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/classLoaderDataGraph.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/cmsVMOperations.hpp"
  36 #include "gc/cms/compactibleFreeListSpace.hpp"
  37 #include "gc/cms/concurrentMarkSweepGeneration.inline.hpp"
  38 #include "gc/cms/concurrentMarkSweepThread.hpp"
  39 #include "gc/cms/parNewGeneration.hpp"
  40 #include "gc/cms/promotionInfo.inline.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/owstTaskTerminator.hpp"
  59 #include "gc/shared/referencePolicy.hpp"
  60 #include "gc/shared/referenceProcessorPhaseTimes.hpp"
  61 #include "gc/shared/space.inline.hpp"
  62 #include "gc/shared/strongRootsScope.hpp"
  63 #include "gc/shared/taskqueue.inline.hpp"
  64 #include "gc/shared/weakProcessor.hpp"
  65 #include "gc/shared/workerPolicy.hpp"
  66 #include "logging/log.hpp"
  67 #include "logging/logStream.hpp"
  68 #include "memory/allocation.hpp"
  69 #include "memory/binaryTreeDictionary.inline.hpp"
  70 #include "memory/iterator.inline.hpp"
  71 #include "memory/padded.hpp"
  72 #include "memory/resourceArea.hpp"
  73 #include "oops/access.inline.hpp"
  74 #include "oops/oop.inline.hpp"
  75 #include "prims/jvmtiExport.hpp"
  76 #include "runtime/atomic.hpp"
  77 #include "runtime/flags/flagSetting.hpp"
  78 #include "runtime/globals_extension.hpp"
  79 #include "runtime/handles.inline.hpp"
  80 #include "runtime/java.hpp"
  81 #include "runtime/orderAccess.hpp"
  82 #include "runtime/timer.hpp"
  83 #include "runtime/vmThread.hpp"
  84 #include "services/memoryService.hpp"
  85 #include "services/runtimeService.hpp"
  86 #include "utilities/align.hpp"
  87 #include "utilities/stack.inline.hpp"
  88 
  89 // statics
  90 CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL;
  91 bool CMSCollector::_full_gc_requested = false;
  92 GCCause::Cause CMSCollector::_full_gc_cause = GCCause::_no_gc;
  93 
  94 //////////////////////////////////////////////////////////////////
  95 // In support of CMS/VM thread synchronization
  96 //////////////////////////////////////////////////////////////////
  97 // We split use of the CGC_lock into 2 "levels".
  98 // The low-level locking is of the usual CGC_lock monitor. We introduce
  99 // a higher level "token" (hereafter "CMS token") built on top of the
 100 // low level monitor (hereafter "CGC lock").
 101 // The token-passing protocol gives priority to the VM thread. The
 102 // CMS-lock doesn't provide any fairness guarantees, but clients
 103 // should ensure that it is only held for very short, bounded
 104 // durations.
 105 //
 106 // When either of the CMS thread or the VM thread is involved in
 107 // collection operations during which it does not want the other
 108 // thread to interfere, it obtains the CMS token.
 109 //
 110 // If either thread tries to get the token while the other has
 111 // it, that thread waits. However, if the VM thread and CMS thread
 112 // both want the token, then the VM thread gets priority while the
 113 // CMS thread waits. This ensures, for instance, that the "concurrent"
 114 // phases of the CMS thread's work do not block out the VM thread
 115 // for long periods of time as the CMS thread continues to hog
 116 // the token. (See bug 4616232).
 117 //
 118 // The baton-passing functions are, however, controlled by the
 119 // flags _foregroundGCShouldWait and _foregroundGCIsActive,
 120 // and here the low-level CMS lock, not the high level token,
 121 // ensures mutual exclusion.
 122 //
 123 // Two important conditions that we have to satisfy:
 124 // 1. if a thread does a low-level wait on the CMS lock, then it
 125 //    relinquishes the CMS token if it were holding that token
 126 //    when it acquired the low-level CMS lock.
 127 // 2. any low-level notifications on the low-level lock
 128 //    should only be sent when a thread has relinquished the token.
 129 //
 130 // In the absence of either property, we'd have potential deadlock.
 131 //
 132 // We protect each of the CMS (concurrent and sequential) phases
 133 // with the CMS _token_, not the CMS _lock_.
 134 //
 135 // The only code protected by CMS lock is the token acquisition code
 136 // itself, see ConcurrentMarkSweepThread::[de]synchronize(), and the
 137 // baton-passing code.
 138 //
 139 // Unfortunately, i couldn't come up with a good abstraction to factor and
 140 // hide the naked CGC_lock manipulation in the baton-passing code
 141 // further below. That's something we should try to do. Also, the proof
 142 // of correctness of this 2-level locking scheme is far from obvious,
 143 // and potentially quite slippery. We have an uneasy suspicion, for instance,
 144 // that there may be a theoretical possibility of delay/starvation in the
 145 // low-level lock/wait/notify scheme used for the baton-passing because of
 146 // potential interference with the priority scheme embodied in the
 147 // CMS-token-passing protocol. See related comments at a CGC_lock->wait()
 148 // invocation further below and marked with "XXX 20011219YSR".
 149 // Indeed, as we note elsewhere, this may become yet more slippery
 150 // in the presence of multiple CMS and/or multiple VM threads. XXX
 151 
 152 class CMSTokenSync: public StackObj {
 153  private:
 154   bool _is_cms_thread;
 155  public:
 156   CMSTokenSync(bool is_cms_thread):
 157     _is_cms_thread(is_cms_thread) {
 158     assert(is_cms_thread == Thread::current()->is_ConcurrentGC_thread(),
 159            "Incorrect argument to constructor");
 160     ConcurrentMarkSweepThread::synchronize(_is_cms_thread);
 161   }
 162 
 163   ~CMSTokenSync() {
 164     assert(_is_cms_thread ?
 165              ConcurrentMarkSweepThread::cms_thread_has_cms_token() :
 166              ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
 167           "Incorrect state");
 168     ConcurrentMarkSweepThread::desynchronize(_is_cms_thread);
 169   }
 170 };
 171 
 172 // Convenience class that does a CMSTokenSync, and then acquires
 173 // upto three locks.
 174 class CMSTokenSyncWithLocks: public CMSTokenSync {
 175  private:
 176   // Note: locks are acquired in textual declaration order
 177   // and released in the opposite order
 178   MutexLockerEx _locker1, _locker2, _locker3;
 179  public:
 180   CMSTokenSyncWithLocks(bool is_cms_thread, Mutex* mutex1,
 181                         Mutex* mutex2 = NULL, Mutex* mutex3 = NULL):
 182     CMSTokenSync(is_cms_thread),
 183     _locker1(mutex1, Mutex::_no_safepoint_check_flag),
 184     _locker2(mutex2, Mutex::_no_safepoint_check_flag),
 185     _locker3(mutex3, Mutex::_no_safepoint_check_flag)
 186   { }
 187 };
 188 
 189 
 190 //////////////////////////////////////////////////////////////////
 191 //  Concurrent Mark-Sweep Generation /////////////////////////////
 192 //////////////////////////////////////////////////////////////////
 193 
 194 NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;)
 195 
 196 // This struct contains per-thread things necessary to support parallel
 197 // young-gen collection.
 198 class CMSParGCThreadState: public CHeapObj<mtGC> {
 199  public:
 200   CompactibleFreeListSpaceLAB lab;
 201   PromotionInfo promo;
 202 
 203   // Constructor.
 204   CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) {
 205     promo.setSpace(cfls);
 206   }
 207 };
 208 
 209 ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration(
 210      ReservedSpace rs, size_t initial_byte_size, CardTableRS* ct) :
 211   CardGeneration(rs, initial_byte_size, ct),
 212   _dilatation_factor(((double)MinChunkSize)/((double)(CollectedHeap::min_fill_size()))),
 213   _did_compact(false)
 214 {
 215   HeapWord* bottom = (HeapWord*) _virtual_space.low();
 216   HeapWord* end    = (HeapWord*) _virtual_space.high();
 217 
 218   _direct_allocated_words = 0;
 219   NOT_PRODUCT(
 220     _numObjectsPromoted = 0;
 221     _numWordsPromoted = 0;
 222     _numObjectsAllocated = 0;
 223     _numWordsAllocated = 0;
 224   )
 225 
 226   _cmsSpace = new CompactibleFreeListSpace(_bts, MemRegion(bottom, end));
 227   NOT_PRODUCT(debug_cms_space = _cmsSpace;)
 228   _cmsSpace->_old_gen = this;
 229 
 230   _gc_stats = new CMSGCStats();
 231 
 232   // Verify the assumption that FreeChunk::_prev and OopDesc::_klass
 233   // offsets match. The ability to tell free chunks from objects
 234   // depends on this property.
 235   debug_only(
 236     FreeChunk* junk = NULL;
 237     assert(UseCompressedClassPointers ||
 238            junk->prev_addr() == (void*)(oop(junk)->klass_addr()),
 239            "Offset of FreeChunk::_prev within FreeChunk must match"
 240            "  that of OopDesc::_klass within OopDesc");
 241   )
 242 
 243   _par_gc_thread_states = NEW_C_HEAP_ARRAY(CMSParGCThreadState*, ParallelGCThreads, mtGC);
 244   for (uint i = 0; i < ParallelGCThreads; i++) {
 245     _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace());
 246   }
 247 
 248   _incremental_collection_failed = false;
 249   // The "dilatation_factor" is the expansion that can occur on
 250   // account of the fact that the minimum object size in the CMS
 251   // generation may be larger than that in, say, a contiguous young
 252   //  generation.
 253   // Ideally, in the calculation below, we'd compute the dilatation
 254   // factor as: MinChunkSize/(promoting_gen's min object size)
 255   // Since we do not have such a general query interface for the
 256   // promoting generation, we'll instead just use the minimum
 257   // object size (which today is a header's worth of space);
 258   // note that all arithmetic is in units of HeapWords.
 259   assert(MinChunkSize >= CollectedHeap::min_fill_size(), "just checking");
 260   assert(_dilatation_factor >= 1.0, "from previous assert");
 261 }
 262 
 263 
 264 // The field "_initiating_occupancy" represents the occupancy percentage
 265 // at which we trigger a new collection cycle.  Unless explicitly specified
 266 // via CMSInitiatingOccupancyFraction (argument "io" below), it
 267 // is calculated by:
 268 //
 269 //   Let "f" be MinHeapFreeRatio in
 270 //
 271 //    _initiating_occupancy = 100-f +
 272 //                           f * (CMSTriggerRatio/100)
 273 //   where CMSTriggerRatio is the argument "tr" below.
 274 //
 275 // That is, if we assume the heap is at its desired maximum occupancy at the
 276 // end of a collection, we let CMSTriggerRatio of the (purported) free
 277 // space be allocated before initiating a new collection cycle.
 278 //
 279 void ConcurrentMarkSweepGeneration::init_initiating_occupancy(intx io, uintx tr) {
 280   assert(io <= 100 && tr <= 100, "Check the arguments");
 281   if (io >= 0) {
 282     _initiating_occupancy = (double)io / 100.0;
 283   } else {
 284     _initiating_occupancy = ((100 - MinHeapFreeRatio) +
 285                              (double)(tr * MinHeapFreeRatio) / 100.0)
 286                             / 100.0;
 287   }
 288 }
 289 
 290 void ConcurrentMarkSweepGeneration::ref_processor_init() {
 291   assert(collector() != NULL, "no collector");
 292   collector()->ref_processor_init();
 293 }
 294 
 295 void CMSCollector::ref_processor_init() {
 296   if (_ref_processor == NULL) {
 297     // Allocate and initialize a reference processor
 298     _ref_processor =
 299       new ReferenceProcessor(&_span_based_discoverer,
 300                              (ParallelGCThreads > 1) && ParallelRefProcEnabled, // mt processing
 301                              ParallelGCThreads,                      // mt processing degree
 302                              _cmsGen->refs_discovery_is_mt(),        // mt discovery
 303                              MAX2(ConcGCThreads, ParallelGCThreads), // mt discovery degree
 304                              _cmsGen->refs_discovery_is_atomic(),    // discovery is not atomic
 305                              &_is_alive_closure,                     // closure for liveness info
 306                              false);                                 // disable adjusting number of processing threads
 307     // Initialize the _ref_processor field of CMSGen
 308     _cmsGen->set_ref_processor(_ref_processor);
 309 
 310   }
 311 }
 312 
 313 AdaptiveSizePolicy* CMSCollector::size_policy() {
 314   return CMSHeap::heap()->size_policy();
 315 }
 316 
 317 void ConcurrentMarkSweepGeneration::initialize_performance_counters() {
 318 
 319   const char* gen_name = "old";
 320   GenCollectorPolicy* gcp = CMSHeap::heap()->gen_policy();
 321   // Generation Counters - generation 1, 1 subspace
 322   _gen_counters = new GenerationCounters(gen_name, 1, 1,
 323       gcp->min_old_size(), gcp->max_old_size(), &_virtual_space);
 324 
 325   _space_counters = new GSpaceCounters(gen_name, 0,
 326                                        _virtual_space.reserved_size(),
 327                                        this, _gen_counters);
 328 }
 329 
 330 CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha):
 331   _cms_gen(cms_gen)
 332 {
 333   assert(alpha <= 100, "bad value");
 334   _saved_alpha = alpha;
 335 
 336   // Initialize the alphas to the bootstrap value of 100.
 337   _gc0_alpha = _cms_alpha = 100;
 338 
 339   _cms_begin_time.update();
 340   _cms_end_time.update();
 341 
 342   _gc0_duration = 0.0;
 343   _gc0_period = 0.0;
 344   _gc0_promoted = 0;
 345 
 346   _cms_duration = 0.0;
 347   _cms_period = 0.0;
 348   _cms_allocated = 0;
 349 
 350   _cms_used_at_gc0_begin = 0;
 351   _cms_used_at_gc0_end = 0;
 352   _allow_duty_cycle_reduction = false;
 353   _valid_bits = 0;
 354 }
 355 
 356 double CMSStats::cms_free_adjustment_factor(size_t free) const {
 357   // TBD: CR 6909490
 358   return 1.0;
 359 }
 360 
 361 void CMSStats::adjust_cms_free_adjustment_factor(bool fail, size_t free) {
 362 }
 363 
 364 // If promotion failure handling is on use
 365 // the padded average size of the promotion for each
 366 // young generation collection.
 367 double CMSStats::time_until_cms_gen_full() const {
 368   size_t cms_free = _cms_gen->cmsSpace()->free();
 369   CMSHeap* heap = CMSHeap::heap();
 370   size_t expected_promotion = MIN2(heap->young_gen()->capacity(),
 371                                    (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average());
 372   if (cms_free > expected_promotion) {
 373     // Start a cms collection if there isn't enough space to promote
 374     // for the next young collection.  Use the padded average as
 375     // a safety factor.
 376     cms_free -= expected_promotion;
 377 
 378     // Adjust by the safety factor.
 379     double cms_free_dbl = (double)cms_free;
 380     double cms_adjustment = (100.0 - CMSIncrementalSafetyFactor) / 100.0;
 381     // Apply a further correction factor which tries to adjust
 382     // for recent occurance of concurrent mode failures.
 383     cms_adjustment = cms_adjustment * cms_free_adjustment_factor(cms_free);
 384     cms_free_dbl = cms_free_dbl * cms_adjustment;
 385 
 386     log_trace(gc)("CMSStats::time_until_cms_gen_full: cms_free " SIZE_FORMAT " expected_promotion " SIZE_FORMAT,
 387                   cms_free, expected_promotion);
 388     log_trace(gc)("  cms_free_dbl %f cms_consumption_rate %f", cms_free_dbl, cms_consumption_rate() + 1.0);
 389     // Add 1 in case the consumption rate goes to zero.
 390     return cms_free_dbl / (cms_consumption_rate() + 1.0);
 391   }
 392   return 0.0;
 393 }
 394 
 395 // Compare the duration of the cms collection to the
 396 // time remaining before the cms generation is empty.
 397 // Note that the time from the start of the cms collection
 398 // to the start of the cms sweep (less than the total
 399 // duration of the cms collection) can be used.  This
 400 // has been tried and some applications experienced
 401 // promotion failures early in execution.  This was
 402 // possibly because the averages were not accurate
 403 // enough at the beginning.
 404 double CMSStats::time_until_cms_start() const {
 405   // We add "gc0_period" to the "work" calculation
 406   // below because this query is done (mostly) at the
 407   // end of a scavenge, so we need to conservatively
 408   // account for that much possible delay
 409   // in the query so as to avoid concurrent mode failures
 410   // due to starting the collection just a wee bit too
 411   // late.
 412   double work = cms_duration() + gc0_period();
 413   double deadline = time_until_cms_gen_full();
 414   // If a concurrent mode failure occurred recently, we want to be
 415   // more conservative and halve our expected time_until_cms_gen_full()
 416   if (work > deadline) {
 417     log_develop_trace(gc)("CMSCollector: collect because of anticipated promotion before full %3.7f + %3.7f > %3.7f ",
 418                           cms_duration(), gc0_period(), time_until_cms_gen_full());
 419     return 0.0;
 420   }
 421   return work - deadline;
 422 }
 423 
 424 #ifndef PRODUCT
 425 void CMSStats::print_on(outputStream *st) const {
 426   st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha);
 427   st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo=" SIZE_FORMAT,
 428                gc0_duration(), gc0_period(), gc0_promoted());
 429   st->print(",cms_dur=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT,
 430             cms_duration(), cms_period(), cms_allocated());
 431   st->print(",cms_since_beg=%g,cms_since_end=%g",
 432             cms_time_since_begin(), cms_time_since_end());
 433   st->print(",cms_used_beg=" SIZE_FORMAT ",cms_used_end=" SIZE_FORMAT,
 434             _cms_used_at_gc0_begin, _cms_used_at_gc0_end);
 435 
 436   if (valid()) {
 437     st->print(",promo_rate=%g,cms_alloc_rate=%g",
 438               promotion_rate(), cms_allocation_rate());
 439     st->print(",cms_consumption_rate=%g,time_until_full=%g",
 440               cms_consumption_rate(), time_until_cms_gen_full());
 441   }
 442   st->cr();
 443 }
 444 #endif // #ifndef PRODUCT
 445 
 446 CMSCollector::CollectorState CMSCollector::_collectorState =
 447                              CMSCollector::Idling;
 448 bool CMSCollector::_foregroundGCIsActive = false;
 449 bool CMSCollector::_foregroundGCShouldWait = false;
 450 
 451 CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
 452                            CardTableRS*                   ct,
 453                            ConcurrentMarkSweepPolicy*     cp):
 454   _overflow_list(NULL),
 455   _conc_workers(NULL),     // may be set later
 456   _completed_initialization(false),
 457   _collection_count_start(0),
 458   _should_unload_classes(CMSClassUnloadingEnabled),
 459   _concurrent_cycles_since_last_unload(0),
 460   _roots_scanning_options(GenCollectedHeap::SO_None),
 461   _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"),
 462   _verifying(false),
 463   _collector_policy(cp),
 464   _inter_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
 465   _intra_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
 466   _gc_tracer_cm(new (ResourceObj::C_HEAP, mtGC) CMSTracer()),
 467   _gc_timer_cm(new (ResourceObj::C_HEAP, mtGC) ConcurrentGCTimer()),
 468   _cms_start_registered(false),
 469   _cmsGen(cmsGen),
 470   // Adjust span to cover old (cms) gen
 471   _span(cmsGen->reserved()),
 472   _ct(ct),
 473   _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"),
 474   _modUnionTable((CardTable::card_shift - LogHeapWordSize),
 475                  -1 /* lock-free */, "No_lock" /* dummy */),
 476   _restart_addr(NULL),
 477   _ser_pmc_preclean_ovflw(0),
 478   _ser_pmc_remark_ovflw(0),
 479   _par_pmc_remark_ovflw(0),
 480   _ser_kac_preclean_ovflw(0),
 481   _ser_kac_ovflw(0),
 482   _par_kac_ovflw(0),
 483 #ifndef PRODUCT
 484   _num_par_pushes(0),
 485 #endif
 486   _span_based_discoverer(_span),
 487   _ref_processor(NULL),    // will be set later
 488   // Construct the is_alive_closure with _span & markBitMap
 489   _is_alive_closure(_span, &_markBitMap),
 490   _modUnionClosurePar(&_modUnionTable),
 491   _between_prologue_and_epilogue(false),
 492   _abort_preclean(false),
 493   _start_sampling(false),
 494   _stats(cmsGen),
 495   _eden_chunk_lock(new Mutex(Mutex::leaf + 1, "CMS_eden_chunk_lock", true,
 496                              //verify that this lock should be acquired with safepoint check.
 497                              Monitor::_safepoint_check_sometimes)),
 498   _eden_chunk_array(NULL),     // may be set in ctor body
 499   _eden_chunk_index(0),        // -- ditto --
 500   _eden_chunk_capacity(0),     // -- ditto --
 501   _survivor_chunk_array(NULL), // -- ditto --
 502   _survivor_chunk_index(0),    // -- ditto --
 503   _survivor_chunk_capacity(0), // -- ditto --
 504   _survivor_plab_array(NULL)   // -- ditto --
 505 {
 506   // Now expand the span and allocate the collection support structures
 507   // (MUT, marking bit map etc.) to cover both generations subject to
 508   // collection.
 509 
 510   // For use by dirty card to oop closures.
 511   _cmsGen->cmsSpace()->set_collector(this);
 512 
 513   // Allocate MUT and marking bit map
 514   {
 515     MutexLockerEx x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag);
 516     if (!_markBitMap.allocate(_span)) {
 517       log_warning(gc)("Failed to allocate CMS Bit Map");
 518       return;
 519     }
 520     assert(_markBitMap.covers(_span), "_markBitMap inconsistency?");
 521   }
 522   {
 523     _modUnionTable.allocate(_span);
 524     assert(_modUnionTable.covers(_span), "_modUnionTable inconsistency?");
 525   }
 526 
 527   if (!_markStack.allocate(MarkStackSize)) {
 528     log_warning(gc)("Failed to allocate CMS Marking Stack");
 529     return;
 530   }
 531 
 532   // Support for multi-threaded concurrent phases
 533   if (CMSConcurrentMTEnabled) {
 534     if (FLAG_IS_DEFAULT(ConcGCThreads)) {
 535       // just for now
 536       FLAG_SET_DEFAULT(ConcGCThreads, (ParallelGCThreads + 3) / 4);
 537     }
 538     if (ConcGCThreads > 1) {
 539       _conc_workers = new YieldingFlexibleWorkGang("CMS Thread",
 540                                  ConcGCThreads, true);
 541       if (_conc_workers == NULL) {
 542         log_warning(gc)("GC/CMS: _conc_workers allocation failure: forcing -CMSConcurrentMTEnabled");
 543         CMSConcurrentMTEnabled = false;
 544       } else {
 545         _conc_workers->initialize_workers();
 546       }
 547     } else {
 548       CMSConcurrentMTEnabled = false;
 549     }
 550   }
 551   if (!CMSConcurrentMTEnabled) {
 552     ConcGCThreads = 0;
 553   } else {
 554     // Turn off CMSCleanOnEnter optimization temporarily for
 555     // the MT case where it's not fixed yet; see 6178663.
 556     CMSCleanOnEnter = false;
 557   }
 558   assert((_conc_workers != NULL) == (ConcGCThreads > 1),
 559          "Inconsistency");
 560   log_debug(gc)("ConcGCThreads: %u", ConcGCThreads);
 561   log_debug(gc)("ParallelGCThreads: %u", ParallelGCThreads);
 562 
 563   // Parallel task queues; these are shared for the
 564   // concurrent and stop-world phases of CMS, but
 565   // are not shared with parallel scavenge (ParNew).
 566   {
 567     uint i;
 568     uint num_queues = MAX2(ParallelGCThreads, ConcGCThreads);
 569 
 570     if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled
 571          || ParallelRefProcEnabled)
 572         && num_queues > 0) {
 573       _task_queues = new OopTaskQueueSet(num_queues);
 574       if (_task_queues == NULL) {
 575         log_warning(gc)("task_queues allocation failure.");
 576         return;
 577       }
 578       typedef Padded<OopTaskQueue> PaddedOopTaskQueue;
 579       for (i = 0; i < num_queues; i++) {
 580         PaddedOopTaskQueue *q = new PaddedOopTaskQueue();
 581         if (q == NULL) {
 582           log_warning(gc)("work_queue allocation failure.");
 583           return;
 584         }
 585         _task_queues->register_queue(i, q);
 586       }
 587       for (i = 0; i < num_queues; i++) {
 588         _task_queues->queue(i)->initialize();
 589       }
 590     }
 591   }
 592 
 593   _cmsGen ->init_initiating_occupancy(CMSInitiatingOccupancyFraction, CMSTriggerRatio);
 594 
 595   // Clip CMSBootstrapOccupancy between 0 and 100.
 596   _bootstrap_occupancy = CMSBootstrapOccupancy / 100.0;
 597 
 598   // Now tell CMS generations the identity of their collector
 599   ConcurrentMarkSweepGeneration::set_collector(this);
 600 
 601   // Create & start a CMS thread for this CMS collector
 602   _cmsThread = ConcurrentMarkSweepThread::start(this);
 603   assert(cmsThread() != NULL, "CMS Thread should have been created");
 604   assert(cmsThread()->collector() == this,
 605          "CMS Thread should refer to this gen");
 606   assert(CGC_lock != NULL, "Where's the CGC_lock?");
 607 
 608   // Support for parallelizing young gen rescan
 609   CMSHeap* heap = CMSHeap::heap();
 610   _young_gen = heap->young_gen();
 611   if (heap->supports_inline_contig_alloc()) {
 612     _top_addr = heap->top_addr();
 613     _end_addr = heap->end_addr();
 614     assert(_young_gen != NULL, "no _young_gen");
 615     _eden_chunk_index = 0;
 616     _eden_chunk_capacity = (_young_gen->max_capacity() + CMSSamplingGrain) / CMSSamplingGrain;
 617     _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity, mtGC);
 618   }
 619 
 620   // Support for parallelizing survivor space rescan
 621   if ((CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) || CMSParallelInitialMarkEnabled) {
 622     const size_t max_plab_samples =
 623       _young_gen->max_survivor_size() / (PLAB::min_size() * HeapWordSize);
 624 
 625     _survivor_plab_array  = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads, mtGC);
 626     _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
 627     _cursor               = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads, mtGC);
 628     _survivor_chunk_capacity = max_plab_samples;
 629     for (uint i = 0; i < ParallelGCThreads; i++) {
 630       HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
 631       ChunkArray* cur = ::new (&_survivor_plab_array[i]) ChunkArray(vec, max_plab_samples);
 632       assert(cur->end() == 0, "Should be 0");
 633       assert(cur->array() == vec, "Should be vec");
 634       assert(cur->capacity() == max_plab_samples, "Error");
 635     }
 636   }
 637 
 638   NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;)
 639   _gc_counters = new CollectorCounters("CMS", 1);
 640   _cgc_counters = new CollectorCounters("CMS stop-the-world phases", 2);
 641   _completed_initialization = true;
 642   _inter_sweep_timer.start();  // start of time
 643 }
 644 
 645 const char* ConcurrentMarkSweepGeneration::name() const {
 646   return "concurrent mark-sweep generation";
 647 }
 648 void ConcurrentMarkSweepGeneration::update_counters() {
 649   if (UsePerfData) {
 650     _space_counters->update_all();
 651     _gen_counters->update_all();
 652   }
 653 }
 654 
 655 // this is an optimized version of update_counters(). it takes the
 656 // used value as a parameter rather than computing it.
 657 //
 658 void ConcurrentMarkSweepGeneration::update_counters(size_t used) {
 659   if (UsePerfData) {
 660     _space_counters->update_used(used);
 661     _space_counters->update_capacity();
 662     _gen_counters->update_all();
 663   }
 664 }
 665 
 666 void ConcurrentMarkSweepGeneration::print() const {
 667   Generation::print();
 668   cmsSpace()->print();
 669 }
 670 
 671 #ifndef PRODUCT
 672 void ConcurrentMarkSweepGeneration::print_statistics() {
 673   cmsSpace()->printFLCensus(0);
 674 }
 675 #endif
 676 
 677 size_t
 678 ConcurrentMarkSweepGeneration::contiguous_available() const {
 679   // dld proposes an improvement in precision here. If the committed
 680   // part of the space ends in a free block we should add that to
 681   // uncommitted size in the calculation below. Will make this
 682   // change later, staying with the approximation below for the
 683   // time being. -- ysr.
 684   return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc());
 685 }
 686 
 687 size_t
 688 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const {
 689   return _cmsSpace->max_alloc_in_words() * HeapWordSize;
 690 }
 691 
 692 size_t ConcurrentMarkSweepGeneration::max_available() const {
 693   return free() + _virtual_space.uncommitted_size();
 694 }
 695 
 696 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(size_t max_promotion_in_bytes) const {
 697   size_t available = max_available();
 698   size_t av_promo  = (size_t)gc_stats()->avg_promoted()->padded_average();
 699   bool   res = (available >= av_promo) || (available >= max_promotion_in_bytes);
 700   log_trace(gc, promotion)("CMS: promo attempt is%s safe: available(" SIZE_FORMAT ") %s av_promo(" SIZE_FORMAT "), max_promo(" SIZE_FORMAT ")",
 701                            res? "":" not", available, res? ">=":"<", av_promo, max_promotion_in_bytes);
 702   return res;
 703 }
 704 
 705 // At a promotion failure dump information on block layout in heap
 706 // (cms old generation).
 707 void ConcurrentMarkSweepGeneration::promotion_failure_occurred() {
 708   Log(gc, promotion) log;
 709   if (log.is_trace()) {
 710     LogStream ls(log.trace());
 711     cmsSpace()->dump_at_safepoint_with_locks(collector(), &ls);
 712   }
 713 }
 714 
 715 void ConcurrentMarkSweepGeneration::reset_after_compaction() {
 716   // Clear the promotion information.  These pointers can be adjusted
 717   // along with all the other pointers into the heap but
 718   // compaction is expected to be a rare event with
 719   // a heap using cms so don't do it without seeing the need.
 720   for (uint i = 0; i < ParallelGCThreads; i++) {
 721     _par_gc_thread_states[i]->promo.reset();
 722   }
 723 }
 724 
 725 void ConcurrentMarkSweepGeneration::compute_new_size() {
 726   assert_locked_or_safepoint(Heap_lock);
 727 
 728   // If incremental collection failed, we just want to expand
 729   // to the limit.
 730   if (incremental_collection_failed()) {
 731     clear_incremental_collection_failed();
 732     grow_to_reserved();
 733     return;
 734   }
 735 
 736   // The heap has been compacted but not reset yet.
 737   // Any metric such as free() or used() will be incorrect.
 738 
 739   CardGeneration::compute_new_size();
 740 
 741   // Reset again after a possible resizing
 742   if (did_compact()) {
 743     cmsSpace()->reset_after_compaction();
 744   }
 745 }
 746 
 747 void ConcurrentMarkSweepGeneration::compute_new_size_free_list() {
 748   assert_locked_or_safepoint(Heap_lock);
 749 
 750   // If incremental collection failed, we just want to expand
 751   // to the limit.
 752   if (incremental_collection_failed()) {
 753     clear_incremental_collection_failed();
 754     grow_to_reserved();
 755     return;
 756   }
 757 
 758   double free_percentage = ((double) free()) / capacity();
 759   double desired_free_percentage = (double) MinHeapFreeRatio / 100;
 760   double maximum_free_percentage = (double) MaxHeapFreeRatio / 100;
 761 
 762   // compute expansion delta needed for reaching desired free percentage
 763   if (free_percentage < desired_free_percentage) {
 764     size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
 765     assert(desired_capacity >= capacity(), "invalid expansion size");
 766     size_t expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes);
 767     Log(gc) log;
 768     if (log.is_trace()) {
 769       size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
 770       log.trace("From compute_new_size: ");
 771       log.trace("  Free fraction %f", free_percentage);
 772       log.trace("  Desired free fraction %f", desired_free_percentage);
 773       log.trace("  Maximum free fraction %f", maximum_free_percentage);
 774       log.trace("  Capacity " SIZE_FORMAT, capacity() / 1000);
 775       log.trace("  Desired capacity " SIZE_FORMAT, desired_capacity / 1000);
 776       CMSHeap* heap = CMSHeap::heap();
 777       size_t young_size = heap->young_gen()->capacity();
 778       log.trace("  Young gen size " SIZE_FORMAT, young_size / 1000);
 779       log.trace("  unsafe_max_alloc_nogc " SIZE_FORMAT, unsafe_max_alloc_nogc() / 1000);
 780       log.trace("  contiguous available " SIZE_FORMAT, contiguous_available() / 1000);
 781       log.trace("  Expand by " SIZE_FORMAT " (bytes)", expand_bytes);
 782     }
 783     // safe if expansion fails
 784     expand_for_gc_cause(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio);
 785     log.trace("  Expanded free fraction %f", ((double) free()) / capacity());
 786   } else {
 787     size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
 788     assert(desired_capacity <= capacity(), "invalid expansion size");
 789     size_t shrink_bytes = capacity() - desired_capacity;
 790     // Don't shrink unless the delta is greater than the minimum shrink we want
 791     if (shrink_bytes >= MinHeapDeltaBytes) {
 792       shrink_free_list_by(shrink_bytes);
 793     }
 794   }
 795 }
 796 
 797 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const {
 798   return cmsSpace()->freelistLock();
 799 }
 800 
 801 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size, bool tlab) {
 802   CMSSynchronousYieldRequest yr;
 803   MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
 804   return have_lock_and_allocate(size, tlab);
 805 }
 806 
 807 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size,
 808                                                                 bool   tlab /* ignored */) {
 809   assert_lock_strong(freelistLock());
 810   size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size);
 811   HeapWord* res = cmsSpace()->allocate(adjustedSize);
 812   // Allocate the object live (grey) if the background collector has
 813   // started marking. This is necessary because the marker may
 814   // have passed this address and consequently this object will
 815   // not otherwise be greyed and would be incorrectly swept up.
 816   // Note that if this object contains references, the writing
 817   // of those references will dirty the card containing this object
 818   // allowing the object to be blackened (and its references scanned)
 819   // either during a preclean phase or at the final checkpoint.
 820   if (res != NULL) {
 821     // We may block here with an uninitialized object with
 822     // its mark-bit or P-bits not yet set. Such objects need
 823     // to be safely navigable by block_start().
 824     assert(oop(res)->klass_or_null() == NULL, "Object should be uninitialized here.");
 825     assert(!((FreeChunk*)res)->is_free(), "Error, block will look free but show wrong size");
 826     collector()->direct_allocated(res, adjustedSize);
 827     _direct_allocated_words += adjustedSize;
 828     // allocation counters
 829     NOT_PRODUCT(
 830       _numObjectsAllocated++;
 831       _numWordsAllocated += (int)adjustedSize;
 832     )
 833   }
 834   return res;
 835 }
 836 
 837 // In the case of direct allocation by mutators in a generation that
 838 // is being concurrently collected, the object must be allocated
 839 // live (grey) if the background collector has started marking.
 840 // This is necessary because the marker may
 841 // have passed this address and consequently this object will
 842 // not otherwise be greyed and would be incorrectly swept up.
 843 // Note that if this object contains references, the writing
 844 // of those references will dirty the card containing this object
 845 // allowing the object to be blackened (and its references scanned)
 846 // either during a preclean phase or at the final checkpoint.
 847 void CMSCollector::direct_allocated(HeapWord* start, size_t size) {
 848   assert(_markBitMap.covers(start, size), "Out of bounds");
 849   if (_collectorState >= Marking) {
 850     MutexLockerEx y(_markBitMap.lock(),
 851                     Mutex::_no_safepoint_check_flag);
 852     // [see comments preceding SweepClosure::do_blk() below for details]
 853     //
 854     // Can the P-bits be deleted now?  JJJ
 855     //
 856     // 1. need to mark the object as live so it isn't collected
 857     // 2. need to mark the 2nd bit to indicate the object may be uninitialized
 858     // 3. need to mark the end of the object so marking, precleaning or sweeping
 859     //    can skip over uninitialized or unparsable objects. An allocated
 860     //    object is considered uninitialized for our purposes as long as
 861     //    its klass word is NULL.  All old gen objects are parsable
 862     //    as soon as they are initialized.)
 863     _markBitMap.mark(start);          // object is live
 864     _markBitMap.mark(start + 1);      // object is potentially uninitialized?
 865     _markBitMap.mark(start + size - 1);
 866                                       // mark end of object
 867   }
 868   // check that oop looks uninitialized
 869   assert(oop(start)->klass_or_null() == NULL, "_klass should be NULL");
 870 }
 871 
 872 void CMSCollector::promoted(bool par, HeapWord* start,
 873                             bool is_obj_array, size_t obj_size) {
 874   assert(_markBitMap.covers(start), "Out of bounds");
 875   // See comment in direct_allocated() about when objects should
 876   // be allocated live.
 877   if (_collectorState >= Marking) {
 878     // we already hold the marking bit map lock, taken in
 879     // the prologue
 880     if (par) {
 881       _markBitMap.par_mark(start);
 882     } else {
 883       _markBitMap.mark(start);
 884     }
 885     // We don't need to mark the object as uninitialized (as
 886     // in direct_allocated above) because this is being done with the
 887     // world stopped and the object will be initialized by the
 888     // time the marking, precleaning or sweeping get to look at it.
 889     // But see the code for copying objects into the CMS generation,
 890     // where we need to ensure that concurrent readers of the
 891     // block offset table are able to safely navigate a block that
 892     // is in flux from being free to being allocated (and in
 893     // transition while being copied into) and subsequently
 894     // becoming a bona-fide object when the copy/promotion is complete.
 895     assert(SafepointSynchronize::is_at_safepoint(),
 896            "expect promotion only at safepoints");
 897 
 898     if (_collectorState < Sweeping) {
 899       // Mark the appropriate cards in the modUnionTable, so that
 900       // this object gets scanned before the sweep. If this is
 901       // not done, CMS generation references in the object might
 902       // not get marked.
 903       // For the case of arrays, which are otherwise precisely
 904       // marked, we need to dirty the entire array, not just its head.
 905       if (is_obj_array) {
 906         // The [par_]mark_range() method expects mr.end() below to
 907         // be aligned to the granularity of a bit's representation
 908         // in the heap. In the case of the MUT below, that's a
 909         // card size.
 910         MemRegion mr(start,
 911                      align_up(start + obj_size,
 912                               CardTable::card_size /* bytes */));
 913         if (par) {
 914           _modUnionTable.par_mark_range(mr);
 915         } else {
 916           _modUnionTable.mark_range(mr);
 917         }
 918       } else {  // not an obj array; we can just mark the head
 919         if (par) {
 920           _modUnionTable.par_mark(start);
 921         } else {
 922           _modUnionTable.mark(start);
 923         }
 924       }
 925     }
 926   }
 927 }
 928 
 929 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size) {
 930   assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
 931   // allocate, copy and if necessary update promoinfo --
 932   // delegate to underlying space.
 933   assert_lock_strong(freelistLock());
 934 
 935 #ifndef PRODUCT
 936   if (CMSHeap::heap()->promotion_should_fail()) {
 937     return NULL;
 938   }
 939 #endif  // #ifndef PRODUCT
 940 
 941   oop res = _cmsSpace->promote(obj, obj_size);
 942   if (res == NULL) {
 943     // expand and retry
 944     size_t s = _cmsSpace->expansionSpaceRequired(obj_size);  // HeapWords
 945     expand_for_gc_cause(s*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_promotion);
 946     // Since this is the old generation, we don't try to promote
 947     // into a more senior generation.
 948     res = _cmsSpace->promote(obj, obj_size);
 949   }
 950   if (res != NULL) {
 951     // See comment in allocate() about when objects should
 952     // be allocated live.
 953     assert(oopDesc::is_oop(obj), "Will dereference klass pointer below");
 954     collector()->promoted(false,           // Not parallel
 955                           (HeapWord*)res, obj->is_objArray(), obj_size);
 956     // promotion counters
 957     NOT_PRODUCT(
 958       _numObjectsPromoted++;
 959       _numWordsPromoted +=
 960         (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size()));
 961     )
 962   }
 963   return res;
 964 }
 965 
 966 
 967 // IMPORTANT: Notes on object size recognition in CMS.
 968 // ---------------------------------------------------
 969 // A block of storage in the CMS generation is always in
 970 // one of three states. A free block (FREE), an allocated
 971 // object (OBJECT) whose size() method reports the correct size,
 972 // and an intermediate state (TRANSIENT) in which its size cannot
 973 // be accurately determined.
 974 // STATE IDENTIFICATION:   (32 bit and 64 bit w/o COOPS)
 975 // -----------------------------------------------------
 976 // FREE:      klass_word & 1 == 1; mark_word holds block size
 977 //
 978 // OBJECT:    klass_word installed; klass_word != 0 && klass_word & 1 == 0;
 979 //            obj->size() computes correct size
 980 //
 981 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
 982 //
 983 // STATE IDENTIFICATION: (64 bit+COOPS)
 984 // ------------------------------------
 985 // FREE:      mark_word & CMS_FREE_BIT == 1; mark_word & ~CMS_FREE_BIT gives block_size
 986 //
 987 // OBJECT:    klass_word installed; klass_word != 0;
 988 //            obj->size() computes correct size
 989 //
 990 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
 991 //
 992 //
 993 // STATE TRANSITION DIAGRAM
 994 //
 995 //        mut / parnew                     mut  /  parnew
 996 // FREE --------------------> TRANSIENT ---------------------> OBJECT --|
 997 //  ^                                                                   |
 998 //  |------------------------ DEAD <------------------------------------|
 999 //         sweep                            mut
1000 //
1001 // While a block is in TRANSIENT state its size cannot be determined
1002 // so readers will either need to come back later or stall until
1003 // the size can be determined. Note that for the case of direct
1004 // allocation, P-bits, when available, may be used to determine the
1005 // size of an object that may not yet have been initialized.
1006 
1007 // Things to support parallel young-gen collection.
1008 oop
1009 ConcurrentMarkSweepGeneration::par_promote(int thread_num,
1010                                            oop old, markOop m,
1011                                            size_t word_sz) {
1012 #ifndef PRODUCT
1013   if (CMSHeap::heap()->promotion_should_fail()) {
1014     return NULL;
1015   }
1016 #endif  // #ifndef PRODUCT
1017 
1018   CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1019   PromotionInfo* promoInfo = &ps->promo;
1020   // if we are tracking promotions, then first ensure space for
1021   // promotion (including spooling space for saving header if necessary).
1022   // then allocate and copy, then track promoted info if needed.
1023   // When tracking (see PromotionInfo::track()), the mark word may
1024   // be displaced and in this case restoration of the mark word
1025   // occurs in the (oop_since_save_marks_)iterate phase.
1026   if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) {
1027     // Out of space for allocating spooling buffers;
1028     // try expanding and allocating spooling buffers.
1029     if (!expand_and_ensure_spooling_space(promoInfo)) {
1030       return NULL;
1031     }
1032   }
1033   assert(!promoInfo->tracking() || promoInfo->has_spooling_space(), "Control point invariant");
1034   const size_t alloc_sz = CompactibleFreeListSpace::adjustObjectSize(word_sz);
1035   HeapWord* obj_ptr = ps->lab.alloc(alloc_sz);
1036   if (obj_ptr == NULL) {
1037      obj_ptr = expand_and_par_lab_allocate(ps, alloc_sz);
1038      if (obj_ptr == NULL) {
1039        return NULL;
1040      }
1041   }
1042   oop obj = oop(obj_ptr);
1043   OrderAccess::storestore();
1044   assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1045   assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1046   // IMPORTANT: See note on object initialization for CMS above.
1047   // Otherwise, copy the object.  Here we must be careful to insert the
1048   // klass pointer last, since this marks the block as an allocated object.
1049   // Except with compressed oops it's the mark word.
1050   HeapWord* old_ptr = (HeapWord*)old;
1051   // Restore the mark word copied above.
1052   obj->set_mark_raw(m);
1053   assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1054   assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1055   OrderAccess::storestore();
1056 
1057   if (UseCompressedClassPointers) {
1058     // Copy gap missed by (aligned) header size calculation below
1059     obj->set_klass_gap(old->klass_gap());
1060   }
1061   if (word_sz > (size_t)oopDesc::header_size()) {
1062     Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1063                                  obj_ptr + oopDesc::header_size(),
1064                                  word_sz - oopDesc::header_size());
1065   }
1066 
1067   // Now we can track the promoted object, if necessary.  We take care
1068   // to delay the transition from uninitialized to full object
1069   // (i.e., insertion of klass pointer) until after, so that it
1070   // atomically becomes a promoted object.
1071   if (promoInfo->tracking()) {
1072     promoInfo->track((PromotedObject*)obj, old->klass());
1073   }
1074   assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1075   assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1076   assert(oopDesc::is_oop(old), "Will use and dereference old klass ptr below");
1077 
1078   // Finally, install the klass pointer (this should be volatile).
1079   OrderAccess::storestore();
1080   obj->set_klass(old->klass());
1081   // We should now be able to calculate the right size for this object
1082   assert(oopDesc::is_oop(obj) && obj->size() == (int)word_sz, "Error, incorrect size computed for promoted object");
1083 
1084   collector()->promoted(true,          // parallel
1085                         obj_ptr, old->is_objArray(), word_sz);
1086 
1087   NOT_PRODUCT(
1088     Atomic::inc(&_numObjectsPromoted);
1089     Atomic::add(alloc_sz, &_numWordsPromoted);
1090   )
1091 
1092   return obj;
1093 }
1094 
1095 void
1096 ConcurrentMarkSweepGeneration::
1097 par_promote_alloc_done(int thread_num) {
1098   CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1099   ps->lab.retire(thread_num);
1100 }
1101 
1102 void
1103 ConcurrentMarkSweepGeneration::
1104 par_oop_since_save_marks_iterate_done(int thread_num) {
1105   CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1106   ParScanWithoutBarrierClosure* dummy_cl = NULL;
1107   ps->promo.promoted_oops_iterate(dummy_cl);
1108 
1109   // Because card-scanning has been completed, subsequent phases
1110   // (e.g., reference processing) will not need to recognize which
1111   // objects have been promoted during this GC. So, we can now disable
1112   // promotion tracking.
1113   ps->promo.stopTrackingPromotions();
1114 }
1115 
1116 bool ConcurrentMarkSweepGeneration::should_collect(bool   full,
1117                                                    size_t size,
1118                                                    bool   tlab)
1119 {
1120   // We allow a STW collection only if a full
1121   // collection was requested.
1122   return full || should_allocate(size, tlab); // FIX ME !!!
1123   // This and promotion failure handling are connected at the
1124   // hip and should be fixed by untying them.
1125 }
1126 
1127 bool CMSCollector::shouldConcurrentCollect() {
1128   LogTarget(Trace, gc) log;
1129 
1130   if (_full_gc_requested) {
1131     log.print("CMSCollector: collect because of explicit  gc request (or GCLocker)");
1132     return true;
1133   }
1134 
1135   FreelistLocker x(this);
1136   // ------------------------------------------------------------------
1137   // Print out lots of information which affects the initiation of
1138   // a collection.
1139   if (log.is_enabled() && stats().valid()) {
1140     log.print("CMSCollector shouldConcurrentCollect: ");
1141 
1142     LogStream out(log);
1143     stats().print_on(&out);
1144 
1145     log.print("time_until_cms_gen_full %3.7f", stats().time_until_cms_gen_full());
1146     log.print("free=" SIZE_FORMAT, _cmsGen->free());
1147     log.print("contiguous_available=" SIZE_FORMAT, _cmsGen->contiguous_available());
1148     log.print("promotion_rate=%g", stats().promotion_rate());
1149     log.print("cms_allocation_rate=%g", stats().cms_allocation_rate());
1150     log.print("occupancy=%3.7f", _cmsGen->occupancy());
1151     log.print("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy());
1152     log.print("cms_time_since_begin=%3.7f", stats().cms_time_since_begin());
1153     log.print("cms_time_since_end=%3.7f", stats().cms_time_since_end());
1154     log.print("metadata initialized %d", MetaspaceGC::should_concurrent_collect());
1155   }
1156   // ------------------------------------------------------------------
1157 
1158   // If the estimated time to complete a cms collection (cms_duration())
1159   // is less than the estimated time remaining until the cms generation
1160   // is full, start a collection.
1161   if (!UseCMSInitiatingOccupancyOnly) {
1162     if (stats().valid()) {
1163       if (stats().time_until_cms_start() == 0.0) {
1164         return true;
1165       }
1166     } else {
1167       // We want to conservatively collect somewhat early in order
1168       // to try and "bootstrap" our CMS/promotion statistics;
1169       // this branch will not fire after the first successful CMS
1170       // collection because the stats should then be valid.
1171       if (_cmsGen->occupancy() >= _bootstrap_occupancy) {
1172         log.print(" CMSCollector: collect for bootstrapping statistics: occupancy = %f, boot occupancy = %f",
1173                   _cmsGen->occupancy(), _bootstrap_occupancy);
1174         return true;
1175       }
1176     }
1177   }
1178 
1179   // Otherwise, we start a collection cycle if
1180   // old gen want a collection cycle started. Each may use
1181   // an appropriate criterion for making this decision.
1182   // XXX We need to make sure that the gen expansion
1183   // criterion dovetails well with this. XXX NEED TO FIX THIS
1184   if (_cmsGen->should_concurrent_collect()) {
1185     log.print("CMS old gen initiated");
1186     return true;
1187   }
1188 
1189   // We start a collection if we believe an incremental collection may fail;
1190   // this is not likely to be productive in practice because it's probably too
1191   // late anyway.
1192   CMSHeap* heap = CMSHeap::heap();
1193   if (heap->incremental_collection_will_fail(true /* consult_young */)) {
1194     log.print("CMSCollector: collect because incremental collection will fail ");
1195     return true;
1196   }
1197 
1198   if (MetaspaceGC::should_concurrent_collect()) {
1199     log.print("CMSCollector: collect for metadata allocation ");
1200     return true;
1201   }
1202 
1203   // CMSTriggerInterval starts a CMS cycle if enough time has passed.
1204   if (CMSTriggerInterval >= 0) {
1205     if (CMSTriggerInterval == 0) {
1206       // Trigger always
1207       return true;
1208     }
1209 
1210     // Check the CMS time since begin (we do not check the stats validity
1211     // as we want to be able to trigger the first CMS cycle as well)
1212     if (stats().cms_time_since_begin() >= (CMSTriggerInterval / ((double) MILLIUNITS))) {
1213       if (stats().valid()) {
1214         log.print("CMSCollector: collect because of trigger interval (time since last begin %3.7f secs)",
1215                   stats().cms_time_since_begin());
1216       } else {
1217         log.print("CMSCollector: collect because of trigger interval (first collection)");
1218       }
1219       return true;
1220     }
1221   }
1222 
1223   return false;
1224 }
1225 
1226 void CMSCollector::set_did_compact(bool v) { _cmsGen->set_did_compact(v); }
1227 
1228 // Clear _expansion_cause fields of constituent generations
1229 void CMSCollector::clear_expansion_cause() {
1230   _cmsGen->clear_expansion_cause();
1231 }
1232 
1233 // We should be conservative in starting a collection cycle.  To
1234 // start too eagerly runs the risk of collecting too often in the
1235 // extreme.  To collect too rarely falls back on full collections,
1236 // which works, even if not optimum in terms of concurrent work.
1237 // As a work around for too eagerly collecting, use the flag
1238 // UseCMSInitiatingOccupancyOnly.  This also has the advantage of
1239 // giving the user an easily understandable way of controlling the
1240 // collections.
1241 // We want to start a new collection cycle if any of the following
1242 // conditions hold:
1243 // . our current occupancy exceeds the configured initiating occupancy
1244 //   for this generation, or
1245 // . we recently needed to expand this space and have not, since that
1246 //   expansion, done a collection of this generation, or
1247 // . the underlying space believes that it may be a good idea to initiate
1248 //   a concurrent collection (this may be based on criteria such as the
1249 //   following: the space uses linear allocation and linear allocation is
1250 //   going to fail, or there is believed to be excessive fragmentation in
1251 //   the generation, etc... or ...
1252 // [.(currently done by CMSCollector::shouldConcurrentCollect() only for
1253 //   the case of the old generation; see CR 6543076):
1254 //   we may be approaching a point at which allocation requests may fail because
1255 //   we will be out of sufficient free space given allocation rate estimates.]
1256 bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const {
1257 
1258   assert_lock_strong(freelistLock());
1259   if (occupancy() > initiating_occupancy()) {
1260     log_trace(gc)(" %s: collect because of occupancy %f / %f  ",
1261                   short_name(), occupancy(), initiating_occupancy());
1262     return true;
1263   }
1264   if (UseCMSInitiatingOccupancyOnly) {
1265     return false;
1266   }
1267   if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) {
1268     log_trace(gc)(" %s: collect because expanded for allocation ", short_name());
1269     return true;
1270   }
1271   return false;
1272 }
1273 
1274 void ConcurrentMarkSweepGeneration::collect(bool   full,
1275                                             bool   clear_all_soft_refs,
1276                                             size_t size,
1277                                             bool   tlab)
1278 {
1279   collector()->collect(full, clear_all_soft_refs, size, tlab);
1280 }
1281 
1282 void CMSCollector::collect(bool   full,
1283                            bool   clear_all_soft_refs,
1284                            size_t size,
1285                            bool   tlab)
1286 {
1287   // The following "if" branch is present for defensive reasons.
1288   // In the current uses of this interface, it can be replaced with:
1289   // assert(!GCLocker.is_active(), "Can't be called otherwise");
1290   // But I am not placing that assert here to allow future
1291   // generality in invoking this interface.
1292   if (GCLocker::is_active()) {
1293     // A consistency test for GCLocker
1294     assert(GCLocker::needs_gc(), "Should have been set already");
1295     // Skip this foreground collection, instead
1296     // expanding the heap if necessary.
1297     // Need the free list locks for the call to free() in compute_new_size()
1298     compute_new_size();
1299     return;
1300   }
1301   acquire_control_and_collect(full, clear_all_soft_refs);
1302 }
1303 
1304 void CMSCollector::request_full_gc(unsigned int full_gc_count, GCCause::Cause cause) {
1305   CMSHeap* heap = CMSHeap::heap();
1306   unsigned int gc_count = heap->total_full_collections();
1307   if (gc_count == full_gc_count) {
1308     MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag);
1309     _full_gc_requested = true;
1310     _full_gc_cause = cause;
1311     CGC_lock->notify();   // nudge CMS thread
1312   } else {
1313     assert(gc_count > full_gc_count, "Error: causal loop");
1314   }
1315 }
1316 
1317 bool CMSCollector::is_external_interruption() {
1318   GCCause::Cause cause = CMSHeap::heap()->gc_cause();
1319   return GCCause::is_user_requested_gc(cause) ||
1320          GCCause::is_serviceability_requested_gc(cause);
1321 }
1322 
1323 void CMSCollector::report_concurrent_mode_interruption() {
1324   if (is_external_interruption()) {
1325     log_debug(gc)("Concurrent mode interrupted");
1326   } else {
1327     log_debug(gc)("Concurrent mode failure");
1328     _gc_tracer_cm->report_concurrent_mode_failure();
1329   }
1330 }
1331 
1332 
1333 // The foreground and background collectors need to coordinate in order
1334 // to make sure that they do not mutually interfere with CMS collections.
1335 // When a background collection is active,
1336 // the foreground collector may need to take over (preempt) and
1337 // synchronously complete an ongoing collection. Depending on the
1338 // frequency of the background collections and the heap usage
1339 // of the application, this preemption can be seldom or frequent.
1340 // There are only certain
1341 // points in the background collection that the "collection-baton"
1342 // can be passed to the foreground collector.
1343 //
1344 // The foreground collector will wait for the baton before
1345 // starting any part of the collection.  The foreground collector
1346 // will only wait at one location.
1347 //
1348 // The background collector will yield the baton before starting a new
1349 // phase of the collection (e.g., before initial marking, marking from roots,
1350 // precleaning, final re-mark, sweep etc.)  This is normally done at the head
1351 // of the loop which switches the phases. The background collector does some
1352 // of the phases (initial mark, final re-mark) with the world stopped.
1353 // Because of locking involved in stopping the world,
1354 // the foreground collector should not block waiting for the background
1355 // collector when it is doing a stop-the-world phase.  The background
1356 // collector will yield the baton at an additional point just before
1357 // it enters a stop-the-world phase.  Once the world is stopped, the
1358 // background collector checks the phase of the collection.  If the
1359 // phase has not changed, it proceeds with the collection.  If the
1360 // phase has changed, it skips that phase of the collection.  See
1361 // the comments on the use of the Heap_lock in collect_in_background().
1362 //
1363 // Variable used in baton passing.
1364 //   _foregroundGCIsActive - Set to true by the foreground collector when
1365 //      it wants the baton.  The foreground clears it when it has finished
1366 //      the collection.
1367 //   _foregroundGCShouldWait - Set to true by the background collector
1368 //        when it is running.  The foreground collector waits while
1369 //      _foregroundGCShouldWait is true.
1370 //  CGC_lock - monitor used to protect access to the above variables
1371 //      and to notify the foreground and background collectors.
1372 //  _collectorState - current state of the CMS collection.
1373 //
1374 // The foreground collector
1375 //   acquires the CGC_lock
1376 //   sets _foregroundGCIsActive
1377 //   waits on the CGC_lock for _foregroundGCShouldWait to be false
1378 //     various locks acquired in preparation for the collection
1379 //     are released so as not to block the background collector
1380 //     that is in the midst of a collection
1381 //   proceeds with the collection
1382 //   clears _foregroundGCIsActive
1383 //   returns
1384 //
1385 // The background collector in a loop iterating on the phases of the
1386 //      collection
1387 //   acquires the CGC_lock
1388 //   sets _foregroundGCShouldWait
1389 //   if _foregroundGCIsActive is set
1390 //     clears _foregroundGCShouldWait, notifies _CGC_lock
1391 //     waits on _CGC_lock for _foregroundGCIsActive to become false
1392 //     and exits the loop.
1393 //   otherwise
1394 //     proceed with that phase of the collection
1395 //     if the phase is a stop-the-world phase,
1396 //       yield the baton once more just before enqueueing
1397 //       the stop-world CMS operation (executed by the VM thread).
1398 //   returns after all phases of the collection are done
1399 //
1400 
1401 void CMSCollector::acquire_control_and_collect(bool full,
1402         bool clear_all_soft_refs) {
1403   assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
1404   assert(!Thread::current()->is_ConcurrentGC_thread(),
1405          "shouldn't try to acquire control from self!");
1406 
1407   // Start the protocol for acquiring control of the
1408   // collection from the background collector (aka CMS thread).
1409   assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1410          "VM thread should have CMS token");
1411   // Remember the possibly interrupted state of an ongoing
1412   // concurrent collection
1413   CollectorState first_state = _collectorState;
1414 
1415   // Signal to a possibly ongoing concurrent collection that
1416   // we want to do a foreground collection.
1417   _foregroundGCIsActive = true;
1418 
1419   // release locks and wait for a notify from the background collector
1420   // releasing the locks in only necessary for phases which
1421   // do yields to improve the granularity of the collection.
1422   assert_lock_strong(bitMapLock());
1423   // We need to lock the Free list lock for the space that we are
1424   // currently collecting.
1425   assert(haveFreelistLocks(), "Must be holding free list locks");
1426   bitMapLock()->unlock();
1427   releaseFreelistLocks();
1428   {
1429     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1430     if (_foregroundGCShouldWait) {
1431       // We are going to be waiting for action for the CMS thread;
1432       // it had better not be gone (for instance at shutdown)!
1433       assert(ConcurrentMarkSweepThread::cmst() != NULL && !ConcurrentMarkSweepThread::cmst()->has_terminated(),
1434              "CMS thread must be running");
1435       // Wait here until the background collector gives us the go-ahead
1436       ConcurrentMarkSweepThread::clear_CMS_flag(
1437         ConcurrentMarkSweepThread::CMS_vm_has_token);  // release token
1438       // Get a possibly blocked CMS thread going:
1439       //   Note that we set _foregroundGCIsActive true above,
1440       //   without protection of the CGC_lock.
1441       CGC_lock->notify();
1442       assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(),
1443              "Possible deadlock");
1444       while (_foregroundGCShouldWait) {
1445         // wait for notification
1446         CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1447         // Possibility of delay/starvation here, since CMS token does
1448         // not know to give priority to VM thread? Actually, i think
1449         // there wouldn't be any delay/starvation, but the proof of
1450         // that "fact" (?) appears non-trivial. XXX 20011219YSR
1451       }
1452       ConcurrentMarkSweepThread::set_CMS_flag(
1453         ConcurrentMarkSweepThread::CMS_vm_has_token);
1454     }
1455   }
1456   // The CMS_token is already held.  Get back the other locks.
1457   assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1458          "VM thread should have CMS token");
1459   getFreelistLocks();
1460   bitMapLock()->lock_without_safepoint_check();
1461   log_debug(gc, state)("CMS foreground collector has asked for control " INTPTR_FORMAT " with first state %d",
1462                        p2i(Thread::current()), first_state);
1463   log_debug(gc, state)("    gets control with state %d", _collectorState);
1464 
1465   // Inform cms gen if this was due to partial collection failing.
1466   // The CMS gen may use this fact to determine its expansion policy.
1467   CMSHeap* heap = CMSHeap::heap();
1468   if (heap->incremental_collection_will_fail(false /* don't consult_young */)) {
1469     assert(!_cmsGen->incremental_collection_failed(),
1470            "Should have been noticed, reacted to and cleared");
1471     _cmsGen->set_incremental_collection_failed();
1472   }
1473 
1474   if (first_state > Idling) {
1475     report_concurrent_mode_interruption();
1476   }
1477 
1478   set_did_compact(true);
1479 
1480   // If the collection is being acquired from the background
1481   // collector, there may be references on the discovered
1482   // references lists.  Abandon those references, since some
1483   // of them may have become unreachable after concurrent
1484   // discovery; the STW compacting collector will redo discovery
1485   // more precisely, without being subject to floating garbage.
1486   // Leaving otherwise unreachable references in the discovered
1487   // lists would require special handling.
1488   ref_processor()->disable_discovery();
1489   ref_processor()->abandon_partial_discovery();
1490   ref_processor()->verify_no_references_recorded();
1491 
1492   if (first_state > Idling) {
1493     save_heap_summary();
1494   }
1495 
1496   do_compaction_work(clear_all_soft_refs);
1497 
1498   // Has the GC time limit been exceeded?
1499   size_t max_eden_size = _young_gen->max_eden_size();
1500   GCCause::Cause gc_cause = heap->gc_cause();
1501   size_policy()->check_gc_overhead_limit(_young_gen->eden()->used(),
1502                                          _cmsGen->max_capacity(),
1503                                          max_eden_size,
1504                                          full,
1505                                          gc_cause,
1506                                          heap->soft_ref_policy());
1507 
1508   // Reset the expansion cause, now that we just completed
1509   // a collection cycle.
1510   clear_expansion_cause();
1511   _foregroundGCIsActive = false;
1512   return;
1513 }
1514 
1515 // Resize the tenured generation
1516 // after obtaining the free list locks for the
1517 // two generations.
1518 void CMSCollector::compute_new_size() {
1519   assert_locked_or_safepoint(Heap_lock);
1520   FreelistLocker z(this);
1521   MetaspaceGC::compute_new_size();
1522   _cmsGen->compute_new_size_free_list();
1523 }
1524 
1525 // A work method used by the foreground collector to do
1526 // a mark-sweep-compact.
1527 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) {
1528   CMSHeap* heap = CMSHeap::heap();
1529 
1530   STWGCTimer* gc_timer = GenMarkSweep::gc_timer();
1531   gc_timer->register_gc_start();
1532 
1533   SerialOldTracer* gc_tracer = GenMarkSweep::gc_tracer();
1534   gc_tracer->report_gc_start(heap->gc_cause(), gc_timer->gc_start());
1535 
1536   heap->pre_full_gc_dump(gc_timer);
1537 
1538   GCTraceTime(Trace, gc, phases) t("CMS:MSC");
1539 
1540   // Temporarily widen the span of the weak reference processing to
1541   // the entire heap.
1542   MemRegion new_span(CMSHeap::heap()->reserved_region());
1543   ReferenceProcessorSpanMutator rp_mut_span(ref_processor(), new_span);
1544   // Temporarily, clear the "is_alive_non_header" field of the
1545   // reference processor.
1546   ReferenceProcessorIsAliveMutator rp_mut_closure(ref_processor(), NULL);
1547   // Temporarily make reference _processing_ single threaded (non-MT).
1548   ReferenceProcessorMTProcMutator rp_mut_mt_processing(ref_processor(), false);
1549   // Temporarily make refs discovery atomic
1550   ReferenceProcessorAtomicMutator rp_mut_atomic(ref_processor(), true);
1551   // Temporarily make reference _discovery_ single threaded (non-MT)
1552   ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
1553 
1554   ref_processor()->set_enqueuing_is_done(false);
1555   ref_processor()->enable_discovery();
1556   ref_processor()->setup_policy(clear_all_soft_refs);
1557   // If an asynchronous collection finishes, the _modUnionTable is
1558   // all clear.  If we are assuming the collection from an asynchronous
1559   // collection, clear the _modUnionTable.
1560   assert(_collectorState != Idling || _modUnionTable.isAllClear(),
1561     "_modUnionTable should be clear if the baton was not passed");
1562   _modUnionTable.clear_all();
1563   assert(_collectorState != Idling || _ct->cld_rem_set()->mod_union_is_clear(),
1564     "mod union for klasses should be clear if the baton was passed");
1565   _ct->cld_rem_set()->clear_mod_union();
1566 
1567 
1568   // We must adjust the allocation statistics being maintained
1569   // in the free list space. We do so by reading and clearing
1570   // the sweep timer and updating the block flux rate estimates below.
1571   assert(!_intra_sweep_timer.is_active(), "_intra_sweep_timer should be inactive");
1572   if (_inter_sweep_timer.is_active()) {
1573     _inter_sweep_timer.stop();
1574     // Note that we do not use this sample to update the _inter_sweep_estimate.
1575     _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
1576                                             _inter_sweep_estimate.padded_average(),
1577                                             _intra_sweep_estimate.padded_average());
1578   }
1579 
1580   GenMarkSweep::invoke_at_safepoint(ref_processor(), clear_all_soft_refs);
1581   #ifdef ASSERT
1582     CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
1583     size_t free_size = cms_space->free();
1584     assert(free_size ==
1585            pointer_delta(cms_space->end(), cms_space->compaction_top())
1586            * HeapWordSize,
1587       "All the free space should be compacted into one chunk at top");
1588     assert(cms_space->dictionary()->total_chunk_size(
1589                                       debug_only(cms_space->freelistLock())) == 0 ||
1590            cms_space->totalSizeInIndexedFreeLists() == 0,
1591       "All the free space should be in a single chunk");
1592     size_t num = cms_space->totalCount();
1593     assert((free_size == 0 && num == 0) ||
1594            (free_size > 0  && (num == 1 || num == 2)),
1595          "There should be at most 2 free chunks after compaction");
1596   #endif // ASSERT
1597   _collectorState = Resetting;
1598   assert(_restart_addr == NULL,
1599          "Should have been NULL'd before baton was passed");
1600   reset_stw();
1601   _cmsGen->reset_after_compaction();
1602   _concurrent_cycles_since_last_unload = 0;
1603 
1604   // Clear any data recorded in the PLAB chunk arrays.
1605   if (_survivor_plab_array != NULL) {
1606     reset_survivor_plab_arrays();
1607   }
1608 
1609   // Adjust the per-size allocation stats for the next epoch.
1610   _cmsGen->cmsSpace()->endSweepFLCensus(sweep_count() /* fake */);
1611   // Restart the "inter sweep timer" for the next epoch.
1612   _inter_sweep_timer.reset();
1613   _inter_sweep_timer.start();
1614 
1615   // No longer a need to do a concurrent collection for Metaspace.
1616   MetaspaceGC::set_should_concurrent_collect(false);
1617 
1618   heap->post_full_gc_dump(gc_timer);
1619 
1620   gc_timer->register_gc_end();
1621 
1622   gc_tracer->report_gc_end(gc_timer->gc_end(), gc_timer->time_partitions());
1623 
1624   // For a mark-sweep-compact, compute_new_size() will be called
1625   // in the heap's do_collection() method.
1626 }
1627 
1628 void CMSCollector::print_eden_and_survivor_chunk_arrays() {
1629   Log(gc, heap) log;
1630   if (!log.is_trace()) {
1631     return;
1632   }
1633 
1634   ContiguousSpace* eden_space = _young_gen->eden();
1635   ContiguousSpace* from_space = _young_gen->from();
1636   ContiguousSpace* to_space   = _young_gen->to();
1637   // Eden
1638   if (_eden_chunk_array != NULL) {
1639     log.trace("eden " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1640               p2i(eden_space->bottom()), p2i(eden_space->top()),
1641               p2i(eden_space->end()), eden_space->capacity());
1642     log.trace("_eden_chunk_index=" SIZE_FORMAT ", _eden_chunk_capacity=" SIZE_FORMAT,
1643               _eden_chunk_index, _eden_chunk_capacity);
1644     for (size_t i = 0; i < _eden_chunk_index; i++) {
1645       log.trace("_eden_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT, i, p2i(_eden_chunk_array[i]));
1646     }
1647   }
1648   // Survivor
1649   if (_survivor_chunk_array != NULL) {
1650     log.trace("survivor " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1651               p2i(from_space->bottom()), p2i(from_space->top()),
1652               p2i(from_space->end()), from_space->capacity());
1653     log.trace("_survivor_chunk_index=" SIZE_FORMAT ", _survivor_chunk_capacity=" SIZE_FORMAT,
1654               _survivor_chunk_index, _survivor_chunk_capacity);
1655     for (size_t i = 0; i < _survivor_chunk_index; i++) {
1656       log.trace("_survivor_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT, i, p2i(_survivor_chunk_array[i]));
1657     }
1658   }
1659 }
1660 
1661 void CMSCollector::getFreelistLocks() const {
1662   // Get locks for all free lists in all generations that this
1663   // collector is responsible for
1664   _cmsGen->freelistLock()->lock_without_safepoint_check();
1665 }
1666 
1667 void CMSCollector::releaseFreelistLocks() const {
1668   // Release locks for all free lists in all generations that this
1669   // collector is responsible for
1670   _cmsGen->freelistLock()->unlock();
1671 }
1672 
1673 bool CMSCollector::haveFreelistLocks() const {
1674   // Check locks for all free lists in all generations that this
1675   // collector is responsible for
1676   assert_lock_strong(_cmsGen->freelistLock());
1677   PRODUCT_ONLY(ShouldNotReachHere());
1678   return true;
1679 }
1680 
1681 // A utility class that is used by the CMS collector to
1682 // temporarily "release" the foreground collector from its
1683 // usual obligation to wait for the background collector to
1684 // complete an ongoing phase before proceeding.
1685 class ReleaseForegroundGC: public StackObj {
1686  private:
1687   CMSCollector* _c;
1688  public:
1689   ReleaseForegroundGC(CMSCollector* c) : _c(c) {
1690     assert(_c->_foregroundGCShouldWait, "Else should not need to call");
1691     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1692     // allow a potentially blocked foreground collector to proceed
1693     _c->_foregroundGCShouldWait = false;
1694     if (_c->_foregroundGCIsActive) {
1695       CGC_lock->notify();
1696     }
1697     assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1698            "Possible deadlock");
1699   }
1700 
1701   ~ReleaseForegroundGC() {
1702     assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?");
1703     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1704     _c->_foregroundGCShouldWait = true;
1705   }
1706 };
1707 
1708 void CMSCollector::collect_in_background(GCCause::Cause cause) {
1709   assert(Thread::current()->is_ConcurrentGC_thread(),
1710     "A CMS asynchronous collection is only allowed on a CMS thread.");
1711 
1712   CMSHeap* heap = CMSHeap::heap();
1713   {
1714     bool safepoint_check = Mutex::_no_safepoint_check_flag;
1715     MutexLockerEx hl(Heap_lock, safepoint_check);
1716     FreelistLocker fll(this);
1717     MutexLockerEx x(CGC_lock, safepoint_check);
1718     if (_foregroundGCIsActive) {
1719       // The foreground collector is. Skip this
1720       // background collection.
1721       assert(!_foregroundGCShouldWait, "Should be clear");
1722       return;
1723     } else {
1724       assert(_collectorState == Idling, "Should be idling before start.");
1725       _collectorState = InitialMarking;
1726       register_gc_start(cause);
1727       // Reset the expansion cause, now that we are about to begin
1728       // a new cycle.
1729       clear_expansion_cause();
1730 
1731       // Clear the MetaspaceGC flag since a concurrent collection
1732       // is starting but also clear it after the collection.
1733       MetaspaceGC::set_should_concurrent_collect(false);
1734     }
1735     // Decide if we want to enable class unloading as part of the
1736     // ensuing concurrent GC cycle.
1737     update_should_unload_classes();
1738     _full_gc_requested = false;           // acks all outstanding full gc requests
1739     _full_gc_cause = GCCause::_no_gc;
1740     // Signal that we are about to start a collection
1741     heap->increment_total_full_collections();  // ... starting a collection cycle
1742     _collection_count_start = heap->total_full_collections();
1743   }
1744 
1745   size_t prev_used = _cmsGen->used();
1746 
1747   // The change of the collection state is normally done at this level;
1748   // the exceptions are phases that are executed while the world is
1749   // stopped.  For those phases the change of state is done while the
1750   // world is stopped.  For baton passing purposes this allows the
1751   // background collector to finish the phase and change state atomically.
1752   // The foreground collector cannot wait on a phase that is done
1753   // while the world is stopped because the foreground collector already
1754   // has the world stopped and would deadlock.
1755   while (_collectorState != Idling) {
1756     log_debug(gc, state)("Thread " INTPTR_FORMAT " in CMS state %d",
1757                          p2i(Thread::current()), _collectorState);
1758     // The foreground collector
1759     //   holds the Heap_lock throughout its collection.
1760     //   holds the CMS token (but not the lock)
1761     //     except while it is waiting for the background collector to yield.
1762     //
1763     // The foreground collector should be blocked (not for long)
1764     //   if the background collector is about to start a phase
1765     //   executed with world stopped.  If the background
1766     //   collector has already started such a phase, the
1767     //   foreground collector is blocked waiting for the
1768     //   Heap_lock.  The stop-world phases (InitialMarking and FinalMarking)
1769     //   are executed in the VM thread.
1770     //
1771     // The locking order is
1772     //   PendingListLock (PLL)  -- if applicable (FinalMarking)
1773     //   Heap_lock  (both this & PLL locked in VM_CMS_Operation::prologue())
1774     //   CMS token  (claimed in
1775     //                stop_world_and_do() -->
1776     //                  safepoint_synchronize() -->
1777     //                    CMSThread::synchronize())
1778 
1779     {
1780       // Check if the FG collector wants us to yield.
1781       CMSTokenSync x(true); // is cms thread
1782       if (waitForForegroundGC()) {
1783         // We yielded to a foreground GC, nothing more to be
1784         // done this round.
1785         assert(_foregroundGCShouldWait == false, "We set it to false in "
1786                "waitForForegroundGC()");
1787         log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " exiting collection CMS state %d",
1788                              p2i(Thread::current()), _collectorState);
1789         return;
1790       } else {
1791         // The background collector can run but check to see if the
1792         // foreground collector has done a collection while the
1793         // background collector was waiting to get the CGC_lock
1794         // above.  If yes, break so that _foregroundGCShouldWait
1795         // is cleared before returning.
1796         if (_collectorState == Idling) {
1797           break;
1798         }
1799       }
1800     }
1801 
1802     assert(_foregroundGCShouldWait, "Foreground collector, if active, "
1803       "should be waiting");
1804 
1805     switch (_collectorState) {
1806       case InitialMarking:
1807         {
1808           ReleaseForegroundGC x(this);
1809           stats().record_cms_begin();
1810           VM_CMS_Initial_Mark initial_mark_op(this);
1811           VMThread::execute(&initial_mark_op);
1812         }
1813         // The collector state may be any legal state at this point
1814         // since the background collector may have yielded to the
1815         // foreground collector.
1816         break;
1817       case Marking:
1818         // initial marking in checkpointRootsInitialWork has been completed
1819         if (markFromRoots()) { // we were successful
1820           assert(_collectorState == Precleaning, "Collector state should "
1821             "have changed");
1822         } else {
1823           assert(_foregroundGCIsActive, "Internal state inconsistency");
1824         }
1825         break;
1826       case Precleaning:
1827         // marking from roots in markFromRoots has been completed
1828         preclean();
1829         assert(_collectorState == AbortablePreclean ||
1830                _collectorState == FinalMarking,
1831                "Collector state should have changed");
1832         break;
1833       case AbortablePreclean:
1834         abortable_preclean();
1835         assert(_collectorState == FinalMarking, "Collector state should "
1836           "have changed");
1837         break;
1838       case FinalMarking:
1839         {
1840           ReleaseForegroundGC x(this);
1841 
1842           VM_CMS_Final_Remark final_remark_op(this);
1843           VMThread::execute(&final_remark_op);
1844         }
1845         assert(_foregroundGCShouldWait, "block post-condition");
1846         break;
1847       case Sweeping:
1848         // final marking in checkpointRootsFinal has been completed
1849         sweep();
1850         assert(_collectorState == Resizing, "Collector state change "
1851           "to Resizing must be done under the free_list_lock");
1852 
1853       case Resizing: {
1854         // Sweeping has been completed...
1855         // At this point the background collection has completed.
1856         // Don't move the call to compute_new_size() down
1857         // into code that might be executed if the background
1858         // collection was preempted.
1859         {
1860           ReleaseForegroundGC x(this);   // unblock FG collection
1861           MutexLockerEx       y(Heap_lock, Mutex::_no_safepoint_check_flag);
1862           CMSTokenSync        z(true);   // not strictly needed.
1863           if (_collectorState == Resizing) {
1864             compute_new_size();
1865             save_heap_summary();
1866             _collectorState = Resetting;
1867           } else {
1868             assert(_collectorState == Idling, "The state should only change"
1869                    " because the foreground collector has finished the collection");
1870           }
1871         }
1872         break;
1873       }
1874       case Resetting:
1875         // CMS heap resizing has been completed
1876         reset_concurrent();
1877         assert(_collectorState == Idling, "Collector state should "
1878           "have changed");
1879 
1880         MetaspaceGC::set_should_concurrent_collect(false);
1881 
1882         stats().record_cms_end();
1883         // Don't move the concurrent_phases_end() and compute_new_size()
1884         // calls to here because a preempted background collection
1885         // has it's state set to "Resetting".
1886         break;
1887       case Idling:
1888       default:
1889         ShouldNotReachHere();
1890         break;
1891     }
1892     log_debug(gc, state)("  Thread " INTPTR_FORMAT " done - next CMS state %d",
1893                          p2i(Thread::current()), _collectorState);
1894     assert(_foregroundGCShouldWait, "block post-condition");
1895   }
1896 
1897   // Should this be in gc_epilogue?
1898   heap->counters()->update_counters();
1899 
1900   {
1901     // Clear _foregroundGCShouldWait and, in the event that the
1902     // foreground collector is waiting, notify it, before
1903     // returning.
1904     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1905     _foregroundGCShouldWait = false;
1906     if (_foregroundGCIsActive) {
1907       CGC_lock->notify();
1908     }
1909     assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1910            "Possible deadlock");
1911   }
1912   log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " exiting collection CMS state %d",
1913                        p2i(Thread::current()), _collectorState);
1914   log_info(gc, heap)("Old: " SIZE_FORMAT "K->" SIZE_FORMAT "K("  SIZE_FORMAT "K)",
1915                      prev_used / K, _cmsGen->used()/K, _cmsGen->capacity() /K);
1916 }
1917 
1918 void CMSCollector::register_gc_start(GCCause::Cause cause) {
1919   _cms_start_registered = true;
1920   _gc_timer_cm->register_gc_start();
1921   _gc_tracer_cm->report_gc_start(cause, _gc_timer_cm->gc_start());
1922 }
1923 
1924 void CMSCollector::register_gc_end() {
1925   if (_cms_start_registered) {
1926     report_heap_summary(GCWhen::AfterGC);
1927 
1928     _gc_timer_cm->register_gc_end();
1929     _gc_tracer_cm->report_gc_end(_gc_timer_cm->gc_end(), _gc_timer_cm->time_partitions());
1930     _cms_start_registered = false;
1931   }
1932 }
1933 
1934 void CMSCollector::save_heap_summary() {
1935   CMSHeap* heap = CMSHeap::heap();
1936   _last_heap_summary = heap->create_heap_summary();
1937   _last_metaspace_summary = heap->create_metaspace_summary();
1938 }
1939 
1940 void CMSCollector::report_heap_summary(GCWhen::Type when) {
1941   _gc_tracer_cm->report_gc_heap_summary(when, _last_heap_summary);
1942   _gc_tracer_cm->report_metaspace_summary(when, _last_metaspace_summary);
1943 }
1944 
1945 bool CMSCollector::waitForForegroundGC() {
1946   bool res = false;
1947   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1948          "CMS thread should have CMS token");
1949   // Block the foreground collector until the
1950   // background collectors decides whether to
1951   // yield.
1952   MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1953   _foregroundGCShouldWait = true;
1954   if (_foregroundGCIsActive) {
1955     // The background collector yields to the
1956     // foreground collector and returns a value
1957     // indicating that it has yielded.  The foreground
1958     // collector can proceed.
1959     res = true;
1960     _foregroundGCShouldWait = false;
1961     ConcurrentMarkSweepThread::clear_CMS_flag(
1962       ConcurrentMarkSweepThread::CMS_cms_has_token);
1963     ConcurrentMarkSweepThread::set_CMS_flag(
1964       ConcurrentMarkSweepThread::CMS_cms_wants_token);
1965     // Get a possibly blocked foreground thread going
1966     CGC_lock->notify();
1967     log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d",
1968                          p2i(Thread::current()), _collectorState);
1969     while (_foregroundGCIsActive) {
1970       CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1971     }
1972     ConcurrentMarkSweepThread::set_CMS_flag(
1973       ConcurrentMarkSweepThread::CMS_cms_has_token);
1974     ConcurrentMarkSweepThread::clear_CMS_flag(
1975       ConcurrentMarkSweepThread::CMS_cms_wants_token);
1976   }
1977   log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d",
1978                        p2i(Thread::current()), _collectorState);
1979   return res;
1980 }
1981 
1982 // Because of the need to lock the free lists and other structures in
1983 // the collector, common to all the generations that the collector is
1984 // collecting, we need the gc_prologues of individual CMS generations
1985 // delegate to their collector. It may have been simpler had the
1986 // current infrastructure allowed one to call a prologue on a
1987 // collector. In the absence of that we have the generation's
1988 // prologue delegate to the collector, which delegates back
1989 // some "local" work to a worker method in the individual generations
1990 // that it's responsible for collecting, while itself doing any
1991 // work common to all generations it's responsible for. A similar
1992 // comment applies to the  gc_epilogue()'s.
1993 // The role of the variable _between_prologue_and_epilogue is to
1994 // enforce the invocation protocol.
1995 void CMSCollector::gc_prologue(bool full) {
1996   // Call gc_prologue_work() for the CMSGen
1997   // we are responsible for.
1998 
1999   // The following locking discipline assumes that we are only called
2000   // when the world is stopped.
2001   assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption");
2002 
2003   // The CMSCollector prologue must call the gc_prologues for the
2004   // "generations" that it's responsible
2005   // for.
2006 
2007   assert(   Thread::current()->is_VM_thread()
2008          || (   CMSScavengeBeforeRemark
2009              && Thread::current()->is_ConcurrentGC_thread()),
2010          "Incorrect thread type for prologue execution");
2011 
2012   if (_between_prologue_and_epilogue) {
2013     // We have already been invoked; this is a gc_prologue delegation
2014     // from yet another CMS generation that we are responsible for, just
2015     // ignore it since all relevant work has already been done.
2016     return;
2017   }
2018 
2019   // set a bit saying prologue has been called; cleared in epilogue
2020   _between_prologue_and_epilogue = true;
2021   // Claim locks for common data structures, then call gc_prologue_work()
2022   // for each CMSGen.
2023 
2024   getFreelistLocks();   // gets free list locks on constituent spaces
2025   bitMapLock()->lock_without_safepoint_check();
2026 
2027   // Should call gc_prologue_work() for all cms gens we are responsible for
2028   bool duringMarking =    _collectorState >= Marking
2029                          && _collectorState < Sweeping;
2030 
2031   // The young collections clear the modified oops state, which tells if
2032   // there are any modified oops in the class. The remark phase also needs
2033   // that information. Tell the young collection to save the union of all
2034   // modified klasses.
2035   if (duringMarking) {
2036     _ct->cld_rem_set()->set_accumulate_modified_oops(true);
2037   }
2038 
2039   bool registerClosure = duringMarking;
2040 
2041   _cmsGen->gc_prologue_work(full, registerClosure, &_modUnionClosurePar);
2042 
2043   if (!full) {
2044     stats().record_gc0_begin();
2045   }
2046 }
2047 
2048 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) {
2049 
2050   _capacity_at_prologue = capacity();
2051   _used_at_prologue = used();
2052 
2053   // We enable promotion tracking so that card-scanning can recognize
2054   // which objects have been promoted during this GC and skip them.
2055   for (uint i = 0; i < ParallelGCThreads; i++) {
2056     _par_gc_thread_states[i]->promo.startTrackingPromotions();
2057   }
2058 
2059   // Delegate to CMScollector which knows how to coordinate between
2060   // this and any other CMS generations that it is responsible for
2061   // collecting.
2062   collector()->gc_prologue(full);
2063 }
2064 
2065 // This is a "private" interface for use by this generation's CMSCollector.
2066 // Not to be called directly by any other entity (for instance,
2067 // GenCollectedHeap, which calls the "public" gc_prologue method above).
2068 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full,
2069   bool registerClosure, ModUnionClosure* modUnionClosure) {
2070   assert(!incremental_collection_failed(), "Shouldn't be set yet");
2071   assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL,
2072     "Should be NULL");
2073   if (registerClosure) {
2074     cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure);
2075   }
2076   cmsSpace()->gc_prologue();
2077   // Clear stat counters
2078   NOT_PRODUCT(
2079     assert(_numObjectsPromoted == 0, "check");
2080     assert(_numWordsPromoted   == 0, "check");
2081     log_develop_trace(gc, alloc)("Allocated " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes concurrently",
2082                                  _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord));
2083     _numObjectsAllocated = 0;
2084     _numWordsAllocated   = 0;
2085   )
2086 }
2087 
2088 void CMSCollector::gc_epilogue(bool full) {
2089   // The following locking discipline assumes that we are only called
2090   // when the world is stopped.
2091   assert(SafepointSynchronize::is_at_safepoint(),
2092          "world is stopped assumption");
2093 
2094   // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks
2095   // if linear allocation blocks need to be appropriately marked to allow the
2096   // the blocks to be parsable. We also check here whether we need to nudge the
2097   // CMS collector thread to start a new cycle (if it's not already active).
2098   assert(   Thread::current()->is_VM_thread()
2099          || (   CMSScavengeBeforeRemark
2100              && Thread::current()->is_ConcurrentGC_thread()),
2101          "Incorrect thread type for epilogue execution");
2102 
2103   if (!_between_prologue_and_epilogue) {
2104     // We have already been invoked; this is a gc_epilogue delegation
2105     // from yet another CMS generation that we are responsible for, just
2106     // ignore it since all relevant work has already been done.
2107     return;
2108   }
2109   assert(haveFreelistLocks(), "must have freelist locks");
2110   assert_lock_strong(bitMapLock());
2111 
2112   _ct->cld_rem_set()->set_accumulate_modified_oops(false);
2113 
2114   _cmsGen->gc_epilogue_work(full);
2115 
2116   if (_collectorState == AbortablePreclean || _collectorState == Precleaning) {
2117     // in case sampling was not already enabled, enable it
2118     _start_sampling = true;
2119   }
2120   // reset _eden_chunk_array so sampling starts afresh
2121   _eden_chunk_index = 0;
2122 
2123   size_t cms_used   = _cmsGen->cmsSpace()->used();
2124 
2125   // update performance counters - this uses a special version of
2126   // update_counters() that allows the utilization to be passed as a
2127   // parameter, avoiding multiple calls to used().
2128   //
2129   _cmsGen->update_counters(cms_used);
2130 
2131   bitMapLock()->unlock();
2132   releaseFreelistLocks();
2133 
2134   if (!CleanChunkPoolAsync) {
2135     Chunk::clean_chunk_pool();
2136   }
2137 
2138   set_did_compact(false);
2139   _between_prologue_and_epilogue = false;  // ready for next cycle
2140 }
2141 
2142 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) {
2143   collector()->gc_epilogue(full);
2144 
2145   // When using ParNew, promotion tracking should have already been
2146   // disabled. However, the prologue (which enables promotion
2147   // tracking) and epilogue are called irrespective of the type of
2148   // GC. So they will also be called before and after Full GCs, during
2149   // which promotion tracking will not be explicitly disabled. So,
2150   // it's safer to also disable it here too (to be symmetric with
2151   // enabling it in the prologue).
2152   for (uint i = 0; i < ParallelGCThreads; i++) {
2153     _par_gc_thread_states[i]->promo.stopTrackingPromotions();
2154   }
2155 }
2156 
2157 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2158   assert(!incremental_collection_failed(), "Should have been cleared");
2159   cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2160   cmsSpace()->gc_epilogue();
2161     // Print stat counters
2162   NOT_PRODUCT(
2163     assert(_numObjectsAllocated == 0, "check");
2164     assert(_numWordsAllocated == 0, "check");
2165     log_develop_trace(gc, promotion)("Promoted " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
2166                                      _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2167     _numObjectsPromoted = 0;
2168     _numWordsPromoted   = 0;
2169   )
2170 
2171   // Call down the chain in contiguous_available needs the freelistLock
2172   // so print this out before releasing the freeListLock.
2173   log_develop_trace(gc)(" Contiguous available " SIZE_FORMAT " bytes ", contiguous_available());
2174 }
2175 
2176 #ifndef PRODUCT
2177 bool CMSCollector::have_cms_token() {
2178   Thread* thr = Thread::current();
2179   if (thr->is_VM_thread()) {
2180     return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2181   } else if (thr->is_ConcurrentGC_thread()) {
2182     return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2183   } else if (thr->is_GC_task_thread()) {
2184     return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2185            ParGCRareEvent_lock->owned_by_self();
2186   }
2187   return false;
2188 }
2189 
2190 // Check reachability of the given heap address in CMS generation,
2191 // treating all other generations as roots.
2192 bool CMSCollector::is_cms_reachable(HeapWord* addr) {
2193   // We could "guarantee" below, rather than assert, but I'll
2194   // leave these as "asserts" so that an adventurous debugger
2195   // could try this in the product build provided some subset of
2196   // the conditions were met, provided they were interested in the
2197   // results and knew that the computation below wouldn't interfere
2198   // with other concurrent computations mutating the structures
2199   // being read or written.
2200   assert(SafepointSynchronize::is_at_safepoint(),
2201          "Else mutations in object graph will make answer suspect");
2202   assert(have_cms_token(), "Should hold cms token");
2203   assert(haveFreelistLocks(), "must hold free list locks");
2204   assert_lock_strong(bitMapLock());
2205 
2206   // Clear the marking bit map array before starting, but, just
2207   // for kicks, first report if the given address is already marked
2208   tty->print_cr("Start: Address " PTR_FORMAT " is%s marked", p2i(addr),
2209                 _markBitMap.isMarked(addr) ? "" : " not");
2210 
2211   if (verify_after_remark()) {
2212     MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2213     bool result = verification_mark_bm()->isMarked(addr);
2214     tty->print_cr("TransitiveMark: Address " PTR_FORMAT " %s marked", p2i(addr),
2215                   result ? "IS" : "is NOT");
2216     return result;
2217   } else {
2218     tty->print_cr("Could not compute result");
2219     return false;
2220   }
2221 }
2222 #endif
2223 
2224 void
2225 CMSCollector::print_on_error(outputStream* st) {
2226   CMSCollector* collector = ConcurrentMarkSweepGeneration::_collector;
2227   if (collector != NULL) {
2228     CMSBitMap* bitmap = &collector->_markBitMap;
2229     st->print_cr("Marking Bits: (CMSBitMap*) " PTR_FORMAT, p2i(bitmap));
2230     bitmap->print_on_error(st, " Bits: ");
2231 
2232     st->cr();
2233 
2234     CMSBitMap* mut_bitmap = &collector->_modUnionTable;
2235     st->print_cr("Mod Union Table: (CMSBitMap*) " PTR_FORMAT, p2i(mut_bitmap));
2236     mut_bitmap->print_on_error(st, " Bits: ");
2237   }
2238 }
2239 
2240 ////////////////////////////////////////////////////////
2241 // CMS Verification Support
2242 ////////////////////////////////////////////////////////
2243 // Following the remark phase, the following invariant
2244 // should hold -- each object in the CMS heap which is
2245 // marked in markBitMap() should be marked in the verification_mark_bm().
2246 
2247 class VerifyMarkedClosure: public BitMapClosure {
2248   CMSBitMap* _marks;
2249   bool       _failed;
2250 
2251  public:
2252   VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2253 
2254   bool do_bit(size_t offset) {
2255     HeapWord* addr = _marks->offsetToHeapWord(offset);
2256     if (!_marks->isMarked(addr)) {
2257       Log(gc, verify) log;
2258       ResourceMark rm;
2259       LogStream ls(log.error());
2260       oop(addr)->print_on(&ls);
2261       log.error(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
2262       _failed = true;
2263     }
2264     return true;
2265   }
2266 
2267   bool failed() { return _failed; }
2268 };
2269 
2270 bool CMSCollector::verify_after_remark() {
2271   GCTraceTime(Info, gc, phases, verify) tm("Verifying CMS Marking.");
2272   MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2273   static bool init = false;
2274 
2275   assert(SafepointSynchronize::is_at_safepoint(),
2276          "Else mutations in object graph will make answer suspect");
2277   assert(have_cms_token(),
2278          "Else there may be mutual interference in use of "
2279          " verification data structures");
2280   assert(_collectorState > Marking && _collectorState <= Sweeping,
2281          "Else marking info checked here may be obsolete");
2282   assert(haveFreelistLocks(), "must hold free list locks");
2283   assert_lock_strong(bitMapLock());
2284 
2285 
2286   // Allocate marking bit map if not already allocated
2287   if (!init) { // first time
2288     if (!verification_mark_bm()->allocate(_span)) {
2289       return false;
2290     }
2291     init = true;
2292   }
2293 
2294   assert(verification_mark_stack()->isEmpty(), "Should be empty");
2295 
2296   // Turn off refs discovery -- so we will be tracing through refs.
2297   // This is as intended, because by this time
2298   // GC must already have cleared any refs that need to be cleared,
2299   // and traced those that need to be marked; moreover,
2300   // the marking done here is not going to interfere in any
2301   // way with the marking information used by GC.
2302   NoRefDiscovery no_discovery(ref_processor());
2303 
2304 #if COMPILER2_OR_JVMCI
2305   DerivedPointerTableDeactivate dpt_deact;
2306 #endif
2307 
2308   // Clear any marks from a previous round
2309   verification_mark_bm()->clear_all();
2310   assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
2311   verify_work_stacks_empty();
2312 
2313   CMSHeap* heap = CMSHeap::heap();
2314   heap->ensure_parsability(false);  // fill TLABs, but no need to retire them
2315   // Update the saved marks which may affect the root scans.
2316   heap->save_marks();
2317 
2318   if (CMSRemarkVerifyVariant == 1) {
2319     // In this first variant of verification, we complete
2320     // all marking, then check if the new marks-vector is
2321     // a subset of the CMS marks-vector.
2322     verify_after_remark_work_1();
2323   } else {
2324     guarantee(CMSRemarkVerifyVariant == 2, "Range checking for CMSRemarkVerifyVariant should guarantee 1 or 2");
2325     // In this second variant of verification, we flag an error
2326     // (i.e. an object reachable in the new marks-vector not reachable
2327     // in the CMS marks-vector) immediately, also indicating the
2328     // identify of an object (A) that references the unmarked object (B) --
2329     // presumably, a mutation to A failed to be picked up by preclean/remark?
2330     verify_after_remark_work_2();
2331   }
2332 
2333   return true;
2334 }
2335 
2336 void CMSCollector::verify_after_remark_work_1() {
2337   ResourceMark rm;
2338   HandleMark  hm;
2339   CMSHeap* heap = CMSHeap::heap();
2340 
2341   // Get a clear set of claim bits for the roots processing to work with.
2342   ClassLoaderDataGraph::clear_claimed_marks();
2343 
2344   // Mark from roots one level into CMS
2345   MarkRefsIntoClosure notOlder(_span, verification_mark_bm());
2346   heap->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2347 
2348   {
2349     StrongRootsScope srs(1);
2350 
2351     heap->cms_process_roots(&srs,
2352                            true,   // young gen as roots
2353                            GenCollectedHeap::ScanningOption(roots_scanning_options()),
2354                            should_unload_classes(),
2355                            &notOlder,
2356                            NULL);
2357   }
2358 
2359   // Now mark from the roots
2360   MarkFromRootsClosure markFromRootsClosure(this, _span,
2361     verification_mark_bm(), verification_mark_stack(),
2362     false /* don't yield */, true /* verifying */);
2363   assert(_restart_addr == NULL, "Expected pre-condition");
2364   verification_mark_bm()->iterate(&markFromRootsClosure);
2365   while (_restart_addr != NULL) {
2366     // Deal with stack overflow: by restarting at the indicated
2367     // address.
2368     HeapWord* ra = _restart_addr;
2369     markFromRootsClosure.reset(ra);
2370     _restart_addr = NULL;
2371     verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2372   }
2373   assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2374   verify_work_stacks_empty();
2375 
2376   // Marking completed -- now verify that each bit marked in
2377   // verification_mark_bm() is also marked in markBitMap(); flag all
2378   // errors by printing corresponding objects.
2379   VerifyMarkedClosure vcl(markBitMap());
2380   verification_mark_bm()->iterate(&vcl);
2381   if (vcl.failed()) {
2382     Log(gc, verify) log;
2383     log.error("Failed marking verification after remark");
2384     ResourceMark rm;
2385     LogStream ls(log.error());
2386     heap->print_on(&ls);
2387     fatal("CMS: failed marking verification after remark");
2388   }
2389 }
2390 
2391 class VerifyCLDOopsCLDClosure : public CLDClosure {
2392   class VerifyCLDOopsClosure : public OopClosure {
2393     CMSBitMap* _bitmap;
2394    public:
2395     VerifyCLDOopsClosure(CMSBitMap* bitmap) : _bitmap(bitmap) { }
2396     void do_oop(oop* p)       { guarantee(*p == NULL || _bitmap->isMarked((HeapWord*) *p), "Should be marked"); }
2397     void do_oop(narrowOop* p) { ShouldNotReachHere(); }
2398   } _oop_closure;
2399  public:
2400   VerifyCLDOopsCLDClosure(CMSBitMap* bitmap) : _oop_closure(bitmap) {}
2401   void do_cld(ClassLoaderData* cld) {
2402     cld->oops_do(&_oop_closure, ClassLoaderData::_claim_none, false);
2403   }
2404 };
2405 
2406 void CMSCollector::verify_after_remark_work_2() {
2407   ResourceMark rm;
2408   HandleMark  hm;
2409   CMSHeap* heap = CMSHeap::heap();
2410 
2411   // Get a clear set of claim bits for the roots processing to work with.
2412   ClassLoaderDataGraph::clear_claimed_marks();
2413 
2414   // Mark from roots one level into CMS
2415   MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
2416                                      markBitMap());
2417   CLDToOopClosure cld_closure(&notOlder, ClassLoaderData::_claim_strong);
2418 
2419   heap->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2420 
2421   {
2422     StrongRootsScope srs(1);
2423 
2424     heap->cms_process_roots(&srs,
2425                            true,   // young gen as roots
2426                            GenCollectedHeap::ScanningOption(roots_scanning_options()),
2427                            should_unload_classes(),
2428                            &notOlder,
2429                            &cld_closure);
2430   }
2431 
2432   // Now mark from the roots
2433   MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
2434     verification_mark_bm(), markBitMap(), verification_mark_stack());
2435   assert(_restart_addr == NULL, "Expected pre-condition");
2436   verification_mark_bm()->iterate(&markFromRootsClosure);
2437   while (_restart_addr != NULL) {
2438     // Deal with stack overflow: by restarting at the indicated
2439     // address.
2440     HeapWord* ra = _restart_addr;
2441     markFromRootsClosure.reset(ra);
2442     _restart_addr = NULL;
2443     verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2444   }
2445   assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2446   verify_work_stacks_empty();
2447 
2448   VerifyCLDOopsCLDClosure verify_cld_oops(verification_mark_bm());
2449   ClassLoaderDataGraph::cld_do(&verify_cld_oops);
2450 
2451   // Marking completed -- now verify that each bit marked in
2452   // verification_mark_bm() is also marked in markBitMap(); flag all
2453   // errors by printing corresponding objects.
2454   VerifyMarkedClosure vcl(markBitMap());
2455   verification_mark_bm()->iterate(&vcl);
2456   assert(!vcl.failed(), "Else verification above should not have succeeded");
2457 }
2458 
2459 void ConcurrentMarkSweepGeneration::save_marks() {
2460   // delegate to CMS space
2461   cmsSpace()->save_marks();
2462 }
2463 
2464 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
2465   return cmsSpace()->no_allocs_since_save_marks();
2466 }
2467 
2468 void
2469 ConcurrentMarkSweepGeneration::oop_iterate(OopIterateClosure* cl) {
2470   if (freelistLock()->owned_by_self()) {
2471     Generation::oop_iterate(cl);
2472   } else {
2473     MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2474     Generation::oop_iterate(cl);
2475   }
2476 }
2477 
2478 void
2479 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
2480   if (freelistLock()->owned_by_self()) {
2481     Generation::object_iterate(cl);
2482   } else {
2483     MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2484     Generation::object_iterate(cl);
2485   }
2486 }
2487 
2488 void
2489 ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) {
2490   if (freelistLock()->owned_by_self()) {
2491     Generation::safe_object_iterate(cl);
2492   } else {
2493     MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2494     Generation::safe_object_iterate(cl);
2495   }
2496 }
2497 
2498 void
2499 ConcurrentMarkSweepGeneration::post_compact() {
2500 }
2501 
2502 void
2503 ConcurrentMarkSweepGeneration::prepare_for_verify() {
2504   // Fix the linear allocation blocks to look like free blocks.
2505 
2506   // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2507   // are not called when the heap is verified during universe initialization and
2508   // at vm shutdown.
2509   if (freelistLock()->owned_by_self()) {
2510     cmsSpace()->prepare_for_verify();
2511   } else {
2512     MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2513     cmsSpace()->prepare_for_verify();
2514   }
2515 }
2516 
2517 void
2518 ConcurrentMarkSweepGeneration::verify() {
2519   // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2520   // are not called when the heap is verified during universe initialization and
2521   // at vm shutdown.
2522   if (freelistLock()->owned_by_self()) {
2523     cmsSpace()->verify();
2524   } else {
2525     MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2526     cmsSpace()->verify();
2527   }
2528 }
2529 
2530 void CMSCollector::verify() {
2531   _cmsGen->verify();
2532 }
2533 
2534 #ifndef PRODUCT
2535 bool CMSCollector::overflow_list_is_empty() const {
2536   assert(_num_par_pushes >= 0, "Inconsistency");
2537   if (_overflow_list == NULL) {
2538     assert(_num_par_pushes == 0, "Inconsistency");
2539   }
2540   return _overflow_list == NULL;
2541 }
2542 
2543 // The methods verify_work_stacks_empty() and verify_overflow_empty()
2544 // merely consolidate assertion checks that appear to occur together frequently.
2545 void CMSCollector::verify_work_stacks_empty() const {
2546   assert(_markStack.isEmpty(), "Marking stack should be empty");
2547   assert(overflow_list_is_empty(), "Overflow list should be empty");
2548 }
2549 
2550 void CMSCollector::verify_overflow_empty() const {
2551   assert(overflow_list_is_empty(), "Overflow list should be empty");
2552   assert(no_preserved_marks(), "No preserved marks");
2553 }
2554 #endif // PRODUCT
2555 
2556 // Decide if we want to enable class unloading as part of the
2557 // ensuing concurrent GC cycle. We will collect and
2558 // unload classes if it's the case that:
2559 //  (a) class unloading is enabled at the command line, and
2560 //  (b) old gen is getting really full
2561 // NOTE: Provided there is no change in the state of the heap between
2562 // calls to this method, it should have idempotent results. Moreover,
2563 // its results should be monotonically increasing (i.e. going from 0 to 1,
2564 // but not 1 to 0) between successive calls between which the heap was
2565 // not collected. For the implementation below, it must thus rely on
2566 // the property that concurrent_cycles_since_last_unload()
2567 // will not decrease unless a collection cycle happened and that
2568 // _cmsGen->is_too_full() are
2569 // themselves also monotonic in that sense. See check_monotonicity()
2570 // below.
2571 void CMSCollector::update_should_unload_classes() {
2572   _should_unload_classes = false;
2573   if (CMSClassUnloadingEnabled) {
2574     _should_unload_classes = (concurrent_cycles_since_last_unload() >=
2575                               CMSClassUnloadingMaxInterval)
2576                            || _cmsGen->is_too_full();
2577   }
2578 }
2579 
2580 bool ConcurrentMarkSweepGeneration::is_too_full() const {
2581   bool res = should_concurrent_collect();
2582   res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
2583   return res;
2584 }
2585 
2586 void CMSCollector::setup_cms_unloading_and_verification_state() {
2587   const  bool should_verify =   VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
2588                              || VerifyBeforeExit;
2589   const  int  rso           =   GenCollectedHeap::SO_AllCodeCache;
2590 
2591   // We set the proper root for this CMS cycle here.
2592   if (should_unload_classes()) {   // Should unload classes this cycle
2593     remove_root_scanning_option(rso);  // Shrink the root set appropriately
2594     set_verifying(should_verify);    // Set verification state for this cycle
2595     return;                            // Nothing else needs to be done at this time
2596   }
2597 
2598   // Not unloading classes this cycle
2599   assert(!should_unload_classes(), "Inconsistency!");
2600 
2601   // If we are not unloading classes then add SO_AllCodeCache to root
2602   // scanning options.
2603   add_root_scanning_option(rso);
2604 
2605   if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
2606     set_verifying(true);
2607   } else if (verifying() && !should_verify) {
2608     // We were verifying, but some verification flags got disabled.
2609     set_verifying(false);
2610     // Exclude symbols, strings and code cache elements from root scanning to
2611     // reduce IM and RM pauses.
2612     remove_root_scanning_option(rso);
2613   }
2614 }
2615 
2616 
2617 #ifndef PRODUCT
2618 HeapWord* CMSCollector::block_start(const void* p) const {
2619   const HeapWord* addr = (HeapWord*)p;
2620   if (_span.contains(p)) {
2621     if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
2622       return _cmsGen->cmsSpace()->block_start(p);
2623     }
2624   }
2625   return NULL;
2626 }
2627 #endif
2628 
2629 HeapWord*
2630 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
2631                                                    bool   tlab,
2632                                                    bool   parallel) {
2633   CMSSynchronousYieldRequest yr;
2634   assert(!tlab, "Can't deal with TLAB allocation");
2635   MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2636   expand_for_gc_cause(word_size*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_allocation);
2637   if (GCExpandToAllocateDelayMillis > 0) {
2638     os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2639   }
2640   return have_lock_and_allocate(word_size, tlab);
2641 }
2642 
2643 void ConcurrentMarkSweepGeneration::expand_for_gc_cause(
2644     size_t bytes,
2645     size_t expand_bytes,
2646     CMSExpansionCause::Cause cause)
2647 {
2648 
2649   bool success = expand(bytes, expand_bytes);
2650 
2651   // remember why we expanded; this information is used
2652   // by shouldConcurrentCollect() when making decisions on whether to start
2653   // a new CMS cycle.
2654   if (success) {
2655     set_expansion_cause(cause);
2656     log_trace(gc)("Expanded CMS gen for %s",  CMSExpansionCause::to_string(cause));
2657   }
2658 }
2659 
2660 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
2661   HeapWord* res = NULL;
2662   MutexLocker x(ParGCRareEvent_lock);
2663   while (true) {
2664     // Expansion by some other thread might make alloc OK now:
2665     res = ps->lab.alloc(word_sz);
2666     if (res != NULL) return res;
2667     // If there's not enough expansion space available, give up.
2668     if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
2669       return NULL;
2670     }
2671     // Otherwise, we try expansion.
2672     expand_for_gc_cause(word_sz*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_lab);
2673     // Now go around the loop and try alloc again;
2674     // A competing par_promote might beat us to the expansion space,
2675     // so we may go around the loop again if promotion fails again.
2676     if (GCExpandToAllocateDelayMillis > 0) {
2677       os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2678     }
2679   }
2680 }
2681 
2682 
2683 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
2684   PromotionInfo* promo) {
2685   MutexLocker x(ParGCRareEvent_lock);
2686   size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
2687   while (true) {
2688     // Expansion by some other thread might make alloc OK now:
2689     if (promo->ensure_spooling_space()) {
2690       assert(promo->has_spooling_space(),
2691              "Post-condition of successful ensure_spooling_space()");
2692       return true;
2693     }
2694     // If there's not enough expansion space available, give up.
2695     if (_virtual_space.uncommitted_size() < refill_size_bytes) {
2696       return false;
2697     }
2698     // Otherwise, we try expansion.
2699     expand_for_gc_cause(refill_size_bytes, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_spooling_space);
2700     // Now go around the loop and try alloc again;
2701     // A competing allocation might beat us to the expansion space,
2702     // so we may go around the loop again if allocation fails again.
2703     if (GCExpandToAllocateDelayMillis > 0) {
2704       os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2705     }
2706   }
2707 }
2708 
2709 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
2710   // Only shrink if a compaction was done so that all the free space
2711   // in the generation is in a contiguous block at the end.
2712   if (did_compact()) {
2713     CardGeneration::shrink(bytes);
2714   }
2715 }
2716 
2717 void ConcurrentMarkSweepGeneration::assert_correct_size_change_locking() {
2718   assert_locked_or_safepoint(Heap_lock);
2719 }
2720 
2721 void ConcurrentMarkSweepGeneration::shrink_free_list_by(size_t bytes) {
2722   assert_locked_or_safepoint(Heap_lock);
2723   assert_lock_strong(freelistLock());
2724   log_trace(gc)("Shrinking of CMS not yet implemented");
2725   return;
2726 }
2727 
2728 
2729 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
2730 // phases.
2731 class CMSPhaseAccounting: public StackObj {
2732  public:
2733   CMSPhaseAccounting(CMSCollector *collector,
2734                      const char *title);
2735   ~CMSPhaseAccounting();
2736 
2737  private:
2738   CMSCollector *_collector;
2739   const char *_title;
2740   GCTraceConcTime(Info, gc) _trace_time;
2741 
2742  public:
2743   // Not MT-safe; so do not pass around these StackObj's
2744   // where they may be accessed by other threads.
2745   double wallclock_millis() {
2746     return TimeHelper::counter_to_millis(os::elapsed_counter() - _trace_time.start_time());
2747   }
2748 };
2749 
2750 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
2751                                        const char *title) :
2752   _collector(collector), _title(title), _trace_time(title) {
2753 
2754   _collector->resetYields();
2755   _collector->resetTimer();
2756   _collector->startTimer();
2757   _collector->gc_timer_cm()->register_gc_concurrent_start(title);
2758 }
2759 
2760 CMSPhaseAccounting::~CMSPhaseAccounting() {
2761   _collector->gc_timer_cm()->register_gc_concurrent_end();
2762   _collector->stopTimer();
2763   log_debug(gc)("Concurrent active time: %.3fms", TimeHelper::counter_to_seconds(_collector->timerTicks()));
2764   log_trace(gc)(" (CMS %s yielded %d times)", _title, _collector->yields());
2765 }
2766 
2767 // CMS work
2768 
2769 // The common parts of CMSParInitialMarkTask and CMSParRemarkTask.
2770 class CMSParMarkTask : public AbstractGangTask {
2771  protected:
2772   CMSCollector*     _collector;
2773   uint              _n_workers;
2774   OopStorage::ParState<false, false> _par_state_string;
2775   CMSParMarkTask(const char* name, CMSCollector* collector, uint n_workers) :
2776       AbstractGangTask(name),
2777       _collector(collector),
2778       _n_workers(n_workers),
2779       _par_state_string(StringTable::weak_storage()) {}
2780   // Work method in support of parallel rescan ... of young gen spaces
2781   void do_young_space_rescan(OopsInGenClosure* cl,
2782                              ContiguousSpace* space,
2783                              HeapWord** chunk_array, size_t chunk_top);
2784   void work_on_young_gen_roots(OopsInGenClosure* cl);
2785 };
2786 
2787 // Parallel initial mark task
2788 class CMSParInitialMarkTask: public CMSParMarkTask {
2789   StrongRootsScope* _strong_roots_scope;
2790  public:
2791   CMSParInitialMarkTask(CMSCollector* collector, StrongRootsScope* strong_roots_scope, uint n_workers) :
2792       CMSParMarkTask("Scan roots and young gen for initial mark in parallel", collector, n_workers),
2793       _strong_roots_scope(strong_roots_scope) {}
2794   void work(uint worker_id);
2795 };
2796 
2797 // Checkpoint the roots into this generation from outside
2798 // this generation. [Note this initial checkpoint need only
2799 // be approximate -- we'll do a catch up phase subsequently.]
2800 void CMSCollector::checkpointRootsInitial() {
2801   assert(_collectorState == InitialMarking, "Wrong collector state");
2802   check_correct_thread_executing();
2803   TraceCMSMemoryManagerStats tms(_collectorState, CMSHeap::heap()->gc_cause());
2804 
2805   save_heap_summary();
2806   report_heap_summary(GCWhen::BeforeGC);
2807 
2808   ReferenceProcessor* rp = ref_processor();
2809   assert(_restart_addr == NULL, "Control point invariant");
2810   {
2811     // acquire locks for subsequent manipulations
2812     MutexLockerEx x(bitMapLock(),
2813                     Mutex::_no_safepoint_check_flag);
2814     checkpointRootsInitialWork();
2815     // enable ("weak") refs discovery
2816     rp->enable_discovery();
2817     _collectorState = Marking;
2818   }
2819 }
2820 
2821 void CMSCollector::checkpointRootsInitialWork() {
2822   assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
2823   assert(_collectorState == InitialMarking, "just checking");
2824 
2825   // Already have locks.
2826   assert_lock_strong(bitMapLock());
2827   assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
2828 
2829   // Setup the verification and class unloading state for this
2830   // CMS collection cycle.
2831   setup_cms_unloading_and_verification_state();
2832 
2833   GCTraceTime(Trace, gc, phases) ts("checkpointRootsInitialWork", _gc_timer_cm);
2834 
2835   // Reset all the PLAB chunk arrays if necessary.
2836   if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
2837     reset_survivor_plab_arrays();
2838   }
2839 
2840   ResourceMark rm;
2841   HandleMark  hm;
2842 
2843   MarkRefsIntoClosure notOlder(_span, &_markBitMap);
2844   CMSHeap* heap = CMSHeap::heap();
2845 
2846   verify_work_stacks_empty();
2847   verify_overflow_empty();
2848 
2849   heap->ensure_parsability(false);  // fill TLABs, but no need to retire them
2850   // Update the saved marks which may affect the root scans.
2851   heap->save_marks();
2852 
2853   // weak reference processing has not started yet.
2854   ref_processor()->set_enqueuing_is_done(false);
2855 
2856   // Need to remember all newly created CLDs,
2857   // so that we can guarantee that the remark finds them.
2858   ClassLoaderDataGraph::remember_new_clds(true);
2859 
2860   // Whenever a CLD is found, it will be claimed before proceeding to mark
2861   // the klasses. The claimed marks need to be cleared before marking starts.
2862   ClassLoaderDataGraph::clear_claimed_marks();
2863 
2864   print_eden_and_survivor_chunk_arrays();
2865 
2866   {
2867 #if COMPILER2_OR_JVMCI
2868     DerivedPointerTableDeactivate dpt_deact;
2869 #endif
2870     if (CMSParallelInitialMarkEnabled) {
2871       // The parallel version.
2872       WorkGang* workers = heap->workers();
2873       assert(workers != NULL, "Need parallel worker threads.");
2874       uint n_workers = workers->active_workers();
2875 
2876       StrongRootsScope srs(n_workers);
2877 
2878       CMSParInitialMarkTask tsk(this, &srs, n_workers);
2879       initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
2880       // If the total workers is greater than 1, then multiple workers
2881       // may be used at some time and the initialization has been set
2882       // such that the single threaded path cannot be used.
2883       if (workers->total_workers() > 1) {
2884         workers->run_task(&tsk);
2885       } else {
2886         tsk.work(0);
2887       }
2888     } else {
2889       // The serial version.
2890       CLDToOopClosure cld_closure(&notOlder, ClassLoaderData::_claim_strong);
2891       heap->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2892 
2893       StrongRootsScope srs(1);
2894 
2895       heap->cms_process_roots(&srs,
2896                              true,   // young gen as roots
2897                              GenCollectedHeap::ScanningOption(roots_scanning_options()),
2898                              should_unload_classes(),
2899                              &notOlder,
2900                              &cld_closure);
2901     }
2902   }
2903 
2904   // Clear mod-union table; it will be dirtied in the prologue of
2905   // CMS generation per each young generation collection.
2906 
2907   assert(_modUnionTable.isAllClear(),
2908        "Was cleared in most recent final checkpoint phase"
2909        " or no bits are set in the gc_prologue before the start of the next "
2910        "subsequent marking phase.");
2911 
2912   assert(_ct->cld_rem_set()->mod_union_is_clear(), "Must be");
2913 
2914   // Save the end of the used_region of the constituent generations
2915   // to be used to limit the extent of sweep in each generation.
2916   save_sweep_limits();
2917   verify_overflow_empty();
2918 }
2919 
2920 bool CMSCollector::markFromRoots() {
2921   // we might be tempted to assert that:
2922   // assert(!SafepointSynchronize::is_at_safepoint(),
2923   //        "inconsistent argument?");
2924   // However that wouldn't be right, because it's possible that
2925   // a safepoint is indeed in progress as a young generation
2926   // stop-the-world GC happens even as we mark in this generation.
2927   assert(_collectorState == Marking, "inconsistent state?");
2928   check_correct_thread_executing();
2929   verify_overflow_empty();
2930 
2931   // Weak ref discovery note: We may be discovering weak
2932   // refs in this generation concurrent (but interleaved) with
2933   // weak ref discovery by the young generation collector.
2934 
2935   CMSTokenSyncWithLocks ts(true, bitMapLock());
2936   GCTraceCPUTime tcpu;
2937   CMSPhaseAccounting pa(this, "Concurrent Mark");
2938   bool res = markFromRootsWork();
2939   if (res) {
2940     _collectorState = Precleaning;
2941   } else { // We failed and a foreground collection wants to take over
2942     assert(_foregroundGCIsActive, "internal state inconsistency");
2943     assert(_restart_addr == NULL,  "foreground will restart from scratch");
2944     log_debug(gc)("bailing out to foreground collection");
2945   }
2946   verify_overflow_empty();
2947   return res;
2948 }
2949 
2950 bool CMSCollector::markFromRootsWork() {
2951   // iterate over marked bits in bit map, doing a full scan and mark
2952   // from these roots using the following algorithm:
2953   // . if oop is to the right of the current scan pointer,
2954   //   mark corresponding bit (we'll process it later)
2955   // . else (oop is to left of current scan pointer)
2956   //   push oop on marking stack
2957   // . drain the marking stack
2958 
2959   // Note that when we do a marking step we need to hold the
2960   // bit map lock -- recall that direct allocation (by mutators)
2961   // and promotion (by the young generation collector) is also
2962   // marking the bit map. [the so-called allocate live policy.]
2963   // Because the implementation of bit map marking is not
2964   // robust wrt simultaneous marking of bits in the same word,
2965   // we need to make sure that there is no such interference
2966   // between concurrent such updates.
2967 
2968   // already have locks
2969   assert_lock_strong(bitMapLock());
2970 
2971   verify_work_stacks_empty();
2972   verify_overflow_empty();
2973   bool result = false;
2974   if (CMSConcurrentMTEnabled && ConcGCThreads > 0) {
2975     result = do_marking_mt();
2976   } else {
2977     result = do_marking_st();
2978   }
2979   return result;
2980 }
2981 
2982 // Forward decl
2983 class CMSConcMarkingTask;
2984 
2985 class CMSConcMarkingParallelTerminator: public ParallelTaskTerminator {
2986   CMSCollector*       _collector;
2987   CMSConcMarkingTask* _task;
2988  public:
2989   virtual void yield();
2990 
2991   // "n_threads" is the number of threads to be terminated.
2992   // "queue_set" is a set of work queues of other threads.
2993   // "collector" is the CMS collector associated with this task terminator.
2994   // "yield" indicates whether we need the gang as a whole to yield.
2995   CMSConcMarkingParallelTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
2996     ParallelTaskTerminator(n_threads, queue_set),
2997     _collector(collector) { }
2998 
2999   void set_task(CMSConcMarkingTask* task) {
3000     _task = task;
3001   }
3002 };
3003 
3004 class CMSConcMarkingOWSTTerminator: public OWSTTaskTerminator {
3005   CMSCollector*       _collector;
3006   CMSConcMarkingTask* _task;
3007  public:
3008   virtual void yield();
3009 
3010   // "n_threads" is the number of threads to be terminated.
3011   // "queue_set" is a set of work queues of other threads.
3012   // "collector" is the CMS collector associated with this task terminator.
3013   // "yield" indicates whether we need the gang as a whole to yield.
3014   CMSConcMarkingOWSTTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
3015     OWSTTaskTerminator(n_threads, queue_set),
3016     _collector(collector) { }
3017 
3018   void set_task(CMSConcMarkingTask* task) {
3019     _task = task;
3020   }
3021 };
3022 
3023 class CMSConcMarkingTaskTerminator {
3024  private:
3025   ParallelTaskTerminator* _term;
3026  public:
3027   CMSConcMarkingTaskTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) {
3028     if (UseOWSTTaskTerminator) {
3029       _term = new CMSConcMarkingOWSTTerminator(n_threads, queue_set, collector);
3030     } else {
3031       _term = new CMSConcMarkingParallelTerminator(n_threads, queue_set, collector);
3032     }
3033   }
3034   ~CMSConcMarkingTaskTerminator() {
3035     assert(_term != NULL, "Must not be NULL");
3036     delete _term;
3037   }
3038 
3039   void set_task(CMSConcMarkingTask* task);
3040   ParallelTaskTerminator* terminator() const { return _term; }
3041 };
3042 
3043 class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator {
3044   CMSConcMarkingTask* _task;
3045  public:
3046   bool should_exit_termination();
3047   void set_task(CMSConcMarkingTask* task) {
3048     _task = task;
3049   }
3050 };
3051 
3052 // MT Concurrent Marking Task
3053 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3054   CMSCollector*             _collector;
3055   uint                      _n_workers;      // requested/desired # workers
3056   bool                      _result;
3057   CompactibleFreeListSpace* _cms_space;
3058   char                      _pad_front[64];   // padding to ...
3059   HeapWord* volatile        _global_finger;   // ... avoid sharing cache line
3060   char                      _pad_back[64];
3061   HeapWord*                 _restart_addr;
3062 
3063   //  Exposed here for yielding support
3064   Mutex* const _bit_map_lock;
3065 
3066   // The per thread work queues, available here for stealing
3067   OopTaskQueueSet*  _task_queues;
3068 
3069   // Termination (and yielding) support
3070   CMSConcMarkingTaskTerminator       _term;
3071   CMSConcMarkingTerminatorTerminator _term_term;
3072 
3073  public:
3074   CMSConcMarkingTask(CMSCollector* collector,
3075                  CompactibleFreeListSpace* cms_space,
3076                  YieldingFlexibleWorkGang* workers,
3077                  OopTaskQueueSet* task_queues):
3078     YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3079     _collector(collector),
3080     _n_workers(0),
3081     _result(true),
3082     _cms_space(cms_space),
3083     _bit_map_lock(collector->bitMapLock()),
3084     _task_queues(task_queues),
3085     _term(_n_workers, task_queues, _collector)
3086   {
3087     _requested_size = _n_workers;
3088     _term.set_task(this);
3089     _term_term.set_task(this);
3090     _restart_addr = _global_finger = _cms_space->bottom();
3091   }
3092 
3093 
3094   OopTaskQueueSet* task_queues()  { return _task_queues; }
3095 
3096   OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3097 
3098   HeapWord* volatile* global_finger_addr() { return &_global_finger; }
3099 
3100   ParallelTaskTerminator* terminator() { return _term.terminator(); }
3101 
3102   virtual void set_for_termination(uint active_workers) {
3103     terminator()->reset_for_reuse(active_workers);
3104   }
3105 
3106   void work(uint worker_id);
3107   bool should_yield() {
3108     return    ConcurrentMarkSweepThread::should_yield()
3109            && !_collector->foregroundGCIsActive();
3110   }
3111 
3112   virtual void coordinator_yield();  // stuff done by coordinator
3113   bool result() { return _result; }
3114 
3115   void reset(HeapWord* ra) {
3116     assert(_global_finger >= _cms_space->end(),  "Postcondition of ::work(i)");
3117     _restart_addr = _global_finger = ra;
3118     _term.terminator()->reset_for_reuse();
3119   }
3120 
3121   static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3122                                            OopTaskQueue* work_q);
3123 
3124  private:
3125   void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3126   void do_work_steal(int i);
3127   void bump_global_finger(HeapWord* f);
3128 };
3129 
3130 bool CMSConcMarkingTerminatorTerminator::should_exit_termination() {
3131   assert(_task != NULL, "Error");
3132   return _task->yielding();
3133   // Note that we do not need the disjunct || _task->should_yield() above
3134   // because we want terminating threads to yield only if the task
3135   // is already in the midst of yielding, which happens only after at least one
3136   // thread has yielded.
3137 }
3138 
3139 void CMSConcMarkingParallelTerminator::yield() {
3140   if (_task->should_yield()) {
3141     _task->yield();
3142   } else {
3143     ParallelTaskTerminator::yield();
3144   }
3145 }
3146 
3147 void CMSConcMarkingOWSTTerminator::yield() {
3148   if (_task->should_yield()) {
3149     _task->yield();
3150   } else {
3151     OWSTTaskTerminator::yield();
3152   }
3153 }
3154 
3155 void CMSConcMarkingTaskTerminator::set_task(CMSConcMarkingTask* task) {
3156   if (UseOWSTTaskTerminator) {
3157     ((CMSConcMarkingOWSTTerminator*)_term)->set_task(task);
3158   } else {
3159     ((CMSConcMarkingParallelTerminator*)_term)->set_task(task);
3160   }
3161 }
3162 
3163 ////////////////////////////////////////////////////////////////
3164 // Concurrent Marking Algorithm Sketch
3165 ////////////////////////////////////////////////////////////////
3166 // Until all tasks exhausted (both spaces):
3167 // -- claim next available chunk
3168 // -- bump global finger via CAS
3169 // -- find first object that starts in this chunk
3170 //    and start scanning bitmap from that position
3171 // -- scan marked objects for oops
3172 // -- CAS-mark target, and if successful:
3173 //    . if target oop is above global finger (volatile read)
3174 //      nothing to do
3175 //    . if target oop is in chunk and above local finger
3176 //        then nothing to do
3177 //    . else push on work-queue
3178 // -- Deal with possible overflow issues:
3179 //    . local work-queue overflow causes stuff to be pushed on
3180 //      global (common) overflow queue
3181 //    . always first empty local work queue
3182 //    . then get a batch of oops from global work queue if any
3183 //    . then do work stealing
3184 // -- When all tasks claimed (both spaces)
3185 //    and local work queue empty,
3186 //    then in a loop do:
3187 //    . check global overflow stack; steal a batch of oops and trace
3188 //    . try to steal from other threads oif GOS is empty
3189 //    . if neither is available, offer termination
3190 // -- Terminate and return result
3191 //
3192 void CMSConcMarkingTask::work(uint worker_id) {
3193   elapsedTimer _timer;
3194   ResourceMark rm;
3195   HandleMark hm;
3196 
3197   DEBUG_ONLY(_collector->verify_overflow_empty();)
3198 
3199   // Before we begin work, our work queue should be empty
3200   assert(work_queue(worker_id)->size() == 0, "Expected to be empty");
3201   // Scan the bitmap covering _cms_space, tracing through grey objects.
3202   _timer.start();
3203   do_scan_and_mark(worker_id, _cms_space);
3204   _timer.stop();
3205   log_trace(gc, task)("Finished cms space scanning in %dth thread: %3.3f sec", worker_id, _timer.seconds());
3206 
3207   // ... do work stealing
3208   _timer.reset();
3209   _timer.start();
3210   do_work_steal(worker_id);
3211   _timer.stop();
3212   log_trace(gc, task)("Finished work stealing in %dth thread: %3.3f sec", worker_id, _timer.seconds());
3213   assert(_collector->_markStack.isEmpty(), "Should have been emptied");
3214   assert(work_queue(worker_id)->size() == 0, "Should have been emptied");
3215   // Note that under the current task protocol, the
3216   // following assertion is true even of the spaces
3217   // expanded since the completion of the concurrent
3218   // marking. XXX This will likely change under a strict
3219   // ABORT semantics.
3220   // After perm removal the comparison was changed to
3221   // greater than or equal to from strictly greater than.
3222   // Before perm removal the highest address sweep would
3223   // have been at the end of perm gen but now is at the
3224   // end of the tenured gen.
3225   assert(_global_finger >=  _cms_space->end(),
3226          "All tasks have been completed");
3227   DEBUG_ONLY(_collector->verify_overflow_empty();)
3228 }
3229 
3230 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
3231   HeapWord* read = _global_finger;
3232   HeapWord* cur  = read;
3233   while (f > read) {
3234     cur = read;
3235     read = Atomic::cmpxchg(f, &_global_finger, cur);
3236     if (cur == read) {
3237       // our cas succeeded
3238       assert(_global_finger >= f, "protocol consistency");
3239       break;
3240     }
3241   }
3242 }
3243 
3244 // This is really inefficient, and should be redone by
3245 // using (not yet available) block-read and -write interfaces to the
3246 // stack and the work_queue. XXX FIX ME !!!
3247 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3248                                                       OopTaskQueue* work_q) {
3249   // Fast lock-free check
3250   if (ovflw_stk->length() == 0) {
3251     return false;
3252   }
3253   assert(work_q->size() == 0, "Shouldn't steal");
3254   MutexLockerEx ml(ovflw_stk->par_lock(),
3255                    Mutex::_no_safepoint_check_flag);
3256   // Grab up to 1/4 the size of the work queue
3257   size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
3258                     (size_t)ParGCDesiredObjsFromOverflowList);
3259   num = MIN2(num, ovflw_stk->length());
3260   for (int i = (int) num; i > 0; i--) {
3261     oop cur = ovflw_stk->pop();
3262     assert(cur != NULL, "Counted wrong?");
3263     work_q->push(cur);
3264   }
3265   return num > 0;
3266 }
3267 
3268 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
3269   SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
3270   int n_tasks = pst->n_tasks();
3271   // We allow that there may be no tasks to do here because
3272   // we are restarting after a stack overflow.
3273   assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
3274   uint nth_task = 0;
3275 
3276   HeapWord* aligned_start = sp->bottom();
3277   if (sp->used_region().contains(_restart_addr)) {
3278     // Align down to a card boundary for the start of 0th task
3279     // for this space.
3280     aligned_start = align_down(_restart_addr, CardTable::card_size);
3281   }
3282 
3283   size_t chunk_size = sp->marking_task_size();
3284   while (pst->try_claim_task(/* reference */ nth_task)) {
3285     // Having claimed the nth task in this space,
3286     // compute the chunk that it corresponds to:
3287     MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
3288                                aligned_start + (nth_task+1)*chunk_size);
3289     // Try and bump the global finger via a CAS;
3290     // note that we need to do the global finger bump
3291     // _before_ taking the intersection below, because
3292     // the task corresponding to that region will be
3293     // deemed done even if the used_region() expands
3294     // because of allocation -- as it almost certainly will
3295     // during start-up while the threads yield in the
3296     // closure below.
3297     HeapWord* finger = span.end();
3298     bump_global_finger(finger);   // atomically
3299     // There are null tasks here corresponding to chunks
3300     // beyond the "top" address of the space.
3301     span = span.intersection(sp->used_region());
3302     if (!span.is_empty()) {  // Non-null task
3303       HeapWord* prev_obj;
3304       assert(!span.contains(_restart_addr) || nth_task == 0,
3305              "Inconsistency");
3306       if (nth_task == 0) {
3307         // For the 0th task, we'll not need to compute a block_start.
3308         if (span.contains(_restart_addr)) {
3309           // In the case of a restart because of stack overflow,
3310           // we might additionally skip a chunk prefix.
3311           prev_obj = _restart_addr;
3312         } else {
3313           prev_obj = span.start();
3314         }
3315       } else {
3316         // We want to skip the first object because
3317         // the protocol is to scan any object in its entirety
3318         // that _starts_ in this span; a fortiori, any
3319         // object starting in an earlier span is scanned
3320         // as part of an earlier claimed task.
3321         // Below we use the "careful" version of block_start
3322         // so we do not try to navigate uninitialized objects.
3323         prev_obj = sp->block_start_careful(span.start());
3324         // Below we use a variant of block_size that uses the
3325         // Printezis bits to avoid waiting for allocated
3326         // objects to become initialized/parsable.
3327         while (prev_obj < span.start()) {
3328           size_t sz = sp->block_size_no_stall(prev_obj, _collector);
3329           if (sz > 0) {
3330             prev_obj += sz;
3331           } else {
3332             // In this case we may end up doing a bit of redundant
3333             // scanning, but that appears unavoidable, short of
3334             // locking the free list locks; see bug 6324141.
3335             break;
3336           }
3337         }
3338       }
3339       if (prev_obj < span.end()) {
3340         MemRegion my_span = MemRegion(prev_obj, span.end());
3341         // Do the marking work within a non-empty span --
3342         // the last argument to the constructor indicates whether the
3343         // iteration should be incremental with periodic yields.
3344         ParMarkFromRootsClosure cl(this, _collector, my_span,
3345                                    &_collector->_markBitMap,
3346                                    work_queue(i),
3347                                    &_collector->_markStack);
3348         _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
3349       } // else nothing to do for this task
3350     }   // else nothing to do for this task
3351   }
3352   // We'd be tempted to assert here that since there are no
3353   // more tasks left to claim in this space, the global_finger
3354   // must exceed space->top() and a fortiori space->end(). However,
3355   // that would not quite be correct because the bumping of
3356   // global_finger occurs strictly after the claiming of a task,
3357   // so by the time we reach here the global finger may not yet
3358   // have been bumped up by the thread that claimed the last
3359   // task.
3360   pst->all_tasks_completed();
3361 }
3362 
3363 class ParConcMarkingClosure: public MetadataVisitingOopIterateClosure {
3364  private:
3365   CMSCollector* _collector;
3366   CMSConcMarkingTask* _task;
3367   MemRegion     _span;
3368   CMSBitMap*    _bit_map;
3369   CMSMarkStack* _overflow_stack;
3370   OopTaskQueue* _work_queue;
3371  protected:
3372   DO_OOP_WORK_DEFN
3373  public:
3374   ParConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue,
3375                         CMSBitMap* bit_map, CMSMarkStack* overflow_stack):
3376     MetadataVisitingOopIterateClosure(collector->ref_processor()),
3377     _collector(collector),
3378     _task(task),
3379     _span(collector->_span),
3380     _bit_map(bit_map),
3381     _overflow_stack(overflow_stack),
3382     _work_queue(work_queue)
3383   { }
3384   virtual void do_oop(oop* p);
3385   virtual void do_oop(narrowOop* p);
3386 
3387   void trim_queue(size_t max);
3388   void handle_stack_overflow(HeapWord* lost);
3389   void do_yield_check() {
3390     if (_task->should_yield()) {
3391       _task->yield();
3392     }
3393   }
3394 };
3395 
3396 DO_OOP_WORK_IMPL(ParConcMarkingClosure)
3397 
3398 // Grey object scanning during work stealing phase --
3399 // the salient assumption here is that any references
3400 // that are in these stolen objects being scanned must
3401 // already have been initialized (else they would not have
3402 // been published), so we do not need to check for
3403 // uninitialized objects before pushing here.
3404 void ParConcMarkingClosure::do_oop(oop obj) {
3405   assert(oopDesc::is_oop_or_null(obj, true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
3406   HeapWord* addr = (HeapWord*)obj;
3407   // Check if oop points into the CMS generation
3408   // and is not marked
3409   if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
3410     // a white object ...
3411     // If we manage to "claim" the object, by being the
3412     // first thread to mark it, then we push it on our
3413     // marking stack
3414     if (_bit_map->par_mark(addr)) {     // ... now grey
3415       // push on work queue (grey set)
3416       bool simulate_overflow = false;
3417       NOT_PRODUCT(
3418         if (CMSMarkStackOverflowALot &&
3419             _collector->simulate_overflow()) {
3420           // simulate a stack overflow
3421           simulate_overflow = true;
3422         }
3423       )
3424       if (simulate_overflow ||
3425           !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
3426         // stack overflow
3427         log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _overflow_stack->capacity());
3428         // We cannot assert that the overflow stack is full because
3429         // it may have been emptied since.
3430         assert(simulate_overflow ||
3431                _work_queue->size() == _work_queue->max_elems(),
3432               "Else push should have succeeded");
3433         handle_stack_overflow(addr);
3434       }
3435     } // Else, some other thread got there first
3436     do_yield_check();
3437   }
3438 }
3439 
3440 void ParConcMarkingClosure::trim_queue(size_t max) {
3441   while (_work_queue->size() > max) {
3442     oop new_oop;
3443     if (_work_queue->pop_local(new_oop)) {
3444       assert(oopDesc::is_oop(new_oop), "Should be an oop");
3445       assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
3446       assert(_span.contains((HeapWord*)new_oop), "Not in span");
3447       new_oop->oop_iterate(this);  // do_oop() above
3448       do_yield_check();
3449     }
3450   }
3451 }
3452 
3453 // Upon stack overflow, we discard (part of) the stack,
3454 // remembering the least address amongst those discarded
3455 // in CMSCollector's _restart_address.
3456 void ParConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
3457   // We need to do this under a mutex to prevent other
3458   // workers from interfering with the work done below.
3459   MutexLockerEx ml(_overflow_stack->par_lock(),
3460                    Mutex::_no_safepoint_check_flag);
3461   // Remember the least grey address discarded
3462   HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
3463   _collector->lower_restart_addr(ra);
3464   _overflow_stack->reset();  // discard stack contents
3465   _overflow_stack->expand(); // expand the stack if possible
3466 }
3467 
3468 
3469 void CMSConcMarkingTask::do_work_steal(int i) {
3470   OopTaskQueue* work_q = work_queue(i);
3471   oop obj_to_scan;
3472   CMSBitMap* bm = &(_collector->_markBitMap);
3473   CMSMarkStack* ovflw = &(_collector->_markStack);
3474   ParConcMarkingClosure cl(_collector, this, work_q, bm, ovflw);
3475   while (true) {
3476     cl.trim_queue(0);
3477     assert(work_q->size() == 0, "Should have been emptied above");
3478     if (get_work_from_overflow_stack(ovflw, work_q)) {
3479       // Can't assert below because the work obtained from the
3480       // overflow stack may already have been stolen from us.
3481       // assert(work_q->size() > 0, "Work from overflow stack");
3482       continue;
3483     } else if (task_queues()->steal(i, /* reference */ obj_to_scan)) {
3484       assert(oopDesc::is_oop(obj_to_scan), "Should be an oop");
3485       assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
3486       obj_to_scan->oop_iterate(&cl);
3487     } else if (terminator()->offer_termination(&_term_term)) {
3488       assert(work_q->size() == 0, "Impossible!");
3489       break;
3490     } else if (yielding() || should_yield()) {
3491       yield();
3492     }
3493   }
3494 }
3495 
3496 // This is run by the CMS (coordinator) thread.
3497 void CMSConcMarkingTask::coordinator_yield() {
3498   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3499          "CMS thread should hold CMS token");
3500   // First give up the locks, then yield, then re-lock
3501   // We should probably use a constructor/destructor idiom to
3502   // do this unlock/lock or modify the MutexUnlocker class to
3503   // serve our purpose. XXX
3504   assert_lock_strong(_bit_map_lock);
3505   _bit_map_lock->unlock();
3506   ConcurrentMarkSweepThread::desynchronize(true);
3507   _collector->stopTimer();
3508   _collector->incrementYields();
3509 
3510   // It is possible for whichever thread initiated the yield request
3511   // not to get a chance to wake up and take the bitmap lock between
3512   // this thread releasing it and reacquiring it. So, while the
3513   // should_yield() flag is on, let's sleep for a bit to give the
3514   // other thread a chance to wake up. The limit imposed on the number
3515   // of iterations is defensive, to avoid any unforseen circumstances
3516   // putting us into an infinite loop. Since it's always been this
3517   // (coordinator_yield()) method that was observed to cause the
3518   // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
3519   // which is by default non-zero. For the other seven methods that
3520   // also perform the yield operation, as are using a different
3521   // parameter (CMSYieldSleepCount) which is by default zero. This way we
3522   // can enable the sleeping for those methods too, if necessary.
3523   // See 6442774.
3524   //
3525   // We really need to reconsider the synchronization between the GC
3526   // thread and the yield-requesting threads in the future and we
3527   // should really use wait/notify, which is the recommended
3528   // way of doing this type of interaction. Additionally, we should
3529   // consolidate the eight methods that do the yield operation and they
3530   // are almost identical into one for better maintainability and
3531   // readability. See 6445193.
3532   //
3533   // Tony 2006.06.29
3534   for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
3535                    ConcurrentMarkSweepThread::should_yield() &&
3536                    !CMSCollector::foregroundGCIsActive(); ++i) {
3537     os::sleep(Thread::current(), 1, false);
3538   }
3539 
3540   ConcurrentMarkSweepThread::synchronize(true);
3541   _bit_map_lock->lock_without_safepoint_check();
3542   _collector->startTimer();
3543 }
3544 
3545 bool CMSCollector::do_marking_mt() {
3546   assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition");
3547   uint num_workers = WorkerPolicy::calc_active_conc_workers(conc_workers()->total_workers(),
3548                                                             conc_workers()->active_workers(),
3549                                                             Threads::number_of_non_daemon_threads());
3550   num_workers = conc_workers()->update_active_workers(num_workers);
3551   log_info(gc,task)("Using %u workers of %u for marking", num_workers, conc_workers()->total_workers());
3552 
3553   CompactibleFreeListSpace* cms_space  = _cmsGen->cmsSpace();
3554 
3555   CMSConcMarkingTask tsk(this,
3556                          cms_space,
3557                          conc_workers(),
3558                          task_queues());
3559 
3560   // Since the actual number of workers we get may be different
3561   // from the number we requested above, do we need to do anything different
3562   // below? In particular, may be we need to subclass the SequantialSubTasksDone
3563   // class?? XXX
3564   cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
3565 
3566   // Refs discovery is already non-atomic.
3567   assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
3568   assert(ref_processor()->discovery_is_mt(), "Discovery should be MT");
3569   conc_workers()->start_task(&tsk);
3570   while (tsk.yielded()) {
3571     tsk.coordinator_yield();
3572     conc_workers()->continue_task(&tsk);
3573   }
3574   // If the task was aborted, _restart_addr will be non-NULL
3575   assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
3576   while (_restart_addr != NULL) {
3577     // XXX For now we do not make use of ABORTED state and have not
3578     // yet implemented the right abort semantics (even in the original
3579     // single-threaded CMS case). That needs some more investigation
3580     // and is deferred for now; see CR# TBF. 07252005YSR. XXX
3581     assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
3582     // If _restart_addr is non-NULL, a marking stack overflow
3583     // occurred; we need to do a fresh marking iteration from the
3584     // indicated restart address.
3585     if (_foregroundGCIsActive) {
3586       // We may be running into repeated stack overflows, having
3587       // reached the limit of the stack size, while making very
3588       // slow forward progress. It may be best to bail out and
3589       // let the foreground collector do its job.
3590       // Clear _restart_addr, so that foreground GC
3591       // works from scratch. This avoids the headache of
3592       // a "rescan" which would otherwise be needed because
3593       // of the dirty mod union table & card table.
3594       _restart_addr = NULL;
3595       return false;
3596     }
3597     // Adjust the task to restart from _restart_addr
3598     tsk.reset(_restart_addr);
3599     cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
3600                   _restart_addr);
3601     _restart_addr = NULL;
3602     // Get the workers going again
3603     conc_workers()->start_task(&tsk);
3604     while (tsk.yielded()) {
3605       tsk.coordinator_yield();
3606       conc_workers()->continue_task(&tsk);
3607     }
3608   }
3609   assert(tsk.completed(), "Inconsistency");
3610   assert(tsk.result() == true, "Inconsistency");
3611   return true;
3612 }
3613 
3614 bool CMSCollector::do_marking_st() {
3615   ResourceMark rm;
3616   HandleMark   hm;
3617 
3618   // Temporarily make refs discovery single threaded (non-MT)
3619   ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
3620   MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
3621     &_markStack, CMSYield);
3622   // the last argument to iterate indicates whether the iteration
3623   // should be incremental with periodic yields.
3624   _markBitMap.iterate(&markFromRootsClosure);
3625   // If _restart_addr is non-NULL, a marking stack overflow
3626   // occurred; we need to do a fresh iteration from the
3627   // indicated restart address.
3628   while (_restart_addr != NULL) {
3629     if (_foregroundGCIsActive) {
3630       // We may be running into repeated stack overflows, having
3631       // reached the limit of the stack size, while making very
3632       // slow forward progress. It may be best to bail out and
3633       // let the foreground collector do its job.
3634       // Clear _restart_addr, so that foreground GC
3635       // works from scratch. This avoids the headache of
3636       // a "rescan" which would otherwise be needed because
3637       // of the dirty mod union table & card table.
3638       _restart_addr = NULL;
3639       return false;  // indicating failure to complete marking
3640     }
3641     // Deal with stack overflow:
3642     // we restart marking from _restart_addr
3643     HeapWord* ra = _restart_addr;
3644     markFromRootsClosure.reset(ra);
3645     _restart_addr = NULL;
3646     _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
3647   }
3648   return true;
3649 }
3650 
3651 void CMSCollector::preclean() {
3652   check_correct_thread_executing();
3653   assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
3654   verify_work_stacks_empty();
3655   verify_overflow_empty();
3656   _abort_preclean = false;
3657   if (CMSPrecleaningEnabled) {
3658     if (!CMSEdenChunksRecordAlways) {
3659       _eden_chunk_index = 0;
3660     }
3661     size_t used = get_eden_used();
3662     size_t capacity = get_eden_capacity();
3663     // Don't start sampling unless we will get sufficiently
3664     // many samples.
3665     if (used < (((capacity / CMSScheduleRemarkSamplingRatio) / 100)
3666                 * CMSScheduleRemarkEdenPenetration)) {
3667       _start_sampling = true;
3668     } else {
3669       _start_sampling = false;
3670     }
3671     GCTraceCPUTime tcpu;
3672     CMSPhaseAccounting pa(this, "Concurrent Preclean");
3673     preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
3674   }
3675   CMSTokenSync x(true); // is cms thread
3676   if (CMSPrecleaningEnabled) {
3677     sample_eden();
3678     _collectorState = AbortablePreclean;
3679   } else {
3680     _collectorState = FinalMarking;
3681   }
3682   verify_work_stacks_empty();
3683   verify_overflow_empty();
3684 }
3685 
3686 // Try and schedule the remark such that young gen
3687 // occupancy is CMSScheduleRemarkEdenPenetration %.
3688 void CMSCollector::abortable_preclean() {
3689   check_correct_thread_executing();
3690   assert(CMSPrecleaningEnabled,  "Inconsistent control state");
3691   assert(_collectorState == AbortablePreclean, "Inconsistent control state");
3692 
3693   // If Eden's current occupancy is below this threshold,
3694   // immediately schedule the remark; else preclean
3695   // past the next scavenge in an effort to
3696   // schedule the pause as described above. By choosing
3697   // CMSScheduleRemarkEdenSizeThreshold >= max eden size
3698   // we will never do an actual abortable preclean cycle.
3699   if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
3700     GCTraceCPUTime tcpu;
3701     CMSPhaseAccounting pa(this, "Concurrent Abortable Preclean");
3702     // We need more smarts in the abortable preclean
3703     // loop below to deal with cases where allocation
3704     // in young gen is very very slow, and our precleaning
3705     // is running a losing race against a horde of
3706     // mutators intent on flooding us with CMS updates
3707     // (dirty cards).
3708     // One, admittedly dumb, strategy is to give up
3709     // after a certain number of abortable precleaning loops
3710     // or after a certain maximum time. We want to make
3711     // this smarter in the next iteration.
3712     // XXX FIX ME!!! YSR
3713     size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
3714     while (!(should_abort_preclean() ||
3715              ConcurrentMarkSweepThread::cmst()->should_terminate())) {
3716       workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
3717       cumworkdone += workdone;
3718       loops++;
3719       // Voluntarily terminate abortable preclean phase if we have
3720       // been at it for too long.
3721       if ((CMSMaxAbortablePrecleanLoops != 0) &&
3722           loops >= CMSMaxAbortablePrecleanLoops) {
3723         log_debug(gc)(" CMS: abort preclean due to loops ");
3724         break;
3725       }
3726       if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
3727         log_debug(gc)(" CMS: abort preclean due to time ");
3728         break;
3729       }
3730       // If we are doing little work each iteration, we should
3731       // take a short break.
3732       if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
3733         // Sleep for some time, waiting for work to accumulate
3734         stopTimer();
3735         cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
3736         startTimer();
3737         waited++;
3738       }
3739     }
3740     log_trace(gc)(" [" SIZE_FORMAT " iterations, " SIZE_FORMAT " waits, " SIZE_FORMAT " cards)] ",
3741                                loops, waited, cumworkdone);
3742   }
3743   CMSTokenSync x(true); // is cms thread
3744   if (_collectorState != Idling) {
3745     assert(_collectorState == AbortablePreclean,
3746            "Spontaneous state transition?");
3747     _collectorState = FinalMarking;
3748   } // Else, a foreground collection completed this CMS cycle.
3749   return;
3750 }
3751 
3752 // Respond to an Eden sampling opportunity
3753 void CMSCollector::sample_eden() {
3754   // Make sure a young gc cannot sneak in between our
3755   // reading and recording of a sample.
3756   assert(Thread::current()->is_ConcurrentGC_thread(),
3757          "Only the cms thread may collect Eden samples");
3758   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3759          "Should collect samples while holding CMS token");
3760   if (!_start_sampling) {
3761     return;
3762   }
3763   // When CMSEdenChunksRecordAlways is true, the eden chunk array
3764   // is populated by the young generation.
3765   if (_eden_chunk_array != NULL && !CMSEdenChunksRecordAlways) {
3766     if (_eden_chunk_index < _eden_chunk_capacity) {
3767       _eden_chunk_array[_eden_chunk_index] = *_top_addr;   // take sample
3768       assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
3769              "Unexpected state of Eden");
3770       // We'd like to check that what we just sampled is an oop-start address;
3771       // however, we cannot do that here since the object may not yet have been
3772       // initialized. So we'll instead do the check when we _use_ this sample
3773       // later.
3774       if (_eden_chunk_index == 0 ||
3775           (pointer_delta(_eden_chunk_array[_eden_chunk_index],
3776                          _eden_chunk_array[_eden_chunk_index-1])
3777            >= CMSSamplingGrain)) {
3778         _eden_chunk_index++;  // commit sample
3779       }
3780     }
3781   }
3782   if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
3783     size_t used = get_eden_used();
3784     size_t capacity = get_eden_capacity();
3785     assert(used <= capacity, "Unexpected state of Eden");
3786     if (used >  (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
3787       _abort_preclean = true;
3788     }
3789   }
3790 }
3791 
3792 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
3793   assert(_collectorState == Precleaning ||
3794          _collectorState == AbortablePreclean, "incorrect state");
3795   ResourceMark rm;
3796   HandleMark   hm;
3797 
3798   // Precleaning is currently not MT but the reference processor
3799   // may be set for MT.  Disable it temporarily here.
3800   ReferenceProcessor* rp = ref_processor();
3801   ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false);
3802 
3803   // Do one pass of scrubbing the discovered reference lists
3804   // to remove any reference objects with strongly-reachable
3805   // referents.
3806   if (clean_refs) {
3807     CMSPrecleanRefsYieldClosure yield_cl(this);
3808     assert(_span_based_discoverer.span().equals(_span), "Spans should be equal");
3809     CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
3810                                    &_markStack, true /* preclean */);
3811     CMSDrainMarkingStackClosure complete_trace(this,
3812                                    _span, &_markBitMap, &_markStack,
3813                                    &keep_alive, true /* preclean */);
3814 
3815     // We don't want this step to interfere with a young
3816     // collection because we don't want to take CPU
3817     // or memory bandwidth away from the young GC threads
3818     // (which may be as many as there are CPUs).
3819     // Note that we don't need to protect ourselves from
3820     // interference with mutators because they can't
3821     // manipulate the discovered reference lists nor affect
3822     // the computed reachability of the referents, the
3823     // only properties manipulated by the precleaning
3824     // of these reference lists.
3825     stopTimer();
3826     CMSTokenSyncWithLocks x(true /* is cms thread */,
3827                             bitMapLock());
3828     startTimer();
3829     sample_eden();
3830 
3831     // The following will yield to allow foreground
3832     // collection to proceed promptly. XXX YSR:
3833     // The code in this method may need further
3834     // tweaking for better performance and some restructuring
3835     // for cleaner interfaces.
3836     GCTimer *gc_timer = NULL; // Currently not tracing concurrent phases
3837     rp->preclean_discovered_references(
3838           rp->is_alive_non_header(), &keep_alive, &complete_trace, &yield_cl,
3839           gc_timer);
3840   }
3841 
3842   if (clean_survivor) {  // preclean the active survivor space(s)
3843     PushAndMarkClosure pam_cl(this, _span, ref_processor(),
3844                              &_markBitMap, &_modUnionTable,
3845                              &_markStack, true /* precleaning phase */);
3846     stopTimer();
3847     CMSTokenSyncWithLocks ts(true /* is cms thread */,
3848                              bitMapLock());
3849     startTimer();
3850     unsigned int before_count =
3851       CMSHeap::heap()->total_collections();
3852     SurvivorSpacePrecleanClosure
3853       sss_cl(this, _span, &_markBitMap, &_markStack,
3854              &pam_cl, before_count, CMSYield);
3855     _young_gen->from()->object_iterate_careful(&sss_cl);
3856     _young_gen->to()->object_iterate_careful(&sss_cl);
3857   }
3858   MarkRefsIntoAndScanClosure
3859     mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
3860              &_markStack, this, CMSYield,
3861              true /* precleaning phase */);
3862   // CAUTION: The following closure has persistent state that may need to
3863   // be reset upon a decrease in the sequence of addresses it
3864   // processes.
3865   ScanMarkedObjectsAgainCarefullyClosure
3866     smoac_cl(this, _span,
3867       &_markBitMap, &_markStack, &mrias_cl, CMSYield);
3868 
3869   // Preclean dirty cards in ModUnionTable and CardTable using
3870   // appropriate convergence criterion;
3871   // repeat CMSPrecleanIter times unless we find that
3872   // we are losing.
3873   assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
3874   assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
3875          "Bad convergence multiplier");
3876   assert(CMSPrecleanThreshold >= 100,
3877          "Unreasonably low CMSPrecleanThreshold");
3878 
3879   size_t numIter, cumNumCards, lastNumCards, curNumCards;
3880   for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
3881        numIter < CMSPrecleanIter;
3882        numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
3883     curNumCards  = preclean_mod_union_table(_cmsGen, &smoac_cl);
3884     log_trace(gc)(" (modUnionTable: " SIZE_FORMAT " cards)", curNumCards);
3885     // Either there are very few dirty cards, so re-mark
3886     // pause will be small anyway, or our pre-cleaning isn't
3887     // that much faster than the rate at which cards are being
3888     // dirtied, so we might as well stop and re-mark since
3889     // precleaning won't improve our re-mark time by much.
3890     if (curNumCards <= CMSPrecleanThreshold ||
3891         (numIter > 0 &&
3892          (curNumCards * CMSPrecleanDenominator >
3893          lastNumCards * CMSPrecleanNumerator))) {
3894       numIter++;
3895       cumNumCards += curNumCards;
3896       break;
3897     }
3898   }
3899 
3900   preclean_cld(&mrias_cl, _cmsGen->freelistLock());
3901 
3902   curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
3903   cumNumCards += curNumCards;
3904   log_trace(gc)(" (cardTable: " SIZE_FORMAT " cards, re-scanned " SIZE_FORMAT " cards, " SIZE_FORMAT " iterations)",
3905                              curNumCards, cumNumCards, numIter);
3906   return cumNumCards;   // as a measure of useful work done
3907 }
3908 
3909 // PRECLEANING NOTES:
3910 // Precleaning involves:
3911 // . reading the bits of the modUnionTable and clearing the set bits.
3912 // . For the cards corresponding to the set bits, we scan the
3913 //   objects on those cards. This means we need the free_list_lock
3914 //   so that we can safely iterate over the CMS space when scanning
3915 //   for oops.
3916 // . When we scan the objects, we'll be both reading and setting
3917 //   marks in the marking bit map, so we'll need the marking bit map.
3918 // . For protecting _collector_state transitions, we take the CGC_lock.
3919 //   Note that any races in the reading of of card table entries by the
3920 //   CMS thread on the one hand and the clearing of those entries by the
3921 //   VM thread or the setting of those entries by the mutator threads on the
3922 //   other are quite benign. However, for efficiency it makes sense to keep
3923 //   the VM thread from racing with the CMS thread while the latter is
3924 //   dirty card info to the modUnionTable. We therefore also use the
3925 //   CGC_lock to protect the reading of the card table and the mod union
3926 //   table by the CM thread.
3927 // . We run concurrently with mutator updates, so scanning
3928 //   needs to be done carefully  -- we should not try to scan
3929 //   potentially uninitialized objects.
3930 //
3931 // Locking strategy: While holding the CGC_lock, we scan over and
3932 // reset a maximal dirty range of the mod union / card tables, then lock
3933 // the free_list_lock and bitmap lock to do a full marking, then
3934 // release these locks; and repeat the cycle. This allows for a
3935 // certain amount of fairness in the sharing of these locks between
3936 // the CMS collector on the one hand, and the VM thread and the
3937 // mutators on the other.
3938 
3939 // NOTE: preclean_mod_union_table() and preclean_card_table()
3940 // further below are largely identical; if you need to modify
3941 // one of these methods, please check the other method too.
3942 
3943 size_t CMSCollector::preclean_mod_union_table(
3944   ConcurrentMarkSweepGeneration* old_gen,
3945   ScanMarkedObjectsAgainCarefullyClosure* cl) {
3946   verify_work_stacks_empty();
3947   verify_overflow_empty();
3948 
3949   // strategy: starting with the first card, accumulate contiguous
3950   // ranges of dirty cards; clear these cards, then scan the region
3951   // covered by these cards.
3952 
3953   // Since all of the MUT is committed ahead, we can just use
3954   // that, in case the generations expand while we are precleaning.
3955   // It might also be fine to just use the committed part of the
3956   // generation, but we might potentially miss cards when the
3957   // generation is rapidly expanding while we are in the midst
3958   // of precleaning.
3959   HeapWord* startAddr = old_gen->reserved().start();
3960   HeapWord* endAddr   = old_gen->reserved().end();
3961 
3962   cl->setFreelistLock(old_gen->freelistLock());   // needed for yielding
3963 
3964   size_t numDirtyCards, cumNumDirtyCards;
3965   HeapWord *nextAddr, *lastAddr;
3966   for (cumNumDirtyCards = numDirtyCards = 0,
3967        nextAddr = lastAddr = startAddr;
3968        nextAddr < endAddr;
3969        nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
3970 
3971     ResourceMark rm;
3972     HandleMark   hm;
3973 
3974     MemRegion dirtyRegion;
3975     {
3976       stopTimer();
3977       // Potential yield point
3978       CMSTokenSync ts(true);
3979       startTimer();
3980       sample_eden();
3981       // Get dirty region starting at nextOffset (inclusive),
3982       // simultaneously clearing it.
3983       dirtyRegion =
3984         _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
3985       assert(dirtyRegion.start() >= nextAddr,
3986              "returned region inconsistent?");
3987     }
3988     // Remember where the next search should begin.
3989     // The returned region (if non-empty) is a right open interval,
3990     // so lastOffset is obtained from the right end of that
3991     // interval.
3992     lastAddr = dirtyRegion.end();
3993     // Should do something more transparent and less hacky XXX
3994     numDirtyCards =
3995       _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
3996 
3997     // We'll scan the cards in the dirty region (with periodic
3998     // yields for foreground GC as needed).
3999     if (!dirtyRegion.is_empty()) {
4000       assert(numDirtyCards > 0, "consistency check");
4001       HeapWord* stop_point = NULL;
4002       stopTimer();
4003       // Potential yield point
4004       CMSTokenSyncWithLocks ts(true, old_gen->freelistLock(),
4005                                bitMapLock());
4006       startTimer();
4007       {
4008         verify_work_stacks_empty();
4009         verify_overflow_empty();
4010         sample_eden();
4011         stop_point =
4012           old_gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4013       }
4014       if (stop_point != NULL) {
4015         // The careful iteration stopped early either because it found an
4016         // uninitialized object, or because we were in the midst of an
4017         // "abortable preclean", which should now be aborted. Redirty
4018         // the bits corresponding to the partially-scanned or unscanned
4019         // cards. We'll either restart at the next block boundary or
4020         // abort the preclean.
4021         assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4022                "Should only be AbortablePreclean.");
4023         _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
4024         if (should_abort_preclean()) {
4025           break; // out of preclean loop
4026         } else {
4027           // Compute the next address at which preclean should pick up;
4028           // might need bitMapLock in order to read P-bits.
4029           lastAddr = next_card_start_after_block(stop_point);
4030         }
4031       }
4032     } else {
4033       assert(lastAddr == endAddr, "consistency check");
4034       assert(numDirtyCards == 0, "consistency check");
4035       break;
4036     }
4037   }
4038   verify_work_stacks_empty();
4039   verify_overflow_empty();
4040   return cumNumDirtyCards;
4041 }
4042 
4043 // NOTE: preclean_mod_union_table() above and preclean_card_table()
4044 // below are largely identical; if you need to modify
4045 // one of these methods, please check the other method too.
4046 
4047 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* old_gen,
4048   ScanMarkedObjectsAgainCarefullyClosure* cl) {
4049   // strategy: it's similar to precleamModUnionTable above, in that
4050   // we accumulate contiguous ranges of dirty cards, mark these cards
4051   // precleaned, then scan the region covered by these cards.
4052   HeapWord* endAddr   = (HeapWord*)(old_gen->_virtual_space.high());
4053   HeapWord* startAddr = (HeapWord*)(old_gen->_virtual_space.low());
4054 
4055   cl->setFreelistLock(old_gen->freelistLock());   // needed for yielding
4056 
4057   size_t numDirtyCards, cumNumDirtyCards;
4058   HeapWord *lastAddr, *nextAddr;
4059 
4060   for (cumNumDirtyCards = numDirtyCards = 0,
4061        nextAddr = lastAddr = startAddr;
4062        nextAddr < endAddr;
4063        nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4064 
4065     ResourceMark rm;
4066     HandleMark   hm;
4067 
4068     MemRegion dirtyRegion;
4069     {
4070       // See comments in "Precleaning notes" above on why we
4071       // do this locking. XXX Could the locking overheads be
4072       // too high when dirty cards are sparse? [I don't think so.]
4073       stopTimer();
4074       CMSTokenSync x(true); // is cms thread
4075       startTimer();
4076       sample_eden();
4077       // Get and clear dirty region from card table
4078       dirtyRegion = _ct->dirty_card_range_after_reset(MemRegion(nextAddr, endAddr),
4079                                                       true,
4080                                                       CardTable::precleaned_card_val());
4081 
4082       assert(dirtyRegion.start() >= nextAddr,
4083              "returned region inconsistent?");
4084     }
4085     lastAddr = dirtyRegion.end();
4086     numDirtyCards =
4087       dirtyRegion.word_size()/CardTable::card_size_in_words;
4088 
4089     if (!dirtyRegion.is_empty()) {
4090       stopTimer();
4091       CMSTokenSyncWithLocks ts(true, old_gen->freelistLock(), bitMapLock());
4092       startTimer();
4093       sample_eden();
4094       verify_work_stacks_empty();
4095       verify_overflow_empty();
4096       HeapWord* stop_point =
4097         old_gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4098       if (stop_point != NULL) {
4099         assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4100                "Should only be AbortablePreclean.");
4101         _ct->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4102         if (should_abort_preclean()) {
4103           break; // out of preclean loop
4104         } else {
4105           // Compute the next address at which preclean should pick up.
4106           lastAddr = next_card_start_after_block(stop_point);
4107         }
4108       }
4109     } else {
4110       break;
4111     }
4112   }
4113   verify_work_stacks_empty();
4114   verify_overflow_empty();
4115   return cumNumDirtyCards;
4116 }
4117 
4118 class PrecleanCLDClosure : public CLDClosure {
4119   MetadataVisitingOopsInGenClosure* _cm_closure;
4120  public:
4121   PrecleanCLDClosure(MetadataVisitingOopsInGenClosure* oop_closure) : _cm_closure(oop_closure) {}
4122   void do_cld(ClassLoaderData* cld) {
4123     if (cld->has_accumulated_modified_oops()) {
4124       cld->clear_accumulated_modified_oops();
4125 
4126       _cm_closure->do_cld(cld);
4127     }
4128   }
4129 };
4130 
4131 // The freelist lock is needed to prevent asserts, is it really needed?
4132 void CMSCollector::preclean_cld(MarkRefsIntoAndScanClosure* cl, Mutex* freelistLock) {
4133   // Needed to walk CLDG
4134   MutexLocker ml(ClassLoaderDataGraph_lock);
4135 
4136   cl->set_freelistLock(freelistLock);
4137 
4138   CMSTokenSyncWithLocks ts(true, freelistLock, bitMapLock());
4139 
4140   // SSS: Add equivalent to ScanMarkedObjectsAgainCarefullyClosure::do_yield_check and should_abort_preclean?
4141   // SSS: We should probably check if precleaning should be aborted, at suitable intervals?
4142   PrecleanCLDClosure preclean_closure(cl);
4143   ClassLoaderDataGraph::cld_do(&preclean_closure);
4144 
4145   verify_work_stacks_empty();
4146   verify_overflow_empty();
4147 }
4148 
4149 void CMSCollector::checkpointRootsFinal() {
4150   assert(_collectorState == FinalMarking, "incorrect state transition?");
4151   check_correct_thread_executing();
4152   // world is stopped at this checkpoint
4153   assert(SafepointSynchronize::is_at_safepoint(),
4154          "world should be stopped");
4155   TraceCMSMemoryManagerStats tms(_collectorState, CMSHeap::heap()->gc_cause());
4156 
4157   verify_work_stacks_empty();
4158   verify_overflow_empty();
4159 
4160   log_debug(gc)("YG occupancy: " SIZE_FORMAT " K (" SIZE_FORMAT " K)",
4161                 _young_gen->used() / K, _young_gen->capacity() / K);
4162   {
4163     if (CMSScavengeBeforeRemark) {
4164       CMSHeap* heap = CMSHeap::heap();
4165       // Temporarily set flag to false, GCH->do_collection will
4166       // expect it to be false and set to true
4167       FlagSetting fl(heap->_is_gc_active, false);
4168 
4169       heap->do_collection(true,                      // full (i.e. force, see below)
4170                           false,                     // !clear_all_soft_refs
4171                           0,                         // size
4172                           false,                     // is_tlab
4173                           GenCollectedHeap::YoungGen // type
4174         );
4175     }
4176     FreelistLocker x(this);
4177     MutexLockerEx y(bitMapLock(),
4178                     Mutex::_no_safepoint_check_flag);
4179     checkpointRootsFinalWork();
4180   }
4181   verify_work_stacks_empty();
4182   verify_overflow_empty();
4183 }
4184 
4185 void CMSCollector::checkpointRootsFinalWork() {
4186   GCTraceTime(Trace, gc, phases) tm("checkpointRootsFinalWork", _gc_timer_cm);
4187 
4188   assert(haveFreelistLocks(), "must have free list locks");
4189   assert_lock_strong(bitMapLock());
4190 
4191   ResourceMark rm;
4192   HandleMark   hm;
4193 
4194   CMSHeap* heap = CMSHeap::heap();
4195 
4196   if (should_unload_classes()) {
4197     CodeCache::gc_prologue();
4198   }
4199   assert(haveFreelistLocks(), "must have free list locks");
4200   assert_lock_strong(bitMapLock());
4201 
4202   // We might assume that we need not fill TLAB's when
4203   // CMSScavengeBeforeRemark is set, because we may have just done
4204   // a scavenge which would have filled all TLAB's -- and besides
4205   // Eden would be empty. This however may not always be the case --
4206   // for instance although we asked for a scavenge, it may not have
4207   // happened because of a JNI critical section. We probably need
4208   // a policy for deciding whether we can in that case wait until
4209   // the critical section releases and then do the remark following
4210   // the scavenge, and skip it here. In the absence of that policy,
4211   // or of an indication of whether the scavenge did indeed occur,
4212   // we cannot rely on TLAB's having been filled and must do
4213   // so here just in case a scavenge did not happen.
4214   heap->ensure_parsability(false);  // fill TLAB's, but no need to retire them
4215   // Update the saved marks which may affect the root scans.
4216   heap->save_marks();
4217 
4218   print_eden_and_survivor_chunk_arrays();
4219 
4220   {
4221 #if COMPILER2_OR_JVMCI
4222     DerivedPointerTableDeactivate dpt_deact;
4223 #endif
4224 
4225     // Note on the role of the mod union table:
4226     // Since the marker in "markFromRoots" marks concurrently with
4227     // mutators, it is possible for some reachable objects not to have been
4228     // scanned. For instance, an only reference to an object A was
4229     // placed in object B after the marker scanned B. Unless B is rescanned,
4230     // A would be collected. Such updates to references in marked objects
4231     // are detected via the mod union table which is the set of all cards
4232     // dirtied since the first checkpoint in this GC cycle and prior to
4233     // the most recent young generation GC, minus those cleaned up by the
4234     // concurrent precleaning.
4235     if (CMSParallelRemarkEnabled) {
4236       GCTraceTime(Debug, gc, phases) t("Rescan (parallel)", _gc_timer_cm);
4237       do_remark_parallel();
4238     } else {
4239       GCTraceTime(Debug, gc, phases) t("Rescan (non-parallel)", _gc_timer_cm);
4240       do_remark_non_parallel();
4241     }
4242   }
4243   verify_work_stacks_empty();
4244   verify_overflow_empty();
4245 
4246   {
4247     GCTraceTime(Trace, gc, phases) ts("refProcessingWork", _gc_timer_cm);
4248     refProcessingWork();
4249   }
4250   verify_work_stacks_empty();
4251   verify_overflow_empty();
4252 
4253   if (should_unload_classes()) {
4254     CodeCache::gc_epilogue();
4255   }
4256   JvmtiExport::gc_epilogue();
4257 
4258   // If we encountered any (marking stack / work queue) overflow
4259   // events during the current CMS cycle, take appropriate
4260   // remedial measures, where possible, so as to try and avoid
4261   // recurrence of that condition.
4262   assert(_markStack.isEmpty(), "No grey objects");
4263   size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
4264                      _ser_kac_ovflw        + _ser_kac_preclean_ovflw;
4265   if (ser_ovflw > 0) {
4266     log_trace(gc)("Marking stack overflow (benign) (pmc_pc=" SIZE_FORMAT ", pmc_rm=" SIZE_FORMAT ", kac=" SIZE_FORMAT ", kac_preclean=" SIZE_FORMAT ")",
4267                          _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw, _ser_kac_ovflw, _ser_kac_preclean_ovflw);
4268     _markStack.expand();
4269     _ser_pmc_remark_ovflw = 0;
4270     _ser_pmc_preclean_ovflw = 0;
4271     _ser_kac_preclean_ovflw = 0;
4272     _ser_kac_ovflw = 0;
4273   }
4274   if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
4275      log_trace(gc)("Work queue overflow (benign) (pmc_rm=" SIZE_FORMAT ", kac=" SIZE_FORMAT ")",
4276                           _par_pmc_remark_ovflw, _par_kac_ovflw);
4277      _par_pmc_remark_ovflw = 0;
4278     _par_kac_ovflw = 0;
4279   }
4280    if (_markStack._hit_limit > 0) {
4281      log_trace(gc)(" (benign) Hit max stack size limit (" SIZE_FORMAT ")",
4282                           _markStack._hit_limit);
4283    }
4284    if (_markStack._failed_double > 0) {
4285      log_trace(gc)(" (benign) Failed stack doubling (" SIZE_FORMAT "), current capacity " SIZE_FORMAT,
4286                           _markStack._failed_double, _markStack.capacity());
4287    }
4288   _markStack._hit_limit = 0;
4289   _markStack._failed_double = 0;
4290 
4291   if ((VerifyAfterGC || VerifyDuringGC) &&
4292       CMSHeap::heap()->total_collections() >= VerifyGCStartAt) {
4293     verify_after_remark();
4294   }
4295 
4296   _gc_tracer_cm->report_object_count_after_gc(&_is_alive_closure);
4297 
4298   // Change under the freelistLocks.
4299   _collectorState = Sweeping;
4300   // Call isAllClear() under bitMapLock
4301   assert(_modUnionTable.isAllClear(),
4302       "Should be clear by end of the final marking");
4303   assert(_ct->cld_rem_set()->mod_union_is_clear(),
4304       "Should be clear by end of the final marking");
4305 }
4306 
4307 void CMSParInitialMarkTask::work(uint worker_id) {
4308   elapsedTimer _timer;
4309   ResourceMark rm;
4310   HandleMark   hm;
4311 
4312   // ---------- scan from roots --------------
4313   _timer.start();
4314   CMSHeap* heap = CMSHeap::heap();
4315   ParMarkRefsIntoClosure par_mri_cl(_collector->_span, &(_collector->_markBitMap));
4316 
4317   // ---------- young gen roots --------------
4318   {
4319     work_on_young_gen_roots(&par_mri_cl);
4320     _timer.stop();
4321     log_trace(gc, task)("Finished young gen initial mark scan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4322   }
4323 
4324   // ---------- remaining roots --------------
4325   _timer.reset();
4326   _timer.start();
4327 
4328   CLDToOopClosure cld_closure(&par_mri_cl, ClassLoaderData::_claim_strong);
4329 
4330   heap->cms_process_roots(_strong_roots_scope,
4331                           false,     // yg was scanned above
4332                           GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4333                           _collector->should_unload_classes(),
4334                           &par_mri_cl,
4335                           &cld_closure,
4336                           &_par_state_string);
4337 
4338   assert(_collector->should_unload_classes()
4339          || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4340          "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4341   _timer.stop();
4342   log_trace(gc, task)("Finished remaining root initial mark scan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4343 }
4344 
4345 // Parallel remark task
4346 class CMSParRemarkTask: public CMSParMarkTask {
4347   CompactibleFreeListSpace* _cms_space;
4348 
4349   // The per-thread work queues, available here for stealing.
4350   OopTaskQueueSet*       _task_queues;
4351   TaskTerminator         _term;
4352   StrongRootsScope*      _strong_roots_scope;
4353 
4354  public:
4355   // A value of 0 passed to n_workers will cause the number of
4356   // workers to be taken from the active workers in the work gang.
4357   CMSParRemarkTask(CMSCollector* collector,
4358                    CompactibleFreeListSpace* cms_space,
4359                    uint n_workers, WorkGang* workers,
4360                    OopTaskQueueSet* task_queues,
4361                    StrongRootsScope* strong_roots_scope):
4362     CMSParMarkTask("Rescan roots and grey objects in parallel",
4363                    collector, n_workers),
4364     _cms_space(cms_space),
4365     _task_queues(task_queues),
4366     _term(n_workers, task_queues),
4367     _strong_roots_scope(strong_roots_scope) { }
4368 
4369   OopTaskQueueSet* task_queues() { return _task_queues; }
4370 
4371   OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
4372 
4373   ParallelTaskTerminator* terminator() { return _term.terminator(); }
4374   uint n_workers() { return _n_workers; }
4375 
4376   void work(uint worker_id);
4377 
4378  private:
4379   // ... of  dirty cards in old space
4380   void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
4381                                   ParMarkRefsIntoAndScanClosure* cl);
4382 
4383   // ... work stealing for the above
4384   void do_work_steal(int i, ParMarkRefsIntoAndScanClosure* cl);
4385 };
4386 
4387 class RemarkCLDClosure : public CLDClosure {
4388   CLDToOopClosure _cm_closure;
4389  public:
4390   RemarkCLDClosure(OopClosure* oop_closure) : _cm_closure(oop_closure, ClassLoaderData::_claim_strong) {}
4391   void do_cld(ClassLoaderData* cld) {
4392     // Check if we have modified any oops in the CLD during the concurrent marking.
4393     if (cld->has_accumulated_modified_oops()) {
4394       cld->clear_accumulated_modified_oops();
4395 
4396       // We could have transfered the current modified marks to the accumulated marks,
4397       // like we do with the Card Table to Mod Union Table. But it's not really necessary.
4398     } else if (cld->has_modified_oops()) {
4399       // Don't clear anything, this info is needed by the next young collection.
4400     } else {
4401       // No modified oops in the ClassLoaderData.
4402       return;
4403     }
4404 
4405     // The klass has modified fields, need to scan the klass.
4406     _cm_closure.do_cld(cld);
4407   }
4408 };
4409 
4410 void CMSParMarkTask::work_on_young_gen_roots(OopsInGenClosure* cl) {
4411   ParNewGeneration* young_gen = _collector->_young_gen;
4412   ContiguousSpace* eden_space = young_gen->eden();
4413   ContiguousSpace* from_space = young_gen->from();
4414   ContiguousSpace* to_space   = young_gen->to();
4415 
4416   HeapWord** eca = _collector->_eden_chunk_array;
4417   size_t     ect = _collector->_eden_chunk_index;
4418   HeapWord** sca = _collector->_survivor_chunk_array;
4419   size_t     sct = _collector->_survivor_chunk_index;
4420 
4421   assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
4422   assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
4423 
4424   do_young_space_rescan(cl, to_space, NULL, 0);
4425   do_young_space_rescan(cl, from_space, sca, sct);
4426   do_young_space_rescan(cl, eden_space, eca, ect);
4427 }
4428 
4429 // work_queue(i) is passed to the closure
4430 // ParMarkRefsIntoAndScanClosure.  The "i" parameter
4431 // also is passed to do_dirty_card_rescan_tasks() and to
4432 // do_work_steal() to select the i-th task_queue.
4433 
4434 void CMSParRemarkTask::work(uint worker_id) {
4435   elapsedTimer _timer;
4436   ResourceMark rm;
4437   HandleMark   hm;
4438 
4439   // ---------- rescan from roots --------------
4440   _timer.start();
4441   CMSHeap* heap = CMSHeap::heap();
4442   ParMarkRefsIntoAndScanClosure par_mrias_cl(_collector,
4443     _collector->_span, _collector->ref_processor(),
4444     &(_collector->_markBitMap),
4445     work_queue(worker_id));
4446 
4447   // Rescan young gen roots first since these are likely
4448   // coarsely partitioned and may, on that account, constitute
4449   // the critical path; thus, it's best to start off that
4450   // work first.
4451   // ---------- young gen roots --------------
4452   {
4453     work_on_young_gen_roots(&par_mrias_cl);
4454     _timer.stop();
4455     log_trace(gc, task)("Finished young gen rescan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4456   }
4457 
4458   // ---------- remaining roots --------------
4459   _timer.reset();
4460   _timer.start();
4461   heap->cms_process_roots(_strong_roots_scope,
4462                           false,     // yg was scanned above
4463                           GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4464                           _collector->should_unload_classes(),
4465                           &par_mrias_cl,
4466                           NULL,     // The dirty klasses will be handled below
4467                           &_par_state_string);
4468 
4469   assert(_collector->should_unload_classes()
4470          || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4471          "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4472   _timer.stop();
4473   log_trace(gc, task)("Finished remaining root rescan work in %dth thread: %3.3f sec",  worker_id, _timer.seconds());
4474 
4475   // ---------- unhandled CLD scanning ----------
4476   if (worker_id == 0) { // Single threaded at the moment.
4477     _timer.reset();
4478     _timer.start();
4479 
4480     // Scan all new class loader data objects and new dependencies that were
4481     // introduced during concurrent marking.
4482     ResourceMark rm;
4483     GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
4484     for (int i = 0; i < array->length(); i++) {
4485       Devirtualizer::do_cld(&par_mrias_cl, array->at(i));
4486     }
4487 
4488     // We don't need to keep track of new CLDs anymore.
4489     ClassLoaderDataGraph::remember_new_clds(false);
4490 
4491     _timer.stop();
4492     log_trace(gc, task)("Finished unhandled CLD scanning work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4493   }
4494 
4495   // We might have added oops to ClassLoaderData::_handles during the
4496   // concurrent marking phase. These oops do not always point to newly allocated objects
4497   // that are guaranteed to be kept alive.  Hence,
4498   // we do have to revisit the _handles block during the remark phase.
4499 
4500   // ---------- dirty CLD scanning ----------
4501   if (worker_id == 0) { // Single threaded at the moment.
4502     _timer.reset();
4503     _timer.start();
4504 
4505     // Scan all classes that was dirtied during the concurrent marking phase.
4506     RemarkCLDClosure remark_closure(&par_mrias_cl);
4507     ClassLoaderDataGraph::cld_do(&remark_closure);
4508 
4509     _timer.stop();
4510     log_trace(gc, task)("Finished dirty CLD scanning work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4511   }
4512 
4513 
4514   // ---------- rescan dirty cards ------------
4515   _timer.reset();
4516   _timer.start();
4517 
4518   // Do the rescan tasks for each of the two spaces
4519   // (cms_space) in turn.
4520   // "worker_id" is passed to select the task_queue for "worker_id"
4521   do_dirty_card_rescan_tasks(_cms_space, worker_id, &par_mrias_cl);
4522   _timer.stop();
4523   log_trace(gc, task)("Finished dirty card rescan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4524 
4525   // ---------- steal work from other threads ...
4526   // ---------- ... and drain overflow list.
4527   _timer.reset();
4528   _timer.start();
4529   do_work_steal(worker_id, &par_mrias_cl);
4530   _timer.stop();
4531   log_trace(gc, task)("Finished work stealing in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4532 }
4533 
4534 void
4535 CMSParMarkTask::do_young_space_rescan(
4536   OopsInGenClosure* cl, ContiguousSpace* space,
4537   HeapWord** chunk_array, size_t chunk_top) {
4538   // Until all tasks completed:
4539   // . claim an unclaimed task
4540   // . compute region boundaries corresponding to task claimed
4541   //   using chunk_array
4542   // . par_oop_iterate(cl) over that region
4543 
4544   ResourceMark rm;
4545   HandleMark   hm;
4546 
4547   SequentialSubTasksDone* pst = space->par_seq_tasks();
4548 
4549   uint nth_task = 0;
4550   uint n_tasks  = pst->n_tasks();
4551 
4552   if (n_tasks > 0) {
4553     assert(pst->valid(), "Uninitialized use?");
4554     HeapWord *start, *end;
4555     while (pst->try_claim_task(/* reference */ nth_task)) {
4556       // We claimed task # nth_task; compute its boundaries.
4557       if (chunk_top == 0) {  // no samples were taken
4558         assert(nth_task == 0 && n_tasks == 1, "Can have only 1 eden task");
4559         start = space->bottom();
4560         end   = space->top();
4561       } else if (nth_task == 0) {
4562         start = space->bottom();
4563         end   = chunk_array[nth_task];
4564       } else if (nth_task < (uint)chunk_top) {
4565         assert(nth_task >= 1, "Control point invariant");
4566         start = chunk_array[nth_task - 1];
4567         end   = chunk_array[nth_task];
4568       } else {
4569         assert(nth_task == (uint)chunk_top, "Control point invariant");
4570         start = chunk_array[chunk_top - 1];
4571         end   = space->top();
4572       }
4573       MemRegion mr(start, end);
4574       // Verify that mr is in space
4575       assert(mr.is_empty() || space->used_region().contains(mr),
4576              "Should be in space");
4577       // Verify that "start" is an object boundary
4578       assert(mr.is_empty() || oopDesc::is_oop(oop(mr.start())),
4579              "Should be an oop");
4580       space->par_oop_iterate(mr, cl);
4581     }
4582     pst->all_tasks_completed();
4583   }
4584 }
4585 
4586 void
4587 CMSParRemarkTask::do_dirty_card_rescan_tasks(
4588   CompactibleFreeListSpace* sp, int i,
4589   ParMarkRefsIntoAndScanClosure* cl) {
4590   // Until all tasks completed:
4591   // . claim an unclaimed task
4592   // . compute region boundaries corresponding to task claimed
4593   // . transfer dirty bits ct->mut for that region
4594   // . apply rescanclosure to dirty mut bits for that region
4595 
4596   ResourceMark rm;
4597   HandleMark   hm;
4598 
4599   OopTaskQueue* work_q = work_queue(i);
4600   ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
4601   // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
4602   // CAUTION: This closure has state that persists across calls to
4603   // the work method dirty_range_iterate_clear() in that it has
4604   // embedded in it a (subtype of) UpwardsObjectClosure. The
4605   // use of that state in the embedded UpwardsObjectClosure instance
4606   // assumes that the cards are always iterated (even if in parallel
4607   // by several threads) in monotonically increasing order per each
4608   // thread. This is true of the implementation below which picks
4609   // card ranges (chunks) in monotonically increasing order globally
4610   // and, a-fortiori, in monotonically increasing order per thread
4611   // (the latter order being a subsequence of the former).
4612   // If the work code below is ever reorganized into a more chaotic
4613   // work-partitioning form than the current "sequential tasks"
4614   // paradigm, the use of that persistent state will have to be
4615   // revisited and modified appropriately. See also related
4616   // bug 4756801 work on which should examine this code to make
4617   // sure that the changes there do not run counter to the
4618   // assumptions made here and necessary for correctness and
4619   // efficiency. Note also that this code might yield inefficient
4620   // behavior in the case of very large objects that span one or
4621   // more work chunks. Such objects would potentially be scanned
4622   // several times redundantly. Work on 4756801 should try and
4623   // address that performance anomaly if at all possible. XXX
4624   MemRegion  full_span  = _collector->_span;
4625   CMSBitMap* bm    = &(_collector->_markBitMap);     // shared
4626   MarkFromDirtyCardsClosure
4627     greyRescanClosure(_collector, full_span, // entire span of interest
4628                       sp, bm, work_q, cl);
4629 
4630   SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
4631   assert(pst->valid(), "Uninitialized use?");
4632   uint nth_task = 0;
4633   const int alignment = CardTable::card_size * BitsPerWord;
4634   MemRegion span = sp->used_region();
4635   HeapWord* start_addr = span.start();
4636   HeapWord* end_addr = align_up(span.end(), alignment);
4637   const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
4638   assert(is_aligned(start_addr, alignment), "Check alignment");
4639   assert(is_aligned(chunk_size, alignment), "Check alignment");
4640 
4641   while (pst->try_claim_task(/* reference */ nth_task)) {
4642     // Having claimed the nth_task, compute corresponding mem-region,
4643     // which is a-fortiori aligned correctly (i.e. at a MUT boundary).
4644     // The alignment restriction ensures that we do not need any
4645     // synchronization with other gang-workers while setting or
4646     // clearing bits in thus chunk of the MUT.
4647     MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
4648                                     start_addr + (nth_task+1)*chunk_size);
4649     // The last chunk's end might be way beyond end of the
4650     // used region. In that case pull back appropriately.
4651     if (this_span.end() > end_addr) {
4652       this_span.set_end(end_addr);
4653       assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
4654     }
4655     // Iterate over the dirty cards covering this chunk, marking them
4656     // precleaned, and setting the corresponding bits in the mod union
4657     // table. Since we have been careful to partition at Card and MUT-word
4658     // boundaries no synchronization is needed between parallel threads.
4659     _collector->_ct->dirty_card_iterate(this_span,
4660                                                  &modUnionClosure);
4661 
4662     // Having transferred these marks into the modUnionTable,
4663     // rescan the marked objects on the dirty cards in the modUnionTable.
4664     // Even if this is at a synchronous collection, the initial marking
4665     // may have been done during an asynchronous collection so there
4666     // may be dirty bits in the mod-union table.
4667     _collector->_modUnionTable.dirty_range_iterate_clear(
4668                   this_span, &greyRescanClosure);
4669     _collector->_modUnionTable.verifyNoOneBitsInRange(
4670                                  this_span.start(),
4671                                  this_span.end());
4672   }
4673   pst->all_tasks_completed();  // declare that i am done
4674 }
4675 
4676 // . see if we can share work_queues with ParNew? XXX
4677 void
4678 CMSParRemarkTask::do_work_steal(int i, ParMarkRefsIntoAndScanClosure* cl) {
4679   OopTaskQueue* work_q = work_queue(i);
4680   NOT_PRODUCT(int num_steals = 0;)
4681   oop obj_to_scan;
4682   CMSBitMap* bm = &(_collector->_markBitMap);
4683 
4684   while (true) {
4685     // Completely finish any left over work from (an) earlier round(s)
4686     cl->trim_queue(0);
4687     size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
4688                                          (size_t)ParGCDesiredObjsFromOverflowList);
4689     // Now check if there's any work in the overflow list
4690     // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
4691     // only affects the number of attempts made to get work from the
4692     // overflow list and does not affect the number of workers.  Just
4693     // pass ParallelGCThreads so this behavior is unchanged.
4694     if (_collector->par_take_from_overflow_list(num_from_overflow_list,
4695                                                 work_q,
4696                                                 ParallelGCThreads)) {
4697       // found something in global overflow list;
4698       // not yet ready to go stealing work from others.
4699       // We'd like to assert(work_q->size() != 0, ...)
4700       // because we just took work from the overflow list,
4701       // but of course we can't since all of that could have
4702       // been already stolen from us.
4703       // "He giveth and He taketh away."
4704       continue;
4705     }
4706     // Verify that we have no work before we resort to stealing
4707     assert(work_q->size() == 0, "Have work, shouldn't steal");
4708     // Try to steal from other queues that have work
4709     if (task_queues()->steal(i, /* reference */ obj_to_scan)) {
4710       NOT_PRODUCT(num_steals++;)
4711       assert(oopDesc::is_oop(obj_to_scan), "Oops, not an oop!");
4712       assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
4713       // Do scanning work
4714       obj_to_scan->oop_iterate(cl);
4715       // Loop around, finish this work, and try to steal some more
4716     } else if (terminator()->offer_termination()) {
4717         break;  // nirvana from the infinite cycle
4718     }
4719   }
4720   log_develop_trace(gc, task)("\t(%d: stole %d oops)", i, num_steals);
4721   assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
4722          "Else our work is not yet done");
4723 }
4724 
4725 // Record object boundaries in _eden_chunk_array by sampling the eden
4726 // top in the slow-path eden object allocation code path and record
4727 // the boundaries, if CMSEdenChunksRecordAlways is true. If
4728 // CMSEdenChunksRecordAlways is false, we use the other asynchronous
4729 // sampling in sample_eden() that activates during the part of the
4730 // preclean phase.
4731 void CMSCollector::sample_eden_chunk() {
4732   if (CMSEdenChunksRecordAlways && _eden_chunk_array != NULL) {
4733     if (_eden_chunk_lock->try_lock()) {
4734       // Record a sample. This is the critical section. The contents
4735       // of the _eden_chunk_array have to be non-decreasing in the
4736       // address order.
4737       _eden_chunk_array[_eden_chunk_index] = *_top_addr;
4738       assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4739              "Unexpected state of Eden");
4740       if (_eden_chunk_index == 0 ||
4741           ((_eden_chunk_array[_eden_chunk_index] > _eden_chunk_array[_eden_chunk_index-1]) &&
4742            (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4743                           _eden_chunk_array[_eden_chunk_index-1]) >= CMSSamplingGrain))) {
4744         _eden_chunk_index++;  // commit sample
4745       }
4746       _eden_chunk_lock->unlock();
4747     }
4748   }
4749 }
4750 
4751 // Return a thread-local PLAB recording array, as appropriate.
4752 void* CMSCollector::get_data_recorder(int thr_num) {
4753   if (_survivor_plab_array != NULL &&
4754       (CMSPLABRecordAlways ||
4755        (_collectorState > Marking && _collectorState < FinalMarking))) {
4756     assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
4757     ChunkArray* ca = &_survivor_plab_array[thr_num];
4758     ca->reset();   // clear it so that fresh data is recorded
4759     return (void*) ca;
4760   } else {
4761     return NULL;
4762   }
4763 }
4764 
4765 // Reset all the thread-local PLAB recording arrays
4766 void CMSCollector::reset_survivor_plab_arrays() {
4767   for (uint i = 0; i < ParallelGCThreads; i++) {
4768     _survivor_plab_array[i].reset();
4769   }
4770 }
4771 
4772 // Merge the per-thread plab arrays into the global survivor chunk
4773 // array which will provide the partitioning of the survivor space
4774 // for CMS initial scan and rescan.
4775 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv,
4776                                               int no_of_gc_threads) {
4777   assert(_survivor_plab_array  != NULL, "Error");
4778   assert(_survivor_chunk_array != NULL, "Error");
4779   assert(_collectorState == FinalMarking ||
4780          (CMSParallelInitialMarkEnabled && _collectorState == InitialMarking), "Error");
4781   for (int j = 0; j < no_of_gc_threads; j++) {
4782     _cursor[j] = 0;
4783   }
4784   HeapWord* top = surv->top();
4785   size_t i;
4786   for (i = 0; i < _survivor_chunk_capacity; i++) {  // all sca entries
4787     HeapWord* min_val = top;          // Higher than any PLAB address
4788     uint      min_tid = 0;            // position of min_val this round
4789     for (int j = 0; j < no_of_gc_threads; j++) {
4790       ChunkArray* cur_sca = &_survivor_plab_array[j];
4791       if (_cursor[j] == cur_sca->end()) {
4792         continue;
4793       }
4794       assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
4795       HeapWord* cur_val = cur_sca->nth(_cursor[j]);
4796       assert(surv->used_region().contains(cur_val), "Out of bounds value");
4797       if (cur_val < min_val) {
4798         min_tid = j;
4799         min_val = cur_val;
4800       } else {
4801         assert(cur_val < top, "All recorded addresses should be less");
4802       }
4803     }
4804     // At this point min_val and min_tid are respectively
4805     // the least address in _survivor_plab_array[j]->nth(_cursor[j])
4806     // and the thread (j) that witnesses that address.
4807     // We record this address in the _survivor_chunk_array[i]
4808     // and increment _cursor[min_tid] prior to the next round i.
4809     if (min_val == top) {
4810       break;
4811     }
4812     _survivor_chunk_array[i] = min_val;
4813     _cursor[min_tid]++;
4814   }
4815   // We are all done; record the size of the _survivor_chunk_array
4816   _survivor_chunk_index = i; // exclusive: [0, i)
4817   log_trace(gc, survivor)(" (Survivor:" SIZE_FORMAT "chunks) ", i);
4818   // Verify that we used up all the recorded entries
4819   #ifdef ASSERT
4820     size_t total = 0;
4821     for (int j = 0; j < no_of_gc_threads; j++) {
4822       assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
4823       total += _cursor[j];
4824     }
4825     assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
4826     // Check that the merged array is in sorted order
4827     if (total > 0) {
4828       for (size_t i = 0; i < total - 1; i++) {
4829         log_develop_trace(gc, survivor)(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
4830                                      i, p2i(_survivor_chunk_array[i]));
4831         assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
4832                "Not sorted");
4833       }
4834     }
4835   #endif // ASSERT
4836 }
4837 
4838 // Set up the space's par_seq_tasks structure for work claiming
4839 // for parallel initial scan and rescan of young gen.
4840 // See ParRescanTask where this is currently used.
4841 void
4842 CMSCollector::
4843 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
4844   assert(n_threads > 0, "Unexpected n_threads argument");
4845 
4846   // Eden space
4847   if (!_young_gen->eden()->is_empty()) {
4848     SequentialSubTasksDone* pst = _young_gen->eden()->par_seq_tasks();
4849     assert(!pst->valid(), "Clobbering existing data?");
4850     // Each valid entry in [0, _eden_chunk_index) represents a task.
4851     size_t n_tasks = _eden_chunk_index + 1;
4852     assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
4853     // Sets the condition for completion of the subtask (how many threads
4854     // need to finish in order to be done).
4855     pst->set_n_threads(n_threads);
4856     pst->set_n_tasks((int)n_tasks);
4857   }
4858 
4859   // Merge the survivor plab arrays into _survivor_chunk_array
4860   if (_survivor_plab_array != NULL) {
4861     merge_survivor_plab_arrays(_young_gen->from(), n_threads);
4862   } else {
4863     assert(_survivor_chunk_index == 0, "Error");
4864   }
4865 
4866   // To space
4867   {
4868     SequentialSubTasksDone* pst = _young_gen->to()->par_seq_tasks();
4869     assert(!pst->valid(), "Clobbering existing data?");
4870     // Sets the condition for completion of the subtask (how many threads
4871     // need to finish in order to be done).
4872     pst->set_n_threads(n_threads);
4873     pst->set_n_tasks(1);
4874     assert(pst->valid(), "Error");
4875   }
4876 
4877   // From space
4878   {
4879     SequentialSubTasksDone* pst = _young_gen->from()->par_seq_tasks();
4880     assert(!pst->valid(), "Clobbering existing data?");
4881     size_t n_tasks = _survivor_chunk_index + 1;
4882     assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
4883     // Sets the condition for completion of the subtask (how many threads
4884     // need to finish in order to be done).
4885     pst->set_n_threads(n_threads);
4886     pst->set_n_tasks((int)n_tasks);
4887     assert(pst->valid(), "Error");
4888   }
4889 }
4890 
4891 // Parallel version of remark
4892 void CMSCollector::do_remark_parallel() {
4893   CMSHeap* heap = CMSHeap::heap();
4894   WorkGang* workers = heap->workers();
4895   assert(workers != NULL, "Need parallel worker threads.");
4896   // Choose to use the number of GC workers most recently set
4897   // into "active_workers".
4898   uint n_workers = workers->active_workers();
4899 
4900   CompactibleFreeListSpace* cms_space  = _cmsGen->cmsSpace();
4901 
4902   StrongRootsScope srs(n_workers);
4903 
4904   CMSParRemarkTask tsk(this, cms_space, n_workers, workers, task_queues(), &srs);
4905 
4906   // We won't be iterating over the cards in the card table updating
4907   // the younger_gen cards, so we shouldn't call the following else
4908   // the verification code as well as subsequent younger_refs_iterate
4909   // code would get confused. XXX
4910   // heap->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
4911 
4912   // The young gen rescan work will not be done as part of
4913   // process_roots (which currently doesn't know how to
4914   // parallelize such a scan), but rather will be broken up into
4915   // a set of parallel tasks (via the sampling that the [abortable]
4916   // preclean phase did of eden, plus the [two] tasks of
4917   // scanning the [two] survivor spaces. Further fine-grain
4918   // parallelization of the scanning of the survivor spaces
4919   // themselves, and of precleaning of the young gen itself
4920   // is deferred to the future.
4921   initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
4922 
4923   // The dirty card rescan work is broken up into a "sequence"
4924   // of parallel tasks (per constituent space) that are dynamically
4925   // claimed by the parallel threads.
4926   cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
4927 
4928   // It turns out that even when we're using 1 thread, doing the work in a
4929   // separate thread causes wide variance in run times.  We can't help this
4930   // in the multi-threaded case, but we special-case n=1 here to get
4931   // repeatable measurements of the 1-thread overhead of the parallel code.
4932   if (n_workers > 1) {
4933     // Make refs discovery MT-safe, if it isn't already: it may not
4934     // necessarily be so, since it's possible that we are doing
4935     // ST marking.
4936     ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), true);
4937     workers->run_task(&tsk);
4938   } else {
4939     ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
4940     tsk.work(0);
4941   }
4942 
4943   // restore, single-threaded for now, any preserved marks
4944   // as a result of work_q overflow
4945   restore_preserved_marks_if_any();
4946 }
4947 
4948 // Non-parallel version of remark
4949 void CMSCollector::do_remark_non_parallel() {
4950   ResourceMark rm;
4951   HandleMark   hm;
4952   CMSHeap* heap = CMSHeap::heap();
4953   ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
4954 
4955   MarkRefsIntoAndScanClosure
4956     mrias_cl(_span, ref_processor(), &_markBitMap, NULL /* not precleaning */,
4957              &_markStack, this,
4958              false /* should_yield */, false /* not precleaning */);
4959   MarkFromDirtyCardsClosure
4960     markFromDirtyCardsClosure(this, _span,
4961                               NULL,  // space is set further below
4962                               &_markBitMap, &_markStack, &mrias_cl);
4963   {
4964     GCTraceTime(Trace, gc, phases) t("Grey Object Rescan", _gc_timer_cm);
4965     // Iterate over the dirty cards, setting the corresponding bits in the
4966     // mod union table.
4967     {
4968       ModUnionClosure modUnionClosure(&_modUnionTable);
4969       _ct->dirty_card_iterate(_cmsGen->used_region(),
4970                               &modUnionClosure);
4971     }
4972     // Having transferred these marks into the modUnionTable, we just need
4973     // to rescan the marked objects on the dirty cards in the modUnionTable.
4974     // The initial marking may have been done during an asynchronous
4975     // collection so there may be dirty bits in the mod-union table.
4976     const int alignment = CardTable::card_size * BitsPerWord;
4977     {
4978       // ... First handle dirty cards in CMS gen
4979       markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
4980       MemRegion ur = _cmsGen->used_region();
4981       HeapWord* lb = ur.start();
4982       HeapWord* ub = align_up(ur.end(), alignment);
4983       MemRegion cms_span(lb, ub);
4984       _modUnionTable.dirty_range_iterate_clear(cms_span,
4985                                                &markFromDirtyCardsClosure);
4986       verify_work_stacks_empty();
4987       log_trace(gc)(" (re-scanned " SIZE_FORMAT " dirty cards in cms gen) ", markFromDirtyCardsClosure.num_dirty_cards());
4988     }
4989   }
4990   if (VerifyDuringGC &&
4991       CMSHeap::heap()->total_collections() >= VerifyGCStartAt) {
4992     HandleMark hm;  // Discard invalid handles created during verification
4993     Universe::verify();
4994   }
4995   {
4996     GCTraceTime(Trace, gc, phases) t("Root Rescan", _gc_timer_cm);
4997 
4998     verify_work_stacks_empty();
4999 
5000     heap->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
5001     StrongRootsScope srs(1);
5002 
5003     heap->cms_process_roots(&srs,
5004                             true,  // young gen as roots
5005                             GenCollectedHeap::ScanningOption(roots_scanning_options()),
5006                             should_unload_classes(),
5007                             &mrias_cl,
5008                             NULL); // The dirty klasses will be handled below
5009 
5010     assert(should_unload_classes()
5011            || (roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
5012            "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5013   }
5014 
5015   {
5016     GCTraceTime(Trace, gc, phases) t("Visit Unhandled CLDs", _gc_timer_cm);
5017 
5018     verify_work_stacks_empty();
5019 
5020     // Scan all class loader data objects that might have been introduced
5021     // during concurrent marking.
5022     ResourceMark rm;
5023     GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
5024     for (int i = 0; i < array->length(); i++) {
5025       Devirtualizer::do_cld(&mrias_cl, array->at(i));
5026     }
5027 
5028     // We don't need to keep track of new CLDs anymore.
5029     ClassLoaderDataGraph::remember_new_clds(false);
5030 
5031     verify_work_stacks_empty();
5032   }
5033 
5034   // We might have added oops to ClassLoaderData::_handles during the
5035   // concurrent marking phase. These oops do not point to newly allocated objects
5036   // that are guaranteed to be kept alive.  Hence,
5037   // we do have to revisit the _handles block during the remark phase.
5038   {
5039     GCTraceTime(Trace, gc, phases) t("Dirty CLD Scan", _gc_timer_cm);
5040 
5041     verify_work_stacks_empty();
5042 
5043     RemarkCLDClosure remark_closure(&mrias_cl);
5044     ClassLoaderDataGraph::cld_do(&remark_closure);
5045 
5046     verify_work_stacks_empty();
5047   }
5048 
5049   verify_work_stacks_empty();
5050   // Restore evacuated mark words, if any, used for overflow list links
5051   restore_preserved_marks_if_any();
5052 
5053   verify_overflow_empty();
5054 }
5055 
5056 ////////////////////////////////////////////////////////
5057 // Parallel Reference Processing Task Proxy Class
5058 ////////////////////////////////////////////////////////
5059 class AbstractGangTaskWOopQueues : public AbstractGangTask {
5060   OopTaskQueueSet*       _queues;
5061   TaskTerminator         _terminator;
5062  public:
5063   AbstractGangTaskWOopQueues(const char* name, OopTaskQueueSet* queues, uint n_threads) :
5064     AbstractGangTask(name), _queues(queues), _terminator(n_threads, _queues) {}
5065   ParallelTaskTerminator* terminator() { return _terminator.terminator(); }
5066   OopTaskQueueSet* queues() { return _queues; }
5067 };
5068 
5069 class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues {
5070   typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
5071   CMSCollector*          _collector;
5072   CMSBitMap*             _mark_bit_map;
5073   const MemRegion        _span;
5074   ProcessTask&           _task;
5075 
5076 public:
5077   CMSRefProcTaskProxy(ProcessTask&     task,
5078                       CMSCollector*    collector,
5079                       const MemRegion& span,
5080                       CMSBitMap*       mark_bit_map,
5081                       AbstractWorkGang* workers,
5082                       OopTaskQueueSet* task_queues):
5083     AbstractGangTaskWOopQueues("Process referents by policy in parallel",
5084       task_queues,
5085       workers->active_workers()),
5086     _collector(collector),
5087     _mark_bit_map(mark_bit_map),
5088     _span(span),
5089     _task(task)
5090   {
5091     assert(_collector->_span.equals(_span) && !_span.is_empty(),
5092            "Inconsistency in _span");
5093   }
5094 
5095   OopTaskQueueSet* task_queues() { return queues(); }
5096 
5097   OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5098 
5099   void do_work_steal(int i,
5100                      CMSParDrainMarkingStackClosure* drain,
5101                      CMSParKeepAliveClosure* keep_alive);
5102 
5103   virtual void work(uint worker_id);
5104 };
5105 
5106 void CMSRefProcTaskProxy::work(uint worker_id) {
5107   ResourceMark rm;
5108   HandleMark hm;
5109   assert(_collector->_span.equals(_span), "Inconsistency in _span");
5110   CMSParKeepAliveClosure par_keep_alive(_collector, _span,
5111                                         _mark_bit_map,
5112                                         work_queue(worker_id));
5113   CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
5114                                                  _mark_bit_map,
5115                                                  work_queue(worker_id));
5116   CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
5117   _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack);
5118   if (_task.marks_oops_alive()) {
5119     do_work_steal(worker_id, &par_drain_stack, &par_keep_alive);
5120   }
5121   assert(work_queue(worker_id)->size() == 0, "work_queue should be empty");
5122   assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
5123 }
5124 
5125 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
5126   MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue):
5127    _span(span),
5128    _work_queue(work_queue),
5129    _bit_map(bit_map),
5130    _mark_and_push(collector, span, bit_map, work_queue),
5131    _low_water_mark(MIN2((work_queue->max_elems()/4),
5132                         ((uint)CMSWorkQueueDrainThreshold * ParallelGCThreads)))
5133 { }
5134 
5135 // . see if we can share work_queues with ParNew? XXX
5136 void CMSRefProcTaskProxy::do_work_steal(int i,
5137   CMSParDrainMarkingStackClosure* drain,
5138   CMSParKeepAliveClosure* keep_alive) {
5139   OopTaskQueue* work_q = work_queue(i);
5140   NOT_PRODUCT(int num_steals = 0;)
5141   oop obj_to_scan;
5142 
5143   while (true) {
5144     // Completely finish any left over work from (an) earlier round(s)
5145     drain->trim_queue(0);
5146     size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5147                                          (size_t)ParGCDesiredObjsFromOverflowList);
5148     // Now check if there's any work in the overflow list
5149     // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5150     // only affects the number of attempts made to get work from the
5151     // overflow list and does not affect the number of workers.  Just
5152     // pass ParallelGCThreads so this behavior is unchanged.
5153     if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5154                                                 work_q,
5155                                                 ParallelGCThreads)) {
5156       // Found something in global overflow list;
5157       // not yet ready to go stealing work from others.
5158       // We'd like to assert(work_q->size() != 0, ...)
5159       // because we just took work from the overflow list,
5160       // but of course we can't, since all of that might have
5161       // been already stolen from us.
5162       continue;
5163     }
5164     // Verify that we have no work before we resort to stealing
5165     assert(work_q->size() == 0, "Have work, shouldn't steal");
5166     // Try to steal from other queues that have work
5167     if (task_queues()->steal(i, /* reference */ obj_to_scan)) {
5168       NOT_PRODUCT(num_steals++;)
5169       assert(oopDesc::is_oop(obj_to_scan), "Oops, not an oop!");
5170       assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5171       // Do scanning work
5172       obj_to_scan->oop_iterate(keep_alive);
5173       // Loop around, finish this work, and try to steal some more
5174     } else if (terminator()->offer_termination()) {
5175       break;  // nirvana from the infinite cycle
5176     }
5177   }
5178   log_develop_trace(gc, task)("\t(%d: stole %d oops)", i, num_steals);
5179 }
5180 
5181 void CMSRefProcTaskExecutor::execute(ProcessTask& task, uint ergo_workers) {
5182   CMSHeap* heap = CMSHeap::heap();
5183   WorkGang* workers = heap->workers();
5184   assert(workers != NULL, "Need parallel worker threads.");
5185   assert(workers->active_workers() == ergo_workers,
5186          "Ergonomically chosen workers (%u) must be equal to active workers (%u)",
5187          ergo_workers, workers->active_workers());
5188   CMSRefProcTaskProxy rp_task(task, &_collector,
5189                               _collector.ref_processor_span(),
5190                               _collector.markBitMap(),
5191                               workers, _collector.task_queues());
5192   workers->run_task(&rp_task, workers->active_workers());
5193 }
5194 
5195 void CMSCollector::refProcessingWork() {
5196   ResourceMark rm;
5197   HandleMark   hm;
5198 
5199   ReferenceProcessor* rp = ref_processor();
5200   assert(_span_based_discoverer.span().equals(_span), "Spans should be equal");
5201   assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
5202   // Process weak references.
5203   rp->setup_policy(false);
5204   verify_work_stacks_empty();
5205 
5206   ReferenceProcessorPhaseTimes pt(_gc_timer_cm, rp->max_num_queues());
5207   {
5208     GCTraceTime(Debug, gc, phases) t("Reference Processing", _gc_timer_cm);
5209 
5210     // Setup keep_alive and complete closures.
5211     CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
5212                                             &_markStack, false /* !preclean */);
5213     CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
5214                                   _span, &_markBitMap, &_markStack,
5215                                   &cmsKeepAliveClosure, false /* !preclean */);
5216 
5217     ReferenceProcessorStats stats;
5218     if (rp->processing_is_mt()) {
5219       // Set the degree of MT here.  If the discovery is done MT, there
5220       // may have been a different number of threads doing the discovery
5221       // and a different number of discovered lists may have Ref objects.
5222       // That is OK as long as the Reference lists are balanced (see
5223       // balance_all_queues() and balance_queues()).
5224       CMSHeap* heap = CMSHeap::heap();
5225       uint active_workers = ParallelGCThreads;
5226       WorkGang* workers = heap->workers();
5227       if (workers != NULL) {
5228         active_workers = workers->active_workers();
5229         // The expectation is that active_workers will have already
5230         // been set to a reasonable value.  If it has not been set,
5231         // investigate.
5232         assert(active_workers > 0, "Should have been set during scavenge");
5233       }
5234       rp->set_active_mt_degree(active_workers);
5235       CMSRefProcTaskExecutor task_executor(*this);
5236       stats = rp->process_discovered_references(&_is_alive_closure,
5237                                         &cmsKeepAliveClosure,
5238                                         &cmsDrainMarkingStackClosure,
5239                                         &task_executor,
5240                                         &pt);
5241     } else {
5242       stats = rp->process_discovered_references(&_is_alive_closure,
5243                                         &cmsKeepAliveClosure,
5244                                         &cmsDrainMarkingStackClosure,
5245                                         NULL,
5246                                         &pt);
5247     }
5248     _gc_tracer_cm->report_gc_reference_stats(stats);
5249     pt.print_all_references();
5250   }
5251 
5252   // This is the point where the entire marking should have completed.
5253   verify_work_stacks_empty();
5254 
5255   {
5256     GCTraceTime(Debug, gc, phases) t("Weak Processing", _gc_timer_cm);
5257     WeakProcessor::weak_oops_do(&_is_alive_closure, &do_nothing_cl);
5258   }
5259 
5260   if (should_unload_classes()) {
5261     {
5262       GCTraceTime(Debug, gc, phases) t("Class Unloading", _gc_timer_cm);
5263 
5264       // Unload classes and purge the SystemDictionary.
5265       bool purged_class = SystemDictionary::do_unloading(_gc_timer_cm);
5266 
5267       // Unload nmethods.
5268       CodeCache::do_unloading(&_is_alive_closure, purged_class);
5269 
5270       // Prune dead klasses from subklass/sibling/implementor lists.
5271       Klass::clean_weak_klass_links(purged_class);
5272     }
5273 
5274     {
5275       GCTraceTime(Debug, gc, phases) t("Scrub Symbol Table", _gc_timer_cm);
5276       // Clean up unreferenced symbols in symbol table.
5277       SymbolTable::unlink();
5278     }
5279 
5280     {
5281       GCTraceTime(Debug, gc, phases) t("Scrub String Table", _gc_timer_cm);
5282       // Delete entries for dead interned strings.
5283       StringTable::unlink(&_is_alive_closure);
5284     }
5285   }
5286 
5287   // Restore any preserved marks as a result of mark stack or
5288   // work queue overflow
5289   restore_preserved_marks_if_any();  // done single-threaded for now
5290 
5291   rp->set_enqueuing_is_done(true);
5292   rp->verify_no_references_recorded();
5293 }
5294 
5295 #ifndef PRODUCT
5296 void CMSCollector::check_correct_thread_executing() {
5297   Thread* t = Thread::current();
5298   // Only the VM thread or the CMS thread should be here.
5299   assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
5300          "Unexpected thread type");
5301   // If this is the vm thread, the foreground process
5302   // should not be waiting.  Note that _foregroundGCIsActive is
5303   // true while the foreground collector is waiting.
5304   if (_foregroundGCShouldWait) {
5305     // We cannot be the VM thread
5306     assert(t->is_ConcurrentGC_thread(),
5307            "Should be CMS thread");
5308   } else {
5309     // We can be the CMS thread only if we are in a stop-world
5310     // phase of CMS collection.
5311     if (t->is_ConcurrentGC_thread()) {
5312       assert(_collectorState == InitialMarking ||
5313              _collectorState == FinalMarking,
5314              "Should be a stop-world phase");
5315       // The CMS thread should be holding the CMS_token.
5316       assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5317              "Potential interference with concurrently "
5318              "executing VM thread");
5319     }
5320   }
5321 }
5322 #endif
5323 
5324 void CMSCollector::sweep() {
5325   assert(_collectorState == Sweeping, "just checking");
5326   check_correct_thread_executing();
5327   verify_work_stacks_empty();
5328   verify_overflow_empty();
5329   increment_sweep_count();
5330   TraceCMSMemoryManagerStats tms(_collectorState, CMSHeap::heap()->gc_cause());
5331 
5332   _inter_sweep_timer.stop();
5333   _inter_sweep_estimate.sample(_inter_sweep_timer.seconds());
5334 
5335   assert(!_intra_sweep_timer.is_active(), "Should not be active");
5336   _intra_sweep_timer.reset();
5337   _intra_sweep_timer.start();
5338   {
5339     GCTraceCPUTime tcpu;
5340     CMSPhaseAccounting pa(this, "Concurrent Sweep");
5341     // First sweep the old gen
5342     {
5343       CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
5344                                bitMapLock());
5345       sweepWork(_cmsGen);
5346     }
5347 
5348     // Update Universe::_heap_*_at_gc figures.
5349     // We need all the free list locks to make the abstract state
5350     // transition from Sweeping to Resetting. See detailed note
5351     // further below.
5352     {
5353       CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock());
5354       // Update heap occupancy information which is used as
5355       // input to soft ref clearing policy at the next gc.
5356       Universe::update_heap_info_at_gc();
5357       _collectorState = Resizing;
5358     }
5359   }
5360   verify_work_stacks_empty();
5361   verify_overflow_empty();
5362 
5363   if (should_unload_classes()) {
5364     // Delay purge to the beginning of the next safepoint.  Metaspace::contains
5365     // requires that the virtual spaces are stable and not deleted.
5366     ClassLoaderDataGraph::set_should_purge(true);
5367   }
5368 
5369   _intra_sweep_timer.stop();
5370   _intra_sweep_estimate.sample(_intra_sweep_timer.seconds());
5371 
5372   _inter_sweep_timer.reset();
5373   _inter_sweep_timer.start();
5374 
5375   // We need to use a monotonically non-decreasing time in ms
5376   // or we will see time-warp warnings and os::javaTimeMillis()
5377   // does not guarantee monotonicity.
5378   jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
5379   update_time_of_last_gc(now);
5380 
5381   // NOTE on abstract state transitions:
5382   // Mutators allocate-live and/or mark the mod-union table dirty
5383   // based on the state of the collection.  The former is done in
5384   // the interval [Marking, Sweeping] and the latter in the interval
5385   // [Marking, Sweeping).  Thus the transitions into the Marking state
5386   // and out of the Sweeping state must be synchronously visible
5387   // globally to the mutators.
5388   // The transition into the Marking state happens with the world
5389   // stopped so the mutators will globally see it.  Sweeping is
5390   // done asynchronously by the background collector so the transition
5391   // from the Sweeping state to the Resizing state must be done
5392   // under the freelistLock (as is the check for whether to
5393   // allocate-live and whether to dirty the mod-union table).
5394   assert(_collectorState == Resizing, "Change of collector state to"
5395     " Resizing must be done under the freelistLocks (plural)");
5396 
5397   // Now that sweeping has been completed, we clear
5398   // the incremental_collection_failed flag,
5399   // thus inviting a younger gen collection to promote into
5400   // this generation. If such a promotion may still fail,
5401   // the flag will be set again when a young collection is
5402   // attempted.
5403   CMSHeap* heap = CMSHeap::heap();
5404   heap->clear_incremental_collection_failed();  // Worth retrying as fresh space may have been freed up
5405   heap->update_full_collections_completed(_collection_count_start);
5406 }
5407 
5408 // FIX ME!!! Looks like this belongs in CFLSpace, with
5409 // CMSGen merely delegating to it.
5410 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
5411   double nearLargestPercent = FLSLargestBlockCoalesceProximity;
5412   HeapWord*  minAddr        = _cmsSpace->bottom();
5413   HeapWord*  largestAddr    =
5414     (HeapWord*) _cmsSpace->dictionary()->find_largest_dict();
5415   if (largestAddr == NULL) {
5416     // The dictionary appears to be empty.  In this case
5417     // try to coalesce at the end of the heap.
5418     largestAddr = _cmsSpace->end();
5419   }
5420   size_t largestOffset     = pointer_delta(largestAddr, minAddr);
5421   size_t nearLargestOffset =
5422     (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
5423   log_debug(gc, freelist)("CMS: Large Block: " PTR_FORMAT "; Proximity: " PTR_FORMAT " -> " PTR_FORMAT,
5424                           p2i(largestAddr), p2i(_cmsSpace->nearLargestChunk()), p2i(minAddr + nearLargestOffset));
5425   _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
5426 }
5427 
5428 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
5429   return addr >= _cmsSpace->nearLargestChunk();
5430 }
5431 
5432 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
5433   return _cmsSpace->find_chunk_at_end();
5434 }
5435 
5436 void ConcurrentMarkSweepGeneration::update_gc_stats(Generation* current_generation,
5437                                                     bool full) {
5438   // If the young generation has been collected, gather any statistics
5439   // that are of interest at this point.
5440   bool current_is_young = CMSHeap::heap()->is_young_gen(current_generation);
5441   if (!full && current_is_young) {
5442     // Gather statistics on the young generation collection.
5443     collector()->stats().record_gc0_end(used());
5444   }
5445 }
5446 
5447 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* old_gen) {
5448   // We iterate over the space(s) underlying this generation,
5449   // checking the mark bit map to see if the bits corresponding
5450   // to specific blocks are marked or not. Blocks that are
5451   // marked are live and are not swept up. All remaining blocks
5452   // are swept up, with coalescing on-the-fly as we sweep up
5453   // contiguous free and/or garbage blocks:
5454   // We need to ensure that the sweeper synchronizes with allocators
5455   // and stop-the-world collectors. In particular, the following
5456   // locks are used:
5457   // . CMS token: if this is held, a stop the world collection cannot occur
5458   // . freelistLock: if this is held no allocation can occur from this
5459   //                 generation by another thread
5460   // . bitMapLock: if this is held, no other thread can access or update
5461   //
5462 
5463   // Note that we need to hold the freelistLock if we use
5464   // block iterate below; else the iterator might go awry if
5465   // a mutator (or promotion) causes block contents to change
5466   // (for instance if the allocator divvies up a block).
5467   // If we hold the free list lock, for all practical purposes
5468   // young generation GC's can't occur (they'll usually need to
5469   // promote), so we might as well prevent all young generation
5470   // GC's while we do a sweeping step. For the same reason, we might
5471   // as well take the bit map lock for the entire duration
5472 
5473   // check that we hold the requisite locks
5474   assert(have_cms_token(), "Should hold cms token");
5475   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), "Should possess CMS token to sweep");
5476   assert_lock_strong(old_gen->freelistLock());
5477   assert_lock_strong(bitMapLock());
5478 
5479   assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context");
5480   assert(_intra_sweep_timer.is_active(),  "Was switched on  in an outer context");
5481   old_gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
5482                                           _inter_sweep_estimate.padded_average(),
5483                                           _intra_sweep_estimate.padded_average());
5484   old_gen->setNearLargestChunk();
5485 
5486   {
5487     SweepClosure sweepClosure(this, old_gen, &_markBitMap, CMSYield);
5488     old_gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
5489     // We need to free-up/coalesce garbage/blocks from a
5490     // co-terminal free run. This is done in the SweepClosure
5491     // destructor; so, do not remove this scope, else the
5492     // end-of-sweep-census below will be off by a little bit.
5493   }
5494   old_gen->cmsSpace()->sweep_completed();
5495   old_gen->cmsSpace()->endSweepFLCensus(sweep_count());
5496   if (should_unload_classes()) {                // unloaded classes this cycle,
5497     _concurrent_cycles_since_last_unload = 0;   // ... reset count
5498   } else {                                      // did not unload classes,
5499     _concurrent_cycles_since_last_unload++;     // ... increment count
5500   }
5501 }
5502 
5503 // Reset CMS data structures (for now just the marking bit map)
5504 // preparatory for the next cycle.
5505 void CMSCollector::reset_concurrent() {
5506   CMSTokenSyncWithLocks ts(true, bitMapLock());
5507 
5508   // If the state is not "Resetting", the foreground  thread
5509   // has done a collection and the resetting.
5510   if (_collectorState != Resetting) {
5511     assert(_collectorState == Idling, "The state should only change"
5512       " because the foreground collector has finished the collection");
5513     return;
5514   }
5515 
5516   {
5517     // Clear the mark bitmap (no grey objects to start with)
5518     // for the next cycle.
5519     GCTraceCPUTime tcpu;
5520     CMSPhaseAccounting cmspa(this, "Concurrent Reset");
5521 
5522     HeapWord* curAddr = _markBitMap.startWord();
5523     while (curAddr < _markBitMap.endWord()) {
5524       size_t remaining  = pointer_delta(_markBitMap.endWord(), curAddr);
5525       MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
5526       _markBitMap.clear_large_range(chunk);
5527       if (ConcurrentMarkSweepThread::should_yield() &&
5528           !foregroundGCIsActive() &&
5529           CMSYield) {
5530         assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5531                "CMS thread should hold CMS token");
5532         assert_lock_strong(bitMapLock());
5533         bitMapLock()->unlock();
5534         ConcurrentMarkSweepThread::desynchronize(true);
5535         stopTimer();
5536         incrementYields();
5537 
5538         // See the comment in coordinator_yield()
5539         for (unsigned i = 0; i < CMSYieldSleepCount &&
5540                          ConcurrentMarkSweepThread::should_yield() &&
5541                          !CMSCollector::foregroundGCIsActive(); ++i) {
5542           os::sleep(Thread::current(), 1, false);
5543         }
5544 
5545         ConcurrentMarkSweepThread::synchronize(true);
5546         bitMapLock()->lock_without_safepoint_check();
5547         startTimer();
5548       }
5549       curAddr = chunk.end();
5550     }
5551     // A successful mostly concurrent collection has been done.
5552     // Because only the full (i.e., concurrent mode failure) collections
5553     // are being measured for gc overhead limits, clean the "near" flag
5554     // and count.
5555     size_policy()->reset_gc_overhead_limit_count();
5556     _collectorState = Idling;
5557   }
5558 
5559   register_gc_end();
5560 }
5561 
5562 // Same as above but for STW paths
5563 void CMSCollector::reset_stw() {
5564   // already have the lock
5565   assert(_collectorState == Resetting, "just checking");
5566   assert_lock_strong(bitMapLock());
5567   GCIdMark gc_id_mark(_cmsThread->gc_id());
5568   _markBitMap.clear_all();
5569   _collectorState = Idling;
5570   register_gc_end();
5571 }
5572 
5573 void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) {
5574   GCTraceCPUTime tcpu;
5575   TraceCollectorStats tcs_cgc(cgc_counters());
5576 
5577   switch (op) {
5578     case CMS_op_checkpointRootsInitial: {
5579       GCTraceTime(Info, gc) t("Pause Initial Mark", NULL, GCCause::_no_gc, true);
5580       SvcGCMarker sgcm(SvcGCMarker::CONCURRENT);
5581       checkpointRootsInitial();
5582       break;
5583     }
5584     case CMS_op_checkpointRootsFinal: {
5585       GCTraceTime(Info, gc) t("Pause Remark", NULL, GCCause::_no_gc, true);
5586       SvcGCMarker sgcm(SvcGCMarker::CONCURRENT);
5587       checkpointRootsFinal();
5588       break;
5589     }
5590     default:
5591       fatal("No such CMS_op");
5592   }
5593 }
5594 
5595 #ifndef PRODUCT
5596 size_t const CMSCollector::skip_header_HeapWords() {
5597   return FreeChunk::header_size();
5598 }
5599 
5600 // Try and collect here conditions that should hold when
5601 // CMS thread is exiting. The idea is that the foreground GC
5602 // thread should not be blocked if it wants to terminate
5603 // the CMS thread and yet continue to run the VM for a while
5604 // after that.
5605 void CMSCollector::verify_ok_to_terminate() const {
5606   assert(Thread::current()->is_ConcurrentGC_thread(),
5607          "should be called by CMS thread");
5608   assert(!_foregroundGCShouldWait, "should be false");
5609   // We could check here that all the various low-level locks
5610   // are not held by the CMS thread, but that is overkill; see
5611   // also CMSThread::verify_ok_to_terminate() where the CGC_lock
5612   // is checked.
5613 }
5614 #endif
5615 
5616 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
5617    assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
5618           "missing Printezis mark?");
5619   HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5620   size_t size = pointer_delta(nextOneAddr + 1, addr);
5621   assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5622          "alignment problem");
5623   assert(size >= 3, "Necessary for Printezis marks to work");
5624   return size;
5625 }
5626 
5627 // A variant of the above (block_size_using_printezis_bits()) except
5628 // that we return 0 if the P-bits are not yet set.
5629 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
5630   if (_markBitMap.isMarked(addr + 1)) {
5631     assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects");
5632     HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5633     size_t size = pointer_delta(nextOneAddr + 1, addr);
5634     assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5635            "alignment problem");
5636     assert(size >= 3, "Necessary for Printezis marks to work");
5637     return size;
5638   }
5639   return 0;
5640 }
5641 
5642 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
5643   size_t sz = 0;
5644   oop p = (oop)addr;
5645   if (p->klass_or_null_acquire() != NULL) {
5646     sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
5647   } else {
5648     sz = block_size_using_printezis_bits(addr);
5649   }
5650   assert(sz > 0, "size must be nonzero");
5651   HeapWord* next_block = addr + sz;
5652   HeapWord* next_card  = align_up(next_block, CardTable::card_size);
5653   assert(align_down((uintptr_t)addr,      CardTable::card_size) <
5654          align_down((uintptr_t)next_card, CardTable::card_size),
5655          "must be different cards");
5656   return next_card;
5657 }
5658 
5659 
5660 // CMS Bit Map Wrapper /////////////////////////////////////////
5661 
5662 // Construct a CMS bit map infrastructure, but don't create the
5663 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
5664 // further below.
5665 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
5666   _shifter(shifter),
5667   _bm(),
5668   _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true,
5669                                     Monitor::_safepoint_check_sometimes) : NULL)
5670 {
5671   _bmStartWord = 0;
5672   _bmWordSize  = 0;
5673 }
5674 
5675 bool CMSBitMap::allocate(MemRegion mr) {
5676   _bmStartWord = mr.start();
5677   _bmWordSize  = mr.word_size();
5678   ReservedSpace brs(ReservedSpace::allocation_align_size_up(
5679                      (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
5680   if (!brs.is_reserved()) {
5681     log_warning(gc)("CMS bit map allocation failure");
5682     return false;
5683   }
5684   // For now we'll just commit all of the bit map up front.
5685   // Later on we'll try to be more parsimonious with swap.
5686   if (!_virtual_space.initialize(brs, brs.size())) {
5687     log_warning(gc)("CMS bit map backing store failure");
5688     return false;
5689   }
5690   assert(_virtual_space.committed_size() == brs.size(),
5691          "didn't reserve backing store for all of CMS bit map?");
5692   assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
5693          _bmWordSize, "inconsistency in bit map sizing");
5694   _bm = BitMapView((BitMap::bm_word_t*)_virtual_space.low(), _bmWordSize >> _shifter);
5695 
5696   // bm.clear(); // can we rely on getting zero'd memory? verify below
5697   assert(isAllClear(),
5698          "Expected zero'd memory from ReservedSpace constructor");
5699   assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
5700          "consistency check");
5701   return true;
5702 }
5703 
5704 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
5705   HeapWord *next_addr, *end_addr, *last_addr;
5706   assert_locked();
5707   assert(covers(mr), "out-of-range error");
5708   // XXX assert that start and end are appropriately aligned
5709   for (next_addr = mr.start(), end_addr = mr.end();
5710        next_addr < end_addr; next_addr = last_addr) {
5711     MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
5712     last_addr = dirty_region.end();
5713     if (!dirty_region.is_empty()) {
5714       cl->do_MemRegion(dirty_region);
5715     } else {
5716       assert(last_addr == end_addr, "program logic");
5717       return;
5718     }
5719   }
5720 }
5721 
5722 void CMSBitMap::print_on_error(outputStream* st, const char* prefix) const {
5723   _bm.print_on_error(st, prefix);
5724 }
5725 
5726 #ifndef PRODUCT
5727 void CMSBitMap::assert_locked() const {
5728   CMSLockVerifier::assert_locked(lock());
5729 }
5730 
5731 bool CMSBitMap::covers(MemRegion mr) const {
5732   // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
5733   assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
5734          "size inconsistency");
5735   return (mr.start() >= _bmStartWord) &&
5736          (mr.end()   <= endWord());
5737 }
5738 
5739 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
5740     return (start >= _bmStartWord && (start + size) <= endWord());
5741 }
5742 
5743 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
5744   // verify that there are no 1 bits in the interval [left, right)
5745   FalseBitMapClosure falseBitMapClosure;
5746   iterate(&falseBitMapClosure, left, right);
5747 }
5748 
5749 void CMSBitMap::region_invariant(MemRegion mr)
5750 {
5751   assert_locked();
5752   // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
5753   assert(!mr.is_empty(), "unexpected empty region");
5754   assert(covers(mr), "mr should be covered by bit map");
5755   // convert address range into offset range
5756   size_t start_ofs = heapWordToOffset(mr.start());
5757   // Make sure that end() is appropriately aligned
5758   assert(mr.end() == align_up(mr.end(), (1 << (_shifter+LogHeapWordSize))),
5759          "Misaligned mr.end()");
5760   size_t end_ofs   = heapWordToOffset(mr.end());
5761   assert(end_ofs > start_ofs, "Should mark at least one bit");
5762 }
5763 
5764 #endif
5765 
5766 bool CMSMarkStack::allocate(size_t size) {
5767   // allocate a stack of the requisite depth
5768   ReservedSpace rs(ReservedSpace::allocation_align_size_up(
5769                    size * sizeof(oop)));
5770   if (!rs.is_reserved()) {
5771     log_warning(gc)("CMSMarkStack allocation failure");
5772     return false;
5773   }
5774   if (!_virtual_space.initialize(rs, rs.size())) {
5775     log_warning(gc)("CMSMarkStack backing store failure");
5776     return false;
5777   }
5778   assert(_virtual_space.committed_size() == rs.size(),
5779          "didn't reserve backing store for all of CMS stack?");
5780   _base = (oop*)(_virtual_space.low());
5781   _index = 0;
5782   _capacity = size;
5783   NOT_PRODUCT(_max_depth = 0);
5784   return true;
5785 }
5786 
5787 // XXX FIX ME !!! In the MT case we come in here holding a
5788 // leaf lock. For printing we need to take a further lock
5789 // which has lower rank. We need to recalibrate the two
5790 // lock-ranks involved in order to be able to print the
5791 // messages below. (Or defer the printing to the caller.
5792 // For now we take the expedient path of just disabling the
5793 // messages for the problematic case.)
5794 void CMSMarkStack::expand() {
5795   assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted");
5796   if (_capacity == MarkStackSizeMax) {
5797     if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled) {
5798       // We print a warning message only once per CMS cycle.
5799       log_debug(gc)(" (benign) Hit CMSMarkStack max size limit");
5800     }
5801     return;
5802   }
5803   // Double capacity if possible
5804   size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax);
5805   // Do not give up existing stack until we have managed to
5806   // get the double capacity that we desired.
5807   ReservedSpace rs(ReservedSpace::allocation_align_size_up(
5808                    new_capacity * sizeof(oop)));
5809   if (rs.is_reserved()) {
5810     // Release the backing store associated with old stack
5811     _virtual_space.release();
5812     // Reinitialize virtual space for new stack
5813     if (!_virtual_space.initialize(rs, rs.size())) {
5814       fatal("Not enough swap for expanded marking stack");
5815     }
5816     _base = (oop*)(_virtual_space.low());
5817     _index = 0;
5818     _capacity = new_capacity;
5819   } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled) {
5820     // Failed to double capacity, continue;
5821     // we print a detail message only once per CMS cycle.
5822     log_debug(gc)(" (benign) Failed to expand marking stack from " SIZE_FORMAT "K to " SIZE_FORMAT "K",
5823                         _capacity / K, new_capacity / K);
5824   }
5825 }
5826 
5827 
5828 // Closures
5829 // XXX: there seems to be a lot of code  duplication here;
5830 // should refactor and consolidate common code.
5831 
5832 // This closure is used to mark refs into the CMS generation in
5833 // the CMS bit map. Called at the first checkpoint. This closure
5834 // assumes that we do not need to re-mark dirty cards; if the CMS
5835 // generation on which this is used is not an oldest
5836 // generation then this will lose younger_gen cards!
5837 
5838 MarkRefsIntoClosure::MarkRefsIntoClosure(
5839   MemRegion span, CMSBitMap* bitMap):
5840     _span(span),
5841     _bitMap(bitMap)
5842 {
5843   assert(ref_discoverer() == NULL, "deliberately left NULL");
5844   assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
5845 }
5846 
5847 void MarkRefsIntoClosure::do_oop(oop obj) {
5848   // if p points into _span, then mark corresponding bit in _markBitMap
5849   assert(oopDesc::is_oop(obj), "expected an oop");
5850   HeapWord* addr = (HeapWord*)obj;
5851   if (_span.contains(addr)) {
5852     // this should be made more efficient
5853     _bitMap->mark(addr);
5854   }
5855 }
5856 
5857 ParMarkRefsIntoClosure::ParMarkRefsIntoClosure(
5858   MemRegion span, CMSBitMap* bitMap):
5859     _span(span),
5860     _bitMap(bitMap)
5861 {
5862   assert(ref_discoverer() == NULL, "deliberately left NULL");
5863   assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
5864 }
5865 
5866 void ParMarkRefsIntoClosure::do_oop(oop obj) {
5867   // if p points into _span, then mark corresponding bit in _markBitMap
5868   assert(oopDesc::is_oop(obj), "expected an oop");
5869   HeapWord* addr = (HeapWord*)obj;
5870   if (_span.contains(addr)) {
5871     // this should be made more efficient
5872     _bitMap->par_mark(addr);
5873   }
5874 }
5875 
5876 // A variant of the above, used for CMS marking verification.
5877 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
5878   MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm):
5879     _span(span),
5880     _verification_bm(verification_bm),
5881     _cms_bm(cms_bm)
5882 {
5883   assert(ref_discoverer() == NULL, "deliberately left NULL");
5884   assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
5885 }
5886 
5887 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
5888   // if p points into _span, then mark corresponding bit in _markBitMap
5889   assert(oopDesc::is_oop(obj), "expected an oop");
5890   HeapWord* addr = (HeapWord*)obj;
5891   if (_span.contains(addr)) {
5892     _verification_bm->mark(addr);
5893     if (!_cms_bm->isMarked(addr)) {
5894       Log(gc, verify) log;
5895       ResourceMark rm;
5896       LogStream ls(log.error());
5897       oop(addr)->print_on(&ls);
5898       log.error(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
5899       fatal("... aborting");
5900     }
5901   }
5902 }
5903 
5904 //////////////////////////////////////////////////
5905 // MarkRefsIntoAndScanClosure
5906 //////////////////////////////////////////////////
5907 
5908 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
5909                                                        ReferenceDiscoverer* rd,
5910                                                        CMSBitMap* bit_map,
5911                                                        CMSBitMap* mod_union_table,
5912                                                        CMSMarkStack*  mark_stack,
5913                                                        CMSCollector* collector,
5914                                                        bool should_yield,
5915                                                        bool concurrent_precleaning):
5916   _span(span),
5917   _bit_map(bit_map),
5918   _mark_stack(mark_stack),
5919   _pushAndMarkClosure(collector, span, rd, bit_map, mod_union_table,
5920                       mark_stack, concurrent_precleaning),
5921   _collector(collector),
5922   _freelistLock(NULL),
5923   _yield(should_yield),
5924   _concurrent_precleaning(concurrent_precleaning)
5925 {
5926   // FIXME: Should initialize in base class constructor.
5927   assert(rd != NULL, "ref_discoverer shouldn't be NULL");
5928   set_ref_discoverer_internal(rd);
5929 }
5930 
5931 // This closure is used to mark refs into the CMS generation at the
5932 // second (final) checkpoint, and to scan and transitively follow
5933 // the unmarked oops. It is also used during the concurrent precleaning
5934 // phase while scanning objects on dirty cards in the CMS generation.
5935 // The marks are made in the marking bit map and the marking stack is
5936 // used for keeping the (newly) grey objects during the scan.
5937 // The parallel version (Par_...) appears further below.
5938 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
5939   if (obj != NULL) {
5940     assert(oopDesc::is_oop(obj), "expected an oop");
5941     HeapWord* addr = (HeapWord*)obj;
5942     assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
5943     assert(_collector->overflow_list_is_empty(),
5944            "overflow list should be empty");
5945     if (_span.contains(addr) &&
5946         !_bit_map->isMarked(addr)) {
5947       // mark bit map (object is now grey)
5948       _bit_map->mark(addr);
5949       // push on marking stack (stack should be empty), and drain the
5950       // stack by applying this closure to the oops in the oops popped
5951       // from the stack (i.e. blacken the grey objects)
5952       bool res = _mark_stack->push(obj);
5953       assert(res, "Should have space to push on empty stack");
5954       do {
5955         oop new_oop = _mark_stack->pop();
5956         assert(new_oop != NULL && oopDesc::is_oop(new_oop), "Expected an oop");
5957         assert(_bit_map->isMarked((HeapWord*)new_oop),
5958                "only grey objects on this stack");
5959         // iterate over the oops in this oop, marking and pushing
5960         // the ones in CMS heap (i.e. in _span).
5961         new_oop->oop_iterate(&_pushAndMarkClosure);
5962         // check if it's time to yield
5963         do_yield_check();
5964       } while (!_mark_stack->isEmpty() ||
5965                (!_concurrent_precleaning && take_from_overflow_list()));
5966         // if marking stack is empty, and we are not doing this
5967         // during precleaning, then check the overflow list
5968     }
5969     assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
5970     assert(_collector->overflow_list_is_empty(),
5971            "overflow list was drained above");
5972 
5973     assert(_collector->no_preserved_marks(),
5974            "All preserved marks should have been restored above");
5975   }
5976 }
5977 
5978 void MarkRefsIntoAndScanClosure::do_yield_work() {
5979   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5980          "CMS thread should hold CMS token");
5981   assert_lock_strong(_freelistLock);
5982   assert_lock_strong(_bit_map->lock());
5983   // relinquish the free_list_lock and bitMaplock()
5984   _bit_map->lock()->unlock();
5985   _freelistLock->unlock();
5986   ConcurrentMarkSweepThread::desynchronize(true);
5987   _collector->stopTimer();
5988   _collector->incrementYields();
5989 
5990   // See the comment in coordinator_yield()
5991   for (unsigned i = 0;
5992        i < CMSYieldSleepCount &&
5993        ConcurrentMarkSweepThread::should_yield() &&
5994        !CMSCollector::foregroundGCIsActive();
5995        ++i) {
5996     os::sleep(Thread::current(), 1, false);
5997   }
5998 
5999   ConcurrentMarkSweepThread::synchronize(true);
6000   _freelistLock->lock_without_safepoint_check();
6001   _bit_map->lock()->lock_without_safepoint_check();
6002   _collector->startTimer();
6003 }
6004 
6005 ///////////////////////////////////////////////////////////
6006 // ParMarkRefsIntoAndScanClosure: a parallel version of
6007 //                                MarkRefsIntoAndScanClosure
6008 ///////////////////////////////////////////////////////////
6009 ParMarkRefsIntoAndScanClosure::ParMarkRefsIntoAndScanClosure(
6010   CMSCollector* collector, MemRegion span, ReferenceDiscoverer* rd,
6011   CMSBitMap* bit_map, OopTaskQueue* work_queue):
6012   _span(span),
6013   _bit_map(bit_map),
6014   _work_queue(work_queue),
6015   _low_water_mark(MIN2((work_queue->max_elems()/4),
6016                        ((uint)CMSWorkQueueDrainThreshold * ParallelGCThreads))),
6017   _parPushAndMarkClosure(collector, span, rd, bit_map, work_queue)
6018 {
6019   // FIXME: Should initialize in base class constructor.
6020   assert(rd != NULL, "ref_discoverer shouldn't be NULL");
6021   set_ref_discoverer_internal(rd);
6022 }
6023 
6024 // This closure is used to mark refs into the CMS generation at the
6025 // second (final) checkpoint, and to scan and transitively follow
6026 // the unmarked oops. The marks are made in the marking bit map and
6027 // the work_queue is used for keeping the (newly) grey objects during
6028 // the scan phase whence they are also available for stealing by parallel
6029 // threads. Since the marking bit map is shared, updates are
6030 // synchronized (via CAS).
6031 void ParMarkRefsIntoAndScanClosure::do_oop(oop obj) {
6032   if (obj != NULL) {
6033     // Ignore mark word because this could be an already marked oop
6034     // that may be chained at the end of the overflow list.
6035     assert(oopDesc::is_oop(obj, true), "expected an oop");
6036     HeapWord* addr = (HeapWord*)obj;
6037     if (_span.contains(addr) &&
6038         !_bit_map->isMarked(addr)) {
6039       // mark bit map (object will become grey):
6040       // It is possible for several threads to be
6041       // trying to "claim" this object concurrently;
6042       // the unique thread that succeeds in marking the
6043       // object first will do the subsequent push on
6044       // to the work queue (or overflow list).
6045       if (_bit_map->par_mark(addr)) {
6046         // push on work_queue (which may not be empty), and trim the
6047         // queue to an appropriate length by applying this closure to
6048         // the oops in the oops popped from the stack (i.e. blacken the
6049         // grey objects)
6050         bool res = _work_queue->push(obj);
6051         assert(res, "Low water mark should be less than capacity?");
6052         trim_queue(_low_water_mark);
6053       } // Else, another thread claimed the object
6054     }
6055   }
6056 }
6057 
6058 // This closure is used to rescan the marked objects on the dirty cards
6059 // in the mod union table and the card table proper.
6060 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
6061   oop p, MemRegion mr) {
6062 
6063   size_t size = 0;
6064   HeapWord* addr = (HeapWord*)p;
6065   DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6066   assert(_span.contains(addr), "we are scanning the CMS generation");
6067   // check if it's time to yield
6068   if (do_yield_check()) {
6069     // We yielded for some foreground stop-world work,
6070     // and we have been asked to abort this ongoing preclean cycle.
6071     return 0;
6072   }
6073   if (_bitMap->isMarked(addr)) {
6074     // it's marked; is it potentially uninitialized?
6075     if (p->klass_or_null_acquire() != NULL) {
6076         // an initialized object; ignore mark word in verification below
6077         // since we are running concurrent with mutators
6078         assert(oopDesc::is_oop(p, true), "should be an oop");
6079         if (p->is_objArray()) {
6080           // objArrays are precisely marked; restrict scanning
6081           // to dirty cards only.
6082           size = CompactibleFreeListSpace::adjustObjectSize(
6083                    p->oop_iterate_size(_scanningClosure, mr));
6084         } else {
6085           // A non-array may have been imprecisely marked; we need
6086           // to scan object in its entirety.
6087           size = CompactibleFreeListSpace::adjustObjectSize(
6088                    p->oop_iterate_size(_scanningClosure));
6089         }
6090       #ifdef ASSERT
6091         size_t direct_size =
6092           CompactibleFreeListSpace::adjustObjectSize(p->size());
6093         assert(size == direct_size, "Inconsistency in size");
6094         assert(size >= 3, "Necessary for Printezis marks to work");
6095         HeapWord* start_pbit = addr + 1;
6096         HeapWord* end_pbit = addr + size - 1;
6097         assert(_bitMap->isMarked(start_pbit) == _bitMap->isMarked(end_pbit),
6098                "inconsistent Printezis mark");
6099         // Verify inner mark bits (between Printezis bits) are clear,
6100         // but don't repeat if there are multiple dirty regions for
6101         // the same object, to avoid potential O(N^2) performance.
6102         if (addr != _last_scanned_object) {
6103           _bitMap->verifyNoOneBitsInRange(start_pbit + 1, end_pbit);
6104           _last_scanned_object = addr;
6105         }
6106       #endif // ASSERT
6107     } else {
6108       // An uninitialized object.
6109       assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
6110       HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
6111       size = pointer_delta(nextOneAddr + 1, addr);
6112       assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6113              "alignment problem");
6114       // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
6115       // will dirty the card when the klass pointer is installed in the
6116       // object (signaling the completion of initialization).
6117     }
6118   } else {
6119     // Either a not yet marked object or an uninitialized object
6120     if (p->klass_or_null_acquire() == NULL) {
6121       // An uninitialized object, skip to the next card, since
6122       // we may not be able to read its P-bits yet.
6123       assert(size == 0, "Initial value");
6124     } else {
6125       // An object not (yet) reached by marking: we merely need to
6126       // compute its size so as to go look at the next block.
6127       assert(oopDesc::is_oop(p, true), "should be an oop");
6128       size = CompactibleFreeListSpace::adjustObjectSize(p->size());
6129     }
6130   }
6131   DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6132   return size;
6133 }
6134 
6135 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
6136   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6137          "CMS thread should hold CMS token");
6138   assert_lock_strong(_freelistLock);
6139   assert_lock_strong(_bitMap->lock());
6140   // relinquish the free_list_lock and bitMaplock()
6141   _bitMap->lock()->unlock();
6142   _freelistLock->unlock();
6143   ConcurrentMarkSweepThread::desynchronize(true);
6144   _collector->stopTimer();
6145   _collector->incrementYields();
6146 
6147   // See the comment in coordinator_yield()
6148   for (unsigned i = 0; i < CMSYieldSleepCount &&
6149                    ConcurrentMarkSweepThread::should_yield() &&
6150                    !CMSCollector::foregroundGCIsActive(); ++i) {
6151     os::sleep(Thread::current(), 1, false);
6152   }
6153 
6154   ConcurrentMarkSweepThread::synchronize(true);
6155   _freelistLock->lock_without_safepoint_check();
6156   _bitMap->lock()->lock_without_safepoint_check();
6157   _collector->startTimer();
6158 }
6159 
6160 
6161 //////////////////////////////////////////////////////////////////
6162 // SurvivorSpacePrecleanClosure
6163 //////////////////////////////////////////////////////////////////
6164 // This (single-threaded) closure is used to preclean the oops in
6165 // the survivor spaces.
6166 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
6167 
6168   HeapWord* addr = (HeapWord*)p;
6169   DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6170   assert(!_span.contains(addr), "we are scanning the survivor spaces");
6171   assert(p->klass_or_null() != NULL, "object should be initialized");
6172   // an initialized object; ignore mark word in verification below
6173   // since we are running concurrent with mutators
6174   assert(oopDesc::is_oop(p, true), "should be an oop");
6175   // Note that we do not yield while we iterate over
6176   // the interior oops of p, pushing the relevant ones
6177   // on our marking stack.
6178   size_t size = p->oop_iterate_size(_scanning_closure);
6179   do_yield_check();
6180   // Observe that below, we do not abandon the preclean
6181   // phase as soon as we should; rather we empty the
6182   // marking stack before returning. This is to satisfy
6183   // some existing assertions. In general, it may be a
6184   // good idea to abort immediately and complete the marking
6185   // from the grey objects at a later time.
6186   while (!_mark_stack->isEmpty()) {
6187     oop new_oop = _mark_stack->pop();
6188     assert(new_oop != NULL && oopDesc::is_oop(new_oop), "Expected an oop");
6189     assert(_bit_map->isMarked((HeapWord*)new_oop),
6190            "only grey objects on this stack");
6191     // iterate over the oops in this oop, marking and pushing
6192     // the ones in CMS heap (i.e. in _span).
6193     new_oop->oop_iterate(_scanning_closure);
6194     // check if it's time to yield
6195     do_yield_check();
6196   }
6197   unsigned int after_count =
6198     CMSHeap::heap()->total_collections();
6199   bool abort = (_before_count != after_count) ||
6200                _collector->should_abort_preclean();
6201   return abort ? 0 : size;
6202 }
6203 
6204 void SurvivorSpacePrecleanClosure::do_yield_work() {
6205   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6206          "CMS thread should hold CMS token");
6207   assert_lock_strong(_bit_map->lock());
6208   // Relinquish the bit map lock
6209   _bit_map->lock()->unlock();
6210   ConcurrentMarkSweepThread::desynchronize(true);
6211   _collector->stopTimer();
6212   _collector->incrementYields();
6213 
6214   // See the comment in coordinator_yield()
6215   for (unsigned i = 0; i < CMSYieldSleepCount &&
6216                        ConcurrentMarkSweepThread::should_yield() &&
6217                        !CMSCollector::foregroundGCIsActive(); ++i) {
6218     os::sleep(Thread::current(), 1, false);
6219   }
6220 
6221   ConcurrentMarkSweepThread::synchronize(true);
6222   _bit_map->lock()->lock_without_safepoint_check();
6223   _collector->startTimer();
6224 }
6225 
6226 // This closure is used to rescan the marked objects on the dirty cards
6227 // in the mod union table and the card table proper. In the parallel
6228 // case, although the bitMap is shared, we do a single read so the
6229 // isMarked() query is "safe".
6230 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
6231   // Ignore mark word because we are running concurrent with mutators
6232   assert(oopDesc::is_oop_or_null(p, true), "Expected an oop or NULL at " PTR_FORMAT, p2i(p));
6233   HeapWord* addr = (HeapWord*)p;
6234   assert(_span.contains(addr), "we are scanning the CMS generation");
6235   bool is_obj_array = false;
6236   #ifdef ASSERT
6237     if (!_parallel) {
6238       assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6239       assert(_collector->overflow_list_is_empty(),
6240              "overflow list should be empty");
6241 
6242     }
6243   #endif // ASSERT
6244   if (_bit_map->isMarked(addr)) {
6245     // Obj arrays are precisely marked, non-arrays are not;
6246     // so we scan objArrays precisely and non-arrays in their
6247     // entirety.
6248     if (p->is_objArray()) {
6249       is_obj_array = true;
6250       if (_parallel) {
6251         p->oop_iterate(_par_scan_closure, mr);
6252       } else {
6253         p->oop_iterate(_scan_closure, mr);
6254       }
6255     } else {
6256       if (_parallel) {
6257         p->oop_iterate(_par_scan_closure);
6258       } else {
6259         p->oop_iterate(_scan_closure);
6260       }
6261     }
6262   }
6263   #ifdef ASSERT
6264     if (!_parallel) {
6265       assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6266       assert(_collector->overflow_list_is_empty(),
6267              "overflow list should be empty");
6268 
6269     }
6270   #endif // ASSERT
6271   return is_obj_array;
6272 }
6273 
6274 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
6275                         MemRegion span,
6276                         CMSBitMap* bitMap, CMSMarkStack*  markStack,
6277                         bool should_yield, bool verifying):
6278   _collector(collector),
6279   _span(span),
6280   _bitMap(bitMap),
6281   _mut(&collector->_modUnionTable),
6282   _markStack(markStack),
6283   _yield(should_yield),
6284   _skipBits(0)
6285 {
6286   assert(_markStack->isEmpty(), "stack should be empty");
6287   _finger = _bitMap->startWord();
6288   _threshold = _finger;
6289   assert(_collector->_restart_addr == NULL, "Sanity check");
6290   assert(_span.contains(_finger), "Out of bounds _finger?");
6291   DEBUG_ONLY(_verifying = verifying;)
6292 }
6293 
6294 void MarkFromRootsClosure::reset(HeapWord* addr) {
6295   assert(_markStack->isEmpty(), "would cause duplicates on stack");
6296   assert(_span.contains(addr), "Out of bounds _finger?");
6297   _finger = addr;
6298   _threshold = align_up(_finger, CardTable::card_size);
6299 }
6300 
6301 // Should revisit to see if this should be restructured for
6302 // greater efficiency.
6303 bool MarkFromRootsClosure::do_bit(size_t offset) {
6304   if (_skipBits > 0) {
6305     _skipBits--;
6306     return true;
6307   }
6308   // convert offset into a HeapWord*
6309   HeapWord* addr = _bitMap->startWord() + offset;
6310   assert(_bitMap->endWord() && addr < _bitMap->endWord(),
6311          "address out of range");
6312   assert(_bitMap->isMarked(addr), "tautology");
6313   if (_bitMap->isMarked(addr+1)) {
6314     // this is an allocated but not yet initialized object
6315     assert(_skipBits == 0, "tautology");
6316     _skipBits = 2;  // skip next two marked bits ("Printezis-marks")
6317     oop p = oop(addr);
6318     if (p->klass_or_null_acquire() == NULL) {
6319       DEBUG_ONLY(if (!_verifying) {)
6320         // We re-dirty the cards on which this object lies and increase
6321         // the _threshold so that we'll come back to scan this object
6322         // during the preclean or remark phase. (CMSCleanOnEnter)
6323         if (CMSCleanOnEnter) {
6324           size_t sz = _collector->block_size_using_printezis_bits(addr);
6325           HeapWord* end_card_addr = align_up(addr + sz, CardTable::card_size);
6326           MemRegion redirty_range = MemRegion(addr, end_card_addr);
6327           assert(!redirty_range.is_empty(), "Arithmetical tautology");
6328           // Bump _threshold to end_card_addr; note that
6329           // _threshold cannot possibly exceed end_card_addr, anyhow.
6330           // This prevents future clearing of the card as the scan proceeds
6331           // to the right.
6332           assert(_threshold <= end_card_addr,
6333                  "Because we are just scanning into this object");
6334           if (_threshold < end_card_addr) {
6335             _threshold = end_card_addr;
6336           }
6337           if (p->klass_or_null_acquire() != NULL) {
6338             // Redirty the range of cards...
6339             _mut->mark_range(redirty_range);
6340           } // ...else the setting of klass will dirty the card anyway.
6341         }
6342       DEBUG_ONLY(})
6343       return true;
6344     }
6345   }
6346   scanOopsInOop(addr);
6347   return true;
6348 }
6349 
6350 // We take a break if we've been at this for a while,
6351 // so as to avoid monopolizing the locks involved.
6352 void MarkFromRootsClosure::do_yield_work() {
6353   // First give up the locks, then yield, then re-lock
6354   // We should probably use a constructor/destructor idiom to
6355   // do this unlock/lock or modify the MutexUnlocker class to
6356   // serve our purpose. XXX
6357   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6358          "CMS thread should hold CMS token");
6359   assert_lock_strong(_bitMap->lock());
6360   _bitMap->lock()->unlock();
6361   ConcurrentMarkSweepThread::desynchronize(true);
6362   _collector->stopTimer();
6363   _collector->incrementYields();
6364 
6365   // See the comment in coordinator_yield()
6366   for (unsigned i = 0; i < CMSYieldSleepCount &&
6367                        ConcurrentMarkSweepThread::should_yield() &&
6368                        !CMSCollector::foregroundGCIsActive(); ++i) {
6369     os::sleep(Thread::current(), 1, false);
6370   }
6371 
6372   ConcurrentMarkSweepThread::synchronize(true);
6373   _bitMap->lock()->lock_without_safepoint_check();
6374   _collector->startTimer();
6375 }
6376 
6377 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
6378   assert(_bitMap->isMarked(ptr), "expected bit to be set");
6379   assert(_markStack->isEmpty(),
6380          "should drain stack to limit stack usage");
6381   // convert ptr to an oop preparatory to scanning
6382   oop obj = oop(ptr);
6383   // Ignore mark word in verification below, since we
6384   // may be running concurrent with mutators.
6385   assert(oopDesc::is_oop(obj, true), "should be an oop");
6386   assert(_finger <= ptr, "_finger runneth ahead");
6387   // advance the finger to right end of this object
6388   _finger = ptr + obj->size();
6389   assert(_finger > ptr, "we just incremented it above");
6390   // On large heaps, it may take us some time to get through
6391   // the marking phase. During
6392   // this time it's possible that a lot of mutations have
6393   // accumulated in the card table and the mod union table --
6394   // these mutation records are redundant until we have
6395   // actually traced into the corresponding card.
6396   // Here, we check whether advancing the finger would make
6397   // us cross into a new card, and if so clear corresponding
6398   // cards in the MUT (preclean them in the card-table in the
6399   // future).
6400 
6401   DEBUG_ONLY(if (!_verifying) {)
6402     // The clean-on-enter optimization is disabled by default,
6403     // until we fix 6178663.
6404     if (CMSCleanOnEnter && (_finger > _threshold)) {
6405       // [_threshold, _finger) represents the interval
6406       // of cards to be cleared  in MUT (or precleaned in card table).
6407       // The set of cards to be cleared is all those that overlap
6408       // with the interval [_threshold, _finger); note that
6409       // _threshold is always kept card-aligned but _finger isn't
6410       // always card-aligned.
6411       HeapWord* old_threshold = _threshold;
6412       assert(is_aligned(old_threshold, CardTable::card_size),
6413              "_threshold should always be card-aligned");
6414       _threshold = align_up(_finger, CardTable::card_size);
6415       MemRegion mr(old_threshold, _threshold);
6416       assert(!mr.is_empty(), "Control point invariant");
6417       assert(_span.contains(mr), "Should clear within span");
6418       _mut->clear_range(mr);
6419     }
6420   DEBUG_ONLY(})
6421   // Note: the finger doesn't advance while we drain
6422   // the stack below.
6423   PushOrMarkClosure pushOrMarkClosure(_collector,
6424                                       _span, _bitMap, _markStack,
6425                                       _finger, this);
6426   bool res = _markStack->push(obj);
6427   assert(res, "Empty non-zero size stack should have space for single push");
6428   while (!_markStack->isEmpty()) {
6429     oop new_oop = _markStack->pop();
6430     // Skip verifying header mark word below because we are
6431     // running concurrent with mutators.
6432     assert(oopDesc::is_oop(new_oop, true), "Oops! expected to pop an oop");
6433     // now scan this oop's oops
6434     new_oop->oop_iterate(&pushOrMarkClosure);
6435     do_yield_check();
6436   }
6437   assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
6438 }
6439 
6440 ParMarkFromRootsClosure::ParMarkFromRootsClosure(CMSConcMarkingTask* task,
6441                        CMSCollector* collector, MemRegion span,
6442                        CMSBitMap* bit_map,
6443                        OopTaskQueue* work_queue,
6444                        CMSMarkStack*  overflow_stack):
6445   _collector(collector),
6446   _whole_span(collector->_span),
6447   _span(span),
6448   _bit_map(bit_map),
6449   _mut(&collector->_modUnionTable),
6450   _work_queue(work_queue),
6451   _overflow_stack(overflow_stack),
6452   _skip_bits(0),
6453   _task(task)
6454 {
6455   assert(_work_queue->size() == 0, "work_queue should be empty");
6456   _finger = span.start();
6457   _threshold = _finger;     // XXX Defer clear-on-enter optimization for now
6458   assert(_span.contains(_finger), "Out of bounds _finger?");
6459 }
6460 
6461 // Should revisit to see if this should be restructured for
6462 // greater efficiency.
6463 bool ParMarkFromRootsClosure::do_bit(size_t offset) {
6464   if (_skip_bits > 0) {
6465     _skip_bits--;
6466     return true;
6467   }
6468   // convert offset into a HeapWord*
6469   HeapWord* addr = _bit_map->startWord() + offset;
6470   assert(_bit_map->endWord() && addr < _bit_map->endWord(),
6471          "address out of range");
6472   assert(_bit_map->isMarked(addr), "tautology");
6473   if (_bit_map->isMarked(addr+1)) {
6474     // this is an allocated object that might not yet be initialized
6475     assert(_skip_bits == 0, "tautology");
6476     _skip_bits = 2;  // skip next two marked bits ("Printezis-marks")
6477     oop p = oop(addr);
6478     if (p->klass_or_null_acquire() == NULL) {
6479       // in the case of Clean-on-Enter optimization, redirty card
6480       // and avoid clearing card by increasing  the threshold.
6481       return true;
6482     }
6483   }
6484   scan_oops_in_oop(addr);
6485   return true;
6486 }
6487 
6488 void ParMarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
6489   assert(_bit_map->isMarked(ptr), "expected bit to be set");
6490   // Should we assert that our work queue is empty or
6491   // below some drain limit?
6492   assert(_work_queue->size() == 0,
6493          "should drain stack to limit stack usage");
6494   // convert ptr to an oop preparatory to scanning
6495   oop obj = oop(ptr);
6496   // Ignore mark word in verification below, since we
6497   // may be running concurrent with mutators.
6498   assert(oopDesc::is_oop(obj, true), "should be an oop");
6499   assert(_finger <= ptr, "_finger runneth ahead");
6500   // advance the finger to right end of this object
6501   _finger = ptr + obj->size();
6502   assert(_finger > ptr, "we just incremented it above");
6503   // On large heaps, it may take us some time to get through
6504   // the marking phase. During
6505   // this time it's possible that a lot of mutations have
6506   // accumulated in the card table and the mod union table --
6507   // these mutation records are redundant until we have
6508   // actually traced into the corresponding card.
6509   // Here, we check whether advancing the finger would make
6510   // us cross into a new card, and if so clear corresponding
6511   // cards in the MUT (preclean them in the card-table in the
6512   // future).
6513 
6514   // The clean-on-enter optimization is disabled by default,
6515   // until we fix 6178663.
6516   if (CMSCleanOnEnter && (_finger > _threshold)) {
6517     // [_threshold, _finger) represents the interval
6518     // of cards to be cleared  in MUT (or precleaned in card table).
6519     // The set of cards to be cleared is all those that overlap
6520     // with the interval [_threshold, _finger); note that
6521     // _threshold is always kept card-aligned but _finger isn't
6522     // always card-aligned.
6523     HeapWord* old_threshold = _threshold;
6524     assert(is_aligned(old_threshold, CardTable::card_size),
6525            "_threshold should always be card-aligned");
6526     _threshold = align_up(_finger, CardTable::card_size);
6527     MemRegion mr(old_threshold, _threshold);
6528     assert(!mr.is_empty(), "Control point invariant");
6529     assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
6530     _mut->clear_range(mr);
6531   }
6532 
6533   // Note: the local finger doesn't advance while we drain
6534   // the stack below, but the global finger sure can and will.
6535   HeapWord* volatile* gfa = _task->global_finger_addr();
6536   ParPushOrMarkClosure pushOrMarkClosure(_collector,
6537                                          _span, _bit_map,
6538                                          _work_queue,
6539                                          _overflow_stack,
6540                                          _finger,
6541                                          gfa, this);
6542   bool res = _work_queue->push(obj);   // overflow could occur here
6543   assert(res, "Will hold once we use workqueues");
6544   while (true) {
6545     oop new_oop;
6546     if (!_work_queue->pop_local(new_oop)) {
6547       // We emptied our work_queue; check if there's stuff that can
6548       // be gotten from the overflow stack.
6549       if (CMSConcMarkingTask::get_work_from_overflow_stack(
6550             _overflow_stack, _work_queue)) {
6551         do_yield_check();
6552         continue;
6553       } else {  // done
6554         break;
6555       }
6556     }
6557     // Skip verifying header mark word below because we are
6558     // running concurrent with mutators.
6559     assert(oopDesc::is_oop(new_oop, true), "Oops! expected to pop an oop");
6560     // now scan this oop's oops
6561     new_oop->oop_iterate(&pushOrMarkClosure);
6562     do_yield_check();
6563   }
6564   assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
6565 }
6566 
6567 // Yield in response to a request from VM Thread or
6568 // from mutators.
6569 void ParMarkFromRootsClosure::do_yield_work() {
6570   assert(_task != NULL, "sanity");
6571   _task->yield();
6572 }
6573 
6574 // A variant of the above used for verifying CMS marking work.
6575 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
6576                         MemRegion span,
6577                         CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6578                         CMSMarkStack*  mark_stack):
6579   _collector(collector),
6580   _span(span),
6581   _verification_bm(verification_bm),
6582   _cms_bm(cms_bm),
6583   _mark_stack(mark_stack),
6584   _pam_verify_closure(collector, span, verification_bm, cms_bm,
6585                       mark_stack)
6586 {
6587   assert(_mark_stack->isEmpty(), "stack should be empty");
6588   _finger = _verification_bm->startWord();
6589   assert(_collector->_restart_addr == NULL, "Sanity check");
6590   assert(_span.contains(_finger), "Out of bounds _finger?");
6591 }
6592 
6593 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
6594   assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
6595   assert(_span.contains(addr), "Out of bounds _finger?");
6596   _finger = addr;
6597 }
6598 
6599 // Should revisit to see if this should be restructured for
6600 // greater efficiency.
6601 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
6602   // convert offset into a HeapWord*
6603   HeapWord* addr = _verification_bm->startWord() + offset;
6604   assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
6605          "address out of range");
6606   assert(_verification_bm->isMarked(addr), "tautology");
6607   assert(_cms_bm->isMarked(addr), "tautology");
6608 
6609   assert(_mark_stack->isEmpty(),
6610          "should drain stack to limit stack usage");
6611   // convert addr to an oop preparatory to scanning
6612   oop obj = oop(addr);
6613   assert(oopDesc::is_oop(obj), "should be an oop");
6614   assert(_finger <= addr, "_finger runneth ahead");
6615   // advance the finger to right end of this object
6616   _finger = addr + obj->size();
6617   assert(_finger > addr, "we just incremented it above");
6618   // Note: the finger doesn't advance while we drain
6619   // the stack below.
6620   bool res = _mark_stack->push(obj);
6621   assert(res, "Empty non-zero size stack should have space for single push");
6622   while (!_mark_stack->isEmpty()) {
6623     oop new_oop = _mark_stack->pop();
6624     assert(oopDesc::is_oop(new_oop), "Oops! expected to pop an oop");
6625     // now scan this oop's oops
6626     new_oop->oop_iterate(&_pam_verify_closure);
6627   }
6628   assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
6629   return true;
6630 }
6631 
6632 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
6633   CMSCollector* collector, MemRegion span,
6634   CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6635   CMSMarkStack*  mark_stack):
6636   MetadataVisitingOopIterateClosure(collector->ref_processor()),
6637   _collector(collector),
6638   _span(span),
6639   _verification_bm(verification_bm),
6640   _cms_bm(cms_bm),
6641   _mark_stack(mark_stack)
6642 { }
6643 
6644 template <class T> void PushAndMarkVerifyClosure::do_oop_work(T *p) {
6645   oop obj = RawAccess<>::oop_load(p);
6646   do_oop(obj);
6647 }
6648 
6649 void PushAndMarkVerifyClosure::do_oop(oop* p)       { PushAndMarkVerifyClosure::do_oop_work(p); }
6650 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
6651 
6652 // Upon stack overflow, we discard (part of) the stack,
6653 // remembering the least address amongst those discarded
6654 // in CMSCollector's _restart_address.
6655 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
6656   // Remember the least grey address discarded
6657   HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
6658   _collector->lower_restart_addr(ra);
6659   _mark_stack->reset();  // discard stack contents
6660   _mark_stack->expand(); // expand the stack if possible
6661 }
6662 
6663 void PushAndMarkVerifyClosure::do_oop(oop obj) {
6664   assert(oopDesc::is_oop_or_null(obj), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6665   HeapWord* addr = (HeapWord*)obj;
6666   if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
6667     // Oop lies in _span and isn't yet grey or black
6668     _verification_bm->mark(addr);            // now grey
6669     if (!_cms_bm->isMarked(addr)) {
6670       Log(gc, verify) log;
6671       ResourceMark rm;
6672       LogStream ls(log.error());
6673       oop(addr)->print_on(&ls);
6674       log.error(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
6675       fatal("... aborting");
6676     }
6677 
6678     if (!_mark_stack->push(obj)) { // stack overflow
6679       log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _mark_stack->capacity());
6680       assert(_mark_stack->isFull(), "Else push should have succeeded");
6681       handle_stack_overflow(addr);
6682     }
6683     // anything including and to the right of _finger
6684     // will be scanned as we iterate over the remainder of the
6685     // bit map
6686   }
6687 }
6688 
6689 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
6690                      MemRegion span,
6691                      CMSBitMap* bitMap, CMSMarkStack*  markStack,
6692                      HeapWord* finger, MarkFromRootsClosure* parent) :
6693   MetadataVisitingOopIterateClosure(collector->ref_processor()),
6694   _collector(collector),
6695   _span(span),
6696   _bitMap(bitMap),
6697   _markStack(markStack),
6698   _finger(finger),
6699   _parent(parent)
6700 { }
6701 
6702 ParPushOrMarkClosure::ParPushOrMarkClosure(CMSCollector* collector,
6703                                            MemRegion span,
6704                                            CMSBitMap* bit_map,
6705                                            OopTaskQueue* work_queue,
6706                                            CMSMarkStack*  overflow_stack,
6707                                            HeapWord* finger,
6708                                            HeapWord* volatile* global_finger_addr,
6709                                            ParMarkFromRootsClosure* parent) :
6710   MetadataVisitingOopIterateClosure(collector->ref_processor()),
6711   _collector(collector),
6712   _whole_span(collector->_span),
6713   _span(span),
6714   _bit_map(bit_map),
6715   _work_queue(work_queue),
6716   _overflow_stack(overflow_stack),
6717   _finger(finger),
6718   _global_finger_addr(global_finger_addr),
6719   _parent(parent)
6720 { }
6721 
6722 // Assumes thread-safe access by callers, who are
6723 // responsible for mutual exclusion.
6724 void CMSCollector::lower_restart_addr(HeapWord* low) {
6725   assert(_span.contains(low), "Out of bounds addr");
6726   if (_restart_addr == NULL) {
6727     _restart_addr = low;
6728   } else {
6729     _restart_addr = MIN2(_restart_addr, low);
6730   }
6731 }
6732 
6733 // Upon stack overflow, we discard (part of) the stack,
6734 // remembering the least address amongst those discarded
6735 // in CMSCollector's _restart_address.
6736 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
6737   // Remember the least grey address discarded
6738   HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
6739   _collector->lower_restart_addr(ra);
6740   _markStack->reset();  // discard stack contents
6741   _markStack->expand(); // expand the stack if possible
6742 }
6743 
6744 // Upon stack overflow, we discard (part of) the stack,
6745 // remembering the least address amongst those discarded
6746 // in CMSCollector's _restart_address.
6747 void ParPushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
6748   // We need to do this under a mutex to prevent other
6749   // workers from interfering with the work done below.
6750   MutexLockerEx ml(_overflow_stack->par_lock(),
6751                    Mutex::_no_safepoint_check_flag);
6752   // Remember the least grey address discarded
6753   HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
6754   _collector->lower_restart_addr(ra);
6755   _overflow_stack->reset();  // discard stack contents
6756   _overflow_stack->expand(); // expand the stack if possible
6757 }
6758 
6759 void PushOrMarkClosure::do_oop(oop obj) {
6760   // Ignore mark word because we are running concurrent with mutators.
6761   assert(oopDesc::is_oop_or_null(obj, true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6762   HeapWord* addr = (HeapWord*)obj;
6763   if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
6764     // Oop lies in _span and isn't yet grey or black
6765     _bitMap->mark(addr);            // now grey
6766     if (addr < _finger) {
6767       // the bit map iteration has already either passed, or
6768       // sampled, this bit in the bit map; we'll need to
6769       // use the marking stack to scan this oop's oops.
6770       bool simulate_overflow = false;
6771       NOT_PRODUCT(
6772         if (CMSMarkStackOverflowALot &&
6773             _collector->simulate_overflow()) {
6774           // simulate a stack overflow
6775           simulate_overflow = true;
6776         }
6777       )
6778       if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
6779         log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _markStack->capacity());
6780         assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
6781         handle_stack_overflow(addr);
6782       }
6783     }
6784     // anything including and to the right of _finger
6785     // will be scanned as we iterate over the remainder of the
6786     // bit map
6787     do_yield_check();
6788   }
6789 }
6790 
6791 void ParPushOrMarkClosure::do_oop(oop obj) {
6792   // Ignore mark word because we are running concurrent with mutators.
6793   assert(oopDesc::is_oop_or_null(obj, true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6794   HeapWord* addr = (HeapWord*)obj;
6795   if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
6796     // Oop lies in _span and isn't yet grey or black
6797     // We read the global_finger (volatile read) strictly after marking oop
6798     bool res = _bit_map->par_mark(addr);    // now grey
6799     volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
6800     // Should we push this marked oop on our stack?
6801     // -- if someone else marked it, nothing to do
6802     // -- if target oop is above global finger nothing to do
6803     // -- if target oop is in chunk and above local finger
6804     //      then nothing to do
6805     // -- else push on work queue
6806     if (   !res       // someone else marked it, they will deal with it
6807         || (addr >= *gfa)  // will be scanned in a later task
6808         || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
6809       return;
6810     }
6811     // the bit map iteration has already either passed, or
6812     // sampled, this bit in the bit map; we'll need to
6813     // use the marking stack to scan this oop's oops.
6814     bool simulate_overflow = false;
6815     NOT_PRODUCT(
6816       if (CMSMarkStackOverflowALot &&
6817           _collector->simulate_overflow()) {
6818         // simulate a stack overflow
6819         simulate_overflow = true;
6820       }
6821     )
6822     if (simulate_overflow ||
6823         !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
6824       // stack overflow
6825       log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _overflow_stack->capacity());
6826       // We cannot assert that the overflow stack is full because
6827       // it may have been emptied since.
6828       assert(simulate_overflow ||
6829              _work_queue->size() == _work_queue->max_elems(),
6830             "Else push should have succeeded");
6831       handle_stack_overflow(addr);
6832     }
6833     do_yield_check();
6834   }
6835 }
6836 
6837 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
6838                                        MemRegion span,
6839                                        ReferenceDiscoverer* rd,
6840                                        CMSBitMap* bit_map,
6841                                        CMSBitMap* mod_union_table,
6842                                        CMSMarkStack*  mark_stack,
6843                                        bool           concurrent_precleaning):
6844   MetadataVisitingOopIterateClosure(rd),
6845   _collector(collector),
6846   _span(span),
6847   _bit_map(bit_map),
6848   _mod_union_table(mod_union_table),
6849   _mark_stack(mark_stack),
6850   _concurrent_precleaning(concurrent_precleaning)
6851 {
6852   assert(ref_discoverer() != NULL, "ref_discoverer shouldn't be NULL");
6853 }
6854 
6855 // Grey object rescan during pre-cleaning and second checkpoint phases --
6856 // the non-parallel version (the parallel version appears further below.)
6857 void PushAndMarkClosure::do_oop(oop obj) {
6858   // Ignore mark word verification. If during concurrent precleaning,
6859   // the object monitor may be locked. If during the checkpoint
6860   // phases, the object may already have been reached by a  different
6861   // path and may be at the end of the global overflow list (so
6862   // the mark word may be NULL).
6863   assert(oopDesc::is_oop_or_null(obj, true /* ignore mark word */),
6864          "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6865   HeapWord* addr = (HeapWord*)obj;
6866   // Check if oop points into the CMS generation
6867   // and is not marked
6868   if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
6869     // a white object ...
6870     _bit_map->mark(addr);         // ... now grey
6871     // push on the marking stack (grey set)
6872     bool simulate_overflow = false;
6873     NOT_PRODUCT(
6874       if (CMSMarkStackOverflowALot &&
6875           _collector->simulate_overflow()) {
6876         // simulate a stack overflow
6877         simulate_overflow = true;
6878       }
6879     )
6880     if (simulate_overflow || !_mark_stack->push(obj)) {
6881       if (_concurrent_precleaning) {
6882          // During precleaning we can just dirty the appropriate card(s)
6883          // in the mod union table, thus ensuring that the object remains
6884          // in the grey set  and continue. In the case of object arrays
6885          // we need to dirty all of the cards that the object spans,
6886          // since the rescan of object arrays will be limited to the
6887          // dirty cards.
6888          // Note that no one can be interfering with us in this action
6889          // of dirtying the mod union table, so no locking or atomics
6890          // are required.
6891          if (obj->is_objArray()) {
6892            size_t sz = obj->size();
6893            HeapWord* end_card_addr = align_up(addr + sz, CardTable::card_size);
6894            MemRegion redirty_range = MemRegion(addr, end_card_addr);
6895            assert(!redirty_range.is_empty(), "Arithmetical tautology");
6896            _mod_union_table->mark_range(redirty_range);
6897          } else {
6898            _mod_union_table->mark(addr);
6899          }
6900          _collector->_ser_pmc_preclean_ovflw++;
6901       } else {
6902          // During the remark phase, we need to remember this oop
6903          // in the overflow list.
6904          _collector->push_on_overflow_list(obj);
6905          _collector->_ser_pmc_remark_ovflw++;
6906       }
6907     }
6908   }
6909 }
6910 
6911 ParPushAndMarkClosure::ParPushAndMarkClosure(CMSCollector* collector,
6912                                              MemRegion span,
6913                                              ReferenceDiscoverer* rd,
6914                                              CMSBitMap* bit_map,
6915                                              OopTaskQueue* work_queue):
6916   MetadataVisitingOopIterateClosure(rd),
6917   _collector(collector),
6918   _span(span),
6919   _bit_map(bit_map),
6920   _work_queue(work_queue)
6921 {
6922   assert(ref_discoverer() != NULL, "ref_discoverer shouldn't be NULL");
6923 }
6924 
6925 // Grey object rescan during second checkpoint phase --
6926 // the parallel version.
6927 void ParPushAndMarkClosure::do_oop(oop obj) {
6928   // In the assert below, we ignore the mark word because
6929   // this oop may point to an already visited object that is
6930   // on the overflow stack (in which case the mark word has
6931   // been hijacked for chaining into the overflow stack --
6932   // if this is the last object in the overflow stack then
6933   // its mark word will be NULL). Because this object may
6934   // have been subsequently popped off the global overflow
6935   // stack, and the mark word possibly restored to the prototypical
6936   // value, by the time we get to examined this failing assert in
6937   // the debugger, is_oop_or_null(false) may subsequently start
6938   // to hold.
6939   assert(oopDesc::is_oop_or_null(obj, true),
6940          "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6941   HeapWord* addr = (HeapWord*)obj;
6942   // Check if oop points into the CMS generation
6943   // and is not marked
6944   if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
6945     // a white object ...
6946     // If we manage to "claim" the object, by being the
6947     // first thread to mark it, then we push it on our
6948     // marking stack
6949     if (_bit_map->par_mark(addr)) {     // ... now grey
6950       // push on work queue (grey set)
6951       bool simulate_overflow = false;
6952       NOT_PRODUCT(
6953         if (CMSMarkStackOverflowALot &&
6954             _collector->par_simulate_overflow()) {
6955           // simulate a stack overflow
6956           simulate_overflow = true;
6957         }
6958       )
6959       if (simulate_overflow || !_work_queue->push(obj)) {
6960         _collector->par_push_on_overflow_list(obj);
6961         _collector->_par_pmc_remark_ovflw++; //  imprecise OK: no need to CAS
6962       }
6963     } // Else, some other thread got there first
6964   }
6965 }
6966 
6967 void CMSPrecleanRefsYieldClosure::do_yield_work() {
6968   Mutex* bml = _collector->bitMapLock();
6969   assert_lock_strong(bml);
6970   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6971          "CMS thread should hold CMS token");
6972 
6973   bml->unlock();
6974   ConcurrentMarkSweepThread::desynchronize(true);
6975 
6976   _collector->stopTimer();
6977   _collector->incrementYields();
6978 
6979   // See the comment in coordinator_yield()
6980   for (unsigned i = 0; i < CMSYieldSleepCount &&
6981                        ConcurrentMarkSweepThread::should_yield() &&
6982                        !CMSCollector::foregroundGCIsActive(); ++i) {
6983     os::sleep(Thread::current(), 1, false);
6984   }
6985 
6986   ConcurrentMarkSweepThread::synchronize(true);
6987   bml->lock();
6988 
6989   _collector->startTimer();
6990 }
6991 
6992 bool CMSPrecleanRefsYieldClosure::should_return() {
6993   if (ConcurrentMarkSweepThread::should_yield()) {
6994     do_yield_work();
6995   }
6996   return _collector->foregroundGCIsActive();
6997 }
6998 
6999 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
7000   assert(((size_t)mr.start())%CardTable::card_size_in_words == 0,
7001          "mr should be aligned to start at a card boundary");
7002   // We'd like to assert:
7003   // assert(mr.word_size()%CardTable::card_size_in_words == 0,
7004   //        "mr should be a range of cards");
7005   // However, that would be too strong in one case -- the last
7006   // partition ends at _unallocated_block which, in general, can be
7007   // an arbitrary boundary, not necessarily card aligned.
7008   _num_dirty_cards += mr.word_size()/CardTable::card_size_in_words;
7009   _space->object_iterate_mem(mr, &_scan_cl);
7010 }
7011 
7012 SweepClosure::SweepClosure(CMSCollector* collector,
7013                            ConcurrentMarkSweepGeneration* g,
7014                            CMSBitMap* bitMap, bool should_yield) :
7015   _collector(collector),
7016   _g(g),
7017   _sp(g->cmsSpace()),
7018   _limit(_sp->sweep_limit()),
7019   _freelistLock(_sp->freelistLock()),
7020   _bitMap(bitMap),
7021   _inFreeRange(false),           // No free range at beginning of sweep
7022   _freeRangeInFreeLists(false),  // No free range at beginning of sweep
7023   _lastFreeRangeCoalesced(false),
7024   _yield(should_yield),
7025   _freeFinger(g->used_region().start())
7026 {
7027   NOT_PRODUCT(
7028     _numObjectsFreed = 0;
7029     _numWordsFreed   = 0;
7030     _numObjectsLive = 0;
7031     _numWordsLive = 0;
7032     _numObjectsAlreadyFree = 0;
7033     _numWordsAlreadyFree = 0;
7034     _last_fc = NULL;
7035 
7036     _sp->initializeIndexedFreeListArrayReturnedBytes();
7037     _sp->dictionary()->initialize_dict_returned_bytes();
7038   )
7039   assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7040          "sweep _limit out of bounds");
7041   log_develop_trace(gc, sweep)("====================");
7042   log_develop_trace(gc, sweep)("Starting new sweep with limit " PTR_FORMAT, p2i(_limit));
7043 }
7044 
7045 void SweepClosure::print_on(outputStream* st) const {
7046   st->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")",
7047                p2i(_sp->bottom()), p2i(_sp->end()));
7048   st->print_cr("_limit = " PTR_FORMAT, p2i(_limit));
7049   st->print_cr("_freeFinger = " PTR_FORMAT, p2i(_freeFinger));
7050   NOT_PRODUCT(st->print_cr("_last_fc = " PTR_FORMAT, p2i(_last_fc));)
7051   st->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d",
7052                _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced);
7053 }
7054 
7055 #ifndef PRODUCT
7056 // Assertion checking only:  no useful work in product mode --
7057 // however, if any of the flags below become product flags,
7058 // you may need to review this code to see if it needs to be
7059 // enabled in product mode.
7060 SweepClosure::~SweepClosure() {
7061   assert_lock_strong(_freelistLock);
7062   assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7063          "sweep _limit out of bounds");
7064   if (inFreeRange()) {
7065     Log(gc, sweep) log;
7066     log.error("inFreeRange() should have been reset; dumping state of SweepClosure");
7067     ResourceMark rm;
7068     LogStream ls(log.error());
7069     print_on(&ls);
7070     ShouldNotReachHere();
7071   }
7072 
7073   if (log_is_enabled(Debug, gc, sweep)) {
7074     log_debug(gc, sweep)("Collected " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
7075                          _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
7076     log_debug(gc, sweep)("Live " SIZE_FORMAT " objects,  " SIZE_FORMAT " bytes  Already free " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
7077                          _numObjectsLive, _numWordsLive*sizeof(HeapWord), _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
7078     size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree) * sizeof(HeapWord);
7079     log_debug(gc, sweep)("Total sweep: " SIZE_FORMAT " bytes", totalBytes);
7080   }
7081 
7082   if (log_is_enabled(Trace, gc, sweep) && CMSVerifyReturnedBytes) {
7083     size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
7084     size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes();
7085     size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes;
7086     log_trace(gc, sweep)("Returned " SIZE_FORMAT " bytes   Indexed List Returned " SIZE_FORMAT " bytes        Dictionary Returned " SIZE_FORMAT " bytes",
7087                          returned_bytes, indexListReturnedBytes, dict_returned_bytes);
7088   }
7089   log_develop_trace(gc, sweep)("end of sweep with _limit = " PTR_FORMAT, p2i(_limit));
7090   log_develop_trace(gc, sweep)("================");
7091 }
7092 #endif  // PRODUCT
7093 
7094 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
7095     bool freeRangeInFreeLists) {
7096   log_develop_trace(gc, sweep)("---- Start free range at " PTR_FORMAT " with free block (%d)",
7097                                p2i(freeFinger), freeRangeInFreeLists);
7098   assert(!inFreeRange(), "Trampling existing free range");
7099   set_inFreeRange(true);
7100   set_lastFreeRangeCoalesced(false);
7101 
7102   set_freeFinger(freeFinger);
7103   set_freeRangeInFreeLists(freeRangeInFreeLists);
7104   if (CMSTestInFreeList) {
7105     if (freeRangeInFreeLists) {
7106       FreeChunk* fc = (FreeChunk*) freeFinger;
7107       assert(fc->is_free(), "A chunk on the free list should be free.");
7108       assert(fc->size() > 0, "Free range should have a size");
7109       assert(_sp->verify_chunk_in_free_list(fc), "Chunk is not in free lists");
7110     }
7111   }
7112 }
7113 
7114 // Note that the sweeper runs concurrently with mutators. Thus,
7115 // it is possible for direct allocation in this generation to happen
7116 // in the middle of the sweep. Note that the sweeper also coalesces
7117 // contiguous free blocks. Thus, unless the sweeper and the allocator
7118 // synchronize appropriately freshly allocated blocks may get swept up.
7119 // This is accomplished by the sweeper locking the free lists while
7120 // it is sweeping. Thus blocks that are determined to be free are
7121 // indeed free. There is however one additional complication:
7122 // blocks that have been allocated since the final checkpoint and
7123 // mark, will not have been marked and so would be treated as
7124 // unreachable and swept up. To prevent this, the allocator marks
7125 // the bit map when allocating during the sweep phase. This leads,
7126 // however, to a further complication -- objects may have been allocated
7127 // but not yet initialized -- in the sense that the header isn't yet
7128 // installed. The sweeper can not then determine the size of the block
7129 // in order to skip over it. To deal with this case, we use a technique
7130 // (due to Printezis) to encode such uninitialized block sizes in the
7131 // bit map. Since the bit map uses a bit per every HeapWord, but the
7132 // CMS generation has a minimum object size of 3 HeapWords, it follows
7133 // that "normal marks" won't be adjacent in the bit map (there will
7134 // always be at least two 0 bits between successive 1 bits). We make use
7135 // of these "unused" bits to represent uninitialized blocks -- the bit
7136 // corresponding to the start of the uninitialized object and the next
7137 // bit are both set. Finally, a 1 bit marks the end of the object that
7138 // started with the two consecutive 1 bits to indicate its potentially
7139 // uninitialized state.
7140 
7141 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
7142   FreeChunk* fc = (FreeChunk*)addr;
7143   size_t res;
7144 
7145   // Check if we are done sweeping. Below we check "addr >= _limit" rather
7146   // than "addr == _limit" because although _limit was a block boundary when
7147   // we started the sweep, it may no longer be one because heap expansion
7148   // may have caused us to coalesce the block ending at the address _limit
7149   // with a newly expanded chunk (this happens when _limit was set to the
7150   // previous _end of the space), so we may have stepped past _limit:
7151   // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740.
7152   if (addr >= _limit) { // we have swept up to or past the limit: finish up
7153     assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7154            "sweep _limit out of bounds");
7155     assert(addr < _sp->end(), "addr out of bounds");
7156     // Flush any free range we might be holding as a single
7157     // coalesced chunk to the appropriate free list.
7158     if (inFreeRange()) {
7159       assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit,
7160              "freeFinger() " PTR_FORMAT " is out of bounds", p2i(freeFinger()));
7161       flush_cur_free_chunk(freeFinger(),
7162                            pointer_delta(addr, freeFinger()));
7163       log_develop_trace(gc, sweep)("Sweep: last chunk: put_free_blk " PTR_FORMAT " (" SIZE_FORMAT ") [coalesced:%d]",
7164                                    p2i(freeFinger()), pointer_delta(addr, freeFinger()),
7165                                    lastFreeRangeCoalesced() ? 1 : 0);
7166     }
7167 
7168     // help the iterator loop finish
7169     return pointer_delta(_sp->end(), addr);
7170   }
7171 
7172   assert(addr < _limit, "sweep invariant");
7173   // check if we should yield
7174   do_yield_check(addr);
7175   if (fc->is_free()) {
7176     // Chunk that is already free
7177     res = fc->size();
7178     do_already_free_chunk(fc);
7179     debug_only(_sp->verifyFreeLists());
7180     // If we flush the chunk at hand in lookahead_and_flush()
7181     // and it's coalesced with a preceding chunk, then the
7182     // process of "mangling" the payload of the coalesced block
7183     // will cause erasure of the size information from the
7184     // (erstwhile) header of all the coalesced blocks but the
7185     // first, so the first disjunct in the assert will not hold
7186     // in that specific case (in which case the second disjunct
7187     // will hold).
7188     assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit,
7189            "Otherwise the size info doesn't change at this step");
7190     NOT_PRODUCT(
7191       _numObjectsAlreadyFree++;
7192       _numWordsAlreadyFree += res;
7193     )
7194     NOT_PRODUCT(_last_fc = fc;)
7195   } else if (!_bitMap->isMarked(addr)) {
7196     // Chunk is fresh garbage
7197     res = do_garbage_chunk(fc);
7198     debug_only(_sp->verifyFreeLists());
7199     NOT_PRODUCT(
7200       _numObjectsFreed++;
7201       _numWordsFreed += res;
7202     )
7203   } else {
7204     // Chunk that is alive.
7205     res = do_live_chunk(fc);
7206     debug_only(_sp->verifyFreeLists());
7207     NOT_PRODUCT(
7208         _numObjectsLive++;
7209         _numWordsLive += res;
7210     )
7211   }
7212   return res;
7213 }
7214 
7215 // For the smart allocation, record following
7216 //  split deaths - a free chunk is removed from its free list because
7217 //      it is being split into two or more chunks.
7218 //  split birth - a free chunk is being added to its free list because
7219 //      a larger free chunk has been split and resulted in this free chunk.
7220 //  coal death - a free chunk is being removed from its free list because
7221 //      it is being coalesced into a large free chunk.
7222 //  coal birth - a free chunk is being added to its free list because
7223 //      it was created when two or more free chunks where coalesced into
7224 //      this free chunk.
7225 //
7226 // These statistics are used to determine the desired number of free
7227 // chunks of a given size.  The desired number is chosen to be relative
7228 // to the end of a CMS sweep.  The desired number at the end of a sweep
7229 // is the
7230 //      count-at-end-of-previous-sweep (an amount that was enough)
7231 //              - count-at-beginning-of-current-sweep  (the excess)
7232 //              + split-births  (gains in this size during interval)
7233 //              - split-deaths  (demands on this size during interval)
7234 // where the interval is from the end of one sweep to the end of the
7235 // next.
7236 //
7237 // When sweeping the sweeper maintains an accumulated chunk which is
7238 // the chunk that is made up of chunks that have been coalesced.  That
7239 // will be termed the left-hand chunk.  A new chunk of garbage that
7240 // is being considered for coalescing will be referred to as the
7241 // right-hand chunk.
7242 //
7243 // When making a decision on whether to coalesce a right-hand chunk with
7244 // the current left-hand chunk, the current count vs. the desired count
7245 // of the left-hand chunk is considered.  Also if the right-hand chunk
7246 // is near the large chunk at the end of the heap (see
7247 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
7248 // left-hand chunk is coalesced.
7249 //
7250 // When making a decision about whether to split a chunk, the desired count
7251 // vs. the current count of the candidate to be split is also considered.
7252 // If the candidate is underpopulated (currently fewer chunks than desired)
7253 // a chunk of an overpopulated (currently more chunks than desired) size may
7254 // be chosen.  The "hint" associated with a free list, if non-null, points
7255 // to a free list which may be overpopulated.
7256 //
7257 
7258 void SweepClosure::do_already_free_chunk(FreeChunk* fc) {
7259   const size_t size = fc->size();
7260   // Chunks that cannot be coalesced are not in the
7261   // free lists.
7262   if (CMSTestInFreeList && !fc->cantCoalesce()) {
7263     assert(_sp->verify_chunk_in_free_list(fc),
7264            "free chunk should be in free lists");
7265   }
7266   // a chunk that is already free, should not have been
7267   // marked in the bit map
7268   HeapWord* const addr = (HeapWord*) fc;
7269   assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
7270   // Verify that the bit map has no bits marked between
7271   // addr and purported end of this block.
7272   _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7273 
7274   // Some chunks cannot be coalesced under any circumstances.
7275   // See the definition of cantCoalesce().
7276   if (!fc->cantCoalesce()) {
7277     // This chunk can potentially be coalesced.
7278     // All the work is done in
7279     do_post_free_or_garbage_chunk(fc, size);
7280     // Note that if the chunk is not coalescable (the else arm
7281     // below), we unconditionally flush, without needing to do
7282     // a "lookahead," as we do below.
7283     if (inFreeRange()) lookahead_and_flush(fc, size);
7284   } else {
7285     // Code path common to both original and adaptive free lists.
7286 
7287     // cant coalesce with previous block; this should be treated
7288     // as the end of a free run if any
7289     if (inFreeRange()) {
7290       // we kicked some butt; time to pick up the garbage
7291       assert(freeFinger() < addr, "freeFinger points too high");
7292       flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7293     }
7294     // else, nothing to do, just continue
7295   }
7296 }
7297 
7298 size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) {
7299   // This is a chunk of garbage.  It is not in any free list.
7300   // Add it to a free list or let it possibly be coalesced into
7301   // a larger chunk.
7302   HeapWord* const addr = (HeapWord*) fc;
7303   const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7304 
7305   // Verify that the bit map has no bits marked between
7306   // addr and purported end of just dead object.
7307   _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7308   do_post_free_or_garbage_chunk(fc, size);
7309 
7310   assert(_limit >= addr + size,
7311          "A freshly garbage chunk can't possibly straddle over _limit");
7312   if (inFreeRange()) lookahead_and_flush(fc, size);
7313   return size;
7314 }
7315 
7316 size_t SweepClosure::do_live_chunk(FreeChunk* fc) {
7317   HeapWord* addr = (HeapWord*) fc;
7318   // The sweeper has just found a live object. Return any accumulated
7319   // left hand chunk to the free lists.
7320   if (inFreeRange()) {
7321     assert(freeFinger() < addr, "freeFinger points too high");
7322     flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7323   }
7324 
7325   // This object is live: we'd normally expect this to be
7326   // an oop, and like to assert the following:
7327   // assert(oopDesc::is_oop(oop(addr)), "live block should be an oop");
7328   // However, as we commented above, this may be an object whose
7329   // header hasn't yet been initialized.
7330   size_t size;
7331   assert(_bitMap->isMarked(addr), "Tautology for this control point");
7332   if (_bitMap->isMarked(addr + 1)) {
7333     // Determine the size from the bit map, rather than trying to
7334     // compute it from the object header.
7335     HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
7336     size = pointer_delta(nextOneAddr + 1, addr);
7337     assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
7338            "alignment problem");
7339 
7340 #ifdef ASSERT
7341       if (oop(addr)->klass_or_null_acquire() != NULL) {
7342         // Ignore mark word because we are running concurrent with mutators
7343         assert(oopDesc::is_oop(oop(addr), true), "live block should be an oop");
7344         assert(size ==
7345                CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
7346                "P-mark and computed size do not agree");
7347       }
7348 #endif
7349 
7350   } else {
7351     // This should be an initialized object that's alive.
7352     assert(oop(addr)->klass_or_null_acquire() != NULL,
7353            "Should be an initialized object");
7354     // Ignore mark word because we are running concurrent with mutators
7355     assert(oopDesc::is_oop(oop(addr), true), "live block should be an oop");
7356     // Verify that the bit map has no bits marked between
7357     // addr and purported end of this block.
7358     size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7359     assert(size >= 3, "Necessary for Printezis marks to work");
7360     assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
7361     DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
7362   }
7363   return size;
7364 }
7365 
7366 void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc,
7367                                                  size_t chunkSize) {
7368   // do_post_free_or_garbage_chunk() should only be called in the case
7369   // of the adaptive free list allocator.
7370   const bool fcInFreeLists = fc->is_free();
7371   assert((HeapWord*)fc <= _limit, "sweep invariant");
7372   if (CMSTestInFreeList && fcInFreeLists) {
7373     assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists");
7374   }
7375 
7376   log_develop_trace(gc, sweep)("  -- pick up another chunk at " PTR_FORMAT " (" SIZE_FORMAT ")", p2i(fc), chunkSize);
7377 
7378   HeapWord* const fc_addr = (HeapWord*) fc;
7379 
7380   bool coalesce = false;
7381   const size_t left  = pointer_delta(fc_addr, freeFinger());
7382   const size_t right = chunkSize;
7383   switch (FLSCoalescePolicy) {
7384     // numeric value forms a coalition aggressiveness metric
7385     case 0:  { // never coalesce
7386       coalesce = false;
7387       break;
7388     }
7389     case 1: { // coalesce if left & right chunks on overpopulated lists
7390       coalesce = _sp->coalOverPopulated(left) &&
7391                  _sp->coalOverPopulated(right);
7392       break;
7393     }
7394     case 2: { // coalesce if left chunk on overpopulated list (default)
7395       coalesce = _sp->coalOverPopulated(left);
7396       break;
7397     }
7398     case 3: { // coalesce if left OR right chunk on overpopulated list
7399       coalesce = _sp->coalOverPopulated(left) ||
7400                  _sp->coalOverPopulated(right);
7401       break;
7402     }
7403     case 4: { // always coalesce
7404       coalesce = true;
7405       break;
7406     }
7407     default:
7408      ShouldNotReachHere();
7409   }
7410 
7411   // Should the current free range be coalesced?
7412   // If the chunk is in a free range and either we decided to coalesce above
7413   // or the chunk is near the large block at the end of the heap
7414   // (isNearLargestChunk() returns true), then coalesce this chunk.
7415   const bool doCoalesce = inFreeRange()
7416                           && (coalesce || _g->isNearLargestChunk(fc_addr));
7417   if (doCoalesce) {
7418     // Coalesce the current free range on the left with the new
7419     // chunk on the right.  If either is on a free list,
7420     // it must be removed from the list and stashed in the closure.
7421     if (freeRangeInFreeLists()) {
7422       FreeChunk* const ffc = (FreeChunk*)freeFinger();
7423       assert(ffc->size() == pointer_delta(fc_addr, freeFinger()),
7424              "Size of free range is inconsistent with chunk size.");
7425       if (CMSTestInFreeList) {
7426         assert(_sp->verify_chunk_in_free_list(ffc),
7427                "Chunk is not in free lists");
7428       }
7429       _sp->coalDeath(ffc->size());
7430       _sp->removeFreeChunkFromFreeLists(ffc);
7431       set_freeRangeInFreeLists(false);
7432     }
7433     if (fcInFreeLists) {
7434       _sp->coalDeath(chunkSize);
7435       assert(fc->size() == chunkSize,
7436         "The chunk has the wrong size or is not in the free lists");
7437       _sp->removeFreeChunkFromFreeLists(fc);
7438     }
7439     set_lastFreeRangeCoalesced(true);
7440     print_free_block_coalesced(fc);
7441   } else {  // not in a free range and/or should not coalesce
7442     // Return the current free range and start a new one.
7443     if (inFreeRange()) {
7444       // In a free range but cannot coalesce with the right hand chunk.
7445       // Put the current free range into the free lists.
7446       flush_cur_free_chunk(freeFinger(),
7447                            pointer_delta(fc_addr, freeFinger()));
7448     }
7449     // Set up for new free range.  Pass along whether the right hand
7450     // chunk is in the free lists.
7451     initialize_free_range((HeapWord*)fc, fcInFreeLists);
7452   }
7453 }
7454 
7455 // Lookahead flush:
7456 // If we are tracking a free range, and this is the last chunk that
7457 // we'll look at because its end crosses past _limit, we'll preemptively
7458 // flush it along with any free range we may be holding on to. Note that
7459 // this can be the case only for an already free or freshly garbage
7460 // chunk. If this block is an object, it can never straddle
7461 // over _limit. The "straddling" occurs when _limit is set at
7462 // the previous end of the space when this cycle started, and
7463 // a subsequent heap expansion caused the previously co-terminal
7464 // free block to be coalesced with the newly expanded portion,
7465 // thus rendering _limit a non-block-boundary making it dangerous
7466 // for the sweeper to step over and examine.
7467 void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) {
7468   assert(inFreeRange(), "Should only be called if currently in a free range.");
7469   HeapWord* const eob = ((HeapWord*)fc) + chunk_size;
7470   assert(_sp->used_region().contains(eob - 1),
7471          "eob = " PTR_FORMAT " eob-1 = " PTR_FORMAT " _limit = " PTR_FORMAT
7472          " out of bounds wrt _sp = [" PTR_FORMAT "," PTR_FORMAT ")"
7473          " when examining fc = " PTR_FORMAT "(" SIZE_FORMAT ")",
7474          p2i(eob), p2i(eob-1), p2i(_limit), p2i(_sp->bottom()), p2i(_sp->end()), p2i(fc), chunk_size);
7475   if (eob >= _limit) {
7476     assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit");
7477     log_develop_trace(gc, sweep)("_limit " PTR_FORMAT " reached or crossed by block "
7478                                  "[" PTR_FORMAT "," PTR_FORMAT ") in space "
7479                                  "[" PTR_FORMAT "," PTR_FORMAT ")",
7480                                  p2i(_limit), p2i(fc), p2i(eob), p2i(_sp->bottom()), p2i(_sp->end()));
7481     // Return the storage we are tracking back into the free lists.
7482     log_develop_trace(gc, sweep)("Flushing ... ");
7483     assert(freeFinger() < eob, "Error");
7484     flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger()));
7485   }
7486 }
7487 
7488 void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) {
7489   assert(inFreeRange(), "Should only be called if currently in a free range.");
7490   assert(size > 0,
7491     "A zero sized chunk cannot be added to the free lists.");
7492   if (!freeRangeInFreeLists()) {
7493     if (CMSTestInFreeList) {
7494       FreeChunk* fc = (FreeChunk*) chunk;
7495       fc->set_size(size);
7496       assert(!_sp->verify_chunk_in_free_list(fc),
7497              "chunk should not be in free lists yet");
7498     }
7499     log_develop_trace(gc, sweep)(" -- add free block " PTR_FORMAT " (" SIZE_FORMAT ") to free lists", p2i(chunk), size);
7500     // A new free range is going to be starting.  The current
7501     // free range has not been added to the free lists yet or
7502     // was removed so add it back.
7503     // If the current free range was coalesced, then the death
7504     // of the free range was recorded.  Record a birth now.
7505     if (lastFreeRangeCoalesced()) {
7506       _sp->coalBirth(size);
7507     }
7508     _sp->addChunkAndRepairOffsetTable(chunk, size,
7509             lastFreeRangeCoalesced());
7510   } else {
7511     log_develop_trace(gc, sweep)("Already in free list: nothing to flush");
7512   }
7513   set_inFreeRange(false);
7514   set_freeRangeInFreeLists(false);
7515 }
7516 
7517 // We take a break if we've been at this for a while,
7518 // so as to avoid monopolizing the locks involved.
7519 void SweepClosure::do_yield_work(HeapWord* addr) {
7520   // Return current free chunk being used for coalescing (if any)
7521   // to the appropriate freelist.  After yielding, the next
7522   // free block encountered will start a coalescing range of
7523   // free blocks.  If the next free block is adjacent to the
7524   // chunk just flushed, they will need to wait for the next
7525   // sweep to be coalesced.
7526   if (inFreeRange()) {
7527     flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7528   }
7529 
7530   // First give up the locks, then yield, then re-lock.
7531   // We should probably use a constructor/destructor idiom to
7532   // do this unlock/lock or modify the MutexUnlocker class to
7533   // serve our purpose. XXX
7534   assert_lock_strong(_bitMap->lock());
7535   assert_lock_strong(_freelistLock);
7536   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7537          "CMS thread should hold CMS token");
7538   _bitMap->lock()->unlock();
7539   _freelistLock->unlock();
7540   ConcurrentMarkSweepThread::desynchronize(true);
7541   _collector->stopTimer();
7542   _collector->incrementYields();
7543 
7544   // See the comment in coordinator_yield()
7545   for (unsigned i = 0; i < CMSYieldSleepCount &&
7546                        ConcurrentMarkSweepThread::should_yield() &&
7547                        !CMSCollector::foregroundGCIsActive(); ++i) {
7548     os::sleep(Thread::current(), 1, false);
7549   }
7550 
7551   ConcurrentMarkSweepThread::synchronize(true);
7552   _freelistLock->lock();
7553   _bitMap->lock()->lock_without_safepoint_check();
7554   _collector->startTimer();
7555 }
7556 
7557 #ifndef PRODUCT
7558 // This is actually very useful in a product build if it can
7559 // be called from the debugger.  Compile it into the product
7560 // as needed.
7561 bool debug_verify_chunk_in_free_list(FreeChunk* fc) {
7562   return debug_cms_space->verify_chunk_in_free_list(fc);
7563 }
7564 #endif
7565 
7566 void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const {
7567   log_develop_trace(gc, sweep)("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")",
7568                                p2i(fc), fc->size());
7569 }
7570 
7571 // CMSIsAliveClosure
7572 bool CMSIsAliveClosure::do_object_b(oop obj) {
7573   HeapWord* addr = (HeapWord*)obj;
7574   return addr != NULL &&
7575          (!_span.contains(addr) || _bit_map->isMarked(addr));
7576 }
7577 
7578 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector,
7579                       MemRegion span,
7580                       CMSBitMap* bit_map, CMSMarkStack* mark_stack,
7581                       bool cpc):
7582   _collector(collector),
7583   _span(span),
7584   _mark_stack(mark_stack),
7585   _bit_map(bit_map),
7586   _concurrent_precleaning(cpc) {
7587   assert(!_span.is_empty(), "Empty span could spell trouble");
7588 }
7589 
7590 
7591 // CMSKeepAliveClosure: the serial version
7592 void CMSKeepAliveClosure::do_oop(oop obj) {
7593   HeapWord* addr = (HeapWord*)obj;
7594   if (_span.contains(addr) &&
7595       !_bit_map->isMarked(addr)) {
7596     _bit_map->mark(addr);
7597     bool simulate_overflow = false;
7598     NOT_PRODUCT(
7599       if (CMSMarkStackOverflowALot &&
7600           _collector->simulate_overflow()) {
7601         // simulate a stack overflow
7602         simulate_overflow = true;
7603       }
7604     )
7605     if (simulate_overflow || !_mark_stack->push(obj)) {
7606       if (_concurrent_precleaning) {
7607         // We dirty the overflown object and let the remark
7608         // phase deal with it.
7609         assert(_collector->overflow_list_is_empty(), "Error");
7610         // In the case of object arrays, we need to dirty all of
7611         // the cards that the object spans. No locking or atomics
7612         // are needed since no one else can be mutating the mod union
7613         // table.
7614         if (obj->is_objArray()) {
7615           size_t sz = obj->size();
7616           HeapWord* end_card_addr = align_up(addr + sz, CardTable::card_size);
7617           MemRegion redirty_range = MemRegion(addr, end_card_addr);
7618           assert(!redirty_range.is_empty(), "Arithmetical tautology");
7619           _collector->_modUnionTable.mark_range(redirty_range);
7620         } else {
7621           _collector->_modUnionTable.mark(addr);
7622         }
7623         _collector->_ser_kac_preclean_ovflw++;
7624       } else {
7625         _collector->push_on_overflow_list(obj);
7626         _collector->_ser_kac_ovflw++;
7627       }
7628     }
7629   }
7630 }
7631 
7632 // CMSParKeepAliveClosure: a parallel version of the above.
7633 // The work queues are private to each closure (thread),
7634 // but (may be) available for stealing by other threads.
7635 void CMSParKeepAliveClosure::do_oop(oop obj) {
7636   HeapWord* addr = (HeapWord*)obj;
7637   if (_span.contains(addr) &&
7638       !_bit_map->isMarked(addr)) {
7639     // In general, during recursive tracing, several threads
7640     // may be concurrently getting here; the first one to
7641     // "tag" it, claims it.
7642     if (_bit_map->par_mark(addr)) {
7643       bool res = _work_queue->push(obj);
7644       assert(res, "Low water mark should be much less than capacity");
7645       // Do a recursive trim in the hope that this will keep
7646       // stack usage lower, but leave some oops for potential stealers
7647       trim_queue(_low_water_mark);
7648     } // Else, another thread got there first
7649   }
7650 }
7651 
7652 void CMSParKeepAliveClosure::trim_queue(uint max) {
7653   while (_work_queue->size() > max) {
7654     oop new_oop;
7655     if (_work_queue->pop_local(new_oop)) {
7656       assert(new_oop != NULL && oopDesc::is_oop(new_oop), "Expected an oop");
7657       assert(_bit_map->isMarked((HeapWord*)new_oop),
7658              "no white objects on this stack!");
7659       assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
7660       // iterate over the oops in this oop, marking and pushing
7661       // the ones in CMS heap (i.e. in _span).
7662       new_oop->oop_iterate(&_mark_and_push);
7663     }
7664   }
7665 }
7666 
7667 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
7668                                 CMSCollector* collector,
7669                                 MemRegion span, CMSBitMap* bit_map,
7670                                 OopTaskQueue* work_queue):
7671   _collector(collector),
7672   _span(span),
7673   _work_queue(work_queue),
7674   _bit_map(bit_map) { }
7675 
7676 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
7677   HeapWord* addr = (HeapWord*)obj;
7678   if (_span.contains(addr) &&
7679       !_bit_map->isMarked(addr)) {
7680     if (_bit_map->par_mark(addr)) {
7681       bool simulate_overflow = false;
7682       NOT_PRODUCT(
7683         if (CMSMarkStackOverflowALot &&
7684             _collector->par_simulate_overflow()) {
7685           // simulate a stack overflow
7686           simulate_overflow = true;
7687         }
7688       )
7689       if (simulate_overflow || !_work_queue->push(obj)) {
7690         _collector->par_push_on_overflow_list(obj);
7691         _collector->_par_kac_ovflw++;
7692       }
7693     } // Else another thread got there already
7694   }
7695 }
7696 
7697 //////////////////////////////////////////////////////////////////
7698 //  CMSExpansionCause                /////////////////////////////
7699 //////////////////////////////////////////////////////////////////
7700 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
7701   switch (cause) {
7702     case _no_expansion:
7703       return "No expansion";
7704     case _satisfy_free_ratio:
7705       return "Free ratio";
7706     case _satisfy_promotion:
7707       return "Satisfy promotion";
7708     case _satisfy_allocation:
7709       return "allocation";
7710     case _allocate_par_lab:
7711       return "Par LAB";
7712     case _allocate_par_spooling_space:
7713       return "Par Spooling Space";
7714     case _adaptive_size_policy:
7715       return "Ergonomics";
7716     default:
7717       return "unknown";
7718   }
7719 }
7720 
7721 void CMSDrainMarkingStackClosure::do_void() {
7722   // the max number to take from overflow list at a time
7723   const size_t num = _mark_stack->capacity()/4;
7724   assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
7725          "Overflow list should be NULL during concurrent phases");
7726   while (!_mark_stack->isEmpty() ||
7727          // if stack is empty, check the overflow list
7728          _collector->take_from_overflow_list(num, _mark_stack)) {
7729     oop obj = _mark_stack->pop();
7730     HeapWord* addr = (HeapWord*)obj;
7731     assert(_span.contains(addr), "Should be within span");
7732     assert(_bit_map->isMarked(addr), "Should be marked");
7733     assert(oopDesc::is_oop(obj), "Should be an oop");
7734     obj->oop_iterate(_keep_alive);
7735   }
7736 }
7737 
7738 void CMSParDrainMarkingStackClosure::do_void() {
7739   // drain queue
7740   trim_queue(0);
7741 }
7742 
7743 // Trim our work_queue so its length is below max at return
7744 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
7745   while (_work_queue->size() > max) {
7746     oop new_oop;
7747     if (_work_queue->pop_local(new_oop)) {
7748       assert(oopDesc::is_oop(new_oop), "Expected an oop");
7749       assert(_bit_map->isMarked((HeapWord*)new_oop),
7750              "no white objects on this stack!");
7751       assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
7752       // iterate over the oops in this oop, marking and pushing
7753       // the ones in CMS heap (i.e. in _span).
7754       new_oop->oop_iterate(&_mark_and_push);
7755     }
7756   }
7757 }
7758 
7759 ////////////////////////////////////////////////////////////////////
7760 // Support for Marking Stack Overflow list handling and related code
7761 ////////////////////////////////////////////////////////////////////
7762 // Much of the following code is similar in shape and spirit to the
7763 // code used in ParNewGC. We should try and share that code
7764 // as much as possible in the future.
7765 
7766 #ifndef PRODUCT
7767 // Debugging support for CMSStackOverflowALot
7768 
7769 // It's OK to call this multi-threaded;  the worst thing
7770 // that can happen is that we'll get a bunch of closely
7771 // spaced simulated overflows, but that's OK, in fact
7772 // probably good as it would exercise the overflow code
7773 // under contention.
7774 bool CMSCollector::simulate_overflow() {
7775   if (_overflow_counter-- <= 0) { // just being defensive
7776     _overflow_counter = CMSMarkStackOverflowInterval;
7777     return true;
7778   } else {
7779     return false;
7780   }
7781 }
7782 
7783 bool CMSCollector::par_simulate_overflow() {
7784   return simulate_overflow();
7785 }
7786 #endif
7787 
7788 // Single-threaded
7789 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
7790   assert(stack->isEmpty(), "Expected precondition");
7791   assert(stack->capacity() > num, "Shouldn't bite more than can chew");
7792   size_t i = num;
7793   oop  cur = _overflow_list;
7794   const markOop proto = markOopDesc::prototype();
7795   NOT_PRODUCT(ssize_t n = 0;)
7796   for (oop next; i > 0 && cur != NULL; cur = next, i--) {
7797     next = oop(cur->mark_raw());
7798     cur->set_mark_raw(proto);   // until proven otherwise
7799     assert(oopDesc::is_oop(cur), "Should be an oop");
7800     bool res = stack->push(cur);
7801     assert(res, "Bit off more than can chew?");
7802     NOT_PRODUCT(n++;)
7803   }
7804   _overflow_list = cur;
7805 #ifndef PRODUCT
7806   assert(_num_par_pushes >= n, "Too many pops?");
7807   _num_par_pushes -=n;
7808 #endif
7809   return !stack->isEmpty();
7810 }
7811 
7812 #define BUSY  (cast_to_oop<intptr_t>(0x1aff1aff))
7813 // (MT-safe) Get a prefix of at most "num" from the list.
7814 // The overflow list is chained through the mark word of
7815 // each object in the list. We fetch the entire list,
7816 // break off a prefix of the right size and return the
7817 // remainder. If other threads try to take objects from
7818 // the overflow list at that time, they will wait for
7819 // some time to see if data becomes available. If (and
7820 // only if) another thread places one or more object(s)
7821 // on the global list before we have returned the suffix
7822 // to the global list, we will walk down our local list
7823 // to find its end and append the global list to
7824 // our suffix before returning it. This suffix walk can
7825 // prove to be expensive (quadratic in the amount of traffic)
7826 // when there are many objects in the overflow list and
7827 // there is much producer-consumer contention on the list.
7828 // *NOTE*: The overflow list manipulation code here and
7829 // in ParNewGeneration:: are very similar in shape,
7830 // except that in the ParNew case we use the old (from/eden)
7831 // copy of the object to thread the list via its klass word.
7832 // Because of the common code, if you make any changes in
7833 // the code below, please check the ParNew version to see if
7834 // similar changes might be needed.
7835 // CR 6797058 has been filed to consolidate the common code.
7836 bool CMSCollector::par_take_from_overflow_list(size_t num,
7837                                                OopTaskQueue* work_q,
7838                                                int no_of_gc_threads) {
7839   assert(work_q->size() == 0, "First empty local work queue");
7840   assert(num < work_q->max_elems(), "Can't bite more than we can chew");
7841   if (_overflow_list == NULL) {
7842     return false;
7843   }
7844   // Grab the entire list; we'll put back a suffix
7845   oop prefix = cast_to_oop(Atomic::xchg((oopDesc*)BUSY, &_overflow_list));
7846   Thread* tid = Thread::current();
7847   // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was
7848   // set to ParallelGCThreads.
7849   size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads;
7850   size_t sleep_time_millis = MAX2((size_t)1, num/100);
7851   // If the list is busy, we spin for a short while,
7852   // sleeping between attempts to get the list.
7853   for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) {
7854     os::sleep(tid, sleep_time_millis, false);
7855     if (_overflow_list == NULL) {
7856       // Nothing left to take
7857       return false;
7858     } else if (_overflow_list != BUSY) {
7859       // Try and grab the prefix
7860       prefix = cast_to_oop(Atomic::xchg((oopDesc*)BUSY, &_overflow_list));
7861     }
7862   }
7863   // If the list was found to be empty, or we spun long
7864   // enough, we give up and return empty-handed. If we leave
7865   // the list in the BUSY state below, it must be the case that
7866   // some other thread holds the overflow list and will set it
7867   // to a non-BUSY state in the future.
7868   if (prefix == NULL || prefix == BUSY) {
7869      // Nothing to take or waited long enough
7870      if (prefix == NULL) {
7871        // Write back the NULL in case we overwrote it with BUSY above
7872        // and it is still the same value.
7873        Atomic::cmpxchg((oopDesc*)NULL, &_overflow_list, (oopDesc*)BUSY);
7874      }
7875      return false;
7876   }
7877   assert(prefix != NULL && prefix != BUSY, "Error");
7878   size_t i = num;
7879   oop cur = prefix;
7880   // Walk down the first "num" objects, unless we reach the end.
7881   for (; i > 1 && cur->mark_raw() != NULL; cur = oop(cur->mark_raw()), i--);
7882   if (cur->mark_raw() == NULL) {
7883     // We have "num" or fewer elements in the list, so there
7884     // is nothing to return to the global list.
7885     // Write back the NULL in lieu of the BUSY we wrote
7886     // above, if it is still the same value.
7887     if (_overflow_list == BUSY) {
7888       Atomic::cmpxchg((oopDesc*)NULL, &_overflow_list, (oopDesc*)BUSY);
7889     }
7890   } else {
7891     // Chop off the suffix and return it to the global list.
7892     assert(cur->mark_raw() != BUSY, "Error");
7893     oop suffix_head = cur->mark_raw(); // suffix will be put back on global list
7894     cur->set_mark_raw(NULL);           // break off suffix
7895     // It's possible that the list is still in the empty(busy) state
7896     // we left it in a short while ago; in that case we may be
7897     // able to place back the suffix without incurring the cost
7898     // of a walk down the list.
7899     oop observed_overflow_list = _overflow_list;
7900     oop cur_overflow_list = observed_overflow_list;
7901     bool attached = false;
7902     while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
7903       observed_overflow_list =
7904         Atomic::cmpxchg((oopDesc*)suffix_head, &_overflow_list, (oopDesc*)cur_overflow_list);
7905       if (cur_overflow_list == observed_overflow_list) {
7906         attached = true;
7907         break;
7908       } else cur_overflow_list = observed_overflow_list;
7909     }
7910     if (!attached) {
7911       // Too bad, someone else sneaked in (at least) an element; we'll need
7912       // to do a splice. Find tail of suffix so we can prepend suffix to global
7913       // list.
7914       for (cur = suffix_head; cur->mark_raw() != NULL; cur = (oop)(cur->mark_raw()));
7915       oop suffix_tail = cur;
7916       assert(suffix_tail != NULL && suffix_tail->mark_raw() == NULL,
7917              "Tautology");
7918       observed_overflow_list = _overflow_list;
7919       do {
7920         cur_overflow_list = observed_overflow_list;
7921         if (cur_overflow_list != BUSY) {
7922           // Do the splice ...
7923           suffix_tail->set_mark_raw(markOop(cur_overflow_list));
7924         } else { // cur_overflow_list == BUSY
7925           suffix_tail->set_mark_raw(NULL);
7926         }
7927         // ... and try to place spliced list back on overflow_list ...
7928         observed_overflow_list =
7929           Atomic::cmpxchg((oopDesc*)suffix_head, &_overflow_list, (oopDesc*)cur_overflow_list);
7930       } while (cur_overflow_list != observed_overflow_list);
7931       // ... until we have succeeded in doing so.
7932     }
7933   }
7934 
7935   // Push the prefix elements on work_q
7936   assert(prefix != NULL, "control point invariant");
7937   const markOop proto = markOopDesc::prototype();
7938   oop next;
7939   NOT_PRODUCT(ssize_t n = 0;)
7940   for (cur = prefix; cur != NULL; cur = next) {
7941     next = oop(cur->mark_raw());
7942     cur->set_mark_raw(proto);   // until proven otherwise
7943     assert(oopDesc::is_oop(cur), "Should be an oop");
7944     bool res = work_q->push(cur);
7945     assert(res, "Bit off more than we can chew?");
7946     NOT_PRODUCT(n++;)
7947   }
7948 #ifndef PRODUCT
7949   assert(_num_par_pushes >= n, "Too many pops?");
7950   Atomic::sub(n, &_num_par_pushes);
7951 #endif
7952   return true;
7953 }
7954 
7955 // Single-threaded
7956 void CMSCollector::push_on_overflow_list(oop p) {
7957   NOT_PRODUCT(_num_par_pushes++;)
7958   assert(oopDesc::is_oop(p), "Not an oop");
7959   preserve_mark_if_necessary(p);
7960   p->set_mark_raw((markOop)_overflow_list);
7961   _overflow_list = p;
7962 }
7963 
7964 // Multi-threaded; use CAS to prepend to overflow list
7965 void CMSCollector::par_push_on_overflow_list(oop p) {
7966   NOT_PRODUCT(Atomic::inc(&_num_par_pushes);)
7967   assert(oopDesc::is_oop(p), "Not an oop");
7968   par_preserve_mark_if_necessary(p);
7969   oop observed_overflow_list = _overflow_list;
7970   oop cur_overflow_list;
7971   do {
7972     cur_overflow_list = observed_overflow_list;
7973     if (cur_overflow_list != BUSY) {
7974       p->set_mark_raw(markOop(cur_overflow_list));
7975     } else {
7976       p->set_mark_raw(NULL);
7977     }
7978     observed_overflow_list =
7979       Atomic::cmpxchg((oopDesc*)p, &_overflow_list, (oopDesc*)cur_overflow_list);
7980   } while (cur_overflow_list != observed_overflow_list);
7981 }
7982 #undef BUSY
7983 
7984 // Single threaded
7985 // General Note on GrowableArray: pushes may silently fail
7986 // because we are (temporarily) out of C-heap for expanding
7987 // the stack. The problem is quite ubiquitous and affects
7988 // a lot of code in the JVM. The prudent thing for GrowableArray
7989 // to do (for now) is to exit with an error. However, that may
7990 // be too draconian in some cases because the caller may be
7991 // able to recover without much harm. For such cases, we
7992 // should probably introduce a "soft_push" method which returns
7993 // an indication of success or failure with the assumption that
7994 // the caller may be able to recover from a failure; code in
7995 // the VM can then be changed, incrementally, to deal with such
7996 // failures where possible, thus, incrementally hardening the VM
7997 // in such low resource situations.
7998 void CMSCollector::preserve_mark_work(oop p, markOop m) {
7999   _preserved_oop_stack.push(p);
8000   _preserved_mark_stack.push(m);
8001   assert(m == p->mark_raw(), "Mark word changed");
8002   assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8003          "bijection");
8004 }
8005 
8006 // Single threaded
8007 void CMSCollector::preserve_mark_if_necessary(oop p) {
8008   markOop m = p->mark_raw();
8009   if (m->must_be_preserved(p)) {
8010     preserve_mark_work(p, m);
8011   }
8012 }
8013 
8014 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
8015   markOop m = p->mark_raw();
8016   if (m->must_be_preserved(p)) {
8017     MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
8018     // Even though we read the mark word without holding
8019     // the lock, we are assured that it will not change
8020     // because we "own" this oop, so no other thread can
8021     // be trying to push it on the overflow list; see
8022     // the assertion in preserve_mark_work() that checks
8023     // that m == p->mark_raw().
8024     preserve_mark_work(p, m);
8025   }
8026 }
8027 
8028 // We should be able to do this multi-threaded,
8029 // a chunk of stack being a task (this is
8030 // correct because each oop only ever appears
8031 // once in the overflow list. However, it's
8032 // not very easy to completely overlap this with
8033 // other operations, so will generally not be done
8034 // until all work's been completed. Because we
8035 // expect the preserved oop stack (set) to be small,
8036 // it's probably fine to do this single-threaded.
8037 // We can explore cleverer concurrent/overlapped/parallel
8038 // processing of preserved marks if we feel the
8039 // need for this in the future. Stack overflow should
8040 // be so rare in practice and, when it happens, its
8041 // effect on performance so great that this will
8042 // likely just be in the noise anyway.
8043 void CMSCollector::restore_preserved_marks_if_any() {
8044   assert(SafepointSynchronize::is_at_safepoint(),
8045          "world should be stopped");
8046   assert(Thread::current()->is_ConcurrentGC_thread() ||
8047          Thread::current()->is_VM_thread(),
8048          "should be single-threaded");
8049   assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8050          "bijection");
8051 
8052   while (!_preserved_oop_stack.is_empty()) {
8053     oop p = _preserved_oop_stack.pop();
8054     assert(oopDesc::is_oop(p), "Should be an oop");
8055     assert(_span.contains(p), "oop should be in _span");
8056     assert(p->mark_raw() == markOopDesc::prototype(),
8057            "Set when taken from overflow list");
8058     markOop m = _preserved_mark_stack.pop();
8059     p->set_mark_raw(m);
8060   }
8061   assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(),
8062          "stacks were cleared above");
8063 }
8064 
8065 #ifndef PRODUCT
8066 bool CMSCollector::no_preserved_marks() const {
8067   return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty();
8068 }
8069 #endif
8070 
8071 // Transfer some number of overflown objects to usual marking
8072 // stack. Return true if some objects were transferred.
8073 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
8074   size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,
8075                     (size_t)ParGCDesiredObjsFromOverflowList);
8076 
8077   bool res = _collector->take_from_overflow_list(num, _mark_stack);
8078   assert(_collector->overflow_list_is_empty() || res,
8079          "If list is not empty, we should have taken something");
8080   assert(!res || !_mark_stack->isEmpty(),
8081          "If we took something, it should now be on our stack");
8082   return res;
8083 }
8084 
8085 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
8086   size_t res = _sp->block_size_no_stall(addr, _collector);
8087   if (_sp->block_is_obj(addr)) {
8088     if (_live_bit_map->isMarked(addr)) {
8089       // It can't have been dead in a previous cycle
8090       guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
8091     } else {
8092       _dead_bit_map->mark(addr);      // mark the dead object
8093     }
8094   }
8095   // Could be 0, if the block size could not be computed without stalling.
8096   return res;
8097 }
8098 
8099 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() {
8100   GCMemoryManager* manager = CMSHeap::heap()->old_manager();
8101   switch (phase) {
8102     case CMSCollector::InitialMarking:
8103       initialize(manager /* GC manager */ ,
8104                  cause   /* cause of the GC */,
8105                  true    /* allMemoryPoolsAffected */,
8106                  true    /* recordGCBeginTime */,
8107                  true    /* recordPreGCUsage */,
8108                  false   /* recordPeakUsage */,
8109                  false   /* recordPostGCusage */,
8110                  true    /* recordAccumulatedGCTime */,
8111                  false   /* recordGCEndTime */,
8112                  false   /* countCollection */  );
8113       break;
8114 
8115     case CMSCollector::FinalMarking:
8116       initialize(manager /* GC manager */ ,
8117                  cause   /* cause of the GC */,
8118                  true    /* allMemoryPoolsAffected */,
8119                  false   /* recordGCBeginTime */,
8120                  false   /* recordPreGCUsage */,
8121                  false   /* recordPeakUsage */,
8122                  false   /* recordPostGCusage */,
8123                  true    /* recordAccumulatedGCTime */,
8124                  false   /* recordGCEndTime */,
8125                  false   /* countCollection */  );
8126       break;
8127 
8128     case CMSCollector::Sweeping:
8129       initialize(manager /* GC manager */ ,
8130                  cause   /* cause of the GC */,
8131                  true    /* allMemoryPoolsAffected */,
8132                  false   /* recordGCBeginTime */,
8133                  false   /* recordPreGCUsage */,
8134                  true    /* recordPeakUsage */,
8135                  true    /* recordPostGCusage */,
8136                  false   /* recordAccumulatedGCTime */,
8137                  true    /* recordGCEndTime */,
8138                  true    /* countCollection */  );
8139       break;
8140 
8141     default:
8142       ShouldNotReachHere();
8143   }
8144 }