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                              (int) ParallelGCThreads,             // mt processing degree
 289                              _cmsGen->refs_discovery_is_mt(),     // mt discovery
 290                              (int) 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 = (uint) 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   // Condition 1 above
2675   if (_full_gc_requested && ExplicitGCInvokesConcurrentAndUnloadsClasses) {
2676     _should_unload_classes = true;
2677   } else if (CMSClassUnloadingEnabled) { // Condition 2.a above
2678     // Disjuncts 2.b.(i,ii,iii) above
2679     _should_unload_classes = (concurrent_cycles_since_last_unload() >=
2680                               CMSClassUnloadingMaxInterval)
2681                            || _cmsGen->is_too_full();
2682   }
2683 }
2684 
2685 bool ConcurrentMarkSweepGeneration::is_too_full() const {
2686   bool res = should_concurrent_collect();
2687   res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
2688   return res;
2689 }
2690 
2691 void CMSCollector::setup_cms_unloading_and_verification_state() {
2692   const  bool should_verify =   VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
2693                              || VerifyBeforeExit;
2694   const  int  rso           =   GenCollectedHeap::SO_AllCodeCache;
2695 
2696   // We set the proper root for this CMS cycle here.
2697   if (should_unload_classes()) {   // Should unload classes this cycle
2698     remove_root_scanning_option(rso);  // Shrink the root set appropriately
2699     set_verifying(should_verify);    // Set verification state for this cycle
2700     return;                            // Nothing else needs to be done at this time
2701   }
2702 
2703   // Not unloading classes this cycle
2704   assert(!should_unload_classes(), "Inconsistency!");
2705 
2706   if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
2707     // Include symbols, strings and code cache elements to prevent their resurrection.
2708     add_root_scanning_option(rso);
2709     set_verifying(true);
2710   } else if (verifying() && !should_verify) {
2711     // We were verifying, but some verification flags got disabled.
2712     set_verifying(false);
2713     // Exclude symbols, strings and code cache elements from root scanning to
2714     // reduce IM and RM pauses.
2715     remove_root_scanning_option(rso);
2716   }
2717 }
2718 
2719 
2720 #ifndef PRODUCT
2721 HeapWord* CMSCollector::block_start(const void* p) const {
2722   const HeapWord* addr = (HeapWord*)p;
2723   if (_span.contains(p)) {
2724     if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
2725       return _cmsGen->cmsSpace()->block_start(p);
2726     }
2727   }
2728   return NULL;
2729 }
2730 #endif
2731 
2732 HeapWord*
2733 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
2734                                                    bool   tlab,
2735                                                    bool   parallel) {
2736   CMSSynchronousYieldRequest yr;
2737   assert(!tlab, "Can't deal with TLAB allocation");
2738   MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2739   expand_for_gc_cause(word_size*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_allocation);
2740   if (GCExpandToAllocateDelayMillis > 0) {
2741     os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2742   }
2743   return have_lock_and_allocate(word_size, tlab);
2744 }
2745 
2746 void ConcurrentMarkSweepGeneration::expand_for_gc_cause(
2747     size_t bytes,
2748     size_t expand_bytes,
2749     CMSExpansionCause::Cause cause)
2750 {
2751 
2752   bool success = expand(bytes, expand_bytes);
2753 
2754   // remember why we expanded; this information is used
2755   // by shouldConcurrentCollect() when making decisions on whether to start
2756   // a new CMS cycle.
2757   if (success) {
2758     set_expansion_cause(cause);
2759     if (PrintGCDetails && Verbose) {
2760       gclog_or_tty->print_cr("Expanded CMS gen for %s",
2761         CMSExpansionCause::to_string(cause));
2762     }
2763   }
2764 }
2765 
2766 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
2767   HeapWord* res = NULL;
2768   MutexLocker x(ParGCRareEvent_lock);
2769   while (true) {
2770     // Expansion by some other thread might make alloc OK now:
2771     res = ps->lab.alloc(word_sz);
2772     if (res != NULL) return res;
2773     // If there's not enough expansion space available, give up.
2774     if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
2775       return NULL;
2776     }
2777     // Otherwise, we try expansion.
2778     expand_for_gc_cause(word_sz*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_lab);
2779     // Now go around the loop and try alloc again;
2780     // A competing par_promote might beat us to the expansion space,
2781     // so we may go around the loop again if promotion fails again.
2782     if (GCExpandToAllocateDelayMillis > 0) {
2783       os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2784     }
2785   }
2786 }
2787 
2788 
2789 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
2790   PromotionInfo* promo) {
2791   MutexLocker x(ParGCRareEvent_lock);
2792   size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
2793   while (true) {
2794     // Expansion by some other thread might make alloc OK now:
2795     if (promo->ensure_spooling_space()) {
2796       assert(promo->has_spooling_space(),
2797              "Post-condition of successful ensure_spooling_space()");
2798       return true;
2799     }
2800     // If there's not enough expansion space available, give up.
2801     if (_virtual_space.uncommitted_size() < refill_size_bytes) {
2802       return false;
2803     }
2804     // Otherwise, we try expansion.
2805     expand_for_gc_cause(refill_size_bytes, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_spooling_space);
2806     // Now go around the loop and try alloc again;
2807     // A competing allocation might beat us to the expansion space,
2808     // so we may go around the loop again if allocation fails again.
2809     if (GCExpandToAllocateDelayMillis > 0) {
2810       os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2811     }
2812   }
2813 }
2814 
2815 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
2816   // Only shrink if a compaction was done so that all the free space
2817   // in the generation is in a contiguous block at the end.
2818   if (did_compact()) {
2819     CardGeneration::shrink(bytes);
2820   }
2821 }
2822 
2823 void ConcurrentMarkSweepGeneration::assert_correct_size_change_locking() {
2824   assert_locked_or_safepoint(Heap_lock);
2825 }
2826 
2827 void ConcurrentMarkSweepGeneration::shrink_free_list_by(size_t bytes) {
2828   assert_locked_or_safepoint(Heap_lock);
2829   assert_lock_strong(freelistLock());
2830   if (PrintGCDetails && Verbose) {
2831     warning("Shrinking of CMS not yet implemented");
2832   }
2833   return;
2834 }
2835 
2836 
2837 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
2838 // phases.
2839 class CMSPhaseAccounting: public StackObj {
2840  public:
2841   CMSPhaseAccounting(CMSCollector *collector,
2842                      const char *phase,
2843                      const GCId gc_id,
2844                      bool print_cr = true);
2845   ~CMSPhaseAccounting();
2846 
2847  private:
2848   CMSCollector *_collector;
2849   const char *_phase;
2850   elapsedTimer _wallclock;
2851   bool _print_cr;
2852   const GCId _gc_id;
2853 
2854  public:
2855   // Not MT-safe; so do not pass around these StackObj's
2856   // where they may be accessed by other threads.
2857   jlong wallclock_millis() {
2858     assert(_wallclock.is_active(), "Wall clock should not stop");
2859     _wallclock.stop();  // to record time
2860     jlong ret = _wallclock.milliseconds();
2861     _wallclock.start(); // restart
2862     return ret;
2863   }
2864 };
2865 
2866 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
2867                                        const char *phase,
2868                                        const GCId gc_id,
2869                                        bool print_cr) :
2870   _collector(collector), _phase(phase), _print_cr(print_cr), _gc_id(gc_id) {
2871 
2872   if (PrintCMSStatistics != 0) {
2873     _collector->resetYields();
2874   }
2875   if (PrintGCDetails) {
2876     gclog_or_tty->gclog_stamp(_gc_id);
2877     gclog_or_tty->print_cr("[%s-concurrent-%s-start]",
2878       _collector->cmsGen()->short_name(), _phase);
2879   }
2880   _collector->resetTimer();
2881   _wallclock.start();
2882   _collector->startTimer();
2883 }
2884 
2885 CMSPhaseAccounting::~CMSPhaseAccounting() {
2886   assert(_wallclock.is_active(), "Wall clock should not have stopped");
2887   _collector->stopTimer();
2888   _wallclock.stop();
2889   if (PrintGCDetails) {
2890     gclog_or_tty->gclog_stamp(_gc_id);
2891     gclog_or_tty->print("[%s-concurrent-%s: %3.3f/%3.3f secs]",
2892                  _collector->cmsGen()->short_name(),
2893                  _phase, _collector->timerValue(), _wallclock.seconds());
2894     if (_print_cr) {
2895       gclog_or_tty->cr();
2896     }
2897     if (PrintCMSStatistics != 0) {
2898       gclog_or_tty->print_cr(" (CMS-concurrent-%s yielded %d times)", _phase,
2899                     _collector->yields());
2900     }
2901   }
2902 }
2903 
2904 // CMS work
2905 
2906 // The common parts of CMSParInitialMarkTask and CMSParRemarkTask.
2907 class CMSParMarkTask : public AbstractGangTask {
2908  protected:
2909   CMSCollector*     _collector;
2910   uint              _n_workers;
2911   CMSParMarkTask(const char* name, CMSCollector* collector, uint n_workers) :
2912       AbstractGangTask(name),
2913       _collector(collector),
2914       _n_workers(n_workers) {}
2915   // Work method in support of parallel rescan ... of young gen spaces
2916   void do_young_space_rescan(uint worker_id, OopsInGenClosure* cl,
2917                              ContiguousSpace* space,
2918                              HeapWord** chunk_array, size_t chunk_top);
2919   void work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl);
2920 };
2921 
2922 // Parallel initial mark task
2923 class CMSParInitialMarkTask: public CMSParMarkTask {
2924   StrongRootsScope* _strong_roots_scope;
2925  public:
2926   CMSParInitialMarkTask(CMSCollector* collector, StrongRootsScope* strong_roots_scope, uint n_workers) :
2927       CMSParMarkTask("Scan roots and young gen for initial mark in parallel", collector, n_workers),
2928       _strong_roots_scope(strong_roots_scope) {}
2929   void work(uint worker_id);
2930 };
2931 
2932 // Checkpoint the roots into this generation from outside
2933 // this generation. [Note this initial checkpoint need only
2934 // be approximate -- we'll do a catch up phase subsequently.]
2935 void CMSCollector::checkpointRootsInitial() {
2936   assert(_collectorState == InitialMarking, "Wrong collector state");
2937   check_correct_thread_executing();
2938   TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
2939 
2940   save_heap_summary();
2941   report_heap_summary(GCWhen::BeforeGC);
2942 
2943   ReferenceProcessor* rp = ref_processor();
2944   assert(_restart_addr == NULL, "Control point invariant");
2945   {
2946     // acquire locks for subsequent manipulations
2947     MutexLockerEx x(bitMapLock(),
2948                     Mutex::_no_safepoint_check_flag);
2949     checkpointRootsInitialWork();
2950     // enable ("weak") refs discovery
2951     rp->enable_discovery();
2952     _collectorState = Marking;
2953   }
2954 }
2955 
2956 void CMSCollector::checkpointRootsInitialWork() {
2957   assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
2958   assert(_collectorState == InitialMarking, "just checking");
2959 
2960   // If there has not been a GC[n-1] since last GC[n] cycle completed,
2961   // precede our marking with a collection of all
2962   // younger generations to keep floating garbage to a minimum.
2963   // XXX: we won't do this for now -- it's an optimization to be done later.
2964 
2965   // already have locks
2966   assert_lock_strong(bitMapLock());
2967   assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
2968 
2969   // Setup the verification and class unloading state for this
2970   // CMS collection cycle.
2971   setup_cms_unloading_and_verification_state();
2972 
2973   NOT_PRODUCT(GCTraceTime t("\ncheckpointRootsInitialWork",
2974     PrintGCDetails && Verbose, true, _gc_timer_cm, _gc_tracer_cm->gc_id());)
2975 
2976   // Reset all the PLAB chunk arrays if necessary.
2977   if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
2978     reset_survivor_plab_arrays();
2979   }
2980 
2981   ResourceMark rm;
2982   HandleMark  hm;
2983 
2984   MarkRefsIntoClosure notOlder(_span, &_markBitMap);
2985   GenCollectedHeap* gch = GenCollectedHeap::heap();
2986 
2987   verify_work_stacks_empty();
2988   verify_overflow_empty();
2989 
2990   gch->ensure_parsability(false);  // fill TLABs, but no need to retire them
2991   // Update the saved marks which may affect the root scans.
2992   gch->save_marks();
2993 
2994   // weak reference processing has not started yet.
2995   ref_processor()->set_enqueuing_is_done(false);
2996 
2997   // Need to remember all newly created CLDs,
2998   // so that we can guarantee that the remark finds them.
2999   ClassLoaderDataGraph::remember_new_clds(true);
3000 
3001   // Whenever a CLD is found, it will be claimed before proceeding to mark
3002   // the klasses. The claimed marks need to be cleared before marking starts.
3003   ClassLoaderDataGraph::clear_claimed_marks();
3004 
3005   if (CMSPrintEdenSurvivorChunks) {
3006     print_eden_and_survivor_chunk_arrays();
3007   }
3008 
3009   {
3010     COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
3011     if (CMSParallelInitialMarkEnabled) {
3012       // The parallel version.
3013       WorkGang* workers = gch->workers();
3014       assert(workers != NULL, "Need parallel worker threads.");
3015       uint n_workers = workers->active_workers();
3016 
3017       StrongRootsScope srs(n_workers);
3018 
3019       CMSParInitialMarkTask tsk(this, &srs, n_workers);
3020       initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
3021       if (n_workers > 1) {
3022         workers->run_task(&tsk);
3023       } else {
3024         tsk.work(0);
3025       }
3026     } else {
3027       // The serial version.
3028       CLDToOopClosure cld_closure(&notOlder, true);
3029       gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3030 
3031       StrongRootsScope srs(1);
3032 
3033       gch->gen_process_roots(&srs,
3034                              _cmsGen->level(),
3035                              true,   // younger gens are roots
3036                              GenCollectedHeap::ScanningOption(roots_scanning_options()),
3037                              should_unload_classes(),
3038                              &notOlder,
3039                              NULL,
3040                              &cld_closure);
3041     }
3042   }
3043 
3044   // Clear mod-union table; it will be dirtied in the prologue of
3045   // CMS generation per each younger generation collection.
3046 
3047   assert(_modUnionTable.isAllClear(),
3048        "Was cleared in most recent final checkpoint phase"
3049        " or no bits are set in the gc_prologue before the start of the next "
3050        "subsequent marking phase.");
3051 
3052   assert(_ct->klass_rem_set()->mod_union_is_clear(), "Must be");
3053 
3054   // Save the end of the used_region of the constituent generations
3055   // to be used to limit the extent of sweep in each generation.
3056   save_sweep_limits();
3057   verify_overflow_empty();
3058 }
3059 
3060 bool CMSCollector::markFromRoots() {
3061   // we might be tempted to assert that:
3062   // assert(!SafepointSynchronize::is_at_safepoint(),
3063   //        "inconsistent argument?");
3064   // However that wouldn't be right, because it's possible that
3065   // a safepoint is indeed in progress as a younger generation
3066   // stop-the-world GC happens even as we mark in this generation.
3067   assert(_collectorState == Marking, "inconsistent state?");
3068   check_correct_thread_executing();
3069   verify_overflow_empty();
3070 
3071   // Weak ref discovery note: We may be discovering weak
3072   // refs in this generation concurrent (but interleaved) with
3073   // weak ref discovery by a younger generation collector.
3074 
3075   CMSTokenSyncWithLocks ts(true, bitMapLock());
3076   TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3077   CMSPhaseAccounting pa(this, "mark", _gc_tracer_cm->gc_id(), !PrintGCDetails);
3078   bool res = markFromRootsWork();
3079   if (res) {
3080     _collectorState = Precleaning;
3081   } else { // We failed and a foreground collection wants to take over
3082     assert(_foregroundGCIsActive, "internal state inconsistency");
3083     assert(_restart_addr == NULL,  "foreground will restart from scratch");
3084     if (PrintGCDetails) {
3085       gclog_or_tty->print_cr("bailing out to foreground collection");
3086     }
3087   }
3088   verify_overflow_empty();
3089   return res;
3090 }
3091 
3092 bool CMSCollector::markFromRootsWork() {
3093   // iterate over marked bits in bit map, doing a full scan and mark
3094   // from these roots using the following algorithm:
3095   // . if oop is to the right of the current scan pointer,
3096   //   mark corresponding bit (we'll process it later)
3097   // . else (oop is to left of current scan pointer)
3098   //   push oop on marking stack
3099   // . drain the marking stack
3100 
3101   // Note that when we do a marking step we need to hold the
3102   // bit map lock -- recall that direct allocation (by mutators)
3103   // and promotion (by younger generation collectors) is also
3104   // marking the bit map. [the so-called allocate live policy.]
3105   // Because the implementation of bit map marking is not
3106   // robust wrt simultaneous marking of bits in the same word,
3107   // we need to make sure that there is no such interference
3108   // between concurrent such updates.
3109 
3110   // already have locks
3111   assert_lock_strong(bitMapLock());
3112 
3113   verify_work_stacks_empty();
3114   verify_overflow_empty();
3115   bool result = false;
3116   if (CMSConcurrentMTEnabled && ConcGCThreads > 0) {
3117     result = do_marking_mt();
3118   } else {
3119     result = do_marking_st();
3120   }
3121   return result;
3122 }
3123 
3124 // Forward decl
3125 class CMSConcMarkingTask;
3126 
3127 class CMSConcMarkingTerminator: public ParallelTaskTerminator {
3128   CMSCollector*       _collector;
3129   CMSConcMarkingTask* _task;
3130  public:
3131   virtual void yield();
3132 
3133   // "n_threads" is the number of threads to be terminated.
3134   // "queue_set" is a set of work queues of other threads.
3135   // "collector" is the CMS collector associated with this task terminator.
3136   // "yield" indicates whether we need the gang as a whole to yield.
3137   CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
3138     ParallelTaskTerminator(n_threads, queue_set),
3139     _collector(collector) { }
3140 
3141   void set_task(CMSConcMarkingTask* task) {
3142     _task = task;
3143   }
3144 };
3145 
3146 class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator {
3147   CMSConcMarkingTask* _task;
3148  public:
3149   bool should_exit_termination();
3150   void set_task(CMSConcMarkingTask* task) {
3151     _task = task;
3152   }
3153 };
3154 
3155 // MT Concurrent Marking Task
3156 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3157   CMSCollector* _collector;
3158   uint          _n_workers;       // requested/desired # workers
3159   bool          _result;
3160   CompactibleFreeListSpace*  _cms_space;
3161   char          _pad_front[64];   // padding to ...
3162   HeapWord*     _global_finger;   // ... avoid sharing cache line
3163   char          _pad_back[64];
3164   HeapWord*     _restart_addr;
3165 
3166   //  Exposed here for yielding support
3167   Mutex* const _bit_map_lock;
3168 
3169   // The per thread work queues, available here for stealing
3170   OopTaskQueueSet*  _task_queues;
3171 
3172   // Termination (and yielding) support
3173   CMSConcMarkingTerminator _term;
3174   CMSConcMarkingTerminatorTerminator _term_term;
3175 
3176  public:
3177   CMSConcMarkingTask(CMSCollector* collector,
3178                  CompactibleFreeListSpace* cms_space,
3179                  YieldingFlexibleWorkGang* workers,
3180                  OopTaskQueueSet* task_queues):
3181     YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3182     _collector(collector),
3183     _cms_space(cms_space),
3184     _n_workers(0), _result(true),
3185     _task_queues(task_queues),
3186     _term(_n_workers, task_queues, _collector),
3187     _bit_map_lock(collector->bitMapLock())
3188   {
3189     _requested_size = _n_workers;
3190     _term.set_task(this);
3191     _term_term.set_task(this);
3192     _restart_addr = _global_finger = _cms_space->bottom();
3193   }
3194 
3195 
3196   OopTaskQueueSet* task_queues()  { return _task_queues; }
3197 
3198   OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3199 
3200   HeapWord** global_finger_addr() { return &_global_finger; }
3201 
3202   CMSConcMarkingTerminator* terminator() { return &_term; }
3203 
3204   virtual void set_for_termination(uint active_workers) {
3205     terminator()->reset_for_reuse(active_workers);
3206   }
3207 
3208   void work(uint worker_id);
3209   bool should_yield() {
3210     return    ConcurrentMarkSweepThread::should_yield()
3211            && !_collector->foregroundGCIsActive();
3212   }
3213 
3214   virtual void coordinator_yield();  // stuff done by coordinator
3215   bool result() { return _result; }
3216 
3217   void reset(HeapWord* ra) {
3218     assert(_global_finger >= _cms_space->end(),  "Postcondition of ::work(i)");
3219     _restart_addr = _global_finger = ra;
3220     _term.reset_for_reuse();
3221   }
3222 
3223   static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3224                                            OopTaskQueue* work_q);
3225 
3226  private:
3227   void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3228   void do_work_steal(int i);
3229   void bump_global_finger(HeapWord* f);
3230 };
3231 
3232 bool CMSConcMarkingTerminatorTerminator::should_exit_termination() {
3233   assert(_task != NULL, "Error");
3234   return _task->yielding();
3235   // Note that we do not need the disjunct || _task->should_yield() above
3236   // because we want terminating threads to yield only if the task
3237   // is already in the midst of yielding, which happens only after at least one
3238   // thread has yielded.
3239 }
3240 
3241 void CMSConcMarkingTerminator::yield() {
3242   if (_task->should_yield()) {
3243     _task->yield();
3244   } else {
3245     ParallelTaskTerminator::yield();
3246   }
3247 }
3248 
3249 ////////////////////////////////////////////////////////////////
3250 // Concurrent Marking Algorithm Sketch
3251 ////////////////////////////////////////////////////////////////
3252 // Until all tasks exhausted (both spaces):
3253 // -- claim next available chunk
3254 // -- bump global finger via CAS
3255 // -- find first object that starts in this chunk
3256 //    and start scanning bitmap from that position
3257 // -- scan marked objects for oops
3258 // -- CAS-mark target, and if successful:
3259 //    . if target oop is above global finger (volatile read)
3260 //      nothing to do
3261 //    . if target oop is in chunk and above local finger
3262 //        then nothing to do
3263 //    . else push on work-queue
3264 // -- Deal with possible overflow issues:
3265 //    . local work-queue overflow causes stuff to be pushed on
3266 //      global (common) overflow queue
3267 //    . always first empty local work queue
3268 //    . then get a batch of oops from global work queue if any
3269 //    . then do work stealing
3270 // -- When all tasks claimed (both spaces)
3271 //    and local work queue empty,
3272 //    then in a loop do:
3273 //    . check global overflow stack; steal a batch of oops and trace
3274 //    . try to steal from other threads oif GOS is empty
3275 //    . if neither is available, offer termination
3276 // -- Terminate and return result
3277 //
3278 void CMSConcMarkingTask::work(uint worker_id) {
3279   elapsedTimer _timer;
3280   ResourceMark rm;
3281   HandleMark hm;
3282 
3283   DEBUG_ONLY(_collector->verify_overflow_empty();)
3284 
3285   // Before we begin work, our work queue should be empty
3286   assert(work_queue(worker_id)->size() == 0, "Expected to be empty");
3287   // Scan the bitmap covering _cms_space, tracing through grey objects.
3288   _timer.start();
3289   do_scan_and_mark(worker_id, _cms_space);
3290   _timer.stop();
3291   if (PrintCMSStatistics != 0) {
3292     gclog_or_tty->print_cr("Finished cms space scanning in %dth thread: %3.3f sec",
3293       worker_id, _timer.seconds());
3294       // XXX: need xxx/xxx type of notation, two timers
3295   }
3296 
3297   // ... do work stealing
3298   _timer.reset();
3299   _timer.start();
3300   do_work_steal(worker_id);
3301   _timer.stop();
3302   if (PrintCMSStatistics != 0) {
3303     gclog_or_tty->print_cr("Finished work stealing in %dth thread: %3.3f sec",
3304       worker_id, _timer.seconds());
3305       // XXX: need xxx/xxx type of notation, two timers
3306   }
3307   assert(_collector->_markStack.isEmpty(), "Should have been emptied");
3308   assert(work_queue(worker_id)->size() == 0, "Should have been emptied");
3309   // Note that under the current task protocol, the
3310   // following assertion is true even of the spaces
3311   // expanded since the completion of the concurrent
3312   // marking. XXX This will likely change under a strict
3313   // ABORT semantics.
3314   // After perm removal the comparison was changed to
3315   // greater than or equal to from strictly greater than.
3316   // Before perm removal the highest address sweep would
3317   // have been at the end of perm gen but now is at the
3318   // end of the tenured gen.
3319   assert(_global_finger >=  _cms_space->end(),
3320          "All tasks have been completed");
3321   DEBUG_ONLY(_collector->verify_overflow_empty();)
3322 }
3323 
3324 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
3325   HeapWord* read = _global_finger;
3326   HeapWord* cur  = read;
3327   while (f > read) {
3328     cur = read;
3329     read = (HeapWord*) Atomic::cmpxchg_ptr(f, &_global_finger, cur);
3330     if (cur == read) {
3331       // our cas succeeded
3332       assert(_global_finger >= f, "protocol consistency");
3333       break;
3334     }
3335   }
3336 }
3337 
3338 // This is really inefficient, and should be redone by
3339 // using (not yet available) block-read and -write interfaces to the
3340 // stack and the work_queue. XXX FIX ME !!!
3341 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3342                                                       OopTaskQueue* work_q) {
3343   // Fast lock-free check
3344   if (ovflw_stk->length() == 0) {
3345     return false;
3346   }
3347   assert(work_q->size() == 0, "Shouldn't steal");
3348   MutexLockerEx ml(ovflw_stk->par_lock(),
3349                    Mutex::_no_safepoint_check_flag);
3350   // Grab up to 1/4 the size of the work queue
3351   size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
3352                     (size_t)ParGCDesiredObjsFromOverflowList);
3353   num = MIN2(num, ovflw_stk->length());
3354   for (int i = (int) num; i > 0; i--) {
3355     oop cur = ovflw_stk->pop();
3356     assert(cur != NULL, "Counted wrong?");
3357     work_q->push(cur);
3358   }
3359   return num > 0;
3360 }
3361 
3362 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
3363   SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
3364   int n_tasks = pst->n_tasks();
3365   // We allow that there may be no tasks to do here because
3366   // we are restarting after a stack overflow.
3367   assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
3368   uint nth_task = 0;
3369 
3370   HeapWord* aligned_start = sp->bottom();
3371   if (sp->used_region().contains(_restart_addr)) {
3372     // Align down to a card boundary for the start of 0th task
3373     // for this space.
3374     aligned_start =
3375       (HeapWord*)align_size_down((uintptr_t)_restart_addr,
3376                                  CardTableModRefBS::card_size);
3377   }
3378 
3379   size_t chunk_size = sp->marking_task_size();
3380   while (!pst->is_task_claimed(/* reference */ nth_task)) {
3381     // Having claimed the nth task in this space,
3382     // compute the chunk that it corresponds to:
3383     MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
3384                                aligned_start + (nth_task+1)*chunk_size);
3385     // Try and bump the global finger via a CAS;
3386     // note that we need to do the global finger bump
3387     // _before_ taking the intersection below, because
3388     // the task corresponding to that region will be
3389     // deemed done even if the used_region() expands
3390     // because of allocation -- as it almost certainly will
3391     // during start-up while the threads yield in the
3392     // closure below.
3393     HeapWord* finger = span.end();
3394     bump_global_finger(finger);   // atomically
3395     // There are null tasks here corresponding to chunks
3396     // beyond the "top" address of the space.
3397     span = span.intersection(sp->used_region());
3398     if (!span.is_empty()) {  // Non-null task
3399       HeapWord* prev_obj;
3400       assert(!span.contains(_restart_addr) || nth_task == 0,
3401              "Inconsistency");
3402       if (nth_task == 0) {
3403         // For the 0th task, we'll not need to compute a block_start.
3404         if (span.contains(_restart_addr)) {
3405           // In the case of a restart because of stack overflow,
3406           // we might additionally skip a chunk prefix.
3407           prev_obj = _restart_addr;
3408         } else {
3409           prev_obj = span.start();
3410         }
3411       } else {
3412         // We want to skip the first object because
3413         // the protocol is to scan any object in its entirety
3414         // that _starts_ in this span; a fortiori, any
3415         // object starting in an earlier span is scanned
3416         // as part of an earlier claimed task.
3417         // Below we use the "careful" version of block_start
3418         // so we do not try to navigate uninitialized objects.
3419         prev_obj = sp->block_start_careful(span.start());
3420         // Below we use a variant of block_size that uses the
3421         // Printezis bits to avoid waiting for allocated
3422         // objects to become initialized/parsable.
3423         while (prev_obj < span.start()) {
3424           size_t sz = sp->block_size_no_stall(prev_obj, _collector);
3425           if (sz > 0) {
3426             prev_obj += sz;
3427           } else {
3428             // In this case we may end up doing a bit of redundant
3429             // scanning, but that appears unavoidable, short of
3430             // locking the free list locks; see bug 6324141.
3431             break;
3432           }
3433         }
3434       }
3435       if (prev_obj < span.end()) {
3436         MemRegion my_span = MemRegion(prev_obj, span.end());
3437         // Do the marking work within a non-empty span --
3438         // the last argument to the constructor indicates whether the
3439         // iteration should be incremental with periodic yields.
3440         Par_MarkFromRootsClosure cl(this, _collector, my_span,
3441                                     &_collector->_markBitMap,
3442                                     work_queue(i),
3443                                     &_collector->_markStack);
3444         _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
3445       } // else nothing to do for this task
3446     }   // else nothing to do for this task
3447   }
3448   // We'd be tempted to assert here that since there are no
3449   // more tasks left to claim in this space, the global_finger
3450   // must exceed space->top() and a fortiori space->end(). However,
3451   // that would not quite be correct because the bumping of
3452   // global_finger occurs strictly after the claiming of a task,
3453   // so by the time we reach here the global finger may not yet
3454   // have been bumped up by the thread that claimed the last
3455   // task.
3456   pst->all_tasks_completed();
3457 }
3458 
3459 class Par_ConcMarkingClosure: public MetadataAwareOopClosure {
3460  private:
3461   CMSCollector* _collector;
3462   CMSConcMarkingTask* _task;
3463   MemRegion     _span;
3464   CMSBitMap*    _bit_map;
3465   CMSMarkStack* _overflow_stack;
3466   OopTaskQueue* _work_queue;
3467  protected:
3468   DO_OOP_WORK_DEFN
3469  public:
3470   Par_ConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue,
3471                          CMSBitMap* bit_map, CMSMarkStack* overflow_stack):
3472     MetadataAwareOopClosure(collector->ref_processor()),
3473     _collector(collector),
3474     _task(task),
3475     _span(collector->_span),
3476     _work_queue(work_queue),
3477     _bit_map(bit_map),
3478     _overflow_stack(overflow_stack)
3479   { }
3480   virtual void do_oop(oop* p);
3481   virtual void do_oop(narrowOop* p);
3482 
3483   void trim_queue(size_t max);
3484   void handle_stack_overflow(HeapWord* lost);
3485   void do_yield_check() {
3486     if (_task->should_yield()) {
3487       _task->yield();
3488     }
3489   }
3490 };
3491 
3492 // Grey object scanning during work stealing phase --
3493 // the salient assumption here is that any references
3494 // that are in these stolen objects being scanned must
3495 // already have been initialized (else they would not have
3496 // been published), so we do not need to check for
3497 // uninitialized objects before pushing here.
3498 void Par_ConcMarkingClosure::do_oop(oop obj) {
3499   assert(obj->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
3500   HeapWord* addr = (HeapWord*)obj;
3501   // Check if oop points into the CMS generation
3502   // and is not marked
3503   if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
3504     // a white object ...
3505     // If we manage to "claim" the object, by being the
3506     // first thread to mark it, then we push it on our
3507     // marking stack
3508     if (_bit_map->par_mark(addr)) {     // ... now grey
3509       // push on work queue (grey set)
3510       bool simulate_overflow = false;
3511       NOT_PRODUCT(
3512         if (CMSMarkStackOverflowALot &&
3513             _collector->simulate_overflow()) {
3514           // simulate a stack overflow
3515           simulate_overflow = true;
3516         }
3517       )
3518       if (simulate_overflow ||
3519           !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
3520         // stack overflow
3521         if (PrintCMSStatistics != 0) {
3522           gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
3523                                  SIZE_FORMAT, _overflow_stack->capacity());
3524         }
3525         // We cannot assert that the overflow stack is full because
3526         // it may have been emptied since.
3527         assert(simulate_overflow ||
3528                _work_queue->size() == _work_queue->max_elems(),
3529               "Else push should have succeeded");
3530         handle_stack_overflow(addr);
3531       }
3532     } // Else, some other thread got there first
3533     do_yield_check();
3534   }
3535 }
3536 
3537 void Par_ConcMarkingClosure::do_oop(oop* p)       { Par_ConcMarkingClosure::do_oop_work(p); }
3538 void Par_ConcMarkingClosure::do_oop(narrowOop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
3539 
3540 void Par_ConcMarkingClosure::trim_queue(size_t max) {
3541   while (_work_queue->size() > max) {
3542     oop new_oop;
3543     if (_work_queue->pop_local(new_oop)) {
3544       assert(new_oop->is_oop(), "Should be an oop");
3545       assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
3546       assert(_span.contains((HeapWord*)new_oop), "Not in span");
3547       new_oop->oop_iterate(this);  // do_oop() above
3548       do_yield_check();
3549     }
3550   }
3551 }
3552 
3553 // Upon stack overflow, we discard (part of) the stack,
3554 // remembering the least address amongst those discarded
3555 // in CMSCollector's _restart_address.
3556 void Par_ConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
3557   // We need to do this under a mutex to prevent other
3558   // workers from interfering with the work done below.
3559   MutexLockerEx ml(_overflow_stack->par_lock(),
3560                    Mutex::_no_safepoint_check_flag);
3561   // Remember the least grey address discarded
3562   HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
3563   _collector->lower_restart_addr(ra);
3564   _overflow_stack->reset();  // discard stack contents
3565   _overflow_stack->expand(); // expand the stack if possible
3566 }
3567 
3568 
3569 void CMSConcMarkingTask::do_work_steal(int i) {
3570   OopTaskQueue* work_q = work_queue(i);
3571   oop obj_to_scan;
3572   CMSBitMap* bm = &(_collector->_markBitMap);
3573   CMSMarkStack* ovflw = &(_collector->_markStack);
3574   int* seed = _collector->hash_seed(i);
3575   Par_ConcMarkingClosure cl(_collector, this, work_q, bm, ovflw);
3576   while (true) {
3577     cl.trim_queue(0);
3578     assert(work_q->size() == 0, "Should have been emptied above");
3579     if (get_work_from_overflow_stack(ovflw, work_q)) {
3580       // Can't assert below because the work obtained from the
3581       // overflow stack may already have been stolen from us.
3582       // assert(work_q->size() > 0, "Work from overflow stack");
3583       continue;
3584     } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
3585       assert(obj_to_scan->is_oop(), "Should be an oop");
3586       assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
3587       obj_to_scan->oop_iterate(&cl);
3588     } else if (terminator()->offer_termination(&_term_term)) {
3589       assert(work_q->size() == 0, "Impossible!");
3590       break;
3591     } else if (yielding() || should_yield()) {
3592       yield();
3593     }
3594   }
3595 }
3596 
3597 // This is run by the CMS (coordinator) thread.
3598 void CMSConcMarkingTask::coordinator_yield() {
3599   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3600          "CMS thread should hold CMS token");
3601   // First give up the locks, then yield, then re-lock
3602   // We should probably use a constructor/destructor idiom to
3603   // do this unlock/lock or modify the MutexUnlocker class to
3604   // serve our purpose. XXX
3605   assert_lock_strong(_bit_map_lock);
3606   _bit_map_lock->unlock();
3607   ConcurrentMarkSweepThread::desynchronize(true);
3608   _collector->stopTimer();
3609   if (PrintCMSStatistics != 0) {
3610     _collector->incrementYields();
3611   }
3612 
3613   // It is possible for whichever thread initiated the yield request
3614   // not to get a chance to wake up and take the bitmap lock between
3615   // this thread releasing it and reacquiring it. So, while the
3616   // should_yield() flag is on, let's sleep for a bit to give the
3617   // other thread a chance to wake up. The limit imposed on the number
3618   // of iterations is defensive, to avoid any unforseen circumstances
3619   // putting us into an infinite loop. Since it's always been this
3620   // (coordinator_yield()) method that was observed to cause the
3621   // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
3622   // which is by default non-zero. For the other seven methods that
3623   // also perform the yield operation, as are using a different
3624   // parameter (CMSYieldSleepCount) which is by default zero. This way we
3625   // can enable the sleeping for those methods too, if necessary.
3626   // See 6442774.
3627   //
3628   // We really need to reconsider the synchronization between the GC
3629   // thread and the yield-requesting threads in the future and we
3630   // should really use wait/notify, which is the recommended
3631   // way of doing this type of interaction. Additionally, we should
3632   // consolidate the eight methods that do the yield operation and they
3633   // are almost identical into one for better maintainability and
3634   // readability. See 6445193.
3635   //
3636   // Tony 2006.06.29
3637   for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
3638                    ConcurrentMarkSweepThread::should_yield() &&
3639                    !CMSCollector::foregroundGCIsActive(); ++i) {
3640     os::sleep(Thread::current(), 1, false);
3641   }
3642 
3643   ConcurrentMarkSweepThread::synchronize(true);
3644   _bit_map_lock->lock_without_safepoint_check();
3645   _collector->startTimer();
3646 }
3647 
3648 bool CMSCollector::do_marking_mt() {
3649   assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition");
3650   uint num_workers = AdaptiveSizePolicy::calc_active_conc_workers(conc_workers()->total_workers(),
3651                                                                   conc_workers()->active_workers(),
3652                                                                   Threads::number_of_non_daemon_threads());
3653   conc_workers()->set_active_workers(num_workers);
3654 
3655   CompactibleFreeListSpace* cms_space  = _cmsGen->cmsSpace();
3656 
3657   CMSConcMarkingTask tsk(this,
3658                          cms_space,
3659                          conc_workers(),
3660                          task_queues());
3661 
3662   // Since the actual number of workers we get may be different
3663   // from the number we requested above, do we need to do anything different
3664   // below? In particular, may be we need to subclass the SequantialSubTasksDone
3665   // class?? XXX
3666   cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
3667 
3668   // Refs discovery is already non-atomic.
3669   assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
3670   assert(ref_processor()->discovery_is_mt(), "Discovery should be MT");
3671   conc_workers()->start_task(&tsk);
3672   while (tsk.yielded()) {
3673     tsk.coordinator_yield();
3674     conc_workers()->continue_task(&tsk);
3675   }
3676   // If the task was aborted, _restart_addr will be non-NULL
3677   assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
3678   while (_restart_addr != NULL) {
3679     // XXX For now we do not make use of ABORTED state and have not
3680     // yet implemented the right abort semantics (even in the original
3681     // single-threaded CMS case). That needs some more investigation
3682     // and is deferred for now; see CR# TBF. 07252005YSR. XXX
3683     assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
3684     // If _restart_addr is non-NULL, a marking stack overflow
3685     // occurred; we need to do a fresh marking iteration from the
3686     // indicated restart address.
3687     if (_foregroundGCIsActive) {
3688       // We may be running into repeated stack overflows, having
3689       // reached the limit of the stack size, while making very
3690       // slow forward progress. It may be best to bail out and
3691       // let the foreground collector do its job.
3692       // Clear _restart_addr, so that foreground GC
3693       // works from scratch. This avoids the headache of
3694       // a "rescan" which would otherwise be needed because
3695       // of the dirty mod union table & card table.
3696       _restart_addr = NULL;
3697       return false;
3698     }
3699     // Adjust the task to restart from _restart_addr
3700     tsk.reset(_restart_addr);
3701     cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
3702                   _restart_addr);
3703     _restart_addr = NULL;
3704     // Get the workers going again
3705     conc_workers()->start_task(&tsk);
3706     while (tsk.yielded()) {
3707       tsk.coordinator_yield();
3708       conc_workers()->continue_task(&tsk);
3709     }
3710   }
3711   assert(tsk.completed(), "Inconsistency");
3712   assert(tsk.result() == true, "Inconsistency");
3713   return true;
3714 }
3715 
3716 bool CMSCollector::do_marking_st() {
3717   ResourceMark rm;
3718   HandleMark   hm;
3719 
3720   // Temporarily make refs discovery single threaded (non-MT)
3721   ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
3722   MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
3723     &_markStack, CMSYield);
3724   // the last argument to iterate indicates whether the iteration
3725   // should be incremental with periodic yields.
3726   _markBitMap.iterate(&markFromRootsClosure);
3727   // If _restart_addr is non-NULL, a marking stack overflow
3728   // occurred; we need to do a fresh iteration from the
3729   // indicated restart address.
3730   while (_restart_addr != NULL) {
3731     if (_foregroundGCIsActive) {
3732       // We may be running into repeated stack overflows, having
3733       // reached the limit of the stack size, while making very
3734       // slow forward progress. It may be best to bail out and
3735       // let the foreground collector do its job.
3736       // Clear _restart_addr, so that foreground GC
3737       // works from scratch. This avoids the headache of
3738       // a "rescan" which would otherwise be needed because
3739       // of the dirty mod union table & card table.
3740       _restart_addr = NULL;
3741       return false;  // indicating failure to complete marking
3742     }
3743     // Deal with stack overflow:
3744     // we restart marking from _restart_addr
3745     HeapWord* ra = _restart_addr;
3746     markFromRootsClosure.reset(ra);
3747     _restart_addr = NULL;
3748     _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
3749   }
3750   return true;
3751 }
3752 
3753 void CMSCollector::preclean() {
3754   check_correct_thread_executing();
3755   assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
3756   verify_work_stacks_empty();
3757   verify_overflow_empty();
3758   _abort_preclean = false;
3759   if (CMSPrecleaningEnabled) {
3760     if (!CMSEdenChunksRecordAlways) {
3761       _eden_chunk_index = 0;
3762     }
3763     size_t used = get_eden_used();
3764     size_t capacity = get_eden_capacity();
3765     // Don't start sampling unless we will get sufficiently
3766     // many samples.
3767     if (used < (capacity/(CMSScheduleRemarkSamplingRatio * 100)
3768                 * CMSScheduleRemarkEdenPenetration)) {
3769       _start_sampling = true;
3770     } else {
3771       _start_sampling = false;
3772     }
3773     TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3774     CMSPhaseAccounting pa(this, "preclean", _gc_tracer_cm->gc_id(), !PrintGCDetails);
3775     preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
3776   }
3777   CMSTokenSync x(true); // is cms thread
3778   if (CMSPrecleaningEnabled) {
3779     sample_eden();
3780     _collectorState = AbortablePreclean;
3781   } else {
3782     _collectorState = FinalMarking;
3783   }
3784   verify_work_stacks_empty();
3785   verify_overflow_empty();
3786 }
3787 
3788 // Try and schedule the remark such that young gen
3789 // occupancy is CMSScheduleRemarkEdenPenetration %.
3790 void CMSCollector::abortable_preclean() {
3791   check_correct_thread_executing();
3792   assert(CMSPrecleaningEnabled,  "Inconsistent control state");
3793   assert(_collectorState == AbortablePreclean, "Inconsistent control state");
3794 
3795   // If Eden's current occupancy is below this threshold,
3796   // immediately schedule the remark; else preclean
3797   // past the next scavenge in an effort to
3798   // schedule the pause as described above. By choosing
3799   // CMSScheduleRemarkEdenSizeThreshold >= max eden size
3800   // we will never do an actual abortable preclean cycle.
3801   if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
3802     TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3803     CMSPhaseAccounting pa(this, "abortable-preclean", _gc_tracer_cm->gc_id(), !PrintGCDetails);
3804     // We need more smarts in the abortable preclean
3805     // loop below to deal with cases where allocation
3806     // in young gen is very very slow, and our precleaning
3807     // is running a losing race against a horde of
3808     // mutators intent on flooding us with CMS updates
3809     // (dirty cards).
3810     // One, admittedly dumb, strategy is to give up
3811     // after a certain number of abortable precleaning loops
3812     // or after a certain maximum time. We want to make
3813     // this smarter in the next iteration.
3814     // XXX FIX ME!!! YSR
3815     size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
3816     while (!(should_abort_preclean() ||
3817              ConcurrentMarkSweepThread::should_terminate())) {
3818       workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
3819       cumworkdone += workdone;
3820       loops++;
3821       // Voluntarily terminate abortable preclean phase if we have
3822       // been at it for too long.
3823       if ((CMSMaxAbortablePrecleanLoops != 0) &&
3824           loops >= CMSMaxAbortablePrecleanLoops) {
3825         if (PrintGCDetails) {
3826           gclog_or_tty->print(" CMS: abort preclean due to loops ");
3827         }
3828         break;
3829       }
3830       if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
3831         if (PrintGCDetails) {
3832           gclog_or_tty->print(" CMS: abort preclean due to time ");
3833         }
3834         break;
3835       }
3836       // If we are doing little work each iteration, we should
3837       // take a short break.
3838       if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
3839         // Sleep for some time, waiting for work to accumulate
3840         stopTimer();
3841         cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
3842         startTimer();
3843         waited++;
3844       }
3845     }
3846     if (PrintCMSStatistics > 0) {
3847       gclog_or_tty->print(" [" SIZE_FORMAT " iterations, " SIZE_FORMAT " waits, " SIZE_FORMAT " cards)] ",
3848                           loops, waited, cumworkdone);
3849     }
3850   }
3851   CMSTokenSync x(true); // is cms thread
3852   if (_collectorState != Idling) {
3853     assert(_collectorState == AbortablePreclean,
3854            "Spontaneous state transition?");
3855     _collectorState = FinalMarking;
3856   } // Else, a foreground collection completed this CMS cycle.
3857   return;
3858 }
3859 
3860 // Respond to an Eden sampling opportunity
3861 void CMSCollector::sample_eden() {
3862   // Make sure a young gc cannot sneak in between our
3863   // reading and recording of a sample.
3864   assert(Thread::current()->is_ConcurrentGC_thread(),
3865          "Only the cms thread may collect Eden samples");
3866   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3867          "Should collect samples while holding CMS token");
3868   if (!_start_sampling) {
3869     return;
3870   }
3871   // When CMSEdenChunksRecordAlways is true, the eden chunk array
3872   // is populated by the young generation.
3873   if (_eden_chunk_array != NULL && !CMSEdenChunksRecordAlways) {
3874     if (_eden_chunk_index < _eden_chunk_capacity) {
3875       _eden_chunk_array[_eden_chunk_index] = *_top_addr;   // take sample
3876       assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
3877              "Unexpected state of Eden");
3878       // We'd like to check that what we just sampled is an oop-start address;
3879       // however, we cannot do that here since the object may not yet have been
3880       // initialized. So we'll instead do the check when we _use_ this sample
3881       // later.
3882       if (_eden_chunk_index == 0 ||
3883           (pointer_delta(_eden_chunk_array[_eden_chunk_index],
3884                          _eden_chunk_array[_eden_chunk_index-1])
3885            >= CMSSamplingGrain)) {
3886         _eden_chunk_index++;  // commit sample
3887       }
3888     }
3889   }
3890   if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
3891     size_t used = get_eden_used();
3892     size_t capacity = get_eden_capacity();
3893     assert(used <= capacity, "Unexpected state of Eden");
3894     if (used >  (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
3895       _abort_preclean = true;
3896     }
3897   }
3898 }
3899 
3900 
3901 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
3902   assert(_collectorState == Precleaning ||
3903          _collectorState == AbortablePreclean, "incorrect state");
3904   ResourceMark rm;
3905   HandleMark   hm;
3906 
3907   // Precleaning is currently not MT but the reference processor
3908   // may be set for MT.  Disable it temporarily here.
3909   ReferenceProcessor* rp = ref_processor();
3910   ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false);
3911 
3912   // Do one pass of scrubbing the discovered reference lists
3913   // to remove any reference objects with strongly-reachable
3914   // referents.
3915   if (clean_refs) {
3916     CMSPrecleanRefsYieldClosure yield_cl(this);
3917     assert(rp->span().equals(_span), "Spans should be equal");
3918     CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
3919                                    &_markStack, true /* preclean */);
3920     CMSDrainMarkingStackClosure complete_trace(this,
3921                                    _span, &_markBitMap, &_markStack,
3922                                    &keep_alive, true /* preclean */);
3923 
3924     // We don't want this step to interfere with a young
3925     // collection because we don't want to take CPU
3926     // or memory bandwidth away from the young GC threads
3927     // (which may be as many as there are CPUs).
3928     // Note that we don't need to protect ourselves from
3929     // interference with mutators because they can't
3930     // manipulate the discovered reference lists nor affect
3931     // the computed reachability of the referents, the
3932     // only properties manipulated by the precleaning
3933     // of these reference lists.
3934     stopTimer();
3935     CMSTokenSyncWithLocks x(true /* is cms thread */,
3936                             bitMapLock());
3937     startTimer();
3938     sample_eden();
3939 
3940     // The following will yield to allow foreground
3941     // collection to proceed promptly. XXX YSR:
3942     // The code in this method may need further
3943     // tweaking for better performance and some restructuring
3944     // for cleaner interfaces.
3945     GCTimer *gc_timer = NULL; // Currently not tracing concurrent phases
3946     rp->preclean_discovered_references(
3947           rp->is_alive_non_header(), &keep_alive, &complete_trace, &yield_cl,
3948           gc_timer, _gc_tracer_cm->gc_id());
3949   }
3950 
3951   if (clean_survivor) {  // preclean the active survivor space(s)
3952     PushAndMarkClosure pam_cl(this, _span, ref_processor(),
3953                              &_markBitMap, &_modUnionTable,
3954                              &_markStack, true /* precleaning phase */);
3955     stopTimer();
3956     CMSTokenSyncWithLocks ts(true /* is cms thread */,
3957                              bitMapLock());
3958     startTimer();
3959     unsigned int before_count =
3960       GenCollectedHeap::heap()->total_collections();
3961     SurvivorSpacePrecleanClosure
3962       sss_cl(this, _span, &_markBitMap, &_markStack,
3963              &pam_cl, before_count, CMSYield);
3964     _young_gen->from()->object_iterate_careful(&sss_cl);
3965     _young_gen->to()->object_iterate_careful(&sss_cl);
3966   }
3967   MarkRefsIntoAndScanClosure
3968     mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
3969              &_markStack, this, CMSYield,
3970              true /* precleaning phase */);
3971   // CAUTION: The following closure has persistent state that may need to
3972   // be reset upon a decrease in the sequence of addresses it
3973   // processes.
3974   ScanMarkedObjectsAgainCarefullyClosure
3975     smoac_cl(this, _span,
3976       &_markBitMap, &_markStack, &mrias_cl, CMSYield);
3977 
3978   // Preclean dirty cards in ModUnionTable and CardTable using
3979   // appropriate convergence criterion;
3980   // repeat CMSPrecleanIter times unless we find that
3981   // we are losing.
3982   assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
3983   assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
3984          "Bad convergence multiplier");
3985   assert(CMSPrecleanThreshold >= 100,
3986          "Unreasonably low CMSPrecleanThreshold");
3987 
3988   size_t numIter, cumNumCards, lastNumCards, curNumCards;
3989   for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
3990        numIter < CMSPrecleanIter;
3991        numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
3992     curNumCards  = preclean_mod_union_table(_cmsGen, &smoac_cl);
3993     if (Verbose && PrintGCDetails) {
3994       gclog_or_tty->print(" (modUnionTable: " SIZE_FORMAT " cards)", curNumCards);
3995     }
3996     // Either there are very few dirty cards, so re-mark
3997     // pause will be small anyway, or our pre-cleaning isn't
3998     // that much faster than the rate at which cards are being
3999     // dirtied, so we might as well stop and re-mark since
4000     // precleaning won't improve our re-mark time by much.
4001     if (curNumCards <= CMSPrecleanThreshold ||
4002         (numIter > 0 &&
4003          (curNumCards * CMSPrecleanDenominator >
4004          lastNumCards * CMSPrecleanNumerator))) {
4005       numIter++;
4006       cumNumCards += curNumCards;
4007       break;
4008     }
4009   }
4010 
4011   preclean_klasses(&mrias_cl, _cmsGen->freelistLock());
4012 
4013   curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
4014   cumNumCards += curNumCards;
4015   if (PrintGCDetails && PrintCMSStatistics != 0) {
4016     gclog_or_tty->print_cr(" (cardTable: " SIZE_FORMAT " cards, re-scanned " SIZE_FORMAT " cards, " SIZE_FORMAT " iterations)",
4017                   curNumCards, cumNumCards, numIter);
4018   }
4019   return cumNumCards;   // as a measure of useful work done
4020 }
4021 
4022 // PRECLEANING NOTES:
4023 // Precleaning involves:
4024 // . reading the bits of the modUnionTable and clearing the set bits.
4025 // . For the cards corresponding to the set bits, we scan the
4026 //   objects on those cards. This means we need the free_list_lock
4027 //   so that we can safely iterate over the CMS space when scanning
4028 //   for oops.
4029 // . When we scan the objects, we'll be both reading and setting
4030 //   marks in the marking bit map, so we'll need the marking bit map.
4031 // . For protecting _collector_state transitions, we take the CGC_lock.
4032 //   Note that any races in the reading of of card table entries by the
4033 //   CMS thread on the one hand and the clearing of those entries by the
4034 //   VM thread or the setting of those entries by the mutator threads on the
4035 //   other are quite benign. However, for efficiency it makes sense to keep
4036 //   the VM thread from racing with the CMS thread while the latter is
4037 //   dirty card info to the modUnionTable. We therefore also use the
4038 //   CGC_lock to protect the reading of the card table and the mod union
4039 //   table by the CM thread.
4040 // . We run concurrently with mutator updates, so scanning
4041 //   needs to be done carefully  -- we should not try to scan
4042 //   potentially uninitialized objects.
4043 //
4044 // Locking strategy: While holding the CGC_lock, we scan over and
4045 // reset a maximal dirty range of the mod union / card tables, then lock
4046 // the free_list_lock and bitmap lock to do a full marking, then
4047 // release these locks; and repeat the cycle. This allows for a
4048 // certain amount of fairness in the sharing of these locks between
4049 // the CMS collector on the one hand, and the VM thread and the
4050 // mutators on the other.
4051 
4052 // NOTE: preclean_mod_union_table() and preclean_card_table()
4053 // further below are largely identical; if you need to modify
4054 // one of these methods, please check the other method too.
4055 
4056 size_t CMSCollector::preclean_mod_union_table(
4057   ConcurrentMarkSweepGeneration* gen,
4058   ScanMarkedObjectsAgainCarefullyClosure* cl) {
4059   verify_work_stacks_empty();
4060   verify_overflow_empty();
4061 
4062   // strategy: starting with the first card, accumulate contiguous
4063   // ranges of dirty cards; clear these cards, then scan the region
4064   // covered by these cards.
4065 
4066   // Since all of the MUT is committed ahead, we can just use
4067   // that, in case the generations expand while we are precleaning.
4068   // It might also be fine to just use the committed part of the
4069   // generation, but we might potentially miss cards when the
4070   // generation is rapidly expanding while we are in the midst
4071   // of precleaning.
4072   HeapWord* startAddr = gen->reserved().start();
4073   HeapWord* endAddr   = gen->reserved().end();
4074 
4075   cl->setFreelistLock(gen->freelistLock());   // needed for yielding
4076 
4077   size_t numDirtyCards, cumNumDirtyCards;
4078   HeapWord *nextAddr, *lastAddr;
4079   for (cumNumDirtyCards = numDirtyCards = 0,
4080        nextAddr = lastAddr = startAddr;
4081        nextAddr < endAddr;
4082        nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4083 
4084     ResourceMark rm;
4085     HandleMark   hm;
4086 
4087     MemRegion dirtyRegion;
4088     {
4089       stopTimer();
4090       // Potential yield point
4091       CMSTokenSync ts(true);
4092       startTimer();
4093       sample_eden();
4094       // Get dirty region starting at nextOffset (inclusive),
4095       // simultaneously clearing it.
4096       dirtyRegion =
4097         _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
4098       assert(dirtyRegion.start() >= nextAddr,
4099              "returned region inconsistent?");
4100     }
4101     // Remember where the next search should begin.
4102     // The returned region (if non-empty) is a right open interval,
4103     // so lastOffset is obtained from the right end of that
4104     // interval.
4105     lastAddr = dirtyRegion.end();
4106     // Should do something more transparent and less hacky XXX
4107     numDirtyCards =
4108       _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
4109 
4110     // We'll scan the cards in the dirty region (with periodic
4111     // yields for foreground GC as needed).
4112     if (!dirtyRegion.is_empty()) {
4113       assert(numDirtyCards > 0, "consistency check");
4114       HeapWord* stop_point = NULL;
4115       stopTimer();
4116       // Potential yield point
4117       CMSTokenSyncWithLocks ts(true, gen->freelistLock(),
4118                                bitMapLock());
4119       startTimer();
4120       {
4121         verify_work_stacks_empty();
4122         verify_overflow_empty();
4123         sample_eden();
4124         stop_point =
4125           gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4126       }
4127       if (stop_point != NULL) {
4128         // The careful iteration stopped early either because it found an
4129         // uninitialized object, or because we were in the midst of an
4130         // "abortable preclean", which should now be aborted. Redirty
4131         // the bits corresponding to the partially-scanned or unscanned
4132         // cards. We'll either restart at the next block boundary or
4133         // abort the preclean.
4134         assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4135                "Should only be AbortablePreclean.");
4136         _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
4137         if (should_abort_preclean()) {
4138           break; // out of preclean loop
4139         } else {
4140           // Compute the next address at which preclean should pick up;
4141           // might need bitMapLock in order to read P-bits.
4142           lastAddr = next_card_start_after_block(stop_point);
4143         }
4144       }
4145     } else {
4146       assert(lastAddr == endAddr, "consistency check");
4147       assert(numDirtyCards == 0, "consistency check");
4148       break;
4149     }
4150   }
4151   verify_work_stacks_empty();
4152   verify_overflow_empty();
4153   return cumNumDirtyCards;
4154 }
4155 
4156 // NOTE: preclean_mod_union_table() above and preclean_card_table()
4157 // below are largely identical; if you need to modify
4158 // one of these methods, please check the other method too.
4159 
4160 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* gen,
4161   ScanMarkedObjectsAgainCarefullyClosure* cl) {
4162   // strategy: it's similar to precleamModUnionTable above, in that
4163   // we accumulate contiguous ranges of dirty cards, mark these cards
4164   // precleaned, then scan the region covered by these cards.
4165   HeapWord* endAddr   = (HeapWord*)(gen->_virtual_space.high());
4166   HeapWord* startAddr = (HeapWord*)(gen->_virtual_space.low());
4167 
4168   cl->setFreelistLock(gen->freelistLock());   // needed for yielding
4169 
4170   size_t numDirtyCards, cumNumDirtyCards;
4171   HeapWord *lastAddr, *nextAddr;
4172 
4173   for (cumNumDirtyCards = numDirtyCards = 0,
4174        nextAddr = lastAddr = startAddr;
4175        nextAddr < endAddr;
4176        nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4177 
4178     ResourceMark rm;
4179     HandleMark   hm;
4180 
4181     MemRegion dirtyRegion;
4182     {
4183       // See comments in "Precleaning notes" above on why we
4184       // do this locking. XXX Could the locking overheads be
4185       // too high when dirty cards are sparse? [I don't think so.]
4186       stopTimer();
4187       CMSTokenSync x(true); // is cms thread
4188       startTimer();
4189       sample_eden();
4190       // Get and clear dirty region from card table
4191       dirtyRegion = _ct->ct_bs()->dirty_card_range_after_reset(
4192                                     MemRegion(nextAddr, endAddr),
4193                                     true,
4194                                     CardTableModRefBS::precleaned_card_val());
4195 
4196       assert(dirtyRegion.start() >= nextAddr,
4197              "returned region inconsistent?");
4198     }
4199     lastAddr = dirtyRegion.end();
4200     numDirtyCards =
4201       dirtyRegion.word_size()/CardTableModRefBS::card_size_in_words;
4202 
4203     if (!dirtyRegion.is_empty()) {
4204       stopTimer();
4205       CMSTokenSyncWithLocks ts(true, gen->freelistLock(), bitMapLock());
4206       startTimer();
4207       sample_eden();
4208       verify_work_stacks_empty();
4209       verify_overflow_empty();
4210       HeapWord* stop_point =
4211         gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4212       if (stop_point != NULL) {
4213         assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4214                "Should only be AbortablePreclean.");
4215         _ct->ct_bs()->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4216         if (should_abort_preclean()) {
4217           break; // out of preclean loop
4218         } else {
4219           // Compute the next address at which preclean should pick up.
4220           lastAddr = next_card_start_after_block(stop_point);
4221         }
4222       }
4223     } else {
4224       break;
4225     }
4226   }
4227   verify_work_stacks_empty();
4228   verify_overflow_empty();
4229   return cumNumDirtyCards;
4230 }
4231 
4232 class PrecleanKlassClosure : public KlassClosure {
4233   KlassToOopClosure _cm_klass_closure;
4234  public:
4235   PrecleanKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4236   void do_klass(Klass* k) {
4237     if (k->has_accumulated_modified_oops()) {
4238       k->clear_accumulated_modified_oops();
4239 
4240       _cm_klass_closure.do_klass(k);
4241     }
4242   }
4243 };
4244 
4245 // The freelist lock is needed to prevent asserts, is it really needed?
4246 void CMSCollector::preclean_klasses(MarkRefsIntoAndScanClosure* cl, Mutex* freelistLock) {
4247 
4248   cl->set_freelistLock(freelistLock);
4249 
4250   CMSTokenSyncWithLocks ts(true, freelistLock, bitMapLock());
4251 
4252   // SSS: Add equivalent to ScanMarkedObjectsAgainCarefullyClosure::do_yield_check and should_abort_preclean?
4253   // SSS: We should probably check if precleaning should be aborted, at suitable intervals?
4254   PrecleanKlassClosure preclean_klass_closure(cl);
4255   ClassLoaderDataGraph::classes_do(&preclean_klass_closure);
4256 
4257   verify_work_stacks_empty();
4258   verify_overflow_empty();
4259 }
4260 
4261 void CMSCollector::checkpointRootsFinal() {
4262   assert(_collectorState == FinalMarking, "incorrect state transition?");
4263   check_correct_thread_executing();
4264   // world is stopped at this checkpoint
4265   assert(SafepointSynchronize::is_at_safepoint(),
4266          "world should be stopped");
4267   TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
4268 
4269   verify_work_stacks_empty();
4270   verify_overflow_empty();
4271 
4272   if (PrintGCDetails) {
4273     gclog_or_tty->print("[YG occupancy: "SIZE_FORMAT" K ("SIZE_FORMAT" K)]",
4274                         _young_gen->used() / K,
4275                         _young_gen->capacity() / K);
4276   }
4277   {
4278     if (CMSScavengeBeforeRemark) {
4279       GenCollectedHeap* gch = GenCollectedHeap::heap();
4280       // Temporarily set flag to false, GCH->do_collection will
4281       // expect it to be false and set to true
4282       FlagSetting fl(gch->_is_gc_active, false);
4283       NOT_PRODUCT(GCTraceTime t("Scavenge-Before-Remark",
4284         PrintGCDetails && Verbose, true, _gc_timer_cm, _gc_tracer_cm->gc_id());)
4285       int level = _cmsGen->level() - 1;
4286       if (level >= 0) {
4287         gch->do_collection(true,        // full (i.e. force, see below)
4288                            false,       // !clear_all_soft_refs
4289                            0,           // size
4290                            false,       // is_tlab
4291                            level        // max_level
4292                           );
4293       }
4294     }
4295     FreelistLocker x(this);
4296     MutexLockerEx y(bitMapLock(),
4297                     Mutex::_no_safepoint_check_flag);
4298     checkpointRootsFinalWork();
4299   }
4300   verify_work_stacks_empty();
4301   verify_overflow_empty();
4302 }
4303 
4304 void CMSCollector::checkpointRootsFinalWork() {
4305   NOT_PRODUCT(GCTraceTime tr("checkpointRootsFinalWork", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());)
4306 
4307   assert(haveFreelistLocks(), "must have free list locks");
4308   assert_lock_strong(bitMapLock());
4309 
4310   ResourceMark rm;
4311   HandleMark   hm;
4312 
4313   GenCollectedHeap* gch = GenCollectedHeap::heap();
4314 
4315   if (should_unload_classes()) {
4316     CodeCache::gc_prologue();
4317   }
4318   assert(haveFreelistLocks(), "must have free list locks");
4319   assert_lock_strong(bitMapLock());
4320 
4321   // We might assume that we need not fill TLAB's when
4322   // CMSScavengeBeforeRemark is set, because we may have just done
4323   // a scavenge which would have filled all TLAB's -- and besides
4324   // Eden would be empty. This however may not always be the case --
4325   // for instance although we asked for a scavenge, it may not have
4326   // happened because of a JNI critical section. We probably need
4327   // a policy for deciding whether we can in that case wait until
4328   // the critical section releases and then do the remark following
4329   // the scavenge, and skip it here. In the absence of that policy,
4330   // or of an indication of whether the scavenge did indeed occur,
4331   // we cannot rely on TLAB's having been filled and must do
4332   // so here just in case a scavenge did not happen.
4333   gch->ensure_parsability(false);  // fill TLAB's, but no need to retire them
4334   // Update the saved marks which may affect the root scans.
4335   gch->save_marks();
4336 
4337   if (CMSPrintEdenSurvivorChunks) {
4338     print_eden_and_survivor_chunk_arrays();
4339   }
4340 
4341   {
4342     COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
4343 
4344     // Note on the role of the mod union table:
4345     // Since the marker in "markFromRoots" marks concurrently with
4346     // mutators, it is possible for some reachable objects not to have been
4347     // scanned. For instance, an only reference to an object A was
4348     // placed in object B after the marker scanned B. Unless B is rescanned,
4349     // A would be collected. Such updates to references in marked objects
4350     // are detected via the mod union table which is the set of all cards
4351     // dirtied since the first checkpoint in this GC cycle and prior to
4352     // the most recent young generation GC, minus those cleaned up by the
4353     // concurrent precleaning.
4354     if (CMSParallelRemarkEnabled) {
4355       GCTraceTime t("Rescan (parallel) ", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
4356       do_remark_parallel();
4357     } else {
4358       GCTraceTime t("Rescan (non-parallel) ", PrintGCDetails, false,
4359                   _gc_timer_cm, _gc_tracer_cm->gc_id());
4360       do_remark_non_parallel();
4361     }
4362   }
4363   verify_work_stacks_empty();
4364   verify_overflow_empty();
4365 
4366   {
4367     NOT_PRODUCT(GCTraceTime ts("refProcessingWork", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());)
4368     refProcessingWork();
4369   }
4370   verify_work_stacks_empty();
4371   verify_overflow_empty();
4372 
4373   if (should_unload_classes()) {
4374     CodeCache::gc_epilogue();
4375   }
4376   JvmtiExport::gc_epilogue();
4377 
4378   // If we encountered any (marking stack / work queue) overflow
4379   // events during the current CMS cycle, take appropriate
4380   // remedial measures, where possible, so as to try and avoid
4381   // recurrence of that condition.
4382   assert(_markStack.isEmpty(), "No grey objects");
4383   size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
4384                      _ser_kac_ovflw        + _ser_kac_preclean_ovflw;
4385   if (ser_ovflw > 0) {
4386     if (PrintCMSStatistics != 0) {
4387       gclog_or_tty->print_cr("Marking stack overflow (benign) "
4388         "(pmc_pc="SIZE_FORMAT", pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT
4389         ", kac_preclean="SIZE_FORMAT")",
4390         _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw,
4391         _ser_kac_ovflw, _ser_kac_preclean_ovflw);
4392     }
4393     _markStack.expand();
4394     _ser_pmc_remark_ovflw = 0;
4395     _ser_pmc_preclean_ovflw = 0;
4396     _ser_kac_preclean_ovflw = 0;
4397     _ser_kac_ovflw = 0;
4398   }
4399   if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
4400     if (PrintCMSStatistics != 0) {
4401       gclog_or_tty->print_cr("Work queue overflow (benign) "
4402         "(pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT")",
4403         _par_pmc_remark_ovflw, _par_kac_ovflw);
4404     }
4405     _par_pmc_remark_ovflw = 0;
4406     _par_kac_ovflw = 0;
4407   }
4408   if (PrintCMSStatistics != 0) {
4409      if (_markStack._hit_limit > 0) {
4410        gclog_or_tty->print_cr(" (benign) Hit max stack size limit ("SIZE_FORMAT")",
4411                               _markStack._hit_limit);
4412      }
4413      if (_markStack._failed_double > 0) {
4414        gclog_or_tty->print_cr(" (benign) Failed stack doubling ("SIZE_FORMAT"),"
4415                               " current capacity "SIZE_FORMAT,
4416                               _markStack._failed_double,
4417                               _markStack.capacity());
4418      }
4419   }
4420   _markStack._hit_limit = 0;
4421   _markStack._failed_double = 0;
4422 
4423   if ((VerifyAfterGC || VerifyDuringGC) &&
4424       GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
4425     verify_after_remark();
4426   }
4427 
4428   _gc_tracer_cm->report_object_count_after_gc(&_is_alive_closure);
4429 
4430   // Change under the freelistLocks.
4431   _collectorState = Sweeping;
4432   // Call isAllClear() under bitMapLock
4433   assert(_modUnionTable.isAllClear(),
4434       "Should be clear by end of the final marking");
4435   assert(_ct->klass_rem_set()->mod_union_is_clear(),
4436       "Should be clear by end of the final marking");
4437 }
4438 
4439 void CMSParInitialMarkTask::work(uint worker_id) {
4440   elapsedTimer _timer;
4441   ResourceMark rm;
4442   HandleMark   hm;
4443 
4444   // ---------- scan from roots --------------
4445   _timer.start();
4446   GenCollectedHeap* gch = GenCollectedHeap::heap();
4447   Par_MarkRefsIntoClosure par_mri_cl(_collector->_span, &(_collector->_markBitMap));
4448 
4449   // ---------- young gen roots --------------
4450   {
4451     work_on_young_gen_roots(worker_id, &par_mri_cl);
4452     _timer.stop();
4453     if (PrintCMSStatistics != 0) {
4454       gclog_or_tty->print_cr(
4455         "Finished young gen initial mark scan work in %dth thread: %3.3f sec",
4456         worker_id, _timer.seconds());
4457     }
4458   }
4459 
4460   // ---------- remaining roots --------------
4461   _timer.reset();
4462   _timer.start();
4463 
4464   CLDToOopClosure cld_closure(&par_mri_cl, true);
4465 
4466   gch->gen_process_roots(_strong_roots_scope,
4467                          _collector->_cmsGen->level(),
4468                          false,     // yg was scanned above
4469                          GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4470                          _collector->should_unload_classes(),
4471                          &par_mri_cl,
4472                          NULL,
4473                          &cld_closure);
4474   assert(_collector->should_unload_classes()
4475          || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4476          "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4477   _timer.stop();
4478   if (PrintCMSStatistics != 0) {
4479     gclog_or_tty->print_cr(
4480       "Finished remaining root initial mark scan work in %dth thread: %3.3f sec",
4481       worker_id, _timer.seconds());
4482   }
4483 }
4484 
4485 // Parallel remark task
4486 class CMSParRemarkTask: public CMSParMarkTask {
4487   CompactibleFreeListSpace* _cms_space;
4488 
4489   // The per-thread work queues, available here for stealing.
4490   OopTaskQueueSet*       _task_queues;
4491   ParallelTaskTerminator _term;
4492   StrongRootsScope*      _strong_roots_scope;
4493 
4494  public:
4495   // A value of 0 passed to n_workers will cause the number of
4496   // workers to be taken from the active workers in the work gang.
4497   CMSParRemarkTask(CMSCollector* collector,
4498                    CompactibleFreeListSpace* cms_space,
4499                    uint n_workers, WorkGang* workers,
4500                    OopTaskQueueSet* task_queues,
4501                    StrongRootsScope* strong_roots_scope):
4502     CMSParMarkTask("Rescan roots and grey objects in parallel",
4503                    collector, n_workers),
4504     _cms_space(cms_space),
4505     _task_queues(task_queues),
4506     _term(n_workers, task_queues),
4507     _strong_roots_scope(strong_roots_scope) { }
4508 
4509   OopTaskQueueSet* task_queues() { return _task_queues; }
4510 
4511   OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
4512 
4513   ParallelTaskTerminator* terminator() { return &_term; }
4514   uint n_workers() { return _n_workers; }
4515 
4516   void work(uint worker_id);
4517 
4518  private:
4519   // ... of  dirty cards in old space
4520   void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
4521                                   Par_MarkRefsIntoAndScanClosure* cl);
4522 
4523   // ... work stealing for the above
4524   void do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl, int* seed);
4525 };
4526 
4527 class RemarkKlassClosure : public KlassClosure {
4528   KlassToOopClosure _cm_klass_closure;
4529  public:
4530   RemarkKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4531   void do_klass(Klass* k) {
4532     // Check if we have modified any oops in the Klass during the concurrent marking.
4533     if (k->has_accumulated_modified_oops()) {
4534       k->clear_accumulated_modified_oops();
4535 
4536       // We could have transfered the current modified marks to the accumulated marks,
4537       // like we do with the Card Table to Mod Union Table. But it's not really necessary.
4538     } else if (k->has_modified_oops()) {
4539       // Don't clear anything, this info is needed by the next young collection.
4540     } else {
4541       // No modified oops in the Klass.
4542       return;
4543     }
4544 
4545     // The klass has modified fields, need to scan the klass.
4546     _cm_klass_closure.do_klass(k);
4547   }
4548 };
4549 
4550 void CMSParMarkTask::work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl) {
4551   ParNewGeneration* young_gen = _collector->_young_gen;
4552   ContiguousSpace* eden_space = young_gen->eden();
4553   ContiguousSpace* from_space = young_gen->from();
4554   ContiguousSpace* to_space   = young_gen->to();
4555 
4556   HeapWord** eca = _collector->_eden_chunk_array;
4557   size_t     ect = _collector->_eden_chunk_index;
4558   HeapWord** sca = _collector->_survivor_chunk_array;
4559   size_t     sct = _collector->_survivor_chunk_index;
4560 
4561   assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
4562   assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
4563 
4564   do_young_space_rescan(worker_id, cl, to_space, NULL, 0);
4565   do_young_space_rescan(worker_id, cl, from_space, sca, sct);
4566   do_young_space_rescan(worker_id, cl, eden_space, eca, ect);
4567 }
4568 
4569 // work_queue(i) is passed to the closure
4570 // Par_MarkRefsIntoAndScanClosure.  The "i" parameter
4571 // also is passed to do_dirty_card_rescan_tasks() and to
4572 // do_work_steal() to select the i-th task_queue.
4573 
4574 void CMSParRemarkTask::work(uint worker_id) {
4575   elapsedTimer _timer;
4576   ResourceMark rm;
4577   HandleMark   hm;
4578 
4579   // ---------- rescan from roots --------------
4580   _timer.start();
4581   GenCollectedHeap* gch = GenCollectedHeap::heap();
4582   Par_MarkRefsIntoAndScanClosure par_mrias_cl(_collector,
4583     _collector->_span, _collector->ref_processor(),
4584     &(_collector->_markBitMap),
4585     work_queue(worker_id));
4586 
4587   // Rescan young gen roots first since these are likely
4588   // coarsely partitioned and may, on that account, constitute
4589   // the critical path; thus, it's best to start off that
4590   // work first.
4591   // ---------- young gen roots --------------
4592   {
4593     work_on_young_gen_roots(worker_id, &par_mrias_cl);
4594     _timer.stop();
4595     if (PrintCMSStatistics != 0) {
4596       gclog_or_tty->print_cr(
4597         "Finished young gen rescan work in %dth thread: %3.3f sec",
4598         worker_id, _timer.seconds());
4599     }
4600   }
4601 
4602   // ---------- remaining roots --------------
4603   _timer.reset();
4604   _timer.start();
4605   gch->gen_process_roots(_strong_roots_scope,
4606                          _collector->_cmsGen->level(),
4607                          false,     // yg was scanned above
4608                          GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4609                          _collector->should_unload_classes(),
4610                          &par_mrias_cl,
4611                          NULL,
4612                          NULL);     // The dirty klasses will be handled below
4613 
4614   assert(_collector->should_unload_classes()
4615          || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4616          "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4617   _timer.stop();
4618   if (PrintCMSStatistics != 0) {
4619     gclog_or_tty->print_cr(
4620       "Finished remaining root rescan work in %dth thread: %3.3f sec",
4621       worker_id, _timer.seconds());
4622   }
4623 
4624   // ---------- unhandled CLD scanning ----------
4625   if (worker_id == 0) { // Single threaded at the moment.
4626     _timer.reset();
4627     _timer.start();
4628 
4629     // Scan all new class loader data objects and new dependencies that were
4630     // introduced during concurrent marking.
4631     ResourceMark rm;
4632     GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
4633     for (int i = 0; i < array->length(); i++) {
4634       par_mrias_cl.do_class_loader_data(array->at(i));
4635     }
4636 
4637     // We don't need to keep track of new CLDs anymore.
4638     ClassLoaderDataGraph::remember_new_clds(false);
4639 
4640     _timer.stop();
4641     if (PrintCMSStatistics != 0) {
4642       gclog_or_tty->print_cr(
4643           "Finished unhandled CLD scanning work in %dth thread: %3.3f sec",
4644           worker_id, _timer.seconds());
4645     }
4646   }
4647 
4648   // ---------- dirty klass scanning ----------
4649   if (worker_id == 0) { // Single threaded at the moment.
4650     _timer.reset();
4651     _timer.start();
4652 
4653     // Scan all classes that was dirtied during the concurrent marking phase.
4654     RemarkKlassClosure remark_klass_closure(&par_mrias_cl);
4655     ClassLoaderDataGraph::classes_do(&remark_klass_closure);
4656 
4657     _timer.stop();
4658     if (PrintCMSStatistics != 0) {
4659       gclog_or_tty->print_cr(
4660           "Finished dirty klass scanning work in %dth thread: %3.3f sec",
4661           worker_id, _timer.seconds());
4662     }
4663   }
4664 
4665   // We might have added oops to ClassLoaderData::_handles during the
4666   // concurrent marking phase. These oops point to newly allocated objects
4667   // that are guaranteed to be kept alive. Either by the direct allocation
4668   // code, or when the young collector processes the roots. Hence,
4669   // we don't have to revisit the _handles block during the remark phase.
4670 
4671   // ---------- rescan dirty cards ------------
4672   _timer.reset();
4673   _timer.start();
4674 
4675   // Do the rescan tasks for each of the two spaces
4676   // (cms_space) in turn.
4677   // "worker_id" is passed to select the task_queue for "worker_id"
4678   do_dirty_card_rescan_tasks(_cms_space, worker_id, &par_mrias_cl);
4679   _timer.stop();
4680   if (PrintCMSStatistics != 0) {
4681     gclog_or_tty->print_cr(
4682       "Finished dirty card rescan work in %dth thread: %3.3f sec",
4683       worker_id, _timer.seconds());
4684   }
4685 
4686   // ---------- steal work from other threads ...
4687   // ---------- ... and drain overflow list.
4688   _timer.reset();
4689   _timer.start();
4690   do_work_steal(worker_id, &par_mrias_cl, _collector->hash_seed(worker_id));
4691   _timer.stop();
4692   if (PrintCMSStatistics != 0) {
4693     gclog_or_tty->print_cr(
4694       "Finished work stealing in %dth thread: %3.3f sec",
4695       worker_id, _timer.seconds());
4696   }
4697 }
4698 
4699 // Note that parameter "i" is not used.
4700 void
4701 CMSParMarkTask::do_young_space_rescan(uint worker_id,
4702   OopsInGenClosure* cl, ContiguousSpace* space,
4703   HeapWord** chunk_array, size_t chunk_top) {
4704   // Until all tasks completed:
4705   // . claim an unclaimed task
4706   // . compute region boundaries corresponding to task claimed
4707   //   using chunk_array
4708   // . par_oop_iterate(cl) over that region
4709 
4710   ResourceMark rm;
4711   HandleMark   hm;
4712 
4713   SequentialSubTasksDone* pst = space->par_seq_tasks();
4714 
4715   uint nth_task = 0;
4716   uint n_tasks  = pst->n_tasks();
4717 
4718   if (n_tasks > 0) {
4719     assert(pst->valid(), "Uninitialized use?");
4720     HeapWord *start, *end;
4721     while (!pst->is_task_claimed(/* reference */ nth_task)) {
4722       // We claimed task # nth_task; compute its boundaries.
4723       if (chunk_top == 0) {  // no samples were taken
4724         assert(nth_task == 0 && n_tasks == 1, "Can have only 1 eden task");
4725         start = space->bottom();
4726         end   = space->top();
4727       } else if (nth_task == 0) {
4728         start = space->bottom();
4729         end   = chunk_array[nth_task];
4730       } else if (nth_task < (uint)chunk_top) {
4731         assert(nth_task >= 1, "Control point invariant");
4732         start = chunk_array[nth_task - 1];
4733         end   = chunk_array[nth_task];
4734       } else {
4735         assert(nth_task == (uint)chunk_top, "Control point invariant");
4736         start = chunk_array[chunk_top - 1];
4737         end   = space->top();
4738       }
4739       MemRegion mr(start, end);
4740       // Verify that mr is in space
4741       assert(mr.is_empty() || space->used_region().contains(mr),
4742              "Should be in space");
4743       // Verify that "start" is an object boundary
4744       assert(mr.is_empty() || oop(mr.start())->is_oop(),
4745              "Should be an oop");
4746       space->par_oop_iterate(mr, cl);
4747     }
4748     pst->all_tasks_completed();
4749   }
4750 }
4751 
4752 void
4753 CMSParRemarkTask::do_dirty_card_rescan_tasks(
4754   CompactibleFreeListSpace* sp, int i,
4755   Par_MarkRefsIntoAndScanClosure* cl) {
4756   // Until all tasks completed:
4757   // . claim an unclaimed task
4758   // . compute region boundaries corresponding to task claimed
4759   // . transfer dirty bits ct->mut for that region
4760   // . apply rescanclosure to dirty mut bits for that region
4761 
4762   ResourceMark rm;
4763   HandleMark   hm;
4764 
4765   OopTaskQueue* work_q = work_queue(i);
4766   ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
4767   // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
4768   // CAUTION: This closure has state that persists across calls to
4769   // the work method dirty_range_iterate_clear() in that it has
4770   // embedded in it a (subtype of) UpwardsObjectClosure. The
4771   // use of that state in the embedded UpwardsObjectClosure instance
4772   // assumes that the cards are always iterated (even if in parallel
4773   // by several threads) in monotonically increasing order per each
4774   // thread. This is true of the implementation below which picks
4775   // card ranges (chunks) in monotonically increasing order globally
4776   // and, a-fortiori, in monotonically increasing order per thread
4777   // (the latter order being a subsequence of the former).
4778   // If the work code below is ever reorganized into a more chaotic
4779   // work-partitioning form than the current "sequential tasks"
4780   // paradigm, the use of that persistent state will have to be
4781   // revisited and modified appropriately. See also related
4782   // bug 4756801 work on which should examine this code to make
4783   // sure that the changes there do not run counter to the
4784   // assumptions made here and necessary for correctness and
4785   // efficiency. Note also that this code might yield inefficient
4786   // behavior in the case of very large objects that span one or
4787   // more work chunks. Such objects would potentially be scanned
4788   // several times redundantly. Work on 4756801 should try and
4789   // address that performance anomaly if at all possible. XXX
4790   MemRegion  full_span  = _collector->_span;
4791   CMSBitMap* bm    = &(_collector->_markBitMap);     // shared
4792   MarkFromDirtyCardsClosure
4793     greyRescanClosure(_collector, full_span, // entire span of interest
4794                       sp, bm, work_q, cl);
4795 
4796   SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
4797   assert(pst->valid(), "Uninitialized use?");
4798   uint nth_task = 0;
4799   const int alignment = CardTableModRefBS::card_size * BitsPerWord;
4800   MemRegion span = sp->used_region();
4801   HeapWord* start_addr = span.start();
4802   HeapWord* end_addr = (HeapWord*)round_to((intptr_t)span.end(),
4803                                            alignment);
4804   const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
4805   assert((HeapWord*)round_to((intptr_t)start_addr, alignment) ==
4806          start_addr, "Check alignment");
4807   assert((size_t)round_to((intptr_t)chunk_size, alignment) ==
4808          chunk_size, "Check alignment");
4809 
4810   while (!pst->is_task_claimed(/* reference */ nth_task)) {
4811     // Having claimed the nth_task, compute corresponding mem-region,
4812     // which is a-fortiori aligned correctly (i.e. at a MUT boundary).
4813     // The alignment restriction ensures that we do not need any
4814     // synchronization with other gang-workers while setting or
4815     // clearing bits in thus chunk of the MUT.
4816     MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
4817                                     start_addr + (nth_task+1)*chunk_size);
4818     // The last chunk's end might be way beyond end of the
4819     // used region. In that case pull back appropriately.
4820     if (this_span.end() > end_addr) {
4821       this_span.set_end(end_addr);
4822       assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
4823     }
4824     // Iterate over the dirty cards covering this chunk, marking them
4825     // precleaned, and setting the corresponding bits in the mod union
4826     // table. Since we have been careful to partition at Card and MUT-word
4827     // boundaries no synchronization is needed between parallel threads.
4828     _collector->_ct->ct_bs()->dirty_card_iterate(this_span,
4829                                                  &modUnionClosure);
4830 
4831     // Having transferred these marks into the modUnionTable,
4832     // rescan the marked objects on the dirty cards in the modUnionTable.
4833     // Even if this is at a synchronous collection, the initial marking
4834     // may have been done during an asynchronous collection so there
4835     // may be dirty bits in the mod-union table.
4836     _collector->_modUnionTable.dirty_range_iterate_clear(
4837                   this_span, &greyRescanClosure);
4838     _collector->_modUnionTable.verifyNoOneBitsInRange(
4839                                  this_span.start(),
4840                                  this_span.end());
4841   }
4842   pst->all_tasks_completed();  // declare that i am done
4843 }
4844 
4845 // . see if we can share work_queues with ParNew? XXX
4846 void
4847 CMSParRemarkTask::do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl,
4848                                 int* seed) {
4849   OopTaskQueue* work_q = work_queue(i);
4850   NOT_PRODUCT(int num_steals = 0;)
4851   oop obj_to_scan;
4852   CMSBitMap* bm = &(_collector->_markBitMap);
4853 
4854   while (true) {
4855     // Completely finish any left over work from (an) earlier round(s)
4856     cl->trim_queue(0);
4857     size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
4858                                          (size_t)ParGCDesiredObjsFromOverflowList);
4859     // Now check if there's any work in the overflow list
4860     // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
4861     // only affects the number of attempts made to get work from the
4862     // overflow list and does not affect the number of workers.  Just
4863     // pass ParallelGCThreads so this behavior is unchanged.
4864     if (_collector->par_take_from_overflow_list(num_from_overflow_list,
4865                                                 work_q,
4866                                                 ParallelGCThreads)) {
4867       // found something in global overflow list;
4868       // not yet ready to go stealing work from others.
4869       // We'd like to assert(work_q->size() != 0, ...)
4870       // because we just took work from the overflow list,
4871       // but of course we can't since all of that could have
4872       // been already stolen from us.
4873       // "He giveth and He taketh away."
4874       continue;
4875     }
4876     // Verify that we have no work before we resort to stealing
4877     assert(work_q->size() == 0, "Have work, shouldn't steal");
4878     // Try to steal from other queues that have work
4879     if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
4880       NOT_PRODUCT(num_steals++;)
4881       assert(obj_to_scan->is_oop(), "Oops, not an oop!");
4882       assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
4883       // Do scanning work
4884       obj_to_scan->oop_iterate(cl);
4885       // Loop around, finish this work, and try to steal some more
4886     } else if (terminator()->offer_termination()) {
4887         break;  // nirvana from the infinite cycle
4888     }
4889   }
4890   NOT_PRODUCT(
4891     if (PrintCMSStatistics != 0) {
4892       gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
4893     }
4894   )
4895   assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
4896          "Else our work is not yet done");
4897 }
4898 
4899 // Record object boundaries in _eden_chunk_array by sampling the eden
4900 // top in the slow-path eden object allocation code path and record
4901 // the boundaries, if CMSEdenChunksRecordAlways is true. If
4902 // CMSEdenChunksRecordAlways is false, we use the other asynchronous
4903 // sampling in sample_eden() that activates during the part of the
4904 // preclean phase.
4905 void CMSCollector::sample_eden_chunk() {
4906   if (CMSEdenChunksRecordAlways && _eden_chunk_array != NULL) {
4907     if (_eden_chunk_lock->try_lock()) {
4908       // Record a sample. This is the critical section. The contents
4909       // of the _eden_chunk_array have to be non-decreasing in the
4910       // address order.
4911       _eden_chunk_array[_eden_chunk_index] = *_top_addr;
4912       assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4913              "Unexpected state of Eden");
4914       if (_eden_chunk_index == 0 ||
4915           ((_eden_chunk_array[_eden_chunk_index] > _eden_chunk_array[_eden_chunk_index-1]) &&
4916            (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4917                           _eden_chunk_array[_eden_chunk_index-1]) >= CMSSamplingGrain))) {
4918         _eden_chunk_index++;  // commit sample
4919       }
4920       _eden_chunk_lock->unlock();
4921     }
4922   }
4923 }
4924 
4925 // Return a thread-local PLAB recording array, as appropriate.
4926 void* CMSCollector::get_data_recorder(int thr_num) {
4927   if (_survivor_plab_array != NULL &&
4928       (CMSPLABRecordAlways ||
4929        (_collectorState > Marking && _collectorState < FinalMarking))) {
4930     assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
4931     ChunkArray* ca = &_survivor_plab_array[thr_num];
4932     ca->reset();   // clear it so that fresh data is recorded
4933     return (void*) ca;
4934   } else {
4935     return NULL;
4936   }
4937 }
4938 
4939 // Reset all the thread-local PLAB recording arrays
4940 void CMSCollector::reset_survivor_plab_arrays() {
4941   for (uint i = 0; i < ParallelGCThreads; i++) {
4942     _survivor_plab_array[i].reset();
4943   }
4944 }
4945 
4946 // Merge the per-thread plab arrays into the global survivor chunk
4947 // array which will provide the partitioning of the survivor space
4948 // for CMS initial scan and rescan.
4949 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv,
4950                                               int no_of_gc_threads) {
4951   assert(_survivor_plab_array  != NULL, "Error");
4952   assert(_survivor_chunk_array != NULL, "Error");
4953   assert(_collectorState == FinalMarking ||
4954          (CMSParallelInitialMarkEnabled && _collectorState == InitialMarking), "Error");
4955   for (int j = 0; j < no_of_gc_threads; j++) {
4956     _cursor[j] = 0;
4957   }
4958   HeapWord* top = surv->top();
4959   size_t i;
4960   for (i = 0; i < _survivor_chunk_capacity; i++) {  // all sca entries
4961     HeapWord* min_val = top;          // Higher than any PLAB address
4962     uint      min_tid = 0;            // position of min_val this round
4963     for (int j = 0; j < no_of_gc_threads; j++) {
4964       ChunkArray* cur_sca = &_survivor_plab_array[j];
4965       if (_cursor[j] == cur_sca->end()) {
4966         continue;
4967       }
4968       assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
4969       HeapWord* cur_val = cur_sca->nth(_cursor[j]);
4970       assert(surv->used_region().contains(cur_val), "Out of bounds value");
4971       if (cur_val < min_val) {
4972         min_tid = j;
4973         min_val = cur_val;
4974       } else {
4975         assert(cur_val < top, "All recorded addresses should be less");
4976       }
4977     }
4978     // At this point min_val and min_tid are respectively
4979     // the least address in _survivor_plab_array[j]->nth(_cursor[j])
4980     // and the thread (j) that witnesses that address.
4981     // We record this address in the _survivor_chunk_array[i]
4982     // and increment _cursor[min_tid] prior to the next round i.
4983     if (min_val == top) {
4984       break;
4985     }
4986     _survivor_chunk_array[i] = min_val;
4987     _cursor[min_tid]++;
4988   }
4989   // We are all done; record the size of the _survivor_chunk_array
4990   _survivor_chunk_index = i; // exclusive: [0, i)
4991   if (PrintCMSStatistics > 0) {
4992     gclog_or_tty->print(" (Survivor:" SIZE_FORMAT "chunks) ", i);
4993   }
4994   // Verify that we used up all the recorded entries
4995   #ifdef ASSERT
4996     size_t total = 0;
4997     for (int j = 0; j < no_of_gc_threads; j++) {
4998       assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
4999       total += _cursor[j];
5000     }
5001     assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
5002     // Check that the merged array is in sorted order
5003     if (total > 0) {
5004       for (size_t i = 0; i < total - 1; i++) {
5005         if (PrintCMSStatistics > 0) {
5006           gclog_or_tty->print(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
5007                               i, p2i(_survivor_chunk_array[i]));
5008         }
5009         assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
5010                "Not sorted");
5011       }
5012     }
5013   #endif // ASSERT
5014 }
5015 
5016 // Set up the space's par_seq_tasks structure for work claiming
5017 // for parallel initial scan and rescan of young gen.
5018 // See ParRescanTask where this is currently used.
5019 void
5020 CMSCollector::
5021 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
5022   assert(n_threads > 0, "Unexpected n_threads argument");
5023 
5024   // Eden space
5025   if (!_young_gen->eden()->is_empty()) {
5026     SequentialSubTasksDone* pst = _young_gen->eden()->par_seq_tasks();
5027     assert(!pst->valid(), "Clobbering existing data?");
5028     // Each valid entry in [0, _eden_chunk_index) represents a task.
5029     size_t n_tasks = _eden_chunk_index + 1;
5030     assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
5031     // Sets the condition for completion of the subtask (how many threads
5032     // need to finish in order to be done).
5033     pst->set_n_threads(n_threads);
5034     pst->set_n_tasks((int)n_tasks);
5035   }
5036 
5037   // Merge the survivor plab arrays into _survivor_chunk_array
5038   if (_survivor_plab_array != NULL) {
5039     merge_survivor_plab_arrays(_young_gen->from(), n_threads);
5040   } else {
5041     assert(_survivor_chunk_index == 0, "Error");
5042   }
5043 
5044   // To space
5045   {
5046     SequentialSubTasksDone* pst = _young_gen->to()->par_seq_tasks();
5047     assert(!pst->valid(), "Clobbering existing data?");
5048     // Sets the condition for completion of the subtask (how many threads
5049     // need to finish in order to be done).
5050     pst->set_n_threads(n_threads);
5051     pst->set_n_tasks(1);
5052     assert(pst->valid(), "Error");
5053   }
5054 
5055   // From space
5056   {
5057     SequentialSubTasksDone* pst = _young_gen->from()->par_seq_tasks();
5058     assert(!pst->valid(), "Clobbering existing data?");
5059     size_t n_tasks = _survivor_chunk_index + 1;
5060     assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
5061     // Sets the condition for completion of the subtask (how many threads
5062     // need to finish in order to be done).
5063     pst->set_n_threads(n_threads);
5064     pst->set_n_tasks((int)n_tasks);
5065     assert(pst->valid(), "Error");
5066   }
5067 }
5068 
5069 // Parallel version of remark
5070 void CMSCollector::do_remark_parallel() {
5071   GenCollectedHeap* gch = GenCollectedHeap::heap();
5072   WorkGang* workers = gch->workers();
5073   assert(workers != NULL, "Need parallel worker threads.");
5074   // Choose to use the number of GC workers most recently set
5075   // into "active_workers".
5076   uint n_workers = workers->active_workers();
5077 
5078   CompactibleFreeListSpace* cms_space  = _cmsGen->cmsSpace();
5079 
5080   StrongRootsScope srs(n_workers);
5081 
5082   CMSParRemarkTask tsk(this, cms_space, n_workers, workers, task_queues(), &srs);
5083 
5084   // We won't be iterating over the cards in the card table updating
5085   // the younger_gen cards, so we shouldn't call the following else
5086   // the verification code as well as subsequent younger_refs_iterate
5087   // code would get confused. XXX
5088   // gch->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
5089 
5090   // The young gen rescan work will not be done as part of
5091   // process_roots (which currently doesn't know how to
5092   // parallelize such a scan), but rather will be broken up into
5093   // a set of parallel tasks (via the sampling that the [abortable]
5094   // preclean phase did of eden, plus the [two] tasks of
5095   // scanning the [two] survivor spaces. Further fine-grain
5096   // parallelization of the scanning of the survivor spaces
5097   // themselves, and of precleaning of the younger gen itself
5098   // is deferred to the future.
5099   initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
5100 
5101   // The dirty card rescan work is broken up into a "sequence"
5102   // of parallel tasks (per constituent space) that are dynamically
5103   // claimed by the parallel threads.
5104   cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
5105 
5106   // It turns out that even when we're using 1 thread, doing the work in a
5107   // separate thread causes wide variance in run times.  We can't help this
5108   // in the multi-threaded case, but we special-case n=1 here to get
5109   // repeatable measurements of the 1-thread overhead of the parallel code.
5110   if (n_workers > 1) {
5111     // Make refs discovery MT-safe, if it isn't already: it may not
5112     // necessarily be so, since it's possible that we are doing
5113     // ST marking.
5114     ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), true);
5115     workers->run_task(&tsk);
5116   } else {
5117     ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5118     tsk.work(0);
5119   }
5120 
5121   // restore, single-threaded for now, any preserved marks
5122   // as a result of work_q overflow
5123   restore_preserved_marks_if_any();
5124 }
5125 
5126 // Non-parallel version of remark
5127 void CMSCollector::do_remark_non_parallel() {
5128   ResourceMark rm;
5129   HandleMark   hm;
5130   GenCollectedHeap* gch = GenCollectedHeap::heap();
5131   ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5132 
5133   MarkRefsIntoAndScanClosure
5134     mrias_cl(_span, ref_processor(), &_markBitMap, NULL /* not precleaning */,
5135              &_markStack, this,
5136              false /* should_yield */, false /* not precleaning */);
5137   MarkFromDirtyCardsClosure
5138     markFromDirtyCardsClosure(this, _span,
5139                               NULL,  // space is set further below
5140                               &_markBitMap, &_markStack, &mrias_cl);
5141   {
5142     GCTraceTime t("grey object rescan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5143     // Iterate over the dirty cards, setting the corresponding bits in the
5144     // mod union table.
5145     {
5146       ModUnionClosure modUnionClosure(&_modUnionTable);
5147       _ct->ct_bs()->dirty_card_iterate(
5148                       _cmsGen->used_region(),
5149                       &modUnionClosure);
5150     }
5151     // Having transferred these marks into the modUnionTable, we just need
5152     // to rescan the marked objects on the dirty cards in the modUnionTable.
5153     // The initial marking may have been done during an asynchronous
5154     // collection so there may be dirty bits in the mod-union table.
5155     const int alignment =
5156       CardTableModRefBS::card_size * BitsPerWord;
5157     {
5158       // ... First handle dirty cards in CMS gen
5159       markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
5160       MemRegion ur = _cmsGen->used_region();
5161       HeapWord* lb = ur.start();
5162       HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
5163       MemRegion cms_span(lb, ub);
5164       _modUnionTable.dirty_range_iterate_clear(cms_span,
5165                                                &markFromDirtyCardsClosure);
5166       verify_work_stacks_empty();
5167       if (PrintCMSStatistics != 0) {
5168         gclog_or_tty->print(" (re-scanned "SIZE_FORMAT" dirty cards in cms gen) ",
5169           markFromDirtyCardsClosure.num_dirty_cards());
5170       }
5171     }
5172   }
5173   if (VerifyDuringGC &&
5174       GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5175     HandleMark hm;  // Discard invalid handles created during verification
5176     Universe::verify();
5177   }
5178   {
5179     GCTraceTime t("root rescan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5180 
5181     verify_work_stacks_empty();
5182 
5183     gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
5184     StrongRootsScope srs(1);
5185 
5186     gch->gen_process_roots(&srs,
5187                            _cmsGen->level(),
5188                            true,  // younger gens as roots
5189                            GenCollectedHeap::ScanningOption(roots_scanning_options()),
5190                            should_unload_classes(),
5191                            &mrias_cl,
5192                            NULL,
5193                            NULL); // The dirty klasses will be handled below
5194 
5195     assert(should_unload_classes()
5196            || (roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
5197            "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5198   }
5199 
5200   {
5201     GCTraceTime t("visit unhandled CLDs", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5202 
5203     verify_work_stacks_empty();
5204 
5205     // Scan all class loader data objects that might have been introduced
5206     // during concurrent marking.
5207     ResourceMark rm;
5208     GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
5209     for (int i = 0; i < array->length(); i++) {
5210       mrias_cl.do_class_loader_data(array->at(i));
5211     }
5212 
5213     // We don't need to keep track of new CLDs anymore.
5214     ClassLoaderDataGraph::remember_new_clds(false);
5215 
5216     verify_work_stacks_empty();
5217   }
5218 
5219   {
5220     GCTraceTime t("dirty klass scan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5221 
5222     verify_work_stacks_empty();
5223 
5224     RemarkKlassClosure remark_klass_closure(&mrias_cl);
5225     ClassLoaderDataGraph::classes_do(&remark_klass_closure);
5226 
5227     verify_work_stacks_empty();
5228   }
5229 
5230   // We might have added oops to ClassLoaderData::_handles during the
5231   // concurrent marking phase. These oops point to newly allocated objects
5232   // that are guaranteed to be kept alive. Either by the direct allocation
5233   // code, or when the young collector processes the roots. Hence,
5234   // we don't have to revisit the _handles block during the remark phase.
5235 
5236   verify_work_stacks_empty();
5237   // Restore evacuated mark words, if any, used for overflow list links
5238   if (!CMSOverflowEarlyRestoration) {
5239     restore_preserved_marks_if_any();
5240   }
5241   verify_overflow_empty();
5242 }
5243 
5244 ////////////////////////////////////////////////////////
5245 // Parallel Reference Processing Task Proxy Class
5246 ////////////////////////////////////////////////////////
5247 class AbstractGangTaskWOopQueues : public AbstractGangTask {
5248   OopTaskQueueSet*       _queues;
5249   ParallelTaskTerminator _terminator;
5250  public:
5251   AbstractGangTaskWOopQueues(const char* name, OopTaskQueueSet* queues, uint n_threads) :
5252     AbstractGangTask(name), _queues(queues), _terminator(n_threads, _queues) {}
5253   ParallelTaskTerminator* terminator() { return &_terminator; }
5254   OopTaskQueueSet* queues() { return _queues; }
5255 };
5256 
5257 class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues {
5258   typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
5259   CMSCollector*          _collector;
5260   CMSBitMap*             _mark_bit_map;
5261   const MemRegion        _span;
5262   ProcessTask&           _task;
5263 
5264 public:
5265   CMSRefProcTaskProxy(ProcessTask&     task,
5266                       CMSCollector*    collector,
5267                       const MemRegion& span,
5268                       CMSBitMap*       mark_bit_map,
5269                       AbstractWorkGang* workers,
5270                       OopTaskQueueSet* task_queues):
5271     AbstractGangTaskWOopQueues("Process referents by policy in parallel",
5272       task_queues,
5273       workers->active_workers()),
5274     _task(task),
5275     _collector(collector), _span(span), _mark_bit_map(mark_bit_map)
5276   {
5277     assert(_collector->_span.equals(_span) && !_span.is_empty(),
5278            "Inconsistency in _span");
5279   }
5280 
5281   OopTaskQueueSet* task_queues() { return queues(); }
5282 
5283   OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5284 
5285   void do_work_steal(int i,
5286                      CMSParDrainMarkingStackClosure* drain,
5287                      CMSParKeepAliveClosure* keep_alive,
5288                      int* seed);
5289 
5290   virtual void work(uint worker_id);
5291 };
5292 
5293 void CMSRefProcTaskProxy::work(uint worker_id) {
5294   ResourceMark rm;
5295   HandleMark hm;
5296   assert(_collector->_span.equals(_span), "Inconsistency in _span");
5297   CMSParKeepAliveClosure par_keep_alive(_collector, _span,
5298                                         _mark_bit_map,
5299                                         work_queue(worker_id));
5300   CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
5301                                                  _mark_bit_map,
5302                                                  work_queue(worker_id));
5303   CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
5304   _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack);
5305   if (_task.marks_oops_alive()) {
5306     do_work_steal(worker_id, &par_drain_stack, &par_keep_alive,
5307                   _collector->hash_seed(worker_id));
5308   }
5309   assert(work_queue(worker_id)->size() == 0, "work_queue should be empty");
5310   assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
5311 }
5312 
5313 class CMSRefEnqueueTaskProxy: public AbstractGangTask {
5314   typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
5315   EnqueueTask& _task;
5316 
5317 public:
5318   CMSRefEnqueueTaskProxy(EnqueueTask& task)
5319     : AbstractGangTask("Enqueue reference objects in parallel"),
5320       _task(task)
5321   { }
5322 
5323   virtual void work(uint worker_id)
5324   {
5325     _task.work(worker_id);
5326   }
5327 };
5328 
5329 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
5330   MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue):
5331    _span(span),
5332    _bit_map(bit_map),
5333    _work_queue(work_queue),
5334    _mark_and_push(collector, span, bit_map, work_queue),
5335    _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
5336                         (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads)))
5337 { }
5338 
5339 // . see if we can share work_queues with ParNew? XXX
5340 void CMSRefProcTaskProxy::do_work_steal(int i,
5341   CMSParDrainMarkingStackClosure* drain,
5342   CMSParKeepAliveClosure* keep_alive,
5343   int* seed) {
5344   OopTaskQueue* work_q = work_queue(i);
5345   NOT_PRODUCT(int num_steals = 0;)
5346   oop obj_to_scan;
5347 
5348   while (true) {
5349     // Completely finish any left over work from (an) earlier round(s)
5350     drain->trim_queue(0);
5351     size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5352                                          (size_t)ParGCDesiredObjsFromOverflowList);
5353     // Now check if there's any work in the overflow list
5354     // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5355     // only affects the number of attempts made to get work from the
5356     // overflow list and does not affect the number of workers.  Just
5357     // pass ParallelGCThreads so this behavior is unchanged.
5358     if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5359                                                 work_q,
5360                                                 ParallelGCThreads)) {
5361       // Found something in global overflow list;
5362       // not yet ready to go stealing work from others.
5363       // We'd like to assert(work_q->size() != 0, ...)
5364       // because we just took work from the overflow list,
5365       // but of course we can't, since all of that might have
5366       // been already stolen from us.
5367       continue;
5368     }
5369     // Verify that we have no work before we resort to stealing
5370     assert(work_q->size() == 0, "Have work, shouldn't steal");
5371     // Try to steal from other queues that have work
5372     if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5373       NOT_PRODUCT(num_steals++;)
5374       assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5375       assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5376       // Do scanning work
5377       obj_to_scan->oop_iterate(keep_alive);
5378       // Loop around, finish this work, and try to steal some more
5379     } else if (terminator()->offer_termination()) {
5380       break;  // nirvana from the infinite cycle
5381     }
5382   }
5383   NOT_PRODUCT(
5384     if (PrintCMSStatistics != 0) {
5385       gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5386     }
5387   )
5388 }
5389 
5390 void CMSRefProcTaskExecutor::execute(ProcessTask& task)
5391 {
5392   GenCollectedHeap* gch = GenCollectedHeap::heap();
5393   WorkGang* workers = gch->workers();
5394   assert(workers != NULL, "Need parallel worker threads.");
5395   CMSRefProcTaskProxy rp_task(task, &_collector,
5396                               _collector.ref_processor()->span(),
5397                               _collector.markBitMap(),
5398                               workers, _collector.task_queues());
5399   workers->run_task(&rp_task);
5400 }
5401 
5402 void CMSRefProcTaskExecutor::execute(EnqueueTask& task)
5403 {
5404 
5405   GenCollectedHeap* gch = GenCollectedHeap::heap();
5406   WorkGang* workers = gch->workers();
5407   assert(workers != NULL, "Need parallel worker threads.");
5408   CMSRefEnqueueTaskProxy enq_task(task);
5409   workers->run_task(&enq_task);
5410 }
5411 
5412 void CMSCollector::refProcessingWork() {
5413   ResourceMark rm;
5414   HandleMark   hm;
5415 
5416   ReferenceProcessor* rp = ref_processor();
5417   assert(rp->span().equals(_span), "Spans should be equal");
5418   assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
5419   // Process weak references.
5420   rp->setup_policy(false);
5421   verify_work_stacks_empty();
5422 
5423   CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
5424                                           &_markStack, false /* !preclean */);
5425   CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
5426                                 _span, &_markBitMap, &_markStack,
5427                                 &cmsKeepAliveClosure, false /* !preclean */);
5428   {
5429     GCTraceTime t("weak refs processing", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5430 
5431     ReferenceProcessorStats stats;
5432     if (rp->processing_is_mt()) {
5433       // Set the degree of MT here.  If the discovery is done MT, there
5434       // may have been a different number of threads doing the discovery
5435       // and a different number of discovered lists may have Ref objects.
5436       // That is OK as long as the Reference lists are balanced (see
5437       // balance_all_queues() and balance_queues()).
5438       GenCollectedHeap* gch = GenCollectedHeap::heap();
5439       uint active_workers = ParallelGCThreads;
5440       WorkGang* workers = gch->workers();
5441       if (workers != NULL) {
5442         active_workers = workers->active_workers();
5443         // The expectation is that active_workers will have already
5444         // been set to a reasonable value.  If it has not been set,
5445         // investigate.
5446         assert(active_workers > 0, "Should have been set during scavenge");
5447       }
5448       rp->set_active_mt_degree(active_workers);
5449       CMSRefProcTaskExecutor task_executor(*this);
5450       stats = rp->process_discovered_references(&_is_alive_closure,
5451                                         &cmsKeepAliveClosure,
5452                                         &cmsDrainMarkingStackClosure,
5453                                         &task_executor,
5454                                         _gc_timer_cm,
5455                                         _gc_tracer_cm->gc_id());
5456     } else {
5457       stats = rp->process_discovered_references(&_is_alive_closure,
5458                                         &cmsKeepAliveClosure,
5459                                         &cmsDrainMarkingStackClosure,
5460                                         NULL,
5461                                         _gc_timer_cm,
5462                                         _gc_tracer_cm->gc_id());
5463     }
5464     _gc_tracer_cm->report_gc_reference_stats(stats);
5465 
5466   }
5467 
5468   // This is the point where the entire marking should have completed.
5469   verify_work_stacks_empty();
5470 
5471   if (should_unload_classes()) {
5472     {
5473       GCTraceTime t("class unloading", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5474 
5475       // Unload classes and purge the SystemDictionary.
5476       bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure);
5477 
5478       // Unload nmethods.
5479       CodeCache::do_unloading(&_is_alive_closure, purged_class);
5480 
5481       // Prune dead klasses from subklass/sibling/implementor lists.
5482       Klass::clean_weak_klass_links(&_is_alive_closure);
5483     }
5484 
5485     {
5486       GCTraceTime t("scrub symbol table", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5487       // Clean up unreferenced symbols in symbol table.
5488       SymbolTable::unlink();
5489     }
5490 
5491     {
5492       GCTraceTime t("scrub string table", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5493       // Delete entries for dead interned strings.
5494       StringTable::unlink(&_is_alive_closure);
5495     }
5496   }
5497 
5498 
5499   // Restore any preserved marks as a result of mark stack or
5500   // work queue overflow
5501   restore_preserved_marks_if_any();  // done single-threaded for now
5502 
5503   rp->set_enqueuing_is_done(true);
5504   if (rp->processing_is_mt()) {
5505     rp->balance_all_queues();
5506     CMSRefProcTaskExecutor task_executor(*this);
5507     rp->enqueue_discovered_references(&task_executor);
5508   } else {
5509     rp->enqueue_discovered_references(NULL);
5510   }
5511   rp->verify_no_references_recorded();
5512   assert(!rp->discovery_enabled(), "should have been disabled");
5513 }
5514 
5515 #ifndef PRODUCT
5516 void CMSCollector::check_correct_thread_executing() {
5517   Thread* t = Thread::current();
5518   // Only the VM thread or the CMS thread should be here.
5519   assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
5520          "Unexpected thread type");
5521   // If this is the vm thread, the foreground process
5522   // should not be waiting.  Note that _foregroundGCIsActive is
5523   // true while the foreground collector is waiting.
5524   if (_foregroundGCShouldWait) {
5525     // We cannot be the VM thread
5526     assert(t->is_ConcurrentGC_thread(),
5527            "Should be CMS thread");
5528   } else {
5529     // We can be the CMS thread only if we are in a stop-world
5530     // phase of CMS collection.
5531     if (t->is_ConcurrentGC_thread()) {
5532       assert(_collectorState == InitialMarking ||
5533              _collectorState == FinalMarking,
5534              "Should be a stop-world phase");
5535       // The CMS thread should be holding the CMS_token.
5536       assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5537              "Potential interference with concurrently "
5538              "executing VM thread");
5539     }
5540   }
5541 }
5542 #endif
5543 
5544 void CMSCollector::sweep() {
5545   assert(_collectorState == Sweeping, "just checking");
5546   check_correct_thread_executing();
5547   verify_work_stacks_empty();
5548   verify_overflow_empty();
5549   increment_sweep_count();
5550   TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
5551 
5552   _inter_sweep_timer.stop();
5553   _inter_sweep_estimate.sample(_inter_sweep_timer.seconds());
5554 
5555   assert(!_intra_sweep_timer.is_active(), "Should not be active");
5556   _intra_sweep_timer.reset();
5557   _intra_sweep_timer.start();
5558   {
5559     TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
5560     CMSPhaseAccounting pa(this, "sweep", _gc_tracer_cm->gc_id(), !PrintGCDetails);
5561     // First sweep the old gen
5562     {
5563       CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
5564                                bitMapLock());
5565       sweepWork(_cmsGen);
5566     }
5567 
5568     // Update Universe::_heap_*_at_gc figures.
5569     // We need all the free list locks to make the abstract state
5570     // transition from Sweeping to Resetting. See detailed note
5571     // further below.
5572     {
5573       CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock());
5574       // Update heap occupancy information which is used as
5575       // input to soft ref clearing policy at the next gc.
5576       Universe::update_heap_info_at_gc();
5577       _collectorState = Resizing;
5578     }
5579   }
5580   verify_work_stacks_empty();
5581   verify_overflow_empty();
5582 
5583   if (should_unload_classes()) {
5584     // Delay purge to the beginning of the next safepoint.  Metaspace::contains
5585     // requires that the virtual spaces are stable and not deleted.
5586     ClassLoaderDataGraph::set_should_purge(true);
5587   }
5588 
5589   _intra_sweep_timer.stop();
5590   _intra_sweep_estimate.sample(_intra_sweep_timer.seconds());
5591 
5592   _inter_sweep_timer.reset();
5593   _inter_sweep_timer.start();
5594 
5595   // We need to use a monotonically non-decreasing time in ms
5596   // or we will see time-warp warnings and os::javaTimeMillis()
5597   // does not guarantee monotonicity.
5598   jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
5599   update_time_of_last_gc(now);
5600 
5601   // NOTE on abstract state transitions:
5602   // Mutators allocate-live and/or mark the mod-union table dirty
5603   // based on the state of the collection.  The former is done in
5604   // the interval [Marking, Sweeping] and the latter in the interval
5605   // [Marking, Sweeping).  Thus the transitions into the Marking state
5606   // and out of the Sweeping state must be synchronously visible
5607   // globally to the mutators.
5608   // The transition into the Marking state happens with the world
5609   // stopped so the mutators will globally see it.  Sweeping is
5610   // done asynchronously by the background collector so the transition
5611   // from the Sweeping state to the Resizing state must be done
5612   // under the freelistLock (as is the check for whether to
5613   // allocate-live and whether to dirty the mod-union table).
5614   assert(_collectorState == Resizing, "Change of collector state to"
5615     " Resizing must be done under the freelistLocks (plural)");
5616 
5617   // Now that sweeping has been completed, we clear
5618   // the incremental_collection_failed flag,
5619   // thus inviting a younger gen collection to promote into
5620   // this generation. If such a promotion may still fail,
5621   // the flag will be set again when a young collection is
5622   // attempted.
5623   GenCollectedHeap* gch = GenCollectedHeap::heap();
5624   gch->clear_incremental_collection_failed();  // Worth retrying as fresh space may have been freed up
5625   gch->update_full_collections_completed(_collection_count_start);
5626 }
5627 
5628 // FIX ME!!! Looks like this belongs in CFLSpace, with
5629 // CMSGen merely delegating to it.
5630 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
5631   double nearLargestPercent = FLSLargestBlockCoalesceProximity;
5632   HeapWord*  minAddr        = _cmsSpace->bottom();
5633   HeapWord*  largestAddr    =
5634     (HeapWord*) _cmsSpace->dictionary()->find_largest_dict();
5635   if (largestAddr == NULL) {
5636     // The dictionary appears to be empty.  In this case
5637     // try to coalesce at the end of the heap.
5638     largestAddr = _cmsSpace->end();
5639   }
5640   size_t largestOffset     = pointer_delta(largestAddr, minAddr);
5641   size_t nearLargestOffset =
5642     (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
5643   if (PrintFLSStatistics != 0) {
5644     gclog_or_tty->print_cr(
5645       "CMS: Large Block: " PTR_FORMAT ";"
5646       " Proximity: " PTR_FORMAT " -> " PTR_FORMAT,
5647       p2i(largestAddr),
5648       p2i(_cmsSpace->nearLargestChunk()), p2i(minAddr + nearLargestOffset));
5649   }
5650   _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
5651 }
5652 
5653 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
5654   return addr >= _cmsSpace->nearLargestChunk();
5655 }
5656 
5657 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
5658   return _cmsSpace->find_chunk_at_end();
5659 }
5660 
5661 void ConcurrentMarkSweepGeneration::update_gc_stats(int current_level,
5662                                                     bool full) {
5663   // The next lower level has been collected.  Gather any statistics
5664   // that are of interest at this point.
5665   if (!full && (current_level + 1) == level()) {
5666     // Gather statistics on the young generation collection.
5667     collector()->stats().record_gc0_end(used());
5668   }
5669 }
5670 
5671 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* gen) {
5672   // We iterate over the space(s) underlying this generation,
5673   // checking the mark bit map to see if the bits corresponding
5674   // to specific blocks are marked or not. Blocks that are
5675   // marked are live and are not swept up. All remaining blocks
5676   // are swept up, with coalescing on-the-fly as we sweep up
5677   // contiguous free and/or garbage blocks:
5678   // We need to ensure that the sweeper synchronizes with allocators
5679   // and stop-the-world collectors. In particular, the following
5680   // locks are used:
5681   // . CMS token: if this is held, a stop the world collection cannot occur
5682   // . freelistLock: if this is held no allocation can occur from this
5683   //                 generation by another thread
5684   // . bitMapLock: if this is held, no other thread can access or update
5685   //
5686 
5687   // Note that we need to hold the freelistLock if we use
5688   // block iterate below; else the iterator might go awry if
5689   // a mutator (or promotion) causes block contents to change
5690   // (for instance if the allocator divvies up a block).
5691   // If we hold the free list lock, for all practical purposes
5692   // young generation GC's can't occur (they'll usually need to
5693   // promote), so we might as well prevent all young generation
5694   // GC's while we do a sweeping step. For the same reason, we might
5695   // as well take the bit map lock for the entire duration
5696 
5697   // check that we hold the requisite locks
5698   assert(have_cms_token(), "Should hold cms token");
5699   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), "Should possess CMS token to sweep");
5700   assert_lock_strong(gen->freelistLock());
5701   assert_lock_strong(bitMapLock());
5702 
5703   assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context");
5704   assert(_intra_sweep_timer.is_active(),  "Was switched on  in an outer context");
5705   gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
5706                                       _inter_sweep_estimate.padded_average(),
5707                                       _intra_sweep_estimate.padded_average());
5708   gen->setNearLargestChunk();
5709 
5710   {
5711     SweepClosure sweepClosure(this, gen, &_markBitMap, CMSYield);
5712     gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
5713     // We need to free-up/coalesce garbage/blocks from a
5714     // co-terminal free run. This is done in the SweepClosure
5715     // destructor; so, do not remove this scope, else the
5716     // end-of-sweep-census below will be off by a little bit.
5717   }
5718   gen->cmsSpace()->sweep_completed();
5719   gen->cmsSpace()->endSweepFLCensus(sweep_count());
5720   if (should_unload_classes()) {                // unloaded classes this cycle,
5721     _concurrent_cycles_since_last_unload = 0;   // ... reset count
5722   } else {                                      // did not unload classes,
5723     _concurrent_cycles_since_last_unload++;     // ... increment count
5724   }
5725 }
5726 
5727 // Reset CMS data structures (for now just the marking bit map)
5728 // preparatory for the next cycle.
5729 void CMSCollector::reset(bool concurrent) {
5730   if (concurrent) {
5731     CMSTokenSyncWithLocks ts(true, bitMapLock());
5732 
5733     // If the state is not "Resetting", the foreground  thread
5734     // has done a collection and the resetting.
5735     if (_collectorState != Resetting) {
5736       assert(_collectorState == Idling, "The state should only change"
5737         " because the foreground collector has finished the collection");
5738       return;
5739     }
5740 
5741     // Clear the mark bitmap (no grey objects to start with)
5742     // for the next cycle.
5743     TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
5744     CMSPhaseAccounting cmspa(this, "reset", _gc_tracer_cm->gc_id(), !PrintGCDetails);
5745 
5746     HeapWord* curAddr = _markBitMap.startWord();
5747     while (curAddr < _markBitMap.endWord()) {
5748       size_t remaining  = pointer_delta(_markBitMap.endWord(), curAddr);
5749       MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
5750       _markBitMap.clear_large_range(chunk);
5751       if (ConcurrentMarkSweepThread::should_yield() &&
5752           !foregroundGCIsActive() &&
5753           CMSYield) {
5754         assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5755                "CMS thread should hold CMS token");
5756         assert_lock_strong(bitMapLock());
5757         bitMapLock()->unlock();
5758         ConcurrentMarkSweepThread::desynchronize(true);
5759         stopTimer();
5760         if (PrintCMSStatistics != 0) {
5761           incrementYields();
5762         }
5763 
5764         // See the comment in coordinator_yield()
5765         for (unsigned i = 0; i < CMSYieldSleepCount &&
5766                          ConcurrentMarkSweepThread::should_yield() &&
5767                          !CMSCollector::foregroundGCIsActive(); ++i) {
5768           os::sleep(Thread::current(), 1, false);
5769         }
5770 
5771         ConcurrentMarkSweepThread::synchronize(true);
5772         bitMapLock()->lock_without_safepoint_check();
5773         startTimer();
5774       }
5775       curAddr = chunk.end();
5776     }
5777     // A successful mostly concurrent collection has been done.
5778     // Because only the full (i.e., concurrent mode failure) collections
5779     // are being measured for gc overhead limits, clean the "near" flag
5780     // and count.
5781     size_policy()->reset_gc_overhead_limit_count();
5782     _collectorState = Idling;
5783   } else {
5784     // already have the lock
5785     assert(_collectorState == Resetting, "just checking");
5786     assert_lock_strong(bitMapLock());
5787     _markBitMap.clear_all();
5788     _collectorState = Idling;
5789   }
5790 
5791   register_gc_end();
5792 }
5793 
5794 void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) {
5795   TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
5796   GCTraceTime t(GCCauseString("GC", gc_cause), PrintGC, !PrintGCDetails, NULL, _gc_tracer_cm->gc_id());
5797   TraceCollectorStats tcs(counters());
5798 
5799   switch (op) {
5800     case CMS_op_checkpointRootsInitial: {
5801       SvcGCMarker sgcm(SvcGCMarker::OTHER);
5802       checkpointRootsInitial();
5803       if (PrintGC) {
5804         _cmsGen->printOccupancy("initial-mark");
5805       }
5806       break;
5807     }
5808     case CMS_op_checkpointRootsFinal: {
5809       SvcGCMarker sgcm(SvcGCMarker::OTHER);
5810       checkpointRootsFinal();
5811       if (PrintGC) {
5812         _cmsGen->printOccupancy("remark");
5813       }
5814       break;
5815     }
5816     default:
5817       fatal("No such CMS_op");
5818   }
5819 }
5820 
5821 #ifndef PRODUCT
5822 size_t const CMSCollector::skip_header_HeapWords() {
5823   return FreeChunk::header_size();
5824 }
5825 
5826 // Try and collect here conditions that should hold when
5827 // CMS thread is exiting. The idea is that the foreground GC
5828 // thread should not be blocked if it wants to terminate
5829 // the CMS thread and yet continue to run the VM for a while
5830 // after that.
5831 void CMSCollector::verify_ok_to_terminate() const {
5832   assert(Thread::current()->is_ConcurrentGC_thread(),
5833          "should be called by CMS thread");
5834   assert(!_foregroundGCShouldWait, "should be false");
5835   // We could check here that all the various low-level locks
5836   // are not held by the CMS thread, but that is overkill; see
5837   // also CMSThread::verify_ok_to_terminate() where the CGC_lock
5838   // is checked.
5839 }
5840 #endif
5841 
5842 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
5843    assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
5844           "missing Printezis mark?");
5845   HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5846   size_t size = pointer_delta(nextOneAddr + 1, addr);
5847   assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5848          "alignment problem");
5849   assert(size >= 3, "Necessary for Printezis marks to work");
5850   return size;
5851 }
5852 
5853 // A variant of the above (block_size_using_printezis_bits()) except
5854 // that we return 0 if the P-bits are not yet set.
5855 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
5856   if (_markBitMap.isMarked(addr + 1)) {
5857     assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects");
5858     HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5859     size_t size = pointer_delta(nextOneAddr + 1, addr);
5860     assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5861            "alignment problem");
5862     assert(size >= 3, "Necessary for Printezis marks to work");
5863     return size;
5864   }
5865   return 0;
5866 }
5867 
5868 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
5869   size_t sz = 0;
5870   oop p = (oop)addr;
5871   if (p->klass_or_null() != NULL) {
5872     sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
5873   } else {
5874     sz = block_size_using_printezis_bits(addr);
5875   }
5876   assert(sz > 0, "size must be nonzero");
5877   HeapWord* next_block = addr + sz;
5878   HeapWord* next_card  = (HeapWord*)round_to((uintptr_t)next_block,
5879                                              CardTableModRefBS::card_size);
5880   assert(round_down((uintptr_t)addr,      CardTableModRefBS::card_size) <
5881          round_down((uintptr_t)next_card, CardTableModRefBS::card_size),
5882          "must be different cards");
5883   return next_card;
5884 }
5885 
5886 
5887 // CMS Bit Map Wrapper /////////////////////////////////////////
5888 
5889 // Construct a CMS bit map infrastructure, but don't create the
5890 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
5891 // further below.
5892 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
5893   _bm(),
5894   _shifter(shifter),
5895   _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true,
5896                                     Monitor::_safepoint_check_sometimes) : NULL)
5897 {
5898   _bmStartWord = 0;
5899   _bmWordSize  = 0;
5900 }
5901 
5902 bool CMSBitMap::allocate(MemRegion mr) {
5903   _bmStartWord = mr.start();
5904   _bmWordSize  = mr.word_size();
5905   ReservedSpace brs(ReservedSpace::allocation_align_size_up(
5906                      (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
5907   if (!brs.is_reserved()) {
5908     warning("CMS bit map allocation failure");
5909     return false;
5910   }
5911   // For now we'll just commit all of the bit map up front.
5912   // Later on we'll try to be more parsimonious with swap.
5913   if (!_virtual_space.initialize(brs, brs.size())) {
5914     warning("CMS bit map backing store failure");
5915     return false;
5916   }
5917   assert(_virtual_space.committed_size() == brs.size(),
5918          "didn't reserve backing store for all of CMS bit map?");
5919   _bm.set_map((BitMap::bm_word_t*)_virtual_space.low());
5920   assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
5921          _bmWordSize, "inconsistency in bit map sizing");
5922   _bm.set_size(_bmWordSize >> _shifter);
5923 
5924   // bm.clear(); // can we rely on getting zero'd memory? verify below
5925   assert(isAllClear(),
5926          "Expected zero'd memory from ReservedSpace constructor");
5927   assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
5928          "consistency check");
5929   return true;
5930 }
5931 
5932 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
5933   HeapWord *next_addr, *end_addr, *last_addr;
5934   assert_locked();
5935   assert(covers(mr), "out-of-range error");
5936   // XXX assert that start and end are appropriately aligned
5937   for (next_addr = mr.start(), end_addr = mr.end();
5938        next_addr < end_addr; next_addr = last_addr) {
5939     MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
5940     last_addr = dirty_region.end();
5941     if (!dirty_region.is_empty()) {
5942       cl->do_MemRegion(dirty_region);
5943     } else {
5944       assert(last_addr == end_addr, "program logic");
5945       return;
5946     }
5947   }
5948 }
5949 
5950 void CMSBitMap::print_on_error(outputStream* st, const char* prefix) const {
5951   _bm.print_on_error(st, prefix);
5952 }
5953 
5954 #ifndef PRODUCT
5955 void CMSBitMap::assert_locked() const {
5956   CMSLockVerifier::assert_locked(lock());
5957 }
5958 
5959 bool CMSBitMap::covers(MemRegion mr) const {
5960   // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
5961   assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
5962          "size inconsistency");
5963   return (mr.start() >= _bmStartWord) &&
5964          (mr.end()   <= endWord());
5965 }
5966 
5967 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
5968     return (start >= _bmStartWord && (start + size) <= endWord());
5969 }
5970 
5971 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
5972   // verify that there are no 1 bits in the interval [left, right)
5973   FalseBitMapClosure falseBitMapClosure;
5974   iterate(&falseBitMapClosure, left, right);
5975 }
5976 
5977 void CMSBitMap::region_invariant(MemRegion mr)
5978 {
5979   assert_locked();
5980   // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
5981   assert(!mr.is_empty(), "unexpected empty region");
5982   assert(covers(mr), "mr should be covered by bit map");
5983   // convert address range into offset range
5984   size_t start_ofs = heapWordToOffset(mr.start());
5985   // Make sure that end() is appropriately aligned
5986   assert(mr.end() == (HeapWord*)round_to((intptr_t)mr.end(),
5987                         (1 << (_shifter+LogHeapWordSize))),
5988          "Misaligned mr.end()");
5989   size_t end_ofs   = heapWordToOffset(mr.end());
5990   assert(end_ofs > start_ofs, "Should mark at least one bit");
5991 }
5992 
5993 #endif
5994 
5995 bool CMSMarkStack::allocate(size_t size) {
5996   // allocate a stack of the requisite depth
5997   ReservedSpace rs(ReservedSpace::allocation_align_size_up(
5998                    size * sizeof(oop)));
5999   if (!rs.is_reserved()) {
6000     warning("CMSMarkStack allocation failure");
6001     return false;
6002   }
6003   if (!_virtual_space.initialize(rs, rs.size())) {
6004     warning("CMSMarkStack backing store failure");
6005     return false;
6006   }
6007   assert(_virtual_space.committed_size() == rs.size(),
6008          "didn't reserve backing store for all of CMS stack?");
6009   _base = (oop*)(_virtual_space.low());
6010   _index = 0;
6011   _capacity = size;
6012   NOT_PRODUCT(_max_depth = 0);
6013   return true;
6014 }
6015 
6016 // XXX FIX ME !!! In the MT case we come in here holding a
6017 // leaf lock. For printing we need to take a further lock
6018 // which has lower rank. We need to recalibrate the two
6019 // lock-ranks involved in order to be able to print the
6020 // messages below. (Or defer the printing to the caller.
6021 // For now we take the expedient path of just disabling the
6022 // messages for the problematic case.)
6023 void CMSMarkStack::expand() {
6024   assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted");
6025   if (_capacity == MarkStackSizeMax) {
6026     if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6027       // We print a warning message only once per CMS cycle.
6028       gclog_or_tty->print_cr(" (benign) Hit CMSMarkStack max size limit");
6029     }
6030     return;
6031   }
6032   // Double capacity if possible
6033   size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax);
6034   // Do not give up existing stack until we have managed to
6035   // get the double capacity that we desired.
6036   ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6037                    new_capacity * sizeof(oop)));
6038   if (rs.is_reserved()) {
6039     // Release the backing store associated with old stack
6040     _virtual_space.release();
6041     // Reinitialize virtual space for new stack
6042     if (!_virtual_space.initialize(rs, rs.size())) {
6043       fatal("Not enough swap for expanded marking stack");
6044     }
6045     _base = (oop*)(_virtual_space.low());
6046     _index = 0;
6047     _capacity = new_capacity;
6048   } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6049     // Failed to double capacity, continue;
6050     // we print a detail message only once per CMS cycle.
6051     gclog_or_tty->print(" (benign) Failed to expand marking stack from "SIZE_FORMAT"K to "
6052             SIZE_FORMAT"K",
6053             _capacity / K, new_capacity / K);
6054   }
6055 }
6056 
6057 
6058 // Closures
6059 // XXX: there seems to be a lot of code  duplication here;
6060 // should refactor and consolidate common code.
6061 
6062 // This closure is used to mark refs into the CMS generation in
6063 // the CMS bit map. Called at the first checkpoint. This closure
6064 // assumes that we do not need to re-mark dirty cards; if the CMS
6065 // generation on which this is used is not an oldest
6066 // generation then this will lose younger_gen cards!
6067 
6068 MarkRefsIntoClosure::MarkRefsIntoClosure(
6069   MemRegion span, CMSBitMap* bitMap):
6070     _span(span),
6071     _bitMap(bitMap)
6072 {
6073     assert(_ref_processor == NULL, "deliberately left NULL");
6074     assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6075 }
6076 
6077 void MarkRefsIntoClosure::do_oop(oop obj) {
6078   // if p points into _span, then mark corresponding bit in _markBitMap
6079   assert(obj->is_oop(), "expected an oop");
6080   HeapWord* addr = (HeapWord*)obj;
6081   if (_span.contains(addr)) {
6082     // this should be made more efficient
6083     _bitMap->mark(addr);
6084   }
6085 }
6086 
6087 void MarkRefsIntoClosure::do_oop(oop* p)       { MarkRefsIntoClosure::do_oop_work(p); }
6088 void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6089 
6090 Par_MarkRefsIntoClosure::Par_MarkRefsIntoClosure(
6091   MemRegion span, CMSBitMap* bitMap):
6092     _span(span),
6093     _bitMap(bitMap)
6094 {
6095     assert(_ref_processor == NULL, "deliberately left NULL");
6096     assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6097 }
6098 
6099 void Par_MarkRefsIntoClosure::do_oop(oop obj) {
6100   // if p points into _span, then mark corresponding bit in _markBitMap
6101   assert(obj->is_oop(), "expected an oop");
6102   HeapWord* addr = (HeapWord*)obj;
6103   if (_span.contains(addr)) {
6104     // this should be made more efficient
6105     _bitMap->par_mark(addr);
6106   }
6107 }
6108 
6109 void Par_MarkRefsIntoClosure::do_oop(oop* p)       { Par_MarkRefsIntoClosure::do_oop_work(p); }
6110 void Par_MarkRefsIntoClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoClosure::do_oop_work(p); }
6111 
6112 // A variant of the above, used for CMS marking verification.
6113 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
6114   MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm):
6115     _span(span),
6116     _verification_bm(verification_bm),
6117     _cms_bm(cms_bm)
6118 {
6119     assert(_ref_processor == NULL, "deliberately left NULL");
6120     assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
6121 }
6122 
6123 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
6124   // if p points into _span, then mark corresponding bit in _markBitMap
6125   assert(obj->is_oop(), "expected an oop");
6126   HeapWord* addr = (HeapWord*)obj;
6127   if (_span.contains(addr)) {
6128     _verification_bm->mark(addr);
6129     if (!_cms_bm->isMarked(addr)) {
6130       oop(addr)->print();
6131       gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
6132       fatal("... aborting");
6133     }
6134   }
6135 }
6136 
6137 void MarkRefsIntoVerifyClosure::do_oop(oop* p)       { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6138 void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6139 
6140 //////////////////////////////////////////////////
6141 // MarkRefsIntoAndScanClosure
6142 //////////////////////////////////////////////////
6143 
6144 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
6145                                                        ReferenceProcessor* rp,
6146                                                        CMSBitMap* bit_map,
6147                                                        CMSBitMap* mod_union_table,
6148                                                        CMSMarkStack*  mark_stack,
6149                                                        CMSCollector* collector,
6150                                                        bool should_yield,
6151                                                        bool concurrent_precleaning):
6152   _collector(collector),
6153   _span(span),
6154   _bit_map(bit_map),
6155   _mark_stack(mark_stack),
6156   _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table,
6157                       mark_stack, concurrent_precleaning),
6158   _yield(should_yield),
6159   _concurrent_precleaning(concurrent_precleaning),
6160   _freelistLock(NULL)
6161 {
6162   _ref_processor = rp;
6163   assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6164 }
6165 
6166 // This closure is used to mark refs into the CMS generation at the
6167 // second (final) checkpoint, and to scan and transitively follow
6168 // the unmarked oops. It is also used during the concurrent precleaning
6169 // phase while scanning objects on dirty cards in the CMS generation.
6170 // The marks are made in the marking bit map and the marking stack is
6171 // used for keeping the (newly) grey objects during the scan.
6172 // The parallel version (Par_...) appears further below.
6173 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6174   if (obj != NULL) {
6175     assert(obj->is_oop(), "expected an oop");
6176     HeapWord* addr = (HeapWord*)obj;
6177     assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6178     assert(_collector->overflow_list_is_empty(),
6179            "overflow list should be empty");
6180     if (_span.contains(addr) &&
6181         !_bit_map->isMarked(addr)) {
6182       // mark bit map (object is now grey)
6183       _bit_map->mark(addr);
6184       // push on marking stack (stack should be empty), and drain the
6185       // stack by applying this closure to the oops in the oops popped
6186       // from the stack (i.e. blacken the grey objects)
6187       bool res = _mark_stack->push(obj);
6188       assert(res, "Should have space to push on empty stack");
6189       do {
6190         oop new_oop = _mark_stack->pop();
6191         assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6192         assert(_bit_map->isMarked((HeapWord*)new_oop),
6193                "only grey objects on this stack");
6194         // iterate over the oops in this oop, marking and pushing
6195         // the ones in CMS heap (i.e. in _span).
6196         new_oop->oop_iterate(&_pushAndMarkClosure);
6197         // check if it's time to yield
6198         do_yield_check();
6199       } while (!_mark_stack->isEmpty() ||
6200                (!_concurrent_precleaning && take_from_overflow_list()));
6201         // if marking stack is empty, and we are not doing this
6202         // during precleaning, then check the overflow list
6203     }
6204     assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6205     assert(_collector->overflow_list_is_empty(),
6206            "overflow list was drained above");
6207     // We could restore evacuated mark words, if any, used for
6208     // overflow list links here because the overflow list is
6209     // provably empty here. That would reduce the maximum
6210     // size requirements for preserved_{oop,mark}_stack.
6211     // But we'll just postpone it until we are all done
6212     // so we can just stream through.
6213     if (!_concurrent_precleaning && CMSOverflowEarlyRestoration) {
6214       _collector->restore_preserved_marks_if_any();
6215       assert(_collector->no_preserved_marks(), "No preserved marks");
6216     }
6217     assert(!CMSOverflowEarlyRestoration || _collector->no_preserved_marks(),
6218            "All preserved marks should have been restored above");
6219   }
6220 }
6221 
6222 void MarkRefsIntoAndScanClosure::do_oop(oop* p)       { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6223 void MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6224 
6225 void MarkRefsIntoAndScanClosure::do_yield_work() {
6226   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6227          "CMS thread should hold CMS token");
6228   assert_lock_strong(_freelistLock);
6229   assert_lock_strong(_bit_map->lock());
6230   // relinquish the free_list_lock and bitMaplock()
6231   _bit_map->lock()->unlock();
6232   _freelistLock->unlock();
6233   ConcurrentMarkSweepThread::desynchronize(true);
6234   _collector->stopTimer();
6235   if (PrintCMSStatistics != 0) {
6236     _collector->incrementYields();
6237   }
6238 
6239   // See the comment in coordinator_yield()
6240   for (unsigned i = 0;
6241        i < CMSYieldSleepCount &&
6242        ConcurrentMarkSweepThread::should_yield() &&
6243        !CMSCollector::foregroundGCIsActive();
6244        ++i) {
6245     os::sleep(Thread::current(), 1, false);
6246   }
6247 
6248   ConcurrentMarkSweepThread::synchronize(true);
6249   _freelistLock->lock_without_safepoint_check();
6250   _bit_map->lock()->lock_without_safepoint_check();
6251   _collector->startTimer();
6252 }
6253 
6254 ///////////////////////////////////////////////////////////
6255 // Par_MarkRefsIntoAndScanClosure: a parallel version of
6256 //                                 MarkRefsIntoAndScanClosure
6257 ///////////////////////////////////////////////////////////
6258 Par_MarkRefsIntoAndScanClosure::Par_MarkRefsIntoAndScanClosure(
6259   CMSCollector* collector, MemRegion span, ReferenceProcessor* rp,
6260   CMSBitMap* bit_map, OopTaskQueue* work_queue):
6261   _span(span),
6262   _bit_map(bit_map),
6263   _work_queue(work_queue),
6264   _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
6265                        (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads))),
6266   _par_pushAndMarkClosure(collector, span, rp, bit_map, work_queue)
6267 {
6268   _ref_processor = rp;
6269   assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6270 }
6271 
6272 // This closure is used to mark refs into the CMS generation at the
6273 // second (final) checkpoint, and to scan and transitively follow
6274 // the unmarked oops. The marks are made in the marking bit map and
6275 // the work_queue is used for keeping the (newly) grey objects during
6276 // the scan phase whence they are also available for stealing by parallel
6277 // threads. Since the marking bit map is shared, updates are
6278 // synchronized (via CAS).
6279 void Par_MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6280   if (obj != NULL) {
6281     // Ignore mark word because this could be an already marked oop
6282     // that may be chained at the end of the overflow list.
6283     assert(obj->is_oop(true), "expected an oop");
6284     HeapWord* addr = (HeapWord*)obj;
6285     if (_span.contains(addr) &&
6286         !_bit_map->isMarked(addr)) {
6287       // mark bit map (object will become grey):
6288       // It is possible for several threads to be
6289       // trying to "claim" this object concurrently;
6290       // the unique thread that succeeds in marking the
6291       // object first will do the subsequent push on
6292       // to the work queue (or overflow list).
6293       if (_bit_map->par_mark(addr)) {
6294         // push on work_queue (which may not be empty), and trim the
6295         // queue to an appropriate length by applying this closure to
6296         // the oops in the oops popped from the stack (i.e. blacken the
6297         // grey objects)
6298         bool res = _work_queue->push(obj);
6299         assert(res, "Low water mark should be less than capacity?");
6300         trim_queue(_low_water_mark);
6301       } // Else, another thread claimed the object
6302     }
6303   }
6304 }
6305 
6306 void Par_MarkRefsIntoAndScanClosure::do_oop(oop* p)       { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6307 void Par_MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6308 
6309 // This closure is used to rescan the marked objects on the dirty cards
6310 // in the mod union table and the card table proper.
6311 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
6312   oop p, MemRegion mr) {
6313 
6314   size_t size = 0;
6315   HeapWord* addr = (HeapWord*)p;
6316   DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6317   assert(_span.contains(addr), "we are scanning the CMS generation");
6318   // check if it's time to yield
6319   if (do_yield_check()) {
6320     // We yielded for some foreground stop-world work,
6321     // and we have been asked to abort this ongoing preclean cycle.
6322     return 0;
6323   }
6324   if (_bitMap->isMarked(addr)) {
6325     // it's marked; is it potentially uninitialized?
6326     if (p->klass_or_null() != NULL) {
6327         // an initialized object; ignore mark word in verification below
6328         // since we are running concurrent with mutators
6329         assert(p->is_oop(true), "should be an oop");
6330         if (p->is_objArray()) {
6331           // objArrays are precisely marked; restrict scanning
6332           // to dirty cards only.
6333           size = CompactibleFreeListSpace::adjustObjectSize(
6334                    p->oop_iterate(_scanningClosure, mr));
6335         } else {
6336           // A non-array may have been imprecisely marked; we need
6337           // to scan object in its entirety.
6338           size = CompactibleFreeListSpace::adjustObjectSize(
6339                    p->oop_iterate(_scanningClosure));
6340         }
6341         #ifdef ASSERT
6342           size_t direct_size =
6343             CompactibleFreeListSpace::adjustObjectSize(p->size());
6344           assert(size == direct_size, "Inconsistency in size");
6345           assert(size >= 3, "Necessary for Printezis marks to work");
6346           if (!_bitMap->isMarked(addr+1)) {
6347             _bitMap->verifyNoOneBitsInRange(addr+2, addr+size);
6348           } else {
6349             _bitMap->verifyNoOneBitsInRange(addr+2, addr+size-1);
6350             assert(_bitMap->isMarked(addr+size-1),
6351                    "inconsistent Printezis mark");
6352           }
6353         #endif // ASSERT
6354     } else {
6355       // An uninitialized object.
6356       assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
6357       HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
6358       size = pointer_delta(nextOneAddr + 1, addr);
6359       assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6360              "alignment problem");
6361       // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
6362       // will dirty the card when the klass pointer is installed in the
6363       // object (signaling the completion of initialization).
6364     }
6365   } else {
6366     // Either a not yet marked object or an uninitialized object
6367     if (p->klass_or_null() == NULL) {
6368       // An uninitialized object, skip to the next card, since
6369       // we may not be able to read its P-bits yet.
6370       assert(size == 0, "Initial value");
6371     } else {
6372       // An object not (yet) reached by marking: we merely need to
6373       // compute its size so as to go look at the next block.
6374       assert(p->is_oop(true), "should be an oop");
6375       size = CompactibleFreeListSpace::adjustObjectSize(p->size());
6376     }
6377   }
6378   DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6379   return size;
6380 }
6381 
6382 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
6383   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6384          "CMS thread should hold CMS token");
6385   assert_lock_strong(_freelistLock);
6386   assert_lock_strong(_bitMap->lock());
6387   // relinquish the free_list_lock and bitMaplock()
6388   _bitMap->lock()->unlock();
6389   _freelistLock->unlock();
6390   ConcurrentMarkSweepThread::desynchronize(true);
6391   _collector->stopTimer();
6392   if (PrintCMSStatistics != 0) {
6393     _collector->incrementYields();
6394   }
6395 
6396   // See the comment in coordinator_yield()
6397   for (unsigned i = 0; i < CMSYieldSleepCount &&
6398                    ConcurrentMarkSweepThread::should_yield() &&
6399                    !CMSCollector::foregroundGCIsActive(); ++i) {
6400     os::sleep(Thread::current(), 1, false);
6401   }
6402 
6403   ConcurrentMarkSweepThread::synchronize(true);
6404   _freelistLock->lock_without_safepoint_check();
6405   _bitMap->lock()->lock_without_safepoint_check();
6406   _collector->startTimer();
6407 }
6408 
6409 
6410 //////////////////////////////////////////////////////////////////
6411 // SurvivorSpacePrecleanClosure
6412 //////////////////////////////////////////////////////////////////
6413 // This (single-threaded) closure is used to preclean the oops in
6414 // the survivor spaces.
6415 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
6416 
6417   HeapWord* addr = (HeapWord*)p;
6418   DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6419   assert(!_span.contains(addr), "we are scanning the survivor spaces");
6420   assert(p->klass_or_null() != NULL, "object should be initialized");
6421   // an initialized object; ignore mark word in verification below
6422   // since we are running concurrent with mutators
6423   assert(p->is_oop(true), "should be an oop");
6424   // Note that we do not yield while we iterate over
6425   // the interior oops of p, pushing the relevant ones
6426   // on our marking stack.
6427   size_t size = p->oop_iterate(_scanning_closure);
6428   do_yield_check();
6429   // Observe that below, we do not abandon the preclean
6430   // phase as soon as we should; rather we empty the
6431   // marking stack before returning. This is to satisfy
6432   // some existing assertions. In general, it may be a
6433   // good idea to abort immediately and complete the marking
6434   // from the grey objects at a later time.
6435   while (!_mark_stack->isEmpty()) {
6436     oop new_oop = _mark_stack->pop();
6437     assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6438     assert(_bit_map->isMarked((HeapWord*)new_oop),
6439            "only grey objects on this stack");
6440     // iterate over the oops in this oop, marking and pushing
6441     // the ones in CMS heap (i.e. in _span).
6442     new_oop->oop_iterate(_scanning_closure);
6443     // check if it's time to yield
6444     do_yield_check();
6445   }
6446   unsigned int after_count =
6447     GenCollectedHeap::heap()->total_collections();
6448   bool abort = (_before_count != after_count) ||
6449                _collector->should_abort_preclean();
6450   return abort ? 0 : size;
6451 }
6452 
6453 void SurvivorSpacePrecleanClosure::do_yield_work() {
6454   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6455          "CMS thread should hold CMS token");
6456   assert_lock_strong(_bit_map->lock());
6457   // Relinquish the bit map lock
6458   _bit_map->lock()->unlock();
6459   ConcurrentMarkSweepThread::desynchronize(true);
6460   _collector->stopTimer();
6461   if (PrintCMSStatistics != 0) {
6462     _collector->incrementYields();
6463   }
6464 
6465   // See the comment in coordinator_yield()
6466   for (unsigned i = 0; i < CMSYieldSleepCount &&
6467                        ConcurrentMarkSweepThread::should_yield() &&
6468                        !CMSCollector::foregroundGCIsActive(); ++i) {
6469     os::sleep(Thread::current(), 1, false);
6470   }
6471 
6472   ConcurrentMarkSweepThread::synchronize(true);
6473   _bit_map->lock()->lock_without_safepoint_check();
6474   _collector->startTimer();
6475 }
6476 
6477 // This closure is used to rescan the marked objects on the dirty cards
6478 // in the mod union table and the card table proper. In the parallel
6479 // case, although the bitMap is shared, we do a single read so the
6480 // isMarked() query is "safe".
6481 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
6482   // Ignore mark word because we are running concurrent with mutators
6483   assert(p->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(p)));
6484   HeapWord* addr = (HeapWord*)p;
6485   assert(_span.contains(addr), "we are scanning the CMS generation");
6486   bool is_obj_array = false;
6487   #ifdef ASSERT
6488     if (!_parallel) {
6489       assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6490       assert(_collector->overflow_list_is_empty(),
6491              "overflow list should be empty");
6492 
6493     }
6494   #endif // ASSERT
6495   if (_bit_map->isMarked(addr)) {
6496     // Obj arrays are precisely marked, non-arrays are not;
6497     // so we scan objArrays precisely and non-arrays in their
6498     // entirety.
6499     if (p->is_objArray()) {
6500       is_obj_array = true;
6501       if (_parallel) {
6502         p->oop_iterate(_par_scan_closure, mr);
6503       } else {
6504         p->oop_iterate(_scan_closure, mr);
6505       }
6506     } else {
6507       if (_parallel) {
6508         p->oop_iterate(_par_scan_closure);
6509       } else {
6510         p->oop_iterate(_scan_closure);
6511       }
6512     }
6513   }
6514   #ifdef ASSERT
6515     if (!_parallel) {
6516       assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6517       assert(_collector->overflow_list_is_empty(),
6518              "overflow list should be empty");
6519 
6520     }
6521   #endif // ASSERT
6522   return is_obj_array;
6523 }
6524 
6525 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
6526                         MemRegion span,
6527                         CMSBitMap* bitMap, CMSMarkStack*  markStack,
6528                         bool should_yield, bool verifying):
6529   _collector(collector),
6530   _span(span),
6531   _bitMap(bitMap),
6532   _mut(&collector->_modUnionTable),
6533   _markStack(markStack),
6534   _yield(should_yield),
6535   _skipBits(0)
6536 {
6537   assert(_markStack->isEmpty(), "stack should be empty");
6538   _finger = _bitMap->startWord();
6539   _threshold = _finger;
6540   assert(_collector->_restart_addr == NULL, "Sanity check");
6541   assert(_span.contains(_finger), "Out of bounds _finger?");
6542   DEBUG_ONLY(_verifying = verifying;)
6543 }
6544 
6545 void MarkFromRootsClosure::reset(HeapWord* addr) {
6546   assert(_markStack->isEmpty(), "would cause duplicates on stack");
6547   assert(_span.contains(addr), "Out of bounds _finger?");
6548   _finger = addr;
6549   _threshold = (HeapWord*)round_to(
6550                  (intptr_t)_finger, CardTableModRefBS::card_size);
6551 }
6552 
6553 // Should revisit to see if this should be restructured for
6554 // greater efficiency.
6555 bool MarkFromRootsClosure::do_bit(size_t offset) {
6556   if (_skipBits > 0) {
6557     _skipBits--;
6558     return true;
6559   }
6560   // convert offset into a HeapWord*
6561   HeapWord* addr = _bitMap->startWord() + offset;
6562   assert(_bitMap->endWord() && addr < _bitMap->endWord(),
6563          "address out of range");
6564   assert(_bitMap->isMarked(addr), "tautology");
6565   if (_bitMap->isMarked(addr+1)) {
6566     // this is an allocated but not yet initialized object
6567     assert(_skipBits == 0, "tautology");
6568     _skipBits = 2;  // skip next two marked bits ("Printezis-marks")
6569     oop p = oop(addr);
6570     if (p->klass_or_null() == NULL) {
6571       DEBUG_ONLY(if (!_verifying) {)
6572         // We re-dirty the cards on which this object lies and increase
6573         // the _threshold so that we'll come back to scan this object
6574         // during the preclean or remark phase. (CMSCleanOnEnter)
6575         if (CMSCleanOnEnter) {
6576           size_t sz = _collector->block_size_using_printezis_bits(addr);
6577           HeapWord* end_card_addr   = (HeapWord*)round_to(
6578                                          (intptr_t)(addr+sz), CardTableModRefBS::card_size);
6579           MemRegion redirty_range = MemRegion(addr, end_card_addr);
6580           assert(!redirty_range.is_empty(), "Arithmetical tautology");
6581           // Bump _threshold to end_card_addr; note that
6582           // _threshold cannot possibly exceed end_card_addr, anyhow.
6583           // This prevents future clearing of the card as the scan proceeds
6584           // to the right.
6585           assert(_threshold <= end_card_addr,
6586                  "Because we are just scanning into this object");
6587           if (_threshold < end_card_addr) {
6588             _threshold = end_card_addr;
6589           }
6590           if (p->klass_or_null() != NULL) {
6591             // Redirty the range of cards...
6592             _mut->mark_range(redirty_range);
6593           } // ...else the setting of klass will dirty the card anyway.
6594         }
6595       DEBUG_ONLY(})
6596       return true;
6597     }
6598   }
6599   scanOopsInOop(addr);
6600   return true;
6601 }
6602 
6603 // We take a break if we've been at this for a while,
6604 // so as to avoid monopolizing the locks involved.
6605 void MarkFromRootsClosure::do_yield_work() {
6606   // First give up the locks, then yield, then re-lock
6607   // We should probably use a constructor/destructor idiom to
6608   // do this unlock/lock or modify the MutexUnlocker class to
6609   // serve our purpose. XXX
6610   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6611          "CMS thread should hold CMS token");
6612   assert_lock_strong(_bitMap->lock());
6613   _bitMap->lock()->unlock();
6614   ConcurrentMarkSweepThread::desynchronize(true);
6615   _collector->stopTimer();
6616   if (PrintCMSStatistics != 0) {
6617     _collector->incrementYields();
6618   }
6619 
6620   // See the comment in coordinator_yield()
6621   for (unsigned i = 0; i < CMSYieldSleepCount &&
6622                        ConcurrentMarkSweepThread::should_yield() &&
6623                        !CMSCollector::foregroundGCIsActive(); ++i) {
6624     os::sleep(Thread::current(), 1, false);
6625   }
6626 
6627   ConcurrentMarkSweepThread::synchronize(true);
6628   _bitMap->lock()->lock_without_safepoint_check();
6629   _collector->startTimer();
6630 }
6631 
6632 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
6633   assert(_bitMap->isMarked(ptr), "expected bit to be set");
6634   assert(_markStack->isEmpty(),
6635          "should drain stack to limit stack usage");
6636   // convert ptr to an oop preparatory to scanning
6637   oop obj = oop(ptr);
6638   // Ignore mark word in verification below, since we
6639   // may be running concurrent with mutators.
6640   assert(obj->is_oop(true), "should be an oop");
6641   assert(_finger <= ptr, "_finger runneth ahead");
6642   // advance the finger to right end of this object
6643   _finger = ptr + obj->size();
6644   assert(_finger > ptr, "we just incremented it above");
6645   // On large heaps, it may take us some time to get through
6646   // the marking phase. During
6647   // this time it's possible that a lot of mutations have
6648   // accumulated in the card table and the mod union table --
6649   // these mutation records are redundant until we have
6650   // actually traced into the corresponding card.
6651   // Here, we check whether advancing the finger would make
6652   // us cross into a new card, and if so clear corresponding
6653   // cards in the MUT (preclean them in the card-table in the
6654   // future).
6655 
6656   DEBUG_ONLY(if (!_verifying) {)
6657     // The clean-on-enter optimization is disabled by default,
6658     // until we fix 6178663.
6659     if (CMSCleanOnEnter && (_finger > _threshold)) {
6660       // [_threshold, _finger) represents the interval
6661       // of cards to be cleared  in MUT (or precleaned in card table).
6662       // The set of cards to be cleared is all those that overlap
6663       // with the interval [_threshold, _finger); note that
6664       // _threshold is always kept card-aligned but _finger isn't
6665       // always card-aligned.
6666       HeapWord* old_threshold = _threshold;
6667       assert(old_threshold == (HeapWord*)round_to(
6668               (intptr_t)old_threshold, CardTableModRefBS::card_size),
6669              "_threshold should always be card-aligned");
6670       _threshold = (HeapWord*)round_to(
6671                      (intptr_t)_finger, CardTableModRefBS::card_size);
6672       MemRegion mr(old_threshold, _threshold);
6673       assert(!mr.is_empty(), "Control point invariant");
6674       assert(_span.contains(mr), "Should clear within span");
6675       _mut->clear_range(mr);
6676     }
6677   DEBUG_ONLY(})
6678   // Note: the finger doesn't advance while we drain
6679   // the stack below.
6680   PushOrMarkClosure pushOrMarkClosure(_collector,
6681                                       _span, _bitMap, _markStack,
6682                                       _finger, this);
6683   bool res = _markStack->push(obj);
6684   assert(res, "Empty non-zero size stack should have space for single push");
6685   while (!_markStack->isEmpty()) {
6686     oop new_oop = _markStack->pop();
6687     // Skip verifying header mark word below because we are
6688     // running concurrent with mutators.
6689     assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
6690     // now scan this oop's oops
6691     new_oop->oop_iterate(&pushOrMarkClosure);
6692     do_yield_check();
6693   }
6694   assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
6695 }
6696 
6697 Par_MarkFromRootsClosure::Par_MarkFromRootsClosure(CMSConcMarkingTask* task,
6698                        CMSCollector* collector, MemRegion span,
6699                        CMSBitMap* bit_map,
6700                        OopTaskQueue* work_queue,
6701                        CMSMarkStack*  overflow_stack):
6702   _collector(collector),
6703   _whole_span(collector->_span),
6704   _span(span),
6705   _bit_map(bit_map),
6706   _mut(&collector->_modUnionTable),
6707   _work_queue(work_queue),
6708   _overflow_stack(overflow_stack),
6709   _skip_bits(0),
6710   _task(task)
6711 {
6712   assert(_work_queue->size() == 0, "work_queue should be empty");
6713   _finger = span.start();
6714   _threshold = _finger;     // XXX Defer clear-on-enter optimization for now
6715   assert(_span.contains(_finger), "Out of bounds _finger?");
6716 }
6717 
6718 // Should revisit to see if this should be restructured for
6719 // greater efficiency.
6720 bool Par_MarkFromRootsClosure::do_bit(size_t offset) {
6721   if (_skip_bits > 0) {
6722     _skip_bits--;
6723     return true;
6724   }
6725   // convert offset into a HeapWord*
6726   HeapWord* addr = _bit_map->startWord() + offset;
6727   assert(_bit_map->endWord() && addr < _bit_map->endWord(),
6728          "address out of range");
6729   assert(_bit_map->isMarked(addr), "tautology");
6730   if (_bit_map->isMarked(addr+1)) {
6731     // this is an allocated object that might not yet be initialized
6732     assert(_skip_bits == 0, "tautology");
6733     _skip_bits = 2;  // skip next two marked bits ("Printezis-marks")
6734     oop p = oop(addr);
6735     if (p->klass_or_null() == NULL) {
6736       // in the case of Clean-on-Enter optimization, redirty card
6737       // and avoid clearing card by increasing  the threshold.
6738       return true;
6739     }
6740   }
6741   scan_oops_in_oop(addr);
6742   return true;
6743 }
6744 
6745 void Par_MarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
6746   assert(_bit_map->isMarked(ptr), "expected bit to be set");
6747   // Should we assert that our work queue is empty or
6748   // below some drain limit?
6749   assert(_work_queue->size() == 0,
6750          "should drain stack to limit stack usage");
6751   // convert ptr to an oop preparatory to scanning
6752   oop obj = oop(ptr);
6753   // Ignore mark word in verification below, since we
6754   // may be running concurrent with mutators.
6755   assert(obj->is_oop(true), "should be an oop");
6756   assert(_finger <= ptr, "_finger runneth ahead");
6757   // advance the finger to right end of this object
6758   _finger = ptr + obj->size();
6759   assert(_finger > ptr, "we just incremented it above");
6760   // On large heaps, it may take us some time to get through
6761   // the marking phase. During
6762   // this time it's possible that a lot of mutations have
6763   // accumulated in the card table and the mod union table --
6764   // these mutation records are redundant until we have
6765   // actually traced into the corresponding card.
6766   // Here, we check whether advancing the finger would make
6767   // us cross into a new card, and if so clear corresponding
6768   // cards in the MUT (preclean them in the card-table in the
6769   // future).
6770 
6771   // The clean-on-enter optimization is disabled by default,
6772   // until we fix 6178663.
6773   if (CMSCleanOnEnter && (_finger > _threshold)) {
6774     // [_threshold, _finger) represents the interval
6775     // of cards to be cleared  in MUT (or precleaned in card table).
6776     // The set of cards to be cleared is all those that overlap
6777     // with the interval [_threshold, _finger); note that
6778     // _threshold is always kept card-aligned but _finger isn't
6779     // always card-aligned.
6780     HeapWord* old_threshold = _threshold;
6781     assert(old_threshold == (HeapWord*)round_to(
6782             (intptr_t)old_threshold, CardTableModRefBS::card_size),
6783            "_threshold should always be card-aligned");
6784     _threshold = (HeapWord*)round_to(
6785                    (intptr_t)_finger, CardTableModRefBS::card_size);
6786     MemRegion mr(old_threshold, _threshold);
6787     assert(!mr.is_empty(), "Control point invariant");
6788     assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
6789     _mut->clear_range(mr);
6790   }
6791 
6792   // Note: the local finger doesn't advance while we drain
6793   // the stack below, but the global finger sure can and will.
6794   HeapWord** gfa = _task->global_finger_addr();
6795   Par_PushOrMarkClosure pushOrMarkClosure(_collector,
6796                                       _span, _bit_map,
6797                                       _work_queue,
6798                                       _overflow_stack,
6799                                       _finger,
6800                                       gfa, this);
6801   bool res = _work_queue->push(obj);   // overflow could occur here
6802   assert(res, "Will hold once we use workqueues");
6803   while (true) {
6804     oop new_oop;
6805     if (!_work_queue->pop_local(new_oop)) {
6806       // We emptied our work_queue; check if there's stuff that can
6807       // be gotten from the overflow stack.
6808       if (CMSConcMarkingTask::get_work_from_overflow_stack(
6809             _overflow_stack, _work_queue)) {
6810         do_yield_check();
6811         continue;
6812       } else {  // done
6813         break;
6814       }
6815     }
6816     // Skip verifying header mark word below because we are
6817     // running concurrent with mutators.
6818     assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
6819     // now scan this oop's oops
6820     new_oop->oop_iterate(&pushOrMarkClosure);
6821     do_yield_check();
6822   }
6823   assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
6824 }
6825 
6826 // Yield in response to a request from VM Thread or
6827 // from mutators.
6828 void Par_MarkFromRootsClosure::do_yield_work() {
6829   assert(_task != NULL, "sanity");
6830   _task->yield();
6831 }
6832 
6833 // A variant of the above used for verifying CMS marking work.
6834 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
6835                         MemRegion span,
6836                         CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6837                         CMSMarkStack*  mark_stack):
6838   _collector(collector),
6839   _span(span),
6840   _verification_bm(verification_bm),
6841   _cms_bm(cms_bm),
6842   _mark_stack(mark_stack),
6843   _pam_verify_closure(collector, span, verification_bm, cms_bm,
6844                       mark_stack)
6845 {
6846   assert(_mark_stack->isEmpty(), "stack should be empty");
6847   _finger = _verification_bm->startWord();
6848   assert(_collector->_restart_addr == NULL, "Sanity check");
6849   assert(_span.contains(_finger), "Out of bounds _finger?");
6850 }
6851 
6852 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
6853   assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
6854   assert(_span.contains(addr), "Out of bounds _finger?");
6855   _finger = addr;
6856 }
6857 
6858 // Should revisit to see if this should be restructured for
6859 // greater efficiency.
6860 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
6861   // convert offset into a HeapWord*
6862   HeapWord* addr = _verification_bm->startWord() + offset;
6863   assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
6864          "address out of range");
6865   assert(_verification_bm->isMarked(addr), "tautology");
6866   assert(_cms_bm->isMarked(addr), "tautology");
6867 
6868   assert(_mark_stack->isEmpty(),
6869          "should drain stack to limit stack usage");
6870   // convert addr to an oop preparatory to scanning
6871   oop obj = oop(addr);
6872   assert(obj->is_oop(), "should be an oop");
6873   assert(_finger <= addr, "_finger runneth ahead");
6874   // advance the finger to right end of this object
6875   _finger = addr + obj->size();
6876   assert(_finger > addr, "we just incremented it above");
6877   // Note: the finger doesn't advance while we drain
6878   // the stack below.
6879   bool res = _mark_stack->push(obj);
6880   assert(res, "Empty non-zero size stack should have space for single push");
6881   while (!_mark_stack->isEmpty()) {
6882     oop new_oop = _mark_stack->pop();
6883     assert(new_oop->is_oop(), "Oops! expected to pop an oop");
6884     // now scan this oop's oops
6885     new_oop->oop_iterate(&_pam_verify_closure);
6886   }
6887   assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
6888   return true;
6889 }
6890 
6891 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
6892   CMSCollector* collector, MemRegion span,
6893   CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6894   CMSMarkStack*  mark_stack):
6895   MetadataAwareOopClosure(collector->ref_processor()),
6896   _collector(collector),
6897   _span(span),
6898   _verification_bm(verification_bm),
6899   _cms_bm(cms_bm),
6900   _mark_stack(mark_stack)
6901 { }
6902 
6903 void PushAndMarkVerifyClosure::do_oop(oop* p)       { PushAndMarkVerifyClosure::do_oop_work(p); }
6904 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
6905 
6906 // Upon stack overflow, we discard (part of) the stack,
6907 // remembering the least address amongst those discarded
6908 // in CMSCollector's _restart_address.
6909 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
6910   // Remember the least grey address discarded
6911   HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
6912   _collector->lower_restart_addr(ra);
6913   _mark_stack->reset();  // discard stack contents
6914   _mark_stack->expand(); // expand the stack if possible
6915 }
6916 
6917 void PushAndMarkVerifyClosure::do_oop(oop obj) {
6918   assert(obj->is_oop_or_null(), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
6919   HeapWord* addr = (HeapWord*)obj;
6920   if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
6921     // Oop lies in _span and isn't yet grey or black
6922     _verification_bm->mark(addr);            // now grey
6923     if (!_cms_bm->isMarked(addr)) {
6924       oop(addr)->print();
6925       gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)",
6926                              p2i(addr));
6927       fatal("... aborting");
6928     }
6929 
6930     if (!_mark_stack->push(obj)) { // stack overflow
6931       if (PrintCMSStatistics != 0) {
6932         gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
6933                                SIZE_FORMAT, _mark_stack->capacity());
6934       }
6935       assert(_mark_stack->isFull(), "Else push should have succeeded");
6936       handle_stack_overflow(addr);
6937     }
6938     // anything including and to the right of _finger
6939     // will be scanned as we iterate over the remainder of the
6940     // bit map
6941   }
6942 }
6943 
6944 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
6945                      MemRegion span,
6946                      CMSBitMap* bitMap, CMSMarkStack*  markStack,
6947                      HeapWord* finger, MarkFromRootsClosure* parent) :
6948   MetadataAwareOopClosure(collector->ref_processor()),
6949   _collector(collector),
6950   _span(span),
6951   _bitMap(bitMap),
6952   _markStack(markStack),
6953   _finger(finger),
6954   _parent(parent)
6955 { }
6956 
6957 Par_PushOrMarkClosure::Par_PushOrMarkClosure(CMSCollector* collector,
6958                      MemRegion span,
6959                      CMSBitMap* bit_map,
6960                      OopTaskQueue* work_queue,
6961                      CMSMarkStack*  overflow_stack,
6962                      HeapWord* finger,
6963                      HeapWord** global_finger_addr,
6964                      Par_MarkFromRootsClosure* parent) :
6965   MetadataAwareOopClosure(collector->ref_processor()),
6966   _collector(collector),
6967   _whole_span(collector->_span),
6968   _span(span),
6969   _bit_map(bit_map),
6970   _work_queue(work_queue),
6971   _overflow_stack(overflow_stack),
6972   _finger(finger),
6973   _global_finger_addr(global_finger_addr),
6974   _parent(parent)
6975 { }
6976 
6977 // Assumes thread-safe access by callers, who are
6978 // responsible for mutual exclusion.
6979 void CMSCollector::lower_restart_addr(HeapWord* low) {
6980   assert(_span.contains(low), "Out of bounds addr");
6981   if (_restart_addr == NULL) {
6982     _restart_addr = low;
6983   } else {
6984     _restart_addr = MIN2(_restart_addr, low);
6985   }
6986 }
6987 
6988 // Upon stack overflow, we discard (part of) the stack,
6989 // remembering the least address amongst those discarded
6990 // in CMSCollector's _restart_address.
6991 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
6992   // Remember the least grey address discarded
6993   HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
6994   _collector->lower_restart_addr(ra);
6995   _markStack->reset();  // discard stack contents
6996   _markStack->expand(); // expand the stack if possible
6997 }
6998 
6999 // Upon stack overflow, we discard (part of) the stack,
7000 // remembering the least address amongst those discarded
7001 // in CMSCollector's _restart_address.
7002 void Par_PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7003   // We need to do this under a mutex to prevent other
7004   // workers from interfering with the work done below.
7005   MutexLockerEx ml(_overflow_stack->par_lock(),
7006                    Mutex::_no_safepoint_check_flag);
7007   // Remember the least grey address discarded
7008   HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
7009   _collector->lower_restart_addr(ra);
7010   _overflow_stack->reset();  // discard stack contents
7011   _overflow_stack->expand(); // expand the stack if possible
7012 }
7013 
7014 void PushOrMarkClosure::do_oop(oop obj) {
7015   // Ignore mark word because we are running concurrent with mutators.
7016   assert(obj->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7017   HeapWord* addr = (HeapWord*)obj;
7018   if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
7019     // Oop lies in _span and isn't yet grey or black
7020     _bitMap->mark(addr);            // now grey
7021     if (addr < _finger) {
7022       // the bit map iteration has already either passed, or
7023       // sampled, this bit in the bit map; we'll need to
7024       // use the marking stack to scan this oop's oops.
7025       bool simulate_overflow = false;
7026       NOT_PRODUCT(
7027         if (CMSMarkStackOverflowALot &&
7028             _collector->simulate_overflow()) {
7029           // simulate a stack overflow
7030           simulate_overflow = true;
7031         }
7032       )
7033       if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
7034         if (PrintCMSStatistics != 0) {
7035           gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7036                                  SIZE_FORMAT, _markStack->capacity());
7037         }
7038         assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
7039         handle_stack_overflow(addr);
7040       }
7041     }
7042     // anything including and to the right of _finger
7043     // will be scanned as we iterate over the remainder of the
7044     // bit map
7045     do_yield_check();
7046   }
7047 }
7048 
7049 void PushOrMarkClosure::do_oop(oop* p)       { PushOrMarkClosure::do_oop_work(p); }
7050 void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); }
7051 
7052 void Par_PushOrMarkClosure::do_oop(oop obj) {
7053   // Ignore mark word because we are running concurrent with mutators.
7054   assert(obj->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7055   HeapWord* addr = (HeapWord*)obj;
7056   if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
7057     // Oop lies in _span and isn't yet grey or black
7058     // We read the global_finger (volatile read) strictly after marking oop
7059     bool res = _bit_map->par_mark(addr);    // now grey
7060     volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
7061     // Should we push this marked oop on our stack?
7062     // -- if someone else marked it, nothing to do
7063     // -- if target oop is above global finger nothing to do
7064     // -- if target oop is in chunk and above local finger
7065     //      then nothing to do
7066     // -- else push on work queue
7067     if (   !res       // someone else marked it, they will deal with it
7068         || (addr >= *gfa)  // will be scanned in a later task
7069         || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
7070       return;
7071     }
7072     // the bit map iteration has already either passed, or
7073     // sampled, this bit in the bit map; we'll need to
7074     // use the marking stack to scan this oop's oops.
7075     bool simulate_overflow = false;
7076     NOT_PRODUCT(
7077       if (CMSMarkStackOverflowALot &&
7078           _collector->simulate_overflow()) {
7079         // simulate a stack overflow
7080         simulate_overflow = true;
7081       }
7082     )
7083     if (simulate_overflow ||
7084         !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
7085       // stack overflow
7086       if (PrintCMSStatistics != 0) {
7087         gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7088                                SIZE_FORMAT, _overflow_stack->capacity());
7089       }
7090       // We cannot assert that the overflow stack is full because
7091       // it may have been emptied since.
7092       assert(simulate_overflow ||
7093              _work_queue->size() == _work_queue->max_elems(),
7094             "Else push should have succeeded");
7095       handle_stack_overflow(addr);
7096     }
7097     do_yield_check();
7098   }
7099 }
7100 
7101 void Par_PushOrMarkClosure::do_oop(oop* p)       { Par_PushOrMarkClosure::do_oop_work(p); }
7102 void Par_PushOrMarkClosure::do_oop(narrowOop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7103 
7104 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
7105                                        MemRegion span,
7106                                        ReferenceProcessor* rp,
7107                                        CMSBitMap* bit_map,
7108                                        CMSBitMap* mod_union_table,
7109                                        CMSMarkStack*  mark_stack,
7110                                        bool           concurrent_precleaning):
7111   MetadataAwareOopClosure(rp),
7112   _collector(collector),
7113   _span(span),
7114   _bit_map(bit_map),
7115   _mod_union_table(mod_union_table),
7116   _mark_stack(mark_stack),
7117   _concurrent_precleaning(concurrent_precleaning)
7118 {
7119   assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7120 }
7121 
7122 // Grey object rescan during pre-cleaning and second checkpoint phases --
7123 // the non-parallel version (the parallel version appears further below.)
7124 void PushAndMarkClosure::do_oop(oop obj) {
7125   // Ignore mark word verification. If during concurrent precleaning,
7126   // the object monitor may be locked. If during the checkpoint
7127   // phases, the object may already have been reached by a  different
7128   // path and may be at the end of the global overflow list (so
7129   // the mark word may be NULL).
7130   assert(obj->is_oop_or_null(true /* ignore mark word */),
7131          err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7132   HeapWord* addr = (HeapWord*)obj;
7133   // Check if oop points into the CMS generation
7134   // and is not marked
7135   if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7136     // a white object ...
7137     _bit_map->mark(addr);         // ... now grey
7138     // push on the marking stack (grey set)
7139     bool simulate_overflow = false;
7140     NOT_PRODUCT(
7141       if (CMSMarkStackOverflowALot &&
7142           _collector->simulate_overflow()) {
7143         // simulate a stack overflow
7144         simulate_overflow = true;
7145       }
7146     )
7147     if (simulate_overflow || !_mark_stack->push(obj)) {
7148       if (_concurrent_precleaning) {
7149          // During precleaning we can just dirty the appropriate card(s)
7150          // in the mod union table, thus ensuring that the object remains
7151          // in the grey set  and continue. In the case of object arrays
7152          // we need to dirty all of the cards that the object spans,
7153          // since the rescan of object arrays will be limited to the
7154          // dirty cards.
7155          // Note that no one can be interfering with us in this action
7156          // of dirtying the mod union table, so no locking or atomics
7157          // are required.
7158          if (obj->is_objArray()) {
7159            size_t sz = obj->size();
7160            HeapWord* end_card_addr = (HeapWord*)round_to(
7161                                         (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7162            MemRegion redirty_range = MemRegion(addr, end_card_addr);
7163            assert(!redirty_range.is_empty(), "Arithmetical tautology");
7164            _mod_union_table->mark_range(redirty_range);
7165          } else {
7166            _mod_union_table->mark(addr);
7167          }
7168          _collector->_ser_pmc_preclean_ovflw++;
7169       } else {
7170          // During the remark phase, we need to remember this oop
7171          // in the overflow list.
7172          _collector->push_on_overflow_list(obj);
7173          _collector->_ser_pmc_remark_ovflw++;
7174       }
7175     }
7176   }
7177 }
7178 
7179 Par_PushAndMarkClosure::Par_PushAndMarkClosure(CMSCollector* collector,
7180                                                MemRegion span,
7181                                                ReferenceProcessor* rp,
7182                                                CMSBitMap* bit_map,
7183                                                OopTaskQueue* work_queue):
7184   MetadataAwareOopClosure(rp),
7185   _collector(collector),
7186   _span(span),
7187   _bit_map(bit_map),
7188   _work_queue(work_queue)
7189 {
7190   assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7191 }
7192 
7193 void PushAndMarkClosure::do_oop(oop* p)       { PushAndMarkClosure::do_oop_work(p); }
7194 void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); }
7195 
7196 // Grey object rescan during second checkpoint phase --
7197 // the parallel version.
7198 void Par_PushAndMarkClosure::do_oop(oop obj) {
7199   // In the assert below, we ignore the mark word because
7200   // this oop may point to an already visited object that is
7201   // on the overflow stack (in which case the mark word has
7202   // been hijacked for chaining into the overflow stack --
7203   // if this is the last object in the overflow stack then
7204   // its mark word will be NULL). Because this object may
7205   // have been subsequently popped off the global overflow
7206   // stack, and the mark word possibly restored to the prototypical
7207   // value, by the time we get to examined this failing assert in
7208   // the debugger, is_oop_or_null(false) may subsequently start
7209   // to hold.
7210   assert(obj->is_oop_or_null(true),
7211          err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7212   HeapWord* addr = (HeapWord*)obj;
7213   // Check if oop points into the CMS generation
7214   // and is not marked
7215   if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7216     // a white object ...
7217     // If we manage to "claim" the object, by being the
7218     // first thread to mark it, then we push it on our
7219     // marking stack
7220     if (_bit_map->par_mark(addr)) {     // ... now grey
7221       // push on work queue (grey set)
7222       bool simulate_overflow = false;
7223       NOT_PRODUCT(
7224         if (CMSMarkStackOverflowALot &&
7225             _collector->par_simulate_overflow()) {
7226           // simulate a stack overflow
7227           simulate_overflow = true;
7228         }
7229       )
7230       if (simulate_overflow || !_work_queue->push(obj)) {
7231         _collector->par_push_on_overflow_list(obj);
7232         _collector->_par_pmc_remark_ovflw++; //  imprecise OK: no need to CAS
7233       }
7234     } // Else, some other thread got there first
7235   }
7236 }
7237 
7238 void Par_PushAndMarkClosure::do_oop(oop* p)       { Par_PushAndMarkClosure::do_oop_work(p); }
7239 void Par_PushAndMarkClosure::do_oop(narrowOop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7240 
7241 void CMSPrecleanRefsYieldClosure::do_yield_work() {
7242   Mutex* bml = _collector->bitMapLock();
7243   assert_lock_strong(bml);
7244   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7245          "CMS thread should hold CMS token");
7246 
7247   bml->unlock();
7248   ConcurrentMarkSweepThread::desynchronize(true);
7249 
7250   _collector->stopTimer();
7251   if (PrintCMSStatistics != 0) {
7252     _collector->incrementYields();
7253   }
7254 
7255   // See the comment in coordinator_yield()
7256   for (unsigned i = 0; i < CMSYieldSleepCount &&
7257                        ConcurrentMarkSweepThread::should_yield() &&
7258                        !CMSCollector::foregroundGCIsActive(); ++i) {
7259     os::sleep(Thread::current(), 1, false);
7260   }
7261 
7262   ConcurrentMarkSweepThread::synchronize(true);
7263   bml->lock();
7264 
7265   _collector->startTimer();
7266 }
7267 
7268 bool CMSPrecleanRefsYieldClosure::should_return() {
7269   if (ConcurrentMarkSweepThread::should_yield()) {
7270     do_yield_work();
7271   }
7272   return _collector->foregroundGCIsActive();
7273 }
7274 
7275 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
7276   assert(((size_t)mr.start())%CardTableModRefBS::card_size_in_words == 0,
7277          "mr should be aligned to start at a card boundary");
7278   // We'd like to assert:
7279   // assert(mr.word_size()%CardTableModRefBS::card_size_in_words == 0,
7280   //        "mr should be a range of cards");
7281   // However, that would be too strong in one case -- the last
7282   // partition ends at _unallocated_block which, in general, can be
7283   // an arbitrary boundary, not necessarily card aligned.
7284   if (PrintCMSStatistics != 0) {
7285     _num_dirty_cards +=
7286          mr.word_size()/CardTableModRefBS::card_size_in_words;
7287   }
7288   _space->object_iterate_mem(mr, &_scan_cl);
7289 }
7290 
7291 SweepClosure::SweepClosure(CMSCollector* collector,
7292                            ConcurrentMarkSweepGeneration* g,
7293                            CMSBitMap* bitMap, bool should_yield) :
7294   _collector(collector),
7295   _g(g),
7296   _sp(g->cmsSpace()),
7297   _limit(_sp->sweep_limit()),
7298   _freelistLock(_sp->freelistLock()),
7299   _bitMap(bitMap),
7300   _yield(should_yield),
7301   _inFreeRange(false),           // No free range at beginning of sweep
7302   _freeRangeInFreeLists(false),  // No free range at beginning of sweep
7303   _lastFreeRangeCoalesced(false),
7304   _freeFinger(g->used_region().start())
7305 {
7306   NOT_PRODUCT(
7307     _numObjectsFreed = 0;
7308     _numWordsFreed   = 0;
7309     _numObjectsLive = 0;
7310     _numWordsLive = 0;
7311     _numObjectsAlreadyFree = 0;
7312     _numWordsAlreadyFree = 0;
7313     _last_fc = NULL;
7314 
7315     _sp->initializeIndexedFreeListArrayReturnedBytes();
7316     _sp->dictionary()->initialize_dict_returned_bytes();
7317   )
7318   assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7319          "sweep _limit out of bounds");
7320   if (CMSTraceSweeper) {
7321     gclog_or_tty->print_cr("\n====================\nStarting new sweep with limit " PTR_FORMAT,
7322                         p2i(_limit));
7323   }
7324 }
7325 
7326 void SweepClosure::print_on(outputStream* st) const {
7327   tty->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")",
7328                 p2i(_sp->bottom()), p2i(_sp->end()));
7329   tty->print_cr("_limit = " PTR_FORMAT, p2i(_limit));
7330   tty->print_cr("_freeFinger = " PTR_FORMAT, p2i(_freeFinger));
7331   NOT_PRODUCT(tty->print_cr("_last_fc = " PTR_FORMAT, p2i(_last_fc));)
7332   tty->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d",
7333                 _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced);
7334 }
7335 
7336 #ifndef PRODUCT
7337 // Assertion checking only:  no useful work in product mode --
7338 // however, if any of the flags below become product flags,
7339 // you may need to review this code to see if it needs to be
7340 // enabled in product mode.
7341 SweepClosure::~SweepClosure() {
7342   assert_lock_strong(_freelistLock);
7343   assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7344          "sweep _limit out of bounds");
7345   if (inFreeRange()) {
7346     warning("inFreeRange() should have been reset; dumping state of SweepClosure");
7347     print();
7348     ShouldNotReachHere();
7349   }
7350   if (Verbose && PrintGC) {
7351     gclog_or_tty->print("Collected "SIZE_FORMAT" objects, " SIZE_FORMAT " bytes",
7352                         _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
7353     gclog_or_tty->print_cr("\nLive "SIZE_FORMAT" objects,  "
7354                            SIZE_FORMAT" bytes  "
7355       "Already free "SIZE_FORMAT" objects, "SIZE_FORMAT" bytes",
7356       _numObjectsLive, _numWordsLive*sizeof(HeapWord),
7357       _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
7358     size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree)
7359                         * sizeof(HeapWord);
7360     gclog_or_tty->print_cr("Total sweep: "SIZE_FORMAT" bytes", totalBytes);
7361 
7362     if (PrintCMSStatistics && CMSVerifyReturnedBytes) {
7363       size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
7364       size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes();
7365       size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes;
7366       gclog_or_tty->print("Returned "SIZE_FORMAT" bytes", returned_bytes);
7367       gclog_or_tty->print("   Indexed List Returned "SIZE_FORMAT" bytes",
7368         indexListReturnedBytes);
7369       gclog_or_tty->print_cr("        Dictionary Returned "SIZE_FORMAT" bytes",
7370         dict_returned_bytes);
7371     }
7372   }
7373   if (CMSTraceSweeper) {
7374     gclog_or_tty->print_cr("end of sweep with _limit = " PTR_FORMAT "\n================",
7375                            p2i(_limit));
7376   }
7377 }
7378 #endif  // PRODUCT
7379 
7380 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
7381     bool freeRangeInFreeLists) {
7382   if (CMSTraceSweeper) {
7383     gclog_or_tty->print("---- Start free range at " PTR_FORMAT " with free block (%d)\n",
7384                p2i(freeFinger), freeRangeInFreeLists);
7385   }
7386   assert(!inFreeRange(), "Trampling existing free range");
7387   set_inFreeRange(true);
7388   set_lastFreeRangeCoalesced(false);
7389 
7390   set_freeFinger(freeFinger);
7391   set_freeRangeInFreeLists(freeRangeInFreeLists);
7392   if (CMSTestInFreeList) {
7393     if (freeRangeInFreeLists) {
7394       FreeChunk* fc = (FreeChunk*) freeFinger;
7395       assert(fc->is_free(), "A chunk on the free list should be free.");
7396       assert(fc->size() > 0, "Free range should have a size");
7397       assert(_sp->verify_chunk_in_free_list(fc), "Chunk is not in free lists");
7398     }
7399   }
7400 }
7401 
7402 // Note that the sweeper runs concurrently with mutators. Thus,
7403 // it is possible for direct allocation in this generation to happen
7404 // in the middle of the sweep. Note that the sweeper also coalesces
7405 // contiguous free blocks. Thus, unless the sweeper and the allocator
7406 // synchronize appropriately freshly allocated blocks may get swept up.
7407 // This is accomplished by the sweeper locking the free lists while
7408 // it is sweeping. Thus blocks that are determined to be free are
7409 // indeed free. There is however one additional complication:
7410 // blocks that have been allocated since the final checkpoint and
7411 // mark, will not have been marked and so would be treated as
7412 // unreachable and swept up. To prevent this, the allocator marks
7413 // the bit map when allocating during the sweep phase. This leads,
7414 // however, to a further complication -- objects may have been allocated
7415 // but not yet initialized -- in the sense that the header isn't yet
7416 // installed. The sweeper can not then determine the size of the block
7417 // in order to skip over it. To deal with this case, we use a technique
7418 // (due to Printezis) to encode such uninitialized block sizes in the
7419 // bit map. Since the bit map uses a bit per every HeapWord, but the
7420 // CMS generation has a minimum object size of 3 HeapWords, it follows
7421 // that "normal marks" won't be adjacent in the bit map (there will
7422 // always be at least two 0 bits between successive 1 bits). We make use
7423 // of these "unused" bits to represent uninitialized blocks -- the bit
7424 // corresponding to the start of the uninitialized object and the next
7425 // bit are both set. Finally, a 1 bit marks the end of the object that
7426 // started with the two consecutive 1 bits to indicate its potentially
7427 // uninitialized state.
7428 
7429 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
7430   FreeChunk* fc = (FreeChunk*)addr;
7431   size_t res;
7432 
7433   // Check if we are done sweeping. Below we check "addr >= _limit" rather
7434   // than "addr == _limit" because although _limit was a block boundary when
7435   // we started the sweep, it may no longer be one because heap expansion
7436   // may have caused us to coalesce the block ending at the address _limit
7437   // with a newly expanded chunk (this happens when _limit was set to the
7438   // previous _end of the space), so we may have stepped past _limit:
7439   // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740.
7440   if (addr >= _limit) { // we have swept up to or past the limit: finish up
7441     assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7442            "sweep _limit out of bounds");
7443     assert(addr < _sp->end(), "addr out of bounds");
7444     // Flush any free range we might be holding as a single
7445     // coalesced chunk to the appropriate free list.
7446     if (inFreeRange()) {
7447       assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit,
7448              err_msg("freeFinger() " PTR_FORMAT" is out-of-bounds", p2i(freeFinger())));
7449       flush_cur_free_chunk(freeFinger(),
7450                            pointer_delta(addr, freeFinger()));
7451       if (CMSTraceSweeper) {
7452         gclog_or_tty->print("Sweep: last chunk: ");
7453         gclog_or_tty->print("put_free_blk " PTR_FORMAT " ("SIZE_FORMAT") "
7454                    "[coalesced:%d]\n",
7455                    p2i(freeFinger()), pointer_delta(addr, freeFinger()),
7456                    lastFreeRangeCoalesced() ? 1 : 0);
7457       }
7458     }
7459 
7460     // help the iterator loop finish
7461     return pointer_delta(_sp->end(), addr);
7462   }
7463 
7464   assert(addr < _limit, "sweep invariant");
7465   // check if we should yield
7466   do_yield_check(addr);
7467   if (fc->is_free()) {
7468     // Chunk that is already free
7469     res = fc->size();
7470     do_already_free_chunk(fc);
7471     debug_only(_sp->verifyFreeLists());
7472     // If we flush the chunk at hand in lookahead_and_flush()
7473     // and it's coalesced with a preceding chunk, then the
7474     // process of "mangling" the payload of the coalesced block
7475     // will cause erasure of the size information from the
7476     // (erstwhile) header of all the coalesced blocks but the
7477     // first, so the first disjunct in the assert will not hold
7478     // in that specific case (in which case the second disjunct
7479     // will hold).
7480     assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit,
7481            "Otherwise the size info doesn't change at this step");
7482     NOT_PRODUCT(
7483       _numObjectsAlreadyFree++;
7484       _numWordsAlreadyFree += res;
7485     )
7486     NOT_PRODUCT(_last_fc = fc;)
7487   } else if (!_bitMap->isMarked(addr)) {
7488     // Chunk is fresh garbage
7489     res = do_garbage_chunk(fc);
7490     debug_only(_sp->verifyFreeLists());
7491     NOT_PRODUCT(
7492       _numObjectsFreed++;
7493       _numWordsFreed += res;
7494     )
7495   } else {
7496     // Chunk that is alive.
7497     res = do_live_chunk(fc);
7498     debug_only(_sp->verifyFreeLists());
7499     NOT_PRODUCT(
7500         _numObjectsLive++;
7501         _numWordsLive += res;
7502     )
7503   }
7504   return res;
7505 }
7506 
7507 // For the smart allocation, record following
7508 //  split deaths - a free chunk is removed from its free list because
7509 //      it is being split into two or more chunks.
7510 //  split birth - a free chunk is being added to its free list because
7511 //      a larger free chunk has been split and resulted in this free chunk.
7512 //  coal death - a free chunk is being removed from its free list because
7513 //      it is being coalesced into a large free chunk.
7514 //  coal birth - a free chunk is being added to its free list because
7515 //      it was created when two or more free chunks where coalesced into
7516 //      this free chunk.
7517 //
7518 // These statistics are used to determine the desired number of free
7519 // chunks of a given size.  The desired number is chosen to be relative
7520 // to the end of a CMS sweep.  The desired number at the end of a sweep
7521 // is the
7522 //      count-at-end-of-previous-sweep (an amount that was enough)
7523 //              - count-at-beginning-of-current-sweep  (the excess)
7524 //              + split-births  (gains in this size during interval)
7525 //              - split-deaths  (demands on this size during interval)
7526 // where the interval is from the end of one sweep to the end of the
7527 // next.
7528 //
7529 // When sweeping the sweeper maintains an accumulated chunk which is
7530 // the chunk that is made up of chunks that have been coalesced.  That
7531 // will be termed the left-hand chunk.  A new chunk of garbage that
7532 // is being considered for coalescing will be referred to as the
7533 // right-hand chunk.
7534 //
7535 // When making a decision on whether to coalesce a right-hand chunk with
7536 // the current left-hand chunk, the current count vs. the desired count
7537 // of the left-hand chunk is considered.  Also if the right-hand chunk
7538 // is near the large chunk at the end of the heap (see
7539 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
7540 // left-hand chunk is coalesced.
7541 //
7542 // When making a decision about whether to split a chunk, the desired count
7543 // vs. the current count of the candidate to be split is also considered.
7544 // If the candidate is underpopulated (currently fewer chunks than desired)
7545 // a chunk of an overpopulated (currently more chunks than desired) size may
7546 // be chosen.  The "hint" associated with a free list, if non-null, points
7547 // to a free list which may be overpopulated.
7548 //
7549 
7550 void SweepClosure::do_already_free_chunk(FreeChunk* fc) {
7551   const size_t size = fc->size();
7552   // Chunks that cannot be coalesced are not in the
7553   // free lists.
7554   if (CMSTestInFreeList && !fc->cantCoalesce()) {
7555     assert(_sp->verify_chunk_in_free_list(fc),
7556       "free chunk should be in free lists");
7557   }
7558   // a chunk that is already free, should not have been
7559   // marked in the bit map
7560   HeapWord* const addr = (HeapWord*) fc;
7561   assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
7562   // Verify that the bit map has no bits marked between
7563   // addr and purported end of this block.
7564   _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7565 
7566   // Some chunks cannot be coalesced under any circumstances.
7567   // See the definition of cantCoalesce().
7568   if (!fc->cantCoalesce()) {
7569     // This chunk can potentially be coalesced.
7570     if (_sp->adaptive_freelists()) {
7571       // All the work is done in
7572       do_post_free_or_garbage_chunk(fc, size);
7573     } else {  // Not adaptive free lists
7574       // this is a free chunk that can potentially be coalesced by the sweeper;
7575       if (!inFreeRange()) {
7576         // if the next chunk is a free block that can't be coalesced
7577         // it doesn't make sense to remove this chunk from the free lists
7578         FreeChunk* nextChunk = (FreeChunk*)(addr + size);
7579         assert((HeapWord*)nextChunk <= _sp->end(), "Chunk size out of bounds?");
7580         if ((HeapWord*)nextChunk < _sp->end() &&     // There is another free chunk to the right ...
7581             nextChunk->is_free()               &&     // ... which is free...
7582             nextChunk->cantCoalesce()) {             // ... but can't be coalesced
7583           // nothing to do
7584         } else {
7585           // Potentially the start of a new free range:
7586           // Don't eagerly remove it from the free lists.
7587           // No need to remove it if it will just be put
7588           // back again.  (Also from a pragmatic point of view
7589           // if it is a free block in a region that is beyond
7590           // any allocated blocks, an assertion will fail)
7591           // Remember the start of a free run.
7592           initialize_free_range(addr, true);
7593           // end - can coalesce with next chunk
7594         }
7595       } else {
7596         // the midst of a free range, we are coalescing
7597         print_free_block_coalesced(fc);
7598         if (CMSTraceSweeper) {
7599           gclog_or_tty->print("  -- pick up free block " PTR_FORMAT " (" SIZE_FORMAT ")\n", p2i(fc), size);
7600         }
7601         // remove it from the free lists
7602         _sp->removeFreeChunkFromFreeLists(fc);
7603         set_lastFreeRangeCoalesced(true);
7604         // If the chunk is being coalesced and the current free range is
7605         // in the free lists, remove the current free range so that it
7606         // will be returned to the free lists in its entirety - all
7607         // the coalesced pieces included.
7608         if (freeRangeInFreeLists()) {
7609           FreeChunk* ffc = (FreeChunk*) freeFinger();
7610           assert(ffc->size() == pointer_delta(addr, freeFinger()),
7611             "Size of free range is inconsistent with chunk size.");
7612           if (CMSTestInFreeList) {
7613             assert(_sp->verify_chunk_in_free_list(ffc),
7614               "free range is not in free lists");
7615           }
7616           _sp->removeFreeChunkFromFreeLists(ffc);
7617           set_freeRangeInFreeLists(false);
7618         }
7619       }
7620     }
7621     // Note that if the chunk is not coalescable (the else arm
7622     // below), we unconditionally flush, without needing to do
7623     // a "lookahead," as we do below.
7624     if (inFreeRange()) lookahead_and_flush(fc, size);
7625   } else {
7626     // Code path common to both original and adaptive free lists.
7627 
7628     // cant coalesce with previous block; this should be treated
7629     // as the end of a free run if any
7630     if (inFreeRange()) {
7631       // we kicked some butt; time to pick up the garbage
7632       assert(freeFinger() < addr, "freeFinger points too high");
7633       flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7634     }
7635     // else, nothing to do, just continue
7636   }
7637 }
7638 
7639 size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) {
7640   // This is a chunk of garbage.  It is not in any free list.
7641   // Add it to a free list or let it possibly be coalesced into
7642   // a larger chunk.
7643   HeapWord* const addr = (HeapWord*) fc;
7644   const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7645 
7646   if (_sp->adaptive_freelists()) {
7647     // Verify that the bit map has no bits marked between
7648     // addr and purported end of just dead object.
7649     _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7650 
7651     do_post_free_or_garbage_chunk(fc, size);
7652   } else {
7653     if (!inFreeRange()) {
7654       // start of a new free range
7655       assert(size > 0, "A free range should have a size");
7656       initialize_free_range(addr, false);
7657     } else {
7658       // this will be swept up when we hit the end of the
7659       // free range
7660       if (CMSTraceSweeper) {
7661         gclog_or_tty->print("  -- pick up garbage " PTR_FORMAT " (" SIZE_FORMAT ")\n", p2i(fc), size);
7662       }
7663       // If the chunk is being coalesced and the current free range is
7664       // in the free lists, remove the current free range so that it
7665       // will be returned to the free lists in its entirety - all
7666       // the coalesced pieces included.
7667       if (freeRangeInFreeLists()) {
7668         FreeChunk* ffc = (FreeChunk*)freeFinger();
7669         assert(ffc->size() == pointer_delta(addr, freeFinger()),
7670           "Size of free range is inconsistent with chunk size.");
7671         if (CMSTestInFreeList) {
7672           assert(_sp->verify_chunk_in_free_list(ffc),
7673             "free range is not in free lists");
7674         }
7675         _sp->removeFreeChunkFromFreeLists(ffc);
7676         set_freeRangeInFreeLists(false);
7677       }
7678       set_lastFreeRangeCoalesced(true);
7679     }
7680     // this will be swept up when we hit the end of the free range
7681 
7682     // Verify that the bit map has no bits marked between
7683     // addr and purported end of just dead object.
7684     _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7685   }
7686   assert(_limit >= addr + size,
7687          "A freshly garbage chunk can't possibly straddle over _limit");
7688   if (inFreeRange()) lookahead_and_flush(fc, size);
7689   return size;
7690 }
7691 
7692 size_t SweepClosure::do_live_chunk(FreeChunk* fc) {
7693   HeapWord* addr = (HeapWord*) fc;
7694   // The sweeper has just found a live object. Return any accumulated
7695   // left hand chunk to the free lists.
7696   if (inFreeRange()) {
7697     assert(freeFinger() < addr, "freeFinger points too high");
7698     flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7699   }
7700 
7701   // This object is live: we'd normally expect this to be
7702   // an oop, and like to assert the following:
7703   // assert(oop(addr)->is_oop(), "live block should be an oop");
7704   // However, as we commented above, this may be an object whose
7705   // header hasn't yet been initialized.
7706   size_t size;
7707   assert(_bitMap->isMarked(addr), "Tautology for this control point");
7708   if (_bitMap->isMarked(addr + 1)) {
7709     // Determine the size from the bit map, rather than trying to
7710     // compute it from the object header.
7711     HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
7712     size = pointer_delta(nextOneAddr + 1, addr);
7713     assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
7714            "alignment problem");
7715 
7716 #ifdef ASSERT
7717       if (oop(addr)->klass_or_null() != NULL) {
7718         // Ignore mark word because we are running concurrent with mutators
7719         assert(oop(addr)->is_oop(true), "live block should be an oop");
7720         assert(size ==
7721                CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
7722                "P-mark and computed size do not agree");
7723       }
7724 #endif
7725 
7726   } else {
7727     // This should be an initialized object that's alive.
7728     assert(oop(addr)->klass_or_null() != NULL,
7729            "Should be an initialized object");
7730     // Ignore mark word because we are running concurrent with mutators
7731     assert(oop(addr)->is_oop(true), "live block should be an oop");
7732     // Verify that the bit map has no bits marked between
7733     // addr and purported end of this block.
7734     size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7735     assert(size >= 3, "Necessary for Printezis marks to work");
7736     assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
7737     DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
7738   }
7739   return size;
7740 }
7741 
7742 void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc,
7743                                                  size_t chunkSize) {
7744   // do_post_free_or_garbage_chunk() should only be called in the case
7745   // of the adaptive free list allocator.
7746   const bool fcInFreeLists = fc->is_free();
7747   assert(_sp->adaptive_freelists(), "Should only be used in this case.");
7748   assert((HeapWord*)fc <= _limit, "sweep invariant");
7749   if (CMSTestInFreeList && fcInFreeLists) {
7750     assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists");
7751   }
7752 
7753   if (CMSTraceSweeper) {
7754     gclog_or_tty->print_cr("  -- pick up another chunk at " PTR_FORMAT " (" SIZE_FORMAT ")", p2i(fc), chunkSize);
7755   }
7756 
7757   HeapWord* const fc_addr = (HeapWord*) fc;
7758 
7759   bool coalesce;
7760   const size_t left  = pointer_delta(fc_addr, freeFinger());
7761   const size_t right = chunkSize;
7762   switch (FLSCoalescePolicy) {
7763     // numeric value forms a coalition aggressiveness metric
7764     case 0:  { // never coalesce
7765       coalesce = false;
7766       break;
7767     }
7768     case 1: { // coalesce if left & right chunks on overpopulated lists
7769       coalesce = _sp->coalOverPopulated(left) &&
7770                  _sp->coalOverPopulated(right);
7771       break;
7772     }
7773     case 2: { // coalesce if left chunk on overpopulated list (default)
7774       coalesce = _sp->coalOverPopulated(left);
7775       break;
7776     }
7777     case 3: { // coalesce if left OR right chunk on overpopulated list
7778       coalesce = _sp->coalOverPopulated(left) ||
7779                  _sp->coalOverPopulated(right);
7780       break;
7781     }
7782     case 4: { // always coalesce
7783       coalesce = true;
7784       break;
7785     }
7786     default:
7787      ShouldNotReachHere();
7788   }
7789 
7790   // Should the current free range be coalesced?
7791   // If the chunk is in a free range and either we decided to coalesce above
7792   // or the chunk is near the large block at the end of the heap
7793   // (isNearLargestChunk() returns true), then coalesce this chunk.
7794   const bool doCoalesce = inFreeRange()
7795                           && (coalesce || _g->isNearLargestChunk(fc_addr));
7796   if (doCoalesce) {
7797     // Coalesce the current free range on the left with the new
7798     // chunk on the right.  If either is on a free list,
7799     // it must be removed from the list and stashed in the closure.
7800     if (freeRangeInFreeLists()) {
7801       FreeChunk* const ffc = (FreeChunk*)freeFinger();
7802       assert(ffc->size() == pointer_delta(fc_addr, freeFinger()),
7803         "Size of free range is inconsistent with chunk size.");
7804       if (CMSTestInFreeList) {
7805         assert(_sp->verify_chunk_in_free_list(ffc),
7806           "Chunk is not in free lists");
7807       }
7808       _sp->coalDeath(ffc->size());
7809       _sp->removeFreeChunkFromFreeLists(ffc);
7810       set_freeRangeInFreeLists(false);
7811     }
7812     if (fcInFreeLists) {
7813       _sp->coalDeath(chunkSize);
7814       assert(fc->size() == chunkSize,
7815         "The chunk has the wrong size or is not in the free lists");
7816       _sp->removeFreeChunkFromFreeLists(fc);
7817     }
7818     set_lastFreeRangeCoalesced(true);
7819     print_free_block_coalesced(fc);
7820   } else {  // not in a free range and/or should not coalesce
7821     // Return the current free range and start a new one.
7822     if (inFreeRange()) {
7823       // In a free range but cannot coalesce with the right hand chunk.
7824       // Put the current free range into the free lists.
7825       flush_cur_free_chunk(freeFinger(),
7826                            pointer_delta(fc_addr, freeFinger()));
7827     }
7828     // Set up for new free range.  Pass along whether the right hand
7829     // chunk is in the free lists.
7830     initialize_free_range((HeapWord*)fc, fcInFreeLists);
7831   }
7832 }
7833 
7834 // Lookahead flush:
7835 // If we are tracking a free range, and this is the last chunk that
7836 // we'll look at because its end crosses past _limit, we'll preemptively
7837 // flush it along with any free range we may be holding on to. Note that
7838 // this can be the case only for an already free or freshly garbage
7839 // chunk. If this block is an object, it can never straddle
7840 // over _limit. The "straddling" occurs when _limit is set at
7841 // the previous end of the space when this cycle started, and
7842 // a subsequent heap expansion caused the previously co-terminal
7843 // free block to be coalesced with the newly expanded portion,
7844 // thus rendering _limit a non-block-boundary making it dangerous
7845 // for the sweeper to step over and examine.
7846 void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) {
7847   assert(inFreeRange(), "Should only be called if currently in a free range.");
7848   HeapWord* const eob = ((HeapWord*)fc) + chunk_size;
7849   assert(_sp->used_region().contains(eob - 1),
7850          err_msg("eob = " PTR_FORMAT " eob-1 = " PTR_FORMAT " _limit = " PTR_FORMAT
7851                  " out of bounds wrt _sp = [" PTR_FORMAT "," PTR_FORMAT ")"
7852                  " when examining fc = " PTR_FORMAT "(" SIZE_FORMAT ")",
7853                  p2i(eob), p2i(eob-1), p2i(_limit), p2i(_sp->bottom()), p2i(_sp->end()), p2i(fc), chunk_size));
7854   if (eob >= _limit) {
7855     assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit");
7856     if (CMSTraceSweeper) {
7857       gclog_or_tty->print_cr("_limit " PTR_FORMAT " reached or crossed by block "
7858                              "[" PTR_FORMAT "," PTR_FORMAT ") in space "
7859                              "[" PTR_FORMAT "," PTR_FORMAT ")",
7860                              p2i(_limit), p2i(fc), p2i(eob), p2i(_sp->bottom()), p2i(_sp->end()));
7861     }
7862     // Return the storage we are tracking back into the free lists.
7863     if (CMSTraceSweeper) {
7864       gclog_or_tty->print_cr("Flushing ... ");
7865     }
7866     assert(freeFinger() < eob, "Error");
7867     flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger()));
7868   }
7869 }
7870 
7871 void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) {
7872   assert(inFreeRange(), "Should only be called if currently in a free range.");
7873   assert(size > 0,
7874     "A zero sized chunk cannot be added to the free lists.");
7875   if (!freeRangeInFreeLists()) {
7876     if (CMSTestInFreeList) {
7877       FreeChunk* fc = (FreeChunk*) chunk;
7878       fc->set_size(size);
7879       assert(!_sp->verify_chunk_in_free_list(fc),
7880         "chunk should not be in free lists yet");
7881     }
7882     if (CMSTraceSweeper) {
7883       gclog_or_tty->print_cr(" -- add free block " PTR_FORMAT " (" SIZE_FORMAT ") to free lists",
7884                     p2i(chunk), size);
7885     }
7886     // A new free range is going to be starting.  The current
7887     // free range has not been added to the free lists yet or
7888     // was removed so add it back.
7889     // If the current free range was coalesced, then the death
7890     // of the free range was recorded.  Record a birth now.
7891     if (lastFreeRangeCoalesced()) {
7892       _sp->coalBirth(size);
7893     }
7894     _sp->addChunkAndRepairOffsetTable(chunk, size,
7895             lastFreeRangeCoalesced());
7896   } else if (CMSTraceSweeper) {
7897     gclog_or_tty->print_cr("Already in free list: nothing to flush");
7898   }
7899   set_inFreeRange(false);
7900   set_freeRangeInFreeLists(false);
7901 }
7902 
7903 // We take a break if we've been at this for a while,
7904 // so as to avoid monopolizing the locks involved.
7905 void SweepClosure::do_yield_work(HeapWord* addr) {
7906   // Return current free chunk being used for coalescing (if any)
7907   // to the appropriate freelist.  After yielding, the next
7908   // free block encountered will start a coalescing range of
7909   // free blocks.  If the next free block is adjacent to the
7910   // chunk just flushed, they will need to wait for the next
7911   // sweep to be coalesced.
7912   if (inFreeRange()) {
7913     flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7914   }
7915 
7916   // First give up the locks, then yield, then re-lock.
7917   // We should probably use a constructor/destructor idiom to
7918   // do this unlock/lock or modify the MutexUnlocker class to
7919   // serve our purpose. XXX
7920   assert_lock_strong(_bitMap->lock());
7921   assert_lock_strong(_freelistLock);
7922   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7923          "CMS thread should hold CMS token");
7924   _bitMap->lock()->unlock();
7925   _freelistLock->unlock();
7926   ConcurrentMarkSweepThread::desynchronize(true);
7927   _collector->stopTimer();
7928   if (PrintCMSStatistics != 0) {
7929     _collector->incrementYields();
7930   }
7931 
7932   // See the comment in coordinator_yield()
7933   for (unsigned i = 0; i < CMSYieldSleepCount &&
7934                        ConcurrentMarkSweepThread::should_yield() &&
7935                        !CMSCollector::foregroundGCIsActive(); ++i) {
7936     os::sleep(Thread::current(), 1, false);
7937   }
7938 
7939   ConcurrentMarkSweepThread::synchronize(true);
7940   _freelistLock->lock();
7941   _bitMap->lock()->lock_without_safepoint_check();
7942   _collector->startTimer();
7943 }
7944 
7945 #ifndef PRODUCT
7946 // This is actually very useful in a product build if it can
7947 // be called from the debugger.  Compile it into the product
7948 // as needed.
7949 bool debug_verify_chunk_in_free_list(FreeChunk* fc) {
7950   return debug_cms_space->verify_chunk_in_free_list(fc);
7951 }
7952 #endif
7953 
7954 void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const {
7955   if (CMSTraceSweeper) {
7956     gclog_or_tty->print_cr("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")",
7957                            p2i(fc), fc->size());
7958   }
7959 }
7960 
7961 // CMSIsAliveClosure
7962 bool CMSIsAliveClosure::do_object_b(oop obj) {
7963   HeapWord* addr = (HeapWord*)obj;
7964   return addr != NULL &&
7965          (!_span.contains(addr) || _bit_map->isMarked(addr));
7966 }
7967 
7968 
7969 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector,
7970                       MemRegion span,
7971                       CMSBitMap* bit_map, CMSMarkStack* mark_stack,
7972                       bool cpc):
7973   _collector(collector),
7974   _span(span),
7975   _bit_map(bit_map),
7976   _mark_stack(mark_stack),
7977   _concurrent_precleaning(cpc) {
7978   assert(!_span.is_empty(), "Empty span could spell trouble");
7979 }
7980 
7981 
7982 // CMSKeepAliveClosure: the serial version
7983 void CMSKeepAliveClosure::do_oop(oop obj) {
7984   HeapWord* addr = (HeapWord*)obj;
7985   if (_span.contains(addr) &&
7986       !_bit_map->isMarked(addr)) {
7987     _bit_map->mark(addr);
7988     bool simulate_overflow = false;
7989     NOT_PRODUCT(
7990       if (CMSMarkStackOverflowALot &&
7991           _collector->simulate_overflow()) {
7992         // simulate a stack overflow
7993         simulate_overflow = true;
7994       }
7995     )
7996     if (simulate_overflow || !_mark_stack->push(obj)) {
7997       if (_concurrent_precleaning) {
7998         // We dirty the overflown object and let the remark
7999         // phase deal with it.
8000         assert(_collector->overflow_list_is_empty(), "Error");
8001         // In the case of object arrays, we need to dirty all of
8002         // the cards that the object spans. No locking or atomics
8003         // are needed since no one else can be mutating the mod union
8004         // table.
8005         if (obj->is_objArray()) {
8006           size_t sz = obj->size();
8007           HeapWord* end_card_addr =
8008             (HeapWord*)round_to((intptr_t)(addr+sz), CardTableModRefBS::card_size);
8009           MemRegion redirty_range = MemRegion(addr, end_card_addr);
8010           assert(!redirty_range.is_empty(), "Arithmetical tautology");
8011           _collector->_modUnionTable.mark_range(redirty_range);
8012         } else {
8013           _collector->_modUnionTable.mark(addr);
8014         }
8015         _collector->_ser_kac_preclean_ovflw++;
8016       } else {
8017         _collector->push_on_overflow_list(obj);
8018         _collector->_ser_kac_ovflw++;
8019       }
8020     }
8021   }
8022 }
8023 
8024 void CMSKeepAliveClosure::do_oop(oop* p)       { CMSKeepAliveClosure::do_oop_work(p); }
8025 void CMSKeepAliveClosure::do_oop(narrowOop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8026 
8027 // CMSParKeepAliveClosure: a parallel version of the above.
8028 // The work queues are private to each closure (thread),
8029 // but (may be) available for stealing by other threads.
8030 void CMSParKeepAliveClosure::do_oop(oop obj) {
8031   HeapWord* addr = (HeapWord*)obj;
8032   if (_span.contains(addr) &&
8033       !_bit_map->isMarked(addr)) {
8034     // In general, during recursive tracing, several threads
8035     // may be concurrently getting here; the first one to
8036     // "tag" it, claims it.
8037     if (_bit_map->par_mark(addr)) {
8038       bool res = _work_queue->push(obj);
8039       assert(res, "Low water mark should be much less than capacity");
8040       // Do a recursive trim in the hope that this will keep
8041       // stack usage lower, but leave some oops for potential stealers
8042       trim_queue(_low_water_mark);
8043     } // Else, another thread got there first
8044   }
8045 }
8046 
8047 void CMSParKeepAliveClosure::do_oop(oop* p)       { CMSParKeepAliveClosure::do_oop_work(p); }
8048 void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8049 
8050 void CMSParKeepAliveClosure::trim_queue(uint max) {
8051   while (_work_queue->size() > max) {
8052     oop new_oop;
8053     if (_work_queue->pop_local(new_oop)) {
8054       assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
8055       assert(_bit_map->isMarked((HeapWord*)new_oop),
8056              "no white objects on this stack!");
8057       assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8058       // iterate over the oops in this oop, marking and pushing
8059       // the ones in CMS heap (i.e. in _span).
8060       new_oop->oop_iterate(&_mark_and_push);
8061     }
8062   }
8063 }
8064 
8065 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
8066                                 CMSCollector* collector,
8067                                 MemRegion span, CMSBitMap* bit_map,
8068                                 OopTaskQueue* work_queue):
8069   _collector(collector),
8070   _span(span),
8071   _bit_map(bit_map),
8072   _work_queue(work_queue) { }
8073 
8074 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
8075   HeapWord* addr = (HeapWord*)obj;
8076   if (_span.contains(addr) &&
8077       !_bit_map->isMarked(addr)) {
8078     if (_bit_map->par_mark(addr)) {
8079       bool simulate_overflow = false;
8080       NOT_PRODUCT(
8081         if (CMSMarkStackOverflowALot &&
8082             _collector->par_simulate_overflow()) {
8083           // simulate a stack overflow
8084           simulate_overflow = true;
8085         }
8086       )
8087       if (simulate_overflow || !_work_queue->push(obj)) {
8088         _collector->par_push_on_overflow_list(obj);
8089         _collector->_par_kac_ovflw++;
8090       }
8091     } // Else another thread got there already
8092   }
8093 }
8094 
8095 void CMSInnerParMarkAndPushClosure::do_oop(oop* p)       { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8096 void CMSInnerParMarkAndPushClosure::do_oop(narrowOop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8097 
8098 //////////////////////////////////////////////////////////////////
8099 //  CMSExpansionCause                /////////////////////////////
8100 //////////////////////////////////////////////////////////////////
8101 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
8102   switch (cause) {
8103     case _no_expansion:
8104       return "No expansion";
8105     case _satisfy_free_ratio:
8106       return "Free ratio";
8107     case _satisfy_promotion:
8108       return "Satisfy promotion";
8109     case _satisfy_allocation:
8110       return "allocation";
8111     case _allocate_par_lab:
8112       return "Par LAB";
8113     case _allocate_par_spooling_space:
8114       return "Par Spooling Space";
8115     case _adaptive_size_policy:
8116       return "Ergonomics";
8117     default:
8118       return "unknown";
8119   }
8120 }
8121 
8122 void CMSDrainMarkingStackClosure::do_void() {
8123   // the max number to take from overflow list at a time
8124   const size_t num = _mark_stack->capacity()/4;
8125   assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
8126          "Overflow list should be NULL during concurrent phases");
8127   while (!_mark_stack->isEmpty() ||
8128          // if stack is empty, check the overflow list
8129          _collector->take_from_overflow_list(num, _mark_stack)) {
8130     oop obj = _mark_stack->pop();
8131     HeapWord* addr = (HeapWord*)obj;
8132     assert(_span.contains(addr), "Should be within span");
8133     assert(_bit_map->isMarked(addr), "Should be marked");
8134     assert(obj->is_oop(), "Should be an oop");
8135     obj->oop_iterate(_keep_alive);
8136   }
8137 }
8138 
8139 void CMSParDrainMarkingStackClosure::do_void() {
8140   // drain queue
8141   trim_queue(0);
8142 }
8143 
8144 // Trim our work_queue so its length is below max at return
8145 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
8146   while (_work_queue->size() > max) {
8147     oop new_oop;
8148     if (_work_queue->pop_local(new_oop)) {
8149       assert(new_oop->is_oop(), "Expected an oop");
8150       assert(_bit_map->isMarked((HeapWord*)new_oop),
8151              "no white objects on this stack!");
8152       assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8153       // iterate over the oops in this oop, marking and pushing
8154       // the ones in CMS heap (i.e. in _span).
8155       new_oop->oop_iterate(&_mark_and_push);
8156     }
8157   }
8158 }
8159 
8160 ////////////////////////////////////////////////////////////////////
8161 // Support for Marking Stack Overflow list handling and related code
8162 ////////////////////////////////////////////////////////////////////
8163 // Much of the following code is similar in shape and spirit to the
8164 // code used in ParNewGC. We should try and share that code
8165 // as much as possible in the future.
8166 
8167 #ifndef PRODUCT
8168 // Debugging support for CMSStackOverflowALot
8169 
8170 // It's OK to call this multi-threaded;  the worst thing
8171 // that can happen is that we'll get a bunch of closely
8172 // spaced simulated overflows, but that's OK, in fact
8173 // probably good as it would exercise the overflow code
8174 // under contention.
8175 bool CMSCollector::simulate_overflow() {
8176   if (_overflow_counter-- <= 0) { // just being defensive
8177     _overflow_counter = CMSMarkStackOverflowInterval;
8178     return true;
8179   } else {
8180     return false;
8181   }
8182 }
8183 
8184 bool CMSCollector::par_simulate_overflow() {
8185   return simulate_overflow();
8186 }
8187 #endif
8188 
8189 // Single-threaded
8190 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
8191   assert(stack->isEmpty(), "Expected precondition");
8192   assert(stack->capacity() > num, "Shouldn't bite more than can chew");
8193   size_t i = num;
8194   oop  cur = _overflow_list;
8195   const markOop proto = markOopDesc::prototype();
8196   NOT_PRODUCT(ssize_t n = 0;)
8197   for (oop next; i > 0 && cur != NULL; cur = next, i--) {
8198     next = oop(cur->mark());
8199     cur->set_mark(proto);   // until proven otherwise
8200     assert(cur->is_oop(), "Should be an oop");
8201     bool res = stack->push(cur);
8202     assert(res, "Bit off more than can chew?");
8203     NOT_PRODUCT(n++;)
8204   }
8205   _overflow_list = cur;
8206 #ifndef PRODUCT
8207   assert(_num_par_pushes >= n, "Too many pops?");
8208   _num_par_pushes -=n;
8209 #endif
8210   return !stack->isEmpty();
8211 }
8212 
8213 #define BUSY  (cast_to_oop<intptr_t>(0x1aff1aff))
8214 // (MT-safe) Get a prefix of at most "num" from the list.
8215 // The overflow list is chained through the mark word of
8216 // each object in the list. We fetch the entire list,
8217 // break off a prefix of the right size and return the
8218 // remainder. If other threads try to take objects from
8219 // the overflow list at that time, they will wait for
8220 // some time to see if data becomes available. If (and
8221 // only if) another thread places one or more object(s)
8222 // on the global list before we have returned the suffix
8223 // to the global list, we will walk down our local list
8224 // to find its end and append the global list to
8225 // our suffix before returning it. This suffix walk can
8226 // prove to be expensive (quadratic in the amount of traffic)
8227 // when there are many objects in the overflow list and
8228 // there is much producer-consumer contention on the list.
8229 // *NOTE*: The overflow list manipulation code here and
8230 // in ParNewGeneration:: are very similar in shape,
8231 // except that in the ParNew case we use the old (from/eden)
8232 // copy of the object to thread the list via its klass word.
8233 // Because of the common code, if you make any changes in
8234 // the code below, please check the ParNew version to see if
8235 // similar changes might be needed.
8236 // CR 6797058 has been filed to consolidate the common code.
8237 bool CMSCollector::par_take_from_overflow_list(size_t num,
8238                                                OopTaskQueue* work_q,
8239                                                int no_of_gc_threads) {
8240   assert(work_q->size() == 0, "First empty local work queue");
8241   assert(num < work_q->max_elems(), "Can't bite more than we can chew");
8242   if (_overflow_list == NULL) {
8243     return false;
8244   }
8245   // Grab the entire list; we'll put back a suffix
8246   oop prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
8247   Thread* tid = Thread::current();
8248   // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was
8249   // set to ParallelGCThreads.
8250   size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads;
8251   size_t sleep_time_millis = MAX2((size_t)1, num/100);
8252   // If the list is busy, we spin for a short while,
8253   // sleeping between attempts to get the list.
8254   for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) {
8255     os::sleep(tid, sleep_time_millis, false);
8256     if (_overflow_list == NULL) {
8257       // Nothing left to take
8258       return false;
8259     } else if (_overflow_list != BUSY) {
8260       // Try and grab the prefix
8261       prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
8262     }
8263   }
8264   // If the list was found to be empty, or we spun long
8265   // enough, we give up and return empty-handed. If we leave
8266   // the list in the BUSY state below, it must be the case that
8267   // some other thread holds the overflow list and will set it
8268   // to a non-BUSY state in the future.
8269   if (prefix == NULL || prefix == BUSY) {
8270      // Nothing to take or waited long enough
8271      if (prefix == NULL) {
8272        // Write back the NULL in case we overwrote it with BUSY above
8273        // and it is still the same value.
8274        (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8275      }
8276      return false;
8277   }
8278   assert(prefix != NULL && prefix != BUSY, "Error");
8279   size_t i = num;
8280   oop cur = prefix;
8281   // Walk down the first "num" objects, unless we reach the end.
8282   for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--);
8283   if (cur->mark() == NULL) {
8284     // We have "num" or fewer elements in the list, so there
8285     // is nothing to return to the global list.
8286     // Write back the NULL in lieu of the BUSY we wrote
8287     // above, if it is still the same value.
8288     if (_overflow_list == BUSY) {
8289       (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8290     }
8291   } else {
8292     // Chop off the suffix and return it to the global list.
8293     assert(cur->mark() != BUSY, "Error");
8294     oop suffix_head = cur->mark(); // suffix will be put back on global list
8295     cur->set_mark(NULL);           // break off suffix
8296     // It's possible that the list is still in the empty(busy) state
8297     // we left it in a short while ago; in that case we may be
8298     // able to place back the suffix without incurring the cost
8299     // of a walk down the list.
8300     oop observed_overflow_list = _overflow_list;
8301     oop cur_overflow_list = observed_overflow_list;
8302     bool attached = false;
8303     while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
8304       observed_overflow_list =
8305         (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
8306       if (cur_overflow_list == observed_overflow_list) {
8307         attached = true;
8308         break;
8309       } else cur_overflow_list = observed_overflow_list;
8310     }
8311     if (!attached) {
8312       // Too bad, someone else sneaked in (at least) an element; we'll need
8313       // to do a splice. Find tail of suffix so we can prepend suffix to global
8314       // list.
8315       for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark()));
8316       oop suffix_tail = cur;
8317       assert(suffix_tail != NULL && suffix_tail->mark() == NULL,
8318              "Tautology");
8319       observed_overflow_list = _overflow_list;
8320       do {
8321         cur_overflow_list = observed_overflow_list;
8322         if (cur_overflow_list != BUSY) {
8323           // Do the splice ...
8324           suffix_tail->set_mark(markOop(cur_overflow_list));
8325         } else { // cur_overflow_list == BUSY
8326           suffix_tail->set_mark(NULL);
8327         }
8328         // ... and try to place spliced list back on overflow_list ...
8329         observed_overflow_list =
8330           (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
8331       } while (cur_overflow_list != observed_overflow_list);
8332       // ... until we have succeeded in doing so.
8333     }
8334   }
8335 
8336   // Push the prefix elements on work_q
8337   assert(prefix != NULL, "control point invariant");
8338   const markOop proto = markOopDesc::prototype();
8339   oop next;
8340   NOT_PRODUCT(ssize_t n = 0;)
8341   for (cur = prefix; cur != NULL; cur = next) {
8342     next = oop(cur->mark());
8343     cur->set_mark(proto);   // until proven otherwise
8344     assert(cur->is_oop(), "Should be an oop");
8345     bool res = work_q->push(cur);
8346     assert(res, "Bit off more than we can chew?");
8347     NOT_PRODUCT(n++;)
8348   }
8349 #ifndef PRODUCT
8350   assert(_num_par_pushes >= n, "Too many pops?");
8351   Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
8352 #endif
8353   return true;
8354 }
8355 
8356 // Single-threaded
8357 void CMSCollector::push_on_overflow_list(oop p) {
8358   NOT_PRODUCT(_num_par_pushes++;)
8359   assert(p->is_oop(), "Not an oop");
8360   preserve_mark_if_necessary(p);
8361   p->set_mark((markOop)_overflow_list);
8362   _overflow_list = p;
8363 }
8364 
8365 // Multi-threaded; use CAS to prepend to overflow list
8366 void CMSCollector::par_push_on_overflow_list(oop p) {
8367   NOT_PRODUCT(Atomic::inc_ptr(&_num_par_pushes);)
8368   assert(p->is_oop(), "Not an oop");
8369   par_preserve_mark_if_necessary(p);
8370   oop observed_overflow_list = _overflow_list;
8371   oop cur_overflow_list;
8372   do {
8373     cur_overflow_list = observed_overflow_list;
8374     if (cur_overflow_list != BUSY) {
8375       p->set_mark(markOop(cur_overflow_list));
8376     } else {
8377       p->set_mark(NULL);
8378     }
8379     observed_overflow_list =
8380       (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list);
8381   } while (cur_overflow_list != observed_overflow_list);
8382 }
8383 #undef BUSY
8384 
8385 // Single threaded
8386 // General Note on GrowableArray: pushes may silently fail
8387 // because we are (temporarily) out of C-heap for expanding
8388 // the stack. The problem is quite ubiquitous and affects
8389 // a lot of code in the JVM. The prudent thing for GrowableArray
8390 // to do (for now) is to exit with an error. However, that may
8391 // be too draconian in some cases because the caller may be
8392 // able to recover without much harm. For such cases, we
8393 // should probably introduce a "soft_push" method which returns
8394 // an indication of success or failure with the assumption that
8395 // the caller may be able to recover from a failure; code in
8396 // the VM can then be changed, incrementally, to deal with such
8397 // failures where possible, thus, incrementally hardening the VM
8398 // in such low resource situations.
8399 void CMSCollector::preserve_mark_work(oop p, markOop m) {
8400   _preserved_oop_stack.push(p);
8401   _preserved_mark_stack.push(m);
8402   assert(m == p->mark(), "Mark word changed");
8403   assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8404          "bijection");
8405 }
8406 
8407 // Single threaded
8408 void CMSCollector::preserve_mark_if_necessary(oop p) {
8409   markOop m = p->mark();
8410   if (m->must_be_preserved(p)) {
8411     preserve_mark_work(p, m);
8412   }
8413 }
8414 
8415 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
8416   markOop m = p->mark();
8417   if (m->must_be_preserved(p)) {
8418     MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
8419     // Even though we read the mark word without holding
8420     // the lock, we are assured that it will not change
8421     // because we "own" this oop, so no other thread can
8422     // be trying to push it on the overflow list; see
8423     // the assertion in preserve_mark_work() that checks
8424     // that m == p->mark().
8425     preserve_mark_work(p, m);
8426   }
8427 }
8428 
8429 // We should be able to do this multi-threaded,
8430 // a chunk of stack being a task (this is
8431 // correct because each oop only ever appears
8432 // once in the overflow list. However, it's
8433 // not very easy to completely overlap this with
8434 // other operations, so will generally not be done
8435 // until all work's been completed. Because we
8436 // expect the preserved oop stack (set) to be small,
8437 // it's probably fine to do this single-threaded.
8438 // We can explore cleverer concurrent/overlapped/parallel
8439 // processing of preserved marks if we feel the
8440 // need for this in the future. Stack overflow should
8441 // be so rare in practice and, when it happens, its
8442 // effect on performance so great that this will
8443 // likely just be in the noise anyway.
8444 void CMSCollector::restore_preserved_marks_if_any() {
8445   assert(SafepointSynchronize::is_at_safepoint(),
8446          "world should be stopped");
8447   assert(Thread::current()->is_ConcurrentGC_thread() ||
8448          Thread::current()->is_VM_thread(),
8449          "should be single-threaded");
8450   assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8451          "bijection");
8452 
8453   while (!_preserved_oop_stack.is_empty()) {
8454     oop p = _preserved_oop_stack.pop();
8455     assert(p->is_oop(), "Should be an oop");
8456     assert(_span.contains(p), "oop should be in _span");
8457     assert(p->mark() == markOopDesc::prototype(),
8458            "Set when taken from overflow list");
8459     markOop m = _preserved_mark_stack.pop();
8460     p->set_mark(m);
8461   }
8462   assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(),
8463          "stacks were cleared above");
8464 }
8465 
8466 #ifndef PRODUCT
8467 bool CMSCollector::no_preserved_marks() const {
8468   return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty();
8469 }
8470 #endif
8471 
8472 // Transfer some number of overflown objects to usual marking
8473 // stack. Return true if some objects were transferred.
8474 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
8475   size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,
8476                     (size_t)ParGCDesiredObjsFromOverflowList);
8477 
8478   bool res = _collector->take_from_overflow_list(num, _mark_stack);
8479   assert(_collector->overflow_list_is_empty() || res,
8480          "If list is not empty, we should have taken something");
8481   assert(!res || !_mark_stack->isEmpty(),
8482          "If we took something, it should now be on our stack");
8483   return res;
8484 }
8485 
8486 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
8487   size_t res = _sp->block_size_no_stall(addr, _collector);
8488   if (_sp->block_is_obj(addr)) {
8489     if (_live_bit_map->isMarked(addr)) {
8490       // It can't have been dead in a previous cycle
8491       guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
8492     } else {
8493       _dead_bit_map->mark(addr);      // mark the dead object
8494     }
8495   }
8496   // Could be 0, if the block size could not be computed without stalling.
8497   return res;
8498 }
8499 
8500 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() {
8501 
8502   switch (phase) {
8503     case CMSCollector::InitialMarking:
8504       initialize(true  /* fullGC */ ,
8505                  cause /* cause of the GC */,
8506                  true  /* recordGCBeginTime */,
8507                  true  /* recordPreGCUsage */,
8508                  false /* recordPeakUsage */,
8509                  false /* recordPostGCusage */,
8510                  true  /* recordAccumulatedGCTime */,
8511                  false /* recordGCEndTime */,
8512                  false /* countCollection */  );
8513       break;
8514 
8515     case CMSCollector::FinalMarking:
8516       initialize(true  /* fullGC */ ,
8517                  cause /* cause of the GC */,
8518                  false /* recordGCBeginTime */,
8519                  false /* recordPreGCUsage */,
8520                  false /* recordPeakUsage */,
8521                  false /* recordPostGCusage */,
8522                  true  /* recordAccumulatedGCTime */,
8523                  false /* recordGCEndTime */,
8524                  false /* countCollection */  );
8525       break;
8526 
8527     case CMSCollector::Sweeping:
8528       initialize(true  /* fullGC */ ,
8529                  cause /* cause of the GC */,
8530                  false /* recordGCBeginTime */,
8531                  false /* recordPreGCUsage */,
8532                  true  /* recordPeakUsage */,
8533                  true  /* recordPostGCusage */,
8534                  false /* recordAccumulatedGCTime */,
8535                  true  /* recordGCEndTime */,
8536                  true  /* countCollection */  );
8537       break;
8538 
8539     default:
8540       ShouldNotReachHere();
8541   }
8542 }