1 /*
   2  * Copyright (c) 2001, 2017, 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/cmsHeap.hpp"
  33 #include "gc/cms/cmsOopClosures.inline.hpp"
  34 #include "gc/cms/compactibleFreeListSpace.hpp"
  35 #include "gc/cms/concurrentMarkSweepGeneration.inline.hpp"
  36 #include "gc/cms/concurrentMarkSweepThread.hpp"
  37 #include "gc/cms/parNewGeneration.hpp"
  38 #include "gc/cms/vmCMSOperations.hpp"
  39 #include "gc/serial/genMarkSweep.hpp"
  40 #include "gc/serial/tenuredGeneration.hpp"
  41 #include "gc/shared/adaptiveSizePolicy.hpp"
  42 #include "gc/shared/cardGeneration.inline.hpp"
  43 #include "gc/shared/cardTableRS.hpp"
  44 #include "gc/shared/collectedHeap.inline.hpp"
  45 #include "gc/shared/collectorCounters.hpp"
  46 #include "gc/shared/collectorPolicy.hpp"
  47 #include "gc/shared/gcLocker.inline.hpp"
  48 #include "gc/shared/gcPolicyCounters.hpp"
  49 #include "gc/shared/gcTimer.hpp"
  50 #include "gc/shared/gcTrace.hpp"
  51 #include "gc/shared/gcTraceTime.inline.hpp"
  52 #include "gc/shared/genCollectedHeap.hpp"
  53 #include "gc/shared/genOopClosures.inline.hpp"
  54 #include "gc/shared/isGCActiveMark.hpp"
  55 #include "gc/shared/referencePolicy.hpp"
  56 #include "gc/shared/strongRootsScope.hpp"
  57 #include "gc/shared/taskqueue.inline.hpp"
  58 #include "gc/shared/weakProcessor.hpp"
  59 #include "logging/log.hpp"
  60 #include "logging/logStream.hpp"
  61 #include "memory/allocation.hpp"
  62 #include "memory/iterator.inline.hpp"
  63 #include "memory/padded.hpp"
  64 #include "memory/resourceArea.hpp"
  65 #include "oops/oop.inline.hpp"
  66 #include "prims/jvmtiExport.hpp"
  67 #include "runtime/atomic.hpp"
  68 #include "runtime/globals_extension.hpp"
  69 #include "runtime/handles.inline.hpp"
  70 #include "runtime/java.hpp"
  71 #include "runtime/orderAccess.inline.hpp"
  72 #include "runtime/timer.hpp"
  73 #include "runtime/vmThread.hpp"
  74 #include "services/memoryService.hpp"
  75 #include "services/runtimeService.hpp"
  76 #include "utilities/align.hpp"
  77 #include "utilities/stack.inline.hpp"
  78 
  79 // statics
  80 CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL;
  81 bool CMSCollector::_full_gc_requested = false;
  82 GCCause::Cause CMSCollector::_full_gc_cause = GCCause::_no_gc;
  83 
  84 //////////////////////////////////////////////////////////////////
  85 // In support of CMS/VM thread synchronization
  86 //////////////////////////////////////////////////////////////////
  87 // We split use of the CGC_lock into 2 "levels".
  88 // The low-level locking is of the usual CGC_lock monitor. We introduce
  89 // a higher level "token" (hereafter "CMS token") built on top of the
  90 // low level monitor (hereafter "CGC lock").
  91 // The token-passing protocol gives priority to the VM thread. The
  92 // CMS-lock doesn't provide any fairness guarantees, but clients
  93 // should ensure that it is only held for very short, bounded
  94 // durations.
  95 //
  96 // When either of the CMS thread or the VM thread is involved in
  97 // collection operations during which it does not want the other
  98 // thread to interfere, it obtains the CMS token.
  99 //
 100 // If either thread tries to get the token while the other has
 101 // it, that thread waits. However, if the VM thread and CMS thread
 102 // both want the token, then the VM thread gets priority while the
 103 // CMS thread waits. This ensures, for instance, that the "concurrent"
 104 // phases of the CMS thread's work do not block out the VM thread
 105 // for long periods of time as the CMS thread continues to hog
 106 // the token. (See bug 4616232).
 107 //
 108 // The baton-passing functions are, however, controlled by the
 109 // flags _foregroundGCShouldWait and _foregroundGCIsActive,
 110 // and here the low-level CMS lock, not the high level token,
 111 // ensures mutual exclusion.
 112 //
 113 // Two important conditions that we have to satisfy:
 114 // 1. if a thread does a low-level wait on the CMS lock, then it
 115 //    relinquishes the CMS token if it were holding that token
 116 //    when it acquired the low-level CMS lock.
 117 // 2. any low-level notifications on the low-level lock
 118 //    should only be sent when a thread has relinquished the token.
 119 //
 120 // In the absence of either property, we'd have potential deadlock.
 121 //
 122 // We protect each of the CMS (concurrent and sequential) phases
 123 // with the CMS _token_, not the CMS _lock_.
 124 //
 125 // The only code protected by CMS lock is the token acquisition code
 126 // itself, see ConcurrentMarkSweepThread::[de]synchronize(), and the
 127 // baton-passing code.
 128 //
 129 // Unfortunately, i couldn't come up with a good abstraction to factor and
 130 // hide the naked CGC_lock manipulation in the baton-passing code
 131 // further below. That's something we should try to do. Also, the proof
 132 // of correctness of this 2-level locking scheme is far from obvious,
 133 // and potentially quite slippery. We have an uneasy suspicion, for instance,
 134 // that there may be a theoretical possibility of delay/starvation in the
 135 // low-level lock/wait/notify scheme used for the baton-passing because of
 136 // potential interference with the priority scheme embodied in the
 137 // CMS-token-passing protocol. See related comments at a CGC_lock->wait()
 138 // invocation further below and marked with "XXX 20011219YSR".
 139 // Indeed, as we note elsewhere, this may become yet more slippery
 140 // in the presence of multiple CMS and/or multiple VM threads. XXX
 141 
 142 class CMSTokenSync: public StackObj {
 143  private:
 144   bool _is_cms_thread;
 145  public:
 146   CMSTokenSync(bool is_cms_thread):
 147     _is_cms_thread(is_cms_thread) {
 148     assert(is_cms_thread == Thread::current()->is_ConcurrentGC_thread(),
 149            "Incorrect argument to constructor");
 150     ConcurrentMarkSweepThread::synchronize(_is_cms_thread);
 151   }
 152 
 153   ~CMSTokenSync() {
 154     assert(_is_cms_thread ?
 155              ConcurrentMarkSweepThread::cms_thread_has_cms_token() :
 156              ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
 157           "Incorrect state");
 158     ConcurrentMarkSweepThread::desynchronize(_is_cms_thread);
 159   }
 160 };
 161 
 162 // Convenience class that does a CMSTokenSync, and then acquires
 163 // upto three locks.
 164 class CMSTokenSyncWithLocks: public CMSTokenSync {
 165  private:
 166   // Note: locks are acquired in textual declaration order
 167   // and released in the opposite order
 168   MutexLockerEx _locker1, _locker2, _locker3;
 169  public:
 170   CMSTokenSyncWithLocks(bool is_cms_thread, Mutex* mutex1,
 171                         Mutex* mutex2 = NULL, Mutex* mutex3 = NULL):
 172     CMSTokenSync(is_cms_thread),
 173     _locker1(mutex1, Mutex::_no_safepoint_check_flag),
 174     _locker2(mutex2, Mutex::_no_safepoint_check_flag),
 175     _locker3(mutex3, Mutex::_no_safepoint_check_flag)
 176   { }
 177 };
 178 
 179 
 180 //////////////////////////////////////////////////////////////////
 181 //  Concurrent Mark-Sweep Generation /////////////////////////////
 182 //////////////////////////////////////////////////////////////////
 183 
 184 NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;)
 185 
 186 // This struct contains per-thread things necessary to support parallel
 187 // young-gen collection.
 188 class CMSParGCThreadState: public CHeapObj<mtGC> {
 189  public:
 190   CompactibleFreeListSpaceLAB lab;
 191   PromotionInfo promo;
 192 
 193   // Constructor.
 194   CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) {
 195     promo.setSpace(cfls);
 196   }
 197 };
 198 
 199 ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration(
 200      ReservedSpace rs, size_t initial_byte_size, CardTableRS* ct) :
 201   CardGeneration(rs, initial_byte_size, ct),
 202   _dilatation_factor(((double)MinChunkSize)/((double)(CollectedHeap::min_fill_size()))),
 203   _did_compact(false)
 204 {
 205   HeapWord* bottom = (HeapWord*) _virtual_space.low();
 206   HeapWord* end    = (HeapWord*) _virtual_space.high();
 207 
 208   _direct_allocated_words = 0;
 209   NOT_PRODUCT(
 210     _numObjectsPromoted = 0;
 211     _numWordsPromoted = 0;
 212     _numObjectsAllocated = 0;
 213     _numWordsAllocated = 0;
 214   )
 215 
 216   _cmsSpace = new CompactibleFreeListSpace(_bts, MemRegion(bottom, end));
 217   NOT_PRODUCT(debug_cms_space = _cmsSpace;)
 218   _cmsSpace->_old_gen = this;
 219 
 220   _gc_stats = new CMSGCStats();
 221 
 222   // Verify the assumption that FreeChunk::_prev and OopDesc::_klass
 223   // offsets match. The ability to tell free chunks from objects
 224   // depends on this property.
 225   debug_only(
 226     FreeChunk* junk = NULL;
 227     assert(UseCompressedClassPointers ||
 228            junk->prev_addr() == (void*)(oop(junk)->klass_addr()),
 229            "Offset of FreeChunk::_prev within FreeChunk must match"
 230            "  that of OopDesc::_klass within OopDesc");
 231   )
 232 
 233   _par_gc_thread_states = NEW_C_HEAP_ARRAY(CMSParGCThreadState*, ParallelGCThreads, mtGC);
 234   for (uint i = 0; i < ParallelGCThreads; i++) {
 235     _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace());
 236   }
 237 
 238   _incremental_collection_failed = false;
 239   // The "dilatation_factor" is the expansion that can occur on
 240   // account of the fact that the minimum object size in the CMS
 241   // generation may be larger than that in, say, a contiguous young
 242   //  generation.
 243   // Ideally, in the calculation below, we'd compute the dilatation
 244   // factor as: MinChunkSize/(promoting_gen's min object size)
 245   // Since we do not have such a general query interface for the
 246   // promoting generation, we'll instead just use the minimum
 247   // object size (which today is a header's worth of space);
 248   // note that all arithmetic is in units of HeapWords.
 249   assert(MinChunkSize >= CollectedHeap::min_fill_size(), "just checking");
 250   assert(_dilatation_factor >= 1.0, "from previous assert");
 251 }
 252 
 253 
 254 // The field "_initiating_occupancy" represents the occupancy percentage
 255 // at which we trigger a new collection cycle.  Unless explicitly specified
 256 // via CMSInitiatingOccupancyFraction (argument "io" below), it
 257 // is calculated by:
 258 //
 259 //   Let "f" be MinHeapFreeRatio in
 260 //
 261 //    _initiating_occupancy = 100-f +
 262 //                           f * (CMSTriggerRatio/100)
 263 //   where CMSTriggerRatio is the argument "tr" below.
 264 //
 265 // That is, if we assume the heap is at its desired maximum occupancy at the
 266 // end of a collection, we let CMSTriggerRatio of the (purported) free
 267 // space be allocated before initiating a new collection cycle.
 268 //
 269 void ConcurrentMarkSweepGeneration::init_initiating_occupancy(intx io, uintx tr) {
 270   assert(io <= 100 && tr <= 100, "Check the arguments");
 271   if (io >= 0) {
 272     _initiating_occupancy = (double)io / 100.0;
 273   } else {
 274     _initiating_occupancy = ((100 - MinHeapFreeRatio) +
 275                              (double)(tr * MinHeapFreeRatio) / 100.0)
 276                             / 100.0;
 277   }
 278 }
 279 
 280 void ConcurrentMarkSweepGeneration::ref_processor_init() {
 281   assert(collector() != NULL, "no collector");
 282   collector()->ref_processor_init();
 283 }
 284 
 285 void CMSCollector::ref_processor_init() {
 286   if (_ref_processor == NULL) {
 287     // Allocate and initialize a reference processor
 288     _ref_processor =
 289       new ReferenceProcessor(_span,                               // span
 290                              (ParallelGCThreads > 1) && ParallelRefProcEnabled, // mt processing
 291                              ParallelGCThreads,                   // mt processing degree
 292                              _cmsGen->refs_discovery_is_mt(),     // mt discovery
 293                              MAX2(ConcGCThreads, ParallelGCThreads), // mt discovery degree
 294                              _cmsGen->refs_discovery_is_atomic(), // discovery is not atomic
 295                              &_is_alive_closure);                 // closure for liveness info
 296     // Initialize the _ref_processor field of CMSGen
 297     _cmsGen->set_ref_processor(_ref_processor);
 298 
 299   }
 300 }
 301 
 302 AdaptiveSizePolicy* CMSCollector::size_policy() {
 303   CMSHeap* heap = CMSHeap::heap();
 304   return heap->gen_policy()->size_policy();
 305 }
 306 
 307 void ConcurrentMarkSweepGeneration::initialize_performance_counters() {
 308 
 309   const char* gen_name = "old";
 310   GenCollectorPolicy* gcp = CMSHeap::heap()->gen_policy();
 311   // Generation Counters - generation 1, 1 subspace
 312   _gen_counters = new GenerationCounters(gen_name, 1, 1,
 313       gcp->min_old_size(), gcp->max_old_size(), &_virtual_space);
 314 
 315   _space_counters = new GSpaceCounters(gen_name, 0,
 316                                        _virtual_space.reserved_size(),
 317                                        this, _gen_counters);
 318 }
 319 
 320 CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha):
 321   _cms_gen(cms_gen)
 322 {
 323   assert(alpha <= 100, "bad value");
 324   _saved_alpha = alpha;
 325 
 326   // Initialize the alphas to the bootstrap value of 100.
 327   _gc0_alpha = _cms_alpha = 100;
 328 
 329   _cms_begin_time.update();
 330   _cms_end_time.update();
 331 
 332   _gc0_duration = 0.0;
 333   _gc0_period = 0.0;
 334   _gc0_promoted = 0;
 335 
 336   _cms_duration = 0.0;
 337   _cms_period = 0.0;
 338   _cms_allocated = 0;
 339 
 340   _cms_used_at_gc0_begin = 0;
 341   _cms_used_at_gc0_end = 0;
 342   _allow_duty_cycle_reduction = false;
 343   _valid_bits = 0;
 344 }
 345 
 346 double CMSStats::cms_free_adjustment_factor(size_t free) const {
 347   // TBD: CR 6909490
 348   return 1.0;
 349 }
 350 
 351 void CMSStats::adjust_cms_free_adjustment_factor(bool fail, size_t free) {
 352 }
 353 
 354 // If promotion failure handling is on use
 355 // the padded average size of the promotion for each
 356 // young generation collection.
 357 double CMSStats::time_until_cms_gen_full() const {
 358   size_t cms_free = _cms_gen->cmsSpace()->free();
 359   CMSHeap* heap = CMSHeap::heap();
 360   size_t expected_promotion = MIN2(heap->young_gen()->capacity(),
 361                                    (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average());
 362   if (cms_free > expected_promotion) {
 363     // Start a cms collection if there isn't enough space to promote
 364     // for the next young collection.  Use the padded average as
 365     // a safety factor.
 366     cms_free -= expected_promotion;
 367 
 368     // Adjust by the safety factor.
 369     double cms_free_dbl = (double)cms_free;
 370     double cms_adjustment = (100.0 - CMSIncrementalSafetyFactor) / 100.0;
 371     // Apply a further correction factor which tries to adjust
 372     // for recent occurance of concurrent mode failures.
 373     cms_adjustment = cms_adjustment * cms_free_adjustment_factor(cms_free);
 374     cms_free_dbl = cms_free_dbl * cms_adjustment;
 375 
 376     log_trace(gc)("CMSStats::time_until_cms_gen_full: cms_free " SIZE_FORMAT " expected_promotion " SIZE_FORMAT,
 377                   cms_free, expected_promotion);
 378     log_trace(gc)("  cms_free_dbl %f cms_consumption_rate %f", cms_free_dbl, cms_consumption_rate() + 1.0);
 379     // Add 1 in case the consumption rate goes to zero.
 380     return cms_free_dbl / (cms_consumption_rate() + 1.0);
 381   }
 382   return 0.0;
 383 }
 384 
 385 // Compare the duration of the cms collection to the
 386 // time remaining before the cms generation is empty.
 387 // Note that the time from the start of the cms collection
 388 // to the start of the cms sweep (less than the total
 389 // duration of the cms collection) can be used.  This
 390 // has been tried and some applications experienced
 391 // promotion failures early in execution.  This was
 392 // possibly because the averages were not accurate
 393 // enough at the beginning.
 394 double CMSStats::time_until_cms_start() const {
 395   // We add "gc0_period" to the "work" calculation
 396   // below because this query is done (mostly) at the
 397   // end of a scavenge, so we need to conservatively
 398   // account for that much possible delay
 399   // in the query so as to avoid concurrent mode failures
 400   // due to starting the collection just a wee bit too
 401   // late.
 402   double work = cms_duration() + gc0_period();
 403   double deadline = time_until_cms_gen_full();
 404   // If a concurrent mode failure occurred recently, we want to be
 405   // more conservative and halve our expected time_until_cms_gen_full()
 406   if (work > deadline) {
 407     log_develop_trace(gc)("CMSCollector: collect because of anticipated promotion before full %3.7f + %3.7f > %3.7f ",
 408                           cms_duration(), gc0_period(), time_until_cms_gen_full());
 409     return 0.0;
 410   }
 411   return work - deadline;
 412 }
 413 
 414 #ifndef PRODUCT
 415 void CMSStats::print_on(outputStream *st) const {
 416   st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha);
 417   st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo=" SIZE_FORMAT,
 418                gc0_duration(), gc0_period(), gc0_promoted());
 419   st->print(",cms_dur=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT,
 420             cms_duration(), cms_period(), cms_allocated());
 421   st->print(",cms_since_beg=%g,cms_since_end=%g",
 422             cms_time_since_begin(), cms_time_since_end());
 423   st->print(",cms_used_beg=" SIZE_FORMAT ",cms_used_end=" SIZE_FORMAT,
 424             _cms_used_at_gc0_begin, _cms_used_at_gc0_end);
 425 
 426   if (valid()) {
 427     st->print(",promo_rate=%g,cms_alloc_rate=%g",
 428               promotion_rate(), cms_allocation_rate());
 429     st->print(",cms_consumption_rate=%g,time_until_full=%g",
 430               cms_consumption_rate(), time_until_cms_gen_full());
 431   }
 432   st->cr();
 433 }
 434 #endif // #ifndef PRODUCT
 435 
 436 CMSCollector::CollectorState CMSCollector::_collectorState =
 437                              CMSCollector::Idling;
 438 bool CMSCollector::_foregroundGCIsActive = false;
 439 bool CMSCollector::_foregroundGCShouldWait = false;
 440 
 441 CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
 442                            CardTableRS*                   ct,
 443                            ConcurrentMarkSweepPolicy*     cp):
 444   _cmsGen(cmsGen),
 445   _ct(ct),
 446   _ref_processor(NULL),    // will be set later
 447   _conc_workers(NULL),     // may be set later
 448   _abort_preclean(false),
 449   _start_sampling(false),
 450   _between_prologue_and_epilogue(false),
 451   _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"),
 452   _modUnionTable((CardTableModRefBS::card_shift - LogHeapWordSize),
 453                  -1 /* lock-free */, "No_lock" /* dummy */),
 454   _modUnionClosurePar(&_modUnionTable),
 455   // Adjust my span to cover old (cms) gen
 456   _span(cmsGen->reserved()),
 457   // Construct the is_alive_closure with _span & markBitMap
 458   _is_alive_closure(_span, &_markBitMap),
 459   _restart_addr(NULL),
 460   _overflow_list(NULL),
 461   _stats(cmsGen),
 462   _eden_chunk_lock(new Mutex(Mutex::leaf + 1, "CMS_eden_chunk_lock", true,
 463                              //verify that this lock should be acquired with safepoint check.
 464                              Monitor::_safepoint_check_sometimes)),
 465   _eden_chunk_array(NULL),     // may be set in ctor body
 466   _eden_chunk_capacity(0),     // -- ditto --
 467   _eden_chunk_index(0),        // -- ditto --
 468   _survivor_plab_array(NULL),  // -- ditto --
 469   _survivor_chunk_array(NULL), // -- ditto --
 470   _survivor_chunk_capacity(0), // -- ditto --
 471   _survivor_chunk_index(0),    // -- ditto --
 472   _ser_pmc_preclean_ovflw(0),
 473   _ser_kac_preclean_ovflw(0),
 474   _ser_pmc_remark_ovflw(0),
 475   _par_pmc_remark_ovflw(0),
 476   _ser_kac_ovflw(0),
 477   _par_kac_ovflw(0),
 478 #ifndef PRODUCT
 479   _num_par_pushes(0),
 480 #endif
 481   _collection_count_start(0),
 482   _verifying(false),
 483   _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"),
 484   _completed_initialization(false),
 485   _collector_policy(cp),
 486   _should_unload_classes(CMSClassUnloadingEnabled),
 487   _concurrent_cycles_since_last_unload(0),
 488   _roots_scanning_options(GenCollectedHeap::SO_None),
 489   _inter_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
 490   _intra_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
 491   _gc_tracer_cm(new (ResourceObj::C_HEAP, mtGC) CMSTracer()),
 492   _gc_timer_cm(new (ResourceObj::C_HEAP, mtGC) ConcurrentGCTimer()),
 493   _cms_start_registered(false)
 494 {
 495   // Now expand the span and allocate the collection support structures
 496   // (MUT, marking bit map etc.) to cover both generations subject to
 497   // collection.
 498 
 499   // For use by dirty card to oop closures.
 500   _cmsGen->cmsSpace()->set_collector(this);
 501 
 502   // Allocate MUT and marking bit map
 503   {
 504     MutexLockerEx x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag);
 505     if (!_markBitMap.allocate(_span)) {
 506       log_warning(gc)("Failed to allocate CMS Bit Map");
 507       return;
 508     }
 509     assert(_markBitMap.covers(_span), "_markBitMap inconsistency?");
 510   }
 511   {
 512     _modUnionTable.allocate(_span);
 513     assert(_modUnionTable.covers(_span), "_modUnionTable inconsistency?");
 514   }
 515 
 516   if (!_markStack.allocate(MarkStackSize)) {
 517     log_warning(gc)("Failed to allocate CMS Marking Stack");
 518     return;
 519   }
 520 
 521   // Support for multi-threaded concurrent phases
 522   if (CMSConcurrentMTEnabled) {
 523     if (FLAG_IS_DEFAULT(ConcGCThreads)) {
 524       // just for now
 525       FLAG_SET_DEFAULT(ConcGCThreads, (ParallelGCThreads + 3) / 4);
 526     }
 527     if (ConcGCThreads > 1) {
 528       _conc_workers = new YieldingFlexibleWorkGang("CMS Thread",
 529                                  ConcGCThreads, true);
 530       if (_conc_workers == NULL) {
 531         log_warning(gc)("GC/CMS: _conc_workers allocation failure: forcing -CMSConcurrentMTEnabled");
 532         CMSConcurrentMTEnabled = false;
 533       } else {
 534         _conc_workers->initialize_workers();
 535       }
 536     } else {
 537       CMSConcurrentMTEnabled = false;
 538     }
 539   }
 540   if (!CMSConcurrentMTEnabled) {
 541     ConcGCThreads = 0;
 542   } else {
 543     // Turn off CMSCleanOnEnter optimization temporarily for
 544     // the MT case where it's not fixed yet; see 6178663.
 545     CMSCleanOnEnter = false;
 546   }
 547   assert((_conc_workers != NULL) == (ConcGCThreads > 1),
 548          "Inconsistency");
 549   log_debug(gc)("ConcGCThreads: %u", ConcGCThreads);
 550   log_debug(gc)("ParallelGCThreads: %u", ParallelGCThreads);
 551 
 552   // Parallel task queues; these are shared for the
 553   // concurrent and stop-world phases of CMS, but
 554   // are not shared with parallel scavenge (ParNew).
 555   {
 556     uint i;
 557     uint num_queues = MAX2(ParallelGCThreads, ConcGCThreads);
 558 
 559     if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled
 560          || ParallelRefProcEnabled)
 561         && num_queues > 0) {
 562       _task_queues = new OopTaskQueueSet(num_queues);
 563       if (_task_queues == NULL) {
 564         log_warning(gc)("task_queues allocation failure.");
 565         return;
 566       }
 567       _hash_seed = NEW_C_HEAP_ARRAY(int, num_queues, mtGC);
 568       typedef Padded<OopTaskQueue> PaddedOopTaskQueue;
 569       for (i = 0; i < num_queues; i++) {
 570         PaddedOopTaskQueue *q = new PaddedOopTaskQueue();
 571         if (q == NULL) {
 572           log_warning(gc)("work_queue allocation failure.");
 573           return;
 574         }
 575         _task_queues->register_queue(i, q);
 576       }
 577       for (i = 0; i < num_queues; i++) {
 578         _task_queues->queue(i)->initialize();
 579         _hash_seed[i] = 17;  // copied from ParNew
 580       }
 581     }
 582   }
 583 
 584   _cmsGen ->init_initiating_occupancy(CMSInitiatingOccupancyFraction, CMSTriggerRatio);
 585 
 586   // Clip CMSBootstrapOccupancy between 0 and 100.
 587   _bootstrap_occupancy = CMSBootstrapOccupancy / 100.0;
 588 
 589   // Now tell CMS generations the identity of their collector
 590   ConcurrentMarkSweepGeneration::set_collector(this);
 591 
 592   // Create & start a CMS thread for this CMS collector
 593   _cmsThread = ConcurrentMarkSweepThread::start(this);
 594   assert(cmsThread() != NULL, "CMS Thread should have been created");
 595   assert(cmsThread()->collector() == this,
 596          "CMS Thread should refer to this gen");
 597   assert(CGC_lock != NULL, "Where's the CGC_lock?");
 598 
 599   // Support for parallelizing young gen rescan
 600   CMSHeap* heap = CMSHeap::heap();
 601   assert(heap->young_gen()->kind() == Generation::ParNew, "CMS can only be used with ParNew");
 602   _young_gen = (ParNewGeneration*)heap->young_gen();
 603   if (heap->supports_inline_contig_alloc()) {
 604     _top_addr = heap->top_addr();
 605     _end_addr = heap->end_addr();
 606     assert(_young_gen != NULL, "no _young_gen");
 607     _eden_chunk_index = 0;
 608     _eden_chunk_capacity = (_young_gen->max_capacity() + CMSSamplingGrain) / CMSSamplingGrain;
 609     _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity, mtGC);
 610   }
 611 
 612   // Support for parallelizing survivor space rescan
 613   if ((CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) || CMSParallelInitialMarkEnabled) {
 614     const size_t max_plab_samples =
 615       _young_gen->max_survivor_size() / (PLAB::min_size() * HeapWordSize);
 616 
 617     _survivor_plab_array  = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads, mtGC);
 618     _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
 619     _cursor               = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads, mtGC);
 620     _survivor_chunk_capacity = max_plab_samples;
 621     for (uint i = 0; i < ParallelGCThreads; i++) {
 622       HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
 623       ChunkArray* cur = ::new (&_survivor_plab_array[i]) ChunkArray(vec, max_plab_samples);
 624       assert(cur->end() == 0, "Should be 0");
 625       assert(cur->array() == vec, "Should be vec");
 626       assert(cur->capacity() == max_plab_samples, "Error");
 627     }
 628   }
 629 
 630   NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;)
 631   _gc_counters = new CollectorCounters("CMS", 1);
 632   _completed_initialization = true;
 633   _inter_sweep_timer.start();  // start of time
 634 }
 635 
 636 const char* ConcurrentMarkSweepGeneration::name() const {
 637   return "concurrent mark-sweep generation";
 638 }
 639 void ConcurrentMarkSweepGeneration::update_counters() {
 640   if (UsePerfData) {
 641     _space_counters->update_all();
 642     _gen_counters->update_all();
 643   }
 644 }
 645 
 646 // this is an optimized version of update_counters(). it takes the
 647 // used value as a parameter rather than computing it.
 648 //
 649 void ConcurrentMarkSweepGeneration::update_counters(size_t used) {
 650   if (UsePerfData) {
 651     _space_counters->update_used(used);
 652     _space_counters->update_capacity();
 653     _gen_counters->update_all();
 654   }
 655 }
 656 
 657 void ConcurrentMarkSweepGeneration::print() const {
 658   Generation::print();
 659   cmsSpace()->print();
 660 }
 661 
 662 #ifndef PRODUCT
 663 void ConcurrentMarkSweepGeneration::print_statistics() {
 664   cmsSpace()->printFLCensus(0);
 665 }
 666 #endif
 667 
 668 size_t
 669 ConcurrentMarkSweepGeneration::contiguous_available() const {
 670   // dld proposes an improvement in precision here. If the committed
 671   // part of the space ends in a free block we should add that to
 672   // uncommitted size in the calculation below. Will make this
 673   // change later, staying with the approximation below for the
 674   // time being. -- ysr.
 675   return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc());
 676 }
 677 
 678 size_t
 679 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const {
 680   return _cmsSpace->max_alloc_in_words() * HeapWordSize;
 681 }
 682 
 683 size_t ConcurrentMarkSweepGeneration::max_available() const {
 684   return free() + _virtual_space.uncommitted_size();
 685 }
 686 
 687 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(size_t max_promotion_in_bytes) const {
 688   size_t available = max_available();
 689   size_t av_promo  = (size_t)gc_stats()->avg_promoted()->padded_average();
 690   bool   res = (available >= av_promo) || (available >= max_promotion_in_bytes);
 691   log_trace(gc, promotion)("CMS: promo attempt is%s safe: available(" SIZE_FORMAT ") %s av_promo(" SIZE_FORMAT "), max_promo(" SIZE_FORMAT ")",
 692                            res? "":" not", available, res? ">=":"<", av_promo, max_promotion_in_bytes);
 693   return res;
 694 }
 695 
 696 // At a promotion failure dump information on block layout in heap
 697 // (cms old generation).
 698 void ConcurrentMarkSweepGeneration::promotion_failure_occurred() {
 699   Log(gc, promotion) log;
 700   if (log.is_trace()) {
 701     LogStream ls(log.trace());
 702     cmsSpace()->dump_at_safepoint_with_locks(collector(), &ls);
 703   }
 704 }
 705 
 706 void ConcurrentMarkSweepGeneration::reset_after_compaction() {
 707   // Clear the promotion information.  These pointers can be adjusted
 708   // along with all the other pointers into the heap but
 709   // compaction is expected to be a rare event with
 710   // a heap using cms so don't do it without seeing the need.
 711   for (uint i = 0; i < ParallelGCThreads; i++) {
 712     _par_gc_thread_states[i]->promo.reset();
 713   }
 714 }
 715 
 716 void ConcurrentMarkSweepGeneration::compute_new_size() {
 717   assert_locked_or_safepoint(Heap_lock);
 718 
 719   // If incremental collection failed, we just want to expand
 720   // to the limit.
 721   if (incremental_collection_failed()) {
 722     clear_incremental_collection_failed();
 723     grow_to_reserved();
 724     return;
 725   }
 726 
 727   // The heap has been compacted but not reset yet.
 728   // Any metric such as free() or used() will be incorrect.
 729 
 730   CardGeneration::compute_new_size();
 731 
 732   // Reset again after a possible resizing
 733   if (did_compact()) {
 734     cmsSpace()->reset_after_compaction();
 735   }
 736 }
 737 
 738 void ConcurrentMarkSweepGeneration::compute_new_size_free_list() {
 739   assert_locked_or_safepoint(Heap_lock);
 740 
 741   // If incremental collection failed, we just want to expand
 742   // to the limit.
 743   if (incremental_collection_failed()) {
 744     clear_incremental_collection_failed();
 745     grow_to_reserved();
 746     return;
 747   }
 748 
 749   double free_percentage = ((double) free()) / capacity();
 750   double desired_free_percentage = (double) MinHeapFreeRatio / 100;
 751   double maximum_free_percentage = (double) MaxHeapFreeRatio / 100;
 752 
 753   // compute expansion delta needed for reaching desired free percentage
 754   if (free_percentage < desired_free_percentage) {
 755     size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
 756     assert(desired_capacity >= capacity(), "invalid expansion size");
 757     size_t expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes);
 758     Log(gc) log;
 759     if (log.is_trace()) {
 760       size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
 761       log.trace("From compute_new_size: ");
 762       log.trace("  Free fraction %f", free_percentage);
 763       log.trace("  Desired free fraction %f", desired_free_percentage);
 764       log.trace("  Maximum free fraction %f", maximum_free_percentage);
 765       log.trace("  Capacity " SIZE_FORMAT, capacity() / 1000);
 766       log.trace("  Desired capacity " SIZE_FORMAT, desired_capacity / 1000);
 767       CMSHeap* heap = CMSHeap::heap();
 768       assert(heap->is_old_gen(this), "The CMS generation should always be the old generation");
 769       size_t young_size = heap->young_gen()->capacity();
 770       log.trace("  Young gen size " SIZE_FORMAT, young_size / 1000);
 771       log.trace("  unsafe_max_alloc_nogc " SIZE_FORMAT, unsafe_max_alloc_nogc() / 1000);
 772       log.trace("  contiguous available " SIZE_FORMAT, contiguous_available() / 1000);
 773       log.trace("  Expand by " SIZE_FORMAT " (bytes)", expand_bytes);
 774     }
 775     // safe if expansion fails
 776     expand_for_gc_cause(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio);
 777     log.trace("  Expanded free fraction %f", ((double) free()) / capacity());
 778   } else {
 779     size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
 780     assert(desired_capacity <= capacity(), "invalid expansion size");
 781     size_t shrink_bytes = capacity() - desired_capacity;
 782     // Don't shrink unless the delta is greater than the minimum shrink we want
 783     if (shrink_bytes >= MinHeapDeltaBytes) {
 784       shrink_free_list_by(shrink_bytes);
 785     }
 786   }
 787 }
 788 
 789 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const {
 790   return cmsSpace()->freelistLock();
 791 }
 792 
 793 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size, bool tlab) {
 794   CMSSynchronousYieldRequest yr;
 795   MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
 796   return have_lock_and_allocate(size, tlab);
 797 }
 798 
 799 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size,
 800                                                                 bool   tlab /* ignored */) {
 801   assert_lock_strong(freelistLock());
 802   size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size);
 803   HeapWord* res = cmsSpace()->allocate(adjustedSize);
 804   // Allocate the object live (grey) if the background collector has
 805   // started marking. This is necessary because the marker may
 806   // have passed this address and consequently this object will
 807   // not otherwise be greyed and would be incorrectly swept up.
 808   // Note that if this object contains references, the writing
 809   // of those references will dirty the card containing this object
 810   // allowing the object to be blackened (and its references scanned)
 811   // either during a preclean phase or at the final checkpoint.
 812   if (res != NULL) {
 813     // We may block here with an uninitialized object with
 814     // its mark-bit or P-bits not yet set. Such objects need
 815     // to be safely navigable by block_start().
 816     assert(oop(res)->klass_or_null() == NULL, "Object should be uninitialized here.");
 817     assert(!((FreeChunk*)res)->is_free(), "Error, block will look free but show wrong size");
 818     collector()->direct_allocated(res, adjustedSize);
 819     _direct_allocated_words += adjustedSize;
 820     // allocation counters
 821     NOT_PRODUCT(
 822       _numObjectsAllocated++;
 823       _numWordsAllocated += (int)adjustedSize;
 824     )
 825   }
 826   return res;
 827 }
 828 
 829 // In the case of direct allocation by mutators in a generation that
 830 // is being concurrently collected, the object must be allocated
 831 // live (grey) if the background collector has started marking.
 832 // This is necessary because the marker may
 833 // have passed this address and consequently this object will
 834 // not otherwise be greyed and would be incorrectly swept up.
 835 // Note that if this object contains references, the writing
 836 // of those references will dirty the card containing this object
 837 // allowing the object to be blackened (and its references scanned)
 838 // either during a preclean phase or at the final checkpoint.
 839 void CMSCollector::direct_allocated(HeapWord* start, size_t size) {
 840   assert(_markBitMap.covers(start, size), "Out of bounds");
 841   if (_collectorState >= Marking) {
 842     MutexLockerEx y(_markBitMap.lock(),
 843                     Mutex::_no_safepoint_check_flag);
 844     // [see comments preceding SweepClosure::do_blk() below for details]
 845     //
 846     // Can the P-bits be deleted now?  JJJ
 847     //
 848     // 1. need to mark the object as live so it isn't collected
 849     // 2. need to mark the 2nd bit to indicate the object may be uninitialized
 850     // 3. need to mark the end of the object so marking, precleaning or sweeping
 851     //    can skip over uninitialized or unparsable objects. An allocated
 852     //    object is considered uninitialized for our purposes as long as
 853     //    its klass word is NULL.  All old gen objects are parsable
 854     //    as soon as they are initialized.)
 855     _markBitMap.mark(start);          // object is live
 856     _markBitMap.mark(start + 1);      // object is potentially uninitialized?
 857     _markBitMap.mark(start + size - 1);
 858                                       // mark end of object
 859   }
 860   // check that oop looks uninitialized
 861   assert(oop(start)->klass_or_null() == NULL, "_klass should be NULL");
 862 }
 863 
 864 void CMSCollector::promoted(bool par, HeapWord* start,
 865                             bool is_obj_array, size_t obj_size) {
 866   assert(_markBitMap.covers(start), "Out of bounds");
 867   // See comment in direct_allocated() about when objects should
 868   // be allocated live.
 869   if (_collectorState >= Marking) {
 870     // we already hold the marking bit map lock, taken in
 871     // the prologue
 872     if (par) {
 873       _markBitMap.par_mark(start);
 874     } else {
 875       _markBitMap.mark(start);
 876     }
 877     // We don't need to mark the object as uninitialized (as
 878     // in direct_allocated above) because this is being done with the
 879     // world stopped and the object will be initialized by the
 880     // time the marking, precleaning or sweeping get to look at it.
 881     // But see the code for copying objects into the CMS generation,
 882     // where we need to ensure that concurrent readers of the
 883     // block offset table are able to safely navigate a block that
 884     // is in flux from being free to being allocated (and in
 885     // transition while being copied into) and subsequently
 886     // becoming a bona-fide object when the copy/promotion is complete.
 887     assert(SafepointSynchronize::is_at_safepoint(),
 888            "expect promotion only at safepoints");
 889 
 890     if (_collectorState < Sweeping) {
 891       // Mark the appropriate cards in the modUnionTable, so that
 892       // this object gets scanned before the sweep. If this is
 893       // not done, CMS generation references in the object might
 894       // not get marked.
 895       // For the case of arrays, which are otherwise precisely
 896       // marked, we need to dirty the entire array, not just its head.
 897       if (is_obj_array) {
 898         // The [par_]mark_range() method expects mr.end() below to
 899         // be aligned to the granularity of a bit's representation
 900         // in the heap. In the case of the MUT below, that's a
 901         // card size.
 902         MemRegion mr(start,
 903                      align_up(start + obj_size,
 904                         CardTableModRefBS::card_size /* bytes */));
 905         if (par) {
 906           _modUnionTable.par_mark_range(mr);
 907         } else {
 908           _modUnionTable.mark_range(mr);
 909         }
 910       } else {  // not an obj array; we can just mark the head
 911         if (par) {
 912           _modUnionTable.par_mark(start);
 913         } else {
 914           _modUnionTable.mark(start);
 915         }
 916       }
 917     }
 918   }
 919 }
 920 
 921 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size) {
 922   assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
 923   // allocate, copy and if necessary update promoinfo --
 924   // delegate to underlying space.
 925   assert_lock_strong(freelistLock());
 926 
 927 #ifndef PRODUCT
 928   if (CMSHeap::heap()->promotion_should_fail()) {
 929     return NULL;
 930   }
 931 #endif  // #ifndef PRODUCT
 932 
 933   oop res = _cmsSpace->promote(obj, obj_size);
 934   if (res == NULL) {
 935     // expand and retry
 936     size_t s = _cmsSpace->expansionSpaceRequired(obj_size);  // HeapWords
 937     expand_for_gc_cause(s*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_promotion);
 938     // Since this is the old generation, we don't try to promote
 939     // into a more senior generation.
 940     res = _cmsSpace->promote(obj, obj_size);
 941   }
 942   if (res != NULL) {
 943     // See comment in allocate() about when objects should
 944     // be allocated live.
 945     assert(oopDesc::is_oop(obj), "Will dereference klass pointer below");
 946     collector()->promoted(false,           // Not parallel
 947                           (HeapWord*)res, obj->is_objArray(), obj_size);
 948     // promotion counters
 949     NOT_PRODUCT(
 950       _numObjectsPromoted++;
 951       _numWordsPromoted +=
 952         (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size()));
 953     )
 954   }
 955   return res;
 956 }
 957 
 958 
 959 // IMPORTANT: Notes on object size recognition in CMS.
 960 // ---------------------------------------------------
 961 // A block of storage in the CMS generation is always in
 962 // one of three states. A free block (FREE), an allocated
 963 // object (OBJECT) whose size() method reports the correct size,
 964 // and an intermediate state (TRANSIENT) in which its size cannot
 965 // be accurately determined.
 966 // STATE IDENTIFICATION:   (32 bit and 64 bit w/o COOPS)
 967 // -----------------------------------------------------
 968 // FREE:      klass_word & 1 == 1; mark_word holds block size
 969 //
 970 // OBJECT:    klass_word installed; klass_word != 0 && klass_word & 1 == 0;
 971 //            obj->size() computes correct size
 972 //
 973 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
 974 //
 975 // STATE IDENTIFICATION: (64 bit+COOPS)
 976 // ------------------------------------
 977 // FREE:      mark_word & CMS_FREE_BIT == 1; mark_word & ~CMS_FREE_BIT gives block_size
 978 //
 979 // OBJECT:    klass_word installed; klass_word != 0;
 980 //            obj->size() computes correct size
 981 //
 982 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
 983 //
 984 //
 985 // STATE TRANSITION DIAGRAM
 986 //
 987 //        mut / parnew                     mut  /  parnew
 988 // FREE --------------------> TRANSIENT ---------------------> OBJECT --|
 989 //  ^                                                                   |
 990 //  |------------------------ DEAD <------------------------------------|
 991 //         sweep                            mut
 992 //
 993 // While a block is in TRANSIENT state its size cannot be determined
 994 // so readers will either need to come back later or stall until
 995 // the size can be determined. Note that for the case of direct
 996 // allocation, P-bits, when available, may be used to determine the
 997 // size of an object that may not yet have been initialized.
 998 
 999 // Things to support parallel young-gen collection.
1000 oop
1001 ConcurrentMarkSweepGeneration::par_promote(int thread_num,
1002                                            oop old, markOop m,
1003                                            size_t word_sz) {
1004 #ifndef PRODUCT
1005   if (CMSHeap::heap()->promotion_should_fail()) {
1006     return NULL;
1007   }
1008 #endif  // #ifndef PRODUCT
1009 
1010   CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1011   PromotionInfo* promoInfo = &ps->promo;
1012   // if we are tracking promotions, then first ensure space for
1013   // promotion (including spooling space for saving header if necessary).
1014   // then allocate and copy, then track promoted info if needed.
1015   // When tracking (see PromotionInfo::track()), the mark word may
1016   // be displaced and in this case restoration of the mark word
1017   // occurs in the (oop_since_save_marks_)iterate phase.
1018   if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) {
1019     // Out of space for allocating spooling buffers;
1020     // try expanding and allocating spooling buffers.
1021     if (!expand_and_ensure_spooling_space(promoInfo)) {
1022       return NULL;
1023     }
1024   }
1025   assert(!promoInfo->tracking() || promoInfo->has_spooling_space(), "Control point invariant");
1026   const size_t alloc_sz = CompactibleFreeListSpace::adjustObjectSize(word_sz);
1027   HeapWord* obj_ptr = ps->lab.alloc(alloc_sz);
1028   if (obj_ptr == NULL) {
1029      obj_ptr = expand_and_par_lab_allocate(ps, alloc_sz);
1030      if (obj_ptr == NULL) {
1031        return NULL;
1032      }
1033   }
1034   oop obj = oop(obj_ptr);
1035   OrderAccess::storestore();
1036   assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1037   assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1038   // IMPORTANT: See note on object initialization for CMS above.
1039   // Otherwise, copy the object.  Here we must be careful to insert the
1040   // klass pointer last, since this marks the block as an allocated object.
1041   // Except with compressed oops it's the mark word.
1042   HeapWord* old_ptr = (HeapWord*)old;
1043   // Restore the mark word copied above.
1044   obj->set_mark(m);
1045   assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1046   assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1047   OrderAccess::storestore();
1048 
1049   if (UseCompressedClassPointers) {
1050     // Copy gap missed by (aligned) header size calculation below
1051     obj->set_klass_gap(old->klass_gap());
1052   }
1053   if (word_sz > (size_t)oopDesc::header_size()) {
1054     Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1055                                  obj_ptr + oopDesc::header_size(),
1056                                  word_sz - oopDesc::header_size());
1057   }
1058 
1059   // Now we can track the promoted object, if necessary.  We take care
1060   // to delay the transition from uninitialized to full object
1061   // (i.e., insertion of klass pointer) until after, so that it
1062   // atomically becomes a promoted object.
1063   if (promoInfo->tracking()) {
1064     promoInfo->track((PromotedObject*)obj, old->klass());
1065   }
1066   assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1067   assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1068   assert(oopDesc::is_oop(old), "Will use and dereference old klass ptr below");
1069 
1070   // Finally, install the klass pointer (this should be volatile).
1071   OrderAccess::storestore();
1072   obj->set_klass(old->klass());
1073   // We should now be able to calculate the right size for this object
1074   assert(oopDesc::is_oop(obj) && obj->size() == (int)word_sz, "Error, incorrect size computed for promoted object");
1075 
1076   collector()->promoted(true,          // parallel
1077                         obj_ptr, old->is_objArray(), word_sz);
1078 
1079   NOT_PRODUCT(
1080     Atomic::inc(&_numObjectsPromoted);
1081     Atomic::add(alloc_sz, &_numWordsPromoted);
1082   )
1083 
1084   return obj;
1085 }
1086 
1087 void
1088 ConcurrentMarkSweepGeneration::
1089 par_promote_alloc_done(int thread_num) {
1090   CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1091   ps->lab.retire(thread_num);
1092 }
1093 
1094 void
1095 ConcurrentMarkSweepGeneration::
1096 par_oop_since_save_marks_iterate_done(int thread_num) {
1097   CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1098   ParScanWithoutBarrierClosure* dummy_cl = NULL;
1099   ps->promo.promoted_oops_iterate_nv(dummy_cl);
1100 
1101   // Because card-scanning has been completed, subsequent phases
1102   // (e.g., reference processing) will not need to recognize which
1103   // objects have been promoted during this GC. So, we can now disable
1104   // promotion tracking.
1105   ps->promo.stopTrackingPromotions();
1106 }
1107 
1108 bool ConcurrentMarkSweepGeneration::should_collect(bool   full,
1109                                                    size_t size,
1110                                                    bool   tlab)
1111 {
1112   // We allow a STW collection only if a full
1113   // collection was requested.
1114   return full || should_allocate(size, tlab); // FIX ME !!!
1115   // This and promotion failure handling are connected at the
1116   // hip and should be fixed by untying them.
1117 }
1118 
1119 bool CMSCollector::shouldConcurrentCollect() {
1120   LogTarget(Trace, gc) log;
1121 
1122   if (_full_gc_requested) {
1123     log.print("CMSCollector: collect because of explicit  gc request (or GCLocker)");
1124     return true;
1125   }
1126 
1127   FreelistLocker x(this);
1128   // ------------------------------------------------------------------
1129   // Print out lots of information which affects the initiation of
1130   // a collection.
1131   if (log.is_enabled() && stats().valid()) {
1132     log.print("CMSCollector shouldConcurrentCollect: ");
1133 
1134     LogStream out(log);
1135     stats().print_on(&out);
1136 
1137     log.print("time_until_cms_gen_full %3.7f", stats().time_until_cms_gen_full());
1138     log.print("free=" SIZE_FORMAT, _cmsGen->free());
1139     log.print("contiguous_available=" SIZE_FORMAT, _cmsGen->contiguous_available());
1140     log.print("promotion_rate=%g", stats().promotion_rate());
1141     log.print("cms_allocation_rate=%g", stats().cms_allocation_rate());
1142     log.print("occupancy=%3.7f", _cmsGen->occupancy());
1143     log.print("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy());
1144     log.print("cms_time_since_begin=%3.7f", stats().cms_time_since_begin());
1145     log.print("cms_time_since_end=%3.7f", stats().cms_time_since_end());
1146     log.print("metadata initialized %d", MetaspaceGC::should_concurrent_collect());
1147   }
1148   // ------------------------------------------------------------------
1149 
1150   // If the estimated time to complete a cms collection (cms_duration())
1151   // is less than the estimated time remaining until the cms generation
1152   // is full, start a collection.
1153   if (!UseCMSInitiatingOccupancyOnly) {
1154     if (stats().valid()) {
1155       if (stats().time_until_cms_start() == 0.0) {
1156         return true;
1157       }
1158     } else {
1159       // We want to conservatively collect somewhat early in order
1160       // to try and "bootstrap" our CMS/promotion statistics;
1161       // this branch will not fire after the first successful CMS
1162       // collection because the stats should then be valid.
1163       if (_cmsGen->occupancy() >= _bootstrap_occupancy) {
1164         log.print(" CMSCollector: collect for bootstrapping statistics: occupancy = %f, boot occupancy = %f",
1165                   _cmsGen->occupancy(), _bootstrap_occupancy);
1166         return true;
1167       }
1168     }
1169   }
1170 
1171   // Otherwise, we start a collection cycle if
1172   // old gen want a collection cycle started. Each may use
1173   // an appropriate criterion for making this decision.
1174   // XXX We need to make sure that the gen expansion
1175   // criterion dovetails well with this. XXX NEED TO FIX THIS
1176   if (_cmsGen->should_concurrent_collect()) {
1177     log.print("CMS old gen initiated");
1178     return true;
1179   }
1180 
1181   // We start a collection if we believe an incremental collection may fail;
1182   // this is not likely to be productive in practice because it's probably too
1183   // late anyway.
1184   CMSHeap* heap = CMSHeap::heap();
1185   assert(heap->collector_policy()->is_generation_policy(),
1186          "You may want to check the correctness of the following");
1187   if (heap->incremental_collection_will_fail(true /* consult_young */)) {
1188     log.print("CMSCollector: collect because incremental collection will fail ");
1189     return true;
1190   }
1191 
1192   if (MetaspaceGC::should_concurrent_collect()) {
1193     log.print("CMSCollector: collect for metadata allocation ");
1194     return true;
1195   }
1196 
1197   // CMSTriggerInterval starts a CMS cycle if enough time has passed.
1198   if (CMSTriggerInterval >= 0) {
1199     if (CMSTriggerInterval == 0) {
1200       // Trigger always
1201       return true;
1202     }
1203 
1204     // Check the CMS time since begin (we do not check the stats validity
1205     // as we want to be able to trigger the first CMS cycle as well)
1206     if (stats().cms_time_since_begin() >= (CMSTriggerInterval / ((double) MILLIUNITS))) {
1207       if (stats().valid()) {
1208         log.print("CMSCollector: collect because of trigger interval (time since last begin %3.7f secs)",
1209                   stats().cms_time_since_begin());
1210       } else {
1211         log.print("CMSCollector: collect because of trigger interval (first collection)");
1212       }
1213       return true;
1214     }
1215   }
1216 
1217   return false;
1218 }
1219 
1220 void CMSCollector::set_did_compact(bool v) { _cmsGen->set_did_compact(v); }
1221 
1222 // Clear _expansion_cause fields of constituent generations
1223 void CMSCollector::clear_expansion_cause() {
1224   _cmsGen->clear_expansion_cause();
1225 }
1226 
1227 // We should be conservative in starting a collection cycle.  To
1228 // start too eagerly runs the risk of collecting too often in the
1229 // extreme.  To collect too rarely falls back on full collections,
1230 // which works, even if not optimum in terms of concurrent work.
1231 // As a work around for too eagerly collecting, use the flag
1232 // UseCMSInitiatingOccupancyOnly.  This also has the advantage of
1233 // giving the user an easily understandable way of controlling the
1234 // collections.
1235 // We want to start a new collection cycle if any of the following
1236 // conditions hold:
1237 // . our current occupancy exceeds the configured initiating occupancy
1238 //   for this generation, or
1239 // . we recently needed to expand this space and have not, since that
1240 //   expansion, done a collection of this generation, or
1241 // . the underlying space believes that it may be a good idea to initiate
1242 //   a concurrent collection (this may be based on criteria such as the
1243 //   following: the space uses linear allocation and linear allocation is
1244 //   going to fail, or there is believed to be excessive fragmentation in
1245 //   the generation, etc... or ...
1246 // [.(currently done by CMSCollector::shouldConcurrentCollect() only for
1247 //   the case of the old generation; see CR 6543076):
1248 //   we may be approaching a point at which allocation requests may fail because
1249 //   we will be out of sufficient free space given allocation rate estimates.]
1250 bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const {
1251 
1252   assert_lock_strong(freelistLock());
1253   if (occupancy() > initiating_occupancy()) {
1254     log_trace(gc)(" %s: collect because of occupancy %f / %f  ",
1255                   short_name(), occupancy(), initiating_occupancy());
1256     return true;
1257   }
1258   if (UseCMSInitiatingOccupancyOnly) {
1259     return false;
1260   }
1261   if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) {
1262     log_trace(gc)(" %s: collect because expanded for allocation ", short_name());
1263     return true;
1264   }
1265   return false;
1266 }
1267 
1268 void ConcurrentMarkSweepGeneration::collect(bool   full,
1269                                             bool   clear_all_soft_refs,
1270                                             size_t size,
1271                                             bool   tlab)
1272 {
1273   collector()->collect(full, clear_all_soft_refs, size, tlab);
1274 }
1275 
1276 void CMSCollector::collect(bool   full,
1277                            bool   clear_all_soft_refs,
1278                            size_t size,
1279                            bool   tlab)
1280 {
1281   // The following "if" branch is present for defensive reasons.
1282   // In the current uses of this interface, it can be replaced with:
1283   // assert(!GCLocker.is_active(), "Can't be called otherwise");
1284   // But I am not placing that assert here to allow future
1285   // generality in invoking this interface.
1286   if (GCLocker::is_active()) {
1287     // A consistency test for GCLocker
1288     assert(GCLocker::needs_gc(), "Should have been set already");
1289     // Skip this foreground collection, instead
1290     // expanding the heap if necessary.
1291     // Need the free list locks for the call to free() in compute_new_size()
1292     compute_new_size();
1293     return;
1294   }
1295   acquire_control_and_collect(full, clear_all_soft_refs);
1296 }
1297 
1298 void CMSCollector::request_full_gc(unsigned int full_gc_count, GCCause::Cause cause) {
1299   CMSHeap* heap = CMSHeap::heap();
1300   unsigned int gc_count = heap->total_full_collections();
1301   if (gc_count == full_gc_count) {
1302     MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag);
1303     _full_gc_requested = true;
1304     _full_gc_cause = cause;
1305     CGC_lock->notify();   // nudge CMS thread
1306   } else {
1307     assert(gc_count > full_gc_count, "Error: causal loop");
1308   }
1309 }
1310 
1311 bool CMSCollector::is_external_interruption() {
1312   GCCause::Cause cause = CMSHeap::heap()->gc_cause();
1313   return GCCause::is_user_requested_gc(cause) ||
1314          GCCause::is_serviceability_requested_gc(cause);
1315 }
1316 
1317 void CMSCollector::report_concurrent_mode_interruption() {
1318   if (is_external_interruption()) {
1319     log_debug(gc)("Concurrent mode interrupted");
1320   } else {
1321     log_debug(gc)("Concurrent mode failure");
1322     _gc_tracer_cm->report_concurrent_mode_failure();
1323   }
1324 }
1325 
1326 
1327 // The foreground and background collectors need to coordinate in order
1328 // to make sure that they do not mutually interfere with CMS collections.
1329 // When a background collection is active,
1330 // the foreground collector may need to take over (preempt) and
1331 // synchronously complete an ongoing collection. Depending on the
1332 // frequency of the background collections and the heap usage
1333 // of the application, this preemption can be seldom or frequent.
1334 // There are only certain
1335 // points in the background collection that the "collection-baton"
1336 // can be passed to the foreground collector.
1337 //
1338 // The foreground collector will wait for the baton before
1339 // starting any part of the collection.  The foreground collector
1340 // will only wait at one location.
1341 //
1342 // The background collector will yield the baton before starting a new
1343 // phase of the collection (e.g., before initial marking, marking from roots,
1344 // precleaning, final re-mark, sweep etc.)  This is normally done at the head
1345 // of the loop which switches the phases. The background collector does some
1346 // of the phases (initial mark, final re-mark) with the world stopped.
1347 // Because of locking involved in stopping the world,
1348 // the foreground collector should not block waiting for the background
1349 // collector when it is doing a stop-the-world phase.  The background
1350 // collector will yield the baton at an additional point just before
1351 // it enters a stop-the-world phase.  Once the world is stopped, the
1352 // background collector checks the phase of the collection.  If the
1353 // phase has not changed, it proceeds with the collection.  If the
1354 // phase has changed, it skips that phase of the collection.  See
1355 // the comments on the use of the Heap_lock in collect_in_background().
1356 //
1357 // Variable used in baton passing.
1358 //   _foregroundGCIsActive - Set to true by the foreground collector when
1359 //      it wants the baton.  The foreground clears it when it has finished
1360 //      the collection.
1361 //   _foregroundGCShouldWait - Set to true by the background collector
1362 //        when it is running.  The foreground collector waits while
1363 //      _foregroundGCShouldWait is true.
1364 //  CGC_lock - monitor used to protect access to the above variables
1365 //      and to notify the foreground and background collectors.
1366 //  _collectorState - current state of the CMS collection.
1367 //
1368 // The foreground collector
1369 //   acquires the CGC_lock
1370 //   sets _foregroundGCIsActive
1371 //   waits on the CGC_lock for _foregroundGCShouldWait to be false
1372 //     various locks acquired in preparation for the collection
1373 //     are released so as not to block the background collector
1374 //     that is in the midst of a collection
1375 //   proceeds with the collection
1376 //   clears _foregroundGCIsActive
1377 //   returns
1378 //
1379 // The background collector in a loop iterating on the phases of the
1380 //      collection
1381 //   acquires the CGC_lock
1382 //   sets _foregroundGCShouldWait
1383 //   if _foregroundGCIsActive is set
1384 //     clears _foregroundGCShouldWait, notifies _CGC_lock
1385 //     waits on _CGC_lock for _foregroundGCIsActive to become false
1386 //     and exits the loop.
1387 //   otherwise
1388 //     proceed with that phase of the collection
1389 //     if the phase is a stop-the-world phase,
1390 //       yield the baton once more just before enqueueing
1391 //       the stop-world CMS operation (executed by the VM thread).
1392 //   returns after all phases of the collection are done
1393 //
1394 
1395 void CMSCollector::acquire_control_and_collect(bool full,
1396         bool clear_all_soft_refs) {
1397   assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
1398   assert(!Thread::current()->is_ConcurrentGC_thread(),
1399          "shouldn't try to acquire control from self!");
1400 
1401   // Start the protocol for acquiring control of the
1402   // collection from the background collector (aka CMS thread).
1403   assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1404          "VM thread should have CMS token");
1405   // Remember the possibly interrupted state of an ongoing
1406   // concurrent collection
1407   CollectorState first_state = _collectorState;
1408 
1409   // Signal to a possibly ongoing concurrent collection that
1410   // we want to do a foreground collection.
1411   _foregroundGCIsActive = true;
1412 
1413   // release locks and wait for a notify from the background collector
1414   // releasing the locks in only necessary for phases which
1415   // do yields to improve the granularity of the collection.
1416   assert_lock_strong(bitMapLock());
1417   // We need to lock the Free list lock for the space that we are
1418   // currently collecting.
1419   assert(haveFreelistLocks(), "Must be holding free list locks");
1420   bitMapLock()->unlock();
1421   releaseFreelistLocks();
1422   {
1423     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1424     if (_foregroundGCShouldWait) {
1425       // We are going to be waiting for action for the CMS thread;
1426       // it had better not be gone (for instance at shutdown)!
1427       assert(ConcurrentMarkSweepThread::cmst() != NULL && !ConcurrentMarkSweepThread::cmst()->has_terminated(),
1428              "CMS thread must be running");
1429       // Wait here until the background collector gives us the go-ahead
1430       ConcurrentMarkSweepThread::clear_CMS_flag(
1431         ConcurrentMarkSweepThread::CMS_vm_has_token);  // release token
1432       // Get a possibly blocked CMS thread going:
1433       //   Note that we set _foregroundGCIsActive true above,
1434       //   without protection of the CGC_lock.
1435       CGC_lock->notify();
1436       assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(),
1437              "Possible deadlock");
1438       while (_foregroundGCShouldWait) {
1439         // wait for notification
1440         CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1441         // Possibility of delay/starvation here, since CMS token does
1442         // not know to give priority to VM thread? Actually, i think
1443         // there wouldn't be any delay/starvation, but the proof of
1444         // that "fact" (?) appears non-trivial. XXX 20011219YSR
1445       }
1446       ConcurrentMarkSweepThread::set_CMS_flag(
1447         ConcurrentMarkSweepThread::CMS_vm_has_token);
1448     }
1449   }
1450   // The CMS_token is already held.  Get back the other locks.
1451   assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1452          "VM thread should have CMS token");
1453   getFreelistLocks();
1454   bitMapLock()->lock_without_safepoint_check();
1455   log_debug(gc, state)("CMS foreground collector has asked for control " INTPTR_FORMAT " with first state %d",
1456                        p2i(Thread::current()), first_state);
1457   log_debug(gc, state)("    gets control with state %d", _collectorState);
1458 
1459   // Inform cms gen if this was due to partial collection failing.
1460   // The CMS gen may use this fact to determine its expansion policy.
1461   CMSHeap* heap = CMSHeap::heap();
1462   if (heap->incremental_collection_will_fail(false /* don't consult_young */)) {
1463     assert(!_cmsGen->incremental_collection_failed(),
1464            "Should have been noticed, reacted to and cleared");
1465     _cmsGen->set_incremental_collection_failed();
1466   }
1467 
1468   if (first_state > Idling) {
1469     report_concurrent_mode_interruption();
1470   }
1471 
1472   set_did_compact(true);
1473 
1474   // If the collection is being acquired from the background
1475   // collector, there may be references on the discovered
1476   // references lists.  Abandon those references, since some
1477   // of them may have become unreachable after concurrent
1478   // discovery; the STW compacting collector will redo discovery
1479   // more precisely, without being subject to floating garbage.
1480   // Leaving otherwise unreachable references in the discovered
1481   // lists would require special handling.
1482   ref_processor()->disable_discovery();
1483   ref_processor()->abandon_partial_discovery();
1484   ref_processor()->verify_no_references_recorded();
1485 
1486   if (first_state > Idling) {
1487     save_heap_summary();
1488   }
1489 
1490   do_compaction_work(clear_all_soft_refs);
1491 
1492   // Has the GC time limit been exceeded?
1493   size_t max_eden_size = _young_gen->max_eden_size();
1494   GCCause::Cause gc_cause = heap->gc_cause();
1495   size_policy()->check_gc_overhead_limit(_young_gen->used(),
1496                                          _young_gen->eden()->used(),
1497                                          _cmsGen->max_capacity(),
1498                                          max_eden_size,
1499                                          full,
1500                                          gc_cause,
1501                                          heap->collector_policy());
1502 
1503   // Reset the expansion cause, now that we just completed
1504   // a collection cycle.
1505   clear_expansion_cause();
1506   _foregroundGCIsActive = false;
1507   return;
1508 }
1509 
1510 // Resize the tenured generation
1511 // after obtaining the free list locks for the
1512 // two generations.
1513 void CMSCollector::compute_new_size() {
1514   assert_locked_or_safepoint(Heap_lock);
1515   FreelistLocker z(this);
1516   MetaspaceGC::compute_new_size();
1517   _cmsGen->compute_new_size_free_list();
1518 }
1519 
1520 // A work method used by the foreground collector to do
1521 // a mark-sweep-compact.
1522 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) {
1523   CMSHeap* heap = CMSHeap::heap();
1524 
1525   STWGCTimer* gc_timer = GenMarkSweep::gc_timer();
1526   gc_timer->register_gc_start();
1527 
1528   SerialOldTracer* gc_tracer = GenMarkSweep::gc_tracer();
1529   gc_tracer->report_gc_start(heap->gc_cause(), gc_timer->gc_start());
1530 
1531   heap->pre_full_gc_dump(gc_timer);
1532 
1533   GCTraceTime(Trace, gc, phases) t("CMS:MSC");
1534 
1535   // Temporarily widen the span of the weak reference processing to
1536   // the entire heap.
1537   MemRegion new_span(CMSHeap::heap()->reserved_region());
1538   ReferenceProcessorSpanMutator rp_mut_span(ref_processor(), new_span);
1539   // Temporarily, clear the "is_alive_non_header" field of the
1540   // reference processor.
1541   ReferenceProcessorIsAliveMutator rp_mut_closure(ref_processor(), NULL);
1542   // Temporarily make reference _processing_ single threaded (non-MT).
1543   ReferenceProcessorMTProcMutator rp_mut_mt_processing(ref_processor(), false);
1544   // Temporarily make refs discovery atomic
1545   ReferenceProcessorAtomicMutator rp_mut_atomic(ref_processor(), true);
1546   // Temporarily make reference _discovery_ single threaded (non-MT)
1547   ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
1548 
1549   ref_processor()->set_enqueuing_is_done(false);
1550   ref_processor()->enable_discovery();
1551   ref_processor()->setup_policy(clear_all_soft_refs);
1552   // If an asynchronous collection finishes, the _modUnionTable is
1553   // all clear.  If we are assuming the collection from an asynchronous
1554   // collection, clear the _modUnionTable.
1555   assert(_collectorState != Idling || _modUnionTable.isAllClear(),
1556     "_modUnionTable should be clear if the baton was not passed");
1557   _modUnionTable.clear_all();
1558   assert(_collectorState != Idling || _ct->cld_rem_set()->mod_union_is_clear(),
1559     "mod union for klasses should be clear if the baton was passed");
1560   _ct->cld_rem_set()->clear_mod_union();
1561 
1562 
1563   // We must adjust the allocation statistics being maintained
1564   // in the free list space. We do so by reading and clearing
1565   // the sweep timer and updating the block flux rate estimates below.
1566   assert(!_intra_sweep_timer.is_active(), "_intra_sweep_timer should be inactive");
1567   if (_inter_sweep_timer.is_active()) {
1568     _inter_sweep_timer.stop();
1569     // Note that we do not use this sample to update the _inter_sweep_estimate.
1570     _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
1571                                             _inter_sweep_estimate.padded_average(),
1572                                             _intra_sweep_estimate.padded_average());
1573   }
1574 
1575   GenMarkSweep::invoke_at_safepoint(ref_processor(), clear_all_soft_refs);
1576   #ifdef ASSERT
1577     CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
1578     size_t free_size = cms_space->free();
1579     assert(free_size ==
1580            pointer_delta(cms_space->end(), cms_space->compaction_top())
1581            * HeapWordSize,
1582       "All the free space should be compacted into one chunk at top");
1583     assert(cms_space->dictionary()->total_chunk_size(
1584                                       debug_only(cms_space->freelistLock())) == 0 ||
1585            cms_space->totalSizeInIndexedFreeLists() == 0,
1586       "All the free space should be in a single chunk");
1587     size_t num = cms_space->totalCount();
1588     assert((free_size == 0 && num == 0) ||
1589            (free_size > 0  && (num == 1 || num == 2)),
1590          "There should be at most 2 free chunks after compaction");
1591   #endif // ASSERT
1592   _collectorState = Resetting;
1593   assert(_restart_addr == NULL,
1594          "Should have been NULL'd before baton was passed");
1595   reset_stw();
1596   _cmsGen->reset_after_compaction();
1597   _concurrent_cycles_since_last_unload = 0;
1598 
1599   // Clear any data recorded in the PLAB chunk arrays.
1600   if (_survivor_plab_array != NULL) {
1601     reset_survivor_plab_arrays();
1602   }
1603 
1604   // Adjust the per-size allocation stats for the next epoch.
1605   _cmsGen->cmsSpace()->endSweepFLCensus(sweep_count() /* fake */);
1606   // Restart the "inter sweep timer" for the next epoch.
1607   _inter_sweep_timer.reset();
1608   _inter_sweep_timer.start();
1609 
1610   // No longer a need to do a concurrent collection for Metaspace.
1611   MetaspaceGC::set_should_concurrent_collect(false);
1612 
1613   heap->post_full_gc_dump(gc_timer);
1614 
1615   gc_timer->register_gc_end();
1616 
1617   gc_tracer->report_gc_end(gc_timer->gc_end(), gc_timer->time_partitions());
1618 
1619   // For a mark-sweep-compact, compute_new_size() will be called
1620   // in the heap's do_collection() method.
1621 }
1622 
1623 void CMSCollector::print_eden_and_survivor_chunk_arrays() {
1624   Log(gc, heap) log;
1625   if (!log.is_trace()) {
1626     return;
1627   }
1628 
1629   ContiguousSpace* eden_space = _young_gen->eden();
1630   ContiguousSpace* from_space = _young_gen->from();
1631   ContiguousSpace* to_space   = _young_gen->to();
1632   // Eden
1633   if (_eden_chunk_array != NULL) {
1634     log.trace("eden " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1635               p2i(eden_space->bottom()), p2i(eden_space->top()),
1636               p2i(eden_space->end()), eden_space->capacity());
1637     log.trace("_eden_chunk_index=" SIZE_FORMAT ", _eden_chunk_capacity=" SIZE_FORMAT,
1638               _eden_chunk_index, _eden_chunk_capacity);
1639     for (size_t i = 0; i < _eden_chunk_index; i++) {
1640       log.trace("_eden_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT, i, p2i(_eden_chunk_array[i]));
1641     }
1642   }
1643   // Survivor
1644   if (_survivor_chunk_array != NULL) {
1645     log.trace("survivor " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1646               p2i(from_space->bottom()), p2i(from_space->top()),
1647               p2i(from_space->end()), from_space->capacity());
1648     log.trace("_survivor_chunk_index=" SIZE_FORMAT ", _survivor_chunk_capacity=" SIZE_FORMAT,
1649               _survivor_chunk_index, _survivor_chunk_capacity);
1650     for (size_t i = 0; i < _survivor_chunk_index; i++) {
1651       log.trace("_survivor_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT, i, p2i(_survivor_chunk_array[i]));
1652     }
1653   }
1654 }
1655 
1656 void CMSCollector::getFreelistLocks() const {
1657   // Get locks for all free lists in all generations that this
1658   // collector is responsible for
1659   _cmsGen->freelistLock()->lock_without_safepoint_check();
1660 }
1661 
1662 void CMSCollector::releaseFreelistLocks() const {
1663   // Release locks for all free lists in all generations that this
1664   // collector is responsible for
1665   _cmsGen->freelistLock()->unlock();
1666 }
1667 
1668 bool CMSCollector::haveFreelistLocks() const {
1669   // Check locks for all free lists in all generations that this
1670   // collector is responsible for
1671   assert_lock_strong(_cmsGen->freelistLock());
1672   PRODUCT_ONLY(ShouldNotReachHere());
1673   return true;
1674 }
1675 
1676 // A utility class that is used by the CMS collector to
1677 // temporarily "release" the foreground collector from its
1678 // usual obligation to wait for the background collector to
1679 // complete an ongoing phase before proceeding.
1680 class ReleaseForegroundGC: public StackObj {
1681  private:
1682   CMSCollector* _c;
1683  public:
1684   ReleaseForegroundGC(CMSCollector* c) : _c(c) {
1685     assert(_c->_foregroundGCShouldWait, "Else should not need to call");
1686     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1687     // allow a potentially blocked foreground collector to proceed
1688     _c->_foregroundGCShouldWait = false;
1689     if (_c->_foregroundGCIsActive) {
1690       CGC_lock->notify();
1691     }
1692     assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1693            "Possible deadlock");
1694   }
1695 
1696   ~ReleaseForegroundGC() {
1697     assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?");
1698     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1699     _c->_foregroundGCShouldWait = true;
1700   }
1701 };
1702 
1703 void CMSCollector::collect_in_background(GCCause::Cause cause) {
1704   assert(Thread::current()->is_ConcurrentGC_thread(),
1705     "A CMS asynchronous collection is only allowed on a CMS thread.");
1706 
1707   CMSHeap* heap = CMSHeap::heap();
1708   {
1709     bool safepoint_check = Mutex::_no_safepoint_check_flag;
1710     MutexLockerEx hl(Heap_lock, safepoint_check);
1711     FreelistLocker fll(this);
1712     MutexLockerEx x(CGC_lock, safepoint_check);
1713     if (_foregroundGCIsActive) {
1714       // The foreground collector is. Skip this
1715       // background collection.
1716       assert(!_foregroundGCShouldWait, "Should be clear");
1717       return;
1718     } else {
1719       assert(_collectorState == Idling, "Should be idling before start.");
1720       _collectorState = InitialMarking;
1721       register_gc_start(cause);
1722       // Reset the expansion cause, now that we are about to begin
1723       // a new cycle.
1724       clear_expansion_cause();
1725 
1726       // Clear the MetaspaceGC flag since a concurrent collection
1727       // is starting but also clear it after the collection.
1728       MetaspaceGC::set_should_concurrent_collect(false);
1729     }
1730     // Decide if we want to enable class unloading as part of the
1731     // ensuing concurrent GC cycle.
1732     update_should_unload_classes();
1733     _full_gc_requested = false;           // acks all outstanding full gc requests
1734     _full_gc_cause = GCCause::_no_gc;
1735     // Signal that we are about to start a collection
1736     heap->increment_total_full_collections();  // ... starting a collection cycle
1737     _collection_count_start = heap->total_full_collections();
1738   }
1739 
1740   size_t prev_used = _cmsGen->used();
1741 
1742   // The change of the collection state is normally done at this level;
1743   // the exceptions are phases that are executed while the world is
1744   // stopped.  For those phases the change of state is done while the
1745   // world is stopped.  For baton passing purposes this allows the
1746   // background collector to finish the phase and change state atomically.
1747   // The foreground collector cannot wait on a phase that is done
1748   // while the world is stopped because the foreground collector already
1749   // has the world stopped and would deadlock.
1750   while (_collectorState != Idling) {
1751     log_debug(gc, state)("Thread " INTPTR_FORMAT " in CMS state %d",
1752                          p2i(Thread::current()), _collectorState);
1753     // The foreground collector
1754     //   holds the Heap_lock throughout its collection.
1755     //   holds the CMS token (but not the lock)
1756     //     except while it is waiting for the background collector to yield.
1757     //
1758     // The foreground collector should be blocked (not for long)
1759     //   if the background collector is about to start a phase
1760     //   executed with world stopped.  If the background
1761     //   collector has already started such a phase, the
1762     //   foreground collector is blocked waiting for the
1763     //   Heap_lock.  The stop-world phases (InitialMarking and FinalMarking)
1764     //   are executed in the VM thread.
1765     //
1766     // The locking order is
1767     //   PendingListLock (PLL)  -- if applicable (FinalMarking)
1768     //   Heap_lock  (both this & PLL locked in VM_CMS_Operation::prologue())
1769     //   CMS token  (claimed in
1770     //                stop_world_and_do() -->
1771     //                  safepoint_synchronize() -->
1772     //                    CMSThread::synchronize())
1773 
1774     {
1775       // Check if the FG collector wants us to yield.
1776       CMSTokenSync x(true); // is cms thread
1777       if (waitForForegroundGC()) {
1778         // We yielded to a foreground GC, nothing more to be
1779         // done this round.
1780         assert(_foregroundGCShouldWait == false, "We set it to false in "
1781                "waitForForegroundGC()");
1782         log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " exiting collection CMS state %d",
1783                              p2i(Thread::current()), _collectorState);
1784         return;
1785       } else {
1786         // The background collector can run but check to see if the
1787         // foreground collector has done a collection while the
1788         // background collector was waiting to get the CGC_lock
1789         // above.  If yes, break so that _foregroundGCShouldWait
1790         // is cleared before returning.
1791         if (_collectorState == Idling) {
1792           break;
1793         }
1794       }
1795     }
1796 
1797     assert(_foregroundGCShouldWait, "Foreground collector, if active, "
1798       "should be waiting");
1799 
1800     switch (_collectorState) {
1801       case InitialMarking:
1802         {
1803           ReleaseForegroundGC x(this);
1804           stats().record_cms_begin();
1805           VM_CMS_Initial_Mark initial_mark_op(this);
1806           VMThread::execute(&initial_mark_op);
1807         }
1808         // The collector state may be any legal state at this point
1809         // since the background collector may have yielded to the
1810         // foreground collector.
1811         break;
1812       case Marking:
1813         // initial marking in checkpointRootsInitialWork has been completed
1814         if (markFromRoots()) { // we were successful
1815           assert(_collectorState == Precleaning, "Collector state should "
1816             "have changed");
1817         } else {
1818           assert(_foregroundGCIsActive, "Internal state inconsistency");
1819         }
1820         break;
1821       case Precleaning:
1822         // marking from roots in markFromRoots has been completed
1823         preclean();
1824         assert(_collectorState == AbortablePreclean ||
1825                _collectorState == FinalMarking,
1826                "Collector state should have changed");
1827         break;
1828       case AbortablePreclean:
1829         abortable_preclean();
1830         assert(_collectorState == FinalMarking, "Collector state should "
1831           "have changed");
1832         break;
1833       case FinalMarking:
1834         {
1835           ReleaseForegroundGC x(this);
1836 
1837           VM_CMS_Final_Remark final_remark_op(this);
1838           VMThread::execute(&final_remark_op);
1839         }
1840         assert(_foregroundGCShouldWait, "block post-condition");
1841         break;
1842       case Sweeping:
1843         // final marking in checkpointRootsFinal has been completed
1844         sweep();
1845         assert(_collectorState == Resizing, "Collector state change "
1846           "to Resizing must be done under the free_list_lock");
1847 
1848       case Resizing: {
1849         // Sweeping has been completed...
1850         // At this point the background collection has completed.
1851         // Don't move the call to compute_new_size() down
1852         // into code that might be executed if the background
1853         // collection was preempted.
1854         {
1855           ReleaseForegroundGC x(this);   // unblock FG collection
1856           MutexLockerEx       y(Heap_lock, Mutex::_no_safepoint_check_flag);
1857           CMSTokenSync        z(true);   // not strictly needed.
1858           if (_collectorState == Resizing) {
1859             compute_new_size();
1860             save_heap_summary();
1861             _collectorState = Resetting;
1862           } else {
1863             assert(_collectorState == Idling, "The state should only change"
1864                    " because the foreground collector has finished the collection");
1865           }
1866         }
1867         break;
1868       }
1869       case Resetting:
1870         // CMS heap resizing has been completed
1871         reset_concurrent();
1872         assert(_collectorState == Idling, "Collector state should "
1873           "have changed");
1874 
1875         MetaspaceGC::set_should_concurrent_collect(false);
1876 
1877         stats().record_cms_end();
1878         // Don't move the concurrent_phases_end() and compute_new_size()
1879         // calls to here because a preempted background collection
1880         // has it's state set to "Resetting".
1881         break;
1882       case Idling:
1883       default:
1884         ShouldNotReachHere();
1885         break;
1886     }
1887     log_debug(gc, state)("  Thread " INTPTR_FORMAT " done - next CMS state %d",
1888                          p2i(Thread::current()), _collectorState);
1889     assert(_foregroundGCShouldWait, "block post-condition");
1890   }
1891 
1892   // Should this be in gc_epilogue?
1893   collector_policy()->counters()->update_counters();
1894 
1895   {
1896     // Clear _foregroundGCShouldWait and, in the event that the
1897     // foreground collector is waiting, notify it, before
1898     // returning.
1899     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1900     _foregroundGCShouldWait = false;
1901     if (_foregroundGCIsActive) {
1902       CGC_lock->notify();
1903     }
1904     assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1905            "Possible deadlock");
1906   }
1907   log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " exiting collection CMS state %d",
1908                        p2i(Thread::current()), _collectorState);
1909   log_info(gc, heap)("Old: " SIZE_FORMAT "K->" SIZE_FORMAT "K("  SIZE_FORMAT "K)",
1910                      prev_used / K, _cmsGen->used()/K, _cmsGen->capacity() /K);
1911 }
1912 
1913 void CMSCollector::register_gc_start(GCCause::Cause cause) {
1914   _cms_start_registered = true;
1915   _gc_timer_cm->register_gc_start();
1916   _gc_tracer_cm->report_gc_start(cause, _gc_timer_cm->gc_start());
1917 }
1918 
1919 void CMSCollector::register_gc_end() {
1920   if (_cms_start_registered) {
1921     report_heap_summary(GCWhen::AfterGC);
1922 
1923     _gc_timer_cm->register_gc_end();
1924     _gc_tracer_cm->report_gc_end(_gc_timer_cm->gc_end(), _gc_timer_cm->time_partitions());
1925     _cms_start_registered = false;
1926   }
1927 }
1928 
1929 void CMSCollector::save_heap_summary() {
1930   CMSHeap* heap = CMSHeap::heap();
1931   _last_heap_summary = heap->create_heap_summary();
1932   _last_metaspace_summary = heap->create_metaspace_summary();
1933 }
1934 
1935 void CMSCollector::report_heap_summary(GCWhen::Type when) {
1936   _gc_tracer_cm->report_gc_heap_summary(when, _last_heap_summary);
1937   _gc_tracer_cm->report_metaspace_summary(when, _last_metaspace_summary);
1938 }
1939 
1940 bool CMSCollector::waitForForegroundGC() {
1941   bool res = false;
1942   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1943          "CMS thread should have CMS token");
1944   // Block the foreground collector until the
1945   // background collectors decides whether to
1946   // yield.
1947   MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1948   _foregroundGCShouldWait = true;
1949   if (_foregroundGCIsActive) {
1950     // The background collector yields to the
1951     // foreground collector and returns a value
1952     // indicating that it has yielded.  The foreground
1953     // collector can proceed.
1954     res = true;
1955     _foregroundGCShouldWait = false;
1956     ConcurrentMarkSweepThread::clear_CMS_flag(
1957       ConcurrentMarkSweepThread::CMS_cms_has_token);
1958     ConcurrentMarkSweepThread::set_CMS_flag(
1959       ConcurrentMarkSweepThread::CMS_cms_wants_token);
1960     // Get a possibly blocked foreground thread going
1961     CGC_lock->notify();
1962     log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d",
1963                          p2i(Thread::current()), _collectorState);
1964     while (_foregroundGCIsActive) {
1965       CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1966     }
1967     ConcurrentMarkSweepThread::set_CMS_flag(
1968       ConcurrentMarkSweepThread::CMS_cms_has_token);
1969     ConcurrentMarkSweepThread::clear_CMS_flag(
1970       ConcurrentMarkSweepThread::CMS_cms_wants_token);
1971   }
1972   log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d",
1973                        p2i(Thread::current()), _collectorState);
1974   return res;
1975 }
1976 
1977 // Because of the need to lock the free lists and other structures in
1978 // the collector, common to all the generations that the collector is
1979 // collecting, we need the gc_prologues of individual CMS generations
1980 // delegate to their collector. It may have been simpler had the
1981 // current infrastructure allowed one to call a prologue on a
1982 // collector. In the absence of that we have the generation's
1983 // prologue delegate to the collector, which delegates back
1984 // some "local" work to a worker method in the individual generations
1985 // that it's responsible for collecting, while itself doing any
1986 // work common to all generations it's responsible for. A similar
1987 // comment applies to the  gc_epilogue()'s.
1988 // The role of the variable _between_prologue_and_epilogue is to
1989 // enforce the invocation protocol.
1990 void CMSCollector::gc_prologue(bool full) {
1991   // Call gc_prologue_work() for the CMSGen
1992   // we are responsible for.
1993 
1994   // The following locking discipline assumes that we are only called
1995   // when the world is stopped.
1996   assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption");
1997 
1998   // The CMSCollector prologue must call the gc_prologues for the
1999   // "generations" that it's responsible
2000   // for.
2001 
2002   assert(   Thread::current()->is_VM_thread()
2003          || (   CMSScavengeBeforeRemark
2004              && Thread::current()->is_ConcurrentGC_thread()),
2005          "Incorrect thread type for prologue execution");
2006 
2007   if (_between_prologue_and_epilogue) {
2008     // We have already been invoked; this is a gc_prologue delegation
2009     // from yet another CMS generation that we are responsible for, just
2010     // ignore it since all relevant work has already been done.
2011     return;
2012   }
2013 
2014   // set a bit saying prologue has been called; cleared in epilogue
2015   _between_prologue_and_epilogue = true;
2016   // Claim locks for common data structures, then call gc_prologue_work()
2017   // for each CMSGen.
2018 
2019   getFreelistLocks();   // gets free list locks on constituent spaces
2020   bitMapLock()->lock_without_safepoint_check();
2021 
2022   // Should call gc_prologue_work() for all cms gens we are responsible for
2023   bool duringMarking =    _collectorState >= Marking
2024                          && _collectorState < Sweeping;
2025 
2026   // The young collections clear the modified oops state, which tells if
2027   // there are any modified oops in the class. The remark phase also needs
2028   // that information. Tell the young collection to save the union of all
2029   // modified klasses.
2030   if (duringMarking) {
2031     _ct->cld_rem_set()->set_accumulate_modified_oops(true);
2032   }
2033 
2034   bool registerClosure = duringMarking;
2035 
2036   _cmsGen->gc_prologue_work(full, registerClosure, &_modUnionClosurePar);
2037 
2038   if (!full) {
2039     stats().record_gc0_begin();
2040   }
2041 }
2042 
2043 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) {
2044 
2045   _capacity_at_prologue = capacity();
2046   _used_at_prologue = used();
2047 
2048   // We enable promotion tracking so that card-scanning can recognize
2049   // which objects have been promoted during this GC and skip them.
2050   for (uint i = 0; i < ParallelGCThreads; i++) {
2051     _par_gc_thread_states[i]->promo.startTrackingPromotions();
2052   }
2053 
2054   // Delegate to CMScollector which knows how to coordinate between
2055   // this and any other CMS generations that it is responsible for
2056   // collecting.
2057   collector()->gc_prologue(full);
2058 }
2059 
2060 // This is a "private" interface for use by this generation's CMSCollector.
2061 // Not to be called directly by any other entity (for instance,
2062 // GenCollectedHeap, which calls the "public" gc_prologue method above).
2063 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full,
2064   bool registerClosure, ModUnionClosure* modUnionClosure) {
2065   assert(!incremental_collection_failed(), "Shouldn't be set yet");
2066   assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL,
2067     "Should be NULL");
2068   if (registerClosure) {
2069     cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure);
2070   }
2071   cmsSpace()->gc_prologue();
2072   // Clear stat counters
2073   NOT_PRODUCT(
2074     assert(_numObjectsPromoted == 0, "check");
2075     assert(_numWordsPromoted   == 0, "check");
2076     log_develop_trace(gc, alloc)("Allocated " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes concurrently",
2077                                  _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord));
2078     _numObjectsAllocated = 0;
2079     _numWordsAllocated   = 0;
2080   )
2081 }
2082 
2083 void CMSCollector::gc_epilogue(bool full) {
2084   // The following locking discipline assumes that we are only called
2085   // when the world is stopped.
2086   assert(SafepointSynchronize::is_at_safepoint(),
2087          "world is stopped assumption");
2088 
2089   // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks
2090   // if linear allocation blocks need to be appropriately marked to allow the
2091   // the blocks to be parsable. We also check here whether we need to nudge the
2092   // CMS collector thread to start a new cycle (if it's not already active).
2093   assert(   Thread::current()->is_VM_thread()
2094          || (   CMSScavengeBeforeRemark
2095              && Thread::current()->is_ConcurrentGC_thread()),
2096          "Incorrect thread type for epilogue execution");
2097 
2098   if (!_between_prologue_and_epilogue) {
2099     // We have already been invoked; this is a gc_epilogue delegation
2100     // from yet another CMS generation that we are responsible for, just
2101     // ignore it since all relevant work has already been done.
2102     return;
2103   }
2104   assert(haveFreelistLocks(), "must have freelist locks");
2105   assert_lock_strong(bitMapLock());
2106 
2107   _ct->cld_rem_set()->set_accumulate_modified_oops(false);
2108 
2109   _cmsGen->gc_epilogue_work(full);
2110 
2111   if (_collectorState == AbortablePreclean || _collectorState == Precleaning) {
2112     // in case sampling was not already enabled, enable it
2113     _start_sampling = true;
2114   }
2115   // reset _eden_chunk_array so sampling starts afresh
2116   _eden_chunk_index = 0;
2117 
2118   size_t cms_used   = _cmsGen->cmsSpace()->used();
2119 
2120   // update performance counters - this uses a special version of
2121   // update_counters() that allows the utilization to be passed as a
2122   // parameter, avoiding multiple calls to used().
2123   //
2124   _cmsGen->update_counters(cms_used);
2125 
2126   bitMapLock()->unlock();
2127   releaseFreelistLocks();
2128 
2129   if (!CleanChunkPoolAsync) {
2130     Chunk::clean_chunk_pool();
2131   }
2132 
2133   set_did_compact(false);
2134   _between_prologue_and_epilogue = false;  // ready for next cycle
2135 }
2136 
2137 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) {
2138   collector()->gc_epilogue(full);
2139 
2140   // When using ParNew, promotion tracking should have already been
2141   // disabled. However, the prologue (which enables promotion
2142   // tracking) and epilogue are called irrespective of the type of
2143   // GC. So they will also be called before and after Full GCs, during
2144   // which promotion tracking will not be explicitly disabled. So,
2145   // it's safer to also disable it here too (to be symmetric with
2146   // enabling it in the prologue).
2147   for (uint i = 0; i < ParallelGCThreads; i++) {
2148     _par_gc_thread_states[i]->promo.stopTrackingPromotions();
2149   }
2150 }
2151 
2152 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2153   assert(!incremental_collection_failed(), "Should have been cleared");
2154   cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2155   cmsSpace()->gc_epilogue();
2156     // Print stat counters
2157   NOT_PRODUCT(
2158     assert(_numObjectsAllocated == 0, "check");
2159     assert(_numWordsAllocated == 0, "check");
2160     log_develop_trace(gc, promotion)("Promoted " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
2161                                      _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2162     _numObjectsPromoted = 0;
2163     _numWordsPromoted   = 0;
2164   )
2165 
2166   // Call down the chain in contiguous_available needs the freelistLock
2167   // so print this out before releasing the freeListLock.
2168   log_develop_trace(gc)(" Contiguous available " SIZE_FORMAT " bytes ", contiguous_available());
2169 }
2170 
2171 #ifndef PRODUCT
2172 bool CMSCollector::have_cms_token() {
2173   Thread* thr = Thread::current();
2174   if (thr->is_VM_thread()) {
2175     return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2176   } else if (thr->is_ConcurrentGC_thread()) {
2177     return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2178   } else if (thr->is_GC_task_thread()) {
2179     return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2180            ParGCRareEvent_lock->owned_by_self();
2181   }
2182   return false;
2183 }
2184 
2185 // Check reachability of the given heap address in CMS generation,
2186 // treating all other generations as roots.
2187 bool CMSCollector::is_cms_reachable(HeapWord* addr) {
2188   // We could "guarantee" below, rather than assert, but I'll
2189   // leave these as "asserts" so that an adventurous debugger
2190   // could try this in the product build provided some subset of
2191   // the conditions were met, provided they were interested in the
2192   // results and knew that the computation below wouldn't interfere
2193   // with other concurrent computations mutating the structures
2194   // being read or written.
2195   assert(SafepointSynchronize::is_at_safepoint(),
2196          "Else mutations in object graph will make answer suspect");
2197   assert(have_cms_token(), "Should hold cms token");
2198   assert(haveFreelistLocks(), "must hold free list locks");
2199   assert_lock_strong(bitMapLock());
2200 
2201   // Clear the marking bit map array before starting, but, just
2202   // for kicks, first report if the given address is already marked
2203   tty->print_cr("Start: Address " PTR_FORMAT " is%s marked", p2i(addr),
2204                 _markBitMap.isMarked(addr) ? "" : " not");
2205 
2206   if (verify_after_remark()) {
2207     MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2208     bool result = verification_mark_bm()->isMarked(addr);
2209     tty->print_cr("TransitiveMark: Address " PTR_FORMAT " %s marked", p2i(addr),
2210                   result ? "IS" : "is NOT");
2211     return result;
2212   } else {
2213     tty->print_cr("Could not compute result");
2214     return false;
2215   }
2216 }
2217 #endif
2218 
2219 void
2220 CMSCollector::print_on_error(outputStream* st) {
2221   CMSCollector* collector = ConcurrentMarkSweepGeneration::_collector;
2222   if (collector != NULL) {
2223     CMSBitMap* bitmap = &collector->_markBitMap;
2224     st->print_cr("Marking Bits: (CMSBitMap*) " PTR_FORMAT, p2i(bitmap));
2225     bitmap->print_on_error(st, " Bits: ");
2226 
2227     st->cr();
2228 
2229     CMSBitMap* mut_bitmap = &collector->_modUnionTable;
2230     st->print_cr("Mod Union Table: (CMSBitMap*) " PTR_FORMAT, p2i(mut_bitmap));
2231     mut_bitmap->print_on_error(st, " Bits: ");
2232   }
2233 }
2234 
2235 ////////////////////////////////////////////////////////
2236 // CMS Verification Support
2237 ////////////////////////////////////////////////////////
2238 // Following the remark phase, the following invariant
2239 // should hold -- each object in the CMS heap which is
2240 // marked in markBitMap() should be marked in the verification_mark_bm().
2241 
2242 class VerifyMarkedClosure: public BitMapClosure {
2243   CMSBitMap* _marks;
2244   bool       _failed;
2245 
2246  public:
2247   VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2248 
2249   bool do_bit(size_t offset) {
2250     HeapWord* addr = _marks->offsetToHeapWord(offset);
2251     if (!_marks->isMarked(addr)) {
2252       Log(gc, verify) log;
2253       ResourceMark rm;
2254       LogStream ls(log.error());
2255       oop(addr)->print_on(&ls);
2256       log.error(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
2257       _failed = true;
2258     }
2259     return true;
2260   }
2261 
2262   bool failed() { return _failed; }
2263 };
2264 
2265 bool CMSCollector::verify_after_remark() {
2266   GCTraceTime(Info, gc, phases, verify) tm("Verifying CMS Marking.");
2267   MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2268   static bool init = false;
2269 
2270   assert(SafepointSynchronize::is_at_safepoint(),
2271          "Else mutations in object graph will make answer suspect");
2272   assert(have_cms_token(),
2273          "Else there may be mutual interference in use of "
2274          " verification data structures");
2275   assert(_collectorState > Marking && _collectorState <= Sweeping,
2276          "Else marking info checked here may be obsolete");
2277   assert(haveFreelistLocks(), "must hold free list locks");
2278   assert_lock_strong(bitMapLock());
2279 
2280 
2281   // Allocate marking bit map if not already allocated
2282   if (!init) { // first time
2283     if (!verification_mark_bm()->allocate(_span)) {
2284       return false;
2285     }
2286     init = true;
2287   }
2288 
2289   assert(verification_mark_stack()->isEmpty(), "Should be empty");
2290 
2291   // Turn off refs discovery -- so we will be tracing through refs.
2292   // This is as intended, because by this time
2293   // GC must already have cleared any refs that need to be cleared,
2294   // and traced those that need to be marked; moreover,
2295   // the marking done here is not going to interfere in any
2296   // way with the marking information used by GC.
2297   NoRefDiscovery no_discovery(ref_processor());
2298 
2299 #if COMPILER2_OR_JVMCI
2300   DerivedPointerTableDeactivate dpt_deact;
2301 #endif
2302 
2303   // Clear any marks from a previous round
2304   verification_mark_bm()->clear_all();
2305   assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
2306   verify_work_stacks_empty();
2307 
2308   CMSHeap* heap = CMSHeap::heap();
2309   heap->ensure_parsability(false);  // fill TLABs, but no need to retire them
2310   // Update the saved marks which may affect the root scans.
2311   heap->save_marks();
2312 
2313   if (CMSRemarkVerifyVariant == 1) {
2314     // In this first variant of verification, we complete
2315     // all marking, then check if the new marks-vector is
2316     // a subset of the CMS marks-vector.
2317     verify_after_remark_work_1();
2318   } else {
2319     guarantee(CMSRemarkVerifyVariant == 2, "Range checking for CMSRemarkVerifyVariant should guarantee 1 or 2");
2320     // In this second variant of verification, we flag an error
2321     // (i.e. an object reachable in the new marks-vector not reachable
2322     // in the CMS marks-vector) immediately, also indicating the
2323     // identify of an object (A) that references the unmarked object (B) --
2324     // presumably, a mutation to A failed to be picked up by preclean/remark?
2325     verify_after_remark_work_2();
2326   }
2327 
2328   return true;
2329 }
2330 
2331 void CMSCollector::verify_after_remark_work_1() {
2332   ResourceMark rm;
2333   HandleMark  hm;
2334   CMSHeap* heap = CMSHeap::heap();
2335 
2336   // Get a clear set of claim bits for the roots processing to work with.
2337   ClassLoaderDataGraph::clear_claimed_marks();
2338 
2339   // Mark from roots one level into CMS
2340   MarkRefsIntoClosure notOlder(_span, verification_mark_bm());
2341   heap->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2342 
2343   {
2344     StrongRootsScope srs(1);
2345 
2346     heap->cms_process_roots(&srs,
2347                            true,   // young gen as roots
2348                            GenCollectedHeap::ScanningOption(roots_scanning_options()),
2349                            should_unload_classes(),
2350                            &notOlder,
2351                            NULL);
2352   }
2353 
2354   // Now mark from the roots
2355   MarkFromRootsClosure markFromRootsClosure(this, _span,
2356     verification_mark_bm(), verification_mark_stack(),
2357     false /* don't yield */, true /* verifying */);
2358   assert(_restart_addr == NULL, "Expected pre-condition");
2359   verification_mark_bm()->iterate(&markFromRootsClosure);
2360   while (_restart_addr != NULL) {
2361     // Deal with stack overflow: by restarting at the indicated
2362     // address.
2363     HeapWord* ra = _restart_addr;
2364     markFromRootsClosure.reset(ra);
2365     _restart_addr = NULL;
2366     verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2367   }
2368   assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2369   verify_work_stacks_empty();
2370 
2371   // Marking completed -- now verify that each bit marked in
2372   // verification_mark_bm() is also marked in markBitMap(); flag all
2373   // errors by printing corresponding objects.
2374   VerifyMarkedClosure vcl(markBitMap());
2375   verification_mark_bm()->iterate(&vcl);
2376   if (vcl.failed()) {
2377     Log(gc, verify) log;
2378     log.error("Failed marking verification after remark");
2379     ResourceMark rm;
2380     LogStream ls(log.error());
2381     heap->print_on(&ls);
2382     fatal("CMS: failed marking verification after remark");
2383   }
2384 }
2385 
2386 class VerifyCLDOopsCLDClosure : public CLDClosure {
2387   class VerifyCLDOopsClosure : public OopClosure {
2388     CMSBitMap* _bitmap;
2389    public:
2390     VerifyCLDOopsClosure(CMSBitMap* bitmap) : _bitmap(bitmap) { }
2391     void do_oop(oop* p)       { guarantee(*p == NULL || _bitmap->isMarked((HeapWord*) *p), "Should be marked"); }
2392     void do_oop(narrowOop* p) { ShouldNotReachHere(); }
2393   } _oop_closure;
2394  public:
2395   VerifyCLDOopsCLDClosure(CMSBitMap* bitmap) : _oop_closure(bitmap) {}
2396   void do_cld(ClassLoaderData* cld) {
2397     cld->oops_do(&_oop_closure, false, false);
2398   }
2399 };
2400 
2401 void CMSCollector::verify_after_remark_work_2() {
2402   ResourceMark rm;
2403   HandleMark  hm;
2404   CMSHeap* heap = CMSHeap::heap();
2405 
2406   // Get a clear set of claim bits for the roots processing to work with.
2407   ClassLoaderDataGraph::clear_claimed_marks();
2408 
2409   // Mark from roots one level into CMS
2410   MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
2411                                      markBitMap());
2412   CLDToOopClosure cld_closure(&notOlder, true);
2413 
2414   heap->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2415 
2416   {
2417     StrongRootsScope srs(1);
2418 
2419     heap->cms_process_roots(&srs,
2420                            true,   // young gen as roots
2421                            GenCollectedHeap::ScanningOption(roots_scanning_options()),
2422                            should_unload_classes(),
2423                            &notOlder,
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   VerifyCLDOopsCLDClosure verify_cld_oops(verification_mark_bm());
2444   ClassLoaderDataGraph::cld_do(&verify_cld_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 //  (a) class unloading is enabled at the command line, and
2567 //  (b) old gen is getting really full
2568 // NOTE: Provided there is no change in the state of the heap between
2569 // calls to this method, it should have idempotent results. Moreover,
2570 // its results should be monotonically increasing (i.e. going from 0 to 1,
2571 // but not 1 to 0) between successive calls between which the heap was
2572 // not collected. For the implementation below, it must thus rely on
2573 // the property that concurrent_cycles_since_last_unload()
2574 // will not decrease unless a collection cycle happened and that
2575 // _cmsGen->is_too_full() are
2576 // themselves also monotonic in that sense. See check_monotonicity()
2577 // below.
2578 void CMSCollector::update_should_unload_classes() {
2579   _should_unload_classes = false;
2580   if (CMSClassUnloadingEnabled) {
2581     _should_unload_classes = (concurrent_cycles_since_last_unload() >=
2582                               CMSClassUnloadingMaxInterval)
2583                            || _cmsGen->is_too_full();
2584   }
2585 }
2586 
2587 bool ConcurrentMarkSweepGeneration::is_too_full() const {
2588   bool res = should_concurrent_collect();
2589   res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
2590   return res;
2591 }
2592 
2593 void CMSCollector::setup_cms_unloading_and_verification_state() {
2594   const  bool should_verify =   VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
2595                              || VerifyBeforeExit;
2596   const  int  rso           =   GenCollectedHeap::SO_AllCodeCache;
2597 
2598   // We set the proper root for this CMS cycle here.
2599   if (should_unload_classes()) {   // Should unload classes this cycle
2600     remove_root_scanning_option(rso);  // Shrink the root set appropriately
2601     set_verifying(should_verify);    // Set verification state for this cycle
2602     return;                            // Nothing else needs to be done at this time
2603   }
2604 
2605   // Not unloading classes this cycle
2606   assert(!should_unload_classes(), "Inconsistency!");
2607 
2608   // If we are not unloading classes then add SO_AllCodeCache to root
2609   // scanning options.
2610   add_root_scanning_option(rso);
2611 
2612   if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
2613     set_verifying(true);
2614   } else if (verifying() && !should_verify) {
2615     // We were verifying, but some verification flags got disabled.
2616     set_verifying(false);
2617     // Exclude symbols, strings and code cache elements from root scanning to
2618     // reduce IM and RM pauses.
2619     remove_root_scanning_option(rso);
2620   }
2621 }
2622 
2623 
2624 #ifndef PRODUCT
2625 HeapWord* CMSCollector::block_start(const void* p) const {
2626   const HeapWord* addr = (HeapWord*)p;
2627   if (_span.contains(p)) {
2628     if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
2629       return _cmsGen->cmsSpace()->block_start(p);
2630     }
2631   }
2632   return NULL;
2633 }
2634 #endif
2635 
2636 HeapWord*
2637 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
2638                                                    bool   tlab,
2639                                                    bool   parallel) {
2640   CMSSynchronousYieldRequest yr;
2641   assert(!tlab, "Can't deal with TLAB allocation");
2642   MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2643   expand_for_gc_cause(word_size*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_allocation);
2644   if (GCExpandToAllocateDelayMillis > 0) {
2645     os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2646   }
2647   return have_lock_and_allocate(word_size, tlab);
2648 }
2649 
2650 void ConcurrentMarkSweepGeneration::expand_for_gc_cause(
2651     size_t bytes,
2652     size_t expand_bytes,
2653     CMSExpansionCause::Cause cause)
2654 {
2655 
2656   bool success = expand(bytes, expand_bytes);
2657 
2658   // remember why we expanded; this information is used
2659   // by shouldConcurrentCollect() when making decisions on whether to start
2660   // a new CMS cycle.
2661   if (success) {
2662     set_expansion_cause(cause);
2663     log_trace(gc)("Expanded CMS gen for %s",  CMSExpansionCause::to_string(cause));
2664   }
2665 }
2666 
2667 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
2668   HeapWord* res = NULL;
2669   MutexLocker x(ParGCRareEvent_lock);
2670   while (true) {
2671     // Expansion by some other thread might make alloc OK now:
2672     res = ps->lab.alloc(word_sz);
2673     if (res != NULL) return res;
2674     // If there's not enough expansion space available, give up.
2675     if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
2676       return NULL;
2677     }
2678     // Otherwise, we try expansion.
2679     expand_for_gc_cause(word_sz*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_lab);
2680     // Now go around the loop and try alloc again;
2681     // A competing par_promote might beat us to the expansion space,
2682     // so we may go around the loop again if promotion fails again.
2683     if (GCExpandToAllocateDelayMillis > 0) {
2684       os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2685     }
2686   }
2687 }
2688 
2689 
2690 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
2691   PromotionInfo* promo) {
2692   MutexLocker x(ParGCRareEvent_lock);
2693   size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
2694   while (true) {
2695     // Expansion by some other thread might make alloc OK now:
2696     if (promo->ensure_spooling_space()) {
2697       assert(promo->has_spooling_space(),
2698              "Post-condition of successful ensure_spooling_space()");
2699       return true;
2700     }
2701     // If there's not enough expansion space available, give up.
2702     if (_virtual_space.uncommitted_size() < refill_size_bytes) {
2703       return false;
2704     }
2705     // Otherwise, we try expansion.
2706     expand_for_gc_cause(refill_size_bytes, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_spooling_space);
2707     // Now go around the loop and try alloc again;
2708     // A competing allocation might beat us to the expansion space,
2709     // so we may go around the loop again if allocation fails again.
2710     if (GCExpandToAllocateDelayMillis > 0) {
2711       os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2712     }
2713   }
2714 }
2715 
2716 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
2717   // Only shrink if a compaction was done so that all the free space
2718   // in the generation is in a contiguous block at the end.
2719   if (did_compact()) {
2720     CardGeneration::shrink(bytes);
2721   }
2722 }
2723 
2724 void ConcurrentMarkSweepGeneration::assert_correct_size_change_locking() {
2725   assert_locked_or_safepoint(Heap_lock);
2726 }
2727 
2728 void ConcurrentMarkSweepGeneration::shrink_free_list_by(size_t bytes) {
2729   assert_locked_or_safepoint(Heap_lock);
2730   assert_lock_strong(freelistLock());
2731   log_trace(gc)("Shrinking of CMS not yet implemented");
2732   return;
2733 }
2734 
2735 
2736 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
2737 // phases.
2738 class CMSPhaseAccounting: public StackObj {
2739  public:
2740   CMSPhaseAccounting(CMSCollector *collector,
2741                      const char *title);
2742   ~CMSPhaseAccounting();
2743 
2744  private:
2745   CMSCollector *_collector;
2746   const char *_title;
2747   GCTraceConcTime(Info, gc) _trace_time;
2748 
2749  public:
2750   // Not MT-safe; so do not pass around these StackObj's
2751   // where they may be accessed by other threads.
2752   double wallclock_millis() {
2753     return TimeHelper::counter_to_millis(os::elapsed_counter() - _trace_time.start_time());
2754   }
2755 };
2756 
2757 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
2758                                        const char *title) :
2759   _collector(collector), _title(title), _trace_time(title) {
2760 
2761   _collector->resetYields();
2762   _collector->resetTimer();
2763   _collector->startTimer();
2764   _collector->gc_timer_cm()->register_gc_concurrent_start(title);
2765 }
2766 
2767 CMSPhaseAccounting::~CMSPhaseAccounting() {
2768   _collector->gc_timer_cm()->register_gc_concurrent_end();
2769   _collector->stopTimer();
2770   log_debug(gc)("Concurrent active time: %.3fms", TimeHelper::counter_to_seconds(_collector->timerTicks()));
2771   log_trace(gc)(" (CMS %s yielded %d times)", _title, _collector->yields());
2772 }
2773 
2774 // CMS work
2775 
2776 // The common parts of CMSParInitialMarkTask and CMSParRemarkTask.
2777 class CMSParMarkTask : public AbstractGangTask {
2778  protected:
2779   CMSCollector*     _collector;
2780   uint              _n_workers;
2781   CMSParMarkTask(const char* name, CMSCollector* collector, uint n_workers) :
2782       AbstractGangTask(name),
2783       _collector(collector),
2784       _n_workers(n_workers) {}
2785   // Work method in support of parallel rescan ... of young gen spaces
2786   void do_young_space_rescan(OopsInGenClosure* cl,
2787                              ContiguousSpace* space,
2788                              HeapWord** chunk_array, size_t chunk_top);
2789   void work_on_young_gen_roots(OopsInGenClosure* cl);
2790 };
2791 
2792 // Parallel initial mark task
2793 class CMSParInitialMarkTask: public CMSParMarkTask {
2794   StrongRootsScope* _strong_roots_scope;
2795  public:
2796   CMSParInitialMarkTask(CMSCollector* collector, StrongRootsScope* strong_roots_scope, uint n_workers) :
2797       CMSParMarkTask("Scan roots and young gen for initial mark in parallel", collector, n_workers),
2798       _strong_roots_scope(strong_roots_scope) {}
2799   void work(uint worker_id);
2800 };
2801 
2802 // Checkpoint the roots into this generation from outside
2803 // this generation. [Note this initial checkpoint need only
2804 // be approximate -- we'll do a catch up phase subsequently.]
2805 void CMSCollector::checkpointRootsInitial() {
2806   assert(_collectorState == InitialMarking, "Wrong collector state");
2807   check_correct_thread_executing();
2808   TraceCMSMemoryManagerStats tms(_collectorState, CMSHeap::heap()->gc_cause());
2809 
2810   save_heap_summary();
2811   report_heap_summary(GCWhen::BeforeGC);
2812 
2813   ReferenceProcessor* rp = ref_processor();
2814   assert(_restart_addr == NULL, "Control point invariant");
2815   {
2816     // acquire locks for subsequent manipulations
2817     MutexLockerEx x(bitMapLock(),
2818                     Mutex::_no_safepoint_check_flag);
2819     checkpointRootsInitialWork();
2820     // enable ("weak") refs discovery
2821     rp->enable_discovery();
2822     _collectorState = Marking;
2823   }
2824 }
2825 
2826 void CMSCollector::checkpointRootsInitialWork() {
2827   assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
2828   assert(_collectorState == InitialMarking, "just checking");
2829 
2830   // Already have locks.
2831   assert_lock_strong(bitMapLock());
2832   assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
2833 
2834   // Setup the verification and class unloading state for this
2835   // CMS collection cycle.
2836   setup_cms_unloading_and_verification_state();
2837 
2838   GCTraceTime(Trace, gc, phases) ts("checkpointRootsInitialWork", _gc_timer_cm);
2839 
2840   // Reset all the PLAB chunk arrays if necessary.
2841   if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
2842     reset_survivor_plab_arrays();
2843   }
2844 
2845   ResourceMark rm;
2846   HandleMark  hm;
2847 
2848   MarkRefsIntoClosure notOlder(_span, &_markBitMap);
2849   CMSHeap* heap = CMSHeap::heap();
2850 
2851   verify_work_stacks_empty();
2852   verify_overflow_empty();
2853 
2854   heap->ensure_parsability(false);  // fill TLABs, but no need to retire them
2855   // Update the saved marks which may affect the root scans.
2856   heap->save_marks();
2857 
2858   // weak reference processing has not started yet.
2859   ref_processor()->set_enqueuing_is_done(false);
2860 
2861   // Need to remember all newly created CLDs,
2862   // so that we can guarantee that the remark finds them.
2863   ClassLoaderDataGraph::remember_new_clds(true);
2864 
2865   // Whenever a CLD is found, it will be claimed before proceeding to mark
2866   // the klasses. The claimed marks need to be cleared before marking starts.
2867   ClassLoaderDataGraph::clear_claimed_marks();
2868 
2869   print_eden_and_survivor_chunk_arrays();
2870 
2871   {
2872 #if COMPILER2_OR_JVMCI
2873     DerivedPointerTableDeactivate dpt_deact;
2874 #endif
2875     if (CMSParallelInitialMarkEnabled) {
2876       // The parallel version.
2877       WorkGang* workers = heap->workers();
2878       assert(workers != NULL, "Need parallel worker threads.");
2879       uint n_workers = workers->active_workers();
2880 
2881       StrongRootsScope srs(n_workers);
2882 
2883       CMSParInitialMarkTask tsk(this, &srs, n_workers);
2884       initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
2885       // If the total workers is greater than 1, then multiple workers
2886       // may be used at some time and the initialization has been set
2887       // such that the single threaded path cannot be used.
2888       if (workers->total_workers() > 1) {
2889         workers->run_task(&tsk);
2890       } else {
2891         tsk.work(0);
2892       }
2893     } else {
2894       // The serial version.
2895       CLDToOopClosure cld_closure(&notOlder, true);
2896       heap->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2897 
2898       StrongRootsScope srs(1);
2899 
2900       heap->cms_process_roots(&srs,
2901                              true,   // young gen as roots
2902                              GenCollectedHeap::ScanningOption(roots_scanning_options()),
2903                              should_unload_classes(),
2904                              &notOlder,
2905                              &cld_closure);
2906     }
2907   }
2908 
2909   // Clear mod-union table; it will be dirtied in the prologue of
2910   // CMS generation per each young generation collection.
2911 
2912   assert(_modUnionTable.isAllClear(),
2913        "Was cleared in most recent final checkpoint phase"
2914        " or no bits are set in the gc_prologue before the start of the next "
2915        "subsequent marking phase.");
2916 
2917   assert(_ct->cld_rem_set()->mod_union_is_clear(), "Must be");
2918 
2919   // Save the end of the used_region of the constituent generations
2920   // to be used to limit the extent of sweep in each generation.
2921   save_sweep_limits();
2922   verify_overflow_empty();
2923 }
2924 
2925 bool CMSCollector::markFromRoots() {
2926   // we might be tempted to assert that:
2927   // assert(!SafepointSynchronize::is_at_safepoint(),
2928   //        "inconsistent argument?");
2929   // However that wouldn't be right, because it's possible that
2930   // a safepoint is indeed in progress as a young generation
2931   // stop-the-world GC happens even as we mark in this generation.
2932   assert(_collectorState == Marking, "inconsistent state?");
2933   check_correct_thread_executing();
2934   verify_overflow_empty();
2935 
2936   // Weak ref discovery note: We may be discovering weak
2937   // refs in this generation concurrent (but interleaved) with
2938   // weak ref discovery by the young generation collector.
2939 
2940   CMSTokenSyncWithLocks ts(true, bitMapLock());
2941   GCTraceCPUTime tcpu;
2942   CMSPhaseAccounting pa(this, "Concurrent Mark");
2943   bool res = markFromRootsWork();
2944   if (res) {
2945     _collectorState = Precleaning;
2946   } else { // We failed and a foreground collection wants to take over
2947     assert(_foregroundGCIsActive, "internal state inconsistency");
2948     assert(_restart_addr == NULL,  "foreground will restart from scratch");
2949     log_debug(gc)("bailing out to foreground collection");
2950   }
2951   verify_overflow_empty();
2952   return res;
2953 }
2954 
2955 bool CMSCollector::markFromRootsWork() {
2956   // iterate over marked bits in bit map, doing a full scan and mark
2957   // from these roots using the following algorithm:
2958   // . if oop is to the right of the current scan pointer,
2959   //   mark corresponding bit (we'll process it later)
2960   // . else (oop is to left of current scan pointer)
2961   //   push oop on marking stack
2962   // . drain the marking stack
2963 
2964   // Note that when we do a marking step we need to hold the
2965   // bit map lock -- recall that direct allocation (by mutators)
2966   // and promotion (by the young generation collector) is also
2967   // marking the bit map. [the so-called allocate live policy.]
2968   // Because the implementation of bit map marking is not
2969   // robust wrt simultaneous marking of bits in the same word,
2970   // we need to make sure that there is no such interference
2971   // between concurrent such updates.
2972 
2973   // already have locks
2974   assert_lock_strong(bitMapLock());
2975 
2976   verify_work_stacks_empty();
2977   verify_overflow_empty();
2978   bool result = false;
2979   if (CMSConcurrentMTEnabled && ConcGCThreads > 0) {
2980     result = do_marking_mt();
2981   } else {
2982     result = do_marking_st();
2983   }
2984   return result;
2985 }
2986 
2987 // Forward decl
2988 class CMSConcMarkingTask;
2989 
2990 class CMSConcMarkingTerminator: public ParallelTaskTerminator {
2991   CMSCollector*       _collector;
2992   CMSConcMarkingTask* _task;
2993  public:
2994   virtual void yield();
2995 
2996   // "n_threads" is the number of threads to be terminated.
2997   // "queue_set" is a set of work queues of other threads.
2998   // "collector" is the CMS collector associated with this task terminator.
2999   // "yield" indicates whether we need the gang as a whole to yield.
3000   CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
3001     ParallelTaskTerminator(n_threads, queue_set),
3002     _collector(collector) { }
3003 
3004   void set_task(CMSConcMarkingTask* task) {
3005     _task = task;
3006   }
3007 };
3008 
3009 class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator {
3010   CMSConcMarkingTask* _task;
3011  public:
3012   bool should_exit_termination();
3013   void set_task(CMSConcMarkingTask* task) {
3014     _task = task;
3015   }
3016 };
3017 
3018 // MT Concurrent Marking Task
3019 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3020   CMSCollector*             _collector;
3021   uint                      _n_workers;      // requested/desired # workers
3022   bool                      _result;
3023   CompactibleFreeListSpace* _cms_space;
3024   char                      _pad_front[64];   // padding to ...
3025   HeapWord* volatile        _global_finger;   // ... avoid sharing cache line
3026   char                      _pad_back[64];
3027   HeapWord*                 _restart_addr;
3028 
3029   //  Exposed here for yielding support
3030   Mutex* const _bit_map_lock;
3031 
3032   // The per thread work queues, available here for stealing
3033   OopTaskQueueSet*  _task_queues;
3034 
3035   // Termination (and yielding) support
3036   CMSConcMarkingTerminator _term;
3037   CMSConcMarkingTerminatorTerminator _term_term;
3038 
3039  public:
3040   CMSConcMarkingTask(CMSCollector* collector,
3041                  CompactibleFreeListSpace* cms_space,
3042                  YieldingFlexibleWorkGang* workers,
3043                  OopTaskQueueSet* task_queues):
3044     YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3045     _collector(collector),
3046     _cms_space(cms_space),
3047     _n_workers(0), _result(true),
3048     _task_queues(task_queues),
3049     _term(_n_workers, task_queues, _collector),
3050     _bit_map_lock(collector->bitMapLock())
3051   {
3052     _requested_size = _n_workers;
3053     _term.set_task(this);
3054     _term_term.set_task(this);
3055     _restart_addr = _global_finger = _cms_space->bottom();
3056   }
3057 
3058 
3059   OopTaskQueueSet* task_queues()  { return _task_queues; }
3060 
3061   OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3062 
3063   HeapWord* volatile* global_finger_addr() { return &_global_finger; }
3064 
3065   CMSConcMarkingTerminator* terminator() { return &_term; }
3066 
3067   virtual void set_for_termination(uint active_workers) {
3068     terminator()->reset_for_reuse(active_workers);
3069   }
3070 
3071   void work(uint worker_id);
3072   bool should_yield() {
3073     return    ConcurrentMarkSweepThread::should_yield()
3074            && !_collector->foregroundGCIsActive();
3075   }
3076 
3077   virtual void coordinator_yield();  // stuff done by coordinator
3078   bool result() { return _result; }
3079 
3080   void reset(HeapWord* ra) {
3081     assert(_global_finger >= _cms_space->end(),  "Postcondition of ::work(i)");
3082     _restart_addr = _global_finger = ra;
3083     _term.reset_for_reuse();
3084   }
3085 
3086   static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3087                                            OopTaskQueue* work_q);
3088 
3089  private:
3090   void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3091   void do_work_steal(int i);
3092   void bump_global_finger(HeapWord* f);
3093 };
3094 
3095 bool CMSConcMarkingTerminatorTerminator::should_exit_termination() {
3096   assert(_task != NULL, "Error");
3097   return _task->yielding();
3098   // Note that we do not need the disjunct || _task->should_yield() above
3099   // because we want terminating threads to yield only if the task
3100   // is already in the midst of yielding, which happens only after at least one
3101   // thread has yielded.
3102 }
3103 
3104 void CMSConcMarkingTerminator::yield() {
3105   if (_task->should_yield()) {
3106     _task->yield();
3107   } else {
3108     ParallelTaskTerminator::yield();
3109   }
3110 }
3111 
3112 ////////////////////////////////////////////////////////////////
3113 // Concurrent Marking Algorithm Sketch
3114 ////////////////////////////////////////////////////////////////
3115 // Until all tasks exhausted (both spaces):
3116 // -- claim next available chunk
3117 // -- bump global finger via CAS
3118 // -- find first object that starts in this chunk
3119 //    and start scanning bitmap from that position
3120 // -- scan marked objects for oops
3121 // -- CAS-mark target, and if successful:
3122 //    . if target oop is above global finger (volatile read)
3123 //      nothing to do
3124 //    . if target oop is in chunk and above local finger
3125 //        then nothing to do
3126 //    . else push on work-queue
3127 // -- Deal with possible overflow issues:
3128 //    . local work-queue overflow causes stuff to be pushed on
3129 //      global (common) overflow queue
3130 //    . always first empty local work queue
3131 //    . then get a batch of oops from global work queue if any
3132 //    . then do work stealing
3133 // -- When all tasks claimed (both spaces)
3134 //    and local work queue empty,
3135 //    then in a loop do:
3136 //    . check global overflow stack; steal a batch of oops and trace
3137 //    . try to steal from other threads oif GOS is empty
3138 //    . if neither is available, offer termination
3139 // -- Terminate and return result
3140 //
3141 void CMSConcMarkingTask::work(uint worker_id) {
3142   elapsedTimer _timer;
3143   ResourceMark rm;
3144   HandleMark hm;
3145 
3146   DEBUG_ONLY(_collector->verify_overflow_empty();)
3147 
3148   // Before we begin work, our work queue should be empty
3149   assert(work_queue(worker_id)->size() == 0, "Expected to be empty");
3150   // Scan the bitmap covering _cms_space, tracing through grey objects.
3151   _timer.start();
3152   do_scan_and_mark(worker_id, _cms_space);
3153   _timer.stop();
3154   log_trace(gc, task)("Finished cms space scanning in %dth thread: %3.3f sec", worker_id, _timer.seconds());
3155 
3156   // ... do work stealing
3157   _timer.reset();
3158   _timer.start();
3159   do_work_steal(worker_id);
3160   _timer.stop();
3161   log_trace(gc, task)("Finished work stealing in %dth thread: %3.3f sec", worker_id, _timer.seconds());
3162   assert(_collector->_markStack.isEmpty(), "Should have been emptied");
3163   assert(work_queue(worker_id)->size() == 0, "Should have been emptied");
3164   // Note that under the current task protocol, the
3165   // following assertion is true even of the spaces
3166   // expanded since the completion of the concurrent
3167   // marking. XXX This will likely change under a strict
3168   // ABORT semantics.
3169   // After perm removal the comparison was changed to
3170   // greater than or equal to from strictly greater than.
3171   // Before perm removal the highest address sweep would
3172   // have been at the end of perm gen but now is at the
3173   // end of the tenured gen.
3174   assert(_global_finger >=  _cms_space->end(),
3175          "All tasks have been completed");
3176   DEBUG_ONLY(_collector->verify_overflow_empty();)
3177 }
3178 
3179 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
3180   HeapWord* read = _global_finger;
3181   HeapWord* cur  = read;
3182   while (f > read) {
3183     cur = read;
3184     read = Atomic::cmpxchg(f, &_global_finger, cur);
3185     if (cur == read) {
3186       // our cas succeeded
3187       assert(_global_finger >= f, "protocol consistency");
3188       break;
3189     }
3190   }
3191 }
3192 
3193 // This is really inefficient, and should be redone by
3194 // using (not yet available) block-read and -write interfaces to the
3195 // stack and the work_queue. XXX FIX ME !!!
3196 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3197                                                       OopTaskQueue* work_q) {
3198   // Fast lock-free check
3199   if (ovflw_stk->length() == 0) {
3200     return false;
3201   }
3202   assert(work_q->size() == 0, "Shouldn't steal");
3203   MutexLockerEx ml(ovflw_stk->par_lock(),
3204                    Mutex::_no_safepoint_check_flag);
3205   // Grab up to 1/4 the size of the work queue
3206   size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
3207                     (size_t)ParGCDesiredObjsFromOverflowList);
3208   num = MIN2(num, ovflw_stk->length());
3209   for (int i = (int) num; i > 0; i--) {
3210     oop cur = ovflw_stk->pop();
3211     assert(cur != NULL, "Counted wrong?");
3212     work_q->push(cur);
3213   }
3214   return num > 0;
3215 }
3216 
3217 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
3218   SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
3219   int n_tasks = pst->n_tasks();
3220   // We allow that there may be no tasks to do here because
3221   // we are restarting after a stack overflow.
3222   assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
3223   uint nth_task = 0;
3224 
3225   HeapWord* aligned_start = sp->bottom();
3226   if (sp->used_region().contains(_restart_addr)) {
3227     // Align down to a card boundary for the start of 0th task
3228     // for this space.
3229     aligned_start = align_down(_restart_addr, CardTableModRefBS::card_size);
3230   }
3231 
3232   size_t chunk_size = sp->marking_task_size();
3233   while (!pst->is_task_claimed(/* reference */ nth_task)) {
3234     // Having claimed the nth task in this space,
3235     // compute the chunk that it corresponds to:
3236     MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
3237                                aligned_start + (nth_task+1)*chunk_size);
3238     // Try and bump the global finger via a CAS;
3239     // note that we need to do the global finger bump
3240     // _before_ taking the intersection below, because
3241     // the task corresponding to that region will be
3242     // deemed done even if the used_region() expands
3243     // because of allocation -- as it almost certainly will
3244     // during start-up while the threads yield in the
3245     // closure below.
3246     HeapWord* finger = span.end();
3247     bump_global_finger(finger);   // atomically
3248     // There are null tasks here corresponding to chunks
3249     // beyond the "top" address of the space.
3250     span = span.intersection(sp->used_region());
3251     if (!span.is_empty()) {  // Non-null task
3252       HeapWord* prev_obj;
3253       assert(!span.contains(_restart_addr) || nth_task == 0,
3254              "Inconsistency");
3255       if (nth_task == 0) {
3256         // For the 0th task, we'll not need to compute a block_start.
3257         if (span.contains(_restart_addr)) {
3258           // In the case of a restart because of stack overflow,
3259           // we might additionally skip a chunk prefix.
3260           prev_obj = _restart_addr;
3261         } else {
3262           prev_obj = span.start();
3263         }
3264       } else {
3265         // We want to skip the first object because
3266         // the protocol is to scan any object in its entirety
3267         // that _starts_ in this span; a fortiori, any
3268         // object starting in an earlier span is scanned
3269         // as part of an earlier claimed task.
3270         // Below we use the "careful" version of block_start
3271         // so we do not try to navigate uninitialized objects.
3272         prev_obj = sp->block_start_careful(span.start());
3273         // Below we use a variant of block_size that uses the
3274         // Printezis bits to avoid waiting for allocated
3275         // objects to become initialized/parsable.
3276         while (prev_obj < span.start()) {
3277           size_t sz = sp->block_size_no_stall(prev_obj, _collector);
3278           if (sz > 0) {
3279             prev_obj += sz;
3280           } else {
3281             // In this case we may end up doing a bit of redundant
3282             // scanning, but that appears unavoidable, short of
3283             // locking the free list locks; see bug 6324141.
3284             break;
3285           }
3286         }
3287       }
3288       if (prev_obj < span.end()) {
3289         MemRegion my_span = MemRegion(prev_obj, span.end());
3290         // Do the marking work within a non-empty span --
3291         // the last argument to the constructor indicates whether the
3292         // iteration should be incremental with periodic yields.
3293         ParMarkFromRootsClosure cl(this, _collector, my_span,
3294                                    &_collector->_markBitMap,
3295                                    work_queue(i),
3296                                    &_collector->_markStack);
3297         _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
3298       } // else nothing to do for this task
3299     }   // else nothing to do for this task
3300   }
3301   // We'd be tempted to assert here that since there are no
3302   // more tasks left to claim in this space, the global_finger
3303   // must exceed space->top() and a fortiori space->end(). However,
3304   // that would not quite be correct because the bumping of
3305   // global_finger occurs strictly after the claiming of a task,
3306   // so by the time we reach here the global finger may not yet
3307   // have been bumped up by the thread that claimed the last
3308   // task.
3309   pst->all_tasks_completed();
3310 }
3311 
3312 class ParConcMarkingClosure: public MetadataAwareOopClosure {
3313  private:
3314   CMSCollector* _collector;
3315   CMSConcMarkingTask* _task;
3316   MemRegion     _span;
3317   CMSBitMap*    _bit_map;
3318   CMSMarkStack* _overflow_stack;
3319   OopTaskQueue* _work_queue;
3320  protected:
3321   DO_OOP_WORK_DEFN
3322  public:
3323   ParConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue,
3324                         CMSBitMap* bit_map, CMSMarkStack* overflow_stack):
3325     MetadataAwareOopClosure(collector->ref_processor()),
3326     _collector(collector),
3327     _task(task),
3328     _span(collector->_span),
3329     _work_queue(work_queue),
3330     _bit_map(bit_map),
3331     _overflow_stack(overflow_stack)
3332   { }
3333   virtual void do_oop(oop* p);
3334   virtual void do_oop(narrowOop* p);
3335 
3336   void trim_queue(size_t max);
3337   void handle_stack_overflow(HeapWord* lost);
3338   void do_yield_check() {
3339     if (_task->should_yield()) {
3340       _task->yield();
3341     }
3342   }
3343 };
3344 
3345 DO_OOP_WORK_IMPL(ParConcMarkingClosure)
3346 
3347 // Grey object scanning during work stealing phase --
3348 // the salient assumption here is that any references
3349 // that are in these stolen objects being scanned must
3350 // already have been initialized (else they would not have
3351 // been published), so we do not need to check for
3352 // uninitialized objects before pushing here.
3353 void ParConcMarkingClosure::do_oop(oop obj) {
3354   assert(oopDesc::is_oop_or_null(obj, true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
3355   HeapWord* addr = (HeapWord*)obj;
3356   // Check if oop points into the CMS generation
3357   // and is not marked
3358   if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
3359     // a white object ...
3360     // If we manage to "claim" the object, by being the
3361     // first thread to mark it, then we push it on our
3362     // marking stack
3363     if (_bit_map->par_mark(addr)) {     // ... now grey
3364       // push on work queue (grey set)
3365       bool simulate_overflow = false;
3366       NOT_PRODUCT(
3367         if (CMSMarkStackOverflowALot &&
3368             _collector->simulate_overflow()) {
3369           // simulate a stack overflow
3370           simulate_overflow = true;
3371         }
3372       )
3373       if (simulate_overflow ||
3374           !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
3375         // stack overflow
3376         log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _overflow_stack->capacity());
3377         // We cannot assert that the overflow stack is full because
3378         // it may have been emptied since.
3379         assert(simulate_overflow ||
3380                _work_queue->size() == _work_queue->max_elems(),
3381               "Else push should have succeeded");
3382         handle_stack_overflow(addr);
3383       }
3384     } // Else, some other thread got there first
3385     do_yield_check();
3386   }
3387 }
3388 
3389 void ParConcMarkingClosure::do_oop(oop* p)       { ParConcMarkingClosure::do_oop_work(p); }
3390 void ParConcMarkingClosure::do_oop(narrowOop* p) { ParConcMarkingClosure::do_oop_work(p); }
3391 
3392 void ParConcMarkingClosure::trim_queue(size_t max) {
3393   while (_work_queue->size() > max) {
3394     oop new_oop;
3395     if (_work_queue->pop_local(new_oop)) {
3396       assert(oopDesc::is_oop(new_oop), "Should be an oop");
3397       assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
3398       assert(_span.contains((HeapWord*)new_oop), "Not in span");
3399       new_oop->oop_iterate(this);  // do_oop() above
3400       do_yield_check();
3401     }
3402   }
3403 }
3404 
3405 // Upon stack overflow, we discard (part of) the stack,
3406 // remembering the least address amongst those discarded
3407 // in CMSCollector's _restart_address.
3408 void ParConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
3409   // We need to do this under a mutex to prevent other
3410   // workers from interfering with the work done below.
3411   MutexLockerEx ml(_overflow_stack->par_lock(),
3412                    Mutex::_no_safepoint_check_flag);
3413   // Remember the least grey address discarded
3414   HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
3415   _collector->lower_restart_addr(ra);
3416   _overflow_stack->reset();  // discard stack contents
3417   _overflow_stack->expand(); // expand the stack if possible
3418 }
3419 
3420 
3421 void CMSConcMarkingTask::do_work_steal(int i) {
3422   OopTaskQueue* work_q = work_queue(i);
3423   oop obj_to_scan;
3424   CMSBitMap* bm = &(_collector->_markBitMap);
3425   CMSMarkStack* ovflw = &(_collector->_markStack);
3426   int* seed = _collector->hash_seed(i);
3427   ParConcMarkingClosure cl(_collector, this, work_q, bm, ovflw);
3428   while (true) {
3429     cl.trim_queue(0);
3430     assert(work_q->size() == 0, "Should have been emptied above");
3431     if (get_work_from_overflow_stack(ovflw, work_q)) {
3432       // Can't assert below because the work obtained from the
3433       // overflow stack may already have been stolen from us.
3434       // assert(work_q->size() > 0, "Work from overflow stack");
3435       continue;
3436     } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
3437       assert(oopDesc::is_oop(obj_to_scan), "Should be an oop");
3438       assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
3439       obj_to_scan->oop_iterate(&cl);
3440     } else if (terminator()->offer_termination(&_term_term)) {
3441       assert(work_q->size() == 0, "Impossible!");
3442       break;
3443     } else if (yielding() || should_yield()) {
3444       yield();
3445     }
3446   }
3447 }
3448 
3449 // This is run by the CMS (coordinator) thread.
3450 void CMSConcMarkingTask::coordinator_yield() {
3451   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3452          "CMS thread should hold CMS token");
3453   // First give up the locks, then yield, then re-lock
3454   // We should probably use a constructor/destructor idiom to
3455   // do this unlock/lock or modify the MutexUnlocker class to
3456   // serve our purpose. XXX
3457   assert_lock_strong(_bit_map_lock);
3458   _bit_map_lock->unlock();
3459   ConcurrentMarkSweepThread::desynchronize(true);
3460   _collector->stopTimer();
3461   _collector->incrementYields();
3462 
3463   // It is possible for whichever thread initiated the yield request
3464   // not to get a chance to wake up and take the bitmap lock between
3465   // this thread releasing it and reacquiring it. So, while the
3466   // should_yield() flag is on, let's sleep for a bit to give the
3467   // other thread a chance to wake up. The limit imposed on the number
3468   // of iterations is defensive, to avoid any unforseen circumstances
3469   // putting us into an infinite loop. Since it's always been this
3470   // (coordinator_yield()) method that was observed to cause the
3471   // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
3472   // which is by default non-zero. For the other seven methods that
3473   // also perform the yield operation, as are using a different
3474   // parameter (CMSYieldSleepCount) which is by default zero. This way we
3475   // can enable the sleeping for those methods too, if necessary.
3476   // See 6442774.
3477   //
3478   // We really need to reconsider the synchronization between the GC
3479   // thread and the yield-requesting threads in the future and we
3480   // should really use wait/notify, which is the recommended
3481   // way of doing this type of interaction. Additionally, we should
3482   // consolidate the eight methods that do the yield operation and they
3483   // are almost identical into one for better maintainability and
3484   // readability. See 6445193.
3485   //
3486   // Tony 2006.06.29
3487   for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
3488                    ConcurrentMarkSweepThread::should_yield() &&
3489                    !CMSCollector::foregroundGCIsActive(); ++i) {
3490     os::sleep(Thread::current(), 1, false);
3491   }
3492 
3493   ConcurrentMarkSweepThread::synchronize(true);
3494   _bit_map_lock->lock_without_safepoint_check();
3495   _collector->startTimer();
3496 }
3497 
3498 bool CMSCollector::do_marking_mt() {
3499   assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition");
3500   uint num_workers = AdaptiveSizePolicy::calc_active_conc_workers(conc_workers()->total_workers(),
3501                                                                   conc_workers()->active_workers(),
3502                                                                   Threads::number_of_non_daemon_threads());
3503   num_workers = conc_workers()->update_active_workers(num_workers);
3504   log_info(gc,task)("Using %u workers of %u for marking", num_workers, conc_workers()->total_workers());
3505 
3506   CompactibleFreeListSpace* cms_space  = _cmsGen->cmsSpace();
3507 
3508   CMSConcMarkingTask tsk(this,
3509                          cms_space,
3510                          conc_workers(),
3511                          task_queues());
3512 
3513   // Since the actual number of workers we get may be different
3514   // from the number we requested above, do we need to do anything different
3515   // below? In particular, may be we need to subclass the SequantialSubTasksDone
3516   // class?? XXX
3517   cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
3518 
3519   // Refs discovery is already non-atomic.
3520   assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
3521   assert(ref_processor()->discovery_is_mt(), "Discovery should be MT");
3522   conc_workers()->start_task(&tsk);
3523   while (tsk.yielded()) {
3524     tsk.coordinator_yield();
3525     conc_workers()->continue_task(&tsk);
3526   }
3527   // If the task was aborted, _restart_addr will be non-NULL
3528   assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
3529   while (_restart_addr != NULL) {
3530     // XXX For now we do not make use of ABORTED state and have not
3531     // yet implemented the right abort semantics (even in the original
3532     // single-threaded CMS case). That needs some more investigation
3533     // and is deferred for now; see CR# TBF. 07252005YSR. XXX
3534     assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
3535     // If _restart_addr is non-NULL, a marking stack overflow
3536     // occurred; we need to do a fresh marking iteration from the
3537     // indicated restart address.
3538     if (_foregroundGCIsActive) {
3539       // We may be running into repeated stack overflows, having
3540       // reached the limit of the stack size, while making very
3541       // slow forward progress. It may be best to bail out and
3542       // let the foreground collector do its job.
3543       // Clear _restart_addr, so that foreground GC
3544       // works from scratch. This avoids the headache of
3545       // a "rescan" which would otherwise be needed because
3546       // of the dirty mod union table & card table.
3547       _restart_addr = NULL;
3548       return false;
3549     }
3550     // Adjust the task to restart from _restart_addr
3551     tsk.reset(_restart_addr);
3552     cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
3553                   _restart_addr);
3554     _restart_addr = NULL;
3555     // Get the workers going again
3556     conc_workers()->start_task(&tsk);
3557     while (tsk.yielded()) {
3558       tsk.coordinator_yield();
3559       conc_workers()->continue_task(&tsk);
3560     }
3561   }
3562   assert(tsk.completed(), "Inconsistency");
3563   assert(tsk.result() == true, "Inconsistency");
3564   return true;
3565 }
3566 
3567 bool CMSCollector::do_marking_st() {
3568   ResourceMark rm;
3569   HandleMark   hm;
3570 
3571   // Temporarily make refs discovery single threaded (non-MT)
3572   ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
3573   MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
3574     &_markStack, CMSYield);
3575   // the last argument to iterate indicates whether the iteration
3576   // should be incremental with periodic yields.
3577   _markBitMap.iterate(&markFromRootsClosure);
3578   // If _restart_addr is non-NULL, a marking stack overflow
3579   // occurred; we need to do a fresh iteration from the
3580   // indicated restart address.
3581   while (_restart_addr != NULL) {
3582     if (_foregroundGCIsActive) {
3583       // We may be running into repeated stack overflows, having
3584       // reached the limit of the stack size, while making very
3585       // slow forward progress. It may be best to bail out and
3586       // let the foreground collector do its job.
3587       // Clear _restart_addr, so that foreground GC
3588       // works from scratch. This avoids the headache of
3589       // a "rescan" which would otherwise be needed because
3590       // of the dirty mod union table & card table.
3591       _restart_addr = NULL;
3592       return false;  // indicating failure to complete marking
3593     }
3594     // Deal with stack overflow:
3595     // we restart marking from _restart_addr
3596     HeapWord* ra = _restart_addr;
3597     markFromRootsClosure.reset(ra);
3598     _restart_addr = NULL;
3599     _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
3600   }
3601   return true;
3602 }
3603 
3604 void CMSCollector::preclean() {
3605   check_correct_thread_executing();
3606   assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
3607   verify_work_stacks_empty();
3608   verify_overflow_empty();
3609   _abort_preclean = false;
3610   if (CMSPrecleaningEnabled) {
3611     if (!CMSEdenChunksRecordAlways) {
3612       _eden_chunk_index = 0;
3613     }
3614     size_t used = get_eden_used();
3615     size_t capacity = get_eden_capacity();
3616     // Don't start sampling unless we will get sufficiently
3617     // many samples.
3618     if (used < (((capacity / CMSScheduleRemarkSamplingRatio) / 100)
3619                 * CMSScheduleRemarkEdenPenetration)) {
3620       _start_sampling = true;
3621     } else {
3622       _start_sampling = false;
3623     }
3624     GCTraceCPUTime tcpu;
3625     CMSPhaseAccounting pa(this, "Concurrent Preclean");
3626     preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
3627   }
3628   CMSTokenSync x(true); // is cms thread
3629   if (CMSPrecleaningEnabled) {
3630     sample_eden();
3631     _collectorState = AbortablePreclean;
3632   } else {
3633     _collectorState = FinalMarking;
3634   }
3635   verify_work_stacks_empty();
3636   verify_overflow_empty();
3637 }
3638 
3639 // Try and schedule the remark such that young gen
3640 // occupancy is CMSScheduleRemarkEdenPenetration %.
3641 void CMSCollector::abortable_preclean() {
3642   check_correct_thread_executing();
3643   assert(CMSPrecleaningEnabled,  "Inconsistent control state");
3644   assert(_collectorState == AbortablePreclean, "Inconsistent control state");
3645 
3646   // If Eden's current occupancy is below this threshold,
3647   // immediately schedule the remark; else preclean
3648   // past the next scavenge in an effort to
3649   // schedule the pause as described above. By choosing
3650   // CMSScheduleRemarkEdenSizeThreshold >= max eden size
3651   // we will never do an actual abortable preclean cycle.
3652   if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
3653     GCTraceCPUTime tcpu;
3654     CMSPhaseAccounting pa(this, "Concurrent Abortable Preclean");
3655     // We need more smarts in the abortable preclean
3656     // loop below to deal with cases where allocation
3657     // in young gen is very very slow, and our precleaning
3658     // is running a losing race against a horde of
3659     // mutators intent on flooding us with CMS updates
3660     // (dirty cards).
3661     // One, admittedly dumb, strategy is to give up
3662     // after a certain number of abortable precleaning loops
3663     // or after a certain maximum time. We want to make
3664     // this smarter in the next iteration.
3665     // XXX FIX ME!!! YSR
3666     size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
3667     while (!(should_abort_preclean() ||
3668              ConcurrentMarkSweepThread::cmst()->should_terminate())) {
3669       workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
3670       cumworkdone += workdone;
3671       loops++;
3672       // Voluntarily terminate abortable preclean phase if we have
3673       // been at it for too long.
3674       if ((CMSMaxAbortablePrecleanLoops != 0) &&
3675           loops >= CMSMaxAbortablePrecleanLoops) {
3676         log_debug(gc)(" CMS: abort preclean due to loops ");
3677         break;
3678       }
3679       if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
3680         log_debug(gc)(" CMS: abort preclean due to time ");
3681         break;
3682       }
3683       // If we are doing little work each iteration, we should
3684       // take a short break.
3685       if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
3686         // Sleep for some time, waiting for work to accumulate
3687         stopTimer();
3688         cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
3689         startTimer();
3690         waited++;
3691       }
3692     }
3693     log_trace(gc)(" [" SIZE_FORMAT " iterations, " SIZE_FORMAT " waits, " SIZE_FORMAT " cards)] ",
3694                                loops, waited, cumworkdone);
3695   }
3696   CMSTokenSync x(true); // is cms thread
3697   if (_collectorState != Idling) {
3698     assert(_collectorState == AbortablePreclean,
3699            "Spontaneous state transition?");
3700     _collectorState = FinalMarking;
3701   } // Else, a foreground collection completed this CMS cycle.
3702   return;
3703 }
3704 
3705 // Respond to an Eden sampling opportunity
3706 void CMSCollector::sample_eden() {
3707   // Make sure a young gc cannot sneak in between our
3708   // reading and recording of a sample.
3709   assert(Thread::current()->is_ConcurrentGC_thread(),
3710          "Only the cms thread may collect Eden samples");
3711   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3712          "Should collect samples while holding CMS token");
3713   if (!_start_sampling) {
3714     return;
3715   }
3716   // When CMSEdenChunksRecordAlways is true, the eden chunk array
3717   // is populated by the young generation.
3718   if (_eden_chunk_array != NULL && !CMSEdenChunksRecordAlways) {
3719     if (_eden_chunk_index < _eden_chunk_capacity) {
3720       _eden_chunk_array[_eden_chunk_index] = *_top_addr;   // take sample
3721       assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
3722              "Unexpected state of Eden");
3723       // We'd like to check that what we just sampled is an oop-start address;
3724       // however, we cannot do that here since the object may not yet have been
3725       // initialized. So we'll instead do the check when we _use_ this sample
3726       // later.
3727       if (_eden_chunk_index == 0 ||
3728           (pointer_delta(_eden_chunk_array[_eden_chunk_index],
3729                          _eden_chunk_array[_eden_chunk_index-1])
3730            >= CMSSamplingGrain)) {
3731         _eden_chunk_index++;  // commit sample
3732       }
3733     }
3734   }
3735   if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
3736     size_t used = get_eden_used();
3737     size_t capacity = get_eden_capacity();
3738     assert(used <= capacity, "Unexpected state of Eden");
3739     if (used >  (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
3740       _abort_preclean = true;
3741     }
3742   }
3743 }
3744 
3745 
3746 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
3747   assert(_collectorState == Precleaning ||
3748          _collectorState == AbortablePreclean, "incorrect state");
3749   ResourceMark rm;
3750   HandleMark   hm;
3751 
3752   // Precleaning is currently not MT but the reference processor
3753   // may be set for MT.  Disable it temporarily here.
3754   ReferenceProcessor* rp = ref_processor();
3755   ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false);
3756 
3757   // Do one pass of scrubbing the discovered reference lists
3758   // to remove any reference objects with strongly-reachable
3759   // referents.
3760   if (clean_refs) {
3761     CMSPrecleanRefsYieldClosure yield_cl(this);
3762     assert(rp->span().equals(_span), "Spans should be equal");
3763     CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
3764                                    &_markStack, true /* preclean */);
3765     CMSDrainMarkingStackClosure complete_trace(this,
3766                                    _span, &_markBitMap, &_markStack,
3767                                    &keep_alive, true /* preclean */);
3768 
3769     // We don't want this step to interfere with a young
3770     // collection because we don't want to take CPU
3771     // or memory bandwidth away from the young GC threads
3772     // (which may be as many as there are CPUs).
3773     // Note that we don't need to protect ourselves from
3774     // interference with mutators because they can't
3775     // manipulate the discovered reference lists nor affect
3776     // the computed reachability of the referents, the
3777     // only properties manipulated by the precleaning
3778     // of these reference lists.
3779     stopTimer();
3780     CMSTokenSyncWithLocks x(true /* is cms thread */,
3781                             bitMapLock());
3782     startTimer();
3783     sample_eden();
3784 
3785     // The following will yield to allow foreground
3786     // collection to proceed promptly. XXX YSR:
3787     // The code in this method may need further
3788     // tweaking for better performance and some restructuring
3789     // for cleaner interfaces.
3790     GCTimer *gc_timer = NULL; // Currently not tracing concurrent phases
3791     rp->preclean_discovered_references(
3792           rp->is_alive_non_header(), &keep_alive, &complete_trace, &yield_cl,
3793           gc_timer);
3794   }
3795 
3796   if (clean_survivor) {  // preclean the active survivor space(s)
3797     PushAndMarkClosure pam_cl(this, _span, ref_processor(),
3798                              &_markBitMap, &_modUnionTable,
3799                              &_markStack, true /* precleaning phase */);
3800     stopTimer();
3801     CMSTokenSyncWithLocks ts(true /* is cms thread */,
3802                              bitMapLock());
3803     startTimer();
3804     unsigned int before_count =
3805       CMSHeap::heap()->total_collections();
3806     SurvivorSpacePrecleanClosure
3807       sss_cl(this, _span, &_markBitMap, &_markStack,
3808              &pam_cl, before_count, CMSYield);
3809     _young_gen->from()->object_iterate_careful(&sss_cl);
3810     _young_gen->to()->object_iterate_careful(&sss_cl);
3811   }
3812   MarkRefsIntoAndScanClosure
3813     mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
3814              &_markStack, this, CMSYield,
3815              true /* precleaning phase */);
3816   // CAUTION: The following closure has persistent state that may need to
3817   // be reset upon a decrease in the sequence of addresses it
3818   // processes.
3819   ScanMarkedObjectsAgainCarefullyClosure
3820     smoac_cl(this, _span,
3821       &_markBitMap, &_markStack, &mrias_cl, CMSYield);
3822 
3823   // Preclean dirty cards in ModUnionTable and CardTable using
3824   // appropriate convergence criterion;
3825   // repeat CMSPrecleanIter times unless we find that
3826   // we are losing.
3827   assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
3828   assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
3829          "Bad convergence multiplier");
3830   assert(CMSPrecleanThreshold >= 100,
3831          "Unreasonably low CMSPrecleanThreshold");
3832 
3833   size_t numIter, cumNumCards, lastNumCards, curNumCards;
3834   for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
3835        numIter < CMSPrecleanIter;
3836        numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
3837     curNumCards  = preclean_mod_union_table(_cmsGen, &smoac_cl);
3838     log_trace(gc)(" (modUnionTable: " SIZE_FORMAT " cards)", curNumCards);
3839     // Either there are very few dirty cards, so re-mark
3840     // pause will be small anyway, or our pre-cleaning isn't
3841     // that much faster than the rate at which cards are being
3842     // dirtied, so we might as well stop and re-mark since
3843     // precleaning won't improve our re-mark time by much.
3844     if (curNumCards <= CMSPrecleanThreshold ||
3845         (numIter > 0 &&
3846          (curNumCards * CMSPrecleanDenominator >
3847          lastNumCards * CMSPrecleanNumerator))) {
3848       numIter++;
3849       cumNumCards += curNumCards;
3850       break;
3851     }
3852   }
3853 
3854   preclean_cld(&mrias_cl, _cmsGen->freelistLock());
3855 
3856   curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
3857   cumNumCards += curNumCards;
3858   log_trace(gc)(" (cardTable: " SIZE_FORMAT " cards, re-scanned " SIZE_FORMAT " cards, " SIZE_FORMAT " iterations)",
3859                              curNumCards, cumNumCards, numIter);
3860   return cumNumCards;   // as a measure of useful work done
3861 }
3862 
3863 // PRECLEANING NOTES:
3864 // Precleaning involves:
3865 // . reading the bits of the modUnionTable and clearing the set bits.
3866 // . For the cards corresponding to the set bits, we scan the
3867 //   objects on those cards. This means we need the free_list_lock
3868 //   so that we can safely iterate over the CMS space when scanning
3869 //   for oops.
3870 // . When we scan the objects, we'll be both reading and setting
3871 //   marks in the marking bit map, so we'll need the marking bit map.
3872 // . For protecting _collector_state transitions, we take the CGC_lock.
3873 //   Note that any races in the reading of of card table entries by the
3874 //   CMS thread on the one hand and the clearing of those entries by the
3875 //   VM thread or the setting of those entries by the mutator threads on the
3876 //   other are quite benign. However, for efficiency it makes sense to keep
3877 //   the VM thread from racing with the CMS thread while the latter is
3878 //   dirty card info to the modUnionTable. We therefore also use the
3879 //   CGC_lock to protect the reading of the card table and the mod union
3880 //   table by the CM thread.
3881 // . We run concurrently with mutator updates, so scanning
3882 //   needs to be done carefully  -- we should not try to scan
3883 //   potentially uninitialized objects.
3884 //
3885 // Locking strategy: While holding the CGC_lock, we scan over and
3886 // reset a maximal dirty range of the mod union / card tables, then lock
3887 // the free_list_lock and bitmap lock to do a full marking, then
3888 // release these locks; and repeat the cycle. This allows for a
3889 // certain amount of fairness in the sharing of these locks between
3890 // the CMS collector on the one hand, and the VM thread and the
3891 // mutators on the other.
3892 
3893 // NOTE: preclean_mod_union_table() and preclean_card_table()
3894 // further below are largely identical; if you need to modify
3895 // one of these methods, please check the other method too.
3896 
3897 size_t CMSCollector::preclean_mod_union_table(
3898   ConcurrentMarkSweepGeneration* old_gen,
3899   ScanMarkedObjectsAgainCarefullyClosure* cl) {
3900   verify_work_stacks_empty();
3901   verify_overflow_empty();
3902 
3903   // strategy: starting with the first card, accumulate contiguous
3904   // ranges of dirty cards; clear these cards, then scan the region
3905   // covered by these cards.
3906 
3907   // Since all of the MUT is committed ahead, we can just use
3908   // that, in case the generations expand while we are precleaning.
3909   // It might also be fine to just use the committed part of the
3910   // generation, but we might potentially miss cards when the
3911   // generation is rapidly expanding while we are in the midst
3912   // of precleaning.
3913   HeapWord* startAddr = old_gen->reserved().start();
3914   HeapWord* endAddr   = old_gen->reserved().end();
3915 
3916   cl->setFreelistLock(old_gen->freelistLock());   // needed for yielding
3917 
3918   size_t numDirtyCards, cumNumDirtyCards;
3919   HeapWord *nextAddr, *lastAddr;
3920   for (cumNumDirtyCards = numDirtyCards = 0,
3921        nextAddr = lastAddr = startAddr;
3922        nextAddr < endAddr;
3923        nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
3924 
3925     ResourceMark rm;
3926     HandleMark   hm;
3927 
3928     MemRegion dirtyRegion;
3929     {
3930       stopTimer();
3931       // Potential yield point
3932       CMSTokenSync ts(true);
3933       startTimer();
3934       sample_eden();
3935       // Get dirty region starting at nextOffset (inclusive),
3936       // simultaneously clearing it.
3937       dirtyRegion =
3938         _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
3939       assert(dirtyRegion.start() >= nextAddr,
3940              "returned region inconsistent?");
3941     }
3942     // Remember where the next search should begin.
3943     // The returned region (if non-empty) is a right open interval,
3944     // so lastOffset is obtained from the right end of that
3945     // interval.
3946     lastAddr = dirtyRegion.end();
3947     // Should do something more transparent and less hacky XXX
3948     numDirtyCards =
3949       _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
3950 
3951     // We'll scan the cards in the dirty region (with periodic
3952     // yields for foreground GC as needed).
3953     if (!dirtyRegion.is_empty()) {
3954       assert(numDirtyCards > 0, "consistency check");
3955       HeapWord* stop_point = NULL;
3956       stopTimer();
3957       // Potential yield point
3958       CMSTokenSyncWithLocks ts(true, old_gen->freelistLock(),
3959                                bitMapLock());
3960       startTimer();
3961       {
3962         verify_work_stacks_empty();
3963         verify_overflow_empty();
3964         sample_eden();
3965         stop_point =
3966           old_gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
3967       }
3968       if (stop_point != NULL) {
3969         // The careful iteration stopped early either because it found an
3970         // uninitialized object, or because we were in the midst of an
3971         // "abortable preclean", which should now be aborted. Redirty
3972         // the bits corresponding to the partially-scanned or unscanned
3973         // cards. We'll either restart at the next block boundary or
3974         // abort the preclean.
3975         assert((_collectorState == AbortablePreclean && should_abort_preclean()),
3976                "Should only be AbortablePreclean.");
3977         _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
3978         if (should_abort_preclean()) {
3979           break; // out of preclean loop
3980         } else {
3981           // Compute the next address at which preclean should pick up;
3982           // might need bitMapLock in order to read P-bits.
3983           lastAddr = next_card_start_after_block(stop_point);
3984         }
3985       }
3986     } else {
3987       assert(lastAddr == endAddr, "consistency check");
3988       assert(numDirtyCards == 0, "consistency check");
3989       break;
3990     }
3991   }
3992   verify_work_stacks_empty();
3993   verify_overflow_empty();
3994   return cumNumDirtyCards;
3995 }
3996 
3997 // NOTE: preclean_mod_union_table() above and preclean_card_table()
3998 // below are largely identical; if you need to modify
3999 // one of these methods, please check the other method too.
4000 
4001 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* old_gen,
4002   ScanMarkedObjectsAgainCarefullyClosure* cl) {
4003   // strategy: it's similar to precleamModUnionTable above, in that
4004   // we accumulate contiguous ranges of dirty cards, mark these cards
4005   // precleaned, then scan the region covered by these cards.
4006   HeapWord* endAddr   = (HeapWord*)(old_gen->_virtual_space.high());
4007   HeapWord* startAddr = (HeapWord*)(old_gen->_virtual_space.low());
4008 
4009   cl->setFreelistLock(old_gen->freelistLock());   // needed for yielding
4010 
4011   size_t numDirtyCards, cumNumDirtyCards;
4012   HeapWord *lastAddr, *nextAddr;
4013 
4014   for (cumNumDirtyCards = numDirtyCards = 0,
4015        nextAddr = lastAddr = startAddr;
4016        nextAddr < endAddr;
4017        nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4018 
4019     ResourceMark rm;
4020     HandleMark   hm;
4021 
4022     MemRegion dirtyRegion;
4023     {
4024       // See comments in "Precleaning notes" above on why we
4025       // do this locking. XXX Could the locking overheads be
4026       // too high when dirty cards are sparse? [I don't think so.]
4027       stopTimer();
4028       CMSTokenSync x(true); // is cms thread
4029       startTimer();
4030       sample_eden();
4031       // Get and clear dirty region from card table
4032       dirtyRegion = _ct->ct_bs()->dirty_card_range_after_reset(
4033                                     MemRegion(nextAddr, endAddr),
4034                                     true,
4035                                     CardTableModRefBS::precleaned_card_val());
4036 
4037       assert(dirtyRegion.start() >= nextAddr,
4038              "returned region inconsistent?");
4039     }
4040     lastAddr = dirtyRegion.end();
4041     numDirtyCards =
4042       dirtyRegion.word_size()/CardTableModRefBS::card_size_in_words;
4043 
4044     if (!dirtyRegion.is_empty()) {
4045       stopTimer();
4046       CMSTokenSyncWithLocks ts(true, old_gen->freelistLock(), bitMapLock());
4047       startTimer();
4048       sample_eden();
4049       verify_work_stacks_empty();
4050       verify_overflow_empty();
4051       HeapWord* stop_point =
4052         old_gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4053       if (stop_point != NULL) {
4054         assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4055                "Should only be AbortablePreclean.");
4056         _ct->ct_bs()->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4057         if (should_abort_preclean()) {
4058           break; // out of preclean loop
4059         } else {
4060           // Compute the next address at which preclean should pick up.
4061           lastAddr = next_card_start_after_block(stop_point);
4062         }
4063       }
4064     } else {
4065       break;
4066     }
4067   }
4068   verify_work_stacks_empty();
4069   verify_overflow_empty();
4070   return cumNumDirtyCards;
4071 }
4072 
4073 class PrecleanCLDClosure : public CLDClosure {
4074   MetadataAwareOopsInGenClosure* _cm_closure;
4075  public:
4076   PrecleanCLDClosure(MetadataAwareOopsInGenClosure* oop_closure) : _cm_closure(oop_closure) {}
4077   void do_cld(ClassLoaderData* cld) {
4078     if (cld->has_accumulated_modified_oops()) {
4079       cld->clear_accumulated_modified_oops();
4080 
4081       _cm_closure->do_cld(cld);
4082     }
4083   }
4084 };
4085 
4086 // The freelist lock is needed to prevent asserts, is it really needed?
4087 void CMSCollector::preclean_cld(MarkRefsIntoAndScanClosure* cl, Mutex* freelistLock) {
4088 
4089   cl->set_freelistLock(freelistLock);
4090 
4091   CMSTokenSyncWithLocks ts(true, freelistLock, bitMapLock());
4092 
4093   // SSS: Add equivalent to ScanMarkedObjectsAgainCarefullyClosure::do_yield_check and should_abort_preclean?
4094   // SSS: We should probably check if precleaning should be aborted, at suitable intervals?
4095   PrecleanCLDClosure preclean_closure(cl);
4096   ClassLoaderDataGraph::cld_do(&preclean_closure);
4097 
4098   verify_work_stacks_empty();
4099   verify_overflow_empty();
4100 }
4101 
4102 void CMSCollector::checkpointRootsFinal() {
4103   assert(_collectorState == FinalMarking, "incorrect state transition?");
4104   check_correct_thread_executing();
4105   // world is stopped at this checkpoint
4106   assert(SafepointSynchronize::is_at_safepoint(),
4107          "world should be stopped");
4108   TraceCMSMemoryManagerStats tms(_collectorState, CMSHeap::heap()->gc_cause());
4109 
4110   verify_work_stacks_empty();
4111   verify_overflow_empty();
4112 
4113   log_debug(gc)("YG occupancy: " SIZE_FORMAT " K (" SIZE_FORMAT " K)",
4114                 _young_gen->used() / K, _young_gen->capacity() / K);
4115   {
4116     if (CMSScavengeBeforeRemark) {
4117       CMSHeap* heap = CMSHeap::heap();
4118       // Temporarily set flag to false, GCH->do_collection will
4119       // expect it to be false and set to true
4120       FlagSetting fl(heap->_is_gc_active, false);
4121 
4122       heap->do_collection(true,                      // full (i.e. force, see below)
4123                           false,                     // !clear_all_soft_refs
4124                           0,                         // size
4125                           false,                     // is_tlab
4126                           GenCollectedHeap::YoungGen // type
4127         );
4128     }
4129     FreelistLocker x(this);
4130     MutexLockerEx y(bitMapLock(),
4131                     Mutex::_no_safepoint_check_flag);
4132     checkpointRootsFinalWork();
4133   }
4134   verify_work_stacks_empty();
4135   verify_overflow_empty();
4136 }
4137 
4138 void CMSCollector::checkpointRootsFinalWork() {
4139   GCTraceTime(Trace, gc, phases) tm("checkpointRootsFinalWork", _gc_timer_cm);
4140 
4141   assert(haveFreelistLocks(), "must have free list locks");
4142   assert_lock_strong(bitMapLock());
4143 
4144   ResourceMark rm;
4145   HandleMark   hm;
4146 
4147   CMSHeap* heap = CMSHeap::heap();
4148 
4149   if (should_unload_classes()) {
4150     CodeCache::gc_prologue();
4151   }
4152   assert(haveFreelistLocks(), "must have free list locks");
4153   assert_lock_strong(bitMapLock());
4154 
4155   // We might assume that we need not fill TLAB's when
4156   // CMSScavengeBeforeRemark is set, because we may have just done
4157   // a scavenge which would have filled all TLAB's -- and besides
4158   // Eden would be empty. This however may not always be the case --
4159   // for instance although we asked for a scavenge, it may not have
4160   // happened because of a JNI critical section. We probably need
4161   // a policy for deciding whether we can in that case wait until
4162   // the critical section releases and then do the remark following
4163   // the scavenge, and skip it here. In the absence of that policy,
4164   // or of an indication of whether the scavenge did indeed occur,
4165   // we cannot rely on TLAB's having been filled and must do
4166   // so here just in case a scavenge did not happen.
4167   heap->ensure_parsability(false);  // fill TLAB's, but no need to retire them
4168   // Update the saved marks which may affect the root scans.
4169   heap->save_marks();
4170 
4171   print_eden_and_survivor_chunk_arrays();
4172 
4173   {
4174 #if COMPILER2_OR_JVMCI
4175     DerivedPointerTableDeactivate dpt_deact;
4176 #endif
4177 
4178     // Note on the role of the mod union table:
4179     // Since the marker in "markFromRoots" marks concurrently with
4180     // mutators, it is possible for some reachable objects not to have been
4181     // scanned. For instance, an only reference to an object A was
4182     // placed in object B after the marker scanned B. Unless B is rescanned,
4183     // A would be collected. Such updates to references in marked objects
4184     // are detected via the mod union table which is the set of all cards
4185     // dirtied since the first checkpoint in this GC cycle and prior to
4186     // the most recent young generation GC, minus those cleaned up by the
4187     // concurrent precleaning.
4188     if (CMSParallelRemarkEnabled) {
4189       GCTraceTime(Debug, gc, phases) t("Rescan (parallel)", _gc_timer_cm);
4190       do_remark_parallel();
4191     } else {
4192       GCTraceTime(Debug, gc, phases) t("Rescan (non-parallel)", _gc_timer_cm);
4193       do_remark_non_parallel();
4194     }
4195   }
4196   verify_work_stacks_empty();
4197   verify_overflow_empty();
4198 
4199   {
4200     GCTraceTime(Trace, gc, phases) ts("refProcessingWork", _gc_timer_cm);
4201     refProcessingWork();
4202   }
4203   verify_work_stacks_empty();
4204   verify_overflow_empty();
4205 
4206   if (should_unload_classes()) {
4207     CodeCache::gc_epilogue();
4208   }
4209   JvmtiExport::gc_epilogue();
4210 
4211   // If we encountered any (marking stack / work queue) overflow
4212   // events during the current CMS cycle, take appropriate
4213   // remedial measures, where possible, so as to try and avoid
4214   // recurrence of that condition.
4215   assert(_markStack.isEmpty(), "No grey objects");
4216   size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
4217                      _ser_kac_ovflw        + _ser_kac_preclean_ovflw;
4218   if (ser_ovflw > 0) {
4219     log_trace(gc)("Marking stack overflow (benign) (pmc_pc=" SIZE_FORMAT ", pmc_rm=" SIZE_FORMAT ", kac=" SIZE_FORMAT ", kac_preclean=" SIZE_FORMAT ")",
4220                          _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw, _ser_kac_ovflw, _ser_kac_preclean_ovflw);
4221     _markStack.expand();
4222     _ser_pmc_remark_ovflw = 0;
4223     _ser_pmc_preclean_ovflw = 0;
4224     _ser_kac_preclean_ovflw = 0;
4225     _ser_kac_ovflw = 0;
4226   }
4227   if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
4228      log_trace(gc)("Work queue overflow (benign) (pmc_rm=" SIZE_FORMAT ", kac=" SIZE_FORMAT ")",
4229                           _par_pmc_remark_ovflw, _par_kac_ovflw);
4230      _par_pmc_remark_ovflw = 0;
4231     _par_kac_ovflw = 0;
4232   }
4233    if (_markStack._hit_limit > 0) {
4234      log_trace(gc)(" (benign) Hit max stack size limit (" SIZE_FORMAT ")",
4235                           _markStack._hit_limit);
4236    }
4237    if (_markStack._failed_double > 0) {
4238      log_trace(gc)(" (benign) Failed stack doubling (" SIZE_FORMAT "), current capacity " SIZE_FORMAT,
4239                           _markStack._failed_double, _markStack.capacity());
4240    }
4241   _markStack._hit_limit = 0;
4242   _markStack._failed_double = 0;
4243 
4244   if ((VerifyAfterGC || VerifyDuringGC) &&
4245       CMSHeap::heap()->total_collections() >= VerifyGCStartAt) {
4246     verify_after_remark();
4247   }
4248 
4249   _gc_tracer_cm->report_object_count_after_gc(&_is_alive_closure);
4250 
4251   // Change under the freelistLocks.
4252   _collectorState = Sweeping;
4253   // Call isAllClear() under bitMapLock
4254   assert(_modUnionTable.isAllClear(),
4255       "Should be clear by end of the final marking");
4256   assert(_ct->cld_rem_set()->mod_union_is_clear(),
4257       "Should be clear by end of the final marking");
4258 }
4259 
4260 void CMSParInitialMarkTask::work(uint worker_id) {
4261   elapsedTimer _timer;
4262   ResourceMark rm;
4263   HandleMark   hm;
4264 
4265   // ---------- scan from roots --------------
4266   _timer.start();
4267   CMSHeap* heap = CMSHeap::heap();
4268   ParMarkRefsIntoClosure par_mri_cl(_collector->_span, &(_collector->_markBitMap));
4269 
4270   // ---------- young gen roots --------------
4271   {
4272     work_on_young_gen_roots(&par_mri_cl);
4273     _timer.stop();
4274     log_trace(gc, task)("Finished young gen initial mark scan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4275   }
4276 
4277   // ---------- remaining roots --------------
4278   _timer.reset();
4279   _timer.start();
4280 
4281   CLDToOopClosure cld_closure(&par_mri_cl, true);
4282 
4283   heap->cms_process_roots(_strong_roots_scope,
4284                           false,     // yg was scanned above
4285                           GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4286                           _collector->should_unload_classes(),
4287                           &par_mri_cl,
4288                           &cld_closure);
4289   assert(_collector->should_unload_classes()
4290          || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4291          "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4292   _timer.stop();
4293   log_trace(gc, task)("Finished remaining root initial mark scan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4294 }
4295 
4296 // Parallel remark task
4297 class CMSParRemarkTask: public CMSParMarkTask {
4298   CompactibleFreeListSpace* _cms_space;
4299 
4300   // The per-thread work queues, available here for stealing.
4301   OopTaskQueueSet*       _task_queues;
4302   ParallelTaskTerminator _term;
4303   StrongRootsScope*      _strong_roots_scope;
4304 
4305  public:
4306   // A value of 0 passed to n_workers will cause the number of
4307   // workers to be taken from the active workers in the work gang.
4308   CMSParRemarkTask(CMSCollector* collector,
4309                    CompactibleFreeListSpace* cms_space,
4310                    uint n_workers, WorkGang* workers,
4311                    OopTaskQueueSet* task_queues,
4312                    StrongRootsScope* strong_roots_scope):
4313     CMSParMarkTask("Rescan roots and grey objects in parallel",
4314                    collector, n_workers),
4315     _cms_space(cms_space),
4316     _task_queues(task_queues),
4317     _term(n_workers, task_queues),
4318     _strong_roots_scope(strong_roots_scope) { }
4319 
4320   OopTaskQueueSet* task_queues() { return _task_queues; }
4321 
4322   OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
4323 
4324   ParallelTaskTerminator* terminator() { return &_term; }
4325   uint n_workers() { return _n_workers; }
4326 
4327   void work(uint worker_id);
4328 
4329  private:
4330   // ... of  dirty cards in old space
4331   void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
4332                                   ParMarkRefsIntoAndScanClosure* cl);
4333 
4334   // ... work stealing for the above
4335   void do_work_steal(int i, ParMarkRefsIntoAndScanClosure* cl, int* seed);
4336 };
4337 
4338 class RemarkCLDClosure : public CLDClosure {
4339   CLDToOopClosure _cm_closure;
4340  public:
4341   RemarkCLDClosure(OopClosure* oop_closure) : _cm_closure(oop_closure) {}
4342   void do_cld(ClassLoaderData* cld) {
4343     // Check if we have modified any oops in the CLD during the concurrent marking.
4344     if (cld->has_accumulated_modified_oops()) {
4345       cld->clear_accumulated_modified_oops();
4346 
4347       // We could have transfered the current modified marks to the accumulated marks,
4348       // like we do with the Card Table to Mod Union Table. But it's not really necessary.
4349     } else if (cld->has_modified_oops()) {
4350       // Don't clear anything, this info is needed by the next young collection.
4351     } else {
4352       // No modified oops in the ClassLoaderData.
4353       return;
4354     }
4355 
4356     // The klass has modified fields, need to scan the klass.
4357     _cm_closure.do_cld(cld);
4358   }
4359 };
4360 
4361 void CMSParMarkTask::work_on_young_gen_roots(OopsInGenClosure* cl) {
4362   ParNewGeneration* young_gen = _collector->_young_gen;
4363   ContiguousSpace* eden_space = young_gen->eden();
4364   ContiguousSpace* from_space = young_gen->from();
4365   ContiguousSpace* to_space   = young_gen->to();
4366 
4367   HeapWord** eca = _collector->_eden_chunk_array;
4368   size_t     ect = _collector->_eden_chunk_index;
4369   HeapWord** sca = _collector->_survivor_chunk_array;
4370   size_t     sct = _collector->_survivor_chunk_index;
4371 
4372   assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
4373   assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
4374 
4375   do_young_space_rescan(cl, to_space, NULL, 0);
4376   do_young_space_rescan(cl, from_space, sca, sct);
4377   do_young_space_rescan(cl, eden_space, eca, ect);
4378 }
4379 
4380 // work_queue(i) is passed to the closure
4381 // ParMarkRefsIntoAndScanClosure.  The "i" parameter
4382 // also is passed to do_dirty_card_rescan_tasks() and to
4383 // do_work_steal() to select the i-th task_queue.
4384 
4385 void CMSParRemarkTask::work(uint worker_id) {
4386   elapsedTimer _timer;
4387   ResourceMark rm;
4388   HandleMark   hm;
4389 
4390   // ---------- rescan from roots --------------
4391   _timer.start();
4392   CMSHeap* heap = CMSHeap::heap();
4393   ParMarkRefsIntoAndScanClosure par_mrias_cl(_collector,
4394     _collector->_span, _collector->ref_processor(),
4395     &(_collector->_markBitMap),
4396     work_queue(worker_id));
4397 
4398   // Rescan young gen roots first since these are likely
4399   // coarsely partitioned and may, on that account, constitute
4400   // the critical path; thus, it's best to start off that
4401   // work first.
4402   // ---------- young gen roots --------------
4403   {
4404     work_on_young_gen_roots(&par_mrias_cl);
4405     _timer.stop();
4406     log_trace(gc, task)("Finished young gen rescan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4407   }
4408 
4409   // ---------- remaining roots --------------
4410   _timer.reset();
4411   _timer.start();
4412   heap->cms_process_roots(_strong_roots_scope,
4413                           false,     // yg was scanned above
4414                           GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4415                           _collector->should_unload_classes(),
4416                           &par_mrias_cl,
4417                           NULL);     // The dirty klasses will be handled below
4418 
4419   assert(_collector->should_unload_classes()
4420          || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4421          "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4422   _timer.stop();
4423   log_trace(gc, task)("Finished remaining root rescan work in %dth thread: %3.3f sec",  worker_id, _timer.seconds());
4424 
4425   // ---------- unhandled CLD scanning ----------
4426   if (worker_id == 0) { // Single threaded at the moment.
4427     _timer.reset();
4428     _timer.start();
4429 
4430     // Scan all new class loader data objects and new dependencies that were
4431     // introduced during concurrent marking.
4432     ResourceMark rm;
4433     GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
4434     for (int i = 0; i < array->length(); i++) {
4435       par_mrias_cl.do_cld_nv(array->at(i));
4436     }
4437 
4438     // We don't need to keep track of new CLDs anymore.
4439     ClassLoaderDataGraph::remember_new_clds(false);
4440 
4441     _timer.stop();
4442     log_trace(gc, task)("Finished unhandled CLD scanning work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4443   }
4444 
4445   // We might have added oops to ClassLoaderData::_handles during the
4446   // concurrent marking phase. These oops do not always point to newly allocated objects
4447   // that are guaranteed to be kept alive.  Hence,
4448   // we do have to revisit the _handles block during the remark phase.
4449 
4450   // ---------- dirty CLD scanning ----------
4451   if (worker_id == 0) { // Single threaded at the moment.
4452     _timer.reset();
4453     _timer.start();
4454 
4455     // Scan all classes that was dirtied during the concurrent marking phase.
4456     RemarkCLDClosure remark_closure(&par_mrias_cl);
4457     ClassLoaderDataGraph::cld_do(&remark_closure);
4458 
4459     _timer.stop();
4460     log_trace(gc, task)("Finished dirty CLD scanning work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4461   }
4462 
4463 
4464   // ---------- rescan dirty cards ------------
4465   _timer.reset();
4466   _timer.start();
4467 
4468   // Do the rescan tasks for each of the two spaces
4469   // (cms_space) in turn.
4470   // "worker_id" is passed to select the task_queue for "worker_id"
4471   do_dirty_card_rescan_tasks(_cms_space, worker_id, &par_mrias_cl);
4472   _timer.stop();
4473   log_trace(gc, task)("Finished dirty card rescan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4474 
4475   // ---------- steal work from other threads ...
4476   // ---------- ... and drain overflow list.
4477   _timer.reset();
4478   _timer.start();
4479   do_work_steal(worker_id, &par_mrias_cl, _collector->hash_seed(worker_id));
4480   _timer.stop();
4481   log_trace(gc, task)("Finished work stealing in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4482 }
4483 
4484 void
4485 CMSParMarkTask::do_young_space_rescan(
4486   OopsInGenClosure* cl, ContiguousSpace* space,
4487   HeapWord** chunk_array, size_t chunk_top) {
4488   // Until all tasks completed:
4489   // . claim an unclaimed task
4490   // . compute region boundaries corresponding to task claimed
4491   //   using chunk_array
4492   // . par_oop_iterate(cl) over that region
4493 
4494   ResourceMark rm;
4495   HandleMark   hm;
4496 
4497   SequentialSubTasksDone* pst = space->par_seq_tasks();
4498 
4499   uint nth_task = 0;
4500   uint n_tasks  = pst->n_tasks();
4501 
4502   if (n_tasks > 0) {
4503     assert(pst->valid(), "Uninitialized use?");
4504     HeapWord *start, *end;
4505     while (!pst->is_task_claimed(/* reference */ nth_task)) {
4506       // We claimed task # nth_task; compute its boundaries.
4507       if (chunk_top == 0) {  // no samples were taken
4508         assert(nth_task == 0 && n_tasks == 1, "Can have only 1 eden task");
4509         start = space->bottom();
4510         end   = space->top();
4511       } else if (nth_task == 0) {
4512         start = space->bottom();
4513         end   = chunk_array[nth_task];
4514       } else if (nth_task < (uint)chunk_top) {
4515         assert(nth_task >= 1, "Control point invariant");
4516         start = chunk_array[nth_task - 1];
4517         end   = chunk_array[nth_task];
4518       } else {
4519         assert(nth_task == (uint)chunk_top, "Control point invariant");
4520         start = chunk_array[chunk_top - 1];
4521         end   = space->top();
4522       }
4523       MemRegion mr(start, end);
4524       // Verify that mr is in space
4525       assert(mr.is_empty() || space->used_region().contains(mr),
4526              "Should be in space");
4527       // Verify that "start" is an object boundary
4528       assert(mr.is_empty() || oopDesc::is_oop(oop(mr.start())),
4529              "Should be an oop");
4530       space->par_oop_iterate(mr, cl);
4531     }
4532     pst->all_tasks_completed();
4533   }
4534 }
4535 
4536 void
4537 CMSParRemarkTask::do_dirty_card_rescan_tasks(
4538   CompactibleFreeListSpace* sp, int i,
4539   ParMarkRefsIntoAndScanClosure* cl) {
4540   // Until all tasks completed:
4541   // . claim an unclaimed task
4542   // . compute region boundaries corresponding to task claimed
4543   // . transfer dirty bits ct->mut for that region
4544   // . apply rescanclosure to dirty mut bits for that region
4545 
4546   ResourceMark rm;
4547   HandleMark   hm;
4548 
4549   OopTaskQueue* work_q = work_queue(i);
4550   ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
4551   // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
4552   // CAUTION: This closure has state that persists across calls to
4553   // the work method dirty_range_iterate_clear() in that it has
4554   // embedded in it a (subtype of) UpwardsObjectClosure. The
4555   // use of that state in the embedded UpwardsObjectClosure instance
4556   // assumes that the cards are always iterated (even if in parallel
4557   // by several threads) in monotonically increasing order per each
4558   // thread. This is true of the implementation below which picks
4559   // card ranges (chunks) in monotonically increasing order globally
4560   // and, a-fortiori, in monotonically increasing order per thread
4561   // (the latter order being a subsequence of the former).
4562   // If the work code below is ever reorganized into a more chaotic
4563   // work-partitioning form than the current "sequential tasks"
4564   // paradigm, the use of that persistent state will have to be
4565   // revisited and modified appropriately. See also related
4566   // bug 4756801 work on which should examine this code to make
4567   // sure that the changes there do not run counter to the
4568   // assumptions made here and necessary for correctness and
4569   // efficiency. Note also that this code might yield inefficient
4570   // behavior in the case of very large objects that span one or
4571   // more work chunks. Such objects would potentially be scanned
4572   // several times redundantly. Work on 4756801 should try and
4573   // address that performance anomaly if at all possible. XXX
4574   MemRegion  full_span  = _collector->_span;
4575   CMSBitMap* bm    = &(_collector->_markBitMap);     // shared
4576   MarkFromDirtyCardsClosure
4577     greyRescanClosure(_collector, full_span, // entire span of interest
4578                       sp, bm, work_q, cl);
4579 
4580   SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
4581   assert(pst->valid(), "Uninitialized use?");
4582   uint nth_task = 0;
4583   const int alignment = CardTableModRefBS::card_size * BitsPerWord;
4584   MemRegion span = sp->used_region();
4585   HeapWord* start_addr = span.start();
4586   HeapWord* end_addr = align_up(span.end(), alignment);
4587   const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
4588   assert(is_aligned(start_addr, alignment), "Check alignment");
4589   assert(is_aligned(chunk_size, alignment), "Check alignment");
4590 
4591   while (!pst->is_task_claimed(/* reference */ nth_task)) {
4592     // Having claimed the nth_task, compute corresponding mem-region,
4593     // which is a-fortiori aligned correctly (i.e. at a MUT boundary).
4594     // The alignment restriction ensures that we do not need any
4595     // synchronization with other gang-workers while setting or
4596     // clearing bits in thus chunk of the MUT.
4597     MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
4598                                     start_addr + (nth_task+1)*chunk_size);
4599     // The last chunk's end might be way beyond end of the
4600     // used region. In that case pull back appropriately.
4601     if (this_span.end() > end_addr) {
4602       this_span.set_end(end_addr);
4603       assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
4604     }
4605     // Iterate over the dirty cards covering this chunk, marking them
4606     // precleaned, and setting the corresponding bits in the mod union
4607     // table. Since we have been careful to partition at Card and MUT-word
4608     // boundaries no synchronization is needed between parallel threads.
4609     _collector->_ct->ct_bs()->dirty_card_iterate(this_span,
4610                                                  &modUnionClosure);
4611 
4612     // Having transferred these marks into the modUnionTable,
4613     // rescan the marked objects on the dirty cards in the modUnionTable.
4614     // Even if this is at a synchronous collection, the initial marking
4615     // may have been done during an asynchronous collection so there
4616     // may be dirty bits in the mod-union table.
4617     _collector->_modUnionTable.dirty_range_iterate_clear(
4618                   this_span, &greyRescanClosure);
4619     _collector->_modUnionTable.verifyNoOneBitsInRange(
4620                                  this_span.start(),
4621                                  this_span.end());
4622   }
4623   pst->all_tasks_completed();  // declare that i am done
4624 }
4625 
4626 // . see if we can share work_queues with ParNew? XXX
4627 void
4628 CMSParRemarkTask::do_work_steal(int i, ParMarkRefsIntoAndScanClosure* cl,
4629                                 int* seed) {
4630   OopTaskQueue* work_q = work_queue(i);
4631   NOT_PRODUCT(int num_steals = 0;)
4632   oop obj_to_scan;
4633   CMSBitMap* bm = &(_collector->_markBitMap);
4634 
4635   while (true) {
4636     // Completely finish any left over work from (an) earlier round(s)
4637     cl->trim_queue(0);
4638     size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
4639                                          (size_t)ParGCDesiredObjsFromOverflowList);
4640     // Now check if there's any work in the overflow list
4641     // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
4642     // only affects the number of attempts made to get work from the
4643     // overflow list and does not affect the number of workers.  Just
4644     // pass ParallelGCThreads so this behavior is unchanged.
4645     if (_collector->par_take_from_overflow_list(num_from_overflow_list,
4646                                                 work_q,
4647                                                 ParallelGCThreads)) {
4648       // found something in global overflow list;
4649       // not yet ready to go stealing work from others.
4650       // We'd like to assert(work_q->size() != 0, ...)
4651       // because we just took work from the overflow list,
4652       // but of course we can't since all of that could have
4653       // been already stolen from us.
4654       // "He giveth and He taketh away."
4655       continue;
4656     }
4657     // Verify that we have no work before we resort to stealing
4658     assert(work_q->size() == 0, "Have work, shouldn't steal");
4659     // Try to steal from other queues that have work
4660     if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
4661       NOT_PRODUCT(num_steals++;)
4662       assert(oopDesc::is_oop(obj_to_scan), "Oops, not an oop!");
4663       assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
4664       // Do scanning work
4665       obj_to_scan->oop_iterate(cl);
4666       // Loop around, finish this work, and try to steal some more
4667     } else if (terminator()->offer_termination()) {
4668         break;  // nirvana from the infinite cycle
4669     }
4670   }
4671   log_develop_trace(gc, task)("\t(%d: stole %d oops)", i, num_steals);
4672   assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
4673          "Else our work is not yet done");
4674 }
4675 
4676 // Record object boundaries in _eden_chunk_array by sampling the eden
4677 // top in the slow-path eden object allocation code path and record
4678 // the boundaries, if CMSEdenChunksRecordAlways is true. If
4679 // CMSEdenChunksRecordAlways is false, we use the other asynchronous
4680 // sampling in sample_eden() that activates during the part of the
4681 // preclean phase.
4682 void CMSCollector::sample_eden_chunk() {
4683   if (CMSEdenChunksRecordAlways && _eden_chunk_array != NULL) {
4684     if (_eden_chunk_lock->try_lock()) {
4685       // Record a sample. This is the critical section. The contents
4686       // of the _eden_chunk_array have to be non-decreasing in the
4687       // address order.
4688       _eden_chunk_array[_eden_chunk_index] = *_top_addr;
4689       assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4690              "Unexpected state of Eden");
4691       if (_eden_chunk_index == 0 ||
4692           ((_eden_chunk_array[_eden_chunk_index] > _eden_chunk_array[_eden_chunk_index-1]) &&
4693            (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4694                           _eden_chunk_array[_eden_chunk_index-1]) >= CMSSamplingGrain))) {
4695         _eden_chunk_index++;  // commit sample
4696       }
4697       _eden_chunk_lock->unlock();
4698     }
4699   }
4700 }
4701 
4702 // Return a thread-local PLAB recording array, as appropriate.
4703 void* CMSCollector::get_data_recorder(int thr_num) {
4704   if (_survivor_plab_array != NULL &&
4705       (CMSPLABRecordAlways ||
4706        (_collectorState > Marking && _collectorState < FinalMarking))) {
4707     assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
4708     ChunkArray* ca = &_survivor_plab_array[thr_num];
4709     ca->reset();   // clear it so that fresh data is recorded
4710     return (void*) ca;
4711   } else {
4712     return NULL;
4713   }
4714 }
4715 
4716 // Reset all the thread-local PLAB recording arrays
4717 void CMSCollector::reset_survivor_plab_arrays() {
4718   for (uint i = 0; i < ParallelGCThreads; i++) {
4719     _survivor_plab_array[i].reset();
4720   }
4721 }
4722 
4723 // Merge the per-thread plab arrays into the global survivor chunk
4724 // array which will provide the partitioning of the survivor space
4725 // for CMS initial scan and rescan.
4726 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv,
4727                                               int no_of_gc_threads) {
4728   assert(_survivor_plab_array  != NULL, "Error");
4729   assert(_survivor_chunk_array != NULL, "Error");
4730   assert(_collectorState == FinalMarking ||
4731          (CMSParallelInitialMarkEnabled && _collectorState == InitialMarking), "Error");
4732   for (int j = 0; j < no_of_gc_threads; j++) {
4733     _cursor[j] = 0;
4734   }
4735   HeapWord* top = surv->top();
4736   size_t i;
4737   for (i = 0; i < _survivor_chunk_capacity; i++) {  // all sca entries
4738     HeapWord* min_val = top;          // Higher than any PLAB address
4739     uint      min_tid = 0;            // position of min_val this round
4740     for (int j = 0; j < no_of_gc_threads; j++) {
4741       ChunkArray* cur_sca = &_survivor_plab_array[j];
4742       if (_cursor[j] == cur_sca->end()) {
4743         continue;
4744       }
4745       assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
4746       HeapWord* cur_val = cur_sca->nth(_cursor[j]);
4747       assert(surv->used_region().contains(cur_val), "Out of bounds value");
4748       if (cur_val < min_val) {
4749         min_tid = j;
4750         min_val = cur_val;
4751       } else {
4752         assert(cur_val < top, "All recorded addresses should be less");
4753       }
4754     }
4755     // At this point min_val and min_tid are respectively
4756     // the least address in _survivor_plab_array[j]->nth(_cursor[j])
4757     // and the thread (j) that witnesses that address.
4758     // We record this address in the _survivor_chunk_array[i]
4759     // and increment _cursor[min_tid] prior to the next round i.
4760     if (min_val == top) {
4761       break;
4762     }
4763     _survivor_chunk_array[i] = min_val;
4764     _cursor[min_tid]++;
4765   }
4766   // We are all done; record the size of the _survivor_chunk_array
4767   _survivor_chunk_index = i; // exclusive: [0, i)
4768   log_trace(gc, survivor)(" (Survivor:" SIZE_FORMAT "chunks) ", i);
4769   // Verify that we used up all the recorded entries
4770   #ifdef ASSERT
4771     size_t total = 0;
4772     for (int j = 0; j < no_of_gc_threads; j++) {
4773       assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
4774       total += _cursor[j];
4775     }
4776     assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
4777     // Check that the merged array is in sorted order
4778     if (total > 0) {
4779       for (size_t i = 0; i < total - 1; i++) {
4780         log_develop_trace(gc, survivor)(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
4781                                      i, p2i(_survivor_chunk_array[i]));
4782         assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
4783                "Not sorted");
4784       }
4785     }
4786   #endif // ASSERT
4787 }
4788 
4789 // Set up the space's par_seq_tasks structure for work claiming
4790 // for parallel initial scan and rescan of young gen.
4791 // See ParRescanTask where this is currently used.
4792 void
4793 CMSCollector::
4794 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
4795   assert(n_threads > 0, "Unexpected n_threads argument");
4796 
4797   // Eden space
4798   if (!_young_gen->eden()->is_empty()) {
4799     SequentialSubTasksDone* pst = _young_gen->eden()->par_seq_tasks();
4800     assert(!pst->valid(), "Clobbering existing data?");
4801     // Each valid entry in [0, _eden_chunk_index) represents a task.
4802     size_t n_tasks = _eden_chunk_index + 1;
4803     assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
4804     // Sets the condition for completion of the subtask (how many threads
4805     // need to finish in order to be done).
4806     pst->set_n_threads(n_threads);
4807     pst->set_n_tasks((int)n_tasks);
4808   }
4809 
4810   // Merge the survivor plab arrays into _survivor_chunk_array
4811   if (_survivor_plab_array != NULL) {
4812     merge_survivor_plab_arrays(_young_gen->from(), n_threads);
4813   } else {
4814     assert(_survivor_chunk_index == 0, "Error");
4815   }
4816 
4817   // To space
4818   {
4819     SequentialSubTasksDone* pst = _young_gen->to()->par_seq_tasks();
4820     assert(!pst->valid(), "Clobbering existing data?");
4821     // Sets the condition for completion of the subtask (how many threads
4822     // need to finish in order to be done).
4823     pst->set_n_threads(n_threads);
4824     pst->set_n_tasks(1);
4825     assert(pst->valid(), "Error");
4826   }
4827 
4828   // From space
4829   {
4830     SequentialSubTasksDone* pst = _young_gen->from()->par_seq_tasks();
4831     assert(!pst->valid(), "Clobbering existing data?");
4832     size_t n_tasks = _survivor_chunk_index + 1;
4833     assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
4834     // Sets the condition for completion of the subtask (how many threads
4835     // need to finish in order to be done).
4836     pst->set_n_threads(n_threads);
4837     pst->set_n_tasks((int)n_tasks);
4838     assert(pst->valid(), "Error");
4839   }
4840 }
4841 
4842 // Parallel version of remark
4843 void CMSCollector::do_remark_parallel() {
4844   CMSHeap* heap = CMSHeap::heap();
4845   WorkGang* workers = heap->workers();
4846   assert(workers != NULL, "Need parallel worker threads.");
4847   // Choose to use the number of GC workers most recently set
4848   // into "active_workers".
4849   uint n_workers = workers->active_workers();
4850 
4851   CompactibleFreeListSpace* cms_space  = _cmsGen->cmsSpace();
4852 
4853   StrongRootsScope srs(n_workers);
4854 
4855   CMSParRemarkTask tsk(this, cms_space, n_workers, workers, task_queues(), &srs);
4856 
4857   // We won't be iterating over the cards in the card table updating
4858   // the younger_gen cards, so we shouldn't call the following else
4859   // the verification code as well as subsequent younger_refs_iterate
4860   // code would get confused. XXX
4861   // heap->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
4862 
4863   // The young gen rescan work will not be done as part of
4864   // process_roots (which currently doesn't know how to
4865   // parallelize such a scan), but rather will be broken up into
4866   // a set of parallel tasks (via the sampling that the [abortable]
4867   // preclean phase did of eden, plus the [two] tasks of
4868   // scanning the [two] survivor spaces. Further fine-grain
4869   // parallelization of the scanning of the survivor spaces
4870   // themselves, and of precleaning of the young gen itself
4871   // is deferred to the future.
4872   initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
4873 
4874   // The dirty card rescan work is broken up into a "sequence"
4875   // of parallel tasks (per constituent space) that are dynamically
4876   // claimed by the parallel threads.
4877   cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
4878 
4879   // It turns out that even when we're using 1 thread, doing the work in a
4880   // separate thread causes wide variance in run times.  We can't help this
4881   // in the multi-threaded case, but we special-case n=1 here to get
4882   // repeatable measurements of the 1-thread overhead of the parallel code.
4883   if (n_workers > 1) {
4884     // Make refs discovery MT-safe, if it isn't already: it may not
4885     // necessarily be so, since it's possible that we are doing
4886     // ST marking.
4887     ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), true);
4888     workers->run_task(&tsk);
4889   } else {
4890     ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
4891     tsk.work(0);
4892   }
4893 
4894   // restore, single-threaded for now, any preserved marks
4895   // as a result of work_q overflow
4896   restore_preserved_marks_if_any();
4897 }
4898 
4899 // Non-parallel version of remark
4900 void CMSCollector::do_remark_non_parallel() {
4901   ResourceMark rm;
4902   HandleMark   hm;
4903   CMSHeap* heap = CMSHeap::heap();
4904   ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
4905 
4906   MarkRefsIntoAndScanClosure
4907     mrias_cl(_span, ref_processor(), &_markBitMap, NULL /* not precleaning */,
4908              &_markStack, this,
4909              false /* should_yield */, false /* not precleaning */);
4910   MarkFromDirtyCardsClosure
4911     markFromDirtyCardsClosure(this, _span,
4912                               NULL,  // space is set further below
4913                               &_markBitMap, &_markStack, &mrias_cl);
4914   {
4915     GCTraceTime(Trace, gc, phases) t("Grey Object Rescan", _gc_timer_cm);
4916     // Iterate over the dirty cards, setting the corresponding bits in the
4917     // mod union table.
4918     {
4919       ModUnionClosure modUnionClosure(&_modUnionTable);
4920       _ct->ct_bs()->dirty_card_iterate(
4921                       _cmsGen->used_region(),
4922                       &modUnionClosure);
4923     }
4924     // Having transferred these marks into the modUnionTable, we just need
4925     // to rescan the marked objects on the dirty cards in the modUnionTable.
4926     // The initial marking may have been done during an asynchronous
4927     // collection so there may be dirty bits in the mod-union table.
4928     const int alignment =
4929       CardTableModRefBS::card_size * BitsPerWord;
4930     {
4931       // ... First handle dirty cards in CMS gen
4932       markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
4933       MemRegion ur = _cmsGen->used_region();
4934       HeapWord* lb = ur.start();
4935       HeapWord* ub = align_up(ur.end(), alignment);
4936       MemRegion cms_span(lb, ub);
4937       _modUnionTable.dirty_range_iterate_clear(cms_span,
4938                                                &markFromDirtyCardsClosure);
4939       verify_work_stacks_empty();
4940       log_trace(gc)(" (re-scanned " SIZE_FORMAT " dirty cards in cms gen) ", markFromDirtyCardsClosure.num_dirty_cards());
4941     }
4942   }
4943   if (VerifyDuringGC &&
4944       CMSHeap::heap()->total_collections() >= VerifyGCStartAt) {
4945     HandleMark hm;  // Discard invalid handles created during verification
4946     Universe::verify();
4947   }
4948   {
4949     GCTraceTime(Trace, gc, phases) t("Root Rescan", _gc_timer_cm);
4950 
4951     verify_work_stacks_empty();
4952 
4953     heap->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
4954     StrongRootsScope srs(1);
4955 
4956     heap->cms_process_roots(&srs,
4957                             true,  // young gen as roots
4958                             GenCollectedHeap::ScanningOption(roots_scanning_options()),
4959                             should_unload_classes(),
4960                             &mrias_cl,
4961                             NULL); // The dirty klasses will be handled below
4962 
4963     assert(should_unload_classes()
4964            || (roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4965            "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4966   }
4967 
4968   {
4969     GCTraceTime(Trace, gc, phases) t("Visit Unhandled CLDs", _gc_timer_cm);
4970 
4971     verify_work_stacks_empty();
4972 
4973     // Scan all class loader data objects that might have been introduced
4974     // during concurrent marking.
4975     ResourceMark rm;
4976     GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
4977     for (int i = 0; i < array->length(); i++) {
4978       mrias_cl.do_cld_nv(array->at(i));
4979     }
4980 
4981     // We don't need to keep track of new CLDs anymore.
4982     ClassLoaderDataGraph::remember_new_clds(false);
4983 
4984     verify_work_stacks_empty();
4985   }
4986 
4987   // We might have added oops to ClassLoaderData::_handles during the
4988   // concurrent marking phase. These oops do not point to newly allocated objects
4989   // that are guaranteed to be kept alive.  Hence,
4990   // we do have to revisit the _handles block during the remark phase.
4991   {
4992     GCTraceTime(Trace, gc, phases) t("Dirty CLD Scan", _gc_timer_cm);
4993 
4994     verify_work_stacks_empty();
4995 
4996     RemarkCLDClosure remark_closure(&mrias_cl);
4997     ClassLoaderDataGraph::cld_do(&remark_closure);
4998 
4999     verify_work_stacks_empty();
5000   }
5001 
5002   verify_work_stacks_empty();
5003   // Restore evacuated mark words, if any, used for overflow list links
5004   restore_preserved_marks_if_any();
5005 
5006   verify_overflow_empty();
5007 }
5008 
5009 ////////////////////////////////////////////////////////
5010 // Parallel Reference Processing Task Proxy Class
5011 ////////////////////////////////////////////////////////
5012 class AbstractGangTaskWOopQueues : public AbstractGangTask {
5013   OopTaskQueueSet*       _queues;
5014   ParallelTaskTerminator _terminator;
5015  public:
5016   AbstractGangTaskWOopQueues(const char* name, OopTaskQueueSet* queues, uint n_threads) :
5017     AbstractGangTask(name), _queues(queues), _terminator(n_threads, _queues) {}
5018   ParallelTaskTerminator* terminator() { return &_terminator; }
5019   OopTaskQueueSet* queues() { return _queues; }
5020 };
5021 
5022 class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues {
5023   typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
5024   CMSCollector*          _collector;
5025   CMSBitMap*             _mark_bit_map;
5026   const MemRegion        _span;
5027   ProcessTask&           _task;
5028 
5029 public:
5030   CMSRefProcTaskProxy(ProcessTask&     task,
5031                       CMSCollector*    collector,
5032                       const MemRegion& span,
5033                       CMSBitMap*       mark_bit_map,
5034                       AbstractWorkGang* workers,
5035                       OopTaskQueueSet* task_queues):
5036     AbstractGangTaskWOopQueues("Process referents by policy in parallel",
5037       task_queues,
5038       workers->active_workers()),
5039     _task(task),
5040     _collector(collector), _span(span), _mark_bit_map(mark_bit_map)
5041   {
5042     assert(_collector->_span.equals(_span) && !_span.is_empty(),
5043            "Inconsistency in _span");
5044   }
5045 
5046   OopTaskQueueSet* task_queues() { return queues(); }
5047 
5048   OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5049 
5050   void do_work_steal(int i,
5051                      CMSParDrainMarkingStackClosure* drain,
5052                      CMSParKeepAliveClosure* keep_alive,
5053                      int* seed);
5054 
5055   virtual void work(uint worker_id);
5056 };
5057 
5058 void CMSRefProcTaskProxy::work(uint worker_id) {
5059   ResourceMark rm;
5060   HandleMark hm;
5061   assert(_collector->_span.equals(_span), "Inconsistency in _span");
5062   CMSParKeepAliveClosure par_keep_alive(_collector, _span,
5063                                         _mark_bit_map,
5064                                         work_queue(worker_id));
5065   CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
5066                                                  _mark_bit_map,
5067                                                  work_queue(worker_id));
5068   CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
5069   _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack);
5070   if (_task.marks_oops_alive()) {
5071     do_work_steal(worker_id, &par_drain_stack, &par_keep_alive,
5072                   _collector->hash_seed(worker_id));
5073   }
5074   assert(work_queue(worker_id)->size() == 0, "work_queue should be empty");
5075   assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
5076 }
5077 
5078 class CMSRefEnqueueTaskProxy: public AbstractGangTask {
5079   typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
5080   EnqueueTask& _task;
5081 
5082 public:
5083   CMSRefEnqueueTaskProxy(EnqueueTask& task)
5084     : AbstractGangTask("Enqueue reference objects in parallel"),
5085       _task(task)
5086   { }
5087 
5088   virtual void work(uint worker_id)
5089   {
5090     _task.work(worker_id);
5091   }
5092 };
5093 
5094 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
5095   MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue):
5096    _span(span),
5097    _bit_map(bit_map),
5098    _work_queue(work_queue),
5099    _mark_and_push(collector, span, bit_map, work_queue),
5100    _low_water_mark(MIN2((work_queue->max_elems()/4),
5101                         ((uint)CMSWorkQueueDrainThreshold * ParallelGCThreads)))
5102 { }
5103 
5104 // . see if we can share work_queues with ParNew? XXX
5105 void CMSRefProcTaskProxy::do_work_steal(int i,
5106   CMSParDrainMarkingStackClosure* drain,
5107   CMSParKeepAliveClosure* keep_alive,
5108   int* seed) {
5109   OopTaskQueue* work_q = work_queue(i);
5110   NOT_PRODUCT(int num_steals = 0;)
5111   oop obj_to_scan;
5112 
5113   while (true) {
5114     // Completely finish any left over work from (an) earlier round(s)
5115     drain->trim_queue(0);
5116     size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5117                                          (size_t)ParGCDesiredObjsFromOverflowList);
5118     // Now check if there's any work in the overflow list
5119     // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5120     // only affects the number of attempts made to get work from the
5121     // overflow list and does not affect the number of workers.  Just
5122     // pass ParallelGCThreads so this behavior is unchanged.
5123     if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5124                                                 work_q,
5125                                                 ParallelGCThreads)) {
5126       // Found something in global overflow list;
5127       // not yet ready to go stealing work from others.
5128       // We'd like to assert(work_q->size() != 0, ...)
5129       // because we just took work from the overflow list,
5130       // but of course we can't, since all of that might have
5131       // been already stolen from us.
5132       continue;
5133     }
5134     // Verify that we have no work before we resort to stealing
5135     assert(work_q->size() == 0, "Have work, shouldn't steal");
5136     // Try to steal from other queues that have work
5137     if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5138       NOT_PRODUCT(num_steals++;)
5139       assert(oopDesc::is_oop(obj_to_scan), "Oops, not an oop!");
5140       assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5141       // Do scanning work
5142       obj_to_scan->oop_iterate(keep_alive);
5143       // Loop around, finish this work, and try to steal some more
5144     } else if (terminator()->offer_termination()) {
5145       break;  // nirvana from the infinite cycle
5146     }
5147   }
5148   log_develop_trace(gc, task)("\t(%d: stole %d oops)", i, num_steals);
5149 }
5150 
5151 void CMSRefProcTaskExecutor::execute(ProcessTask& task)
5152 {
5153   CMSHeap* heap = CMSHeap::heap();
5154   WorkGang* workers = heap->workers();
5155   assert(workers != NULL, "Need parallel worker threads.");
5156   CMSRefProcTaskProxy rp_task(task, &_collector,
5157                               _collector.ref_processor()->span(),
5158                               _collector.markBitMap(),
5159                               workers, _collector.task_queues());
5160   workers->run_task(&rp_task);
5161 }
5162 
5163 void CMSRefProcTaskExecutor::execute(EnqueueTask& task)
5164 {
5165 
5166   CMSHeap* heap = CMSHeap::heap();
5167   WorkGang* workers = heap->workers();
5168   assert(workers != NULL, "Need parallel worker threads.");
5169   CMSRefEnqueueTaskProxy enq_task(task);
5170   workers->run_task(&enq_task);
5171 }
5172 
5173 void CMSCollector::refProcessingWork() {
5174   ResourceMark rm;
5175   HandleMark   hm;
5176 
5177   ReferenceProcessor* rp = ref_processor();
5178   assert(rp->span().equals(_span), "Spans should be equal");
5179   assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
5180   // Process weak references.
5181   rp->setup_policy(false);
5182   verify_work_stacks_empty();
5183 
5184   ReferenceProcessorPhaseTimes pt(_gc_timer_cm, rp->num_q());
5185   {
5186     GCTraceTime(Debug, gc, phases) t("Reference Processing", _gc_timer_cm);
5187 
5188     // Setup keep_alive and complete closures.
5189     CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
5190                                             &_markStack, false /* !preclean */);
5191     CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
5192                                   _span, &_markBitMap, &_markStack,
5193                                   &cmsKeepAliveClosure, false /* !preclean */);
5194 
5195     ReferenceProcessorStats stats;
5196     if (rp->processing_is_mt()) {
5197       // Set the degree of MT here.  If the discovery is done MT, there
5198       // may have been a different number of threads doing the discovery
5199       // and a different number of discovered lists may have Ref objects.
5200       // That is OK as long as the Reference lists are balanced (see
5201       // balance_all_queues() and balance_queues()).
5202       CMSHeap* heap = CMSHeap::heap();
5203       uint active_workers = ParallelGCThreads;
5204       WorkGang* workers = heap->workers();
5205       if (workers != NULL) {
5206         active_workers = workers->active_workers();
5207         // The expectation is that active_workers will have already
5208         // been set to a reasonable value.  If it has not been set,
5209         // investigate.
5210         assert(active_workers > 0, "Should have been set during scavenge");
5211       }
5212       rp->set_active_mt_degree(active_workers);
5213       CMSRefProcTaskExecutor task_executor(*this);
5214       stats = rp->process_discovered_references(&_is_alive_closure,
5215                                         &cmsKeepAliveClosure,
5216                                         &cmsDrainMarkingStackClosure,
5217                                         &task_executor,
5218                                         &pt);
5219     } else {
5220       stats = rp->process_discovered_references(&_is_alive_closure,
5221                                         &cmsKeepAliveClosure,
5222                                         &cmsDrainMarkingStackClosure,
5223                                         NULL,
5224                                         &pt);
5225     }
5226     _gc_tracer_cm->report_gc_reference_stats(stats);
5227     pt.print_all_references();
5228   }
5229 
5230   // This is the point where the entire marking should have completed.
5231   verify_work_stacks_empty();
5232 
5233   {
5234     GCTraceTime(Debug, gc, phases) t("Weak Processing", _gc_timer_cm);
5235     WeakProcessor::weak_oops_do(&_is_alive_closure, &do_nothing_cl);
5236   }
5237 
5238   if (should_unload_classes()) {
5239     {
5240       GCTraceTime(Debug, gc, phases) t("Class Unloading", _gc_timer_cm);
5241 
5242       // Unload classes and purge the SystemDictionary.
5243       bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure, _gc_timer_cm);
5244 
5245       // Unload nmethods.
5246       CodeCache::do_unloading(&_is_alive_closure, purged_class);
5247 
5248       // Prune dead klasses from subklass/sibling/implementor lists.
5249       Klass::clean_weak_klass_links(&_is_alive_closure);
5250     }
5251 
5252     {
5253       GCTraceTime(Debug, gc, phases) t("Scrub Symbol Table", _gc_timer_cm);
5254       // Clean up unreferenced symbols in symbol table.
5255       SymbolTable::unlink();
5256     }
5257 
5258     {
5259       GCTraceTime(Debug, gc, phases) t("Scrub String Table", _gc_timer_cm);
5260       // Delete entries for dead interned strings.
5261       StringTable::unlink(&_is_alive_closure);
5262     }
5263   }
5264 
5265   // Restore any preserved marks as a result of mark stack or
5266   // work queue overflow
5267   restore_preserved_marks_if_any();  // done single-threaded for now
5268 
5269   rp->set_enqueuing_is_done(true);
5270   if (rp->processing_is_mt()) {
5271     rp->balance_all_queues();
5272     CMSRefProcTaskExecutor task_executor(*this);
5273     rp->enqueue_discovered_references(&task_executor, &pt);
5274   } else {
5275     rp->enqueue_discovered_references(NULL, &pt);
5276   }
5277   rp->verify_no_references_recorded();
5278   pt.print_enqueue_phase();
5279   assert(!rp->discovery_enabled(), "should have been disabled");
5280 }
5281 
5282 #ifndef PRODUCT
5283 void CMSCollector::check_correct_thread_executing() {
5284   Thread* t = Thread::current();
5285   // Only the VM thread or the CMS thread should be here.
5286   assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
5287          "Unexpected thread type");
5288   // If this is the vm thread, the foreground process
5289   // should not be waiting.  Note that _foregroundGCIsActive is
5290   // true while the foreground collector is waiting.
5291   if (_foregroundGCShouldWait) {
5292     // We cannot be the VM thread
5293     assert(t->is_ConcurrentGC_thread(),
5294            "Should be CMS thread");
5295   } else {
5296     // We can be the CMS thread only if we are in a stop-world
5297     // phase of CMS collection.
5298     if (t->is_ConcurrentGC_thread()) {
5299       assert(_collectorState == InitialMarking ||
5300              _collectorState == FinalMarking,
5301              "Should be a stop-world phase");
5302       // The CMS thread should be holding the CMS_token.
5303       assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5304              "Potential interference with concurrently "
5305              "executing VM thread");
5306     }
5307   }
5308 }
5309 #endif
5310 
5311 void CMSCollector::sweep() {
5312   assert(_collectorState == Sweeping, "just checking");
5313   check_correct_thread_executing();
5314   verify_work_stacks_empty();
5315   verify_overflow_empty();
5316   increment_sweep_count();
5317   TraceCMSMemoryManagerStats tms(_collectorState, CMSHeap::heap()->gc_cause());
5318 
5319   _inter_sweep_timer.stop();
5320   _inter_sweep_estimate.sample(_inter_sweep_timer.seconds());
5321 
5322   assert(!_intra_sweep_timer.is_active(), "Should not be active");
5323   _intra_sweep_timer.reset();
5324   _intra_sweep_timer.start();
5325   {
5326     GCTraceCPUTime tcpu;
5327     CMSPhaseAccounting pa(this, "Concurrent Sweep");
5328     // First sweep the old gen
5329     {
5330       CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
5331                                bitMapLock());
5332       sweepWork(_cmsGen);
5333     }
5334 
5335     // Update Universe::_heap_*_at_gc figures.
5336     // We need all the free list locks to make the abstract state
5337     // transition from Sweeping to Resetting. See detailed note
5338     // further below.
5339     {
5340       CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock());
5341       // Update heap occupancy information which is used as
5342       // input to soft ref clearing policy at the next gc.
5343       Universe::update_heap_info_at_gc();
5344       _collectorState = Resizing;
5345     }
5346   }
5347   verify_work_stacks_empty();
5348   verify_overflow_empty();
5349 
5350   if (should_unload_classes()) {
5351     // Delay purge to the beginning of the next safepoint.  Metaspace::contains
5352     // requires that the virtual spaces are stable and not deleted.
5353     ClassLoaderDataGraph::set_should_purge(true);
5354   }
5355 
5356   _intra_sweep_timer.stop();
5357   _intra_sweep_estimate.sample(_intra_sweep_timer.seconds());
5358 
5359   _inter_sweep_timer.reset();
5360   _inter_sweep_timer.start();
5361 
5362   // We need to use a monotonically non-decreasing time in ms
5363   // or we will see time-warp warnings and os::javaTimeMillis()
5364   // does not guarantee monotonicity.
5365   jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
5366   update_time_of_last_gc(now);
5367 
5368   // NOTE on abstract state transitions:
5369   // Mutators allocate-live and/or mark the mod-union table dirty
5370   // based on the state of the collection.  The former is done in
5371   // the interval [Marking, Sweeping] and the latter in the interval
5372   // [Marking, Sweeping).  Thus the transitions into the Marking state
5373   // and out of the Sweeping state must be synchronously visible
5374   // globally to the mutators.
5375   // The transition into the Marking state happens with the world
5376   // stopped so the mutators will globally see it.  Sweeping is
5377   // done asynchronously by the background collector so the transition
5378   // from the Sweeping state to the Resizing state must be done
5379   // under the freelistLock (as is the check for whether to
5380   // allocate-live and whether to dirty the mod-union table).
5381   assert(_collectorState == Resizing, "Change of collector state to"
5382     " Resizing must be done under the freelistLocks (plural)");
5383 
5384   // Now that sweeping has been completed, we clear
5385   // the incremental_collection_failed flag,
5386   // thus inviting a younger gen collection to promote into
5387   // this generation. If such a promotion may still fail,
5388   // the flag will be set again when a young collection is
5389   // attempted.
5390   CMSHeap* heap = CMSHeap::heap();
5391   heap->clear_incremental_collection_failed();  // Worth retrying as fresh space may have been freed up
5392   heap->update_full_collections_completed(_collection_count_start);
5393 }
5394 
5395 // FIX ME!!! Looks like this belongs in CFLSpace, with
5396 // CMSGen merely delegating to it.
5397 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
5398   double nearLargestPercent = FLSLargestBlockCoalesceProximity;
5399   HeapWord*  minAddr        = _cmsSpace->bottom();
5400   HeapWord*  largestAddr    =
5401     (HeapWord*) _cmsSpace->dictionary()->find_largest_dict();
5402   if (largestAddr == NULL) {
5403     // The dictionary appears to be empty.  In this case
5404     // try to coalesce at the end of the heap.
5405     largestAddr = _cmsSpace->end();
5406   }
5407   size_t largestOffset     = pointer_delta(largestAddr, minAddr);
5408   size_t nearLargestOffset =
5409     (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
5410   log_debug(gc, freelist)("CMS: Large Block: " PTR_FORMAT "; Proximity: " PTR_FORMAT " -> " PTR_FORMAT,
5411                           p2i(largestAddr), p2i(_cmsSpace->nearLargestChunk()), p2i(minAddr + nearLargestOffset));
5412   _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
5413 }
5414 
5415 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
5416   return addr >= _cmsSpace->nearLargestChunk();
5417 }
5418 
5419 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
5420   return _cmsSpace->find_chunk_at_end();
5421 }
5422 
5423 void ConcurrentMarkSweepGeneration::update_gc_stats(Generation* current_generation,
5424                                                     bool full) {
5425   // If the young generation has been collected, gather any statistics
5426   // that are of interest at this point.
5427   bool current_is_young = CMSHeap::heap()->is_young_gen(current_generation);
5428   if (!full && current_is_young) {
5429     // Gather statistics on the young generation collection.
5430     collector()->stats().record_gc0_end(used());
5431   }
5432 }
5433 
5434 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* old_gen) {
5435   // We iterate over the space(s) underlying this generation,
5436   // checking the mark bit map to see if the bits corresponding
5437   // to specific blocks are marked or not. Blocks that are
5438   // marked are live and are not swept up. All remaining blocks
5439   // are swept up, with coalescing on-the-fly as we sweep up
5440   // contiguous free and/or garbage blocks:
5441   // We need to ensure that the sweeper synchronizes with allocators
5442   // and stop-the-world collectors. In particular, the following
5443   // locks are used:
5444   // . CMS token: if this is held, a stop the world collection cannot occur
5445   // . freelistLock: if this is held no allocation can occur from this
5446   //                 generation by another thread
5447   // . bitMapLock: if this is held, no other thread can access or update
5448   //
5449 
5450   // Note that we need to hold the freelistLock if we use
5451   // block iterate below; else the iterator might go awry if
5452   // a mutator (or promotion) causes block contents to change
5453   // (for instance if the allocator divvies up a block).
5454   // If we hold the free list lock, for all practical purposes
5455   // young generation GC's can't occur (they'll usually need to
5456   // promote), so we might as well prevent all young generation
5457   // GC's while we do a sweeping step. For the same reason, we might
5458   // as well take the bit map lock for the entire duration
5459 
5460   // check that we hold the requisite locks
5461   assert(have_cms_token(), "Should hold cms token");
5462   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), "Should possess CMS token to sweep");
5463   assert_lock_strong(old_gen->freelistLock());
5464   assert_lock_strong(bitMapLock());
5465 
5466   assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context");
5467   assert(_intra_sweep_timer.is_active(),  "Was switched on  in an outer context");
5468   old_gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
5469                                           _inter_sweep_estimate.padded_average(),
5470                                           _intra_sweep_estimate.padded_average());
5471   old_gen->setNearLargestChunk();
5472 
5473   {
5474     SweepClosure sweepClosure(this, old_gen, &_markBitMap, CMSYield);
5475     old_gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
5476     // We need to free-up/coalesce garbage/blocks from a
5477     // co-terminal free run. This is done in the SweepClosure
5478     // destructor; so, do not remove this scope, else the
5479     // end-of-sweep-census below will be off by a little bit.
5480   }
5481   old_gen->cmsSpace()->sweep_completed();
5482   old_gen->cmsSpace()->endSweepFLCensus(sweep_count());
5483   if (should_unload_classes()) {                // unloaded classes this cycle,
5484     _concurrent_cycles_since_last_unload = 0;   // ... reset count
5485   } else {                                      // did not unload classes,
5486     _concurrent_cycles_since_last_unload++;     // ... increment count
5487   }
5488 }
5489 
5490 // Reset CMS data structures (for now just the marking bit map)
5491 // preparatory for the next cycle.
5492 void CMSCollector::reset_concurrent() {
5493   CMSTokenSyncWithLocks ts(true, bitMapLock());
5494 
5495   // If the state is not "Resetting", the foreground  thread
5496   // has done a collection and the resetting.
5497   if (_collectorState != Resetting) {
5498     assert(_collectorState == Idling, "The state should only change"
5499       " because the foreground collector has finished the collection");
5500     return;
5501   }
5502 
5503   {
5504     // Clear the mark bitmap (no grey objects to start with)
5505     // for the next cycle.
5506     GCTraceCPUTime tcpu;
5507     CMSPhaseAccounting cmspa(this, "Concurrent Reset");
5508 
5509     HeapWord* curAddr = _markBitMap.startWord();
5510     while (curAddr < _markBitMap.endWord()) {
5511       size_t remaining  = pointer_delta(_markBitMap.endWord(), curAddr);
5512       MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
5513       _markBitMap.clear_large_range(chunk);
5514       if (ConcurrentMarkSweepThread::should_yield() &&
5515           !foregroundGCIsActive() &&
5516           CMSYield) {
5517         assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5518                "CMS thread should hold CMS token");
5519         assert_lock_strong(bitMapLock());
5520         bitMapLock()->unlock();
5521         ConcurrentMarkSweepThread::desynchronize(true);
5522         stopTimer();
5523         incrementYields();
5524 
5525         // See the comment in coordinator_yield()
5526         for (unsigned i = 0; i < CMSYieldSleepCount &&
5527                          ConcurrentMarkSweepThread::should_yield() &&
5528                          !CMSCollector::foregroundGCIsActive(); ++i) {
5529           os::sleep(Thread::current(), 1, false);
5530         }
5531 
5532         ConcurrentMarkSweepThread::synchronize(true);
5533         bitMapLock()->lock_without_safepoint_check();
5534         startTimer();
5535       }
5536       curAddr = chunk.end();
5537     }
5538     // A successful mostly concurrent collection has been done.
5539     // Because only the full (i.e., concurrent mode failure) collections
5540     // are being measured for gc overhead limits, clean the "near" flag
5541     // and count.
5542     size_policy()->reset_gc_overhead_limit_count();
5543     _collectorState = Idling;
5544   }
5545 
5546   register_gc_end();
5547 }
5548 
5549 // Same as above but for STW paths
5550 void CMSCollector::reset_stw() {
5551   // already have the lock
5552   assert(_collectorState == Resetting, "just checking");
5553   assert_lock_strong(bitMapLock());
5554   GCIdMarkAndRestore gc_id_mark(_cmsThread->gc_id());
5555   _markBitMap.clear_all();
5556   _collectorState = Idling;
5557   register_gc_end();
5558 }
5559 
5560 void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) {
5561   GCTraceCPUTime tcpu;
5562   TraceCollectorStats tcs(counters());
5563 
5564   switch (op) {
5565     case CMS_op_checkpointRootsInitial: {
5566       GCTraceTime(Info, gc) t("Pause Initial Mark", NULL, GCCause::_no_gc, true);
5567       SvcGCMarker sgcm(SvcGCMarker::OTHER);
5568       checkpointRootsInitial();
5569       break;
5570     }
5571     case CMS_op_checkpointRootsFinal: {
5572       GCTraceTime(Info, gc) t("Pause Remark", NULL, GCCause::_no_gc, true);
5573       SvcGCMarker sgcm(SvcGCMarker::OTHER);
5574       checkpointRootsFinal();
5575       break;
5576     }
5577     default:
5578       fatal("No such CMS_op");
5579   }
5580 }
5581 
5582 #ifndef PRODUCT
5583 size_t const CMSCollector::skip_header_HeapWords() {
5584   return FreeChunk::header_size();
5585 }
5586 
5587 // Try and collect here conditions that should hold when
5588 // CMS thread is exiting. The idea is that the foreground GC
5589 // thread should not be blocked if it wants to terminate
5590 // the CMS thread and yet continue to run the VM for a while
5591 // after that.
5592 void CMSCollector::verify_ok_to_terminate() const {
5593   assert(Thread::current()->is_ConcurrentGC_thread(),
5594          "should be called by CMS thread");
5595   assert(!_foregroundGCShouldWait, "should be false");
5596   // We could check here that all the various low-level locks
5597   // are not held by the CMS thread, but that is overkill; see
5598   // also CMSThread::verify_ok_to_terminate() where the CGC_lock
5599   // is checked.
5600 }
5601 #endif
5602 
5603 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
5604    assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
5605           "missing Printezis mark?");
5606   HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5607   size_t size = pointer_delta(nextOneAddr + 1, addr);
5608   assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5609          "alignment problem");
5610   assert(size >= 3, "Necessary for Printezis marks to work");
5611   return size;
5612 }
5613 
5614 // A variant of the above (block_size_using_printezis_bits()) except
5615 // that we return 0 if the P-bits are not yet set.
5616 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
5617   if (_markBitMap.isMarked(addr + 1)) {
5618     assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects");
5619     HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5620     size_t size = pointer_delta(nextOneAddr + 1, addr);
5621     assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5622            "alignment problem");
5623     assert(size >= 3, "Necessary for Printezis marks to work");
5624     return size;
5625   }
5626   return 0;
5627 }
5628 
5629 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
5630   size_t sz = 0;
5631   oop p = (oop)addr;
5632   if (p->klass_or_null_acquire() != NULL) {
5633     sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
5634   } else {
5635     sz = block_size_using_printezis_bits(addr);
5636   }
5637   assert(sz > 0, "size must be nonzero");
5638   HeapWord* next_block = addr + sz;
5639   HeapWord* next_card  = align_up(next_block, CardTableModRefBS::card_size);
5640   assert(align_down((uintptr_t)addr,      CardTableModRefBS::card_size) <
5641          align_down((uintptr_t)next_card, CardTableModRefBS::card_size),
5642          "must be different cards");
5643   return next_card;
5644 }
5645 
5646 
5647 // CMS Bit Map Wrapper /////////////////////////////////////////
5648 
5649 // Construct a CMS bit map infrastructure, but don't create the
5650 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
5651 // further below.
5652 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
5653   _bm(),
5654   _shifter(shifter),
5655   _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true,
5656                                     Monitor::_safepoint_check_sometimes) : NULL)
5657 {
5658   _bmStartWord = 0;
5659   _bmWordSize  = 0;
5660 }
5661 
5662 bool CMSBitMap::allocate(MemRegion mr) {
5663   _bmStartWord = mr.start();
5664   _bmWordSize  = mr.word_size();
5665   ReservedSpace brs(ReservedSpace::allocation_align_size_up(
5666                      (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
5667   if (!brs.is_reserved()) {
5668     log_warning(gc)("CMS bit map allocation failure");
5669     return false;
5670   }
5671   // For now we'll just commit all of the bit map up front.
5672   // Later on we'll try to be more parsimonious with swap.
5673   if (!_virtual_space.initialize(brs, brs.size())) {
5674     log_warning(gc)("CMS bit map backing store failure");
5675     return false;
5676   }
5677   assert(_virtual_space.committed_size() == brs.size(),
5678          "didn't reserve backing store for all of CMS bit map?");
5679   assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
5680          _bmWordSize, "inconsistency in bit map sizing");
5681   _bm = BitMapView((BitMap::bm_word_t*)_virtual_space.low(), _bmWordSize >> _shifter);
5682 
5683   // bm.clear(); // can we rely on getting zero'd memory? verify below
5684   assert(isAllClear(),
5685          "Expected zero'd memory from ReservedSpace constructor");
5686   assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
5687          "consistency check");
5688   return true;
5689 }
5690 
5691 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
5692   HeapWord *next_addr, *end_addr, *last_addr;
5693   assert_locked();
5694   assert(covers(mr), "out-of-range error");
5695   // XXX assert that start and end are appropriately aligned
5696   for (next_addr = mr.start(), end_addr = mr.end();
5697        next_addr < end_addr; next_addr = last_addr) {
5698     MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
5699     last_addr = dirty_region.end();
5700     if (!dirty_region.is_empty()) {
5701       cl->do_MemRegion(dirty_region);
5702     } else {
5703       assert(last_addr == end_addr, "program logic");
5704       return;
5705     }
5706   }
5707 }
5708 
5709 void CMSBitMap::print_on_error(outputStream* st, const char* prefix) const {
5710   _bm.print_on_error(st, prefix);
5711 }
5712 
5713 #ifndef PRODUCT
5714 void CMSBitMap::assert_locked() const {
5715   CMSLockVerifier::assert_locked(lock());
5716 }
5717 
5718 bool CMSBitMap::covers(MemRegion mr) const {
5719   // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
5720   assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
5721          "size inconsistency");
5722   return (mr.start() >= _bmStartWord) &&
5723          (mr.end()   <= endWord());
5724 }
5725 
5726 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
5727     return (start >= _bmStartWord && (start + size) <= endWord());
5728 }
5729 
5730 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
5731   // verify that there are no 1 bits in the interval [left, right)
5732   FalseBitMapClosure falseBitMapClosure;
5733   iterate(&falseBitMapClosure, left, right);
5734 }
5735 
5736 void CMSBitMap::region_invariant(MemRegion mr)
5737 {
5738   assert_locked();
5739   // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
5740   assert(!mr.is_empty(), "unexpected empty region");
5741   assert(covers(mr), "mr should be covered by bit map");
5742   // convert address range into offset range
5743   size_t start_ofs = heapWordToOffset(mr.start());
5744   // Make sure that end() is appropriately aligned
5745   assert(mr.end() == align_up(mr.end(), (1 << (_shifter+LogHeapWordSize))),
5746          "Misaligned mr.end()");
5747   size_t end_ofs   = heapWordToOffset(mr.end());
5748   assert(end_ofs > start_ofs, "Should mark at least one bit");
5749 }
5750 
5751 #endif
5752 
5753 bool CMSMarkStack::allocate(size_t size) {
5754   // allocate a stack of the requisite depth
5755   ReservedSpace rs(ReservedSpace::allocation_align_size_up(
5756                    size * sizeof(oop)));
5757   if (!rs.is_reserved()) {
5758     log_warning(gc)("CMSMarkStack allocation failure");
5759     return false;
5760   }
5761   if (!_virtual_space.initialize(rs, rs.size())) {
5762     log_warning(gc)("CMSMarkStack backing store failure");
5763     return false;
5764   }
5765   assert(_virtual_space.committed_size() == rs.size(),
5766          "didn't reserve backing store for all of CMS stack?");
5767   _base = (oop*)(_virtual_space.low());
5768   _index = 0;
5769   _capacity = size;
5770   NOT_PRODUCT(_max_depth = 0);
5771   return true;
5772 }
5773 
5774 // XXX FIX ME !!! In the MT case we come in here holding a
5775 // leaf lock. For printing we need to take a further lock
5776 // which has lower rank. We need to recalibrate the two
5777 // lock-ranks involved in order to be able to print the
5778 // messages below. (Or defer the printing to the caller.
5779 // For now we take the expedient path of just disabling the
5780 // messages for the problematic case.)
5781 void CMSMarkStack::expand() {
5782   assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted");
5783   if (_capacity == MarkStackSizeMax) {
5784     if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled) {
5785       // We print a warning message only once per CMS cycle.
5786       log_debug(gc)(" (benign) Hit CMSMarkStack max size limit");
5787     }
5788     return;
5789   }
5790   // Double capacity if possible
5791   size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax);
5792   // Do not give up existing stack until we have managed to
5793   // get the double capacity that we desired.
5794   ReservedSpace rs(ReservedSpace::allocation_align_size_up(
5795                    new_capacity * sizeof(oop)));
5796   if (rs.is_reserved()) {
5797     // Release the backing store associated with old stack
5798     _virtual_space.release();
5799     // Reinitialize virtual space for new stack
5800     if (!_virtual_space.initialize(rs, rs.size())) {
5801       fatal("Not enough swap for expanded marking stack");
5802     }
5803     _base = (oop*)(_virtual_space.low());
5804     _index = 0;
5805     _capacity = new_capacity;
5806   } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled) {
5807     // Failed to double capacity, continue;
5808     // we print a detail message only once per CMS cycle.
5809     log_debug(gc)(" (benign) Failed to expand marking stack from " SIZE_FORMAT "K to " SIZE_FORMAT "K",
5810                         _capacity / K, new_capacity / K);
5811   }
5812 }
5813 
5814 
5815 // Closures
5816 // XXX: there seems to be a lot of code  duplication here;
5817 // should refactor and consolidate common code.
5818 
5819 // This closure is used to mark refs into the CMS generation in
5820 // the CMS bit map. Called at the first checkpoint. This closure
5821 // assumes that we do not need to re-mark dirty cards; if the CMS
5822 // generation on which this is used is not an oldest
5823 // generation then this will lose younger_gen cards!
5824 
5825 MarkRefsIntoClosure::MarkRefsIntoClosure(
5826   MemRegion span, CMSBitMap* bitMap):
5827     _span(span),
5828     _bitMap(bitMap)
5829 {
5830   assert(ref_processor() == NULL, "deliberately left NULL");
5831   assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
5832 }
5833 
5834 void MarkRefsIntoClosure::do_oop(oop obj) {
5835   // if p points into _span, then mark corresponding bit in _markBitMap
5836   assert(oopDesc::is_oop(obj), "expected an oop");
5837   HeapWord* addr = (HeapWord*)obj;
5838   if (_span.contains(addr)) {
5839     // this should be made more efficient
5840     _bitMap->mark(addr);
5841   }
5842 }
5843 
5844 void MarkRefsIntoClosure::do_oop(oop* p)       { MarkRefsIntoClosure::do_oop_work(p); }
5845 void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); }
5846 
5847 ParMarkRefsIntoClosure::ParMarkRefsIntoClosure(
5848   MemRegion span, CMSBitMap* bitMap):
5849     _span(span),
5850     _bitMap(bitMap)
5851 {
5852   assert(ref_processor() == NULL, "deliberately left NULL");
5853   assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
5854 }
5855 
5856 void ParMarkRefsIntoClosure::do_oop(oop obj) {
5857   // if p points into _span, then mark corresponding bit in _markBitMap
5858   assert(oopDesc::is_oop(obj), "expected an oop");
5859   HeapWord* addr = (HeapWord*)obj;
5860   if (_span.contains(addr)) {
5861     // this should be made more efficient
5862     _bitMap->par_mark(addr);
5863   }
5864 }
5865 
5866 void ParMarkRefsIntoClosure::do_oop(oop* p)       { ParMarkRefsIntoClosure::do_oop_work(p); }
5867 void ParMarkRefsIntoClosure::do_oop(narrowOop* p) { ParMarkRefsIntoClosure::do_oop_work(p); }
5868 
5869 // A variant of the above, used for CMS marking verification.
5870 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
5871   MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm):
5872     _span(span),
5873     _verification_bm(verification_bm),
5874     _cms_bm(cms_bm)
5875 {
5876   assert(ref_processor() == NULL, "deliberately left NULL");
5877   assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
5878 }
5879 
5880 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
5881   // if p points into _span, then mark corresponding bit in _markBitMap
5882   assert(oopDesc::is_oop(obj), "expected an oop");
5883   HeapWord* addr = (HeapWord*)obj;
5884   if (_span.contains(addr)) {
5885     _verification_bm->mark(addr);
5886     if (!_cms_bm->isMarked(addr)) {
5887       Log(gc, verify) log;
5888       ResourceMark rm;
5889       LogStream ls(log.error());
5890       oop(addr)->print_on(&ls);
5891       log.error(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
5892       fatal("... aborting");
5893     }
5894   }
5895 }
5896 
5897 void MarkRefsIntoVerifyClosure::do_oop(oop* p)       { MarkRefsIntoVerifyClosure::do_oop_work(p); }
5898 void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
5899 
5900 //////////////////////////////////////////////////
5901 // MarkRefsIntoAndScanClosure
5902 //////////////////////////////////////////////////
5903 
5904 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
5905                                                        ReferenceProcessor* rp,
5906                                                        CMSBitMap* bit_map,
5907                                                        CMSBitMap* mod_union_table,
5908                                                        CMSMarkStack*  mark_stack,
5909                                                        CMSCollector* collector,
5910                                                        bool should_yield,
5911                                                        bool concurrent_precleaning):
5912   _collector(collector),
5913   _span(span),
5914   _bit_map(bit_map),
5915   _mark_stack(mark_stack),
5916   _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table,
5917                       mark_stack, concurrent_precleaning),
5918   _yield(should_yield),
5919   _concurrent_precleaning(concurrent_precleaning),
5920   _freelistLock(NULL)
5921 {
5922   // FIXME: Should initialize in base class constructor.
5923   assert(rp != NULL, "ref_processor shouldn't be NULL");
5924   set_ref_processor_internal(rp);
5925 }
5926 
5927 // This closure is used to mark refs into the CMS generation at the
5928 // second (final) checkpoint, and to scan and transitively follow
5929 // the unmarked oops. It is also used during the concurrent precleaning
5930 // phase while scanning objects on dirty cards in the CMS generation.
5931 // The marks are made in the marking bit map and the marking stack is
5932 // used for keeping the (newly) grey objects during the scan.
5933 // The parallel version (Par_...) appears further below.
5934 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
5935   if (obj != NULL) {
5936     assert(oopDesc::is_oop(obj), "expected an oop");
5937     HeapWord* addr = (HeapWord*)obj;
5938     assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
5939     assert(_collector->overflow_list_is_empty(),
5940            "overflow list should be empty");
5941     if (_span.contains(addr) &&
5942         !_bit_map->isMarked(addr)) {
5943       // mark bit map (object is now grey)
5944       _bit_map->mark(addr);
5945       // push on marking stack (stack should be empty), and drain the
5946       // stack by applying this closure to the oops in the oops popped
5947       // from the stack (i.e. blacken the grey objects)
5948       bool res = _mark_stack->push(obj);
5949       assert(res, "Should have space to push on empty stack");
5950       do {
5951         oop new_oop = _mark_stack->pop();
5952         assert(new_oop != NULL && oopDesc::is_oop(new_oop), "Expected an oop");
5953         assert(_bit_map->isMarked((HeapWord*)new_oop),
5954                "only grey objects on this stack");
5955         // iterate over the oops in this oop, marking and pushing
5956         // the ones in CMS heap (i.e. in _span).
5957         new_oop->oop_iterate(&_pushAndMarkClosure);
5958         // check if it's time to yield
5959         do_yield_check();
5960       } while (!_mark_stack->isEmpty() ||
5961                (!_concurrent_precleaning && take_from_overflow_list()));
5962         // if marking stack is empty, and we are not doing this
5963         // during precleaning, then check the overflow list
5964     }
5965     assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
5966     assert(_collector->overflow_list_is_empty(),
5967            "overflow list was drained above");
5968 
5969     assert(_collector->no_preserved_marks(),
5970            "All preserved marks should have been restored above");
5971   }
5972 }
5973 
5974 void MarkRefsIntoAndScanClosure::do_oop(oop* p)       { MarkRefsIntoAndScanClosure::do_oop_work(p); }
5975 void MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
5976 
5977 void MarkRefsIntoAndScanClosure::do_yield_work() {
5978   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5979          "CMS thread should hold CMS token");
5980   assert_lock_strong(_freelistLock);
5981   assert_lock_strong(_bit_map->lock());
5982   // relinquish the free_list_lock and bitMaplock()
5983   _bit_map->lock()->unlock();
5984   _freelistLock->unlock();
5985   ConcurrentMarkSweepThread::desynchronize(true);
5986   _collector->stopTimer();
5987   _collector->incrementYields();
5988 
5989   // See the comment in coordinator_yield()
5990   for (unsigned i = 0;
5991        i < CMSYieldSleepCount &&
5992        ConcurrentMarkSweepThread::should_yield() &&
5993        !CMSCollector::foregroundGCIsActive();
5994        ++i) {
5995     os::sleep(Thread::current(), 1, false);
5996   }
5997 
5998   ConcurrentMarkSweepThread::synchronize(true);
5999   _freelistLock->lock_without_safepoint_check();
6000   _bit_map->lock()->lock_without_safepoint_check();
6001   _collector->startTimer();
6002 }
6003 
6004 ///////////////////////////////////////////////////////////
6005 // ParMarkRefsIntoAndScanClosure: a parallel version of
6006 //                                MarkRefsIntoAndScanClosure
6007 ///////////////////////////////////////////////////////////
6008 ParMarkRefsIntoAndScanClosure::ParMarkRefsIntoAndScanClosure(
6009   CMSCollector* collector, MemRegion span, ReferenceProcessor* rp,
6010   CMSBitMap* bit_map, OopTaskQueue* work_queue):
6011   _span(span),
6012   _bit_map(bit_map),
6013   _work_queue(work_queue),
6014   _low_water_mark(MIN2((work_queue->max_elems()/4),
6015                        ((uint)CMSWorkQueueDrainThreshold * ParallelGCThreads))),
6016   _parPushAndMarkClosure(collector, span, rp, bit_map, work_queue)
6017 {
6018   // FIXME: Should initialize in base class constructor.
6019   assert(rp != NULL, "ref_processor shouldn't be NULL");
6020   set_ref_processor_internal(rp);
6021 }
6022 
6023 // This closure is used to mark refs into the CMS generation at the
6024 // second (final) checkpoint, and to scan and transitively follow
6025 // the unmarked oops. The marks are made in the marking bit map and
6026 // the work_queue is used for keeping the (newly) grey objects during
6027 // the scan phase whence they are also available for stealing by parallel
6028 // threads. Since the marking bit map is shared, updates are
6029 // synchronized (via CAS).
6030 void ParMarkRefsIntoAndScanClosure::do_oop(oop obj) {
6031   if (obj != NULL) {
6032     // Ignore mark word because this could be an already marked oop
6033     // that may be chained at the end of the overflow list.
6034     assert(oopDesc::is_oop(obj, true), "expected an oop");
6035     HeapWord* addr = (HeapWord*)obj;
6036     if (_span.contains(addr) &&
6037         !_bit_map->isMarked(addr)) {
6038       // mark bit map (object will become grey):
6039       // It is possible for several threads to be
6040       // trying to "claim" this object concurrently;
6041       // the unique thread that succeeds in marking the
6042       // object first will do the subsequent push on
6043       // to the work queue (or overflow list).
6044       if (_bit_map->par_mark(addr)) {
6045         // push on work_queue (which may not be empty), and trim the
6046         // queue to an appropriate length by applying this closure to
6047         // the oops in the oops popped from the stack (i.e. blacken the
6048         // grey objects)
6049         bool res = _work_queue->push(obj);
6050         assert(res, "Low water mark should be less than capacity?");
6051         trim_queue(_low_water_mark);
6052       } // Else, another thread claimed the object
6053     }
6054   }
6055 }
6056 
6057 void ParMarkRefsIntoAndScanClosure::do_oop(oop* p)       { ParMarkRefsIntoAndScanClosure::do_oop_work(p); }
6058 void ParMarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { ParMarkRefsIntoAndScanClosure::do_oop_work(p); }
6059 
6060 // This closure is used to rescan the marked objects on the dirty cards
6061 // in the mod union table and the card table proper.
6062 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
6063   oop p, MemRegion mr) {
6064 
6065   size_t size = 0;
6066   HeapWord* addr = (HeapWord*)p;
6067   DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6068   assert(_span.contains(addr), "we are scanning the CMS generation");
6069   // check if it's time to yield
6070   if (do_yield_check()) {
6071     // We yielded for some foreground stop-world work,
6072     // and we have been asked to abort this ongoing preclean cycle.
6073     return 0;
6074   }
6075   if (_bitMap->isMarked(addr)) {
6076     // it's marked; is it potentially uninitialized?
6077     if (p->klass_or_null_acquire() != NULL) {
6078         // an initialized object; ignore mark word in verification below
6079         // since we are running concurrent with mutators
6080         assert(oopDesc::is_oop(p, true), "should be an oop");
6081         if (p->is_objArray()) {
6082           // objArrays are precisely marked; restrict scanning
6083           // to dirty cards only.
6084           size = CompactibleFreeListSpace::adjustObjectSize(
6085                    p->oop_iterate_size(_scanningClosure, mr));
6086         } else {
6087           // A non-array may have been imprecisely marked; we need
6088           // to scan object in its entirety.
6089           size = CompactibleFreeListSpace::adjustObjectSize(
6090                    p->oop_iterate_size(_scanningClosure));
6091         }
6092       #ifdef ASSERT
6093         size_t direct_size =
6094           CompactibleFreeListSpace::adjustObjectSize(p->size());
6095         assert(size == direct_size, "Inconsistency in size");
6096         assert(size >= 3, "Necessary for Printezis marks to work");
6097         HeapWord* start_pbit = addr + 1;
6098         HeapWord* end_pbit = addr + size - 1;
6099         assert(_bitMap->isMarked(start_pbit) == _bitMap->isMarked(end_pbit),
6100                "inconsistent Printezis mark");
6101         // Verify inner mark bits (between Printezis bits) are clear,
6102         // but don't repeat if there are multiple dirty regions for
6103         // the same object, to avoid potential O(N^2) performance.
6104         if (addr != _last_scanned_object) {
6105           _bitMap->verifyNoOneBitsInRange(start_pbit + 1, end_pbit);
6106           _last_scanned_object = addr;
6107         }
6108       #endif // ASSERT
6109     } else {
6110       // An uninitialized object.
6111       assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
6112       HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
6113       size = pointer_delta(nextOneAddr + 1, addr);
6114       assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6115              "alignment problem");
6116       // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
6117       // will dirty the card when the klass pointer is installed in the
6118       // object (signaling the completion of initialization).
6119     }
6120   } else {
6121     // Either a not yet marked object or an uninitialized object
6122     if (p->klass_or_null_acquire() == NULL) {
6123       // An uninitialized object, skip to the next card, since
6124       // we may not be able to read its P-bits yet.
6125       assert(size == 0, "Initial value");
6126     } else {
6127       // An object not (yet) reached by marking: we merely need to
6128       // compute its size so as to go look at the next block.
6129       assert(oopDesc::is_oop(p, true), "should be an oop");
6130       size = CompactibleFreeListSpace::adjustObjectSize(p->size());
6131     }
6132   }
6133   DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6134   return size;
6135 }
6136 
6137 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
6138   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6139          "CMS thread should hold CMS token");
6140   assert_lock_strong(_freelistLock);
6141   assert_lock_strong(_bitMap->lock());
6142   // relinquish the free_list_lock and bitMaplock()
6143   _bitMap->lock()->unlock();
6144   _freelistLock->unlock();
6145   ConcurrentMarkSweepThread::desynchronize(true);
6146   _collector->stopTimer();
6147   _collector->incrementYields();
6148 
6149   // See the comment in coordinator_yield()
6150   for (unsigned i = 0; i < CMSYieldSleepCount &&
6151                    ConcurrentMarkSweepThread::should_yield() &&
6152                    !CMSCollector::foregroundGCIsActive(); ++i) {
6153     os::sleep(Thread::current(), 1, false);
6154   }
6155 
6156   ConcurrentMarkSweepThread::synchronize(true);
6157   _freelistLock->lock_without_safepoint_check();
6158   _bitMap->lock()->lock_without_safepoint_check();
6159   _collector->startTimer();
6160 }
6161 
6162 
6163 //////////////////////////////////////////////////////////////////
6164 // SurvivorSpacePrecleanClosure
6165 //////////////////////////////////////////////////////////////////
6166 // This (single-threaded) closure is used to preclean the oops in
6167 // the survivor spaces.
6168 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
6169 
6170   HeapWord* addr = (HeapWord*)p;
6171   DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6172   assert(!_span.contains(addr), "we are scanning the survivor spaces");
6173   assert(p->klass_or_null() != NULL, "object should be initialized");
6174   // an initialized object; ignore mark word in verification below
6175   // since we are running concurrent with mutators
6176   assert(oopDesc::is_oop(p, true), "should be an oop");
6177   // Note that we do not yield while we iterate over
6178   // the interior oops of p, pushing the relevant ones
6179   // on our marking stack.
6180   size_t size = p->oop_iterate_size(_scanning_closure);
6181   do_yield_check();
6182   // Observe that below, we do not abandon the preclean
6183   // phase as soon as we should; rather we empty the
6184   // marking stack before returning. This is to satisfy
6185   // some existing assertions. In general, it may be a
6186   // good idea to abort immediately and complete the marking
6187   // from the grey objects at a later time.
6188   while (!_mark_stack->isEmpty()) {
6189     oop new_oop = _mark_stack->pop();
6190     assert(new_oop != NULL && oopDesc::is_oop(new_oop), "Expected an oop");
6191     assert(_bit_map->isMarked((HeapWord*)new_oop),
6192            "only grey objects on this stack");
6193     // iterate over the oops in this oop, marking and pushing
6194     // the ones in CMS heap (i.e. in _span).
6195     new_oop->oop_iterate(_scanning_closure);
6196     // check if it's time to yield
6197     do_yield_check();
6198   }
6199   unsigned int after_count =
6200     CMSHeap::heap()->total_collections();
6201   bool abort = (_before_count != after_count) ||
6202                _collector->should_abort_preclean();
6203   return abort ? 0 : size;
6204 }
6205 
6206 void SurvivorSpacePrecleanClosure::do_yield_work() {
6207   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6208          "CMS thread should hold CMS token");
6209   assert_lock_strong(_bit_map->lock());
6210   // Relinquish the bit map lock
6211   _bit_map->lock()->unlock();
6212   ConcurrentMarkSweepThread::desynchronize(true);
6213   _collector->stopTimer();
6214   _collector->incrementYields();
6215 
6216   // See the comment in coordinator_yield()
6217   for (unsigned i = 0; i < CMSYieldSleepCount &&
6218                        ConcurrentMarkSweepThread::should_yield() &&
6219                        !CMSCollector::foregroundGCIsActive(); ++i) {
6220     os::sleep(Thread::current(), 1, false);
6221   }
6222 
6223   ConcurrentMarkSweepThread::synchronize(true);
6224   _bit_map->lock()->lock_without_safepoint_check();
6225   _collector->startTimer();
6226 }
6227 
6228 // This closure is used to rescan the marked objects on the dirty cards
6229 // in the mod union table and the card table proper. In the parallel
6230 // case, although the bitMap is shared, we do a single read so the
6231 // isMarked() query is "safe".
6232 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
6233   // Ignore mark word because we are running concurrent with mutators
6234   assert(oopDesc::is_oop_or_null(p, true), "Expected an oop or NULL at " PTR_FORMAT, p2i(p));
6235   HeapWord* addr = (HeapWord*)p;
6236   assert(_span.contains(addr), "we are scanning the CMS generation");
6237   bool is_obj_array = false;
6238   #ifdef ASSERT
6239     if (!_parallel) {
6240       assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6241       assert(_collector->overflow_list_is_empty(),
6242              "overflow list should be empty");
6243 
6244     }
6245   #endif // ASSERT
6246   if (_bit_map->isMarked(addr)) {
6247     // Obj arrays are precisely marked, non-arrays are not;
6248     // so we scan objArrays precisely and non-arrays in their
6249     // entirety.
6250     if (p->is_objArray()) {
6251       is_obj_array = true;
6252       if (_parallel) {
6253         p->oop_iterate(_par_scan_closure, mr);
6254       } else {
6255         p->oop_iterate(_scan_closure, mr);
6256       }
6257     } else {
6258       if (_parallel) {
6259         p->oop_iterate(_par_scan_closure);
6260       } else {
6261         p->oop_iterate(_scan_closure);
6262       }
6263     }
6264   }
6265   #ifdef ASSERT
6266     if (!_parallel) {
6267       assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6268       assert(_collector->overflow_list_is_empty(),
6269              "overflow list should be empty");
6270 
6271     }
6272   #endif // ASSERT
6273   return is_obj_array;
6274 }
6275 
6276 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
6277                         MemRegion span,
6278                         CMSBitMap* bitMap, CMSMarkStack*  markStack,
6279                         bool should_yield, bool verifying):
6280   _collector(collector),
6281   _span(span),
6282   _bitMap(bitMap),
6283   _mut(&collector->_modUnionTable),
6284   _markStack(markStack),
6285   _yield(should_yield),
6286   _skipBits(0)
6287 {
6288   assert(_markStack->isEmpty(), "stack should be empty");
6289   _finger = _bitMap->startWord();
6290   _threshold = _finger;
6291   assert(_collector->_restart_addr == NULL, "Sanity check");
6292   assert(_span.contains(_finger), "Out of bounds _finger?");
6293   DEBUG_ONLY(_verifying = verifying;)
6294 }
6295 
6296 void MarkFromRootsClosure::reset(HeapWord* addr) {
6297   assert(_markStack->isEmpty(), "would cause duplicates on stack");
6298   assert(_span.contains(addr), "Out of bounds _finger?");
6299   _finger = addr;
6300   _threshold = align_up(_finger, CardTableModRefBS::card_size);
6301 }
6302 
6303 // Should revisit to see if this should be restructured for
6304 // greater efficiency.
6305 bool MarkFromRootsClosure::do_bit(size_t offset) {
6306   if (_skipBits > 0) {
6307     _skipBits--;
6308     return true;
6309   }
6310   // convert offset into a HeapWord*
6311   HeapWord* addr = _bitMap->startWord() + offset;
6312   assert(_bitMap->endWord() && addr < _bitMap->endWord(),
6313          "address out of range");
6314   assert(_bitMap->isMarked(addr), "tautology");
6315   if (_bitMap->isMarked(addr+1)) {
6316     // this is an allocated but not yet initialized object
6317     assert(_skipBits == 0, "tautology");
6318     _skipBits = 2;  // skip next two marked bits ("Printezis-marks")
6319     oop p = oop(addr);
6320     if (p->klass_or_null_acquire() == NULL) {
6321       DEBUG_ONLY(if (!_verifying) {)
6322         // We re-dirty the cards on which this object lies and increase
6323         // the _threshold so that we'll come back to scan this object
6324         // during the preclean or remark phase. (CMSCleanOnEnter)
6325         if (CMSCleanOnEnter) {
6326           size_t sz = _collector->block_size_using_printezis_bits(addr);
6327           HeapWord* end_card_addr = align_up(addr + sz, CardTableModRefBS::card_size);
6328           MemRegion redirty_range = MemRegion(addr, end_card_addr);
6329           assert(!redirty_range.is_empty(), "Arithmetical tautology");
6330           // Bump _threshold to end_card_addr; note that
6331           // _threshold cannot possibly exceed end_card_addr, anyhow.
6332           // This prevents future clearing of the card as the scan proceeds
6333           // to the right.
6334           assert(_threshold <= end_card_addr,
6335                  "Because we are just scanning into this object");
6336           if (_threshold < end_card_addr) {
6337             _threshold = end_card_addr;
6338           }
6339           if (p->klass_or_null_acquire() != NULL) {
6340             // Redirty the range of cards...
6341             _mut->mark_range(redirty_range);
6342           } // ...else the setting of klass will dirty the card anyway.
6343         }
6344       DEBUG_ONLY(})
6345       return true;
6346     }
6347   }
6348   scanOopsInOop(addr);
6349   return true;
6350 }
6351 
6352 // We take a break if we've been at this for a while,
6353 // so as to avoid monopolizing the locks involved.
6354 void MarkFromRootsClosure::do_yield_work() {
6355   // First give up the locks, then yield, then re-lock
6356   // We should probably use a constructor/destructor idiom to
6357   // do this unlock/lock or modify the MutexUnlocker class to
6358   // serve our purpose. XXX
6359   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6360          "CMS thread should hold CMS token");
6361   assert_lock_strong(_bitMap->lock());
6362   _bitMap->lock()->unlock();
6363   ConcurrentMarkSweepThread::desynchronize(true);
6364   _collector->stopTimer();
6365   _collector->incrementYields();
6366 
6367   // See the comment in coordinator_yield()
6368   for (unsigned i = 0; i < CMSYieldSleepCount &&
6369                        ConcurrentMarkSweepThread::should_yield() &&
6370                        !CMSCollector::foregroundGCIsActive(); ++i) {
6371     os::sleep(Thread::current(), 1, false);
6372   }
6373 
6374   ConcurrentMarkSweepThread::synchronize(true);
6375   _bitMap->lock()->lock_without_safepoint_check();
6376   _collector->startTimer();
6377 }
6378 
6379 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
6380   assert(_bitMap->isMarked(ptr), "expected bit to be set");
6381   assert(_markStack->isEmpty(),
6382          "should drain stack to limit stack usage");
6383   // convert ptr to an oop preparatory to scanning
6384   oop obj = oop(ptr);
6385   // Ignore mark word in verification below, since we
6386   // may be running concurrent with mutators.
6387   assert(oopDesc::is_oop(obj, true), "should be an oop");
6388   assert(_finger <= ptr, "_finger runneth ahead");
6389   // advance the finger to right end of this object
6390   _finger = ptr + obj->size();
6391   assert(_finger > ptr, "we just incremented it above");
6392   // On large heaps, it may take us some time to get through
6393   // the marking phase. During
6394   // this time it's possible that a lot of mutations have
6395   // accumulated in the card table and the mod union table --
6396   // these mutation records are redundant until we have
6397   // actually traced into the corresponding card.
6398   // Here, we check whether advancing the finger would make
6399   // us cross into a new card, and if so clear corresponding
6400   // cards in the MUT (preclean them in the card-table in the
6401   // future).
6402 
6403   DEBUG_ONLY(if (!_verifying) {)
6404     // The clean-on-enter optimization is disabled by default,
6405     // until we fix 6178663.
6406     if (CMSCleanOnEnter && (_finger > _threshold)) {
6407       // [_threshold, _finger) represents the interval
6408       // of cards to be cleared  in MUT (or precleaned in card table).
6409       // The set of cards to be cleared is all those that overlap
6410       // with the interval [_threshold, _finger); note that
6411       // _threshold is always kept card-aligned but _finger isn't
6412       // always card-aligned.
6413       HeapWord* old_threshold = _threshold;
6414       assert(is_aligned(old_threshold, CardTableModRefBS::card_size),
6415              "_threshold should always be card-aligned");
6416       _threshold = align_up(_finger, CardTableModRefBS::card_size);
6417       MemRegion mr(old_threshold, _threshold);
6418       assert(!mr.is_empty(), "Control point invariant");
6419       assert(_span.contains(mr), "Should clear within span");
6420       _mut->clear_range(mr);
6421     }
6422   DEBUG_ONLY(})
6423   // Note: the finger doesn't advance while we drain
6424   // the stack below.
6425   PushOrMarkClosure pushOrMarkClosure(_collector,
6426                                       _span, _bitMap, _markStack,
6427                                       _finger, this);
6428   bool res = _markStack->push(obj);
6429   assert(res, "Empty non-zero size stack should have space for single push");
6430   while (!_markStack->isEmpty()) {
6431     oop new_oop = _markStack->pop();
6432     // Skip verifying header mark word below because we are
6433     // running concurrent with mutators.
6434     assert(oopDesc::is_oop(new_oop, true), "Oops! expected to pop an oop");
6435     // now scan this oop's oops
6436     new_oop->oop_iterate(&pushOrMarkClosure);
6437     do_yield_check();
6438   }
6439   assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
6440 }
6441 
6442 ParMarkFromRootsClosure::ParMarkFromRootsClosure(CMSConcMarkingTask* task,
6443                        CMSCollector* collector, MemRegion span,
6444                        CMSBitMap* bit_map,
6445                        OopTaskQueue* work_queue,
6446                        CMSMarkStack*  overflow_stack):
6447   _collector(collector),
6448   _whole_span(collector->_span),
6449   _span(span),
6450   _bit_map(bit_map),
6451   _mut(&collector->_modUnionTable),
6452   _work_queue(work_queue),
6453   _overflow_stack(overflow_stack),
6454   _skip_bits(0),
6455   _task(task)
6456 {
6457   assert(_work_queue->size() == 0, "work_queue should be empty");
6458   _finger = span.start();
6459   _threshold = _finger;     // XXX Defer clear-on-enter optimization for now
6460   assert(_span.contains(_finger), "Out of bounds _finger?");
6461 }
6462 
6463 // Should revisit to see if this should be restructured for
6464 // greater efficiency.
6465 bool ParMarkFromRootsClosure::do_bit(size_t offset) {
6466   if (_skip_bits > 0) {
6467     _skip_bits--;
6468     return true;
6469   }
6470   // convert offset into a HeapWord*
6471   HeapWord* addr = _bit_map->startWord() + offset;
6472   assert(_bit_map->endWord() && addr < _bit_map->endWord(),
6473          "address out of range");
6474   assert(_bit_map->isMarked(addr), "tautology");
6475   if (_bit_map->isMarked(addr+1)) {
6476     // this is an allocated object that might not yet be initialized
6477     assert(_skip_bits == 0, "tautology");
6478     _skip_bits = 2;  // skip next two marked bits ("Printezis-marks")
6479     oop p = oop(addr);
6480     if (p->klass_or_null_acquire() == NULL) {
6481       // in the case of Clean-on-Enter optimization, redirty card
6482       // and avoid clearing card by increasing  the threshold.
6483       return true;
6484     }
6485   }
6486   scan_oops_in_oop(addr);
6487   return true;
6488 }
6489 
6490 void ParMarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
6491   assert(_bit_map->isMarked(ptr), "expected bit to be set");
6492   // Should we assert that our work queue is empty or
6493   // below some drain limit?
6494   assert(_work_queue->size() == 0,
6495          "should drain stack to limit stack usage");
6496   // convert ptr to an oop preparatory to scanning
6497   oop obj = oop(ptr);
6498   // Ignore mark word in verification below, since we
6499   // may be running concurrent with mutators.
6500   assert(oopDesc::is_oop(obj, true), "should be an oop");
6501   assert(_finger <= ptr, "_finger runneth ahead");
6502   // advance the finger to right end of this object
6503   _finger = ptr + obj->size();
6504   assert(_finger > ptr, "we just incremented it above");
6505   // On large heaps, it may take us some time to get through
6506   // the marking phase. During
6507   // this time it's possible that a lot of mutations have
6508   // accumulated in the card table and the mod union table --
6509   // these mutation records are redundant until we have
6510   // actually traced into the corresponding card.
6511   // Here, we check whether advancing the finger would make
6512   // us cross into a new card, and if so clear corresponding
6513   // cards in the MUT (preclean them in the card-table in the
6514   // future).
6515 
6516   // The clean-on-enter optimization is disabled by default,
6517   // until we fix 6178663.
6518   if (CMSCleanOnEnter && (_finger > _threshold)) {
6519     // [_threshold, _finger) represents the interval
6520     // of cards to be cleared  in MUT (or precleaned in card table).
6521     // The set of cards to be cleared is all those that overlap
6522     // with the interval [_threshold, _finger); note that
6523     // _threshold is always kept card-aligned but _finger isn't
6524     // always card-aligned.
6525     HeapWord* old_threshold = _threshold;
6526     assert(is_aligned(old_threshold, CardTableModRefBS::card_size),
6527            "_threshold should always be card-aligned");
6528     _threshold = align_up(_finger, CardTableModRefBS::card_size);
6529     MemRegion mr(old_threshold, _threshold);
6530     assert(!mr.is_empty(), "Control point invariant");
6531     assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
6532     _mut->clear_range(mr);
6533   }
6534 
6535   // Note: the local finger doesn't advance while we drain
6536   // the stack below, but the global finger sure can and will.
6537   HeapWord* volatile* gfa = _task->global_finger_addr();
6538   ParPushOrMarkClosure pushOrMarkClosure(_collector,
6539                                          _span, _bit_map,
6540                                          _work_queue,
6541                                          _overflow_stack,
6542                                          _finger,
6543                                          gfa, this);
6544   bool res = _work_queue->push(obj);   // overflow could occur here
6545   assert(res, "Will hold once we use workqueues");
6546   while (true) {
6547     oop new_oop;
6548     if (!_work_queue->pop_local(new_oop)) {
6549       // We emptied our work_queue; check if there's stuff that can
6550       // be gotten from the overflow stack.
6551       if (CMSConcMarkingTask::get_work_from_overflow_stack(
6552             _overflow_stack, _work_queue)) {
6553         do_yield_check();
6554         continue;
6555       } else {  // done
6556         break;
6557       }
6558     }
6559     // Skip verifying header mark word below because we are
6560     // running concurrent with mutators.
6561     assert(oopDesc::is_oop(new_oop, true), "Oops! expected to pop an oop");
6562     // now scan this oop's oops
6563     new_oop->oop_iterate(&pushOrMarkClosure);
6564     do_yield_check();
6565   }
6566   assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
6567 }
6568 
6569 // Yield in response to a request from VM Thread or
6570 // from mutators.
6571 void ParMarkFromRootsClosure::do_yield_work() {
6572   assert(_task != NULL, "sanity");
6573   _task->yield();
6574 }
6575 
6576 // A variant of the above used for verifying CMS marking work.
6577 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
6578                         MemRegion span,
6579                         CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6580                         CMSMarkStack*  mark_stack):
6581   _collector(collector),
6582   _span(span),
6583   _verification_bm(verification_bm),
6584   _cms_bm(cms_bm),
6585   _mark_stack(mark_stack),
6586   _pam_verify_closure(collector, span, verification_bm, cms_bm,
6587                       mark_stack)
6588 {
6589   assert(_mark_stack->isEmpty(), "stack should be empty");
6590   _finger = _verification_bm->startWord();
6591   assert(_collector->_restart_addr == NULL, "Sanity check");
6592   assert(_span.contains(_finger), "Out of bounds _finger?");
6593 }
6594 
6595 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
6596   assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
6597   assert(_span.contains(addr), "Out of bounds _finger?");
6598   _finger = addr;
6599 }
6600 
6601 // Should revisit to see if this should be restructured for
6602 // greater efficiency.
6603 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
6604   // convert offset into a HeapWord*
6605   HeapWord* addr = _verification_bm->startWord() + offset;
6606   assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
6607          "address out of range");
6608   assert(_verification_bm->isMarked(addr), "tautology");
6609   assert(_cms_bm->isMarked(addr), "tautology");
6610 
6611   assert(_mark_stack->isEmpty(),
6612          "should drain stack to limit stack usage");
6613   // convert addr to an oop preparatory to scanning
6614   oop obj = oop(addr);
6615   assert(oopDesc::is_oop(obj), "should be an oop");
6616   assert(_finger <= addr, "_finger runneth ahead");
6617   // advance the finger to right end of this object
6618   _finger = addr + obj->size();
6619   assert(_finger > addr, "we just incremented it above");
6620   // Note: the finger doesn't advance while we drain
6621   // the stack below.
6622   bool res = _mark_stack->push(obj);
6623   assert(res, "Empty non-zero size stack should have space for single push");
6624   while (!_mark_stack->isEmpty()) {
6625     oop new_oop = _mark_stack->pop();
6626     assert(oopDesc::is_oop(new_oop), "Oops! expected to pop an oop");
6627     // now scan this oop's oops
6628     new_oop->oop_iterate(&_pam_verify_closure);
6629   }
6630   assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
6631   return true;
6632 }
6633 
6634 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
6635   CMSCollector* collector, MemRegion span,
6636   CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6637   CMSMarkStack*  mark_stack):
6638   MetadataAwareOopClosure(collector->ref_processor()),
6639   _collector(collector),
6640   _span(span),
6641   _verification_bm(verification_bm),
6642   _cms_bm(cms_bm),
6643   _mark_stack(mark_stack)
6644 { }
6645 
6646 void PushAndMarkVerifyClosure::do_oop(oop* p)       { PushAndMarkVerifyClosure::do_oop_work(p); }
6647 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
6648 
6649 // Upon stack overflow, we discard (part of) the stack,
6650 // remembering the least address amongst those discarded
6651 // in CMSCollector's _restart_address.
6652 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
6653   // Remember the least grey address discarded
6654   HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
6655   _collector->lower_restart_addr(ra);
6656   _mark_stack->reset();  // discard stack contents
6657   _mark_stack->expand(); // expand the stack if possible
6658 }
6659 
6660 void PushAndMarkVerifyClosure::do_oop(oop obj) {
6661   assert(oopDesc::is_oop_or_null(obj), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6662   HeapWord* addr = (HeapWord*)obj;
6663   if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
6664     // Oop lies in _span and isn't yet grey or black
6665     _verification_bm->mark(addr);            // now grey
6666     if (!_cms_bm->isMarked(addr)) {
6667       Log(gc, verify) log;
6668       ResourceMark rm;
6669       LogStream ls(log.error());
6670       oop(addr)->print_on(&ls);
6671       log.error(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
6672       fatal("... aborting");
6673     }
6674 
6675     if (!_mark_stack->push(obj)) { // stack overflow
6676       log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _mark_stack->capacity());
6677       assert(_mark_stack->isFull(), "Else push should have succeeded");
6678       handle_stack_overflow(addr);
6679     }
6680     // anything including and to the right of _finger
6681     // will be scanned as we iterate over the remainder of the
6682     // bit map
6683   }
6684 }
6685 
6686 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
6687                      MemRegion span,
6688                      CMSBitMap* bitMap, CMSMarkStack*  markStack,
6689                      HeapWord* finger, MarkFromRootsClosure* parent) :
6690   MetadataAwareOopClosure(collector->ref_processor()),
6691   _collector(collector),
6692   _span(span),
6693   _bitMap(bitMap),
6694   _markStack(markStack),
6695   _finger(finger),
6696   _parent(parent)
6697 { }
6698 
6699 ParPushOrMarkClosure::ParPushOrMarkClosure(CMSCollector* collector,
6700                                            MemRegion span,
6701                                            CMSBitMap* bit_map,
6702                                            OopTaskQueue* work_queue,
6703                                            CMSMarkStack*  overflow_stack,
6704                                            HeapWord* finger,
6705                                            HeapWord* volatile* global_finger_addr,
6706                                            ParMarkFromRootsClosure* parent) :
6707   MetadataAwareOopClosure(collector->ref_processor()),
6708   _collector(collector),
6709   _whole_span(collector->_span),
6710   _span(span),
6711   _bit_map(bit_map),
6712   _work_queue(work_queue),
6713   _overflow_stack(overflow_stack),
6714   _finger(finger),
6715   _global_finger_addr(global_finger_addr),
6716   _parent(parent)
6717 { }
6718 
6719 // Assumes thread-safe access by callers, who are
6720 // responsible for mutual exclusion.
6721 void CMSCollector::lower_restart_addr(HeapWord* low) {
6722   assert(_span.contains(low), "Out of bounds addr");
6723   if (_restart_addr == NULL) {
6724     _restart_addr = low;
6725   } else {
6726     _restart_addr = MIN2(_restart_addr, low);
6727   }
6728 }
6729 
6730 // Upon stack overflow, we discard (part of) the stack,
6731 // remembering the least address amongst those discarded
6732 // in CMSCollector's _restart_address.
6733 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
6734   // Remember the least grey address discarded
6735   HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
6736   _collector->lower_restart_addr(ra);
6737   _markStack->reset();  // discard stack contents
6738   _markStack->expand(); // expand the stack if possible
6739 }
6740 
6741 // Upon stack overflow, we discard (part of) the stack,
6742 // remembering the least address amongst those discarded
6743 // in CMSCollector's _restart_address.
6744 void ParPushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
6745   // We need to do this under a mutex to prevent other
6746   // workers from interfering with the work done below.
6747   MutexLockerEx ml(_overflow_stack->par_lock(),
6748                    Mutex::_no_safepoint_check_flag);
6749   // Remember the least grey address discarded
6750   HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
6751   _collector->lower_restart_addr(ra);
6752   _overflow_stack->reset();  // discard stack contents
6753   _overflow_stack->expand(); // expand the stack if possible
6754 }
6755 
6756 void PushOrMarkClosure::do_oop(oop obj) {
6757   // Ignore mark word because we are running concurrent with mutators.
6758   assert(oopDesc::is_oop_or_null(obj, true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6759   HeapWord* addr = (HeapWord*)obj;
6760   if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
6761     // Oop lies in _span and isn't yet grey or black
6762     _bitMap->mark(addr);            // now grey
6763     if (addr < _finger) {
6764       // the bit map iteration has already either passed, or
6765       // sampled, this bit in the bit map; we'll need to
6766       // use the marking stack to scan this oop's oops.
6767       bool simulate_overflow = false;
6768       NOT_PRODUCT(
6769         if (CMSMarkStackOverflowALot &&
6770             _collector->simulate_overflow()) {
6771           // simulate a stack overflow
6772           simulate_overflow = true;
6773         }
6774       )
6775       if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
6776         log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _markStack->capacity());
6777         assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
6778         handle_stack_overflow(addr);
6779       }
6780     }
6781     // anything including and to the right of _finger
6782     // will be scanned as we iterate over the remainder of the
6783     // bit map
6784     do_yield_check();
6785   }
6786 }
6787 
6788 void PushOrMarkClosure::do_oop(oop* p)       { PushOrMarkClosure::do_oop_work(p); }
6789 void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); }
6790 
6791 void ParPushOrMarkClosure::do_oop(oop obj) {
6792   // Ignore mark word because we are running concurrent with mutators.
6793   assert(oopDesc::is_oop_or_null(obj, true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6794   HeapWord* addr = (HeapWord*)obj;
6795   if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
6796     // Oop lies in _span and isn't yet grey or black
6797     // We read the global_finger (volatile read) strictly after marking oop
6798     bool res = _bit_map->par_mark(addr);    // now grey
6799     volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
6800     // Should we push this marked oop on our stack?
6801     // -- if someone else marked it, nothing to do
6802     // -- if target oop is above global finger nothing to do
6803     // -- if target oop is in chunk and above local finger
6804     //      then nothing to do
6805     // -- else push on work queue
6806     if (   !res       // someone else marked it, they will deal with it
6807         || (addr >= *gfa)  // will be scanned in a later task
6808         || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
6809       return;
6810     }
6811     // the bit map iteration has already either passed, or
6812     // sampled, this bit in the bit map; we'll need to
6813     // use the marking stack to scan this oop's oops.
6814     bool simulate_overflow = false;
6815     NOT_PRODUCT(
6816       if (CMSMarkStackOverflowALot &&
6817           _collector->simulate_overflow()) {
6818         // simulate a stack overflow
6819         simulate_overflow = true;
6820       }
6821     )
6822     if (simulate_overflow ||
6823         !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
6824       // stack overflow
6825       log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _overflow_stack->capacity());
6826       // We cannot assert that the overflow stack is full because
6827       // it may have been emptied since.
6828       assert(simulate_overflow ||
6829              _work_queue->size() == _work_queue->max_elems(),
6830             "Else push should have succeeded");
6831       handle_stack_overflow(addr);
6832     }
6833     do_yield_check();
6834   }
6835 }
6836 
6837 void ParPushOrMarkClosure::do_oop(oop* p)       { ParPushOrMarkClosure::do_oop_work(p); }
6838 void ParPushOrMarkClosure::do_oop(narrowOop* p) { ParPushOrMarkClosure::do_oop_work(p); }
6839 
6840 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
6841                                        MemRegion span,
6842                                        ReferenceProcessor* rp,
6843                                        CMSBitMap* bit_map,
6844                                        CMSBitMap* mod_union_table,
6845                                        CMSMarkStack*  mark_stack,
6846                                        bool           concurrent_precleaning):
6847   MetadataAwareOopClosure(rp),
6848   _collector(collector),
6849   _span(span),
6850   _bit_map(bit_map),
6851   _mod_union_table(mod_union_table),
6852   _mark_stack(mark_stack),
6853   _concurrent_precleaning(concurrent_precleaning)
6854 {
6855   assert(ref_processor() != NULL, "ref_processor shouldn't be NULL");
6856 }
6857 
6858 // Grey object rescan during pre-cleaning and second checkpoint phases --
6859 // the non-parallel version (the parallel version appears further below.)
6860 void PushAndMarkClosure::do_oop(oop obj) {
6861   // Ignore mark word verification. If during concurrent precleaning,
6862   // the object monitor may be locked. If during the checkpoint
6863   // phases, the object may already have been reached by a  different
6864   // path and may be at the end of the global overflow list (so
6865   // the mark word may be NULL).
6866   assert(oopDesc::is_oop_or_null(obj, true /* ignore mark word */),
6867          "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6868   HeapWord* addr = (HeapWord*)obj;
6869   // Check if oop points into the CMS generation
6870   // and is not marked
6871   if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
6872     // a white object ...
6873     _bit_map->mark(addr);         // ... now grey
6874     // push on the marking stack (grey set)
6875     bool simulate_overflow = false;
6876     NOT_PRODUCT(
6877       if (CMSMarkStackOverflowALot &&
6878           _collector->simulate_overflow()) {
6879         // simulate a stack overflow
6880         simulate_overflow = true;
6881       }
6882     )
6883     if (simulate_overflow || !_mark_stack->push(obj)) {
6884       if (_concurrent_precleaning) {
6885          // During precleaning we can just dirty the appropriate card(s)
6886          // in the mod union table, thus ensuring that the object remains
6887          // in the grey set  and continue. In the case of object arrays
6888          // we need to dirty all of the cards that the object spans,
6889          // since the rescan of object arrays will be limited to the
6890          // dirty cards.
6891          // Note that no one can be interfering with us in this action
6892          // of dirtying the mod union table, so no locking or atomics
6893          // are required.
6894          if (obj->is_objArray()) {
6895            size_t sz = obj->size();
6896            HeapWord* end_card_addr = align_up(addr + sz, CardTableModRefBS::card_size);
6897            MemRegion redirty_range = MemRegion(addr, end_card_addr);
6898            assert(!redirty_range.is_empty(), "Arithmetical tautology");
6899            _mod_union_table->mark_range(redirty_range);
6900          } else {
6901            _mod_union_table->mark(addr);
6902          }
6903          _collector->_ser_pmc_preclean_ovflw++;
6904       } else {
6905          // During the remark phase, we need to remember this oop
6906          // in the overflow list.
6907          _collector->push_on_overflow_list(obj);
6908          _collector->_ser_pmc_remark_ovflw++;
6909       }
6910     }
6911   }
6912 }
6913 
6914 ParPushAndMarkClosure::ParPushAndMarkClosure(CMSCollector* collector,
6915                                              MemRegion span,
6916                                              ReferenceProcessor* rp,
6917                                              CMSBitMap* bit_map,
6918                                              OopTaskQueue* work_queue):
6919   MetadataAwareOopClosure(rp),
6920   _collector(collector),
6921   _span(span),
6922   _bit_map(bit_map),
6923   _work_queue(work_queue)
6924 {
6925   assert(ref_processor() != NULL, "ref_processor shouldn't be NULL");
6926 }
6927 
6928 void PushAndMarkClosure::do_oop(oop* p)       { PushAndMarkClosure::do_oop_work(p); }
6929 void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); }
6930 
6931 // Grey object rescan during second checkpoint phase --
6932 // the parallel version.
6933 void ParPushAndMarkClosure::do_oop(oop obj) {
6934   // In the assert below, we ignore the mark word because
6935   // this oop may point to an already visited object that is
6936   // on the overflow stack (in which case the mark word has
6937   // been hijacked for chaining into the overflow stack --
6938   // if this is the last object in the overflow stack then
6939   // its mark word will be NULL). Because this object may
6940   // have been subsequently popped off the global overflow
6941   // stack, and the mark word possibly restored to the prototypical
6942   // value, by the time we get to examined this failing assert in
6943   // the debugger, is_oop_or_null(false) may subsequently start
6944   // to hold.
6945   assert(oopDesc::is_oop_or_null(obj, true),
6946          "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6947   HeapWord* addr = (HeapWord*)obj;
6948   // Check if oop points into the CMS generation
6949   // and is not marked
6950   if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
6951     // a white object ...
6952     // If we manage to "claim" the object, by being the
6953     // first thread to mark it, then we push it on our
6954     // marking stack
6955     if (_bit_map->par_mark(addr)) {     // ... now grey
6956       // push on work queue (grey set)
6957       bool simulate_overflow = false;
6958       NOT_PRODUCT(
6959         if (CMSMarkStackOverflowALot &&
6960             _collector->par_simulate_overflow()) {
6961           // simulate a stack overflow
6962           simulate_overflow = true;
6963         }
6964       )
6965       if (simulate_overflow || !_work_queue->push(obj)) {
6966         _collector->par_push_on_overflow_list(obj);
6967         _collector->_par_pmc_remark_ovflw++; //  imprecise OK: no need to CAS
6968       }
6969     } // Else, some other thread got there first
6970   }
6971 }
6972 
6973 void ParPushAndMarkClosure::do_oop(oop* p)       { ParPushAndMarkClosure::do_oop_work(p); }
6974 void ParPushAndMarkClosure::do_oop(narrowOop* p) { ParPushAndMarkClosure::do_oop_work(p); }
6975 
6976 void CMSPrecleanRefsYieldClosure::do_yield_work() {
6977   Mutex* bml = _collector->bitMapLock();
6978   assert_lock_strong(bml);
6979   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6980          "CMS thread should hold CMS token");
6981 
6982   bml->unlock();
6983   ConcurrentMarkSweepThread::desynchronize(true);
6984 
6985   _collector->stopTimer();
6986   _collector->incrementYields();
6987 
6988   // See the comment in coordinator_yield()
6989   for (unsigned i = 0; i < CMSYieldSleepCount &&
6990                        ConcurrentMarkSweepThread::should_yield() &&
6991                        !CMSCollector::foregroundGCIsActive(); ++i) {
6992     os::sleep(Thread::current(), 1, false);
6993   }
6994 
6995   ConcurrentMarkSweepThread::synchronize(true);
6996   bml->lock();
6997 
6998   _collector->startTimer();
6999 }
7000 
7001 bool CMSPrecleanRefsYieldClosure::should_return() {
7002   if (ConcurrentMarkSweepThread::should_yield()) {
7003     do_yield_work();
7004   }
7005   return _collector->foregroundGCIsActive();
7006 }
7007 
7008 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
7009   assert(((size_t)mr.start())%CardTableModRefBS::card_size_in_words == 0,
7010          "mr should be aligned to start at a card boundary");
7011   // We'd like to assert:
7012   // assert(mr.word_size()%CardTableModRefBS::card_size_in_words == 0,
7013   //        "mr should be a range of cards");
7014   // However, that would be too strong in one case -- the last
7015   // partition ends at _unallocated_block which, in general, can be
7016   // an arbitrary boundary, not necessarily card aligned.
7017   _num_dirty_cards += mr.word_size()/CardTableModRefBS::card_size_in_words;
7018   _space->object_iterate_mem(mr, &_scan_cl);
7019 }
7020 
7021 SweepClosure::SweepClosure(CMSCollector* collector,
7022                            ConcurrentMarkSweepGeneration* g,
7023                            CMSBitMap* bitMap, bool should_yield) :
7024   _collector(collector),
7025   _g(g),
7026   _sp(g->cmsSpace()),
7027   _limit(_sp->sweep_limit()),
7028   _freelistLock(_sp->freelistLock()),
7029   _bitMap(bitMap),
7030   _yield(should_yield),
7031   _inFreeRange(false),           // No free range at beginning of sweep
7032   _freeRangeInFreeLists(false),  // No free range at beginning of sweep
7033   _lastFreeRangeCoalesced(false),
7034   _freeFinger(g->used_region().start())
7035 {
7036   NOT_PRODUCT(
7037     _numObjectsFreed = 0;
7038     _numWordsFreed   = 0;
7039     _numObjectsLive = 0;
7040     _numWordsLive = 0;
7041     _numObjectsAlreadyFree = 0;
7042     _numWordsAlreadyFree = 0;
7043     _last_fc = NULL;
7044 
7045     _sp->initializeIndexedFreeListArrayReturnedBytes();
7046     _sp->dictionary()->initialize_dict_returned_bytes();
7047   )
7048   assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7049          "sweep _limit out of bounds");
7050   log_develop_trace(gc, sweep)("====================");
7051   log_develop_trace(gc, sweep)("Starting new sweep with limit " PTR_FORMAT, p2i(_limit));
7052 }
7053 
7054 void SweepClosure::print_on(outputStream* st) const {
7055   st->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")",
7056                p2i(_sp->bottom()), p2i(_sp->end()));
7057   st->print_cr("_limit = " PTR_FORMAT, p2i(_limit));
7058   st->print_cr("_freeFinger = " PTR_FORMAT, p2i(_freeFinger));
7059   NOT_PRODUCT(st->print_cr("_last_fc = " PTR_FORMAT, p2i(_last_fc));)
7060   st->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d",
7061                _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced);
7062 }
7063 
7064 #ifndef PRODUCT
7065 // Assertion checking only:  no useful work in product mode --
7066 // however, if any of the flags below become product flags,
7067 // you may need to review this code to see if it needs to be
7068 // enabled in product mode.
7069 SweepClosure::~SweepClosure() {
7070   assert_lock_strong(_freelistLock);
7071   assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7072          "sweep _limit out of bounds");
7073   if (inFreeRange()) {
7074     Log(gc, sweep) log;
7075     log.error("inFreeRange() should have been reset; dumping state of SweepClosure");
7076     ResourceMark rm;
7077     LogStream ls(log.error());
7078     print_on(&ls);
7079     ShouldNotReachHere();
7080   }
7081 
7082   if (log_is_enabled(Debug, gc, sweep)) {
7083     log_debug(gc, sweep)("Collected " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
7084                          _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
7085     log_debug(gc, sweep)("Live " SIZE_FORMAT " objects,  " SIZE_FORMAT " bytes  Already free " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
7086                          _numObjectsLive, _numWordsLive*sizeof(HeapWord), _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
7087     size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree) * sizeof(HeapWord);
7088     log_debug(gc, sweep)("Total sweep: " SIZE_FORMAT " bytes", totalBytes);
7089   }
7090 
7091   if (log_is_enabled(Trace, gc, sweep) && CMSVerifyReturnedBytes) {
7092     size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
7093     size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes();
7094     size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes;
7095     log_trace(gc, sweep)("Returned " SIZE_FORMAT " bytes   Indexed List Returned " SIZE_FORMAT " bytes        Dictionary Returned " SIZE_FORMAT " bytes",
7096                          returned_bytes, indexListReturnedBytes, dict_returned_bytes);
7097   }
7098   log_develop_trace(gc, sweep)("end of sweep with _limit = " PTR_FORMAT, p2i(_limit));
7099   log_develop_trace(gc, sweep)("================");
7100 }
7101 #endif  // PRODUCT
7102 
7103 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
7104     bool freeRangeInFreeLists) {
7105   log_develop_trace(gc, sweep)("---- Start free range at " PTR_FORMAT " with free block (%d)",
7106                                p2i(freeFinger), freeRangeInFreeLists);
7107   assert(!inFreeRange(), "Trampling existing free range");
7108   set_inFreeRange(true);
7109   set_lastFreeRangeCoalesced(false);
7110 
7111   set_freeFinger(freeFinger);
7112   set_freeRangeInFreeLists(freeRangeInFreeLists);
7113   if (CMSTestInFreeList) {
7114     if (freeRangeInFreeLists) {
7115       FreeChunk* fc = (FreeChunk*) freeFinger;
7116       assert(fc->is_free(), "A chunk on the free list should be free.");
7117       assert(fc->size() > 0, "Free range should have a size");
7118       assert(_sp->verify_chunk_in_free_list(fc), "Chunk is not in free lists");
7119     }
7120   }
7121 }
7122 
7123 // Note that the sweeper runs concurrently with mutators. Thus,
7124 // it is possible for direct allocation in this generation to happen
7125 // in the middle of the sweep. Note that the sweeper also coalesces
7126 // contiguous free blocks. Thus, unless the sweeper and the allocator
7127 // synchronize appropriately freshly allocated blocks may get swept up.
7128 // This is accomplished by the sweeper locking the free lists while
7129 // it is sweeping. Thus blocks that are determined to be free are
7130 // indeed free. There is however one additional complication:
7131 // blocks that have been allocated since the final checkpoint and
7132 // mark, will not have been marked and so would be treated as
7133 // unreachable and swept up. To prevent this, the allocator marks
7134 // the bit map when allocating during the sweep phase. This leads,
7135 // however, to a further complication -- objects may have been allocated
7136 // but not yet initialized -- in the sense that the header isn't yet
7137 // installed. The sweeper can not then determine the size of the block
7138 // in order to skip over it. To deal with this case, we use a technique
7139 // (due to Printezis) to encode such uninitialized block sizes in the
7140 // bit map. Since the bit map uses a bit per every HeapWord, but the
7141 // CMS generation has a minimum object size of 3 HeapWords, it follows
7142 // that "normal marks" won't be adjacent in the bit map (there will
7143 // always be at least two 0 bits between successive 1 bits). We make use
7144 // of these "unused" bits to represent uninitialized blocks -- the bit
7145 // corresponding to the start of the uninitialized object and the next
7146 // bit are both set. Finally, a 1 bit marks the end of the object that
7147 // started with the two consecutive 1 bits to indicate its potentially
7148 // uninitialized state.
7149 
7150 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
7151   FreeChunk* fc = (FreeChunk*)addr;
7152   size_t res;
7153 
7154   // Check if we are done sweeping. Below we check "addr >= _limit" rather
7155   // than "addr == _limit" because although _limit was a block boundary when
7156   // we started the sweep, it may no longer be one because heap expansion
7157   // may have caused us to coalesce the block ending at the address _limit
7158   // with a newly expanded chunk (this happens when _limit was set to the
7159   // previous _end of the space), so we may have stepped past _limit:
7160   // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740.
7161   if (addr >= _limit) { // we have swept up to or past the limit: finish up
7162     assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7163            "sweep _limit out of bounds");
7164     assert(addr < _sp->end(), "addr out of bounds");
7165     // Flush any free range we might be holding as a single
7166     // coalesced chunk to the appropriate free list.
7167     if (inFreeRange()) {
7168       assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit,
7169              "freeFinger() " PTR_FORMAT " is out-of-bounds", p2i(freeFinger()));
7170       flush_cur_free_chunk(freeFinger(),
7171                            pointer_delta(addr, freeFinger()));
7172       log_develop_trace(gc, sweep)("Sweep: last chunk: put_free_blk " PTR_FORMAT " (" SIZE_FORMAT ") [coalesced:%d]",
7173                                    p2i(freeFinger()), pointer_delta(addr, freeFinger()),
7174                                    lastFreeRangeCoalesced() ? 1 : 0);
7175     }
7176 
7177     // help the iterator loop finish
7178     return pointer_delta(_sp->end(), addr);
7179   }
7180 
7181   assert(addr < _limit, "sweep invariant");
7182   // check if we should yield
7183   do_yield_check(addr);
7184   if (fc->is_free()) {
7185     // Chunk that is already free
7186     res = fc->size();
7187     do_already_free_chunk(fc);
7188     debug_only(_sp->verifyFreeLists());
7189     // If we flush the chunk at hand in lookahead_and_flush()
7190     // and it's coalesced with a preceding chunk, then the
7191     // process of "mangling" the payload of the coalesced block
7192     // will cause erasure of the size information from the
7193     // (erstwhile) header of all the coalesced blocks but the
7194     // first, so the first disjunct in the assert will not hold
7195     // in that specific case (in which case the second disjunct
7196     // will hold).
7197     assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit,
7198            "Otherwise the size info doesn't change at this step");
7199     NOT_PRODUCT(
7200       _numObjectsAlreadyFree++;
7201       _numWordsAlreadyFree += res;
7202     )
7203     NOT_PRODUCT(_last_fc = fc;)
7204   } else if (!_bitMap->isMarked(addr)) {
7205     // Chunk is fresh garbage
7206     res = do_garbage_chunk(fc);
7207     debug_only(_sp->verifyFreeLists());
7208     NOT_PRODUCT(
7209       _numObjectsFreed++;
7210       _numWordsFreed += res;
7211     )
7212   } else {
7213     // Chunk that is alive.
7214     res = do_live_chunk(fc);
7215     debug_only(_sp->verifyFreeLists());
7216     NOT_PRODUCT(
7217         _numObjectsLive++;
7218         _numWordsLive += res;
7219     )
7220   }
7221   return res;
7222 }
7223 
7224 // For the smart allocation, record following
7225 //  split deaths - a free chunk is removed from its free list because
7226 //      it is being split into two or more chunks.
7227 //  split birth - a free chunk is being added to its free list because
7228 //      a larger free chunk has been split and resulted in this free chunk.
7229 //  coal death - a free chunk is being removed from its free list because
7230 //      it is being coalesced into a large free chunk.
7231 //  coal birth - a free chunk is being added to its free list because
7232 //      it was created when two or more free chunks where coalesced into
7233 //      this free chunk.
7234 //
7235 // These statistics are used to determine the desired number of free
7236 // chunks of a given size.  The desired number is chosen to be relative
7237 // to the end of a CMS sweep.  The desired number at the end of a sweep
7238 // is the
7239 //      count-at-end-of-previous-sweep (an amount that was enough)
7240 //              - count-at-beginning-of-current-sweep  (the excess)
7241 //              + split-births  (gains in this size during interval)
7242 //              - split-deaths  (demands on this size during interval)
7243 // where the interval is from the end of one sweep to the end of the
7244 // next.
7245 //
7246 // When sweeping the sweeper maintains an accumulated chunk which is
7247 // the chunk that is made up of chunks that have been coalesced.  That
7248 // will be termed the left-hand chunk.  A new chunk of garbage that
7249 // is being considered for coalescing will be referred to as the
7250 // right-hand chunk.
7251 //
7252 // When making a decision on whether to coalesce a right-hand chunk with
7253 // the current left-hand chunk, the current count vs. the desired count
7254 // of the left-hand chunk is considered.  Also if the right-hand chunk
7255 // is near the large chunk at the end of the heap (see
7256 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
7257 // left-hand chunk is coalesced.
7258 //
7259 // When making a decision about whether to split a chunk, the desired count
7260 // vs. the current count of the candidate to be split is also considered.
7261 // If the candidate is underpopulated (currently fewer chunks than desired)
7262 // a chunk of an overpopulated (currently more chunks than desired) size may
7263 // be chosen.  The "hint" associated with a free list, if non-null, points
7264 // to a free list which may be overpopulated.
7265 //
7266 
7267 void SweepClosure::do_already_free_chunk(FreeChunk* fc) {
7268   const size_t size = fc->size();
7269   // Chunks that cannot be coalesced are not in the
7270   // free lists.
7271   if (CMSTestInFreeList && !fc->cantCoalesce()) {
7272     assert(_sp->verify_chunk_in_free_list(fc),
7273            "free chunk should be in free lists");
7274   }
7275   // a chunk that is already free, should not have been
7276   // marked in the bit map
7277   HeapWord* const addr = (HeapWord*) fc;
7278   assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
7279   // Verify that the bit map has no bits marked between
7280   // addr and purported end of this block.
7281   _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7282 
7283   // Some chunks cannot be coalesced under any circumstances.
7284   // See the definition of cantCoalesce().
7285   if (!fc->cantCoalesce()) {
7286     // This chunk can potentially be coalesced.
7287     // All the work is done in
7288     do_post_free_or_garbage_chunk(fc, size);
7289     // Note that if the chunk is not coalescable (the else arm
7290     // below), we unconditionally flush, without needing to do
7291     // a "lookahead," as we do below.
7292     if (inFreeRange()) lookahead_and_flush(fc, size);
7293   } else {
7294     // Code path common to both original and adaptive free lists.
7295 
7296     // cant coalesce with previous block; this should be treated
7297     // as the end of a free run if any
7298     if (inFreeRange()) {
7299       // we kicked some butt; time to pick up the garbage
7300       assert(freeFinger() < addr, "freeFinger points too high");
7301       flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7302     }
7303     // else, nothing to do, just continue
7304   }
7305 }
7306 
7307 size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) {
7308   // This is a chunk of garbage.  It is not in any free list.
7309   // Add it to a free list or let it possibly be coalesced into
7310   // a larger chunk.
7311   HeapWord* const addr = (HeapWord*) fc;
7312   const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7313 
7314   // Verify that the bit map has no bits marked between
7315   // addr and purported end of just dead object.
7316   _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7317   do_post_free_or_garbage_chunk(fc, size);
7318 
7319   assert(_limit >= addr + size,
7320          "A freshly garbage chunk can't possibly straddle over _limit");
7321   if (inFreeRange()) lookahead_and_flush(fc, size);
7322   return size;
7323 }
7324 
7325 size_t SweepClosure::do_live_chunk(FreeChunk* fc) {
7326   HeapWord* addr = (HeapWord*) fc;
7327   // The sweeper has just found a live object. Return any accumulated
7328   // left hand chunk to the free lists.
7329   if (inFreeRange()) {
7330     assert(freeFinger() < addr, "freeFinger points too high");
7331     flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7332   }
7333 
7334   // This object is live: we'd normally expect this to be
7335   // an oop, and like to assert the following:
7336   // assert(oopDesc::is_oop(oop(addr)), "live block should be an oop");
7337   // However, as we commented above, this may be an object whose
7338   // header hasn't yet been initialized.
7339   size_t size;
7340   assert(_bitMap->isMarked(addr), "Tautology for this control point");
7341   if (_bitMap->isMarked(addr + 1)) {
7342     // Determine the size from the bit map, rather than trying to
7343     // compute it from the object header.
7344     HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
7345     size = pointer_delta(nextOneAddr + 1, addr);
7346     assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
7347            "alignment problem");
7348 
7349 #ifdef ASSERT
7350       if (oop(addr)->klass_or_null_acquire() != NULL) {
7351         // Ignore mark word because we are running concurrent with mutators
7352         assert(oopDesc::is_oop(oop(addr), true), "live block should be an oop");
7353         assert(size ==
7354                CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
7355                "P-mark and computed size do not agree");
7356       }
7357 #endif
7358 
7359   } else {
7360     // This should be an initialized object that's alive.
7361     assert(oop(addr)->klass_or_null_acquire() != NULL,
7362            "Should be an initialized object");
7363     // Ignore mark word because we are running concurrent with mutators
7364     assert(oopDesc::is_oop(oop(addr), true), "live block should be an oop");
7365     // Verify that the bit map has no bits marked between
7366     // addr and purported end of this block.
7367     size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7368     assert(size >= 3, "Necessary for Printezis marks to work");
7369     assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
7370     DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
7371   }
7372   return size;
7373 }
7374 
7375 void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc,
7376                                                  size_t chunkSize) {
7377   // do_post_free_or_garbage_chunk() should only be called in the case
7378   // of the adaptive free list allocator.
7379   const bool fcInFreeLists = fc->is_free();
7380   assert((HeapWord*)fc <= _limit, "sweep invariant");
7381   if (CMSTestInFreeList && fcInFreeLists) {
7382     assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists");
7383   }
7384 
7385   log_develop_trace(gc, sweep)("  -- pick up another chunk at " PTR_FORMAT " (" SIZE_FORMAT ")", p2i(fc), chunkSize);
7386 
7387   HeapWord* const fc_addr = (HeapWord*) fc;
7388 
7389   bool coalesce = false;
7390   const size_t left  = pointer_delta(fc_addr, freeFinger());
7391   const size_t right = chunkSize;
7392   switch (FLSCoalescePolicy) {
7393     // numeric value forms a coalition aggressiveness metric
7394     case 0:  { // never coalesce
7395       coalesce = false;
7396       break;
7397     }
7398     case 1: { // coalesce if left & right chunks on overpopulated lists
7399       coalesce = _sp->coalOverPopulated(left) &&
7400                  _sp->coalOverPopulated(right);
7401       break;
7402     }
7403     case 2: { // coalesce if left chunk on overpopulated list (default)
7404       coalesce = _sp->coalOverPopulated(left);
7405       break;
7406     }
7407     case 3: { // coalesce if left OR right chunk on overpopulated list
7408       coalesce = _sp->coalOverPopulated(left) ||
7409                  _sp->coalOverPopulated(right);
7410       break;
7411     }
7412     case 4: { // always coalesce
7413       coalesce = true;
7414       break;
7415     }
7416     default:
7417      ShouldNotReachHere();
7418   }
7419 
7420   // Should the current free range be coalesced?
7421   // If the chunk is in a free range and either we decided to coalesce above
7422   // or the chunk is near the large block at the end of the heap
7423   // (isNearLargestChunk() returns true), then coalesce this chunk.
7424   const bool doCoalesce = inFreeRange()
7425                           && (coalesce || _g->isNearLargestChunk(fc_addr));
7426   if (doCoalesce) {
7427     // Coalesce the current free range on the left with the new
7428     // chunk on the right.  If either is on a free list,
7429     // it must be removed from the list and stashed in the closure.
7430     if (freeRangeInFreeLists()) {
7431       FreeChunk* const ffc = (FreeChunk*)freeFinger();
7432       assert(ffc->size() == pointer_delta(fc_addr, freeFinger()),
7433              "Size of free range is inconsistent with chunk size.");
7434       if (CMSTestInFreeList) {
7435         assert(_sp->verify_chunk_in_free_list(ffc),
7436                "Chunk is not in free lists");
7437       }
7438       _sp->coalDeath(ffc->size());
7439       _sp->removeFreeChunkFromFreeLists(ffc);
7440       set_freeRangeInFreeLists(false);
7441     }
7442     if (fcInFreeLists) {
7443       _sp->coalDeath(chunkSize);
7444       assert(fc->size() == chunkSize,
7445         "The chunk has the wrong size or is not in the free lists");
7446       _sp->removeFreeChunkFromFreeLists(fc);
7447     }
7448     set_lastFreeRangeCoalesced(true);
7449     print_free_block_coalesced(fc);
7450   } else {  // not in a free range and/or should not coalesce
7451     // Return the current free range and start a new one.
7452     if (inFreeRange()) {
7453       // In a free range but cannot coalesce with the right hand chunk.
7454       // Put the current free range into the free lists.
7455       flush_cur_free_chunk(freeFinger(),
7456                            pointer_delta(fc_addr, freeFinger()));
7457     }
7458     // Set up for new free range.  Pass along whether the right hand
7459     // chunk is in the free lists.
7460     initialize_free_range((HeapWord*)fc, fcInFreeLists);
7461   }
7462 }
7463 
7464 // Lookahead flush:
7465 // If we are tracking a free range, and this is the last chunk that
7466 // we'll look at because its end crosses past _limit, we'll preemptively
7467 // flush it along with any free range we may be holding on to. Note that
7468 // this can be the case only for an already free or freshly garbage
7469 // chunk. If this block is an object, it can never straddle
7470 // over _limit. The "straddling" occurs when _limit is set at
7471 // the previous end of the space when this cycle started, and
7472 // a subsequent heap expansion caused the previously co-terminal
7473 // free block to be coalesced with the newly expanded portion,
7474 // thus rendering _limit a non-block-boundary making it dangerous
7475 // for the sweeper to step over and examine.
7476 void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) {
7477   assert(inFreeRange(), "Should only be called if currently in a free range.");
7478   HeapWord* const eob = ((HeapWord*)fc) + chunk_size;
7479   assert(_sp->used_region().contains(eob - 1),
7480          "eob = " PTR_FORMAT " eob-1 = " PTR_FORMAT " _limit = " PTR_FORMAT
7481          " out of bounds wrt _sp = [" PTR_FORMAT "," PTR_FORMAT ")"
7482          " when examining fc = " PTR_FORMAT "(" SIZE_FORMAT ")",
7483          p2i(eob), p2i(eob-1), p2i(_limit), p2i(_sp->bottom()), p2i(_sp->end()), p2i(fc), chunk_size);
7484   if (eob >= _limit) {
7485     assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit");
7486     log_develop_trace(gc, sweep)("_limit " PTR_FORMAT " reached or crossed by block "
7487                                  "[" PTR_FORMAT "," PTR_FORMAT ") in space "
7488                                  "[" PTR_FORMAT "," PTR_FORMAT ")",
7489                                  p2i(_limit), p2i(fc), p2i(eob), p2i(_sp->bottom()), p2i(_sp->end()));
7490     // Return the storage we are tracking back into the free lists.
7491     log_develop_trace(gc, sweep)("Flushing ... ");
7492     assert(freeFinger() < eob, "Error");
7493     flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger()));
7494   }
7495 }
7496 
7497 void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) {
7498   assert(inFreeRange(), "Should only be called if currently in a free range.");
7499   assert(size > 0,
7500     "A zero sized chunk cannot be added to the free lists.");
7501   if (!freeRangeInFreeLists()) {
7502     if (CMSTestInFreeList) {
7503       FreeChunk* fc = (FreeChunk*) chunk;
7504       fc->set_size(size);
7505       assert(!_sp->verify_chunk_in_free_list(fc),
7506              "chunk should not be in free lists yet");
7507     }
7508     log_develop_trace(gc, sweep)(" -- add free block " PTR_FORMAT " (" SIZE_FORMAT ") to free lists", p2i(chunk), size);
7509     // A new free range is going to be starting.  The current
7510     // free range has not been added to the free lists yet or
7511     // was removed so add it back.
7512     // If the current free range was coalesced, then the death
7513     // of the free range was recorded.  Record a birth now.
7514     if (lastFreeRangeCoalesced()) {
7515       _sp->coalBirth(size);
7516     }
7517     _sp->addChunkAndRepairOffsetTable(chunk, size,
7518             lastFreeRangeCoalesced());
7519   } else {
7520     log_develop_trace(gc, sweep)("Already in free list: nothing to flush");
7521   }
7522   set_inFreeRange(false);
7523   set_freeRangeInFreeLists(false);
7524 }
7525 
7526 // We take a break if we've been at this for a while,
7527 // so as to avoid monopolizing the locks involved.
7528 void SweepClosure::do_yield_work(HeapWord* addr) {
7529   // Return current free chunk being used for coalescing (if any)
7530   // to the appropriate freelist.  After yielding, the next
7531   // free block encountered will start a coalescing range of
7532   // free blocks.  If the next free block is adjacent to the
7533   // chunk just flushed, they will need to wait for the next
7534   // sweep to be coalesced.
7535   if (inFreeRange()) {
7536     flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7537   }
7538 
7539   // First give up the locks, then yield, then re-lock.
7540   // We should probably use a constructor/destructor idiom to
7541   // do this unlock/lock or modify the MutexUnlocker class to
7542   // serve our purpose. XXX
7543   assert_lock_strong(_bitMap->lock());
7544   assert_lock_strong(_freelistLock);
7545   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7546          "CMS thread should hold CMS token");
7547   _bitMap->lock()->unlock();
7548   _freelistLock->unlock();
7549   ConcurrentMarkSweepThread::desynchronize(true);
7550   _collector->stopTimer();
7551   _collector->incrementYields();
7552 
7553   // See the comment in coordinator_yield()
7554   for (unsigned i = 0; i < CMSYieldSleepCount &&
7555                        ConcurrentMarkSweepThread::should_yield() &&
7556                        !CMSCollector::foregroundGCIsActive(); ++i) {
7557     os::sleep(Thread::current(), 1, false);
7558   }
7559 
7560   ConcurrentMarkSweepThread::synchronize(true);
7561   _freelistLock->lock();
7562   _bitMap->lock()->lock_without_safepoint_check();
7563   _collector->startTimer();
7564 }
7565 
7566 #ifndef PRODUCT
7567 // This is actually very useful in a product build if it can
7568 // be called from the debugger.  Compile it into the product
7569 // as needed.
7570 bool debug_verify_chunk_in_free_list(FreeChunk* fc) {
7571   return debug_cms_space->verify_chunk_in_free_list(fc);
7572 }
7573 #endif
7574 
7575 void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const {
7576   log_develop_trace(gc, sweep)("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")",
7577                                p2i(fc), fc->size());
7578 }
7579 
7580 // CMSIsAliveClosure
7581 bool CMSIsAliveClosure::do_object_b(oop obj) {
7582   HeapWord* addr = (HeapWord*)obj;
7583   return addr != NULL &&
7584          (!_span.contains(addr) || _bit_map->isMarked(addr));
7585 }
7586 
7587 
7588 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector,
7589                       MemRegion span,
7590                       CMSBitMap* bit_map, CMSMarkStack* mark_stack,
7591                       bool cpc):
7592   _collector(collector),
7593   _span(span),
7594   _bit_map(bit_map),
7595   _mark_stack(mark_stack),
7596   _concurrent_precleaning(cpc) {
7597   assert(!_span.is_empty(), "Empty span could spell trouble");
7598 }
7599 
7600 
7601 // CMSKeepAliveClosure: the serial version
7602 void CMSKeepAliveClosure::do_oop(oop obj) {
7603   HeapWord* addr = (HeapWord*)obj;
7604   if (_span.contains(addr) &&
7605       !_bit_map->isMarked(addr)) {
7606     _bit_map->mark(addr);
7607     bool simulate_overflow = false;
7608     NOT_PRODUCT(
7609       if (CMSMarkStackOverflowALot &&
7610           _collector->simulate_overflow()) {
7611         // simulate a stack overflow
7612         simulate_overflow = true;
7613       }
7614     )
7615     if (simulate_overflow || !_mark_stack->push(obj)) {
7616       if (_concurrent_precleaning) {
7617         // We dirty the overflown object and let the remark
7618         // phase deal with it.
7619         assert(_collector->overflow_list_is_empty(), "Error");
7620         // In the case of object arrays, we need to dirty all of
7621         // the cards that the object spans. No locking or atomics
7622         // are needed since no one else can be mutating the mod union
7623         // table.
7624         if (obj->is_objArray()) {
7625           size_t sz = obj->size();
7626           HeapWord* end_card_addr = align_up(addr + sz, CardTableModRefBS::card_size);
7627           MemRegion redirty_range = MemRegion(addr, end_card_addr);
7628           assert(!redirty_range.is_empty(), "Arithmetical tautology");
7629           _collector->_modUnionTable.mark_range(redirty_range);
7630         } else {
7631           _collector->_modUnionTable.mark(addr);
7632         }
7633         _collector->_ser_kac_preclean_ovflw++;
7634       } else {
7635         _collector->push_on_overflow_list(obj);
7636         _collector->_ser_kac_ovflw++;
7637       }
7638     }
7639   }
7640 }
7641 
7642 void CMSKeepAliveClosure::do_oop(oop* p)       { CMSKeepAliveClosure::do_oop_work(p); }
7643 void CMSKeepAliveClosure::do_oop(narrowOop* p) { CMSKeepAliveClosure::do_oop_work(p); }
7644 
7645 // CMSParKeepAliveClosure: a parallel version of the above.
7646 // The work queues are private to each closure (thread),
7647 // but (may be) available for stealing by other threads.
7648 void CMSParKeepAliveClosure::do_oop(oop obj) {
7649   HeapWord* addr = (HeapWord*)obj;
7650   if (_span.contains(addr) &&
7651       !_bit_map->isMarked(addr)) {
7652     // In general, during recursive tracing, several threads
7653     // may be concurrently getting here; the first one to
7654     // "tag" it, claims it.
7655     if (_bit_map->par_mark(addr)) {
7656       bool res = _work_queue->push(obj);
7657       assert(res, "Low water mark should be much less than capacity");
7658       // Do a recursive trim in the hope that this will keep
7659       // stack usage lower, but leave some oops for potential stealers
7660       trim_queue(_low_water_mark);
7661     } // Else, another thread got there first
7662   }
7663 }
7664 
7665 void CMSParKeepAliveClosure::do_oop(oop* p)       { CMSParKeepAliveClosure::do_oop_work(p); }
7666 void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
7667 
7668 void CMSParKeepAliveClosure::trim_queue(uint max) {
7669   while (_work_queue->size() > max) {
7670     oop new_oop;
7671     if (_work_queue->pop_local(new_oop)) {
7672       assert(new_oop != NULL && oopDesc::is_oop(new_oop), "Expected an oop");
7673       assert(_bit_map->isMarked((HeapWord*)new_oop),
7674              "no white objects on this stack!");
7675       assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
7676       // iterate over the oops in this oop, marking and pushing
7677       // the ones in CMS heap (i.e. in _span).
7678       new_oop->oop_iterate(&_mark_and_push);
7679     }
7680   }
7681 }
7682 
7683 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
7684                                 CMSCollector* collector,
7685                                 MemRegion span, CMSBitMap* bit_map,
7686                                 OopTaskQueue* work_queue):
7687   _collector(collector),
7688   _span(span),
7689   _bit_map(bit_map),
7690   _work_queue(work_queue) { }
7691 
7692 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
7693   HeapWord* addr = (HeapWord*)obj;
7694   if (_span.contains(addr) &&
7695       !_bit_map->isMarked(addr)) {
7696     if (_bit_map->par_mark(addr)) {
7697       bool simulate_overflow = false;
7698       NOT_PRODUCT(
7699         if (CMSMarkStackOverflowALot &&
7700             _collector->par_simulate_overflow()) {
7701           // simulate a stack overflow
7702           simulate_overflow = true;
7703         }
7704       )
7705       if (simulate_overflow || !_work_queue->push(obj)) {
7706         _collector->par_push_on_overflow_list(obj);
7707         _collector->_par_kac_ovflw++;
7708       }
7709     } // Else another thread got there already
7710   }
7711 }
7712 
7713 void CMSInnerParMarkAndPushClosure::do_oop(oop* p)       { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
7714 void CMSInnerParMarkAndPushClosure::do_oop(narrowOop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
7715 
7716 //////////////////////////////////////////////////////////////////
7717 //  CMSExpansionCause                /////////////////////////////
7718 //////////////////////////////////////////////////////////////////
7719 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
7720   switch (cause) {
7721     case _no_expansion:
7722       return "No expansion";
7723     case _satisfy_free_ratio:
7724       return "Free ratio";
7725     case _satisfy_promotion:
7726       return "Satisfy promotion";
7727     case _satisfy_allocation:
7728       return "allocation";
7729     case _allocate_par_lab:
7730       return "Par LAB";
7731     case _allocate_par_spooling_space:
7732       return "Par Spooling Space";
7733     case _adaptive_size_policy:
7734       return "Ergonomics";
7735     default:
7736       return "unknown";
7737   }
7738 }
7739 
7740 void CMSDrainMarkingStackClosure::do_void() {
7741   // the max number to take from overflow list at a time
7742   const size_t num = _mark_stack->capacity()/4;
7743   assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
7744          "Overflow list should be NULL during concurrent phases");
7745   while (!_mark_stack->isEmpty() ||
7746          // if stack is empty, check the overflow list
7747          _collector->take_from_overflow_list(num, _mark_stack)) {
7748     oop obj = _mark_stack->pop();
7749     HeapWord* addr = (HeapWord*)obj;
7750     assert(_span.contains(addr), "Should be within span");
7751     assert(_bit_map->isMarked(addr), "Should be marked");
7752     assert(oopDesc::is_oop(obj), "Should be an oop");
7753     obj->oop_iterate(_keep_alive);
7754   }
7755 }
7756 
7757 void CMSParDrainMarkingStackClosure::do_void() {
7758   // drain queue
7759   trim_queue(0);
7760 }
7761 
7762 // Trim our work_queue so its length is below max at return
7763 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
7764   while (_work_queue->size() > max) {
7765     oop new_oop;
7766     if (_work_queue->pop_local(new_oop)) {
7767       assert(oopDesc::is_oop(new_oop), "Expected an oop");
7768       assert(_bit_map->isMarked((HeapWord*)new_oop),
7769              "no white objects on this stack!");
7770       assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
7771       // iterate over the oops in this oop, marking and pushing
7772       // the ones in CMS heap (i.e. in _span).
7773       new_oop->oop_iterate(&_mark_and_push);
7774     }
7775   }
7776 }
7777 
7778 ////////////////////////////////////////////////////////////////////
7779 // Support for Marking Stack Overflow list handling and related code
7780 ////////////////////////////////////////////////////////////////////
7781 // Much of the following code is similar in shape and spirit to the
7782 // code used in ParNewGC. We should try and share that code
7783 // as much as possible in the future.
7784 
7785 #ifndef PRODUCT
7786 // Debugging support for CMSStackOverflowALot
7787 
7788 // It's OK to call this multi-threaded;  the worst thing
7789 // that can happen is that we'll get a bunch of closely
7790 // spaced simulated overflows, but that's OK, in fact
7791 // probably good as it would exercise the overflow code
7792 // under contention.
7793 bool CMSCollector::simulate_overflow() {
7794   if (_overflow_counter-- <= 0) { // just being defensive
7795     _overflow_counter = CMSMarkStackOverflowInterval;
7796     return true;
7797   } else {
7798     return false;
7799   }
7800 }
7801 
7802 bool CMSCollector::par_simulate_overflow() {
7803   return simulate_overflow();
7804 }
7805 #endif
7806 
7807 // Single-threaded
7808 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
7809   assert(stack->isEmpty(), "Expected precondition");
7810   assert(stack->capacity() > num, "Shouldn't bite more than can chew");
7811   size_t i = num;
7812   oop  cur = _overflow_list;
7813   const markOop proto = markOopDesc::prototype();
7814   NOT_PRODUCT(ssize_t n = 0;)
7815   for (oop next; i > 0 && cur != NULL; cur = next, i--) {
7816     next = oop(cur->mark());
7817     cur->set_mark(proto);   // until proven otherwise
7818     assert(oopDesc::is_oop(cur), "Should be an oop");
7819     bool res = stack->push(cur);
7820     assert(res, "Bit off more than can chew?");
7821     NOT_PRODUCT(n++;)
7822   }
7823   _overflow_list = cur;
7824 #ifndef PRODUCT
7825   assert(_num_par_pushes >= n, "Too many pops?");
7826   _num_par_pushes -=n;
7827 #endif
7828   return !stack->isEmpty();
7829 }
7830 
7831 #define BUSY  (cast_to_oop<intptr_t>(0x1aff1aff))
7832 // (MT-safe) Get a prefix of at most "num" from the list.
7833 // The overflow list is chained through the mark word of
7834 // each object in the list. We fetch the entire list,
7835 // break off a prefix of the right size and return the
7836 // remainder. If other threads try to take objects from
7837 // the overflow list at that time, they will wait for
7838 // some time to see if data becomes available. If (and
7839 // only if) another thread places one or more object(s)
7840 // on the global list before we have returned the suffix
7841 // to the global list, we will walk down our local list
7842 // to find its end and append the global list to
7843 // our suffix before returning it. This suffix walk can
7844 // prove to be expensive (quadratic in the amount of traffic)
7845 // when there are many objects in the overflow list and
7846 // there is much producer-consumer contention on the list.
7847 // *NOTE*: The overflow list manipulation code here and
7848 // in ParNewGeneration:: are very similar in shape,
7849 // except that in the ParNew case we use the old (from/eden)
7850 // copy of the object to thread the list via its klass word.
7851 // Because of the common code, if you make any changes in
7852 // the code below, please check the ParNew version to see if
7853 // similar changes might be needed.
7854 // CR 6797058 has been filed to consolidate the common code.
7855 bool CMSCollector::par_take_from_overflow_list(size_t num,
7856                                                OopTaskQueue* work_q,
7857                                                int no_of_gc_threads) {
7858   assert(work_q->size() == 0, "First empty local work queue");
7859   assert(num < work_q->max_elems(), "Can't bite more than we can chew");
7860   if (_overflow_list == NULL) {
7861     return false;
7862   }
7863   // Grab the entire list; we'll put back a suffix
7864   oop prefix = cast_to_oop(Atomic::xchg((oopDesc*)BUSY, &_overflow_list));
7865   Thread* tid = Thread::current();
7866   // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was
7867   // set to ParallelGCThreads.
7868   size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads;
7869   size_t sleep_time_millis = MAX2((size_t)1, num/100);
7870   // If the list is busy, we spin for a short while,
7871   // sleeping between attempts to get the list.
7872   for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) {
7873     os::sleep(tid, sleep_time_millis, false);
7874     if (_overflow_list == NULL) {
7875       // Nothing left to take
7876       return false;
7877     } else if (_overflow_list != BUSY) {
7878       // Try and grab the prefix
7879       prefix = cast_to_oop(Atomic::xchg((oopDesc*)BUSY, &_overflow_list));
7880     }
7881   }
7882   // If the list was found to be empty, or we spun long
7883   // enough, we give up and return empty-handed. If we leave
7884   // the list in the BUSY state below, it must be the case that
7885   // some other thread holds the overflow list and will set it
7886   // to a non-BUSY state in the future.
7887   if (prefix == NULL || prefix == BUSY) {
7888      // Nothing to take or waited long enough
7889      if (prefix == NULL) {
7890        // Write back the NULL in case we overwrote it with BUSY above
7891        // and it is still the same value.
7892        Atomic::cmpxchg((oopDesc*)NULL, &_overflow_list, (oopDesc*)BUSY);
7893      }
7894      return false;
7895   }
7896   assert(prefix != NULL && prefix != BUSY, "Error");
7897   size_t i = num;
7898   oop cur = prefix;
7899   // Walk down the first "num" objects, unless we reach the end.
7900   for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--);
7901   if (cur->mark() == NULL) {
7902     // We have "num" or fewer elements in the list, so there
7903     // is nothing to return to the global list.
7904     // Write back the NULL in lieu of the BUSY we wrote
7905     // above, if it is still the same value.
7906     if (_overflow_list == BUSY) {
7907       Atomic::cmpxchg((oopDesc*)NULL, &_overflow_list, (oopDesc*)BUSY);
7908     }
7909   } else {
7910     // Chop off the suffix and return it to the global list.
7911     assert(cur->mark() != BUSY, "Error");
7912     oop suffix_head = cur->mark(); // suffix will be put back on global list
7913     cur->set_mark(NULL);           // break off suffix
7914     // It's possible that the list is still in the empty(busy) state
7915     // we left it in a short while ago; in that case we may be
7916     // able to place back the suffix without incurring the cost
7917     // of a walk down the list.
7918     oop observed_overflow_list = _overflow_list;
7919     oop cur_overflow_list = observed_overflow_list;
7920     bool attached = false;
7921     while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
7922       observed_overflow_list =
7923         Atomic::cmpxchg((oopDesc*)suffix_head, &_overflow_list, (oopDesc*)cur_overflow_list);
7924       if (cur_overflow_list == observed_overflow_list) {
7925         attached = true;
7926         break;
7927       } else cur_overflow_list = observed_overflow_list;
7928     }
7929     if (!attached) {
7930       // Too bad, someone else sneaked in (at least) an element; we'll need
7931       // to do a splice. Find tail of suffix so we can prepend suffix to global
7932       // list.
7933       for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark()));
7934       oop suffix_tail = cur;
7935       assert(suffix_tail != NULL && suffix_tail->mark() == NULL,
7936              "Tautology");
7937       observed_overflow_list = _overflow_list;
7938       do {
7939         cur_overflow_list = observed_overflow_list;
7940         if (cur_overflow_list != BUSY) {
7941           // Do the splice ...
7942           suffix_tail->set_mark(markOop(cur_overflow_list));
7943         } else { // cur_overflow_list == BUSY
7944           suffix_tail->set_mark(NULL);
7945         }
7946         // ... and try to place spliced list back on overflow_list ...
7947         observed_overflow_list =
7948           Atomic::cmpxchg((oopDesc*)suffix_head, &_overflow_list, (oopDesc*)cur_overflow_list);
7949       } while (cur_overflow_list != observed_overflow_list);
7950       // ... until we have succeeded in doing so.
7951     }
7952   }
7953 
7954   // Push the prefix elements on work_q
7955   assert(prefix != NULL, "control point invariant");
7956   const markOop proto = markOopDesc::prototype();
7957   oop next;
7958   NOT_PRODUCT(ssize_t n = 0;)
7959   for (cur = prefix; cur != NULL; cur = next) {
7960     next = oop(cur->mark());
7961     cur->set_mark(proto);   // until proven otherwise
7962     assert(oopDesc::is_oop(cur), "Should be an oop");
7963     bool res = work_q->push(cur);
7964     assert(res, "Bit off more than we can chew?");
7965     NOT_PRODUCT(n++;)
7966   }
7967 #ifndef PRODUCT
7968   assert(_num_par_pushes >= n, "Too many pops?");
7969   Atomic::sub(n, &_num_par_pushes);
7970 #endif
7971   return true;
7972 }
7973 
7974 // Single-threaded
7975 void CMSCollector::push_on_overflow_list(oop p) {
7976   NOT_PRODUCT(_num_par_pushes++;)
7977   assert(oopDesc::is_oop(p), "Not an oop");
7978   preserve_mark_if_necessary(p);
7979   p->set_mark((markOop)_overflow_list);
7980   _overflow_list = p;
7981 }
7982 
7983 // Multi-threaded; use CAS to prepend to overflow list
7984 void CMSCollector::par_push_on_overflow_list(oop p) {
7985   NOT_PRODUCT(Atomic::inc(&_num_par_pushes);)
7986   assert(oopDesc::is_oop(p), "Not an oop");
7987   par_preserve_mark_if_necessary(p);
7988   oop observed_overflow_list = _overflow_list;
7989   oop cur_overflow_list;
7990   do {
7991     cur_overflow_list = observed_overflow_list;
7992     if (cur_overflow_list != BUSY) {
7993       p->set_mark(markOop(cur_overflow_list));
7994     } else {
7995       p->set_mark(NULL);
7996     }
7997     observed_overflow_list =
7998       Atomic::cmpxchg((oopDesc*)p, &_overflow_list, (oopDesc*)cur_overflow_list);
7999   } while (cur_overflow_list != observed_overflow_list);
8000 }
8001 #undef BUSY
8002 
8003 // Single threaded
8004 // General Note on GrowableArray: pushes may silently fail
8005 // because we are (temporarily) out of C-heap for expanding
8006 // the stack. The problem is quite ubiquitous and affects
8007 // a lot of code in the JVM. The prudent thing for GrowableArray
8008 // to do (for now) is to exit with an error. However, that may
8009 // be too draconian in some cases because the caller may be
8010 // able to recover without much harm. For such cases, we
8011 // should probably introduce a "soft_push" method which returns
8012 // an indication of success or failure with the assumption that
8013 // the caller may be able to recover from a failure; code in
8014 // the VM can then be changed, incrementally, to deal with such
8015 // failures where possible, thus, incrementally hardening the VM
8016 // in such low resource situations.
8017 void CMSCollector::preserve_mark_work(oop p, markOop m) {
8018   _preserved_oop_stack.push(p);
8019   _preserved_mark_stack.push(m);
8020   assert(m == p->mark(), "Mark word changed");
8021   assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8022          "bijection");
8023 }
8024 
8025 // Single threaded
8026 void CMSCollector::preserve_mark_if_necessary(oop p) {
8027   markOop m = p->mark();
8028   if (m->must_be_preserved(p)) {
8029     preserve_mark_work(p, m);
8030   }
8031 }
8032 
8033 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
8034   markOop m = p->mark();
8035   if (m->must_be_preserved(p)) {
8036     MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
8037     // Even though we read the mark word without holding
8038     // the lock, we are assured that it will not change
8039     // because we "own" this oop, so no other thread can
8040     // be trying to push it on the overflow list; see
8041     // the assertion in preserve_mark_work() that checks
8042     // that m == p->mark().
8043     preserve_mark_work(p, m);
8044   }
8045 }
8046 
8047 // We should be able to do this multi-threaded,
8048 // a chunk of stack being a task (this is
8049 // correct because each oop only ever appears
8050 // once in the overflow list. However, it's
8051 // not very easy to completely overlap this with
8052 // other operations, so will generally not be done
8053 // until all work's been completed. Because we
8054 // expect the preserved oop stack (set) to be small,
8055 // it's probably fine to do this single-threaded.
8056 // We can explore cleverer concurrent/overlapped/parallel
8057 // processing of preserved marks if we feel the
8058 // need for this in the future. Stack overflow should
8059 // be so rare in practice and, when it happens, its
8060 // effect on performance so great that this will
8061 // likely just be in the noise anyway.
8062 void CMSCollector::restore_preserved_marks_if_any() {
8063   assert(SafepointSynchronize::is_at_safepoint(),
8064          "world should be stopped");
8065   assert(Thread::current()->is_ConcurrentGC_thread() ||
8066          Thread::current()->is_VM_thread(),
8067          "should be single-threaded");
8068   assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8069          "bijection");
8070 
8071   while (!_preserved_oop_stack.is_empty()) {
8072     oop p = _preserved_oop_stack.pop();
8073     assert(oopDesc::is_oop(p), "Should be an oop");
8074     assert(_span.contains(p), "oop should be in _span");
8075     assert(p->mark() == markOopDesc::prototype(),
8076            "Set when taken from overflow list");
8077     markOop m = _preserved_mark_stack.pop();
8078     p->set_mark(m);
8079   }
8080   assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(),
8081          "stacks were cleared above");
8082 }
8083 
8084 #ifndef PRODUCT
8085 bool CMSCollector::no_preserved_marks() const {
8086   return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty();
8087 }
8088 #endif
8089 
8090 // Transfer some number of overflown objects to usual marking
8091 // stack. Return true if some objects were transferred.
8092 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
8093   size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,
8094                     (size_t)ParGCDesiredObjsFromOverflowList);
8095 
8096   bool res = _collector->take_from_overflow_list(num, _mark_stack);
8097   assert(_collector->overflow_list_is_empty() || res,
8098          "If list is not empty, we should have taken something");
8099   assert(!res || !_mark_stack->isEmpty(),
8100          "If we took something, it should now be on our stack");
8101   return res;
8102 }
8103 
8104 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
8105   size_t res = _sp->block_size_no_stall(addr, _collector);
8106   if (_sp->block_is_obj(addr)) {
8107     if (_live_bit_map->isMarked(addr)) {
8108       // It can't have been dead in a previous cycle
8109       guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
8110     } else {
8111       _dead_bit_map->mark(addr);      // mark the dead object
8112     }
8113   }
8114   // Could be 0, if the block size could not be computed without stalling.
8115   return res;
8116 }
8117 
8118 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() {
8119 
8120   switch (phase) {
8121     case CMSCollector::InitialMarking:
8122       initialize(true  /* fullGC */ ,
8123                  cause /* cause of the GC */,
8124                  true  /* recordGCBeginTime */,
8125                  true  /* recordPreGCUsage */,
8126                  false /* recordPeakUsage */,
8127                  false /* recordPostGCusage */,
8128                  true  /* recordAccumulatedGCTime */,
8129                  false /* recordGCEndTime */,
8130                  false /* countCollection */  );
8131       break;
8132 
8133     case CMSCollector::FinalMarking:
8134       initialize(true  /* fullGC */ ,
8135                  cause /* cause of the GC */,
8136                  false /* recordGCBeginTime */,
8137                  false /* recordPreGCUsage */,
8138                  false /* recordPeakUsage */,
8139                  false /* recordPostGCusage */,
8140                  true  /* recordAccumulatedGCTime */,
8141                  false /* recordGCEndTime */,
8142                  false /* countCollection */  );
8143       break;
8144 
8145     case CMSCollector::Sweeping:
8146       initialize(true  /* fullGC */ ,
8147                  cause /* cause of the GC */,
8148                  false /* recordGCBeginTime */,
8149                  false /* recordPreGCUsage */,
8150                  true  /* recordPeakUsage */,
8151                  true  /* recordPostGCusage */,
8152                  false /* recordAccumulatedGCTime */,
8153                  true  /* recordGCEndTime */,
8154                  true  /* countCollection */  );
8155       break;
8156 
8157     default:
8158       ShouldNotReachHere();
8159   }
8160 }