1 /*
   2  * Copyright (c) 2001, 2015, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
  21  * questions.
  22  *
  23  */
  24 
  25 #include "precompiled.hpp"
  26 #include "classfile/classLoaderData.hpp"
  27 #include "classfile/stringTable.hpp"
  28 #include "classfile/systemDictionary.hpp"
  29 #include "code/codeCache.hpp"
  30 #include "gc/cms/cmsCollectorPolicy.hpp"
  31 #include "gc/cms/cmsOopClosures.inline.hpp"
  32 #include "gc/cms/compactibleFreeListSpace.hpp"
  33 #include "gc/cms/concurrentMarkSweepGeneration.inline.hpp"
  34 #include "gc/cms/concurrentMarkSweepThread.hpp"
  35 #include "gc/cms/parNewGeneration.hpp"
  36 #include "gc/cms/vmCMSOperations.hpp"
  37 #include "gc/serial/genMarkSweep.hpp"
  38 #include "gc/serial/tenuredGeneration.hpp"
  39 #include "gc/shared/adaptiveSizePolicy.hpp"
  40 #include "gc/shared/cardGeneration.inline.hpp"
  41 #include "gc/shared/cardTableRS.hpp"
  42 #include "gc/shared/collectedHeap.inline.hpp"
  43 #include "gc/shared/collectorCounters.hpp"
  44 #include "gc/shared/collectorPolicy.hpp"
  45 #include "gc/shared/gcLocker.inline.hpp"
  46 #include "gc/shared/gcPolicyCounters.hpp"
  47 #include "gc/shared/gcTimer.hpp"
  48 #include "gc/shared/gcTrace.hpp"
  49 #include "gc/shared/gcTraceTime.hpp"
  50 #include "gc/shared/genCollectedHeap.hpp"
  51 #include "gc/shared/genOopClosures.inline.hpp"
  52 #include "gc/shared/isGCActiveMark.hpp"
  53 #include "gc/shared/referencePolicy.hpp"
  54 #include "gc/shared/strongRootsScope.hpp"
  55 #include "gc/shared/taskqueue.inline.hpp"
  56 #include "memory/allocation.hpp"
  57 #include "memory/iterator.inline.hpp"
  58 #include "memory/padded.hpp"
  59 #include "memory/resourceArea.hpp"
  60 #include "oops/oop.inline.hpp"
  61 #include "prims/jvmtiExport.hpp"
  62 #include "runtime/atomic.inline.hpp"
  63 #include "runtime/globals_extension.hpp"
  64 #include "runtime/handles.inline.hpp"
  65 #include "runtime/java.hpp"
  66 #include "runtime/orderAccess.inline.hpp"
  67 #include "runtime/vmThread.hpp"
  68 #include "services/memoryService.hpp"
  69 #include "services/runtimeService.hpp"
  70 #include "utilities/stack.inline.hpp"
  71 
  72 // statics
  73 CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL;
  74 bool CMSCollector::_full_gc_requested = false;
  75 GCCause::Cause CMSCollector::_full_gc_cause = GCCause::_no_gc;
  76 
  77 //////////////////////////////////////////////////////////////////
  78 // In support of CMS/VM thread synchronization
  79 //////////////////////////////////////////////////////////////////
  80 // We split use of the CGC_lock into 2 "levels".
  81 // The low-level locking is of the usual CGC_lock monitor. We introduce
  82 // a higher level "token" (hereafter "CMS token") built on top of the
  83 // low level monitor (hereafter "CGC lock").
  84 // The token-passing protocol gives priority to the VM thread. The
  85 // CMS-lock doesn't provide any fairness guarantees, but clients
  86 // should ensure that it is only held for very short, bounded
  87 // durations.
  88 //
  89 // When either of the CMS thread or the VM thread is involved in
  90 // collection operations during which it does not want the other
  91 // thread to interfere, it obtains the CMS token.
  92 //
  93 // If either thread tries to get the token while the other has
  94 // it, that thread waits. However, if the VM thread and CMS thread
  95 // both want the token, then the VM thread gets priority while the
  96 // CMS thread waits. This ensures, for instance, that the "concurrent"
  97 // phases of the CMS thread's work do not block out the VM thread
  98 // for long periods of time as the CMS thread continues to hog
  99 // the token. (See bug 4616232).
 100 //
 101 // The baton-passing functions are, however, controlled by the
 102 // flags _foregroundGCShouldWait and _foregroundGCIsActive,
 103 // and here the low-level CMS lock, not the high level token,
 104 // ensures mutual exclusion.
 105 //
 106 // Two important conditions that we have to satisfy:
 107 // 1. if a thread does a low-level wait on the CMS lock, then it
 108 //    relinquishes the CMS token if it were holding that token
 109 //    when it acquired the low-level CMS lock.
 110 // 2. any low-level notifications on the low-level lock
 111 //    should only be sent when a thread has relinquished the token.
 112 //
 113 // In the absence of either property, we'd have potential deadlock.
 114 //
 115 // We protect each of the CMS (concurrent and sequential) phases
 116 // with the CMS _token_, not the CMS _lock_.
 117 //
 118 // The only code protected by CMS lock is the token acquisition code
 119 // itself, see ConcurrentMarkSweepThread::[de]synchronize(), and the
 120 // baton-passing code.
 121 //
 122 // Unfortunately, i couldn't come up with a good abstraction to factor and
 123 // hide the naked CGC_lock manipulation in the baton-passing code
 124 // further below. That's something we should try to do. Also, the proof
 125 // of correctness of this 2-level locking scheme is far from obvious,
 126 // and potentially quite slippery. We have an uneasy suspicion, for instance,
 127 // that there may be a theoretical possibility of delay/starvation in the
 128 // low-level lock/wait/notify scheme used for the baton-passing because of
 129 // potential interference with the priority scheme embodied in the
 130 // CMS-token-passing protocol. See related comments at a CGC_lock->wait()
 131 // invocation further below and marked with "XXX 20011219YSR".
 132 // Indeed, as we note elsewhere, this may become yet more slippery
 133 // in the presence of multiple CMS and/or multiple VM threads. XXX
 134 
 135 class CMSTokenSync: public StackObj {
 136  private:
 137   bool _is_cms_thread;
 138  public:
 139   CMSTokenSync(bool is_cms_thread):
 140     _is_cms_thread(is_cms_thread) {
 141     assert(is_cms_thread == Thread::current()->is_ConcurrentGC_thread(),
 142            "Incorrect argument to constructor");
 143     ConcurrentMarkSweepThread::synchronize(_is_cms_thread);
 144   }
 145 
 146   ~CMSTokenSync() {
 147     assert(_is_cms_thread ?
 148              ConcurrentMarkSweepThread::cms_thread_has_cms_token() :
 149              ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
 150           "Incorrect state");
 151     ConcurrentMarkSweepThread::desynchronize(_is_cms_thread);
 152   }
 153 };
 154 
 155 // Convenience class that does a CMSTokenSync, and then acquires
 156 // upto three locks.
 157 class CMSTokenSyncWithLocks: public CMSTokenSync {
 158  private:
 159   // Note: locks are acquired in textual declaration order
 160   // and released in the opposite order
 161   MutexLockerEx _locker1, _locker2, _locker3;
 162  public:
 163   CMSTokenSyncWithLocks(bool is_cms_thread, Mutex* mutex1,
 164                         Mutex* mutex2 = NULL, Mutex* mutex3 = NULL):
 165     CMSTokenSync(is_cms_thread),
 166     _locker1(mutex1, Mutex::_no_safepoint_check_flag),
 167     _locker2(mutex2, Mutex::_no_safepoint_check_flag),
 168     _locker3(mutex3, Mutex::_no_safepoint_check_flag)
 169   { }
 170 };
 171 
 172 
 173 //////////////////////////////////////////////////////////////////
 174 //  Concurrent Mark-Sweep Generation /////////////////////////////
 175 //////////////////////////////////////////////////////////////////
 176 
 177 NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;)
 178 
 179 // This struct contains per-thread things necessary to support parallel
 180 // young-gen collection.
 181 class CMSParGCThreadState: public CHeapObj<mtGC> {
 182  public:
 183   CFLS_LAB lab;
 184   PromotionInfo promo;
 185 
 186   // Constructor.
 187   CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) {
 188     promo.setSpace(cfls);
 189   }
 190 };
 191 
 192 ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration(
 193      ReservedSpace rs, size_t initial_byte_size, int level,
 194      CardTableRS* ct, bool use_adaptive_freelists,
 195      FreeBlockDictionary<FreeChunk>::DictionaryChoice dictionaryChoice) :
 196   CardGeneration(rs, initial_byte_size, level, ct),
 197   _dilatation_factor(((double)MinChunkSize)/((double)(CollectedHeap::min_fill_size()))),
 198   _did_compact(false)
 199 {
 200   HeapWord* bottom = (HeapWord*) _virtual_space.low();
 201   HeapWord* end    = (HeapWord*) _virtual_space.high();
 202 
 203   _direct_allocated_words = 0;
 204   NOT_PRODUCT(
 205     _numObjectsPromoted = 0;
 206     _numWordsPromoted = 0;
 207     _numObjectsAllocated = 0;
 208     _numWordsAllocated = 0;
 209   )
 210 
 211   _cmsSpace = new CompactibleFreeListSpace(_bts, MemRegion(bottom, end),
 212                                            use_adaptive_freelists,
 213                                            dictionaryChoice);
 214   NOT_PRODUCT(debug_cms_space = _cmsSpace;)
 215   _cmsSpace->_gen = this;
 216 
 217   _gc_stats = new CMSGCStats();
 218 
 219   // Verify the assumption that FreeChunk::_prev and OopDesc::_klass
 220   // offsets match. The ability to tell free chunks from objects
 221   // depends on this property.
 222   debug_only(
 223     FreeChunk* junk = NULL;
 224     assert(UseCompressedClassPointers ||
 225            junk->prev_addr() == (void*)(oop(junk)->klass_addr()),
 226            "Offset of FreeChunk::_prev within FreeChunk must match"
 227            "  that of OopDesc::_klass within OopDesc");
 228   )
 229 
 230   _par_gc_thread_states = NEW_C_HEAP_ARRAY(CMSParGCThreadState*, ParallelGCThreads, mtGC);
 231   for (uint i = 0; i < ParallelGCThreads; i++) {
 232     _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace());
 233   }
 234 
 235   _incremental_collection_failed = false;
 236   // The "dilatation_factor" is the expansion that can occur on
 237   // account of the fact that the minimum object size in the CMS
 238   // generation may be larger than that in, say, a contiguous young
 239   //  generation.
 240   // Ideally, in the calculation below, we'd compute the dilatation
 241   // factor as: MinChunkSize/(promoting_gen's min object size)
 242   // Since we do not have such a general query interface for the
 243   // promoting generation, we'll instead just use the minimum
 244   // object size (which today is a header's worth of space);
 245   // note that all arithmetic is in units of HeapWords.
 246   assert(MinChunkSize >= CollectedHeap::min_fill_size(), "just checking");
 247   assert(_dilatation_factor >= 1.0, "from previous assert");
 248 }
 249 
 250 
 251 // The field "_initiating_occupancy" represents the occupancy percentage
 252 // at which we trigger a new collection cycle.  Unless explicitly specified
 253 // via CMSInitiatingOccupancyFraction (argument "io" below), it
 254 // is calculated by:
 255 //
 256 //   Let "f" be MinHeapFreeRatio in
 257 //
 258 //    _initiating_occupancy = 100-f +
 259 //                           f * (CMSTriggerRatio/100)
 260 //   where CMSTriggerRatio is the argument "tr" below.
 261 //
 262 // That is, if we assume the heap is at its desired maximum occupancy at the
 263 // end of a collection, we let CMSTriggerRatio of the (purported) free
 264 // space be allocated before initiating a new collection cycle.
 265 //
 266 void ConcurrentMarkSweepGeneration::init_initiating_occupancy(intx io, uintx tr) {
 267   assert(io <= 100 && tr <= 100, "Check the arguments");
 268   if (io >= 0) {
 269     _initiating_occupancy = (double)io / 100.0;
 270   } else {
 271     _initiating_occupancy = ((100 - MinHeapFreeRatio) +
 272                              (double)(tr * MinHeapFreeRatio) / 100.0)
 273                             / 100.0;
 274   }
 275 }
 276 
 277 void ConcurrentMarkSweepGeneration::ref_processor_init() {
 278   assert(collector() != NULL, "no collector");
 279   collector()->ref_processor_init();
 280 }
 281 
 282 void CMSCollector::ref_processor_init() {
 283   if (_ref_processor == NULL) {
 284     // Allocate and initialize a reference processor
 285     _ref_processor =
 286       new ReferenceProcessor(_span,                               // span
 287                              (ParallelGCThreads > 1) && ParallelRefProcEnabled, // mt processing
 288                              ParallelGCThreads,                   // mt processing degree
 289                              _cmsGen->refs_discovery_is_mt(),     // mt discovery
 290                              MAX2(ConcGCThreads, ParallelGCThreads), // mt discovery degree
 291                              _cmsGen->refs_discovery_is_atomic(), // discovery is not atomic
 292                              &_is_alive_closure);                 // closure for liveness info
 293     // Initialize the _ref_processor field of CMSGen
 294     _cmsGen->set_ref_processor(_ref_processor);
 295 
 296   }
 297 }
 298 
 299 AdaptiveSizePolicy* CMSCollector::size_policy() {
 300   GenCollectedHeap* gch = GenCollectedHeap::heap();
 301   return gch->gen_policy()->size_policy();
 302 }
 303 
 304 void ConcurrentMarkSweepGeneration::initialize_performance_counters() {
 305 
 306   const char* gen_name = "old";
 307   GenCollectorPolicy* gcp = (GenCollectorPolicy*) GenCollectedHeap::heap()->collector_policy();
 308 
 309   // Generation Counters - generation 1, 1 subspace
 310   _gen_counters = new GenerationCounters(gen_name, 1, 1,
 311       gcp->min_old_size(), gcp->max_old_size(), &_virtual_space);
 312 
 313   _space_counters = new GSpaceCounters(gen_name, 0,
 314                                        _virtual_space.reserved_size(),
 315                                        this, _gen_counters);
 316 }
 317 
 318 CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha):
 319   _cms_gen(cms_gen)
 320 {
 321   assert(alpha <= 100, "bad value");
 322   _saved_alpha = alpha;
 323 
 324   // Initialize the alphas to the bootstrap value of 100.
 325   _gc0_alpha = _cms_alpha = 100;
 326 
 327   _cms_begin_time.update();
 328   _cms_end_time.update();
 329 
 330   _gc0_duration = 0.0;
 331   _gc0_period = 0.0;
 332   _gc0_promoted = 0;
 333 
 334   _cms_duration = 0.0;
 335   _cms_period = 0.0;
 336   _cms_allocated = 0;
 337 
 338   _cms_used_at_gc0_begin = 0;
 339   _cms_used_at_gc0_end = 0;
 340   _allow_duty_cycle_reduction = false;
 341   _valid_bits = 0;
 342 }
 343 
 344 double CMSStats::cms_free_adjustment_factor(size_t free) const {
 345   // TBD: CR 6909490
 346   return 1.0;
 347 }
 348 
 349 void CMSStats::adjust_cms_free_adjustment_factor(bool fail, size_t free) {
 350 }
 351 
 352 // If promotion failure handling is on use
 353 // the padded average size of the promotion for each
 354 // young generation collection.
 355 double CMSStats::time_until_cms_gen_full() const {
 356   size_t cms_free = _cms_gen->cmsSpace()->free();
 357   GenCollectedHeap* gch = GenCollectedHeap::heap();
 358   size_t expected_promotion = MIN2(gch->young_gen()->capacity(),
 359                                    (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average());
 360   if (cms_free > expected_promotion) {
 361     // Start a cms collection if there isn't enough space to promote
 362     // for the next minor collection.  Use the padded average as
 363     // a safety factor.
 364     cms_free -= expected_promotion;
 365 
 366     // Adjust by the safety factor.
 367     double cms_free_dbl = (double)cms_free;
 368     double cms_adjustment = (100.0 - CMSIncrementalSafetyFactor)/100.0;
 369     // Apply a further correction factor which tries to adjust
 370     // for recent occurance of concurrent mode failures.
 371     cms_adjustment = cms_adjustment * cms_free_adjustment_factor(cms_free);
 372     cms_free_dbl = cms_free_dbl * cms_adjustment;
 373 
 374     if (PrintGCDetails && Verbose) {
 375       gclog_or_tty->print_cr("CMSStats::time_until_cms_gen_full: cms_free "
 376         SIZE_FORMAT " expected_promotion " SIZE_FORMAT,
 377         cms_free, expected_promotion);
 378       gclog_or_tty->print_cr("  cms_free_dbl %f cms_consumption_rate %f",
 379         cms_free_dbl, cms_consumption_rate() + 1.0);
 380     }
 381     // Add 1 in case the consumption rate goes to zero.
 382     return cms_free_dbl / (cms_consumption_rate() + 1.0);
 383   }
 384   return 0.0;
 385 }
 386 
 387 // Compare the duration of the cms collection to the
 388 // time remaining before the cms generation is empty.
 389 // Note that the time from the start of the cms collection
 390 // to the start of the cms sweep (less than the total
 391 // duration of the cms collection) can be used.  This
 392 // has been tried and some applications experienced
 393 // promotion failures early in execution.  This was
 394 // possibly because the averages were not accurate
 395 // enough at the beginning.
 396 double CMSStats::time_until_cms_start() const {
 397   // We add "gc0_period" to the "work" calculation
 398   // below because this query is done (mostly) at the
 399   // end of a scavenge, so we need to conservatively
 400   // account for that much possible delay
 401   // in the query so as to avoid concurrent mode failures
 402   // due to starting the collection just a wee bit too
 403   // late.
 404   double work = cms_duration() + gc0_period();
 405   double deadline = time_until_cms_gen_full();
 406   // If a concurrent mode failure occurred recently, we want to be
 407   // more conservative and halve our expected time_until_cms_gen_full()
 408   if (work > deadline) {
 409     if (Verbose && PrintGCDetails) {
 410       gclog_or_tty->print(
 411         " CMSCollector: collect because of anticipated promotion "
 412         "before full %3.7f + %3.7f > %3.7f ", cms_duration(),
 413         gc0_period(), time_until_cms_gen_full());
 414     }
 415     return 0.0;
 416   }
 417   return work - deadline;
 418 }
 419 
 420 #ifndef PRODUCT
 421 void CMSStats::print_on(outputStream *st) const {
 422   st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha);
 423   st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo=" SIZE_FORMAT,
 424                gc0_duration(), gc0_period(), gc0_promoted());
 425   st->print(",cms_dur=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT,
 426             cms_duration(), cms_period(), cms_allocated());
 427   st->print(",cms_since_beg=%g,cms_since_end=%g",
 428             cms_time_since_begin(), cms_time_since_end());
 429   st->print(",cms_used_beg=" SIZE_FORMAT ",cms_used_end=" SIZE_FORMAT,
 430             _cms_used_at_gc0_begin, _cms_used_at_gc0_end);
 431 
 432   if (valid()) {
 433     st->print(",promo_rate=%g,cms_alloc_rate=%g",
 434               promotion_rate(), cms_allocation_rate());
 435     st->print(",cms_consumption_rate=%g,time_until_full=%g",
 436               cms_consumption_rate(), time_until_cms_gen_full());
 437   }
 438   st->print(" ");
 439 }
 440 #endif // #ifndef PRODUCT
 441 
 442 CMSCollector::CollectorState CMSCollector::_collectorState =
 443                              CMSCollector::Idling;
 444 bool CMSCollector::_foregroundGCIsActive = false;
 445 bool CMSCollector::_foregroundGCShouldWait = false;
 446 
 447 CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
 448                            CardTableRS*                   ct,
 449                            ConcurrentMarkSweepPolicy*     cp):
 450   _cmsGen(cmsGen),
 451   _ct(ct),
 452   _ref_processor(NULL),    // will be set later
 453   _conc_workers(NULL),     // may be set later
 454   _abort_preclean(false),
 455   _start_sampling(false),
 456   _between_prologue_and_epilogue(false),
 457   _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"),
 458   _modUnionTable((CardTableModRefBS::card_shift - LogHeapWordSize),
 459                  -1 /* lock-free */, "No_lock" /* dummy */),
 460   _modUnionClosurePar(&_modUnionTable),
 461   // Adjust my span to cover old (cms) gen
 462   _span(cmsGen->reserved()),
 463   // Construct the is_alive_closure with _span & markBitMap
 464   _is_alive_closure(_span, &_markBitMap),
 465   _restart_addr(NULL),
 466   _overflow_list(NULL),
 467   _stats(cmsGen),
 468   _eden_chunk_lock(new Mutex(Mutex::leaf + 1, "CMS_eden_chunk_lock", true,
 469                              //verify that this lock should be acquired with safepoint check.
 470                              Monitor::_safepoint_check_sometimes)),
 471   _eden_chunk_array(NULL),     // may be set in ctor body
 472   _eden_chunk_capacity(0),     // -- ditto --
 473   _eden_chunk_index(0),        // -- ditto --
 474   _survivor_plab_array(NULL),  // -- ditto --
 475   _survivor_chunk_array(NULL), // -- ditto --
 476   _survivor_chunk_capacity(0), // -- ditto --
 477   _survivor_chunk_index(0),    // -- ditto --
 478   _ser_pmc_preclean_ovflw(0),
 479   _ser_kac_preclean_ovflw(0),
 480   _ser_pmc_remark_ovflw(0),
 481   _par_pmc_remark_ovflw(0),
 482   _ser_kac_ovflw(0),
 483   _par_kac_ovflw(0),
 484 #ifndef PRODUCT
 485   _num_par_pushes(0),
 486 #endif
 487   _collection_count_start(0),
 488   _verifying(false),
 489   _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"),
 490   _completed_initialization(false),
 491   _collector_policy(cp),
 492   _should_unload_classes(CMSClassUnloadingEnabled),
 493   _concurrent_cycles_since_last_unload(0),
 494   _roots_scanning_options(GenCollectedHeap::SO_None),
 495   _inter_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
 496   _intra_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
 497   _gc_tracer_cm(new (ResourceObj::C_HEAP, mtGC) CMSTracer()),
 498   _gc_timer_cm(new (ResourceObj::C_HEAP, mtGC) ConcurrentGCTimer()),
 499   _cms_start_registered(false)
 500 {
 501   if (ExplicitGCInvokesConcurrentAndUnloadsClasses) {
 502     ExplicitGCInvokesConcurrent = true;
 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       warning("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     warning("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         warning("GC/CMS: _conc_workers allocation failure: "
 541               "forcing -CMSConcurrentMTEnabled");
 542         CMSConcurrentMTEnabled = false;
 543       } else {
 544         _conc_workers->initialize_workers();
 545       }
 546     } else {
 547       CMSConcurrentMTEnabled = false;
 548     }
 549   }
 550   if (!CMSConcurrentMTEnabled) {
 551     ConcGCThreads = 0;
 552   } else {
 553     // Turn off CMSCleanOnEnter optimization temporarily for
 554     // the MT case where it's not fixed yet; see 6178663.
 555     CMSCleanOnEnter = false;
 556   }
 557   assert((_conc_workers != NULL) == (ConcGCThreads > 1),
 558          "Inconsistency");
 559 
 560   // Parallel task queues; these are shared for the
 561   // concurrent and stop-world phases of CMS, but
 562   // are not shared with parallel scavenge (ParNew).
 563   {
 564     uint i;
 565     uint num_queues = MAX2(ParallelGCThreads, ConcGCThreads);
 566 
 567     if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled
 568          || ParallelRefProcEnabled)
 569         && num_queues > 0) {
 570       _task_queues = new OopTaskQueueSet(num_queues);
 571       if (_task_queues == NULL) {
 572         warning("task_queues allocation failure.");
 573         return;
 574       }
 575       _hash_seed = NEW_C_HEAP_ARRAY(int, num_queues, mtGC);
 576       typedef Padded<OopTaskQueue> PaddedOopTaskQueue;
 577       for (i = 0; i < num_queues; i++) {
 578         PaddedOopTaskQueue *q = new PaddedOopTaskQueue();
 579         if (q == NULL) {
 580           warning("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         _hash_seed[i] = 17;  // copied from ParNew
 588       }
 589     }
 590   }
 591 
 592   _cmsGen ->init_initiating_occupancy(CMSInitiatingOccupancyFraction, CMSTriggerRatio);
 593 
 594   // Clip CMSBootstrapOccupancy between 0 and 100.
 595   _bootstrap_occupancy = ((double)CMSBootstrapOccupancy)/(double)100;
 596 
 597   // Now tell CMS generations the identity of their collector
 598   ConcurrentMarkSweepGeneration::set_collector(this);
 599 
 600   // Create & start a CMS thread for this CMS collector
 601   _cmsThread = ConcurrentMarkSweepThread::start(this);
 602   assert(cmsThread() != NULL, "CMS Thread should have been created");
 603   assert(cmsThread()->collector() == this,
 604          "CMS Thread should refer to this gen");
 605   assert(CGC_lock != NULL, "Where's the CGC_lock?");
 606 
 607   // Support for parallelizing young gen rescan
 608   GenCollectedHeap* gch = GenCollectedHeap::heap();
 609   assert(gch->young_gen()->kind() == Generation::ParNew, "CMS can only be used with ParNew");
 610   _young_gen = (ParNewGeneration*)gch->young_gen();
 611   if (gch->supports_inline_contig_alloc()) {
 612     _top_addr = gch->top_addr();
 613     _end_addr = gch->end_addr();
 614     assert(_young_gen != NULL, "no _young_gen");
 615     _eden_chunk_index = 0;
 616     _eden_chunk_capacity = (_young_gen->max_capacity()+CMSSamplingGrain)/CMSSamplingGrain;
 617     _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity, mtGC);
 618   }
 619 
 620   // Support for parallelizing survivor space rescan
 621   if ((CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) || CMSParallelInitialMarkEnabled) {
 622     const size_t max_plab_samples =
 623       ((DefNewGeneration*)_young_gen)->max_survivor_size() / plab_sample_minimum_size();
 624 
 625     _survivor_plab_array  = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads, mtGC);
 626     _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, 2*max_plab_samples, mtGC);
 627     _cursor               = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads, mtGC);
 628     _survivor_chunk_capacity = 2*max_plab_samples;
 629     for (uint i = 0; i < ParallelGCThreads; i++) {
 630       HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
 631       ChunkArray* cur = ::new (&_survivor_plab_array[i]) ChunkArray(vec, max_plab_samples);
 632       assert(cur->end() == 0, "Should be 0");
 633       assert(cur->array() == vec, "Should be vec");
 634       assert(cur->capacity() == max_plab_samples, "Error");
 635     }
 636   }
 637 
 638   NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;)
 639   _gc_counters = new CollectorCounters("CMS", 1);
 640   _completed_initialization = true;
 641   _inter_sweep_timer.start();  // start of time
 642 }
 643 
 644 size_t CMSCollector::plab_sample_minimum_size() {
 645   // The default value of MinTLABSize is 2k, but there is
 646   // no way to get the default value if the flag has been overridden.
 647   return MAX2(ThreadLocalAllocBuffer::min_size() * HeapWordSize, 2 * K);
 648 }
 649 
 650 const char* ConcurrentMarkSweepGeneration::name() const {
 651   return "concurrent mark-sweep generation";
 652 }
 653 void ConcurrentMarkSweepGeneration::update_counters() {
 654   if (UsePerfData) {
 655     _space_counters->update_all();
 656     _gen_counters->update_all();
 657   }
 658 }
 659 
 660 // this is an optimized version of update_counters(). it takes the
 661 // used value as a parameter rather than computing it.
 662 //
 663 void ConcurrentMarkSweepGeneration::update_counters(size_t used) {
 664   if (UsePerfData) {
 665     _space_counters->update_used(used);
 666     _space_counters->update_capacity();
 667     _gen_counters->update_all();
 668   }
 669 }
 670 
 671 void ConcurrentMarkSweepGeneration::print() const {
 672   Generation::print();
 673   cmsSpace()->print();
 674 }
 675 
 676 #ifndef PRODUCT
 677 void ConcurrentMarkSweepGeneration::print_statistics() {
 678   cmsSpace()->printFLCensus(0);
 679 }
 680 #endif
 681 
 682 void ConcurrentMarkSweepGeneration::printOccupancy(const char *s) {
 683   GenCollectedHeap* gch = GenCollectedHeap::heap();
 684   if (PrintGCDetails) {
 685     if (Verbose) {
 686       gclog_or_tty->print("[%d %s-%s: "SIZE_FORMAT"("SIZE_FORMAT")]",
 687         level(), short_name(), s, used(), capacity());
 688     } else {
 689       gclog_or_tty->print("[%d %s-%s: "SIZE_FORMAT"K("SIZE_FORMAT"K)]",
 690         level(), short_name(), s, used() / K, capacity() / K);
 691     }
 692   }
 693   if (Verbose) {
 694     gclog_or_tty->print(" "SIZE_FORMAT"("SIZE_FORMAT")",
 695               gch->used(), gch->capacity());
 696   } else {
 697     gclog_or_tty->print(" "SIZE_FORMAT"K("SIZE_FORMAT"K)",
 698               gch->used() / K, gch->capacity() / K);
 699   }
 700 }
 701 
 702 size_t
 703 ConcurrentMarkSweepGeneration::contiguous_available() const {
 704   // dld proposes an improvement in precision here. If the committed
 705   // part of the space ends in a free block we should add that to
 706   // uncommitted size in the calculation below. Will make this
 707   // change later, staying with the approximation below for the
 708   // time being. -- ysr.
 709   return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc());
 710 }
 711 
 712 size_t
 713 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const {
 714   return _cmsSpace->max_alloc_in_words() * HeapWordSize;
 715 }
 716 
 717 size_t ConcurrentMarkSweepGeneration::max_available() const {
 718   return free() + _virtual_space.uncommitted_size();
 719 }
 720 
 721 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(size_t max_promotion_in_bytes) const {
 722   size_t available = max_available();
 723   size_t av_promo  = (size_t)gc_stats()->avg_promoted()->padded_average();
 724   bool   res = (available >= av_promo) || (available >= max_promotion_in_bytes);
 725   if (Verbose && PrintGCDetails) {
 726     gclog_or_tty->print_cr(
 727       "CMS: promo attempt is%s safe: available("SIZE_FORMAT") %s av_promo("SIZE_FORMAT"),"
 728       "max_promo("SIZE_FORMAT")",
 729       res? "":" not", available, res? ">=":"<",
 730       av_promo, max_promotion_in_bytes);
 731   }
 732   return res;
 733 }
 734 
 735 // At a promotion failure dump information on block layout in heap
 736 // (cms old generation).
 737 void ConcurrentMarkSweepGeneration::promotion_failure_occurred() {
 738   if (CMSDumpAtPromotionFailure) {
 739     cmsSpace()->dump_at_safepoint_with_locks(collector(), gclog_or_tty);
 740   }
 741 }
 742 
 743 void ConcurrentMarkSweepGeneration::reset_after_compaction() {
 744   // Clear the promotion information.  These pointers can be adjusted
 745   // along with all the other pointers into the heap but
 746   // compaction is expected to be a rare event with
 747   // a heap using cms so don't do it without seeing the need.
 748   for (uint i = 0; i < ParallelGCThreads; i++) {
 749     _par_gc_thread_states[i]->promo.reset();
 750   }
 751 }
 752 
 753 void ConcurrentMarkSweepGeneration::compute_new_size() {
 754   assert_locked_or_safepoint(Heap_lock);
 755 
 756   // If incremental collection failed, we just want to expand
 757   // to the limit.
 758   if (incremental_collection_failed()) {
 759     clear_incremental_collection_failed();
 760     grow_to_reserved();
 761     return;
 762   }
 763 
 764   // The heap has been compacted but not reset yet.
 765   // Any metric such as free() or used() will be incorrect.
 766 
 767   CardGeneration::compute_new_size();
 768 
 769   // Reset again after a possible resizing
 770   if (did_compact()) {
 771     cmsSpace()->reset_after_compaction();
 772   }
 773 }
 774 
 775 void ConcurrentMarkSweepGeneration::compute_new_size_free_list() {
 776   assert_locked_or_safepoint(Heap_lock);
 777 
 778   // If incremental collection failed, we just want to expand
 779   // to the limit.
 780   if (incremental_collection_failed()) {
 781     clear_incremental_collection_failed();
 782     grow_to_reserved();
 783     return;
 784   }
 785 
 786   double free_percentage = ((double) free()) / capacity();
 787   double desired_free_percentage = (double) MinHeapFreeRatio / 100;
 788   double maximum_free_percentage = (double) MaxHeapFreeRatio / 100;
 789 
 790   // compute expansion delta needed for reaching desired free percentage
 791   if (free_percentage < desired_free_percentage) {
 792     size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
 793     assert(desired_capacity >= capacity(), "invalid expansion size");
 794     size_t expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes);
 795     if (PrintGCDetails && Verbose) {
 796       size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
 797       gclog_or_tty->print_cr("\nFrom compute_new_size: ");
 798       gclog_or_tty->print_cr("  Free fraction %f", free_percentage);
 799       gclog_or_tty->print_cr("  Desired free fraction %f",
 800         desired_free_percentage);
 801       gclog_or_tty->print_cr("  Maximum free fraction %f",
 802         maximum_free_percentage);
 803       gclog_or_tty->print_cr("  Capacity "SIZE_FORMAT, capacity()/1000);
 804       gclog_or_tty->print_cr("  Desired capacity "SIZE_FORMAT,
 805         desired_capacity/1000);
 806       int prev_level = level() - 1;
 807       if (prev_level >= 0) {
 808         size_t prev_size = 0;
 809         GenCollectedHeap* gch = GenCollectedHeap::heap();
 810         Generation* prev_gen = gch->young_gen();
 811         prev_size = prev_gen->capacity();
 812           gclog_or_tty->print_cr("  Younger gen size "SIZE_FORMAT,
 813                                  prev_size/1000);
 814       }
 815       gclog_or_tty->print_cr("  unsafe_max_alloc_nogc "SIZE_FORMAT,
 816         unsafe_max_alloc_nogc()/1000);
 817       gclog_or_tty->print_cr("  contiguous available "SIZE_FORMAT,
 818         contiguous_available()/1000);
 819       gclog_or_tty->print_cr("  Expand by "SIZE_FORMAT" (bytes)",
 820         expand_bytes);
 821     }
 822     // safe if expansion fails
 823     expand_for_gc_cause(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio);
 824     if (PrintGCDetails && Verbose) {
 825       gclog_or_tty->print_cr("  Expanded free fraction %f",
 826         ((double) free()) / capacity());
 827     }
 828   } else {
 829     size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
 830     assert(desired_capacity <= capacity(), "invalid expansion size");
 831     size_t shrink_bytes = capacity() - desired_capacity;
 832     // Don't shrink unless the delta is greater than the minimum shrink we want
 833     if (shrink_bytes >= MinHeapDeltaBytes) {
 834       shrink_free_list_by(shrink_bytes);
 835     }
 836   }
 837 }
 838 
 839 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const {
 840   return cmsSpace()->freelistLock();
 841 }
 842 
 843 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size,
 844                                                   bool   tlab) {
 845   CMSSynchronousYieldRequest yr;
 846   MutexLockerEx x(freelistLock(),
 847                   Mutex::_no_safepoint_check_flag);
 848   return have_lock_and_allocate(size, tlab);
 849 }
 850 
 851 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size,
 852                                                   bool   tlab /* ignored */) {
 853   assert_lock_strong(freelistLock());
 854   size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size);
 855   HeapWord* res = cmsSpace()->allocate(adjustedSize);
 856   // Allocate the object live (grey) if the background collector has
 857   // started marking. This is necessary because the marker may
 858   // have passed this address and consequently this object will
 859   // not otherwise be greyed and would be incorrectly swept up.
 860   // Note that if this object contains references, the writing
 861   // of those references will dirty the card containing this object
 862   // allowing the object to be blackened (and its references scanned)
 863   // either during a preclean phase or at the final checkpoint.
 864   if (res != NULL) {
 865     // We may block here with an uninitialized object with
 866     // its mark-bit or P-bits not yet set. Such objects need
 867     // to be safely navigable by block_start().
 868     assert(oop(res)->klass_or_null() == NULL, "Object should be uninitialized here.");
 869     assert(!((FreeChunk*)res)->is_free(), "Error, block will look free but show wrong size");
 870     collector()->direct_allocated(res, adjustedSize);
 871     _direct_allocated_words += adjustedSize;
 872     // allocation counters
 873     NOT_PRODUCT(
 874       _numObjectsAllocated++;
 875       _numWordsAllocated += (int)adjustedSize;
 876     )
 877   }
 878   return res;
 879 }
 880 
 881 // In the case of direct allocation by mutators in a generation that
 882 // is being concurrently collected, the object must be allocated
 883 // live (grey) if the background collector has started marking.
 884 // This is necessary because the marker may
 885 // have passed this address and consequently this object will
 886 // not otherwise be greyed and would be incorrectly swept up.
 887 // Note that if this object contains references, the writing
 888 // of those references will dirty the card containing this object
 889 // allowing the object to be blackened (and its references scanned)
 890 // either during a preclean phase or at the final checkpoint.
 891 void CMSCollector::direct_allocated(HeapWord* start, size_t size) {
 892   assert(_markBitMap.covers(start, size), "Out of bounds");
 893   if (_collectorState >= Marking) {
 894     MutexLockerEx y(_markBitMap.lock(),
 895                     Mutex::_no_safepoint_check_flag);
 896     // [see comments preceding SweepClosure::do_blk() below for details]
 897     //
 898     // Can the P-bits be deleted now?  JJJ
 899     //
 900     // 1. need to mark the object as live so it isn't collected
 901     // 2. need to mark the 2nd bit to indicate the object may be uninitialized
 902     // 3. need to mark the end of the object so marking, precleaning or sweeping
 903     //    can skip over uninitialized or unparsable objects. An allocated
 904     //    object is considered uninitialized for our purposes as long as
 905     //    its klass word is NULL.  All old gen objects are parsable
 906     //    as soon as they are initialized.)
 907     _markBitMap.mark(start);          // object is live
 908     _markBitMap.mark(start + 1);      // object is potentially uninitialized?
 909     _markBitMap.mark(start + size - 1);
 910                                       // mark end of object
 911   }
 912   // check that oop looks uninitialized
 913   assert(oop(start)->klass_or_null() == NULL, "_klass should be NULL");
 914 }
 915 
 916 void CMSCollector::promoted(bool par, HeapWord* start,
 917                             bool is_obj_array, size_t obj_size) {
 918   assert(_markBitMap.covers(start), "Out of bounds");
 919   // See comment in direct_allocated() about when objects should
 920   // be allocated live.
 921   if (_collectorState >= Marking) {
 922     // we already hold the marking bit map lock, taken in
 923     // the prologue
 924     if (par) {
 925       _markBitMap.par_mark(start);
 926     } else {
 927       _markBitMap.mark(start);
 928     }
 929     // We don't need to mark the object as uninitialized (as
 930     // in direct_allocated above) because this is being done with the
 931     // world stopped and the object will be initialized by the
 932     // time the marking, precleaning or sweeping get to look at it.
 933     // But see the code for copying objects into the CMS generation,
 934     // where we need to ensure that concurrent readers of the
 935     // block offset table are able to safely navigate a block that
 936     // is in flux from being free to being allocated (and in
 937     // transition while being copied into) and subsequently
 938     // becoming a bona-fide object when the copy/promotion is complete.
 939     assert(SafepointSynchronize::is_at_safepoint(),
 940            "expect promotion only at safepoints");
 941 
 942     if (_collectorState < Sweeping) {
 943       // Mark the appropriate cards in the modUnionTable, so that
 944       // this object gets scanned before the sweep. If this is
 945       // not done, CMS generation references in the object might
 946       // not get marked.
 947       // For the case of arrays, which are otherwise precisely
 948       // marked, we need to dirty the entire array, not just its head.
 949       if (is_obj_array) {
 950         // The [par_]mark_range() method expects mr.end() below to
 951         // be aligned to the granularity of a bit's representation
 952         // in the heap. In the case of the MUT below, that's a
 953         // card size.
 954         MemRegion mr(start,
 955                      (HeapWord*)round_to((intptr_t)(start + obj_size),
 956                         CardTableModRefBS::card_size /* bytes */));
 957         if (par) {
 958           _modUnionTable.par_mark_range(mr);
 959         } else {
 960           _modUnionTable.mark_range(mr);
 961         }
 962       } else {  // not an obj array; we can just mark the head
 963         if (par) {
 964           _modUnionTable.par_mark(start);
 965         } else {
 966           _modUnionTable.mark(start);
 967         }
 968       }
 969     }
 970   }
 971 }
 972 
 973 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size) {
 974   assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
 975   // allocate, copy and if necessary update promoinfo --
 976   // delegate to underlying space.
 977   assert_lock_strong(freelistLock());
 978 
 979 #ifndef PRODUCT
 980   if (GenCollectedHeap::heap()->promotion_should_fail()) {
 981     return NULL;
 982   }
 983 #endif  // #ifndef PRODUCT
 984 
 985   oop res = _cmsSpace->promote(obj, obj_size);
 986   if (res == NULL) {
 987     // expand and retry
 988     size_t s = _cmsSpace->expansionSpaceRequired(obj_size);  // HeapWords
 989     expand_for_gc_cause(s*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_promotion);
 990     // Since this is the old generation, we don't try to promote
 991     // into a more senior generation.
 992     res = _cmsSpace->promote(obj, obj_size);
 993   }
 994   if (res != NULL) {
 995     // See comment in allocate() about when objects should
 996     // be allocated live.
 997     assert(obj->is_oop(), "Will dereference klass pointer below");
 998     collector()->promoted(false,           // Not parallel
 999                           (HeapWord*)res, obj->is_objArray(), obj_size);
1000     // promotion counters
1001     NOT_PRODUCT(
1002       _numObjectsPromoted++;
1003       _numWordsPromoted +=
1004         (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size()));
1005     )
1006   }
1007   return res;
1008 }
1009 
1010 
1011 // IMPORTANT: Notes on object size recognition in CMS.
1012 // ---------------------------------------------------
1013 // A block of storage in the CMS generation is always in
1014 // one of three states. A free block (FREE), an allocated
1015 // object (OBJECT) whose size() method reports the correct size,
1016 // and an intermediate state (TRANSIENT) in which its size cannot
1017 // be accurately determined.
1018 // STATE IDENTIFICATION:   (32 bit and 64 bit w/o COOPS)
1019 // -----------------------------------------------------
1020 // FREE:      klass_word & 1 == 1; mark_word holds block size
1021 //
1022 // OBJECT:    klass_word installed; klass_word != 0 && klass_word & 1 == 0;
1023 //            obj->size() computes correct size
1024 //
1025 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1026 //
1027 // STATE IDENTIFICATION: (64 bit+COOPS)
1028 // ------------------------------------
1029 // FREE:      mark_word & CMS_FREE_BIT == 1; mark_word & ~CMS_FREE_BIT gives block_size
1030 //
1031 // OBJECT:    klass_word installed; klass_word != 0;
1032 //            obj->size() computes correct size
1033 //
1034 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1035 //
1036 //
1037 // STATE TRANSITION DIAGRAM
1038 //
1039 //        mut / parnew                     mut  /  parnew
1040 // FREE --------------------> TRANSIENT ---------------------> OBJECT --|
1041 //  ^                                                                   |
1042 //  |------------------------ DEAD <------------------------------------|
1043 //         sweep                            mut
1044 //
1045 // While a block is in TRANSIENT state its size cannot be determined
1046 // so readers will either need to come back later or stall until
1047 // the size can be determined. Note that for the case of direct
1048 // allocation, P-bits, when available, may be used to determine the
1049 // size of an object that may not yet have been initialized.
1050 
1051 // Things to support parallel young-gen collection.
1052 oop
1053 ConcurrentMarkSweepGeneration::par_promote(int thread_num,
1054                                            oop old, markOop m,
1055                                            size_t word_sz) {
1056 #ifndef PRODUCT
1057   if (GenCollectedHeap::heap()->promotion_should_fail()) {
1058     return NULL;
1059   }
1060 #endif  // #ifndef PRODUCT
1061 
1062   CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1063   PromotionInfo* promoInfo = &ps->promo;
1064   // if we are tracking promotions, then first ensure space for
1065   // promotion (including spooling space for saving header if necessary).
1066   // then allocate and copy, then track promoted info if needed.
1067   // When tracking (see PromotionInfo::track()), the mark word may
1068   // be displaced and in this case restoration of the mark word
1069   // occurs in the (oop_since_save_marks_)iterate phase.
1070   if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) {
1071     // Out of space for allocating spooling buffers;
1072     // try expanding and allocating spooling buffers.
1073     if (!expand_and_ensure_spooling_space(promoInfo)) {
1074       return NULL;
1075     }
1076   }
1077   assert(promoInfo->has_spooling_space(), "Control point invariant");
1078   const size_t alloc_sz = CompactibleFreeListSpace::adjustObjectSize(word_sz);
1079   HeapWord* obj_ptr = ps->lab.alloc(alloc_sz);
1080   if (obj_ptr == NULL) {
1081      obj_ptr = expand_and_par_lab_allocate(ps, alloc_sz);
1082      if (obj_ptr == NULL) {
1083        return NULL;
1084      }
1085   }
1086   oop obj = oop(obj_ptr);
1087   OrderAccess::storestore();
1088   assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1089   assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1090   // IMPORTANT: See note on object initialization for CMS above.
1091   // Otherwise, copy the object.  Here we must be careful to insert the
1092   // klass pointer last, since this marks the block as an allocated object.
1093   // Except with compressed oops it's the mark word.
1094   HeapWord* old_ptr = (HeapWord*)old;
1095   // Restore the mark word copied above.
1096   obj->set_mark(m);
1097   assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1098   assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1099   OrderAccess::storestore();
1100 
1101   if (UseCompressedClassPointers) {
1102     // Copy gap missed by (aligned) header size calculation below
1103     obj->set_klass_gap(old->klass_gap());
1104   }
1105   if (word_sz > (size_t)oopDesc::header_size()) {
1106     Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1107                                  obj_ptr + oopDesc::header_size(),
1108                                  word_sz - oopDesc::header_size());
1109   }
1110 
1111   // Now we can track the promoted object, if necessary.  We take care
1112   // to delay the transition from uninitialized to full object
1113   // (i.e., insertion of klass pointer) until after, so that it
1114   // atomically becomes a promoted object.
1115   if (promoInfo->tracking()) {
1116     promoInfo->track((PromotedObject*)obj, old->klass());
1117   }
1118   assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1119   assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1120   assert(old->is_oop(), "Will use and dereference old klass ptr below");
1121 
1122   // Finally, install the klass pointer (this should be volatile).
1123   OrderAccess::storestore();
1124   obj->set_klass(old->klass());
1125   // We should now be able to calculate the right size for this object
1126   assert(obj->is_oop() && obj->size() == (int)word_sz, "Error, incorrect size computed for promoted object");
1127 
1128   collector()->promoted(true,          // parallel
1129                         obj_ptr, old->is_objArray(), word_sz);
1130 
1131   NOT_PRODUCT(
1132     Atomic::inc_ptr(&_numObjectsPromoted);
1133     Atomic::add_ptr(alloc_sz, &_numWordsPromoted);
1134   )
1135 
1136   return obj;
1137 }
1138 
1139 void
1140 ConcurrentMarkSweepGeneration::
1141 par_promote_alloc_done(int thread_num) {
1142   CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1143   ps->lab.retire(thread_num);
1144 }
1145 
1146 void
1147 ConcurrentMarkSweepGeneration::
1148 par_oop_since_save_marks_iterate_done(int thread_num) {
1149   CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1150   ParScanWithoutBarrierClosure* dummy_cl = NULL;
1151   ps->promo.promoted_oops_iterate_nv(dummy_cl);
1152 }
1153 
1154 bool ConcurrentMarkSweepGeneration::should_collect(bool   full,
1155                                                    size_t size,
1156                                                    bool   tlab)
1157 {
1158   // We allow a STW collection only if a full
1159   // collection was requested.
1160   return full || should_allocate(size, tlab); // FIX ME !!!
1161   // This and promotion failure handling are connected at the
1162   // hip and should be fixed by untying them.
1163 }
1164 
1165 bool CMSCollector::shouldConcurrentCollect() {
1166   if (_full_gc_requested) {
1167     if (Verbose && PrintGCDetails) {
1168       gclog_or_tty->print_cr("CMSCollector: collect because of explicit "
1169                              " gc request (or gc_locker)");
1170     }
1171     return true;
1172   }
1173 
1174   FreelistLocker x(this);
1175   // ------------------------------------------------------------------
1176   // Print out lots of information which affects the initiation of
1177   // a collection.
1178   if (PrintCMSInitiationStatistics && stats().valid()) {
1179     gclog_or_tty->print("CMSCollector shouldConcurrentCollect: ");
1180     gclog_or_tty->stamp();
1181     gclog_or_tty->cr();
1182     stats().print_on(gclog_or_tty);
1183     gclog_or_tty->print_cr("time_until_cms_gen_full %3.7f",
1184       stats().time_until_cms_gen_full());
1185     gclog_or_tty->print_cr("free="SIZE_FORMAT, _cmsGen->free());
1186     gclog_or_tty->print_cr("contiguous_available="SIZE_FORMAT,
1187                            _cmsGen->contiguous_available());
1188     gclog_or_tty->print_cr("promotion_rate=%g", stats().promotion_rate());
1189     gclog_or_tty->print_cr("cms_allocation_rate=%g", stats().cms_allocation_rate());
1190     gclog_or_tty->print_cr("occupancy=%3.7f", _cmsGen->occupancy());
1191     gclog_or_tty->print_cr("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy());
1192     gclog_or_tty->print_cr("cms_time_since_begin=%3.7f", stats().cms_time_since_begin());
1193     gclog_or_tty->print_cr("cms_time_since_end=%3.7f", stats().cms_time_since_end());
1194     gclog_or_tty->print_cr("metadata initialized %d",
1195       MetaspaceGC::should_concurrent_collect());
1196   }
1197   // ------------------------------------------------------------------
1198 
1199   // If the estimated time to complete a cms collection (cms_duration())
1200   // is less than the estimated time remaining until the cms generation
1201   // is full, start a collection.
1202   if (!UseCMSInitiatingOccupancyOnly) {
1203     if (stats().valid()) {
1204       if (stats().time_until_cms_start() == 0.0) {
1205         return true;
1206       }
1207     } else {
1208       // We want to conservatively collect somewhat early in order
1209       // to try and "bootstrap" our CMS/promotion statistics;
1210       // this branch will not fire after the first successful CMS
1211       // collection because the stats should then be valid.
1212       if (_cmsGen->occupancy() >= _bootstrap_occupancy) {
1213         if (Verbose && PrintGCDetails) {
1214           gclog_or_tty->print_cr(
1215             " CMSCollector: collect for bootstrapping statistics:"
1216             " occupancy = %f, boot occupancy = %f", _cmsGen->occupancy(),
1217             _bootstrap_occupancy);
1218         }
1219         return true;
1220       }
1221     }
1222   }
1223 
1224   // Otherwise, we start a collection cycle if
1225   // old gen want a collection cycle started. Each may use
1226   // an appropriate criterion for making this decision.
1227   // XXX We need to make sure that the gen expansion
1228   // criterion dovetails well with this. XXX NEED TO FIX THIS
1229   if (_cmsGen->should_concurrent_collect()) {
1230     if (Verbose && PrintGCDetails) {
1231       gclog_or_tty->print_cr("CMS old gen initiated");
1232     }
1233     return true;
1234   }
1235 
1236   // We start a collection if we believe an incremental collection may fail;
1237   // this is not likely to be productive in practice because it's probably too
1238   // late anyway.
1239   GenCollectedHeap* gch = GenCollectedHeap::heap();
1240   assert(gch->collector_policy()->is_generation_policy(),
1241          "You may want to check the correctness of the following");
1242   if (gch->incremental_collection_will_fail(true /* consult_young */)) {
1243     if (Verbose && PrintGCDetails) {
1244       gclog_or_tty->print("CMSCollector: collect because incremental collection will fail ");
1245     }
1246     return true;
1247   }
1248 
1249   if (MetaspaceGC::should_concurrent_collect()) {
1250     if (Verbose && PrintGCDetails) {
1251       gclog_or_tty->print("CMSCollector: collect for metadata allocation ");
1252     }
1253     return true;
1254   }
1255 
1256   // CMSTriggerInterval starts a CMS cycle if enough time has passed.
1257   if (CMSTriggerInterval >= 0) {
1258     if (CMSTriggerInterval == 0) {
1259       // Trigger always
1260       return true;
1261     }
1262 
1263     // Check the CMS time since begin (we do not check the stats validity
1264     // as we want to be able to trigger the first CMS cycle as well)
1265     if (stats().cms_time_since_begin() >= (CMSTriggerInterval / ((double) MILLIUNITS))) {
1266       if (Verbose && PrintGCDetails) {
1267         if (stats().valid()) {
1268           gclog_or_tty->print_cr("CMSCollector: collect because of trigger interval (time since last begin %3.7f secs)",
1269                                  stats().cms_time_since_begin());
1270         } else {
1271           gclog_or_tty->print_cr("CMSCollector: collect because of trigger interval (first collection)");
1272         }
1273       }
1274       return true;
1275     }
1276   }
1277 
1278   return false;
1279 }
1280 
1281 void CMSCollector::set_did_compact(bool v) { _cmsGen->set_did_compact(v); }
1282 
1283 // Clear _expansion_cause fields of constituent generations
1284 void CMSCollector::clear_expansion_cause() {
1285   _cmsGen->clear_expansion_cause();
1286 }
1287 
1288 // We should be conservative in starting a collection cycle.  To
1289 // start too eagerly runs the risk of collecting too often in the
1290 // extreme.  To collect too rarely falls back on full collections,
1291 // which works, even if not optimum in terms of concurrent work.
1292 // As a work around for too eagerly collecting, use the flag
1293 // UseCMSInitiatingOccupancyOnly.  This also has the advantage of
1294 // giving the user an easily understandable way of controlling the
1295 // collections.
1296 // We want to start a new collection cycle if any of the following
1297 // conditions hold:
1298 // . our current occupancy exceeds the configured initiating occupancy
1299 //   for this generation, or
1300 // . we recently needed to expand this space and have not, since that
1301 //   expansion, done a collection of this generation, or
1302 // . the underlying space believes that it may be a good idea to initiate
1303 //   a concurrent collection (this may be based on criteria such as the
1304 //   following: the space uses linear allocation and linear allocation is
1305 //   going to fail, or there is believed to be excessive fragmentation in
1306 //   the generation, etc... or ...
1307 // [.(currently done by CMSCollector::shouldConcurrentCollect() only for
1308 //   the case of the old generation; see CR 6543076):
1309 //   we may be approaching a point at which allocation requests may fail because
1310 //   we will be out of sufficient free space given allocation rate estimates.]
1311 bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const {
1312 
1313   assert_lock_strong(freelistLock());
1314   if (occupancy() > initiating_occupancy()) {
1315     if (PrintGCDetails && Verbose) {
1316       gclog_or_tty->print(" %s: collect because of occupancy %f / %f  ",
1317         short_name(), occupancy(), initiating_occupancy());
1318     }
1319     return true;
1320   }
1321   if (UseCMSInitiatingOccupancyOnly) {
1322     return false;
1323   }
1324   if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) {
1325     if (PrintGCDetails && Verbose) {
1326       gclog_or_tty->print(" %s: collect because expanded for allocation ",
1327         short_name());
1328     }
1329     return true;
1330   }
1331   if (_cmsSpace->should_concurrent_collect()) {
1332     if (PrintGCDetails && Verbose) {
1333       gclog_or_tty->print(" %s: collect because cmsSpace says so ",
1334         short_name());
1335     }
1336     return true;
1337   }
1338   return false;
1339 }
1340 
1341 void ConcurrentMarkSweepGeneration::collect(bool   full,
1342                                             bool   clear_all_soft_refs,
1343                                             size_t size,
1344                                             bool   tlab)
1345 {
1346   collector()->collect(full, clear_all_soft_refs, size, tlab);
1347 }
1348 
1349 void CMSCollector::collect(bool   full,
1350                            bool   clear_all_soft_refs,
1351                            size_t size,
1352                            bool   tlab)
1353 {
1354   // The following "if" branch is present for defensive reasons.
1355   // In the current uses of this interface, it can be replaced with:
1356   // assert(!GC_locker.is_active(), "Can't be called otherwise");
1357   // But I am not placing that assert here to allow future
1358   // generality in invoking this interface.
1359   if (GC_locker::is_active()) {
1360     // A consistency test for GC_locker
1361     assert(GC_locker::needs_gc(), "Should have been set already");
1362     // Skip this foreground collection, instead
1363     // expanding the heap if necessary.
1364     // Need the free list locks for the call to free() in compute_new_size()
1365     compute_new_size();
1366     return;
1367   }
1368   acquire_control_and_collect(full, clear_all_soft_refs);
1369 }
1370 
1371 void CMSCollector::request_full_gc(unsigned int full_gc_count, GCCause::Cause cause) {
1372   GenCollectedHeap* gch = GenCollectedHeap::heap();
1373   unsigned int gc_count = gch->total_full_collections();
1374   if (gc_count == full_gc_count) {
1375     MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag);
1376     _full_gc_requested = true;
1377     _full_gc_cause = cause;
1378     CGC_lock->notify();   // nudge CMS thread
1379   } else {
1380     assert(gc_count > full_gc_count, "Error: causal loop");
1381   }
1382 }
1383 
1384 bool CMSCollector::is_external_interruption() {
1385   GCCause::Cause cause = GenCollectedHeap::heap()->gc_cause();
1386   return GCCause::is_user_requested_gc(cause) ||
1387          GCCause::is_serviceability_requested_gc(cause);
1388 }
1389 
1390 void CMSCollector::report_concurrent_mode_interruption() {
1391   if (is_external_interruption()) {
1392     if (PrintGCDetails) {
1393       gclog_or_tty->print(" (concurrent mode interrupted)");
1394     }
1395   } else {
1396     if (PrintGCDetails) {
1397       gclog_or_tty->print(" (concurrent mode failure)");
1398     }
1399     _gc_tracer_cm->report_concurrent_mode_failure();
1400   }
1401 }
1402 
1403 
1404 // The foreground and background collectors need to coordinate in order
1405 // to make sure that they do not mutually interfere with CMS collections.
1406 // When a background collection is active,
1407 // the foreground collector may need to take over (preempt) and
1408 // synchronously complete an ongoing collection. Depending on the
1409 // frequency of the background collections and the heap usage
1410 // of the application, this preemption can be seldom or frequent.
1411 // There are only certain
1412 // points in the background collection that the "collection-baton"
1413 // can be passed to the foreground collector.
1414 //
1415 // The foreground collector will wait for the baton before
1416 // starting any part of the collection.  The foreground collector
1417 // will only wait at one location.
1418 //
1419 // The background collector will yield the baton before starting a new
1420 // phase of the collection (e.g., before initial marking, marking from roots,
1421 // precleaning, final re-mark, sweep etc.)  This is normally done at the head
1422 // of the loop which switches the phases. The background collector does some
1423 // of the phases (initial mark, final re-mark) with the world stopped.
1424 // Because of locking involved in stopping the world,
1425 // the foreground collector should not block waiting for the background
1426 // collector when it is doing a stop-the-world phase.  The background
1427 // collector will yield the baton at an additional point just before
1428 // it enters a stop-the-world phase.  Once the world is stopped, the
1429 // background collector checks the phase of the collection.  If the
1430 // phase has not changed, it proceeds with the collection.  If the
1431 // phase has changed, it skips that phase of the collection.  See
1432 // the comments on the use of the Heap_lock in collect_in_background().
1433 //
1434 // Variable used in baton passing.
1435 //   _foregroundGCIsActive - Set to true by the foreground collector when
1436 //      it wants the baton.  The foreground clears it when it has finished
1437 //      the collection.
1438 //   _foregroundGCShouldWait - Set to true by the background collector
1439 //        when it is running.  The foreground collector waits while
1440 //      _foregroundGCShouldWait is true.
1441 //  CGC_lock - monitor used to protect access to the above variables
1442 //      and to notify the foreground and background collectors.
1443 //  _collectorState - current state of the CMS collection.
1444 //
1445 // The foreground collector
1446 //   acquires the CGC_lock
1447 //   sets _foregroundGCIsActive
1448 //   waits on the CGC_lock for _foregroundGCShouldWait to be false
1449 //     various locks acquired in preparation for the collection
1450 //     are released so as not to block the background collector
1451 //     that is in the midst of a collection
1452 //   proceeds with the collection
1453 //   clears _foregroundGCIsActive
1454 //   returns
1455 //
1456 // The background collector in a loop iterating on the phases of the
1457 //      collection
1458 //   acquires the CGC_lock
1459 //   sets _foregroundGCShouldWait
1460 //   if _foregroundGCIsActive is set
1461 //     clears _foregroundGCShouldWait, notifies _CGC_lock
1462 //     waits on _CGC_lock for _foregroundGCIsActive to become false
1463 //     and exits the loop.
1464 //   otherwise
1465 //     proceed with that phase of the collection
1466 //     if the phase is a stop-the-world phase,
1467 //       yield the baton once more just before enqueueing
1468 //       the stop-world CMS operation (executed by the VM thread).
1469 //   returns after all phases of the collection are done
1470 //
1471 
1472 void CMSCollector::acquire_control_and_collect(bool full,
1473         bool clear_all_soft_refs) {
1474   assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
1475   assert(!Thread::current()->is_ConcurrentGC_thread(),
1476          "shouldn't try to acquire control from self!");
1477 
1478   // Start the protocol for acquiring control of the
1479   // collection from the background collector (aka CMS thread).
1480   assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1481          "VM thread should have CMS token");
1482   // Remember the possibly interrupted state of an ongoing
1483   // concurrent collection
1484   CollectorState first_state = _collectorState;
1485 
1486   // Signal to a possibly ongoing concurrent collection that
1487   // we want to do a foreground collection.
1488   _foregroundGCIsActive = true;
1489 
1490   // release locks and wait for a notify from the background collector
1491   // releasing the locks in only necessary for phases which
1492   // do yields to improve the granularity of the collection.
1493   assert_lock_strong(bitMapLock());
1494   // We need to lock the Free list lock for the space that we are
1495   // currently collecting.
1496   assert(haveFreelistLocks(), "Must be holding free list locks");
1497   bitMapLock()->unlock();
1498   releaseFreelistLocks();
1499   {
1500     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1501     if (_foregroundGCShouldWait) {
1502       // We are going to be waiting for action for the CMS thread;
1503       // it had better not be gone (for instance at shutdown)!
1504       assert(ConcurrentMarkSweepThread::cmst() != NULL,
1505              "CMS thread must be running");
1506       // Wait here until the background collector gives us the go-ahead
1507       ConcurrentMarkSweepThread::clear_CMS_flag(
1508         ConcurrentMarkSweepThread::CMS_vm_has_token);  // release token
1509       // Get a possibly blocked CMS thread going:
1510       //   Note that we set _foregroundGCIsActive true above,
1511       //   without protection of the CGC_lock.
1512       CGC_lock->notify();
1513       assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(),
1514              "Possible deadlock");
1515       while (_foregroundGCShouldWait) {
1516         // wait for notification
1517         CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1518         // Possibility of delay/starvation here, since CMS token does
1519         // not know to give priority to VM thread? Actually, i think
1520         // there wouldn't be any delay/starvation, but the proof of
1521         // that "fact" (?) appears non-trivial. XXX 20011219YSR
1522       }
1523       ConcurrentMarkSweepThread::set_CMS_flag(
1524         ConcurrentMarkSweepThread::CMS_vm_has_token);
1525     }
1526   }
1527   // The CMS_token is already held.  Get back the other locks.
1528   assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1529          "VM thread should have CMS token");
1530   getFreelistLocks();
1531   bitMapLock()->lock_without_safepoint_check();
1532   if (TraceCMSState) {
1533     gclog_or_tty->print_cr("CMS foreground collector has asked for control "
1534       INTPTR_FORMAT " with first state %d", p2i(Thread::current()), first_state);
1535     gclog_or_tty->print_cr("    gets control with state %d", _collectorState);
1536   }
1537 
1538   // Inform cms gen if this was due to partial collection failing.
1539   // The CMS gen may use this fact to determine its expansion policy.
1540   GenCollectedHeap* gch = GenCollectedHeap::heap();
1541   if (gch->incremental_collection_will_fail(false /* don't consult_young */)) {
1542     assert(!_cmsGen->incremental_collection_failed(),
1543            "Should have been noticed, reacted to and cleared");
1544     _cmsGen->set_incremental_collection_failed();
1545   }
1546 
1547   if (first_state > Idling) {
1548     report_concurrent_mode_interruption();
1549   }
1550 
1551   set_did_compact(true);
1552 
1553   // If the collection is being acquired from the background
1554   // collector, there may be references on the discovered
1555   // references lists.  Abandon those references, since some
1556   // of them may have become unreachable after concurrent
1557   // discovery; the STW compacting collector will redo discovery
1558   // more precisely, without being subject to floating garbage.
1559   // Leaving otherwise unreachable references in the discovered
1560   // lists would require special handling.
1561   ref_processor()->disable_discovery();
1562   ref_processor()->abandon_partial_discovery();
1563   ref_processor()->verify_no_references_recorded();
1564 
1565   if (first_state > Idling) {
1566     save_heap_summary();
1567   }
1568 
1569   do_compaction_work(clear_all_soft_refs);
1570 
1571   // Has the GC time limit been exceeded?
1572   size_t max_eden_size = _young_gen->max_capacity() -
1573                          _young_gen->to()->capacity() -
1574                          _young_gen->from()->capacity();
1575   GCCause::Cause gc_cause = gch->gc_cause();
1576   size_policy()->check_gc_overhead_limit(_young_gen->used(),
1577                                          _young_gen->eden()->used(),
1578                                          _cmsGen->max_capacity(),
1579                                          max_eden_size,
1580                                          full,
1581                                          gc_cause,
1582                                          gch->collector_policy());
1583 
1584   // Reset the expansion cause, now that we just completed
1585   // a collection cycle.
1586   clear_expansion_cause();
1587   _foregroundGCIsActive = false;
1588   return;
1589 }
1590 
1591 // Resize the tenured generation
1592 // after obtaining the free list locks for the
1593 // two generations.
1594 void CMSCollector::compute_new_size() {
1595   assert_locked_or_safepoint(Heap_lock);
1596   FreelistLocker z(this);
1597   MetaspaceGC::compute_new_size();
1598   _cmsGen->compute_new_size_free_list();
1599 }
1600 
1601 // A work method used by the foreground collector to do
1602 // a mark-sweep-compact.
1603 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) {
1604   GenCollectedHeap* gch = GenCollectedHeap::heap();
1605 
1606   STWGCTimer* gc_timer = GenMarkSweep::gc_timer();
1607   gc_timer->register_gc_start();
1608 
1609   SerialOldTracer* gc_tracer = GenMarkSweep::gc_tracer();
1610   gc_tracer->report_gc_start(gch->gc_cause(), gc_timer->gc_start());
1611 
1612   GCTraceTime t("CMS:MSC ", PrintGCDetails && Verbose, true, NULL, gc_tracer->gc_id());
1613 
1614   // Temporarily widen the span of the weak reference processing to
1615   // the entire heap.
1616   MemRegion new_span(GenCollectedHeap::heap()->reserved_region());
1617   ReferenceProcessorSpanMutator rp_mut_span(ref_processor(), new_span);
1618   // Temporarily, clear the "is_alive_non_header" field of the
1619   // reference processor.
1620   ReferenceProcessorIsAliveMutator rp_mut_closure(ref_processor(), NULL);
1621   // Temporarily make reference _processing_ single threaded (non-MT).
1622   ReferenceProcessorMTProcMutator rp_mut_mt_processing(ref_processor(), false);
1623   // Temporarily make refs discovery atomic
1624   ReferenceProcessorAtomicMutator rp_mut_atomic(ref_processor(), true);
1625   // Temporarily make reference _discovery_ single threaded (non-MT)
1626   ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
1627 
1628   ref_processor()->set_enqueuing_is_done(false);
1629   ref_processor()->enable_discovery();
1630   ref_processor()->setup_policy(clear_all_soft_refs);
1631   // If an asynchronous collection finishes, the _modUnionTable is
1632   // all clear.  If we are assuming the collection from an asynchronous
1633   // collection, clear the _modUnionTable.
1634   assert(_collectorState != Idling || _modUnionTable.isAllClear(),
1635     "_modUnionTable should be clear if the baton was not passed");
1636   _modUnionTable.clear_all();
1637   assert(_collectorState != Idling || _ct->klass_rem_set()->mod_union_is_clear(),
1638     "mod union for klasses should be clear if the baton was passed");
1639   _ct->klass_rem_set()->clear_mod_union();
1640 
1641   // We must adjust the allocation statistics being maintained
1642   // in the free list space. We do so by reading and clearing
1643   // the sweep timer and updating the block flux rate estimates below.
1644   assert(!_intra_sweep_timer.is_active(), "_intra_sweep_timer should be inactive");
1645   if (_inter_sweep_timer.is_active()) {
1646     _inter_sweep_timer.stop();
1647     // Note that we do not use this sample to update the _inter_sweep_estimate.
1648     _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
1649                                             _inter_sweep_estimate.padded_average(),
1650                                             _intra_sweep_estimate.padded_average());
1651   }
1652 
1653   GenMarkSweep::invoke_at_safepoint(_cmsGen->level(),
1654     ref_processor(), clear_all_soft_refs);
1655   #ifdef ASSERT
1656     CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
1657     size_t free_size = cms_space->free();
1658     assert(free_size ==
1659            pointer_delta(cms_space->end(), cms_space->compaction_top())
1660            * HeapWordSize,
1661       "All the free space should be compacted into one chunk at top");
1662     assert(cms_space->dictionary()->total_chunk_size(
1663                                       debug_only(cms_space->freelistLock())) == 0 ||
1664            cms_space->totalSizeInIndexedFreeLists() == 0,
1665       "All the free space should be in a single chunk");
1666     size_t num = cms_space->totalCount();
1667     assert((free_size == 0 && num == 0) ||
1668            (free_size > 0  && (num == 1 || num == 2)),
1669          "There should be at most 2 free chunks after compaction");
1670   #endif // ASSERT
1671   _collectorState = Resetting;
1672   assert(_restart_addr == NULL,
1673          "Should have been NULL'd before baton was passed");
1674   reset(false /* == !concurrent */);
1675   _cmsGen->reset_after_compaction();
1676   _concurrent_cycles_since_last_unload = 0;
1677 
1678   // Clear any data recorded in the PLAB chunk arrays.
1679   if (_survivor_plab_array != NULL) {
1680     reset_survivor_plab_arrays();
1681   }
1682 
1683   // Adjust the per-size allocation stats for the next epoch.
1684   _cmsGen->cmsSpace()->endSweepFLCensus(sweep_count() /* fake */);
1685   // Restart the "inter sweep timer" for the next epoch.
1686   _inter_sweep_timer.reset();
1687   _inter_sweep_timer.start();
1688 
1689   gc_timer->register_gc_end();
1690 
1691   gc_tracer->report_gc_end(gc_timer->gc_end(), gc_timer->time_partitions());
1692 
1693   // For a mark-sweep-compact, compute_new_size() will be called
1694   // in the heap's do_collection() method.
1695 }
1696 
1697 void CMSCollector::print_eden_and_survivor_chunk_arrays() {
1698   ContiguousSpace* eden_space = _young_gen->eden();
1699   ContiguousSpace* from_space = _young_gen->from();
1700   ContiguousSpace* to_space   = _young_gen->to();
1701   // Eden
1702   if (_eden_chunk_array != NULL) {
1703     gclog_or_tty->print_cr("eden " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1704                            p2i(eden_space->bottom()), p2i(eden_space->top()),
1705                            p2i(eden_space->end()), eden_space->capacity());
1706     gclog_or_tty->print_cr("_eden_chunk_index=" SIZE_FORMAT ", "
1707                            "_eden_chunk_capacity=" SIZE_FORMAT,
1708                            _eden_chunk_index, _eden_chunk_capacity);
1709     for (size_t i = 0; i < _eden_chunk_index; i++) {
1710       gclog_or_tty->print_cr("_eden_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT,
1711                              i, p2i(_eden_chunk_array[i]));
1712     }
1713   }
1714   // Survivor
1715   if (_survivor_chunk_array != NULL) {
1716     gclog_or_tty->print_cr("survivor " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1717                            p2i(from_space->bottom()), p2i(from_space->top()),
1718                            p2i(from_space->end()), from_space->capacity());
1719     gclog_or_tty->print_cr("_survivor_chunk_index=" SIZE_FORMAT ", "
1720                            "_survivor_chunk_capacity=" SIZE_FORMAT,
1721                            _survivor_chunk_index, _survivor_chunk_capacity);
1722     for (size_t i = 0; i < _survivor_chunk_index; i++) {
1723       gclog_or_tty->print_cr("_survivor_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT,
1724                              i, p2i(_survivor_chunk_array[i]));
1725     }
1726   }
1727 }
1728 
1729 void CMSCollector::getFreelistLocks() const {
1730   // Get locks for all free lists in all generations that this
1731   // collector is responsible for
1732   _cmsGen->freelistLock()->lock_without_safepoint_check();
1733 }
1734 
1735 void CMSCollector::releaseFreelistLocks() const {
1736   // Release locks for all free lists in all generations that this
1737   // collector is responsible for
1738   _cmsGen->freelistLock()->unlock();
1739 }
1740 
1741 bool CMSCollector::haveFreelistLocks() const {
1742   // Check locks for all free lists in all generations that this
1743   // collector is responsible for
1744   assert_lock_strong(_cmsGen->freelistLock());
1745   PRODUCT_ONLY(ShouldNotReachHere());
1746   return true;
1747 }
1748 
1749 // A utility class that is used by the CMS collector to
1750 // temporarily "release" the foreground collector from its
1751 // usual obligation to wait for the background collector to
1752 // complete an ongoing phase before proceeding.
1753 class ReleaseForegroundGC: public StackObj {
1754  private:
1755   CMSCollector* _c;
1756  public:
1757   ReleaseForegroundGC(CMSCollector* c) : _c(c) {
1758     assert(_c->_foregroundGCShouldWait, "Else should not need to call");
1759     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1760     // allow a potentially blocked foreground collector to proceed
1761     _c->_foregroundGCShouldWait = false;
1762     if (_c->_foregroundGCIsActive) {
1763       CGC_lock->notify();
1764     }
1765     assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1766            "Possible deadlock");
1767   }
1768 
1769   ~ReleaseForegroundGC() {
1770     assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?");
1771     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1772     _c->_foregroundGCShouldWait = true;
1773   }
1774 };
1775 
1776 void CMSCollector::collect_in_background(GCCause::Cause cause) {
1777   assert(Thread::current()->is_ConcurrentGC_thread(),
1778     "A CMS asynchronous collection is only allowed on a CMS thread.");
1779 
1780   GenCollectedHeap* gch = GenCollectedHeap::heap();
1781   {
1782     bool safepoint_check = Mutex::_no_safepoint_check_flag;
1783     MutexLockerEx hl(Heap_lock, safepoint_check);
1784     FreelistLocker fll(this);
1785     MutexLockerEx x(CGC_lock, safepoint_check);
1786     if (_foregroundGCIsActive || !UseAsyncConcMarkSweepGC) {
1787       // The foreground collector is active or we're
1788       // not using asynchronous collections.  Skip this
1789       // background collection.
1790       assert(!_foregroundGCShouldWait, "Should be clear");
1791       return;
1792     } else {
1793       assert(_collectorState == Idling, "Should be idling before start.");
1794       _collectorState = InitialMarking;
1795       register_gc_start(cause);
1796       // Reset the expansion cause, now that we are about to begin
1797       // a new cycle.
1798       clear_expansion_cause();
1799 
1800       // Clear the MetaspaceGC flag since a concurrent collection
1801       // is starting but also clear it after the collection.
1802       MetaspaceGC::set_should_concurrent_collect(false);
1803     }
1804     // Decide if we want to enable class unloading as part of the
1805     // ensuing concurrent GC cycle.
1806     update_should_unload_classes();
1807     _full_gc_requested = false;           // acks all outstanding full gc requests
1808     _full_gc_cause = GCCause::_no_gc;
1809     // Signal that we are about to start a collection
1810     gch->increment_total_full_collections();  // ... starting a collection cycle
1811     _collection_count_start = gch->total_full_collections();
1812   }
1813 
1814   // Used for PrintGC
1815   size_t prev_used;
1816   if (PrintGC && Verbose) {
1817     prev_used = _cmsGen->used();
1818   }
1819 
1820   // The change of the collection state is normally done at this level;
1821   // the exceptions are phases that are executed while the world is
1822   // stopped.  For those phases the change of state is done while the
1823   // world is stopped.  For baton passing purposes this allows the
1824   // background collector to finish the phase and change state atomically.
1825   // The foreground collector cannot wait on a phase that is done
1826   // while the world is stopped because the foreground collector already
1827   // has the world stopped and would deadlock.
1828   while (_collectorState != Idling) {
1829     if (TraceCMSState) {
1830       gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
1831         p2i(Thread::current()), _collectorState);
1832     }
1833     // The foreground collector
1834     //   holds the Heap_lock throughout its collection.
1835     //   holds the CMS token (but not the lock)
1836     //     except while it is waiting for the background collector to yield.
1837     //
1838     // The foreground collector should be blocked (not for long)
1839     //   if the background collector is about to start a phase
1840     //   executed with world stopped.  If the background
1841     //   collector has already started such a phase, the
1842     //   foreground collector is blocked waiting for the
1843     //   Heap_lock.  The stop-world phases (InitialMarking and FinalMarking)
1844     //   are executed in the VM thread.
1845     //
1846     // The locking order is
1847     //   PendingListLock (PLL)  -- if applicable (FinalMarking)
1848     //   Heap_lock  (both this & PLL locked in VM_CMS_Operation::prologue())
1849     //   CMS token  (claimed in
1850     //                stop_world_and_do() -->
1851     //                  safepoint_synchronize() -->
1852     //                    CMSThread::synchronize())
1853 
1854     {
1855       // Check if the FG collector wants us to yield.
1856       CMSTokenSync x(true); // is cms thread
1857       if (waitForForegroundGC()) {
1858         // We yielded to a foreground GC, nothing more to be
1859         // done this round.
1860         assert(_foregroundGCShouldWait == false, "We set it to false in "
1861                "waitForForegroundGC()");
1862         if (TraceCMSState) {
1863           gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
1864             " exiting collection CMS state %d",
1865             p2i(Thread::current()), _collectorState);
1866         }
1867         return;
1868       } else {
1869         // The background collector can run but check to see if the
1870         // foreground collector has done a collection while the
1871         // background collector was waiting to get the CGC_lock
1872         // above.  If yes, break so that _foregroundGCShouldWait
1873         // is cleared before returning.
1874         if (_collectorState == Idling) {
1875           break;
1876         }
1877       }
1878     }
1879 
1880     assert(_foregroundGCShouldWait, "Foreground collector, if active, "
1881       "should be waiting");
1882 
1883     switch (_collectorState) {
1884       case InitialMarking:
1885         {
1886           ReleaseForegroundGC x(this);
1887           stats().record_cms_begin();
1888           VM_CMS_Initial_Mark initial_mark_op(this);
1889           VMThread::execute(&initial_mark_op);
1890         }
1891         // The collector state may be any legal state at this point
1892         // since the background collector may have yielded to the
1893         // foreground collector.
1894         break;
1895       case Marking:
1896         // initial marking in checkpointRootsInitialWork has been completed
1897         if (markFromRoots()) { // we were successful
1898           assert(_collectorState == Precleaning, "Collector state should "
1899             "have changed");
1900         } else {
1901           assert(_foregroundGCIsActive, "Internal state inconsistency");
1902         }
1903         break;
1904       case Precleaning:
1905         // marking from roots in markFromRoots has been completed
1906         preclean();
1907         assert(_collectorState == AbortablePreclean ||
1908                _collectorState == FinalMarking,
1909                "Collector state should have changed");
1910         break;
1911       case AbortablePreclean:
1912         abortable_preclean();
1913         assert(_collectorState == FinalMarking, "Collector state should "
1914           "have changed");
1915         break;
1916       case FinalMarking:
1917         {
1918           ReleaseForegroundGC x(this);
1919 
1920           VM_CMS_Final_Remark final_remark_op(this);
1921           VMThread::execute(&final_remark_op);
1922         }
1923         assert(_foregroundGCShouldWait, "block post-condition");
1924         break;
1925       case Sweeping:
1926         // final marking in checkpointRootsFinal has been completed
1927         sweep();
1928         assert(_collectorState == Resizing, "Collector state change "
1929           "to Resizing must be done under the free_list_lock");
1930 
1931       case Resizing: {
1932         // Sweeping has been completed...
1933         // At this point the background collection has completed.
1934         // Don't move the call to compute_new_size() down
1935         // into code that might be executed if the background
1936         // collection was preempted.
1937         {
1938           ReleaseForegroundGC x(this);   // unblock FG collection
1939           MutexLockerEx       y(Heap_lock, Mutex::_no_safepoint_check_flag);
1940           CMSTokenSync        z(true);   // not strictly needed.
1941           if (_collectorState == Resizing) {
1942             compute_new_size();
1943             save_heap_summary();
1944             _collectorState = Resetting;
1945           } else {
1946             assert(_collectorState == Idling, "The state should only change"
1947                    " because the foreground collector has finished the collection");
1948           }
1949         }
1950         break;
1951       }
1952       case Resetting:
1953         // CMS heap resizing has been completed
1954         reset(true);
1955         assert(_collectorState == Idling, "Collector state should "
1956           "have changed");
1957 
1958         MetaspaceGC::set_should_concurrent_collect(false);
1959 
1960         stats().record_cms_end();
1961         // Don't move the concurrent_phases_end() and compute_new_size()
1962         // calls to here because a preempted background collection
1963         // has it's state set to "Resetting".
1964         break;
1965       case Idling:
1966       default:
1967         ShouldNotReachHere();
1968         break;
1969     }
1970     if (TraceCMSState) {
1971       gclog_or_tty->print_cr("  Thread " INTPTR_FORMAT " done - next CMS state %d",
1972         p2i(Thread::current()), _collectorState);
1973     }
1974     assert(_foregroundGCShouldWait, "block post-condition");
1975   }
1976 
1977   // Should this be in gc_epilogue?
1978   collector_policy()->counters()->update_counters();
1979 
1980   {
1981     // Clear _foregroundGCShouldWait and, in the event that the
1982     // foreground collector is waiting, notify it, before
1983     // returning.
1984     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1985     _foregroundGCShouldWait = false;
1986     if (_foregroundGCIsActive) {
1987       CGC_lock->notify();
1988     }
1989     assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1990            "Possible deadlock");
1991   }
1992   if (TraceCMSState) {
1993     gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
1994       " exiting collection CMS state %d",
1995       p2i(Thread::current()), _collectorState);
1996   }
1997   if (PrintGC && Verbose) {
1998     _cmsGen->print_heap_change(prev_used);
1999   }
2000 }
2001 
2002 void CMSCollector::register_gc_start(GCCause::Cause cause) {
2003   _cms_start_registered = true;
2004   _gc_timer_cm->register_gc_start();
2005   _gc_tracer_cm->report_gc_start(cause, _gc_timer_cm->gc_start());
2006 }
2007 
2008 void CMSCollector::register_gc_end() {
2009   if (_cms_start_registered) {
2010     report_heap_summary(GCWhen::AfterGC);
2011 
2012     _gc_timer_cm->register_gc_end();
2013     _gc_tracer_cm->report_gc_end(_gc_timer_cm->gc_end(), _gc_timer_cm->time_partitions());
2014     _cms_start_registered = false;
2015   }
2016 }
2017 
2018 void CMSCollector::save_heap_summary() {
2019   GenCollectedHeap* gch = GenCollectedHeap::heap();
2020   _last_heap_summary = gch->create_heap_summary();
2021   _last_metaspace_summary = gch->create_metaspace_summary();
2022 }
2023 
2024 void CMSCollector::report_heap_summary(GCWhen::Type when) {
2025   _gc_tracer_cm->report_gc_heap_summary(when, _last_heap_summary);
2026   _gc_tracer_cm->report_metaspace_summary(when, _last_metaspace_summary);
2027 }
2028 
2029 bool CMSCollector::waitForForegroundGC() {
2030   bool res = false;
2031   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2032          "CMS thread should have CMS token");
2033   // Block the foreground collector until the
2034   // background collectors decides whether to
2035   // yield.
2036   MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2037   _foregroundGCShouldWait = true;
2038   if (_foregroundGCIsActive) {
2039     // The background collector yields to the
2040     // foreground collector and returns a value
2041     // indicating that it has yielded.  The foreground
2042     // collector can proceed.
2043     res = true;
2044     _foregroundGCShouldWait = false;
2045     ConcurrentMarkSweepThread::clear_CMS_flag(
2046       ConcurrentMarkSweepThread::CMS_cms_has_token);
2047     ConcurrentMarkSweepThread::set_CMS_flag(
2048       ConcurrentMarkSweepThread::CMS_cms_wants_token);
2049     // Get a possibly blocked foreground thread going
2050     CGC_lock->notify();
2051     if (TraceCMSState) {
2052       gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d",
2053         p2i(Thread::current()), _collectorState);
2054     }
2055     while (_foregroundGCIsActive) {
2056       CGC_lock->wait(Mutex::_no_safepoint_check_flag);
2057     }
2058     ConcurrentMarkSweepThread::set_CMS_flag(
2059       ConcurrentMarkSweepThread::CMS_cms_has_token);
2060     ConcurrentMarkSweepThread::clear_CMS_flag(
2061       ConcurrentMarkSweepThread::CMS_cms_wants_token);
2062   }
2063   if (TraceCMSState) {
2064     gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d",
2065       p2i(Thread::current()), _collectorState);
2066   }
2067   return res;
2068 }
2069 
2070 // Because of the need to lock the free lists and other structures in
2071 // the collector, common to all the generations that the collector is
2072 // collecting, we need the gc_prologues of individual CMS generations
2073 // delegate to their collector. It may have been simpler had the
2074 // current infrastructure allowed one to call a prologue on a
2075 // collector. In the absence of that we have the generation's
2076 // prologue delegate to the collector, which delegates back
2077 // some "local" work to a worker method in the individual generations
2078 // that it's responsible for collecting, while itself doing any
2079 // work common to all generations it's responsible for. A similar
2080 // comment applies to the  gc_epilogue()'s.
2081 // The role of the variable _between_prologue_and_epilogue is to
2082 // enforce the invocation protocol.
2083 void CMSCollector::gc_prologue(bool full) {
2084   // Call gc_prologue_work() for the CMSGen
2085   // we are responsible for.
2086 
2087   // The following locking discipline assumes that we are only called
2088   // when the world is stopped.
2089   assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption");
2090 
2091   // The CMSCollector prologue must call the gc_prologues for the
2092   // "generations" that it's responsible
2093   // for.
2094 
2095   assert(   Thread::current()->is_VM_thread()
2096          || (   CMSScavengeBeforeRemark
2097              && Thread::current()->is_ConcurrentGC_thread()),
2098          "Incorrect thread type for prologue execution");
2099 
2100   if (_between_prologue_and_epilogue) {
2101     // We have already been invoked; this is a gc_prologue delegation
2102     // from yet another CMS generation that we are responsible for, just
2103     // ignore it since all relevant work has already been done.
2104     return;
2105   }
2106 
2107   // set a bit saying prologue has been called; cleared in epilogue
2108   _between_prologue_and_epilogue = true;
2109   // Claim locks for common data structures, then call gc_prologue_work()
2110   // for each CMSGen.
2111 
2112   getFreelistLocks();   // gets free list locks on constituent spaces
2113   bitMapLock()->lock_without_safepoint_check();
2114 
2115   // Should call gc_prologue_work() for all cms gens we are responsible for
2116   bool duringMarking =    _collectorState >= Marking
2117                          && _collectorState < Sweeping;
2118 
2119   // The young collections clear the modified oops state, which tells if
2120   // there are any modified oops in the class. The remark phase also needs
2121   // that information. Tell the young collection to save the union of all
2122   // modified klasses.
2123   if (duringMarking) {
2124     _ct->klass_rem_set()->set_accumulate_modified_oops(true);
2125   }
2126 
2127   bool registerClosure = duringMarking;
2128 
2129   _cmsGen->gc_prologue_work(full, registerClosure, &_modUnionClosurePar);
2130 
2131   if (!full) {
2132     stats().record_gc0_begin();
2133   }
2134 }
2135 
2136 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) {
2137 
2138   _capacity_at_prologue = capacity();
2139   _used_at_prologue = used();
2140 
2141   // Delegate to CMScollector which knows how to coordinate between
2142   // this and any other CMS generations that it is responsible for
2143   // collecting.
2144   collector()->gc_prologue(full);
2145 }
2146 
2147 // This is a "private" interface for use by this generation's CMSCollector.
2148 // Not to be called directly by any other entity (for instance,
2149 // GenCollectedHeap, which calls the "public" gc_prologue method above).
2150 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full,
2151   bool registerClosure, ModUnionClosure* modUnionClosure) {
2152   assert(!incremental_collection_failed(), "Shouldn't be set yet");
2153   assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL,
2154     "Should be NULL");
2155   if (registerClosure) {
2156     cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure);
2157   }
2158   cmsSpace()->gc_prologue();
2159   // Clear stat counters
2160   NOT_PRODUCT(
2161     assert(_numObjectsPromoted == 0, "check");
2162     assert(_numWordsPromoted   == 0, "check");
2163     if (Verbose && PrintGC) {
2164       gclog_or_tty->print("Allocated "SIZE_FORMAT" objects, "
2165                           SIZE_FORMAT" bytes concurrently",
2166       _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord));
2167     }
2168     _numObjectsAllocated = 0;
2169     _numWordsAllocated   = 0;
2170   )
2171 }
2172 
2173 void CMSCollector::gc_epilogue(bool full) {
2174   // The following locking discipline assumes that we are only called
2175   // when the world is stopped.
2176   assert(SafepointSynchronize::is_at_safepoint(),
2177          "world is stopped assumption");
2178 
2179   // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks
2180   // if linear allocation blocks need to be appropriately marked to allow the
2181   // the blocks to be parsable. We also check here whether we need to nudge the
2182   // CMS collector thread to start a new cycle (if it's not already active).
2183   assert(   Thread::current()->is_VM_thread()
2184          || (   CMSScavengeBeforeRemark
2185              && Thread::current()->is_ConcurrentGC_thread()),
2186          "Incorrect thread type for epilogue execution");
2187 
2188   if (!_between_prologue_and_epilogue) {
2189     // We have already been invoked; this is a gc_epilogue delegation
2190     // from yet another CMS generation that we are responsible for, just
2191     // ignore it since all relevant work has already been done.
2192     return;
2193   }
2194   assert(haveFreelistLocks(), "must have freelist locks");
2195   assert_lock_strong(bitMapLock());
2196 
2197   _ct->klass_rem_set()->set_accumulate_modified_oops(false);
2198 
2199   _cmsGen->gc_epilogue_work(full);
2200 
2201   if (_collectorState == AbortablePreclean || _collectorState == Precleaning) {
2202     // in case sampling was not already enabled, enable it
2203     _start_sampling = true;
2204   }
2205   // reset _eden_chunk_array so sampling starts afresh
2206   _eden_chunk_index = 0;
2207 
2208   size_t cms_used   = _cmsGen->cmsSpace()->used();
2209 
2210   // update performance counters - this uses a special version of
2211   // update_counters() that allows the utilization to be passed as a
2212   // parameter, avoiding multiple calls to used().
2213   //
2214   _cmsGen->update_counters(cms_used);
2215 
2216   bitMapLock()->unlock();
2217   releaseFreelistLocks();
2218 
2219   if (!CleanChunkPoolAsync) {
2220     Chunk::clean_chunk_pool();
2221   }
2222 
2223   set_did_compact(false);
2224   _between_prologue_and_epilogue = false;  // ready for next cycle
2225 }
2226 
2227 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) {
2228   collector()->gc_epilogue(full);
2229 
2230   // Also reset promotion tracking in par gc thread states.
2231   for (uint i = 0; i < ParallelGCThreads; i++) {
2232     _par_gc_thread_states[i]->promo.stopTrackingPromotions(i);
2233   }
2234 }
2235 
2236 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2237   assert(!incremental_collection_failed(), "Should have been cleared");
2238   cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2239   cmsSpace()->gc_epilogue();
2240     // Print stat counters
2241   NOT_PRODUCT(
2242     assert(_numObjectsAllocated == 0, "check");
2243     assert(_numWordsAllocated == 0, "check");
2244     if (Verbose && PrintGC) {
2245       gclog_or_tty->print("Promoted "SIZE_FORMAT" objects, "
2246                           SIZE_FORMAT" bytes",
2247                  _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2248     }
2249     _numObjectsPromoted = 0;
2250     _numWordsPromoted   = 0;
2251   )
2252 
2253   if (PrintGC && Verbose) {
2254     // Call down the chain in contiguous_available needs the freelistLock
2255     // so print this out before releasing the freeListLock.
2256     gclog_or_tty->print(" Contiguous available "SIZE_FORMAT" bytes ",
2257                         contiguous_available());
2258   }
2259 }
2260 
2261 #ifndef PRODUCT
2262 bool CMSCollector::have_cms_token() {
2263   Thread* thr = Thread::current();
2264   if (thr->is_VM_thread()) {
2265     return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2266   } else if (thr->is_ConcurrentGC_thread()) {
2267     return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2268   } else if (thr->is_GC_task_thread()) {
2269     return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2270            ParGCRareEvent_lock->owned_by_self();
2271   }
2272   return false;
2273 }
2274 #endif
2275 
2276 // Check reachability of the given heap address in CMS generation,
2277 // treating all other generations as roots.
2278 bool CMSCollector::is_cms_reachable(HeapWord* addr) {
2279   // We could "guarantee" below, rather than assert, but I'll
2280   // leave these as "asserts" so that an adventurous debugger
2281   // could try this in the product build provided some subset of
2282   // the conditions were met, provided they were interested in the
2283   // results and knew that the computation below wouldn't interfere
2284   // with other concurrent computations mutating the structures
2285   // being read or written.
2286   assert(SafepointSynchronize::is_at_safepoint(),
2287          "Else mutations in object graph will make answer suspect");
2288   assert(have_cms_token(), "Should hold cms token");
2289   assert(haveFreelistLocks(), "must hold free list locks");
2290   assert_lock_strong(bitMapLock());
2291 
2292   // Clear the marking bit map array before starting, but, just
2293   // for kicks, first report if the given address is already marked
2294   gclog_or_tty->print_cr("Start: Address " PTR_FORMAT " is%s marked", p2i(addr),
2295                 _markBitMap.isMarked(addr) ? "" : " not");
2296 
2297   if (verify_after_remark()) {
2298     MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2299     bool result = verification_mark_bm()->isMarked(addr);
2300     gclog_or_tty->print_cr("TransitiveMark: Address " PTR_FORMAT " %s marked", p2i(addr),
2301                            result ? "IS" : "is NOT");
2302     return result;
2303   } else {
2304     gclog_or_tty->print_cr("Could not compute result");
2305     return false;
2306   }
2307 }
2308 
2309 
2310 void
2311 CMSCollector::print_on_error(outputStream* st) {
2312   CMSCollector* collector = ConcurrentMarkSweepGeneration::_collector;
2313   if (collector != NULL) {
2314     CMSBitMap* bitmap = &collector->_markBitMap;
2315     st->print_cr("Marking Bits: (CMSBitMap*) " PTR_FORMAT, p2i(bitmap));
2316     bitmap->print_on_error(st, " Bits: ");
2317 
2318     st->cr();
2319 
2320     CMSBitMap* mut_bitmap = &collector->_modUnionTable;
2321     st->print_cr("Mod Union Table: (CMSBitMap*) " PTR_FORMAT, p2i(mut_bitmap));
2322     mut_bitmap->print_on_error(st, " Bits: ");
2323   }
2324 }
2325 
2326 ////////////////////////////////////////////////////////
2327 // CMS Verification Support
2328 ////////////////////////////////////////////////////////
2329 // Following the remark phase, the following invariant
2330 // should hold -- each object in the CMS heap which is
2331 // marked in markBitMap() should be marked in the verification_mark_bm().
2332 
2333 class VerifyMarkedClosure: public BitMapClosure {
2334   CMSBitMap* _marks;
2335   bool       _failed;
2336 
2337  public:
2338   VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2339 
2340   bool do_bit(size_t offset) {
2341     HeapWord* addr = _marks->offsetToHeapWord(offset);
2342     if (!_marks->isMarked(addr)) {
2343       oop(addr)->print_on(gclog_or_tty);
2344       gclog_or_tty->print_cr(" ("INTPTR_FORMAT" should have been marked)", p2i(addr));
2345       _failed = true;
2346     }
2347     return true;
2348   }
2349 
2350   bool failed() { return _failed; }
2351 };
2352 
2353 bool CMSCollector::verify_after_remark(bool silent) {
2354   if (!silent) gclog_or_tty->print(" [Verifying CMS Marking... ");
2355   MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2356   static bool init = false;
2357 
2358   assert(SafepointSynchronize::is_at_safepoint(),
2359          "Else mutations in object graph will make answer suspect");
2360   assert(have_cms_token(),
2361          "Else there may be mutual interference in use of "
2362          " verification data structures");
2363   assert(_collectorState > Marking && _collectorState <= Sweeping,
2364          "Else marking info checked here may be obsolete");
2365   assert(haveFreelistLocks(), "must hold free list locks");
2366   assert_lock_strong(bitMapLock());
2367 
2368 
2369   // Allocate marking bit map if not already allocated
2370   if (!init) { // first time
2371     if (!verification_mark_bm()->allocate(_span)) {
2372       return false;
2373     }
2374     init = true;
2375   }
2376 
2377   assert(verification_mark_stack()->isEmpty(), "Should be empty");
2378 
2379   // Turn off refs discovery -- so we will be tracing through refs.
2380   // This is as intended, because by this time
2381   // GC must already have cleared any refs that need to be cleared,
2382   // and traced those that need to be marked; moreover,
2383   // the marking done here is not going to interfere in any
2384   // way with the marking information used by GC.
2385   NoRefDiscovery no_discovery(ref_processor());
2386 
2387   COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
2388 
2389   // Clear any marks from a previous round
2390   verification_mark_bm()->clear_all();
2391   assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
2392   verify_work_stacks_empty();
2393 
2394   GenCollectedHeap* gch = GenCollectedHeap::heap();
2395   gch->ensure_parsability(false);  // fill TLABs, but no need to retire them
2396   // Update the saved marks which may affect the root scans.
2397   gch->save_marks();
2398 
2399   if (CMSRemarkVerifyVariant == 1) {
2400     // In this first variant of verification, we complete
2401     // all marking, then check if the new marks-vector is
2402     // a subset of the CMS marks-vector.
2403     verify_after_remark_work_1();
2404   } else if (CMSRemarkVerifyVariant == 2) {
2405     // In this second variant of verification, we flag an error
2406     // (i.e. an object reachable in the new marks-vector not reachable
2407     // in the CMS marks-vector) immediately, also indicating the
2408     // identify of an object (A) that references the unmarked object (B) --
2409     // presumably, a mutation to A failed to be picked up by preclean/remark?
2410     verify_after_remark_work_2();
2411   } else {
2412     warning("Unrecognized value " UINTX_FORMAT " for CMSRemarkVerifyVariant",
2413             CMSRemarkVerifyVariant);
2414   }
2415   if (!silent) gclog_or_tty->print(" done] ");
2416   return true;
2417 }
2418 
2419 void CMSCollector::verify_after_remark_work_1() {
2420   ResourceMark rm;
2421   HandleMark  hm;
2422   GenCollectedHeap* gch = GenCollectedHeap::heap();
2423 
2424   // Get a clear set of claim bits for the roots processing to work with.
2425   ClassLoaderDataGraph::clear_claimed_marks();
2426 
2427   // Mark from roots one level into CMS
2428   MarkRefsIntoClosure notOlder(_span, verification_mark_bm());
2429   gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2430 
2431   {
2432     StrongRootsScope srs(1);
2433 
2434     gch->gen_process_roots(&srs,
2435                            _cmsGen->level(),
2436                            true,   // younger gens are roots
2437                            GenCollectedHeap::ScanningOption(roots_scanning_options()),
2438                            should_unload_classes(),
2439                            &notOlder,
2440                            NULL,
2441                            NULL);
2442   }
2443 
2444   // Now mark from the roots
2445   MarkFromRootsClosure markFromRootsClosure(this, _span,
2446     verification_mark_bm(), verification_mark_stack(),
2447     false /* don't yield */, true /* verifying */);
2448   assert(_restart_addr == NULL, "Expected pre-condition");
2449   verification_mark_bm()->iterate(&markFromRootsClosure);
2450   while (_restart_addr != NULL) {
2451     // Deal with stack overflow: by restarting at the indicated
2452     // address.
2453     HeapWord* ra = _restart_addr;
2454     markFromRootsClosure.reset(ra);
2455     _restart_addr = NULL;
2456     verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2457   }
2458   assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2459   verify_work_stacks_empty();
2460 
2461   // Marking completed -- now verify that each bit marked in
2462   // verification_mark_bm() is also marked in markBitMap(); flag all
2463   // errors by printing corresponding objects.
2464   VerifyMarkedClosure vcl(markBitMap());
2465   verification_mark_bm()->iterate(&vcl);
2466   if (vcl.failed()) {
2467     gclog_or_tty->print("Verification failed");
2468     gch->print_on(gclog_or_tty);
2469     fatal("CMS: failed marking verification after remark");
2470   }
2471 }
2472 
2473 class VerifyKlassOopsKlassClosure : public KlassClosure {
2474   class VerifyKlassOopsClosure : public OopClosure {
2475     CMSBitMap* _bitmap;
2476    public:
2477     VerifyKlassOopsClosure(CMSBitMap* bitmap) : _bitmap(bitmap) { }
2478     void do_oop(oop* p)       { guarantee(*p == NULL || _bitmap->isMarked((HeapWord*) *p), "Should be marked"); }
2479     void do_oop(narrowOop* p) { ShouldNotReachHere(); }
2480   } _oop_closure;
2481  public:
2482   VerifyKlassOopsKlassClosure(CMSBitMap* bitmap) : _oop_closure(bitmap) {}
2483   void do_klass(Klass* k) {
2484     k->oops_do(&_oop_closure);
2485   }
2486 };
2487 
2488 void CMSCollector::verify_after_remark_work_2() {
2489   ResourceMark rm;
2490   HandleMark  hm;
2491   GenCollectedHeap* gch = GenCollectedHeap::heap();
2492 
2493   // Get a clear set of claim bits for the roots processing to work with.
2494   ClassLoaderDataGraph::clear_claimed_marks();
2495 
2496   // Mark from roots one level into CMS
2497   MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
2498                                      markBitMap());
2499   CLDToOopClosure cld_closure(&notOlder, true);
2500 
2501   gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2502 
2503   {
2504     StrongRootsScope srs(1);
2505 
2506     gch->gen_process_roots(&srs,
2507                            _cmsGen->level(),
2508                            true,   // younger gens are roots
2509                            GenCollectedHeap::ScanningOption(roots_scanning_options()),
2510                            should_unload_classes(),
2511                            &notOlder,
2512                            NULL,
2513                            &cld_closure);
2514   }
2515 
2516   // Now mark from the roots
2517   MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
2518     verification_mark_bm(), markBitMap(), verification_mark_stack());
2519   assert(_restart_addr == NULL, "Expected pre-condition");
2520   verification_mark_bm()->iterate(&markFromRootsClosure);
2521   while (_restart_addr != NULL) {
2522     // Deal with stack overflow: by restarting at the indicated
2523     // address.
2524     HeapWord* ra = _restart_addr;
2525     markFromRootsClosure.reset(ra);
2526     _restart_addr = NULL;
2527     verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2528   }
2529   assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2530   verify_work_stacks_empty();
2531 
2532   VerifyKlassOopsKlassClosure verify_klass_oops(verification_mark_bm());
2533   ClassLoaderDataGraph::classes_do(&verify_klass_oops);
2534 
2535   // Marking completed -- now verify that each bit marked in
2536   // verification_mark_bm() is also marked in markBitMap(); flag all
2537   // errors by printing corresponding objects.
2538   VerifyMarkedClosure vcl(markBitMap());
2539   verification_mark_bm()->iterate(&vcl);
2540   assert(!vcl.failed(), "Else verification above should not have succeeded");
2541 }
2542 
2543 void ConcurrentMarkSweepGeneration::save_marks() {
2544   // delegate to CMS space
2545   cmsSpace()->save_marks();
2546   for (uint i = 0; i < ParallelGCThreads; i++) {
2547     _par_gc_thread_states[i]->promo.startTrackingPromotions();
2548   }
2549 }
2550 
2551 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
2552   return cmsSpace()->no_allocs_since_save_marks();
2553 }
2554 
2555 #define CMS_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix)    \
2556                                                                 \
2557 void ConcurrentMarkSweepGeneration::                            \
2558 oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) {   \
2559   cl->set_generation(this);                                     \
2560   cmsSpace()->oop_since_save_marks_iterate##nv_suffix(cl);      \
2561   cl->reset_generation();                                       \
2562   save_marks();                                                 \
2563 }
2564 
2565 ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DEFN)
2566 
2567 void
2568 ConcurrentMarkSweepGeneration::oop_iterate(ExtendedOopClosure* cl) {
2569   if (freelistLock()->owned_by_self()) {
2570     Generation::oop_iterate(cl);
2571   } else {
2572     MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2573     Generation::oop_iterate(cl);
2574   }
2575 }
2576 
2577 void
2578 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
2579   if (freelistLock()->owned_by_self()) {
2580     Generation::object_iterate(cl);
2581   } else {
2582     MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2583     Generation::object_iterate(cl);
2584   }
2585 }
2586 
2587 void
2588 ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) {
2589   if (freelistLock()->owned_by_self()) {
2590     Generation::safe_object_iterate(cl);
2591   } else {
2592     MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2593     Generation::safe_object_iterate(cl);
2594   }
2595 }
2596 
2597 void
2598 ConcurrentMarkSweepGeneration::post_compact() {
2599 }
2600 
2601 void
2602 ConcurrentMarkSweepGeneration::prepare_for_verify() {
2603   // Fix the linear allocation blocks to look like free blocks.
2604 
2605   // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2606   // are not called when the heap is verified during universe initialization and
2607   // at vm shutdown.
2608   if (freelistLock()->owned_by_self()) {
2609     cmsSpace()->prepare_for_verify();
2610   } else {
2611     MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2612     cmsSpace()->prepare_for_verify();
2613   }
2614 }
2615 
2616 void
2617 ConcurrentMarkSweepGeneration::verify() {
2618   // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2619   // are not called when the heap is verified during universe initialization and
2620   // at vm shutdown.
2621   if (freelistLock()->owned_by_self()) {
2622     cmsSpace()->verify();
2623   } else {
2624     MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2625     cmsSpace()->verify();
2626   }
2627 }
2628 
2629 void CMSCollector::verify() {
2630   _cmsGen->verify();
2631 }
2632 
2633 #ifndef PRODUCT
2634 bool CMSCollector::overflow_list_is_empty() const {
2635   assert(_num_par_pushes >= 0, "Inconsistency");
2636   if (_overflow_list == NULL) {
2637     assert(_num_par_pushes == 0, "Inconsistency");
2638   }
2639   return _overflow_list == NULL;
2640 }
2641 
2642 // The methods verify_work_stacks_empty() and verify_overflow_empty()
2643 // merely consolidate assertion checks that appear to occur together frequently.
2644 void CMSCollector::verify_work_stacks_empty() const {
2645   assert(_markStack.isEmpty(), "Marking stack should be empty");
2646   assert(overflow_list_is_empty(), "Overflow list should be empty");
2647 }
2648 
2649 void CMSCollector::verify_overflow_empty() const {
2650   assert(overflow_list_is_empty(), "Overflow list should be empty");
2651   assert(no_preserved_marks(), "No preserved marks");
2652 }
2653 #endif // PRODUCT
2654 
2655 // Decide if we want to enable class unloading as part of the
2656 // ensuing concurrent GC cycle. We will collect and
2657 // unload classes if it's the case that:
2658 // (1) an explicit gc request has been made and the flag
2659 //     ExplicitGCInvokesConcurrentAndUnloadsClasses is set, OR
2660 // (2) (a) class unloading is enabled at the command line, and
2661 //     (b) old gen is getting really full
2662 // NOTE: Provided there is no change in the state of the heap between
2663 // calls to this method, it should have idempotent results. Moreover,
2664 // its results should be monotonically increasing (i.e. going from 0 to 1,
2665 // but not 1 to 0) between successive calls between which the heap was
2666 // not collected. For the implementation below, it must thus rely on
2667 // the property that concurrent_cycles_since_last_unload()
2668 // will not decrease unless a collection cycle happened and that
2669 // _cmsGen->is_too_full() are
2670 // themselves also monotonic in that sense. See check_monotonicity()
2671 // below.
2672 void CMSCollector::update_should_unload_classes() {
2673   _should_unload_classes = false;
2674   if (!ClassUnloading) {
2675     return;
2676   }
2677 
2678   // Condition 1 above
2679   if (_full_gc_requested && ExplicitGCInvokesConcurrentAndUnloadsClasses) {
2680     _should_unload_classes = true;
2681   } else if (CMSClassUnloadingEnabled) { // Condition 2.a above
2682     // Disjuncts 2.b.(i,ii,iii) above
2683     _should_unload_classes = (concurrent_cycles_since_last_unload() >=
2684                               CMSClassUnloadingMaxInterval)
2685                            || _cmsGen->is_too_full();
2686   }
2687 }
2688 
2689 bool ConcurrentMarkSweepGeneration::is_too_full() const {
2690   bool res = should_concurrent_collect();
2691   res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
2692   return res;
2693 }
2694 
2695 void CMSCollector::setup_cms_unloading_and_verification_state() {
2696   const  bool should_verify =   VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
2697                              || VerifyBeforeExit;
2698   const  int  rso           =   GenCollectedHeap::SO_AllCodeCache;
2699 
2700   // We set the proper root for this CMS cycle here.
2701   if (should_unload_classes()) {   // Should unload classes this cycle
2702     remove_root_scanning_option(rso);  // Shrink the root set appropriately
2703     set_verifying(should_verify);    // Set verification state for this cycle
2704     return;                            // Nothing else needs to be done at this time
2705   }
2706 
2707   // Not unloading classes this cycle
2708   assert(!should_unload_classes(), "Inconsistency!");
2709 
2710   if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
2711     // Include symbols, strings and code cache elements to prevent their resurrection.
2712     add_root_scanning_option(rso);
2713     set_verifying(true);
2714   } else if (verifying() && !should_verify) {
2715     // We were verifying, but some verification flags got disabled.
2716     set_verifying(false);
2717     // Exclude symbols, strings and code cache elements from root scanning to
2718     // reduce IM and RM pauses.
2719     remove_root_scanning_option(rso);
2720   }
2721 }
2722 
2723 
2724 #ifndef PRODUCT
2725 HeapWord* CMSCollector::block_start(const void* p) const {
2726   const HeapWord* addr = (HeapWord*)p;
2727   if (_span.contains(p)) {
2728     if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
2729       return _cmsGen->cmsSpace()->block_start(p);
2730     }
2731   }
2732   return NULL;
2733 }
2734 #endif
2735 
2736 HeapWord*
2737 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
2738                                                    bool   tlab,
2739                                                    bool   parallel) {
2740   CMSSynchronousYieldRequest yr;
2741   assert(!tlab, "Can't deal with TLAB allocation");
2742   MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2743   expand_for_gc_cause(word_size*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_allocation);
2744   if (GCExpandToAllocateDelayMillis > 0) {
2745     os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2746   }
2747   return have_lock_and_allocate(word_size, tlab);
2748 }
2749 
2750 void ConcurrentMarkSweepGeneration::expand_for_gc_cause(
2751     size_t bytes,
2752     size_t expand_bytes,
2753     CMSExpansionCause::Cause cause)
2754 {
2755 
2756   bool success = expand(bytes, expand_bytes);
2757 
2758   // remember why we expanded; this information is used
2759   // by shouldConcurrentCollect() when making decisions on whether to start
2760   // a new CMS cycle.
2761   if (success) {
2762     set_expansion_cause(cause);
2763     if (PrintGCDetails && Verbose) {
2764       gclog_or_tty->print_cr("Expanded CMS gen for %s",
2765         CMSExpansionCause::to_string(cause));
2766     }
2767   }
2768 }
2769 
2770 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
2771   HeapWord* res = NULL;
2772   MutexLocker x(ParGCRareEvent_lock);
2773   while (true) {
2774     // Expansion by some other thread might make alloc OK now:
2775     res = ps->lab.alloc(word_sz);
2776     if (res != NULL) return res;
2777     // If there's not enough expansion space available, give up.
2778     if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
2779       return NULL;
2780     }
2781     // Otherwise, we try expansion.
2782     expand_for_gc_cause(word_sz*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_lab);
2783     // Now go around the loop and try alloc again;
2784     // A competing par_promote might beat us to the expansion space,
2785     // so we may go around the loop again if promotion fails again.
2786     if (GCExpandToAllocateDelayMillis > 0) {
2787       os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2788     }
2789   }
2790 }
2791 
2792 
2793 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
2794   PromotionInfo* promo) {
2795   MutexLocker x(ParGCRareEvent_lock);
2796   size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
2797   while (true) {
2798     // Expansion by some other thread might make alloc OK now:
2799     if (promo->ensure_spooling_space()) {
2800       assert(promo->has_spooling_space(),
2801              "Post-condition of successful ensure_spooling_space()");
2802       return true;
2803     }
2804     // If there's not enough expansion space available, give up.
2805     if (_virtual_space.uncommitted_size() < refill_size_bytes) {
2806       return false;
2807     }
2808     // Otherwise, we try expansion.
2809     expand_for_gc_cause(refill_size_bytes, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_spooling_space);
2810     // Now go around the loop and try alloc again;
2811     // A competing allocation might beat us to the expansion space,
2812     // so we may go around the loop again if allocation fails again.
2813     if (GCExpandToAllocateDelayMillis > 0) {
2814       os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2815     }
2816   }
2817 }
2818 
2819 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
2820   // Only shrink if a compaction was done so that all the free space
2821   // in the generation is in a contiguous block at the end.
2822   if (did_compact()) {
2823     CardGeneration::shrink(bytes);
2824   }
2825 }
2826 
2827 void ConcurrentMarkSweepGeneration::assert_correct_size_change_locking() {
2828   assert_locked_or_safepoint(Heap_lock);
2829 }
2830 
2831 void ConcurrentMarkSweepGeneration::shrink_free_list_by(size_t bytes) {
2832   assert_locked_or_safepoint(Heap_lock);
2833   assert_lock_strong(freelistLock());
2834   if (PrintGCDetails && Verbose) {
2835     warning("Shrinking of CMS not yet implemented");
2836   }
2837   return;
2838 }
2839 
2840 
2841 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
2842 // phases.
2843 class CMSPhaseAccounting: public StackObj {
2844  public:
2845   CMSPhaseAccounting(CMSCollector *collector,
2846                      const char *phase,
2847                      const GCId gc_id,
2848                      bool print_cr = true);
2849   ~CMSPhaseAccounting();
2850 
2851  private:
2852   CMSCollector *_collector;
2853   const char *_phase;
2854   elapsedTimer _wallclock;
2855   bool _print_cr;
2856   const GCId _gc_id;
2857 
2858  public:
2859   // Not MT-safe; so do not pass around these StackObj's
2860   // where they may be accessed by other threads.
2861   jlong wallclock_millis() {
2862     assert(_wallclock.is_active(), "Wall clock should not stop");
2863     _wallclock.stop();  // to record time
2864     jlong ret = _wallclock.milliseconds();
2865     _wallclock.start(); // restart
2866     return ret;
2867   }
2868 };
2869 
2870 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
2871                                        const char *phase,
2872                                        const GCId gc_id,
2873                                        bool print_cr) :
2874   _collector(collector), _phase(phase), _print_cr(print_cr), _gc_id(gc_id) {
2875 
2876   if (PrintCMSStatistics != 0) {
2877     _collector->resetYields();
2878   }
2879   if (PrintGCDetails) {
2880     gclog_or_tty->gclog_stamp(_gc_id);
2881     gclog_or_tty->print_cr("[%s-concurrent-%s-start]",
2882       _collector->cmsGen()->short_name(), _phase);
2883   }
2884   _collector->resetTimer();
2885   _wallclock.start();
2886   _collector->startTimer();
2887 }
2888 
2889 CMSPhaseAccounting::~CMSPhaseAccounting() {
2890   assert(_wallclock.is_active(), "Wall clock should not have stopped");
2891   _collector->stopTimer();
2892   _wallclock.stop();
2893   if (PrintGCDetails) {
2894     gclog_or_tty->gclog_stamp(_gc_id);
2895     gclog_or_tty->print("[%s-concurrent-%s: %3.3f/%3.3f secs]",
2896                  _collector->cmsGen()->short_name(),
2897                  _phase, _collector->timerValue(), _wallclock.seconds());
2898     if (_print_cr) {
2899       gclog_or_tty->cr();
2900     }
2901     if (PrintCMSStatistics != 0) {
2902       gclog_or_tty->print_cr(" (CMS-concurrent-%s yielded %d times)", _phase,
2903                     _collector->yields());
2904     }
2905   }
2906 }
2907 
2908 // CMS work
2909 
2910 // The common parts of CMSParInitialMarkTask and CMSParRemarkTask.
2911 class CMSParMarkTask : public AbstractGangTask {
2912  protected:
2913   CMSCollector*     _collector;
2914   uint              _n_workers;
2915   CMSParMarkTask(const char* name, CMSCollector* collector, uint n_workers) :
2916       AbstractGangTask(name),
2917       _collector(collector),
2918       _n_workers(n_workers) {}
2919   // Work method in support of parallel rescan ... of young gen spaces
2920   void do_young_space_rescan(uint worker_id, OopsInGenClosure* cl,
2921                              ContiguousSpace* space,
2922                              HeapWord** chunk_array, size_t chunk_top);
2923   void work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl);
2924 };
2925 
2926 // Parallel initial mark task
2927 class CMSParInitialMarkTask: public CMSParMarkTask {
2928   StrongRootsScope* _strong_roots_scope;
2929  public:
2930   CMSParInitialMarkTask(CMSCollector* collector, StrongRootsScope* strong_roots_scope, uint n_workers) :
2931       CMSParMarkTask("Scan roots and young gen for initial mark in parallel", collector, n_workers),
2932       _strong_roots_scope(strong_roots_scope) {}
2933   void work(uint worker_id);
2934 };
2935 
2936 // Checkpoint the roots into this generation from outside
2937 // this generation. [Note this initial checkpoint need only
2938 // be approximate -- we'll do a catch up phase subsequently.]
2939 void CMSCollector::checkpointRootsInitial() {
2940   assert(_collectorState == InitialMarking, "Wrong collector state");
2941   check_correct_thread_executing();
2942   TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
2943 
2944   save_heap_summary();
2945   report_heap_summary(GCWhen::BeforeGC);
2946 
2947   ReferenceProcessor* rp = ref_processor();
2948   assert(_restart_addr == NULL, "Control point invariant");
2949   {
2950     // acquire locks for subsequent manipulations
2951     MutexLockerEx x(bitMapLock(),
2952                     Mutex::_no_safepoint_check_flag);
2953     checkpointRootsInitialWork();
2954     // enable ("weak") refs discovery
2955     rp->enable_discovery();
2956     _collectorState = Marking;
2957   }
2958 }
2959 
2960 void CMSCollector::checkpointRootsInitialWork() {
2961   assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
2962   assert(_collectorState == InitialMarking, "just checking");
2963 
2964   // If there has not been a GC[n-1] since last GC[n] cycle completed,
2965   // precede our marking with a collection of all
2966   // younger generations to keep floating garbage to a minimum.
2967   // XXX: we won't do this for now -- it's an optimization to be done later.
2968 
2969   // already have locks
2970   assert_lock_strong(bitMapLock());
2971   assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
2972 
2973   // Setup the verification and class unloading state for this
2974   // CMS collection cycle.
2975   setup_cms_unloading_and_verification_state();
2976 
2977   NOT_PRODUCT(GCTraceTime t("\ncheckpointRootsInitialWork",
2978     PrintGCDetails && Verbose, true, _gc_timer_cm, _gc_tracer_cm->gc_id());)
2979 
2980   // Reset all the PLAB chunk arrays if necessary.
2981   if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
2982     reset_survivor_plab_arrays();
2983   }
2984 
2985   ResourceMark rm;
2986   HandleMark  hm;
2987 
2988   MarkRefsIntoClosure notOlder(_span, &_markBitMap);
2989   GenCollectedHeap* gch = GenCollectedHeap::heap();
2990 
2991   verify_work_stacks_empty();
2992   verify_overflow_empty();
2993 
2994   gch->ensure_parsability(false);  // fill TLABs, but no need to retire them
2995   // Update the saved marks which may affect the root scans.
2996   gch->save_marks();
2997 
2998   // weak reference processing has not started yet.
2999   ref_processor()->set_enqueuing_is_done(false);
3000 
3001   // Need to remember all newly created CLDs,
3002   // so that we can guarantee that the remark finds them.
3003   ClassLoaderDataGraph::remember_new_clds(true);
3004 
3005   // Whenever a CLD is found, it will be claimed before proceeding to mark
3006   // the klasses. The claimed marks need to be cleared before marking starts.
3007   ClassLoaderDataGraph::clear_claimed_marks();
3008 
3009   if (CMSPrintEdenSurvivorChunks) {
3010     print_eden_and_survivor_chunk_arrays();
3011   }
3012 
3013   {
3014     COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
3015     if (CMSParallelInitialMarkEnabled) {
3016       // The parallel version.
3017       FlexibleWorkGang* workers = gch->workers();
3018       assert(workers != NULL, "Need parallel worker threads.");
3019       uint n_workers = workers->active_workers();
3020 
3021       StrongRootsScope srs(n_workers);
3022 
3023       CMSParInitialMarkTask tsk(this, &srs, n_workers);
3024       initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
3025       if (n_workers > 1) {
3026         workers->run_task(&tsk);
3027       } else {
3028         tsk.work(0);
3029       }
3030     } else {
3031       // The serial version.
3032       CLDToOopClosure cld_closure(&notOlder, true);
3033       gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3034 
3035       StrongRootsScope srs(1);
3036 
3037       gch->gen_process_roots(&srs,
3038                              _cmsGen->level(),
3039                              true,   // younger gens are roots
3040                              GenCollectedHeap::ScanningOption(roots_scanning_options()),
3041                              should_unload_classes(),
3042                              &notOlder,
3043                              NULL,
3044                              &cld_closure);
3045     }
3046   }
3047 
3048   // Clear mod-union table; it will be dirtied in the prologue of
3049   // CMS generation per each younger generation collection.
3050 
3051   assert(_modUnionTable.isAllClear(),
3052        "Was cleared in most recent final checkpoint phase"
3053        " or no bits are set in the gc_prologue before the start of the next "
3054        "subsequent marking phase.");
3055 
3056   assert(_ct->klass_rem_set()->mod_union_is_clear(), "Must be");
3057 
3058   // Save the end of the used_region of the constituent generations
3059   // to be used to limit the extent of sweep in each generation.
3060   save_sweep_limits();
3061   verify_overflow_empty();
3062 }
3063 
3064 bool CMSCollector::markFromRoots() {
3065   // we might be tempted to assert that:
3066   // assert(!SafepointSynchronize::is_at_safepoint(),
3067   //        "inconsistent argument?");
3068   // However that wouldn't be right, because it's possible that
3069   // a safepoint is indeed in progress as a younger generation
3070   // stop-the-world GC happens even as we mark in this generation.
3071   assert(_collectorState == Marking, "inconsistent state?");
3072   check_correct_thread_executing();
3073   verify_overflow_empty();
3074 
3075   // Weak ref discovery note: We may be discovering weak
3076   // refs in this generation concurrent (but interleaved) with
3077   // weak ref discovery by a younger generation collector.
3078 
3079   CMSTokenSyncWithLocks ts(true, bitMapLock());
3080   TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3081   CMSPhaseAccounting pa(this, "mark", _gc_tracer_cm->gc_id(), !PrintGCDetails);
3082   bool res = markFromRootsWork();
3083   if (res) {
3084     _collectorState = Precleaning;
3085   } else { // We failed and a foreground collection wants to take over
3086     assert(_foregroundGCIsActive, "internal state inconsistency");
3087     assert(_restart_addr == NULL,  "foreground will restart from scratch");
3088     if (PrintGCDetails) {
3089       gclog_or_tty->print_cr("bailing out to foreground collection");
3090     }
3091   }
3092   verify_overflow_empty();
3093   return res;
3094 }
3095 
3096 bool CMSCollector::markFromRootsWork() {
3097   // iterate over marked bits in bit map, doing a full scan and mark
3098   // from these roots using the following algorithm:
3099   // . if oop is to the right of the current scan pointer,
3100   //   mark corresponding bit (we'll process it later)
3101   // . else (oop is to left of current scan pointer)
3102   //   push oop on marking stack
3103   // . drain the marking stack
3104 
3105   // Note that when we do a marking step we need to hold the
3106   // bit map lock -- recall that direct allocation (by mutators)
3107   // and promotion (by younger generation collectors) is also
3108   // marking the bit map. [the so-called allocate live policy.]
3109   // Because the implementation of bit map marking is not
3110   // robust wrt simultaneous marking of bits in the same word,
3111   // we need to make sure that there is no such interference
3112   // between concurrent such updates.
3113 
3114   // already have locks
3115   assert_lock_strong(bitMapLock());
3116 
3117   verify_work_stacks_empty();
3118   verify_overflow_empty();
3119   bool result = false;
3120   if (CMSConcurrentMTEnabled && ConcGCThreads > 0) {
3121     result = do_marking_mt();
3122   } else {
3123     result = do_marking_st();
3124   }
3125   return result;
3126 }
3127 
3128 // Forward decl
3129 class CMSConcMarkingTask;
3130 
3131 class CMSConcMarkingTerminator: public ParallelTaskTerminator {
3132   CMSCollector*       _collector;
3133   CMSConcMarkingTask* _task;
3134  public:
3135   virtual void yield();
3136 
3137   // "n_threads" is the number of threads to be terminated.
3138   // "queue_set" is a set of work queues of other threads.
3139   // "collector" is the CMS collector associated with this task terminator.
3140   // "yield" indicates whether we need the gang as a whole to yield.
3141   CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
3142     ParallelTaskTerminator(n_threads, queue_set),
3143     _collector(collector) { }
3144 
3145   void set_task(CMSConcMarkingTask* task) {
3146     _task = task;
3147   }
3148 };
3149 
3150 class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator {
3151   CMSConcMarkingTask* _task;
3152  public:
3153   bool should_exit_termination();
3154   void set_task(CMSConcMarkingTask* task) {
3155     _task = task;
3156   }
3157 };
3158 
3159 // MT Concurrent Marking Task
3160 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3161   CMSCollector* _collector;
3162   uint          _n_workers;       // requested/desired # workers
3163   bool          _result;
3164   CompactibleFreeListSpace*  _cms_space;
3165   char          _pad_front[64];   // padding to ...
3166   HeapWord*     _global_finger;   // ... avoid sharing cache line
3167   char          _pad_back[64];
3168   HeapWord*     _restart_addr;
3169 
3170   //  Exposed here for yielding support
3171   Mutex* const _bit_map_lock;
3172 
3173   // The per thread work queues, available here for stealing
3174   OopTaskQueueSet*  _task_queues;
3175 
3176   // Termination (and yielding) support
3177   CMSConcMarkingTerminator _term;
3178   CMSConcMarkingTerminatorTerminator _term_term;
3179 
3180  public:
3181   CMSConcMarkingTask(CMSCollector* collector,
3182                  CompactibleFreeListSpace* cms_space,
3183                  YieldingFlexibleWorkGang* workers,
3184                  OopTaskQueueSet* task_queues):
3185     YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3186     _collector(collector),
3187     _cms_space(cms_space),
3188     _n_workers(0), _result(true),
3189     _task_queues(task_queues),
3190     _term(_n_workers, task_queues, _collector),
3191     _bit_map_lock(collector->bitMapLock())
3192   {
3193     _requested_size = _n_workers;
3194     _term.set_task(this);
3195     _term_term.set_task(this);
3196     _restart_addr = _global_finger = _cms_space->bottom();
3197   }
3198 
3199 
3200   OopTaskQueueSet* task_queues()  { return _task_queues; }
3201 
3202   OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3203 
3204   HeapWord** global_finger_addr() { return &_global_finger; }
3205 
3206   CMSConcMarkingTerminator* terminator() { return &_term; }
3207 
3208   virtual void set_for_termination(uint active_workers) {
3209     terminator()->reset_for_reuse(active_workers);
3210   }
3211 
3212   void work(uint worker_id);
3213   bool should_yield() {
3214     return    ConcurrentMarkSweepThread::should_yield()
3215            && !_collector->foregroundGCIsActive();
3216   }
3217 
3218   virtual void coordinator_yield();  // stuff done by coordinator
3219   bool result() { return _result; }
3220 
3221   void reset(HeapWord* ra) {
3222     assert(_global_finger >= _cms_space->end(),  "Postcondition of ::work(i)");
3223     _restart_addr = _global_finger = ra;
3224     _term.reset_for_reuse();
3225   }
3226 
3227   static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3228                                            OopTaskQueue* work_q);
3229 
3230  private:
3231   void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3232   void do_work_steal(int i);
3233   void bump_global_finger(HeapWord* f);
3234 };
3235 
3236 bool CMSConcMarkingTerminatorTerminator::should_exit_termination() {
3237   assert(_task != NULL, "Error");
3238   return _task->yielding();
3239   // Note that we do not need the disjunct || _task->should_yield() above
3240   // because we want terminating threads to yield only if the task
3241   // is already in the midst of yielding, which happens only after at least one
3242   // thread has yielded.
3243 }
3244 
3245 void CMSConcMarkingTerminator::yield() {
3246   if (_task->should_yield()) {
3247     _task->yield();
3248   } else {
3249     ParallelTaskTerminator::yield();
3250   }
3251 }
3252 
3253 ////////////////////////////////////////////////////////////////
3254 // Concurrent Marking Algorithm Sketch
3255 ////////////////////////////////////////////////////////////////
3256 // Until all tasks exhausted (both spaces):
3257 // -- claim next available chunk
3258 // -- bump global finger via CAS
3259 // -- find first object that starts in this chunk
3260 //    and start scanning bitmap from that position
3261 // -- scan marked objects for oops
3262 // -- CAS-mark target, and if successful:
3263 //    . if target oop is above global finger (volatile read)
3264 //      nothing to do
3265 //    . if target oop is in chunk and above local finger
3266 //        then nothing to do
3267 //    . else push on work-queue
3268 // -- Deal with possible overflow issues:
3269 //    . local work-queue overflow causes stuff to be pushed on
3270 //      global (common) overflow queue
3271 //    . always first empty local work queue
3272 //    . then get a batch of oops from global work queue if any
3273 //    . then do work stealing
3274 // -- When all tasks claimed (both spaces)
3275 //    and local work queue empty,
3276 //    then in a loop do:
3277 //    . check global overflow stack; steal a batch of oops and trace
3278 //    . try to steal from other threads oif GOS is empty
3279 //    . if neither is available, offer termination
3280 // -- Terminate and return result
3281 //
3282 void CMSConcMarkingTask::work(uint worker_id) {
3283   elapsedTimer _timer;
3284   ResourceMark rm;
3285   HandleMark hm;
3286 
3287   DEBUG_ONLY(_collector->verify_overflow_empty();)
3288 
3289   // Before we begin work, our work queue should be empty
3290   assert(work_queue(worker_id)->size() == 0, "Expected to be empty");
3291   // Scan the bitmap covering _cms_space, tracing through grey objects.
3292   _timer.start();
3293   do_scan_and_mark(worker_id, _cms_space);
3294   _timer.stop();
3295   if (PrintCMSStatistics != 0) {
3296     gclog_or_tty->print_cr("Finished cms space scanning in %dth thread: %3.3f sec",
3297       worker_id, _timer.seconds());
3298       // XXX: need xxx/xxx type of notation, two timers
3299   }
3300 
3301   // ... do work stealing
3302   _timer.reset();
3303   _timer.start();
3304   do_work_steal(worker_id);
3305   _timer.stop();
3306   if (PrintCMSStatistics != 0) {
3307     gclog_or_tty->print_cr("Finished work stealing in %dth thread: %3.3f sec",
3308       worker_id, _timer.seconds());
3309       // XXX: need xxx/xxx type of notation, two timers
3310   }
3311   assert(_collector->_markStack.isEmpty(), "Should have been emptied");
3312   assert(work_queue(worker_id)->size() == 0, "Should have been emptied");
3313   // Note that under the current task protocol, the
3314   // following assertion is true even of the spaces
3315   // expanded since the completion of the concurrent
3316   // marking. XXX This will likely change under a strict
3317   // ABORT semantics.
3318   // After perm removal the comparison was changed to
3319   // greater than or equal to from strictly greater than.
3320   // Before perm removal the highest address sweep would
3321   // have been at the end of perm gen but now is at the
3322   // end of the tenured gen.
3323   assert(_global_finger >=  _cms_space->end(),
3324          "All tasks have been completed");
3325   DEBUG_ONLY(_collector->verify_overflow_empty();)
3326 }
3327 
3328 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
3329   HeapWord* read = _global_finger;
3330   HeapWord* cur  = read;
3331   while (f > read) {
3332     cur = read;
3333     read = (HeapWord*) Atomic::cmpxchg_ptr(f, &_global_finger, cur);
3334     if (cur == read) {
3335       // our cas succeeded
3336       assert(_global_finger >= f, "protocol consistency");
3337       break;
3338     }
3339   }
3340 }
3341 
3342 // This is really inefficient, and should be redone by
3343 // using (not yet available) block-read and -write interfaces to the
3344 // stack and the work_queue. XXX FIX ME !!!
3345 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3346                                                       OopTaskQueue* work_q) {
3347   // Fast lock-free check
3348   if (ovflw_stk->length() == 0) {
3349     return false;
3350   }
3351   assert(work_q->size() == 0, "Shouldn't steal");
3352   MutexLockerEx ml(ovflw_stk->par_lock(),
3353                    Mutex::_no_safepoint_check_flag);
3354   // Grab up to 1/4 the size of the work queue
3355   size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
3356                     (size_t)ParGCDesiredObjsFromOverflowList);
3357   num = MIN2(num, ovflw_stk->length());
3358   for (int i = (int) num; i > 0; i--) {
3359     oop cur = ovflw_stk->pop();
3360     assert(cur != NULL, "Counted wrong?");
3361     work_q->push(cur);
3362   }
3363   return num > 0;
3364 }
3365 
3366 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
3367   SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
3368   int n_tasks = pst->n_tasks();
3369   // We allow that there may be no tasks to do here because
3370   // we are restarting after a stack overflow.
3371   assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
3372   uint nth_task = 0;
3373 
3374   HeapWord* aligned_start = sp->bottom();
3375   if (sp->used_region().contains(_restart_addr)) {
3376     // Align down to a card boundary for the start of 0th task
3377     // for this space.
3378     aligned_start =
3379       (HeapWord*)align_size_down((uintptr_t)_restart_addr,
3380                                  CardTableModRefBS::card_size);
3381   }
3382 
3383   size_t chunk_size = sp->marking_task_size();
3384   while (!pst->is_task_claimed(/* reference */ nth_task)) {
3385     // Having claimed the nth task in this space,
3386     // compute the chunk that it corresponds to:
3387     MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
3388                                aligned_start + (nth_task+1)*chunk_size);
3389     // Try and bump the global finger via a CAS;
3390     // note that we need to do the global finger bump
3391     // _before_ taking the intersection below, because
3392     // the task corresponding to that region will be
3393     // deemed done even if the used_region() expands
3394     // because of allocation -- as it almost certainly will
3395     // during start-up while the threads yield in the
3396     // closure below.
3397     HeapWord* finger = span.end();
3398     bump_global_finger(finger);   // atomically
3399     // There are null tasks here corresponding to chunks
3400     // beyond the "top" address of the space.
3401     span = span.intersection(sp->used_region());
3402     if (!span.is_empty()) {  // Non-null task
3403       HeapWord* prev_obj;
3404       assert(!span.contains(_restart_addr) || nth_task == 0,
3405              "Inconsistency");
3406       if (nth_task == 0) {
3407         // For the 0th task, we'll not need to compute a block_start.
3408         if (span.contains(_restart_addr)) {
3409           // In the case of a restart because of stack overflow,
3410           // we might additionally skip a chunk prefix.
3411           prev_obj = _restart_addr;
3412         } else {
3413           prev_obj = span.start();
3414         }
3415       } else {
3416         // We want to skip the first object because
3417         // the protocol is to scan any object in its entirety
3418         // that _starts_ in this span; a fortiori, any
3419         // object starting in an earlier span is scanned
3420         // as part of an earlier claimed task.
3421         // Below we use the "careful" version of block_start
3422         // so we do not try to navigate uninitialized objects.
3423         prev_obj = sp->block_start_careful(span.start());
3424         // Below we use a variant of block_size that uses the
3425         // Printezis bits to avoid waiting for allocated
3426         // objects to become initialized/parsable.
3427         while (prev_obj < span.start()) {
3428           size_t sz = sp->block_size_no_stall(prev_obj, _collector);
3429           if (sz > 0) {
3430             prev_obj += sz;
3431           } else {
3432             // In this case we may end up doing a bit of redundant
3433             // scanning, but that appears unavoidable, short of
3434             // locking the free list locks; see bug 6324141.
3435             break;
3436           }
3437         }
3438       }
3439       if (prev_obj < span.end()) {
3440         MemRegion my_span = MemRegion(prev_obj, span.end());
3441         // Do the marking work within a non-empty span --
3442         // the last argument to the constructor indicates whether the
3443         // iteration should be incremental with periodic yields.
3444         Par_MarkFromRootsClosure cl(this, _collector, my_span,
3445                                     &_collector->_markBitMap,
3446                                     work_queue(i),
3447                                     &_collector->_markStack);
3448         _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
3449       } // else nothing to do for this task
3450     }   // else nothing to do for this task
3451   }
3452   // We'd be tempted to assert here that since there are no
3453   // more tasks left to claim in this space, the global_finger
3454   // must exceed space->top() and a fortiori space->end(). However,
3455   // that would not quite be correct because the bumping of
3456   // global_finger occurs strictly after the claiming of a task,
3457   // so by the time we reach here the global finger may not yet
3458   // have been bumped up by the thread that claimed the last
3459   // task.
3460   pst->all_tasks_completed();
3461 }
3462 
3463 class Par_ConcMarkingClosure: public MetadataAwareOopClosure {
3464  private:
3465   CMSCollector* _collector;
3466   CMSConcMarkingTask* _task;
3467   MemRegion     _span;
3468   CMSBitMap*    _bit_map;
3469   CMSMarkStack* _overflow_stack;
3470   OopTaskQueue* _work_queue;
3471  protected:
3472   DO_OOP_WORK_DEFN
3473  public:
3474   Par_ConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue,
3475                          CMSBitMap* bit_map, CMSMarkStack* overflow_stack):
3476     MetadataAwareOopClosure(collector->ref_processor()),
3477     _collector(collector),
3478     _task(task),
3479     _span(collector->_span),
3480     _work_queue(work_queue),
3481     _bit_map(bit_map),
3482     _overflow_stack(overflow_stack)
3483   { }
3484   virtual void do_oop(oop* p);
3485   virtual void do_oop(narrowOop* p);
3486 
3487   void trim_queue(size_t max);
3488   void handle_stack_overflow(HeapWord* lost);
3489   void do_yield_check() {
3490     if (_task->should_yield()) {
3491       _task->yield();
3492     }
3493   }
3494 };
3495 
3496 // Grey object scanning during work stealing phase --
3497 // the salient assumption here is that any references
3498 // that are in these stolen objects being scanned must
3499 // already have been initialized (else they would not have
3500 // been published), so we do not need to check for
3501 // uninitialized objects before pushing here.
3502 void Par_ConcMarkingClosure::do_oop(oop obj) {
3503   assert(obj->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
3504   HeapWord* addr = (HeapWord*)obj;
3505   // Check if oop points into the CMS generation
3506   // and is not marked
3507   if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
3508     // a white object ...
3509     // If we manage to "claim" the object, by being the
3510     // first thread to mark it, then we push it on our
3511     // marking stack
3512     if (_bit_map->par_mark(addr)) {     // ... now grey
3513       // push on work queue (grey set)
3514       bool simulate_overflow = false;
3515       NOT_PRODUCT(
3516         if (CMSMarkStackOverflowALot &&
3517             _collector->simulate_overflow()) {
3518           // simulate a stack overflow
3519           simulate_overflow = true;
3520         }
3521       )
3522       if (simulate_overflow ||
3523           !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
3524         // stack overflow
3525         if (PrintCMSStatistics != 0) {
3526           gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
3527                                  SIZE_FORMAT, _overflow_stack->capacity());
3528         }
3529         // We cannot assert that the overflow stack is full because
3530         // it may have been emptied since.
3531         assert(simulate_overflow ||
3532                _work_queue->size() == _work_queue->max_elems(),
3533               "Else push should have succeeded");
3534         handle_stack_overflow(addr);
3535       }
3536     } // Else, some other thread got there first
3537     do_yield_check();
3538   }
3539 }
3540 
3541 void Par_ConcMarkingClosure::do_oop(oop* p)       { Par_ConcMarkingClosure::do_oop_work(p); }
3542 void Par_ConcMarkingClosure::do_oop(narrowOop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
3543 
3544 void Par_ConcMarkingClosure::trim_queue(size_t max) {
3545   while (_work_queue->size() > max) {
3546     oop new_oop;
3547     if (_work_queue->pop_local(new_oop)) {
3548       assert(new_oop->is_oop(), "Should be an oop");
3549       assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
3550       assert(_span.contains((HeapWord*)new_oop), "Not in span");
3551       new_oop->oop_iterate(this);  // do_oop() above
3552       do_yield_check();
3553     }
3554   }
3555 }
3556 
3557 // Upon stack overflow, we discard (part of) the stack,
3558 // remembering the least address amongst those discarded
3559 // in CMSCollector's _restart_address.
3560 void Par_ConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
3561   // We need to do this under a mutex to prevent other
3562   // workers from interfering with the work done below.
3563   MutexLockerEx ml(_overflow_stack->par_lock(),
3564                    Mutex::_no_safepoint_check_flag);
3565   // Remember the least grey address discarded
3566   HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
3567   _collector->lower_restart_addr(ra);
3568   _overflow_stack->reset();  // discard stack contents
3569   _overflow_stack->expand(); // expand the stack if possible
3570 }
3571 
3572 
3573 void CMSConcMarkingTask::do_work_steal(int i) {
3574   OopTaskQueue* work_q = work_queue(i);
3575   oop obj_to_scan;
3576   CMSBitMap* bm = &(_collector->_markBitMap);
3577   CMSMarkStack* ovflw = &(_collector->_markStack);
3578   int* seed = _collector->hash_seed(i);
3579   Par_ConcMarkingClosure cl(_collector, this, work_q, bm, ovflw);
3580   while (true) {
3581     cl.trim_queue(0);
3582     assert(work_q->size() == 0, "Should have been emptied above");
3583     if (get_work_from_overflow_stack(ovflw, work_q)) {
3584       // Can't assert below because the work obtained from the
3585       // overflow stack may already have been stolen from us.
3586       // assert(work_q->size() > 0, "Work from overflow stack");
3587       continue;
3588     } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
3589       assert(obj_to_scan->is_oop(), "Should be an oop");
3590       assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
3591       obj_to_scan->oop_iterate(&cl);
3592     } else if (terminator()->offer_termination(&_term_term)) {
3593       assert(work_q->size() == 0, "Impossible!");
3594       break;
3595     } else if (yielding() || should_yield()) {
3596       yield();
3597     }
3598   }
3599 }
3600 
3601 // This is run by the CMS (coordinator) thread.
3602 void CMSConcMarkingTask::coordinator_yield() {
3603   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3604          "CMS thread should hold CMS token");
3605   // First give up the locks, then yield, then re-lock
3606   // We should probably use a constructor/destructor idiom to
3607   // do this unlock/lock or modify the MutexUnlocker class to
3608   // serve our purpose. XXX
3609   assert_lock_strong(_bit_map_lock);
3610   _bit_map_lock->unlock();
3611   ConcurrentMarkSweepThread::desynchronize(true);
3612   _collector->stopTimer();
3613   if (PrintCMSStatistics != 0) {
3614     _collector->incrementYields();
3615   }
3616 
3617   // It is possible for whichever thread initiated the yield request
3618   // not to get a chance to wake up and take the bitmap lock between
3619   // this thread releasing it and reacquiring it. So, while the
3620   // should_yield() flag is on, let's sleep for a bit to give the
3621   // other thread a chance to wake up. The limit imposed on the number
3622   // of iterations is defensive, to avoid any unforseen circumstances
3623   // putting us into an infinite loop. Since it's always been this
3624   // (coordinator_yield()) method that was observed to cause the
3625   // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
3626   // which is by default non-zero. For the other seven methods that
3627   // also perform the yield operation, as are using a different
3628   // parameter (CMSYieldSleepCount) which is by default zero. This way we
3629   // can enable the sleeping for those methods too, if necessary.
3630   // See 6442774.
3631   //
3632   // We really need to reconsider the synchronization between the GC
3633   // thread and the yield-requesting threads in the future and we
3634   // should really use wait/notify, which is the recommended
3635   // way of doing this type of interaction. Additionally, we should
3636   // consolidate the eight methods that do the yield operation and they
3637   // are almost identical into one for better maintainability and
3638   // readability. See 6445193.
3639   //
3640   // Tony 2006.06.29
3641   for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
3642                    ConcurrentMarkSweepThread::should_yield() &&
3643                    !CMSCollector::foregroundGCIsActive(); ++i) {
3644     os::sleep(Thread::current(), 1, false);
3645   }
3646 
3647   ConcurrentMarkSweepThread::synchronize(true);
3648   _bit_map_lock->lock_without_safepoint_check();
3649   _collector->startTimer();
3650 }
3651 
3652 bool CMSCollector::do_marking_mt() {
3653   assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition");
3654   uint num_workers = AdaptiveSizePolicy::calc_active_conc_workers(conc_workers()->total_workers(),
3655                                                                   conc_workers()->active_workers(),
3656                                                                   Threads::number_of_non_daemon_threads());
3657   conc_workers()->set_active_workers(num_workers);
3658 
3659   CompactibleFreeListSpace* cms_space  = _cmsGen->cmsSpace();
3660 
3661   CMSConcMarkingTask tsk(this,
3662                          cms_space,
3663                          conc_workers(),
3664                          task_queues());
3665 
3666   // Since the actual number of workers we get may be different
3667   // from the number we requested above, do we need to do anything different
3668   // below? In particular, may be we need to subclass the SequantialSubTasksDone
3669   // class?? XXX
3670   cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
3671 
3672   // Refs discovery is already non-atomic.
3673   assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
3674   assert(ref_processor()->discovery_is_mt(), "Discovery should be MT");
3675   conc_workers()->start_task(&tsk);
3676   while (tsk.yielded()) {
3677     tsk.coordinator_yield();
3678     conc_workers()->continue_task(&tsk);
3679   }
3680   // If the task was aborted, _restart_addr will be non-NULL
3681   assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
3682   while (_restart_addr != NULL) {
3683     // XXX For now we do not make use of ABORTED state and have not
3684     // yet implemented the right abort semantics (even in the original
3685     // single-threaded CMS case). That needs some more investigation
3686     // and is deferred for now; see CR# TBF. 07252005YSR. XXX
3687     assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
3688     // If _restart_addr is non-NULL, a marking stack overflow
3689     // occurred; we need to do a fresh marking iteration from the
3690     // indicated restart address.
3691     if (_foregroundGCIsActive) {
3692       // We may be running into repeated stack overflows, having
3693       // reached the limit of the stack size, while making very
3694       // slow forward progress. It may be best to bail out and
3695       // let the foreground collector do its job.
3696       // Clear _restart_addr, so that foreground GC
3697       // works from scratch. This avoids the headache of
3698       // a "rescan" which would otherwise be needed because
3699       // of the dirty mod union table & card table.
3700       _restart_addr = NULL;
3701       return false;
3702     }
3703     // Adjust the task to restart from _restart_addr
3704     tsk.reset(_restart_addr);
3705     cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
3706                   _restart_addr);
3707     _restart_addr = NULL;
3708     // Get the workers going again
3709     conc_workers()->start_task(&tsk);
3710     while (tsk.yielded()) {
3711       tsk.coordinator_yield();
3712       conc_workers()->continue_task(&tsk);
3713     }
3714   }
3715   assert(tsk.completed(), "Inconsistency");
3716   assert(tsk.result() == true, "Inconsistency");
3717   return true;
3718 }
3719 
3720 bool CMSCollector::do_marking_st() {
3721   ResourceMark rm;
3722   HandleMark   hm;
3723 
3724   // Temporarily make refs discovery single threaded (non-MT)
3725   ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
3726   MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
3727     &_markStack, CMSYield);
3728   // the last argument to iterate indicates whether the iteration
3729   // should be incremental with periodic yields.
3730   _markBitMap.iterate(&markFromRootsClosure);
3731   // If _restart_addr is non-NULL, a marking stack overflow
3732   // occurred; we need to do a fresh iteration from the
3733   // indicated restart address.
3734   while (_restart_addr != NULL) {
3735     if (_foregroundGCIsActive) {
3736       // We may be running into repeated stack overflows, having
3737       // reached the limit of the stack size, while making very
3738       // slow forward progress. It may be best to bail out and
3739       // let the foreground collector do its job.
3740       // Clear _restart_addr, so that foreground GC
3741       // works from scratch. This avoids the headache of
3742       // a "rescan" which would otherwise be needed because
3743       // of the dirty mod union table & card table.
3744       _restart_addr = NULL;
3745       return false;  // indicating failure to complete marking
3746     }
3747     // Deal with stack overflow:
3748     // we restart marking from _restart_addr
3749     HeapWord* ra = _restart_addr;
3750     markFromRootsClosure.reset(ra);
3751     _restart_addr = NULL;
3752     _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
3753   }
3754   return true;
3755 }
3756 
3757 void CMSCollector::preclean() {
3758   check_correct_thread_executing();
3759   assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
3760   verify_work_stacks_empty();
3761   verify_overflow_empty();
3762   _abort_preclean = false;
3763   if (CMSPrecleaningEnabled) {
3764     if (!CMSEdenChunksRecordAlways) {
3765       _eden_chunk_index = 0;
3766     }
3767     size_t used = get_eden_used();
3768     size_t capacity = get_eden_capacity();
3769     // Don't start sampling unless we will get sufficiently
3770     // many samples.
3771     if (used < (capacity/(CMSScheduleRemarkSamplingRatio * 100)
3772                 * CMSScheduleRemarkEdenPenetration)) {
3773       _start_sampling = true;
3774     } else {
3775       _start_sampling = false;
3776     }
3777     TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3778     CMSPhaseAccounting pa(this, "preclean", _gc_tracer_cm->gc_id(), !PrintGCDetails);
3779     preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
3780   }
3781   CMSTokenSync x(true); // is cms thread
3782   if (CMSPrecleaningEnabled) {
3783     sample_eden();
3784     _collectorState = AbortablePreclean;
3785   } else {
3786     _collectorState = FinalMarking;
3787   }
3788   verify_work_stacks_empty();
3789   verify_overflow_empty();
3790 }
3791 
3792 // Try and schedule the remark such that young gen
3793 // occupancy is CMSScheduleRemarkEdenPenetration %.
3794 void CMSCollector::abortable_preclean() {
3795   check_correct_thread_executing();
3796   assert(CMSPrecleaningEnabled,  "Inconsistent control state");
3797   assert(_collectorState == AbortablePreclean, "Inconsistent control state");
3798 
3799   // If Eden's current occupancy is below this threshold,
3800   // immediately schedule the remark; else preclean
3801   // past the next scavenge in an effort to
3802   // schedule the pause as described above. By choosing
3803   // CMSScheduleRemarkEdenSizeThreshold >= max eden size
3804   // we will never do an actual abortable preclean cycle.
3805   if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
3806     TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3807     CMSPhaseAccounting pa(this, "abortable-preclean", _gc_tracer_cm->gc_id(), !PrintGCDetails);
3808     // We need more smarts in the abortable preclean
3809     // loop below to deal with cases where allocation
3810     // in young gen is very very slow, and our precleaning
3811     // is running a losing race against a horde of
3812     // mutators intent on flooding us with CMS updates
3813     // (dirty cards).
3814     // One, admittedly dumb, strategy is to give up
3815     // after a certain number of abortable precleaning loops
3816     // or after a certain maximum time. We want to make
3817     // this smarter in the next iteration.
3818     // XXX FIX ME!!! YSR
3819     size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
3820     while (!(should_abort_preclean() ||
3821              ConcurrentMarkSweepThread::should_terminate())) {
3822       workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
3823       cumworkdone += workdone;
3824       loops++;
3825       // Voluntarily terminate abortable preclean phase if we have
3826       // been at it for too long.
3827       if ((CMSMaxAbortablePrecleanLoops != 0) &&
3828           loops >= CMSMaxAbortablePrecleanLoops) {
3829         if (PrintGCDetails) {
3830           gclog_or_tty->print(" CMS: abort preclean due to loops ");
3831         }
3832         break;
3833       }
3834       if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
3835         if (PrintGCDetails) {
3836           gclog_or_tty->print(" CMS: abort preclean due to time ");
3837         }
3838         break;
3839       }
3840       // If we are doing little work each iteration, we should
3841       // take a short break.
3842       if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
3843         // Sleep for some time, waiting for work to accumulate
3844         stopTimer();
3845         cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
3846         startTimer();
3847         waited++;
3848       }
3849     }
3850     if (PrintCMSStatistics > 0) {
3851       gclog_or_tty->print(" [" SIZE_FORMAT " iterations, " SIZE_FORMAT " waits, " SIZE_FORMAT " cards)] ",
3852                           loops, waited, cumworkdone);
3853     }
3854   }
3855   CMSTokenSync x(true); // is cms thread
3856   if (_collectorState != Idling) {
3857     assert(_collectorState == AbortablePreclean,
3858            "Spontaneous state transition?");
3859     _collectorState = FinalMarking;
3860   } // Else, a foreground collection completed this CMS cycle.
3861   return;
3862 }
3863 
3864 // Respond to an Eden sampling opportunity
3865 void CMSCollector::sample_eden() {
3866   // Make sure a young gc cannot sneak in between our
3867   // reading and recording of a sample.
3868   assert(Thread::current()->is_ConcurrentGC_thread(),
3869          "Only the cms thread may collect Eden samples");
3870   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3871          "Should collect samples while holding CMS token");
3872   if (!_start_sampling) {
3873     return;
3874   }
3875   // When CMSEdenChunksRecordAlways is true, the eden chunk array
3876   // is populated by the young generation.
3877   if (_eden_chunk_array != NULL && !CMSEdenChunksRecordAlways) {
3878     if (_eden_chunk_index < _eden_chunk_capacity) {
3879       _eden_chunk_array[_eden_chunk_index] = *_top_addr;   // take sample
3880       assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
3881              "Unexpected state of Eden");
3882       // We'd like to check that what we just sampled is an oop-start address;
3883       // however, we cannot do that here since the object may not yet have been
3884       // initialized. So we'll instead do the check when we _use_ this sample
3885       // later.
3886       if (_eden_chunk_index == 0 ||
3887           (pointer_delta(_eden_chunk_array[_eden_chunk_index],
3888                          _eden_chunk_array[_eden_chunk_index-1])
3889            >= CMSSamplingGrain)) {
3890         _eden_chunk_index++;  // commit sample
3891       }
3892     }
3893   }
3894   if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
3895     size_t used = get_eden_used();
3896     size_t capacity = get_eden_capacity();
3897     assert(used <= capacity, "Unexpected state of Eden");
3898     if (used >  (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
3899       _abort_preclean = true;
3900     }
3901   }
3902 }
3903 
3904 
3905 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
3906   assert(_collectorState == Precleaning ||
3907          _collectorState == AbortablePreclean, "incorrect state");
3908   ResourceMark rm;
3909   HandleMark   hm;
3910 
3911   // Precleaning is currently not MT but the reference processor
3912   // may be set for MT.  Disable it temporarily here.
3913   ReferenceProcessor* rp = ref_processor();
3914   ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false);
3915 
3916   // Do one pass of scrubbing the discovered reference lists
3917   // to remove any reference objects with strongly-reachable
3918   // referents.
3919   if (clean_refs) {
3920     CMSPrecleanRefsYieldClosure yield_cl(this);
3921     assert(rp->span().equals(_span), "Spans should be equal");
3922     CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
3923                                    &_markStack, true /* preclean */);
3924     CMSDrainMarkingStackClosure complete_trace(this,
3925                                    _span, &_markBitMap, &_markStack,
3926                                    &keep_alive, true /* preclean */);
3927 
3928     // We don't want this step to interfere with a young
3929     // collection because we don't want to take CPU
3930     // or memory bandwidth away from the young GC threads
3931     // (which may be as many as there are CPUs).
3932     // Note that we don't need to protect ourselves from
3933     // interference with mutators because they can't
3934     // manipulate the discovered reference lists nor affect
3935     // the computed reachability of the referents, the
3936     // only properties manipulated by the precleaning
3937     // of these reference lists.
3938     stopTimer();
3939     CMSTokenSyncWithLocks x(true /* is cms thread */,
3940                             bitMapLock());
3941     startTimer();
3942     sample_eden();
3943 
3944     // The following will yield to allow foreground
3945     // collection to proceed promptly. XXX YSR:
3946     // The code in this method may need further
3947     // tweaking for better performance and some restructuring
3948     // for cleaner interfaces.
3949     GCTimer *gc_timer = NULL; // Currently not tracing concurrent phases
3950     rp->preclean_discovered_references(
3951           rp->is_alive_non_header(), &keep_alive, &complete_trace, &yield_cl,
3952           gc_timer, _gc_tracer_cm->gc_id());
3953   }
3954 
3955   if (clean_survivor) {  // preclean the active survivor space(s)
3956     PushAndMarkClosure pam_cl(this, _span, ref_processor(),
3957                              &_markBitMap, &_modUnionTable,
3958                              &_markStack, true /* precleaning phase */);
3959     stopTimer();
3960     CMSTokenSyncWithLocks ts(true /* is cms thread */,
3961                              bitMapLock());
3962     startTimer();
3963     unsigned int before_count =
3964       GenCollectedHeap::heap()->total_collections();
3965     SurvivorSpacePrecleanClosure
3966       sss_cl(this, _span, &_markBitMap, &_markStack,
3967              &pam_cl, before_count, CMSYield);
3968     _young_gen->from()->object_iterate_careful(&sss_cl);
3969     _young_gen->to()->object_iterate_careful(&sss_cl);
3970   }
3971   MarkRefsIntoAndScanClosure
3972     mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
3973              &_markStack, this, CMSYield,
3974              true /* precleaning phase */);
3975   // CAUTION: The following closure has persistent state that may need to
3976   // be reset upon a decrease in the sequence of addresses it
3977   // processes.
3978   ScanMarkedObjectsAgainCarefullyClosure
3979     smoac_cl(this, _span,
3980       &_markBitMap, &_markStack, &mrias_cl, CMSYield);
3981 
3982   // Preclean dirty cards in ModUnionTable and CardTable using
3983   // appropriate convergence criterion;
3984   // repeat CMSPrecleanIter times unless we find that
3985   // we are losing.
3986   assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
3987   assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
3988          "Bad convergence multiplier");
3989   assert(CMSPrecleanThreshold >= 100,
3990          "Unreasonably low CMSPrecleanThreshold");
3991 
3992   size_t numIter, cumNumCards, lastNumCards, curNumCards;
3993   for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
3994        numIter < CMSPrecleanIter;
3995        numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
3996     curNumCards  = preclean_mod_union_table(_cmsGen, &smoac_cl);
3997     if (Verbose && PrintGCDetails) {
3998       gclog_or_tty->print(" (modUnionTable: " SIZE_FORMAT " cards)", curNumCards);
3999     }
4000     // Either there are very few dirty cards, so re-mark
4001     // pause will be small anyway, or our pre-cleaning isn't
4002     // that much faster than the rate at which cards are being
4003     // dirtied, so we might as well stop and re-mark since
4004     // precleaning won't improve our re-mark time by much.
4005     if (curNumCards <= CMSPrecleanThreshold ||
4006         (numIter > 0 &&
4007          (curNumCards * CMSPrecleanDenominator >
4008          lastNumCards * CMSPrecleanNumerator))) {
4009       numIter++;
4010       cumNumCards += curNumCards;
4011       break;
4012     }
4013   }
4014 
4015   preclean_klasses(&mrias_cl, _cmsGen->freelistLock());
4016 
4017   curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
4018   cumNumCards += curNumCards;
4019   if (PrintGCDetails && PrintCMSStatistics != 0) {
4020     gclog_or_tty->print_cr(" (cardTable: " SIZE_FORMAT " cards, re-scanned " SIZE_FORMAT " cards, " SIZE_FORMAT " iterations)",
4021                   curNumCards, cumNumCards, numIter);
4022   }
4023   return cumNumCards;   // as a measure of useful work done
4024 }
4025 
4026 // PRECLEANING NOTES:
4027 // Precleaning involves:
4028 // . reading the bits of the modUnionTable and clearing the set bits.
4029 // . For the cards corresponding to the set bits, we scan the
4030 //   objects on those cards. This means we need the free_list_lock
4031 //   so that we can safely iterate over the CMS space when scanning
4032 //   for oops.
4033 // . When we scan the objects, we'll be both reading and setting
4034 //   marks in the marking bit map, so we'll need the marking bit map.
4035 // . For protecting _collector_state transitions, we take the CGC_lock.
4036 //   Note that any races in the reading of of card table entries by the
4037 //   CMS thread on the one hand and the clearing of those entries by the
4038 //   VM thread or the setting of those entries by the mutator threads on the
4039 //   other are quite benign. However, for efficiency it makes sense to keep
4040 //   the VM thread from racing with the CMS thread while the latter is
4041 //   dirty card info to the modUnionTable. We therefore also use the
4042 //   CGC_lock to protect the reading of the card table and the mod union
4043 //   table by the CM thread.
4044 // . We run concurrently with mutator updates, so scanning
4045 //   needs to be done carefully  -- we should not try to scan
4046 //   potentially uninitialized objects.
4047 //
4048 // Locking strategy: While holding the CGC_lock, we scan over and
4049 // reset a maximal dirty range of the mod union / card tables, then lock
4050 // the free_list_lock and bitmap lock to do a full marking, then
4051 // release these locks; and repeat the cycle. This allows for a
4052 // certain amount of fairness in the sharing of these locks between
4053 // the CMS collector on the one hand, and the VM thread and the
4054 // mutators on the other.
4055 
4056 // NOTE: preclean_mod_union_table() and preclean_card_table()
4057 // further below are largely identical; if you need to modify
4058 // one of these methods, please check the other method too.
4059 
4060 size_t CMSCollector::preclean_mod_union_table(
4061   ConcurrentMarkSweepGeneration* gen,
4062   ScanMarkedObjectsAgainCarefullyClosure* cl) {
4063   verify_work_stacks_empty();
4064   verify_overflow_empty();
4065 
4066   // strategy: starting with the first card, accumulate contiguous
4067   // ranges of dirty cards; clear these cards, then scan the region
4068   // covered by these cards.
4069 
4070   // Since all of the MUT is committed ahead, we can just use
4071   // that, in case the generations expand while we are precleaning.
4072   // It might also be fine to just use the committed part of the
4073   // generation, but we might potentially miss cards when the
4074   // generation is rapidly expanding while we are in the midst
4075   // of precleaning.
4076   HeapWord* startAddr = gen->reserved().start();
4077   HeapWord* endAddr   = gen->reserved().end();
4078 
4079   cl->setFreelistLock(gen->freelistLock());   // needed for yielding
4080 
4081   size_t numDirtyCards, cumNumDirtyCards;
4082   HeapWord *nextAddr, *lastAddr;
4083   for (cumNumDirtyCards = numDirtyCards = 0,
4084        nextAddr = lastAddr = startAddr;
4085        nextAddr < endAddr;
4086        nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4087 
4088     ResourceMark rm;
4089     HandleMark   hm;
4090 
4091     MemRegion dirtyRegion;
4092     {
4093       stopTimer();
4094       // Potential yield point
4095       CMSTokenSync ts(true);
4096       startTimer();
4097       sample_eden();
4098       // Get dirty region starting at nextOffset (inclusive),
4099       // simultaneously clearing it.
4100       dirtyRegion =
4101         _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
4102       assert(dirtyRegion.start() >= nextAddr,
4103              "returned region inconsistent?");
4104     }
4105     // Remember where the next search should begin.
4106     // The returned region (if non-empty) is a right open interval,
4107     // so lastOffset is obtained from the right end of that
4108     // interval.
4109     lastAddr = dirtyRegion.end();
4110     // Should do something more transparent and less hacky XXX
4111     numDirtyCards =
4112       _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
4113 
4114     // We'll scan the cards in the dirty region (with periodic
4115     // yields for foreground GC as needed).
4116     if (!dirtyRegion.is_empty()) {
4117       assert(numDirtyCards > 0, "consistency check");
4118       HeapWord* stop_point = NULL;
4119       stopTimer();
4120       // Potential yield point
4121       CMSTokenSyncWithLocks ts(true, gen->freelistLock(),
4122                                bitMapLock());
4123       startTimer();
4124       {
4125         verify_work_stacks_empty();
4126         verify_overflow_empty();
4127         sample_eden();
4128         stop_point =
4129           gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4130       }
4131       if (stop_point != NULL) {
4132         // The careful iteration stopped early either because it found an
4133         // uninitialized object, or because we were in the midst of an
4134         // "abortable preclean", which should now be aborted. Redirty
4135         // the bits corresponding to the partially-scanned or unscanned
4136         // cards. We'll either restart at the next block boundary or
4137         // abort the preclean.
4138         assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4139                "Should only be AbortablePreclean.");
4140         _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
4141         if (should_abort_preclean()) {
4142           break; // out of preclean loop
4143         } else {
4144           // Compute the next address at which preclean should pick up;
4145           // might need bitMapLock in order to read P-bits.
4146           lastAddr = next_card_start_after_block(stop_point);
4147         }
4148       }
4149     } else {
4150       assert(lastAddr == endAddr, "consistency check");
4151       assert(numDirtyCards == 0, "consistency check");
4152       break;
4153     }
4154   }
4155   verify_work_stacks_empty();
4156   verify_overflow_empty();
4157   return cumNumDirtyCards;
4158 }
4159 
4160 // NOTE: preclean_mod_union_table() above and preclean_card_table()
4161 // below are largely identical; if you need to modify
4162 // one of these methods, please check the other method too.
4163 
4164 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* gen,
4165   ScanMarkedObjectsAgainCarefullyClosure* cl) {
4166   // strategy: it's similar to precleamModUnionTable above, in that
4167   // we accumulate contiguous ranges of dirty cards, mark these cards
4168   // precleaned, then scan the region covered by these cards.
4169   HeapWord* endAddr   = (HeapWord*)(gen->_virtual_space.high());
4170   HeapWord* startAddr = (HeapWord*)(gen->_virtual_space.low());
4171 
4172   cl->setFreelistLock(gen->freelistLock());   // needed for yielding
4173 
4174   size_t numDirtyCards, cumNumDirtyCards;
4175   HeapWord *lastAddr, *nextAddr;
4176 
4177   for (cumNumDirtyCards = numDirtyCards = 0,
4178        nextAddr = lastAddr = startAddr;
4179        nextAddr < endAddr;
4180        nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4181 
4182     ResourceMark rm;
4183     HandleMark   hm;
4184 
4185     MemRegion dirtyRegion;
4186     {
4187       // See comments in "Precleaning notes" above on why we
4188       // do this locking. XXX Could the locking overheads be
4189       // too high when dirty cards are sparse? [I don't think so.]
4190       stopTimer();
4191       CMSTokenSync x(true); // is cms thread
4192       startTimer();
4193       sample_eden();
4194       // Get and clear dirty region from card table
4195       dirtyRegion = _ct->ct_bs()->dirty_card_range_after_reset(
4196                                     MemRegion(nextAddr, endAddr),
4197                                     true,
4198                                     CardTableModRefBS::precleaned_card_val());
4199 
4200       assert(dirtyRegion.start() >= nextAddr,
4201              "returned region inconsistent?");
4202     }
4203     lastAddr = dirtyRegion.end();
4204     numDirtyCards =
4205       dirtyRegion.word_size()/CardTableModRefBS::card_size_in_words;
4206 
4207     if (!dirtyRegion.is_empty()) {
4208       stopTimer();
4209       CMSTokenSyncWithLocks ts(true, gen->freelistLock(), bitMapLock());
4210       startTimer();
4211       sample_eden();
4212       verify_work_stacks_empty();
4213       verify_overflow_empty();
4214       HeapWord* stop_point =
4215         gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4216       if (stop_point != NULL) {
4217         assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4218                "Should only be AbortablePreclean.");
4219         _ct->ct_bs()->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4220         if (should_abort_preclean()) {
4221           break; // out of preclean loop
4222         } else {
4223           // Compute the next address at which preclean should pick up.
4224           lastAddr = next_card_start_after_block(stop_point);
4225         }
4226       }
4227     } else {
4228       break;
4229     }
4230   }
4231   verify_work_stacks_empty();
4232   verify_overflow_empty();
4233   return cumNumDirtyCards;
4234 }
4235 
4236 class PrecleanKlassClosure : public KlassClosure {
4237   KlassToOopClosure _cm_klass_closure;
4238  public:
4239   PrecleanKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4240   void do_klass(Klass* k) {
4241     if (k->has_accumulated_modified_oops()) {
4242       k->clear_accumulated_modified_oops();
4243 
4244       _cm_klass_closure.do_klass(k);
4245     }
4246   }
4247 };
4248 
4249 // The freelist lock is needed to prevent asserts, is it really needed?
4250 void CMSCollector::preclean_klasses(MarkRefsIntoAndScanClosure* cl, Mutex* freelistLock) {
4251 
4252   cl->set_freelistLock(freelistLock);
4253 
4254   CMSTokenSyncWithLocks ts(true, freelistLock, bitMapLock());
4255 
4256   // SSS: Add equivalent to ScanMarkedObjectsAgainCarefullyClosure::do_yield_check and should_abort_preclean?
4257   // SSS: We should probably check if precleaning should be aborted, at suitable intervals?
4258   PrecleanKlassClosure preclean_klass_closure(cl);
4259   ClassLoaderDataGraph::classes_do(&preclean_klass_closure);
4260 
4261   verify_work_stacks_empty();
4262   verify_overflow_empty();
4263 }
4264 
4265 void CMSCollector::checkpointRootsFinal() {
4266   assert(_collectorState == FinalMarking, "incorrect state transition?");
4267   check_correct_thread_executing();
4268   // world is stopped at this checkpoint
4269   assert(SafepointSynchronize::is_at_safepoint(),
4270          "world should be stopped");
4271   TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
4272 
4273   verify_work_stacks_empty();
4274   verify_overflow_empty();
4275 
4276   if (PrintGCDetails) {
4277     gclog_or_tty->print("[YG occupancy: "SIZE_FORMAT" K ("SIZE_FORMAT" K)]",
4278                         _young_gen->used() / K,
4279                         _young_gen->capacity() / K);
4280   }
4281   {
4282     if (CMSScavengeBeforeRemark) {
4283       GenCollectedHeap* gch = GenCollectedHeap::heap();
4284       // Temporarily set flag to false, GCH->do_collection will
4285       // expect it to be false and set to true
4286       FlagSetting fl(gch->_is_gc_active, false);
4287       NOT_PRODUCT(GCTraceTime t("Scavenge-Before-Remark",
4288         PrintGCDetails && Verbose, true, _gc_timer_cm, _gc_tracer_cm->gc_id());)
4289       int level = _cmsGen->level() - 1;
4290       if (level >= 0) {
4291         gch->do_collection(true,        // full (i.e. force, see below)
4292                            false,       // !clear_all_soft_refs
4293                            0,           // size
4294                            false,       // is_tlab
4295                            level        // max_level
4296                           );
4297       }
4298     }
4299     FreelistLocker x(this);
4300     MutexLockerEx y(bitMapLock(),
4301                     Mutex::_no_safepoint_check_flag);
4302     checkpointRootsFinalWork();
4303   }
4304   verify_work_stacks_empty();
4305   verify_overflow_empty();
4306 }
4307 
4308 void CMSCollector::checkpointRootsFinalWork() {
4309   NOT_PRODUCT(GCTraceTime tr("checkpointRootsFinalWork", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());)
4310 
4311   assert(haveFreelistLocks(), "must have free list locks");
4312   assert_lock_strong(bitMapLock());
4313 
4314   ResourceMark rm;
4315   HandleMark   hm;
4316 
4317   GenCollectedHeap* gch = GenCollectedHeap::heap();
4318 
4319   if (should_unload_classes()) {
4320     CodeCache::gc_prologue();
4321   }
4322   assert(haveFreelistLocks(), "must have free list locks");
4323   assert_lock_strong(bitMapLock());
4324 
4325   // We might assume that we need not fill TLAB's when
4326   // CMSScavengeBeforeRemark is set, because we may have just done
4327   // a scavenge which would have filled all TLAB's -- and besides
4328   // Eden would be empty. This however may not always be the case --
4329   // for instance although we asked for a scavenge, it may not have
4330   // happened because of a JNI critical section. We probably need
4331   // a policy for deciding whether we can in that case wait until
4332   // the critical section releases and then do the remark following
4333   // the scavenge, and skip it here. In the absence of that policy,
4334   // or of an indication of whether the scavenge did indeed occur,
4335   // we cannot rely on TLAB's having been filled and must do
4336   // so here just in case a scavenge did not happen.
4337   gch->ensure_parsability(false);  // fill TLAB's, but no need to retire them
4338   // Update the saved marks which may affect the root scans.
4339   gch->save_marks();
4340 
4341   if (CMSPrintEdenSurvivorChunks) {
4342     print_eden_and_survivor_chunk_arrays();
4343   }
4344 
4345   {
4346     COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
4347 
4348     // Note on the role of the mod union table:
4349     // Since the marker in "markFromRoots" marks concurrently with
4350     // mutators, it is possible for some reachable objects not to have been
4351     // scanned. For instance, an only reference to an object A was
4352     // placed in object B after the marker scanned B. Unless B is rescanned,
4353     // A would be collected. Such updates to references in marked objects
4354     // are detected via the mod union table which is the set of all cards
4355     // dirtied since the first checkpoint in this GC cycle and prior to
4356     // the most recent young generation GC, minus those cleaned up by the
4357     // concurrent precleaning.
4358     if (CMSParallelRemarkEnabled) {
4359       GCTraceTime t("Rescan (parallel) ", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
4360       do_remark_parallel();
4361     } else {
4362       GCTraceTime t("Rescan (non-parallel) ", PrintGCDetails, false,
4363                   _gc_timer_cm, _gc_tracer_cm->gc_id());
4364       do_remark_non_parallel();
4365     }
4366   }
4367   verify_work_stacks_empty();
4368   verify_overflow_empty();
4369 
4370   {
4371     NOT_PRODUCT(GCTraceTime ts("refProcessingWork", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());)
4372     refProcessingWork();
4373   }
4374   verify_work_stacks_empty();
4375   verify_overflow_empty();
4376 
4377   if (should_unload_classes()) {
4378     CodeCache::gc_epilogue();
4379   }
4380   JvmtiExport::gc_epilogue();
4381 
4382   // If we encountered any (marking stack / work queue) overflow
4383   // events during the current CMS cycle, take appropriate
4384   // remedial measures, where possible, so as to try and avoid
4385   // recurrence of that condition.
4386   assert(_markStack.isEmpty(), "No grey objects");
4387   size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
4388                      _ser_kac_ovflw        + _ser_kac_preclean_ovflw;
4389   if (ser_ovflw > 0) {
4390     if (PrintCMSStatistics != 0) {
4391       gclog_or_tty->print_cr("Marking stack overflow (benign) "
4392         "(pmc_pc="SIZE_FORMAT", pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT
4393         ", kac_preclean="SIZE_FORMAT")",
4394         _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw,
4395         _ser_kac_ovflw, _ser_kac_preclean_ovflw);
4396     }
4397     _markStack.expand();
4398     _ser_pmc_remark_ovflw = 0;
4399     _ser_pmc_preclean_ovflw = 0;
4400     _ser_kac_preclean_ovflw = 0;
4401     _ser_kac_ovflw = 0;
4402   }
4403   if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
4404     if (PrintCMSStatistics != 0) {
4405       gclog_or_tty->print_cr("Work queue overflow (benign) "
4406         "(pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT")",
4407         _par_pmc_remark_ovflw, _par_kac_ovflw);
4408     }
4409     _par_pmc_remark_ovflw = 0;
4410     _par_kac_ovflw = 0;
4411   }
4412   if (PrintCMSStatistics != 0) {
4413      if (_markStack._hit_limit > 0) {
4414        gclog_or_tty->print_cr(" (benign) Hit max stack size limit ("SIZE_FORMAT")",
4415                               _markStack._hit_limit);
4416      }
4417      if (_markStack._failed_double > 0) {
4418        gclog_or_tty->print_cr(" (benign) Failed stack doubling ("SIZE_FORMAT"),"
4419                               " current capacity "SIZE_FORMAT,
4420                               _markStack._failed_double,
4421                               _markStack.capacity());
4422      }
4423   }
4424   _markStack._hit_limit = 0;
4425   _markStack._failed_double = 0;
4426 
4427   if ((VerifyAfterGC || VerifyDuringGC) &&
4428       GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
4429     verify_after_remark();
4430   }
4431 
4432   _gc_tracer_cm->report_object_count_after_gc(&_is_alive_closure);
4433 
4434   // Change under the freelistLocks.
4435   _collectorState = Sweeping;
4436   // Call isAllClear() under bitMapLock
4437   assert(_modUnionTable.isAllClear(),
4438       "Should be clear by end of the final marking");
4439   assert(_ct->klass_rem_set()->mod_union_is_clear(),
4440       "Should be clear by end of the final marking");
4441 }
4442 
4443 void CMSParInitialMarkTask::work(uint worker_id) {
4444   elapsedTimer _timer;
4445   ResourceMark rm;
4446   HandleMark   hm;
4447 
4448   // ---------- scan from roots --------------
4449   _timer.start();
4450   GenCollectedHeap* gch = GenCollectedHeap::heap();
4451   Par_MarkRefsIntoClosure par_mri_cl(_collector->_span, &(_collector->_markBitMap));
4452 
4453   // ---------- young gen roots --------------
4454   {
4455     work_on_young_gen_roots(worker_id, &par_mri_cl);
4456     _timer.stop();
4457     if (PrintCMSStatistics != 0) {
4458       gclog_or_tty->print_cr(
4459         "Finished young gen initial mark scan work in %dth thread: %3.3f sec",
4460         worker_id, _timer.seconds());
4461     }
4462   }
4463 
4464   // ---------- remaining roots --------------
4465   _timer.reset();
4466   _timer.start();
4467 
4468   CLDToOopClosure cld_closure(&par_mri_cl, true);
4469 
4470   gch->gen_process_roots(_strong_roots_scope,
4471                          _collector->_cmsGen->level(),
4472                          false,     // yg was scanned above
4473                          GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4474                          _collector->should_unload_classes(),
4475                          &par_mri_cl,
4476                          NULL,
4477                          &cld_closure);
4478   assert(_collector->should_unload_classes()
4479          || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4480          "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4481   _timer.stop();
4482   if (PrintCMSStatistics != 0) {
4483     gclog_or_tty->print_cr(
4484       "Finished remaining root initial mark scan work in %dth thread: %3.3f sec",
4485       worker_id, _timer.seconds());
4486   }
4487 }
4488 
4489 // Parallel remark task
4490 class CMSParRemarkTask: public CMSParMarkTask {
4491   CompactibleFreeListSpace* _cms_space;
4492 
4493   // The per-thread work queues, available here for stealing.
4494   OopTaskQueueSet*       _task_queues;
4495   ParallelTaskTerminator _term;
4496   StrongRootsScope*      _strong_roots_scope;
4497 
4498  public:
4499   // A value of 0 passed to n_workers will cause the number of
4500   // workers to be taken from the active workers in the work gang.
4501   CMSParRemarkTask(CMSCollector* collector,
4502                    CompactibleFreeListSpace* cms_space,
4503                    uint n_workers, FlexibleWorkGang* workers,
4504                    OopTaskQueueSet* task_queues,
4505                    StrongRootsScope* strong_roots_scope):
4506     CMSParMarkTask("Rescan roots and grey objects in parallel",
4507                    collector, n_workers),
4508     _cms_space(cms_space),
4509     _task_queues(task_queues),
4510     _term(n_workers, task_queues),
4511     _strong_roots_scope(strong_roots_scope) { }
4512 
4513   OopTaskQueueSet* task_queues() { return _task_queues; }
4514 
4515   OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
4516 
4517   ParallelTaskTerminator* terminator() { return &_term; }
4518   uint n_workers() { return _n_workers; }
4519 
4520   void work(uint worker_id);
4521 
4522  private:
4523   // ... of  dirty cards in old space
4524   void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
4525                                   Par_MarkRefsIntoAndScanClosure* cl);
4526 
4527   // ... work stealing for the above
4528   void do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl, int* seed);
4529 };
4530 
4531 class RemarkKlassClosure : public KlassClosure {
4532   KlassToOopClosure _cm_klass_closure;
4533  public:
4534   RemarkKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4535   void do_klass(Klass* k) {
4536     // Check if we have modified any oops in the Klass during the concurrent marking.
4537     if (k->has_accumulated_modified_oops()) {
4538       k->clear_accumulated_modified_oops();
4539 
4540       // We could have transfered the current modified marks to the accumulated marks,
4541       // like we do with the Card Table to Mod Union Table. But it's not really necessary.
4542     } else if (k->has_modified_oops()) {
4543       // Don't clear anything, this info is needed by the next young collection.
4544     } else {
4545       // No modified oops in the Klass.
4546       return;
4547     }
4548 
4549     // The klass has modified fields, need to scan the klass.
4550     _cm_klass_closure.do_klass(k);
4551   }
4552 };
4553 
4554 void CMSParMarkTask::work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl) {
4555   ParNewGeneration* young_gen = _collector->_young_gen;
4556   ContiguousSpace* eden_space = young_gen->eden();
4557   ContiguousSpace* from_space = young_gen->from();
4558   ContiguousSpace* to_space   = young_gen->to();
4559 
4560   HeapWord** eca = _collector->_eden_chunk_array;
4561   size_t     ect = _collector->_eden_chunk_index;
4562   HeapWord** sca = _collector->_survivor_chunk_array;
4563   size_t     sct = _collector->_survivor_chunk_index;
4564 
4565   assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
4566   assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
4567 
4568   do_young_space_rescan(worker_id, cl, to_space, NULL, 0);
4569   do_young_space_rescan(worker_id, cl, from_space, sca, sct);
4570   do_young_space_rescan(worker_id, cl, eden_space, eca, ect);
4571 }
4572 
4573 // work_queue(i) is passed to the closure
4574 // Par_MarkRefsIntoAndScanClosure.  The "i" parameter
4575 // also is passed to do_dirty_card_rescan_tasks() and to
4576 // do_work_steal() to select the i-th task_queue.
4577 
4578 void CMSParRemarkTask::work(uint worker_id) {
4579   elapsedTimer _timer;
4580   ResourceMark rm;
4581   HandleMark   hm;
4582 
4583   // ---------- rescan from roots --------------
4584   _timer.start();
4585   GenCollectedHeap* gch = GenCollectedHeap::heap();
4586   Par_MarkRefsIntoAndScanClosure par_mrias_cl(_collector,
4587     _collector->_span, _collector->ref_processor(),
4588     &(_collector->_markBitMap),
4589     work_queue(worker_id));
4590 
4591   // Rescan young gen roots first since these are likely
4592   // coarsely partitioned and may, on that account, constitute
4593   // the critical path; thus, it's best to start off that
4594   // work first.
4595   // ---------- young gen roots --------------
4596   {
4597     work_on_young_gen_roots(worker_id, &par_mrias_cl);
4598     _timer.stop();
4599     if (PrintCMSStatistics != 0) {
4600       gclog_or_tty->print_cr(
4601         "Finished young gen rescan work in %dth thread: %3.3f sec",
4602         worker_id, _timer.seconds());
4603     }
4604   }
4605 
4606   // ---------- remaining roots --------------
4607   _timer.reset();
4608   _timer.start();
4609   gch->gen_process_roots(_strong_roots_scope,
4610                          _collector->_cmsGen->level(),
4611                          false,     // yg was scanned above
4612                          GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4613                          _collector->should_unload_classes(),
4614                          &par_mrias_cl,
4615                          NULL,
4616                          NULL);     // The dirty klasses will be handled below
4617 
4618   assert(_collector->should_unload_classes()
4619          || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4620          "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4621   _timer.stop();
4622   if (PrintCMSStatistics != 0) {
4623     gclog_or_tty->print_cr(
4624       "Finished remaining root rescan work in %dth thread: %3.3f sec",
4625       worker_id, _timer.seconds());
4626   }
4627 
4628   // ---------- unhandled CLD scanning ----------
4629   if (worker_id == 0) { // Single threaded at the moment.
4630     _timer.reset();
4631     _timer.start();
4632 
4633     // Scan all new class loader data objects and new dependencies that were
4634     // introduced during concurrent marking.
4635     ResourceMark rm;
4636     GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
4637     for (int i = 0; i < array->length(); i++) {
4638       par_mrias_cl.do_class_loader_data(array->at(i));
4639     }
4640 
4641     // We don't need to keep track of new CLDs anymore.
4642     ClassLoaderDataGraph::remember_new_clds(false);
4643 
4644     _timer.stop();
4645     if (PrintCMSStatistics != 0) {
4646       gclog_or_tty->print_cr(
4647           "Finished unhandled CLD scanning work in %dth thread: %3.3f sec",
4648           worker_id, _timer.seconds());
4649     }
4650   }
4651 
4652   // ---------- dirty klass scanning ----------
4653   if (worker_id == 0) { // Single threaded at the moment.
4654     _timer.reset();
4655     _timer.start();
4656 
4657     // Scan all classes that was dirtied during the concurrent marking phase.
4658     RemarkKlassClosure remark_klass_closure(&par_mrias_cl);
4659     ClassLoaderDataGraph::classes_do(&remark_klass_closure);
4660 
4661     _timer.stop();
4662     if (PrintCMSStatistics != 0) {
4663       gclog_or_tty->print_cr(
4664           "Finished dirty klass scanning work in %dth thread: %3.3f sec",
4665           worker_id, _timer.seconds());
4666     }
4667   }
4668 
4669   // We might have added oops to ClassLoaderData::_handles during the
4670   // concurrent marking phase. These oops point to newly allocated objects
4671   // that are guaranteed to be kept alive. Either by the direct allocation
4672   // code, or when the young collector processes the roots. Hence,
4673   // we don't have to revisit the _handles block during the remark phase.
4674 
4675   // ---------- rescan dirty cards ------------
4676   _timer.reset();
4677   _timer.start();
4678 
4679   // Do the rescan tasks for each of the two spaces
4680   // (cms_space) in turn.
4681   // "worker_id" is passed to select the task_queue for "worker_id"
4682   do_dirty_card_rescan_tasks(_cms_space, worker_id, &par_mrias_cl);
4683   _timer.stop();
4684   if (PrintCMSStatistics != 0) {
4685     gclog_or_tty->print_cr(
4686       "Finished dirty card rescan work in %dth thread: %3.3f sec",
4687       worker_id, _timer.seconds());
4688   }
4689 
4690   // ---------- steal work from other threads ...
4691   // ---------- ... and drain overflow list.
4692   _timer.reset();
4693   _timer.start();
4694   do_work_steal(worker_id, &par_mrias_cl, _collector->hash_seed(worker_id));
4695   _timer.stop();
4696   if (PrintCMSStatistics != 0) {
4697     gclog_or_tty->print_cr(
4698       "Finished work stealing in %dth thread: %3.3f sec",
4699       worker_id, _timer.seconds());
4700   }
4701 }
4702 
4703 // Note that parameter "i" is not used.
4704 void
4705 CMSParMarkTask::do_young_space_rescan(uint worker_id,
4706   OopsInGenClosure* cl, ContiguousSpace* space,
4707   HeapWord** chunk_array, size_t chunk_top) {
4708   // Until all tasks completed:
4709   // . claim an unclaimed task
4710   // . compute region boundaries corresponding to task claimed
4711   //   using chunk_array
4712   // . par_oop_iterate(cl) over that region
4713 
4714   ResourceMark rm;
4715   HandleMark   hm;
4716 
4717   SequentialSubTasksDone* pst = space->par_seq_tasks();
4718 
4719   uint nth_task = 0;
4720   uint n_tasks  = pst->n_tasks();
4721 
4722   if (n_tasks > 0) {
4723     assert(pst->valid(), "Uninitialized use?");
4724     HeapWord *start, *end;
4725     while (!pst->is_task_claimed(/* reference */ nth_task)) {
4726       // We claimed task # nth_task; compute its boundaries.
4727       if (chunk_top == 0) {  // no samples were taken
4728         assert(nth_task == 0 && n_tasks == 1, "Can have only 1 eden task");
4729         start = space->bottom();
4730         end   = space->top();
4731       } else if (nth_task == 0) {
4732         start = space->bottom();
4733         end   = chunk_array[nth_task];
4734       } else if (nth_task < (uint)chunk_top) {
4735         assert(nth_task >= 1, "Control point invariant");
4736         start = chunk_array[nth_task - 1];
4737         end   = chunk_array[nth_task];
4738       } else {
4739         assert(nth_task == (uint)chunk_top, "Control point invariant");
4740         start = chunk_array[chunk_top - 1];
4741         end   = space->top();
4742       }
4743       MemRegion mr(start, end);
4744       // Verify that mr is in space
4745       assert(mr.is_empty() || space->used_region().contains(mr),
4746              "Should be in space");
4747       // Verify that "start" is an object boundary
4748       assert(mr.is_empty() || oop(mr.start())->is_oop(),
4749              "Should be an oop");
4750       space->par_oop_iterate(mr, cl);
4751     }
4752     pst->all_tasks_completed();
4753   }
4754 }
4755 
4756 void
4757 CMSParRemarkTask::do_dirty_card_rescan_tasks(
4758   CompactibleFreeListSpace* sp, int i,
4759   Par_MarkRefsIntoAndScanClosure* cl) {
4760   // Until all tasks completed:
4761   // . claim an unclaimed task
4762   // . compute region boundaries corresponding to task claimed
4763   // . transfer dirty bits ct->mut for that region
4764   // . apply rescanclosure to dirty mut bits for that region
4765 
4766   ResourceMark rm;
4767   HandleMark   hm;
4768 
4769   OopTaskQueue* work_q = work_queue(i);
4770   ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
4771   // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
4772   // CAUTION: This closure has state that persists across calls to
4773   // the work method dirty_range_iterate_clear() in that it has
4774   // embedded in it a (subtype of) UpwardsObjectClosure. The
4775   // use of that state in the embedded UpwardsObjectClosure instance
4776   // assumes that the cards are always iterated (even if in parallel
4777   // by several threads) in monotonically increasing order per each
4778   // thread. This is true of the implementation below which picks
4779   // card ranges (chunks) in monotonically increasing order globally
4780   // and, a-fortiori, in monotonically increasing order per thread
4781   // (the latter order being a subsequence of the former).
4782   // If the work code below is ever reorganized into a more chaotic
4783   // work-partitioning form than the current "sequential tasks"
4784   // paradigm, the use of that persistent state will have to be
4785   // revisited and modified appropriately. See also related
4786   // bug 4756801 work on which should examine this code to make
4787   // sure that the changes there do not run counter to the
4788   // assumptions made here and necessary for correctness and
4789   // efficiency. Note also that this code might yield inefficient
4790   // behavior in the case of very large objects that span one or
4791   // more work chunks. Such objects would potentially be scanned
4792   // several times redundantly. Work on 4756801 should try and
4793   // address that performance anomaly if at all possible. XXX
4794   MemRegion  full_span  = _collector->_span;
4795   CMSBitMap* bm    = &(_collector->_markBitMap);     // shared
4796   MarkFromDirtyCardsClosure
4797     greyRescanClosure(_collector, full_span, // entire span of interest
4798                       sp, bm, work_q, cl);
4799 
4800   SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
4801   assert(pst->valid(), "Uninitialized use?");
4802   uint nth_task = 0;
4803   const int alignment = CardTableModRefBS::card_size * BitsPerWord;
4804   MemRegion span = sp->used_region();
4805   HeapWord* start_addr = span.start();
4806   HeapWord* end_addr = (HeapWord*)round_to((intptr_t)span.end(),
4807                                            alignment);
4808   const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
4809   assert((HeapWord*)round_to((intptr_t)start_addr, alignment) ==
4810          start_addr, "Check alignment");
4811   assert((size_t)round_to((intptr_t)chunk_size, alignment) ==
4812          chunk_size, "Check alignment");
4813 
4814   while (!pst->is_task_claimed(/* reference */ nth_task)) {
4815     // Having claimed the nth_task, compute corresponding mem-region,
4816     // which is a-fortiori aligned correctly (i.e. at a MUT boundary).
4817     // The alignment restriction ensures that we do not need any
4818     // synchronization with other gang-workers while setting or
4819     // clearing bits in thus chunk of the MUT.
4820     MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
4821                                     start_addr + (nth_task+1)*chunk_size);
4822     // The last chunk's end might be way beyond end of the
4823     // used region. In that case pull back appropriately.
4824     if (this_span.end() > end_addr) {
4825       this_span.set_end(end_addr);
4826       assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
4827     }
4828     // Iterate over the dirty cards covering this chunk, marking them
4829     // precleaned, and setting the corresponding bits in the mod union
4830     // table. Since we have been careful to partition at Card and MUT-word
4831     // boundaries no synchronization is needed between parallel threads.
4832     _collector->_ct->ct_bs()->dirty_card_iterate(this_span,
4833                                                  &modUnionClosure);
4834 
4835     // Having transferred these marks into the modUnionTable,
4836     // rescan the marked objects on the dirty cards in the modUnionTable.
4837     // Even if this is at a synchronous collection, the initial marking
4838     // may have been done during an asynchronous collection so there
4839     // may be dirty bits in the mod-union table.
4840     _collector->_modUnionTable.dirty_range_iterate_clear(
4841                   this_span, &greyRescanClosure);
4842     _collector->_modUnionTable.verifyNoOneBitsInRange(
4843                                  this_span.start(),
4844                                  this_span.end());
4845   }
4846   pst->all_tasks_completed();  // declare that i am done
4847 }
4848 
4849 // . see if we can share work_queues with ParNew? XXX
4850 void
4851 CMSParRemarkTask::do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl,
4852                                 int* seed) {
4853   OopTaskQueue* work_q = work_queue(i);
4854   NOT_PRODUCT(int num_steals = 0;)
4855   oop obj_to_scan;
4856   CMSBitMap* bm = &(_collector->_markBitMap);
4857 
4858   while (true) {
4859     // Completely finish any left over work from (an) earlier round(s)
4860     cl->trim_queue(0);
4861     size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
4862                                          (size_t)ParGCDesiredObjsFromOverflowList);
4863     // Now check if there's any work in the overflow list
4864     // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
4865     // only affects the number of attempts made to get work from the
4866     // overflow list and does not affect the number of workers.  Just
4867     // pass ParallelGCThreads so this behavior is unchanged.
4868     if (_collector->par_take_from_overflow_list(num_from_overflow_list,
4869                                                 work_q,
4870                                                 ParallelGCThreads)) {
4871       // found something in global overflow list;
4872       // not yet ready to go stealing work from others.
4873       // We'd like to assert(work_q->size() != 0, ...)
4874       // because we just took work from the overflow list,
4875       // but of course we can't since all of that could have
4876       // been already stolen from us.
4877       // "He giveth and He taketh away."
4878       continue;
4879     }
4880     // Verify that we have no work before we resort to stealing
4881     assert(work_q->size() == 0, "Have work, shouldn't steal");
4882     // Try to steal from other queues that have work
4883     if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
4884       NOT_PRODUCT(num_steals++;)
4885       assert(obj_to_scan->is_oop(), "Oops, not an oop!");
4886       assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
4887       // Do scanning work
4888       obj_to_scan->oop_iterate(cl);
4889       // Loop around, finish this work, and try to steal some more
4890     } else if (terminator()->offer_termination()) {
4891         break;  // nirvana from the infinite cycle
4892     }
4893   }
4894   NOT_PRODUCT(
4895     if (PrintCMSStatistics != 0) {
4896       gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
4897     }
4898   )
4899   assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
4900          "Else our work is not yet done");
4901 }
4902 
4903 // Record object boundaries in _eden_chunk_array by sampling the eden
4904 // top in the slow-path eden object allocation code path and record
4905 // the boundaries, if CMSEdenChunksRecordAlways is true. If
4906 // CMSEdenChunksRecordAlways is false, we use the other asynchronous
4907 // sampling in sample_eden() that activates during the part of the
4908 // preclean phase.
4909 void CMSCollector::sample_eden_chunk() {
4910   if (CMSEdenChunksRecordAlways && _eden_chunk_array != NULL) {
4911     if (_eden_chunk_lock->try_lock()) {
4912       // Record a sample. This is the critical section. The contents
4913       // of the _eden_chunk_array have to be non-decreasing in the
4914       // address order.
4915       _eden_chunk_array[_eden_chunk_index] = *_top_addr;
4916       assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4917              "Unexpected state of Eden");
4918       if (_eden_chunk_index == 0 ||
4919           ((_eden_chunk_array[_eden_chunk_index] > _eden_chunk_array[_eden_chunk_index-1]) &&
4920            (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4921                           _eden_chunk_array[_eden_chunk_index-1]) >= CMSSamplingGrain))) {
4922         _eden_chunk_index++;  // commit sample
4923       }
4924       _eden_chunk_lock->unlock();
4925     }
4926   }
4927 }
4928 
4929 // Return a thread-local PLAB recording array, as appropriate.
4930 void* CMSCollector::get_data_recorder(int thr_num) {
4931   if (_survivor_plab_array != NULL &&
4932       (CMSPLABRecordAlways ||
4933        (_collectorState > Marking && _collectorState < FinalMarking))) {
4934     assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
4935     ChunkArray* ca = &_survivor_plab_array[thr_num];
4936     ca->reset();   // clear it so that fresh data is recorded
4937     return (void*) ca;
4938   } else {
4939     return NULL;
4940   }
4941 }
4942 
4943 // Reset all the thread-local PLAB recording arrays
4944 void CMSCollector::reset_survivor_plab_arrays() {
4945   for (uint i = 0; i < ParallelGCThreads; i++) {
4946     _survivor_plab_array[i].reset();
4947   }
4948 }
4949 
4950 // Merge the per-thread plab arrays into the global survivor chunk
4951 // array which will provide the partitioning of the survivor space
4952 // for CMS initial scan and rescan.
4953 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv,
4954                                               int no_of_gc_threads) {
4955   assert(_survivor_plab_array  != NULL, "Error");
4956   assert(_survivor_chunk_array != NULL, "Error");
4957   assert(_collectorState == FinalMarking ||
4958          (CMSParallelInitialMarkEnabled && _collectorState == InitialMarking), "Error");
4959   for (int j = 0; j < no_of_gc_threads; j++) {
4960     _cursor[j] = 0;
4961   }
4962   HeapWord* top = surv->top();
4963   size_t i;
4964   for (i = 0; i < _survivor_chunk_capacity; i++) {  // all sca entries
4965     HeapWord* min_val = top;          // Higher than any PLAB address
4966     uint      min_tid = 0;            // position of min_val this round
4967     for (int j = 0; j < no_of_gc_threads; j++) {
4968       ChunkArray* cur_sca = &_survivor_plab_array[j];
4969       if (_cursor[j] == cur_sca->end()) {
4970         continue;
4971       }
4972       assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
4973       HeapWord* cur_val = cur_sca->nth(_cursor[j]);
4974       assert(surv->used_region().contains(cur_val), "Out of bounds value");
4975       if (cur_val < min_val) {
4976         min_tid = j;
4977         min_val = cur_val;
4978       } else {
4979         assert(cur_val < top, "All recorded addresses should be less");
4980       }
4981     }
4982     // At this point min_val and min_tid are respectively
4983     // the least address in _survivor_plab_array[j]->nth(_cursor[j])
4984     // and the thread (j) that witnesses that address.
4985     // We record this address in the _survivor_chunk_array[i]
4986     // and increment _cursor[min_tid] prior to the next round i.
4987     if (min_val == top) {
4988       break;
4989     }
4990     _survivor_chunk_array[i] = min_val;
4991     _cursor[min_tid]++;
4992   }
4993   // We are all done; record the size of the _survivor_chunk_array
4994   _survivor_chunk_index = i; // exclusive: [0, i)
4995   if (PrintCMSStatistics > 0) {
4996     gclog_or_tty->print(" (Survivor:" SIZE_FORMAT "chunks) ", i);
4997   }
4998   // Verify that we used up all the recorded entries
4999   #ifdef ASSERT
5000     size_t total = 0;
5001     for (int j = 0; j < no_of_gc_threads; j++) {
5002       assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
5003       total += _cursor[j];
5004     }
5005     assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
5006     // Check that the merged array is in sorted order
5007     if (total > 0) {
5008       for (size_t i = 0; i < total - 1; i++) {
5009         if (PrintCMSStatistics > 0) {
5010           gclog_or_tty->print(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
5011                               i, p2i(_survivor_chunk_array[i]));
5012         }
5013         assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
5014                "Not sorted");
5015       }
5016     }
5017   #endif // ASSERT
5018 }
5019 
5020 // Set up the space's par_seq_tasks structure for work claiming
5021 // for parallel initial scan and rescan of young gen.
5022 // See ParRescanTask where this is currently used.
5023 void
5024 CMSCollector::
5025 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
5026   assert(n_threads > 0, "Unexpected n_threads argument");
5027 
5028   // Eden space
5029   if (!_young_gen->eden()->is_empty()) {
5030     SequentialSubTasksDone* pst = _young_gen->eden()->par_seq_tasks();
5031     assert(!pst->valid(), "Clobbering existing data?");
5032     // Each valid entry in [0, _eden_chunk_index) represents a task.
5033     size_t n_tasks = _eden_chunk_index + 1;
5034     assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
5035     // Sets the condition for completion of the subtask (how many threads
5036     // need to finish in order to be done).
5037     pst->set_n_threads(n_threads);
5038     pst->set_n_tasks((int)n_tasks);
5039   }
5040 
5041   // Merge the survivor plab arrays into _survivor_chunk_array
5042   if (_survivor_plab_array != NULL) {
5043     merge_survivor_plab_arrays(_young_gen->from(), n_threads);
5044   } else {
5045     assert(_survivor_chunk_index == 0, "Error");
5046   }
5047 
5048   // To space
5049   {
5050     SequentialSubTasksDone* pst = _young_gen->to()->par_seq_tasks();
5051     assert(!pst->valid(), "Clobbering existing data?");
5052     // Sets the condition for completion of the subtask (how many threads
5053     // need to finish in order to be done).
5054     pst->set_n_threads(n_threads);
5055     pst->set_n_tasks(1);
5056     assert(pst->valid(), "Error");
5057   }
5058 
5059   // From space
5060   {
5061     SequentialSubTasksDone* pst = _young_gen->from()->par_seq_tasks();
5062     assert(!pst->valid(), "Clobbering existing data?");
5063     size_t n_tasks = _survivor_chunk_index + 1;
5064     assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
5065     // Sets the condition for completion of the subtask (how many threads
5066     // need to finish in order to be done).
5067     pst->set_n_threads(n_threads);
5068     pst->set_n_tasks((int)n_tasks);
5069     assert(pst->valid(), "Error");
5070   }
5071 }
5072 
5073 // Parallel version of remark
5074 void CMSCollector::do_remark_parallel() {
5075   GenCollectedHeap* gch = GenCollectedHeap::heap();
5076   FlexibleWorkGang* workers = gch->workers();
5077   assert(workers != NULL, "Need parallel worker threads.");
5078   // Choose to use the number of GC workers most recently set
5079   // into "active_workers".
5080   uint n_workers = workers->active_workers();
5081 
5082   CompactibleFreeListSpace* cms_space  = _cmsGen->cmsSpace();
5083 
5084   StrongRootsScope srs(n_workers);
5085 
5086   CMSParRemarkTask tsk(this, cms_space, n_workers, workers, task_queues(), &srs);
5087 
5088   // We won't be iterating over the cards in the card table updating
5089   // the younger_gen cards, so we shouldn't call the following else
5090   // the verification code as well as subsequent younger_refs_iterate
5091   // code would get confused. XXX
5092   // gch->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
5093 
5094   // The young gen rescan work will not be done as part of
5095   // process_roots (which currently doesn't know how to
5096   // parallelize such a scan), but rather will be broken up into
5097   // a set of parallel tasks (via the sampling that the [abortable]
5098   // preclean phase did of eden, plus the [two] tasks of
5099   // scanning the [two] survivor spaces. Further fine-grain
5100   // parallelization of the scanning of the survivor spaces
5101   // themselves, and of precleaning of the younger gen itself
5102   // is deferred to the future.
5103   initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
5104 
5105   // The dirty card rescan work is broken up into a "sequence"
5106   // of parallel tasks (per constituent space) that are dynamically
5107   // claimed by the parallel threads.
5108   cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
5109 
5110   // It turns out that even when we're using 1 thread, doing the work in a
5111   // separate thread causes wide variance in run times.  We can't help this
5112   // in the multi-threaded case, but we special-case n=1 here to get
5113   // repeatable measurements of the 1-thread overhead of the parallel code.
5114   if (n_workers > 1) {
5115     // Make refs discovery MT-safe, if it isn't already: it may not
5116     // necessarily be so, since it's possible that we are doing
5117     // ST marking.
5118     ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), true);
5119     workers->run_task(&tsk);
5120   } else {
5121     ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5122     tsk.work(0);
5123   }
5124 
5125   // restore, single-threaded for now, any preserved marks
5126   // as a result of work_q overflow
5127   restore_preserved_marks_if_any();
5128 }
5129 
5130 // Non-parallel version of remark
5131 void CMSCollector::do_remark_non_parallel() {
5132   ResourceMark rm;
5133   HandleMark   hm;
5134   GenCollectedHeap* gch = GenCollectedHeap::heap();
5135   ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5136 
5137   MarkRefsIntoAndScanClosure
5138     mrias_cl(_span, ref_processor(), &_markBitMap, NULL /* not precleaning */,
5139              &_markStack, this,
5140              false /* should_yield */, false /* not precleaning */);
5141   MarkFromDirtyCardsClosure
5142     markFromDirtyCardsClosure(this, _span,
5143                               NULL,  // space is set further below
5144                               &_markBitMap, &_markStack, &mrias_cl);
5145   {
5146     GCTraceTime t("grey object rescan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5147     // Iterate over the dirty cards, setting the corresponding bits in the
5148     // mod union table.
5149     {
5150       ModUnionClosure modUnionClosure(&_modUnionTable);
5151       _ct->ct_bs()->dirty_card_iterate(
5152                       _cmsGen->used_region(),
5153                       &modUnionClosure);
5154     }
5155     // Having transferred these marks into the modUnionTable, we just need
5156     // to rescan the marked objects on the dirty cards in the modUnionTable.
5157     // The initial marking may have been done during an asynchronous
5158     // collection so there may be dirty bits in the mod-union table.
5159     const int alignment =
5160       CardTableModRefBS::card_size * BitsPerWord;
5161     {
5162       // ... First handle dirty cards in CMS gen
5163       markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
5164       MemRegion ur = _cmsGen->used_region();
5165       HeapWord* lb = ur.start();
5166       HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
5167       MemRegion cms_span(lb, ub);
5168       _modUnionTable.dirty_range_iterate_clear(cms_span,
5169                                                &markFromDirtyCardsClosure);
5170       verify_work_stacks_empty();
5171       if (PrintCMSStatistics != 0) {
5172         gclog_or_tty->print(" (re-scanned "SIZE_FORMAT" dirty cards in cms gen) ",
5173           markFromDirtyCardsClosure.num_dirty_cards());
5174       }
5175     }
5176   }
5177   if (VerifyDuringGC &&
5178       GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5179     HandleMark hm;  // Discard invalid handles created during verification
5180     Universe::verify();
5181   }
5182   {
5183     GCTraceTime t("root rescan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5184 
5185     verify_work_stacks_empty();
5186 
5187     gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
5188     StrongRootsScope srs(1);
5189 
5190     gch->gen_process_roots(&srs,
5191                            _cmsGen->level(),
5192                            true,  // younger gens as roots
5193                            GenCollectedHeap::ScanningOption(roots_scanning_options()),
5194                            should_unload_classes(),
5195                            &mrias_cl,
5196                            NULL,
5197                            NULL); // The dirty klasses will be handled below
5198 
5199     assert(should_unload_classes()
5200            || (roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
5201            "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5202   }
5203 
5204   {
5205     GCTraceTime t("visit unhandled CLDs", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5206 
5207     verify_work_stacks_empty();
5208 
5209     // Scan all class loader data objects that might have been introduced
5210     // during concurrent marking.
5211     ResourceMark rm;
5212     GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
5213     for (int i = 0; i < array->length(); i++) {
5214       mrias_cl.do_class_loader_data(array->at(i));
5215     }
5216 
5217     // We don't need to keep track of new CLDs anymore.
5218     ClassLoaderDataGraph::remember_new_clds(false);
5219 
5220     verify_work_stacks_empty();
5221   }
5222 
5223   {
5224     GCTraceTime t("dirty klass scan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5225 
5226     verify_work_stacks_empty();
5227 
5228     RemarkKlassClosure remark_klass_closure(&mrias_cl);
5229     ClassLoaderDataGraph::classes_do(&remark_klass_closure);
5230 
5231     verify_work_stacks_empty();
5232   }
5233 
5234   // We might have added oops to ClassLoaderData::_handles during the
5235   // concurrent marking phase. These oops point to newly allocated objects
5236   // that are guaranteed to be kept alive. Either by the direct allocation
5237   // code, or when the young collector processes the roots. Hence,
5238   // we don't have to revisit the _handles block during the remark phase.
5239 
5240   verify_work_stacks_empty();
5241   // Restore evacuated mark words, if any, used for overflow list links
5242   if (!CMSOverflowEarlyRestoration) {
5243     restore_preserved_marks_if_any();
5244   }
5245   verify_overflow_empty();
5246 }
5247 
5248 ////////////////////////////////////////////////////////
5249 // Parallel Reference Processing Task Proxy Class
5250 ////////////////////////////////////////////////////////
5251 class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues {
5252   typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
5253   CMSCollector*          _collector;
5254   CMSBitMap*             _mark_bit_map;
5255   const MemRegion        _span;
5256   ProcessTask&           _task;
5257 
5258 public:
5259   CMSRefProcTaskProxy(ProcessTask&     task,
5260                       CMSCollector*    collector,
5261                       const MemRegion& span,
5262                       CMSBitMap*       mark_bit_map,
5263                       AbstractWorkGang* workers,
5264                       OopTaskQueueSet* task_queues):
5265     AbstractGangTaskWOopQueues("Process referents by policy in parallel",
5266       task_queues,
5267       workers->active_workers()),
5268     _task(task),
5269     _collector(collector), _span(span), _mark_bit_map(mark_bit_map)
5270   {
5271     assert(_collector->_span.equals(_span) && !_span.is_empty(),
5272            "Inconsistency in _span");
5273   }
5274 
5275   OopTaskQueueSet* task_queues() { return queues(); }
5276 
5277   OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5278 
5279   void do_work_steal(int i,
5280                      CMSParDrainMarkingStackClosure* drain,
5281                      CMSParKeepAliveClosure* keep_alive,
5282                      int* seed);
5283 
5284   virtual void work(uint worker_id);
5285 };
5286 
5287 void CMSRefProcTaskProxy::work(uint worker_id) {
5288   ResourceMark rm;
5289   HandleMark hm;
5290   assert(_collector->_span.equals(_span), "Inconsistency in _span");
5291   CMSParKeepAliveClosure par_keep_alive(_collector, _span,
5292                                         _mark_bit_map,
5293                                         work_queue(worker_id));
5294   CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
5295                                                  _mark_bit_map,
5296                                                  work_queue(worker_id));
5297   CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
5298   _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack);
5299   if (_task.marks_oops_alive()) {
5300     do_work_steal(worker_id, &par_drain_stack, &par_keep_alive,
5301                   _collector->hash_seed(worker_id));
5302   }
5303   assert(work_queue(worker_id)->size() == 0, "work_queue should be empty");
5304   assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
5305 }
5306 
5307 class CMSRefEnqueueTaskProxy: public AbstractGangTask {
5308   typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
5309   EnqueueTask& _task;
5310 
5311 public:
5312   CMSRefEnqueueTaskProxy(EnqueueTask& task)
5313     : AbstractGangTask("Enqueue reference objects in parallel"),
5314       _task(task)
5315   { }
5316 
5317   virtual void work(uint worker_id)
5318   {
5319     _task.work(worker_id);
5320   }
5321 };
5322 
5323 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
5324   MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue):
5325    _span(span),
5326    _bit_map(bit_map),
5327    _work_queue(work_queue),
5328    _mark_and_push(collector, span, bit_map, work_queue),
5329    _low_water_mark(MIN2((work_queue->max_elems()/4),
5330                         ((uint)CMSWorkQueueDrainThreshold * ParallelGCThreads)))
5331 { }
5332 
5333 // . see if we can share work_queues with ParNew? XXX
5334 void CMSRefProcTaskProxy::do_work_steal(int i,
5335   CMSParDrainMarkingStackClosure* drain,
5336   CMSParKeepAliveClosure* keep_alive,
5337   int* seed) {
5338   OopTaskQueue* work_q = work_queue(i);
5339   NOT_PRODUCT(int num_steals = 0;)
5340   oop obj_to_scan;
5341 
5342   while (true) {
5343     // Completely finish any left over work from (an) earlier round(s)
5344     drain->trim_queue(0);
5345     size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5346                                          (size_t)ParGCDesiredObjsFromOverflowList);
5347     // Now check if there's any work in the overflow list
5348     // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5349     // only affects the number of attempts made to get work from the
5350     // overflow list and does not affect the number of workers.  Just
5351     // pass ParallelGCThreads so this behavior is unchanged.
5352     if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5353                                                 work_q,
5354                                                 ParallelGCThreads)) {
5355       // Found something in global overflow list;
5356       // not yet ready to go stealing work from others.
5357       // We'd like to assert(work_q->size() != 0, ...)
5358       // because we just took work from the overflow list,
5359       // but of course we can't, since all of that might have
5360       // been already stolen from us.
5361       continue;
5362     }
5363     // Verify that we have no work before we resort to stealing
5364     assert(work_q->size() == 0, "Have work, shouldn't steal");
5365     // Try to steal from other queues that have work
5366     if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5367       NOT_PRODUCT(num_steals++;)
5368       assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5369       assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5370       // Do scanning work
5371       obj_to_scan->oop_iterate(keep_alive);
5372       // Loop around, finish this work, and try to steal some more
5373     } else if (terminator()->offer_termination()) {
5374       break;  // nirvana from the infinite cycle
5375     }
5376   }
5377   NOT_PRODUCT(
5378     if (PrintCMSStatistics != 0) {
5379       gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5380     }
5381   )
5382 }
5383 
5384 void CMSRefProcTaskExecutor::execute(ProcessTask& task)
5385 {
5386   GenCollectedHeap* gch = GenCollectedHeap::heap();
5387   FlexibleWorkGang* workers = gch->workers();
5388   assert(workers != NULL, "Need parallel worker threads.");
5389   CMSRefProcTaskProxy rp_task(task, &_collector,
5390                               _collector.ref_processor()->span(),
5391                               _collector.markBitMap(),
5392                               workers, _collector.task_queues());
5393   workers->run_task(&rp_task);
5394 }
5395 
5396 void CMSRefProcTaskExecutor::execute(EnqueueTask& task)
5397 {
5398 
5399   GenCollectedHeap* gch = GenCollectedHeap::heap();
5400   FlexibleWorkGang* workers = gch->workers();
5401   assert(workers != NULL, "Need parallel worker threads.");
5402   CMSRefEnqueueTaskProxy enq_task(task);
5403   workers->run_task(&enq_task);
5404 }
5405 
5406 void CMSCollector::refProcessingWork() {
5407   ResourceMark rm;
5408   HandleMark   hm;
5409 
5410   ReferenceProcessor* rp = ref_processor();
5411   assert(rp->span().equals(_span), "Spans should be equal");
5412   assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
5413   // Process weak references.
5414   rp->setup_policy(false);
5415   verify_work_stacks_empty();
5416 
5417   CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
5418                                           &_markStack, false /* !preclean */);
5419   CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
5420                                 _span, &_markBitMap, &_markStack,
5421                                 &cmsKeepAliveClosure, false /* !preclean */);
5422   {
5423     GCTraceTime t("weak refs processing", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5424 
5425     ReferenceProcessorStats stats;
5426     if (rp->processing_is_mt()) {
5427       // Set the degree of MT here.  If the discovery is done MT, there
5428       // may have been a different number of threads doing the discovery
5429       // and a different number of discovered lists may have Ref objects.
5430       // That is OK as long as the Reference lists are balanced (see
5431       // balance_all_queues() and balance_queues()).
5432       GenCollectedHeap* gch = GenCollectedHeap::heap();
5433       uint active_workers = ParallelGCThreads;
5434       FlexibleWorkGang* workers = gch->workers();
5435       if (workers != NULL) {
5436         active_workers = workers->active_workers();
5437         // The expectation is that active_workers will have already
5438         // been set to a reasonable value.  If it has not been set,
5439         // investigate.
5440         assert(active_workers > 0, "Should have been set during scavenge");
5441       }
5442       rp->set_active_mt_degree(active_workers);
5443       CMSRefProcTaskExecutor task_executor(*this);
5444       stats = rp->process_discovered_references(&_is_alive_closure,
5445                                         &cmsKeepAliveClosure,
5446                                         &cmsDrainMarkingStackClosure,
5447                                         &task_executor,
5448                                         _gc_timer_cm,
5449                                         _gc_tracer_cm->gc_id());
5450     } else {
5451       stats = rp->process_discovered_references(&_is_alive_closure,
5452                                         &cmsKeepAliveClosure,
5453                                         &cmsDrainMarkingStackClosure,
5454                                         NULL,
5455                                         _gc_timer_cm,
5456                                         _gc_tracer_cm->gc_id());
5457     }
5458     _gc_tracer_cm->report_gc_reference_stats(stats);
5459 
5460   }
5461 
5462   // This is the point where the entire marking should have completed.
5463   verify_work_stacks_empty();
5464 
5465   if (should_unload_classes()) {
5466     {
5467       GCTraceTime t("class unloading", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5468 
5469       // Unload classes and purge the SystemDictionary.
5470       bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure);
5471 
5472       // Unload nmethods.
5473       CodeCache::do_unloading(&_is_alive_closure, purged_class);
5474 
5475       // Prune dead klasses from subklass/sibling/implementor lists.
5476       Klass::clean_weak_klass_links(&_is_alive_closure);
5477     }
5478 
5479     {
5480       GCTraceTime t("scrub symbol table", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5481       // Clean up unreferenced symbols in symbol table.
5482       SymbolTable::unlink();
5483     }
5484 
5485     {
5486       GCTraceTime t("scrub string table", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5487       // Delete entries for dead interned strings.
5488       StringTable::unlink(&_is_alive_closure);
5489     }
5490   }
5491 
5492 
5493   // Restore any preserved marks as a result of mark stack or
5494   // work queue overflow
5495   restore_preserved_marks_if_any();  // done single-threaded for now
5496 
5497   rp->set_enqueuing_is_done(true);
5498   if (rp->processing_is_mt()) {
5499     rp->balance_all_queues();
5500     CMSRefProcTaskExecutor task_executor(*this);
5501     rp->enqueue_discovered_references(&task_executor);
5502   } else {
5503     rp->enqueue_discovered_references(NULL);
5504   }
5505   rp->verify_no_references_recorded();
5506   assert(!rp->discovery_enabled(), "should have been disabled");
5507 }
5508 
5509 #ifndef PRODUCT
5510 void CMSCollector::check_correct_thread_executing() {
5511   Thread* t = Thread::current();
5512   // Only the VM thread or the CMS thread should be here.
5513   assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
5514          "Unexpected thread type");
5515   // If this is the vm thread, the foreground process
5516   // should not be waiting.  Note that _foregroundGCIsActive is
5517   // true while the foreground collector is waiting.
5518   if (_foregroundGCShouldWait) {
5519     // We cannot be the VM thread
5520     assert(t->is_ConcurrentGC_thread(),
5521            "Should be CMS thread");
5522   } else {
5523     // We can be the CMS thread only if we are in a stop-world
5524     // phase of CMS collection.
5525     if (t->is_ConcurrentGC_thread()) {
5526       assert(_collectorState == InitialMarking ||
5527              _collectorState == FinalMarking,
5528              "Should be a stop-world phase");
5529       // The CMS thread should be holding the CMS_token.
5530       assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5531              "Potential interference with concurrently "
5532              "executing VM thread");
5533     }
5534   }
5535 }
5536 #endif
5537 
5538 void CMSCollector::sweep() {
5539   assert(_collectorState == Sweeping, "just checking");
5540   check_correct_thread_executing();
5541   verify_work_stacks_empty();
5542   verify_overflow_empty();
5543   increment_sweep_count();
5544   TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
5545 
5546   _inter_sweep_timer.stop();
5547   _inter_sweep_estimate.sample(_inter_sweep_timer.seconds());
5548 
5549   assert(!_intra_sweep_timer.is_active(), "Should not be active");
5550   _intra_sweep_timer.reset();
5551   _intra_sweep_timer.start();
5552   {
5553     TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
5554     CMSPhaseAccounting pa(this, "sweep", _gc_tracer_cm->gc_id(), !PrintGCDetails);
5555     // First sweep the old gen
5556     {
5557       CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
5558                                bitMapLock());
5559       sweepWork(_cmsGen);
5560     }
5561 
5562     // Update Universe::_heap_*_at_gc figures.
5563     // We need all the free list locks to make the abstract state
5564     // transition from Sweeping to Resetting. See detailed note
5565     // further below.
5566     {
5567       CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock());
5568       // Update heap occupancy information which is used as
5569       // input to soft ref clearing policy at the next gc.
5570       Universe::update_heap_info_at_gc();
5571       _collectorState = Resizing;
5572     }
5573   }
5574   verify_work_stacks_empty();
5575   verify_overflow_empty();
5576 
5577   if (should_unload_classes()) {
5578     // Delay purge to the beginning of the next safepoint.  Metaspace::contains
5579     // requires that the virtual spaces are stable and not deleted.
5580     ClassLoaderDataGraph::set_should_purge(true);
5581   }
5582 
5583   _intra_sweep_timer.stop();
5584   _intra_sweep_estimate.sample(_intra_sweep_timer.seconds());
5585 
5586   _inter_sweep_timer.reset();
5587   _inter_sweep_timer.start();
5588 
5589   // We need to use a monotonically non-decreasing time in ms
5590   // or we will see time-warp warnings and os::javaTimeMillis()
5591   // does not guarantee monotonicity.
5592   jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
5593   update_time_of_last_gc(now);
5594 
5595   // NOTE on abstract state transitions:
5596   // Mutators allocate-live and/or mark the mod-union table dirty
5597   // based on the state of the collection.  The former is done in
5598   // the interval [Marking, Sweeping] and the latter in the interval
5599   // [Marking, Sweeping).  Thus the transitions into the Marking state
5600   // and out of the Sweeping state must be synchronously visible
5601   // globally to the mutators.
5602   // The transition into the Marking state happens with the world
5603   // stopped so the mutators will globally see it.  Sweeping is
5604   // done asynchronously by the background collector so the transition
5605   // from the Sweeping state to the Resizing state must be done
5606   // under the freelistLock (as is the check for whether to
5607   // allocate-live and whether to dirty the mod-union table).
5608   assert(_collectorState == Resizing, "Change of collector state to"
5609     " Resizing must be done under the freelistLocks (plural)");
5610 
5611   // Now that sweeping has been completed, we clear
5612   // the incremental_collection_failed flag,
5613   // thus inviting a younger gen collection to promote into
5614   // this generation. If such a promotion may still fail,
5615   // the flag will be set again when a young collection is
5616   // attempted.
5617   GenCollectedHeap* gch = GenCollectedHeap::heap();
5618   gch->clear_incremental_collection_failed();  // Worth retrying as fresh space may have been freed up
5619   gch->update_full_collections_completed(_collection_count_start);
5620 }
5621 
5622 // FIX ME!!! Looks like this belongs in CFLSpace, with
5623 // CMSGen merely delegating to it.
5624 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
5625   double nearLargestPercent = FLSLargestBlockCoalesceProximity;
5626   HeapWord*  minAddr        = _cmsSpace->bottom();
5627   HeapWord*  largestAddr    =
5628     (HeapWord*) _cmsSpace->dictionary()->find_largest_dict();
5629   if (largestAddr == NULL) {
5630     // The dictionary appears to be empty.  In this case
5631     // try to coalesce at the end of the heap.
5632     largestAddr = _cmsSpace->end();
5633   }
5634   size_t largestOffset     = pointer_delta(largestAddr, minAddr);
5635   size_t nearLargestOffset =
5636     (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
5637   if (PrintFLSStatistics != 0) {
5638     gclog_or_tty->print_cr(
5639       "CMS: Large Block: " PTR_FORMAT ";"
5640       " Proximity: " PTR_FORMAT " -> " PTR_FORMAT,
5641       p2i(largestAddr),
5642       p2i(_cmsSpace->nearLargestChunk()), p2i(minAddr + nearLargestOffset));
5643   }
5644   _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
5645 }
5646 
5647 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
5648   return addr >= _cmsSpace->nearLargestChunk();
5649 }
5650 
5651 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
5652   return _cmsSpace->find_chunk_at_end();
5653 }
5654 
5655 void ConcurrentMarkSweepGeneration::update_gc_stats(int current_level,
5656                                                     bool full) {
5657   // The next lower level has been collected.  Gather any statistics
5658   // that are of interest at this point.
5659   if (!full && (current_level + 1) == level()) {
5660     // Gather statistics on the young generation collection.
5661     collector()->stats().record_gc0_end(used());
5662   }
5663 }
5664 
5665 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* gen) {
5666   // We iterate over the space(s) underlying this generation,
5667   // checking the mark bit map to see if the bits corresponding
5668   // to specific blocks are marked or not. Blocks that are
5669   // marked are live and are not swept up. All remaining blocks
5670   // are swept up, with coalescing on-the-fly as we sweep up
5671   // contiguous free and/or garbage blocks:
5672   // We need to ensure that the sweeper synchronizes with allocators
5673   // and stop-the-world collectors. In particular, the following
5674   // locks are used:
5675   // . CMS token: if this is held, a stop the world collection cannot occur
5676   // . freelistLock: if this is held no allocation can occur from this
5677   //                 generation by another thread
5678   // . bitMapLock: if this is held, no other thread can access or update
5679   //
5680 
5681   // Note that we need to hold the freelistLock if we use
5682   // block iterate below; else the iterator might go awry if
5683   // a mutator (or promotion) causes block contents to change
5684   // (for instance if the allocator divvies up a block).
5685   // If we hold the free list lock, for all practical purposes
5686   // young generation GC's can't occur (they'll usually need to
5687   // promote), so we might as well prevent all young generation
5688   // GC's while we do a sweeping step. For the same reason, we might
5689   // as well take the bit map lock for the entire duration
5690 
5691   // check that we hold the requisite locks
5692   assert(have_cms_token(), "Should hold cms token");
5693   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), "Should possess CMS token to sweep");
5694   assert_lock_strong(gen->freelistLock());
5695   assert_lock_strong(bitMapLock());
5696 
5697   assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context");
5698   assert(_intra_sweep_timer.is_active(),  "Was switched on  in an outer context");
5699   gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
5700                                       _inter_sweep_estimate.padded_average(),
5701                                       _intra_sweep_estimate.padded_average());
5702   gen->setNearLargestChunk();
5703 
5704   {
5705     SweepClosure sweepClosure(this, gen, &_markBitMap, CMSYield);
5706     gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
5707     // We need to free-up/coalesce garbage/blocks from a
5708     // co-terminal free run. This is done in the SweepClosure
5709     // destructor; so, do not remove this scope, else the
5710     // end-of-sweep-census below will be off by a little bit.
5711   }
5712   gen->cmsSpace()->sweep_completed();
5713   gen->cmsSpace()->endSweepFLCensus(sweep_count());
5714   if (should_unload_classes()) {                // unloaded classes this cycle,
5715     _concurrent_cycles_since_last_unload = 0;   // ... reset count
5716   } else {                                      // did not unload classes,
5717     _concurrent_cycles_since_last_unload++;     // ... increment count
5718   }
5719 }
5720 
5721 // Reset CMS data structures (for now just the marking bit map)
5722 // preparatory for the next cycle.
5723 void CMSCollector::reset(bool concurrent) {
5724   if (concurrent) {
5725     CMSTokenSyncWithLocks ts(true, bitMapLock());
5726 
5727     // If the state is not "Resetting", the foreground  thread
5728     // has done a collection and the resetting.
5729     if (_collectorState != Resetting) {
5730       assert(_collectorState == Idling, "The state should only change"
5731         " because the foreground collector has finished the collection");
5732       return;
5733     }
5734 
5735     // Clear the mark bitmap (no grey objects to start with)
5736     // for the next cycle.
5737     TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
5738     CMSPhaseAccounting cmspa(this, "reset", _gc_tracer_cm->gc_id(), !PrintGCDetails);
5739 
5740     HeapWord* curAddr = _markBitMap.startWord();
5741     while (curAddr < _markBitMap.endWord()) {
5742       size_t remaining  = pointer_delta(_markBitMap.endWord(), curAddr);
5743       MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
5744       _markBitMap.clear_large_range(chunk);
5745       if (ConcurrentMarkSweepThread::should_yield() &&
5746           !foregroundGCIsActive() &&
5747           CMSYield) {
5748         assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5749                "CMS thread should hold CMS token");
5750         assert_lock_strong(bitMapLock());
5751         bitMapLock()->unlock();
5752         ConcurrentMarkSweepThread::desynchronize(true);
5753         stopTimer();
5754         if (PrintCMSStatistics != 0) {
5755           incrementYields();
5756         }
5757 
5758         // See the comment in coordinator_yield()
5759         for (unsigned i = 0; i < CMSYieldSleepCount &&
5760                          ConcurrentMarkSweepThread::should_yield() &&
5761                          !CMSCollector::foregroundGCIsActive(); ++i) {
5762           os::sleep(Thread::current(), 1, false);
5763         }
5764 
5765         ConcurrentMarkSweepThread::synchronize(true);
5766         bitMapLock()->lock_without_safepoint_check();
5767         startTimer();
5768       }
5769       curAddr = chunk.end();
5770     }
5771     // A successful mostly concurrent collection has been done.
5772     // Because only the full (i.e., concurrent mode failure) collections
5773     // are being measured for gc overhead limits, clean the "near" flag
5774     // and count.
5775     size_policy()->reset_gc_overhead_limit_count();
5776     _collectorState = Idling;
5777   } else {
5778     // already have the lock
5779     assert(_collectorState == Resetting, "just checking");
5780     assert_lock_strong(bitMapLock());
5781     _markBitMap.clear_all();
5782     _collectorState = Idling;
5783   }
5784 
5785   register_gc_end();
5786 }
5787 
5788 void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) {
5789   TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
5790   GCTraceTime t(GCCauseString("GC", gc_cause), PrintGC, !PrintGCDetails, NULL, _gc_tracer_cm->gc_id());
5791   TraceCollectorStats tcs(counters());
5792 
5793   switch (op) {
5794     case CMS_op_checkpointRootsInitial: {
5795       SvcGCMarker sgcm(SvcGCMarker::OTHER);
5796       checkpointRootsInitial();
5797       if (PrintGC) {
5798         _cmsGen->printOccupancy("initial-mark");
5799       }
5800       break;
5801     }
5802     case CMS_op_checkpointRootsFinal: {
5803       SvcGCMarker sgcm(SvcGCMarker::OTHER);
5804       checkpointRootsFinal();
5805       if (PrintGC) {
5806         _cmsGen->printOccupancy("remark");
5807       }
5808       break;
5809     }
5810     default:
5811       fatal("No such CMS_op");
5812   }
5813 }
5814 
5815 #ifndef PRODUCT
5816 size_t const CMSCollector::skip_header_HeapWords() {
5817   return FreeChunk::header_size();
5818 }
5819 
5820 // Try and collect here conditions that should hold when
5821 // CMS thread is exiting. The idea is that the foreground GC
5822 // thread should not be blocked if it wants to terminate
5823 // the CMS thread and yet continue to run the VM for a while
5824 // after that.
5825 void CMSCollector::verify_ok_to_terminate() const {
5826   assert(Thread::current()->is_ConcurrentGC_thread(),
5827          "should be called by CMS thread");
5828   assert(!_foregroundGCShouldWait, "should be false");
5829   // We could check here that all the various low-level locks
5830   // are not held by the CMS thread, but that is overkill; see
5831   // also CMSThread::verify_ok_to_terminate() where the CGC_lock
5832   // is checked.
5833 }
5834 #endif
5835 
5836 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
5837    assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
5838           "missing Printezis mark?");
5839   HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5840   size_t size = pointer_delta(nextOneAddr + 1, addr);
5841   assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5842          "alignment problem");
5843   assert(size >= 3, "Necessary for Printezis marks to work");
5844   return size;
5845 }
5846 
5847 // A variant of the above (block_size_using_printezis_bits()) except
5848 // that we return 0 if the P-bits are not yet set.
5849 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
5850   if (_markBitMap.isMarked(addr + 1)) {
5851     assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects");
5852     HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5853     size_t size = pointer_delta(nextOneAddr + 1, addr);
5854     assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5855            "alignment problem");
5856     assert(size >= 3, "Necessary for Printezis marks to work");
5857     return size;
5858   }
5859   return 0;
5860 }
5861 
5862 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
5863   size_t sz = 0;
5864   oop p = (oop)addr;
5865   if (p->klass_or_null() != NULL) {
5866     sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
5867   } else {
5868     sz = block_size_using_printezis_bits(addr);
5869   }
5870   assert(sz > 0, "size must be nonzero");
5871   HeapWord* next_block = addr + sz;
5872   HeapWord* next_card  = (HeapWord*)round_to((uintptr_t)next_block,
5873                                              CardTableModRefBS::card_size);
5874   assert(round_down((uintptr_t)addr,      CardTableModRefBS::card_size) <
5875          round_down((uintptr_t)next_card, CardTableModRefBS::card_size),
5876          "must be different cards");
5877   return next_card;
5878 }
5879 
5880 
5881 // CMS Bit Map Wrapper /////////////////////////////////////////
5882 
5883 // Construct a CMS bit map infrastructure, but don't create the
5884 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
5885 // further below.
5886 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
5887   _bm(),
5888   _shifter(shifter),
5889   _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true,
5890                                     Monitor::_safepoint_check_sometimes) : NULL)
5891 {
5892   _bmStartWord = 0;
5893   _bmWordSize  = 0;
5894 }
5895 
5896 bool CMSBitMap::allocate(MemRegion mr) {
5897   _bmStartWord = mr.start();
5898   _bmWordSize  = mr.word_size();
5899   ReservedSpace brs(ReservedSpace::allocation_align_size_up(
5900                      (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
5901   if (!brs.is_reserved()) {
5902     warning("CMS bit map allocation failure");
5903     return false;
5904   }
5905   // For now we'll just commit all of the bit map up front.
5906   // Later on we'll try to be more parsimonious with swap.
5907   if (!_virtual_space.initialize(brs, brs.size())) {
5908     warning("CMS bit map backing store failure");
5909     return false;
5910   }
5911   assert(_virtual_space.committed_size() == brs.size(),
5912          "didn't reserve backing store for all of CMS bit map?");
5913   _bm.set_map((BitMap::bm_word_t*)_virtual_space.low());
5914   assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
5915          _bmWordSize, "inconsistency in bit map sizing");
5916   _bm.set_size(_bmWordSize >> _shifter);
5917 
5918   // bm.clear(); // can we rely on getting zero'd memory? verify below
5919   assert(isAllClear(),
5920          "Expected zero'd memory from ReservedSpace constructor");
5921   assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
5922          "consistency check");
5923   return true;
5924 }
5925 
5926 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
5927   HeapWord *next_addr, *end_addr, *last_addr;
5928   assert_locked();
5929   assert(covers(mr), "out-of-range error");
5930   // XXX assert that start and end are appropriately aligned
5931   for (next_addr = mr.start(), end_addr = mr.end();
5932        next_addr < end_addr; next_addr = last_addr) {
5933     MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
5934     last_addr = dirty_region.end();
5935     if (!dirty_region.is_empty()) {
5936       cl->do_MemRegion(dirty_region);
5937     } else {
5938       assert(last_addr == end_addr, "program logic");
5939       return;
5940     }
5941   }
5942 }
5943 
5944 void CMSBitMap::print_on_error(outputStream* st, const char* prefix) const {
5945   _bm.print_on_error(st, prefix);
5946 }
5947 
5948 #ifndef PRODUCT
5949 void CMSBitMap::assert_locked() const {
5950   CMSLockVerifier::assert_locked(lock());
5951 }
5952 
5953 bool CMSBitMap::covers(MemRegion mr) const {
5954   // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
5955   assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
5956          "size inconsistency");
5957   return (mr.start() >= _bmStartWord) &&
5958          (mr.end()   <= endWord());
5959 }
5960 
5961 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
5962     return (start >= _bmStartWord && (start + size) <= endWord());
5963 }
5964 
5965 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
5966   // verify that there are no 1 bits in the interval [left, right)
5967   FalseBitMapClosure falseBitMapClosure;
5968   iterate(&falseBitMapClosure, left, right);
5969 }
5970 
5971 void CMSBitMap::region_invariant(MemRegion mr)
5972 {
5973   assert_locked();
5974   // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
5975   assert(!mr.is_empty(), "unexpected empty region");
5976   assert(covers(mr), "mr should be covered by bit map");
5977   // convert address range into offset range
5978   size_t start_ofs = heapWordToOffset(mr.start());
5979   // Make sure that end() is appropriately aligned
5980   assert(mr.end() == (HeapWord*)round_to((intptr_t)mr.end(),
5981                         (1 << (_shifter+LogHeapWordSize))),
5982          "Misaligned mr.end()");
5983   size_t end_ofs   = heapWordToOffset(mr.end());
5984   assert(end_ofs > start_ofs, "Should mark at least one bit");
5985 }
5986 
5987 #endif
5988 
5989 bool CMSMarkStack::allocate(size_t size) {
5990   // allocate a stack of the requisite depth
5991   ReservedSpace rs(ReservedSpace::allocation_align_size_up(
5992                    size * sizeof(oop)));
5993   if (!rs.is_reserved()) {
5994     warning("CMSMarkStack allocation failure");
5995     return false;
5996   }
5997   if (!_virtual_space.initialize(rs, rs.size())) {
5998     warning("CMSMarkStack backing store failure");
5999     return false;
6000   }
6001   assert(_virtual_space.committed_size() == rs.size(),
6002          "didn't reserve backing store for all of CMS stack?");
6003   _base = (oop*)(_virtual_space.low());
6004   _index = 0;
6005   _capacity = size;
6006   NOT_PRODUCT(_max_depth = 0);
6007   return true;
6008 }
6009 
6010 // XXX FIX ME !!! In the MT case we come in here holding a
6011 // leaf lock. For printing we need to take a further lock
6012 // which has lower rank. We need to recalibrate the two
6013 // lock-ranks involved in order to be able to print the
6014 // messages below. (Or defer the printing to the caller.
6015 // For now we take the expedient path of just disabling the
6016 // messages for the problematic case.)
6017 void CMSMarkStack::expand() {
6018   assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted");
6019   if (_capacity == MarkStackSizeMax) {
6020     if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6021       // We print a warning message only once per CMS cycle.
6022       gclog_or_tty->print_cr(" (benign) Hit CMSMarkStack max size limit");
6023     }
6024     return;
6025   }
6026   // Double capacity if possible
6027   size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax);
6028   // Do not give up existing stack until we have managed to
6029   // get the double capacity that we desired.
6030   ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6031                    new_capacity * sizeof(oop)));
6032   if (rs.is_reserved()) {
6033     // Release the backing store associated with old stack
6034     _virtual_space.release();
6035     // Reinitialize virtual space for new stack
6036     if (!_virtual_space.initialize(rs, rs.size())) {
6037       fatal("Not enough swap for expanded marking stack");
6038     }
6039     _base = (oop*)(_virtual_space.low());
6040     _index = 0;
6041     _capacity = new_capacity;
6042   } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6043     // Failed to double capacity, continue;
6044     // we print a detail message only once per CMS cycle.
6045     gclog_or_tty->print(" (benign) Failed to expand marking stack from "SIZE_FORMAT"K to "
6046             SIZE_FORMAT"K",
6047             _capacity / K, new_capacity / K);
6048   }
6049 }
6050 
6051 
6052 // Closures
6053 // XXX: there seems to be a lot of code  duplication here;
6054 // should refactor and consolidate common code.
6055 
6056 // This closure is used to mark refs into the CMS generation in
6057 // the CMS bit map. Called at the first checkpoint. This closure
6058 // assumes that we do not need to re-mark dirty cards; if the CMS
6059 // generation on which this is used is not an oldest
6060 // generation then this will lose younger_gen cards!
6061 
6062 MarkRefsIntoClosure::MarkRefsIntoClosure(
6063   MemRegion span, CMSBitMap* bitMap):
6064     _span(span),
6065     _bitMap(bitMap)
6066 {
6067     assert(_ref_processor == NULL, "deliberately left NULL");
6068     assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6069 }
6070 
6071 void MarkRefsIntoClosure::do_oop(oop obj) {
6072   // if p points into _span, then mark corresponding bit in _markBitMap
6073   assert(obj->is_oop(), "expected an oop");
6074   HeapWord* addr = (HeapWord*)obj;
6075   if (_span.contains(addr)) {
6076     // this should be made more efficient
6077     _bitMap->mark(addr);
6078   }
6079 }
6080 
6081 void MarkRefsIntoClosure::do_oop(oop* p)       { MarkRefsIntoClosure::do_oop_work(p); }
6082 void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6083 
6084 Par_MarkRefsIntoClosure::Par_MarkRefsIntoClosure(
6085   MemRegion span, CMSBitMap* bitMap):
6086     _span(span),
6087     _bitMap(bitMap)
6088 {
6089     assert(_ref_processor == NULL, "deliberately left NULL");
6090     assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6091 }
6092 
6093 void Par_MarkRefsIntoClosure::do_oop(oop obj) {
6094   // if p points into _span, then mark corresponding bit in _markBitMap
6095   assert(obj->is_oop(), "expected an oop");
6096   HeapWord* addr = (HeapWord*)obj;
6097   if (_span.contains(addr)) {
6098     // this should be made more efficient
6099     _bitMap->par_mark(addr);
6100   }
6101 }
6102 
6103 void Par_MarkRefsIntoClosure::do_oop(oop* p)       { Par_MarkRefsIntoClosure::do_oop_work(p); }
6104 void Par_MarkRefsIntoClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoClosure::do_oop_work(p); }
6105 
6106 // A variant of the above, used for CMS marking verification.
6107 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
6108   MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm):
6109     _span(span),
6110     _verification_bm(verification_bm),
6111     _cms_bm(cms_bm)
6112 {
6113     assert(_ref_processor == NULL, "deliberately left NULL");
6114     assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
6115 }
6116 
6117 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
6118   // if p points into _span, then mark corresponding bit in _markBitMap
6119   assert(obj->is_oop(), "expected an oop");
6120   HeapWord* addr = (HeapWord*)obj;
6121   if (_span.contains(addr)) {
6122     _verification_bm->mark(addr);
6123     if (!_cms_bm->isMarked(addr)) {
6124       oop(addr)->print();
6125       gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
6126       fatal("... aborting");
6127     }
6128   }
6129 }
6130 
6131 void MarkRefsIntoVerifyClosure::do_oop(oop* p)       { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6132 void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6133 
6134 //////////////////////////////////////////////////
6135 // MarkRefsIntoAndScanClosure
6136 //////////////////////////////////////////////////
6137 
6138 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
6139                                                        ReferenceProcessor* rp,
6140                                                        CMSBitMap* bit_map,
6141                                                        CMSBitMap* mod_union_table,
6142                                                        CMSMarkStack*  mark_stack,
6143                                                        CMSCollector* collector,
6144                                                        bool should_yield,
6145                                                        bool concurrent_precleaning):
6146   _collector(collector),
6147   _span(span),
6148   _bit_map(bit_map),
6149   _mark_stack(mark_stack),
6150   _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table,
6151                       mark_stack, concurrent_precleaning),
6152   _yield(should_yield),
6153   _concurrent_precleaning(concurrent_precleaning),
6154   _freelistLock(NULL)
6155 {
6156   _ref_processor = rp;
6157   assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6158 }
6159 
6160 // This closure is used to mark refs into the CMS generation at the
6161 // second (final) checkpoint, and to scan and transitively follow
6162 // the unmarked oops. It is also used during the concurrent precleaning
6163 // phase while scanning objects on dirty cards in the CMS generation.
6164 // The marks are made in the marking bit map and the marking stack is
6165 // used for keeping the (newly) grey objects during the scan.
6166 // The parallel version (Par_...) appears further below.
6167 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6168   if (obj != NULL) {
6169     assert(obj->is_oop(), "expected an oop");
6170     HeapWord* addr = (HeapWord*)obj;
6171     assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6172     assert(_collector->overflow_list_is_empty(),
6173            "overflow list should be empty");
6174     if (_span.contains(addr) &&
6175         !_bit_map->isMarked(addr)) {
6176       // mark bit map (object is now grey)
6177       _bit_map->mark(addr);
6178       // push on marking stack (stack should be empty), and drain the
6179       // stack by applying this closure to the oops in the oops popped
6180       // from the stack (i.e. blacken the grey objects)
6181       bool res = _mark_stack->push(obj);
6182       assert(res, "Should have space to push on empty stack");
6183       do {
6184         oop new_oop = _mark_stack->pop();
6185         assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6186         assert(_bit_map->isMarked((HeapWord*)new_oop),
6187                "only grey objects on this stack");
6188         // iterate over the oops in this oop, marking and pushing
6189         // the ones in CMS heap (i.e. in _span).
6190         new_oop->oop_iterate(&_pushAndMarkClosure);
6191         // check if it's time to yield
6192         do_yield_check();
6193       } while (!_mark_stack->isEmpty() ||
6194                (!_concurrent_precleaning && take_from_overflow_list()));
6195         // if marking stack is empty, and we are not doing this
6196         // during precleaning, then check the overflow list
6197     }
6198     assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6199     assert(_collector->overflow_list_is_empty(),
6200            "overflow list was drained above");
6201     // We could restore evacuated mark words, if any, used for
6202     // overflow list links here because the overflow list is
6203     // provably empty here. That would reduce the maximum
6204     // size requirements for preserved_{oop,mark}_stack.
6205     // But we'll just postpone it until we are all done
6206     // so we can just stream through.
6207     if (!_concurrent_precleaning && CMSOverflowEarlyRestoration) {
6208       _collector->restore_preserved_marks_if_any();
6209       assert(_collector->no_preserved_marks(), "No preserved marks");
6210     }
6211     assert(!CMSOverflowEarlyRestoration || _collector->no_preserved_marks(),
6212            "All preserved marks should have been restored above");
6213   }
6214 }
6215 
6216 void MarkRefsIntoAndScanClosure::do_oop(oop* p)       { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6217 void MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6218 
6219 void MarkRefsIntoAndScanClosure::do_yield_work() {
6220   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6221          "CMS thread should hold CMS token");
6222   assert_lock_strong(_freelistLock);
6223   assert_lock_strong(_bit_map->lock());
6224   // relinquish the free_list_lock and bitMaplock()
6225   _bit_map->lock()->unlock();
6226   _freelistLock->unlock();
6227   ConcurrentMarkSweepThread::desynchronize(true);
6228   _collector->stopTimer();
6229   if (PrintCMSStatistics != 0) {
6230     _collector->incrementYields();
6231   }
6232 
6233   // See the comment in coordinator_yield()
6234   for (unsigned i = 0;
6235        i < CMSYieldSleepCount &&
6236        ConcurrentMarkSweepThread::should_yield() &&
6237        !CMSCollector::foregroundGCIsActive();
6238        ++i) {
6239     os::sleep(Thread::current(), 1, false);
6240   }
6241 
6242   ConcurrentMarkSweepThread::synchronize(true);
6243   _freelistLock->lock_without_safepoint_check();
6244   _bit_map->lock()->lock_without_safepoint_check();
6245   _collector->startTimer();
6246 }
6247 
6248 ///////////////////////////////////////////////////////////
6249 // Par_MarkRefsIntoAndScanClosure: a parallel version of
6250 //                                 MarkRefsIntoAndScanClosure
6251 ///////////////////////////////////////////////////////////
6252 Par_MarkRefsIntoAndScanClosure::Par_MarkRefsIntoAndScanClosure(
6253   CMSCollector* collector, MemRegion span, ReferenceProcessor* rp,
6254   CMSBitMap* bit_map, OopTaskQueue* work_queue):
6255   _span(span),
6256   _bit_map(bit_map),
6257   _work_queue(work_queue),
6258   _low_water_mark(MIN2((work_queue->max_elems()/4),
6259                        ((uint)CMSWorkQueueDrainThreshold * ParallelGCThreads))),
6260   _par_pushAndMarkClosure(collector, span, rp, bit_map, work_queue)
6261 {
6262   _ref_processor = rp;
6263   assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6264 }
6265 
6266 // This closure is used to mark refs into the CMS generation at the
6267 // second (final) checkpoint, and to scan and transitively follow
6268 // the unmarked oops. The marks are made in the marking bit map and
6269 // the work_queue is used for keeping the (newly) grey objects during
6270 // the scan phase whence they are also available for stealing by parallel
6271 // threads. Since the marking bit map is shared, updates are
6272 // synchronized (via CAS).
6273 void Par_MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6274   if (obj != NULL) {
6275     // Ignore mark word because this could be an already marked oop
6276     // that may be chained at the end of the overflow list.
6277     assert(obj->is_oop(true), "expected an oop");
6278     HeapWord* addr = (HeapWord*)obj;
6279     if (_span.contains(addr) &&
6280         !_bit_map->isMarked(addr)) {
6281       // mark bit map (object will become grey):
6282       // It is possible for several threads to be
6283       // trying to "claim" this object concurrently;
6284       // the unique thread that succeeds in marking the
6285       // object first will do the subsequent push on
6286       // to the work queue (or overflow list).
6287       if (_bit_map->par_mark(addr)) {
6288         // push on work_queue (which may not be empty), and trim the
6289         // queue to an appropriate length by applying this closure to
6290         // the oops in the oops popped from the stack (i.e. blacken the
6291         // grey objects)
6292         bool res = _work_queue->push(obj);
6293         assert(res, "Low water mark should be less than capacity?");
6294         trim_queue(_low_water_mark);
6295       } // Else, another thread claimed the object
6296     }
6297   }
6298 }
6299 
6300 void Par_MarkRefsIntoAndScanClosure::do_oop(oop* p)       { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6301 void Par_MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6302 
6303 // This closure is used to rescan the marked objects on the dirty cards
6304 // in the mod union table and the card table proper.
6305 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
6306   oop p, MemRegion mr) {
6307 
6308   size_t size = 0;
6309   HeapWord* addr = (HeapWord*)p;
6310   DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6311   assert(_span.contains(addr), "we are scanning the CMS generation");
6312   // check if it's time to yield
6313   if (do_yield_check()) {
6314     // We yielded for some foreground stop-world work,
6315     // and we have been asked to abort this ongoing preclean cycle.
6316     return 0;
6317   }
6318   if (_bitMap->isMarked(addr)) {
6319     // it's marked; is it potentially uninitialized?
6320     if (p->klass_or_null() != NULL) {
6321         // an initialized object; ignore mark word in verification below
6322         // since we are running concurrent with mutators
6323         assert(p->is_oop(true), "should be an oop");
6324         if (p->is_objArray()) {
6325           // objArrays are precisely marked; restrict scanning
6326           // to dirty cards only.
6327           size = CompactibleFreeListSpace::adjustObjectSize(
6328                    p->oop_iterate(_scanningClosure, mr));
6329         } else {
6330           // A non-array may have been imprecisely marked; we need
6331           // to scan object in its entirety.
6332           size = CompactibleFreeListSpace::adjustObjectSize(
6333                    p->oop_iterate(_scanningClosure));
6334         }
6335         #ifdef ASSERT
6336           size_t direct_size =
6337             CompactibleFreeListSpace::adjustObjectSize(p->size());
6338           assert(size == direct_size, "Inconsistency in size");
6339           assert(size >= 3, "Necessary for Printezis marks to work");
6340           if (!_bitMap->isMarked(addr+1)) {
6341             _bitMap->verifyNoOneBitsInRange(addr+2, addr+size);
6342           } else {
6343             _bitMap->verifyNoOneBitsInRange(addr+2, addr+size-1);
6344             assert(_bitMap->isMarked(addr+size-1),
6345                    "inconsistent Printezis mark");
6346           }
6347         #endif // ASSERT
6348     } else {
6349       // An uninitialized object.
6350       assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
6351       HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
6352       size = pointer_delta(nextOneAddr + 1, addr);
6353       assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6354              "alignment problem");
6355       // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
6356       // will dirty the card when the klass pointer is installed in the
6357       // object (signaling the completion of initialization).
6358     }
6359   } else {
6360     // Either a not yet marked object or an uninitialized object
6361     if (p->klass_or_null() == NULL) {
6362       // An uninitialized object, skip to the next card, since
6363       // we may not be able to read its P-bits yet.
6364       assert(size == 0, "Initial value");
6365     } else {
6366       // An object not (yet) reached by marking: we merely need to
6367       // compute its size so as to go look at the next block.
6368       assert(p->is_oop(true), "should be an oop");
6369       size = CompactibleFreeListSpace::adjustObjectSize(p->size());
6370     }
6371   }
6372   DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6373   return size;
6374 }
6375 
6376 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
6377   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6378          "CMS thread should hold CMS token");
6379   assert_lock_strong(_freelistLock);
6380   assert_lock_strong(_bitMap->lock());
6381   // relinquish the free_list_lock and bitMaplock()
6382   _bitMap->lock()->unlock();
6383   _freelistLock->unlock();
6384   ConcurrentMarkSweepThread::desynchronize(true);
6385   _collector->stopTimer();
6386   if (PrintCMSStatistics != 0) {
6387     _collector->incrementYields();
6388   }
6389 
6390   // See the comment in coordinator_yield()
6391   for (unsigned i = 0; i < CMSYieldSleepCount &&
6392                    ConcurrentMarkSweepThread::should_yield() &&
6393                    !CMSCollector::foregroundGCIsActive(); ++i) {
6394     os::sleep(Thread::current(), 1, false);
6395   }
6396 
6397   ConcurrentMarkSweepThread::synchronize(true);
6398   _freelistLock->lock_without_safepoint_check();
6399   _bitMap->lock()->lock_without_safepoint_check();
6400   _collector->startTimer();
6401 }
6402 
6403 
6404 //////////////////////////////////////////////////////////////////
6405 // SurvivorSpacePrecleanClosure
6406 //////////////////////////////////////////////////////////////////
6407 // This (single-threaded) closure is used to preclean the oops in
6408 // the survivor spaces.
6409 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
6410 
6411   HeapWord* addr = (HeapWord*)p;
6412   DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6413   assert(!_span.contains(addr), "we are scanning the survivor spaces");
6414   assert(p->klass_or_null() != NULL, "object should be initialized");
6415   // an initialized object; ignore mark word in verification below
6416   // since we are running concurrent with mutators
6417   assert(p->is_oop(true), "should be an oop");
6418   // Note that we do not yield while we iterate over
6419   // the interior oops of p, pushing the relevant ones
6420   // on our marking stack.
6421   size_t size = p->oop_iterate(_scanning_closure);
6422   do_yield_check();
6423   // Observe that below, we do not abandon the preclean
6424   // phase as soon as we should; rather we empty the
6425   // marking stack before returning. This is to satisfy
6426   // some existing assertions. In general, it may be a
6427   // good idea to abort immediately and complete the marking
6428   // from the grey objects at a later time.
6429   while (!_mark_stack->isEmpty()) {
6430     oop new_oop = _mark_stack->pop();
6431     assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6432     assert(_bit_map->isMarked((HeapWord*)new_oop),
6433            "only grey objects on this stack");
6434     // iterate over the oops in this oop, marking and pushing
6435     // the ones in CMS heap (i.e. in _span).
6436     new_oop->oop_iterate(_scanning_closure);
6437     // check if it's time to yield
6438     do_yield_check();
6439   }
6440   unsigned int after_count =
6441     GenCollectedHeap::heap()->total_collections();
6442   bool abort = (_before_count != after_count) ||
6443                _collector->should_abort_preclean();
6444   return abort ? 0 : size;
6445 }
6446 
6447 void SurvivorSpacePrecleanClosure::do_yield_work() {
6448   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6449          "CMS thread should hold CMS token");
6450   assert_lock_strong(_bit_map->lock());
6451   // Relinquish the bit map lock
6452   _bit_map->lock()->unlock();
6453   ConcurrentMarkSweepThread::desynchronize(true);
6454   _collector->stopTimer();
6455   if (PrintCMSStatistics != 0) {
6456     _collector->incrementYields();
6457   }
6458 
6459   // See the comment in coordinator_yield()
6460   for (unsigned i = 0; i < CMSYieldSleepCount &&
6461                        ConcurrentMarkSweepThread::should_yield() &&
6462                        !CMSCollector::foregroundGCIsActive(); ++i) {
6463     os::sleep(Thread::current(), 1, false);
6464   }
6465 
6466   ConcurrentMarkSweepThread::synchronize(true);
6467   _bit_map->lock()->lock_without_safepoint_check();
6468   _collector->startTimer();
6469 }
6470 
6471 // This closure is used to rescan the marked objects on the dirty cards
6472 // in the mod union table and the card table proper. In the parallel
6473 // case, although the bitMap is shared, we do a single read so the
6474 // isMarked() query is "safe".
6475 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
6476   // Ignore mark word because we are running concurrent with mutators
6477   assert(p->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(p)));
6478   HeapWord* addr = (HeapWord*)p;
6479   assert(_span.contains(addr), "we are scanning the CMS generation");
6480   bool is_obj_array = false;
6481   #ifdef ASSERT
6482     if (!_parallel) {
6483       assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6484       assert(_collector->overflow_list_is_empty(),
6485              "overflow list should be empty");
6486 
6487     }
6488   #endif // ASSERT
6489   if (_bit_map->isMarked(addr)) {
6490     // Obj arrays are precisely marked, non-arrays are not;
6491     // so we scan objArrays precisely and non-arrays in their
6492     // entirety.
6493     if (p->is_objArray()) {
6494       is_obj_array = true;
6495       if (_parallel) {
6496         p->oop_iterate(_par_scan_closure, mr);
6497       } else {
6498         p->oop_iterate(_scan_closure, mr);
6499       }
6500     } else {
6501       if (_parallel) {
6502         p->oop_iterate(_par_scan_closure);
6503       } else {
6504         p->oop_iterate(_scan_closure);
6505       }
6506     }
6507   }
6508   #ifdef ASSERT
6509     if (!_parallel) {
6510       assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6511       assert(_collector->overflow_list_is_empty(),
6512              "overflow list should be empty");
6513 
6514     }
6515   #endif // ASSERT
6516   return is_obj_array;
6517 }
6518 
6519 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
6520                         MemRegion span,
6521                         CMSBitMap* bitMap, CMSMarkStack*  markStack,
6522                         bool should_yield, bool verifying):
6523   _collector(collector),
6524   _span(span),
6525   _bitMap(bitMap),
6526   _mut(&collector->_modUnionTable),
6527   _markStack(markStack),
6528   _yield(should_yield),
6529   _skipBits(0)
6530 {
6531   assert(_markStack->isEmpty(), "stack should be empty");
6532   _finger = _bitMap->startWord();
6533   _threshold = _finger;
6534   assert(_collector->_restart_addr == NULL, "Sanity check");
6535   assert(_span.contains(_finger), "Out of bounds _finger?");
6536   DEBUG_ONLY(_verifying = verifying;)
6537 }
6538 
6539 void MarkFromRootsClosure::reset(HeapWord* addr) {
6540   assert(_markStack->isEmpty(), "would cause duplicates on stack");
6541   assert(_span.contains(addr), "Out of bounds _finger?");
6542   _finger = addr;
6543   _threshold = (HeapWord*)round_to(
6544                  (intptr_t)_finger, CardTableModRefBS::card_size);
6545 }
6546 
6547 // Should revisit to see if this should be restructured for
6548 // greater efficiency.
6549 bool MarkFromRootsClosure::do_bit(size_t offset) {
6550   if (_skipBits > 0) {
6551     _skipBits--;
6552     return true;
6553   }
6554   // convert offset into a HeapWord*
6555   HeapWord* addr = _bitMap->startWord() + offset;
6556   assert(_bitMap->endWord() && addr < _bitMap->endWord(),
6557          "address out of range");
6558   assert(_bitMap->isMarked(addr), "tautology");
6559   if (_bitMap->isMarked(addr+1)) {
6560     // this is an allocated but not yet initialized object
6561     assert(_skipBits == 0, "tautology");
6562     _skipBits = 2;  // skip next two marked bits ("Printezis-marks")
6563     oop p = oop(addr);
6564     if (p->klass_or_null() == NULL) {
6565       DEBUG_ONLY(if (!_verifying) {)
6566         // We re-dirty the cards on which this object lies and increase
6567         // the _threshold so that we'll come back to scan this object
6568         // during the preclean or remark phase. (CMSCleanOnEnter)
6569         if (CMSCleanOnEnter) {
6570           size_t sz = _collector->block_size_using_printezis_bits(addr);
6571           HeapWord* end_card_addr   = (HeapWord*)round_to(
6572                                          (intptr_t)(addr+sz), CardTableModRefBS::card_size);
6573           MemRegion redirty_range = MemRegion(addr, end_card_addr);
6574           assert(!redirty_range.is_empty(), "Arithmetical tautology");
6575           // Bump _threshold to end_card_addr; note that
6576           // _threshold cannot possibly exceed end_card_addr, anyhow.
6577           // This prevents future clearing of the card as the scan proceeds
6578           // to the right.
6579           assert(_threshold <= end_card_addr,
6580                  "Because we are just scanning into this object");
6581           if (_threshold < end_card_addr) {
6582             _threshold = end_card_addr;
6583           }
6584           if (p->klass_or_null() != NULL) {
6585             // Redirty the range of cards...
6586             _mut->mark_range(redirty_range);
6587           } // ...else the setting of klass will dirty the card anyway.
6588         }
6589       DEBUG_ONLY(})
6590       return true;
6591     }
6592   }
6593   scanOopsInOop(addr);
6594   return true;
6595 }
6596 
6597 // We take a break if we've been at this for a while,
6598 // so as to avoid monopolizing the locks involved.
6599 void MarkFromRootsClosure::do_yield_work() {
6600   // First give up the locks, then yield, then re-lock
6601   // We should probably use a constructor/destructor idiom to
6602   // do this unlock/lock or modify the MutexUnlocker class to
6603   // serve our purpose. XXX
6604   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6605          "CMS thread should hold CMS token");
6606   assert_lock_strong(_bitMap->lock());
6607   _bitMap->lock()->unlock();
6608   ConcurrentMarkSweepThread::desynchronize(true);
6609   _collector->stopTimer();
6610   if (PrintCMSStatistics != 0) {
6611     _collector->incrementYields();
6612   }
6613 
6614   // See the comment in coordinator_yield()
6615   for (unsigned i = 0; i < CMSYieldSleepCount &&
6616                        ConcurrentMarkSweepThread::should_yield() &&
6617                        !CMSCollector::foregroundGCIsActive(); ++i) {
6618     os::sleep(Thread::current(), 1, false);
6619   }
6620 
6621   ConcurrentMarkSweepThread::synchronize(true);
6622   _bitMap->lock()->lock_without_safepoint_check();
6623   _collector->startTimer();
6624 }
6625 
6626 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
6627   assert(_bitMap->isMarked(ptr), "expected bit to be set");
6628   assert(_markStack->isEmpty(),
6629          "should drain stack to limit stack usage");
6630   // convert ptr to an oop preparatory to scanning
6631   oop obj = oop(ptr);
6632   // Ignore mark word in verification below, since we
6633   // may be running concurrent with mutators.
6634   assert(obj->is_oop(true), "should be an oop");
6635   assert(_finger <= ptr, "_finger runneth ahead");
6636   // advance the finger to right end of this object
6637   _finger = ptr + obj->size();
6638   assert(_finger > ptr, "we just incremented it above");
6639   // On large heaps, it may take us some time to get through
6640   // the marking phase. During
6641   // this time it's possible that a lot of mutations have
6642   // accumulated in the card table and the mod union table --
6643   // these mutation records are redundant until we have
6644   // actually traced into the corresponding card.
6645   // Here, we check whether advancing the finger would make
6646   // us cross into a new card, and if so clear corresponding
6647   // cards in the MUT (preclean them in the card-table in the
6648   // future).
6649 
6650   DEBUG_ONLY(if (!_verifying) {)
6651     // The clean-on-enter optimization is disabled by default,
6652     // until we fix 6178663.
6653     if (CMSCleanOnEnter && (_finger > _threshold)) {
6654       // [_threshold, _finger) represents the interval
6655       // of cards to be cleared  in MUT (or precleaned in card table).
6656       // The set of cards to be cleared is all those that overlap
6657       // with the interval [_threshold, _finger); note that
6658       // _threshold is always kept card-aligned but _finger isn't
6659       // always card-aligned.
6660       HeapWord* old_threshold = _threshold;
6661       assert(old_threshold == (HeapWord*)round_to(
6662               (intptr_t)old_threshold, CardTableModRefBS::card_size),
6663              "_threshold should always be card-aligned");
6664       _threshold = (HeapWord*)round_to(
6665                      (intptr_t)_finger, CardTableModRefBS::card_size);
6666       MemRegion mr(old_threshold, _threshold);
6667       assert(!mr.is_empty(), "Control point invariant");
6668       assert(_span.contains(mr), "Should clear within span");
6669       _mut->clear_range(mr);
6670     }
6671   DEBUG_ONLY(})
6672   // Note: the finger doesn't advance while we drain
6673   // the stack below.
6674   PushOrMarkClosure pushOrMarkClosure(_collector,
6675                                       _span, _bitMap, _markStack,
6676                                       _finger, this);
6677   bool res = _markStack->push(obj);
6678   assert(res, "Empty non-zero size stack should have space for single push");
6679   while (!_markStack->isEmpty()) {
6680     oop new_oop = _markStack->pop();
6681     // Skip verifying header mark word below because we are
6682     // running concurrent with mutators.
6683     assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
6684     // now scan this oop's oops
6685     new_oop->oop_iterate(&pushOrMarkClosure);
6686     do_yield_check();
6687   }
6688   assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
6689 }
6690 
6691 Par_MarkFromRootsClosure::Par_MarkFromRootsClosure(CMSConcMarkingTask* task,
6692                        CMSCollector* collector, MemRegion span,
6693                        CMSBitMap* bit_map,
6694                        OopTaskQueue* work_queue,
6695                        CMSMarkStack*  overflow_stack):
6696   _collector(collector),
6697   _whole_span(collector->_span),
6698   _span(span),
6699   _bit_map(bit_map),
6700   _mut(&collector->_modUnionTable),
6701   _work_queue(work_queue),
6702   _overflow_stack(overflow_stack),
6703   _skip_bits(0),
6704   _task(task)
6705 {
6706   assert(_work_queue->size() == 0, "work_queue should be empty");
6707   _finger = span.start();
6708   _threshold = _finger;     // XXX Defer clear-on-enter optimization for now
6709   assert(_span.contains(_finger), "Out of bounds _finger?");
6710 }
6711 
6712 // Should revisit to see if this should be restructured for
6713 // greater efficiency.
6714 bool Par_MarkFromRootsClosure::do_bit(size_t offset) {
6715   if (_skip_bits > 0) {
6716     _skip_bits--;
6717     return true;
6718   }
6719   // convert offset into a HeapWord*
6720   HeapWord* addr = _bit_map->startWord() + offset;
6721   assert(_bit_map->endWord() && addr < _bit_map->endWord(),
6722          "address out of range");
6723   assert(_bit_map->isMarked(addr), "tautology");
6724   if (_bit_map->isMarked(addr+1)) {
6725     // this is an allocated object that might not yet be initialized
6726     assert(_skip_bits == 0, "tautology");
6727     _skip_bits = 2;  // skip next two marked bits ("Printezis-marks")
6728     oop p = oop(addr);
6729     if (p->klass_or_null() == NULL) {
6730       // in the case of Clean-on-Enter optimization, redirty card
6731       // and avoid clearing card by increasing  the threshold.
6732       return true;
6733     }
6734   }
6735   scan_oops_in_oop(addr);
6736   return true;
6737 }
6738 
6739 void Par_MarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
6740   assert(_bit_map->isMarked(ptr), "expected bit to be set");
6741   // Should we assert that our work queue is empty or
6742   // below some drain limit?
6743   assert(_work_queue->size() == 0,
6744          "should drain stack to limit stack usage");
6745   // convert ptr to an oop preparatory to scanning
6746   oop obj = oop(ptr);
6747   // Ignore mark word in verification below, since we
6748   // may be running concurrent with mutators.
6749   assert(obj->is_oop(true), "should be an oop");
6750   assert(_finger <= ptr, "_finger runneth ahead");
6751   // advance the finger to right end of this object
6752   _finger = ptr + obj->size();
6753   assert(_finger > ptr, "we just incremented it above");
6754   // On large heaps, it may take us some time to get through
6755   // the marking phase. During
6756   // this time it's possible that a lot of mutations have
6757   // accumulated in the card table and the mod union table --
6758   // these mutation records are redundant until we have
6759   // actually traced into the corresponding card.
6760   // Here, we check whether advancing the finger would make
6761   // us cross into a new card, and if so clear corresponding
6762   // cards in the MUT (preclean them in the card-table in the
6763   // future).
6764 
6765   // The clean-on-enter optimization is disabled by default,
6766   // until we fix 6178663.
6767   if (CMSCleanOnEnter && (_finger > _threshold)) {
6768     // [_threshold, _finger) represents the interval
6769     // of cards to be cleared  in MUT (or precleaned in card table).
6770     // The set of cards to be cleared is all those that overlap
6771     // with the interval [_threshold, _finger); note that
6772     // _threshold is always kept card-aligned but _finger isn't
6773     // always card-aligned.
6774     HeapWord* old_threshold = _threshold;
6775     assert(old_threshold == (HeapWord*)round_to(
6776             (intptr_t)old_threshold, CardTableModRefBS::card_size),
6777            "_threshold should always be card-aligned");
6778     _threshold = (HeapWord*)round_to(
6779                    (intptr_t)_finger, CardTableModRefBS::card_size);
6780     MemRegion mr(old_threshold, _threshold);
6781     assert(!mr.is_empty(), "Control point invariant");
6782     assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
6783     _mut->clear_range(mr);
6784   }
6785 
6786   // Note: the local finger doesn't advance while we drain
6787   // the stack below, but the global finger sure can and will.
6788   HeapWord** gfa = _task->global_finger_addr();
6789   Par_PushOrMarkClosure pushOrMarkClosure(_collector,
6790                                       _span, _bit_map,
6791                                       _work_queue,
6792                                       _overflow_stack,
6793                                       _finger,
6794                                       gfa, this);
6795   bool res = _work_queue->push(obj);   // overflow could occur here
6796   assert(res, "Will hold once we use workqueues");
6797   while (true) {
6798     oop new_oop;
6799     if (!_work_queue->pop_local(new_oop)) {
6800       // We emptied our work_queue; check if there's stuff that can
6801       // be gotten from the overflow stack.
6802       if (CMSConcMarkingTask::get_work_from_overflow_stack(
6803             _overflow_stack, _work_queue)) {
6804         do_yield_check();
6805         continue;
6806       } else {  // done
6807         break;
6808       }
6809     }
6810     // Skip verifying header mark word below because we are
6811     // running concurrent with mutators.
6812     assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
6813     // now scan this oop's oops
6814     new_oop->oop_iterate(&pushOrMarkClosure);
6815     do_yield_check();
6816   }
6817   assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
6818 }
6819 
6820 // Yield in response to a request from VM Thread or
6821 // from mutators.
6822 void Par_MarkFromRootsClosure::do_yield_work() {
6823   assert(_task != NULL, "sanity");
6824   _task->yield();
6825 }
6826 
6827 // A variant of the above used for verifying CMS marking work.
6828 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
6829                         MemRegion span,
6830                         CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6831                         CMSMarkStack*  mark_stack):
6832   _collector(collector),
6833   _span(span),
6834   _verification_bm(verification_bm),
6835   _cms_bm(cms_bm),
6836   _mark_stack(mark_stack),
6837   _pam_verify_closure(collector, span, verification_bm, cms_bm,
6838                       mark_stack)
6839 {
6840   assert(_mark_stack->isEmpty(), "stack should be empty");
6841   _finger = _verification_bm->startWord();
6842   assert(_collector->_restart_addr == NULL, "Sanity check");
6843   assert(_span.contains(_finger), "Out of bounds _finger?");
6844 }
6845 
6846 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
6847   assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
6848   assert(_span.contains(addr), "Out of bounds _finger?");
6849   _finger = addr;
6850 }
6851 
6852 // Should revisit to see if this should be restructured for
6853 // greater efficiency.
6854 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
6855   // convert offset into a HeapWord*
6856   HeapWord* addr = _verification_bm->startWord() + offset;
6857   assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
6858          "address out of range");
6859   assert(_verification_bm->isMarked(addr), "tautology");
6860   assert(_cms_bm->isMarked(addr), "tautology");
6861 
6862   assert(_mark_stack->isEmpty(),
6863          "should drain stack to limit stack usage");
6864   // convert addr to an oop preparatory to scanning
6865   oop obj = oop(addr);
6866   assert(obj->is_oop(), "should be an oop");
6867   assert(_finger <= addr, "_finger runneth ahead");
6868   // advance the finger to right end of this object
6869   _finger = addr + obj->size();
6870   assert(_finger > addr, "we just incremented it above");
6871   // Note: the finger doesn't advance while we drain
6872   // the stack below.
6873   bool res = _mark_stack->push(obj);
6874   assert(res, "Empty non-zero size stack should have space for single push");
6875   while (!_mark_stack->isEmpty()) {
6876     oop new_oop = _mark_stack->pop();
6877     assert(new_oop->is_oop(), "Oops! expected to pop an oop");
6878     // now scan this oop's oops
6879     new_oop->oop_iterate(&_pam_verify_closure);
6880   }
6881   assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
6882   return true;
6883 }
6884 
6885 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
6886   CMSCollector* collector, MemRegion span,
6887   CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6888   CMSMarkStack*  mark_stack):
6889   MetadataAwareOopClosure(collector->ref_processor()),
6890   _collector(collector),
6891   _span(span),
6892   _verification_bm(verification_bm),
6893   _cms_bm(cms_bm),
6894   _mark_stack(mark_stack)
6895 { }
6896 
6897 void PushAndMarkVerifyClosure::do_oop(oop* p)       { PushAndMarkVerifyClosure::do_oop_work(p); }
6898 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
6899 
6900 // Upon stack overflow, we discard (part of) the stack,
6901 // remembering the least address amongst those discarded
6902 // in CMSCollector's _restart_address.
6903 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
6904   // Remember the least grey address discarded
6905   HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
6906   _collector->lower_restart_addr(ra);
6907   _mark_stack->reset();  // discard stack contents
6908   _mark_stack->expand(); // expand the stack if possible
6909 }
6910 
6911 void PushAndMarkVerifyClosure::do_oop(oop obj) {
6912   assert(obj->is_oop_or_null(), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
6913   HeapWord* addr = (HeapWord*)obj;
6914   if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
6915     // Oop lies in _span and isn't yet grey or black
6916     _verification_bm->mark(addr);            // now grey
6917     if (!_cms_bm->isMarked(addr)) {
6918       oop(addr)->print();
6919       gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)",
6920                              p2i(addr));
6921       fatal("... aborting");
6922     }
6923 
6924     if (!_mark_stack->push(obj)) { // stack overflow
6925       if (PrintCMSStatistics != 0) {
6926         gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
6927                                SIZE_FORMAT, _mark_stack->capacity());
6928       }
6929       assert(_mark_stack->isFull(), "Else push should have succeeded");
6930       handle_stack_overflow(addr);
6931     }
6932     // anything including and to the right of _finger
6933     // will be scanned as we iterate over the remainder of the
6934     // bit map
6935   }
6936 }
6937 
6938 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
6939                      MemRegion span,
6940                      CMSBitMap* bitMap, CMSMarkStack*  markStack,
6941                      HeapWord* finger, MarkFromRootsClosure* parent) :
6942   MetadataAwareOopClosure(collector->ref_processor()),
6943   _collector(collector),
6944   _span(span),
6945   _bitMap(bitMap),
6946   _markStack(markStack),
6947   _finger(finger),
6948   _parent(parent)
6949 { }
6950 
6951 Par_PushOrMarkClosure::Par_PushOrMarkClosure(CMSCollector* collector,
6952                      MemRegion span,
6953                      CMSBitMap* bit_map,
6954                      OopTaskQueue* work_queue,
6955                      CMSMarkStack*  overflow_stack,
6956                      HeapWord* finger,
6957                      HeapWord** global_finger_addr,
6958                      Par_MarkFromRootsClosure* parent) :
6959   MetadataAwareOopClosure(collector->ref_processor()),
6960   _collector(collector),
6961   _whole_span(collector->_span),
6962   _span(span),
6963   _bit_map(bit_map),
6964   _work_queue(work_queue),
6965   _overflow_stack(overflow_stack),
6966   _finger(finger),
6967   _global_finger_addr(global_finger_addr),
6968   _parent(parent)
6969 { }
6970 
6971 // Assumes thread-safe access by callers, who are
6972 // responsible for mutual exclusion.
6973 void CMSCollector::lower_restart_addr(HeapWord* low) {
6974   assert(_span.contains(low), "Out of bounds addr");
6975   if (_restart_addr == NULL) {
6976     _restart_addr = low;
6977   } else {
6978     _restart_addr = MIN2(_restart_addr, low);
6979   }
6980 }
6981 
6982 // Upon stack overflow, we discard (part of) the stack,
6983 // remembering the least address amongst those discarded
6984 // in CMSCollector's _restart_address.
6985 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
6986   // Remember the least grey address discarded
6987   HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
6988   _collector->lower_restart_addr(ra);
6989   _markStack->reset();  // discard stack contents
6990   _markStack->expand(); // expand the stack if possible
6991 }
6992 
6993 // Upon stack overflow, we discard (part of) the stack,
6994 // remembering the least address amongst those discarded
6995 // in CMSCollector's _restart_address.
6996 void Par_PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
6997   // We need to do this under a mutex to prevent other
6998   // workers from interfering with the work done below.
6999   MutexLockerEx ml(_overflow_stack->par_lock(),
7000                    Mutex::_no_safepoint_check_flag);
7001   // Remember the least grey address discarded
7002   HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
7003   _collector->lower_restart_addr(ra);
7004   _overflow_stack->reset();  // discard stack contents
7005   _overflow_stack->expand(); // expand the stack if possible
7006 }
7007 
7008 void PushOrMarkClosure::do_oop(oop obj) {
7009   // Ignore mark word because we are running concurrent with mutators.
7010   assert(obj->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7011   HeapWord* addr = (HeapWord*)obj;
7012   if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
7013     // Oop lies in _span and isn't yet grey or black
7014     _bitMap->mark(addr);            // now grey
7015     if (addr < _finger) {
7016       // the bit map iteration has already either passed, or
7017       // sampled, this bit in the bit map; we'll need to
7018       // use the marking stack to scan this oop's oops.
7019       bool simulate_overflow = false;
7020       NOT_PRODUCT(
7021         if (CMSMarkStackOverflowALot &&
7022             _collector->simulate_overflow()) {
7023           // simulate a stack overflow
7024           simulate_overflow = true;
7025         }
7026       )
7027       if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
7028         if (PrintCMSStatistics != 0) {
7029           gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7030                                  SIZE_FORMAT, _markStack->capacity());
7031         }
7032         assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
7033         handle_stack_overflow(addr);
7034       }
7035     }
7036     // anything including and to the right of _finger
7037     // will be scanned as we iterate over the remainder of the
7038     // bit map
7039     do_yield_check();
7040   }
7041 }
7042 
7043 void PushOrMarkClosure::do_oop(oop* p)       { PushOrMarkClosure::do_oop_work(p); }
7044 void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); }
7045 
7046 void Par_PushOrMarkClosure::do_oop(oop obj) {
7047   // Ignore mark word because we are running concurrent with mutators.
7048   assert(obj->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7049   HeapWord* addr = (HeapWord*)obj;
7050   if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
7051     // Oop lies in _span and isn't yet grey or black
7052     // We read the global_finger (volatile read) strictly after marking oop
7053     bool res = _bit_map->par_mark(addr);    // now grey
7054     volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
7055     // Should we push this marked oop on our stack?
7056     // -- if someone else marked it, nothing to do
7057     // -- if target oop is above global finger nothing to do
7058     // -- if target oop is in chunk and above local finger
7059     //      then nothing to do
7060     // -- else push on work queue
7061     if (   !res       // someone else marked it, they will deal with it
7062         || (addr >= *gfa)  // will be scanned in a later task
7063         || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
7064       return;
7065     }
7066     // the bit map iteration has already either passed, or
7067     // sampled, this bit in the bit map; we'll need to
7068     // use the marking stack to scan this oop's oops.
7069     bool simulate_overflow = false;
7070     NOT_PRODUCT(
7071       if (CMSMarkStackOverflowALot &&
7072           _collector->simulate_overflow()) {
7073         // simulate a stack overflow
7074         simulate_overflow = true;
7075       }
7076     )
7077     if (simulate_overflow ||
7078         !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
7079       // stack overflow
7080       if (PrintCMSStatistics != 0) {
7081         gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7082                                SIZE_FORMAT, _overflow_stack->capacity());
7083       }
7084       // We cannot assert that the overflow stack is full because
7085       // it may have been emptied since.
7086       assert(simulate_overflow ||
7087              _work_queue->size() == _work_queue->max_elems(),
7088             "Else push should have succeeded");
7089       handle_stack_overflow(addr);
7090     }
7091     do_yield_check();
7092   }
7093 }
7094 
7095 void Par_PushOrMarkClosure::do_oop(oop* p)       { Par_PushOrMarkClosure::do_oop_work(p); }
7096 void Par_PushOrMarkClosure::do_oop(narrowOop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7097 
7098 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
7099                                        MemRegion span,
7100                                        ReferenceProcessor* rp,
7101                                        CMSBitMap* bit_map,
7102                                        CMSBitMap* mod_union_table,
7103                                        CMSMarkStack*  mark_stack,
7104                                        bool           concurrent_precleaning):
7105   MetadataAwareOopClosure(rp),
7106   _collector(collector),
7107   _span(span),
7108   _bit_map(bit_map),
7109   _mod_union_table(mod_union_table),
7110   _mark_stack(mark_stack),
7111   _concurrent_precleaning(concurrent_precleaning)
7112 {
7113   assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7114 }
7115 
7116 // Grey object rescan during pre-cleaning and second checkpoint phases --
7117 // the non-parallel version (the parallel version appears further below.)
7118 void PushAndMarkClosure::do_oop(oop obj) {
7119   // Ignore mark word verification. If during concurrent precleaning,
7120   // the object monitor may be locked. If during the checkpoint
7121   // phases, the object may already have been reached by a  different
7122   // path and may be at the end of the global overflow list (so
7123   // the mark word may be NULL).
7124   assert(obj->is_oop_or_null(true /* ignore mark word */),
7125          err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7126   HeapWord* addr = (HeapWord*)obj;
7127   // Check if oop points into the CMS generation
7128   // and is not marked
7129   if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7130     // a white object ...
7131     _bit_map->mark(addr);         // ... now grey
7132     // push on the marking stack (grey set)
7133     bool simulate_overflow = false;
7134     NOT_PRODUCT(
7135       if (CMSMarkStackOverflowALot &&
7136           _collector->simulate_overflow()) {
7137         // simulate a stack overflow
7138         simulate_overflow = true;
7139       }
7140     )
7141     if (simulate_overflow || !_mark_stack->push(obj)) {
7142       if (_concurrent_precleaning) {
7143          // During precleaning we can just dirty the appropriate card(s)
7144          // in the mod union table, thus ensuring that the object remains
7145          // in the grey set  and continue. In the case of object arrays
7146          // we need to dirty all of the cards that the object spans,
7147          // since the rescan of object arrays will be limited to the
7148          // dirty cards.
7149          // Note that no one can be interfering with us in this action
7150          // of dirtying the mod union table, so no locking or atomics
7151          // are required.
7152          if (obj->is_objArray()) {
7153            size_t sz = obj->size();
7154            HeapWord* end_card_addr = (HeapWord*)round_to(
7155                                         (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7156            MemRegion redirty_range = MemRegion(addr, end_card_addr);
7157            assert(!redirty_range.is_empty(), "Arithmetical tautology");
7158            _mod_union_table->mark_range(redirty_range);
7159          } else {
7160            _mod_union_table->mark(addr);
7161          }
7162          _collector->_ser_pmc_preclean_ovflw++;
7163       } else {
7164          // During the remark phase, we need to remember this oop
7165          // in the overflow list.
7166          _collector->push_on_overflow_list(obj);
7167          _collector->_ser_pmc_remark_ovflw++;
7168       }
7169     }
7170   }
7171 }
7172 
7173 Par_PushAndMarkClosure::Par_PushAndMarkClosure(CMSCollector* collector,
7174                                                MemRegion span,
7175                                                ReferenceProcessor* rp,
7176                                                CMSBitMap* bit_map,
7177                                                OopTaskQueue* work_queue):
7178   MetadataAwareOopClosure(rp),
7179   _collector(collector),
7180   _span(span),
7181   _bit_map(bit_map),
7182   _work_queue(work_queue)
7183 {
7184   assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7185 }
7186 
7187 void PushAndMarkClosure::do_oop(oop* p)       { PushAndMarkClosure::do_oop_work(p); }
7188 void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); }
7189 
7190 // Grey object rescan during second checkpoint phase --
7191 // the parallel version.
7192 void Par_PushAndMarkClosure::do_oop(oop obj) {
7193   // In the assert below, we ignore the mark word because
7194   // this oop may point to an already visited object that is
7195   // on the overflow stack (in which case the mark word has
7196   // been hijacked for chaining into the overflow stack --
7197   // if this is the last object in the overflow stack then
7198   // its mark word will be NULL). Because this object may
7199   // have been subsequently popped off the global overflow
7200   // stack, and the mark word possibly restored to the prototypical
7201   // value, by the time we get to examined this failing assert in
7202   // the debugger, is_oop_or_null(false) may subsequently start
7203   // to hold.
7204   assert(obj->is_oop_or_null(true),
7205          err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7206   HeapWord* addr = (HeapWord*)obj;
7207   // Check if oop points into the CMS generation
7208   // and is not marked
7209   if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7210     // a white object ...
7211     // If we manage to "claim" the object, by being the
7212     // first thread to mark it, then we push it on our
7213     // marking stack
7214     if (_bit_map->par_mark(addr)) {     // ... now grey
7215       // push on work queue (grey set)
7216       bool simulate_overflow = false;
7217       NOT_PRODUCT(
7218         if (CMSMarkStackOverflowALot &&
7219             _collector->par_simulate_overflow()) {
7220           // simulate a stack overflow
7221           simulate_overflow = true;
7222         }
7223       )
7224       if (simulate_overflow || !_work_queue->push(obj)) {
7225         _collector->par_push_on_overflow_list(obj);
7226         _collector->_par_pmc_remark_ovflw++; //  imprecise OK: no need to CAS
7227       }
7228     } // Else, some other thread got there first
7229   }
7230 }
7231 
7232 void Par_PushAndMarkClosure::do_oop(oop* p)       { Par_PushAndMarkClosure::do_oop_work(p); }
7233 void Par_PushAndMarkClosure::do_oop(narrowOop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7234 
7235 void CMSPrecleanRefsYieldClosure::do_yield_work() {
7236   Mutex* bml = _collector->bitMapLock();
7237   assert_lock_strong(bml);
7238   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7239          "CMS thread should hold CMS token");
7240 
7241   bml->unlock();
7242   ConcurrentMarkSweepThread::desynchronize(true);
7243 
7244   _collector->stopTimer();
7245   if (PrintCMSStatistics != 0) {
7246     _collector->incrementYields();
7247   }
7248 
7249   // See the comment in coordinator_yield()
7250   for (unsigned i = 0; i < CMSYieldSleepCount &&
7251                        ConcurrentMarkSweepThread::should_yield() &&
7252                        !CMSCollector::foregroundGCIsActive(); ++i) {
7253     os::sleep(Thread::current(), 1, false);
7254   }
7255 
7256   ConcurrentMarkSweepThread::synchronize(true);
7257   bml->lock();
7258 
7259   _collector->startTimer();
7260 }
7261 
7262 bool CMSPrecleanRefsYieldClosure::should_return() {
7263   if (ConcurrentMarkSweepThread::should_yield()) {
7264     do_yield_work();
7265   }
7266   return _collector->foregroundGCIsActive();
7267 }
7268 
7269 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
7270   assert(((size_t)mr.start())%CardTableModRefBS::card_size_in_words == 0,
7271          "mr should be aligned to start at a card boundary");
7272   // We'd like to assert:
7273   // assert(mr.word_size()%CardTableModRefBS::card_size_in_words == 0,
7274   //        "mr should be a range of cards");
7275   // However, that would be too strong in one case -- the last
7276   // partition ends at _unallocated_block which, in general, can be
7277   // an arbitrary boundary, not necessarily card aligned.
7278   if (PrintCMSStatistics != 0) {
7279     _num_dirty_cards +=
7280          mr.word_size()/CardTableModRefBS::card_size_in_words;
7281   }
7282   _space->object_iterate_mem(mr, &_scan_cl);
7283 }
7284 
7285 SweepClosure::SweepClosure(CMSCollector* collector,
7286                            ConcurrentMarkSweepGeneration* g,
7287                            CMSBitMap* bitMap, bool should_yield) :
7288   _collector(collector),
7289   _g(g),
7290   _sp(g->cmsSpace()),
7291   _limit(_sp->sweep_limit()),
7292   _freelistLock(_sp->freelistLock()),
7293   _bitMap(bitMap),
7294   _yield(should_yield),
7295   _inFreeRange(false),           // No free range at beginning of sweep
7296   _freeRangeInFreeLists(false),  // No free range at beginning of sweep
7297   _lastFreeRangeCoalesced(false),
7298   _freeFinger(g->used_region().start())
7299 {
7300   NOT_PRODUCT(
7301     _numObjectsFreed = 0;
7302     _numWordsFreed   = 0;
7303     _numObjectsLive = 0;
7304     _numWordsLive = 0;
7305     _numObjectsAlreadyFree = 0;
7306     _numWordsAlreadyFree = 0;
7307     _last_fc = NULL;
7308 
7309     _sp->initializeIndexedFreeListArrayReturnedBytes();
7310     _sp->dictionary()->initialize_dict_returned_bytes();
7311   )
7312   assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7313          "sweep _limit out of bounds");
7314   if (CMSTraceSweeper) {
7315     gclog_or_tty->print_cr("\n====================\nStarting new sweep with limit " PTR_FORMAT,
7316                         p2i(_limit));
7317   }
7318 }
7319 
7320 void SweepClosure::print_on(outputStream* st) const {
7321   tty->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")",
7322                 p2i(_sp->bottom()), p2i(_sp->end()));
7323   tty->print_cr("_limit = " PTR_FORMAT, p2i(_limit));
7324   tty->print_cr("_freeFinger = " PTR_FORMAT, p2i(_freeFinger));
7325   NOT_PRODUCT(tty->print_cr("_last_fc = " PTR_FORMAT, p2i(_last_fc));)
7326   tty->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d",
7327                 _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced);
7328 }
7329 
7330 #ifndef PRODUCT
7331 // Assertion checking only:  no useful work in product mode --
7332 // however, if any of the flags below become product flags,
7333 // you may need to review this code to see if it needs to be
7334 // enabled in product mode.
7335 SweepClosure::~SweepClosure() {
7336   assert_lock_strong(_freelistLock);
7337   assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7338          "sweep _limit out of bounds");
7339   if (inFreeRange()) {
7340     warning("inFreeRange() should have been reset; dumping state of SweepClosure");
7341     print();
7342     ShouldNotReachHere();
7343   }
7344   if (Verbose && PrintGC) {
7345     gclog_or_tty->print("Collected "SIZE_FORMAT" objects, " SIZE_FORMAT " bytes",
7346                         _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
7347     gclog_or_tty->print_cr("\nLive "SIZE_FORMAT" objects,  "
7348                            SIZE_FORMAT" bytes  "
7349       "Already free "SIZE_FORMAT" objects, "SIZE_FORMAT" bytes",
7350       _numObjectsLive, _numWordsLive*sizeof(HeapWord),
7351       _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
7352     size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree)
7353                         * sizeof(HeapWord);
7354     gclog_or_tty->print_cr("Total sweep: "SIZE_FORMAT" bytes", totalBytes);
7355 
7356     if (PrintCMSStatistics && CMSVerifyReturnedBytes) {
7357       size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
7358       size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes();
7359       size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes;
7360       gclog_or_tty->print("Returned "SIZE_FORMAT" bytes", returned_bytes);
7361       gclog_or_tty->print("   Indexed List Returned "SIZE_FORMAT" bytes",
7362         indexListReturnedBytes);
7363       gclog_or_tty->print_cr("        Dictionary Returned "SIZE_FORMAT" bytes",
7364         dict_returned_bytes);
7365     }
7366   }
7367   if (CMSTraceSweeper) {
7368     gclog_or_tty->print_cr("end of sweep with _limit = " PTR_FORMAT "\n================",
7369                            p2i(_limit));
7370   }
7371 }
7372 #endif  // PRODUCT
7373 
7374 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
7375     bool freeRangeInFreeLists) {
7376   if (CMSTraceSweeper) {
7377     gclog_or_tty->print("---- Start free range at " PTR_FORMAT " with free block (%d)\n",
7378                p2i(freeFinger), freeRangeInFreeLists);
7379   }
7380   assert(!inFreeRange(), "Trampling existing free range");
7381   set_inFreeRange(true);
7382   set_lastFreeRangeCoalesced(false);
7383 
7384   set_freeFinger(freeFinger);
7385   set_freeRangeInFreeLists(freeRangeInFreeLists);
7386   if (CMSTestInFreeList) {
7387     if (freeRangeInFreeLists) {
7388       FreeChunk* fc = (FreeChunk*) freeFinger;
7389       assert(fc->is_free(), "A chunk on the free list should be free.");
7390       assert(fc->size() > 0, "Free range should have a size");
7391       assert(_sp->verify_chunk_in_free_list(fc), "Chunk is not in free lists");
7392     }
7393   }
7394 }
7395 
7396 // Note that the sweeper runs concurrently with mutators. Thus,
7397 // it is possible for direct allocation in this generation to happen
7398 // in the middle of the sweep. Note that the sweeper also coalesces
7399 // contiguous free blocks. Thus, unless the sweeper and the allocator
7400 // synchronize appropriately freshly allocated blocks may get swept up.
7401 // This is accomplished by the sweeper locking the free lists while
7402 // it is sweeping. Thus blocks that are determined to be free are
7403 // indeed free. There is however one additional complication:
7404 // blocks that have been allocated since the final checkpoint and
7405 // mark, will not have been marked and so would be treated as
7406 // unreachable and swept up. To prevent this, the allocator marks
7407 // the bit map when allocating during the sweep phase. This leads,
7408 // however, to a further complication -- objects may have been allocated
7409 // but not yet initialized -- in the sense that the header isn't yet
7410 // installed. The sweeper can not then determine the size of the block
7411 // in order to skip over it. To deal with this case, we use a technique
7412 // (due to Printezis) to encode such uninitialized block sizes in the
7413 // bit map. Since the bit map uses a bit per every HeapWord, but the
7414 // CMS generation has a minimum object size of 3 HeapWords, it follows
7415 // that "normal marks" won't be adjacent in the bit map (there will
7416 // always be at least two 0 bits between successive 1 bits). We make use
7417 // of these "unused" bits to represent uninitialized blocks -- the bit
7418 // corresponding to the start of the uninitialized object and the next
7419 // bit are both set. Finally, a 1 bit marks the end of the object that
7420 // started with the two consecutive 1 bits to indicate its potentially
7421 // uninitialized state.
7422 
7423 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
7424   FreeChunk* fc = (FreeChunk*)addr;
7425   size_t res;
7426 
7427   // Check if we are done sweeping. Below we check "addr >= _limit" rather
7428   // than "addr == _limit" because although _limit was a block boundary when
7429   // we started the sweep, it may no longer be one because heap expansion
7430   // may have caused us to coalesce the block ending at the address _limit
7431   // with a newly expanded chunk (this happens when _limit was set to the
7432   // previous _end of the space), so we may have stepped past _limit:
7433   // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740.
7434   if (addr >= _limit) { // we have swept up to or past the limit: finish up
7435     assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7436            "sweep _limit out of bounds");
7437     assert(addr < _sp->end(), "addr out of bounds");
7438     // Flush any free range we might be holding as a single
7439     // coalesced chunk to the appropriate free list.
7440     if (inFreeRange()) {
7441       assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit,
7442              err_msg("freeFinger() " PTR_FORMAT" is out-of-bounds", p2i(freeFinger())));
7443       flush_cur_free_chunk(freeFinger(),
7444                            pointer_delta(addr, freeFinger()));
7445       if (CMSTraceSweeper) {
7446         gclog_or_tty->print("Sweep: last chunk: ");
7447         gclog_or_tty->print("put_free_blk " PTR_FORMAT " ("SIZE_FORMAT") "
7448                    "[coalesced:%d]\n",
7449                    p2i(freeFinger()), pointer_delta(addr, freeFinger()),
7450                    lastFreeRangeCoalesced() ? 1 : 0);
7451       }
7452     }
7453 
7454     // help the iterator loop finish
7455     return pointer_delta(_sp->end(), addr);
7456   }
7457 
7458   assert(addr < _limit, "sweep invariant");
7459   // check if we should yield
7460   do_yield_check(addr);
7461   if (fc->is_free()) {
7462     // Chunk that is already free
7463     res = fc->size();
7464     do_already_free_chunk(fc);
7465     debug_only(_sp->verifyFreeLists());
7466     // If we flush the chunk at hand in lookahead_and_flush()
7467     // and it's coalesced with a preceding chunk, then the
7468     // process of "mangling" the payload of the coalesced block
7469     // will cause erasure of the size information from the
7470     // (erstwhile) header of all the coalesced blocks but the
7471     // first, so the first disjunct in the assert will not hold
7472     // in that specific case (in which case the second disjunct
7473     // will hold).
7474     assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit,
7475            "Otherwise the size info doesn't change at this step");
7476     NOT_PRODUCT(
7477       _numObjectsAlreadyFree++;
7478       _numWordsAlreadyFree += res;
7479     )
7480     NOT_PRODUCT(_last_fc = fc;)
7481   } else if (!_bitMap->isMarked(addr)) {
7482     // Chunk is fresh garbage
7483     res = do_garbage_chunk(fc);
7484     debug_only(_sp->verifyFreeLists());
7485     NOT_PRODUCT(
7486       _numObjectsFreed++;
7487       _numWordsFreed += res;
7488     )
7489   } else {
7490     // Chunk that is alive.
7491     res = do_live_chunk(fc);
7492     debug_only(_sp->verifyFreeLists());
7493     NOT_PRODUCT(
7494         _numObjectsLive++;
7495         _numWordsLive += res;
7496     )
7497   }
7498   return res;
7499 }
7500 
7501 // For the smart allocation, record following
7502 //  split deaths - a free chunk is removed from its free list because
7503 //      it is being split into two or more chunks.
7504 //  split birth - a free chunk is being added to its free list because
7505 //      a larger free chunk has been split and resulted in this free chunk.
7506 //  coal death - a free chunk is being removed from its free list because
7507 //      it is being coalesced into a large free chunk.
7508 //  coal birth - a free chunk is being added to its free list because
7509 //      it was created when two or more free chunks where coalesced into
7510 //      this free chunk.
7511 //
7512 // These statistics are used to determine the desired number of free
7513 // chunks of a given size.  The desired number is chosen to be relative
7514 // to the end of a CMS sweep.  The desired number at the end of a sweep
7515 // is the
7516 //      count-at-end-of-previous-sweep (an amount that was enough)
7517 //              - count-at-beginning-of-current-sweep  (the excess)
7518 //              + split-births  (gains in this size during interval)
7519 //              - split-deaths  (demands on this size during interval)
7520 // where the interval is from the end of one sweep to the end of the
7521 // next.
7522 //
7523 // When sweeping the sweeper maintains an accumulated chunk which is
7524 // the chunk that is made up of chunks that have been coalesced.  That
7525 // will be termed the left-hand chunk.  A new chunk of garbage that
7526 // is being considered for coalescing will be referred to as the
7527 // right-hand chunk.
7528 //
7529 // When making a decision on whether to coalesce a right-hand chunk with
7530 // the current left-hand chunk, the current count vs. the desired count
7531 // of the left-hand chunk is considered.  Also if the right-hand chunk
7532 // is near the large chunk at the end of the heap (see
7533 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
7534 // left-hand chunk is coalesced.
7535 //
7536 // When making a decision about whether to split a chunk, the desired count
7537 // vs. the current count of the candidate to be split is also considered.
7538 // If the candidate is underpopulated (currently fewer chunks than desired)
7539 // a chunk of an overpopulated (currently more chunks than desired) size may
7540 // be chosen.  The "hint" associated with a free list, if non-null, points
7541 // to a free list which may be overpopulated.
7542 //
7543 
7544 void SweepClosure::do_already_free_chunk(FreeChunk* fc) {
7545   const size_t size = fc->size();
7546   // Chunks that cannot be coalesced are not in the
7547   // free lists.
7548   if (CMSTestInFreeList && !fc->cantCoalesce()) {
7549     assert(_sp->verify_chunk_in_free_list(fc),
7550       "free chunk should be in free lists");
7551   }
7552   // a chunk that is already free, should not have been
7553   // marked in the bit map
7554   HeapWord* const addr = (HeapWord*) fc;
7555   assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
7556   // Verify that the bit map has no bits marked between
7557   // addr and purported end of this block.
7558   _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7559 
7560   // Some chunks cannot be coalesced under any circumstances.
7561   // See the definition of cantCoalesce().
7562   if (!fc->cantCoalesce()) {
7563     // This chunk can potentially be coalesced.
7564     if (_sp->adaptive_freelists()) {
7565       // All the work is done in
7566       do_post_free_or_garbage_chunk(fc, size);
7567     } else {  // Not adaptive free lists
7568       // this is a free chunk that can potentially be coalesced by the sweeper;
7569       if (!inFreeRange()) {
7570         // if the next chunk is a free block that can't be coalesced
7571         // it doesn't make sense to remove this chunk from the free lists
7572         FreeChunk* nextChunk = (FreeChunk*)(addr + size);
7573         assert((HeapWord*)nextChunk <= _sp->end(), "Chunk size out of bounds?");
7574         if ((HeapWord*)nextChunk < _sp->end() &&     // There is another free chunk to the right ...
7575             nextChunk->is_free()               &&     // ... which is free...
7576             nextChunk->cantCoalesce()) {             // ... but can't be coalesced
7577           // nothing to do
7578         } else {
7579           // Potentially the start of a new free range:
7580           // Don't eagerly remove it from the free lists.
7581           // No need to remove it if it will just be put
7582           // back again.  (Also from a pragmatic point of view
7583           // if it is a free block in a region that is beyond
7584           // any allocated blocks, an assertion will fail)
7585           // Remember the start of a free run.
7586           initialize_free_range(addr, true);
7587           // end - can coalesce with next chunk
7588         }
7589       } else {
7590         // the midst of a free range, we are coalescing
7591         print_free_block_coalesced(fc);
7592         if (CMSTraceSweeper) {
7593           gclog_or_tty->print("  -- pick up free block " PTR_FORMAT " (" SIZE_FORMAT ")\n", p2i(fc), size);
7594         }
7595         // remove it from the free lists
7596         _sp->removeFreeChunkFromFreeLists(fc);
7597         set_lastFreeRangeCoalesced(true);
7598         // If the chunk is being coalesced and the current free range is
7599         // in the free lists, remove the current free range so that it
7600         // will be returned to the free lists in its entirety - all
7601         // the coalesced pieces included.
7602         if (freeRangeInFreeLists()) {
7603           FreeChunk* ffc = (FreeChunk*) freeFinger();
7604           assert(ffc->size() == pointer_delta(addr, freeFinger()),
7605             "Size of free range is inconsistent with chunk size.");
7606           if (CMSTestInFreeList) {
7607             assert(_sp->verify_chunk_in_free_list(ffc),
7608               "free range is not in free lists");
7609           }
7610           _sp->removeFreeChunkFromFreeLists(ffc);
7611           set_freeRangeInFreeLists(false);
7612         }
7613       }
7614     }
7615     // Note that if the chunk is not coalescable (the else arm
7616     // below), we unconditionally flush, without needing to do
7617     // a "lookahead," as we do below.
7618     if (inFreeRange()) lookahead_and_flush(fc, size);
7619   } else {
7620     // Code path common to both original and adaptive free lists.
7621 
7622     // cant coalesce with previous block; this should be treated
7623     // as the end of a free run if any
7624     if (inFreeRange()) {
7625       // we kicked some butt; time to pick up the garbage
7626       assert(freeFinger() < addr, "freeFinger points too high");
7627       flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7628     }
7629     // else, nothing to do, just continue
7630   }
7631 }
7632 
7633 size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) {
7634   // This is a chunk of garbage.  It is not in any free list.
7635   // Add it to a free list or let it possibly be coalesced into
7636   // a larger chunk.
7637   HeapWord* const addr = (HeapWord*) fc;
7638   const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7639 
7640   if (_sp->adaptive_freelists()) {
7641     // Verify that the bit map has no bits marked between
7642     // addr and purported end of just dead object.
7643     _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7644 
7645     do_post_free_or_garbage_chunk(fc, size);
7646   } else {
7647     if (!inFreeRange()) {
7648       // start of a new free range
7649       assert(size > 0, "A free range should have a size");
7650       initialize_free_range(addr, false);
7651     } else {
7652       // this will be swept up when we hit the end of the
7653       // free range
7654       if (CMSTraceSweeper) {
7655         gclog_or_tty->print("  -- pick up garbage " PTR_FORMAT " (" SIZE_FORMAT ")\n", p2i(fc), size);
7656       }
7657       // If the chunk is being coalesced and the current free range is
7658       // in the free lists, remove the current free range so that it
7659       // will be returned to the free lists in its entirety - all
7660       // the coalesced pieces included.
7661       if (freeRangeInFreeLists()) {
7662         FreeChunk* ffc = (FreeChunk*)freeFinger();
7663         assert(ffc->size() == pointer_delta(addr, freeFinger()),
7664           "Size of free range is inconsistent with chunk size.");
7665         if (CMSTestInFreeList) {
7666           assert(_sp->verify_chunk_in_free_list(ffc),
7667             "free range is not in free lists");
7668         }
7669         _sp->removeFreeChunkFromFreeLists(ffc);
7670         set_freeRangeInFreeLists(false);
7671       }
7672       set_lastFreeRangeCoalesced(true);
7673     }
7674     // this will be swept up when we hit the end of the free range
7675 
7676     // Verify that the bit map has no bits marked between
7677     // addr and purported end of just dead object.
7678     _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7679   }
7680   assert(_limit >= addr + size,
7681          "A freshly garbage chunk can't possibly straddle over _limit");
7682   if (inFreeRange()) lookahead_and_flush(fc, size);
7683   return size;
7684 }
7685 
7686 size_t SweepClosure::do_live_chunk(FreeChunk* fc) {
7687   HeapWord* addr = (HeapWord*) fc;
7688   // The sweeper has just found a live object. Return any accumulated
7689   // left hand chunk to the free lists.
7690   if (inFreeRange()) {
7691     assert(freeFinger() < addr, "freeFinger points too high");
7692     flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7693   }
7694 
7695   // This object is live: we'd normally expect this to be
7696   // an oop, and like to assert the following:
7697   // assert(oop(addr)->is_oop(), "live block should be an oop");
7698   // However, as we commented above, this may be an object whose
7699   // header hasn't yet been initialized.
7700   size_t size;
7701   assert(_bitMap->isMarked(addr), "Tautology for this control point");
7702   if (_bitMap->isMarked(addr + 1)) {
7703     // Determine the size from the bit map, rather than trying to
7704     // compute it from the object header.
7705     HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
7706     size = pointer_delta(nextOneAddr + 1, addr);
7707     assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
7708            "alignment problem");
7709 
7710 #ifdef ASSERT
7711       if (oop(addr)->klass_or_null() != NULL) {
7712         // Ignore mark word because we are running concurrent with mutators
7713         assert(oop(addr)->is_oop(true), "live block should be an oop");
7714         assert(size ==
7715                CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
7716                "P-mark and computed size do not agree");
7717       }
7718 #endif
7719 
7720   } else {
7721     // This should be an initialized object that's alive.
7722     assert(oop(addr)->klass_or_null() != NULL,
7723            "Should be an initialized object");
7724     // Ignore mark word because we are running concurrent with mutators
7725     assert(oop(addr)->is_oop(true), "live block should be an oop");
7726     // Verify that the bit map has no bits marked between
7727     // addr and purported end of this block.
7728     size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7729     assert(size >= 3, "Necessary for Printezis marks to work");
7730     assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
7731     DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
7732   }
7733   return size;
7734 }
7735 
7736 void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc,
7737                                                  size_t chunkSize) {
7738   // do_post_free_or_garbage_chunk() should only be called in the case
7739   // of the adaptive free list allocator.
7740   const bool fcInFreeLists = fc->is_free();
7741   assert(_sp->adaptive_freelists(), "Should only be used in this case.");
7742   assert((HeapWord*)fc <= _limit, "sweep invariant");
7743   if (CMSTestInFreeList && fcInFreeLists) {
7744     assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists");
7745   }
7746 
7747   if (CMSTraceSweeper) {
7748     gclog_or_tty->print_cr("  -- pick up another chunk at " PTR_FORMAT " (" SIZE_FORMAT ")", p2i(fc), chunkSize);
7749   }
7750 
7751   HeapWord* const fc_addr = (HeapWord*) fc;
7752 
7753   bool coalesce;
7754   const size_t left  = pointer_delta(fc_addr, freeFinger());
7755   const size_t right = chunkSize;
7756   switch (FLSCoalescePolicy) {
7757     // numeric value forms a coalition aggressiveness metric
7758     case 0:  { // never coalesce
7759       coalesce = false;
7760       break;
7761     }
7762     case 1: { // coalesce if left & right chunks on overpopulated lists
7763       coalesce = _sp->coalOverPopulated(left) &&
7764                  _sp->coalOverPopulated(right);
7765       break;
7766     }
7767     case 2: { // coalesce if left chunk on overpopulated list (default)
7768       coalesce = _sp->coalOverPopulated(left);
7769       break;
7770     }
7771     case 3: { // coalesce if left OR right chunk on overpopulated list
7772       coalesce = _sp->coalOverPopulated(left) ||
7773                  _sp->coalOverPopulated(right);
7774       break;
7775     }
7776     case 4: { // always coalesce
7777       coalesce = true;
7778       break;
7779     }
7780     default:
7781      ShouldNotReachHere();
7782   }
7783 
7784   // Should the current free range be coalesced?
7785   // If the chunk is in a free range and either we decided to coalesce above
7786   // or the chunk is near the large block at the end of the heap
7787   // (isNearLargestChunk() returns true), then coalesce this chunk.
7788   const bool doCoalesce = inFreeRange()
7789                           && (coalesce || _g->isNearLargestChunk(fc_addr));
7790   if (doCoalesce) {
7791     // Coalesce the current free range on the left with the new
7792     // chunk on the right.  If either is on a free list,
7793     // it must be removed from the list and stashed in the closure.
7794     if (freeRangeInFreeLists()) {
7795       FreeChunk* const ffc = (FreeChunk*)freeFinger();
7796       assert(ffc->size() == pointer_delta(fc_addr, freeFinger()),
7797         "Size of free range is inconsistent with chunk size.");
7798       if (CMSTestInFreeList) {
7799         assert(_sp->verify_chunk_in_free_list(ffc),
7800           "Chunk is not in free lists");
7801       }
7802       _sp->coalDeath(ffc->size());
7803       _sp->removeFreeChunkFromFreeLists(ffc);
7804       set_freeRangeInFreeLists(false);
7805     }
7806     if (fcInFreeLists) {
7807       _sp->coalDeath(chunkSize);
7808       assert(fc->size() == chunkSize,
7809         "The chunk has the wrong size or is not in the free lists");
7810       _sp->removeFreeChunkFromFreeLists(fc);
7811     }
7812     set_lastFreeRangeCoalesced(true);
7813     print_free_block_coalesced(fc);
7814   } else {  // not in a free range and/or should not coalesce
7815     // Return the current free range and start a new one.
7816     if (inFreeRange()) {
7817       // In a free range but cannot coalesce with the right hand chunk.
7818       // Put the current free range into the free lists.
7819       flush_cur_free_chunk(freeFinger(),
7820                            pointer_delta(fc_addr, freeFinger()));
7821     }
7822     // Set up for new free range.  Pass along whether the right hand
7823     // chunk is in the free lists.
7824     initialize_free_range((HeapWord*)fc, fcInFreeLists);
7825   }
7826 }
7827 
7828 // Lookahead flush:
7829 // If we are tracking a free range, and this is the last chunk that
7830 // we'll look at because its end crosses past _limit, we'll preemptively
7831 // flush it along with any free range we may be holding on to. Note that
7832 // this can be the case only for an already free or freshly garbage
7833 // chunk. If this block is an object, it can never straddle
7834 // over _limit. The "straddling" occurs when _limit is set at
7835 // the previous end of the space when this cycle started, and
7836 // a subsequent heap expansion caused the previously co-terminal
7837 // free block to be coalesced with the newly expanded portion,
7838 // thus rendering _limit a non-block-boundary making it dangerous
7839 // for the sweeper to step over and examine.
7840 void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) {
7841   assert(inFreeRange(), "Should only be called if currently in a free range.");
7842   HeapWord* const eob = ((HeapWord*)fc) + chunk_size;
7843   assert(_sp->used_region().contains(eob - 1),
7844          err_msg("eob = " PTR_FORMAT " eob-1 = " PTR_FORMAT " _limit = " PTR_FORMAT
7845                  " out of bounds wrt _sp = [" PTR_FORMAT "," PTR_FORMAT ")"
7846                  " when examining fc = " PTR_FORMAT "(" SIZE_FORMAT ")",
7847                  p2i(eob), p2i(eob-1), p2i(_limit), p2i(_sp->bottom()), p2i(_sp->end()), p2i(fc), chunk_size));
7848   if (eob >= _limit) {
7849     assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit");
7850     if (CMSTraceSweeper) {
7851       gclog_or_tty->print_cr("_limit " PTR_FORMAT " reached or crossed by block "
7852                              "[" PTR_FORMAT "," PTR_FORMAT ") in space "
7853                              "[" PTR_FORMAT "," PTR_FORMAT ")",
7854                              p2i(_limit), p2i(fc), p2i(eob), p2i(_sp->bottom()), p2i(_sp->end()));
7855     }
7856     // Return the storage we are tracking back into the free lists.
7857     if (CMSTraceSweeper) {
7858       gclog_or_tty->print_cr("Flushing ... ");
7859     }
7860     assert(freeFinger() < eob, "Error");
7861     flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger()));
7862   }
7863 }
7864 
7865 void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) {
7866   assert(inFreeRange(), "Should only be called if currently in a free range.");
7867   assert(size > 0,
7868     "A zero sized chunk cannot be added to the free lists.");
7869   if (!freeRangeInFreeLists()) {
7870     if (CMSTestInFreeList) {
7871       FreeChunk* fc = (FreeChunk*) chunk;
7872       fc->set_size(size);
7873       assert(!_sp->verify_chunk_in_free_list(fc),
7874         "chunk should not be in free lists yet");
7875     }
7876     if (CMSTraceSweeper) {
7877       gclog_or_tty->print_cr(" -- add free block " PTR_FORMAT " (" SIZE_FORMAT ") to free lists",
7878                     p2i(chunk), size);
7879     }
7880     // A new free range is going to be starting.  The current
7881     // free range has not been added to the free lists yet or
7882     // was removed so add it back.
7883     // If the current free range was coalesced, then the death
7884     // of the free range was recorded.  Record a birth now.
7885     if (lastFreeRangeCoalesced()) {
7886       _sp->coalBirth(size);
7887     }
7888     _sp->addChunkAndRepairOffsetTable(chunk, size,
7889             lastFreeRangeCoalesced());
7890   } else if (CMSTraceSweeper) {
7891     gclog_or_tty->print_cr("Already in free list: nothing to flush");
7892   }
7893   set_inFreeRange(false);
7894   set_freeRangeInFreeLists(false);
7895 }
7896 
7897 // We take a break if we've been at this for a while,
7898 // so as to avoid monopolizing the locks involved.
7899 void SweepClosure::do_yield_work(HeapWord* addr) {
7900   // Return current free chunk being used for coalescing (if any)
7901   // to the appropriate freelist.  After yielding, the next
7902   // free block encountered will start a coalescing range of
7903   // free blocks.  If the next free block is adjacent to the
7904   // chunk just flushed, they will need to wait for the next
7905   // sweep to be coalesced.
7906   if (inFreeRange()) {
7907     flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7908   }
7909 
7910   // First give up the locks, then yield, then re-lock.
7911   // We should probably use a constructor/destructor idiom to
7912   // do this unlock/lock or modify the MutexUnlocker class to
7913   // serve our purpose. XXX
7914   assert_lock_strong(_bitMap->lock());
7915   assert_lock_strong(_freelistLock);
7916   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7917          "CMS thread should hold CMS token");
7918   _bitMap->lock()->unlock();
7919   _freelistLock->unlock();
7920   ConcurrentMarkSweepThread::desynchronize(true);
7921   _collector->stopTimer();
7922   if (PrintCMSStatistics != 0) {
7923     _collector->incrementYields();
7924   }
7925 
7926   // See the comment in coordinator_yield()
7927   for (unsigned i = 0; i < CMSYieldSleepCount &&
7928                        ConcurrentMarkSweepThread::should_yield() &&
7929                        !CMSCollector::foregroundGCIsActive(); ++i) {
7930     os::sleep(Thread::current(), 1, false);
7931   }
7932 
7933   ConcurrentMarkSweepThread::synchronize(true);
7934   _freelistLock->lock();
7935   _bitMap->lock()->lock_without_safepoint_check();
7936   _collector->startTimer();
7937 }
7938 
7939 #ifndef PRODUCT
7940 // This is actually very useful in a product build if it can
7941 // be called from the debugger.  Compile it into the product
7942 // as needed.
7943 bool debug_verify_chunk_in_free_list(FreeChunk* fc) {
7944   return debug_cms_space->verify_chunk_in_free_list(fc);
7945 }
7946 #endif
7947 
7948 void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const {
7949   if (CMSTraceSweeper) {
7950     gclog_or_tty->print_cr("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")",
7951                            p2i(fc), fc->size());
7952   }
7953 }
7954 
7955 // CMSIsAliveClosure
7956 bool CMSIsAliveClosure::do_object_b(oop obj) {
7957   HeapWord* addr = (HeapWord*)obj;
7958   return addr != NULL &&
7959          (!_span.contains(addr) || _bit_map->isMarked(addr));
7960 }
7961 
7962 
7963 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector,
7964                       MemRegion span,
7965                       CMSBitMap* bit_map, CMSMarkStack* mark_stack,
7966                       bool cpc):
7967   _collector(collector),
7968   _span(span),
7969   _bit_map(bit_map),
7970   _mark_stack(mark_stack),
7971   _concurrent_precleaning(cpc) {
7972   assert(!_span.is_empty(), "Empty span could spell trouble");
7973 }
7974 
7975 
7976 // CMSKeepAliveClosure: the serial version
7977 void CMSKeepAliveClosure::do_oop(oop obj) {
7978   HeapWord* addr = (HeapWord*)obj;
7979   if (_span.contains(addr) &&
7980       !_bit_map->isMarked(addr)) {
7981     _bit_map->mark(addr);
7982     bool simulate_overflow = false;
7983     NOT_PRODUCT(
7984       if (CMSMarkStackOverflowALot &&
7985           _collector->simulate_overflow()) {
7986         // simulate a stack overflow
7987         simulate_overflow = true;
7988       }
7989     )
7990     if (simulate_overflow || !_mark_stack->push(obj)) {
7991       if (_concurrent_precleaning) {
7992         // We dirty the overflown object and let the remark
7993         // phase deal with it.
7994         assert(_collector->overflow_list_is_empty(), "Error");
7995         // In the case of object arrays, we need to dirty all of
7996         // the cards that the object spans. No locking or atomics
7997         // are needed since no one else can be mutating the mod union
7998         // table.
7999         if (obj->is_objArray()) {
8000           size_t sz = obj->size();
8001           HeapWord* end_card_addr =
8002             (HeapWord*)round_to((intptr_t)(addr+sz), CardTableModRefBS::card_size);
8003           MemRegion redirty_range = MemRegion(addr, end_card_addr);
8004           assert(!redirty_range.is_empty(), "Arithmetical tautology");
8005           _collector->_modUnionTable.mark_range(redirty_range);
8006         } else {
8007           _collector->_modUnionTable.mark(addr);
8008         }
8009         _collector->_ser_kac_preclean_ovflw++;
8010       } else {
8011         _collector->push_on_overflow_list(obj);
8012         _collector->_ser_kac_ovflw++;
8013       }
8014     }
8015   }
8016 }
8017 
8018 void CMSKeepAliveClosure::do_oop(oop* p)       { CMSKeepAliveClosure::do_oop_work(p); }
8019 void CMSKeepAliveClosure::do_oop(narrowOop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8020 
8021 // CMSParKeepAliveClosure: a parallel version of the above.
8022 // The work queues are private to each closure (thread),
8023 // but (may be) available for stealing by other threads.
8024 void CMSParKeepAliveClosure::do_oop(oop obj) {
8025   HeapWord* addr = (HeapWord*)obj;
8026   if (_span.contains(addr) &&
8027       !_bit_map->isMarked(addr)) {
8028     // In general, during recursive tracing, several threads
8029     // may be concurrently getting here; the first one to
8030     // "tag" it, claims it.
8031     if (_bit_map->par_mark(addr)) {
8032       bool res = _work_queue->push(obj);
8033       assert(res, "Low water mark should be much less than capacity");
8034       // Do a recursive trim in the hope that this will keep
8035       // stack usage lower, but leave some oops for potential stealers
8036       trim_queue(_low_water_mark);
8037     } // Else, another thread got there first
8038   }
8039 }
8040 
8041 void CMSParKeepAliveClosure::do_oop(oop* p)       { CMSParKeepAliveClosure::do_oop_work(p); }
8042 void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8043 
8044 void CMSParKeepAliveClosure::trim_queue(uint max) {
8045   while (_work_queue->size() > max) {
8046     oop new_oop;
8047     if (_work_queue->pop_local(new_oop)) {
8048       assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
8049       assert(_bit_map->isMarked((HeapWord*)new_oop),
8050              "no white objects on this stack!");
8051       assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8052       // iterate over the oops in this oop, marking and pushing
8053       // the ones in CMS heap (i.e. in _span).
8054       new_oop->oop_iterate(&_mark_and_push);
8055     }
8056   }
8057 }
8058 
8059 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
8060                                 CMSCollector* collector,
8061                                 MemRegion span, CMSBitMap* bit_map,
8062                                 OopTaskQueue* work_queue):
8063   _collector(collector),
8064   _span(span),
8065   _bit_map(bit_map),
8066   _work_queue(work_queue) { }
8067 
8068 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
8069   HeapWord* addr = (HeapWord*)obj;
8070   if (_span.contains(addr) &&
8071       !_bit_map->isMarked(addr)) {
8072     if (_bit_map->par_mark(addr)) {
8073       bool simulate_overflow = false;
8074       NOT_PRODUCT(
8075         if (CMSMarkStackOverflowALot &&
8076             _collector->par_simulate_overflow()) {
8077           // simulate a stack overflow
8078           simulate_overflow = true;
8079         }
8080       )
8081       if (simulate_overflow || !_work_queue->push(obj)) {
8082         _collector->par_push_on_overflow_list(obj);
8083         _collector->_par_kac_ovflw++;
8084       }
8085     } // Else another thread got there already
8086   }
8087 }
8088 
8089 void CMSInnerParMarkAndPushClosure::do_oop(oop* p)       { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8090 void CMSInnerParMarkAndPushClosure::do_oop(narrowOop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8091 
8092 //////////////////////////////////////////////////////////////////
8093 //  CMSExpansionCause                /////////////////////////////
8094 //////////////////////////////////////////////////////////////////
8095 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
8096   switch (cause) {
8097     case _no_expansion:
8098       return "No expansion";
8099     case _satisfy_free_ratio:
8100       return "Free ratio";
8101     case _satisfy_promotion:
8102       return "Satisfy promotion";
8103     case _satisfy_allocation:
8104       return "allocation";
8105     case _allocate_par_lab:
8106       return "Par LAB";
8107     case _allocate_par_spooling_space:
8108       return "Par Spooling Space";
8109     case _adaptive_size_policy:
8110       return "Ergonomics";
8111     default:
8112       return "unknown";
8113   }
8114 }
8115 
8116 void CMSDrainMarkingStackClosure::do_void() {
8117   // the max number to take from overflow list at a time
8118   const size_t num = _mark_stack->capacity()/4;
8119   assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
8120          "Overflow list should be NULL during concurrent phases");
8121   while (!_mark_stack->isEmpty() ||
8122          // if stack is empty, check the overflow list
8123          _collector->take_from_overflow_list(num, _mark_stack)) {
8124     oop obj = _mark_stack->pop();
8125     HeapWord* addr = (HeapWord*)obj;
8126     assert(_span.contains(addr), "Should be within span");
8127     assert(_bit_map->isMarked(addr), "Should be marked");
8128     assert(obj->is_oop(), "Should be an oop");
8129     obj->oop_iterate(_keep_alive);
8130   }
8131 }
8132 
8133 void CMSParDrainMarkingStackClosure::do_void() {
8134   // drain queue
8135   trim_queue(0);
8136 }
8137 
8138 // Trim our work_queue so its length is below max at return
8139 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
8140   while (_work_queue->size() > max) {
8141     oop new_oop;
8142     if (_work_queue->pop_local(new_oop)) {
8143       assert(new_oop->is_oop(), "Expected an oop");
8144       assert(_bit_map->isMarked((HeapWord*)new_oop),
8145              "no white objects on this stack!");
8146       assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8147       // iterate over the oops in this oop, marking and pushing
8148       // the ones in CMS heap (i.e. in _span).
8149       new_oop->oop_iterate(&_mark_and_push);
8150     }
8151   }
8152 }
8153 
8154 ////////////////////////////////////////////////////////////////////
8155 // Support for Marking Stack Overflow list handling and related code
8156 ////////////////////////////////////////////////////////////////////
8157 // Much of the following code is similar in shape and spirit to the
8158 // code used in ParNewGC. We should try and share that code
8159 // as much as possible in the future.
8160 
8161 #ifndef PRODUCT
8162 // Debugging support for CMSStackOverflowALot
8163 
8164 // It's OK to call this multi-threaded;  the worst thing
8165 // that can happen is that we'll get a bunch of closely
8166 // spaced simulated overflows, but that's OK, in fact
8167 // probably good as it would exercise the overflow code
8168 // under contention.
8169 bool CMSCollector::simulate_overflow() {
8170   if (_overflow_counter-- <= 0) { // just being defensive
8171     _overflow_counter = CMSMarkStackOverflowInterval;
8172     return true;
8173   } else {
8174     return false;
8175   }
8176 }
8177 
8178 bool CMSCollector::par_simulate_overflow() {
8179   return simulate_overflow();
8180 }
8181 #endif
8182 
8183 // Single-threaded
8184 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
8185   assert(stack->isEmpty(), "Expected precondition");
8186   assert(stack->capacity() > num, "Shouldn't bite more than can chew");
8187   size_t i = num;
8188   oop  cur = _overflow_list;
8189   const markOop proto = markOopDesc::prototype();
8190   NOT_PRODUCT(ssize_t n = 0;)
8191   for (oop next; i > 0 && cur != NULL; cur = next, i--) {
8192     next = oop(cur->mark());
8193     cur->set_mark(proto);   // until proven otherwise
8194     assert(cur->is_oop(), "Should be an oop");
8195     bool res = stack->push(cur);
8196     assert(res, "Bit off more than can chew?");
8197     NOT_PRODUCT(n++;)
8198   }
8199   _overflow_list = cur;
8200 #ifndef PRODUCT
8201   assert(_num_par_pushes >= n, "Too many pops?");
8202   _num_par_pushes -=n;
8203 #endif
8204   return !stack->isEmpty();
8205 }
8206 
8207 #define BUSY  (cast_to_oop<intptr_t>(0x1aff1aff))
8208 // (MT-safe) Get a prefix of at most "num" from the list.
8209 // The overflow list is chained through the mark word of
8210 // each object in the list. We fetch the entire list,
8211 // break off a prefix of the right size and return the
8212 // remainder. If other threads try to take objects from
8213 // the overflow list at that time, they will wait for
8214 // some time to see if data becomes available. If (and
8215 // only if) another thread places one or more object(s)
8216 // on the global list before we have returned the suffix
8217 // to the global list, we will walk down our local list
8218 // to find its end and append the global list to
8219 // our suffix before returning it. This suffix walk can
8220 // prove to be expensive (quadratic in the amount of traffic)
8221 // when there are many objects in the overflow list and
8222 // there is much producer-consumer contention on the list.
8223 // *NOTE*: The overflow list manipulation code here and
8224 // in ParNewGeneration:: are very similar in shape,
8225 // except that in the ParNew case we use the old (from/eden)
8226 // copy of the object to thread the list via its klass word.
8227 // Because of the common code, if you make any changes in
8228 // the code below, please check the ParNew version to see if
8229 // similar changes might be needed.
8230 // CR 6797058 has been filed to consolidate the common code.
8231 bool CMSCollector::par_take_from_overflow_list(size_t num,
8232                                                OopTaskQueue* work_q,
8233                                                int no_of_gc_threads) {
8234   assert(work_q->size() == 0, "First empty local work queue");
8235   assert(num < work_q->max_elems(), "Can't bite more than we can chew");
8236   if (_overflow_list == NULL) {
8237     return false;
8238   }
8239   // Grab the entire list; we'll put back a suffix
8240   oop prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
8241   Thread* tid = Thread::current();
8242   // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was
8243   // set to ParallelGCThreads.
8244   size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads;
8245   size_t sleep_time_millis = MAX2((size_t)1, num/100);
8246   // If the list is busy, we spin for a short while,
8247   // sleeping between attempts to get the list.
8248   for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) {
8249     os::sleep(tid, sleep_time_millis, false);
8250     if (_overflow_list == NULL) {
8251       // Nothing left to take
8252       return false;
8253     } else if (_overflow_list != BUSY) {
8254       // Try and grab the prefix
8255       prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
8256     }
8257   }
8258   // If the list was found to be empty, or we spun long
8259   // enough, we give up and return empty-handed. If we leave
8260   // the list in the BUSY state below, it must be the case that
8261   // some other thread holds the overflow list and will set it
8262   // to a non-BUSY state in the future.
8263   if (prefix == NULL || prefix == BUSY) {
8264      // Nothing to take or waited long enough
8265      if (prefix == NULL) {
8266        // Write back the NULL in case we overwrote it with BUSY above
8267        // and it is still the same value.
8268        (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8269      }
8270      return false;
8271   }
8272   assert(prefix != NULL && prefix != BUSY, "Error");
8273   size_t i = num;
8274   oop cur = prefix;
8275   // Walk down the first "num" objects, unless we reach the end.
8276   for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--);
8277   if (cur->mark() == NULL) {
8278     // We have "num" or fewer elements in the list, so there
8279     // is nothing to return to the global list.
8280     // Write back the NULL in lieu of the BUSY we wrote
8281     // above, if it is still the same value.
8282     if (_overflow_list == BUSY) {
8283       (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8284     }
8285   } else {
8286     // Chop off the suffix and return it to the global list.
8287     assert(cur->mark() != BUSY, "Error");
8288     oop suffix_head = cur->mark(); // suffix will be put back on global list
8289     cur->set_mark(NULL);           // break off suffix
8290     // It's possible that the list is still in the empty(busy) state
8291     // we left it in a short while ago; in that case we may be
8292     // able to place back the suffix without incurring the cost
8293     // of a walk down the list.
8294     oop observed_overflow_list = _overflow_list;
8295     oop cur_overflow_list = observed_overflow_list;
8296     bool attached = false;
8297     while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
8298       observed_overflow_list =
8299         (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
8300       if (cur_overflow_list == observed_overflow_list) {
8301         attached = true;
8302         break;
8303       } else cur_overflow_list = observed_overflow_list;
8304     }
8305     if (!attached) {
8306       // Too bad, someone else sneaked in (at least) an element; we'll need
8307       // to do a splice. Find tail of suffix so we can prepend suffix to global
8308       // list.
8309       for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark()));
8310       oop suffix_tail = cur;
8311       assert(suffix_tail != NULL && suffix_tail->mark() == NULL,
8312              "Tautology");
8313       observed_overflow_list = _overflow_list;
8314       do {
8315         cur_overflow_list = observed_overflow_list;
8316         if (cur_overflow_list != BUSY) {
8317           // Do the splice ...
8318           suffix_tail->set_mark(markOop(cur_overflow_list));
8319         } else { // cur_overflow_list == BUSY
8320           suffix_tail->set_mark(NULL);
8321         }
8322         // ... and try to place spliced list back on overflow_list ...
8323         observed_overflow_list =
8324           (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
8325       } while (cur_overflow_list != observed_overflow_list);
8326       // ... until we have succeeded in doing so.
8327     }
8328   }
8329 
8330   // Push the prefix elements on work_q
8331   assert(prefix != NULL, "control point invariant");
8332   const markOop proto = markOopDesc::prototype();
8333   oop next;
8334   NOT_PRODUCT(ssize_t n = 0;)
8335   for (cur = prefix; cur != NULL; cur = next) {
8336     next = oop(cur->mark());
8337     cur->set_mark(proto);   // until proven otherwise
8338     assert(cur->is_oop(), "Should be an oop");
8339     bool res = work_q->push(cur);
8340     assert(res, "Bit off more than we can chew?");
8341     NOT_PRODUCT(n++;)
8342   }
8343 #ifndef PRODUCT
8344   assert(_num_par_pushes >= n, "Too many pops?");
8345   Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
8346 #endif
8347   return true;
8348 }
8349 
8350 // Single-threaded
8351 void CMSCollector::push_on_overflow_list(oop p) {
8352   NOT_PRODUCT(_num_par_pushes++;)
8353   assert(p->is_oop(), "Not an oop");
8354   preserve_mark_if_necessary(p);
8355   p->set_mark((markOop)_overflow_list);
8356   _overflow_list = p;
8357 }
8358 
8359 // Multi-threaded; use CAS to prepend to overflow list
8360 void CMSCollector::par_push_on_overflow_list(oop p) {
8361   NOT_PRODUCT(Atomic::inc_ptr(&_num_par_pushes);)
8362   assert(p->is_oop(), "Not an oop");
8363   par_preserve_mark_if_necessary(p);
8364   oop observed_overflow_list = _overflow_list;
8365   oop cur_overflow_list;
8366   do {
8367     cur_overflow_list = observed_overflow_list;
8368     if (cur_overflow_list != BUSY) {
8369       p->set_mark(markOop(cur_overflow_list));
8370     } else {
8371       p->set_mark(NULL);
8372     }
8373     observed_overflow_list =
8374       (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list);
8375   } while (cur_overflow_list != observed_overflow_list);
8376 }
8377 #undef BUSY
8378 
8379 // Single threaded
8380 // General Note on GrowableArray: pushes may silently fail
8381 // because we are (temporarily) out of C-heap for expanding
8382 // the stack. The problem is quite ubiquitous and affects
8383 // a lot of code in the JVM. The prudent thing for GrowableArray
8384 // to do (for now) is to exit with an error. However, that may
8385 // be too draconian in some cases because the caller may be
8386 // able to recover without much harm. For such cases, we
8387 // should probably introduce a "soft_push" method which returns
8388 // an indication of success or failure with the assumption that
8389 // the caller may be able to recover from a failure; code in
8390 // the VM can then be changed, incrementally, to deal with such
8391 // failures where possible, thus, incrementally hardening the VM
8392 // in such low resource situations.
8393 void CMSCollector::preserve_mark_work(oop p, markOop m) {
8394   _preserved_oop_stack.push(p);
8395   _preserved_mark_stack.push(m);
8396   assert(m == p->mark(), "Mark word changed");
8397   assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8398          "bijection");
8399 }
8400 
8401 // Single threaded
8402 void CMSCollector::preserve_mark_if_necessary(oop p) {
8403   markOop m = p->mark();
8404   if (m->must_be_preserved(p)) {
8405     preserve_mark_work(p, m);
8406   }
8407 }
8408 
8409 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
8410   markOop m = p->mark();
8411   if (m->must_be_preserved(p)) {
8412     MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
8413     // Even though we read the mark word without holding
8414     // the lock, we are assured that it will not change
8415     // because we "own" this oop, so no other thread can
8416     // be trying to push it on the overflow list; see
8417     // the assertion in preserve_mark_work() that checks
8418     // that m == p->mark().
8419     preserve_mark_work(p, m);
8420   }
8421 }
8422 
8423 // We should be able to do this multi-threaded,
8424 // a chunk of stack being a task (this is
8425 // correct because each oop only ever appears
8426 // once in the overflow list. However, it's
8427 // not very easy to completely overlap this with
8428 // other operations, so will generally not be done
8429 // until all work's been completed. Because we
8430 // expect the preserved oop stack (set) to be small,
8431 // it's probably fine to do this single-threaded.
8432 // We can explore cleverer concurrent/overlapped/parallel
8433 // processing of preserved marks if we feel the
8434 // need for this in the future. Stack overflow should
8435 // be so rare in practice and, when it happens, its
8436 // effect on performance so great that this will
8437 // likely just be in the noise anyway.
8438 void CMSCollector::restore_preserved_marks_if_any() {
8439   assert(SafepointSynchronize::is_at_safepoint(),
8440          "world should be stopped");
8441   assert(Thread::current()->is_ConcurrentGC_thread() ||
8442          Thread::current()->is_VM_thread(),
8443          "should be single-threaded");
8444   assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8445          "bijection");
8446 
8447   while (!_preserved_oop_stack.is_empty()) {
8448     oop p = _preserved_oop_stack.pop();
8449     assert(p->is_oop(), "Should be an oop");
8450     assert(_span.contains(p), "oop should be in _span");
8451     assert(p->mark() == markOopDesc::prototype(),
8452            "Set when taken from overflow list");
8453     markOop m = _preserved_mark_stack.pop();
8454     p->set_mark(m);
8455   }
8456   assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(),
8457          "stacks were cleared above");
8458 }
8459 
8460 #ifndef PRODUCT
8461 bool CMSCollector::no_preserved_marks() const {
8462   return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty();
8463 }
8464 #endif
8465 
8466 // Transfer some number of overflown objects to usual marking
8467 // stack. Return true if some objects were transferred.
8468 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
8469   size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,
8470                     (size_t)ParGCDesiredObjsFromOverflowList);
8471 
8472   bool res = _collector->take_from_overflow_list(num, _mark_stack);
8473   assert(_collector->overflow_list_is_empty() || res,
8474          "If list is not empty, we should have taken something");
8475   assert(!res || !_mark_stack->isEmpty(),
8476          "If we took something, it should now be on our stack");
8477   return res;
8478 }
8479 
8480 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
8481   size_t res = _sp->block_size_no_stall(addr, _collector);
8482   if (_sp->block_is_obj(addr)) {
8483     if (_live_bit_map->isMarked(addr)) {
8484       // It can't have been dead in a previous cycle
8485       guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
8486     } else {
8487       _dead_bit_map->mark(addr);      // mark the dead object
8488     }
8489   }
8490   // Could be 0, if the block size could not be computed without stalling.
8491   return res;
8492 }
8493 
8494 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() {
8495 
8496   switch (phase) {
8497     case CMSCollector::InitialMarking:
8498       initialize(true  /* fullGC */ ,
8499                  cause /* cause of the GC */,
8500                  true  /* recordGCBeginTime */,
8501                  true  /* recordPreGCUsage */,
8502                  false /* recordPeakUsage */,
8503                  false /* recordPostGCusage */,
8504                  true  /* recordAccumulatedGCTime */,
8505                  false /* recordGCEndTime */,
8506                  false /* countCollection */  );
8507       break;
8508 
8509     case CMSCollector::FinalMarking:
8510       initialize(true  /* fullGC */ ,
8511                  cause /* cause of the GC */,
8512                  false /* recordGCBeginTime */,
8513                  false /* recordPreGCUsage */,
8514                  false /* recordPeakUsage */,
8515                  false /* recordPostGCusage */,
8516                  true  /* recordAccumulatedGCTime */,
8517                  false /* recordGCEndTime */,
8518                  false /* countCollection */  );
8519       break;
8520 
8521     case CMSCollector::Sweeping:
8522       initialize(true  /* fullGC */ ,
8523                  cause /* cause of the GC */,
8524                  false /* recordGCBeginTime */,
8525                  false /* recordPreGCUsage */,
8526                  true  /* recordPeakUsage */,
8527                  true  /* recordPostGCusage */,
8528                  false /* recordAccumulatedGCTime */,
8529                  true  /* recordGCEndTime */,
8530                  true  /* countCollection */  );
8531       break;
8532 
8533     default:
8534       ShouldNotReachHere();
8535   }
8536 }