1 /*
   2  * Copyright (c) 2001, 2015, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
  21  * questions.
  22  *
  23  */
  24 
  25 #include "precompiled.hpp"
  26 #include "classfile/classLoaderData.hpp"
  27 #include "classfile/stringTable.hpp"
  28 #include "classfile/systemDictionary.hpp"
  29 #include "code/codeCache.hpp"
  30 #include "gc/cms/cmsCollectorPolicy.hpp"
  31 #include "gc/cms/cmsOopClosures.inline.hpp"
  32 #include "gc/cms/compactibleFreeListSpace.hpp"
  33 #include "gc/cms/concurrentMarkSweepGeneration.inline.hpp"
  34 #include "gc/cms/concurrentMarkSweepThread.hpp"
  35 #include "gc/cms/parNewGeneration.hpp"
  36 #include "gc/cms/vmCMSOperations.hpp"
  37 #include "gc/serial/genMarkSweep.hpp"
  38 #include "gc/serial/tenuredGeneration.hpp"
  39 #include "gc/shared/adaptiveSizePolicy.hpp"
  40 #include "gc/shared/cardGeneration.inline.hpp"
  41 #include "gc/shared/cardTableRS.hpp"
  42 #include "gc/shared/collectedHeap.inline.hpp"
  43 #include "gc/shared/collectorCounters.hpp"
  44 #include "gc/shared/collectorPolicy.hpp"
  45 #include "gc/shared/gcLocker.inline.hpp"
  46 #include "gc/shared/gcTimer.hpp"
  47 #include "gc/shared/gcTrace.hpp"
  48 #include "gc/shared/gcTraceTime.hpp"
  49 #include "gc/shared/genCollectedHeap.hpp"
  50 #include "gc/shared/genOopClosures.inline.hpp"
  51 #include "gc/shared/isGCActiveMark.hpp"
  52 #include "gc/shared/referencePolicy.hpp"
  53 #include "gc/shared/strongRootsScope.hpp"
  54 #include "gc/shared/taskqueue.inline.hpp"
  55 #include "memory/allocation.hpp"
  56 #include "memory/iterator.inline.hpp"
  57 #include "memory/padded.hpp"
  58 #include "memory/resourceArea.hpp"
  59 #include "oops/oop.inline.hpp"
  60 #include "prims/jvmtiExport.hpp"
  61 #include "runtime/atomic.inline.hpp"
  62 #include "runtime/globals_extension.hpp"
  63 #include "runtime/handles.inline.hpp"
  64 #include "runtime/java.hpp"
  65 #include "runtime/orderAccess.inline.hpp"
  66 #include "runtime/vmThread.hpp"
  67 #include "services/memoryService.hpp"
  68 #include "services/runtimeService.hpp"
  69 #include "utilities/stack.inline.hpp"
  70 
  71 // statics
  72 CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL;
  73 bool CMSCollector::_full_gc_requested = false;
  74 GCCause::Cause CMSCollector::_full_gc_cause = GCCause::_no_gc;
  75 
  76 //////////////////////////////////////////////////////////////////
  77 // In support of CMS/VM thread synchronization
  78 //////////////////////////////////////////////////////////////////
  79 // We split use of the CGC_lock into 2 "levels".
  80 // The low-level locking is of the usual CGC_lock monitor. We introduce
  81 // a higher level "token" (hereafter "CMS token") built on top of the
  82 // low level monitor (hereafter "CGC lock").
  83 // The token-passing protocol gives priority to the VM thread. The
  84 // CMS-lock doesn't provide any fairness guarantees, but clients
  85 // should ensure that it is only held for very short, bounded
  86 // durations.
  87 //
  88 // When either of the CMS thread or the VM thread is involved in
  89 // collection operations during which it does not want the other
  90 // thread to interfere, it obtains the CMS token.
  91 //
  92 // If either thread tries to get the token while the other has
  93 // it, that thread waits. However, if the VM thread and CMS thread
  94 // both want the token, then the VM thread gets priority while the
  95 // CMS thread waits. This ensures, for instance, that the "concurrent"
  96 // phases of the CMS thread's work do not block out the VM thread
  97 // for long periods of time as the CMS thread continues to hog
  98 // the token. (See bug 4616232).
  99 //
 100 // The baton-passing functions are, however, controlled by the
 101 // flags _foregroundGCShouldWait and _foregroundGCIsActive,
 102 // and here the low-level CMS lock, not the high level token,
 103 // ensures mutual exclusion.
 104 //
 105 // Two important conditions that we have to satisfy:
 106 // 1. if a thread does a low-level wait on the CMS lock, then it
 107 //    relinquishes the CMS token if it were holding that token
 108 //    when it acquired the low-level CMS lock.
 109 // 2. any low-level notifications on the low-level lock
 110 //    should only be sent when a thread has relinquished the token.
 111 //
 112 // In the absence of either property, we'd have potential deadlock.
 113 //
 114 // We protect each of the CMS (concurrent and sequential) phases
 115 // with the CMS _token_, not the CMS _lock_.
 116 //
 117 // The only code protected by CMS lock is the token acquisition code
 118 // itself, see ConcurrentMarkSweepThread::[de]synchronize(), and the
 119 // baton-passing code.
 120 //
 121 // Unfortunately, i couldn't come up with a good abstraction to factor and
 122 // hide the naked CGC_lock manipulation in the baton-passing code
 123 // further below. That's something we should try to do. Also, the proof
 124 // of correctness of this 2-level locking scheme is far from obvious,
 125 // and potentially quite slippery. We have an uneasy suspicion, for instance,
 126 // that there may be a theoretical possibility of delay/starvation in the
 127 // low-level lock/wait/notify scheme used for the baton-passing because of
 128 // potential interference with the priority scheme embodied in the
 129 // CMS-token-passing protocol. See related comments at a CGC_lock->wait()
 130 // invocation further below and marked with "XXX 20011219YSR".
 131 // Indeed, as we note elsewhere, this may become yet more slippery
 132 // in the presence of multiple CMS and/or multiple VM threads. XXX
 133 
 134 class CMSTokenSync: public StackObj {
 135  private:
 136   bool _is_cms_thread;
 137  public:
 138   CMSTokenSync(bool is_cms_thread):
 139     _is_cms_thread(is_cms_thread) {
 140     assert(is_cms_thread == Thread::current()->is_ConcurrentGC_thread(),
 141            "Incorrect argument to constructor");
 142     ConcurrentMarkSweepThread::synchronize(_is_cms_thread);
 143   }
 144 
 145   ~CMSTokenSync() {
 146     assert(_is_cms_thread ?
 147              ConcurrentMarkSweepThread::cms_thread_has_cms_token() :
 148              ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
 149           "Incorrect state");
 150     ConcurrentMarkSweepThread::desynchronize(_is_cms_thread);
 151   }
 152 };
 153 
 154 // Convenience class that does a CMSTokenSync, and then acquires
 155 // upto three locks.
 156 class CMSTokenSyncWithLocks: public CMSTokenSync {
 157  private:
 158   // Note: locks are acquired in textual declaration order
 159   // and released in the opposite order
 160   MutexLockerEx _locker1, _locker2, _locker3;
 161  public:
 162   CMSTokenSyncWithLocks(bool is_cms_thread, Mutex* mutex1,
 163                         Mutex* mutex2 = NULL, Mutex* mutex3 = NULL):
 164     CMSTokenSync(is_cms_thread),
 165     _locker1(mutex1, Mutex::_no_safepoint_check_flag),
 166     _locker2(mutex2, Mutex::_no_safepoint_check_flag),
 167     _locker3(mutex3, Mutex::_no_safepoint_check_flag)
 168   { }
 169 };
 170 
 171 
 172 //////////////////////////////////////////////////////////////////
 173 //  Concurrent Mark-Sweep Generation /////////////////////////////
 174 //////////////////////////////////////////////////////////////////
 175 
 176 NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;)
 177 
 178 // This struct contains per-thread things necessary to support parallel
 179 // young-gen collection.
 180 class CMSParGCThreadState: public CHeapObj<mtGC> {
 181  public:
 182   CFLS_LAB lab;
 183   PromotionInfo promo;
 184 
 185   // Constructor.
 186   CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) {
 187     promo.setSpace(cfls);
 188   }
 189 };
 190 
 191 ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration(
 192      ReservedSpace rs, size_t initial_byte_size, int level,
 193      CardTableRS* ct, bool use_adaptive_freelists,
 194      FreeBlockDictionary<FreeChunk>::DictionaryChoice dictionaryChoice) :
 195   CardGeneration(rs, initial_byte_size, level, ct),
 196   _dilatation_factor(((double)MinChunkSize)/((double)(CollectedHeap::min_fill_size()))),
 197   _did_compact(false)
 198 {
 199   HeapWord* bottom = (HeapWord*) _virtual_space.low();
 200   HeapWord* end    = (HeapWord*) _virtual_space.high();
 201 
 202   _direct_allocated_words = 0;
 203   NOT_PRODUCT(
 204     _numObjectsPromoted = 0;
 205     _numWordsPromoted = 0;
 206     _numObjectsAllocated = 0;
 207     _numWordsAllocated = 0;
 208   )
 209 
 210   _cmsSpace = new CompactibleFreeListSpace(_bts, MemRegion(bottom, end),
 211                                            use_adaptive_freelists,
 212                                            dictionaryChoice);
 213   NOT_PRODUCT(debug_cms_space = _cmsSpace;)
 214   _cmsSpace->_gen = this;
 215 
 216   _gc_stats = new CMSGCStats();
 217 
 218   // Verify the assumption that FreeChunk::_prev and OopDesc::_klass
 219   // offsets match. The ability to tell free chunks from objects
 220   // depends on this property.
 221   debug_only(
 222     FreeChunk* junk = NULL;
 223     assert(UseCompressedClassPointers ||
 224            junk->prev_addr() == (void*)(oop(junk)->klass_addr()),
 225            "Offset of FreeChunk::_prev within FreeChunk must match"
 226            "  that of OopDesc::_klass within OopDesc");
 227   )
 228 
 229   _par_gc_thread_states = NEW_C_HEAP_ARRAY(CMSParGCThreadState*, ParallelGCThreads, mtGC);
 230   for (uint i = 0; i < ParallelGCThreads; i++) {
 231     _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace());
 232   }
 233 
 234   _incremental_collection_failed = false;
 235   // The "dilatation_factor" is the expansion that can occur on
 236   // account of the fact that the minimum object size in the CMS
 237   // generation may be larger than that in, say, a contiguous young
 238   //  generation.
 239   // Ideally, in the calculation below, we'd compute the dilatation
 240   // factor as: MinChunkSize/(promoting_gen's min object size)
 241   // Since we do not have such a general query interface for the
 242   // promoting generation, we'll instead just use the minimum
 243   // object size (which today is a header's worth of space);
 244   // note that all arithmetic is in units of HeapWords.
 245   assert(MinChunkSize >= CollectedHeap::min_fill_size(), "just checking");
 246   assert(_dilatation_factor >= 1.0, "from previous assert");
 247 }
 248 
 249 
 250 // The field "_initiating_occupancy" represents the occupancy percentage
 251 // at which we trigger a new collection cycle.  Unless explicitly specified
 252 // via CMSInitiatingOccupancyFraction (argument "io" below), it
 253 // is calculated by:
 254 //
 255 //   Let "f" be MinHeapFreeRatio in
 256 //
 257 //    _initiating_occupancy = 100-f +
 258 //                           f * (CMSTriggerRatio/100)
 259 //   where CMSTriggerRatio is the argument "tr" below.
 260 //
 261 // That is, if we assume the heap is at its desired maximum occupancy at the
 262 // end of a collection, we let CMSTriggerRatio of the (purported) free
 263 // space be allocated before initiating a new collection cycle.
 264 //
 265 void ConcurrentMarkSweepGeneration::init_initiating_occupancy(intx io, uintx tr) {
 266   assert(io <= 100 && tr <= 100, "Check the arguments");
 267   if (io >= 0) {
 268     _initiating_occupancy = (double)io / 100.0;
 269   } else {
 270     _initiating_occupancy = ((100 - MinHeapFreeRatio) +
 271                              (double)(tr * MinHeapFreeRatio) / 100.0)
 272                             / 100.0;
 273   }
 274 }
 275 
 276 void ConcurrentMarkSweepGeneration::ref_processor_init() {
 277   assert(collector() != NULL, "no collector");
 278   collector()->ref_processor_init();
 279 }
 280 
 281 void CMSCollector::ref_processor_init() {
 282   if (_ref_processor == NULL) {
 283     // Allocate and initialize a reference processor
 284     _ref_processor =
 285       new ReferenceProcessor(_span,                               // span
 286                              (ParallelGCThreads > 1) && ParallelRefProcEnabled, // mt processing
 287                              (int) ParallelGCThreads,             // mt processing degree
 288                              _cmsGen->refs_discovery_is_mt(),     // mt discovery
 289                              (int) MAX2(ConcGCThreads, ParallelGCThreads), // mt discovery degree
 290                              _cmsGen->refs_discovery_is_atomic(), // discovery is not atomic
 291                              &_is_alive_closure);                 // closure for liveness info
 292     // Initialize the _ref_processor field of CMSGen
 293     _cmsGen->set_ref_processor(_ref_processor);
 294 
 295   }
 296 }
 297 
 298 AdaptiveSizePolicy* CMSCollector::size_policy() {
 299   GenCollectedHeap* gch = GenCollectedHeap::heap();
 300   return gch->gen_policy()->size_policy();
 301 }
 302 
 303 void ConcurrentMarkSweepGeneration::initialize_performance_counters() {
 304 
 305   const char* gen_name = "old";
 306   GenCollectorPolicy* gcp = (GenCollectorPolicy*) GenCollectedHeap::heap()->collector_policy();
 307 
 308   // Generation Counters - generation 1, 1 subspace
 309   _gen_counters = new GenerationCounters(gen_name, 1, 1,
 310       gcp->min_old_size(), gcp->max_old_size(), &_virtual_space);
 311 
 312   _space_counters = new GSpaceCounters(gen_name, 0,
 313                                        _virtual_space.reserved_size(),
 314                                        this, _gen_counters);
 315 }
 316 
 317 CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha):
 318   _cms_gen(cms_gen)
 319 {
 320   assert(alpha <= 100, "bad value");
 321   _saved_alpha = alpha;
 322 
 323   // Initialize the alphas to the bootstrap value of 100.
 324   _gc0_alpha = _cms_alpha = 100;
 325 
 326   _cms_begin_time.update();
 327   _cms_end_time.update();
 328 
 329   _gc0_duration = 0.0;
 330   _gc0_period = 0.0;
 331   _gc0_promoted = 0;
 332 
 333   _cms_duration = 0.0;
 334   _cms_period = 0.0;
 335   _cms_allocated = 0;
 336 
 337   _cms_used_at_gc0_begin = 0;
 338   _cms_used_at_gc0_end = 0;
 339   _allow_duty_cycle_reduction = false;
 340   _valid_bits = 0;
 341 }
 342 
 343 double CMSStats::cms_free_adjustment_factor(size_t free) const {
 344   // TBD: CR 6909490
 345   return 1.0;
 346 }
 347 
 348 void CMSStats::adjust_cms_free_adjustment_factor(bool fail, size_t free) {
 349 }
 350 
 351 // If promotion failure handling is on use
 352 // the padded average size of the promotion for each
 353 // young generation collection.
 354 double CMSStats::time_until_cms_gen_full() const {
 355   size_t cms_free = _cms_gen->cmsSpace()->free();
 356   GenCollectedHeap* gch = GenCollectedHeap::heap();
 357   size_t expected_promotion = MIN2(gch->young_gen()->capacity(),
 358                                    (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average());
 359   if (cms_free > expected_promotion) {
 360     // Start a cms collection if there isn't enough space to promote
 361     // for the next minor collection.  Use the padded average as
 362     // a safety factor.
 363     cms_free -= expected_promotion;
 364 
 365     // Adjust by the safety factor.
 366     double cms_free_dbl = (double)cms_free;
 367     double cms_adjustment = (100.0 - CMSIncrementalSafetyFactor)/100.0;
 368     // Apply a further correction factor which tries to adjust
 369     // for recent occurance of concurrent mode failures.
 370     cms_adjustment = cms_adjustment * cms_free_adjustment_factor(cms_free);
 371     cms_free_dbl = cms_free_dbl * cms_adjustment;
 372 
 373     if (PrintGCDetails && Verbose) {
 374       gclog_or_tty->print_cr("CMSStats::time_until_cms_gen_full: cms_free "
 375         SIZE_FORMAT " expected_promotion " SIZE_FORMAT,
 376         cms_free, expected_promotion);
 377       gclog_or_tty->print_cr("  cms_free_dbl %f cms_consumption_rate %f",
 378         cms_free_dbl, cms_consumption_rate() + 1.0);
 379     }
 380     // Add 1 in case the consumption rate goes to zero.
 381     return cms_free_dbl / (cms_consumption_rate() + 1.0);
 382   }
 383   return 0.0;
 384 }
 385 
 386 // Compare the duration of the cms collection to the
 387 // time remaining before the cms generation is empty.
 388 // Note that the time from the start of the cms collection
 389 // to the start of the cms sweep (less than the total
 390 // duration of the cms collection) can be used.  This
 391 // has been tried and some applications experienced
 392 // promotion failures early in execution.  This was
 393 // possibly because the averages were not accurate
 394 // enough at the beginning.
 395 double CMSStats::time_until_cms_start() const {
 396   // We add "gc0_period" to the "work" calculation
 397   // below because this query is done (mostly) at the
 398   // end of a scavenge, so we need to conservatively
 399   // account for that much possible delay
 400   // in the query so as to avoid concurrent mode failures
 401   // due to starting the collection just a wee bit too
 402   // late.
 403   double work = cms_duration() + gc0_period();
 404   double deadline = time_until_cms_gen_full();
 405   // If a concurrent mode failure occurred recently, we want to be
 406   // more conservative and halve our expected time_until_cms_gen_full()
 407   if (work > deadline) {
 408     if (Verbose && PrintGCDetails) {
 409       gclog_or_tty->print(
 410         " CMSCollector: collect because of anticipated promotion "
 411         "before full %3.7f + %3.7f > %3.7f ", cms_duration(),
 412         gc0_period(), time_until_cms_gen_full());
 413     }
 414     return 0.0;
 415   }
 416   return work - deadline;
 417 }
 418 
 419 #ifndef PRODUCT
 420 void CMSStats::print_on(outputStream *st) const {
 421   st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha);
 422   st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo=" SIZE_FORMAT,
 423                gc0_duration(), gc0_period(), gc0_promoted());
 424   st->print(",cms_dur=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT,
 425             cms_duration(), cms_period(), cms_allocated());
 426   st->print(",cms_since_beg=%g,cms_since_end=%g",
 427             cms_time_since_begin(), cms_time_since_end());
 428   st->print(",cms_used_beg=" SIZE_FORMAT ",cms_used_end=" SIZE_FORMAT,
 429             _cms_used_at_gc0_begin, _cms_used_at_gc0_end);
 430 
 431   if (valid()) {
 432     st->print(",promo_rate=%g,cms_alloc_rate=%g",
 433               promotion_rate(), cms_allocation_rate());
 434     st->print(",cms_consumption_rate=%g,time_until_full=%g",
 435               cms_consumption_rate(), time_until_cms_gen_full());
 436   }
 437   st->print(" ");
 438 }
 439 #endif // #ifndef PRODUCT
 440 
 441 CMSCollector::CollectorState CMSCollector::_collectorState =
 442                              CMSCollector::Idling;
 443 bool CMSCollector::_foregroundGCIsActive = false;
 444 bool CMSCollector::_foregroundGCShouldWait = false;
 445 
 446 CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
 447                            CardTableRS*                   ct,
 448                            ConcurrentMarkSweepPolicy*     cp):
 449   _cmsGen(cmsGen),
 450   _ct(ct),
 451   _ref_processor(NULL),    // will be set later
 452   _conc_workers(NULL),     // may be set later
 453   _abort_preclean(false),
 454   _start_sampling(false),
 455   _between_prologue_and_epilogue(false),
 456   _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"),
 457   _modUnionTable((CardTableModRefBS::card_shift - LogHeapWordSize),
 458                  -1 /* lock-free */, "No_lock" /* dummy */),
 459   _modUnionClosurePar(&_modUnionTable),
 460   // Adjust my span to cover old (cms) gen
 461   _span(cmsGen->reserved()),
 462   // Construct the is_alive_closure with _span & markBitMap
 463   _is_alive_closure(_span, &_markBitMap),
 464   _restart_addr(NULL),
 465   _overflow_list(NULL),
 466   _stats(cmsGen),
 467   _eden_chunk_lock(new Mutex(Mutex::leaf + 1, "CMS_eden_chunk_lock", true,
 468                              //verify that this lock should be acquired with safepoint check.
 469                              Monitor::_safepoint_check_sometimes)),
 470   _eden_chunk_array(NULL),     // may be set in ctor body
 471   _eden_chunk_capacity(0),     // -- ditto --
 472   _eden_chunk_index(0),        // -- ditto --
 473   _survivor_plab_array(NULL),  // -- ditto --
 474   _survivor_chunk_array(NULL), // -- ditto --
 475   _survivor_chunk_capacity(0), // -- ditto --
 476   _survivor_chunk_index(0),    // -- ditto --
 477   _ser_pmc_preclean_ovflw(0),
 478   _ser_kac_preclean_ovflw(0),
 479   _ser_pmc_remark_ovflw(0),
 480   _par_pmc_remark_ovflw(0),
 481   _ser_kac_ovflw(0),
 482   _par_kac_ovflw(0),
 483 #ifndef PRODUCT
 484   _num_par_pushes(0),
 485 #endif
 486   _collection_count_start(0),
 487   _verifying(false),
 488   _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"),
 489   _completed_initialization(false),
 490   _collector_policy(cp),
 491   _should_unload_classes(CMSClassUnloadingEnabled),
 492   _concurrent_cycles_since_last_unload(0),
 493   _roots_scanning_options(GenCollectedHeap::SO_None),
 494   _inter_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
 495   _intra_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
 496   _gc_tracer_cm(new (ResourceObj::C_HEAP, mtGC) CMSTracer()),
 497   _gc_timer_cm(new (ResourceObj::C_HEAP, mtGC) ConcurrentGCTimer()),
 498   _cms_start_registered(false)
 499 {
 500   if (ExplicitGCInvokesConcurrentAndUnloadsClasses) {
 501     ExplicitGCInvokesConcurrent = true;
 502   }
 503   // Now expand the span and allocate the collection support structures
 504   // (MUT, marking bit map etc.) to cover both generations subject to
 505   // collection.
 506 
 507   // For use by dirty card to oop closures.
 508   _cmsGen->cmsSpace()->set_collector(this);
 509 
 510   // Allocate MUT and marking bit map
 511   {
 512     MutexLockerEx x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag);
 513     if (!_markBitMap.allocate(_span)) {
 514       warning("Failed to allocate CMS Bit Map");
 515       return;
 516     }
 517     assert(_markBitMap.covers(_span), "_markBitMap inconsistency?");
 518   }
 519   {
 520     _modUnionTable.allocate(_span);
 521     assert(_modUnionTable.covers(_span), "_modUnionTable inconsistency?");
 522   }
 523 
 524   if (!_markStack.allocate(MarkStackSize)) {
 525     warning("Failed to allocate CMS Marking Stack");
 526     return;
 527   }
 528 
 529   // Support for multi-threaded concurrent phases
 530   if (CMSConcurrentMTEnabled) {
 531     if (FLAG_IS_DEFAULT(ConcGCThreads)) {
 532       // just for now
 533       FLAG_SET_DEFAULT(ConcGCThreads, (ParallelGCThreads + 3)/4);
 534     }
 535     if (ConcGCThreads > 1) {
 536       _conc_workers = new YieldingFlexibleWorkGang("CMS Thread",
 537                                  ConcGCThreads, true);
 538       if (_conc_workers == NULL) {
 539         warning("GC/CMS: _conc_workers allocation failure: "
 540               "forcing -CMSConcurrentMTEnabled");
 541         CMSConcurrentMTEnabled = false;
 542       } else {
 543         _conc_workers->initialize_workers();
 544       }
 545     } else {
 546       CMSConcurrentMTEnabled = false;
 547     }
 548   }
 549   if (!CMSConcurrentMTEnabled) {
 550     ConcGCThreads = 0;
 551   } else {
 552     // Turn off CMSCleanOnEnter optimization temporarily for
 553     // the MT case where it's not fixed yet; see 6178663.
 554     CMSCleanOnEnter = false;
 555   }
 556   assert((_conc_workers != NULL) == (ConcGCThreads > 1),
 557          "Inconsistency");
 558 
 559   // Parallel task queues; these are shared for the
 560   // concurrent and stop-world phases of CMS, but
 561   // are not shared with parallel scavenge (ParNew).
 562   {
 563     uint i;
 564     uint num_queues = (uint) MAX2(ParallelGCThreads, ConcGCThreads);
 565 
 566     if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled
 567          || ParallelRefProcEnabled)
 568         && num_queues > 0) {
 569       _task_queues = new OopTaskQueueSet(num_queues);
 570       if (_task_queues == NULL) {
 571         warning("task_queues allocation failure.");
 572         return;
 573       }
 574       _hash_seed = NEW_C_HEAP_ARRAY(int, num_queues, mtGC);
 575       typedef Padded<OopTaskQueue> PaddedOopTaskQueue;
 576       for (i = 0; i < num_queues; i++) {
 577         PaddedOopTaskQueue *q = new PaddedOopTaskQueue();
 578         if (q == NULL) {
 579           warning("work_queue allocation failure.");
 580           return;
 581         }
 582         _task_queues->register_queue(i, q);
 583       }
 584       for (i = 0; i < num_queues; i++) {
 585         _task_queues->queue(i)->initialize();
 586         _hash_seed[i] = 17;  // copied from ParNew
 587       }
 588     }
 589   }
 590 
 591   _cmsGen ->init_initiating_occupancy(CMSInitiatingOccupancyFraction, CMSTriggerRatio);
 592 
 593   // Clip CMSBootstrapOccupancy between 0 and 100.
 594   _bootstrap_occupancy = ((double)CMSBootstrapOccupancy)/(double)100;
 595 
 596   // Now tell CMS generations the identity of their collector
 597   ConcurrentMarkSweepGeneration::set_collector(this);
 598 
 599   // Create & start a CMS thread for this CMS collector
 600   _cmsThread = ConcurrentMarkSweepThread::start(this);
 601   assert(cmsThread() != NULL, "CMS Thread should have been created");
 602   assert(cmsThread()->collector() == this,
 603          "CMS Thread should refer to this gen");
 604   assert(CGC_lock != NULL, "Where's the CGC_lock?");
 605 
 606   // Support for parallelizing young gen rescan
 607   GenCollectedHeap* gch = GenCollectedHeap::heap();
 608   assert(gch->young_gen()->kind() == Generation::ParNew, "CMS can only be used with ParNew");
 609   _young_gen = (ParNewGeneration*)gch->young_gen();
 610   if (gch->supports_inline_contig_alloc()) {
 611     _top_addr = gch->top_addr();
 612     _end_addr = gch->end_addr();
 613     assert(_young_gen != NULL, "no _young_gen");
 614     _eden_chunk_index = 0;
 615     _eden_chunk_capacity = (_young_gen->max_capacity()+CMSSamplingGrain)/CMSSamplingGrain;
 616     _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity, mtGC);
 617   }
 618 
 619   // Support for parallelizing survivor space rescan
 620   if ((CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) || CMSParallelInitialMarkEnabled) {
 621     const size_t max_plab_samples =
 622       ((DefNewGeneration*)_young_gen)->max_survivor_size() / plab_sample_minimum_size();
 623 
 624     _survivor_plab_array  = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads, mtGC);
 625     _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, 2*max_plab_samples, mtGC);
 626     _cursor               = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads, mtGC);
 627     _survivor_chunk_capacity = 2*max_plab_samples;
 628     for (uint i = 0; i < ParallelGCThreads; i++) {
 629       HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
 630       ChunkArray* cur = ::new (&_survivor_plab_array[i]) ChunkArray(vec, max_plab_samples);
 631       assert(cur->end() == 0, "Should be 0");
 632       assert(cur->array() == vec, "Should be vec");
 633       assert(cur->capacity() == max_plab_samples, "Error");
 634     }
 635   }
 636 
 637   NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;)
 638   _gc_counters = new CollectorCounters("CMS", 1);
 639   _completed_initialization = true;
 640   _inter_sweep_timer.start();  // start of time
 641 }
 642 
 643 size_t CMSCollector::plab_sample_minimum_size() {
 644   // The default value of MinTLABSize is 2k, but there is
 645   // no way to get the default value if the flag has been overridden.
 646   return MAX2(ThreadLocalAllocBuffer::min_size() * HeapWordSize, 2 * K);
 647 }
 648 
 649 const char* ConcurrentMarkSweepGeneration::name() const {
 650   return "concurrent mark-sweep generation";
 651 }
 652 void ConcurrentMarkSweepGeneration::update_counters() {
 653   if (UsePerfData) {
 654     _space_counters->update_all();
 655     _gen_counters->update_all();
 656   }
 657 }
 658 
 659 // this is an optimized version of update_counters(). it takes the
 660 // used value as a parameter rather than computing it.
 661 //
 662 void ConcurrentMarkSweepGeneration::update_counters(size_t used) {
 663   if (UsePerfData) {
 664     _space_counters->update_used(used);
 665     _space_counters->update_capacity();
 666     _gen_counters->update_all();
 667   }
 668 }
 669 
 670 void ConcurrentMarkSweepGeneration::print() const {
 671   Generation::print();
 672   cmsSpace()->print();
 673 }
 674 
 675 #ifndef PRODUCT
 676 void ConcurrentMarkSweepGeneration::print_statistics() {
 677   cmsSpace()->printFLCensus(0);
 678 }
 679 #endif
 680 
 681 void ConcurrentMarkSweepGeneration::printOccupancy(const char *s) {
 682   GenCollectedHeap* gch = GenCollectedHeap::heap();
 683   if (PrintGCDetails) {
 684     if (Verbose) {
 685       gclog_or_tty->print("[%d %s-%s: "SIZE_FORMAT"("SIZE_FORMAT")]",
 686         level(), short_name(), s, used(), capacity());
 687     } else {
 688       gclog_or_tty->print("[%d %s-%s: "SIZE_FORMAT"K("SIZE_FORMAT"K)]",
 689         level(), short_name(), s, used() / K, capacity() / K);
 690     }
 691   }
 692   if (Verbose) {
 693     gclog_or_tty->print(" "SIZE_FORMAT"("SIZE_FORMAT")",
 694               gch->used(), gch->capacity());
 695   } else {
 696     gclog_or_tty->print(" "SIZE_FORMAT"K("SIZE_FORMAT"K)",
 697               gch->used() / K, gch->capacity() / K);
 698   }
 699 }
 700 
 701 size_t
 702 ConcurrentMarkSweepGeneration::contiguous_available() const {
 703   // dld proposes an improvement in precision here. If the committed
 704   // part of the space ends in a free block we should add that to
 705   // uncommitted size in the calculation below. Will make this
 706   // change later, staying with the approximation below for the
 707   // time being. -- ysr.
 708   return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc());
 709 }
 710 
 711 size_t
 712 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const {
 713   return _cmsSpace->max_alloc_in_words() * HeapWordSize;
 714 }
 715 
 716 size_t ConcurrentMarkSweepGeneration::max_available() const {
 717   return free() + _virtual_space.uncommitted_size();
 718 }
 719 
 720 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(size_t max_promotion_in_bytes) const {
 721   size_t available = max_available();
 722   size_t av_promo  = (size_t)gc_stats()->avg_promoted()->padded_average();
 723   bool   res = (available >= av_promo) || (available >= max_promotion_in_bytes);
 724   if (Verbose && PrintGCDetails) {
 725     gclog_or_tty->print_cr(
 726       "CMS: promo attempt is%s safe: available("SIZE_FORMAT") %s av_promo("SIZE_FORMAT"),"
 727       "max_promo("SIZE_FORMAT")",
 728       res? "":" not", available, res? ">=":"<",
 729       av_promo, max_promotion_in_bytes);
 730   }
 731   return res;
 732 }
 733 
 734 // At a promotion failure dump information on block layout in heap
 735 // (cms old generation).
 736 void ConcurrentMarkSweepGeneration::promotion_failure_occurred() {
 737   if (CMSDumpAtPromotionFailure) {
 738     cmsSpace()->dump_at_safepoint_with_locks(collector(), gclog_or_tty);
 739   }
 740 }
 741 
 742 void ConcurrentMarkSweepGeneration::reset_after_compaction() {
 743   // Clear the promotion information.  These pointers can be adjusted
 744   // along with all the other pointers into the heap but
 745   // compaction is expected to be a rare event with
 746   // a heap using cms so don't do it without seeing the need.
 747   for (uint i = 0; i < ParallelGCThreads; i++) {
 748     _par_gc_thread_states[i]->promo.reset();
 749   }
 750 }
 751 
 752 void ConcurrentMarkSweepGeneration::compute_new_size() {
 753   assert_locked_or_safepoint(Heap_lock);
 754 
 755   // If incremental collection failed, we just want to expand
 756   // to the limit.
 757   if (incremental_collection_failed()) {
 758     clear_incremental_collection_failed();
 759     grow_to_reserved();
 760     return;
 761   }
 762 
 763   // The heap has been compacted but not reset yet.
 764   // Any metric such as free() or used() will be incorrect.
 765 
 766   CardGeneration::compute_new_size();
 767 
 768   // Reset again after a possible resizing
 769   if (did_compact()) {
 770     cmsSpace()->reset_after_compaction();
 771   }
 772 }
 773 
 774 void ConcurrentMarkSweepGeneration::compute_new_size_free_list() {
 775   assert_locked_or_safepoint(Heap_lock);
 776 
 777   // If incremental collection failed, we just want to expand
 778   // to the limit.
 779   if (incremental_collection_failed()) {
 780     clear_incremental_collection_failed();
 781     grow_to_reserved();
 782     return;
 783   }
 784 
 785   double free_percentage = ((double) free()) / capacity();
 786   double desired_free_percentage = (double) MinHeapFreeRatio / 100;
 787   double maximum_free_percentage = (double) MaxHeapFreeRatio / 100;
 788 
 789   // compute expansion delta needed for reaching desired free percentage
 790   if (free_percentage < desired_free_percentage) {
 791     size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
 792     assert(desired_capacity >= capacity(), "invalid expansion size");
 793     size_t expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes);
 794     if (PrintGCDetails && Verbose) {
 795       size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
 796       gclog_or_tty->print_cr("\nFrom compute_new_size: ");
 797       gclog_or_tty->print_cr("  Free fraction %f", free_percentage);
 798       gclog_or_tty->print_cr("  Desired free fraction %f",
 799         desired_free_percentage);
 800       gclog_or_tty->print_cr("  Maximum free fraction %f",
 801         maximum_free_percentage);
 802       gclog_or_tty->print_cr("  Capacity "SIZE_FORMAT, capacity()/1000);
 803       gclog_or_tty->print_cr("  Desired capacity "SIZE_FORMAT,
 804         desired_capacity/1000);
 805       int prev_level = level() - 1;
 806       if (prev_level >= 0) {
 807         size_t prev_size = 0;
 808         GenCollectedHeap* gch = GenCollectedHeap::heap();
 809         Generation* prev_gen = gch->young_gen();
 810         prev_size = prev_gen->capacity();
 811           gclog_or_tty->print_cr("  Younger gen size "SIZE_FORMAT,
 812                                  prev_size/1000);
 813       }
 814       gclog_or_tty->print_cr("  unsafe_max_alloc_nogc "SIZE_FORMAT,
 815         unsafe_max_alloc_nogc()/1000);
 816       gclog_or_tty->print_cr("  contiguous available "SIZE_FORMAT,
 817         contiguous_available()/1000);
 818       gclog_or_tty->print_cr("  Expand by "SIZE_FORMAT" (bytes)",
 819         expand_bytes);
 820     }
 821     // safe if expansion fails
 822     expand_for_gc_cause(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio);
 823     if (PrintGCDetails && Verbose) {
 824       gclog_or_tty->print_cr("  Expanded free fraction %f",
 825         ((double) free()) / capacity());
 826     }
 827   } else {
 828     size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
 829     assert(desired_capacity <= capacity(), "invalid expansion size");
 830     size_t shrink_bytes = capacity() - desired_capacity;
 831     // Don't shrink unless the delta is greater than the minimum shrink we want
 832     if (shrink_bytes >= MinHeapDeltaBytes) {
 833       shrink_free_list_by(shrink_bytes);
 834     }
 835   }
 836 }
 837 
 838 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const {
 839   return cmsSpace()->freelistLock();
 840 }
 841 
 842 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size,
 843                                                   bool   tlab) {
 844   CMSSynchronousYieldRequest yr;
 845   MutexLockerEx x(freelistLock(),
 846                   Mutex::_no_safepoint_check_flag);
 847   return have_lock_and_allocate(size, tlab);
 848 }
 849 
 850 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size,
 851                                                   bool   tlab /* ignored */) {
 852   assert_lock_strong(freelistLock());
 853   size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size);
 854   HeapWord* res = cmsSpace()->allocate(adjustedSize);
 855   // Allocate the object live (grey) if the background collector has
 856   // started marking. This is necessary because the marker may
 857   // have passed this address and consequently this object will
 858   // not otherwise be greyed and would be incorrectly swept up.
 859   // Note that if this object contains references, the writing
 860   // of those references will dirty the card containing this object
 861   // allowing the object to be blackened (and its references scanned)
 862   // either during a preclean phase or at the final checkpoint.
 863   if (res != NULL) {
 864     // We may block here with an uninitialized object with
 865     // its mark-bit or P-bits not yet set. Such objects need
 866     // to be safely navigable by block_start().
 867     assert(oop(res)->klass_or_null() == NULL, "Object should be uninitialized here.");
 868     assert(!((FreeChunk*)res)->is_free(), "Error, block will look free but show wrong size");
 869     collector()->direct_allocated(res, adjustedSize);
 870     _direct_allocated_words += adjustedSize;
 871     // allocation counters
 872     NOT_PRODUCT(
 873       _numObjectsAllocated++;
 874       _numWordsAllocated += (int)adjustedSize;
 875     )
 876   }
 877   return res;
 878 }
 879 
 880 // In the case of direct allocation by mutators in a generation that
 881 // is being concurrently collected, the object must be allocated
 882 // live (grey) if the background collector has started marking.
 883 // This is necessary because the marker may
 884 // have passed this address and consequently this object will
 885 // not otherwise be greyed and would be incorrectly swept up.
 886 // Note that if this object contains references, the writing
 887 // of those references will dirty the card containing this object
 888 // allowing the object to be blackened (and its references scanned)
 889 // either during a preclean phase or at the final checkpoint.
 890 void CMSCollector::direct_allocated(HeapWord* start, size_t size) {
 891   assert(_markBitMap.covers(start, size), "Out of bounds");
 892   if (_collectorState >= Marking) {
 893     MutexLockerEx y(_markBitMap.lock(),
 894                     Mutex::_no_safepoint_check_flag);
 895     // [see comments preceding SweepClosure::do_blk() below for details]
 896     //
 897     // Can the P-bits be deleted now?  JJJ
 898     //
 899     // 1. need to mark the object as live so it isn't collected
 900     // 2. need to mark the 2nd bit to indicate the object may be uninitialized
 901     // 3. need to mark the end of the object so marking, precleaning or sweeping
 902     //    can skip over uninitialized or unparsable objects. An allocated
 903     //    object is considered uninitialized for our purposes as long as
 904     //    its klass word is NULL.  All old gen objects are parsable
 905     //    as soon as they are initialized.)
 906     _markBitMap.mark(start);          // object is live
 907     _markBitMap.mark(start + 1);      // object is potentially uninitialized?
 908     _markBitMap.mark(start + size - 1);
 909                                       // mark end of object
 910   }
 911   // check that oop looks uninitialized
 912   assert(oop(start)->klass_or_null() == NULL, "_klass should be NULL");
 913 }
 914 
 915 void CMSCollector::promoted(bool par, HeapWord* start,
 916                             bool is_obj_array, size_t obj_size) {
 917   assert(_markBitMap.covers(start), "Out of bounds");
 918   // See comment in direct_allocated() about when objects should
 919   // be allocated live.
 920   if (_collectorState >= Marking) {
 921     // we already hold the marking bit map lock, taken in
 922     // the prologue
 923     if (par) {
 924       _markBitMap.par_mark(start);
 925     } else {
 926       _markBitMap.mark(start);
 927     }
 928     // We don't need to mark the object as uninitialized (as
 929     // in direct_allocated above) because this is being done with the
 930     // world stopped and the object will be initialized by the
 931     // time the marking, precleaning or sweeping get to look at it.
 932     // But see the code for copying objects into the CMS generation,
 933     // where we need to ensure that concurrent readers of the
 934     // block offset table are able to safely navigate a block that
 935     // is in flux from being free to being allocated (and in
 936     // transition while being copied into) and subsequently
 937     // becoming a bona-fide object when the copy/promotion is complete.
 938     assert(SafepointSynchronize::is_at_safepoint(),
 939            "expect promotion only at safepoints");
 940 
 941     if (_collectorState < Sweeping) {
 942       // Mark the appropriate cards in the modUnionTable, so that
 943       // this object gets scanned before the sweep. If this is
 944       // not done, CMS generation references in the object might
 945       // not get marked.
 946       // For the case of arrays, which are otherwise precisely
 947       // marked, we need to dirty the entire array, not just its head.
 948       if (is_obj_array) {
 949         // The [par_]mark_range() method expects mr.end() below to
 950         // be aligned to the granularity of a bit's representation
 951         // in the heap. In the case of the MUT below, that's a
 952         // card size.
 953         MemRegion mr(start,
 954                      (HeapWord*)round_to((intptr_t)(start + obj_size),
 955                         CardTableModRefBS::card_size /* bytes */));
 956         if (par) {
 957           _modUnionTable.par_mark_range(mr);
 958         } else {
 959           _modUnionTable.mark_range(mr);
 960         }
 961       } else {  // not an obj array; we can just mark the head
 962         if (par) {
 963           _modUnionTable.par_mark(start);
 964         } else {
 965           _modUnionTable.mark(start);
 966         }
 967       }
 968     }
 969   }
 970 }
 971 
 972 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size) {
 973   assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
 974   // allocate, copy and if necessary update promoinfo --
 975   // delegate to underlying space.
 976   assert_lock_strong(freelistLock());
 977 
 978 #ifndef PRODUCT
 979   if (GenCollectedHeap::heap()->promotion_should_fail()) {
 980     return NULL;
 981   }
 982 #endif  // #ifndef PRODUCT
 983 
 984   oop res = _cmsSpace->promote(obj, obj_size);
 985   if (res == NULL) {
 986     // expand and retry
 987     size_t s = _cmsSpace->expansionSpaceRequired(obj_size);  // HeapWords
 988     expand_for_gc_cause(s*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_promotion);
 989     // Since this is the old generation, we don't try to promote
 990     // into a more senior generation.
 991     res = _cmsSpace->promote(obj, obj_size);
 992   }
 993   if (res != NULL) {
 994     // See comment in allocate() about when objects should
 995     // be allocated live.
 996     assert(obj->is_oop(), "Will dereference klass pointer below");
 997     collector()->promoted(false,           // Not parallel
 998                           (HeapWord*)res, obj->is_objArray(), obj_size);
 999     // promotion counters
1000     NOT_PRODUCT(
1001       _numObjectsPromoted++;
1002       _numWordsPromoted +=
1003         (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size()));
1004     )
1005   }
1006   return res;
1007 }
1008 
1009 
1010 // IMPORTANT: Notes on object size recognition in CMS.
1011 // ---------------------------------------------------
1012 // A block of storage in the CMS generation is always in
1013 // one of three states. A free block (FREE), an allocated
1014 // object (OBJECT) whose size() method reports the correct size,
1015 // and an intermediate state (TRANSIENT) in which its size cannot
1016 // be accurately determined.
1017 // STATE IDENTIFICATION:   (32 bit and 64 bit w/o COOPS)
1018 // -----------------------------------------------------
1019 // FREE:      klass_word & 1 == 1; mark_word holds block size
1020 //
1021 // OBJECT:    klass_word installed; klass_word != 0 && klass_word & 1 == 0;
1022 //            obj->size() computes correct size
1023 //
1024 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1025 //
1026 // STATE IDENTIFICATION: (64 bit+COOPS)
1027 // ------------------------------------
1028 // FREE:      mark_word & CMS_FREE_BIT == 1; mark_word & ~CMS_FREE_BIT gives block_size
1029 //
1030 // OBJECT:    klass_word installed; klass_word != 0;
1031 //            obj->size() computes correct size
1032 //
1033 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1034 //
1035 //
1036 // STATE TRANSITION DIAGRAM
1037 //
1038 //        mut / parnew                     mut  /  parnew
1039 // FREE --------------------> TRANSIENT ---------------------> OBJECT --|
1040 //  ^                                                                   |
1041 //  |------------------------ DEAD <------------------------------------|
1042 //         sweep                            mut
1043 //
1044 // While a block is in TRANSIENT state its size cannot be determined
1045 // so readers will either need to come back later or stall until
1046 // the size can be determined. Note that for the case of direct
1047 // allocation, P-bits, when available, may be used to determine the
1048 // size of an object that may not yet have been initialized.
1049 
1050 // Things to support parallel young-gen collection.
1051 oop
1052 ConcurrentMarkSweepGeneration::par_promote(int thread_num,
1053                                            oop old, markOop m,
1054                                            size_t word_sz) {
1055 #ifndef PRODUCT
1056   if (GenCollectedHeap::heap()->promotion_should_fail()) {
1057     return NULL;
1058   }
1059 #endif  // #ifndef PRODUCT
1060 
1061   CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1062   PromotionInfo* promoInfo = &ps->promo;
1063   // if we are tracking promotions, then first ensure space for
1064   // promotion (including spooling space for saving header if necessary).
1065   // then allocate and copy, then track promoted info if needed.
1066   // When tracking (see PromotionInfo::track()), the mark word may
1067   // be displaced and in this case restoration of the mark word
1068   // occurs in the (oop_since_save_marks_)iterate phase.
1069   if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) {
1070     // Out of space for allocating spooling buffers;
1071     // try expanding and allocating spooling buffers.
1072     if (!expand_and_ensure_spooling_space(promoInfo)) {
1073       return NULL;
1074     }
1075   }
1076   assert(promoInfo->has_spooling_space(), "Control point invariant");
1077   const size_t alloc_sz = CompactibleFreeListSpace::adjustObjectSize(word_sz);
1078   HeapWord* obj_ptr = ps->lab.alloc(alloc_sz);
1079   if (obj_ptr == NULL) {
1080      obj_ptr = expand_and_par_lab_allocate(ps, alloc_sz);
1081      if (obj_ptr == NULL) {
1082        return NULL;
1083      }
1084   }
1085   oop obj = oop(obj_ptr);
1086   OrderAccess::storestore();
1087   assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1088   assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1089   // IMPORTANT: See note on object initialization for CMS above.
1090   // Otherwise, copy the object.  Here we must be careful to insert the
1091   // klass pointer last, since this marks the block as an allocated object.
1092   // Except with compressed oops it's the mark word.
1093   HeapWord* old_ptr = (HeapWord*)old;
1094   // Restore the mark word copied above.
1095   obj->set_mark(m);
1096   assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1097   assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1098   OrderAccess::storestore();
1099 
1100   if (UseCompressedClassPointers) {
1101     // Copy gap missed by (aligned) header size calculation below
1102     obj->set_klass_gap(old->klass_gap());
1103   }
1104   if (word_sz > (size_t)oopDesc::header_size()) {
1105     Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1106                                  obj_ptr + oopDesc::header_size(),
1107                                  word_sz - oopDesc::header_size());
1108   }
1109 
1110   // Now we can track the promoted object, if necessary.  We take care
1111   // to delay the transition from uninitialized to full object
1112   // (i.e., insertion of klass pointer) until after, so that it
1113   // atomically becomes a promoted object.
1114   if (promoInfo->tracking()) {
1115     promoInfo->track((PromotedObject*)obj, old->klass());
1116   }
1117   assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1118   assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1119   assert(old->is_oop(), "Will use and dereference old klass ptr below");
1120 
1121   // Finally, install the klass pointer (this should be volatile).
1122   OrderAccess::storestore();
1123   obj->set_klass(old->klass());
1124   // We should now be able to calculate the right size for this object
1125   assert(obj->is_oop() && obj->size() == (int)word_sz, "Error, incorrect size computed for promoted object");
1126 
1127   collector()->promoted(true,          // parallel
1128                         obj_ptr, old->is_objArray(), word_sz);
1129 
1130   NOT_PRODUCT(
1131     Atomic::inc_ptr(&_numObjectsPromoted);
1132     Atomic::add_ptr(alloc_sz, &_numWordsPromoted);
1133   )
1134 
1135   return obj;
1136 }
1137 
1138 void
1139 ConcurrentMarkSweepGeneration::
1140 par_promote_alloc_done(int thread_num) {
1141   CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1142   ps->lab.retire(thread_num);
1143 }
1144 
1145 void
1146 ConcurrentMarkSweepGeneration::
1147 par_oop_since_save_marks_iterate_done(int thread_num) {
1148   CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1149   ParScanWithoutBarrierClosure* dummy_cl = NULL;
1150   ps->promo.promoted_oops_iterate_nv(dummy_cl);
1151 }
1152 
1153 bool ConcurrentMarkSweepGeneration::should_collect(bool   full,
1154                                                    size_t size,
1155                                                    bool   tlab)
1156 {
1157   // We allow a STW collection only if a full
1158   // collection was requested.
1159   return full || should_allocate(size, tlab); // FIX ME !!!
1160   // This and promotion failure handling are connected at the
1161   // hip and should be fixed by untying them.
1162 }
1163 
1164 bool CMSCollector::shouldConcurrentCollect() {
1165   if (_full_gc_requested) {
1166     if (Verbose && PrintGCDetails) {
1167       gclog_or_tty->print_cr("CMSCollector: collect because of explicit "
1168                              " gc request (or gc_locker)");
1169     }
1170     return true;
1171   }
1172 
1173   FreelistLocker x(this);
1174   // ------------------------------------------------------------------
1175   // Print out lots of information which affects the initiation of
1176   // a collection.
1177   if (PrintCMSInitiationStatistics && stats().valid()) {
1178     gclog_or_tty->print("CMSCollector shouldConcurrentCollect: ");
1179     gclog_or_tty->stamp();
1180     gclog_or_tty->cr();
1181     stats().print_on(gclog_or_tty);
1182     gclog_or_tty->print_cr("time_until_cms_gen_full %3.7f",
1183       stats().time_until_cms_gen_full());
1184     gclog_or_tty->print_cr("free="SIZE_FORMAT, _cmsGen->free());
1185     gclog_or_tty->print_cr("contiguous_available="SIZE_FORMAT,
1186                            _cmsGen->contiguous_available());
1187     gclog_or_tty->print_cr("promotion_rate=%g", stats().promotion_rate());
1188     gclog_or_tty->print_cr("cms_allocation_rate=%g", stats().cms_allocation_rate());
1189     gclog_or_tty->print_cr("occupancy=%3.7f", _cmsGen->occupancy());
1190     gclog_or_tty->print_cr("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy());
1191     gclog_or_tty->print_cr("cms_time_since_begin=%3.7f", stats().cms_time_since_begin());
1192     gclog_or_tty->print_cr("cms_time_since_end=%3.7f", stats().cms_time_since_end());
1193     gclog_or_tty->print_cr("metadata initialized %d",
1194       MetaspaceGC::should_concurrent_collect());
1195   }
1196   // ------------------------------------------------------------------
1197 
1198   // If the estimated time to complete a cms collection (cms_duration())
1199   // is less than the estimated time remaining until the cms generation
1200   // is full, start a collection.
1201   if (!UseCMSInitiatingOccupancyOnly) {
1202     if (stats().valid()) {
1203       if (stats().time_until_cms_start() == 0.0) {
1204         return true;
1205       }
1206     } else {
1207       // We want to conservatively collect somewhat early in order
1208       // to try and "bootstrap" our CMS/promotion statistics;
1209       // this branch will not fire after the first successful CMS
1210       // collection because the stats should then be valid.
1211       if (_cmsGen->occupancy() >= _bootstrap_occupancy) {
1212         if (Verbose && PrintGCDetails) {
1213           gclog_or_tty->print_cr(
1214             " CMSCollector: collect for bootstrapping statistics:"
1215             " occupancy = %f, boot occupancy = %f", _cmsGen->occupancy(),
1216             _bootstrap_occupancy);
1217         }
1218         return true;
1219       }
1220     }
1221   }
1222 
1223   // Otherwise, we start a collection cycle if
1224   // old gen want a collection cycle started. Each may use
1225   // an appropriate criterion for making this decision.
1226   // XXX We need to make sure that the gen expansion
1227   // criterion dovetails well with this. XXX NEED TO FIX THIS
1228   if (_cmsGen->should_concurrent_collect()) {
1229     if (Verbose && PrintGCDetails) {
1230       gclog_or_tty->print_cr("CMS old gen initiated");
1231     }
1232     return true;
1233   }
1234 
1235   // We start a collection if we believe an incremental collection may fail;
1236   // this is not likely to be productive in practice because it's probably too
1237   // late anyway.
1238   GenCollectedHeap* gch = GenCollectedHeap::heap();
1239   assert(gch->collector_policy()->is_generation_policy(),
1240          "You may want to check the correctness of the following");
1241   if (gch->incremental_collection_will_fail(true /* consult_young */)) {
1242     if (Verbose && PrintGCDetails) {
1243       gclog_or_tty->print("CMSCollector: collect because incremental collection will fail ");
1244     }
1245     return true;
1246   }
1247 
1248   if (MetaspaceGC::should_concurrent_collect()) {
1249     if (Verbose && PrintGCDetails) {
1250       gclog_or_tty->print("CMSCollector: collect for metadata allocation ");
1251     }
1252     return true;
1253   }
1254 
1255   // CMSTriggerInterval starts a CMS cycle if enough time has passed.
1256   if (CMSTriggerInterval >= 0) {
1257     if (CMSTriggerInterval == 0) {
1258       // Trigger always
1259       return true;
1260     }
1261 
1262     // Check the CMS time since begin (we do not check the stats validity
1263     // as we want to be able to trigger the first CMS cycle as well)
1264     if (stats().cms_time_since_begin() >= (CMSTriggerInterval / ((double) MILLIUNITS))) {
1265       if (Verbose && PrintGCDetails) {
1266         if (stats().valid()) {
1267           gclog_or_tty->print_cr("CMSCollector: collect because of trigger interval (time since last begin %3.7f secs)",
1268                                  stats().cms_time_since_begin());
1269         } else {
1270           gclog_or_tty->print_cr("CMSCollector: collect because of trigger interval (first collection)");
1271         }
1272       }
1273       return true;
1274     }
1275   }
1276 
1277   return false;
1278 }
1279 
1280 void CMSCollector::set_did_compact(bool v) { _cmsGen->set_did_compact(v); }
1281 
1282 // Clear _expansion_cause fields of constituent generations
1283 void CMSCollector::clear_expansion_cause() {
1284   _cmsGen->clear_expansion_cause();
1285 }
1286 
1287 // We should be conservative in starting a collection cycle.  To
1288 // start too eagerly runs the risk of collecting too often in the
1289 // extreme.  To collect too rarely falls back on full collections,
1290 // which works, even if not optimum in terms of concurrent work.
1291 // As a work around for too eagerly collecting, use the flag
1292 // UseCMSInitiatingOccupancyOnly.  This also has the advantage of
1293 // giving the user an easily understandable way of controlling the
1294 // collections.
1295 // We want to start a new collection cycle if any of the following
1296 // conditions hold:
1297 // . our current occupancy exceeds the configured initiating occupancy
1298 //   for this generation, or
1299 // . we recently needed to expand this space and have not, since that
1300 //   expansion, done a collection of this generation, or
1301 // . the underlying space believes that it may be a good idea to initiate
1302 //   a concurrent collection (this may be based on criteria such as the
1303 //   following: the space uses linear allocation and linear allocation is
1304 //   going to fail, or there is believed to be excessive fragmentation in
1305 //   the generation, etc... or ...
1306 // [.(currently done by CMSCollector::shouldConcurrentCollect() only for
1307 //   the case of the old generation; see CR 6543076):
1308 //   we may be approaching a point at which allocation requests may fail because
1309 //   we will be out of sufficient free space given allocation rate estimates.]
1310 bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const {
1311 
1312   assert_lock_strong(freelistLock());
1313   if (occupancy() > initiating_occupancy()) {
1314     if (PrintGCDetails && Verbose) {
1315       gclog_or_tty->print(" %s: collect because of occupancy %f / %f  ",
1316         short_name(), occupancy(), initiating_occupancy());
1317     }
1318     return true;
1319   }
1320   if (UseCMSInitiatingOccupancyOnly) {
1321     return false;
1322   }
1323   if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) {
1324     if (PrintGCDetails && Verbose) {
1325       gclog_or_tty->print(" %s: collect because expanded for allocation ",
1326         short_name());
1327     }
1328     return true;
1329   }
1330   if (_cmsSpace->should_concurrent_collect()) {
1331     if (PrintGCDetails && Verbose) {
1332       gclog_or_tty->print(" %s: collect because cmsSpace says so ",
1333         short_name());
1334     }
1335     return true;
1336   }
1337   return false;
1338 }
1339 
1340 void ConcurrentMarkSweepGeneration::collect(bool   full,
1341                                             bool   clear_all_soft_refs,
1342                                             size_t size,
1343                                             bool   tlab)
1344 {
1345   collector()->collect(full, clear_all_soft_refs, size, tlab);
1346 }
1347 
1348 void CMSCollector::collect(bool   full,
1349                            bool   clear_all_soft_refs,
1350                            size_t size,
1351                            bool   tlab)
1352 {
1353   // The following "if" branch is present for defensive reasons.
1354   // In the current uses of this interface, it can be replaced with:
1355   // assert(!GC_locker.is_active(), "Can't be called otherwise");
1356   // But I am not placing that assert here to allow future
1357   // generality in invoking this interface.
1358   if (GC_locker::is_active()) {
1359     // A consistency test for GC_locker
1360     assert(GC_locker::needs_gc(), "Should have been set already");
1361     // Skip this foreground collection, instead
1362     // expanding the heap if necessary.
1363     // Need the free list locks for the call to free() in compute_new_size()
1364     compute_new_size();
1365     return;
1366   }
1367   acquire_control_and_collect(full, clear_all_soft_refs);
1368 }
1369 
1370 void CMSCollector::request_full_gc(unsigned int full_gc_count, GCCause::Cause cause) {
1371   GenCollectedHeap* gch = GenCollectedHeap::heap();
1372   unsigned int gc_count = gch->total_full_collections();
1373   if (gc_count == full_gc_count) {
1374     MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag);
1375     _full_gc_requested = true;
1376     _full_gc_cause = cause;
1377     CGC_lock->notify();   // nudge CMS thread
1378   } else {
1379     assert(gc_count > full_gc_count, "Error: causal loop");
1380   }
1381 }
1382 
1383 bool CMSCollector::is_external_interruption() {
1384   GCCause::Cause cause = GenCollectedHeap::heap()->gc_cause();
1385   return GCCause::is_user_requested_gc(cause) ||
1386          GCCause::is_serviceability_requested_gc(cause);
1387 }
1388 
1389 void CMSCollector::report_concurrent_mode_interruption() {
1390   if (is_external_interruption()) {
1391     if (PrintGCDetails) {
1392       gclog_or_tty->print(" (concurrent mode interrupted)");
1393     }
1394   } else {
1395     if (PrintGCDetails) {
1396       gclog_or_tty->print(" (concurrent mode failure)");
1397     }
1398     _gc_tracer_cm->report_concurrent_mode_failure();
1399   }
1400 }
1401 
1402 
1403 // The foreground and background collectors need to coordinate in order
1404 // to make sure that they do not mutually interfere with CMS collections.
1405 // When a background collection is active,
1406 // the foreground collector may need to take over (preempt) and
1407 // synchronously complete an ongoing collection. Depending on the
1408 // frequency of the background collections and the heap usage
1409 // of the application, this preemption can be seldom or frequent.
1410 // There are only certain
1411 // points in the background collection that the "collection-baton"
1412 // can be passed to the foreground collector.
1413 //
1414 // The foreground collector will wait for the baton before
1415 // starting any part of the collection.  The foreground collector
1416 // will only wait at one location.
1417 //
1418 // The background collector will yield the baton before starting a new
1419 // phase of the collection (e.g., before initial marking, marking from roots,
1420 // precleaning, final re-mark, sweep etc.)  This is normally done at the head
1421 // of the loop which switches the phases. The background collector does some
1422 // of the phases (initial mark, final re-mark) with the world stopped.
1423 // Because of locking involved in stopping the world,
1424 // the foreground collector should not block waiting for the background
1425 // collector when it is doing a stop-the-world phase.  The background
1426 // collector will yield the baton at an additional point just before
1427 // it enters a stop-the-world phase.  Once the world is stopped, the
1428 // background collector checks the phase of the collection.  If the
1429 // phase has not changed, it proceeds with the collection.  If the
1430 // phase has changed, it skips that phase of the collection.  See
1431 // the comments on the use of the Heap_lock in collect_in_background().
1432 //
1433 // Variable used in baton passing.
1434 //   _foregroundGCIsActive - Set to true by the foreground collector when
1435 //      it wants the baton.  The foreground clears it when it has finished
1436 //      the collection.
1437 //   _foregroundGCShouldWait - Set to true by the background collector
1438 //        when it is running.  The foreground collector waits while
1439 //      _foregroundGCShouldWait is true.
1440 //  CGC_lock - monitor used to protect access to the above variables
1441 //      and to notify the foreground and background collectors.
1442 //  _collectorState - current state of the CMS collection.
1443 //
1444 // The foreground collector
1445 //   acquires the CGC_lock
1446 //   sets _foregroundGCIsActive
1447 //   waits on the CGC_lock for _foregroundGCShouldWait to be false
1448 //     various locks acquired in preparation for the collection
1449 //     are released so as not to block the background collector
1450 //     that is in the midst of a collection
1451 //   proceeds with the collection
1452 //   clears _foregroundGCIsActive
1453 //   returns
1454 //
1455 // The background collector in a loop iterating on the phases of the
1456 //      collection
1457 //   acquires the CGC_lock
1458 //   sets _foregroundGCShouldWait
1459 //   if _foregroundGCIsActive is set
1460 //     clears _foregroundGCShouldWait, notifies _CGC_lock
1461 //     waits on _CGC_lock for _foregroundGCIsActive to become false
1462 //     and exits the loop.
1463 //   otherwise
1464 //     proceed with that phase of the collection
1465 //     if the phase is a stop-the-world phase,
1466 //       yield the baton once more just before enqueueing
1467 //       the stop-world CMS operation (executed by the VM thread).
1468 //   returns after all phases of the collection are done
1469 //
1470 
1471 void CMSCollector::acquire_control_and_collect(bool full,
1472         bool clear_all_soft_refs) {
1473   assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
1474   assert(!Thread::current()->is_ConcurrentGC_thread(),
1475          "shouldn't try to acquire control from self!");
1476 
1477   // Start the protocol for acquiring control of the
1478   // collection from the background collector (aka CMS thread).
1479   assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1480          "VM thread should have CMS token");
1481   // Remember the possibly interrupted state of an ongoing
1482   // concurrent collection
1483   CollectorState first_state = _collectorState;
1484 
1485   // Signal to a possibly ongoing concurrent collection that
1486   // we want to do a foreground collection.
1487   _foregroundGCIsActive = true;
1488 
1489   // release locks and wait for a notify from the background collector
1490   // releasing the locks in only necessary for phases which
1491   // do yields to improve the granularity of the collection.
1492   assert_lock_strong(bitMapLock());
1493   // We need to lock the Free list lock for the space that we are
1494   // currently collecting.
1495   assert(haveFreelistLocks(), "Must be holding free list locks");
1496   bitMapLock()->unlock();
1497   releaseFreelistLocks();
1498   {
1499     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1500     if (_foregroundGCShouldWait) {
1501       // We are going to be waiting for action for the CMS thread;
1502       // it had better not be gone (for instance at shutdown)!
1503       assert(ConcurrentMarkSweepThread::cmst() != NULL,
1504              "CMS thread must be running");
1505       // Wait here until the background collector gives us the go-ahead
1506       ConcurrentMarkSweepThread::clear_CMS_flag(
1507         ConcurrentMarkSweepThread::CMS_vm_has_token);  // release token
1508       // Get a possibly blocked CMS thread going:
1509       //   Note that we set _foregroundGCIsActive true above,
1510       //   without protection of the CGC_lock.
1511       CGC_lock->notify();
1512       assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(),
1513              "Possible deadlock");
1514       while (_foregroundGCShouldWait) {
1515         // wait for notification
1516         CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1517         // Possibility of delay/starvation here, since CMS token does
1518         // not know to give priority to VM thread? Actually, i think
1519         // there wouldn't be any delay/starvation, but the proof of
1520         // that "fact" (?) appears non-trivial. XXX 20011219YSR
1521       }
1522       ConcurrentMarkSweepThread::set_CMS_flag(
1523         ConcurrentMarkSweepThread::CMS_vm_has_token);
1524     }
1525   }
1526   // The CMS_token is already held.  Get back the other locks.
1527   assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1528          "VM thread should have CMS token");
1529   getFreelistLocks();
1530   bitMapLock()->lock_without_safepoint_check();
1531   if (TraceCMSState) {
1532     gclog_or_tty->print_cr("CMS foreground collector has asked for control "
1533       INTPTR_FORMAT " with first state %d", p2i(Thread::current()), first_state);
1534     gclog_or_tty->print_cr("    gets control with state %d", _collectorState);
1535   }
1536 
1537   // Inform cms gen if this was due to partial collection failing.
1538   // The CMS gen may use this fact to determine its expansion policy.
1539   GenCollectedHeap* gch = GenCollectedHeap::heap();
1540   if (gch->incremental_collection_will_fail(false /* don't consult_young */)) {
1541     assert(!_cmsGen->incremental_collection_failed(),
1542            "Should have been noticed, reacted to and cleared");
1543     _cmsGen->set_incremental_collection_failed();
1544   }
1545 
1546   if (first_state > Idling) {
1547     report_concurrent_mode_interruption();
1548   }
1549 
1550   set_did_compact(true);
1551 
1552   // If the collection is being acquired from the background
1553   // collector, there may be references on the discovered
1554   // references lists.  Abandon those references, since some
1555   // of them may have become unreachable after concurrent
1556   // discovery; the STW compacting collector will redo discovery
1557   // more precisely, without being subject to floating garbage.
1558   // Leaving otherwise unreachable references in the discovered
1559   // lists would require special handling.
1560   ref_processor()->disable_discovery();
1561   ref_processor()->abandon_partial_discovery();
1562   ref_processor()->verify_no_references_recorded();
1563 
1564   if (first_state > Idling) {
1565     save_heap_summary();
1566   }
1567 
1568   do_compaction_work(clear_all_soft_refs);
1569 
1570   // Has the GC time limit been exceeded?
1571   size_t max_eden_size = _young_gen->max_capacity() -
1572                          _young_gen->to()->capacity() -
1573                          _young_gen->from()->capacity();
1574   GCCause::Cause gc_cause = gch->gc_cause();
1575   size_policy()->check_gc_overhead_limit(_young_gen->used(),
1576                                          _young_gen->eden()->used(),
1577                                          _cmsGen->max_capacity(),
1578                                          max_eden_size,
1579                                          full,
1580                                          gc_cause,
1581                                          gch->collector_policy());
1582 
1583   // Reset the expansion cause, now that we just completed
1584   // a collection cycle.
1585   clear_expansion_cause();
1586   _foregroundGCIsActive = false;
1587   return;
1588 }
1589 
1590 // Resize the tenured generation
1591 // after obtaining the free list locks for the
1592 // two generations.
1593 void CMSCollector::compute_new_size() {
1594   assert_locked_or_safepoint(Heap_lock);
1595   FreelistLocker z(this);
1596   MetaspaceGC::compute_new_size();
1597   _cmsGen->compute_new_size_free_list();
1598 }
1599 
1600 // A work method used by the foreground collector to do
1601 // a mark-sweep-compact.
1602 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) {
1603   GenCollectedHeap* gch = GenCollectedHeap::heap();
1604 
1605   STWGCTimer* gc_timer = GenMarkSweep::gc_timer();
1606   gc_timer->register_gc_start();
1607 
1608   SerialOldTracer* gc_tracer = GenMarkSweep::gc_tracer();
1609   gc_tracer->report_gc_start(gch->gc_cause(), gc_timer->gc_start());
1610 
1611   GCTraceTime t("CMS:MSC ", PrintGCDetails && Verbose, true, NULL, gc_tracer->gc_id());
1612 
1613   // Temporarily widen the span of the weak reference processing to
1614   // the entire heap.
1615   MemRegion new_span(GenCollectedHeap::heap()->reserved_region());
1616   ReferenceProcessorSpanMutator rp_mut_span(ref_processor(), new_span);
1617   // Temporarily, clear the "is_alive_non_header" field of the
1618   // reference processor.
1619   ReferenceProcessorIsAliveMutator rp_mut_closure(ref_processor(), NULL);
1620   // Temporarily make reference _processing_ single threaded (non-MT).
1621   ReferenceProcessorMTProcMutator rp_mut_mt_processing(ref_processor(), false);
1622   // Temporarily make refs discovery atomic
1623   ReferenceProcessorAtomicMutator rp_mut_atomic(ref_processor(), true);
1624   // Temporarily make reference _discovery_ single threaded (non-MT)
1625   ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
1626 
1627   ref_processor()->set_enqueuing_is_done(false);
1628   ref_processor()->enable_discovery();
1629   ref_processor()->setup_policy(clear_all_soft_refs);
1630   // If an asynchronous collection finishes, the _modUnionTable is
1631   // all clear.  If we are assuming the collection from an asynchronous
1632   // collection, clear the _modUnionTable.
1633   assert(_collectorState != Idling || _modUnionTable.isAllClear(),
1634     "_modUnionTable should be clear if the baton was not passed");
1635   _modUnionTable.clear_all();
1636   assert(_collectorState != Idling || _ct->klass_rem_set()->mod_union_is_clear(),
1637     "mod union for klasses should be clear if the baton was passed");
1638   _ct->klass_rem_set()->clear_mod_union();
1639 
1640   // We must adjust the allocation statistics being maintained
1641   // in the free list space. We do so by reading and clearing
1642   // the sweep timer and updating the block flux rate estimates below.
1643   assert(!_intra_sweep_timer.is_active(), "_intra_sweep_timer should be inactive");
1644   if (_inter_sweep_timer.is_active()) {
1645     _inter_sweep_timer.stop();
1646     // Note that we do not use this sample to update the _inter_sweep_estimate.
1647     _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
1648                                             _inter_sweep_estimate.padded_average(),
1649                                             _intra_sweep_estimate.padded_average());
1650   }
1651 
1652   GenMarkSweep::invoke_at_safepoint(_cmsGen->level(),
1653     ref_processor(), clear_all_soft_refs);
1654   #ifdef ASSERT
1655     CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
1656     size_t free_size = cms_space->free();
1657     assert(free_size ==
1658            pointer_delta(cms_space->end(), cms_space->compaction_top())
1659            * HeapWordSize,
1660       "All the free space should be compacted into one chunk at top");
1661     assert(cms_space->dictionary()->total_chunk_size(
1662                                       debug_only(cms_space->freelistLock())) == 0 ||
1663            cms_space->totalSizeInIndexedFreeLists() == 0,
1664       "All the free space should be in a single chunk");
1665     size_t num = cms_space->totalCount();
1666     assert((free_size == 0 && num == 0) ||
1667            (free_size > 0  && (num == 1 || num == 2)),
1668          "There should be at most 2 free chunks after compaction");
1669   #endif // ASSERT
1670   _collectorState = Resetting;
1671   assert(_restart_addr == NULL,
1672          "Should have been NULL'd before baton was passed");
1673   reset(false /* == !concurrent */);
1674   _cmsGen->reset_after_compaction();
1675   _concurrent_cycles_since_last_unload = 0;
1676 
1677   // Clear any data recorded in the PLAB chunk arrays.
1678   if (_survivor_plab_array != NULL) {
1679     reset_survivor_plab_arrays();
1680   }
1681 
1682   // Adjust the per-size allocation stats for the next epoch.
1683   _cmsGen->cmsSpace()->endSweepFLCensus(sweep_count() /* fake */);
1684   // Restart the "inter sweep timer" for the next epoch.
1685   _inter_sweep_timer.reset();
1686   _inter_sweep_timer.start();
1687 
1688   gc_timer->register_gc_end();
1689 
1690   gc_tracer->report_gc_end(gc_timer->gc_end(), gc_timer->time_partitions());
1691 
1692   // For a mark-sweep-compact, compute_new_size() will be called
1693   // in the heap's do_collection() method.
1694 }
1695 
1696 void CMSCollector::print_eden_and_survivor_chunk_arrays() {
1697   ContiguousSpace* eden_space = _young_gen->eden();
1698   ContiguousSpace* from_space = _young_gen->from();
1699   ContiguousSpace* to_space   = _young_gen->to();
1700   // Eden
1701   if (_eden_chunk_array != NULL) {
1702     gclog_or_tty->print_cr("eden " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1703                            p2i(eden_space->bottom()), p2i(eden_space->top()),
1704                            p2i(eden_space->end()), eden_space->capacity());
1705     gclog_or_tty->print_cr("_eden_chunk_index=" SIZE_FORMAT ", "
1706                            "_eden_chunk_capacity=" SIZE_FORMAT,
1707                            _eden_chunk_index, _eden_chunk_capacity);
1708     for (size_t i = 0; i < _eden_chunk_index; i++) {
1709       gclog_or_tty->print_cr("_eden_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT,
1710                              i, p2i(_eden_chunk_array[i]));
1711     }
1712   }
1713   // Survivor
1714   if (_survivor_chunk_array != NULL) {
1715     gclog_or_tty->print_cr("survivor " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1716                            p2i(from_space->bottom()), p2i(from_space->top()),
1717                            p2i(from_space->end()), from_space->capacity());
1718     gclog_or_tty->print_cr("_survivor_chunk_index=" SIZE_FORMAT ", "
1719                            "_survivor_chunk_capacity=" SIZE_FORMAT,
1720                            _survivor_chunk_index, _survivor_chunk_capacity);
1721     for (size_t i = 0; i < _survivor_chunk_index; i++) {
1722       gclog_or_tty->print_cr("_survivor_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT,
1723                              i, p2i(_survivor_chunk_array[i]));
1724     }
1725   }
1726 }
1727 
1728 void CMSCollector::getFreelistLocks() const {
1729   // Get locks for all free lists in all generations that this
1730   // collector is responsible for
1731   _cmsGen->freelistLock()->lock_without_safepoint_check();
1732 }
1733 
1734 void CMSCollector::releaseFreelistLocks() const {
1735   // Release locks for all free lists in all generations that this
1736   // collector is responsible for
1737   _cmsGen->freelistLock()->unlock();
1738 }
1739 
1740 bool CMSCollector::haveFreelistLocks() const {
1741   // Check locks for all free lists in all generations that this
1742   // collector is responsible for
1743   assert_lock_strong(_cmsGen->freelistLock());
1744   PRODUCT_ONLY(ShouldNotReachHere());
1745   return true;
1746 }
1747 
1748 // A utility class that is used by the CMS collector to
1749 // temporarily "release" the foreground collector from its
1750 // usual obligation to wait for the background collector to
1751 // complete an ongoing phase before proceeding.
1752 class ReleaseForegroundGC: public StackObj {
1753  private:
1754   CMSCollector* _c;
1755  public:
1756   ReleaseForegroundGC(CMSCollector* c) : _c(c) {
1757     assert(_c->_foregroundGCShouldWait, "Else should not need to call");
1758     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1759     // allow a potentially blocked foreground collector to proceed
1760     _c->_foregroundGCShouldWait = false;
1761     if (_c->_foregroundGCIsActive) {
1762       CGC_lock->notify();
1763     }
1764     assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1765            "Possible deadlock");
1766   }
1767 
1768   ~ReleaseForegroundGC() {
1769     assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?");
1770     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1771     _c->_foregroundGCShouldWait = true;
1772   }
1773 };
1774 
1775 void CMSCollector::collect_in_background(GCCause::Cause cause) {
1776   assert(Thread::current()->is_ConcurrentGC_thread(),
1777     "A CMS asynchronous collection is only allowed on a CMS thread.");
1778 
1779   GenCollectedHeap* gch = GenCollectedHeap::heap();
1780   {
1781     bool safepoint_check = Mutex::_no_safepoint_check_flag;
1782     MutexLockerEx hl(Heap_lock, safepoint_check);
1783     FreelistLocker fll(this);
1784     MutexLockerEx x(CGC_lock, safepoint_check);
1785     if (_foregroundGCIsActive || !UseAsyncConcMarkSweepGC) {
1786       // The foreground collector is active or we're
1787       // not using asynchronous collections.  Skip this
1788       // background collection.
1789       assert(!_foregroundGCShouldWait, "Should be clear");
1790       return;
1791     } else {
1792       assert(_collectorState == Idling, "Should be idling before start.");
1793       _collectorState = InitialMarking;
1794       register_gc_start(cause);
1795       // Reset the expansion cause, now that we are about to begin
1796       // a new cycle.
1797       clear_expansion_cause();
1798 
1799       // Clear the MetaspaceGC flag since a concurrent collection
1800       // is starting but also clear it after the collection.
1801       MetaspaceGC::set_should_concurrent_collect(false);
1802     }
1803     // Decide if we want to enable class unloading as part of the
1804     // ensuing concurrent GC cycle.
1805     update_should_unload_classes();
1806     _full_gc_requested = false;           // acks all outstanding full gc requests
1807     _full_gc_cause = GCCause::_no_gc;
1808     // Signal that we are about to start a collection
1809     gch->increment_total_full_collections();  // ... starting a collection cycle
1810     _collection_count_start = gch->total_full_collections();
1811   }
1812 
1813   // Used for PrintGC
1814   size_t prev_used;
1815   if (PrintGC && Verbose) {
1816     prev_used = _cmsGen->used();
1817   }
1818 
1819   // The change of the collection state is normally done at this level;
1820   // the exceptions are phases that are executed while the world is
1821   // stopped.  For those phases the change of state is done while the
1822   // world is stopped.  For baton passing purposes this allows the
1823   // background collector to finish the phase and change state atomically.
1824   // The foreground collector cannot wait on a phase that is done
1825   // while the world is stopped because the foreground collector already
1826   // has the world stopped and would deadlock.
1827   while (_collectorState != Idling) {
1828     if (TraceCMSState) {
1829       gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
1830         p2i(Thread::current()), _collectorState);
1831     }
1832     // The foreground collector
1833     //   holds the Heap_lock throughout its collection.
1834     //   holds the CMS token (but not the lock)
1835     //     except while it is waiting for the background collector to yield.
1836     //
1837     // The foreground collector should be blocked (not for long)
1838     //   if the background collector is about to start a phase
1839     //   executed with world stopped.  If the background
1840     //   collector has already started such a phase, the
1841     //   foreground collector is blocked waiting for the
1842     //   Heap_lock.  The stop-world phases (InitialMarking and FinalMarking)
1843     //   are executed in the VM thread.
1844     //
1845     // The locking order is
1846     //   PendingListLock (PLL)  -- if applicable (FinalMarking)
1847     //   Heap_lock  (both this & PLL locked in VM_CMS_Operation::prologue())
1848     //   CMS token  (claimed in
1849     //                stop_world_and_do() -->
1850     //                  safepoint_synchronize() -->
1851     //                    CMSThread::synchronize())
1852 
1853     {
1854       // Check if the FG collector wants us to yield.
1855       CMSTokenSync x(true); // is cms thread
1856       if (waitForForegroundGC()) {
1857         // We yielded to a foreground GC, nothing more to be
1858         // done this round.
1859         assert(_foregroundGCShouldWait == false, "We set it to false in "
1860                "waitForForegroundGC()");
1861         if (TraceCMSState) {
1862           gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
1863             " exiting collection CMS state %d",
1864             p2i(Thread::current()), _collectorState);
1865         }
1866         return;
1867       } else {
1868         // The background collector can run but check to see if the
1869         // foreground collector has done a collection while the
1870         // background collector was waiting to get the CGC_lock
1871         // above.  If yes, break so that _foregroundGCShouldWait
1872         // is cleared before returning.
1873         if (_collectorState == Idling) {
1874           break;
1875         }
1876       }
1877     }
1878 
1879     assert(_foregroundGCShouldWait, "Foreground collector, if active, "
1880       "should be waiting");
1881 
1882     switch (_collectorState) {
1883       case InitialMarking:
1884         {
1885           ReleaseForegroundGC x(this);
1886           stats().record_cms_begin();
1887           VM_CMS_Initial_Mark initial_mark_op(this);
1888           VMThread::execute(&initial_mark_op);
1889         }
1890         // The collector state may be any legal state at this point
1891         // since the background collector may have yielded to the
1892         // foreground collector.
1893         break;
1894       case Marking:
1895         // initial marking in checkpointRootsInitialWork has been completed
1896         if (markFromRoots()) { // we were successful
1897           assert(_collectorState == Precleaning, "Collector state should "
1898             "have changed");
1899         } else {
1900           assert(_foregroundGCIsActive, "Internal state inconsistency");
1901         }
1902         break;
1903       case Precleaning:
1904         // marking from roots in markFromRoots has been completed
1905         preclean();
1906         assert(_collectorState == AbortablePreclean ||
1907                _collectorState == FinalMarking,
1908                "Collector state should have changed");
1909         break;
1910       case AbortablePreclean:
1911         abortable_preclean();
1912         assert(_collectorState == FinalMarking, "Collector state should "
1913           "have changed");
1914         break;
1915       case FinalMarking:
1916         {
1917           ReleaseForegroundGC x(this);
1918 
1919           VM_CMS_Final_Remark final_remark_op(this);
1920           VMThread::execute(&final_remark_op);
1921         }
1922         assert(_foregroundGCShouldWait, "block post-condition");
1923         break;
1924       case Sweeping:
1925         // final marking in checkpointRootsFinal has been completed
1926         sweep();
1927         assert(_collectorState == Resizing, "Collector state change "
1928           "to Resizing must be done under the free_list_lock");
1929 
1930       case Resizing: {
1931         // Sweeping has been completed...
1932         // At this point the background collection has completed.
1933         // Don't move the call to compute_new_size() down
1934         // into code that might be executed if the background
1935         // collection was preempted.
1936         {
1937           ReleaseForegroundGC x(this);   // unblock FG collection
1938           MutexLockerEx       y(Heap_lock, Mutex::_no_safepoint_check_flag);
1939           CMSTokenSync        z(true);   // not strictly needed.
1940           if (_collectorState == Resizing) {
1941             compute_new_size();
1942             save_heap_summary();
1943             _collectorState = Resetting;
1944           } else {
1945             assert(_collectorState == Idling, "The state should only change"
1946                    " because the foreground collector has finished the collection");
1947           }
1948         }
1949         break;
1950       }
1951       case Resetting:
1952         // CMS heap resizing has been completed
1953         reset(true);
1954         assert(_collectorState == Idling, "Collector state should "
1955           "have changed");
1956 
1957         MetaspaceGC::set_should_concurrent_collect(false);
1958 
1959         stats().record_cms_end();
1960         // Don't move the concurrent_phases_end() and compute_new_size()
1961         // calls to here because a preempted background collection
1962         // has it's state set to "Resetting".
1963         break;
1964       case Idling:
1965       default:
1966         ShouldNotReachHere();
1967         break;
1968     }
1969     if (TraceCMSState) {
1970       gclog_or_tty->print_cr("  Thread " INTPTR_FORMAT " done - next CMS state %d",
1971         p2i(Thread::current()), _collectorState);
1972     }
1973     assert(_foregroundGCShouldWait, "block post-condition");
1974   }
1975 
1976   // Should this be in gc_epilogue?
1977   collector_policy()->counters()->update_counters();
1978 
1979   {
1980     // Clear _foregroundGCShouldWait and, in the event that the
1981     // foreground collector is waiting, notify it, before
1982     // returning.
1983     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1984     _foregroundGCShouldWait = false;
1985     if (_foregroundGCIsActive) {
1986       CGC_lock->notify();
1987     }
1988     assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1989            "Possible deadlock");
1990   }
1991   if (TraceCMSState) {
1992     gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
1993       " exiting collection CMS state %d",
1994       p2i(Thread::current()), _collectorState);
1995   }
1996   if (PrintGC && Verbose) {
1997     _cmsGen->print_heap_change(prev_used);
1998   }
1999 }
2000 
2001 void CMSCollector::register_gc_start(GCCause::Cause cause) {
2002   _cms_start_registered = true;
2003   _gc_timer_cm->register_gc_start();
2004   _gc_tracer_cm->report_gc_start(cause, _gc_timer_cm->gc_start());
2005 }
2006 
2007 void CMSCollector::register_gc_end() {
2008   if (_cms_start_registered) {
2009     report_heap_summary(GCWhen::AfterGC);
2010 
2011     _gc_timer_cm->register_gc_end();
2012     _gc_tracer_cm->report_gc_end(_gc_timer_cm->gc_end(), _gc_timer_cm->time_partitions());
2013     _cms_start_registered = false;
2014   }
2015 }
2016 
2017 void CMSCollector::save_heap_summary() {
2018   GenCollectedHeap* gch = GenCollectedHeap::heap();
2019   _last_heap_summary = gch->create_heap_summary();
2020   _last_metaspace_summary = gch->create_metaspace_summary();
2021 }
2022 
2023 void CMSCollector::report_heap_summary(GCWhen::Type when) {
2024   _gc_tracer_cm->report_gc_heap_summary(when, _last_heap_summary);
2025   _gc_tracer_cm->report_metaspace_summary(when, _last_metaspace_summary);
2026 }
2027 
2028 bool CMSCollector::waitForForegroundGC() {
2029   bool res = false;
2030   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2031          "CMS thread should have CMS token");
2032   // Block the foreground collector until the
2033   // background collectors decides whether to
2034   // yield.
2035   MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2036   _foregroundGCShouldWait = true;
2037   if (_foregroundGCIsActive) {
2038     // The background collector yields to the
2039     // foreground collector and returns a value
2040     // indicating that it has yielded.  The foreground
2041     // collector can proceed.
2042     res = true;
2043     _foregroundGCShouldWait = false;
2044     ConcurrentMarkSweepThread::clear_CMS_flag(
2045       ConcurrentMarkSweepThread::CMS_cms_has_token);
2046     ConcurrentMarkSweepThread::set_CMS_flag(
2047       ConcurrentMarkSweepThread::CMS_cms_wants_token);
2048     // Get a possibly blocked foreground thread going
2049     CGC_lock->notify();
2050     if (TraceCMSState) {
2051       gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d",
2052         p2i(Thread::current()), _collectorState);
2053     }
2054     while (_foregroundGCIsActive) {
2055       CGC_lock->wait(Mutex::_no_safepoint_check_flag);
2056     }
2057     ConcurrentMarkSweepThread::set_CMS_flag(
2058       ConcurrentMarkSweepThread::CMS_cms_has_token);
2059     ConcurrentMarkSweepThread::clear_CMS_flag(
2060       ConcurrentMarkSweepThread::CMS_cms_wants_token);
2061   }
2062   if (TraceCMSState) {
2063     gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d",
2064       p2i(Thread::current()), _collectorState);
2065   }
2066   return res;
2067 }
2068 
2069 // Because of the need to lock the free lists and other structures in
2070 // the collector, common to all the generations that the collector is
2071 // collecting, we need the gc_prologues of individual CMS generations
2072 // delegate to their collector. It may have been simpler had the
2073 // current infrastructure allowed one to call a prologue on a
2074 // collector. In the absence of that we have the generation's
2075 // prologue delegate to the collector, which delegates back
2076 // some "local" work to a worker method in the individual generations
2077 // that it's responsible for collecting, while itself doing any
2078 // work common to all generations it's responsible for. A similar
2079 // comment applies to the  gc_epilogue()'s.
2080 // The role of the variable _between_prologue_and_epilogue is to
2081 // enforce the invocation protocol.
2082 void CMSCollector::gc_prologue(bool full) {
2083   // Call gc_prologue_work() for the CMSGen
2084   // we are responsible for.
2085 
2086   // The following locking discipline assumes that we are only called
2087   // when the world is stopped.
2088   assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption");
2089 
2090   // The CMSCollector prologue must call the gc_prologues for the
2091   // "generations" that it's responsible
2092   // for.
2093 
2094   assert(   Thread::current()->is_VM_thread()
2095          || (   CMSScavengeBeforeRemark
2096              && Thread::current()->is_ConcurrentGC_thread()),
2097          "Incorrect thread type for prologue execution");
2098 
2099   if (_between_prologue_and_epilogue) {
2100     // We have already been invoked; this is a gc_prologue delegation
2101     // from yet another CMS generation that we are responsible for, just
2102     // ignore it since all relevant work has already been done.
2103     return;
2104   }
2105 
2106   // set a bit saying prologue has been called; cleared in epilogue
2107   _between_prologue_and_epilogue = true;
2108   // Claim locks for common data structures, then call gc_prologue_work()
2109   // for each CMSGen.
2110 
2111   getFreelistLocks();   // gets free list locks on constituent spaces
2112   bitMapLock()->lock_without_safepoint_check();
2113 
2114   // Should call gc_prologue_work() for all cms gens we are responsible for
2115   bool duringMarking =    _collectorState >= Marking
2116                          && _collectorState < Sweeping;
2117 
2118   // The young collections clear the modified oops state, which tells if
2119   // there are any modified oops in the class. The remark phase also needs
2120   // that information. Tell the young collection to save the union of all
2121   // modified klasses.
2122   if (duringMarking) {
2123     _ct->klass_rem_set()->set_accumulate_modified_oops(true);
2124   }
2125 
2126   bool registerClosure = duringMarking;
2127 
2128   _cmsGen->gc_prologue_work(full, registerClosure, &_modUnionClosurePar);
2129 
2130   if (!full) {
2131     stats().record_gc0_begin();
2132   }
2133 }
2134 
2135 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) {
2136 
2137   _capacity_at_prologue = capacity();
2138   _used_at_prologue = used();
2139 
2140   // Delegate to CMScollector which knows how to coordinate between
2141   // this and any other CMS generations that it is responsible for
2142   // collecting.
2143   collector()->gc_prologue(full);
2144 }
2145 
2146 // This is a "private" interface for use by this generation's CMSCollector.
2147 // Not to be called directly by any other entity (for instance,
2148 // GenCollectedHeap, which calls the "public" gc_prologue method above).
2149 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full,
2150   bool registerClosure, ModUnionClosure* modUnionClosure) {
2151   assert(!incremental_collection_failed(), "Shouldn't be set yet");
2152   assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL,
2153     "Should be NULL");
2154   if (registerClosure) {
2155     cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure);
2156   }
2157   cmsSpace()->gc_prologue();
2158   // Clear stat counters
2159   NOT_PRODUCT(
2160     assert(_numObjectsPromoted == 0, "check");
2161     assert(_numWordsPromoted   == 0, "check");
2162     if (Verbose && PrintGC) {
2163       gclog_or_tty->print("Allocated "SIZE_FORMAT" objects, "
2164                           SIZE_FORMAT" bytes concurrently",
2165       _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord));
2166     }
2167     _numObjectsAllocated = 0;
2168     _numWordsAllocated   = 0;
2169   )
2170 }
2171 
2172 void CMSCollector::gc_epilogue(bool full) {
2173   // The following locking discipline assumes that we are only called
2174   // when the world is stopped.
2175   assert(SafepointSynchronize::is_at_safepoint(),
2176          "world is stopped assumption");
2177 
2178   // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks
2179   // if linear allocation blocks need to be appropriately marked to allow the
2180   // the blocks to be parsable. We also check here whether we need to nudge the
2181   // CMS collector thread to start a new cycle (if it's not already active).
2182   assert(   Thread::current()->is_VM_thread()
2183          || (   CMSScavengeBeforeRemark
2184              && Thread::current()->is_ConcurrentGC_thread()),
2185          "Incorrect thread type for epilogue execution");
2186 
2187   if (!_between_prologue_and_epilogue) {
2188     // We have already been invoked; this is a gc_epilogue delegation
2189     // from yet another CMS generation that we are responsible for, just
2190     // ignore it since all relevant work has already been done.
2191     return;
2192   }
2193   assert(haveFreelistLocks(), "must have freelist locks");
2194   assert_lock_strong(bitMapLock());
2195 
2196   _ct->klass_rem_set()->set_accumulate_modified_oops(false);
2197 
2198   _cmsGen->gc_epilogue_work(full);
2199 
2200   if (_collectorState == AbortablePreclean || _collectorState == Precleaning) {
2201     // in case sampling was not already enabled, enable it
2202     _start_sampling = true;
2203   }
2204   // reset _eden_chunk_array so sampling starts afresh
2205   _eden_chunk_index = 0;
2206 
2207   size_t cms_used   = _cmsGen->cmsSpace()->used();
2208 
2209   // update performance counters - this uses a special version of
2210   // update_counters() that allows the utilization to be passed as a
2211   // parameter, avoiding multiple calls to used().
2212   //
2213   _cmsGen->update_counters(cms_used);
2214 
2215   bitMapLock()->unlock();
2216   releaseFreelistLocks();
2217 
2218   if (!CleanChunkPoolAsync) {
2219     Chunk::clean_chunk_pool();
2220   }
2221 
2222   set_did_compact(false);
2223   _between_prologue_and_epilogue = false;  // ready for next cycle
2224 }
2225 
2226 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) {
2227   collector()->gc_epilogue(full);
2228 
2229   // Also reset promotion tracking in par gc thread states.
2230   for (uint i = 0; i < ParallelGCThreads; i++) {
2231     _par_gc_thread_states[i]->promo.stopTrackingPromotions(i);
2232   }
2233 }
2234 
2235 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2236   assert(!incremental_collection_failed(), "Should have been cleared");
2237   cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2238   cmsSpace()->gc_epilogue();
2239     // Print stat counters
2240   NOT_PRODUCT(
2241     assert(_numObjectsAllocated == 0, "check");
2242     assert(_numWordsAllocated == 0, "check");
2243     if (Verbose && PrintGC) {
2244       gclog_or_tty->print("Promoted "SIZE_FORMAT" objects, "
2245                           SIZE_FORMAT" bytes",
2246                  _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2247     }
2248     _numObjectsPromoted = 0;
2249     _numWordsPromoted   = 0;
2250   )
2251 
2252   if (PrintGC && Verbose) {
2253     // Call down the chain in contiguous_available needs the freelistLock
2254     // so print this out before releasing the freeListLock.
2255     gclog_or_tty->print(" Contiguous available "SIZE_FORMAT" bytes ",
2256                         contiguous_available());
2257   }
2258 }
2259 
2260 #ifndef PRODUCT
2261 bool CMSCollector::have_cms_token() {
2262   Thread* thr = Thread::current();
2263   if (thr->is_VM_thread()) {
2264     return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2265   } else if (thr->is_ConcurrentGC_thread()) {
2266     return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2267   } else if (thr->is_GC_task_thread()) {
2268     return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2269            ParGCRareEvent_lock->owned_by_self();
2270   }
2271   return false;
2272 }
2273 #endif
2274 
2275 // Check reachability of the given heap address in CMS generation,
2276 // treating all other generations as roots.
2277 bool CMSCollector::is_cms_reachable(HeapWord* addr) {
2278   // We could "guarantee" below, rather than assert, but I'll
2279   // leave these as "asserts" so that an adventurous debugger
2280   // could try this in the product build provided some subset of
2281   // the conditions were met, provided they were interested in the
2282   // results and knew that the computation below wouldn't interfere
2283   // with other concurrent computations mutating the structures
2284   // being read or written.
2285   assert(SafepointSynchronize::is_at_safepoint(),
2286          "Else mutations in object graph will make answer suspect");
2287   assert(have_cms_token(), "Should hold cms token");
2288   assert(haveFreelistLocks(), "must hold free list locks");
2289   assert_lock_strong(bitMapLock());
2290 
2291   // Clear the marking bit map array before starting, but, just
2292   // for kicks, first report if the given address is already marked
2293   gclog_or_tty->print_cr("Start: Address " PTR_FORMAT " is%s marked", p2i(addr),
2294                 _markBitMap.isMarked(addr) ? "" : " not");
2295 
2296   if (verify_after_remark()) {
2297     MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2298     bool result = verification_mark_bm()->isMarked(addr);
2299     gclog_or_tty->print_cr("TransitiveMark: Address " PTR_FORMAT " %s marked", p2i(addr),
2300                            result ? "IS" : "is NOT");
2301     return result;
2302   } else {
2303     gclog_or_tty->print_cr("Could not compute result");
2304     return false;
2305   }
2306 }
2307 
2308 
2309 void
2310 CMSCollector::print_on_error(outputStream* st) {
2311   CMSCollector* collector = ConcurrentMarkSweepGeneration::_collector;
2312   if (collector != NULL) {
2313     CMSBitMap* bitmap = &collector->_markBitMap;
2314     st->print_cr("Marking Bits: (CMSBitMap*) " PTR_FORMAT, p2i(bitmap));
2315     bitmap->print_on_error(st, " Bits: ");
2316 
2317     st->cr();
2318 
2319     CMSBitMap* mut_bitmap = &collector->_modUnionTable;
2320     st->print_cr("Mod Union Table: (CMSBitMap*) " PTR_FORMAT, p2i(mut_bitmap));
2321     mut_bitmap->print_on_error(st, " Bits: ");
2322   }
2323 }
2324 
2325 ////////////////////////////////////////////////////////
2326 // CMS Verification Support
2327 ////////////////////////////////////////////////////////
2328 // Following the remark phase, the following invariant
2329 // should hold -- each object in the CMS heap which is
2330 // marked in markBitMap() should be marked in the verification_mark_bm().
2331 
2332 class VerifyMarkedClosure: public BitMapClosure {
2333   CMSBitMap* _marks;
2334   bool       _failed;
2335 
2336  public:
2337   VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2338 
2339   bool do_bit(size_t offset) {
2340     HeapWord* addr = _marks->offsetToHeapWord(offset);
2341     if (!_marks->isMarked(addr)) {
2342       oop(addr)->print_on(gclog_or_tty);
2343       gclog_or_tty->print_cr(" ("INTPTR_FORMAT" should have been marked)", p2i(addr));
2344       _failed = true;
2345     }
2346     return true;
2347   }
2348 
2349   bool failed() { return _failed; }
2350 };
2351 
2352 bool CMSCollector::verify_after_remark(bool silent) {
2353   if (!silent) gclog_or_tty->print(" [Verifying CMS Marking... ");
2354   MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2355   static bool init = false;
2356 
2357   assert(SafepointSynchronize::is_at_safepoint(),
2358          "Else mutations in object graph will make answer suspect");
2359   assert(have_cms_token(),
2360          "Else there may be mutual interference in use of "
2361          " verification data structures");
2362   assert(_collectorState > Marking && _collectorState <= Sweeping,
2363          "Else marking info checked here may be obsolete");
2364   assert(haveFreelistLocks(), "must hold free list locks");
2365   assert_lock_strong(bitMapLock());
2366 
2367 
2368   // Allocate marking bit map if not already allocated
2369   if (!init) { // first time
2370     if (!verification_mark_bm()->allocate(_span)) {
2371       return false;
2372     }
2373     init = true;
2374   }
2375 
2376   assert(verification_mark_stack()->isEmpty(), "Should be empty");
2377 
2378   // Turn off refs discovery -- so we will be tracing through refs.
2379   // This is as intended, because by this time
2380   // GC must already have cleared any refs that need to be cleared,
2381   // and traced those that need to be marked; moreover,
2382   // the marking done here is not going to interfere in any
2383   // way with the marking information used by GC.
2384   NoRefDiscovery no_discovery(ref_processor());
2385 
2386   COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
2387 
2388   // Clear any marks from a previous round
2389   verification_mark_bm()->clear_all();
2390   assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
2391   verify_work_stacks_empty();
2392 
2393   GenCollectedHeap* gch = GenCollectedHeap::heap();
2394   gch->ensure_parsability(false);  // fill TLABs, but no need to retire them
2395   // Update the saved marks which may affect the root scans.
2396   gch->save_marks();
2397 
2398   if (CMSRemarkVerifyVariant == 1) {
2399     // In this first variant of verification, we complete
2400     // all marking, then check if the new marks-vector is
2401     // a subset of the CMS marks-vector.
2402     verify_after_remark_work_1();
2403   } else if (CMSRemarkVerifyVariant == 2) {
2404     // In this second variant of verification, we flag an error
2405     // (i.e. an object reachable in the new marks-vector not reachable
2406     // in the CMS marks-vector) immediately, also indicating the
2407     // identify of an object (A) that references the unmarked object (B) --
2408     // presumably, a mutation to A failed to be picked up by preclean/remark?
2409     verify_after_remark_work_2();
2410   } else {
2411     warning("Unrecognized value " UINTX_FORMAT " for CMSRemarkVerifyVariant",
2412             CMSRemarkVerifyVariant);
2413   }
2414   if (!silent) gclog_or_tty->print(" done] ");
2415   return true;
2416 }
2417 
2418 void CMSCollector::verify_after_remark_work_1() {
2419   ResourceMark rm;
2420   HandleMark  hm;
2421   GenCollectedHeap* gch = GenCollectedHeap::heap();
2422 
2423   // Get a clear set of claim bits for the roots processing to work with.
2424   ClassLoaderDataGraph::clear_claimed_marks();
2425 
2426   // Mark from roots one level into CMS
2427   MarkRefsIntoClosure notOlder(_span, verification_mark_bm());
2428   gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2429 
2430   gch->gen_process_roots(_cmsGen->level(),
2431                          true,   // younger gens are roots
2432                          true,   // activate StrongRootsScope
2433                          GenCollectedHeap::ScanningOption(roots_scanning_options()),
2434                          should_unload_classes(),
2435                          &notOlder,
2436                          NULL,
2437                          NULL);  // SSS: Provide correct closure
2438 
2439   // Now mark from the roots
2440   MarkFromRootsClosure markFromRootsClosure(this, _span,
2441     verification_mark_bm(), verification_mark_stack(),
2442     false /* don't yield */, true /* verifying */);
2443   assert(_restart_addr == NULL, "Expected pre-condition");
2444   verification_mark_bm()->iterate(&markFromRootsClosure);
2445   while (_restart_addr != NULL) {
2446     // Deal with stack overflow: by restarting at the indicated
2447     // address.
2448     HeapWord* ra = _restart_addr;
2449     markFromRootsClosure.reset(ra);
2450     _restart_addr = NULL;
2451     verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2452   }
2453   assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2454   verify_work_stacks_empty();
2455 
2456   // Marking completed -- now verify that each bit marked in
2457   // verification_mark_bm() is also marked in markBitMap(); flag all
2458   // errors by printing corresponding objects.
2459   VerifyMarkedClosure vcl(markBitMap());
2460   verification_mark_bm()->iterate(&vcl);
2461   if (vcl.failed()) {
2462     gclog_or_tty->print("Verification failed");
2463     gch->print_on(gclog_or_tty);
2464     fatal("CMS: failed marking verification after remark");
2465   }
2466 }
2467 
2468 class VerifyKlassOopsKlassClosure : public KlassClosure {
2469   class VerifyKlassOopsClosure : public OopClosure {
2470     CMSBitMap* _bitmap;
2471    public:
2472     VerifyKlassOopsClosure(CMSBitMap* bitmap) : _bitmap(bitmap) { }
2473     void do_oop(oop* p)       { guarantee(*p == NULL || _bitmap->isMarked((HeapWord*) *p), "Should be marked"); }
2474     void do_oop(narrowOop* p) { ShouldNotReachHere(); }
2475   } _oop_closure;
2476  public:
2477   VerifyKlassOopsKlassClosure(CMSBitMap* bitmap) : _oop_closure(bitmap) {}
2478   void do_klass(Klass* k) {
2479     k->oops_do(&_oop_closure);
2480   }
2481 };
2482 
2483 void CMSCollector::verify_after_remark_work_2() {
2484   ResourceMark rm;
2485   HandleMark  hm;
2486   GenCollectedHeap* gch = GenCollectedHeap::heap();
2487 
2488   // Get a clear set of claim bits for the roots processing to work with.
2489   ClassLoaderDataGraph::clear_claimed_marks();
2490 
2491   // Mark from roots one level into CMS
2492   MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
2493                                      markBitMap());
2494   CLDToOopClosure cld_closure(&notOlder, true);
2495 
2496   gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2497 
2498   gch->gen_process_roots(_cmsGen->level(),
2499                          true,   // younger gens are roots
2500                          true,   // activate StrongRootsScope
2501                          GenCollectedHeap::ScanningOption(roots_scanning_options()),
2502                          should_unload_classes(),
2503                          &notOlder,
2504                          NULL,
2505                          &cld_closure);
2506 
2507   // Now mark from the roots
2508   MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
2509     verification_mark_bm(), markBitMap(), verification_mark_stack());
2510   assert(_restart_addr == NULL, "Expected pre-condition");
2511   verification_mark_bm()->iterate(&markFromRootsClosure);
2512   while (_restart_addr != NULL) {
2513     // Deal with stack overflow: by restarting at the indicated
2514     // address.
2515     HeapWord* ra = _restart_addr;
2516     markFromRootsClosure.reset(ra);
2517     _restart_addr = NULL;
2518     verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2519   }
2520   assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2521   verify_work_stacks_empty();
2522 
2523   VerifyKlassOopsKlassClosure verify_klass_oops(verification_mark_bm());
2524   ClassLoaderDataGraph::classes_do(&verify_klass_oops);
2525 
2526   // Marking completed -- now verify that each bit marked in
2527   // verification_mark_bm() is also marked in markBitMap(); flag all
2528   // errors by printing corresponding objects.
2529   VerifyMarkedClosure vcl(markBitMap());
2530   verification_mark_bm()->iterate(&vcl);
2531   assert(!vcl.failed(), "Else verification above should not have succeeded");
2532 }
2533 
2534 void ConcurrentMarkSweepGeneration::save_marks() {
2535   // delegate to CMS space
2536   cmsSpace()->save_marks();
2537   for (uint i = 0; i < ParallelGCThreads; i++) {
2538     _par_gc_thread_states[i]->promo.startTrackingPromotions();
2539   }
2540 }
2541 
2542 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
2543   return cmsSpace()->no_allocs_since_save_marks();
2544 }
2545 
2546 #define CMS_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix)    \
2547                                                                 \
2548 void ConcurrentMarkSweepGeneration::                            \
2549 oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) {   \
2550   cl->set_generation(this);                                     \
2551   cmsSpace()->oop_since_save_marks_iterate##nv_suffix(cl);      \
2552   cl->reset_generation();                                       \
2553   save_marks();                                                 \
2554 }
2555 
2556 ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DEFN)
2557 
2558 void
2559 ConcurrentMarkSweepGeneration::oop_iterate(ExtendedOopClosure* cl) {
2560   if (freelistLock()->owned_by_self()) {
2561     Generation::oop_iterate(cl);
2562   } else {
2563     MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2564     Generation::oop_iterate(cl);
2565   }
2566 }
2567 
2568 void
2569 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
2570   if (freelistLock()->owned_by_self()) {
2571     Generation::object_iterate(cl);
2572   } else {
2573     MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2574     Generation::object_iterate(cl);
2575   }
2576 }
2577 
2578 void
2579 ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) {
2580   if (freelistLock()->owned_by_self()) {
2581     Generation::safe_object_iterate(cl);
2582   } else {
2583     MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2584     Generation::safe_object_iterate(cl);
2585   }
2586 }
2587 
2588 void
2589 ConcurrentMarkSweepGeneration::post_compact() {
2590 }
2591 
2592 void
2593 ConcurrentMarkSweepGeneration::prepare_for_verify() {
2594   // Fix the linear allocation blocks to look like free blocks.
2595 
2596   // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2597   // are not called when the heap is verified during universe initialization and
2598   // at vm shutdown.
2599   if (freelistLock()->owned_by_self()) {
2600     cmsSpace()->prepare_for_verify();
2601   } else {
2602     MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2603     cmsSpace()->prepare_for_verify();
2604   }
2605 }
2606 
2607 void
2608 ConcurrentMarkSweepGeneration::verify() {
2609   // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2610   // are not called when the heap is verified during universe initialization and
2611   // at vm shutdown.
2612   if (freelistLock()->owned_by_self()) {
2613     cmsSpace()->verify();
2614   } else {
2615     MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2616     cmsSpace()->verify();
2617   }
2618 }
2619 
2620 void CMSCollector::verify() {
2621   _cmsGen->verify();
2622 }
2623 
2624 #ifndef PRODUCT
2625 bool CMSCollector::overflow_list_is_empty() const {
2626   assert(_num_par_pushes >= 0, "Inconsistency");
2627   if (_overflow_list == NULL) {
2628     assert(_num_par_pushes == 0, "Inconsistency");
2629   }
2630   return _overflow_list == NULL;
2631 }
2632 
2633 // The methods verify_work_stacks_empty() and verify_overflow_empty()
2634 // merely consolidate assertion checks that appear to occur together frequently.
2635 void CMSCollector::verify_work_stacks_empty() const {
2636   assert(_markStack.isEmpty(), "Marking stack should be empty");
2637   assert(overflow_list_is_empty(), "Overflow list should be empty");
2638 }
2639 
2640 void CMSCollector::verify_overflow_empty() const {
2641   assert(overflow_list_is_empty(), "Overflow list should be empty");
2642   assert(no_preserved_marks(), "No preserved marks");
2643 }
2644 #endif // PRODUCT
2645 
2646 // Decide if we want to enable class unloading as part of the
2647 // ensuing concurrent GC cycle. We will collect and
2648 // unload classes if it's the case that:
2649 // (1) an explicit gc request has been made and the flag
2650 //     ExplicitGCInvokesConcurrentAndUnloadsClasses is set, OR
2651 // (2) (a) class unloading is enabled at the command line, and
2652 //     (b) old gen is getting really full
2653 // NOTE: Provided there is no change in the state of the heap between
2654 // calls to this method, it should have idempotent results. Moreover,
2655 // its results should be monotonically increasing (i.e. going from 0 to 1,
2656 // but not 1 to 0) between successive calls between which the heap was
2657 // not collected. For the implementation below, it must thus rely on
2658 // the property that concurrent_cycles_since_last_unload()
2659 // will not decrease unless a collection cycle happened and that
2660 // _cmsGen->is_too_full() are
2661 // themselves also monotonic in that sense. See check_monotonicity()
2662 // below.
2663 void CMSCollector::update_should_unload_classes() {
2664   _should_unload_classes = false;
2665   // Condition 1 above
2666   if (_full_gc_requested && ExplicitGCInvokesConcurrentAndUnloadsClasses) {
2667     _should_unload_classes = true;
2668   } else if (CMSClassUnloadingEnabled) { // Condition 2.a above
2669     // Disjuncts 2.b.(i,ii,iii) above
2670     _should_unload_classes = (concurrent_cycles_since_last_unload() >=
2671                               CMSClassUnloadingMaxInterval)
2672                            || _cmsGen->is_too_full();
2673   }
2674 }
2675 
2676 bool ConcurrentMarkSweepGeneration::is_too_full() const {
2677   bool res = should_concurrent_collect();
2678   res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
2679   return res;
2680 }
2681 
2682 void CMSCollector::setup_cms_unloading_and_verification_state() {
2683   const  bool should_verify =   VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
2684                              || VerifyBeforeExit;
2685   const  int  rso           =   GenCollectedHeap::SO_AllCodeCache;
2686 
2687   // We set the proper root for this CMS cycle here.
2688   if (should_unload_classes()) {   // Should unload classes this cycle
2689     remove_root_scanning_option(rso);  // Shrink the root set appropriately
2690     set_verifying(should_verify);    // Set verification state for this cycle
2691     return;                            // Nothing else needs to be done at this time
2692   }
2693 
2694   // Not unloading classes this cycle
2695   assert(!should_unload_classes(), "Inconsistency!");
2696 
2697   if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
2698     // Include symbols, strings and code cache elements to prevent their resurrection.
2699     add_root_scanning_option(rso);
2700     set_verifying(true);
2701   } else if (verifying() && !should_verify) {
2702     // We were verifying, but some verification flags got disabled.
2703     set_verifying(false);
2704     // Exclude symbols, strings and code cache elements from root scanning to
2705     // reduce IM and RM pauses.
2706     remove_root_scanning_option(rso);
2707   }
2708 }
2709 
2710 
2711 #ifndef PRODUCT
2712 HeapWord* CMSCollector::block_start(const void* p) const {
2713   const HeapWord* addr = (HeapWord*)p;
2714   if (_span.contains(p)) {
2715     if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
2716       return _cmsGen->cmsSpace()->block_start(p);
2717     }
2718   }
2719   return NULL;
2720 }
2721 #endif
2722 
2723 HeapWord*
2724 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
2725                                                    bool   tlab,
2726                                                    bool   parallel) {
2727   CMSSynchronousYieldRequest yr;
2728   assert(!tlab, "Can't deal with TLAB allocation");
2729   MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2730   expand_for_gc_cause(word_size*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_allocation);
2731   if (GCExpandToAllocateDelayMillis > 0) {
2732     os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2733   }
2734   return have_lock_and_allocate(word_size, tlab);
2735 }
2736 
2737 void ConcurrentMarkSweepGeneration::expand_for_gc_cause(
2738     size_t bytes,
2739     size_t expand_bytes,
2740     CMSExpansionCause::Cause cause)
2741 {
2742 
2743   bool success = expand(bytes, expand_bytes);
2744 
2745   // remember why we expanded; this information is used
2746   // by shouldConcurrentCollect() when making decisions on whether to start
2747   // a new CMS cycle.
2748   if (success) {
2749     set_expansion_cause(cause);
2750     if (PrintGCDetails && Verbose) {
2751       gclog_or_tty->print_cr("Expanded CMS gen for %s",
2752         CMSExpansionCause::to_string(cause));
2753     }
2754   }
2755 }
2756 
2757 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
2758   HeapWord* res = NULL;
2759   MutexLocker x(ParGCRareEvent_lock);
2760   while (true) {
2761     // Expansion by some other thread might make alloc OK now:
2762     res = ps->lab.alloc(word_sz);
2763     if (res != NULL) return res;
2764     // If there's not enough expansion space available, give up.
2765     if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
2766       return NULL;
2767     }
2768     // Otherwise, we try expansion.
2769     expand_for_gc_cause(word_sz*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_lab);
2770     // Now go around the loop and try alloc again;
2771     // A competing par_promote might beat us to the expansion space,
2772     // so we may go around the loop again if promotion fails again.
2773     if (GCExpandToAllocateDelayMillis > 0) {
2774       os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2775     }
2776   }
2777 }
2778 
2779 
2780 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
2781   PromotionInfo* promo) {
2782   MutexLocker x(ParGCRareEvent_lock);
2783   size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
2784   while (true) {
2785     // Expansion by some other thread might make alloc OK now:
2786     if (promo->ensure_spooling_space()) {
2787       assert(promo->has_spooling_space(),
2788              "Post-condition of successful ensure_spooling_space()");
2789       return true;
2790     }
2791     // If there's not enough expansion space available, give up.
2792     if (_virtual_space.uncommitted_size() < refill_size_bytes) {
2793       return false;
2794     }
2795     // Otherwise, we try expansion.
2796     expand_for_gc_cause(refill_size_bytes, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_spooling_space);
2797     // Now go around the loop and try alloc again;
2798     // A competing allocation might beat us to the expansion space,
2799     // so we may go around the loop again if allocation fails again.
2800     if (GCExpandToAllocateDelayMillis > 0) {
2801       os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2802     }
2803   }
2804 }
2805 
2806 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
2807   // Only shrink if a compaction was done so that all the free space
2808   // in the generation is in a contiguous block at the end.
2809   if (did_compact()) {
2810     CardGeneration::shrink(bytes);
2811   }
2812 }
2813 
2814 void ConcurrentMarkSweepGeneration::assert_correct_size_change_locking() {
2815   assert_locked_or_safepoint(Heap_lock);
2816 }
2817 
2818 void ConcurrentMarkSweepGeneration::shrink_free_list_by(size_t bytes) {
2819   assert_locked_or_safepoint(Heap_lock);
2820   assert_lock_strong(freelistLock());
2821   if (PrintGCDetails && Verbose) {
2822     warning("Shrinking of CMS not yet implemented");
2823   }
2824   return;
2825 }
2826 
2827 
2828 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
2829 // phases.
2830 class CMSPhaseAccounting: public StackObj {
2831  public:
2832   CMSPhaseAccounting(CMSCollector *collector,
2833                      const char *phase,
2834                      const GCId gc_id,
2835                      bool print_cr = true);
2836   ~CMSPhaseAccounting();
2837 
2838  private:
2839   CMSCollector *_collector;
2840   const char *_phase;
2841   elapsedTimer _wallclock;
2842   bool _print_cr;
2843   const GCId _gc_id;
2844 
2845  public:
2846   // Not MT-safe; so do not pass around these StackObj's
2847   // where they may be accessed by other threads.
2848   jlong wallclock_millis() {
2849     assert(_wallclock.is_active(), "Wall clock should not stop");
2850     _wallclock.stop();  // to record time
2851     jlong ret = _wallclock.milliseconds();
2852     _wallclock.start(); // restart
2853     return ret;
2854   }
2855 };
2856 
2857 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
2858                                        const char *phase,
2859                                        const GCId gc_id,
2860                                        bool print_cr) :
2861   _collector(collector), _phase(phase), _print_cr(print_cr), _gc_id(gc_id) {
2862 
2863   if (PrintCMSStatistics != 0) {
2864     _collector->resetYields();
2865   }
2866   if (PrintGCDetails) {
2867     gclog_or_tty->gclog_stamp(_gc_id);
2868     gclog_or_tty->print_cr("[%s-concurrent-%s-start]",
2869       _collector->cmsGen()->short_name(), _phase);
2870   }
2871   _collector->resetTimer();
2872   _wallclock.start();
2873   _collector->startTimer();
2874 }
2875 
2876 CMSPhaseAccounting::~CMSPhaseAccounting() {
2877   assert(_wallclock.is_active(), "Wall clock should not have stopped");
2878   _collector->stopTimer();
2879   _wallclock.stop();
2880   if (PrintGCDetails) {
2881     gclog_or_tty->gclog_stamp(_gc_id);
2882     gclog_or_tty->print("[%s-concurrent-%s: %3.3f/%3.3f secs]",
2883                  _collector->cmsGen()->short_name(),
2884                  _phase, _collector->timerValue(), _wallclock.seconds());
2885     if (_print_cr) {
2886       gclog_or_tty->cr();
2887     }
2888     if (PrintCMSStatistics != 0) {
2889       gclog_or_tty->print_cr(" (CMS-concurrent-%s yielded %d times)", _phase,
2890                     _collector->yields());
2891     }
2892   }
2893 }
2894 
2895 // CMS work
2896 
2897 // The common parts of CMSParInitialMarkTask and CMSParRemarkTask.
2898 class CMSParMarkTask : public AbstractGangTask {
2899  protected:
2900   CMSCollector*     _collector;
2901   uint              _n_workers;
2902   CMSParMarkTask(const char* name, CMSCollector* collector, uint n_workers) :
2903       AbstractGangTask(name),
2904       _collector(collector),
2905       _n_workers(n_workers) {}
2906   // Work method in support of parallel rescan ... of young gen spaces
2907   void do_young_space_rescan(uint worker_id, OopsInGenClosure* cl,
2908                              ContiguousSpace* space,
2909                              HeapWord** chunk_array, size_t chunk_top);
2910   void work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl);
2911 };
2912 
2913 // Parallel initial mark task
2914 class CMSParInitialMarkTask: public CMSParMarkTask {
2915  public:
2916   CMSParInitialMarkTask(CMSCollector* collector, uint n_workers) :
2917       CMSParMarkTask("Scan roots and young gen for initial mark in parallel",
2918                      collector, n_workers) {}
2919   void work(uint worker_id);
2920 };
2921 
2922 // Checkpoint the roots into this generation from outside
2923 // this generation. [Note this initial checkpoint need only
2924 // be approximate -- we'll do a catch up phase subsequently.]
2925 void CMSCollector::checkpointRootsInitial() {
2926   assert(_collectorState == InitialMarking, "Wrong collector state");
2927   check_correct_thread_executing();
2928   TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
2929 
2930   save_heap_summary();
2931   report_heap_summary(GCWhen::BeforeGC);
2932 
2933   ReferenceProcessor* rp = ref_processor();
2934   assert(_restart_addr == NULL, "Control point invariant");
2935   {
2936     // acquire locks for subsequent manipulations
2937     MutexLockerEx x(bitMapLock(),
2938                     Mutex::_no_safepoint_check_flag);
2939     checkpointRootsInitialWork();
2940     // enable ("weak") refs discovery
2941     rp->enable_discovery();
2942     _collectorState = Marking;
2943   }
2944 }
2945 
2946 void CMSCollector::checkpointRootsInitialWork() {
2947   assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
2948   assert(_collectorState == InitialMarking, "just checking");
2949 
2950   // If there has not been a GC[n-1] since last GC[n] cycle completed,
2951   // precede our marking with a collection of all
2952   // younger generations to keep floating garbage to a minimum.
2953   // XXX: we won't do this for now -- it's an optimization to be done later.
2954 
2955   // already have locks
2956   assert_lock_strong(bitMapLock());
2957   assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
2958 
2959   // Setup the verification and class unloading state for this
2960   // CMS collection cycle.
2961   setup_cms_unloading_and_verification_state();
2962 
2963   NOT_PRODUCT(GCTraceTime t("\ncheckpointRootsInitialWork",
2964     PrintGCDetails && Verbose, true, _gc_timer_cm, _gc_tracer_cm->gc_id());)
2965 
2966   // Reset all the PLAB chunk arrays if necessary.
2967   if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
2968     reset_survivor_plab_arrays();
2969   }
2970 
2971   ResourceMark rm;
2972   HandleMark  hm;
2973 
2974   MarkRefsIntoClosure notOlder(_span, &_markBitMap);
2975   GenCollectedHeap* gch = GenCollectedHeap::heap();
2976 
2977   verify_work_stacks_empty();
2978   verify_overflow_empty();
2979 
2980   gch->ensure_parsability(false);  // fill TLABs, but no need to retire them
2981   // Update the saved marks which may affect the root scans.
2982   gch->save_marks();
2983 
2984   // weak reference processing has not started yet.
2985   ref_processor()->set_enqueuing_is_done(false);
2986 
2987   // Need to remember all newly created CLDs,
2988   // so that we can guarantee that the remark finds them.
2989   ClassLoaderDataGraph::remember_new_clds(true);
2990 
2991   // Whenever a CLD is found, it will be claimed before proceeding to mark
2992   // the klasses. The claimed marks need to be cleared before marking starts.
2993   ClassLoaderDataGraph::clear_claimed_marks();
2994 
2995   if (CMSPrintEdenSurvivorChunks) {
2996     print_eden_and_survivor_chunk_arrays();
2997   }
2998 
2999   {
3000     COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
3001     if (CMSParallelInitialMarkEnabled) {
3002       // The parallel version.
3003       FlexibleWorkGang* workers = gch->workers();
3004       assert(workers != NULL, "Need parallel worker threads.");
3005       uint n_workers = workers->active_workers();
3006       CMSParInitialMarkTask tsk(this, n_workers);
3007       gch->set_par_threads(n_workers);
3008       initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
3009       if (n_workers > 1) {
3010         StrongRootsScope srs;
3011         workers->run_task(&tsk);
3012       } else {
3013         StrongRootsScope srs;
3014         tsk.work(0);
3015       }
3016       gch->set_par_threads(0);
3017     } else {
3018       // The serial version.
3019       CLDToOopClosure cld_closure(&notOlder, true);
3020       gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3021       gch->gen_process_roots(_cmsGen->level(),
3022                              true,   // younger gens are roots
3023                              true,   // activate StrongRootsScope
3024                              GenCollectedHeap::ScanningOption(roots_scanning_options()),
3025                              should_unload_classes(),
3026                              &notOlder,
3027                              NULL,
3028                              &cld_closure);
3029     }
3030   }
3031 
3032   // Clear mod-union table; it will be dirtied in the prologue of
3033   // CMS generation per each younger generation collection.
3034 
3035   assert(_modUnionTable.isAllClear(),
3036        "Was cleared in most recent final checkpoint phase"
3037        " or no bits are set in the gc_prologue before the start of the next "
3038        "subsequent marking phase.");
3039 
3040   assert(_ct->klass_rem_set()->mod_union_is_clear(), "Must be");
3041 
3042   // Save the end of the used_region of the constituent generations
3043   // to be used to limit the extent of sweep in each generation.
3044   save_sweep_limits();
3045   verify_overflow_empty();
3046 }
3047 
3048 bool CMSCollector::markFromRoots() {
3049   // we might be tempted to assert that:
3050   // assert(!SafepointSynchronize::is_at_safepoint(),
3051   //        "inconsistent argument?");
3052   // However that wouldn't be right, because it's possible that
3053   // a safepoint is indeed in progress as a younger generation
3054   // stop-the-world GC happens even as we mark in this generation.
3055   assert(_collectorState == Marking, "inconsistent state?");
3056   check_correct_thread_executing();
3057   verify_overflow_empty();
3058 
3059   // Weak ref discovery note: We may be discovering weak
3060   // refs in this generation concurrent (but interleaved) with
3061   // weak ref discovery by a younger generation collector.
3062 
3063   CMSTokenSyncWithLocks ts(true, bitMapLock());
3064   TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3065   CMSPhaseAccounting pa(this, "mark", _gc_tracer_cm->gc_id(), !PrintGCDetails);
3066   bool res = markFromRootsWork();
3067   if (res) {
3068     _collectorState = Precleaning;
3069   } else { // We failed and a foreground collection wants to take over
3070     assert(_foregroundGCIsActive, "internal state inconsistency");
3071     assert(_restart_addr == NULL,  "foreground will restart from scratch");
3072     if (PrintGCDetails) {
3073       gclog_or_tty->print_cr("bailing out to foreground collection");
3074     }
3075   }
3076   verify_overflow_empty();
3077   return res;
3078 }
3079 
3080 bool CMSCollector::markFromRootsWork() {
3081   // iterate over marked bits in bit map, doing a full scan and mark
3082   // from these roots using the following algorithm:
3083   // . if oop is to the right of the current scan pointer,
3084   //   mark corresponding bit (we'll process it later)
3085   // . else (oop is to left of current scan pointer)
3086   //   push oop on marking stack
3087   // . drain the marking stack
3088 
3089   // Note that when we do a marking step we need to hold the
3090   // bit map lock -- recall that direct allocation (by mutators)
3091   // and promotion (by younger generation collectors) is also
3092   // marking the bit map. [the so-called allocate live policy.]
3093   // Because the implementation of bit map marking is not
3094   // robust wrt simultaneous marking of bits in the same word,
3095   // we need to make sure that there is no such interference
3096   // between concurrent such updates.
3097 
3098   // already have locks
3099   assert_lock_strong(bitMapLock());
3100 
3101   verify_work_stacks_empty();
3102   verify_overflow_empty();
3103   bool result = false;
3104   if (CMSConcurrentMTEnabled && ConcGCThreads > 0) {
3105     result = do_marking_mt();
3106   } else {
3107     result = do_marking_st();
3108   }
3109   return result;
3110 }
3111 
3112 // Forward decl
3113 class CMSConcMarkingTask;
3114 
3115 class CMSConcMarkingTerminator: public ParallelTaskTerminator {
3116   CMSCollector*       _collector;
3117   CMSConcMarkingTask* _task;
3118  public:
3119   virtual void yield();
3120 
3121   // "n_threads" is the number of threads to be terminated.
3122   // "queue_set" is a set of work queues of other threads.
3123   // "collector" is the CMS collector associated with this task terminator.
3124   // "yield" indicates whether we need the gang as a whole to yield.
3125   CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
3126     ParallelTaskTerminator(n_threads, queue_set),
3127     _collector(collector) { }
3128 
3129   void set_task(CMSConcMarkingTask* task) {
3130     _task = task;
3131   }
3132 };
3133 
3134 class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator {
3135   CMSConcMarkingTask* _task;
3136  public:
3137   bool should_exit_termination();
3138   void set_task(CMSConcMarkingTask* task) {
3139     _task = task;
3140   }
3141 };
3142 
3143 // MT Concurrent Marking Task
3144 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3145   CMSCollector* _collector;
3146   uint          _n_workers;       // requested/desired # workers
3147   bool          _result;
3148   CompactibleFreeListSpace*  _cms_space;
3149   char          _pad_front[64];   // padding to ...
3150   HeapWord*     _global_finger;   // ... avoid sharing cache line
3151   char          _pad_back[64];
3152   HeapWord*     _restart_addr;
3153 
3154   //  Exposed here for yielding support
3155   Mutex* const _bit_map_lock;
3156 
3157   // The per thread work queues, available here for stealing
3158   OopTaskQueueSet*  _task_queues;
3159 
3160   // Termination (and yielding) support
3161   CMSConcMarkingTerminator _term;
3162   CMSConcMarkingTerminatorTerminator _term_term;
3163 
3164  public:
3165   CMSConcMarkingTask(CMSCollector* collector,
3166                  CompactibleFreeListSpace* cms_space,
3167                  YieldingFlexibleWorkGang* workers,
3168                  OopTaskQueueSet* task_queues):
3169     YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3170     _collector(collector),
3171     _cms_space(cms_space),
3172     _n_workers(0), _result(true),
3173     _task_queues(task_queues),
3174     _term(_n_workers, task_queues, _collector),
3175     _bit_map_lock(collector->bitMapLock())
3176   {
3177     _requested_size = _n_workers;
3178     _term.set_task(this);
3179     _term_term.set_task(this);
3180     _restart_addr = _global_finger = _cms_space->bottom();
3181   }
3182 
3183 
3184   OopTaskQueueSet* task_queues()  { return _task_queues; }
3185 
3186   OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3187 
3188   HeapWord** global_finger_addr() { return &_global_finger; }
3189 
3190   CMSConcMarkingTerminator* terminator() { return &_term; }
3191 
3192   virtual void set_for_termination(uint active_workers) {
3193     terminator()->reset_for_reuse(active_workers);
3194   }
3195 
3196   void work(uint worker_id);
3197   bool should_yield() {
3198     return    ConcurrentMarkSweepThread::should_yield()
3199            && !_collector->foregroundGCIsActive();
3200   }
3201 
3202   virtual void coordinator_yield();  // stuff done by coordinator
3203   bool result() { return _result; }
3204 
3205   void reset(HeapWord* ra) {
3206     assert(_global_finger >= _cms_space->end(),  "Postcondition of ::work(i)");
3207     _restart_addr = _global_finger = ra;
3208     _term.reset_for_reuse();
3209   }
3210 
3211   static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3212                                            OopTaskQueue* work_q);
3213 
3214  private:
3215   void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3216   void do_work_steal(int i);
3217   void bump_global_finger(HeapWord* f);
3218 };
3219 
3220 bool CMSConcMarkingTerminatorTerminator::should_exit_termination() {
3221   assert(_task != NULL, "Error");
3222   return _task->yielding();
3223   // Note that we do not need the disjunct || _task->should_yield() above
3224   // because we want terminating threads to yield only if the task
3225   // is already in the midst of yielding, which happens only after at least one
3226   // thread has yielded.
3227 }
3228 
3229 void CMSConcMarkingTerminator::yield() {
3230   if (_task->should_yield()) {
3231     _task->yield();
3232   } else {
3233     ParallelTaskTerminator::yield();
3234   }
3235 }
3236 
3237 ////////////////////////////////////////////////////////////////
3238 // Concurrent Marking Algorithm Sketch
3239 ////////////////////////////////////////////////////////////////
3240 // Until all tasks exhausted (both spaces):
3241 // -- claim next available chunk
3242 // -- bump global finger via CAS
3243 // -- find first object that starts in this chunk
3244 //    and start scanning bitmap from that position
3245 // -- scan marked objects for oops
3246 // -- CAS-mark target, and if successful:
3247 //    . if target oop is above global finger (volatile read)
3248 //      nothing to do
3249 //    . if target oop is in chunk and above local finger
3250 //        then nothing to do
3251 //    . else push on work-queue
3252 // -- Deal with possible overflow issues:
3253 //    . local work-queue overflow causes stuff to be pushed on
3254 //      global (common) overflow queue
3255 //    . always first empty local work queue
3256 //    . then get a batch of oops from global work queue if any
3257 //    . then do work stealing
3258 // -- When all tasks claimed (both spaces)
3259 //    and local work queue empty,
3260 //    then in a loop do:
3261 //    . check global overflow stack; steal a batch of oops and trace
3262 //    . try to steal from other threads oif GOS is empty
3263 //    . if neither is available, offer termination
3264 // -- Terminate and return result
3265 //
3266 void CMSConcMarkingTask::work(uint worker_id) {
3267   elapsedTimer _timer;
3268   ResourceMark rm;
3269   HandleMark hm;
3270 
3271   DEBUG_ONLY(_collector->verify_overflow_empty();)
3272 
3273   // Before we begin work, our work queue should be empty
3274   assert(work_queue(worker_id)->size() == 0, "Expected to be empty");
3275   // Scan the bitmap covering _cms_space, tracing through grey objects.
3276   _timer.start();
3277   do_scan_and_mark(worker_id, _cms_space);
3278   _timer.stop();
3279   if (PrintCMSStatistics != 0) {
3280     gclog_or_tty->print_cr("Finished cms space scanning in %dth thread: %3.3f sec",
3281       worker_id, _timer.seconds());
3282       // XXX: need xxx/xxx type of notation, two timers
3283   }
3284 
3285   // ... do work stealing
3286   _timer.reset();
3287   _timer.start();
3288   do_work_steal(worker_id);
3289   _timer.stop();
3290   if (PrintCMSStatistics != 0) {
3291     gclog_or_tty->print_cr("Finished work stealing in %dth thread: %3.3f sec",
3292       worker_id, _timer.seconds());
3293       // XXX: need xxx/xxx type of notation, two timers
3294   }
3295   assert(_collector->_markStack.isEmpty(), "Should have been emptied");
3296   assert(work_queue(worker_id)->size() == 0, "Should have been emptied");
3297   // Note that under the current task protocol, the
3298   // following assertion is true even of the spaces
3299   // expanded since the completion of the concurrent
3300   // marking. XXX This will likely change under a strict
3301   // ABORT semantics.
3302   // After perm removal the comparison was changed to
3303   // greater than or equal to from strictly greater than.
3304   // Before perm removal the highest address sweep would
3305   // have been at the end of perm gen but now is at the
3306   // end of the tenured gen.
3307   assert(_global_finger >=  _cms_space->end(),
3308          "All tasks have been completed");
3309   DEBUG_ONLY(_collector->verify_overflow_empty();)
3310 }
3311 
3312 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
3313   HeapWord* read = _global_finger;
3314   HeapWord* cur  = read;
3315   while (f > read) {
3316     cur = read;
3317     read = (HeapWord*) Atomic::cmpxchg_ptr(f, &_global_finger, cur);
3318     if (cur == read) {
3319       // our cas succeeded
3320       assert(_global_finger >= f, "protocol consistency");
3321       break;
3322     }
3323   }
3324 }
3325 
3326 // This is really inefficient, and should be redone by
3327 // using (not yet available) block-read and -write interfaces to the
3328 // stack and the work_queue. XXX FIX ME !!!
3329 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3330                                                       OopTaskQueue* work_q) {
3331   // Fast lock-free check
3332   if (ovflw_stk->length() == 0) {
3333     return false;
3334   }
3335   assert(work_q->size() == 0, "Shouldn't steal");
3336   MutexLockerEx ml(ovflw_stk->par_lock(),
3337                    Mutex::_no_safepoint_check_flag);
3338   // Grab up to 1/4 the size of the work queue
3339   size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
3340                     (size_t)ParGCDesiredObjsFromOverflowList);
3341   num = MIN2(num, ovflw_stk->length());
3342   for (int i = (int) num; i > 0; i--) {
3343     oop cur = ovflw_stk->pop();
3344     assert(cur != NULL, "Counted wrong?");
3345     work_q->push(cur);
3346   }
3347   return num > 0;
3348 }
3349 
3350 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
3351   SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
3352   int n_tasks = pst->n_tasks();
3353   // We allow that there may be no tasks to do here because
3354   // we are restarting after a stack overflow.
3355   assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
3356   uint nth_task = 0;
3357 
3358   HeapWord* aligned_start = sp->bottom();
3359   if (sp->used_region().contains(_restart_addr)) {
3360     // Align down to a card boundary for the start of 0th task
3361     // for this space.
3362     aligned_start =
3363       (HeapWord*)align_size_down((uintptr_t)_restart_addr,
3364                                  CardTableModRefBS::card_size);
3365   }
3366 
3367   size_t chunk_size = sp->marking_task_size();
3368   while (!pst->is_task_claimed(/* reference */ nth_task)) {
3369     // Having claimed the nth task in this space,
3370     // compute the chunk that it corresponds to:
3371     MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
3372                                aligned_start + (nth_task+1)*chunk_size);
3373     // Try and bump the global finger via a CAS;
3374     // note that we need to do the global finger bump
3375     // _before_ taking the intersection below, because
3376     // the task corresponding to that region will be
3377     // deemed done even if the used_region() expands
3378     // because of allocation -- as it almost certainly will
3379     // during start-up while the threads yield in the
3380     // closure below.
3381     HeapWord* finger = span.end();
3382     bump_global_finger(finger);   // atomically
3383     // There are null tasks here corresponding to chunks
3384     // beyond the "top" address of the space.
3385     span = span.intersection(sp->used_region());
3386     if (!span.is_empty()) {  // Non-null task
3387       HeapWord* prev_obj;
3388       assert(!span.contains(_restart_addr) || nth_task == 0,
3389              "Inconsistency");
3390       if (nth_task == 0) {
3391         // For the 0th task, we'll not need to compute a block_start.
3392         if (span.contains(_restart_addr)) {
3393           // In the case of a restart because of stack overflow,
3394           // we might additionally skip a chunk prefix.
3395           prev_obj = _restart_addr;
3396         } else {
3397           prev_obj = span.start();
3398         }
3399       } else {
3400         // We want to skip the first object because
3401         // the protocol is to scan any object in its entirety
3402         // that _starts_ in this span; a fortiori, any
3403         // object starting in an earlier span is scanned
3404         // as part of an earlier claimed task.
3405         // Below we use the "careful" version of block_start
3406         // so we do not try to navigate uninitialized objects.
3407         prev_obj = sp->block_start_careful(span.start());
3408         // Below we use a variant of block_size that uses the
3409         // Printezis bits to avoid waiting for allocated
3410         // objects to become initialized/parsable.
3411         while (prev_obj < span.start()) {
3412           size_t sz = sp->block_size_no_stall(prev_obj, _collector);
3413           if (sz > 0) {
3414             prev_obj += sz;
3415           } else {
3416             // In this case we may end up doing a bit of redundant
3417             // scanning, but that appears unavoidable, short of
3418             // locking the free list locks; see bug 6324141.
3419             break;
3420           }
3421         }
3422       }
3423       if (prev_obj < span.end()) {
3424         MemRegion my_span = MemRegion(prev_obj, span.end());
3425         // Do the marking work within a non-empty span --
3426         // the last argument to the constructor indicates whether the
3427         // iteration should be incremental with periodic yields.
3428         Par_MarkFromRootsClosure cl(this, _collector, my_span,
3429                                     &_collector->_markBitMap,
3430                                     work_queue(i),
3431                                     &_collector->_markStack);
3432         _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
3433       } // else nothing to do for this task
3434     }   // else nothing to do for this task
3435   }
3436   // We'd be tempted to assert here that since there are no
3437   // more tasks left to claim in this space, the global_finger
3438   // must exceed space->top() and a fortiori space->end(). However,
3439   // that would not quite be correct because the bumping of
3440   // global_finger occurs strictly after the claiming of a task,
3441   // so by the time we reach here the global finger may not yet
3442   // have been bumped up by the thread that claimed the last
3443   // task.
3444   pst->all_tasks_completed();
3445 }
3446 
3447 class Par_ConcMarkingClosure: public MetadataAwareOopClosure {
3448  private:
3449   CMSCollector* _collector;
3450   CMSConcMarkingTask* _task;
3451   MemRegion     _span;
3452   CMSBitMap*    _bit_map;
3453   CMSMarkStack* _overflow_stack;
3454   OopTaskQueue* _work_queue;
3455  protected:
3456   DO_OOP_WORK_DEFN
3457  public:
3458   Par_ConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue,
3459                          CMSBitMap* bit_map, CMSMarkStack* overflow_stack):
3460     MetadataAwareOopClosure(collector->ref_processor()),
3461     _collector(collector),
3462     _task(task),
3463     _span(collector->_span),
3464     _work_queue(work_queue),
3465     _bit_map(bit_map),
3466     _overflow_stack(overflow_stack)
3467   { }
3468   virtual void do_oop(oop* p);
3469   virtual void do_oop(narrowOop* p);
3470 
3471   void trim_queue(size_t max);
3472   void handle_stack_overflow(HeapWord* lost);
3473   void do_yield_check() {
3474     if (_task->should_yield()) {
3475       _task->yield();
3476     }
3477   }
3478 };
3479 
3480 // Grey object scanning during work stealing phase --
3481 // the salient assumption here is that any references
3482 // that are in these stolen objects being scanned must
3483 // already have been initialized (else they would not have
3484 // been published), so we do not need to check for
3485 // uninitialized objects before pushing here.
3486 void Par_ConcMarkingClosure::do_oop(oop obj) {
3487   assert(obj->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
3488   HeapWord* addr = (HeapWord*)obj;
3489   // Check if oop points into the CMS generation
3490   // and is not marked
3491   if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
3492     // a white object ...
3493     // If we manage to "claim" the object, by being the
3494     // first thread to mark it, then we push it on our
3495     // marking stack
3496     if (_bit_map->par_mark(addr)) {     // ... now grey
3497       // push on work queue (grey set)
3498       bool simulate_overflow = false;
3499       NOT_PRODUCT(
3500         if (CMSMarkStackOverflowALot &&
3501             _collector->simulate_overflow()) {
3502           // simulate a stack overflow
3503           simulate_overflow = true;
3504         }
3505       )
3506       if (simulate_overflow ||
3507           !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
3508         // stack overflow
3509         if (PrintCMSStatistics != 0) {
3510           gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
3511                                  SIZE_FORMAT, _overflow_stack->capacity());
3512         }
3513         // We cannot assert that the overflow stack is full because
3514         // it may have been emptied since.
3515         assert(simulate_overflow ||
3516                _work_queue->size() == _work_queue->max_elems(),
3517               "Else push should have succeeded");
3518         handle_stack_overflow(addr);
3519       }
3520     } // Else, some other thread got there first
3521     do_yield_check();
3522   }
3523 }
3524 
3525 void Par_ConcMarkingClosure::do_oop(oop* p)       { Par_ConcMarkingClosure::do_oop_work(p); }
3526 void Par_ConcMarkingClosure::do_oop(narrowOop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
3527 
3528 void Par_ConcMarkingClosure::trim_queue(size_t max) {
3529   while (_work_queue->size() > max) {
3530     oop new_oop;
3531     if (_work_queue->pop_local(new_oop)) {
3532       assert(new_oop->is_oop(), "Should be an oop");
3533       assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
3534       assert(_span.contains((HeapWord*)new_oop), "Not in span");
3535       new_oop->oop_iterate(this);  // do_oop() above
3536       do_yield_check();
3537     }
3538   }
3539 }
3540 
3541 // Upon stack overflow, we discard (part of) the stack,
3542 // remembering the least address amongst those discarded
3543 // in CMSCollector's _restart_address.
3544 void Par_ConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
3545   // We need to do this under a mutex to prevent other
3546   // workers from interfering with the work done below.
3547   MutexLockerEx ml(_overflow_stack->par_lock(),
3548                    Mutex::_no_safepoint_check_flag);
3549   // Remember the least grey address discarded
3550   HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
3551   _collector->lower_restart_addr(ra);
3552   _overflow_stack->reset();  // discard stack contents
3553   _overflow_stack->expand(); // expand the stack if possible
3554 }
3555 
3556 
3557 void CMSConcMarkingTask::do_work_steal(int i) {
3558   OopTaskQueue* work_q = work_queue(i);
3559   oop obj_to_scan;
3560   CMSBitMap* bm = &(_collector->_markBitMap);
3561   CMSMarkStack* ovflw = &(_collector->_markStack);
3562   int* seed = _collector->hash_seed(i);
3563   Par_ConcMarkingClosure cl(_collector, this, work_q, bm, ovflw);
3564   while (true) {
3565     cl.trim_queue(0);
3566     assert(work_q->size() == 0, "Should have been emptied above");
3567     if (get_work_from_overflow_stack(ovflw, work_q)) {
3568       // Can't assert below because the work obtained from the
3569       // overflow stack may already have been stolen from us.
3570       // assert(work_q->size() > 0, "Work from overflow stack");
3571       continue;
3572     } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
3573       assert(obj_to_scan->is_oop(), "Should be an oop");
3574       assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
3575       obj_to_scan->oop_iterate(&cl);
3576     } else if (terminator()->offer_termination(&_term_term)) {
3577       assert(work_q->size() == 0, "Impossible!");
3578       break;
3579     } else if (yielding() || should_yield()) {
3580       yield();
3581     }
3582   }
3583 }
3584 
3585 // This is run by the CMS (coordinator) thread.
3586 void CMSConcMarkingTask::coordinator_yield() {
3587   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3588          "CMS thread should hold CMS token");
3589   // First give up the locks, then yield, then re-lock
3590   // We should probably use a constructor/destructor idiom to
3591   // do this unlock/lock or modify the MutexUnlocker class to
3592   // serve our purpose. XXX
3593   assert_lock_strong(_bit_map_lock);
3594   _bit_map_lock->unlock();
3595   ConcurrentMarkSweepThread::desynchronize(true);
3596   _collector->stopTimer();
3597   if (PrintCMSStatistics != 0) {
3598     _collector->incrementYields();
3599   }
3600 
3601   // It is possible for whichever thread initiated the yield request
3602   // not to get a chance to wake up and take the bitmap lock between
3603   // this thread releasing it and reacquiring it. So, while the
3604   // should_yield() flag is on, let's sleep for a bit to give the
3605   // other thread a chance to wake up. The limit imposed on the number
3606   // of iterations is defensive, to avoid any unforseen circumstances
3607   // putting us into an infinite loop. Since it's always been this
3608   // (coordinator_yield()) method that was observed to cause the
3609   // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
3610   // which is by default non-zero. For the other seven methods that
3611   // also perform the yield operation, as are using a different
3612   // parameter (CMSYieldSleepCount) which is by default zero. This way we
3613   // can enable the sleeping for those methods too, if necessary.
3614   // See 6442774.
3615   //
3616   // We really need to reconsider the synchronization between the GC
3617   // thread and the yield-requesting threads in the future and we
3618   // should really use wait/notify, which is the recommended
3619   // way of doing this type of interaction. Additionally, we should
3620   // consolidate the eight methods that do the yield operation and they
3621   // are almost identical into one for better maintainability and
3622   // readability. See 6445193.
3623   //
3624   // Tony 2006.06.29
3625   for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
3626                    ConcurrentMarkSweepThread::should_yield() &&
3627                    !CMSCollector::foregroundGCIsActive(); ++i) {
3628     os::sleep(Thread::current(), 1, false);
3629   }
3630 
3631   ConcurrentMarkSweepThread::synchronize(true);
3632   _bit_map_lock->lock_without_safepoint_check();
3633   _collector->startTimer();
3634 }
3635 
3636 bool CMSCollector::do_marking_mt() {
3637   assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition");
3638   uint num_workers = AdaptiveSizePolicy::calc_active_conc_workers(conc_workers()->total_workers(),
3639                                                                   conc_workers()->active_workers(),
3640                                                                   Threads::number_of_non_daemon_threads());
3641   conc_workers()->set_active_workers(num_workers);
3642 
3643   CompactibleFreeListSpace* cms_space  = _cmsGen->cmsSpace();
3644 
3645   CMSConcMarkingTask tsk(this,
3646                          cms_space,
3647                          conc_workers(),
3648                          task_queues());
3649 
3650   // Since the actual number of workers we get may be different
3651   // from the number we requested above, do we need to do anything different
3652   // below? In particular, may be we need to subclass the SequantialSubTasksDone
3653   // class?? XXX
3654   cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
3655 
3656   // Refs discovery is already non-atomic.
3657   assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
3658   assert(ref_processor()->discovery_is_mt(), "Discovery should be MT");
3659   conc_workers()->start_task(&tsk);
3660   while (tsk.yielded()) {
3661     tsk.coordinator_yield();
3662     conc_workers()->continue_task(&tsk);
3663   }
3664   // If the task was aborted, _restart_addr will be non-NULL
3665   assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
3666   while (_restart_addr != NULL) {
3667     // XXX For now we do not make use of ABORTED state and have not
3668     // yet implemented the right abort semantics (even in the original
3669     // single-threaded CMS case). That needs some more investigation
3670     // and is deferred for now; see CR# TBF. 07252005YSR. XXX
3671     assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
3672     // If _restart_addr is non-NULL, a marking stack overflow
3673     // occurred; we need to do a fresh marking iteration from the
3674     // indicated restart address.
3675     if (_foregroundGCIsActive) {
3676       // We may be running into repeated stack overflows, having
3677       // reached the limit of the stack size, while making very
3678       // slow forward progress. It may be best to bail out and
3679       // let the foreground collector do its job.
3680       // Clear _restart_addr, so that foreground GC
3681       // works from scratch. This avoids the headache of
3682       // a "rescan" which would otherwise be needed because
3683       // of the dirty mod union table & card table.
3684       _restart_addr = NULL;
3685       return false;
3686     }
3687     // Adjust the task to restart from _restart_addr
3688     tsk.reset(_restart_addr);
3689     cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
3690                   _restart_addr);
3691     _restart_addr = NULL;
3692     // Get the workers going again
3693     conc_workers()->start_task(&tsk);
3694     while (tsk.yielded()) {
3695       tsk.coordinator_yield();
3696       conc_workers()->continue_task(&tsk);
3697     }
3698   }
3699   assert(tsk.completed(), "Inconsistency");
3700   assert(tsk.result() == true, "Inconsistency");
3701   return true;
3702 }
3703 
3704 bool CMSCollector::do_marking_st() {
3705   ResourceMark rm;
3706   HandleMark   hm;
3707 
3708   // Temporarily make refs discovery single threaded (non-MT)
3709   ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
3710   MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
3711     &_markStack, CMSYield);
3712   // the last argument to iterate indicates whether the iteration
3713   // should be incremental with periodic yields.
3714   _markBitMap.iterate(&markFromRootsClosure);
3715   // If _restart_addr is non-NULL, a marking stack overflow
3716   // occurred; we need to do a fresh iteration from the
3717   // indicated restart address.
3718   while (_restart_addr != NULL) {
3719     if (_foregroundGCIsActive) {
3720       // We may be running into repeated stack overflows, having
3721       // reached the limit of the stack size, while making very
3722       // slow forward progress. It may be best to bail out and
3723       // let the foreground collector do its job.
3724       // Clear _restart_addr, so that foreground GC
3725       // works from scratch. This avoids the headache of
3726       // a "rescan" which would otherwise be needed because
3727       // of the dirty mod union table & card table.
3728       _restart_addr = NULL;
3729       return false;  // indicating failure to complete marking
3730     }
3731     // Deal with stack overflow:
3732     // we restart marking from _restart_addr
3733     HeapWord* ra = _restart_addr;
3734     markFromRootsClosure.reset(ra);
3735     _restart_addr = NULL;
3736     _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
3737   }
3738   return true;
3739 }
3740 
3741 void CMSCollector::preclean() {
3742   check_correct_thread_executing();
3743   assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
3744   verify_work_stacks_empty();
3745   verify_overflow_empty();
3746   _abort_preclean = false;
3747   if (CMSPrecleaningEnabled) {
3748     if (!CMSEdenChunksRecordAlways) {
3749       _eden_chunk_index = 0;
3750     }
3751     size_t used = get_eden_used();
3752     size_t capacity = get_eden_capacity();
3753     // Don't start sampling unless we will get sufficiently
3754     // many samples.
3755     if (used < (capacity/(CMSScheduleRemarkSamplingRatio * 100)
3756                 * CMSScheduleRemarkEdenPenetration)) {
3757       _start_sampling = true;
3758     } else {
3759       _start_sampling = false;
3760     }
3761     TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3762     CMSPhaseAccounting pa(this, "preclean", _gc_tracer_cm->gc_id(), !PrintGCDetails);
3763     preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
3764   }
3765   CMSTokenSync x(true); // is cms thread
3766   if (CMSPrecleaningEnabled) {
3767     sample_eden();
3768     _collectorState = AbortablePreclean;
3769   } else {
3770     _collectorState = FinalMarking;
3771   }
3772   verify_work_stacks_empty();
3773   verify_overflow_empty();
3774 }
3775 
3776 // Try and schedule the remark such that young gen
3777 // occupancy is CMSScheduleRemarkEdenPenetration %.
3778 void CMSCollector::abortable_preclean() {
3779   check_correct_thread_executing();
3780   assert(CMSPrecleaningEnabled,  "Inconsistent control state");
3781   assert(_collectorState == AbortablePreclean, "Inconsistent control state");
3782 
3783   // If Eden's current occupancy is below this threshold,
3784   // immediately schedule the remark; else preclean
3785   // past the next scavenge in an effort to
3786   // schedule the pause as described above. By choosing
3787   // CMSScheduleRemarkEdenSizeThreshold >= max eden size
3788   // we will never do an actual abortable preclean cycle.
3789   if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
3790     TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3791     CMSPhaseAccounting pa(this, "abortable-preclean", _gc_tracer_cm->gc_id(), !PrintGCDetails);
3792     // We need more smarts in the abortable preclean
3793     // loop below to deal with cases where allocation
3794     // in young gen is very very slow, and our precleaning
3795     // is running a losing race against a horde of
3796     // mutators intent on flooding us with CMS updates
3797     // (dirty cards).
3798     // One, admittedly dumb, strategy is to give up
3799     // after a certain number of abortable precleaning loops
3800     // or after a certain maximum time. We want to make
3801     // this smarter in the next iteration.
3802     // XXX FIX ME!!! YSR
3803     size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
3804     while (!(should_abort_preclean() ||
3805              ConcurrentMarkSweepThread::should_terminate())) {
3806       workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
3807       cumworkdone += workdone;
3808       loops++;
3809       // Voluntarily terminate abortable preclean phase if we have
3810       // been at it for too long.
3811       if ((CMSMaxAbortablePrecleanLoops != 0) &&
3812           loops >= CMSMaxAbortablePrecleanLoops) {
3813         if (PrintGCDetails) {
3814           gclog_or_tty->print(" CMS: abort preclean due to loops ");
3815         }
3816         break;
3817       }
3818       if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
3819         if (PrintGCDetails) {
3820           gclog_or_tty->print(" CMS: abort preclean due to time ");
3821         }
3822         break;
3823       }
3824       // If we are doing little work each iteration, we should
3825       // take a short break.
3826       if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
3827         // Sleep for some time, waiting for work to accumulate
3828         stopTimer();
3829         cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
3830         startTimer();
3831         waited++;
3832       }
3833     }
3834     if (PrintCMSStatistics > 0) {
3835       gclog_or_tty->print(" [" SIZE_FORMAT " iterations, " SIZE_FORMAT " waits, " SIZE_FORMAT " cards)] ",
3836                           loops, waited, cumworkdone);
3837     }
3838   }
3839   CMSTokenSync x(true); // is cms thread
3840   if (_collectorState != Idling) {
3841     assert(_collectorState == AbortablePreclean,
3842            "Spontaneous state transition?");
3843     _collectorState = FinalMarking;
3844   } // Else, a foreground collection completed this CMS cycle.
3845   return;
3846 }
3847 
3848 // Respond to an Eden sampling opportunity
3849 void CMSCollector::sample_eden() {
3850   // Make sure a young gc cannot sneak in between our
3851   // reading and recording of a sample.
3852   assert(Thread::current()->is_ConcurrentGC_thread(),
3853          "Only the cms thread may collect Eden samples");
3854   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3855          "Should collect samples while holding CMS token");
3856   if (!_start_sampling) {
3857     return;
3858   }
3859   // When CMSEdenChunksRecordAlways is true, the eden chunk array
3860   // is populated by the young generation.
3861   if (_eden_chunk_array != NULL && !CMSEdenChunksRecordAlways) {
3862     if (_eden_chunk_index < _eden_chunk_capacity) {
3863       _eden_chunk_array[_eden_chunk_index] = *_top_addr;   // take sample
3864       assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
3865              "Unexpected state of Eden");
3866       // We'd like to check that what we just sampled is an oop-start address;
3867       // however, we cannot do that here since the object may not yet have been
3868       // initialized. So we'll instead do the check when we _use_ this sample
3869       // later.
3870       if (_eden_chunk_index == 0 ||
3871           (pointer_delta(_eden_chunk_array[_eden_chunk_index],
3872                          _eden_chunk_array[_eden_chunk_index-1])
3873            >= CMSSamplingGrain)) {
3874         _eden_chunk_index++;  // commit sample
3875       }
3876     }
3877   }
3878   if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
3879     size_t used = get_eden_used();
3880     size_t capacity = get_eden_capacity();
3881     assert(used <= capacity, "Unexpected state of Eden");
3882     if (used >  (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
3883       _abort_preclean = true;
3884     }
3885   }
3886 }
3887 
3888 
3889 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
3890   assert(_collectorState == Precleaning ||
3891          _collectorState == AbortablePreclean, "incorrect state");
3892   ResourceMark rm;
3893   HandleMark   hm;
3894 
3895   // Precleaning is currently not MT but the reference processor
3896   // may be set for MT.  Disable it temporarily here.
3897   ReferenceProcessor* rp = ref_processor();
3898   ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false);
3899 
3900   // Do one pass of scrubbing the discovered reference lists
3901   // to remove any reference objects with strongly-reachable
3902   // referents.
3903   if (clean_refs) {
3904     CMSPrecleanRefsYieldClosure yield_cl(this);
3905     assert(rp->span().equals(_span), "Spans should be equal");
3906     CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
3907                                    &_markStack, true /* preclean */);
3908     CMSDrainMarkingStackClosure complete_trace(this,
3909                                    _span, &_markBitMap, &_markStack,
3910                                    &keep_alive, true /* preclean */);
3911 
3912     // We don't want this step to interfere with a young
3913     // collection because we don't want to take CPU
3914     // or memory bandwidth away from the young GC threads
3915     // (which may be as many as there are CPUs).
3916     // Note that we don't need to protect ourselves from
3917     // interference with mutators because they can't
3918     // manipulate the discovered reference lists nor affect
3919     // the computed reachability of the referents, the
3920     // only properties manipulated by the precleaning
3921     // of these reference lists.
3922     stopTimer();
3923     CMSTokenSyncWithLocks x(true /* is cms thread */,
3924                             bitMapLock());
3925     startTimer();
3926     sample_eden();
3927 
3928     // The following will yield to allow foreground
3929     // collection to proceed promptly. XXX YSR:
3930     // The code in this method may need further
3931     // tweaking for better performance and some restructuring
3932     // for cleaner interfaces.
3933     GCTimer *gc_timer = NULL; // Currently not tracing concurrent phases
3934     rp->preclean_discovered_references(
3935           rp->is_alive_non_header(), &keep_alive, &complete_trace, &yield_cl,
3936           gc_timer, _gc_tracer_cm->gc_id());
3937   }
3938 
3939   if (clean_survivor) {  // preclean the active survivor space(s)
3940     PushAndMarkClosure pam_cl(this, _span, ref_processor(),
3941                              &_markBitMap, &_modUnionTable,
3942                              &_markStack, true /* precleaning phase */);
3943     stopTimer();
3944     CMSTokenSyncWithLocks ts(true /* is cms thread */,
3945                              bitMapLock());
3946     startTimer();
3947     unsigned int before_count =
3948       GenCollectedHeap::heap()->total_collections();
3949     SurvivorSpacePrecleanClosure
3950       sss_cl(this, _span, &_markBitMap, &_markStack,
3951              &pam_cl, before_count, CMSYield);
3952     _young_gen->from()->object_iterate_careful(&sss_cl);
3953     _young_gen->to()->object_iterate_careful(&sss_cl);
3954   }
3955   MarkRefsIntoAndScanClosure
3956     mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
3957              &_markStack, this, CMSYield,
3958              true /* precleaning phase */);
3959   // CAUTION: The following closure has persistent state that may need to
3960   // be reset upon a decrease in the sequence of addresses it
3961   // processes.
3962   ScanMarkedObjectsAgainCarefullyClosure
3963     smoac_cl(this, _span,
3964       &_markBitMap, &_markStack, &mrias_cl, CMSYield);
3965 
3966   // Preclean dirty cards in ModUnionTable and CardTable using
3967   // appropriate convergence criterion;
3968   // repeat CMSPrecleanIter times unless we find that
3969   // we are losing.
3970   assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
3971   assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
3972          "Bad convergence multiplier");
3973   assert(CMSPrecleanThreshold >= 100,
3974          "Unreasonably low CMSPrecleanThreshold");
3975 
3976   size_t numIter, cumNumCards, lastNumCards, curNumCards;
3977   for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
3978        numIter < CMSPrecleanIter;
3979        numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
3980     curNumCards  = preclean_mod_union_table(_cmsGen, &smoac_cl);
3981     if (Verbose && PrintGCDetails) {
3982       gclog_or_tty->print(" (modUnionTable: " SIZE_FORMAT " cards)", curNumCards);
3983     }
3984     // Either there are very few dirty cards, so re-mark
3985     // pause will be small anyway, or our pre-cleaning isn't
3986     // that much faster than the rate at which cards are being
3987     // dirtied, so we might as well stop and re-mark since
3988     // precleaning won't improve our re-mark time by much.
3989     if (curNumCards <= CMSPrecleanThreshold ||
3990         (numIter > 0 &&
3991          (curNumCards * CMSPrecleanDenominator >
3992          lastNumCards * CMSPrecleanNumerator))) {
3993       numIter++;
3994       cumNumCards += curNumCards;
3995       break;
3996     }
3997   }
3998 
3999   preclean_klasses(&mrias_cl, _cmsGen->freelistLock());
4000 
4001   curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
4002   cumNumCards += curNumCards;
4003   if (PrintGCDetails && PrintCMSStatistics != 0) {
4004     gclog_or_tty->print_cr(" (cardTable: " SIZE_FORMAT " cards, re-scanned " SIZE_FORMAT " cards, " SIZE_FORMAT " iterations)",
4005                   curNumCards, cumNumCards, numIter);
4006   }
4007   return cumNumCards;   // as a measure of useful work done
4008 }
4009 
4010 // PRECLEANING NOTES:
4011 // Precleaning involves:
4012 // . reading the bits of the modUnionTable and clearing the set bits.
4013 // . For the cards corresponding to the set bits, we scan the
4014 //   objects on those cards. This means we need the free_list_lock
4015 //   so that we can safely iterate over the CMS space when scanning
4016 //   for oops.
4017 // . When we scan the objects, we'll be both reading and setting
4018 //   marks in the marking bit map, so we'll need the marking bit map.
4019 // . For protecting _collector_state transitions, we take the CGC_lock.
4020 //   Note that any races in the reading of of card table entries by the
4021 //   CMS thread on the one hand and the clearing of those entries by the
4022 //   VM thread or the setting of those entries by the mutator threads on the
4023 //   other are quite benign. However, for efficiency it makes sense to keep
4024 //   the VM thread from racing with the CMS thread while the latter is
4025 //   dirty card info to the modUnionTable. We therefore also use the
4026 //   CGC_lock to protect the reading of the card table and the mod union
4027 //   table by the CM thread.
4028 // . We run concurrently with mutator updates, so scanning
4029 //   needs to be done carefully  -- we should not try to scan
4030 //   potentially uninitialized objects.
4031 //
4032 // Locking strategy: While holding the CGC_lock, we scan over and
4033 // reset a maximal dirty range of the mod union / card tables, then lock
4034 // the free_list_lock and bitmap lock to do a full marking, then
4035 // release these locks; and repeat the cycle. This allows for a
4036 // certain amount of fairness in the sharing of these locks between
4037 // the CMS collector on the one hand, and the VM thread and the
4038 // mutators on the other.
4039 
4040 // NOTE: preclean_mod_union_table() and preclean_card_table()
4041 // further below are largely identical; if you need to modify
4042 // one of these methods, please check the other method too.
4043 
4044 size_t CMSCollector::preclean_mod_union_table(
4045   ConcurrentMarkSweepGeneration* gen,
4046   ScanMarkedObjectsAgainCarefullyClosure* cl) {
4047   verify_work_stacks_empty();
4048   verify_overflow_empty();
4049 
4050   // strategy: starting with the first card, accumulate contiguous
4051   // ranges of dirty cards; clear these cards, then scan the region
4052   // covered by these cards.
4053 
4054   // Since all of the MUT is committed ahead, we can just use
4055   // that, in case the generations expand while we are precleaning.
4056   // It might also be fine to just use the committed part of the
4057   // generation, but we might potentially miss cards when the
4058   // generation is rapidly expanding while we are in the midst
4059   // of precleaning.
4060   HeapWord* startAddr = gen->reserved().start();
4061   HeapWord* endAddr   = gen->reserved().end();
4062 
4063   cl->setFreelistLock(gen->freelistLock());   // needed for yielding
4064 
4065   size_t numDirtyCards, cumNumDirtyCards;
4066   HeapWord *nextAddr, *lastAddr;
4067   for (cumNumDirtyCards = numDirtyCards = 0,
4068        nextAddr = lastAddr = startAddr;
4069        nextAddr < endAddr;
4070        nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4071 
4072     ResourceMark rm;
4073     HandleMark   hm;
4074 
4075     MemRegion dirtyRegion;
4076     {
4077       stopTimer();
4078       // Potential yield point
4079       CMSTokenSync ts(true);
4080       startTimer();
4081       sample_eden();
4082       // Get dirty region starting at nextOffset (inclusive),
4083       // simultaneously clearing it.
4084       dirtyRegion =
4085         _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
4086       assert(dirtyRegion.start() >= nextAddr,
4087              "returned region inconsistent?");
4088     }
4089     // Remember where the next search should begin.
4090     // The returned region (if non-empty) is a right open interval,
4091     // so lastOffset is obtained from the right end of that
4092     // interval.
4093     lastAddr = dirtyRegion.end();
4094     // Should do something more transparent and less hacky XXX
4095     numDirtyCards =
4096       _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
4097 
4098     // We'll scan the cards in the dirty region (with periodic
4099     // yields for foreground GC as needed).
4100     if (!dirtyRegion.is_empty()) {
4101       assert(numDirtyCards > 0, "consistency check");
4102       HeapWord* stop_point = NULL;
4103       stopTimer();
4104       // Potential yield point
4105       CMSTokenSyncWithLocks ts(true, gen->freelistLock(),
4106                                bitMapLock());
4107       startTimer();
4108       {
4109         verify_work_stacks_empty();
4110         verify_overflow_empty();
4111         sample_eden();
4112         stop_point =
4113           gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4114       }
4115       if (stop_point != NULL) {
4116         // The careful iteration stopped early either because it found an
4117         // uninitialized object, or because we were in the midst of an
4118         // "abortable preclean", which should now be aborted. Redirty
4119         // the bits corresponding to the partially-scanned or unscanned
4120         // cards. We'll either restart at the next block boundary or
4121         // abort the preclean.
4122         assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4123                "Should only be AbortablePreclean.");
4124         _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
4125         if (should_abort_preclean()) {
4126           break; // out of preclean loop
4127         } else {
4128           // Compute the next address at which preclean should pick up;
4129           // might need bitMapLock in order to read P-bits.
4130           lastAddr = next_card_start_after_block(stop_point);
4131         }
4132       }
4133     } else {
4134       assert(lastAddr == endAddr, "consistency check");
4135       assert(numDirtyCards == 0, "consistency check");
4136       break;
4137     }
4138   }
4139   verify_work_stacks_empty();
4140   verify_overflow_empty();
4141   return cumNumDirtyCards;
4142 }
4143 
4144 // NOTE: preclean_mod_union_table() above and preclean_card_table()
4145 // below are largely identical; if you need to modify
4146 // one of these methods, please check the other method too.
4147 
4148 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* gen,
4149   ScanMarkedObjectsAgainCarefullyClosure* cl) {
4150   // strategy: it's similar to precleamModUnionTable above, in that
4151   // we accumulate contiguous ranges of dirty cards, mark these cards
4152   // precleaned, then scan the region covered by these cards.
4153   HeapWord* endAddr   = (HeapWord*)(gen->_virtual_space.high());
4154   HeapWord* startAddr = (HeapWord*)(gen->_virtual_space.low());
4155 
4156   cl->setFreelistLock(gen->freelistLock());   // needed for yielding
4157 
4158   size_t numDirtyCards, cumNumDirtyCards;
4159   HeapWord *lastAddr, *nextAddr;
4160 
4161   for (cumNumDirtyCards = numDirtyCards = 0,
4162        nextAddr = lastAddr = startAddr;
4163        nextAddr < endAddr;
4164        nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4165 
4166     ResourceMark rm;
4167     HandleMark   hm;
4168 
4169     MemRegion dirtyRegion;
4170     {
4171       // See comments in "Precleaning notes" above on why we
4172       // do this locking. XXX Could the locking overheads be
4173       // too high when dirty cards are sparse? [I don't think so.]
4174       stopTimer();
4175       CMSTokenSync x(true); // is cms thread
4176       startTimer();
4177       sample_eden();
4178       // Get and clear dirty region from card table
4179       dirtyRegion = _ct->ct_bs()->dirty_card_range_after_reset(
4180                                     MemRegion(nextAddr, endAddr),
4181                                     true,
4182                                     CardTableModRefBS::precleaned_card_val());
4183 
4184       assert(dirtyRegion.start() >= nextAddr,
4185              "returned region inconsistent?");
4186     }
4187     lastAddr = dirtyRegion.end();
4188     numDirtyCards =
4189       dirtyRegion.word_size()/CardTableModRefBS::card_size_in_words;
4190 
4191     if (!dirtyRegion.is_empty()) {
4192       stopTimer();
4193       CMSTokenSyncWithLocks ts(true, gen->freelistLock(), bitMapLock());
4194       startTimer();
4195       sample_eden();
4196       verify_work_stacks_empty();
4197       verify_overflow_empty();
4198       HeapWord* stop_point =
4199         gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4200       if (stop_point != NULL) {
4201         assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4202                "Should only be AbortablePreclean.");
4203         _ct->ct_bs()->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4204         if (should_abort_preclean()) {
4205           break; // out of preclean loop
4206         } else {
4207           // Compute the next address at which preclean should pick up.
4208           lastAddr = next_card_start_after_block(stop_point);
4209         }
4210       }
4211     } else {
4212       break;
4213     }
4214   }
4215   verify_work_stacks_empty();
4216   verify_overflow_empty();
4217   return cumNumDirtyCards;
4218 }
4219 
4220 class PrecleanKlassClosure : public KlassClosure {
4221   KlassToOopClosure _cm_klass_closure;
4222  public:
4223   PrecleanKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4224   void do_klass(Klass* k) {
4225     if (k->has_accumulated_modified_oops()) {
4226       k->clear_accumulated_modified_oops();
4227 
4228       _cm_klass_closure.do_klass(k);
4229     }
4230   }
4231 };
4232 
4233 // The freelist lock is needed to prevent asserts, is it really needed?
4234 void CMSCollector::preclean_klasses(MarkRefsIntoAndScanClosure* cl, Mutex* freelistLock) {
4235 
4236   cl->set_freelistLock(freelistLock);
4237 
4238   CMSTokenSyncWithLocks ts(true, freelistLock, bitMapLock());
4239 
4240   // SSS: Add equivalent to ScanMarkedObjectsAgainCarefullyClosure::do_yield_check and should_abort_preclean?
4241   // SSS: We should probably check if precleaning should be aborted, at suitable intervals?
4242   PrecleanKlassClosure preclean_klass_closure(cl);
4243   ClassLoaderDataGraph::classes_do(&preclean_klass_closure);
4244 
4245   verify_work_stacks_empty();
4246   verify_overflow_empty();
4247 }
4248 
4249 void CMSCollector::checkpointRootsFinal() {
4250   assert(_collectorState == FinalMarking, "incorrect state transition?");
4251   check_correct_thread_executing();
4252   // world is stopped at this checkpoint
4253   assert(SafepointSynchronize::is_at_safepoint(),
4254          "world should be stopped");
4255   TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
4256 
4257   verify_work_stacks_empty();
4258   verify_overflow_empty();
4259 
4260   if (PrintGCDetails) {
4261     gclog_or_tty->print("[YG occupancy: "SIZE_FORMAT" K ("SIZE_FORMAT" K)]",
4262                         _young_gen->used() / K,
4263                         _young_gen->capacity() / K);
4264   }
4265   {
4266     if (CMSScavengeBeforeRemark) {
4267       GenCollectedHeap* gch = GenCollectedHeap::heap();
4268       // Temporarily set flag to false, GCH->do_collection will
4269       // expect it to be false and set to true
4270       FlagSetting fl(gch->_is_gc_active, false);
4271       NOT_PRODUCT(GCTraceTime t("Scavenge-Before-Remark",
4272         PrintGCDetails && Verbose, true, _gc_timer_cm, _gc_tracer_cm->gc_id());)
4273       int level = _cmsGen->level() - 1;
4274       if (level >= 0) {
4275         gch->do_collection(true,        // full (i.e. force, see below)
4276                            false,       // !clear_all_soft_refs
4277                            0,           // size
4278                            false,       // is_tlab
4279                            level        // max_level
4280                           );
4281       }
4282     }
4283     FreelistLocker x(this);
4284     MutexLockerEx y(bitMapLock(),
4285                     Mutex::_no_safepoint_check_flag);
4286     checkpointRootsFinalWork();
4287   }
4288   verify_work_stacks_empty();
4289   verify_overflow_empty();
4290 }
4291 
4292 void CMSCollector::checkpointRootsFinalWork() {
4293   NOT_PRODUCT(GCTraceTime tr("checkpointRootsFinalWork", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());)
4294 
4295   assert(haveFreelistLocks(), "must have free list locks");
4296   assert_lock_strong(bitMapLock());
4297 
4298   ResourceMark rm;
4299   HandleMark   hm;
4300 
4301   GenCollectedHeap* gch = GenCollectedHeap::heap();
4302 
4303   if (should_unload_classes()) {
4304     CodeCache::gc_prologue();
4305   }
4306   assert(haveFreelistLocks(), "must have free list locks");
4307   assert_lock_strong(bitMapLock());
4308 
4309   // We might assume that we need not fill TLAB's when
4310   // CMSScavengeBeforeRemark is set, because we may have just done
4311   // a scavenge which would have filled all TLAB's -- and besides
4312   // Eden would be empty. This however may not always be the case --
4313   // for instance although we asked for a scavenge, it may not have
4314   // happened because of a JNI critical section. We probably need
4315   // a policy for deciding whether we can in that case wait until
4316   // the critical section releases and then do the remark following
4317   // the scavenge, and skip it here. In the absence of that policy,
4318   // or of an indication of whether the scavenge did indeed occur,
4319   // we cannot rely on TLAB's having been filled and must do
4320   // so here just in case a scavenge did not happen.
4321   gch->ensure_parsability(false);  // fill TLAB's, but no need to retire them
4322   // Update the saved marks which may affect the root scans.
4323   gch->save_marks();
4324 
4325   if (CMSPrintEdenSurvivorChunks) {
4326     print_eden_and_survivor_chunk_arrays();
4327   }
4328 
4329   {
4330     COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
4331 
4332     // Note on the role of the mod union table:
4333     // Since the marker in "markFromRoots" marks concurrently with
4334     // mutators, it is possible for some reachable objects not to have been
4335     // scanned. For instance, an only reference to an object A was
4336     // placed in object B after the marker scanned B. Unless B is rescanned,
4337     // A would be collected. Such updates to references in marked objects
4338     // are detected via the mod union table which is the set of all cards
4339     // dirtied since the first checkpoint in this GC cycle and prior to
4340     // the most recent young generation GC, minus those cleaned up by the
4341     // concurrent precleaning.
4342     if (CMSParallelRemarkEnabled) {
4343       GCTraceTime t("Rescan (parallel) ", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
4344       do_remark_parallel();
4345     } else {
4346       GCTraceTime t("Rescan (non-parallel) ", PrintGCDetails, false,
4347                   _gc_timer_cm, _gc_tracer_cm->gc_id());
4348       do_remark_non_parallel();
4349     }
4350   }
4351   verify_work_stacks_empty();
4352   verify_overflow_empty();
4353 
4354   {
4355     NOT_PRODUCT(GCTraceTime ts("refProcessingWork", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());)
4356     refProcessingWork();
4357   }
4358   verify_work_stacks_empty();
4359   verify_overflow_empty();
4360 
4361   if (should_unload_classes()) {
4362     CodeCache::gc_epilogue();
4363   }
4364   JvmtiExport::gc_epilogue();
4365 
4366   // If we encountered any (marking stack / work queue) overflow
4367   // events during the current CMS cycle, take appropriate
4368   // remedial measures, where possible, so as to try and avoid
4369   // recurrence of that condition.
4370   assert(_markStack.isEmpty(), "No grey objects");
4371   size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
4372                      _ser_kac_ovflw        + _ser_kac_preclean_ovflw;
4373   if (ser_ovflw > 0) {
4374     if (PrintCMSStatistics != 0) {
4375       gclog_or_tty->print_cr("Marking stack overflow (benign) "
4376         "(pmc_pc="SIZE_FORMAT", pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT
4377         ", kac_preclean="SIZE_FORMAT")",
4378         _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw,
4379         _ser_kac_ovflw, _ser_kac_preclean_ovflw);
4380     }
4381     _markStack.expand();
4382     _ser_pmc_remark_ovflw = 0;
4383     _ser_pmc_preclean_ovflw = 0;
4384     _ser_kac_preclean_ovflw = 0;
4385     _ser_kac_ovflw = 0;
4386   }
4387   if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
4388     if (PrintCMSStatistics != 0) {
4389       gclog_or_tty->print_cr("Work queue overflow (benign) "
4390         "(pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT")",
4391         _par_pmc_remark_ovflw, _par_kac_ovflw);
4392     }
4393     _par_pmc_remark_ovflw = 0;
4394     _par_kac_ovflw = 0;
4395   }
4396   if (PrintCMSStatistics != 0) {
4397      if (_markStack._hit_limit > 0) {
4398        gclog_or_tty->print_cr(" (benign) Hit max stack size limit ("SIZE_FORMAT")",
4399                               _markStack._hit_limit);
4400      }
4401      if (_markStack._failed_double > 0) {
4402        gclog_or_tty->print_cr(" (benign) Failed stack doubling ("SIZE_FORMAT"),"
4403                               " current capacity "SIZE_FORMAT,
4404                               _markStack._failed_double,
4405                               _markStack.capacity());
4406      }
4407   }
4408   _markStack._hit_limit = 0;
4409   _markStack._failed_double = 0;
4410 
4411   if ((VerifyAfterGC || VerifyDuringGC) &&
4412       GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
4413     verify_after_remark();
4414   }
4415 
4416   _gc_tracer_cm->report_object_count_after_gc(&_is_alive_closure);
4417 
4418   // Change under the freelistLocks.
4419   _collectorState = Sweeping;
4420   // Call isAllClear() under bitMapLock
4421   assert(_modUnionTable.isAllClear(),
4422       "Should be clear by end of the final marking");
4423   assert(_ct->klass_rem_set()->mod_union_is_clear(),
4424       "Should be clear by end of the final marking");
4425 }
4426 
4427 void CMSParInitialMarkTask::work(uint worker_id) {
4428   elapsedTimer _timer;
4429   ResourceMark rm;
4430   HandleMark   hm;
4431 
4432   // ---------- scan from roots --------------
4433   _timer.start();
4434   GenCollectedHeap* gch = GenCollectedHeap::heap();
4435   Par_MarkRefsIntoClosure par_mri_cl(_collector->_span, &(_collector->_markBitMap));
4436 
4437   // ---------- young gen roots --------------
4438   {
4439     work_on_young_gen_roots(worker_id, &par_mri_cl);
4440     _timer.stop();
4441     if (PrintCMSStatistics != 0) {
4442       gclog_or_tty->print_cr(
4443         "Finished young gen initial mark scan work in %dth thread: %3.3f sec",
4444         worker_id, _timer.seconds());
4445     }
4446   }
4447 
4448   // ---------- remaining roots --------------
4449   _timer.reset();
4450   _timer.start();
4451 
4452   CLDToOopClosure cld_closure(&par_mri_cl, true);
4453 
4454   gch->gen_process_roots(_collector->_cmsGen->level(),
4455                          false,     // yg was scanned above
4456                          false,     // this is parallel code
4457                          GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4458                          _collector->should_unload_classes(),
4459                          &par_mri_cl,
4460                          NULL,
4461                          &cld_closure);
4462   assert(_collector->should_unload_classes()
4463          || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4464          "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4465   _timer.stop();
4466   if (PrintCMSStatistics != 0) {
4467     gclog_or_tty->print_cr(
4468       "Finished remaining root initial mark scan work in %dth thread: %3.3f sec",
4469       worker_id, _timer.seconds());
4470   }
4471 }
4472 
4473 // Parallel remark task
4474 class CMSParRemarkTask: public CMSParMarkTask {
4475   CompactibleFreeListSpace* _cms_space;
4476 
4477   // The per-thread work queues, available here for stealing.
4478   OopTaskQueueSet*       _task_queues;
4479   ParallelTaskTerminator _term;
4480 
4481  public:
4482   // A value of 0 passed to n_workers will cause the number of
4483   // workers to be taken from the active workers in the work gang.
4484   CMSParRemarkTask(CMSCollector* collector,
4485                    CompactibleFreeListSpace* cms_space,
4486                    uint n_workers, FlexibleWorkGang* workers,
4487                    OopTaskQueueSet* task_queues):
4488     CMSParMarkTask("Rescan roots and grey objects in parallel",
4489                    collector, n_workers),
4490     _cms_space(cms_space),
4491     _task_queues(task_queues),
4492     _term(n_workers, task_queues) { }
4493 
4494   OopTaskQueueSet* task_queues() { return _task_queues; }
4495 
4496   OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
4497 
4498   ParallelTaskTerminator* terminator() { return &_term; }
4499   uint n_workers() { return _n_workers; }
4500 
4501   void work(uint worker_id);
4502 
4503  private:
4504   // ... of  dirty cards in old space
4505   void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
4506                                   Par_MarkRefsIntoAndScanClosure* cl);
4507 
4508   // ... work stealing for the above
4509   void do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl, int* seed);
4510 };
4511 
4512 class RemarkKlassClosure : public KlassClosure {
4513   KlassToOopClosure _cm_klass_closure;
4514  public:
4515   RemarkKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4516   void do_klass(Klass* k) {
4517     // Check if we have modified any oops in the Klass during the concurrent marking.
4518     if (k->has_accumulated_modified_oops()) {
4519       k->clear_accumulated_modified_oops();
4520 
4521       // We could have transfered the current modified marks to the accumulated marks,
4522       // like we do with the Card Table to Mod Union Table. But it's not really necessary.
4523     } else if (k->has_modified_oops()) {
4524       // Don't clear anything, this info is needed by the next young collection.
4525     } else {
4526       // No modified oops in the Klass.
4527       return;
4528     }
4529 
4530     // The klass has modified fields, need to scan the klass.
4531     _cm_klass_closure.do_klass(k);
4532   }
4533 };
4534 
4535 void CMSParMarkTask::work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl) {
4536   ParNewGeneration* young_gen = _collector->_young_gen;
4537   ContiguousSpace* eden_space = young_gen->eden();
4538   ContiguousSpace* from_space = young_gen->from();
4539   ContiguousSpace* to_space   = young_gen->to();
4540 
4541   HeapWord** eca = _collector->_eden_chunk_array;
4542   size_t     ect = _collector->_eden_chunk_index;
4543   HeapWord** sca = _collector->_survivor_chunk_array;
4544   size_t     sct = _collector->_survivor_chunk_index;
4545 
4546   assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
4547   assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
4548 
4549   do_young_space_rescan(worker_id, cl, to_space, NULL, 0);
4550   do_young_space_rescan(worker_id, cl, from_space, sca, sct);
4551   do_young_space_rescan(worker_id, cl, eden_space, eca, ect);
4552 }
4553 
4554 // work_queue(i) is passed to the closure
4555 // Par_MarkRefsIntoAndScanClosure.  The "i" parameter
4556 // also is passed to do_dirty_card_rescan_tasks() and to
4557 // do_work_steal() to select the i-th task_queue.
4558 
4559 void CMSParRemarkTask::work(uint worker_id) {
4560   elapsedTimer _timer;
4561   ResourceMark rm;
4562   HandleMark   hm;
4563 
4564   // ---------- rescan from roots --------------
4565   _timer.start();
4566   GenCollectedHeap* gch = GenCollectedHeap::heap();
4567   Par_MarkRefsIntoAndScanClosure par_mrias_cl(_collector,
4568     _collector->_span, _collector->ref_processor(),
4569     &(_collector->_markBitMap),
4570     work_queue(worker_id));
4571 
4572   // Rescan young gen roots first since these are likely
4573   // coarsely partitioned and may, on that account, constitute
4574   // the critical path; thus, it's best to start off that
4575   // work first.
4576   // ---------- young gen roots --------------
4577   {
4578     work_on_young_gen_roots(worker_id, &par_mrias_cl);
4579     _timer.stop();
4580     if (PrintCMSStatistics != 0) {
4581       gclog_or_tty->print_cr(
4582         "Finished young gen rescan work in %dth thread: %3.3f sec",
4583         worker_id, _timer.seconds());
4584     }
4585   }
4586 
4587   // ---------- remaining roots --------------
4588   _timer.reset();
4589   _timer.start();
4590   gch->gen_process_roots(_collector->_cmsGen->level(),
4591                          false,     // yg was scanned above
4592                          false,     // this is parallel code
4593                          GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4594                          _collector->should_unload_classes(),
4595                          &par_mrias_cl,
4596                          NULL,
4597                          NULL);     // The dirty klasses will be handled below
4598 
4599   assert(_collector->should_unload_classes()
4600          || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4601          "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4602   _timer.stop();
4603   if (PrintCMSStatistics != 0) {
4604     gclog_or_tty->print_cr(
4605       "Finished remaining root rescan work in %dth thread: %3.3f sec",
4606       worker_id, _timer.seconds());
4607   }
4608 
4609   // ---------- unhandled CLD scanning ----------
4610   if (worker_id == 0) { // Single threaded at the moment.
4611     _timer.reset();
4612     _timer.start();
4613 
4614     // Scan all new class loader data objects and new dependencies that were
4615     // introduced during concurrent marking.
4616     ResourceMark rm;
4617     GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
4618     for (int i = 0; i < array->length(); i++) {
4619       par_mrias_cl.do_class_loader_data(array->at(i));
4620     }
4621 
4622     // We don't need to keep track of new CLDs anymore.
4623     ClassLoaderDataGraph::remember_new_clds(false);
4624 
4625     _timer.stop();
4626     if (PrintCMSStatistics != 0) {
4627       gclog_or_tty->print_cr(
4628           "Finished unhandled CLD scanning work in %dth thread: %3.3f sec",
4629           worker_id, _timer.seconds());
4630     }
4631   }
4632 
4633   // ---------- dirty klass scanning ----------
4634   if (worker_id == 0) { // Single threaded at the moment.
4635     _timer.reset();
4636     _timer.start();
4637 
4638     // Scan all classes that was dirtied during the concurrent marking phase.
4639     RemarkKlassClosure remark_klass_closure(&par_mrias_cl);
4640     ClassLoaderDataGraph::classes_do(&remark_klass_closure);
4641 
4642     _timer.stop();
4643     if (PrintCMSStatistics != 0) {
4644       gclog_or_tty->print_cr(
4645           "Finished dirty klass scanning work in %dth thread: %3.3f sec",
4646           worker_id, _timer.seconds());
4647     }
4648   }
4649 
4650   // We might have added oops to ClassLoaderData::_handles during the
4651   // concurrent marking phase. These oops point to newly allocated objects
4652   // that are guaranteed to be kept alive. Either by the direct allocation
4653   // code, or when the young collector processes the roots. Hence,
4654   // we don't have to revisit the _handles block during the remark phase.
4655 
4656   // ---------- rescan dirty cards ------------
4657   _timer.reset();
4658   _timer.start();
4659 
4660   // Do the rescan tasks for each of the two spaces
4661   // (cms_space) in turn.
4662   // "worker_id" is passed to select the task_queue for "worker_id"
4663   do_dirty_card_rescan_tasks(_cms_space, worker_id, &par_mrias_cl);
4664   _timer.stop();
4665   if (PrintCMSStatistics != 0) {
4666     gclog_or_tty->print_cr(
4667       "Finished dirty card rescan work in %dth thread: %3.3f sec",
4668       worker_id, _timer.seconds());
4669   }
4670 
4671   // ---------- steal work from other threads ...
4672   // ---------- ... and drain overflow list.
4673   _timer.reset();
4674   _timer.start();
4675   do_work_steal(worker_id, &par_mrias_cl, _collector->hash_seed(worker_id));
4676   _timer.stop();
4677   if (PrintCMSStatistics != 0) {
4678     gclog_or_tty->print_cr(
4679       "Finished work stealing in %dth thread: %3.3f sec",
4680       worker_id, _timer.seconds());
4681   }
4682 }
4683 
4684 // Note that parameter "i" is not used.
4685 void
4686 CMSParMarkTask::do_young_space_rescan(uint worker_id,
4687   OopsInGenClosure* cl, ContiguousSpace* space,
4688   HeapWord** chunk_array, size_t chunk_top) {
4689   // Until all tasks completed:
4690   // . claim an unclaimed task
4691   // . compute region boundaries corresponding to task claimed
4692   //   using chunk_array
4693   // . par_oop_iterate(cl) over that region
4694 
4695   ResourceMark rm;
4696   HandleMark   hm;
4697 
4698   SequentialSubTasksDone* pst = space->par_seq_tasks();
4699 
4700   uint nth_task = 0;
4701   uint n_tasks  = pst->n_tasks();
4702 
4703   if (n_tasks > 0) {
4704     assert(pst->valid(), "Uninitialized use?");
4705     HeapWord *start, *end;
4706     while (!pst->is_task_claimed(/* reference */ nth_task)) {
4707       // We claimed task # nth_task; compute its boundaries.
4708       if (chunk_top == 0) {  // no samples were taken
4709         assert(nth_task == 0 && n_tasks == 1, "Can have only 1 eden task");
4710         start = space->bottom();
4711         end   = space->top();
4712       } else if (nth_task == 0) {
4713         start = space->bottom();
4714         end   = chunk_array[nth_task];
4715       } else if (nth_task < (uint)chunk_top) {
4716         assert(nth_task >= 1, "Control point invariant");
4717         start = chunk_array[nth_task - 1];
4718         end   = chunk_array[nth_task];
4719       } else {
4720         assert(nth_task == (uint)chunk_top, "Control point invariant");
4721         start = chunk_array[chunk_top - 1];
4722         end   = space->top();
4723       }
4724       MemRegion mr(start, end);
4725       // Verify that mr is in space
4726       assert(mr.is_empty() || space->used_region().contains(mr),
4727              "Should be in space");
4728       // Verify that "start" is an object boundary
4729       assert(mr.is_empty() || oop(mr.start())->is_oop(),
4730              "Should be an oop");
4731       space->par_oop_iterate(mr, cl);
4732     }
4733     pst->all_tasks_completed();
4734   }
4735 }
4736 
4737 void
4738 CMSParRemarkTask::do_dirty_card_rescan_tasks(
4739   CompactibleFreeListSpace* sp, int i,
4740   Par_MarkRefsIntoAndScanClosure* cl) {
4741   // Until all tasks completed:
4742   // . claim an unclaimed task
4743   // . compute region boundaries corresponding to task claimed
4744   // . transfer dirty bits ct->mut for that region
4745   // . apply rescanclosure to dirty mut bits for that region
4746 
4747   ResourceMark rm;
4748   HandleMark   hm;
4749 
4750   OopTaskQueue* work_q = work_queue(i);
4751   ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
4752   // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
4753   // CAUTION: This closure has state that persists across calls to
4754   // the work method dirty_range_iterate_clear() in that it has
4755   // embedded in it a (subtype of) UpwardsObjectClosure. The
4756   // use of that state in the embedded UpwardsObjectClosure instance
4757   // assumes that the cards are always iterated (even if in parallel
4758   // by several threads) in monotonically increasing order per each
4759   // thread. This is true of the implementation below which picks
4760   // card ranges (chunks) in monotonically increasing order globally
4761   // and, a-fortiori, in monotonically increasing order per thread
4762   // (the latter order being a subsequence of the former).
4763   // If the work code below is ever reorganized into a more chaotic
4764   // work-partitioning form than the current "sequential tasks"
4765   // paradigm, the use of that persistent state will have to be
4766   // revisited and modified appropriately. See also related
4767   // bug 4756801 work on which should examine this code to make
4768   // sure that the changes there do not run counter to the
4769   // assumptions made here and necessary for correctness and
4770   // efficiency. Note also that this code might yield inefficient
4771   // behavior in the case of very large objects that span one or
4772   // more work chunks. Such objects would potentially be scanned
4773   // several times redundantly. Work on 4756801 should try and
4774   // address that performance anomaly if at all possible. XXX
4775   MemRegion  full_span  = _collector->_span;
4776   CMSBitMap* bm    = &(_collector->_markBitMap);     // shared
4777   MarkFromDirtyCardsClosure
4778     greyRescanClosure(_collector, full_span, // entire span of interest
4779                       sp, bm, work_q, cl);
4780 
4781   SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
4782   assert(pst->valid(), "Uninitialized use?");
4783   uint nth_task = 0;
4784   const int alignment = CardTableModRefBS::card_size * BitsPerWord;
4785   MemRegion span = sp->used_region();
4786   HeapWord* start_addr = span.start();
4787   HeapWord* end_addr = (HeapWord*)round_to((intptr_t)span.end(),
4788                                            alignment);
4789   const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
4790   assert((HeapWord*)round_to((intptr_t)start_addr, alignment) ==
4791          start_addr, "Check alignment");
4792   assert((size_t)round_to((intptr_t)chunk_size, alignment) ==
4793          chunk_size, "Check alignment");
4794 
4795   while (!pst->is_task_claimed(/* reference */ nth_task)) {
4796     // Having claimed the nth_task, compute corresponding mem-region,
4797     // which is a-fortiori aligned correctly (i.e. at a MUT boundary).
4798     // The alignment restriction ensures that we do not need any
4799     // synchronization with other gang-workers while setting or
4800     // clearing bits in thus chunk of the MUT.
4801     MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
4802                                     start_addr + (nth_task+1)*chunk_size);
4803     // The last chunk's end might be way beyond end of the
4804     // used region. In that case pull back appropriately.
4805     if (this_span.end() > end_addr) {
4806       this_span.set_end(end_addr);
4807       assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
4808     }
4809     // Iterate over the dirty cards covering this chunk, marking them
4810     // precleaned, and setting the corresponding bits in the mod union
4811     // table. Since we have been careful to partition at Card and MUT-word
4812     // boundaries no synchronization is needed between parallel threads.
4813     _collector->_ct->ct_bs()->dirty_card_iterate(this_span,
4814                                                  &modUnionClosure);
4815 
4816     // Having transferred these marks into the modUnionTable,
4817     // rescan the marked objects on the dirty cards in the modUnionTable.
4818     // Even if this is at a synchronous collection, the initial marking
4819     // may have been done during an asynchronous collection so there
4820     // may be dirty bits in the mod-union table.
4821     _collector->_modUnionTable.dirty_range_iterate_clear(
4822                   this_span, &greyRescanClosure);
4823     _collector->_modUnionTable.verifyNoOneBitsInRange(
4824                                  this_span.start(),
4825                                  this_span.end());
4826   }
4827   pst->all_tasks_completed();  // declare that i am done
4828 }
4829 
4830 // . see if we can share work_queues with ParNew? XXX
4831 void
4832 CMSParRemarkTask::do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl,
4833                                 int* seed) {
4834   OopTaskQueue* work_q = work_queue(i);
4835   NOT_PRODUCT(int num_steals = 0;)
4836   oop obj_to_scan;
4837   CMSBitMap* bm = &(_collector->_markBitMap);
4838 
4839   while (true) {
4840     // Completely finish any left over work from (an) earlier round(s)
4841     cl->trim_queue(0);
4842     size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
4843                                          (size_t)ParGCDesiredObjsFromOverflowList);
4844     // Now check if there's any work in the overflow list
4845     // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
4846     // only affects the number of attempts made to get work from the
4847     // overflow list and does not affect the number of workers.  Just
4848     // pass ParallelGCThreads so this behavior is unchanged.
4849     if (_collector->par_take_from_overflow_list(num_from_overflow_list,
4850                                                 work_q,
4851                                                 ParallelGCThreads)) {
4852       // found something in global overflow list;
4853       // not yet ready to go stealing work from others.
4854       // We'd like to assert(work_q->size() != 0, ...)
4855       // because we just took work from the overflow list,
4856       // but of course we can't since all of that could have
4857       // been already stolen from us.
4858       // "He giveth and He taketh away."
4859       continue;
4860     }
4861     // Verify that we have no work before we resort to stealing
4862     assert(work_q->size() == 0, "Have work, shouldn't steal");
4863     // Try to steal from other queues that have work
4864     if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
4865       NOT_PRODUCT(num_steals++;)
4866       assert(obj_to_scan->is_oop(), "Oops, not an oop!");
4867       assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
4868       // Do scanning work
4869       obj_to_scan->oop_iterate(cl);
4870       // Loop around, finish this work, and try to steal some more
4871     } else if (terminator()->offer_termination()) {
4872         break;  // nirvana from the infinite cycle
4873     }
4874   }
4875   NOT_PRODUCT(
4876     if (PrintCMSStatistics != 0) {
4877       gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
4878     }
4879   )
4880   assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
4881          "Else our work is not yet done");
4882 }
4883 
4884 // Record object boundaries in _eden_chunk_array by sampling the eden
4885 // top in the slow-path eden object allocation code path and record
4886 // the boundaries, if CMSEdenChunksRecordAlways is true. If
4887 // CMSEdenChunksRecordAlways is false, we use the other asynchronous
4888 // sampling in sample_eden() that activates during the part of the
4889 // preclean phase.
4890 void CMSCollector::sample_eden_chunk() {
4891   if (CMSEdenChunksRecordAlways && _eden_chunk_array != NULL) {
4892     if (_eden_chunk_lock->try_lock()) {
4893       // Record a sample. This is the critical section. The contents
4894       // of the _eden_chunk_array have to be non-decreasing in the
4895       // address order.
4896       _eden_chunk_array[_eden_chunk_index] = *_top_addr;
4897       assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4898              "Unexpected state of Eden");
4899       if (_eden_chunk_index == 0 ||
4900           ((_eden_chunk_array[_eden_chunk_index] > _eden_chunk_array[_eden_chunk_index-1]) &&
4901            (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4902                           _eden_chunk_array[_eden_chunk_index-1]) >= CMSSamplingGrain))) {
4903         _eden_chunk_index++;  // commit sample
4904       }
4905       _eden_chunk_lock->unlock();
4906     }
4907   }
4908 }
4909 
4910 // Return a thread-local PLAB recording array, as appropriate.
4911 void* CMSCollector::get_data_recorder(int thr_num) {
4912   if (_survivor_plab_array != NULL &&
4913       (CMSPLABRecordAlways ||
4914        (_collectorState > Marking && _collectorState < FinalMarking))) {
4915     assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
4916     ChunkArray* ca = &_survivor_plab_array[thr_num];
4917     ca->reset();   // clear it so that fresh data is recorded
4918     return (void*) ca;
4919   } else {
4920     return NULL;
4921   }
4922 }
4923 
4924 // Reset all the thread-local PLAB recording arrays
4925 void CMSCollector::reset_survivor_plab_arrays() {
4926   for (uint i = 0; i < ParallelGCThreads; i++) {
4927     _survivor_plab_array[i].reset();
4928   }
4929 }
4930 
4931 // Merge the per-thread plab arrays into the global survivor chunk
4932 // array which will provide the partitioning of the survivor space
4933 // for CMS initial scan and rescan.
4934 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv,
4935                                               int no_of_gc_threads) {
4936   assert(_survivor_plab_array  != NULL, "Error");
4937   assert(_survivor_chunk_array != NULL, "Error");
4938   assert(_collectorState == FinalMarking ||
4939          (CMSParallelInitialMarkEnabled && _collectorState == InitialMarking), "Error");
4940   for (int j = 0; j < no_of_gc_threads; j++) {
4941     _cursor[j] = 0;
4942   }
4943   HeapWord* top = surv->top();
4944   size_t i;
4945   for (i = 0; i < _survivor_chunk_capacity; i++) {  // all sca entries
4946     HeapWord* min_val = top;          // Higher than any PLAB address
4947     uint      min_tid = 0;            // position of min_val this round
4948     for (int j = 0; j < no_of_gc_threads; j++) {
4949       ChunkArray* cur_sca = &_survivor_plab_array[j];
4950       if (_cursor[j] == cur_sca->end()) {
4951         continue;
4952       }
4953       assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
4954       HeapWord* cur_val = cur_sca->nth(_cursor[j]);
4955       assert(surv->used_region().contains(cur_val), "Out of bounds value");
4956       if (cur_val < min_val) {
4957         min_tid = j;
4958         min_val = cur_val;
4959       } else {
4960         assert(cur_val < top, "All recorded addresses should be less");
4961       }
4962     }
4963     // At this point min_val and min_tid are respectively
4964     // the least address in _survivor_plab_array[j]->nth(_cursor[j])
4965     // and the thread (j) that witnesses that address.
4966     // We record this address in the _survivor_chunk_array[i]
4967     // and increment _cursor[min_tid] prior to the next round i.
4968     if (min_val == top) {
4969       break;
4970     }
4971     _survivor_chunk_array[i] = min_val;
4972     _cursor[min_tid]++;
4973   }
4974   // We are all done; record the size of the _survivor_chunk_array
4975   _survivor_chunk_index = i; // exclusive: [0, i)
4976   if (PrintCMSStatistics > 0) {
4977     gclog_or_tty->print(" (Survivor:" SIZE_FORMAT "chunks) ", i);
4978   }
4979   // Verify that we used up all the recorded entries
4980   #ifdef ASSERT
4981     size_t total = 0;
4982     for (int j = 0; j < no_of_gc_threads; j++) {
4983       assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
4984       total += _cursor[j];
4985     }
4986     assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
4987     // Check that the merged array is in sorted order
4988     if (total > 0) {
4989       for (size_t i = 0; i < total - 1; i++) {
4990         if (PrintCMSStatistics > 0) {
4991           gclog_or_tty->print(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
4992                               i, p2i(_survivor_chunk_array[i]));
4993         }
4994         assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
4995                "Not sorted");
4996       }
4997     }
4998   #endif // ASSERT
4999 }
5000 
5001 // Set up the space's par_seq_tasks structure for work claiming
5002 // for parallel initial scan and rescan of young gen.
5003 // See ParRescanTask where this is currently used.
5004 void
5005 CMSCollector::
5006 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
5007   assert(n_threads > 0, "Unexpected n_threads argument");
5008 
5009   // Eden space
5010   if (!_young_gen->eden()->is_empty()) {
5011     SequentialSubTasksDone* pst = _young_gen->eden()->par_seq_tasks();
5012     assert(!pst->valid(), "Clobbering existing data?");
5013     // Each valid entry in [0, _eden_chunk_index) represents a task.
5014     size_t n_tasks = _eden_chunk_index + 1;
5015     assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
5016     // Sets the condition for completion of the subtask (how many threads
5017     // need to finish in order to be done).
5018     pst->set_n_threads(n_threads);
5019     pst->set_n_tasks((int)n_tasks);
5020   }
5021 
5022   // Merge the survivor plab arrays into _survivor_chunk_array
5023   if (_survivor_plab_array != NULL) {
5024     merge_survivor_plab_arrays(_young_gen->from(), n_threads);
5025   } else {
5026     assert(_survivor_chunk_index == 0, "Error");
5027   }
5028 
5029   // To space
5030   {
5031     SequentialSubTasksDone* pst = _young_gen->to()->par_seq_tasks();
5032     assert(!pst->valid(), "Clobbering existing data?");
5033     // Sets the condition for completion of the subtask (how many threads
5034     // need to finish in order to be done).
5035     pst->set_n_threads(n_threads);
5036     pst->set_n_tasks(1);
5037     assert(pst->valid(), "Error");
5038   }
5039 
5040   // From space
5041   {
5042     SequentialSubTasksDone* pst = _young_gen->from()->par_seq_tasks();
5043     assert(!pst->valid(), "Clobbering existing data?");
5044     size_t n_tasks = _survivor_chunk_index + 1;
5045     assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
5046     // Sets the condition for completion of the subtask (how many threads
5047     // need to finish in order to be done).
5048     pst->set_n_threads(n_threads);
5049     pst->set_n_tasks((int)n_tasks);
5050     assert(pst->valid(), "Error");
5051   }
5052 }
5053 
5054 // Parallel version of remark
5055 void CMSCollector::do_remark_parallel() {
5056   GenCollectedHeap* gch = GenCollectedHeap::heap();
5057   FlexibleWorkGang* workers = gch->workers();
5058   assert(workers != NULL, "Need parallel worker threads.");
5059   // Choose to use the number of GC workers most recently set
5060   // into "active_workers".  If active_workers is not set, set it
5061   // to ParallelGCThreads.
5062   uint n_workers = workers->active_workers();
5063   if (n_workers == 0) {
5064     assert(n_workers > 0, "Should have been set during scavenge");
5065     n_workers = ParallelGCThreads;
5066     workers->set_active_workers(n_workers);
5067   }
5068   CompactibleFreeListSpace* cms_space  = _cmsGen->cmsSpace();
5069 
5070   CMSParRemarkTask tsk(this,
5071     cms_space,
5072     n_workers, workers, task_queues());
5073 
5074   // Set up for parallel process_roots work.
5075   gch->set_par_threads(n_workers);
5076   // We won't be iterating over the cards in the card table updating
5077   // the younger_gen cards, so we shouldn't call the following else
5078   // the verification code as well as subsequent younger_refs_iterate
5079   // code would get confused. XXX
5080   // gch->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
5081 
5082   // The young gen rescan work will not be done as part of
5083   // process_roots (which currently doesn't know how to
5084   // parallelize such a scan), but rather will be broken up into
5085   // a set of parallel tasks (via the sampling that the [abortable]
5086   // preclean phase did of eden, plus the [two] tasks of
5087   // scanning the [two] survivor spaces. Further fine-grain
5088   // parallelization of the scanning of the survivor spaces
5089   // themselves, and of precleaning of the younger gen itself
5090   // is deferred to the future.
5091   initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
5092 
5093   // The dirty card rescan work is broken up into a "sequence"
5094   // of parallel tasks (per constituent space) that are dynamically
5095   // claimed by the parallel threads.
5096   cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
5097 
5098   // It turns out that even when we're using 1 thread, doing the work in a
5099   // separate thread causes wide variance in run times.  We can't help this
5100   // in the multi-threaded case, but we special-case n=1 here to get
5101   // repeatable measurements of the 1-thread overhead of the parallel code.
5102   if (n_workers > 1) {
5103     // Make refs discovery MT-safe, if it isn't already: it may not
5104     // necessarily be so, since it's possible that we are doing
5105     // ST marking.
5106     ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), true);
5107     StrongRootsScope srs;
5108     workers->run_task(&tsk);
5109   } else {
5110     ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5111     StrongRootsScope srs;
5112     tsk.work(0);
5113   }
5114 
5115   gch->set_par_threads(0);  // 0 ==> non-parallel.
5116   // restore, single-threaded for now, any preserved marks
5117   // as a result of work_q overflow
5118   restore_preserved_marks_if_any();
5119 }
5120 
5121 // Non-parallel version of remark
5122 void CMSCollector::do_remark_non_parallel() {
5123   ResourceMark rm;
5124   HandleMark   hm;
5125   GenCollectedHeap* gch = GenCollectedHeap::heap();
5126   ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5127 
5128   MarkRefsIntoAndScanClosure
5129     mrias_cl(_span, ref_processor(), &_markBitMap, NULL /* not precleaning */,
5130              &_markStack, this,
5131              false /* should_yield */, false /* not precleaning */);
5132   MarkFromDirtyCardsClosure
5133     markFromDirtyCardsClosure(this, _span,
5134                               NULL,  // space is set further below
5135                               &_markBitMap, &_markStack, &mrias_cl);
5136   {
5137     GCTraceTime t("grey object rescan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5138     // Iterate over the dirty cards, setting the corresponding bits in the
5139     // mod union table.
5140     {
5141       ModUnionClosure modUnionClosure(&_modUnionTable);
5142       _ct->ct_bs()->dirty_card_iterate(
5143                       _cmsGen->used_region(),
5144                       &modUnionClosure);
5145     }
5146     // Having transferred these marks into the modUnionTable, we just need
5147     // to rescan the marked objects on the dirty cards in the modUnionTable.
5148     // The initial marking may have been done during an asynchronous
5149     // collection so there may be dirty bits in the mod-union table.
5150     const int alignment =
5151       CardTableModRefBS::card_size * BitsPerWord;
5152     {
5153       // ... First handle dirty cards in CMS gen
5154       markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
5155       MemRegion ur = _cmsGen->used_region();
5156       HeapWord* lb = ur.start();
5157       HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
5158       MemRegion cms_span(lb, ub);
5159       _modUnionTable.dirty_range_iterate_clear(cms_span,
5160                                                &markFromDirtyCardsClosure);
5161       verify_work_stacks_empty();
5162       if (PrintCMSStatistics != 0) {
5163         gclog_or_tty->print(" (re-scanned "SIZE_FORMAT" dirty cards in cms gen) ",
5164           markFromDirtyCardsClosure.num_dirty_cards());
5165       }
5166     }
5167   }
5168   if (VerifyDuringGC &&
5169       GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5170     HandleMark hm;  // Discard invalid handles created during verification
5171     Universe::verify();
5172   }
5173   {
5174     GCTraceTime t("root rescan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5175 
5176     verify_work_stacks_empty();
5177 
5178     gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
5179     StrongRootsScope srs;
5180 
5181     gch->gen_process_roots(_cmsGen->level(),
5182                            true,  // younger gens as roots
5183                            false, // use the local StrongRootsScope
5184                            GenCollectedHeap::ScanningOption(roots_scanning_options()),
5185                            should_unload_classes(),
5186                            &mrias_cl,
5187                            NULL,
5188                            NULL); // The dirty klasses will be handled below
5189 
5190     assert(should_unload_classes()
5191            || (roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
5192            "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5193   }
5194 
5195   {
5196     GCTraceTime t("visit unhandled CLDs", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5197 
5198     verify_work_stacks_empty();
5199 
5200     // Scan all class loader data objects that might have been introduced
5201     // during concurrent marking.
5202     ResourceMark rm;
5203     GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
5204     for (int i = 0; i < array->length(); i++) {
5205       mrias_cl.do_class_loader_data(array->at(i));
5206     }
5207 
5208     // We don't need to keep track of new CLDs anymore.
5209     ClassLoaderDataGraph::remember_new_clds(false);
5210 
5211     verify_work_stacks_empty();
5212   }
5213 
5214   {
5215     GCTraceTime t("dirty klass scan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5216 
5217     verify_work_stacks_empty();
5218 
5219     RemarkKlassClosure remark_klass_closure(&mrias_cl);
5220     ClassLoaderDataGraph::classes_do(&remark_klass_closure);
5221 
5222     verify_work_stacks_empty();
5223   }
5224 
5225   // We might have added oops to ClassLoaderData::_handles during the
5226   // concurrent marking phase. These oops point to newly allocated objects
5227   // that are guaranteed to be kept alive. Either by the direct allocation
5228   // code, or when the young collector processes the roots. Hence,
5229   // we don't have to revisit the _handles block during the remark phase.
5230 
5231   verify_work_stacks_empty();
5232   // Restore evacuated mark words, if any, used for overflow list links
5233   if (!CMSOverflowEarlyRestoration) {
5234     restore_preserved_marks_if_any();
5235   }
5236   verify_overflow_empty();
5237 }
5238 
5239 ////////////////////////////////////////////////////////
5240 // Parallel Reference Processing Task Proxy Class
5241 ////////////////////////////////////////////////////////
5242 class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues {
5243   typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
5244   CMSCollector*          _collector;
5245   CMSBitMap*             _mark_bit_map;
5246   const MemRegion        _span;
5247   ProcessTask&           _task;
5248 
5249 public:
5250   CMSRefProcTaskProxy(ProcessTask&     task,
5251                       CMSCollector*    collector,
5252                       const MemRegion& span,
5253                       CMSBitMap*       mark_bit_map,
5254                       AbstractWorkGang* workers,
5255                       OopTaskQueueSet* task_queues):
5256     // XXX Should superclass AGTWOQ also know about AWG since it knows
5257     // about the task_queues used by the AWG? Then it could initialize
5258     // the terminator() object. See 6984287. The set_for_termination()
5259     // below is a temporary band-aid for the regression in 6984287.
5260     AbstractGangTaskWOopQueues("Process referents by policy in parallel",
5261       task_queues),
5262     _task(task),
5263     _collector(collector), _span(span), _mark_bit_map(mark_bit_map)
5264   {
5265     assert(_collector->_span.equals(_span) && !_span.is_empty(),
5266            "Inconsistency in _span");
5267     set_for_termination(workers->active_workers());
5268   }
5269 
5270   OopTaskQueueSet* task_queues() { return queues(); }
5271 
5272   OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5273 
5274   void do_work_steal(int i,
5275                      CMSParDrainMarkingStackClosure* drain,
5276                      CMSParKeepAliveClosure* keep_alive,
5277                      int* seed);
5278 
5279   virtual void work(uint worker_id);
5280 };
5281 
5282 void CMSRefProcTaskProxy::work(uint worker_id) {
5283   ResourceMark rm;
5284   HandleMark hm;
5285   assert(_collector->_span.equals(_span), "Inconsistency in _span");
5286   CMSParKeepAliveClosure par_keep_alive(_collector, _span,
5287                                         _mark_bit_map,
5288                                         work_queue(worker_id));
5289   CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
5290                                                  _mark_bit_map,
5291                                                  work_queue(worker_id));
5292   CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
5293   _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack);
5294   if (_task.marks_oops_alive()) {
5295     do_work_steal(worker_id, &par_drain_stack, &par_keep_alive,
5296                   _collector->hash_seed(worker_id));
5297   }
5298   assert(work_queue(worker_id)->size() == 0, "work_queue should be empty");
5299   assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
5300 }
5301 
5302 class CMSRefEnqueueTaskProxy: public AbstractGangTask {
5303   typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
5304   EnqueueTask& _task;
5305 
5306 public:
5307   CMSRefEnqueueTaskProxy(EnqueueTask& task)
5308     : AbstractGangTask("Enqueue reference objects in parallel"),
5309       _task(task)
5310   { }
5311 
5312   virtual void work(uint worker_id)
5313   {
5314     _task.work(worker_id);
5315   }
5316 };
5317 
5318 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
5319   MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue):
5320    _span(span),
5321    _bit_map(bit_map),
5322    _work_queue(work_queue),
5323    _mark_and_push(collector, span, bit_map, work_queue),
5324    _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
5325                         (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads)))
5326 { }
5327 
5328 // . see if we can share work_queues with ParNew? XXX
5329 void CMSRefProcTaskProxy::do_work_steal(int i,
5330   CMSParDrainMarkingStackClosure* drain,
5331   CMSParKeepAliveClosure* keep_alive,
5332   int* seed) {
5333   OopTaskQueue* work_q = work_queue(i);
5334   NOT_PRODUCT(int num_steals = 0;)
5335   oop obj_to_scan;
5336 
5337   while (true) {
5338     // Completely finish any left over work from (an) earlier round(s)
5339     drain->trim_queue(0);
5340     size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5341                                          (size_t)ParGCDesiredObjsFromOverflowList);
5342     // Now check if there's any work in the overflow list
5343     // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5344     // only affects the number of attempts made to get work from the
5345     // overflow list and does not affect the number of workers.  Just
5346     // pass ParallelGCThreads so this behavior is unchanged.
5347     if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5348                                                 work_q,
5349                                                 ParallelGCThreads)) {
5350       // Found something in global overflow list;
5351       // not yet ready to go stealing work from others.
5352       // We'd like to assert(work_q->size() != 0, ...)
5353       // because we just took work from the overflow list,
5354       // but of course we can't, since all of that might have
5355       // been already stolen from us.
5356       continue;
5357     }
5358     // Verify that we have no work before we resort to stealing
5359     assert(work_q->size() == 0, "Have work, shouldn't steal");
5360     // Try to steal from other queues that have work
5361     if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5362       NOT_PRODUCT(num_steals++;)
5363       assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5364       assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5365       // Do scanning work
5366       obj_to_scan->oop_iterate(keep_alive);
5367       // Loop around, finish this work, and try to steal some more
5368     } else if (terminator()->offer_termination()) {
5369       break;  // nirvana from the infinite cycle
5370     }
5371   }
5372   NOT_PRODUCT(
5373     if (PrintCMSStatistics != 0) {
5374       gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5375     }
5376   )
5377 }
5378 
5379 void CMSRefProcTaskExecutor::execute(ProcessTask& task)
5380 {
5381   GenCollectedHeap* gch = GenCollectedHeap::heap();
5382   FlexibleWorkGang* workers = gch->workers();
5383   assert(workers != NULL, "Need parallel worker threads.");
5384   CMSRefProcTaskProxy rp_task(task, &_collector,
5385                               _collector.ref_processor()->span(),
5386                               _collector.markBitMap(),
5387                               workers, _collector.task_queues());
5388   workers->run_task(&rp_task);
5389 }
5390 
5391 void CMSRefProcTaskExecutor::execute(EnqueueTask& task)
5392 {
5393 
5394   GenCollectedHeap* gch = GenCollectedHeap::heap();
5395   FlexibleWorkGang* workers = gch->workers();
5396   assert(workers != NULL, "Need parallel worker threads.");
5397   CMSRefEnqueueTaskProxy enq_task(task);
5398   workers->run_task(&enq_task);
5399 }
5400 
5401 void CMSCollector::refProcessingWork() {
5402   ResourceMark rm;
5403   HandleMark   hm;
5404 
5405   ReferenceProcessor* rp = ref_processor();
5406   assert(rp->span().equals(_span), "Spans should be equal");
5407   assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
5408   // Process weak references.
5409   rp->setup_policy(false);
5410   verify_work_stacks_empty();
5411 
5412   CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
5413                                           &_markStack, false /* !preclean */);
5414   CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
5415                                 _span, &_markBitMap, &_markStack,
5416                                 &cmsKeepAliveClosure, false /* !preclean */);
5417   {
5418     GCTraceTime t("weak refs processing", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5419 
5420     ReferenceProcessorStats stats;
5421     if (rp->processing_is_mt()) {
5422       // Set the degree of MT here.  If the discovery is done MT, there
5423       // may have been a different number of threads doing the discovery
5424       // and a different number of discovered lists may have Ref objects.
5425       // That is OK as long as the Reference lists are balanced (see
5426       // balance_all_queues() and balance_queues()).
5427       GenCollectedHeap* gch = GenCollectedHeap::heap();
5428       uint active_workers = ParallelGCThreads;
5429       FlexibleWorkGang* workers = gch->workers();
5430       if (workers != NULL) {
5431         active_workers = workers->active_workers();
5432         // The expectation is that active_workers will have already
5433         // been set to a reasonable value.  If it has not been set,
5434         // investigate.
5435         assert(active_workers > 0, "Should have been set during scavenge");
5436       }
5437       rp->set_active_mt_degree(active_workers);
5438       CMSRefProcTaskExecutor task_executor(*this);
5439       stats = rp->process_discovered_references(&_is_alive_closure,
5440                                         &cmsKeepAliveClosure,
5441                                         &cmsDrainMarkingStackClosure,
5442                                         &task_executor,
5443                                         _gc_timer_cm,
5444                                         _gc_tracer_cm->gc_id());
5445     } else {
5446       stats = rp->process_discovered_references(&_is_alive_closure,
5447                                         &cmsKeepAliveClosure,
5448                                         &cmsDrainMarkingStackClosure,
5449                                         NULL,
5450                                         _gc_timer_cm,
5451                                         _gc_tracer_cm->gc_id());
5452     }
5453     _gc_tracer_cm->report_gc_reference_stats(stats);
5454 
5455   }
5456 
5457   // This is the point where the entire marking should have completed.
5458   verify_work_stacks_empty();
5459 
5460   if (should_unload_classes()) {
5461     {
5462       GCTraceTime t("class unloading", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5463 
5464       // Unload classes and purge the SystemDictionary.
5465       bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure);
5466 
5467       // Unload nmethods.
5468       CodeCache::do_unloading(&_is_alive_closure, purged_class);
5469 
5470       // Prune dead klasses from subklass/sibling/implementor lists.
5471       Klass::clean_weak_klass_links(&_is_alive_closure);
5472     }
5473 
5474     {
5475       GCTraceTime t("scrub symbol table", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5476       // Clean up unreferenced symbols in symbol table.
5477       SymbolTable::unlink();
5478     }
5479 
5480     {
5481       GCTraceTime t("scrub string table", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5482       // Delete entries for dead interned strings.
5483       StringTable::unlink(&_is_alive_closure);
5484     }
5485   }
5486 
5487 
5488   // Restore any preserved marks as a result of mark stack or
5489   // work queue overflow
5490   restore_preserved_marks_if_any();  // done single-threaded for now
5491 
5492   rp->set_enqueuing_is_done(true);
5493   if (rp->processing_is_mt()) {
5494     rp->balance_all_queues();
5495     CMSRefProcTaskExecutor task_executor(*this);
5496     rp->enqueue_discovered_references(&task_executor);
5497   } else {
5498     rp->enqueue_discovered_references(NULL);
5499   }
5500   rp->verify_no_references_recorded();
5501   assert(!rp->discovery_enabled(), "should have been disabled");
5502 }
5503 
5504 #ifndef PRODUCT
5505 void CMSCollector::check_correct_thread_executing() {
5506   Thread* t = Thread::current();
5507   // Only the VM thread or the CMS thread should be here.
5508   assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
5509          "Unexpected thread type");
5510   // If this is the vm thread, the foreground process
5511   // should not be waiting.  Note that _foregroundGCIsActive is
5512   // true while the foreground collector is waiting.
5513   if (_foregroundGCShouldWait) {
5514     // We cannot be the VM thread
5515     assert(t->is_ConcurrentGC_thread(),
5516            "Should be CMS thread");
5517   } else {
5518     // We can be the CMS thread only if we are in a stop-world
5519     // phase of CMS collection.
5520     if (t->is_ConcurrentGC_thread()) {
5521       assert(_collectorState == InitialMarking ||
5522              _collectorState == FinalMarking,
5523              "Should be a stop-world phase");
5524       // The CMS thread should be holding the CMS_token.
5525       assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5526              "Potential interference with concurrently "
5527              "executing VM thread");
5528     }
5529   }
5530 }
5531 #endif
5532 
5533 void CMSCollector::sweep() {
5534   assert(_collectorState == Sweeping, "just checking");
5535   check_correct_thread_executing();
5536   verify_work_stacks_empty();
5537   verify_overflow_empty();
5538   increment_sweep_count();
5539   TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
5540 
5541   _inter_sweep_timer.stop();
5542   _inter_sweep_estimate.sample(_inter_sweep_timer.seconds());
5543 
5544   assert(!_intra_sweep_timer.is_active(), "Should not be active");
5545   _intra_sweep_timer.reset();
5546   _intra_sweep_timer.start();
5547   {
5548     TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
5549     CMSPhaseAccounting pa(this, "sweep", _gc_tracer_cm->gc_id(), !PrintGCDetails);
5550     // First sweep the old gen
5551     {
5552       CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
5553                                bitMapLock());
5554       sweepWork(_cmsGen);
5555     }
5556 
5557     // Update Universe::_heap_*_at_gc figures.
5558     // We need all the free list locks to make the abstract state
5559     // transition from Sweeping to Resetting. See detailed note
5560     // further below.
5561     {
5562       CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock());
5563       // Update heap occupancy information which is used as
5564       // input to soft ref clearing policy at the next gc.
5565       Universe::update_heap_info_at_gc();
5566       _collectorState = Resizing;
5567     }
5568   }
5569   verify_work_stacks_empty();
5570   verify_overflow_empty();
5571 
5572   if (should_unload_classes()) {
5573     // Delay purge to the beginning of the next safepoint.  Metaspace::contains
5574     // requires that the virtual spaces are stable and not deleted.
5575     ClassLoaderDataGraph::set_should_purge(true);
5576   }
5577 
5578   _intra_sweep_timer.stop();
5579   _intra_sweep_estimate.sample(_intra_sweep_timer.seconds());
5580 
5581   _inter_sweep_timer.reset();
5582   _inter_sweep_timer.start();
5583 
5584   // We need to use a monotonically non-decreasing time in ms
5585   // or we will see time-warp warnings and os::javaTimeMillis()
5586   // does not guarantee monotonicity.
5587   jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
5588   update_time_of_last_gc(now);
5589 
5590   // NOTE on abstract state transitions:
5591   // Mutators allocate-live and/or mark the mod-union table dirty
5592   // based on the state of the collection.  The former is done in
5593   // the interval [Marking, Sweeping] and the latter in the interval
5594   // [Marking, Sweeping).  Thus the transitions into the Marking state
5595   // and out of the Sweeping state must be synchronously visible
5596   // globally to the mutators.
5597   // The transition into the Marking state happens with the world
5598   // stopped so the mutators will globally see it.  Sweeping is
5599   // done asynchronously by the background collector so the transition
5600   // from the Sweeping state to the Resizing state must be done
5601   // under the freelistLock (as is the check for whether to
5602   // allocate-live and whether to dirty the mod-union table).
5603   assert(_collectorState == Resizing, "Change of collector state to"
5604     " Resizing must be done under the freelistLocks (plural)");
5605 
5606   // Now that sweeping has been completed, we clear
5607   // the incremental_collection_failed flag,
5608   // thus inviting a younger gen collection to promote into
5609   // this generation. If such a promotion may still fail,
5610   // the flag will be set again when a young collection is
5611   // attempted.
5612   GenCollectedHeap* gch = GenCollectedHeap::heap();
5613   gch->clear_incremental_collection_failed();  // Worth retrying as fresh space may have been freed up
5614   gch->update_full_collections_completed(_collection_count_start);
5615 }
5616 
5617 // FIX ME!!! Looks like this belongs in CFLSpace, with
5618 // CMSGen merely delegating to it.
5619 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
5620   double nearLargestPercent = FLSLargestBlockCoalesceProximity;
5621   HeapWord*  minAddr        = _cmsSpace->bottom();
5622   HeapWord*  largestAddr    =
5623     (HeapWord*) _cmsSpace->dictionary()->find_largest_dict();
5624   if (largestAddr == NULL) {
5625     // The dictionary appears to be empty.  In this case
5626     // try to coalesce at the end of the heap.
5627     largestAddr = _cmsSpace->end();
5628   }
5629   size_t largestOffset     = pointer_delta(largestAddr, minAddr);
5630   size_t nearLargestOffset =
5631     (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
5632   if (PrintFLSStatistics != 0) {
5633     gclog_or_tty->print_cr(
5634       "CMS: Large Block: " PTR_FORMAT ";"
5635       " Proximity: " PTR_FORMAT " -> " PTR_FORMAT,
5636       p2i(largestAddr),
5637       p2i(_cmsSpace->nearLargestChunk()), p2i(minAddr + nearLargestOffset));
5638   }
5639   _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
5640 }
5641 
5642 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
5643   return addr >= _cmsSpace->nearLargestChunk();
5644 }
5645 
5646 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
5647   return _cmsSpace->find_chunk_at_end();
5648 }
5649 
5650 void ConcurrentMarkSweepGeneration::update_gc_stats(int current_level,
5651                                                     bool full) {
5652   // The next lower level has been collected.  Gather any statistics
5653   // that are of interest at this point.
5654   if (!full && (current_level + 1) == level()) {
5655     // Gather statistics on the young generation collection.
5656     collector()->stats().record_gc0_end(used());
5657   }
5658 }
5659 
5660 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* gen) {
5661   // We iterate over the space(s) underlying this generation,
5662   // checking the mark bit map to see if the bits corresponding
5663   // to specific blocks are marked or not. Blocks that are
5664   // marked are live and are not swept up. All remaining blocks
5665   // are swept up, with coalescing on-the-fly as we sweep up
5666   // contiguous free and/or garbage blocks:
5667   // We need to ensure that the sweeper synchronizes with allocators
5668   // and stop-the-world collectors. In particular, the following
5669   // locks are used:
5670   // . CMS token: if this is held, a stop the world collection cannot occur
5671   // . freelistLock: if this is held no allocation can occur from this
5672   //                 generation by another thread
5673   // . bitMapLock: if this is held, no other thread can access or update
5674   //
5675 
5676   // Note that we need to hold the freelistLock if we use
5677   // block iterate below; else the iterator might go awry if
5678   // a mutator (or promotion) causes block contents to change
5679   // (for instance if the allocator divvies up a block).
5680   // If we hold the free list lock, for all practical purposes
5681   // young generation GC's can't occur (they'll usually need to
5682   // promote), so we might as well prevent all young generation
5683   // GC's while we do a sweeping step. For the same reason, we might
5684   // as well take the bit map lock for the entire duration
5685 
5686   // check that we hold the requisite locks
5687   assert(have_cms_token(), "Should hold cms token");
5688   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), "Should possess CMS token to sweep");
5689   assert_lock_strong(gen->freelistLock());
5690   assert_lock_strong(bitMapLock());
5691 
5692   assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context");
5693   assert(_intra_sweep_timer.is_active(),  "Was switched on  in an outer context");
5694   gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
5695                                       _inter_sweep_estimate.padded_average(),
5696                                       _intra_sweep_estimate.padded_average());
5697   gen->setNearLargestChunk();
5698 
5699   {
5700     SweepClosure sweepClosure(this, gen, &_markBitMap, CMSYield);
5701     gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
5702     // We need to free-up/coalesce garbage/blocks from a
5703     // co-terminal free run. This is done in the SweepClosure
5704     // destructor; so, do not remove this scope, else the
5705     // end-of-sweep-census below will be off by a little bit.
5706   }
5707   gen->cmsSpace()->sweep_completed();
5708   gen->cmsSpace()->endSweepFLCensus(sweep_count());
5709   if (should_unload_classes()) {                // unloaded classes this cycle,
5710     _concurrent_cycles_since_last_unload = 0;   // ... reset count
5711   } else {                                      // did not unload classes,
5712     _concurrent_cycles_since_last_unload++;     // ... increment count
5713   }
5714 }
5715 
5716 // Reset CMS data structures (for now just the marking bit map)
5717 // preparatory for the next cycle.
5718 void CMSCollector::reset(bool concurrent) {
5719   if (concurrent) {
5720     CMSTokenSyncWithLocks ts(true, bitMapLock());
5721 
5722     // If the state is not "Resetting", the foreground  thread
5723     // has done a collection and the resetting.
5724     if (_collectorState != Resetting) {
5725       assert(_collectorState == Idling, "The state should only change"
5726         " because the foreground collector has finished the collection");
5727       return;
5728     }
5729 
5730     // Clear the mark bitmap (no grey objects to start with)
5731     // for the next cycle.
5732     TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
5733     CMSPhaseAccounting cmspa(this, "reset", _gc_tracer_cm->gc_id(), !PrintGCDetails);
5734 
5735     HeapWord* curAddr = _markBitMap.startWord();
5736     while (curAddr < _markBitMap.endWord()) {
5737       size_t remaining  = pointer_delta(_markBitMap.endWord(), curAddr);
5738       MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
5739       _markBitMap.clear_large_range(chunk);
5740       if (ConcurrentMarkSweepThread::should_yield() &&
5741           !foregroundGCIsActive() &&
5742           CMSYield) {
5743         assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5744                "CMS thread should hold CMS token");
5745         assert_lock_strong(bitMapLock());
5746         bitMapLock()->unlock();
5747         ConcurrentMarkSweepThread::desynchronize(true);
5748         stopTimer();
5749         if (PrintCMSStatistics != 0) {
5750           incrementYields();
5751         }
5752 
5753         // See the comment in coordinator_yield()
5754         for (unsigned i = 0; i < CMSYieldSleepCount &&
5755                          ConcurrentMarkSweepThread::should_yield() &&
5756                          !CMSCollector::foregroundGCIsActive(); ++i) {
5757           os::sleep(Thread::current(), 1, false);
5758         }
5759 
5760         ConcurrentMarkSweepThread::synchronize(true);
5761         bitMapLock()->lock_without_safepoint_check();
5762         startTimer();
5763       }
5764       curAddr = chunk.end();
5765     }
5766     // A successful mostly concurrent collection has been done.
5767     // Because only the full (i.e., concurrent mode failure) collections
5768     // are being measured for gc overhead limits, clean the "near" flag
5769     // and count.
5770     size_policy()->reset_gc_overhead_limit_count();
5771     _collectorState = Idling;
5772   } else {
5773     // already have the lock
5774     assert(_collectorState == Resetting, "just checking");
5775     assert_lock_strong(bitMapLock());
5776     _markBitMap.clear_all();
5777     _collectorState = Idling;
5778   }
5779 
5780   register_gc_end();
5781 }
5782 
5783 void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) {
5784   TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
5785   GCTraceTime t(GCCauseString("GC", gc_cause), PrintGC, !PrintGCDetails, NULL, _gc_tracer_cm->gc_id());
5786   TraceCollectorStats tcs(counters());
5787 
5788   switch (op) {
5789     case CMS_op_checkpointRootsInitial: {
5790       SvcGCMarker sgcm(SvcGCMarker::OTHER);
5791       checkpointRootsInitial();
5792       if (PrintGC) {
5793         _cmsGen->printOccupancy("initial-mark");
5794       }
5795       break;
5796     }
5797     case CMS_op_checkpointRootsFinal: {
5798       SvcGCMarker sgcm(SvcGCMarker::OTHER);
5799       checkpointRootsFinal();
5800       if (PrintGC) {
5801         _cmsGen->printOccupancy("remark");
5802       }
5803       break;
5804     }
5805     default:
5806       fatal("No such CMS_op");
5807   }
5808 }
5809 
5810 #ifndef PRODUCT
5811 size_t const CMSCollector::skip_header_HeapWords() {
5812   return FreeChunk::header_size();
5813 }
5814 
5815 // Try and collect here conditions that should hold when
5816 // CMS thread is exiting. The idea is that the foreground GC
5817 // thread should not be blocked if it wants to terminate
5818 // the CMS thread and yet continue to run the VM for a while
5819 // after that.
5820 void CMSCollector::verify_ok_to_terminate() const {
5821   assert(Thread::current()->is_ConcurrentGC_thread(),
5822          "should be called by CMS thread");
5823   assert(!_foregroundGCShouldWait, "should be false");
5824   // We could check here that all the various low-level locks
5825   // are not held by the CMS thread, but that is overkill; see
5826   // also CMSThread::verify_ok_to_terminate() where the CGC_lock
5827   // is checked.
5828 }
5829 #endif
5830 
5831 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
5832    assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
5833           "missing Printezis mark?");
5834   HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5835   size_t size = pointer_delta(nextOneAddr + 1, addr);
5836   assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5837          "alignment problem");
5838   assert(size >= 3, "Necessary for Printezis marks to work");
5839   return size;
5840 }
5841 
5842 // A variant of the above (block_size_using_printezis_bits()) except
5843 // that we return 0 if the P-bits are not yet set.
5844 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
5845   if (_markBitMap.isMarked(addr + 1)) {
5846     assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects");
5847     HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5848     size_t size = pointer_delta(nextOneAddr + 1, addr);
5849     assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5850            "alignment problem");
5851     assert(size >= 3, "Necessary for Printezis marks to work");
5852     return size;
5853   }
5854   return 0;
5855 }
5856 
5857 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
5858   size_t sz = 0;
5859   oop p = (oop)addr;
5860   if (p->klass_or_null() != NULL) {
5861     sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
5862   } else {
5863     sz = block_size_using_printezis_bits(addr);
5864   }
5865   assert(sz > 0, "size must be nonzero");
5866   HeapWord* next_block = addr + sz;
5867   HeapWord* next_card  = (HeapWord*)round_to((uintptr_t)next_block,
5868                                              CardTableModRefBS::card_size);
5869   assert(round_down((uintptr_t)addr,      CardTableModRefBS::card_size) <
5870          round_down((uintptr_t)next_card, CardTableModRefBS::card_size),
5871          "must be different cards");
5872   return next_card;
5873 }
5874 
5875 
5876 // CMS Bit Map Wrapper /////////////////////////////////////////
5877 
5878 // Construct a CMS bit map infrastructure, but don't create the
5879 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
5880 // further below.
5881 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
5882   _bm(),
5883   _shifter(shifter),
5884   _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true,
5885                                     Monitor::_safepoint_check_sometimes) : NULL)
5886 {
5887   _bmStartWord = 0;
5888   _bmWordSize  = 0;
5889 }
5890 
5891 bool CMSBitMap::allocate(MemRegion mr) {
5892   _bmStartWord = mr.start();
5893   _bmWordSize  = mr.word_size();
5894   ReservedSpace brs(ReservedSpace::allocation_align_size_up(
5895                      (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
5896   if (!brs.is_reserved()) {
5897     warning("CMS bit map allocation failure");
5898     return false;
5899   }
5900   // For now we'll just commit all of the bit map up front.
5901   // Later on we'll try to be more parsimonious with swap.
5902   if (!_virtual_space.initialize(brs, brs.size())) {
5903     warning("CMS bit map backing store failure");
5904     return false;
5905   }
5906   assert(_virtual_space.committed_size() == brs.size(),
5907          "didn't reserve backing store for all of CMS bit map?");
5908   _bm.set_map((BitMap::bm_word_t*)_virtual_space.low());
5909   assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
5910          _bmWordSize, "inconsistency in bit map sizing");
5911   _bm.set_size(_bmWordSize >> _shifter);
5912 
5913   // bm.clear(); // can we rely on getting zero'd memory? verify below
5914   assert(isAllClear(),
5915          "Expected zero'd memory from ReservedSpace constructor");
5916   assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
5917          "consistency check");
5918   return true;
5919 }
5920 
5921 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
5922   HeapWord *next_addr, *end_addr, *last_addr;
5923   assert_locked();
5924   assert(covers(mr), "out-of-range error");
5925   // XXX assert that start and end are appropriately aligned
5926   for (next_addr = mr.start(), end_addr = mr.end();
5927        next_addr < end_addr; next_addr = last_addr) {
5928     MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
5929     last_addr = dirty_region.end();
5930     if (!dirty_region.is_empty()) {
5931       cl->do_MemRegion(dirty_region);
5932     } else {
5933       assert(last_addr == end_addr, "program logic");
5934       return;
5935     }
5936   }
5937 }
5938 
5939 void CMSBitMap::print_on_error(outputStream* st, const char* prefix) const {
5940   _bm.print_on_error(st, prefix);
5941 }
5942 
5943 #ifndef PRODUCT
5944 void CMSBitMap::assert_locked() const {
5945   CMSLockVerifier::assert_locked(lock());
5946 }
5947 
5948 bool CMSBitMap::covers(MemRegion mr) const {
5949   // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
5950   assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
5951          "size inconsistency");
5952   return (mr.start() >= _bmStartWord) &&
5953          (mr.end()   <= endWord());
5954 }
5955 
5956 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
5957     return (start >= _bmStartWord && (start + size) <= endWord());
5958 }
5959 
5960 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
5961   // verify that there are no 1 bits in the interval [left, right)
5962   FalseBitMapClosure falseBitMapClosure;
5963   iterate(&falseBitMapClosure, left, right);
5964 }
5965 
5966 void CMSBitMap::region_invariant(MemRegion mr)
5967 {
5968   assert_locked();
5969   // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
5970   assert(!mr.is_empty(), "unexpected empty region");
5971   assert(covers(mr), "mr should be covered by bit map");
5972   // convert address range into offset range
5973   size_t start_ofs = heapWordToOffset(mr.start());
5974   // Make sure that end() is appropriately aligned
5975   assert(mr.end() == (HeapWord*)round_to((intptr_t)mr.end(),
5976                         (1 << (_shifter+LogHeapWordSize))),
5977          "Misaligned mr.end()");
5978   size_t end_ofs   = heapWordToOffset(mr.end());
5979   assert(end_ofs > start_ofs, "Should mark at least one bit");
5980 }
5981 
5982 #endif
5983 
5984 bool CMSMarkStack::allocate(size_t size) {
5985   // allocate a stack of the requisite depth
5986   ReservedSpace rs(ReservedSpace::allocation_align_size_up(
5987                    size * sizeof(oop)));
5988   if (!rs.is_reserved()) {
5989     warning("CMSMarkStack allocation failure");
5990     return false;
5991   }
5992   if (!_virtual_space.initialize(rs, rs.size())) {
5993     warning("CMSMarkStack backing store failure");
5994     return false;
5995   }
5996   assert(_virtual_space.committed_size() == rs.size(),
5997          "didn't reserve backing store for all of CMS stack?");
5998   _base = (oop*)(_virtual_space.low());
5999   _index = 0;
6000   _capacity = size;
6001   NOT_PRODUCT(_max_depth = 0);
6002   return true;
6003 }
6004 
6005 // XXX FIX ME !!! In the MT case we come in here holding a
6006 // leaf lock. For printing we need to take a further lock
6007 // which has lower rank. We need to recalibrate the two
6008 // lock-ranks involved in order to be able to print the
6009 // messages below. (Or defer the printing to the caller.
6010 // For now we take the expedient path of just disabling the
6011 // messages for the problematic case.)
6012 void CMSMarkStack::expand() {
6013   assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted");
6014   if (_capacity == MarkStackSizeMax) {
6015     if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6016       // We print a warning message only once per CMS cycle.
6017       gclog_or_tty->print_cr(" (benign) Hit CMSMarkStack max size limit");
6018     }
6019     return;
6020   }
6021   // Double capacity if possible
6022   size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax);
6023   // Do not give up existing stack until we have managed to
6024   // get the double capacity that we desired.
6025   ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6026                    new_capacity * sizeof(oop)));
6027   if (rs.is_reserved()) {
6028     // Release the backing store associated with old stack
6029     _virtual_space.release();
6030     // Reinitialize virtual space for new stack
6031     if (!_virtual_space.initialize(rs, rs.size())) {
6032       fatal("Not enough swap for expanded marking stack");
6033     }
6034     _base = (oop*)(_virtual_space.low());
6035     _index = 0;
6036     _capacity = new_capacity;
6037   } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6038     // Failed to double capacity, continue;
6039     // we print a detail message only once per CMS cycle.
6040     gclog_or_tty->print(" (benign) Failed to expand marking stack from "SIZE_FORMAT"K to "
6041             SIZE_FORMAT"K",
6042             _capacity / K, new_capacity / K);
6043   }
6044 }
6045 
6046 
6047 // Closures
6048 // XXX: there seems to be a lot of code  duplication here;
6049 // should refactor and consolidate common code.
6050 
6051 // This closure is used to mark refs into the CMS generation in
6052 // the CMS bit map. Called at the first checkpoint. This closure
6053 // assumes that we do not need to re-mark dirty cards; if the CMS
6054 // generation on which this is used is not an oldest
6055 // generation then this will lose younger_gen cards!
6056 
6057 MarkRefsIntoClosure::MarkRefsIntoClosure(
6058   MemRegion span, CMSBitMap* bitMap):
6059     _span(span),
6060     _bitMap(bitMap)
6061 {
6062     assert(_ref_processor == NULL, "deliberately left NULL");
6063     assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6064 }
6065 
6066 void MarkRefsIntoClosure::do_oop(oop obj) {
6067   // if p points into _span, then mark corresponding bit in _markBitMap
6068   assert(obj->is_oop(), "expected an oop");
6069   HeapWord* addr = (HeapWord*)obj;
6070   if (_span.contains(addr)) {
6071     // this should be made more efficient
6072     _bitMap->mark(addr);
6073   }
6074 }
6075 
6076 void MarkRefsIntoClosure::do_oop(oop* p)       { MarkRefsIntoClosure::do_oop_work(p); }
6077 void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6078 
6079 Par_MarkRefsIntoClosure::Par_MarkRefsIntoClosure(
6080   MemRegion span, CMSBitMap* bitMap):
6081     _span(span),
6082     _bitMap(bitMap)
6083 {
6084     assert(_ref_processor == NULL, "deliberately left NULL");
6085     assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6086 }
6087 
6088 void Par_MarkRefsIntoClosure::do_oop(oop obj) {
6089   // if p points into _span, then mark corresponding bit in _markBitMap
6090   assert(obj->is_oop(), "expected an oop");
6091   HeapWord* addr = (HeapWord*)obj;
6092   if (_span.contains(addr)) {
6093     // this should be made more efficient
6094     _bitMap->par_mark(addr);
6095   }
6096 }
6097 
6098 void Par_MarkRefsIntoClosure::do_oop(oop* p)       { Par_MarkRefsIntoClosure::do_oop_work(p); }
6099 void Par_MarkRefsIntoClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoClosure::do_oop_work(p); }
6100 
6101 // A variant of the above, used for CMS marking verification.
6102 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
6103   MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm):
6104     _span(span),
6105     _verification_bm(verification_bm),
6106     _cms_bm(cms_bm)
6107 {
6108     assert(_ref_processor == NULL, "deliberately left NULL");
6109     assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
6110 }
6111 
6112 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
6113   // if p points into _span, then mark corresponding bit in _markBitMap
6114   assert(obj->is_oop(), "expected an oop");
6115   HeapWord* addr = (HeapWord*)obj;
6116   if (_span.contains(addr)) {
6117     _verification_bm->mark(addr);
6118     if (!_cms_bm->isMarked(addr)) {
6119       oop(addr)->print();
6120       gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
6121       fatal("... aborting");
6122     }
6123   }
6124 }
6125 
6126 void MarkRefsIntoVerifyClosure::do_oop(oop* p)       { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6127 void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6128 
6129 //////////////////////////////////////////////////
6130 // MarkRefsIntoAndScanClosure
6131 //////////////////////////////////////////////////
6132 
6133 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
6134                                                        ReferenceProcessor* rp,
6135                                                        CMSBitMap* bit_map,
6136                                                        CMSBitMap* mod_union_table,
6137                                                        CMSMarkStack*  mark_stack,
6138                                                        CMSCollector* collector,
6139                                                        bool should_yield,
6140                                                        bool concurrent_precleaning):
6141   _collector(collector),
6142   _span(span),
6143   _bit_map(bit_map),
6144   _mark_stack(mark_stack),
6145   _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table,
6146                       mark_stack, concurrent_precleaning),
6147   _yield(should_yield),
6148   _concurrent_precleaning(concurrent_precleaning),
6149   _freelistLock(NULL)
6150 {
6151   _ref_processor = rp;
6152   assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6153 }
6154 
6155 // This closure is used to mark refs into the CMS generation at the
6156 // second (final) checkpoint, and to scan and transitively follow
6157 // the unmarked oops. It is also used during the concurrent precleaning
6158 // phase while scanning objects on dirty cards in the CMS generation.
6159 // The marks are made in the marking bit map and the marking stack is
6160 // used for keeping the (newly) grey objects during the scan.
6161 // The parallel version (Par_...) appears further below.
6162 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6163   if (obj != NULL) {
6164     assert(obj->is_oop(), "expected an oop");
6165     HeapWord* addr = (HeapWord*)obj;
6166     assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6167     assert(_collector->overflow_list_is_empty(),
6168            "overflow list should be empty");
6169     if (_span.contains(addr) &&
6170         !_bit_map->isMarked(addr)) {
6171       // mark bit map (object is now grey)
6172       _bit_map->mark(addr);
6173       // push on marking stack (stack should be empty), and drain the
6174       // stack by applying this closure to the oops in the oops popped
6175       // from the stack (i.e. blacken the grey objects)
6176       bool res = _mark_stack->push(obj);
6177       assert(res, "Should have space to push on empty stack");
6178       do {
6179         oop new_oop = _mark_stack->pop();
6180         assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6181         assert(_bit_map->isMarked((HeapWord*)new_oop),
6182                "only grey objects on this stack");
6183         // iterate over the oops in this oop, marking and pushing
6184         // the ones in CMS heap (i.e. in _span).
6185         new_oop->oop_iterate(&_pushAndMarkClosure);
6186         // check if it's time to yield
6187         do_yield_check();
6188       } while (!_mark_stack->isEmpty() ||
6189                (!_concurrent_precleaning && take_from_overflow_list()));
6190         // if marking stack is empty, and we are not doing this
6191         // during precleaning, then check the overflow list
6192     }
6193     assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6194     assert(_collector->overflow_list_is_empty(),
6195            "overflow list was drained above");
6196     // We could restore evacuated mark words, if any, used for
6197     // overflow list links here because the overflow list is
6198     // provably empty here. That would reduce the maximum
6199     // size requirements for preserved_{oop,mark}_stack.
6200     // But we'll just postpone it until we are all done
6201     // so we can just stream through.
6202     if (!_concurrent_precleaning && CMSOverflowEarlyRestoration) {
6203       _collector->restore_preserved_marks_if_any();
6204       assert(_collector->no_preserved_marks(), "No preserved marks");
6205     }
6206     assert(!CMSOverflowEarlyRestoration || _collector->no_preserved_marks(),
6207            "All preserved marks should have been restored above");
6208   }
6209 }
6210 
6211 void MarkRefsIntoAndScanClosure::do_oop(oop* p)       { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6212 void MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6213 
6214 void MarkRefsIntoAndScanClosure::do_yield_work() {
6215   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6216          "CMS thread should hold CMS token");
6217   assert_lock_strong(_freelistLock);
6218   assert_lock_strong(_bit_map->lock());
6219   // relinquish the free_list_lock and bitMaplock()
6220   _bit_map->lock()->unlock();
6221   _freelistLock->unlock();
6222   ConcurrentMarkSweepThread::desynchronize(true);
6223   _collector->stopTimer();
6224   if (PrintCMSStatistics != 0) {
6225     _collector->incrementYields();
6226   }
6227 
6228   // See the comment in coordinator_yield()
6229   for (unsigned i = 0;
6230        i < CMSYieldSleepCount &&
6231        ConcurrentMarkSweepThread::should_yield() &&
6232        !CMSCollector::foregroundGCIsActive();
6233        ++i) {
6234     os::sleep(Thread::current(), 1, false);
6235   }
6236 
6237   ConcurrentMarkSweepThread::synchronize(true);
6238   _freelistLock->lock_without_safepoint_check();
6239   _bit_map->lock()->lock_without_safepoint_check();
6240   _collector->startTimer();
6241 }
6242 
6243 ///////////////////////////////////////////////////////////
6244 // Par_MarkRefsIntoAndScanClosure: a parallel version of
6245 //                                 MarkRefsIntoAndScanClosure
6246 ///////////////////////////////////////////////////////////
6247 Par_MarkRefsIntoAndScanClosure::Par_MarkRefsIntoAndScanClosure(
6248   CMSCollector* collector, MemRegion span, ReferenceProcessor* rp,
6249   CMSBitMap* bit_map, OopTaskQueue* work_queue):
6250   _span(span),
6251   _bit_map(bit_map),
6252   _work_queue(work_queue),
6253   _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
6254                        (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads))),
6255   _par_pushAndMarkClosure(collector, span, rp, bit_map, work_queue)
6256 {
6257   _ref_processor = rp;
6258   assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6259 }
6260 
6261 // This closure is used to mark refs into the CMS generation at the
6262 // second (final) checkpoint, and to scan and transitively follow
6263 // the unmarked oops. The marks are made in the marking bit map and
6264 // the work_queue is used for keeping the (newly) grey objects during
6265 // the scan phase whence they are also available for stealing by parallel
6266 // threads. Since the marking bit map is shared, updates are
6267 // synchronized (via CAS).
6268 void Par_MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6269   if (obj != NULL) {
6270     // Ignore mark word because this could be an already marked oop
6271     // that may be chained at the end of the overflow list.
6272     assert(obj->is_oop(true), "expected an oop");
6273     HeapWord* addr = (HeapWord*)obj;
6274     if (_span.contains(addr) &&
6275         !_bit_map->isMarked(addr)) {
6276       // mark bit map (object will become grey):
6277       // It is possible for several threads to be
6278       // trying to "claim" this object concurrently;
6279       // the unique thread that succeeds in marking the
6280       // object first will do the subsequent push on
6281       // to the work queue (or overflow list).
6282       if (_bit_map->par_mark(addr)) {
6283         // push on work_queue (which may not be empty), and trim the
6284         // queue to an appropriate length by applying this closure to
6285         // the oops in the oops popped from the stack (i.e. blacken the
6286         // grey objects)
6287         bool res = _work_queue->push(obj);
6288         assert(res, "Low water mark should be less than capacity?");
6289         trim_queue(_low_water_mark);
6290       } // Else, another thread claimed the object
6291     }
6292   }
6293 }
6294 
6295 void Par_MarkRefsIntoAndScanClosure::do_oop(oop* p)       { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6296 void Par_MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6297 
6298 // This closure is used to rescan the marked objects on the dirty cards
6299 // in the mod union table and the card table proper.
6300 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
6301   oop p, MemRegion mr) {
6302 
6303   size_t size = 0;
6304   HeapWord* addr = (HeapWord*)p;
6305   DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6306   assert(_span.contains(addr), "we are scanning the CMS generation");
6307   // check if it's time to yield
6308   if (do_yield_check()) {
6309     // We yielded for some foreground stop-world work,
6310     // and we have been asked to abort this ongoing preclean cycle.
6311     return 0;
6312   }
6313   if (_bitMap->isMarked(addr)) {
6314     // it's marked; is it potentially uninitialized?
6315     if (p->klass_or_null() != NULL) {
6316         // an initialized object; ignore mark word in verification below
6317         // since we are running concurrent with mutators
6318         assert(p->is_oop(true), "should be an oop");
6319         if (p->is_objArray()) {
6320           // objArrays are precisely marked; restrict scanning
6321           // to dirty cards only.
6322           size = CompactibleFreeListSpace::adjustObjectSize(
6323                    p->oop_iterate(_scanningClosure, mr));
6324         } else {
6325           // A non-array may have been imprecisely marked; we need
6326           // to scan object in its entirety.
6327           size = CompactibleFreeListSpace::adjustObjectSize(
6328                    p->oop_iterate(_scanningClosure));
6329         }
6330         #ifdef ASSERT
6331           size_t direct_size =
6332             CompactibleFreeListSpace::adjustObjectSize(p->size());
6333           assert(size == direct_size, "Inconsistency in size");
6334           assert(size >= 3, "Necessary for Printezis marks to work");
6335           if (!_bitMap->isMarked(addr+1)) {
6336             _bitMap->verifyNoOneBitsInRange(addr+2, addr+size);
6337           } else {
6338             _bitMap->verifyNoOneBitsInRange(addr+2, addr+size-1);
6339             assert(_bitMap->isMarked(addr+size-1),
6340                    "inconsistent Printezis mark");
6341           }
6342         #endif // ASSERT
6343     } else {
6344       // An uninitialized object.
6345       assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
6346       HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
6347       size = pointer_delta(nextOneAddr + 1, addr);
6348       assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6349              "alignment problem");
6350       // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
6351       // will dirty the card when the klass pointer is installed in the
6352       // object (signaling the completion of initialization).
6353     }
6354   } else {
6355     // Either a not yet marked object or an uninitialized object
6356     if (p->klass_or_null() == NULL) {
6357       // An uninitialized object, skip to the next card, since
6358       // we may not be able to read its P-bits yet.
6359       assert(size == 0, "Initial value");
6360     } else {
6361       // An object not (yet) reached by marking: we merely need to
6362       // compute its size so as to go look at the next block.
6363       assert(p->is_oop(true), "should be an oop");
6364       size = CompactibleFreeListSpace::adjustObjectSize(p->size());
6365     }
6366   }
6367   DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6368   return size;
6369 }
6370 
6371 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
6372   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6373          "CMS thread should hold CMS token");
6374   assert_lock_strong(_freelistLock);
6375   assert_lock_strong(_bitMap->lock());
6376   // relinquish the free_list_lock and bitMaplock()
6377   _bitMap->lock()->unlock();
6378   _freelistLock->unlock();
6379   ConcurrentMarkSweepThread::desynchronize(true);
6380   _collector->stopTimer();
6381   if (PrintCMSStatistics != 0) {
6382     _collector->incrementYields();
6383   }
6384 
6385   // See the comment in coordinator_yield()
6386   for (unsigned i = 0; i < CMSYieldSleepCount &&
6387                    ConcurrentMarkSweepThread::should_yield() &&
6388                    !CMSCollector::foregroundGCIsActive(); ++i) {
6389     os::sleep(Thread::current(), 1, false);
6390   }
6391 
6392   ConcurrentMarkSweepThread::synchronize(true);
6393   _freelistLock->lock_without_safepoint_check();
6394   _bitMap->lock()->lock_without_safepoint_check();
6395   _collector->startTimer();
6396 }
6397 
6398 
6399 //////////////////////////////////////////////////////////////////
6400 // SurvivorSpacePrecleanClosure
6401 //////////////////////////////////////////////////////////////////
6402 // This (single-threaded) closure is used to preclean the oops in
6403 // the survivor spaces.
6404 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
6405 
6406   HeapWord* addr = (HeapWord*)p;
6407   DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6408   assert(!_span.contains(addr), "we are scanning the survivor spaces");
6409   assert(p->klass_or_null() != NULL, "object should be initialized");
6410   // an initialized object; ignore mark word in verification below
6411   // since we are running concurrent with mutators
6412   assert(p->is_oop(true), "should be an oop");
6413   // Note that we do not yield while we iterate over
6414   // the interior oops of p, pushing the relevant ones
6415   // on our marking stack.
6416   size_t size = p->oop_iterate(_scanning_closure);
6417   do_yield_check();
6418   // Observe that below, we do not abandon the preclean
6419   // phase as soon as we should; rather we empty the
6420   // marking stack before returning. This is to satisfy
6421   // some existing assertions. In general, it may be a
6422   // good idea to abort immediately and complete the marking
6423   // from the grey objects at a later time.
6424   while (!_mark_stack->isEmpty()) {
6425     oop new_oop = _mark_stack->pop();
6426     assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6427     assert(_bit_map->isMarked((HeapWord*)new_oop),
6428            "only grey objects on this stack");
6429     // iterate over the oops in this oop, marking and pushing
6430     // the ones in CMS heap (i.e. in _span).
6431     new_oop->oop_iterate(_scanning_closure);
6432     // check if it's time to yield
6433     do_yield_check();
6434   }
6435   unsigned int after_count =
6436     GenCollectedHeap::heap()->total_collections();
6437   bool abort = (_before_count != after_count) ||
6438                _collector->should_abort_preclean();
6439   return abort ? 0 : size;
6440 }
6441 
6442 void SurvivorSpacePrecleanClosure::do_yield_work() {
6443   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6444          "CMS thread should hold CMS token");
6445   assert_lock_strong(_bit_map->lock());
6446   // Relinquish the bit map lock
6447   _bit_map->lock()->unlock();
6448   ConcurrentMarkSweepThread::desynchronize(true);
6449   _collector->stopTimer();
6450   if (PrintCMSStatistics != 0) {
6451     _collector->incrementYields();
6452   }
6453 
6454   // See the comment in coordinator_yield()
6455   for (unsigned i = 0; i < CMSYieldSleepCount &&
6456                        ConcurrentMarkSweepThread::should_yield() &&
6457                        !CMSCollector::foregroundGCIsActive(); ++i) {
6458     os::sleep(Thread::current(), 1, false);
6459   }
6460 
6461   ConcurrentMarkSweepThread::synchronize(true);
6462   _bit_map->lock()->lock_without_safepoint_check();
6463   _collector->startTimer();
6464 }
6465 
6466 // This closure is used to rescan the marked objects on the dirty cards
6467 // in the mod union table and the card table proper. In the parallel
6468 // case, although the bitMap is shared, we do a single read so the
6469 // isMarked() query is "safe".
6470 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
6471   // Ignore mark word because we are running concurrent with mutators
6472   assert(p->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(p)));
6473   HeapWord* addr = (HeapWord*)p;
6474   assert(_span.contains(addr), "we are scanning the CMS generation");
6475   bool is_obj_array = false;
6476   #ifdef ASSERT
6477     if (!_parallel) {
6478       assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6479       assert(_collector->overflow_list_is_empty(),
6480              "overflow list should be empty");
6481 
6482     }
6483   #endif // ASSERT
6484   if (_bit_map->isMarked(addr)) {
6485     // Obj arrays are precisely marked, non-arrays are not;
6486     // so we scan objArrays precisely and non-arrays in their
6487     // entirety.
6488     if (p->is_objArray()) {
6489       is_obj_array = true;
6490       if (_parallel) {
6491         p->oop_iterate(_par_scan_closure, mr);
6492       } else {
6493         p->oop_iterate(_scan_closure, mr);
6494       }
6495     } else {
6496       if (_parallel) {
6497         p->oop_iterate(_par_scan_closure);
6498       } else {
6499         p->oop_iterate(_scan_closure);
6500       }
6501     }
6502   }
6503   #ifdef ASSERT
6504     if (!_parallel) {
6505       assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6506       assert(_collector->overflow_list_is_empty(),
6507              "overflow list should be empty");
6508 
6509     }
6510   #endif // ASSERT
6511   return is_obj_array;
6512 }
6513 
6514 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
6515                         MemRegion span,
6516                         CMSBitMap* bitMap, CMSMarkStack*  markStack,
6517                         bool should_yield, bool verifying):
6518   _collector(collector),
6519   _span(span),
6520   _bitMap(bitMap),
6521   _mut(&collector->_modUnionTable),
6522   _markStack(markStack),
6523   _yield(should_yield),
6524   _skipBits(0)
6525 {
6526   assert(_markStack->isEmpty(), "stack should be empty");
6527   _finger = _bitMap->startWord();
6528   _threshold = _finger;
6529   assert(_collector->_restart_addr == NULL, "Sanity check");
6530   assert(_span.contains(_finger), "Out of bounds _finger?");
6531   DEBUG_ONLY(_verifying = verifying;)
6532 }
6533 
6534 void MarkFromRootsClosure::reset(HeapWord* addr) {
6535   assert(_markStack->isEmpty(), "would cause duplicates on stack");
6536   assert(_span.contains(addr), "Out of bounds _finger?");
6537   _finger = addr;
6538   _threshold = (HeapWord*)round_to(
6539                  (intptr_t)_finger, CardTableModRefBS::card_size);
6540 }
6541 
6542 // Should revisit to see if this should be restructured for
6543 // greater efficiency.
6544 bool MarkFromRootsClosure::do_bit(size_t offset) {
6545   if (_skipBits > 0) {
6546     _skipBits--;
6547     return true;
6548   }
6549   // convert offset into a HeapWord*
6550   HeapWord* addr = _bitMap->startWord() + offset;
6551   assert(_bitMap->endWord() && addr < _bitMap->endWord(),
6552          "address out of range");
6553   assert(_bitMap->isMarked(addr), "tautology");
6554   if (_bitMap->isMarked(addr+1)) {
6555     // this is an allocated but not yet initialized object
6556     assert(_skipBits == 0, "tautology");
6557     _skipBits = 2;  // skip next two marked bits ("Printezis-marks")
6558     oop p = oop(addr);
6559     if (p->klass_or_null() == NULL) {
6560       DEBUG_ONLY(if (!_verifying) {)
6561         // We re-dirty the cards on which this object lies and increase
6562         // the _threshold so that we'll come back to scan this object
6563         // during the preclean or remark phase. (CMSCleanOnEnter)
6564         if (CMSCleanOnEnter) {
6565           size_t sz = _collector->block_size_using_printezis_bits(addr);
6566           HeapWord* end_card_addr   = (HeapWord*)round_to(
6567                                          (intptr_t)(addr+sz), CardTableModRefBS::card_size);
6568           MemRegion redirty_range = MemRegion(addr, end_card_addr);
6569           assert(!redirty_range.is_empty(), "Arithmetical tautology");
6570           // Bump _threshold to end_card_addr; note that
6571           // _threshold cannot possibly exceed end_card_addr, anyhow.
6572           // This prevents future clearing of the card as the scan proceeds
6573           // to the right.
6574           assert(_threshold <= end_card_addr,
6575                  "Because we are just scanning into this object");
6576           if (_threshold < end_card_addr) {
6577             _threshold = end_card_addr;
6578           }
6579           if (p->klass_or_null() != NULL) {
6580             // Redirty the range of cards...
6581             _mut->mark_range(redirty_range);
6582           } // ...else the setting of klass will dirty the card anyway.
6583         }
6584       DEBUG_ONLY(})
6585       return true;
6586     }
6587   }
6588   scanOopsInOop(addr);
6589   return true;
6590 }
6591 
6592 // We take a break if we've been at this for a while,
6593 // so as to avoid monopolizing the locks involved.
6594 void MarkFromRootsClosure::do_yield_work() {
6595   // First give up the locks, then yield, then re-lock
6596   // We should probably use a constructor/destructor idiom to
6597   // do this unlock/lock or modify the MutexUnlocker class to
6598   // serve our purpose. XXX
6599   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6600          "CMS thread should hold CMS token");
6601   assert_lock_strong(_bitMap->lock());
6602   _bitMap->lock()->unlock();
6603   ConcurrentMarkSweepThread::desynchronize(true);
6604   _collector->stopTimer();
6605   if (PrintCMSStatistics != 0) {
6606     _collector->incrementYields();
6607   }
6608 
6609   // See the comment in coordinator_yield()
6610   for (unsigned i = 0; i < CMSYieldSleepCount &&
6611                        ConcurrentMarkSweepThread::should_yield() &&
6612                        !CMSCollector::foregroundGCIsActive(); ++i) {
6613     os::sleep(Thread::current(), 1, false);
6614   }
6615 
6616   ConcurrentMarkSweepThread::synchronize(true);
6617   _bitMap->lock()->lock_without_safepoint_check();
6618   _collector->startTimer();
6619 }
6620 
6621 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
6622   assert(_bitMap->isMarked(ptr), "expected bit to be set");
6623   assert(_markStack->isEmpty(),
6624          "should drain stack to limit stack usage");
6625   // convert ptr to an oop preparatory to scanning
6626   oop obj = oop(ptr);
6627   // Ignore mark word in verification below, since we
6628   // may be running concurrent with mutators.
6629   assert(obj->is_oop(true), "should be an oop");
6630   assert(_finger <= ptr, "_finger runneth ahead");
6631   // advance the finger to right end of this object
6632   _finger = ptr + obj->size();
6633   assert(_finger > ptr, "we just incremented it above");
6634   // On large heaps, it may take us some time to get through
6635   // the marking phase. During
6636   // this time it's possible that a lot of mutations have
6637   // accumulated in the card table and the mod union table --
6638   // these mutation records are redundant until we have
6639   // actually traced into the corresponding card.
6640   // Here, we check whether advancing the finger would make
6641   // us cross into a new card, and if so clear corresponding
6642   // cards in the MUT (preclean them in the card-table in the
6643   // future).
6644 
6645   DEBUG_ONLY(if (!_verifying) {)
6646     // The clean-on-enter optimization is disabled by default,
6647     // until we fix 6178663.
6648     if (CMSCleanOnEnter && (_finger > _threshold)) {
6649       // [_threshold, _finger) represents the interval
6650       // of cards to be cleared  in MUT (or precleaned in card table).
6651       // The set of cards to be cleared is all those that overlap
6652       // with the interval [_threshold, _finger); note that
6653       // _threshold is always kept card-aligned but _finger isn't
6654       // always card-aligned.
6655       HeapWord* old_threshold = _threshold;
6656       assert(old_threshold == (HeapWord*)round_to(
6657               (intptr_t)old_threshold, CardTableModRefBS::card_size),
6658              "_threshold should always be card-aligned");
6659       _threshold = (HeapWord*)round_to(
6660                      (intptr_t)_finger, CardTableModRefBS::card_size);
6661       MemRegion mr(old_threshold, _threshold);
6662       assert(!mr.is_empty(), "Control point invariant");
6663       assert(_span.contains(mr), "Should clear within span");
6664       _mut->clear_range(mr);
6665     }
6666   DEBUG_ONLY(})
6667   // Note: the finger doesn't advance while we drain
6668   // the stack below.
6669   PushOrMarkClosure pushOrMarkClosure(_collector,
6670                                       _span, _bitMap, _markStack,
6671                                       _finger, this);
6672   bool res = _markStack->push(obj);
6673   assert(res, "Empty non-zero size stack should have space for single push");
6674   while (!_markStack->isEmpty()) {
6675     oop new_oop = _markStack->pop();
6676     // Skip verifying header mark word below because we are
6677     // running concurrent with mutators.
6678     assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
6679     // now scan this oop's oops
6680     new_oop->oop_iterate(&pushOrMarkClosure);
6681     do_yield_check();
6682   }
6683   assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
6684 }
6685 
6686 Par_MarkFromRootsClosure::Par_MarkFromRootsClosure(CMSConcMarkingTask* task,
6687                        CMSCollector* collector, MemRegion span,
6688                        CMSBitMap* bit_map,
6689                        OopTaskQueue* work_queue,
6690                        CMSMarkStack*  overflow_stack):
6691   _collector(collector),
6692   _whole_span(collector->_span),
6693   _span(span),
6694   _bit_map(bit_map),
6695   _mut(&collector->_modUnionTable),
6696   _work_queue(work_queue),
6697   _overflow_stack(overflow_stack),
6698   _skip_bits(0),
6699   _task(task)
6700 {
6701   assert(_work_queue->size() == 0, "work_queue should be empty");
6702   _finger = span.start();
6703   _threshold = _finger;     // XXX Defer clear-on-enter optimization for now
6704   assert(_span.contains(_finger), "Out of bounds _finger?");
6705 }
6706 
6707 // Should revisit to see if this should be restructured for
6708 // greater efficiency.
6709 bool Par_MarkFromRootsClosure::do_bit(size_t offset) {
6710   if (_skip_bits > 0) {
6711     _skip_bits--;
6712     return true;
6713   }
6714   // convert offset into a HeapWord*
6715   HeapWord* addr = _bit_map->startWord() + offset;
6716   assert(_bit_map->endWord() && addr < _bit_map->endWord(),
6717          "address out of range");
6718   assert(_bit_map->isMarked(addr), "tautology");
6719   if (_bit_map->isMarked(addr+1)) {
6720     // this is an allocated object that might not yet be initialized
6721     assert(_skip_bits == 0, "tautology");
6722     _skip_bits = 2;  // skip next two marked bits ("Printezis-marks")
6723     oop p = oop(addr);
6724     if (p->klass_or_null() == NULL) {
6725       // in the case of Clean-on-Enter optimization, redirty card
6726       // and avoid clearing card by increasing  the threshold.
6727       return true;
6728     }
6729   }
6730   scan_oops_in_oop(addr);
6731   return true;
6732 }
6733 
6734 void Par_MarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
6735   assert(_bit_map->isMarked(ptr), "expected bit to be set");
6736   // Should we assert that our work queue is empty or
6737   // below some drain limit?
6738   assert(_work_queue->size() == 0,
6739          "should drain stack to limit stack usage");
6740   // convert ptr to an oop preparatory to scanning
6741   oop obj = oop(ptr);
6742   // Ignore mark word in verification below, since we
6743   // may be running concurrent with mutators.
6744   assert(obj->is_oop(true), "should be an oop");
6745   assert(_finger <= ptr, "_finger runneth ahead");
6746   // advance the finger to right end of this object
6747   _finger = ptr + obj->size();
6748   assert(_finger > ptr, "we just incremented it above");
6749   // On large heaps, it may take us some time to get through
6750   // the marking phase. During
6751   // this time it's possible that a lot of mutations have
6752   // accumulated in the card table and the mod union table --
6753   // these mutation records are redundant until we have
6754   // actually traced into the corresponding card.
6755   // Here, we check whether advancing the finger would make
6756   // us cross into a new card, and if so clear corresponding
6757   // cards in the MUT (preclean them in the card-table in the
6758   // future).
6759 
6760   // The clean-on-enter optimization is disabled by default,
6761   // until we fix 6178663.
6762   if (CMSCleanOnEnter && (_finger > _threshold)) {
6763     // [_threshold, _finger) represents the interval
6764     // of cards to be cleared  in MUT (or precleaned in card table).
6765     // The set of cards to be cleared is all those that overlap
6766     // with the interval [_threshold, _finger); note that
6767     // _threshold is always kept card-aligned but _finger isn't
6768     // always card-aligned.
6769     HeapWord* old_threshold = _threshold;
6770     assert(old_threshold == (HeapWord*)round_to(
6771             (intptr_t)old_threshold, CardTableModRefBS::card_size),
6772            "_threshold should always be card-aligned");
6773     _threshold = (HeapWord*)round_to(
6774                    (intptr_t)_finger, CardTableModRefBS::card_size);
6775     MemRegion mr(old_threshold, _threshold);
6776     assert(!mr.is_empty(), "Control point invariant");
6777     assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
6778     _mut->clear_range(mr);
6779   }
6780 
6781   // Note: the local finger doesn't advance while we drain
6782   // the stack below, but the global finger sure can and will.
6783   HeapWord** gfa = _task->global_finger_addr();
6784   Par_PushOrMarkClosure pushOrMarkClosure(_collector,
6785                                       _span, _bit_map,
6786                                       _work_queue,
6787                                       _overflow_stack,
6788                                       _finger,
6789                                       gfa, this);
6790   bool res = _work_queue->push(obj);   // overflow could occur here
6791   assert(res, "Will hold once we use workqueues");
6792   while (true) {
6793     oop new_oop;
6794     if (!_work_queue->pop_local(new_oop)) {
6795       // We emptied our work_queue; check if there's stuff that can
6796       // be gotten from the overflow stack.
6797       if (CMSConcMarkingTask::get_work_from_overflow_stack(
6798             _overflow_stack, _work_queue)) {
6799         do_yield_check();
6800         continue;
6801       } else {  // done
6802         break;
6803       }
6804     }
6805     // Skip verifying header mark word below because we are
6806     // running concurrent with mutators.
6807     assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
6808     // now scan this oop's oops
6809     new_oop->oop_iterate(&pushOrMarkClosure);
6810     do_yield_check();
6811   }
6812   assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
6813 }
6814 
6815 // Yield in response to a request from VM Thread or
6816 // from mutators.
6817 void Par_MarkFromRootsClosure::do_yield_work() {
6818   assert(_task != NULL, "sanity");
6819   _task->yield();
6820 }
6821 
6822 // A variant of the above used for verifying CMS marking work.
6823 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
6824                         MemRegion span,
6825                         CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6826                         CMSMarkStack*  mark_stack):
6827   _collector(collector),
6828   _span(span),
6829   _verification_bm(verification_bm),
6830   _cms_bm(cms_bm),
6831   _mark_stack(mark_stack),
6832   _pam_verify_closure(collector, span, verification_bm, cms_bm,
6833                       mark_stack)
6834 {
6835   assert(_mark_stack->isEmpty(), "stack should be empty");
6836   _finger = _verification_bm->startWord();
6837   assert(_collector->_restart_addr == NULL, "Sanity check");
6838   assert(_span.contains(_finger), "Out of bounds _finger?");
6839 }
6840 
6841 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
6842   assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
6843   assert(_span.contains(addr), "Out of bounds _finger?");
6844   _finger = addr;
6845 }
6846 
6847 // Should revisit to see if this should be restructured for
6848 // greater efficiency.
6849 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
6850   // convert offset into a HeapWord*
6851   HeapWord* addr = _verification_bm->startWord() + offset;
6852   assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
6853          "address out of range");
6854   assert(_verification_bm->isMarked(addr), "tautology");
6855   assert(_cms_bm->isMarked(addr), "tautology");
6856 
6857   assert(_mark_stack->isEmpty(),
6858          "should drain stack to limit stack usage");
6859   // convert addr to an oop preparatory to scanning
6860   oop obj = oop(addr);
6861   assert(obj->is_oop(), "should be an oop");
6862   assert(_finger <= addr, "_finger runneth ahead");
6863   // advance the finger to right end of this object
6864   _finger = addr + obj->size();
6865   assert(_finger > addr, "we just incremented it above");
6866   // Note: the finger doesn't advance while we drain
6867   // the stack below.
6868   bool res = _mark_stack->push(obj);
6869   assert(res, "Empty non-zero size stack should have space for single push");
6870   while (!_mark_stack->isEmpty()) {
6871     oop new_oop = _mark_stack->pop();
6872     assert(new_oop->is_oop(), "Oops! expected to pop an oop");
6873     // now scan this oop's oops
6874     new_oop->oop_iterate(&_pam_verify_closure);
6875   }
6876   assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
6877   return true;
6878 }
6879 
6880 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
6881   CMSCollector* collector, MemRegion span,
6882   CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6883   CMSMarkStack*  mark_stack):
6884   MetadataAwareOopClosure(collector->ref_processor()),
6885   _collector(collector),
6886   _span(span),
6887   _verification_bm(verification_bm),
6888   _cms_bm(cms_bm),
6889   _mark_stack(mark_stack)
6890 { }
6891 
6892 void PushAndMarkVerifyClosure::do_oop(oop* p)       { PushAndMarkVerifyClosure::do_oop_work(p); }
6893 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
6894 
6895 // Upon stack overflow, we discard (part of) the stack,
6896 // remembering the least address amongst those discarded
6897 // in CMSCollector's _restart_address.
6898 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
6899   // Remember the least grey address discarded
6900   HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
6901   _collector->lower_restart_addr(ra);
6902   _mark_stack->reset();  // discard stack contents
6903   _mark_stack->expand(); // expand the stack if possible
6904 }
6905 
6906 void PushAndMarkVerifyClosure::do_oop(oop obj) {
6907   assert(obj->is_oop_or_null(), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
6908   HeapWord* addr = (HeapWord*)obj;
6909   if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
6910     // Oop lies in _span and isn't yet grey or black
6911     _verification_bm->mark(addr);            // now grey
6912     if (!_cms_bm->isMarked(addr)) {
6913       oop(addr)->print();
6914       gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)",
6915                              p2i(addr));
6916       fatal("... aborting");
6917     }
6918 
6919     if (!_mark_stack->push(obj)) { // stack overflow
6920       if (PrintCMSStatistics != 0) {
6921         gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
6922                                SIZE_FORMAT, _mark_stack->capacity());
6923       }
6924       assert(_mark_stack->isFull(), "Else push should have succeeded");
6925       handle_stack_overflow(addr);
6926     }
6927     // anything including and to the right of _finger
6928     // will be scanned as we iterate over the remainder of the
6929     // bit map
6930   }
6931 }
6932 
6933 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
6934                      MemRegion span,
6935                      CMSBitMap* bitMap, CMSMarkStack*  markStack,
6936                      HeapWord* finger, MarkFromRootsClosure* parent) :
6937   MetadataAwareOopClosure(collector->ref_processor()),
6938   _collector(collector),
6939   _span(span),
6940   _bitMap(bitMap),
6941   _markStack(markStack),
6942   _finger(finger),
6943   _parent(parent)
6944 { }
6945 
6946 Par_PushOrMarkClosure::Par_PushOrMarkClosure(CMSCollector* collector,
6947                      MemRegion span,
6948                      CMSBitMap* bit_map,
6949                      OopTaskQueue* work_queue,
6950                      CMSMarkStack*  overflow_stack,
6951                      HeapWord* finger,
6952                      HeapWord** global_finger_addr,
6953                      Par_MarkFromRootsClosure* parent) :
6954   MetadataAwareOopClosure(collector->ref_processor()),
6955   _collector(collector),
6956   _whole_span(collector->_span),
6957   _span(span),
6958   _bit_map(bit_map),
6959   _work_queue(work_queue),
6960   _overflow_stack(overflow_stack),
6961   _finger(finger),
6962   _global_finger_addr(global_finger_addr),
6963   _parent(parent)
6964 { }
6965 
6966 // Assumes thread-safe access by callers, who are
6967 // responsible for mutual exclusion.
6968 void CMSCollector::lower_restart_addr(HeapWord* low) {
6969   assert(_span.contains(low), "Out of bounds addr");
6970   if (_restart_addr == NULL) {
6971     _restart_addr = low;
6972   } else {
6973     _restart_addr = MIN2(_restart_addr, low);
6974   }
6975 }
6976 
6977 // Upon stack overflow, we discard (part of) the stack,
6978 // remembering the least address amongst those discarded
6979 // in CMSCollector's _restart_address.
6980 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
6981   // Remember the least grey address discarded
6982   HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
6983   _collector->lower_restart_addr(ra);
6984   _markStack->reset();  // discard stack contents
6985   _markStack->expand(); // expand the stack if possible
6986 }
6987 
6988 // Upon stack overflow, we discard (part of) the stack,
6989 // remembering the least address amongst those discarded
6990 // in CMSCollector's _restart_address.
6991 void Par_PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
6992   // We need to do this under a mutex to prevent other
6993   // workers from interfering with the work done below.
6994   MutexLockerEx ml(_overflow_stack->par_lock(),
6995                    Mutex::_no_safepoint_check_flag);
6996   // Remember the least grey address discarded
6997   HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
6998   _collector->lower_restart_addr(ra);
6999   _overflow_stack->reset();  // discard stack contents
7000   _overflow_stack->expand(); // expand the stack if possible
7001 }
7002 
7003 void PushOrMarkClosure::do_oop(oop obj) {
7004   // Ignore mark word because we are running concurrent with mutators.
7005   assert(obj->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7006   HeapWord* addr = (HeapWord*)obj;
7007   if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
7008     // Oop lies in _span and isn't yet grey or black
7009     _bitMap->mark(addr);            // now grey
7010     if (addr < _finger) {
7011       // the bit map iteration has already either passed, or
7012       // sampled, this bit in the bit map; we'll need to
7013       // use the marking stack to scan this oop's oops.
7014       bool simulate_overflow = false;
7015       NOT_PRODUCT(
7016         if (CMSMarkStackOverflowALot &&
7017             _collector->simulate_overflow()) {
7018           // simulate a stack overflow
7019           simulate_overflow = true;
7020         }
7021       )
7022       if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
7023         if (PrintCMSStatistics != 0) {
7024           gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7025                                  SIZE_FORMAT, _markStack->capacity());
7026         }
7027         assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
7028         handle_stack_overflow(addr);
7029       }
7030     }
7031     // anything including and to the right of _finger
7032     // will be scanned as we iterate over the remainder of the
7033     // bit map
7034     do_yield_check();
7035   }
7036 }
7037 
7038 void PushOrMarkClosure::do_oop(oop* p)       { PushOrMarkClosure::do_oop_work(p); }
7039 void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); }
7040 
7041 void Par_PushOrMarkClosure::do_oop(oop obj) {
7042   // Ignore mark word because we are running concurrent with mutators.
7043   assert(obj->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7044   HeapWord* addr = (HeapWord*)obj;
7045   if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
7046     // Oop lies in _span and isn't yet grey or black
7047     // We read the global_finger (volatile read) strictly after marking oop
7048     bool res = _bit_map->par_mark(addr);    // now grey
7049     volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
7050     // Should we push this marked oop on our stack?
7051     // -- if someone else marked it, nothing to do
7052     // -- if target oop is above global finger nothing to do
7053     // -- if target oop is in chunk and above local finger
7054     //      then nothing to do
7055     // -- else push on work queue
7056     if (   !res       // someone else marked it, they will deal with it
7057         || (addr >= *gfa)  // will be scanned in a later task
7058         || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
7059       return;
7060     }
7061     // the bit map iteration has already either passed, or
7062     // sampled, this bit in the bit map; we'll need to
7063     // use the marking stack to scan this oop's oops.
7064     bool simulate_overflow = false;
7065     NOT_PRODUCT(
7066       if (CMSMarkStackOverflowALot &&
7067           _collector->simulate_overflow()) {
7068         // simulate a stack overflow
7069         simulate_overflow = true;
7070       }
7071     )
7072     if (simulate_overflow ||
7073         !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
7074       // stack overflow
7075       if (PrintCMSStatistics != 0) {
7076         gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7077                                SIZE_FORMAT, _overflow_stack->capacity());
7078       }
7079       // We cannot assert that the overflow stack is full because
7080       // it may have been emptied since.
7081       assert(simulate_overflow ||
7082              _work_queue->size() == _work_queue->max_elems(),
7083             "Else push should have succeeded");
7084       handle_stack_overflow(addr);
7085     }
7086     do_yield_check();
7087   }
7088 }
7089 
7090 void Par_PushOrMarkClosure::do_oop(oop* p)       { Par_PushOrMarkClosure::do_oop_work(p); }
7091 void Par_PushOrMarkClosure::do_oop(narrowOop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7092 
7093 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
7094                                        MemRegion span,
7095                                        ReferenceProcessor* rp,
7096                                        CMSBitMap* bit_map,
7097                                        CMSBitMap* mod_union_table,
7098                                        CMSMarkStack*  mark_stack,
7099                                        bool           concurrent_precleaning):
7100   MetadataAwareOopClosure(rp),
7101   _collector(collector),
7102   _span(span),
7103   _bit_map(bit_map),
7104   _mod_union_table(mod_union_table),
7105   _mark_stack(mark_stack),
7106   _concurrent_precleaning(concurrent_precleaning)
7107 {
7108   assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7109 }
7110 
7111 // Grey object rescan during pre-cleaning and second checkpoint phases --
7112 // the non-parallel version (the parallel version appears further below.)
7113 void PushAndMarkClosure::do_oop(oop obj) {
7114   // Ignore mark word verification. If during concurrent precleaning,
7115   // the object monitor may be locked. If during the checkpoint
7116   // phases, the object may already have been reached by a  different
7117   // path and may be at the end of the global overflow list (so
7118   // the mark word may be NULL).
7119   assert(obj->is_oop_or_null(true /* ignore mark word */),
7120          err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7121   HeapWord* addr = (HeapWord*)obj;
7122   // Check if oop points into the CMS generation
7123   // and is not marked
7124   if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7125     // a white object ...
7126     _bit_map->mark(addr);         // ... now grey
7127     // push on the marking stack (grey set)
7128     bool simulate_overflow = false;
7129     NOT_PRODUCT(
7130       if (CMSMarkStackOverflowALot &&
7131           _collector->simulate_overflow()) {
7132         // simulate a stack overflow
7133         simulate_overflow = true;
7134       }
7135     )
7136     if (simulate_overflow || !_mark_stack->push(obj)) {
7137       if (_concurrent_precleaning) {
7138          // During precleaning we can just dirty the appropriate card(s)
7139          // in the mod union table, thus ensuring that the object remains
7140          // in the grey set  and continue. In the case of object arrays
7141          // we need to dirty all of the cards that the object spans,
7142          // since the rescan of object arrays will be limited to the
7143          // dirty cards.
7144          // Note that no one can be interfering with us in this action
7145          // of dirtying the mod union table, so no locking or atomics
7146          // are required.
7147          if (obj->is_objArray()) {
7148            size_t sz = obj->size();
7149            HeapWord* end_card_addr = (HeapWord*)round_to(
7150                                         (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7151            MemRegion redirty_range = MemRegion(addr, end_card_addr);
7152            assert(!redirty_range.is_empty(), "Arithmetical tautology");
7153            _mod_union_table->mark_range(redirty_range);
7154          } else {
7155            _mod_union_table->mark(addr);
7156          }
7157          _collector->_ser_pmc_preclean_ovflw++;
7158       } else {
7159          // During the remark phase, we need to remember this oop
7160          // in the overflow list.
7161          _collector->push_on_overflow_list(obj);
7162          _collector->_ser_pmc_remark_ovflw++;
7163       }
7164     }
7165   }
7166 }
7167 
7168 Par_PushAndMarkClosure::Par_PushAndMarkClosure(CMSCollector* collector,
7169                                                MemRegion span,
7170                                                ReferenceProcessor* rp,
7171                                                CMSBitMap* bit_map,
7172                                                OopTaskQueue* work_queue):
7173   MetadataAwareOopClosure(rp),
7174   _collector(collector),
7175   _span(span),
7176   _bit_map(bit_map),
7177   _work_queue(work_queue)
7178 {
7179   assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7180 }
7181 
7182 void PushAndMarkClosure::do_oop(oop* p)       { PushAndMarkClosure::do_oop_work(p); }
7183 void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); }
7184 
7185 // Grey object rescan during second checkpoint phase --
7186 // the parallel version.
7187 void Par_PushAndMarkClosure::do_oop(oop obj) {
7188   // In the assert below, we ignore the mark word because
7189   // this oop may point to an already visited object that is
7190   // on the overflow stack (in which case the mark word has
7191   // been hijacked for chaining into the overflow stack --
7192   // if this is the last object in the overflow stack then
7193   // its mark word will be NULL). Because this object may
7194   // have been subsequently popped off the global overflow
7195   // stack, and the mark word possibly restored to the prototypical
7196   // value, by the time we get to examined this failing assert in
7197   // the debugger, is_oop_or_null(false) may subsequently start
7198   // to hold.
7199   assert(obj->is_oop_or_null(true),
7200          err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7201   HeapWord* addr = (HeapWord*)obj;
7202   // Check if oop points into the CMS generation
7203   // and is not marked
7204   if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7205     // a white object ...
7206     // If we manage to "claim" the object, by being the
7207     // first thread to mark it, then we push it on our
7208     // marking stack
7209     if (_bit_map->par_mark(addr)) {     // ... now grey
7210       // push on work queue (grey set)
7211       bool simulate_overflow = false;
7212       NOT_PRODUCT(
7213         if (CMSMarkStackOverflowALot &&
7214             _collector->par_simulate_overflow()) {
7215           // simulate a stack overflow
7216           simulate_overflow = true;
7217         }
7218       )
7219       if (simulate_overflow || !_work_queue->push(obj)) {
7220         _collector->par_push_on_overflow_list(obj);
7221         _collector->_par_pmc_remark_ovflw++; //  imprecise OK: no need to CAS
7222       }
7223     } // Else, some other thread got there first
7224   }
7225 }
7226 
7227 void Par_PushAndMarkClosure::do_oop(oop* p)       { Par_PushAndMarkClosure::do_oop_work(p); }
7228 void Par_PushAndMarkClosure::do_oop(narrowOop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7229 
7230 void CMSPrecleanRefsYieldClosure::do_yield_work() {
7231   Mutex* bml = _collector->bitMapLock();
7232   assert_lock_strong(bml);
7233   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7234          "CMS thread should hold CMS token");
7235 
7236   bml->unlock();
7237   ConcurrentMarkSweepThread::desynchronize(true);
7238 
7239   _collector->stopTimer();
7240   if (PrintCMSStatistics != 0) {
7241     _collector->incrementYields();
7242   }
7243 
7244   // See the comment in coordinator_yield()
7245   for (unsigned i = 0; i < CMSYieldSleepCount &&
7246                        ConcurrentMarkSweepThread::should_yield() &&
7247                        !CMSCollector::foregroundGCIsActive(); ++i) {
7248     os::sleep(Thread::current(), 1, false);
7249   }
7250 
7251   ConcurrentMarkSweepThread::synchronize(true);
7252   bml->lock();
7253 
7254   _collector->startTimer();
7255 }
7256 
7257 bool CMSPrecleanRefsYieldClosure::should_return() {
7258   if (ConcurrentMarkSweepThread::should_yield()) {
7259     do_yield_work();
7260   }
7261   return _collector->foregroundGCIsActive();
7262 }
7263 
7264 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
7265   assert(((size_t)mr.start())%CardTableModRefBS::card_size_in_words == 0,
7266          "mr should be aligned to start at a card boundary");
7267   // We'd like to assert:
7268   // assert(mr.word_size()%CardTableModRefBS::card_size_in_words == 0,
7269   //        "mr should be a range of cards");
7270   // However, that would be too strong in one case -- the last
7271   // partition ends at _unallocated_block which, in general, can be
7272   // an arbitrary boundary, not necessarily card aligned.
7273   if (PrintCMSStatistics != 0) {
7274     _num_dirty_cards +=
7275          mr.word_size()/CardTableModRefBS::card_size_in_words;
7276   }
7277   _space->object_iterate_mem(mr, &_scan_cl);
7278 }
7279 
7280 SweepClosure::SweepClosure(CMSCollector* collector,
7281                            ConcurrentMarkSweepGeneration* g,
7282                            CMSBitMap* bitMap, bool should_yield) :
7283   _collector(collector),
7284   _g(g),
7285   _sp(g->cmsSpace()),
7286   _limit(_sp->sweep_limit()),
7287   _freelistLock(_sp->freelistLock()),
7288   _bitMap(bitMap),
7289   _yield(should_yield),
7290   _inFreeRange(false),           // No free range at beginning of sweep
7291   _freeRangeInFreeLists(false),  // No free range at beginning of sweep
7292   _lastFreeRangeCoalesced(false),
7293   _freeFinger(g->used_region().start())
7294 {
7295   NOT_PRODUCT(
7296     _numObjectsFreed = 0;
7297     _numWordsFreed   = 0;
7298     _numObjectsLive = 0;
7299     _numWordsLive = 0;
7300     _numObjectsAlreadyFree = 0;
7301     _numWordsAlreadyFree = 0;
7302     _last_fc = NULL;
7303 
7304     _sp->initializeIndexedFreeListArrayReturnedBytes();
7305     _sp->dictionary()->initialize_dict_returned_bytes();
7306   )
7307   assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7308          "sweep _limit out of bounds");
7309   if (CMSTraceSweeper) {
7310     gclog_or_tty->print_cr("\n====================\nStarting new sweep with limit " PTR_FORMAT,
7311                         p2i(_limit));
7312   }
7313 }
7314 
7315 void SweepClosure::print_on(outputStream* st) const {
7316   tty->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")",
7317                 p2i(_sp->bottom()), p2i(_sp->end()));
7318   tty->print_cr("_limit = " PTR_FORMAT, p2i(_limit));
7319   tty->print_cr("_freeFinger = " PTR_FORMAT, p2i(_freeFinger));
7320   NOT_PRODUCT(tty->print_cr("_last_fc = " PTR_FORMAT, p2i(_last_fc));)
7321   tty->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d",
7322                 _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced);
7323 }
7324 
7325 #ifndef PRODUCT
7326 // Assertion checking only:  no useful work in product mode --
7327 // however, if any of the flags below become product flags,
7328 // you may need to review this code to see if it needs to be
7329 // enabled in product mode.
7330 SweepClosure::~SweepClosure() {
7331   assert_lock_strong(_freelistLock);
7332   assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7333          "sweep _limit out of bounds");
7334   if (inFreeRange()) {
7335     warning("inFreeRange() should have been reset; dumping state of SweepClosure");
7336     print();
7337     ShouldNotReachHere();
7338   }
7339   if (Verbose && PrintGC) {
7340     gclog_or_tty->print("Collected "SIZE_FORMAT" objects, " SIZE_FORMAT " bytes",
7341                         _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
7342     gclog_or_tty->print_cr("\nLive "SIZE_FORMAT" objects,  "
7343                            SIZE_FORMAT" bytes  "
7344       "Already free "SIZE_FORMAT" objects, "SIZE_FORMAT" bytes",
7345       _numObjectsLive, _numWordsLive*sizeof(HeapWord),
7346       _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
7347     size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree)
7348                         * sizeof(HeapWord);
7349     gclog_or_tty->print_cr("Total sweep: "SIZE_FORMAT" bytes", totalBytes);
7350 
7351     if (PrintCMSStatistics && CMSVerifyReturnedBytes) {
7352       size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
7353       size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes();
7354       size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes;
7355       gclog_or_tty->print("Returned "SIZE_FORMAT" bytes", returned_bytes);
7356       gclog_or_tty->print("   Indexed List Returned "SIZE_FORMAT" bytes",
7357         indexListReturnedBytes);
7358       gclog_or_tty->print_cr("        Dictionary Returned "SIZE_FORMAT" bytes",
7359         dict_returned_bytes);
7360     }
7361   }
7362   if (CMSTraceSweeper) {
7363     gclog_or_tty->print_cr("end of sweep with _limit = " PTR_FORMAT "\n================",
7364                            p2i(_limit));
7365   }
7366 }
7367 #endif  // PRODUCT
7368 
7369 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
7370     bool freeRangeInFreeLists) {
7371   if (CMSTraceSweeper) {
7372     gclog_or_tty->print("---- Start free range at " PTR_FORMAT " with free block (%d)\n",
7373                p2i(freeFinger), freeRangeInFreeLists);
7374   }
7375   assert(!inFreeRange(), "Trampling existing free range");
7376   set_inFreeRange(true);
7377   set_lastFreeRangeCoalesced(false);
7378 
7379   set_freeFinger(freeFinger);
7380   set_freeRangeInFreeLists(freeRangeInFreeLists);
7381   if (CMSTestInFreeList) {
7382     if (freeRangeInFreeLists) {
7383       FreeChunk* fc = (FreeChunk*) freeFinger;
7384       assert(fc->is_free(), "A chunk on the free list should be free.");
7385       assert(fc->size() > 0, "Free range should have a size");
7386       assert(_sp->verify_chunk_in_free_list(fc), "Chunk is not in free lists");
7387     }
7388   }
7389 }
7390 
7391 // Note that the sweeper runs concurrently with mutators. Thus,
7392 // it is possible for direct allocation in this generation to happen
7393 // in the middle of the sweep. Note that the sweeper also coalesces
7394 // contiguous free blocks. Thus, unless the sweeper and the allocator
7395 // synchronize appropriately freshly allocated blocks may get swept up.
7396 // This is accomplished by the sweeper locking the free lists while
7397 // it is sweeping. Thus blocks that are determined to be free are
7398 // indeed free. There is however one additional complication:
7399 // blocks that have been allocated since the final checkpoint and
7400 // mark, will not have been marked and so would be treated as
7401 // unreachable and swept up. To prevent this, the allocator marks
7402 // the bit map when allocating during the sweep phase. This leads,
7403 // however, to a further complication -- objects may have been allocated
7404 // but not yet initialized -- in the sense that the header isn't yet
7405 // installed. The sweeper can not then determine the size of the block
7406 // in order to skip over it. To deal with this case, we use a technique
7407 // (due to Printezis) to encode such uninitialized block sizes in the
7408 // bit map. Since the bit map uses a bit per every HeapWord, but the
7409 // CMS generation has a minimum object size of 3 HeapWords, it follows
7410 // that "normal marks" won't be adjacent in the bit map (there will
7411 // always be at least two 0 bits between successive 1 bits). We make use
7412 // of these "unused" bits to represent uninitialized blocks -- the bit
7413 // corresponding to the start of the uninitialized object and the next
7414 // bit are both set. Finally, a 1 bit marks the end of the object that
7415 // started with the two consecutive 1 bits to indicate its potentially
7416 // uninitialized state.
7417 
7418 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
7419   FreeChunk* fc = (FreeChunk*)addr;
7420   size_t res;
7421 
7422   // Check if we are done sweeping. Below we check "addr >= _limit" rather
7423   // than "addr == _limit" because although _limit was a block boundary when
7424   // we started the sweep, it may no longer be one because heap expansion
7425   // may have caused us to coalesce the block ending at the address _limit
7426   // with a newly expanded chunk (this happens when _limit was set to the
7427   // previous _end of the space), so we may have stepped past _limit:
7428   // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740.
7429   if (addr >= _limit) { // we have swept up to or past the limit: finish up
7430     assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7431            "sweep _limit out of bounds");
7432     assert(addr < _sp->end(), "addr out of bounds");
7433     // Flush any free range we might be holding as a single
7434     // coalesced chunk to the appropriate free list.
7435     if (inFreeRange()) {
7436       assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit,
7437              err_msg("freeFinger() " PTR_FORMAT" is out-of-bounds", p2i(freeFinger())));
7438       flush_cur_free_chunk(freeFinger(),
7439                            pointer_delta(addr, freeFinger()));
7440       if (CMSTraceSweeper) {
7441         gclog_or_tty->print("Sweep: last chunk: ");
7442         gclog_or_tty->print("put_free_blk " PTR_FORMAT " ("SIZE_FORMAT") "
7443                    "[coalesced:%d]\n",
7444                    p2i(freeFinger()), pointer_delta(addr, freeFinger()),
7445                    lastFreeRangeCoalesced() ? 1 : 0);
7446       }
7447     }
7448 
7449     // help the iterator loop finish
7450     return pointer_delta(_sp->end(), addr);
7451   }
7452 
7453   assert(addr < _limit, "sweep invariant");
7454   // check if we should yield
7455   do_yield_check(addr);
7456   if (fc->is_free()) {
7457     // Chunk that is already free
7458     res = fc->size();
7459     do_already_free_chunk(fc);
7460     debug_only(_sp->verifyFreeLists());
7461     // If we flush the chunk at hand in lookahead_and_flush()
7462     // and it's coalesced with a preceding chunk, then the
7463     // process of "mangling" the payload of the coalesced block
7464     // will cause erasure of the size information from the
7465     // (erstwhile) header of all the coalesced blocks but the
7466     // first, so the first disjunct in the assert will not hold
7467     // in that specific case (in which case the second disjunct
7468     // will hold).
7469     assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit,
7470            "Otherwise the size info doesn't change at this step");
7471     NOT_PRODUCT(
7472       _numObjectsAlreadyFree++;
7473       _numWordsAlreadyFree += res;
7474     )
7475     NOT_PRODUCT(_last_fc = fc;)
7476   } else if (!_bitMap->isMarked(addr)) {
7477     // Chunk is fresh garbage
7478     res = do_garbage_chunk(fc);
7479     debug_only(_sp->verifyFreeLists());
7480     NOT_PRODUCT(
7481       _numObjectsFreed++;
7482       _numWordsFreed += res;
7483     )
7484   } else {
7485     // Chunk that is alive.
7486     res = do_live_chunk(fc);
7487     debug_only(_sp->verifyFreeLists());
7488     NOT_PRODUCT(
7489         _numObjectsLive++;
7490         _numWordsLive += res;
7491     )
7492   }
7493   return res;
7494 }
7495 
7496 // For the smart allocation, record following
7497 //  split deaths - a free chunk is removed from its free list because
7498 //      it is being split into two or more chunks.
7499 //  split birth - a free chunk is being added to its free list because
7500 //      a larger free chunk has been split and resulted in this free chunk.
7501 //  coal death - a free chunk is being removed from its free list because
7502 //      it is being coalesced into a large free chunk.
7503 //  coal birth - a free chunk is being added to its free list because
7504 //      it was created when two or more free chunks where coalesced into
7505 //      this free chunk.
7506 //
7507 // These statistics are used to determine the desired number of free
7508 // chunks of a given size.  The desired number is chosen to be relative
7509 // to the end of a CMS sweep.  The desired number at the end of a sweep
7510 // is the
7511 //      count-at-end-of-previous-sweep (an amount that was enough)
7512 //              - count-at-beginning-of-current-sweep  (the excess)
7513 //              + split-births  (gains in this size during interval)
7514 //              - split-deaths  (demands on this size during interval)
7515 // where the interval is from the end of one sweep to the end of the
7516 // next.
7517 //
7518 // When sweeping the sweeper maintains an accumulated chunk which is
7519 // the chunk that is made up of chunks that have been coalesced.  That
7520 // will be termed the left-hand chunk.  A new chunk of garbage that
7521 // is being considered for coalescing will be referred to as the
7522 // right-hand chunk.
7523 //
7524 // When making a decision on whether to coalesce a right-hand chunk with
7525 // the current left-hand chunk, the current count vs. the desired count
7526 // of the left-hand chunk is considered.  Also if the right-hand chunk
7527 // is near the large chunk at the end of the heap (see
7528 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
7529 // left-hand chunk is coalesced.
7530 //
7531 // When making a decision about whether to split a chunk, the desired count
7532 // vs. the current count of the candidate to be split is also considered.
7533 // If the candidate is underpopulated (currently fewer chunks than desired)
7534 // a chunk of an overpopulated (currently more chunks than desired) size may
7535 // be chosen.  The "hint" associated with a free list, if non-null, points
7536 // to a free list which may be overpopulated.
7537 //
7538 
7539 void SweepClosure::do_already_free_chunk(FreeChunk* fc) {
7540   const size_t size = fc->size();
7541   // Chunks that cannot be coalesced are not in the
7542   // free lists.
7543   if (CMSTestInFreeList && !fc->cantCoalesce()) {
7544     assert(_sp->verify_chunk_in_free_list(fc),
7545       "free chunk should be in free lists");
7546   }
7547   // a chunk that is already free, should not have been
7548   // marked in the bit map
7549   HeapWord* const addr = (HeapWord*) fc;
7550   assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
7551   // Verify that the bit map has no bits marked between
7552   // addr and purported end of this block.
7553   _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7554 
7555   // Some chunks cannot be coalesced under any circumstances.
7556   // See the definition of cantCoalesce().
7557   if (!fc->cantCoalesce()) {
7558     // This chunk can potentially be coalesced.
7559     if (_sp->adaptive_freelists()) {
7560       // All the work is done in
7561       do_post_free_or_garbage_chunk(fc, size);
7562     } else {  // Not adaptive free lists
7563       // this is a free chunk that can potentially be coalesced by the sweeper;
7564       if (!inFreeRange()) {
7565         // if the next chunk is a free block that can't be coalesced
7566         // it doesn't make sense to remove this chunk from the free lists
7567         FreeChunk* nextChunk = (FreeChunk*)(addr + size);
7568         assert((HeapWord*)nextChunk <= _sp->end(), "Chunk size out of bounds?");
7569         if ((HeapWord*)nextChunk < _sp->end() &&     // There is another free chunk to the right ...
7570             nextChunk->is_free()               &&     // ... which is free...
7571             nextChunk->cantCoalesce()) {             // ... but can't be coalesced
7572           // nothing to do
7573         } else {
7574           // Potentially the start of a new free range:
7575           // Don't eagerly remove it from the free lists.
7576           // No need to remove it if it will just be put
7577           // back again.  (Also from a pragmatic point of view
7578           // if it is a free block in a region that is beyond
7579           // any allocated blocks, an assertion will fail)
7580           // Remember the start of a free run.
7581           initialize_free_range(addr, true);
7582           // end - can coalesce with next chunk
7583         }
7584       } else {
7585         // the midst of a free range, we are coalescing
7586         print_free_block_coalesced(fc);
7587         if (CMSTraceSweeper) {
7588           gclog_or_tty->print("  -- pick up free block " PTR_FORMAT " (" SIZE_FORMAT ")\n", p2i(fc), size);
7589         }
7590         // remove it from the free lists
7591         _sp->removeFreeChunkFromFreeLists(fc);
7592         set_lastFreeRangeCoalesced(true);
7593         // If the chunk is being coalesced and the current free range is
7594         // in the free lists, remove the current free range so that it
7595         // will be returned to the free lists in its entirety - all
7596         // the coalesced pieces included.
7597         if (freeRangeInFreeLists()) {
7598           FreeChunk* ffc = (FreeChunk*) freeFinger();
7599           assert(ffc->size() == pointer_delta(addr, freeFinger()),
7600             "Size of free range is inconsistent with chunk size.");
7601           if (CMSTestInFreeList) {
7602             assert(_sp->verify_chunk_in_free_list(ffc),
7603               "free range is not in free lists");
7604           }
7605           _sp->removeFreeChunkFromFreeLists(ffc);
7606           set_freeRangeInFreeLists(false);
7607         }
7608       }
7609     }
7610     // Note that if the chunk is not coalescable (the else arm
7611     // below), we unconditionally flush, without needing to do
7612     // a "lookahead," as we do below.
7613     if (inFreeRange()) lookahead_and_flush(fc, size);
7614   } else {
7615     // Code path common to both original and adaptive free lists.
7616 
7617     // cant coalesce with previous block; this should be treated
7618     // as the end of a free run if any
7619     if (inFreeRange()) {
7620       // we kicked some butt; time to pick up the garbage
7621       assert(freeFinger() < addr, "freeFinger points too high");
7622       flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7623     }
7624     // else, nothing to do, just continue
7625   }
7626 }
7627 
7628 size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) {
7629   // This is a chunk of garbage.  It is not in any free list.
7630   // Add it to a free list or let it possibly be coalesced into
7631   // a larger chunk.
7632   HeapWord* const addr = (HeapWord*) fc;
7633   const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7634 
7635   if (_sp->adaptive_freelists()) {
7636     // Verify that the bit map has no bits marked between
7637     // addr and purported end of just dead object.
7638     _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7639 
7640     do_post_free_or_garbage_chunk(fc, size);
7641   } else {
7642     if (!inFreeRange()) {
7643       // start of a new free range
7644       assert(size > 0, "A free range should have a size");
7645       initialize_free_range(addr, false);
7646     } else {
7647       // this will be swept up when we hit the end of the
7648       // free range
7649       if (CMSTraceSweeper) {
7650         gclog_or_tty->print("  -- pick up garbage " PTR_FORMAT " (" SIZE_FORMAT ")\n", p2i(fc), size);
7651       }
7652       // If the chunk is being coalesced and the current free range is
7653       // in the free lists, remove the current free range so that it
7654       // will be returned to the free lists in its entirety - all
7655       // the coalesced pieces included.
7656       if (freeRangeInFreeLists()) {
7657         FreeChunk* ffc = (FreeChunk*)freeFinger();
7658         assert(ffc->size() == pointer_delta(addr, freeFinger()),
7659           "Size of free range is inconsistent with chunk size.");
7660         if (CMSTestInFreeList) {
7661           assert(_sp->verify_chunk_in_free_list(ffc),
7662             "free range is not in free lists");
7663         }
7664         _sp->removeFreeChunkFromFreeLists(ffc);
7665         set_freeRangeInFreeLists(false);
7666       }
7667       set_lastFreeRangeCoalesced(true);
7668     }
7669     // this will be swept up when we hit the end of the free range
7670 
7671     // Verify that the bit map has no bits marked between
7672     // addr and purported end of just dead object.
7673     _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7674   }
7675   assert(_limit >= addr + size,
7676          "A freshly garbage chunk can't possibly straddle over _limit");
7677   if (inFreeRange()) lookahead_and_flush(fc, size);
7678   return size;
7679 }
7680 
7681 size_t SweepClosure::do_live_chunk(FreeChunk* fc) {
7682   HeapWord* addr = (HeapWord*) fc;
7683   // The sweeper has just found a live object. Return any accumulated
7684   // left hand chunk to the free lists.
7685   if (inFreeRange()) {
7686     assert(freeFinger() < addr, "freeFinger points too high");
7687     flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7688   }
7689 
7690   // This object is live: we'd normally expect this to be
7691   // an oop, and like to assert the following:
7692   // assert(oop(addr)->is_oop(), "live block should be an oop");
7693   // However, as we commented above, this may be an object whose
7694   // header hasn't yet been initialized.
7695   size_t size;
7696   assert(_bitMap->isMarked(addr), "Tautology for this control point");
7697   if (_bitMap->isMarked(addr + 1)) {
7698     // Determine the size from the bit map, rather than trying to
7699     // compute it from the object header.
7700     HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
7701     size = pointer_delta(nextOneAddr + 1, addr);
7702     assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
7703            "alignment problem");
7704 
7705 #ifdef ASSERT
7706       if (oop(addr)->klass_or_null() != NULL) {
7707         // Ignore mark word because we are running concurrent with mutators
7708         assert(oop(addr)->is_oop(true), "live block should be an oop");
7709         assert(size ==
7710                CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
7711                "P-mark and computed size do not agree");
7712       }
7713 #endif
7714 
7715   } else {
7716     // This should be an initialized object that's alive.
7717     assert(oop(addr)->klass_or_null() != NULL,
7718            "Should be an initialized object");
7719     // Ignore mark word because we are running concurrent with mutators
7720     assert(oop(addr)->is_oop(true), "live block should be an oop");
7721     // Verify that the bit map has no bits marked between
7722     // addr and purported end of this block.
7723     size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7724     assert(size >= 3, "Necessary for Printezis marks to work");
7725     assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
7726     DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
7727   }
7728   return size;
7729 }
7730 
7731 void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc,
7732                                                  size_t chunkSize) {
7733   // do_post_free_or_garbage_chunk() should only be called in the case
7734   // of the adaptive free list allocator.
7735   const bool fcInFreeLists = fc->is_free();
7736   assert(_sp->adaptive_freelists(), "Should only be used in this case.");
7737   assert((HeapWord*)fc <= _limit, "sweep invariant");
7738   if (CMSTestInFreeList && fcInFreeLists) {
7739     assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists");
7740   }
7741 
7742   if (CMSTraceSweeper) {
7743     gclog_or_tty->print_cr("  -- pick up another chunk at " PTR_FORMAT " (" SIZE_FORMAT ")", p2i(fc), chunkSize);
7744   }
7745 
7746   HeapWord* const fc_addr = (HeapWord*) fc;
7747 
7748   bool coalesce;
7749   const size_t left  = pointer_delta(fc_addr, freeFinger());
7750   const size_t right = chunkSize;
7751   switch (FLSCoalescePolicy) {
7752     // numeric value forms a coalition aggressiveness metric
7753     case 0:  { // never coalesce
7754       coalesce = false;
7755       break;
7756     }
7757     case 1: { // coalesce if left & right chunks on overpopulated lists
7758       coalesce = _sp->coalOverPopulated(left) &&
7759                  _sp->coalOverPopulated(right);
7760       break;
7761     }
7762     case 2: { // coalesce if left chunk on overpopulated list (default)
7763       coalesce = _sp->coalOverPopulated(left);
7764       break;
7765     }
7766     case 3: { // coalesce if left OR right chunk on overpopulated list
7767       coalesce = _sp->coalOverPopulated(left) ||
7768                  _sp->coalOverPopulated(right);
7769       break;
7770     }
7771     case 4: { // always coalesce
7772       coalesce = true;
7773       break;
7774     }
7775     default:
7776      ShouldNotReachHere();
7777   }
7778 
7779   // Should the current free range be coalesced?
7780   // If the chunk is in a free range and either we decided to coalesce above
7781   // or the chunk is near the large block at the end of the heap
7782   // (isNearLargestChunk() returns true), then coalesce this chunk.
7783   const bool doCoalesce = inFreeRange()
7784                           && (coalesce || _g->isNearLargestChunk(fc_addr));
7785   if (doCoalesce) {
7786     // Coalesce the current free range on the left with the new
7787     // chunk on the right.  If either is on a free list,
7788     // it must be removed from the list and stashed in the closure.
7789     if (freeRangeInFreeLists()) {
7790       FreeChunk* const ffc = (FreeChunk*)freeFinger();
7791       assert(ffc->size() == pointer_delta(fc_addr, freeFinger()),
7792         "Size of free range is inconsistent with chunk size.");
7793       if (CMSTestInFreeList) {
7794         assert(_sp->verify_chunk_in_free_list(ffc),
7795           "Chunk is not in free lists");
7796       }
7797       _sp->coalDeath(ffc->size());
7798       _sp->removeFreeChunkFromFreeLists(ffc);
7799       set_freeRangeInFreeLists(false);
7800     }
7801     if (fcInFreeLists) {
7802       _sp->coalDeath(chunkSize);
7803       assert(fc->size() == chunkSize,
7804         "The chunk has the wrong size or is not in the free lists");
7805       _sp->removeFreeChunkFromFreeLists(fc);
7806     }
7807     set_lastFreeRangeCoalesced(true);
7808     print_free_block_coalesced(fc);
7809   } else {  // not in a free range and/or should not coalesce
7810     // Return the current free range and start a new one.
7811     if (inFreeRange()) {
7812       // In a free range but cannot coalesce with the right hand chunk.
7813       // Put the current free range into the free lists.
7814       flush_cur_free_chunk(freeFinger(),
7815                            pointer_delta(fc_addr, freeFinger()));
7816     }
7817     // Set up for new free range.  Pass along whether the right hand
7818     // chunk is in the free lists.
7819     initialize_free_range((HeapWord*)fc, fcInFreeLists);
7820   }
7821 }
7822 
7823 // Lookahead flush:
7824 // If we are tracking a free range, and this is the last chunk that
7825 // we'll look at because its end crosses past _limit, we'll preemptively
7826 // flush it along with any free range we may be holding on to. Note that
7827 // this can be the case only for an already free or freshly garbage
7828 // chunk. If this block is an object, it can never straddle
7829 // over _limit. The "straddling" occurs when _limit is set at
7830 // the previous end of the space when this cycle started, and
7831 // a subsequent heap expansion caused the previously co-terminal
7832 // free block to be coalesced with the newly expanded portion,
7833 // thus rendering _limit a non-block-boundary making it dangerous
7834 // for the sweeper to step over and examine.
7835 void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) {
7836   assert(inFreeRange(), "Should only be called if currently in a free range.");
7837   HeapWord* const eob = ((HeapWord*)fc) + chunk_size;
7838   assert(_sp->used_region().contains(eob - 1),
7839          err_msg("eob = " PTR_FORMAT " eob-1 = " PTR_FORMAT " _limit = " PTR_FORMAT
7840                  " out of bounds wrt _sp = [" PTR_FORMAT "," PTR_FORMAT ")"
7841                  " when examining fc = " PTR_FORMAT "(" SIZE_FORMAT ")",
7842                  p2i(eob), p2i(eob-1), p2i(_limit), p2i(_sp->bottom()), p2i(_sp->end()), p2i(fc), chunk_size));
7843   if (eob >= _limit) {
7844     assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit");
7845     if (CMSTraceSweeper) {
7846       gclog_or_tty->print_cr("_limit " PTR_FORMAT " reached or crossed by block "
7847                              "[" PTR_FORMAT "," PTR_FORMAT ") in space "
7848                              "[" PTR_FORMAT "," PTR_FORMAT ")",
7849                              p2i(_limit), p2i(fc), p2i(eob), p2i(_sp->bottom()), p2i(_sp->end()));
7850     }
7851     // Return the storage we are tracking back into the free lists.
7852     if (CMSTraceSweeper) {
7853       gclog_or_tty->print_cr("Flushing ... ");
7854     }
7855     assert(freeFinger() < eob, "Error");
7856     flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger()));
7857   }
7858 }
7859 
7860 void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) {
7861   assert(inFreeRange(), "Should only be called if currently in a free range.");
7862   assert(size > 0,
7863     "A zero sized chunk cannot be added to the free lists.");
7864   if (!freeRangeInFreeLists()) {
7865     if (CMSTestInFreeList) {
7866       FreeChunk* fc = (FreeChunk*) chunk;
7867       fc->set_size(size);
7868       assert(!_sp->verify_chunk_in_free_list(fc),
7869         "chunk should not be in free lists yet");
7870     }
7871     if (CMSTraceSweeper) {
7872       gclog_or_tty->print_cr(" -- add free block " PTR_FORMAT " (" SIZE_FORMAT ") to free lists",
7873                     p2i(chunk), size);
7874     }
7875     // A new free range is going to be starting.  The current
7876     // free range has not been added to the free lists yet or
7877     // was removed so add it back.
7878     // If the current free range was coalesced, then the death
7879     // of the free range was recorded.  Record a birth now.
7880     if (lastFreeRangeCoalesced()) {
7881       _sp->coalBirth(size);
7882     }
7883     _sp->addChunkAndRepairOffsetTable(chunk, size,
7884             lastFreeRangeCoalesced());
7885   } else if (CMSTraceSweeper) {
7886     gclog_or_tty->print_cr("Already in free list: nothing to flush");
7887   }
7888   set_inFreeRange(false);
7889   set_freeRangeInFreeLists(false);
7890 }
7891 
7892 // We take a break if we've been at this for a while,
7893 // so as to avoid monopolizing the locks involved.
7894 void SweepClosure::do_yield_work(HeapWord* addr) {
7895   // Return current free chunk being used for coalescing (if any)
7896   // to the appropriate freelist.  After yielding, the next
7897   // free block encountered will start a coalescing range of
7898   // free blocks.  If the next free block is adjacent to the
7899   // chunk just flushed, they will need to wait for the next
7900   // sweep to be coalesced.
7901   if (inFreeRange()) {
7902     flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7903   }
7904 
7905   // First give up the locks, then yield, then re-lock.
7906   // We should probably use a constructor/destructor idiom to
7907   // do this unlock/lock or modify the MutexUnlocker class to
7908   // serve our purpose. XXX
7909   assert_lock_strong(_bitMap->lock());
7910   assert_lock_strong(_freelistLock);
7911   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7912          "CMS thread should hold CMS token");
7913   _bitMap->lock()->unlock();
7914   _freelistLock->unlock();
7915   ConcurrentMarkSweepThread::desynchronize(true);
7916   _collector->stopTimer();
7917   if (PrintCMSStatistics != 0) {
7918     _collector->incrementYields();
7919   }
7920 
7921   // See the comment in coordinator_yield()
7922   for (unsigned i = 0; i < CMSYieldSleepCount &&
7923                        ConcurrentMarkSweepThread::should_yield() &&
7924                        !CMSCollector::foregroundGCIsActive(); ++i) {
7925     os::sleep(Thread::current(), 1, false);
7926   }
7927 
7928   ConcurrentMarkSweepThread::synchronize(true);
7929   _freelistLock->lock();
7930   _bitMap->lock()->lock_without_safepoint_check();
7931   _collector->startTimer();
7932 }
7933 
7934 #ifndef PRODUCT
7935 // This is actually very useful in a product build if it can
7936 // be called from the debugger.  Compile it into the product
7937 // as needed.
7938 bool debug_verify_chunk_in_free_list(FreeChunk* fc) {
7939   return debug_cms_space->verify_chunk_in_free_list(fc);
7940 }
7941 #endif
7942 
7943 void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const {
7944   if (CMSTraceSweeper) {
7945     gclog_or_tty->print_cr("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")",
7946                            p2i(fc), fc->size());
7947   }
7948 }
7949 
7950 // CMSIsAliveClosure
7951 bool CMSIsAliveClosure::do_object_b(oop obj) {
7952   HeapWord* addr = (HeapWord*)obj;
7953   return addr != NULL &&
7954          (!_span.contains(addr) || _bit_map->isMarked(addr));
7955 }
7956 
7957 
7958 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector,
7959                       MemRegion span,
7960                       CMSBitMap* bit_map, CMSMarkStack* mark_stack,
7961                       bool cpc):
7962   _collector(collector),
7963   _span(span),
7964   _bit_map(bit_map),
7965   _mark_stack(mark_stack),
7966   _concurrent_precleaning(cpc) {
7967   assert(!_span.is_empty(), "Empty span could spell trouble");
7968 }
7969 
7970 
7971 // CMSKeepAliveClosure: the serial version
7972 void CMSKeepAliveClosure::do_oop(oop obj) {
7973   HeapWord* addr = (HeapWord*)obj;
7974   if (_span.contains(addr) &&
7975       !_bit_map->isMarked(addr)) {
7976     _bit_map->mark(addr);
7977     bool simulate_overflow = false;
7978     NOT_PRODUCT(
7979       if (CMSMarkStackOverflowALot &&
7980           _collector->simulate_overflow()) {
7981         // simulate a stack overflow
7982         simulate_overflow = true;
7983       }
7984     )
7985     if (simulate_overflow || !_mark_stack->push(obj)) {
7986       if (_concurrent_precleaning) {
7987         // We dirty the overflown object and let the remark
7988         // phase deal with it.
7989         assert(_collector->overflow_list_is_empty(), "Error");
7990         // In the case of object arrays, we need to dirty all of
7991         // the cards that the object spans. No locking or atomics
7992         // are needed since no one else can be mutating the mod union
7993         // table.
7994         if (obj->is_objArray()) {
7995           size_t sz = obj->size();
7996           HeapWord* end_card_addr =
7997             (HeapWord*)round_to((intptr_t)(addr+sz), CardTableModRefBS::card_size);
7998           MemRegion redirty_range = MemRegion(addr, end_card_addr);
7999           assert(!redirty_range.is_empty(), "Arithmetical tautology");
8000           _collector->_modUnionTable.mark_range(redirty_range);
8001         } else {
8002           _collector->_modUnionTable.mark(addr);
8003         }
8004         _collector->_ser_kac_preclean_ovflw++;
8005       } else {
8006         _collector->push_on_overflow_list(obj);
8007         _collector->_ser_kac_ovflw++;
8008       }
8009     }
8010   }
8011 }
8012 
8013 void CMSKeepAliveClosure::do_oop(oop* p)       { CMSKeepAliveClosure::do_oop_work(p); }
8014 void CMSKeepAliveClosure::do_oop(narrowOop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8015 
8016 // CMSParKeepAliveClosure: a parallel version of the above.
8017 // The work queues are private to each closure (thread),
8018 // but (may be) available for stealing by other threads.
8019 void CMSParKeepAliveClosure::do_oop(oop obj) {
8020   HeapWord* addr = (HeapWord*)obj;
8021   if (_span.contains(addr) &&
8022       !_bit_map->isMarked(addr)) {
8023     // In general, during recursive tracing, several threads
8024     // may be concurrently getting here; the first one to
8025     // "tag" it, claims it.
8026     if (_bit_map->par_mark(addr)) {
8027       bool res = _work_queue->push(obj);
8028       assert(res, "Low water mark should be much less than capacity");
8029       // Do a recursive trim in the hope that this will keep
8030       // stack usage lower, but leave some oops for potential stealers
8031       trim_queue(_low_water_mark);
8032     } // Else, another thread got there first
8033   }
8034 }
8035 
8036 void CMSParKeepAliveClosure::do_oop(oop* p)       { CMSParKeepAliveClosure::do_oop_work(p); }
8037 void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8038 
8039 void CMSParKeepAliveClosure::trim_queue(uint max) {
8040   while (_work_queue->size() > max) {
8041     oop new_oop;
8042     if (_work_queue->pop_local(new_oop)) {
8043       assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
8044       assert(_bit_map->isMarked((HeapWord*)new_oop),
8045              "no white objects on this stack!");
8046       assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8047       // iterate over the oops in this oop, marking and pushing
8048       // the ones in CMS heap (i.e. in _span).
8049       new_oop->oop_iterate(&_mark_and_push);
8050     }
8051   }
8052 }
8053 
8054 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
8055                                 CMSCollector* collector,
8056                                 MemRegion span, CMSBitMap* bit_map,
8057                                 OopTaskQueue* work_queue):
8058   _collector(collector),
8059   _span(span),
8060   _bit_map(bit_map),
8061   _work_queue(work_queue) { }
8062 
8063 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
8064   HeapWord* addr = (HeapWord*)obj;
8065   if (_span.contains(addr) &&
8066       !_bit_map->isMarked(addr)) {
8067     if (_bit_map->par_mark(addr)) {
8068       bool simulate_overflow = false;
8069       NOT_PRODUCT(
8070         if (CMSMarkStackOverflowALot &&
8071             _collector->par_simulate_overflow()) {
8072           // simulate a stack overflow
8073           simulate_overflow = true;
8074         }
8075       )
8076       if (simulate_overflow || !_work_queue->push(obj)) {
8077         _collector->par_push_on_overflow_list(obj);
8078         _collector->_par_kac_ovflw++;
8079       }
8080     } // Else another thread got there already
8081   }
8082 }
8083 
8084 void CMSInnerParMarkAndPushClosure::do_oop(oop* p)       { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8085 void CMSInnerParMarkAndPushClosure::do_oop(narrowOop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8086 
8087 //////////////////////////////////////////////////////////////////
8088 //  CMSExpansionCause                /////////////////////////////
8089 //////////////////////////////////////////////////////////////////
8090 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
8091   switch (cause) {
8092     case _no_expansion:
8093       return "No expansion";
8094     case _satisfy_free_ratio:
8095       return "Free ratio";
8096     case _satisfy_promotion:
8097       return "Satisfy promotion";
8098     case _satisfy_allocation:
8099       return "allocation";
8100     case _allocate_par_lab:
8101       return "Par LAB";
8102     case _allocate_par_spooling_space:
8103       return "Par Spooling Space";
8104     case _adaptive_size_policy:
8105       return "Ergonomics";
8106     default:
8107       return "unknown";
8108   }
8109 }
8110 
8111 void CMSDrainMarkingStackClosure::do_void() {
8112   // the max number to take from overflow list at a time
8113   const size_t num = _mark_stack->capacity()/4;
8114   assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
8115          "Overflow list should be NULL during concurrent phases");
8116   while (!_mark_stack->isEmpty() ||
8117          // if stack is empty, check the overflow list
8118          _collector->take_from_overflow_list(num, _mark_stack)) {
8119     oop obj = _mark_stack->pop();
8120     HeapWord* addr = (HeapWord*)obj;
8121     assert(_span.contains(addr), "Should be within span");
8122     assert(_bit_map->isMarked(addr), "Should be marked");
8123     assert(obj->is_oop(), "Should be an oop");
8124     obj->oop_iterate(_keep_alive);
8125   }
8126 }
8127 
8128 void CMSParDrainMarkingStackClosure::do_void() {
8129   // drain queue
8130   trim_queue(0);
8131 }
8132 
8133 // Trim our work_queue so its length is below max at return
8134 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
8135   while (_work_queue->size() > max) {
8136     oop new_oop;
8137     if (_work_queue->pop_local(new_oop)) {
8138       assert(new_oop->is_oop(), "Expected an oop");
8139       assert(_bit_map->isMarked((HeapWord*)new_oop),
8140              "no white objects on this stack!");
8141       assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8142       // iterate over the oops in this oop, marking and pushing
8143       // the ones in CMS heap (i.e. in _span).
8144       new_oop->oop_iterate(&_mark_and_push);
8145     }
8146   }
8147 }
8148 
8149 ////////////////////////////////////////////////////////////////////
8150 // Support for Marking Stack Overflow list handling and related code
8151 ////////////////////////////////////////////////////////////////////
8152 // Much of the following code is similar in shape and spirit to the
8153 // code used in ParNewGC. We should try and share that code
8154 // as much as possible in the future.
8155 
8156 #ifndef PRODUCT
8157 // Debugging support for CMSStackOverflowALot
8158 
8159 // It's OK to call this multi-threaded;  the worst thing
8160 // that can happen is that we'll get a bunch of closely
8161 // spaced simulated overflows, but that's OK, in fact
8162 // probably good as it would exercise the overflow code
8163 // under contention.
8164 bool CMSCollector::simulate_overflow() {
8165   if (_overflow_counter-- <= 0) { // just being defensive
8166     _overflow_counter = CMSMarkStackOverflowInterval;
8167     return true;
8168   } else {
8169     return false;
8170   }
8171 }
8172 
8173 bool CMSCollector::par_simulate_overflow() {
8174   return simulate_overflow();
8175 }
8176 #endif
8177 
8178 // Single-threaded
8179 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
8180   assert(stack->isEmpty(), "Expected precondition");
8181   assert(stack->capacity() > num, "Shouldn't bite more than can chew");
8182   size_t i = num;
8183   oop  cur = _overflow_list;
8184   const markOop proto = markOopDesc::prototype();
8185   NOT_PRODUCT(ssize_t n = 0;)
8186   for (oop next; i > 0 && cur != NULL; cur = next, i--) {
8187     next = oop(cur->mark());
8188     cur->set_mark(proto);   // until proven otherwise
8189     assert(cur->is_oop(), "Should be an oop");
8190     bool res = stack->push(cur);
8191     assert(res, "Bit off more than can chew?");
8192     NOT_PRODUCT(n++;)
8193   }
8194   _overflow_list = cur;
8195 #ifndef PRODUCT
8196   assert(_num_par_pushes >= n, "Too many pops?");
8197   _num_par_pushes -=n;
8198 #endif
8199   return !stack->isEmpty();
8200 }
8201 
8202 #define BUSY  (cast_to_oop<intptr_t>(0x1aff1aff))
8203 // (MT-safe) Get a prefix of at most "num" from the list.
8204 // The overflow list is chained through the mark word of
8205 // each object in the list. We fetch the entire list,
8206 // break off a prefix of the right size and return the
8207 // remainder. If other threads try to take objects from
8208 // the overflow list at that time, they will wait for
8209 // some time to see if data becomes available. If (and
8210 // only if) another thread places one or more object(s)
8211 // on the global list before we have returned the suffix
8212 // to the global list, we will walk down our local list
8213 // to find its end and append the global list to
8214 // our suffix before returning it. This suffix walk can
8215 // prove to be expensive (quadratic in the amount of traffic)
8216 // when there are many objects in the overflow list and
8217 // there is much producer-consumer contention on the list.
8218 // *NOTE*: The overflow list manipulation code here and
8219 // in ParNewGeneration:: are very similar in shape,
8220 // except that in the ParNew case we use the old (from/eden)
8221 // copy of the object to thread the list via its klass word.
8222 // Because of the common code, if you make any changes in
8223 // the code below, please check the ParNew version to see if
8224 // similar changes might be needed.
8225 // CR 6797058 has been filed to consolidate the common code.
8226 bool CMSCollector::par_take_from_overflow_list(size_t num,
8227                                                OopTaskQueue* work_q,
8228                                                int no_of_gc_threads) {
8229   assert(work_q->size() == 0, "First empty local work queue");
8230   assert(num < work_q->max_elems(), "Can't bite more than we can chew");
8231   if (_overflow_list == NULL) {
8232     return false;
8233   }
8234   // Grab the entire list; we'll put back a suffix
8235   oop prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
8236   Thread* tid = Thread::current();
8237   // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was
8238   // set to ParallelGCThreads.
8239   size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads;
8240   size_t sleep_time_millis = MAX2((size_t)1, num/100);
8241   // If the list is busy, we spin for a short while,
8242   // sleeping between attempts to get the list.
8243   for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) {
8244     os::sleep(tid, sleep_time_millis, false);
8245     if (_overflow_list == NULL) {
8246       // Nothing left to take
8247       return false;
8248     } else if (_overflow_list != BUSY) {
8249       // Try and grab the prefix
8250       prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
8251     }
8252   }
8253   // If the list was found to be empty, or we spun long
8254   // enough, we give up and return empty-handed. If we leave
8255   // the list in the BUSY state below, it must be the case that
8256   // some other thread holds the overflow list and will set it
8257   // to a non-BUSY state in the future.
8258   if (prefix == NULL || prefix == BUSY) {
8259      // Nothing to take or waited long enough
8260      if (prefix == NULL) {
8261        // Write back the NULL in case we overwrote it with BUSY above
8262        // and it is still the same value.
8263        (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8264      }
8265      return false;
8266   }
8267   assert(prefix != NULL && prefix != BUSY, "Error");
8268   size_t i = num;
8269   oop cur = prefix;
8270   // Walk down the first "num" objects, unless we reach the end.
8271   for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--);
8272   if (cur->mark() == NULL) {
8273     // We have "num" or fewer elements in the list, so there
8274     // is nothing to return to the global list.
8275     // Write back the NULL in lieu of the BUSY we wrote
8276     // above, if it is still the same value.
8277     if (_overflow_list == BUSY) {
8278       (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8279     }
8280   } else {
8281     // Chop off the suffix and return it to the global list.
8282     assert(cur->mark() != BUSY, "Error");
8283     oop suffix_head = cur->mark(); // suffix will be put back on global list
8284     cur->set_mark(NULL);           // break off suffix
8285     // It's possible that the list is still in the empty(busy) state
8286     // we left it in a short while ago; in that case we may be
8287     // able to place back the suffix without incurring the cost
8288     // of a walk down the list.
8289     oop observed_overflow_list = _overflow_list;
8290     oop cur_overflow_list = observed_overflow_list;
8291     bool attached = false;
8292     while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
8293       observed_overflow_list =
8294         (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
8295       if (cur_overflow_list == observed_overflow_list) {
8296         attached = true;
8297         break;
8298       } else cur_overflow_list = observed_overflow_list;
8299     }
8300     if (!attached) {
8301       // Too bad, someone else sneaked in (at least) an element; we'll need
8302       // to do a splice. Find tail of suffix so we can prepend suffix to global
8303       // list.
8304       for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark()));
8305       oop suffix_tail = cur;
8306       assert(suffix_tail != NULL && suffix_tail->mark() == NULL,
8307              "Tautology");
8308       observed_overflow_list = _overflow_list;
8309       do {
8310         cur_overflow_list = observed_overflow_list;
8311         if (cur_overflow_list != BUSY) {
8312           // Do the splice ...
8313           suffix_tail->set_mark(markOop(cur_overflow_list));
8314         } else { // cur_overflow_list == BUSY
8315           suffix_tail->set_mark(NULL);
8316         }
8317         // ... and try to place spliced list back on overflow_list ...
8318         observed_overflow_list =
8319           (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
8320       } while (cur_overflow_list != observed_overflow_list);
8321       // ... until we have succeeded in doing so.
8322     }
8323   }
8324 
8325   // Push the prefix elements on work_q
8326   assert(prefix != NULL, "control point invariant");
8327   const markOop proto = markOopDesc::prototype();
8328   oop next;
8329   NOT_PRODUCT(ssize_t n = 0;)
8330   for (cur = prefix; cur != NULL; cur = next) {
8331     next = oop(cur->mark());
8332     cur->set_mark(proto);   // until proven otherwise
8333     assert(cur->is_oop(), "Should be an oop");
8334     bool res = work_q->push(cur);
8335     assert(res, "Bit off more than we can chew?");
8336     NOT_PRODUCT(n++;)
8337   }
8338 #ifndef PRODUCT
8339   assert(_num_par_pushes >= n, "Too many pops?");
8340   Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
8341 #endif
8342   return true;
8343 }
8344 
8345 // Single-threaded
8346 void CMSCollector::push_on_overflow_list(oop p) {
8347   NOT_PRODUCT(_num_par_pushes++;)
8348   assert(p->is_oop(), "Not an oop");
8349   preserve_mark_if_necessary(p);
8350   p->set_mark((markOop)_overflow_list);
8351   _overflow_list = p;
8352 }
8353 
8354 // Multi-threaded; use CAS to prepend to overflow list
8355 void CMSCollector::par_push_on_overflow_list(oop p) {
8356   NOT_PRODUCT(Atomic::inc_ptr(&_num_par_pushes);)
8357   assert(p->is_oop(), "Not an oop");
8358   par_preserve_mark_if_necessary(p);
8359   oop observed_overflow_list = _overflow_list;
8360   oop cur_overflow_list;
8361   do {
8362     cur_overflow_list = observed_overflow_list;
8363     if (cur_overflow_list != BUSY) {
8364       p->set_mark(markOop(cur_overflow_list));
8365     } else {
8366       p->set_mark(NULL);
8367     }
8368     observed_overflow_list =
8369       (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list);
8370   } while (cur_overflow_list != observed_overflow_list);
8371 }
8372 #undef BUSY
8373 
8374 // Single threaded
8375 // General Note on GrowableArray: pushes may silently fail
8376 // because we are (temporarily) out of C-heap for expanding
8377 // the stack. The problem is quite ubiquitous and affects
8378 // a lot of code in the JVM. The prudent thing for GrowableArray
8379 // to do (for now) is to exit with an error. However, that may
8380 // be too draconian in some cases because the caller may be
8381 // able to recover without much harm. For such cases, we
8382 // should probably introduce a "soft_push" method which returns
8383 // an indication of success or failure with the assumption that
8384 // the caller may be able to recover from a failure; code in
8385 // the VM can then be changed, incrementally, to deal with such
8386 // failures where possible, thus, incrementally hardening the VM
8387 // in such low resource situations.
8388 void CMSCollector::preserve_mark_work(oop p, markOop m) {
8389   _preserved_oop_stack.push(p);
8390   _preserved_mark_stack.push(m);
8391   assert(m == p->mark(), "Mark word changed");
8392   assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8393          "bijection");
8394 }
8395 
8396 // Single threaded
8397 void CMSCollector::preserve_mark_if_necessary(oop p) {
8398   markOop m = p->mark();
8399   if (m->must_be_preserved(p)) {
8400     preserve_mark_work(p, m);
8401   }
8402 }
8403 
8404 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
8405   markOop m = p->mark();
8406   if (m->must_be_preserved(p)) {
8407     MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
8408     // Even though we read the mark word without holding
8409     // the lock, we are assured that it will not change
8410     // because we "own" this oop, so no other thread can
8411     // be trying to push it on the overflow list; see
8412     // the assertion in preserve_mark_work() that checks
8413     // that m == p->mark().
8414     preserve_mark_work(p, m);
8415   }
8416 }
8417 
8418 // We should be able to do this multi-threaded,
8419 // a chunk of stack being a task (this is
8420 // correct because each oop only ever appears
8421 // once in the overflow list. However, it's
8422 // not very easy to completely overlap this with
8423 // other operations, so will generally not be done
8424 // until all work's been completed. Because we
8425 // expect the preserved oop stack (set) to be small,
8426 // it's probably fine to do this single-threaded.
8427 // We can explore cleverer concurrent/overlapped/parallel
8428 // processing of preserved marks if we feel the
8429 // need for this in the future. Stack overflow should
8430 // be so rare in practice and, when it happens, its
8431 // effect on performance so great that this will
8432 // likely just be in the noise anyway.
8433 void CMSCollector::restore_preserved_marks_if_any() {
8434   assert(SafepointSynchronize::is_at_safepoint(),
8435          "world should be stopped");
8436   assert(Thread::current()->is_ConcurrentGC_thread() ||
8437          Thread::current()->is_VM_thread(),
8438          "should be single-threaded");
8439   assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8440          "bijection");
8441 
8442   while (!_preserved_oop_stack.is_empty()) {
8443     oop p = _preserved_oop_stack.pop();
8444     assert(p->is_oop(), "Should be an oop");
8445     assert(_span.contains(p), "oop should be in _span");
8446     assert(p->mark() == markOopDesc::prototype(),
8447            "Set when taken from overflow list");
8448     markOop m = _preserved_mark_stack.pop();
8449     p->set_mark(m);
8450   }
8451   assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(),
8452          "stacks were cleared above");
8453 }
8454 
8455 #ifndef PRODUCT
8456 bool CMSCollector::no_preserved_marks() const {
8457   return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty();
8458 }
8459 #endif
8460 
8461 // Transfer some number of overflown objects to usual marking
8462 // stack. Return true if some objects were transferred.
8463 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
8464   size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,
8465                     (size_t)ParGCDesiredObjsFromOverflowList);
8466 
8467   bool res = _collector->take_from_overflow_list(num, _mark_stack);
8468   assert(_collector->overflow_list_is_empty() || res,
8469          "If list is not empty, we should have taken something");
8470   assert(!res || !_mark_stack->isEmpty(),
8471          "If we took something, it should now be on our stack");
8472   return res;
8473 }
8474 
8475 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
8476   size_t res = _sp->block_size_no_stall(addr, _collector);
8477   if (_sp->block_is_obj(addr)) {
8478     if (_live_bit_map->isMarked(addr)) {
8479       // It can't have been dead in a previous cycle
8480       guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
8481     } else {
8482       _dead_bit_map->mark(addr);      // mark the dead object
8483     }
8484   }
8485   // Could be 0, if the block size could not be computed without stalling.
8486   return res;
8487 }
8488 
8489 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() {
8490 
8491   switch (phase) {
8492     case CMSCollector::InitialMarking:
8493       initialize(true  /* fullGC */ ,
8494                  cause /* cause of the GC */,
8495                  true  /* recordGCBeginTime */,
8496                  true  /* recordPreGCUsage */,
8497                  false /* recordPeakUsage */,
8498                  false /* recordPostGCusage */,
8499                  true  /* recordAccumulatedGCTime */,
8500                  false /* recordGCEndTime */,
8501                  false /* countCollection */  );
8502       break;
8503 
8504     case CMSCollector::FinalMarking:
8505       initialize(true  /* fullGC */ ,
8506                  cause /* cause of the GC */,
8507                  false /* recordGCBeginTime */,
8508                  false /* recordPreGCUsage */,
8509                  false /* recordPeakUsage */,
8510                  false /* recordPostGCusage */,
8511                  true  /* recordAccumulatedGCTime */,
8512                  false /* recordGCEndTime */,
8513                  false /* countCollection */  );
8514       break;
8515 
8516     case CMSCollector::Sweeping:
8517       initialize(true  /* fullGC */ ,
8518                  cause /* cause of the GC */,
8519                  false /* recordGCBeginTime */,
8520                  false /* recordPreGCUsage */,
8521                  true  /* recordPeakUsage */,
8522                  true  /* recordPostGCusage */,
8523                  false /* recordAccumulatedGCTime */,
8524                  true  /* recordGCEndTime */,
8525                  true  /* countCollection */  );
8526       break;
8527 
8528     default:
8529       ShouldNotReachHere();
8530   }
8531 }