1 /*
   2  * Copyright (c) 2001, 2016, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
  21  * questions.
  22  *
  23  */
  24 
  25 #include "precompiled.hpp"
  26 #include "classfile/classLoaderData.hpp"
  27 #include "classfile/stringTable.hpp"
  28 #include "classfile/symbolTable.hpp"
  29 #include "classfile/systemDictionary.hpp"
  30 #include "code/codeCache.hpp"
  31 #include "gc/cms/cmsCollectorPolicy.hpp"
  32 #include "gc/cms/cmsOopClosures.inline.hpp"
  33 #include "gc/cms/compactibleFreeListSpace.hpp"
  34 #include "gc/cms/concurrentMarkSweepGeneration.inline.hpp"
  35 #include "gc/cms/concurrentMarkSweepThread.hpp"
  36 #include "gc/cms/parNewGeneration.hpp"
  37 #include "gc/cms/vmCMSOperations.hpp"
  38 #include "gc/serial/genMarkSweep.hpp"
  39 #include "gc/serial/tenuredGeneration.hpp"
  40 #include "gc/shared/adaptiveSizePolicy.hpp"
  41 #include "gc/shared/cardGeneration.inline.hpp"
  42 #include "gc/shared/cardTableRS.hpp"
  43 #include "gc/shared/collectedHeap.inline.hpp"
  44 #include "gc/shared/collectorCounters.hpp"
  45 #include "gc/shared/collectorPolicy.hpp"
  46 #include "gc/shared/gcLocker.inline.hpp"
  47 #include "gc/shared/gcPolicyCounters.hpp"
  48 #include "gc/shared/gcTimer.hpp"
  49 #include "gc/shared/gcTrace.hpp"
  50 #include "gc/shared/gcTraceTime.inline.hpp"
  51 #include "gc/shared/genCollectedHeap.hpp"
  52 #include "gc/shared/genOopClosures.inline.hpp"
  53 #include "gc/shared/isGCActiveMark.hpp"
  54 #include "gc/shared/referencePolicy.hpp"
  55 #include "gc/shared/strongRootsScope.hpp"
  56 #include "gc/shared/taskqueue.inline.hpp"
  57 #include "logging/log.hpp"
  58 #include "memory/allocation.hpp"
  59 #include "memory/iterator.inline.hpp"
  60 #include "memory/padded.hpp"
  61 #include "memory/resourceArea.hpp"
  62 #include "oops/oop.inline.hpp"
  63 #include "prims/jvmtiExport.hpp"
  64 #include "runtime/atomic.hpp"
  65 #include "runtime/globals_extension.hpp"
  66 #include "runtime/handles.inline.hpp"
  67 #include "runtime/java.hpp"
  68 #include "runtime/orderAccess.inline.hpp"
  69 #include "runtime/timer.hpp"
  70 #include "runtime/vmThread.hpp"
  71 #include "services/memoryService.hpp"
  72 #include "services/runtimeService.hpp"
  73 #include "utilities/stack.inline.hpp"
  74 
  75 // statics
  76 CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL;
  77 bool CMSCollector::_full_gc_requested = false;
  78 GCCause::Cause CMSCollector::_full_gc_cause = GCCause::_no_gc;
  79 
  80 //////////////////////////////////////////////////////////////////
  81 // In support of CMS/VM thread synchronization
  82 //////////////////////////////////////////////////////////////////
  83 // We split use of the CGC_lock into 2 "levels".
  84 // The low-level locking is of the usual CGC_lock monitor. We introduce
  85 // a higher level "token" (hereafter "CMS token") built on top of the
  86 // low level monitor (hereafter "CGC lock").
  87 // The token-passing protocol gives priority to the VM thread. The
  88 // CMS-lock doesn't provide any fairness guarantees, but clients
  89 // should ensure that it is only held for very short, bounded
  90 // durations.
  91 //
  92 // When either of the CMS thread or the VM thread is involved in
  93 // collection operations during which it does not want the other
  94 // thread to interfere, it obtains the CMS token.
  95 //
  96 // If either thread tries to get the token while the other has
  97 // it, that thread waits. However, if the VM thread and CMS thread
  98 // both want the token, then the VM thread gets priority while the
  99 // CMS thread waits. This ensures, for instance, that the "concurrent"
 100 // phases of the CMS thread's work do not block out the VM thread
 101 // for long periods of time as the CMS thread continues to hog
 102 // the token. (See bug 4616232).
 103 //
 104 // The baton-passing functions are, however, controlled by the
 105 // flags _foregroundGCShouldWait and _foregroundGCIsActive,
 106 // and here the low-level CMS lock, not the high level token,
 107 // ensures mutual exclusion.
 108 //
 109 // Two important conditions that we have to satisfy:
 110 // 1. if a thread does a low-level wait on the CMS lock, then it
 111 //    relinquishes the CMS token if it were holding that token
 112 //    when it acquired the low-level CMS lock.
 113 // 2. any low-level notifications on the low-level lock
 114 //    should only be sent when a thread has relinquished the token.
 115 //
 116 // In the absence of either property, we'd have potential deadlock.
 117 //
 118 // We protect each of the CMS (concurrent and sequential) phases
 119 // with the CMS _token_, not the CMS _lock_.
 120 //
 121 // The only code protected by CMS lock is the token acquisition code
 122 // itself, see ConcurrentMarkSweepThread::[de]synchronize(), and the
 123 // baton-passing code.
 124 //
 125 // Unfortunately, i couldn't come up with a good abstraction to factor and
 126 // hide the naked CGC_lock manipulation in the baton-passing code
 127 // further below. That's something we should try to do. Also, the proof
 128 // of correctness of this 2-level locking scheme is far from obvious,
 129 // and potentially quite slippery. We have an uneasy suspicion, for instance,
 130 // that there may be a theoretical possibility of delay/starvation in the
 131 // low-level lock/wait/notify scheme used for the baton-passing because of
 132 // potential interference with the priority scheme embodied in the
 133 // CMS-token-passing protocol. See related comments at a CGC_lock->wait()
 134 // invocation further below and marked with "XXX 20011219YSR".
 135 // Indeed, as we note elsewhere, this may become yet more slippery
 136 // in the presence of multiple CMS and/or multiple VM threads. XXX
 137 
 138 class CMSTokenSync: public StackObj {
 139  private:
 140   bool _is_cms_thread;
 141  public:
 142   CMSTokenSync(bool is_cms_thread):
 143     _is_cms_thread(is_cms_thread) {
 144     assert(is_cms_thread == Thread::current()->is_ConcurrentGC_thread(),
 145            "Incorrect argument to constructor");
 146     ConcurrentMarkSweepThread::synchronize(_is_cms_thread);
 147   }
 148 
 149   ~CMSTokenSync() {
 150     assert(_is_cms_thread ?
 151              ConcurrentMarkSweepThread::cms_thread_has_cms_token() :
 152              ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
 153           "Incorrect state");
 154     ConcurrentMarkSweepThread::desynchronize(_is_cms_thread);
 155   }
 156 };
 157 
 158 // Convenience class that does a CMSTokenSync, and then acquires
 159 // upto three locks.
 160 class CMSTokenSyncWithLocks: public CMSTokenSync {
 161  private:
 162   // Note: locks are acquired in textual declaration order
 163   // and released in the opposite order
 164   MutexLockerEx _locker1, _locker2, _locker3;
 165  public:
 166   CMSTokenSyncWithLocks(bool is_cms_thread, Mutex* mutex1,
 167                         Mutex* mutex2 = NULL, Mutex* mutex3 = NULL):
 168     CMSTokenSync(is_cms_thread),
 169     _locker1(mutex1, Mutex::_no_safepoint_check_flag),
 170     _locker2(mutex2, Mutex::_no_safepoint_check_flag),
 171     _locker3(mutex3, Mutex::_no_safepoint_check_flag)
 172   { }
 173 };
 174 
 175 
 176 //////////////////////////////////////////////////////////////////
 177 //  Concurrent Mark-Sweep Generation /////////////////////////////
 178 //////////////////////////////////////////////////////////////////
 179 
 180 NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;)
 181 
 182 // This struct contains per-thread things necessary to support parallel
 183 // young-gen collection.
 184 class CMSParGCThreadState: public CHeapObj<mtGC> {
 185  public:
 186   CompactibleFreeListSpaceLAB lab;
 187   PromotionInfo promo;
 188 
 189   // Constructor.
 190   CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) {
 191     promo.setSpace(cfls);
 192   }
 193 };
 194 
 195 ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration(
 196      ReservedSpace rs, size_t initial_byte_size, CardTableRS* ct) :
 197   CardGeneration(rs, initial_byte_size, ct),
 198   _dilatation_factor(((double)MinChunkSize)/((double)(CollectedHeap::min_fill_size()))),
 199   _did_compact(false)
 200 {
 201   HeapWord* bottom = (HeapWord*) _virtual_space.low();
 202   HeapWord* end    = (HeapWord*) _virtual_space.high();
 203 
 204   _direct_allocated_words = 0;
 205   NOT_PRODUCT(
 206     _numObjectsPromoted = 0;
 207     _numWordsPromoted = 0;
 208     _numObjectsAllocated = 0;
 209     _numWordsAllocated = 0;
 210   )
 211 
 212   _cmsSpace = new CompactibleFreeListSpace(_bts, MemRegion(bottom, end));
 213   NOT_PRODUCT(debug_cms_space = _cmsSpace;)
 214   _cmsSpace->_old_gen = this;
 215 
 216   _gc_stats = new CMSGCStats();
 217 
 218   // Verify the assumption that FreeChunk::_prev and OopDesc::_klass
 219   // offsets match. The ability to tell free chunks from objects
 220   // depends on this property.
 221   debug_only(
 222     FreeChunk* junk = NULL;
 223     assert(UseCompressedClassPointers ||
 224            junk->prev_addr() == (void*)(oop(junk)->klass_addr()),
 225            "Offset of FreeChunk::_prev within FreeChunk must match"
 226            "  that of OopDesc::_klass within OopDesc");
 227   )
 228 
 229   _par_gc_thread_states = NEW_C_HEAP_ARRAY(CMSParGCThreadState*, ParallelGCThreads, mtGC);
 230   for (uint i = 0; i < ParallelGCThreads; i++) {
 231     _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace());
 232   }
 233 
 234   _incremental_collection_failed = false;
 235   // The "dilatation_factor" is the expansion that can occur on
 236   // account of the fact that the minimum object size in the CMS
 237   // generation may be larger than that in, say, a contiguous young
 238   //  generation.
 239   // Ideally, in the calculation below, we'd compute the dilatation
 240   // factor as: MinChunkSize/(promoting_gen's min object size)
 241   // Since we do not have such a general query interface for the
 242   // promoting generation, we'll instead just use the minimum
 243   // object size (which today is a header's worth of space);
 244   // note that all arithmetic is in units of HeapWords.
 245   assert(MinChunkSize >= CollectedHeap::min_fill_size(), "just checking");
 246   assert(_dilatation_factor >= 1.0, "from previous assert");
 247 }
 248 
 249 
 250 // The field "_initiating_occupancy" represents the occupancy percentage
 251 // at which we trigger a new collection cycle.  Unless explicitly specified
 252 // via CMSInitiatingOccupancyFraction (argument "io" below), it
 253 // is calculated by:
 254 //
 255 //   Let "f" be MinHeapFreeRatio in
 256 //
 257 //    _initiating_occupancy = 100-f +
 258 //                           f * (CMSTriggerRatio/100)
 259 //   where CMSTriggerRatio is the argument "tr" below.
 260 //
 261 // That is, if we assume the heap is at its desired maximum occupancy at the
 262 // end of a collection, we let CMSTriggerRatio of the (purported) free
 263 // space be allocated before initiating a new collection cycle.
 264 //
 265 void ConcurrentMarkSweepGeneration::init_initiating_occupancy(intx io, uintx tr) {
 266   assert(io <= 100 && tr <= 100, "Check the arguments");
 267   if (io >= 0) {
 268     _initiating_occupancy = (double)io / 100.0;
 269   } else {
 270     _initiating_occupancy = ((100 - MinHeapFreeRatio) +
 271                              (double)(tr * MinHeapFreeRatio) / 100.0)
 272                             / 100.0;
 273   }
 274 }
 275 
 276 void ConcurrentMarkSweepGeneration::ref_processor_init() {
 277   assert(collector() != NULL, "no collector");
 278   collector()->ref_processor_init();
 279 }
 280 
 281 void CMSCollector::ref_processor_init() {
 282   if (_ref_processor == NULL) {
 283     // Allocate and initialize a reference processor
 284     _ref_processor =
 285       new ReferenceProcessor(_span,                               // span
 286                              (ParallelGCThreads > 1) && ParallelRefProcEnabled, // mt processing
 287                              ParallelGCThreads,                   // mt processing degree
 288                              _cmsGen->refs_discovery_is_mt(),     // mt discovery
 289                              MAX2(ConcGCThreads, ParallelGCThreads), // mt discovery degree
 290                              _cmsGen->refs_discovery_is_atomic(), // discovery is not atomic
 291                              &_is_alive_closure);                 // closure for liveness info
 292     // Initialize the _ref_processor field of CMSGen
 293     _cmsGen->set_ref_processor(_ref_processor);
 294 
 295   }
 296 }
 297 
 298 AdaptiveSizePolicy* CMSCollector::size_policy() {
 299   GenCollectedHeap* gch = GenCollectedHeap::heap();
 300   return gch->gen_policy()->size_policy();
 301 }
 302 
 303 void ConcurrentMarkSweepGeneration::initialize_performance_counters() {
 304 
 305   const char* gen_name = "old";
 306   GenCollectorPolicy* gcp = GenCollectedHeap::heap()->gen_policy();
 307   // Generation Counters - generation 1, 1 subspace
 308   _gen_counters = new GenerationCounters(gen_name, 1, 1,
 309       gcp->min_old_size(), gcp->max_old_size(), &_virtual_space);
 310 
 311   _space_counters = new GSpaceCounters(gen_name, 0,
 312                                        _virtual_space.reserved_size(),
 313                                        this, _gen_counters);
 314 }
 315 
 316 CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha):
 317   _cms_gen(cms_gen)
 318 {
 319   assert(alpha <= 100, "bad value");
 320   _saved_alpha = alpha;
 321 
 322   // Initialize the alphas to the bootstrap value of 100.
 323   _gc0_alpha = _cms_alpha = 100;
 324 
 325   _cms_begin_time.update();
 326   _cms_end_time.update();
 327 
 328   _gc0_duration = 0.0;
 329   _gc0_period = 0.0;
 330   _gc0_promoted = 0;
 331 
 332   _cms_duration = 0.0;
 333   _cms_period = 0.0;
 334   _cms_allocated = 0;
 335 
 336   _cms_used_at_gc0_begin = 0;
 337   _cms_used_at_gc0_end = 0;
 338   _allow_duty_cycle_reduction = false;
 339   _valid_bits = 0;
 340 }
 341 
 342 double CMSStats::cms_free_adjustment_factor(size_t free) const {
 343   // TBD: CR 6909490
 344   return 1.0;
 345 }
 346 
 347 void CMSStats::adjust_cms_free_adjustment_factor(bool fail, size_t free) {
 348 }
 349 
 350 // If promotion failure handling is on use
 351 // the padded average size of the promotion for each
 352 // young generation collection.
 353 double CMSStats::time_until_cms_gen_full() const {
 354   size_t cms_free = _cms_gen->cmsSpace()->free();
 355   GenCollectedHeap* gch = GenCollectedHeap::heap();
 356   size_t expected_promotion = MIN2(gch->young_gen()->capacity(),
 357                                    (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average());
 358   if (cms_free > expected_promotion) {
 359     // Start a cms collection if there isn't enough space to promote
 360     // for the next young collection.  Use the padded average as
 361     // a safety factor.
 362     cms_free -= expected_promotion;
 363 
 364     // Adjust by the safety factor.
 365     double cms_free_dbl = (double)cms_free;
 366     double cms_adjustment = (100.0 - CMSIncrementalSafetyFactor) / 100.0;
 367     // Apply a further correction factor which tries to adjust
 368     // for recent occurance of concurrent mode failures.
 369     cms_adjustment = cms_adjustment * cms_free_adjustment_factor(cms_free);
 370     cms_free_dbl = cms_free_dbl * cms_adjustment;
 371 
 372     log_trace(gc)("CMSStats::time_until_cms_gen_full: cms_free " SIZE_FORMAT " expected_promotion " SIZE_FORMAT,
 373                   cms_free, expected_promotion);
 374     log_trace(gc)("  cms_free_dbl %f cms_consumption_rate %f", cms_free_dbl, cms_consumption_rate() + 1.0);
 375     // Add 1 in case the consumption rate goes to zero.
 376     return cms_free_dbl / (cms_consumption_rate() + 1.0);
 377   }
 378   return 0.0;
 379 }
 380 
 381 // Compare the duration of the cms collection to the
 382 // time remaining before the cms generation is empty.
 383 // Note that the time from the start of the cms collection
 384 // to the start of the cms sweep (less than the total
 385 // duration of the cms collection) can be used.  This
 386 // has been tried and some applications experienced
 387 // promotion failures early in execution.  This was
 388 // possibly because the averages were not accurate
 389 // enough at the beginning.
 390 double CMSStats::time_until_cms_start() const {
 391   // We add "gc0_period" to the "work" calculation
 392   // below because this query is done (mostly) at the
 393   // end of a scavenge, so we need to conservatively
 394   // account for that much possible delay
 395   // in the query so as to avoid concurrent mode failures
 396   // due to starting the collection just a wee bit too
 397   // late.
 398   double work = cms_duration() + gc0_period();
 399   double deadline = time_until_cms_gen_full();
 400   // If a concurrent mode failure occurred recently, we want to be
 401   // more conservative and halve our expected time_until_cms_gen_full()
 402   if (work > deadline) {
 403     log_develop_trace(gc)("CMSCollector: collect because of anticipated promotion before full %3.7f + %3.7f > %3.7f ",
 404                           cms_duration(), gc0_period(), time_until_cms_gen_full());
 405     return 0.0;
 406   }
 407   return work - deadline;
 408 }
 409 
 410 #ifndef PRODUCT
 411 void CMSStats::print_on(outputStream *st) const {
 412   st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha);
 413   st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo=" SIZE_FORMAT,
 414                gc0_duration(), gc0_period(), gc0_promoted());
 415   st->print(",cms_dur=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT,
 416             cms_duration(), cms_period(), cms_allocated());
 417   st->print(",cms_since_beg=%g,cms_since_end=%g",
 418             cms_time_since_begin(), cms_time_since_end());
 419   st->print(",cms_used_beg=" SIZE_FORMAT ",cms_used_end=" SIZE_FORMAT,
 420             _cms_used_at_gc0_begin, _cms_used_at_gc0_end);
 421 
 422   if (valid()) {
 423     st->print(",promo_rate=%g,cms_alloc_rate=%g",
 424               promotion_rate(), cms_allocation_rate());
 425     st->print(",cms_consumption_rate=%g,time_until_full=%g",
 426               cms_consumption_rate(), time_until_cms_gen_full());
 427   }
 428   st->cr();
 429 }
 430 #endif // #ifndef PRODUCT
 431 
 432 CMSCollector::CollectorState CMSCollector::_collectorState =
 433                              CMSCollector::Idling;
 434 bool CMSCollector::_foregroundGCIsActive = false;
 435 bool CMSCollector::_foregroundGCShouldWait = false;
 436 
 437 CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
 438                            CardTableRS*                   ct,
 439                            ConcurrentMarkSweepPolicy*     cp):
 440   _cmsGen(cmsGen),
 441   _ct(ct),
 442   _ref_processor(NULL),    // will be set later
 443   _conc_workers(NULL),     // may be set later
 444   _abort_preclean(false),
 445   _start_sampling(false),
 446   _between_prologue_and_epilogue(false),
 447   _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"),
 448   _modUnionTable((CardTableModRefBS::card_shift - LogHeapWordSize),
 449                  -1 /* lock-free */, "No_lock" /* dummy */),
 450   _modUnionClosurePar(&_modUnionTable),
 451   // Adjust my span to cover old (cms) gen
 452   _span(cmsGen->reserved()),
 453   // Construct the is_alive_closure with _span & markBitMap
 454   _is_alive_closure(_span, &_markBitMap),
 455   _restart_addr(NULL),
 456   _overflow_list(NULL),
 457   _stats(cmsGen),
 458   _eden_chunk_lock(new Mutex(Mutex::leaf + 1, "CMS_eden_chunk_lock", true,
 459                              //verify that this lock should be acquired with safepoint check.
 460                              Monitor::_safepoint_check_sometimes)),
 461   _eden_chunk_array(NULL),     // may be set in ctor body
 462   _eden_chunk_capacity(0),     // -- ditto --
 463   _eden_chunk_index(0),        // -- ditto --
 464   _survivor_plab_array(NULL),  // -- ditto --
 465   _survivor_chunk_array(NULL), // -- ditto --
 466   _survivor_chunk_capacity(0), // -- ditto --
 467   _survivor_chunk_index(0),    // -- ditto --
 468   _ser_pmc_preclean_ovflw(0),
 469   _ser_kac_preclean_ovflw(0),
 470   _ser_pmc_remark_ovflw(0),
 471   _par_pmc_remark_ovflw(0),
 472   _ser_kac_ovflw(0),
 473   _par_kac_ovflw(0),
 474 #ifndef PRODUCT
 475   _num_par_pushes(0),
 476 #endif
 477   _collection_count_start(0),
 478   _verifying(false),
 479   _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"),
 480   _completed_initialization(false),
 481   _collector_policy(cp),
 482   _should_unload_classes(CMSClassUnloadingEnabled),
 483   _concurrent_cycles_since_last_unload(0),
 484   _roots_scanning_options(GenCollectedHeap::SO_None),
 485   _inter_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
 486   _intra_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
 487   _gc_tracer_cm(new (ResourceObj::C_HEAP, mtGC) CMSTracer()),
 488   _gc_timer_cm(new (ResourceObj::C_HEAP, mtGC) ConcurrentGCTimer()),
 489   _cms_start_registered(false)
 490 {
 491   if (ExplicitGCInvokesConcurrentAndUnloadsClasses) {
 492     ExplicitGCInvokesConcurrent = true;
 493   }
 494   // Now expand the span and allocate the collection support structures
 495   // (MUT, marking bit map etc.) to cover both generations subject to
 496   // collection.
 497 
 498   // For use by dirty card to oop closures.
 499   _cmsGen->cmsSpace()->set_collector(this);
 500 
 501   // Allocate MUT and marking bit map
 502   {
 503     MutexLockerEx x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag);
 504     if (!_markBitMap.allocate(_span)) {
 505       log_warning(gc)("Failed to allocate CMS Bit Map");
 506       return;
 507     }
 508     assert(_markBitMap.covers(_span), "_markBitMap inconsistency?");
 509   }
 510   {
 511     _modUnionTable.allocate(_span);
 512     assert(_modUnionTable.covers(_span), "_modUnionTable inconsistency?");
 513   }
 514 
 515   if (!_markStack.allocate(MarkStackSize)) {
 516     log_warning(gc)("Failed to allocate CMS Marking Stack");
 517     return;
 518   }
 519 
 520   // Support for multi-threaded concurrent phases
 521   if (CMSConcurrentMTEnabled) {
 522     if (FLAG_IS_DEFAULT(ConcGCThreads)) {
 523       // just for now
 524       FLAG_SET_DEFAULT(ConcGCThreads, (ParallelGCThreads + 3) / 4);
 525     }
 526     if (ConcGCThreads > 1) {
 527       _conc_workers = new YieldingFlexibleWorkGang("CMS Thread",
 528                                  ConcGCThreads, true);
 529       if (_conc_workers == NULL) {
 530         log_warning(gc)("GC/CMS: _conc_workers allocation failure: forcing -CMSConcurrentMTEnabled");
 531         CMSConcurrentMTEnabled = false;
 532       } else {
 533         _conc_workers->initialize_workers();
 534       }
 535     } else {
 536       CMSConcurrentMTEnabled = false;
 537     }
 538   }
 539   if (!CMSConcurrentMTEnabled) {
 540     ConcGCThreads = 0;
 541   } else {
 542     // Turn off CMSCleanOnEnter optimization temporarily for
 543     // the MT case where it's not fixed yet; see 6178663.
 544     CMSCleanOnEnter = false;
 545   }
 546   assert((_conc_workers != NULL) == (ConcGCThreads > 1),
 547          "Inconsistency");
 548   log_debug(gc)("ConcGCThreads: %u", ConcGCThreads);
 549   log_debug(gc)("ParallelGCThreads: %u", ParallelGCThreads);
 550 
 551   // Parallel task queues; these are shared for the
 552   // concurrent and stop-world phases of CMS, but
 553   // are not shared with parallel scavenge (ParNew).
 554   {
 555     uint i;
 556     uint num_queues = MAX2(ParallelGCThreads, ConcGCThreads);
 557 
 558     if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled
 559          || ParallelRefProcEnabled)
 560         && num_queues > 0) {
 561       _task_queues = new OopTaskQueueSet(num_queues);
 562       if (_task_queues == NULL) {
 563         log_warning(gc)("task_queues allocation failure.");
 564         return;
 565       }
 566       _hash_seed = NEW_C_HEAP_ARRAY(int, num_queues, mtGC);
 567       typedef Padded<OopTaskQueue> PaddedOopTaskQueue;
 568       for (i = 0; i < num_queues; i++) {
 569         PaddedOopTaskQueue *q = new PaddedOopTaskQueue();
 570         if (q == NULL) {
 571           log_warning(gc)("work_queue allocation failure.");
 572           return;
 573         }
 574         _task_queues->register_queue(i, q);
 575       }
 576       for (i = 0; i < num_queues; i++) {
 577         _task_queues->queue(i)->initialize();
 578         _hash_seed[i] = 17;  // copied from ParNew
 579       }
 580     }
 581   }
 582 
 583   _cmsGen ->init_initiating_occupancy(CMSInitiatingOccupancyFraction, CMSTriggerRatio);
 584 
 585   // Clip CMSBootstrapOccupancy between 0 and 100.
 586   _bootstrap_occupancy = CMSBootstrapOccupancy / 100.0;
 587 
 588   // Now tell CMS generations the identity of their collector
 589   ConcurrentMarkSweepGeneration::set_collector(this);
 590 
 591   // Create & start a CMS thread for this CMS collector
 592   _cmsThread = ConcurrentMarkSweepThread::start(this);
 593   assert(cmsThread() != NULL, "CMS Thread should have been created");
 594   assert(cmsThread()->collector() == this,
 595          "CMS Thread should refer to this gen");
 596   assert(CGC_lock != NULL, "Where's the CGC_lock?");
 597 
 598   // Support for parallelizing young gen rescan
 599   GenCollectedHeap* gch = GenCollectedHeap::heap();
 600   assert(gch->young_gen()->kind() == Generation::ParNew, "CMS can only be used with ParNew");
 601   _young_gen = (ParNewGeneration*)gch->young_gen();
 602   if (gch->supports_inline_contig_alloc()) {
 603     _top_addr = gch->top_addr();
 604     _end_addr = gch->end_addr();
 605     assert(_young_gen != NULL, "no _young_gen");
 606     _eden_chunk_index = 0;
 607     _eden_chunk_capacity = (_young_gen->max_capacity() + CMSSamplingGrain) / CMSSamplingGrain;
 608     _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity, mtGC);
 609   }
 610 
 611   // Support for parallelizing survivor space rescan
 612   if ((CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) || CMSParallelInitialMarkEnabled) {
 613     const size_t max_plab_samples =
 614       _young_gen->max_survivor_size() / (PLAB::min_size() * HeapWordSize);
 615 
 616     _survivor_plab_array  = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads, mtGC);
 617     _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
 618     _cursor               = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads, mtGC);
 619     _survivor_chunk_capacity = max_plab_samples;
 620     for (uint i = 0; i < ParallelGCThreads; i++) {
 621       HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
 622       ChunkArray* cur = ::new (&_survivor_plab_array[i]) ChunkArray(vec, max_plab_samples);
 623       assert(cur->end() == 0, "Should be 0");
 624       assert(cur->array() == vec, "Should be vec");
 625       assert(cur->capacity() == max_plab_samples, "Error");
 626     }
 627   }
 628 
 629   NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;)
 630   _gc_counters = new CollectorCounters("CMS", 1);
 631   _completed_initialization = true;
 632   _inter_sweep_timer.start();  // start of time
 633 }
 634 
 635 const char* ConcurrentMarkSweepGeneration::name() const {
 636   return "concurrent mark-sweep generation";
 637 }
 638 void ConcurrentMarkSweepGeneration::update_counters() {
 639   if (UsePerfData) {
 640     _space_counters->update_all();
 641     _gen_counters->update_all();
 642   }
 643 }
 644 
 645 // this is an optimized version of update_counters(). it takes the
 646 // used value as a parameter rather than computing it.
 647 //
 648 void ConcurrentMarkSweepGeneration::update_counters(size_t used) {
 649   if (UsePerfData) {
 650     _space_counters->update_used(used);
 651     _space_counters->update_capacity();
 652     _gen_counters->update_all();
 653   }
 654 }
 655 
 656 void ConcurrentMarkSweepGeneration::print() const {
 657   Generation::print();
 658   cmsSpace()->print();
 659 }
 660 
 661 #ifndef PRODUCT
 662 void ConcurrentMarkSweepGeneration::print_statistics() {
 663   cmsSpace()->printFLCensus(0);
 664 }
 665 #endif
 666 
 667 size_t
 668 ConcurrentMarkSweepGeneration::contiguous_available() const {
 669   // dld proposes an improvement in precision here. If the committed
 670   // part of the space ends in a free block we should add that to
 671   // uncommitted size in the calculation below. Will make this
 672   // change later, staying with the approximation below for the
 673   // time being. -- ysr.
 674   return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc());
 675 }
 676 
 677 size_t
 678 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const {
 679   return _cmsSpace->max_alloc_in_words() * HeapWordSize;
 680 }
 681 
 682 size_t ConcurrentMarkSweepGeneration::max_available() const {
 683   return free() + _virtual_space.uncommitted_size();
 684 }
 685 
 686 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(size_t max_promotion_in_bytes) const {
 687   size_t available = max_available();
 688   size_t av_promo  = (size_t)gc_stats()->avg_promoted()->padded_average();
 689   bool   res = (available >= av_promo) || (available >= max_promotion_in_bytes);
 690   log_trace(gc, promotion)("CMS: promo attempt is%s safe: available(" SIZE_FORMAT ") %s av_promo(" SIZE_FORMAT "), max_promo(" SIZE_FORMAT ")",
 691                            res? "":" not", available, res? ">=":"<", av_promo, max_promotion_in_bytes);
 692   return res;
 693 }
 694 
 695 // At a promotion failure dump information on block layout in heap
 696 // (cms old generation).
 697 void ConcurrentMarkSweepGeneration::promotion_failure_occurred() {
 698   Log(gc, promotion) log;
 699   if (log.is_trace()) {
 700     ResourceMark rm;
 701     cmsSpace()->dump_at_safepoint_with_locks(collector(), log.trace_stream());
 702   }
 703 }
 704 
 705 void ConcurrentMarkSweepGeneration::reset_after_compaction() {
 706   // Clear the promotion information.  These pointers can be adjusted
 707   // along with all the other pointers into the heap but
 708   // compaction is expected to be a rare event with
 709   // a heap using cms so don't do it without seeing the need.
 710   for (uint i = 0; i < ParallelGCThreads; i++) {
 711     _par_gc_thread_states[i]->promo.reset();
 712   }
 713 }
 714 
 715 void ConcurrentMarkSweepGeneration::compute_new_size() {
 716   assert_locked_or_safepoint(Heap_lock);
 717 
 718   // If incremental collection failed, we just want to expand
 719   // to the limit.
 720   if (incremental_collection_failed()) {
 721     clear_incremental_collection_failed();
 722     grow_to_reserved();
 723     return;
 724   }
 725 
 726   // The heap has been compacted but not reset yet.
 727   // Any metric such as free() or used() will be incorrect.
 728 
 729   CardGeneration::compute_new_size();
 730 
 731   // Reset again after a possible resizing
 732   if (did_compact()) {
 733     cmsSpace()->reset_after_compaction();
 734   }
 735 }
 736 
 737 void ConcurrentMarkSweepGeneration::compute_new_size_free_list() {
 738   assert_locked_or_safepoint(Heap_lock);
 739 
 740   // If incremental collection failed, we just want to expand
 741   // to the limit.
 742   if (incremental_collection_failed()) {
 743     clear_incremental_collection_failed();
 744     grow_to_reserved();
 745     return;
 746   }
 747 
 748   double free_percentage = ((double) free()) / capacity();
 749   double desired_free_percentage = (double) MinHeapFreeRatio / 100;
 750   double maximum_free_percentage = (double) MaxHeapFreeRatio / 100;
 751 
 752   // compute expansion delta needed for reaching desired free percentage
 753   if (free_percentage < desired_free_percentage) {
 754     size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
 755     assert(desired_capacity >= capacity(), "invalid expansion size");
 756     size_t expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes);
 757     Log(gc) log;
 758     if (log.is_trace()) {
 759       size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
 760       log.trace("From compute_new_size: ");
 761       log.trace("  Free fraction %f", free_percentage);
 762       log.trace("  Desired free fraction %f", desired_free_percentage);
 763       log.trace("  Maximum free fraction %f", maximum_free_percentage);
 764       log.trace("  Capacity " SIZE_FORMAT, capacity() / 1000);
 765       log.trace("  Desired capacity " SIZE_FORMAT, desired_capacity / 1000);
 766       GenCollectedHeap* gch = GenCollectedHeap::heap();
 767       assert(gch->is_old_gen(this), "The CMS generation should always be the old generation");
 768       size_t young_size = gch->young_gen()->capacity();
 769       log.trace("  Young gen size " SIZE_FORMAT, young_size / 1000);
 770       log.trace("  unsafe_max_alloc_nogc " SIZE_FORMAT, unsafe_max_alloc_nogc() / 1000);
 771       log.trace("  contiguous available " SIZE_FORMAT, contiguous_available() / 1000);
 772       log.trace("  Expand by " SIZE_FORMAT " (bytes)", expand_bytes);
 773     }
 774     // safe if expansion fails
 775     expand_for_gc_cause(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio);
 776     log.trace("  Expanded free fraction %f", ((double) free()) / capacity());
 777   } else {
 778     size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
 779     assert(desired_capacity <= capacity(), "invalid expansion size");
 780     size_t shrink_bytes = capacity() - desired_capacity;
 781     // Don't shrink unless the delta is greater than the minimum shrink we want
 782     if (shrink_bytes >= MinHeapDeltaBytes) {
 783       shrink_free_list_by(shrink_bytes);
 784     }
 785   }
 786 }
 787 
 788 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const {
 789   return cmsSpace()->freelistLock();
 790 }
 791 
 792 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size, bool tlab) {
 793   CMSSynchronousYieldRequest yr;
 794   MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
 795   return have_lock_and_allocate(size, tlab);
 796 }
 797 
 798 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size,
 799                                                                 bool   tlab /* ignored */) {
 800   assert_lock_strong(freelistLock());
 801   size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size);
 802   HeapWord* res = cmsSpace()->allocate(adjustedSize);
 803   // Allocate the object live (grey) if the background collector has
 804   // started marking. This is necessary because the marker may
 805   // have passed this address and consequently this object will
 806   // not otherwise be greyed and would be incorrectly swept up.
 807   // Note that if this object contains references, the writing
 808   // of those references will dirty the card containing this object
 809   // allowing the object to be blackened (and its references scanned)
 810   // either during a preclean phase or at the final checkpoint.
 811   if (res != NULL) {
 812     // We may block here with an uninitialized object with
 813     // its mark-bit or P-bits not yet set. Such objects need
 814     // to be safely navigable by block_start().
 815     assert(oop(res)->klass_or_null() == NULL, "Object should be uninitialized here.");
 816     assert(!((FreeChunk*)res)->is_free(), "Error, block will look free but show wrong size");
 817     collector()->direct_allocated(res, adjustedSize);
 818     _direct_allocated_words += adjustedSize;
 819     // allocation counters
 820     NOT_PRODUCT(
 821       _numObjectsAllocated++;
 822       _numWordsAllocated += (int)adjustedSize;
 823     )
 824   }
 825   return res;
 826 }
 827 
 828 // In the case of direct allocation by mutators in a generation that
 829 // is being concurrently collected, the object must be allocated
 830 // live (grey) if the background collector has started marking.
 831 // This is necessary because the marker may
 832 // have passed this address and consequently this object will
 833 // not otherwise be greyed and would be incorrectly swept up.
 834 // Note that if this object contains references, the writing
 835 // of those references will dirty the card containing this object
 836 // allowing the object to be blackened (and its references scanned)
 837 // either during a preclean phase or at the final checkpoint.
 838 void CMSCollector::direct_allocated(HeapWord* start, size_t size) {
 839   assert(_markBitMap.covers(start, size), "Out of bounds");
 840   if (_collectorState >= Marking) {
 841     MutexLockerEx y(_markBitMap.lock(),
 842                     Mutex::_no_safepoint_check_flag);
 843     // [see comments preceding SweepClosure::do_blk() below for details]
 844     //
 845     // Can the P-bits be deleted now?  JJJ
 846     //
 847     // 1. need to mark the object as live so it isn't collected
 848     // 2. need to mark the 2nd bit to indicate the object may be uninitialized
 849     // 3. need to mark the end of the object so marking, precleaning or sweeping
 850     //    can skip over uninitialized or unparsable objects. An allocated
 851     //    object is considered uninitialized for our purposes as long as
 852     //    its klass word is NULL.  All old gen objects are parsable
 853     //    as soon as they are initialized.)
 854     _markBitMap.mark(start);          // object is live
 855     _markBitMap.mark(start + 1);      // object is potentially uninitialized?
 856     _markBitMap.mark(start + size - 1);
 857                                       // mark end of object
 858   }
 859   // check that oop looks uninitialized
 860   assert(oop(start)->klass_or_null() == NULL, "_klass should be NULL");
 861 }
 862 
 863 void CMSCollector::promoted(bool par, HeapWord* start,
 864                             bool is_obj_array, size_t obj_size) {
 865   assert(_markBitMap.covers(start), "Out of bounds");
 866   // See comment in direct_allocated() about when objects should
 867   // be allocated live.
 868   if (_collectorState >= Marking) {
 869     // we already hold the marking bit map lock, taken in
 870     // the prologue
 871     if (par) {
 872       _markBitMap.par_mark(start);
 873     } else {
 874       _markBitMap.mark(start);
 875     }
 876     // We don't need to mark the object as uninitialized (as
 877     // in direct_allocated above) because this is being done with the
 878     // world stopped and the object will be initialized by the
 879     // time the marking, precleaning or sweeping get to look at it.
 880     // But see the code for copying objects into the CMS generation,
 881     // where we need to ensure that concurrent readers of the
 882     // block offset table are able to safely navigate a block that
 883     // is in flux from being free to being allocated (and in
 884     // transition while being copied into) and subsequently
 885     // becoming a bona-fide object when the copy/promotion is complete.
 886     assert(SafepointSynchronize::is_at_safepoint(),
 887            "expect promotion only at safepoints");
 888 
 889     if (_collectorState < Sweeping) {
 890       // Mark the appropriate cards in the modUnionTable, so that
 891       // this object gets scanned before the sweep. If this is
 892       // not done, CMS generation references in the object might
 893       // not get marked.
 894       // For the case of arrays, which are otherwise precisely
 895       // marked, we need to dirty the entire array, not just its head.
 896       if (is_obj_array) {
 897         // The [par_]mark_range() method expects mr.end() below to
 898         // be aligned to the granularity of a bit's representation
 899         // in the heap. In the case of the MUT below, that's a
 900         // card size.
 901         MemRegion mr(start,
 902                      (HeapWord*)round_to((intptr_t)(start + obj_size),
 903                         CardTableModRefBS::card_size /* bytes */));
 904         if (par) {
 905           _modUnionTable.par_mark_range(mr);
 906         } else {
 907           _modUnionTable.mark_range(mr);
 908         }
 909       } else {  // not an obj array; we can just mark the head
 910         if (par) {
 911           _modUnionTable.par_mark(start);
 912         } else {
 913           _modUnionTable.mark(start);
 914         }
 915       }
 916     }
 917   }
 918 }
 919 
 920 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size) {
 921   assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
 922   // allocate, copy and if necessary update promoinfo --
 923   // delegate to underlying space.
 924   assert_lock_strong(freelistLock());
 925 
 926 #ifndef PRODUCT
 927   if (GenCollectedHeap::heap()->promotion_should_fail()) {
 928     return NULL;
 929   }
 930 #endif  // #ifndef PRODUCT
 931 
 932   oop res = _cmsSpace->promote(obj, obj_size);
 933   if (res == NULL) {
 934     // expand and retry
 935     size_t s = _cmsSpace->expansionSpaceRequired(obj_size);  // HeapWords
 936     expand_for_gc_cause(s*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_promotion);
 937     // Since this is the old generation, we don't try to promote
 938     // into a more senior generation.
 939     res = _cmsSpace->promote(obj, obj_size);
 940   }
 941   if (res != NULL) {
 942     // See comment in allocate() about when objects should
 943     // be allocated live.
 944     assert(obj->is_oop(), "Will dereference klass pointer below");
 945     collector()->promoted(false,           // Not parallel
 946                           (HeapWord*)res, obj->is_objArray(), obj_size);
 947     // promotion counters
 948     NOT_PRODUCT(
 949       _numObjectsPromoted++;
 950       _numWordsPromoted +=
 951         (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size()));
 952     )
 953   }
 954   return res;
 955 }
 956 
 957 
 958 // IMPORTANT: Notes on object size recognition in CMS.
 959 // ---------------------------------------------------
 960 // A block of storage in the CMS generation is always in
 961 // one of three states. A free block (FREE), an allocated
 962 // object (OBJECT) whose size() method reports the correct size,
 963 // and an intermediate state (TRANSIENT) in which its size cannot
 964 // be accurately determined.
 965 // STATE IDENTIFICATION:   (32 bit and 64 bit w/o COOPS)
 966 // -----------------------------------------------------
 967 // FREE:      klass_word & 1 == 1; mark_word holds block size
 968 //
 969 // OBJECT:    klass_word installed; klass_word != 0 && klass_word & 1 == 0;
 970 //            obj->size() computes correct size
 971 //
 972 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
 973 //
 974 // STATE IDENTIFICATION: (64 bit+COOPS)
 975 // ------------------------------------
 976 // FREE:      mark_word & CMS_FREE_BIT == 1; mark_word & ~CMS_FREE_BIT gives block_size
 977 //
 978 // OBJECT:    klass_word installed; klass_word != 0;
 979 //            obj->size() computes correct size
 980 //
 981 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
 982 //
 983 //
 984 // STATE TRANSITION DIAGRAM
 985 //
 986 //        mut / parnew                     mut  /  parnew
 987 // FREE --------------------> TRANSIENT ---------------------> OBJECT --|
 988 //  ^                                                                   |
 989 //  |------------------------ DEAD <------------------------------------|
 990 //         sweep                            mut
 991 //
 992 // While a block is in TRANSIENT state its size cannot be determined
 993 // so readers will either need to come back later or stall until
 994 // the size can be determined. Note that for the case of direct
 995 // allocation, P-bits, when available, may be used to determine the
 996 // size of an object that may not yet have been initialized.
 997 
 998 // Things to support parallel young-gen collection.
 999 oop
1000 ConcurrentMarkSweepGeneration::par_promote(int thread_num,
1001                                            oop old, markOop m,
1002                                            size_t word_sz) {
1003 #ifndef PRODUCT
1004   if (GenCollectedHeap::heap()->promotion_should_fail()) {
1005     return NULL;
1006   }
1007 #endif  // #ifndef PRODUCT
1008 
1009   CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1010   PromotionInfo* promoInfo = &ps->promo;
1011   // if we are tracking promotions, then first ensure space for
1012   // promotion (including spooling space for saving header if necessary).
1013   // then allocate and copy, then track promoted info if needed.
1014   // When tracking (see PromotionInfo::track()), the mark word may
1015   // be displaced and in this case restoration of the mark word
1016   // occurs in the (oop_since_save_marks_)iterate phase.
1017   if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) {
1018     // Out of space for allocating spooling buffers;
1019     // try expanding and allocating spooling buffers.
1020     if (!expand_and_ensure_spooling_space(promoInfo)) {
1021       return NULL;
1022     }
1023   }
1024   assert(!promoInfo->tracking() || promoInfo->has_spooling_space(), "Control point invariant");
1025   const size_t alloc_sz = CompactibleFreeListSpace::adjustObjectSize(word_sz);
1026   HeapWord* obj_ptr = ps->lab.alloc(alloc_sz);
1027   if (obj_ptr == NULL) {
1028      obj_ptr = expand_and_par_lab_allocate(ps, alloc_sz);
1029      if (obj_ptr == NULL) {
1030        return NULL;
1031      }
1032   }
1033   oop obj = oop(obj_ptr);
1034   OrderAccess::storestore();
1035   assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1036   assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1037   // IMPORTANT: See note on object initialization for CMS above.
1038   // Otherwise, copy the object.  Here we must be careful to insert the
1039   // klass pointer last, since this marks the block as an allocated object.
1040   // Except with compressed oops it's the mark word.
1041   HeapWord* old_ptr = (HeapWord*)old;
1042   // Restore the mark word copied above.
1043   obj->set_mark(m);
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   OrderAccess::storestore();
1047 
1048   if (UseCompressedClassPointers) {
1049     // Copy gap missed by (aligned) header size calculation below
1050     obj->set_klass_gap(old->klass_gap());
1051   }
1052   if (word_sz > (size_t)oopDesc::header_size()) {
1053     Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1054                                  obj_ptr + oopDesc::header_size(),
1055                                  word_sz - oopDesc::header_size());
1056   }
1057 
1058   // Now we can track the promoted object, if necessary.  We take care
1059   // to delay the transition from uninitialized to full object
1060   // (i.e., insertion of klass pointer) until after, so that it
1061   // atomically becomes a promoted object.
1062   if (promoInfo->tracking()) {
1063     promoInfo->track((PromotedObject*)obj, old->klass());
1064   }
1065   assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1066   assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1067   assert(old->is_oop(), "Will use and dereference old klass ptr below");
1068 
1069   // Finally, install the klass pointer (this should be volatile).
1070   OrderAccess::storestore();
1071   obj->set_klass(old->klass());
1072   // We should now be able to calculate the right size for this object
1073   assert(obj->is_oop() && obj->size() == (int)word_sz, "Error, incorrect size computed for promoted object");
1074 
1075   collector()->promoted(true,          // parallel
1076                         obj_ptr, old->is_objArray(), word_sz);
1077 
1078   NOT_PRODUCT(
1079     Atomic::inc_ptr(&_numObjectsPromoted);
1080     Atomic::add_ptr(alloc_sz, &_numWordsPromoted);
1081   )
1082 
1083   return obj;
1084 }
1085 
1086 void
1087 ConcurrentMarkSweepGeneration::
1088 par_promote_alloc_done(int thread_num) {
1089   CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1090   ps->lab.retire(thread_num);
1091 }
1092 
1093 void
1094 ConcurrentMarkSweepGeneration::
1095 par_oop_since_save_marks_iterate_done(int thread_num) {
1096   CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1097   ParScanWithoutBarrierClosure* dummy_cl = NULL;
1098   ps->promo.promoted_oops_iterate_nv(dummy_cl);
1099 
1100   // Because card-scanning has been completed, subsequent phases
1101   // (e.g., reference processing) will not need to recognize which
1102   // objects have been promoted during this GC. So, we can now disable
1103   // promotion tracking.
1104   ps->promo.stopTrackingPromotions();
1105 }
1106 
1107 bool ConcurrentMarkSweepGeneration::should_collect(bool   full,
1108                                                    size_t size,
1109                                                    bool   tlab)
1110 {
1111   // We allow a STW collection only if a full
1112   // collection was requested.
1113   return full || should_allocate(size, tlab); // FIX ME !!!
1114   // This and promotion failure handling are connected at the
1115   // hip and should be fixed by untying them.
1116 }
1117 
1118 bool CMSCollector::shouldConcurrentCollect() {
1119   LogTarget(Trace, gc) log;
1120 
1121   if (_full_gc_requested) {
1122     log.print("CMSCollector: collect because of explicit  gc request (or GCLocker)");
1123     return true;
1124   }
1125 
1126   FreelistLocker x(this);
1127   // ------------------------------------------------------------------
1128   // Print out lots of information which affects the initiation of
1129   // a collection.
1130   if (log.is_enabled() && stats().valid()) {
1131     log.print("CMSCollector shouldConcurrentCollect: ");
1132 
1133     LogStream out(log);
1134     stats().print_on(&out);
1135 
1136     log.print("time_until_cms_gen_full %3.7f", stats().time_until_cms_gen_full());
1137     log.print("free=" SIZE_FORMAT, _cmsGen->free());
1138     log.print("contiguous_available=" SIZE_FORMAT, _cmsGen->contiguous_available());
1139     log.print("promotion_rate=%g", stats().promotion_rate());
1140     log.print("cms_allocation_rate=%g", stats().cms_allocation_rate());
1141     log.print("occupancy=%3.7f", _cmsGen->occupancy());
1142     log.print("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy());
1143     log.print("cms_time_since_begin=%3.7f", stats().cms_time_since_begin());
1144     log.print("cms_time_since_end=%3.7f", stats().cms_time_since_end());
1145     log.print("metadata initialized %d", MetaspaceGC::should_concurrent_collect());
1146   }
1147   // ------------------------------------------------------------------
1148 
1149   // If the estimated time to complete a cms collection (cms_duration())
1150   // is less than the estimated time remaining until the cms generation
1151   // is full, start a collection.
1152   if (!UseCMSInitiatingOccupancyOnly) {
1153     if (stats().valid()) {
1154       if (stats().time_until_cms_start() == 0.0) {
1155         return true;
1156       }
1157     } else {
1158       // We want to conservatively collect somewhat early in order
1159       // to try and "bootstrap" our CMS/promotion statistics;
1160       // this branch will not fire after the first successful CMS
1161       // collection because the stats should then be valid.
1162       if (_cmsGen->occupancy() >= _bootstrap_occupancy) {
1163         log.print(" CMSCollector: collect for bootstrapping statistics: occupancy = %f, boot occupancy = %f",
1164                   _cmsGen->occupancy(), _bootstrap_occupancy);
1165         return true;
1166       }
1167     }
1168   }
1169 
1170   // Otherwise, we start a collection cycle if
1171   // old gen want a collection cycle started. Each may use
1172   // an appropriate criterion for making this decision.
1173   // XXX We need to make sure that the gen expansion
1174   // criterion dovetails well with this. XXX NEED TO FIX THIS
1175   if (_cmsGen->should_concurrent_collect()) {
1176     log.print("CMS old gen initiated");
1177     return true;
1178   }
1179 
1180   // We start a collection if we believe an incremental collection may fail;
1181   // this is not likely to be productive in practice because it's probably too
1182   // late anyway.
1183   GenCollectedHeap* gch = GenCollectedHeap::heap();
1184   assert(gch->collector_policy()->is_generation_policy(),
1185          "You may want to check the correctness of the following");
1186   if (gch->incremental_collection_will_fail(true /* consult_young */)) {
1187     log.print("CMSCollector: collect because incremental collection will fail ");
1188     return true;
1189   }
1190 
1191   if (MetaspaceGC::should_concurrent_collect()) {
1192     log.print("CMSCollector: collect for metadata allocation ");
1193     return true;
1194   }
1195 
1196   // CMSTriggerInterval starts a CMS cycle if enough time has passed.
1197   if (CMSTriggerInterval >= 0) {
1198     if (CMSTriggerInterval == 0) {
1199       // Trigger always
1200       return true;
1201     }
1202 
1203     // Check the CMS time since begin (we do not check the stats validity
1204     // as we want to be able to trigger the first CMS cycle as well)
1205     if (stats().cms_time_since_begin() >= (CMSTriggerInterval / ((double) MILLIUNITS))) {
1206       if (stats().valid()) {
1207         log.print("CMSCollector: collect because of trigger interval (time since last begin %3.7f secs)",
1208                   stats().cms_time_since_begin());
1209       } else {
1210         log.print("CMSCollector: collect because of trigger interval (first collection)");
1211       }
1212       return true;
1213     }
1214   }
1215 
1216   return false;
1217 }
1218 
1219 void CMSCollector::set_did_compact(bool v) { _cmsGen->set_did_compact(v); }
1220 
1221 // Clear _expansion_cause fields of constituent generations
1222 void CMSCollector::clear_expansion_cause() {
1223   _cmsGen->clear_expansion_cause();
1224 }
1225 
1226 // We should be conservative in starting a collection cycle.  To
1227 // start too eagerly runs the risk of collecting too often in the
1228 // extreme.  To collect too rarely falls back on full collections,
1229 // which works, even if not optimum in terms of concurrent work.
1230 // As a work around for too eagerly collecting, use the flag
1231 // UseCMSInitiatingOccupancyOnly.  This also has the advantage of
1232 // giving the user an easily understandable way of controlling the
1233 // collections.
1234 // We want to start a new collection cycle if any of the following
1235 // conditions hold:
1236 // . our current occupancy exceeds the configured initiating occupancy
1237 //   for this generation, or
1238 // . we recently needed to expand this space and have not, since that
1239 //   expansion, done a collection of this generation, or
1240 // . the underlying space believes that it may be a good idea to initiate
1241 //   a concurrent collection (this may be based on criteria such as the
1242 //   following: the space uses linear allocation and linear allocation is
1243 //   going to fail, or there is believed to be excessive fragmentation in
1244 //   the generation, etc... or ...
1245 // [.(currently done by CMSCollector::shouldConcurrentCollect() only for
1246 //   the case of the old generation; see CR 6543076):
1247 //   we may be approaching a point at which allocation requests may fail because
1248 //   we will be out of sufficient free space given allocation rate estimates.]
1249 bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const {
1250 
1251   assert_lock_strong(freelistLock());
1252   if (occupancy() > initiating_occupancy()) {
1253     log_trace(gc)(" %s: collect because of occupancy %f / %f  ",
1254                   short_name(), occupancy(), initiating_occupancy());
1255     return true;
1256   }
1257   if (UseCMSInitiatingOccupancyOnly) {
1258     return false;
1259   }
1260   if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) {
1261     log_trace(gc)(" %s: collect because expanded for allocation ", short_name());
1262     return true;
1263   }
1264   return false;
1265 }
1266 
1267 void ConcurrentMarkSweepGeneration::collect(bool   full,
1268                                             bool   clear_all_soft_refs,
1269                                             size_t size,
1270                                             bool   tlab)
1271 {
1272   collector()->collect(full, clear_all_soft_refs, size, tlab);
1273 }
1274 
1275 void CMSCollector::collect(bool   full,
1276                            bool   clear_all_soft_refs,
1277                            size_t size,
1278                            bool   tlab)
1279 {
1280   // The following "if" branch is present for defensive reasons.
1281   // In the current uses of this interface, it can be replaced with:
1282   // assert(!GCLocker.is_active(), "Can't be called otherwise");
1283   // But I am not placing that assert here to allow future
1284   // generality in invoking this interface.
1285   if (GCLocker::is_active()) {
1286     // A consistency test for GCLocker
1287     assert(GCLocker::needs_gc(), "Should have been set already");
1288     // Skip this foreground collection, instead
1289     // expanding the heap if necessary.
1290     // Need the free list locks for the call to free() in compute_new_size()
1291     compute_new_size();
1292     return;
1293   }
1294   acquire_control_and_collect(full, clear_all_soft_refs);
1295 }
1296 
1297 void CMSCollector::request_full_gc(unsigned int full_gc_count, GCCause::Cause cause) {
1298   GenCollectedHeap* gch = GenCollectedHeap::heap();
1299   unsigned int gc_count = gch->total_full_collections();
1300   if (gc_count == full_gc_count) {
1301     MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag);
1302     _full_gc_requested = true;
1303     _full_gc_cause = cause;
1304     CGC_lock->notify();   // nudge CMS thread
1305   } else {
1306     assert(gc_count > full_gc_count, "Error: causal loop");
1307   }
1308 }
1309 
1310 bool CMSCollector::is_external_interruption() {
1311   GCCause::Cause cause = GenCollectedHeap::heap()->gc_cause();
1312   return GCCause::is_user_requested_gc(cause) ||
1313          GCCause::is_serviceability_requested_gc(cause);
1314 }
1315 
1316 void CMSCollector::report_concurrent_mode_interruption() {
1317   if (is_external_interruption()) {
1318     log_debug(gc)("Concurrent mode interrupted");
1319   } else {
1320     log_debug(gc)("Concurrent mode failure");
1321     _gc_tracer_cm->report_concurrent_mode_failure();
1322   }
1323 }
1324 
1325 
1326 // The foreground and background collectors need to coordinate in order
1327 // to make sure that they do not mutually interfere with CMS collections.
1328 // When a background collection is active,
1329 // the foreground collector may need to take over (preempt) and
1330 // synchronously complete an ongoing collection. Depending on the
1331 // frequency of the background collections and the heap usage
1332 // of the application, this preemption can be seldom or frequent.
1333 // There are only certain
1334 // points in the background collection that the "collection-baton"
1335 // can be passed to the foreground collector.
1336 //
1337 // The foreground collector will wait for the baton before
1338 // starting any part of the collection.  The foreground collector
1339 // will only wait at one location.
1340 //
1341 // The background collector will yield the baton before starting a new
1342 // phase of the collection (e.g., before initial marking, marking from roots,
1343 // precleaning, final re-mark, sweep etc.)  This is normally done at the head
1344 // of the loop which switches the phases. The background collector does some
1345 // of the phases (initial mark, final re-mark) with the world stopped.
1346 // Because of locking involved in stopping the world,
1347 // the foreground collector should not block waiting for the background
1348 // collector when it is doing a stop-the-world phase.  The background
1349 // collector will yield the baton at an additional point just before
1350 // it enters a stop-the-world phase.  Once the world is stopped, the
1351 // background collector checks the phase of the collection.  If the
1352 // phase has not changed, it proceeds with the collection.  If the
1353 // phase has changed, it skips that phase of the collection.  See
1354 // the comments on the use of the Heap_lock in collect_in_background().
1355 //
1356 // Variable used in baton passing.
1357 //   _foregroundGCIsActive - Set to true by the foreground collector when
1358 //      it wants the baton.  The foreground clears it when it has finished
1359 //      the collection.
1360 //   _foregroundGCShouldWait - Set to true by the background collector
1361 //        when it is running.  The foreground collector waits while
1362 //      _foregroundGCShouldWait is true.
1363 //  CGC_lock - monitor used to protect access to the above variables
1364 //      and to notify the foreground and background collectors.
1365 //  _collectorState - current state of the CMS collection.
1366 //
1367 // The foreground collector
1368 //   acquires the CGC_lock
1369 //   sets _foregroundGCIsActive
1370 //   waits on the CGC_lock for _foregroundGCShouldWait to be false
1371 //     various locks acquired in preparation for the collection
1372 //     are released so as not to block the background collector
1373 //     that is in the midst of a collection
1374 //   proceeds with the collection
1375 //   clears _foregroundGCIsActive
1376 //   returns
1377 //
1378 // The background collector in a loop iterating on the phases of the
1379 //      collection
1380 //   acquires the CGC_lock
1381 //   sets _foregroundGCShouldWait
1382 //   if _foregroundGCIsActive is set
1383 //     clears _foregroundGCShouldWait, notifies _CGC_lock
1384 //     waits on _CGC_lock for _foregroundGCIsActive to become false
1385 //     and exits the loop.
1386 //   otherwise
1387 //     proceed with that phase of the collection
1388 //     if the phase is a stop-the-world phase,
1389 //       yield the baton once more just before enqueueing
1390 //       the stop-world CMS operation (executed by the VM thread).
1391 //   returns after all phases of the collection are done
1392 //
1393 
1394 void CMSCollector::acquire_control_and_collect(bool full,
1395         bool clear_all_soft_refs) {
1396   assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
1397   assert(!Thread::current()->is_ConcurrentGC_thread(),
1398          "shouldn't try to acquire control from self!");
1399 
1400   // Start the protocol for acquiring control of the
1401   // collection from the background collector (aka CMS thread).
1402   assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1403          "VM thread should have CMS token");
1404   // Remember the possibly interrupted state of an ongoing
1405   // concurrent collection
1406   CollectorState first_state = _collectorState;
1407 
1408   // Signal to a possibly ongoing concurrent collection that
1409   // we want to do a foreground collection.
1410   _foregroundGCIsActive = true;
1411 
1412   // release locks and wait for a notify from the background collector
1413   // releasing the locks in only necessary for phases which
1414   // do yields to improve the granularity of the collection.
1415   assert_lock_strong(bitMapLock());
1416   // We need to lock the Free list lock for the space that we are
1417   // currently collecting.
1418   assert(haveFreelistLocks(), "Must be holding free list locks");
1419   bitMapLock()->unlock();
1420   releaseFreelistLocks();
1421   {
1422     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1423     if (_foregroundGCShouldWait) {
1424       // We are going to be waiting for action for the CMS thread;
1425       // it had better not be gone (for instance at shutdown)!
1426       assert(ConcurrentMarkSweepThread::cmst() != NULL && !ConcurrentMarkSweepThread::cmst()->has_terminated(),
1427              "CMS thread must be running");
1428       // Wait here until the background collector gives us the go-ahead
1429       ConcurrentMarkSweepThread::clear_CMS_flag(
1430         ConcurrentMarkSweepThread::CMS_vm_has_token);  // release token
1431       // Get a possibly blocked CMS thread going:
1432       //   Note that we set _foregroundGCIsActive true above,
1433       //   without protection of the CGC_lock.
1434       CGC_lock->notify();
1435       assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(),
1436              "Possible deadlock");
1437       while (_foregroundGCShouldWait) {
1438         // wait for notification
1439         CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1440         // Possibility of delay/starvation here, since CMS token does
1441         // not know to give priority to VM thread? Actually, i think
1442         // there wouldn't be any delay/starvation, but the proof of
1443         // that "fact" (?) appears non-trivial. XXX 20011219YSR
1444       }
1445       ConcurrentMarkSweepThread::set_CMS_flag(
1446         ConcurrentMarkSweepThread::CMS_vm_has_token);
1447     }
1448   }
1449   // The CMS_token is already held.  Get back the other locks.
1450   assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1451          "VM thread should have CMS token");
1452   getFreelistLocks();
1453   bitMapLock()->lock_without_safepoint_check();
1454   log_debug(gc, state)("CMS foreground collector has asked for control " INTPTR_FORMAT " with first state %d",
1455                        p2i(Thread::current()), first_state);
1456   log_debug(gc, state)("    gets control with state %d", _collectorState);
1457 
1458   // Inform cms gen if this was due to partial collection failing.
1459   // The CMS gen may use this fact to determine its expansion policy.
1460   GenCollectedHeap* gch = GenCollectedHeap::heap();
1461   if (gch->incremental_collection_will_fail(false /* don't consult_young */)) {
1462     assert(!_cmsGen->incremental_collection_failed(),
1463            "Should have been noticed, reacted to and cleared");
1464     _cmsGen->set_incremental_collection_failed();
1465   }
1466 
1467   if (first_state > Idling) {
1468     report_concurrent_mode_interruption();
1469   }
1470 
1471   set_did_compact(true);
1472 
1473   // If the collection is being acquired from the background
1474   // collector, there may be references on the discovered
1475   // references lists.  Abandon those references, since some
1476   // of them may have become unreachable after concurrent
1477   // discovery; the STW compacting collector will redo discovery
1478   // more precisely, without being subject to floating garbage.
1479   // Leaving otherwise unreachable references in the discovered
1480   // lists would require special handling.
1481   ref_processor()->disable_discovery();
1482   ref_processor()->abandon_partial_discovery();
1483   ref_processor()->verify_no_references_recorded();
1484 
1485   if (first_state > Idling) {
1486     save_heap_summary();
1487   }
1488 
1489   do_compaction_work(clear_all_soft_refs);
1490 
1491   // Has the GC time limit been exceeded?
1492   size_t max_eden_size = _young_gen->max_eden_size();
1493   GCCause::Cause gc_cause = gch->gc_cause();
1494   size_policy()->check_gc_overhead_limit(_young_gen->used(),
1495                                          _young_gen->eden()->used(),
1496                                          _cmsGen->max_capacity(),
1497                                          max_eden_size,
1498                                          full,
1499                                          gc_cause,
1500                                          gch->collector_policy());
1501 
1502   // Reset the expansion cause, now that we just completed
1503   // a collection cycle.
1504   clear_expansion_cause();
1505   _foregroundGCIsActive = false;
1506   return;
1507 }
1508 
1509 // Resize the tenured generation
1510 // after obtaining the free list locks for the
1511 // two generations.
1512 void CMSCollector::compute_new_size() {
1513   assert_locked_or_safepoint(Heap_lock);
1514   FreelistLocker z(this);
1515   MetaspaceGC::compute_new_size();
1516   _cmsGen->compute_new_size_free_list();
1517 }
1518 
1519 // A work method used by the foreground collector to do
1520 // a mark-sweep-compact.
1521 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) {
1522   GenCollectedHeap* gch = GenCollectedHeap::heap();
1523 
1524   STWGCTimer* gc_timer = GenMarkSweep::gc_timer();
1525   gc_timer->register_gc_start();
1526 
1527   SerialOldTracer* gc_tracer = GenMarkSweep::gc_tracer();
1528   gc_tracer->report_gc_start(gch->gc_cause(), gc_timer->gc_start());
1529 
1530   gch->pre_full_gc_dump(gc_timer);
1531 
1532   GCTraceTime(Trace, gc, phases) t("CMS:MSC");
1533 
1534   // Temporarily widen the span of the weak reference processing to
1535   // the entire heap.
1536   MemRegion new_span(GenCollectedHeap::heap()->reserved_region());
1537   ReferenceProcessorSpanMutator rp_mut_span(ref_processor(), new_span);
1538   // Temporarily, clear the "is_alive_non_header" field of the
1539   // reference processor.
1540   ReferenceProcessorIsAliveMutator rp_mut_closure(ref_processor(), NULL);
1541   // Temporarily make reference _processing_ single threaded (non-MT).
1542   ReferenceProcessorMTProcMutator rp_mut_mt_processing(ref_processor(), false);
1543   // Temporarily make refs discovery atomic
1544   ReferenceProcessorAtomicMutator rp_mut_atomic(ref_processor(), true);
1545   // Temporarily make reference _discovery_ single threaded (non-MT)
1546   ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
1547 
1548   ref_processor()->set_enqueuing_is_done(false);
1549   ref_processor()->enable_discovery();
1550   ref_processor()->setup_policy(clear_all_soft_refs);
1551   // If an asynchronous collection finishes, the _modUnionTable is
1552   // all clear.  If we are assuming the collection from an asynchronous
1553   // collection, clear the _modUnionTable.
1554   assert(_collectorState != Idling || _modUnionTable.isAllClear(),
1555     "_modUnionTable should be clear if the baton was not passed");
1556   _modUnionTable.clear_all();
1557   assert(_collectorState != Idling || _ct->klass_rem_set()->mod_union_is_clear(),
1558     "mod union for klasses should be clear if the baton was passed");
1559   _ct->klass_rem_set()->clear_mod_union();
1560 
1561   // We must adjust the allocation statistics being maintained
1562   // in the free list space. We do so by reading and clearing
1563   // the sweep timer and updating the block flux rate estimates below.
1564   assert(!_intra_sweep_timer.is_active(), "_intra_sweep_timer should be inactive");
1565   if (_inter_sweep_timer.is_active()) {
1566     _inter_sweep_timer.stop();
1567     // Note that we do not use this sample to update the _inter_sweep_estimate.
1568     _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
1569                                             _inter_sweep_estimate.padded_average(),
1570                                             _intra_sweep_estimate.padded_average());
1571   }
1572 
1573   GenMarkSweep::invoke_at_safepoint(ref_processor(), clear_all_soft_refs);
1574   #ifdef ASSERT
1575     CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
1576     size_t free_size = cms_space->free();
1577     assert(free_size ==
1578            pointer_delta(cms_space->end(), cms_space->compaction_top())
1579            * HeapWordSize,
1580       "All the free space should be compacted into one chunk at top");
1581     assert(cms_space->dictionary()->total_chunk_size(
1582                                       debug_only(cms_space->freelistLock())) == 0 ||
1583            cms_space->totalSizeInIndexedFreeLists() == 0,
1584       "All the free space should be in a single chunk");
1585     size_t num = cms_space->totalCount();
1586     assert((free_size == 0 && num == 0) ||
1587            (free_size > 0  && (num == 1 || num == 2)),
1588          "There should be at most 2 free chunks after compaction");
1589   #endif // ASSERT
1590   _collectorState = Resetting;
1591   assert(_restart_addr == NULL,
1592          "Should have been NULL'd before baton was passed");
1593   reset_stw();
1594   _cmsGen->reset_after_compaction();
1595   _concurrent_cycles_since_last_unload = 0;
1596 
1597   // Clear any data recorded in the PLAB chunk arrays.
1598   if (_survivor_plab_array != NULL) {
1599     reset_survivor_plab_arrays();
1600   }
1601 
1602   // Adjust the per-size allocation stats for the next epoch.
1603   _cmsGen->cmsSpace()->endSweepFLCensus(sweep_count() /* fake */);
1604   // Restart the "inter sweep timer" for the next epoch.
1605   _inter_sweep_timer.reset();
1606   _inter_sweep_timer.start();
1607 
1608   // No longer a need to do a concurrent collection for Metaspace.
1609   MetaspaceGC::set_should_concurrent_collect(false);
1610 
1611   gch->post_full_gc_dump(gc_timer);
1612 
1613   gc_timer->register_gc_end();
1614 
1615   gc_tracer->report_gc_end(gc_timer->gc_end(), gc_timer->time_partitions());
1616 
1617   // For a mark-sweep-compact, compute_new_size() will be called
1618   // in the heap's do_collection() method.
1619 }
1620 
1621 void CMSCollector::print_eden_and_survivor_chunk_arrays() {
1622   Log(gc, heap) log;
1623   if (!log.is_trace()) {
1624     return;
1625   }
1626 
1627   ContiguousSpace* eden_space = _young_gen->eden();
1628   ContiguousSpace* from_space = _young_gen->from();
1629   ContiguousSpace* to_space   = _young_gen->to();
1630   // Eden
1631   if (_eden_chunk_array != NULL) {
1632     log.trace("eden " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1633               p2i(eden_space->bottom()), p2i(eden_space->top()),
1634               p2i(eden_space->end()), eden_space->capacity());
1635     log.trace("_eden_chunk_index=" SIZE_FORMAT ", _eden_chunk_capacity=" SIZE_FORMAT,
1636               _eden_chunk_index, _eden_chunk_capacity);
1637     for (size_t i = 0; i < _eden_chunk_index; i++) {
1638       log.trace("_eden_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT, i, p2i(_eden_chunk_array[i]));
1639     }
1640   }
1641   // Survivor
1642   if (_survivor_chunk_array != NULL) {
1643     log.trace("survivor " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1644               p2i(from_space->bottom()), p2i(from_space->top()),
1645               p2i(from_space->end()), from_space->capacity());
1646     log.trace("_survivor_chunk_index=" SIZE_FORMAT ", _survivor_chunk_capacity=" SIZE_FORMAT,
1647               _survivor_chunk_index, _survivor_chunk_capacity);
1648     for (size_t i = 0; i < _survivor_chunk_index; i++) {
1649       log.trace("_survivor_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT, i, p2i(_survivor_chunk_array[i]));
1650     }
1651   }
1652 }
1653 
1654 void CMSCollector::getFreelistLocks() const {
1655   // Get locks for all free lists in all generations that this
1656   // collector is responsible for
1657   _cmsGen->freelistLock()->lock_without_safepoint_check();
1658 }
1659 
1660 void CMSCollector::releaseFreelistLocks() const {
1661   // Release locks for all free lists in all generations that this
1662   // collector is responsible for
1663   _cmsGen->freelistLock()->unlock();
1664 }
1665 
1666 bool CMSCollector::haveFreelistLocks() const {
1667   // Check locks for all free lists in all generations that this
1668   // collector is responsible for
1669   assert_lock_strong(_cmsGen->freelistLock());
1670   PRODUCT_ONLY(ShouldNotReachHere());
1671   return true;
1672 }
1673 
1674 // A utility class that is used by the CMS collector to
1675 // temporarily "release" the foreground collector from its
1676 // usual obligation to wait for the background collector to
1677 // complete an ongoing phase before proceeding.
1678 class ReleaseForegroundGC: public StackObj {
1679  private:
1680   CMSCollector* _c;
1681  public:
1682   ReleaseForegroundGC(CMSCollector* c) : _c(c) {
1683     assert(_c->_foregroundGCShouldWait, "Else should not need to call");
1684     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1685     // allow a potentially blocked foreground collector to proceed
1686     _c->_foregroundGCShouldWait = false;
1687     if (_c->_foregroundGCIsActive) {
1688       CGC_lock->notify();
1689     }
1690     assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1691            "Possible deadlock");
1692   }
1693 
1694   ~ReleaseForegroundGC() {
1695     assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?");
1696     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1697     _c->_foregroundGCShouldWait = true;
1698   }
1699 };
1700 
1701 void CMSCollector::collect_in_background(GCCause::Cause cause) {
1702   assert(Thread::current()->is_ConcurrentGC_thread(),
1703     "A CMS asynchronous collection is only allowed on a CMS thread.");
1704 
1705   GenCollectedHeap* gch = GenCollectedHeap::heap();
1706   {
1707     bool safepoint_check = Mutex::_no_safepoint_check_flag;
1708     MutexLockerEx hl(Heap_lock, safepoint_check);
1709     FreelistLocker fll(this);
1710     MutexLockerEx x(CGC_lock, safepoint_check);
1711     if (_foregroundGCIsActive) {
1712       // The foreground collector is. Skip this
1713       // background collection.
1714       assert(!_foregroundGCShouldWait, "Should be clear");
1715       return;
1716     } else {
1717       assert(_collectorState == Idling, "Should be idling before start.");
1718       _collectorState = InitialMarking;
1719       register_gc_start(cause);
1720       // Reset the expansion cause, now that we are about to begin
1721       // a new cycle.
1722       clear_expansion_cause();
1723 
1724       // Clear the MetaspaceGC flag since a concurrent collection
1725       // is starting but also clear it after the collection.
1726       MetaspaceGC::set_should_concurrent_collect(false);
1727     }
1728     // Decide if we want to enable class unloading as part of the
1729     // ensuing concurrent GC cycle.
1730     update_should_unload_classes();
1731     _full_gc_requested = false;           // acks all outstanding full gc requests
1732     _full_gc_cause = GCCause::_no_gc;
1733     // Signal that we are about to start a collection
1734     gch->increment_total_full_collections();  // ... starting a collection cycle
1735     _collection_count_start = gch->total_full_collections();
1736   }
1737 
1738   size_t prev_used = _cmsGen->used();
1739 
1740   // The change of the collection state is normally done at this level;
1741   // the exceptions are phases that are executed while the world is
1742   // stopped.  For those phases the change of state is done while the
1743   // world is stopped.  For baton passing purposes this allows the
1744   // background collector to finish the phase and change state atomically.
1745   // The foreground collector cannot wait on a phase that is done
1746   // while the world is stopped because the foreground collector already
1747   // has the world stopped and would deadlock.
1748   while (_collectorState != Idling) {
1749     log_debug(gc, state)("Thread " INTPTR_FORMAT " in CMS state %d",
1750                          p2i(Thread::current()), _collectorState);
1751     // The foreground collector
1752     //   holds the Heap_lock throughout its collection.
1753     //   holds the CMS token (but not the lock)
1754     //     except while it is waiting for the background collector to yield.
1755     //
1756     // The foreground collector should be blocked (not for long)
1757     //   if the background collector is about to start a phase
1758     //   executed with world stopped.  If the background
1759     //   collector has already started such a phase, the
1760     //   foreground collector is blocked waiting for the
1761     //   Heap_lock.  The stop-world phases (InitialMarking and FinalMarking)
1762     //   are executed in the VM thread.
1763     //
1764     // The locking order is
1765     //   PendingListLock (PLL)  -- if applicable (FinalMarking)
1766     //   Heap_lock  (both this & PLL locked in VM_CMS_Operation::prologue())
1767     //   CMS token  (claimed in
1768     //                stop_world_and_do() -->
1769     //                  safepoint_synchronize() -->
1770     //                    CMSThread::synchronize())
1771 
1772     {
1773       // Check if the FG collector wants us to yield.
1774       CMSTokenSync x(true); // is cms thread
1775       if (waitForForegroundGC()) {
1776         // We yielded to a foreground GC, nothing more to be
1777         // done this round.
1778         assert(_foregroundGCShouldWait == false, "We set it to false in "
1779                "waitForForegroundGC()");
1780         log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " exiting collection CMS state %d",
1781                              p2i(Thread::current()), _collectorState);
1782         return;
1783       } else {
1784         // The background collector can run but check to see if the
1785         // foreground collector has done a collection while the
1786         // background collector was waiting to get the CGC_lock
1787         // above.  If yes, break so that _foregroundGCShouldWait
1788         // is cleared before returning.
1789         if (_collectorState == Idling) {
1790           break;
1791         }
1792       }
1793     }
1794 
1795     assert(_foregroundGCShouldWait, "Foreground collector, if active, "
1796       "should be waiting");
1797 
1798     switch (_collectorState) {
1799       case InitialMarking:
1800         {
1801           ReleaseForegroundGC x(this);
1802           stats().record_cms_begin();
1803           VM_CMS_Initial_Mark initial_mark_op(this);
1804           VMThread::execute(&initial_mark_op);
1805         }
1806         // The collector state may be any legal state at this point
1807         // since the background collector may have yielded to the
1808         // foreground collector.
1809         break;
1810       case Marking:
1811         // initial marking in checkpointRootsInitialWork has been completed
1812         if (markFromRoots()) { // we were successful
1813           assert(_collectorState == Precleaning, "Collector state should "
1814             "have changed");
1815         } else {
1816           assert(_foregroundGCIsActive, "Internal state inconsistency");
1817         }
1818         break;
1819       case Precleaning:
1820         // marking from roots in markFromRoots has been completed
1821         preclean();
1822         assert(_collectorState == AbortablePreclean ||
1823                _collectorState == FinalMarking,
1824                "Collector state should have changed");
1825         break;
1826       case AbortablePreclean:
1827         abortable_preclean();
1828         assert(_collectorState == FinalMarking, "Collector state should "
1829           "have changed");
1830         break;
1831       case FinalMarking:
1832         {
1833           ReleaseForegroundGC x(this);
1834 
1835           VM_CMS_Final_Remark final_remark_op(this);
1836           VMThread::execute(&final_remark_op);
1837         }
1838         assert(_foregroundGCShouldWait, "block post-condition");
1839         break;
1840       case Sweeping:
1841         // final marking in checkpointRootsFinal has been completed
1842         sweep();
1843         assert(_collectorState == Resizing, "Collector state change "
1844           "to Resizing must be done under the free_list_lock");
1845 
1846       case Resizing: {
1847         // Sweeping has been completed...
1848         // At this point the background collection has completed.
1849         // Don't move the call to compute_new_size() down
1850         // into code that might be executed if the background
1851         // collection was preempted.
1852         {
1853           ReleaseForegroundGC x(this);   // unblock FG collection
1854           MutexLockerEx       y(Heap_lock, Mutex::_no_safepoint_check_flag);
1855           CMSTokenSync        z(true);   // not strictly needed.
1856           if (_collectorState == Resizing) {
1857             compute_new_size();
1858             save_heap_summary();
1859             _collectorState = Resetting;
1860           } else {
1861             assert(_collectorState == Idling, "The state should only change"
1862                    " because the foreground collector has finished the collection");
1863           }
1864         }
1865         break;
1866       }
1867       case Resetting:
1868         // CMS heap resizing has been completed
1869         reset_concurrent();
1870         assert(_collectorState == Idling, "Collector state should "
1871           "have changed");
1872 
1873         MetaspaceGC::set_should_concurrent_collect(false);
1874 
1875         stats().record_cms_end();
1876         // Don't move the concurrent_phases_end() and compute_new_size()
1877         // calls to here because a preempted background collection
1878         // has it's state set to "Resetting".
1879         break;
1880       case Idling:
1881       default:
1882         ShouldNotReachHere();
1883         break;
1884     }
1885     log_debug(gc, state)("  Thread " INTPTR_FORMAT " done - next CMS state %d",
1886                          p2i(Thread::current()), _collectorState);
1887     assert(_foregroundGCShouldWait, "block post-condition");
1888   }
1889 
1890   // Should this be in gc_epilogue?
1891   collector_policy()->counters()->update_counters();
1892 
1893   {
1894     // Clear _foregroundGCShouldWait and, in the event that the
1895     // foreground collector is waiting, notify it, before
1896     // returning.
1897     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1898     _foregroundGCShouldWait = false;
1899     if (_foregroundGCIsActive) {
1900       CGC_lock->notify();
1901     }
1902     assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1903            "Possible deadlock");
1904   }
1905   log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " exiting collection CMS state %d",
1906                        p2i(Thread::current()), _collectorState);
1907   log_info(gc, heap)("Old: " SIZE_FORMAT "K->" SIZE_FORMAT "K("  SIZE_FORMAT "K)",
1908                      prev_used / K, _cmsGen->used()/K, _cmsGen->capacity() /K);
1909 }
1910 
1911 void CMSCollector::register_gc_start(GCCause::Cause cause) {
1912   _cms_start_registered = true;
1913   _gc_timer_cm->register_gc_start();
1914   _gc_tracer_cm->report_gc_start(cause, _gc_timer_cm->gc_start());
1915 }
1916 
1917 void CMSCollector::register_gc_end() {
1918   if (_cms_start_registered) {
1919     report_heap_summary(GCWhen::AfterGC);
1920 
1921     _gc_timer_cm->register_gc_end();
1922     _gc_tracer_cm->report_gc_end(_gc_timer_cm->gc_end(), _gc_timer_cm->time_partitions());
1923     _cms_start_registered = false;
1924   }
1925 }
1926 
1927 void CMSCollector::save_heap_summary() {
1928   GenCollectedHeap* gch = GenCollectedHeap::heap();
1929   _last_heap_summary = gch->create_heap_summary();
1930   _last_metaspace_summary = gch->create_metaspace_summary();
1931 }
1932 
1933 void CMSCollector::report_heap_summary(GCWhen::Type when) {
1934   _gc_tracer_cm->report_gc_heap_summary(when, _last_heap_summary);
1935   _gc_tracer_cm->report_metaspace_summary(when, _last_metaspace_summary);
1936 }
1937 
1938 bool CMSCollector::waitForForegroundGC() {
1939   bool res = false;
1940   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1941          "CMS thread should have CMS token");
1942   // Block the foreground collector until the
1943   // background collectors decides whether to
1944   // yield.
1945   MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1946   _foregroundGCShouldWait = true;
1947   if (_foregroundGCIsActive) {
1948     // The background collector yields to the
1949     // foreground collector and returns a value
1950     // indicating that it has yielded.  The foreground
1951     // collector can proceed.
1952     res = true;
1953     _foregroundGCShouldWait = false;
1954     ConcurrentMarkSweepThread::clear_CMS_flag(
1955       ConcurrentMarkSweepThread::CMS_cms_has_token);
1956     ConcurrentMarkSweepThread::set_CMS_flag(
1957       ConcurrentMarkSweepThread::CMS_cms_wants_token);
1958     // Get a possibly blocked foreground thread going
1959     CGC_lock->notify();
1960     log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d",
1961                          p2i(Thread::current()), _collectorState);
1962     while (_foregroundGCIsActive) {
1963       CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1964     }
1965     ConcurrentMarkSweepThread::set_CMS_flag(
1966       ConcurrentMarkSweepThread::CMS_cms_has_token);
1967     ConcurrentMarkSweepThread::clear_CMS_flag(
1968       ConcurrentMarkSweepThread::CMS_cms_wants_token);
1969   }
1970   log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d",
1971                        p2i(Thread::current()), _collectorState);
1972   return res;
1973 }
1974 
1975 // Because of the need to lock the free lists and other structures in
1976 // the collector, common to all the generations that the collector is
1977 // collecting, we need the gc_prologues of individual CMS generations
1978 // delegate to their collector. It may have been simpler had the
1979 // current infrastructure allowed one to call a prologue on a
1980 // collector. In the absence of that we have the generation's
1981 // prologue delegate to the collector, which delegates back
1982 // some "local" work to a worker method in the individual generations
1983 // that it's responsible for collecting, while itself doing any
1984 // work common to all generations it's responsible for. A similar
1985 // comment applies to the  gc_epilogue()'s.
1986 // The role of the variable _between_prologue_and_epilogue is to
1987 // enforce the invocation protocol.
1988 void CMSCollector::gc_prologue(bool full) {
1989   // Call gc_prologue_work() for the CMSGen
1990   // we are responsible for.
1991 
1992   // The following locking discipline assumes that we are only called
1993   // when the world is stopped.
1994   assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption");
1995 
1996   // The CMSCollector prologue must call the gc_prologues for the
1997   // "generations" that it's responsible
1998   // for.
1999 
2000   assert(   Thread::current()->is_VM_thread()
2001          || (   CMSScavengeBeforeRemark
2002              && Thread::current()->is_ConcurrentGC_thread()),
2003          "Incorrect thread type for prologue execution");
2004 
2005   if (_between_prologue_and_epilogue) {
2006     // We have already been invoked; this is a gc_prologue delegation
2007     // from yet another CMS generation that we are responsible for, just
2008     // ignore it since all relevant work has already been done.
2009     return;
2010   }
2011 
2012   // set a bit saying prologue has been called; cleared in epilogue
2013   _between_prologue_and_epilogue = true;
2014   // Claim locks for common data structures, then call gc_prologue_work()
2015   // for each CMSGen.
2016 
2017   getFreelistLocks();   // gets free list locks on constituent spaces
2018   bitMapLock()->lock_without_safepoint_check();
2019 
2020   // Should call gc_prologue_work() for all cms gens we are responsible for
2021   bool duringMarking =    _collectorState >= Marking
2022                          && _collectorState < Sweeping;
2023 
2024   // The young collections clear the modified oops state, which tells if
2025   // there are any modified oops in the class. The remark phase also needs
2026   // that information. Tell the young collection to save the union of all
2027   // modified klasses.
2028   if (duringMarking) {
2029     _ct->klass_rem_set()->set_accumulate_modified_oops(true);
2030   }
2031 
2032   bool registerClosure = duringMarking;
2033 
2034   _cmsGen->gc_prologue_work(full, registerClosure, &_modUnionClosurePar);
2035 
2036   if (!full) {
2037     stats().record_gc0_begin();
2038   }
2039 }
2040 
2041 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) {
2042 
2043   _capacity_at_prologue = capacity();
2044   _used_at_prologue = used();
2045 
2046   // We enable promotion tracking so that card-scanning can recognize
2047   // which objects have been promoted during this GC and skip them.
2048   for (uint i = 0; i < ParallelGCThreads; i++) {
2049     _par_gc_thread_states[i]->promo.startTrackingPromotions();
2050   }
2051 
2052   // Delegate to CMScollector which knows how to coordinate between
2053   // this and any other CMS generations that it is responsible for
2054   // collecting.
2055   collector()->gc_prologue(full);
2056 }
2057 
2058 // This is a "private" interface for use by this generation's CMSCollector.
2059 // Not to be called directly by any other entity (for instance,
2060 // GenCollectedHeap, which calls the "public" gc_prologue method above).
2061 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full,
2062   bool registerClosure, ModUnionClosure* modUnionClosure) {
2063   assert(!incremental_collection_failed(), "Shouldn't be set yet");
2064   assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL,
2065     "Should be NULL");
2066   if (registerClosure) {
2067     cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure);
2068   }
2069   cmsSpace()->gc_prologue();
2070   // Clear stat counters
2071   NOT_PRODUCT(
2072     assert(_numObjectsPromoted == 0, "check");
2073     assert(_numWordsPromoted   == 0, "check");
2074     log_develop_trace(gc, alloc)("Allocated " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes concurrently",
2075                                  _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord));
2076     _numObjectsAllocated = 0;
2077     _numWordsAllocated   = 0;
2078   )
2079 }
2080 
2081 void CMSCollector::gc_epilogue(bool full) {
2082   // The following locking discipline assumes that we are only called
2083   // when the world is stopped.
2084   assert(SafepointSynchronize::is_at_safepoint(),
2085          "world is stopped assumption");
2086 
2087   // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks
2088   // if linear allocation blocks need to be appropriately marked to allow the
2089   // the blocks to be parsable. We also check here whether we need to nudge the
2090   // CMS collector thread to start a new cycle (if it's not already active).
2091   assert(   Thread::current()->is_VM_thread()
2092          || (   CMSScavengeBeforeRemark
2093              && Thread::current()->is_ConcurrentGC_thread()),
2094          "Incorrect thread type for epilogue execution");
2095 
2096   if (!_between_prologue_and_epilogue) {
2097     // We have already been invoked; this is a gc_epilogue delegation
2098     // from yet another CMS generation that we are responsible for, just
2099     // ignore it since all relevant work has already been done.
2100     return;
2101   }
2102   assert(haveFreelistLocks(), "must have freelist locks");
2103   assert_lock_strong(bitMapLock());
2104 
2105   _ct->klass_rem_set()->set_accumulate_modified_oops(false);
2106 
2107   _cmsGen->gc_epilogue_work(full);
2108 
2109   if (_collectorState == AbortablePreclean || _collectorState == Precleaning) {
2110     // in case sampling was not already enabled, enable it
2111     _start_sampling = true;
2112   }
2113   // reset _eden_chunk_array so sampling starts afresh
2114   _eden_chunk_index = 0;
2115 
2116   size_t cms_used   = _cmsGen->cmsSpace()->used();
2117 
2118   // update performance counters - this uses a special version of
2119   // update_counters() that allows the utilization to be passed as a
2120   // parameter, avoiding multiple calls to used().
2121   //
2122   _cmsGen->update_counters(cms_used);
2123 
2124   bitMapLock()->unlock();
2125   releaseFreelistLocks();
2126 
2127   if (!CleanChunkPoolAsync) {
2128     Chunk::clean_chunk_pool();
2129   }
2130 
2131   set_did_compact(false);
2132   _between_prologue_and_epilogue = false;  // ready for next cycle
2133 }
2134 
2135 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) {
2136   collector()->gc_epilogue(full);
2137 
2138   // When using ParNew, promotion tracking should have already been
2139   // disabled. However, the prologue (which enables promotion
2140   // tracking) and epilogue are called irrespective of the type of
2141   // GC. So they will also be called before and after Full GCs, during
2142   // which promotion tracking will not be explicitly disabled. So,
2143   // it's safer to also disable it here too (to be symmetric with
2144   // enabling it in the prologue).
2145   for (uint i = 0; i < ParallelGCThreads; i++) {
2146     _par_gc_thread_states[i]->promo.stopTrackingPromotions();
2147   }
2148 }
2149 
2150 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2151   assert(!incremental_collection_failed(), "Should have been cleared");
2152   cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2153   cmsSpace()->gc_epilogue();
2154     // Print stat counters
2155   NOT_PRODUCT(
2156     assert(_numObjectsAllocated == 0, "check");
2157     assert(_numWordsAllocated == 0, "check");
2158     log_develop_trace(gc, promotion)("Promoted " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
2159                                      _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2160     _numObjectsPromoted = 0;
2161     _numWordsPromoted   = 0;
2162   )
2163 
2164   // Call down the chain in contiguous_available needs the freelistLock
2165   // so print this out before releasing the freeListLock.
2166   log_develop_trace(gc)(" Contiguous available " SIZE_FORMAT " bytes ", contiguous_available());
2167 }
2168 
2169 #ifndef PRODUCT
2170 bool CMSCollector::have_cms_token() {
2171   Thread* thr = Thread::current();
2172   if (thr->is_VM_thread()) {
2173     return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2174   } else if (thr->is_ConcurrentGC_thread()) {
2175     return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2176   } else if (thr->is_GC_task_thread()) {
2177     return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2178            ParGCRareEvent_lock->owned_by_self();
2179   }
2180   return false;
2181 }
2182 
2183 // Check reachability of the given heap address in CMS generation,
2184 // treating all other generations as roots.
2185 bool CMSCollector::is_cms_reachable(HeapWord* addr) {
2186   // We could "guarantee" below, rather than assert, but I'll
2187   // leave these as "asserts" so that an adventurous debugger
2188   // could try this in the product build provided some subset of
2189   // the conditions were met, provided they were interested in the
2190   // results and knew that the computation below wouldn't interfere
2191   // with other concurrent computations mutating the structures
2192   // being read or written.
2193   assert(SafepointSynchronize::is_at_safepoint(),
2194          "Else mutations in object graph will make answer suspect");
2195   assert(have_cms_token(), "Should hold cms token");
2196   assert(haveFreelistLocks(), "must hold free list locks");
2197   assert_lock_strong(bitMapLock());
2198 
2199   // Clear the marking bit map array before starting, but, just
2200   // for kicks, first report if the given address is already marked
2201   tty->print_cr("Start: Address " PTR_FORMAT " is%s marked", p2i(addr),
2202                 _markBitMap.isMarked(addr) ? "" : " not");
2203 
2204   if (verify_after_remark()) {
2205     MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2206     bool result = verification_mark_bm()->isMarked(addr);
2207     tty->print_cr("TransitiveMark: Address " PTR_FORMAT " %s marked", p2i(addr),
2208                   result ? "IS" : "is NOT");
2209     return result;
2210   } else {
2211     tty->print_cr("Could not compute result");
2212     return false;
2213   }
2214 }
2215 #endif
2216 
2217 void
2218 CMSCollector::print_on_error(outputStream* st) {
2219   CMSCollector* collector = ConcurrentMarkSweepGeneration::_collector;
2220   if (collector != NULL) {
2221     CMSBitMap* bitmap = &collector->_markBitMap;
2222     st->print_cr("Marking Bits: (CMSBitMap*) " PTR_FORMAT, p2i(bitmap));
2223     bitmap->print_on_error(st, " Bits: ");
2224 
2225     st->cr();
2226 
2227     CMSBitMap* mut_bitmap = &collector->_modUnionTable;
2228     st->print_cr("Mod Union Table: (CMSBitMap*) " PTR_FORMAT, p2i(mut_bitmap));
2229     mut_bitmap->print_on_error(st, " Bits: ");
2230   }
2231 }
2232 
2233 ////////////////////////////////////////////////////////
2234 // CMS Verification Support
2235 ////////////////////////////////////////////////////////
2236 // Following the remark phase, the following invariant
2237 // should hold -- each object in the CMS heap which is
2238 // marked in markBitMap() should be marked in the verification_mark_bm().
2239 
2240 class VerifyMarkedClosure: public BitMapClosure {
2241   CMSBitMap* _marks;
2242   bool       _failed;
2243 
2244  public:
2245   VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2246 
2247   bool do_bit(size_t offset) {
2248     HeapWord* addr = _marks->offsetToHeapWord(offset);
2249     if (!_marks->isMarked(addr)) {
2250       Log(gc, verify) log;
2251       ResourceMark rm;
2252       oop(addr)->print_on(log.error_stream());
2253       log.error(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
2254       _failed = true;
2255     }
2256     return true;
2257   }
2258 
2259   bool failed() { return _failed; }
2260 };
2261 
2262 bool CMSCollector::verify_after_remark() {
2263   GCTraceTime(Info, gc, phases, verify) tm("Verifying CMS Marking.");
2264   MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2265   static bool init = false;
2266 
2267   assert(SafepointSynchronize::is_at_safepoint(),
2268          "Else mutations in object graph will make answer suspect");
2269   assert(have_cms_token(),
2270          "Else there may be mutual interference in use of "
2271          " verification data structures");
2272   assert(_collectorState > Marking && _collectorState <= Sweeping,
2273          "Else marking info checked here may be obsolete");
2274   assert(haveFreelistLocks(), "must hold free list locks");
2275   assert_lock_strong(bitMapLock());
2276 
2277 
2278   // Allocate marking bit map if not already allocated
2279   if (!init) { // first time
2280     if (!verification_mark_bm()->allocate(_span)) {
2281       return false;
2282     }
2283     init = true;
2284   }
2285 
2286   assert(verification_mark_stack()->isEmpty(), "Should be empty");
2287 
2288   // Turn off refs discovery -- so we will be tracing through refs.
2289   // This is as intended, because by this time
2290   // GC must already have cleared any refs that need to be cleared,
2291   // and traced those that need to be marked; moreover,
2292   // the marking done here is not going to interfere in any
2293   // way with the marking information used by GC.
2294   NoRefDiscovery no_discovery(ref_processor());
2295 
2296 #if defined(COMPILER2) || INCLUDE_JVMCI
2297   DerivedPointerTableDeactivate dpt_deact;
2298 #endif
2299 
2300   // Clear any marks from a previous round
2301   verification_mark_bm()->clear_all();
2302   assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
2303   verify_work_stacks_empty();
2304 
2305   GenCollectedHeap* gch = GenCollectedHeap::heap();
2306   gch->ensure_parsability(false);  // fill TLABs, but no need to retire them
2307   // Update the saved marks which may affect the root scans.
2308   gch->save_marks();
2309 
2310   if (CMSRemarkVerifyVariant == 1) {
2311     // In this first variant of verification, we complete
2312     // all marking, then check if the new marks-vector is
2313     // a subset of the CMS marks-vector.
2314     verify_after_remark_work_1();
2315   } else {
2316     guarantee(CMSRemarkVerifyVariant == 2, "Range checking for CMSRemarkVerifyVariant should guarantee 1 or 2");
2317     // In this second variant of verification, we flag an error
2318     // (i.e. an object reachable in the new marks-vector not reachable
2319     // in the CMS marks-vector) immediately, also indicating the
2320     // identify of an object (A) that references the unmarked object (B) --
2321     // presumably, a mutation to A failed to be picked up by preclean/remark?
2322     verify_after_remark_work_2();
2323   }
2324 
2325   return true;
2326 }
2327 
2328 void CMSCollector::verify_after_remark_work_1() {
2329   ResourceMark rm;
2330   HandleMark  hm;
2331   GenCollectedHeap* gch = GenCollectedHeap::heap();
2332 
2333   // Get a clear set of claim bits for the roots processing to work with.
2334   ClassLoaderDataGraph::clear_claimed_marks();
2335 
2336   // Mark from roots one level into CMS
2337   MarkRefsIntoClosure notOlder(_span, verification_mark_bm());
2338   gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2339 
2340   {
2341     StrongRootsScope srs(1);
2342 
2343     gch->gen_process_roots(&srs,
2344                            GenCollectedHeap::OldGen,
2345                            true,   // young gen as roots
2346                            GenCollectedHeap::ScanningOption(roots_scanning_options()),
2347                            should_unload_classes(),
2348                            &notOlder,
2349                            NULL,
2350                            NULL);
2351   }
2352 
2353   // Now mark from the roots
2354   MarkFromRootsClosure markFromRootsClosure(this, _span,
2355     verification_mark_bm(), verification_mark_stack(),
2356     false /* don't yield */, true /* verifying */);
2357   assert(_restart_addr == NULL, "Expected pre-condition");
2358   verification_mark_bm()->iterate(&markFromRootsClosure);
2359   while (_restart_addr != NULL) {
2360     // Deal with stack overflow: by restarting at the indicated
2361     // address.
2362     HeapWord* ra = _restart_addr;
2363     markFromRootsClosure.reset(ra);
2364     _restart_addr = NULL;
2365     verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2366   }
2367   assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2368   verify_work_stacks_empty();
2369 
2370   // Marking completed -- now verify that each bit marked in
2371   // verification_mark_bm() is also marked in markBitMap(); flag all
2372   // errors by printing corresponding objects.
2373   VerifyMarkedClosure vcl(markBitMap());
2374   verification_mark_bm()->iterate(&vcl);
2375   if (vcl.failed()) {
2376     Log(gc, verify) log;
2377     log.error("Failed marking verification after remark");
2378     ResourceMark rm;
2379     gch->print_on(log.error_stream());
2380     fatal("CMS: failed marking verification after remark");
2381   }
2382 }
2383 
2384 class VerifyKlassOopsKlassClosure : public KlassClosure {
2385   class VerifyKlassOopsClosure : public OopClosure {
2386     CMSBitMap* _bitmap;
2387    public:
2388     VerifyKlassOopsClosure(CMSBitMap* bitmap) : _bitmap(bitmap) { }
2389     void do_oop(oop* p)       { guarantee(*p == NULL || _bitmap->isMarked((HeapWord*) *p), "Should be marked"); }
2390     void do_oop(narrowOop* p) { ShouldNotReachHere(); }
2391   } _oop_closure;
2392  public:
2393   VerifyKlassOopsKlassClosure(CMSBitMap* bitmap) : _oop_closure(bitmap) {}
2394   void do_klass(Klass* k) {
2395     k->oops_do(&_oop_closure);
2396   }
2397 };
2398 
2399 void CMSCollector::verify_after_remark_work_2() {
2400   ResourceMark rm;
2401   HandleMark  hm;
2402   GenCollectedHeap* gch = GenCollectedHeap::heap();
2403 
2404   // Get a clear set of claim bits for the roots processing to work with.
2405   ClassLoaderDataGraph::clear_claimed_marks();
2406 
2407   // Mark from roots one level into CMS
2408   MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
2409                                      markBitMap());
2410   CLDToOopClosure cld_closure(&notOlder, true);
2411 
2412   gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2413 
2414   {
2415     StrongRootsScope srs(1);
2416 
2417     gch->gen_process_roots(&srs,
2418                            GenCollectedHeap::OldGen,
2419                            true,   // young gen as roots
2420                            GenCollectedHeap::ScanningOption(roots_scanning_options()),
2421                            should_unload_classes(),
2422                            &notOlder,
2423                            NULL,
2424                            &cld_closure);
2425   }
2426 
2427   // Now mark from the roots
2428   MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
2429     verification_mark_bm(), markBitMap(), verification_mark_stack());
2430   assert(_restart_addr == NULL, "Expected pre-condition");
2431   verification_mark_bm()->iterate(&markFromRootsClosure);
2432   while (_restart_addr != NULL) {
2433     // Deal with stack overflow: by restarting at the indicated
2434     // address.
2435     HeapWord* ra = _restart_addr;
2436     markFromRootsClosure.reset(ra);
2437     _restart_addr = NULL;
2438     verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2439   }
2440   assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2441   verify_work_stacks_empty();
2442 
2443   VerifyKlassOopsKlassClosure verify_klass_oops(verification_mark_bm());
2444   ClassLoaderDataGraph::classes_do(&verify_klass_oops);
2445 
2446   // Marking completed -- now verify that each bit marked in
2447   // verification_mark_bm() is also marked in markBitMap(); flag all
2448   // errors by printing corresponding objects.
2449   VerifyMarkedClosure vcl(markBitMap());
2450   verification_mark_bm()->iterate(&vcl);
2451   assert(!vcl.failed(), "Else verification above should not have succeeded");
2452 }
2453 
2454 void ConcurrentMarkSweepGeneration::save_marks() {
2455   // delegate to CMS space
2456   cmsSpace()->save_marks();
2457 }
2458 
2459 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
2460   return cmsSpace()->no_allocs_since_save_marks();
2461 }
2462 
2463 #define CMS_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix)    \
2464                                                                 \
2465 void ConcurrentMarkSweepGeneration::                            \
2466 oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) {   \
2467   cl->set_generation(this);                                     \
2468   cmsSpace()->oop_since_save_marks_iterate##nv_suffix(cl);      \
2469   cl->reset_generation();                                       \
2470   save_marks();                                                 \
2471 }
2472 
2473 ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DEFN)
2474 
2475 void
2476 ConcurrentMarkSweepGeneration::oop_iterate(ExtendedOopClosure* cl) {
2477   if (freelistLock()->owned_by_self()) {
2478     Generation::oop_iterate(cl);
2479   } else {
2480     MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2481     Generation::oop_iterate(cl);
2482   }
2483 }
2484 
2485 void
2486 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
2487   if (freelistLock()->owned_by_self()) {
2488     Generation::object_iterate(cl);
2489   } else {
2490     MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2491     Generation::object_iterate(cl);
2492   }
2493 }
2494 
2495 void
2496 ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) {
2497   if (freelistLock()->owned_by_self()) {
2498     Generation::safe_object_iterate(cl);
2499   } else {
2500     MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2501     Generation::safe_object_iterate(cl);
2502   }
2503 }
2504 
2505 void
2506 ConcurrentMarkSweepGeneration::post_compact() {
2507 }
2508 
2509 void
2510 ConcurrentMarkSweepGeneration::prepare_for_verify() {
2511   // Fix the linear allocation blocks to look like free blocks.
2512 
2513   // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2514   // are not called when the heap is verified during universe initialization and
2515   // at vm shutdown.
2516   if (freelistLock()->owned_by_self()) {
2517     cmsSpace()->prepare_for_verify();
2518   } else {
2519     MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2520     cmsSpace()->prepare_for_verify();
2521   }
2522 }
2523 
2524 void
2525 ConcurrentMarkSweepGeneration::verify() {
2526   // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2527   // are not called when the heap is verified during universe initialization and
2528   // at vm shutdown.
2529   if (freelistLock()->owned_by_self()) {
2530     cmsSpace()->verify();
2531   } else {
2532     MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2533     cmsSpace()->verify();
2534   }
2535 }
2536 
2537 void CMSCollector::verify() {
2538   _cmsGen->verify();
2539 }
2540 
2541 #ifndef PRODUCT
2542 bool CMSCollector::overflow_list_is_empty() const {
2543   assert(_num_par_pushes >= 0, "Inconsistency");
2544   if (_overflow_list == NULL) {
2545     assert(_num_par_pushes == 0, "Inconsistency");
2546   }
2547   return _overflow_list == NULL;
2548 }
2549 
2550 // The methods verify_work_stacks_empty() and verify_overflow_empty()
2551 // merely consolidate assertion checks that appear to occur together frequently.
2552 void CMSCollector::verify_work_stacks_empty() const {
2553   assert(_markStack.isEmpty(), "Marking stack should be empty");
2554   assert(overflow_list_is_empty(), "Overflow list should be empty");
2555 }
2556 
2557 void CMSCollector::verify_overflow_empty() const {
2558   assert(overflow_list_is_empty(), "Overflow list should be empty");
2559   assert(no_preserved_marks(), "No preserved marks");
2560 }
2561 #endif // PRODUCT
2562 
2563 // Decide if we want to enable class unloading as part of the
2564 // ensuing concurrent GC cycle. We will collect and
2565 // unload classes if it's the case that:
2566 // (1) an explicit gc request has been made and the flag
2567 //     ExplicitGCInvokesConcurrentAndUnloadsClasses is set, OR
2568 // (2) (a) class unloading is enabled at the command line, and
2569 //     (b) old gen is getting really full
2570 // NOTE: Provided there is no change in the state of the heap between
2571 // calls to this method, it should have idempotent results. Moreover,
2572 // its results should be monotonically increasing (i.e. going from 0 to 1,
2573 // but not 1 to 0) between successive calls between which the heap was
2574 // not collected. For the implementation below, it must thus rely on
2575 // the property that concurrent_cycles_since_last_unload()
2576 // will not decrease unless a collection cycle happened and that
2577 // _cmsGen->is_too_full() are
2578 // themselves also monotonic in that sense. See check_monotonicity()
2579 // below.
2580 void CMSCollector::update_should_unload_classes() {
2581   _should_unload_classes = false;
2582   // Condition 1 above
2583   if (_full_gc_requested && ExplicitGCInvokesConcurrentAndUnloadsClasses) {
2584     _should_unload_classes = true;
2585   } else if (CMSClassUnloadingEnabled) { // Condition 2.a above
2586     // Disjuncts 2.b.(i,ii,iii) above
2587     _should_unload_classes = (concurrent_cycles_since_last_unload() >=
2588                               CMSClassUnloadingMaxInterval)
2589                            || _cmsGen->is_too_full();
2590   }
2591 }
2592 
2593 bool ConcurrentMarkSweepGeneration::is_too_full() const {
2594   bool res = should_concurrent_collect();
2595   res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
2596   return res;
2597 }
2598 
2599 void CMSCollector::setup_cms_unloading_and_verification_state() {
2600   const  bool should_verify =   VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
2601                              || VerifyBeforeExit;
2602   const  int  rso           =   GenCollectedHeap::SO_AllCodeCache;
2603 
2604   // We set the proper root for this CMS cycle here.
2605   if (should_unload_classes()) {   // Should unload classes this cycle
2606     remove_root_scanning_option(rso);  // Shrink the root set appropriately
2607     set_verifying(should_verify);    // Set verification state for this cycle
2608     return;                            // Nothing else needs to be done at this time
2609   }
2610 
2611   // Not unloading classes this cycle
2612   assert(!should_unload_classes(), "Inconsistency!");
2613 
2614   // If we are not unloading classes then add SO_AllCodeCache to root
2615   // scanning options.
2616   add_root_scanning_option(rso);
2617 
2618   if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
2619     set_verifying(true);
2620   } else if (verifying() && !should_verify) {
2621     // We were verifying, but some verification flags got disabled.
2622     set_verifying(false);
2623     // Exclude symbols, strings and code cache elements from root scanning to
2624     // reduce IM and RM pauses.
2625     remove_root_scanning_option(rso);
2626   }
2627 }
2628 
2629 
2630 #ifndef PRODUCT
2631 HeapWord* CMSCollector::block_start(const void* p) const {
2632   const HeapWord* addr = (HeapWord*)p;
2633   if (_span.contains(p)) {
2634     if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
2635       return _cmsGen->cmsSpace()->block_start(p);
2636     }
2637   }
2638   return NULL;
2639 }
2640 #endif
2641 
2642 HeapWord*
2643 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
2644                                                    bool   tlab,
2645                                                    bool   parallel) {
2646   CMSSynchronousYieldRequest yr;
2647   assert(!tlab, "Can't deal with TLAB allocation");
2648   MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2649   expand_for_gc_cause(word_size*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_allocation);
2650   if (GCExpandToAllocateDelayMillis > 0) {
2651     os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2652   }
2653   return have_lock_and_allocate(word_size, tlab);
2654 }
2655 
2656 void ConcurrentMarkSweepGeneration::expand_for_gc_cause(
2657     size_t bytes,
2658     size_t expand_bytes,
2659     CMSExpansionCause::Cause cause)
2660 {
2661 
2662   bool success = expand(bytes, expand_bytes);
2663 
2664   // remember why we expanded; this information is used
2665   // by shouldConcurrentCollect() when making decisions on whether to start
2666   // a new CMS cycle.
2667   if (success) {
2668     set_expansion_cause(cause);
2669     log_trace(gc)("Expanded CMS gen for %s",  CMSExpansionCause::to_string(cause));
2670   }
2671 }
2672 
2673 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
2674   HeapWord* res = NULL;
2675   MutexLocker x(ParGCRareEvent_lock);
2676   while (true) {
2677     // Expansion by some other thread might make alloc OK now:
2678     res = ps->lab.alloc(word_sz);
2679     if (res != NULL) return res;
2680     // If there's not enough expansion space available, give up.
2681     if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
2682       return NULL;
2683     }
2684     // Otherwise, we try expansion.
2685     expand_for_gc_cause(word_sz*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_lab);
2686     // Now go around the loop and try alloc again;
2687     // A competing par_promote might beat us to the expansion space,
2688     // so we may go around the loop again if promotion fails again.
2689     if (GCExpandToAllocateDelayMillis > 0) {
2690       os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2691     }
2692   }
2693 }
2694 
2695 
2696 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
2697   PromotionInfo* promo) {
2698   MutexLocker x(ParGCRareEvent_lock);
2699   size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
2700   while (true) {
2701     // Expansion by some other thread might make alloc OK now:
2702     if (promo->ensure_spooling_space()) {
2703       assert(promo->has_spooling_space(),
2704              "Post-condition of successful ensure_spooling_space()");
2705       return true;
2706     }
2707     // If there's not enough expansion space available, give up.
2708     if (_virtual_space.uncommitted_size() < refill_size_bytes) {
2709       return false;
2710     }
2711     // Otherwise, we try expansion.
2712     expand_for_gc_cause(refill_size_bytes, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_spooling_space);
2713     // Now go around the loop and try alloc again;
2714     // A competing allocation might beat us to the expansion space,
2715     // so we may go around the loop again if allocation fails again.
2716     if (GCExpandToAllocateDelayMillis > 0) {
2717       os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2718     }
2719   }
2720 }
2721 
2722 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
2723   // Only shrink if a compaction was done so that all the free space
2724   // in the generation is in a contiguous block at the end.
2725   if (did_compact()) {
2726     CardGeneration::shrink(bytes);
2727   }
2728 }
2729 
2730 void ConcurrentMarkSweepGeneration::assert_correct_size_change_locking() {
2731   assert_locked_or_safepoint(Heap_lock);
2732 }
2733 
2734 void ConcurrentMarkSweepGeneration::shrink_free_list_by(size_t bytes) {
2735   assert_locked_or_safepoint(Heap_lock);
2736   assert_lock_strong(freelistLock());
2737   log_trace(gc)("Shrinking of CMS not yet implemented");
2738   return;
2739 }
2740 
2741 
2742 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
2743 // phases.
2744 class CMSPhaseAccounting: public StackObj {
2745  public:
2746   CMSPhaseAccounting(CMSCollector *collector,
2747                      const char *title);
2748   ~CMSPhaseAccounting();
2749 
2750  private:
2751   CMSCollector *_collector;
2752   const char *_title;
2753   GCTraceConcTime(Info, gc) _trace_time;
2754 
2755  public:
2756   // Not MT-safe; so do not pass around these StackObj's
2757   // where they may be accessed by other threads.
2758   double wallclock_millis() {
2759     return TimeHelper::counter_to_millis(os::elapsed_counter() - _trace_time.start_time());
2760   }
2761 };
2762 
2763 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
2764                                        const char *title) :
2765   _collector(collector), _title(title), _trace_time(title) {
2766 
2767   _collector->resetYields();
2768   _collector->resetTimer();
2769   _collector->startTimer();
2770   _collector->gc_timer_cm()->register_gc_concurrent_start(title);
2771 }
2772 
2773 CMSPhaseAccounting::~CMSPhaseAccounting() {
2774   _collector->gc_timer_cm()->register_gc_concurrent_end();
2775   _collector->stopTimer();
2776   log_debug(gc)("Concurrent active time: %.3fms", TimeHelper::counter_to_seconds(_collector->timerTicks()));
2777   log_trace(gc)(" (CMS %s yielded %d times)", _title, _collector->yields());
2778 }
2779 
2780 // CMS work
2781 
2782 // The common parts of CMSParInitialMarkTask and CMSParRemarkTask.
2783 class CMSParMarkTask : public AbstractGangTask {
2784  protected:
2785   CMSCollector*     _collector;
2786   uint              _n_workers;
2787   CMSParMarkTask(const char* name, CMSCollector* collector, uint n_workers) :
2788       AbstractGangTask(name),
2789       _collector(collector),
2790       _n_workers(n_workers) {}
2791   // Work method in support of parallel rescan ... of young gen spaces
2792   void do_young_space_rescan(OopsInGenClosure* cl,
2793                              ContiguousSpace* space,
2794                              HeapWord** chunk_array, size_t chunk_top);
2795   void work_on_young_gen_roots(OopsInGenClosure* cl);
2796 };
2797 
2798 // Parallel initial mark task
2799 class CMSParInitialMarkTask: public CMSParMarkTask {
2800   StrongRootsScope* _strong_roots_scope;
2801  public:
2802   CMSParInitialMarkTask(CMSCollector* collector, StrongRootsScope* strong_roots_scope, uint n_workers) :
2803       CMSParMarkTask("Scan roots and young gen for initial mark in parallel", collector, n_workers),
2804       _strong_roots_scope(strong_roots_scope) {}
2805   void work(uint worker_id);
2806 };
2807 
2808 // Checkpoint the roots into this generation from outside
2809 // this generation. [Note this initial checkpoint need only
2810 // be approximate -- we'll do a catch up phase subsequently.]
2811 void CMSCollector::checkpointRootsInitial() {
2812   assert(_collectorState == InitialMarking, "Wrong collector state");
2813   check_correct_thread_executing();
2814   TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
2815 
2816   save_heap_summary();
2817   report_heap_summary(GCWhen::BeforeGC);
2818 
2819   ReferenceProcessor* rp = ref_processor();
2820   assert(_restart_addr == NULL, "Control point invariant");
2821   {
2822     // acquire locks for subsequent manipulations
2823     MutexLockerEx x(bitMapLock(),
2824                     Mutex::_no_safepoint_check_flag);
2825     checkpointRootsInitialWork();
2826     // enable ("weak") refs discovery
2827     rp->enable_discovery();
2828     _collectorState = Marking;
2829   }
2830 }
2831 
2832 void CMSCollector::checkpointRootsInitialWork() {
2833   assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
2834   assert(_collectorState == InitialMarking, "just checking");
2835 
2836   // Already have locks.
2837   assert_lock_strong(bitMapLock());
2838   assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
2839 
2840   // Setup the verification and class unloading state for this
2841   // CMS collection cycle.
2842   setup_cms_unloading_and_verification_state();
2843 
2844   GCTraceTime(Trace, gc, phases) ts("checkpointRootsInitialWork", _gc_timer_cm);
2845 
2846   // Reset all the PLAB chunk arrays if necessary.
2847   if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
2848     reset_survivor_plab_arrays();
2849   }
2850 
2851   ResourceMark rm;
2852   HandleMark  hm;
2853 
2854   MarkRefsIntoClosure notOlder(_span, &_markBitMap);
2855   GenCollectedHeap* gch = GenCollectedHeap::heap();
2856 
2857   verify_work_stacks_empty();
2858   verify_overflow_empty();
2859 
2860   gch->ensure_parsability(false);  // fill TLABs, but no need to retire them
2861   // Update the saved marks which may affect the root scans.
2862   gch->save_marks();
2863 
2864   // weak reference processing has not started yet.
2865   ref_processor()->set_enqueuing_is_done(false);
2866 
2867   // Need to remember all newly created CLDs,
2868   // so that we can guarantee that the remark finds them.
2869   ClassLoaderDataGraph::remember_new_clds(true);
2870 
2871   // Whenever a CLD is found, it will be claimed before proceeding to mark
2872   // the klasses. The claimed marks need to be cleared before marking starts.
2873   ClassLoaderDataGraph::clear_claimed_marks();
2874 
2875   print_eden_and_survivor_chunk_arrays();
2876 
2877   {
2878 #if defined(COMPILER2) || INCLUDE_JVMCI
2879     DerivedPointerTableDeactivate dpt_deact;
2880 #endif
2881     if (CMSParallelInitialMarkEnabled) {
2882       // The parallel version.
2883       WorkGang* workers = gch->workers();
2884       assert(workers != NULL, "Need parallel worker threads.");
2885       uint n_workers = workers->active_workers();
2886 
2887       StrongRootsScope srs(n_workers);
2888 
2889       CMSParInitialMarkTask tsk(this, &srs, n_workers);
2890       initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
2891       // If the total workers is greater than 1, then multiple workers
2892       // may be used at some time and the initialization has been set
2893       // such that the single threaded path cannot be used.
2894       if (workers->total_workers() > 1) {
2895         workers->run_task(&tsk);
2896       } else {
2897         tsk.work(0);
2898       }
2899     } else {
2900       // The serial version.
2901       CLDToOopClosure cld_closure(&notOlder, true);
2902       gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2903 
2904       StrongRootsScope srs(1);
2905 
2906       gch->gen_process_roots(&srs,
2907                              GenCollectedHeap::OldGen,
2908                              true,   // young gen as roots
2909                              GenCollectedHeap::ScanningOption(roots_scanning_options()),
2910                              should_unload_classes(),
2911                              &notOlder,
2912                              NULL,
2913                              &cld_closure);
2914     }
2915   }
2916 
2917   // Clear mod-union table; it will be dirtied in the prologue of
2918   // CMS generation per each young generation collection.
2919 
2920   assert(_modUnionTable.isAllClear(),
2921        "Was cleared in most recent final checkpoint phase"
2922        " or no bits are set in the gc_prologue before the start of the next "
2923        "subsequent marking phase.");
2924 
2925   assert(_ct->klass_rem_set()->mod_union_is_clear(), "Must be");
2926 
2927   // Save the end of the used_region of the constituent generations
2928   // to be used to limit the extent of sweep in each generation.
2929   save_sweep_limits();
2930   verify_overflow_empty();
2931 }
2932 
2933 bool CMSCollector::markFromRoots() {
2934   // we might be tempted to assert that:
2935   // assert(!SafepointSynchronize::is_at_safepoint(),
2936   //        "inconsistent argument?");
2937   // However that wouldn't be right, because it's possible that
2938   // a safepoint is indeed in progress as a young generation
2939   // stop-the-world GC happens even as we mark in this generation.
2940   assert(_collectorState == Marking, "inconsistent state?");
2941   check_correct_thread_executing();
2942   verify_overflow_empty();
2943 
2944   // Weak ref discovery note: We may be discovering weak
2945   // refs in this generation concurrent (but interleaved) with
2946   // weak ref discovery by the young generation collector.
2947 
2948   CMSTokenSyncWithLocks ts(true, bitMapLock());
2949   GCTraceCPUTime tcpu;
2950   CMSPhaseAccounting pa(this, "Concurrent Mark");
2951   bool res = markFromRootsWork();
2952   if (res) {
2953     _collectorState = Precleaning;
2954   } else { // We failed and a foreground collection wants to take over
2955     assert(_foregroundGCIsActive, "internal state inconsistency");
2956     assert(_restart_addr == NULL,  "foreground will restart from scratch");
2957     log_debug(gc)("bailing out to foreground collection");
2958   }
2959   verify_overflow_empty();
2960   return res;
2961 }
2962 
2963 bool CMSCollector::markFromRootsWork() {
2964   // iterate over marked bits in bit map, doing a full scan and mark
2965   // from these roots using the following algorithm:
2966   // . if oop is to the right of the current scan pointer,
2967   //   mark corresponding bit (we'll process it later)
2968   // . else (oop is to left of current scan pointer)
2969   //   push oop on marking stack
2970   // . drain the marking stack
2971 
2972   // Note that when we do a marking step we need to hold the
2973   // bit map lock -- recall that direct allocation (by mutators)
2974   // and promotion (by the young generation collector) is also
2975   // marking the bit map. [the so-called allocate live policy.]
2976   // Because the implementation of bit map marking is not
2977   // robust wrt simultaneous marking of bits in the same word,
2978   // we need to make sure that there is no such interference
2979   // between concurrent such updates.
2980 
2981   // already have locks
2982   assert_lock_strong(bitMapLock());
2983 
2984   verify_work_stacks_empty();
2985   verify_overflow_empty();
2986   bool result = false;
2987   if (CMSConcurrentMTEnabled && ConcGCThreads > 0) {
2988     result = do_marking_mt();
2989   } else {
2990     result = do_marking_st();
2991   }
2992   return result;
2993 }
2994 
2995 // Forward decl
2996 class CMSConcMarkingTask;
2997 
2998 class CMSConcMarkingTerminator: public ParallelTaskTerminator {
2999   CMSCollector*       _collector;
3000   CMSConcMarkingTask* _task;
3001  public:
3002   virtual void yield();
3003 
3004   // "n_threads" is the number of threads to be terminated.
3005   // "queue_set" is a set of work queues of other threads.
3006   // "collector" is the CMS collector associated with this task terminator.
3007   // "yield" indicates whether we need the gang as a whole to yield.
3008   CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
3009     ParallelTaskTerminator(n_threads, queue_set),
3010     _collector(collector) { }
3011 
3012   void set_task(CMSConcMarkingTask* task) {
3013     _task = task;
3014   }
3015 };
3016 
3017 class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator {
3018   CMSConcMarkingTask* _task;
3019  public:
3020   bool should_exit_termination();
3021   void set_task(CMSConcMarkingTask* task) {
3022     _task = task;
3023   }
3024 };
3025 
3026 // MT Concurrent Marking Task
3027 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3028   CMSCollector* _collector;
3029   uint          _n_workers;       // requested/desired # workers
3030   bool          _result;
3031   CompactibleFreeListSpace*  _cms_space;
3032   char          _pad_front[64];   // padding to ...
3033   HeapWord*     _global_finger;   // ... avoid sharing cache line
3034   char          _pad_back[64];
3035   HeapWord*     _restart_addr;
3036 
3037   //  Exposed here for yielding support
3038   Mutex* const _bit_map_lock;
3039 
3040   // The per thread work queues, available here for stealing
3041   OopTaskQueueSet*  _task_queues;
3042 
3043   // Termination (and yielding) support
3044   CMSConcMarkingTerminator _term;
3045   CMSConcMarkingTerminatorTerminator _term_term;
3046 
3047  public:
3048   CMSConcMarkingTask(CMSCollector* collector,
3049                  CompactibleFreeListSpace* cms_space,
3050                  YieldingFlexibleWorkGang* workers,
3051                  OopTaskQueueSet* task_queues):
3052     YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3053     _collector(collector),
3054     _cms_space(cms_space),
3055     _n_workers(0), _result(true),
3056     _task_queues(task_queues),
3057     _term(_n_workers, task_queues, _collector),
3058     _bit_map_lock(collector->bitMapLock())
3059   {
3060     _requested_size = _n_workers;
3061     _term.set_task(this);
3062     _term_term.set_task(this);
3063     _restart_addr = _global_finger = _cms_space->bottom();
3064   }
3065 
3066 
3067   OopTaskQueueSet* task_queues()  { return _task_queues; }
3068 
3069   OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3070 
3071   HeapWord** global_finger_addr() { return &_global_finger; }
3072 
3073   CMSConcMarkingTerminator* terminator() { return &_term; }
3074 
3075   virtual void set_for_termination(uint active_workers) {
3076     terminator()->reset_for_reuse(active_workers);
3077   }
3078 
3079   void work(uint worker_id);
3080   bool should_yield() {
3081     return    ConcurrentMarkSweepThread::should_yield()
3082            && !_collector->foregroundGCIsActive();
3083   }
3084 
3085   virtual void coordinator_yield();  // stuff done by coordinator
3086   bool result() { return _result; }
3087 
3088   void reset(HeapWord* ra) {
3089     assert(_global_finger >= _cms_space->end(),  "Postcondition of ::work(i)");
3090     _restart_addr = _global_finger = ra;
3091     _term.reset_for_reuse();
3092   }
3093 
3094   static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3095                                            OopTaskQueue* work_q);
3096 
3097  private:
3098   void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3099   void do_work_steal(int i);
3100   void bump_global_finger(HeapWord* f);
3101 };
3102 
3103 bool CMSConcMarkingTerminatorTerminator::should_exit_termination() {
3104   assert(_task != NULL, "Error");
3105   return _task->yielding();
3106   // Note that we do not need the disjunct || _task->should_yield() above
3107   // because we want terminating threads to yield only if the task
3108   // is already in the midst of yielding, which happens only after at least one
3109   // thread has yielded.
3110 }
3111 
3112 void CMSConcMarkingTerminator::yield() {
3113   if (_task->should_yield()) {
3114     _task->yield();
3115   } else {
3116     ParallelTaskTerminator::yield();
3117   }
3118 }
3119 
3120 ////////////////////////////////////////////////////////////////
3121 // Concurrent Marking Algorithm Sketch
3122 ////////////////////////////////////////////////////////////////
3123 // Until all tasks exhausted (both spaces):
3124 // -- claim next available chunk
3125 // -- bump global finger via CAS
3126 // -- find first object that starts in this chunk
3127 //    and start scanning bitmap from that position
3128 // -- scan marked objects for oops
3129 // -- CAS-mark target, and if successful:
3130 //    . if target oop is above global finger (volatile read)
3131 //      nothing to do
3132 //    . if target oop is in chunk and above local finger
3133 //        then nothing to do
3134 //    . else push on work-queue
3135 // -- Deal with possible overflow issues:
3136 //    . local work-queue overflow causes stuff to be pushed on
3137 //      global (common) overflow queue
3138 //    . always first empty local work queue
3139 //    . then get a batch of oops from global work queue if any
3140 //    . then do work stealing
3141 // -- When all tasks claimed (both spaces)
3142 //    and local work queue empty,
3143 //    then in a loop do:
3144 //    . check global overflow stack; steal a batch of oops and trace
3145 //    . try to steal from other threads oif GOS is empty
3146 //    . if neither is available, offer termination
3147 // -- Terminate and return result
3148 //
3149 void CMSConcMarkingTask::work(uint worker_id) {
3150   elapsedTimer _timer;
3151   ResourceMark rm;
3152   HandleMark hm;
3153 
3154   DEBUG_ONLY(_collector->verify_overflow_empty();)
3155 
3156   // Before we begin work, our work queue should be empty
3157   assert(work_queue(worker_id)->size() == 0, "Expected to be empty");
3158   // Scan the bitmap covering _cms_space, tracing through grey objects.
3159   _timer.start();
3160   do_scan_and_mark(worker_id, _cms_space);
3161   _timer.stop();
3162   log_trace(gc, task)("Finished cms space scanning in %dth thread: %3.3f sec", worker_id, _timer.seconds());
3163 
3164   // ... do work stealing
3165   _timer.reset();
3166   _timer.start();
3167   do_work_steal(worker_id);
3168   _timer.stop();
3169   log_trace(gc, task)("Finished work stealing in %dth thread: %3.3f sec", worker_id, _timer.seconds());
3170   assert(_collector->_markStack.isEmpty(), "Should have been emptied");
3171   assert(work_queue(worker_id)->size() == 0, "Should have been emptied");
3172   // Note that under the current task protocol, the
3173   // following assertion is true even of the spaces
3174   // expanded since the completion of the concurrent
3175   // marking. XXX This will likely change under a strict
3176   // ABORT semantics.
3177   // After perm removal the comparison was changed to
3178   // greater than or equal to from strictly greater than.
3179   // Before perm removal the highest address sweep would
3180   // have been at the end of perm gen but now is at the
3181   // end of the tenured gen.
3182   assert(_global_finger >=  _cms_space->end(),
3183          "All tasks have been completed");
3184   DEBUG_ONLY(_collector->verify_overflow_empty();)
3185 }
3186 
3187 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
3188   HeapWord* read = _global_finger;
3189   HeapWord* cur  = read;
3190   while (f > read) {
3191     cur = read;
3192     read = (HeapWord*) Atomic::cmpxchg_ptr(f, &_global_finger, cur);
3193     if (cur == read) {
3194       // our cas succeeded
3195       assert(_global_finger >= f, "protocol consistency");
3196       break;
3197     }
3198   }
3199 }
3200 
3201 // This is really inefficient, and should be redone by
3202 // using (not yet available) block-read and -write interfaces to the
3203 // stack and the work_queue. XXX FIX ME !!!
3204 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3205                                                       OopTaskQueue* work_q) {
3206   // Fast lock-free check
3207   if (ovflw_stk->length() == 0) {
3208     return false;
3209   }
3210   assert(work_q->size() == 0, "Shouldn't steal");
3211   MutexLockerEx ml(ovflw_stk->par_lock(),
3212                    Mutex::_no_safepoint_check_flag);
3213   // Grab up to 1/4 the size of the work queue
3214   size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
3215                     (size_t)ParGCDesiredObjsFromOverflowList);
3216   num = MIN2(num, ovflw_stk->length());
3217   for (int i = (int) num; i > 0; i--) {
3218     oop cur = ovflw_stk->pop();
3219     assert(cur != NULL, "Counted wrong?");
3220     work_q->push(cur);
3221   }
3222   return num > 0;
3223 }
3224 
3225 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
3226   SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
3227   int n_tasks = pst->n_tasks();
3228   // We allow that there may be no tasks to do here because
3229   // we are restarting after a stack overflow.
3230   assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
3231   uint nth_task = 0;
3232 
3233   HeapWord* aligned_start = sp->bottom();
3234   if (sp->used_region().contains(_restart_addr)) {
3235     // Align down to a card boundary for the start of 0th task
3236     // for this space.
3237     aligned_start =
3238       (HeapWord*)align_size_down((uintptr_t)_restart_addr,
3239                                  CardTableModRefBS::card_size);
3240   }
3241 
3242   size_t chunk_size = sp->marking_task_size();
3243   while (!pst->is_task_claimed(/* reference */ nth_task)) {
3244     // Having claimed the nth task in this space,
3245     // compute the chunk that it corresponds to:
3246     MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
3247                                aligned_start + (nth_task+1)*chunk_size);
3248     // Try and bump the global finger via a CAS;
3249     // note that we need to do the global finger bump
3250     // _before_ taking the intersection below, because
3251     // the task corresponding to that region will be
3252     // deemed done even if the used_region() expands
3253     // because of allocation -- as it almost certainly will
3254     // during start-up while the threads yield in the
3255     // closure below.
3256     HeapWord* finger = span.end();
3257     bump_global_finger(finger);   // atomically
3258     // There are null tasks here corresponding to chunks
3259     // beyond the "top" address of the space.
3260     span = span.intersection(sp->used_region());
3261     if (!span.is_empty()) {  // Non-null task
3262       HeapWord* prev_obj;
3263       assert(!span.contains(_restart_addr) || nth_task == 0,
3264              "Inconsistency");
3265       if (nth_task == 0) {
3266         // For the 0th task, we'll not need to compute a block_start.
3267         if (span.contains(_restart_addr)) {
3268           // In the case of a restart because of stack overflow,
3269           // we might additionally skip a chunk prefix.
3270           prev_obj = _restart_addr;
3271         } else {
3272           prev_obj = span.start();
3273         }
3274       } else {
3275         // We want to skip the first object because
3276         // the protocol is to scan any object in its entirety
3277         // that _starts_ in this span; a fortiori, any
3278         // object starting in an earlier span is scanned
3279         // as part of an earlier claimed task.
3280         // Below we use the "careful" version of block_start
3281         // so we do not try to navigate uninitialized objects.
3282         prev_obj = sp->block_start_careful(span.start());
3283         // Below we use a variant of block_size that uses the
3284         // Printezis bits to avoid waiting for allocated
3285         // objects to become initialized/parsable.
3286         while (prev_obj < span.start()) {
3287           size_t sz = sp->block_size_no_stall(prev_obj, _collector);
3288           if (sz > 0) {
3289             prev_obj += sz;
3290           } else {
3291             // In this case we may end up doing a bit of redundant
3292             // scanning, but that appears unavoidable, short of
3293             // locking the free list locks; see bug 6324141.
3294             break;
3295           }
3296         }
3297       }
3298       if (prev_obj < span.end()) {
3299         MemRegion my_span = MemRegion(prev_obj, span.end());
3300         // Do the marking work within a non-empty span --
3301         // the last argument to the constructor indicates whether the
3302         // iteration should be incremental with periodic yields.
3303         ParMarkFromRootsClosure cl(this, _collector, my_span,
3304                                    &_collector->_markBitMap,
3305                                    work_queue(i),
3306                                    &_collector->_markStack);
3307         _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
3308       } // else nothing to do for this task
3309     }   // else nothing to do for this task
3310   }
3311   // We'd be tempted to assert here that since there are no
3312   // more tasks left to claim in this space, the global_finger
3313   // must exceed space->top() and a fortiori space->end(). However,
3314   // that would not quite be correct because the bumping of
3315   // global_finger occurs strictly after the claiming of a task,
3316   // so by the time we reach here the global finger may not yet
3317   // have been bumped up by the thread that claimed the last
3318   // task.
3319   pst->all_tasks_completed();
3320 }
3321 
3322 class ParConcMarkingClosure: public MetadataAwareOopClosure {
3323  private:
3324   CMSCollector* _collector;
3325   CMSConcMarkingTask* _task;
3326   MemRegion     _span;
3327   CMSBitMap*    _bit_map;
3328   CMSMarkStack* _overflow_stack;
3329   OopTaskQueue* _work_queue;
3330  protected:
3331   DO_OOP_WORK_DEFN
3332  public:
3333   ParConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue,
3334                         CMSBitMap* bit_map, CMSMarkStack* overflow_stack):
3335     MetadataAwareOopClosure(collector->ref_processor()),
3336     _collector(collector),
3337     _task(task),
3338     _span(collector->_span),
3339     _work_queue(work_queue),
3340     _bit_map(bit_map),
3341     _overflow_stack(overflow_stack)
3342   { }
3343   virtual void do_oop(oop* p);
3344   virtual void do_oop(narrowOop* p);
3345 
3346   void trim_queue(size_t max);
3347   void handle_stack_overflow(HeapWord* lost);
3348   void do_yield_check() {
3349     if (_task->should_yield()) {
3350       _task->yield();
3351     }
3352   }
3353 };
3354 
3355 DO_OOP_WORK_IMPL(ParConcMarkingClosure)
3356 
3357 // Grey object scanning during work stealing phase --
3358 // the salient assumption here is that any references
3359 // that are in these stolen objects being scanned must
3360 // already have been initialized (else they would not have
3361 // been published), so we do not need to check for
3362 // uninitialized objects before pushing here.
3363 void ParConcMarkingClosure::do_oop(oop obj) {
3364   assert(obj->is_oop_or_null(true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
3365   HeapWord* addr = (HeapWord*)obj;
3366   // Check if oop points into the CMS generation
3367   // and is not marked
3368   if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
3369     // a white object ...
3370     // If we manage to "claim" the object, by being the
3371     // first thread to mark it, then we push it on our
3372     // marking stack
3373     if (_bit_map->par_mark(addr)) {     // ... now grey
3374       // push on work queue (grey set)
3375       bool simulate_overflow = false;
3376       NOT_PRODUCT(
3377         if (CMSMarkStackOverflowALot &&
3378             _collector->simulate_overflow()) {
3379           // simulate a stack overflow
3380           simulate_overflow = true;
3381         }
3382       )
3383       if (simulate_overflow ||
3384           !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
3385         // stack overflow
3386         log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _overflow_stack->capacity());
3387         // We cannot assert that the overflow stack is full because
3388         // it may have been emptied since.
3389         assert(simulate_overflow ||
3390                _work_queue->size() == _work_queue->max_elems(),
3391               "Else push should have succeeded");
3392         handle_stack_overflow(addr);
3393       }
3394     } // Else, some other thread got there first
3395     do_yield_check();
3396   }
3397 }
3398 
3399 void ParConcMarkingClosure::do_oop(oop* p)       { ParConcMarkingClosure::do_oop_work(p); }
3400 void ParConcMarkingClosure::do_oop(narrowOop* p) { ParConcMarkingClosure::do_oop_work(p); }
3401 
3402 void ParConcMarkingClosure::trim_queue(size_t max) {
3403   while (_work_queue->size() > max) {
3404     oop new_oop;
3405     if (_work_queue->pop_local(new_oop)) {
3406       assert(new_oop->is_oop(), "Should be an oop");
3407       assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
3408       assert(_span.contains((HeapWord*)new_oop), "Not in span");
3409       new_oop->oop_iterate(this);  // do_oop() above
3410       do_yield_check();
3411     }
3412   }
3413 }
3414 
3415 // Upon stack overflow, we discard (part of) the stack,
3416 // remembering the least address amongst those discarded
3417 // in CMSCollector's _restart_address.
3418 void ParConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
3419   // We need to do this under a mutex to prevent other
3420   // workers from interfering with the work done below.
3421   MutexLockerEx ml(_overflow_stack->par_lock(),
3422                    Mutex::_no_safepoint_check_flag);
3423   // Remember the least grey address discarded
3424   HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
3425   _collector->lower_restart_addr(ra);
3426   _overflow_stack->reset();  // discard stack contents
3427   _overflow_stack->expand(); // expand the stack if possible
3428 }
3429 
3430 
3431 void CMSConcMarkingTask::do_work_steal(int i) {
3432   OopTaskQueue* work_q = work_queue(i);
3433   oop obj_to_scan;
3434   CMSBitMap* bm = &(_collector->_markBitMap);
3435   CMSMarkStack* ovflw = &(_collector->_markStack);
3436   int* seed = _collector->hash_seed(i);
3437   ParConcMarkingClosure cl(_collector, this, work_q, bm, ovflw);
3438   while (true) {
3439     cl.trim_queue(0);
3440     assert(work_q->size() == 0, "Should have been emptied above");
3441     if (get_work_from_overflow_stack(ovflw, work_q)) {
3442       // Can't assert below because the work obtained from the
3443       // overflow stack may already have been stolen from us.
3444       // assert(work_q->size() > 0, "Work from overflow stack");
3445       continue;
3446     } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
3447       assert(obj_to_scan->is_oop(), "Should be an oop");
3448       assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
3449       obj_to_scan->oop_iterate(&cl);
3450     } else if (terminator()->offer_termination(&_term_term)) {
3451       assert(work_q->size() == 0, "Impossible!");
3452       break;
3453     } else if (yielding() || should_yield()) {
3454       yield();
3455     }
3456   }
3457 }
3458 
3459 // This is run by the CMS (coordinator) thread.
3460 void CMSConcMarkingTask::coordinator_yield() {
3461   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3462          "CMS thread should hold CMS token");
3463   // First give up the locks, then yield, then re-lock
3464   // We should probably use a constructor/destructor idiom to
3465   // do this unlock/lock or modify the MutexUnlocker class to
3466   // serve our purpose. XXX
3467   assert_lock_strong(_bit_map_lock);
3468   _bit_map_lock->unlock();
3469   ConcurrentMarkSweepThread::desynchronize(true);
3470   _collector->stopTimer();
3471   _collector->incrementYields();
3472 
3473   // It is possible for whichever thread initiated the yield request
3474   // not to get a chance to wake up and take the bitmap lock between
3475   // this thread releasing it and reacquiring it. So, while the
3476   // should_yield() flag is on, let's sleep for a bit to give the
3477   // other thread a chance to wake up. The limit imposed on the number
3478   // of iterations is defensive, to avoid any unforseen circumstances
3479   // putting us into an infinite loop. Since it's always been this
3480   // (coordinator_yield()) method that was observed to cause the
3481   // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
3482   // which is by default non-zero. For the other seven methods that
3483   // also perform the yield operation, as are using a different
3484   // parameter (CMSYieldSleepCount) which is by default zero. This way we
3485   // can enable the sleeping for those methods too, if necessary.
3486   // See 6442774.
3487   //
3488   // We really need to reconsider the synchronization between the GC
3489   // thread and the yield-requesting threads in the future and we
3490   // should really use wait/notify, which is the recommended
3491   // way of doing this type of interaction. Additionally, we should
3492   // consolidate the eight methods that do the yield operation and they
3493   // are almost identical into one for better maintainability and
3494   // readability. See 6445193.
3495   //
3496   // Tony 2006.06.29
3497   for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
3498                    ConcurrentMarkSweepThread::should_yield() &&
3499                    !CMSCollector::foregroundGCIsActive(); ++i) {
3500     os::sleep(Thread::current(), 1, false);
3501   }
3502 
3503   ConcurrentMarkSweepThread::synchronize(true);
3504   _bit_map_lock->lock_without_safepoint_check();
3505   _collector->startTimer();
3506 }
3507 
3508 bool CMSCollector::do_marking_mt() {
3509   assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition");
3510   uint num_workers = AdaptiveSizePolicy::calc_active_conc_workers(conc_workers()->total_workers(),
3511                                                                   conc_workers()->active_workers(),
3512                                                                   Threads::number_of_non_daemon_threads());
3513   num_workers = conc_workers()->update_active_workers(num_workers);
3514 
3515   CompactibleFreeListSpace* cms_space  = _cmsGen->cmsSpace();
3516 
3517   CMSConcMarkingTask tsk(this,
3518                          cms_space,
3519                          conc_workers(),
3520                          task_queues());
3521 
3522   // Since the actual number of workers we get may be different
3523   // from the number we requested above, do we need to do anything different
3524   // below? In particular, may be we need to subclass the SequantialSubTasksDone
3525   // class?? XXX
3526   cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
3527 
3528   // Refs discovery is already non-atomic.
3529   assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
3530   assert(ref_processor()->discovery_is_mt(), "Discovery should be MT");
3531   conc_workers()->start_task(&tsk);
3532   while (tsk.yielded()) {
3533     tsk.coordinator_yield();
3534     conc_workers()->continue_task(&tsk);
3535   }
3536   // If the task was aborted, _restart_addr will be non-NULL
3537   assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
3538   while (_restart_addr != NULL) {
3539     // XXX For now we do not make use of ABORTED state and have not
3540     // yet implemented the right abort semantics (even in the original
3541     // single-threaded CMS case). That needs some more investigation
3542     // and is deferred for now; see CR# TBF. 07252005YSR. XXX
3543     assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
3544     // If _restart_addr is non-NULL, a marking stack overflow
3545     // occurred; we need to do a fresh marking iteration from the
3546     // indicated restart address.
3547     if (_foregroundGCIsActive) {
3548       // We may be running into repeated stack overflows, having
3549       // reached the limit of the stack size, while making very
3550       // slow forward progress. It may be best to bail out and
3551       // let the foreground collector do its job.
3552       // Clear _restart_addr, so that foreground GC
3553       // works from scratch. This avoids the headache of
3554       // a "rescan" which would otherwise be needed because
3555       // of the dirty mod union table & card table.
3556       _restart_addr = NULL;
3557       return false;
3558     }
3559     // Adjust the task to restart from _restart_addr
3560     tsk.reset(_restart_addr);
3561     cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
3562                   _restart_addr);
3563     _restart_addr = NULL;
3564     // Get the workers going again
3565     conc_workers()->start_task(&tsk);
3566     while (tsk.yielded()) {
3567       tsk.coordinator_yield();
3568       conc_workers()->continue_task(&tsk);
3569     }
3570   }
3571   assert(tsk.completed(), "Inconsistency");
3572   assert(tsk.result() == true, "Inconsistency");
3573   return true;
3574 }
3575 
3576 bool CMSCollector::do_marking_st() {
3577   ResourceMark rm;
3578   HandleMark   hm;
3579 
3580   // Temporarily make refs discovery single threaded (non-MT)
3581   ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
3582   MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
3583     &_markStack, CMSYield);
3584   // the last argument to iterate indicates whether the iteration
3585   // should be incremental with periodic yields.
3586   _markBitMap.iterate(&markFromRootsClosure);
3587   // If _restart_addr is non-NULL, a marking stack overflow
3588   // occurred; we need to do a fresh iteration from the
3589   // indicated restart address.
3590   while (_restart_addr != NULL) {
3591     if (_foregroundGCIsActive) {
3592       // We may be running into repeated stack overflows, having
3593       // reached the limit of the stack size, while making very
3594       // slow forward progress. It may be best to bail out and
3595       // let the foreground collector do its job.
3596       // Clear _restart_addr, so that foreground GC
3597       // works from scratch. This avoids the headache of
3598       // a "rescan" which would otherwise be needed because
3599       // of the dirty mod union table & card table.
3600       _restart_addr = NULL;
3601       return false;  // indicating failure to complete marking
3602     }
3603     // Deal with stack overflow:
3604     // we restart marking from _restart_addr
3605     HeapWord* ra = _restart_addr;
3606     markFromRootsClosure.reset(ra);
3607     _restart_addr = NULL;
3608     _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
3609   }
3610   return true;
3611 }
3612 
3613 void CMSCollector::preclean() {
3614   check_correct_thread_executing();
3615   assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
3616   verify_work_stacks_empty();
3617   verify_overflow_empty();
3618   _abort_preclean = false;
3619   if (CMSPrecleaningEnabled) {
3620     if (!CMSEdenChunksRecordAlways) {
3621       _eden_chunk_index = 0;
3622     }
3623     size_t used = get_eden_used();
3624     size_t capacity = get_eden_capacity();
3625     // Don't start sampling unless we will get sufficiently
3626     // many samples.
3627     if (used < (((capacity / CMSScheduleRemarkSamplingRatio) / 100)
3628                 * CMSScheduleRemarkEdenPenetration)) {
3629       _start_sampling = true;
3630     } else {
3631       _start_sampling = false;
3632     }
3633     GCTraceCPUTime tcpu;
3634     CMSPhaseAccounting pa(this, "Concurrent Preclean");
3635     preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
3636   }
3637   CMSTokenSync x(true); // is cms thread
3638   if (CMSPrecleaningEnabled) {
3639     sample_eden();
3640     _collectorState = AbortablePreclean;
3641   } else {
3642     _collectorState = FinalMarking;
3643   }
3644   verify_work_stacks_empty();
3645   verify_overflow_empty();
3646 }
3647 
3648 // Try and schedule the remark such that young gen
3649 // occupancy is CMSScheduleRemarkEdenPenetration %.
3650 void CMSCollector::abortable_preclean() {
3651   check_correct_thread_executing();
3652   assert(CMSPrecleaningEnabled,  "Inconsistent control state");
3653   assert(_collectorState == AbortablePreclean, "Inconsistent control state");
3654 
3655   // If Eden's current occupancy is below this threshold,
3656   // immediately schedule the remark; else preclean
3657   // past the next scavenge in an effort to
3658   // schedule the pause as described above. By choosing
3659   // CMSScheduleRemarkEdenSizeThreshold >= max eden size
3660   // we will never do an actual abortable preclean cycle.
3661   if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
3662     GCTraceCPUTime tcpu;
3663     CMSPhaseAccounting pa(this, "Concurrent Abortable Preclean");
3664     // We need more smarts in the abortable preclean
3665     // loop below to deal with cases where allocation
3666     // in young gen is very very slow, and our precleaning
3667     // is running a losing race against a horde of
3668     // mutators intent on flooding us with CMS updates
3669     // (dirty cards).
3670     // One, admittedly dumb, strategy is to give up
3671     // after a certain number of abortable precleaning loops
3672     // or after a certain maximum time. We want to make
3673     // this smarter in the next iteration.
3674     // XXX FIX ME!!! YSR
3675     size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
3676     while (!(should_abort_preclean() ||
3677              ConcurrentMarkSweepThread::cmst()->should_terminate())) {
3678       workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
3679       cumworkdone += workdone;
3680       loops++;
3681       // Voluntarily terminate abortable preclean phase if we have
3682       // been at it for too long.
3683       if ((CMSMaxAbortablePrecleanLoops != 0) &&
3684           loops >= CMSMaxAbortablePrecleanLoops) {
3685         log_debug(gc)(" CMS: abort preclean due to loops ");
3686         break;
3687       }
3688       if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
3689         log_debug(gc)(" CMS: abort preclean due to time ");
3690         break;
3691       }
3692       // If we are doing little work each iteration, we should
3693       // take a short break.
3694       if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
3695         // Sleep for some time, waiting for work to accumulate
3696         stopTimer();
3697         cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
3698         startTimer();
3699         waited++;
3700       }
3701     }
3702     log_trace(gc)(" [" SIZE_FORMAT " iterations, " SIZE_FORMAT " waits, " SIZE_FORMAT " cards)] ",
3703                                loops, waited, cumworkdone);
3704   }
3705   CMSTokenSync x(true); // is cms thread
3706   if (_collectorState != Idling) {
3707     assert(_collectorState == AbortablePreclean,
3708            "Spontaneous state transition?");
3709     _collectorState = FinalMarking;
3710   } // Else, a foreground collection completed this CMS cycle.
3711   return;
3712 }
3713 
3714 // Respond to an Eden sampling opportunity
3715 void CMSCollector::sample_eden() {
3716   // Make sure a young gc cannot sneak in between our
3717   // reading and recording of a sample.
3718   assert(Thread::current()->is_ConcurrentGC_thread(),
3719          "Only the cms thread may collect Eden samples");
3720   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3721          "Should collect samples while holding CMS token");
3722   if (!_start_sampling) {
3723     return;
3724   }
3725   // When CMSEdenChunksRecordAlways is true, the eden chunk array
3726   // is populated by the young generation.
3727   if (_eden_chunk_array != NULL && !CMSEdenChunksRecordAlways) {
3728     if (_eden_chunk_index < _eden_chunk_capacity) {
3729       _eden_chunk_array[_eden_chunk_index] = *_top_addr;   // take sample
3730       assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
3731              "Unexpected state of Eden");
3732       // We'd like to check that what we just sampled is an oop-start address;
3733       // however, we cannot do that here since the object may not yet have been
3734       // initialized. So we'll instead do the check when we _use_ this sample
3735       // later.
3736       if (_eden_chunk_index == 0 ||
3737           (pointer_delta(_eden_chunk_array[_eden_chunk_index],
3738                          _eden_chunk_array[_eden_chunk_index-1])
3739            >= CMSSamplingGrain)) {
3740         _eden_chunk_index++;  // commit sample
3741       }
3742     }
3743   }
3744   if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
3745     size_t used = get_eden_used();
3746     size_t capacity = get_eden_capacity();
3747     assert(used <= capacity, "Unexpected state of Eden");
3748     if (used >  (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
3749       _abort_preclean = true;
3750     }
3751   }
3752 }
3753 
3754 
3755 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
3756   assert(_collectorState == Precleaning ||
3757          _collectorState == AbortablePreclean, "incorrect state");
3758   ResourceMark rm;
3759   HandleMark   hm;
3760 
3761   // Precleaning is currently not MT but the reference processor
3762   // may be set for MT.  Disable it temporarily here.
3763   ReferenceProcessor* rp = ref_processor();
3764   ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false);
3765 
3766   // Do one pass of scrubbing the discovered reference lists
3767   // to remove any reference objects with strongly-reachable
3768   // referents.
3769   if (clean_refs) {
3770     CMSPrecleanRefsYieldClosure yield_cl(this);
3771     assert(rp->span().equals(_span), "Spans should be equal");
3772     CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
3773                                    &_markStack, true /* preclean */);
3774     CMSDrainMarkingStackClosure complete_trace(this,
3775                                    _span, &_markBitMap, &_markStack,
3776                                    &keep_alive, true /* preclean */);
3777 
3778     // We don't want this step to interfere with a young
3779     // collection because we don't want to take CPU
3780     // or memory bandwidth away from the young GC threads
3781     // (which may be as many as there are CPUs).
3782     // Note that we don't need to protect ourselves from
3783     // interference with mutators because they can't
3784     // manipulate the discovered reference lists nor affect
3785     // the computed reachability of the referents, the
3786     // only properties manipulated by the precleaning
3787     // of these reference lists.
3788     stopTimer();
3789     CMSTokenSyncWithLocks x(true /* is cms thread */,
3790                             bitMapLock());
3791     startTimer();
3792     sample_eden();
3793 
3794     // The following will yield to allow foreground
3795     // collection to proceed promptly. XXX YSR:
3796     // The code in this method may need further
3797     // tweaking for better performance and some restructuring
3798     // for cleaner interfaces.
3799     GCTimer *gc_timer = NULL; // Currently not tracing concurrent phases
3800     rp->preclean_discovered_references(
3801           rp->is_alive_non_header(), &keep_alive, &complete_trace, &yield_cl,
3802           gc_timer);
3803   }
3804 
3805   if (clean_survivor) {  // preclean the active survivor space(s)
3806     PushAndMarkClosure pam_cl(this, _span, ref_processor(),
3807                              &_markBitMap, &_modUnionTable,
3808                              &_markStack, true /* precleaning phase */);
3809     stopTimer();
3810     CMSTokenSyncWithLocks ts(true /* is cms thread */,
3811                              bitMapLock());
3812     startTimer();
3813     unsigned int before_count =
3814       GenCollectedHeap::heap()->total_collections();
3815     SurvivorSpacePrecleanClosure
3816       sss_cl(this, _span, &_markBitMap, &_markStack,
3817              &pam_cl, before_count, CMSYield);
3818     _young_gen->from()->object_iterate_careful(&sss_cl);
3819     _young_gen->to()->object_iterate_careful(&sss_cl);
3820   }
3821   MarkRefsIntoAndScanClosure
3822     mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
3823              &_markStack, this, CMSYield,
3824              true /* precleaning phase */);
3825   // CAUTION: The following closure has persistent state that may need to
3826   // be reset upon a decrease in the sequence of addresses it
3827   // processes.
3828   ScanMarkedObjectsAgainCarefullyClosure
3829     smoac_cl(this, _span,
3830       &_markBitMap, &_markStack, &mrias_cl, CMSYield);
3831 
3832   // Preclean dirty cards in ModUnionTable and CardTable using
3833   // appropriate convergence criterion;
3834   // repeat CMSPrecleanIter times unless we find that
3835   // we are losing.
3836   assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
3837   assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
3838          "Bad convergence multiplier");
3839   assert(CMSPrecleanThreshold >= 100,
3840          "Unreasonably low CMSPrecleanThreshold");
3841 
3842   size_t numIter, cumNumCards, lastNumCards, curNumCards;
3843   for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
3844        numIter < CMSPrecleanIter;
3845        numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
3846     curNumCards  = preclean_mod_union_table(_cmsGen, &smoac_cl);
3847     log_trace(gc)(" (modUnionTable: " SIZE_FORMAT " cards)", curNumCards);
3848     // Either there are very few dirty cards, so re-mark
3849     // pause will be small anyway, or our pre-cleaning isn't
3850     // that much faster than the rate at which cards are being
3851     // dirtied, so we might as well stop and re-mark since
3852     // precleaning won't improve our re-mark time by much.
3853     if (curNumCards <= CMSPrecleanThreshold ||
3854         (numIter > 0 &&
3855          (curNumCards * CMSPrecleanDenominator >
3856          lastNumCards * CMSPrecleanNumerator))) {
3857       numIter++;
3858       cumNumCards += curNumCards;
3859       break;
3860     }
3861   }
3862 
3863   preclean_klasses(&mrias_cl, _cmsGen->freelistLock());
3864 
3865   curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
3866   cumNumCards += curNumCards;
3867   log_trace(gc)(" (cardTable: " SIZE_FORMAT " cards, re-scanned " SIZE_FORMAT " cards, " SIZE_FORMAT " iterations)",
3868                              curNumCards, cumNumCards, numIter);
3869   return cumNumCards;   // as a measure of useful work done
3870 }
3871 
3872 // PRECLEANING NOTES:
3873 // Precleaning involves:
3874 // . reading the bits of the modUnionTable and clearing the set bits.
3875 // . For the cards corresponding to the set bits, we scan the
3876 //   objects on those cards. This means we need the free_list_lock
3877 //   so that we can safely iterate over the CMS space when scanning
3878 //   for oops.
3879 // . When we scan the objects, we'll be both reading and setting
3880 //   marks in the marking bit map, so we'll need the marking bit map.
3881 // . For protecting _collector_state transitions, we take the CGC_lock.
3882 //   Note that any races in the reading of of card table entries by the
3883 //   CMS thread on the one hand and the clearing of those entries by the
3884 //   VM thread or the setting of those entries by the mutator threads on the
3885 //   other are quite benign. However, for efficiency it makes sense to keep
3886 //   the VM thread from racing with the CMS thread while the latter is
3887 //   dirty card info to the modUnionTable. We therefore also use the
3888 //   CGC_lock to protect the reading of the card table and the mod union
3889 //   table by the CM thread.
3890 // . We run concurrently with mutator updates, so scanning
3891 //   needs to be done carefully  -- we should not try to scan
3892 //   potentially uninitialized objects.
3893 //
3894 // Locking strategy: While holding the CGC_lock, we scan over and
3895 // reset a maximal dirty range of the mod union / card tables, then lock
3896 // the free_list_lock and bitmap lock to do a full marking, then
3897 // release these locks; and repeat the cycle. This allows for a
3898 // certain amount of fairness in the sharing of these locks between
3899 // the CMS collector on the one hand, and the VM thread and the
3900 // mutators on the other.
3901 
3902 // NOTE: preclean_mod_union_table() and preclean_card_table()
3903 // further below are largely identical; if you need to modify
3904 // one of these methods, please check the other method too.
3905 
3906 size_t CMSCollector::preclean_mod_union_table(
3907   ConcurrentMarkSweepGeneration* old_gen,
3908   ScanMarkedObjectsAgainCarefullyClosure* cl) {
3909   verify_work_stacks_empty();
3910   verify_overflow_empty();
3911 
3912   // strategy: starting with the first card, accumulate contiguous
3913   // ranges of dirty cards; clear these cards, then scan the region
3914   // covered by these cards.
3915 
3916   // Since all of the MUT is committed ahead, we can just use
3917   // that, in case the generations expand while we are precleaning.
3918   // It might also be fine to just use the committed part of the
3919   // generation, but we might potentially miss cards when the
3920   // generation is rapidly expanding while we are in the midst
3921   // of precleaning.
3922   HeapWord* startAddr = old_gen->reserved().start();
3923   HeapWord* endAddr   = old_gen->reserved().end();
3924 
3925   cl->setFreelistLock(old_gen->freelistLock());   // needed for yielding
3926 
3927   size_t numDirtyCards, cumNumDirtyCards;
3928   HeapWord *nextAddr, *lastAddr;
3929   for (cumNumDirtyCards = numDirtyCards = 0,
3930        nextAddr = lastAddr = startAddr;
3931        nextAddr < endAddr;
3932        nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
3933 
3934     ResourceMark rm;
3935     HandleMark   hm;
3936 
3937     MemRegion dirtyRegion;
3938     {
3939       stopTimer();
3940       // Potential yield point
3941       CMSTokenSync ts(true);
3942       startTimer();
3943       sample_eden();
3944       // Get dirty region starting at nextOffset (inclusive),
3945       // simultaneously clearing it.
3946       dirtyRegion =
3947         _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
3948       assert(dirtyRegion.start() >= nextAddr,
3949              "returned region inconsistent?");
3950     }
3951     // Remember where the next search should begin.
3952     // The returned region (if non-empty) is a right open interval,
3953     // so lastOffset is obtained from the right end of that
3954     // interval.
3955     lastAddr = dirtyRegion.end();
3956     // Should do something more transparent and less hacky XXX
3957     numDirtyCards =
3958       _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
3959 
3960     // We'll scan the cards in the dirty region (with periodic
3961     // yields for foreground GC as needed).
3962     if (!dirtyRegion.is_empty()) {
3963       assert(numDirtyCards > 0, "consistency check");
3964       HeapWord* stop_point = NULL;
3965       stopTimer();
3966       // Potential yield point
3967       CMSTokenSyncWithLocks ts(true, old_gen->freelistLock(),
3968                                bitMapLock());
3969       startTimer();
3970       {
3971         verify_work_stacks_empty();
3972         verify_overflow_empty();
3973         sample_eden();
3974         stop_point =
3975           old_gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
3976       }
3977       if (stop_point != NULL) {
3978         // The careful iteration stopped early either because it found an
3979         // uninitialized object, or because we were in the midst of an
3980         // "abortable preclean", which should now be aborted. Redirty
3981         // the bits corresponding to the partially-scanned or unscanned
3982         // cards. We'll either restart at the next block boundary or
3983         // abort the preclean.
3984         assert((_collectorState == AbortablePreclean && should_abort_preclean()),
3985                "Should only be AbortablePreclean.");
3986         _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
3987         if (should_abort_preclean()) {
3988           break; // out of preclean loop
3989         } else {
3990           // Compute the next address at which preclean should pick up;
3991           // might need bitMapLock in order to read P-bits.
3992           lastAddr = next_card_start_after_block(stop_point);
3993         }
3994       }
3995     } else {
3996       assert(lastAddr == endAddr, "consistency check");
3997       assert(numDirtyCards == 0, "consistency check");
3998       break;
3999     }
4000   }
4001   verify_work_stacks_empty();
4002   verify_overflow_empty();
4003   return cumNumDirtyCards;
4004 }
4005 
4006 // NOTE: preclean_mod_union_table() above and preclean_card_table()
4007 // below are largely identical; if you need to modify
4008 // one of these methods, please check the other method too.
4009 
4010 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* old_gen,
4011   ScanMarkedObjectsAgainCarefullyClosure* cl) {
4012   // strategy: it's similar to precleamModUnionTable above, in that
4013   // we accumulate contiguous ranges of dirty cards, mark these cards
4014   // precleaned, then scan the region covered by these cards.
4015   HeapWord* endAddr   = (HeapWord*)(old_gen->_virtual_space.high());
4016   HeapWord* startAddr = (HeapWord*)(old_gen->_virtual_space.low());
4017 
4018   cl->setFreelistLock(old_gen->freelistLock());   // needed for yielding
4019 
4020   size_t numDirtyCards, cumNumDirtyCards;
4021   HeapWord *lastAddr, *nextAddr;
4022 
4023   for (cumNumDirtyCards = numDirtyCards = 0,
4024        nextAddr = lastAddr = startAddr;
4025        nextAddr < endAddr;
4026        nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4027 
4028     ResourceMark rm;
4029     HandleMark   hm;
4030 
4031     MemRegion dirtyRegion;
4032     {
4033       // See comments in "Precleaning notes" above on why we
4034       // do this locking. XXX Could the locking overheads be
4035       // too high when dirty cards are sparse? [I don't think so.]
4036       stopTimer();
4037       CMSTokenSync x(true); // is cms thread
4038       startTimer();
4039       sample_eden();
4040       // Get and clear dirty region from card table
4041       dirtyRegion = _ct->ct_bs()->dirty_card_range_after_reset(
4042                                     MemRegion(nextAddr, endAddr),
4043                                     true,
4044                                     CardTableModRefBS::precleaned_card_val());
4045 
4046       assert(dirtyRegion.start() >= nextAddr,
4047              "returned region inconsistent?");
4048     }
4049     lastAddr = dirtyRegion.end();
4050     numDirtyCards =
4051       dirtyRegion.word_size()/CardTableModRefBS::card_size_in_words;
4052 
4053     if (!dirtyRegion.is_empty()) {
4054       stopTimer();
4055       CMSTokenSyncWithLocks ts(true, old_gen->freelistLock(), bitMapLock());
4056       startTimer();
4057       sample_eden();
4058       verify_work_stacks_empty();
4059       verify_overflow_empty();
4060       HeapWord* stop_point =
4061         old_gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4062       if (stop_point != NULL) {
4063         assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4064                "Should only be AbortablePreclean.");
4065         _ct->ct_bs()->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4066         if (should_abort_preclean()) {
4067           break; // out of preclean loop
4068         } else {
4069           // Compute the next address at which preclean should pick up.
4070           lastAddr = next_card_start_after_block(stop_point);
4071         }
4072       }
4073     } else {
4074       break;
4075     }
4076   }
4077   verify_work_stacks_empty();
4078   verify_overflow_empty();
4079   return cumNumDirtyCards;
4080 }
4081 
4082 class PrecleanKlassClosure : public KlassClosure {
4083   KlassToOopClosure _cm_klass_closure;
4084  public:
4085   PrecleanKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4086   void do_klass(Klass* k) {
4087     if (k->has_accumulated_modified_oops()) {
4088       k->clear_accumulated_modified_oops();
4089 
4090       _cm_klass_closure.do_klass(k);
4091     }
4092   }
4093 };
4094 
4095 // The freelist lock is needed to prevent asserts, is it really needed?
4096 void CMSCollector::preclean_klasses(MarkRefsIntoAndScanClosure* cl, Mutex* freelistLock) {
4097 
4098   cl->set_freelistLock(freelistLock);
4099 
4100   CMSTokenSyncWithLocks ts(true, freelistLock, bitMapLock());
4101 
4102   // SSS: Add equivalent to ScanMarkedObjectsAgainCarefullyClosure::do_yield_check and should_abort_preclean?
4103   // SSS: We should probably check if precleaning should be aborted, at suitable intervals?
4104   PrecleanKlassClosure preclean_klass_closure(cl);
4105   ClassLoaderDataGraph::classes_do(&preclean_klass_closure);
4106 
4107   verify_work_stacks_empty();
4108   verify_overflow_empty();
4109 }
4110 
4111 void CMSCollector::checkpointRootsFinal() {
4112   assert(_collectorState == FinalMarking, "incorrect state transition?");
4113   check_correct_thread_executing();
4114   // world is stopped at this checkpoint
4115   assert(SafepointSynchronize::is_at_safepoint(),
4116          "world should be stopped");
4117   TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
4118 
4119   verify_work_stacks_empty();
4120   verify_overflow_empty();
4121 
4122   log_debug(gc)("YG occupancy: " SIZE_FORMAT " K (" SIZE_FORMAT " K)",
4123                 _young_gen->used() / K, _young_gen->capacity() / K);
4124   {
4125     if (CMSScavengeBeforeRemark) {
4126       GenCollectedHeap* gch = GenCollectedHeap::heap();
4127       // Temporarily set flag to false, GCH->do_collection will
4128       // expect it to be false and set to true
4129       FlagSetting fl(gch->_is_gc_active, false);
4130 
4131       gch->do_collection(true,                      // full (i.e. force, see below)
4132                          false,                     // !clear_all_soft_refs
4133                          0,                         // size
4134                          false,                     // is_tlab
4135                          GenCollectedHeap::YoungGen // type
4136         );
4137     }
4138     FreelistLocker x(this);
4139     MutexLockerEx y(bitMapLock(),
4140                     Mutex::_no_safepoint_check_flag);
4141     checkpointRootsFinalWork();
4142   }
4143   verify_work_stacks_empty();
4144   verify_overflow_empty();
4145 }
4146 
4147 void CMSCollector::checkpointRootsFinalWork() {
4148   GCTraceTime(Trace, gc, phases) tm("checkpointRootsFinalWork", _gc_timer_cm);
4149 
4150   assert(haveFreelistLocks(), "must have free list locks");
4151   assert_lock_strong(bitMapLock());
4152 
4153   ResourceMark rm;
4154   HandleMark   hm;
4155 
4156   GenCollectedHeap* gch = GenCollectedHeap::heap();
4157 
4158   if (should_unload_classes()) {
4159     CodeCache::gc_prologue();
4160   }
4161   assert(haveFreelistLocks(), "must have free list locks");
4162   assert_lock_strong(bitMapLock());
4163 
4164   // We might assume that we need not fill TLAB's when
4165   // CMSScavengeBeforeRemark is set, because we may have just done
4166   // a scavenge which would have filled all TLAB's -- and besides
4167   // Eden would be empty. This however may not always be the case --
4168   // for instance although we asked for a scavenge, it may not have
4169   // happened because of a JNI critical section. We probably need
4170   // a policy for deciding whether we can in that case wait until
4171   // the critical section releases and then do the remark following
4172   // the scavenge, and skip it here. In the absence of that policy,
4173   // or of an indication of whether the scavenge did indeed occur,
4174   // we cannot rely on TLAB's having been filled and must do
4175   // so here just in case a scavenge did not happen.
4176   gch->ensure_parsability(false);  // fill TLAB's, but no need to retire them
4177   // Update the saved marks which may affect the root scans.
4178   gch->save_marks();
4179 
4180   print_eden_and_survivor_chunk_arrays();
4181 
4182   {
4183 #if defined(COMPILER2) || INCLUDE_JVMCI
4184     DerivedPointerTableDeactivate dpt_deact;
4185 #endif
4186 
4187     // Note on the role of the mod union table:
4188     // Since the marker in "markFromRoots" marks concurrently with
4189     // mutators, it is possible for some reachable objects not to have been
4190     // scanned. For instance, an only reference to an object A was
4191     // placed in object B after the marker scanned B. Unless B is rescanned,
4192     // A would be collected. Such updates to references in marked objects
4193     // are detected via the mod union table which is the set of all cards
4194     // dirtied since the first checkpoint in this GC cycle and prior to
4195     // the most recent young generation GC, minus those cleaned up by the
4196     // concurrent precleaning.
4197     if (CMSParallelRemarkEnabled) {
4198       GCTraceTime(Debug, gc, phases) t("Rescan (parallel)", _gc_timer_cm);
4199       do_remark_parallel();
4200     } else {
4201       GCTraceTime(Debug, gc, phases) t("Rescan (non-parallel)", _gc_timer_cm);
4202       do_remark_non_parallel();
4203     }
4204   }
4205   verify_work_stacks_empty();
4206   verify_overflow_empty();
4207 
4208   {
4209     GCTraceTime(Trace, gc, phases) ts("refProcessingWork", _gc_timer_cm);
4210     refProcessingWork();
4211   }
4212   verify_work_stacks_empty();
4213   verify_overflow_empty();
4214 
4215   if (should_unload_classes()) {
4216     CodeCache::gc_epilogue();
4217   }
4218   JvmtiExport::gc_epilogue();
4219 
4220   // If we encountered any (marking stack / work queue) overflow
4221   // events during the current CMS cycle, take appropriate
4222   // remedial measures, where possible, so as to try and avoid
4223   // recurrence of that condition.
4224   assert(_markStack.isEmpty(), "No grey objects");
4225   size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
4226                      _ser_kac_ovflw        + _ser_kac_preclean_ovflw;
4227   if (ser_ovflw > 0) {
4228     log_trace(gc)("Marking stack overflow (benign) (pmc_pc=" SIZE_FORMAT ", pmc_rm=" SIZE_FORMAT ", kac=" SIZE_FORMAT ", kac_preclean=" SIZE_FORMAT ")",
4229                          _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw, _ser_kac_ovflw, _ser_kac_preclean_ovflw);
4230     _markStack.expand();
4231     _ser_pmc_remark_ovflw = 0;
4232     _ser_pmc_preclean_ovflw = 0;
4233     _ser_kac_preclean_ovflw = 0;
4234     _ser_kac_ovflw = 0;
4235   }
4236   if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
4237      log_trace(gc)("Work queue overflow (benign) (pmc_rm=" SIZE_FORMAT ", kac=" SIZE_FORMAT ")",
4238                           _par_pmc_remark_ovflw, _par_kac_ovflw);
4239      _par_pmc_remark_ovflw = 0;
4240     _par_kac_ovflw = 0;
4241   }
4242    if (_markStack._hit_limit > 0) {
4243      log_trace(gc)(" (benign) Hit max stack size limit (" SIZE_FORMAT ")",
4244                           _markStack._hit_limit);
4245    }
4246    if (_markStack._failed_double > 0) {
4247      log_trace(gc)(" (benign) Failed stack doubling (" SIZE_FORMAT "), current capacity " SIZE_FORMAT,
4248                           _markStack._failed_double, _markStack.capacity());
4249    }
4250   _markStack._hit_limit = 0;
4251   _markStack._failed_double = 0;
4252 
4253   if ((VerifyAfterGC || VerifyDuringGC) &&
4254       GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
4255     verify_after_remark();
4256   }
4257 
4258   _gc_tracer_cm->report_object_count_after_gc(&_is_alive_closure);
4259 
4260   // Change under the freelistLocks.
4261   _collectorState = Sweeping;
4262   // Call isAllClear() under bitMapLock
4263   assert(_modUnionTable.isAllClear(),
4264       "Should be clear by end of the final marking");
4265   assert(_ct->klass_rem_set()->mod_union_is_clear(),
4266       "Should be clear by end of the final marking");
4267 }
4268 
4269 void CMSParInitialMarkTask::work(uint worker_id) {
4270   elapsedTimer _timer;
4271   ResourceMark rm;
4272   HandleMark   hm;
4273 
4274   // ---------- scan from roots --------------
4275   _timer.start();
4276   GenCollectedHeap* gch = GenCollectedHeap::heap();
4277   ParMarkRefsIntoClosure par_mri_cl(_collector->_span, &(_collector->_markBitMap));
4278 
4279   // ---------- young gen roots --------------
4280   {
4281     work_on_young_gen_roots(&par_mri_cl);
4282     _timer.stop();
4283     log_trace(gc, task)("Finished young gen initial mark scan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4284   }
4285 
4286   // ---------- remaining roots --------------
4287   _timer.reset();
4288   _timer.start();
4289 
4290   CLDToOopClosure cld_closure(&par_mri_cl, true);
4291 
4292   gch->gen_process_roots(_strong_roots_scope,
4293                          GenCollectedHeap::OldGen,
4294                          false,     // yg was scanned above
4295                          GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4296                          _collector->should_unload_classes(),
4297                          &par_mri_cl,
4298                          NULL,
4299                          &cld_closure);
4300   assert(_collector->should_unload_classes()
4301          || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4302          "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4303   _timer.stop();
4304   log_trace(gc, task)("Finished remaining root initial mark scan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4305 }
4306 
4307 // Parallel remark task
4308 class CMSParRemarkTask: public CMSParMarkTask {
4309   CompactibleFreeListSpace* _cms_space;
4310 
4311   // The per-thread work queues, available here for stealing.
4312   OopTaskQueueSet*       _task_queues;
4313   ParallelTaskTerminator _term;
4314   StrongRootsScope*      _strong_roots_scope;
4315 
4316  public:
4317   // A value of 0 passed to n_workers will cause the number of
4318   // workers to be taken from the active workers in the work gang.
4319   CMSParRemarkTask(CMSCollector* collector,
4320                    CompactibleFreeListSpace* cms_space,
4321                    uint n_workers, WorkGang* workers,
4322                    OopTaskQueueSet* task_queues,
4323                    StrongRootsScope* strong_roots_scope):
4324     CMSParMarkTask("Rescan roots and grey objects in parallel",
4325                    collector, n_workers),
4326     _cms_space(cms_space),
4327     _task_queues(task_queues),
4328     _term(n_workers, task_queues),
4329     _strong_roots_scope(strong_roots_scope) { }
4330 
4331   OopTaskQueueSet* task_queues() { return _task_queues; }
4332 
4333   OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
4334 
4335   ParallelTaskTerminator* terminator() { return &_term; }
4336   uint n_workers() { return _n_workers; }
4337 
4338   void work(uint worker_id);
4339 
4340  private:
4341   // ... of  dirty cards in old space
4342   void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
4343                                   ParMarkRefsIntoAndScanClosure* cl);
4344 
4345   // ... work stealing for the above
4346   void do_work_steal(int i, ParMarkRefsIntoAndScanClosure* cl, int* seed);
4347 };
4348 
4349 class RemarkKlassClosure : public KlassClosure {
4350   KlassToOopClosure _cm_klass_closure;
4351  public:
4352   RemarkKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4353   void do_klass(Klass* k) {
4354     // Check if we have modified any oops in the Klass during the concurrent marking.
4355     if (k->has_accumulated_modified_oops()) {
4356       k->clear_accumulated_modified_oops();
4357 
4358       // We could have transfered the current modified marks to the accumulated marks,
4359       // like we do with the Card Table to Mod Union Table. But it's not really necessary.
4360     } else if (k->has_modified_oops()) {
4361       // Don't clear anything, this info is needed by the next young collection.
4362     } else {
4363       // No modified oops in the Klass.
4364       return;
4365     }
4366 
4367     // The klass has modified fields, need to scan the klass.
4368     _cm_klass_closure.do_klass(k);
4369   }
4370 };
4371 
4372 void CMSParMarkTask::work_on_young_gen_roots(OopsInGenClosure* cl) {
4373   ParNewGeneration* young_gen = _collector->_young_gen;
4374   ContiguousSpace* eden_space = young_gen->eden();
4375   ContiguousSpace* from_space = young_gen->from();
4376   ContiguousSpace* to_space   = young_gen->to();
4377 
4378   HeapWord** eca = _collector->_eden_chunk_array;
4379   size_t     ect = _collector->_eden_chunk_index;
4380   HeapWord** sca = _collector->_survivor_chunk_array;
4381   size_t     sct = _collector->_survivor_chunk_index;
4382 
4383   assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
4384   assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
4385 
4386   do_young_space_rescan(cl, to_space, NULL, 0);
4387   do_young_space_rescan(cl, from_space, sca, sct);
4388   do_young_space_rescan(cl, eden_space, eca, ect);
4389 }
4390 
4391 // work_queue(i) is passed to the closure
4392 // ParMarkRefsIntoAndScanClosure.  The "i" parameter
4393 // also is passed to do_dirty_card_rescan_tasks() and to
4394 // do_work_steal() to select the i-th task_queue.
4395 
4396 void CMSParRemarkTask::work(uint worker_id) {
4397   elapsedTimer _timer;
4398   ResourceMark rm;
4399   HandleMark   hm;
4400 
4401   // ---------- rescan from roots --------------
4402   _timer.start();
4403   GenCollectedHeap* gch = GenCollectedHeap::heap();
4404   ParMarkRefsIntoAndScanClosure par_mrias_cl(_collector,
4405     _collector->_span, _collector->ref_processor(),
4406     &(_collector->_markBitMap),
4407     work_queue(worker_id));
4408 
4409   // Rescan young gen roots first since these are likely
4410   // coarsely partitioned and may, on that account, constitute
4411   // the critical path; thus, it's best to start off that
4412   // work first.
4413   // ---------- young gen roots --------------
4414   {
4415     work_on_young_gen_roots(&par_mrias_cl);
4416     _timer.stop();
4417     log_trace(gc, task)("Finished young gen rescan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4418   }
4419 
4420   // ---------- remaining roots --------------
4421   _timer.reset();
4422   _timer.start();
4423   gch->gen_process_roots(_strong_roots_scope,
4424                          GenCollectedHeap::OldGen,
4425                          false,     // yg was scanned above
4426                          GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4427                          _collector->should_unload_classes(),
4428                          &par_mrias_cl,
4429                          NULL,
4430                          NULL);     // The dirty klasses will be handled below
4431 
4432   assert(_collector->should_unload_classes()
4433          || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4434          "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4435   _timer.stop();
4436   log_trace(gc, task)("Finished remaining root rescan work in %dth thread: %3.3f sec",  worker_id, _timer.seconds());
4437 
4438   // ---------- unhandled CLD scanning ----------
4439   if (worker_id == 0) { // Single threaded at the moment.
4440     _timer.reset();
4441     _timer.start();
4442 
4443     // Scan all new class loader data objects and new dependencies that were
4444     // introduced during concurrent marking.
4445     ResourceMark rm;
4446     GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
4447     for (int i = 0; i < array->length(); i++) {
4448       par_mrias_cl.do_cld_nv(array->at(i));
4449     }
4450 
4451     // We don't need to keep track of new CLDs anymore.
4452     ClassLoaderDataGraph::remember_new_clds(false);
4453 
4454     _timer.stop();
4455     log_trace(gc, task)("Finished unhandled CLD scanning work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4456   }
4457 
4458   // ---------- dirty klass scanning ----------
4459   if (worker_id == 0) { // Single threaded at the moment.
4460     _timer.reset();
4461     _timer.start();
4462 
4463     // Scan all classes that was dirtied during the concurrent marking phase.
4464     RemarkKlassClosure remark_klass_closure(&par_mrias_cl);
4465     ClassLoaderDataGraph::classes_do(&remark_klass_closure);
4466 
4467     _timer.stop();
4468     log_trace(gc, task)("Finished dirty klass scanning work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4469   }
4470 
4471   // We might have added oops to ClassLoaderData::_handles during the
4472   // concurrent marking phase. These oops point to newly allocated objects
4473   // that are guaranteed to be kept alive. Either by the direct allocation
4474   // code, or when the young collector processes the roots. Hence,
4475   // we don't have to revisit the _handles block during the remark phase.
4476 
4477   // ---------- rescan dirty cards ------------
4478   _timer.reset();
4479   _timer.start();
4480 
4481   // Do the rescan tasks for each of the two spaces
4482   // (cms_space) in turn.
4483   // "worker_id" is passed to select the task_queue for "worker_id"
4484   do_dirty_card_rescan_tasks(_cms_space, worker_id, &par_mrias_cl);
4485   _timer.stop();
4486   log_trace(gc, task)("Finished dirty card rescan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4487 
4488   // ---------- steal work from other threads ...
4489   // ---------- ... and drain overflow list.
4490   _timer.reset();
4491   _timer.start();
4492   do_work_steal(worker_id, &par_mrias_cl, _collector->hash_seed(worker_id));
4493   _timer.stop();
4494   log_trace(gc, task)("Finished work stealing in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4495 }
4496 
4497 void
4498 CMSParMarkTask::do_young_space_rescan(
4499   OopsInGenClosure* cl, ContiguousSpace* space,
4500   HeapWord** chunk_array, size_t chunk_top) {
4501   // Until all tasks completed:
4502   // . claim an unclaimed task
4503   // . compute region boundaries corresponding to task claimed
4504   //   using chunk_array
4505   // . par_oop_iterate(cl) over that region
4506 
4507   ResourceMark rm;
4508   HandleMark   hm;
4509 
4510   SequentialSubTasksDone* pst = space->par_seq_tasks();
4511 
4512   uint nth_task = 0;
4513   uint n_tasks  = pst->n_tasks();
4514 
4515   if (n_tasks > 0) {
4516     assert(pst->valid(), "Uninitialized use?");
4517     HeapWord *start, *end;
4518     while (!pst->is_task_claimed(/* reference */ nth_task)) {
4519       // We claimed task # nth_task; compute its boundaries.
4520       if (chunk_top == 0) {  // no samples were taken
4521         assert(nth_task == 0 && n_tasks == 1, "Can have only 1 eden task");
4522         start = space->bottom();
4523         end   = space->top();
4524       } else if (nth_task == 0) {
4525         start = space->bottom();
4526         end   = chunk_array[nth_task];
4527       } else if (nth_task < (uint)chunk_top) {
4528         assert(nth_task >= 1, "Control point invariant");
4529         start = chunk_array[nth_task - 1];
4530         end   = chunk_array[nth_task];
4531       } else {
4532         assert(nth_task == (uint)chunk_top, "Control point invariant");
4533         start = chunk_array[chunk_top - 1];
4534         end   = space->top();
4535       }
4536       MemRegion mr(start, end);
4537       // Verify that mr is in space
4538       assert(mr.is_empty() || space->used_region().contains(mr),
4539              "Should be in space");
4540       // Verify that "start" is an object boundary
4541       assert(mr.is_empty() || oop(mr.start())->is_oop(),
4542              "Should be an oop");
4543       space->par_oop_iterate(mr, cl);
4544     }
4545     pst->all_tasks_completed();
4546   }
4547 }
4548 
4549 void
4550 CMSParRemarkTask::do_dirty_card_rescan_tasks(
4551   CompactibleFreeListSpace* sp, int i,
4552   ParMarkRefsIntoAndScanClosure* cl) {
4553   // Until all tasks completed:
4554   // . claim an unclaimed task
4555   // . compute region boundaries corresponding to task claimed
4556   // . transfer dirty bits ct->mut for that region
4557   // . apply rescanclosure to dirty mut bits for that region
4558 
4559   ResourceMark rm;
4560   HandleMark   hm;
4561 
4562   OopTaskQueue* work_q = work_queue(i);
4563   ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
4564   // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
4565   // CAUTION: This closure has state that persists across calls to
4566   // the work method dirty_range_iterate_clear() in that it has
4567   // embedded in it a (subtype of) UpwardsObjectClosure. The
4568   // use of that state in the embedded UpwardsObjectClosure instance
4569   // assumes that the cards are always iterated (even if in parallel
4570   // by several threads) in monotonically increasing order per each
4571   // thread. This is true of the implementation below which picks
4572   // card ranges (chunks) in monotonically increasing order globally
4573   // and, a-fortiori, in monotonically increasing order per thread
4574   // (the latter order being a subsequence of the former).
4575   // If the work code below is ever reorganized into a more chaotic
4576   // work-partitioning form than the current "sequential tasks"
4577   // paradigm, the use of that persistent state will have to be
4578   // revisited and modified appropriately. See also related
4579   // bug 4756801 work on which should examine this code to make
4580   // sure that the changes there do not run counter to the
4581   // assumptions made here and necessary for correctness and
4582   // efficiency. Note also that this code might yield inefficient
4583   // behavior in the case of very large objects that span one or
4584   // more work chunks. Such objects would potentially be scanned
4585   // several times redundantly. Work on 4756801 should try and
4586   // address that performance anomaly if at all possible. XXX
4587   MemRegion  full_span  = _collector->_span;
4588   CMSBitMap* bm    = &(_collector->_markBitMap);     // shared
4589   MarkFromDirtyCardsClosure
4590     greyRescanClosure(_collector, full_span, // entire span of interest
4591                       sp, bm, work_q, cl);
4592 
4593   SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
4594   assert(pst->valid(), "Uninitialized use?");
4595   uint nth_task = 0;
4596   const int alignment = CardTableModRefBS::card_size * BitsPerWord;
4597   MemRegion span = sp->used_region();
4598   HeapWord* start_addr = span.start();
4599   HeapWord* end_addr = (HeapWord*)round_to((intptr_t)span.end(),
4600                                            alignment);
4601   const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
4602   assert((HeapWord*)round_to((intptr_t)start_addr, alignment) ==
4603          start_addr, "Check alignment");
4604   assert((size_t)round_to((intptr_t)chunk_size, alignment) ==
4605          chunk_size, "Check alignment");
4606 
4607   while (!pst->is_task_claimed(/* reference */ nth_task)) {
4608     // Having claimed the nth_task, compute corresponding mem-region,
4609     // which is a-fortiori aligned correctly (i.e. at a MUT boundary).
4610     // The alignment restriction ensures that we do not need any
4611     // synchronization with other gang-workers while setting or
4612     // clearing bits in thus chunk of the MUT.
4613     MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
4614                                     start_addr + (nth_task+1)*chunk_size);
4615     // The last chunk's end might be way beyond end of the
4616     // used region. In that case pull back appropriately.
4617     if (this_span.end() > end_addr) {
4618       this_span.set_end(end_addr);
4619       assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
4620     }
4621     // Iterate over the dirty cards covering this chunk, marking them
4622     // precleaned, and setting the corresponding bits in the mod union
4623     // table. Since we have been careful to partition at Card and MUT-word
4624     // boundaries no synchronization is needed between parallel threads.
4625     _collector->_ct->ct_bs()->dirty_card_iterate(this_span,
4626                                                  &modUnionClosure);
4627 
4628     // Having transferred these marks into the modUnionTable,
4629     // rescan the marked objects on the dirty cards in the modUnionTable.
4630     // Even if this is at a synchronous collection, the initial marking
4631     // may have been done during an asynchronous collection so there
4632     // may be dirty bits in the mod-union table.
4633     _collector->_modUnionTable.dirty_range_iterate_clear(
4634                   this_span, &greyRescanClosure);
4635     _collector->_modUnionTable.verifyNoOneBitsInRange(
4636                                  this_span.start(),
4637                                  this_span.end());
4638   }
4639   pst->all_tasks_completed();  // declare that i am done
4640 }
4641 
4642 // . see if we can share work_queues with ParNew? XXX
4643 void
4644 CMSParRemarkTask::do_work_steal(int i, ParMarkRefsIntoAndScanClosure* cl,
4645                                 int* seed) {
4646   OopTaskQueue* work_q = work_queue(i);
4647   NOT_PRODUCT(int num_steals = 0;)
4648   oop obj_to_scan;
4649   CMSBitMap* bm = &(_collector->_markBitMap);
4650 
4651   while (true) {
4652     // Completely finish any left over work from (an) earlier round(s)
4653     cl->trim_queue(0);
4654     size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
4655                                          (size_t)ParGCDesiredObjsFromOverflowList);
4656     // Now check if there's any work in the overflow list
4657     // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
4658     // only affects the number of attempts made to get work from the
4659     // overflow list and does not affect the number of workers.  Just
4660     // pass ParallelGCThreads so this behavior is unchanged.
4661     if (_collector->par_take_from_overflow_list(num_from_overflow_list,
4662                                                 work_q,
4663                                                 ParallelGCThreads)) {
4664       // found something in global overflow list;
4665       // not yet ready to go stealing work from others.
4666       // We'd like to assert(work_q->size() != 0, ...)
4667       // because we just took work from the overflow list,
4668       // but of course we can't since all of that could have
4669       // been already stolen from us.
4670       // "He giveth and He taketh away."
4671       continue;
4672     }
4673     // Verify that we have no work before we resort to stealing
4674     assert(work_q->size() == 0, "Have work, shouldn't steal");
4675     // Try to steal from other queues that have work
4676     if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
4677       NOT_PRODUCT(num_steals++;)
4678       assert(obj_to_scan->is_oop(), "Oops, not an oop!");
4679       assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
4680       // Do scanning work
4681       obj_to_scan->oop_iterate(cl);
4682       // Loop around, finish this work, and try to steal some more
4683     } else if (terminator()->offer_termination()) {
4684         break;  // nirvana from the infinite cycle
4685     }
4686   }
4687   log_develop_trace(gc, task)("\t(%d: stole %d oops)", i, num_steals);
4688   assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
4689          "Else our work is not yet done");
4690 }
4691 
4692 // Record object boundaries in _eden_chunk_array by sampling the eden
4693 // top in the slow-path eden object allocation code path and record
4694 // the boundaries, if CMSEdenChunksRecordAlways is true. If
4695 // CMSEdenChunksRecordAlways is false, we use the other asynchronous
4696 // sampling in sample_eden() that activates during the part of the
4697 // preclean phase.
4698 void CMSCollector::sample_eden_chunk() {
4699   if (CMSEdenChunksRecordAlways && _eden_chunk_array != NULL) {
4700     if (_eden_chunk_lock->try_lock()) {
4701       // Record a sample. This is the critical section. The contents
4702       // of the _eden_chunk_array have to be non-decreasing in the
4703       // address order.
4704       _eden_chunk_array[_eden_chunk_index] = *_top_addr;
4705       assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4706              "Unexpected state of Eden");
4707       if (_eden_chunk_index == 0 ||
4708           ((_eden_chunk_array[_eden_chunk_index] > _eden_chunk_array[_eden_chunk_index-1]) &&
4709            (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4710                           _eden_chunk_array[_eden_chunk_index-1]) >= CMSSamplingGrain))) {
4711         _eden_chunk_index++;  // commit sample
4712       }
4713       _eden_chunk_lock->unlock();
4714     }
4715   }
4716 }
4717 
4718 // Return a thread-local PLAB recording array, as appropriate.
4719 void* CMSCollector::get_data_recorder(int thr_num) {
4720   if (_survivor_plab_array != NULL &&
4721       (CMSPLABRecordAlways ||
4722        (_collectorState > Marking && _collectorState < FinalMarking))) {
4723     assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
4724     ChunkArray* ca = &_survivor_plab_array[thr_num];
4725     ca->reset();   // clear it so that fresh data is recorded
4726     return (void*) ca;
4727   } else {
4728     return NULL;
4729   }
4730 }
4731 
4732 // Reset all the thread-local PLAB recording arrays
4733 void CMSCollector::reset_survivor_plab_arrays() {
4734   for (uint i = 0; i < ParallelGCThreads; i++) {
4735     _survivor_plab_array[i].reset();
4736   }
4737 }
4738 
4739 // Merge the per-thread plab arrays into the global survivor chunk
4740 // array which will provide the partitioning of the survivor space
4741 // for CMS initial scan and rescan.
4742 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv,
4743                                               int no_of_gc_threads) {
4744   assert(_survivor_plab_array  != NULL, "Error");
4745   assert(_survivor_chunk_array != NULL, "Error");
4746   assert(_collectorState == FinalMarking ||
4747          (CMSParallelInitialMarkEnabled && _collectorState == InitialMarking), "Error");
4748   for (int j = 0; j < no_of_gc_threads; j++) {
4749     _cursor[j] = 0;
4750   }
4751   HeapWord* top = surv->top();
4752   size_t i;
4753   for (i = 0; i < _survivor_chunk_capacity; i++) {  // all sca entries
4754     HeapWord* min_val = top;          // Higher than any PLAB address
4755     uint      min_tid = 0;            // position of min_val this round
4756     for (int j = 0; j < no_of_gc_threads; j++) {
4757       ChunkArray* cur_sca = &_survivor_plab_array[j];
4758       if (_cursor[j] == cur_sca->end()) {
4759         continue;
4760       }
4761       assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
4762       HeapWord* cur_val = cur_sca->nth(_cursor[j]);
4763       assert(surv->used_region().contains(cur_val), "Out of bounds value");
4764       if (cur_val < min_val) {
4765         min_tid = j;
4766         min_val = cur_val;
4767       } else {
4768         assert(cur_val < top, "All recorded addresses should be less");
4769       }
4770     }
4771     // At this point min_val and min_tid are respectively
4772     // the least address in _survivor_plab_array[j]->nth(_cursor[j])
4773     // and the thread (j) that witnesses that address.
4774     // We record this address in the _survivor_chunk_array[i]
4775     // and increment _cursor[min_tid] prior to the next round i.
4776     if (min_val == top) {
4777       break;
4778     }
4779     _survivor_chunk_array[i] = min_val;
4780     _cursor[min_tid]++;
4781   }
4782   // We are all done; record the size of the _survivor_chunk_array
4783   _survivor_chunk_index = i; // exclusive: [0, i)
4784   log_trace(gc, survivor)(" (Survivor:" SIZE_FORMAT "chunks) ", i);
4785   // Verify that we used up all the recorded entries
4786   #ifdef ASSERT
4787     size_t total = 0;
4788     for (int j = 0; j < no_of_gc_threads; j++) {
4789       assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
4790       total += _cursor[j];
4791     }
4792     assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
4793     // Check that the merged array is in sorted order
4794     if (total > 0) {
4795       for (size_t i = 0; i < total - 1; i++) {
4796         log_develop_trace(gc, survivor)(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
4797                                      i, p2i(_survivor_chunk_array[i]));
4798         assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
4799                "Not sorted");
4800       }
4801     }
4802   #endif // ASSERT
4803 }
4804 
4805 // Set up the space's par_seq_tasks structure for work claiming
4806 // for parallel initial scan and rescan of young gen.
4807 // See ParRescanTask where this is currently used.
4808 void
4809 CMSCollector::
4810 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
4811   assert(n_threads > 0, "Unexpected n_threads argument");
4812 
4813   // Eden space
4814   if (!_young_gen->eden()->is_empty()) {
4815     SequentialSubTasksDone* pst = _young_gen->eden()->par_seq_tasks();
4816     assert(!pst->valid(), "Clobbering existing data?");
4817     // Each valid entry in [0, _eden_chunk_index) represents a task.
4818     size_t n_tasks = _eden_chunk_index + 1;
4819     assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
4820     // Sets the condition for completion of the subtask (how many threads
4821     // need to finish in order to be done).
4822     pst->set_n_threads(n_threads);
4823     pst->set_n_tasks((int)n_tasks);
4824   }
4825 
4826   // Merge the survivor plab arrays into _survivor_chunk_array
4827   if (_survivor_plab_array != NULL) {
4828     merge_survivor_plab_arrays(_young_gen->from(), n_threads);
4829   } else {
4830     assert(_survivor_chunk_index == 0, "Error");
4831   }
4832 
4833   // To space
4834   {
4835     SequentialSubTasksDone* pst = _young_gen->to()->par_seq_tasks();
4836     assert(!pst->valid(), "Clobbering existing data?");
4837     // Sets the condition for completion of the subtask (how many threads
4838     // need to finish in order to be done).
4839     pst->set_n_threads(n_threads);
4840     pst->set_n_tasks(1);
4841     assert(pst->valid(), "Error");
4842   }
4843 
4844   // From space
4845   {
4846     SequentialSubTasksDone* pst = _young_gen->from()->par_seq_tasks();
4847     assert(!pst->valid(), "Clobbering existing data?");
4848     size_t n_tasks = _survivor_chunk_index + 1;
4849     assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
4850     // Sets the condition for completion of the subtask (how many threads
4851     // need to finish in order to be done).
4852     pst->set_n_threads(n_threads);
4853     pst->set_n_tasks((int)n_tasks);
4854     assert(pst->valid(), "Error");
4855   }
4856 }
4857 
4858 // Parallel version of remark
4859 void CMSCollector::do_remark_parallel() {
4860   GenCollectedHeap* gch = GenCollectedHeap::heap();
4861   WorkGang* workers = gch->workers();
4862   assert(workers != NULL, "Need parallel worker threads.");
4863   // Choose to use the number of GC workers most recently set
4864   // into "active_workers".
4865   uint n_workers = workers->active_workers();
4866 
4867   CompactibleFreeListSpace* cms_space  = _cmsGen->cmsSpace();
4868 
4869   StrongRootsScope srs(n_workers);
4870 
4871   CMSParRemarkTask tsk(this, cms_space, n_workers, workers, task_queues(), &srs);
4872 
4873   // We won't be iterating over the cards in the card table updating
4874   // the younger_gen cards, so we shouldn't call the following else
4875   // the verification code as well as subsequent younger_refs_iterate
4876   // code would get confused. XXX
4877   // gch->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
4878 
4879   // The young gen rescan work will not be done as part of
4880   // process_roots (which currently doesn't know how to
4881   // parallelize such a scan), but rather will be broken up into
4882   // a set of parallel tasks (via the sampling that the [abortable]
4883   // preclean phase did of eden, plus the [two] tasks of
4884   // scanning the [two] survivor spaces. Further fine-grain
4885   // parallelization of the scanning of the survivor spaces
4886   // themselves, and of precleaning of the young gen itself
4887   // is deferred to the future.
4888   initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
4889 
4890   // The dirty card rescan work is broken up into a "sequence"
4891   // of parallel tasks (per constituent space) that are dynamically
4892   // claimed by the parallel threads.
4893   cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
4894 
4895   // It turns out that even when we're using 1 thread, doing the work in a
4896   // separate thread causes wide variance in run times.  We can't help this
4897   // in the multi-threaded case, but we special-case n=1 here to get
4898   // repeatable measurements of the 1-thread overhead of the parallel code.
4899   if (n_workers > 1) {
4900     // Make refs discovery MT-safe, if it isn't already: it may not
4901     // necessarily be so, since it's possible that we are doing
4902     // ST marking.
4903     ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), true);
4904     workers->run_task(&tsk);
4905   } else {
4906     ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
4907     tsk.work(0);
4908   }
4909 
4910   // restore, single-threaded for now, any preserved marks
4911   // as a result of work_q overflow
4912   restore_preserved_marks_if_any();
4913 }
4914 
4915 // Non-parallel version of remark
4916 void CMSCollector::do_remark_non_parallel() {
4917   ResourceMark rm;
4918   HandleMark   hm;
4919   GenCollectedHeap* gch = GenCollectedHeap::heap();
4920   ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
4921 
4922   MarkRefsIntoAndScanClosure
4923     mrias_cl(_span, ref_processor(), &_markBitMap, NULL /* not precleaning */,
4924              &_markStack, this,
4925              false /* should_yield */, false /* not precleaning */);
4926   MarkFromDirtyCardsClosure
4927     markFromDirtyCardsClosure(this, _span,
4928                               NULL,  // space is set further below
4929                               &_markBitMap, &_markStack, &mrias_cl);
4930   {
4931     GCTraceTime(Trace, gc, phases) t("Grey Object Rescan", _gc_timer_cm);
4932     // Iterate over the dirty cards, setting the corresponding bits in the
4933     // mod union table.
4934     {
4935       ModUnionClosure modUnionClosure(&_modUnionTable);
4936       _ct->ct_bs()->dirty_card_iterate(
4937                       _cmsGen->used_region(),
4938                       &modUnionClosure);
4939     }
4940     // Having transferred these marks into the modUnionTable, we just need
4941     // to rescan the marked objects on the dirty cards in the modUnionTable.
4942     // The initial marking may have been done during an asynchronous
4943     // collection so there may be dirty bits in the mod-union table.
4944     const int alignment =
4945       CardTableModRefBS::card_size * BitsPerWord;
4946     {
4947       // ... First handle dirty cards in CMS gen
4948       markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
4949       MemRegion ur = _cmsGen->used_region();
4950       HeapWord* lb = ur.start();
4951       HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
4952       MemRegion cms_span(lb, ub);
4953       _modUnionTable.dirty_range_iterate_clear(cms_span,
4954                                                &markFromDirtyCardsClosure);
4955       verify_work_stacks_empty();
4956       log_trace(gc)(" (re-scanned " SIZE_FORMAT " dirty cards in cms gen) ", markFromDirtyCardsClosure.num_dirty_cards());
4957     }
4958   }
4959   if (VerifyDuringGC &&
4960       GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
4961     HandleMark hm;  // Discard invalid handles created during verification
4962     Universe::verify();
4963   }
4964   {
4965     GCTraceTime(Trace, gc, phases) t("Root Rescan", _gc_timer_cm);
4966 
4967     verify_work_stacks_empty();
4968 
4969     gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
4970     StrongRootsScope srs(1);
4971 
4972     gch->gen_process_roots(&srs,
4973                            GenCollectedHeap::OldGen,
4974                            true,  // young gen as roots
4975                            GenCollectedHeap::ScanningOption(roots_scanning_options()),
4976                            should_unload_classes(),
4977                            &mrias_cl,
4978                            NULL,
4979                            NULL); // The dirty klasses will be handled below
4980 
4981     assert(should_unload_classes()
4982            || (roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4983            "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4984   }
4985 
4986   {
4987     GCTraceTime(Trace, gc, phases) t("Visit Unhandled CLDs", _gc_timer_cm);
4988 
4989     verify_work_stacks_empty();
4990 
4991     // Scan all class loader data objects that might have been introduced
4992     // during concurrent marking.
4993     ResourceMark rm;
4994     GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
4995     for (int i = 0; i < array->length(); i++) {
4996       mrias_cl.do_cld_nv(array->at(i));
4997     }
4998 
4999     // We don't need to keep track of new CLDs anymore.
5000     ClassLoaderDataGraph::remember_new_clds(false);
5001 
5002     verify_work_stacks_empty();
5003   }
5004 
5005   {
5006     GCTraceTime(Trace, gc, phases) t("Dirty Klass Scan", _gc_timer_cm);
5007 
5008     verify_work_stacks_empty();
5009 
5010     RemarkKlassClosure remark_klass_closure(&mrias_cl);
5011     ClassLoaderDataGraph::classes_do(&remark_klass_closure);
5012 
5013     verify_work_stacks_empty();
5014   }
5015 
5016   // We might have added oops to ClassLoaderData::_handles during the
5017   // concurrent marking phase. These oops point to newly allocated objects
5018   // that are guaranteed to be kept alive. Either by the direct allocation
5019   // code, or when the young collector processes the roots. Hence,
5020   // we don't have to revisit the _handles block during the remark phase.
5021 
5022   verify_work_stacks_empty();
5023   // Restore evacuated mark words, if any, used for overflow list links
5024   restore_preserved_marks_if_any();
5025 
5026   verify_overflow_empty();
5027 }
5028 
5029 ////////////////////////////////////////////////////////
5030 // Parallel Reference Processing Task Proxy Class
5031 ////////////////////////////////////////////////////////
5032 class AbstractGangTaskWOopQueues : public AbstractGangTask {
5033   OopTaskQueueSet*       _queues;
5034   ParallelTaskTerminator _terminator;
5035  public:
5036   AbstractGangTaskWOopQueues(const char* name, OopTaskQueueSet* queues, uint n_threads) :
5037     AbstractGangTask(name), _queues(queues), _terminator(n_threads, _queues) {}
5038   ParallelTaskTerminator* terminator() { return &_terminator; }
5039   OopTaskQueueSet* queues() { return _queues; }
5040 };
5041 
5042 class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues {
5043   typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
5044   CMSCollector*          _collector;
5045   CMSBitMap*             _mark_bit_map;
5046   const MemRegion        _span;
5047   ProcessTask&           _task;
5048 
5049 public:
5050   CMSRefProcTaskProxy(ProcessTask&     task,
5051                       CMSCollector*    collector,
5052                       const MemRegion& span,
5053                       CMSBitMap*       mark_bit_map,
5054                       AbstractWorkGang* workers,
5055                       OopTaskQueueSet* task_queues):
5056     AbstractGangTaskWOopQueues("Process referents by policy in parallel",
5057       task_queues,
5058       workers->active_workers()),
5059     _task(task),
5060     _collector(collector), _span(span), _mark_bit_map(mark_bit_map)
5061   {
5062     assert(_collector->_span.equals(_span) && !_span.is_empty(),
5063            "Inconsistency in _span");
5064   }
5065 
5066   OopTaskQueueSet* task_queues() { return queues(); }
5067 
5068   OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5069 
5070   void do_work_steal(int i,
5071                      CMSParDrainMarkingStackClosure* drain,
5072                      CMSParKeepAliveClosure* keep_alive,
5073                      int* seed);
5074 
5075   virtual void work(uint worker_id);
5076 };
5077 
5078 void CMSRefProcTaskProxy::work(uint worker_id) {
5079   ResourceMark rm;
5080   HandleMark hm;
5081   assert(_collector->_span.equals(_span), "Inconsistency in _span");
5082   CMSParKeepAliveClosure par_keep_alive(_collector, _span,
5083                                         _mark_bit_map,
5084                                         work_queue(worker_id));
5085   CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
5086                                                  _mark_bit_map,
5087                                                  work_queue(worker_id));
5088   CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
5089   _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack);
5090   if (_task.marks_oops_alive()) {
5091     do_work_steal(worker_id, &par_drain_stack, &par_keep_alive,
5092                   _collector->hash_seed(worker_id));
5093   }
5094   assert(work_queue(worker_id)->size() == 0, "work_queue should be empty");
5095   assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
5096 }
5097 
5098 class CMSRefEnqueueTaskProxy: public AbstractGangTask {
5099   typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
5100   EnqueueTask& _task;
5101 
5102 public:
5103   CMSRefEnqueueTaskProxy(EnqueueTask& task)
5104     : AbstractGangTask("Enqueue reference objects in parallel"),
5105       _task(task)
5106   { }
5107 
5108   virtual void work(uint worker_id)
5109   {
5110     _task.work(worker_id);
5111   }
5112 };
5113 
5114 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
5115   MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue):
5116    _span(span),
5117    _bit_map(bit_map),
5118    _work_queue(work_queue),
5119    _mark_and_push(collector, span, bit_map, work_queue),
5120    _low_water_mark(MIN2((work_queue->max_elems()/4),
5121                         ((uint)CMSWorkQueueDrainThreshold * ParallelGCThreads)))
5122 { }
5123 
5124 // . see if we can share work_queues with ParNew? XXX
5125 void CMSRefProcTaskProxy::do_work_steal(int i,
5126   CMSParDrainMarkingStackClosure* drain,
5127   CMSParKeepAliveClosure* keep_alive,
5128   int* seed) {
5129   OopTaskQueue* work_q = work_queue(i);
5130   NOT_PRODUCT(int num_steals = 0;)
5131   oop obj_to_scan;
5132 
5133   while (true) {
5134     // Completely finish any left over work from (an) earlier round(s)
5135     drain->trim_queue(0);
5136     size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5137                                          (size_t)ParGCDesiredObjsFromOverflowList);
5138     // Now check if there's any work in the overflow list
5139     // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5140     // only affects the number of attempts made to get work from the
5141     // overflow list and does not affect the number of workers.  Just
5142     // pass ParallelGCThreads so this behavior is unchanged.
5143     if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5144                                                 work_q,
5145                                                 ParallelGCThreads)) {
5146       // Found something in global overflow list;
5147       // not yet ready to go stealing work from others.
5148       // We'd like to assert(work_q->size() != 0, ...)
5149       // because we just took work from the overflow list,
5150       // but of course we can't, since all of that might have
5151       // been already stolen from us.
5152       continue;
5153     }
5154     // Verify that we have no work before we resort to stealing
5155     assert(work_q->size() == 0, "Have work, shouldn't steal");
5156     // Try to steal from other queues that have work
5157     if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5158       NOT_PRODUCT(num_steals++;)
5159       assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5160       assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5161       // Do scanning work
5162       obj_to_scan->oop_iterate(keep_alive);
5163       // Loop around, finish this work, and try to steal some more
5164     } else if (terminator()->offer_termination()) {
5165       break;  // nirvana from the infinite cycle
5166     }
5167   }
5168   log_develop_trace(gc, task)("\t(%d: stole %d oops)", i, num_steals);
5169 }
5170 
5171 void CMSRefProcTaskExecutor::execute(ProcessTask& task)
5172 {
5173   GenCollectedHeap* gch = GenCollectedHeap::heap();
5174   WorkGang* workers = gch->workers();
5175   assert(workers != NULL, "Need parallel worker threads.");
5176   CMSRefProcTaskProxy rp_task(task, &_collector,
5177                               _collector.ref_processor()->span(),
5178                               _collector.markBitMap(),
5179                               workers, _collector.task_queues());
5180   workers->run_task(&rp_task);
5181 }
5182 
5183 void CMSRefProcTaskExecutor::execute(EnqueueTask& task)
5184 {
5185 
5186   GenCollectedHeap* gch = GenCollectedHeap::heap();
5187   WorkGang* workers = gch->workers();
5188   assert(workers != NULL, "Need parallel worker threads.");
5189   CMSRefEnqueueTaskProxy enq_task(task);
5190   workers->run_task(&enq_task);
5191 }
5192 
5193 void CMSCollector::refProcessingWork() {
5194   ResourceMark rm;
5195   HandleMark   hm;
5196 
5197   ReferenceProcessor* rp = ref_processor();
5198   assert(rp->span().equals(_span), "Spans should be equal");
5199   assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
5200   // Process weak references.
5201   rp->setup_policy(false);
5202   verify_work_stacks_empty();
5203 
5204   CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
5205                                           &_markStack, false /* !preclean */);
5206   CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
5207                                 _span, &_markBitMap, &_markStack,
5208                                 &cmsKeepAliveClosure, false /* !preclean */);
5209   {
5210     GCTraceTime(Debug, gc, phases) t("Reference Processing", _gc_timer_cm);
5211 
5212     ReferenceProcessorStats stats;
5213     if (rp->processing_is_mt()) {
5214       // Set the degree of MT here.  If the discovery is done MT, there
5215       // may have been a different number of threads doing the discovery
5216       // and a different number of discovered lists may have Ref objects.
5217       // That is OK as long as the Reference lists are balanced (see
5218       // balance_all_queues() and balance_queues()).
5219       GenCollectedHeap* gch = GenCollectedHeap::heap();
5220       uint active_workers = ParallelGCThreads;
5221       WorkGang* workers = gch->workers();
5222       if (workers != NULL) {
5223         active_workers = workers->active_workers();
5224         // The expectation is that active_workers will have already
5225         // been set to a reasonable value.  If it has not been set,
5226         // investigate.
5227         assert(active_workers > 0, "Should have been set during scavenge");
5228       }
5229       rp->set_active_mt_degree(active_workers);
5230       CMSRefProcTaskExecutor task_executor(*this);
5231       stats = rp->process_discovered_references(&_is_alive_closure,
5232                                         &cmsKeepAliveClosure,
5233                                         &cmsDrainMarkingStackClosure,
5234                                         &task_executor,
5235                                         _gc_timer_cm);
5236     } else {
5237       stats = rp->process_discovered_references(&_is_alive_closure,
5238                                         &cmsKeepAliveClosure,
5239                                         &cmsDrainMarkingStackClosure,
5240                                         NULL,
5241                                         _gc_timer_cm);
5242     }
5243     _gc_tracer_cm->report_gc_reference_stats(stats);
5244 
5245   }
5246 
5247   // This is the point where the entire marking should have completed.
5248   verify_work_stacks_empty();
5249 
5250   if (should_unload_classes()) {
5251     {
5252       GCTraceTime(Debug, gc, phases) t("Class Unloading", _gc_timer_cm);
5253 
5254       // Unload classes and purge the SystemDictionary.
5255       bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure);
5256 
5257       // Unload nmethods.
5258       CodeCache::do_unloading(&_is_alive_closure, purged_class);
5259 
5260       // Prune dead klasses from subklass/sibling/implementor lists.
5261       Klass::clean_weak_klass_links(&_is_alive_closure);
5262     }
5263 
5264     {
5265       GCTraceTime(Debug, gc, phases) t("Scrub Symbol Table", _gc_timer_cm);
5266       // Clean up unreferenced symbols in symbol table.
5267       SymbolTable::unlink();
5268     }
5269 
5270     {
5271       GCTraceTime(Debug, gc, phases) t("Scrub String Table", _gc_timer_cm);
5272       // Delete entries for dead interned strings.
5273       StringTable::unlink(&_is_alive_closure);
5274     }
5275   }
5276 
5277 
5278   // Restore any preserved marks as a result of mark stack or
5279   // work queue overflow
5280   restore_preserved_marks_if_any();  // done single-threaded for now
5281 
5282   rp->set_enqueuing_is_done(true);
5283   if (rp->processing_is_mt()) {
5284     rp->balance_all_queues();
5285     CMSRefProcTaskExecutor task_executor(*this);
5286     rp->enqueue_discovered_references(&task_executor);
5287   } else {
5288     rp->enqueue_discovered_references(NULL);
5289   }
5290   rp->verify_no_references_recorded();
5291   assert(!rp->discovery_enabled(), "should have been disabled");
5292 }
5293 
5294 #ifndef PRODUCT
5295 void CMSCollector::check_correct_thread_executing() {
5296   Thread* t = Thread::current();
5297   // Only the VM thread or the CMS thread should be here.
5298   assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
5299          "Unexpected thread type");
5300   // If this is the vm thread, the foreground process
5301   // should not be waiting.  Note that _foregroundGCIsActive is
5302   // true while the foreground collector is waiting.
5303   if (_foregroundGCShouldWait) {
5304     // We cannot be the VM thread
5305     assert(t->is_ConcurrentGC_thread(),
5306            "Should be CMS thread");
5307   } else {
5308     // We can be the CMS thread only if we are in a stop-world
5309     // phase of CMS collection.
5310     if (t->is_ConcurrentGC_thread()) {
5311       assert(_collectorState == InitialMarking ||
5312              _collectorState == FinalMarking,
5313              "Should be a stop-world phase");
5314       // The CMS thread should be holding the CMS_token.
5315       assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5316              "Potential interference with concurrently "
5317              "executing VM thread");
5318     }
5319   }
5320 }
5321 #endif
5322 
5323 void CMSCollector::sweep() {
5324   assert(_collectorState == Sweeping, "just checking");
5325   check_correct_thread_executing();
5326   verify_work_stacks_empty();
5327   verify_overflow_empty();
5328   increment_sweep_count();
5329   TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
5330 
5331   _inter_sweep_timer.stop();
5332   _inter_sweep_estimate.sample(_inter_sweep_timer.seconds());
5333 
5334   assert(!_intra_sweep_timer.is_active(), "Should not be active");
5335   _intra_sweep_timer.reset();
5336   _intra_sweep_timer.start();
5337   {
5338     GCTraceCPUTime tcpu;
5339     CMSPhaseAccounting pa(this, "Concurrent Sweep");
5340     // First sweep the old gen
5341     {
5342       CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
5343                                bitMapLock());
5344       sweepWork(_cmsGen);
5345     }
5346 
5347     // Update Universe::_heap_*_at_gc figures.
5348     // We need all the free list locks to make the abstract state
5349     // transition from Sweeping to Resetting. See detailed note
5350     // further below.
5351     {
5352       CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock());
5353       // Update heap occupancy information which is used as
5354       // input to soft ref clearing policy at the next gc.
5355       Universe::update_heap_info_at_gc();
5356       _collectorState = Resizing;
5357     }
5358   }
5359   verify_work_stacks_empty();
5360   verify_overflow_empty();
5361 
5362   if (should_unload_classes()) {
5363     // Delay purge to the beginning of the next safepoint.  Metaspace::contains
5364     // requires that the virtual spaces are stable and not deleted.
5365     ClassLoaderDataGraph::set_should_purge(true);
5366   }
5367 
5368   _intra_sweep_timer.stop();
5369   _intra_sweep_estimate.sample(_intra_sweep_timer.seconds());
5370 
5371   _inter_sweep_timer.reset();
5372   _inter_sweep_timer.start();
5373 
5374   // We need to use a monotonically non-decreasing time in ms
5375   // or we will see time-warp warnings and os::javaTimeMillis()
5376   // does not guarantee monotonicity.
5377   jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
5378   update_time_of_last_gc(now);
5379 
5380   // NOTE on abstract state transitions:
5381   // Mutators allocate-live and/or mark the mod-union table dirty
5382   // based on the state of the collection.  The former is done in
5383   // the interval [Marking, Sweeping] and the latter in the interval
5384   // [Marking, Sweeping).  Thus the transitions into the Marking state
5385   // and out of the Sweeping state must be synchronously visible
5386   // globally to the mutators.
5387   // The transition into the Marking state happens with the world
5388   // stopped so the mutators will globally see it.  Sweeping is
5389   // done asynchronously by the background collector so the transition
5390   // from the Sweeping state to the Resizing state must be done
5391   // under the freelistLock (as is the check for whether to
5392   // allocate-live and whether to dirty the mod-union table).
5393   assert(_collectorState == Resizing, "Change of collector state to"
5394     " Resizing must be done under the freelistLocks (plural)");
5395 
5396   // Now that sweeping has been completed, we clear
5397   // the incremental_collection_failed flag,
5398   // thus inviting a younger gen collection to promote into
5399   // this generation. If such a promotion may still fail,
5400   // the flag will be set again when a young collection is
5401   // attempted.
5402   GenCollectedHeap* gch = GenCollectedHeap::heap();
5403   gch->clear_incremental_collection_failed();  // Worth retrying as fresh space may have been freed up
5404   gch->update_full_collections_completed(_collection_count_start);
5405 }
5406 
5407 // FIX ME!!! Looks like this belongs in CFLSpace, with
5408 // CMSGen merely delegating to it.
5409 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
5410   double nearLargestPercent = FLSLargestBlockCoalesceProximity;
5411   HeapWord*  minAddr        = _cmsSpace->bottom();
5412   HeapWord*  largestAddr    =
5413     (HeapWord*) _cmsSpace->dictionary()->find_largest_dict();
5414   if (largestAddr == NULL) {
5415     // The dictionary appears to be empty.  In this case
5416     // try to coalesce at the end of the heap.
5417     largestAddr = _cmsSpace->end();
5418   }
5419   size_t largestOffset     = pointer_delta(largestAddr, minAddr);
5420   size_t nearLargestOffset =
5421     (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
5422   log_debug(gc, freelist)("CMS: Large Block: " PTR_FORMAT "; Proximity: " PTR_FORMAT " -> " PTR_FORMAT,
5423                           p2i(largestAddr), p2i(_cmsSpace->nearLargestChunk()), p2i(minAddr + nearLargestOffset));
5424   _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
5425 }
5426 
5427 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
5428   return addr >= _cmsSpace->nearLargestChunk();
5429 }
5430 
5431 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
5432   return _cmsSpace->find_chunk_at_end();
5433 }
5434 
5435 void ConcurrentMarkSweepGeneration::update_gc_stats(Generation* current_generation,
5436                                                     bool full) {
5437   // If the young generation has been collected, gather any statistics
5438   // that are of interest at this point.
5439   bool current_is_young = GenCollectedHeap::heap()->is_young_gen(current_generation);
5440   if (!full && current_is_young) {
5441     // Gather statistics on the young generation collection.
5442     collector()->stats().record_gc0_end(used());
5443   }
5444 }
5445 
5446 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* old_gen) {
5447   // We iterate over the space(s) underlying this generation,
5448   // checking the mark bit map to see if the bits corresponding
5449   // to specific blocks are marked or not. Blocks that are
5450   // marked are live and are not swept up. All remaining blocks
5451   // are swept up, with coalescing on-the-fly as we sweep up
5452   // contiguous free and/or garbage blocks:
5453   // We need to ensure that the sweeper synchronizes with allocators
5454   // and stop-the-world collectors. In particular, the following
5455   // locks are used:
5456   // . CMS token: if this is held, a stop the world collection cannot occur
5457   // . freelistLock: if this is held no allocation can occur from this
5458   //                 generation by another thread
5459   // . bitMapLock: if this is held, no other thread can access or update
5460   //
5461 
5462   // Note that we need to hold the freelistLock if we use
5463   // block iterate below; else the iterator might go awry if
5464   // a mutator (or promotion) causes block contents to change
5465   // (for instance if the allocator divvies up a block).
5466   // If we hold the free list lock, for all practical purposes
5467   // young generation GC's can't occur (they'll usually need to
5468   // promote), so we might as well prevent all young generation
5469   // GC's while we do a sweeping step. For the same reason, we might
5470   // as well take the bit map lock for the entire duration
5471 
5472   // check that we hold the requisite locks
5473   assert(have_cms_token(), "Should hold cms token");
5474   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), "Should possess CMS token to sweep");
5475   assert_lock_strong(old_gen->freelistLock());
5476   assert_lock_strong(bitMapLock());
5477 
5478   assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context");
5479   assert(_intra_sweep_timer.is_active(),  "Was switched on  in an outer context");
5480   old_gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
5481                                           _inter_sweep_estimate.padded_average(),
5482                                           _intra_sweep_estimate.padded_average());
5483   old_gen->setNearLargestChunk();
5484 
5485   {
5486     SweepClosure sweepClosure(this, old_gen, &_markBitMap, CMSYield);
5487     old_gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
5488     // We need to free-up/coalesce garbage/blocks from a
5489     // co-terminal free run. This is done in the SweepClosure
5490     // destructor; so, do not remove this scope, else the
5491     // end-of-sweep-census below will be off by a little bit.
5492   }
5493   old_gen->cmsSpace()->sweep_completed();
5494   old_gen->cmsSpace()->endSweepFLCensus(sweep_count());
5495   if (should_unload_classes()) {                // unloaded classes this cycle,
5496     _concurrent_cycles_since_last_unload = 0;   // ... reset count
5497   } else {                                      // did not unload classes,
5498     _concurrent_cycles_since_last_unload++;     // ... increment count
5499   }
5500 }
5501 
5502 // Reset CMS data structures (for now just the marking bit map)
5503 // preparatory for the next cycle.
5504 void CMSCollector::reset_concurrent() {
5505   CMSTokenSyncWithLocks ts(true, bitMapLock());
5506 
5507   // If the state is not "Resetting", the foreground  thread
5508   // has done a collection and the resetting.
5509   if (_collectorState != Resetting) {
5510     assert(_collectorState == Idling, "The state should only change"
5511       " because the foreground collector has finished the collection");
5512     return;
5513   }
5514 
5515   {
5516     // Clear the mark bitmap (no grey objects to start with)
5517     // for the next cycle.
5518     GCTraceCPUTime tcpu;
5519     CMSPhaseAccounting cmspa(this, "Concurrent Reset");
5520 
5521     HeapWord* curAddr = _markBitMap.startWord();
5522     while (curAddr < _markBitMap.endWord()) {
5523       size_t remaining  = pointer_delta(_markBitMap.endWord(), curAddr);
5524       MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
5525       _markBitMap.clear_large_range(chunk);
5526       if (ConcurrentMarkSweepThread::should_yield() &&
5527           !foregroundGCIsActive() &&
5528           CMSYield) {
5529         assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5530                "CMS thread should hold CMS token");
5531         assert_lock_strong(bitMapLock());
5532         bitMapLock()->unlock();
5533         ConcurrentMarkSweepThread::desynchronize(true);
5534         stopTimer();
5535         incrementYields();
5536 
5537         // See the comment in coordinator_yield()
5538         for (unsigned i = 0; i < CMSYieldSleepCount &&
5539                          ConcurrentMarkSweepThread::should_yield() &&
5540                          !CMSCollector::foregroundGCIsActive(); ++i) {
5541           os::sleep(Thread::current(), 1, false);
5542         }
5543 
5544         ConcurrentMarkSweepThread::synchronize(true);
5545         bitMapLock()->lock_without_safepoint_check();
5546         startTimer();
5547       }
5548       curAddr = chunk.end();
5549     }
5550     // A successful mostly concurrent collection has been done.
5551     // Because only the full (i.e., concurrent mode failure) collections
5552     // are being measured for gc overhead limits, clean the "near" flag
5553     // and count.
5554     size_policy()->reset_gc_overhead_limit_count();
5555     _collectorState = Idling;
5556   }
5557 
5558   register_gc_end();
5559 }
5560 
5561 // Same as above but for STW paths
5562 void CMSCollector::reset_stw() {
5563   // already have the lock
5564   assert(_collectorState == Resetting, "just checking");
5565   assert_lock_strong(bitMapLock());
5566   GCIdMarkAndRestore gc_id_mark(_cmsThread->gc_id());
5567   _markBitMap.clear_all();
5568   _collectorState = Idling;
5569   register_gc_end();
5570 }
5571 
5572 void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) {
5573   GCTraceCPUTime tcpu;
5574   TraceCollectorStats tcs(counters());
5575 
5576   switch (op) {
5577     case CMS_op_checkpointRootsInitial: {
5578       GCTraceTime(Info, gc) t("Pause Initial Mark", NULL, GCCause::_no_gc, true);
5579       SvcGCMarker sgcm(SvcGCMarker::OTHER);
5580       checkpointRootsInitial();
5581       break;
5582     }
5583     case CMS_op_checkpointRootsFinal: {
5584       GCTraceTime(Info, gc) t("Pause Remark", NULL, GCCause::_no_gc, true);
5585       SvcGCMarker sgcm(SvcGCMarker::OTHER);
5586       checkpointRootsFinal();
5587       break;
5588     }
5589     default:
5590       fatal("No such CMS_op");
5591   }
5592 }
5593 
5594 #ifndef PRODUCT
5595 size_t const CMSCollector::skip_header_HeapWords() {
5596   return FreeChunk::header_size();
5597 }
5598 
5599 // Try and collect here conditions that should hold when
5600 // CMS thread is exiting. The idea is that the foreground GC
5601 // thread should not be blocked if it wants to terminate
5602 // the CMS thread and yet continue to run the VM for a while
5603 // after that.
5604 void CMSCollector::verify_ok_to_terminate() const {
5605   assert(Thread::current()->is_ConcurrentGC_thread(),
5606          "should be called by CMS thread");
5607   assert(!_foregroundGCShouldWait, "should be false");
5608   // We could check here that all the various low-level locks
5609   // are not held by the CMS thread, but that is overkill; see
5610   // also CMSThread::verify_ok_to_terminate() where the CGC_lock
5611   // is checked.
5612 }
5613 #endif
5614 
5615 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
5616    assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
5617           "missing Printezis mark?");
5618   HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5619   size_t size = pointer_delta(nextOneAddr + 1, addr);
5620   assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5621          "alignment problem");
5622   assert(size >= 3, "Necessary for Printezis marks to work");
5623   return size;
5624 }
5625 
5626 // A variant of the above (block_size_using_printezis_bits()) except
5627 // that we return 0 if the P-bits are not yet set.
5628 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
5629   if (_markBitMap.isMarked(addr + 1)) {
5630     assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects");
5631     HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5632     size_t size = pointer_delta(nextOneAddr + 1, addr);
5633     assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5634            "alignment problem");
5635     assert(size >= 3, "Necessary for Printezis marks to work");
5636     return size;
5637   }
5638   return 0;
5639 }
5640 
5641 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
5642   size_t sz = 0;
5643   oop p = (oop)addr;
5644   if (p->klass_or_null() != NULL) {
5645     sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
5646   } else {
5647     sz = block_size_using_printezis_bits(addr);
5648   }
5649   assert(sz > 0, "size must be nonzero");
5650   HeapWord* next_block = addr + sz;
5651   HeapWord* next_card  = (HeapWord*)round_to((uintptr_t)next_block,
5652                                              CardTableModRefBS::card_size);
5653   assert(round_down((uintptr_t)addr,      CardTableModRefBS::card_size) <
5654          round_down((uintptr_t)next_card, CardTableModRefBS::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   _bm(),
5667   _shifter(shifter),
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() == (HeapWord*)round_to((intptr_t)mr.end(),
5759                         (1 << (_shifter+LogHeapWordSize))),
5760          "Misaligned mr.end()");
5761   size_t end_ofs   = heapWordToOffset(mr.end());
5762   assert(end_ofs > start_ofs, "Should mark at least one bit");
5763 }
5764 
5765 #endif
5766 
5767 bool CMSMarkStack::allocate(size_t size) {
5768   // allocate a stack of the requisite depth
5769   ReservedSpace rs(ReservedSpace::allocation_align_size_up(
5770                    size * sizeof(oop)));
5771   if (!rs.is_reserved()) {
5772     log_warning(gc)("CMSMarkStack allocation failure");
5773     return false;
5774   }
5775   if (!_virtual_space.initialize(rs, rs.size())) {
5776     log_warning(gc)("CMSMarkStack backing store failure");
5777     return false;
5778   }
5779   assert(_virtual_space.committed_size() == rs.size(),
5780          "didn't reserve backing store for all of CMS stack?");
5781   _base = (oop*)(_virtual_space.low());
5782   _index = 0;
5783   _capacity = size;
5784   NOT_PRODUCT(_max_depth = 0);
5785   return true;
5786 }
5787 
5788 // XXX FIX ME !!! In the MT case we come in here holding a
5789 // leaf lock. For printing we need to take a further lock
5790 // which has lower rank. We need to recalibrate the two
5791 // lock-ranks involved in order to be able to print the
5792 // messages below. (Or defer the printing to the caller.
5793 // For now we take the expedient path of just disabling the
5794 // messages for the problematic case.)
5795 void CMSMarkStack::expand() {
5796   assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted");
5797   if (_capacity == MarkStackSizeMax) {
5798     if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled) {
5799       // We print a warning message only once per CMS cycle.
5800       log_debug(gc)(" (benign) Hit CMSMarkStack max size limit");
5801     }
5802     return;
5803   }
5804   // Double capacity if possible
5805   size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax);
5806   // Do not give up existing stack until we have managed to
5807   // get the double capacity that we desired.
5808   ReservedSpace rs(ReservedSpace::allocation_align_size_up(
5809                    new_capacity * sizeof(oop)));
5810   if (rs.is_reserved()) {
5811     // Release the backing store associated with old stack
5812     _virtual_space.release();
5813     // Reinitialize virtual space for new stack
5814     if (!_virtual_space.initialize(rs, rs.size())) {
5815       fatal("Not enough swap for expanded marking stack");
5816     }
5817     _base = (oop*)(_virtual_space.low());
5818     _index = 0;
5819     _capacity = new_capacity;
5820   } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled) {
5821     // Failed to double capacity, continue;
5822     // we print a detail message only once per CMS cycle.
5823     log_debug(gc)(" (benign) Failed to expand marking stack from " SIZE_FORMAT "K to " SIZE_FORMAT "K",
5824                         _capacity / K, new_capacity / K);
5825   }
5826 }
5827 
5828 
5829 // Closures
5830 // XXX: there seems to be a lot of code  duplication here;
5831 // should refactor and consolidate common code.
5832 
5833 // This closure is used to mark refs into the CMS generation in
5834 // the CMS bit map. Called at the first checkpoint. This closure
5835 // assumes that we do not need to re-mark dirty cards; if the CMS
5836 // generation on which this is used is not an oldest
5837 // generation then this will lose younger_gen cards!
5838 
5839 MarkRefsIntoClosure::MarkRefsIntoClosure(
5840   MemRegion span, CMSBitMap* bitMap):
5841     _span(span),
5842     _bitMap(bitMap)
5843 {
5844   assert(ref_processor() == NULL, "deliberately left NULL");
5845   assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
5846 }
5847 
5848 void MarkRefsIntoClosure::do_oop(oop obj) {
5849   // if p points into _span, then mark corresponding bit in _markBitMap
5850   assert(obj->is_oop(), "expected an oop");
5851   HeapWord* addr = (HeapWord*)obj;
5852   if (_span.contains(addr)) {
5853     // this should be made more efficient
5854     _bitMap->mark(addr);
5855   }
5856 }
5857 
5858 void MarkRefsIntoClosure::do_oop(oop* p)       { MarkRefsIntoClosure::do_oop_work(p); }
5859 void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); }
5860 
5861 ParMarkRefsIntoClosure::ParMarkRefsIntoClosure(
5862   MemRegion span, CMSBitMap* bitMap):
5863     _span(span),
5864     _bitMap(bitMap)
5865 {
5866   assert(ref_processor() == NULL, "deliberately left NULL");
5867   assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
5868 }
5869 
5870 void ParMarkRefsIntoClosure::do_oop(oop obj) {
5871   // if p points into _span, then mark corresponding bit in _markBitMap
5872   assert(obj->is_oop(), "expected an oop");
5873   HeapWord* addr = (HeapWord*)obj;
5874   if (_span.contains(addr)) {
5875     // this should be made more efficient
5876     _bitMap->par_mark(addr);
5877   }
5878 }
5879 
5880 void ParMarkRefsIntoClosure::do_oop(oop* p)       { ParMarkRefsIntoClosure::do_oop_work(p); }
5881 void ParMarkRefsIntoClosure::do_oop(narrowOop* p) { ParMarkRefsIntoClosure::do_oop_work(p); }
5882 
5883 // A variant of the above, used for CMS marking verification.
5884 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
5885   MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm):
5886     _span(span),
5887     _verification_bm(verification_bm),
5888     _cms_bm(cms_bm)
5889 {
5890   assert(ref_processor() == NULL, "deliberately left NULL");
5891   assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
5892 }
5893 
5894 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
5895   // if p points into _span, then mark corresponding bit in _markBitMap
5896   assert(obj->is_oop(), "expected an oop");
5897   HeapWord* addr = (HeapWord*)obj;
5898   if (_span.contains(addr)) {
5899     _verification_bm->mark(addr);
5900     if (!_cms_bm->isMarked(addr)) {
5901       Log(gc, verify) log;
5902       ResourceMark rm;
5903       oop(addr)->print_on(log.error_stream());
5904       log.error(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
5905       fatal("... aborting");
5906     }
5907   }
5908 }
5909 
5910 void MarkRefsIntoVerifyClosure::do_oop(oop* p)       { MarkRefsIntoVerifyClosure::do_oop_work(p); }
5911 void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
5912 
5913 //////////////////////////////////////////////////
5914 // MarkRefsIntoAndScanClosure
5915 //////////////////////////////////////////////////
5916 
5917 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
5918                                                        ReferenceProcessor* rp,
5919                                                        CMSBitMap* bit_map,
5920                                                        CMSBitMap* mod_union_table,
5921                                                        CMSMarkStack*  mark_stack,
5922                                                        CMSCollector* collector,
5923                                                        bool should_yield,
5924                                                        bool concurrent_precleaning):
5925   _collector(collector),
5926   _span(span),
5927   _bit_map(bit_map),
5928   _mark_stack(mark_stack),
5929   _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table,
5930                       mark_stack, concurrent_precleaning),
5931   _yield(should_yield),
5932   _concurrent_precleaning(concurrent_precleaning),
5933   _freelistLock(NULL)
5934 {
5935   // FIXME: Should initialize in base class constructor.
5936   assert(rp != NULL, "ref_processor shouldn't be NULL");
5937   set_ref_processor_internal(rp);
5938 }
5939 
5940 // This closure is used to mark refs into the CMS generation at the
5941 // second (final) checkpoint, and to scan and transitively follow
5942 // the unmarked oops. It is also used during the concurrent precleaning
5943 // phase while scanning objects on dirty cards in the CMS generation.
5944 // The marks are made in the marking bit map and the marking stack is
5945 // used for keeping the (newly) grey objects during the scan.
5946 // The parallel version (Par_...) appears further below.
5947 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
5948   if (obj != NULL) {
5949     assert(obj->is_oop(), "expected an oop");
5950     HeapWord* addr = (HeapWord*)obj;
5951     assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
5952     assert(_collector->overflow_list_is_empty(),
5953            "overflow list should be empty");
5954     if (_span.contains(addr) &&
5955         !_bit_map->isMarked(addr)) {
5956       // mark bit map (object is now grey)
5957       _bit_map->mark(addr);
5958       // push on marking stack (stack should be empty), and drain the
5959       // stack by applying this closure to the oops in the oops popped
5960       // from the stack (i.e. blacken the grey objects)
5961       bool res = _mark_stack->push(obj);
5962       assert(res, "Should have space to push on empty stack");
5963       do {
5964         oop new_oop = _mark_stack->pop();
5965         assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
5966         assert(_bit_map->isMarked((HeapWord*)new_oop),
5967                "only grey objects on this stack");
5968         // iterate over the oops in this oop, marking and pushing
5969         // the ones in CMS heap (i.e. in _span).
5970         new_oop->oop_iterate(&_pushAndMarkClosure);
5971         // check if it's time to yield
5972         do_yield_check();
5973       } while (!_mark_stack->isEmpty() ||
5974                (!_concurrent_precleaning && take_from_overflow_list()));
5975         // if marking stack is empty, and we are not doing this
5976         // during precleaning, then check the overflow list
5977     }
5978     assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
5979     assert(_collector->overflow_list_is_empty(),
5980            "overflow list was drained above");
5981 
5982     assert(_collector->no_preserved_marks(),
5983            "All preserved marks should have been restored above");
5984   }
5985 }
5986 
5987 void MarkRefsIntoAndScanClosure::do_oop(oop* p)       { MarkRefsIntoAndScanClosure::do_oop_work(p); }
5988 void MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
5989 
5990 void MarkRefsIntoAndScanClosure::do_yield_work() {
5991   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5992          "CMS thread should hold CMS token");
5993   assert_lock_strong(_freelistLock);
5994   assert_lock_strong(_bit_map->lock());
5995   // relinquish the free_list_lock and bitMaplock()
5996   _bit_map->lock()->unlock();
5997   _freelistLock->unlock();
5998   ConcurrentMarkSweepThread::desynchronize(true);
5999   _collector->stopTimer();
6000   _collector->incrementYields();
6001 
6002   // See the comment in coordinator_yield()
6003   for (unsigned i = 0;
6004        i < CMSYieldSleepCount &&
6005        ConcurrentMarkSweepThread::should_yield() &&
6006        !CMSCollector::foregroundGCIsActive();
6007        ++i) {
6008     os::sleep(Thread::current(), 1, false);
6009   }
6010 
6011   ConcurrentMarkSweepThread::synchronize(true);
6012   _freelistLock->lock_without_safepoint_check();
6013   _bit_map->lock()->lock_without_safepoint_check();
6014   _collector->startTimer();
6015 }
6016 
6017 ///////////////////////////////////////////////////////////
6018 // ParMarkRefsIntoAndScanClosure: a parallel version of
6019 //                                MarkRefsIntoAndScanClosure
6020 ///////////////////////////////////////////////////////////
6021 ParMarkRefsIntoAndScanClosure::ParMarkRefsIntoAndScanClosure(
6022   CMSCollector* collector, MemRegion span, ReferenceProcessor* rp,
6023   CMSBitMap* bit_map, OopTaskQueue* work_queue):
6024   _span(span),
6025   _bit_map(bit_map),
6026   _work_queue(work_queue),
6027   _low_water_mark(MIN2((work_queue->max_elems()/4),
6028                        ((uint)CMSWorkQueueDrainThreshold * ParallelGCThreads))),
6029   _parPushAndMarkClosure(collector, span, rp, bit_map, work_queue)
6030 {
6031   // FIXME: Should initialize in base class constructor.
6032   assert(rp != NULL, "ref_processor shouldn't be NULL");
6033   set_ref_processor_internal(rp);
6034 }
6035 
6036 // This closure is used to mark refs into the CMS generation at the
6037 // second (final) checkpoint, and to scan and transitively follow
6038 // the unmarked oops. The marks are made in the marking bit map and
6039 // the work_queue is used for keeping the (newly) grey objects during
6040 // the scan phase whence they are also available for stealing by parallel
6041 // threads. Since the marking bit map is shared, updates are
6042 // synchronized (via CAS).
6043 void ParMarkRefsIntoAndScanClosure::do_oop(oop obj) {
6044   if (obj != NULL) {
6045     // Ignore mark word because this could be an already marked oop
6046     // that may be chained at the end of the overflow list.
6047     assert(obj->is_oop(true), "expected an oop");
6048     HeapWord* addr = (HeapWord*)obj;
6049     if (_span.contains(addr) &&
6050         !_bit_map->isMarked(addr)) {
6051       // mark bit map (object will become grey):
6052       // It is possible for several threads to be
6053       // trying to "claim" this object concurrently;
6054       // the unique thread that succeeds in marking the
6055       // object first will do the subsequent push on
6056       // to the work queue (or overflow list).
6057       if (_bit_map->par_mark(addr)) {
6058         // push on work_queue (which may not be empty), and trim the
6059         // queue to an appropriate length by applying this closure to
6060         // the oops in the oops popped from the stack (i.e. blacken the
6061         // grey objects)
6062         bool res = _work_queue->push(obj);
6063         assert(res, "Low water mark should be less than capacity?");
6064         trim_queue(_low_water_mark);
6065       } // Else, another thread claimed the object
6066     }
6067   }
6068 }
6069 
6070 void ParMarkRefsIntoAndScanClosure::do_oop(oop* p)       { ParMarkRefsIntoAndScanClosure::do_oop_work(p); }
6071 void ParMarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { ParMarkRefsIntoAndScanClosure::do_oop_work(p); }
6072 
6073 // This closure is used to rescan the marked objects on the dirty cards
6074 // in the mod union table and the card table proper.
6075 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
6076   oop p, MemRegion mr) {
6077 
6078   size_t size = 0;
6079   HeapWord* addr = (HeapWord*)p;
6080   DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6081   assert(_span.contains(addr), "we are scanning the CMS generation");
6082   // check if it's time to yield
6083   if (do_yield_check()) {
6084     // We yielded for some foreground stop-world work,
6085     // and we have been asked to abort this ongoing preclean cycle.
6086     return 0;
6087   }
6088   if (_bitMap->isMarked(addr)) {
6089     // it's marked; is it potentially uninitialized?
6090     if (p->klass_or_null() != NULL) {
6091         // an initialized object; ignore mark word in verification below
6092         // since we are running concurrent with mutators
6093         assert(p->is_oop(true), "should be an oop");
6094         if (p->is_objArray()) {
6095           // objArrays are precisely marked; restrict scanning
6096           // to dirty cards only.
6097           size = CompactibleFreeListSpace::adjustObjectSize(
6098                    p->oop_iterate_size(_scanningClosure, mr));
6099         } else {
6100           // A non-array may have been imprecisely marked; we need
6101           // to scan object in its entirety.
6102           size = CompactibleFreeListSpace::adjustObjectSize(
6103                    p->oop_iterate_size(_scanningClosure));
6104         }
6105       #ifdef ASSERT
6106         size_t direct_size =
6107           CompactibleFreeListSpace::adjustObjectSize(p->size());
6108         assert(size == direct_size, "Inconsistency in size");
6109         assert(size >= 3, "Necessary for Printezis marks to work");
6110         HeapWord* start_pbit = addr + 1;
6111         HeapWord* end_pbit = addr + size - 1;
6112         assert(_bitMap->isMarked(start_pbit) == _bitMap->isMarked(end_pbit),
6113                "inconsistent Printezis mark");
6114         // Verify inner mark bits (between Printezis bits) are clear,
6115         // but don't repeat if there are multiple dirty regions for
6116         // the same object, to avoid potential O(N^2) performance.
6117         if (addr != _last_scanned_object) {
6118           _bitMap->verifyNoOneBitsInRange(start_pbit + 1, end_pbit);
6119           _last_scanned_object = addr;
6120         }
6121       #endif // ASSERT
6122     } else {
6123       // An uninitialized object.
6124       assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
6125       HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
6126       size = pointer_delta(nextOneAddr + 1, addr);
6127       assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6128              "alignment problem");
6129       // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
6130       // will dirty the card when the klass pointer is installed in the
6131       // object (signaling the completion of initialization).
6132     }
6133   } else {
6134     // Either a not yet marked object or an uninitialized object
6135     if (p->klass_or_null() == NULL) {
6136       // An uninitialized object, skip to the next card, since
6137       // we may not be able to read its P-bits yet.
6138       assert(size == 0, "Initial value");
6139     } else {
6140       // An object not (yet) reached by marking: we merely need to
6141       // compute its size so as to go look at the next block.
6142       assert(p->is_oop(true), "should be an oop");
6143       size = CompactibleFreeListSpace::adjustObjectSize(p->size());
6144     }
6145   }
6146   DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6147   return size;
6148 }
6149 
6150 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
6151   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6152          "CMS thread should hold CMS token");
6153   assert_lock_strong(_freelistLock);
6154   assert_lock_strong(_bitMap->lock());
6155   // relinquish the free_list_lock and bitMaplock()
6156   _bitMap->lock()->unlock();
6157   _freelistLock->unlock();
6158   ConcurrentMarkSweepThread::desynchronize(true);
6159   _collector->stopTimer();
6160   _collector->incrementYields();
6161 
6162   // See the comment in coordinator_yield()
6163   for (unsigned i = 0; i < CMSYieldSleepCount &&
6164                    ConcurrentMarkSweepThread::should_yield() &&
6165                    !CMSCollector::foregroundGCIsActive(); ++i) {
6166     os::sleep(Thread::current(), 1, false);
6167   }
6168 
6169   ConcurrentMarkSweepThread::synchronize(true);
6170   _freelistLock->lock_without_safepoint_check();
6171   _bitMap->lock()->lock_without_safepoint_check();
6172   _collector->startTimer();
6173 }
6174 
6175 
6176 //////////////////////////////////////////////////////////////////
6177 // SurvivorSpacePrecleanClosure
6178 //////////////////////////////////////////////////////////////////
6179 // This (single-threaded) closure is used to preclean the oops in
6180 // the survivor spaces.
6181 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
6182 
6183   HeapWord* addr = (HeapWord*)p;
6184   DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6185   assert(!_span.contains(addr), "we are scanning the survivor spaces");
6186   assert(p->klass_or_null() != NULL, "object should be initialized");
6187   // an initialized object; ignore mark word in verification below
6188   // since we are running concurrent with mutators
6189   assert(p->is_oop(true), "should be an oop");
6190   // Note that we do not yield while we iterate over
6191   // the interior oops of p, pushing the relevant ones
6192   // on our marking stack.
6193   size_t size = p->oop_iterate_size(_scanning_closure);
6194   do_yield_check();
6195   // Observe that below, we do not abandon the preclean
6196   // phase as soon as we should; rather we empty the
6197   // marking stack before returning. This is to satisfy
6198   // some existing assertions. In general, it may be a
6199   // good idea to abort immediately and complete the marking
6200   // from the grey objects at a later time.
6201   while (!_mark_stack->isEmpty()) {
6202     oop new_oop = _mark_stack->pop();
6203     assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6204     assert(_bit_map->isMarked((HeapWord*)new_oop),
6205            "only grey objects on this stack");
6206     // iterate over the oops in this oop, marking and pushing
6207     // the ones in CMS heap (i.e. in _span).
6208     new_oop->oop_iterate(_scanning_closure);
6209     // check if it's time to yield
6210     do_yield_check();
6211   }
6212   unsigned int after_count =
6213     GenCollectedHeap::heap()->total_collections();
6214   bool abort = (_before_count != after_count) ||
6215                _collector->should_abort_preclean();
6216   return abort ? 0 : size;
6217 }
6218 
6219 void SurvivorSpacePrecleanClosure::do_yield_work() {
6220   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6221          "CMS thread should hold CMS token");
6222   assert_lock_strong(_bit_map->lock());
6223   // Relinquish the bit map lock
6224   _bit_map->lock()->unlock();
6225   ConcurrentMarkSweepThread::desynchronize(true);
6226   _collector->stopTimer();
6227   _collector->incrementYields();
6228 
6229   // See the comment in coordinator_yield()
6230   for (unsigned i = 0; i < CMSYieldSleepCount &&
6231                        ConcurrentMarkSweepThread::should_yield() &&
6232                        !CMSCollector::foregroundGCIsActive(); ++i) {
6233     os::sleep(Thread::current(), 1, false);
6234   }
6235 
6236   ConcurrentMarkSweepThread::synchronize(true);
6237   _bit_map->lock()->lock_without_safepoint_check();
6238   _collector->startTimer();
6239 }
6240 
6241 // This closure is used to rescan the marked objects on the dirty cards
6242 // in the mod union table and the card table proper. In the parallel
6243 // case, although the bitMap is shared, we do a single read so the
6244 // isMarked() query is "safe".
6245 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
6246   // Ignore mark word because we are running concurrent with mutators
6247   assert(p->is_oop_or_null(true), "Expected an oop or NULL at " PTR_FORMAT, p2i(p));
6248   HeapWord* addr = (HeapWord*)p;
6249   assert(_span.contains(addr), "we are scanning the CMS generation");
6250   bool is_obj_array = false;
6251   #ifdef ASSERT
6252     if (!_parallel) {
6253       assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6254       assert(_collector->overflow_list_is_empty(),
6255              "overflow list should be empty");
6256 
6257     }
6258   #endif // ASSERT
6259   if (_bit_map->isMarked(addr)) {
6260     // Obj arrays are precisely marked, non-arrays are not;
6261     // so we scan objArrays precisely and non-arrays in their
6262     // entirety.
6263     if (p->is_objArray()) {
6264       is_obj_array = true;
6265       if (_parallel) {
6266         p->oop_iterate(_par_scan_closure, mr);
6267       } else {
6268         p->oop_iterate(_scan_closure, mr);
6269       }
6270     } else {
6271       if (_parallel) {
6272         p->oop_iterate(_par_scan_closure);
6273       } else {
6274         p->oop_iterate(_scan_closure);
6275       }
6276     }
6277   }
6278   #ifdef ASSERT
6279     if (!_parallel) {
6280       assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6281       assert(_collector->overflow_list_is_empty(),
6282              "overflow list should be empty");
6283 
6284     }
6285   #endif // ASSERT
6286   return is_obj_array;
6287 }
6288 
6289 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
6290                         MemRegion span,
6291                         CMSBitMap* bitMap, CMSMarkStack*  markStack,
6292                         bool should_yield, bool verifying):
6293   _collector(collector),
6294   _span(span),
6295   _bitMap(bitMap),
6296   _mut(&collector->_modUnionTable),
6297   _markStack(markStack),
6298   _yield(should_yield),
6299   _skipBits(0)
6300 {
6301   assert(_markStack->isEmpty(), "stack should be empty");
6302   _finger = _bitMap->startWord();
6303   _threshold = _finger;
6304   assert(_collector->_restart_addr == NULL, "Sanity check");
6305   assert(_span.contains(_finger), "Out of bounds _finger?");
6306   DEBUG_ONLY(_verifying = verifying;)
6307 }
6308 
6309 void MarkFromRootsClosure::reset(HeapWord* addr) {
6310   assert(_markStack->isEmpty(), "would cause duplicates on stack");
6311   assert(_span.contains(addr), "Out of bounds _finger?");
6312   _finger = addr;
6313   _threshold = (HeapWord*)round_to(
6314                  (intptr_t)_finger, CardTableModRefBS::card_size);
6315 }
6316 
6317 // Should revisit to see if this should be restructured for
6318 // greater efficiency.
6319 bool MarkFromRootsClosure::do_bit(size_t offset) {
6320   if (_skipBits > 0) {
6321     _skipBits--;
6322     return true;
6323   }
6324   // convert offset into a HeapWord*
6325   HeapWord* addr = _bitMap->startWord() + offset;
6326   assert(_bitMap->endWord() && addr < _bitMap->endWord(),
6327          "address out of range");
6328   assert(_bitMap->isMarked(addr), "tautology");
6329   if (_bitMap->isMarked(addr+1)) {
6330     // this is an allocated but not yet initialized object
6331     assert(_skipBits == 0, "tautology");
6332     _skipBits = 2;  // skip next two marked bits ("Printezis-marks")
6333     oop p = oop(addr);
6334     if (p->klass_or_null() == NULL) {
6335       DEBUG_ONLY(if (!_verifying) {)
6336         // We re-dirty the cards on which this object lies and increase
6337         // the _threshold so that we'll come back to scan this object
6338         // during the preclean or remark phase. (CMSCleanOnEnter)
6339         if (CMSCleanOnEnter) {
6340           size_t sz = _collector->block_size_using_printezis_bits(addr);
6341           HeapWord* end_card_addr   = (HeapWord*)round_to(
6342                                          (intptr_t)(addr+sz), CardTableModRefBS::card_size);
6343           MemRegion redirty_range = MemRegion(addr, end_card_addr);
6344           assert(!redirty_range.is_empty(), "Arithmetical tautology");
6345           // Bump _threshold to end_card_addr; note that
6346           // _threshold cannot possibly exceed end_card_addr, anyhow.
6347           // This prevents future clearing of the card as the scan proceeds
6348           // to the right.
6349           assert(_threshold <= end_card_addr,
6350                  "Because we are just scanning into this object");
6351           if (_threshold < end_card_addr) {
6352             _threshold = end_card_addr;
6353           }
6354           if (p->klass_or_null() != NULL) {
6355             // Redirty the range of cards...
6356             _mut->mark_range(redirty_range);
6357           } // ...else the setting of klass will dirty the card anyway.
6358         }
6359       DEBUG_ONLY(})
6360       return true;
6361     }
6362   }
6363   scanOopsInOop(addr);
6364   return true;
6365 }
6366 
6367 // We take a break if we've been at this for a while,
6368 // so as to avoid monopolizing the locks involved.
6369 void MarkFromRootsClosure::do_yield_work() {
6370   // First give up the locks, then yield, then re-lock
6371   // We should probably use a constructor/destructor idiom to
6372   // do this unlock/lock or modify the MutexUnlocker class to
6373   // serve our purpose. XXX
6374   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6375          "CMS thread should hold CMS token");
6376   assert_lock_strong(_bitMap->lock());
6377   _bitMap->lock()->unlock();
6378   ConcurrentMarkSweepThread::desynchronize(true);
6379   _collector->stopTimer();
6380   _collector->incrementYields();
6381 
6382   // See the comment in coordinator_yield()
6383   for (unsigned i = 0; i < CMSYieldSleepCount &&
6384                        ConcurrentMarkSweepThread::should_yield() &&
6385                        !CMSCollector::foregroundGCIsActive(); ++i) {
6386     os::sleep(Thread::current(), 1, false);
6387   }
6388 
6389   ConcurrentMarkSweepThread::synchronize(true);
6390   _bitMap->lock()->lock_without_safepoint_check();
6391   _collector->startTimer();
6392 }
6393 
6394 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
6395   assert(_bitMap->isMarked(ptr), "expected bit to be set");
6396   assert(_markStack->isEmpty(),
6397          "should drain stack to limit stack usage");
6398   // convert ptr to an oop preparatory to scanning
6399   oop obj = oop(ptr);
6400   // Ignore mark word in verification below, since we
6401   // may be running concurrent with mutators.
6402   assert(obj->is_oop(true), "should be an oop");
6403   assert(_finger <= ptr, "_finger runneth ahead");
6404   // advance the finger to right end of this object
6405   _finger = ptr + obj->size();
6406   assert(_finger > ptr, "we just incremented it above");
6407   // On large heaps, it may take us some time to get through
6408   // the marking phase. During
6409   // this time it's possible that a lot of mutations have
6410   // accumulated in the card table and the mod union table --
6411   // these mutation records are redundant until we have
6412   // actually traced into the corresponding card.
6413   // Here, we check whether advancing the finger would make
6414   // us cross into a new card, and if so clear corresponding
6415   // cards in the MUT (preclean them in the card-table in the
6416   // future).
6417 
6418   DEBUG_ONLY(if (!_verifying) {)
6419     // The clean-on-enter optimization is disabled by default,
6420     // until we fix 6178663.
6421     if (CMSCleanOnEnter && (_finger > _threshold)) {
6422       // [_threshold, _finger) represents the interval
6423       // of cards to be cleared  in MUT (or precleaned in card table).
6424       // The set of cards to be cleared is all those that overlap
6425       // with the interval [_threshold, _finger); note that
6426       // _threshold is always kept card-aligned but _finger isn't
6427       // always card-aligned.
6428       HeapWord* old_threshold = _threshold;
6429       assert(old_threshold == (HeapWord*)round_to(
6430               (intptr_t)old_threshold, CardTableModRefBS::card_size),
6431              "_threshold should always be card-aligned");
6432       _threshold = (HeapWord*)round_to(
6433                      (intptr_t)_finger, CardTableModRefBS::card_size);
6434       MemRegion mr(old_threshold, _threshold);
6435       assert(!mr.is_empty(), "Control point invariant");
6436       assert(_span.contains(mr), "Should clear within span");
6437       _mut->clear_range(mr);
6438     }
6439   DEBUG_ONLY(})
6440   // Note: the finger doesn't advance while we drain
6441   // the stack below.
6442   PushOrMarkClosure pushOrMarkClosure(_collector,
6443                                       _span, _bitMap, _markStack,
6444                                       _finger, this);
6445   bool res = _markStack->push(obj);
6446   assert(res, "Empty non-zero size stack should have space for single push");
6447   while (!_markStack->isEmpty()) {
6448     oop new_oop = _markStack->pop();
6449     // Skip verifying header mark word below because we are
6450     // running concurrent with mutators.
6451     assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
6452     // now scan this oop's oops
6453     new_oop->oop_iterate(&pushOrMarkClosure);
6454     do_yield_check();
6455   }
6456   assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
6457 }
6458 
6459 ParMarkFromRootsClosure::ParMarkFromRootsClosure(CMSConcMarkingTask* task,
6460                        CMSCollector* collector, MemRegion span,
6461                        CMSBitMap* bit_map,
6462                        OopTaskQueue* work_queue,
6463                        CMSMarkStack*  overflow_stack):
6464   _collector(collector),
6465   _whole_span(collector->_span),
6466   _span(span),
6467   _bit_map(bit_map),
6468   _mut(&collector->_modUnionTable),
6469   _work_queue(work_queue),
6470   _overflow_stack(overflow_stack),
6471   _skip_bits(0),
6472   _task(task)
6473 {
6474   assert(_work_queue->size() == 0, "work_queue should be empty");
6475   _finger = span.start();
6476   _threshold = _finger;     // XXX Defer clear-on-enter optimization for now
6477   assert(_span.contains(_finger), "Out of bounds _finger?");
6478 }
6479 
6480 // Should revisit to see if this should be restructured for
6481 // greater efficiency.
6482 bool ParMarkFromRootsClosure::do_bit(size_t offset) {
6483   if (_skip_bits > 0) {
6484     _skip_bits--;
6485     return true;
6486   }
6487   // convert offset into a HeapWord*
6488   HeapWord* addr = _bit_map->startWord() + offset;
6489   assert(_bit_map->endWord() && addr < _bit_map->endWord(),
6490          "address out of range");
6491   assert(_bit_map->isMarked(addr), "tautology");
6492   if (_bit_map->isMarked(addr+1)) {
6493     // this is an allocated object that might not yet be initialized
6494     assert(_skip_bits == 0, "tautology");
6495     _skip_bits = 2;  // skip next two marked bits ("Printezis-marks")
6496     oop p = oop(addr);
6497     if (p->klass_or_null() == NULL) {
6498       // in the case of Clean-on-Enter optimization, redirty card
6499       // and avoid clearing card by increasing  the threshold.
6500       return true;
6501     }
6502   }
6503   scan_oops_in_oop(addr);
6504   return true;
6505 }
6506 
6507 void ParMarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
6508   assert(_bit_map->isMarked(ptr), "expected bit to be set");
6509   // Should we assert that our work queue is empty or
6510   // below some drain limit?
6511   assert(_work_queue->size() == 0,
6512          "should drain stack to limit stack usage");
6513   // convert ptr to an oop preparatory to scanning
6514   oop obj = oop(ptr);
6515   // Ignore mark word in verification below, since we
6516   // may be running concurrent with mutators.
6517   assert(obj->is_oop(true), "should be an oop");
6518   assert(_finger <= ptr, "_finger runneth ahead");
6519   // advance the finger to right end of this object
6520   _finger = ptr + obj->size();
6521   assert(_finger > ptr, "we just incremented it above");
6522   // On large heaps, it may take us some time to get through
6523   // the marking phase. During
6524   // this time it's possible that a lot of mutations have
6525   // accumulated in the card table and the mod union table --
6526   // these mutation records are redundant until we have
6527   // actually traced into the corresponding card.
6528   // Here, we check whether advancing the finger would make
6529   // us cross into a new card, and if so clear corresponding
6530   // cards in the MUT (preclean them in the card-table in the
6531   // future).
6532 
6533   // The clean-on-enter optimization is disabled by default,
6534   // until we fix 6178663.
6535   if (CMSCleanOnEnter && (_finger > _threshold)) {
6536     // [_threshold, _finger) represents the interval
6537     // of cards to be cleared  in MUT (or precleaned in card table).
6538     // The set of cards to be cleared is all those that overlap
6539     // with the interval [_threshold, _finger); note that
6540     // _threshold is always kept card-aligned but _finger isn't
6541     // always card-aligned.
6542     HeapWord* old_threshold = _threshold;
6543     assert(old_threshold == (HeapWord*)round_to(
6544             (intptr_t)old_threshold, CardTableModRefBS::card_size),
6545            "_threshold should always be card-aligned");
6546     _threshold = (HeapWord*)round_to(
6547                    (intptr_t)_finger, CardTableModRefBS::card_size);
6548     MemRegion mr(old_threshold, _threshold);
6549     assert(!mr.is_empty(), "Control point invariant");
6550     assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
6551     _mut->clear_range(mr);
6552   }
6553 
6554   // Note: the local finger doesn't advance while we drain
6555   // the stack below, but the global finger sure can and will.
6556   HeapWord** gfa = _task->global_finger_addr();
6557   ParPushOrMarkClosure pushOrMarkClosure(_collector,
6558                                          _span, _bit_map,
6559                                          _work_queue,
6560                                          _overflow_stack,
6561                                          _finger,
6562                                          gfa, this);
6563   bool res = _work_queue->push(obj);   // overflow could occur here
6564   assert(res, "Will hold once we use workqueues");
6565   while (true) {
6566     oop new_oop;
6567     if (!_work_queue->pop_local(new_oop)) {
6568       // We emptied our work_queue; check if there's stuff that can
6569       // be gotten from the overflow stack.
6570       if (CMSConcMarkingTask::get_work_from_overflow_stack(
6571             _overflow_stack, _work_queue)) {
6572         do_yield_check();
6573         continue;
6574       } else {  // done
6575         break;
6576       }
6577     }
6578     // Skip verifying header mark word below because we are
6579     // running concurrent with mutators.
6580     assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
6581     // now scan this oop's oops
6582     new_oop->oop_iterate(&pushOrMarkClosure);
6583     do_yield_check();
6584   }
6585   assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
6586 }
6587 
6588 // Yield in response to a request from VM Thread or
6589 // from mutators.
6590 void ParMarkFromRootsClosure::do_yield_work() {
6591   assert(_task != NULL, "sanity");
6592   _task->yield();
6593 }
6594 
6595 // A variant of the above used for verifying CMS marking work.
6596 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
6597                         MemRegion span,
6598                         CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6599                         CMSMarkStack*  mark_stack):
6600   _collector(collector),
6601   _span(span),
6602   _verification_bm(verification_bm),
6603   _cms_bm(cms_bm),
6604   _mark_stack(mark_stack),
6605   _pam_verify_closure(collector, span, verification_bm, cms_bm,
6606                       mark_stack)
6607 {
6608   assert(_mark_stack->isEmpty(), "stack should be empty");
6609   _finger = _verification_bm->startWord();
6610   assert(_collector->_restart_addr == NULL, "Sanity check");
6611   assert(_span.contains(_finger), "Out of bounds _finger?");
6612 }
6613 
6614 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
6615   assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
6616   assert(_span.contains(addr), "Out of bounds _finger?");
6617   _finger = addr;
6618 }
6619 
6620 // Should revisit to see if this should be restructured for
6621 // greater efficiency.
6622 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
6623   // convert offset into a HeapWord*
6624   HeapWord* addr = _verification_bm->startWord() + offset;
6625   assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
6626          "address out of range");
6627   assert(_verification_bm->isMarked(addr), "tautology");
6628   assert(_cms_bm->isMarked(addr), "tautology");
6629 
6630   assert(_mark_stack->isEmpty(),
6631          "should drain stack to limit stack usage");
6632   // convert addr to an oop preparatory to scanning
6633   oop obj = oop(addr);
6634   assert(obj->is_oop(), "should be an oop");
6635   assert(_finger <= addr, "_finger runneth ahead");
6636   // advance the finger to right end of this object
6637   _finger = addr + obj->size();
6638   assert(_finger > addr, "we just incremented it above");
6639   // Note: the finger doesn't advance while we drain
6640   // the stack below.
6641   bool res = _mark_stack->push(obj);
6642   assert(res, "Empty non-zero size stack should have space for single push");
6643   while (!_mark_stack->isEmpty()) {
6644     oop new_oop = _mark_stack->pop();
6645     assert(new_oop->is_oop(), "Oops! expected to pop an oop");
6646     // now scan this oop's oops
6647     new_oop->oop_iterate(&_pam_verify_closure);
6648   }
6649   assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
6650   return true;
6651 }
6652 
6653 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
6654   CMSCollector* collector, MemRegion span,
6655   CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6656   CMSMarkStack*  mark_stack):
6657   MetadataAwareOopClosure(collector->ref_processor()),
6658   _collector(collector),
6659   _span(span),
6660   _verification_bm(verification_bm),
6661   _cms_bm(cms_bm),
6662   _mark_stack(mark_stack)
6663 { }
6664 
6665 void PushAndMarkVerifyClosure::do_oop(oop* p)       { PushAndMarkVerifyClosure::do_oop_work(p); }
6666 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
6667 
6668 // Upon stack overflow, we discard (part of) the stack,
6669 // remembering the least address amongst those discarded
6670 // in CMSCollector's _restart_address.
6671 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
6672   // Remember the least grey address discarded
6673   HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
6674   _collector->lower_restart_addr(ra);
6675   _mark_stack->reset();  // discard stack contents
6676   _mark_stack->expand(); // expand the stack if possible
6677 }
6678 
6679 void PushAndMarkVerifyClosure::do_oop(oop obj) {
6680   assert(obj->is_oop_or_null(), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6681   HeapWord* addr = (HeapWord*)obj;
6682   if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
6683     // Oop lies in _span and isn't yet grey or black
6684     _verification_bm->mark(addr);            // now grey
6685     if (!_cms_bm->isMarked(addr)) {
6686       Log(gc, verify) log;
6687       ResourceMark rm;
6688       oop(addr)->print_on(log.error_stream());
6689       log.error(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
6690       fatal("... aborting");
6691     }
6692 
6693     if (!_mark_stack->push(obj)) { // stack overflow
6694       log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _mark_stack->capacity());
6695       assert(_mark_stack->isFull(), "Else push should have succeeded");
6696       handle_stack_overflow(addr);
6697     }
6698     // anything including and to the right of _finger
6699     // will be scanned as we iterate over the remainder of the
6700     // bit map
6701   }
6702 }
6703 
6704 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
6705                      MemRegion span,
6706                      CMSBitMap* bitMap, CMSMarkStack*  markStack,
6707                      HeapWord* finger, MarkFromRootsClosure* parent) :
6708   MetadataAwareOopClosure(collector->ref_processor()),
6709   _collector(collector),
6710   _span(span),
6711   _bitMap(bitMap),
6712   _markStack(markStack),
6713   _finger(finger),
6714   _parent(parent)
6715 { }
6716 
6717 ParPushOrMarkClosure::ParPushOrMarkClosure(CMSCollector* collector,
6718                                            MemRegion span,
6719                                            CMSBitMap* bit_map,
6720                                            OopTaskQueue* work_queue,
6721                                            CMSMarkStack*  overflow_stack,
6722                                            HeapWord* finger,
6723                                            HeapWord** global_finger_addr,
6724                                            ParMarkFromRootsClosure* parent) :
6725   MetadataAwareOopClosure(collector->ref_processor()),
6726   _collector(collector),
6727   _whole_span(collector->_span),
6728   _span(span),
6729   _bit_map(bit_map),
6730   _work_queue(work_queue),
6731   _overflow_stack(overflow_stack),
6732   _finger(finger),
6733   _global_finger_addr(global_finger_addr),
6734   _parent(parent)
6735 { }
6736 
6737 // Assumes thread-safe access by callers, who are
6738 // responsible for mutual exclusion.
6739 void CMSCollector::lower_restart_addr(HeapWord* low) {
6740   assert(_span.contains(low), "Out of bounds addr");
6741   if (_restart_addr == NULL) {
6742     _restart_addr = low;
6743   } else {
6744     _restart_addr = MIN2(_restart_addr, low);
6745   }
6746 }
6747 
6748 // Upon stack overflow, we discard (part of) the stack,
6749 // remembering the least address amongst those discarded
6750 // in CMSCollector's _restart_address.
6751 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
6752   // Remember the least grey address discarded
6753   HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
6754   _collector->lower_restart_addr(ra);
6755   _markStack->reset();  // discard stack contents
6756   _markStack->expand(); // expand the stack if possible
6757 }
6758 
6759 // Upon stack overflow, we discard (part of) the stack,
6760 // remembering the least address amongst those discarded
6761 // in CMSCollector's _restart_address.
6762 void ParPushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
6763   // We need to do this under a mutex to prevent other
6764   // workers from interfering with the work done below.
6765   MutexLockerEx ml(_overflow_stack->par_lock(),
6766                    Mutex::_no_safepoint_check_flag);
6767   // Remember the least grey address discarded
6768   HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
6769   _collector->lower_restart_addr(ra);
6770   _overflow_stack->reset();  // discard stack contents
6771   _overflow_stack->expand(); // expand the stack if possible
6772 }
6773 
6774 void PushOrMarkClosure::do_oop(oop obj) {
6775   // Ignore mark word because we are running concurrent with mutators.
6776   assert(obj->is_oop_or_null(true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6777   HeapWord* addr = (HeapWord*)obj;
6778   if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
6779     // Oop lies in _span and isn't yet grey or black
6780     _bitMap->mark(addr);            // now grey
6781     if (addr < _finger) {
6782       // the bit map iteration has already either passed, or
6783       // sampled, this bit in the bit map; we'll need to
6784       // use the marking stack to scan this oop's oops.
6785       bool simulate_overflow = false;
6786       NOT_PRODUCT(
6787         if (CMSMarkStackOverflowALot &&
6788             _collector->simulate_overflow()) {
6789           // simulate a stack overflow
6790           simulate_overflow = true;
6791         }
6792       )
6793       if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
6794         log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _markStack->capacity());
6795         assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
6796         handle_stack_overflow(addr);
6797       }
6798     }
6799     // anything including and to the right of _finger
6800     // will be scanned as we iterate over the remainder of the
6801     // bit map
6802     do_yield_check();
6803   }
6804 }
6805 
6806 void PushOrMarkClosure::do_oop(oop* p)       { PushOrMarkClosure::do_oop_work(p); }
6807 void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); }
6808 
6809 void ParPushOrMarkClosure::do_oop(oop obj) {
6810   // Ignore mark word because we are running concurrent with mutators.
6811   assert(obj->is_oop_or_null(true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6812   HeapWord* addr = (HeapWord*)obj;
6813   if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
6814     // Oop lies in _span and isn't yet grey or black
6815     // We read the global_finger (volatile read) strictly after marking oop
6816     bool res = _bit_map->par_mark(addr);    // now grey
6817     volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
6818     // Should we push this marked oop on our stack?
6819     // -- if someone else marked it, nothing to do
6820     // -- if target oop is above global finger nothing to do
6821     // -- if target oop is in chunk and above local finger
6822     //      then nothing to do
6823     // -- else push on work queue
6824     if (   !res       // someone else marked it, they will deal with it
6825         || (addr >= *gfa)  // will be scanned in a later task
6826         || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
6827       return;
6828     }
6829     // the bit map iteration has already either passed, or
6830     // sampled, this bit in the bit map; we'll need to
6831     // use the marking stack to scan this oop's oops.
6832     bool simulate_overflow = false;
6833     NOT_PRODUCT(
6834       if (CMSMarkStackOverflowALot &&
6835           _collector->simulate_overflow()) {
6836         // simulate a stack overflow
6837         simulate_overflow = true;
6838       }
6839     )
6840     if (simulate_overflow ||
6841         !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
6842       // stack overflow
6843       log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _overflow_stack->capacity());
6844       // We cannot assert that the overflow stack is full because
6845       // it may have been emptied since.
6846       assert(simulate_overflow ||
6847              _work_queue->size() == _work_queue->max_elems(),
6848             "Else push should have succeeded");
6849       handle_stack_overflow(addr);
6850     }
6851     do_yield_check();
6852   }
6853 }
6854 
6855 void ParPushOrMarkClosure::do_oop(oop* p)       { ParPushOrMarkClosure::do_oop_work(p); }
6856 void ParPushOrMarkClosure::do_oop(narrowOop* p) { ParPushOrMarkClosure::do_oop_work(p); }
6857 
6858 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
6859                                        MemRegion span,
6860                                        ReferenceProcessor* rp,
6861                                        CMSBitMap* bit_map,
6862                                        CMSBitMap* mod_union_table,
6863                                        CMSMarkStack*  mark_stack,
6864                                        bool           concurrent_precleaning):
6865   MetadataAwareOopClosure(rp),
6866   _collector(collector),
6867   _span(span),
6868   _bit_map(bit_map),
6869   _mod_union_table(mod_union_table),
6870   _mark_stack(mark_stack),
6871   _concurrent_precleaning(concurrent_precleaning)
6872 {
6873   assert(ref_processor() != NULL, "ref_processor shouldn't be NULL");
6874 }
6875 
6876 // Grey object rescan during pre-cleaning and second checkpoint phases --
6877 // the non-parallel version (the parallel version appears further below.)
6878 void PushAndMarkClosure::do_oop(oop obj) {
6879   // Ignore mark word verification. If during concurrent precleaning,
6880   // the object monitor may be locked. If during the checkpoint
6881   // phases, the object may already have been reached by a  different
6882   // path and may be at the end of the global overflow list (so
6883   // the mark word may be NULL).
6884   assert(obj->is_oop_or_null(true /* ignore mark word */),
6885          "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6886   HeapWord* addr = (HeapWord*)obj;
6887   // Check if oop points into the CMS generation
6888   // and is not marked
6889   if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
6890     // a white object ...
6891     _bit_map->mark(addr);         // ... now grey
6892     // push on the marking stack (grey set)
6893     bool simulate_overflow = false;
6894     NOT_PRODUCT(
6895       if (CMSMarkStackOverflowALot &&
6896           _collector->simulate_overflow()) {
6897         // simulate a stack overflow
6898         simulate_overflow = true;
6899       }
6900     )
6901     if (simulate_overflow || !_mark_stack->push(obj)) {
6902       if (_concurrent_precleaning) {
6903          // During precleaning we can just dirty the appropriate card(s)
6904          // in the mod union table, thus ensuring that the object remains
6905          // in the grey set  and continue. In the case of object arrays
6906          // we need to dirty all of the cards that the object spans,
6907          // since the rescan of object arrays will be limited to the
6908          // dirty cards.
6909          // Note that no one can be interfering with us in this action
6910          // of dirtying the mod union table, so no locking or atomics
6911          // are required.
6912          if (obj->is_objArray()) {
6913            size_t sz = obj->size();
6914            HeapWord* end_card_addr = (HeapWord*)round_to(
6915                                         (intptr_t)(addr+sz), CardTableModRefBS::card_size);
6916            MemRegion redirty_range = MemRegion(addr, end_card_addr);
6917            assert(!redirty_range.is_empty(), "Arithmetical tautology");
6918            _mod_union_table->mark_range(redirty_range);
6919          } else {
6920            _mod_union_table->mark(addr);
6921          }
6922          _collector->_ser_pmc_preclean_ovflw++;
6923       } else {
6924          // During the remark phase, we need to remember this oop
6925          // in the overflow list.
6926          _collector->push_on_overflow_list(obj);
6927          _collector->_ser_pmc_remark_ovflw++;
6928       }
6929     }
6930   }
6931 }
6932 
6933 ParPushAndMarkClosure::ParPushAndMarkClosure(CMSCollector* collector,
6934                                              MemRegion span,
6935                                              ReferenceProcessor* rp,
6936                                              CMSBitMap* bit_map,
6937                                              OopTaskQueue* work_queue):
6938   MetadataAwareOopClosure(rp),
6939   _collector(collector),
6940   _span(span),
6941   _bit_map(bit_map),
6942   _work_queue(work_queue)
6943 {
6944   assert(ref_processor() != NULL, "ref_processor shouldn't be NULL");
6945 }
6946 
6947 void PushAndMarkClosure::do_oop(oop* p)       { PushAndMarkClosure::do_oop_work(p); }
6948 void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); }
6949 
6950 // Grey object rescan during second checkpoint phase --
6951 // the parallel version.
6952 void ParPushAndMarkClosure::do_oop(oop obj) {
6953   // In the assert below, we ignore the mark word because
6954   // this oop may point to an already visited object that is
6955   // on the overflow stack (in which case the mark word has
6956   // been hijacked for chaining into the overflow stack --
6957   // if this is the last object in the overflow stack then
6958   // its mark word will be NULL). Because this object may
6959   // have been subsequently popped off the global overflow
6960   // stack, and the mark word possibly restored to the prototypical
6961   // value, by the time we get to examined this failing assert in
6962   // the debugger, is_oop_or_null(false) may subsequently start
6963   // to hold.
6964   assert(obj->is_oop_or_null(true),
6965          "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6966   HeapWord* addr = (HeapWord*)obj;
6967   // Check if oop points into the CMS generation
6968   // and is not marked
6969   if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
6970     // a white object ...
6971     // If we manage to "claim" the object, by being the
6972     // first thread to mark it, then we push it on our
6973     // marking stack
6974     if (_bit_map->par_mark(addr)) {     // ... now grey
6975       // push on work queue (grey set)
6976       bool simulate_overflow = false;
6977       NOT_PRODUCT(
6978         if (CMSMarkStackOverflowALot &&
6979             _collector->par_simulate_overflow()) {
6980           // simulate a stack overflow
6981           simulate_overflow = true;
6982         }
6983       )
6984       if (simulate_overflow || !_work_queue->push(obj)) {
6985         _collector->par_push_on_overflow_list(obj);
6986         _collector->_par_pmc_remark_ovflw++; //  imprecise OK: no need to CAS
6987       }
6988     } // Else, some other thread got there first
6989   }
6990 }
6991 
6992 void ParPushAndMarkClosure::do_oop(oop* p)       { ParPushAndMarkClosure::do_oop_work(p); }
6993 void ParPushAndMarkClosure::do_oop(narrowOop* p) { ParPushAndMarkClosure::do_oop_work(p); }
6994 
6995 void CMSPrecleanRefsYieldClosure::do_yield_work() {
6996   Mutex* bml = _collector->bitMapLock();
6997   assert_lock_strong(bml);
6998   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6999          "CMS thread should hold CMS token");
7000 
7001   bml->unlock();
7002   ConcurrentMarkSweepThread::desynchronize(true);
7003 
7004   _collector->stopTimer();
7005   _collector->incrementYields();
7006 
7007   // See the comment in coordinator_yield()
7008   for (unsigned i = 0; i < CMSYieldSleepCount &&
7009                        ConcurrentMarkSweepThread::should_yield() &&
7010                        !CMSCollector::foregroundGCIsActive(); ++i) {
7011     os::sleep(Thread::current(), 1, false);
7012   }
7013 
7014   ConcurrentMarkSweepThread::synchronize(true);
7015   bml->lock();
7016 
7017   _collector->startTimer();
7018 }
7019 
7020 bool CMSPrecleanRefsYieldClosure::should_return() {
7021   if (ConcurrentMarkSweepThread::should_yield()) {
7022     do_yield_work();
7023   }
7024   return _collector->foregroundGCIsActive();
7025 }
7026 
7027 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
7028   assert(((size_t)mr.start())%CardTableModRefBS::card_size_in_words == 0,
7029          "mr should be aligned to start at a card boundary");
7030   // We'd like to assert:
7031   // assert(mr.word_size()%CardTableModRefBS::card_size_in_words == 0,
7032   //        "mr should be a range of cards");
7033   // However, that would be too strong in one case -- the last
7034   // partition ends at _unallocated_block which, in general, can be
7035   // an arbitrary boundary, not necessarily card aligned.
7036   _num_dirty_cards += mr.word_size()/CardTableModRefBS::card_size_in_words;
7037   _space->object_iterate_mem(mr, &_scan_cl);
7038 }
7039 
7040 SweepClosure::SweepClosure(CMSCollector* collector,
7041                            ConcurrentMarkSweepGeneration* g,
7042                            CMSBitMap* bitMap, bool should_yield) :
7043   _collector(collector),
7044   _g(g),
7045   _sp(g->cmsSpace()),
7046   _limit(_sp->sweep_limit()),
7047   _freelistLock(_sp->freelistLock()),
7048   _bitMap(bitMap),
7049   _yield(should_yield),
7050   _inFreeRange(false),           // No free range at beginning of sweep
7051   _freeRangeInFreeLists(false),  // No free range at beginning of sweep
7052   _lastFreeRangeCoalesced(false),
7053   _freeFinger(g->used_region().start())
7054 {
7055   NOT_PRODUCT(
7056     _numObjectsFreed = 0;
7057     _numWordsFreed   = 0;
7058     _numObjectsLive = 0;
7059     _numWordsLive = 0;
7060     _numObjectsAlreadyFree = 0;
7061     _numWordsAlreadyFree = 0;
7062     _last_fc = NULL;
7063 
7064     _sp->initializeIndexedFreeListArrayReturnedBytes();
7065     _sp->dictionary()->initialize_dict_returned_bytes();
7066   )
7067   assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7068          "sweep _limit out of bounds");
7069   log_develop_trace(gc, sweep)("====================");
7070   log_develop_trace(gc, sweep)("Starting new sweep with limit " PTR_FORMAT, p2i(_limit));
7071 }
7072 
7073 void SweepClosure::print_on(outputStream* st) const {
7074   st->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")",
7075                p2i(_sp->bottom()), p2i(_sp->end()));
7076   st->print_cr("_limit = " PTR_FORMAT, p2i(_limit));
7077   st->print_cr("_freeFinger = " PTR_FORMAT, p2i(_freeFinger));
7078   NOT_PRODUCT(st->print_cr("_last_fc = " PTR_FORMAT, p2i(_last_fc));)
7079   st->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d",
7080                _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced);
7081 }
7082 
7083 #ifndef PRODUCT
7084 // Assertion checking only:  no useful work in product mode --
7085 // however, if any of the flags below become product flags,
7086 // you may need to review this code to see if it needs to be
7087 // enabled in product mode.
7088 SweepClosure::~SweepClosure() {
7089   assert_lock_strong(_freelistLock);
7090   assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7091          "sweep _limit out of bounds");
7092   if (inFreeRange()) {
7093     Log(gc, sweep) log;
7094     log.error("inFreeRange() should have been reset; dumping state of SweepClosure");
7095     ResourceMark rm;
7096     print_on(log.error_stream());
7097     ShouldNotReachHere();
7098   }
7099 
7100   if (log_is_enabled(Debug, gc, sweep)) {
7101     log_debug(gc, sweep)("Collected " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
7102                          _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
7103     log_debug(gc, sweep)("Live " SIZE_FORMAT " objects,  " SIZE_FORMAT " bytes  Already free " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
7104                          _numObjectsLive, _numWordsLive*sizeof(HeapWord), _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
7105     size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree) * sizeof(HeapWord);
7106     log_debug(gc, sweep)("Total sweep: " SIZE_FORMAT " bytes", totalBytes);
7107   }
7108 
7109   if (log_is_enabled(Trace, gc, sweep) && CMSVerifyReturnedBytes) {
7110     size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
7111     size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes();
7112     size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes;
7113     log_trace(gc, sweep)("Returned " SIZE_FORMAT " bytes   Indexed List Returned " SIZE_FORMAT " bytes        Dictionary Returned " SIZE_FORMAT " bytes",
7114                          returned_bytes, indexListReturnedBytes, dict_returned_bytes);
7115   }
7116   log_develop_trace(gc, sweep)("end of sweep with _limit = " PTR_FORMAT, p2i(_limit));
7117   log_develop_trace(gc, sweep)("================");
7118 }
7119 #endif  // PRODUCT
7120 
7121 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
7122     bool freeRangeInFreeLists) {
7123   log_develop_trace(gc, sweep)("---- Start free range at " PTR_FORMAT " with free block (%d)",
7124                                p2i(freeFinger), freeRangeInFreeLists);
7125   assert(!inFreeRange(), "Trampling existing free range");
7126   set_inFreeRange(true);
7127   set_lastFreeRangeCoalesced(false);
7128 
7129   set_freeFinger(freeFinger);
7130   set_freeRangeInFreeLists(freeRangeInFreeLists);
7131   if (CMSTestInFreeList) {
7132     if (freeRangeInFreeLists) {
7133       FreeChunk* fc = (FreeChunk*) freeFinger;
7134       assert(fc->is_free(), "A chunk on the free list should be free.");
7135       assert(fc->size() > 0, "Free range should have a size");
7136       assert(_sp->verify_chunk_in_free_list(fc), "Chunk is not in free lists");
7137     }
7138   }
7139 }
7140 
7141 // Note that the sweeper runs concurrently with mutators. Thus,
7142 // it is possible for direct allocation in this generation to happen
7143 // in the middle of the sweep. Note that the sweeper also coalesces
7144 // contiguous free blocks. Thus, unless the sweeper and the allocator
7145 // synchronize appropriately freshly allocated blocks may get swept up.
7146 // This is accomplished by the sweeper locking the free lists while
7147 // it is sweeping. Thus blocks that are determined to be free are
7148 // indeed free. There is however one additional complication:
7149 // blocks that have been allocated since the final checkpoint and
7150 // mark, will not have been marked and so would be treated as
7151 // unreachable and swept up. To prevent this, the allocator marks
7152 // the bit map when allocating during the sweep phase. This leads,
7153 // however, to a further complication -- objects may have been allocated
7154 // but not yet initialized -- in the sense that the header isn't yet
7155 // installed. The sweeper can not then determine the size of the block
7156 // in order to skip over it. To deal with this case, we use a technique
7157 // (due to Printezis) to encode such uninitialized block sizes in the
7158 // bit map. Since the bit map uses a bit per every HeapWord, but the
7159 // CMS generation has a minimum object size of 3 HeapWords, it follows
7160 // that "normal marks" won't be adjacent in the bit map (there will
7161 // always be at least two 0 bits between successive 1 bits). We make use
7162 // of these "unused" bits to represent uninitialized blocks -- the bit
7163 // corresponding to the start of the uninitialized object and the next
7164 // bit are both set. Finally, a 1 bit marks the end of the object that
7165 // started with the two consecutive 1 bits to indicate its potentially
7166 // uninitialized state.
7167 
7168 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
7169   FreeChunk* fc = (FreeChunk*)addr;
7170   size_t res;
7171 
7172   // Check if we are done sweeping. Below we check "addr >= _limit" rather
7173   // than "addr == _limit" because although _limit was a block boundary when
7174   // we started the sweep, it may no longer be one because heap expansion
7175   // may have caused us to coalesce the block ending at the address _limit
7176   // with a newly expanded chunk (this happens when _limit was set to the
7177   // previous _end of the space), so we may have stepped past _limit:
7178   // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740.
7179   if (addr >= _limit) { // we have swept up to or past the limit: finish up
7180     assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7181            "sweep _limit out of bounds");
7182     assert(addr < _sp->end(), "addr out of bounds");
7183     // Flush any free range we might be holding as a single
7184     // coalesced chunk to the appropriate free list.
7185     if (inFreeRange()) {
7186       assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit,
7187              "freeFinger() " PTR_FORMAT " is out-of-bounds", p2i(freeFinger()));
7188       flush_cur_free_chunk(freeFinger(),
7189                            pointer_delta(addr, freeFinger()));
7190       log_develop_trace(gc, sweep)("Sweep: last chunk: put_free_blk " PTR_FORMAT " (" SIZE_FORMAT ") [coalesced:%d]",
7191                                    p2i(freeFinger()), pointer_delta(addr, freeFinger()),
7192                                    lastFreeRangeCoalesced() ? 1 : 0);
7193     }
7194 
7195     // help the iterator loop finish
7196     return pointer_delta(_sp->end(), addr);
7197   }
7198 
7199   assert(addr < _limit, "sweep invariant");
7200   // check if we should yield
7201   do_yield_check(addr);
7202   if (fc->is_free()) {
7203     // Chunk that is already free
7204     res = fc->size();
7205     do_already_free_chunk(fc);
7206     debug_only(_sp->verifyFreeLists());
7207     // If we flush the chunk at hand in lookahead_and_flush()
7208     // and it's coalesced with a preceding chunk, then the
7209     // process of "mangling" the payload of the coalesced block
7210     // will cause erasure of the size information from the
7211     // (erstwhile) header of all the coalesced blocks but the
7212     // first, so the first disjunct in the assert will not hold
7213     // in that specific case (in which case the second disjunct
7214     // will hold).
7215     assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit,
7216            "Otherwise the size info doesn't change at this step");
7217     NOT_PRODUCT(
7218       _numObjectsAlreadyFree++;
7219       _numWordsAlreadyFree += res;
7220     )
7221     NOT_PRODUCT(_last_fc = fc;)
7222   } else if (!_bitMap->isMarked(addr)) {
7223     // Chunk is fresh garbage
7224     res = do_garbage_chunk(fc);
7225     debug_only(_sp->verifyFreeLists());
7226     NOT_PRODUCT(
7227       _numObjectsFreed++;
7228       _numWordsFreed += res;
7229     )
7230   } else {
7231     // Chunk that is alive.
7232     res = do_live_chunk(fc);
7233     debug_only(_sp->verifyFreeLists());
7234     NOT_PRODUCT(
7235         _numObjectsLive++;
7236         _numWordsLive += res;
7237     )
7238   }
7239   return res;
7240 }
7241 
7242 // For the smart allocation, record following
7243 //  split deaths - a free chunk is removed from its free list because
7244 //      it is being split into two or more chunks.
7245 //  split birth - a free chunk is being added to its free list because
7246 //      a larger free chunk has been split and resulted in this free chunk.
7247 //  coal death - a free chunk is being removed from its free list because
7248 //      it is being coalesced into a large free chunk.
7249 //  coal birth - a free chunk is being added to its free list because
7250 //      it was created when two or more free chunks where coalesced into
7251 //      this free chunk.
7252 //
7253 // These statistics are used to determine the desired number of free
7254 // chunks of a given size.  The desired number is chosen to be relative
7255 // to the end of a CMS sweep.  The desired number at the end of a sweep
7256 // is the
7257 //      count-at-end-of-previous-sweep (an amount that was enough)
7258 //              - count-at-beginning-of-current-sweep  (the excess)
7259 //              + split-births  (gains in this size during interval)
7260 //              - split-deaths  (demands on this size during interval)
7261 // where the interval is from the end of one sweep to the end of the
7262 // next.
7263 //
7264 // When sweeping the sweeper maintains an accumulated chunk which is
7265 // the chunk that is made up of chunks that have been coalesced.  That
7266 // will be termed the left-hand chunk.  A new chunk of garbage that
7267 // is being considered for coalescing will be referred to as the
7268 // right-hand chunk.
7269 //
7270 // When making a decision on whether to coalesce a right-hand chunk with
7271 // the current left-hand chunk, the current count vs. the desired count
7272 // of the left-hand chunk is considered.  Also if the right-hand chunk
7273 // is near the large chunk at the end of the heap (see
7274 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
7275 // left-hand chunk is coalesced.
7276 //
7277 // When making a decision about whether to split a chunk, the desired count
7278 // vs. the current count of the candidate to be split is also considered.
7279 // If the candidate is underpopulated (currently fewer chunks than desired)
7280 // a chunk of an overpopulated (currently more chunks than desired) size may
7281 // be chosen.  The "hint" associated with a free list, if non-null, points
7282 // to a free list which may be overpopulated.
7283 //
7284 
7285 void SweepClosure::do_already_free_chunk(FreeChunk* fc) {
7286   const size_t size = fc->size();
7287   // Chunks that cannot be coalesced are not in the
7288   // free lists.
7289   if (CMSTestInFreeList && !fc->cantCoalesce()) {
7290     assert(_sp->verify_chunk_in_free_list(fc),
7291            "free chunk should be in free lists");
7292   }
7293   // a chunk that is already free, should not have been
7294   // marked in the bit map
7295   HeapWord* const addr = (HeapWord*) fc;
7296   assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
7297   // Verify that the bit map has no bits marked between
7298   // addr and purported end of this block.
7299   _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7300 
7301   // Some chunks cannot be coalesced under any circumstances.
7302   // See the definition of cantCoalesce().
7303   if (!fc->cantCoalesce()) {
7304     // This chunk can potentially be coalesced.
7305     // All the work is done in
7306     do_post_free_or_garbage_chunk(fc, size);
7307     // Note that if the chunk is not coalescable (the else arm
7308     // below), we unconditionally flush, without needing to do
7309     // a "lookahead," as we do below.
7310     if (inFreeRange()) lookahead_and_flush(fc, size);
7311   } else {
7312     // Code path common to both original and adaptive free lists.
7313 
7314     // cant coalesce with previous block; this should be treated
7315     // as the end of a free run if any
7316     if (inFreeRange()) {
7317       // we kicked some butt; time to pick up the garbage
7318       assert(freeFinger() < addr, "freeFinger points too high");
7319       flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7320     }
7321     // else, nothing to do, just continue
7322   }
7323 }
7324 
7325 size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) {
7326   // This is a chunk of garbage.  It is not in any free list.
7327   // Add it to a free list or let it possibly be coalesced into
7328   // a larger chunk.
7329   HeapWord* const addr = (HeapWord*) fc;
7330   const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7331 
7332   // Verify that the bit map has no bits marked between
7333   // addr and purported end of just dead object.
7334   _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7335   do_post_free_or_garbage_chunk(fc, size);
7336 
7337   assert(_limit >= addr + size,
7338          "A freshly garbage chunk can't possibly straddle over _limit");
7339   if (inFreeRange()) lookahead_and_flush(fc, size);
7340   return size;
7341 }
7342 
7343 size_t SweepClosure::do_live_chunk(FreeChunk* fc) {
7344   HeapWord* addr = (HeapWord*) fc;
7345   // The sweeper has just found a live object. Return any accumulated
7346   // left hand chunk to the free lists.
7347   if (inFreeRange()) {
7348     assert(freeFinger() < addr, "freeFinger points too high");
7349     flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7350   }
7351 
7352   // This object is live: we'd normally expect this to be
7353   // an oop, and like to assert the following:
7354   // assert(oop(addr)->is_oop(), "live block should be an oop");
7355   // However, as we commented above, this may be an object whose
7356   // header hasn't yet been initialized.
7357   size_t size;
7358   assert(_bitMap->isMarked(addr), "Tautology for this control point");
7359   if (_bitMap->isMarked(addr + 1)) {
7360     // Determine the size from the bit map, rather than trying to
7361     // compute it from the object header.
7362     HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
7363     size = pointer_delta(nextOneAddr + 1, addr);
7364     assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
7365            "alignment problem");
7366 
7367 #ifdef ASSERT
7368       if (oop(addr)->klass_or_null() != NULL) {
7369         // Ignore mark word because we are running concurrent with mutators
7370         assert(oop(addr)->is_oop(true), "live block should be an oop");
7371         assert(size ==
7372                CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
7373                "P-mark and computed size do not agree");
7374       }
7375 #endif
7376 
7377   } else {
7378     // This should be an initialized object that's alive.
7379     assert(oop(addr)->klass_or_null() != NULL,
7380            "Should be an initialized object");
7381     // Ignore mark word because we are running concurrent with mutators
7382     assert(oop(addr)->is_oop(true), "live block should be an oop");
7383     // Verify that the bit map has no bits marked between
7384     // addr and purported end of this block.
7385     size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7386     assert(size >= 3, "Necessary for Printezis marks to work");
7387     assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
7388     DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
7389   }
7390   return size;
7391 }
7392 
7393 void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc,
7394                                                  size_t chunkSize) {
7395   // do_post_free_or_garbage_chunk() should only be called in the case
7396   // of the adaptive free list allocator.
7397   const bool fcInFreeLists = fc->is_free();
7398   assert((HeapWord*)fc <= _limit, "sweep invariant");
7399   if (CMSTestInFreeList && fcInFreeLists) {
7400     assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists");
7401   }
7402 
7403   log_develop_trace(gc, sweep)("  -- pick up another chunk at " PTR_FORMAT " (" SIZE_FORMAT ")", p2i(fc), chunkSize);
7404 
7405   HeapWord* const fc_addr = (HeapWord*) fc;
7406 
7407   bool coalesce = false;
7408   const size_t left  = pointer_delta(fc_addr, freeFinger());
7409   const size_t right = chunkSize;
7410   switch (FLSCoalescePolicy) {
7411     // numeric value forms a coalition aggressiveness metric
7412     case 0:  { // never coalesce
7413       coalesce = false;
7414       break;
7415     }
7416     case 1: { // coalesce if left & right chunks on overpopulated lists
7417       coalesce = _sp->coalOverPopulated(left) &&
7418                  _sp->coalOverPopulated(right);
7419       break;
7420     }
7421     case 2: { // coalesce if left chunk on overpopulated list (default)
7422       coalesce = _sp->coalOverPopulated(left);
7423       break;
7424     }
7425     case 3: { // coalesce if left OR right chunk on overpopulated list
7426       coalesce = _sp->coalOverPopulated(left) ||
7427                  _sp->coalOverPopulated(right);
7428       break;
7429     }
7430     case 4: { // always coalesce
7431       coalesce = true;
7432       break;
7433     }
7434     default:
7435      ShouldNotReachHere();
7436   }
7437 
7438   // Should the current free range be coalesced?
7439   // If the chunk is in a free range and either we decided to coalesce above
7440   // or the chunk is near the large block at the end of the heap
7441   // (isNearLargestChunk() returns true), then coalesce this chunk.
7442   const bool doCoalesce = inFreeRange()
7443                           && (coalesce || _g->isNearLargestChunk(fc_addr));
7444   if (doCoalesce) {
7445     // Coalesce the current free range on the left with the new
7446     // chunk on the right.  If either is on a free list,
7447     // it must be removed from the list and stashed in the closure.
7448     if (freeRangeInFreeLists()) {
7449       FreeChunk* const ffc = (FreeChunk*)freeFinger();
7450       assert(ffc->size() == pointer_delta(fc_addr, freeFinger()),
7451              "Size of free range is inconsistent with chunk size.");
7452       if (CMSTestInFreeList) {
7453         assert(_sp->verify_chunk_in_free_list(ffc),
7454                "Chunk is not in free lists");
7455       }
7456       _sp->coalDeath(ffc->size());
7457       _sp->removeFreeChunkFromFreeLists(ffc);
7458       set_freeRangeInFreeLists(false);
7459     }
7460     if (fcInFreeLists) {
7461       _sp->coalDeath(chunkSize);
7462       assert(fc->size() == chunkSize,
7463         "The chunk has the wrong size or is not in the free lists");
7464       _sp->removeFreeChunkFromFreeLists(fc);
7465     }
7466     set_lastFreeRangeCoalesced(true);
7467     print_free_block_coalesced(fc);
7468   } else {  // not in a free range and/or should not coalesce
7469     // Return the current free range and start a new one.
7470     if (inFreeRange()) {
7471       // In a free range but cannot coalesce with the right hand chunk.
7472       // Put the current free range into the free lists.
7473       flush_cur_free_chunk(freeFinger(),
7474                            pointer_delta(fc_addr, freeFinger()));
7475     }
7476     // Set up for new free range.  Pass along whether the right hand
7477     // chunk is in the free lists.
7478     initialize_free_range((HeapWord*)fc, fcInFreeLists);
7479   }
7480 }
7481 
7482 // Lookahead flush:
7483 // If we are tracking a free range, and this is the last chunk that
7484 // we'll look at because its end crosses past _limit, we'll preemptively
7485 // flush it along with any free range we may be holding on to. Note that
7486 // this can be the case only for an already free or freshly garbage
7487 // chunk. If this block is an object, it can never straddle
7488 // over _limit. The "straddling" occurs when _limit is set at
7489 // the previous end of the space when this cycle started, and
7490 // a subsequent heap expansion caused the previously co-terminal
7491 // free block to be coalesced with the newly expanded portion,
7492 // thus rendering _limit a non-block-boundary making it dangerous
7493 // for the sweeper to step over and examine.
7494 void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) {
7495   assert(inFreeRange(), "Should only be called if currently in a free range.");
7496   HeapWord* const eob = ((HeapWord*)fc) + chunk_size;
7497   assert(_sp->used_region().contains(eob - 1),
7498          "eob = " PTR_FORMAT " eob-1 = " PTR_FORMAT " _limit = " PTR_FORMAT
7499          " out of bounds wrt _sp = [" PTR_FORMAT "," PTR_FORMAT ")"
7500          " when examining fc = " PTR_FORMAT "(" SIZE_FORMAT ")",
7501          p2i(eob), p2i(eob-1), p2i(_limit), p2i(_sp->bottom()), p2i(_sp->end()), p2i(fc), chunk_size);
7502   if (eob >= _limit) {
7503     assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit");
7504     log_develop_trace(gc, sweep)("_limit " PTR_FORMAT " reached or crossed by block "
7505                                  "[" PTR_FORMAT "," PTR_FORMAT ") in space "
7506                                  "[" PTR_FORMAT "," PTR_FORMAT ")",
7507                                  p2i(_limit), p2i(fc), p2i(eob), p2i(_sp->bottom()), p2i(_sp->end()));
7508     // Return the storage we are tracking back into the free lists.
7509     log_develop_trace(gc, sweep)("Flushing ... ");
7510     assert(freeFinger() < eob, "Error");
7511     flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger()));
7512   }
7513 }
7514 
7515 void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) {
7516   assert(inFreeRange(), "Should only be called if currently in a free range.");
7517   assert(size > 0,
7518     "A zero sized chunk cannot be added to the free lists.");
7519   if (!freeRangeInFreeLists()) {
7520     if (CMSTestInFreeList) {
7521       FreeChunk* fc = (FreeChunk*) chunk;
7522       fc->set_size(size);
7523       assert(!_sp->verify_chunk_in_free_list(fc),
7524              "chunk should not be in free lists yet");
7525     }
7526     log_develop_trace(gc, sweep)(" -- add free block " PTR_FORMAT " (" SIZE_FORMAT ") to free lists", p2i(chunk), size);
7527     // A new free range is going to be starting.  The current
7528     // free range has not been added to the free lists yet or
7529     // was removed so add it back.
7530     // If the current free range was coalesced, then the death
7531     // of the free range was recorded.  Record a birth now.
7532     if (lastFreeRangeCoalesced()) {
7533       _sp->coalBirth(size);
7534     }
7535     _sp->addChunkAndRepairOffsetTable(chunk, size,
7536             lastFreeRangeCoalesced());
7537   } else {
7538     log_develop_trace(gc, sweep)("Already in free list: nothing to flush");
7539   }
7540   set_inFreeRange(false);
7541   set_freeRangeInFreeLists(false);
7542 }
7543 
7544 // We take a break if we've been at this for a while,
7545 // so as to avoid monopolizing the locks involved.
7546 void SweepClosure::do_yield_work(HeapWord* addr) {
7547   // Return current free chunk being used for coalescing (if any)
7548   // to the appropriate freelist.  After yielding, the next
7549   // free block encountered will start a coalescing range of
7550   // free blocks.  If the next free block is adjacent to the
7551   // chunk just flushed, they will need to wait for the next
7552   // sweep to be coalesced.
7553   if (inFreeRange()) {
7554     flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7555   }
7556 
7557   // First give up the locks, then yield, then re-lock.
7558   // We should probably use a constructor/destructor idiom to
7559   // do this unlock/lock or modify the MutexUnlocker class to
7560   // serve our purpose. XXX
7561   assert_lock_strong(_bitMap->lock());
7562   assert_lock_strong(_freelistLock);
7563   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7564          "CMS thread should hold CMS token");
7565   _bitMap->lock()->unlock();
7566   _freelistLock->unlock();
7567   ConcurrentMarkSweepThread::desynchronize(true);
7568   _collector->stopTimer();
7569   _collector->incrementYields();
7570 
7571   // See the comment in coordinator_yield()
7572   for (unsigned i = 0; i < CMSYieldSleepCount &&
7573                        ConcurrentMarkSweepThread::should_yield() &&
7574                        !CMSCollector::foregroundGCIsActive(); ++i) {
7575     os::sleep(Thread::current(), 1, false);
7576   }
7577 
7578   ConcurrentMarkSweepThread::synchronize(true);
7579   _freelistLock->lock();
7580   _bitMap->lock()->lock_without_safepoint_check();
7581   _collector->startTimer();
7582 }
7583 
7584 #ifndef PRODUCT
7585 // This is actually very useful in a product build if it can
7586 // be called from the debugger.  Compile it into the product
7587 // as needed.
7588 bool debug_verify_chunk_in_free_list(FreeChunk* fc) {
7589   return debug_cms_space->verify_chunk_in_free_list(fc);
7590 }
7591 #endif
7592 
7593 void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const {
7594   log_develop_trace(gc, sweep)("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")",
7595                                p2i(fc), fc->size());
7596 }
7597 
7598 // CMSIsAliveClosure
7599 bool CMSIsAliveClosure::do_object_b(oop obj) {
7600   HeapWord* addr = (HeapWord*)obj;
7601   return addr != NULL &&
7602          (!_span.contains(addr) || _bit_map->isMarked(addr));
7603 }
7604 
7605 
7606 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector,
7607                       MemRegion span,
7608                       CMSBitMap* bit_map, CMSMarkStack* mark_stack,
7609                       bool cpc):
7610   _collector(collector),
7611   _span(span),
7612   _bit_map(bit_map),
7613   _mark_stack(mark_stack),
7614   _concurrent_precleaning(cpc) {
7615   assert(!_span.is_empty(), "Empty span could spell trouble");
7616 }
7617 
7618 
7619 // CMSKeepAliveClosure: the serial version
7620 void CMSKeepAliveClosure::do_oop(oop obj) {
7621   HeapWord* addr = (HeapWord*)obj;
7622   if (_span.contains(addr) &&
7623       !_bit_map->isMarked(addr)) {
7624     _bit_map->mark(addr);
7625     bool simulate_overflow = false;
7626     NOT_PRODUCT(
7627       if (CMSMarkStackOverflowALot &&
7628           _collector->simulate_overflow()) {
7629         // simulate a stack overflow
7630         simulate_overflow = true;
7631       }
7632     )
7633     if (simulate_overflow || !_mark_stack->push(obj)) {
7634       if (_concurrent_precleaning) {
7635         // We dirty the overflown object and let the remark
7636         // phase deal with it.
7637         assert(_collector->overflow_list_is_empty(), "Error");
7638         // In the case of object arrays, we need to dirty all of
7639         // the cards that the object spans. No locking or atomics
7640         // are needed since no one else can be mutating the mod union
7641         // table.
7642         if (obj->is_objArray()) {
7643           size_t sz = obj->size();
7644           HeapWord* end_card_addr =
7645             (HeapWord*)round_to((intptr_t)(addr+sz), CardTableModRefBS::card_size);
7646           MemRegion redirty_range = MemRegion(addr, end_card_addr);
7647           assert(!redirty_range.is_empty(), "Arithmetical tautology");
7648           _collector->_modUnionTable.mark_range(redirty_range);
7649         } else {
7650           _collector->_modUnionTable.mark(addr);
7651         }
7652         _collector->_ser_kac_preclean_ovflw++;
7653       } else {
7654         _collector->push_on_overflow_list(obj);
7655         _collector->_ser_kac_ovflw++;
7656       }
7657     }
7658   }
7659 }
7660 
7661 void CMSKeepAliveClosure::do_oop(oop* p)       { CMSKeepAliveClosure::do_oop_work(p); }
7662 void CMSKeepAliveClosure::do_oop(narrowOop* p) { CMSKeepAliveClosure::do_oop_work(p); }
7663 
7664 // CMSParKeepAliveClosure: a parallel version of the above.
7665 // The work queues are private to each closure (thread),
7666 // but (may be) available for stealing by other threads.
7667 void CMSParKeepAliveClosure::do_oop(oop obj) {
7668   HeapWord* addr = (HeapWord*)obj;
7669   if (_span.contains(addr) &&
7670       !_bit_map->isMarked(addr)) {
7671     // In general, during recursive tracing, several threads
7672     // may be concurrently getting here; the first one to
7673     // "tag" it, claims it.
7674     if (_bit_map->par_mark(addr)) {
7675       bool res = _work_queue->push(obj);
7676       assert(res, "Low water mark should be much less than capacity");
7677       // Do a recursive trim in the hope that this will keep
7678       // stack usage lower, but leave some oops for potential stealers
7679       trim_queue(_low_water_mark);
7680     } // Else, another thread got there first
7681   }
7682 }
7683 
7684 void CMSParKeepAliveClosure::do_oop(oop* p)       { CMSParKeepAliveClosure::do_oop_work(p); }
7685 void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
7686 
7687 void CMSParKeepAliveClosure::trim_queue(uint max) {
7688   while (_work_queue->size() > max) {
7689     oop new_oop;
7690     if (_work_queue->pop_local(new_oop)) {
7691       assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
7692       assert(_bit_map->isMarked((HeapWord*)new_oop),
7693              "no white objects on this stack!");
7694       assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
7695       // iterate over the oops in this oop, marking and pushing
7696       // the ones in CMS heap (i.e. in _span).
7697       new_oop->oop_iterate(&_mark_and_push);
7698     }
7699   }
7700 }
7701 
7702 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
7703                                 CMSCollector* collector,
7704                                 MemRegion span, CMSBitMap* bit_map,
7705                                 OopTaskQueue* work_queue):
7706   _collector(collector),
7707   _span(span),
7708   _bit_map(bit_map),
7709   _work_queue(work_queue) { }
7710 
7711 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
7712   HeapWord* addr = (HeapWord*)obj;
7713   if (_span.contains(addr) &&
7714       !_bit_map->isMarked(addr)) {
7715     if (_bit_map->par_mark(addr)) {
7716       bool simulate_overflow = false;
7717       NOT_PRODUCT(
7718         if (CMSMarkStackOverflowALot &&
7719             _collector->par_simulate_overflow()) {
7720           // simulate a stack overflow
7721           simulate_overflow = true;
7722         }
7723       )
7724       if (simulate_overflow || !_work_queue->push(obj)) {
7725         _collector->par_push_on_overflow_list(obj);
7726         _collector->_par_kac_ovflw++;
7727       }
7728     } // Else another thread got there already
7729   }
7730 }
7731 
7732 void CMSInnerParMarkAndPushClosure::do_oop(oop* p)       { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
7733 void CMSInnerParMarkAndPushClosure::do_oop(narrowOop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
7734 
7735 //////////////////////////////////////////////////////////////////
7736 //  CMSExpansionCause                /////////////////////////////
7737 //////////////////////////////////////////////////////////////////
7738 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
7739   switch (cause) {
7740     case _no_expansion:
7741       return "No expansion";
7742     case _satisfy_free_ratio:
7743       return "Free ratio";
7744     case _satisfy_promotion:
7745       return "Satisfy promotion";
7746     case _satisfy_allocation:
7747       return "allocation";
7748     case _allocate_par_lab:
7749       return "Par LAB";
7750     case _allocate_par_spooling_space:
7751       return "Par Spooling Space";
7752     case _adaptive_size_policy:
7753       return "Ergonomics";
7754     default:
7755       return "unknown";
7756   }
7757 }
7758 
7759 void CMSDrainMarkingStackClosure::do_void() {
7760   // the max number to take from overflow list at a time
7761   const size_t num = _mark_stack->capacity()/4;
7762   assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
7763          "Overflow list should be NULL during concurrent phases");
7764   while (!_mark_stack->isEmpty() ||
7765          // if stack is empty, check the overflow list
7766          _collector->take_from_overflow_list(num, _mark_stack)) {
7767     oop obj = _mark_stack->pop();
7768     HeapWord* addr = (HeapWord*)obj;
7769     assert(_span.contains(addr), "Should be within span");
7770     assert(_bit_map->isMarked(addr), "Should be marked");
7771     assert(obj->is_oop(), "Should be an oop");
7772     obj->oop_iterate(_keep_alive);
7773   }
7774 }
7775 
7776 void CMSParDrainMarkingStackClosure::do_void() {
7777   // drain queue
7778   trim_queue(0);
7779 }
7780 
7781 // Trim our work_queue so its length is below max at return
7782 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
7783   while (_work_queue->size() > max) {
7784     oop new_oop;
7785     if (_work_queue->pop_local(new_oop)) {
7786       assert(new_oop->is_oop(), "Expected an oop");
7787       assert(_bit_map->isMarked((HeapWord*)new_oop),
7788              "no white objects on this stack!");
7789       assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
7790       // iterate over the oops in this oop, marking and pushing
7791       // the ones in CMS heap (i.e. in _span).
7792       new_oop->oop_iterate(&_mark_and_push);
7793     }
7794   }
7795 }
7796 
7797 ////////////////////////////////////////////////////////////////////
7798 // Support for Marking Stack Overflow list handling and related code
7799 ////////////////////////////////////////////////////////////////////
7800 // Much of the following code is similar in shape and spirit to the
7801 // code used in ParNewGC. We should try and share that code
7802 // as much as possible in the future.
7803 
7804 #ifndef PRODUCT
7805 // Debugging support for CMSStackOverflowALot
7806 
7807 // It's OK to call this multi-threaded;  the worst thing
7808 // that can happen is that we'll get a bunch of closely
7809 // spaced simulated overflows, but that's OK, in fact
7810 // probably good as it would exercise the overflow code
7811 // under contention.
7812 bool CMSCollector::simulate_overflow() {
7813   if (_overflow_counter-- <= 0) { // just being defensive
7814     _overflow_counter = CMSMarkStackOverflowInterval;
7815     return true;
7816   } else {
7817     return false;
7818   }
7819 }
7820 
7821 bool CMSCollector::par_simulate_overflow() {
7822   return simulate_overflow();
7823 }
7824 #endif
7825 
7826 // Single-threaded
7827 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
7828   assert(stack->isEmpty(), "Expected precondition");
7829   assert(stack->capacity() > num, "Shouldn't bite more than can chew");
7830   size_t i = num;
7831   oop  cur = _overflow_list;
7832   const markOop proto = markOopDesc::prototype();
7833   NOT_PRODUCT(ssize_t n = 0;)
7834   for (oop next; i > 0 && cur != NULL; cur = next, i--) {
7835     next = oop(cur->mark());
7836     cur->set_mark(proto);   // until proven otherwise
7837     assert(cur->is_oop(), "Should be an oop");
7838     bool res = stack->push(cur);
7839     assert(res, "Bit off more than can chew?");
7840     NOT_PRODUCT(n++;)
7841   }
7842   _overflow_list = cur;
7843 #ifndef PRODUCT
7844   assert(_num_par_pushes >= n, "Too many pops?");
7845   _num_par_pushes -=n;
7846 #endif
7847   return !stack->isEmpty();
7848 }
7849 
7850 #define BUSY  (cast_to_oop<intptr_t>(0x1aff1aff))
7851 // (MT-safe) Get a prefix of at most "num" from the list.
7852 // The overflow list is chained through the mark word of
7853 // each object in the list. We fetch the entire list,
7854 // break off a prefix of the right size and return the
7855 // remainder. If other threads try to take objects from
7856 // the overflow list at that time, they will wait for
7857 // some time to see if data becomes available. If (and
7858 // only if) another thread places one or more object(s)
7859 // on the global list before we have returned the suffix
7860 // to the global list, we will walk down our local list
7861 // to find its end and append the global list to
7862 // our suffix before returning it. This suffix walk can
7863 // prove to be expensive (quadratic in the amount of traffic)
7864 // when there are many objects in the overflow list and
7865 // there is much producer-consumer contention on the list.
7866 // *NOTE*: The overflow list manipulation code here and
7867 // in ParNewGeneration:: are very similar in shape,
7868 // except that in the ParNew case we use the old (from/eden)
7869 // copy of the object to thread the list via its klass word.
7870 // Because of the common code, if you make any changes in
7871 // the code below, please check the ParNew version to see if
7872 // similar changes might be needed.
7873 // CR 6797058 has been filed to consolidate the common code.
7874 bool CMSCollector::par_take_from_overflow_list(size_t num,
7875                                                OopTaskQueue* work_q,
7876                                                int no_of_gc_threads) {
7877   assert(work_q->size() == 0, "First empty local work queue");
7878   assert(num < work_q->max_elems(), "Can't bite more than we can chew");
7879   if (_overflow_list == NULL) {
7880     return false;
7881   }
7882   // Grab the entire list; we'll put back a suffix
7883   oop prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
7884   Thread* tid = Thread::current();
7885   // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was
7886   // set to ParallelGCThreads.
7887   size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads;
7888   size_t sleep_time_millis = MAX2((size_t)1, num/100);
7889   // If the list is busy, we spin for a short while,
7890   // sleeping between attempts to get the list.
7891   for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) {
7892     os::sleep(tid, sleep_time_millis, false);
7893     if (_overflow_list == NULL) {
7894       // Nothing left to take
7895       return false;
7896     } else if (_overflow_list != BUSY) {
7897       // Try and grab the prefix
7898       prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
7899     }
7900   }
7901   // If the list was found to be empty, or we spun long
7902   // enough, we give up and return empty-handed. If we leave
7903   // the list in the BUSY state below, it must be the case that
7904   // some other thread holds the overflow list and will set it
7905   // to a non-BUSY state in the future.
7906   if (prefix == NULL || prefix == BUSY) {
7907      // Nothing to take or waited long enough
7908      if (prefix == NULL) {
7909        // Write back the NULL in case we overwrote it with BUSY above
7910        // and it is still the same value.
7911        (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
7912      }
7913      return false;
7914   }
7915   assert(prefix != NULL && prefix != BUSY, "Error");
7916   size_t i = num;
7917   oop cur = prefix;
7918   // Walk down the first "num" objects, unless we reach the end.
7919   for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--);
7920   if (cur->mark() == NULL) {
7921     // We have "num" or fewer elements in the list, so there
7922     // is nothing to return to the global list.
7923     // Write back the NULL in lieu of the BUSY we wrote
7924     // above, if it is still the same value.
7925     if (_overflow_list == BUSY) {
7926       (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
7927     }
7928   } else {
7929     // Chop off the suffix and return it to the global list.
7930     assert(cur->mark() != BUSY, "Error");
7931     oop suffix_head = cur->mark(); // suffix will be put back on global list
7932     cur->set_mark(NULL);           // break off suffix
7933     // It's possible that the list is still in the empty(busy) state
7934     // we left it in a short while ago; in that case we may be
7935     // able to place back the suffix without incurring the cost
7936     // of a walk down the list.
7937     oop observed_overflow_list = _overflow_list;
7938     oop cur_overflow_list = observed_overflow_list;
7939     bool attached = false;
7940     while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
7941       observed_overflow_list =
7942         (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
7943       if (cur_overflow_list == observed_overflow_list) {
7944         attached = true;
7945         break;
7946       } else cur_overflow_list = observed_overflow_list;
7947     }
7948     if (!attached) {
7949       // Too bad, someone else sneaked in (at least) an element; we'll need
7950       // to do a splice. Find tail of suffix so we can prepend suffix to global
7951       // list.
7952       for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark()));
7953       oop suffix_tail = cur;
7954       assert(suffix_tail != NULL && suffix_tail->mark() == NULL,
7955              "Tautology");
7956       observed_overflow_list = _overflow_list;
7957       do {
7958         cur_overflow_list = observed_overflow_list;
7959         if (cur_overflow_list != BUSY) {
7960           // Do the splice ...
7961           suffix_tail->set_mark(markOop(cur_overflow_list));
7962         } else { // cur_overflow_list == BUSY
7963           suffix_tail->set_mark(NULL);
7964         }
7965         // ... and try to place spliced list back on overflow_list ...
7966         observed_overflow_list =
7967           (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
7968       } while (cur_overflow_list != observed_overflow_list);
7969       // ... until we have succeeded in doing so.
7970     }
7971   }
7972 
7973   // Push the prefix elements on work_q
7974   assert(prefix != NULL, "control point invariant");
7975   const markOop proto = markOopDesc::prototype();
7976   oop next;
7977   NOT_PRODUCT(ssize_t n = 0;)
7978   for (cur = prefix; cur != NULL; cur = next) {
7979     next = oop(cur->mark());
7980     cur->set_mark(proto);   // until proven otherwise
7981     assert(cur->is_oop(), "Should be an oop");
7982     bool res = work_q->push(cur);
7983     assert(res, "Bit off more than we can chew?");
7984     NOT_PRODUCT(n++;)
7985   }
7986 #ifndef PRODUCT
7987   assert(_num_par_pushes >= n, "Too many pops?");
7988   Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
7989 #endif
7990   return true;
7991 }
7992 
7993 // Single-threaded
7994 void CMSCollector::push_on_overflow_list(oop p) {
7995   NOT_PRODUCT(_num_par_pushes++;)
7996   assert(p->is_oop(), "Not an oop");
7997   preserve_mark_if_necessary(p);
7998   p->set_mark((markOop)_overflow_list);
7999   _overflow_list = p;
8000 }
8001 
8002 // Multi-threaded; use CAS to prepend to overflow list
8003 void CMSCollector::par_push_on_overflow_list(oop p) {
8004   NOT_PRODUCT(Atomic::inc_ptr(&_num_par_pushes);)
8005   assert(p->is_oop(), "Not an oop");
8006   par_preserve_mark_if_necessary(p);
8007   oop observed_overflow_list = _overflow_list;
8008   oop cur_overflow_list;
8009   do {
8010     cur_overflow_list = observed_overflow_list;
8011     if (cur_overflow_list != BUSY) {
8012       p->set_mark(markOop(cur_overflow_list));
8013     } else {
8014       p->set_mark(NULL);
8015     }
8016     observed_overflow_list =
8017       (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list);
8018   } while (cur_overflow_list != observed_overflow_list);
8019 }
8020 #undef BUSY
8021 
8022 // Single threaded
8023 // General Note on GrowableArray: pushes may silently fail
8024 // because we are (temporarily) out of C-heap for expanding
8025 // the stack. The problem is quite ubiquitous and affects
8026 // a lot of code in the JVM. The prudent thing for GrowableArray
8027 // to do (for now) is to exit with an error. However, that may
8028 // be too draconian in some cases because the caller may be
8029 // able to recover without much harm. For such cases, we
8030 // should probably introduce a "soft_push" method which returns
8031 // an indication of success or failure with the assumption that
8032 // the caller may be able to recover from a failure; code in
8033 // the VM can then be changed, incrementally, to deal with such
8034 // failures where possible, thus, incrementally hardening the VM
8035 // in such low resource situations.
8036 void CMSCollector::preserve_mark_work(oop p, markOop m) {
8037   _preserved_oop_stack.push(p);
8038   _preserved_mark_stack.push(m);
8039   assert(m == p->mark(), "Mark word changed");
8040   assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8041          "bijection");
8042 }
8043 
8044 // Single threaded
8045 void CMSCollector::preserve_mark_if_necessary(oop p) {
8046   markOop m = p->mark();
8047   if (m->must_be_preserved(p)) {
8048     preserve_mark_work(p, m);
8049   }
8050 }
8051 
8052 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
8053   markOop m = p->mark();
8054   if (m->must_be_preserved(p)) {
8055     MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
8056     // Even though we read the mark word without holding
8057     // the lock, we are assured that it will not change
8058     // because we "own" this oop, so no other thread can
8059     // be trying to push it on the overflow list; see
8060     // the assertion in preserve_mark_work() that checks
8061     // that m == p->mark().
8062     preserve_mark_work(p, m);
8063   }
8064 }
8065 
8066 // We should be able to do this multi-threaded,
8067 // a chunk of stack being a task (this is
8068 // correct because each oop only ever appears
8069 // once in the overflow list. However, it's
8070 // not very easy to completely overlap this with
8071 // other operations, so will generally not be done
8072 // until all work's been completed. Because we
8073 // expect the preserved oop stack (set) to be small,
8074 // it's probably fine to do this single-threaded.
8075 // We can explore cleverer concurrent/overlapped/parallel
8076 // processing of preserved marks if we feel the
8077 // need for this in the future. Stack overflow should
8078 // be so rare in practice and, when it happens, its
8079 // effect on performance so great that this will
8080 // likely just be in the noise anyway.
8081 void CMSCollector::restore_preserved_marks_if_any() {
8082   assert(SafepointSynchronize::is_at_safepoint(),
8083          "world should be stopped");
8084   assert(Thread::current()->is_ConcurrentGC_thread() ||
8085          Thread::current()->is_VM_thread(),
8086          "should be single-threaded");
8087   assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8088          "bijection");
8089 
8090   while (!_preserved_oop_stack.is_empty()) {
8091     oop p = _preserved_oop_stack.pop();
8092     assert(p->is_oop(), "Should be an oop");
8093     assert(_span.contains(p), "oop should be in _span");
8094     assert(p->mark() == markOopDesc::prototype(),
8095            "Set when taken from overflow list");
8096     markOop m = _preserved_mark_stack.pop();
8097     p->set_mark(m);
8098   }
8099   assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(),
8100          "stacks were cleared above");
8101 }
8102 
8103 #ifndef PRODUCT
8104 bool CMSCollector::no_preserved_marks() const {
8105   return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty();
8106 }
8107 #endif
8108 
8109 // Transfer some number of overflown objects to usual marking
8110 // stack. Return true if some objects were transferred.
8111 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
8112   size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,
8113                     (size_t)ParGCDesiredObjsFromOverflowList);
8114 
8115   bool res = _collector->take_from_overflow_list(num, _mark_stack);
8116   assert(_collector->overflow_list_is_empty() || res,
8117          "If list is not empty, we should have taken something");
8118   assert(!res || !_mark_stack->isEmpty(),
8119          "If we took something, it should now be on our stack");
8120   return res;
8121 }
8122 
8123 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
8124   size_t res = _sp->block_size_no_stall(addr, _collector);
8125   if (_sp->block_is_obj(addr)) {
8126     if (_live_bit_map->isMarked(addr)) {
8127       // It can't have been dead in a previous cycle
8128       guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
8129     } else {
8130       _dead_bit_map->mark(addr);      // mark the dead object
8131     }
8132   }
8133   // Could be 0, if the block size could not be computed without stalling.
8134   return res;
8135 }
8136 
8137 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() {
8138 
8139   switch (phase) {
8140     case CMSCollector::InitialMarking:
8141       initialize(true  /* fullGC */ ,
8142                  cause /* cause of the GC */,
8143                  true  /* recordGCBeginTime */,
8144                  true  /* recordPreGCUsage */,
8145                  false /* recordPeakUsage */,
8146                  false /* recordPostGCusage */,
8147                  true  /* recordAccumulatedGCTime */,
8148                  false /* recordGCEndTime */,
8149                  false /* countCollection */  );
8150       break;
8151 
8152     case CMSCollector::FinalMarking:
8153       initialize(true  /* fullGC */ ,
8154                  cause /* cause of the GC */,
8155                  false /* recordGCBeginTime */,
8156                  false /* recordPreGCUsage */,
8157                  false /* recordPeakUsage */,
8158                  false /* recordPostGCusage */,
8159                  true  /* recordAccumulatedGCTime */,
8160                  false /* recordGCEndTime */,
8161                  false /* countCollection */  );
8162       break;
8163 
8164     case CMSCollector::Sweeping:
8165       initialize(true  /* fullGC */ ,
8166                  cause /* cause of the GC */,
8167                  false /* recordGCBeginTime */,
8168                  false /* recordPreGCUsage */,
8169                  true  /* recordPeakUsage */,
8170                  true  /* recordPostGCusage */,
8171                  false /* recordAccumulatedGCTime */,
8172                  true  /* recordGCEndTime */,
8173                  true  /* countCollection */  );
8174       break;
8175 
8176     default:
8177       ShouldNotReachHere();
8178   }
8179 }