than capacity?");
6009         trim_queue(_low_water_mark);
6010       } // Else, another thread claimed the object
6011     }
6012   }
6013 }
6014 
6015 void ParMarkRefsIntoAndScanClosure::do_oop(oop* p)       { ParMarkRefsIntoAndScanClosure::do_oop_work(p); }
6016 void ParMarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { ParMarkRefsIntoAndScanClosure::do_oop_work(p); }
6017 
6018 // This closure is used to rescan the marked objects on the dirty cards
6019 // in the mod union table and the card table proper.
6020 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
6021   oop p, MemRegion mr) {
6022 
6023   size_t size = 0;
6024   HeapWord* addr = (HeapWord*)p;
6025   DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6026   assert(_span.contains(addr), "we are scanning the CMS generation");
6027   // check if it's time to yield
6028   if (do_yield_check()) {
6029     // We yielded for some foreground stop-world work,
6030     // and we have been asked to abort this ongoing preclean cycle.
6031     return 0;
6032   }
6033   if (_bitMap->isMarked(addr)) {
6034     // it's marked; is it potentially uninitialized?
6035     if (p->klass_or_null_acquire() != NULL) {
6036         // an initialized object; ignore mark word in verification below
6037         // since we are running concurrent with mutators
6038         assert(oopDesc::is_oop(p, true), "should be an oop");
6039         if (p->is_objArray()) {
6040           // objArrays are precisely marked; restrict scanning
6041           // to dirty cards only.
6042           size = CompactibleFreeListSpace::adjustObjectSize(
6043                    p->oop_iterate_size(_scanningClosure, mr));
6044         } else {
6045           // A non-array may have been imprecisely marked; we need
6046           // to scan object in its entirety.
6047           size = CompactibleFreeListSpace::adjustObjectSize(
6048                    p->oop_iterate_size(_scanningClosure));
6049         }
6050       #ifdef ASSERT
6051         size_t direct_size =
6052           CompactibleFreeListSpace::adjustObjectSize(p->size());
6053         assert(size == direct_size, "Inconsistency in size");
6054         assert(size >= 3, "Necessary for Printezis marks to work");
6055         HeapWord* start_pbit = addr + 1;
6056         HeapWord* end_pbit = addr + size - 1;
6057         assert(_bitMap->isMarked(start_pbit) == _bitMap->isMarked(end_pbit),
6058                "inconsistent Printezis mark");
6059         // Verify inner mark bits (between Printezis bits) are clear,
6060         // but don't repeat if there are multiple dirty regions for
6061         // the same object, to avoid potential O(N^2) performance.
6062         if (addr != _last_scanned_object) {
6063           _bitMap->verifyNoOneBitsInRange(start_pbit + 1, end_pbit);
6064           _last_scanned_object = addr;
6065         }
6066       #endif // ASSERT
6067     } else {
6068       // An uninitialized object.
6069       assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
6070       HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
6071       size = pointer_delta(nextOneAddr + 1, addr);
6072       assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6073              "alignment problem");
6074       // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
6075       // will dirty the card when the klass pointer is installed in the
6076       // object (signaling the completion of initialization).
6077     }
6078   } else {
6079     // Either a not yet marked object or an uninitialized object
6080     if (p->klass_or_null_acquire() == NULL) {
6081       // An uninitialized object, skip to the next card, since
6082       // we may not be able to read its P-bits yet.
6083       assert(size == 0, "Initial value");
6084     } else {
6085       // An object not (yet) reached by marking: we merely need to
6086       // compute its size so as to go look at the next block.
6087       assert(oopDesc::is_oop(p, true), "should be an oop");
6088       size = CompactibleFreeListSpace::adjustObjectSize(p->size());
6089     }
6090   }
6091   DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6092   return size;
6093 }
6094 
6095 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
6096   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6097          "CMS thread should hold CMS token");
6098   assert_lock_strong(_freelistLock);
6099   assert_lock_strong(_bitMap->lock());
6100   // relinquish the free_list_lock and bitMaplock()
6101   _bitMap->lock()->unlock();
6102   _freelistLock->unlock();
6103   ConcurrentMarkSweepThread::desynchronize(true);
6104   _collector->stopTimer();
6105   _collector->incrementYields();
6106 
6107   // See the comment in coordinator_yield()
6108   for (unsigned i = 0; i < CMSYieldSleepCount &&
6109                    ConcurrentMarkSweepThread::should_yield() &&
6110                    !CMSCollector::foregroundGCIsActive(); ++i) {
6111     os::sleep(Thread::current(), 1, false);
6112   }
6113 
6114   ConcurrentMarkSweepThread::synchronize(true);
6115   _freelistLock->lock_without_safepoint_check();
6116   _bitMap->lock()->lock_without_safepoint_check();
6117   _collector->startTimer();
6118 }
6119 
6120 
6121 //////////////////////////////////////////////////////////////////
6122 // SurvivorSpacePrecleanClosure
6123 //////////////////////////////////////////////////////////////////
6124 // This (single-threaded) closure is used to preclean the oops in
6125 // the survivor spaces.
6126 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
6127 
6128   HeapWord* addr = (HeapWord*)p;
6129   DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6130   assert(!_span.contains(addr), "we are scanning the survivor spaces");
6131   assert(p->klass_or_null() != NULL, "object should be initialized");
6132   // an initialized object; ignore mark word in verification below
6133   // since we are running concurrent with mutators
6134   assert(oopDesc::is_oop(p, true), "should be an oop");
6135   // Note that we do not yield while we iterate over
6136   // the interior oops of p, pushing the relevant ones
6137   // on our marking stack.
6138   size_t size = p->oop_iterate_size(_scanning_closure);
6139   do_yield_check();
6140   // Observe that below, we do not abandon the preclean
6141   // phase as soon as we should; rather we empty the
6142   // marking stack before returning. This is to satisfy
6143   // some existing assertions. In general, it may be a
6144   // good idea to abort immediately and complete the marking
6145   // from the grey objects at a later time.
6146   while (!_mark_stack->isEmpty()) {
6147     oop new_oop = _mark_stack->pop();
6148     assert(new_oop != NULL && oopDesc::is_oop(new_oop), "Expected an oop");
6149     assert(_bit_map->isMarked((HeapWord*)new_oop),
6150            "only grey objects on this stack");
6151     // iterate over the oops in this oop, marking and pushing
6152     // the ones in CMS heap (i.e. in _span).
6153     new_oop->oop_iterate(_scanning_closure);
6154     // check if it's time to yield
6155     do_yield_check();
6156   }
6157   unsigned int after_count =
6158     CMSHeap::heap()->total_collections();
6159   bool abort = (_before_count != after_count) ||
6160                _collector->should_abort_preclean();
6161   return abort ? 0 : size;
6162 }
6163 
6164 void SurvivorSpacePrecleanClosure::do_yield_work() {
6165   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6166          "CMS thread should hold CMS token");
6167   assert_lock_strong(_bit_map->lock());
6168   // Relinquish the bit map lock
6169   _bit_map->lock()->unlock();
6170   ConcurrentMarkSweepThread::desynchronize(true);
6171   _collector->stopTimer();
6172   _collector->incrementYields();
6173 
6174   // See the comment in coordinator_yield()
6175   for (unsigned i = 0; i < CMSYieldSleepCount &&
6176                        ConcurrentMarkSweepThread::should_yield() &&
6177                        !CMSCollector::foregroundGCIsActive(); ++i) {
6178     os::sleep(Thread::current(), 1, false);
6179   }
6180 
6181   ConcurrentMarkSweepThread::synchronize(true);
6182   _bit_map->lock()->lock_without_safepoint_check();
6183   _collector->startTimer();
6184 }
6185 
6186 // This closure is used to rescan the marked objects on the dirty cards
6187 // in the mod union table and the card table proper. In the parallel
6188 // case, although the bitMap is shared, we do a single read so the
6189 // isMarked() query is "safe".
6190 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
6191   // Ignore mark word because we are running concurrent with mutators
6192   assert(oopDesc::is_oop_or_null(p, true), "Expected an oop or NULL at " PTR_FORMAT, p2i(p));
6193   HeapWord* addr = (HeapWord*)p;
6194   assert(_span.contains(addr), "we are scanning the CMS generation");
6195   bool is_obj_array = false;
6196   #ifdef ASSERT
6197     if (!_parallel) {
6198       assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6199       assert(_collector->overflow_list_is_empty(),
6200              "overflow list should be empty");
6201 
6202     }
6203   #endif // ASSERT
6204   if (_bit_map->isMarked(addr)) {
6205     // Obj arrays are precisely marked, non-arrays are not;
6206     // so we scan objArrays precisely and non-arrays in their
6207     // entirety.
6208     if (p->is_objArray()) {
6209       is_obj_array = true;
6210       if (_parallel) {
6211         p->oop_iterate(_par_scan_closure, mr);
6212       } else {
6213         p->oop_iterate(_scan_closure, mr);
6214       }
6215     } else {
6216       if (_parallel) {
6217         p->oop_iterate(_par_scan_closure);
6218       } else {
6219         p->oop_iterate(_scan_closure);
6220       }
6221     }
6222   }
6223   #ifdef ASSERT
6224     if (!_parallel) {
6225       assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6226       assert(_collector->overflow_list_is_empty(),
6227              "overflow list should be empty");
6228 
6229     }
6230   #endif // ASSERT
6231   return is_obj_array;
6232 }
6233 
6234 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
6235                         MemRegion span,
6236                         CMSBitMap* bitMap, CMSMarkStack*  markStack,
6237                         bool should_yield, bool verifying):
6238   _collector(collector),
6239   _span(span),
6240   _bitMap(bitMap),
6241   _mut(&collector->_modUnionTable),
6242   _markStack(markStack),
6243   _yield(should_yield),
6244   _skipBits(0)
6245 {
6246   assert(_markStack->isEmpty(), "stack should be empty");
6247   _finger = _bitMap->startWord();
6248   _threshold = _finger;
6249   assert(_collector->_restart_addr == NULL, "Sanity check");
6250   assert(_span.contains(_finger), "Out of bounds _finger?");
6251   DEBUG_ONLY(_verifying = verifying;)
6252 }
6253 
6254 void MarkFromRootsClosure::reset(HeapWord* addr) {
6255   assert(_markStack->isEmpty(), "would cause duplicates on stack");
6256   assert(_span.contains(addr), "Out of bounds _finger?");
6257   _finger = addr;
6258   _threshold = align_up(_finger, CardTable::card_size);
6259 }
6260 
6261 // Should revisit to see if this should be restructured for
6262 // greater efficiency.
6263 bool MarkFromRootsClosure::do_bit(size_t offset) {
6264   if (_skipBits > 0) {
6265     _skipBits--;
6266     return true;
6267   }
6268   // convert offset into a HeapWord*
6269   HeapWord* addr = _bitMap->startWord() + offset;
6270   assert(_bitMap->endWord() && addr < _bitMap->endWord(),
6271          "address out of range");
6272   assert(_bitMap->isMarked(addr), "tautology");
6273   if (_bitMap->isMarked(addr+1)) {
6274     // this is an allocated but not yet initialized object
6275     assert(_skipBits == 0, "tautology");
6276     _skipBits = 2;  // skip next two marked bits ("Printezis-marks")
6277     oop p = oop(addr);
6278     if (p->klass_or_null_acquire() == NULL) {
6279       DEBUG_ONLY(if (!_verifying) {)
6280         // We re-dirty the cards on which this object lies and increase
6281         // the _threshold so that we'll come back to scan this object
6282         // during the preclean or remark phase. (CMSCleanOnEnter)
6283         if (CMSCleanOnEnter) {
6284           size_t sz = _collector->block_size_using_printezis_bits(addr);
6285           HeapWord* end_card_addr = align_up(addr + sz, CardTable::card_size);
6286           MemRegion redirty_range = MemRegion(addr, end_card_addr);
6287           assert(!redirty_range.is_empty(), "Arithmetical tautology");
6288           // Bump _threshold to end_card_addr; note that
6289           // _threshold cannot possibly exceed end_card_addr, anyhow.
6290           // This prevents future clearing of the card as the scan proceeds
6291           // to the right.
6292           assert(_threshold <= end_card_addr,
6293                  "Because we are just scanning into this object");
6294           if (_threshold < end_card_addr) {
6295             _threshold = end_card_addr;
6296           }
6297           if (p->klass_or_null_acquire() != NULL) {
6298             // Redirty the range of cards...
6299             _mut->mark_range(redirty_range);
6300           } // ...else the setting of klass will dirty the card anyway.
6301         }
6302       DEBUG_ONLY(})
6303       return true;
6304     }
6305   }
6306   scanOopsInOop(addr);
6307   return true;
6308 }
6309 
6310 // We take a break if we've been at this for a while,
6311 // so as to avoid monopolizing the locks involved.
6312 void MarkFromRootsClosure::do_yield_work() {
6313   // First give up the locks, then yield, then re-lock
6314   // We should probably use a constructor/destructor idiom to
6315   // do this unlock/lock or modify the MutexUnlocker class to
6316   // serve our purpose. XXX
6317   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6318          "CMS thread should hold CMS token");
6319   assert_lock_strong(_bitMap->lock());
6320   _bitMap->lock()->unlock();
6321   ConcurrentMarkSweepThread::desynchronize(true);
6322   _collector->stopTimer();
6323   _collector->incrementYields();
6324 
6325   // See the comment in coordinator_yield()
6326   for (unsigned i = 0; i < CMSYieldSleepCount &&
6327                        ConcurrentMarkSweepThread::should_yield() &&
6328                        !CMSCollector::foregroundGCIsActive(); ++i) {
6329     os::sleep(Thread::current(), 1, false);
6330   }
6331 
6332   ConcurrentMarkSweepThread::synchronize(true);
6333   _bitMap->lock()->lock_without_safepoint_check();
6334   _collector->startTimer();
6335 }
6336 
6337 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
6338   assert(_bitMap->isMarked(ptr), "expected bit to be set");
6339   assert(_markStack->isEmpty(),
6340          "should drain stack to limit stack usage");
6341   // convert ptr to an oop preparatory to scanning
6342   oop obj = oop(ptr);
6343   // Ignore mark word in verification below, since we
6344   // may be running concurrent with mutators.
6345   assert(oopDesc::is_oop(obj, true), "should be an oop");
6346   assert(_finger <= ptr, "_finger runneth ahead");
6347   // advance the finger to right end of this object
6348   _finger = ptr + obj->size();
6349   assert(_finger > ptr, "we just incremented it above");
6350   // On large heaps, it may take us some time to get through
6351   // the marking phase. During
6352   // this time it's possible that a lot of mutations have
6353   // accumulated in the card table and the mod union table --
6354   // these mutation records are redundant until we have
6355   // actually traced into the corresponding card.
6356   // Here, we check whether advancing the finger would make
6357   // us cross into a new card, and if so clear corresponding
6358   // cards in the MUT (preclean them in the card-table in the
6359   // future).
6360 
6361   DEBUG_ONLY(if (!_verifying) {)
6362     // The clean-on-enter optimization is disabled by default,
6363     // until we fix 6178663.
6364     if (CMSCleanOnEnter && (_finger > _threshold)) {
6365       // [_threshold, _finger) represents the interval
6366       // of cards to be cleared  in MUT (or precleaned in card table).
6367       // The set of cards to be cleared is all those that overlap
6368       // with the interval [_threshold, _finger); note that
6369       // _threshold is always kept card-aligned but _finger isn't
6370       // always card-aligned.
6371       HeapWord* old_threshold = _threshold;
6372       assert(is_aligned(old_threshold, CardTable::card_size),
6373              "_threshold should always be card-aligned");
6374       _threshold = align_up(_finger, CardTable::card_size);
6375       MemRegion mr(old_threshold, _threshold);
6376       assert(!mr.is_empty(), "Control point invariant");
6377       assert(_span.contains(mr), "Should clear within span");
6378       _mut->clear_range(mr);
6379     }
6380   DEBUG_ONLY(})
6381   // Note: the finger doesn't advance while we drain
6382   // the stack below.
6383   PushOrMarkClosure pushOrMarkClosure(_collector,
6384                                       _span, _bitMap, _markStack,
6385                                       _finger, this);
6386   bool res = _markStack->push(obj);
6387   assert(res, "Empty non-zero size stack should have space for single push");
6388   while (!_markStack->isEmpty()) {
6389     oop new_oop = _markStack->pop();
6390     // Skip verifying header mark word below because we are
6391     // running concurrent with mutators.
6392     assert(oopDesc::is_oop(new_oop, true), "Oops! expected to pop an oop");
6393     // now scan this oop's oops
6394     new_oop->oop_iterate(&pushOrMarkClosure);
6395     do_yield_check();
6396   }
6397   assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
6398 }
6399 
6400 ParMarkFromRootsClosure::ParMarkFromRootsClosure(CMSConcMarkingTask* task,
6401                        CMSCollector* collector, MemRegion span,
6402                        CMSBitMap* bit_map,
6403                        OopTaskQueue* work_queue,
6404                        CMSMarkStack*  overflow_stack):
6405   _collector(collector),
6406   _whole_span(collector->_span),
6407   _span(span),
6408   _bit_map(bit_map),
6409   _mut(&collector->_modUnionTable),
6410   _work_queue(work_queue),
6411   _overflow_stack(overflow_stack),
6412   _skip_bits(0),
6413   _task(task)
6414 {
6415   assert(_work_queue->size() == 0, "work_queue should be empty");
6416   _finger = span.start();
6417   _threshold = _finger;     // XXX Defer clear-on-enter optimization for now
6418   assert(_span.contains(_finger), "Out of bounds _finger?");
6419 }
6420 
6421 // Should revisit to see if this should be restructured for
6422 // greater efficiency.
6423 bool ParMarkFromRootsClosure::do_bit(size_t offset) {
6424   if (_skip_bits > 0) {
6425     _skip_bits--;
6426     return true;
6427   }
6428   // convert offset into a HeapWord*
6429   HeapWord* addr = _bit_map->startWord() + offset;
6430   assert(_bit_map->endWord() && addr < _bit_map->endWord(),
6431          "address out of range");
6432   assert(_bit_map->isMarked(addr), "tautology");
6433   if (_bit_map->isMarked(addr+1)) {
6434     // this is an allocated object that might not yet be initialized
6435     assert(_skip_bits == 0, "tautology");
6436     _skip_bits = 2;  // skip next two marked bits ("Printezis-marks")
6437     oop p = oop(addr);
6438     if (p->klass_or_null_acquire() == NULL) {
6439       // in the case of Clean-on-Enter optimization, redirty card
6440       // and avoid clearing card by increasing  the threshold.
6441       return true;
6442     }
6443   }
6444   scan_oops_in_oop(addr);
6445   return true;
6446 }
6447 
6448 void ParMarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
6449   assert(_bit_map->isMarked(ptr), "expected bit to be set");
6450   // Should we assert that our work queue is empty or
6451   // below some drain limit?
6452   assert(_work_queue->size() == 0,
6453          "should drain stack to limit stack usage");
6454   // convert ptr to an oop preparatory to scanning
6455   oop obj = oop(ptr);
6456   // Ignore mark word in verification below, since we
6457   // may be running concurrent with mutators.
6458   assert(oopDesc::is_oop(obj, true), "should be an oop");
6459   assert(_finger <= ptr, "_finger runneth ahead");
6460   // advance the finger to right end of this object
6461   _finger = ptr + obj->size();
6462   assert(_finger > ptr, "we just incremented it above");
6463   // On large heaps, it may take us some time to get through
6464   // the marking phase. During
6465   // this time it's possible that a lot of mutations have
6466   // accumulated in the card table and the mod union table --
6467   // these mutation records are redundant until we have
6468   // actually traced into the corresponding card.
6469   // Here, we check whether advancing the finger would make
6470   // us cross into a new card, and if so clear corresponding
6471   // cards in the MUT (preclean them in the card-table in the
6472   // future).
6473 
6474   // The clean-on-enter optimization is disabled by default,
6475   // until we fix 6178663.
6476   if (CMSCleanOnEnter && (_finger > _threshold)) {
6477     // [_threshold, _finger) represents the interval
6478     // of cards to be cleared  in MUT (or precleaned in card table).
6479     // The set of cards to be cleared is all those that overlap
6480     // with the interval [_threshold, _finger); note that
6481     // _threshold is always kept card-aligned but _finger isn't
6482     // always card-aligned.
6483     HeapWord* old_threshold = _threshold;
6484     assert(is_aligned(old_threshold, CardTable::card_size),
6485            "_threshold should always be card-aligned");
6486     _threshold = align_up(_finger, CardTable::card_size);
6487     MemRegion mr(old_threshold, _threshold);
6488     assert(!mr.is_empty(), "Control point invariant");
6489     assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
6490     _mut->clear_range(mr);
6491   }
6492 
6493   // Note: the local finger doesn't advance while we drain
6494   // the stack below, but the global finger sure can and will.
6495   HeapWord* volatile* gfa = _task->global_finger_addr();
6496   ParPushOrMarkClosure pushOrMarkClosure(_collector,
6497                                          _span, _bit_map,
6498                                          _work_queue,
6499                                          _overflow_stack,
6500                                          _finger,
6501                                          gfa, this);
6502   bool res = _work_queue->push(obj);   // overflow could occur here
6503   assert(res, "Will hold once we use workqueues");
6504   while (true) {
6505     oop new_oop;
6506     if (!_work_queue->pop_local(new_oop)) {
6507       // We emptied our work_queue; check if there's stuff that can
6508       // be gotten from the overflow stack.
6509       if (CMSConcMarkingTask::get_work_from_overflow_stack(
6510             _overflow_stack, _work_queue)) {
6511         do_yield_check();
6512         continue;
6513       } else {  // done
6514         break;
6515       }
6516     }
6517     // Skip verifying header mark word below because we are
6518     // running concurrent with mutators.
6519     assert(oopDesc::is_oop(new_oop, true), "Oops! expected to pop an oop");
6520     // now scan this oop's oops
6521     new_oop->oop_iterate(&pushOrMarkClosure);
6522     do_yield_check();
6523   }
6524   assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
6525 }
6526 
6527 // Yield in response to a request from VM Thread or
6528 // from mutators.
6529 void ParMarkFromRootsClosure::do_yield_work() {
6530   assert(_task != NULL, "sanity");
6531   _task->yield();
6532 }
6533 
6534 // A variant of the above used for verifying CMS marking work.
6535 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
6536                         MemRegion span,
6537                         CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6538                         CMSMarkStack*  mark_stack):
6539   _collector(collector),
6540   _span(span),
6541   _verification_bm(verification_bm),
6542   _cms_bm(cms_bm),
6543   _mark_stack(mark_stack),
6544   _pam_verify_closure(collector, span, verification_bm, cms_bm,
6545                       mark_stack)
6546 {
6547   assert(_mark_stack->isEmpty(), "stack should be empty");
6548   _finger = _verification_bm->startWord();
6549   assert(_collector->_restart_addr == NULL, "Sanity check");
6550   assert(_span.contains(_finger), "Out of bounds _finger?");
6551 }
6552 
6553 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
6554   assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
6555   assert(_span.contains(addr), "Out of bounds _finger?");
6556   _finger = addr;
6557 }
6558 
6559 // Should revisit to see if this should be restructured for
6560 // greater efficiency.
6561 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
6562   // convert offset into a HeapWord*
6563   HeapWord* addr = _verification_bm->startWord() + offset;
6564   assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
6565          "address out of range");
6566   assert(_verification_bm->isMarked(addr), "tautology");
6567   assert(_cms_bm->isMarked(addr), "tautology");
6568 
6569   assert(_mark_stack->isEmpty(),
6570          "should drain stack to limit stack usage");
6571   // convert addr to an oop preparatory to scanning
6572   oop obj = oop(addr);
6573   assert(oopDesc::is_oop(obj), "should be an oop");
6574   assert(_finger <= addr, "_finger runneth ahead");
6575   // advance the finger to right end of this object
6576   _finger = addr + obj->size();
6577   assert(_finger > addr, "we just incremented it above");
6578   // Note: the finger doesn't advance while we drain
6579   // the stack below.
6580   bool res = _mark_stack->push(obj);
6581   assert(res, "Empty non-zero size stack should have space for single push");
6582   while (!_mark_stack->isEmpty()) {
6583     oop new_oop = _mark_stack->pop();
6584     assert(oopDesc::is_oop(new_oop), "Oops! expected to pop an oop");
6585     // now scan this oop's oops
6586     new_oop->oop_iterate(&_pam_verify_closure);
6587   }
6588   assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
6589   return true;
6590 }
6591 
6592 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
6593   CMSCollector* collector, MemRegion span,
6594   CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6595   CMSMarkStack*  mark_stack):
6596   MetadataAwareOopClosure(collector->ref_processor()),
6597   _collector(collector),
6598   _span(span),
6599   _verification_bm(verification_bm),
6600   _cms_bm(cms_bm),
6601   _mark_stack(mark_stack)
6602 { }
6603 
6604 template <class T> void PushAndMarkVerifyClosure::do_oop_work(T *p) {
6605   oop obj = RawAccess<>::oop_load(p);
6606   do_oop(obj);
6607 }
6608 
6609 void PushAndMarkVerifyClosure::do_oop(oop* p)       { PushAndMarkVerifyClosure::do_oop_work(p); }
6610 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
6611 
6612 // Upon stack overflow, we discard (part of) the stack,
6613 // remembering the least address amongst those discarded
6614 // in CMSCollector's _restart_address.
6615 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
6616   // Remember the least grey address discarded
6617   HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
6618   _collector->lower_restart_addr(ra);
6619   _mark_stack->reset();  // discard stack contents
6620   _mark_stack->expand(); // expand the stack if possible
6621 }
6622 
6623 void PushAndMarkVerifyClosure::do_oop(oop obj) {
6624   assert(oopDesc::is_oop_or_null(obj), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6625   HeapWord* addr = (HeapWord*)obj;
6626   if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
6627     // Oop lies in _span and isn't yet grey or black
6628     _verification_bm->mark(addr);            // now grey
6629     if (!_cms_bm->isMarked(addr)) {
6630       Log(gc, verify) log;
6631       ResourceMark rm;
6632       LogStream ls(log.error());
6633       oop(addr)->print_on(&ls);
6634       log.error(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
6635       fatal("... aborting");
6636     }
6637 
6638     if (!_mark_stack->push(obj)) { // stack overflow
6639       log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _mark_stack->capacity());
6640       assert(_mark_stack->isFull(), "Else push should have succeeded");
6641       handle_stack_overflow(addr);
6642     }
6643     // anything including and to the right of _finger
6644     // will be scanned as we iterate over the remainder of the
6645     // bit map
6646   }
6647 }
6648 
6649 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
6650                      MemRegion span,
6651                      CMSBitMap* bitMap, CMSMarkStack*  markStack,
6652                      HeapWord* finger, MarkFromRootsClosure* parent) :
6653   MetadataAwareOopClosure(collector->ref_processor()),
6654   _collector(collector),
6655   _span(span),
6656   _bitMap(bitMap),
6657   _markStack(markStack),
6658   _finger(finger),
6659   _parent(parent)
6660 { }
6661 
6662 ParPushOrMarkClosure::ParPushOrMarkClosure(CMSCollector* collector,
6663                                            MemRegion span,
6664                                            CMSBitMap* bit_map,
6665                                            OopTaskQueue* work_queue,
6666                                            CMSMarkStack*  overflow_stack,
6667                                            HeapWord* finger,
6668                                            HeapWord* volatile* global_finger_addr,
6669                                            ParMarkFromRootsClosure* parent) :
6670   MetadataAwareOopClosure(collector->ref_processor()),
6671   _collector(collector),
6672   _whole_span(collector->_span),
6673   _span(span),
6674   _bit_map(bit_map),
6675   _work_queue(work_queue),
6676   _overflow_stack(overflow_stack),
6677   _finger(finger),
6678   _global_finger_addr(global_finger_addr),
6679   _parent(parent)
6680 { }
6681 
6682 // Assumes thread-safe access by callers, who are
6683 // responsible for mutual exclusion.
6684 void CMSCollector::lower_restart_addr(HeapWord* low) {
6685   assert(_span.contains(low), "Out of bounds addr");
6686   if (_restart_addr == NULL) {
6687     _restart_addr = low;
6688   } else {
6689     _restart_addr = MIN2(_restart_addr, low);
6690   }
6691 }
6692 
6693 // Upon stack overflow, we discard (part of) the stack,
6694 // remembering the least address amongst those discarded
6695 // in CMSCollector's _restart_address.
6696 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
6697   // Remember the least grey address discarded
6698   HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
6699   _collector->lower_restart_addr(ra);
6700   _markStack->reset();  // discard stack contents
6701   _markStack->expand(); // expand the stack if possible
6702 }
6703 
6704 // Upon stack overflow, we discard (part of) the stack,
6705 // remembering the least address amongst those discarded
6706 // in CMSCollector's _restart_address.
6707 void ParPushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
6708   // We need to do this under a mutex to prevent other
6709   // workers from interfering with the work done below.
6710   MutexLockerEx ml(_overflow_stack->par_lock(),
6711                    Mutex::_no_safepoint_check_flag);
6712   // Remember the least grey address discarded
6713   HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
6714   _collector->lower_restart_addr(ra);
6715   _overflow_stack->reset();  // discard stack contents
6716   _overflow_stack->expand(); // expand the stack if possible
6717 }
6718 
6719 void PushOrMarkClosure::do_oop(oop obj) {
6720   // Ignore mark word because we are running concurrent with mutators.
6721   assert(oopDesc::is_oop_or_null(obj, true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6722   HeapWord* addr = (HeapWord*)obj;
6723   if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
6724     // Oop lies in _span and isn't yet grey or black
6725     _bitMap->mark(addr);            // now grey
6726     if (addr < _finger) {
6727       // the bit map iteration has already either passed, or
6728       // sampled, this bit in the bit map; we'll need to
6729       // use the marking stack to scan this oop's oops.
6730       bool simulate_overflow = false;
6731       NOT_PRODUCT(
6732         if (CMSMarkStackOverflowALot &&
6733             _collector->simulate_overflow()) {
6734           // simulate a stack overflow
6735           simulate_overflow = true;
6736         }
6737       )
6738       if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
6739         log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _markStack->capacity());
6740         assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
6741         handle_stack_overflow(addr);
6742       }
6743     }
6744     // anything including and to the right of _finger
6745     // will be scanned as we iterate over the remainder of the
6746     // bit map
6747     do_yield_check();
6748   }
6749 }
6750 
6751 void PushOrMarkClosure::do_oop(oop* p)       { PushOrMarkClosure::do_oop_work(p); }
6752 void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); }
6753 
6754 void ParPushOrMarkClosure::do_oop(oop obj) {
6755   // Ignore mark word because we are running concurrent with mutators.
6756   assert(oopDesc::is_oop_or_null(obj, true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6757   HeapWord* addr = (HeapWord*)obj;
6758   if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
6759     // Oop lies in _span and isn't yet grey or black
6760     // We read the global_finger (volatile read) strictly after marking oop
6761     bool res = _bit_map->par_mark(addr);    // now grey
6762     volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
6763     // Should we push this marked oop on our stack?
6764     // -- if someone else marked it, nothing to do
6765     // -- if target oop is above global finger nothing to do
6766     // -- if target oop is in chunk and above local finger
6767     //      then nothing to do
6768     // -- else push on work queue
6769     if (   !res       // someone else marked it, they will deal with it
6770         || (addr >= *gfa)  // will be scanned in a later task
6771         || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
6772       return;
6773     }
6774     // the bit map iteration has already either passed, or
6775     // sampled, this bit in the bit map; we'll need to
6776     // use the marking stack to scan this oop's oops.
6777     bool simulate_overflow = false;
6778     NOT_PRODUCT(
6779       if (CMSMarkStackOverflowALot &&
6780           _collector->simulate_overflow()) {
6781         // simulate a stack overflow
6782         simulate_overflow = true;
6783       }
6784     )
6785     if (simulate_overflow ||
6786         !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
6787       // stack overflow
6788       log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _overflow_stack->capacity());
6789       // We cannot assert that the overflow stack is full because
6790       // it may have been emptied since.
6791       assert(simulate_overflow ||
6792              _work_queue->size() == _work_queue->max_elems(),
6793             "Else push should have succeeded");
6794       handle_stack_overflow(addr);
6795     }
6796     do_yield_check();
6797   }
6798 }
6799 
6800 void ParPushOrMarkClosure::do_oop(oop* p)       { ParPushOrMarkClosure::do_oop_work(p); }
6801 void ParPushOrMarkClosure::do_oop(narrowOop* p) { ParPushOrMarkClosure::do_oop_work(p); }
6802 
6803 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
6804                                        MemRegion span,
6805                                        ReferenceDiscoverer* rd,
6806                                        CMSBitMap* bit_map,
6807                                        CMSBitMap* mod_union_table,
6808                                        CMSMarkStack*  mark_stack,
6809                                        bool           concurrent_precleaning):
6810   MetadataAwareOopClosure(rd),
6811   _collector(collector),
6812   _span(span),
6813   _bit_map(bit_map),
6814   _mod_union_table(mod_union_table),
6815   _mark_stack(mark_stack),
6816   _concurrent_precleaning(concurrent_precleaning)
6817 {
6818   assert(ref_discoverer() != NULL, "ref_discoverer shouldn't be NULL");
6819 }
6820 
6821 // Grey object rescan during pre-cleaning and second checkpoint phases --
6822 // the non-parallel version (the parallel version appears further below.)
6823 void PushAndMarkClosure::do_oop(oop obj) {
6824   // Ignore mark word verification. If during concurrent precleaning,
6825   // the object monitor may be locked. If during the checkpoint
6826   // phases, the object may already have been reached by a  different
6827   // path and may be at the end of the global overflow list (so
6828   // the mark word may be NULL).
6829   assert(oopDesc::is_oop_or_null(obj, true /* ignore mark word */),
6830          "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6831   HeapWord* addr = (HeapWord*)obj;
6832   // Check if oop points into the CMS generation
6833   // and is not marked
6834   if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
6835     // a white object ...
6836     _bit_map->mark(addr);         // ... now grey
6837     // push on the marking stack (grey set)
6838     bool simulate_overflow = false;
6839     NOT_PRODUCT(
6840       if (CMSMarkStackOverflowALot &&
6841           _collector->simulate_overflow()) {
6842         // simulate a stack overflow
6843         simulate_overflow = true;
6844       }
6845     )
6846     if (simulate_overflow || !_mark_stack->push(obj)) {
6847       if (_concurrent_precleaning) {
6848          // During precleaning we can just dirty the appropriate card(s)
6849          // in the mod union table, thus ensuring that the object remains
6850          // in the grey set  and continue. In the case of object arrays
6851          // we need to dirty all of the cards that the object spans,
6852          // since the rescan of object arrays will be limited to the
6853          // dirty cards.
6854          // Note that no one can be interfering with us in this action
6855          // of dirtying the mod union table, so no locking or atomics
6856          // are required.
6857          if (obj->is_objArray()) {
6858            size_t sz = obj->size();
6859            HeapWord* end_card_addr = align_up(addr + sz, CardTable::card_size);
6860            MemRegion redirty_range = MemRegion(addr, end_card_addr);
6861            assert(!redirty_range.is_empty(), "Arithmetical tautology");
6862            _mod_union_table->mark_range(redirty_range);
6863          } else {
6864            _mod_union_table->mark(addr);
6865          }
6866          _collector->_ser_pmc_preclean_ovflw++;
6867       } else {
6868          // During the remark phase, we need to remember this oop
6869          // in the overflow list.
6870          _collector->push_on_overflow_list(obj);
6871          _collector->_ser_pmc_remark_ovflw++;
6872       }
6873     }
6874   }
6875 }
6876 
6877 ParPushAndMarkClosure::ParPushAndMarkClosure(CMSCollector* collector,
6878                                              MemRegion span,
6879                                              ReferenceDiscoverer* rd,
6880                                              CMSBitMap* bit_map,
6881                                              OopTaskQueue* work_queue):
6882   MetadataAwareOopClosure(rd),
6883   _collector(collector),
6884   _span(span),
6885   _bit_map(bit_map),
6886   _work_queue(work_queue)
6887 {
6888   assert(ref_discoverer() != NULL, "ref_discoverer shouldn't be NULL");
6889 }
6890 
6891 void PushAndMarkClosure::do_oop(oop* p)       { PushAndMarkClosure::do_oop_work(p); }
6892 void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); }
6893 
6894 // Grey object rescan during second checkpoint phase --
6895 // the parallel version.
6896 void ParPushAndMarkClosure::do_oop(oop obj) {
6897   // In the assert below, we ignore the mark word because
6898   // this oop may point to an already visited object that is
6899   // on the overflow stack (in which case the mark word has
6900   // been hijacked for chaining into the overflow stack --
6901   // if this is the last object in the overflow stack then
6902   // its mark word will be NULL). Because this object may
6903   // have been subsequently popped off the global overflow
6904   // stack, and the mark word possibly restored to the prototypical
6905   // value, by the time we get to examined this failing assert in
6906   // the debugger, is_oop_or_null(false) may subsequently start
6907   // to hold.
6908   assert(oopDesc::is_oop_or_null(obj, true),
6909          "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6910   HeapWord* addr = (HeapWord*)obj;
6911   // Check if oop points into the CMS generation
6912   // and is not marked
6913   if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
6914     // a white object ...
6915     // If we manage to "claim" the object, by being the
6916     // first thread to mark it, then we push it on our
6917     // marking stack
6918     if (_bit_map->par_mark(addr)) {     // ... now grey
6919       // push on work queue (grey set)
6920       bool simulate_overflow = false;
6921       NOT_PRODUCT(
6922         if (CMSMarkStackOverflowALot &&
6923             _collector->par_simulate_overflow()) {
6924           // simulate a stack overflow
6925           simulate_overflow = true;
6926         }
6927       )
6928       if (simulate_overflow || !_work_queue->push(obj)) {
6929         _collector->par_push_on_overflow_list(obj);
6930         _collector->_par_pmc_remark_ovflw++; //  imprecise OK: no need to CAS
6931       }
6932     } // Else, some other thread got there first
6933   }
6934 }
6935 
6936 void ParPushAndMarkClosure::do_oop(oop* p)       { ParPushAndMarkClosure::do_oop_work(p); }
6937 void ParPushAndMarkClosure::do_oop(narrowOop* p) { ParPushAndMarkClosure::do_oop_work(p); }
6938 
6939 void CMSPrecleanRefsYieldClosure::do_yield_work() {
6940   Mutex* bml = _collector->bitMapLock();
6941   assert_lock_strong(bml);
6942   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6943          "CMS thread should hold CMS token");
6944 
6945   bml->unlock();
6946   ConcurrentMarkSweepThread::desynchronize(true);
6947 
6948   _collector->stopTimer();
6949   _collector->incrementYields();
6950 
6951   // See the comment in coordinator_yield()
6952   for (unsigned i = 0; i < CMSYieldSleepCount &&
6953                        ConcurrentMarkSweepThread::should_yield() &&
6954                        !CMSCollector::foregroundGCIsActive(); ++i) {
6955     os::sleep(Thread::current(), 1, false);
6956   }
6957 
6958   ConcurrentMarkSweepThread::synchronize(true);
6959   bml->lock();
6960 
6961   _collector->startTimer();
6962 }
6963 
6964 bool CMSPrecleanRefsYieldClosure::should_return() {
6965   if (ConcurrentMarkSweepThread::should_yield()) {
6966     do_yield_work();
6967   }
6968   return _collector->foregroundGCIsActive();
6969 }
6970 
6971 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
6972   assert(((size_t)mr.start())%CardTable::card_size_in_words == 0,
6973          "mr should be aligned to start at a card boundary");
6974   // We'd like to assert:
6975   // assert(mr.word_size()%CardTable::card_size_in_words == 0,
6976   //        "mr should be a range of cards");
6977   // However, that would be too strong in one case -- the last
6978   // partition ends at _unallocated_block which, in general, can be
6979   // an arbitrary boundary, not necessarily card aligned.
6980   _num_dirty_cards += mr.word_size()/CardTable::card_size_in_words;
6981   _space->object_iterate_mem(mr, &_scan_cl);
6982 }
6983 
6984 SweepClosure::SweepClosure(CMSCollector* collector,
6985                            ConcurrentMarkSweepGeneration* g,
6986                            CMSBitMap* bitMap, bool should_yield) :
6987   _collector(collector),
6988   _g(g),
6989   _sp(g->cmsSpace()),
6990   _limit(_sp->sweep_limit()),
6991   _freelistLock(_sp->freelistLock()),
6992   _bitMap(bitMap),
6993   _yield(should_yield),
6994   _inFreeRange(false),           // No free range at beginning of sweep
6995   _freeRangeInFreeLists(false),  // No free range at beginning of sweep
6996   _lastFreeRangeCoalesced(false),
6997   _freeFinger(g->used_region().start())
6998 {
6999   NOT_PRODUCT(
7000     _numObjectsFreed = 0;
7001     _numWordsFreed   = 0;
7002     _numObjectsLive = 0;
7003     _numWordsLive = 0;
7004     _numObjectsAlreadyFree = 0;
7005     _numWordsAlreadyFree = 0;
7006     _last_fc = NULL;
7007 
7008     _sp->initializeIndexedFreeListArrayReturnedBytes();
7009     _sp->dictionary()->initialize_dict_returned_bytes();
7010   )
7011   assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7012          "sweep _limit out of bounds");
7013   log_develop_trace(gc, sweep)("====================");
7014   log_develop_trace(gc, sweep)("Starting new sweep with limit " PTR_FORMAT, p2i(_limit));
7015 }
7016 
7017 void SweepClosure::print_on(outputStream* st) const {
7018   st->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")",
7019                p2i(_sp->bottom()), p2i(_sp->end()));
7020   st->print_cr("_limit = " PTR_FORMAT, p2i(_limit));
7021   st->print_cr("_freeFinger = " PTR_FORMAT, p2i(_freeFinger));
7022   NOT_PRODUCT(st->print_cr("_last_fc = " PTR_FORMAT, p2i(_last_fc));)
7023   st->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d",
7024                _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced);
7025 }
7026 
7027 #ifndef PRODUCT
7028 // Assertion checking only:  no useful work in product mode --
7029 // however, if any of the flags below become product flags,
7030 // you may need to review this code to see if it needs to be
7031 // enabled in product mode.
7032 SweepClosure::~SweepClosure() {
7033   assert_lock_strong(_freelistLock);
7034   assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7035          "sweep _limit out of bounds");
7036   if (inFreeRange()) {
7037     Log(gc, sweep) log;
7038     log.error("inFreeRange() should have been reset; dumping state of SweepClosure");
7039     ResourceMark rm;
7040     LogStream ls(log.error());
7041     print_on(&ls);
7042     ShouldNotReachHere();
7043   }
7044 
7045   if (log_is_enabled(Debug, gc, sweep)) {
7046     log_debug(gc, sweep)("Collected " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
7047                          _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
7048     log_debug(gc, sweep)("Live " SIZE_FORMAT " objects,  " SIZE_FORMAT " bytes  Already free " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
7049                          _numObjectsLive, _numWordsLive*sizeof(HeapWord), _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
7050     size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree) * sizeof(HeapWord);
7051     log_debug(gc, sweep)("Total sweep: " SIZE_FORMAT " bytes", totalBytes);
7052   }
7053 
7054   if (log_is_enabled(Trace, gc, sweep) && CMSVerifyReturnedBytes) {
7055     size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
7056     size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes();
7057     size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes;
7058     log_trace(gc, sweep)("Returned " SIZE_FORMAT " bytes   Indexed List Returned " SIZE_FORMAT " bytes        Dictionary Returned " SIZE_FORMAT " bytes",
7059                          returned_bytes, indexListReturnedBytes, dict_returned_bytes);
7060   }
7061   log_develop_trace(gc, sweep)("end of sweep with _limit = " PTR_FORMAT, p2i(_limit));
7062   log_develop_trace(gc, sweep)("================");
7063 }
7064 #endif  // PRODUCT
7065 
7066 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
7067     bool freeRangeInFreeLists) {
7068   log_develop_trace(gc, sweep)("---- Start free range at " PTR_FORMAT " with free block (%d)",
7069                                p2i(freeFinger), freeRangeInFreeLists);
7070   assert(!inFreeRange(), "Trampling existing free range");
7071   set_inFreeRange(true);
7072   set_lastFreeRangeCoalesced(false);
7073 
7074   set_freeFinger(freeFinger);
7075   set_freeRangeInFreeLists(freeRangeInFreeLists);
7076   if (CMSTestInFreeList) {
7077     if (freeRangeInFreeLists) {
7078       FreeChunk* fc = (FreeChunk*) freeFinger;
7079       assert(fc->is_free(), "A chunk on the free list should be free.");
7080       assert(fc->size() > 0, "Free range should have a size");
7081       assert(_sp->verify_chunk_in_free_list(fc), "Chunk is not in free lists");
7082     }
7083   }
7084 }
7085 
7086 // Note that the sweeper runs concurrently with mutators. Thus,
7087 // it is possible for direct allocation in this generation to happen
7088 // in the middle of the sweep. Note that the sweeper also coalesces
7089 // contiguous free blocks. Thus, unless the sweeper and the allocator
7090 // synchronize appropriately freshly allocated blocks may get swept up.
7091 // This is accomplished by the sweeper locking the free lists while
7092 // it is sweeping. Thus blocks that are determined to be free are
7093 // indeed free. There is however one additional complication:
7094 // blocks that have been allocated since the final checkpoint and
7095 // mark, will not have been marked and so would be treated as
7096 // unreachable and swept up. To prevent this, the allocator marks
7097 // the bit map when allocating during the sweep phase. This leads,
7098 // however, to a further complication -- objects may have been allocated
7099 // but not yet initialized -- in the sense that the header isn't yet
7100 // installed. The sweeper can not then determine the size of the block
7101 // in order to skip over it. To deal with this case, we use a technique
7102 // (due to Printezis) to encode such uninitialized block sizes in the
7103 // bit map. Since the bit map uses a bit per every HeapWord, but the
7104 // CMS generation has a minimum object size of 3 HeapWords, it follows
7105 // that "normal marks" won't be adjacent in the bit map (there will
7106 // always be at least two 0 bits between successive 1 bits). We make use
7107 // of these "unused" bits to represent uninitialized blocks -- the bit
7108 // corresponding to the start of the uninitialized object and the next
7109 // bit are both set. Finally, a 1 bit marks the end of the object that
7110 // started with the two consecutive 1 bits to indicate its potentially
7111 // uninitialized state.
7112 
7113 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
7114   FreeChunk* fc = (FreeChunk*)addr;
7115   size_t res;
7116 
7117   // Check if we are done sweeping. Below we check "addr >= _limit" rather
7118   // than "addr == _limit" because although _limit was a block boundary when
7119   // we started the sweep, it may no longer be one because heap expansion
7120   // may have caused us to coalesce the block ending at the address _limit
7121   // with a newly expanded chunk (this happens when _limit was set to the
7122   // previous _end of the space), so we may have stepped past _limit:
7123   // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740.
7124   if (addr >= _limit) { // we have swept up to or past the limit: finish up
7125     assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7126            "sweep _limit out of bounds");
7127     assert(addr < _sp->end(), "addr out of bounds");
7128     // Flush any free range we might be holding as a single
7129     // coalesced chunk to the appropriate free list.
7130     if (inFreeRange()) {
7131       assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit,
7132              "freeFinger() " PTR_FORMAT " is out of bounds", p2i(freeFinger()));
7133       flush_cur_free_chunk(freeFinger(),
7134                            pointer_delta(addr, freeFinger()));
7135       log_develop_trace(gc, sweep)("Sweep: last chunk: put_free_blk " PTR_FORMAT " (" SIZE_FORMAT ") [coalesced:%d]",
7136                                    p2i(freeFinger()), pointer_delta(addr, freeFinger()),
7137                                    lastFreeRangeCoalesced() ? 1 : 0);
7138     }
7139 
7140     // help the iterator loop finish
7141     return pointer_delta(_sp->end(), addr);
7142   }
7143 
7144   assert(addr < _limit, "sweep invariant");
7145   // check if we should yield
7146   do_yield_check(addr);
7147   if (fc->is_free()) {
7148     // Chunk that is already free
7149     res = fc->size();
7150     do_already_free_chunk(fc);
7151     debug_only(_sp->verifyFreeLists());
7152     // If we flush the chunk at hand in lookahead_and_flush()
7153     // and it's coalesced with a preceding chunk, then the
7154     // process of "mangling" the payload of the coalesced block
7155     // will cause erasure of the size information from the
7156     // (erstwhile) header of all the coalesced blocks but the
7157     // first, so the first disjunct in the assert will not hold
7158     // in that specific case (in which case the second disjunct
7159     // will hold).
7160     assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit,
7161            "Otherwise the size info doesn't change at this step");
7162     NOT_PRODUCT(
7163       _numObjectsAlreadyFree++;
7164       _numWordsAlreadyFree += res;
7165     )
7166     NOT_PRODUCT(_last_fc = fc;)
7167   } else if (!_bitMap->isMarked(addr)) {
7168     // Chunk is fresh garbage
7169     res = do_garbage_chunk(fc);
7170     debug_only(_sp->verifyFreeLists());
7171     NOT_PRODUCT(
7172       _numObjectsFreed++;
7173       _numWordsFreed += res;
7174     )
7175   } else {
7176     // Chunk that is alive.
7177     res = do_live_chunk(fc);
7178     debug_only(_sp->verifyFreeLists());
7179     NOT_PRODUCT(
7180         _numObjectsLive++;
7181         _numWordsLive += res;
7182     )
7183   }
7184   return res;
7185 }
7186 
7187 // For the smart allocation, record following
7188 //  split deaths - a free chunk is removed from its free list because
7189 //      it is being split into two or more chunks.
7190 //  split birth - a free chunk is being added to its free list because
7191 //      a larger free chunk has been split and resulted in this free chunk.
7192 //  coal death - a free chunk is being removed from its free list because
7193 //      it is being coalesced into a large free chunk.
7194 //  coal birth - a free chunk is being added to its free list because
7195 //      it was created when two or more free chunks where coalesced into
7196 //      this free chunk.
7197 //
7198 // These statistics are used to determine the desired number of free
7199 // chunks of a given size.  The desired number is chosen to be relative
7200 // to the end of a CMS sweep.  The desired number at the end of a sweep
7201 // is the
7202 //      count-at-end-of-previous-sweep (an amount that was enough)
7203 //              - count-at-beginning-of-current-sweep  (the excess)
7204 //              + split-births  (gains in this size during interval)
7205 //              - split-deaths  (demands on this size during interval)
7206 // where the interval is from the end of one sweep to the end of the
7207 // next.
7208 //
7209 // When sweeping the sweeper maintains an accumulated chunk which is
7210 // the chunk that is made up of chunks that have been coalesced.  That
7211 // will be termed the left-hand chunk.  A new chunk of garbage that
7212 // is being considered for coalescing will be referred to as the
7213 // right-hand chunk.
7214 //
7215 // When making a decision on whether to coalesce a right-hand chunk with
7216 // the current left-hand chunk, the current count vs. the desired count
7217 // of the left-hand chunk is considered.  Also if the right-hand chunk
7218 // is near the large chunk at the end of the heap (see
7219 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
7220 // left-hand chunk is coalesced.
7221 //
7222 // When making a decision about whether to split a chunk, the desired count
7223 // vs. the current count of the candidate to be split is also considered.
7224 // If the candidate is underpopulated (currently fewer chunks than desired)
7225 // a chunk of an overpopulated (currently more chunks than desired) size may
7226 // be chosen.  The "hint" associated with a free list, if non-null, points
7227 // to a free list which may be overpopulated.
7228 //
7229 
7230 void SweepClosure::do_already_free_chunk(FreeChunk* fc) {
7231   const size_t size = fc->size();
7232   // Chunks that cannot be coalesced are not in the
7233   // free lists.
7234   if (CMSTestInFreeList && !fc->cantCoalesce()) {
7235     assert(_sp->verify_chunk_in_free_list(fc),
7236            "free chunk should be in free lists");
7237   }
7238   // a chunk that is already free, should not have been
7239   // marked in the bit map
7240   HeapWord* const addr = (HeapWord*) fc;
7241   assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
7242   // Verify that the bit map has no bits marked between
7243   // addr and purported end of this block.
7244   _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7245 
7246   // Some chunks cannot be coalesced under any circumstances.
7247   // See the definition of cantCoalesce().
7248   if (!fc->cantCoalesce()) {
7249     // This chunk can potentially be coalesced.
7250     // All the work is done in
7251     do_post_free_or_garbage_chunk(fc, size);
7252     // Note that if the chunk is not coalescable (the else arm
7253     // below), we unconditionally flush, without needing to do
7254     // a "lookahead," as we do below.
7255     if (inFreeRange()) lookahead_and_flush(fc, size);
7256   } else {
7257     // Code path common to both original and adaptive free lists.
7258 
7259     // cant coalesce with previous block; this should be treated
7260     // as the end of a free run if any
7261     if (inFreeRange()) {
7262       // we kicked some butt; time to pick up the garbage
7263       assert(freeFinger() < addr, "freeFinger points too high");
7264       flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7265     }
7266     // else, nothing to do, just continue
7267   }
7268 }
7269 
7270 size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) {
7271   // This is a chunk of garbage.  It is not in any free list.
7272   // Add it to a free list or let it possibly be coalesced into
7273   // a larger chunk.
7274   HeapWord* const addr = (HeapWord*) fc;
7275   const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7276 
7277   // Verify that the bit map has no bits marked between
7278   // addr and purported end of just dead object.
7279   _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7280   do_post_free_or_garbage_chunk(fc, size);
7281 
7282   assert(_limit >= addr + size,
7283          "A freshly garbage chunk can't possibly straddle over _limit");
7284   if (inFreeRange()) lookahead_and_flush(fc, size);
7285   return size;
7286 }
7287 
7288 size_t SweepClosure::do_live_chunk(FreeChunk* fc) {
7289   HeapWord* addr = (HeapWord*) fc;
7290   // The sweeper has just found a live object. Return any accumulated
7291   // left hand chunk to the free lists.
7292   if (inFreeRange()) {
7293     assert(freeFinger() < addr, "freeFinger points too high");
7294     flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7295   }
7296 
7297   // This object is live: we'd normally expect this to be
7298   // an oop, and like to assert the following:
7299   // assert(oopDesc::is_oop(oop(addr)), "live block should be an oop");
7300   // However, as we commented above, this may be an object whose
7301   // header hasn't yet been initialized.
7302   size_t size;
7303   assert(_bitMap->isMarked(addr), "Tautology for this control point");
7304   if (_bitMap->isMarked(addr + 1)) {
7305     // Determine the size from the bit map, rather than trying to
7306     // compute it from the object header.
7307     HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
7308     size = pointer_delta(nextOneAddr + 1, addr);
7309     assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
7310            "alignment problem");
7311 
7312 #ifdef ASSERT
7313       if (oop(addr)->klass_or_null_acquire() != NULL) {
7314         // Ignore mark word because we are running concurrent with mutators
7315         assert(oopDesc::is_oop(oop(addr), true), "live block should be an oop");
7316         assert(size ==
7317                CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
7318                "P-mark and computed size do not agree");
7319       }
7320 #endif
7321 
7322   } else {
7323     // This should be an initialized object that's alive.
7324     assert(oop(addr)->klass_or_null_acquire() != NULL,
7325            "Should be an initialized object");
7326     // Ignore mark word because we are running concurrent with mutators
7327     assert(oopDesc::is_oop(oop(addr), true), "live block should be an oop");
7328     // Verify that the bit map has no bits marked between
7329     // addr and purported end of this block.
7330     size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7331     assert(size >= 3, "Necessary for Printezis marks to work");
7332     assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
7333     DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
7334   }
7335   return size;
7336 }
7337 
7338 void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc,
7339                                                  size_t chunkSize) {
7340   // do_post_free_or_garbage_chunk() should only be called in the case
7341   // of the adaptive free list allocator.
7342   const bool fcInFreeLists = fc->is_free();
7343   assert((HeapWord*)fc <= _limit, "sweep invariant");
7344   if (CMSTestInFreeList && fcInFreeLists) {
7345     assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists");
7346   }
7347 
7348   log_develop_trace(gc, sweep)("  -- pick up another chunk at " PTR_FORMAT " (" SIZE_FORMAT ")", p2i(fc), chunkSize);
7349 
7350   HeapWord* const fc_addr = (HeapWord*) fc;
7351 
7352   bool coalesce = false;
7353   const size_t left  = pointer_delta(fc_addr, freeFinger());
7354   const size_t right = chunkSize;
7355   switch (FLSCoalescePolicy) {
7356     // numeric value forms a coalition aggressiveness metric
7357     case 0:  { // never coalesce
7358       coalesce = false;
7359       break;
7360     }
7361     case 1: { // coalesce if left & right chunks on overpopulated lists
7362       coalesce = _sp->coalOverPopulated(left) &&
7363                  _sp->coalOverPopulated(right);
7364       break;
7365     }
7366     case 2: { // coalesce if left chunk on overpopulated list (default)
7367       coalesce = _sp->coalOverPopulated(left);
7368       break;
7369     }
7370     case 3: { // coalesce if left OR right chunk on overpopulated list
7371       coalesce = _sp->coalOverPopulated(left) ||
7372                  _sp->coalOverPopulated(right);
7373       break;
7374     }
7375     case 4: { // always coalesce
7376       coalesce = true;
7377       break;
7378     }
7379     default:
7380      ShouldNotReachHere();
7381   }
7382 
7383   // Should the current free range be coalesced?
7384   // If the chunk is in a free range and either we decided to coalesce above
7385   // or the chunk is near the large block at the end of the heap
7386   // (isNearLargestChunk() returns true), then coalesce this chunk.
7387   const bool doCoalesce = inFreeRange()
7388                           && (coalesce || _g->isNearLargestChunk(fc_addr));
7389   if (doCoalesce) {
7390     // Coalesce the current free range on the left with the new
7391     // chunk on the right.  If either is on a free list,
7392     // it must be removed from the list and stashed in the closure.
7393     if (freeRangeInFreeLists()) {
7394       FreeChunk* const ffc = (FreeChunk*)freeFinger();
7395       assert(ffc->size() == pointer_delta(fc_addr, freeFinger()),
7396              "Size of free range is inconsistent with chunk size.");
7397       if (CMSTestInFreeList) {
7398         assert(_sp->verify_chunk_in_free_list(ffc),
7399                "Chunk is not in free lists");
7400       }
7401       _sp->coalDeath(ffc->size());
7402       _sp->removeFreeChunkFromFreeLists(ffc);
7403       set_freeRangeInFreeLists(false);
7404     }
7405     if (fcInFreeLists) {
7406       _sp->coalDeath(chunkSize);
7407       assert(fc->size() == chunkSize,
7408         "The chunk has the wrong size or is not in the free lists");
7409       _sp->removeFreeChunkFromFreeLists(fc);
7410     }
7411     set_lastFreeRangeCoalesced(true);
7412     print_free_block_coalesced(fc);
7413   } else {  // not in a free range and/or should not coalesce
7414     // Return the current free range and start a new one.
7415     if (inFreeRange()) {
7416       // In a free range but cannot coalesce with the right hand chunk.
7417       // Put the current free range into the free lists.
7418       flush_cur_free_chunk(freeFinger(),
7419                            pointer_delta(fc_addr, freeFinger()));
7420     }
7421     // Set up for new free range.  Pass along whether the right hand
7422     // chunk is in the free lists.
7423     initialize_free_range((HeapWord*)fc, fcInFreeLists);
7424   }
7425 }
7426 
7427 // Lookahead flush:
7428 // If we are tracking a free range, and this is the last chunk that
7429 // we'll look at because its end crosses past _limit, we'll preemptively
7430 // flush it along with any free range we may be holding on to. Note that
7431 // this can be the case only for an already free or freshly garbage
7432 // chunk. If this block is an object, it can never straddle
7433 // over _limit. The "straddling" occurs when _limit is set at
7434 // the previous end of the space when this cycle started, and
7435 // a subsequent heap expansion caused the previously co-terminal
7436 // free block to be coalesced with the newly expanded portion,
7437 // thus rendering _limit a non-block-boundary making it dangerous
7438 // for the sweeper to step over and examine.
7439 void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) {
7440   assert(inFreeRange(), "Should only be called if currently in a free range.");
7441   HeapWord* const eob = ((HeapWord*)fc) + chunk_size;
7442   assert(_sp->used_region().contains(eob - 1),
7443          "eob = " PTR_FORMAT " eob-1 = " PTR_FORMAT " _limit = " PTR_FORMAT
7444          " out of bounds wrt _sp = [" PTR_FORMAT "," PTR_FORMAT ")"
7445          " when examining fc = " PTR_FORMAT "(" SIZE_FORMAT ")",
7446          p2i(eob), p2i(eob-1), p2i(_limit), p2i(_sp->bottom()), p2i(_sp->end()), p2i(fc), chunk_size);
7447   if (eob >= _limit) {
7448     assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit");
7449     log_develop_trace(gc, sweep)("_limit " PTR_FORMAT " reached or crossed by block "
7450                                  "[" PTR_FORMAT "," PTR_FORMAT ") in space "
7451                                  "[" PTR_FORMAT "," PTR_FORMAT ")",
7452                                  p2i(_limit), p2i(fc), p2i(eob), p2i(_sp->bottom()), p2i(_sp->end()));
7453     // Return the storage we are tracking back into the free lists.
7454     log_develop_trace(gc, sweep)("Flushing ... ");
7455     assert(freeFinger() < eob, "Error");
7456     flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger()));
7457   }
7458 }
7459 
7460 void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) {
7461   assert(inFreeRange(), "Should only be called if currently in a free range.");
7462   assert(size > 0,
7463     "A zero sized chunk cannot be added to the free lists.");
7464   if (!freeRangeInFreeLists()) {
7465     if (CMSTestInFreeList) {
7466       FreeChunk* fc = (FreeChunk*) chunk;
7467       fc->set_size(size);
7468       assert(!_sp->verify_chunk_in_free_list(fc),
7469              "chunk should not be in free lists yet");
7470     }
7471     log_develop_trace(gc, sweep)(" -- add free block " PTR_FORMAT " (" SIZE_FORMAT ") to free lists", p2i(chunk), size);
7472     // A new free range is going to be starting.  The current
7473     // free range has not been added to the free lists yet or
7474     // was removed so add it back.
7475     // If the current free range was coalesced, then the death
7476     // of the free range was recorded.  Record a birth now.
7477     if (lastFreeRangeCoalesced()) {
7478       _sp->coalBirth(size);
7479     }
7480     _sp->addChunkAndRepairOffsetTable(chunk, size,
7481             lastFreeRangeCoalesced());
7482   } else {
7483     log_develop_trace(gc, sweep)("Already in free list: nothing to flush");
7484   }
7485   set_inFreeRange(false);
7486   set_freeRangeInFreeLists(false);
7487 }
7488 
7489 // We take a break if we've been at this for a while,
7490 // so as to avoid monopolizing the locks involved.
7491 void SweepClosure::do_yield_work(HeapWord* addr) {
7492   // Return current free chunk being used for coalescing (if any)
7493   // to the appropriate freelist.  After yielding, the next
7494   // free block encountered will start a coalescing range of
7495   // free blocks.  If the next free block is adjacent to the
7496   // chunk just flushed, they will need to wait for the next
7497   // sweep to be coalesced.
7498   if (inFreeRange()) {
7499     flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7500   }
7501 
7502   // First give up the locks, then yield, then re-lock.
7503   // We should probably use a constructor/destructor idiom to
7504   // do this unlock/lock or modify the MutexUnlocker class to
7505   // serve our purpose. XXX
7506   assert_lock_strong(_bitMap->lock());
7507   assert_lock_strong(_freelistLock);
7508   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7509          "CMS thread should hold CMS token");
7510   _bitMap->lock()->unlock();
7511   _freelistLock->unlock();
7512   ConcurrentMarkSweepThread::desynchronize(true);
7513   _collector->stopTimer();
7514   _collector->incrementYields();
7515 
7516   // See the comment in coordinator_yield()
7517   for (unsigned i = 0; i < CMSYieldSleepCount &&
7518                        ConcurrentMarkSweepThread::should_yield() &&
7519                        !CMSCollector::foregroundGCIsActive(); ++i) {
7520     os::sleep(Thread::current(), 1, false);
7521   }
7522 
7523   ConcurrentMarkSweepThread::synchronize(true);
7524   _freelistLock->lock();
7525   _bitMap->lock()->lock_without_safepoint_check();
7526   _collector->startTimer();
7527 }
7528 
7529 #ifndef PRODUCT
7530 // This is actually very useful in a product build if it can
7531 // be called from the debugger.  Compile it into the product
7532 // as needed.
7533 bool debug_verify_chunk_in_free_list(FreeChunk* fc) {
7534   return debug_cms_space->verify_chunk_in_free_list(fc);
7535 }
7536 #endif
7537 
7538 void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const {
7539   log_develop_trace(gc, sweep)("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")",
7540                                p2i(fc), fc->size());
7541 }
7542 
7543 // CMSIsAliveClosure
7544 bool CMSIsAliveClosure::do_object_b(oop obj) {
7545   HeapWord* addr = (HeapWord*)obj;
7546   return addr != NULL &&
7547          (!_span.contains(addr) || _bit_map->isMarked(addr));
7548 }
7549 
7550 
7551 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector,
7552                       MemRegion span,
7553                       CMSBitMap* bit_map, CMSMarkStack* mark_stack,
7554                       bool cpc):
7555   _collector(collector),
7556   _span(span),
7557   _bit_map(bit_map),
7558   _mark_stack(mark_stack),
7559   _concurrent_precleaning(cpc) {
7560   assert(!_span.is_empty(), "Empty span could spell trouble");
7561 }
7562 
7563 
7564 // CMSKeepAliveClosure: the serial version
7565 void CMSKeepAliveClosure::do_oop(oop obj) {
7566   HeapWord* addr = (HeapWord*)obj;
7567   if (_span.contains(addr) &&
7568       !_bit_map->isMarked(addr)) {
7569     _bit_map->mark(addr);
7570     bool simulate_overflow = false;
7571     NOT_PRODUCT(
7572       if (CMSMarkStackOverflowALot &&
7573           _collector->simulate_overflow()) {
7574         // simulate a stack overflow
7575         simulate_overflow = true;
7576       }
7577     )
7578     if (simulate_overflow || !_mark_stack->push(obj)) {
7579       if (_concurrent_precleaning) {
7580         // We dirty the overflown object and let the remark
7581         // phase deal with it.
7582         assert(_collector->overflow_list_is_empty(), "Error");
7583         // In the case of object arrays, we need to dirty all of
7584         // the cards that the object spans. No locking or atomics
7585         // are needed since no one else can be mutating the mod union
7586         // table.
7587         if (obj->is_objArray()) {
7588           size_t sz = obj->size();
7589           HeapWord* end_card_addr = align_up(addr + sz, CardTable::card_size);
7590           MemRegion redirty_range = MemRegion(addr, end_card_addr);
7591           assert(!redirty_range.is_empty(), "Arithmetical tautology");
7592           _collector->_modUnionTable.mark_range(redirty_range);
7593         } else {
7594           _collector->_modUnionTable.mark(addr);
7595         }
7596         _collector->_ser_kac_preclean_ovflw++;
7597       } else {
7598         _collector->push_on_overflow_list(obj);
7599         _collector->_ser_kac_ovflw++;
7600       }
7601     }
7602   }
7603 }
7604 
7605 void CMSKeepAliveClosure::do_oop(oop* p)       { CMSKeepAliveClosure::do_oop_work(p); }
7606 void CMSKeepAliveClosure::do_oop(narrowOop* p) { CMSKeepAliveClosure::do_oop_work(p); }
7607 
7608 // CMSParKeepAliveClosure: a parallel version of the above.
7609 // The work queues are private to each closure (thread),
7610 // but (may be) available for stealing by other threads.
7611 void CMSParKeepAliveClosure::do_oop(oop obj) {
7612   HeapWord* addr = (HeapWord*)obj;
7613   if (_span.contains(addr) &&
7614       !_bit_map->isMarked(addr)) {
7615     // In general, during recursive tracing, several threads
7616     // may be concurrently getting here; the first one to
7617     // "tag" it, claims it.
7618     if (_bit_map->par_mark(addr)) {
7619       bool res = _work_queue->push(obj);
7620       assert(res, "Low water mark should be much less than capacity");
7621       // Do a recursive trim in the hope that this will keep
7622       // stack usage lower, but leave some oops for potential stealers
7623       trim_queue(_low_water_mark);
7624     } // Else, another thread got there first
7625   }
7626 }
7627 
7628 void CMSParKeepAliveClosure::do_oop(oop* p)       { CMSParKeepAliveClosure::do_oop_work(p); }
7629 void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
7630 
7631 void CMSParKeepAliveClosure::trim_queue(uint max) {
7632   while (_work_queue->size() > max) {
7633     oop new_oop;
7634     if (_work_queue->pop_local(new_oop)) {
7635       assert(new_oop != NULL && oopDesc::is_oop(new_oop), "Expected an oop");
7636       assert(_bit_map->isMarked((HeapWord*)new_oop),
7637              "no white objects on this stack!");
7638       assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
7639       // iterate over the oops in this oop, marking and pushing
7640       // the ones in CMS heap (i.e. in _span).
7641       new_oop->oop_iterate(&_mark_and_push);
7642     }
7643   }
7644 }
7645 
7646 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
7647                                 CMSCollector* collector,
7648                                 MemRegion span, CMSBitMap* bit_map,
7649                                 OopTaskQueue* work_queue):
7650   _collector(collector),
7651   _span(span),
7652   _bit_map(bit_map),
7653   _work_queue(work_queue) { }
7654 
7655 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
7656   HeapWord* addr = (HeapWord*)obj;
7657   if (_span.contains(addr) &&
7658       !_bit_map->isMarked(addr)) {
7659     if (_bit_map->par_mark(addr)) {
7660       bool simulate_overflow = false;
7661       NOT_PRODUCT(
7662         if (CMSMarkStackOverflowALot &&
7663             _collector->par_simulate_overflow()) {
7664           // simulate a stack overflow
7665           simulate_overflow = true;
7666         }
7667       )
7668       if (simulate_overflow || !_work_queue->push(obj)) {
7669         _collector->par_push_on_overflow_list(obj);
7670         _collector->_par_kac_ovflw++;
7671       }
7672     } // Else another thread got there already
7673   }
7674 }
7675 
7676 void CMSInnerParMarkAndPushClosure::do_oop(oop* p)       { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
7677 void CMSInnerParMarkAndPushClosure::do_oop(narrowOop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
7678 
7679 //////////////////////////////////////////////////////////////////
7680 //  CMSExpansionCause                /////////////////////////////
7681 //////////////////////////////////////////////////////////////////
7682 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
7683   switch (cause) {
7684     case _no_expansion:
7685       return "No expansion";
7686     case _satisfy_free_ratio:
7687       return "Free ratio";
7688     case _satisfy_promotion:
7689       return "Satisfy promotion";
7690     case _satisfy_allocation:
7691       return "allocation";
7692     case _allocate_par_lab:
7693       return "Par LAB";
7694     case _allocate_par_spooling_space:
7695       return "Par Spooling Space";
7696     case _adaptive_size_policy:
7697       return "Ergonomics";
7698     default:
7699       return "unknown";
7700   }
7701 }
7702 
7703 void CMSDrainMarkingStackClosure::do_void() {
7704   // the max number to take from overflow list at a time
7705   const size_t num = _mark_stack->capacity()/4;
7706   assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
7707          "Overflow list should be NULL during concurrent phases");
7708   while (!_mark_stack->isEmpty() ||
7709          // if stack is empty, check the overflow list
7710          _collector->take_from_overflow_list(num, _mark_stack)) {
7711     oop obj = _mark_stack->pop();
7712     HeapWord* addr = (HeapWord*)obj;
7713     assert(_span.contains(addr), "Should be within span");
7714     assert(_bit_map->isMarked(addr), "Should be marked");
7715     assert(oopDesc::is_oop(obj), "Should be an oop");
7716     obj->oop_iterate(_keep_alive);
7717   }
7718 }
7719 
7720 void CMSParDrainMarkingStackClosure::do_void() {
7721   // drain queue
7722   trim_queue(0);
7723 }
7724 
7725 // Trim our work_queue so its length is below max at return
7726 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
7727   while (_work_queue->size() > max) {
7728     oop new_oop;
7729     if (_work_queue->pop_local(new_oop)) {
7730       assert(oopDesc::is_oop(new_oop), "Expected an oop");
7731       assert(_bit_map->isMarked((HeapWord*)new_oop),
7732              "no white objects on this stack!");
7733       assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
7734       // iterate over the oops in this oop, marking and pushing
7735       // the ones in CMS heap (i.e. in _span).
7736       new_oop->oop_iterate(&_mark_and_push);
7737     }
7738   }
7739 }
7740 
7741 ////////////////////////////////////////////////////////////////////
7742 // Support for Marking Stack Overflow list handling and related code
7743 ////////////////////////////////////////////////////////////////////
7744 // Much of the following code is similar in shape and spirit to the
7745 // code used in ParNewGC. We should try and share that code
7746 // as much as possible in the future.
7747 
7748 #ifndef PRODUCT
7749 // Debugging support for CMSStackOverflowALot
7750 
7751 // It's OK to call this multi-threaded;  the worst thing
7752 // that can happen is that we'll get a bunch of closely
7753 // spaced simulated overflows, but that's OK, in fact
7754 // probably good as it would exercise the overflow code
7755 // under contention.
7756 bool CMSCollector::simulate_overflow() {
7757   if (_overflow_counter-- <= 0) { // just being defensive
7758     _overflow_counter = CMSMarkStackOverflowInterval;
7759     return true;
7760   } else {
7761     return false;
7762   }
7763 }
7764 
7765 bool CMSCollector::par_simulate_overflow() {
7766   return simulate_overflow();
7767 }
7768 #endif
7769 
7770 // Single-threaded
7771 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
7772   assert(stack->isEmpty(), "Expected precondition");
7773   assert(stack->capacity() > num, "Shouldn't bite more than can chew");
7774   size_t i = num;
7775   oop  cur = _overflow_list;
7776   const markOop proto = markOopDesc::prototype();
7777   NOT_PRODUCT(ssize_t n = 0;)
7778   for (oop next; i > 0 && cur != NULL; cur = next, i--) {
7779     next = oop(cur->mark_raw());
7780     cur->set_mark_raw(proto);   // until proven otherwise
7781     assert(oopDesc::is_oop(cur), "Should be an oop");
7782     bool res = stack->push(cur);
7783     assert(res, "Bit off more than can chew?");
7784     NOT_PRODUCT(n++;)
7785   }
7786   _overflow_list = cur;
7787 #ifndef PRODUCT
7788   assert(_num_par_pushes >= n, "Too many pops?");
7789   _num_par_pushes -=n;
7790 #endif
7791   return !stack->isEmpty();
7792 }
7793 
7794 #define BUSY  (cast_to_oop<intptr_t>(0x1aff1aff))
7795 // (MT-safe) Get a prefix of at most "num" from the list.
7796 // The overflow list is chained through the mark word of
7797 // each object in the list. We fetch the entire list,
7798 // break off a prefix of the right size and return the
7799 // remainder. If other threads try to take objects from
7800 // the overflow list at that time, they will wait for
7801 // some time to see if data becomes available. If (and
7802 // only if) another thread places one or more object(s)
7803 // on the global list before we have returned the suffix
7804 // to the global list, we will walk down our local list
7805 // to find its end and append the global list to
7806 // our suffix before returning it. This suffix walk can
7807 // prove to be expensive (quadratic in the amount of traffic)
7808 // when there are many objects in the overflow list and
7809 // there is much producer-consumer contention on the list.
7810 // *NOTE*: The overflow list manipulation code here and
7811 // in ParNewGeneration:: are very similar in shape,
7812 // except that in the ParNew case we use the old (from/eden)
7813 // copy of the object to thread the list via its klass word.
7814 // Because of the common code, if you make any changes in
7815 // the code below, please check the ParNew version to see if
7816 // similar changes might be needed.
7817 // CR 6797058 has been filed to consolidate the common code.
7818 bool CMSCollector::par_take_from_overflow_list(size_t num,
7819                                                OopTaskQueue* work_q,
7820                                                int no_of_gc_threads) {
7821   assert(work_q->size() == 0, "First empty local work queue");
7822   assert(num < work_q->max_elems(), "Can't bite more than we can chew");
7823   if (_overflow_list == NULL) {
7824     return false;
7825   }
7826   // Grab the entire list; we'll put back a suffix
7827   oop prefix = cast_to_oop(Atomic::xchg((oopDesc*)BUSY, &_overflow_list));
7828   Thread* tid = Thread::current();
7829   // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was
7830   // set to ParallelGCThreads.
7831   size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads;
7832   size_t sleep_time_millis = MAX2((size_t)1, num/100);
7833   // If the list is busy, we spin for a short while,
7834   // sleeping between attempts to get the list.
7835   for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) {
7836     os::sleep(tid, sleep_time_millis, false);
7837     if (_overflow_list == NULL) {
7838       // Nothing left to take
7839       return false;
7840     } else if (_overflow_list != BUSY) {
7841       // Try and grab the prefix
7842       prefix = cast_to_oop(Atomic::xchg((oopDesc*)BUSY, &_overflow_list));
7843     }
7844   }
7845   // If the list was found to be empty, or we spun long
7846   // enough, we give up and return empty-handed. If we leave
7847   // the list in the BUSY state below, it must be the case that
7848   // some other thread holds the overflow list and will set it
7849   // to a non-BUSY state in the future.
7850   if (prefix == NULL || prefix == BUSY) {
7851      // Nothing to take or waited long enough
7852      if (prefix == NULL) {
7853        // Write back the NULL in case we overwrote it with BUSY above
7854        // and it is still the same value.
7855        Atomic::cmpxchg((oopDesc*)NULL, &_overflow_list, (oopDesc*)BUSY);
7856      }
7857      return false;
7858   }
7859   assert(prefix != NULL && prefix != BUSY, "Error");
7860   size_t i = num;
7861   oop cur = prefix;
7862   // Walk down the first "num" objects, unless we reach the end.
7863   for (; i > 1 && cur->mark_raw() != NULL; cur = oop(cur->mark_raw()), i--);
7864   if (cur->mark_raw() == NULL) {
7865     // We have "num" or fewer elements in the list, so there
7866     // is nothing to return to the global list.
7867     // Write back the NULL in lieu of the BUSY we wrote
7868     // above, if it is still the same value.
7869     if (_overflow_list == BUSY) {
7870       Atomic::cmpxchg((oopDesc*)NULL, &_overflow_list, (oopDesc*)BUSY);
7871     }
7872   } else {
7873     // Chop off the suffix and return it to the global list.
7874     assert(cur->mark_raw() != BUSY, "Error");
7875     oop suffix_head = cur->mark_raw(); // suffix will be put back on global list
7876     cur->set_mark_raw(NULL);           // break off suffix
7877     // It's possible that the list is still in the empty(busy) state
7878     // we left it in a short while ago; in that case we may be
7879     // able to place back the suffix without incurring the cost
7880     // of a walk down the list.
7881     oop observed_overflow_list = _overflow_list;
7882     oop cur_overflow_list = observed_overflow_list;
7883     bool attached = false;
7884     while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
7885       observed_overflow_list =
7886         Atomic::cmpxchg((oopDesc*)suffix_head, &_overflow_list, (oopDesc*)cur_overflow_list);
7887       if (cur_overflow_list == observed_overflow_list) {
7888         attached = true;
7889         break;
7890       } else cur_overflow_list = observed_overflow_list;
7891     }
7892     if (!attached) {
7893       // Too bad, someone else sneaked in (at least) an element; we'll need
7894       // to do a splice. Find tail of suffix so we can prepend suffix to global
7895       // list.
7896       for (cur = suffix_head; cur->mark_raw() != NULL; cur = (oop)(cur->mark_raw()));
7897       oop suffix_tail = cur;
7898       assert(suffix_tail != NULL && suffix_tail->mark_raw() == NULL,
7899              "Tautology");
7900       observed_overflow_list = _overflow_list;
7901       do {
7902         cur_overflow_list = observed_overflow_list;
7903         if (cur_overflow_list != BUSY) {
7904           // Do the splice ...
7905           suffix_tail->set_mark_raw(markOop(cur_overflow_list));
7906         } else { // cur_overflow_list == BUSY
7907           suffix_tail->set_mark_raw(NULL);
7908         }
7909         // ... and try to place spliced list back on overflow_list ...
7910         observed_overflow_list =
7911           Atomic::cmpxchg((oopDesc*)suffix_head, &_overflow_list, (oopDesc*)cur_overflow_list);
7912       } while (cur_overflow_list != observed_overflow_list);
7913       // ... until we have succeeded in doing so.
7914     }
7915   }
7916 
7917   // Push the prefix elements on work_q
7918   assert(prefix != NULL, "control point invariant");
7919   const markOop proto = markOopDesc::prototype();
7920   oop next;
7921   NOT_PRODUCT(ssize_t n = 0;)
7922   for (cur = prefix; cur != NULL; cur = next) {
7923     next = oop(cur->mark_raw());
7924     cur->set_mark_raw(proto);   // until proven otherwise
7925     assert(oopDesc::is_oop(cur), "Should be an oop");
7926     bool res = work_q->push(cur);
7927     assert(res, "Bit off more than we can chew?");
7928     NOT_PRODUCT(n++;)
7929   }
7930 #ifndef PRODUCT
7931   assert(_num_par_pushes >= n, "Too many pops?");
7932   Atomic::sub(n, &_num_par_pushes);
7933 #endif
7934   return true;
7935 }
7936 
7937 // Single-threaded
7938 void CMSCollector::push_on_overflow_list(oop p) {
7939   NOT_PRODUCT(_num_par_pushes++;)
7940   assert(oopDesc::is_oop(p), "Not an oop");
7941   preserve_mark_if_necessary(p);
7942   p->set_mark_raw((markOop)_overflow_list);
7943   _overflow_list = p;
7944 }
7945 
7946 // Multi-threaded; use CAS to prepend to overflow list
7947 void CMSCollector::par_push_on_overflow_list(oop p) {
7948   NOT_PRODUCT(Atomic::inc(&_num_par_pushes);)
7949   assert(oopDesc::is_oop(p), "Not an oop");
7950   par_preserve_mark_if_necessary(p);
7951   oop observed_overflow_list = _overflow_list;
7952   oop cur_overflow_list;
7953   do {
7954     cur_overflow_list = observed_overflow_list;
7955     if (cur_overflow_list != BUSY) {
7956       p->set_mark_raw(markOop(cur_overflow_list));
7957     } else {
7958       p->set_mark_raw(NULL);
7959     }
7960     observed_overflow_list =
7961       Atomic::cmpxchg((oopDesc*)p, &_overflow_list, (oopDesc*)cur_overflow_list);
7962   } while (cur_overflow_list != observed_overflow_list);
7963 }
7964 #undef BUSY
7965 
7966 // Single threaded
7967 // General Note on GrowableArray: pushes may silently fail
7968 // because we are (temporarily) out of C-heap for expanding
7969 // the stack. The problem is quite ubiquitous and affects
7970 // a lot of code in the JVM. The prudent thing for GrowableArray
7971 // to do (for now) is to exit with an error. However, that may
7972 // be too draconian in some cases because the caller may be
7973 // able to recover without much harm. For such cases, we
7974 // should probably introduce a "soft_push" method which returns
7975 // an indication of success or failure with the assumption that
7976 // the caller may be able to recover from a failure; code in
7977 // the VM can then be changed, incrementally, to deal with such
7978 // failures where possible, thus, incrementally hardening the VM
7979 // in such low resource situations.
7980 void CMSCollector::preserve_mark_work(oop p, markOop m) {
7981   _preserved_oop_stack.push(p);
7982   _preserved_mark_stack.push(m);
7983   assert(m == p->mark_raw(), "Mark word changed");
7984   assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
7985          "bijection");
7986 }
7987 
7988 // Single threaded
7989 void CMSCollector::preserve_mark_if_necessary(oop p) {
7990   markOop m = p->mark_raw();
7991   if (m->must_be_preserved(p)) {
7992     preserve_mark_work(p, m);
7993   }
7994 }
7995 
7996 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
7997   markOop m = p->mark_raw();
7998   if (m->must_be_preserved(p)) {
7999     MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
8000     // Even though we read the mark word without holding
8001     // the lock, we are assured that it will not change
8002     // because we "own" this oop, so no other thread can
8003     // be trying to push it on the overflow list; see
8004     // the assertion in preserve_mark_work() that checks
8005     // that m == p->mark_raw().
8006     preserve_mark_work(p, m);
8007   }
8008 }
8009 
8010 // We should be able to do this multi-threaded,
8011 // a chunk of stack being a task (this is
8012 // correct because each oop only ever appears
8013 // once in the overflow list. However, it's
8014 // not very easy to completely overlap this with
8015 // other operations, so will generally not be done
8016 // until all work's been completed. Because we
8017 // expect the preserved oop stack (set) to be small,
8018 // it's probably fine to do this single-threaded.
8019 // We can explore cleverer concurrent/overlapped/parallel
8020 // processing of preserved marks if we feel the
8021 // need for this in the future. Stack overflow should
8022 // be so rare in practice and, when it happens, its
8023 // effect on performance so great that this will
8024 // likely just be in the noise anyway.
8025 void CMSCollector::restore_preserved_marks_if_any() {
8026   assert(SafepointSynchronize::is_at_safepoint(),
8027          "world should be stopped");
8028   assert(Thread::current()->is_ConcurrentGC_thread() ||
8029          Thread::current()->is_VM_thread(),
8030          "should be single-threaded");
8031   assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8032          "bijection");
8033 
8034   while (!_preserved_oop_stack.is_empty()) {
8035     oop p = _preserved_oop_stack.pop();
8036     assert(oopDesc::is_oop(p), "Should be an oop");
8037     assert(_span.contains(p), "oop should be in _span");
8038     assert(p->mark_raw() == markOopDesc::prototype(),
8039            "Set when taken from overflow list");
8040     markOop m = _preserved_mark_stack.pop();
8041     p->set_mark_raw(m);
8042   }
8043   assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(),
8044          "stacks were cleared above");
8045 }
8046 
8047 #ifndef PRODUCT
8048 bool CMSCollector::no_preserved_marks() const {
8049   return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty();
8050 }
8051 #endif
8052 
8053 // Transfer some number of overflown objects to usual marking
8054 // stack. Return true if some objects were transferred.
8055 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
8056   size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,
8057                     (size_t)ParGCDesiredObjsFromOverflowList);
8058 
8059   bool res = _collector->take_from_overflow_list(num, _mark_stack);
8060   assert(_collector->overflow_list_is_empty() || res,
8061          "If list is not empty, we should have taken something");
8062   assert(!res || !_mark_stack->isEmpty(),
8063          "If we took something, it should now be on our stack");
8064   return res;
8065 }
8066 
8067 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
8068   size_t res = _sp->block_size_no_stall(addr, _collector);
8069   if (_sp->block_is_obj(addr)) {
8070     if (_live_bit_map->isMarked(addr)) {
8071       // It can't have been dead in a previous cycle
8072       guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
8073     } else {
8074       _dead_bit_map->mark(addr);      // mark the dead object
8075     }
8076   }
8077   // Could be 0, if the block size could not be computed without stalling.
8078   return res;
8079 }
8080 
8081 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() {
8082   GCMemoryManager* manager = CMSHeap::heap()->old_manager();
8083   switch (phase) {
8084     case CMSCollector::InitialMarking:
8085       initialize(manager /* GC manager */ ,
8086                  cause   /* cause of the GC */,
8087                  true    /* recordGCBeginTime */,
8088                  true    /* recordPreGCUsage */,
8089                  false   /* recordPeakUsage */,
8090                  false   /* recordPostGCusage */,
8091                  true    /* recordAccumulatedGCTime */,
8092                  false   /* recordGCEndTime */,
8093                  false   /* countCollection */  );
8094       break;
8095 
8096     case CMSCollector::FinalMarking:
8097       initialize(manager /* GC manager */ ,
8098                  cause   /* cause of the GC */,
8099                  false   /* recordGCBeginTime */,
8100                  false   /* recordPreGCUsage */,
8101                  false   /* recordPeakUsage */,
8102                  false   /* recordPostGCusage */,
8103                  true    /* recordAccumulatedGCTime */,
8104                  false   /* recordGCEndTime */,
8105                  false   /* countCollection */  );
8106       break;
8107 
8108     case CMSCollector::Sweeping:
8109       initialize(manager /* GC manager */ ,
8110                  cause   /* cause of the GC */,
8111                  false   /* recordGCBeginTime */,
8112                  false   /* recordPreGCUsage */,
8113                  true    /* recordPeakUsage */,
8114                  true    /* recordPostGCusage */,
8115                  false   /* recordAccumulatedGCTime */,
8116                  true    /* recordGCEndTime */,
8117                  true    /* countCollection */  );
8118       break;
8119 
8120     default:
8121       ShouldNotReachHere();
8122   }
8123 }