1 /*
   2  * Copyright (c) 2001, 2018, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
  21  * questions.
  22  *
  23  */
  24 
  25 #include "precompiled.hpp"
  26 #include "classfile/classLoaderDataGraph.hpp"
  27 #include "classfile/stringTable.hpp"
  28 #include "classfile/symbolTable.hpp"
  29 #include "classfile/systemDictionary.hpp"
  30 #include "code/codeCache.hpp"
  31 #include "gc/cms/cmsCollectorPolicy.hpp"
  32 #include "gc/cms/cmsGCStats.hpp"
  33 #include "gc/cms/cmsHeap.hpp"
  34 #include "gc/cms/cmsOopClosures.inline.hpp"
  35 #include "gc/cms/compactibleFreeListSpace.hpp"
  36 #include "gc/cms/concurrentMarkSweepGeneration.inline.hpp"
  37 #include "gc/cms/concurrentMarkSweepThread.hpp"
  38 #include "gc/cms/parNewGeneration.hpp"
  39 #include "gc/cms/promotionInfo.inline.hpp"
  40 #include "gc/cms/vmCMSOperations.hpp"
  41 #include "gc/serial/genMarkSweep.hpp"
  42 #include "gc/serial/tenuredGeneration.hpp"
  43 #include "gc/shared/adaptiveSizePolicy.hpp"
  44 #include "gc/shared/cardGeneration.inline.hpp"
  45 #include "gc/shared/cardTableRS.hpp"
  46 #include "gc/shared/collectedHeap.inline.hpp"
  47 #include "gc/shared/collectorCounters.hpp"
  48 #include "gc/shared/collectorPolicy.hpp"
  49 #include "gc/shared/gcLocker.hpp"
  50 #include "gc/shared/gcPolicyCounters.hpp"
  51 #include "gc/shared/gcTimer.hpp"
  52 #include "gc/shared/gcTrace.hpp"
  53 #include "gc/shared/gcTraceTime.inline.hpp"
  54 #include "gc/shared/genCollectedHeap.hpp"
  55 #include "gc/shared/genOopClosures.inline.hpp"
  56 #include "gc/shared/isGCActiveMark.hpp"
  57 #include "gc/shared/oopStorageParState.hpp"
  58 #include "gc/shared/referencePolicy.hpp"
  59 #include "gc/shared/referenceProcessorPhaseTimes.hpp"
  60 #include "gc/shared/space.inline.hpp"
  61 #include "gc/shared/strongRootsScope.hpp"
  62 #include "gc/shared/taskqueue.inline.hpp"
  63 #include "gc/shared/weakProcessor.hpp"
  64 #include "logging/log.hpp"
  65 #include "logging/logStream.hpp"
  66 #include "memory/allocation.hpp"
  67 #include "memory/binaryTreeDictionary.inline.hpp"
  68 #include "memory/iterator.inline.hpp"
  69 #include "memory/padded.hpp"
  70 #include "memory/resourceArea.hpp"
  71 #include "oops/access.inline.hpp"
  72 #include "oops/oop.inline.hpp"
  73 #include "prims/jvmtiExport.hpp"
  74 #include "runtime/atomic.hpp"
  75 #include "runtime/flags/flagSetting.hpp"
  76 #include "runtime/globals_extension.hpp"
  77 #include "runtime/handles.inline.hpp"
  78 #include "runtime/java.hpp"
  79 #include "runtime/orderAccess.hpp"
  80 #include "runtime/timer.hpp"
  81 #include "runtime/vmThread.hpp"
  82 #include "services/memoryService.hpp"
  83 #include "services/runtimeService.hpp"
  84 #include "utilities/align.hpp"
  85 #include "utilities/stack.inline.hpp"
  86 
  87 // statics
  88 CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL;
  89 bool CMSCollector::_full_gc_requested = false;
  90 GCCause::Cause CMSCollector::_full_gc_cause = GCCause::_no_gc;
  91 
  92 //////////////////////////////////////////////////////////////////
  93 // In support of CMS/VM thread synchronization
  94 //////////////////////////////////////////////////////////////////
  95 // We split use of the CGC_lock into 2 "levels".
  96 // The low-level locking is of the usual CGC_lock monitor. We introduce
  97 // a higher level "token" (hereafter "CMS token") built on top of the
  98 // low level monitor (hereafter "CGC lock").
  99 // The token-passing protocol gives priority to the VM thread. The
 100 // CMS-lock doesn't provide any fairness guarantees, but clients
 101 // should ensure that it is only held for very short, bounded
 102 // durations.
 103 //
 104 // When either of the CMS thread or the VM thread is involved in
 105 // collection operations during which it does not want the other
 106 // thread to interfere, it obtains the CMS token.
 107 //
 108 // If either thread tries to get the token while the other has
 109 // it, that thread waits. However, if the VM thread and CMS thread
 110 // both want the token, then the VM thread gets priority while the
 111 // CMS thread waits. This ensures, for instance, that the "concurrent"
 112 // phases of the CMS thread's work do not block out the VM thread
 113 // for long periods of time as the CMS thread continues to hog
 114 // the token. (See bug 4616232).
 115 //
 116 // The baton-passing functions are, however, controlled by the
 117 // flags _foregroundGCShouldWait and _foregroundGCIsActive,
 118 // and here the low-level CMS lock, not the high level token,
 119 // ensures mutual exclusion.
 120 //
 121 // Two important conditions that we have to satisfy:
 122 // 1. if a thread does a low-level wait on the CMS lock, then it
 123 //    relinquishes the CMS token if it were holding that token
 124 //    when it acquired the low-level CMS lock.
 125 // 2. any low-level notifications on the low-level lock
 126 //    should only be sent when a thread has relinquished the token.
 127 //
 128 // In the absence of either property, we'd have potential deadlock.
 129 //
 130 // We protect each of the CMS (concurrent and sequential) phases
 131 // with the CMS _token_, not the CMS _lock_.
 132 //
 133 // The only code protected by CMS lock is the token acquisition code
 134 // itself, see ConcurrentMarkSweepThread::[de]synchronize(), and the
 135 // baton-passing code.
 136 //
 137 // Unfortunately, i couldn't come up with a good abstraction to factor and
 138 // hide the naked CGC_lock manipulation in the baton-passing code
 139 // further below. That's something we should try to do. Also, the proof
 140 // of correctness of this 2-level locking scheme is far from obvious,
 141 // and potentially quite slippery. We have an uneasy suspicion, for instance,
 142 // that there may be a theoretical possibility of delay/starvation in the
 143 // low-level lock/wait/notify scheme used for the baton-passing because of
 144 // potential interference with the priority scheme embodied in the
 145 // CMS-token-passing protocol. See related comments at a CGC_lock->wait()
 146 // invocation further below and marked with "XXX 20011219YSR".
 147 // Indeed, as we note elsewhere, this may become yet more slippery
 148 // in the presence of multiple CMS and/or multiple VM threads. XXX
 149 
 150 class CMSTokenSync: public StackObj {
 151  private:
 152   bool _is_cms_thread;
 153  public:
 154   CMSTokenSync(bool is_cms_thread):
 155     _is_cms_thread(is_cms_thread) {
 156     assert(is_cms_thread == Thread::current()->is_ConcurrentGC_thread(),
 157            "Incorrect argument to constructor");
 158     ConcurrentMarkSweepThread::synchronize(_is_cms_thread);
 159   }
 160 
 161   ~CMSTokenSync() {
 162     assert(_is_cms_thread ?
 163              ConcurrentMarkSweepThread::cms_thread_has_cms_token() :
 164              ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
 165           "Incorrect state");
 166     ConcurrentMarkSweepThread::desynchronize(_is_cms_thread);
 167   }
 168 };
 169 
 170 // Convenience class that does a CMSTokenSync, and then acquires
 171 // upto three locks.
 172 class CMSTokenSyncWithLocks: public CMSTokenSync {
 173  private:
 174   // Note: locks are acquired in textual declaration order
 175   // and released in the opposite order
 176   MutexLockerEx _locker1, _locker2, _locker3;
 177  public:
 178   CMSTokenSyncWithLocks(bool is_cms_thread, Mutex* mutex1,
 179                         Mutex* mutex2 = NULL, Mutex* mutex3 = NULL):
 180     CMSTokenSync(is_cms_thread),
 181     _locker1(mutex1, Mutex::_no_safepoint_check_flag),
 182     _locker2(mutex2, Mutex::_no_safepoint_check_flag),
 183     _locker3(mutex3, Mutex::_no_safepoint_check_flag)
 184   { }
 185 };
 186 
 187 
 188 //////////////////////////////////////////////////////////////////
 189 //  Concurrent Mark-Sweep Generation /////////////////////////////
 190 //////////////////////////////////////////////////////////////////
 191 
 192 NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;)
 193 
 194 // This struct contains per-thread things necessary to support parallel
 195 // young-gen collection.
 196 class CMSParGCThreadState: public CHeapObj<mtGC> {
 197  public:
 198   CompactibleFreeListSpaceLAB lab;
 199   PromotionInfo promo;
 200 
 201   // Constructor.
 202   CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) {
 203     promo.setSpace(cfls);
 204   }
 205 };
 206 
 207 ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration(
 208      ReservedSpace rs, size_t initial_byte_size, CardTableRS* ct) :
 209   CardGeneration(rs, initial_byte_size, ct),
 210   _dilatation_factor(((double)MinChunkSize)/((double)(CollectedHeap::min_fill_size()))),
 211   _did_compact(false)
 212 {
 213   HeapWord* bottom = (HeapWord*) _virtual_space.low();
 214   HeapWord* end    = (HeapWord*) _virtual_space.high();
 215 
 216   _direct_allocated_words = 0;
 217   NOT_PRODUCT(
 218     _numObjectsPromoted = 0;
 219     _numWordsPromoted = 0;
 220     _numObjectsAllocated = 0;
 221     _numWordsAllocated = 0;
 222   )
 223 
 224   _cmsSpace = new CompactibleFreeListSpace(_bts, MemRegion(bottom, end));
 225   NOT_PRODUCT(debug_cms_space = _cmsSpace;)
 226   _cmsSpace->_old_gen = this;
 227 
 228   _gc_stats = new CMSGCStats();
 229 
 230   // Verify the assumption that FreeChunk::_prev and OopDesc::_klass
 231   // offsets match. The ability to tell free chunks from objects
 232   // depends on this property.
 233   debug_only(
 234     FreeChunk* junk = NULL;
 235     assert(UseCompressedClassPointers ||
 236            junk->prev_addr() == (void*)(oop(junk)->klass_addr()),
 237            "Offset of FreeChunk::_prev within FreeChunk must match"
 238            "  that of OopDesc::_klass within OopDesc");
 239   )
 240 
 241   _par_gc_thread_states = NEW_C_HEAP_ARRAY(CMSParGCThreadState*, ParallelGCThreads, mtGC);
 242   for (uint i = 0; i < ParallelGCThreads; i++) {
 243     _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace());
 244   }
 245 
 246   _incremental_collection_failed = false;
 247   // The "dilatation_factor" is the expansion that can occur on
 248   // account of the fact that the minimum object size in the CMS
 249   // generation may be larger than that in, say, a contiguous young
 250   //  generation.
 251   // Ideally, in the calculation below, we'd compute the dilatation
 252   // factor as: MinChunkSize/(promoting_gen's min object size)
 253   // Since we do not have such a general query interface for the
 254   // promoting generation, we'll instead just use the minimum
 255   // object size (which today is a header's worth of space);
 256   // note that all arithmetic is in units of HeapWords.
 257   assert(MinChunkSize >= CollectedHeap::min_fill_size(), "just checking");
 258   assert(_dilatation_factor >= 1.0, "from previous assert");
 259 }
 260 
 261 
 262 // The field "_initiating_occupancy" represents the occupancy percentage
 263 // at which we trigger a new collection cycle.  Unless explicitly specified
 264 // via CMSInitiatingOccupancyFraction (argument "io" below), it
 265 // is calculated by:
 266 //
 267 //   Let "f" be MinHeapFreeRatio in
 268 //
 269 //    _initiating_occupancy = 100-f +
 270 //                           f * (CMSTriggerRatio/100)
 271 //   where CMSTriggerRatio is the argument "tr" below.
 272 //
 273 // That is, if we assume the heap is at its desired maximum occupancy at the
 274 // end of a collection, we let CMSTriggerRatio of the (purported) free
 275 // space be allocated before initiating a new collection cycle.
 276 //
 277 void ConcurrentMarkSweepGeneration::init_initiating_occupancy(intx io, uintx tr) {
 278   assert(io <= 100 && tr <= 100, "Check the arguments");
 279   if (io >= 0) {
 280     _initiating_occupancy = (double)io / 100.0;
 281   } else {
 282     _initiating_occupancy = ((100 - MinHeapFreeRatio) +
 283                              (double)(tr * MinHeapFreeRatio) / 100.0)
 284                             / 100.0;
 285   }
 286 }
 287 
 288 void ConcurrentMarkSweepGeneration::ref_processor_init() {
 289   assert(collector() != NULL, "no collector");
 290   collector()->ref_processor_init();
 291 }
 292 
 293 void CMSCollector::ref_processor_init() {
 294   if (_ref_processor == NULL) {
 295     // Allocate and initialize a reference processor
 296     _ref_processor =
 297       new ReferenceProcessor(&_span_based_discoverer,
 298                              (ParallelGCThreads > 1) && ParallelRefProcEnabled, // mt processing
 299                              ParallelGCThreads,                      // mt processing degree
 300                              _cmsGen->refs_discovery_is_mt(),        // mt discovery
 301                              MAX2(ConcGCThreads, ParallelGCThreads), // mt discovery degree
 302                              _cmsGen->refs_discovery_is_atomic(),    // discovery is not atomic
 303                              &_is_alive_closure,                     // closure for liveness info
 304                              false);                                 // disable adjusting number of processing threads
 305     // Initialize the _ref_processor field of CMSGen
 306     _cmsGen->set_ref_processor(_ref_processor);
 307 
 308   }
 309 }
 310 
 311 AdaptiveSizePolicy* CMSCollector::size_policy() {
 312   return CMSHeap::heap()->size_policy();
 313 }
 314 
 315 void ConcurrentMarkSweepGeneration::initialize_performance_counters() {
 316 
 317   const char* gen_name = "old";
 318   GenCollectorPolicy* gcp = CMSHeap::heap()->gen_policy();
 319   // Generation Counters - generation 1, 1 subspace
 320   _gen_counters = new GenerationCounters(gen_name, 1, 1,
 321       gcp->min_old_size(), gcp->max_old_size(), &_virtual_space);
 322 
 323   _space_counters = new GSpaceCounters(gen_name, 0,
 324                                        _virtual_space.reserved_size(),
 325                                        this, _gen_counters);
 326 }
 327 
 328 CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha):
 329   _cms_gen(cms_gen)
 330 {
 331   assert(alpha <= 100, "bad value");
 332   _saved_alpha = alpha;
 333 
 334   // Initialize the alphas to the bootstrap value of 100.
 335   _gc0_alpha = _cms_alpha = 100;
 336 
 337   _cms_begin_time.update();
 338   _cms_end_time.update();
 339 
 340   _gc0_duration = 0.0;
 341   _gc0_period = 0.0;
 342   _gc0_promoted = 0;
 343 
 344   _cms_duration = 0.0;
 345   _cms_period = 0.0;
 346   _cms_allocated = 0;
 347 
 348   _cms_used_at_gc0_begin = 0;
 349   _cms_used_at_gc0_end = 0;
 350   _allow_duty_cycle_reduction = false;
 351   _valid_bits = 0;
 352 }
 353 
 354 double CMSStats::cms_free_adjustment_factor(size_t free) const {
 355   // TBD: CR 6909490
 356   return 1.0;
 357 }
 358 
 359 void CMSStats::adjust_cms_free_adjustment_factor(bool fail, size_t free) {
 360 }
 361 
 362 // If promotion failure handling is on use
 363 // the padded average size of the promotion for each
 364 // young generation collection.
 365 double CMSStats::time_until_cms_gen_full() const {
 366   size_t cms_free = _cms_gen->cmsSpace()->free();
 367   CMSHeap* heap = CMSHeap::heap();
 368   size_t expected_promotion = MIN2(heap->young_gen()->capacity(),
 369                                    (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average());
 370   if (cms_free > expected_promotion) {
 371     // Start a cms collection if there isn't enough space to promote
 372     // for the next young collection.  Use the padded average as
 373     // a safety factor.
 374     cms_free -= expected_promotion;
 375 
 376     // Adjust by the safety factor.
 377     double cms_free_dbl = (double)cms_free;
 378     double cms_adjustment = (100.0 - CMSIncrementalSafetyFactor) / 100.0;
 379     // Apply a further correction factor which tries to adjust
 380     // for recent occurance of concurrent mode failures.
 381     cms_adjustment = cms_adjustment * cms_free_adjustment_factor(cms_free);
 382     cms_free_dbl = cms_free_dbl * cms_adjustment;
 383 
 384     log_trace(gc)("CMSStats::time_until_cms_gen_full: cms_free " SIZE_FORMAT " expected_promotion " SIZE_FORMAT,
 385                   cms_free, expected_promotion);
 386     log_trace(gc)("  cms_free_dbl %f cms_consumption_rate %f", cms_free_dbl, cms_consumption_rate() + 1.0);
 387     // Add 1 in case the consumption rate goes to zero.
 388     return cms_free_dbl / (cms_consumption_rate() + 1.0);
 389   }
 390   return 0.0;
 391 }
 392 
 393 // Compare the duration of the cms collection to the
 394 // time remaining before the cms generation is empty.
 395 // Note that the time from the start of the cms collection
 396 // to the start of the cms sweep (less than the total
 397 // duration of the cms collection) can be used.  This
 398 // has been tried and some applications experienced
 399 // promotion failures early in execution.  This was
 400 // possibly because the averages were not accurate
 401 // enough at the beginning.
 402 double CMSStats::time_until_cms_start() const {
 403   // We add "gc0_period" to the "work" calculation
 404   // below because this query is done (mostly) at the
 405   // end of a scavenge, so we need to conservatively
 406   // account for that much possible delay
 407   // in the query so as to avoid concurrent mode failures
 408   // due to starting the collection just a wee bit too
 409   // late.
 410   double work = cms_duration() + gc0_period();
 411   double deadline = time_until_cms_gen_full();
 412   // If a concurrent mode failure occurred recently, we want to be
 413   // more conservative and halve our expected time_until_cms_gen_full()
 414   if (work > deadline) {
 415     log_develop_trace(gc)("CMSCollector: collect because of anticipated promotion before full %3.7f + %3.7f > %3.7f ",
 416                           cms_duration(), gc0_period(), time_until_cms_gen_full());
 417     return 0.0;
 418   }
 419   return work - deadline;
 420 }
 421 
 422 #ifndef PRODUCT
 423 void CMSStats::print_on(outputStream *st) const {
 424   st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha);
 425   st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo=" SIZE_FORMAT,
 426                gc0_duration(), gc0_period(), gc0_promoted());
 427   st->print(",cms_dur=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT,
 428             cms_duration(), cms_period(), cms_allocated());
 429   st->print(",cms_since_beg=%g,cms_since_end=%g",
 430             cms_time_since_begin(), cms_time_since_end());
 431   st->print(",cms_used_beg=" SIZE_FORMAT ",cms_used_end=" SIZE_FORMAT,
 432             _cms_used_at_gc0_begin, _cms_used_at_gc0_end);
 433 
 434   if (valid()) {
 435     st->print(",promo_rate=%g,cms_alloc_rate=%g",
 436               promotion_rate(), cms_allocation_rate());
 437     st->print(",cms_consumption_rate=%g,time_until_full=%g",
 438               cms_consumption_rate(), time_until_cms_gen_full());
 439   }
 440   st->cr();
 441 }
 442 #endif // #ifndef PRODUCT
 443 
 444 CMSCollector::CollectorState CMSCollector::_collectorState =
 445                              CMSCollector::Idling;
 446 bool CMSCollector::_foregroundGCIsActive = false;
 447 bool CMSCollector::_foregroundGCShouldWait = false;
 448 
 449 CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
 450                            CardTableRS*                   ct,
 451                            ConcurrentMarkSweepPolicy*     cp):
 452   _overflow_list(NULL),
 453   _conc_workers(NULL),     // may be set later
 454   _completed_initialization(false),
 455   _collection_count_start(0),
 456   _should_unload_classes(CMSClassUnloadingEnabled),
 457   _concurrent_cycles_since_last_unload(0),
 458   _roots_scanning_options(GenCollectedHeap::SO_None),
 459   _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"),
 460   _verifying(false),
 461   _collector_policy(cp),
 462   _inter_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
 463   _intra_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
 464   _gc_tracer_cm(new (ResourceObj::C_HEAP, mtGC) CMSTracer()),
 465   _gc_timer_cm(new (ResourceObj::C_HEAP, mtGC) ConcurrentGCTimer()),
 466   _cms_start_registered(false),
 467   _cmsGen(cmsGen),
 468   // Adjust span to cover old (cms) gen
 469   _span(cmsGen->reserved()),
 470   _ct(ct),
 471   _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"),
 472   _modUnionTable((CardTable::card_shift - LogHeapWordSize),
 473                  -1 /* lock-free */, "No_lock" /* dummy */),
 474   _restart_addr(NULL),
 475   _ser_pmc_preclean_ovflw(0),
 476   _ser_pmc_remark_ovflw(0),
 477   _par_pmc_remark_ovflw(0),
 478   _ser_kac_preclean_ovflw(0),
 479   _ser_kac_ovflw(0),
 480   _par_kac_ovflw(0),
 481 #ifndef PRODUCT
 482   _num_par_pushes(0),
 483 #endif
 484   _span_based_discoverer(_span),
 485   _ref_processor(NULL),    // will be set later
 486   // Construct the is_alive_closure with _span & markBitMap
 487   _is_alive_closure(_span, &_markBitMap),
 488   _modUnionClosurePar(&_modUnionTable),
 489   _between_prologue_and_epilogue(false),
 490   _abort_preclean(false),
 491   _start_sampling(false),
 492   _stats(cmsGen),
 493   _eden_chunk_lock(new Mutex(Mutex::leaf + 1, "CMS_eden_chunk_lock", true,
 494                              //verify that this lock should be acquired with safepoint check.
 495                              Monitor::_safepoint_check_sometimes)),
 496   _eden_chunk_array(NULL),     // may be set in ctor body
 497   _eden_chunk_index(0),        // -- ditto --
 498   _eden_chunk_capacity(0),     // -- ditto --
 499   _survivor_chunk_array(NULL), // -- ditto --
 500   _survivor_chunk_index(0),    // -- ditto --
 501   _survivor_chunk_capacity(0), // -- ditto --
 502   _survivor_plab_array(NULL)   // -- ditto --
 503 {
 504   // Now expand the span and allocate the collection support structures
 505   // (MUT, marking bit map etc.) to cover both generations subject to
 506   // collection.
 507 
 508   // For use by dirty card to oop closures.
 509   _cmsGen->cmsSpace()->set_collector(this);
 510 
 511   // Allocate MUT and marking bit map
 512   {
 513     MutexLockerEx x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag);
 514     if (!_markBitMap.allocate(_span)) {
 515       log_warning(gc)("Failed to allocate CMS Bit Map");
 516       return;
 517     }
 518     assert(_markBitMap.covers(_span), "_markBitMap inconsistency?");
 519   }
 520   {
 521     _modUnionTable.allocate(_span);
 522     assert(_modUnionTable.covers(_span), "_modUnionTable inconsistency?");
 523   }
 524 
 525   if (!_markStack.allocate(MarkStackSize)) {
 526     log_warning(gc)("Failed to allocate CMS Marking Stack");
 527     return;
 528   }
 529 
 530   // Support for multi-threaded concurrent phases
 531   if (CMSConcurrentMTEnabled) {
 532     if (FLAG_IS_DEFAULT(ConcGCThreads)) {
 533       // just for now
 534       FLAG_SET_DEFAULT(ConcGCThreads, (ParallelGCThreads + 3) / 4);
 535     }
 536     if (ConcGCThreads > 1) {
 537       _conc_workers = new YieldingFlexibleWorkGang("CMS Thread",
 538                                  ConcGCThreads, true);
 539       if (_conc_workers == NULL) {
 540         log_warning(gc)("GC/CMS: _conc_workers allocation failure: forcing -CMSConcurrentMTEnabled");
 541         CMSConcurrentMTEnabled = false;
 542       } else {
 543         _conc_workers->initialize_workers();
 544       }
 545     } else {
 546       CMSConcurrentMTEnabled = false;
 547     }
 548   }
 549   if (!CMSConcurrentMTEnabled) {
 550     ConcGCThreads = 0;
 551   } else {
 552     // Turn off CMSCleanOnEnter optimization temporarily for
 553     // the MT case where it's not fixed yet; see 6178663.
 554     CMSCleanOnEnter = false;
 555   }
 556   assert((_conc_workers != NULL) == (ConcGCThreads > 1),
 557          "Inconsistency");
 558   log_debug(gc)("ConcGCThreads: %u", ConcGCThreads);
 559   log_debug(gc)("ParallelGCThreads: %u", ParallelGCThreads);
 560 
 561   // Parallel task queues; these are shared for the
 562   // concurrent and stop-world phases of CMS, but
 563   // are not shared with parallel scavenge (ParNew).
 564   {
 565     uint i;
 566     uint num_queues = MAX2(ParallelGCThreads, ConcGCThreads);
 567 
 568     if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled
 569          || ParallelRefProcEnabled)
 570         && num_queues > 0) {
 571       _task_queues = new OopTaskQueueSet(num_queues);
 572       if (_task_queues == NULL) {
 573         log_warning(gc)("task_queues allocation failure.");
 574         return;
 575       }
 576       typedef Padded<OopTaskQueue> PaddedOopTaskQueue;
 577       for (i = 0; i < num_queues; i++) {
 578         PaddedOopTaskQueue *q = new PaddedOopTaskQueue();
 579         if (q == NULL) {
 580           log_warning(gc)("work_queue allocation failure.");
 581           return;
 582         }
 583         _task_queues->register_queue(i, q);
 584       }
 585       for (i = 0; i < num_queues; i++) {
 586         _task_queues->queue(i)->initialize();
 587       }
 588     }
 589   }
 590 
 591   _cmsGen ->init_initiating_occupancy(CMSInitiatingOccupancyFraction, CMSTriggerRatio);
 592 
 593   // Clip CMSBootstrapOccupancy between 0 and 100.
 594   _bootstrap_occupancy = CMSBootstrapOccupancy / 100.0;
 595 
 596   // Now tell CMS generations the identity of their collector
 597   ConcurrentMarkSweepGeneration::set_collector(this);
 598 
 599   // Create & start a CMS thread for this CMS collector
 600   _cmsThread = ConcurrentMarkSweepThread::start(this);
 601   assert(cmsThread() != NULL, "CMS Thread should have been created");
 602   assert(cmsThread()->collector() == this,
 603          "CMS Thread should refer to this gen");
 604   assert(CGC_lock != NULL, "Where's the CGC_lock?");
 605 
 606   // Support for parallelizing young gen rescan
 607   CMSHeap* heap = CMSHeap::heap();
 608   _young_gen = heap->young_gen();
 609   if (heap->supports_inline_contig_alloc()) {
 610     _top_addr = heap->top_addr();
 611     _end_addr = heap->end_addr();
 612     assert(_young_gen != NULL, "no _young_gen");
 613     _eden_chunk_index = 0;
 614     _eden_chunk_capacity = (_young_gen->max_capacity() + CMSSamplingGrain) / CMSSamplingGrain;
 615     _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity, mtGC);
 616   }
 617 
 618   // Support for parallelizing survivor space rescan
 619   if ((CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) || CMSParallelInitialMarkEnabled) {
 620     const size_t max_plab_samples =
 621       _young_gen->max_survivor_size() / (PLAB::min_size() * HeapWordSize);
 622 
 623     _survivor_plab_array  = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads, mtGC);
 624     _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
 625     _cursor               = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads, mtGC);
 626     _survivor_chunk_capacity = max_plab_samples;
 627     for (uint i = 0; i < ParallelGCThreads; i++) {
 628       HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
 629       ChunkArray* cur = ::new (&_survivor_plab_array[i]) ChunkArray(vec, max_plab_samples);
 630       assert(cur->end() == 0, "Should be 0");
 631       assert(cur->array() == vec, "Should be vec");
 632       assert(cur->capacity() == max_plab_samples, "Error");
 633     }
 634   }
 635 
 636   NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;)
 637   _gc_counters = new CollectorCounters("CMS", 1);
 638   _cgc_counters = new CollectorCounters("CMS stop-the-world phases", 2);
 639   _completed_initialization = true;
 640   _inter_sweep_timer.start();  // start of time
 641 }
 642 
 643 const char* ConcurrentMarkSweepGeneration::name() const {
 644   return "concurrent mark-sweep generation";
 645 }
 646 void ConcurrentMarkSweepGeneration::update_counters() {
 647   if (UsePerfData) {
 648     _space_counters->update_all();
 649     _gen_counters->update_all();
 650   }
 651 }
 652 
 653 // this is an optimized version of update_counters(). it takes the
 654 // used value as a parameter rather than computing it.
 655 //
 656 void ConcurrentMarkSweepGeneration::update_counters(size_t used) {
 657   if (UsePerfData) {
 658     _space_counters->update_used(used);
 659     _space_counters->update_capacity();
 660     _gen_counters->update_all();
 661   }
 662 }
 663 
 664 void ConcurrentMarkSweepGeneration::print() const {
 665   Generation::print();
 666   cmsSpace()->print();
 667 }
 668 
 669 #ifndef PRODUCT
 670 void ConcurrentMarkSweepGeneration::print_statistics() {
 671   cmsSpace()->printFLCensus(0);
 672 }
 673 #endif
 674 
 675 size_t
 676 ConcurrentMarkSweepGeneration::contiguous_available() const {
 677   // dld proposes an improvement in precision here. If the committed
 678   // part of the space ends in a free block we should add that to
 679   // uncommitted size in the calculation below. Will make this
 680   // change later, staying with the approximation below for the
 681   // time being. -- ysr.
 682   return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc());
 683 }
 684 
 685 size_t
 686 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const {
 687   return _cmsSpace->max_alloc_in_words() * HeapWordSize;
 688 }
 689 
 690 size_t ConcurrentMarkSweepGeneration::max_available() const {
 691   return free() + _virtual_space.uncommitted_size();
 692 }
 693 
 694 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(size_t max_promotion_in_bytes) const {
 695   size_t available = max_available();
 696   size_t av_promo  = (size_t)gc_stats()->avg_promoted()->padded_average();
 697   bool   res = (available >= av_promo) || (available >= max_promotion_in_bytes);
 698   log_trace(gc, promotion)("CMS: promo attempt is%s safe: available(" SIZE_FORMAT ") %s av_promo(" SIZE_FORMAT "), max_promo(" SIZE_FORMAT ")",
 699                            res? "":" not", available, res? ">=":"<", av_promo, max_promotion_in_bytes);
 700   return res;
 701 }
 702 
 703 // At a promotion failure dump information on block layout in heap
 704 // (cms old generation).
 705 void ConcurrentMarkSweepGeneration::promotion_failure_occurred() {
 706   Log(gc, promotion) log;
 707   if (log.is_trace()) {
 708     LogStream ls(log.trace());
 709     cmsSpace()->dump_at_safepoint_with_locks(collector(), &ls);
 710   }
 711 }
 712 
 713 void ConcurrentMarkSweepGeneration::reset_after_compaction() {
 714   // Clear the promotion information.  These pointers can be adjusted
 715   // along with all the other pointers into the heap but
 716   // compaction is expected to be a rare event with
 717   // a heap using cms so don't do it without seeing the need.
 718   for (uint i = 0; i < ParallelGCThreads; i++) {
 719     _par_gc_thread_states[i]->promo.reset();
 720   }
 721 }
 722 
 723 void ConcurrentMarkSweepGeneration::compute_new_size() {
 724   assert_locked_or_safepoint(Heap_lock);
 725 
 726   // If incremental collection failed, we just want to expand
 727   // to the limit.
 728   if (incremental_collection_failed()) {
 729     clear_incremental_collection_failed();
 730     grow_to_reserved();
 731     return;
 732   }
 733 
 734   // The heap has been compacted but not reset yet.
 735   // Any metric such as free() or used() will be incorrect.
 736 
 737   CardGeneration::compute_new_size();
 738 
 739   // Reset again after a possible resizing
 740   if (did_compact()) {
 741     cmsSpace()->reset_after_compaction();
 742   }
 743 }
 744 
 745 void ConcurrentMarkSweepGeneration::compute_new_size_free_list() {
 746   assert_locked_or_safepoint(Heap_lock);
 747 
 748   // If incremental collection failed, we just want to expand
 749   // to the limit.
 750   if (incremental_collection_failed()) {
 751     clear_incremental_collection_failed();
 752     grow_to_reserved();
 753     return;
 754   }
 755 
 756   double free_percentage = ((double) free()) / capacity();
 757   double desired_free_percentage = (double) MinHeapFreeRatio / 100;
 758   double maximum_free_percentage = (double) MaxHeapFreeRatio / 100;
 759 
 760   // compute expansion delta needed for reaching desired free percentage
 761   if (free_percentage < desired_free_percentage) {
 762     size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
 763     assert(desired_capacity >= capacity(), "invalid expansion size");
 764     size_t expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes);
 765     Log(gc) log;
 766     if (log.is_trace()) {
 767       size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
 768       log.trace("From compute_new_size: ");
 769       log.trace("  Free fraction %f", free_percentage);
 770       log.trace("  Desired free fraction %f", desired_free_percentage);
 771       log.trace("  Maximum free fraction %f", maximum_free_percentage);
 772       log.trace("  Capacity " SIZE_FORMAT, capacity() / 1000);
 773       log.trace("  Desired capacity " SIZE_FORMAT, desired_capacity / 1000);
 774       CMSHeap* heap = CMSHeap::heap();
 775       size_t young_size = heap->young_gen()->capacity();
 776       log.trace("  Young gen size " SIZE_FORMAT, young_size / 1000);
 777       log.trace("  unsafe_max_alloc_nogc " SIZE_FORMAT, unsafe_max_alloc_nogc() / 1000);
 778       log.trace("  contiguous available " SIZE_FORMAT, contiguous_available() / 1000);
 779       log.trace("  Expand by " SIZE_FORMAT " (bytes)", expand_bytes);
 780     }
 781     // safe if expansion fails
 782     expand_for_gc_cause(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio);
 783     log.trace("  Expanded free fraction %f", ((double) free()) / capacity());
 784   } else {
 785     size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
 786     assert(desired_capacity <= capacity(), "invalid expansion size");
 787     size_t shrink_bytes = capacity() - desired_capacity;
 788     // Don't shrink unless the delta is greater than the minimum shrink we want
 789     if (shrink_bytes >= MinHeapDeltaBytes) {
 790       shrink_free_list_by(shrink_bytes);
 791     }
 792   }
 793 }
 794 
 795 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const {
 796   return cmsSpace()->freelistLock();
 797 }
 798 
 799 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size, bool tlab) {
 800   CMSSynchronousYieldRequest yr;
 801   MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
 802   return have_lock_and_allocate(size, tlab);
 803 }
 804 
 805 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size,
 806                                                                 bool   tlab /* ignored */) {
 807   assert_lock_strong(freelistLock());
 808   size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size);
 809   HeapWord* res = cmsSpace()->allocate(adjustedSize);
 810   // Allocate the object live (grey) if the background collector has
 811   // started marking. This is necessary because the marker may
 812   // have passed this address and consequently this object will
 813   // not otherwise be greyed and would be incorrectly swept up.
 814   // Note that if this object contains references, the writing
 815   // of those references will dirty the card containing this object
 816   // allowing the object to be blackened (and its references scanned)
 817   // either during a preclean phase or at the final checkpoint.
 818   if (res != NULL) {
 819     // We may block here with an uninitialized object with
 820     // its mark-bit or P-bits not yet set. Such objects need
 821     // to be safely navigable by block_start().
 822     assert(oop(res)->klass_or_null() == NULL, "Object should be uninitialized here.");
 823     assert(!((FreeChunk*)res)->is_free(), "Error, block will look free but show wrong size");
 824     collector()->direct_allocated(res, adjustedSize);
 825     _direct_allocated_words += adjustedSize;
 826     // allocation counters
 827     NOT_PRODUCT(
 828       _numObjectsAllocated++;
 829       _numWordsAllocated += (int)adjustedSize;
 830     )
 831   }
 832   return res;
 833 }
 834 
 835 // In the case of direct allocation by mutators in a generation that
 836 // is being concurrently collected, the object must be allocated
 837 // live (grey) if the background collector has started marking.
 838 // This is necessary because the marker may
 839 // have passed this address and consequently this object will
 840 // not otherwise be greyed and would be incorrectly swept up.
 841 // Note that if this object contains references, the writing
 842 // of those references will dirty the card containing this object
 843 // allowing the object to be blackened (and its references scanned)
 844 // either during a preclean phase or at the final checkpoint.
 845 void CMSCollector::direct_allocated(HeapWord* start, size_t size) {
 846   assert(_markBitMap.covers(start, size), "Out of bounds");
 847   if (_collectorState >= Marking) {
 848     MutexLockerEx y(_markBitMap.lock(),
 849                     Mutex::_no_safepoint_check_flag);
 850     // [see comments preceding SweepClosure::do_blk() below for details]
 851     //
 852     // Can the P-bits be deleted now?  JJJ
 853     //
 854     // 1. need to mark the object as live so it isn't collected
 855     // 2. need to mark the 2nd bit to indicate the object may be uninitialized
 856     // 3. need to mark the end of the object so marking, precleaning or sweeping
 857     //    can skip over uninitialized or unparsable objects. An allocated
 858     //    object is considered uninitialized for our purposes as long as
 859     //    its klass word is NULL.  All old gen objects are parsable
 860     //    as soon as they are initialized.)
 861     _markBitMap.mark(start);          // object is live
 862     _markBitMap.mark(start + 1);      // object is potentially uninitialized?
 863     _markBitMap.mark(start + size - 1);
 864                                       // mark end of object
 865   }
 866   // check that oop looks uninitialized
 867   assert(oop(start)->klass_or_null() == NULL, "_klass should be NULL");
 868 }
 869 
 870 void CMSCollector::promoted(bool par, HeapWord* start,
 871                             bool is_obj_array, size_t obj_size) {
 872   assert(_markBitMap.covers(start), "Out of bounds");
 873   // See comment in direct_allocated() about when objects should
 874   // be allocated live.
 875   if (_collectorState >= Marking) {
 876     // we already hold the marking bit map lock, taken in
 877     // the prologue
 878     if (par) {
 879       _markBitMap.par_mark(start);
 880     } else {
 881       _markBitMap.mark(start);
 882     }
 883     // We don't need to mark the object as uninitialized (as
 884     // in direct_allocated above) because this is being done with the
 885     // world stopped and the object will be initialized by the
 886     // time the marking, precleaning or sweeping get to look at it.
 887     // But see the code for copying objects into the CMS generation,
 888     // where we need to ensure that concurrent readers of the
 889     // block offset table are able to safely navigate a block that
 890     // is in flux from being free to being allocated (and in
 891     // transition while being copied into) and subsequently
 892     // becoming a bona-fide object when the copy/promotion is complete.
 893     assert(SafepointSynchronize::is_at_safepoint(),
 894            "expect promotion only at safepoints");
 895 
 896     if (_collectorState < Sweeping) {
 897       // Mark the appropriate cards in the modUnionTable, so that
 898       // this object gets scanned before the sweep. If this is
 899       // not done, CMS generation references in the object might
 900       // not get marked.
 901       // For the case of arrays, which are otherwise precisely
 902       // marked, we need to dirty the entire array, not just its head.
 903       if (is_obj_array) {
 904         // The [par_]mark_range() method expects mr.end() below to
 905         // be aligned to the granularity of a bit's representation
 906         // in the heap. In the case of the MUT below, that's a
 907         // card size.
 908         MemRegion mr(start,
 909                      align_up(start + obj_size,
 910                               CardTable::card_size /* bytes */));
 911         if (par) {
 912           _modUnionTable.par_mark_range(mr);
 913         } else {
 914           _modUnionTable.mark_range(mr);
 915         }
 916       } else {  // not an obj array; we can just mark the head
 917         if (par) {
 918           _modUnionTable.par_mark(start);
 919         } else {
 920           _modUnionTable.mark(start);
 921         }
 922       }
 923     }
 924   }
 925 }
 926 
 927 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size) {
 928   assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
 929   // allocate, copy and if necessary update promoinfo --
 930   // delegate to underlying space.
 931   assert_lock_strong(freelistLock());
 932 
 933 #ifndef PRODUCT
 934   if (CMSHeap::heap()->promotion_should_fail()) {
 935     return NULL;
 936   }
 937 #endif  // #ifndef PRODUCT
 938 
 939   oop res = _cmsSpace->promote(obj, obj_size);
 940   if (res == NULL) {
 941     // expand and retry
 942     size_t s = _cmsSpace->expansionSpaceRequired(obj_size);  // HeapWords
 943     expand_for_gc_cause(s*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_promotion);
 944     // Since this is the old generation, we don't try to promote
 945     // into a more senior generation.
 946     res = _cmsSpace->promote(obj, obj_size);
 947   }
 948   if (res != NULL) {
 949     // See comment in allocate() about when objects should
 950     // be allocated live.
 951     assert(oopDesc::is_oop(obj), "Will dereference klass pointer below");
 952     collector()->promoted(false,           // Not parallel
 953                           (HeapWord*)res, obj->is_objArray(), obj_size);
 954     // promotion counters
 955     NOT_PRODUCT(
 956       _numObjectsPromoted++;
 957       _numWordsPromoted +=
 958         (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size()));
 959     )
 960   }
 961   return res;
 962 }
 963 
 964 
 965 // IMPORTANT: Notes on object size recognition in CMS.
 966 // ---------------------------------------------------
 967 // A block of storage in the CMS generation is always in
 968 // one of three states. A free block (FREE), an allocated
 969 // object (OBJECT) whose size() method reports the correct size,
 970 // and an intermediate state (TRANSIENT) in which its size cannot
 971 // be accurately determined.
 972 // STATE IDENTIFICATION:   (32 bit and 64 bit w/o COOPS)
 973 // -----------------------------------------------------
 974 // FREE:      klass_word & 1 == 1; mark_word holds block size
 975 //
 976 // OBJECT:    klass_word installed; klass_word != 0 && klass_word & 1 == 0;
 977 //            obj->size() computes correct size
 978 //
 979 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
 980 //
 981 // STATE IDENTIFICATION: (64 bit+COOPS)
 982 // ------------------------------------
 983 // FREE:      mark_word & CMS_FREE_BIT == 1; mark_word & ~CMS_FREE_BIT gives block_size
 984 //
 985 // OBJECT:    klass_word installed; klass_word != 0;
 986 //            obj->size() computes correct size
 987 //
 988 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
 989 //
 990 //
 991 // STATE TRANSITION DIAGRAM
 992 //
 993 //        mut / parnew                     mut  /  parnew
 994 // FREE --------------------> TRANSIENT ---------------------> OBJECT --|
 995 //  ^                                                                   |
 996 //  |------------------------ DEAD <------------------------------------|
 997 //         sweep                            mut
 998 //
 999 // While a block is in TRANSIENT state its size cannot be determined
1000 // so readers will either need to come back later or stall until
1001 // the size can be determined. Note that for the case of direct
1002 // allocation, P-bits, when available, may be used to determine the
1003 // size of an object that may not yet have been initialized.
1004 
1005 // Things to support parallel young-gen collection.
1006 oop
1007 ConcurrentMarkSweepGeneration::par_promote(int thread_num,
1008                                            oop old, markOop m,
1009                                            size_t word_sz) {
1010 #ifndef PRODUCT
1011   if (CMSHeap::heap()->promotion_should_fail()) {
1012     return NULL;
1013   }
1014 #endif  // #ifndef PRODUCT
1015 
1016   CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1017   PromotionInfo* promoInfo = &ps->promo;
1018   // if we are tracking promotions, then first ensure space for
1019   // promotion (including spooling space for saving header if necessary).
1020   // then allocate and copy, then track promoted info if needed.
1021   // When tracking (see PromotionInfo::track()), the mark word may
1022   // be displaced and in this case restoration of the mark word
1023   // occurs in the (oop_since_save_marks_)iterate phase.
1024   if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) {
1025     // Out of space for allocating spooling buffers;
1026     // try expanding and allocating spooling buffers.
1027     if (!expand_and_ensure_spooling_space(promoInfo)) {
1028       return NULL;
1029     }
1030   }
1031   assert(!promoInfo->tracking() || promoInfo->has_spooling_space(), "Control point invariant");
1032   const size_t alloc_sz = CompactibleFreeListSpace::adjustObjectSize(word_sz);
1033   HeapWord* obj_ptr = ps->lab.alloc(alloc_sz);
1034   if (obj_ptr == NULL) {
1035      obj_ptr = expand_and_par_lab_allocate(ps, alloc_sz);
1036      if (obj_ptr == NULL) {
1037        return NULL;
1038      }
1039   }
1040   oop obj = oop(obj_ptr);
1041   OrderAccess::storestore();
1042   assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1043   assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1044   // IMPORTANT: See note on object initialization for CMS above.
1045   // Otherwise, copy the object.  Here we must be careful to insert the
1046   // klass pointer last, since this marks the block as an allocated object.
1047   // Except with compressed oops it's the mark word.
1048   HeapWord* old_ptr = (HeapWord*)old;
1049   // Restore the mark word copied above.
1050   obj->set_mark_raw(m);
1051   assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1052   assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1053   OrderAccess::storestore();
1054 
1055   if (UseCompressedClassPointers) {
1056     // Copy gap missed by (aligned) header size calculation below
1057     obj->set_klass_gap(old->klass_gap());
1058   }
1059   if (word_sz > (size_t)oopDesc::header_size()) {
1060     Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1061                                  obj_ptr + oopDesc::header_size(),
1062                                  word_sz - oopDesc::header_size());
1063   }
1064 
1065   // Now we can track the promoted object, if necessary.  We take care
1066   // to delay the transition from uninitialized to full object
1067   // (i.e., insertion of klass pointer) until after, so that it
1068   // atomically becomes a promoted object.
1069   if (promoInfo->tracking()) {
1070     promoInfo->track((PromotedObject*)obj, old->klass());
1071   }
1072   assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1073   assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1074   assert(oopDesc::is_oop(old), "Will use and dereference old klass ptr below");
1075 
1076   // Finally, install the klass pointer (this should be volatile).
1077   OrderAccess::storestore();
1078   obj->set_klass(old->klass());
1079   // We should now be able to calculate the right size for this object
1080   assert(oopDesc::is_oop(obj) && obj->size() == (int)word_sz, "Error, incorrect size computed for promoted object");
1081 
1082   collector()->promoted(true,          // parallel
1083                         obj_ptr, old->is_objArray(), word_sz);
1084 
1085   NOT_PRODUCT(
1086     Atomic::inc(&_numObjectsPromoted);
1087     Atomic::add(alloc_sz, &_numWordsPromoted);
1088   )
1089 
1090   return obj;
1091 }
1092 
1093 void
1094 ConcurrentMarkSweepGeneration::
1095 par_promote_alloc_done(int thread_num) {
1096   CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1097   ps->lab.retire(thread_num);
1098 }
1099 
1100 void
1101 ConcurrentMarkSweepGeneration::
1102 par_oop_since_save_marks_iterate_done(int thread_num) {
1103   CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1104   ParScanWithoutBarrierClosure* dummy_cl = NULL;
1105   ps->promo.promoted_oops_iterate(dummy_cl);
1106 
1107   // Because card-scanning has been completed, subsequent phases
1108   // (e.g., reference processing) will not need to recognize which
1109   // objects have been promoted during this GC. So, we can now disable
1110   // promotion tracking.
1111   ps->promo.stopTrackingPromotions();
1112 }
1113 
1114 bool ConcurrentMarkSweepGeneration::should_collect(bool   full,
1115                                                    size_t size,
1116                                                    bool   tlab)
1117 {
1118   // We allow a STW collection only if a full
1119   // collection was requested.
1120   return full || should_allocate(size, tlab); // FIX ME !!!
1121   // This and promotion failure handling are connected at the
1122   // hip and should be fixed by untying them.
1123 }
1124 
1125 bool CMSCollector::shouldConcurrentCollect() {
1126   LogTarget(Trace, gc) log;
1127 
1128   if (_full_gc_requested) {
1129     log.print("CMSCollector: collect because of explicit  gc request (or GCLocker)");
1130     return true;
1131   }
1132 
1133   FreelistLocker x(this);
1134   // ------------------------------------------------------------------
1135   // Print out lots of information which affects the initiation of
1136   // a collection.
1137   if (log.is_enabled() && stats().valid()) {
1138     log.print("CMSCollector shouldConcurrentCollect: ");
1139 
1140     LogStream out(log);
1141     stats().print_on(&out);
1142 
1143     log.print("time_until_cms_gen_full %3.7f", stats().time_until_cms_gen_full());
1144     log.print("free=" SIZE_FORMAT, _cmsGen->free());
1145     log.print("contiguous_available=" SIZE_FORMAT, _cmsGen->contiguous_available());
1146     log.print("promotion_rate=%g", stats().promotion_rate());
1147     log.print("cms_allocation_rate=%g", stats().cms_allocation_rate());
1148     log.print("occupancy=%3.7f", _cmsGen->occupancy());
1149     log.print("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy());
1150     log.print("cms_time_since_begin=%3.7f", stats().cms_time_since_begin());
1151     log.print("cms_time_since_end=%3.7f", stats().cms_time_since_end());
1152     log.print("metadata initialized %d", MetaspaceGC::should_concurrent_collect());
1153   }
1154   // ------------------------------------------------------------------
1155 
1156   // If the estimated time to complete a cms collection (cms_duration())
1157   // is less than the estimated time remaining until the cms generation
1158   // is full, start a collection.
1159   if (!UseCMSInitiatingOccupancyOnly) {
1160     if (stats().valid()) {
1161       if (stats().time_until_cms_start() == 0.0) {
1162         return true;
1163       }
1164     } else {
1165       // We want to conservatively collect somewhat early in order
1166       // to try and "bootstrap" our CMS/promotion statistics;
1167       // this branch will not fire after the first successful CMS
1168       // collection because the stats should then be valid.
1169       if (_cmsGen->occupancy() >= _bootstrap_occupancy) {
1170         log.print(" CMSCollector: collect for bootstrapping statistics: occupancy = %f, boot occupancy = %f",
1171                   _cmsGen->occupancy(), _bootstrap_occupancy);
1172         return true;
1173       }
1174     }
1175   }
1176 
1177   // Otherwise, we start a collection cycle if
1178   // old gen want a collection cycle started. Each may use
1179   // an appropriate criterion for making this decision.
1180   // XXX We need to make sure that the gen expansion
1181   // criterion dovetails well with this. XXX NEED TO FIX THIS
1182   if (_cmsGen->should_concurrent_collect()) {
1183     log.print("CMS old gen initiated");
1184     return true;
1185   }
1186 
1187   // We start a collection if we believe an incremental collection may fail;
1188   // this is not likely to be productive in practice because it's probably too
1189   // late anyway.
1190   CMSHeap* heap = CMSHeap::heap();
1191   if (heap->incremental_collection_will_fail(true /* consult_young */)) {
1192     log.print("CMSCollector: collect because incremental collection will fail ");
1193     return true;
1194   }
1195 
1196   if (MetaspaceGC::should_concurrent_collect()) {
1197     log.print("CMSCollector: collect for metadata allocation ");
1198     return true;
1199   }
1200 
1201   // CMSTriggerInterval starts a CMS cycle if enough time has passed.
1202   if (CMSTriggerInterval >= 0) {
1203     if (CMSTriggerInterval == 0) {
1204       // Trigger always
1205       return true;
1206     }
1207 
1208     // Check the CMS time since begin (we do not check the stats validity
1209     // as we want to be able to trigger the first CMS cycle as well)
1210     if (stats().cms_time_since_begin() >= (CMSTriggerInterval / ((double) MILLIUNITS))) {
1211       if (stats().valid()) {
1212         log.print("CMSCollector: collect because of trigger interval (time since last begin %3.7f secs)",
1213                   stats().cms_time_since_begin());
1214       } else {
1215         log.print("CMSCollector: collect because of trigger interval (first collection)");
1216       }
1217       return true;
1218     }
1219   }
1220 
1221   return false;
1222 }
1223 
1224 void CMSCollector::set_did_compact(bool v) { _cmsGen->set_did_compact(v); }
1225 
1226 // Clear _expansion_cause fields of constituent generations
1227 void CMSCollector::clear_expansion_cause() {
1228   _cmsGen->clear_expansion_cause();
1229 }
1230 
1231 // We should be conservative in starting a collection cycle.  To
1232 // start too eagerly runs the risk of collecting too often in the
1233 // extreme.  To collect too rarely falls back on full collections,
1234 // which works, even if not optimum in terms of concurrent work.
1235 // As a work around for too eagerly collecting, use the flag
1236 // UseCMSInitiatingOccupancyOnly.  This also has the advantage of
1237 // giving the user an easily understandable way of controlling the
1238 // collections.
1239 // We want to start a new collection cycle if any of the following
1240 // conditions hold:
1241 // . our current occupancy exceeds the configured initiating occupancy
1242 //   for this generation, or
1243 // . we recently needed to expand this space and have not, since that
1244 //   expansion, done a collection of this generation, or
1245 // . the underlying space believes that it may be a good idea to initiate
1246 //   a concurrent collection (this may be based on criteria such as the
1247 //   following: the space uses linear allocation and linear allocation is
1248 //   going to fail, or there is believed to be excessive fragmentation in
1249 //   the generation, etc... or ...
1250 // [.(currently done by CMSCollector::shouldConcurrentCollect() only for
1251 //   the case of the old generation; see CR 6543076):
1252 //   we may be approaching a point at which allocation requests may fail because
1253 //   we will be out of sufficient free space given allocation rate estimates.]
1254 bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const {
1255 
1256   assert_lock_strong(freelistLock());
1257   if (occupancy() > initiating_occupancy()) {
1258     log_trace(gc)(" %s: collect because of occupancy %f / %f  ",
1259                   short_name(), occupancy(), initiating_occupancy());
1260     return true;
1261   }
1262   if (UseCMSInitiatingOccupancyOnly) {
1263     return false;
1264   }
1265   if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) {
1266     log_trace(gc)(" %s: collect because expanded for allocation ", short_name());
1267     return true;
1268   }
1269   return false;
1270 }
1271 
1272 void ConcurrentMarkSweepGeneration::collect(bool   full,
1273                                             bool   clear_all_soft_refs,
1274                                             size_t size,
1275                                             bool   tlab)
1276 {
1277   collector()->collect(full, clear_all_soft_refs, size, tlab);
1278 }
1279 
1280 void CMSCollector::collect(bool   full,
1281                            bool   clear_all_soft_refs,
1282                            size_t size,
1283                            bool   tlab)
1284 {
1285   // The following "if" branch is present for defensive reasons.
1286   // In the current uses of this interface, it can be replaced with:
1287   // assert(!GCLocker.is_active(), "Can't be called otherwise");
1288   // But I am not placing that assert here to allow future
1289   // generality in invoking this interface.
1290   if (GCLocker::is_active()) {
1291     // A consistency test for GCLocker
1292     assert(GCLocker::needs_gc(), "Should have been set already");
1293     // Skip this foreground collection, instead
1294     // expanding the heap if necessary.
1295     // Need the free list locks for the call to free() in compute_new_size()
1296     compute_new_size();
1297     return;
1298   }
1299   acquire_control_and_collect(full, clear_all_soft_refs);
1300 }
1301 
1302 void CMSCollector::request_full_gc(unsigned int full_gc_count, GCCause::Cause cause) {
1303   CMSHeap* heap = CMSHeap::heap();
1304   unsigned int gc_count = heap->total_full_collections();
1305   if (gc_count == full_gc_count) {
1306     MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag);
1307     _full_gc_requested = true;
1308     _full_gc_cause = cause;
1309     CGC_lock->notify();   // nudge CMS thread
1310   } else {
1311     assert(gc_count > full_gc_count, "Error: causal loop");
1312   }
1313 }
1314 
1315 bool CMSCollector::is_external_interruption() {
1316   GCCause::Cause cause = CMSHeap::heap()->gc_cause();
1317   return GCCause::is_user_requested_gc(cause) ||
1318          GCCause::is_serviceability_requested_gc(cause);
1319 }
1320 
1321 void CMSCollector::report_concurrent_mode_interruption() {
1322   if (is_external_interruption()) {
1323     log_debug(gc)("Concurrent mode interrupted");
1324   } else {
1325     log_debug(gc)("Concurrent mode failure");
1326     _gc_tracer_cm->report_concurrent_mode_failure();
1327   }
1328 }
1329 
1330 
1331 // The foreground and background collectors need to coordinate in order
1332 // to make sure that they do not mutually interfere with CMS collections.
1333 // When a background collection is active,
1334 // the foreground collector may need to take over (preempt) and
1335 // synchronously complete an ongoing collection. Depending on the
1336 // frequency of the background collections and the heap usage
1337 // of the application, this preemption can be seldom or frequent.
1338 // There are only certain
1339 // points in the background collection that the "collection-baton"
1340 // can be passed to the foreground collector.
1341 //
1342 // The foreground collector will wait for the baton before
1343 // starting any part of the collection.  The foreground collector
1344 // will only wait at one location.
1345 //
1346 // The background collector will yield the baton before starting a new
1347 // phase of the collection (e.g., before initial marking, marking from roots,
1348 // precleaning, final re-mark, sweep etc.)  This is normally done at the head
1349 // of the loop which switches the phases. The background collector does some
1350 // of the phases (initial mark, final re-mark) with the world stopped.
1351 // Because of locking involved in stopping the world,
1352 // the foreground collector should not block waiting for the background
1353 // collector when it is doing a stop-the-world phase.  The background
1354 // collector will yield the baton at an additional point just before
1355 // it enters a stop-the-world phase.  Once the world is stopped, the
1356 // background collector checks the phase of the collection.  If the
1357 // phase has not changed, it proceeds with the collection.  If the
1358 // phase has changed, it skips that phase of the collection.  See
1359 // the comments on the use of the Heap_lock in collect_in_background().
1360 //
1361 // Variable used in baton passing.
1362 //   _foregroundGCIsActive - Set to true by the foreground collector when
1363 //      it wants the baton.  The foreground clears it when it has finished
1364 //      the collection.
1365 //   _foregroundGCShouldWait - Set to true by the background collector
1366 //        when it is running.  The foreground collector waits while
1367 //      _foregroundGCShouldWait is true.
1368 //  CGC_lock - monitor used to protect access to the above variables
1369 //      and to notify the foreground and background collectors.
1370 //  _collectorState - current state of the CMS collection.
1371 //
1372 // The foreground collector
1373 //   acquires the CGC_lock
1374 //   sets _foregroundGCIsActive
1375 //   waits on the CGC_lock for _foregroundGCShouldWait to be false
1376 //     various locks acquired in preparation for the collection
1377 //     are released so as not to block the background collector
1378 //     that is in the midst of a collection
1379 //   proceeds with the collection
1380 //   clears _foregroundGCIsActive
1381 //   returns
1382 //
1383 // The background collector in a loop iterating on the phases of the
1384 //      collection
1385 //   acquires the CGC_lock
1386 //   sets _foregroundGCShouldWait
1387 //   if _foregroundGCIsActive is set
1388 //     clears _foregroundGCShouldWait, notifies _CGC_lock
1389 //     waits on _CGC_lock for _foregroundGCIsActive to become false
1390 //     and exits the loop.
1391 //   otherwise
1392 //     proceed with that phase of the collection
1393 //     if the phase is a stop-the-world phase,
1394 //       yield the baton once more just before enqueueing
1395 //       the stop-world CMS operation (executed by the VM thread).
1396 //   returns after all phases of the collection are done
1397 //
1398 
1399 void CMSCollector::acquire_control_and_collect(bool full,
1400         bool clear_all_soft_refs) {
1401   assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
1402   assert(!Thread::current()->is_ConcurrentGC_thread(),
1403          "shouldn't try to acquire control from self!");
1404 
1405   // Start the protocol for acquiring control of the
1406   // collection from the background collector (aka CMS thread).
1407   assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1408          "VM thread should have CMS token");
1409   // Remember the possibly interrupted state of an ongoing
1410   // concurrent collection
1411   CollectorState first_state = _collectorState;
1412 
1413   // Signal to a possibly ongoing concurrent collection that
1414   // we want to do a foreground collection.
1415   _foregroundGCIsActive = true;
1416 
1417   // release locks and wait for a notify from the background collector
1418   // releasing the locks in only necessary for phases which
1419   // do yields to improve the granularity of the collection.
1420   assert_lock_strong(bitMapLock());
1421   // We need to lock the Free list lock for the space that we are
1422   // currently collecting.
1423   assert(haveFreelistLocks(), "Must be holding free list locks");
1424   bitMapLock()->unlock();
1425   releaseFreelistLocks();
1426   {
1427     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1428     if (_foregroundGCShouldWait) {
1429       // We are going to be waiting for action for the CMS thread;
1430       // it had better not be gone (for instance at shutdown)!
1431       assert(ConcurrentMarkSweepThread::cmst() != NULL && !ConcurrentMarkSweepThread::cmst()->has_terminated(),
1432              "CMS thread must be running");
1433       // Wait here until the background collector gives us the go-ahead
1434       ConcurrentMarkSweepThread::clear_CMS_flag(
1435         ConcurrentMarkSweepThread::CMS_vm_has_token);  // release token
1436       // Get a possibly blocked CMS thread going:
1437       //   Note that we set _foregroundGCIsActive true above,
1438       //   without protection of the CGC_lock.
1439       CGC_lock->notify();
1440       assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(),
1441              "Possible deadlock");
1442       while (_foregroundGCShouldWait) {
1443         // wait for notification
1444         CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1445         // Possibility of delay/starvation here, since CMS token does
1446         // not know to give priority to VM thread? Actually, i think
1447         // there wouldn't be any delay/starvation, but the proof of
1448         // that "fact" (?) appears non-trivial. XXX 20011219YSR
1449       }
1450       ConcurrentMarkSweepThread::set_CMS_flag(
1451         ConcurrentMarkSweepThread::CMS_vm_has_token);
1452     }
1453   }
1454   // The CMS_token is already held.  Get back the other locks.
1455   assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1456          "VM thread should have CMS token");
1457   getFreelistLocks();
1458   bitMapLock()->lock_without_safepoint_check();
1459   log_debug(gc, state)("CMS foreground collector has asked for control " INTPTR_FORMAT " with first state %d",
1460                        p2i(Thread::current()), first_state);
1461   log_debug(gc, state)("    gets control with state %d", _collectorState);
1462 
1463   // Inform cms gen if this was due to partial collection failing.
1464   // The CMS gen may use this fact to determine its expansion policy.
1465   CMSHeap* heap = CMSHeap::heap();
1466   if (heap->incremental_collection_will_fail(false /* don't consult_young */)) {
1467     assert(!_cmsGen->incremental_collection_failed(),
1468            "Should have been noticed, reacted to and cleared");
1469     _cmsGen->set_incremental_collection_failed();
1470   }
1471 
1472   if (first_state > Idling) {
1473     report_concurrent_mode_interruption();
1474   }
1475 
1476   set_did_compact(true);
1477 
1478   // If the collection is being acquired from the background
1479   // collector, there may be references on the discovered
1480   // references lists.  Abandon those references, since some
1481   // of them may have become unreachable after concurrent
1482   // discovery; the STW compacting collector will redo discovery
1483   // more precisely, without being subject to floating garbage.
1484   // Leaving otherwise unreachable references in the discovered
1485   // lists would require special handling.
1486   ref_processor()->disable_discovery();
1487   ref_processor()->abandon_partial_discovery();
1488   ref_processor()->verify_no_references_recorded();
1489 
1490   if (first_state > Idling) {
1491     save_heap_summary();
1492   }
1493 
1494   do_compaction_work(clear_all_soft_refs);
1495 
1496   // Has the GC time limit been exceeded?
1497   size_t max_eden_size = _young_gen->max_eden_size();
1498   GCCause::Cause gc_cause = heap->gc_cause();
1499   size_policy()->check_gc_overhead_limit(_young_gen->used(),
1500                                          _young_gen->eden()->used(),
1501                                          _cmsGen->max_capacity(),
1502                                          max_eden_size,
1503                                          full,
1504                                          gc_cause,
1505                                          heap->soft_ref_policy());
1506 
1507   // Reset the expansion cause, now that we just completed
1508   // a collection cycle.
1509   clear_expansion_cause();
1510   _foregroundGCIsActive = false;
1511   return;
1512 }
1513 
1514 // Resize the tenured generation
1515 // after obtaining the free list locks for the
1516 // two generations.
1517 void CMSCollector::compute_new_size() {
1518   assert_locked_or_safepoint(Heap_lock);
1519   FreelistLocker z(this);
1520   MetaspaceGC::compute_new_size();
1521   _cmsGen->compute_new_size_free_list();
1522 }
1523 
1524 // A work method used by the foreground collector to do
1525 // a mark-sweep-compact.
1526 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) {
1527   CMSHeap* heap = CMSHeap::heap();
1528 
1529   STWGCTimer* gc_timer = GenMarkSweep::gc_timer();
1530   gc_timer->register_gc_start();
1531 
1532   SerialOldTracer* gc_tracer = GenMarkSweep::gc_tracer();
1533   gc_tracer->report_gc_start(heap->gc_cause(), gc_timer->gc_start());
1534 
1535   heap->pre_full_gc_dump(gc_timer);
1536 
1537   GCTraceTime(Trace, gc, phases) t("CMS:MSC");
1538 
1539   // Temporarily widen the span of the weak reference processing to
1540   // the entire heap.
1541   MemRegion new_span(CMSHeap::heap()->reserved_region());
1542   ReferenceProcessorSpanMutator rp_mut_span(ref_processor(), new_span);
1543   // Temporarily, clear the "is_alive_non_header" field of the
1544   // reference processor.
1545   ReferenceProcessorIsAliveMutator rp_mut_closure(ref_processor(), NULL);
1546   // Temporarily make reference _processing_ single threaded (non-MT).
1547   ReferenceProcessorMTProcMutator rp_mut_mt_processing(ref_processor(), false);
1548   // Temporarily make refs discovery atomic
1549   ReferenceProcessorAtomicMutator rp_mut_atomic(ref_processor(), true);
1550   // Temporarily make reference _discovery_ single threaded (non-MT)
1551   ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
1552 
1553   ref_processor()->set_enqueuing_is_done(false);
1554   ref_processor()->enable_discovery();
1555   ref_processor()->setup_policy(clear_all_soft_refs);
1556   // If an asynchronous collection finishes, the _modUnionTable is
1557   // all clear.  If we are assuming the collection from an asynchronous
1558   // collection, clear the _modUnionTable.
1559   assert(_collectorState != Idling || _modUnionTable.isAllClear(),
1560     "_modUnionTable should be clear if the baton was not passed");
1561   _modUnionTable.clear_all();
1562   assert(_collectorState != Idling || _ct->cld_rem_set()->mod_union_is_clear(),
1563     "mod union for klasses should be clear if the baton was passed");
1564   _ct->cld_rem_set()->clear_mod_union();
1565 
1566 
1567   // We must adjust the allocation statistics being maintained
1568   // in the free list space. We do so by reading and clearing
1569   // the sweep timer and updating the block flux rate estimates below.
1570   assert(!_intra_sweep_timer.is_active(), "_intra_sweep_timer should be inactive");
1571   if (_inter_sweep_timer.is_active()) {
1572     _inter_sweep_timer.stop();
1573     // Note that we do not use this sample to update the _inter_sweep_estimate.
1574     _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
1575                                             _inter_sweep_estimate.padded_average(),
1576                                             _intra_sweep_estimate.padded_average());
1577   }
1578 
1579   GenMarkSweep::invoke_at_safepoint(ref_processor(), clear_all_soft_refs);
1580   #ifdef ASSERT
1581     CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
1582     size_t free_size = cms_space->free();
1583     assert(free_size ==
1584            pointer_delta(cms_space->end(), cms_space->compaction_top())
1585            * HeapWordSize,
1586       "All the free space should be compacted into one chunk at top");
1587     assert(cms_space->dictionary()->total_chunk_size(
1588                                       debug_only(cms_space->freelistLock())) == 0 ||
1589            cms_space->totalSizeInIndexedFreeLists() == 0,
1590       "All the free space should be in a single chunk");
1591     size_t num = cms_space->totalCount();
1592     assert((free_size == 0 && num == 0) ||
1593            (free_size > 0  && (num == 1 || num == 2)),
1594          "There should be at most 2 free chunks after compaction");
1595   #endif // ASSERT
1596   _collectorState = Resetting;
1597   assert(_restart_addr == NULL,
1598          "Should have been NULL'd before baton was passed");
1599   reset_stw();
1600   _cmsGen->reset_after_compaction();
1601   _concurrent_cycles_since_last_unload = 0;
1602 
1603   // Clear any data recorded in the PLAB chunk arrays.
1604   if (_survivor_plab_array != NULL) {
1605     reset_survivor_plab_arrays();
1606   }
1607 
1608   // Adjust the per-size allocation stats for the next epoch.
1609   _cmsGen->cmsSpace()->endSweepFLCensus(sweep_count() /* fake */);
1610   // Restart the "inter sweep timer" for the next epoch.
1611   _inter_sweep_timer.reset();
1612   _inter_sweep_timer.start();
1613 
1614   // No longer a need to do a concurrent collection for Metaspace.
1615   MetaspaceGC::set_should_concurrent_collect(false);
1616 
1617   heap->post_full_gc_dump(gc_timer);
1618 
1619   gc_timer->register_gc_end();
1620 
1621   gc_tracer->report_gc_end(gc_timer->gc_end(), gc_timer->time_partitions());
1622 
1623   // For a mark-sweep-compact, compute_new_size() will be called
1624   // in the heap's do_collection() method.
1625 }
1626 
1627 void CMSCollector::print_eden_and_survivor_chunk_arrays() {
1628   Log(gc, heap) log;
1629   if (!log.is_trace()) {
1630     return;
1631   }
1632 
1633   ContiguousSpace* eden_space = _young_gen->eden();
1634   ContiguousSpace* from_space = _young_gen->from();
1635   ContiguousSpace* to_space   = _young_gen->to();
1636   // Eden
1637   if (_eden_chunk_array != NULL) {
1638     log.trace("eden " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1639               p2i(eden_space->bottom()), p2i(eden_space->top()),
1640               p2i(eden_space->end()), eden_space->capacity());
1641     log.trace("_eden_chunk_index=" SIZE_FORMAT ", _eden_chunk_capacity=" SIZE_FORMAT,
1642               _eden_chunk_index, _eden_chunk_capacity);
1643     for (size_t i = 0; i < _eden_chunk_index; i++) {
1644       log.trace("_eden_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT, i, p2i(_eden_chunk_array[i]));
1645     }
1646   }
1647   // Survivor
1648   if (_survivor_chunk_array != NULL) {
1649     log.trace("survivor " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1650               p2i(from_space->bottom()), p2i(from_space->top()),
1651               p2i(from_space->end()), from_space->capacity());
1652     log.trace("_survivor_chunk_index=" SIZE_FORMAT ", _survivor_chunk_capacity=" SIZE_FORMAT,
1653               _survivor_chunk_index, _survivor_chunk_capacity);
1654     for (size_t i = 0; i < _survivor_chunk_index; i++) {
1655       log.trace("_survivor_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT, i, p2i(_survivor_chunk_array[i]));
1656     }
1657   }
1658 }
1659 
1660 void CMSCollector::getFreelistLocks() const {
1661   // Get locks for all free lists in all generations that this
1662   // collector is responsible for
1663   _cmsGen->freelistLock()->lock_without_safepoint_check();
1664 }
1665 
1666 void CMSCollector::releaseFreelistLocks() const {
1667   // Release locks for all free lists in all generations that this
1668   // collector is responsible for
1669   _cmsGen->freelistLock()->unlock();
1670 }
1671 
1672 bool CMSCollector::haveFreelistLocks() const {
1673   // Check locks for all free lists in all generations that this
1674   // collector is responsible for
1675   assert_lock_strong(_cmsGen->freelistLock());
1676   PRODUCT_ONLY(ShouldNotReachHere());
1677   return true;
1678 }
1679 
1680 // A utility class that is used by the CMS collector to
1681 // temporarily "release" the foreground collector from its
1682 // usual obligation to wait for the background collector to
1683 // complete an ongoing phase before proceeding.
1684 class ReleaseForegroundGC: public StackObj {
1685  private:
1686   CMSCollector* _c;
1687  public:
1688   ReleaseForegroundGC(CMSCollector* c) : _c(c) {
1689     assert(_c->_foregroundGCShouldWait, "Else should not need to call");
1690     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1691     // allow a potentially blocked foreground collector to proceed
1692     _c->_foregroundGCShouldWait = false;
1693     if (_c->_foregroundGCIsActive) {
1694       CGC_lock->notify();
1695     }
1696     assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1697            "Possible deadlock");
1698   }
1699 
1700   ~ReleaseForegroundGC() {
1701     assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?");
1702     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1703     _c->_foregroundGCShouldWait = true;
1704   }
1705 };
1706 
1707 void CMSCollector::collect_in_background(GCCause::Cause cause) {
1708   assert(Thread::current()->is_ConcurrentGC_thread(),
1709     "A CMS asynchronous collection is only allowed on a CMS thread.");
1710 
1711   CMSHeap* heap = CMSHeap::heap();
1712   {
1713     bool safepoint_check = Mutex::_no_safepoint_check_flag;
1714     MutexLockerEx hl(Heap_lock, safepoint_check);
1715     FreelistLocker fll(this);
1716     MutexLockerEx x(CGC_lock, safepoint_check);
1717     if (_foregroundGCIsActive) {
1718       // The foreground collector is. Skip this
1719       // background collection.
1720       assert(!_foregroundGCShouldWait, "Should be clear");
1721       return;
1722     } else {
1723       assert(_collectorState == Idling, "Should be idling before start.");
1724       _collectorState = InitialMarking;
1725       register_gc_start(cause);
1726       // Reset the expansion cause, now that we are about to begin
1727       // a new cycle.
1728       clear_expansion_cause();
1729 
1730       // Clear the MetaspaceGC flag since a concurrent collection
1731       // is starting but also clear it after the collection.
1732       MetaspaceGC::set_should_concurrent_collect(false);
1733     }
1734     // Decide if we want to enable class unloading as part of the
1735     // ensuing concurrent GC cycle.
1736     update_should_unload_classes();
1737     _full_gc_requested = false;           // acks all outstanding full gc requests
1738     _full_gc_cause = GCCause::_no_gc;
1739     // Signal that we are about to start a collection
1740     heap->increment_total_full_collections();  // ... starting a collection cycle
1741     _collection_count_start = heap->total_full_collections();
1742   }
1743 
1744   size_t prev_used = _cmsGen->used();
1745 
1746   // The change of the collection state is normally done at this level;
1747   // the exceptions are phases that are executed while the world is
1748   // stopped.  For those phases the change of state is done while the
1749   // world is stopped.  For baton passing purposes this allows the
1750   // background collector to finish the phase and change state atomically.
1751   // The foreground collector cannot wait on a phase that is done
1752   // while the world is stopped because the foreground collector already
1753   // has the world stopped and would deadlock.
1754   while (_collectorState != Idling) {
1755     log_debug(gc, state)("Thread " INTPTR_FORMAT " in CMS state %d",
1756                          p2i(Thread::current()), _collectorState);
1757     // The foreground collector
1758     //   holds the Heap_lock throughout its collection.
1759     //   holds the CMS token (but not the lock)
1760     //     except while it is waiting for the background collector to yield.
1761     //
1762     // The foreground collector should be blocked (not for long)
1763     //   if the background collector is about to start a phase
1764     //   executed with world stopped.  If the background
1765     //   collector has already started such a phase, the
1766     //   foreground collector is blocked waiting for the
1767     //   Heap_lock.  The stop-world phases (InitialMarking and FinalMarking)
1768     //   are executed in the VM thread.
1769     //
1770     // The locking order is
1771     //   PendingListLock (PLL)  -- if applicable (FinalMarking)
1772     //   Heap_lock  (both this & PLL locked in VM_CMS_Operation::prologue())
1773     //   CMS token  (claimed in
1774     //                stop_world_and_do() -->
1775     //                  safepoint_synchronize() -->
1776     //                    CMSThread::synchronize())
1777 
1778     {
1779       // Check if the FG collector wants us to yield.
1780       CMSTokenSync x(true); // is cms thread
1781       if (waitForForegroundGC()) {
1782         // We yielded to a foreground GC, nothing more to be
1783         // done this round.
1784         assert(_foregroundGCShouldWait == false, "We set it to false in "
1785                "waitForForegroundGC()");
1786         log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " exiting collection CMS state %d",
1787                              p2i(Thread::current()), _collectorState);
1788         return;
1789       } else {
1790         // The background collector can run but check to see if the
1791         // foreground collector has done a collection while the
1792         // background collector was waiting to get the CGC_lock
1793         // above.  If yes, break so that _foregroundGCShouldWait
1794         // is cleared before returning.
1795         if (_collectorState == Idling) {
1796           break;
1797         }
1798       }
1799     }
1800 
1801     assert(_foregroundGCShouldWait, "Foreground collector, if active, "
1802       "should be waiting");
1803 
1804     switch (_collectorState) {
1805       case InitialMarking:
1806         {
1807           ReleaseForegroundGC x(this);
1808           stats().record_cms_begin();
1809           VM_CMS_Initial_Mark initial_mark_op(this);
1810           VMThread::execute(&initial_mark_op);
1811         }
1812         // The collector state may be any legal state at this point
1813         // since the background collector may have yielded to the
1814         // foreground collector.
1815         break;
1816       case Marking:
1817         // initial marking in checkpointRootsInitialWork has been completed
1818         if (markFromRoots()) { // we were successful
1819           assert(_collectorState == Precleaning, "Collector state should "
1820             "have changed");
1821         } else {
1822           assert(_foregroundGCIsActive, "Internal state inconsistency");
1823         }
1824         break;
1825       case Precleaning:
1826         // marking from roots in markFromRoots has been completed
1827         preclean();
1828         assert(_collectorState == AbortablePreclean ||
1829                _collectorState == FinalMarking,
1830                "Collector state should have changed");
1831         break;
1832       case AbortablePreclean:
1833         abortable_preclean();
1834         assert(_collectorState == FinalMarking, "Collector state should "
1835           "have changed");
1836         break;
1837       case FinalMarking:
1838         {
1839           ReleaseForegroundGC x(this);
1840 
1841           VM_CMS_Final_Remark final_remark_op(this);
1842           VMThread::execute(&final_remark_op);
1843         }
1844         assert(_foregroundGCShouldWait, "block post-condition");
1845         break;
1846       case Sweeping:
1847         // final marking in checkpointRootsFinal has been completed
1848         sweep();
1849         assert(_collectorState == Resizing, "Collector state change "
1850           "to Resizing must be done under the free_list_lock");
1851 
1852       case Resizing: {
1853         // Sweeping has been completed...
1854         // At this point the background collection has completed.
1855         // Don't move the call to compute_new_size() down
1856         // into code that might be executed if the background
1857         // collection was preempted.
1858         {
1859           ReleaseForegroundGC x(this);   // unblock FG collection
1860           MutexLockerEx       y(Heap_lock, Mutex::_no_safepoint_check_flag);
1861           CMSTokenSync        z(true);   // not strictly needed.
1862           if (_collectorState == Resizing) {
1863             compute_new_size();
1864             save_heap_summary();
1865             _collectorState = Resetting;
1866           } else {
1867             assert(_collectorState == Idling, "The state should only change"
1868                    " because the foreground collector has finished the collection");
1869           }
1870         }
1871         break;
1872       }
1873       case Resetting:
1874         // CMS heap resizing has been completed
1875         reset_concurrent();
1876         assert(_collectorState == Idling, "Collector state should "
1877           "have changed");
1878 
1879         MetaspaceGC::set_should_concurrent_collect(false);
1880 
1881         stats().record_cms_end();
1882         // Don't move the concurrent_phases_end() and compute_new_size()
1883         // calls to here because a preempted background collection
1884         // has it's state set to "Resetting".
1885         break;
1886       case Idling:
1887       default:
1888         ShouldNotReachHere();
1889         break;
1890     }
1891     log_debug(gc, state)("  Thread " INTPTR_FORMAT " done - next CMS state %d",
1892                          p2i(Thread::current()), _collectorState);
1893     assert(_foregroundGCShouldWait, "block post-condition");
1894   }
1895 
1896   // Should this be in gc_epilogue?
1897   heap->counters()->update_counters();
1898 
1899   {
1900     // Clear _foregroundGCShouldWait and, in the event that the
1901     // foreground collector is waiting, notify it, before
1902     // returning.
1903     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1904     _foregroundGCShouldWait = false;
1905     if (_foregroundGCIsActive) {
1906       CGC_lock->notify();
1907     }
1908     assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1909            "Possible deadlock");
1910   }
1911   log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " exiting collection CMS state %d",
1912                        p2i(Thread::current()), _collectorState);
1913   log_info(gc, heap)("Old: " SIZE_FORMAT "K->" SIZE_FORMAT "K("  SIZE_FORMAT "K)",
1914                      prev_used / K, _cmsGen->used()/K, _cmsGen->capacity() /K);
1915 }
1916 
1917 void CMSCollector::register_gc_start(GCCause::Cause cause) {
1918   _cms_start_registered = true;
1919   _gc_timer_cm->register_gc_start();
1920   _gc_tracer_cm->report_gc_start(cause, _gc_timer_cm->gc_start());
1921 }
1922 
1923 void CMSCollector::register_gc_end() {
1924   if (_cms_start_registered) {
1925     report_heap_summary(GCWhen::AfterGC);
1926 
1927     _gc_timer_cm->register_gc_end();
1928     _gc_tracer_cm->report_gc_end(_gc_timer_cm->gc_end(), _gc_timer_cm->time_partitions());
1929     _cms_start_registered = false;
1930   }
1931 }
1932 
1933 void CMSCollector::save_heap_summary() {
1934   CMSHeap* heap = CMSHeap::heap();
1935   _last_heap_summary = heap->create_heap_summary();
1936   _last_metaspace_summary = heap->create_metaspace_summary();
1937 }
1938 
1939 void CMSCollector::report_heap_summary(GCWhen::Type when) {
1940   _gc_tracer_cm->report_gc_heap_summary(when, _last_heap_summary);
1941   _gc_tracer_cm->report_metaspace_summary(when, _last_metaspace_summary);
1942 }
1943 
1944 bool CMSCollector::waitForForegroundGC() {
1945   bool res = false;
1946   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1947          "CMS thread should have CMS token");
1948   // Block the foreground collector until the
1949   // background collectors decides whether to
1950   // yield.
1951   MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1952   _foregroundGCShouldWait = true;
1953   if (_foregroundGCIsActive) {
1954     // The background collector yields to the
1955     // foreground collector and returns a value
1956     // indicating that it has yielded.  The foreground
1957     // collector can proceed.
1958     res = true;
1959     _foregroundGCShouldWait = false;
1960     ConcurrentMarkSweepThread::clear_CMS_flag(
1961       ConcurrentMarkSweepThread::CMS_cms_has_token);
1962     ConcurrentMarkSweepThread::set_CMS_flag(
1963       ConcurrentMarkSweepThread::CMS_cms_wants_token);
1964     // Get a possibly blocked foreground thread going
1965     CGC_lock->notify();
1966     log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d",
1967                          p2i(Thread::current()), _collectorState);
1968     while (_foregroundGCIsActive) {
1969       CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1970     }
1971     ConcurrentMarkSweepThread::set_CMS_flag(
1972       ConcurrentMarkSweepThread::CMS_cms_has_token);
1973     ConcurrentMarkSweepThread::clear_CMS_flag(
1974       ConcurrentMarkSweepThread::CMS_cms_wants_token);
1975   }
1976   log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d",
1977                        p2i(Thread::current()), _collectorState);
1978   return res;
1979 }
1980 
1981 // Because of the need to lock the free lists and other structures in
1982 // the collector, common to all the generations that the collector is
1983 // collecting, we need the gc_prologues of individual CMS generations
1984 // delegate to their collector. It may have been simpler had the
1985 // current infrastructure allowed one to call a prologue on a
1986 // collector. In the absence of that we have the generation's
1987 // prologue delegate to the collector, which delegates back
1988 // some "local" work to a worker method in the individual generations
1989 // that it's responsible for collecting, while itself doing any
1990 // work common to all generations it's responsible for. A similar
1991 // comment applies to the  gc_epilogue()'s.
1992 // The role of the variable _between_prologue_and_epilogue is to
1993 // enforce the invocation protocol.
1994 void CMSCollector::gc_prologue(bool full) {
1995   // Call gc_prologue_work() for the CMSGen
1996   // we are responsible for.
1997 
1998   // The following locking discipline assumes that we are only called
1999   // when the world is stopped.
2000   assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption");
2001 
2002   // The CMSCollector prologue must call the gc_prologues for the
2003   // "generations" that it's responsible
2004   // for.
2005 
2006   assert(   Thread::current()->is_VM_thread()
2007          || (   CMSScavengeBeforeRemark
2008              && Thread::current()->is_ConcurrentGC_thread()),
2009          "Incorrect thread type for prologue execution");
2010 
2011   if (_between_prologue_and_epilogue) {
2012     // We have already been invoked; this is a gc_prologue delegation
2013     // from yet another CMS generation that we are responsible for, just
2014     // ignore it since all relevant work has already been done.
2015     return;
2016   }
2017 
2018   // set a bit saying prologue has been called; cleared in epilogue
2019   _between_prologue_and_epilogue = true;
2020   // Claim locks for common data structures, then call gc_prologue_work()
2021   // for each CMSGen.
2022 
2023   getFreelistLocks();   // gets free list locks on constituent spaces
2024   bitMapLock()->lock_without_safepoint_check();
2025 
2026   // Should call gc_prologue_work() for all cms gens we are responsible for
2027   bool duringMarking =    _collectorState >= Marking
2028                          && _collectorState < Sweeping;
2029 
2030   // The young collections clear the modified oops state, which tells if
2031   // there are any modified oops in the class. The remark phase also needs
2032   // that information. Tell the young collection to save the union of all
2033   // modified klasses.
2034   if (duringMarking) {
2035     _ct->cld_rem_set()->set_accumulate_modified_oops(true);
2036   }
2037 
2038   bool registerClosure = duringMarking;
2039 
2040   _cmsGen->gc_prologue_work(full, registerClosure, &_modUnionClosurePar);
2041 
2042   if (!full) {
2043     stats().record_gc0_begin();
2044   }
2045 }
2046 
2047 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) {
2048 
2049   _capacity_at_prologue = capacity();
2050   _used_at_prologue = used();
2051 
2052   // We enable promotion tracking so that card-scanning can recognize
2053   // which objects have been promoted during this GC and skip them.
2054   for (uint i = 0; i < ParallelGCThreads; i++) {
2055     _par_gc_thread_states[i]->promo.startTrackingPromotions();
2056   }
2057 
2058   // Delegate to CMScollector which knows how to coordinate between
2059   // this and any other CMS generations that it is responsible for
2060   // collecting.
2061   collector()->gc_prologue(full);
2062 }
2063 
2064 // This is a "private" interface for use by this generation's CMSCollector.
2065 // Not to be called directly by any other entity (for instance,
2066 // GenCollectedHeap, which calls the "public" gc_prologue method above).
2067 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full,
2068   bool registerClosure, ModUnionClosure* modUnionClosure) {
2069   assert(!incremental_collection_failed(), "Shouldn't be set yet");
2070   assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL,
2071     "Should be NULL");
2072   if (registerClosure) {
2073     cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure);
2074   }
2075   cmsSpace()->gc_prologue();
2076   // Clear stat counters
2077   NOT_PRODUCT(
2078     assert(_numObjectsPromoted == 0, "check");
2079     assert(_numWordsPromoted   == 0, "check");
2080     log_develop_trace(gc, alloc)("Allocated " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes concurrently",
2081                                  _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord));
2082     _numObjectsAllocated = 0;
2083     _numWordsAllocated   = 0;
2084   )
2085 }
2086 
2087 void CMSCollector::gc_epilogue(bool full) {
2088   // The following locking discipline assumes that we are only called
2089   // when the world is stopped.
2090   assert(SafepointSynchronize::is_at_safepoint(),
2091          "world is stopped assumption");
2092 
2093   // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks
2094   // if linear allocation blocks need to be appropriately marked to allow the
2095   // the blocks to be parsable. We also check here whether we need to nudge the
2096   // CMS collector thread to start a new cycle (if it's not already active).
2097   assert(   Thread::current()->is_VM_thread()
2098          || (   CMSScavengeBeforeRemark
2099              && Thread::current()->is_ConcurrentGC_thread()),
2100          "Incorrect thread type for epilogue execution");
2101 
2102   if (!_between_prologue_and_epilogue) {
2103     // We have already been invoked; this is a gc_epilogue delegation
2104     // from yet another CMS generation that we are responsible for, just
2105     // ignore it since all relevant work has already been done.
2106     return;
2107   }
2108   assert(haveFreelistLocks(), "must have freelist locks");
2109   assert_lock_strong(bitMapLock());
2110 
2111   _ct->cld_rem_set()->set_accumulate_modified_oops(false);
2112 
2113   _cmsGen->gc_epilogue_work(full);
2114 
2115   if (_collectorState == AbortablePreclean || _collectorState == Precleaning) {
2116     // in case sampling was not already enabled, enable it
2117     _start_sampling = true;
2118   }
2119   // reset _eden_chunk_array so sampling starts afresh
2120   _eden_chunk_index = 0;
2121 
2122   size_t cms_used   = _cmsGen->cmsSpace()->used();
2123 
2124   // update performance counters - this uses a special version of
2125   // update_counters() that allows the utilization to be passed as a
2126   // parameter, avoiding multiple calls to used().
2127   //
2128   _cmsGen->update_counters(cms_used);
2129 
2130   bitMapLock()->unlock();
2131   releaseFreelistLocks();
2132 
2133   if (!CleanChunkPoolAsync) {
2134     Chunk::clean_chunk_pool();
2135   }
2136 
2137   set_did_compact(false);
2138   _between_prologue_and_epilogue = false;  // ready for next cycle
2139 }
2140 
2141 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) {
2142   collector()->gc_epilogue(full);
2143 
2144   // When using ParNew, promotion tracking should have already been
2145   // disabled. However, the prologue (which enables promotion
2146   // tracking) and epilogue are called irrespective of the type of
2147   // GC. So they will also be called before and after Full GCs, during
2148   // which promotion tracking will not be explicitly disabled. So,
2149   // it's safer to also disable it here too (to be symmetric with
2150   // enabling it in the prologue).
2151   for (uint i = 0; i < ParallelGCThreads; i++) {
2152     _par_gc_thread_states[i]->promo.stopTrackingPromotions();
2153   }
2154 }
2155 
2156 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2157   assert(!incremental_collection_failed(), "Should have been cleared");
2158   cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2159   cmsSpace()->gc_epilogue();
2160     // Print stat counters
2161   NOT_PRODUCT(
2162     assert(_numObjectsAllocated == 0, "check");
2163     assert(_numWordsAllocated == 0, "check");
2164     log_develop_trace(gc, promotion)("Promoted " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
2165                                      _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2166     _numObjectsPromoted = 0;
2167     _numWordsPromoted   = 0;
2168   )
2169 
2170   // Call down the chain in contiguous_available needs the freelistLock
2171   // so print this out before releasing the freeListLock.
2172   log_develop_trace(gc)(" Contiguous available " SIZE_FORMAT " bytes ", contiguous_available());
2173 }
2174 
2175 #ifndef PRODUCT
2176 bool CMSCollector::have_cms_token() {
2177   Thread* thr = Thread::current();
2178   if (thr->is_VM_thread()) {
2179     return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2180   } else if (thr->is_ConcurrentGC_thread()) {
2181     return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2182   } else if (thr->is_GC_task_thread()) {
2183     return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2184            ParGCRareEvent_lock->owned_by_self();
2185   }
2186   return false;
2187 }
2188 
2189 // Check reachability of the given heap address in CMS generation,
2190 // treating all other generations as roots.
2191 bool CMSCollector::is_cms_reachable(HeapWord* addr) {
2192   // We could "guarantee" below, rather than assert, but I'll
2193   // leave these as "asserts" so that an adventurous debugger
2194   // could try this in the product build provided some subset of
2195   // the conditions were met, provided they were interested in the
2196   // results and knew that the computation below wouldn't interfere
2197   // with other concurrent computations mutating the structures
2198   // being read or written.
2199   assert(SafepointSynchronize::is_at_safepoint(),
2200          "Else mutations in object graph will make answer suspect");
2201   assert(have_cms_token(), "Should hold cms token");
2202   assert(haveFreelistLocks(), "must hold free list locks");
2203   assert_lock_strong(bitMapLock());
2204 
2205   // Clear the marking bit map array before starting, but, just
2206   // for kicks, first report if the given address is already marked
2207   tty->print_cr("Start: Address " PTR_FORMAT " is%s marked", p2i(addr),
2208                 _markBitMap.isMarked(addr) ? "" : " not");
2209 
2210   if (verify_after_remark()) {
2211     MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2212     bool result = verification_mark_bm()->isMarked(addr);
2213     tty->print_cr("TransitiveMark: Address " PTR_FORMAT " %s marked", p2i(addr),
2214                   result ? "IS" : "is NOT");
2215     return result;
2216   } else {
2217     tty->print_cr("Could not compute result");
2218     return false;
2219   }
2220 }
2221 #endif
2222 
2223 void
2224 CMSCollector::print_on_error(outputStream* st) {
2225   CMSCollector* collector = ConcurrentMarkSweepGeneration::_collector;
2226   if (collector != NULL) {
2227     CMSBitMap* bitmap = &collector->_markBitMap;
2228     st->print_cr("Marking Bits: (CMSBitMap*) " PTR_FORMAT, p2i(bitmap));
2229     bitmap->print_on_error(st, " Bits: ");
2230 
2231     st->cr();
2232 
2233     CMSBitMap* mut_bitmap = &collector->_modUnionTable;
2234     st->print_cr("Mod Union Table: (CMSBitMap*) " PTR_FORMAT, p2i(mut_bitmap));
2235     mut_bitmap->print_on_error(st, " Bits: ");
2236   }
2237 }
2238 
2239 ////////////////////////////////////////////////////////
2240 // CMS Verification Support
2241 ////////////////////////////////////////////////////////
2242 // Following the remark phase, the following invariant
2243 // should hold -- each object in the CMS heap which is
2244 // marked in markBitMap() should be marked in the verification_mark_bm().
2245 
2246 class VerifyMarkedClosure: public BitMapClosure {
2247   CMSBitMap* _marks;
2248   bool       _failed;
2249 
2250  public:
2251   VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2252 
2253   bool do_bit(size_t offset) {
2254     HeapWord* addr = _marks->offsetToHeapWord(offset);
2255     if (!_marks->isMarked(addr)) {
2256       Log(gc, verify) log;
2257       ResourceMark rm;
2258       LogStream ls(log.error());
2259       oop(addr)->print_on(&ls);
2260       log.error(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
2261       _failed = true;
2262     }
2263     return true;
2264   }
2265 
2266   bool failed() { return _failed; }
2267 };
2268 
2269 bool CMSCollector::verify_after_remark() {
2270   GCTraceTime(Info, gc, phases, verify) tm("Verifying CMS Marking.");
2271   MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2272   static bool init = false;
2273 
2274   assert(SafepointSynchronize::is_at_safepoint(),
2275          "Else mutations in object graph will make answer suspect");
2276   assert(have_cms_token(),
2277          "Else there may be mutual interference in use of "
2278          " verification data structures");
2279   assert(_collectorState > Marking && _collectorState <= Sweeping,
2280          "Else marking info checked here may be obsolete");
2281   assert(haveFreelistLocks(), "must hold free list locks");
2282   assert_lock_strong(bitMapLock());
2283 
2284 
2285   // Allocate marking bit map if not already allocated
2286   if (!init) { // first time
2287     if (!verification_mark_bm()->allocate(_span)) {
2288       return false;
2289     }
2290     init = true;
2291   }
2292 
2293   assert(verification_mark_stack()->isEmpty(), "Should be empty");
2294 
2295   // Turn off refs discovery -- so we will be tracing through refs.
2296   // This is as intended, because by this time
2297   // GC must already have cleared any refs that need to be cleared,
2298   // and traced those that need to be marked; moreover,
2299   // the marking done here is not going to interfere in any
2300   // way with the marking information used by GC.
2301   NoRefDiscovery no_discovery(ref_processor());
2302 
2303 #if COMPILER2_OR_JVMCI
2304   DerivedPointerTableDeactivate dpt_deact;
2305 #endif
2306 
2307   // Clear any marks from a previous round
2308   verification_mark_bm()->clear_all();
2309   assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
2310   verify_work_stacks_empty();
2311 
2312   CMSHeap* heap = CMSHeap::heap();
2313   heap->ensure_parsability(false);  // fill TLABs, but no need to retire them
2314   // Update the saved marks which may affect the root scans.
2315   heap->save_marks();
2316 
2317   if (CMSRemarkVerifyVariant == 1) {
2318     // In this first variant of verification, we complete
2319     // all marking, then check if the new marks-vector is
2320     // a subset of the CMS marks-vector.
2321     verify_after_remark_work_1();
2322   } else {
2323     guarantee(CMSRemarkVerifyVariant == 2, "Range checking for CMSRemarkVerifyVariant should guarantee 1 or 2");
2324     // In this second variant of verification, we flag an error
2325     // (i.e. an object reachable in the new marks-vector not reachable
2326     // in the CMS marks-vector) immediately, also indicating the
2327     // identify of an object (A) that references the unmarked object (B) --
2328     // presumably, a mutation to A failed to be picked up by preclean/remark?
2329     verify_after_remark_work_2();
2330   }
2331 
2332   return true;
2333 }
2334 
2335 void CMSCollector::verify_after_remark_work_1() {
2336   ResourceMark rm;
2337   HandleMark  hm;
2338   CMSHeap* heap = CMSHeap::heap();
2339 
2340   // Get a clear set of claim bits for the roots processing to work with.
2341   ClassLoaderDataGraph::clear_claimed_marks();
2342 
2343   // Mark from roots one level into CMS
2344   MarkRefsIntoClosure notOlder(_span, verification_mark_bm());
2345   heap->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2346 
2347   {
2348     StrongRootsScope srs(1);
2349 
2350     heap->cms_process_roots(&srs,
2351                            true,   // young gen as roots
2352                            GenCollectedHeap::ScanningOption(roots_scanning_options()),
2353                            should_unload_classes(),
2354                            &notOlder,
2355                            NULL);
2356   }
2357 
2358   // Now mark from the roots
2359   MarkFromRootsClosure markFromRootsClosure(this, _span,
2360     verification_mark_bm(), verification_mark_stack(),
2361     false /* don't yield */, true /* verifying */);
2362   assert(_restart_addr == NULL, "Expected pre-condition");
2363   verification_mark_bm()->iterate(&markFromRootsClosure);
2364   while (_restart_addr != NULL) {
2365     // Deal with stack overflow: by restarting at the indicated
2366     // address.
2367     HeapWord* ra = _restart_addr;
2368     markFromRootsClosure.reset(ra);
2369     _restart_addr = NULL;
2370     verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2371   }
2372   assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2373   verify_work_stacks_empty();
2374 
2375   // Marking completed -- now verify that each bit marked in
2376   // verification_mark_bm() is also marked in markBitMap(); flag all
2377   // errors by printing corresponding objects.
2378   VerifyMarkedClosure vcl(markBitMap());
2379   verification_mark_bm()->iterate(&vcl);
2380   if (vcl.failed()) {
2381     Log(gc, verify) log;
2382     log.error("Failed marking verification after remark");
2383     ResourceMark rm;
2384     LogStream ls(log.error());
2385     heap->print_on(&ls);
2386     fatal("CMS: failed marking verification after remark");
2387   }
2388 }
2389 
2390 class VerifyCLDOopsCLDClosure : public CLDClosure {
2391   class VerifyCLDOopsClosure : public OopClosure {
2392     CMSBitMap* _bitmap;
2393    public:
2394     VerifyCLDOopsClosure(CMSBitMap* bitmap) : _bitmap(bitmap) { }
2395     void do_oop(oop* p)       { guarantee(*p == NULL || _bitmap->isMarked((HeapWord*) *p), "Should be marked"); }
2396     void do_oop(narrowOop* p) { ShouldNotReachHere(); }
2397   } _oop_closure;
2398  public:
2399   VerifyCLDOopsCLDClosure(CMSBitMap* bitmap) : _oop_closure(bitmap) {}
2400   void do_cld(ClassLoaderData* cld) {
2401     cld->oops_do(&_oop_closure, ClassLoaderData::_claim_none, false);
2402   }
2403 };
2404 
2405 void CMSCollector::verify_after_remark_work_2() {
2406   ResourceMark rm;
2407   HandleMark  hm;
2408   CMSHeap* heap = CMSHeap::heap();
2409 
2410   // Get a clear set of claim bits for the roots processing to work with.
2411   ClassLoaderDataGraph::clear_claimed_marks();
2412 
2413   // Mark from roots one level into CMS
2414   MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
2415                                      markBitMap());
2416   CLDToOopClosure cld_closure(&notOlder, ClassLoaderData::_claim_strong);
2417 
2418   heap->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2419 
2420   {
2421     StrongRootsScope srs(1);
2422 
2423     heap->cms_process_roots(&srs,
2424                            true,   // young gen as roots
2425                            GenCollectedHeap::ScanningOption(roots_scanning_options()),
2426                            should_unload_classes(),
2427                            &notOlder,
2428                            &cld_closure);
2429   }
2430 
2431   // Now mark from the roots
2432   MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
2433     verification_mark_bm(), markBitMap(), verification_mark_stack());
2434   assert(_restart_addr == NULL, "Expected pre-condition");
2435   verification_mark_bm()->iterate(&markFromRootsClosure);
2436   while (_restart_addr != NULL) {
2437     // Deal with stack overflow: by restarting at the indicated
2438     // address.
2439     HeapWord* ra = _restart_addr;
2440     markFromRootsClosure.reset(ra);
2441     _restart_addr = NULL;
2442     verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2443   }
2444   assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2445   verify_work_stacks_empty();
2446 
2447   VerifyCLDOopsCLDClosure verify_cld_oops(verification_mark_bm());
2448   ClassLoaderDataGraph::cld_oops_do(&verify_cld_oops);
2449 
2450   // Marking completed -- now verify that each bit marked in
2451   // verification_mark_bm() is also marked in markBitMap(); flag all
2452   // errors by printing corresponding objects.
2453   VerifyMarkedClosure vcl(markBitMap());
2454   verification_mark_bm()->iterate(&vcl);
2455   assert(!vcl.failed(), "Else verification above should not have succeeded");
2456 }
2457 
2458 void ConcurrentMarkSweepGeneration::save_marks() {
2459   // delegate to CMS space
2460   cmsSpace()->save_marks();
2461 }
2462 
2463 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
2464   return cmsSpace()->no_allocs_since_save_marks();
2465 }
2466 
2467 void
2468 ConcurrentMarkSweepGeneration::oop_iterate(OopIterateClosure* cl) {
2469   if (freelistLock()->owned_by_self()) {
2470     Generation::oop_iterate(cl);
2471   } else {
2472     MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2473     Generation::oop_iterate(cl);
2474   }
2475 }
2476 
2477 void
2478 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
2479   if (freelistLock()->owned_by_self()) {
2480     Generation::object_iterate(cl);
2481   } else {
2482     MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2483     Generation::object_iterate(cl);
2484   }
2485 }
2486 
2487 void
2488 ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) {
2489   if (freelistLock()->owned_by_self()) {
2490     Generation::safe_object_iterate(cl);
2491   } else {
2492     MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2493     Generation::safe_object_iterate(cl);
2494   }
2495 }
2496 
2497 void
2498 ConcurrentMarkSweepGeneration::post_compact() {
2499 }
2500 
2501 void
2502 ConcurrentMarkSweepGeneration::prepare_for_verify() {
2503   // Fix the linear allocation blocks to look like free blocks.
2504 
2505   // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2506   // are not called when the heap is verified during universe initialization and
2507   // at vm shutdown.
2508   if (freelistLock()->owned_by_self()) {
2509     cmsSpace()->prepare_for_verify();
2510   } else {
2511     MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2512     cmsSpace()->prepare_for_verify();
2513   }
2514 }
2515 
2516 void
2517 ConcurrentMarkSweepGeneration::verify() {
2518   // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2519   // are not called when the heap is verified during universe initialization and
2520   // at vm shutdown.
2521   if (freelistLock()->owned_by_self()) {
2522     cmsSpace()->verify();
2523   } else {
2524     MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2525     cmsSpace()->verify();
2526   }
2527 }
2528 
2529 void CMSCollector::verify() {
2530   _cmsGen->verify();
2531 }
2532 
2533 #ifndef PRODUCT
2534 bool CMSCollector::overflow_list_is_empty() const {
2535   assert(_num_par_pushes >= 0, "Inconsistency");
2536   if (_overflow_list == NULL) {
2537     assert(_num_par_pushes == 0, "Inconsistency");
2538   }
2539   return _overflow_list == NULL;
2540 }
2541 
2542 // The methods verify_work_stacks_empty() and verify_overflow_empty()
2543 // merely consolidate assertion checks that appear to occur together frequently.
2544 void CMSCollector::verify_work_stacks_empty() const {
2545   assert(_markStack.isEmpty(), "Marking stack should be empty");
2546   assert(overflow_list_is_empty(), "Overflow list should be empty");
2547 }
2548 
2549 void CMSCollector::verify_overflow_empty() const {
2550   assert(overflow_list_is_empty(), "Overflow list should be empty");
2551   assert(no_preserved_marks(), "No preserved marks");
2552 }
2553 #endif // PRODUCT
2554 
2555 // Decide if we want to enable class unloading as part of the
2556 // ensuing concurrent GC cycle. We will collect and
2557 // unload classes if it's the case that:
2558 //  (a) class unloading is enabled at the command line, and
2559 //  (b) old gen is getting really full
2560 // NOTE: Provided there is no change in the state of the heap between
2561 // calls to this method, it should have idempotent results. Moreover,
2562 // its results should be monotonically increasing (i.e. going from 0 to 1,
2563 // but not 1 to 0) between successive calls between which the heap was
2564 // not collected. For the implementation below, it must thus rely on
2565 // the property that concurrent_cycles_since_last_unload()
2566 // will not decrease unless a collection cycle happened and that
2567 // _cmsGen->is_too_full() are
2568 // themselves also monotonic in that sense. See check_monotonicity()
2569 // below.
2570 void CMSCollector::update_should_unload_classes() {
2571   _should_unload_classes = false;
2572   if (CMSClassUnloadingEnabled) {
2573     _should_unload_classes = (concurrent_cycles_since_last_unload() >=
2574                               CMSClassUnloadingMaxInterval)
2575                            || _cmsGen->is_too_full();
2576   }
2577 }
2578 
2579 bool ConcurrentMarkSweepGeneration::is_too_full() const {
2580   bool res = should_concurrent_collect();
2581   res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
2582   return res;
2583 }
2584 
2585 void CMSCollector::setup_cms_unloading_and_verification_state() {
2586   const  bool should_verify =   VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
2587                              || VerifyBeforeExit;
2588   const  int  rso           =   GenCollectedHeap::SO_AllCodeCache;
2589 
2590   // We set the proper root for this CMS cycle here.
2591   if (should_unload_classes()) {   // Should unload classes this cycle
2592     remove_root_scanning_option(rso);  // Shrink the root set appropriately
2593     set_verifying(should_verify);    // Set verification state for this cycle
2594     return;                            // Nothing else needs to be done at this time
2595   }
2596 
2597   // Not unloading classes this cycle
2598   assert(!should_unload_classes(), "Inconsistency!");
2599 
2600   // If we are not unloading classes then add SO_AllCodeCache to root
2601   // scanning options.
2602   add_root_scanning_option(rso);
2603 
2604   if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
2605     set_verifying(true);
2606   } else if (verifying() && !should_verify) {
2607     // We were verifying, but some verification flags got disabled.
2608     set_verifying(false);
2609     // Exclude symbols, strings and code cache elements from root scanning to
2610     // reduce IM and RM pauses.
2611     remove_root_scanning_option(rso);
2612   }
2613 }
2614 
2615 
2616 #ifndef PRODUCT
2617 HeapWord* CMSCollector::block_start(const void* p) const {
2618   const HeapWord* addr = (HeapWord*)p;
2619   if (_span.contains(p)) {
2620     if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
2621       return _cmsGen->cmsSpace()->block_start(p);
2622     }
2623   }
2624   return NULL;
2625 }
2626 #endif
2627 
2628 HeapWord*
2629 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
2630                                                    bool   tlab,
2631                                                    bool   parallel) {
2632   CMSSynchronousYieldRequest yr;
2633   assert(!tlab, "Can't deal with TLAB allocation");
2634   MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2635   expand_for_gc_cause(word_size*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_allocation);
2636   if (GCExpandToAllocateDelayMillis > 0) {
2637     os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2638   }
2639   return have_lock_and_allocate(word_size, tlab);
2640 }
2641 
2642 void ConcurrentMarkSweepGeneration::expand_for_gc_cause(
2643     size_t bytes,
2644     size_t expand_bytes,
2645     CMSExpansionCause::Cause cause)
2646 {
2647 
2648   bool success = expand(bytes, expand_bytes);
2649 
2650   // remember why we expanded; this information is used
2651   // by shouldConcurrentCollect() when making decisions on whether to start
2652   // a new CMS cycle.
2653   if (success) {
2654     set_expansion_cause(cause);
2655     log_trace(gc)("Expanded CMS gen for %s",  CMSExpansionCause::to_string(cause));
2656   }
2657 }
2658 
2659 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
2660   HeapWord* res = NULL;
2661   MutexLocker x(ParGCRareEvent_lock);
2662   while (true) {
2663     // Expansion by some other thread might make alloc OK now:
2664     res = ps->lab.alloc(word_sz);
2665     if (res != NULL) return res;
2666     // If there's not enough expansion space available, give up.
2667     if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
2668       return NULL;
2669     }
2670     // Otherwise, we try expansion.
2671     expand_for_gc_cause(word_sz*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_lab);
2672     // Now go around the loop and try alloc again;
2673     // A competing par_promote might beat us to the expansion space,
2674     // so we may go around the loop again if promotion fails again.
2675     if (GCExpandToAllocateDelayMillis > 0) {
2676       os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2677     }
2678   }
2679 }
2680 
2681 
2682 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
2683   PromotionInfo* promo) {
2684   MutexLocker x(ParGCRareEvent_lock);
2685   size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
2686   while (true) {
2687     // Expansion by some other thread might make alloc OK now:
2688     if (promo->ensure_spooling_space()) {
2689       assert(promo->has_spooling_space(),
2690              "Post-condition of successful ensure_spooling_space()");
2691       return true;
2692     }
2693     // If there's not enough expansion space available, give up.
2694     if (_virtual_space.uncommitted_size() < refill_size_bytes) {
2695       return false;
2696     }
2697     // Otherwise, we try expansion.
2698     expand_for_gc_cause(refill_size_bytes, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_spooling_space);
2699     // Now go around the loop and try alloc again;
2700     // A competing allocation might beat us to the expansion space,
2701     // so we may go around the loop again if allocation fails again.
2702     if (GCExpandToAllocateDelayMillis > 0) {
2703       os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2704     }
2705   }
2706 }
2707 
2708 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
2709   // Only shrink if a compaction was done so that all the free space
2710   // in the generation is in a contiguous block at the end.
2711   if (did_compact()) {
2712     CardGeneration::shrink(bytes);
2713   }
2714 }
2715 
2716 void ConcurrentMarkSweepGeneration::assert_correct_size_change_locking() {
2717   assert_locked_or_safepoint(Heap_lock);
2718 }
2719 
2720 void ConcurrentMarkSweepGeneration::shrink_free_list_by(size_t bytes) {
2721   assert_locked_or_safepoint(Heap_lock);
2722   assert_lock_strong(freelistLock());
2723   log_trace(gc)("Shrinking of CMS not yet implemented");
2724   return;
2725 }
2726 
2727 
2728 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
2729 // phases.
2730 class CMSPhaseAccounting: public StackObj {
2731  public:
2732   CMSPhaseAccounting(CMSCollector *collector,
2733                      const char *title);
2734   ~CMSPhaseAccounting();
2735 
2736  private:
2737   CMSCollector *_collector;
2738   const char *_title;
2739   GCTraceConcTime(Info, gc) _trace_time;
2740 
2741  public:
2742   // Not MT-safe; so do not pass around these StackObj's
2743   // where they may be accessed by other threads.
2744   double wallclock_millis() {
2745     return TimeHelper::counter_to_millis(os::elapsed_counter() - _trace_time.start_time());
2746   }
2747 };
2748 
2749 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
2750                                        const char *title) :
2751   _collector(collector), _title(title), _trace_time(title) {
2752 
2753   _collector->resetYields();
2754   _collector->resetTimer();
2755   _collector->startTimer();
2756   _collector->gc_timer_cm()->register_gc_concurrent_start(title);
2757 }
2758 
2759 CMSPhaseAccounting::~CMSPhaseAccounting() {
2760   _collector->gc_timer_cm()->register_gc_concurrent_end();
2761   _collector->stopTimer();
2762   log_debug(gc)("Concurrent active time: %.3fms", TimeHelper::counter_to_seconds(_collector->timerTicks()));
2763   log_trace(gc)(" (CMS %s yielded %d times)", _title, _collector->yields());
2764 }
2765 
2766 // CMS work
2767 
2768 // The common parts of CMSParInitialMarkTask and CMSParRemarkTask.
2769 class CMSParMarkTask : public AbstractGangTask {
2770  protected:
2771   CMSCollector*     _collector;
2772   uint              _n_workers;
2773   OopStorage::ParState<false, false> _par_state_string;
2774   CMSParMarkTask(const char* name, CMSCollector* collector, uint n_workers) :
2775       AbstractGangTask(name),
2776       _collector(collector),
2777       _n_workers(n_workers),
2778       _par_state_string(StringTable::weak_storage()) {}
2779   // Work method in support of parallel rescan ... of young gen spaces
2780   void do_young_space_rescan(OopsInGenClosure* cl,
2781                              ContiguousSpace* space,
2782                              HeapWord** chunk_array, size_t chunk_top);
2783   void work_on_young_gen_roots(OopsInGenClosure* cl);
2784 };
2785 
2786 // Parallel initial mark task
2787 class CMSParInitialMarkTask: public CMSParMarkTask {
2788   StrongRootsScope* _strong_roots_scope;
2789  public:
2790   CMSParInitialMarkTask(CMSCollector* collector, StrongRootsScope* strong_roots_scope, uint n_workers) :
2791       CMSParMarkTask("Scan roots and young gen for initial mark in parallel", collector, n_workers),
2792       _strong_roots_scope(strong_roots_scope) {}
2793   void work(uint worker_id);
2794 };
2795 
2796 // Checkpoint the roots into this generation from outside
2797 // this generation. [Note this initial checkpoint need only
2798 // be approximate -- we'll do a catch up phase subsequently.]
2799 void CMSCollector::checkpointRootsInitial() {
2800   assert(_collectorState == InitialMarking, "Wrong collector state");
2801   check_correct_thread_executing();
2802   TraceCMSMemoryManagerStats tms(_collectorState, CMSHeap::heap()->gc_cause());
2803 
2804   save_heap_summary();
2805   report_heap_summary(GCWhen::BeforeGC);
2806 
2807   ReferenceProcessor* rp = ref_processor();
2808   assert(_restart_addr == NULL, "Control point invariant");
2809   {
2810     // acquire locks for subsequent manipulations
2811     MutexLockerEx x(bitMapLock(),
2812                     Mutex::_no_safepoint_check_flag);
2813     checkpointRootsInitialWork();
2814     // enable ("weak") refs discovery
2815     rp->enable_discovery();
2816     _collectorState = Marking;
2817   }
2818 }
2819 
2820 void CMSCollector::checkpointRootsInitialWork() {
2821   assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
2822   assert(_collectorState == InitialMarking, "just checking");
2823 
2824   // Already have locks.
2825   assert_lock_strong(bitMapLock());
2826   assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
2827 
2828   // Setup the verification and class unloading state for this
2829   // CMS collection cycle.
2830   setup_cms_unloading_and_verification_state();
2831 
2832   GCTraceTime(Trace, gc, phases) ts("checkpointRootsInitialWork", _gc_timer_cm);
2833 
2834   // Reset all the PLAB chunk arrays if necessary.
2835   if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
2836     reset_survivor_plab_arrays();
2837   }
2838 
2839   ResourceMark rm;
2840   HandleMark  hm;
2841 
2842   MarkRefsIntoClosure notOlder(_span, &_markBitMap);
2843   CMSHeap* heap = CMSHeap::heap();
2844 
2845   verify_work_stacks_empty();
2846   verify_overflow_empty();
2847 
2848   heap->ensure_parsability(false);  // fill TLABs, but no need to retire them
2849   // Update the saved marks which may affect the root scans.
2850   heap->save_marks();
2851 
2852   // weak reference processing has not started yet.
2853   ref_processor()->set_enqueuing_is_done(false);
2854 
2855   // Need to remember all newly created CLDs,
2856   // so that we can guarantee that the remark finds them.
2857   ClassLoaderDataGraph::remember_new_clds(true);
2858 
2859   // Whenever a CLD is found, it will be claimed before proceeding to mark
2860   // the klasses. The claimed marks need to be cleared before marking starts.
2861   ClassLoaderDataGraph::clear_claimed_marks();
2862 
2863   print_eden_and_survivor_chunk_arrays();
2864 
2865   {
2866 #if COMPILER2_OR_JVMCI
2867     DerivedPointerTableDeactivate dpt_deact;
2868 #endif
2869     if (CMSParallelInitialMarkEnabled) {
2870       // The parallel version.
2871       WorkGang* workers = heap->workers();
2872       assert(workers != NULL, "Need parallel worker threads.");
2873       uint n_workers = workers->active_workers();
2874 
2875       StrongRootsScope srs(n_workers);
2876 
2877       CMSParInitialMarkTask tsk(this, &srs, n_workers);
2878       initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
2879       // If the total workers is greater than 1, then multiple workers
2880       // may be used at some time and the initialization has been set
2881       // such that the single threaded path cannot be used.
2882       if (workers->total_workers() > 1) {
2883         workers->run_task(&tsk);
2884       } else {
2885         tsk.work(0);
2886       }
2887     } else {
2888       // The serial version.
2889       CLDToOopClosure cld_closure(&notOlder, ClassLoaderData::_claim_strong);
2890       heap->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2891 
2892       StrongRootsScope srs(1);
2893 
2894       heap->cms_process_roots(&srs,
2895                              true,   // young gen as roots
2896                              GenCollectedHeap::ScanningOption(roots_scanning_options()),
2897                              should_unload_classes(),
2898                              &notOlder,
2899                              &cld_closure);
2900     }
2901   }
2902 
2903   // Clear mod-union table; it will be dirtied in the prologue of
2904   // CMS generation per each young generation collection.
2905 
2906   assert(_modUnionTable.isAllClear(),
2907        "Was cleared in most recent final checkpoint phase"
2908        " or no bits are set in the gc_prologue before the start of the next "
2909        "subsequent marking phase.");
2910 
2911   assert(_ct->cld_rem_set()->mod_union_is_clear(), "Must be");
2912 
2913   // Save the end of the used_region of the constituent generations
2914   // to be used to limit the extent of sweep in each generation.
2915   save_sweep_limits();
2916   verify_overflow_empty();
2917 }
2918 
2919 bool CMSCollector::markFromRoots() {
2920   // we might be tempted to assert that:
2921   // assert(!SafepointSynchronize::is_at_safepoint(),
2922   //        "inconsistent argument?");
2923   // However that wouldn't be right, because it's possible that
2924   // a safepoint is indeed in progress as a young generation
2925   // stop-the-world GC happens even as we mark in this generation.
2926   assert(_collectorState == Marking, "inconsistent state?");
2927   check_correct_thread_executing();
2928   verify_overflow_empty();
2929 
2930   // Weak ref discovery note: We may be discovering weak
2931   // refs in this generation concurrent (but interleaved) with
2932   // weak ref discovery by the young generation collector.
2933 
2934   CMSTokenSyncWithLocks ts(true, bitMapLock());
2935   GCTraceCPUTime tcpu;
2936   CMSPhaseAccounting pa(this, "Concurrent Mark");
2937   bool res = markFromRootsWork();
2938   if (res) {
2939     _collectorState = Precleaning;
2940   } else { // We failed and a foreground collection wants to take over
2941     assert(_foregroundGCIsActive, "internal state inconsistency");
2942     assert(_restart_addr == NULL,  "foreground will restart from scratch");
2943     log_debug(gc)("bailing out to foreground collection");
2944   }
2945   verify_overflow_empty();
2946   return res;
2947 }
2948 
2949 bool CMSCollector::markFromRootsWork() {
2950   // iterate over marked bits in bit map, doing a full scan and mark
2951   // from these roots using the following algorithm:
2952   // . if oop is to the right of the current scan pointer,
2953   //   mark corresponding bit (we'll process it later)
2954   // . else (oop is to left of current scan pointer)
2955   //   push oop on marking stack
2956   // . drain the marking stack
2957 
2958   // Note that when we do a marking step we need to hold the
2959   // bit map lock -- recall that direct allocation (by mutators)
2960   // and promotion (by the young generation collector) is also
2961   // marking the bit map. [the so-called allocate live policy.]
2962   // Because the implementation of bit map marking is not
2963   // robust wrt simultaneous marking of bits in the same word,
2964   // we need to make sure that there is no such interference
2965   // between concurrent such updates.
2966 
2967   // already have locks
2968   assert_lock_strong(bitMapLock());
2969 
2970   verify_work_stacks_empty();
2971   verify_overflow_empty();
2972   bool result = false;
2973   if (CMSConcurrentMTEnabled && ConcGCThreads > 0) {
2974     result = do_marking_mt();
2975   } else {
2976     result = do_marking_st();
2977   }
2978   return result;
2979 }
2980 
2981 // Forward decl
2982 class CMSConcMarkingTask;
2983 
2984 class CMSConcMarkingTerminator: public ParallelTaskTerminator {
2985   CMSCollector*       _collector;
2986   CMSConcMarkingTask* _task;
2987  public:
2988   virtual void yield();
2989 
2990   // "n_threads" is the number of threads to be terminated.
2991   // "queue_set" is a set of work queues of other threads.
2992   // "collector" is the CMS collector associated with this task terminator.
2993   // "yield" indicates whether we need the gang as a whole to yield.
2994   CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
2995     ParallelTaskTerminator(n_threads, queue_set),
2996     _collector(collector) { }
2997 
2998   void set_task(CMSConcMarkingTask* task) {
2999     _task = task;
3000   }
3001 };
3002 
3003 class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator {
3004   CMSConcMarkingTask* _task;
3005  public:
3006   bool should_exit_termination();
3007   void set_task(CMSConcMarkingTask* task) {
3008     _task = task;
3009   }
3010 };
3011 
3012 // MT Concurrent Marking Task
3013 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3014   CMSCollector*             _collector;
3015   uint                      _n_workers;      // requested/desired # workers
3016   bool                      _result;
3017   CompactibleFreeListSpace* _cms_space;
3018   char                      _pad_front[64];   // padding to ...
3019   HeapWord* volatile        _global_finger;   // ... avoid sharing cache line
3020   char                      _pad_back[64];
3021   HeapWord*                 _restart_addr;
3022 
3023   //  Exposed here for yielding support
3024   Mutex* const _bit_map_lock;
3025 
3026   // The per thread work queues, available here for stealing
3027   OopTaskQueueSet*  _task_queues;
3028 
3029   // Termination (and yielding) support
3030   CMSConcMarkingTerminator _term;
3031   CMSConcMarkingTerminatorTerminator _term_term;
3032 
3033  public:
3034   CMSConcMarkingTask(CMSCollector* collector,
3035                  CompactibleFreeListSpace* cms_space,
3036                  YieldingFlexibleWorkGang* workers,
3037                  OopTaskQueueSet* task_queues):
3038     YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3039     _collector(collector),
3040     _n_workers(0),
3041     _result(true),
3042     _cms_space(cms_space),
3043     _bit_map_lock(collector->bitMapLock()),
3044     _task_queues(task_queues),
3045     _term(_n_workers, task_queues, _collector)
3046   {
3047     _requested_size = _n_workers;
3048     _term.set_task(this);
3049     _term_term.set_task(this);
3050     _restart_addr = _global_finger = _cms_space->bottom();
3051   }
3052 
3053 
3054   OopTaskQueueSet* task_queues()  { return _task_queues; }
3055 
3056   OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3057 
3058   HeapWord* volatile* global_finger_addr() { return &_global_finger; }
3059 
3060   CMSConcMarkingTerminator* terminator() { return &_term; }
3061 
3062   virtual void set_for_termination(uint active_workers) {
3063     terminator()->reset_for_reuse(active_workers);
3064   }
3065 
3066   void work(uint worker_id);
3067   bool should_yield() {
3068     return    ConcurrentMarkSweepThread::should_yield()
3069            && !_collector->foregroundGCIsActive();
3070   }
3071 
3072   virtual void coordinator_yield();  // stuff done by coordinator
3073   bool result() { return _result; }
3074 
3075   void reset(HeapWord* ra) {
3076     assert(_global_finger >= _cms_space->end(),  "Postcondition of ::work(i)");
3077     _restart_addr = _global_finger = ra;
3078     _term.reset_for_reuse();
3079   }
3080 
3081   static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3082                                            OopTaskQueue* work_q);
3083 
3084  private:
3085   void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3086   void do_work_steal(int i);
3087   void bump_global_finger(HeapWord* f);
3088 };
3089 
3090 bool CMSConcMarkingTerminatorTerminator::should_exit_termination() {
3091   assert(_task != NULL, "Error");
3092   return _task->yielding();
3093   // Note that we do not need the disjunct || _task->should_yield() above
3094   // because we want terminating threads to yield only if the task
3095   // is already in the midst of yielding, which happens only after at least one
3096   // thread has yielded.
3097 }
3098 
3099 void CMSConcMarkingTerminator::yield() {
3100   if (_task->should_yield()) {
3101     _task->yield();
3102   } else {
3103     ParallelTaskTerminator::yield();
3104   }
3105 }
3106 
3107 ////////////////////////////////////////////////////////////////
3108 // Concurrent Marking Algorithm Sketch
3109 ////////////////////////////////////////////////////////////////
3110 // Until all tasks exhausted (both spaces):
3111 // -- claim next available chunk
3112 // -- bump global finger via CAS
3113 // -- find first object that starts in this chunk
3114 //    and start scanning bitmap from that position
3115 // -- scan marked objects for oops
3116 // -- CAS-mark target, and if successful:
3117 //    . if target oop is above global finger (volatile read)
3118 //      nothing to do
3119 //    . if target oop is in chunk and above local finger
3120 //        then nothing to do
3121 //    . else push on work-queue
3122 // -- Deal with possible overflow issues:
3123 //    . local work-queue overflow causes stuff to be pushed on
3124 //      global (common) overflow queue
3125 //    . always first empty local work queue
3126 //    . then get a batch of oops from global work queue if any
3127 //    . then do work stealing
3128 // -- When all tasks claimed (both spaces)
3129 //    and local work queue empty,
3130 //    then in a loop do:
3131 //    . check global overflow stack; steal a batch of oops and trace
3132 //    . try to steal from other threads oif GOS is empty
3133 //    . if neither is available, offer termination
3134 // -- Terminate and return result
3135 //
3136 void CMSConcMarkingTask::work(uint worker_id) {
3137   elapsedTimer _timer;
3138   ResourceMark rm;
3139   HandleMark hm;
3140 
3141   DEBUG_ONLY(_collector->verify_overflow_empty();)
3142 
3143   // Before we begin work, our work queue should be empty
3144   assert(work_queue(worker_id)->size() == 0, "Expected to be empty");
3145   // Scan the bitmap covering _cms_space, tracing through grey objects.
3146   _timer.start();
3147   do_scan_and_mark(worker_id, _cms_space);
3148   _timer.stop();
3149   log_trace(gc, task)("Finished cms space scanning in %dth thread: %3.3f sec", worker_id, _timer.seconds());
3150 
3151   // ... do work stealing
3152   _timer.reset();
3153   _timer.start();
3154   do_work_steal(worker_id);
3155   _timer.stop();
3156   log_trace(gc, task)("Finished work stealing in %dth thread: %3.3f sec", worker_id, _timer.seconds());
3157   assert(_collector->_markStack.isEmpty(), "Should have been emptied");
3158   assert(work_queue(worker_id)->size() == 0, "Should have been emptied");
3159   // Note that under the current task protocol, the
3160   // following assertion is true even of the spaces
3161   // expanded since the completion of the concurrent
3162   // marking. XXX This will likely change under a strict
3163   // ABORT semantics.
3164   // After perm removal the comparison was changed to
3165   // greater than or equal to from strictly greater than.
3166   // Before perm removal the highest address sweep would
3167   // have been at the end of perm gen but now is at the
3168   // end of the tenured gen.
3169   assert(_global_finger >=  _cms_space->end(),
3170          "All tasks have been completed");
3171   DEBUG_ONLY(_collector->verify_overflow_empty();)
3172 }
3173 
3174 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
3175   HeapWord* read = _global_finger;
3176   HeapWord* cur  = read;
3177   while (f > read) {
3178     cur = read;
3179     read = Atomic::cmpxchg(f, &_global_finger, cur);
3180     if (cur == read) {
3181       // our cas succeeded
3182       assert(_global_finger >= f, "protocol consistency");
3183       break;
3184     }
3185   }
3186 }
3187 
3188 // This is really inefficient, and should be redone by
3189 // using (not yet available) block-read and -write interfaces to the
3190 // stack and the work_queue. XXX FIX ME !!!
3191 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3192                                                       OopTaskQueue* work_q) {
3193   // Fast lock-free check
3194   if (ovflw_stk->length() == 0) {
3195     return false;
3196   }
3197   assert(work_q->size() == 0, "Shouldn't steal");
3198   MutexLockerEx ml(ovflw_stk->par_lock(),
3199                    Mutex::_no_safepoint_check_flag);
3200   // Grab up to 1/4 the size of the work queue
3201   size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
3202                     (size_t)ParGCDesiredObjsFromOverflowList);
3203   num = MIN2(num, ovflw_stk->length());
3204   for (int i = (int) num; i > 0; i--) {
3205     oop cur = ovflw_stk->pop();
3206     assert(cur != NULL, "Counted wrong?");
3207     work_q->push(cur);
3208   }
3209   return num > 0;
3210 }
3211 
3212 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
3213   SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
3214   int n_tasks = pst->n_tasks();
3215   // We allow that there may be no tasks to do here because
3216   // we are restarting after a stack overflow.
3217   assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
3218   uint nth_task = 0;
3219 
3220   HeapWord* aligned_start = sp->bottom();
3221   if (sp->used_region().contains(_restart_addr)) {
3222     // Align down to a card boundary for the start of 0th task
3223     // for this space.
3224     aligned_start = align_down(_restart_addr, CardTable::card_size);
3225   }
3226 
3227   size_t chunk_size = sp->marking_task_size();
3228   while (pst->try_claim_task(/* reference */ nth_task)) {
3229     // Having claimed the nth task in this space,
3230     // compute the chunk that it corresponds to:
3231     MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
3232                                aligned_start + (nth_task+1)*chunk_size);
3233     // Try and bump the global finger via a CAS;
3234     // note that we need to do the global finger bump
3235     // _before_ taking the intersection below, because
3236     // the task corresponding to that region will be
3237     // deemed done even if the used_region() expands
3238     // because of allocation -- as it almost certainly will
3239     // during start-up while the threads yield in the
3240     // closure below.
3241     HeapWord* finger = span.end();
3242     bump_global_finger(finger);   // atomically
3243     // There are null tasks here corresponding to chunks
3244     // beyond the "top" address of the space.
3245     span = span.intersection(sp->used_region());
3246     if (!span.is_empty()) {  // Non-null task
3247       HeapWord* prev_obj;
3248       assert(!span.contains(_restart_addr) || nth_task == 0,
3249              "Inconsistency");
3250       if (nth_task == 0) {
3251         // For the 0th task, we'll not need to compute a block_start.
3252         if (span.contains(_restart_addr)) {
3253           // In the case of a restart because of stack overflow,
3254           // we might additionally skip a chunk prefix.
3255           prev_obj = _restart_addr;
3256         } else {
3257           prev_obj = span.start();
3258         }
3259       } else {
3260         // We want to skip the first object because
3261         // the protocol is to scan any object in its entirety
3262         // that _starts_ in this span; a fortiori, any
3263         // object starting in an earlier span is scanned
3264         // as part of an earlier claimed task.
3265         // Below we use the "careful" version of block_start
3266         // so we do not try to navigate uninitialized objects.
3267         prev_obj = sp->block_start_careful(span.start());
3268         // Below we use a variant of block_size that uses the
3269         // Printezis bits to avoid waiting for allocated
3270         // objects to become initialized/parsable.
3271         while (prev_obj < span.start()) {
3272           size_t sz = sp->block_size_no_stall(prev_obj, _collector);
3273           if (sz > 0) {
3274             prev_obj += sz;
3275           } else {
3276             // In this case we may end up doing a bit of redundant
3277             // scanning, but that appears unavoidable, short of
3278             // locking the free list locks; see bug 6324141.
3279             break;
3280           }
3281         }
3282       }
3283       if (prev_obj < span.end()) {
3284         MemRegion my_span = MemRegion(prev_obj, span.end());
3285         // Do the marking work within a non-empty span --
3286         // the last argument to the constructor indicates whether the
3287         // iteration should be incremental with periodic yields.
3288         ParMarkFromRootsClosure cl(this, _collector, my_span,
3289                                    &_collector->_markBitMap,
3290                                    work_queue(i),
3291                                    &_collector->_markStack);
3292         _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
3293       } // else nothing to do for this task
3294     }   // else nothing to do for this task
3295   }
3296   // We'd be tempted to assert here that since there are no
3297   // more tasks left to claim in this space, the global_finger
3298   // must exceed space->top() and a fortiori space->end(). However,
3299   // that would not quite be correct because the bumping of
3300   // global_finger occurs strictly after the claiming of a task,
3301   // so by the time we reach here the global finger may not yet
3302   // have been bumped up by the thread that claimed the last
3303   // task.
3304   pst->all_tasks_completed();
3305 }
3306 
3307 class ParConcMarkingClosure: public MetadataVisitingOopIterateClosure {
3308  private:
3309   CMSCollector* _collector;
3310   CMSConcMarkingTask* _task;
3311   MemRegion     _span;
3312   CMSBitMap*    _bit_map;
3313   CMSMarkStack* _overflow_stack;
3314   OopTaskQueue* _work_queue;
3315  protected:
3316   DO_OOP_WORK_DEFN
3317  public:
3318   ParConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue,
3319                         CMSBitMap* bit_map, CMSMarkStack* overflow_stack):
3320     MetadataVisitingOopIterateClosure(collector->ref_processor()),
3321     _collector(collector),
3322     _task(task),
3323     _span(collector->_span),
3324     _bit_map(bit_map),
3325     _overflow_stack(overflow_stack),
3326     _work_queue(work_queue)
3327   { }
3328   virtual void do_oop(oop* p);
3329   virtual void do_oop(narrowOop* p);
3330 
3331   void trim_queue(size_t max);
3332   void handle_stack_overflow(HeapWord* lost);
3333   void do_yield_check() {
3334     if (_task->should_yield()) {
3335       _task->yield();
3336     }
3337   }
3338 };
3339 
3340 DO_OOP_WORK_IMPL(ParConcMarkingClosure)
3341 
3342 // Grey object scanning during work stealing phase --
3343 // the salient assumption here is that any references
3344 // that are in these stolen objects being scanned must
3345 // already have been initialized (else they would not have
3346 // been published), so we do not need to check for
3347 // uninitialized objects before pushing here.
3348 void ParConcMarkingClosure::do_oop(oop obj) {
3349   assert(oopDesc::is_oop_or_null(obj, true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
3350   HeapWord* addr = (HeapWord*)obj;
3351   // Check if oop points into the CMS generation
3352   // and is not marked
3353   if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
3354     // a white object ...
3355     // If we manage to "claim" the object, by being the
3356     // first thread to mark it, then we push it on our
3357     // marking stack
3358     if (_bit_map->par_mark(addr)) {     // ... now grey
3359       // push on work queue (grey set)
3360       bool simulate_overflow = false;
3361       NOT_PRODUCT(
3362         if (CMSMarkStackOverflowALot &&
3363             _collector->simulate_overflow()) {
3364           // simulate a stack overflow
3365           simulate_overflow = true;
3366         }
3367       )
3368       if (simulate_overflow ||
3369           !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
3370         // stack overflow
3371         log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _overflow_stack->capacity());
3372         // We cannot assert that the overflow stack is full because
3373         // it may have been emptied since.
3374         assert(simulate_overflow ||
3375                _work_queue->size() == _work_queue->max_elems(),
3376               "Else push should have succeeded");
3377         handle_stack_overflow(addr);
3378       }
3379     } // Else, some other thread got there first
3380     do_yield_check();
3381   }
3382 }
3383 
3384 void ParConcMarkingClosure::trim_queue(size_t max) {
3385   while (_work_queue->size() > max) {
3386     oop new_oop;
3387     if (_work_queue->pop_local(new_oop)) {
3388       assert(oopDesc::is_oop(new_oop), "Should be an oop");
3389       assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
3390       assert(_span.contains((HeapWord*)new_oop), "Not in span");
3391       new_oop->oop_iterate(this);  // do_oop() above
3392       do_yield_check();
3393     }
3394   }
3395 }
3396 
3397 // Upon stack overflow, we discard (part of) the stack,
3398 // remembering the least address amongst those discarded
3399 // in CMSCollector's _restart_address.
3400 void ParConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
3401   // We need to do this under a mutex to prevent other
3402   // workers from interfering with the work done below.
3403   MutexLockerEx ml(_overflow_stack->par_lock(),
3404                    Mutex::_no_safepoint_check_flag);
3405   // Remember the least grey address discarded
3406   HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
3407   _collector->lower_restart_addr(ra);
3408   _overflow_stack->reset();  // discard stack contents
3409   _overflow_stack->expand(); // expand the stack if possible
3410 }
3411 
3412 
3413 void CMSConcMarkingTask::do_work_steal(int i) {
3414   OopTaskQueue* work_q = work_queue(i);
3415   oop obj_to_scan;
3416   CMSBitMap* bm = &(_collector->_markBitMap);
3417   CMSMarkStack* ovflw = &(_collector->_markStack);
3418   ParConcMarkingClosure cl(_collector, this, work_q, bm, ovflw);
3419   while (true) {
3420     cl.trim_queue(0);
3421     assert(work_q->size() == 0, "Should have been emptied above");
3422     if (get_work_from_overflow_stack(ovflw, work_q)) {
3423       // Can't assert below because the work obtained from the
3424       // overflow stack may already have been stolen from us.
3425       // assert(work_q->size() > 0, "Work from overflow stack");
3426       continue;
3427     } else if (task_queues()->steal(i, /* reference */ obj_to_scan)) {
3428       assert(oopDesc::is_oop(obj_to_scan), "Should be an oop");
3429       assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
3430       obj_to_scan->oop_iterate(&cl);
3431     } else if (terminator()->offer_termination(&_term_term)) {
3432       assert(work_q->size() == 0, "Impossible!");
3433       break;
3434     } else if (yielding() || should_yield()) {
3435       yield();
3436     }
3437   }
3438 }
3439 
3440 // This is run by the CMS (coordinator) thread.
3441 void CMSConcMarkingTask::coordinator_yield() {
3442   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3443          "CMS thread should hold CMS token");
3444   // First give up the locks, then yield, then re-lock
3445   // We should probably use a constructor/destructor idiom to
3446   // do this unlock/lock or modify the MutexUnlocker class to
3447   // serve our purpose. XXX
3448   assert_lock_strong(_bit_map_lock);
3449   _bit_map_lock->unlock();
3450   ConcurrentMarkSweepThread::desynchronize(true);
3451   _collector->stopTimer();
3452   _collector->incrementYields();
3453 
3454   // It is possible for whichever thread initiated the yield request
3455   // not to get a chance to wake up and take the bitmap lock between
3456   // this thread releasing it and reacquiring it. So, while the
3457   // should_yield() flag is on, let's sleep for a bit to give the
3458   // other thread a chance to wake up. The limit imposed on the number
3459   // of iterations is defensive, to avoid any unforseen circumstances
3460   // putting us into an infinite loop. Since it's always been this
3461   // (coordinator_yield()) method that was observed to cause the
3462   // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
3463   // which is by default non-zero. For the other seven methods that
3464   // also perform the yield operation, as are using a different
3465   // parameter (CMSYieldSleepCount) which is by default zero. This way we
3466   // can enable the sleeping for those methods too, if necessary.
3467   // See 6442774.
3468   //
3469   // We really need to reconsider the synchronization between the GC
3470   // thread and the yield-requesting threads in the future and we
3471   // should really use wait/notify, which is the recommended
3472   // way of doing this type of interaction. Additionally, we should
3473   // consolidate the eight methods that do the yield operation and they
3474   // are almost identical into one for better maintainability and
3475   // readability. See 6445193.
3476   //
3477   // Tony 2006.06.29
3478   for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
3479                    ConcurrentMarkSweepThread::should_yield() &&
3480                    !CMSCollector::foregroundGCIsActive(); ++i) {
3481     os::sleep(Thread::current(), 1, false);
3482   }
3483 
3484   ConcurrentMarkSweepThread::synchronize(true);
3485   _bit_map_lock->lock_without_safepoint_check();
3486   _collector->startTimer();
3487 }
3488 
3489 bool CMSCollector::do_marking_mt() {
3490   assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition");
3491   uint num_workers = AdaptiveSizePolicy::calc_active_conc_workers(conc_workers()->total_workers(),
3492                                                                   conc_workers()->active_workers(),
3493                                                                   Threads::number_of_non_daemon_threads());
3494   num_workers = conc_workers()->update_active_workers(num_workers);
3495   log_info(gc,task)("Using %u workers of %u for marking", num_workers, conc_workers()->total_workers());
3496 
3497   CompactibleFreeListSpace* cms_space  = _cmsGen->cmsSpace();
3498 
3499   CMSConcMarkingTask tsk(this,
3500                          cms_space,
3501                          conc_workers(),
3502                          task_queues());
3503 
3504   // Since the actual number of workers we get may be different
3505   // from the number we requested above, do we need to do anything different
3506   // below? In particular, may be we need to subclass the SequantialSubTasksDone
3507   // class?? XXX
3508   cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
3509 
3510   // Refs discovery is already non-atomic.
3511   assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
3512   assert(ref_processor()->discovery_is_mt(), "Discovery should be MT");
3513   conc_workers()->start_task(&tsk);
3514   while (tsk.yielded()) {
3515     tsk.coordinator_yield();
3516     conc_workers()->continue_task(&tsk);
3517   }
3518   // If the task was aborted, _restart_addr will be non-NULL
3519   assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
3520   while (_restart_addr != NULL) {
3521     // XXX For now we do not make use of ABORTED state and have not
3522     // yet implemented the right abort semantics (even in the original
3523     // single-threaded CMS case). That needs some more investigation
3524     // and is deferred for now; see CR# TBF. 07252005YSR. XXX
3525     assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
3526     // If _restart_addr is non-NULL, a marking stack overflow
3527     // occurred; we need to do a fresh marking iteration from the
3528     // indicated restart address.
3529     if (_foregroundGCIsActive) {
3530       // We may be running into repeated stack overflows, having
3531       // reached the limit of the stack size, while making very
3532       // slow forward progress. It may be best to bail out and
3533       // let the foreground collector do its job.
3534       // Clear _restart_addr, so that foreground GC
3535       // works from scratch. This avoids the headache of
3536       // a "rescan" which would otherwise be needed because
3537       // of the dirty mod union table & card table.
3538       _restart_addr = NULL;
3539       return false;
3540     }
3541     // Adjust the task to restart from _restart_addr
3542     tsk.reset(_restart_addr);
3543     cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
3544                   _restart_addr);
3545     _restart_addr = NULL;
3546     // Get the workers going again
3547     conc_workers()->start_task(&tsk);
3548     while (tsk.yielded()) {
3549       tsk.coordinator_yield();
3550       conc_workers()->continue_task(&tsk);
3551     }
3552   }
3553   assert(tsk.completed(), "Inconsistency");
3554   assert(tsk.result() == true, "Inconsistency");
3555   return true;
3556 }
3557 
3558 bool CMSCollector::do_marking_st() {
3559   ResourceMark rm;
3560   HandleMark   hm;
3561 
3562   // Temporarily make refs discovery single threaded (non-MT)
3563   ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
3564   MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
3565     &_markStack, CMSYield);
3566   // the last argument to iterate indicates whether the iteration
3567   // should be incremental with periodic yields.
3568   _markBitMap.iterate(&markFromRootsClosure);
3569   // If _restart_addr is non-NULL, a marking stack overflow
3570   // occurred; we need to do a fresh iteration from the
3571   // indicated restart address.
3572   while (_restart_addr != NULL) {
3573     if (_foregroundGCIsActive) {
3574       // We may be running into repeated stack overflows, having
3575       // reached the limit of the stack size, while making very
3576       // slow forward progress. It may be best to bail out and
3577       // let the foreground collector do its job.
3578       // Clear _restart_addr, so that foreground GC
3579       // works from scratch. This avoids the headache of
3580       // a "rescan" which would otherwise be needed because
3581       // of the dirty mod union table & card table.
3582       _restart_addr = NULL;
3583       return false;  // indicating failure to complete marking
3584     }
3585     // Deal with stack overflow:
3586     // we restart marking from _restart_addr
3587     HeapWord* ra = _restart_addr;
3588     markFromRootsClosure.reset(ra);
3589     _restart_addr = NULL;
3590     _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
3591   }
3592   return true;
3593 }
3594 
3595 void CMSCollector::preclean() {
3596   check_correct_thread_executing();
3597   assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
3598   verify_work_stacks_empty();
3599   verify_overflow_empty();
3600   _abort_preclean = false;
3601   if (CMSPrecleaningEnabled) {
3602     if (!CMSEdenChunksRecordAlways) {
3603       _eden_chunk_index = 0;
3604     }
3605     size_t used = get_eden_used();
3606     size_t capacity = get_eden_capacity();
3607     // Don't start sampling unless we will get sufficiently
3608     // many samples.
3609     if (used < (((capacity / CMSScheduleRemarkSamplingRatio) / 100)
3610                 * CMSScheduleRemarkEdenPenetration)) {
3611       _start_sampling = true;
3612     } else {
3613       _start_sampling = false;
3614     }
3615     GCTraceCPUTime tcpu;
3616     CMSPhaseAccounting pa(this, "Concurrent Preclean");
3617     preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
3618   }
3619   CMSTokenSync x(true); // is cms thread
3620   if (CMSPrecleaningEnabled) {
3621     sample_eden();
3622     _collectorState = AbortablePreclean;
3623   } else {
3624     _collectorState = FinalMarking;
3625   }
3626   verify_work_stacks_empty();
3627   verify_overflow_empty();
3628 }
3629 
3630 // Try and schedule the remark such that young gen
3631 // occupancy is CMSScheduleRemarkEdenPenetration %.
3632 void CMSCollector::abortable_preclean() {
3633   check_correct_thread_executing();
3634   assert(CMSPrecleaningEnabled,  "Inconsistent control state");
3635   assert(_collectorState == AbortablePreclean, "Inconsistent control state");
3636 
3637   // If Eden's current occupancy is below this threshold,
3638   // immediately schedule the remark; else preclean
3639   // past the next scavenge in an effort to
3640   // schedule the pause as described above. By choosing
3641   // CMSScheduleRemarkEdenSizeThreshold >= max eden size
3642   // we will never do an actual abortable preclean cycle.
3643   if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
3644     GCTraceCPUTime tcpu;
3645     CMSPhaseAccounting pa(this, "Concurrent Abortable Preclean");
3646     // We need more smarts in the abortable preclean
3647     // loop below to deal with cases where allocation
3648     // in young gen is very very slow, and our precleaning
3649     // is running a losing race against a horde of
3650     // mutators intent on flooding us with CMS updates
3651     // (dirty cards).
3652     // One, admittedly dumb, strategy is to give up
3653     // after a certain number of abortable precleaning loops
3654     // or after a certain maximum time. We want to make
3655     // this smarter in the next iteration.
3656     // XXX FIX ME!!! YSR
3657     size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
3658     while (!(should_abort_preclean() ||
3659              ConcurrentMarkSweepThread::cmst()->should_terminate())) {
3660       workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
3661       cumworkdone += workdone;
3662       loops++;
3663       // Voluntarily terminate abortable preclean phase if we have
3664       // been at it for too long.
3665       if ((CMSMaxAbortablePrecleanLoops != 0) &&
3666           loops >= CMSMaxAbortablePrecleanLoops) {
3667         log_debug(gc)(" CMS: abort preclean due to loops ");
3668         break;
3669       }
3670       if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
3671         log_debug(gc)(" CMS: abort preclean due to time ");
3672         break;
3673       }
3674       // If we are doing little work each iteration, we should
3675       // take a short break.
3676       if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
3677         // Sleep for some time, waiting for work to accumulate
3678         stopTimer();
3679         cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
3680         startTimer();
3681         waited++;
3682       }
3683     }
3684     log_trace(gc)(" [" SIZE_FORMAT " iterations, " SIZE_FORMAT " waits, " SIZE_FORMAT " cards)] ",
3685                                loops, waited, cumworkdone);
3686   }
3687   CMSTokenSync x(true); // is cms thread
3688   if (_collectorState != Idling) {
3689     assert(_collectorState == AbortablePreclean,
3690            "Spontaneous state transition?");
3691     _collectorState = FinalMarking;
3692   } // Else, a foreground collection completed this CMS cycle.
3693   return;
3694 }
3695 
3696 // Respond to an Eden sampling opportunity
3697 void CMSCollector::sample_eden() {
3698   // Make sure a young gc cannot sneak in between our
3699   // reading and recording of a sample.
3700   assert(Thread::current()->is_ConcurrentGC_thread(),
3701          "Only the cms thread may collect Eden samples");
3702   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3703          "Should collect samples while holding CMS token");
3704   if (!_start_sampling) {
3705     return;
3706   }
3707   // When CMSEdenChunksRecordAlways is true, the eden chunk array
3708   // is populated by the young generation.
3709   if (_eden_chunk_array != NULL && !CMSEdenChunksRecordAlways) {
3710     if (_eden_chunk_index < _eden_chunk_capacity) {
3711       _eden_chunk_array[_eden_chunk_index] = *_top_addr;   // take sample
3712       assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
3713              "Unexpected state of Eden");
3714       // We'd like to check that what we just sampled is an oop-start address;
3715       // however, we cannot do that here since the object may not yet have been
3716       // initialized. So we'll instead do the check when we _use_ this sample
3717       // later.
3718       if (_eden_chunk_index == 0 ||
3719           (pointer_delta(_eden_chunk_array[_eden_chunk_index],
3720                          _eden_chunk_array[_eden_chunk_index-1])
3721            >= CMSSamplingGrain)) {
3722         _eden_chunk_index++;  // commit sample
3723       }
3724     }
3725   }
3726   if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
3727     size_t used = get_eden_used();
3728     size_t capacity = get_eden_capacity();
3729     assert(used <= capacity, "Unexpected state of Eden");
3730     if (used >  (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
3731       _abort_preclean = true;
3732     }
3733   }
3734 }
3735 
3736 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
3737   assert(_collectorState == Precleaning ||
3738          _collectorState == AbortablePreclean, "incorrect state");
3739   ResourceMark rm;
3740   HandleMark   hm;
3741 
3742   // Precleaning is currently not MT but the reference processor
3743   // may be set for MT.  Disable it temporarily here.
3744   ReferenceProcessor* rp = ref_processor();
3745   ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false);
3746 
3747   // Do one pass of scrubbing the discovered reference lists
3748   // to remove any reference objects with strongly-reachable
3749   // referents.
3750   if (clean_refs) {
3751     CMSPrecleanRefsYieldClosure yield_cl(this);
3752     assert(_span_based_discoverer.span().equals(_span), "Spans should be equal");
3753     CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
3754                                    &_markStack, true /* preclean */);
3755     CMSDrainMarkingStackClosure complete_trace(this,
3756                                    _span, &_markBitMap, &_markStack,
3757                                    &keep_alive, true /* preclean */);
3758 
3759     // We don't want this step to interfere with a young
3760     // collection because we don't want to take CPU
3761     // or memory bandwidth away from the young GC threads
3762     // (which may be as many as there are CPUs).
3763     // Note that we don't need to protect ourselves from
3764     // interference with mutators because they can't
3765     // manipulate the discovered reference lists nor affect
3766     // the computed reachability of the referents, the
3767     // only properties manipulated by the precleaning
3768     // of these reference lists.
3769     stopTimer();
3770     CMSTokenSyncWithLocks x(true /* is cms thread */,
3771                             bitMapLock());
3772     startTimer();
3773     sample_eden();
3774 
3775     // The following will yield to allow foreground
3776     // collection to proceed promptly. XXX YSR:
3777     // The code in this method may need further
3778     // tweaking for better performance and some restructuring
3779     // for cleaner interfaces.
3780     GCTimer *gc_timer = NULL; // Currently not tracing concurrent phases
3781     rp->preclean_discovered_references(
3782           rp->is_alive_non_header(), &keep_alive, &complete_trace, &yield_cl,
3783           gc_timer);
3784   }
3785 
3786   if (clean_survivor) {  // preclean the active survivor space(s)
3787     PushAndMarkClosure pam_cl(this, _span, ref_processor(),
3788                              &_markBitMap, &_modUnionTable,
3789                              &_markStack, true /* precleaning phase */);
3790     stopTimer();
3791     CMSTokenSyncWithLocks ts(true /* is cms thread */,
3792                              bitMapLock());
3793     startTimer();
3794     unsigned int before_count =
3795       CMSHeap::heap()->total_collections();
3796     SurvivorSpacePrecleanClosure
3797       sss_cl(this, _span, &_markBitMap, &_markStack,
3798              &pam_cl, before_count, CMSYield);
3799     _young_gen->from()->object_iterate_careful(&sss_cl);
3800     _young_gen->to()->object_iterate_careful(&sss_cl);
3801   }
3802   MarkRefsIntoAndScanClosure
3803     mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
3804              &_markStack, this, CMSYield,
3805              true /* precleaning phase */);
3806   // CAUTION: The following closure has persistent state that may need to
3807   // be reset upon a decrease in the sequence of addresses it
3808   // processes.
3809   ScanMarkedObjectsAgainCarefullyClosure
3810     smoac_cl(this, _span,
3811       &_markBitMap, &_markStack, &mrias_cl, CMSYield);
3812 
3813   // Preclean dirty cards in ModUnionTable and CardTable using
3814   // appropriate convergence criterion;
3815   // repeat CMSPrecleanIter times unless we find that
3816   // we are losing.
3817   assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
3818   assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
3819          "Bad convergence multiplier");
3820   assert(CMSPrecleanThreshold >= 100,
3821          "Unreasonably low CMSPrecleanThreshold");
3822 
3823   size_t numIter, cumNumCards, lastNumCards, curNumCards;
3824   for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
3825        numIter < CMSPrecleanIter;
3826        numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
3827     curNumCards  = preclean_mod_union_table(_cmsGen, &smoac_cl);
3828     log_trace(gc)(" (modUnionTable: " SIZE_FORMAT " cards)", curNumCards);
3829     // Either there are very few dirty cards, so re-mark
3830     // pause will be small anyway, or our pre-cleaning isn't
3831     // that much faster than the rate at which cards are being
3832     // dirtied, so we might as well stop and re-mark since
3833     // precleaning won't improve our re-mark time by much.
3834     if (curNumCards <= CMSPrecleanThreshold ||
3835         (numIter > 0 &&
3836          (curNumCards * CMSPrecleanDenominator >
3837          lastNumCards * CMSPrecleanNumerator))) {
3838       numIter++;
3839       cumNumCards += curNumCards;
3840       break;
3841     }
3842   }
3843 
3844   preclean_cld(&mrias_cl, _cmsGen->freelistLock());
3845 
3846   curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
3847   cumNumCards += curNumCards;
3848   log_trace(gc)(" (cardTable: " SIZE_FORMAT " cards, re-scanned " SIZE_FORMAT " cards, " SIZE_FORMAT " iterations)",
3849                              curNumCards, cumNumCards, numIter);
3850   return cumNumCards;   // as a measure of useful work done
3851 }
3852 
3853 // PRECLEANING NOTES:
3854 // Precleaning involves:
3855 // . reading the bits of the modUnionTable and clearing the set bits.
3856 // . For the cards corresponding to the set bits, we scan the
3857 //   objects on those cards. This means we need the free_list_lock
3858 //   so that we can safely iterate over the CMS space when scanning
3859 //   for oops.
3860 // . When we scan the objects, we'll be both reading and setting
3861 //   marks in the marking bit map, so we'll need the marking bit map.
3862 // . For protecting _collector_state transitions, we take the CGC_lock.
3863 //   Note that any races in the reading of of card table entries by the
3864 //   CMS thread on the one hand and the clearing of those entries by the
3865 //   VM thread or the setting of those entries by the mutator threads on the
3866 //   other are quite benign. However, for efficiency it makes sense to keep
3867 //   the VM thread from racing with the CMS thread while the latter is
3868 //   dirty card info to the modUnionTable. We therefore also use the
3869 //   CGC_lock to protect the reading of the card table and the mod union
3870 //   table by the CM thread.
3871 // . We run concurrently with mutator updates, so scanning
3872 //   needs to be done carefully  -- we should not try to scan
3873 //   potentially uninitialized objects.
3874 //
3875 // Locking strategy: While holding the CGC_lock, we scan over and
3876 // reset a maximal dirty range of the mod union / card tables, then lock
3877 // the free_list_lock and bitmap lock to do a full marking, then
3878 // release these locks; and repeat the cycle. This allows for a
3879 // certain amount of fairness in the sharing of these locks between
3880 // the CMS collector on the one hand, and the VM thread and the
3881 // mutators on the other.
3882 
3883 // NOTE: preclean_mod_union_table() and preclean_card_table()
3884 // further below are largely identical; if you need to modify
3885 // one of these methods, please check the other method too.
3886 
3887 size_t CMSCollector::preclean_mod_union_table(
3888   ConcurrentMarkSweepGeneration* old_gen,
3889   ScanMarkedObjectsAgainCarefullyClosure* cl) {
3890   verify_work_stacks_empty();
3891   verify_overflow_empty();
3892 
3893   // strategy: starting with the first card, accumulate contiguous
3894   // ranges of dirty cards; clear these cards, then scan the region
3895   // covered by these cards.
3896 
3897   // Since all of the MUT is committed ahead, we can just use
3898   // that, in case the generations expand while we are precleaning.
3899   // It might also be fine to just use the committed part of the
3900   // generation, but we might potentially miss cards when the
3901   // generation is rapidly expanding while we are in the midst
3902   // of precleaning.
3903   HeapWord* startAddr = old_gen->reserved().start();
3904   HeapWord* endAddr   = old_gen->reserved().end();
3905 
3906   cl->setFreelistLock(old_gen->freelistLock());   // needed for yielding
3907 
3908   size_t numDirtyCards, cumNumDirtyCards;
3909   HeapWord *nextAddr, *lastAddr;
3910   for (cumNumDirtyCards = numDirtyCards = 0,
3911        nextAddr = lastAddr = startAddr;
3912        nextAddr < endAddr;
3913        nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
3914 
3915     ResourceMark rm;
3916     HandleMark   hm;
3917 
3918     MemRegion dirtyRegion;
3919     {
3920       stopTimer();
3921       // Potential yield point
3922       CMSTokenSync ts(true);
3923       startTimer();
3924       sample_eden();
3925       // Get dirty region starting at nextOffset (inclusive),
3926       // simultaneously clearing it.
3927       dirtyRegion =
3928         _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
3929       assert(dirtyRegion.start() >= nextAddr,
3930              "returned region inconsistent?");
3931     }
3932     // Remember where the next search should begin.
3933     // The returned region (if non-empty) is a right open interval,
3934     // so lastOffset is obtained from the right end of that
3935     // interval.
3936     lastAddr = dirtyRegion.end();
3937     // Should do something more transparent and less hacky XXX
3938     numDirtyCards =
3939       _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
3940 
3941     // We'll scan the cards in the dirty region (with periodic
3942     // yields for foreground GC as needed).
3943     if (!dirtyRegion.is_empty()) {
3944       assert(numDirtyCards > 0, "consistency check");
3945       HeapWord* stop_point = NULL;
3946       stopTimer();
3947       // Potential yield point
3948       CMSTokenSyncWithLocks ts(true, old_gen->freelistLock(),
3949                                bitMapLock());
3950       startTimer();
3951       {
3952         verify_work_stacks_empty();
3953         verify_overflow_empty();
3954         sample_eden();
3955         stop_point =
3956           old_gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
3957       }
3958       if (stop_point != NULL) {
3959         // The careful iteration stopped early either because it found an
3960         // uninitialized object, or because we were in the midst of an
3961         // "abortable preclean", which should now be aborted. Redirty
3962         // the bits corresponding to the partially-scanned or unscanned
3963         // cards. We'll either restart at the next block boundary or
3964         // abort the preclean.
3965         assert((_collectorState == AbortablePreclean && should_abort_preclean()),
3966                "Should only be AbortablePreclean.");
3967         _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
3968         if (should_abort_preclean()) {
3969           break; // out of preclean loop
3970         } else {
3971           // Compute the next address at which preclean should pick up;
3972           // might need bitMapLock in order to read P-bits.
3973           lastAddr = next_card_start_after_block(stop_point);
3974         }
3975       }
3976     } else {
3977       assert(lastAddr == endAddr, "consistency check");
3978       assert(numDirtyCards == 0, "consistency check");
3979       break;
3980     }
3981   }
3982   verify_work_stacks_empty();
3983   verify_overflow_empty();
3984   return cumNumDirtyCards;
3985 }
3986 
3987 // NOTE: preclean_mod_union_table() above and preclean_card_table()
3988 // below are largely identical; if you need to modify
3989 // one of these methods, please check the other method too.
3990 
3991 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* old_gen,
3992   ScanMarkedObjectsAgainCarefullyClosure* cl) {
3993   // strategy: it's similar to precleamModUnionTable above, in that
3994   // we accumulate contiguous ranges of dirty cards, mark these cards
3995   // precleaned, then scan the region covered by these cards.
3996   HeapWord* endAddr   = (HeapWord*)(old_gen->_virtual_space.high());
3997   HeapWord* startAddr = (HeapWord*)(old_gen->_virtual_space.low());
3998 
3999   cl->setFreelistLock(old_gen->freelistLock());   // needed for yielding
4000 
4001   size_t numDirtyCards, cumNumDirtyCards;
4002   HeapWord *lastAddr, *nextAddr;
4003 
4004   for (cumNumDirtyCards = numDirtyCards = 0,
4005        nextAddr = lastAddr = startAddr;
4006        nextAddr < endAddr;
4007        nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4008 
4009     ResourceMark rm;
4010     HandleMark   hm;
4011 
4012     MemRegion dirtyRegion;
4013     {
4014       // See comments in "Precleaning notes" above on why we
4015       // do this locking. XXX Could the locking overheads be
4016       // too high when dirty cards are sparse? [I don't think so.]
4017       stopTimer();
4018       CMSTokenSync x(true); // is cms thread
4019       startTimer();
4020       sample_eden();
4021       // Get and clear dirty region from card table
4022       dirtyRegion = _ct->dirty_card_range_after_reset(MemRegion(nextAddr, endAddr),
4023                                                       true,
4024                                                       CardTable::precleaned_card_val());
4025 
4026       assert(dirtyRegion.start() >= nextAddr,
4027              "returned region inconsistent?");
4028     }
4029     lastAddr = dirtyRegion.end();
4030     numDirtyCards =
4031       dirtyRegion.word_size()/CardTable::card_size_in_words;
4032 
4033     if (!dirtyRegion.is_empty()) {
4034       stopTimer();
4035       CMSTokenSyncWithLocks ts(true, old_gen->freelistLock(), bitMapLock());
4036       startTimer();
4037       sample_eden();
4038       verify_work_stacks_empty();
4039       verify_overflow_empty();
4040       HeapWord* stop_point =
4041         old_gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4042       if (stop_point != NULL) {
4043         assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4044                "Should only be AbortablePreclean.");
4045         _ct->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4046         if (should_abort_preclean()) {
4047           break; // out of preclean loop
4048         } else {
4049           // Compute the next address at which preclean should pick up.
4050           lastAddr = next_card_start_after_block(stop_point);
4051         }
4052       }
4053     } else {
4054       break;
4055     }
4056   }
4057   verify_work_stacks_empty();
4058   verify_overflow_empty();
4059   return cumNumDirtyCards;
4060 }
4061 
4062 class PrecleanCLDClosure : public CLDClosure {
4063   MetadataVisitingOopsInGenClosure* _cm_closure;
4064  public:
4065   PrecleanCLDClosure(MetadataVisitingOopsInGenClosure* oop_closure) : _cm_closure(oop_closure) {}
4066   void do_cld(ClassLoaderData* cld) {
4067     if (cld->has_accumulated_modified_oops()) {
4068       cld->clear_accumulated_modified_oops();
4069 
4070       _cm_closure->do_cld(cld);
4071     }
4072   }
4073 };
4074 
4075 // The freelist lock is needed to prevent asserts, is it really needed?
4076 void CMSCollector::preclean_cld(MarkRefsIntoAndScanClosure* cl, Mutex* freelistLock) {
4077   // Needed to walk CLDG
4078   MutexLocker ml(ClassLoaderDataGraph_lock);
4079 
4080   cl->set_freelistLock(freelistLock);
4081 
4082   CMSTokenSyncWithLocks ts(true, freelistLock, bitMapLock());
4083 
4084   // SSS: Add equivalent to ScanMarkedObjectsAgainCarefullyClosure::do_yield_check and should_abort_preclean?
4085   // SSS: We should probably check if precleaning should be aborted, at suitable intervals?
4086   PrecleanCLDClosure preclean_closure(cl);
4087   ClassLoaderDataGraph::cld_oops_do(&preclean_closure);
4088 
4089   verify_work_stacks_empty();
4090   verify_overflow_empty();
4091 }
4092 
4093 void CMSCollector::checkpointRootsFinal() {
4094   assert(_collectorState == FinalMarking, "incorrect state transition?");
4095   check_correct_thread_executing();
4096   // world is stopped at this checkpoint
4097   assert(SafepointSynchronize::is_at_safepoint(),
4098          "world should be stopped");
4099   TraceCMSMemoryManagerStats tms(_collectorState, CMSHeap::heap()->gc_cause());
4100 
4101   verify_work_stacks_empty();
4102   verify_overflow_empty();
4103 
4104   log_debug(gc)("YG occupancy: " SIZE_FORMAT " K (" SIZE_FORMAT " K)",
4105                 _young_gen->used() / K, _young_gen->capacity() / K);
4106   {
4107     if (CMSScavengeBeforeRemark) {
4108       CMSHeap* heap = CMSHeap::heap();
4109       // Temporarily set flag to false, GCH->do_collection will
4110       // expect it to be false and set to true
4111       FlagSetting fl(heap->_is_gc_active, false);
4112 
4113       heap->do_collection(true,                      // full (i.e. force, see below)
4114                           false,                     // !clear_all_soft_refs
4115                           0,                         // size
4116                           false,                     // is_tlab
4117                           GenCollectedHeap::YoungGen // type
4118         );
4119     }
4120     FreelistLocker x(this);
4121     MutexLockerEx y(bitMapLock(),
4122                     Mutex::_no_safepoint_check_flag);
4123     checkpointRootsFinalWork();
4124   }
4125   verify_work_stacks_empty();
4126   verify_overflow_empty();
4127 }
4128 
4129 void CMSCollector::checkpointRootsFinalWork() {
4130   GCTraceTime(Trace, gc, phases) tm("checkpointRootsFinalWork", _gc_timer_cm);
4131 
4132   assert(haveFreelistLocks(), "must have free list locks");
4133   assert_lock_strong(bitMapLock());
4134 
4135   ResourceMark rm;
4136   HandleMark   hm;
4137 
4138   CMSHeap* heap = CMSHeap::heap();
4139 
4140   if (should_unload_classes()) {
4141     CodeCache::gc_prologue();
4142   }
4143   assert(haveFreelistLocks(), "must have free list locks");
4144   assert_lock_strong(bitMapLock());
4145 
4146   // We might assume that we need not fill TLAB's when
4147   // CMSScavengeBeforeRemark is set, because we may have just done
4148   // a scavenge which would have filled all TLAB's -- and besides
4149   // Eden would be empty. This however may not always be the case --
4150   // for instance although we asked for a scavenge, it may not have
4151   // happened because of a JNI critical section. We probably need
4152   // a policy for deciding whether we can in that case wait until
4153   // the critical section releases and then do the remark following
4154   // the scavenge, and skip it here. In the absence of that policy,
4155   // or of an indication of whether the scavenge did indeed occur,
4156   // we cannot rely on TLAB's having been filled and must do
4157   // so here just in case a scavenge did not happen.
4158   heap->ensure_parsability(false);  // fill TLAB's, but no need to retire them
4159   // Update the saved marks which may affect the root scans.
4160   heap->save_marks();
4161 
4162   print_eden_and_survivor_chunk_arrays();
4163 
4164   {
4165 #if COMPILER2_OR_JVMCI
4166     DerivedPointerTableDeactivate dpt_deact;
4167 #endif
4168 
4169     // Note on the role of the mod union table:
4170     // Since the marker in "markFromRoots" marks concurrently with
4171     // mutators, it is possible for some reachable objects not to have been
4172     // scanned. For instance, an only reference to an object A was
4173     // placed in object B after the marker scanned B. Unless B is rescanned,
4174     // A would be collected. Such updates to references in marked objects
4175     // are detected via the mod union table which is the set of all cards
4176     // dirtied since the first checkpoint in this GC cycle and prior to
4177     // the most recent young generation GC, minus those cleaned up by the
4178     // concurrent precleaning.
4179     if (CMSParallelRemarkEnabled) {
4180       GCTraceTime(Debug, gc, phases) t("Rescan (parallel)", _gc_timer_cm);
4181       do_remark_parallel();
4182     } else {
4183       GCTraceTime(Debug, gc, phases) t("Rescan (non-parallel)", _gc_timer_cm);
4184       do_remark_non_parallel();
4185     }
4186   }
4187   verify_work_stacks_empty();
4188   verify_overflow_empty();
4189 
4190   {
4191     GCTraceTime(Trace, gc, phases) ts("refProcessingWork", _gc_timer_cm);
4192     refProcessingWork();
4193   }
4194   verify_work_stacks_empty();
4195   verify_overflow_empty();
4196 
4197   if (should_unload_classes()) {
4198     CodeCache::gc_epilogue();
4199   }
4200   JvmtiExport::gc_epilogue();
4201 
4202   // If we encountered any (marking stack / work queue) overflow
4203   // events during the current CMS cycle, take appropriate
4204   // remedial measures, where possible, so as to try and avoid
4205   // recurrence of that condition.
4206   assert(_markStack.isEmpty(), "No grey objects");
4207   size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
4208                      _ser_kac_ovflw        + _ser_kac_preclean_ovflw;
4209   if (ser_ovflw > 0) {
4210     log_trace(gc)("Marking stack overflow (benign) (pmc_pc=" SIZE_FORMAT ", pmc_rm=" SIZE_FORMAT ", kac=" SIZE_FORMAT ", kac_preclean=" SIZE_FORMAT ")",
4211                          _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw, _ser_kac_ovflw, _ser_kac_preclean_ovflw);
4212     _markStack.expand();
4213     _ser_pmc_remark_ovflw = 0;
4214     _ser_pmc_preclean_ovflw = 0;
4215     _ser_kac_preclean_ovflw = 0;
4216     _ser_kac_ovflw = 0;
4217   }
4218   if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
4219      log_trace(gc)("Work queue overflow (benign) (pmc_rm=" SIZE_FORMAT ", kac=" SIZE_FORMAT ")",
4220                           _par_pmc_remark_ovflw, _par_kac_ovflw);
4221      _par_pmc_remark_ovflw = 0;
4222     _par_kac_ovflw = 0;
4223   }
4224    if (_markStack._hit_limit > 0) {
4225      log_trace(gc)(" (benign) Hit max stack size limit (" SIZE_FORMAT ")",
4226                           _markStack._hit_limit);
4227    }
4228    if (_markStack._failed_double > 0) {
4229      log_trace(gc)(" (benign) Failed stack doubling (" SIZE_FORMAT "), current capacity " SIZE_FORMAT,
4230                           _markStack._failed_double, _markStack.capacity());
4231    }
4232   _markStack._hit_limit = 0;
4233   _markStack._failed_double = 0;
4234 
4235   if ((VerifyAfterGC || VerifyDuringGC) &&
4236       CMSHeap::heap()->total_collections() >= VerifyGCStartAt) {
4237     verify_after_remark();
4238   }
4239 
4240   _gc_tracer_cm->report_object_count_after_gc(&_is_alive_closure);
4241 
4242   // Change under the freelistLocks.
4243   _collectorState = Sweeping;
4244   // Call isAllClear() under bitMapLock
4245   assert(_modUnionTable.isAllClear(),
4246       "Should be clear by end of the final marking");
4247   assert(_ct->cld_rem_set()->mod_union_is_clear(),
4248       "Should be clear by end of the final marking");
4249 }
4250 
4251 void CMSParInitialMarkTask::work(uint worker_id) {
4252   elapsedTimer _timer;
4253   ResourceMark rm;
4254   HandleMark   hm;
4255 
4256   // ---------- scan from roots --------------
4257   _timer.start();
4258   CMSHeap* heap = CMSHeap::heap();
4259   ParMarkRefsIntoClosure par_mri_cl(_collector->_span, &(_collector->_markBitMap));
4260 
4261   // ---------- young gen roots --------------
4262   {
4263     work_on_young_gen_roots(&par_mri_cl);
4264     _timer.stop();
4265     log_trace(gc, task)("Finished young gen initial mark scan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4266   }
4267 
4268   // ---------- remaining roots --------------
4269   _timer.reset();
4270   _timer.start();
4271 
4272   CLDToOopClosure cld_closure(&par_mri_cl, ClassLoaderData::_claim_strong);
4273 
4274   heap->cms_process_roots(_strong_roots_scope,
4275                           false,     // yg was scanned above
4276                           GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4277                           _collector->should_unload_classes(),
4278                           &par_mri_cl,
4279                           &cld_closure,
4280                           &_par_state_string);
4281 
4282   assert(_collector->should_unload_classes()
4283          || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4284          "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4285   _timer.stop();
4286   log_trace(gc, task)("Finished remaining root initial mark scan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4287 }
4288 
4289 // Parallel remark task
4290 class CMSParRemarkTask: public CMSParMarkTask {
4291   CompactibleFreeListSpace* _cms_space;
4292 
4293   // The per-thread work queues, available here for stealing.
4294   OopTaskQueueSet*       _task_queues;
4295   ParallelTaskTerminator _term;
4296   StrongRootsScope*      _strong_roots_scope;
4297 
4298  public:
4299   // A value of 0 passed to n_workers will cause the number of
4300   // workers to be taken from the active workers in the work gang.
4301   CMSParRemarkTask(CMSCollector* collector,
4302                    CompactibleFreeListSpace* cms_space,
4303                    uint n_workers, WorkGang* workers,
4304                    OopTaskQueueSet* task_queues,
4305                    StrongRootsScope* strong_roots_scope):
4306     CMSParMarkTask("Rescan roots and grey objects in parallel",
4307                    collector, n_workers),
4308     _cms_space(cms_space),
4309     _task_queues(task_queues),
4310     _term(n_workers, task_queues),
4311     _strong_roots_scope(strong_roots_scope) { }
4312 
4313   OopTaskQueueSet* task_queues() { return _task_queues; }
4314 
4315   OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
4316 
4317   ParallelTaskTerminator* terminator() { return &_term; }
4318   uint n_workers() { return _n_workers; }
4319 
4320   void work(uint worker_id);
4321 
4322  private:
4323   // ... of  dirty cards in old space
4324   void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
4325                                   ParMarkRefsIntoAndScanClosure* cl);
4326 
4327   // ... work stealing for the above
4328   void do_work_steal(int i, ParMarkRefsIntoAndScanClosure* cl);
4329 };
4330 
4331 class RemarkCLDClosure : public CLDClosure {
4332   CLDToOopClosure _cm_closure;
4333  public:
4334   RemarkCLDClosure(OopClosure* oop_closure) : _cm_closure(oop_closure, ClassLoaderData::_claim_strong) {}
4335   void do_cld(ClassLoaderData* cld) {
4336     // Check if we have modified any oops in the CLD during the concurrent marking.
4337     if (cld->has_accumulated_modified_oops()) {
4338       cld->clear_accumulated_modified_oops();
4339 
4340       // We could have transfered the current modified marks to the accumulated marks,
4341       // like we do with the Card Table to Mod Union Table. But it's not really necessary.
4342     } else if (cld->has_modified_oops()) {
4343       // Don't clear anything, this info is needed by the next young collection.
4344     } else {
4345       // No modified oops in the ClassLoaderData.
4346       return;
4347     }
4348 
4349     // The klass has modified fields, need to scan the klass.
4350     _cm_closure.do_cld(cld);
4351   }
4352 };
4353 
4354 void CMSParMarkTask::work_on_young_gen_roots(OopsInGenClosure* cl) {
4355   ParNewGeneration* young_gen = _collector->_young_gen;
4356   ContiguousSpace* eden_space = young_gen->eden();
4357   ContiguousSpace* from_space = young_gen->from();
4358   ContiguousSpace* to_space   = young_gen->to();
4359 
4360   HeapWord** eca = _collector->_eden_chunk_array;
4361   size_t     ect = _collector->_eden_chunk_index;
4362   HeapWord** sca = _collector->_survivor_chunk_array;
4363   size_t     sct = _collector->_survivor_chunk_index;
4364 
4365   assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
4366   assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
4367 
4368   do_young_space_rescan(cl, to_space, NULL, 0);
4369   do_young_space_rescan(cl, from_space, sca, sct);
4370   do_young_space_rescan(cl, eden_space, eca, ect);
4371 }
4372 
4373 // work_queue(i) is passed to the closure
4374 // ParMarkRefsIntoAndScanClosure.  The "i" parameter
4375 // also is passed to do_dirty_card_rescan_tasks() and to
4376 // do_work_steal() to select the i-th task_queue.
4377 
4378 void CMSParRemarkTask::work(uint worker_id) {
4379   elapsedTimer _timer;
4380   ResourceMark rm;
4381   HandleMark   hm;
4382 
4383   // ---------- rescan from roots --------------
4384   _timer.start();
4385   CMSHeap* heap = CMSHeap::heap();
4386   ParMarkRefsIntoAndScanClosure par_mrias_cl(_collector,
4387     _collector->_span, _collector->ref_processor(),
4388     &(_collector->_markBitMap),
4389     work_queue(worker_id));
4390 
4391   // Rescan young gen roots first since these are likely
4392   // coarsely partitioned and may, on that account, constitute
4393   // the critical path; thus, it's best to start off that
4394   // work first.
4395   // ---------- young gen roots --------------
4396   {
4397     work_on_young_gen_roots(&par_mrias_cl);
4398     _timer.stop();
4399     log_trace(gc, task)("Finished young gen rescan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4400   }
4401 
4402   // ---------- remaining roots --------------
4403   _timer.reset();
4404   _timer.start();
4405   heap->cms_process_roots(_strong_roots_scope,
4406                           false,     // yg was scanned above
4407                           GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4408                           _collector->should_unload_classes(),
4409                           &par_mrias_cl,
4410                           NULL,     // The dirty klasses will be handled below
4411                           &_par_state_string);
4412 
4413   assert(_collector->should_unload_classes()
4414          || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4415          "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4416   _timer.stop();
4417   log_trace(gc, task)("Finished remaining root rescan work in %dth thread: %3.3f sec",  worker_id, _timer.seconds());
4418 
4419   // ---------- unhandled CLD scanning ----------
4420   if (worker_id == 0) { // Single threaded at the moment.
4421     _timer.reset();
4422     _timer.start();
4423 
4424     // Scan all new class loader data objects and new dependencies that were
4425     // introduced during concurrent marking.
4426     ResourceMark rm;
4427     GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
4428     for (int i = 0; i < array->length(); i++) {
4429       Devirtualizer::do_cld(&par_mrias_cl, array->at(i));
4430     }
4431 
4432     // We don't need to keep track of new CLDs anymore.
4433     ClassLoaderDataGraph::remember_new_clds(false);
4434 
4435     _timer.stop();
4436     log_trace(gc, task)("Finished unhandled CLD scanning work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4437   }
4438 
4439   // We might have added oops to ClassLoaderData::_handles during the
4440   // concurrent marking phase. These oops do not always point to newly allocated objects
4441   // that are guaranteed to be kept alive.  Hence,
4442   // we do have to revisit the _handles block during the remark phase.
4443 
4444   // ---------- dirty CLD scanning ----------
4445   if (worker_id == 0) { // Single threaded at the moment.
4446     _timer.reset();
4447     _timer.start();
4448 
4449     // Scan all classes that was dirtied during the concurrent marking phase.
4450     RemarkCLDClosure remark_closure(&par_mrias_cl);
4451     ClassLoaderDataGraph::cld_oops_do(&remark_closure);
4452 
4453     _timer.stop();
4454     log_trace(gc, task)("Finished dirty CLD scanning work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4455   }
4456 
4457 
4458   // ---------- rescan dirty cards ------------
4459   _timer.reset();
4460   _timer.start();
4461 
4462   // Do the rescan tasks for each of the two spaces
4463   // (cms_space) in turn.
4464   // "worker_id" is passed to select the task_queue for "worker_id"
4465   do_dirty_card_rescan_tasks(_cms_space, worker_id, &par_mrias_cl);
4466   _timer.stop();
4467   log_trace(gc, task)("Finished dirty card rescan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4468 
4469   // ---------- steal work from other threads ...
4470   // ---------- ... and drain overflow list.
4471   _timer.reset();
4472   _timer.start();
4473   do_work_steal(worker_id, &par_mrias_cl);
4474   _timer.stop();
4475   log_trace(gc, task)("Finished work stealing in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4476 }
4477 
4478 void
4479 CMSParMarkTask::do_young_space_rescan(
4480   OopsInGenClosure* cl, ContiguousSpace* space,
4481   HeapWord** chunk_array, size_t chunk_top) {
4482   // Until all tasks completed:
4483   // . claim an unclaimed task
4484   // . compute region boundaries corresponding to task claimed
4485   //   using chunk_array
4486   // . par_oop_iterate(cl) over that region
4487 
4488   ResourceMark rm;
4489   HandleMark   hm;
4490 
4491   SequentialSubTasksDone* pst = space->par_seq_tasks();
4492 
4493   uint nth_task = 0;
4494   uint n_tasks  = pst->n_tasks();
4495 
4496   if (n_tasks > 0) {
4497     assert(pst->valid(), "Uninitialized use?");
4498     HeapWord *start, *end;
4499     while (pst->try_claim_task(/* reference */ nth_task)) {
4500       // We claimed task # nth_task; compute its boundaries.
4501       if (chunk_top == 0) {  // no samples were taken
4502         assert(nth_task == 0 && n_tasks == 1, "Can have only 1 eden task");
4503         start = space->bottom();
4504         end   = space->top();
4505       } else if (nth_task == 0) {
4506         start = space->bottom();
4507         end   = chunk_array[nth_task];
4508       } else if (nth_task < (uint)chunk_top) {
4509         assert(nth_task >= 1, "Control point invariant");
4510         start = chunk_array[nth_task - 1];
4511         end   = chunk_array[nth_task];
4512       } else {
4513         assert(nth_task == (uint)chunk_top, "Control point invariant");
4514         start = chunk_array[chunk_top - 1];
4515         end   = space->top();
4516       }
4517       MemRegion mr(start, end);
4518       // Verify that mr is in space
4519       assert(mr.is_empty() || space->used_region().contains(mr),
4520              "Should be in space");
4521       // Verify that "start" is an object boundary
4522       assert(mr.is_empty() || oopDesc::is_oop(oop(mr.start())),
4523              "Should be an oop");
4524       space->par_oop_iterate(mr, cl);
4525     }
4526     pst->all_tasks_completed();
4527   }
4528 }
4529 
4530 void
4531 CMSParRemarkTask::do_dirty_card_rescan_tasks(
4532   CompactibleFreeListSpace* sp, int i,
4533   ParMarkRefsIntoAndScanClosure* cl) {
4534   // Until all tasks completed:
4535   // . claim an unclaimed task
4536   // . compute region boundaries corresponding to task claimed
4537   // . transfer dirty bits ct->mut for that region
4538   // . apply rescanclosure to dirty mut bits for that region
4539 
4540   ResourceMark rm;
4541   HandleMark   hm;
4542 
4543   OopTaskQueue* work_q = work_queue(i);
4544   ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
4545   // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
4546   // CAUTION: This closure has state that persists across calls to
4547   // the work method dirty_range_iterate_clear() in that it has
4548   // embedded in it a (subtype of) UpwardsObjectClosure. The
4549   // use of that state in the embedded UpwardsObjectClosure instance
4550   // assumes that the cards are always iterated (even if in parallel
4551   // by several threads) in monotonically increasing order per each
4552   // thread. This is true of the implementation below which picks
4553   // card ranges (chunks) in monotonically increasing order globally
4554   // and, a-fortiori, in monotonically increasing order per thread
4555   // (the latter order being a subsequence of the former).
4556   // If the work code below is ever reorganized into a more chaotic
4557   // work-partitioning form than the current "sequential tasks"
4558   // paradigm, the use of that persistent state will have to be
4559   // revisited and modified appropriately. See also related
4560   // bug 4756801 work on which should examine this code to make
4561   // sure that the changes there do not run counter to the
4562   // assumptions made here and necessary for correctness and
4563   // efficiency. Note also that this code might yield inefficient
4564   // behavior in the case of very large objects that span one or
4565   // more work chunks. Such objects would potentially be scanned
4566   // several times redundantly. Work on 4756801 should try and
4567   // address that performance anomaly if at all possible. XXX
4568   MemRegion  full_span  = _collector->_span;
4569   CMSBitMap* bm    = &(_collector->_markBitMap);     // shared
4570   MarkFromDirtyCardsClosure
4571     greyRescanClosure(_collector, full_span, // entire span of interest
4572                       sp, bm, work_q, cl);
4573 
4574   SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
4575   assert(pst->valid(), "Uninitialized use?");
4576   uint nth_task = 0;
4577   const int alignment = CardTable::card_size * BitsPerWord;
4578   MemRegion span = sp->used_region();
4579   HeapWord* start_addr = span.start();
4580   HeapWord* end_addr = align_up(span.end(), alignment);
4581   const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
4582   assert(is_aligned(start_addr, alignment), "Check alignment");
4583   assert(is_aligned(chunk_size, alignment), "Check alignment");
4584 
4585   while (pst->try_claim_task(/* reference */ nth_task)) {
4586     // Having claimed the nth_task, compute corresponding mem-region,
4587     // which is a-fortiori aligned correctly (i.e. at a MUT boundary).
4588     // The alignment restriction ensures that we do not need any
4589     // synchronization with other gang-workers while setting or
4590     // clearing bits in thus chunk of the MUT.
4591     MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
4592                                     start_addr + (nth_task+1)*chunk_size);
4593     // The last chunk's end might be way beyond end of the
4594     // used region. In that case pull back appropriately.
4595     if (this_span.end() > end_addr) {
4596       this_span.set_end(end_addr);
4597       assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
4598     }
4599     // Iterate over the dirty cards covering this chunk, marking them
4600     // precleaned, and setting the corresponding bits in the mod union
4601     // table. Since we have been careful to partition at Card and MUT-word
4602     // boundaries no synchronization is needed between parallel threads.
4603     _collector->_ct->dirty_card_iterate(this_span,
4604                                                  &modUnionClosure);
4605 
4606     // Having transferred these marks into the modUnionTable,
4607     // rescan the marked objects on the dirty cards in the modUnionTable.
4608     // Even if this is at a synchronous collection, the initial marking
4609     // may have been done during an asynchronous collection so there
4610     // may be dirty bits in the mod-union table.
4611     _collector->_modUnionTable.dirty_range_iterate_clear(
4612                   this_span, &greyRescanClosure);
4613     _collector->_modUnionTable.verifyNoOneBitsInRange(
4614                                  this_span.start(),
4615                                  this_span.end());
4616   }
4617   pst->all_tasks_completed();  // declare that i am done
4618 }
4619 
4620 // . see if we can share work_queues with ParNew? XXX
4621 void
4622 CMSParRemarkTask::do_work_steal(int i, ParMarkRefsIntoAndScanClosure* cl) {
4623   OopTaskQueue* work_q = work_queue(i);
4624   NOT_PRODUCT(int num_steals = 0;)
4625   oop obj_to_scan;
4626   CMSBitMap* bm = &(_collector->_markBitMap);
4627 
4628   while (true) {
4629     // Completely finish any left over work from (an) earlier round(s)
4630     cl->trim_queue(0);
4631     size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
4632                                          (size_t)ParGCDesiredObjsFromOverflowList);
4633     // Now check if there's any work in the overflow list
4634     // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
4635     // only affects the number of attempts made to get work from the
4636     // overflow list and does not affect the number of workers.  Just
4637     // pass ParallelGCThreads so this behavior is unchanged.
4638     if (_collector->par_take_from_overflow_list(num_from_overflow_list,
4639                                                 work_q,
4640                                                 ParallelGCThreads)) {
4641       // found something in global overflow list;
4642       // not yet ready to go stealing work from others.
4643       // We'd like to assert(work_q->size() != 0, ...)
4644       // because we just took work from the overflow list,
4645       // but of course we can't since all of that could have
4646       // been already stolen from us.
4647       // "He giveth and He taketh away."
4648       continue;
4649     }
4650     // Verify that we have no work before we resort to stealing
4651     assert(work_q->size() == 0, "Have work, shouldn't steal");
4652     // Try to steal from other queues that have work
4653     if (task_queues()->steal(i, /* reference */ obj_to_scan)) {
4654       NOT_PRODUCT(num_steals++;)
4655       assert(oopDesc::is_oop(obj_to_scan), "Oops, not an oop!");
4656       assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
4657       // Do scanning work
4658       obj_to_scan->oop_iterate(cl);
4659       // Loop around, finish this work, and try to steal some more
4660     } else if (terminator()->offer_termination()) {
4661         break;  // nirvana from the infinite cycle
4662     }
4663   }
4664   log_develop_trace(gc, task)("\t(%d: stole %d oops)", i, num_steals);
4665   assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
4666          "Else our work is not yet done");
4667 }
4668 
4669 // Record object boundaries in _eden_chunk_array by sampling the eden
4670 // top in the slow-path eden object allocation code path and record
4671 // the boundaries, if CMSEdenChunksRecordAlways is true. If
4672 // CMSEdenChunksRecordAlways is false, we use the other asynchronous
4673 // sampling in sample_eden() that activates during the part of the
4674 // preclean phase.
4675 void CMSCollector::sample_eden_chunk() {
4676   if (CMSEdenChunksRecordAlways && _eden_chunk_array != NULL) {
4677     if (_eden_chunk_lock->try_lock()) {
4678       // Record a sample. This is the critical section. The contents
4679       // of the _eden_chunk_array have to be non-decreasing in the
4680       // address order.
4681       _eden_chunk_array[_eden_chunk_index] = *_top_addr;
4682       assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4683              "Unexpected state of Eden");
4684       if (_eden_chunk_index == 0 ||
4685           ((_eden_chunk_array[_eden_chunk_index] > _eden_chunk_array[_eden_chunk_index-1]) &&
4686            (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4687                           _eden_chunk_array[_eden_chunk_index-1]) >= CMSSamplingGrain))) {
4688         _eden_chunk_index++;  // commit sample
4689       }
4690       _eden_chunk_lock->unlock();
4691     }
4692   }
4693 }
4694 
4695 // Return a thread-local PLAB recording array, as appropriate.
4696 void* CMSCollector::get_data_recorder(int thr_num) {
4697   if (_survivor_plab_array != NULL &&
4698       (CMSPLABRecordAlways ||
4699        (_collectorState > Marking && _collectorState < FinalMarking))) {
4700     assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
4701     ChunkArray* ca = &_survivor_plab_array[thr_num];
4702     ca->reset();   // clear it so that fresh data is recorded
4703     return (void*) ca;
4704   } else {
4705     return NULL;
4706   }
4707 }
4708 
4709 // Reset all the thread-local PLAB recording arrays
4710 void CMSCollector::reset_survivor_plab_arrays() {
4711   for (uint i = 0; i < ParallelGCThreads; i++) {
4712     _survivor_plab_array[i].reset();
4713   }
4714 }
4715 
4716 // Merge the per-thread plab arrays into the global survivor chunk
4717 // array which will provide the partitioning of the survivor space
4718 // for CMS initial scan and rescan.
4719 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv,
4720                                               int no_of_gc_threads) {
4721   assert(_survivor_plab_array  != NULL, "Error");
4722   assert(_survivor_chunk_array != NULL, "Error");
4723   assert(_collectorState == FinalMarking ||
4724          (CMSParallelInitialMarkEnabled && _collectorState == InitialMarking), "Error");
4725   for (int j = 0; j < no_of_gc_threads; j++) {
4726     _cursor[j] = 0;
4727   }
4728   HeapWord* top = surv->top();
4729   size_t i;
4730   for (i = 0; i < _survivor_chunk_capacity; i++) {  // all sca entries
4731     HeapWord* min_val = top;          // Higher than any PLAB address
4732     uint      min_tid = 0;            // position of min_val this round
4733     for (int j = 0; j < no_of_gc_threads; j++) {
4734       ChunkArray* cur_sca = &_survivor_plab_array[j];
4735       if (_cursor[j] == cur_sca->end()) {
4736         continue;
4737       }
4738       assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
4739       HeapWord* cur_val = cur_sca->nth(_cursor[j]);
4740       assert(surv->used_region().contains(cur_val), "Out of bounds value");
4741       if (cur_val < min_val) {
4742         min_tid = j;
4743         min_val = cur_val;
4744       } else {
4745         assert(cur_val < top, "All recorded addresses should be less");
4746       }
4747     }
4748     // At this point min_val and min_tid are respectively
4749     // the least address in _survivor_plab_array[j]->nth(_cursor[j])
4750     // and the thread (j) that witnesses that address.
4751     // We record this address in the _survivor_chunk_array[i]
4752     // and increment _cursor[min_tid] prior to the next round i.
4753     if (min_val == top) {
4754       break;
4755     }
4756     _survivor_chunk_array[i] = min_val;
4757     _cursor[min_tid]++;
4758   }
4759   // We are all done; record the size of the _survivor_chunk_array
4760   _survivor_chunk_index = i; // exclusive: [0, i)
4761   log_trace(gc, survivor)(" (Survivor:" SIZE_FORMAT "chunks) ", i);
4762   // Verify that we used up all the recorded entries
4763   #ifdef ASSERT
4764     size_t total = 0;
4765     for (int j = 0; j < no_of_gc_threads; j++) {
4766       assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
4767       total += _cursor[j];
4768     }
4769     assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
4770     // Check that the merged array is in sorted order
4771     if (total > 0) {
4772       for (size_t i = 0; i < total - 1; i++) {
4773         log_develop_trace(gc, survivor)(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
4774                                      i, p2i(_survivor_chunk_array[i]));
4775         assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
4776                "Not sorted");
4777       }
4778     }
4779   #endif // ASSERT
4780 }
4781 
4782 // Set up the space's par_seq_tasks structure for work claiming
4783 // for parallel initial scan and rescan of young gen.
4784 // See ParRescanTask where this is currently used.
4785 void
4786 CMSCollector::
4787 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
4788   assert(n_threads > 0, "Unexpected n_threads argument");
4789 
4790   // Eden space
4791   if (!_young_gen->eden()->is_empty()) {
4792     SequentialSubTasksDone* pst = _young_gen->eden()->par_seq_tasks();
4793     assert(!pst->valid(), "Clobbering existing data?");
4794     // Each valid entry in [0, _eden_chunk_index) represents a task.
4795     size_t n_tasks = _eden_chunk_index + 1;
4796     assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
4797     // Sets the condition for completion of the subtask (how many threads
4798     // need to finish in order to be done).
4799     pst->set_n_threads(n_threads);
4800     pst->set_n_tasks((int)n_tasks);
4801   }
4802 
4803   // Merge the survivor plab arrays into _survivor_chunk_array
4804   if (_survivor_plab_array != NULL) {
4805     merge_survivor_plab_arrays(_young_gen->from(), n_threads);
4806   } else {
4807     assert(_survivor_chunk_index == 0, "Error");
4808   }
4809 
4810   // To space
4811   {
4812     SequentialSubTasksDone* pst = _young_gen->to()->par_seq_tasks();
4813     assert(!pst->valid(), "Clobbering existing data?");
4814     // Sets the condition for completion of the subtask (how many threads
4815     // need to finish in order to be done).
4816     pst->set_n_threads(n_threads);
4817     pst->set_n_tasks(1);
4818     assert(pst->valid(), "Error");
4819   }
4820 
4821   // From space
4822   {
4823     SequentialSubTasksDone* pst = _young_gen->from()->par_seq_tasks();
4824     assert(!pst->valid(), "Clobbering existing data?");
4825     size_t n_tasks = _survivor_chunk_index + 1;
4826     assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
4827     // Sets the condition for completion of the subtask (how many threads
4828     // need to finish in order to be done).
4829     pst->set_n_threads(n_threads);
4830     pst->set_n_tasks((int)n_tasks);
4831     assert(pst->valid(), "Error");
4832   }
4833 }
4834 
4835 // Parallel version of remark
4836 void CMSCollector::do_remark_parallel() {
4837   CMSHeap* heap = CMSHeap::heap();
4838   WorkGang* workers = heap->workers();
4839   assert(workers != NULL, "Need parallel worker threads.");
4840   // Choose to use the number of GC workers most recently set
4841   // into "active_workers".
4842   uint n_workers = workers->active_workers();
4843 
4844   CompactibleFreeListSpace* cms_space  = _cmsGen->cmsSpace();
4845 
4846   StrongRootsScope srs(n_workers);
4847 
4848   CMSParRemarkTask tsk(this, cms_space, n_workers, workers, task_queues(), &srs);
4849 
4850   // We won't be iterating over the cards in the card table updating
4851   // the younger_gen cards, so we shouldn't call the following else
4852   // the verification code as well as subsequent younger_refs_iterate
4853   // code would get confused. XXX
4854   // heap->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
4855 
4856   // The young gen rescan work will not be done as part of
4857   // process_roots (which currently doesn't know how to
4858   // parallelize such a scan), but rather will be broken up into
4859   // a set of parallel tasks (via the sampling that the [abortable]
4860   // preclean phase did of eden, plus the [two] tasks of
4861   // scanning the [two] survivor spaces. Further fine-grain
4862   // parallelization of the scanning of the survivor spaces
4863   // themselves, and of precleaning of the young gen itself
4864   // is deferred to the future.
4865   initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
4866 
4867   // The dirty card rescan work is broken up into a "sequence"
4868   // of parallel tasks (per constituent space) that are dynamically
4869   // claimed by the parallel threads.
4870   cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
4871 
4872   // It turns out that even when we're using 1 thread, doing the work in a
4873   // separate thread causes wide variance in run times.  We can't help this
4874   // in the multi-threaded case, but we special-case n=1 here to get
4875   // repeatable measurements of the 1-thread overhead of the parallel code.
4876   if (n_workers > 1) {
4877     // Make refs discovery MT-safe, if it isn't already: it may not
4878     // necessarily be so, since it's possible that we are doing
4879     // ST marking.
4880     ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), true);
4881     workers->run_task(&tsk);
4882   } else {
4883     ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
4884     tsk.work(0);
4885   }
4886 
4887   // restore, single-threaded for now, any preserved marks
4888   // as a result of work_q overflow
4889   restore_preserved_marks_if_any();
4890 }
4891 
4892 // Non-parallel version of remark
4893 void CMSCollector::do_remark_non_parallel() {
4894   ResourceMark rm;
4895   HandleMark   hm;
4896   CMSHeap* heap = CMSHeap::heap();
4897   ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
4898 
4899   MarkRefsIntoAndScanClosure
4900     mrias_cl(_span, ref_processor(), &_markBitMap, NULL /* not precleaning */,
4901              &_markStack, this,
4902              false /* should_yield */, false /* not precleaning */);
4903   MarkFromDirtyCardsClosure
4904     markFromDirtyCardsClosure(this, _span,
4905                               NULL,  // space is set further below
4906                               &_markBitMap, &_markStack, &mrias_cl);
4907   {
4908     GCTraceTime(Trace, gc, phases) t("Grey Object Rescan", _gc_timer_cm);
4909     // Iterate over the dirty cards, setting the corresponding bits in the
4910     // mod union table.
4911     {
4912       ModUnionClosure modUnionClosure(&_modUnionTable);
4913       _ct->dirty_card_iterate(_cmsGen->used_region(),
4914                               &modUnionClosure);
4915     }
4916     // Having transferred these marks into the modUnionTable, we just need
4917     // to rescan the marked objects on the dirty cards in the modUnionTable.
4918     // The initial marking may have been done during an asynchronous
4919     // collection so there may be dirty bits in the mod-union table.
4920     const int alignment = CardTable::card_size * BitsPerWord;
4921     {
4922       // ... First handle dirty cards in CMS gen
4923       markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
4924       MemRegion ur = _cmsGen->used_region();
4925       HeapWord* lb = ur.start();
4926       HeapWord* ub = align_up(ur.end(), alignment);
4927       MemRegion cms_span(lb, ub);
4928       _modUnionTable.dirty_range_iterate_clear(cms_span,
4929                                                &markFromDirtyCardsClosure);
4930       verify_work_stacks_empty();
4931       log_trace(gc)(" (re-scanned " SIZE_FORMAT " dirty cards in cms gen) ", markFromDirtyCardsClosure.num_dirty_cards());
4932     }
4933   }
4934   if (VerifyDuringGC &&
4935       CMSHeap::heap()->total_collections() >= VerifyGCStartAt) {
4936     HandleMark hm;  // Discard invalid handles created during verification
4937     Universe::verify();
4938   }
4939   {
4940     GCTraceTime(Trace, gc, phases) t("Root Rescan", _gc_timer_cm);
4941 
4942     verify_work_stacks_empty();
4943 
4944     heap->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
4945     StrongRootsScope srs(1);
4946 
4947     heap->cms_process_roots(&srs,
4948                             true,  // young gen as roots
4949                             GenCollectedHeap::ScanningOption(roots_scanning_options()),
4950                             should_unload_classes(),
4951                             &mrias_cl,
4952                             NULL); // The dirty klasses will be handled below
4953 
4954     assert(should_unload_classes()
4955            || (roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4956            "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4957   }
4958 
4959   {
4960     GCTraceTime(Trace, gc, phases) t("Visit Unhandled CLDs", _gc_timer_cm);
4961 
4962     verify_work_stacks_empty();
4963 
4964     // Scan all class loader data objects that might have been introduced
4965     // during concurrent marking.
4966     ResourceMark rm;
4967     GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
4968     for (int i = 0; i < array->length(); i++) {
4969       Devirtualizer::do_cld(&mrias_cl, array->at(i));
4970     }
4971 
4972     // We don't need to keep track of new CLDs anymore.
4973     ClassLoaderDataGraph::remember_new_clds(false);
4974 
4975     verify_work_stacks_empty();
4976   }
4977 
4978   // We might have added oops to ClassLoaderData::_handles during the
4979   // concurrent marking phase. These oops do not point to newly allocated objects
4980   // that are guaranteed to be kept alive.  Hence,
4981   // we do have to revisit the _handles block during the remark phase.
4982   {
4983     GCTraceTime(Trace, gc, phases) t("Dirty CLD Scan", _gc_timer_cm);
4984 
4985     verify_work_stacks_empty();
4986 
4987     RemarkCLDClosure remark_closure(&mrias_cl);
4988     ClassLoaderDataGraph::cld_oops_do(&remark_closure);
4989 
4990     verify_work_stacks_empty();
4991   }
4992 
4993   verify_work_stacks_empty();
4994   // Restore evacuated mark words, if any, used for overflow list links
4995   restore_preserved_marks_if_any();
4996 
4997   verify_overflow_empty();
4998 }
4999 
5000 ////////////////////////////////////////////////////////
5001 // Parallel Reference Processing Task Proxy Class
5002 ////////////////////////////////////////////////////////
5003 class AbstractGangTaskWOopQueues : public AbstractGangTask {
5004   OopTaskQueueSet*       _queues;
5005   ParallelTaskTerminator _terminator;
5006  public:
5007   AbstractGangTaskWOopQueues(const char* name, OopTaskQueueSet* queues, uint n_threads) :
5008     AbstractGangTask(name), _queues(queues), _terminator(n_threads, _queues) {}
5009   ParallelTaskTerminator* terminator() { return &_terminator; }
5010   OopTaskQueueSet* queues() { return _queues; }
5011 };
5012 
5013 class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues {
5014   typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
5015   CMSCollector*          _collector;
5016   CMSBitMap*             _mark_bit_map;
5017   const MemRegion        _span;
5018   ProcessTask&           _task;
5019 
5020 public:
5021   CMSRefProcTaskProxy(ProcessTask&     task,
5022                       CMSCollector*    collector,
5023                       const MemRegion& span,
5024                       CMSBitMap*       mark_bit_map,
5025                       AbstractWorkGang* workers,
5026                       OopTaskQueueSet* task_queues):
5027     AbstractGangTaskWOopQueues("Process referents by policy in parallel",
5028       task_queues,
5029       workers->active_workers()),
5030     _collector(collector),
5031     _mark_bit_map(mark_bit_map),
5032     _span(span),
5033     _task(task)
5034   {
5035     assert(_collector->_span.equals(_span) && !_span.is_empty(),
5036            "Inconsistency in _span");
5037   }
5038 
5039   OopTaskQueueSet* task_queues() { return queues(); }
5040 
5041   OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5042 
5043   void do_work_steal(int i,
5044                      CMSParDrainMarkingStackClosure* drain,
5045                      CMSParKeepAliveClosure* keep_alive);
5046 
5047   virtual void work(uint worker_id);
5048 };
5049 
5050 void CMSRefProcTaskProxy::work(uint worker_id) {
5051   ResourceMark rm;
5052   HandleMark hm;
5053   assert(_collector->_span.equals(_span), "Inconsistency in _span");
5054   CMSParKeepAliveClosure par_keep_alive(_collector, _span,
5055                                         _mark_bit_map,
5056                                         work_queue(worker_id));
5057   CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
5058                                                  _mark_bit_map,
5059                                                  work_queue(worker_id));
5060   CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
5061   _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack);
5062   if (_task.marks_oops_alive()) {
5063     do_work_steal(worker_id, &par_drain_stack, &par_keep_alive);
5064   }
5065   assert(work_queue(worker_id)->size() == 0, "work_queue should be empty");
5066   assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
5067 }
5068 
5069 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
5070   MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue):
5071    _span(span),
5072    _work_queue(work_queue),
5073    _bit_map(bit_map),
5074    _mark_and_push(collector, span, bit_map, work_queue),
5075    _low_water_mark(MIN2((work_queue->max_elems()/4),
5076                         ((uint)CMSWorkQueueDrainThreshold * ParallelGCThreads)))
5077 { }
5078 
5079 // . see if we can share work_queues with ParNew? XXX
5080 void CMSRefProcTaskProxy::do_work_steal(int i,
5081   CMSParDrainMarkingStackClosure* drain,
5082   CMSParKeepAliveClosure* keep_alive) {
5083   OopTaskQueue* work_q = work_queue(i);
5084   NOT_PRODUCT(int num_steals = 0;)
5085   oop obj_to_scan;
5086 
5087   while (true) {
5088     // Completely finish any left over work from (an) earlier round(s)
5089     drain->trim_queue(0);
5090     size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5091                                          (size_t)ParGCDesiredObjsFromOverflowList);
5092     // Now check if there's any work in the overflow list
5093     // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5094     // only affects the number of attempts made to get work from the
5095     // overflow list and does not affect the number of workers.  Just
5096     // pass ParallelGCThreads so this behavior is unchanged.
5097     if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5098                                                 work_q,
5099                                                 ParallelGCThreads)) {
5100       // Found something in global overflow list;
5101       // not yet ready to go stealing work from others.
5102       // We'd like to assert(work_q->size() != 0, ...)
5103       // because we just took work from the overflow list,
5104       // but of course we can't, since all of that might have
5105       // been already stolen from us.
5106       continue;
5107     }
5108     // Verify that we have no work before we resort to stealing
5109     assert(work_q->size() == 0, "Have work, shouldn't steal");
5110     // Try to steal from other queues that have work
5111     if (task_queues()->steal(i, /* reference */ obj_to_scan)) {
5112       NOT_PRODUCT(num_steals++;)
5113       assert(oopDesc::is_oop(obj_to_scan), "Oops, not an oop!");
5114       assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5115       // Do scanning work
5116       obj_to_scan->oop_iterate(keep_alive);
5117       // Loop around, finish this work, and try to steal some more
5118     } else if (terminator()->offer_termination()) {
5119       break;  // nirvana from the infinite cycle
5120     }
5121   }
5122   log_develop_trace(gc, task)("\t(%d: stole %d oops)", i, num_steals);
5123 }
5124 
5125 void CMSRefProcTaskExecutor::execute(ProcessTask& task, uint ergo_workers) {
5126   CMSHeap* heap = CMSHeap::heap();
5127   WorkGang* workers = heap->workers();
5128   assert(workers != NULL, "Need parallel worker threads.");
5129   assert(workers->active_workers() == ergo_workers,
5130          "Ergonomically chosen workers (%u) must be equal to active workers (%u)",
5131          ergo_workers, workers->active_workers());
5132   CMSRefProcTaskProxy rp_task(task, &_collector,
5133                               _collector.ref_processor_span(),
5134                               _collector.markBitMap(),
5135                               workers, _collector.task_queues());
5136   workers->run_task(&rp_task, workers->active_workers());
5137 }
5138 
5139 void CMSCollector::refProcessingWork() {
5140   ResourceMark rm;
5141   HandleMark   hm;
5142 
5143   ReferenceProcessor* rp = ref_processor();
5144   assert(_span_based_discoverer.span().equals(_span), "Spans should be equal");
5145   assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
5146   // Process weak references.
5147   rp->setup_policy(false);
5148   verify_work_stacks_empty();
5149 
5150   ReferenceProcessorPhaseTimes pt(_gc_timer_cm, rp->max_num_queues());
5151   {
5152     GCTraceTime(Debug, gc, phases) t("Reference Processing", _gc_timer_cm);
5153 
5154     // Setup keep_alive and complete closures.
5155     CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
5156                                             &_markStack, false /* !preclean */);
5157     CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
5158                                   _span, &_markBitMap, &_markStack,
5159                                   &cmsKeepAliveClosure, false /* !preclean */);
5160 
5161     ReferenceProcessorStats stats;
5162     if (rp->processing_is_mt()) {
5163       // Set the degree of MT here.  If the discovery is done MT, there
5164       // may have been a different number of threads doing the discovery
5165       // and a different number of discovered lists may have Ref objects.
5166       // That is OK as long as the Reference lists are balanced (see
5167       // balance_all_queues() and balance_queues()).
5168       CMSHeap* heap = CMSHeap::heap();
5169       uint active_workers = ParallelGCThreads;
5170       WorkGang* workers = heap->workers();
5171       if (workers != NULL) {
5172         active_workers = workers->active_workers();
5173         // The expectation is that active_workers will have already
5174         // been set to a reasonable value.  If it has not been set,
5175         // investigate.
5176         assert(active_workers > 0, "Should have been set during scavenge");
5177       }
5178       rp->set_active_mt_degree(active_workers);
5179       CMSRefProcTaskExecutor task_executor(*this);
5180       stats = rp->process_discovered_references(&_is_alive_closure,
5181                                         &cmsKeepAliveClosure,
5182                                         &cmsDrainMarkingStackClosure,
5183                                         &task_executor,
5184                                         &pt);
5185     } else {
5186       stats = rp->process_discovered_references(&_is_alive_closure,
5187                                         &cmsKeepAliveClosure,
5188                                         &cmsDrainMarkingStackClosure,
5189                                         NULL,
5190                                         &pt);
5191     }
5192     _gc_tracer_cm->report_gc_reference_stats(stats);
5193     pt.print_all_references();
5194   }
5195 
5196   // This is the point where the entire marking should have completed.
5197   verify_work_stacks_empty();
5198 
5199   {
5200     GCTraceTime(Debug, gc, phases) t("Weak Processing", _gc_timer_cm);
5201     WeakProcessor::weak_oops_do(&_is_alive_closure, &do_nothing_cl);
5202   }
5203 
5204   if (should_unload_classes()) {
5205     {
5206       GCTraceTime(Debug, gc, phases) t("Class Unloading", _gc_timer_cm);
5207 
5208       // Unload classes and purge the SystemDictionary.
5209       bool purged_class = SystemDictionary::do_unloading(_gc_timer_cm);
5210 
5211       // Unload nmethods.
5212       CodeCache::do_unloading(&_is_alive_closure, purged_class);
5213 
5214       // Prune dead klasses from subklass/sibling/implementor lists.
5215       Klass::clean_weak_klass_links(purged_class);
5216     }
5217 
5218     {
5219       GCTraceTime(Debug, gc, phases) t("Scrub Symbol Table", _gc_timer_cm);
5220       // Clean up unreferenced symbols in symbol table.
5221       SymbolTable::unlink();
5222     }
5223 
5224     {
5225       GCTraceTime(Debug, gc, phases) t("Scrub String Table", _gc_timer_cm);
5226       // Delete entries for dead interned strings.
5227       StringTable::unlink(&_is_alive_closure);
5228     }
5229   }
5230 
5231   // Restore any preserved marks as a result of mark stack or
5232   // work queue overflow
5233   restore_preserved_marks_if_any();  // done single-threaded for now
5234 
5235   rp->set_enqueuing_is_done(true);
5236   rp->verify_no_references_recorded();
5237 }
5238 
5239 #ifndef PRODUCT
5240 void CMSCollector::check_correct_thread_executing() {
5241   Thread* t = Thread::current();
5242   // Only the VM thread or the CMS thread should be here.
5243   assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
5244          "Unexpected thread type");
5245   // If this is the vm thread, the foreground process
5246   // should not be waiting.  Note that _foregroundGCIsActive is
5247   // true while the foreground collector is waiting.
5248   if (_foregroundGCShouldWait) {
5249     // We cannot be the VM thread
5250     assert(t->is_ConcurrentGC_thread(),
5251            "Should be CMS thread");
5252   } else {
5253     // We can be the CMS thread only if we are in a stop-world
5254     // phase of CMS collection.
5255     if (t->is_ConcurrentGC_thread()) {
5256       assert(_collectorState == InitialMarking ||
5257              _collectorState == FinalMarking,
5258              "Should be a stop-world phase");
5259       // The CMS thread should be holding the CMS_token.
5260       assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5261              "Potential interference with concurrently "
5262              "executing VM thread");
5263     }
5264   }
5265 }
5266 #endif
5267 
5268 void CMSCollector::sweep() {
5269   assert(_collectorState == Sweeping, "just checking");
5270   check_correct_thread_executing();
5271   verify_work_stacks_empty();
5272   verify_overflow_empty();
5273   increment_sweep_count();
5274   TraceCMSMemoryManagerStats tms(_collectorState, CMSHeap::heap()->gc_cause());
5275 
5276   _inter_sweep_timer.stop();
5277   _inter_sweep_estimate.sample(_inter_sweep_timer.seconds());
5278 
5279   assert(!_intra_sweep_timer.is_active(), "Should not be active");
5280   _intra_sweep_timer.reset();
5281   _intra_sweep_timer.start();
5282   {
5283     GCTraceCPUTime tcpu;
5284     CMSPhaseAccounting pa(this, "Concurrent Sweep");
5285     // First sweep the old gen
5286     {
5287       CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
5288                                bitMapLock());
5289       sweepWork(_cmsGen);
5290     }
5291 
5292     // Update Universe::_heap_*_at_gc figures.
5293     // We need all the free list locks to make the abstract state
5294     // transition from Sweeping to Resetting. See detailed note
5295     // further below.
5296     {
5297       CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock());
5298       // Update heap occupancy information which is used as
5299       // input to soft ref clearing policy at the next gc.
5300       Universe::update_heap_info_at_gc();
5301       _collectorState = Resizing;
5302     }
5303   }
5304   verify_work_stacks_empty();
5305   verify_overflow_empty();
5306 
5307   if (should_unload_classes()) {
5308     // Delay purge to the beginning of the next safepoint.  Metaspace::contains
5309     // requires that the virtual spaces are stable and not deleted.
5310     ClassLoaderDataGraph::set_should_purge(true);
5311   }
5312 
5313   _intra_sweep_timer.stop();
5314   _intra_sweep_estimate.sample(_intra_sweep_timer.seconds());
5315 
5316   _inter_sweep_timer.reset();
5317   _inter_sweep_timer.start();
5318 
5319   // We need to use a monotonically non-decreasing time in ms
5320   // or we will see time-warp warnings and os::javaTimeMillis()
5321   // does not guarantee monotonicity.
5322   jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
5323   update_time_of_last_gc(now);
5324 
5325   // NOTE on abstract state transitions:
5326   // Mutators allocate-live and/or mark the mod-union table dirty
5327   // based on the state of the collection.  The former is done in
5328   // the interval [Marking, Sweeping] and the latter in the interval
5329   // [Marking, Sweeping).  Thus the transitions into the Marking state
5330   // and out of the Sweeping state must be synchronously visible
5331   // globally to the mutators.
5332   // The transition into the Marking state happens with the world
5333   // stopped so the mutators will globally see it.  Sweeping is
5334   // done asynchronously by the background collector so the transition
5335   // from the Sweeping state to the Resizing state must be done
5336   // under the freelistLock (as is the check for whether to
5337   // allocate-live and whether to dirty the mod-union table).
5338   assert(_collectorState == Resizing, "Change of collector state to"
5339     " Resizing must be done under the freelistLocks (plural)");
5340 
5341   // Now that sweeping has been completed, we clear
5342   // the incremental_collection_failed flag,
5343   // thus inviting a younger gen collection to promote into
5344   // this generation. If such a promotion may still fail,
5345   // the flag will be set again when a young collection is
5346   // attempted.
5347   CMSHeap* heap = CMSHeap::heap();
5348   heap->clear_incremental_collection_failed();  // Worth retrying as fresh space may have been freed up
5349   heap->update_full_collections_completed(_collection_count_start);
5350 }
5351 
5352 // FIX ME!!! Looks like this belongs in CFLSpace, with
5353 // CMSGen merely delegating to it.
5354 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
5355   double nearLargestPercent = FLSLargestBlockCoalesceProximity;
5356   HeapWord*  minAddr        = _cmsSpace->bottom();
5357   HeapWord*  largestAddr    =
5358     (HeapWord*) _cmsSpace->dictionary()->find_largest_dict();
5359   if (largestAddr == NULL) {
5360     // The dictionary appears to be empty.  In this case
5361     // try to coalesce at the end of the heap.
5362     largestAddr = _cmsSpace->end();
5363   }
5364   size_t largestOffset     = pointer_delta(largestAddr, minAddr);
5365   size_t nearLargestOffset =
5366     (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
5367   log_debug(gc, freelist)("CMS: Large Block: " PTR_FORMAT "; Proximity: " PTR_FORMAT " -> " PTR_FORMAT,
5368                           p2i(largestAddr), p2i(_cmsSpace->nearLargestChunk()), p2i(minAddr + nearLargestOffset));
5369   _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
5370 }
5371 
5372 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
5373   return addr >= _cmsSpace->nearLargestChunk();
5374 }
5375 
5376 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
5377   return _cmsSpace->find_chunk_at_end();
5378 }
5379 
5380 void ConcurrentMarkSweepGeneration::update_gc_stats(Generation* current_generation,
5381                                                     bool full) {
5382   // If the young generation has been collected, gather any statistics
5383   // that are of interest at this point.
5384   bool current_is_young = CMSHeap::heap()->is_young_gen(current_generation);
5385   if (!full && current_is_young) {
5386     // Gather statistics on the young generation collection.
5387     collector()->stats().record_gc0_end(used());
5388   }
5389 }
5390 
5391 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* old_gen) {
5392   // We iterate over the space(s) underlying this generation,
5393   // checking the mark bit map to see if the bits corresponding
5394   // to specific blocks are marked or not. Blocks that are
5395   // marked are live and are not swept up. All remaining blocks
5396   // are swept up, with coalescing on-the-fly as we sweep up
5397   // contiguous free and/or garbage blocks:
5398   // We need to ensure that the sweeper synchronizes with allocators
5399   // and stop-the-world collectors. In particular, the following
5400   // locks are used:
5401   // . CMS token: if this is held, a stop the world collection cannot occur
5402   // . freelistLock: if this is held no allocation can occur from this
5403   //                 generation by another thread
5404   // . bitMapLock: if this is held, no other thread can access or update
5405   //
5406 
5407   // Note that we need to hold the freelistLock if we use
5408   // block iterate below; else the iterator might go awry if
5409   // a mutator (or promotion) causes block contents to change
5410   // (for instance if the allocator divvies up a block).
5411   // If we hold the free list lock, for all practical purposes
5412   // young generation GC's can't occur (they'll usually need to
5413   // promote), so we might as well prevent all young generation
5414   // GC's while we do a sweeping step. For the same reason, we might
5415   // as well take the bit map lock for the entire duration
5416 
5417   // check that we hold the requisite locks
5418   assert(have_cms_token(), "Should hold cms token");
5419   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), "Should possess CMS token to sweep");
5420   assert_lock_strong(old_gen->freelistLock());
5421   assert_lock_strong(bitMapLock());
5422 
5423   assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context");
5424   assert(_intra_sweep_timer.is_active(),  "Was switched on  in an outer context");
5425   old_gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
5426                                           _inter_sweep_estimate.padded_average(),
5427                                           _intra_sweep_estimate.padded_average());
5428   old_gen->setNearLargestChunk();
5429 
5430   {
5431     SweepClosure sweepClosure(this, old_gen, &_markBitMap, CMSYield);
5432     old_gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
5433     // We need to free-up/coalesce garbage/blocks from a
5434     // co-terminal free run. This is done in the SweepClosure
5435     // destructor; so, do not remove this scope, else the
5436     // end-of-sweep-census below will be off by a little bit.
5437   }
5438   old_gen->cmsSpace()->sweep_completed();
5439   old_gen->cmsSpace()->endSweepFLCensus(sweep_count());
5440   if (should_unload_classes()) {                // unloaded classes this cycle,
5441     _concurrent_cycles_since_last_unload = 0;   // ... reset count
5442   } else {                                      // did not unload classes,
5443     _concurrent_cycles_since_last_unload++;     // ... increment count
5444   }
5445 }
5446 
5447 // Reset CMS data structures (for now just the marking bit map)
5448 // preparatory for the next cycle.
5449 void CMSCollector::reset_concurrent() {
5450   CMSTokenSyncWithLocks ts(true, bitMapLock());
5451 
5452   // If the state is not "Resetting", the foreground  thread
5453   // has done a collection and the resetting.
5454   if (_collectorState != Resetting) {
5455     assert(_collectorState == Idling, "The state should only change"
5456       " because the foreground collector has finished the collection");
5457     return;
5458   }
5459 
5460   {
5461     // Clear the mark bitmap (no grey objects to start with)
5462     // for the next cycle.
5463     GCTraceCPUTime tcpu;
5464     CMSPhaseAccounting cmspa(this, "Concurrent Reset");
5465 
5466     HeapWord* curAddr = _markBitMap.startWord();
5467     while (curAddr < _markBitMap.endWord()) {
5468       size_t remaining  = pointer_delta(_markBitMap.endWord(), curAddr);
5469       MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
5470       _markBitMap.clear_large_range(chunk);
5471       if (ConcurrentMarkSweepThread::should_yield() &&
5472           !foregroundGCIsActive() &&
5473           CMSYield) {
5474         assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5475                "CMS thread should hold CMS token");
5476         assert_lock_strong(bitMapLock());
5477         bitMapLock()->unlock();
5478         ConcurrentMarkSweepThread::desynchronize(true);
5479         stopTimer();
5480         incrementYields();
5481 
5482         // See the comment in coordinator_yield()
5483         for (unsigned i = 0; i < CMSYieldSleepCount &&
5484                          ConcurrentMarkSweepThread::should_yield() &&
5485                          !CMSCollector::foregroundGCIsActive(); ++i) {
5486           os::sleep(Thread::current(), 1, false);
5487         }
5488 
5489         ConcurrentMarkSweepThread::synchronize(true);
5490         bitMapLock()->lock_without_safepoint_check();
5491         startTimer();
5492       }
5493       curAddr = chunk.end();
5494     }
5495     // A successful mostly concurrent collection has been done.
5496     // Because only the full (i.e., concurrent mode failure) collections
5497     // are being measured for gc overhead limits, clean the "near" flag
5498     // and count.
5499     size_policy()->reset_gc_overhead_limit_count();
5500     _collectorState = Idling;
5501   }
5502 
5503   register_gc_end();
5504 }
5505 
5506 // Same as above but for STW paths
5507 void CMSCollector::reset_stw() {
5508   // already have the lock
5509   assert(_collectorState == Resetting, "just checking");
5510   assert_lock_strong(bitMapLock());
5511   GCIdMark gc_id_mark(_cmsThread->gc_id());
5512   _markBitMap.clear_all();
5513   _collectorState = Idling;
5514   register_gc_end();
5515 }
5516 
5517 void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) {
5518   GCTraceCPUTime tcpu;
5519   TraceCollectorStats tcs_cgc(cgc_counters());
5520 
5521   switch (op) {
5522     case CMS_op_checkpointRootsInitial: {
5523       GCTraceTime(Info, gc) t("Pause Initial Mark", NULL, GCCause::_no_gc, true);
5524       SvcGCMarker sgcm(SvcGCMarker::CONCURRENT);
5525       checkpointRootsInitial();
5526       break;
5527     }
5528     case CMS_op_checkpointRootsFinal: {
5529       GCTraceTime(Info, gc) t("Pause Remark", NULL, GCCause::_no_gc, true);
5530       SvcGCMarker sgcm(SvcGCMarker::CONCURRENT);
5531       checkpointRootsFinal();
5532       break;
5533     }
5534     default:
5535       fatal("No such CMS_op");
5536   }
5537 }
5538 
5539 #ifndef PRODUCT
5540 size_t const CMSCollector::skip_header_HeapWords() {
5541   return FreeChunk::header_size();
5542 }
5543 
5544 // Try and collect here conditions that should hold when
5545 // CMS thread is exiting. The idea is that the foreground GC
5546 // thread should not be blocked if it wants to terminate
5547 // the CMS thread and yet continue to run the VM for a while
5548 // after that.
5549 void CMSCollector::verify_ok_to_terminate() const {
5550   assert(Thread::current()->is_ConcurrentGC_thread(),
5551          "should be called by CMS thread");
5552   assert(!_foregroundGCShouldWait, "should be false");
5553   // We could check here that all the various low-level locks
5554   // are not held by the CMS thread, but that is overkill; see
5555   // also CMSThread::verify_ok_to_terminate() where the CGC_lock
5556   // is checked.
5557 }
5558 #endif
5559 
5560 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
5561    assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
5562           "missing Printezis mark?");
5563   HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5564   size_t size = pointer_delta(nextOneAddr + 1, addr);
5565   assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5566          "alignment problem");
5567   assert(size >= 3, "Necessary for Printezis marks to work");
5568   return size;
5569 }
5570 
5571 // A variant of the above (block_size_using_printezis_bits()) except
5572 // that we return 0 if the P-bits are not yet set.
5573 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
5574   if (_markBitMap.isMarked(addr + 1)) {
5575     assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects");
5576     HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5577     size_t size = pointer_delta(nextOneAddr + 1, addr);
5578     assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5579            "alignment problem");
5580     assert(size >= 3, "Necessary for Printezis marks to work");
5581     return size;
5582   }
5583   return 0;
5584 }
5585 
5586 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
5587   size_t sz = 0;
5588   oop p = (oop)addr;
5589   if (p->klass_or_null_acquire() != NULL) {
5590     sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
5591   } else {
5592     sz = block_size_using_printezis_bits(addr);
5593   }
5594   assert(sz > 0, "size must be nonzero");
5595   HeapWord* next_block = addr + sz;
5596   HeapWord* next_card  = align_up(next_block, CardTable::card_size);
5597   assert(align_down((uintptr_t)addr,      CardTable::card_size) <
5598          align_down((uintptr_t)next_card, CardTable::card_size),
5599          "must be different cards");
5600   return next_card;
5601 }
5602 
5603 
5604 // CMS Bit Map Wrapper /////////////////////////////////////////
5605 
5606 // Construct a CMS bit map infrastructure, but don't create the
5607 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
5608 // further below.
5609 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
5610   _shifter(shifter),
5611   _bm(),
5612   _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true,
5613                                     Monitor::_safepoint_check_sometimes) : NULL)
5614 {
5615   _bmStartWord = 0;
5616   _bmWordSize  = 0;
5617 }
5618 
5619 bool CMSBitMap::allocate(MemRegion mr) {
5620   _bmStartWord = mr.start();
5621   _bmWordSize  = mr.word_size();
5622   ReservedSpace brs(ReservedSpace::allocation_align_size_up(
5623                      (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
5624   if (!brs.is_reserved()) {
5625     log_warning(gc)("CMS bit map allocation failure");
5626     return false;
5627   }
5628   // For now we'll just commit all of the bit map up front.
5629   // Later on we'll try to be more parsimonious with swap.
5630   if (!_virtual_space.initialize(brs, brs.size())) {
5631     log_warning(gc)("CMS bit map backing store failure");
5632     return false;
5633   }
5634   assert(_virtual_space.committed_size() == brs.size(),
5635          "didn't reserve backing store for all of CMS bit map?");
5636   assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
5637          _bmWordSize, "inconsistency in bit map sizing");
5638   _bm = BitMapView((BitMap::bm_word_t*)_virtual_space.low(), _bmWordSize >> _shifter);
5639 
5640   // bm.clear(); // can we rely on getting zero'd memory? verify below
5641   assert(isAllClear(),
5642          "Expected zero'd memory from ReservedSpace constructor");
5643   assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
5644          "consistency check");
5645   return true;
5646 }
5647 
5648 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
5649   HeapWord *next_addr, *end_addr, *last_addr;
5650   assert_locked();
5651   assert(covers(mr), "out-of-range error");
5652   // XXX assert that start and end are appropriately aligned
5653   for (next_addr = mr.start(), end_addr = mr.end();
5654        next_addr < end_addr; next_addr = last_addr) {
5655     MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
5656     last_addr = dirty_region.end();
5657     if (!dirty_region.is_empty()) {
5658       cl->do_MemRegion(dirty_region);
5659     } else {
5660       assert(last_addr == end_addr, "program logic");
5661       return;
5662     }
5663   }
5664 }
5665 
5666 void CMSBitMap::print_on_error(outputStream* st, const char* prefix) const {
5667   _bm.print_on_error(st, prefix);
5668 }
5669 
5670 #ifndef PRODUCT
5671 void CMSBitMap::assert_locked() const {
5672   CMSLockVerifier::assert_locked(lock());
5673 }
5674 
5675 bool CMSBitMap::covers(MemRegion mr) const {
5676   // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
5677   assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
5678          "size inconsistency");
5679   return (mr.start() >= _bmStartWord) &&
5680          (mr.end()   <= endWord());
5681 }
5682 
5683 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
5684     return (start >= _bmStartWord && (start + size) <= endWord());
5685 }
5686 
5687 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
5688   // verify that there are no 1 bits in the interval [left, right)
5689   FalseBitMapClosure falseBitMapClosure;
5690   iterate(&falseBitMapClosure, left, right);
5691 }
5692 
5693 void CMSBitMap::region_invariant(MemRegion mr)
5694 {
5695   assert_locked();
5696   // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
5697   assert(!mr.is_empty(), "unexpected empty region");
5698   assert(covers(mr), "mr should be covered by bit map");
5699   // convert address range into offset range
5700   size_t start_ofs = heapWordToOffset(mr.start());
5701   // Make sure that end() is appropriately aligned
5702   assert(mr.end() == align_up(mr.end(), (1 << (_shifter+LogHeapWordSize))),
5703          "Misaligned mr.end()");
5704   size_t end_ofs   = heapWordToOffset(mr.end());
5705   assert(end_ofs > start_ofs, "Should mark at least one bit");
5706 }
5707 
5708 #endif
5709 
5710 bool CMSMarkStack::allocate(size_t size) {
5711   // allocate a stack of the requisite depth
5712   ReservedSpace rs(ReservedSpace::allocation_align_size_up(
5713                    size * sizeof(oop)));
5714   if (!rs.is_reserved()) {
5715     log_warning(gc)("CMSMarkStack allocation failure");
5716     return false;
5717   }
5718   if (!_virtual_space.initialize(rs, rs.size())) {
5719     log_warning(gc)("CMSMarkStack backing store failure");
5720     return false;
5721   }
5722   assert(_virtual_space.committed_size() == rs.size(),
5723          "didn't reserve backing store for all of CMS stack?");
5724   _base = (oop*)(_virtual_space.low());
5725   _index = 0;
5726   _capacity = size;
5727   NOT_PRODUCT(_max_depth = 0);
5728   return true;
5729 }
5730 
5731 // XXX FIX ME !!! In the MT case we come in here holding a
5732 // leaf lock. For printing we need to take a further lock
5733 // which has lower rank. We need to recalibrate the two
5734 // lock-ranks involved in order to be able to print the
5735 // messages below. (Or defer the printing to the caller.
5736 // For now we take the expedient path of just disabling the
5737 // messages for the problematic case.)
5738 void CMSMarkStack::expand() {
5739   assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted");
5740   if (_capacity == MarkStackSizeMax) {
5741     if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled) {
5742       // We print a warning message only once per CMS cycle.
5743       log_debug(gc)(" (benign) Hit CMSMarkStack max size limit");
5744     }
5745     return;
5746   }
5747   // Double capacity if possible
5748   size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax);
5749   // Do not give up existing stack until we have managed to
5750   // get the double capacity that we desired.
5751   ReservedSpace rs(ReservedSpace::allocation_align_size_up(
5752                    new_capacity * sizeof(oop)));
5753   if (rs.is_reserved()) {
5754     // Release the backing store associated with old stack
5755     _virtual_space.release();
5756     // Reinitialize virtual space for new stack
5757     if (!_virtual_space.initialize(rs, rs.size())) {
5758       fatal("Not enough swap for expanded marking stack");
5759     }
5760     _base = (oop*)(_virtual_space.low());
5761     _index = 0;
5762     _capacity = new_capacity;
5763   } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled) {
5764     // Failed to double capacity, continue;
5765     // we print a detail message only once per CMS cycle.
5766     log_debug(gc)(" (benign) Failed to expand marking stack from " SIZE_FORMAT "K to " SIZE_FORMAT "K",
5767                         _capacity / K, new_capacity / K);
5768   }
5769 }
5770 
5771 
5772 // Closures
5773 // XXX: there seems to be a lot of code  duplication here;
5774 // should refactor and consolidate common code.
5775 
5776 // This closure is used to mark refs into the CMS generation in
5777 // the CMS bit map. Called at the first checkpoint. This closure
5778 // assumes that we do not need to re-mark dirty cards; if the CMS
5779 // generation on which this is used is not an oldest
5780 // generation then this will lose younger_gen cards!
5781 
5782 MarkRefsIntoClosure::MarkRefsIntoClosure(
5783   MemRegion span, CMSBitMap* bitMap):
5784     _span(span),
5785     _bitMap(bitMap)
5786 {
5787   assert(ref_discoverer() == NULL, "deliberately left NULL");
5788   assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
5789 }
5790 
5791 void MarkRefsIntoClosure::do_oop(oop obj) {
5792   // if p points into _span, then mark corresponding bit in _markBitMap
5793   assert(oopDesc::is_oop(obj), "expected an oop");
5794   HeapWord* addr = (HeapWord*)obj;
5795   if (_span.contains(addr)) {
5796     // this should be made more efficient
5797     _bitMap->mark(addr);
5798   }
5799 }
5800 
5801 ParMarkRefsIntoClosure::ParMarkRefsIntoClosure(
5802   MemRegion span, CMSBitMap* bitMap):
5803     _span(span),
5804     _bitMap(bitMap)
5805 {
5806   assert(ref_discoverer() == NULL, "deliberately left NULL");
5807   assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
5808 }
5809 
5810 void ParMarkRefsIntoClosure::do_oop(oop obj) {
5811   // if p points into _span, then mark corresponding bit in _markBitMap
5812   assert(oopDesc::is_oop(obj), "expected an oop");
5813   HeapWord* addr = (HeapWord*)obj;
5814   if (_span.contains(addr)) {
5815     // this should be made more efficient
5816     _bitMap->par_mark(addr);
5817   }
5818 }
5819 
5820 // A variant of the above, used for CMS marking verification.
5821 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
5822   MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm):
5823     _span(span),
5824     _verification_bm(verification_bm),
5825     _cms_bm(cms_bm)
5826 {
5827   assert(ref_discoverer() == NULL, "deliberately left NULL");
5828   assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
5829 }
5830 
5831 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
5832   // if p points into _span, then mark corresponding bit in _markBitMap
5833   assert(oopDesc::is_oop(obj), "expected an oop");
5834   HeapWord* addr = (HeapWord*)obj;
5835   if (_span.contains(addr)) {
5836     _verification_bm->mark(addr);
5837     if (!_cms_bm->isMarked(addr)) {
5838       Log(gc, verify) log;
5839       ResourceMark rm;
5840       LogStream ls(log.error());
5841       oop(addr)->print_on(&ls);
5842       log.error(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
5843       fatal("... aborting");
5844     }
5845   }
5846 }
5847 
5848 //////////////////////////////////////////////////
5849 // MarkRefsIntoAndScanClosure
5850 //////////////////////////////////////////////////
5851 
5852 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
5853                                                        ReferenceDiscoverer* rd,
5854                                                        CMSBitMap* bit_map,
5855                                                        CMSBitMap* mod_union_table,
5856                                                        CMSMarkStack*  mark_stack,
5857                                                        CMSCollector* collector,
5858                                                        bool should_yield,
5859                                                        bool concurrent_precleaning):
5860   _span(span),
5861   _bit_map(bit_map),
5862   _mark_stack(mark_stack),
5863   _pushAndMarkClosure(collector, span, rd, bit_map, mod_union_table,
5864                       mark_stack, concurrent_precleaning),
5865   _collector(collector),
5866   _freelistLock(NULL),
5867   _yield(should_yield),
5868   _concurrent_precleaning(concurrent_precleaning)
5869 {
5870   // FIXME: Should initialize in base class constructor.
5871   assert(rd != NULL, "ref_discoverer shouldn't be NULL");
5872   set_ref_discoverer_internal(rd);
5873 }
5874 
5875 // This closure is used to mark refs into the CMS generation at the
5876 // second (final) checkpoint, and to scan and transitively follow
5877 // the unmarked oops. It is also used during the concurrent precleaning
5878 // phase while scanning objects on dirty cards in the CMS generation.
5879 // The marks are made in the marking bit map and the marking stack is
5880 // used for keeping the (newly) grey objects during the scan.
5881 // The parallel version (Par_...) appears further below.
5882 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
5883   if (obj != NULL) {
5884     assert(oopDesc::is_oop(obj), "expected an oop");
5885     HeapWord* addr = (HeapWord*)obj;
5886     assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
5887     assert(_collector->overflow_list_is_empty(),
5888            "overflow list should be empty");
5889     if (_span.contains(addr) &&
5890         !_bit_map->isMarked(addr)) {
5891       // mark bit map (object is now grey)
5892       _bit_map->mark(addr);
5893       // push on marking stack (stack should be empty), and drain the
5894       // stack by applying this closure to the oops in the oops popped
5895       // from the stack (i.e. blacken the grey objects)
5896       bool res = _mark_stack->push(obj);
5897       assert(res, "Should have space to push on empty stack");
5898       do {
5899         oop new_oop = _mark_stack->pop();
5900         assert(new_oop != NULL && oopDesc::is_oop(new_oop), "Expected an oop");
5901         assert(_bit_map->isMarked((HeapWord*)new_oop),
5902                "only grey objects on this stack");
5903         // iterate over the oops in this oop, marking and pushing
5904         // the ones in CMS heap (i.e. in _span).
5905         new_oop->oop_iterate(&_pushAndMarkClosure);
5906         // check if it's time to yield
5907         do_yield_check();
5908       } while (!_mark_stack->isEmpty() ||
5909                (!_concurrent_precleaning && take_from_overflow_list()));
5910         // if marking stack is empty, and we are not doing this
5911         // during precleaning, then check the overflow list
5912     }
5913     assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
5914     assert(_collector->overflow_list_is_empty(),
5915            "overflow list was drained above");
5916 
5917     assert(_collector->no_preserved_marks(),
5918            "All preserved marks should have been restored above");
5919   }
5920 }
5921 
5922 void MarkRefsIntoAndScanClosure::do_yield_work() {
5923   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5924          "CMS thread should hold CMS token");
5925   assert_lock_strong(_freelistLock);
5926   assert_lock_strong(_bit_map->lock());
5927   // relinquish the free_list_lock and bitMaplock()
5928   _bit_map->lock()->unlock();
5929   _freelistLock->unlock();
5930   ConcurrentMarkSweepThread::desynchronize(true);
5931   _collector->stopTimer();
5932   _collector->incrementYields();
5933 
5934   // See the comment in coordinator_yield()
5935   for (unsigned i = 0;
5936        i < CMSYieldSleepCount &&
5937        ConcurrentMarkSweepThread::should_yield() &&
5938        !CMSCollector::foregroundGCIsActive();
5939        ++i) {
5940     os::sleep(Thread::current(), 1, false);
5941   }
5942 
5943   ConcurrentMarkSweepThread::synchronize(true);
5944   _freelistLock->lock_without_safepoint_check();
5945   _bit_map->lock()->lock_without_safepoint_check();
5946   _collector->startTimer();
5947 }
5948 
5949 ///////////////////////////////////////////////////////////
5950 // ParMarkRefsIntoAndScanClosure: a parallel version of
5951 //                                MarkRefsIntoAndScanClosure
5952 ///////////////////////////////////////////////////////////
5953 ParMarkRefsIntoAndScanClosure::ParMarkRefsIntoAndScanClosure(
5954   CMSCollector* collector, MemRegion span, ReferenceDiscoverer* rd,
5955   CMSBitMap* bit_map, OopTaskQueue* work_queue):
5956   _span(span),
5957   _bit_map(bit_map),
5958   _work_queue(work_queue),
5959   _low_water_mark(MIN2((work_queue->max_elems()/4),
5960                        ((uint)CMSWorkQueueDrainThreshold * ParallelGCThreads))),
5961   _parPushAndMarkClosure(collector, span, rd, bit_map, work_queue)
5962 {
5963   // FIXME: Should initialize in base class constructor.
5964   assert(rd != NULL, "ref_discoverer shouldn't be NULL");
5965   set_ref_discoverer_internal(rd);
5966 }
5967 
5968 // This closure is used to mark refs into the CMS generation at the
5969 // second (final) checkpoint, and to scan and transitively follow
5970 // the unmarked oops. The marks are made in the marking bit map and
5971 // the work_queue is used for keeping the (newly) grey objects during
5972 // the scan phase whence they are also available for stealing by parallel
5973 // threads. Since the marking bit map is shared, updates are
5974 // synchronized (via CAS).
5975 void ParMarkRefsIntoAndScanClosure::do_oop(oop obj) {
5976   if (obj != NULL) {
5977     // Ignore mark word because this could be an already marked oop
5978     // that may be chained at the end of the overflow list.
5979     assert(oopDesc::is_oop(obj, true), "expected an oop");
5980     HeapWord* addr = (HeapWord*)obj;
5981     if (_span.contains(addr) &&
5982         !_bit_map->isMarked(addr)) {
5983       // mark bit map (object will become grey):
5984       // It is possible for several threads to be
5985       // trying to "claim" this object concurrently;
5986       // the unique thread that succeeds in marking the
5987       // object first will do the subsequent push on
5988       // to the work queue (or overflow list).
5989       if (_bit_map->par_mark(addr)) {
5990         // push on work_queue (which may not be empty), and trim the
5991         // queue to an appropriate length by applying this closure to
5992         // the oops in the oops popped from the stack (i.e. blacken the
5993         // grey objects)
5994         bool res = _work_queue->push(obj);
5995         assert(res, "Low water mark should be less than capacity?");
5996         trim_queue(_low_water_mark);
5997       } // Else, another thread claimed the object
5998     }
5999   }
6000 }
6001 
6002 // This closure is used to rescan the marked objects on the dirty cards
6003 // in the mod union table and the card table proper.
6004 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
6005   oop p, MemRegion mr) {
6006 
6007   size_t size = 0;
6008   HeapWord* addr = (HeapWord*)p;
6009   DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6010   assert(_span.contains(addr), "we are scanning the CMS generation");
6011   // check if it's time to yield
6012   if (do_yield_check()) {
6013     // We yielded for some foreground stop-world work,
6014     // and we have been asked to abort this ongoing preclean cycle.
6015     return 0;
6016   }
6017   if (_bitMap->isMarked(addr)) {
6018     // it's marked; is it potentially uninitialized?
6019     if (p->klass_or_null_acquire() != NULL) {
6020         // an initialized object; ignore mark word in verification below
6021         // since we are running concurrent with mutators
6022         assert(oopDesc::is_oop(p, true), "should be an oop");
6023         if (p->is_objArray()) {
6024           // objArrays are precisely marked; restrict scanning
6025           // to dirty cards only.
6026           size = CompactibleFreeListSpace::adjustObjectSize(
6027                    p->oop_iterate_size(_scanningClosure, mr));
6028         } else {
6029           // A non-array may have been imprecisely marked; we need
6030           // to scan object in its entirety.
6031           size = CompactibleFreeListSpace::adjustObjectSize(
6032                    p->oop_iterate_size(_scanningClosure));
6033         }
6034       #ifdef ASSERT
6035         size_t direct_size =
6036           CompactibleFreeListSpace::adjustObjectSize(p->size());
6037         assert(size == direct_size, "Inconsistency in size");
6038         assert(size >= 3, "Necessary for Printezis marks to work");
6039         HeapWord* start_pbit = addr + 1;
6040         HeapWord* end_pbit = addr + size - 1;
6041         assert(_bitMap->isMarked(start_pbit) == _bitMap->isMarked(end_pbit),
6042                "inconsistent Printezis mark");
6043         // Verify inner mark bits (between Printezis bits) are clear,
6044         // but don't repeat if there are multiple dirty regions for
6045         // the same object, to avoid potential O(N^2) performance.
6046         if (addr != _last_scanned_object) {
6047           _bitMap->verifyNoOneBitsInRange(start_pbit + 1, end_pbit);
6048           _last_scanned_object = addr;
6049         }
6050       #endif // ASSERT
6051     } else {
6052       // An uninitialized object.
6053       assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
6054       HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
6055       size = pointer_delta(nextOneAddr + 1, addr);
6056       assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6057              "alignment problem");
6058       // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
6059       // will dirty the card when the klass pointer is installed in the
6060       // object (signaling the completion of initialization).
6061     }
6062   } else {
6063     // Either a not yet marked object or an uninitialized object
6064     if (p->klass_or_null_acquire() == NULL) {
6065       // An uninitialized object, skip to the next card, since
6066       // we may not be able to read its P-bits yet.
6067       assert(size == 0, "Initial value");
6068     } else {
6069       // An object not (yet) reached by marking: we merely need to
6070       // compute its size so as to go look at the next block.
6071       assert(oopDesc::is_oop(p, true), "should be an oop");
6072       size = CompactibleFreeListSpace::adjustObjectSize(p->size());
6073     }
6074   }
6075   DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6076   return size;
6077 }
6078 
6079 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
6080   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6081          "CMS thread should hold CMS token");
6082   assert_lock_strong(_freelistLock);
6083   assert_lock_strong(_bitMap->lock());
6084   // relinquish the free_list_lock and bitMaplock()
6085   _bitMap->lock()->unlock();
6086   _freelistLock->unlock();
6087   ConcurrentMarkSweepThread::desynchronize(true);
6088   _collector->stopTimer();
6089   _collector->incrementYields();
6090 
6091   // See the comment in coordinator_yield()
6092   for (unsigned i = 0; i < CMSYieldSleepCount &&
6093                    ConcurrentMarkSweepThread::should_yield() &&
6094                    !CMSCollector::foregroundGCIsActive(); ++i) {
6095     os::sleep(Thread::current(), 1, false);
6096   }
6097 
6098   ConcurrentMarkSweepThread::synchronize(true);
6099   _freelistLock->lock_without_safepoint_check();
6100   _bitMap->lock()->lock_without_safepoint_check();
6101   _collector->startTimer();
6102 }
6103 
6104 
6105 //////////////////////////////////////////////////////////////////
6106 // SurvivorSpacePrecleanClosure
6107 //////////////////////////////////////////////////////////////////
6108 // This (single-threaded) closure is used to preclean the oops in
6109 // the survivor spaces.
6110 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
6111 
6112   HeapWord* addr = (HeapWord*)p;
6113   DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6114   assert(!_span.contains(addr), "we are scanning the survivor spaces");
6115   assert(p->klass_or_null() != NULL, "object should be initialized");
6116   // an initialized object; ignore mark word in verification below
6117   // since we are running concurrent with mutators
6118   assert(oopDesc::is_oop(p, true), "should be an oop");
6119   // Note that we do not yield while we iterate over
6120   // the interior oops of p, pushing the relevant ones
6121   // on our marking stack.
6122   size_t size = p->oop_iterate_size(_scanning_closure);
6123   do_yield_check();
6124   // Observe that below, we do not abandon the preclean
6125   // phase as soon as we should; rather we empty the
6126   // marking stack before returning. This is to satisfy
6127   // some existing assertions. In general, it may be a
6128   // good idea to abort immediately and complete the marking
6129   // from the grey objects at a later time.
6130   while (!_mark_stack->isEmpty()) {
6131     oop new_oop = _mark_stack->pop();
6132     assert(new_oop != NULL && oopDesc::is_oop(new_oop), "Expected an oop");
6133     assert(_bit_map->isMarked((HeapWord*)new_oop),
6134            "only grey objects on this stack");
6135     // iterate over the oops in this oop, marking and pushing
6136     // the ones in CMS heap (i.e. in _span).
6137     new_oop->oop_iterate(_scanning_closure);
6138     // check if it's time to yield
6139     do_yield_check();
6140   }
6141   unsigned int after_count =
6142     CMSHeap::heap()->total_collections();
6143   bool abort = (_before_count != after_count) ||
6144                _collector->should_abort_preclean();
6145   return abort ? 0 : size;
6146 }
6147 
6148 void SurvivorSpacePrecleanClosure::do_yield_work() {
6149   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6150          "CMS thread should hold CMS token");
6151   assert_lock_strong(_bit_map->lock());
6152   // Relinquish the bit map lock
6153   _bit_map->lock()->unlock();
6154   ConcurrentMarkSweepThread::desynchronize(true);
6155   _collector->stopTimer();
6156   _collector->incrementYields();
6157 
6158   // See the comment in coordinator_yield()
6159   for (unsigned i = 0; i < CMSYieldSleepCount &&
6160                        ConcurrentMarkSweepThread::should_yield() &&
6161                        !CMSCollector::foregroundGCIsActive(); ++i) {
6162     os::sleep(Thread::current(), 1, false);
6163   }
6164 
6165   ConcurrentMarkSweepThread::synchronize(true);
6166   _bit_map->lock()->lock_without_safepoint_check();
6167   _collector->startTimer();
6168 }
6169 
6170 // This closure is used to rescan the marked objects on the dirty cards
6171 // in the mod union table and the card table proper. In the parallel
6172 // case, although the bitMap is shared, we do a single read so the
6173 // isMarked() query is "safe".
6174 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
6175   // Ignore mark word because we are running concurrent with mutators
6176   assert(oopDesc::is_oop_or_null(p, true), "Expected an oop or NULL at " PTR_FORMAT, p2i(p));
6177   HeapWord* addr = (HeapWord*)p;
6178   assert(_span.contains(addr), "we are scanning the CMS generation");
6179   bool is_obj_array = false;
6180   #ifdef ASSERT
6181     if (!_parallel) {
6182       assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6183       assert(_collector->overflow_list_is_empty(),
6184              "overflow list should be empty");
6185 
6186     }
6187   #endif // ASSERT
6188   if (_bit_map->isMarked(addr)) {
6189     // Obj arrays are precisely marked, non-arrays are not;
6190     // so we scan objArrays precisely and non-arrays in their
6191     // entirety.
6192     if (p->is_objArray()) {
6193       is_obj_array = true;
6194       if (_parallel) {
6195         p->oop_iterate(_par_scan_closure, mr);
6196       } else {
6197         p->oop_iterate(_scan_closure, mr);
6198       }
6199     } else {
6200       if (_parallel) {
6201         p->oop_iterate(_par_scan_closure);
6202       } else {
6203         p->oop_iterate(_scan_closure);
6204       }
6205     }
6206   }
6207   #ifdef ASSERT
6208     if (!_parallel) {
6209       assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6210       assert(_collector->overflow_list_is_empty(),
6211              "overflow list should be empty");
6212 
6213     }
6214   #endif // ASSERT
6215   return is_obj_array;
6216 }
6217 
6218 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
6219                         MemRegion span,
6220                         CMSBitMap* bitMap, CMSMarkStack*  markStack,
6221                         bool should_yield, bool verifying):
6222   _collector(collector),
6223   _span(span),
6224   _bitMap(bitMap),
6225   _mut(&collector->_modUnionTable),
6226   _markStack(markStack),
6227   _yield(should_yield),
6228   _skipBits(0)
6229 {
6230   assert(_markStack->isEmpty(), "stack should be empty");
6231   _finger = _bitMap->startWord();
6232   _threshold = _finger;
6233   assert(_collector->_restart_addr == NULL, "Sanity check");
6234   assert(_span.contains(_finger), "Out of bounds _finger?");
6235   DEBUG_ONLY(_verifying = verifying;)
6236 }
6237 
6238 void MarkFromRootsClosure::reset(HeapWord* addr) {
6239   assert(_markStack->isEmpty(), "would cause duplicates on stack");
6240   assert(_span.contains(addr), "Out of bounds _finger?");
6241   _finger = addr;
6242   _threshold = align_up(_finger, CardTable::card_size);
6243 }
6244 
6245 // Should revisit to see if this should be restructured for
6246 // greater efficiency.
6247 bool MarkFromRootsClosure::do_bit(size_t offset) {
6248   if (_skipBits > 0) {
6249     _skipBits--;
6250     return true;
6251   }
6252   // convert offset into a HeapWord*
6253   HeapWord* addr = _bitMap->startWord() + offset;
6254   assert(_bitMap->endWord() && addr < _bitMap->endWord(),
6255          "address out of range");
6256   assert(_bitMap->isMarked(addr), "tautology");
6257   if (_bitMap->isMarked(addr+1)) {
6258     // this is an allocated but not yet initialized object
6259     assert(_skipBits == 0, "tautology");
6260     _skipBits = 2;  // skip next two marked bits ("Printezis-marks")
6261     oop p = oop(addr);
6262     if (p->klass_or_null_acquire() == NULL) {
6263       DEBUG_ONLY(if (!_verifying) {)
6264         // We re-dirty the cards on which this object lies and increase
6265         // the _threshold so that we'll come back to scan this object
6266         // during the preclean or remark phase. (CMSCleanOnEnter)
6267         if (CMSCleanOnEnter) {
6268           size_t sz = _collector->block_size_using_printezis_bits(addr);
6269           HeapWord* end_card_addr = align_up(addr + sz, CardTable::card_size);
6270           MemRegion redirty_range = MemRegion(addr, end_card_addr);
6271           assert(!redirty_range.is_empty(), "Arithmetical tautology");
6272           // Bump _threshold to end_card_addr; note that
6273           // _threshold cannot possibly exceed end_card_addr, anyhow.
6274           // This prevents future clearing of the card as the scan proceeds
6275           // to the right.
6276           assert(_threshold <= end_card_addr,
6277                  "Because we are just scanning into this object");
6278           if (_threshold < end_card_addr) {
6279             _threshold = end_card_addr;
6280           }
6281           if (p->klass_or_null_acquire() != NULL) {
6282             // Redirty the range of cards...
6283             _mut->mark_range(redirty_range);
6284           } // ...else the setting of klass will dirty the card anyway.
6285         }
6286       DEBUG_ONLY(})
6287       return true;
6288     }
6289   }
6290   scanOopsInOop(addr);
6291   return true;
6292 }
6293 
6294 // We take a break if we've been at this for a while,
6295 // so as to avoid monopolizing the locks involved.
6296 void MarkFromRootsClosure::do_yield_work() {
6297   // First give up the locks, then yield, then re-lock
6298   // We should probably use a constructor/destructor idiom to
6299   // do this unlock/lock or modify the MutexUnlocker class to
6300   // serve our purpose. XXX
6301   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6302          "CMS thread should hold CMS token");
6303   assert_lock_strong(_bitMap->lock());
6304   _bitMap->lock()->unlock();
6305   ConcurrentMarkSweepThread::desynchronize(true);
6306   _collector->stopTimer();
6307   _collector->incrementYields();
6308 
6309   // See the comment in coordinator_yield()
6310   for (unsigned i = 0; i < CMSYieldSleepCount &&
6311                        ConcurrentMarkSweepThread::should_yield() &&
6312                        !CMSCollector::foregroundGCIsActive(); ++i) {
6313     os::sleep(Thread::current(), 1, false);
6314   }
6315 
6316   ConcurrentMarkSweepThread::synchronize(true);
6317   _bitMap->lock()->lock_without_safepoint_check();
6318   _collector->startTimer();
6319 }
6320 
6321 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
6322   assert(_bitMap->isMarked(ptr), "expected bit to be set");
6323   assert(_markStack->isEmpty(),
6324          "should drain stack to limit stack usage");
6325   // convert ptr to an oop preparatory to scanning
6326   oop obj = oop(ptr);
6327   // Ignore mark word in verification below, since we
6328   // may be running concurrent with mutators.
6329   assert(oopDesc::is_oop(obj, true), "should be an oop");
6330   assert(_finger <= ptr, "_finger runneth ahead");
6331   // advance the finger to right end of this object
6332   _finger = ptr + obj->size();
6333   assert(_finger > ptr, "we just incremented it above");
6334   // On large heaps, it may take us some time to get through
6335   // the marking phase. During
6336   // this time it's possible that a lot of mutations have
6337   // accumulated in the card table and the mod union table --
6338   // these mutation records are redundant until we have
6339   // actually traced into the corresponding card.
6340   // Here, we check whether advancing the finger would make
6341   // us cross into a new card, and if so clear corresponding
6342   // cards in the MUT (preclean them in the card-table in the
6343   // future).
6344 
6345   DEBUG_ONLY(if (!_verifying) {)
6346     // The clean-on-enter optimization is disabled by default,
6347     // until we fix 6178663.
6348     if (CMSCleanOnEnter && (_finger > _threshold)) {
6349       // [_threshold, _finger) represents the interval
6350       // of cards to be cleared  in MUT (or precleaned in card table).
6351       // The set of cards to be cleared is all those that overlap
6352       // with the interval [_threshold, _finger); note that
6353       // _threshold is always kept card-aligned but _finger isn't
6354       // always card-aligned.
6355       HeapWord* old_threshold = _threshold;
6356       assert(is_aligned(old_threshold, CardTable::card_size),
6357              "_threshold should always be card-aligned");
6358       _threshold = align_up(_finger, CardTable::card_size);
6359       MemRegion mr(old_threshold, _threshold);
6360       assert(!mr.is_empty(), "Control point invariant");
6361       assert(_span.contains(mr), "Should clear within span");
6362       _mut->clear_range(mr);
6363     }
6364   DEBUG_ONLY(})
6365   // Note: the finger doesn't advance while we drain
6366   // the stack below.
6367   PushOrMarkClosure pushOrMarkClosure(_collector,
6368                                       _span, _bitMap, _markStack,
6369                                       _finger, this);
6370   bool res = _markStack->push(obj);
6371   assert(res, "Empty non-zero size stack should have space for single push");
6372   while (!_markStack->isEmpty()) {
6373     oop new_oop = _markStack->pop();
6374     // Skip verifying header mark word below because we are
6375     // running concurrent with mutators.
6376     assert(oopDesc::is_oop(new_oop, true), "Oops! expected to pop an oop");
6377     // now scan this oop's oops
6378     new_oop->oop_iterate(&pushOrMarkClosure);
6379     do_yield_check();
6380   }
6381   assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
6382 }
6383 
6384 ParMarkFromRootsClosure::ParMarkFromRootsClosure(CMSConcMarkingTask* task,
6385                        CMSCollector* collector, MemRegion span,
6386                        CMSBitMap* bit_map,
6387                        OopTaskQueue* work_queue,
6388                        CMSMarkStack*  overflow_stack):
6389   _collector(collector),
6390   _whole_span(collector->_span),
6391   _span(span),
6392   _bit_map(bit_map),
6393   _mut(&collector->_modUnionTable),
6394   _work_queue(work_queue),
6395   _overflow_stack(overflow_stack),
6396   _skip_bits(0),
6397   _task(task)
6398 {
6399   assert(_work_queue->size() == 0, "work_queue should be empty");
6400   _finger = span.start();
6401   _threshold = _finger;     // XXX Defer clear-on-enter optimization for now
6402   assert(_span.contains(_finger), "Out of bounds _finger?");
6403 }
6404 
6405 // Should revisit to see if this should be restructured for
6406 // greater efficiency.
6407 bool ParMarkFromRootsClosure::do_bit(size_t offset) {
6408   if (_skip_bits > 0) {
6409     _skip_bits--;
6410     return true;
6411   }
6412   // convert offset into a HeapWord*
6413   HeapWord* addr = _bit_map->startWord() + offset;
6414   assert(_bit_map->endWord() && addr < _bit_map->endWord(),
6415          "address out of range");
6416   assert(_bit_map->isMarked(addr), "tautology");
6417   if (_bit_map->isMarked(addr+1)) {
6418     // this is an allocated object that might not yet be initialized
6419     assert(_skip_bits == 0, "tautology");
6420     _skip_bits = 2;  // skip next two marked bits ("Printezis-marks")
6421     oop p = oop(addr);
6422     if (p->klass_or_null_acquire() == NULL) {
6423       // in the case of Clean-on-Enter optimization, redirty card
6424       // and avoid clearing card by increasing  the threshold.
6425       return true;
6426     }
6427   }
6428   scan_oops_in_oop(addr);
6429   return true;
6430 }
6431 
6432 void ParMarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
6433   assert(_bit_map->isMarked(ptr), "expected bit to be set");
6434   // Should we assert that our work queue is empty or
6435   // below some drain limit?
6436   assert(_work_queue->size() == 0,
6437          "should drain stack to limit stack usage");
6438   // convert ptr to an oop preparatory to scanning
6439   oop obj = oop(ptr);
6440   // Ignore mark word in verification below, since we
6441   // may be running concurrent with mutators.
6442   assert(oopDesc::is_oop(obj, true), "should be an oop");
6443   assert(_finger <= ptr, "_finger runneth ahead");
6444   // advance the finger to right end of this object
6445   _finger = ptr + obj->size();
6446   assert(_finger > ptr, "we just incremented it above");
6447   // On large heaps, it may take us some time to get through
6448   // the marking phase. During
6449   // this time it's possible that a lot of mutations have
6450   // accumulated in the card table and the mod union table --
6451   // these mutation records are redundant until we have
6452   // actually traced into the corresponding card.
6453   // Here, we check whether advancing the finger would make
6454   // us cross into a new card, and if so clear corresponding
6455   // cards in the MUT (preclean them in the card-table in the
6456   // future).
6457 
6458   // The clean-on-enter optimization is disabled by default,
6459   // until we fix 6178663.
6460   if (CMSCleanOnEnter && (_finger > _threshold)) {
6461     // [_threshold, _finger) represents the interval
6462     // of cards to be cleared  in MUT (or precleaned in card table).
6463     // The set of cards to be cleared is all those that overlap
6464     // with the interval [_threshold, _finger); note that
6465     // _threshold is always kept card-aligned but _finger isn't
6466     // always card-aligned.
6467     HeapWord* old_threshold = _threshold;
6468     assert(is_aligned(old_threshold, CardTable::card_size),
6469            "_threshold should always be card-aligned");
6470     _threshold = align_up(_finger, CardTable::card_size);
6471     MemRegion mr(old_threshold, _threshold);
6472     assert(!mr.is_empty(), "Control point invariant");
6473     assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
6474     _mut->clear_range(mr);
6475   }
6476 
6477   // Note: the local finger doesn't advance while we drain
6478   // the stack below, but the global finger sure can and will.
6479   HeapWord* volatile* gfa = _task->global_finger_addr();
6480   ParPushOrMarkClosure pushOrMarkClosure(_collector,
6481                                          _span, _bit_map,
6482                                          _work_queue,
6483                                          _overflow_stack,
6484                                          _finger,
6485                                          gfa, this);
6486   bool res = _work_queue->push(obj);   // overflow could occur here
6487   assert(res, "Will hold once we use workqueues");
6488   while (true) {
6489     oop new_oop;
6490     if (!_work_queue->pop_local(new_oop)) {
6491       // We emptied our work_queue; check if there's stuff that can
6492       // be gotten from the overflow stack.
6493       if (CMSConcMarkingTask::get_work_from_overflow_stack(
6494             _overflow_stack, _work_queue)) {
6495         do_yield_check();
6496         continue;
6497       } else {  // done
6498         break;
6499       }
6500     }
6501     // Skip verifying header mark word below because we are
6502     // running concurrent with mutators.
6503     assert(oopDesc::is_oop(new_oop, true), "Oops! expected to pop an oop");
6504     // now scan this oop's oops
6505     new_oop->oop_iterate(&pushOrMarkClosure);
6506     do_yield_check();
6507   }
6508   assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
6509 }
6510 
6511 // Yield in response to a request from VM Thread or
6512 // from mutators.
6513 void ParMarkFromRootsClosure::do_yield_work() {
6514   assert(_task != NULL, "sanity");
6515   _task->yield();
6516 }
6517 
6518 // A variant of the above used for verifying CMS marking work.
6519 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
6520                         MemRegion span,
6521                         CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6522                         CMSMarkStack*  mark_stack):
6523   _collector(collector),
6524   _span(span),
6525   _verification_bm(verification_bm),
6526   _cms_bm(cms_bm),
6527   _mark_stack(mark_stack),
6528   _pam_verify_closure(collector, span, verification_bm, cms_bm,
6529                       mark_stack)
6530 {
6531   assert(_mark_stack->isEmpty(), "stack should be empty");
6532   _finger = _verification_bm->startWord();
6533   assert(_collector->_restart_addr == NULL, "Sanity check");
6534   assert(_span.contains(_finger), "Out of bounds _finger?");
6535 }
6536 
6537 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
6538   assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
6539   assert(_span.contains(addr), "Out of bounds _finger?");
6540   _finger = addr;
6541 }
6542 
6543 // Should revisit to see if this should be restructured for
6544 // greater efficiency.
6545 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
6546   // convert offset into a HeapWord*
6547   HeapWord* addr = _verification_bm->startWord() + offset;
6548   assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
6549          "address out of range");
6550   assert(_verification_bm->isMarked(addr), "tautology");
6551   assert(_cms_bm->isMarked(addr), "tautology");
6552 
6553   assert(_mark_stack->isEmpty(),
6554          "should drain stack to limit stack usage");
6555   // convert addr to an oop preparatory to scanning
6556   oop obj = oop(addr);
6557   assert(oopDesc::is_oop(obj), "should be an oop");
6558   assert(_finger <= addr, "_finger runneth ahead");
6559   // advance the finger to right end of this object
6560   _finger = addr + obj->size();
6561   assert(_finger > addr, "we just incremented it above");
6562   // Note: the finger doesn't advance while we drain
6563   // the stack below.
6564   bool res = _mark_stack->push(obj);
6565   assert(res, "Empty non-zero size stack should have space for single push");
6566   while (!_mark_stack->isEmpty()) {
6567     oop new_oop = _mark_stack->pop();
6568     assert(oopDesc::is_oop(new_oop), "Oops! expected to pop an oop");
6569     // now scan this oop's oops
6570     new_oop->oop_iterate(&_pam_verify_closure);
6571   }
6572   assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
6573   return true;
6574 }
6575 
6576 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
6577   CMSCollector* collector, MemRegion span,
6578   CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6579   CMSMarkStack*  mark_stack):
6580   MetadataVisitingOopIterateClosure(collector->ref_processor()),
6581   _collector(collector),
6582   _span(span),
6583   _verification_bm(verification_bm),
6584   _cms_bm(cms_bm),
6585   _mark_stack(mark_stack)
6586 { }
6587 
6588 template <class T> void PushAndMarkVerifyClosure::do_oop_work(T *p) {
6589   oop obj = RawAccess<>::oop_load(p);
6590   do_oop(obj);
6591 }
6592 
6593 void PushAndMarkVerifyClosure::do_oop(oop* p)       { PushAndMarkVerifyClosure::do_oop_work(p); }
6594 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
6595 
6596 // Upon stack overflow, we discard (part of) the stack,
6597 // remembering the least address amongst those discarded
6598 // in CMSCollector's _restart_address.
6599 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
6600   // Remember the least grey address discarded
6601   HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
6602   _collector->lower_restart_addr(ra);
6603   _mark_stack->reset();  // discard stack contents
6604   _mark_stack->expand(); // expand the stack if possible
6605 }
6606 
6607 void PushAndMarkVerifyClosure::do_oop(oop obj) {
6608   assert(oopDesc::is_oop_or_null(obj), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6609   HeapWord* addr = (HeapWord*)obj;
6610   if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
6611     // Oop lies in _span and isn't yet grey or black
6612     _verification_bm->mark(addr);            // now grey
6613     if (!_cms_bm->isMarked(addr)) {
6614       Log(gc, verify) log;
6615       ResourceMark rm;
6616       LogStream ls(log.error());
6617       oop(addr)->print_on(&ls);
6618       log.error(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
6619       fatal("... aborting");
6620     }
6621 
6622     if (!_mark_stack->push(obj)) { // stack overflow
6623       log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _mark_stack->capacity());
6624       assert(_mark_stack->isFull(), "Else push should have succeeded");
6625       handle_stack_overflow(addr);
6626     }
6627     // anything including and to the right of _finger
6628     // will be scanned as we iterate over the remainder of the
6629     // bit map
6630   }
6631 }
6632 
6633 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
6634                      MemRegion span,
6635                      CMSBitMap* bitMap, CMSMarkStack*  markStack,
6636                      HeapWord* finger, MarkFromRootsClosure* parent) :
6637   MetadataVisitingOopIterateClosure(collector->ref_processor()),
6638   _collector(collector),
6639   _span(span),
6640   _bitMap(bitMap),
6641   _markStack(markStack),
6642   _finger(finger),
6643   _parent(parent)
6644 { }
6645 
6646 ParPushOrMarkClosure::ParPushOrMarkClosure(CMSCollector* collector,
6647                                            MemRegion span,
6648                                            CMSBitMap* bit_map,
6649                                            OopTaskQueue* work_queue,
6650                                            CMSMarkStack*  overflow_stack,
6651                                            HeapWord* finger,
6652                                            HeapWord* volatile* global_finger_addr,
6653                                            ParMarkFromRootsClosure* parent) :
6654   MetadataVisitingOopIterateClosure(collector->ref_processor()),
6655   _collector(collector),
6656   _whole_span(collector->_span),
6657   _span(span),
6658   _bit_map(bit_map),
6659   _work_queue(work_queue),
6660   _overflow_stack(overflow_stack),
6661   _finger(finger),
6662   _global_finger_addr(global_finger_addr),
6663   _parent(parent)
6664 { }
6665 
6666 // Assumes thread-safe access by callers, who are
6667 // responsible for mutual exclusion.
6668 void CMSCollector::lower_restart_addr(HeapWord* low) {
6669   assert(_span.contains(low), "Out of bounds addr");
6670   if (_restart_addr == NULL) {
6671     _restart_addr = low;
6672   } else {
6673     _restart_addr = MIN2(_restart_addr, low);
6674   }
6675 }
6676 
6677 // Upon stack overflow, we discard (part of) the stack,
6678 // remembering the least address amongst those discarded
6679 // in CMSCollector's _restart_address.
6680 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
6681   // Remember the least grey address discarded
6682   HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
6683   _collector->lower_restart_addr(ra);
6684   _markStack->reset();  // discard stack contents
6685   _markStack->expand(); // expand the stack if possible
6686 }
6687 
6688 // Upon stack overflow, we discard (part of) the stack,
6689 // remembering the least address amongst those discarded
6690 // in CMSCollector's _restart_address.
6691 void ParPushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
6692   // We need to do this under a mutex to prevent other
6693   // workers from interfering with the work done below.
6694   MutexLockerEx ml(_overflow_stack->par_lock(),
6695                    Mutex::_no_safepoint_check_flag);
6696   // Remember the least grey address discarded
6697   HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
6698   _collector->lower_restart_addr(ra);
6699   _overflow_stack->reset();  // discard stack contents
6700   _overflow_stack->expand(); // expand the stack if possible
6701 }
6702 
6703 void PushOrMarkClosure::do_oop(oop obj) {
6704   // Ignore mark word because we are running concurrent with mutators.
6705   assert(oopDesc::is_oop_or_null(obj, true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6706   HeapWord* addr = (HeapWord*)obj;
6707   if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
6708     // Oop lies in _span and isn't yet grey or black
6709     _bitMap->mark(addr);            // now grey
6710     if (addr < _finger) {
6711       // the bit map iteration has already either passed, or
6712       // sampled, this bit in the bit map; we'll need to
6713       // use the marking stack to scan this oop's oops.
6714       bool simulate_overflow = false;
6715       NOT_PRODUCT(
6716         if (CMSMarkStackOverflowALot &&
6717             _collector->simulate_overflow()) {
6718           // simulate a stack overflow
6719           simulate_overflow = true;
6720         }
6721       )
6722       if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
6723         log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _markStack->capacity());
6724         assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
6725         handle_stack_overflow(addr);
6726       }
6727     }
6728     // anything including and to the right of _finger
6729     // will be scanned as we iterate over the remainder of the
6730     // bit map
6731     do_yield_check();
6732   }
6733 }
6734 
6735 void ParPushOrMarkClosure::do_oop(oop obj) {
6736   // Ignore mark word because we are running concurrent with mutators.
6737   assert(oopDesc::is_oop_or_null(obj, true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6738   HeapWord* addr = (HeapWord*)obj;
6739   if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
6740     // Oop lies in _span and isn't yet grey or black
6741     // We read the global_finger (volatile read) strictly after marking oop
6742     bool res = _bit_map->par_mark(addr);    // now grey
6743     volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
6744     // Should we push this marked oop on our stack?
6745     // -- if someone else marked it, nothing to do
6746     // -- if target oop is above global finger nothing to do
6747     // -- if target oop is in chunk and above local finger
6748     //      then nothing to do
6749     // -- else push on work queue
6750     if (   !res       // someone else marked it, they will deal with it
6751         || (addr >= *gfa)  // will be scanned in a later task
6752         || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
6753       return;
6754     }
6755     // the bit map iteration has already either passed, or
6756     // sampled, this bit in the bit map; we'll need to
6757     // use the marking stack to scan this oop's oops.
6758     bool simulate_overflow = false;
6759     NOT_PRODUCT(
6760       if (CMSMarkStackOverflowALot &&
6761           _collector->simulate_overflow()) {
6762         // simulate a stack overflow
6763         simulate_overflow = true;
6764       }
6765     )
6766     if (simulate_overflow ||
6767         !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
6768       // stack overflow
6769       log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _overflow_stack->capacity());
6770       // We cannot assert that the overflow stack is full because
6771       // it may have been emptied since.
6772       assert(simulate_overflow ||
6773              _work_queue->size() == _work_queue->max_elems(),
6774             "Else push should have succeeded");
6775       handle_stack_overflow(addr);
6776     }
6777     do_yield_check();
6778   }
6779 }
6780 
6781 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
6782                                        MemRegion span,
6783                                        ReferenceDiscoverer* rd,
6784                                        CMSBitMap* bit_map,
6785                                        CMSBitMap* mod_union_table,
6786                                        CMSMarkStack*  mark_stack,
6787                                        bool           concurrent_precleaning):
6788   MetadataVisitingOopIterateClosure(rd),
6789   _collector(collector),
6790   _span(span),
6791   _bit_map(bit_map),
6792   _mod_union_table(mod_union_table),
6793   _mark_stack(mark_stack),
6794   _concurrent_precleaning(concurrent_precleaning)
6795 {
6796   assert(ref_discoverer() != NULL, "ref_discoverer shouldn't be NULL");
6797 }
6798 
6799 // Grey object rescan during pre-cleaning and second checkpoint phases --
6800 // the non-parallel version (the parallel version appears further below.)
6801 void PushAndMarkClosure::do_oop(oop obj) {
6802   // Ignore mark word verification. If during concurrent precleaning,
6803   // the object monitor may be locked. If during the checkpoint
6804   // phases, the object may already have been reached by a  different
6805   // path and may be at the end of the global overflow list (so
6806   // the mark word may be NULL).
6807   assert(oopDesc::is_oop_or_null(obj, true /* ignore mark word */),
6808          "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6809   HeapWord* addr = (HeapWord*)obj;
6810   // Check if oop points into the CMS generation
6811   // and is not marked
6812   if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
6813     // a white object ...
6814     _bit_map->mark(addr);         // ... now grey
6815     // push on the marking stack (grey set)
6816     bool simulate_overflow = false;
6817     NOT_PRODUCT(
6818       if (CMSMarkStackOverflowALot &&
6819           _collector->simulate_overflow()) {
6820         // simulate a stack overflow
6821         simulate_overflow = true;
6822       }
6823     )
6824     if (simulate_overflow || !_mark_stack->push(obj)) {
6825       if (_concurrent_precleaning) {
6826          // During precleaning we can just dirty the appropriate card(s)
6827          // in the mod union table, thus ensuring that the object remains
6828          // in the grey set  and continue. In the case of object arrays
6829          // we need to dirty all of the cards that the object spans,
6830          // since the rescan of object arrays will be limited to the
6831          // dirty cards.
6832          // Note that no one can be interfering with us in this action
6833          // of dirtying the mod union table, so no locking or atomics
6834          // are required.
6835          if (obj->is_objArray()) {
6836            size_t sz = obj->size();
6837            HeapWord* end_card_addr = align_up(addr + sz, CardTable::card_size);
6838            MemRegion redirty_range = MemRegion(addr, end_card_addr);
6839            assert(!redirty_range.is_empty(), "Arithmetical tautology");
6840            _mod_union_table->mark_range(redirty_range);
6841          } else {
6842            _mod_union_table->mark(addr);
6843          }
6844          _collector->_ser_pmc_preclean_ovflw++;
6845       } else {
6846          // During the remark phase, we need to remember this oop
6847          // in the overflow list.
6848          _collector->push_on_overflow_list(obj);
6849          _collector->_ser_pmc_remark_ovflw++;
6850       }
6851     }
6852   }
6853 }
6854 
6855 ParPushAndMarkClosure::ParPushAndMarkClosure(CMSCollector* collector,
6856                                              MemRegion span,
6857                                              ReferenceDiscoverer* rd,
6858                                              CMSBitMap* bit_map,
6859                                              OopTaskQueue* work_queue):
6860   MetadataVisitingOopIterateClosure(rd),
6861   _collector(collector),
6862   _span(span),
6863   _bit_map(bit_map),
6864   _work_queue(work_queue)
6865 {
6866   assert(ref_discoverer() != NULL, "ref_discoverer shouldn't be NULL");
6867 }
6868 
6869 // Grey object rescan during second checkpoint phase --
6870 // the parallel version.
6871 void ParPushAndMarkClosure::do_oop(oop obj) {
6872   // In the assert below, we ignore the mark word because
6873   // this oop may point to an already visited object that is
6874   // on the overflow stack (in which case the mark word has
6875   // been hijacked for chaining into the overflow stack --
6876   // if this is the last object in the overflow stack then
6877   // its mark word will be NULL). Because this object may
6878   // have been subsequently popped off the global overflow
6879   // stack, and the mark word possibly restored to the prototypical
6880   // value, by the time we get to examined this failing assert in
6881   // the debugger, is_oop_or_null(false) may subsequently start
6882   // to hold.
6883   assert(oopDesc::is_oop_or_null(obj, true),
6884          "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6885   HeapWord* addr = (HeapWord*)obj;
6886   // Check if oop points into the CMS generation
6887   // and is not marked
6888   if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
6889     // a white object ...
6890     // If we manage to "claim" the object, by being the
6891     // first thread to mark it, then we push it on our
6892     // marking stack
6893     if (_bit_map->par_mark(addr)) {     // ... now grey
6894       // push on work queue (grey set)
6895       bool simulate_overflow = false;
6896       NOT_PRODUCT(
6897         if (CMSMarkStackOverflowALot &&
6898             _collector->par_simulate_overflow()) {
6899           // simulate a stack overflow
6900           simulate_overflow = true;
6901         }
6902       )
6903       if (simulate_overflow || !_work_queue->push(obj)) {
6904         _collector->par_push_on_overflow_list(obj);
6905         _collector->_par_pmc_remark_ovflw++; //  imprecise OK: no need to CAS
6906       }
6907     } // Else, some other thread got there first
6908   }
6909 }
6910 
6911 void CMSPrecleanRefsYieldClosure::do_yield_work() {
6912   Mutex* bml = _collector->bitMapLock();
6913   assert_lock_strong(bml);
6914   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6915          "CMS thread should hold CMS token");
6916 
6917   bml->unlock();
6918   ConcurrentMarkSweepThread::desynchronize(true);
6919 
6920   _collector->stopTimer();
6921   _collector->incrementYields();
6922 
6923   // See the comment in coordinator_yield()
6924   for (unsigned i = 0; i < CMSYieldSleepCount &&
6925                        ConcurrentMarkSweepThread::should_yield() &&
6926                        !CMSCollector::foregroundGCIsActive(); ++i) {
6927     os::sleep(Thread::current(), 1, false);
6928   }
6929 
6930   ConcurrentMarkSweepThread::synchronize(true);
6931   bml->lock();
6932 
6933   _collector->startTimer();
6934 }
6935 
6936 bool CMSPrecleanRefsYieldClosure::should_return() {
6937   if (ConcurrentMarkSweepThread::should_yield()) {
6938     do_yield_work();
6939   }
6940   return _collector->foregroundGCIsActive();
6941 }
6942 
6943 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
6944   assert(((size_t)mr.start())%CardTable::card_size_in_words == 0,
6945          "mr should be aligned to start at a card boundary");
6946   // We'd like to assert:
6947   // assert(mr.word_size()%CardTable::card_size_in_words == 0,
6948   //        "mr should be a range of cards");
6949   // However, that would be too strong in one case -- the last
6950   // partition ends at _unallocated_block which, in general, can be
6951   // an arbitrary boundary, not necessarily card aligned.
6952   _num_dirty_cards += mr.word_size()/CardTable::card_size_in_words;
6953   _space->object_iterate_mem(mr, &_scan_cl);
6954 }
6955 
6956 SweepClosure::SweepClosure(CMSCollector* collector,
6957                            ConcurrentMarkSweepGeneration* g,
6958                            CMSBitMap* bitMap, bool should_yield) :
6959   _collector(collector),
6960   _g(g),
6961   _sp(g->cmsSpace()),
6962   _limit(_sp->sweep_limit()),
6963   _freelistLock(_sp->freelistLock()),
6964   _bitMap(bitMap),
6965   _inFreeRange(false),           // No free range at beginning of sweep
6966   _freeRangeInFreeLists(false),  // No free range at beginning of sweep
6967   _lastFreeRangeCoalesced(false),
6968   _yield(should_yield),
6969   _freeFinger(g->used_region().start())
6970 {
6971   NOT_PRODUCT(
6972     _numObjectsFreed = 0;
6973     _numWordsFreed   = 0;
6974     _numObjectsLive = 0;
6975     _numWordsLive = 0;
6976     _numObjectsAlreadyFree = 0;
6977     _numWordsAlreadyFree = 0;
6978     _last_fc = NULL;
6979 
6980     _sp->initializeIndexedFreeListArrayReturnedBytes();
6981     _sp->dictionary()->initialize_dict_returned_bytes();
6982   )
6983   assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
6984          "sweep _limit out of bounds");
6985   log_develop_trace(gc, sweep)("====================");
6986   log_develop_trace(gc, sweep)("Starting new sweep with limit " PTR_FORMAT, p2i(_limit));
6987 }
6988 
6989 void SweepClosure::print_on(outputStream* st) const {
6990   st->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")",
6991                p2i(_sp->bottom()), p2i(_sp->end()));
6992   st->print_cr("_limit = " PTR_FORMAT, p2i(_limit));
6993   st->print_cr("_freeFinger = " PTR_FORMAT, p2i(_freeFinger));
6994   NOT_PRODUCT(st->print_cr("_last_fc = " PTR_FORMAT, p2i(_last_fc));)
6995   st->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d",
6996                _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced);
6997 }
6998 
6999 #ifndef PRODUCT
7000 // Assertion checking only:  no useful work in product mode --
7001 // however, if any of the flags below become product flags,
7002 // you may need to review this code to see if it needs to be
7003 // enabled in product mode.
7004 SweepClosure::~SweepClosure() {
7005   assert_lock_strong(_freelistLock);
7006   assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7007          "sweep _limit out of bounds");
7008   if (inFreeRange()) {
7009     Log(gc, sweep) log;
7010     log.error("inFreeRange() should have been reset; dumping state of SweepClosure");
7011     ResourceMark rm;
7012     LogStream ls(log.error());
7013     print_on(&ls);
7014     ShouldNotReachHere();
7015   }
7016 
7017   if (log_is_enabled(Debug, gc, sweep)) {
7018     log_debug(gc, sweep)("Collected " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
7019                          _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
7020     log_debug(gc, sweep)("Live " SIZE_FORMAT " objects,  " SIZE_FORMAT " bytes  Already free " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
7021                          _numObjectsLive, _numWordsLive*sizeof(HeapWord), _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
7022     size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree) * sizeof(HeapWord);
7023     log_debug(gc, sweep)("Total sweep: " SIZE_FORMAT " bytes", totalBytes);
7024   }
7025 
7026   if (log_is_enabled(Trace, gc, sweep) && CMSVerifyReturnedBytes) {
7027     size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
7028     size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes();
7029     size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes;
7030     log_trace(gc, sweep)("Returned " SIZE_FORMAT " bytes   Indexed List Returned " SIZE_FORMAT " bytes        Dictionary Returned " SIZE_FORMAT " bytes",
7031                          returned_bytes, indexListReturnedBytes, dict_returned_bytes);
7032   }
7033   log_develop_trace(gc, sweep)("end of sweep with _limit = " PTR_FORMAT, p2i(_limit));
7034   log_develop_trace(gc, sweep)("================");
7035 }
7036 #endif  // PRODUCT
7037 
7038 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
7039     bool freeRangeInFreeLists) {
7040   log_develop_trace(gc, sweep)("---- Start free range at " PTR_FORMAT " with free block (%d)",
7041                                p2i(freeFinger), freeRangeInFreeLists);
7042   assert(!inFreeRange(), "Trampling existing free range");
7043   set_inFreeRange(true);
7044   set_lastFreeRangeCoalesced(false);
7045 
7046   set_freeFinger(freeFinger);
7047   set_freeRangeInFreeLists(freeRangeInFreeLists);
7048   if (CMSTestInFreeList) {
7049     if (freeRangeInFreeLists) {
7050       FreeChunk* fc = (FreeChunk*) freeFinger;
7051       assert(fc->is_free(), "A chunk on the free list should be free.");
7052       assert(fc->size() > 0, "Free range should have a size");
7053       assert(_sp->verify_chunk_in_free_list(fc), "Chunk is not in free lists");
7054     }
7055   }
7056 }
7057 
7058 // Note that the sweeper runs concurrently with mutators. Thus,
7059 // it is possible for direct allocation in this generation to happen
7060 // in the middle of the sweep. Note that the sweeper also coalesces
7061 // contiguous free blocks. Thus, unless the sweeper and the allocator
7062 // synchronize appropriately freshly allocated blocks may get swept up.
7063 // This is accomplished by the sweeper locking the free lists while
7064 // it is sweeping. Thus blocks that are determined to be free are
7065 // indeed free. There is however one additional complication:
7066 // blocks that have been allocated since the final checkpoint and
7067 // mark, will not have been marked and so would be treated as
7068 // unreachable and swept up. To prevent this, the allocator marks
7069 // the bit map when allocating during the sweep phase. This leads,
7070 // however, to a further complication -- objects may have been allocated
7071 // but not yet initialized -- in the sense that the header isn't yet
7072 // installed. The sweeper can not then determine the size of the block
7073 // in order to skip over it. To deal with this case, we use a technique
7074 // (due to Printezis) to encode such uninitialized block sizes in the
7075 // bit map. Since the bit map uses a bit per every HeapWord, but the
7076 // CMS generation has a minimum object size of 3 HeapWords, it follows
7077 // that "normal marks" won't be adjacent in the bit map (there will
7078 // always be at least two 0 bits between successive 1 bits). We make use
7079 // of these "unused" bits to represent uninitialized blocks -- the bit
7080 // corresponding to the start of the uninitialized object and the next
7081 // bit are both set. Finally, a 1 bit marks the end of the object that
7082 // started with the two consecutive 1 bits to indicate its potentially
7083 // uninitialized state.
7084 
7085 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
7086   FreeChunk* fc = (FreeChunk*)addr;
7087   size_t res;
7088 
7089   // Check if we are done sweeping. Below we check "addr >= _limit" rather
7090   // than "addr == _limit" because although _limit was a block boundary when
7091   // we started the sweep, it may no longer be one because heap expansion
7092   // may have caused us to coalesce the block ending at the address _limit
7093   // with a newly expanded chunk (this happens when _limit was set to the
7094   // previous _end of the space), so we may have stepped past _limit:
7095   // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740.
7096   if (addr >= _limit) { // we have swept up to or past the limit: finish up
7097     assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7098            "sweep _limit out of bounds");
7099     assert(addr < _sp->end(), "addr out of bounds");
7100     // Flush any free range we might be holding as a single
7101     // coalesced chunk to the appropriate free list.
7102     if (inFreeRange()) {
7103       assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit,
7104              "freeFinger() " PTR_FORMAT " is out of bounds", p2i(freeFinger()));
7105       flush_cur_free_chunk(freeFinger(),
7106                            pointer_delta(addr, freeFinger()));
7107       log_develop_trace(gc, sweep)("Sweep: last chunk: put_free_blk " PTR_FORMAT " (" SIZE_FORMAT ") [coalesced:%d]",
7108                                    p2i(freeFinger()), pointer_delta(addr, freeFinger()),
7109                                    lastFreeRangeCoalesced() ? 1 : 0);
7110     }
7111 
7112     // help the iterator loop finish
7113     return pointer_delta(_sp->end(), addr);
7114   }
7115 
7116   assert(addr < _limit, "sweep invariant");
7117   // check if we should yield
7118   do_yield_check(addr);
7119   if (fc->is_free()) {
7120     // Chunk that is already free
7121     res = fc->size();
7122     do_already_free_chunk(fc);
7123     debug_only(_sp->verifyFreeLists());
7124     // If we flush the chunk at hand in lookahead_and_flush()
7125     // and it's coalesced with a preceding chunk, then the
7126     // process of "mangling" the payload of the coalesced block
7127     // will cause erasure of the size information from the
7128     // (erstwhile) header of all the coalesced blocks but the
7129     // first, so the first disjunct in the assert will not hold
7130     // in that specific case (in which case the second disjunct
7131     // will hold).
7132     assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit,
7133            "Otherwise the size info doesn't change at this step");
7134     NOT_PRODUCT(
7135       _numObjectsAlreadyFree++;
7136       _numWordsAlreadyFree += res;
7137     )
7138     NOT_PRODUCT(_last_fc = fc;)
7139   } else if (!_bitMap->isMarked(addr)) {
7140     // Chunk is fresh garbage
7141     res = do_garbage_chunk(fc);
7142     debug_only(_sp->verifyFreeLists());
7143     NOT_PRODUCT(
7144       _numObjectsFreed++;
7145       _numWordsFreed += res;
7146     )
7147   } else {
7148     // Chunk that is alive.
7149     res = do_live_chunk(fc);
7150     debug_only(_sp->verifyFreeLists());
7151     NOT_PRODUCT(
7152         _numObjectsLive++;
7153         _numWordsLive += res;
7154     )
7155   }
7156   return res;
7157 }
7158 
7159 // For the smart allocation, record following
7160 //  split deaths - a free chunk is removed from its free list because
7161 //      it is being split into two or more chunks.
7162 //  split birth - a free chunk is being added to its free list because
7163 //      a larger free chunk has been split and resulted in this free chunk.
7164 //  coal death - a free chunk is being removed from its free list because
7165 //      it is being coalesced into a large free chunk.
7166 //  coal birth - a free chunk is being added to its free list because
7167 //      it was created when two or more free chunks where coalesced into
7168 //      this free chunk.
7169 //
7170 // These statistics are used to determine the desired number of free
7171 // chunks of a given size.  The desired number is chosen to be relative
7172 // to the end of a CMS sweep.  The desired number at the end of a sweep
7173 // is the
7174 //      count-at-end-of-previous-sweep (an amount that was enough)
7175 //              - count-at-beginning-of-current-sweep  (the excess)
7176 //              + split-births  (gains in this size during interval)
7177 //              - split-deaths  (demands on this size during interval)
7178 // where the interval is from the end of one sweep to the end of the
7179 // next.
7180 //
7181 // When sweeping the sweeper maintains an accumulated chunk which is
7182 // the chunk that is made up of chunks that have been coalesced.  That
7183 // will be termed the left-hand chunk.  A new chunk of garbage that
7184 // is being considered for coalescing will be referred to as the
7185 // right-hand chunk.
7186 //
7187 // When making a decision on whether to coalesce a right-hand chunk with
7188 // the current left-hand chunk, the current count vs. the desired count
7189 // of the left-hand chunk is considered.  Also if the right-hand chunk
7190 // is near the large chunk at the end of the heap (see
7191 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
7192 // left-hand chunk is coalesced.
7193 //
7194 // When making a decision about whether to split a chunk, the desired count
7195 // vs. the current count of the candidate to be split is also considered.
7196 // If the candidate is underpopulated (currently fewer chunks than desired)
7197 // a chunk of an overpopulated (currently more chunks than desired) size may
7198 // be chosen.  The "hint" associated with a free list, if non-null, points
7199 // to a free list which may be overpopulated.
7200 //
7201 
7202 void SweepClosure::do_already_free_chunk(FreeChunk* fc) {
7203   const size_t size = fc->size();
7204   // Chunks that cannot be coalesced are not in the
7205   // free lists.
7206   if (CMSTestInFreeList && !fc->cantCoalesce()) {
7207     assert(_sp->verify_chunk_in_free_list(fc),
7208            "free chunk should be in free lists");
7209   }
7210   // a chunk that is already free, should not have been
7211   // marked in the bit map
7212   HeapWord* const addr = (HeapWord*) fc;
7213   assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
7214   // Verify that the bit map has no bits marked between
7215   // addr and purported end of this block.
7216   _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7217 
7218   // Some chunks cannot be coalesced under any circumstances.
7219   // See the definition of cantCoalesce().
7220   if (!fc->cantCoalesce()) {
7221     // This chunk can potentially be coalesced.
7222     // All the work is done in
7223     do_post_free_or_garbage_chunk(fc, size);
7224     // Note that if the chunk is not coalescable (the else arm
7225     // below), we unconditionally flush, without needing to do
7226     // a "lookahead," as we do below.
7227     if (inFreeRange()) lookahead_and_flush(fc, size);
7228   } else {
7229     // Code path common to both original and adaptive free lists.
7230 
7231     // cant coalesce with previous block; this should be treated
7232     // as the end of a free run if any
7233     if (inFreeRange()) {
7234       // we kicked some butt; time to pick up the garbage
7235       assert(freeFinger() < addr, "freeFinger points too high");
7236       flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7237     }
7238     // else, nothing to do, just continue
7239   }
7240 }
7241 
7242 size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) {
7243   // This is a chunk of garbage.  It is not in any free list.
7244   // Add it to a free list or let it possibly be coalesced into
7245   // a larger chunk.
7246   HeapWord* const addr = (HeapWord*) fc;
7247   const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7248 
7249   // Verify that the bit map has no bits marked between
7250   // addr and purported end of just dead object.
7251   _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7252   do_post_free_or_garbage_chunk(fc, size);
7253 
7254   assert(_limit >= addr + size,
7255          "A freshly garbage chunk can't possibly straddle over _limit");
7256   if (inFreeRange()) lookahead_and_flush(fc, size);
7257   return size;
7258 }
7259 
7260 size_t SweepClosure::do_live_chunk(FreeChunk* fc) {
7261   HeapWord* addr = (HeapWord*) fc;
7262   // The sweeper has just found a live object. Return any accumulated
7263   // left hand chunk to the free lists.
7264   if (inFreeRange()) {
7265     assert(freeFinger() < addr, "freeFinger points too high");
7266     flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7267   }
7268 
7269   // This object is live: we'd normally expect this to be
7270   // an oop, and like to assert the following:
7271   // assert(oopDesc::is_oop(oop(addr)), "live block should be an oop");
7272   // However, as we commented above, this may be an object whose
7273   // header hasn't yet been initialized.
7274   size_t size;
7275   assert(_bitMap->isMarked(addr), "Tautology for this control point");
7276   if (_bitMap->isMarked(addr + 1)) {
7277     // Determine the size from the bit map, rather than trying to
7278     // compute it from the object header.
7279     HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
7280     size = pointer_delta(nextOneAddr + 1, addr);
7281     assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
7282            "alignment problem");
7283 
7284 #ifdef ASSERT
7285       if (oop(addr)->klass_or_null_acquire() != NULL) {
7286         // Ignore mark word because we are running concurrent with mutators
7287         assert(oopDesc::is_oop(oop(addr), true), "live block should be an oop");
7288         assert(size ==
7289                CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
7290                "P-mark and computed size do not agree");
7291       }
7292 #endif
7293 
7294   } else {
7295     // This should be an initialized object that's alive.
7296     assert(oop(addr)->klass_or_null_acquire() != NULL,
7297            "Should be an initialized object");
7298     // Ignore mark word because we are running concurrent with mutators
7299     assert(oopDesc::is_oop(oop(addr), true), "live block should be an oop");
7300     // Verify that the bit map has no bits marked between
7301     // addr and purported end of this block.
7302     size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7303     assert(size >= 3, "Necessary for Printezis marks to work");
7304     assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
7305     DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
7306   }
7307   return size;
7308 }
7309 
7310 void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc,
7311                                                  size_t chunkSize) {
7312   // do_post_free_or_garbage_chunk() should only be called in the case
7313   // of the adaptive free list allocator.
7314   const bool fcInFreeLists = fc->is_free();
7315   assert((HeapWord*)fc <= _limit, "sweep invariant");
7316   if (CMSTestInFreeList && fcInFreeLists) {
7317     assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists");
7318   }
7319 
7320   log_develop_trace(gc, sweep)("  -- pick up another chunk at " PTR_FORMAT " (" SIZE_FORMAT ")", p2i(fc), chunkSize);
7321 
7322   HeapWord* const fc_addr = (HeapWord*) fc;
7323 
7324   bool coalesce = false;
7325   const size_t left  = pointer_delta(fc_addr, freeFinger());
7326   const size_t right = chunkSize;
7327   switch (FLSCoalescePolicy) {
7328     // numeric value forms a coalition aggressiveness metric
7329     case 0:  { // never coalesce
7330       coalesce = false;
7331       break;
7332     }
7333     case 1: { // coalesce if left & right chunks on overpopulated lists
7334       coalesce = _sp->coalOverPopulated(left) &&
7335                  _sp->coalOverPopulated(right);
7336       break;
7337     }
7338     case 2: { // coalesce if left chunk on overpopulated list (default)
7339       coalesce = _sp->coalOverPopulated(left);
7340       break;
7341     }
7342     case 3: { // coalesce if left OR right chunk on overpopulated list
7343       coalesce = _sp->coalOverPopulated(left) ||
7344                  _sp->coalOverPopulated(right);
7345       break;
7346     }
7347     case 4: { // always coalesce
7348       coalesce = true;
7349       break;
7350     }
7351     default:
7352      ShouldNotReachHere();
7353   }
7354 
7355   // Should the current free range be coalesced?
7356   // If the chunk is in a free range and either we decided to coalesce above
7357   // or the chunk is near the large block at the end of the heap
7358   // (isNearLargestChunk() returns true), then coalesce this chunk.
7359   const bool doCoalesce = inFreeRange()
7360                           && (coalesce || _g->isNearLargestChunk(fc_addr));
7361   if (doCoalesce) {
7362     // Coalesce the current free range on the left with the new
7363     // chunk on the right.  If either is on a free list,
7364     // it must be removed from the list and stashed in the closure.
7365     if (freeRangeInFreeLists()) {
7366       FreeChunk* const ffc = (FreeChunk*)freeFinger();
7367       assert(ffc->size() == pointer_delta(fc_addr, freeFinger()),
7368              "Size of free range is inconsistent with chunk size.");
7369       if (CMSTestInFreeList) {
7370         assert(_sp->verify_chunk_in_free_list(ffc),
7371                "Chunk is not in free lists");
7372       }
7373       _sp->coalDeath(ffc->size());
7374       _sp->removeFreeChunkFromFreeLists(ffc);
7375       set_freeRangeInFreeLists(false);
7376     }
7377     if (fcInFreeLists) {
7378       _sp->coalDeath(chunkSize);
7379       assert(fc->size() == chunkSize,
7380         "The chunk has the wrong size or is not in the free lists");
7381       _sp->removeFreeChunkFromFreeLists(fc);
7382     }
7383     set_lastFreeRangeCoalesced(true);
7384     print_free_block_coalesced(fc);
7385   } else {  // not in a free range and/or should not coalesce
7386     // Return the current free range and start a new one.
7387     if (inFreeRange()) {
7388       // In a free range but cannot coalesce with the right hand chunk.
7389       // Put the current free range into the free lists.
7390       flush_cur_free_chunk(freeFinger(),
7391                            pointer_delta(fc_addr, freeFinger()));
7392     }
7393     // Set up for new free range.  Pass along whether the right hand
7394     // chunk is in the free lists.
7395     initialize_free_range((HeapWord*)fc, fcInFreeLists);
7396   }
7397 }
7398 
7399 // Lookahead flush:
7400 // If we are tracking a free range, and this is the last chunk that
7401 // we'll look at because its end crosses past _limit, we'll preemptively
7402 // flush it along with any free range we may be holding on to. Note that
7403 // this can be the case only for an already free or freshly garbage
7404 // chunk. If this block is an object, it can never straddle
7405 // over _limit. The "straddling" occurs when _limit is set at
7406 // the previous end of the space when this cycle started, and
7407 // a subsequent heap expansion caused the previously co-terminal
7408 // free block to be coalesced with the newly expanded portion,
7409 // thus rendering _limit a non-block-boundary making it dangerous
7410 // for the sweeper to step over and examine.
7411 void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) {
7412   assert(inFreeRange(), "Should only be called if currently in a free range.");
7413   HeapWord* const eob = ((HeapWord*)fc) + chunk_size;
7414   assert(_sp->used_region().contains(eob - 1),
7415          "eob = " PTR_FORMAT " eob-1 = " PTR_FORMAT " _limit = " PTR_FORMAT
7416          " out of bounds wrt _sp = [" PTR_FORMAT "," PTR_FORMAT ")"
7417          " when examining fc = " PTR_FORMAT "(" SIZE_FORMAT ")",
7418          p2i(eob), p2i(eob-1), p2i(_limit), p2i(_sp->bottom()), p2i(_sp->end()), p2i(fc), chunk_size);
7419   if (eob >= _limit) {
7420     assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit");
7421     log_develop_trace(gc, sweep)("_limit " PTR_FORMAT " reached or crossed by block "
7422                                  "[" PTR_FORMAT "," PTR_FORMAT ") in space "
7423                                  "[" PTR_FORMAT "," PTR_FORMAT ")",
7424                                  p2i(_limit), p2i(fc), p2i(eob), p2i(_sp->bottom()), p2i(_sp->end()));
7425     // Return the storage we are tracking back into the free lists.
7426     log_develop_trace(gc, sweep)("Flushing ... ");
7427     assert(freeFinger() < eob, "Error");
7428     flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger()));
7429   }
7430 }
7431 
7432 void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) {
7433   assert(inFreeRange(), "Should only be called if currently in a free range.");
7434   assert(size > 0,
7435     "A zero sized chunk cannot be added to the free lists.");
7436   if (!freeRangeInFreeLists()) {
7437     if (CMSTestInFreeList) {
7438       FreeChunk* fc = (FreeChunk*) chunk;
7439       fc->set_size(size);
7440       assert(!_sp->verify_chunk_in_free_list(fc),
7441              "chunk should not be in free lists yet");
7442     }
7443     log_develop_trace(gc, sweep)(" -- add free block " PTR_FORMAT " (" SIZE_FORMAT ") to free lists", p2i(chunk), size);
7444     // A new free range is going to be starting.  The current
7445     // free range has not been added to the free lists yet or
7446     // was removed so add it back.
7447     // If the current free range was coalesced, then the death
7448     // of the free range was recorded.  Record a birth now.
7449     if (lastFreeRangeCoalesced()) {
7450       _sp->coalBirth(size);
7451     }
7452     _sp->addChunkAndRepairOffsetTable(chunk, size,
7453             lastFreeRangeCoalesced());
7454   } else {
7455     log_develop_trace(gc, sweep)("Already in free list: nothing to flush");
7456   }
7457   set_inFreeRange(false);
7458   set_freeRangeInFreeLists(false);
7459 }
7460 
7461 // We take a break if we've been at this for a while,
7462 // so as to avoid monopolizing the locks involved.
7463 void SweepClosure::do_yield_work(HeapWord* addr) {
7464   // Return current free chunk being used for coalescing (if any)
7465   // to the appropriate freelist.  After yielding, the next
7466   // free block encountered will start a coalescing range of
7467   // free blocks.  If the next free block is adjacent to the
7468   // chunk just flushed, they will need to wait for the next
7469   // sweep to be coalesced.
7470   if (inFreeRange()) {
7471     flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7472   }
7473 
7474   // First give up the locks, then yield, then re-lock.
7475   // We should probably use a constructor/destructor idiom to
7476   // do this unlock/lock or modify the MutexUnlocker class to
7477   // serve our purpose. XXX
7478   assert_lock_strong(_bitMap->lock());
7479   assert_lock_strong(_freelistLock);
7480   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7481          "CMS thread should hold CMS token");
7482   _bitMap->lock()->unlock();
7483   _freelistLock->unlock();
7484   ConcurrentMarkSweepThread::desynchronize(true);
7485   _collector->stopTimer();
7486   _collector->incrementYields();
7487 
7488   // See the comment in coordinator_yield()
7489   for (unsigned i = 0; i < CMSYieldSleepCount &&
7490                        ConcurrentMarkSweepThread::should_yield() &&
7491                        !CMSCollector::foregroundGCIsActive(); ++i) {
7492     os::sleep(Thread::current(), 1, false);
7493   }
7494 
7495   ConcurrentMarkSweepThread::synchronize(true);
7496   _freelistLock->lock();
7497   _bitMap->lock()->lock_without_safepoint_check();
7498   _collector->startTimer();
7499 }
7500 
7501 #ifndef PRODUCT
7502 // This is actually very useful in a product build if it can
7503 // be called from the debugger.  Compile it into the product
7504 // as needed.
7505 bool debug_verify_chunk_in_free_list(FreeChunk* fc) {
7506   return debug_cms_space->verify_chunk_in_free_list(fc);
7507 }
7508 #endif
7509 
7510 void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const {
7511   log_develop_trace(gc, sweep)("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")",
7512                                p2i(fc), fc->size());
7513 }
7514 
7515 // CMSIsAliveClosure
7516 bool CMSIsAliveClosure::do_object_b(oop obj) {
7517   HeapWord* addr = (HeapWord*)obj;
7518   return addr != NULL &&
7519          (!_span.contains(addr) || _bit_map->isMarked(addr));
7520 }
7521 
7522 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector,
7523                       MemRegion span,
7524                       CMSBitMap* bit_map, CMSMarkStack* mark_stack,
7525                       bool cpc):
7526   _collector(collector),
7527   _span(span),
7528   _mark_stack(mark_stack),
7529   _bit_map(bit_map),
7530   _concurrent_precleaning(cpc) {
7531   assert(!_span.is_empty(), "Empty span could spell trouble");
7532 }
7533 
7534 
7535 // CMSKeepAliveClosure: the serial version
7536 void CMSKeepAliveClosure::do_oop(oop obj) {
7537   HeapWord* addr = (HeapWord*)obj;
7538   if (_span.contains(addr) &&
7539       !_bit_map->isMarked(addr)) {
7540     _bit_map->mark(addr);
7541     bool simulate_overflow = false;
7542     NOT_PRODUCT(
7543       if (CMSMarkStackOverflowALot &&
7544           _collector->simulate_overflow()) {
7545         // simulate a stack overflow
7546         simulate_overflow = true;
7547       }
7548     )
7549     if (simulate_overflow || !_mark_stack->push(obj)) {
7550       if (_concurrent_precleaning) {
7551         // We dirty the overflown object and let the remark
7552         // phase deal with it.
7553         assert(_collector->overflow_list_is_empty(), "Error");
7554         // In the case of object arrays, we need to dirty all of
7555         // the cards that the object spans. No locking or atomics
7556         // are needed since no one else can be mutating the mod union
7557         // table.
7558         if (obj->is_objArray()) {
7559           size_t sz = obj->size();
7560           HeapWord* end_card_addr = align_up(addr + sz, CardTable::card_size);
7561           MemRegion redirty_range = MemRegion(addr, end_card_addr);
7562           assert(!redirty_range.is_empty(), "Arithmetical tautology");
7563           _collector->_modUnionTable.mark_range(redirty_range);
7564         } else {
7565           _collector->_modUnionTable.mark(addr);
7566         }
7567         _collector->_ser_kac_preclean_ovflw++;
7568       } else {
7569         _collector->push_on_overflow_list(obj);
7570         _collector->_ser_kac_ovflw++;
7571       }
7572     }
7573   }
7574 }
7575 
7576 // CMSParKeepAliveClosure: a parallel version of the above.
7577 // The work queues are private to each closure (thread),
7578 // but (may be) available for stealing by other threads.
7579 void CMSParKeepAliveClosure::do_oop(oop obj) {
7580   HeapWord* addr = (HeapWord*)obj;
7581   if (_span.contains(addr) &&
7582       !_bit_map->isMarked(addr)) {
7583     // In general, during recursive tracing, several threads
7584     // may be concurrently getting here; the first one to
7585     // "tag" it, claims it.
7586     if (_bit_map->par_mark(addr)) {
7587       bool res = _work_queue->push(obj);
7588       assert(res, "Low water mark should be much less than capacity");
7589       // Do a recursive trim in the hope that this will keep
7590       // stack usage lower, but leave some oops for potential stealers
7591       trim_queue(_low_water_mark);
7592     } // Else, another thread got there first
7593   }
7594 }
7595 
7596 void CMSParKeepAliveClosure::trim_queue(uint max) {
7597   while (_work_queue->size() > max) {
7598     oop new_oop;
7599     if (_work_queue->pop_local(new_oop)) {
7600       assert(new_oop != NULL && oopDesc::is_oop(new_oop), "Expected an oop");
7601       assert(_bit_map->isMarked((HeapWord*)new_oop),
7602              "no white objects on this stack!");
7603       assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
7604       // iterate over the oops in this oop, marking and pushing
7605       // the ones in CMS heap (i.e. in _span).
7606       new_oop->oop_iterate(&_mark_and_push);
7607     }
7608   }
7609 }
7610 
7611 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
7612                                 CMSCollector* collector,
7613                                 MemRegion span, CMSBitMap* bit_map,
7614                                 OopTaskQueue* work_queue):
7615   _collector(collector),
7616   _span(span),
7617   _work_queue(work_queue),
7618   _bit_map(bit_map) { }
7619 
7620 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
7621   HeapWord* addr = (HeapWord*)obj;
7622   if (_span.contains(addr) &&
7623       !_bit_map->isMarked(addr)) {
7624     if (_bit_map->par_mark(addr)) {
7625       bool simulate_overflow = false;
7626       NOT_PRODUCT(
7627         if (CMSMarkStackOverflowALot &&
7628             _collector->par_simulate_overflow()) {
7629           // simulate a stack overflow
7630           simulate_overflow = true;
7631         }
7632       )
7633       if (simulate_overflow || !_work_queue->push(obj)) {
7634         _collector->par_push_on_overflow_list(obj);
7635         _collector->_par_kac_ovflw++;
7636       }
7637     } // Else another thread got there already
7638   }
7639 }
7640 
7641 //////////////////////////////////////////////////////////////////
7642 //  CMSExpansionCause                /////////////////////////////
7643 //////////////////////////////////////////////////////////////////
7644 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
7645   switch (cause) {
7646     case _no_expansion:
7647       return "No expansion";
7648     case _satisfy_free_ratio:
7649       return "Free ratio";
7650     case _satisfy_promotion:
7651       return "Satisfy promotion";
7652     case _satisfy_allocation:
7653       return "allocation";
7654     case _allocate_par_lab:
7655       return "Par LAB";
7656     case _allocate_par_spooling_space:
7657       return "Par Spooling Space";
7658     case _adaptive_size_policy:
7659       return "Ergonomics";
7660     default:
7661       return "unknown";
7662   }
7663 }
7664 
7665 void CMSDrainMarkingStackClosure::do_void() {
7666   // the max number to take from overflow list at a time
7667   const size_t num = _mark_stack->capacity()/4;
7668   assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
7669          "Overflow list should be NULL during concurrent phases");
7670   while (!_mark_stack->isEmpty() ||
7671          // if stack is empty, check the overflow list
7672          _collector->take_from_overflow_list(num, _mark_stack)) {
7673     oop obj = _mark_stack->pop();
7674     HeapWord* addr = (HeapWord*)obj;
7675     assert(_span.contains(addr), "Should be within span");
7676     assert(_bit_map->isMarked(addr), "Should be marked");
7677     assert(oopDesc::is_oop(obj), "Should be an oop");
7678     obj->oop_iterate(_keep_alive);
7679   }
7680 }
7681 
7682 void CMSParDrainMarkingStackClosure::do_void() {
7683   // drain queue
7684   trim_queue(0);
7685 }
7686 
7687 // Trim our work_queue so its length is below max at return
7688 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
7689   while (_work_queue->size() > max) {
7690     oop new_oop;
7691     if (_work_queue->pop_local(new_oop)) {
7692       assert(oopDesc::is_oop(new_oop), "Expected an oop");
7693       assert(_bit_map->isMarked((HeapWord*)new_oop),
7694              "no white objects on this stack!");
7695       assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
7696       // iterate over the oops in this oop, marking and pushing
7697       // the ones in CMS heap (i.e. in _span).
7698       new_oop->oop_iterate(&_mark_and_push);
7699     }
7700   }
7701 }
7702 
7703 ////////////////////////////////////////////////////////////////////
7704 // Support for Marking Stack Overflow list handling and related code
7705 ////////////////////////////////////////////////////////////////////
7706 // Much of the following code is similar in shape and spirit to the
7707 // code used in ParNewGC. We should try and share that code
7708 // as much as possible in the future.
7709 
7710 #ifndef PRODUCT
7711 // Debugging support for CMSStackOverflowALot
7712 
7713 // It's OK to call this multi-threaded;  the worst thing
7714 // that can happen is that we'll get a bunch of closely
7715 // spaced simulated overflows, but that's OK, in fact
7716 // probably good as it would exercise the overflow code
7717 // under contention.
7718 bool CMSCollector::simulate_overflow() {
7719   if (_overflow_counter-- <= 0) { // just being defensive
7720     _overflow_counter = CMSMarkStackOverflowInterval;
7721     return true;
7722   } else {
7723     return false;
7724   }
7725 }
7726 
7727 bool CMSCollector::par_simulate_overflow() {
7728   return simulate_overflow();
7729 }
7730 #endif
7731 
7732 // Single-threaded
7733 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
7734   assert(stack->isEmpty(), "Expected precondition");
7735   assert(stack->capacity() > num, "Shouldn't bite more than can chew");
7736   size_t i = num;
7737   oop  cur = _overflow_list;
7738   const markOop proto = markOopDesc::prototype();
7739   NOT_PRODUCT(ssize_t n = 0;)
7740   for (oop next; i > 0 && cur != NULL; cur = next, i--) {
7741     next = oop(cur->mark_raw());
7742     cur->set_mark_raw(proto);   // until proven otherwise
7743     assert(oopDesc::is_oop(cur), "Should be an oop");
7744     bool res = stack->push(cur);
7745     assert(res, "Bit off more than can chew?");
7746     NOT_PRODUCT(n++;)
7747   }
7748   _overflow_list = cur;
7749 #ifndef PRODUCT
7750   assert(_num_par_pushes >= n, "Too many pops?");
7751   _num_par_pushes -=n;
7752 #endif
7753   return !stack->isEmpty();
7754 }
7755 
7756 #define BUSY  (cast_to_oop<intptr_t>(0x1aff1aff))
7757 // (MT-safe) Get a prefix of at most "num" from the list.
7758 // The overflow list is chained through the mark word of
7759 // each object in the list. We fetch the entire list,
7760 // break off a prefix of the right size and return the
7761 // remainder. If other threads try to take objects from
7762 // the overflow list at that time, they will wait for
7763 // some time to see if data becomes available. If (and
7764 // only if) another thread places one or more object(s)
7765 // on the global list before we have returned the suffix
7766 // to the global list, we will walk down our local list
7767 // to find its end and append the global list to
7768 // our suffix before returning it. This suffix walk can
7769 // prove to be expensive (quadratic in the amount of traffic)
7770 // when there are many objects in the overflow list and
7771 // there is much producer-consumer contention on the list.
7772 // *NOTE*: The overflow list manipulation code here and
7773 // in ParNewGeneration:: are very similar in shape,
7774 // except that in the ParNew case we use the old (from/eden)
7775 // copy of the object to thread the list via its klass word.
7776 // Because of the common code, if you make any changes in
7777 // the code below, please check the ParNew version to see if
7778 // similar changes might be needed.
7779 // CR 6797058 has been filed to consolidate the common code.
7780 bool CMSCollector::par_take_from_overflow_list(size_t num,
7781                                                OopTaskQueue* work_q,
7782                                                int no_of_gc_threads) {
7783   assert(work_q->size() == 0, "First empty local work queue");
7784   assert(num < work_q->max_elems(), "Can't bite more than we can chew");
7785   if (_overflow_list == NULL) {
7786     return false;
7787   }
7788   // Grab the entire list; we'll put back a suffix
7789   oop prefix = cast_to_oop(Atomic::xchg((oopDesc*)BUSY, &_overflow_list));
7790   Thread* tid = Thread::current();
7791   // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was
7792   // set to ParallelGCThreads.
7793   size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads;
7794   size_t sleep_time_millis = MAX2((size_t)1, num/100);
7795   // If the list is busy, we spin for a short while,
7796   // sleeping between attempts to get the list.
7797   for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) {
7798     os::sleep(tid, sleep_time_millis, false);
7799     if (_overflow_list == NULL) {
7800       // Nothing left to take
7801       return false;
7802     } else if (_overflow_list != BUSY) {
7803       // Try and grab the prefix
7804       prefix = cast_to_oop(Atomic::xchg((oopDesc*)BUSY, &_overflow_list));
7805     }
7806   }
7807   // If the list was found to be empty, or we spun long
7808   // enough, we give up and return empty-handed. If we leave
7809   // the list in the BUSY state below, it must be the case that
7810   // some other thread holds the overflow list and will set it
7811   // to a non-BUSY state in the future.
7812   if (prefix == NULL || prefix == BUSY) {
7813      // Nothing to take or waited long enough
7814      if (prefix == NULL) {
7815        // Write back the NULL in case we overwrote it with BUSY above
7816        // and it is still the same value.
7817        Atomic::cmpxchg((oopDesc*)NULL, &_overflow_list, (oopDesc*)BUSY);
7818      }
7819      return false;
7820   }
7821   assert(prefix != NULL && prefix != BUSY, "Error");
7822   size_t i = num;
7823   oop cur = prefix;
7824   // Walk down the first "num" objects, unless we reach the end.
7825   for (; i > 1 && cur->mark_raw() != NULL; cur = oop(cur->mark_raw()), i--);
7826   if (cur->mark_raw() == NULL) {
7827     // We have "num" or fewer elements in the list, so there
7828     // is nothing to return to the global list.
7829     // Write back the NULL in lieu of the BUSY we wrote
7830     // above, if it is still the same value.
7831     if (_overflow_list == BUSY) {
7832       Atomic::cmpxchg((oopDesc*)NULL, &_overflow_list, (oopDesc*)BUSY);
7833     }
7834   } else {
7835     // Chop off the suffix and return it to the global list.
7836     assert(cur->mark_raw() != BUSY, "Error");
7837     oop suffix_head = cur->mark_raw(); // suffix will be put back on global list
7838     cur->set_mark_raw(NULL);           // break off suffix
7839     // It's possible that the list is still in the empty(busy) state
7840     // we left it in a short while ago; in that case we may be
7841     // able to place back the suffix without incurring the cost
7842     // of a walk down the list.
7843     oop observed_overflow_list = _overflow_list;
7844     oop cur_overflow_list = observed_overflow_list;
7845     bool attached = false;
7846     while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
7847       observed_overflow_list =
7848         Atomic::cmpxchg((oopDesc*)suffix_head, &_overflow_list, (oopDesc*)cur_overflow_list);
7849       if (cur_overflow_list == observed_overflow_list) {
7850         attached = true;
7851         break;
7852       } else cur_overflow_list = observed_overflow_list;
7853     }
7854     if (!attached) {
7855       // Too bad, someone else sneaked in (at least) an element; we'll need
7856       // to do a splice. Find tail of suffix so we can prepend suffix to global
7857       // list.
7858       for (cur = suffix_head; cur->mark_raw() != NULL; cur = (oop)(cur->mark_raw()));
7859       oop suffix_tail = cur;
7860       assert(suffix_tail != NULL && suffix_tail->mark_raw() == NULL,
7861              "Tautology");
7862       observed_overflow_list = _overflow_list;
7863       do {
7864         cur_overflow_list = observed_overflow_list;
7865         if (cur_overflow_list != BUSY) {
7866           // Do the splice ...
7867           suffix_tail->set_mark_raw(markOop(cur_overflow_list));
7868         } else { // cur_overflow_list == BUSY
7869           suffix_tail->set_mark_raw(NULL);
7870         }
7871         // ... and try to place spliced list back on overflow_list ...
7872         observed_overflow_list =
7873           Atomic::cmpxchg((oopDesc*)suffix_head, &_overflow_list, (oopDesc*)cur_overflow_list);
7874       } while (cur_overflow_list != observed_overflow_list);
7875       // ... until we have succeeded in doing so.
7876     }
7877   }
7878 
7879   // Push the prefix elements on work_q
7880   assert(prefix != NULL, "control point invariant");
7881   const markOop proto = markOopDesc::prototype();
7882   oop next;
7883   NOT_PRODUCT(ssize_t n = 0;)
7884   for (cur = prefix; cur != NULL; cur = next) {
7885     next = oop(cur->mark_raw());
7886     cur->set_mark_raw(proto);   // until proven otherwise
7887     assert(oopDesc::is_oop(cur), "Should be an oop");
7888     bool res = work_q->push(cur);
7889     assert(res, "Bit off more than we can chew?");
7890     NOT_PRODUCT(n++;)
7891   }
7892 #ifndef PRODUCT
7893   assert(_num_par_pushes >= n, "Too many pops?");
7894   Atomic::sub(n, &_num_par_pushes);
7895 #endif
7896   return true;
7897 }
7898 
7899 // Single-threaded
7900 void CMSCollector::push_on_overflow_list(oop p) {
7901   NOT_PRODUCT(_num_par_pushes++;)
7902   assert(oopDesc::is_oop(p), "Not an oop");
7903   preserve_mark_if_necessary(p);
7904   p->set_mark_raw((markOop)_overflow_list);
7905   _overflow_list = p;
7906 }
7907 
7908 // Multi-threaded; use CAS to prepend to overflow list
7909 void CMSCollector::par_push_on_overflow_list(oop p) {
7910   NOT_PRODUCT(Atomic::inc(&_num_par_pushes);)
7911   assert(oopDesc::is_oop(p), "Not an oop");
7912   par_preserve_mark_if_necessary(p);
7913   oop observed_overflow_list = _overflow_list;
7914   oop cur_overflow_list;
7915   do {
7916     cur_overflow_list = observed_overflow_list;
7917     if (cur_overflow_list != BUSY) {
7918       p->set_mark_raw(markOop(cur_overflow_list));
7919     } else {
7920       p->set_mark_raw(NULL);
7921     }
7922     observed_overflow_list =
7923       Atomic::cmpxchg((oopDesc*)p, &_overflow_list, (oopDesc*)cur_overflow_list);
7924   } while (cur_overflow_list != observed_overflow_list);
7925 }
7926 #undef BUSY
7927 
7928 // Single threaded
7929 // General Note on GrowableArray: pushes may silently fail
7930 // because we are (temporarily) out of C-heap for expanding
7931 // the stack. The problem is quite ubiquitous and affects
7932 // a lot of code in the JVM. The prudent thing for GrowableArray
7933 // to do (for now) is to exit with an error. However, that may
7934 // be too draconian in some cases because the caller may be
7935 // able to recover without much harm. For such cases, we
7936 // should probably introduce a "soft_push" method which returns
7937 // an indication of success or failure with the assumption that
7938 // the caller may be able to recover from a failure; code in
7939 // the VM can then be changed, incrementally, to deal with such
7940 // failures where possible, thus, incrementally hardening the VM
7941 // in such low resource situations.
7942 void CMSCollector::preserve_mark_work(oop p, markOop m) {
7943   _preserved_oop_stack.push(p);
7944   _preserved_mark_stack.push(m);
7945   assert(m == p->mark_raw(), "Mark word changed");
7946   assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
7947          "bijection");
7948 }
7949 
7950 // Single threaded
7951 void CMSCollector::preserve_mark_if_necessary(oop p) {
7952   markOop m = p->mark_raw();
7953   if (m->must_be_preserved(p)) {
7954     preserve_mark_work(p, m);
7955   }
7956 }
7957 
7958 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
7959   markOop m = p->mark_raw();
7960   if (m->must_be_preserved(p)) {
7961     MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
7962     // Even though we read the mark word without holding
7963     // the lock, we are assured that it will not change
7964     // because we "own" this oop, so no other thread can
7965     // be trying to push it on the overflow list; see
7966     // the assertion in preserve_mark_work() that checks
7967     // that m == p->mark_raw().
7968     preserve_mark_work(p, m);
7969   }
7970 }
7971 
7972 // We should be able to do this multi-threaded,
7973 // a chunk of stack being a task (this is
7974 // correct because each oop only ever appears
7975 // once in the overflow list. However, it's
7976 // not very easy to completely overlap this with
7977 // other operations, so will generally not be done
7978 // until all work's been completed. Because we
7979 // expect the preserved oop stack (set) to be small,
7980 // it's probably fine to do this single-threaded.
7981 // We can explore cleverer concurrent/overlapped/parallel
7982 // processing of preserved marks if we feel the
7983 // need for this in the future. Stack overflow should
7984 // be so rare in practice and, when it happens, its
7985 // effect on performance so great that this will
7986 // likely just be in the noise anyway.
7987 void CMSCollector::restore_preserved_marks_if_any() {
7988   assert(SafepointSynchronize::is_at_safepoint(),
7989          "world should be stopped");
7990   assert(Thread::current()->is_ConcurrentGC_thread() ||
7991          Thread::current()->is_VM_thread(),
7992          "should be single-threaded");
7993   assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
7994          "bijection");
7995 
7996   while (!_preserved_oop_stack.is_empty()) {
7997     oop p = _preserved_oop_stack.pop();
7998     assert(oopDesc::is_oop(p), "Should be an oop");
7999     assert(_span.contains(p), "oop should be in _span");
8000     assert(p->mark_raw() == markOopDesc::prototype(),
8001            "Set when taken from overflow list");
8002     markOop m = _preserved_mark_stack.pop();
8003     p->set_mark_raw(m);
8004   }
8005   assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(),
8006          "stacks were cleared above");
8007 }
8008 
8009 #ifndef PRODUCT
8010 bool CMSCollector::no_preserved_marks() const {
8011   return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty();
8012 }
8013 #endif
8014 
8015 // Transfer some number of overflown objects to usual marking
8016 // stack. Return true if some objects were transferred.
8017 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
8018   size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,
8019                     (size_t)ParGCDesiredObjsFromOverflowList);
8020 
8021   bool res = _collector->take_from_overflow_list(num, _mark_stack);
8022   assert(_collector->overflow_list_is_empty() || res,
8023          "If list is not empty, we should have taken something");
8024   assert(!res || !_mark_stack->isEmpty(),
8025          "If we took something, it should now be on our stack");
8026   return res;
8027 }
8028 
8029 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
8030   size_t res = _sp->block_size_no_stall(addr, _collector);
8031   if (_sp->block_is_obj(addr)) {
8032     if (_live_bit_map->isMarked(addr)) {
8033       // It can't have been dead in a previous cycle
8034       guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
8035     } else {
8036       _dead_bit_map->mark(addr);      // mark the dead object
8037     }
8038   }
8039   // Could be 0, if the block size could not be computed without stalling.
8040   return res;
8041 }
8042 
8043 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() {
8044   GCMemoryManager* manager = CMSHeap::heap()->old_manager();
8045   switch (phase) {
8046     case CMSCollector::InitialMarking:
8047       initialize(manager /* GC manager */ ,
8048                  cause   /* cause of the GC */,
8049                  true    /* allMemoryPoolsAffected */,
8050                  true    /* recordGCBeginTime */,
8051                  true    /* recordPreGCUsage */,
8052                  false   /* recordPeakUsage */,
8053                  false   /* recordPostGCusage */,
8054                  true    /* recordAccumulatedGCTime */,
8055                  false   /* recordGCEndTime */,
8056                  false   /* countCollection */  );
8057       break;
8058 
8059     case CMSCollector::FinalMarking:
8060       initialize(manager /* GC manager */ ,
8061                  cause   /* cause of the GC */,
8062                  true    /* allMemoryPoolsAffected */,
8063                  false   /* recordGCBeginTime */,
8064                  false   /* recordPreGCUsage */,
8065                  false   /* recordPeakUsage */,
8066                  false   /* recordPostGCusage */,
8067                  true    /* recordAccumulatedGCTime */,
8068                  false   /* recordGCEndTime */,
8069                  false   /* countCollection */  );
8070       break;
8071 
8072     case CMSCollector::Sweeping:
8073       initialize(manager /* GC manager */ ,
8074                  cause   /* cause of the GC */,
8075                  true    /* allMemoryPoolsAffected */,
8076                  false   /* recordGCBeginTime */,
8077                  false   /* recordPreGCUsage */,
8078                  true    /* recordPeakUsage */,
8079                  true    /* recordPostGCusage */,
8080                  false   /* recordAccumulatedGCTime */,
8081                  true    /* recordGCEndTime */,
8082                  true    /* countCollection */  );
8083       break;
8084 
8085     default:
8086       ShouldNotReachHere();
8087   }
8088 }
--- EOF ---