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_implementation/shared/adaptiveSizePolicy.hpp"
  31 #include "gc_implementation/concurrentMarkSweep/cmsCollectorPolicy.hpp"
  32 #include "gc_implementation/concurrentMarkSweep/cmsOopClosures.inline.hpp"
  33 #include "gc_implementation/concurrentMarkSweep/compactibleFreeListSpace.hpp"
  34 #include "gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.inline.hpp"
  35 #include "gc_implementation/concurrentMarkSweep/concurrentMarkSweepThread.hpp"
  36 #include "gc_implementation/concurrentMarkSweep/vmCMSOperations.hpp"
  37 #include "gc_implementation/parNew/parNewGeneration.hpp"
  38 #include "gc_implementation/shared/collectorCounters.hpp"
  39 #include "gc_implementation/shared/gcTimer.hpp"
  40 #include "gc_implementation/shared/gcTrace.hpp"
  41 #include "gc_implementation/shared/gcTraceTime.hpp"
  42 #include "gc_implementation/shared/isGCActiveMark.hpp"
  43 #include "gc_interface/collectedHeap.inline.hpp"
  44 #include "memory/allocation.hpp"
  45 #include "memory/cardGeneration.inline.hpp"
  46 #include "memory/cardTableRS.hpp"
  47 #include "memory/collectorPolicy.hpp"
  48 #include "memory/gcLocker.inline.hpp"
  49 #include "memory/genCollectedHeap.hpp"
  50 #include "memory/genMarkSweep.hpp"
  51 #include "memory/genOopClosures.inline.hpp"
  52 #include "memory/iterator.inline.hpp"
  53 #include "memory/padded.hpp"
  54 #include "memory/referencePolicy.hpp"
  55 #include "memory/resourceArea.hpp"
  56 #include "memory/strongRootsScope.hpp"
  57 #include "memory/tenuredGeneration.hpp"
  58 #include "oops/oop.inline.hpp"
  59 #include "prims/jvmtiExport.hpp"
  60 #include "runtime/atomic.inline.hpp"
  61 #include "runtime/globals_extension.hpp"
  62 #include "runtime/handles.inline.hpp"
  63 #include "runtime/java.hpp"
  64 #include "runtime/orderAccess.inline.hpp"
  65 #include "runtime/vmThread.hpp"
  66 #include "services/memoryService.hpp"
  67 #include "services/runtimeService.hpp"
  68 
  69 // statics
  70 CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL;
  71 bool CMSCollector::_full_gc_requested = false;
  72 GCCause::Cause CMSCollector::_full_gc_cause = GCCause::_no_gc;
  73 
  74 //////////////////////////////////////////////////////////////////
  75 // In support of CMS/VM thread synchronization
  76 //////////////////////////////////////////////////////////////////
  77 // We split use of the CGC_lock into 2 "levels".
  78 // The low-level locking is of the usual CGC_lock monitor. We introduce
  79 // a higher level "token" (hereafter "CMS token") built on top of the
  80 // low level monitor (hereafter "CGC lock").
  81 // The token-passing protocol gives priority to the VM thread. The
  82 // CMS-lock doesn't provide any fairness guarantees, but clients
  83 // should ensure that it is only held for very short, bounded
  84 // durations.
  85 //
  86 // When either of the CMS thread or the VM thread is involved in
  87 // collection operations during which it does not want the other
  88 // thread to interfere, it obtains the CMS token.
  89 //
  90 // If either thread tries to get the token while the other has
  91 // it, that thread waits. However, if the VM thread and CMS thread
  92 // both want the token, then the VM thread gets priority while the
  93 // CMS thread waits. This ensures, for instance, that the "concurrent"
  94 // phases of the CMS thread's work do not block out the VM thread
  95 // for long periods of time as the CMS thread continues to hog
  96 // the token. (See bug 4616232).
  97 //
  98 // The baton-passing functions are, however, controlled by the
  99 // flags _foregroundGCShouldWait and _foregroundGCIsActive,
 100 // and here the low-level CMS lock, not the high level token,
 101 // ensures mutual exclusion.
 102 //
 103 // Two important conditions that we have to satisfy:
 104 // 1. if a thread does a low-level wait on the CMS lock, then it
 105 //    relinquishes the CMS token if it were holding that token
 106 //    when it acquired the low-level CMS lock.
 107 // 2. any low-level notifications on the low-level lock
 108 //    should only be sent when a thread has relinquished the token.
 109 //
 110 // In the absence of either property, we'd have potential deadlock.
 111 //
 112 // We protect each of the CMS (concurrent and sequential) phases
 113 // with the CMS _token_, not the CMS _lock_.
 114 //
 115 // The only code protected by CMS lock is the token acquisition code
 116 // itself, see ConcurrentMarkSweepThread::[de]synchronize(), and the
 117 // baton-passing code.
 118 //
 119 // Unfortunately, i couldn't come up with a good abstraction to factor and
 120 // hide the naked CGC_lock manipulation in the baton-passing code
 121 // further below. That's something we should try to do. Also, the proof
 122 // of correctness of this 2-level locking scheme is far from obvious,
 123 // and potentially quite slippery. We have an uneasy suspicion, for instance,
 124 // that there may be a theoretical possibility of delay/starvation in the
 125 // low-level lock/wait/notify scheme used for the baton-passing because of
 126 // potential interference with the priority scheme embodied in the
 127 // CMS-token-passing protocol. See related comments at a CGC_lock->wait()
 128 // invocation further below and marked with "XXX 20011219YSR".
 129 // Indeed, as we note elsewhere, this may become yet more slippery
 130 // in the presence of multiple CMS and/or multiple VM threads. XXX
 131 
 132 class CMSTokenSync: public StackObj {
 133  private:
 134   bool _is_cms_thread;
 135  public:
 136   CMSTokenSync(bool is_cms_thread):
 137     _is_cms_thread(is_cms_thread) {
 138     assert(is_cms_thread == Thread::current()->is_ConcurrentGC_thread(),
 139            "Incorrect argument to constructor");
 140     ConcurrentMarkSweepThread::synchronize(_is_cms_thread);
 141   }
 142 
 143   ~CMSTokenSync() {
 144     assert(_is_cms_thread ?
 145              ConcurrentMarkSweepThread::cms_thread_has_cms_token() :
 146              ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
 147           "Incorrect state");
 148     ConcurrentMarkSweepThread::desynchronize(_is_cms_thread);
 149   }
 150 };
 151 
 152 // Convenience class that does a CMSTokenSync, and then acquires
 153 // upto three locks.
 154 class CMSTokenSyncWithLocks: public CMSTokenSync {
 155  private:
 156   // Note: locks are acquired in textual declaration order
 157   // and released in the opposite order
 158   MutexLockerEx _locker1, _locker2, _locker3;
 159  public:
 160   CMSTokenSyncWithLocks(bool is_cms_thread, Mutex* mutex1,
 161                         Mutex* mutex2 = NULL, Mutex* mutex3 = NULL):
 162     CMSTokenSync(is_cms_thread),
 163     _locker1(mutex1, Mutex::_no_safepoint_check_flag),
 164     _locker2(mutex2, Mutex::_no_safepoint_check_flag),
 165     _locker3(mutex3, Mutex::_no_safepoint_check_flag)
 166   { }
 167 };
 168 
 169 
 170 //////////////////////////////////////////////////////////////////
 171 //  Concurrent Mark-Sweep Generation /////////////////////////////
 172 //////////////////////////////////////////////////////////////////
 173 
 174 NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;)
 175 
 176 // This struct contains per-thread things necessary to support parallel
 177 // young-gen collection.
 178 class CMSParGCThreadState: public CHeapObj<mtGC> {
 179  public:
 180   CFLS_LAB lab;
 181   PromotionInfo promo;
 182 
 183   // Constructor.
 184   CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) {
 185     promo.setSpace(cfls);
 186   }
 187 };
 188 
 189 ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration(
 190      ReservedSpace rs, size_t initial_byte_size, int level,
 191      CardTableRS* ct, bool use_adaptive_freelists,
 192      FreeBlockDictionary<FreeChunk>::DictionaryChoice dictionaryChoice) :
 193   CardGeneration(rs, initial_byte_size, level, ct),
 194   _dilatation_factor(((double)MinChunkSize)/((double)(CollectedHeap::min_fill_size()))),
 195   _did_compact(false)
 196 {
 197   HeapWord* bottom = (HeapWord*) _virtual_space.low();
 198   HeapWord* end    = (HeapWord*) _virtual_space.high();
 199 
 200   _direct_allocated_words = 0;
 201   NOT_PRODUCT(
 202     _numObjectsPromoted = 0;
 203     _numWordsPromoted = 0;
 204     _numObjectsAllocated = 0;
 205     _numWordsAllocated = 0;
 206   )
 207 
 208   _cmsSpace = new CompactibleFreeListSpace(_bts, MemRegion(bottom, end),
 209                                            use_adaptive_freelists,
 210                                            dictionaryChoice);
 211   NOT_PRODUCT(debug_cms_space = _cmsSpace;)
 212   _cmsSpace->_gen = this;
 213 
 214   _gc_stats = new CMSGCStats();
 215 
 216   // Verify the assumption that FreeChunk::_prev and OopDesc::_klass
 217   // offsets match. The ability to tell free chunks from objects
 218   // depends on this property.
 219   debug_only(
 220     FreeChunk* junk = NULL;
 221     assert(UseCompressedClassPointers ||
 222            junk->prev_addr() == (void*)(oop(junk)->klass_addr()),
 223            "Offset of FreeChunk::_prev within FreeChunk must match"
 224            "  that of OopDesc::_klass within OopDesc");
 225   )
 226   if (CollectedHeap::use_parallel_gc_threads()) {
 227     typedef CMSParGCThreadState* CMSParGCThreadStatePtr;
 228     _par_gc_thread_states =
 229       NEW_C_HEAP_ARRAY(CMSParGCThreadStatePtr, ParallelGCThreads, mtGC);
 230     for (uint i = 0; i < ParallelGCThreads; i++) {
 231       _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace());
 232     }
 233   } else {
 234     _par_gc_thread_states = NULL;
 235   }
 236   _incremental_collection_failed = false;
 237   // The "dilatation_factor" is the expansion that can occur on
 238   // account of the fact that the minimum object size in the CMS
 239   // generation may be larger than that in, say, a contiguous young
 240   //  generation.
 241   // Ideally, in the calculation below, we'd compute the dilatation
 242   // factor as: MinChunkSize/(promoting_gen's min object size)
 243   // Since we do not have such a general query interface for the
 244   // promoting generation, we'll instead just use the minimum
 245   // object size (which today is a header's worth of space);
 246   // note that all arithmetic is in units of HeapWords.
 247   assert(MinChunkSize >= CollectedHeap::min_fill_size(), "just checking");
 248   assert(_dilatation_factor >= 1.0, "from previous assert");
 249 }
 250 
 251 
 252 // The field "_initiating_occupancy" represents the occupancy percentage
 253 // at which we trigger a new collection cycle.  Unless explicitly specified
 254 // via CMSInitiatingOccupancyFraction (argument "io" below), it
 255 // is calculated by:
 256 //
 257 //   Let "f" be MinHeapFreeRatio in
 258 //
 259 //    _initiating_occupancy = 100-f +
 260 //                           f * (CMSTriggerRatio/100)
 261 //   where CMSTriggerRatio is the argument "tr" below.
 262 //
 263 // That is, if we assume the heap is at its desired maximum occupancy at the
 264 // end of a collection, we let CMSTriggerRatio of the (purported) free
 265 // space be allocated before initiating a new collection cycle.
 266 //
 267 void ConcurrentMarkSweepGeneration::init_initiating_occupancy(intx io, uintx tr) {
 268   assert(io <= 100 && tr <= 100, "Check the arguments");
 269   if (io >= 0) {
 270     _initiating_occupancy = (double)io / 100.0;
 271   } else {
 272     _initiating_occupancy = ((100 - MinHeapFreeRatio) +
 273                              (double)(tr * MinHeapFreeRatio) / 100.0)
 274                             / 100.0;
 275   }
 276 }
 277 
 278 void ConcurrentMarkSweepGeneration::ref_processor_init() {
 279   assert(collector() != NULL, "no collector");
 280   collector()->ref_processor_init();
 281 }
 282 
 283 void CMSCollector::ref_processor_init() {
 284   if (_ref_processor == NULL) {
 285     // Allocate and initialize a reference processor
 286     _ref_processor =
 287       new ReferenceProcessor(_span,                               // span
 288                              (ParallelGCThreads > 1) && ParallelRefProcEnabled, // mt processing
 289                              (int) ParallelGCThreads,             // mt processing degree
 290                              _cmsGen->refs_discovery_is_mt(),     // mt discovery
 291                              (int) MAX2(ConcGCThreads, ParallelGCThreads), // mt discovery degree
 292                              _cmsGen->refs_discovery_is_atomic(), // discovery is not atomic
 293                              &_is_alive_closure);                 // closure for liveness info
 294     // Initialize the _ref_processor field of CMSGen
 295     _cmsGen->set_ref_processor(_ref_processor);
 296 
 297   }
 298 }
 299 
 300 AdaptiveSizePolicy* CMSCollector::size_policy() {
 301   GenCollectedHeap* gch = GenCollectedHeap::heap();
 302   assert(gch->kind() == CollectedHeap::GenCollectedHeap,
 303     "Wrong type of heap");
 304   return gch->gen_policy()->size_policy();
 305 }
 306 
 307 void ConcurrentMarkSweepGeneration::initialize_performance_counters() {
 308 
 309   const char* gen_name = "old";
 310   GenCollectorPolicy* gcp = (GenCollectorPolicy*) GenCollectedHeap::heap()->collector_policy();
 311 
 312   // Generation Counters - generation 1, 1 subspace
 313   _gen_counters = new GenerationCounters(gen_name, 1, 1,
 314       gcp->min_old_size(), gcp->max_old_size(), &_virtual_space);
 315 
 316   _space_counters = new GSpaceCounters(gen_name, 0,
 317                                        _virtual_space.reserved_size(),
 318                                        this, _gen_counters);
 319 }
 320 
 321 CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha):
 322   _cms_gen(cms_gen)
 323 {
 324   assert(alpha <= 100, "bad value");
 325   _saved_alpha = alpha;
 326 
 327   // Initialize the alphas to the bootstrap value of 100.
 328   _gc0_alpha = _cms_alpha = 100;
 329 
 330   _cms_begin_time.update();
 331   _cms_end_time.update();
 332 
 333   _gc0_duration = 0.0;
 334   _gc0_period = 0.0;
 335   _gc0_promoted = 0;
 336 
 337   _cms_duration = 0.0;
 338   _cms_period = 0.0;
 339   _cms_allocated = 0;
 340 
 341   _cms_used_at_gc0_begin = 0;
 342   _cms_used_at_gc0_end = 0;
 343   _allow_duty_cycle_reduction = false;
 344   _valid_bits = 0;
 345 }
 346 
 347 double CMSStats::cms_free_adjustment_factor(size_t free) const {
 348   // TBD: CR 6909490
 349   return 1.0;
 350 }
 351 
 352 void CMSStats::adjust_cms_free_adjustment_factor(bool fail, size_t free) {
 353 }
 354 
 355 // If promotion failure handling is on use
 356 // the padded average size of the promotion for each
 357 // young generation collection.
 358 double CMSStats::time_until_cms_gen_full() const {
 359   size_t cms_free = _cms_gen->cmsSpace()->free();
 360   GenCollectedHeap* gch = GenCollectedHeap::heap();
 361   size_t expected_promotion = MIN2(gch->young_gen()->capacity(),
 362                                    (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average());
 363   if (cms_free > expected_promotion) {
 364     // Start a cms collection if there isn't enough space to promote
 365     // for the next minor collection.  Use the padded average as
 366     // a safety factor.
 367     cms_free -= expected_promotion;
 368 
 369     // Adjust by the safety factor.
 370     double cms_free_dbl = (double)cms_free;
 371     double cms_adjustment = (100.0 - CMSIncrementalSafetyFactor)/100.0;
 372     // Apply a further correction factor which tries to adjust
 373     // for recent occurance of concurrent mode failures.
 374     cms_adjustment = cms_adjustment * cms_free_adjustment_factor(cms_free);
 375     cms_free_dbl = cms_free_dbl * cms_adjustment;
 376 
 377     if (PrintGCDetails && Verbose) {
 378       gclog_or_tty->print_cr("CMSStats::time_until_cms_gen_full: cms_free "
 379         SIZE_FORMAT " expected_promotion " SIZE_FORMAT,
 380         cms_free, expected_promotion);
 381       gclog_or_tty->print_cr("  cms_free_dbl %f cms_consumption_rate %f",
 382         cms_free_dbl, cms_consumption_rate() + 1.0);
 383     }
 384     // Add 1 in case the consumption rate goes to zero.
 385     return cms_free_dbl / (cms_consumption_rate() + 1.0);
 386   }
 387   return 0.0;
 388 }
 389 
 390 // Compare the duration of the cms collection to the
 391 // time remaining before the cms generation is empty.
 392 // Note that the time from the start of the cms collection
 393 // to the start of the cms sweep (less than the total
 394 // duration of the cms collection) can be used.  This
 395 // has been tried and some applications experienced
 396 // promotion failures early in execution.  This was
 397 // possibly because the averages were not accurate
 398 // enough at the beginning.
 399 double CMSStats::time_until_cms_start() const {
 400   // We add "gc0_period" to the "work" calculation
 401   // below because this query is done (mostly) at the
 402   // end of a scavenge, so we need to conservatively
 403   // account for that much possible delay
 404   // in the query so as to avoid concurrent mode failures
 405   // due to starting the collection just a wee bit too
 406   // late.
 407   double work = cms_duration() + gc0_period();
 408   double deadline = time_until_cms_gen_full();
 409   // If a concurrent mode failure occurred recently, we want to be
 410   // more conservative and halve our expected time_until_cms_gen_full()
 411   if (work > deadline) {
 412     if (Verbose && PrintGCDetails) {
 413       gclog_or_tty->print(
 414         " CMSCollector: collect because of anticipated promotion "
 415         "before full %3.7f + %3.7f > %3.7f ", cms_duration(),
 416         gc0_period(), time_until_cms_gen_full());
 417     }
 418     return 0.0;
 419   }
 420   return work - deadline;
 421 }
 422 
 423 #ifndef PRODUCT
 424 void CMSStats::print_on(outputStream *st) const {
 425   st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha);
 426   st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo=" SIZE_FORMAT,
 427                gc0_duration(), gc0_period(), gc0_promoted());
 428   st->print(",cms_dur=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT,
 429             cms_duration(), cms_period(), cms_allocated());
 430   st->print(",cms_since_beg=%g,cms_since_end=%g",
 431             cms_time_since_begin(), cms_time_since_end());
 432   st->print(",cms_used_beg=" SIZE_FORMAT ",cms_used_end=" SIZE_FORMAT,
 433             _cms_used_at_gc0_begin, _cms_used_at_gc0_end);
 434 
 435   if (valid()) {
 436     st->print(",promo_rate=%g,cms_alloc_rate=%g",
 437               promotion_rate(), cms_allocation_rate());
 438     st->print(",cms_consumption_rate=%g,time_until_full=%g",
 439               cms_consumption_rate(), time_until_cms_gen_full());
 440   }
 441   st->print(" ");
 442 }
 443 #endif // #ifndef PRODUCT
 444 
 445 CMSCollector::CollectorState CMSCollector::_collectorState =
 446                              CMSCollector::Idling;
 447 bool CMSCollector::_foregroundGCIsActive = false;
 448 bool CMSCollector::_foregroundGCShouldWait = false;
 449 
 450 CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
 451                            CardTableRS*                   ct,
 452                            ConcurrentMarkSweepPolicy*     cp):
 453   _cmsGen(cmsGen),
 454   _ct(ct),
 455   _ref_processor(NULL),    // will be set later
 456   _conc_workers(NULL),     // may be set later
 457   _abort_preclean(false),
 458   _start_sampling(false),
 459   _between_prologue_and_epilogue(false),
 460   _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"),
 461   _modUnionTable((CardTableModRefBS::card_shift - LogHeapWordSize),
 462                  -1 /* lock-free */, "No_lock" /* dummy */),
 463   _modUnionClosure(&_modUnionTable),
 464   _modUnionClosurePar(&_modUnionTable),
 465   // Adjust my span to cover old (cms) gen
 466   _span(cmsGen->reserved()),
 467   // Construct the is_alive_closure with _span & markBitMap
 468   _is_alive_closure(_span, &_markBitMap),
 469   _restart_addr(NULL),
 470   _overflow_list(NULL),
 471   _stats(cmsGen),
 472   _eden_chunk_lock(new Mutex(Mutex::leaf + 1, "CMS_eden_chunk_lock", true,
 473                              //verify that this lock should be acquired with safepoint check.
 474                              Monitor::_safepoint_check_sometimes)),
 475   _eden_chunk_array(NULL),     // may be set in ctor body
 476   _eden_chunk_capacity(0),     // -- ditto --
 477   _eden_chunk_index(0),        // -- ditto --
 478   _survivor_plab_array(NULL),  // -- ditto --
 479   _survivor_chunk_array(NULL), // -- ditto --
 480   _survivor_chunk_capacity(0), // -- ditto --
 481   _survivor_chunk_index(0),    // -- ditto --
 482   _ser_pmc_preclean_ovflw(0),
 483   _ser_kac_preclean_ovflw(0),
 484   _ser_pmc_remark_ovflw(0),
 485   _par_pmc_remark_ovflw(0),
 486   _ser_kac_ovflw(0),
 487   _par_kac_ovflw(0),
 488 #ifndef PRODUCT
 489   _num_par_pushes(0),
 490 #endif
 491   _collection_count_start(0),
 492   _verifying(false),
 493   _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"),
 494   _completed_initialization(false),
 495   _collector_policy(cp),
 496   _should_unload_classes(CMSClassUnloadingEnabled),
 497   _concurrent_cycles_since_last_unload(0),
 498   _roots_scanning_options(GenCollectedHeap::SO_None),
 499   _inter_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
 500   _intra_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
 501   _gc_tracer_cm(new (ResourceObj::C_HEAP, mtGC) CMSTracer()),
 502   _gc_timer_cm(new (ResourceObj::C_HEAP, mtGC) ConcurrentGCTimer()),
 503   _cms_start_registered(false)
 504 {
 505   if (ExplicitGCInvokesConcurrentAndUnloadsClasses) {
 506     ExplicitGCInvokesConcurrent = true;
 507   }
 508   // Now expand the span and allocate the collection support structures
 509   // (MUT, marking bit map etc.) to cover both generations subject to
 510   // collection.
 511 
 512   // For use by dirty card to oop closures.
 513   _cmsGen->cmsSpace()->set_collector(this);
 514 
 515   // Allocate MUT and marking bit map
 516   {
 517     MutexLockerEx x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag);
 518     if (!_markBitMap.allocate(_span)) {
 519       warning("Failed to allocate CMS Bit Map");
 520       return;
 521     }
 522     assert(_markBitMap.covers(_span), "_markBitMap inconsistency?");
 523   }
 524   {
 525     _modUnionTable.allocate(_span);
 526     assert(_modUnionTable.covers(_span), "_modUnionTable inconsistency?");
 527   }
 528 
 529   if (!_markStack.allocate(MarkStackSize)) {
 530     warning("Failed to allocate CMS Marking Stack");
 531     return;
 532   }
 533 
 534   // Support for multi-threaded concurrent phases
 535   if (CMSConcurrentMTEnabled) {
 536     if (FLAG_IS_DEFAULT(ConcGCThreads)) {
 537       // just for now
 538       FLAG_SET_DEFAULT(ConcGCThreads, (ParallelGCThreads + 3)/4);
 539     }
 540     if (ConcGCThreads > 1) {
 541       _conc_workers = new YieldingFlexibleWorkGang("CMS Thread",
 542                                  ConcGCThreads, true);
 543       if (_conc_workers == NULL) {
 544         warning("GC/CMS: _conc_workers allocation failure: "
 545               "forcing -CMSConcurrentMTEnabled");
 546         CMSConcurrentMTEnabled = false;
 547       } else {
 548         _conc_workers->initialize_workers();
 549       }
 550     } else {
 551       CMSConcurrentMTEnabled = false;
 552     }
 553   }
 554   if (!CMSConcurrentMTEnabled) {
 555     ConcGCThreads = 0;
 556   } else {
 557     // Turn off CMSCleanOnEnter optimization temporarily for
 558     // the MT case where it's not fixed yet; see 6178663.
 559     CMSCleanOnEnter = false;
 560   }
 561   assert((_conc_workers != NULL) == (ConcGCThreads > 1),
 562          "Inconsistency");
 563 
 564   // Parallel task queues; these are shared for the
 565   // concurrent and stop-world phases of CMS, but
 566   // are not shared with parallel scavenge (ParNew).
 567   {
 568     uint i;
 569     uint num_queues = (uint) MAX2(ParallelGCThreads, ConcGCThreads);
 570 
 571     if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled
 572          || ParallelRefProcEnabled)
 573         && num_queues > 0) {
 574       _task_queues = new OopTaskQueueSet(num_queues);
 575       if (_task_queues == NULL) {
 576         warning("task_queues allocation failure.");
 577         return;
 578       }
 579       _hash_seed = NEW_C_HEAP_ARRAY(int, num_queues, mtGC);
 580       typedef Padded<OopTaskQueue> PaddedOopTaskQueue;
 581       for (i = 0; i < num_queues; i++) {
 582         PaddedOopTaskQueue *q = new PaddedOopTaskQueue();
 583         if (q == NULL) {
 584           warning("work_queue allocation failure.");
 585           return;
 586         }
 587         _task_queues->register_queue(i, q);
 588       }
 589       for (i = 0; i < num_queues; i++) {
 590         _task_queues->queue(i)->initialize();
 591         _hash_seed[i] = 17;  // copied from ParNew
 592       }
 593     }
 594   }
 595 
 596   _cmsGen ->init_initiating_occupancy(CMSInitiatingOccupancyFraction, CMSTriggerRatio);
 597 
 598   // Clip CMSBootstrapOccupancy between 0 and 100.
 599   _bootstrap_occupancy = ((double)CMSBootstrapOccupancy)/(double)100;
 600 
 601   // Now tell CMS generations the identity of their collector
 602   ConcurrentMarkSweepGeneration::set_collector(this);
 603 
 604   // Create & start a CMS thread for this CMS collector
 605   _cmsThread = ConcurrentMarkSweepThread::start(this);
 606   assert(cmsThread() != NULL, "CMS Thread should have been created");
 607   assert(cmsThread()->collector() == this,
 608          "CMS Thread should refer to this gen");
 609   assert(CGC_lock != NULL, "Where's the CGC_lock?");
 610 
 611   // Support for parallelizing young gen rescan
 612   GenCollectedHeap* gch = GenCollectedHeap::heap();
 613   assert(gch->young_gen()->kind() == Generation::ParNew, "CMS can only be used with ParNew");
 614   _young_gen = (ParNewGeneration*)gch->young_gen();
 615   if (gch->supports_inline_contig_alloc()) {
 616     _top_addr = gch->top_addr();
 617     _end_addr = gch->end_addr();
 618     assert(_young_gen != NULL, "no _young_gen");
 619     _eden_chunk_index = 0;
 620     _eden_chunk_capacity = (_young_gen->max_capacity()+CMSSamplingGrain)/CMSSamplingGrain;
 621     _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity, mtGC);
 622   }
 623 
 624   // Support for parallelizing survivor space rescan
 625   if ((CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) || CMSParallelInitialMarkEnabled) {
 626     const size_t max_plab_samples =
 627       ((DefNewGeneration*)_young_gen)->max_survivor_size() / plab_sample_minimum_size();
 628 
 629     _survivor_plab_array  = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads, mtGC);
 630     _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, 2*max_plab_samples, mtGC);
 631     _cursor               = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads, mtGC);
 632     _survivor_chunk_capacity = 2*max_plab_samples;
 633     for (uint i = 0; i < ParallelGCThreads; i++) {
 634       HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
 635       ChunkArray* cur = ::new (&_survivor_plab_array[i]) ChunkArray(vec, max_plab_samples);
 636       assert(cur->end() == 0, "Should be 0");
 637       assert(cur->array() == vec, "Should be vec");
 638       assert(cur->capacity() == max_plab_samples, "Error");
 639     }
 640   }
 641 
 642   NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;)
 643   _gc_counters = new CollectorCounters("CMS", 1);
 644   _completed_initialization = true;
 645   _inter_sweep_timer.start();  // start of time
 646 }
 647 
 648 size_t CMSCollector::plab_sample_minimum_size() {
 649   // The default value of MinTLABSize is 2k, but there is
 650   // no way to get the default value if the flag has been overridden.
 651   return MAX2(ThreadLocalAllocBuffer::min_size() * HeapWordSize, 2 * K);
 652 }
 653 
 654 const char* ConcurrentMarkSweepGeneration::name() const {
 655   return "concurrent mark-sweep generation";
 656 }
 657 void ConcurrentMarkSweepGeneration::update_counters() {
 658   if (UsePerfData) {
 659     _space_counters->update_all();
 660     _gen_counters->update_all();
 661   }
 662 }
 663 
 664 // this is an optimized version of update_counters(). it takes the
 665 // used value as a parameter rather than computing it.
 666 //
 667 void ConcurrentMarkSweepGeneration::update_counters(size_t used) {
 668   if (UsePerfData) {
 669     _space_counters->update_used(used);
 670     _space_counters->update_capacity();
 671     _gen_counters->update_all();
 672   }
 673 }
 674 
 675 void ConcurrentMarkSweepGeneration::print() const {
 676   Generation::print();
 677   cmsSpace()->print();
 678 }
 679 
 680 #ifndef PRODUCT
 681 void ConcurrentMarkSweepGeneration::print_statistics() {
 682   cmsSpace()->printFLCensus(0);
 683 }
 684 #endif
 685 
 686 void ConcurrentMarkSweepGeneration::printOccupancy(const char *s) {
 687   GenCollectedHeap* gch = GenCollectedHeap::heap();
 688   if (PrintGCDetails) {
 689     if (Verbose) {
 690       gclog_or_tty->print("[%d %s-%s: "SIZE_FORMAT"("SIZE_FORMAT")]",
 691         level(), short_name(), s, used(), capacity());
 692     } else {
 693       gclog_or_tty->print("[%d %s-%s: "SIZE_FORMAT"K("SIZE_FORMAT"K)]",
 694         level(), short_name(), s, used() / K, capacity() / K);
 695     }
 696   }
 697   if (Verbose) {
 698     gclog_or_tty->print(" "SIZE_FORMAT"("SIZE_FORMAT")",
 699               gch->used(), gch->capacity());
 700   } else {
 701     gclog_or_tty->print(" "SIZE_FORMAT"K("SIZE_FORMAT"K)",
 702               gch->used() / K, gch->capacity() / K);
 703   }
 704 }
 705 
 706 size_t
 707 ConcurrentMarkSweepGeneration::contiguous_available() const {
 708   // dld proposes an improvement in precision here. If the committed
 709   // part of the space ends in a free block we should add that to
 710   // uncommitted size in the calculation below. Will make this
 711   // change later, staying with the approximation below for the
 712   // time being. -- ysr.
 713   return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc());
 714 }
 715 
 716 size_t
 717 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const {
 718   return _cmsSpace->max_alloc_in_words() * HeapWordSize;
 719 }
 720 
 721 size_t ConcurrentMarkSweepGeneration::max_available() const {
 722   return free() + _virtual_space.uncommitted_size();
 723 }
 724 
 725 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(size_t max_promotion_in_bytes) const {
 726   size_t available = max_available();
 727   size_t av_promo  = (size_t)gc_stats()->avg_promoted()->padded_average();
 728   bool   res = (available >= av_promo) || (available >= max_promotion_in_bytes);
 729   if (Verbose && PrintGCDetails) {
 730     gclog_or_tty->print_cr(
 731       "CMS: promo attempt is%s safe: available("SIZE_FORMAT") %s av_promo("SIZE_FORMAT"),"
 732       "max_promo("SIZE_FORMAT")",
 733       res? "":" not", available, res? ">=":"<",
 734       av_promo, max_promotion_in_bytes);
 735   }
 736   return res;
 737 }
 738 
 739 // At a promotion failure dump information on block layout in heap
 740 // (cms old generation).
 741 void ConcurrentMarkSweepGeneration::promotion_failure_occurred() {
 742   if (CMSDumpAtPromotionFailure) {
 743     cmsSpace()->dump_at_safepoint_with_locks(collector(), gclog_or_tty);
 744   }
 745 }
 746 
 747 void ConcurrentMarkSweepGeneration::reset_after_compaction() {
 748   // Clear the promotion information.  These pointers can be adjusted
 749   // along with all the other pointers into the heap but
 750   // compaction is expected to be a rare event with
 751   // a heap using cms so don't do it without seeing the need.
 752   for (uint i = 0; i < ParallelGCThreads; i++) {
 753     _par_gc_thread_states[i]->promo.reset();
 754   }
 755 }
 756 
 757 void ConcurrentMarkSweepGeneration::compute_new_size() {
 758   assert_locked_or_safepoint(Heap_lock);
 759 
 760   // If incremental collection failed, we just want to expand
 761   // to the limit.
 762   if (incremental_collection_failed()) {
 763     clear_incremental_collection_failed();
 764     grow_to_reserved();
 765     return;
 766   }
 767 
 768   // The heap has been compacted but not reset yet.
 769   // Any metric such as free() or used() will be incorrect.
 770 
 771   CardGeneration::compute_new_size();
 772 
 773   // Reset again after a possible resizing
 774   if (did_compact()) {
 775     cmsSpace()->reset_after_compaction();
 776   }
 777 }
 778 
 779 void ConcurrentMarkSweepGeneration::compute_new_size_free_list() {
 780   assert_locked_or_safepoint(Heap_lock);
 781 
 782   // If incremental collection failed, we just want to expand
 783   // to the limit.
 784   if (incremental_collection_failed()) {
 785     clear_incremental_collection_failed();
 786     grow_to_reserved();
 787     return;
 788   }
 789 
 790   double free_percentage = ((double) free()) / capacity();
 791   double desired_free_percentage = (double) MinHeapFreeRatio / 100;
 792   double maximum_free_percentage = (double) MaxHeapFreeRatio / 100;
 793 
 794   // compute expansion delta needed for reaching desired free percentage
 795   if (free_percentage < desired_free_percentage) {
 796     size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
 797     assert(desired_capacity >= capacity(), "invalid expansion size");
 798     size_t expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes);
 799     if (PrintGCDetails && Verbose) {
 800       size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
 801       gclog_or_tty->print_cr("\nFrom compute_new_size: ");
 802       gclog_or_tty->print_cr("  Free fraction %f", free_percentage);
 803       gclog_or_tty->print_cr("  Desired free fraction %f",
 804         desired_free_percentage);
 805       gclog_or_tty->print_cr("  Maximum free fraction %f",
 806         maximum_free_percentage);
 807       gclog_or_tty->print_cr("  Capacity "SIZE_FORMAT, capacity()/1000);
 808       gclog_or_tty->print_cr("  Desired capacity "SIZE_FORMAT,
 809         desired_capacity/1000);
 810       int prev_level = level() - 1;
 811       if (prev_level >= 0) {
 812         size_t prev_size = 0;
 813         GenCollectedHeap* gch = GenCollectedHeap::heap();
 814         Generation* prev_gen = gch->young_gen();
 815         prev_size = prev_gen->capacity();
 816           gclog_or_tty->print_cr("  Younger gen size "SIZE_FORMAT,
 817                                  prev_size/1000);
 818       }
 819       gclog_or_tty->print_cr("  unsafe_max_alloc_nogc "SIZE_FORMAT,
 820         unsafe_max_alloc_nogc()/1000);
 821       gclog_or_tty->print_cr("  contiguous available "SIZE_FORMAT,
 822         contiguous_available()/1000);
 823       gclog_or_tty->print_cr("  Expand by "SIZE_FORMAT" (bytes)",
 824         expand_bytes);
 825     }
 826     // safe if expansion fails
 827     expand_for_gc_cause(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio);
 828     if (PrintGCDetails && Verbose) {
 829       gclog_or_tty->print_cr("  Expanded free fraction %f",
 830         ((double) free()) / capacity());
 831     }
 832   } else {
 833     size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
 834     assert(desired_capacity <= capacity(), "invalid expansion size");
 835     size_t shrink_bytes = capacity() - desired_capacity;
 836     // Don't shrink unless the delta is greater than the minimum shrink we want
 837     if (shrink_bytes >= MinHeapDeltaBytes) {
 838       shrink_free_list_by(shrink_bytes);
 839     }
 840   }
 841 }
 842 
 843 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const {
 844   return cmsSpace()->freelistLock();
 845 }
 846 
 847 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size,
 848                                                   bool   tlab) {
 849   CMSSynchronousYieldRequest yr;
 850   MutexLockerEx x(freelistLock(),
 851                   Mutex::_no_safepoint_check_flag);
 852   return have_lock_and_allocate(size, tlab);
 853 }
 854 
 855 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size,
 856                                                   bool   tlab /* ignored */) {
 857   assert_lock_strong(freelistLock());
 858   size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size);
 859   HeapWord* res = cmsSpace()->allocate(adjustedSize);
 860   // Allocate the object live (grey) if the background collector has
 861   // started marking. This is necessary because the marker may
 862   // have passed this address and consequently this object will
 863   // not otherwise be greyed and would be incorrectly swept up.
 864   // Note that if this object contains references, the writing
 865   // of those references will dirty the card containing this object
 866   // allowing the object to be blackened (and its references scanned)
 867   // either during a preclean phase or at the final checkpoint.
 868   if (res != NULL) {
 869     // We may block here with an uninitialized object with
 870     // its mark-bit or P-bits not yet set. Such objects need
 871     // to be safely navigable by block_start().
 872     assert(oop(res)->klass_or_null() == NULL, "Object should be uninitialized here.");
 873     assert(!((FreeChunk*)res)->is_free(), "Error, block will look free but show wrong size");
 874     collector()->direct_allocated(res, adjustedSize);
 875     _direct_allocated_words += adjustedSize;
 876     // allocation counters
 877     NOT_PRODUCT(
 878       _numObjectsAllocated++;
 879       _numWordsAllocated += (int)adjustedSize;
 880     )
 881   }
 882   return res;
 883 }
 884 
 885 // In the case of direct allocation by mutators in a generation that
 886 // is being concurrently collected, the object must be allocated
 887 // live (grey) if the background collector has started marking.
 888 // This is necessary because the marker may
 889 // have passed this address and consequently this object will
 890 // not otherwise be greyed and would be incorrectly swept up.
 891 // Note that if this object contains references, the writing
 892 // of those references will dirty the card containing this object
 893 // allowing the object to be blackened (and its references scanned)
 894 // either during a preclean phase or at the final checkpoint.
 895 void CMSCollector::direct_allocated(HeapWord* start, size_t size) {
 896   assert(_markBitMap.covers(start, size), "Out of bounds");
 897   if (_collectorState >= Marking) {
 898     MutexLockerEx y(_markBitMap.lock(),
 899                     Mutex::_no_safepoint_check_flag);
 900     // [see comments preceding SweepClosure::do_blk() below for details]
 901     //
 902     // Can the P-bits be deleted now?  JJJ
 903     //
 904     // 1. need to mark the object as live so it isn't collected
 905     // 2. need to mark the 2nd bit to indicate the object may be uninitialized
 906     // 3. need to mark the end of the object so marking, precleaning or sweeping
 907     //    can skip over uninitialized or unparsable objects. An allocated
 908     //    object is considered uninitialized for our purposes as long as
 909     //    its klass word is NULL.  All old gen objects are parsable
 910     //    as soon as they are initialized.)
 911     _markBitMap.mark(start);          // object is live
 912     _markBitMap.mark(start + 1);      // object is potentially uninitialized?
 913     _markBitMap.mark(start + size - 1);
 914                                       // mark end of object
 915   }
 916   // check that oop looks uninitialized
 917   assert(oop(start)->klass_or_null() == NULL, "_klass should be NULL");
 918 }
 919 
 920 void CMSCollector::promoted(bool par, HeapWord* start,
 921                             bool is_obj_array, size_t obj_size) {
 922   assert(_markBitMap.covers(start), "Out of bounds");
 923   // See comment in direct_allocated() about when objects should
 924   // be allocated live.
 925   if (_collectorState >= Marking) {
 926     // we already hold the marking bit map lock, taken in
 927     // the prologue
 928     if (par) {
 929       _markBitMap.par_mark(start);
 930     } else {
 931       _markBitMap.mark(start);
 932     }
 933     // We don't need to mark the object as uninitialized (as
 934     // in direct_allocated above) because this is being done with the
 935     // world stopped and the object will be initialized by the
 936     // time the marking, precleaning or sweeping get to look at it.
 937     // But see the code for copying objects into the CMS generation,
 938     // where we need to ensure that concurrent readers of the
 939     // block offset table are able to safely navigate a block that
 940     // is in flux from being free to being allocated (and in
 941     // transition while being copied into) and subsequently
 942     // becoming a bona-fide object when the copy/promotion is complete.
 943     assert(SafepointSynchronize::is_at_safepoint(),
 944            "expect promotion only at safepoints");
 945 
 946     if (_collectorState < Sweeping) {
 947       // Mark the appropriate cards in the modUnionTable, so that
 948       // this object gets scanned before the sweep. If this is
 949       // not done, CMS generation references in the object might
 950       // not get marked.
 951       // For the case of arrays, which are otherwise precisely
 952       // marked, we need to dirty the entire array, not just its head.
 953       if (is_obj_array) {
 954         // The [par_]mark_range() method expects mr.end() below to
 955         // be aligned to the granularity of a bit's representation
 956         // in the heap. In the case of the MUT below, that's a
 957         // card size.
 958         MemRegion mr(start,
 959                      (HeapWord*)round_to((intptr_t)(start + obj_size),
 960                         CardTableModRefBS::card_size /* bytes */));
 961         if (par) {
 962           _modUnionTable.par_mark_range(mr);
 963         } else {
 964           _modUnionTable.mark_range(mr);
 965         }
 966       } else {  // not an obj array; we can just mark the head
 967         if (par) {
 968           _modUnionTable.par_mark(start);
 969         } else {
 970           _modUnionTable.mark(start);
 971         }
 972       }
 973     }
 974   }
 975 }
 976 
 977 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size) {
 978   assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
 979   // allocate, copy and if necessary update promoinfo --
 980   // delegate to underlying space.
 981   assert_lock_strong(freelistLock());
 982 
 983 #ifndef PRODUCT
 984   if (Universe::heap()->promotion_should_fail()) {
 985     return NULL;
 986   }
 987 #endif  // #ifndef PRODUCT
 988 
 989   oop res = _cmsSpace->promote(obj, obj_size);
 990   if (res == NULL) {
 991     // expand and retry
 992     size_t s = _cmsSpace->expansionSpaceRequired(obj_size);  // HeapWords
 993     expand_for_gc_cause(s*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_promotion);
 994     // Since this is the old generation, we don't try to promote
 995     // into a more senior generation.
 996     res = _cmsSpace->promote(obj, obj_size);
 997   }
 998   if (res != NULL) {
 999     // See comment in allocate() about when objects should
1000     // be allocated live.
1001     assert(obj->is_oop(), "Will dereference klass pointer below");
1002     collector()->promoted(false,           // Not parallel
1003                           (HeapWord*)res, obj->is_objArray(), obj_size);
1004     // promotion counters
1005     NOT_PRODUCT(
1006       _numObjectsPromoted++;
1007       _numWordsPromoted +=
1008         (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size()));
1009     )
1010   }
1011   return res;
1012 }
1013 
1014 
1015 // IMPORTANT: Notes on object size recognition in CMS.
1016 // ---------------------------------------------------
1017 // A block of storage in the CMS generation is always in
1018 // one of three states. A free block (FREE), an allocated
1019 // object (OBJECT) whose size() method reports the correct size,
1020 // and an intermediate state (TRANSIENT) in which its size cannot
1021 // be accurately determined.
1022 // STATE IDENTIFICATION:   (32 bit and 64 bit w/o COOPS)
1023 // -----------------------------------------------------
1024 // FREE:      klass_word & 1 == 1; mark_word holds block size
1025 //
1026 // OBJECT:    klass_word installed; klass_word != 0 && klass_word & 1 == 0;
1027 //            obj->size() computes correct size
1028 //
1029 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1030 //
1031 // STATE IDENTIFICATION: (64 bit+COOPS)
1032 // ------------------------------------
1033 // FREE:      mark_word & CMS_FREE_BIT == 1; mark_word & ~CMS_FREE_BIT gives block_size
1034 //
1035 // OBJECT:    klass_word installed; klass_word != 0;
1036 //            obj->size() computes correct size
1037 //
1038 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1039 //
1040 //
1041 // STATE TRANSITION DIAGRAM
1042 //
1043 //        mut / parnew                     mut  /  parnew
1044 // FREE --------------------> TRANSIENT ---------------------> OBJECT --|
1045 //  ^                                                                   |
1046 //  |------------------------ DEAD <------------------------------------|
1047 //         sweep                            mut
1048 //
1049 // While a block is in TRANSIENT state its size cannot be determined
1050 // so readers will either need to come back later or stall until
1051 // the size can be determined. Note that for the case of direct
1052 // allocation, P-bits, when available, may be used to determine the
1053 // size of an object that may not yet have been initialized.
1054 
1055 // Things to support parallel young-gen collection.
1056 oop
1057 ConcurrentMarkSweepGeneration::par_promote(int thread_num,
1058                                            oop old, markOop m,
1059                                            size_t word_sz) {
1060 #ifndef PRODUCT
1061   if (Universe::heap()->promotion_should_fail()) {
1062     return NULL;
1063   }
1064 #endif  // #ifndef PRODUCT
1065 
1066   CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1067   PromotionInfo* promoInfo = &ps->promo;
1068   // if we are tracking promotions, then first ensure space for
1069   // promotion (including spooling space for saving header if necessary).
1070   // then allocate and copy, then track promoted info if needed.
1071   // When tracking (see PromotionInfo::track()), the mark word may
1072   // be displaced and in this case restoration of the mark word
1073   // occurs in the (oop_since_save_marks_)iterate phase.
1074   if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) {
1075     // Out of space for allocating spooling buffers;
1076     // try expanding and allocating spooling buffers.
1077     if (!expand_and_ensure_spooling_space(promoInfo)) {
1078       return NULL;
1079     }
1080   }
1081   assert(promoInfo->has_spooling_space(), "Control point invariant");
1082   const size_t alloc_sz = CompactibleFreeListSpace::adjustObjectSize(word_sz);
1083   HeapWord* obj_ptr = ps->lab.alloc(alloc_sz);
1084   if (obj_ptr == NULL) {
1085      obj_ptr = expand_and_par_lab_allocate(ps, alloc_sz);
1086      if (obj_ptr == NULL) {
1087        return NULL;
1088      }
1089   }
1090   oop obj = oop(obj_ptr);
1091   OrderAccess::storestore();
1092   assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1093   assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1094   // IMPORTANT: See note on object initialization for CMS above.
1095   // Otherwise, copy the object.  Here we must be careful to insert the
1096   // klass pointer last, since this marks the block as an allocated object.
1097   // Except with compressed oops it's the mark word.
1098   HeapWord* old_ptr = (HeapWord*)old;
1099   // Restore the mark word copied above.
1100   obj->set_mark(m);
1101   assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1102   assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1103   OrderAccess::storestore();
1104 
1105   if (UseCompressedClassPointers) {
1106     // Copy gap missed by (aligned) header size calculation below
1107     obj->set_klass_gap(old->klass_gap());
1108   }
1109   if (word_sz > (size_t)oopDesc::header_size()) {
1110     Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1111                                  obj_ptr + oopDesc::header_size(),
1112                                  word_sz - oopDesc::header_size());
1113   }
1114 
1115   // Now we can track the promoted object, if necessary.  We take care
1116   // to delay the transition from uninitialized to full object
1117   // (i.e., insertion of klass pointer) until after, so that it
1118   // atomically becomes a promoted object.
1119   if (promoInfo->tracking()) {
1120     promoInfo->track((PromotedObject*)obj, old->klass());
1121   }
1122   assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1123   assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1124   assert(old->is_oop(), "Will use and dereference old klass ptr below");
1125 
1126   // Finally, install the klass pointer (this should be volatile).
1127   OrderAccess::storestore();
1128   obj->set_klass(old->klass());
1129   // We should now be able to calculate the right size for this object
1130   assert(obj->is_oop() && obj->size() == (int)word_sz, "Error, incorrect size computed for promoted object");
1131 
1132   collector()->promoted(true,          // parallel
1133                         obj_ptr, old->is_objArray(), word_sz);
1134 
1135   NOT_PRODUCT(
1136     Atomic::inc_ptr(&_numObjectsPromoted);
1137     Atomic::add_ptr(alloc_sz, &_numWordsPromoted);
1138   )
1139 
1140   return obj;
1141 }
1142 
1143 void
1144 ConcurrentMarkSweepGeneration::
1145 par_promote_alloc_done(int thread_num) {
1146   CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1147   ps->lab.retire(thread_num);
1148 }
1149 
1150 void
1151 ConcurrentMarkSweepGeneration::
1152 par_oop_since_save_marks_iterate_done(int thread_num) {
1153   CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1154   ParScanWithoutBarrierClosure* dummy_cl = NULL;
1155   ps->promo.promoted_oops_iterate_nv(dummy_cl);
1156 }
1157 
1158 bool ConcurrentMarkSweepGeneration::should_collect(bool   full,
1159                                                    size_t size,
1160                                                    bool   tlab)
1161 {
1162   // We allow a STW collection only if a full
1163   // collection was requested.
1164   return full || should_allocate(size, tlab); // FIX ME !!!
1165   // This and promotion failure handling are connected at the
1166   // hip and should be fixed by untying them.
1167 }
1168 
1169 bool CMSCollector::shouldConcurrentCollect() {
1170   if (_full_gc_requested) {
1171     if (Verbose && PrintGCDetails) {
1172       gclog_or_tty->print_cr("CMSCollector: collect because of explicit "
1173                              " gc request (or gc_locker)");
1174     }
1175     return true;
1176   }
1177 
1178   FreelistLocker x(this);
1179   // ------------------------------------------------------------------
1180   // Print out lots of information which affects the initiation of
1181   // a collection.
1182   if (PrintCMSInitiationStatistics && stats().valid()) {
1183     gclog_or_tty->print("CMSCollector shouldConcurrentCollect: ");
1184     gclog_or_tty->stamp();
1185     gclog_or_tty->cr();
1186     stats().print_on(gclog_or_tty);
1187     gclog_or_tty->print_cr("time_until_cms_gen_full %3.7f",
1188       stats().time_until_cms_gen_full());
1189     gclog_or_tty->print_cr("free="SIZE_FORMAT, _cmsGen->free());
1190     gclog_or_tty->print_cr("contiguous_available="SIZE_FORMAT,
1191                            _cmsGen->contiguous_available());
1192     gclog_or_tty->print_cr("promotion_rate=%g", stats().promotion_rate());
1193     gclog_or_tty->print_cr("cms_allocation_rate=%g", stats().cms_allocation_rate());
1194     gclog_or_tty->print_cr("occupancy=%3.7f", _cmsGen->occupancy());
1195     gclog_or_tty->print_cr("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy());
1196     gclog_or_tty->print_cr("cms_time_since_begin=%3.7f", stats().cms_time_since_begin());
1197     gclog_or_tty->print_cr("cms_time_since_end=%3.7f", stats().cms_time_since_end());
1198     gclog_or_tty->print_cr("metadata initialized %d",
1199       MetaspaceGC::should_concurrent_collect());
1200   }
1201   // ------------------------------------------------------------------
1202 
1203   // If the estimated time to complete a cms collection (cms_duration())
1204   // is less than the estimated time remaining until the cms generation
1205   // is full, start a collection.
1206   if (!UseCMSInitiatingOccupancyOnly) {
1207     if (stats().valid()) {
1208       if (stats().time_until_cms_start() == 0.0) {
1209         return true;
1210       }
1211     } else {
1212       // We want to conservatively collect somewhat early in order
1213       // to try and "bootstrap" our CMS/promotion statistics;
1214       // this branch will not fire after the first successful CMS
1215       // collection because the stats should then be valid.
1216       if (_cmsGen->occupancy() >= _bootstrap_occupancy) {
1217         if (Verbose && PrintGCDetails) {
1218           gclog_or_tty->print_cr(
1219             " CMSCollector: collect for bootstrapping statistics:"
1220             " occupancy = %f, boot occupancy = %f", _cmsGen->occupancy(),
1221             _bootstrap_occupancy);
1222         }
1223         return true;
1224       }
1225     }
1226   }
1227 
1228   // Otherwise, we start a collection cycle if
1229   // old gen want a collection cycle started. Each may use
1230   // an appropriate criterion for making this decision.
1231   // XXX We need to make sure that the gen expansion
1232   // criterion dovetails well with this. XXX NEED TO FIX THIS
1233   if (_cmsGen->should_concurrent_collect()) {
1234     if (Verbose && PrintGCDetails) {
1235       gclog_or_tty->print_cr("CMS old gen initiated");
1236     }
1237     return true;
1238   }
1239 
1240   // We start a collection if we believe an incremental collection may fail;
1241   // this is not likely to be productive in practice because it's probably too
1242   // late anyway.
1243   GenCollectedHeap* gch = GenCollectedHeap::heap();
1244   assert(gch->collector_policy()->is_generation_policy(),
1245          "You may want to check the correctness of the following");
1246   if (gch->incremental_collection_will_fail(true /* consult_young */)) {
1247     if (Verbose && PrintGCDetails) {
1248       gclog_or_tty->print("CMSCollector: collect because incremental collection will fail ");
1249     }
1250     return true;
1251   }
1252 
1253   if (MetaspaceGC::should_concurrent_collect()) {
1254     if (Verbose && PrintGCDetails) {
1255       gclog_or_tty->print("CMSCollector: collect for metadata allocation ");
1256     }
1257     return true;
1258   }
1259 
1260   // CMSTriggerInterval starts a CMS cycle if enough time has passed.
1261   if (CMSTriggerInterval >= 0) {
1262     if (CMSTriggerInterval == 0) {
1263       // Trigger always
1264       return true;
1265     }
1266 
1267     // Check the CMS time since begin (we do not check the stats validity
1268     // as we want to be able to trigger the first CMS cycle as well)
1269     if (stats().cms_time_since_begin() >= (CMSTriggerInterval / ((double) MILLIUNITS))) {
1270       if (Verbose && PrintGCDetails) {
1271         if (stats().valid()) {
1272           gclog_or_tty->print_cr("CMSCollector: collect because of trigger interval (time since last begin %3.7f secs)",
1273                                  stats().cms_time_since_begin());
1274         } else {
1275           gclog_or_tty->print_cr("CMSCollector: collect because of trigger interval (first collection)");
1276         }
1277       }
1278       return true;
1279     }
1280   }
1281 
1282   return false;
1283 }
1284 
1285 void CMSCollector::set_did_compact(bool v) { _cmsGen->set_did_compact(v); }
1286 
1287 // Clear _expansion_cause fields of constituent generations
1288 void CMSCollector::clear_expansion_cause() {
1289   _cmsGen->clear_expansion_cause();
1290 }
1291 
1292 // We should be conservative in starting a collection cycle.  To
1293 // start too eagerly runs the risk of collecting too often in the
1294 // extreme.  To collect too rarely falls back on full collections,
1295 // which works, even if not optimum in terms of concurrent work.
1296 // As a work around for too eagerly collecting, use the flag
1297 // UseCMSInitiatingOccupancyOnly.  This also has the advantage of
1298 // giving the user an easily understandable way of controlling the
1299 // collections.
1300 // We want to start a new collection cycle if any of the following
1301 // conditions hold:
1302 // . our current occupancy exceeds the configured initiating occupancy
1303 //   for this generation, or
1304 // . we recently needed to expand this space and have not, since that
1305 //   expansion, done a collection of this generation, or
1306 // . the underlying space believes that it may be a good idea to initiate
1307 //   a concurrent collection (this may be based on criteria such as the
1308 //   following: the space uses linear allocation and linear allocation is
1309 //   going to fail, or there is believed to be excessive fragmentation in
1310 //   the generation, etc... or ...
1311 // [.(currently done by CMSCollector::shouldConcurrentCollect() only for
1312 //   the case of the old generation; see CR 6543076):
1313 //   we may be approaching a point at which allocation requests may fail because
1314 //   we will be out of sufficient free space given allocation rate estimates.]
1315 bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const {
1316 
1317   assert_lock_strong(freelistLock());
1318   if (occupancy() > initiating_occupancy()) {
1319     if (PrintGCDetails && Verbose) {
1320       gclog_or_tty->print(" %s: collect because of occupancy %f / %f  ",
1321         short_name(), occupancy(), initiating_occupancy());
1322     }
1323     return true;
1324   }
1325   if (UseCMSInitiatingOccupancyOnly) {
1326     return false;
1327   }
1328   if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) {
1329     if (PrintGCDetails && Verbose) {
1330       gclog_or_tty->print(" %s: collect because expanded for allocation ",
1331         short_name());
1332     }
1333     return true;
1334   }
1335   if (_cmsSpace->should_concurrent_collect()) {
1336     if (PrintGCDetails && Verbose) {
1337       gclog_or_tty->print(" %s: collect because cmsSpace says so ",
1338         short_name());
1339     }
1340     return true;
1341   }
1342   return false;
1343 }
1344 
1345 void ConcurrentMarkSweepGeneration::collect(bool   full,
1346                                             bool   clear_all_soft_refs,
1347                                             size_t size,
1348                                             bool   tlab)
1349 {
1350   collector()->collect(full, clear_all_soft_refs, size, tlab);
1351 }
1352 
1353 void CMSCollector::collect(bool   full,
1354                            bool   clear_all_soft_refs,
1355                            size_t size,
1356                            bool   tlab)
1357 {
1358   // The following "if" branch is present for defensive reasons.
1359   // In the current uses of this interface, it can be replaced with:
1360   // assert(!GC_locker.is_active(), "Can't be called otherwise");
1361   // But I am not placing that assert here to allow future
1362   // generality in invoking this interface.
1363   if (GC_locker::is_active()) {
1364     // A consistency test for GC_locker
1365     assert(GC_locker::needs_gc(), "Should have been set already");
1366     // Skip this foreground collection, instead
1367     // expanding the heap if necessary.
1368     // Need the free list locks for the call to free() in compute_new_size()
1369     compute_new_size();
1370     return;
1371   }
1372   acquire_control_and_collect(full, clear_all_soft_refs);
1373 }
1374 
1375 void CMSCollector::request_full_gc(unsigned int full_gc_count, GCCause::Cause cause) {
1376   GenCollectedHeap* gch = GenCollectedHeap::heap();
1377   unsigned int gc_count = gch->total_full_collections();
1378   if (gc_count == full_gc_count) {
1379     MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag);
1380     _full_gc_requested = true;
1381     _full_gc_cause = cause;
1382     CGC_lock->notify();   // nudge CMS thread
1383   } else {
1384     assert(gc_count > full_gc_count, "Error: causal loop");
1385   }
1386 }
1387 
1388 bool CMSCollector::is_external_interruption() {
1389   GCCause::Cause cause = GenCollectedHeap::heap()->gc_cause();
1390   return GCCause::is_user_requested_gc(cause) ||
1391          GCCause::is_serviceability_requested_gc(cause);
1392 }
1393 
1394 void CMSCollector::report_concurrent_mode_interruption() {
1395   if (is_external_interruption()) {
1396     if (PrintGCDetails) {
1397       gclog_or_tty->print(" (concurrent mode interrupted)");
1398     }
1399   } else {
1400     if (PrintGCDetails) {
1401       gclog_or_tty->print(" (concurrent mode failure)");
1402     }
1403     _gc_tracer_cm->report_concurrent_mode_failure();
1404   }
1405 }
1406 
1407 
1408 // The foreground and background collectors need to coordinate in order
1409 // to make sure that they do not mutually interfere with CMS collections.
1410 // When a background collection is active,
1411 // the foreground collector may need to take over (preempt) and
1412 // synchronously complete an ongoing collection. Depending on the
1413 // frequency of the background collections and the heap usage
1414 // of the application, this preemption can be seldom or frequent.
1415 // There are only certain
1416 // points in the background collection that the "collection-baton"
1417 // can be passed to the foreground collector.
1418 //
1419 // The foreground collector will wait for the baton before
1420 // starting any part of the collection.  The foreground collector
1421 // will only wait at one location.
1422 //
1423 // The background collector will yield the baton before starting a new
1424 // phase of the collection (e.g., before initial marking, marking from roots,
1425 // precleaning, final re-mark, sweep etc.)  This is normally done at the head
1426 // of the loop which switches the phases. The background collector does some
1427 // of the phases (initial mark, final re-mark) with the world stopped.
1428 // Because of locking involved in stopping the world,
1429 // the foreground collector should not block waiting for the background
1430 // collector when it is doing a stop-the-world phase.  The background
1431 // collector will yield the baton at an additional point just before
1432 // it enters a stop-the-world phase.  Once the world is stopped, the
1433 // background collector checks the phase of the collection.  If the
1434 // phase has not changed, it proceeds with the collection.  If the
1435 // phase has changed, it skips that phase of the collection.  See
1436 // the comments on the use of the Heap_lock in collect_in_background().
1437 //
1438 // Variable used in baton passing.
1439 //   _foregroundGCIsActive - Set to true by the foreground collector when
1440 //      it wants the baton.  The foreground clears it when it has finished
1441 //      the collection.
1442 //   _foregroundGCShouldWait - Set to true by the background collector
1443 //        when it is running.  The foreground collector waits while
1444 //      _foregroundGCShouldWait is true.
1445 //  CGC_lock - monitor used to protect access to the above variables
1446 //      and to notify the foreground and background collectors.
1447 //  _collectorState - current state of the CMS collection.
1448 //
1449 // The foreground collector
1450 //   acquires the CGC_lock
1451 //   sets _foregroundGCIsActive
1452 //   waits on the CGC_lock for _foregroundGCShouldWait to be false
1453 //     various locks acquired in preparation for the collection
1454 //     are released so as not to block the background collector
1455 //     that is in the midst of a collection
1456 //   proceeds with the collection
1457 //   clears _foregroundGCIsActive
1458 //   returns
1459 //
1460 // The background collector in a loop iterating on the phases of the
1461 //      collection
1462 //   acquires the CGC_lock
1463 //   sets _foregroundGCShouldWait
1464 //   if _foregroundGCIsActive is set
1465 //     clears _foregroundGCShouldWait, notifies _CGC_lock
1466 //     waits on _CGC_lock for _foregroundGCIsActive to become false
1467 //     and exits the loop.
1468 //   otherwise
1469 //     proceed with that phase of the collection
1470 //     if the phase is a stop-the-world phase,
1471 //       yield the baton once more just before enqueueing
1472 //       the stop-world CMS operation (executed by the VM thread).
1473 //   returns after all phases of the collection are done
1474 //
1475 
1476 void CMSCollector::acquire_control_and_collect(bool full,
1477         bool clear_all_soft_refs) {
1478   assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
1479   assert(!Thread::current()->is_ConcurrentGC_thread(),
1480          "shouldn't try to acquire control from self!");
1481 
1482   // Start the protocol for acquiring control of the
1483   // collection from the background collector (aka CMS thread).
1484   assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1485          "VM thread should have CMS token");
1486   // Remember the possibly interrupted state of an ongoing
1487   // concurrent collection
1488   CollectorState first_state = _collectorState;
1489 
1490   // Signal to a possibly ongoing concurrent collection that
1491   // we want to do a foreground collection.
1492   _foregroundGCIsActive = true;
1493 
1494   // release locks and wait for a notify from the background collector
1495   // releasing the locks in only necessary for phases which
1496   // do yields to improve the granularity of the collection.
1497   assert_lock_strong(bitMapLock());
1498   // We need to lock the Free list lock for the space that we are
1499   // currently collecting.
1500   assert(haveFreelistLocks(), "Must be holding free list locks");
1501   bitMapLock()->unlock();
1502   releaseFreelistLocks();
1503   {
1504     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1505     if (_foregroundGCShouldWait) {
1506       // We are going to be waiting for action for the CMS thread;
1507       // it had better not be gone (for instance at shutdown)!
1508       assert(ConcurrentMarkSweepThread::cmst() != NULL,
1509              "CMS thread must be running");
1510       // Wait here until the background collector gives us the go-ahead
1511       ConcurrentMarkSweepThread::clear_CMS_flag(
1512         ConcurrentMarkSweepThread::CMS_vm_has_token);  // release token
1513       // Get a possibly blocked CMS thread going:
1514       //   Note that we set _foregroundGCIsActive true above,
1515       //   without protection of the CGC_lock.
1516       CGC_lock->notify();
1517       assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(),
1518              "Possible deadlock");
1519       while (_foregroundGCShouldWait) {
1520         // wait for notification
1521         CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1522         // Possibility of delay/starvation here, since CMS token does
1523         // not know to give priority to VM thread? Actually, i think
1524         // there wouldn't be any delay/starvation, but the proof of
1525         // that "fact" (?) appears non-trivial. XXX 20011219YSR
1526       }
1527       ConcurrentMarkSweepThread::set_CMS_flag(
1528         ConcurrentMarkSweepThread::CMS_vm_has_token);
1529     }
1530   }
1531   // The CMS_token is already held.  Get back the other locks.
1532   assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1533          "VM thread should have CMS token");
1534   getFreelistLocks();
1535   bitMapLock()->lock_without_safepoint_check();
1536   if (TraceCMSState) {
1537     gclog_or_tty->print_cr("CMS foreground collector has asked for control "
1538       INTPTR_FORMAT " with first state %d", p2i(Thread::current()), first_state);
1539     gclog_or_tty->print_cr("    gets control with state %d", _collectorState);
1540   }
1541 
1542   // Inform cms gen if this was due to partial collection failing.
1543   // The CMS gen may use this fact to determine its expansion policy.
1544   GenCollectedHeap* gch = GenCollectedHeap::heap();
1545   if (gch->incremental_collection_will_fail(false /* don't consult_young */)) {
1546     assert(!_cmsGen->incremental_collection_failed(),
1547            "Should have been noticed, reacted to and cleared");
1548     _cmsGen->set_incremental_collection_failed();
1549   }
1550 
1551   if (first_state > Idling) {
1552     report_concurrent_mode_interruption();
1553   }
1554 
1555   set_did_compact(true);
1556 
1557   // If the collection is being acquired from the background
1558   // collector, there may be references on the discovered
1559   // references lists.  Abandon those references, since some
1560   // of them may have become unreachable after concurrent
1561   // discovery; the STW compacting collector will redo discovery
1562   // more precisely, without being subject to floating garbage.
1563   // Leaving otherwise unreachable references in the discovered
1564   // lists would require special handling.
1565   ref_processor()->disable_discovery();
1566   ref_processor()->abandon_partial_discovery();
1567   ref_processor()->verify_no_references_recorded();
1568 
1569   if (first_state > Idling) {
1570     save_heap_summary();
1571   }
1572 
1573   do_compaction_work(clear_all_soft_refs);
1574 
1575   // Has the GC time limit been exceeded?
1576   size_t max_eden_size = _young_gen->max_capacity() -
1577                          _young_gen->to()->capacity() -
1578                          _young_gen->from()->capacity();
1579   GCCause::Cause gc_cause = gch->gc_cause();
1580   size_policy()->check_gc_overhead_limit(_young_gen->used(),
1581                                          _young_gen->eden()->used(),
1582                                          _cmsGen->max_capacity(),
1583                                          max_eden_size,
1584                                          full,
1585                                          gc_cause,
1586                                          gch->collector_policy());
1587 
1588   // Reset the expansion cause, now that we just completed
1589   // a collection cycle.
1590   clear_expansion_cause();
1591   _foregroundGCIsActive = false;
1592   return;
1593 }
1594 
1595 // Resize the tenured generation
1596 // after obtaining the free list locks for the
1597 // two generations.
1598 void CMSCollector::compute_new_size() {
1599   assert_locked_or_safepoint(Heap_lock);
1600   FreelistLocker z(this);
1601   MetaspaceGC::compute_new_size();
1602   _cmsGen->compute_new_size_free_list();
1603 }
1604 
1605 // A work method used by the foreground collector to do
1606 // a mark-sweep-compact.
1607 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) {
1608   GenCollectedHeap* gch = GenCollectedHeap::heap();
1609 
1610   STWGCTimer* gc_timer = GenMarkSweep::gc_timer();
1611   gc_timer->register_gc_start();
1612 
1613   SerialOldTracer* gc_tracer = GenMarkSweep::gc_tracer();
1614   gc_tracer->report_gc_start(gch->gc_cause(), gc_timer->gc_start());
1615 
1616   GCTraceTime t("CMS:MSC ", PrintGCDetails && Verbose, true, NULL, gc_tracer->gc_id());
1617 
1618   // Temporarily widen the span of the weak reference processing to
1619   // the entire heap.
1620   MemRegion new_span(GenCollectedHeap::heap()->reserved_region());
1621   ReferenceProcessorSpanMutator rp_mut_span(ref_processor(), new_span);
1622   // Temporarily, clear the "is_alive_non_header" field of the
1623   // reference processor.
1624   ReferenceProcessorIsAliveMutator rp_mut_closure(ref_processor(), NULL);
1625   // Temporarily make reference _processing_ single threaded (non-MT).
1626   ReferenceProcessorMTProcMutator rp_mut_mt_processing(ref_processor(), false);
1627   // Temporarily make refs discovery atomic
1628   ReferenceProcessorAtomicMutator rp_mut_atomic(ref_processor(), true);
1629   // Temporarily make reference _discovery_ single threaded (non-MT)
1630   ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
1631 
1632   ref_processor()->set_enqueuing_is_done(false);
1633   ref_processor()->enable_discovery();
1634   ref_processor()->setup_policy(clear_all_soft_refs);
1635   // If an asynchronous collection finishes, the _modUnionTable is
1636   // all clear.  If we are assuming the collection from an asynchronous
1637   // collection, clear the _modUnionTable.
1638   assert(_collectorState != Idling || _modUnionTable.isAllClear(),
1639     "_modUnionTable should be clear if the baton was not passed");
1640   _modUnionTable.clear_all();
1641   assert(_collectorState != Idling || _ct->klass_rem_set()->mod_union_is_clear(),
1642     "mod union for klasses should be clear if the baton was passed");
1643   _ct->klass_rem_set()->clear_mod_union();
1644 
1645   // We must adjust the allocation statistics being maintained
1646   // in the free list space. We do so by reading and clearing
1647   // the sweep timer and updating the block flux rate estimates below.
1648   assert(!_intra_sweep_timer.is_active(), "_intra_sweep_timer should be inactive");
1649   if (_inter_sweep_timer.is_active()) {
1650     _inter_sweep_timer.stop();
1651     // Note that we do not use this sample to update the _inter_sweep_estimate.
1652     _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
1653                                             _inter_sweep_estimate.padded_average(),
1654                                             _intra_sweep_estimate.padded_average());
1655   }
1656 
1657   GenMarkSweep::invoke_at_safepoint(_cmsGen->level(),
1658     ref_processor(), clear_all_soft_refs);
1659   #ifdef ASSERT
1660     CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
1661     size_t free_size = cms_space->free();
1662     assert(free_size ==
1663            pointer_delta(cms_space->end(), cms_space->compaction_top())
1664            * HeapWordSize,
1665       "All the free space should be compacted into one chunk at top");
1666     assert(cms_space->dictionary()->total_chunk_size(
1667                                       debug_only(cms_space->freelistLock())) == 0 ||
1668            cms_space->totalSizeInIndexedFreeLists() == 0,
1669       "All the free space should be in a single chunk");
1670     size_t num = cms_space->totalCount();
1671     assert((free_size == 0 && num == 0) ||
1672            (free_size > 0  && (num == 1 || num == 2)),
1673          "There should be at most 2 free chunks after compaction");
1674   #endif // ASSERT
1675   _collectorState = Resetting;
1676   assert(_restart_addr == NULL,
1677          "Should have been NULL'd before baton was passed");
1678   reset(false /* == !concurrent */);
1679   _cmsGen->reset_after_compaction();
1680   _concurrent_cycles_since_last_unload = 0;
1681 
1682   // Clear any data recorded in the PLAB chunk arrays.
1683   if (_survivor_plab_array != NULL) {
1684     reset_survivor_plab_arrays();
1685   }
1686 
1687   // Adjust the per-size allocation stats for the next epoch.
1688   _cmsGen->cmsSpace()->endSweepFLCensus(sweep_count() /* fake */);
1689   // Restart the "inter sweep timer" for the next epoch.
1690   _inter_sweep_timer.reset();
1691   _inter_sweep_timer.start();
1692 
1693   gc_timer->register_gc_end();
1694 
1695   gc_tracer->report_gc_end(gc_timer->gc_end(), gc_timer->time_partitions());
1696 
1697   // For a mark-sweep-compact, compute_new_size() will be called
1698   // in the heap's do_collection() method.
1699 }
1700 
1701 void CMSCollector::print_eden_and_survivor_chunk_arrays() {
1702   ContiguousSpace* eden_space = _young_gen->eden();
1703   ContiguousSpace* from_space = _young_gen->from();
1704   ContiguousSpace* to_space   = _young_gen->to();
1705   // Eden
1706   if (_eden_chunk_array != NULL) {
1707     gclog_or_tty->print_cr("eden " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1708                            p2i(eden_space->bottom()), p2i(eden_space->top()),
1709                            p2i(eden_space->end()), eden_space->capacity());
1710     gclog_or_tty->print_cr("_eden_chunk_index=" SIZE_FORMAT ", "
1711                            "_eden_chunk_capacity=" SIZE_FORMAT,
1712                            _eden_chunk_index, _eden_chunk_capacity);
1713     for (size_t i = 0; i < _eden_chunk_index; i++) {
1714       gclog_or_tty->print_cr("_eden_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT,
1715                              i, p2i(_eden_chunk_array[i]));
1716     }
1717   }
1718   // Survivor
1719   if (_survivor_chunk_array != NULL) {
1720     gclog_or_tty->print_cr("survivor " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1721                            p2i(from_space->bottom()), p2i(from_space->top()),
1722                            p2i(from_space->end()), from_space->capacity());
1723     gclog_or_tty->print_cr("_survivor_chunk_index=" SIZE_FORMAT ", "
1724                            "_survivor_chunk_capacity=" SIZE_FORMAT,
1725                            _survivor_chunk_index, _survivor_chunk_capacity);
1726     for (size_t i = 0; i < _survivor_chunk_index; i++) {
1727       gclog_or_tty->print_cr("_survivor_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT,
1728                              i, p2i(_survivor_chunk_array[i]));
1729     }
1730   }
1731 }
1732 
1733 void CMSCollector::getFreelistLocks() const {
1734   // Get locks for all free lists in all generations that this
1735   // collector is responsible for
1736   _cmsGen->freelistLock()->lock_without_safepoint_check();
1737 }
1738 
1739 void CMSCollector::releaseFreelistLocks() const {
1740   // Release locks for all free lists in all generations that this
1741   // collector is responsible for
1742   _cmsGen->freelistLock()->unlock();
1743 }
1744 
1745 bool CMSCollector::haveFreelistLocks() const {
1746   // Check locks for all free lists in all generations that this
1747   // collector is responsible for
1748   assert_lock_strong(_cmsGen->freelistLock());
1749   PRODUCT_ONLY(ShouldNotReachHere());
1750   return true;
1751 }
1752 
1753 // A utility class that is used by the CMS collector to
1754 // temporarily "release" the foreground collector from its
1755 // usual obligation to wait for the background collector to
1756 // complete an ongoing phase before proceeding.
1757 class ReleaseForegroundGC: public StackObj {
1758  private:
1759   CMSCollector* _c;
1760  public:
1761   ReleaseForegroundGC(CMSCollector* c) : _c(c) {
1762     assert(_c->_foregroundGCShouldWait, "Else should not need to call");
1763     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1764     // allow a potentially blocked foreground collector to proceed
1765     _c->_foregroundGCShouldWait = false;
1766     if (_c->_foregroundGCIsActive) {
1767       CGC_lock->notify();
1768     }
1769     assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1770            "Possible deadlock");
1771   }
1772 
1773   ~ReleaseForegroundGC() {
1774     assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?");
1775     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1776     _c->_foregroundGCShouldWait = true;
1777   }
1778 };
1779 
1780 void CMSCollector::collect_in_background(GCCause::Cause cause) {
1781   assert(Thread::current()->is_ConcurrentGC_thread(),
1782     "A CMS asynchronous collection is only allowed on a CMS thread.");
1783 
1784   GenCollectedHeap* gch = GenCollectedHeap::heap();
1785   {
1786     bool safepoint_check = Mutex::_no_safepoint_check_flag;
1787     MutexLockerEx hl(Heap_lock, safepoint_check);
1788     FreelistLocker fll(this);
1789     MutexLockerEx x(CGC_lock, safepoint_check);
1790     if (_foregroundGCIsActive || !UseAsyncConcMarkSweepGC) {
1791       // The foreground collector is active or we're
1792       // not using asynchronous collections.  Skip this
1793       // background collection.
1794       assert(!_foregroundGCShouldWait, "Should be clear");
1795       return;
1796     } else {
1797       assert(_collectorState == Idling, "Should be idling before start.");
1798       _collectorState = InitialMarking;
1799       register_gc_start(cause);
1800       // Reset the expansion cause, now that we are about to begin
1801       // a new cycle.
1802       clear_expansion_cause();
1803 
1804       // Clear the MetaspaceGC flag since a concurrent collection
1805       // is starting but also clear it after the collection.
1806       MetaspaceGC::set_should_concurrent_collect(false);
1807     }
1808     // Decide if we want to enable class unloading as part of the
1809     // ensuing concurrent GC cycle.
1810     update_should_unload_classes();
1811     _full_gc_requested = false;           // acks all outstanding full gc requests
1812     _full_gc_cause = GCCause::_no_gc;
1813     // Signal that we are about to start a collection
1814     gch->increment_total_full_collections();  // ... starting a collection cycle
1815     _collection_count_start = gch->total_full_collections();
1816   }
1817 
1818   // Used for PrintGC
1819   size_t prev_used;
1820   if (PrintGC && Verbose) {
1821     prev_used = _cmsGen->used();
1822   }
1823 
1824   // The change of the collection state is normally done at this level;
1825   // the exceptions are phases that are executed while the world is
1826   // stopped.  For those phases the change of state is done while the
1827   // world is stopped.  For baton passing purposes this allows the
1828   // background collector to finish the phase and change state atomically.
1829   // The foreground collector cannot wait on a phase that is done
1830   // while the world is stopped because the foreground collector already
1831   // has the world stopped and would deadlock.
1832   while (_collectorState != Idling) {
1833     if (TraceCMSState) {
1834       gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
1835         p2i(Thread::current()), _collectorState);
1836     }
1837     // The foreground collector
1838     //   holds the Heap_lock throughout its collection.
1839     //   holds the CMS token (but not the lock)
1840     //     except while it is waiting for the background collector to yield.
1841     //
1842     // The foreground collector should be blocked (not for long)
1843     //   if the background collector is about to start a phase
1844     //   executed with world stopped.  If the background
1845     //   collector has already started such a phase, the
1846     //   foreground collector is blocked waiting for the
1847     //   Heap_lock.  The stop-world phases (InitialMarking and FinalMarking)
1848     //   are executed in the VM thread.
1849     //
1850     // The locking order is
1851     //   PendingListLock (PLL)  -- if applicable (FinalMarking)
1852     //   Heap_lock  (both this & PLL locked in VM_CMS_Operation::prologue())
1853     //   CMS token  (claimed in
1854     //                stop_world_and_do() -->
1855     //                  safepoint_synchronize() -->
1856     //                    CMSThread::synchronize())
1857 
1858     {
1859       // Check if the FG collector wants us to yield.
1860       CMSTokenSync x(true); // is cms thread
1861       if (waitForForegroundGC()) {
1862         // We yielded to a foreground GC, nothing more to be
1863         // done this round.
1864         assert(_foregroundGCShouldWait == false, "We set it to false in "
1865                "waitForForegroundGC()");
1866         if (TraceCMSState) {
1867           gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
1868             " exiting collection CMS state %d",
1869             p2i(Thread::current()), _collectorState);
1870         }
1871         return;
1872       } else {
1873         // The background collector can run but check to see if the
1874         // foreground collector has done a collection while the
1875         // background collector was waiting to get the CGC_lock
1876         // above.  If yes, break so that _foregroundGCShouldWait
1877         // is cleared before returning.
1878         if (_collectorState == Idling) {
1879           break;
1880         }
1881       }
1882     }
1883 
1884     assert(_foregroundGCShouldWait, "Foreground collector, if active, "
1885       "should be waiting");
1886 
1887     switch (_collectorState) {
1888       case InitialMarking:
1889         {
1890           ReleaseForegroundGC x(this);
1891           stats().record_cms_begin();
1892           VM_CMS_Initial_Mark initial_mark_op(this);
1893           VMThread::execute(&initial_mark_op);
1894         }
1895         // The collector state may be any legal state at this point
1896         // since the background collector may have yielded to the
1897         // foreground collector.
1898         break;
1899       case Marking:
1900         // initial marking in checkpointRootsInitialWork has been completed
1901         if (markFromRoots()) { // we were successful
1902           assert(_collectorState == Precleaning, "Collector state should "
1903             "have changed");
1904         } else {
1905           assert(_foregroundGCIsActive, "Internal state inconsistency");
1906         }
1907         break;
1908       case Precleaning:
1909         // marking from roots in markFromRoots has been completed
1910         preclean();
1911         assert(_collectorState == AbortablePreclean ||
1912                _collectorState == FinalMarking,
1913                "Collector state should have changed");
1914         break;
1915       case AbortablePreclean:
1916         abortable_preclean();
1917         assert(_collectorState == FinalMarking, "Collector state should "
1918           "have changed");
1919         break;
1920       case FinalMarking:
1921         {
1922           ReleaseForegroundGC x(this);
1923 
1924           VM_CMS_Final_Remark final_remark_op(this);
1925           VMThread::execute(&final_remark_op);
1926         }
1927         assert(_foregroundGCShouldWait, "block post-condition");
1928         break;
1929       case Sweeping:
1930         // final marking in checkpointRootsFinal has been completed
1931         sweep();
1932         assert(_collectorState == Resizing, "Collector state change "
1933           "to Resizing must be done under the free_list_lock");
1934 
1935       case Resizing: {
1936         // Sweeping has been completed...
1937         // At this point the background collection has completed.
1938         // Don't move the call to compute_new_size() down
1939         // into code that might be executed if the background
1940         // collection was preempted.
1941         {
1942           ReleaseForegroundGC x(this);   // unblock FG collection
1943           MutexLockerEx       y(Heap_lock, Mutex::_no_safepoint_check_flag);
1944           CMSTokenSync        z(true);   // not strictly needed.
1945           if (_collectorState == Resizing) {
1946             compute_new_size();
1947             save_heap_summary();
1948             _collectorState = Resetting;
1949           } else {
1950             assert(_collectorState == Idling, "The state should only change"
1951                    " because the foreground collector has finished the collection");
1952           }
1953         }
1954         break;
1955       }
1956       case Resetting:
1957         // CMS heap resizing has been completed
1958         reset(true);
1959         assert(_collectorState == Idling, "Collector state should "
1960           "have changed");
1961 
1962         MetaspaceGC::set_should_concurrent_collect(false);
1963 
1964         stats().record_cms_end();
1965         // Don't move the concurrent_phases_end() and compute_new_size()
1966         // calls to here because a preempted background collection
1967         // has it's state set to "Resetting".
1968         break;
1969       case Idling:
1970       default:
1971         ShouldNotReachHere();
1972         break;
1973     }
1974     if (TraceCMSState) {
1975       gclog_or_tty->print_cr("  Thread " INTPTR_FORMAT " done - next CMS state %d",
1976         p2i(Thread::current()), _collectorState);
1977     }
1978     assert(_foregroundGCShouldWait, "block post-condition");
1979   }
1980 
1981   // Should this be in gc_epilogue?
1982   collector_policy()->counters()->update_counters();
1983 
1984   {
1985     // Clear _foregroundGCShouldWait and, in the event that the
1986     // foreground collector is waiting, notify it, before
1987     // returning.
1988     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1989     _foregroundGCShouldWait = false;
1990     if (_foregroundGCIsActive) {
1991       CGC_lock->notify();
1992     }
1993     assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1994            "Possible deadlock");
1995   }
1996   if (TraceCMSState) {
1997     gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
1998       " exiting collection CMS state %d",
1999       p2i(Thread::current()), _collectorState);
2000   }
2001   if (PrintGC && Verbose) {
2002     _cmsGen->print_heap_change(prev_used);
2003   }
2004 }
2005 
2006 void CMSCollector::register_gc_start(GCCause::Cause cause) {
2007   _cms_start_registered = true;
2008   _gc_timer_cm->register_gc_start();
2009   _gc_tracer_cm->report_gc_start(cause, _gc_timer_cm->gc_start());
2010 }
2011 
2012 void CMSCollector::register_gc_end() {
2013   if (_cms_start_registered) {
2014     report_heap_summary(GCWhen::AfterGC);
2015 
2016     _gc_timer_cm->register_gc_end();
2017     _gc_tracer_cm->report_gc_end(_gc_timer_cm->gc_end(), _gc_timer_cm->time_partitions());
2018     _cms_start_registered = false;
2019   }
2020 }
2021 
2022 void CMSCollector::save_heap_summary() {
2023   GenCollectedHeap* gch = GenCollectedHeap::heap();
2024   _last_heap_summary = gch->create_heap_summary();
2025   _last_metaspace_summary = gch->create_metaspace_summary();
2026 }
2027 
2028 void CMSCollector::report_heap_summary(GCWhen::Type when) {
2029   _gc_tracer_cm->report_gc_heap_summary(when, _last_heap_summary);
2030   _gc_tracer_cm->report_metaspace_summary(when, _last_metaspace_summary);
2031 }
2032 
2033 bool CMSCollector::waitForForegroundGC() {
2034   bool res = false;
2035   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2036          "CMS thread should have CMS token");
2037   // Block the foreground collector until the
2038   // background collectors decides whether to
2039   // yield.
2040   MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2041   _foregroundGCShouldWait = true;
2042   if (_foregroundGCIsActive) {
2043     // The background collector yields to the
2044     // foreground collector and returns a value
2045     // indicating that it has yielded.  The foreground
2046     // collector can proceed.
2047     res = true;
2048     _foregroundGCShouldWait = false;
2049     ConcurrentMarkSweepThread::clear_CMS_flag(
2050       ConcurrentMarkSweepThread::CMS_cms_has_token);
2051     ConcurrentMarkSweepThread::set_CMS_flag(
2052       ConcurrentMarkSweepThread::CMS_cms_wants_token);
2053     // Get a possibly blocked foreground thread going
2054     CGC_lock->notify();
2055     if (TraceCMSState) {
2056       gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d",
2057         p2i(Thread::current()), _collectorState);
2058     }
2059     while (_foregroundGCIsActive) {
2060       CGC_lock->wait(Mutex::_no_safepoint_check_flag);
2061     }
2062     ConcurrentMarkSweepThread::set_CMS_flag(
2063       ConcurrentMarkSweepThread::CMS_cms_has_token);
2064     ConcurrentMarkSweepThread::clear_CMS_flag(
2065       ConcurrentMarkSweepThread::CMS_cms_wants_token);
2066   }
2067   if (TraceCMSState) {
2068     gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d",
2069       p2i(Thread::current()), _collectorState);
2070   }
2071   return res;
2072 }
2073 
2074 // Because of the need to lock the free lists and other structures in
2075 // the collector, common to all the generations that the collector is
2076 // collecting, we need the gc_prologues of individual CMS generations
2077 // delegate to their collector. It may have been simpler had the
2078 // current infrastructure allowed one to call a prologue on a
2079 // collector. In the absence of that we have the generation's
2080 // prologue delegate to the collector, which delegates back
2081 // some "local" work to a worker method in the individual generations
2082 // that it's responsible for collecting, while itself doing any
2083 // work common to all generations it's responsible for. A similar
2084 // comment applies to the  gc_epilogue()'s.
2085 // The role of the variable _between_prologue_and_epilogue is to
2086 // enforce the invocation protocol.
2087 void CMSCollector::gc_prologue(bool full) {
2088   // Call gc_prologue_work() for the CMSGen
2089   // we are responsible for.
2090 
2091   // The following locking discipline assumes that we are only called
2092   // when the world is stopped.
2093   assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption");
2094 
2095   // The CMSCollector prologue must call the gc_prologues for the
2096   // "generations" that it's responsible
2097   // for.
2098 
2099   assert(   Thread::current()->is_VM_thread()
2100          || (   CMSScavengeBeforeRemark
2101              && Thread::current()->is_ConcurrentGC_thread()),
2102          "Incorrect thread type for prologue execution");
2103 
2104   if (_between_prologue_and_epilogue) {
2105     // We have already been invoked; this is a gc_prologue delegation
2106     // from yet another CMS generation that we are responsible for, just
2107     // ignore it since all relevant work has already been done.
2108     return;
2109   }
2110 
2111   // set a bit saying prologue has been called; cleared in epilogue
2112   _between_prologue_and_epilogue = true;
2113   // Claim locks for common data structures, then call gc_prologue_work()
2114   // for each CMSGen.
2115 
2116   getFreelistLocks();   // gets free list locks on constituent spaces
2117   bitMapLock()->lock_without_safepoint_check();
2118 
2119   // Should call gc_prologue_work() for all cms gens we are responsible for
2120   bool duringMarking =    _collectorState >= Marking
2121                          && _collectorState < Sweeping;
2122 
2123   // The young collections clear the modified oops state, which tells if
2124   // there are any modified oops in the class. The remark phase also needs
2125   // that information. Tell the young collection to save the union of all
2126   // modified klasses.
2127   if (duringMarking) {
2128     _ct->klass_rem_set()->set_accumulate_modified_oops(true);
2129   }
2130 
2131   bool registerClosure = duringMarking;
2132 
2133   ModUnionClosure* muc = CollectedHeap::use_parallel_gc_threads() ?
2134                                                &_modUnionClosurePar
2135                                                : &_modUnionClosure;
2136   _cmsGen->gc_prologue_work(full, registerClosure, muc);
2137 
2138   if (!full) {
2139     stats().record_gc0_begin();
2140   }
2141 }
2142 
2143 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) {
2144 
2145   _capacity_at_prologue = capacity();
2146   _used_at_prologue = used();
2147 
2148   // Delegate to CMScollector which knows how to coordinate between
2149   // this and any other CMS generations that it is responsible for
2150   // collecting.
2151   collector()->gc_prologue(full);
2152 }
2153 
2154 // This is a "private" interface for use by this generation's CMSCollector.
2155 // Not to be called directly by any other entity (for instance,
2156 // GenCollectedHeap, which calls the "public" gc_prologue method above).
2157 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full,
2158   bool registerClosure, ModUnionClosure* modUnionClosure) {
2159   assert(!incremental_collection_failed(), "Shouldn't be set yet");
2160   assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL,
2161     "Should be NULL");
2162   if (registerClosure) {
2163     cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure);
2164   }
2165   cmsSpace()->gc_prologue();
2166   // Clear stat counters
2167   NOT_PRODUCT(
2168     assert(_numObjectsPromoted == 0, "check");
2169     assert(_numWordsPromoted   == 0, "check");
2170     if (Verbose && PrintGC) {
2171       gclog_or_tty->print("Allocated "SIZE_FORMAT" objects, "
2172                           SIZE_FORMAT" bytes concurrently",
2173       _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord));
2174     }
2175     _numObjectsAllocated = 0;
2176     _numWordsAllocated   = 0;
2177   )
2178 }
2179 
2180 void CMSCollector::gc_epilogue(bool full) {
2181   // The following locking discipline assumes that we are only called
2182   // when the world is stopped.
2183   assert(SafepointSynchronize::is_at_safepoint(),
2184          "world is stopped assumption");
2185 
2186   // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks
2187   // if linear allocation blocks need to be appropriately marked to allow the
2188   // the blocks to be parsable. We also check here whether we need to nudge the
2189   // CMS collector thread to start a new cycle (if it's not already active).
2190   assert(   Thread::current()->is_VM_thread()
2191          || (   CMSScavengeBeforeRemark
2192              && Thread::current()->is_ConcurrentGC_thread()),
2193          "Incorrect thread type for epilogue execution");
2194 
2195   if (!_between_prologue_and_epilogue) {
2196     // We have already been invoked; this is a gc_epilogue delegation
2197     // from yet another CMS generation that we are responsible for, just
2198     // ignore it since all relevant work has already been done.
2199     return;
2200   }
2201   assert(haveFreelistLocks(), "must have freelist locks");
2202   assert_lock_strong(bitMapLock());
2203 
2204   _ct->klass_rem_set()->set_accumulate_modified_oops(false);
2205 
2206   _cmsGen->gc_epilogue_work(full);
2207 
2208   if (_collectorState == AbortablePreclean || _collectorState == Precleaning) {
2209     // in case sampling was not already enabled, enable it
2210     _start_sampling = true;
2211   }
2212   // reset _eden_chunk_array so sampling starts afresh
2213   _eden_chunk_index = 0;
2214 
2215   size_t cms_used   = _cmsGen->cmsSpace()->used();
2216 
2217   // update performance counters - this uses a special version of
2218   // update_counters() that allows the utilization to be passed as a
2219   // parameter, avoiding multiple calls to used().
2220   //
2221   _cmsGen->update_counters(cms_used);
2222 
2223   bitMapLock()->unlock();
2224   releaseFreelistLocks();
2225 
2226   if (!CleanChunkPoolAsync) {
2227     Chunk::clean_chunk_pool();
2228   }
2229 
2230   set_did_compact(false);
2231   _between_prologue_and_epilogue = false;  // ready for next cycle
2232 }
2233 
2234 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) {
2235   collector()->gc_epilogue(full);
2236 
2237   // Also reset promotion tracking in par gc thread states.
2238   for (uint i = 0; i < ParallelGCThreads; i++) {
2239     _par_gc_thread_states[i]->promo.stopTrackingPromotions(i);
2240   }
2241 }
2242 
2243 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2244   assert(!incremental_collection_failed(), "Should have been cleared");
2245   cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2246   cmsSpace()->gc_epilogue();
2247     // Print stat counters
2248   NOT_PRODUCT(
2249     assert(_numObjectsAllocated == 0, "check");
2250     assert(_numWordsAllocated == 0, "check");
2251     if (Verbose && PrintGC) {
2252       gclog_or_tty->print("Promoted "SIZE_FORMAT" objects, "
2253                           SIZE_FORMAT" bytes",
2254                  _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2255     }
2256     _numObjectsPromoted = 0;
2257     _numWordsPromoted   = 0;
2258   )
2259 
2260   if (PrintGC && Verbose) {
2261     // Call down the chain in contiguous_available needs the freelistLock
2262     // so print this out before releasing the freeListLock.
2263     gclog_or_tty->print(" Contiguous available "SIZE_FORMAT" bytes ",
2264                         contiguous_available());
2265   }
2266 }
2267 
2268 #ifndef PRODUCT
2269 bool CMSCollector::have_cms_token() {
2270   Thread* thr = Thread::current();
2271   if (thr->is_VM_thread()) {
2272     return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2273   } else if (thr->is_ConcurrentGC_thread()) {
2274     return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2275   } else if (thr->is_GC_task_thread()) {
2276     return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2277            ParGCRareEvent_lock->owned_by_self();
2278   }
2279   return false;
2280 }
2281 #endif
2282 
2283 // Check reachability of the given heap address in CMS generation,
2284 // treating all other generations as roots.
2285 bool CMSCollector::is_cms_reachable(HeapWord* addr) {
2286   // We could "guarantee" below, rather than assert, but I'll
2287   // leave these as "asserts" so that an adventurous debugger
2288   // could try this in the product build provided some subset of
2289   // the conditions were met, provided they were interested in the
2290   // results and knew that the computation below wouldn't interfere
2291   // with other concurrent computations mutating the structures
2292   // being read or written.
2293   assert(SafepointSynchronize::is_at_safepoint(),
2294          "Else mutations in object graph will make answer suspect");
2295   assert(have_cms_token(), "Should hold cms token");
2296   assert(haveFreelistLocks(), "must hold free list locks");
2297   assert_lock_strong(bitMapLock());
2298 
2299   // Clear the marking bit map array before starting, but, just
2300   // for kicks, first report if the given address is already marked
2301   gclog_or_tty->print_cr("Start: Address " PTR_FORMAT " is%s marked", p2i(addr),
2302                 _markBitMap.isMarked(addr) ? "" : " not");
2303 
2304   if (verify_after_remark()) {
2305     MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2306     bool result = verification_mark_bm()->isMarked(addr);
2307     gclog_or_tty->print_cr("TransitiveMark: Address " PTR_FORMAT " %s marked", p2i(addr),
2308                            result ? "IS" : "is NOT");
2309     return result;
2310   } else {
2311     gclog_or_tty->print_cr("Could not compute result");
2312     return false;
2313   }
2314 }
2315 
2316 
2317 void
2318 CMSCollector::print_on_error(outputStream* st) {
2319   CMSCollector* collector = ConcurrentMarkSweepGeneration::_collector;
2320   if (collector != NULL) {
2321     CMSBitMap* bitmap = &collector->_markBitMap;
2322     st->print_cr("Marking Bits: (CMSBitMap*) " PTR_FORMAT, p2i(bitmap));
2323     bitmap->print_on_error(st, " Bits: ");
2324 
2325     st->cr();
2326 
2327     CMSBitMap* mut_bitmap = &collector->_modUnionTable;
2328     st->print_cr("Mod Union Table: (CMSBitMap*) " PTR_FORMAT, p2i(mut_bitmap));
2329     mut_bitmap->print_on_error(st, " Bits: ");
2330   }
2331 }
2332 
2333 ////////////////////////////////////////////////////////
2334 // CMS Verification Support
2335 ////////////////////////////////////////////////////////
2336 // Following the remark phase, the following invariant
2337 // should hold -- each object in the CMS heap which is
2338 // marked in markBitMap() should be marked in the verification_mark_bm().
2339 
2340 class VerifyMarkedClosure: public BitMapClosure {
2341   CMSBitMap* _marks;
2342   bool       _failed;
2343 
2344  public:
2345   VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2346 
2347   bool do_bit(size_t offset) {
2348     HeapWord* addr = _marks->offsetToHeapWord(offset);
2349     if (!_marks->isMarked(addr)) {
2350       oop(addr)->print_on(gclog_or_tty);
2351       gclog_or_tty->print_cr(" ("INTPTR_FORMAT" should have been marked)", p2i(addr));
2352       _failed = true;
2353     }
2354     return true;
2355   }
2356 
2357   bool failed() { return _failed; }
2358 };
2359 
2360 bool CMSCollector::verify_after_remark(bool silent) {
2361   if (!silent) gclog_or_tty->print(" [Verifying CMS Marking... ");
2362   MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2363   static bool init = false;
2364 
2365   assert(SafepointSynchronize::is_at_safepoint(),
2366          "Else mutations in object graph will make answer suspect");
2367   assert(have_cms_token(),
2368          "Else there may be mutual interference in use of "
2369          " verification data structures");
2370   assert(_collectorState > Marking && _collectorState <= Sweeping,
2371          "Else marking info checked here may be obsolete");
2372   assert(haveFreelistLocks(), "must hold free list locks");
2373   assert_lock_strong(bitMapLock());
2374 
2375 
2376   // Allocate marking bit map if not already allocated
2377   if (!init) { // first time
2378     if (!verification_mark_bm()->allocate(_span)) {
2379       return false;
2380     }
2381     init = true;
2382   }
2383 
2384   assert(verification_mark_stack()->isEmpty(), "Should be empty");
2385 
2386   // Turn off refs discovery -- so we will be tracing through refs.
2387   // This is as intended, because by this time
2388   // GC must already have cleared any refs that need to be cleared,
2389   // and traced those that need to be marked; moreover,
2390   // the marking done here is not going to interfere in any
2391   // way with the marking information used by GC.
2392   NoRefDiscovery no_discovery(ref_processor());
2393 
2394   COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
2395 
2396   // Clear any marks from a previous round
2397   verification_mark_bm()->clear_all();
2398   assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
2399   verify_work_stacks_empty();
2400 
2401   GenCollectedHeap* gch = GenCollectedHeap::heap();
2402   gch->ensure_parsability(false);  // fill TLABs, but no need to retire them
2403   // Update the saved marks which may affect the root scans.
2404   gch->save_marks();
2405 
2406   if (CMSRemarkVerifyVariant == 1) {
2407     // In this first variant of verification, we complete
2408     // all marking, then check if the new marks-vector is
2409     // a subset of the CMS marks-vector.
2410     verify_after_remark_work_1();
2411   } else if (CMSRemarkVerifyVariant == 2) {
2412     // In this second variant of verification, we flag an error
2413     // (i.e. an object reachable in the new marks-vector not reachable
2414     // in the CMS marks-vector) immediately, also indicating the
2415     // identify of an object (A) that references the unmarked object (B) --
2416     // presumably, a mutation to A failed to be picked up by preclean/remark?
2417     verify_after_remark_work_2();
2418   } else {
2419     warning("Unrecognized value " UINTX_FORMAT " for CMSRemarkVerifyVariant",
2420             CMSRemarkVerifyVariant);
2421   }
2422   if (!silent) gclog_or_tty->print(" done] ");
2423   return true;
2424 }
2425 
2426 void CMSCollector::verify_after_remark_work_1() {
2427   ResourceMark rm;
2428   HandleMark  hm;
2429   GenCollectedHeap* gch = GenCollectedHeap::heap();
2430 
2431   // Get a clear set of claim bits for the roots processing to work with.
2432   ClassLoaderDataGraph::clear_claimed_marks();
2433 
2434   // Mark from roots one level into CMS
2435   MarkRefsIntoClosure notOlder(_span, verification_mark_bm());
2436   gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2437 
2438   gch->gen_process_roots(_cmsGen->level(),
2439                          true,   // younger gens are roots
2440                          true,   // activate StrongRootsScope
2441                          GenCollectedHeap::ScanningOption(roots_scanning_options()),
2442                          should_unload_classes(),
2443                          &notOlder,
2444                          NULL,
2445                          NULL);  // SSS: Provide correct closure
2446 
2447   // Now mark from the roots
2448   MarkFromRootsClosure markFromRootsClosure(this, _span,
2449     verification_mark_bm(), verification_mark_stack(),
2450     false /* don't yield */, true /* verifying */);
2451   assert(_restart_addr == NULL, "Expected pre-condition");
2452   verification_mark_bm()->iterate(&markFromRootsClosure);
2453   while (_restart_addr != NULL) {
2454     // Deal with stack overflow: by restarting at the indicated
2455     // address.
2456     HeapWord* ra = _restart_addr;
2457     markFromRootsClosure.reset(ra);
2458     _restart_addr = NULL;
2459     verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2460   }
2461   assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2462   verify_work_stacks_empty();
2463 
2464   // Marking completed -- now verify that each bit marked in
2465   // verification_mark_bm() is also marked in markBitMap(); flag all
2466   // errors by printing corresponding objects.
2467   VerifyMarkedClosure vcl(markBitMap());
2468   verification_mark_bm()->iterate(&vcl);
2469   if (vcl.failed()) {
2470     gclog_or_tty->print("Verification failed");
2471     Universe::heap()->print_on(gclog_or_tty);
2472     fatal("CMS: failed marking verification after remark");
2473   }
2474 }
2475 
2476 class VerifyKlassOopsKlassClosure : public KlassClosure {
2477   class VerifyKlassOopsClosure : public OopClosure {
2478     CMSBitMap* _bitmap;
2479    public:
2480     VerifyKlassOopsClosure(CMSBitMap* bitmap) : _bitmap(bitmap) { }
2481     void do_oop(oop* p)       { guarantee(*p == NULL || _bitmap->isMarked((HeapWord*) *p), "Should be marked"); }
2482     void do_oop(narrowOop* p) { ShouldNotReachHere(); }
2483   } _oop_closure;
2484  public:
2485   VerifyKlassOopsKlassClosure(CMSBitMap* bitmap) : _oop_closure(bitmap) {}
2486   void do_klass(Klass* k) {
2487     k->oops_do(&_oop_closure);
2488   }
2489 };
2490 
2491 void CMSCollector::verify_after_remark_work_2() {
2492   ResourceMark rm;
2493   HandleMark  hm;
2494   GenCollectedHeap* gch = GenCollectedHeap::heap();
2495 
2496   // Get a clear set of claim bits for the roots processing to work with.
2497   ClassLoaderDataGraph::clear_claimed_marks();
2498 
2499   // Mark from roots one level into CMS
2500   MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
2501                                      markBitMap());
2502   CLDToOopClosure cld_closure(&notOlder, true);
2503 
2504   gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2505 
2506   gch->gen_process_roots(_cmsGen->level(),
2507                          true,   // younger gens are roots
2508                          true,   // activate StrongRootsScope
2509                          GenCollectedHeap::ScanningOption(roots_scanning_options()),
2510                          should_unload_classes(),
2511                          &notOlder,
2512                          NULL,
2513                          &cld_closure);
2514 
2515   // Now mark from the roots
2516   MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
2517     verification_mark_bm(), markBitMap(), verification_mark_stack());
2518   assert(_restart_addr == NULL, "Expected pre-condition");
2519   verification_mark_bm()->iterate(&markFromRootsClosure);
2520   while (_restart_addr != NULL) {
2521     // Deal with stack overflow: by restarting at the indicated
2522     // address.
2523     HeapWord* ra = _restart_addr;
2524     markFromRootsClosure.reset(ra);
2525     _restart_addr = NULL;
2526     verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2527   }
2528   assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2529   verify_work_stacks_empty();
2530 
2531   VerifyKlassOopsKlassClosure verify_klass_oops(verification_mark_bm());
2532   ClassLoaderDataGraph::classes_do(&verify_klass_oops);
2533 
2534   // Marking completed -- now verify that each bit marked in
2535   // verification_mark_bm() is also marked in markBitMap(); flag all
2536   // errors by printing corresponding objects.
2537   VerifyMarkedClosure vcl(markBitMap());
2538   verification_mark_bm()->iterate(&vcl);
2539   assert(!vcl.failed(), "Else verification above should not have succeeded");
2540 }
2541 
2542 void ConcurrentMarkSweepGeneration::save_marks() {
2543   // delegate to CMS space
2544   cmsSpace()->save_marks();
2545   for (uint i = 0; i < ParallelGCThreads; i++) {
2546     _par_gc_thread_states[i]->promo.startTrackingPromotions();
2547   }
2548 }
2549 
2550 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
2551   return cmsSpace()->no_allocs_since_save_marks();
2552 }
2553 
2554 #define CMS_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix)    \
2555                                                                 \
2556 void ConcurrentMarkSweepGeneration::                            \
2557 oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) {   \
2558   cl->set_generation(this);                                     \
2559   cmsSpace()->oop_since_save_marks_iterate##nv_suffix(cl);      \
2560   cl->reset_generation();                                       \
2561   save_marks();                                                 \
2562 }
2563 
2564 ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DEFN)
2565 
2566 void
2567 ConcurrentMarkSweepGeneration::oop_iterate(ExtendedOopClosure* cl) {
2568   if (freelistLock()->owned_by_self()) {
2569     Generation::oop_iterate(cl);
2570   } else {
2571     MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2572     Generation::oop_iterate(cl);
2573   }
2574 }
2575 
2576 void
2577 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
2578   if (freelistLock()->owned_by_self()) {
2579     Generation::object_iterate(cl);
2580   } else {
2581     MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2582     Generation::object_iterate(cl);
2583   }
2584 }
2585 
2586 void
2587 ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) {
2588   if (freelistLock()->owned_by_self()) {
2589     Generation::safe_object_iterate(cl);
2590   } else {
2591     MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2592     Generation::safe_object_iterate(cl);
2593   }
2594 }
2595 
2596 void
2597 ConcurrentMarkSweepGeneration::post_compact() {
2598 }
2599 
2600 void
2601 ConcurrentMarkSweepGeneration::prepare_for_verify() {
2602   // Fix the linear allocation blocks to look like free blocks.
2603 
2604   // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2605   // are not called when the heap is verified during universe initialization and
2606   // at vm shutdown.
2607   if (freelistLock()->owned_by_self()) {
2608     cmsSpace()->prepare_for_verify();
2609   } else {
2610     MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2611     cmsSpace()->prepare_for_verify();
2612   }
2613 }
2614 
2615 void
2616 ConcurrentMarkSweepGeneration::verify() {
2617   // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2618   // are not called when the heap is verified during universe initialization and
2619   // at vm shutdown.
2620   if (freelistLock()->owned_by_self()) {
2621     cmsSpace()->verify();
2622   } else {
2623     MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2624     cmsSpace()->verify();
2625   }
2626 }
2627 
2628 void CMSCollector::verify() {
2629   _cmsGen->verify();
2630 }
2631 
2632 #ifndef PRODUCT
2633 bool CMSCollector::overflow_list_is_empty() const {
2634   assert(_num_par_pushes >= 0, "Inconsistency");
2635   if (_overflow_list == NULL) {
2636     assert(_num_par_pushes == 0, "Inconsistency");
2637   }
2638   return _overflow_list == NULL;
2639 }
2640 
2641 // The methods verify_work_stacks_empty() and verify_overflow_empty()
2642 // merely consolidate assertion checks that appear to occur together frequently.
2643 void CMSCollector::verify_work_stacks_empty() const {
2644   assert(_markStack.isEmpty(), "Marking stack should be empty");
2645   assert(overflow_list_is_empty(), "Overflow list should be empty");
2646 }
2647 
2648 void CMSCollector::verify_overflow_empty() const {
2649   assert(overflow_list_is_empty(), "Overflow list should be empty");
2650   assert(no_preserved_marks(), "No preserved marks");
2651 }
2652 #endif // PRODUCT
2653 
2654 // Decide if we want to enable class unloading as part of the
2655 // ensuing concurrent GC cycle. We will collect and
2656 // unload classes if it's the case that:
2657 // (1) an explicit gc request has been made and the flag
2658 //     ExplicitGCInvokesConcurrentAndUnloadsClasses is set, OR
2659 // (2) (a) class unloading is enabled at the command line, and
2660 //     (b) old gen is getting really full
2661 // NOTE: Provided there is no change in the state of the heap between
2662 // calls to this method, it should have idempotent results. Moreover,
2663 // its results should be monotonically increasing (i.e. going from 0 to 1,
2664 // but not 1 to 0) between successive calls between which the heap was
2665 // not collected. For the implementation below, it must thus rely on
2666 // the property that concurrent_cycles_since_last_unload()
2667 // will not decrease unless a collection cycle happened and that
2668 // _cmsGen->is_too_full() are
2669 // themselves also monotonic in that sense. See check_monotonicity()
2670 // below.
2671 void CMSCollector::update_should_unload_classes() {
2672   _should_unload_classes = false;
2673   // Condition 1 above
2674   if (_full_gc_requested && ExplicitGCInvokesConcurrentAndUnloadsClasses) {
2675     _should_unload_classes = true;
2676   } else if (CMSClassUnloadingEnabled) { // Condition 2.a above
2677     // Disjuncts 2.b.(i,ii,iii) above
2678     _should_unload_classes = (concurrent_cycles_since_last_unload() >=
2679                               CMSClassUnloadingMaxInterval)
2680                            || _cmsGen->is_too_full();
2681   }
2682 }
2683 
2684 bool ConcurrentMarkSweepGeneration::is_too_full() const {
2685   bool res = should_concurrent_collect();
2686   res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
2687   return res;
2688 }
2689 
2690 void CMSCollector::setup_cms_unloading_and_verification_state() {
2691   const  bool should_verify =   VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
2692                              || VerifyBeforeExit;
2693   const  int  rso           =   GenCollectedHeap::SO_AllCodeCache;
2694 
2695   // We set the proper root for this CMS cycle here.
2696   if (should_unload_classes()) {   // Should unload classes this cycle
2697     remove_root_scanning_option(rso);  // Shrink the root set appropriately
2698     set_verifying(should_verify);    // Set verification state for this cycle
2699     return;                            // Nothing else needs to be done at this time
2700   }
2701 
2702   // Not unloading classes this cycle
2703   assert(!should_unload_classes(), "Inconsistency!");
2704 
2705   if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
2706     // Include symbols, strings and code cache elements to prevent their resurrection.
2707     add_root_scanning_option(rso);
2708     set_verifying(true);
2709   } else if (verifying() && !should_verify) {
2710     // We were verifying, but some verification flags got disabled.
2711     set_verifying(false);
2712     // Exclude symbols, strings and code cache elements from root scanning to
2713     // reduce IM and RM pauses.
2714     remove_root_scanning_option(rso);
2715   }
2716 }
2717 
2718 
2719 #ifndef PRODUCT
2720 HeapWord* CMSCollector::block_start(const void* p) const {
2721   const HeapWord* addr = (HeapWord*)p;
2722   if (_span.contains(p)) {
2723     if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
2724       return _cmsGen->cmsSpace()->block_start(p);
2725     }
2726   }
2727   return NULL;
2728 }
2729 #endif
2730 
2731 HeapWord*
2732 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
2733                                                    bool   tlab,
2734                                                    bool   parallel) {
2735   CMSSynchronousYieldRequest yr;
2736   assert(!tlab, "Can't deal with TLAB allocation");
2737   MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2738   expand_for_gc_cause(word_size*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_allocation);
2739   if (GCExpandToAllocateDelayMillis > 0) {
2740     os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2741   }
2742   return have_lock_and_allocate(word_size, tlab);
2743 }
2744 
2745 void ConcurrentMarkSweepGeneration::expand_for_gc_cause(
2746     size_t bytes,
2747     size_t expand_bytes,
2748     CMSExpansionCause::Cause cause)
2749 {
2750 
2751   bool success = expand(bytes, expand_bytes);
2752 
2753   // remember why we expanded; this information is used
2754   // by shouldConcurrentCollect() when making decisions on whether to start
2755   // a new CMS cycle.
2756   if (success) {
2757     set_expansion_cause(cause);
2758     if (PrintGCDetails && Verbose) {
2759       gclog_or_tty->print_cr("Expanded CMS gen for %s",
2760         CMSExpansionCause::to_string(cause));
2761     }
2762   }
2763 }
2764 
2765 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
2766   HeapWord* res = NULL;
2767   MutexLocker x(ParGCRareEvent_lock);
2768   while (true) {
2769     // Expansion by some other thread might make alloc OK now:
2770     res = ps->lab.alloc(word_sz);
2771     if (res != NULL) return res;
2772     // If there's not enough expansion space available, give up.
2773     if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
2774       return NULL;
2775     }
2776     // Otherwise, we try expansion.
2777     expand_for_gc_cause(word_sz*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_lab);
2778     // Now go around the loop and try alloc again;
2779     // A competing par_promote might beat us to the expansion space,
2780     // so we may go around the loop again if promotion fails again.
2781     if (GCExpandToAllocateDelayMillis > 0) {
2782       os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2783     }
2784   }
2785 }
2786 
2787 
2788 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
2789   PromotionInfo* promo) {
2790   MutexLocker x(ParGCRareEvent_lock);
2791   size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
2792   while (true) {
2793     // Expansion by some other thread might make alloc OK now:
2794     if (promo->ensure_spooling_space()) {
2795       assert(promo->has_spooling_space(),
2796              "Post-condition of successful ensure_spooling_space()");
2797       return true;
2798     }
2799     // If there's not enough expansion space available, give up.
2800     if (_virtual_space.uncommitted_size() < refill_size_bytes) {
2801       return false;
2802     }
2803     // Otherwise, we try expansion.
2804     expand_for_gc_cause(refill_size_bytes, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_spooling_space);
2805     // Now go around the loop and try alloc again;
2806     // A competing allocation might beat us to the expansion space,
2807     // so we may go around the loop again if allocation fails again.
2808     if (GCExpandToAllocateDelayMillis > 0) {
2809       os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2810     }
2811   }
2812 }
2813 
2814 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
2815   // Only shrink if a compaction was done so that all the free space
2816   // in the generation is in a contiguous block at the end.
2817   if (did_compact()) {
2818     CardGeneration::shrink(bytes);
2819   }
2820 }
2821 
2822 void ConcurrentMarkSweepGeneration::assert_correct_size_change_locking() {
2823   assert_locked_or_safepoint(Heap_lock);
2824 }
2825 
2826 void ConcurrentMarkSweepGeneration::shrink_free_list_by(size_t bytes) {
2827   assert_locked_or_safepoint(Heap_lock);
2828   assert_lock_strong(freelistLock());
2829   if (PrintGCDetails && Verbose) {
2830     warning("Shrinking of CMS not yet implemented");
2831   }
2832   return;
2833 }
2834 
2835 
2836 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
2837 // phases.
2838 class CMSPhaseAccounting: public StackObj {
2839  public:
2840   CMSPhaseAccounting(CMSCollector *collector,
2841                      const char *phase,
2842                      const GCId gc_id,
2843                      bool print_cr = true);
2844   ~CMSPhaseAccounting();
2845 
2846  private:
2847   CMSCollector *_collector;
2848   const char *_phase;
2849   elapsedTimer _wallclock;
2850   bool _print_cr;
2851   const GCId _gc_id;
2852 
2853  public:
2854   // Not MT-safe; so do not pass around these StackObj's
2855   // where they may be accessed by other threads.
2856   jlong wallclock_millis() {
2857     assert(_wallclock.is_active(), "Wall clock should not stop");
2858     _wallclock.stop();  // to record time
2859     jlong ret = _wallclock.milliseconds();
2860     _wallclock.start(); // restart
2861     return ret;
2862   }
2863 };
2864 
2865 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
2866                                        const char *phase,
2867                                        const GCId gc_id,
2868                                        bool print_cr) :
2869   _collector(collector), _phase(phase), _print_cr(print_cr), _gc_id(gc_id) {
2870 
2871   if (PrintCMSStatistics != 0) {
2872     _collector->resetYields();
2873   }
2874   if (PrintGCDetails) {
2875     gclog_or_tty->gclog_stamp(_gc_id);
2876     gclog_or_tty->print_cr("[%s-concurrent-%s-start]",
2877       _collector->cmsGen()->short_name(), _phase);
2878   }
2879   _collector->resetTimer();
2880   _wallclock.start();
2881   _collector->startTimer();
2882 }
2883 
2884 CMSPhaseAccounting::~CMSPhaseAccounting() {
2885   assert(_wallclock.is_active(), "Wall clock should not have stopped");
2886   _collector->stopTimer();
2887   _wallclock.stop();
2888   if (PrintGCDetails) {
2889     gclog_or_tty->gclog_stamp(_gc_id);
2890     gclog_or_tty->print("[%s-concurrent-%s: %3.3f/%3.3f secs]",
2891                  _collector->cmsGen()->short_name(),
2892                  _phase, _collector->timerValue(), _wallclock.seconds());
2893     if (_print_cr) {
2894       gclog_or_tty->cr();
2895     }
2896     if (PrintCMSStatistics != 0) {
2897       gclog_or_tty->print_cr(" (CMS-concurrent-%s yielded %d times)", _phase,
2898                     _collector->yields());
2899     }
2900   }
2901 }
2902 
2903 // CMS work
2904 
2905 // The common parts of CMSParInitialMarkTask and CMSParRemarkTask.
2906 class CMSParMarkTask : public AbstractGangTask {
2907  protected:
2908   CMSCollector*     _collector;
2909   int               _n_workers;
2910   CMSParMarkTask(const char* name, CMSCollector* collector, int n_workers) :
2911       AbstractGangTask(name),
2912       _collector(collector),
2913       _n_workers(n_workers) {}
2914   // Work method in support of parallel rescan ... of young gen spaces
2915   void do_young_space_rescan(uint worker_id, OopsInGenClosure* cl,
2916                              ContiguousSpace* space,
2917                              HeapWord** chunk_array, size_t chunk_top);
2918   void work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl);
2919 };
2920 
2921 // Parallel initial mark task
2922 class CMSParInitialMarkTask: public CMSParMarkTask {
2923  public:
2924   CMSParInitialMarkTask(CMSCollector* collector, int n_workers) :
2925       CMSParMarkTask("Scan roots and young gen for initial mark in parallel",
2926                      collector, n_workers) {}
2927   void work(uint worker_id);
2928 };
2929 
2930 // Checkpoint the roots into this generation from outside
2931 // this generation. [Note this initial checkpoint need only
2932 // be approximate -- we'll do a catch up phase subsequently.]
2933 void CMSCollector::checkpointRootsInitial() {
2934   assert(_collectorState == InitialMarking, "Wrong collector state");
2935   check_correct_thread_executing();
2936   TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
2937 
2938   save_heap_summary();
2939   report_heap_summary(GCWhen::BeforeGC);
2940 
2941   ReferenceProcessor* rp = ref_processor();
2942   assert(_restart_addr == NULL, "Control point invariant");
2943   {
2944     // acquire locks for subsequent manipulations
2945     MutexLockerEx x(bitMapLock(),
2946                     Mutex::_no_safepoint_check_flag);
2947     checkpointRootsInitialWork();
2948     // enable ("weak") refs discovery
2949     rp->enable_discovery();
2950     _collectorState = Marking;
2951   }
2952 }
2953 
2954 void CMSCollector::checkpointRootsInitialWork() {
2955   assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
2956   assert(_collectorState == InitialMarking, "just checking");
2957 
2958   // If there has not been a GC[n-1] since last GC[n] cycle completed,
2959   // precede our marking with a collection of all
2960   // younger generations to keep floating garbage to a minimum.
2961   // XXX: we won't do this for now -- it's an optimization to be done later.
2962 
2963   // already have locks
2964   assert_lock_strong(bitMapLock());
2965   assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
2966 
2967   // Setup the verification and class unloading state for this
2968   // CMS collection cycle.
2969   setup_cms_unloading_and_verification_state();
2970 
2971   NOT_PRODUCT(GCTraceTime t("\ncheckpointRootsInitialWork",
2972     PrintGCDetails && Verbose, true, _gc_timer_cm, _gc_tracer_cm->gc_id());)
2973 
2974   // Reset all the PLAB chunk arrays if necessary.
2975   if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
2976     reset_survivor_plab_arrays();
2977   }
2978 
2979   ResourceMark rm;
2980   HandleMark  hm;
2981 
2982   MarkRefsIntoClosure notOlder(_span, &_markBitMap);
2983   GenCollectedHeap* gch = GenCollectedHeap::heap();
2984 
2985   verify_work_stacks_empty();
2986   verify_overflow_empty();
2987 
2988   gch->ensure_parsability(false);  // fill TLABs, but no need to retire them
2989   // Update the saved marks which may affect the root scans.
2990   gch->save_marks();
2991 
2992   // weak reference processing has not started yet.
2993   ref_processor()->set_enqueuing_is_done(false);
2994 
2995   // Need to remember all newly created CLDs,
2996   // so that we can guarantee that the remark finds them.
2997   ClassLoaderDataGraph::remember_new_clds(true);
2998 
2999   // Whenever a CLD is found, it will be claimed before proceeding to mark
3000   // the klasses. The claimed marks need to be cleared before marking starts.
3001   ClassLoaderDataGraph::clear_claimed_marks();
3002 
3003   if (CMSPrintEdenSurvivorChunks) {
3004     print_eden_and_survivor_chunk_arrays();
3005   }
3006 
3007   {
3008     COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
3009     if (CMSParallelInitialMarkEnabled && CollectedHeap::use_parallel_gc_threads()) {
3010       // The parallel version.
3011       FlexibleWorkGang* workers = gch->workers();
3012       assert(workers != NULL, "Need parallel worker threads.");
3013       int n_workers = workers->active_workers();
3014       CMSParInitialMarkTask tsk(this, n_workers);
3015       gch->set_par_threads(n_workers);
3016       initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
3017       if (n_workers > 1) {
3018         StrongRootsScope srs;
3019         workers->run_task(&tsk);
3020       } else {
3021         StrongRootsScope srs;
3022         tsk.work(0);
3023       }
3024       gch->set_par_threads(0);
3025     } else {
3026       // The serial version.
3027       CLDToOopClosure cld_closure(&notOlder, true);
3028       gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3029       gch->gen_process_roots(_cmsGen->level(),
3030                              true,   // younger gens are roots
3031                              true,   // activate StrongRootsScope
3032                              GenCollectedHeap::ScanningOption(roots_scanning_options()),
3033                              should_unload_classes(),
3034                              &notOlder,
3035                              NULL,
3036                              &cld_closure);
3037     }
3038   }
3039 
3040   // Clear mod-union table; it will be dirtied in the prologue of
3041   // CMS generation per each younger generation collection.
3042 
3043   assert(_modUnionTable.isAllClear(),
3044        "Was cleared in most recent final checkpoint phase"
3045        " or no bits are set in the gc_prologue before the start of the next "
3046        "subsequent marking phase.");
3047 
3048   assert(_ct->klass_rem_set()->mod_union_is_clear(), "Must be");
3049 
3050   // Save the end of the used_region of the constituent generations
3051   // to be used to limit the extent of sweep in each generation.
3052   save_sweep_limits();
3053   verify_overflow_empty();
3054 }
3055 
3056 bool CMSCollector::markFromRoots() {
3057   // we might be tempted to assert that:
3058   // assert(!SafepointSynchronize::is_at_safepoint(),
3059   //        "inconsistent argument?");
3060   // However that wouldn't be right, because it's possible that
3061   // a safepoint is indeed in progress as a younger generation
3062   // stop-the-world GC happens even as we mark in this generation.
3063   assert(_collectorState == Marking, "inconsistent state?");
3064   check_correct_thread_executing();
3065   verify_overflow_empty();
3066 
3067   // Weak ref discovery note: We may be discovering weak
3068   // refs in this generation concurrent (but interleaved) with
3069   // weak ref discovery by a younger generation collector.
3070 
3071   CMSTokenSyncWithLocks ts(true, bitMapLock());
3072   TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3073   CMSPhaseAccounting pa(this, "mark", _gc_tracer_cm->gc_id(), !PrintGCDetails);
3074   bool res = markFromRootsWork();
3075   if (res) {
3076     _collectorState = Precleaning;
3077   } else { // We failed and a foreground collection wants to take over
3078     assert(_foregroundGCIsActive, "internal state inconsistency");
3079     assert(_restart_addr == NULL,  "foreground will restart from scratch");
3080     if (PrintGCDetails) {
3081       gclog_or_tty->print_cr("bailing out to foreground collection");
3082     }
3083   }
3084   verify_overflow_empty();
3085   return res;
3086 }
3087 
3088 bool CMSCollector::markFromRootsWork() {
3089   // iterate over marked bits in bit map, doing a full scan and mark
3090   // from these roots using the following algorithm:
3091   // . if oop is to the right of the current scan pointer,
3092   //   mark corresponding bit (we'll process it later)
3093   // . else (oop is to left of current scan pointer)
3094   //   push oop on marking stack
3095   // . drain the marking stack
3096 
3097   // Note that when we do a marking step we need to hold the
3098   // bit map lock -- recall that direct allocation (by mutators)
3099   // and promotion (by younger generation collectors) is also
3100   // marking the bit map. [the so-called allocate live policy.]
3101   // Because the implementation of bit map marking is not
3102   // robust wrt simultaneous marking of bits in the same word,
3103   // we need to make sure that there is no such interference
3104   // between concurrent such updates.
3105 
3106   // already have locks
3107   assert_lock_strong(bitMapLock());
3108 
3109   verify_work_stacks_empty();
3110   verify_overflow_empty();
3111   bool result = false;
3112   if (CMSConcurrentMTEnabled && ConcGCThreads > 0) {
3113     result = do_marking_mt();
3114   } else {
3115     result = do_marking_st();
3116   }
3117   return result;
3118 }
3119 
3120 // Forward decl
3121 class CMSConcMarkingTask;
3122 
3123 class CMSConcMarkingTerminator: public ParallelTaskTerminator {
3124   CMSCollector*       _collector;
3125   CMSConcMarkingTask* _task;
3126  public:
3127   virtual void yield();
3128 
3129   // "n_threads" is the number of threads to be terminated.
3130   // "queue_set" is a set of work queues of other threads.
3131   // "collector" is the CMS collector associated with this task terminator.
3132   // "yield" indicates whether we need the gang as a whole to yield.
3133   CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
3134     ParallelTaskTerminator(n_threads, queue_set),
3135     _collector(collector) { }
3136 
3137   void set_task(CMSConcMarkingTask* task) {
3138     _task = task;
3139   }
3140 };
3141 
3142 class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator {
3143   CMSConcMarkingTask* _task;
3144  public:
3145   bool should_exit_termination();
3146   void set_task(CMSConcMarkingTask* task) {
3147     _task = task;
3148   }
3149 };
3150 
3151 // MT Concurrent Marking Task
3152 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3153   CMSCollector* _collector;
3154   int           _n_workers;                  // requested/desired # workers
3155   bool          _result;
3156   CompactibleFreeListSpace*  _cms_space;
3157   char          _pad_front[64];   // padding to ...
3158   HeapWord*     _global_finger;   // ... avoid sharing cache line
3159   char          _pad_back[64];
3160   HeapWord*     _restart_addr;
3161 
3162   //  Exposed here for yielding support
3163   Mutex* const _bit_map_lock;
3164 
3165   // The per thread work queues, available here for stealing
3166   OopTaskQueueSet*  _task_queues;
3167 
3168   // Termination (and yielding) support
3169   CMSConcMarkingTerminator _term;
3170   CMSConcMarkingTerminatorTerminator _term_term;
3171 
3172  public:
3173   CMSConcMarkingTask(CMSCollector* collector,
3174                  CompactibleFreeListSpace* cms_space,
3175                  YieldingFlexibleWorkGang* workers,
3176                  OopTaskQueueSet* task_queues):
3177     YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3178     _collector(collector),
3179     _cms_space(cms_space),
3180     _n_workers(0), _result(true),
3181     _task_queues(task_queues),
3182     _term(_n_workers, task_queues, _collector),
3183     _bit_map_lock(collector->bitMapLock())
3184   {
3185     _requested_size = _n_workers;
3186     _term.set_task(this);
3187     _term_term.set_task(this);
3188     _restart_addr = _global_finger = _cms_space->bottom();
3189   }
3190 
3191 
3192   OopTaskQueueSet* task_queues()  { return _task_queues; }
3193 
3194   OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3195 
3196   HeapWord** global_finger_addr() { return &_global_finger; }
3197 
3198   CMSConcMarkingTerminator* terminator() { return &_term; }
3199 
3200   virtual void set_for_termination(int active_workers) {
3201     terminator()->reset_for_reuse(active_workers);
3202   }
3203 
3204   void work(uint worker_id);
3205   bool should_yield() {
3206     return    ConcurrentMarkSweepThread::should_yield()
3207            && !_collector->foregroundGCIsActive();
3208   }
3209 
3210   virtual void coordinator_yield();  // stuff done by coordinator
3211   bool result() { return _result; }
3212 
3213   void reset(HeapWord* ra) {
3214     assert(_global_finger >= _cms_space->end(),  "Postcondition of ::work(i)");
3215     _restart_addr = _global_finger = ra;
3216     _term.reset_for_reuse();
3217   }
3218 
3219   static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3220                                            OopTaskQueue* work_q);
3221 
3222  private:
3223   void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3224   void do_work_steal(int i);
3225   void bump_global_finger(HeapWord* f);
3226 };
3227 
3228 bool CMSConcMarkingTerminatorTerminator::should_exit_termination() {
3229   assert(_task != NULL, "Error");
3230   return _task->yielding();
3231   // Note that we do not need the disjunct || _task->should_yield() above
3232   // because we want terminating threads to yield only if the task
3233   // is already in the midst of yielding, which happens only after at least one
3234   // thread has yielded.
3235 }
3236 
3237 void CMSConcMarkingTerminator::yield() {
3238   if (_task->should_yield()) {
3239     _task->yield();
3240   } else {
3241     ParallelTaskTerminator::yield();
3242   }
3243 }
3244 
3245 ////////////////////////////////////////////////////////////////
3246 // Concurrent Marking Algorithm Sketch
3247 ////////////////////////////////////////////////////////////////
3248 // Until all tasks exhausted (both spaces):
3249 // -- claim next available chunk
3250 // -- bump global finger via CAS
3251 // -- find first object that starts in this chunk
3252 //    and start scanning bitmap from that position
3253 // -- scan marked objects for oops
3254 // -- CAS-mark target, and if successful:
3255 //    . if target oop is above global finger (volatile read)
3256 //      nothing to do
3257 //    . if target oop is in chunk and above local finger
3258 //        then nothing to do
3259 //    . else push on work-queue
3260 // -- Deal with possible overflow issues:
3261 //    . local work-queue overflow causes stuff to be pushed on
3262 //      global (common) overflow queue
3263 //    . always first empty local work queue
3264 //    . then get a batch of oops from global work queue if any
3265 //    . then do work stealing
3266 // -- When all tasks claimed (both spaces)
3267 //    and local work queue empty,
3268 //    then in a loop do:
3269 //    . check global overflow stack; steal a batch of oops and trace
3270 //    . try to steal from other threads oif GOS is empty
3271 //    . if neither is available, offer termination
3272 // -- Terminate and return result
3273 //
3274 void CMSConcMarkingTask::work(uint worker_id) {
3275   elapsedTimer _timer;
3276   ResourceMark rm;
3277   HandleMark hm;
3278 
3279   DEBUG_ONLY(_collector->verify_overflow_empty();)
3280 
3281   // Before we begin work, our work queue should be empty
3282   assert(work_queue(worker_id)->size() == 0, "Expected to be empty");
3283   // Scan the bitmap covering _cms_space, tracing through grey objects.
3284   _timer.start();
3285   do_scan_and_mark(worker_id, _cms_space);
3286   _timer.stop();
3287   if (PrintCMSStatistics != 0) {
3288     gclog_or_tty->print_cr("Finished cms space scanning in %dth thread: %3.3f sec",
3289       worker_id, _timer.seconds());
3290       // XXX: need xxx/xxx type of notation, two timers
3291   }
3292 
3293   // ... do work stealing
3294   _timer.reset();
3295   _timer.start();
3296   do_work_steal(worker_id);
3297   _timer.stop();
3298   if (PrintCMSStatistics != 0) {
3299     gclog_or_tty->print_cr("Finished work stealing in %dth thread: %3.3f sec",
3300       worker_id, _timer.seconds());
3301       // XXX: need xxx/xxx type of notation, two timers
3302   }
3303   assert(_collector->_markStack.isEmpty(), "Should have been emptied");
3304   assert(work_queue(worker_id)->size() == 0, "Should have been emptied");
3305   // Note that under the current task protocol, the
3306   // following assertion is true even of the spaces
3307   // expanded since the completion of the concurrent
3308   // marking. XXX This will likely change under a strict
3309   // ABORT semantics.
3310   // After perm removal the comparison was changed to
3311   // greater than or equal to from strictly greater than.
3312   // Before perm removal the highest address sweep would
3313   // have been at the end of perm gen but now is at the
3314   // end of the tenured gen.
3315   assert(_global_finger >=  _cms_space->end(),
3316          "All tasks have been completed");
3317   DEBUG_ONLY(_collector->verify_overflow_empty();)
3318 }
3319 
3320 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
3321   HeapWord* read = _global_finger;
3322   HeapWord* cur  = read;
3323   while (f > read) {
3324     cur = read;
3325     read = (HeapWord*) Atomic::cmpxchg_ptr(f, &_global_finger, cur);
3326     if (cur == read) {
3327       // our cas succeeded
3328       assert(_global_finger >= f, "protocol consistency");
3329       break;
3330     }
3331   }
3332 }
3333 
3334 // This is really inefficient, and should be redone by
3335 // using (not yet available) block-read and -write interfaces to the
3336 // stack and the work_queue. XXX FIX ME !!!
3337 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3338                                                       OopTaskQueue* work_q) {
3339   // Fast lock-free check
3340   if (ovflw_stk->length() == 0) {
3341     return false;
3342   }
3343   assert(work_q->size() == 0, "Shouldn't steal");
3344   MutexLockerEx ml(ovflw_stk->par_lock(),
3345                    Mutex::_no_safepoint_check_flag);
3346   // Grab up to 1/4 the size of the work queue
3347   size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
3348                     (size_t)ParGCDesiredObjsFromOverflowList);
3349   num = MIN2(num, ovflw_stk->length());
3350   for (int i = (int) num; i > 0; i--) {
3351     oop cur = ovflw_stk->pop();
3352     assert(cur != NULL, "Counted wrong?");
3353     work_q->push(cur);
3354   }
3355   return num > 0;
3356 }
3357 
3358 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
3359   SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
3360   int n_tasks = pst->n_tasks();
3361   // We allow that there may be no tasks to do here because
3362   // we are restarting after a stack overflow.
3363   assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
3364   uint nth_task = 0;
3365 
3366   HeapWord* aligned_start = sp->bottom();
3367   if (sp->used_region().contains(_restart_addr)) {
3368     // Align down to a card boundary for the start of 0th task
3369     // for this space.
3370     aligned_start =
3371       (HeapWord*)align_size_down((uintptr_t)_restart_addr,
3372                                  CardTableModRefBS::card_size);
3373   }
3374 
3375   size_t chunk_size = sp->marking_task_size();
3376   while (!pst->is_task_claimed(/* reference */ nth_task)) {
3377     // Having claimed the nth task in this space,
3378     // compute the chunk that it corresponds to:
3379     MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
3380                                aligned_start + (nth_task+1)*chunk_size);
3381     // Try and bump the global finger via a CAS;
3382     // note that we need to do the global finger bump
3383     // _before_ taking the intersection below, because
3384     // the task corresponding to that region will be
3385     // deemed done even if the used_region() expands
3386     // because of allocation -- as it almost certainly will
3387     // during start-up while the threads yield in the
3388     // closure below.
3389     HeapWord* finger = span.end();
3390     bump_global_finger(finger);   // atomically
3391     // There are null tasks here corresponding to chunks
3392     // beyond the "top" address of the space.
3393     span = span.intersection(sp->used_region());
3394     if (!span.is_empty()) {  // Non-null task
3395       HeapWord* prev_obj;
3396       assert(!span.contains(_restart_addr) || nth_task == 0,
3397              "Inconsistency");
3398       if (nth_task == 0) {
3399         // For the 0th task, we'll not need to compute a block_start.
3400         if (span.contains(_restart_addr)) {
3401           // In the case of a restart because of stack overflow,
3402           // we might additionally skip a chunk prefix.
3403           prev_obj = _restart_addr;
3404         } else {
3405           prev_obj = span.start();
3406         }
3407       } else {
3408         // We want to skip the first object because
3409         // the protocol is to scan any object in its entirety
3410         // that _starts_ in this span; a fortiori, any
3411         // object starting in an earlier span is scanned
3412         // as part of an earlier claimed task.
3413         // Below we use the "careful" version of block_start
3414         // so we do not try to navigate uninitialized objects.
3415         prev_obj = sp->block_start_careful(span.start());
3416         // Below we use a variant of block_size that uses the
3417         // Printezis bits to avoid waiting for allocated
3418         // objects to become initialized/parsable.
3419         while (prev_obj < span.start()) {
3420           size_t sz = sp->block_size_no_stall(prev_obj, _collector);
3421           if (sz > 0) {
3422             prev_obj += sz;
3423           } else {
3424             // In this case we may end up doing a bit of redundant
3425             // scanning, but that appears unavoidable, short of
3426             // locking the free list locks; see bug 6324141.
3427             break;
3428           }
3429         }
3430       }
3431       if (prev_obj < span.end()) {
3432         MemRegion my_span = MemRegion(prev_obj, span.end());
3433         // Do the marking work within a non-empty span --
3434         // the last argument to the constructor indicates whether the
3435         // iteration should be incremental with periodic yields.
3436         Par_MarkFromRootsClosure cl(this, _collector, my_span,
3437                                     &_collector->_markBitMap,
3438                                     work_queue(i),
3439                                     &_collector->_markStack);
3440         _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
3441       } // else nothing to do for this task
3442     }   // else nothing to do for this task
3443   }
3444   // We'd be tempted to assert here that since there are no
3445   // more tasks left to claim in this space, the global_finger
3446   // must exceed space->top() and a fortiori space->end(). However,
3447   // that would not quite be correct because the bumping of
3448   // global_finger occurs strictly after the claiming of a task,
3449   // so by the time we reach here the global finger may not yet
3450   // have been bumped up by the thread that claimed the last
3451   // task.
3452   pst->all_tasks_completed();
3453 }
3454 
3455 class Par_ConcMarkingClosure: public MetadataAwareOopClosure {
3456  private:
3457   CMSCollector* _collector;
3458   CMSConcMarkingTask* _task;
3459   MemRegion     _span;
3460   CMSBitMap*    _bit_map;
3461   CMSMarkStack* _overflow_stack;
3462   OopTaskQueue* _work_queue;
3463  protected:
3464   DO_OOP_WORK_DEFN
3465  public:
3466   Par_ConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue,
3467                          CMSBitMap* bit_map, CMSMarkStack* overflow_stack):
3468     MetadataAwareOopClosure(collector->ref_processor()),
3469     _collector(collector),
3470     _task(task),
3471     _span(collector->_span),
3472     _work_queue(work_queue),
3473     _bit_map(bit_map),
3474     _overflow_stack(overflow_stack)
3475   { }
3476   virtual void do_oop(oop* p);
3477   virtual void do_oop(narrowOop* p);
3478 
3479   void trim_queue(size_t max);
3480   void handle_stack_overflow(HeapWord* lost);
3481   void do_yield_check() {
3482     if (_task->should_yield()) {
3483       _task->yield();
3484     }
3485   }
3486 };
3487 
3488 // Grey object scanning during work stealing phase --
3489 // the salient assumption here is that any references
3490 // that are in these stolen objects being scanned must
3491 // already have been initialized (else they would not have
3492 // been published), so we do not need to check for
3493 // uninitialized objects before pushing here.
3494 void Par_ConcMarkingClosure::do_oop(oop obj) {
3495   assert(obj->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
3496   HeapWord* addr = (HeapWord*)obj;
3497   // Check if oop points into the CMS generation
3498   // and is not marked
3499   if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
3500     // a white object ...
3501     // If we manage to "claim" the object, by being the
3502     // first thread to mark it, then we push it on our
3503     // marking stack
3504     if (_bit_map->par_mark(addr)) {     // ... now grey
3505       // push on work queue (grey set)
3506       bool simulate_overflow = false;
3507       NOT_PRODUCT(
3508         if (CMSMarkStackOverflowALot &&
3509             _collector->simulate_overflow()) {
3510           // simulate a stack overflow
3511           simulate_overflow = true;
3512         }
3513       )
3514       if (simulate_overflow ||
3515           !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
3516         // stack overflow
3517         if (PrintCMSStatistics != 0) {
3518           gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
3519                                  SIZE_FORMAT, _overflow_stack->capacity());
3520         }
3521         // We cannot assert that the overflow stack is full because
3522         // it may have been emptied since.
3523         assert(simulate_overflow ||
3524                _work_queue->size() == _work_queue->max_elems(),
3525               "Else push should have succeeded");
3526         handle_stack_overflow(addr);
3527       }
3528     } // Else, some other thread got there first
3529     do_yield_check();
3530   }
3531 }
3532 
3533 void Par_ConcMarkingClosure::do_oop(oop* p)       { Par_ConcMarkingClosure::do_oop_work(p); }
3534 void Par_ConcMarkingClosure::do_oop(narrowOop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
3535 
3536 void Par_ConcMarkingClosure::trim_queue(size_t max) {
3537   while (_work_queue->size() > max) {
3538     oop new_oop;
3539     if (_work_queue->pop_local(new_oop)) {
3540       assert(new_oop->is_oop(), "Should be an oop");
3541       assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
3542       assert(_span.contains((HeapWord*)new_oop), "Not in span");
3543       new_oop->oop_iterate(this);  // do_oop() above
3544       do_yield_check();
3545     }
3546   }
3547 }
3548 
3549 // Upon stack overflow, we discard (part of) the stack,
3550 // remembering the least address amongst those discarded
3551 // in CMSCollector's _restart_address.
3552 void Par_ConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
3553   // We need to do this under a mutex to prevent other
3554   // workers from interfering with the work done below.
3555   MutexLockerEx ml(_overflow_stack->par_lock(),
3556                    Mutex::_no_safepoint_check_flag);
3557   // Remember the least grey address discarded
3558   HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
3559   _collector->lower_restart_addr(ra);
3560   _overflow_stack->reset();  // discard stack contents
3561   _overflow_stack->expand(); // expand the stack if possible
3562 }
3563 
3564 
3565 void CMSConcMarkingTask::do_work_steal(int i) {
3566   OopTaskQueue* work_q = work_queue(i);
3567   oop obj_to_scan;
3568   CMSBitMap* bm = &(_collector->_markBitMap);
3569   CMSMarkStack* ovflw = &(_collector->_markStack);
3570   int* seed = _collector->hash_seed(i);
3571   Par_ConcMarkingClosure cl(_collector, this, work_q, bm, ovflw);
3572   while (true) {
3573     cl.trim_queue(0);
3574     assert(work_q->size() == 0, "Should have been emptied above");
3575     if (get_work_from_overflow_stack(ovflw, work_q)) {
3576       // Can't assert below because the work obtained from the
3577       // overflow stack may already have been stolen from us.
3578       // assert(work_q->size() > 0, "Work from overflow stack");
3579       continue;
3580     } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
3581       assert(obj_to_scan->is_oop(), "Should be an oop");
3582       assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
3583       obj_to_scan->oop_iterate(&cl);
3584     } else if (terminator()->offer_termination(&_term_term)) {
3585       assert(work_q->size() == 0, "Impossible!");
3586       break;
3587     } else if (yielding() || should_yield()) {
3588       yield();
3589     }
3590   }
3591 }
3592 
3593 // This is run by the CMS (coordinator) thread.
3594 void CMSConcMarkingTask::coordinator_yield() {
3595   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3596          "CMS thread should hold CMS token");
3597   // First give up the locks, then yield, then re-lock
3598   // We should probably use a constructor/destructor idiom to
3599   // do this unlock/lock or modify the MutexUnlocker class to
3600   // serve our purpose. XXX
3601   assert_lock_strong(_bit_map_lock);
3602   _bit_map_lock->unlock();
3603   ConcurrentMarkSweepThread::desynchronize(true);
3604   _collector->stopTimer();
3605   if (PrintCMSStatistics != 0) {
3606     _collector->incrementYields();
3607   }
3608 
3609   // It is possible for whichever thread initiated the yield request
3610   // not to get a chance to wake up and take the bitmap lock between
3611   // this thread releasing it and reacquiring it. So, while the
3612   // should_yield() flag is on, let's sleep for a bit to give the
3613   // other thread a chance to wake up. The limit imposed on the number
3614   // of iterations is defensive, to avoid any unforseen circumstances
3615   // putting us into an infinite loop. Since it's always been this
3616   // (coordinator_yield()) method that was observed to cause the
3617   // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
3618   // which is by default non-zero. For the other seven methods that
3619   // also perform the yield operation, as are using a different
3620   // parameter (CMSYieldSleepCount) which is by default zero. This way we
3621   // can enable the sleeping for those methods too, if necessary.
3622   // See 6442774.
3623   //
3624   // We really need to reconsider the synchronization between the GC
3625   // thread and the yield-requesting threads in the future and we
3626   // should really use wait/notify, which is the recommended
3627   // way of doing this type of interaction. Additionally, we should
3628   // consolidate the eight methods that do the yield operation and they
3629   // are almost identical into one for better maintainability and
3630   // readability. See 6445193.
3631   //
3632   // Tony 2006.06.29
3633   for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
3634                    ConcurrentMarkSweepThread::should_yield() &&
3635                    !CMSCollector::foregroundGCIsActive(); ++i) {
3636     os::sleep(Thread::current(), 1, false);
3637   }
3638 
3639   ConcurrentMarkSweepThread::synchronize(true);
3640   _bit_map_lock->lock_without_safepoint_check();
3641   _collector->startTimer();
3642 }
3643 
3644 bool CMSCollector::do_marking_mt() {
3645   assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition");
3646   int num_workers = AdaptiveSizePolicy::calc_active_conc_workers(
3647                                        conc_workers()->total_workers(),
3648                                        conc_workers()->active_workers(),
3649                                        Threads::number_of_non_daemon_threads());
3650   conc_workers()->set_active_workers(num_workers);
3651 
3652   CompactibleFreeListSpace* cms_space  = _cmsGen->cmsSpace();
3653 
3654   CMSConcMarkingTask tsk(this,
3655                          cms_space,
3656                          conc_workers(),
3657                          task_queues());
3658 
3659   // Since the actual number of workers we get may be different
3660   // from the number we requested above, do we need to do anything different
3661   // below? In particular, may be we need to subclass the SequantialSubTasksDone
3662   // class?? XXX
3663   cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
3664 
3665   // Refs discovery is already non-atomic.
3666   assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
3667   assert(ref_processor()->discovery_is_mt(), "Discovery should be MT");
3668   conc_workers()->start_task(&tsk);
3669   while (tsk.yielded()) {
3670     tsk.coordinator_yield();
3671     conc_workers()->continue_task(&tsk);
3672   }
3673   // If the task was aborted, _restart_addr will be non-NULL
3674   assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
3675   while (_restart_addr != NULL) {
3676     // XXX For now we do not make use of ABORTED state and have not
3677     // yet implemented the right abort semantics (even in the original
3678     // single-threaded CMS case). That needs some more investigation
3679     // and is deferred for now; see CR# TBF. 07252005YSR. XXX
3680     assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
3681     // If _restart_addr is non-NULL, a marking stack overflow
3682     // occurred; we need to do a fresh marking iteration from the
3683     // indicated restart address.
3684     if (_foregroundGCIsActive) {
3685       // We may be running into repeated stack overflows, having
3686       // reached the limit of the stack size, while making very
3687       // slow forward progress. It may be best to bail out and
3688       // let the foreground collector do its job.
3689       // Clear _restart_addr, so that foreground GC
3690       // works from scratch. This avoids the headache of
3691       // a "rescan" which would otherwise be needed because
3692       // of the dirty mod union table & card table.
3693       _restart_addr = NULL;
3694       return false;
3695     }
3696     // Adjust the task to restart from _restart_addr
3697     tsk.reset(_restart_addr);
3698     cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
3699                   _restart_addr);
3700     _restart_addr = NULL;
3701     // Get the workers going again
3702     conc_workers()->start_task(&tsk);
3703     while (tsk.yielded()) {
3704       tsk.coordinator_yield();
3705       conc_workers()->continue_task(&tsk);
3706     }
3707   }
3708   assert(tsk.completed(), "Inconsistency");
3709   assert(tsk.result() == true, "Inconsistency");
3710   return true;
3711 }
3712 
3713 bool CMSCollector::do_marking_st() {
3714   ResourceMark rm;
3715   HandleMark   hm;
3716 
3717   // Temporarily make refs discovery single threaded (non-MT)
3718   ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
3719   MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
3720     &_markStack, CMSYield);
3721   // the last argument to iterate indicates whether the iteration
3722   // should be incremental with periodic yields.
3723   _markBitMap.iterate(&markFromRootsClosure);
3724   // If _restart_addr is non-NULL, a marking stack overflow
3725   // occurred; we need to do a fresh iteration from the
3726   // indicated restart address.
3727   while (_restart_addr != NULL) {
3728     if (_foregroundGCIsActive) {
3729       // We may be running into repeated stack overflows, having
3730       // reached the limit of the stack size, while making very
3731       // slow forward progress. It may be best to bail out and
3732       // let the foreground collector do its job.
3733       // Clear _restart_addr, so that foreground GC
3734       // works from scratch. This avoids the headache of
3735       // a "rescan" which would otherwise be needed because
3736       // of the dirty mod union table & card table.
3737       _restart_addr = NULL;
3738       return false;  // indicating failure to complete marking
3739     }
3740     // Deal with stack overflow:
3741     // we restart marking from _restart_addr
3742     HeapWord* ra = _restart_addr;
3743     markFromRootsClosure.reset(ra);
3744     _restart_addr = NULL;
3745     _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
3746   }
3747   return true;
3748 }
3749 
3750 void CMSCollector::preclean() {
3751   check_correct_thread_executing();
3752   assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
3753   verify_work_stacks_empty();
3754   verify_overflow_empty();
3755   _abort_preclean = false;
3756   if (CMSPrecleaningEnabled) {
3757     if (!CMSEdenChunksRecordAlways) {
3758       _eden_chunk_index = 0;
3759     }
3760     size_t used = get_eden_used();
3761     size_t capacity = get_eden_capacity();
3762     // Don't start sampling unless we will get sufficiently
3763     // many samples.
3764     if (used < (capacity/(CMSScheduleRemarkSamplingRatio * 100)
3765                 * CMSScheduleRemarkEdenPenetration)) {
3766       _start_sampling = true;
3767     } else {
3768       _start_sampling = false;
3769     }
3770     TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3771     CMSPhaseAccounting pa(this, "preclean", _gc_tracer_cm->gc_id(), !PrintGCDetails);
3772     preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
3773   }
3774   CMSTokenSync x(true); // is cms thread
3775   if (CMSPrecleaningEnabled) {
3776     sample_eden();
3777     _collectorState = AbortablePreclean;
3778   } else {
3779     _collectorState = FinalMarking;
3780   }
3781   verify_work_stacks_empty();
3782   verify_overflow_empty();
3783 }
3784 
3785 // Try and schedule the remark such that young gen
3786 // occupancy is CMSScheduleRemarkEdenPenetration %.
3787 void CMSCollector::abortable_preclean() {
3788   check_correct_thread_executing();
3789   assert(CMSPrecleaningEnabled,  "Inconsistent control state");
3790   assert(_collectorState == AbortablePreclean, "Inconsistent control state");
3791 
3792   // If Eden's current occupancy is below this threshold,
3793   // immediately schedule the remark; else preclean
3794   // past the next scavenge in an effort to
3795   // schedule the pause as described above. By choosing
3796   // CMSScheduleRemarkEdenSizeThreshold >= max eden size
3797   // we will never do an actual abortable preclean cycle.
3798   if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
3799     TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3800     CMSPhaseAccounting pa(this, "abortable-preclean", _gc_tracer_cm->gc_id(), !PrintGCDetails);
3801     // We need more smarts in the abortable preclean
3802     // loop below to deal with cases where allocation
3803     // in young gen is very very slow, and our precleaning
3804     // is running a losing race against a horde of
3805     // mutators intent on flooding us with CMS updates
3806     // (dirty cards).
3807     // One, admittedly dumb, strategy is to give up
3808     // after a certain number of abortable precleaning loops
3809     // or after a certain maximum time. We want to make
3810     // this smarter in the next iteration.
3811     // XXX FIX ME!!! YSR
3812     size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
3813     while (!(should_abort_preclean() ||
3814              ConcurrentMarkSweepThread::should_terminate())) {
3815       workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
3816       cumworkdone += workdone;
3817       loops++;
3818       // Voluntarily terminate abortable preclean phase if we have
3819       // been at it for too long.
3820       if ((CMSMaxAbortablePrecleanLoops != 0) &&
3821           loops >= CMSMaxAbortablePrecleanLoops) {
3822         if (PrintGCDetails) {
3823           gclog_or_tty->print(" CMS: abort preclean due to loops ");
3824         }
3825         break;
3826       }
3827       if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
3828         if (PrintGCDetails) {
3829           gclog_or_tty->print(" CMS: abort preclean due to time ");
3830         }
3831         break;
3832       }
3833       // If we are doing little work each iteration, we should
3834       // take a short break.
3835       if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
3836         // Sleep for some time, waiting for work to accumulate
3837         stopTimer();
3838         cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
3839         startTimer();
3840         waited++;
3841       }
3842     }
3843     if (PrintCMSStatistics > 0) {
3844       gclog_or_tty->print(" [" SIZE_FORMAT " iterations, " SIZE_FORMAT " waits, " SIZE_FORMAT " cards)] ",
3845                           loops, waited, cumworkdone);
3846     }
3847   }
3848   CMSTokenSync x(true); // is cms thread
3849   if (_collectorState != Idling) {
3850     assert(_collectorState == AbortablePreclean,
3851            "Spontaneous state transition?");
3852     _collectorState = FinalMarking;
3853   } // Else, a foreground collection completed this CMS cycle.
3854   return;
3855 }
3856 
3857 // Respond to an Eden sampling opportunity
3858 void CMSCollector::sample_eden() {
3859   // Make sure a young gc cannot sneak in between our
3860   // reading and recording of a sample.
3861   assert(Thread::current()->is_ConcurrentGC_thread(),
3862          "Only the cms thread may collect Eden samples");
3863   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3864          "Should collect samples while holding CMS token");
3865   if (!_start_sampling) {
3866     return;
3867   }
3868   // When CMSEdenChunksRecordAlways is true, the eden chunk array
3869   // is populated by the young generation.
3870   if (_eden_chunk_array != NULL && !CMSEdenChunksRecordAlways) {
3871     if (_eden_chunk_index < _eden_chunk_capacity) {
3872       _eden_chunk_array[_eden_chunk_index] = *_top_addr;   // take sample
3873       assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
3874              "Unexpected state of Eden");
3875       // We'd like to check that what we just sampled is an oop-start address;
3876       // however, we cannot do that here since the object may not yet have been
3877       // initialized. So we'll instead do the check when we _use_ this sample
3878       // later.
3879       if (_eden_chunk_index == 0 ||
3880           (pointer_delta(_eden_chunk_array[_eden_chunk_index],
3881                          _eden_chunk_array[_eden_chunk_index-1])
3882            >= CMSSamplingGrain)) {
3883         _eden_chunk_index++;  // commit sample
3884       }
3885     }
3886   }
3887   if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
3888     size_t used = get_eden_used();
3889     size_t capacity = get_eden_capacity();
3890     assert(used <= capacity, "Unexpected state of Eden");
3891     if (used >  (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
3892       _abort_preclean = true;
3893     }
3894   }
3895 }
3896 
3897 
3898 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
3899   assert(_collectorState == Precleaning ||
3900          _collectorState == AbortablePreclean, "incorrect state");
3901   ResourceMark rm;
3902   HandleMark   hm;
3903 
3904   // Precleaning is currently not MT but the reference processor
3905   // may be set for MT.  Disable it temporarily here.
3906   ReferenceProcessor* rp = ref_processor();
3907   ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false);
3908 
3909   // Do one pass of scrubbing the discovered reference lists
3910   // to remove any reference objects with strongly-reachable
3911   // referents.
3912   if (clean_refs) {
3913     CMSPrecleanRefsYieldClosure yield_cl(this);
3914     assert(rp->span().equals(_span), "Spans should be equal");
3915     CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
3916                                    &_markStack, true /* preclean */);
3917     CMSDrainMarkingStackClosure complete_trace(this,
3918                                    _span, &_markBitMap, &_markStack,
3919                                    &keep_alive, true /* preclean */);
3920 
3921     // We don't want this step to interfere with a young
3922     // collection because we don't want to take CPU
3923     // or memory bandwidth away from the young GC threads
3924     // (which may be as many as there are CPUs).
3925     // Note that we don't need to protect ourselves from
3926     // interference with mutators because they can't
3927     // manipulate the discovered reference lists nor affect
3928     // the computed reachability of the referents, the
3929     // only properties manipulated by the precleaning
3930     // of these reference lists.
3931     stopTimer();
3932     CMSTokenSyncWithLocks x(true /* is cms thread */,
3933                             bitMapLock());
3934     startTimer();
3935     sample_eden();
3936 
3937     // The following will yield to allow foreground
3938     // collection to proceed promptly. XXX YSR:
3939     // The code in this method may need further
3940     // tweaking for better performance and some restructuring
3941     // for cleaner interfaces.
3942     GCTimer *gc_timer = NULL; // Currently not tracing concurrent phases
3943     rp->preclean_discovered_references(
3944           rp->is_alive_non_header(), &keep_alive, &complete_trace, &yield_cl,
3945           gc_timer, _gc_tracer_cm->gc_id());
3946   }
3947 
3948   if (clean_survivor) {  // preclean the active survivor space(s)
3949     PushAndMarkClosure pam_cl(this, _span, ref_processor(),
3950                              &_markBitMap, &_modUnionTable,
3951                              &_markStack, true /* precleaning phase */);
3952     stopTimer();
3953     CMSTokenSyncWithLocks ts(true /* is cms thread */,
3954                              bitMapLock());
3955     startTimer();
3956     unsigned int before_count =
3957       GenCollectedHeap::heap()->total_collections();
3958     SurvivorSpacePrecleanClosure
3959       sss_cl(this, _span, &_markBitMap, &_markStack,
3960              &pam_cl, before_count, CMSYield);
3961     _young_gen->from()->object_iterate_careful(&sss_cl);
3962     _young_gen->to()->object_iterate_careful(&sss_cl);
3963   }
3964   MarkRefsIntoAndScanClosure
3965     mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
3966              &_markStack, this, CMSYield,
3967              true /* precleaning phase */);
3968   // CAUTION: The following closure has persistent state that may need to
3969   // be reset upon a decrease in the sequence of addresses it
3970   // processes.
3971   ScanMarkedObjectsAgainCarefullyClosure
3972     smoac_cl(this, _span,
3973       &_markBitMap, &_markStack, &mrias_cl, CMSYield);
3974 
3975   // Preclean dirty cards in ModUnionTable and CardTable using
3976   // appropriate convergence criterion;
3977   // repeat CMSPrecleanIter times unless we find that
3978   // we are losing.
3979   assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
3980   assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
3981          "Bad convergence multiplier");
3982   assert(CMSPrecleanThreshold >= 100,
3983          "Unreasonably low CMSPrecleanThreshold");
3984 
3985   size_t numIter, cumNumCards, lastNumCards, curNumCards;
3986   for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
3987        numIter < CMSPrecleanIter;
3988        numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
3989     curNumCards  = preclean_mod_union_table(_cmsGen, &smoac_cl);
3990     if (Verbose && PrintGCDetails) {
3991       gclog_or_tty->print(" (modUnionTable: " SIZE_FORMAT " cards)", curNumCards);
3992     }
3993     // Either there are very few dirty cards, so re-mark
3994     // pause will be small anyway, or our pre-cleaning isn't
3995     // that much faster than the rate at which cards are being
3996     // dirtied, so we might as well stop and re-mark since
3997     // precleaning won't improve our re-mark time by much.
3998     if (curNumCards <= CMSPrecleanThreshold ||
3999         (numIter > 0 &&
4000          (curNumCards * CMSPrecleanDenominator >
4001          lastNumCards * CMSPrecleanNumerator))) {
4002       numIter++;
4003       cumNumCards += curNumCards;
4004       break;
4005     }
4006   }
4007 
4008   preclean_klasses(&mrias_cl, _cmsGen->freelistLock());
4009 
4010   curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
4011   cumNumCards += curNumCards;
4012   if (PrintGCDetails && PrintCMSStatistics != 0) {
4013     gclog_or_tty->print_cr(" (cardTable: " SIZE_FORMAT " cards, re-scanned " SIZE_FORMAT " cards, " SIZE_FORMAT " iterations)",
4014                   curNumCards, cumNumCards, numIter);
4015   }
4016   return cumNumCards;   // as a measure of useful work done
4017 }
4018 
4019 // PRECLEANING NOTES:
4020 // Precleaning involves:
4021 // . reading the bits of the modUnionTable and clearing the set bits.
4022 // . For the cards corresponding to the set bits, we scan the
4023 //   objects on those cards. This means we need the free_list_lock
4024 //   so that we can safely iterate over the CMS space when scanning
4025 //   for oops.
4026 // . When we scan the objects, we'll be both reading and setting
4027 //   marks in the marking bit map, so we'll need the marking bit map.
4028 // . For protecting _collector_state transitions, we take the CGC_lock.
4029 //   Note that any races in the reading of of card table entries by the
4030 //   CMS thread on the one hand and the clearing of those entries by the
4031 //   VM thread or the setting of those entries by the mutator threads on the
4032 //   other are quite benign. However, for efficiency it makes sense to keep
4033 //   the VM thread from racing with the CMS thread while the latter is
4034 //   dirty card info to the modUnionTable. We therefore also use the
4035 //   CGC_lock to protect the reading of the card table and the mod union
4036 //   table by the CM thread.
4037 // . We run concurrently with mutator updates, so scanning
4038 //   needs to be done carefully  -- we should not try to scan
4039 //   potentially uninitialized objects.
4040 //
4041 // Locking strategy: While holding the CGC_lock, we scan over and
4042 // reset a maximal dirty range of the mod union / card tables, then lock
4043 // the free_list_lock and bitmap lock to do a full marking, then
4044 // release these locks; and repeat the cycle. This allows for a
4045 // certain amount of fairness in the sharing of these locks between
4046 // the CMS collector on the one hand, and the VM thread and the
4047 // mutators on the other.
4048 
4049 // NOTE: preclean_mod_union_table() and preclean_card_table()
4050 // further below are largely identical; if you need to modify
4051 // one of these methods, please check the other method too.
4052 
4053 size_t CMSCollector::preclean_mod_union_table(
4054   ConcurrentMarkSweepGeneration* gen,
4055   ScanMarkedObjectsAgainCarefullyClosure* cl) {
4056   verify_work_stacks_empty();
4057   verify_overflow_empty();
4058 
4059   // strategy: starting with the first card, accumulate contiguous
4060   // ranges of dirty cards; clear these cards, then scan the region
4061   // covered by these cards.
4062 
4063   // Since all of the MUT is committed ahead, we can just use
4064   // that, in case the generations expand while we are precleaning.
4065   // It might also be fine to just use the committed part of the
4066   // generation, but we might potentially miss cards when the
4067   // generation is rapidly expanding while we are in the midst
4068   // of precleaning.
4069   HeapWord* startAddr = gen->reserved().start();
4070   HeapWord* endAddr   = gen->reserved().end();
4071 
4072   cl->setFreelistLock(gen->freelistLock());   // needed for yielding
4073 
4074   size_t numDirtyCards, cumNumDirtyCards;
4075   HeapWord *nextAddr, *lastAddr;
4076   for (cumNumDirtyCards = numDirtyCards = 0,
4077        nextAddr = lastAddr = startAddr;
4078        nextAddr < endAddr;
4079        nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4080 
4081     ResourceMark rm;
4082     HandleMark   hm;
4083 
4084     MemRegion dirtyRegion;
4085     {
4086       stopTimer();
4087       // Potential yield point
4088       CMSTokenSync ts(true);
4089       startTimer();
4090       sample_eden();
4091       // Get dirty region starting at nextOffset (inclusive),
4092       // simultaneously clearing it.
4093       dirtyRegion =
4094         _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
4095       assert(dirtyRegion.start() >= nextAddr,
4096              "returned region inconsistent?");
4097     }
4098     // Remember where the next search should begin.
4099     // The returned region (if non-empty) is a right open interval,
4100     // so lastOffset is obtained from the right end of that
4101     // interval.
4102     lastAddr = dirtyRegion.end();
4103     // Should do something more transparent and less hacky XXX
4104     numDirtyCards =
4105       _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
4106 
4107     // We'll scan the cards in the dirty region (with periodic
4108     // yields for foreground GC as needed).
4109     if (!dirtyRegion.is_empty()) {
4110       assert(numDirtyCards > 0, "consistency check");
4111       HeapWord* stop_point = NULL;
4112       stopTimer();
4113       // Potential yield point
4114       CMSTokenSyncWithLocks ts(true, gen->freelistLock(),
4115                                bitMapLock());
4116       startTimer();
4117       {
4118         verify_work_stacks_empty();
4119         verify_overflow_empty();
4120         sample_eden();
4121         stop_point =
4122           gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4123       }
4124       if (stop_point != NULL) {
4125         // The careful iteration stopped early either because it found an
4126         // uninitialized object, or because we were in the midst of an
4127         // "abortable preclean", which should now be aborted. Redirty
4128         // the bits corresponding to the partially-scanned or unscanned
4129         // cards. We'll either restart at the next block boundary or
4130         // abort the preclean.
4131         assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4132                "Should only be AbortablePreclean.");
4133         _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
4134         if (should_abort_preclean()) {
4135           break; // out of preclean loop
4136         } else {
4137           // Compute the next address at which preclean should pick up;
4138           // might need bitMapLock in order to read P-bits.
4139           lastAddr = next_card_start_after_block(stop_point);
4140         }
4141       }
4142     } else {
4143       assert(lastAddr == endAddr, "consistency check");
4144       assert(numDirtyCards == 0, "consistency check");
4145       break;
4146     }
4147   }
4148   verify_work_stacks_empty();
4149   verify_overflow_empty();
4150   return cumNumDirtyCards;
4151 }
4152 
4153 // NOTE: preclean_mod_union_table() above and preclean_card_table()
4154 // below are largely identical; if you need to modify
4155 // one of these methods, please check the other method too.
4156 
4157 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* gen,
4158   ScanMarkedObjectsAgainCarefullyClosure* cl) {
4159   // strategy: it's similar to precleamModUnionTable above, in that
4160   // we accumulate contiguous ranges of dirty cards, mark these cards
4161   // precleaned, then scan the region covered by these cards.
4162   HeapWord* endAddr   = (HeapWord*)(gen->_virtual_space.high());
4163   HeapWord* startAddr = (HeapWord*)(gen->_virtual_space.low());
4164 
4165   cl->setFreelistLock(gen->freelistLock());   // needed for yielding
4166 
4167   size_t numDirtyCards, cumNumDirtyCards;
4168   HeapWord *lastAddr, *nextAddr;
4169 
4170   for (cumNumDirtyCards = numDirtyCards = 0,
4171        nextAddr = lastAddr = startAddr;
4172        nextAddr < endAddr;
4173        nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4174 
4175     ResourceMark rm;
4176     HandleMark   hm;
4177 
4178     MemRegion dirtyRegion;
4179     {
4180       // See comments in "Precleaning notes" above on why we
4181       // do this locking. XXX Could the locking overheads be
4182       // too high when dirty cards are sparse? [I don't think so.]
4183       stopTimer();
4184       CMSTokenSync x(true); // is cms thread
4185       startTimer();
4186       sample_eden();
4187       // Get and clear dirty region from card table
4188       dirtyRegion = _ct->ct_bs()->dirty_card_range_after_reset(
4189                                     MemRegion(nextAddr, endAddr),
4190                                     true,
4191                                     CardTableModRefBS::precleaned_card_val());
4192 
4193       assert(dirtyRegion.start() >= nextAddr,
4194              "returned region inconsistent?");
4195     }
4196     lastAddr = dirtyRegion.end();
4197     numDirtyCards =
4198       dirtyRegion.word_size()/CardTableModRefBS::card_size_in_words;
4199 
4200     if (!dirtyRegion.is_empty()) {
4201       stopTimer();
4202       CMSTokenSyncWithLocks ts(true, gen->freelistLock(), bitMapLock());
4203       startTimer();
4204       sample_eden();
4205       verify_work_stacks_empty();
4206       verify_overflow_empty();
4207       HeapWord* stop_point =
4208         gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4209       if (stop_point != NULL) {
4210         assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4211                "Should only be AbortablePreclean.");
4212         _ct->ct_bs()->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4213         if (should_abort_preclean()) {
4214           break; // out of preclean loop
4215         } else {
4216           // Compute the next address at which preclean should pick up.
4217           lastAddr = next_card_start_after_block(stop_point);
4218         }
4219       }
4220     } else {
4221       break;
4222     }
4223   }
4224   verify_work_stacks_empty();
4225   verify_overflow_empty();
4226   return cumNumDirtyCards;
4227 }
4228 
4229 class PrecleanKlassClosure : public KlassClosure {
4230   KlassToOopClosure _cm_klass_closure;
4231  public:
4232   PrecleanKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4233   void do_klass(Klass* k) {
4234     if (k->has_accumulated_modified_oops()) {
4235       k->clear_accumulated_modified_oops();
4236 
4237       _cm_klass_closure.do_klass(k);
4238     }
4239   }
4240 };
4241 
4242 // The freelist lock is needed to prevent asserts, is it really needed?
4243 void CMSCollector::preclean_klasses(MarkRefsIntoAndScanClosure* cl, Mutex* freelistLock) {
4244 
4245   cl->set_freelistLock(freelistLock);
4246 
4247   CMSTokenSyncWithLocks ts(true, freelistLock, bitMapLock());
4248 
4249   // SSS: Add equivalent to ScanMarkedObjectsAgainCarefullyClosure::do_yield_check and should_abort_preclean?
4250   // SSS: We should probably check if precleaning should be aborted, at suitable intervals?
4251   PrecleanKlassClosure preclean_klass_closure(cl);
4252   ClassLoaderDataGraph::classes_do(&preclean_klass_closure);
4253 
4254   verify_work_stacks_empty();
4255   verify_overflow_empty();
4256 }
4257 
4258 void CMSCollector::checkpointRootsFinal() {
4259   assert(_collectorState == FinalMarking, "incorrect state transition?");
4260   check_correct_thread_executing();
4261   // world is stopped at this checkpoint
4262   assert(SafepointSynchronize::is_at_safepoint(),
4263          "world should be stopped");
4264   TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
4265 
4266   verify_work_stacks_empty();
4267   verify_overflow_empty();
4268 
4269   if (PrintGCDetails) {
4270     gclog_or_tty->print("[YG occupancy: "SIZE_FORMAT" K ("SIZE_FORMAT" K)]",
4271                         _young_gen->used() / K,
4272                         _young_gen->capacity() / K);
4273   }
4274   {
4275     if (CMSScavengeBeforeRemark) {
4276       GenCollectedHeap* gch = GenCollectedHeap::heap();
4277       // Temporarily set flag to false, GCH->do_collection will
4278       // expect it to be false and set to true
4279       FlagSetting fl(gch->_is_gc_active, false);
4280       NOT_PRODUCT(GCTraceTime t("Scavenge-Before-Remark",
4281         PrintGCDetails && Verbose, true, _gc_timer_cm, _gc_tracer_cm->gc_id());)
4282       int level = _cmsGen->level() - 1;
4283       if (level >= 0) {
4284         gch->do_collection(true,        // full (i.e. force, see below)
4285                            false,       // !clear_all_soft_refs
4286                            0,           // size
4287                            false,       // is_tlab
4288                            level        // max_level
4289                           );
4290       }
4291     }
4292     FreelistLocker x(this);
4293     MutexLockerEx y(bitMapLock(),
4294                     Mutex::_no_safepoint_check_flag);
4295     checkpointRootsFinalWork();
4296   }
4297   verify_work_stacks_empty();
4298   verify_overflow_empty();
4299 }
4300 
4301 void CMSCollector::checkpointRootsFinalWork() {
4302   NOT_PRODUCT(GCTraceTime tr("checkpointRootsFinalWork", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());)
4303 
4304   assert(haveFreelistLocks(), "must have free list locks");
4305   assert_lock_strong(bitMapLock());
4306 
4307   ResourceMark rm;
4308   HandleMark   hm;
4309 
4310   GenCollectedHeap* gch = GenCollectedHeap::heap();
4311 
4312   if (should_unload_classes()) {
4313     CodeCache::gc_prologue();
4314   }
4315   assert(haveFreelistLocks(), "must have free list locks");
4316   assert_lock_strong(bitMapLock());
4317 
4318   // We might assume that we need not fill TLAB's when
4319   // CMSScavengeBeforeRemark is set, because we may have just done
4320   // a scavenge which would have filled all TLAB's -- and besides
4321   // Eden would be empty. This however may not always be the case --
4322   // for instance although we asked for a scavenge, it may not have
4323   // happened because of a JNI critical section. We probably need
4324   // a policy for deciding whether we can in that case wait until
4325   // the critical section releases and then do the remark following
4326   // the scavenge, and skip it here. In the absence of that policy,
4327   // or of an indication of whether the scavenge did indeed occur,
4328   // we cannot rely on TLAB's having been filled and must do
4329   // so here just in case a scavenge did not happen.
4330   gch->ensure_parsability(false);  // fill TLAB's, but no need to retire them
4331   // Update the saved marks which may affect the root scans.
4332   gch->save_marks();
4333 
4334   if (CMSPrintEdenSurvivorChunks) {
4335     print_eden_and_survivor_chunk_arrays();
4336   }
4337 
4338   {
4339     COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
4340 
4341     // Note on the role of the mod union table:
4342     // Since the marker in "markFromRoots" marks concurrently with
4343     // mutators, it is possible for some reachable objects not to have been
4344     // scanned. For instance, an only reference to an object A was
4345     // placed in object B after the marker scanned B. Unless B is rescanned,
4346     // A would be collected. Such updates to references in marked objects
4347     // are detected via the mod union table which is the set of all cards
4348     // dirtied since the first checkpoint in this GC cycle and prior to
4349     // the most recent young generation GC, minus those cleaned up by the
4350     // concurrent precleaning.
4351     if (CMSParallelRemarkEnabled && CollectedHeap::use_parallel_gc_threads()) {
4352       GCTraceTime t("Rescan (parallel) ", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
4353       do_remark_parallel();
4354     } else {
4355       GCTraceTime t("Rescan (non-parallel) ", PrintGCDetails, false,
4356                   _gc_timer_cm, _gc_tracer_cm->gc_id());
4357       do_remark_non_parallel();
4358     }
4359   }
4360   verify_work_stacks_empty();
4361   verify_overflow_empty();
4362 
4363   {
4364     NOT_PRODUCT(GCTraceTime ts("refProcessingWork", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());)
4365     refProcessingWork();
4366   }
4367   verify_work_stacks_empty();
4368   verify_overflow_empty();
4369 
4370   if (should_unload_classes()) {
4371     CodeCache::gc_epilogue();
4372   }
4373   JvmtiExport::gc_epilogue();
4374 
4375   // If we encountered any (marking stack / work queue) overflow
4376   // events during the current CMS cycle, take appropriate
4377   // remedial measures, where possible, so as to try and avoid
4378   // recurrence of that condition.
4379   assert(_markStack.isEmpty(), "No grey objects");
4380   size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
4381                      _ser_kac_ovflw        + _ser_kac_preclean_ovflw;
4382   if (ser_ovflw > 0) {
4383     if (PrintCMSStatistics != 0) {
4384       gclog_or_tty->print_cr("Marking stack overflow (benign) "
4385         "(pmc_pc="SIZE_FORMAT", pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT
4386         ", kac_preclean="SIZE_FORMAT")",
4387         _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw,
4388         _ser_kac_ovflw, _ser_kac_preclean_ovflw);
4389     }
4390     _markStack.expand();
4391     _ser_pmc_remark_ovflw = 0;
4392     _ser_pmc_preclean_ovflw = 0;
4393     _ser_kac_preclean_ovflw = 0;
4394     _ser_kac_ovflw = 0;
4395   }
4396   if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
4397     if (PrintCMSStatistics != 0) {
4398       gclog_or_tty->print_cr("Work queue overflow (benign) "
4399         "(pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT")",
4400         _par_pmc_remark_ovflw, _par_kac_ovflw);
4401     }
4402     _par_pmc_remark_ovflw = 0;
4403     _par_kac_ovflw = 0;
4404   }
4405   if (PrintCMSStatistics != 0) {
4406      if (_markStack._hit_limit > 0) {
4407        gclog_or_tty->print_cr(" (benign) Hit max stack size limit ("SIZE_FORMAT")",
4408                               _markStack._hit_limit);
4409      }
4410      if (_markStack._failed_double > 0) {
4411        gclog_or_tty->print_cr(" (benign) Failed stack doubling ("SIZE_FORMAT"),"
4412                               " current capacity "SIZE_FORMAT,
4413                               _markStack._failed_double,
4414                               _markStack.capacity());
4415      }
4416   }
4417   _markStack._hit_limit = 0;
4418   _markStack._failed_double = 0;
4419 
4420   if ((VerifyAfterGC || VerifyDuringGC) &&
4421       GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
4422     verify_after_remark();
4423   }
4424 
4425   _gc_tracer_cm->report_object_count_after_gc(&_is_alive_closure);
4426 
4427   // Change under the freelistLocks.
4428   _collectorState = Sweeping;
4429   // Call isAllClear() under bitMapLock
4430   assert(_modUnionTable.isAllClear(),
4431       "Should be clear by end of the final marking");
4432   assert(_ct->klass_rem_set()->mod_union_is_clear(),
4433       "Should be clear by end of the final marking");
4434 }
4435 
4436 void CMSParInitialMarkTask::work(uint worker_id) {
4437   elapsedTimer _timer;
4438   ResourceMark rm;
4439   HandleMark   hm;
4440 
4441   // ---------- scan from roots --------------
4442   _timer.start();
4443   GenCollectedHeap* gch = GenCollectedHeap::heap();
4444   Par_MarkRefsIntoClosure par_mri_cl(_collector->_span, &(_collector->_markBitMap));
4445 
4446   // ---------- young gen roots --------------
4447   {
4448     work_on_young_gen_roots(worker_id, &par_mri_cl);
4449     _timer.stop();
4450     if (PrintCMSStatistics != 0) {
4451       gclog_or_tty->print_cr(
4452         "Finished young gen initial mark scan work in %dth thread: %3.3f sec",
4453         worker_id, _timer.seconds());
4454     }
4455   }
4456 
4457   // ---------- remaining roots --------------
4458   _timer.reset();
4459   _timer.start();
4460 
4461   CLDToOopClosure cld_closure(&par_mri_cl, true);
4462 
4463   gch->gen_process_roots(_collector->_cmsGen->level(),
4464                          false,     // yg was scanned above
4465                          false,     // this is parallel code
4466                          GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4467                          _collector->should_unload_classes(),
4468                          &par_mri_cl,
4469                          NULL,
4470                          &cld_closure);
4471   assert(_collector->should_unload_classes()
4472          || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4473          "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4474   _timer.stop();
4475   if (PrintCMSStatistics != 0) {
4476     gclog_or_tty->print_cr(
4477       "Finished remaining root initial mark scan work in %dth thread: %3.3f sec",
4478       worker_id, _timer.seconds());
4479   }
4480 }
4481 
4482 // Parallel remark task
4483 class CMSParRemarkTask: public CMSParMarkTask {
4484   CompactibleFreeListSpace* _cms_space;
4485 
4486   // The per-thread work queues, available here for stealing.
4487   OopTaskQueueSet*       _task_queues;
4488   ParallelTaskTerminator _term;
4489 
4490  public:
4491   // A value of 0 passed to n_workers will cause the number of
4492   // workers to be taken from the active workers in the work gang.
4493   CMSParRemarkTask(CMSCollector* collector,
4494                    CompactibleFreeListSpace* cms_space,
4495                    int n_workers, FlexibleWorkGang* workers,
4496                    OopTaskQueueSet* task_queues):
4497     CMSParMarkTask("Rescan roots and grey objects in parallel",
4498                    collector, n_workers),
4499     _cms_space(cms_space),
4500     _task_queues(task_queues),
4501     _term(n_workers, task_queues) { }
4502 
4503   OopTaskQueueSet* task_queues() { return _task_queues; }
4504 
4505   OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
4506 
4507   ParallelTaskTerminator* terminator() { return &_term; }
4508   int n_workers() { return _n_workers; }
4509 
4510   void work(uint worker_id);
4511 
4512  private:
4513   // ... of  dirty cards in old space
4514   void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
4515                                   Par_MarkRefsIntoAndScanClosure* cl);
4516 
4517   // ... work stealing for the above
4518   void do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl, int* seed);
4519 };
4520 
4521 class RemarkKlassClosure : public KlassClosure {
4522   KlassToOopClosure _cm_klass_closure;
4523  public:
4524   RemarkKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4525   void do_klass(Klass* k) {
4526     // Check if we have modified any oops in the Klass during the concurrent marking.
4527     if (k->has_accumulated_modified_oops()) {
4528       k->clear_accumulated_modified_oops();
4529 
4530       // We could have transfered the current modified marks to the accumulated marks,
4531       // like we do with the Card Table to Mod Union Table. But it's not really necessary.
4532     } else if (k->has_modified_oops()) {
4533       // Don't clear anything, this info is needed by the next young collection.
4534     } else {
4535       // No modified oops in the Klass.
4536       return;
4537     }
4538 
4539     // The klass has modified fields, need to scan the klass.
4540     _cm_klass_closure.do_klass(k);
4541   }
4542 };
4543 
4544 void CMSParMarkTask::work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl) {
4545   ParNewGeneration* young_gen = _collector->_young_gen;
4546   ContiguousSpace* eden_space = young_gen->eden();
4547   ContiguousSpace* from_space = young_gen->from();
4548   ContiguousSpace* to_space   = young_gen->to();
4549 
4550   HeapWord** eca = _collector->_eden_chunk_array;
4551   size_t     ect = _collector->_eden_chunk_index;
4552   HeapWord** sca = _collector->_survivor_chunk_array;
4553   size_t     sct = _collector->_survivor_chunk_index;
4554 
4555   assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
4556   assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
4557 
4558   do_young_space_rescan(worker_id, cl, to_space, NULL, 0);
4559   do_young_space_rescan(worker_id, cl, from_space, sca, sct);
4560   do_young_space_rescan(worker_id, cl, eden_space, eca, ect);
4561 }
4562 
4563 // work_queue(i) is passed to the closure
4564 // Par_MarkRefsIntoAndScanClosure.  The "i" parameter
4565 // also is passed to do_dirty_card_rescan_tasks() and to
4566 // do_work_steal() to select the i-th task_queue.
4567 
4568 void CMSParRemarkTask::work(uint worker_id) {
4569   elapsedTimer _timer;
4570   ResourceMark rm;
4571   HandleMark   hm;
4572 
4573   // ---------- rescan from roots --------------
4574   _timer.start();
4575   GenCollectedHeap* gch = GenCollectedHeap::heap();
4576   Par_MarkRefsIntoAndScanClosure par_mrias_cl(_collector,
4577     _collector->_span, _collector->ref_processor(),
4578     &(_collector->_markBitMap),
4579     work_queue(worker_id));
4580 
4581   // Rescan young gen roots first since these are likely
4582   // coarsely partitioned and may, on that account, constitute
4583   // the critical path; thus, it's best to start off that
4584   // work first.
4585   // ---------- young gen roots --------------
4586   {
4587     work_on_young_gen_roots(worker_id, &par_mrias_cl);
4588     _timer.stop();
4589     if (PrintCMSStatistics != 0) {
4590       gclog_or_tty->print_cr(
4591         "Finished young gen rescan work in %dth thread: %3.3f sec",
4592         worker_id, _timer.seconds());
4593     }
4594   }
4595 
4596   // ---------- remaining roots --------------
4597   _timer.reset();
4598   _timer.start();
4599   gch->gen_process_roots(_collector->_cmsGen->level(),
4600                          false,     // yg was scanned above
4601                          false,     // this is parallel code
4602                          GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4603                          _collector->should_unload_classes(),
4604                          &par_mrias_cl,
4605                          NULL,
4606                          NULL);     // The dirty klasses will be handled below
4607 
4608   assert(_collector->should_unload_classes()
4609          || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4610          "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4611   _timer.stop();
4612   if (PrintCMSStatistics != 0) {
4613     gclog_or_tty->print_cr(
4614       "Finished remaining root rescan work in %dth thread: %3.3f sec",
4615       worker_id, _timer.seconds());
4616   }
4617 
4618   // ---------- unhandled CLD scanning ----------
4619   if (worker_id == 0) { // Single threaded at the moment.
4620     _timer.reset();
4621     _timer.start();
4622 
4623     // Scan all new class loader data objects and new dependencies that were
4624     // introduced during concurrent marking.
4625     ResourceMark rm;
4626     GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
4627     for (int i = 0; i < array->length(); i++) {
4628       par_mrias_cl.do_class_loader_data(array->at(i));
4629     }
4630 
4631     // We don't need to keep track of new CLDs anymore.
4632     ClassLoaderDataGraph::remember_new_clds(false);
4633 
4634     _timer.stop();
4635     if (PrintCMSStatistics != 0) {
4636       gclog_or_tty->print_cr(
4637           "Finished unhandled CLD scanning work in %dth thread: %3.3f sec",
4638           worker_id, _timer.seconds());
4639     }
4640   }
4641 
4642   // ---------- dirty klass scanning ----------
4643   if (worker_id == 0) { // Single threaded at the moment.
4644     _timer.reset();
4645     _timer.start();
4646 
4647     // Scan all classes that was dirtied during the concurrent marking phase.
4648     RemarkKlassClosure remark_klass_closure(&par_mrias_cl);
4649     ClassLoaderDataGraph::classes_do(&remark_klass_closure);
4650 
4651     _timer.stop();
4652     if (PrintCMSStatistics != 0) {
4653       gclog_or_tty->print_cr(
4654           "Finished dirty klass scanning work in %dth thread: %3.3f sec",
4655           worker_id, _timer.seconds());
4656     }
4657   }
4658 
4659   // We might have added oops to ClassLoaderData::_handles during the
4660   // concurrent marking phase. These oops point to newly allocated objects
4661   // that are guaranteed to be kept alive. Either by the direct allocation
4662   // code, or when the young collector processes the roots. Hence,
4663   // we don't have to revisit the _handles block during the remark phase.
4664 
4665   // ---------- rescan dirty cards ------------
4666   _timer.reset();
4667   _timer.start();
4668 
4669   // Do the rescan tasks for each of the two spaces
4670   // (cms_space) in turn.
4671   // "worker_id" is passed to select the task_queue for "worker_id"
4672   do_dirty_card_rescan_tasks(_cms_space, worker_id, &par_mrias_cl);
4673   _timer.stop();
4674   if (PrintCMSStatistics != 0) {
4675     gclog_or_tty->print_cr(
4676       "Finished dirty card rescan work in %dth thread: %3.3f sec",
4677       worker_id, _timer.seconds());
4678   }
4679 
4680   // ---------- steal work from other threads ...
4681   // ---------- ... and drain overflow list.
4682   _timer.reset();
4683   _timer.start();
4684   do_work_steal(worker_id, &par_mrias_cl, _collector->hash_seed(worker_id));
4685   _timer.stop();
4686   if (PrintCMSStatistics != 0) {
4687     gclog_or_tty->print_cr(
4688       "Finished work stealing in %dth thread: %3.3f sec",
4689       worker_id, _timer.seconds());
4690   }
4691 }
4692 
4693 // Note that parameter "i" is not used.
4694 void
4695 CMSParMarkTask::do_young_space_rescan(uint worker_id,
4696   OopsInGenClosure* cl, ContiguousSpace* space,
4697   HeapWord** chunk_array, size_t chunk_top) {
4698   // Until all tasks completed:
4699   // . claim an unclaimed task
4700   // . compute region boundaries corresponding to task claimed
4701   //   using chunk_array
4702   // . par_oop_iterate(cl) over that region
4703 
4704   ResourceMark rm;
4705   HandleMark   hm;
4706 
4707   SequentialSubTasksDone* pst = space->par_seq_tasks();
4708 
4709   uint nth_task = 0;
4710   uint n_tasks  = pst->n_tasks();
4711 
4712   if (n_tasks > 0) {
4713     assert(pst->valid(), "Uninitialized use?");
4714     HeapWord *start, *end;
4715     while (!pst->is_task_claimed(/* reference */ nth_task)) {
4716       // We claimed task # nth_task; compute its boundaries.
4717       if (chunk_top == 0) {  // no samples were taken
4718         assert(nth_task == 0 && n_tasks == 1, "Can have only 1 eden task");
4719         start = space->bottom();
4720         end   = space->top();
4721       } else if (nth_task == 0) {
4722         start = space->bottom();
4723         end   = chunk_array[nth_task];
4724       } else if (nth_task < (uint)chunk_top) {
4725         assert(nth_task >= 1, "Control point invariant");
4726         start = chunk_array[nth_task - 1];
4727         end   = chunk_array[nth_task];
4728       } else {
4729         assert(nth_task == (uint)chunk_top, "Control point invariant");
4730         start = chunk_array[chunk_top - 1];
4731         end   = space->top();
4732       }
4733       MemRegion mr(start, end);
4734       // Verify that mr is in space
4735       assert(mr.is_empty() || space->used_region().contains(mr),
4736              "Should be in space");
4737       // Verify that "start" is an object boundary
4738       assert(mr.is_empty() || oop(mr.start())->is_oop(),
4739              "Should be an oop");
4740       space->par_oop_iterate(mr, cl);
4741     }
4742     pst->all_tasks_completed();
4743   }
4744 }
4745 
4746 void
4747 CMSParRemarkTask::do_dirty_card_rescan_tasks(
4748   CompactibleFreeListSpace* sp, int i,
4749   Par_MarkRefsIntoAndScanClosure* cl) {
4750   // Until all tasks completed:
4751   // . claim an unclaimed task
4752   // . compute region boundaries corresponding to task claimed
4753   // . transfer dirty bits ct->mut for that region
4754   // . apply rescanclosure to dirty mut bits for that region
4755 
4756   ResourceMark rm;
4757   HandleMark   hm;
4758 
4759   OopTaskQueue* work_q = work_queue(i);
4760   ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
4761   // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
4762   // CAUTION: This closure has state that persists across calls to
4763   // the work method dirty_range_iterate_clear() in that it has
4764   // embedded in it a (subtype of) UpwardsObjectClosure. The
4765   // use of that state in the embedded UpwardsObjectClosure instance
4766   // assumes that the cards are always iterated (even if in parallel
4767   // by several threads) in monotonically increasing order per each
4768   // thread. This is true of the implementation below which picks
4769   // card ranges (chunks) in monotonically increasing order globally
4770   // and, a-fortiori, in monotonically increasing order per thread
4771   // (the latter order being a subsequence of the former).
4772   // If the work code below is ever reorganized into a more chaotic
4773   // work-partitioning form than the current "sequential tasks"
4774   // paradigm, the use of that persistent state will have to be
4775   // revisited and modified appropriately. See also related
4776   // bug 4756801 work on which should examine this code to make
4777   // sure that the changes there do not run counter to the
4778   // assumptions made here and necessary for correctness and
4779   // efficiency. Note also that this code might yield inefficient
4780   // behavior in the case of very large objects that span one or
4781   // more work chunks. Such objects would potentially be scanned
4782   // several times redundantly. Work on 4756801 should try and
4783   // address that performance anomaly if at all possible. XXX
4784   MemRegion  full_span  = _collector->_span;
4785   CMSBitMap* bm    = &(_collector->_markBitMap);     // shared
4786   MarkFromDirtyCardsClosure
4787     greyRescanClosure(_collector, full_span, // entire span of interest
4788                       sp, bm, work_q, cl);
4789 
4790   SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
4791   assert(pst->valid(), "Uninitialized use?");
4792   uint nth_task = 0;
4793   const int alignment = CardTableModRefBS::card_size * BitsPerWord;
4794   MemRegion span = sp->used_region();
4795   HeapWord* start_addr = span.start();
4796   HeapWord* end_addr = (HeapWord*)round_to((intptr_t)span.end(),
4797                                            alignment);
4798   const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
4799   assert((HeapWord*)round_to((intptr_t)start_addr, alignment) ==
4800          start_addr, "Check alignment");
4801   assert((size_t)round_to((intptr_t)chunk_size, alignment) ==
4802          chunk_size, "Check alignment");
4803 
4804   while (!pst->is_task_claimed(/* reference */ nth_task)) {
4805     // Having claimed the nth_task, compute corresponding mem-region,
4806     // which is a-fortiori aligned correctly (i.e. at a MUT boundary).
4807     // The alignment restriction ensures that we do not need any
4808     // synchronization with other gang-workers while setting or
4809     // clearing bits in thus chunk of the MUT.
4810     MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
4811                                     start_addr + (nth_task+1)*chunk_size);
4812     // The last chunk's end might be way beyond end of the
4813     // used region. In that case pull back appropriately.
4814     if (this_span.end() > end_addr) {
4815       this_span.set_end(end_addr);
4816       assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
4817     }
4818     // Iterate over the dirty cards covering this chunk, marking them
4819     // precleaned, and setting the corresponding bits in the mod union
4820     // table. Since we have been careful to partition at Card and MUT-word
4821     // boundaries no synchronization is needed between parallel threads.
4822     _collector->_ct->ct_bs()->dirty_card_iterate(this_span,
4823                                                  &modUnionClosure);
4824 
4825     // Having transferred these marks into the modUnionTable,
4826     // rescan the marked objects on the dirty cards in the modUnionTable.
4827     // Even if this is at a synchronous collection, the initial marking
4828     // may have been done during an asynchronous collection so there
4829     // may be dirty bits in the mod-union table.
4830     _collector->_modUnionTable.dirty_range_iterate_clear(
4831                   this_span, &greyRescanClosure);
4832     _collector->_modUnionTable.verifyNoOneBitsInRange(
4833                                  this_span.start(),
4834                                  this_span.end());
4835   }
4836   pst->all_tasks_completed();  // declare that i am done
4837 }
4838 
4839 // . see if we can share work_queues with ParNew? XXX
4840 void
4841 CMSParRemarkTask::do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl,
4842                                 int* seed) {
4843   OopTaskQueue* work_q = work_queue(i);
4844   NOT_PRODUCT(int num_steals = 0;)
4845   oop obj_to_scan;
4846   CMSBitMap* bm = &(_collector->_markBitMap);
4847 
4848   while (true) {
4849     // Completely finish any left over work from (an) earlier round(s)
4850     cl->trim_queue(0);
4851     size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
4852                                          (size_t)ParGCDesiredObjsFromOverflowList);
4853     // Now check if there's any work in the overflow list
4854     // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
4855     // only affects the number of attempts made to get work from the
4856     // overflow list and does not affect the number of workers.  Just
4857     // pass ParallelGCThreads so this behavior is unchanged.
4858     if (_collector->par_take_from_overflow_list(num_from_overflow_list,
4859                                                 work_q,
4860                                                 ParallelGCThreads)) {
4861       // found something in global overflow list;
4862       // not yet ready to go stealing work from others.
4863       // We'd like to assert(work_q->size() != 0, ...)
4864       // because we just took work from the overflow list,
4865       // but of course we can't since all of that could have
4866       // been already stolen from us.
4867       // "He giveth and He taketh away."
4868       continue;
4869     }
4870     // Verify that we have no work before we resort to stealing
4871     assert(work_q->size() == 0, "Have work, shouldn't steal");
4872     // Try to steal from other queues that have work
4873     if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
4874       NOT_PRODUCT(num_steals++;)
4875       assert(obj_to_scan->is_oop(), "Oops, not an oop!");
4876       assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
4877       // Do scanning work
4878       obj_to_scan->oop_iterate(cl);
4879       // Loop around, finish this work, and try to steal some more
4880     } else if (terminator()->offer_termination()) {
4881         break;  // nirvana from the infinite cycle
4882     }
4883   }
4884   NOT_PRODUCT(
4885     if (PrintCMSStatistics != 0) {
4886       gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
4887     }
4888   )
4889   assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
4890          "Else our work is not yet done");
4891 }
4892 
4893 // Record object boundaries in _eden_chunk_array by sampling the eden
4894 // top in the slow-path eden object allocation code path and record
4895 // the boundaries, if CMSEdenChunksRecordAlways is true. If
4896 // CMSEdenChunksRecordAlways is false, we use the other asynchronous
4897 // sampling in sample_eden() that activates during the part of the
4898 // preclean phase.
4899 void CMSCollector::sample_eden_chunk() {
4900   if (CMSEdenChunksRecordAlways && _eden_chunk_array != NULL) {
4901     if (_eden_chunk_lock->try_lock()) {
4902       // Record a sample. This is the critical section. The contents
4903       // of the _eden_chunk_array have to be non-decreasing in the
4904       // address order.
4905       _eden_chunk_array[_eden_chunk_index] = *_top_addr;
4906       assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4907              "Unexpected state of Eden");
4908       if (_eden_chunk_index == 0 ||
4909           ((_eden_chunk_array[_eden_chunk_index] > _eden_chunk_array[_eden_chunk_index-1]) &&
4910            (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4911                           _eden_chunk_array[_eden_chunk_index-1]) >= CMSSamplingGrain))) {
4912         _eden_chunk_index++;  // commit sample
4913       }
4914       _eden_chunk_lock->unlock();
4915     }
4916   }
4917 }
4918 
4919 // Return a thread-local PLAB recording array, as appropriate.
4920 void* CMSCollector::get_data_recorder(int thr_num) {
4921   if (_survivor_plab_array != NULL &&
4922       (CMSPLABRecordAlways ||
4923        (_collectorState > Marking && _collectorState < FinalMarking))) {
4924     assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
4925     ChunkArray* ca = &_survivor_plab_array[thr_num];
4926     ca->reset();   // clear it so that fresh data is recorded
4927     return (void*) ca;
4928   } else {
4929     return NULL;
4930   }
4931 }
4932 
4933 // Reset all the thread-local PLAB recording arrays
4934 void CMSCollector::reset_survivor_plab_arrays() {
4935   for (uint i = 0; i < ParallelGCThreads; i++) {
4936     _survivor_plab_array[i].reset();
4937   }
4938 }
4939 
4940 // Merge the per-thread plab arrays into the global survivor chunk
4941 // array which will provide the partitioning of the survivor space
4942 // for CMS initial scan and rescan.
4943 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv,
4944                                               int no_of_gc_threads) {
4945   assert(_survivor_plab_array  != NULL, "Error");
4946   assert(_survivor_chunk_array != NULL, "Error");
4947   assert(_collectorState == FinalMarking ||
4948          (CMSParallelInitialMarkEnabled && _collectorState == InitialMarking), "Error");
4949   for (int j = 0; j < no_of_gc_threads; j++) {
4950     _cursor[j] = 0;
4951   }
4952   HeapWord* top = surv->top();
4953   size_t i;
4954   for (i = 0; i < _survivor_chunk_capacity; i++) {  // all sca entries
4955     HeapWord* min_val = top;          // Higher than any PLAB address
4956     uint      min_tid = 0;            // position of min_val this round
4957     for (int j = 0; j < no_of_gc_threads; j++) {
4958       ChunkArray* cur_sca = &_survivor_plab_array[j];
4959       if (_cursor[j] == cur_sca->end()) {
4960         continue;
4961       }
4962       assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
4963       HeapWord* cur_val = cur_sca->nth(_cursor[j]);
4964       assert(surv->used_region().contains(cur_val), "Out of bounds value");
4965       if (cur_val < min_val) {
4966         min_tid = j;
4967         min_val = cur_val;
4968       } else {
4969         assert(cur_val < top, "All recorded addresses should be less");
4970       }
4971     }
4972     // At this point min_val and min_tid are respectively
4973     // the least address in _survivor_plab_array[j]->nth(_cursor[j])
4974     // and the thread (j) that witnesses that address.
4975     // We record this address in the _survivor_chunk_array[i]
4976     // and increment _cursor[min_tid] prior to the next round i.
4977     if (min_val == top) {
4978       break;
4979     }
4980     _survivor_chunk_array[i] = min_val;
4981     _cursor[min_tid]++;
4982   }
4983   // We are all done; record the size of the _survivor_chunk_array
4984   _survivor_chunk_index = i; // exclusive: [0, i)
4985   if (PrintCMSStatistics > 0) {
4986     gclog_or_tty->print(" (Survivor:" SIZE_FORMAT "chunks) ", i);
4987   }
4988   // Verify that we used up all the recorded entries
4989   #ifdef ASSERT
4990     size_t total = 0;
4991     for (int j = 0; j < no_of_gc_threads; j++) {
4992       assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
4993       total += _cursor[j];
4994     }
4995     assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
4996     // Check that the merged array is in sorted order
4997     if (total > 0) {
4998       for (size_t i = 0; i < total - 1; i++) {
4999         if (PrintCMSStatistics > 0) {
5000           gclog_or_tty->print(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
5001                               i, p2i(_survivor_chunk_array[i]));
5002         }
5003         assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
5004                "Not sorted");
5005       }
5006     }
5007   #endif // ASSERT
5008 }
5009 
5010 // Set up the space's par_seq_tasks structure for work claiming
5011 // for parallel initial scan and rescan of young gen.
5012 // See ParRescanTask where this is currently used.
5013 void
5014 CMSCollector::
5015 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
5016   assert(n_threads > 0, "Unexpected n_threads argument");
5017 
5018   // Eden space
5019   if (!_young_gen->eden()->is_empty()) {
5020     SequentialSubTasksDone* pst = _young_gen->eden()->par_seq_tasks();
5021     assert(!pst->valid(), "Clobbering existing data?");
5022     // Each valid entry in [0, _eden_chunk_index) represents a task.
5023     size_t n_tasks = _eden_chunk_index + 1;
5024     assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
5025     // Sets the condition for completion of the subtask (how many threads
5026     // need to finish in order to be done).
5027     pst->set_n_threads(n_threads);
5028     pst->set_n_tasks((int)n_tasks);
5029   }
5030 
5031   // Merge the survivor plab arrays into _survivor_chunk_array
5032   if (_survivor_plab_array != NULL) {
5033     merge_survivor_plab_arrays(_young_gen->from(), n_threads);
5034   } else {
5035     assert(_survivor_chunk_index == 0, "Error");
5036   }
5037 
5038   // To space
5039   {
5040     SequentialSubTasksDone* pst = _young_gen->to()->par_seq_tasks();
5041     assert(!pst->valid(), "Clobbering existing data?");
5042     // Sets the condition for completion of the subtask (how many threads
5043     // need to finish in order to be done).
5044     pst->set_n_threads(n_threads);
5045     pst->set_n_tasks(1);
5046     assert(pst->valid(), "Error");
5047   }
5048 
5049   // From space
5050   {
5051     SequentialSubTasksDone* pst = _young_gen->from()->par_seq_tasks();
5052     assert(!pst->valid(), "Clobbering existing data?");
5053     size_t n_tasks = _survivor_chunk_index + 1;
5054     assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
5055     // Sets the condition for completion of the subtask (how many threads
5056     // need to finish in order to be done).
5057     pst->set_n_threads(n_threads);
5058     pst->set_n_tasks((int)n_tasks);
5059     assert(pst->valid(), "Error");
5060   }
5061 }
5062 
5063 // Parallel version of remark
5064 void CMSCollector::do_remark_parallel() {
5065   GenCollectedHeap* gch = GenCollectedHeap::heap();
5066   FlexibleWorkGang* workers = gch->workers();
5067   assert(workers != NULL, "Need parallel worker threads.");
5068   // Choose to use the number of GC workers most recently set
5069   // into "active_workers".  If active_workers is not set, set it
5070   // to ParallelGCThreads.
5071   int n_workers = workers->active_workers();
5072   if (n_workers == 0) {
5073     assert(n_workers > 0, "Should have been set during scavenge");
5074     n_workers = ParallelGCThreads;
5075     workers->set_active_workers(n_workers);
5076   }
5077   CompactibleFreeListSpace* cms_space  = _cmsGen->cmsSpace();
5078 
5079   CMSParRemarkTask tsk(this,
5080     cms_space,
5081     n_workers, workers, task_queues());
5082 
5083   // Set up for parallel process_roots work.
5084   gch->set_par_threads(n_workers);
5085   // We won't be iterating over the cards in the card table updating
5086   // the younger_gen cards, so we shouldn't call the following else
5087   // the verification code as well as subsequent younger_refs_iterate
5088   // code would get confused. XXX
5089   // gch->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
5090 
5091   // The young gen rescan work will not be done as part of
5092   // process_roots (which currently doesn't know how to
5093   // parallelize such a scan), but rather will be broken up into
5094   // a set of parallel tasks (via the sampling that the [abortable]
5095   // preclean phase did of eden, plus the [two] tasks of
5096   // scanning the [two] survivor spaces. Further fine-grain
5097   // parallelization of the scanning of the survivor spaces
5098   // themselves, and of precleaning of the younger gen itself
5099   // is deferred to the future.
5100   initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
5101 
5102   // The dirty card rescan work is broken up into a "sequence"
5103   // of parallel tasks (per constituent space) that are dynamically
5104   // claimed by the parallel threads.
5105   cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
5106 
5107   // It turns out that even when we're using 1 thread, doing the work in a
5108   // separate thread causes wide variance in run times.  We can't help this
5109   // in the multi-threaded case, but we special-case n=1 here to get
5110   // repeatable measurements of the 1-thread overhead of the parallel code.
5111   if (n_workers > 1) {
5112     // Make refs discovery MT-safe, if it isn't already: it may not
5113     // necessarily be so, since it's possible that we are doing
5114     // ST marking.
5115     ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), true);
5116     StrongRootsScope srs;
5117     workers->run_task(&tsk);
5118   } else {
5119     ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5120     StrongRootsScope srs;
5121     tsk.work(0);
5122   }
5123 
5124   gch->set_par_threads(0);  // 0 ==> non-parallel.
5125   // restore, single-threaded for now, any preserved marks
5126   // as a result of work_q overflow
5127   restore_preserved_marks_if_any();
5128 }
5129 
5130 // Non-parallel version of remark
5131 void CMSCollector::do_remark_non_parallel() {
5132   ResourceMark rm;
5133   HandleMark   hm;
5134   GenCollectedHeap* gch = GenCollectedHeap::heap();
5135   ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5136 
5137   MarkRefsIntoAndScanClosure
5138     mrias_cl(_span, ref_processor(), &_markBitMap, NULL /* not precleaning */,
5139              &_markStack, this,
5140              false /* should_yield */, false /* not precleaning */);
5141   MarkFromDirtyCardsClosure
5142     markFromDirtyCardsClosure(this, _span,
5143                               NULL,  // space is set further below
5144                               &_markBitMap, &_markStack, &mrias_cl);
5145   {
5146     GCTraceTime t("grey object rescan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5147     // Iterate over the dirty cards, setting the corresponding bits in the
5148     // mod union table.
5149     {
5150       ModUnionClosure modUnionClosure(&_modUnionTable);
5151       _ct->ct_bs()->dirty_card_iterate(
5152                       _cmsGen->used_region(),
5153                       &modUnionClosure);
5154     }
5155     // Having transferred these marks into the modUnionTable, we just need
5156     // to rescan the marked objects on the dirty cards in the modUnionTable.
5157     // The initial marking may have been done during an asynchronous
5158     // collection so there may be dirty bits in the mod-union table.
5159     const int alignment =
5160       CardTableModRefBS::card_size * BitsPerWord;
5161     {
5162       // ... First handle dirty cards in CMS gen
5163       markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
5164       MemRegion ur = _cmsGen->used_region();
5165       HeapWord* lb = ur.start();
5166       HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
5167       MemRegion cms_span(lb, ub);
5168       _modUnionTable.dirty_range_iterate_clear(cms_span,
5169                                                &markFromDirtyCardsClosure);
5170       verify_work_stacks_empty();
5171       if (PrintCMSStatistics != 0) {
5172         gclog_or_tty->print(" (re-scanned "SIZE_FORMAT" dirty cards in cms gen) ",
5173           markFromDirtyCardsClosure.num_dirty_cards());
5174       }
5175     }
5176   }
5177   if (VerifyDuringGC &&
5178       GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5179     HandleMark hm;  // Discard invalid handles created during verification
5180     Universe::verify();
5181   }
5182   {
5183     GCTraceTime t("root rescan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5184 
5185     verify_work_stacks_empty();
5186 
5187     gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
5188     StrongRootsScope srs;
5189 
5190     gch->gen_process_roots(_cmsGen->level(),
5191                            true,  // younger gens as roots
5192                            false, // use the local StrongRootsScope
5193                            GenCollectedHeap::ScanningOption(roots_scanning_options()),
5194                            should_unload_classes(),
5195                            &mrias_cl,
5196                            NULL,
5197                            NULL); // The dirty klasses will be handled below
5198 
5199     assert(should_unload_classes()
5200            || (roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
5201            "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5202   }
5203 
5204   {
5205     GCTraceTime t("visit unhandled CLDs", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5206 
5207     verify_work_stacks_empty();
5208 
5209     // Scan all class loader data objects that might have been introduced
5210     // during concurrent marking.
5211     ResourceMark rm;
5212     GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
5213     for (int i = 0; i < array->length(); i++) {
5214       mrias_cl.do_class_loader_data(array->at(i));
5215     }
5216 
5217     // We don't need to keep track of new CLDs anymore.
5218     ClassLoaderDataGraph::remember_new_clds(false);
5219 
5220     verify_work_stacks_empty();
5221   }
5222 
5223   {
5224     GCTraceTime t("dirty klass scan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5225 
5226     verify_work_stacks_empty();
5227 
5228     RemarkKlassClosure remark_klass_closure(&mrias_cl);
5229     ClassLoaderDataGraph::classes_do(&remark_klass_closure);
5230 
5231     verify_work_stacks_empty();
5232   }
5233 
5234   // We might have added oops to ClassLoaderData::_handles during the
5235   // concurrent marking phase. These oops point to newly allocated objects
5236   // that are guaranteed to be kept alive. Either by the direct allocation
5237   // code, or when the young collector processes the roots. Hence,
5238   // we don't have to revisit the _handles block during the remark phase.
5239 
5240   verify_work_stacks_empty();
5241   // Restore evacuated mark words, if any, used for overflow list links
5242   if (!CMSOverflowEarlyRestoration) {
5243     restore_preserved_marks_if_any();
5244   }
5245   verify_overflow_empty();
5246 }
5247 
5248 ////////////////////////////////////////////////////////
5249 // Parallel Reference Processing Task Proxy Class
5250 ////////////////////////////////////////////////////////
5251 class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues {
5252   typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
5253   CMSCollector*          _collector;
5254   CMSBitMap*             _mark_bit_map;
5255   const MemRegion        _span;
5256   ProcessTask&           _task;
5257 
5258 public:
5259   CMSRefProcTaskProxy(ProcessTask&     task,
5260                       CMSCollector*    collector,
5261                       const MemRegion& span,
5262                       CMSBitMap*       mark_bit_map,
5263                       AbstractWorkGang* workers,
5264                       OopTaskQueueSet* task_queues):
5265     // XXX Should superclass AGTWOQ also know about AWG since it knows
5266     // about the task_queues used by the AWG? Then it could initialize
5267     // the terminator() object. See 6984287. The set_for_termination()
5268     // below is a temporary band-aid for the regression in 6984287.
5269     AbstractGangTaskWOopQueues("Process referents by policy in parallel",
5270       task_queues),
5271     _task(task),
5272     _collector(collector), _span(span), _mark_bit_map(mark_bit_map)
5273   {
5274     assert(_collector->_span.equals(_span) && !_span.is_empty(),
5275            "Inconsistency in _span");
5276     set_for_termination(workers->active_workers());
5277   }
5278 
5279   OopTaskQueueSet* task_queues() { return queues(); }
5280 
5281   OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5282 
5283   void do_work_steal(int i,
5284                      CMSParDrainMarkingStackClosure* drain,
5285                      CMSParKeepAliveClosure* keep_alive,
5286                      int* seed);
5287 
5288   virtual void work(uint worker_id);
5289 };
5290 
5291 void CMSRefProcTaskProxy::work(uint worker_id) {
5292   ResourceMark rm;
5293   HandleMark hm;
5294   assert(_collector->_span.equals(_span), "Inconsistency in _span");
5295   CMSParKeepAliveClosure par_keep_alive(_collector, _span,
5296                                         _mark_bit_map,
5297                                         work_queue(worker_id));
5298   CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
5299                                                  _mark_bit_map,
5300                                                  work_queue(worker_id));
5301   CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
5302   _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack);
5303   if (_task.marks_oops_alive()) {
5304     do_work_steal(worker_id, &par_drain_stack, &par_keep_alive,
5305                   _collector->hash_seed(worker_id));
5306   }
5307   assert(work_queue(worker_id)->size() == 0, "work_queue should be empty");
5308   assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
5309 }
5310 
5311 class CMSRefEnqueueTaskProxy: public AbstractGangTask {
5312   typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
5313   EnqueueTask& _task;
5314 
5315 public:
5316   CMSRefEnqueueTaskProxy(EnqueueTask& task)
5317     : AbstractGangTask("Enqueue reference objects in parallel"),
5318       _task(task)
5319   { }
5320 
5321   virtual void work(uint worker_id)
5322   {
5323     _task.work(worker_id);
5324   }
5325 };
5326 
5327 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
5328   MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue):
5329    _span(span),
5330    _bit_map(bit_map),
5331    _work_queue(work_queue),
5332    _mark_and_push(collector, span, bit_map, work_queue),
5333    _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
5334                         (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads)))
5335 { }
5336 
5337 // . see if we can share work_queues with ParNew? XXX
5338 void CMSRefProcTaskProxy::do_work_steal(int i,
5339   CMSParDrainMarkingStackClosure* drain,
5340   CMSParKeepAliveClosure* keep_alive,
5341   int* seed) {
5342   OopTaskQueue* work_q = work_queue(i);
5343   NOT_PRODUCT(int num_steals = 0;)
5344   oop obj_to_scan;
5345 
5346   while (true) {
5347     // Completely finish any left over work from (an) earlier round(s)
5348     drain->trim_queue(0);
5349     size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5350                                          (size_t)ParGCDesiredObjsFromOverflowList);
5351     // Now check if there's any work in the overflow list
5352     // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5353     // only affects the number of attempts made to get work from the
5354     // overflow list and does not affect the number of workers.  Just
5355     // pass ParallelGCThreads so this behavior is unchanged.
5356     if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5357                                                 work_q,
5358                                                 ParallelGCThreads)) {
5359       // Found something in global overflow list;
5360       // not yet ready to go stealing work from others.
5361       // We'd like to assert(work_q->size() != 0, ...)
5362       // because we just took work from the overflow list,
5363       // but of course we can't, since all of that might have
5364       // been already stolen from us.
5365       continue;
5366     }
5367     // Verify that we have no work before we resort to stealing
5368     assert(work_q->size() == 0, "Have work, shouldn't steal");
5369     // Try to steal from other queues that have work
5370     if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5371       NOT_PRODUCT(num_steals++;)
5372       assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5373       assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5374       // Do scanning work
5375       obj_to_scan->oop_iterate(keep_alive);
5376       // Loop around, finish this work, and try to steal some more
5377     } else if (terminator()->offer_termination()) {
5378       break;  // nirvana from the infinite cycle
5379     }
5380   }
5381   NOT_PRODUCT(
5382     if (PrintCMSStatistics != 0) {
5383       gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5384     }
5385   )
5386 }
5387 
5388 void CMSRefProcTaskExecutor::execute(ProcessTask& task)
5389 {
5390   GenCollectedHeap* gch = GenCollectedHeap::heap();
5391   FlexibleWorkGang* workers = gch->workers();
5392   assert(workers != NULL, "Need parallel worker threads.");
5393   CMSRefProcTaskProxy rp_task(task, &_collector,
5394                               _collector.ref_processor()->span(),
5395                               _collector.markBitMap(),
5396                               workers, _collector.task_queues());
5397   workers->run_task(&rp_task);
5398 }
5399 
5400 void CMSRefProcTaskExecutor::execute(EnqueueTask& task)
5401 {
5402 
5403   GenCollectedHeap* gch = GenCollectedHeap::heap();
5404   FlexibleWorkGang* workers = gch->workers();
5405   assert(workers != NULL, "Need parallel worker threads.");
5406   CMSRefEnqueueTaskProxy enq_task(task);
5407   workers->run_task(&enq_task);
5408 }
5409 
5410 void CMSCollector::refProcessingWork() {
5411   ResourceMark rm;
5412   HandleMark   hm;
5413 
5414   ReferenceProcessor* rp = ref_processor();
5415   assert(rp->span().equals(_span), "Spans should be equal");
5416   assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
5417   // Process weak references.
5418   rp->setup_policy(false);
5419   verify_work_stacks_empty();
5420 
5421   CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
5422                                           &_markStack, false /* !preclean */);
5423   CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
5424                                 _span, &_markBitMap, &_markStack,
5425                                 &cmsKeepAliveClosure, false /* !preclean */);
5426   {
5427     GCTraceTime t("weak refs processing", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5428 
5429     ReferenceProcessorStats stats;
5430     if (rp->processing_is_mt()) {
5431       // Set the degree of MT here.  If the discovery is done MT, there
5432       // may have been a different number of threads doing the discovery
5433       // and a different number of discovered lists may have Ref objects.
5434       // That is OK as long as the Reference lists are balanced (see
5435       // balance_all_queues() and balance_queues()).
5436       GenCollectedHeap* gch = GenCollectedHeap::heap();
5437       int active_workers = ParallelGCThreads;
5438       FlexibleWorkGang* workers = gch->workers();
5439       if (workers != NULL) {
5440         active_workers = workers->active_workers();
5441         // The expectation is that active_workers will have already
5442         // been set to a reasonable value.  If it has not been set,
5443         // investigate.
5444         assert(active_workers > 0, "Should have been set during scavenge");
5445       }
5446       rp->set_active_mt_degree(active_workers);
5447       CMSRefProcTaskExecutor task_executor(*this);
5448       stats = rp->process_discovered_references(&_is_alive_closure,
5449                                         &cmsKeepAliveClosure,
5450                                         &cmsDrainMarkingStackClosure,
5451                                         &task_executor,
5452                                         _gc_timer_cm,
5453                                         _gc_tracer_cm->gc_id());
5454     } else {
5455       stats = rp->process_discovered_references(&_is_alive_closure,
5456                                         &cmsKeepAliveClosure,
5457                                         &cmsDrainMarkingStackClosure,
5458                                         NULL,
5459                                         _gc_timer_cm,
5460                                         _gc_tracer_cm->gc_id());
5461     }
5462     _gc_tracer_cm->report_gc_reference_stats(stats);
5463 
5464   }
5465 
5466   // This is the point where the entire marking should have completed.
5467   verify_work_stacks_empty();
5468 
5469   if (should_unload_classes()) {
5470     {
5471       GCTraceTime t("class unloading", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5472 
5473       // Unload classes and purge the SystemDictionary.
5474       bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure);
5475 
5476       // Unload nmethods.
5477       CodeCache::do_unloading(&_is_alive_closure, purged_class);
5478 
5479       // Prune dead klasses from subklass/sibling/implementor lists.
5480       Klass::clean_weak_klass_links(&_is_alive_closure);
5481     }
5482 
5483     {
5484       GCTraceTime t("scrub symbol table", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5485       // Clean up unreferenced symbols in symbol table.
5486       SymbolTable::unlink();
5487     }
5488 
5489     {
5490       GCTraceTime t("scrub string table", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5491       // Delete entries for dead interned strings.
5492       StringTable::unlink(&_is_alive_closure);
5493     }
5494   }
5495 
5496 
5497   // Restore any preserved marks as a result of mark stack or
5498   // work queue overflow
5499   restore_preserved_marks_if_any();  // done single-threaded for now
5500 
5501   rp->set_enqueuing_is_done(true);
5502   if (rp->processing_is_mt()) {
5503     rp->balance_all_queues();
5504     CMSRefProcTaskExecutor task_executor(*this);
5505     rp->enqueue_discovered_references(&task_executor);
5506   } else {
5507     rp->enqueue_discovered_references(NULL);
5508   }
5509   rp->verify_no_references_recorded();
5510   assert(!rp->discovery_enabled(), "should have been disabled");
5511 }
5512 
5513 #ifndef PRODUCT
5514 void CMSCollector::check_correct_thread_executing() {
5515   Thread* t = Thread::current();
5516   // Only the VM thread or the CMS thread should be here.
5517   assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
5518          "Unexpected thread type");
5519   // If this is the vm thread, the foreground process
5520   // should not be waiting.  Note that _foregroundGCIsActive is
5521   // true while the foreground collector is waiting.
5522   if (_foregroundGCShouldWait) {
5523     // We cannot be the VM thread
5524     assert(t->is_ConcurrentGC_thread(),
5525            "Should be CMS thread");
5526   } else {
5527     // We can be the CMS thread only if we are in a stop-world
5528     // phase of CMS collection.
5529     if (t->is_ConcurrentGC_thread()) {
5530       assert(_collectorState == InitialMarking ||
5531              _collectorState == FinalMarking,
5532              "Should be a stop-world phase");
5533       // The CMS thread should be holding the CMS_token.
5534       assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5535              "Potential interference with concurrently "
5536              "executing VM thread");
5537     }
5538   }
5539 }
5540 #endif
5541 
5542 void CMSCollector::sweep() {
5543   assert(_collectorState == Sweeping, "just checking");
5544   check_correct_thread_executing();
5545   verify_work_stacks_empty();
5546   verify_overflow_empty();
5547   increment_sweep_count();
5548   TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
5549 
5550   _inter_sweep_timer.stop();
5551   _inter_sweep_estimate.sample(_inter_sweep_timer.seconds());
5552 
5553   assert(!_intra_sweep_timer.is_active(), "Should not be active");
5554   _intra_sweep_timer.reset();
5555   _intra_sweep_timer.start();
5556   {
5557     TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
5558     CMSPhaseAccounting pa(this, "sweep", _gc_tracer_cm->gc_id(), !PrintGCDetails);
5559     // First sweep the old gen
5560     {
5561       CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
5562                                bitMapLock());
5563       sweepWork(_cmsGen);
5564     }
5565 
5566     // Update Universe::_heap_*_at_gc figures.
5567     // We need all the free list locks to make the abstract state
5568     // transition from Sweeping to Resetting. See detailed note
5569     // further below.
5570     {
5571       CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock());
5572       // Update heap occupancy information which is used as
5573       // input to soft ref clearing policy at the next gc.
5574       Universe::update_heap_info_at_gc();
5575       _collectorState = Resizing;
5576     }
5577   }
5578   verify_work_stacks_empty();
5579   verify_overflow_empty();
5580 
5581   if (should_unload_classes()) {
5582     // Delay purge to the beginning of the next safepoint.  Metaspace::contains
5583     // requires that the virtual spaces are stable and not deleted.
5584     ClassLoaderDataGraph::set_should_purge(true);
5585   }
5586 
5587   _intra_sweep_timer.stop();
5588   _intra_sweep_estimate.sample(_intra_sweep_timer.seconds());
5589 
5590   _inter_sweep_timer.reset();
5591   _inter_sweep_timer.start();
5592 
5593   // We need to use a monotonically non-decreasing time in ms
5594   // or we will see time-warp warnings and os::javaTimeMillis()
5595   // does not guarantee monotonicity.
5596   jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
5597   update_time_of_last_gc(now);
5598 
5599   // NOTE on abstract state transitions:
5600   // Mutators allocate-live and/or mark the mod-union table dirty
5601   // based on the state of the collection.  The former is done in
5602   // the interval [Marking, Sweeping] and the latter in the interval
5603   // [Marking, Sweeping).  Thus the transitions into the Marking state
5604   // and out of the Sweeping state must be synchronously visible
5605   // globally to the mutators.
5606   // The transition into the Marking state happens with the world
5607   // stopped so the mutators will globally see it.  Sweeping is
5608   // done asynchronously by the background collector so the transition
5609   // from the Sweeping state to the Resizing state must be done
5610   // under the freelistLock (as is the check for whether to
5611   // allocate-live and whether to dirty the mod-union table).
5612   assert(_collectorState == Resizing, "Change of collector state to"
5613     " Resizing must be done under the freelistLocks (plural)");
5614 
5615   // Now that sweeping has been completed, we clear
5616   // the incremental_collection_failed flag,
5617   // thus inviting a younger gen collection to promote into
5618   // this generation. If such a promotion may still fail,
5619   // the flag will be set again when a young collection is
5620   // attempted.
5621   GenCollectedHeap* gch = GenCollectedHeap::heap();
5622   gch->clear_incremental_collection_failed();  // Worth retrying as fresh space may have been freed up
5623   gch->update_full_collections_completed(_collection_count_start);
5624 }
5625 
5626 // FIX ME!!! Looks like this belongs in CFLSpace, with
5627 // CMSGen merely delegating to it.
5628 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
5629   double nearLargestPercent = FLSLargestBlockCoalesceProximity;
5630   HeapWord*  minAddr        = _cmsSpace->bottom();
5631   HeapWord*  largestAddr    =
5632     (HeapWord*) _cmsSpace->dictionary()->find_largest_dict();
5633   if (largestAddr == NULL) {
5634     // The dictionary appears to be empty.  In this case
5635     // try to coalesce at the end of the heap.
5636     largestAddr = _cmsSpace->end();
5637   }
5638   size_t largestOffset     = pointer_delta(largestAddr, minAddr);
5639   size_t nearLargestOffset =
5640     (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
5641   if (PrintFLSStatistics != 0) {
5642     gclog_or_tty->print_cr(
5643       "CMS: Large Block: " PTR_FORMAT ";"
5644       " Proximity: " PTR_FORMAT " -> " PTR_FORMAT,
5645       p2i(largestAddr),
5646       p2i(_cmsSpace->nearLargestChunk()), p2i(minAddr + nearLargestOffset));
5647   }
5648   _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
5649 }
5650 
5651 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
5652   return addr >= _cmsSpace->nearLargestChunk();
5653 }
5654 
5655 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
5656   return _cmsSpace->find_chunk_at_end();
5657 }
5658 
5659 void ConcurrentMarkSweepGeneration::update_gc_stats(int current_level,
5660                                                     bool full) {
5661   // The next lower level has been collected.  Gather any statistics
5662   // that are of interest at this point.
5663   if (!full && (current_level + 1) == level()) {
5664     // Gather statistics on the young generation collection.
5665     collector()->stats().record_gc0_end(used());
5666   }
5667 }
5668 
5669 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* gen) {
5670   // We iterate over the space(s) underlying this generation,
5671   // checking the mark bit map to see if the bits corresponding
5672   // to specific blocks are marked or not. Blocks that are
5673   // marked are live and are not swept up. All remaining blocks
5674   // are swept up, with coalescing on-the-fly as we sweep up
5675   // contiguous free and/or garbage blocks:
5676   // We need to ensure that the sweeper synchronizes with allocators
5677   // and stop-the-world collectors. In particular, the following
5678   // locks are used:
5679   // . CMS token: if this is held, a stop the world collection cannot occur
5680   // . freelistLock: if this is held no allocation can occur from this
5681   //                 generation by another thread
5682   // . bitMapLock: if this is held, no other thread can access or update
5683   //
5684 
5685   // Note that we need to hold the freelistLock if we use
5686   // block iterate below; else the iterator might go awry if
5687   // a mutator (or promotion) causes block contents to change
5688   // (for instance if the allocator divvies up a block).
5689   // If we hold the free list lock, for all practical purposes
5690   // young generation GC's can't occur (they'll usually need to
5691   // promote), so we might as well prevent all young generation
5692   // GC's while we do a sweeping step. For the same reason, we might
5693   // as well take the bit map lock for the entire duration
5694 
5695   // check that we hold the requisite locks
5696   assert(have_cms_token(), "Should hold cms token");
5697   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), "Should possess CMS token to sweep");
5698   assert_lock_strong(gen->freelistLock());
5699   assert_lock_strong(bitMapLock());
5700 
5701   assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context");
5702   assert(_intra_sweep_timer.is_active(),  "Was switched on  in an outer context");
5703   gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
5704                                       _inter_sweep_estimate.padded_average(),
5705                                       _intra_sweep_estimate.padded_average());
5706   gen->setNearLargestChunk();
5707 
5708   {
5709     SweepClosure sweepClosure(this, gen, &_markBitMap, CMSYield);
5710     gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
5711     // We need to free-up/coalesce garbage/blocks from a
5712     // co-terminal free run. This is done in the SweepClosure
5713     // destructor; so, do not remove this scope, else the
5714     // end-of-sweep-census below will be off by a little bit.
5715   }
5716   gen->cmsSpace()->sweep_completed();
5717   gen->cmsSpace()->endSweepFLCensus(sweep_count());
5718   if (should_unload_classes()) {                // unloaded classes this cycle,
5719     _concurrent_cycles_since_last_unload = 0;   // ... reset count
5720   } else {                                      // did not unload classes,
5721     _concurrent_cycles_since_last_unload++;     // ... increment count
5722   }
5723 }
5724 
5725 // Reset CMS data structures (for now just the marking bit map)
5726 // preparatory for the next cycle.
5727 void CMSCollector::reset(bool concurrent) {
5728   if (concurrent) {
5729     CMSTokenSyncWithLocks ts(true, bitMapLock());
5730 
5731     // If the state is not "Resetting", the foreground  thread
5732     // has done a collection and the resetting.
5733     if (_collectorState != Resetting) {
5734       assert(_collectorState == Idling, "The state should only change"
5735         " because the foreground collector has finished the collection");
5736       return;
5737     }
5738 
5739     // Clear the mark bitmap (no grey objects to start with)
5740     // for the next cycle.
5741     TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
5742     CMSPhaseAccounting cmspa(this, "reset", _gc_tracer_cm->gc_id(), !PrintGCDetails);
5743 
5744     HeapWord* curAddr = _markBitMap.startWord();
5745     while (curAddr < _markBitMap.endWord()) {
5746       size_t remaining  = pointer_delta(_markBitMap.endWord(), curAddr);
5747       MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
5748       _markBitMap.clear_large_range(chunk);
5749       if (ConcurrentMarkSweepThread::should_yield() &&
5750           !foregroundGCIsActive() &&
5751           CMSYield) {
5752         assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5753                "CMS thread should hold CMS token");
5754         assert_lock_strong(bitMapLock());
5755         bitMapLock()->unlock();
5756         ConcurrentMarkSweepThread::desynchronize(true);
5757         stopTimer();
5758         if (PrintCMSStatistics != 0) {
5759           incrementYields();
5760         }
5761 
5762         // See the comment in coordinator_yield()
5763         for (unsigned i = 0; i < CMSYieldSleepCount &&
5764                          ConcurrentMarkSweepThread::should_yield() &&
5765                          !CMSCollector::foregroundGCIsActive(); ++i) {
5766           os::sleep(Thread::current(), 1, false);
5767         }
5768 
5769         ConcurrentMarkSweepThread::synchronize(true);
5770         bitMapLock()->lock_without_safepoint_check();
5771         startTimer();
5772       }
5773       curAddr = chunk.end();
5774     }
5775     // A successful mostly concurrent collection has been done.
5776     // Because only the full (i.e., concurrent mode failure) collections
5777     // are being measured for gc overhead limits, clean the "near" flag
5778     // and count.
5779     size_policy()->reset_gc_overhead_limit_count();
5780     _collectorState = Idling;
5781   } else {
5782     // already have the lock
5783     assert(_collectorState == Resetting, "just checking");
5784     assert_lock_strong(bitMapLock());
5785     _markBitMap.clear_all();
5786     _collectorState = Idling;
5787   }
5788 
5789   register_gc_end();
5790 }
5791 
5792 void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) {
5793   TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
5794   GCTraceTime t(GCCauseString("GC", gc_cause), PrintGC, !PrintGCDetails, NULL, _gc_tracer_cm->gc_id());
5795   TraceCollectorStats tcs(counters());
5796 
5797   switch (op) {
5798     case CMS_op_checkpointRootsInitial: {
5799       SvcGCMarker sgcm(SvcGCMarker::OTHER);
5800       checkpointRootsInitial();
5801       if (PrintGC) {
5802         _cmsGen->printOccupancy("initial-mark");
5803       }
5804       break;
5805     }
5806     case CMS_op_checkpointRootsFinal: {
5807       SvcGCMarker sgcm(SvcGCMarker::OTHER);
5808       checkpointRootsFinal();
5809       if (PrintGC) {
5810         _cmsGen->printOccupancy("remark");
5811       }
5812       break;
5813     }
5814     default:
5815       fatal("No such CMS_op");
5816   }
5817 }
5818 
5819 #ifndef PRODUCT
5820 size_t const CMSCollector::skip_header_HeapWords() {
5821   return FreeChunk::header_size();
5822 }
5823 
5824 // Try and collect here conditions that should hold when
5825 // CMS thread is exiting. The idea is that the foreground GC
5826 // thread should not be blocked if it wants to terminate
5827 // the CMS thread and yet continue to run the VM for a while
5828 // after that.
5829 void CMSCollector::verify_ok_to_terminate() const {
5830   assert(Thread::current()->is_ConcurrentGC_thread(),
5831          "should be called by CMS thread");
5832   assert(!_foregroundGCShouldWait, "should be false");
5833   // We could check here that all the various low-level locks
5834   // are not held by the CMS thread, but that is overkill; see
5835   // also CMSThread::verify_ok_to_terminate() where the CGC_lock
5836   // is checked.
5837 }
5838 #endif
5839 
5840 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
5841    assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
5842           "missing Printezis mark?");
5843   HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5844   size_t size = pointer_delta(nextOneAddr + 1, addr);
5845   assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5846          "alignment problem");
5847   assert(size >= 3, "Necessary for Printezis marks to work");
5848   return size;
5849 }
5850 
5851 // A variant of the above (block_size_using_printezis_bits()) except
5852 // that we return 0 if the P-bits are not yet set.
5853 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
5854   if (_markBitMap.isMarked(addr + 1)) {
5855     assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects");
5856     HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5857     size_t size = pointer_delta(nextOneAddr + 1, addr);
5858     assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5859            "alignment problem");
5860     assert(size >= 3, "Necessary for Printezis marks to work");
5861     return size;
5862   }
5863   return 0;
5864 }
5865 
5866 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
5867   size_t sz = 0;
5868   oop p = (oop)addr;
5869   if (p->klass_or_null() != NULL) {
5870     sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
5871   } else {
5872     sz = block_size_using_printezis_bits(addr);
5873   }
5874   assert(sz > 0, "size must be nonzero");
5875   HeapWord* next_block = addr + sz;
5876   HeapWord* next_card  = (HeapWord*)round_to((uintptr_t)next_block,
5877                                              CardTableModRefBS::card_size);
5878   assert(round_down((uintptr_t)addr,      CardTableModRefBS::card_size) <
5879          round_down((uintptr_t)next_card, CardTableModRefBS::card_size),
5880          "must be different cards");
5881   return next_card;
5882 }
5883 
5884 
5885 // CMS Bit Map Wrapper /////////////////////////////////////////
5886 
5887 // Construct a CMS bit map infrastructure, but don't create the
5888 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
5889 // further below.
5890 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
5891   _bm(),
5892   _shifter(shifter),
5893   _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true,
5894                                     Monitor::_safepoint_check_sometimes) : NULL)
5895 {
5896   _bmStartWord = 0;
5897   _bmWordSize  = 0;
5898 }
5899 
5900 bool CMSBitMap::allocate(MemRegion mr) {
5901   _bmStartWord = mr.start();
5902   _bmWordSize  = mr.word_size();
5903   ReservedSpace brs(ReservedSpace::allocation_align_size_up(
5904                      (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
5905   if (!brs.is_reserved()) {
5906     warning("CMS bit map allocation failure");
5907     return false;
5908   }
5909   // For now we'll just commit all of the bit map up front.
5910   // Later on we'll try to be more parsimonious with swap.
5911   if (!_virtual_space.initialize(brs, brs.size())) {
5912     warning("CMS bit map backing store failure");
5913     return false;
5914   }
5915   assert(_virtual_space.committed_size() == brs.size(),
5916          "didn't reserve backing store for all of CMS bit map?");
5917   _bm.set_map((BitMap::bm_word_t*)_virtual_space.low());
5918   assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
5919          _bmWordSize, "inconsistency in bit map sizing");
5920   _bm.set_size(_bmWordSize >> _shifter);
5921 
5922   // bm.clear(); // can we rely on getting zero'd memory? verify below
5923   assert(isAllClear(),
5924          "Expected zero'd memory from ReservedSpace constructor");
5925   assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
5926          "consistency check");
5927   return true;
5928 }
5929 
5930 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
5931   HeapWord *next_addr, *end_addr, *last_addr;
5932   assert_locked();
5933   assert(covers(mr), "out-of-range error");
5934   // XXX assert that start and end are appropriately aligned
5935   for (next_addr = mr.start(), end_addr = mr.end();
5936        next_addr < end_addr; next_addr = last_addr) {
5937     MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
5938     last_addr = dirty_region.end();
5939     if (!dirty_region.is_empty()) {
5940       cl->do_MemRegion(dirty_region);
5941     } else {
5942       assert(last_addr == end_addr, "program logic");
5943       return;
5944     }
5945   }
5946 }
5947 
5948 void CMSBitMap::print_on_error(outputStream* st, const char* prefix) const {
5949   _bm.print_on_error(st, prefix);
5950 }
5951 
5952 #ifndef PRODUCT
5953 void CMSBitMap::assert_locked() const {
5954   CMSLockVerifier::assert_locked(lock());
5955 }
5956 
5957 bool CMSBitMap::covers(MemRegion mr) const {
5958   // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
5959   assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
5960          "size inconsistency");
5961   return (mr.start() >= _bmStartWord) &&
5962          (mr.end()   <= endWord());
5963 }
5964 
5965 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
5966     return (start >= _bmStartWord && (start + size) <= endWord());
5967 }
5968 
5969 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
5970   // verify that there are no 1 bits in the interval [left, right)
5971   FalseBitMapClosure falseBitMapClosure;
5972   iterate(&falseBitMapClosure, left, right);
5973 }
5974 
5975 void CMSBitMap::region_invariant(MemRegion mr)
5976 {
5977   assert_locked();
5978   // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
5979   assert(!mr.is_empty(), "unexpected empty region");
5980   assert(covers(mr), "mr should be covered by bit map");
5981   // convert address range into offset range
5982   size_t start_ofs = heapWordToOffset(mr.start());
5983   // Make sure that end() is appropriately aligned
5984   assert(mr.end() == (HeapWord*)round_to((intptr_t)mr.end(),
5985                         (1 << (_shifter+LogHeapWordSize))),
5986          "Misaligned mr.end()");
5987   size_t end_ofs   = heapWordToOffset(mr.end());
5988   assert(end_ofs > start_ofs, "Should mark at least one bit");
5989 }
5990 
5991 #endif
5992 
5993 bool CMSMarkStack::allocate(size_t size) {
5994   // allocate a stack of the requisite depth
5995   ReservedSpace rs(ReservedSpace::allocation_align_size_up(
5996                    size * sizeof(oop)));
5997   if (!rs.is_reserved()) {
5998     warning("CMSMarkStack allocation failure");
5999     return false;
6000   }
6001   if (!_virtual_space.initialize(rs, rs.size())) {
6002     warning("CMSMarkStack backing store failure");
6003     return false;
6004   }
6005   assert(_virtual_space.committed_size() == rs.size(),
6006          "didn't reserve backing store for all of CMS stack?");
6007   _base = (oop*)(_virtual_space.low());
6008   _index = 0;
6009   _capacity = size;
6010   NOT_PRODUCT(_max_depth = 0);
6011   return true;
6012 }
6013 
6014 // XXX FIX ME !!! In the MT case we come in here holding a
6015 // leaf lock. For printing we need to take a further lock
6016 // which has lower rank. We need to recalibrate the two
6017 // lock-ranks involved in order to be able to print the
6018 // messages below. (Or defer the printing to the caller.
6019 // For now we take the expedient path of just disabling the
6020 // messages for the problematic case.)
6021 void CMSMarkStack::expand() {
6022   assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted");
6023   if (_capacity == MarkStackSizeMax) {
6024     if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6025       // We print a warning message only once per CMS cycle.
6026       gclog_or_tty->print_cr(" (benign) Hit CMSMarkStack max size limit");
6027     }
6028     return;
6029   }
6030   // Double capacity if possible
6031   size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax);
6032   // Do not give up existing stack until we have managed to
6033   // get the double capacity that we desired.
6034   ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6035                    new_capacity * sizeof(oop)));
6036   if (rs.is_reserved()) {
6037     // Release the backing store associated with old stack
6038     _virtual_space.release();
6039     // Reinitialize virtual space for new stack
6040     if (!_virtual_space.initialize(rs, rs.size())) {
6041       fatal("Not enough swap for expanded marking stack");
6042     }
6043     _base = (oop*)(_virtual_space.low());
6044     _index = 0;
6045     _capacity = new_capacity;
6046   } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6047     // Failed to double capacity, continue;
6048     // we print a detail message only once per CMS cycle.
6049     gclog_or_tty->print(" (benign) Failed to expand marking stack from "SIZE_FORMAT"K to "
6050             SIZE_FORMAT"K",
6051             _capacity / K, new_capacity / K);
6052   }
6053 }
6054 
6055 
6056 // Closures
6057 // XXX: there seems to be a lot of code  duplication here;
6058 // should refactor and consolidate common code.
6059 
6060 // This closure is used to mark refs into the CMS generation in
6061 // the CMS bit map. Called at the first checkpoint. This closure
6062 // assumes that we do not need to re-mark dirty cards; if the CMS
6063 // generation on which this is used is not an oldest
6064 // generation then this will lose younger_gen cards!
6065 
6066 MarkRefsIntoClosure::MarkRefsIntoClosure(
6067   MemRegion span, CMSBitMap* bitMap):
6068     _span(span),
6069     _bitMap(bitMap)
6070 {
6071     assert(_ref_processor == NULL, "deliberately left NULL");
6072     assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6073 }
6074 
6075 void MarkRefsIntoClosure::do_oop(oop obj) {
6076   // if p points into _span, then mark corresponding bit in _markBitMap
6077   assert(obj->is_oop(), "expected an oop");
6078   HeapWord* addr = (HeapWord*)obj;
6079   if (_span.contains(addr)) {
6080     // this should be made more efficient
6081     _bitMap->mark(addr);
6082   }
6083 }
6084 
6085 void MarkRefsIntoClosure::do_oop(oop* p)       { MarkRefsIntoClosure::do_oop_work(p); }
6086 void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6087 
6088 Par_MarkRefsIntoClosure::Par_MarkRefsIntoClosure(
6089   MemRegion span, CMSBitMap* bitMap):
6090     _span(span),
6091     _bitMap(bitMap)
6092 {
6093     assert(_ref_processor == NULL, "deliberately left NULL");
6094     assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6095 }
6096 
6097 void Par_MarkRefsIntoClosure::do_oop(oop obj) {
6098   // if p points into _span, then mark corresponding bit in _markBitMap
6099   assert(obj->is_oop(), "expected an oop");
6100   HeapWord* addr = (HeapWord*)obj;
6101   if (_span.contains(addr)) {
6102     // this should be made more efficient
6103     _bitMap->par_mark(addr);
6104   }
6105 }
6106 
6107 void Par_MarkRefsIntoClosure::do_oop(oop* p)       { Par_MarkRefsIntoClosure::do_oop_work(p); }
6108 void Par_MarkRefsIntoClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoClosure::do_oop_work(p); }
6109 
6110 // A variant of the above, used for CMS marking verification.
6111 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
6112   MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm):
6113     _span(span),
6114     _verification_bm(verification_bm),
6115     _cms_bm(cms_bm)
6116 {
6117     assert(_ref_processor == NULL, "deliberately left NULL");
6118     assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
6119 }
6120 
6121 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
6122   // if p points into _span, then mark corresponding bit in _markBitMap
6123   assert(obj->is_oop(), "expected an oop");
6124   HeapWord* addr = (HeapWord*)obj;
6125   if (_span.contains(addr)) {
6126     _verification_bm->mark(addr);
6127     if (!_cms_bm->isMarked(addr)) {
6128       oop(addr)->print();
6129       gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
6130       fatal("... aborting");
6131     }
6132   }
6133 }
6134 
6135 void MarkRefsIntoVerifyClosure::do_oop(oop* p)       { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6136 void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6137 
6138 //////////////////////////////////////////////////
6139 // MarkRefsIntoAndScanClosure
6140 //////////////////////////////////////////////////
6141 
6142 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
6143                                                        ReferenceProcessor* rp,
6144                                                        CMSBitMap* bit_map,
6145                                                        CMSBitMap* mod_union_table,
6146                                                        CMSMarkStack*  mark_stack,
6147                                                        CMSCollector* collector,
6148                                                        bool should_yield,
6149                                                        bool concurrent_precleaning):
6150   _collector(collector),
6151   _span(span),
6152   _bit_map(bit_map),
6153   _mark_stack(mark_stack),
6154   _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table,
6155                       mark_stack, concurrent_precleaning),
6156   _yield(should_yield),
6157   _concurrent_precleaning(concurrent_precleaning),
6158   _freelistLock(NULL)
6159 {
6160   _ref_processor = rp;
6161   assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6162 }
6163 
6164 // This closure is used to mark refs into the CMS generation at the
6165 // second (final) checkpoint, and to scan and transitively follow
6166 // the unmarked oops. It is also used during the concurrent precleaning
6167 // phase while scanning objects on dirty cards in the CMS generation.
6168 // The marks are made in the marking bit map and the marking stack is
6169 // used for keeping the (newly) grey objects during the scan.
6170 // The parallel version (Par_...) appears further below.
6171 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6172   if (obj != NULL) {
6173     assert(obj->is_oop(), "expected an oop");
6174     HeapWord* addr = (HeapWord*)obj;
6175     assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6176     assert(_collector->overflow_list_is_empty(),
6177            "overflow list should be empty");
6178     if (_span.contains(addr) &&
6179         !_bit_map->isMarked(addr)) {
6180       // mark bit map (object is now grey)
6181       _bit_map->mark(addr);
6182       // push on marking stack (stack should be empty), and drain the
6183       // stack by applying this closure to the oops in the oops popped
6184       // from the stack (i.e. blacken the grey objects)
6185       bool res = _mark_stack->push(obj);
6186       assert(res, "Should have space to push on empty stack");
6187       do {
6188         oop new_oop = _mark_stack->pop();
6189         assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6190         assert(_bit_map->isMarked((HeapWord*)new_oop),
6191                "only grey objects on this stack");
6192         // iterate over the oops in this oop, marking and pushing
6193         // the ones in CMS heap (i.e. in _span).
6194         new_oop->oop_iterate(&_pushAndMarkClosure);
6195         // check if it's time to yield
6196         do_yield_check();
6197       } while (!_mark_stack->isEmpty() ||
6198                (!_concurrent_precleaning && take_from_overflow_list()));
6199         // if marking stack is empty, and we are not doing this
6200         // during precleaning, then check the overflow list
6201     }
6202     assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6203     assert(_collector->overflow_list_is_empty(),
6204            "overflow list was drained above");
6205     // We could restore evacuated mark words, if any, used for
6206     // overflow list links here because the overflow list is
6207     // provably empty here. That would reduce the maximum
6208     // size requirements for preserved_{oop,mark}_stack.
6209     // But we'll just postpone it until we are all done
6210     // so we can just stream through.
6211     if (!_concurrent_precleaning && CMSOverflowEarlyRestoration) {
6212       _collector->restore_preserved_marks_if_any();
6213       assert(_collector->no_preserved_marks(), "No preserved marks");
6214     }
6215     assert(!CMSOverflowEarlyRestoration || _collector->no_preserved_marks(),
6216            "All preserved marks should have been restored above");
6217   }
6218 }
6219 
6220 void MarkRefsIntoAndScanClosure::do_oop(oop* p)       { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6221 void MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6222 
6223 void MarkRefsIntoAndScanClosure::do_yield_work() {
6224   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6225          "CMS thread should hold CMS token");
6226   assert_lock_strong(_freelistLock);
6227   assert_lock_strong(_bit_map->lock());
6228   // relinquish the free_list_lock and bitMaplock()
6229   _bit_map->lock()->unlock();
6230   _freelistLock->unlock();
6231   ConcurrentMarkSweepThread::desynchronize(true);
6232   _collector->stopTimer();
6233   if (PrintCMSStatistics != 0) {
6234     _collector->incrementYields();
6235   }
6236 
6237   // See the comment in coordinator_yield()
6238   for (unsigned i = 0;
6239        i < CMSYieldSleepCount &&
6240        ConcurrentMarkSweepThread::should_yield() &&
6241        !CMSCollector::foregroundGCIsActive();
6242        ++i) {
6243     os::sleep(Thread::current(), 1, false);
6244   }
6245 
6246   ConcurrentMarkSweepThread::synchronize(true);
6247   _freelistLock->lock_without_safepoint_check();
6248   _bit_map->lock()->lock_without_safepoint_check();
6249   _collector->startTimer();
6250 }
6251 
6252 ///////////////////////////////////////////////////////////
6253 // Par_MarkRefsIntoAndScanClosure: a parallel version of
6254 //                                 MarkRefsIntoAndScanClosure
6255 ///////////////////////////////////////////////////////////
6256 Par_MarkRefsIntoAndScanClosure::Par_MarkRefsIntoAndScanClosure(
6257   CMSCollector* collector, MemRegion span, ReferenceProcessor* rp,
6258   CMSBitMap* bit_map, OopTaskQueue* work_queue):
6259   _span(span),
6260   _bit_map(bit_map),
6261   _work_queue(work_queue),
6262   _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
6263                        (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads))),
6264   _par_pushAndMarkClosure(collector, span, rp, bit_map, work_queue)
6265 {
6266   _ref_processor = rp;
6267   assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6268 }
6269 
6270 // This closure is used to mark refs into the CMS generation at the
6271 // second (final) checkpoint, and to scan and transitively follow
6272 // the unmarked oops. The marks are made in the marking bit map and
6273 // the work_queue is used for keeping the (newly) grey objects during
6274 // the scan phase whence they are also available for stealing by parallel
6275 // threads. Since the marking bit map is shared, updates are
6276 // synchronized (via CAS).
6277 void Par_MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6278   if (obj != NULL) {
6279     // Ignore mark word because this could be an already marked oop
6280     // that may be chained at the end of the overflow list.
6281     assert(obj->is_oop(true), "expected an oop");
6282     HeapWord* addr = (HeapWord*)obj;
6283     if (_span.contains(addr) &&
6284         !_bit_map->isMarked(addr)) {
6285       // mark bit map (object will become grey):
6286       // It is possible for several threads to be
6287       // trying to "claim" this object concurrently;
6288       // the unique thread that succeeds in marking the
6289       // object first will do the subsequent push on
6290       // to the work queue (or overflow list).
6291       if (_bit_map->par_mark(addr)) {
6292         // push on work_queue (which may not be empty), and trim the
6293         // queue to an appropriate length by applying this closure to
6294         // the oops in the oops popped from the stack (i.e. blacken the
6295         // grey objects)
6296         bool res = _work_queue->push(obj);
6297         assert(res, "Low water mark should be less than capacity?");
6298         trim_queue(_low_water_mark);
6299       } // Else, another thread claimed the object
6300     }
6301   }
6302 }
6303 
6304 void Par_MarkRefsIntoAndScanClosure::do_oop(oop* p)       { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6305 void Par_MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6306 
6307 // This closure is used to rescan the marked objects on the dirty cards
6308 // in the mod union table and the card table proper.
6309 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
6310   oop p, MemRegion mr) {
6311 
6312   size_t size = 0;
6313   HeapWord* addr = (HeapWord*)p;
6314   DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6315   assert(_span.contains(addr), "we are scanning the CMS generation");
6316   // check if it's time to yield
6317   if (do_yield_check()) {
6318     // We yielded for some foreground stop-world work,
6319     // and we have been asked to abort this ongoing preclean cycle.
6320     return 0;
6321   }
6322   if (_bitMap->isMarked(addr)) {
6323     // it's marked; is it potentially uninitialized?
6324     if (p->klass_or_null() != NULL) {
6325         // an initialized object; ignore mark word in verification below
6326         // since we are running concurrent with mutators
6327         assert(p->is_oop(true), "should be an oop");
6328         if (p->is_objArray()) {
6329           // objArrays are precisely marked; restrict scanning
6330           // to dirty cards only.
6331           size = CompactibleFreeListSpace::adjustObjectSize(
6332                    p->oop_iterate(_scanningClosure, mr));
6333         } else {
6334           // A non-array may have been imprecisely marked; we need
6335           // to scan object in its entirety.
6336           size = CompactibleFreeListSpace::adjustObjectSize(
6337                    p->oop_iterate(_scanningClosure));
6338         }
6339         #ifdef ASSERT
6340           size_t direct_size =
6341             CompactibleFreeListSpace::adjustObjectSize(p->size());
6342           assert(size == direct_size, "Inconsistency in size");
6343           assert(size >= 3, "Necessary for Printezis marks to work");
6344           if (!_bitMap->isMarked(addr+1)) {
6345             _bitMap->verifyNoOneBitsInRange(addr+2, addr+size);
6346           } else {
6347             _bitMap->verifyNoOneBitsInRange(addr+2, addr+size-1);
6348             assert(_bitMap->isMarked(addr+size-1),
6349                    "inconsistent Printezis mark");
6350           }
6351         #endif // ASSERT
6352     } else {
6353       // An uninitialized object.
6354       assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
6355       HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
6356       size = pointer_delta(nextOneAddr + 1, addr);
6357       assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6358              "alignment problem");
6359       // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
6360       // will dirty the card when the klass pointer is installed in the
6361       // object (signaling the completion of initialization).
6362     }
6363   } else {
6364     // Either a not yet marked object or an uninitialized object
6365     if (p->klass_or_null() == NULL) {
6366       // An uninitialized object, skip to the next card, since
6367       // we may not be able to read its P-bits yet.
6368       assert(size == 0, "Initial value");
6369     } else {
6370       // An object not (yet) reached by marking: we merely need to
6371       // compute its size so as to go look at the next block.
6372       assert(p->is_oop(true), "should be an oop");
6373       size = CompactibleFreeListSpace::adjustObjectSize(p->size());
6374     }
6375   }
6376   DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6377   return size;
6378 }
6379 
6380 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
6381   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6382          "CMS thread should hold CMS token");
6383   assert_lock_strong(_freelistLock);
6384   assert_lock_strong(_bitMap->lock());
6385   // relinquish the free_list_lock and bitMaplock()
6386   _bitMap->lock()->unlock();
6387   _freelistLock->unlock();
6388   ConcurrentMarkSweepThread::desynchronize(true);
6389   _collector->stopTimer();
6390   if (PrintCMSStatistics != 0) {
6391     _collector->incrementYields();
6392   }
6393 
6394   // See the comment in coordinator_yield()
6395   for (unsigned i = 0; i < CMSYieldSleepCount &&
6396                    ConcurrentMarkSweepThread::should_yield() &&
6397                    !CMSCollector::foregroundGCIsActive(); ++i) {
6398     os::sleep(Thread::current(), 1, false);
6399   }
6400 
6401   ConcurrentMarkSweepThread::synchronize(true);
6402   _freelistLock->lock_without_safepoint_check();
6403   _bitMap->lock()->lock_without_safepoint_check();
6404   _collector->startTimer();
6405 }
6406 
6407 
6408 //////////////////////////////////////////////////////////////////
6409 // SurvivorSpacePrecleanClosure
6410 //////////////////////////////////////////////////////////////////
6411 // This (single-threaded) closure is used to preclean the oops in
6412 // the survivor spaces.
6413 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
6414 
6415   HeapWord* addr = (HeapWord*)p;
6416   DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6417   assert(!_span.contains(addr), "we are scanning the survivor spaces");
6418   assert(p->klass_or_null() != NULL, "object should be initialized");
6419   // an initialized object; ignore mark word in verification below
6420   // since we are running concurrent with mutators
6421   assert(p->is_oop(true), "should be an oop");
6422   // Note that we do not yield while we iterate over
6423   // the interior oops of p, pushing the relevant ones
6424   // on our marking stack.
6425   size_t size = p->oop_iterate(_scanning_closure);
6426   do_yield_check();
6427   // Observe that below, we do not abandon the preclean
6428   // phase as soon as we should; rather we empty the
6429   // marking stack before returning. This is to satisfy
6430   // some existing assertions. In general, it may be a
6431   // good idea to abort immediately and complete the marking
6432   // from the grey objects at a later time.
6433   while (!_mark_stack->isEmpty()) {
6434     oop new_oop = _mark_stack->pop();
6435     assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6436     assert(_bit_map->isMarked((HeapWord*)new_oop),
6437            "only grey objects on this stack");
6438     // iterate over the oops in this oop, marking and pushing
6439     // the ones in CMS heap (i.e. in _span).
6440     new_oop->oop_iterate(_scanning_closure);
6441     // check if it's time to yield
6442     do_yield_check();
6443   }
6444   unsigned int after_count =
6445     GenCollectedHeap::heap()->total_collections();
6446   bool abort = (_before_count != after_count) ||
6447                _collector->should_abort_preclean();
6448   return abort ? 0 : size;
6449 }
6450 
6451 void SurvivorSpacePrecleanClosure::do_yield_work() {
6452   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6453          "CMS thread should hold CMS token");
6454   assert_lock_strong(_bit_map->lock());
6455   // Relinquish the bit map lock
6456   _bit_map->lock()->unlock();
6457   ConcurrentMarkSweepThread::desynchronize(true);
6458   _collector->stopTimer();
6459   if (PrintCMSStatistics != 0) {
6460     _collector->incrementYields();
6461   }
6462 
6463   // See the comment in coordinator_yield()
6464   for (unsigned i = 0; i < CMSYieldSleepCount &&
6465                        ConcurrentMarkSweepThread::should_yield() &&
6466                        !CMSCollector::foregroundGCIsActive(); ++i) {
6467     os::sleep(Thread::current(), 1, false);
6468   }
6469 
6470   ConcurrentMarkSweepThread::synchronize(true);
6471   _bit_map->lock()->lock_without_safepoint_check();
6472   _collector->startTimer();
6473 }
6474 
6475 // This closure is used to rescan the marked objects on the dirty cards
6476 // in the mod union table and the card table proper. In the parallel
6477 // case, although the bitMap is shared, we do a single read so the
6478 // isMarked() query is "safe".
6479 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
6480   // Ignore mark word because we are running concurrent with mutators
6481   assert(p->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(p)));
6482   HeapWord* addr = (HeapWord*)p;
6483   assert(_span.contains(addr), "we are scanning the CMS generation");
6484   bool is_obj_array = false;
6485   #ifdef ASSERT
6486     if (!_parallel) {
6487       assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6488       assert(_collector->overflow_list_is_empty(),
6489              "overflow list should be empty");
6490 
6491     }
6492   #endif // ASSERT
6493   if (_bit_map->isMarked(addr)) {
6494     // Obj arrays are precisely marked, non-arrays are not;
6495     // so we scan objArrays precisely and non-arrays in their
6496     // entirety.
6497     if (p->is_objArray()) {
6498       is_obj_array = true;
6499       if (_parallel) {
6500         p->oop_iterate(_par_scan_closure, mr);
6501       } else {
6502         p->oop_iterate(_scan_closure, mr);
6503       }
6504     } else {
6505       if (_parallel) {
6506         p->oop_iterate(_par_scan_closure);
6507       } else {
6508         p->oop_iterate(_scan_closure);
6509       }
6510     }
6511   }
6512   #ifdef ASSERT
6513     if (!_parallel) {
6514       assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6515       assert(_collector->overflow_list_is_empty(),
6516              "overflow list should be empty");
6517 
6518     }
6519   #endif // ASSERT
6520   return is_obj_array;
6521 }
6522 
6523 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
6524                         MemRegion span,
6525                         CMSBitMap* bitMap, CMSMarkStack*  markStack,
6526                         bool should_yield, bool verifying):
6527   _collector(collector),
6528   _span(span),
6529   _bitMap(bitMap),
6530   _mut(&collector->_modUnionTable),
6531   _markStack(markStack),
6532   _yield(should_yield),
6533   _skipBits(0)
6534 {
6535   assert(_markStack->isEmpty(), "stack should be empty");
6536   _finger = _bitMap->startWord();
6537   _threshold = _finger;
6538   assert(_collector->_restart_addr == NULL, "Sanity check");
6539   assert(_span.contains(_finger), "Out of bounds _finger?");
6540   DEBUG_ONLY(_verifying = verifying;)
6541 }
6542 
6543 void MarkFromRootsClosure::reset(HeapWord* addr) {
6544   assert(_markStack->isEmpty(), "would cause duplicates on stack");
6545   assert(_span.contains(addr), "Out of bounds _finger?");
6546   _finger = addr;
6547   _threshold = (HeapWord*)round_to(
6548                  (intptr_t)_finger, CardTableModRefBS::card_size);
6549 }
6550 
6551 // Should revisit to see if this should be restructured for
6552 // greater efficiency.
6553 bool MarkFromRootsClosure::do_bit(size_t offset) {
6554   if (_skipBits > 0) {
6555     _skipBits--;
6556     return true;
6557   }
6558   // convert offset into a HeapWord*
6559   HeapWord* addr = _bitMap->startWord() + offset;
6560   assert(_bitMap->endWord() && addr < _bitMap->endWord(),
6561          "address out of range");
6562   assert(_bitMap->isMarked(addr), "tautology");
6563   if (_bitMap->isMarked(addr+1)) {
6564     // this is an allocated but not yet initialized object
6565     assert(_skipBits == 0, "tautology");
6566     _skipBits = 2;  // skip next two marked bits ("Printezis-marks")
6567     oop p = oop(addr);
6568     if (p->klass_or_null() == NULL) {
6569       DEBUG_ONLY(if (!_verifying) {)
6570         // We re-dirty the cards on which this object lies and increase
6571         // the _threshold so that we'll come back to scan this object
6572         // during the preclean or remark phase. (CMSCleanOnEnter)
6573         if (CMSCleanOnEnter) {
6574           size_t sz = _collector->block_size_using_printezis_bits(addr);
6575           HeapWord* end_card_addr   = (HeapWord*)round_to(
6576                                          (intptr_t)(addr+sz), CardTableModRefBS::card_size);
6577           MemRegion redirty_range = MemRegion(addr, end_card_addr);
6578           assert(!redirty_range.is_empty(), "Arithmetical tautology");
6579           // Bump _threshold to end_card_addr; note that
6580           // _threshold cannot possibly exceed end_card_addr, anyhow.
6581           // This prevents future clearing of the card as the scan proceeds
6582           // to the right.
6583           assert(_threshold <= end_card_addr,
6584                  "Because we are just scanning into this object");
6585           if (_threshold < end_card_addr) {
6586             _threshold = end_card_addr;
6587           }
6588           if (p->klass_or_null() != NULL) {
6589             // Redirty the range of cards...
6590             _mut->mark_range(redirty_range);
6591           } // ...else the setting of klass will dirty the card anyway.
6592         }
6593       DEBUG_ONLY(})
6594       return true;
6595     }
6596   }
6597   scanOopsInOop(addr);
6598   return true;
6599 }
6600 
6601 // We take a break if we've been at this for a while,
6602 // so as to avoid monopolizing the locks involved.
6603 void MarkFromRootsClosure::do_yield_work() {
6604   // First give up the locks, then yield, then re-lock
6605   // We should probably use a constructor/destructor idiom to
6606   // do this unlock/lock or modify the MutexUnlocker class to
6607   // serve our purpose. XXX
6608   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6609          "CMS thread should hold CMS token");
6610   assert_lock_strong(_bitMap->lock());
6611   _bitMap->lock()->unlock();
6612   ConcurrentMarkSweepThread::desynchronize(true);
6613   _collector->stopTimer();
6614   if (PrintCMSStatistics != 0) {
6615     _collector->incrementYields();
6616   }
6617 
6618   // See the comment in coordinator_yield()
6619   for (unsigned i = 0; i < CMSYieldSleepCount &&
6620                        ConcurrentMarkSweepThread::should_yield() &&
6621                        !CMSCollector::foregroundGCIsActive(); ++i) {
6622     os::sleep(Thread::current(), 1, false);
6623   }
6624 
6625   ConcurrentMarkSweepThread::synchronize(true);
6626   _bitMap->lock()->lock_without_safepoint_check();
6627   _collector->startTimer();
6628 }
6629 
6630 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
6631   assert(_bitMap->isMarked(ptr), "expected bit to be set");
6632   assert(_markStack->isEmpty(),
6633          "should drain stack to limit stack usage");
6634   // convert ptr to an oop preparatory to scanning
6635   oop obj = oop(ptr);
6636   // Ignore mark word in verification below, since we
6637   // may be running concurrent with mutators.
6638   assert(obj->is_oop(true), "should be an oop");
6639   assert(_finger <= ptr, "_finger runneth ahead");
6640   // advance the finger to right end of this object
6641   _finger = ptr + obj->size();
6642   assert(_finger > ptr, "we just incremented it above");
6643   // On large heaps, it may take us some time to get through
6644   // the marking phase. During
6645   // this time it's possible that a lot of mutations have
6646   // accumulated in the card table and the mod union table --
6647   // these mutation records are redundant until we have
6648   // actually traced into the corresponding card.
6649   // Here, we check whether advancing the finger would make
6650   // us cross into a new card, and if so clear corresponding
6651   // cards in the MUT (preclean them in the card-table in the
6652   // future).
6653 
6654   DEBUG_ONLY(if (!_verifying) {)
6655     // The clean-on-enter optimization is disabled by default,
6656     // until we fix 6178663.
6657     if (CMSCleanOnEnter && (_finger > _threshold)) {
6658       // [_threshold, _finger) represents the interval
6659       // of cards to be cleared  in MUT (or precleaned in card table).
6660       // The set of cards to be cleared is all those that overlap
6661       // with the interval [_threshold, _finger); note that
6662       // _threshold is always kept card-aligned but _finger isn't
6663       // always card-aligned.
6664       HeapWord* old_threshold = _threshold;
6665       assert(old_threshold == (HeapWord*)round_to(
6666               (intptr_t)old_threshold, CardTableModRefBS::card_size),
6667              "_threshold should always be card-aligned");
6668       _threshold = (HeapWord*)round_to(
6669                      (intptr_t)_finger, CardTableModRefBS::card_size);
6670       MemRegion mr(old_threshold, _threshold);
6671       assert(!mr.is_empty(), "Control point invariant");
6672       assert(_span.contains(mr), "Should clear within span");
6673       _mut->clear_range(mr);
6674     }
6675   DEBUG_ONLY(})
6676   // Note: the finger doesn't advance while we drain
6677   // the stack below.
6678   PushOrMarkClosure pushOrMarkClosure(_collector,
6679                                       _span, _bitMap, _markStack,
6680                                       _finger, this);
6681   bool res = _markStack->push(obj);
6682   assert(res, "Empty non-zero size stack should have space for single push");
6683   while (!_markStack->isEmpty()) {
6684     oop new_oop = _markStack->pop();
6685     // Skip verifying header mark word below because we are
6686     // running concurrent with mutators.
6687     assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
6688     // now scan this oop's oops
6689     new_oop->oop_iterate(&pushOrMarkClosure);
6690     do_yield_check();
6691   }
6692   assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
6693 }
6694 
6695 Par_MarkFromRootsClosure::Par_MarkFromRootsClosure(CMSConcMarkingTask* task,
6696                        CMSCollector* collector, MemRegion span,
6697                        CMSBitMap* bit_map,
6698                        OopTaskQueue* work_queue,
6699                        CMSMarkStack*  overflow_stack):
6700   _collector(collector),
6701   _whole_span(collector->_span),
6702   _span(span),
6703   _bit_map(bit_map),
6704   _mut(&collector->_modUnionTable),
6705   _work_queue(work_queue),
6706   _overflow_stack(overflow_stack),
6707   _skip_bits(0),
6708   _task(task)
6709 {
6710   assert(_work_queue->size() == 0, "work_queue should be empty");
6711   _finger = span.start();
6712   _threshold = _finger;     // XXX Defer clear-on-enter optimization for now
6713   assert(_span.contains(_finger), "Out of bounds _finger?");
6714 }
6715 
6716 // Should revisit to see if this should be restructured for
6717 // greater efficiency.
6718 bool Par_MarkFromRootsClosure::do_bit(size_t offset) {
6719   if (_skip_bits > 0) {
6720     _skip_bits--;
6721     return true;
6722   }
6723   // convert offset into a HeapWord*
6724   HeapWord* addr = _bit_map->startWord() + offset;
6725   assert(_bit_map->endWord() && addr < _bit_map->endWord(),
6726          "address out of range");
6727   assert(_bit_map->isMarked(addr), "tautology");
6728   if (_bit_map->isMarked(addr+1)) {
6729     // this is an allocated object that might not yet be initialized
6730     assert(_skip_bits == 0, "tautology");
6731     _skip_bits = 2;  // skip next two marked bits ("Printezis-marks")
6732     oop p = oop(addr);
6733     if (p->klass_or_null() == NULL) {
6734       // in the case of Clean-on-Enter optimization, redirty card
6735       // and avoid clearing card by increasing  the threshold.
6736       return true;
6737     }
6738   }
6739   scan_oops_in_oop(addr);
6740   return true;
6741 }
6742 
6743 void Par_MarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
6744   assert(_bit_map->isMarked(ptr), "expected bit to be set");
6745   // Should we assert that our work queue is empty or
6746   // below some drain limit?
6747   assert(_work_queue->size() == 0,
6748          "should drain stack to limit stack usage");
6749   // convert ptr to an oop preparatory to scanning
6750   oop obj = oop(ptr);
6751   // Ignore mark word in verification below, since we
6752   // may be running concurrent with mutators.
6753   assert(obj->is_oop(true), "should be an oop");
6754   assert(_finger <= ptr, "_finger runneth ahead");
6755   // advance the finger to right end of this object
6756   _finger = ptr + obj->size();
6757   assert(_finger > ptr, "we just incremented it above");
6758   // On large heaps, it may take us some time to get through
6759   // the marking phase. During
6760   // this time it's possible that a lot of mutations have
6761   // accumulated in the card table and the mod union table --
6762   // these mutation records are redundant until we have
6763   // actually traced into the corresponding card.
6764   // Here, we check whether advancing the finger would make
6765   // us cross into a new card, and if so clear corresponding
6766   // cards in the MUT (preclean them in the card-table in the
6767   // future).
6768 
6769   // The clean-on-enter optimization is disabled by default,
6770   // until we fix 6178663.
6771   if (CMSCleanOnEnter && (_finger > _threshold)) {
6772     // [_threshold, _finger) represents the interval
6773     // of cards to be cleared  in MUT (or precleaned in card table).
6774     // The set of cards to be cleared is all those that overlap
6775     // with the interval [_threshold, _finger); note that
6776     // _threshold is always kept card-aligned but _finger isn't
6777     // always card-aligned.
6778     HeapWord* old_threshold = _threshold;
6779     assert(old_threshold == (HeapWord*)round_to(
6780             (intptr_t)old_threshold, CardTableModRefBS::card_size),
6781            "_threshold should always be card-aligned");
6782     _threshold = (HeapWord*)round_to(
6783                    (intptr_t)_finger, CardTableModRefBS::card_size);
6784     MemRegion mr(old_threshold, _threshold);
6785     assert(!mr.is_empty(), "Control point invariant");
6786     assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
6787     _mut->clear_range(mr);
6788   }
6789 
6790   // Note: the local finger doesn't advance while we drain
6791   // the stack below, but the global finger sure can and will.
6792   HeapWord** gfa = _task->global_finger_addr();
6793   Par_PushOrMarkClosure pushOrMarkClosure(_collector,
6794                                       _span, _bit_map,
6795                                       _work_queue,
6796                                       _overflow_stack,
6797                                       _finger,
6798                                       gfa, this);
6799   bool res = _work_queue->push(obj);   // overflow could occur here
6800   assert(res, "Will hold once we use workqueues");
6801   while (true) {
6802     oop new_oop;
6803     if (!_work_queue->pop_local(new_oop)) {
6804       // We emptied our work_queue; check if there's stuff that can
6805       // be gotten from the overflow stack.
6806       if (CMSConcMarkingTask::get_work_from_overflow_stack(
6807             _overflow_stack, _work_queue)) {
6808         do_yield_check();
6809         continue;
6810       } else {  // done
6811         break;
6812       }
6813     }
6814     // Skip verifying header mark word below because we are
6815     // running concurrent with mutators.
6816     assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
6817     // now scan this oop's oops
6818     new_oop->oop_iterate(&pushOrMarkClosure);
6819     do_yield_check();
6820   }
6821   assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
6822 }
6823 
6824 // Yield in response to a request from VM Thread or
6825 // from mutators.
6826 void Par_MarkFromRootsClosure::do_yield_work() {
6827   assert(_task != NULL, "sanity");
6828   _task->yield();
6829 }
6830 
6831 // A variant of the above used for verifying CMS marking work.
6832 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
6833                         MemRegion span,
6834                         CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6835                         CMSMarkStack*  mark_stack):
6836   _collector(collector),
6837   _span(span),
6838   _verification_bm(verification_bm),
6839   _cms_bm(cms_bm),
6840   _mark_stack(mark_stack),
6841   _pam_verify_closure(collector, span, verification_bm, cms_bm,
6842                       mark_stack)
6843 {
6844   assert(_mark_stack->isEmpty(), "stack should be empty");
6845   _finger = _verification_bm->startWord();
6846   assert(_collector->_restart_addr == NULL, "Sanity check");
6847   assert(_span.contains(_finger), "Out of bounds _finger?");
6848 }
6849 
6850 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
6851   assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
6852   assert(_span.contains(addr), "Out of bounds _finger?");
6853   _finger = addr;
6854 }
6855 
6856 // Should revisit to see if this should be restructured for
6857 // greater efficiency.
6858 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
6859   // convert offset into a HeapWord*
6860   HeapWord* addr = _verification_bm->startWord() + offset;
6861   assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
6862          "address out of range");
6863   assert(_verification_bm->isMarked(addr), "tautology");
6864   assert(_cms_bm->isMarked(addr), "tautology");
6865 
6866   assert(_mark_stack->isEmpty(),
6867          "should drain stack to limit stack usage");
6868   // convert addr to an oop preparatory to scanning
6869   oop obj = oop(addr);
6870   assert(obj->is_oop(), "should be an oop");
6871   assert(_finger <= addr, "_finger runneth ahead");
6872   // advance the finger to right end of this object
6873   _finger = addr + obj->size();
6874   assert(_finger > addr, "we just incremented it above");
6875   // Note: the finger doesn't advance while we drain
6876   // the stack below.
6877   bool res = _mark_stack->push(obj);
6878   assert(res, "Empty non-zero size stack should have space for single push");
6879   while (!_mark_stack->isEmpty()) {
6880     oop new_oop = _mark_stack->pop();
6881     assert(new_oop->is_oop(), "Oops! expected to pop an oop");
6882     // now scan this oop's oops
6883     new_oop->oop_iterate(&_pam_verify_closure);
6884   }
6885   assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
6886   return true;
6887 }
6888 
6889 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
6890   CMSCollector* collector, MemRegion span,
6891   CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6892   CMSMarkStack*  mark_stack):
6893   MetadataAwareOopClosure(collector->ref_processor()),
6894   _collector(collector),
6895   _span(span),
6896   _verification_bm(verification_bm),
6897   _cms_bm(cms_bm),
6898   _mark_stack(mark_stack)
6899 { }
6900 
6901 void PushAndMarkVerifyClosure::do_oop(oop* p)       { PushAndMarkVerifyClosure::do_oop_work(p); }
6902 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
6903 
6904 // Upon stack overflow, we discard (part of) the stack,
6905 // remembering the least address amongst those discarded
6906 // in CMSCollector's _restart_address.
6907 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
6908   // Remember the least grey address discarded
6909   HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
6910   _collector->lower_restart_addr(ra);
6911   _mark_stack->reset();  // discard stack contents
6912   _mark_stack->expand(); // expand the stack if possible
6913 }
6914 
6915 void PushAndMarkVerifyClosure::do_oop(oop obj) {
6916   assert(obj->is_oop_or_null(), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
6917   HeapWord* addr = (HeapWord*)obj;
6918   if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
6919     // Oop lies in _span and isn't yet grey or black
6920     _verification_bm->mark(addr);            // now grey
6921     if (!_cms_bm->isMarked(addr)) {
6922       oop(addr)->print();
6923       gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)",
6924                              p2i(addr));
6925       fatal("... aborting");
6926     }
6927 
6928     if (!_mark_stack->push(obj)) { // stack overflow
6929       if (PrintCMSStatistics != 0) {
6930         gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
6931                                SIZE_FORMAT, _mark_stack->capacity());
6932       }
6933       assert(_mark_stack->isFull(), "Else push should have succeeded");
6934       handle_stack_overflow(addr);
6935     }
6936     // anything including and to the right of _finger
6937     // will be scanned as we iterate over the remainder of the
6938     // bit map
6939   }
6940 }
6941 
6942 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
6943                      MemRegion span,
6944                      CMSBitMap* bitMap, CMSMarkStack*  markStack,
6945                      HeapWord* finger, MarkFromRootsClosure* parent) :
6946   MetadataAwareOopClosure(collector->ref_processor()),
6947   _collector(collector),
6948   _span(span),
6949   _bitMap(bitMap),
6950   _markStack(markStack),
6951   _finger(finger),
6952   _parent(parent)
6953 { }
6954 
6955 Par_PushOrMarkClosure::Par_PushOrMarkClosure(CMSCollector* collector,
6956                      MemRegion span,
6957                      CMSBitMap* bit_map,
6958                      OopTaskQueue* work_queue,
6959                      CMSMarkStack*  overflow_stack,
6960                      HeapWord* finger,
6961                      HeapWord** global_finger_addr,
6962                      Par_MarkFromRootsClosure* parent) :
6963   MetadataAwareOopClosure(collector->ref_processor()),
6964   _collector(collector),
6965   _whole_span(collector->_span),
6966   _span(span),
6967   _bit_map(bit_map),
6968   _work_queue(work_queue),
6969   _overflow_stack(overflow_stack),
6970   _finger(finger),
6971   _global_finger_addr(global_finger_addr),
6972   _parent(parent)
6973 { }
6974 
6975 // Assumes thread-safe access by callers, who are
6976 // responsible for mutual exclusion.
6977 void CMSCollector::lower_restart_addr(HeapWord* low) {
6978   assert(_span.contains(low), "Out of bounds addr");
6979   if (_restart_addr == NULL) {
6980     _restart_addr = low;
6981   } else {
6982     _restart_addr = MIN2(_restart_addr, low);
6983   }
6984 }
6985 
6986 // Upon stack overflow, we discard (part of) the stack,
6987 // remembering the least address amongst those discarded
6988 // in CMSCollector's _restart_address.
6989 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
6990   // Remember the least grey address discarded
6991   HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
6992   _collector->lower_restart_addr(ra);
6993   _markStack->reset();  // discard stack contents
6994   _markStack->expand(); // expand the stack if possible
6995 }
6996 
6997 // Upon stack overflow, we discard (part of) the stack,
6998 // remembering the least address amongst those discarded
6999 // in CMSCollector's _restart_address.
7000 void Par_PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7001   // We need to do this under a mutex to prevent other
7002   // workers from interfering with the work done below.
7003   MutexLockerEx ml(_overflow_stack->par_lock(),
7004                    Mutex::_no_safepoint_check_flag);
7005   // Remember the least grey address discarded
7006   HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
7007   _collector->lower_restart_addr(ra);
7008   _overflow_stack->reset();  // discard stack contents
7009   _overflow_stack->expand(); // expand the stack if possible
7010 }
7011 
7012 void PushOrMarkClosure::do_oop(oop obj) {
7013   // Ignore mark word because we are running concurrent with mutators.
7014   assert(obj->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7015   HeapWord* addr = (HeapWord*)obj;
7016   if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
7017     // Oop lies in _span and isn't yet grey or black
7018     _bitMap->mark(addr);            // now grey
7019     if (addr < _finger) {
7020       // the bit map iteration has already either passed, or
7021       // sampled, this bit in the bit map; we'll need to
7022       // use the marking stack to scan this oop's oops.
7023       bool simulate_overflow = false;
7024       NOT_PRODUCT(
7025         if (CMSMarkStackOverflowALot &&
7026             _collector->simulate_overflow()) {
7027           // simulate a stack overflow
7028           simulate_overflow = true;
7029         }
7030       )
7031       if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
7032         if (PrintCMSStatistics != 0) {
7033           gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7034                                  SIZE_FORMAT, _markStack->capacity());
7035         }
7036         assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
7037         handle_stack_overflow(addr);
7038       }
7039     }
7040     // anything including and to the right of _finger
7041     // will be scanned as we iterate over the remainder of the
7042     // bit map
7043     do_yield_check();
7044   }
7045 }
7046 
7047 void PushOrMarkClosure::do_oop(oop* p)       { PushOrMarkClosure::do_oop_work(p); }
7048 void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); }
7049 
7050 void Par_PushOrMarkClosure::do_oop(oop obj) {
7051   // Ignore mark word because we are running concurrent with mutators.
7052   assert(obj->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7053   HeapWord* addr = (HeapWord*)obj;
7054   if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
7055     // Oop lies in _span and isn't yet grey or black
7056     // We read the global_finger (volatile read) strictly after marking oop
7057     bool res = _bit_map->par_mark(addr);    // now grey
7058     volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
7059     // Should we push this marked oop on our stack?
7060     // -- if someone else marked it, nothing to do
7061     // -- if target oop is above global finger nothing to do
7062     // -- if target oop is in chunk and above local finger
7063     //      then nothing to do
7064     // -- else push on work queue
7065     if (   !res       // someone else marked it, they will deal with it
7066         || (addr >= *gfa)  // will be scanned in a later task
7067         || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
7068       return;
7069     }
7070     // the bit map iteration has already either passed, or
7071     // sampled, this bit in the bit map; we'll need to
7072     // use the marking stack to scan this oop's oops.
7073     bool simulate_overflow = false;
7074     NOT_PRODUCT(
7075       if (CMSMarkStackOverflowALot &&
7076           _collector->simulate_overflow()) {
7077         // simulate a stack overflow
7078         simulate_overflow = true;
7079       }
7080     )
7081     if (simulate_overflow ||
7082         !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
7083       // stack overflow
7084       if (PrintCMSStatistics != 0) {
7085         gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7086                                SIZE_FORMAT, _overflow_stack->capacity());
7087       }
7088       // We cannot assert that the overflow stack is full because
7089       // it may have been emptied since.
7090       assert(simulate_overflow ||
7091              _work_queue->size() == _work_queue->max_elems(),
7092             "Else push should have succeeded");
7093       handle_stack_overflow(addr);
7094     }
7095     do_yield_check();
7096   }
7097 }
7098 
7099 void Par_PushOrMarkClosure::do_oop(oop* p)       { Par_PushOrMarkClosure::do_oop_work(p); }
7100 void Par_PushOrMarkClosure::do_oop(narrowOop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7101 
7102 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
7103                                        MemRegion span,
7104                                        ReferenceProcessor* rp,
7105                                        CMSBitMap* bit_map,
7106                                        CMSBitMap* mod_union_table,
7107                                        CMSMarkStack*  mark_stack,
7108                                        bool           concurrent_precleaning):
7109   MetadataAwareOopClosure(rp),
7110   _collector(collector),
7111   _span(span),
7112   _bit_map(bit_map),
7113   _mod_union_table(mod_union_table),
7114   _mark_stack(mark_stack),
7115   _concurrent_precleaning(concurrent_precleaning)
7116 {
7117   assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7118 }
7119 
7120 // Grey object rescan during pre-cleaning and second checkpoint phases --
7121 // the non-parallel version (the parallel version appears further below.)
7122 void PushAndMarkClosure::do_oop(oop obj) {
7123   // Ignore mark word verification. If during concurrent precleaning,
7124   // the object monitor may be locked. If during the checkpoint
7125   // phases, the object may already have been reached by a  different
7126   // path and may be at the end of the global overflow list (so
7127   // the mark word may be NULL).
7128   assert(obj->is_oop_or_null(true /* ignore mark word */),
7129          err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7130   HeapWord* addr = (HeapWord*)obj;
7131   // Check if oop points into the CMS generation
7132   // and is not marked
7133   if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7134     // a white object ...
7135     _bit_map->mark(addr);         // ... now grey
7136     // push on the marking stack (grey set)
7137     bool simulate_overflow = false;
7138     NOT_PRODUCT(
7139       if (CMSMarkStackOverflowALot &&
7140           _collector->simulate_overflow()) {
7141         // simulate a stack overflow
7142         simulate_overflow = true;
7143       }
7144     )
7145     if (simulate_overflow || !_mark_stack->push(obj)) {
7146       if (_concurrent_precleaning) {
7147          // During precleaning we can just dirty the appropriate card(s)
7148          // in the mod union table, thus ensuring that the object remains
7149          // in the grey set  and continue. In the case of object arrays
7150          // we need to dirty all of the cards that the object spans,
7151          // since the rescan of object arrays will be limited to the
7152          // dirty cards.
7153          // Note that no one can be interfering with us in this action
7154          // of dirtying the mod union table, so no locking or atomics
7155          // are required.
7156          if (obj->is_objArray()) {
7157            size_t sz = obj->size();
7158            HeapWord* end_card_addr = (HeapWord*)round_to(
7159                                         (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7160            MemRegion redirty_range = MemRegion(addr, end_card_addr);
7161            assert(!redirty_range.is_empty(), "Arithmetical tautology");
7162            _mod_union_table->mark_range(redirty_range);
7163          } else {
7164            _mod_union_table->mark(addr);
7165          }
7166          _collector->_ser_pmc_preclean_ovflw++;
7167       } else {
7168          // During the remark phase, we need to remember this oop
7169          // in the overflow list.
7170          _collector->push_on_overflow_list(obj);
7171          _collector->_ser_pmc_remark_ovflw++;
7172       }
7173     }
7174   }
7175 }
7176 
7177 Par_PushAndMarkClosure::Par_PushAndMarkClosure(CMSCollector* collector,
7178                                                MemRegion span,
7179                                                ReferenceProcessor* rp,
7180                                                CMSBitMap* bit_map,
7181                                                OopTaskQueue* work_queue):
7182   MetadataAwareOopClosure(rp),
7183   _collector(collector),
7184   _span(span),
7185   _bit_map(bit_map),
7186   _work_queue(work_queue)
7187 {
7188   assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7189 }
7190 
7191 void PushAndMarkClosure::do_oop(oop* p)       { PushAndMarkClosure::do_oop_work(p); }
7192 void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); }
7193 
7194 // Grey object rescan during second checkpoint phase --
7195 // the parallel version.
7196 void Par_PushAndMarkClosure::do_oop(oop obj) {
7197   // In the assert below, we ignore the mark word because
7198   // this oop may point to an already visited object that is
7199   // on the overflow stack (in which case the mark word has
7200   // been hijacked for chaining into the overflow stack --
7201   // if this is the last object in the overflow stack then
7202   // its mark word will be NULL). Because this object may
7203   // have been subsequently popped off the global overflow
7204   // stack, and the mark word possibly restored to the prototypical
7205   // value, by the time we get to examined this failing assert in
7206   // the debugger, is_oop_or_null(false) may subsequently start
7207   // to hold.
7208   assert(obj->is_oop_or_null(true),
7209          err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7210   HeapWord* addr = (HeapWord*)obj;
7211   // Check if oop points into the CMS generation
7212   // and is not marked
7213   if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7214     // a white object ...
7215     // If we manage to "claim" the object, by being the
7216     // first thread to mark it, then we push it on our
7217     // marking stack
7218     if (_bit_map->par_mark(addr)) {     // ... now grey
7219       // push on work queue (grey set)
7220       bool simulate_overflow = false;
7221       NOT_PRODUCT(
7222         if (CMSMarkStackOverflowALot &&
7223             _collector->par_simulate_overflow()) {
7224           // simulate a stack overflow
7225           simulate_overflow = true;
7226         }
7227       )
7228       if (simulate_overflow || !_work_queue->push(obj)) {
7229         _collector->par_push_on_overflow_list(obj);
7230         _collector->_par_pmc_remark_ovflw++; //  imprecise OK: no need to CAS
7231       }
7232     } // Else, some other thread got there first
7233   }
7234 }
7235 
7236 void Par_PushAndMarkClosure::do_oop(oop* p)       { Par_PushAndMarkClosure::do_oop_work(p); }
7237 void Par_PushAndMarkClosure::do_oop(narrowOop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7238 
7239 void CMSPrecleanRefsYieldClosure::do_yield_work() {
7240   Mutex* bml = _collector->bitMapLock();
7241   assert_lock_strong(bml);
7242   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7243          "CMS thread should hold CMS token");
7244 
7245   bml->unlock();
7246   ConcurrentMarkSweepThread::desynchronize(true);
7247 
7248   _collector->stopTimer();
7249   if (PrintCMSStatistics != 0) {
7250     _collector->incrementYields();
7251   }
7252 
7253   // See the comment in coordinator_yield()
7254   for (unsigned i = 0; i < CMSYieldSleepCount &&
7255                        ConcurrentMarkSweepThread::should_yield() &&
7256                        !CMSCollector::foregroundGCIsActive(); ++i) {
7257     os::sleep(Thread::current(), 1, false);
7258   }
7259 
7260   ConcurrentMarkSweepThread::synchronize(true);
7261   bml->lock();
7262 
7263   _collector->startTimer();
7264 }
7265 
7266 bool CMSPrecleanRefsYieldClosure::should_return() {
7267   if (ConcurrentMarkSweepThread::should_yield()) {
7268     do_yield_work();
7269   }
7270   return _collector->foregroundGCIsActive();
7271 }
7272 
7273 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
7274   assert(((size_t)mr.start())%CardTableModRefBS::card_size_in_words == 0,
7275          "mr should be aligned to start at a card boundary");
7276   // We'd like to assert:
7277   // assert(mr.word_size()%CardTableModRefBS::card_size_in_words == 0,
7278   //        "mr should be a range of cards");
7279   // However, that would be too strong in one case -- the last
7280   // partition ends at _unallocated_block which, in general, can be
7281   // an arbitrary boundary, not necessarily card aligned.
7282   if (PrintCMSStatistics != 0) {
7283     _num_dirty_cards +=
7284          mr.word_size()/CardTableModRefBS::card_size_in_words;
7285   }
7286   _space->object_iterate_mem(mr, &_scan_cl);
7287 }
7288 
7289 SweepClosure::SweepClosure(CMSCollector* collector,
7290                            ConcurrentMarkSweepGeneration* g,
7291                            CMSBitMap* bitMap, bool should_yield) :
7292   _collector(collector),
7293   _g(g),
7294   _sp(g->cmsSpace()),
7295   _limit(_sp->sweep_limit()),
7296   _freelistLock(_sp->freelistLock()),
7297   _bitMap(bitMap),
7298   _yield(should_yield),
7299   _inFreeRange(false),           // No free range at beginning of sweep
7300   _freeRangeInFreeLists(false),  // No free range at beginning of sweep
7301   _lastFreeRangeCoalesced(false),
7302   _freeFinger(g->used_region().start())
7303 {
7304   NOT_PRODUCT(
7305     _numObjectsFreed = 0;
7306     _numWordsFreed   = 0;
7307     _numObjectsLive = 0;
7308     _numWordsLive = 0;
7309     _numObjectsAlreadyFree = 0;
7310     _numWordsAlreadyFree = 0;
7311     _last_fc = NULL;
7312 
7313     _sp->initializeIndexedFreeListArrayReturnedBytes();
7314     _sp->dictionary()->initialize_dict_returned_bytes();
7315   )
7316   assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7317          "sweep _limit out of bounds");
7318   if (CMSTraceSweeper) {
7319     gclog_or_tty->print_cr("\n====================\nStarting new sweep with limit " PTR_FORMAT,
7320                         p2i(_limit));
7321   }
7322 }
7323 
7324 void SweepClosure::print_on(outputStream* st) const {
7325   tty->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")",
7326                 p2i(_sp->bottom()), p2i(_sp->end()));
7327   tty->print_cr("_limit = " PTR_FORMAT, p2i(_limit));
7328   tty->print_cr("_freeFinger = " PTR_FORMAT, p2i(_freeFinger));
7329   NOT_PRODUCT(tty->print_cr("_last_fc = " PTR_FORMAT, p2i(_last_fc));)
7330   tty->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d",
7331                 _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced);
7332 }
7333 
7334 #ifndef PRODUCT
7335 // Assertion checking only:  no useful work in product mode --
7336 // however, if any of the flags below become product flags,
7337 // you may need to review this code to see if it needs to be
7338 // enabled in product mode.
7339 SweepClosure::~SweepClosure() {
7340   assert_lock_strong(_freelistLock);
7341   assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7342          "sweep _limit out of bounds");
7343   if (inFreeRange()) {
7344     warning("inFreeRange() should have been reset; dumping state of SweepClosure");
7345     print();
7346     ShouldNotReachHere();
7347   }
7348   if (Verbose && PrintGC) {
7349     gclog_or_tty->print("Collected "SIZE_FORMAT" objects, " SIZE_FORMAT " bytes",
7350                         _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
7351     gclog_or_tty->print_cr("\nLive "SIZE_FORMAT" objects,  "
7352                            SIZE_FORMAT" bytes  "
7353       "Already free "SIZE_FORMAT" objects, "SIZE_FORMAT" bytes",
7354       _numObjectsLive, _numWordsLive*sizeof(HeapWord),
7355       _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
7356     size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree)
7357                         * sizeof(HeapWord);
7358     gclog_or_tty->print_cr("Total sweep: "SIZE_FORMAT" bytes", totalBytes);
7359 
7360     if (PrintCMSStatistics && CMSVerifyReturnedBytes) {
7361       size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
7362       size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes();
7363       size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes;
7364       gclog_or_tty->print("Returned "SIZE_FORMAT" bytes", returned_bytes);
7365       gclog_or_tty->print("   Indexed List Returned "SIZE_FORMAT" bytes",
7366         indexListReturnedBytes);
7367       gclog_or_tty->print_cr("        Dictionary Returned "SIZE_FORMAT" bytes",
7368         dict_returned_bytes);
7369     }
7370   }
7371   if (CMSTraceSweeper) {
7372     gclog_or_tty->print_cr("end of sweep with _limit = " PTR_FORMAT "\n================",
7373                            p2i(_limit));
7374   }
7375 }
7376 #endif  // PRODUCT
7377 
7378 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
7379     bool freeRangeInFreeLists) {
7380   if (CMSTraceSweeper) {
7381     gclog_or_tty->print("---- Start free range at " PTR_FORMAT " with free block (%d)\n",
7382                p2i(freeFinger), freeRangeInFreeLists);
7383   }
7384   assert(!inFreeRange(), "Trampling existing free range");
7385   set_inFreeRange(true);
7386   set_lastFreeRangeCoalesced(false);
7387 
7388   set_freeFinger(freeFinger);
7389   set_freeRangeInFreeLists(freeRangeInFreeLists);
7390   if (CMSTestInFreeList) {
7391     if (freeRangeInFreeLists) {
7392       FreeChunk* fc = (FreeChunk*) freeFinger;
7393       assert(fc->is_free(), "A chunk on the free list should be free.");
7394       assert(fc->size() > 0, "Free range should have a size");
7395       assert(_sp->verify_chunk_in_free_list(fc), "Chunk is not in free lists");
7396     }
7397   }
7398 }
7399 
7400 // Note that the sweeper runs concurrently with mutators. Thus,
7401 // it is possible for direct allocation in this generation to happen
7402 // in the middle of the sweep. Note that the sweeper also coalesces
7403 // contiguous free blocks. Thus, unless the sweeper and the allocator
7404 // synchronize appropriately freshly allocated blocks may get swept up.
7405 // This is accomplished by the sweeper locking the free lists while
7406 // it is sweeping. Thus blocks that are determined to be free are
7407 // indeed free. There is however one additional complication:
7408 // blocks that have been allocated since the final checkpoint and
7409 // mark, will not have been marked and so would be treated as
7410 // unreachable and swept up. To prevent this, the allocator marks
7411 // the bit map when allocating during the sweep phase. This leads,
7412 // however, to a further complication -- objects may have been allocated
7413 // but not yet initialized -- in the sense that the header isn't yet
7414 // installed. The sweeper can not then determine the size of the block
7415 // in order to skip over it. To deal with this case, we use a technique
7416 // (due to Printezis) to encode such uninitialized block sizes in the
7417 // bit map. Since the bit map uses a bit per every HeapWord, but the
7418 // CMS generation has a minimum object size of 3 HeapWords, it follows
7419 // that "normal marks" won't be adjacent in the bit map (there will
7420 // always be at least two 0 bits between successive 1 bits). We make use
7421 // of these "unused" bits to represent uninitialized blocks -- the bit
7422 // corresponding to the start of the uninitialized object and the next
7423 // bit are both set. Finally, a 1 bit marks the end of the object that
7424 // started with the two consecutive 1 bits to indicate its potentially
7425 // uninitialized state.
7426 
7427 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
7428   FreeChunk* fc = (FreeChunk*)addr;
7429   size_t res;
7430 
7431   // Check if we are done sweeping. Below we check "addr >= _limit" rather
7432   // than "addr == _limit" because although _limit was a block boundary when
7433   // we started the sweep, it may no longer be one because heap expansion
7434   // may have caused us to coalesce the block ending at the address _limit
7435   // with a newly expanded chunk (this happens when _limit was set to the
7436   // previous _end of the space), so we may have stepped past _limit:
7437   // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740.
7438   if (addr >= _limit) { // we have swept up to or past the limit: finish up
7439     assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7440            "sweep _limit out of bounds");
7441     assert(addr < _sp->end(), "addr out of bounds");
7442     // Flush any free range we might be holding as a single
7443     // coalesced chunk to the appropriate free list.
7444     if (inFreeRange()) {
7445       assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit,
7446              err_msg("freeFinger() " PTR_FORMAT" is out-of-bounds", p2i(freeFinger())));
7447       flush_cur_free_chunk(freeFinger(),
7448                            pointer_delta(addr, freeFinger()));
7449       if (CMSTraceSweeper) {
7450         gclog_or_tty->print("Sweep: last chunk: ");
7451         gclog_or_tty->print("put_free_blk " PTR_FORMAT " ("SIZE_FORMAT") "
7452                    "[coalesced:%d]\n",
7453                    p2i(freeFinger()), pointer_delta(addr, freeFinger()),
7454                    lastFreeRangeCoalesced() ? 1 : 0);
7455       }
7456     }
7457 
7458     // help the iterator loop finish
7459     return pointer_delta(_sp->end(), addr);
7460   }
7461 
7462   assert(addr < _limit, "sweep invariant");
7463   // check if we should yield
7464   do_yield_check(addr);
7465   if (fc->is_free()) {
7466     // Chunk that is already free
7467     res = fc->size();
7468     do_already_free_chunk(fc);
7469     debug_only(_sp->verifyFreeLists());
7470     // If we flush the chunk at hand in lookahead_and_flush()
7471     // and it's coalesced with a preceding chunk, then the
7472     // process of "mangling" the payload of the coalesced block
7473     // will cause erasure of the size information from the
7474     // (erstwhile) header of all the coalesced blocks but the
7475     // first, so the first disjunct in the assert will not hold
7476     // in that specific case (in which case the second disjunct
7477     // will hold).
7478     assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit,
7479            "Otherwise the size info doesn't change at this step");
7480     NOT_PRODUCT(
7481       _numObjectsAlreadyFree++;
7482       _numWordsAlreadyFree += res;
7483     )
7484     NOT_PRODUCT(_last_fc = fc;)
7485   } else if (!_bitMap->isMarked(addr)) {
7486     // Chunk is fresh garbage
7487     res = do_garbage_chunk(fc);
7488     debug_only(_sp->verifyFreeLists());
7489     NOT_PRODUCT(
7490       _numObjectsFreed++;
7491       _numWordsFreed += res;
7492     )
7493   } else {
7494     // Chunk that is alive.
7495     res = do_live_chunk(fc);
7496     debug_only(_sp->verifyFreeLists());
7497     NOT_PRODUCT(
7498         _numObjectsLive++;
7499         _numWordsLive += res;
7500     )
7501   }
7502   return res;
7503 }
7504 
7505 // For the smart allocation, record following
7506 //  split deaths - a free chunk is removed from its free list because
7507 //      it is being split into two or more chunks.
7508 //  split birth - a free chunk is being added to its free list because
7509 //      a larger free chunk has been split and resulted in this free chunk.
7510 //  coal death - a free chunk is being removed from its free list because
7511 //      it is being coalesced into a large free chunk.
7512 //  coal birth - a free chunk is being added to its free list because
7513 //      it was created when two or more free chunks where coalesced into
7514 //      this free chunk.
7515 //
7516 // These statistics are used to determine the desired number of free
7517 // chunks of a given size.  The desired number is chosen to be relative
7518 // to the end of a CMS sweep.  The desired number at the end of a sweep
7519 // is the
7520 //      count-at-end-of-previous-sweep (an amount that was enough)
7521 //              - count-at-beginning-of-current-sweep  (the excess)
7522 //              + split-births  (gains in this size during interval)
7523 //              - split-deaths  (demands on this size during interval)
7524 // where the interval is from the end of one sweep to the end of the
7525 // next.
7526 //
7527 // When sweeping the sweeper maintains an accumulated chunk which is
7528 // the chunk that is made up of chunks that have been coalesced.  That
7529 // will be termed the left-hand chunk.  A new chunk of garbage that
7530 // is being considered for coalescing will be referred to as the
7531 // right-hand chunk.
7532 //
7533 // When making a decision on whether to coalesce a right-hand chunk with
7534 // the current left-hand chunk, the current count vs. the desired count
7535 // of the left-hand chunk is considered.  Also if the right-hand chunk
7536 // is near the large chunk at the end of the heap (see
7537 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
7538 // left-hand chunk is coalesced.
7539 //
7540 // When making a decision about whether to split a chunk, the desired count
7541 // vs. the current count of the candidate to be split is also considered.
7542 // If the candidate is underpopulated (currently fewer chunks than desired)
7543 // a chunk of an overpopulated (currently more chunks than desired) size may
7544 // be chosen.  The "hint" associated with a free list, if non-null, points
7545 // to a free list which may be overpopulated.
7546 //
7547 
7548 void SweepClosure::do_already_free_chunk(FreeChunk* fc) {
7549   const size_t size = fc->size();
7550   // Chunks that cannot be coalesced are not in the
7551   // free lists.
7552   if (CMSTestInFreeList && !fc->cantCoalesce()) {
7553     assert(_sp->verify_chunk_in_free_list(fc),
7554       "free chunk should be in free lists");
7555   }
7556   // a chunk that is already free, should not have been
7557   // marked in the bit map
7558   HeapWord* const addr = (HeapWord*) fc;
7559   assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
7560   // Verify that the bit map has no bits marked between
7561   // addr and purported end of this block.
7562   _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7563 
7564   // Some chunks cannot be coalesced under any circumstances.
7565   // See the definition of cantCoalesce().
7566   if (!fc->cantCoalesce()) {
7567     // This chunk can potentially be coalesced.
7568     if (_sp->adaptive_freelists()) {
7569       // All the work is done in
7570       do_post_free_or_garbage_chunk(fc, size);
7571     } else {  // Not adaptive free lists
7572       // this is a free chunk that can potentially be coalesced by the sweeper;
7573       if (!inFreeRange()) {
7574         // if the next chunk is a free block that can't be coalesced
7575         // it doesn't make sense to remove this chunk from the free lists
7576         FreeChunk* nextChunk = (FreeChunk*)(addr + size);
7577         assert((HeapWord*)nextChunk <= _sp->end(), "Chunk size out of bounds?");
7578         if ((HeapWord*)nextChunk < _sp->end() &&     // There is another free chunk to the right ...
7579             nextChunk->is_free()               &&     // ... which is free...
7580             nextChunk->cantCoalesce()) {             // ... but can't be coalesced
7581           // nothing to do
7582         } else {
7583           // Potentially the start of a new free range:
7584           // Don't eagerly remove it from the free lists.
7585           // No need to remove it if it will just be put
7586           // back again.  (Also from a pragmatic point of view
7587           // if it is a free block in a region that is beyond
7588           // any allocated blocks, an assertion will fail)
7589           // Remember the start of a free run.
7590           initialize_free_range(addr, true);
7591           // end - can coalesce with next chunk
7592         }
7593       } else {
7594         // the midst of a free range, we are coalescing
7595         print_free_block_coalesced(fc);
7596         if (CMSTraceSweeper) {
7597           gclog_or_tty->print("  -- pick up free block " PTR_FORMAT " (" SIZE_FORMAT ")\n", p2i(fc), size);
7598         }
7599         // remove it from the free lists
7600         _sp->removeFreeChunkFromFreeLists(fc);
7601         set_lastFreeRangeCoalesced(true);
7602         // If the chunk is being coalesced and the current free range is
7603         // in the free lists, remove the current free range so that it
7604         // will be returned to the free lists in its entirety - all
7605         // the coalesced pieces included.
7606         if (freeRangeInFreeLists()) {
7607           FreeChunk* ffc = (FreeChunk*) freeFinger();
7608           assert(ffc->size() == pointer_delta(addr, freeFinger()),
7609             "Size of free range is inconsistent with chunk size.");
7610           if (CMSTestInFreeList) {
7611             assert(_sp->verify_chunk_in_free_list(ffc),
7612               "free range is not in free lists");
7613           }
7614           _sp->removeFreeChunkFromFreeLists(ffc);
7615           set_freeRangeInFreeLists(false);
7616         }
7617       }
7618     }
7619     // Note that if the chunk is not coalescable (the else arm
7620     // below), we unconditionally flush, without needing to do
7621     // a "lookahead," as we do below.
7622     if (inFreeRange()) lookahead_and_flush(fc, size);
7623   } else {
7624     // Code path common to both original and adaptive free lists.
7625 
7626     // cant coalesce with previous block; this should be treated
7627     // as the end of a free run if any
7628     if (inFreeRange()) {
7629       // we kicked some butt; time to pick up the garbage
7630       assert(freeFinger() < addr, "freeFinger points too high");
7631       flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7632     }
7633     // else, nothing to do, just continue
7634   }
7635 }
7636 
7637 size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) {
7638   // This is a chunk of garbage.  It is not in any free list.
7639   // Add it to a free list or let it possibly be coalesced into
7640   // a larger chunk.
7641   HeapWord* const addr = (HeapWord*) fc;
7642   const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7643 
7644   if (_sp->adaptive_freelists()) {
7645     // Verify that the bit map has no bits marked between
7646     // addr and purported end of just dead object.
7647     _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7648 
7649     do_post_free_or_garbage_chunk(fc, size);
7650   } else {
7651     if (!inFreeRange()) {
7652       // start of a new free range
7653       assert(size > 0, "A free range should have a size");
7654       initialize_free_range(addr, false);
7655     } else {
7656       // this will be swept up when we hit the end of the
7657       // free range
7658       if (CMSTraceSweeper) {
7659         gclog_or_tty->print("  -- pick up garbage " PTR_FORMAT " (" SIZE_FORMAT ")\n", p2i(fc), size);
7660       }
7661       // If the chunk is being coalesced and the current free range is
7662       // in the free lists, remove the current free range so that it
7663       // will be returned to the free lists in its entirety - all
7664       // the coalesced pieces included.
7665       if (freeRangeInFreeLists()) {
7666         FreeChunk* ffc = (FreeChunk*)freeFinger();
7667         assert(ffc->size() == pointer_delta(addr, freeFinger()),
7668           "Size of free range is inconsistent with chunk size.");
7669         if (CMSTestInFreeList) {
7670           assert(_sp->verify_chunk_in_free_list(ffc),
7671             "free range is not in free lists");
7672         }
7673         _sp->removeFreeChunkFromFreeLists(ffc);
7674         set_freeRangeInFreeLists(false);
7675       }
7676       set_lastFreeRangeCoalesced(true);
7677     }
7678     // this will be swept up when we hit the end of the free range
7679 
7680     // Verify that the bit map has no bits marked between
7681     // addr and purported end of just dead object.
7682     _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7683   }
7684   assert(_limit >= addr + size,
7685          "A freshly garbage chunk can't possibly straddle over _limit");
7686   if (inFreeRange()) lookahead_and_flush(fc, size);
7687   return size;
7688 }
7689 
7690 size_t SweepClosure::do_live_chunk(FreeChunk* fc) {
7691   HeapWord* addr = (HeapWord*) fc;
7692   // The sweeper has just found a live object. Return any accumulated
7693   // left hand chunk to the free lists.
7694   if (inFreeRange()) {
7695     assert(freeFinger() < addr, "freeFinger points too high");
7696     flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7697   }
7698 
7699   // This object is live: we'd normally expect this to be
7700   // an oop, and like to assert the following:
7701   // assert(oop(addr)->is_oop(), "live block should be an oop");
7702   // However, as we commented above, this may be an object whose
7703   // header hasn't yet been initialized.
7704   size_t size;
7705   assert(_bitMap->isMarked(addr), "Tautology for this control point");
7706   if (_bitMap->isMarked(addr + 1)) {
7707     // Determine the size from the bit map, rather than trying to
7708     // compute it from the object header.
7709     HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
7710     size = pointer_delta(nextOneAddr + 1, addr);
7711     assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
7712            "alignment problem");
7713 
7714 #ifdef ASSERT
7715       if (oop(addr)->klass_or_null() != NULL) {
7716         // Ignore mark word because we are running concurrent with mutators
7717         assert(oop(addr)->is_oop(true), "live block should be an oop");
7718         assert(size ==
7719                CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
7720                "P-mark and computed size do not agree");
7721       }
7722 #endif
7723 
7724   } else {
7725     // This should be an initialized object that's alive.
7726     assert(oop(addr)->klass_or_null() != NULL,
7727            "Should be an initialized object");
7728     // Ignore mark word because we are running concurrent with mutators
7729     assert(oop(addr)->is_oop(true), "live block should be an oop");
7730     // Verify that the bit map has no bits marked between
7731     // addr and purported end of this block.
7732     size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7733     assert(size >= 3, "Necessary for Printezis marks to work");
7734     assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
7735     DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
7736   }
7737   return size;
7738 }
7739 
7740 void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc,
7741                                                  size_t chunkSize) {
7742   // do_post_free_or_garbage_chunk() should only be called in the case
7743   // of the adaptive free list allocator.
7744   const bool fcInFreeLists = fc->is_free();
7745   assert(_sp->adaptive_freelists(), "Should only be used in this case.");
7746   assert((HeapWord*)fc <= _limit, "sweep invariant");
7747   if (CMSTestInFreeList && fcInFreeLists) {
7748     assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists");
7749   }
7750 
7751   if (CMSTraceSweeper) {
7752     gclog_or_tty->print_cr("  -- pick up another chunk at " PTR_FORMAT " (" SIZE_FORMAT ")", p2i(fc), chunkSize);
7753   }
7754 
7755   HeapWord* const fc_addr = (HeapWord*) fc;
7756 
7757   bool coalesce;
7758   const size_t left  = pointer_delta(fc_addr, freeFinger());
7759   const size_t right = chunkSize;
7760   switch (FLSCoalescePolicy) {
7761     // numeric value forms a coalition aggressiveness metric
7762     case 0:  { // never coalesce
7763       coalesce = false;
7764       break;
7765     }
7766     case 1: { // coalesce if left & right chunks on overpopulated lists
7767       coalesce = _sp->coalOverPopulated(left) &&
7768                  _sp->coalOverPopulated(right);
7769       break;
7770     }
7771     case 2: { // coalesce if left chunk on overpopulated list (default)
7772       coalesce = _sp->coalOverPopulated(left);
7773       break;
7774     }
7775     case 3: { // coalesce if left OR right chunk on overpopulated list
7776       coalesce = _sp->coalOverPopulated(left) ||
7777                  _sp->coalOverPopulated(right);
7778       break;
7779     }
7780     case 4: { // always coalesce
7781       coalesce = true;
7782       break;
7783     }
7784     default:
7785      ShouldNotReachHere();
7786   }
7787 
7788   // Should the current free range be coalesced?
7789   // If the chunk is in a free range and either we decided to coalesce above
7790   // or the chunk is near the large block at the end of the heap
7791   // (isNearLargestChunk() returns true), then coalesce this chunk.
7792   const bool doCoalesce = inFreeRange()
7793                           && (coalesce || _g->isNearLargestChunk(fc_addr));
7794   if (doCoalesce) {
7795     // Coalesce the current free range on the left with the new
7796     // chunk on the right.  If either is on a free list,
7797     // it must be removed from the list and stashed in the closure.
7798     if (freeRangeInFreeLists()) {
7799       FreeChunk* const ffc = (FreeChunk*)freeFinger();
7800       assert(ffc->size() == pointer_delta(fc_addr, freeFinger()),
7801         "Size of free range is inconsistent with chunk size.");
7802       if (CMSTestInFreeList) {
7803         assert(_sp->verify_chunk_in_free_list(ffc),
7804           "Chunk is not in free lists");
7805       }
7806       _sp->coalDeath(ffc->size());
7807       _sp->removeFreeChunkFromFreeLists(ffc);
7808       set_freeRangeInFreeLists(false);
7809     }
7810     if (fcInFreeLists) {
7811       _sp->coalDeath(chunkSize);
7812       assert(fc->size() == chunkSize,
7813         "The chunk has the wrong size or is not in the free lists");
7814       _sp->removeFreeChunkFromFreeLists(fc);
7815     }
7816     set_lastFreeRangeCoalesced(true);
7817     print_free_block_coalesced(fc);
7818   } else {  // not in a free range and/or should not coalesce
7819     // Return the current free range and start a new one.
7820     if (inFreeRange()) {
7821       // In a free range but cannot coalesce with the right hand chunk.
7822       // Put the current free range into the free lists.
7823       flush_cur_free_chunk(freeFinger(),
7824                            pointer_delta(fc_addr, freeFinger()));
7825     }
7826     // Set up for new free range.  Pass along whether the right hand
7827     // chunk is in the free lists.
7828     initialize_free_range((HeapWord*)fc, fcInFreeLists);
7829   }
7830 }
7831 
7832 // Lookahead flush:
7833 // If we are tracking a free range, and this is the last chunk that
7834 // we'll look at because its end crosses past _limit, we'll preemptively
7835 // flush it along with any free range we may be holding on to. Note that
7836 // this can be the case only for an already free or freshly garbage
7837 // chunk. If this block is an object, it can never straddle
7838 // over _limit. The "straddling" occurs when _limit is set at
7839 // the previous end of the space when this cycle started, and
7840 // a subsequent heap expansion caused the previously co-terminal
7841 // free block to be coalesced with the newly expanded portion,
7842 // thus rendering _limit a non-block-boundary making it dangerous
7843 // for the sweeper to step over and examine.
7844 void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) {
7845   assert(inFreeRange(), "Should only be called if currently in a free range.");
7846   HeapWord* const eob = ((HeapWord*)fc) + chunk_size;
7847   assert(_sp->used_region().contains(eob - 1),
7848          err_msg("eob = " PTR_FORMAT " eob-1 = " PTR_FORMAT " _limit = " PTR_FORMAT
7849                  " out of bounds wrt _sp = [" PTR_FORMAT "," PTR_FORMAT ")"
7850                  " when examining fc = " PTR_FORMAT "(" SIZE_FORMAT ")",
7851                  p2i(eob), p2i(eob-1), p2i(_limit), p2i(_sp->bottom()), p2i(_sp->end()), p2i(fc), chunk_size));
7852   if (eob >= _limit) {
7853     assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit");
7854     if (CMSTraceSweeper) {
7855       gclog_or_tty->print_cr("_limit " PTR_FORMAT " reached or crossed by block "
7856                              "[" PTR_FORMAT "," PTR_FORMAT ") in space "
7857                              "[" PTR_FORMAT "," PTR_FORMAT ")",
7858                              p2i(_limit), p2i(fc), p2i(eob), p2i(_sp->bottom()), p2i(_sp->end()));
7859     }
7860     // Return the storage we are tracking back into the free lists.
7861     if (CMSTraceSweeper) {
7862       gclog_or_tty->print_cr("Flushing ... ");
7863     }
7864     assert(freeFinger() < eob, "Error");
7865     flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger()));
7866   }
7867 }
7868 
7869 void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) {
7870   assert(inFreeRange(), "Should only be called if currently in a free range.");
7871   assert(size > 0,
7872     "A zero sized chunk cannot be added to the free lists.");
7873   if (!freeRangeInFreeLists()) {
7874     if (CMSTestInFreeList) {
7875       FreeChunk* fc = (FreeChunk*) chunk;
7876       fc->set_size(size);
7877       assert(!_sp->verify_chunk_in_free_list(fc),
7878         "chunk should not be in free lists yet");
7879     }
7880     if (CMSTraceSweeper) {
7881       gclog_or_tty->print_cr(" -- add free block " PTR_FORMAT " (" SIZE_FORMAT ") to free lists",
7882                     p2i(chunk), size);
7883     }
7884     // A new free range is going to be starting.  The current
7885     // free range has not been added to the free lists yet or
7886     // was removed so add it back.
7887     // If the current free range was coalesced, then the death
7888     // of the free range was recorded.  Record a birth now.
7889     if (lastFreeRangeCoalesced()) {
7890       _sp->coalBirth(size);
7891     }
7892     _sp->addChunkAndRepairOffsetTable(chunk, size,
7893             lastFreeRangeCoalesced());
7894   } else if (CMSTraceSweeper) {
7895     gclog_or_tty->print_cr("Already in free list: nothing to flush");
7896   }
7897   set_inFreeRange(false);
7898   set_freeRangeInFreeLists(false);
7899 }
7900 
7901 // We take a break if we've been at this for a while,
7902 // so as to avoid monopolizing the locks involved.
7903 void SweepClosure::do_yield_work(HeapWord* addr) {
7904   // Return current free chunk being used for coalescing (if any)
7905   // to the appropriate freelist.  After yielding, the next
7906   // free block encountered will start a coalescing range of
7907   // free blocks.  If the next free block is adjacent to the
7908   // chunk just flushed, they will need to wait for the next
7909   // sweep to be coalesced.
7910   if (inFreeRange()) {
7911     flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7912   }
7913 
7914   // First give up the locks, then yield, then re-lock.
7915   // We should probably use a constructor/destructor idiom to
7916   // do this unlock/lock or modify the MutexUnlocker class to
7917   // serve our purpose. XXX
7918   assert_lock_strong(_bitMap->lock());
7919   assert_lock_strong(_freelistLock);
7920   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7921          "CMS thread should hold CMS token");
7922   _bitMap->lock()->unlock();
7923   _freelistLock->unlock();
7924   ConcurrentMarkSweepThread::desynchronize(true);
7925   _collector->stopTimer();
7926   if (PrintCMSStatistics != 0) {
7927     _collector->incrementYields();
7928   }
7929 
7930   // See the comment in coordinator_yield()
7931   for (unsigned i = 0; i < CMSYieldSleepCount &&
7932                        ConcurrentMarkSweepThread::should_yield() &&
7933                        !CMSCollector::foregroundGCIsActive(); ++i) {
7934     os::sleep(Thread::current(), 1, false);
7935   }
7936 
7937   ConcurrentMarkSweepThread::synchronize(true);
7938   _freelistLock->lock();
7939   _bitMap->lock()->lock_without_safepoint_check();
7940   _collector->startTimer();
7941 }
7942 
7943 #ifndef PRODUCT
7944 // This is actually very useful in a product build if it can
7945 // be called from the debugger.  Compile it into the product
7946 // as needed.
7947 bool debug_verify_chunk_in_free_list(FreeChunk* fc) {
7948   return debug_cms_space->verify_chunk_in_free_list(fc);
7949 }
7950 #endif
7951 
7952 void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const {
7953   if (CMSTraceSweeper) {
7954     gclog_or_tty->print_cr("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")",
7955                            p2i(fc), fc->size());
7956   }
7957 }
7958 
7959 // CMSIsAliveClosure
7960 bool CMSIsAliveClosure::do_object_b(oop obj) {
7961   HeapWord* addr = (HeapWord*)obj;
7962   return addr != NULL &&
7963          (!_span.contains(addr) || _bit_map->isMarked(addr));
7964 }
7965 
7966 
7967 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector,
7968                       MemRegion span,
7969                       CMSBitMap* bit_map, CMSMarkStack* mark_stack,
7970                       bool cpc):
7971   _collector(collector),
7972   _span(span),
7973   _bit_map(bit_map),
7974   _mark_stack(mark_stack),
7975   _concurrent_precleaning(cpc) {
7976   assert(!_span.is_empty(), "Empty span could spell trouble");
7977 }
7978 
7979 
7980 // CMSKeepAliveClosure: the serial version
7981 void CMSKeepAliveClosure::do_oop(oop obj) {
7982   HeapWord* addr = (HeapWord*)obj;
7983   if (_span.contains(addr) &&
7984       !_bit_map->isMarked(addr)) {
7985     _bit_map->mark(addr);
7986     bool simulate_overflow = false;
7987     NOT_PRODUCT(
7988       if (CMSMarkStackOverflowALot &&
7989           _collector->simulate_overflow()) {
7990         // simulate a stack overflow
7991         simulate_overflow = true;
7992       }
7993     )
7994     if (simulate_overflow || !_mark_stack->push(obj)) {
7995       if (_concurrent_precleaning) {
7996         // We dirty the overflown object and let the remark
7997         // phase deal with it.
7998         assert(_collector->overflow_list_is_empty(), "Error");
7999         // In the case of object arrays, we need to dirty all of
8000         // the cards that the object spans. No locking or atomics
8001         // are needed since no one else can be mutating the mod union
8002         // table.
8003         if (obj->is_objArray()) {
8004           size_t sz = obj->size();
8005           HeapWord* end_card_addr =
8006             (HeapWord*)round_to((intptr_t)(addr+sz), CardTableModRefBS::card_size);
8007           MemRegion redirty_range = MemRegion(addr, end_card_addr);
8008           assert(!redirty_range.is_empty(), "Arithmetical tautology");
8009           _collector->_modUnionTable.mark_range(redirty_range);
8010         } else {
8011           _collector->_modUnionTable.mark(addr);
8012         }
8013         _collector->_ser_kac_preclean_ovflw++;
8014       } else {
8015         _collector->push_on_overflow_list(obj);
8016         _collector->_ser_kac_ovflw++;
8017       }
8018     }
8019   }
8020 }
8021 
8022 void CMSKeepAliveClosure::do_oop(oop* p)       { CMSKeepAliveClosure::do_oop_work(p); }
8023 void CMSKeepAliveClosure::do_oop(narrowOop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8024 
8025 // CMSParKeepAliveClosure: a parallel version of the above.
8026 // The work queues are private to each closure (thread),
8027 // but (may be) available for stealing by other threads.
8028 void CMSParKeepAliveClosure::do_oop(oop obj) {
8029   HeapWord* addr = (HeapWord*)obj;
8030   if (_span.contains(addr) &&
8031       !_bit_map->isMarked(addr)) {
8032     // In general, during recursive tracing, several threads
8033     // may be concurrently getting here; the first one to
8034     // "tag" it, claims it.
8035     if (_bit_map->par_mark(addr)) {
8036       bool res = _work_queue->push(obj);
8037       assert(res, "Low water mark should be much less than capacity");
8038       // Do a recursive trim in the hope that this will keep
8039       // stack usage lower, but leave some oops for potential stealers
8040       trim_queue(_low_water_mark);
8041     } // Else, another thread got there first
8042   }
8043 }
8044 
8045 void CMSParKeepAliveClosure::do_oop(oop* p)       { CMSParKeepAliveClosure::do_oop_work(p); }
8046 void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8047 
8048 void CMSParKeepAliveClosure::trim_queue(uint max) {
8049   while (_work_queue->size() > max) {
8050     oop new_oop;
8051     if (_work_queue->pop_local(new_oop)) {
8052       assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
8053       assert(_bit_map->isMarked((HeapWord*)new_oop),
8054              "no white objects on this stack!");
8055       assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8056       // iterate over the oops in this oop, marking and pushing
8057       // the ones in CMS heap (i.e. in _span).
8058       new_oop->oop_iterate(&_mark_and_push);
8059     }
8060   }
8061 }
8062 
8063 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
8064                                 CMSCollector* collector,
8065                                 MemRegion span, CMSBitMap* bit_map,
8066                                 OopTaskQueue* work_queue):
8067   _collector(collector),
8068   _span(span),
8069   _bit_map(bit_map),
8070   _work_queue(work_queue) { }
8071 
8072 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
8073   HeapWord* addr = (HeapWord*)obj;
8074   if (_span.contains(addr) &&
8075       !_bit_map->isMarked(addr)) {
8076     if (_bit_map->par_mark(addr)) {
8077       bool simulate_overflow = false;
8078       NOT_PRODUCT(
8079         if (CMSMarkStackOverflowALot &&
8080             _collector->par_simulate_overflow()) {
8081           // simulate a stack overflow
8082           simulate_overflow = true;
8083         }
8084       )
8085       if (simulate_overflow || !_work_queue->push(obj)) {
8086         _collector->par_push_on_overflow_list(obj);
8087         _collector->_par_kac_ovflw++;
8088       }
8089     } // Else another thread got there already
8090   }
8091 }
8092 
8093 void CMSInnerParMarkAndPushClosure::do_oop(oop* p)       { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8094 void CMSInnerParMarkAndPushClosure::do_oop(narrowOop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8095 
8096 //////////////////////////////////////////////////////////////////
8097 //  CMSExpansionCause                /////////////////////////////
8098 //////////////////////////////////////////////////////////////////
8099 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
8100   switch (cause) {
8101     case _no_expansion:
8102       return "No expansion";
8103     case _satisfy_free_ratio:
8104       return "Free ratio";
8105     case _satisfy_promotion:
8106       return "Satisfy promotion";
8107     case _satisfy_allocation:
8108       return "allocation";
8109     case _allocate_par_lab:
8110       return "Par LAB";
8111     case _allocate_par_spooling_space:
8112       return "Par Spooling Space";
8113     case _adaptive_size_policy:
8114       return "Ergonomics";
8115     default:
8116       return "unknown";
8117   }
8118 }
8119 
8120 void CMSDrainMarkingStackClosure::do_void() {
8121   // the max number to take from overflow list at a time
8122   const size_t num = _mark_stack->capacity()/4;
8123   assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
8124          "Overflow list should be NULL during concurrent phases");
8125   while (!_mark_stack->isEmpty() ||
8126          // if stack is empty, check the overflow list
8127          _collector->take_from_overflow_list(num, _mark_stack)) {
8128     oop obj = _mark_stack->pop();
8129     HeapWord* addr = (HeapWord*)obj;
8130     assert(_span.contains(addr), "Should be within span");
8131     assert(_bit_map->isMarked(addr), "Should be marked");
8132     assert(obj->is_oop(), "Should be an oop");
8133     obj->oop_iterate(_keep_alive);
8134   }
8135 }
8136 
8137 void CMSParDrainMarkingStackClosure::do_void() {
8138   // drain queue
8139   trim_queue(0);
8140 }
8141 
8142 // Trim our work_queue so its length is below max at return
8143 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
8144   while (_work_queue->size() > max) {
8145     oop new_oop;
8146     if (_work_queue->pop_local(new_oop)) {
8147       assert(new_oop->is_oop(), "Expected an oop");
8148       assert(_bit_map->isMarked((HeapWord*)new_oop),
8149              "no white objects on this stack!");
8150       assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8151       // iterate over the oops in this oop, marking and pushing
8152       // the ones in CMS heap (i.e. in _span).
8153       new_oop->oop_iterate(&_mark_and_push);
8154     }
8155   }
8156 }
8157 
8158 ////////////////////////////////////////////////////////////////////
8159 // Support for Marking Stack Overflow list handling and related code
8160 ////////////////////////////////////////////////////////////////////
8161 // Much of the following code is similar in shape and spirit to the
8162 // code used in ParNewGC. We should try and share that code
8163 // as much as possible in the future.
8164 
8165 #ifndef PRODUCT
8166 // Debugging support for CMSStackOverflowALot
8167 
8168 // It's OK to call this multi-threaded;  the worst thing
8169 // that can happen is that we'll get a bunch of closely
8170 // spaced simulated overflows, but that's OK, in fact
8171 // probably good as it would exercise the overflow code
8172 // under contention.
8173 bool CMSCollector::simulate_overflow() {
8174   if (_overflow_counter-- <= 0) { // just being defensive
8175     _overflow_counter = CMSMarkStackOverflowInterval;
8176     return true;
8177   } else {
8178     return false;
8179   }
8180 }
8181 
8182 bool CMSCollector::par_simulate_overflow() {
8183   return simulate_overflow();
8184 }
8185 #endif
8186 
8187 // Single-threaded
8188 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
8189   assert(stack->isEmpty(), "Expected precondition");
8190   assert(stack->capacity() > num, "Shouldn't bite more than can chew");
8191   size_t i = num;
8192   oop  cur = _overflow_list;
8193   const markOop proto = markOopDesc::prototype();
8194   NOT_PRODUCT(ssize_t n = 0;)
8195   for (oop next; i > 0 && cur != NULL; cur = next, i--) {
8196     next = oop(cur->mark());
8197     cur->set_mark(proto);   // until proven otherwise
8198     assert(cur->is_oop(), "Should be an oop");
8199     bool res = stack->push(cur);
8200     assert(res, "Bit off more than can chew?");
8201     NOT_PRODUCT(n++;)
8202   }
8203   _overflow_list = cur;
8204 #ifndef PRODUCT
8205   assert(_num_par_pushes >= n, "Too many pops?");
8206   _num_par_pushes -=n;
8207 #endif
8208   return !stack->isEmpty();
8209 }
8210 
8211 #define BUSY  (cast_to_oop<intptr_t>(0x1aff1aff))
8212 // (MT-safe) Get a prefix of at most "num" from the list.
8213 // The overflow list is chained through the mark word of
8214 // each object in the list. We fetch the entire list,
8215 // break off a prefix of the right size and return the
8216 // remainder. If other threads try to take objects from
8217 // the overflow list at that time, they will wait for
8218 // some time to see if data becomes available. If (and
8219 // only if) another thread places one or more object(s)
8220 // on the global list before we have returned the suffix
8221 // to the global list, we will walk down our local list
8222 // to find its end and append the global list to
8223 // our suffix before returning it. This suffix walk can
8224 // prove to be expensive (quadratic in the amount of traffic)
8225 // when there are many objects in the overflow list and
8226 // there is much producer-consumer contention on the list.
8227 // *NOTE*: The overflow list manipulation code here and
8228 // in ParNewGeneration:: are very similar in shape,
8229 // except that in the ParNew case we use the old (from/eden)
8230 // copy of the object to thread the list via its klass word.
8231 // Because of the common code, if you make any changes in
8232 // the code below, please check the ParNew version to see if
8233 // similar changes might be needed.
8234 // CR 6797058 has been filed to consolidate the common code.
8235 bool CMSCollector::par_take_from_overflow_list(size_t num,
8236                                                OopTaskQueue* work_q,
8237                                                int no_of_gc_threads) {
8238   assert(work_q->size() == 0, "First empty local work queue");
8239   assert(num < work_q->max_elems(), "Can't bite more than we can chew");
8240   if (_overflow_list == NULL) {
8241     return false;
8242   }
8243   // Grab the entire list; we'll put back a suffix
8244   oop prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
8245   Thread* tid = Thread::current();
8246   // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was
8247   // set to ParallelGCThreads.
8248   size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads;
8249   size_t sleep_time_millis = MAX2((size_t)1, num/100);
8250   // If the list is busy, we spin for a short while,
8251   // sleeping between attempts to get the list.
8252   for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) {
8253     os::sleep(tid, sleep_time_millis, false);
8254     if (_overflow_list == NULL) {
8255       // Nothing left to take
8256       return false;
8257     } else if (_overflow_list != BUSY) {
8258       // Try and grab the prefix
8259       prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
8260     }
8261   }
8262   // If the list was found to be empty, or we spun long
8263   // enough, we give up and return empty-handed. If we leave
8264   // the list in the BUSY state below, it must be the case that
8265   // some other thread holds the overflow list and will set it
8266   // to a non-BUSY state in the future.
8267   if (prefix == NULL || prefix == BUSY) {
8268      // Nothing to take or waited long enough
8269      if (prefix == NULL) {
8270        // Write back the NULL in case we overwrote it with BUSY above
8271        // and it is still the same value.
8272        (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8273      }
8274      return false;
8275   }
8276   assert(prefix != NULL && prefix != BUSY, "Error");
8277   size_t i = num;
8278   oop cur = prefix;
8279   // Walk down the first "num" objects, unless we reach the end.
8280   for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--);
8281   if (cur->mark() == NULL) {
8282     // We have "num" or fewer elements in the list, so there
8283     // is nothing to return to the global list.
8284     // Write back the NULL in lieu of the BUSY we wrote
8285     // above, if it is still the same value.
8286     if (_overflow_list == BUSY) {
8287       (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8288     }
8289   } else {
8290     // Chop off the suffix and return it to the global list.
8291     assert(cur->mark() != BUSY, "Error");
8292     oop suffix_head = cur->mark(); // suffix will be put back on global list
8293     cur->set_mark(NULL);           // break off suffix
8294     // It's possible that the list is still in the empty(busy) state
8295     // we left it in a short while ago; in that case we may be
8296     // able to place back the suffix without incurring the cost
8297     // of a walk down the list.
8298     oop observed_overflow_list = _overflow_list;
8299     oop cur_overflow_list = observed_overflow_list;
8300     bool attached = false;
8301     while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
8302       observed_overflow_list =
8303         (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
8304       if (cur_overflow_list == observed_overflow_list) {
8305         attached = true;
8306         break;
8307       } else cur_overflow_list = observed_overflow_list;
8308     }
8309     if (!attached) {
8310       // Too bad, someone else sneaked in (at least) an element; we'll need
8311       // to do a splice. Find tail of suffix so we can prepend suffix to global
8312       // list.
8313       for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark()));
8314       oop suffix_tail = cur;
8315       assert(suffix_tail != NULL && suffix_tail->mark() == NULL,
8316              "Tautology");
8317       observed_overflow_list = _overflow_list;
8318       do {
8319         cur_overflow_list = observed_overflow_list;
8320         if (cur_overflow_list != BUSY) {
8321           // Do the splice ...
8322           suffix_tail->set_mark(markOop(cur_overflow_list));
8323         } else { // cur_overflow_list == BUSY
8324           suffix_tail->set_mark(NULL);
8325         }
8326         // ... and try to place spliced list back on overflow_list ...
8327         observed_overflow_list =
8328           (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
8329       } while (cur_overflow_list != observed_overflow_list);
8330       // ... until we have succeeded in doing so.
8331     }
8332   }
8333 
8334   // Push the prefix elements on work_q
8335   assert(prefix != NULL, "control point invariant");
8336   const markOop proto = markOopDesc::prototype();
8337   oop next;
8338   NOT_PRODUCT(ssize_t n = 0;)
8339   for (cur = prefix; cur != NULL; cur = next) {
8340     next = oop(cur->mark());
8341     cur->set_mark(proto);   // until proven otherwise
8342     assert(cur->is_oop(), "Should be an oop");
8343     bool res = work_q->push(cur);
8344     assert(res, "Bit off more than we can chew?");
8345     NOT_PRODUCT(n++;)
8346   }
8347 #ifndef PRODUCT
8348   assert(_num_par_pushes >= n, "Too many pops?");
8349   Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
8350 #endif
8351   return true;
8352 }
8353 
8354 // Single-threaded
8355 void CMSCollector::push_on_overflow_list(oop p) {
8356   NOT_PRODUCT(_num_par_pushes++;)
8357   assert(p->is_oop(), "Not an oop");
8358   preserve_mark_if_necessary(p);
8359   p->set_mark((markOop)_overflow_list);
8360   _overflow_list = p;
8361 }
8362 
8363 // Multi-threaded; use CAS to prepend to overflow list
8364 void CMSCollector::par_push_on_overflow_list(oop p) {
8365   NOT_PRODUCT(Atomic::inc_ptr(&_num_par_pushes);)
8366   assert(p->is_oop(), "Not an oop");
8367   par_preserve_mark_if_necessary(p);
8368   oop observed_overflow_list = _overflow_list;
8369   oop cur_overflow_list;
8370   do {
8371     cur_overflow_list = observed_overflow_list;
8372     if (cur_overflow_list != BUSY) {
8373       p->set_mark(markOop(cur_overflow_list));
8374     } else {
8375       p->set_mark(NULL);
8376     }
8377     observed_overflow_list =
8378       (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list);
8379   } while (cur_overflow_list != observed_overflow_list);
8380 }
8381 #undef BUSY
8382 
8383 // Single threaded
8384 // General Note on GrowableArray: pushes may silently fail
8385 // because we are (temporarily) out of C-heap for expanding
8386 // the stack. The problem is quite ubiquitous and affects
8387 // a lot of code in the JVM. The prudent thing for GrowableArray
8388 // to do (for now) is to exit with an error. However, that may
8389 // be too draconian in some cases because the caller may be
8390 // able to recover without much harm. For such cases, we
8391 // should probably introduce a "soft_push" method which returns
8392 // an indication of success or failure with the assumption that
8393 // the caller may be able to recover from a failure; code in
8394 // the VM can then be changed, incrementally, to deal with such
8395 // failures where possible, thus, incrementally hardening the VM
8396 // in such low resource situations.
8397 void CMSCollector::preserve_mark_work(oop p, markOop m) {
8398   _preserved_oop_stack.push(p);
8399   _preserved_mark_stack.push(m);
8400   assert(m == p->mark(), "Mark word changed");
8401   assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8402          "bijection");
8403 }
8404 
8405 // Single threaded
8406 void CMSCollector::preserve_mark_if_necessary(oop p) {
8407   markOop m = p->mark();
8408   if (m->must_be_preserved(p)) {
8409     preserve_mark_work(p, m);
8410   }
8411 }
8412 
8413 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
8414   markOop m = p->mark();
8415   if (m->must_be_preserved(p)) {
8416     MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
8417     // Even though we read the mark word without holding
8418     // the lock, we are assured that it will not change
8419     // because we "own" this oop, so no other thread can
8420     // be trying to push it on the overflow list; see
8421     // the assertion in preserve_mark_work() that checks
8422     // that m == p->mark().
8423     preserve_mark_work(p, m);
8424   }
8425 }
8426 
8427 // We should be able to do this multi-threaded,
8428 // a chunk of stack being a task (this is
8429 // correct because each oop only ever appears
8430 // once in the overflow list. However, it's
8431 // not very easy to completely overlap this with
8432 // other operations, so will generally not be done
8433 // until all work's been completed. Because we
8434 // expect the preserved oop stack (set) to be small,
8435 // it's probably fine to do this single-threaded.
8436 // We can explore cleverer concurrent/overlapped/parallel
8437 // processing of preserved marks if we feel the
8438 // need for this in the future. Stack overflow should
8439 // be so rare in practice and, when it happens, its
8440 // effect on performance so great that this will
8441 // likely just be in the noise anyway.
8442 void CMSCollector::restore_preserved_marks_if_any() {
8443   assert(SafepointSynchronize::is_at_safepoint(),
8444          "world should be stopped");
8445   assert(Thread::current()->is_ConcurrentGC_thread() ||
8446          Thread::current()->is_VM_thread(),
8447          "should be single-threaded");
8448   assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8449          "bijection");
8450 
8451   while (!_preserved_oop_stack.is_empty()) {
8452     oop p = _preserved_oop_stack.pop();
8453     assert(p->is_oop(), "Should be an oop");
8454     assert(_span.contains(p), "oop should be in _span");
8455     assert(p->mark() == markOopDesc::prototype(),
8456            "Set when taken from overflow list");
8457     markOop m = _preserved_mark_stack.pop();
8458     p->set_mark(m);
8459   }
8460   assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(),
8461          "stacks were cleared above");
8462 }
8463 
8464 #ifndef PRODUCT
8465 bool CMSCollector::no_preserved_marks() const {
8466   return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty();
8467 }
8468 #endif
8469 
8470 // Transfer some number of overflown objects to usual marking
8471 // stack. Return true if some objects were transferred.
8472 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
8473   size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,
8474                     (size_t)ParGCDesiredObjsFromOverflowList);
8475 
8476   bool res = _collector->take_from_overflow_list(num, _mark_stack);
8477   assert(_collector->overflow_list_is_empty() || res,
8478          "If list is not empty, we should have taken something");
8479   assert(!res || !_mark_stack->isEmpty(),
8480          "If we took something, it should now be on our stack");
8481   return res;
8482 }
8483 
8484 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
8485   size_t res = _sp->block_size_no_stall(addr, _collector);
8486   if (_sp->block_is_obj(addr)) {
8487     if (_live_bit_map->isMarked(addr)) {
8488       // It can't have been dead in a previous cycle
8489       guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
8490     } else {
8491       _dead_bit_map->mark(addr);      // mark the dead object
8492     }
8493   }
8494   // Could be 0, if the block size could not be computed without stalling.
8495   return res;
8496 }
8497 
8498 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() {
8499 
8500   switch (phase) {
8501     case CMSCollector::InitialMarking:
8502       initialize(true  /* fullGC */ ,
8503                  cause /* cause of the GC */,
8504                  true  /* recordGCBeginTime */,
8505                  true  /* recordPreGCUsage */,
8506                  false /* recordPeakUsage */,
8507                  false /* recordPostGCusage */,
8508                  true  /* recordAccumulatedGCTime */,
8509                  false /* recordGCEndTime */,
8510                  false /* countCollection */  );
8511       break;
8512 
8513     case CMSCollector::FinalMarking:
8514       initialize(true  /* fullGC */ ,
8515                  cause /* cause of the GC */,
8516                  false /* recordGCBeginTime */,
8517                  false /* recordPreGCUsage */,
8518                  false /* recordPeakUsage */,
8519                  false /* recordPostGCusage */,
8520                  true  /* recordAccumulatedGCTime */,
8521                  false /* recordGCEndTime */,
8522                  false /* countCollection */  );
8523       break;
8524 
8525     case CMSCollector::Sweeping:
8526       initialize(true  /* fullGC */ ,
8527                  cause /* cause of the GC */,
8528                  false /* recordGCBeginTime */,
8529                  false /* recordPreGCUsage */,
8530                  true  /* recordPeakUsage */,
8531                  true  /* recordPostGCusage */,
8532                  false /* recordAccumulatedGCTime */,
8533                  true  /* recordGCEndTime */,
8534                  true  /* countCollection */  );
8535       break;
8536 
8537     default:
8538       ShouldNotReachHere();
8539   }
8540 }