1 /*
   2  * Copyright (c) 2001, 2010, 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
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  24 
  25 # include "incls/_precompiled.incl"
  26 # include "incls/_concurrentMarkSweepGeneration.cpp.incl"
  27 
  28 // statics
  29 CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL;
  30 bool          CMSCollector::_full_gc_requested          = false;
  31 
  32 //////////////////////////////////////////////////////////////////
  33 // In support of CMS/VM thread synchronization
  34 //////////////////////////////////////////////////////////////////
  35 // We split use of the CGC_lock into 2 "levels".
  36 // The low-level locking is of the usual CGC_lock monitor. We introduce
  37 // a higher level "token" (hereafter "CMS token") built on top of the
  38 // low level monitor (hereafter "CGC lock").
  39 // The token-passing protocol gives priority to the VM thread. The
  40 // CMS-lock doesn't provide any fairness guarantees, but clients
  41 // should ensure that it is only held for very short, bounded
  42 // durations.
  43 //
  44 // When either of the CMS thread or the VM thread is involved in
  45 // collection operations during which it does not want the other
  46 // thread to interfere, it obtains the CMS token.
  47 //
  48 // If either thread tries to get the token while the other has
  49 // it, that thread waits. However, if the VM thread and CMS thread
  50 // both want the token, then the VM thread gets priority while the
  51 // CMS thread waits. This ensures, for instance, that the "concurrent"
  52 // phases of the CMS thread's work do not block out the VM thread
  53 // for long periods of time as the CMS thread continues to hog
  54 // the token. (See bug 4616232).
  55 //
  56 // The baton-passing functions are, however, controlled by the
  57 // flags _foregroundGCShouldWait and _foregroundGCIsActive,
  58 // and here the low-level CMS lock, not the high level token,
  59 // ensures mutual exclusion.
  60 //
  61 // Two important conditions that we have to satisfy:
  62 // 1. if a thread does a low-level wait on the CMS lock, then it
  63 //    relinquishes the CMS token if it were holding that token
  64 //    when it acquired the low-level CMS lock.
  65 // 2. any low-level notifications on the low-level lock
  66 //    should only be sent when a thread has relinquished the token.
  67 //
  68 // In the absence of either property, we'd have potential deadlock.
  69 //
  70 // We protect each of the CMS (concurrent and sequential) phases
  71 // with the CMS _token_, not the CMS _lock_.
  72 //
  73 // The only code protected by CMS lock is the token acquisition code
  74 // itself, see ConcurrentMarkSweepThread::[de]synchronize(), and the
  75 // baton-passing code.
  76 //
  77 // Unfortunately, i couldn't come up with a good abstraction to factor and
  78 // hide the naked CGC_lock manipulation in the baton-passing code
  79 // further below. That's something we should try to do. Also, the proof
  80 // of correctness of this 2-level locking scheme is far from obvious,
  81 // and potentially quite slippery. We have an uneasy supsicion, for instance,
  82 // that there may be a theoretical possibility of delay/starvation in the
  83 // low-level lock/wait/notify scheme used for the baton-passing because of
  84 // potential intereference with the priority scheme embodied in the
  85 // CMS-token-passing protocol. See related comments at a CGC_lock->wait()
  86 // invocation further below and marked with "XXX 20011219YSR".
  87 // Indeed, as we note elsewhere, this may become yet more slippery
  88 // in the presence of multiple CMS and/or multiple VM threads. XXX
  89 
  90 class CMSTokenSync: public StackObj {
  91  private:
  92   bool _is_cms_thread;
  93  public:
  94   CMSTokenSync(bool is_cms_thread):
  95     _is_cms_thread(is_cms_thread) {
  96     assert(is_cms_thread == Thread::current()->is_ConcurrentGC_thread(),
  97            "Incorrect argument to constructor");
  98     ConcurrentMarkSweepThread::synchronize(_is_cms_thread);
  99   }
 100 
 101   ~CMSTokenSync() {
 102     assert(_is_cms_thread ?
 103              ConcurrentMarkSweepThread::cms_thread_has_cms_token() :
 104              ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
 105           "Incorrect state");
 106     ConcurrentMarkSweepThread::desynchronize(_is_cms_thread);
 107   }
 108 };
 109 
 110 // Convenience class that does a CMSTokenSync, and then acquires
 111 // upto three locks.
 112 class CMSTokenSyncWithLocks: public CMSTokenSync {
 113  private:
 114   // Note: locks are acquired in textual declaration order
 115   // and released in the opposite order
 116   MutexLockerEx _locker1, _locker2, _locker3;
 117  public:
 118   CMSTokenSyncWithLocks(bool is_cms_thread, Mutex* mutex1,
 119                         Mutex* mutex2 = NULL, Mutex* mutex3 = NULL):
 120     CMSTokenSync(is_cms_thread),
 121     _locker1(mutex1, Mutex::_no_safepoint_check_flag),
 122     _locker2(mutex2, Mutex::_no_safepoint_check_flag),
 123     _locker3(mutex3, Mutex::_no_safepoint_check_flag)
 124   { }
 125 };
 126 
 127 
 128 // Wrapper class to temporarily disable icms during a foreground cms collection.
 129 class ICMSDisabler: public StackObj {
 130  public:
 131   // The ctor disables icms and wakes up the thread so it notices the change;
 132   // the dtor re-enables icms.  Note that the CMSCollector methods will check
 133   // CMSIncrementalMode.
 134   ICMSDisabler()  { CMSCollector::disable_icms(); CMSCollector::start_icms(); }
 135   ~ICMSDisabler() { CMSCollector::enable_icms(); }
 136 };
 137 
 138 //////////////////////////////////////////////////////////////////
 139 //  Concurrent Mark-Sweep Generation /////////////////////////////
 140 //////////////////////////////////////////////////////////////////
 141 
 142 NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;)
 143 
 144 // This struct contains per-thread things necessary to support parallel
 145 // young-gen collection.
 146 class CMSParGCThreadState: public CHeapObj {
 147  public:
 148   CFLS_LAB lab;
 149   PromotionInfo promo;
 150 
 151   // Constructor.
 152   CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) {
 153     promo.setSpace(cfls);
 154   }
 155 };
 156 
 157 ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration(
 158      ReservedSpace rs, size_t initial_byte_size, int level,
 159      CardTableRS* ct, bool use_adaptive_freelists,
 160      FreeBlockDictionary::DictionaryChoice dictionaryChoice) :
 161   CardGeneration(rs, initial_byte_size, level, ct),
 162   _dilatation_factor(((double)MinChunkSize)/((double)(CollectedHeap::min_fill_size()))),
 163   _debug_collection_type(Concurrent_collection_type)
 164 {
 165   HeapWord* bottom = (HeapWord*) _virtual_space.low();
 166   HeapWord* end    = (HeapWord*) _virtual_space.high();
 167 
 168   _direct_allocated_words = 0;
 169   NOT_PRODUCT(
 170     _numObjectsPromoted = 0;
 171     _numWordsPromoted = 0;
 172     _numObjectsAllocated = 0;
 173     _numWordsAllocated = 0;
 174   )
 175 
 176   _cmsSpace = new CompactibleFreeListSpace(_bts, MemRegion(bottom, end),
 177                                            use_adaptive_freelists,
 178                                            dictionaryChoice);
 179   NOT_PRODUCT(debug_cms_space = _cmsSpace;)
 180   if (_cmsSpace == NULL) {
 181     vm_exit_during_initialization(
 182       "CompactibleFreeListSpace allocation failure");
 183   }
 184   _cmsSpace->_gen = this;
 185 
 186   _gc_stats = new CMSGCStats();
 187 
 188   // Verify the assumption that FreeChunk::_prev and OopDesc::_klass
 189   // offsets match. The ability to tell free chunks from objects
 190   // depends on this property.
 191   debug_only(
 192     FreeChunk* junk = NULL;
 193     assert(UseCompressedOops ||
 194            junk->prev_addr() == (void*)(oop(junk)->klass_addr()),
 195            "Offset of FreeChunk::_prev within FreeChunk must match"
 196            "  that of OopDesc::_klass within OopDesc");
 197   )
 198   if (ParallelGCThreads > 0) {
 199     typedef CMSParGCThreadState* CMSParGCThreadStatePtr;
 200     _par_gc_thread_states =
 201       NEW_C_HEAP_ARRAY(CMSParGCThreadStatePtr, ParallelGCThreads);
 202     if (_par_gc_thread_states == NULL) {
 203       vm_exit_during_initialization("Could not allocate par gc structs");
 204     }
 205     for (uint i = 0; i < ParallelGCThreads; i++) {
 206       _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace());
 207       if (_par_gc_thread_states[i] == NULL) {
 208         vm_exit_during_initialization("Could not allocate par gc structs");
 209       }
 210     }
 211   } else {
 212     _par_gc_thread_states = NULL;
 213   }
 214   _incremental_collection_failed = false;
 215   // The "dilatation_factor" is the expansion that can occur on
 216   // account of the fact that the minimum object size in the CMS
 217   // generation may be larger than that in, say, a contiguous young
 218   //  generation.
 219   // Ideally, in the calculation below, we'd compute the dilatation
 220   // factor as: MinChunkSize/(promoting_gen's min object size)
 221   // Since we do not have such a general query interface for the
 222   // promoting generation, we'll instead just use the mimimum
 223   // object size (which today is a header's worth of space);
 224   // note that all arithmetic is in units of HeapWords.
 225   assert(MinChunkSize >= CollectedHeap::min_fill_size(), "just checking");
 226   assert(_dilatation_factor >= 1.0, "from previous assert");
 227 }
 228 
 229 
 230 // The field "_initiating_occupancy" represents the occupancy percentage
 231 // at which we trigger a new collection cycle.  Unless explicitly specified
 232 // via CMSInitiating[Perm]OccupancyFraction (argument "io" below), it
 233 // is calculated by:
 234 //
 235 //   Let "f" be MinHeapFreeRatio in
 236 //
 237 //    _intiating_occupancy = 100-f +
 238 //                           f * (CMSTrigger[Perm]Ratio/100)
 239 //   where CMSTrigger[Perm]Ratio is the argument "tr" below.
 240 //
 241 // That is, if we assume the heap is at its desired maximum occupancy at the
 242 // end of a collection, we let CMSTrigger[Perm]Ratio of the (purported) free
 243 // space be allocated before initiating a new collection cycle.
 244 //
 245 void ConcurrentMarkSweepGeneration::init_initiating_occupancy(intx io, intx tr) {
 246   assert(io <= 100 && tr >= 0 && tr <= 100, "Check the arguments");
 247   if (io >= 0) {
 248     _initiating_occupancy = (double)io / 100.0;
 249   } else {
 250     _initiating_occupancy = ((100 - MinHeapFreeRatio) +
 251                              (double)(tr * MinHeapFreeRatio) / 100.0)
 252                             / 100.0;
 253   }
 254 }
 255 
 256 void ConcurrentMarkSweepGeneration::ref_processor_init() {
 257   assert(collector() != NULL, "no collector");
 258   collector()->ref_processor_init();
 259 }
 260 
 261 void CMSCollector::ref_processor_init() {
 262   if (_ref_processor == NULL) {
 263     // Allocate and initialize a reference processor
 264     _ref_processor = ReferenceProcessor::create_ref_processor(
 265         _span,                               // span
 266         _cmsGen->refs_discovery_is_atomic(), // atomic_discovery
 267         _cmsGen->refs_discovery_is_mt(),     // mt_discovery
 268         &_is_alive_closure,
 269         ParallelGCThreads,
 270         ParallelRefProcEnabled);
 271     // Initialize the _ref_processor field of CMSGen
 272     _cmsGen->set_ref_processor(_ref_processor);
 273 
 274     // Allocate a dummy ref processor for perm gen.
 275     ReferenceProcessor* rp2 = new ReferenceProcessor();
 276     if (rp2 == NULL) {
 277       vm_exit_during_initialization("Could not allocate ReferenceProcessor object");
 278     }
 279     _permGen->set_ref_processor(rp2);
 280   }
 281 }
 282 
 283 CMSAdaptiveSizePolicy* CMSCollector::size_policy() {
 284   GenCollectedHeap* gch = GenCollectedHeap::heap();
 285   assert(gch->kind() == CollectedHeap::GenCollectedHeap,
 286     "Wrong type of heap");
 287   CMSAdaptiveSizePolicy* sp = (CMSAdaptiveSizePolicy*)
 288     gch->gen_policy()->size_policy();
 289   assert(sp->is_gc_cms_adaptive_size_policy(),
 290     "Wrong type of size policy");
 291   return sp;
 292 }
 293 
 294 CMSGCAdaptivePolicyCounters* CMSCollector::gc_adaptive_policy_counters() {
 295   CMSGCAdaptivePolicyCounters* results =
 296     (CMSGCAdaptivePolicyCounters*) collector_policy()->counters();
 297   assert(
 298     results->kind() == GCPolicyCounters::CMSGCAdaptivePolicyCountersKind,
 299     "Wrong gc policy counter kind");
 300   return results;
 301 }
 302 
 303 
 304 void ConcurrentMarkSweepGeneration::initialize_performance_counters() {
 305 
 306   const char* gen_name = "old";
 307 
 308   // Generation Counters - generation 1, 1 subspace
 309   _gen_counters = new GenerationCounters(gen_name, 1, 1, &_virtual_space);
 310 
 311   _space_counters = new GSpaceCounters(gen_name, 0,
 312                                        _virtual_space.reserved_size(),
 313                                        this, _gen_counters);
 314 }
 315 
 316 CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha):
 317   _cms_gen(cms_gen)
 318 {
 319   assert(alpha <= 100, "bad value");
 320   _saved_alpha = alpha;
 321 
 322   // Initialize the alphas to the bootstrap value of 100.
 323   _gc0_alpha = _cms_alpha = 100;
 324 
 325   _cms_begin_time.update();
 326   _cms_end_time.update();
 327 
 328   _gc0_duration = 0.0;
 329   _gc0_period = 0.0;
 330   _gc0_promoted = 0;
 331 
 332   _cms_duration = 0.0;
 333   _cms_period = 0.0;
 334   _cms_allocated = 0;
 335 
 336   _cms_used_at_gc0_begin = 0;
 337   _cms_used_at_gc0_end = 0;
 338   _allow_duty_cycle_reduction = false;
 339   _valid_bits = 0;
 340   _icms_duty_cycle = CMSIncrementalDutyCycle;
 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 = gch->get_gen(0)->capacity();
 358   if (HandlePromotionFailure) {
 359     expected_promotion = MIN2(
 360         (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average(),
 361         expected_promotion);
 362   }
 363   if (cms_free > expected_promotion) {
 364     // Start a cms collection if there isn't enough space to promote
 365     // for the next minor collection.  Use the padded average as
 366     // a safety factor.
 367     cms_free -= expected_promotion;
 368 
 369     // Adjust by the safety factor.
 370     double cms_free_dbl = (double)cms_free;
 371     double cms_adjustment = (100.0 - CMSIncrementalSafetyFactor)/100.0;
 372     // Apply a further correction factor which tries to adjust
 373     // for recent occurance of concurrent mode failures.
 374     cms_adjustment = cms_adjustment * cms_free_adjustment_factor(cms_free);
 375     cms_free_dbl = cms_free_dbl * cms_adjustment;
 376 
 377     if (PrintGCDetails && Verbose) {
 378       gclog_or_tty->print_cr("CMSStats::time_until_cms_gen_full: cms_free "
 379         SIZE_FORMAT " expected_promotion " SIZE_FORMAT,
 380         cms_free, expected_promotion);
 381       gclog_or_tty->print_cr("  cms_free_dbl %f cms_consumption_rate %f",
 382         cms_free_dbl, cms_consumption_rate() + 1.0);
 383     }
 384     // Add 1 in case the consumption rate goes to zero.
 385     return cms_free_dbl / (cms_consumption_rate() + 1.0);
 386   }
 387   return 0.0;
 388 }
 389 
 390 // Compare the duration of the cms collection to the
 391 // time remaining before the cms generation is empty.
 392 // Note that the time from the start of the cms collection
 393 // to the start of the cms sweep (less than the total
 394 // duration of the cms collection) can be used.  This
 395 // has been tried and some applications experienced
 396 // promotion failures early in execution.  This was
 397 // possibly because the averages were not accurate
 398 // enough at the beginning.
 399 double CMSStats::time_until_cms_start() const {
 400   // We add "gc0_period" to the "work" calculation
 401   // below because this query is done (mostly) at the
 402   // end of a scavenge, so we need to conservatively
 403   // account for that much possible delay
 404   // in the query so as to avoid concurrent mode failures
 405   // due to starting the collection just a wee bit too
 406   // late.
 407   double work = cms_duration() + gc0_period();
 408   double deadline = time_until_cms_gen_full();
 409   // If a concurrent mode failure occurred recently, we want to be
 410   // more conservative and halve our expected time_until_cms_gen_full()
 411   if (work > deadline) {
 412     if (Verbose && PrintGCDetails) {
 413       gclog_or_tty->print(
 414         " CMSCollector: collect because of anticipated promotion "
 415         "before full %3.7f + %3.7f > %3.7f ", cms_duration(),
 416         gc0_period(), time_until_cms_gen_full());
 417     }
 418     return 0.0;
 419   }
 420   return work - deadline;
 421 }
 422 
 423 // Return a duty cycle based on old_duty_cycle and new_duty_cycle, limiting the
 424 // amount of change to prevent wild oscillation.
 425 unsigned int CMSStats::icms_damped_duty_cycle(unsigned int old_duty_cycle,
 426                                               unsigned int new_duty_cycle) {
 427   assert(old_duty_cycle <= 100, "bad input value");
 428   assert(new_duty_cycle <= 100, "bad input value");
 429 
 430   // Note:  use subtraction with caution since it may underflow (values are
 431   // unsigned).  Addition is safe since we're in the range 0-100.
 432   unsigned int damped_duty_cycle = new_duty_cycle;
 433   if (new_duty_cycle < old_duty_cycle) {
 434     const unsigned int largest_delta = MAX2(old_duty_cycle / 4, 5U);
 435     if (new_duty_cycle + largest_delta < old_duty_cycle) {
 436       damped_duty_cycle = old_duty_cycle - largest_delta;
 437     }
 438   } else if (new_duty_cycle > old_duty_cycle) {
 439     const unsigned int largest_delta = MAX2(old_duty_cycle / 4, 15U);
 440     if (new_duty_cycle > old_duty_cycle + largest_delta) {
 441       damped_duty_cycle = MIN2(old_duty_cycle + largest_delta, 100U);
 442     }
 443   }
 444   assert(damped_duty_cycle <= 100, "invalid duty cycle computed");
 445 
 446   if (CMSTraceIncrementalPacing) {
 447     gclog_or_tty->print(" [icms_damped_duty_cycle(%d,%d) = %d] ",
 448                            old_duty_cycle, new_duty_cycle, damped_duty_cycle);
 449   }
 450   return damped_duty_cycle;
 451 }
 452 
 453 unsigned int CMSStats::icms_update_duty_cycle_impl() {
 454   assert(CMSIncrementalPacing && valid(),
 455          "should be handled in icms_update_duty_cycle()");
 456 
 457   double cms_time_so_far = cms_timer().seconds();
 458   double scaled_duration = cms_duration_per_mb() * _cms_used_at_gc0_end / M;
 459   double scaled_duration_remaining = fabsd(scaled_duration - cms_time_so_far);
 460 
 461   // Avoid division by 0.
 462   double time_until_full = MAX2(time_until_cms_gen_full(), 0.01);
 463   double duty_cycle_dbl = 100.0 * scaled_duration_remaining / time_until_full;
 464 
 465   unsigned int new_duty_cycle = MIN2((unsigned int)duty_cycle_dbl, 100U);
 466   if (new_duty_cycle > _icms_duty_cycle) {
 467     // Avoid very small duty cycles (1 or 2); 0 is allowed.
 468     if (new_duty_cycle > 2) {
 469       _icms_duty_cycle = icms_damped_duty_cycle(_icms_duty_cycle,
 470                                                 new_duty_cycle);
 471     }
 472   } else if (_allow_duty_cycle_reduction) {
 473     // The duty cycle is reduced only once per cms cycle (see record_cms_end()).
 474     new_duty_cycle = icms_damped_duty_cycle(_icms_duty_cycle, new_duty_cycle);
 475     // Respect the minimum duty cycle.
 476     unsigned int min_duty_cycle = (unsigned int)CMSIncrementalDutyCycleMin;
 477     _icms_duty_cycle = MAX2(new_duty_cycle, min_duty_cycle);
 478   }
 479 
 480   if (PrintGCDetails || CMSTraceIncrementalPacing) {
 481     gclog_or_tty->print(" icms_dc=%d ", _icms_duty_cycle);
 482   }
 483 
 484   _allow_duty_cycle_reduction = false;
 485   return _icms_duty_cycle;
 486 }
 487 
 488 #ifndef PRODUCT
 489 void CMSStats::print_on(outputStream *st) const {
 490   st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha);
 491   st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo=" SIZE_FORMAT,
 492                gc0_duration(), gc0_period(), gc0_promoted());
 493   st->print(",cms_dur=%g,cms_dur_per_mb=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT,
 494             cms_duration(), cms_duration_per_mb(),
 495             cms_period(), cms_allocated());
 496   st->print(",cms_since_beg=%g,cms_since_end=%g",
 497             cms_time_since_begin(), cms_time_since_end());
 498   st->print(",cms_used_beg=" SIZE_FORMAT ",cms_used_end=" SIZE_FORMAT,
 499             _cms_used_at_gc0_begin, _cms_used_at_gc0_end);
 500   if (CMSIncrementalMode) {
 501     st->print(",dc=%d", icms_duty_cycle());
 502   }
 503 
 504   if (valid()) {
 505     st->print(",promo_rate=%g,cms_alloc_rate=%g",
 506               promotion_rate(), cms_allocation_rate());
 507     st->print(",cms_consumption_rate=%g,time_until_full=%g",
 508               cms_consumption_rate(), time_until_cms_gen_full());
 509   }
 510   st->print(" ");
 511 }
 512 #endif // #ifndef PRODUCT
 513 
 514 CMSCollector::CollectorState CMSCollector::_collectorState =
 515                              CMSCollector::Idling;
 516 bool CMSCollector::_foregroundGCIsActive = false;
 517 bool CMSCollector::_foregroundGCShouldWait = false;
 518 
 519 CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
 520                            ConcurrentMarkSweepGeneration* permGen,
 521                            CardTableRS*                   ct,
 522                            ConcurrentMarkSweepPolicy*     cp):
 523   _cmsGen(cmsGen),
 524   _permGen(permGen),
 525   _ct(ct),
 526   _ref_processor(NULL),    // will be set later
 527   _conc_workers(NULL),     // may be set later
 528   _abort_preclean(false),
 529   _start_sampling(false),
 530   _between_prologue_and_epilogue(false),
 531   _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"),
 532   _perm_gen_verify_bit_map(0, -1 /* no mutex */, "No_lock"),
 533   _modUnionTable((CardTableModRefBS::card_shift - LogHeapWordSize),
 534                  -1 /* lock-free */, "No_lock" /* dummy */),
 535   _modUnionClosure(&_modUnionTable),
 536   _modUnionClosurePar(&_modUnionTable),
 537   // Adjust my span to cover old (cms) gen and perm gen
 538   _span(cmsGen->reserved()._union(permGen->reserved())),
 539   // Construct the is_alive_closure with _span & markBitMap
 540   _is_alive_closure(_span, &_markBitMap),
 541   _restart_addr(NULL),
 542   _overflow_list(NULL),
 543   _preserved_oop_stack(NULL),
 544   _preserved_mark_stack(NULL),
 545   _stats(cmsGen),
 546   _eden_chunk_array(NULL),     // may be set in ctor body
 547   _eden_chunk_capacity(0),     // -- ditto --
 548   _eden_chunk_index(0),        // -- ditto --
 549   _survivor_plab_array(NULL),  // -- ditto --
 550   _survivor_chunk_array(NULL), // -- ditto --
 551   _survivor_chunk_capacity(0), // -- ditto --
 552   _survivor_chunk_index(0),    // -- ditto --
 553   _ser_pmc_preclean_ovflw(0),
 554   _ser_kac_preclean_ovflw(0),
 555   _ser_pmc_remark_ovflw(0),
 556   _par_pmc_remark_ovflw(0),
 557   _ser_kac_ovflw(0),
 558   _par_kac_ovflw(0),
 559 #ifndef PRODUCT
 560   _num_par_pushes(0),
 561 #endif
 562   _collection_count_start(0),
 563   _verifying(false),
 564   _icms_start_limit(NULL),
 565   _icms_stop_limit(NULL),
 566   _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"),
 567   _completed_initialization(false),
 568   _collector_policy(cp),
 569   _should_unload_classes(false),
 570   _concurrent_cycles_since_last_unload(0),
 571   _roots_scanning_options(0),
 572   _inter_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
 573   _intra_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding)
 574 {
 575   if (ExplicitGCInvokesConcurrentAndUnloadsClasses) {
 576     ExplicitGCInvokesConcurrent = true;
 577   }
 578   // Now expand the span and allocate the collection support structures
 579   // (MUT, marking bit map etc.) to cover both generations subject to
 580   // collection.
 581 
 582   // First check that _permGen is adjacent to _cmsGen and above it.
 583   assert(   _cmsGen->reserved().word_size()  > 0
 584          && _permGen->reserved().word_size() > 0,
 585          "generations should not be of zero size");
 586   assert(_cmsGen->reserved().intersection(_permGen->reserved()).is_empty(),
 587          "_cmsGen and _permGen should not overlap");
 588   assert(_cmsGen->reserved().end() == _permGen->reserved().start(),
 589          "_cmsGen->end() different from _permGen->start()");
 590 
 591   // For use by dirty card to oop closures.
 592   _cmsGen->cmsSpace()->set_collector(this);
 593   _permGen->cmsSpace()->set_collector(this);
 594 
 595   // Allocate MUT and marking bit map
 596   {
 597     MutexLockerEx x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag);
 598     if (!_markBitMap.allocate(_span)) {
 599       warning("Failed to allocate CMS Bit Map");
 600       return;
 601     }
 602     assert(_markBitMap.covers(_span), "_markBitMap inconsistency?");
 603   }
 604   {
 605     _modUnionTable.allocate(_span);
 606     assert(_modUnionTable.covers(_span), "_modUnionTable inconsistency?");
 607   }
 608 
 609   if (!_markStack.allocate(MarkStackSize)) {
 610     warning("Failed to allocate CMS Marking Stack");
 611     return;
 612   }
 613   if (!_revisitStack.allocate(CMSRevisitStackSize)) {
 614     warning("Failed to allocate CMS Revisit Stack");
 615     return;
 616   }
 617 
 618   // Support for multi-threaded concurrent phases
 619   if (ParallelGCThreads > 0 && CMSConcurrentMTEnabled) {
 620     if (FLAG_IS_DEFAULT(ConcGCThreads)) {
 621       // just for now
 622       FLAG_SET_DEFAULT(ConcGCThreads, (ParallelGCThreads + 3)/4);
 623     }
 624     if (ConcGCThreads > 1) {
 625       _conc_workers = new YieldingFlexibleWorkGang("Parallel CMS Threads",
 626                                  ConcGCThreads, true);
 627       if (_conc_workers == NULL) {
 628         warning("GC/CMS: _conc_workers allocation failure: "
 629               "forcing -CMSConcurrentMTEnabled");
 630         CMSConcurrentMTEnabled = false;
 631       }
 632     } else {
 633       CMSConcurrentMTEnabled = false;
 634     }
 635   }
 636   if (!CMSConcurrentMTEnabled) {
 637     ConcGCThreads = 0;
 638   } else {
 639     // Turn off CMSCleanOnEnter optimization temporarily for
 640     // the MT case where it's not fixed yet; see 6178663.
 641     CMSCleanOnEnter = false;
 642   }
 643   assert((_conc_workers != NULL) == (ConcGCThreads > 1),
 644          "Inconsistency");
 645 
 646   // Parallel task queues; these are shared for the
 647   // concurrent and stop-world phases of CMS, but
 648   // are not shared with parallel scavenge (ParNew).
 649   {
 650     uint i;
 651     uint num_queues = (uint) MAX2(ParallelGCThreads, ConcGCThreads);
 652 
 653     if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled
 654          || ParallelRefProcEnabled)
 655         && num_queues > 0) {
 656       _task_queues = new OopTaskQueueSet(num_queues);
 657       if (_task_queues == NULL) {
 658         warning("task_queues allocation failure.");
 659         return;
 660       }
 661       _hash_seed = NEW_C_HEAP_ARRAY(int, num_queues);
 662       if (_hash_seed == NULL) {
 663         warning("_hash_seed array allocation failure");
 664         return;
 665       }
 666 
 667       // XXX use a global constant instead of 64!
 668       typedef struct OopTaskQueuePadded {
 669         OopTaskQueue work_queue;
 670         char pad[64 - sizeof(OopTaskQueue)];  // prevent false sharing
 671       } OopTaskQueuePadded;
 672 
 673       for (i = 0; i < num_queues; i++) {
 674         OopTaskQueuePadded *q_padded = new OopTaskQueuePadded();
 675         if (q_padded == NULL) {
 676           warning("work_queue allocation failure.");
 677           return;
 678         }
 679         _task_queues->register_queue(i, &q_padded->work_queue);
 680       }
 681       for (i = 0; i < num_queues; i++) {
 682         _task_queues->queue(i)->initialize();
 683         _hash_seed[i] = 17;  // copied from ParNew
 684       }
 685     }
 686   }
 687 
 688   _cmsGen ->init_initiating_occupancy(CMSInitiatingOccupancyFraction, CMSTriggerRatio);
 689   _permGen->init_initiating_occupancy(CMSInitiatingPermOccupancyFraction, CMSTriggerPermRatio);
 690 
 691   // Clip CMSBootstrapOccupancy between 0 and 100.
 692   _bootstrap_occupancy = ((double)MIN2((uintx)100, MAX2((uintx)0, CMSBootstrapOccupancy)))
 693                          /(double)100;
 694 
 695   _full_gcs_since_conc_gc = 0;
 696 
 697   // Now tell CMS generations the identity of their collector
 698   ConcurrentMarkSweepGeneration::set_collector(this);
 699 
 700   // Create & start a CMS thread for this CMS collector
 701   _cmsThread = ConcurrentMarkSweepThread::start(this);
 702   assert(cmsThread() != NULL, "CMS Thread should have been created");
 703   assert(cmsThread()->collector() == this,
 704          "CMS Thread should refer to this gen");
 705   assert(CGC_lock != NULL, "Where's the CGC_lock?");
 706 
 707   // Support for parallelizing young gen rescan
 708   GenCollectedHeap* gch = GenCollectedHeap::heap();
 709   _young_gen = gch->prev_gen(_cmsGen);
 710   if (gch->supports_inline_contig_alloc()) {
 711     _top_addr = gch->top_addr();
 712     _end_addr = gch->end_addr();
 713     assert(_young_gen != NULL, "no _young_gen");
 714     _eden_chunk_index = 0;
 715     _eden_chunk_capacity = (_young_gen->max_capacity()+CMSSamplingGrain)/CMSSamplingGrain;
 716     _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity);
 717     if (_eden_chunk_array == NULL) {
 718       _eden_chunk_capacity = 0;
 719       warning("GC/CMS: _eden_chunk_array allocation failure");
 720     }
 721   }
 722   assert(_eden_chunk_array != NULL || _eden_chunk_capacity == 0, "Error");
 723 
 724   // Support for parallelizing survivor space rescan
 725   if (CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) {
 726     const size_t max_plab_samples =
 727       ((DefNewGeneration*)_young_gen)->max_survivor_size()/MinTLABSize;
 728 
 729     _survivor_plab_array  = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads);
 730     _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, 2*max_plab_samples);
 731     _cursor               = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads);
 732     if (_survivor_plab_array == NULL || _survivor_chunk_array == NULL
 733         || _cursor == NULL) {
 734       warning("Failed to allocate survivor plab/chunk array");
 735       if (_survivor_plab_array  != NULL) {
 736         FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array);
 737         _survivor_plab_array = NULL;
 738       }
 739       if (_survivor_chunk_array != NULL) {
 740         FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array);
 741         _survivor_chunk_array = NULL;
 742       }
 743       if (_cursor != NULL) {
 744         FREE_C_HEAP_ARRAY(size_t, _cursor);
 745         _cursor = NULL;
 746       }
 747     } else {
 748       _survivor_chunk_capacity = 2*max_plab_samples;
 749       for (uint i = 0; i < ParallelGCThreads; i++) {
 750         HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples);
 751         if (vec == NULL) {
 752           warning("Failed to allocate survivor plab array");
 753           for (int j = i; j > 0; j--) {
 754             FREE_C_HEAP_ARRAY(HeapWord*, _survivor_plab_array[j-1].array());
 755           }
 756           FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array);
 757           FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array);
 758           _survivor_plab_array = NULL;
 759           _survivor_chunk_array = NULL;
 760           _survivor_chunk_capacity = 0;
 761           break;
 762         } else {
 763           ChunkArray* cur =
 764             ::new (&_survivor_plab_array[i]) ChunkArray(vec,
 765                                                         max_plab_samples);
 766           assert(cur->end() == 0, "Should be 0");
 767           assert(cur->array() == vec, "Should be vec");
 768           assert(cur->capacity() == max_plab_samples, "Error");
 769         }
 770       }
 771     }
 772   }
 773   assert(   (   _survivor_plab_array  != NULL
 774              && _survivor_chunk_array != NULL)
 775          || (   _survivor_chunk_capacity == 0
 776              && _survivor_chunk_index == 0),
 777          "Error");
 778 
 779   // Choose what strong roots should be scanned depending on verification options
 780   // and perm gen collection mode.
 781   if (!CMSClassUnloadingEnabled) {
 782     // If class unloading is disabled we want to include all classes into the root set.
 783     add_root_scanning_option(SharedHeap::SO_AllClasses);
 784   } else {
 785     add_root_scanning_option(SharedHeap::SO_SystemClasses);
 786   }
 787 
 788   NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;)
 789   _gc_counters = new CollectorCounters("CMS", 1);
 790   _completed_initialization = true;
 791   _inter_sweep_timer.start();  // start of time
 792 #ifdef SPARC
 793   // Issue a stern warning, but allow use for experimentation and debugging.
 794   if (VM_Version::is_sun4v() && UseMemSetInBOT) {
 795     assert(!FLAG_IS_DEFAULT(UseMemSetInBOT), "Error");
 796     warning("Experimental flag -XX:+UseMemSetInBOT is known to cause instability"
 797             " on sun4v; please understand that you are using at your own risk!");
 798   }
 799 #endif
 800 }
 801 
 802 const char* ConcurrentMarkSweepGeneration::name() const {
 803   return "concurrent mark-sweep generation";
 804 }
 805 void ConcurrentMarkSweepGeneration::update_counters() {
 806   if (UsePerfData) {
 807     _space_counters->update_all();
 808     _gen_counters->update_all();
 809   }
 810 }
 811 
 812 // this is an optimized version of update_counters(). it takes the
 813 // used value as a parameter rather than computing it.
 814 //
 815 void ConcurrentMarkSweepGeneration::update_counters(size_t used) {
 816   if (UsePerfData) {
 817     _space_counters->update_used(used);
 818     _space_counters->update_capacity();
 819     _gen_counters->update_all();
 820   }
 821 }
 822 
 823 void ConcurrentMarkSweepGeneration::print() const {
 824   Generation::print();
 825   cmsSpace()->print();
 826 }
 827 
 828 #ifndef PRODUCT
 829 void ConcurrentMarkSweepGeneration::print_statistics() {
 830   cmsSpace()->printFLCensus(0);
 831 }
 832 #endif
 833 
 834 void ConcurrentMarkSweepGeneration::printOccupancy(const char *s) {
 835   GenCollectedHeap* gch = GenCollectedHeap::heap();
 836   if (PrintGCDetails) {
 837     if (Verbose) {
 838       gclog_or_tty->print(" [%d %s-%s: "SIZE_FORMAT"("SIZE_FORMAT")]",
 839         level(), short_name(), s, used(), capacity());
 840     } else {
 841       gclog_or_tty->print(" [%d %s-%s: "SIZE_FORMAT"K("SIZE_FORMAT"K)]",
 842         level(), short_name(), s, used() / K, capacity() / K);
 843     }
 844   }
 845   if (Verbose) {
 846     gclog_or_tty->print(" "SIZE_FORMAT"("SIZE_FORMAT")",
 847               gch->used(), gch->capacity());
 848   } else {
 849     gclog_or_tty->print(" "SIZE_FORMAT"K("SIZE_FORMAT"K)",
 850               gch->used() / K, gch->capacity() / K);
 851   }
 852 }
 853 
 854 size_t
 855 ConcurrentMarkSweepGeneration::contiguous_available() const {
 856   // dld proposes an improvement in precision here. If the committed
 857   // part of the space ends in a free block we should add that to
 858   // uncommitted size in the calculation below. Will make this
 859   // change later, staying with the approximation below for the
 860   // time being. -- ysr.
 861   return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc());
 862 }
 863 
 864 size_t
 865 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const {
 866   return _cmsSpace->max_alloc_in_words() * HeapWordSize;
 867 }
 868 
 869 size_t ConcurrentMarkSweepGeneration::max_available() const {
 870   return free() + _virtual_space.uncommitted_size();
 871 }
 872 
 873 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(
 874     size_t max_promotion_in_bytes,
 875     bool younger_handles_promotion_failure) const {
 876 
 877   // This is the most conservative test.  Full promotion is
 878   // guaranteed if this is used. The multiplicative factor is to
 879   // account for the worst case "dilatation".
 880   double adjusted_max_promo_bytes = _dilatation_factor * max_promotion_in_bytes;
 881   if (adjusted_max_promo_bytes > (double)max_uintx) { // larger than size_t
 882     adjusted_max_promo_bytes = (double)max_uintx;
 883   }
 884   bool result = (max_contiguous_available() >= (size_t)adjusted_max_promo_bytes);
 885 
 886   if (younger_handles_promotion_failure && !result) {
 887     // Full promotion is not guaranteed because fragmentation
 888     // of the cms generation can prevent the full promotion.
 889     result = (max_available() >= (size_t)adjusted_max_promo_bytes);
 890 
 891     if (!result) {
 892       // With promotion failure handling the test for the ability
 893       // to support the promotion does not have to be guaranteed.
 894       // Use an average of the amount promoted.
 895       result = max_available() >= (size_t)
 896         gc_stats()->avg_promoted()->padded_average();
 897       if (PrintGC && Verbose && result) {
 898         gclog_or_tty->print_cr(
 899           "\nConcurrentMarkSweepGeneration::promotion_attempt_is_safe"
 900           " max_available: " SIZE_FORMAT
 901           " avg_promoted: " SIZE_FORMAT,
 902           max_available(), (size_t)
 903           gc_stats()->avg_promoted()->padded_average());
 904       }
 905     } else {
 906       if (PrintGC && Verbose) {
 907         gclog_or_tty->print_cr(
 908           "\nConcurrentMarkSweepGeneration::promotion_attempt_is_safe"
 909           " max_available: " SIZE_FORMAT
 910           " adj_max_promo_bytes: " SIZE_FORMAT,
 911           max_available(), (size_t)adjusted_max_promo_bytes);
 912       }
 913     }
 914   } else {
 915     if (PrintGC && Verbose) {
 916       gclog_or_tty->print_cr(
 917         "\nConcurrentMarkSweepGeneration::promotion_attempt_is_safe"
 918         " contiguous_available: " SIZE_FORMAT
 919         " adj_max_promo_bytes: " SIZE_FORMAT,
 920         max_contiguous_available(), (size_t)adjusted_max_promo_bytes);
 921     }
 922   }
 923   return result;
 924 }
 925 
 926 // At a promotion failure dump information on block layout in heap
 927 // (cms old generation).
 928 void ConcurrentMarkSweepGeneration::promotion_failure_occurred() {
 929   if (CMSDumpAtPromotionFailure) {
 930     cmsSpace()->dump_at_safepoint_with_locks(collector(), gclog_or_tty);
 931   }
 932 }
 933 
 934 CompactibleSpace*
 935 ConcurrentMarkSweepGeneration::first_compaction_space() const {
 936   return _cmsSpace;
 937 }
 938 
 939 void ConcurrentMarkSweepGeneration::reset_after_compaction() {
 940   // Clear the promotion information.  These pointers can be adjusted
 941   // along with all the other pointers into the heap but
 942   // compaction is expected to be a rare event with
 943   // a heap using cms so don't do it without seeing the need.
 944   if (ParallelGCThreads > 0) {
 945     for (uint i = 0; i < ParallelGCThreads; i++) {
 946       _par_gc_thread_states[i]->promo.reset();
 947     }
 948   }
 949 }
 950 
 951 void ConcurrentMarkSweepGeneration::space_iterate(SpaceClosure* blk, bool usedOnly) {
 952   blk->do_space(_cmsSpace);
 953 }
 954 
 955 void ConcurrentMarkSweepGeneration::compute_new_size() {
 956   assert_locked_or_safepoint(Heap_lock);
 957 
 958   // If incremental collection failed, we just want to expand
 959   // to the limit.
 960   if (incremental_collection_failed()) {
 961     clear_incremental_collection_failed();
 962     grow_to_reserved();
 963     return;
 964   }
 965 
 966   size_t expand_bytes = 0;
 967   double free_percentage = ((double) free()) / capacity();
 968   double desired_free_percentage = (double) MinHeapFreeRatio / 100;
 969   double maximum_free_percentage = (double) MaxHeapFreeRatio / 100;
 970 
 971   // compute expansion delta needed for reaching desired free percentage
 972   if (free_percentage < desired_free_percentage) {
 973     size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
 974     assert(desired_capacity >= capacity(), "invalid expansion size");
 975     expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes);
 976   }
 977   if (expand_bytes > 0) {
 978     if (PrintGCDetails && Verbose) {
 979       size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
 980       gclog_or_tty->print_cr("\nFrom compute_new_size: ");
 981       gclog_or_tty->print_cr("  Free fraction %f", free_percentage);
 982       gclog_or_tty->print_cr("  Desired free fraction %f",
 983         desired_free_percentage);
 984       gclog_or_tty->print_cr("  Maximum free fraction %f",
 985         maximum_free_percentage);
 986       gclog_or_tty->print_cr("  Capactiy "SIZE_FORMAT, capacity()/1000);
 987       gclog_or_tty->print_cr("  Desired capacity "SIZE_FORMAT,
 988         desired_capacity/1000);
 989       int prev_level = level() - 1;
 990       if (prev_level >= 0) {
 991         size_t prev_size = 0;
 992         GenCollectedHeap* gch = GenCollectedHeap::heap();
 993         Generation* prev_gen = gch->_gens[prev_level];
 994         prev_size = prev_gen->capacity();
 995           gclog_or_tty->print_cr("  Younger gen size "SIZE_FORMAT,
 996                                  prev_size/1000);
 997       }
 998       gclog_or_tty->print_cr("  unsafe_max_alloc_nogc "SIZE_FORMAT,
 999         unsafe_max_alloc_nogc()/1000);
1000       gclog_or_tty->print_cr("  contiguous available "SIZE_FORMAT,
1001         contiguous_available()/1000);
1002       gclog_or_tty->print_cr("  Expand by "SIZE_FORMAT" (bytes)",
1003         expand_bytes);
1004     }
1005     // safe if expansion fails
1006     expand(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio);
1007     if (PrintGCDetails && Verbose) {
1008       gclog_or_tty->print_cr("  Expanded free fraction %f",
1009         ((double) free()) / capacity());
1010     }
1011   }
1012 }
1013 
1014 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const {
1015   return cmsSpace()->freelistLock();
1016 }
1017 
1018 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size,
1019                                                   bool   tlab) {
1020   CMSSynchronousYieldRequest yr;
1021   MutexLockerEx x(freelistLock(),
1022                   Mutex::_no_safepoint_check_flag);
1023   return have_lock_and_allocate(size, tlab);
1024 }
1025 
1026 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size,
1027                                                   bool   tlab) {
1028   assert_lock_strong(freelistLock());
1029   size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size);
1030   HeapWord* res = cmsSpace()->allocate(adjustedSize);
1031   // Allocate the object live (grey) if the background collector has
1032   // started marking. This is necessary because the marker may
1033   // have passed this address and consequently this object will
1034   // not otherwise be greyed and would be incorrectly swept up.
1035   // Note that if this object contains references, the writing
1036   // of those references will dirty the card containing this object
1037   // allowing the object to be blackened (and its references scanned)
1038   // either during a preclean phase or at the final checkpoint.
1039   if (res != NULL) {
1040     collector()->direct_allocated(res, adjustedSize);
1041     _direct_allocated_words += adjustedSize;
1042     // allocation counters
1043     NOT_PRODUCT(
1044       _numObjectsAllocated++;
1045       _numWordsAllocated += (int)adjustedSize;
1046     )
1047   }
1048   return res;
1049 }
1050 
1051 // In the case of direct allocation by mutators in a generation that
1052 // is being concurrently collected, the object must be allocated
1053 // live (grey) if the background collector has started marking.
1054 // This is necessary because the marker may
1055 // have passed this address and consequently this object will
1056 // not otherwise be greyed and would be incorrectly swept up.
1057 // Note that if this object contains references, the writing
1058 // of those references will dirty the card containing this object
1059 // allowing the object to be blackened (and its references scanned)
1060 // either during a preclean phase or at the final checkpoint.
1061 void CMSCollector::direct_allocated(HeapWord* start, size_t size) {
1062   assert(_markBitMap.covers(start, size), "Out of bounds");
1063   if (_collectorState >= Marking) {
1064     MutexLockerEx y(_markBitMap.lock(),
1065                     Mutex::_no_safepoint_check_flag);
1066     // [see comments preceding SweepClosure::do_blk() below for details]
1067     // 1. need to mark the object as live so it isn't collected
1068     // 2. need to mark the 2nd bit to indicate the object may be uninitialized
1069     // 3. need to mark the end of the object so sweeper can skip over it
1070     //    if it's uninitialized when the sweeper reaches it.
1071     _markBitMap.mark(start);          // object is live
1072     _markBitMap.mark(start + 1);      // object is potentially uninitialized?
1073     _markBitMap.mark(start + size - 1);
1074                                       // mark end of object
1075   }
1076   // check that oop looks uninitialized
1077   assert(oop(start)->klass_or_null() == NULL, "_klass should be NULL");
1078 }
1079 
1080 void CMSCollector::promoted(bool par, HeapWord* start,
1081                             bool is_obj_array, size_t obj_size) {
1082   assert(_markBitMap.covers(start), "Out of bounds");
1083   // See comment in direct_allocated() about when objects should
1084   // be allocated live.
1085   if (_collectorState >= Marking) {
1086     // we already hold the marking bit map lock, taken in
1087     // the prologue
1088     if (par) {
1089       _markBitMap.par_mark(start);
1090     } else {
1091       _markBitMap.mark(start);
1092     }
1093     // We don't need to mark the object as uninitialized (as
1094     // in direct_allocated above) because this is being done with the
1095     // world stopped and the object will be initialized by the
1096     // time the sweeper gets to look at it.
1097     assert(SafepointSynchronize::is_at_safepoint(),
1098            "expect promotion only at safepoints");
1099 
1100     if (_collectorState < Sweeping) {
1101       // Mark the appropriate cards in the modUnionTable, so that
1102       // this object gets scanned before the sweep. If this is
1103       // not done, CMS generation references in the object might
1104       // not get marked.
1105       // For the case of arrays, which are otherwise precisely
1106       // marked, we need to dirty the entire array, not just its head.
1107       if (is_obj_array) {
1108         // The [par_]mark_range() method expects mr.end() below to
1109         // be aligned to the granularity of a bit's representation
1110         // in the heap. In the case of the MUT below, that's a
1111         // card size.
1112         MemRegion mr(start,
1113                      (HeapWord*)round_to((intptr_t)(start + obj_size),
1114                         CardTableModRefBS::card_size /* bytes */));
1115         if (par) {
1116           _modUnionTable.par_mark_range(mr);
1117         } else {
1118           _modUnionTable.mark_range(mr);
1119         }
1120       } else {  // not an obj array; we can just mark the head
1121         if (par) {
1122           _modUnionTable.par_mark(start);
1123         } else {
1124           _modUnionTable.mark(start);
1125         }
1126       }
1127     }
1128   }
1129 }
1130 
1131 static inline size_t percent_of_space(Space* space, HeapWord* addr)
1132 {
1133   size_t delta = pointer_delta(addr, space->bottom());
1134   return (size_t)(delta * 100.0 / (space->capacity() / HeapWordSize));
1135 }
1136 
1137 void CMSCollector::icms_update_allocation_limits()
1138 {
1139   Generation* gen0 = GenCollectedHeap::heap()->get_gen(0);
1140   EdenSpace* eden = gen0->as_DefNewGeneration()->eden();
1141 
1142   const unsigned int duty_cycle = stats().icms_update_duty_cycle();
1143   if (CMSTraceIncrementalPacing) {
1144     stats().print();
1145   }
1146 
1147   assert(duty_cycle <= 100, "invalid duty cycle");
1148   if (duty_cycle != 0) {
1149     // The duty_cycle is a percentage between 0 and 100; convert to words and
1150     // then compute the offset from the endpoints of the space.
1151     size_t free_words = eden->free() / HeapWordSize;
1152     double free_words_dbl = (double)free_words;
1153     size_t duty_cycle_words = (size_t)(free_words_dbl * duty_cycle / 100.0);
1154     size_t offset_words = (free_words - duty_cycle_words) / 2;
1155 
1156     _icms_start_limit = eden->top() + offset_words;
1157     _icms_stop_limit = eden->end() - offset_words;
1158 
1159     // The limits may be adjusted (shifted to the right) by
1160     // CMSIncrementalOffset, to allow the application more mutator time after a
1161     // young gen gc (when all mutators were stopped) and before CMS starts and
1162     // takes away one or more cpus.
1163     if (CMSIncrementalOffset != 0) {
1164       double adjustment_dbl = free_words_dbl * CMSIncrementalOffset / 100.0;
1165       size_t adjustment = (size_t)adjustment_dbl;
1166       HeapWord* tmp_stop = _icms_stop_limit + adjustment;
1167       if (tmp_stop > _icms_stop_limit && tmp_stop < eden->end()) {
1168         _icms_start_limit += adjustment;
1169         _icms_stop_limit = tmp_stop;
1170       }
1171     }
1172   }
1173   if (duty_cycle == 0 || (_icms_start_limit == _icms_stop_limit)) {
1174     _icms_start_limit = _icms_stop_limit = eden->end();
1175   }
1176 
1177   // Install the new start limit.
1178   eden->set_soft_end(_icms_start_limit);
1179 
1180   if (CMSTraceIncrementalMode) {
1181     gclog_or_tty->print(" icms alloc limits:  "
1182                            PTR_FORMAT "," PTR_FORMAT
1183                            " (" SIZE_FORMAT "%%," SIZE_FORMAT "%%) ",
1184                            _icms_start_limit, _icms_stop_limit,
1185                            percent_of_space(eden, _icms_start_limit),
1186                            percent_of_space(eden, _icms_stop_limit));
1187     if (Verbose) {
1188       gclog_or_tty->print("eden:  ");
1189       eden->print_on(gclog_or_tty);
1190     }
1191   }
1192 }
1193 
1194 // Any changes here should try to maintain the invariant
1195 // that if this method is called with _icms_start_limit
1196 // and _icms_stop_limit both NULL, then it should return NULL
1197 // and not notify the icms thread.
1198 HeapWord*
1199 CMSCollector::allocation_limit_reached(Space* space, HeapWord* top,
1200                                        size_t word_size)
1201 {
1202   // A start_limit equal to end() means the duty cycle is 0, so treat that as a
1203   // nop.
1204   if (CMSIncrementalMode && _icms_start_limit != space->end()) {
1205     if (top <= _icms_start_limit) {
1206       if (CMSTraceIncrementalMode) {
1207         space->print_on(gclog_or_tty);
1208         gclog_or_tty->stamp();
1209         gclog_or_tty->print_cr(" start limit top=" PTR_FORMAT
1210                                ", new limit=" PTR_FORMAT
1211                                " (" SIZE_FORMAT "%%)",
1212                                top, _icms_stop_limit,
1213                                percent_of_space(space, _icms_stop_limit));
1214       }
1215       ConcurrentMarkSweepThread::start_icms();
1216       assert(top < _icms_stop_limit, "Tautology");
1217       if (word_size < pointer_delta(_icms_stop_limit, top)) {
1218         return _icms_stop_limit;
1219       }
1220 
1221       // The allocation will cross both the _start and _stop limits, so do the
1222       // stop notification also and return end().
1223       if (CMSTraceIncrementalMode) {
1224         space->print_on(gclog_or_tty);
1225         gclog_or_tty->stamp();
1226         gclog_or_tty->print_cr(" +stop limit top=" PTR_FORMAT
1227                                ", new limit=" PTR_FORMAT
1228                                " (" SIZE_FORMAT "%%)",
1229                                top, space->end(),
1230                                percent_of_space(space, space->end()));
1231       }
1232       ConcurrentMarkSweepThread::stop_icms();
1233       return space->end();
1234     }
1235 
1236     if (top <= _icms_stop_limit) {
1237       if (CMSTraceIncrementalMode) {
1238         space->print_on(gclog_or_tty);
1239         gclog_or_tty->stamp();
1240         gclog_or_tty->print_cr(" stop limit top=" PTR_FORMAT
1241                                ", new limit=" PTR_FORMAT
1242                                " (" SIZE_FORMAT "%%)",
1243                                top, space->end(),
1244                                percent_of_space(space, space->end()));
1245       }
1246       ConcurrentMarkSweepThread::stop_icms();
1247       return space->end();
1248     }
1249 
1250     if (CMSTraceIncrementalMode) {
1251       space->print_on(gclog_or_tty);
1252       gclog_or_tty->stamp();
1253       gclog_or_tty->print_cr(" end limit top=" PTR_FORMAT
1254                              ", new limit=" PTR_FORMAT,
1255                              top, NULL);
1256     }
1257   }
1258 
1259   return NULL;
1260 }
1261 
1262 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size) {
1263   assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
1264   // allocate, copy and if necessary update promoinfo --
1265   // delegate to underlying space.
1266   assert_lock_strong(freelistLock());
1267 
1268 #ifndef PRODUCT
1269   if (Universe::heap()->promotion_should_fail()) {
1270     return NULL;
1271   }
1272 #endif  // #ifndef PRODUCT
1273 
1274   oop res = _cmsSpace->promote(obj, obj_size);
1275   if (res == NULL) {
1276     // expand and retry
1277     size_t s = _cmsSpace->expansionSpaceRequired(obj_size);  // HeapWords
1278     expand(s*HeapWordSize, MinHeapDeltaBytes,
1279       CMSExpansionCause::_satisfy_promotion);
1280     // Since there's currently no next generation, we don't try to promote
1281     // into a more senior generation.
1282     assert(next_gen() == NULL, "assumption, based upon which no attempt "
1283                                "is made to pass on a possibly failing "
1284                                "promotion to next generation");
1285     res = _cmsSpace->promote(obj, obj_size);
1286   }
1287   if (res != NULL) {
1288     // See comment in allocate() about when objects should
1289     // be allocated live.
1290     assert(obj->is_oop(), "Will dereference klass pointer below");
1291     collector()->promoted(false,           // Not parallel
1292                           (HeapWord*)res, obj->is_objArray(), obj_size);
1293     // promotion counters
1294     NOT_PRODUCT(
1295       _numObjectsPromoted++;
1296       _numWordsPromoted +=
1297         (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size()));
1298     )
1299   }
1300   return res;
1301 }
1302 
1303 
1304 HeapWord*
1305 ConcurrentMarkSweepGeneration::allocation_limit_reached(Space* space,
1306                                              HeapWord* top,
1307                                              size_t word_sz)
1308 {
1309   return collector()->allocation_limit_reached(space, top, word_sz);
1310 }
1311 
1312 // Things to support parallel young-gen collection.
1313 oop
1314 ConcurrentMarkSweepGeneration::par_promote(int thread_num,
1315                                            oop old, markOop m,
1316                                            size_t word_sz) {
1317 #ifndef PRODUCT
1318   if (Universe::heap()->promotion_should_fail()) {
1319     return NULL;
1320   }
1321 #endif  // #ifndef PRODUCT
1322 
1323   CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1324   PromotionInfo* promoInfo = &ps->promo;
1325   // if we are tracking promotions, then first ensure space for
1326   // promotion (including spooling space for saving header if necessary).
1327   // then allocate and copy, then track promoted info if needed.
1328   // When tracking (see PromotionInfo::track()), the mark word may
1329   // be displaced and in this case restoration of the mark word
1330   // occurs in the (oop_since_save_marks_)iterate phase.
1331   if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) {
1332     // Out of space for allocating spooling buffers;
1333     // try expanding and allocating spooling buffers.
1334     if (!expand_and_ensure_spooling_space(promoInfo)) {
1335       return NULL;
1336     }
1337   }
1338   assert(promoInfo->has_spooling_space(), "Control point invariant");
1339   HeapWord* obj_ptr = ps->lab.alloc(word_sz);
1340   if (obj_ptr == NULL) {
1341      obj_ptr = expand_and_par_lab_allocate(ps, word_sz);
1342      if (obj_ptr == NULL) {
1343        return NULL;
1344      }
1345   }
1346   oop obj = oop(obj_ptr);
1347   assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1348   // Otherwise, copy the object.  Here we must be careful to insert the
1349   // klass pointer last, since this marks the block as an allocated object.
1350   // Except with compressed oops it's the mark word.
1351   HeapWord* old_ptr = (HeapWord*)old;
1352   if (word_sz > (size_t)oopDesc::header_size()) {
1353     Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1354                                  obj_ptr + oopDesc::header_size(),
1355                                  word_sz - oopDesc::header_size());
1356   }
1357 
1358   if (UseCompressedOops) {
1359     // Copy gap missed by (aligned) header size calculation above
1360     obj->set_klass_gap(old->klass_gap());
1361   }
1362 
1363   // Restore the mark word copied above.
1364   obj->set_mark(m);
1365 
1366   // Now we can track the promoted object, if necessary.  We take care
1367   // to delay the transition from uninitialized to full object
1368   // (i.e., insertion of klass pointer) until after, so that it
1369   // atomically becomes a promoted object.
1370   if (promoInfo->tracking()) {
1371     promoInfo->track((PromotedObject*)obj, old->klass());
1372   }
1373 
1374   // Finally, install the klass pointer (this should be volatile).
1375   obj->set_klass(old->klass());
1376 
1377   assert(old->is_oop(), "Will dereference klass ptr below");
1378   collector()->promoted(true,          // parallel
1379                         obj_ptr, old->is_objArray(), word_sz);
1380 
1381   NOT_PRODUCT(
1382     Atomic::inc(&_numObjectsPromoted);
1383     Atomic::add((jint)CompactibleFreeListSpace::adjustObjectSize(obj->size()),
1384                 &_numWordsPromoted);
1385   )
1386 
1387   return obj;
1388 }
1389 
1390 void
1391 ConcurrentMarkSweepGeneration::
1392 par_promote_alloc_undo(int thread_num,
1393                        HeapWord* obj, size_t word_sz) {
1394   // CMS does not support promotion undo.
1395   ShouldNotReachHere();
1396 }
1397 
1398 void
1399 ConcurrentMarkSweepGeneration::
1400 par_promote_alloc_done(int thread_num) {
1401   CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1402   ps->lab.retire(thread_num);
1403 }
1404 
1405 void
1406 ConcurrentMarkSweepGeneration::
1407 par_oop_since_save_marks_iterate_done(int thread_num) {
1408   CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1409   ParScanWithoutBarrierClosure* dummy_cl = NULL;
1410   ps->promo.promoted_oops_iterate_nv(dummy_cl);
1411 }
1412 
1413 // XXXPERM
1414 bool ConcurrentMarkSweepGeneration::should_collect(bool   full,
1415                                                    size_t size,
1416                                                    bool   tlab)
1417 {
1418   // We allow a STW collection only if a full
1419   // collection was requested.
1420   return full || should_allocate(size, tlab); // FIX ME !!!
1421   // This and promotion failure handling are connected at the
1422   // hip and should be fixed by untying them.
1423 }
1424 
1425 bool CMSCollector::shouldConcurrentCollect() {
1426   if (_full_gc_requested) {
1427     if (Verbose && PrintGCDetails) {
1428       gclog_or_tty->print_cr("CMSCollector: collect because of explicit "
1429                              " gc request (or gc_locker)");
1430     }
1431     return true;
1432   }
1433 
1434   // For debugging purposes, change the type of collection.
1435   // If the rotation is not on the concurrent collection
1436   // type, don't start a concurrent collection.
1437   NOT_PRODUCT(
1438     if (RotateCMSCollectionTypes &&
1439         (_cmsGen->debug_collection_type() !=
1440           ConcurrentMarkSweepGeneration::Concurrent_collection_type)) {
1441       assert(_cmsGen->debug_collection_type() !=
1442         ConcurrentMarkSweepGeneration::Unknown_collection_type,
1443         "Bad cms collection type");
1444       return false;
1445     }
1446   )
1447 
1448   FreelistLocker x(this);
1449   // ------------------------------------------------------------------
1450   // Print out lots of information which affects the initiation of
1451   // a collection.
1452   if (PrintCMSInitiationStatistics && stats().valid()) {
1453     gclog_or_tty->print("CMSCollector shouldConcurrentCollect: ");
1454     gclog_or_tty->stamp();
1455     gclog_or_tty->print_cr("");
1456     stats().print_on(gclog_or_tty);
1457     gclog_or_tty->print_cr("time_until_cms_gen_full %3.7f",
1458       stats().time_until_cms_gen_full());
1459     gclog_or_tty->print_cr("free="SIZE_FORMAT, _cmsGen->free());
1460     gclog_or_tty->print_cr("contiguous_available="SIZE_FORMAT,
1461                            _cmsGen->contiguous_available());
1462     gclog_or_tty->print_cr("promotion_rate=%g", stats().promotion_rate());
1463     gclog_or_tty->print_cr("cms_allocation_rate=%g", stats().cms_allocation_rate());
1464     gclog_or_tty->print_cr("occupancy=%3.7f", _cmsGen->occupancy());
1465     gclog_or_tty->print_cr("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy());
1466     gclog_or_tty->print_cr("initiatingPermOccupancy=%3.7f", _permGen->initiating_occupancy());
1467   }
1468   // ------------------------------------------------------------------
1469 
1470   // If the estimated time to complete a cms collection (cms_duration())
1471   // is less than the estimated time remaining until the cms generation
1472   // is full, start a collection.
1473   if (!UseCMSInitiatingOccupancyOnly) {
1474     if (stats().valid()) {
1475       if (stats().time_until_cms_start() == 0.0) {
1476         return true;
1477       }
1478     } else {
1479       // We want to conservatively collect somewhat early in order
1480       // to try and "bootstrap" our CMS/promotion statistics;
1481       // this branch will not fire after the first successful CMS
1482       // collection because the stats should then be valid.
1483       if (_cmsGen->occupancy() >= _bootstrap_occupancy) {
1484         if (Verbose && PrintGCDetails) {
1485           gclog_or_tty->print_cr(
1486             " CMSCollector: collect for bootstrapping statistics:"
1487             " occupancy = %f, boot occupancy = %f", _cmsGen->occupancy(),
1488             _bootstrap_occupancy);
1489         }
1490         return true;
1491       }
1492     }
1493   }
1494 
1495   // Otherwise, we start a collection cycle if either the perm gen or
1496   // old gen want a collection cycle started. Each may use
1497   // an appropriate criterion for making this decision.
1498   // XXX We need to make sure that the gen expansion
1499   // criterion dovetails well with this. XXX NEED TO FIX THIS
1500   if (_cmsGen->should_concurrent_collect()) {
1501     if (Verbose && PrintGCDetails) {
1502       gclog_or_tty->print_cr("CMS old gen initiated");
1503     }
1504     return true;
1505   }
1506 
1507   // We start a collection if we believe an incremental collection may fail;
1508   // this is not likely to be productive in practice because it's probably too
1509   // late anyway.
1510   GenCollectedHeap* gch = GenCollectedHeap::heap();
1511   assert(gch->collector_policy()->is_two_generation_policy(),
1512          "You may want to check the correctness of the following");
1513   if (gch->incremental_collection_will_fail()) {
1514     if (PrintGCDetails && Verbose) {
1515       gclog_or_tty->print("CMSCollector: collect because incremental collection will fail ");
1516     }
1517     return true;
1518   }
1519 
1520   if (CMSClassUnloadingEnabled && _permGen->should_concurrent_collect()) {
1521     bool res = update_should_unload_classes();
1522     if (res) {
1523       if (Verbose && PrintGCDetails) {
1524         gclog_or_tty->print_cr("CMS perm gen initiated");
1525       }
1526       return true;
1527     }
1528   }
1529   return false;
1530 }
1531 
1532 // Clear _expansion_cause fields of constituent generations
1533 void CMSCollector::clear_expansion_cause() {
1534   _cmsGen->clear_expansion_cause();
1535   _permGen->clear_expansion_cause();
1536 }
1537 
1538 // We should be conservative in starting a collection cycle.  To
1539 // start too eagerly runs the risk of collecting too often in the
1540 // extreme.  To collect too rarely falls back on full collections,
1541 // which works, even if not optimum in terms of concurrent work.
1542 // As a work around for too eagerly collecting, use the flag
1543 // UseCMSInitiatingOccupancyOnly.  This also has the advantage of
1544 // giving the user an easily understandable way of controlling the
1545 // collections.
1546 // We want to start a new collection cycle if any of the following
1547 // conditions hold:
1548 // . our current occupancy exceeds the configured initiating occupancy
1549 //   for this generation, or
1550 // . we recently needed to expand this space and have not, since that
1551 //   expansion, done a collection of this generation, or
1552 // . the underlying space believes that it may be a good idea to initiate
1553 //   a concurrent collection (this may be based on criteria such as the
1554 //   following: the space uses linear allocation and linear allocation is
1555 //   going to fail, or there is believed to be excessive fragmentation in
1556 //   the generation, etc... or ...
1557 // [.(currently done by CMSCollector::shouldConcurrentCollect() only for
1558 //   the case of the old generation, not the perm generation; see CR 6543076):
1559 //   we may be approaching a point at which allocation requests may fail because
1560 //   we will be out of sufficient free space given allocation rate estimates.]
1561 bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const {
1562 
1563   assert_lock_strong(freelistLock());
1564   if (occupancy() > initiating_occupancy()) {
1565     if (PrintGCDetails && Verbose) {
1566       gclog_or_tty->print(" %s: collect because of occupancy %f / %f  ",
1567         short_name(), occupancy(), initiating_occupancy());
1568     }
1569     return true;
1570   }
1571   if (UseCMSInitiatingOccupancyOnly) {
1572     return false;
1573   }
1574   if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) {
1575     if (PrintGCDetails && Verbose) {
1576       gclog_or_tty->print(" %s: collect because expanded for allocation ",
1577         short_name());
1578     }
1579     return true;
1580   }
1581   if (_cmsSpace->should_concurrent_collect()) {
1582     if (PrintGCDetails && Verbose) {
1583       gclog_or_tty->print(" %s: collect because cmsSpace says so ",
1584         short_name());
1585     }
1586     return true;
1587   }
1588   return false;
1589 }
1590 
1591 void ConcurrentMarkSweepGeneration::collect(bool   full,
1592                                             bool   clear_all_soft_refs,
1593                                             size_t size,
1594                                             bool   tlab)
1595 {
1596   collector()->collect(full, clear_all_soft_refs, size, tlab);
1597 }
1598 
1599 void CMSCollector::collect(bool   full,
1600                            bool   clear_all_soft_refs,
1601                            size_t size,
1602                            bool   tlab)
1603 {
1604   if (!UseCMSCollectionPassing && _collectorState > Idling) {
1605     // For debugging purposes skip the collection if the state
1606     // is not currently idle
1607     if (TraceCMSState) {
1608       gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " skipped full:%d CMS state %d",
1609         Thread::current(), full, _collectorState);
1610     }
1611     return;
1612   }
1613 
1614   // The following "if" branch is present for defensive reasons.
1615   // In the current uses of this interface, it can be replaced with:
1616   // assert(!GC_locker.is_active(), "Can't be called otherwise");
1617   // But I am not placing that assert here to allow future
1618   // generality in invoking this interface.
1619   if (GC_locker::is_active()) {
1620     // A consistency test for GC_locker
1621     assert(GC_locker::needs_gc(), "Should have been set already");
1622     // Skip this foreground collection, instead
1623     // expanding the heap if necessary.
1624     // Need the free list locks for the call to free() in compute_new_size()
1625     compute_new_size();
1626     return;
1627   }
1628   acquire_control_and_collect(full, clear_all_soft_refs);
1629   _full_gcs_since_conc_gc++;
1630 
1631 }
1632 
1633 void CMSCollector::request_full_gc(unsigned int full_gc_count) {
1634   GenCollectedHeap* gch = GenCollectedHeap::heap();
1635   unsigned int gc_count = gch->total_full_collections();
1636   if (gc_count == full_gc_count) {
1637     MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag);
1638     _full_gc_requested = true;
1639     CGC_lock->notify();   // nudge CMS thread
1640   }
1641 }
1642 
1643 
1644 // The foreground and background collectors need to coordinate in order
1645 // to make sure that they do not mutually interfere with CMS collections.
1646 // When a background collection is active,
1647 // the foreground collector may need to take over (preempt) and
1648 // synchronously complete an ongoing collection. Depending on the
1649 // frequency of the background collections and the heap usage
1650 // of the application, this preemption can be seldom or frequent.
1651 // There are only certain
1652 // points in the background collection that the "collection-baton"
1653 // can be passed to the foreground collector.
1654 //
1655 // The foreground collector will wait for the baton before
1656 // starting any part of the collection.  The foreground collector
1657 // will only wait at one location.
1658 //
1659 // The background collector will yield the baton before starting a new
1660 // phase of the collection (e.g., before initial marking, marking from roots,
1661 // precleaning, final re-mark, sweep etc.)  This is normally done at the head
1662 // of the loop which switches the phases. The background collector does some
1663 // of the phases (initial mark, final re-mark) with the world stopped.
1664 // Because of locking involved in stopping the world,
1665 // the foreground collector should not block waiting for the background
1666 // collector when it is doing a stop-the-world phase.  The background
1667 // collector will yield the baton at an additional point just before
1668 // it enters a stop-the-world phase.  Once the world is stopped, the
1669 // background collector checks the phase of the collection.  If the
1670 // phase has not changed, it proceeds with the collection.  If the
1671 // phase has changed, it skips that phase of the collection.  See
1672 // the comments on the use of the Heap_lock in collect_in_background().
1673 //
1674 // Variable used in baton passing.
1675 //   _foregroundGCIsActive - Set to true by the foreground collector when
1676 //      it wants the baton.  The foreground clears it when it has finished
1677 //      the collection.
1678 //   _foregroundGCShouldWait - Set to true by the background collector
1679 //        when it is running.  The foreground collector waits while
1680 //      _foregroundGCShouldWait is true.
1681 //  CGC_lock - monitor used to protect access to the above variables
1682 //      and to notify the foreground and background collectors.
1683 //  _collectorState - current state of the CMS collection.
1684 //
1685 // The foreground collector
1686 //   acquires the CGC_lock
1687 //   sets _foregroundGCIsActive
1688 //   waits on the CGC_lock for _foregroundGCShouldWait to be false
1689 //     various locks acquired in preparation for the collection
1690 //     are released so as not to block the background collector
1691 //     that is in the midst of a collection
1692 //   proceeds with the collection
1693 //   clears _foregroundGCIsActive
1694 //   returns
1695 //
1696 // The background collector in a loop iterating on the phases of the
1697 //      collection
1698 //   acquires the CGC_lock
1699 //   sets _foregroundGCShouldWait
1700 //   if _foregroundGCIsActive is set
1701 //     clears _foregroundGCShouldWait, notifies _CGC_lock
1702 //     waits on _CGC_lock for _foregroundGCIsActive to become false
1703 //     and exits the loop.
1704 //   otherwise
1705 //     proceed with that phase of the collection
1706 //     if the phase is a stop-the-world phase,
1707 //       yield the baton once more just before enqueueing
1708 //       the stop-world CMS operation (executed by the VM thread).
1709 //   returns after all phases of the collection are done
1710 //
1711 
1712 void CMSCollector::acquire_control_and_collect(bool full,
1713         bool clear_all_soft_refs) {
1714   assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
1715   assert(!Thread::current()->is_ConcurrentGC_thread(),
1716          "shouldn't try to acquire control from self!");
1717 
1718   // Start the protocol for acquiring control of the
1719   // collection from the background collector (aka CMS thread).
1720   assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1721          "VM thread should have CMS token");
1722   // Remember the possibly interrupted state of an ongoing
1723   // concurrent collection
1724   CollectorState first_state = _collectorState;
1725 
1726   // Signal to a possibly ongoing concurrent collection that
1727   // we want to do a foreground collection.
1728   _foregroundGCIsActive = true;
1729 
1730   // Disable incremental mode during a foreground collection.
1731   ICMSDisabler icms_disabler;
1732 
1733   // release locks and wait for a notify from the background collector
1734   // releasing the locks in only necessary for phases which
1735   // do yields to improve the granularity of the collection.
1736   assert_lock_strong(bitMapLock());
1737   // We need to lock the Free list lock for the space that we are
1738   // currently collecting.
1739   assert(haveFreelistLocks(), "Must be holding free list locks");
1740   bitMapLock()->unlock();
1741   releaseFreelistLocks();
1742   {
1743     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1744     if (_foregroundGCShouldWait) {
1745       // We are going to be waiting for action for the CMS thread;
1746       // it had better not be gone (for instance at shutdown)!
1747       assert(ConcurrentMarkSweepThread::cmst() != NULL,
1748              "CMS thread must be running");
1749       // Wait here until the background collector gives us the go-ahead
1750       ConcurrentMarkSweepThread::clear_CMS_flag(
1751         ConcurrentMarkSweepThread::CMS_vm_has_token);  // release token
1752       // Get a possibly blocked CMS thread going:
1753       //   Note that we set _foregroundGCIsActive true above,
1754       //   without protection of the CGC_lock.
1755       CGC_lock->notify();
1756       assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(),
1757              "Possible deadlock");
1758       while (_foregroundGCShouldWait) {
1759         // wait for notification
1760         CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1761         // Possibility of delay/starvation here, since CMS token does
1762         // not know to give priority to VM thread? Actually, i think
1763         // there wouldn't be any delay/starvation, but the proof of
1764         // that "fact" (?) appears non-trivial. XXX 20011219YSR
1765       }
1766       ConcurrentMarkSweepThread::set_CMS_flag(
1767         ConcurrentMarkSweepThread::CMS_vm_has_token);
1768     }
1769   }
1770   // The CMS_token is already held.  Get back the other locks.
1771   assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1772          "VM thread should have CMS token");
1773   getFreelistLocks();
1774   bitMapLock()->lock_without_safepoint_check();
1775   if (TraceCMSState) {
1776     gclog_or_tty->print_cr("CMS foreground collector has asked for control "
1777       INTPTR_FORMAT " with first state %d", Thread::current(), first_state);
1778     gclog_or_tty->print_cr("    gets control with state %d", _collectorState);
1779   }
1780 
1781   // Check if we need to do a compaction, or if not, whether
1782   // we need to start the mark-sweep from scratch.
1783   bool should_compact    = false;
1784   bool should_start_over = false;
1785   decide_foreground_collection_type(clear_all_soft_refs,
1786     &should_compact, &should_start_over);
1787 
1788 NOT_PRODUCT(
1789   if (RotateCMSCollectionTypes) {
1790     if (_cmsGen->debug_collection_type() ==
1791         ConcurrentMarkSweepGeneration::MSC_foreground_collection_type) {
1792       should_compact = true;
1793     } else if (_cmsGen->debug_collection_type() ==
1794                ConcurrentMarkSweepGeneration::MS_foreground_collection_type) {
1795       should_compact = false;
1796     }
1797   }
1798 )
1799 
1800   if (PrintGCDetails && first_state > Idling) {
1801     GCCause::Cause cause = GenCollectedHeap::heap()->gc_cause();
1802     if (GCCause::is_user_requested_gc(cause) ||
1803         GCCause::is_serviceability_requested_gc(cause)) {
1804       gclog_or_tty->print(" (concurrent mode interrupted)");
1805     } else {
1806       gclog_or_tty->print(" (concurrent mode failure)");
1807     }
1808   }
1809 
1810   if (should_compact) {
1811     // If the collection is being acquired from the background
1812     // collector, there may be references on the discovered
1813     // references lists that have NULL referents (being those
1814     // that were concurrently cleared by a mutator) or
1815     // that are no longer active (having been enqueued concurrently
1816     // by the mutator).
1817     // Scrub the list of those references because Mark-Sweep-Compact
1818     // code assumes referents are not NULL and that all discovered
1819     // Reference objects are active.
1820     ref_processor()->clean_up_discovered_references();
1821 
1822     do_compaction_work(clear_all_soft_refs);
1823 
1824     // Has the GC time limit been exceeded?
1825     DefNewGeneration* young_gen = _young_gen->as_DefNewGeneration();
1826     size_t max_eden_size = young_gen->max_capacity() -
1827                            young_gen->to()->capacity() -
1828                            young_gen->from()->capacity();
1829     GenCollectedHeap* gch = GenCollectedHeap::heap();
1830     GCCause::Cause gc_cause = gch->gc_cause();
1831     size_policy()->check_gc_overhead_limit(_young_gen->used(),
1832                                            young_gen->eden()->used(),
1833                                            _cmsGen->max_capacity(),
1834                                            max_eden_size,
1835                                            full,
1836                                            gc_cause,
1837                                            gch->collector_policy());
1838   } else {
1839     do_mark_sweep_work(clear_all_soft_refs, first_state,
1840       should_start_over);
1841   }
1842   // Reset the expansion cause, now that we just completed
1843   // a collection cycle.
1844   clear_expansion_cause();
1845   _foregroundGCIsActive = false;
1846   return;
1847 }
1848 
1849 // Resize the perm generation and the tenured generation
1850 // after obtaining the free list locks for the
1851 // two generations.
1852 void CMSCollector::compute_new_size() {
1853   assert_locked_or_safepoint(Heap_lock);
1854   FreelistLocker z(this);
1855   _permGen->compute_new_size();
1856   _cmsGen->compute_new_size();
1857 }
1858 
1859 // A work method used by foreground collection to determine
1860 // what type of collection (compacting or not, continuing or fresh)
1861 // it should do.
1862 // NOTE: the intent is to make UseCMSCompactAtFullCollection
1863 // and CMSCompactWhenClearAllSoftRefs the default in the future
1864 // and do away with the flags after a suitable period.
1865 void CMSCollector::decide_foreground_collection_type(
1866   bool clear_all_soft_refs, bool* should_compact,
1867   bool* should_start_over) {
1868   // Normally, we'll compact only if the UseCMSCompactAtFullCollection
1869   // flag is set, and we have either requested a System.gc() or
1870   // the number of full gc's since the last concurrent cycle
1871   // has exceeded the threshold set by CMSFullGCsBeforeCompaction,
1872   // or if an incremental collection has failed
1873   GenCollectedHeap* gch = GenCollectedHeap::heap();
1874   assert(gch->collector_policy()->is_two_generation_policy(),
1875          "You may want to check the correctness of the following");
1876   // Inform cms gen if this was due to partial collection failing.
1877   // The CMS gen may use this fact to determine its expansion policy.
1878   if (gch->incremental_collection_will_fail()) {
1879     assert(!_cmsGen->incremental_collection_failed(),
1880            "Should have been noticed, reacted to and cleared");
1881     _cmsGen->set_incremental_collection_failed();
1882   }
1883   *should_compact =
1884     UseCMSCompactAtFullCollection &&
1885     ((_full_gcs_since_conc_gc >= CMSFullGCsBeforeCompaction) ||
1886      GCCause::is_user_requested_gc(gch->gc_cause()) ||
1887      gch->incremental_collection_will_fail());
1888   *should_start_over = false;
1889   if (clear_all_soft_refs && !*should_compact) {
1890     // We are about to do a last ditch collection attempt
1891     // so it would normally make sense to do a compaction
1892     // to reclaim as much space as possible.
1893     if (CMSCompactWhenClearAllSoftRefs) {
1894       // Default: The rationale is that in this case either
1895       // we are past the final marking phase, in which case
1896       // we'd have to start over, or so little has been done
1897       // that there's little point in saving that work. Compaction
1898       // appears to be the sensible choice in either case.
1899       *should_compact = true;
1900     } else {
1901       // We have been asked to clear all soft refs, but not to
1902       // compact. Make sure that we aren't past the final checkpoint
1903       // phase, for that is where we process soft refs. If we are already
1904       // past that phase, we'll need to redo the refs discovery phase and
1905       // if necessary clear soft refs that weren't previously
1906       // cleared. We do so by remembering the phase in which
1907       // we came in, and if we are past the refs processing
1908       // phase, we'll choose to just redo the mark-sweep
1909       // collection from scratch.
1910       if (_collectorState > FinalMarking) {
1911         // We are past the refs processing phase;
1912         // start over and do a fresh synchronous CMS cycle
1913         _collectorState = Resetting; // skip to reset to start new cycle
1914         reset(false /* == !asynch */);
1915         *should_start_over = true;
1916       } // else we can continue a possibly ongoing current cycle
1917     }
1918   }
1919 }
1920 
1921 // A work method used by the foreground collector to do
1922 // a mark-sweep-compact.
1923 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) {
1924   GenCollectedHeap* gch = GenCollectedHeap::heap();
1925   TraceTime t("CMS:MSC ", PrintGCDetails && Verbose, true, gclog_or_tty);
1926   if (PrintGC && Verbose && !(GCCause::is_user_requested_gc(gch->gc_cause()))) {
1927     gclog_or_tty->print_cr("Compact ConcurrentMarkSweepGeneration after %d "
1928       "collections passed to foreground collector", _full_gcs_since_conc_gc);
1929   }
1930 
1931   // Sample collection interval time and reset for collection pause.
1932   if (UseAdaptiveSizePolicy) {
1933     size_policy()->msc_collection_begin();
1934   }
1935 
1936   // Temporarily widen the span of the weak reference processing to
1937   // the entire heap.
1938   MemRegion new_span(GenCollectedHeap::heap()->reserved_region());
1939   ReferenceProcessorSpanMutator x(ref_processor(), new_span);
1940 
1941   // Temporarily, clear the "is_alive_non_header" field of the
1942   // reference processor.
1943   ReferenceProcessorIsAliveMutator y(ref_processor(), NULL);
1944 
1945   // Temporarily make reference _processing_ single threaded (non-MT).
1946   ReferenceProcessorMTProcMutator z(ref_processor(), false);
1947 
1948   // Temporarily make refs discovery atomic
1949   ReferenceProcessorAtomicMutator w(ref_processor(), true);
1950 
1951   ref_processor()->set_enqueuing_is_done(false);
1952   ref_processor()->enable_discovery();
1953   ref_processor()->setup_policy(clear_all_soft_refs);
1954   // If an asynchronous collection finishes, the _modUnionTable is
1955   // all clear.  If we are assuming the collection from an asynchronous
1956   // collection, clear the _modUnionTable.
1957   assert(_collectorState != Idling || _modUnionTable.isAllClear(),
1958     "_modUnionTable should be clear if the baton was not passed");
1959   _modUnionTable.clear_all();
1960 
1961   // We must adjust the allocation statistics being maintained
1962   // in the free list space. We do so by reading and clearing
1963   // the sweep timer and updating the block flux rate estimates below.
1964   assert(!_intra_sweep_timer.is_active(), "_intra_sweep_timer should be inactive");
1965   if (_inter_sweep_timer.is_active()) {
1966     _inter_sweep_timer.stop();
1967     // Note that we do not use this sample to update the _inter_sweep_estimate.
1968     _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
1969                                             _inter_sweep_estimate.padded_average(),
1970                                             _intra_sweep_estimate.padded_average());
1971   }
1972 



1973   GenMarkSweep::invoke_at_safepoint(_cmsGen->level(),
1974     ref_processor(), clear_all_soft_refs);
1975   #ifdef ASSERT
1976     CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
1977     size_t free_size = cms_space->free();
1978     assert(free_size ==
1979            pointer_delta(cms_space->end(), cms_space->compaction_top())
1980            * HeapWordSize,
1981       "All the free space should be compacted into one chunk at top");
1982     assert(cms_space->dictionary()->totalChunkSize(
1983                                       debug_only(cms_space->freelistLock())) == 0 ||
1984            cms_space->totalSizeInIndexedFreeLists() == 0,
1985       "All the free space should be in a single chunk");
1986     size_t num = cms_space->totalCount();
1987     assert((free_size == 0 && num == 0) ||
1988            (free_size > 0  && (num == 1 || num == 2)),
1989          "There should be at most 2 free chunks after compaction");
1990   #endif // ASSERT
1991   _collectorState = Resetting;
1992   assert(_restart_addr == NULL,
1993          "Should have been NULL'd before baton was passed");
1994   reset(false /* == !asynch */);
1995   _cmsGen->reset_after_compaction();
1996   _concurrent_cycles_since_last_unload = 0;
1997 
1998   if (verifying() && !should_unload_classes()) {
1999     perm_gen_verify_bit_map()->clear_all();
2000   }
2001 
2002   // Clear any data recorded in the PLAB chunk arrays.
2003   if (_survivor_plab_array != NULL) {
2004     reset_survivor_plab_arrays();
2005   }
2006 
2007   // Adjust the per-size allocation stats for the next epoch.
2008   _cmsGen->cmsSpace()->endSweepFLCensus(sweep_count() /* fake */);
2009   // Restart the "inter sweep timer" for the next epoch.
2010   _inter_sweep_timer.reset();
2011   _inter_sweep_timer.start();
2012 
2013   // Sample collection pause time and reset for collection interval.
2014   if (UseAdaptiveSizePolicy) {
2015     size_policy()->msc_collection_end(gch->gc_cause());
2016   }
2017 
2018   // For a mark-sweep-compact, compute_new_size() will be called
2019   // in the heap's do_collection() method.
2020 }
2021 
2022 // A work method used by the foreground collector to do
2023 // a mark-sweep, after taking over from a possibly on-going
2024 // concurrent mark-sweep collection.
2025 void CMSCollector::do_mark_sweep_work(bool clear_all_soft_refs,
2026   CollectorState first_state, bool should_start_over) {
2027   if (PrintGC && Verbose) {
2028     gclog_or_tty->print_cr("Pass concurrent collection to foreground "
2029       "collector with count %d",
2030       _full_gcs_since_conc_gc);
2031   }
2032   switch (_collectorState) {
2033     case Idling:
2034       if (first_state == Idling || should_start_over) {
2035         // The background GC was not active, or should
2036         // restarted from scratch;  start the cycle.
2037         _collectorState = InitialMarking;
2038       }
2039       // If first_state was not Idling, then a background GC
2040       // was in progress and has now finished.  No need to do it
2041       // again.  Leave the state as Idling.
2042       break;
2043     case Precleaning:
2044       // In the foreground case don't do the precleaning since
2045       // it is not done concurrently and there is extra work
2046       // required.
2047       _collectorState = FinalMarking;
2048   }
2049   if (PrintGCDetails &&
2050       (_collectorState > Idling ||
2051        !GCCause::is_user_requested_gc(GenCollectedHeap::heap()->gc_cause()))) {
2052     gclog_or_tty->print(" (concurrent mode failure)");
2053   }
2054   collect_in_foreground(clear_all_soft_refs);
2055 
2056   // For a mark-sweep, compute_new_size() will be called
2057   // in the heap's do_collection() method.
2058 }
2059 
2060 
2061 void CMSCollector::getFreelistLocks() const {
2062   // Get locks for all free lists in all generations that this
2063   // collector is responsible for
2064   _cmsGen->freelistLock()->lock_without_safepoint_check();
2065   _permGen->freelistLock()->lock_without_safepoint_check();
2066 }
2067 
2068 void CMSCollector::releaseFreelistLocks() const {
2069   // Release locks for all free lists in all generations that this
2070   // collector is responsible for
2071   _cmsGen->freelistLock()->unlock();
2072   _permGen->freelistLock()->unlock();
2073 }
2074 
2075 bool CMSCollector::haveFreelistLocks() const {
2076   // Check locks for all free lists in all generations that this
2077   // collector is responsible for
2078   assert_lock_strong(_cmsGen->freelistLock());
2079   assert_lock_strong(_permGen->freelistLock());
2080   PRODUCT_ONLY(ShouldNotReachHere());
2081   return true;
2082 }
2083 
2084 // A utility class that is used by the CMS collector to
2085 // temporarily "release" the foreground collector from its
2086 // usual obligation to wait for the background collector to
2087 // complete an ongoing phase before proceeding.
2088 class ReleaseForegroundGC: public StackObj {
2089  private:
2090   CMSCollector* _c;
2091  public:
2092   ReleaseForegroundGC(CMSCollector* c) : _c(c) {
2093     assert(_c->_foregroundGCShouldWait, "Else should not need to call");
2094     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2095     // allow a potentially blocked foreground collector to proceed
2096     _c->_foregroundGCShouldWait = false;
2097     if (_c->_foregroundGCIsActive) {
2098       CGC_lock->notify();
2099     }
2100     assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2101            "Possible deadlock");
2102   }
2103 
2104   ~ReleaseForegroundGC() {
2105     assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?");
2106     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2107     _c->_foregroundGCShouldWait = true;
2108   }
2109 };
2110 
2111 // There are separate collect_in_background and collect_in_foreground because of
2112 // the different locking requirements of the background collector and the
2113 // foreground collector.  There was originally an attempt to share
2114 // one "collect" method between the background collector and the foreground
2115 // collector but the if-then-else required made it cleaner to have
2116 // separate methods.
2117 void CMSCollector::collect_in_background(bool clear_all_soft_refs) {
2118   assert(Thread::current()->is_ConcurrentGC_thread(),
2119     "A CMS asynchronous collection is only allowed on a CMS thread.");
2120 
2121   GenCollectedHeap* gch = GenCollectedHeap::heap();
2122   {
2123     bool safepoint_check = Mutex::_no_safepoint_check_flag;
2124     MutexLockerEx hl(Heap_lock, safepoint_check);
2125     FreelistLocker fll(this);
2126     MutexLockerEx x(CGC_lock, safepoint_check);
2127     if (_foregroundGCIsActive || !UseAsyncConcMarkSweepGC) {
2128       // The foreground collector is active or we're
2129       // not using asynchronous collections.  Skip this
2130       // background collection.
2131       assert(!_foregroundGCShouldWait, "Should be clear");
2132       return;
2133     } else {
2134       assert(_collectorState == Idling, "Should be idling before start.");
2135       _collectorState = InitialMarking;
2136       // Reset the expansion cause, now that we are about to begin
2137       // a new cycle.
2138       clear_expansion_cause();
2139     }
2140     // Decide if we want to enable class unloading as part of the
2141     // ensuing concurrent GC cycle.
2142     update_should_unload_classes();
2143     _full_gc_requested = false;           // acks all outstanding full gc requests
2144     // Signal that we are about to start a collection
2145     gch->increment_total_full_collections();  // ... starting a collection cycle
2146     _collection_count_start = gch->total_full_collections();
2147   }
2148 
2149   // Used for PrintGC
2150   size_t prev_used;
2151   if (PrintGC && Verbose) {
2152     prev_used = _cmsGen->used(); // XXXPERM
2153   }
2154 
2155   // The change of the collection state is normally done at this level;
2156   // the exceptions are phases that are executed while the world is
2157   // stopped.  For those phases the change of state is done while the
2158   // world is stopped.  For baton passing purposes this allows the
2159   // background collector to finish the phase and change state atomically.
2160   // The foreground collector cannot wait on a phase that is done
2161   // while the world is stopped because the foreground collector already
2162   // has the world stopped and would deadlock.
2163   while (_collectorState != Idling) {
2164     if (TraceCMSState) {
2165       gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
2166         Thread::current(), _collectorState);
2167     }
2168     // The foreground collector
2169     //   holds the Heap_lock throughout its collection.
2170     //   holds the CMS token (but not the lock)
2171     //     except while it is waiting for the background collector to yield.
2172     //
2173     // The foreground collector should be blocked (not for long)
2174     //   if the background collector is about to start a phase
2175     //   executed with world stopped.  If the background
2176     //   collector has already started such a phase, the
2177     //   foreground collector is blocked waiting for the
2178     //   Heap_lock.  The stop-world phases (InitialMarking and FinalMarking)
2179     //   are executed in the VM thread.
2180     //
2181     // The locking order is
2182     //   PendingListLock (PLL)  -- if applicable (FinalMarking)
2183     //   Heap_lock  (both this & PLL locked in VM_CMS_Operation::prologue())
2184     //   CMS token  (claimed in
2185     //                stop_world_and_do() -->
2186     //                  safepoint_synchronize() -->
2187     //                    CMSThread::synchronize())
2188 
2189     {
2190       // Check if the FG collector wants us to yield.
2191       CMSTokenSync x(true); // is cms thread
2192       if (waitForForegroundGC()) {
2193         // We yielded to a foreground GC, nothing more to be
2194         // done this round.
2195         assert(_foregroundGCShouldWait == false, "We set it to false in "
2196                "waitForForegroundGC()");
2197         if (TraceCMSState) {
2198           gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2199             " exiting collection CMS state %d",
2200             Thread::current(), _collectorState);
2201         }
2202         return;
2203       } else {
2204         // The background collector can run but check to see if the
2205         // foreground collector has done a collection while the
2206         // background collector was waiting to get the CGC_lock
2207         // above.  If yes, break so that _foregroundGCShouldWait
2208         // is cleared before returning.
2209         if (_collectorState == Idling) {
2210           break;
2211         }
2212       }
2213     }
2214 
2215     assert(_foregroundGCShouldWait, "Foreground collector, if active, "
2216       "should be waiting");
2217 
2218     switch (_collectorState) {
2219       case InitialMarking:
2220         {
2221           ReleaseForegroundGC x(this);
2222           stats().record_cms_begin();
2223 
2224           VM_CMS_Initial_Mark initial_mark_op(this);
2225           VMThread::execute(&initial_mark_op);
2226         }
2227         // The collector state may be any legal state at this point
2228         // since the background collector may have yielded to the
2229         // foreground collector.
2230         break;
2231       case Marking:
2232         // initial marking in checkpointRootsInitialWork has been completed
2233         if (markFromRoots(true)) { // we were successful
2234           assert(_collectorState == Precleaning, "Collector state should "
2235             "have changed");
2236         } else {
2237           assert(_foregroundGCIsActive, "Internal state inconsistency");
2238         }
2239         break;
2240       case Precleaning:
2241         if (UseAdaptiveSizePolicy) {
2242           size_policy()->concurrent_precleaning_begin();
2243         }
2244         // marking from roots in markFromRoots has been completed
2245         preclean();
2246         if (UseAdaptiveSizePolicy) {
2247           size_policy()->concurrent_precleaning_end();
2248         }
2249         assert(_collectorState == AbortablePreclean ||
2250                _collectorState == FinalMarking,
2251                "Collector state should have changed");
2252         break;
2253       case AbortablePreclean:
2254         if (UseAdaptiveSizePolicy) {
2255         size_policy()->concurrent_phases_resume();
2256         }
2257         abortable_preclean();
2258         if (UseAdaptiveSizePolicy) {
2259           size_policy()->concurrent_precleaning_end();
2260         }
2261         assert(_collectorState == FinalMarking, "Collector state should "
2262           "have changed");
2263         break;
2264       case FinalMarking:
2265         {
2266           ReleaseForegroundGC x(this);
2267 
2268           VM_CMS_Final_Remark final_remark_op(this);
2269           VMThread::execute(&final_remark_op);
2270         }
2271         assert(_foregroundGCShouldWait, "block post-condition");
2272         break;
2273       case Sweeping:
2274         if (UseAdaptiveSizePolicy) {
2275           size_policy()->concurrent_sweeping_begin();
2276         }
2277         // final marking in checkpointRootsFinal has been completed
2278         sweep(true);
2279         assert(_collectorState == Resizing, "Collector state change "
2280           "to Resizing must be done under the free_list_lock");
2281         _full_gcs_since_conc_gc = 0;
2282 
2283         // Stop the timers for adaptive size policy for the concurrent phases
2284         if (UseAdaptiveSizePolicy) {
2285           size_policy()->concurrent_sweeping_end();
2286           size_policy()->concurrent_phases_end(gch->gc_cause(),
2287                                              gch->prev_gen(_cmsGen)->capacity(),
2288                                              _cmsGen->free());
2289         }
2290 
2291       case Resizing: {
2292         // Sweeping has been completed...
2293         // At this point the background collection has completed.
2294         // Don't move the call to compute_new_size() down
2295         // into code that might be executed if the background
2296         // collection was preempted.
2297         {
2298           ReleaseForegroundGC x(this);   // unblock FG collection
2299           MutexLockerEx       y(Heap_lock, Mutex::_no_safepoint_check_flag);
2300           CMSTokenSync        z(true);   // not strictly needed.
2301           if (_collectorState == Resizing) {
2302             compute_new_size();
2303             _collectorState = Resetting;
2304           } else {
2305             assert(_collectorState == Idling, "The state should only change"
2306                    " because the foreground collector has finished the collection");
2307           }
2308         }
2309         break;
2310       }
2311       case Resetting:
2312         // CMS heap resizing has been completed
2313         reset(true);
2314         assert(_collectorState == Idling, "Collector state should "
2315           "have changed");
2316         stats().record_cms_end();
2317         // Don't move the concurrent_phases_end() and compute_new_size()
2318         // calls to here because a preempted background collection
2319         // has it's state set to "Resetting".
2320         break;
2321       case Idling:
2322       default:
2323         ShouldNotReachHere();
2324         break;
2325     }
2326     if (TraceCMSState) {
2327       gclog_or_tty->print_cr("  Thread " INTPTR_FORMAT " done - next CMS state %d",
2328         Thread::current(), _collectorState);
2329     }
2330     assert(_foregroundGCShouldWait, "block post-condition");
2331   }
2332 
2333   // Should this be in gc_epilogue?
2334   collector_policy()->counters()->update_counters();
2335 
2336   {
2337     // Clear _foregroundGCShouldWait and, in the event that the
2338     // foreground collector is waiting, notify it, before
2339     // returning.
2340     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2341     _foregroundGCShouldWait = false;
2342     if (_foregroundGCIsActive) {
2343       CGC_lock->notify();
2344     }
2345     assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2346            "Possible deadlock");
2347   }
2348   if (TraceCMSState) {
2349     gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2350       " exiting collection CMS state %d",
2351       Thread::current(), _collectorState);
2352   }
2353   if (PrintGC && Verbose) {
2354     _cmsGen->print_heap_change(prev_used);
2355   }
2356 }
2357 
2358 void CMSCollector::collect_in_foreground(bool clear_all_soft_refs) {
2359   assert(_foregroundGCIsActive && !_foregroundGCShouldWait,
2360          "Foreground collector should be waiting, not executing");
2361   assert(Thread::current()->is_VM_thread(), "A foreground collection"
2362     "may only be done by the VM Thread with the world stopped");
2363   assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
2364          "VM thread should have CMS token");
2365 
2366   NOT_PRODUCT(TraceTime t("CMS:MS (foreground) ", PrintGCDetails && Verbose,
2367     true, gclog_or_tty);)
2368   if (UseAdaptiveSizePolicy) {
2369     size_policy()->ms_collection_begin();
2370   }
2371   COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact);
2372 
2373   HandleMark hm;  // Discard invalid handles created during verification
2374 
2375   if (VerifyBeforeGC &&
2376       GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2377     Universe::verify(true);
2378   }
2379 
2380   // Snapshot the soft reference policy to be used in this collection cycle.
2381   ref_processor()->setup_policy(clear_all_soft_refs);
2382 
2383   bool init_mark_was_synchronous = false; // until proven otherwise
2384   while (_collectorState != Idling) {
2385     if (TraceCMSState) {
2386       gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
2387         Thread::current(), _collectorState);
2388     }
2389     switch (_collectorState) {
2390       case InitialMarking:
2391         init_mark_was_synchronous = true;  // fact to be exploited in re-mark
2392         checkpointRootsInitial(false);
2393         assert(_collectorState == Marking, "Collector state should have changed"
2394           " within checkpointRootsInitial()");
2395         break;
2396       case Marking:
2397         // initial marking in checkpointRootsInitialWork has been completed
2398         if (VerifyDuringGC &&
2399             GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2400           gclog_or_tty->print("Verify before initial mark: ");
2401           Universe::verify(true);
2402         }
2403         {
2404           bool res = markFromRoots(false);
2405           assert(res && _collectorState == FinalMarking, "Collector state should "
2406             "have changed");
2407           break;
2408         }
2409       case FinalMarking:
2410         if (VerifyDuringGC &&
2411             GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2412           gclog_or_tty->print("Verify before re-mark: ");
2413           Universe::verify(true);
2414         }
2415         checkpointRootsFinal(false, clear_all_soft_refs,
2416                              init_mark_was_synchronous);
2417         assert(_collectorState == Sweeping, "Collector state should not "
2418           "have changed within checkpointRootsFinal()");
2419         break;
2420       case Sweeping:
2421         // final marking in checkpointRootsFinal has been completed
2422         if (VerifyDuringGC &&
2423             GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2424           gclog_or_tty->print("Verify before sweep: ");
2425           Universe::verify(true);
2426         }
2427         sweep(false);
2428         assert(_collectorState == Resizing, "Incorrect state");
2429         break;
2430       case Resizing: {
2431         // Sweeping has been completed; the actual resize in this case
2432         // is done separately; nothing to be done in this state.
2433         _collectorState = Resetting;
2434         break;
2435       }
2436       case Resetting:
2437         // The heap has been resized.
2438         if (VerifyDuringGC &&
2439             GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2440           gclog_or_tty->print("Verify before reset: ");
2441           Universe::verify(true);
2442         }
2443         reset(false);
2444         assert(_collectorState == Idling, "Collector state should "
2445           "have changed");
2446         break;
2447       case Precleaning:
2448       case AbortablePreclean:
2449         // Elide the preclean phase
2450         _collectorState = FinalMarking;
2451         break;
2452       default:
2453         ShouldNotReachHere();
2454     }
2455     if (TraceCMSState) {
2456       gclog_or_tty->print_cr("  Thread " INTPTR_FORMAT " done - next CMS state %d",
2457         Thread::current(), _collectorState);
2458     }
2459   }
2460 
2461   if (UseAdaptiveSizePolicy) {
2462     GenCollectedHeap* gch = GenCollectedHeap::heap();
2463     size_policy()->ms_collection_end(gch->gc_cause());
2464   }
2465 
2466   if (VerifyAfterGC &&
2467       GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2468     Universe::verify(true);
2469   }
2470   if (TraceCMSState) {
2471     gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2472       " exiting collection CMS state %d",
2473       Thread::current(), _collectorState);
2474   }
2475 }
2476 
2477 bool CMSCollector::waitForForegroundGC() {
2478   bool res = false;
2479   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2480          "CMS thread should have CMS token");
2481   // Block the foreground collector until the
2482   // background collectors decides whether to
2483   // yield.
2484   MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2485   _foregroundGCShouldWait = true;
2486   if (_foregroundGCIsActive) {
2487     // The background collector yields to the
2488     // foreground collector and returns a value
2489     // indicating that it has yielded.  The foreground
2490     // collector can proceed.
2491     res = true;
2492     _foregroundGCShouldWait = false;
2493     ConcurrentMarkSweepThread::clear_CMS_flag(
2494       ConcurrentMarkSweepThread::CMS_cms_has_token);
2495     ConcurrentMarkSweepThread::set_CMS_flag(
2496       ConcurrentMarkSweepThread::CMS_cms_wants_token);
2497     // Get a possibly blocked foreground thread going
2498     CGC_lock->notify();
2499     if (TraceCMSState) {
2500       gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d",
2501         Thread::current(), _collectorState);
2502     }
2503     while (_foregroundGCIsActive) {
2504       CGC_lock->wait(Mutex::_no_safepoint_check_flag);
2505     }
2506     ConcurrentMarkSweepThread::set_CMS_flag(
2507       ConcurrentMarkSweepThread::CMS_cms_has_token);
2508     ConcurrentMarkSweepThread::clear_CMS_flag(
2509       ConcurrentMarkSweepThread::CMS_cms_wants_token);
2510   }
2511   if (TraceCMSState) {
2512     gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d",
2513       Thread::current(), _collectorState);
2514   }
2515   return res;
2516 }
2517 
2518 // Because of the need to lock the free lists and other structures in
2519 // the collector, common to all the generations that the collector is
2520 // collecting, we need the gc_prologues of individual CMS generations
2521 // delegate to their collector. It may have been simpler had the
2522 // current infrastructure allowed one to call a prologue on a
2523 // collector. In the absence of that we have the generation's
2524 // prologue delegate to the collector, which delegates back
2525 // some "local" work to a worker method in the individual generations
2526 // that it's responsible for collecting, while itself doing any
2527 // work common to all generations it's responsible for. A similar
2528 // comment applies to the  gc_epilogue()'s.
2529 // The role of the varaible _between_prologue_and_epilogue is to
2530 // enforce the invocation protocol.
2531 void CMSCollector::gc_prologue(bool full) {
2532   // Call gc_prologue_work() for each CMSGen and PermGen that
2533   // we are responsible for.
2534 
2535   // The following locking discipline assumes that we are only called
2536   // when the world is stopped.
2537   assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption");
2538 
2539   // The CMSCollector prologue must call the gc_prologues for the
2540   // "generations" (including PermGen if any) that it's responsible
2541   // for.
2542 
2543   assert(   Thread::current()->is_VM_thread()
2544          || (   CMSScavengeBeforeRemark
2545              && Thread::current()->is_ConcurrentGC_thread()),
2546          "Incorrect thread type for prologue execution");
2547 
2548   if (_between_prologue_and_epilogue) {
2549     // We have already been invoked; this is a gc_prologue delegation
2550     // from yet another CMS generation that we are responsible for, just
2551     // ignore it since all relevant work has already been done.
2552     return;
2553   }
2554 
2555   // set a bit saying prologue has been called; cleared in epilogue
2556   _between_prologue_and_epilogue = true;
2557   // Claim locks for common data structures, then call gc_prologue_work()
2558   // for each CMSGen and PermGen that we are responsible for.
2559 
2560   getFreelistLocks();   // gets free list locks on constituent spaces
2561   bitMapLock()->lock_without_safepoint_check();
2562 
2563   // Should call gc_prologue_work() for all cms gens we are responsible for
2564   bool registerClosure =    _collectorState >= Marking
2565                          && _collectorState < Sweeping;
2566   ModUnionClosure* muc = ParallelGCThreads > 0 ? &_modUnionClosurePar
2567                                                : &_modUnionClosure;
2568   _cmsGen->gc_prologue_work(full, registerClosure, muc);
2569   _permGen->gc_prologue_work(full, registerClosure, muc);
2570 
2571   if (!full) {
2572     stats().record_gc0_begin();
2573   }
2574 }
2575 
2576 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) {
2577   // Delegate to CMScollector which knows how to coordinate between
2578   // this and any other CMS generations that it is responsible for
2579   // collecting.
2580   collector()->gc_prologue(full);
2581 }
2582 
2583 // This is a "private" interface for use by this generation's CMSCollector.
2584 // Not to be called directly by any other entity (for instance,
2585 // GenCollectedHeap, which calls the "public" gc_prologue method above).
2586 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full,
2587   bool registerClosure, ModUnionClosure* modUnionClosure) {
2588   assert(!incremental_collection_failed(), "Shouldn't be set yet");
2589   assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL,
2590     "Should be NULL");
2591   if (registerClosure) {
2592     cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure);
2593   }
2594   cmsSpace()->gc_prologue();
2595   // Clear stat counters
2596   NOT_PRODUCT(
2597     assert(_numObjectsPromoted == 0, "check");
2598     assert(_numWordsPromoted   == 0, "check");
2599     if (Verbose && PrintGC) {
2600       gclog_or_tty->print("Allocated "SIZE_FORMAT" objects, "
2601                           SIZE_FORMAT" bytes concurrently",
2602       _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord));
2603     }
2604     _numObjectsAllocated = 0;
2605     _numWordsAllocated   = 0;
2606   )
2607 }
2608 
2609 void CMSCollector::gc_epilogue(bool full) {
2610   // The following locking discipline assumes that we are only called
2611   // when the world is stopped.
2612   assert(SafepointSynchronize::is_at_safepoint(),
2613          "world is stopped assumption");
2614 
2615   // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks
2616   // if linear allocation blocks need to be appropriately marked to allow the
2617   // the blocks to be parsable. We also check here whether we need to nudge the
2618   // CMS collector thread to start a new cycle (if it's not already active).
2619   assert(   Thread::current()->is_VM_thread()
2620          || (   CMSScavengeBeforeRemark
2621              && Thread::current()->is_ConcurrentGC_thread()),
2622          "Incorrect thread type for epilogue execution");
2623 
2624   if (!_between_prologue_and_epilogue) {
2625     // We have already been invoked; this is a gc_epilogue delegation
2626     // from yet another CMS generation that we are responsible for, just
2627     // ignore it since all relevant work has already been done.
2628     return;
2629   }
2630   assert(haveFreelistLocks(), "must have freelist locks");
2631   assert_lock_strong(bitMapLock());
2632 
2633   _cmsGen->gc_epilogue_work(full);
2634   _permGen->gc_epilogue_work(full);
2635 
2636   if (_collectorState == AbortablePreclean || _collectorState == Precleaning) {
2637     // in case sampling was not already enabled, enable it
2638     _start_sampling = true;
2639   }
2640   // reset _eden_chunk_array so sampling starts afresh
2641   _eden_chunk_index = 0;
2642 
2643   size_t cms_used   = _cmsGen->cmsSpace()->used();
2644   size_t perm_used  = _permGen->cmsSpace()->used();
2645 
2646   // update performance counters - this uses a special version of
2647   // update_counters() that allows the utilization to be passed as a
2648   // parameter, avoiding multiple calls to used().
2649   //
2650   _cmsGen->update_counters(cms_used);
2651   _permGen->update_counters(perm_used);
2652 
2653   if (CMSIncrementalMode) {
2654     icms_update_allocation_limits();
2655   }
2656 
2657   bitMapLock()->unlock();
2658   releaseFreelistLocks();
2659 
2660   _between_prologue_and_epilogue = false;  // ready for next cycle
2661 }
2662 
2663 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) {
2664   collector()->gc_epilogue(full);
2665 
2666   // Also reset promotion tracking in par gc thread states.
2667   if (ParallelGCThreads > 0) {
2668     for (uint i = 0; i < ParallelGCThreads; i++) {
2669       _par_gc_thread_states[i]->promo.stopTrackingPromotions(i);
2670     }
2671   }
2672 }
2673 
2674 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2675   assert(!incremental_collection_failed(), "Should have been cleared");
2676   cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2677   cmsSpace()->gc_epilogue();
2678     // Print stat counters
2679   NOT_PRODUCT(
2680     assert(_numObjectsAllocated == 0, "check");
2681     assert(_numWordsAllocated == 0, "check");
2682     if (Verbose && PrintGC) {
2683       gclog_or_tty->print("Promoted "SIZE_FORMAT" objects, "
2684                           SIZE_FORMAT" bytes",
2685                  _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2686     }
2687     _numObjectsPromoted = 0;
2688     _numWordsPromoted   = 0;
2689   )
2690 
2691   if (PrintGC && Verbose) {
2692     // Call down the chain in contiguous_available needs the freelistLock
2693     // so print this out before releasing the freeListLock.
2694     gclog_or_tty->print(" Contiguous available "SIZE_FORMAT" bytes ",
2695                         contiguous_available());
2696   }
2697 }
2698 
2699 #ifndef PRODUCT
2700 bool CMSCollector::have_cms_token() {
2701   Thread* thr = Thread::current();
2702   if (thr->is_VM_thread()) {
2703     return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2704   } else if (thr->is_ConcurrentGC_thread()) {
2705     return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2706   } else if (thr->is_GC_task_thread()) {
2707     return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2708            ParGCRareEvent_lock->owned_by_self();
2709   }
2710   return false;
2711 }
2712 #endif
2713 
2714 // Check reachability of the given heap address in CMS generation,
2715 // treating all other generations as roots.
2716 bool CMSCollector::is_cms_reachable(HeapWord* addr) {
2717   // We could "guarantee" below, rather than assert, but i'll
2718   // leave these as "asserts" so that an adventurous debugger
2719   // could try this in the product build provided some subset of
2720   // the conditions were met, provided they were intersted in the
2721   // results and knew that the computation below wouldn't interfere
2722   // with other concurrent computations mutating the structures
2723   // being read or written.
2724   assert(SafepointSynchronize::is_at_safepoint(),
2725          "Else mutations in object graph will make answer suspect");
2726   assert(have_cms_token(), "Should hold cms token");
2727   assert(haveFreelistLocks(), "must hold free list locks");
2728   assert_lock_strong(bitMapLock());
2729 
2730   // Clear the marking bit map array before starting, but, just
2731   // for kicks, first report if the given address is already marked
2732   gclog_or_tty->print_cr("Start: Address 0x%x is%s marked", addr,
2733                 _markBitMap.isMarked(addr) ? "" : " not");
2734 
2735   if (verify_after_remark()) {
2736     MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2737     bool result = verification_mark_bm()->isMarked(addr);
2738     gclog_or_tty->print_cr("TransitiveMark: Address 0x%x %s marked", addr,
2739                            result ? "IS" : "is NOT");
2740     return result;
2741   } else {
2742     gclog_or_tty->print_cr("Could not compute result");
2743     return false;
2744   }
2745 }
2746 
2747 ////////////////////////////////////////////////////////
2748 // CMS Verification Support
2749 ////////////////////////////////////////////////////////
2750 // Following the remark phase, the following invariant
2751 // should hold -- each object in the CMS heap which is
2752 // marked in markBitMap() should be marked in the verification_mark_bm().
2753 
2754 class VerifyMarkedClosure: public BitMapClosure {
2755   CMSBitMap* _marks;
2756   bool       _failed;
2757 
2758  public:
2759   VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2760 
2761   bool do_bit(size_t offset) {
2762     HeapWord* addr = _marks->offsetToHeapWord(offset);
2763     if (!_marks->isMarked(addr)) {
2764       oop(addr)->print_on(gclog_or_tty);
2765       gclog_or_tty->print_cr(" ("INTPTR_FORMAT" should have been marked)", addr);
2766       _failed = true;
2767     }
2768     return true;
2769   }
2770 
2771   bool failed() { return _failed; }
2772 };
2773 
2774 bool CMSCollector::verify_after_remark() {
2775   gclog_or_tty->print(" [Verifying CMS Marking... ");
2776   MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2777   static bool init = false;
2778 
2779   assert(SafepointSynchronize::is_at_safepoint(),
2780          "Else mutations in object graph will make answer suspect");
2781   assert(have_cms_token(),
2782          "Else there may be mutual interference in use of "
2783          " verification data structures");
2784   assert(_collectorState > Marking && _collectorState <= Sweeping,
2785          "Else marking info checked here may be obsolete");
2786   assert(haveFreelistLocks(), "must hold free list locks");
2787   assert_lock_strong(bitMapLock());
2788 
2789 
2790   // Allocate marking bit map if not already allocated
2791   if (!init) { // first time
2792     if (!verification_mark_bm()->allocate(_span)) {
2793       return false;
2794     }
2795     init = true;
2796   }
2797 
2798   assert(verification_mark_stack()->isEmpty(), "Should be empty");
2799 
2800   // Turn off refs discovery -- so we will be tracing through refs.
2801   // This is as intended, because by this time
2802   // GC must already have cleared any refs that need to be cleared,
2803   // and traced those that need to be marked; moreover,
2804   // the marking done here is not going to intefere in any
2805   // way with the marking information used by GC.
2806   NoRefDiscovery no_discovery(ref_processor());
2807 
2808   COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
2809 
2810   // Clear any marks from a previous round
2811   verification_mark_bm()->clear_all();
2812   assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
2813   verify_work_stacks_empty();
2814 
2815   GenCollectedHeap* gch = GenCollectedHeap::heap();
2816   gch->ensure_parsability(false);  // fill TLABs, but no need to retire them
2817   // Update the saved marks which may affect the root scans.
2818   gch->save_marks();
2819 
2820   if (CMSRemarkVerifyVariant == 1) {
2821     // In this first variant of verification, we complete
2822     // all marking, then check if the new marks-verctor is
2823     // a subset of the CMS marks-vector.
2824     verify_after_remark_work_1();
2825   } else if (CMSRemarkVerifyVariant == 2) {
2826     // In this second variant of verification, we flag an error
2827     // (i.e. an object reachable in the new marks-vector not reachable
2828     // in the CMS marks-vector) immediately, also indicating the
2829     // identify of an object (A) that references the unmarked object (B) --
2830     // presumably, a mutation to A failed to be picked up by preclean/remark?
2831     verify_after_remark_work_2();
2832   } else {
2833     warning("Unrecognized value %d for CMSRemarkVerifyVariant",
2834             CMSRemarkVerifyVariant);
2835   }
2836   gclog_or_tty->print(" done] ");
2837   return true;
2838 }
2839 
2840 void CMSCollector::verify_after_remark_work_1() {
2841   ResourceMark rm;
2842   HandleMark  hm;
2843   GenCollectedHeap* gch = GenCollectedHeap::heap();
2844 
2845   // Mark from roots one level into CMS
2846   MarkRefsIntoClosure notOlder(_span, verification_mark_bm());
2847   gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2848 
2849   gch->gen_process_strong_roots(_cmsGen->level(),
2850                                 true,   // younger gens are roots
2851                                 true,   // activate StrongRootsScope
2852                                 true,   // collecting perm gen
2853                                 SharedHeap::ScanningOption(roots_scanning_options()),
2854                                 &notOlder,
2855                                 true,   // walk code active on stacks
2856                                 NULL);
2857 
2858   // Now mark from the roots
2859   assert(_revisitStack.isEmpty(), "Should be empty");
2860   MarkFromRootsClosure markFromRootsClosure(this, _span,
2861     verification_mark_bm(), verification_mark_stack(), &_revisitStack,
2862     false /* don't yield */, true /* verifying */);
2863   assert(_restart_addr == NULL, "Expected pre-condition");
2864   verification_mark_bm()->iterate(&markFromRootsClosure);
2865   while (_restart_addr != NULL) {
2866     // Deal with stack overflow: by restarting at the indicated
2867     // address.
2868     HeapWord* ra = _restart_addr;
2869     markFromRootsClosure.reset(ra);
2870     _restart_addr = NULL;
2871     verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2872   }
2873   assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2874   verify_work_stacks_empty();
2875   // Should reset the revisit stack above, since no class tree
2876   // surgery is forthcoming.
2877   _revisitStack.reset(); // throwing away all contents
2878 
2879   // Marking completed -- now verify that each bit marked in
2880   // verification_mark_bm() is also marked in markBitMap(); flag all
2881   // errors by printing corresponding objects.
2882   VerifyMarkedClosure vcl(markBitMap());
2883   verification_mark_bm()->iterate(&vcl);
2884   if (vcl.failed()) {
2885     gclog_or_tty->print("Verification failed");
2886     Universe::heap()->print_on(gclog_or_tty);
2887     fatal("CMS: failed marking verification after remark");
2888   }
2889 }
2890 
2891 void CMSCollector::verify_after_remark_work_2() {
2892   ResourceMark rm;
2893   HandleMark  hm;
2894   GenCollectedHeap* gch = GenCollectedHeap::heap();
2895 
2896   // Mark from roots one level into CMS
2897   MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
2898                                      markBitMap());
2899   gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2900   gch->gen_process_strong_roots(_cmsGen->level(),
2901                                 true,   // younger gens are roots
2902                                 true,   // activate StrongRootsScope
2903                                 true,   // collecting perm gen
2904                                 SharedHeap::ScanningOption(roots_scanning_options()),
2905                                 &notOlder,
2906                                 true,   // walk code active on stacks
2907                                 NULL);
2908 
2909   // Now mark from the roots
2910   assert(_revisitStack.isEmpty(), "Should be empty");
2911   MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
2912     verification_mark_bm(), markBitMap(), verification_mark_stack());
2913   assert(_restart_addr == NULL, "Expected pre-condition");
2914   verification_mark_bm()->iterate(&markFromRootsClosure);
2915   while (_restart_addr != NULL) {
2916     // Deal with stack overflow: by restarting at the indicated
2917     // address.
2918     HeapWord* ra = _restart_addr;
2919     markFromRootsClosure.reset(ra);
2920     _restart_addr = NULL;
2921     verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2922   }
2923   assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2924   verify_work_stacks_empty();
2925   // Should reset the revisit stack above, since no class tree
2926   // surgery is forthcoming.
2927   _revisitStack.reset(); // throwing away all contents
2928 
2929   // Marking completed -- now verify that each bit marked in
2930   // verification_mark_bm() is also marked in markBitMap(); flag all
2931   // errors by printing corresponding objects.
2932   VerifyMarkedClosure vcl(markBitMap());
2933   verification_mark_bm()->iterate(&vcl);
2934   assert(!vcl.failed(), "Else verification above should not have succeeded");
2935 }
2936 
2937 void ConcurrentMarkSweepGeneration::save_marks() {
2938   // delegate to CMS space
2939   cmsSpace()->save_marks();
2940   for (uint i = 0; i < ParallelGCThreads; i++) {
2941     _par_gc_thread_states[i]->promo.startTrackingPromotions();
2942   }
2943 }
2944 
2945 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
2946   return cmsSpace()->no_allocs_since_save_marks();
2947 }
2948 
2949 #define CMS_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix)    \
2950                                                                 \
2951 void ConcurrentMarkSweepGeneration::                            \
2952 oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) {   \
2953   cl->set_generation(this);                                     \
2954   cmsSpace()->oop_since_save_marks_iterate##nv_suffix(cl);      \
2955   cl->reset_generation();                                       \
2956   save_marks();                                                 \
2957 }
2958 
2959 ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DEFN)
2960 
2961 void
2962 ConcurrentMarkSweepGeneration::object_iterate_since_last_GC(ObjectClosure* blk)
2963 {
2964   // Not currently implemented; need to do the following. -- ysr.
2965   // dld -- I think that is used for some sort of allocation profiler.  So it
2966   // really means the objects allocated by the mutator since the last
2967   // GC.  We could potentially implement this cheaply by recording only
2968   // the direct allocations in a side data structure.
2969   //
2970   // I think we probably ought not to be required to support these
2971   // iterations at any arbitrary point; I think there ought to be some
2972   // call to enable/disable allocation profiling in a generation/space,
2973   // and the iterator ought to return the objects allocated in the
2974   // gen/space since the enable call, or the last iterator call (which
2975   // will probably be at a GC.)  That way, for gens like CM&S that would
2976   // require some extra data structure to support this, we only pay the
2977   // cost when it's in use...
2978   cmsSpace()->object_iterate_since_last_GC(blk);
2979 }
2980 
2981 void
2982 ConcurrentMarkSweepGeneration::younger_refs_iterate(OopsInGenClosure* cl) {
2983   cl->set_generation(this);
2984   younger_refs_in_space_iterate(_cmsSpace, cl);
2985   cl->reset_generation();
2986 }
2987 
2988 void
2989 ConcurrentMarkSweepGeneration::oop_iterate(MemRegion mr, OopClosure* cl) {
2990   if (freelistLock()->owned_by_self()) {
2991     Generation::oop_iterate(mr, cl);
2992   } else {
2993     MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2994     Generation::oop_iterate(mr, cl);
2995   }
2996 }
2997 
2998 void
2999 ConcurrentMarkSweepGeneration::oop_iterate(OopClosure* cl) {
3000   if (freelistLock()->owned_by_self()) {
3001     Generation::oop_iterate(cl);
3002   } else {
3003     MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3004     Generation::oop_iterate(cl);
3005   }
3006 }
3007 
3008 void
3009 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
3010   if (freelistLock()->owned_by_self()) {
3011     Generation::object_iterate(cl);
3012   } else {
3013     MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3014     Generation::object_iterate(cl);
3015   }
3016 }
3017 
3018 void
3019 ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) {
3020   if (freelistLock()->owned_by_self()) {
3021     Generation::safe_object_iterate(cl);
3022   } else {
3023     MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3024     Generation::safe_object_iterate(cl);
3025   }
3026 }
3027 
3028 void
3029 ConcurrentMarkSweepGeneration::pre_adjust_pointers() {
3030 }
3031 
3032 void
3033 ConcurrentMarkSweepGeneration::post_compact() {
3034 }
3035 
3036 void
3037 ConcurrentMarkSweepGeneration::prepare_for_verify() {
3038   // Fix the linear allocation blocks to look like free blocks.
3039 
3040   // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
3041   // are not called when the heap is verified during universe initialization and
3042   // at vm shutdown.
3043   if (freelistLock()->owned_by_self()) {
3044     cmsSpace()->prepare_for_verify();
3045   } else {
3046     MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
3047     cmsSpace()->prepare_for_verify();
3048   }
3049 }
3050 
3051 void
3052 ConcurrentMarkSweepGeneration::verify(bool allow_dirty /* ignored */) {
3053   // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
3054   // are not called when the heap is verified during universe initialization and
3055   // at vm shutdown.
3056   if (freelistLock()->owned_by_self()) {
3057     cmsSpace()->verify(false /* ignored */);
3058   } else {
3059     MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
3060     cmsSpace()->verify(false /* ignored */);
3061   }
3062 }
3063 
3064 void CMSCollector::verify(bool allow_dirty /* ignored */) {
3065   _cmsGen->verify(allow_dirty);
3066   _permGen->verify(allow_dirty);
3067 }
3068 
3069 #ifndef PRODUCT
3070 bool CMSCollector::overflow_list_is_empty() const {
3071   assert(_num_par_pushes >= 0, "Inconsistency");
3072   if (_overflow_list == NULL) {
3073     assert(_num_par_pushes == 0, "Inconsistency");
3074   }
3075   return _overflow_list == NULL;
3076 }
3077 
3078 // The methods verify_work_stacks_empty() and verify_overflow_empty()
3079 // merely consolidate assertion checks that appear to occur together frequently.
3080 void CMSCollector::verify_work_stacks_empty() const {
3081   assert(_markStack.isEmpty(), "Marking stack should be empty");
3082   assert(overflow_list_is_empty(), "Overflow list should be empty");
3083 }
3084 
3085 void CMSCollector::verify_overflow_empty() const {
3086   assert(overflow_list_is_empty(), "Overflow list should be empty");
3087   assert(no_preserved_marks(), "No preserved marks");
3088 }
3089 #endif // PRODUCT
3090 
3091 // Decide if we want to enable class unloading as part of the
3092 // ensuing concurrent GC cycle. We will collect the perm gen and
3093 // unload classes if it's the case that:
3094 // (1) an explicit gc request has been made and the flag
3095 //     ExplicitGCInvokesConcurrentAndUnloadsClasses is set, OR
3096 // (2) (a) class unloading is enabled at the command line, and
3097 //     (b) (i)   perm gen threshold has been crossed, or
3098 //         (ii)  old gen is getting really full, or
3099 //         (iii) the previous N CMS collections did not collect the
3100 //               perm gen
3101 // NOTE: Provided there is no change in the state of the heap between
3102 // calls to this method, it should have idempotent results. Moreover,
3103 // its results should be monotonically increasing (i.e. going from 0 to 1,
3104 // but not 1 to 0) between successive calls between which the heap was
3105 // not collected. For the implementation below, it must thus rely on
3106 // the property that concurrent_cycles_since_last_unload()
3107 // will not decrease unless a collection cycle happened and that
3108 // _permGen->should_concurrent_collect() and _cmsGen->is_too_full() are
3109 // themselves also monotonic in that sense. See check_monotonicity()
3110 // below.
3111 bool CMSCollector::update_should_unload_classes() {
3112   _should_unload_classes = false;
3113   // Condition 1 above
3114   if (_full_gc_requested && ExplicitGCInvokesConcurrentAndUnloadsClasses) {
3115     _should_unload_classes = true;
3116   } else if (CMSClassUnloadingEnabled) { // Condition 2.a above
3117     // Disjuncts 2.b.(i,ii,iii) above
3118     _should_unload_classes = (concurrent_cycles_since_last_unload() >=
3119                               CMSClassUnloadingMaxInterval)
3120                            || _permGen->should_concurrent_collect()
3121                            || _cmsGen->is_too_full();
3122   }
3123   return _should_unload_classes;
3124 }
3125 
3126 bool ConcurrentMarkSweepGeneration::is_too_full() const {
3127   bool res = should_concurrent_collect();
3128   res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
3129   return res;
3130 }
3131 
3132 void CMSCollector::setup_cms_unloading_and_verification_state() {
3133   const  bool should_verify =    VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
3134                              || VerifyBeforeExit;
3135   const  int  rso           =    SharedHeap::SO_Symbols | SharedHeap::SO_Strings
3136                              |   SharedHeap::SO_CodeCache;
3137 
3138   if (should_unload_classes()) {   // Should unload classes this cycle
3139     remove_root_scanning_option(rso);  // Shrink the root set appropriately
3140     set_verifying(should_verify);    // Set verification state for this cycle
3141     return;                            // Nothing else needs to be done at this time
3142   }
3143 
3144   // Not unloading classes this cycle
3145   assert(!should_unload_classes(), "Inconsitency!");
3146   if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
3147     // We were not verifying, or we _were_ unloading classes in the last cycle,
3148     // AND some verification options are enabled this cycle; in this case,
3149     // we must make sure that the deadness map is allocated if not already so,
3150     // and cleared (if already allocated previously --
3151     // CMSBitMap::sizeInBits() is used to determine if it's allocated).
3152     if (perm_gen_verify_bit_map()->sizeInBits() == 0) {
3153       if (!perm_gen_verify_bit_map()->allocate(_permGen->reserved())) {
3154         warning("Failed to allocate permanent generation verification CMS Bit Map;\n"
3155                 "permanent generation verification disabled");
3156         return;  // Note that we leave verification disabled, so we'll retry this
3157                  // allocation next cycle. We _could_ remember this failure
3158                  // and skip further attempts and permanently disable verification
3159                  // attempts if that is considered more desirable.
3160       }
3161       assert(perm_gen_verify_bit_map()->covers(_permGen->reserved()),
3162               "_perm_gen_ver_bit_map inconsistency?");
3163     } else {
3164       perm_gen_verify_bit_map()->clear_all();
3165     }
3166     // Include symbols, strings and code cache elements to prevent their resurrection.
3167     add_root_scanning_option(rso);
3168     set_verifying(true);
3169   } else if (verifying() && !should_verify) {
3170     // We were verifying, but some verification flags got disabled.
3171     set_verifying(false);
3172     // Exclude symbols, strings and code cache elements from root scanning to
3173     // reduce IM and RM pauses.
3174     remove_root_scanning_option(rso);
3175   }
3176 }
3177 
3178 
3179 #ifndef PRODUCT
3180 HeapWord* CMSCollector::block_start(const void* p) const {
3181   const HeapWord* addr = (HeapWord*)p;
3182   if (_span.contains(p)) {
3183     if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
3184       return _cmsGen->cmsSpace()->block_start(p);
3185     } else {
3186       assert(_permGen->cmsSpace()->is_in_reserved(addr),
3187              "Inconsistent _span?");
3188       return _permGen->cmsSpace()->block_start(p);
3189     }
3190   }
3191   return NULL;
3192 }
3193 #endif
3194 
3195 HeapWord*
3196 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
3197                                                    bool   tlab,
3198                                                    bool   parallel) {
3199   assert(!tlab, "Can't deal with TLAB allocation");
3200   MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3201   expand(word_size*HeapWordSize, MinHeapDeltaBytes,
3202     CMSExpansionCause::_satisfy_allocation);
3203   if (GCExpandToAllocateDelayMillis > 0) {
3204     os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3205   }
3206   return have_lock_and_allocate(word_size, tlab);
3207 }
3208 
3209 // YSR: All of this generation expansion/shrinking stuff is an exact copy of
3210 // OneContigSpaceCardGeneration, which makes me wonder if we should move this
3211 // to CardGeneration and share it...
3212 bool ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes) {
3213   return CardGeneration::expand(bytes, expand_bytes);
3214 }
3215 
3216 void ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes,
3217   CMSExpansionCause::Cause cause)
3218 {
3219 
3220   bool success = expand(bytes, expand_bytes);
3221 
3222   // remember why we expanded; this information is used
3223   // by shouldConcurrentCollect() when making decisions on whether to start
3224   // a new CMS cycle.
3225   if (success) {
3226     set_expansion_cause(cause);
3227     if (PrintGCDetails && Verbose) {
3228       gclog_or_tty->print_cr("Expanded CMS gen for %s",
3229         CMSExpansionCause::to_string(cause));
3230     }
3231   }
3232 }
3233 
3234 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
3235   HeapWord* res = NULL;
3236   MutexLocker x(ParGCRareEvent_lock);
3237   while (true) {
3238     // Expansion by some other thread might make alloc OK now:
3239     res = ps->lab.alloc(word_sz);
3240     if (res != NULL) return res;
3241     // If there's not enough expansion space available, give up.
3242     if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
3243       return NULL;
3244     }
3245     // Otherwise, we try expansion.
3246     expand(word_sz*HeapWordSize, MinHeapDeltaBytes,
3247       CMSExpansionCause::_allocate_par_lab);
3248     // Now go around the loop and try alloc again;
3249     // A competing par_promote might beat us to the expansion space,
3250     // so we may go around the loop again if promotion fails agaion.
3251     if (GCExpandToAllocateDelayMillis > 0) {
3252       os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3253     }
3254   }
3255 }
3256 
3257 
3258 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
3259   PromotionInfo* promo) {
3260   MutexLocker x(ParGCRareEvent_lock);
3261   size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
3262   while (true) {
3263     // Expansion by some other thread might make alloc OK now:
3264     if (promo->ensure_spooling_space()) {
3265       assert(promo->has_spooling_space(),
3266              "Post-condition of successful ensure_spooling_space()");
3267       return true;
3268     }
3269     // If there's not enough expansion space available, give up.
3270     if (_virtual_space.uncommitted_size() < refill_size_bytes) {
3271       return false;
3272     }
3273     // Otherwise, we try expansion.
3274     expand(refill_size_bytes, MinHeapDeltaBytes,
3275       CMSExpansionCause::_allocate_par_spooling_space);
3276     // Now go around the loop and try alloc again;
3277     // A competing allocation might beat us to the expansion space,
3278     // so we may go around the loop again if allocation fails again.
3279     if (GCExpandToAllocateDelayMillis > 0) {
3280       os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3281     }
3282   }
3283 }
3284 
3285 
3286 
3287 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
3288   assert_locked_or_safepoint(Heap_lock);
3289   size_t size = ReservedSpace::page_align_size_down(bytes);
3290   if (size > 0) {
3291     shrink_by(size);
3292   }
3293 }
3294 
3295 bool ConcurrentMarkSweepGeneration::grow_by(size_t bytes) {
3296   assert_locked_or_safepoint(Heap_lock);
3297   bool result = _virtual_space.expand_by(bytes);
3298   if (result) {
3299     HeapWord* old_end = _cmsSpace->end();
3300     size_t new_word_size =
3301       heap_word_size(_virtual_space.committed_size());
3302     MemRegion mr(_cmsSpace->bottom(), new_word_size);
3303     _bts->resize(new_word_size);  // resize the block offset shared array
3304     Universe::heap()->barrier_set()->resize_covered_region(mr);
3305     // Hmmmm... why doesn't CFLS::set_end verify locking?
3306     // This is quite ugly; FIX ME XXX
3307     _cmsSpace->assert_locked(freelistLock());
3308     _cmsSpace->set_end((HeapWord*)_virtual_space.high());
3309 
3310     // update the space and generation capacity counters
3311     if (UsePerfData) {
3312       _space_counters->update_capacity();
3313       _gen_counters->update_all();
3314     }
3315 
3316     if (Verbose && PrintGC) {
3317       size_t new_mem_size = _virtual_space.committed_size();
3318       size_t old_mem_size = new_mem_size - bytes;
3319       gclog_or_tty->print_cr("Expanding %s from %ldK by %ldK to %ldK",
3320                     name(), old_mem_size/K, bytes/K, new_mem_size/K);
3321     }
3322   }
3323   return result;
3324 }
3325 
3326 bool ConcurrentMarkSweepGeneration::grow_to_reserved() {
3327   assert_locked_or_safepoint(Heap_lock);
3328   bool success = true;
3329   const size_t remaining_bytes = _virtual_space.uncommitted_size();
3330   if (remaining_bytes > 0) {
3331     success = grow_by(remaining_bytes);
3332     DEBUG_ONLY(if (!success) warning("grow to reserved failed");)
3333   }
3334   return success;
3335 }
3336 
3337 void ConcurrentMarkSweepGeneration::shrink_by(size_t bytes) {
3338   assert_locked_or_safepoint(Heap_lock);
3339   assert_lock_strong(freelistLock());
3340   // XXX Fix when compaction is implemented.
3341   warning("Shrinking of CMS not yet implemented");
3342   return;
3343 }
3344 
3345 
3346 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
3347 // phases.
3348 class CMSPhaseAccounting: public StackObj {
3349  public:
3350   CMSPhaseAccounting(CMSCollector *collector,
3351                      const char *phase,
3352                      bool print_cr = true);
3353   ~CMSPhaseAccounting();
3354 
3355  private:
3356   CMSCollector *_collector;
3357   const char *_phase;
3358   elapsedTimer _wallclock;
3359   bool _print_cr;
3360 
3361  public:
3362   // Not MT-safe; so do not pass around these StackObj's
3363   // where they may be accessed by other threads.
3364   jlong wallclock_millis() {
3365     assert(_wallclock.is_active(), "Wall clock should not stop");
3366     _wallclock.stop();  // to record time
3367     jlong ret = _wallclock.milliseconds();
3368     _wallclock.start(); // restart
3369     return ret;
3370   }
3371 };
3372 
3373 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
3374                                        const char *phase,
3375                                        bool print_cr) :
3376   _collector(collector), _phase(phase), _print_cr(print_cr) {
3377 
3378   if (PrintCMSStatistics != 0) {
3379     _collector->resetYields();
3380   }
3381   if (PrintGCDetails && PrintGCTimeStamps) {
3382     gclog_or_tty->date_stamp(PrintGCDateStamps);
3383     gclog_or_tty->stamp();
3384     gclog_or_tty->print_cr(": [%s-concurrent-%s-start]",
3385       _collector->cmsGen()->short_name(), _phase);
3386   }
3387   _collector->resetTimer();
3388   _wallclock.start();
3389   _collector->startTimer();
3390 }
3391 
3392 CMSPhaseAccounting::~CMSPhaseAccounting() {
3393   assert(_wallclock.is_active(), "Wall clock should not have stopped");
3394   _collector->stopTimer();
3395   _wallclock.stop();
3396   if (PrintGCDetails) {
3397     gclog_or_tty->date_stamp(PrintGCDateStamps);
3398     if (PrintGCTimeStamps) {
3399       gclog_or_tty->stamp();
3400       gclog_or_tty->print(": ");
3401     }
3402     gclog_or_tty->print("[%s-concurrent-%s: %3.3f/%3.3f secs]",
3403                  _collector->cmsGen()->short_name(),
3404                  _phase, _collector->timerValue(), _wallclock.seconds());
3405     if (_print_cr) {
3406       gclog_or_tty->print_cr("");
3407     }
3408     if (PrintCMSStatistics != 0) {
3409       gclog_or_tty->print_cr(" (CMS-concurrent-%s yielded %d times)", _phase,
3410                     _collector->yields());
3411     }
3412   }
3413 }
3414 
3415 // CMS work
3416 
3417 // Checkpoint the roots into this generation from outside
3418 // this generation. [Note this initial checkpoint need only
3419 // be approximate -- we'll do a catch up phase subsequently.]
3420 void CMSCollector::checkpointRootsInitial(bool asynch) {
3421   assert(_collectorState == InitialMarking, "Wrong collector state");
3422   check_correct_thread_executing();

3423   ReferenceProcessor* rp = ref_processor();
3424   SpecializationStats::clear();
3425   assert(_restart_addr == NULL, "Control point invariant");
3426   if (asynch) {
3427     // acquire locks for subsequent manipulations
3428     MutexLockerEx x(bitMapLock(),
3429                     Mutex::_no_safepoint_check_flag);
3430     checkpointRootsInitialWork(asynch);
3431     rp->verify_no_references_recorded();
3432     rp->enable_discovery(); // enable ("weak") refs discovery
3433     _collectorState = Marking;
3434   } else {
3435     // (Weak) Refs discovery: this is controlled from genCollectedHeap::do_collection
3436     // which recognizes if we are a CMS generation, and doesn't try to turn on
3437     // discovery; verify that they aren't meddling.
3438     assert(!rp->discovery_is_atomic(),
3439            "incorrect setting of discovery predicate");
3440     assert(!rp->discovery_enabled(), "genCollectedHeap shouldn't control "
3441            "ref discovery for this generation kind");
3442     // already have locks
3443     checkpointRootsInitialWork(asynch);
3444     rp->enable_discovery(); // now enable ("weak") refs discovery
3445     _collectorState = Marking;
3446   }
3447   SpecializationStats::print();
3448 }
3449 
3450 void CMSCollector::checkpointRootsInitialWork(bool asynch) {
3451   assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
3452   assert(_collectorState == InitialMarking, "just checking");
3453 
3454   // If there has not been a GC[n-1] since last GC[n] cycle completed,
3455   // precede our marking with a collection of all
3456   // younger generations to keep floating garbage to a minimum.
3457   // XXX: we won't do this for now -- it's an optimization to be done later.
3458 
3459   // already have locks
3460   assert_lock_strong(bitMapLock());
3461   assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
3462 
3463   // Setup the verification and class unloading state for this
3464   // CMS collection cycle.
3465   setup_cms_unloading_and_verification_state();
3466 
3467   NOT_PRODUCT(TraceTime t("\ncheckpointRootsInitialWork",
3468     PrintGCDetails && Verbose, true, gclog_or_tty);)
3469   if (UseAdaptiveSizePolicy) {
3470     size_policy()->checkpoint_roots_initial_begin();
3471   }
3472 
3473   // Reset all the PLAB chunk arrays if necessary.
3474   if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
3475     reset_survivor_plab_arrays();
3476   }
3477 
3478   ResourceMark rm;
3479   HandleMark  hm;
3480 
3481   FalseClosure falseClosure;
3482   // In the case of a synchronous collection, we will elide the
3483   // remark step, so it's important to catch all the nmethod oops
3484   // in this step.
3485   // The final 'true' flag to gen_process_strong_roots will ensure this.
3486   // If 'async' is true, we can relax the nmethod tracing.
3487   MarkRefsIntoClosure notOlder(_span, &_markBitMap);
3488   GenCollectedHeap* gch = GenCollectedHeap::heap();
3489 
3490   verify_work_stacks_empty();
3491   verify_overflow_empty();
3492 
3493   gch->ensure_parsability(false);  // fill TLABs, but no need to retire them
3494   // Update the saved marks which may affect the root scans.
3495   gch->save_marks();
3496 
3497   // weak reference processing has not started yet.
3498   ref_processor()->set_enqueuing_is_done(false);
3499 
3500   {
3501     // This is not needed. DEBUG_ONLY(RememberKlassesChecker imx(true);)
3502     COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
3503     gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3504     gch->gen_process_strong_roots(_cmsGen->level(),
3505                                   true,   // younger gens are roots
3506                                   true,   // activate StrongRootsScope
3507                                   true,   // collecting perm gen
3508                                   SharedHeap::ScanningOption(roots_scanning_options()),
3509                                   &notOlder,
3510                                   true,   // walk all of code cache if (so & SO_CodeCache)
3511                                   NULL);
3512   }
3513 
3514   // Clear mod-union table; it will be dirtied in the prologue of
3515   // CMS generation per each younger generation collection.
3516 
3517   assert(_modUnionTable.isAllClear(),
3518        "Was cleared in most recent final checkpoint phase"
3519        " or no bits are set in the gc_prologue before the start of the next "
3520        "subsequent marking phase.");
3521 
3522   // Temporarily disabled, since pre/post-consumption closures don't
3523   // care about precleaned cards
3524   #if 0
3525   {
3526     MemRegion mr = MemRegion((HeapWord*)_virtual_space.low(),
3527                              (HeapWord*)_virtual_space.high());
3528     _ct->ct_bs()->preclean_dirty_cards(mr);
3529   }
3530   #endif
3531 
3532   // Save the end of the used_region of the constituent generations
3533   // to be used to limit the extent of sweep in each generation.
3534   save_sweep_limits();
3535   if (UseAdaptiveSizePolicy) {
3536     size_policy()->checkpoint_roots_initial_end(gch->gc_cause());
3537   }
3538   verify_overflow_empty();
3539 }
3540 
3541 bool CMSCollector::markFromRoots(bool asynch) {
3542   // we might be tempted to assert that:
3543   // assert(asynch == !SafepointSynchronize::is_at_safepoint(),
3544   //        "inconsistent argument?");
3545   // However that wouldn't be right, because it's possible that
3546   // a safepoint is indeed in progress as a younger generation
3547   // stop-the-world GC happens even as we mark in this generation.
3548   assert(_collectorState == Marking, "inconsistent state?");
3549   check_correct_thread_executing();
3550   verify_overflow_empty();
3551 
3552   bool res;
3553   if (asynch) {
3554 
3555     // Start the timers for adaptive size policy for the concurrent phases
3556     // Do it here so that the foreground MS can use the concurrent
3557     // timer since a foreground MS might has the sweep done concurrently
3558     // or STW.
3559     if (UseAdaptiveSizePolicy) {
3560       size_policy()->concurrent_marking_begin();
3561     }
3562 
3563     // Weak ref discovery note: We may be discovering weak
3564     // refs in this generation concurrent (but interleaved) with
3565     // weak ref discovery by a younger generation collector.
3566 
3567     CMSTokenSyncWithLocks ts(true, bitMapLock());
3568     TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3569     CMSPhaseAccounting pa(this, "mark", !PrintGCDetails);
3570     res = markFromRootsWork(asynch);
3571     if (res) {
3572       _collectorState = Precleaning;
3573     } else { // We failed and a foreground collection wants to take over
3574       assert(_foregroundGCIsActive, "internal state inconsistency");
3575       assert(_restart_addr == NULL,  "foreground will restart from scratch");
3576       if (PrintGCDetails) {
3577         gclog_or_tty->print_cr("bailing out to foreground collection");
3578       }
3579     }
3580     if (UseAdaptiveSizePolicy) {
3581       size_policy()->concurrent_marking_end();
3582     }
3583   } else {
3584     assert(SafepointSynchronize::is_at_safepoint(),
3585            "inconsistent with asynch == false");
3586     if (UseAdaptiveSizePolicy) {
3587       size_policy()->ms_collection_marking_begin();
3588     }
3589     // already have locks
3590     res = markFromRootsWork(asynch);
3591     _collectorState = FinalMarking;
3592     if (UseAdaptiveSizePolicy) {
3593       GenCollectedHeap* gch = GenCollectedHeap::heap();
3594       size_policy()->ms_collection_marking_end(gch->gc_cause());
3595     }
3596   }
3597   verify_overflow_empty();
3598   return res;
3599 }
3600 
3601 bool CMSCollector::markFromRootsWork(bool asynch) {
3602   // iterate over marked bits in bit map, doing a full scan and mark
3603   // from these roots using the following algorithm:
3604   // . if oop is to the right of the current scan pointer,
3605   //   mark corresponding bit (we'll process it later)
3606   // . else (oop is to left of current scan pointer)
3607   //   push oop on marking stack
3608   // . drain the marking stack
3609 
3610   // Note that when we do a marking step we need to hold the
3611   // bit map lock -- recall that direct allocation (by mutators)
3612   // and promotion (by younger generation collectors) is also
3613   // marking the bit map. [the so-called allocate live policy.]
3614   // Because the implementation of bit map marking is not
3615   // robust wrt simultaneous marking of bits in the same word,
3616   // we need to make sure that there is no such interference
3617   // between concurrent such updates.
3618 
3619   // already have locks
3620   assert_lock_strong(bitMapLock());
3621 
3622   // Clear the revisit stack, just in case there are any
3623   // obsolete contents from a short-circuited previous CMS cycle.
3624   _revisitStack.reset();
3625   verify_work_stacks_empty();
3626   verify_overflow_empty();
3627   assert(_revisitStack.isEmpty(), "tabula rasa");
3628   DEBUG_ONLY(RememberKlassesChecker cmx(should_unload_classes());)
3629   bool result = false;
3630   if (CMSConcurrentMTEnabled && ConcGCThreads > 0) {
3631     result = do_marking_mt(asynch);
3632   } else {
3633     result = do_marking_st(asynch);
3634   }
3635   return result;
3636 }
3637 
3638 // Forward decl
3639 class CMSConcMarkingTask;
3640 
3641 class CMSConcMarkingTerminator: public ParallelTaskTerminator {
3642   CMSCollector*       _collector;
3643   CMSConcMarkingTask* _task;
3644   bool _yield;
3645  protected:
3646   virtual void yield();
3647  public:
3648   // "n_threads" is the number of threads to be terminated.
3649   // "queue_set" is a set of work queues of other threads.
3650   // "collector" is the CMS collector associated with this task terminator.
3651   // "yield" indicates whether we need the gang as a whole to yield.
3652   CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set,
3653                            CMSCollector* collector, bool yield) :
3654     ParallelTaskTerminator(n_threads, queue_set),
3655     _collector(collector),
3656     _yield(yield) { }
3657 
3658   void set_task(CMSConcMarkingTask* task) {
3659     _task = task;
3660   }
3661 };
3662 
3663 // MT Concurrent Marking Task
3664 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3665   CMSCollector* _collector;
3666   YieldingFlexibleWorkGang* _workers;        // the whole gang
3667   int           _n_workers;                  // requested/desired # workers
3668   bool          _asynch;
3669   bool          _result;
3670   CompactibleFreeListSpace*  _cms_space;
3671   CompactibleFreeListSpace* _perm_space;
3672   HeapWord*     _global_finger;
3673   HeapWord*     _restart_addr;
3674 
3675   //  Exposed here for yielding support
3676   Mutex* const _bit_map_lock;
3677 
3678   // The per thread work queues, available here for stealing
3679   OopTaskQueueSet*  _task_queues;
3680   CMSConcMarkingTerminator _term;
3681 
3682  public:
3683   CMSConcMarkingTask(CMSCollector* collector,
3684                  CompactibleFreeListSpace* cms_space,
3685                  CompactibleFreeListSpace* perm_space,
3686                  bool asynch, int n_workers,
3687                  YieldingFlexibleWorkGang* workers,
3688                  OopTaskQueueSet* task_queues):
3689     YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3690     _collector(collector),
3691     _cms_space(cms_space),
3692     _perm_space(perm_space),
3693     _asynch(asynch), _n_workers(n_workers), _result(true),
3694     _workers(workers), _task_queues(task_queues),
3695     _term(n_workers, task_queues, _collector, asynch),
3696     _bit_map_lock(collector->bitMapLock())
3697   {
3698     assert(n_workers <= workers->total_workers(),
3699            "Else termination won't work correctly today"); // XXX FIX ME!
3700     _requested_size = n_workers;
3701     _term.set_task(this);
3702     assert(_cms_space->bottom() < _perm_space->bottom(),
3703            "Finger incorrectly initialized below");
3704     _restart_addr = _global_finger = _cms_space->bottom();
3705   }
3706 
3707 
3708   OopTaskQueueSet* task_queues()  { return _task_queues; }
3709 
3710   OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3711 
3712   HeapWord** global_finger_addr() { return &_global_finger; }
3713 
3714   CMSConcMarkingTerminator* terminator() { return &_term; }
3715 
3716   void work(int i);
3717 
3718   virtual void coordinator_yield();  // stuff done by coordinator
3719   bool result() { return _result; }
3720 
3721   void reset(HeapWord* ra) {
3722     assert(_global_finger >= _cms_space->end(),  "Postcondition of ::work(i)");
3723     assert(_global_finger >= _perm_space->end(), "Postcondition of ::work(i)");
3724     assert(ra             <  _perm_space->end(), "ra too large");
3725     _restart_addr = _global_finger = ra;
3726     _term.reset_for_reuse();
3727   }
3728 
3729   static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3730                                            OopTaskQueue* work_q);
3731 
3732  private:
3733   void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3734   void do_work_steal(int i);
3735   void bump_global_finger(HeapWord* f);
3736 };
3737 
3738 void CMSConcMarkingTerminator::yield() {
3739   if (ConcurrentMarkSweepThread::should_yield() &&
3740       !_collector->foregroundGCIsActive() &&
3741       _yield) {
3742     _task->yield();
3743   } else {
3744     ParallelTaskTerminator::yield();
3745   }
3746 }
3747 
3748 ////////////////////////////////////////////////////////////////
3749 // Concurrent Marking Algorithm Sketch
3750 ////////////////////////////////////////////////////////////////
3751 // Until all tasks exhausted (both spaces):
3752 // -- claim next available chunk
3753 // -- bump global finger via CAS
3754 // -- find first object that starts in this chunk
3755 //    and start scanning bitmap from that position
3756 // -- scan marked objects for oops
3757 // -- CAS-mark target, and if successful:
3758 //    . if target oop is above global finger (volatile read)
3759 //      nothing to do
3760 //    . if target oop is in chunk and above local finger
3761 //        then nothing to do
3762 //    . else push on work-queue
3763 // -- Deal with possible overflow issues:
3764 //    . local work-queue overflow causes stuff to be pushed on
3765 //      global (common) overflow queue
3766 //    . always first empty local work queue
3767 //    . then get a batch of oops from global work queue if any
3768 //    . then do work stealing
3769 // -- When all tasks claimed (both spaces)
3770 //    and local work queue empty,
3771 //    then in a loop do:
3772 //    . check global overflow stack; steal a batch of oops and trace
3773 //    . try to steal from other threads oif GOS is empty
3774 //    . if neither is available, offer termination
3775 // -- Terminate and return result
3776 //
3777 void CMSConcMarkingTask::work(int i) {
3778   elapsedTimer _timer;
3779   ResourceMark rm;
3780   HandleMark hm;
3781 
3782   DEBUG_ONLY(_collector->verify_overflow_empty();)
3783 
3784   // Before we begin work, our work queue should be empty
3785   assert(work_queue(i)->size() == 0, "Expected to be empty");
3786   // Scan the bitmap covering _cms_space, tracing through grey objects.
3787   _timer.start();
3788   do_scan_and_mark(i, _cms_space);
3789   _timer.stop();
3790   if (PrintCMSStatistics != 0) {
3791     gclog_or_tty->print_cr("Finished cms space scanning in %dth thread: %3.3f sec",
3792       i, _timer.seconds()); // XXX: need xxx/xxx type of notation, two timers
3793   }
3794 
3795   // ... do the same for the _perm_space
3796   _timer.reset();
3797   _timer.start();
3798   do_scan_and_mark(i, _perm_space);
3799   _timer.stop();
3800   if (PrintCMSStatistics != 0) {
3801     gclog_or_tty->print_cr("Finished perm space scanning in %dth thread: %3.3f sec",
3802       i, _timer.seconds()); // XXX: need xxx/xxx type of notation, two timers
3803   }
3804 
3805   // ... do work stealing
3806   _timer.reset();
3807   _timer.start();
3808   do_work_steal(i);
3809   _timer.stop();
3810   if (PrintCMSStatistics != 0) {
3811     gclog_or_tty->print_cr("Finished work stealing in %dth thread: %3.3f sec",
3812       i, _timer.seconds()); // XXX: need xxx/xxx type of notation, two timers
3813   }
3814   assert(_collector->_markStack.isEmpty(), "Should have been emptied");
3815   assert(work_queue(i)->size() == 0, "Should have been emptied");
3816   // Note that under the current task protocol, the
3817   // following assertion is true even of the spaces
3818   // expanded since the completion of the concurrent
3819   // marking. XXX This will likely change under a strict
3820   // ABORT semantics.
3821   assert(_global_finger >  _cms_space->end() &&
3822          _global_finger >= _perm_space->end(),
3823          "All tasks have been completed");
3824   DEBUG_ONLY(_collector->verify_overflow_empty();)
3825 }
3826 
3827 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
3828   HeapWord* read = _global_finger;
3829   HeapWord* cur  = read;
3830   while (f > read) {
3831     cur = read;
3832     read = (HeapWord*) Atomic::cmpxchg_ptr(f, &_global_finger, cur);
3833     if (cur == read) {
3834       // our cas succeeded
3835       assert(_global_finger >= f, "protocol consistency");
3836       break;
3837     }
3838   }
3839 }
3840 
3841 // This is really inefficient, and should be redone by
3842 // using (not yet available) block-read and -write interfaces to the
3843 // stack and the work_queue. XXX FIX ME !!!
3844 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3845                                                       OopTaskQueue* work_q) {
3846   // Fast lock-free check
3847   if (ovflw_stk->length() == 0) {
3848     return false;
3849   }
3850   assert(work_q->size() == 0, "Shouldn't steal");
3851   MutexLockerEx ml(ovflw_stk->par_lock(),
3852                    Mutex::_no_safepoint_check_flag);
3853   // Grab up to 1/4 the size of the work queue
3854   size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
3855                     (size_t)ParGCDesiredObjsFromOverflowList);
3856   num = MIN2(num, ovflw_stk->length());
3857   for (int i = (int) num; i > 0; i--) {
3858     oop cur = ovflw_stk->pop();
3859     assert(cur != NULL, "Counted wrong?");
3860     work_q->push(cur);
3861   }
3862   return num > 0;
3863 }
3864 
3865 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
3866   SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
3867   int n_tasks = pst->n_tasks();
3868   // We allow that there may be no tasks to do here because
3869   // we are restarting after a stack overflow.
3870   assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
3871   int nth_task = 0;
3872 
3873   HeapWord* aligned_start = sp->bottom();
3874   if (sp->used_region().contains(_restart_addr)) {
3875     // Align down to a card boundary for the start of 0th task
3876     // for this space.
3877     aligned_start =
3878       (HeapWord*)align_size_down((uintptr_t)_restart_addr,
3879                                  CardTableModRefBS::card_size);
3880   }
3881 
3882   size_t chunk_size = sp->marking_task_size();
3883   while (!pst->is_task_claimed(/* reference */ nth_task)) {
3884     // Having claimed the nth task in this space,
3885     // compute the chunk that it corresponds to:
3886     MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
3887                                aligned_start + (nth_task+1)*chunk_size);
3888     // Try and bump the global finger via a CAS;
3889     // note that we need to do the global finger bump
3890     // _before_ taking the intersection below, because
3891     // the task corresponding to that region will be
3892     // deemed done even if the used_region() expands
3893     // because of allocation -- as it almost certainly will
3894     // during start-up while the threads yield in the
3895     // closure below.
3896     HeapWord* finger = span.end();
3897     bump_global_finger(finger);   // atomically
3898     // There are null tasks here corresponding to chunks
3899     // beyond the "top" address of the space.
3900     span = span.intersection(sp->used_region());
3901     if (!span.is_empty()) {  // Non-null task
3902       HeapWord* prev_obj;
3903       assert(!span.contains(_restart_addr) || nth_task == 0,
3904              "Inconsistency");
3905       if (nth_task == 0) {
3906         // For the 0th task, we'll not need to compute a block_start.
3907         if (span.contains(_restart_addr)) {
3908           // In the case of a restart because of stack overflow,
3909           // we might additionally skip a chunk prefix.
3910           prev_obj = _restart_addr;
3911         } else {
3912           prev_obj = span.start();
3913         }
3914       } else {
3915         // We want to skip the first object because
3916         // the protocol is to scan any object in its entirety
3917         // that _starts_ in this span; a fortiori, any
3918         // object starting in an earlier span is scanned
3919         // as part of an earlier claimed task.
3920         // Below we use the "careful" version of block_start
3921         // so we do not try to navigate uninitialized objects.
3922         prev_obj = sp->block_start_careful(span.start());
3923         // Below we use a variant of block_size that uses the
3924         // Printezis bits to avoid waiting for allocated
3925         // objects to become initialized/parsable.
3926         while (prev_obj < span.start()) {
3927           size_t sz = sp->block_size_no_stall(prev_obj, _collector);
3928           if (sz > 0) {
3929             prev_obj += sz;
3930           } else {
3931             // In this case we may end up doing a bit of redundant
3932             // scanning, but that appears unavoidable, short of
3933             // locking the free list locks; see bug 6324141.
3934             break;
3935           }
3936         }
3937       }
3938       if (prev_obj < span.end()) {
3939         MemRegion my_span = MemRegion(prev_obj, span.end());
3940         // Do the marking work within a non-empty span --
3941         // the last argument to the constructor indicates whether the
3942         // iteration should be incremental with periodic yields.
3943         Par_MarkFromRootsClosure cl(this, _collector, my_span,
3944                                     &_collector->_markBitMap,
3945                                     work_queue(i),
3946                                     &_collector->_markStack,
3947                                     &_collector->_revisitStack,
3948                                     _asynch);
3949         _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
3950       } // else nothing to do for this task
3951     }   // else nothing to do for this task
3952   }
3953   // We'd be tempted to assert here that since there are no
3954   // more tasks left to claim in this space, the global_finger
3955   // must exceed space->top() and a fortiori space->end(). However,
3956   // that would not quite be correct because the bumping of
3957   // global_finger occurs strictly after the claiming of a task,
3958   // so by the time we reach here the global finger may not yet
3959   // have been bumped up by the thread that claimed the last
3960   // task.
3961   pst->all_tasks_completed();
3962 }
3963 
3964 class Par_ConcMarkingClosure: public Par_KlassRememberingOopClosure {
3965  private:
3966   MemRegion     _span;
3967   CMSBitMap*    _bit_map;
3968   CMSMarkStack* _overflow_stack;
3969   OopTaskQueue* _work_queue;
3970  protected:
3971   DO_OOP_WORK_DEFN
3972  public:
3973   Par_ConcMarkingClosure(CMSCollector* collector, OopTaskQueue* work_queue,
3974                          CMSBitMap* bit_map, CMSMarkStack* overflow_stack,
3975                          CMSMarkStack* revisit_stack):
3976     Par_KlassRememberingOopClosure(collector, NULL, revisit_stack),
3977     _span(_collector->_span),
3978     _work_queue(work_queue),
3979     _bit_map(bit_map),
3980     _overflow_stack(overflow_stack)
3981   { }
3982   virtual void do_oop(oop* p);
3983   virtual void do_oop(narrowOop* p);
3984   void trim_queue(size_t max);
3985   void handle_stack_overflow(HeapWord* lost);
3986 };
3987 
3988 // Grey object scanning during work stealing phase --
3989 // the salient assumption here is that any references
3990 // that are in these stolen objects being scanned must
3991 // already have been initialized (else they would not have
3992 // been published), so we do not need to check for
3993 // uninitialized objects before pushing here.
3994 void Par_ConcMarkingClosure::do_oop(oop obj) {
3995   assert(obj->is_oop_or_null(true), "expected an oop or NULL");
3996   HeapWord* addr = (HeapWord*)obj;
3997   // Check if oop points into the CMS generation
3998   // and is not marked
3999   if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
4000     // a white object ...
4001     // If we manage to "claim" the object, by being the
4002     // first thread to mark it, then we push it on our
4003     // marking stack
4004     if (_bit_map->par_mark(addr)) {     // ... now grey
4005       // push on work queue (grey set)
4006       bool simulate_overflow = false;
4007       NOT_PRODUCT(
4008         if (CMSMarkStackOverflowALot &&
4009             _collector->simulate_overflow()) {
4010           // simulate a stack overflow
4011           simulate_overflow = true;
4012         }
4013       )
4014       if (simulate_overflow ||
4015           !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
4016         // stack overflow
4017         if (PrintCMSStatistics != 0) {
4018           gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
4019                                  SIZE_FORMAT, _overflow_stack->capacity());
4020         }
4021         // We cannot assert that the overflow stack is full because
4022         // it may have been emptied since.
4023         assert(simulate_overflow ||
4024                _work_queue->size() == _work_queue->max_elems(),
4025               "Else push should have succeeded");
4026         handle_stack_overflow(addr);
4027       }
4028     } // Else, some other thread got there first
4029   }
4030 }
4031 
4032 void Par_ConcMarkingClosure::do_oop(oop* p)       { Par_ConcMarkingClosure::do_oop_work(p); }
4033 void Par_ConcMarkingClosure::do_oop(narrowOop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
4034 
4035 void Par_ConcMarkingClosure::trim_queue(size_t max) {
4036   while (_work_queue->size() > max) {
4037     oop new_oop;
4038     if (_work_queue->pop_local(new_oop)) {
4039       assert(new_oop->is_oop(), "Should be an oop");
4040       assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
4041       assert(_span.contains((HeapWord*)new_oop), "Not in span");
4042       assert(new_oop->is_parsable(), "Should be parsable");
4043       new_oop->oop_iterate(this);  // do_oop() above
4044     }
4045   }
4046 }
4047 
4048 // Upon stack overflow, we discard (part of) the stack,
4049 // remembering the least address amongst those discarded
4050 // in CMSCollector's _restart_address.
4051 void Par_ConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
4052   // We need to do this under a mutex to prevent other
4053   // workers from interfering with the work done below.
4054   MutexLockerEx ml(_overflow_stack->par_lock(),
4055                    Mutex::_no_safepoint_check_flag);
4056   // Remember the least grey address discarded
4057   HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
4058   _collector->lower_restart_addr(ra);
4059   _overflow_stack->reset();  // discard stack contents
4060   _overflow_stack->expand(); // expand the stack if possible
4061 }
4062 
4063 
4064 void CMSConcMarkingTask::do_work_steal(int i) {
4065   OopTaskQueue* work_q = work_queue(i);
4066   oop obj_to_scan;
4067   CMSBitMap* bm = &(_collector->_markBitMap);
4068   CMSMarkStack* ovflw = &(_collector->_markStack);
4069   CMSMarkStack* revisit = &(_collector->_revisitStack);
4070   int* seed = _collector->hash_seed(i);
4071   Par_ConcMarkingClosure cl(_collector, work_q, bm, ovflw, revisit);
4072   while (true) {
4073     cl.trim_queue(0);
4074     assert(work_q->size() == 0, "Should have been emptied above");
4075     if (get_work_from_overflow_stack(ovflw, work_q)) {
4076       // Can't assert below because the work obtained from the
4077       // overflow stack may already have been stolen from us.
4078       // assert(work_q->size() > 0, "Work from overflow stack");
4079       continue;
4080     } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
4081       assert(obj_to_scan->is_oop(), "Should be an oop");
4082       assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
4083       obj_to_scan->oop_iterate(&cl);
4084     } else if (terminator()->offer_termination()) {
4085       assert(work_q->size() == 0, "Impossible!");
4086       break;
4087     }
4088   }
4089 }
4090 
4091 // This is run by the CMS (coordinator) thread.
4092 void CMSConcMarkingTask::coordinator_yield() {
4093   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
4094          "CMS thread should hold CMS token");
4095   DEBUG_ONLY(RememberKlassesChecker mux(false);)
4096   // First give up the locks, then yield, then re-lock
4097   // We should probably use a constructor/destructor idiom to
4098   // do this unlock/lock or modify the MutexUnlocker class to
4099   // serve our purpose. XXX
4100   assert_lock_strong(_bit_map_lock);
4101   _bit_map_lock->unlock();
4102   ConcurrentMarkSweepThread::desynchronize(true);
4103   ConcurrentMarkSweepThread::acknowledge_yield_request();
4104   _collector->stopTimer();
4105   if (PrintCMSStatistics != 0) {
4106     _collector->incrementYields();
4107   }
4108   _collector->icms_wait();
4109 
4110   // It is possible for whichever thread initiated the yield request
4111   // not to get a chance to wake up and take the bitmap lock between
4112   // this thread releasing it and reacquiring it. So, while the
4113   // should_yield() flag is on, let's sleep for a bit to give the
4114   // other thread a chance to wake up. The limit imposed on the number
4115   // of iterations is defensive, to avoid any unforseen circumstances
4116   // putting us into an infinite loop. Since it's always been this
4117   // (coordinator_yield()) method that was observed to cause the
4118   // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
4119   // which is by default non-zero. For the other seven methods that
4120   // also perform the yield operation, as are using a different
4121   // parameter (CMSYieldSleepCount) which is by default zero. This way we
4122   // can enable the sleeping for those methods too, if necessary.
4123   // See 6442774.
4124   //
4125   // We really need to reconsider the synchronization between the GC
4126   // thread and the yield-requesting threads in the future and we
4127   // should really use wait/notify, which is the recommended
4128   // way of doing this type of interaction. Additionally, we should
4129   // consolidate the eight methods that do the yield operation and they
4130   // are almost identical into one for better maintenability and
4131   // readability. See 6445193.
4132   //
4133   // Tony 2006.06.29
4134   for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
4135                    ConcurrentMarkSweepThread::should_yield() &&
4136                    !CMSCollector::foregroundGCIsActive(); ++i) {
4137     os::sleep(Thread::current(), 1, false);
4138     ConcurrentMarkSweepThread::acknowledge_yield_request();
4139   }
4140 
4141   ConcurrentMarkSweepThread::synchronize(true);
4142   _bit_map_lock->lock_without_safepoint_check();
4143   _collector->startTimer();
4144 }
4145 
4146 bool CMSCollector::do_marking_mt(bool asynch) {
4147   assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition");
4148   // In the future this would be determined ergonomically, based
4149   // on #cpu's, # active mutator threads (and load), and mutation rate.
4150   int num_workers = ConcGCThreads;
4151 
4152   CompactibleFreeListSpace* cms_space  = _cmsGen->cmsSpace();
4153   CompactibleFreeListSpace* perm_space = _permGen->cmsSpace();
4154 
4155   CMSConcMarkingTask tsk(this, cms_space, perm_space,
4156                          asynch, num_workers /* number requested XXX */,
4157                          conc_workers(), task_queues());
4158 
4159   // Since the actual number of workers we get may be different
4160   // from the number we requested above, do we need to do anything different
4161   // below? In particular, may be we need to subclass the SequantialSubTasksDone
4162   // class?? XXX
4163   cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
4164   perm_space->initialize_sequential_subtasks_for_marking(num_workers);
4165 
4166   // Refs discovery is already non-atomic.
4167   assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
4168   // Mutate the Refs discovery so it is MT during the
4169   // multi-threaded marking phase.
4170   ReferenceProcessorMTMutator mt(ref_processor(), num_workers > 1);
4171   DEBUG_ONLY(RememberKlassesChecker cmx(should_unload_classes());)
4172   conc_workers()->start_task(&tsk);
4173   while (tsk.yielded()) {
4174     tsk.coordinator_yield();
4175     conc_workers()->continue_task(&tsk);
4176   }
4177   // If the task was aborted, _restart_addr will be non-NULL
4178   assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
4179   while (_restart_addr != NULL) {
4180     // XXX For now we do not make use of ABORTED state and have not
4181     // yet implemented the right abort semantics (even in the original
4182     // single-threaded CMS case). That needs some more investigation
4183     // and is deferred for now; see CR# TBF. 07252005YSR. XXX
4184     assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
4185     // If _restart_addr is non-NULL, a marking stack overflow
4186     // occurred; we need to do a fresh marking iteration from the
4187     // indicated restart address.
4188     if (_foregroundGCIsActive && asynch) {
4189       // We may be running into repeated stack overflows, having
4190       // reached the limit of the stack size, while making very
4191       // slow forward progress. It may be best to bail out and
4192       // let the foreground collector do its job.
4193       // Clear _restart_addr, so that foreground GC
4194       // works from scratch. This avoids the headache of
4195       // a "rescan" which would otherwise be needed because
4196       // of the dirty mod union table & card table.
4197       _restart_addr = NULL;
4198       return false;
4199     }
4200     // Adjust the task to restart from _restart_addr
4201     tsk.reset(_restart_addr);
4202     cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
4203                   _restart_addr);
4204     perm_space->initialize_sequential_subtasks_for_marking(num_workers,
4205                   _restart_addr);
4206     _restart_addr = NULL;
4207     // Get the workers going again
4208     conc_workers()->start_task(&tsk);
4209     while (tsk.yielded()) {
4210       tsk.coordinator_yield();
4211       conc_workers()->continue_task(&tsk);
4212     }
4213   }
4214   assert(tsk.completed(), "Inconsistency");
4215   assert(tsk.result() == true, "Inconsistency");
4216   return true;
4217 }
4218 
4219 bool CMSCollector::do_marking_st(bool asynch) {
4220   ResourceMark rm;
4221   HandleMark   hm;
4222 
4223   MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
4224     &_markStack, &_revisitStack, CMSYield && asynch);
4225   // the last argument to iterate indicates whether the iteration
4226   // should be incremental with periodic yields.
4227   _markBitMap.iterate(&markFromRootsClosure);
4228   // If _restart_addr is non-NULL, a marking stack overflow
4229   // occurred; we need to do a fresh iteration from the
4230   // indicated restart address.
4231   while (_restart_addr != NULL) {
4232     if (_foregroundGCIsActive && asynch) {
4233       // We may be running into repeated stack overflows, having
4234       // reached the limit of the stack size, while making very
4235       // slow forward progress. It may be best to bail out and
4236       // let the foreground collector do its job.
4237       // Clear _restart_addr, so that foreground GC
4238       // works from scratch. This avoids the headache of
4239       // a "rescan" which would otherwise be needed because
4240       // of the dirty mod union table & card table.
4241       _restart_addr = NULL;
4242       return false;  // indicating failure to complete marking
4243     }
4244     // Deal with stack overflow:
4245     // we restart marking from _restart_addr
4246     HeapWord* ra = _restart_addr;
4247     markFromRootsClosure.reset(ra);
4248     _restart_addr = NULL;
4249     _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
4250   }
4251   return true;
4252 }
4253 
4254 void CMSCollector::preclean() {
4255   check_correct_thread_executing();
4256   assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
4257   verify_work_stacks_empty();
4258   verify_overflow_empty();
4259   _abort_preclean = false;
4260   if (CMSPrecleaningEnabled) {
4261     _eden_chunk_index = 0;
4262     size_t used = get_eden_used();
4263     size_t capacity = get_eden_capacity();
4264     // Don't start sampling unless we will get sufficiently
4265     // many samples.
4266     if (used < (capacity/(CMSScheduleRemarkSamplingRatio * 100)
4267                 * CMSScheduleRemarkEdenPenetration)) {
4268       _start_sampling = true;
4269     } else {
4270       _start_sampling = false;
4271     }
4272     TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
4273     CMSPhaseAccounting pa(this, "preclean", !PrintGCDetails);
4274     preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
4275   }
4276   CMSTokenSync x(true); // is cms thread
4277   if (CMSPrecleaningEnabled) {
4278     sample_eden();
4279     _collectorState = AbortablePreclean;
4280   } else {
4281     _collectorState = FinalMarking;
4282   }
4283   verify_work_stacks_empty();
4284   verify_overflow_empty();
4285 }
4286 
4287 // Try and schedule the remark such that young gen
4288 // occupancy is CMSScheduleRemarkEdenPenetration %.
4289 void CMSCollector::abortable_preclean() {
4290   check_correct_thread_executing();
4291   assert(CMSPrecleaningEnabled,  "Inconsistent control state");
4292   assert(_collectorState == AbortablePreclean, "Inconsistent control state");
4293 
4294   // If Eden's current occupancy is below this threshold,
4295   // immediately schedule the remark; else preclean
4296   // past the next scavenge in an effort to
4297   // schedule the pause as described avove. By choosing
4298   // CMSScheduleRemarkEdenSizeThreshold >= max eden size
4299   // we will never do an actual abortable preclean cycle.
4300   if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
4301     TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
4302     CMSPhaseAccounting pa(this, "abortable-preclean", !PrintGCDetails);
4303     // We need more smarts in the abortable preclean
4304     // loop below to deal with cases where allocation
4305     // in young gen is very very slow, and our precleaning
4306     // is running a losing race against a horde of
4307     // mutators intent on flooding us with CMS updates
4308     // (dirty cards).
4309     // One, admittedly dumb, strategy is to give up
4310     // after a certain number of abortable precleaning loops
4311     // or after a certain maximum time. We want to make
4312     // this smarter in the next iteration.
4313     // XXX FIX ME!!! YSR
4314     size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
4315     while (!(should_abort_preclean() ||
4316              ConcurrentMarkSweepThread::should_terminate())) {
4317       workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
4318       cumworkdone += workdone;
4319       loops++;
4320       // Voluntarily terminate abortable preclean phase if we have
4321       // been at it for too long.
4322       if ((CMSMaxAbortablePrecleanLoops != 0) &&
4323           loops >= CMSMaxAbortablePrecleanLoops) {
4324         if (PrintGCDetails) {
4325           gclog_or_tty->print(" CMS: abort preclean due to loops ");
4326         }
4327         break;
4328       }
4329       if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
4330         if (PrintGCDetails) {
4331           gclog_or_tty->print(" CMS: abort preclean due to time ");
4332         }
4333         break;
4334       }
4335       // If we are doing little work each iteration, we should
4336       // take a short break.
4337       if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
4338         // Sleep for some time, waiting for work to accumulate
4339         stopTimer();
4340         cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
4341         startTimer();
4342         waited++;
4343       }
4344     }
4345     if (PrintCMSStatistics > 0) {
4346       gclog_or_tty->print(" [%d iterations, %d waits, %d cards)] ",
4347                           loops, waited, cumworkdone);
4348     }
4349   }
4350   CMSTokenSync x(true); // is cms thread
4351   if (_collectorState != Idling) {
4352     assert(_collectorState == AbortablePreclean,
4353            "Spontaneous state transition?");
4354     _collectorState = FinalMarking;
4355   } // Else, a foreground collection completed this CMS cycle.
4356   return;
4357 }
4358 
4359 // Respond to an Eden sampling opportunity
4360 void CMSCollector::sample_eden() {
4361   // Make sure a young gc cannot sneak in between our
4362   // reading and recording of a sample.
4363   assert(Thread::current()->is_ConcurrentGC_thread(),
4364          "Only the cms thread may collect Eden samples");
4365   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
4366          "Should collect samples while holding CMS token");
4367   if (!_start_sampling) {
4368     return;
4369   }
4370   if (_eden_chunk_array) {
4371     if (_eden_chunk_index < _eden_chunk_capacity) {
4372       _eden_chunk_array[_eden_chunk_index] = *_top_addr;   // take sample
4373       assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4374              "Unexpected state of Eden");
4375       // We'd like to check that what we just sampled is an oop-start address;
4376       // however, we cannot do that here since the object may not yet have been
4377       // initialized. So we'll instead do the check when we _use_ this sample
4378       // later.
4379       if (_eden_chunk_index == 0 ||
4380           (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4381                          _eden_chunk_array[_eden_chunk_index-1])
4382            >= CMSSamplingGrain)) {
4383         _eden_chunk_index++;  // commit sample
4384       }
4385     }
4386   }
4387   if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
4388     size_t used = get_eden_used();
4389     size_t capacity = get_eden_capacity();
4390     assert(used <= capacity, "Unexpected state of Eden");
4391     if (used >  (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
4392       _abort_preclean = true;
4393     }
4394   }
4395 }
4396 
4397 
4398 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
4399   assert(_collectorState == Precleaning ||
4400          _collectorState == AbortablePreclean, "incorrect state");
4401   ResourceMark rm;
4402   HandleMark   hm;
4403   // Do one pass of scrubbing the discovered reference lists
4404   // to remove any reference objects with strongly-reachable
4405   // referents.
4406   if (clean_refs) {
4407     ReferenceProcessor* rp = ref_processor();
4408     CMSPrecleanRefsYieldClosure yield_cl(this);
4409     assert(rp->span().equals(_span), "Spans should be equal");
4410     CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
4411                                    &_markStack, &_revisitStack,
4412                                    true /* preclean */);
4413     CMSDrainMarkingStackClosure complete_trace(this,
4414                                    _span, &_markBitMap, &_markStack,
4415                                    &keep_alive, true /* preclean */);
4416 
4417     // We don't want this step to interfere with a young
4418     // collection because we don't want to take CPU
4419     // or memory bandwidth away from the young GC threads
4420     // (which may be as many as there are CPUs).
4421     // Note that we don't need to protect ourselves from
4422     // interference with mutators because they can't
4423     // manipulate the discovered reference lists nor affect
4424     // the computed reachability of the referents, the
4425     // only properties manipulated by the precleaning
4426     // of these reference lists.
4427     stopTimer();
4428     CMSTokenSyncWithLocks x(true /* is cms thread */,
4429                             bitMapLock());
4430     startTimer();
4431     sample_eden();
4432 
4433     // The following will yield to allow foreground
4434     // collection to proceed promptly. XXX YSR:
4435     // The code in this method may need further
4436     // tweaking for better performance and some restructuring
4437     // for cleaner interfaces.
4438     rp->preclean_discovered_references(
4439           rp->is_alive_non_header(), &keep_alive, &complete_trace,
4440           &yield_cl, should_unload_classes());
4441   }
4442 
4443   if (clean_survivor) {  // preclean the active survivor space(s)
4444     assert(_young_gen->kind() == Generation::DefNew ||
4445            _young_gen->kind() == Generation::ParNew ||
4446            _young_gen->kind() == Generation::ASParNew,
4447          "incorrect type for cast");
4448     DefNewGeneration* dng = (DefNewGeneration*)_young_gen;
4449     PushAndMarkClosure pam_cl(this, _span, ref_processor(),
4450                              &_markBitMap, &_modUnionTable,
4451                              &_markStack, &_revisitStack,
4452                              true /* precleaning phase */);
4453     stopTimer();
4454     CMSTokenSyncWithLocks ts(true /* is cms thread */,
4455                              bitMapLock());
4456     startTimer();
4457     unsigned int before_count =
4458       GenCollectedHeap::heap()->total_collections();
4459     SurvivorSpacePrecleanClosure
4460       sss_cl(this, _span, &_markBitMap, &_markStack,
4461              &pam_cl, before_count, CMSYield);
4462     DEBUG_ONLY(RememberKlassesChecker mx(should_unload_classes());)
4463     dng->from()->object_iterate_careful(&sss_cl);
4464     dng->to()->object_iterate_careful(&sss_cl);
4465   }
4466   MarkRefsIntoAndScanClosure
4467     mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
4468              &_markStack, &_revisitStack, this, CMSYield,
4469              true /* precleaning phase */);
4470   // CAUTION: The following closure has persistent state that may need to
4471   // be reset upon a decrease in the sequence of addresses it
4472   // processes.
4473   ScanMarkedObjectsAgainCarefullyClosure
4474     smoac_cl(this, _span,
4475       &_markBitMap, &_markStack, &_revisitStack, &mrias_cl, CMSYield);
4476 
4477   // Preclean dirty cards in ModUnionTable and CardTable using
4478   // appropriate convergence criterion;
4479   // repeat CMSPrecleanIter times unless we find that
4480   // we are losing.
4481   assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
4482   assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
4483          "Bad convergence multiplier");
4484   assert(CMSPrecleanThreshold >= 100,
4485          "Unreasonably low CMSPrecleanThreshold");
4486 
4487   size_t numIter, cumNumCards, lastNumCards, curNumCards;
4488   for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
4489        numIter < CMSPrecleanIter;
4490        numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
4491     curNumCards  = preclean_mod_union_table(_cmsGen, &smoac_cl);
4492     if (CMSPermGenPrecleaningEnabled) {
4493       curNumCards  += preclean_mod_union_table(_permGen, &smoac_cl);
4494     }
4495     if (Verbose && PrintGCDetails) {
4496       gclog_or_tty->print(" (modUnionTable: %d cards)", curNumCards);
4497     }
4498     // Either there are very few dirty cards, so re-mark
4499     // pause will be small anyway, or our pre-cleaning isn't
4500     // that much faster than the rate at which cards are being
4501     // dirtied, so we might as well stop and re-mark since
4502     // precleaning won't improve our re-mark time by much.
4503     if (curNumCards <= CMSPrecleanThreshold ||
4504         (numIter > 0 &&
4505          (curNumCards * CMSPrecleanDenominator >
4506          lastNumCards * CMSPrecleanNumerator))) {
4507       numIter++;
4508       cumNumCards += curNumCards;
4509       break;
4510     }
4511   }
4512   curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
4513   if (CMSPermGenPrecleaningEnabled) {
4514     curNumCards += preclean_card_table(_permGen, &smoac_cl);
4515   }
4516   cumNumCards += curNumCards;
4517   if (PrintGCDetails && PrintCMSStatistics != 0) {
4518     gclog_or_tty->print_cr(" (cardTable: %d cards, re-scanned %d cards, %d iterations)",
4519                   curNumCards, cumNumCards, numIter);
4520   }
4521   return cumNumCards;   // as a measure of useful work done
4522 }
4523 
4524 // PRECLEANING NOTES:
4525 // Precleaning involves:
4526 // . reading the bits of the modUnionTable and clearing the set bits.
4527 // . For the cards corresponding to the set bits, we scan the
4528 //   objects on those cards. This means we need the free_list_lock
4529 //   so that we can safely iterate over the CMS space when scanning
4530 //   for oops.
4531 // . When we scan the objects, we'll be both reading and setting
4532 //   marks in the marking bit map, so we'll need the marking bit map.
4533 // . For protecting _collector_state transitions, we take the CGC_lock.
4534 //   Note that any races in the reading of of card table entries by the
4535 //   CMS thread on the one hand and the clearing of those entries by the
4536 //   VM thread or the setting of those entries by the mutator threads on the
4537 //   other are quite benign. However, for efficiency it makes sense to keep
4538 //   the VM thread from racing with the CMS thread while the latter is
4539 //   dirty card info to the modUnionTable. We therefore also use the
4540 //   CGC_lock to protect the reading of the card table and the mod union
4541 //   table by the CM thread.
4542 // . We run concurrently with mutator updates, so scanning
4543 //   needs to be done carefully  -- we should not try to scan
4544 //   potentially uninitialized objects.
4545 //
4546 // Locking strategy: While holding the CGC_lock, we scan over and
4547 // reset a maximal dirty range of the mod union / card tables, then lock
4548 // the free_list_lock and bitmap lock to do a full marking, then
4549 // release these locks; and repeat the cycle. This allows for a
4550 // certain amount of fairness in the sharing of these locks between
4551 // the CMS collector on the one hand, and the VM thread and the
4552 // mutators on the other.
4553 
4554 // NOTE: preclean_mod_union_table() and preclean_card_table()
4555 // further below are largely identical; if you need to modify
4556 // one of these methods, please check the other method too.
4557 
4558 size_t CMSCollector::preclean_mod_union_table(
4559   ConcurrentMarkSweepGeneration* gen,
4560   ScanMarkedObjectsAgainCarefullyClosure* cl) {
4561   verify_work_stacks_empty();
4562   verify_overflow_empty();
4563 
4564   // Turn off checking for this method but turn it back on
4565   // selectively.  There are yield points in this method
4566   // but it is difficult to turn the checking off just around
4567   // the yield points.  It is simpler to selectively turn
4568   // it on.
4569   DEBUG_ONLY(RememberKlassesChecker mux(false);)
4570 
4571   // strategy: starting with the first card, accumulate contiguous
4572   // ranges of dirty cards; clear these cards, then scan the region
4573   // covered by these cards.
4574 
4575   // Since all of the MUT is committed ahead, we can just use
4576   // that, in case the generations expand while we are precleaning.
4577   // It might also be fine to just use the committed part of the
4578   // generation, but we might potentially miss cards when the
4579   // generation is rapidly expanding while we are in the midst
4580   // of precleaning.
4581   HeapWord* startAddr = gen->reserved().start();
4582   HeapWord* endAddr   = gen->reserved().end();
4583 
4584   cl->setFreelistLock(gen->freelistLock());   // needed for yielding
4585 
4586   size_t numDirtyCards, cumNumDirtyCards;
4587   HeapWord *nextAddr, *lastAddr;
4588   for (cumNumDirtyCards = numDirtyCards = 0,
4589        nextAddr = lastAddr = startAddr;
4590        nextAddr < endAddr;
4591        nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4592 
4593     ResourceMark rm;
4594     HandleMark   hm;
4595 
4596     MemRegion dirtyRegion;
4597     {
4598       stopTimer();
4599       // Potential yield point
4600       CMSTokenSync ts(true);
4601       startTimer();
4602       sample_eden();
4603       // Get dirty region starting at nextOffset (inclusive),
4604       // simultaneously clearing it.
4605       dirtyRegion =
4606         _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
4607       assert(dirtyRegion.start() >= nextAddr,
4608              "returned region inconsistent?");
4609     }
4610     // Remember where the next search should begin.
4611     // The returned region (if non-empty) is a right open interval,
4612     // so lastOffset is obtained from the right end of that
4613     // interval.
4614     lastAddr = dirtyRegion.end();
4615     // Should do something more transparent and less hacky XXX
4616     numDirtyCards =
4617       _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
4618 
4619     // We'll scan the cards in the dirty region (with periodic
4620     // yields for foreground GC as needed).
4621     if (!dirtyRegion.is_empty()) {
4622       assert(numDirtyCards > 0, "consistency check");
4623       HeapWord* stop_point = NULL;
4624       stopTimer();
4625       // Potential yield point
4626       CMSTokenSyncWithLocks ts(true, gen->freelistLock(),
4627                                bitMapLock());
4628       startTimer();
4629       {
4630         verify_work_stacks_empty();
4631         verify_overflow_empty();
4632         sample_eden();
4633         DEBUG_ONLY(RememberKlassesChecker mx(should_unload_classes());)
4634         stop_point =
4635           gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4636       }
4637       if (stop_point != NULL) {
4638         // The careful iteration stopped early either because it found an
4639         // uninitialized object, or because we were in the midst of an
4640         // "abortable preclean", which should now be aborted. Redirty
4641         // the bits corresponding to the partially-scanned or unscanned
4642         // cards. We'll either restart at the next block boundary or
4643         // abort the preclean.
4644         assert((CMSPermGenPrecleaningEnabled && (gen == _permGen)) ||
4645                (_collectorState == AbortablePreclean && should_abort_preclean()),
4646                "Unparsable objects should only be in perm gen.");
4647         _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
4648         if (should_abort_preclean()) {
4649           break; // out of preclean loop
4650         } else {
4651           // Compute the next address at which preclean should pick up;
4652           // might need bitMapLock in order to read P-bits.
4653           lastAddr = next_card_start_after_block(stop_point);
4654         }
4655       }
4656     } else {
4657       assert(lastAddr == endAddr, "consistency check");
4658       assert(numDirtyCards == 0, "consistency check");
4659       break;
4660     }
4661   }
4662   verify_work_stacks_empty();
4663   verify_overflow_empty();
4664   return cumNumDirtyCards;
4665 }
4666 
4667 // NOTE: preclean_mod_union_table() above and preclean_card_table()
4668 // below are largely identical; if you need to modify
4669 // one of these methods, please check the other method too.
4670 
4671 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* gen,
4672   ScanMarkedObjectsAgainCarefullyClosure* cl) {
4673   // strategy: it's similar to precleamModUnionTable above, in that
4674   // we accumulate contiguous ranges of dirty cards, mark these cards
4675   // precleaned, then scan the region covered by these cards.
4676   HeapWord* endAddr   = (HeapWord*)(gen->_virtual_space.high());
4677   HeapWord* startAddr = (HeapWord*)(gen->_virtual_space.low());
4678 
4679   cl->setFreelistLock(gen->freelistLock());   // needed for yielding
4680 
4681   size_t numDirtyCards, cumNumDirtyCards;
4682   HeapWord *lastAddr, *nextAddr;
4683 
4684   for (cumNumDirtyCards = numDirtyCards = 0,
4685        nextAddr = lastAddr = startAddr;
4686        nextAddr < endAddr;
4687        nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4688 
4689     ResourceMark rm;
4690     HandleMark   hm;
4691 
4692     MemRegion dirtyRegion;
4693     {
4694       // See comments in "Precleaning notes" above on why we
4695       // do this locking. XXX Could the locking overheads be
4696       // too high when dirty cards are sparse? [I don't think so.]
4697       stopTimer();
4698       CMSTokenSync x(true); // is cms thread
4699       startTimer();
4700       sample_eden();
4701       // Get and clear dirty region from card table
4702       dirtyRegion = _ct->ct_bs()->dirty_card_range_after_reset(
4703                                     MemRegion(nextAddr, endAddr),
4704                                     true,
4705                                     CardTableModRefBS::precleaned_card_val());
4706 
4707       assert(dirtyRegion.start() >= nextAddr,
4708              "returned region inconsistent?");
4709     }
4710     lastAddr = dirtyRegion.end();
4711     numDirtyCards =
4712       dirtyRegion.word_size()/CardTableModRefBS::card_size_in_words;
4713 
4714     if (!dirtyRegion.is_empty()) {
4715       stopTimer();
4716       CMSTokenSyncWithLocks ts(true, gen->freelistLock(), bitMapLock());
4717       startTimer();
4718       sample_eden();
4719       verify_work_stacks_empty();
4720       verify_overflow_empty();
4721       DEBUG_ONLY(RememberKlassesChecker mx(should_unload_classes());)
4722       HeapWord* stop_point =
4723         gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4724       if (stop_point != NULL) {
4725         // The careful iteration stopped early because it found an
4726         // uninitialized object.  Redirty the bits corresponding to the
4727         // partially-scanned or unscanned cards, and start again at the
4728         // next block boundary.
4729         assert(CMSPermGenPrecleaningEnabled ||
4730                (_collectorState == AbortablePreclean && should_abort_preclean()),
4731                "Unparsable objects should only be in perm gen.");
4732         _ct->ct_bs()->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4733         if (should_abort_preclean()) {
4734           break; // out of preclean loop
4735         } else {
4736           // Compute the next address at which preclean should pick up.
4737           lastAddr = next_card_start_after_block(stop_point);
4738         }
4739       }
4740     } else {
4741       break;
4742     }
4743   }
4744   verify_work_stacks_empty();
4745   verify_overflow_empty();
4746   return cumNumDirtyCards;
4747 }
4748 
4749 void CMSCollector::checkpointRootsFinal(bool asynch,
4750   bool clear_all_soft_refs, bool init_mark_was_synchronous) {
4751   assert(_collectorState == FinalMarking, "incorrect state transition?");
4752   check_correct_thread_executing();
4753   // world is stopped at this checkpoint
4754   assert(SafepointSynchronize::is_at_safepoint(),
4755          "world should be stopped");

4756   verify_work_stacks_empty();
4757   verify_overflow_empty();
4758 
4759   SpecializationStats::clear();
4760   if (PrintGCDetails) {
4761     gclog_or_tty->print("[YG occupancy: "SIZE_FORMAT" K ("SIZE_FORMAT" K)]",
4762                         _young_gen->used() / K,
4763                         _young_gen->capacity() / K);
4764   }
4765   if (asynch) {
4766     if (CMSScavengeBeforeRemark) {
4767       GenCollectedHeap* gch = GenCollectedHeap::heap();
4768       // Temporarily set flag to false, GCH->do_collection will
4769       // expect it to be false and set to true
4770       FlagSetting fl(gch->_is_gc_active, false);
4771       NOT_PRODUCT(TraceTime t("Scavenge-Before-Remark",
4772         PrintGCDetails && Verbose, true, gclog_or_tty);)
4773       int level = _cmsGen->level() - 1;
4774       if (level >= 0) {
4775         gch->do_collection(true,        // full (i.e. force, see below)
4776                            false,       // !clear_all_soft_refs
4777                            0,           // size
4778                            false,       // is_tlab
4779                            level        // max_level
4780                           );
4781       }
4782     }
4783     FreelistLocker x(this);
4784     MutexLockerEx y(bitMapLock(),
4785                     Mutex::_no_safepoint_check_flag);
4786     assert(!init_mark_was_synchronous, "but that's impossible!");
4787     checkpointRootsFinalWork(asynch, clear_all_soft_refs, false);
4788   } else {
4789     // already have all the locks
4790     checkpointRootsFinalWork(asynch, clear_all_soft_refs,
4791                              init_mark_was_synchronous);
4792   }
4793   verify_work_stacks_empty();
4794   verify_overflow_empty();
4795   SpecializationStats::print();
4796 }
4797 
4798 void CMSCollector::checkpointRootsFinalWork(bool asynch,
4799   bool clear_all_soft_refs, bool init_mark_was_synchronous) {
4800 
4801   NOT_PRODUCT(TraceTime tr("checkpointRootsFinalWork", PrintGCDetails, false, gclog_or_tty);)
4802 
4803   assert(haveFreelistLocks(), "must have free list locks");
4804   assert_lock_strong(bitMapLock());
4805 
4806   if (UseAdaptiveSizePolicy) {
4807     size_policy()->checkpoint_roots_final_begin();
4808   }
4809 
4810   ResourceMark rm;
4811   HandleMark   hm;
4812 
4813   GenCollectedHeap* gch = GenCollectedHeap::heap();
4814 
4815   if (should_unload_classes()) {
4816     CodeCache::gc_prologue();
4817   }
4818   assert(haveFreelistLocks(), "must have free list locks");
4819   assert_lock_strong(bitMapLock());
4820 
4821   DEBUG_ONLY(RememberKlassesChecker fmx(should_unload_classes());)
4822   if (!init_mark_was_synchronous) {
4823     // We might assume that we need not fill TLAB's when
4824     // CMSScavengeBeforeRemark is set, because we may have just done
4825     // a scavenge which would have filled all TLAB's -- and besides
4826     // Eden would be empty. This however may not always be the case --
4827     // for instance although we asked for a scavenge, it may not have
4828     // happened because of a JNI critical section. We probably need
4829     // a policy for deciding whether we can in that case wait until
4830     // the critical section releases and then do the remark following
4831     // the scavenge, and skip it here. In the absence of that policy,
4832     // or of an indication of whether the scavenge did indeed occur,
4833     // we cannot rely on TLAB's having been filled and must do
4834     // so here just in case a scavenge did not happen.
4835     gch->ensure_parsability(false);  // fill TLAB's, but no need to retire them
4836     // Update the saved marks which may affect the root scans.
4837     gch->save_marks();
4838 
4839     {
4840       COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
4841 
4842       // Note on the role of the mod union table:
4843       // Since the marker in "markFromRoots" marks concurrently with
4844       // mutators, it is possible for some reachable objects not to have been
4845       // scanned. For instance, an only reference to an object A was
4846       // placed in object B after the marker scanned B. Unless B is rescanned,
4847       // A would be collected. Such updates to references in marked objects
4848       // are detected via the mod union table which is the set of all cards
4849       // dirtied since the first checkpoint in this GC cycle and prior to
4850       // the most recent young generation GC, minus those cleaned up by the
4851       // concurrent precleaning.
4852       if (CMSParallelRemarkEnabled && ParallelGCThreads > 0) {
4853         TraceTime t("Rescan (parallel) ", PrintGCDetails, false, gclog_or_tty);
4854         do_remark_parallel();
4855       } else {
4856         TraceTime t("Rescan (non-parallel) ", PrintGCDetails, false,
4857                     gclog_or_tty);
4858         do_remark_non_parallel();
4859       }
4860     }
4861   } else {
4862     assert(!asynch, "Can't have init_mark_was_synchronous in asynch mode");
4863     // The initial mark was stop-world, so there's no rescanning to
4864     // do; go straight on to the next step below.
4865   }
4866   verify_work_stacks_empty();
4867   verify_overflow_empty();
4868 
4869   {
4870     NOT_PRODUCT(TraceTime ts("refProcessingWork", PrintGCDetails, false, gclog_or_tty);)
4871     refProcessingWork(asynch, clear_all_soft_refs);
4872   }
4873   verify_work_stacks_empty();
4874   verify_overflow_empty();
4875 
4876   if (should_unload_classes()) {
4877     CodeCache::gc_epilogue();
4878   }
4879 
4880   // If we encountered any (marking stack / work queue) overflow
4881   // events during the current CMS cycle, take appropriate
4882   // remedial measures, where possible, so as to try and avoid
4883   // recurrence of that condition.
4884   assert(_markStack.isEmpty(), "No grey objects");
4885   size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
4886                      _ser_kac_ovflw        + _ser_kac_preclean_ovflw;
4887   if (ser_ovflw > 0) {
4888     if (PrintCMSStatistics != 0) {
4889       gclog_or_tty->print_cr("Marking stack overflow (benign) "
4890         "(pmc_pc="SIZE_FORMAT", pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT
4891         ", kac_preclean="SIZE_FORMAT")",
4892         _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw,
4893         _ser_kac_ovflw, _ser_kac_preclean_ovflw);
4894     }
4895     _markStack.expand();
4896     _ser_pmc_remark_ovflw = 0;
4897     _ser_pmc_preclean_ovflw = 0;
4898     _ser_kac_preclean_ovflw = 0;
4899     _ser_kac_ovflw = 0;
4900   }
4901   if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
4902     if (PrintCMSStatistics != 0) {
4903       gclog_or_tty->print_cr("Work queue overflow (benign) "
4904         "(pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT")",
4905         _par_pmc_remark_ovflw, _par_kac_ovflw);
4906     }
4907     _par_pmc_remark_ovflw = 0;
4908     _par_kac_ovflw = 0;
4909   }
4910   if (PrintCMSStatistics != 0) {
4911      if (_markStack._hit_limit > 0) {
4912        gclog_or_tty->print_cr(" (benign) Hit max stack size limit ("SIZE_FORMAT")",
4913                               _markStack._hit_limit);
4914      }
4915      if (_markStack._failed_double > 0) {
4916        gclog_or_tty->print_cr(" (benign) Failed stack doubling ("SIZE_FORMAT"),"
4917                               " current capacity "SIZE_FORMAT,
4918                               _markStack._failed_double,
4919                               _markStack.capacity());
4920      }
4921   }
4922   _markStack._hit_limit = 0;
4923   _markStack._failed_double = 0;
4924 
4925   // Check that all the klasses have been checked
4926   assert(_revisitStack.isEmpty(), "Not all klasses revisited");
4927 
4928   if ((VerifyAfterGC || VerifyDuringGC) &&
4929       GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
4930     verify_after_remark();
4931   }
4932 
4933   // Change under the freelistLocks.
4934   _collectorState = Sweeping;
4935   // Call isAllClear() under bitMapLock
4936   assert(_modUnionTable.isAllClear(), "Should be clear by end of the"
4937     " final marking");
4938   if (UseAdaptiveSizePolicy) {
4939     size_policy()->checkpoint_roots_final_end(gch->gc_cause());
4940   }
4941 }
4942 
4943 // Parallel remark task
4944 class CMSParRemarkTask: public AbstractGangTask {
4945   CMSCollector* _collector;
4946   WorkGang*     _workers;
4947   int           _n_workers;
4948   CompactibleFreeListSpace* _cms_space;
4949   CompactibleFreeListSpace* _perm_space;
4950 
4951   // The per-thread work queues, available here for stealing.
4952   OopTaskQueueSet*       _task_queues;
4953   ParallelTaskTerminator _term;
4954 
4955  public:
4956   CMSParRemarkTask(CMSCollector* collector,
4957                    CompactibleFreeListSpace* cms_space,
4958                    CompactibleFreeListSpace* perm_space,
4959                    int n_workers, WorkGang* workers,
4960                    OopTaskQueueSet* task_queues):
4961     AbstractGangTask("Rescan roots and grey objects in parallel"),
4962     _collector(collector),
4963     _cms_space(cms_space), _perm_space(perm_space),
4964     _n_workers(n_workers),
4965     _workers(workers),
4966     _task_queues(task_queues),
4967     _term(workers->total_workers(), task_queues) { }
4968 
4969   OopTaskQueueSet* task_queues() { return _task_queues; }
4970 
4971   OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
4972 
4973   ParallelTaskTerminator* terminator() { return &_term; }
4974 
4975   void work(int i);
4976 
4977  private:
4978   // Work method in support of parallel rescan ... of young gen spaces
4979   void do_young_space_rescan(int i, Par_MarkRefsIntoAndScanClosure* cl,
4980                              ContiguousSpace* space,
4981                              HeapWord** chunk_array, size_t chunk_top);
4982 
4983   // ... of  dirty cards in old space
4984   void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
4985                                   Par_MarkRefsIntoAndScanClosure* cl);
4986 
4987   // ... work stealing for the above
4988   void do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl, int* seed);
4989 };
4990 
4991 void CMSParRemarkTask::work(int i) {
4992   elapsedTimer _timer;
4993   ResourceMark rm;
4994   HandleMark   hm;
4995 
4996   // ---------- rescan from roots --------------
4997   _timer.start();
4998   GenCollectedHeap* gch = GenCollectedHeap::heap();
4999   Par_MarkRefsIntoAndScanClosure par_mrias_cl(_collector,
5000     _collector->_span, _collector->ref_processor(),
5001     &(_collector->_markBitMap),
5002     work_queue(i), &(_collector->_revisitStack));
5003 
5004   // Rescan young gen roots first since these are likely
5005   // coarsely partitioned and may, on that account, constitute
5006   // the critical path; thus, it's best to start off that
5007   // work first.
5008   // ---------- young gen roots --------------
5009   {
5010     DefNewGeneration* dng = _collector->_young_gen->as_DefNewGeneration();
5011     EdenSpace* eden_space = dng->eden();
5012     ContiguousSpace* from_space = dng->from();
5013     ContiguousSpace* to_space   = dng->to();
5014 
5015     HeapWord** eca = _collector->_eden_chunk_array;
5016     size_t     ect = _collector->_eden_chunk_index;
5017     HeapWord** sca = _collector->_survivor_chunk_array;
5018     size_t     sct = _collector->_survivor_chunk_index;
5019 
5020     assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
5021     assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
5022 
5023     do_young_space_rescan(i, &par_mrias_cl, to_space, NULL, 0);
5024     do_young_space_rescan(i, &par_mrias_cl, from_space, sca, sct);
5025     do_young_space_rescan(i, &par_mrias_cl, eden_space, eca, ect);
5026 
5027     _timer.stop();
5028     if (PrintCMSStatistics != 0) {
5029       gclog_or_tty->print_cr(
5030         "Finished young gen rescan work in %dth thread: %3.3f sec",
5031         i, _timer.seconds());
5032     }
5033   }
5034 
5035   // ---------- remaining roots --------------
5036   _timer.reset();
5037   _timer.start();
5038   gch->gen_process_strong_roots(_collector->_cmsGen->level(),
5039                                 false,     // yg was scanned above
5040                                 false,     // this is parallel code
5041                                 true,      // collecting perm gen
5042                                 SharedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
5043                                 &par_mrias_cl,
5044                                 true,   // walk all of code cache if (so & SO_CodeCache)
5045                                 NULL);
5046   assert(_collector->should_unload_classes()
5047          || (_collector->CMSCollector::roots_scanning_options() & SharedHeap::SO_CodeCache),
5048          "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5049   _timer.stop();
5050   if (PrintCMSStatistics != 0) {
5051     gclog_or_tty->print_cr(
5052       "Finished remaining root rescan work in %dth thread: %3.3f sec",
5053       i, _timer.seconds());
5054   }
5055 
5056   // ---------- rescan dirty cards ------------
5057   _timer.reset();
5058   _timer.start();
5059 
5060   // Do the rescan tasks for each of the two spaces
5061   // (cms_space and perm_space) in turn.
5062   do_dirty_card_rescan_tasks(_cms_space, i, &par_mrias_cl);
5063   do_dirty_card_rescan_tasks(_perm_space, i, &par_mrias_cl);
5064   _timer.stop();
5065   if (PrintCMSStatistics != 0) {
5066     gclog_or_tty->print_cr(
5067       "Finished dirty card rescan work in %dth thread: %3.3f sec",
5068       i, _timer.seconds());
5069   }
5070 
5071   // ---------- steal work from other threads ...
5072   // ---------- ... and drain overflow list.
5073   _timer.reset();
5074   _timer.start();
5075   do_work_steal(i, &par_mrias_cl, _collector->hash_seed(i));
5076   _timer.stop();
5077   if (PrintCMSStatistics != 0) {
5078     gclog_or_tty->print_cr(
5079       "Finished work stealing in %dth thread: %3.3f sec",
5080       i, _timer.seconds());
5081   }
5082 }
5083 
5084 void
5085 CMSParRemarkTask::do_young_space_rescan(int i,
5086   Par_MarkRefsIntoAndScanClosure* cl, ContiguousSpace* space,
5087   HeapWord** chunk_array, size_t chunk_top) {
5088   // Until all tasks completed:
5089   // . claim an unclaimed task
5090   // . compute region boundaries corresponding to task claimed
5091   //   using chunk_array
5092   // . par_oop_iterate(cl) over that region
5093 
5094   ResourceMark rm;
5095   HandleMark   hm;
5096 
5097   SequentialSubTasksDone* pst = space->par_seq_tasks();
5098   assert(pst->valid(), "Uninitialized use?");
5099 
5100   int nth_task = 0;
5101   int n_tasks  = pst->n_tasks();
5102 
5103   HeapWord *start, *end;
5104   while (!pst->is_task_claimed(/* reference */ nth_task)) {
5105     // We claimed task # nth_task; compute its boundaries.
5106     if (chunk_top == 0) {  // no samples were taken
5107       assert(nth_task == 0 && n_tasks == 1, "Can have only 1 EdenSpace task");
5108       start = space->bottom();
5109       end   = space->top();
5110     } else if (nth_task == 0) {
5111       start = space->bottom();
5112       end   = chunk_array[nth_task];
5113     } else if (nth_task < (jint)chunk_top) {
5114       assert(nth_task >= 1, "Control point invariant");
5115       start = chunk_array[nth_task - 1];
5116       end   = chunk_array[nth_task];
5117     } else {
5118       assert(nth_task == (jint)chunk_top, "Control point invariant");
5119       start = chunk_array[chunk_top - 1];
5120       end   = space->top();
5121     }
5122     MemRegion mr(start, end);
5123     // Verify that mr is in space
5124     assert(mr.is_empty() || space->used_region().contains(mr),
5125            "Should be in space");
5126     // Verify that "start" is an object boundary
5127     assert(mr.is_empty() || oop(mr.start())->is_oop(),
5128            "Should be an oop");
5129     space->par_oop_iterate(mr, cl);
5130   }
5131   pst->all_tasks_completed();
5132 }
5133 
5134 void
5135 CMSParRemarkTask::do_dirty_card_rescan_tasks(
5136   CompactibleFreeListSpace* sp, int i,
5137   Par_MarkRefsIntoAndScanClosure* cl) {
5138   // Until all tasks completed:
5139   // . claim an unclaimed task
5140   // . compute region boundaries corresponding to task claimed
5141   // . transfer dirty bits ct->mut for that region
5142   // . apply rescanclosure to dirty mut bits for that region
5143 
5144   ResourceMark rm;
5145   HandleMark   hm;
5146 
5147   OopTaskQueue* work_q = work_queue(i);
5148   ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
5149   // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
5150   // CAUTION: This closure has state that persists across calls to
5151   // the work method dirty_range_iterate_clear() in that it has
5152   // imbedded in it a (subtype of) UpwardsObjectClosure. The
5153   // use of that state in the imbedded UpwardsObjectClosure instance
5154   // assumes that the cards are always iterated (even if in parallel
5155   // by several threads) in monotonically increasing order per each
5156   // thread. This is true of the implementation below which picks
5157   // card ranges (chunks) in monotonically increasing order globally
5158   // and, a-fortiori, in monotonically increasing order per thread
5159   // (the latter order being a subsequence of the former).
5160   // If the work code below is ever reorganized into a more chaotic
5161   // work-partitioning form than the current "sequential tasks"
5162   // paradigm, the use of that persistent state will have to be
5163   // revisited and modified appropriately. See also related
5164   // bug 4756801 work on which should examine this code to make
5165   // sure that the changes there do not run counter to the
5166   // assumptions made here and necessary for correctness and
5167   // efficiency. Note also that this code might yield inefficient
5168   // behaviour in the case of very large objects that span one or
5169   // more work chunks. Such objects would potentially be scanned
5170   // several times redundantly. Work on 4756801 should try and
5171   // address that performance anomaly if at all possible. XXX
5172   MemRegion  full_span  = _collector->_span;
5173   CMSBitMap* bm    = &(_collector->_markBitMap);     // shared
5174   CMSMarkStack* rs = &(_collector->_revisitStack);   // shared
5175   MarkFromDirtyCardsClosure
5176     greyRescanClosure(_collector, full_span, // entire span of interest
5177                       sp, bm, work_q, rs, cl);
5178 
5179   SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
5180   assert(pst->valid(), "Uninitialized use?");
5181   int nth_task = 0;
5182   const int alignment = CardTableModRefBS::card_size * BitsPerWord;
5183   MemRegion span = sp->used_region();
5184   HeapWord* start_addr = span.start();
5185   HeapWord* end_addr = (HeapWord*)round_to((intptr_t)span.end(),
5186                                            alignment);
5187   const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
5188   assert((HeapWord*)round_to((intptr_t)start_addr, alignment) ==
5189          start_addr, "Check alignment");
5190   assert((size_t)round_to((intptr_t)chunk_size, alignment) ==
5191          chunk_size, "Check alignment");
5192 
5193   while (!pst->is_task_claimed(/* reference */ nth_task)) {
5194     // Having claimed the nth_task, compute corresponding mem-region,
5195     // which is a-fortiori aligned correctly (i.e. at a MUT bopundary).
5196     // The alignment restriction ensures that we do not need any
5197     // synchronization with other gang-workers while setting or
5198     // clearing bits in thus chunk of the MUT.
5199     MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
5200                                     start_addr + (nth_task+1)*chunk_size);
5201     // The last chunk's end might be way beyond end of the
5202     // used region. In that case pull back appropriately.
5203     if (this_span.end() > end_addr) {
5204       this_span.set_end(end_addr);
5205       assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
5206     }
5207     // Iterate over the dirty cards covering this chunk, marking them
5208     // precleaned, and setting the corresponding bits in the mod union
5209     // table. Since we have been careful to partition at Card and MUT-word
5210     // boundaries no synchronization is needed between parallel threads.
5211     _collector->_ct->ct_bs()->dirty_card_iterate(this_span,
5212                                                  &modUnionClosure);
5213 
5214     // Having transferred these marks into the modUnionTable,
5215     // rescan the marked objects on the dirty cards in the modUnionTable.
5216     // Even if this is at a synchronous collection, the initial marking
5217     // may have been done during an asynchronous collection so there
5218     // may be dirty bits in the mod-union table.
5219     _collector->_modUnionTable.dirty_range_iterate_clear(
5220                   this_span, &greyRescanClosure);
5221     _collector->_modUnionTable.verifyNoOneBitsInRange(
5222                                  this_span.start(),
5223                                  this_span.end());
5224   }
5225   pst->all_tasks_completed();  // declare that i am done
5226 }
5227 
5228 // . see if we can share work_queues with ParNew? XXX
5229 void
5230 CMSParRemarkTask::do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl,
5231                                 int* seed) {
5232   OopTaskQueue* work_q = work_queue(i);
5233   NOT_PRODUCT(int num_steals = 0;)
5234   oop obj_to_scan;
5235   CMSBitMap* bm = &(_collector->_markBitMap);
5236 
5237   while (true) {
5238     // Completely finish any left over work from (an) earlier round(s)
5239     cl->trim_queue(0);
5240     size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5241                                          (size_t)ParGCDesiredObjsFromOverflowList);
5242     // Now check if there's any work in the overflow list
5243     if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5244                                                 work_q)) {
5245       // found something in global overflow list;
5246       // not yet ready to go stealing work from others.
5247       // We'd like to assert(work_q->size() != 0, ...)
5248       // because we just took work from the overflow list,
5249       // but of course we can't since all of that could have
5250       // been already stolen from us.
5251       // "He giveth and He taketh away."
5252       continue;
5253     }
5254     // Verify that we have no work before we resort to stealing
5255     assert(work_q->size() == 0, "Have work, shouldn't steal");
5256     // Try to steal from other queues that have work
5257     if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5258       NOT_PRODUCT(num_steals++;)
5259       assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5260       assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5261       // Do scanning work
5262       obj_to_scan->oop_iterate(cl);
5263       // Loop around, finish this work, and try to steal some more
5264     } else if (terminator()->offer_termination()) {
5265         break;  // nirvana from the infinite cycle
5266     }
5267   }
5268   NOT_PRODUCT(
5269     if (PrintCMSStatistics != 0) {
5270       gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5271     }
5272   )
5273   assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
5274          "Else our work is not yet done");
5275 }
5276 
5277 // Return a thread-local PLAB recording array, as appropriate.
5278 void* CMSCollector::get_data_recorder(int thr_num) {
5279   if (_survivor_plab_array != NULL &&
5280       (CMSPLABRecordAlways ||
5281        (_collectorState > Marking && _collectorState < FinalMarking))) {
5282     assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
5283     ChunkArray* ca = &_survivor_plab_array[thr_num];
5284     ca->reset();   // clear it so that fresh data is recorded
5285     return (void*) ca;
5286   } else {
5287     return NULL;
5288   }
5289 }
5290 
5291 // Reset all the thread-local PLAB recording arrays
5292 void CMSCollector::reset_survivor_plab_arrays() {
5293   for (uint i = 0; i < ParallelGCThreads; i++) {
5294     _survivor_plab_array[i].reset();
5295   }
5296 }
5297 
5298 // Merge the per-thread plab arrays into the global survivor chunk
5299 // array which will provide the partitioning of the survivor space
5300 // for CMS rescan.
5301 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv) {
5302   assert(_survivor_plab_array  != NULL, "Error");
5303   assert(_survivor_chunk_array != NULL, "Error");
5304   assert(_collectorState == FinalMarking, "Error");
5305   for (uint j = 0; j < ParallelGCThreads; j++) {
5306     _cursor[j] = 0;
5307   }
5308   HeapWord* top = surv->top();
5309   size_t i;
5310   for (i = 0; i < _survivor_chunk_capacity; i++) {  // all sca entries
5311     HeapWord* min_val = top;          // Higher than any PLAB address
5312     uint      min_tid = 0;            // position of min_val this round
5313     for (uint j = 0; j < ParallelGCThreads; j++) {
5314       ChunkArray* cur_sca = &_survivor_plab_array[j];
5315       if (_cursor[j] == cur_sca->end()) {
5316         continue;
5317       }
5318       assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
5319       HeapWord* cur_val = cur_sca->nth(_cursor[j]);
5320       assert(surv->used_region().contains(cur_val), "Out of bounds value");
5321       if (cur_val < min_val) {
5322         min_tid = j;
5323         min_val = cur_val;
5324       } else {
5325         assert(cur_val < top, "All recorded addresses should be less");
5326       }
5327     }
5328     // At this point min_val and min_tid are respectively
5329     // the least address in _survivor_plab_array[j]->nth(_cursor[j])
5330     // and the thread (j) that witnesses that address.
5331     // We record this address in the _survivor_chunk_array[i]
5332     // and increment _cursor[min_tid] prior to the next round i.
5333     if (min_val == top) {
5334       break;
5335     }
5336     _survivor_chunk_array[i] = min_val;
5337     _cursor[min_tid]++;
5338   }
5339   // We are all done; record the size of the _survivor_chunk_array
5340   _survivor_chunk_index = i; // exclusive: [0, i)
5341   if (PrintCMSStatistics > 0) {
5342     gclog_or_tty->print(" (Survivor:" SIZE_FORMAT "chunks) ", i);
5343   }
5344   // Verify that we used up all the recorded entries
5345   #ifdef ASSERT
5346     size_t total = 0;
5347     for (uint j = 0; j < ParallelGCThreads; j++) {
5348       assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
5349       total += _cursor[j];
5350     }
5351     assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
5352     // Check that the merged array is in sorted order
5353     if (total > 0) {
5354       for (size_t i = 0; i < total - 1; i++) {
5355         if (PrintCMSStatistics > 0) {
5356           gclog_or_tty->print(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
5357                               i, _survivor_chunk_array[i]);
5358         }
5359         assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
5360                "Not sorted");
5361       }
5362     }
5363   #endif // ASSERT
5364 }
5365 
5366 // Set up the space's par_seq_tasks structure for work claiming
5367 // for parallel rescan of young gen.
5368 // See ParRescanTask where this is currently used.
5369 void
5370 CMSCollector::
5371 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
5372   assert(n_threads > 0, "Unexpected n_threads argument");
5373   DefNewGeneration* dng = (DefNewGeneration*)_young_gen;
5374 
5375   // Eden space
5376   {
5377     SequentialSubTasksDone* pst = dng->eden()->par_seq_tasks();
5378     assert(!pst->valid(), "Clobbering existing data?");
5379     // Each valid entry in [0, _eden_chunk_index) represents a task.
5380     size_t n_tasks = _eden_chunk_index + 1;
5381     assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
5382     pst->set_par_threads(n_threads);
5383     pst->set_n_tasks((int)n_tasks);
5384   }
5385 
5386   // Merge the survivor plab arrays into _survivor_chunk_array
5387   if (_survivor_plab_array != NULL) {
5388     merge_survivor_plab_arrays(dng->from());
5389   } else {
5390     assert(_survivor_chunk_index == 0, "Error");
5391   }
5392 
5393   // To space
5394   {
5395     SequentialSubTasksDone* pst = dng->to()->par_seq_tasks();
5396     assert(!pst->valid(), "Clobbering existing data?");
5397     pst->set_par_threads(n_threads);
5398     pst->set_n_tasks(1);
5399     assert(pst->valid(), "Error");
5400   }
5401 
5402   // From space
5403   {
5404     SequentialSubTasksDone* pst = dng->from()->par_seq_tasks();
5405     assert(!pst->valid(), "Clobbering existing data?");
5406     size_t n_tasks = _survivor_chunk_index + 1;
5407     assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
5408     pst->set_par_threads(n_threads);
5409     pst->set_n_tasks((int)n_tasks);
5410     assert(pst->valid(), "Error");
5411   }
5412 }
5413 
5414 // Parallel version of remark
5415 void CMSCollector::do_remark_parallel() {
5416   GenCollectedHeap* gch = GenCollectedHeap::heap();
5417   WorkGang* workers = gch->workers();
5418   assert(workers != NULL, "Need parallel worker threads.");
5419   int n_workers = workers->total_workers();
5420   CompactibleFreeListSpace* cms_space  = _cmsGen->cmsSpace();
5421   CompactibleFreeListSpace* perm_space = _permGen->cmsSpace();
5422 
5423   CMSParRemarkTask tsk(this,
5424     cms_space, perm_space,
5425     n_workers, workers, task_queues());
5426 
5427   // Set up for parallel process_strong_roots work.
5428   gch->set_par_threads(n_workers);
5429   // We won't be iterating over the cards in the card table updating
5430   // the younger_gen cards, so we shouldn't call the following else
5431   // the verification code as well as subsequent younger_refs_iterate
5432   // code would get confused. XXX
5433   // gch->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
5434 
5435   // The young gen rescan work will not be done as part of
5436   // process_strong_roots (which currently doesn't knw how to
5437   // parallelize such a scan), but rather will be broken up into
5438   // a set of parallel tasks (via the sampling that the [abortable]
5439   // preclean phase did of EdenSpace, plus the [two] tasks of
5440   // scanning the [two] survivor spaces. Further fine-grain
5441   // parallelization of the scanning of the survivor spaces
5442   // themselves, and of precleaning of the younger gen itself
5443   // is deferred to the future.
5444   initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
5445 
5446   // The dirty card rescan work is broken up into a "sequence"
5447   // of parallel tasks (per constituent space) that are dynamically
5448   // claimed by the parallel threads.
5449   cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
5450   perm_space->initialize_sequential_subtasks_for_rescan(n_workers);
5451 
5452   // It turns out that even when we're using 1 thread, doing the work in a
5453   // separate thread causes wide variance in run times.  We can't help this
5454   // in the multi-threaded case, but we special-case n=1 here to get
5455   // repeatable measurements of the 1-thread overhead of the parallel code.
5456   if (n_workers > 1) {
5457     // Make refs discovery MT-safe
5458     ReferenceProcessorMTMutator mt(ref_processor(), true);
5459     GenCollectedHeap::StrongRootsScope srs(gch);
5460     workers->run_task(&tsk);
5461   } else {
5462     GenCollectedHeap::StrongRootsScope srs(gch);
5463     tsk.work(0);
5464   }
5465   gch->set_par_threads(0);  // 0 ==> non-parallel.
5466   // restore, single-threaded for now, any preserved marks
5467   // as a result of work_q overflow
5468   restore_preserved_marks_if_any();
5469 }
5470 
5471 // Non-parallel version of remark
5472 void CMSCollector::do_remark_non_parallel() {
5473   ResourceMark rm;
5474   HandleMark   hm;
5475   GenCollectedHeap* gch = GenCollectedHeap::heap();
5476   MarkRefsIntoAndScanClosure
5477     mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
5478              &_markStack, &_revisitStack, this,
5479              false /* should_yield */, false /* not precleaning */);
5480   MarkFromDirtyCardsClosure
5481     markFromDirtyCardsClosure(this, _span,
5482                               NULL,  // space is set further below
5483                               &_markBitMap, &_markStack, &_revisitStack,
5484                               &mrias_cl);
5485   {
5486     TraceTime t("grey object rescan", PrintGCDetails, false, gclog_or_tty);
5487     // Iterate over the dirty cards, setting the corresponding bits in the
5488     // mod union table.
5489     {
5490       ModUnionClosure modUnionClosure(&_modUnionTable);
5491       _ct->ct_bs()->dirty_card_iterate(
5492                       _cmsGen->used_region(),
5493                       &modUnionClosure);
5494       _ct->ct_bs()->dirty_card_iterate(
5495                       _permGen->used_region(),
5496                       &modUnionClosure);
5497     }
5498     // Having transferred these marks into the modUnionTable, we just need
5499     // to rescan the marked objects on the dirty cards in the modUnionTable.
5500     // The initial marking may have been done during an asynchronous
5501     // collection so there may be dirty bits in the mod-union table.
5502     const int alignment =
5503       CardTableModRefBS::card_size * BitsPerWord;
5504     {
5505       // ... First handle dirty cards in CMS gen
5506       markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
5507       MemRegion ur = _cmsGen->used_region();
5508       HeapWord* lb = ur.start();
5509       HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
5510       MemRegion cms_span(lb, ub);
5511       _modUnionTable.dirty_range_iterate_clear(cms_span,
5512                                                &markFromDirtyCardsClosure);
5513       verify_work_stacks_empty();
5514       if (PrintCMSStatistics != 0) {
5515         gclog_or_tty->print(" (re-scanned "SIZE_FORMAT" dirty cards in cms gen) ",
5516           markFromDirtyCardsClosure.num_dirty_cards());
5517       }
5518     }
5519     {
5520       // .. and then repeat for dirty cards in perm gen
5521       markFromDirtyCardsClosure.set_space(_permGen->cmsSpace());
5522       MemRegion ur = _permGen->used_region();
5523       HeapWord* lb = ur.start();
5524       HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
5525       MemRegion perm_span(lb, ub);
5526       _modUnionTable.dirty_range_iterate_clear(perm_span,
5527                                                &markFromDirtyCardsClosure);
5528       verify_work_stacks_empty();
5529       if (PrintCMSStatistics != 0) {
5530         gclog_or_tty->print(" (re-scanned "SIZE_FORMAT" dirty cards in perm gen) ",
5531           markFromDirtyCardsClosure.num_dirty_cards());
5532       }
5533     }
5534   }
5535   if (VerifyDuringGC &&
5536       GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5537     HandleMark hm;  // Discard invalid handles created during verification
5538     Universe::verify(true);
5539   }
5540   {
5541     TraceTime t("root rescan", PrintGCDetails, false, gclog_or_tty);
5542 
5543     verify_work_stacks_empty();
5544 
5545     gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
5546     GenCollectedHeap::StrongRootsScope srs(gch);
5547     gch->gen_process_strong_roots(_cmsGen->level(),
5548                                   true,  // younger gens as roots
5549                                   false, // use the local StrongRootsScope
5550                                   true,  // collecting perm gen
5551                                   SharedHeap::ScanningOption(roots_scanning_options()),
5552                                   &mrias_cl,
5553                                   true,   // walk code active on stacks
5554                                   NULL);
5555     assert(should_unload_classes()
5556            || (roots_scanning_options() & SharedHeap::SO_CodeCache),
5557            "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5558   }
5559   verify_work_stacks_empty();
5560   // Restore evacuated mark words, if any, used for overflow list links
5561   if (!CMSOverflowEarlyRestoration) {
5562     restore_preserved_marks_if_any();
5563   }
5564   verify_overflow_empty();
5565 }
5566 
5567 ////////////////////////////////////////////////////////
5568 // Parallel Reference Processing Task Proxy Class
5569 ////////////////////////////////////////////////////////
5570 class CMSRefProcTaskProxy: public AbstractGangTask {
5571   typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
5572   CMSCollector*          _collector;
5573   CMSBitMap*             _mark_bit_map;
5574   const MemRegion        _span;
5575   OopTaskQueueSet*       _task_queues;
5576   ParallelTaskTerminator _term;
5577   ProcessTask&           _task;
5578 
5579 public:
5580   CMSRefProcTaskProxy(ProcessTask&     task,
5581                       CMSCollector*    collector,
5582                       const MemRegion& span,
5583                       CMSBitMap*       mark_bit_map,
5584                       int              total_workers,
5585                       OopTaskQueueSet* task_queues):
5586     AbstractGangTask("Process referents by policy in parallel"),
5587     _task(task),
5588     _collector(collector), _span(span), _mark_bit_map(mark_bit_map),
5589     _task_queues(task_queues),
5590     _term(total_workers, task_queues)
5591     {
5592       assert(_collector->_span.equals(_span) && !_span.is_empty(),
5593              "Inconsistency in _span");
5594     }
5595 
5596   OopTaskQueueSet* task_queues() { return _task_queues; }
5597 
5598   OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5599 
5600   ParallelTaskTerminator* terminator() { return &_term; }
5601 
5602   void do_work_steal(int i,
5603                      CMSParDrainMarkingStackClosure* drain,
5604                      CMSParKeepAliveClosure* keep_alive,
5605                      int* seed);
5606 
5607   virtual void work(int i);
5608 };
5609 
5610 void CMSRefProcTaskProxy::work(int i) {
5611   assert(_collector->_span.equals(_span), "Inconsistency in _span");
5612   CMSParKeepAliveClosure par_keep_alive(_collector, _span,
5613                                         _mark_bit_map,
5614                                         &_collector->_revisitStack,
5615                                         work_queue(i));
5616   CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
5617                                                  _mark_bit_map,
5618                                                  &_collector->_revisitStack,
5619                                                  work_queue(i));
5620   CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
5621   _task.work(i, is_alive_closure, par_keep_alive, par_drain_stack);
5622   if (_task.marks_oops_alive()) {
5623     do_work_steal(i, &par_drain_stack, &par_keep_alive,
5624                   _collector->hash_seed(i));
5625   }
5626   assert(work_queue(i)->size() == 0, "work_queue should be empty");
5627   assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
5628 }
5629 
5630 class CMSRefEnqueueTaskProxy: public AbstractGangTask {
5631   typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
5632   EnqueueTask& _task;
5633 
5634 public:
5635   CMSRefEnqueueTaskProxy(EnqueueTask& task)
5636     : AbstractGangTask("Enqueue reference objects in parallel"),
5637       _task(task)
5638   { }
5639 
5640   virtual void work(int i)
5641   {
5642     _task.work(i);
5643   }
5644 };
5645 
5646 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
5647   MemRegion span, CMSBitMap* bit_map, CMSMarkStack* revisit_stack,
5648   OopTaskQueue* work_queue):
5649    Par_KlassRememberingOopClosure(collector, NULL, revisit_stack),
5650    _span(span),
5651    _bit_map(bit_map),
5652    _work_queue(work_queue),
5653    _mark_and_push(collector, span, bit_map, revisit_stack, work_queue),
5654    _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
5655                         (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads)))
5656 { }
5657 
5658 // . see if we can share work_queues with ParNew? XXX
5659 void CMSRefProcTaskProxy::do_work_steal(int i,
5660   CMSParDrainMarkingStackClosure* drain,
5661   CMSParKeepAliveClosure* keep_alive,
5662   int* seed) {
5663   OopTaskQueue* work_q = work_queue(i);
5664   NOT_PRODUCT(int num_steals = 0;)
5665   oop obj_to_scan;
5666 
5667   while (true) {
5668     // Completely finish any left over work from (an) earlier round(s)
5669     drain->trim_queue(0);
5670     size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5671                                          (size_t)ParGCDesiredObjsFromOverflowList);
5672     // Now check if there's any work in the overflow list
5673     if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5674                                                 work_q)) {
5675       // Found something in global overflow list;
5676       // not yet ready to go stealing work from others.
5677       // We'd like to assert(work_q->size() != 0, ...)
5678       // because we just took work from the overflow list,
5679       // but of course we can't, since all of that might have
5680       // been already stolen from us.
5681       continue;
5682     }
5683     // Verify that we have no work before we resort to stealing
5684     assert(work_q->size() == 0, "Have work, shouldn't steal");
5685     // Try to steal from other queues that have work
5686     if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5687       NOT_PRODUCT(num_steals++;)
5688       assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5689       assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5690       // Do scanning work
5691       obj_to_scan->oop_iterate(keep_alive);
5692       // Loop around, finish this work, and try to steal some more
5693     } else if (terminator()->offer_termination()) {
5694       break;  // nirvana from the infinite cycle
5695     }
5696   }
5697   NOT_PRODUCT(
5698     if (PrintCMSStatistics != 0) {
5699       gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5700     }
5701   )
5702 }
5703 
5704 void CMSRefProcTaskExecutor::execute(ProcessTask& task)
5705 {
5706   GenCollectedHeap* gch = GenCollectedHeap::heap();
5707   WorkGang* workers = gch->workers();
5708   assert(workers != NULL, "Need parallel worker threads.");
5709   int n_workers = workers->total_workers();
5710   CMSRefProcTaskProxy rp_task(task, &_collector,
5711                               _collector.ref_processor()->span(),
5712                               _collector.markBitMap(),
5713                               n_workers, _collector.task_queues());
5714   workers->run_task(&rp_task);
5715 }
5716 
5717 void CMSRefProcTaskExecutor::execute(EnqueueTask& task)
5718 {
5719 
5720   GenCollectedHeap* gch = GenCollectedHeap::heap();
5721   WorkGang* workers = gch->workers();
5722   assert(workers != NULL, "Need parallel worker threads.");
5723   CMSRefEnqueueTaskProxy enq_task(task);
5724   workers->run_task(&enq_task);
5725 }
5726 
5727 void CMSCollector::refProcessingWork(bool asynch, bool clear_all_soft_refs) {
5728 
5729   ResourceMark rm;
5730   HandleMark   hm;
5731 
5732   ReferenceProcessor* rp = ref_processor();
5733   assert(rp->span().equals(_span), "Spans should be equal");
5734   assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
5735   // Process weak references.
5736   rp->setup_policy(clear_all_soft_refs);
5737   verify_work_stacks_empty();
5738 
5739   CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
5740                                           &_markStack, &_revisitStack,
5741                                           false /* !preclean */);
5742   CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
5743                                 _span, &_markBitMap, &_markStack,
5744                                 &cmsKeepAliveClosure, false /* !preclean */);
5745   {
5746     TraceTime t("weak refs processing", PrintGCDetails, false, gclog_or_tty);
5747     if (rp->processing_is_mt()) {
5748       CMSRefProcTaskExecutor task_executor(*this);
5749       rp->process_discovered_references(&_is_alive_closure,
5750                                         &cmsKeepAliveClosure,
5751                                         &cmsDrainMarkingStackClosure,
5752                                         &task_executor);
5753     } else {
5754       rp->process_discovered_references(&_is_alive_closure,
5755                                         &cmsKeepAliveClosure,
5756                                         &cmsDrainMarkingStackClosure,
5757                                         NULL);
5758     }
5759     verify_work_stacks_empty();
5760   }
5761 
5762   if (should_unload_classes()) {
5763     {
5764       TraceTime t("class unloading", PrintGCDetails, false, gclog_or_tty);
5765 
5766       // Follow SystemDictionary roots and unload classes
5767       bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure);
5768 
5769       // Follow CodeCache roots and unload any methods marked for unloading
5770       CodeCache::do_unloading(&_is_alive_closure,
5771                               &cmsKeepAliveClosure,
5772                               purged_class);
5773 
5774       cmsDrainMarkingStackClosure.do_void();
5775       verify_work_stacks_empty();
5776 
5777       // Update subklass/sibling/implementor links in KlassKlass descendants
5778       assert(!_revisitStack.isEmpty(), "revisit stack should not be empty");
5779       oop k;
5780       while ((k = _revisitStack.pop()) != NULL) {
5781         ((Klass*)(oopDesc*)k)->follow_weak_klass_links(
5782                        &_is_alive_closure,
5783                        &cmsKeepAliveClosure);
5784       }
5785       assert(!ClassUnloading ||
5786              (_markStack.isEmpty() && overflow_list_is_empty()),
5787              "Should not have found new reachable objects");
5788       assert(_revisitStack.isEmpty(), "revisit stack should have been drained");
5789       cmsDrainMarkingStackClosure.do_void();
5790       verify_work_stacks_empty();
5791     }
5792 
5793     {
5794       TraceTime t("scrub symbol & string tables", PrintGCDetails, false, gclog_or_tty);
5795       // Now clean up stale oops in SymbolTable and StringTable
5796       SymbolTable::unlink(&_is_alive_closure);
5797       StringTable::unlink(&_is_alive_closure);
5798     }
5799   }
5800 
5801   verify_work_stacks_empty();
5802   // Restore any preserved marks as a result of mark stack or
5803   // work queue overflow
5804   restore_preserved_marks_if_any();  // done single-threaded for now
5805 
5806   rp->set_enqueuing_is_done(true);
5807   if (rp->processing_is_mt()) {
5808     CMSRefProcTaskExecutor task_executor(*this);
5809     rp->enqueue_discovered_references(&task_executor);
5810   } else {
5811     rp->enqueue_discovered_references(NULL);
5812   }
5813   rp->verify_no_references_recorded();
5814   assert(!rp->discovery_enabled(), "should have been disabled");
5815 
5816   // JVMTI object tagging is based on JNI weak refs. If any of these
5817   // refs were cleared then JVMTI needs to update its maps and
5818   // maybe post ObjectFrees to agents.
5819   JvmtiExport::cms_ref_processing_epilogue();
5820 }
5821 
5822 #ifndef PRODUCT
5823 void CMSCollector::check_correct_thread_executing() {
5824   Thread* t = Thread::current();
5825   // Only the VM thread or the CMS thread should be here.
5826   assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
5827          "Unexpected thread type");
5828   // If this is the vm thread, the foreground process
5829   // should not be waiting.  Note that _foregroundGCIsActive is
5830   // true while the foreground collector is waiting.
5831   if (_foregroundGCShouldWait) {
5832     // We cannot be the VM thread
5833     assert(t->is_ConcurrentGC_thread(),
5834            "Should be CMS thread");
5835   } else {
5836     // We can be the CMS thread only if we are in a stop-world
5837     // phase of CMS collection.
5838     if (t->is_ConcurrentGC_thread()) {
5839       assert(_collectorState == InitialMarking ||
5840              _collectorState == FinalMarking,
5841              "Should be a stop-world phase");
5842       // The CMS thread should be holding the CMS_token.
5843       assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5844              "Potential interference with concurrently "
5845              "executing VM thread");
5846     }
5847   }
5848 }
5849 #endif
5850 
5851 void CMSCollector::sweep(bool asynch) {
5852   assert(_collectorState == Sweeping, "just checking");
5853   check_correct_thread_executing();
5854   verify_work_stacks_empty();
5855   verify_overflow_empty();
5856   increment_sweep_count();


5857   _inter_sweep_timer.stop();
5858   _inter_sweep_estimate.sample(_inter_sweep_timer.seconds());
5859   size_policy()->avg_cms_free_at_sweep()->sample(_cmsGen->free());
5860 
5861   // PermGen verification support: If perm gen sweeping is disabled in
5862   // this cycle, we preserve the perm gen object "deadness" information
5863   // in the perm_gen_verify_bit_map. In order to do that we traverse
5864   // all blocks in perm gen and mark all dead objects.
5865   if (verifying() && !should_unload_classes()) {
5866     assert(perm_gen_verify_bit_map()->sizeInBits() != 0,
5867            "Should have already been allocated");
5868     MarkDeadObjectsClosure mdo(this, _permGen->cmsSpace(),
5869                                markBitMap(), perm_gen_verify_bit_map());
5870     if (asynch) {
5871       CMSTokenSyncWithLocks ts(true, _permGen->freelistLock(),
5872                                bitMapLock());
5873       _permGen->cmsSpace()->blk_iterate(&mdo);
5874     } else {
5875       // In the case of synchronous sweep, we already have
5876       // the requisite locks/tokens.
5877       _permGen->cmsSpace()->blk_iterate(&mdo);
5878     }
5879   }
5880 
5881   assert(!_intra_sweep_timer.is_active(), "Should not be active");
5882   _intra_sweep_timer.reset();
5883   _intra_sweep_timer.start();
5884   if (asynch) {
5885     TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
5886     CMSPhaseAccounting pa(this, "sweep", !PrintGCDetails);
5887     // First sweep the old gen then the perm gen
5888     {
5889       CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
5890                                bitMapLock());
5891       sweepWork(_cmsGen, asynch);
5892     }
5893 
5894     // Now repeat for perm gen
5895     if (should_unload_classes()) {
5896       CMSTokenSyncWithLocks ts(true, _permGen->freelistLock(),
5897                              bitMapLock());
5898       sweepWork(_permGen, asynch);
5899     }
5900 
5901     // Update Universe::_heap_*_at_gc figures.
5902     // We need all the free list locks to make the abstract state
5903     // transition from Sweeping to Resetting. See detailed note
5904     // further below.
5905     {
5906       CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
5907                                _permGen->freelistLock());
5908       // Update heap occupancy information which is used as
5909       // input to soft ref clearing policy at the next gc.
5910       Universe::update_heap_info_at_gc();
5911       _collectorState = Resizing;
5912     }
5913   } else {
5914     // already have needed locks
5915     sweepWork(_cmsGen,  asynch);
5916 
5917     if (should_unload_classes()) {
5918       sweepWork(_permGen, asynch);
5919     }
5920     // Update heap occupancy information which is used as
5921     // input to soft ref clearing policy at the next gc.
5922     Universe::update_heap_info_at_gc();
5923     _collectorState = Resizing;
5924   }
5925   verify_work_stacks_empty();
5926   verify_overflow_empty();
5927 
5928   _intra_sweep_timer.stop();
5929   _intra_sweep_estimate.sample(_intra_sweep_timer.seconds());
5930 
5931   _inter_sweep_timer.reset();
5932   _inter_sweep_timer.start();
5933 
5934   update_time_of_last_gc(os::javaTimeMillis());
5935 
5936   // NOTE on abstract state transitions:
5937   // Mutators allocate-live and/or mark the mod-union table dirty
5938   // based on the state of the collection.  The former is done in
5939   // the interval [Marking, Sweeping] and the latter in the interval
5940   // [Marking, Sweeping).  Thus the transitions into the Marking state
5941   // and out of the Sweeping state must be synchronously visible
5942   // globally to the mutators.
5943   // The transition into the Marking state happens with the world
5944   // stopped so the mutators will globally see it.  Sweeping is
5945   // done asynchronously by the background collector so the transition
5946   // from the Sweeping state to the Resizing state must be done
5947   // under the freelistLock (as is the check for whether to
5948   // allocate-live and whether to dirty the mod-union table).
5949   assert(_collectorState == Resizing, "Change of collector state to"
5950     " Resizing must be done under the freelistLocks (plural)");
5951 
5952   // Now that sweeping has been completed, if the GCH's
5953   // incremental_collection_will_fail flag is set, clear it,
5954   // thus inviting a younger gen collection to promote into
5955   // this generation. If such a promotion may still fail,
5956   // the flag will be set again when a young collection is
5957   // attempted.
5958   // I think the incremental_collection_will_fail flag's use
5959   // is specific to a 2 generation collection policy, so i'll
5960   // assert that that's the configuration we are operating within.
5961   // The use of the flag can and should be generalized appropriately
5962   // in the future to deal with a general n-generation system.
5963 
5964   GenCollectedHeap* gch = GenCollectedHeap::heap();
5965   assert(gch->collector_policy()->is_two_generation_policy(),
5966          "Resetting of incremental_collection_will_fail flag"
5967          " may be incorrect otherwise");
5968   gch->clear_incremental_collection_will_fail();
5969   gch->update_full_collections_completed(_collection_count_start);
5970 }
5971 
5972 // FIX ME!!! Looks like this belongs in CFLSpace, with
5973 // CMSGen merely delegating to it.
5974 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
5975   double nearLargestPercent = FLSLargestBlockCoalesceProximity;
5976   HeapWord*  minAddr        = _cmsSpace->bottom();
5977   HeapWord*  largestAddr    =
5978     (HeapWord*) _cmsSpace->dictionary()->findLargestDict();
5979   if (largestAddr == NULL) {
5980     // The dictionary appears to be empty.  In this case
5981     // try to coalesce at the end of the heap.
5982     largestAddr = _cmsSpace->end();
5983   }
5984   size_t largestOffset     = pointer_delta(largestAddr, minAddr);
5985   size_t nearLargestOffset =
5986     (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
5987   if (PrintFLSStatistics != 0) {
5988     gclog_or_tty->print_cr(
5989       "CMS: Large Block: " PTR_FORMAT ";"
5990       " Proximity: " PTR_FORMAT " -> " PTR_FORMAT,
5991       largestAddr,
5992       _cmsSpace->nearLargestChunk(), minAddr + nearLargestOffset);
5993   }
5994   _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
5995 }
5996 
5997 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
5998   return addr >= _cmsSpace->nearLargestChunk();
5999 }
6000 
6001 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
6002   return _cmsSpace->find_chunk_at_end();
6003 }
6004 
6005 void ConcurrentMarkSweepGeneration::update_gc_stats(int current_level,
6006                                                     bool full) {
6007   // The next lower level has been collected.  Gather any statistics
6008   // that are of interest at this point.
6009   if (!full && (current_level + 1) == level()) {
6010     // Gather statistics on the young generation collection.
6011     collector()->stats().record_gc0_end(used());
6012   }
6013 }
6014 
6015 CMSAdaptiveSizePolicy* ConcurrentMarkSweepGeneration::size_policy() {
6016   GenCollectedHeap* gch = GenCollectedHeap::heap();
6017   assert(gch->kind() == CollectedHeap::GenCollectedHeap,
6018     "Wrong type of heap");
6019   CMSAdaptiveSizePolicy* sp = (CMSAdaptiveSizePolicy*)
6020     gch->gen_policy()->size_policy();
6021   assert(sp->is_gc_cms_adaptive_size_policy(),
6022     "Wrong type of size policy");
6023   return sp;
6024 }
6025 
6026 void ConcurrentMarkSweepGeneration::rotate_debug_collection_type() {
6027   if (PrintGCDetails && Verbose) {
6028     gclog_or_tty->print("Rotate from %d ", _debug_collection_type);
6029   }
6030   _debug_collection_type = (CollectionTypes) (_debug_collection_type + 1);
6031   _debug_collection_type =
6032     (CollectionTypes) (_debug_collection_type % Unknown_collection_type);
6033   if (PrintGCDetails && Verbose) {
6034     gclog_or_tty->print_cr("to %d ", _debug_collection_type);
6035   }
6036 }
6037 
6038 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* gen,
6039   bool asynch) {
6040   // We iterate over the space(s) underlying this generation,
6041   // checking the mark bit map to see if the bits corresponding
6042   // to specific blocks are marked or not. Blocks that are
6043   // marked are live and are not swept up. All remaining blocks
6044   // are swept up, with coalescing on-the-fly as we sweep up
6045   // contiguous free and/or garbage blocks:
6046   // We need to ensure that the sweeper synchronizes with allocators
6047   // and stop-the-world collectors. In particular, the following
6048   // locks are used:
6049   // . CMS token: if this is held, a stop the world collection cannot occur
6050   // . freelistLock: if this is held no allocation can occur from this
6051   //                 generation by another thread
6052   // . bitMapLock: if this is held, no other thread can access or update
6053   //
6054 
6055   // Note that we need to hold the freelistLock if we use
6056   // block iterate below; else the iterator might go awry if
6057   // a mutator (or promotion) causes block contents to change
6058   // (for instance if the allocator divvies up a block).
6059   // If we hold the free list lock, for all practical purposes
6060   // young generation GC's can't occur (they'll usually need to
6061   // promote), so we might as well prevent all young generation
6062   // GC's while we do a sweeping step. For the same reason, we might
6063   // as well take the bit map lock for the entire duration
6064 
6065   // check that we hold the requisite locks
6066   assert(have_cms_token(), "Should hold cms token");
6067   assert(   (asynch && ConcurrentMarkSweepThread::cms_thread_has_cms_token())
6068          || (!asynch && ConcurrentMarkSweepThread::vm_thread_has_cms_token()),
6069         "Should possess CMS token to sweep");
6070   assert_lock_strong(gen->freelistLock());
6071   assert_lock_strong(bitMapLock());
6072 
6073   assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context");
6074   assert(_intra_sweep_timer.is_active(),  "Was switched on  in an outer context");
6075   gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
6076                                       _inter_sweep_estimate.padded_average(),
6077                                       _intra_sweep_estimate.padded_average());
6078   gen->setNearLargestChunk();
6079 
6080   {
6081     SweepClosure sweepClosure(this, gen, &_markBitMap,
6082                             CMSYield && asynch);
6083     gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
6084     // We need to free-up/coalesce garbage/blocks from a
6085     // co-terminal free run. This is done in the SweepClosure
6086     // destructor; so, do not remove this scope, else the
6087     // end-of-sweep-census below will be off by a little bit.
6088   }
6089   gen->cmsSpace()->sweep_completed();
6090   gen->cmsSpace()->endSweepFLCensus(sweep_count());
6091   if (should_unload_classes()) {                // unloaded classes this cycle,
6092     _concurrent_cycles_since_last_unload = 0;   // ... reset count
6093   } else {                                      // did not unload classes,
6094     _concurrent_cycles_since_last_unload++;     // ... increment count
6095   }
6096 }
6097 
6098 // Reset CMS data structures (for now just the marking bit map)
6099 // preparatory for the next cycle.
6100 void CMSCollector::reset(bool asynch) {
6101   GenCollectedHeap* gch = GenCollectedHeap::heap();
6102   CMSAdaptiveSizePolicy* sp = size_policy();
6103   AdaptiveSizePolicyOutput(sp, gch->total_collections());
6104   if (asynch) {
6105     CMSTokenSyncWithLocks ts(true, bitMapLock());
6106 
6107     // If the state is not "Resetting", the foreground  thread
6108     // has done a collection and the resetting.
6109     if (_collectorState != Resetting) {
6110       assert(_collectorState == Idling, "The state should only change"
6111         " because the foreground collector has finished the collection");
6112       return;
6113     }
6114 
6115     // Clear the mark bitmap (no grey objects to start with)
6116     // for the next cycle.
6117     TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6118     CMSPhaseAccounting cmspa(this, "reset", !PrintGCDetails);
6119 
6120     HeapWord* curAddr = _markBitMap.startWord();
6121     while (curAddr < _markBitMap.endWord()) {
6122       size_t remaining  = pointer_delta(_markBitMap.endWord(), curAddr);
6123       MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
6124       _markBitMap.clear_large_range(chunk);
6125       if (ConcurrentMarkSweepThread::should_yield() &&
6126           !foregroundGCIsActive() &&
6127           CMSYield) {
6128         assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6129                "CMS thread should hold CMS token");
6130         assert_lock_strong(bitMapLock());
6131         bitMapLock()->unlock();
6132         ConcurrentMarkSweepThread::desynchronize(true);
6133         ConcurrentMarkSweepThread::acknowledge_yield_request();
6134         stopTimer();
6135         if (PrintCMSStatistics != 0) {
6136           incrementYields();
6137         }
6138         icms_wait();
6139 
6140         // See the comment in coordinator_yield()
6141         for (unsigned i = 0; i < CMSYieldSleepCount &&
6142                          ConcurrentMarkSweepThread::should_yield() &&
6143                          !CMSCollector::foregroundGCIsActive(); ++i) {
6144           os::sleep(Thread::current(), 1, false);
6145           ConcurrentMarkSweepThread::acknowledge_yield_request();
6146         }
6147 
6148         ConcurrentMarkSweepThread::synchronize(true);
6149         bitMapLock()->lock_without_safepoint_check();
6150         startTimer();
6151       }
6152       curAddr = chunk.end();
6153     }
6154     // A successful mostly concurrent collection has been done.
6155     // Because only the full (i.e., concurrent mode failure) collections
6156     // are being measured for gc overhead limits, clean the "near" flag
6157     // and count.
6158     sp->reset_gc_overhead_limit_count();
6159     _collectorState = Idling;
6160   } else {
6161     // already have the lock
6162     assert(_collectorState == Resetting, "just checking");
6163     assert_lock_strong(bitMapLock());
6164     _markBitMap.clear_all();
6165     _collectorState = Idling;
6166   }
6167 
6168   // Stop incremental mode after a cycle completes, so that any future cycles
6169   // are triggered by allocation.
6170   stop_icms();
6171 
6172   NOT_PRODUCT(
6173     if (RotateCMSCollectionTypes) {
6174       _cmsGen->rotate_debug_collection_type();
6175     }
6176   )
6177 }
6178 
6179 void CMSCollector::do_CMS_operation(CMS_op_type op) {
6180   gclog_or_tty->date_stamp(PrintGC && PrintGCDateStamps);
6181   TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6182   TraceTime t("GC", PrintGC, !PrintGCDetails, gclog_or_tty);
6183   TraceCollectorStats tcs(counters());
6184 
6185   switch (op) {
6186     case CMS_op_checkpointRootsInitial: {
6187       checkpointRootsInitial(true);       // asynch
6188       if (PrintGC) {
6189         _cmsGen->printOccupancy("initial-mark");
6190       }
6191       break;
6192     }
6193     case CMS_op_checkpointRootsFinal: {
6194       checkpointRootsFinal(true,    // asynch
6195                            false,   // !clear_all_soft_refs
6196                            false);  // !init_mark_was_synchronous
6197       if (PrintGC) {
6198         _cmsGen->printOccupancy("remark");
6199       }
6200       break;
6201     }
6202     default:
6203       fatal("No such CMS_op");
6204   }
6205 }
6206 
6207 #ifndef PRODUCT
6208 size_t const CMSCollector::skip_header_HeapWords() {
6209   return FreeChunk::header_size();
6210 }
6211 
6212 // Try and collect here conditions that should hold when
6213 // CMS thread is exiting. The idea is that the foreground GC
6214 // thread should not be blocked if it wants to terminate
6215 // the CMS thread and yet continue to run the VM for a while
6216 // after that.
6217 void CMSCollector::verify_ok_to_terminate() const {
6218   assert(Thread::current()->is_ConcurrentGC_thread(),
6219          "should be called by CMS thread");
6220   assert(!_foregroundGCShouldWait, "should be false");
6221   // We could check here that all the various low-level locks
6222   // are not held by the CMS thread, but that is overkill; see
6223   // also CMSThread::verify_ok_to_terminate() where the CGC_lock
6224   // is checked.
6225 }
6226 #endif
6227 
6228 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
6229    assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
6230           "missing Printezis mark?");
6231   HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
6232   size_t size = pointer_delta(nextOneAddr + 1, addr);
6233   assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6234          "alignment problem");
6235   assert(size >= 3, "Necessary for Printezis marks to work");
6236   return size;
6237 }
6238 
6239 // A variant of the above (block_size_using_printezis_bits()) except
6240 // that we return 0 if the P-bits are not yet set.
6241 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
6242   if (_markBitMap.isMarked(addr)) {
6243     assert(_markBitMap.isMarked(addr + 1), "Missing Printezis bit?");
6244     HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
6245     size_t size = pointer_delta(nextOneAddr + 1, addr);
6246     assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6247            "alignment problem");
6248     assert(size >= 3, "Necessary for Printezis marks to work");
6249     return size;
6250   } else {
6251     assert(!_markBitMap.isMarked(addr + 1), "Bit map inconsistency?");
6252     return 0;
6253   }
6254 }
6255 
6256 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
6257   size_t sz = 0;
6258   oop p = (oop)addr;
6259   if (p->klass_or_null() != NULL && p->is_parsable()) {
6260     sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
6261   } else {
6262     sz = block_size_using_printezis_bits(addr);
6263   }
6264   assert(sz > 0, "size must be nonzero");
6265   HeapWord* next_block = addr + sz;
6266   HeapWord* next_card  = (HeapWord*)round_to((uintptr_t)next_block,
6267                                              CardTableModRefBS::card_size);
6268   assert(round_down((uintptr_t)addr,      CardTableModRefBS::card_size) <
6269          round_down((uintptr_t)next_card, CardTableModRefBS::card_size),
6270          "must be different cards");
6271   return next_card;
6272 }
6273 
6274 
6275 // CMS Bit Map Wrapper /////////////////////////////////////////
6276 
6277 // Construct a CMS bit map infrastructure, but don't create the
6278 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
6279 // further below.
6280 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
6281   _bm(),
6282   _shifter(shifter),
6283   _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true) : NULL)
6284 {
6285   _bmStartWord = 0;
6286   _bmWordSize  = 0;
6287 }
6288 
6289 bool CMSBitMap::allocate(MemRegion mr) {
6290   _bmStartWord = mr.start();
6291   _bmWordSize  = mr.word_size();
6292   ReservedSpace brs(ReservedSpace::allocation_align_size_up(
6293                      (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
6294   if (!brs.is_reserved()) {
6295     warning("CMS bit map allocation failure");
6296     return false;
6297   }
6298   // For now we'll just commit all of the bit map up fromt.
6299   // Later on we'll try to be more parsimonious with swap.
6300   if (!_virtual_space.initialize(brs, brs.size())) {
6301     warning("CMS bit map backing store failure");
6302     return false;
6303   }
6304   assert(_virtual_space.committed_size() == brs.size(),
6305          "didn't reserve backing store for all of CMS bit map?");
6306   _bm.set_map((BitMap::bm_word_t*)_virtual_space.low());
6307   assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
6308          _bmWordSize, "inconsistency in bit map sizing");
6309   _bm.set_size(_bmWordSize >> _shifter);
6310 
6311   // bm.clear(); // can we rely on getting zero'd memory? verify below
6312   assert(isAllClear(),
6313          "Expected zero'd memory from ReservedSpace constructor");
6314   assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
6315          "consistency check");
6316   return true;
6317 }
6318 
6319 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
6320   HeapWord *next_addr, *end_addr, *last_addr;
6321   assert_locked();
6322   assert(covers(mr), "out-of-range error");
6323   // XXX assert that start and end are appropriately aligned
6324   for (next_addr = mr.start(), end_addr = mr.end();
6325        next_addr < end_addr; next_addr = last_addr) {
6326     MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
6327     last_addr = dirty_region.end();
6328     if (!dirty_region.is_empty()) {
6329       cl->do_MemRegion(dirty_region);
6330     } else {
6331       assert(last_addr == end_addr, "program logic");
6332       return;
6333     }
6334   }
6335 }
6336 
6337 #ifndef PRODUCT
6338 void CMSBitMap::assert_locked() const {
6339   CMSLockVerifier::assert_locked(lock());
6340 }
6341 
6342 bool CMSBitMap::covers(MemRegion mr) const {
6343   // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
6344   assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
6345          "size inconsistency");
6346   return (mr.start() >= _bmStartWord) &&
6347          (mr.end()   <= endWord());
6348 }
6349 
6350 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
6351     return (start >= _bmStartWord && (start + size) <= endWord());
6352 }
6353 
6354 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
6355   // verify that there are no 1 bits in the interval [left, right)
6356   FalseBitMapClosure falseBitMapClosure;
6357   iterate(&falseBitMapClosure, left, right);
6358 }
6359 
6360 void CMSBitMap::region_invariant(MemRegion mr)
6361 {
6362   assert_locked();
6363   // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
6364   assert(!mr.is_empty(), "unexpected empty region");
6365   assert(covers(mr), "mr should be covered by bit map");
6366   // convert address range into offset range
6367   size_t start_ofs = heapWordToOffset(mr.start());
6368   // Make sure that end() is appropriately aligned
6369   assert(mr.end() == (HeapWord*)round_to((intptr_t)mr.end(),
6370                         (1 << (_shifter+LogHeapWordSize))),
6371          "Misaligned mr.end()");
6372   size_t end_ofs   = heapWordToOffset(mr.end());
6373   assert(end_ofs > start_ofs, "Should mark at least one bit");
6374 }
6375 
6376 #endif
6377 
6378 bool CMSMarkStack::allocate(size_t size) {
6379   // allocate a stack of the requisite depth
6380   ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6381                    size * sizeof(oop)));
6382   if (!rs.is_reserved()) {
6383     warning("CMSMarkStack allocation failure");
6384     return false;
6385   }
6386   if (!_virtual_space.initialize(rs, rs.size())) {
6387     warning("CMSMarkStack backing store failure");
6388     return false;
6389   }
6390   assert(_virtual_space.committed_size() == rs.size(),
6391          "didn't reserve backing store for all of CMS stack?");
6392   _base = (oop*)(_virtual_space.low());
6393   _index = 0;
6394   _capacity = size;
6395   NOT_PRODUCT(_max_depth = 0);
6396   return true;
6397 }
6398 
6399 // XXX FIX ME !!! In the MT case we come in here holding a
6400 // leaf lock. For printing we need to take a further lock
6401 // which has lower rank. We need to recallibrate the two
6402 // lock-ranks involved in order to be able to rpint the
6403 // messages below. (Or defer the printing to the caller.
6404 // For now we take the expedient path of just disabling the
6405 // messages for the problematic case.)
6406 void CMSMarkStack::expand() {
6407   assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted");
6408   if (_capacity == MarkStackSizeMax) {
6409     if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6410       // We print a warning message only once per CMS cycle.
6411       gclog_or_tty->print_cr(" (benign) Hit CMSMarkStack max size limit");
6412     }
6413     return;
6414   }
6415   // Double capacity if possible
6416   size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax);
6417   // Do not give up existing stack until we have managed to
6418   // get the double capacity that we desired.
6419   ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6420                    new_capacity * sizeof(oop)));
6421   if (rs.is_reserved()) {
6422     // Release the backing store associated with old stack
6423     _virtual_space.release();
6424     // Reinitialize virtual space for new stack
6425     if (!_virtual_space.initialize(rs, rs.size())) {
6426       fatal("Not enough swap for expanded marking stack");
6427     }
6428     _base = (oop*)(_virtual_space.low());
6429     _index = 0;
6430     _capacity = new_capacity;
6431   } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6432     // Failed to double capacity, continue;
6433     // we print a detail message only once per CMS cycle.
6434     gclog_or_tty->print(" (benign) Failed to expand marking stack from "SIZE_FORMAT"K to "
6435             SIZE_FORMAT"K",
6436             _capacity / K, new_capacity / K);
6437   }
6438 }
6439 
6440 
6441 // Closures
6442 // XXX: there seems to be a lot of code  duplication here;
6443 // should refactor and consolidate common code.
6444 
6445 // This closure is used to mark refs into the CMS generation in
6446 // the CMS bit map. Called at the first checkpoint. This closure
6447 // assumes that we do not need to re-mark dirty cards; if the CMS
6448 // generation on which this is used is not an oldest (modulo perm gen)
6449 // generation then this will lose younger_gen cards!
6450 
6451 MarkRefsIntoClosure::MarkRefsIntoClosure(
6452   MemRegion span, CMSBitMap* bitMap):
6453     _span(span),
6454     _bitMap(bitMap)
6455 {
6456     assert(_ref_processor == NULL, "deliberately left NULL");
6457     assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6458 }
6459 
6460 void MarkRefsIntoClosure::do_oop(oop obj) {
6461   // if p points into _span, then mark corresponding bit in _markBitMap
6462   assert(obj->is_oop(), "expected an oop");
6463   HeapWord* addr = (HeapWord*)obj;
6464   if (_span.contains(addr)) {
6465     // this should be made more efficient
6466     _bitMap->mark(addr);
6467   }
6468 }
6469 
6470 void MarkRefsIntoClosure::do_oop(oop* p)       { MarkRefsIntoClosure::do_oop_work(p); }
6471 void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6472 
6473 // A variant of the above, used for CMS marking verification.
6474 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
6475   MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm):
6476     _span(span),
6477     _verification_bm(verification_bm),
6478     _cms_bm(cms_bm)
6479 {
6480     assert(_ref_processor == NULL, "deliberately left NULL");
6481     assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
6482 }
6483 
6484 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
6485   // if p points into _span, then mark corresponding bit in _markBitMap
6486   assert(obj->is_oop(), "expected an oop");
6487   HeapWord* addr = (HeapWord*)obj;
6488   if (_span.contains(addr)) {
6489     _verification_bm->mark(addr);
6490     if (!_cms_bm->isMarked(addr)) {
6491       oop(addr)->print();
6492       gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)", addr);
6493       fatal("... aborting");
6494     }
6495   }
6496 }
6497 
6498 void MarkRefsIntoVerifyClosure::do_oop(oop* p)       { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6499 void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6500 
6501 //////////////////////////////////////////////////
6502 // MarkRefsIntoAndScanClosure
6503 //////////////////////////////////////////////////
6504 
6505 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
6506                                                        ReferenceProcessor* rp,
6507                                                        CMSBitMap* bit_map,
6508                                                        CMSBitMap* mod_union_table,
6509                                                        CMSMarkStack*  mark_stack,
6510                                                        CMSMarkStack*  revisit_stack,
6511                                                        CMSCollector* collector,
6512                                                        bool should_yield,
6513                                                        bool concurrent_precleaning):
6514   _collector(collector),
6515   _span(span),
6516   _bit_map(bit_map),
6517   _mark_stack(mark_stack),
6518   _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table,
6519                       mark_stack, revisit_stack, concurrent_precleaning),
6520   _yield(should_yield),
6521   _concurrent_precleaning(concurrent_precleaning),
6522   _freelistLock(NULL)
6523 {
6524   _ref_processor = rp;
6525   assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6526 }
6527 
6528 // This closure is used to mark refs into the CMS generation at the
6529 // second (final) checkpoint, and to scan and transitively follow
6530 // the unmarked oops. It is also used during the concurrent precleaning
6531 // phase while scanning objects on dirty cards in the CMS generation.
6532 // The marks are made in the marking bit map and the marking stack is
6533 // used for keeping the (newly) grey objects during the scan.
6534 // The parallel version (Par_...) appears further below.
6535 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6536   if (obj != NULL) {
6537     assert(obj->is_oop(), "expected an oop");
6538     HeapWord* addr = (HeapWord*)obj;
6539     assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6540     assert(_collector->overflow_list_is_empty(),
6541            "overflow list should be empty");
6542     if (_span.contains(addr) &&
6543         !_bit_map->isMarked(addr)) {
6544       // mark bit map (object is now grey)
6545       _bit_map->mark(addr);
6546       // push on marking stack (stack should be empty), and drain the
6547       // stack by applying this closure to the oops in the oops popped
6548       // from the stack (i.e. blacken the grey objects)
6549       bool res = _mark_stack->push(obj);
6550       assert(res, "Should have space to push on empty stack");
6551       do {
6552         oop new_oop = _mark_stack->pop();
6553         assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6554         assert(new_oop->is_parsable(), "Found unparsable oop");
6555         assert(_bit_map->isMarked((HeapWord*)new_oop),
6556                "only grey objects on this stack");
6557         // iterate over the oops in this oop, marking and pushing
6558         // the ones in CMS heap (i.e. in _span).
6559         new_oop->oop_iterate(&_pushAndMarkClosure);
6560         // check if it's time to yield
6561         do_yield_check();
6562       } while (!_mark_stack->isEmpty() ||
6563                (!_concurrent_precleaning && take_from_overflow_list()));
6564         // if marking stack is empty, and we are not doing this
6565         // during precleaning, then check the overflow list
6566     }
6567     assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6568     assert(_collector->overflow_list_is_empty(),
6569            "overflow list was drained above");
6570     // We could restore evacuated mark words, if any, used for
6571     // overflow list links here because the overflow list is
6572     // provably empty here. That would reduce the maximum
6573     // size requirements for preserved_{oop,mark}_stack.
6574     // But we'll just postpone it until we are all done
6575     // so we can just stream through.
6576     if (!_concurrent_precleaning && CMSOverflowEarlyRestoration) {
6577       _collector->restore_preserved_marks_if_any();
6578       assert(_collector->no_preserved_marks(), "No preserved marks");
6579     }
6580     assert(!CMSOverflowEarlyRestoration || _collector->no_preserved_marks(),
6581            "All preserved marks should have been restored above");
6582   }
6583 }
6584 
6585 void MarkRefsIntoAndScanClosure::do_oop(oop* p)       { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6586 void MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6587 
6588 void MarkRefsIntoAndScanClosure::do_yield_work() {
6589   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6590          "CMS thread should hold CMS token");
6591   assert_lock_strong(_freelistLock);
6592   assert_lock_strong(_bit_map->lock());
6593   // relinquish the free_list_lock and bitMaplock()
6594   DEBUG_ONLY(RememberKlassesChecker mux(false);)
6595   _bit_map->lock()->unlock();
6596   _freelistLock->unlock();
6597   ConcurrentMarkSweepThread::desynchronize(true);
6598   ConcurrentMarkSweepThread::acknowledge_yield_request();
6599   _collector->stopTimer();
6600   GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
6601   if (PrintCMSStatistics != 0) {
6602     _collector->incrementYields();
6603   }
6604   _collector->icms_wait();
6605 
6606   // See the comment in coordinator_yield()
6607   for (unsigned i = 0;
6608        i < CMSYieldSleepCount &&
6609        ConcurrentMarkSweepThread::should_yield() &&
6610        !CMSCollector::foregroundGCIsActive();
6611        ++i) {
6612     os::sleep(Thread::current(), 1, false);
6613     ConcurrentMarkSweepThread::acknowledge_yield_request();
6614   }
6615 
6616   ConcurrentMarkSweepThread::synchronize(true);
6617   _freelistLock->lock_without_safepoint_check();
6618   _bit_map->lock()->lock_without_safepoint_check();
6619   _collector->startTimer();
6620 }
6621 
6622 ///////////////////////////////////////////////////////////
6623 // Par_MarkRefsIntoAndScanClosure: a parallel version of
6624 //                                 MarkRefsIntoAndScanClosure
6625 ///////////////////////////////////////////////////////////
6626 Par_MarkRefsIntoAndScanClosure::Par_MarkRefsIntoAndScanClosure(
6627   CMSCollector* collector, MemRegion span, ReferenceProcessor* rp,
6628   CMSBitMap* bit_map, OopTaskQueue* work_queue, CMSMarkStack*  revisit_stack):
6629   _span(span),
6630   _bit_map(bit_map),
6631   _work_queue(work_queue),
6632   _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
6633                        (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads))),
6634   _par_pushAndMarkClosure(collector, span, rp, bit_map, work_queue,
6635                           revisit_stack)
6636 {
6637   _ref_processor = rp;
6638   assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6639 }
6640 
6641 // This closure is used to mark refs into the CMS generation at the
6642 // second (final) checkpoint, and to scan and transitively follow
6643 // the unmarked oops. The marks are made in the marking bit map and
6644 // the work_queue is used for keeping the (newly) grey objects during
6645 // the scan phase whence they are also available for stealing by parallel
6646 // threads. Since the marking bit map is shared, updates are
6647 // synchronized (via CAS).
6648 void Par_MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6649   if (obj != NULL) {
6650     // Ignore mark word because this could be an already marked oop
6651     // that may be chained at the end of the overflow list.
6652     assert(obj->is_oop(true), "expected an oop");
6653     HeapWord* addr = (HeapWord*)obj;
6654     if (_span.contains(addr) &&
6655         !_bit_map->isMarked(addr)) {
6656       // mark bit map (object will become grey):
6657       // It is possible for several threads to be
6658       // trying to "claim" this object concurrently;
6659       // the unique thread that succeeds in marking the
6660       // object first will do the subsequent push on
6661       // to the work queue (or overflow list).
6662       if (_bit_map->par_mark(addr)) {
6663         // push on work_queue (which may not be empty), and trim the
6664         // queue to an appropriate length by applying this closure to
6665         // the oops in the oops popped from the stack (i.e. blacken the
6666         // grey objects)
6667         bool res = _work_queue->push(obj);
6668         assert(res, "Low water mark should be less than capacity?");
6669         trim_queue(_low_water_mark);
6670       } // Else, another thread claimed the object
6671     }
6672   }
6673 }
6674 
6675 void Par_MarkRefsIntoAndScanClosure::do_oop(oop* p)       { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6676 void Par_MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6677 
6678 // This closure is used to rescan the marked objects on the dirty cards
6679 // in the mod union table and the card table proper.
6680 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
6681   oop p, MemRegion mr) {
6682 
6683   size_t size = 0;
6684   HeapWord* addr = (HeapWord*)p;
6685   DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6686   assert(_span.contains(addr), "we are scanning the CMS generation");
6687   // check if it's time to yield
6688   if (do_yield_check()) {
6689     // We yielded for some foreground stop-world work,
6690     // and we have been asked to abort this ongoing preclean cycle.
6691     return 0;
6692   }
6693   if (_bitMap->isMarked(addr)) {
6694     // it's marked; is it potentially uninitialized?
6695     if (p->klass_or_null() != NULL) {
6696       // If is_conc_safe is false, the object may be undergoing
6697       // change by the VM outside a safepoint.  Don't try to
6698       // scan it, but rather leave it for the remark phase.
6699       if (CMSPermGenPrecleaningEnabled &&
6700           (!p->is_conc_safe() || !p->is_parsable())) {
6701         // Signal precleaning to redirty the card since
6702         // the klass pointer is already installed.
6703         assert(size == 0, "Initial value");
6704       } else {
6705         assert(p->is_parsable(), "must be parsable.");
6706         // an initialized object; ignore mark word in verification below
6707         // since we are running concurrent with mutators
6708         assert(p->is_oop(true), "should be an oop");
6709         if (p->is_objArray()) {
6710           // objArrays are precisely marked; restrict scanning
6711           // to dirty cards only.
6712           size = CompactibleFreeListSpace::adjustObjectSize(
6713                    p->oop_iterate(_scanningClosure, mr));
6714         } else {
6715           // A non-array may have been imprecisely marked; we need
6716           // to scan object in its entirety.
6717           size = CompactibleFreeListSpace::adjustObjectSize(
6718                    p->oop_iterate(_scanningClosure));
6719         }
6720         #ifdef DEBUG
6721           size_t direct_size =
6722             CompactibleFreeListSpace::adjustObjectSize(p->size());
6723           assert(size == direct_size, "Inconsistency in size");
6724           assert(size >= 3, "Necessary for Printezis marks to work");
6725           if (!_bitMap->isMarked(addr+1)) {
6726             _bitMap->verifyNoOneBitsInRange(addr+2, addr+size);
6727           } else {
6728             _bitMap->verifyNoOneBitsInRange(addr+2, addr+size-1);
6729             assert(_bitMap->isMarked(addr+size-1),
6730                    "inconsistent Printezis mark");
6731           }
6732         #endif // DEBUG
6733       }
6734     } else {
6735       // an unitialized object
6736       assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
6737       HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
6738       size = pointer_delta(nextOneAddr + 1, addr);
6739       assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6740              "alignment problem");
6741       // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
6742       // will dirty the card when the klass pointer is installed in the
6743       // object (signalling the completion of initialization).
6744     }
6745   } else {
6746     // Either a not yet marked object or an uninitialized object
6747     if (p->klass_or_null() == NULL || !p->is_parsable()) {
6748       // An uninitialized object, skip to the next card, since
6749       // we may not be able to read its P-bits yet.
6750       assert(size == 0, "Initial value");
6751     } else {
6752       // An object not (yet) reached by marking: we merely need to
6753       // compute its size so as to go look at the next block.
6754       assert(p->is_oop(true), "should be an oop");
6755       size = CompactibleFreeListSpace::adjustObjectSize(p->size());
6756     }
6757   }
6758   DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6759   return size;
6760 }
6761 
6762 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
6763   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6764          "CMS thread should hold CMS token");
6765   assert_lock_strong(_freelistLock);
6766   assert_lock_strong(_bitMap->lock());
6767   DEBUG_ONLY(RememberKlassesChecker mux(false);)
6768   // relinquish the free_list_lock and bitMaplock()
6769   _bitMap->lock()->unlock();
6770   _freelistLock->unlock();
6771   ConcurrentMarkSweepThread::desynchronize(true);
6772   ConcurrentMarkSweepThread::acknowledge_yield_request();
6773   _collector->stopTimer();
6774   GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
6775   if (PrintCMSStatistics != 0) {
6776     _collector->incrementYields();
6777   }
6778   _collector->icms_wait();
6779 
6780   // See the comment in coordinator_yield()
6781   for (unsigned i = 0; i < CMSYieldSleepCount &&
6782                    ConcurrentMarkSweepThread::should_yield() &&
6783                    !CMSCollector::foregroundGCIsActive(); ++i) {
6784     os::sleep(Thread::current(), 1, false);
6785     ConcurrentMarkSweepThread::acknowledge_yield_request();
6786   }
6787 
6788   ConcurrentMarkSweepThread::synchronize(true);
6789   _freelistLock->lock_without_safepoint_check();
6790   _bitMap->lock()->lock_without_safepoint_check();
6791   _collector->startTimer();
6792 }
6793 
6794 
6795 //////////////////////////////////////////////////////////////////
6796 // SurvivorSpacePrecleanClosure
6797 //////////////////////////////////////////////////////////////////
6798 // This (single-threaded) closure is used to preclean the oops in
6799 // the survivor spaces.
6800 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
6801 
6802   HeapWord* addr = (HeapWord*)p;
6803   DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6804   assert(!_span.contains(addr), "we are scanning the survivor spaces");
6805   assert(p->klass_or_null() != NULL, "object should be initializd");
6806   assert(p->is_parsable(), "must be parsable.");
6807   // an initialized object; ignore mark word in verification below
6808   // since we are running concurrent with mutators
6809   assert(p->is_oop(true), "should be an oop");
6810   // Note that we do not yield while we iterate over
6811   // the interior oops of p, pushing the relevant ones
6812   // on our marking stack.
6813   size_t size = p->oop_iterate(_scanning_closure);
6814   do_yield_check();
6815   // Observe that below, we do not abandon the preclean
6816   // phase as soon as we should; rather we empty the
6817   // marking stack before returning. This is to satisfy
6818   // some existing assertions. In general, it may be a
6819   // good idea to abort immediately and complete the marking
6820   // from the grey objects at a later time.
6821   while (!_mark_stack->isEmpty()) {
6822     oop new_oop = _mark_stack->pop();
6823     assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6824     assert(new_oop->is_parsable(), "Found unparsable oop");
6825     assert(_bit_map->isMarked((HeapWord*)new_oop),
6826            "only grey objects on this stack");
6827     // iterate over the oops in this oop, marking and pushing
6828     // the ones in CMS heap (i.e. in _span).
6829     new_oop->oop_iterate(_scanning_closure);
6830     // check if it's time to yield
6831     do_yield_check();
6832   }
6833   unsigned int after_count =
6834     GenCollectedHeap::heap()->total_collections();
6835   bool abort = (_before_count != after_count) ||
6836                _collector->should_abort_preclean();
6837   return abort ? 0 : size;
6838 }
6839 
6840 void SurvivorSpacePrecleanClosure::do_yield_work() {
6841   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6842          "CMS thread should hold CMS token");
6843   assert_lock_strong(_bit_map->lock());
6844   DEBUG_ONLY(RememberKlassesChecker smx(false);)
6845   // Relinquish the bit map lock
6846   _bit_map->lock()->unlock();
6847   ConcurrentMarkSweepThread::desynchronize(true);
6848   ConcurrentMarkSweepThread::acknowledge_yield_request();
6849   _collector->stopTimer();
6850   GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
6851   if (PrintCMSStatistics != 0) {
6852     _collector->incrementYields();
6853   }
6854   _collector->icms_wait();
6855 
6856   // See the comment in coordinator_yield()
6857   for (unsigned i = 0; i < CMSYieldSleepCount &&
6858                        ConcurrentMarkSweepThread::should_yield() &&
6859                        !CMSCollector::foregroundGCIsActive(); ++i) {
6860     os::sleep(Thread::current(), 1, false);
6861     ConcurrentMarkSweepThread::acknowledge_yield_request();
6862   }
6863 
6864   ConcurrentMarkSweepThread::synchronize(true);
6865   _bit_map->lock()->lock_without_safepoint_check();
6866   _collector->startTimer();
6867 }
6868 
6869 // This closure is used to rescan the marked objects on the dirty cards
6870 // in the mod union table and the card table proper. In the parallel
6871 // case, although the bitMap is shared, we do a single read so the
6872 // isMarked() query is "safe".
6873 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
6874   // Ignore mark word because we are running concurrent with mutators
6875   assert(p->is_oop_or_null(true), "expected an oop or null");
6876   HeapWord* addr = (HeapWord*)p;
6877   assert(_span.contains(addr), "we are scanning the CMS generation");
6878   bool is_obj_array = false;
6879   #ifdef DEBUG
6880     if (!_parallel) {
6881       assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6882       assert(_collector->overflow_list_is_empty(),
6883              "overflow list should be empty");
6884 
6885     }
6886   #endif // DEBUG
6887   if (_bit_map->isMarked(addr)) {
6888     // Obj arrays are precisely marked, non-arrays are not;
6889     // so we scan objArrays precisely and non-arrays in their
6890     // entirety.
6891     if (p->is_objArray()) {
6892       is_obj_array = true;
6893       if (_parallel) {
6894         p->oop_iterate(_par_scan_closure, mr);
6895       } else {
6896         p->oop_iterate(_scan_closure, mr);
6897       }
6898     } else {
6899       if (_parallel) {
6900         p->oop_iterate(_par_scan_closure);
6901       } else {
6902         p->oop_iterate(_scan_closure);
6903       }
6904     }
6905   }
6906   #ifdef DEBUG
6907     if (!_parallel) {
6908       assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6909       assert(_collector->overflow_list_is_empty(),
6910              "overflow list should be empty");
6911 
6912     }
6913   #endif // DEBUG
6914   return is_obj_array;
6915 }
6916 
6917 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
6918                         MemRegion span,
6919                         CMSBitMap* bitMap, CMSMarkStack*  markStack,
6920                         CMSMarkStack*  revisitStack,
6921                         bool should_yield, bool verifying):
6922   _collector(collector),
6923   _span(span),
6924   _bitMap(bitMap),
6925   _mut(&collector->_modUnionTable),
6926   _markStack(markStack),
6927   _revisitStack(revisitStack),
6928   _yield(should_yield),
6929   _skipBits(0)
6930 {
6931   assert(_markStack->isEmpty(), "stack should be empty");
6932   _finger = _bitMap->startWord();
6933   _threshold = _finger;
6934   assert(_collector->_restart_addr == NULL, "Sanity check");
6935   assert(_span.contains(_finger), "Out of bounds _finger?");
6936   DEBUG_ONLY(_verifying = verifying;)
6937 }
6938 
6939 void MarkFromRootsClosure::reset(HeapWord* addr) {
6940   assert(_markStack->isEmpty(), "would cause duplicates on stack");
6941   assert(_span.contains(addr), "Out of bounds _finger?");
6942   _finger = addr;
6943   _threshold = (HeapWord*)round_to(
6944                  (intptr_t)_finger, CardTableModRefBS::card_size);
6945 }
6946 
6947 // Should revisit to see if this should be restructured for
6948 // greater efficiency.
6949 bool MarkFromRootsClosure::do_bit(size_t offset) {
6950   if (_skipBits > 0) {
6951     _skipBits--;
6952     return true;
6953   }
6954   // convert offset into a HeapWord*
6955   HeapWord* addr = _bitMap->startWord() + offset;
6956   assert(_bitMap->endWord() && addr < _bitMap->endWord(),
6957          "address out of range");
6958   assert(_bitMap->isMarked(addr), "tautology");
6959   if (_bitMap->isMarked(addr+1)) {
6960     // this is an allocated but not yet initialized object
6961     assert(_skipBits == 0, "tautology");
6962     _skipBits = 2;  // skip next two marked bits ("Printezis-marks")
6963     oop p = oop(addr);
6964     if (p->klass_or_null() == NULL || !p->is_parsable()) {
6965       DEBUG_ONLY(if (!_verifying) {)
6966         // We re-dirty the cards on which this object lies and increase
6967         // the _threshold so that we'll come back to scan this object
6968         // during the preclean or remark phase. (CMSCleanOnEnter)
6969         if (CMSCleanOnEnter) {
6970           size_t sz = _collector->block_size_using_printezis_bits(addr);
6971           HeapWord* end_card_addr   = (HeapWord*)round_to(
6972                                          (intptr_t)(addr+sz), CardTableModRefBS::card_size);
6973           MemRegion redirty_range = MemRegion(addr, end_card_addr);
6974           assert(!redirty_range.is_empty(), "Arithmetical tautology");
6975           // Bump _threshold to end_card_addr; note that
6976           // _threshold cannot possibly exceed end_card_addr, anyhow.
6977           // This prevents future clearing of the card as the scan proceeds
6978           // to the right.
6979           assert(_threshold <= end_card_addr,
6980                  "Because we are just scanning into this object");
6981           if (_threshold < end_card_addr) {
6982             _threshold = end_card_addr;
6983           }
6984           if (p->klass_or_null() != NULL) {
6985             // Redirty the range of cards...
6986             _mut->mark_range(redirty_range);
6987           } // ...else the setting of klass will dirty the card anyway.
6988         }
6989       DEBUG_ONLY(})
6990       return true;
6991     }
6992   }
6993   scanOopsInOop(addr);
6994   return true;
6995 }
6996 
6997 // We take a break if we've been at this for a while,
6998 // so as to avoid monopolizing the locks involved.
6999 void MarkFromRootsClosure::do_yield_work() {
7000   // First give up the locks, then yield, then re-lock
7001   // We should probably use a constructor/destructor idiom to
7002   // do this unlock/lock or modify the MutexUnlocker class to
7003   // serve our purpose. XXX
7004   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7005          "CMS thread should hold CMS token");
7006   assert_lock_strong(_bitMap->lock());
7007   DEBUG_ONLY(RememberKlassesChecker mux(false);)
7008   _bitMap->lock()->unlock();
7009   ConcurrentMarkSweepThread::desynchronize(true);
7010   ConcurrentMarkSweepThread::acknowledge_yield_request();
7011   _collector->stopTimer();
7012   GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7013   if (PrintCMSStatistics != 0) {
7014     _collector->incrementYields();
7015   }
7016   _collector->icms_wait();
7017 
7018   // See the comment in coordinator_yield()
7019   for (unsigned i = 0; i < CMSYieldSleepCount &&
7020                        ConcurrentMarkSweepThread::should_yield() &&
7021                        !CMSCollector::foregroundGCIsActive(); ++i) {
7022     os::sleep(Thread::current(), 1, false);
7023     ConcurrentMarkSweepThread::acknowledge_yield_request();
7024   }
7025 
7026   ConcurrentMarkSweepThread::synchronize(true);
7027   _bitMap->lock()->lock_without_safepoint_check();
7028   _collector->startTimer();
7029 }
7030 
7031 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
7032   assert(_bitMap->isMarked(ptr), "expected bit to be set");
7033   assert(_markStack->isEmpty(),
7034          "should drain stack to limit stack usage");
7035   // convert ptr to an oop preparatory to scanning
7036   oop obj = oop(ptr);
7037   // Ignore mark word in verification below, since we
7038   // may be running concurrent with mutators.
7039   assert(obj->is_oop(true), "should be an oop");
7040   assert(_finger <= ptr, "_finger runneth ahead");
7041   // advance the finger to right end of this object
7042   _finger = ptr + obj->size();
7043   assert(_finger > ptr, "we just incremented it above");
7044   // On large heaps, it may take us some time to get through
7045   // the marking phase (especially if running iCMS). During
7046   // this time it's possible that a lot of mutations have
7047   // accumulated in the card table and the mod union table --
7048   // these mutation records are redundant until we have
7049   // actually traced into the corresponding card.
7050   // Here, we check whether advancing the finger would make
7051   // us cross into a new card, and if so clear corresponding
7052   // cards in the MUT (preclean them in the card-table in the
7053   // future).
7054 
7055   DEBUG_ONLY(if (!_verifying) {)
7056     // The clean-on-enter optimization is disabled by default,
7057     // until we fix 6178663.
7058     if (CMSCleanOnEnter && (_finger > _threshold)) {
7059       // [_threshold, _finger) represents the interval
7060       // of cards to be cleared  in MUT (or precleaned in card table).
7061       // The set of cards to be cleared is all those that overlap
7062       // with the interval [_threshold, _finger); note that
7063       // _threshold is always kept card-aligned but _finger isn't
7064       // always card-aligned.
7065       HeapWord* old_threshold = _threshold;
7066       assert(old_threshold == (HeapWord*)round_to(
7067               (intptr_t)old_threshold, CardTableModRefBS::card_size),
7068              "_threshold should always be card-aligned");
7069       _threshold = (HeapWord*)round_to(
7070                      (intptr_t)_finger, CardTableModRefBS::card_size);
7071       MemRegion mr(old_threshold, _threshold);
7072       assert(!mr.is_empty(), "Control point invariant");
7073       assert(_span.contains(mr), "Should clear within span");
7074       // XXX When _finger crosses from old gen into perm gen
7075       // we may be doing unnecessary cleaning; do better in the
7076       // future by detecting that condition and clearing fewer
7077       // MUT/CT entries.
7078       _mut->clear_range(mr);
7079     }
7080   DEBUG_ONLY(})
7081   // Note: the finger doesn't advance while we drain
7082   // the stack below.
7083   PushOrMarkClosure pushOrMarkClosure(_collector,
7084                                       _span, _bitMap, _markStack,
7085                                       _revisitStack,
7086                                       _finger, this);
7087   bool res = _markStack->push(obj);
7088   assert(res, "Empty non-zero size stack should have space for single push");
7089   while (!_markStack->isEmpty()) {
7090     oop new_oop = _markStack->pop();
7091     // Skip verifying header mark word below because we are
7092     // running concurrent with mutators.
7093     assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
7094     // now scan this oop's oops
7095     new_oop->oop_iterate(&pushOrMarkClosure);
7096     do_yield_check();
7097   }
7098   assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
7099 }
7100 
7101 Par_MarkFromRootsClosure::Par_MarkFromRootsClosure(CMSConcMarkingTask* task,
7102                        CMSCollector* collector, MemRegion span,
7103                        CMSBitMap* bit_map,
7104                        OopTaskQueue* work_queue,
7105                        CMSMarkStack*  overflow_stack,
7106                        CMSMarkStack*  revisit_stack,
7107                        bool should_yield):
7108   _collector(collector),
7109   _whole_span(collector->_span),
7110   _span(span),
7111   _bit_map(bit_map),
7112   _mut(&collector->_modUnionTable),
7113   _work_queue(work_queue),
7114   _overflow_stack(overflow_stack),
7115   _revisit_stack(revisit_stack),
7116   _yield(should_yield),
7117   _skip_bits(0),
7118   _task(task)
7119 {
7120   assert(_work_queue->size() == 0, "work_queue should be empty");
7121   _finger = span.start();
7122   _threshold = _finger;     // XXX Defer clear-on-enter optimization for now
7123   assert(_span.contains(_finger), "Out of bounds _finger?");
7124 }
7125 
7126 // Should revisit to see if this should be restructured for
7127 // greater efficiency.
7128 bool Par_MarkFromRootsClosure::do_bit(size_t offset) {
7129   if (_skip_bits > 0) {
7130     _skip_bits--;
7131     return true;
7132   }
7133   // convert offset into a HeapWord*
7134   HeapWord* addr = _bit_map->startWord() + offset;
7135   assert(_bit_map->endWord() && addr < _bit_map->endWord(),
7136          "address out of range");
7137   assert(_bit_map->isMarked(addr), "tautology");
7138   if (_bit_map->isMarked(addr+1)) {
7139     // this is an allocated object that might not yet be initialized
7140     assert(_skip_bits == 0, "tautology");
7141     _skip_bits = 2;  // skip next two marked bits ("Printezis-marks")
7142     oop p = oop(addr);
7143     if (p->klass_or_null() == NULL || !p->is_parsable()) {
7144       // in the case of Clean-on-Enter optimization, redirty card
7145       // and avoid clearing card by increasing  the threshold.
7146       return true;
7147     }
7148   }
7149   scan_oops_in_oop(addr);
7150   return true;
7151 }
7152 
7153 void Par_MarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
7154   assert(_bit_map->isMarked(ptr), "expected bit to be set");
7155   // Should we assert that our work queue is empty or
7156   // below some drain limit?
7157   assert(_work_queue->size() == 0,
7158          "should drain stack to limit stack usage");
7159   // convert ptr to an oop preparatory to scanning
7160   oop obj = oop(ptr);
7161   // Ignore mark word in verification below, since we
7162   // may be running concurrent with mutators.
7163   assert(obj->is_oop(true), "should be an oop");
7164   assert(_finger <= ptr, "_finger runneth ahead");
7165   // advance the finger to right end of this object
7166   _finger = ptr + obj->size();
7167   assert(_finger > ptr, "we just incremented it above");
7168   // On large heaps, it may take us some time to get through
7169   // the marking phase (especially if running iCMS). During
7170   // this time it's possible that a lot of mutations have
7171   // accumulated in the card table and the mod union table --
7172   // these mutation records are redundant until we have
7173   // actually traced into the corresponding card.
7174   // Here, we check whether advancing the finger would make
7175   // us cross into a new card, and if so clear corresponding
7176   // cards in the MUT (preclean them in the card-table in the
7177   // future).
7178 
7179   // The clean-on-enter optimization is disabled by default,
7180   // until we fix 6178663.
7181   if (CMSCleanOnEnter && (_finger > _threshold)) {
7182     // [_threshold, _finger) represents the interval
7183     // of cards to be cleared  in MUT (or precleaned in card table).
7184     // The set of cards to be cleared is all those that overlap
7185     // with the interval [_threshold, _finger); note that
7186     // _threshold is always kept card-aligned but _finger isn't
7187     // always card-aligned.
7188     HeapWord* old_threshold = _threshold;
7189     assert(old_threshold == (HeapWord*)round_to(
7190             (intptr_t)old_threshold, CardTableModRefBS::card_size),
7191            "_threshold should always be card-aligned");
7192     _threshold = (HeapWord*)round_to(
7193                    (intptr_t)_finger, CardTableModRefBS::card_size);
7194     MemRegion mr(old_threshold, _threshold);
7195     assert(!mr.is_empty(), "Control point invariant");
7196     assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
7197     // XXX When _finger crosses from old gen into perm gen
7198     // we may be doing unnecessary cleaning; do better in the
7199     // future by detecting that condition and clearing fewer
7200     // MUT/CT entries.
7201     _mut->clear_range(mr);
7202   }
7203 
7204   // Note: the local finger doesn't advance while we drain
7205   // the stack below, but the global finger sure can and will.
7206   HeapWord** gfa = _task->global_finger_addr();
7207   Par_PushOrMarkClosure pushOrMarkClosure(_collector,
7208                                       _span, _bit_map,
7209                                       _work_queue,
7210                                       _overflow_stack,
7211                                       _revisit_stack,
7212                                       _finger,
7213                                       gfa, this);
7214   bool res = _work_queue->push(obj);   // overflow could occur here
7215   assert(res, "Will hold once we use workqueues");
7216   while (true) {
7217     oop new_oop;
7218     if (!_work_queue->pop_local(new_oop)) {
7219       // We emptied our work_queue; check if there's stuff that can
7220       // be gotten from the overflow stack.
7221       if (CMSConcMarkingTask::get_work_from_overflow_stack(
7222             _overflow_stack, _work_queue)) {
7223         do_yield_check();
7224         continue;
7225       } else {  // done
7226         break;
7227       }
7228     }
7229     // Skip verifying header mark word below because we are
7230     // running concurrent with mutators.
7231     assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
7232     // now scan this oop's oops
7233     new_oop->oop_iterate(&pushOrMarkClosure);
7234     do_yield_check();
7235   }
7236   assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
7237 }
7238 
7239 // Yield in response to a request from VM Thread or
7240 // from mutators.
7241 void Par_MarkFromRootsClosure::do_yield_work() {
7242   assert(_task != NULL, "sanity");
7243   _task->yield();
7244 }
7245 
7246 // A variant of the above used for verifying CMS marking work.
7247 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
7248                         MemRegion span,
7249                         CMSBitMap* verification_bm, CMSBitMap* cms_bm,
7250                         CMSMarkStack*  mark_stack):
7251   _collector(collector),
7252   _span(span),
7253   _verification_bm(verification_bm),
7254   _cms_bm(cms_bm),
7255   _mark_stack(mark_stack),
7256   _pam_verify_closure(collector, span, verification_bm, cms_bm,
7257                       mark_stack)
7258 {
7259   assert(_mark_stack->isEmpty(), "stack should be empty");
7260   _finger = _verification_bm->startWord();
7261   assert(_collector->_restart_addr == NULL, "Sanity check");
7262   assert(_span.contains(_finger), "Out of bounds _finger?");
7263 }
7264 
7265 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
7266   assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
7267   assert(_span.contains(addr), "Out of bounds _finger?");
7268   _finger = addr;
7269 }
7270 
7271 // Should revisit to see if this should be restructured for
7272 // greater efficiency.
7273 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
7274   // convert offset into a HeapWord*
7275   HeapWord* addr = _verification_bm->startWord() + offset;
7276   assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
7277          "address out of range");
7278   assert(_verification_bm->isMarked(addr), "tautology");
7279   assert(_cms_bm->isMarked(addr), "tautology");
7280 
7281   assert(_mark_stack->isEmpty(),
7282          "should drain stack to limit stack usage");
7283   // convert addr to an oop preparatory to scanning
7284   oop obj = oop(addr);
7285   assert(obj->is_oop(), "should be an oop");
7286   assert(_finger <= addr, "_finger runneth ahead");
7287   // advance the finger to right end of this object
7288   _finger = addr + obj->size();
7289   assert(_finger > addr, "we just incremented it above");
7290   // Note: the finger doesn't advance while we drain
7291   // the stack below.
7292   bool res = _mark_stack->push(obj);
7293   assert(res, "Empty non-zero size stack should have space for single push");
7294   while (!_mark_stack->isEmpty()) {
7295     oop new_oop = _mark_stack->pop();
7296     assert(new_oop->is_oop(), "Oops! expected to pop an oop");
7297     // now scan this oop's oops
7298     new_oop->oop_iterate(&_pam_verify_closure);
7299   }
7300   assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
7301   return true;
7302 }
7303 
7304 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
7305   CMSCollector* collector, MemRegion span,
7306   CMSBitMap* verification_bm, CMSBitMap* cms_bm,
7307   CMSMarkStack*  mark_stack):
7308   OopClosure(collector->ref_processor()),
7309   _collector(collector),
7310   _span(span),
7311   _verification_bm(verification_bm),
7312   _cms_bm(cms_bm),
7313   _mark_stack(mark_stack)
7314 { }
7315 
7316 void PushAndMarkVerifyClosure::do_oop(oop* p)       { PushAndMarkVerifyClosure::do_oop_work(p); }
7317 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
7318 
7319 // Upon stack overflow, we discard (part of) the stack,
7320 // remembering the least address amongst those discarded
7321 // in CMSCollector's _restart_address.
7322 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
7323   // Remember the least grey address discarded
7324   HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
7325   _collector->lower_restart_addr(ra);
7326   _mark_stack->reset();  // discard stack contents
7327   _mark_stack->expand(); // expand the stack if possible
7328 }
7329 
7330 void PushAndMarkVerifyClosure::do_oop(oop obj) {
7331   assert(obj->is_oop_or_null(), "expected an oop or NULL");
7332   HeapWord* addr = (HeapWord*)obj;
7333   if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
7334     // Oop lies in _span and isn't yet grey or black
7335     _verification_bm->mark(addr);            // now grey
7336     if (!_cms_bm->isMarked(addr)) {
7337       oop(addr)->print();
7338       gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)",
7339                              addr);
7340       fatal("... aborting");
7341     }
7342 
7343     if (!_mark_stack->push(obj)) { // stack overflow
7344       if (PrintCMSStatistics != 0) {
7345         gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7346                                SIZE_FORMAT, _mark_stack->capacity());
7347       }
7348       assert(_mark_stack->isFull(), "Else push should have succeeded");
7349       handle_stack_overflow(addr);
7350     }
7351     // anything including and to the right of _finger
7352     // will be scanned as we iterate over the remainder of the
7353     // bit map
7354   }
7355 }
7356 
7357 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
7358                      MemRegion span,
7359                      CMSBitMap* bitMap, CMSMarkStack*  markStack,
7360                      CMSMarkStack*  revisitStack,
7361                      HeapWord* finger, MarkFromRootsClosure* parent) :
7362   KlassRememberingOopClosure(collector, collector->ref_processor(), revisitStack),
7363   _span(span),
7364   _bitMap(bitMap),
7365   _markStack(markStack),
7366   _finger(finger),
7367   _parent(parent)
7368 { }
7369 
7370 Par_PushOrMarkClosure::Par_PushOrMarkClosure(CMSCollector* collector,
7371                      MemRegion span,
7372                      CMSBitMap* bit_map,
7373                      OopTaskQueue* work_queue,
7374                      CMSMarkStack*  overflow_stack,
7375                      CMSMarkStack*  revisit_stack,
7376                      HeapWord* finger,
7377                      HeapWord** global_finger_addr,
7378                      Par_MarkFromRootsClosure* parent) :
7379   Par_KlassRememberingOopClosure(collector,
7380                             collector->ref_processor(),
7381                             revisit_stack),
7382   _whole_span(collector->_span),
7383   _span(span),
7384   _bit_map(bit_map),
7385   _work_queue(work_queue),
7386   _overflow_stack(overflow_stack),
7387   _finger(finger),
7388   _global_finger_addr(global_finger_addr),
7389   _parent(parent)
7390 { }
7391 
7392 // Assumes thread-safe access by callers, who are
7393 // responsible for mutual exclusion.
7394 void CMSCollector::lower_restart_addr(HeapWord* low) {
7395   assert(_span.contains(low), "Out of bounds addr");
7396   if (_restart_addr == NULL) {
7397     _restart_addr = low;
7398   } else {
7399     _restart_addr = MIN2(_restart_addr, low);
7400   }
7401 }
7402 
7403 // Upon stack overflow, we discard (part of) the stack,
7404 // remembering the least address amongst those discarded
7405 // in CMSCollector's _restart_address.
7406 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7407   // Remember the least grey address discarded
7408   HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
7409   _collector->lower_restart_addr(ra);
7410   _markStack->reset();  // discard stack contents
7411   _markStack->expand(); // expand the stack if possible
7412 }
7413 
7414 // Upon stack overflow, we discard (part of) the stack,
7415 // remembering the least address amongst those discarded
7416 // in CMSCollector's _restart_address.
7417 void Par_PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7418   // We need to do this under a mutex to prevent other
7419   // workers from interfering with the work done below.
7420   MutexLockerEx ml(_overflow_stack->par_lock(),
7421                    Mutex::_no_safepoint_check_flag);
7422   // Remember the least grey address discarded
7423   HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
7424   _collector->lower_restart_addr(ra);
7425   _overflow_stack->reset();  // discard stack contents
7426   _overflow_stack->expand(); // expand the stack if possible
7427 }
7428 
7429 void PushOrMarkClosure::do_oop(oop obj) {
7430   // Ignore mark word because we are running concurrent with mutators.
7431   assert(obj->is_oop_or_null(true), "expected an oop or NULL");
7432   HeapWord* addr = (HeapWord*)obj;
7433   if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
7434     // Oop lies in _span and isn't yet grey or black
7435     _bitMap->mark(addr);            // now grey
7436     if (addr < _finger) {
7437       // the bit map iteration has already either passed, or
7438       // sampled, this bit in the bit map; we'll need to
7439       // use the marking stack to scan this oop's oops.
7440       bool simulate_overflow = false;
7441       NOT_PRODUCT(
7442         if (CMSMarkStackOverflowALot &&
7443             _collector->simulate_overflow()) {
7444           // simulate a stack overflow
7445           simulate_overflow = true;
7446         }
7447       )
7448       if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
7449         if (PrintCMSStatistics != 0) {
7450           gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7451                                  SIZE_FORMAT, _markStack->capacity());
7452         }
7453         assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
7454         handle_stack_overflow(addr);
7455       }
7456     }
7457     // anything including and to the right of _finger
7458     // will be scanned as we iterate over the remainder of the
7459     // bit map
7460     do_yield_check();
7461   }
7462 }
7463 
7464 void PushOrMarkClosure::do_oop(oop* p)       { PushOrMarkClosure::do_oop_work(p); }
7465 void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); }
7466 
7467 void Par_PushOrMarkClosure::do_oop(oop obj) {
7468   // Ignore mark word because we are running concurrent with mutators.
7469   assert(obj->is_oop_or_null(true), "expected an oop or NULL");
7470   HeapWord* addr = (HeapWord*)obj;
7471   if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
7472     // Oop lies in _span and isn't yet grey or black
7473     // We read the global_finger (volatile read) strictly after marking oop
7474     bool res = _bit_map->par_mark(addr);    // now grey
7475     volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
7476     // Should we push this marked oop on our stack?
7477     // -- if someone else marked it, nothing to do
7478     // -- if target oop is above global finger nothing to do
7479     // -- if target oop is in chunk and above local finger
7480     //      then nothing to do
7481     // -- else push on work queue
7482     if (   !res       // someone else marked it, they will deal with it
7483         || (addr >= *gfa)  // will be scanned in a later task
7484         || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
7485       return;
7486     }
7487     // the bit map iteration has already either passed, or
7488     // sampled, this bit in the bit map; we'll need to
7489     // use the marking stack to scan this oop's oops.
7490     bool simulate_overflow = false;
7491     NOT_PRODUCT(
7492       if (CMSMarkStackOverflowALot &&
7493           _collector->simulate_overflow()) {
7494         // simulate a stack overflow
7495         simulate_overflow = true;
7496       }
7497     )
7498     if (simulate_overflow ||
7499         !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
7500       // stack overflow
7501       if (PrintCMSStatistics != 0) {
7502         gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7503                                SIZE_FORMAT, _overflow_stack->capacity());
7504       }
7505       // We cannot assert that the overflow stack is full because
7506       // it may have been emptied since.
7507       assert(simulate_overflow ||
7508              _work_queue->size() == _work_queue->max_elems(),
7509             "Else push should have succeeded");
7510       handle_stack_overflow(addr);
7511     }
7512     do_yield_check();
7513   }
7514 }
7515 
7516 void Par_PushOrMarkClosure::do_oop(oop* p)       { Par_PushOrMarkClosure::do_oop_work(p); }
7517 void Par_PushOrMarkClosure::do_oop(narrowOop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7518 
7519 KlassRememberingOopClosure::KlassRememberingOopClosure(CMSCollector* collector,
7520                                              ReferenceProcessor* rp,
7521                                              CMSMarkStack* revisit_stack) :
7522   OopClosure(rp),
7523   _collector(collector),
7524   _revisit_stack(revisit_stack),
7525   _should_remember_klasses(collector->should_unload_classes()) {}
7526 
7527 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
7528                                        MemRegion span,
7529                                        ReferenceProcessor* rp,
7530                                        CMSBitMap* bit_map,
7531                                        CMSBitMap* mod_union_table,
7532                                        CMSMarkStack*  mark_stack,
7533                                        CMSMarkStack*  revisit_stack,
7534                                        bool           concurrent_precleaning):
7535   KlassRememberingOopClosure(collector, rp, revisit_stack),
7536   _span(span),
7537   _bit_map(bit_map),
7538   _mod_union_table(mod_union_table),
7539   _mark_stack(mark_stack),
7540   _concurrent_precleaning(concurrent_precleaning)
7541 {
7542   assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7543 }
7544 
7545 // Grey object rescan during pre-cleaning and second checkpoint phases --
7546 // the non-parallel version (the parallel version appears further below.)
7547 void PushAndMarkClosure::do_oop(oop obj) {
7548   // Ignore mark word verification. If during concurrent precleaning,
7549   // the object monitor may be locked. If during the checkpoint
7550   // phases, the object may already have been reached by a  different
7551   // path and may be at the end of the global overflow list (so
7552   // the mark word may be NULL).
7553   assert(obj->is_oop_or_null(true /* ignore mark word */),
7554          "expected an oop or NULL");
7555   HeapWord* addr = (HeapWord*)obj;
7556   // Check if oop points into the CMS generation
7557   // and is not marked
7558   if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7559     // a white object ...
7560     _bit_map->mark(addr);         // ... now grey
7561     // push on the marking stack (grey set)
7562     bool simulate_overflow = false;
7563     NOT_PRODUCT(
7564       if (CMSMarkStackOverflowALot &&
7565           _collector->simulate_overflow()) {
7566         // simulate a stack overflow
7567         simulate_overflow = true;
7568       }
7569     )
7570     if (simulate_overflow || !_mark_stack->push(obj)) {
7571       if (_concurrent_precleaning) {
7572          // During precleaning we can just dirty the appropriate card(s)
7573          // in the mod union table, thus ensuring that the object remains
7574          // in the grey set  and continue. In the case of object arrays
7575          // we need to dirty all of the cards that the object spans,
7576          // since the rescan of object arrays will be limited to the
7577          // dirty cards.
7578          // Note that no one can be intefering with us in this action
7579          // of dirtying the mod union table, so no locking or atomics
7580          // are required.
7581          if (obj->is_objArray()) {
7582            size_t sz = obj->size();
7583            HeapWord* end_card_addr = (HeapWord*)round_to(
7584                                         (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7585            MemRegion redirty_range = MemRegion(addr, end_card_addr);
7586            assert(!redirty_range.is_empty(), "Arithmetical tautology");
7587            _mod_union_table->mark_range(redirty_range);
7588          } else {
7589            _mod_union_table->mark(addr);
7590          }
7591          _collector->_ser_pmc_preclean_ovflw++;
7592       } else {
7593          // During the remark phase, we need to remember this oop
7594          // in the overflow list.
7595          _collector->push_on_overflow_list(obj);
7596          _collector->_ser_pmc_remark_ovflw++;
7597       }
7598     }
7599   }
7600 }
7601 
7602 Par_PushAndMarkClosure::Par_PushAndMarkClosure(CMSCollector* collector,
7603                                                MemRegion span,
7604                                                ReferenceProcessor* rp,
7605                                                CMSBitMap* bit_map,
7606                                                OopTaskQueue* work_queue,
7607                                                CMSMarkStack* revisit_stack):
7608   Par_KlassRememberingOopClosure(collector, rp, revisit_stack),
7609   _span(span),
7610   _bit_map(bit_map),
7611   _work_queue(work_queue)
7612 {
7613   assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7614 }
7615 
7616 void PushAndMarkClosure::do_oop(oop* p)       { PushAndMarkClosure::do_oop_work(p); }
7617 void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); }
7618 
7619 // Grey object rescan during second checkpoint phase --
7620 // the parallel version.
7621 void Par_PushAndMarkClosure::do_oop(oop obj) {
7622   // In the assert below, we ignore the mark word because
7623   // this oop may point to an already visited object that is
7624   // on the overflow stack (in which case the mark word has
7625   // been hijacked for chaining into the overflow stack --
7626   // if this is the last object in the overflow stack then
7627   // its mark word will be NULL). Because this object may
7628   // have been subsequently popped off the global overflow
7629   // stack, and the mark word possibly restored to the prototypical
7630   // value, by the time we get to examined this failing assert in
7631   // the debugger, is_oop_or_null(false) may subsequently start
7632   // to hold.
7633   assert(obj->is_oop_or_null(true),
7634          "expected an oop or NULL");
7635   HeapWord* addr = (HeapWord*)obj;
7636   // Check if oop points into the CMS generation
7637   // and is not marked
7638   if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7639     // a white object ...
7640     // If we manage to "claim" the object, by being the
7641     // first thread to mark it, then we push it on our
7642     // marking stack
7643     if (_bit_map->par_mark(addr)) {     // ... now grey
7644       // push on work queue (grey set)
7645       bool simulate_overflow = false;
7646       NOT_PRODUCT(
7647         if (CMSMarkStackOverflowALot &&
7648             _collector->par_simulate_overflow()) {
7649           // simulate a stack overflow
7650           simulate_overflow = true;
7651         }
7652       )
7653       if (simulate_overflow || !_work_queue->push(obj)) {
7654         _collector->par_push_on_overflow_list(obj);
7655         _collector->_par_pmc_remark_ovflw++; //  imprecise OK: no need to CAS
7656       }
7657     } // Else, some other thread got there first
7658   }
7659 }
7660 
7661 void Par_PushAndMarkClosure::do_oop(oop* p)       { Par_PushAndMarkClosure::do_oop_work(p); }
7662 void Par_PushAndMarkClosure::do_oop(narrowOop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7663 
7664 void PushAndMarkClosure::remember_mdo(DataLayout* v) {
7665   // TBD
7666 }
7667 
7668 void Par_PushAndMarkClosure::remember_mdo(DataLayout* v) {
7669   // TBD
7670 }
7671 
7672 void CMSPrecleanRefsYieldClosure::do_yield_work() {
7673   DEBUG_ONLY(RememberKlassesChecker mux(false);)
7674   Mutex* bml = _collector->bitMapLock();
7675   assert_lock_strong(bml);
7676   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7677          "CMS thread should hold CMS token");
7678 
7679   bml->unlock();
7680   ConcurrentMarkSweepThread::desynchronize(true);
7681 
7682   ConcurrentMarkSweepThread::acknowledge_yield_request();
7683 
7684   _collector->stopTimer();
7685   GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7686   if (PrintCMSStatistics != 0) {
7687     _collector->incrementYields();
7688   }
7689   _collector->icms_wait();
7690 
7691   // See the comment in coordinator_yield()
7692   for (unsigned i = 0; i < CMSYieldSleepCount &&
7693                        ConcurrentMarkSweepThread::should_yield() &&
7694                        !CMSCollector::foregroundGCIsActive(); ++i) {
7695     os::sleep(Thread::current(), 1, false);
7696     ConcurrentMarkSweepThread::acknowledge_yield_request();
7697   }
7698 
7699   ConcurrentMarkSweepThread::synchronize(true);
7700   bml->lock();
7701 
7702   _collector->startTimer();
7703 }
7704 
7705 bool CMSPrecleanRefsYieldClosure::should_return() {
7706   if (ConcurrentMarkSweepThread::should_yield()) {
7707     do_yield_work();
7708   }
7709   return _collector->foregroundGCIsActive();
7710 }
7711 
7712 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
7713   assert(((size_t)mr.start())%CardTableModRefBS::card_size_in_words == 0,
7714          "mr should be aligned to start at a card boundary");
7715   // We'd like to assert:
7716   // assert(mr.word_size()%CardTableModRefBS::card_size_in_words == 0,
7717   //        "mr should be a range of cards");
7718   // However, that would be too strong in one case -- the last
7719   // partition ends at _unallocated_block which, in general, can be
7720   // an arbitrary boundary, not necessarily card aligned.
7721   if (PrintCMSStatistics != 0) {
7722     _num_dirty_cards +=
7723          mr.word_size()/CardTableModRefBS::card_size_in_words;
7724   }
7725   _space->object_iterate_mem(mr, &_scan_cl);
7726 }
7727 
7728 SweepClosure::SweepClosure(CMSCollector* collector,
7729                            ConcurrentMarkSweepGeneration* g,
7730                            CMSBitMap* bitMap, bool should_yield) :
7731   _collector(collector),
7732   _g(g),
7733   _sp(g->cmsSpace()),
7734   _limit(_sp->sweep_limit()),
7735   _freelistLock(_sp->freelistLock()),
7736   _bitMap(bitMap),
7737   _yield(should_yield),
7738   _inFreeRange(false),           // No free range at beginning of sweep
7739   _freeRangeInFreeLists(false),  // No free range at beginning of sweep
7740   _lastFreeRangeCoalesced(false),
7741   _freeFinger(g->used_region().start())
7742 {
7743   NOT_PRODUCT(
7744     _numObjectsFreed = 0;
7745     _numWordsFreed   = 0;
7746     _numObjectsLive = 0;
7747     _numWordsLive = 0;
7748     _numObjectsAlreadyFree = 0;
7749     _numWordsAlreadyFree = 0;
7750     _last_fc = NULL;
7751 
7752     _sp->initializeIndexedFreeListArrayReturnedBytes();
7753     _sp->dictionary()->initializeDictReturnedBytes();
7754   )
7755   assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7756          "sweep _limit out of bounds");
7757   if (CMSTraceSweeper) {
7758     gclog_or_tty->print("\n====================\nStarting new sweep\n");
7759   }
7760 }
7761 
7762 // We need this destructor to reclaim any space at the end
7763 // of the space, which do_blk below may not have added back to
7764 // the free lists. [basically dealing with the "fringe effect"]
7765 SweepClosure::~SweepClosure() {
7766   assert_lock_strong(_freelistLock);
7767   // this should be treated as the end of a free run if any
7768   // The current free range should be returned to the free lists
7769   // as one coalesced chunk.
7770   if (inFreeRange()) {
7771     flushCurFreeChunk(freeFinger(),
7772       pointer_delta(_limit, freeFinger()));
7773     assert(freeFinger() < _limit, "the finger pointeth off base");
7774     if (CMSTraceSweeper) {
7775       gclog_or_tty->print("destructor:");
7776       gclog_or_tty->print("Sweep:put_free_blk 0x%x ("SIZE_FORMAT") "
7777                  "[coalesced:"SIZE_FORMAT"]\n",
7778                  freeFinger(), pointer_delta(_limit, freeFinger()),
7779                  lastFreeRangeCoalesced());
7780     }
7781   }
7782   NOT_PRODUCT(
7783     if (Verbose && PrintGC) {
7784       gclog_or_tty->print("Collected "SIZE_FORMAT" objects, "
7785                           SIZE_FORMAT " bytes",
7786                  _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
7787       gclog_or_tty->print_cr("\nLive "SIZE_FORMAT" objects,  "
7788                              SIZE_FORMAT" bytes  "
7789         "Already free "SIZE_FORMAT" objects, "SIZE_FORMAT" bytes",
7790         _numObjectsLive, _numWordsLive*sizeof(HeapWord),
7791         _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
7792       size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree) *
7793         sizeof(HeapWord);
7794       gclog_or_tty->print_cr("Total sweep: "SIZE_FORMAT" bytes", totalBytes);
7795 
7796       if (PrintCMSStatistics && CMSVerifyReturnedBytes) {
7797         size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
7798         size_t dictReturnedBytes = _sp->dictionary()->sumDictReturnedBytes();
7799         size_t returnedBytes = indexListReturnedBytes + dictReturnedBytes;
7800         gclog_or_tty->print("Returned "SIZE_FORMAT" bytes", returnedBytes);
7801         gclog_or_tty->print("   Indexed List Returned "SIZE_FORMAT" bytes",
7802           indexListReturnedBytes);
7803         gclog_or_tty->print_cr("        Dictionary Returned "SIZE_FORMAT" bytes",
7804           dictReturnedBytes);
7805       }
7806     }
7807   )
7808   // Now, in debug mode, just null out the sweep_limit
7809   NOT_PRODUCT(_sp->clear_sweep_limit();)
7810   if (CMSTraceSweeper) {
7811     gclog_or_tty->print("end of sweep\n================\n");
7812   }
7813 }
7814 
7815 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
7816     bool freeRangeInFreeLists) {
7817   if (CMSTraceSweeper) {
7818     gclog_or_tty->print("---- Start free range 0x%x with free block [%d] (%d)\n",
7819                freeFinger, _sp->block_size(freeFinger),
7820                freeRangeInFreeLists);
7821   }
7822   assert(!inFreeRange(), "Trampling existing free range");
7823   set_inFreeRange(true);
7824   set_lastFreeRangeCoalesced(false);
7825 
7826   set_freeFinger(freeFinger);
7827   set_freeRangeInFreeLists(freeRangeInFreeLists);
7828   if (CMSTestInFreeList) {
7829     if (freeRangeInFreeLists) {
7830       FreeChunk* fc = (FreeChunk*) freeFinger;
7831       assert(fc->isFree(), "A chunk on the free list should be free.");
7832       assert(fc->size() > 0, "Free range should have a size");
7833       assert(_sp->verifyChunkInFreeLists(fc), "Chunk is not in free lists");
7834     }
7835   }
7836 }
7837 
7838 // Note that the sweeper runs concurrently with mutators. Thus,
7839 // it is possible for direct allocation in this generation to happen
7840 // in the middle of the sweep. Note that the sweeper also coalesces
7841 // contiguous free blocks. Thus, unless the sweeper and the allocator
7842 // synchronize appropriately freshly allocated blocks may get swept up.
7843 // This is accomplished by the sweeper locking the free lists while
7844 // it is sweeping. Thus blocks that are determined to be free are
7845 // indeed free. There is however one additional complication:
7846 // blocks that have been allocated since the final checkpoint and
7847 // mark, will not have been marked and so would be treated as
7848 // unreachable and swept up. To prevent this, the allocator marks
7849 // the bit map when allocating during the sweep phase. This leads,
7850 // however, to a further complication -- objects may have been allocated
7851 // but not yet initialized -- in the sense that the header isn't yet
7852 // installed. The sweeper can not then determine the size of the block
7853 // in order to skip over it. To deal with this case, we use a technique
7854 // (due to Printezis) to encode such uninitialized block sizes in the
7855 // bit map. Since the bit map uses a bit per every HeapWord, but the
7856 // CMS generation has a minimum object size of 3 HeapWords, it follows
7857 // that "normal marks" won't be adjacent in the bit map (there will
7858 // always be at least two 0 bits between successive 1 bits). We make use
7859 // of these "unused" bits to represent uninitialized blocks -- the bit
7860 // corresponding to the start of the uninitialized object and the next
7861 // bit are both set. Finally, a 1 bit marks the end of the object that
7862 // started with the two consecutive 1 bits to indicate its potentially
7863 // uninitialized state.
7864 
7865 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
7866   FreeChunk* fc = (FreeChunk*)addr;
7867   size_t res;
7868 
7869   // check if we are done sweepinrg
7870   if (addr == _limit) { // we have swept up to the limit, do nothing more
7871     assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7872            "sweep _limit out of bounds");
7873     // help the closure application finish
7874     return pointer_delta(_sp->end(), _limit);
7875   }
7876   assert(addr <= _limit, "sweep invariant");
7877 
7878   // check if we should yield
7879   do_yield_check(addr);
7880   if (fc->isFree()) {
7881     // Chunk that is already free
7882     res = fc->size();
7883     doAlreadyFreeChunk(fc);
7884     debug_only(_sp->verifyFreeLists());
7885     assert(res == fc->size(), "Don't expect the size to change");
7886     NOT_PRODUCT(
7887       _numObjectsAlreadyFree++;
7888       _numWordsAlreadyFree += res;
7889     )
7890     NOT_PRODUCT(_last_fc = fc;)
7891   } else if (!_bitMap->isMarked(addr)) {
7892     // Chunk is fresh garbage
7893     res = doGarbageChunk(fc);
7894     debug_only(_sp->verifyFreeLists());
7895     NOT_PRODUCT(
7896       _numObjectsFreed++;
7897       _numWordsFreed += res;
7898     )
7899   } else {
7900     // Chunk that is alive.
7901     res = doLiveChunk(fc);
7902     debug_only(_sp->verifyFreeLists());
7903     NOT_PRODUCT(
7904         _numObjectsLive++;
7905         _numWordsLive += res;
7906     )
7907   }
7908   return res;
7909 }
7910 
7911 // For the smart allocation, record following
7912 //  split deaths - a free chunk is removed from its free list because
7913 //      it is being split into two or more chunks.
7914 //  split birth - a free chunk is being added to its free list because
7915 //      a larger free chunk has been split and resulted in this free chunk.
7916 //  coal death - a free chunk is being removed from its free list because
7917 //      it is being coalesced into a large free chunk.
7918 //  coal birth - a free chunk is being added to its free list because
7919 //      it was created when two or more free chunks where coalesced into
7920 //      this free chunk.
7921 //
7922 // These statistics are used to determine the desired number of free
7923 // chunks of a given size.  The desired number is chosen to be relative
7924 // to the end of a CMS sweep.  The desired number at the end of a sweep
7925 // is the
7926 //      count-at-end-of-previous-sweep (an amount that was enough)
7927 //              - count-at-beginning-of-current-sweep  (the excess)
7928 //              + split-births  (gains in this size during interval)
7929 //              - split-deaths  (demands on this size during interval)
7930 // where the interval is from the end of one sweep to the end of the
7931 // next.
7932 //
7933 // When sweeping the sweeper maintains an accumulated chunk which is
7934 // the chunk that is made up of chunks that have been coalesced.  That
7935 // will be termed the left-hand chunk.  A new chunk of garbage that
7936 // is being considered for coalescing will be referred to as the
7937 // right-hand chunk.
7938 //
7939 // When making a decision on whether to coalesce a right-hand chunk with
7940 // the current left-hand chunk, the current count vs. the desired count
7941 // of the left-hand chunk is considered.  Also if the right-hand chunk
7942 // is near the large chunk at the end of the heap (see
7943 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
7944 // left-hand chunk is coalesced.
7945 //
7946 // When making a decision about whether to split a chunk, the desired count
7947 // vs. the current count of the candidate to be split is also considered.
7948 // If the candidate is underpopulated (currently fewer chunks than desired)
7949 // a chunk of an overpopulated (currently more chunks than desired) size may
7950 // be chosen.  The "hint" associated with a free list, if non-null, points
7951 // to a free list which may be overpopulated.
7952 //
7953 
7954 void SweepClosure::doAlreadyFreeChunk(FreeChunk* fc) {
7955   size_t size = fc->size();
7956   // Chunks that cannot be coalesced are not in the
7957   // free lists.
7958   if (CMSTestInFreeList && !fc->cantCoalesce()) {
7959     assert(_sp->verifyChunkInFreeLists(fc),
7960       "free chunk should be in free lists");
7961   }
7962   // a chunk that is already free, should not have been
7963   // marked in the bit map
7964   HeapWord* addr = (HeapWord*) fc;
7965   assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
7966   // Verify that the bit map has no bits marked between
7967   // addr and purported end of this block.
7968   _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7969 
7970   // Some chunks cannot be coalesced in under any circumstances.
7971   // See the definition of cantCoalesce().
7972   if (!fc->cantCoalesce()) {
7973     // This chunk can potentially be coalesced.
7974     if (_sp->adaptive_freelists()) {
7975       // All the work is done in
7976       doPostIsFreeOrGarbageChunk(fc, size);
7977     } else {  // Not adaptive free lists
7978       // this is a free chunk that can potentially be coalesced by the sweeper;
7979       if (!inFreeRange()) {
7980         // if the next chunk is a free block that can't be coalesced
7981         // it doesn't make sense to remove this chunk from the free lists
7982         FreeChunk* nextChunk = (FreeChunk*)(addr + size);
7983         assert((HeapWord*)nextChunk <= _limit, "sweep invariant");
7984         if ((HeapWord*)nextChunk < _limit  &&    // there's a next chunk...
7985             nextChunk->isFree()    &&            // which is free...
7986             nextChunk->cantCoalesce()) {         // ... but cant be coalesced
7987           // nothing to do
7988         } else {
7989           // Potentially the start of a new free range:
7990           // Don't eagerly remove it from the free lists.
7991           // No need to remove it if it will just be put
7992           // back again.  (Also from a pragmatic point of view
7993           // if it is a free block in a region that is beyond
7994           // any allocated blocks, an assertion will fail)
7995           // Remember the start of a free run.
7996           initialize_free_range(addr, true);
7997           // end - can coalesce with next chunk
7998         }
7999       } else {
8000         // the midst of a free range, we are coalescing
8001         debug_only(record_free_block_coalesced(fc);)
8002         if (CMSTraceSweeper) {
8003           gclog_or_tty->print("  -- pick up free block 0x%x (%d)\n", fc, size);
8004         }
8005         // remove it from the free lists
8006         _sp->removeFreeChunkFromFreeLists(fc);
8007         set_lastFreeRangeCoalesced(true);
8008         // If the chunk is being coalesced and the current free range is
8009         // in the free lists, remove the current free range so that it
8010         // will be returned to the free lists in its entirety - all
8011         // the coalesced pieces included.
8012         if (freeRangeInFreeLists()) {
8013           FreeChunk* ffc = (FreeChunk*) freeFinger();
8014           assert(ffc->size() == pointer_delta(addr, freeFinger()),
8015             "Size of free range is inconsistent with chunk size.");
8016           if (CMSTestInFreeList) {
8017             assert(_sp->verifyChunkInFreeLists(ffc),
8018               "free range is not in free lists");
8019           }
8020           _sp->removeFreeChunkFromFreeLists(ffc);
8021           set_freeRangeInFreeLists(false);
8022         }
8023       }
8024     }
8025   } else {
8026     // Code path common to both original and adaptive free lists.
8027 
8028     // cant coalesce with previous block; this should be treated
8029     // as the end of a free run if any
8030     if (inFreeRange()) {
8031       // we kicked some butt; time to pick up the garbage
8032       assert(freeFinger() < addr, "the finger pointeth off base");
8033       flushCurFreeChunk(freeFinger(), pointer_delta(addr, freeFinger()));
8034     }
8035     // else, nothing to do, just continue
8036   }
8037 }
8038 
8039 size_t SweepClosure::doGarbageChunk(FreeChunk* fc) {
8040   // This is a chunk of garbage.  It is not in any free list.
8041   // Add it to a free list or let it possibly be coalesced into
8042   // a larger chunk.
8043   HeapWord* addr = (HeapWord*) fc;
8044   size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
8045 
8046   if (_sp->adaptive_freelists()) {
8047     // Verify that the bit map has no bits marked between
8048     // addr and purported end of just dead object.
8049     _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8050 
8051     doPostIsFreeOrGarbageChunk(fc, size);
8052   } else {
8053     if (!inFreeRange()) {
8054       // start of a new free range
8055       assert(size > 0, "A free range should have a size");
8056       initialize_free_range(addr, false);
8057 
8058     } else {
8059       // this will be swept up when we hit the end of the
8060       // free range
8061       if (CMSTraceSweeper) {
8062         gclog_or_tty->print("  -- pick up garbage 0x%x (%d) \n", fc, size);
8063       }
8064       // If the chunk is being coalesced and the current free range is
8065       // in the free lists, remove the current free range so that it
8066       // will be returned to the free lists in its entirety - all
8067       // the coalesced pieces included.
8068       if (freeRangeInFreeLists()) {
8069         FreeChunk* ffc = (FreeChunk*)freeFinger();
8070         assert(ffc->size() == pointer_delta(addr, freeFinger()),
8071           "Size of free range is inconsistent with chunk size.");
8072         if (CMSTestInFreeList) {
8073           assert(_sp->verifyChunkInFreeLists(ffc),
8074             "free range is not in free lists");
8075         }
8076         _sp->removeFreeChunkFromFreeLists(ffc);
8077         set_freeRangeInFreeLists(false);
8078       }
8079       set_lastFreeRangeCoalesced(true);
8080     }
8081     // this will be swept up when we hit the end of the free range
8082 
8083     // Verify that the bit map has no bits marked between
8084     // addr and purported end of just dead object.
8085     _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8086   }
8087   return size;
8088 }
8089 
8090 size_t SweepClosure::doLiveChunk(FreeChunk* fc) {
8091   HeapWord* addr = (HeapWord*) fc;
8092   // The sweeper has just found a live object. Return any accumulated
8093   // left hand chunk to the free lists.
8094   if (inFreeRange()) {
8095     if (_sp->adaptive_freelists()) {
8096       flushCurFreeChunk(freeFinger(),
8097                         pointer_delta(addr, freeFinger()));
8098     } else { // not adaptive freelists
8099       set_inFreeRange(false);
8100       // Add the free range back to the free list if it is not already
8101       // there.
8102       if (!freeRangeInFreeLists()) {
8103         assert(freeFinger() < addr, "the finger pointeth off base");
8104         if (CMSTraceSweeper) {
8105           gclog_or_tty->print("Sweep:put_free_blk 0x%x (%d) "
8106             "[coalesced:%d]\n",
8107             freeFinger(), pointer_delta(addr, freeFinger()),
8108             lastFreeRangeCoalesced());
8109         }
8110         _sp->addChunkAndRepairOffsetTable(freeFinger(),
8111           pointer_delta(addr, freeFinger()), lastFreeRangeCoalesced());
8112       }
8113     }
8114   }
8115 
8116   // Common code path for original and adaptive free lists.
8117 
8118   // this object is live: we'd normally expect this to be
8119   // an oop, and like to assert the following:
8120   // assert(oop(addr)->is_oop(), "live block should be an oop");
8121   // However, as we commented above, this may be an object whose
8122   // header hasn't yet been initialized.
8123   size_t size;
8124   assert(_bitMap->isMarked(addr), "Tautology for this control point");
8125   if (_bitMap->isMarked(addr + 1)) {
8126     // Determine the size from the bit map, rather than trying to
8127     // compute it from the object header.
8128     HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
8129     size = pointer_delta(nextOneAddr + 1, addr);
8130     assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
8131            "alignment problem");
8132 
8133     #ifdef DEBUG
8134       if (oop(addr)->klass_or_null() != NULL &&
8135           (   !_collector->should_unload_classes()
8136            || (oop(addr)->is_parsable()) &&
8137                oop(addr)->is_conc_safe())) {
8138         // Ignore mark word because we are running concurrent with mutators
8139         assert(oop(addr)->is_oop(true), "live block should be an oop");
8140         // is_conc_safe is checked before performing this assertion
8141         // because an object that is not is_conc_safe may yet have
8142         // the return from size() correct.
8143         assert(size ==
8144                CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
8145                "P-mark and computed size do not agree");
8146       }
8147     #endif
8148 
8149   } else {
8150     // This should be an initialized object that's alive.
8151     assert(oop(addr)->klass_or_null() != NULL &&
8152            (!_collector->should_unload_classes()
8153             || oop(addr)->is_parsable()),
8154            "Should be an initialized object");
8155     // Note that there are objects used during class redefinition
8156     // (e.g., merge_cp in VM_RedefineClasses::merge_cp_and_rewrite()
8157     // which are discarded with their is_conc_safe state still
8158     // false.  These object may be floating garbage so may be
8159     // seen here.  If they are floating garbage their size
8160     // should be attainable from their klass.  Do not that
8161     // is_conc_safe() is true for oop(addr).
8162     // Ignore mark word because we are running concurrent with mutators
8163     assert(oop(addr)->is_oop(true), "live block should be an oop");
8164     // Verify that the bit map has no bits marked between
8165     // addr and purported end of this block.
8166     size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
8167     assert(size >= 3, "Necessary for Printezis marks to work");
8168     assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
8169     DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
8170   }
8171   return size;
8172 }
8173 
8174 void SweepClosure::doPostIsFreeOrGarbageChunk(FreeChunk* fc,
8175                                             size_t chunkSize) {
8176   // doPostIsFreeOrGarbageChunk() should only be called in the smart allocation
8177   // scheme.
8178   bool fcInFreeLists = fc->isFree();
8179   assert(_sp->adaptive_freelists(), "Should only be used in this case.");
8180   assert((HeapWord*)fc <= _limit, "sweep invariant");
8181   if (CMSTestInFreeList && fcInFreeLists) {
8182     assert(_sp->verifyChunkInFreeLists(fc),
8183       "free chunk is not in free lists");
8184   }
8185 
8186 
8187   if (CMSTraceSweeper) {
8188     gclog_or_tty->print_cr("  -- pick up another chunk at 0x%x (%d)", fc, chunkSize);
8189   }
8190 
8191   HeapWord* addr = (HeapWord*) fc;
8192 
8193   bool coalesce;
8194   size_t left  = pointer_delta(addr, freeFinger());
8195   size_t right = chunkSize;
8196   switch (FLSCoalescePolicy) {
8197     // numeric value forms a coalition aggressiveness metric
8198     case 0:  { // never coalesce
8199       coalesce = false;
8200       break;
8201     }
8202     case 1: { // coalesce if left & right chunks on overpopulated lists
8203       coalesce = _sp->coalOverPopulated(left) &&
8204                  _sp->coalOverPopulated(right);
8205       break;
8206     }
8207     case 2: { // coalesce if left chunk on overpopulated list (default)
8208       coalesce = _sp->coalOverPopulated(left);
8209       break;
8210     }
8211     case 3: { // coalesce if left OR right chunk on overpopulated list
8212       coalesce = _sp->coalOverPopulated(left) ||
8213                  _sp->coalOverPopulated(right);
8214       break;
8215     }
8216     case 4: { // always coalesce
8217       coalesce = true;
8218       break;
8219     }
8220     default:
8221      ShouldNotReachHere();
8222   }
8223 
8224   // Should the current free range be coalesced?
8225   // If the chunk is in a free range and either we decided to coalesce above
8226   // or the chunk is near the large block at the end of the heap
8227   // (isNearLargestChunk() returns true), then coalesce this chunk.
8228   bool doCoalesce = inFreeRange() &&
8229     (coalesce || _g->isNearLargestChunk((HeapWord*)fc));
8230   if (doCoalesce) {
8231     // Coalesce the current free range on the left with the new
8232     // chunk on the right.  If either is on a free list,
8233     // it must be removed from the list and stashed in the closure.
8234     if (freeRangeInFreeLists()) {
8235       FreeChunk* ffc = (FreeChunk*)freeFinger();
8236       assert(ffc->size() == pointer_delta(addr, freeFinger()),
8237         "Size of free range is inconsistent with chunk size.");
8238       if (CMSTestInFreeList) {
8239         assert(_sp->verifyChunkInFreeLists(ffc),
8240           "Chunk is not in free lists");
8241       }
8242       _sp->coalDeath(ffc->size());
8243       _sp->removeFreeChunkFromFreeLists(ffc);
8244       set_freeRangeInFreeLists(false);
8245     }
8246     if (fcInFreeLists) {
8247       _sp->coalDeath(chunkSize);
8248       assert(fc->size() == chunkSize,
8249         "The chunk has the wrong size or is not in the free lists");
8250       _sp->removeFreeChunkFromFreeLists(fc);
8251     }
8252     set_lastFreeRangeCoalesced(true);
8253   } else {  // not in a free range and/or should not coalesce
8254     // Return the current free range and start a new one.
8255     if (inFreeRange()) {
8256       // In a free range but cannot coalesce with the right hand chunk.
8257       // Put the current free range into the free lists.
8258       flushCurFreeChunk(freeFinger(),
8259         pointer_delta(addr, freeFinger()));
8260     }
8261     // Set up for new free range.  Pass along whether the right hand
8262     // chunk is in the free lists.
8263     initialize_free_range((HeapWord*)fc, fcInFreeLists);
8264   }
8265 }
8266 void SweepClosure::flushCurFreeChunk(HeapWord* chunk, size_t size) {
8267   assert(inFreeRange(), "Should only be called if currently in a free range.");
8268   assert(size > 0,
8269     "A zero sized chunk cannot be added to the free lists.");
8270   if (!freeRangeInFreeLists()) {
8271     if(CMSTestInFreeList) {
8272       FreeChunk* fc = (FreeChunk*) chunk;
8273       fc->setSize(size);
8274       assert(!_sp->verifyChunkInFreeLists(fc),
8275         "chunk should not be in free lists yet");
8276     }
8277     if (CMSTraceSweeper) {
8278       gclog_or_tty->print_cr(" -- add free block 0x%x (%d) to free lists",
8279                     chunk, size);
8280     }
8281     // A new free range is going to be starting.  The current
8282     // free range has not been added to the free lists yet or
8283     // was removed so add it back.
8284     // If the current free range was coalesced, then the death
8285     // of the free range was recorded.  Record a birth now.
8286     if (lastFreeRangeCoalesced()) {
8287       _sp->coalBirth(size);
8288     }
8289     _sp->addChunkAndRepairOffsetTable(chunk, size,
8290             lastFreeRangeCoalesced());
8291   }
8292   set_inFreeRange(false);
8293   set_freeRangeInFreeLists(false);
8294 }
8295 
8296 // We take a break if we've been at this for a while,
8297 // so as to avoid monopolizing the locks involved.
8298 void SweepClosure::do_yield_work(HeapWord* addr) {
8299   // Return current free chunk being used for coalescing (if any)
8300   // to the appropriate freelist.  After yielding, the next
8301   // free block encountered will start a coalescing range of
8302   // free blocks.  If the next free block is adjacent to the
8303   // chunk just flushed, they will need to wait for the next
8304   // sweep to be coalesced.
8305   if (inFreeRange()) {
8306     flushCurFreeChunk(freeFinger(), pointer_delta(addr, freeFinger()));
8307   }
8308 
8309   // First give up the locks, then yield, then re-lock.
8310   // We should probably use a constructor/destructor idiom to
8311   // do this unlock/lock or modify the MutexUnlocker class to
8312   // serve our purpose. XXX
8313   assert_lock_strong(_bitMap->lock());
8314   assert_lock_strong(_freelistLock);
8315   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
8316          "CMS thread should hold CMS token");
8317   _bitMap->lock()->unlock();
8318   _freelistLock->unlock();
8319   ConcurrentMarkSweepThread::desynchronize(true);
8320   ConcurrentMarkSweepThread::acknowledge_yield_request();
8321   _collector->stopTimer();
8322   GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
8323   if (PrintCMSStatistics != 0) {
8324     _collector->incrementYields();
8325   }
8326   _collector->icms_wait();
8327 
8328   // See the comment in coordinator_yield()
8329   for (unsigned i = 0; i < CMSYieldSleepCount &&
8330                        ConcurrentMarkSweepThread::should_yield() &&
8331                        !CMSCollector::foregroundGCIsActive(); ++i) {
8332     os::sleep(Thread::current(), 1, false);
8333     ConcurrentMarkSweepThread::acknowledge_yield_request();
8334   }
8335 
8336   ConcurrentMarkSweepThread::synchronize(true);
8337   _freelistLock->lock();
8338   _bitMap->lock()->lock_without_safepoint_check();
8339   _collector->startTimer();
8340 }
8341 
8342 #ifndef PRODUCT
8343 // This is actually very useful in a product build if it can
8344 // be called from the debugger.  Compile it into the product
8345 // as needed.
8346 bool debug_verifyChunkInFreeLists(FreeChunk* fc) {
8347   return debug_cms_space->verifyChunkInFreeLists(fc);
8348 }
8349 
8350 void SweepClosure::record_free_block_coalesced(FreeChunk* fc) const {
8351   if (CMSTraceSweeper) {
8352     gclog_or_tty->print("Sweep:coal_free_blk 0x%x (%d)\n", fc, fc->size());
8353   }
8354 }
8355 #endif
8356 
8357 // CMSIsAliveClosure
8358 bool CMSIsAliveClosure::do_object_b(oop obj) {
8359   HeapWord* addr = (HeapWord*)obj;
8360   return addr != NULL &&
8361          (!_span.contains(addr) || _bit_map->isMarked(addr));
8362 }
8363 
8364 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector,
8365                       MemRegion span,
8366                       CMSBitMap* bit_map, CMSMarkStack* mark_stack,
8367                       CMSMarkStack* revisit_stack, bool cpc):
8368   KlassRememberingOopClosure(collector, NULL, revisit_stack),
8369   _span(span),
8370   _bit_map(bit_map),
8371   _mark_stack(mark_stack),
8372   _concurrent_precleaning(cpc) {
8373   assert(!_span.is_empty(), "Empty span could spell trouble");
8374 }
8375 
8376 
8377 // CMSKeepAliveClosure: the serial version
8378 void CMSKeepAliveClosure::do_oop(oop obj) {
8379   HeapWord* addr = (HeapWord*)obj;
8380   if (_span.contains(addr) &&
8381       !_bit_map->isMarked(addr)) {
8382     _bit_map->mark(addr);
8383     bool simulate_overflow = false;
8384     NOT_PRODUCT(
8385       if (CMSMarkStackOverflowALot &&
8386           _collector->simulate_overflow()) {
8387         // simulate a stack overflow
8388         simulate_overflow = true;
8389       }
8390     )
8391     if (simulate_overflow || !_mark_stack->push(obj)) {
8392       if (_concurrent_precleaning) {
8393         // We dirty the overflown object and let the remark
8394         // phase deal with it.
8395         assert(_collector->overflow_list_is_empty(), "Error");
8396         // In the case of object arrays, we need to dirty all of
8397         // the cards that the object spans. No locking or atomics
8398         // are needed since no one else can be mutating the mod union
8399         // table.
8400         if (obj->is_objArray()) {
8401           size_t sz = obj->size();
8402           HeapWord* end_card_addr =
8403             (HeapWord*)round_to((intptr_t)(addr+sz), CardTableModRefBS::card_size);
8404           MemRegion redirty_range = MemRegion(addr, end_card_addr);
8405           assert(!redirty_range.is_empty(), "Arithmetical tautology");
8406           _collector->_modUnionTable.mark_range(redirty_range);
8407         } else {
8408           _collector->_modUnionTable.mark(addr);
8409         }
8410         _collector->_ser_kac_preclean_ovflw++;
8411       } else {
8412         _collector->push_on_overflow_list(obj);
8413         _collector->_ser_kac_ovflw++;
8414       }
8415     }
8416   }
8417 }
8418 
8419 void CMSKeepAliveClosure::do_oop(oop* p)       { CMSKeepAliveClosure::do_oop_work(p); }
8420 void CMSKeepAliveClosure::do_oop(narrowOop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8421 
8422 // CMSParKeepAliveClosure: a parallel version of the above.
8423 // The work queues are private to each closure (thread),
8424 // but (may be) available for stealing by other threads.
8425 void CMSParKeepAliveClosure::do_oop(oop obj) {
8426   HeapWord* addr = (HeapWord*)obj;
8427   if (_span.contains(addr) &&
8428       !_bit_map->isMarked(addr)) {
8429     // In general, during recursive tracing, several threads
8430     // may be concurrently getting here; the first one to
8431     // "tag" it, claims it.
8432     if (_bit_map->par_mark(addr)) {
8433       bool res = _work_queue->push(obj);
8434       assert(res, "Low water mark should be much less than capacity");
8435       // Do a recursive trim in the hope that this will keep
8436       // stack usage lower, but leave some oops for potential stealers
8437       trim_queue(_low_water_mark);
8438     } // Else, another thread got there first
8439   }
8440 }
8441 
8442 void CMSParKeepAliveClosure::do_oop(oop* p)       { CMSParKeepAliveClosure::do_oop_work(p); }
8443 void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8444 
8445 void CMSParKeepAliveClosure::trim_queue(uint max) {
8446   while (_work_queue->size() > max) {
8447     oop new_oop;
8448     if (_work_queue->pop_local(new_oop)) {
8449       assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
8450       assert(_bit_map->isMarked((HeapWord*)new_oop),
8451              "no white objects on this stack!");
8452       assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8453       // iterate over the oops in this oop, marking and pushing
8454       // the ones in CMS heap (i.e. in _span).
8455       new_oop->oop_iterate(&_mark_and_push);
8456     }
8457   }
8458 }
8459 
8460 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
8461                                 CMSCollector* collector,
8462                                 MemRegion span, CMSBitMap* bit_map,
8463                                 CMSMarkStack* revisit_stack,
8464                                 OopTaskQueue* work_queue):
8465   Par_KlassRememberingOopClosure(collector, NULL, revisit_stack),
8466   _span(span),
8467   _bit_map(bit_map),
8468   _work_queue(work_queue) { }
8469 
8470 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
8471   HeapWord* addr = (HeapWord*)obj;
8472   if (_span.contains(addr) &&
8473       !_bit_map->isMarked(addr)) {
8474     if (_bit_map->par_mark(addr)) {
8475       bool simulate_overflow = false;
8476       NOT_PRODUCT(
8477         if (CMSMarkStackOverflowALot &&
8478             _collector->par_simulate_overflow()) {
8479           // simulate a stack overflow
8480           simulate_overflow = true;
8481         }
8482       )
8483       if (simulate_overflow || !_work_queue->push(obj)) {
8484         _collector->par_push_on_overflow_list(obj);
8485         _collector->_par_kac_ovflw++;
8486       }
8487     } // Else another thread got there already
8488   }
8489 }
8490 
8491 void CMSInnerParMarkAndPushClosure::do_oop(oop* p)       { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8492 void CMSInnerParMarkAndPushClosure::do_oop(narrowOop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8493 
8494 //////////////////////////////////////////////////////////////////
8495 //  CMSExpansionCause                /////////////////////////////
8496 //////////////////////////////////////////////////////////////////
8497 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
8498   switch (cause) {
8499     case _no_expansion:
8500       return "No expansion";
8501     case _satisfy_free_ratio:
8502       return "Free ratio";
8503     case _satisfy_promotion:
8504       return "Satisfy promotion";
8505     case _satisfy_allocation:
8506       return "allocation";
8507     case _allocate_par_lab:
8508       return "Par LAB";
8509     case _allocate_par_spooling_space:
8510       return "Par Spooling Space";
8511     case _adaptive_size_policy:
8512       return "Ergonomics";
8513     default:
8514       return "unknown";
8515   }
8516 }
8517 
8518 void CMSDrainMarkingStackClosure::do_void() {
8519   // the max number to take from overflow list at a time
8520   const size_t num = _mark_stack->capacity()/4;
8521   assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
8522          "Overflow list should be NULL during concurrent phases");
8523   while (!_mark_stack->isEmpty() ||
8524          // if stack is empty, check the overflow list
8525          _collector->take_from_overflow_list(num, _mark_stack)) {
8526     oop obj = _mark_stack->pop();
8527     HeapWord* addr = (HeapWord*)obj;
8528     assert(_span.contains(addr), "Should be within span");
8529     assert(_bit_map->isMarked(addr), "Should be marked");
8530     assert(obj->is_oop(), "Should be an oop");
8531     obj->oop_iterate(_keep_alive);
8532   }
8533 }
8534 
8535 void CMSParDrainMarkingStackClosure::do_void() {
8536   // drain queue
8537   trim_queue(0);
8538 }
8539 
8540 // Trim our work_queue so its length is below max at return
8541 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
8542   while (_work_queue->size() > max) {
8543     oop new_oop;
8544     if (_work_queue->pop_local(new_oop)) {
8545       assert(new_oop->is_oop(), "Expected an oop");
8546       assert(_bit_map->isMarked((HeapWord*)new_oop),
8547              "no white objects on this stack!");
8548       assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8549       // iterate over the oops in this oop, marking and pushing
8550       // the ones in CMS heap (i.e. in _span).
8551       new_oop->oop_iterate(&_mark_and_push);
8552     }
8553   }
8554 }
8555 
8556 ////////////////////////////////////////////////////////////////////
8557 // Support for Marking Stack Overflow list handling and related code
8558 ////////////////////////////////////////////////////////////////////
8559 // Much of the following code is similar in shape and spirit to the
8560 // code used in ParNewGC. We should try and share that code
8561 // as much as possible in the future.
8562 
8563 #ifndef PRODUCT
8564 // Debugging support for CMSStackOverflowALot
8565 
8566 // It's OK to call this multi-threaded;  the worst thing
8567 // that can happen is that we'll get a bunch of closely
8568 // spaced simulated oveflows, but that's OK, in fact
8569 // probably good as it would exercise the overflow code
8570 // under contention.
8571 bool CMSCollector::simulate_overflow() {
8572   if (_overflow_counter-- <= 0) { // just being defensive
8573     _overflow_counter = CMSMarkStackOverflowInterval;
8574     return true;
8575   } else {
8576     return false;
8577   }
8578 }
8579 
8580 bool CMSCollector::par_simulate_overflow() {
8581   return simulate_overflow();
8582 }
8583 #endif
8584 
8585 // Single-threaded
8586 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
8587   assert(stack->isEmpty(), "Expected precondition");
8588   assert(stack->capacity() > num, "Shouldn't bite more than can chew");
8589   size_t i = num;
8590   oop  cur = _overflow_list;
8591   const markOop proto = markOopDesc::prototype();
8592   NOT_PRODUCT(ssize_t n = 0;)
8593   for (oop next; i > 0 && cur != NULL; cur = next, i--) {
8594     next = oop(cur->mark());
8595     cur->set_mark(proto);   // until proven otherwise
8596     assert(cur->is_oop(), "Should be an oop");
8597     bool res = stack->push(cur);
8598     assert(res, "Bit off more than can chew?");
8599     NOT_PRODUCT(n++;)
8600   }
8601   _overflow_list = cur;
8602 #ifndef PRODUCT
8603   assert(_num_par_pushes >= n, "Too many pops?");
8604   _num_par_pushes -=n;
8605 #endif
8606   return !stack->isEmpty();
8607 }
8608 
8609 #define BUSY  (oop(0x1aff1aff))
8610 // (MT-safe) Get a prefix of at most "num" from the list.
8611 // The overflow list is chained through the mark word of
8612 // each object in the list. We fetch the entire list,
8613 // break off a prefix of the right size and return the
8614 // remainder. If other threads try to take objects from
8615 // the overflow list at that time, they will wait for
8616 // some time to see if data becomes available. If (and
8617 // only if) another thread places one or more object(s)
8618 // on the global list before we have returned the suffix
8619 // to the global list, we will walk down our local list
8620 // to find its end and append the global list to
8621 // our suffix before returning it. This suffix walk can
8622 // prove to be expensive (quadratic in the amount of traffic)
8623 // when there are many objects in the overflow list and
8624 // there is much producer-consumer contention on the list.
8625 // *NOTE*: The overflow list manipulation code here and
8626 // in ParNewGeneration:: are very similar in shape,
8627 // except that in the ParNew case we use the old (from/eden)
8628 // copy of the object to thread the list via its klass word.
8629 // Because of the common code, if you make any changes in
8630 // the code below, please check the ParNew version to see if
8631 // similar changes might be needed.
8632 // CR 6797058 has been filed to consolidate the common code.
8633 bool CMSCollector::par_take_from_overflow_list(size_t num,
8634                                                OopTaskQueue* work_q) {
8635   assert(work_q->size() == 0, "First empty local work queue");
8636   assert(num < work_q->max_elems(), "Can't bite more than we can chew");
8637   if (_overflow_list == NULL) {
8638     return false;
8639   }
8640   // Grab the entire list; we'll put back a suffix
8641   oop prefix = (oop)Atomic::xchg_ptr(BUSY, &_overflow_list);
8642   Thread* tid = Thread::current();
8643   size_t CMSOverflowSpinCount = (size_t)ParallelGCThreads;
8644   size_t sleep_time_millis = MAX2((size_t)1, num/100);
8645   // If the list is busy, we spin for a short while,
8646   // sleeping between attempts to get the list.
8647   for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) {
8648     os::sleep(tid, sleep_time_millis, false);
8649     if (_overflow_list == NULL) {
8650       // Nothing left to take
8651       return false;
8652     } else if (_overflow_list != BUSY) {
8653       // Try and grab the prefix
8654       prefix = (oop)Atomic::xchg_ptr(BUSY, &_overflow_list);
8655     }
8656   }
8657   // If the list was found to be empty, or we spun long
8658   // enough, we give up and return empty-handed. If we leave
8659   // the list in the BUSY state below, it must be the case that
8660   // some other thread holds the overflow list and will set it
8661   // to a non-BUSY state in the future.
8662   if (prefix == NULL || prefix == BUSY) {
8663      // Nothing to take or waited long enough
8664      if (prefix == NULL) {
8665        // Write back the NULL in case we overwrote it with BUSY above
8666        // and it is still the same value.
8667        (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8668      }
8669      return false;
8670   }
8671   assert(prefix != NULL && prefix != BUSY, "Error");
8672   size_t i = num;
8673   oop cur = prefix;
8674   // Walk down the first "num" objects, unless we reach the end.
8675   for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--);
8676   if (cur->mark() == NULL) {
8677     // We have "num" or fewer elements in the list, so there
8678     // is nothing to return to the global list.
8679     // Write back the NULL in lieu of the BUSY we wrote
8680     // above, if it is still the same value.
8681     if (_overflow_list == BUSY) {
8682       (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8683     }
8684   } else {
8685     // Chop off the suffix and rerturn it to the global list.
8686     assert(cur->mark() != BUSY, "Error");
8687     oop suffix_head = cur->mark(); // suffix will be put back on global list
8688     cur->set_mark(NULL);           // break off suffix
8689     // It's possible that the list is still in the empty(busy) state
8690     // we left it in a short while ago; in that case we may be
8691     // able to place back the suffix without incurring the cost
8692     // of a walk down the list.
8693     oop observed_overflow_list = _overflow_list;
8694     oop cur_overflow_list = observed_overflow_list;
8695     bool attached = false;
8696     while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
8697       observed_overflow_list =
8698         (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
8699       if (cur_overflow_list == observed_overflow_list) {
8700         attached = true;
8701         break;
8702       } else cur_overflow_list = observed_overflow_list;
8703     }
8704     if (!attached) {
8705       // Too bad, someone else sneaked in (at least) an element; we'll need
8706       // to do a splice. Find tail of suffix so we can prepend suffix to global
8707       // list.
8708       for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark()));
8709       oop suffix_tail = cur;
8710       assert(suffix_tail != NULL && suffix_tail->mark() == NULL,
8711              "Tautology");
8712       observed_overflow_list = _overflow_list;
8713       do {
8714         cur_overflow_list = observed_overflow_list;
8715         if (cur_overflow_list != BUSY) {
8716           // Do the splice ...
8717           suffix_tail->set_mark(markOop(cur_overflow_list));
8718         } else { // cur_overflow_list == BUSY
8719           suffix_tail->set_mark(NULL);
8720         }
8721         // ... and try to place spliced list back on overflow_list ...
8722         observed_overflow_list =
8723           (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
8724       } while (cur_overflow_list != observed_overflow_list);
8725       // ... until we have succeeded in doing so.
8726     }
8727   }
8728 
8729   // Push the prefix elements on work_q
8730   assert(prefix != NULL, "control point invariant");
8731   const markOop proto = markOopDesc::prototype();
8732   oop next;
8733   NOT_PRODUCT(ssize_t n = 0;)
8734   for (cur = prefix; cur != NULL; cur = next) {
8735     next = oop(cur->mark());
8736     cur->set_mark(proto);   // until proven otherwise
8737     assert(cur->is_oop(), "Should be an oop");
8738     bool res = work_q->push(cur);
8739     assert(res, "Bit off more than we can chew?");
8740     NOT_PRODUCT(n++;)
8741   }
8742 #ifndef PRODUCT
8743   assert(_num_par_pushes >= n, "Too many pops?");
8744   Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
8745 #endif
8746   return true;
8747 }
8748 
8749 // Single-threaded
8750 void CMSCollector::push_on_overflow_list(oop p) {
8751   NOT_PRODUCT(_num_par_pushes++;)
8752   assert(p->is_oop(), "Not an oop");
8753   preserve_mark_if_necessary(p);
8754   p->set_mark((markOop)_overflow_list);
8755   _overflow_list = p;
8756 }
8757 
8758 // Multi-threaded; use CAS to prepend to overflow list
8759 void CMSCollector::par_push_on_overflow_list(oop p) {
8760   NOT_PRODUCT(Atomic::inc_ptr(&_num_par_pushes);)
8761   assert(p->is_oop(), "Not an oop");
8762   par_preserve_mark_if_necessary(p);
8763   oop observed_overflow_list = _overflow_list;
8764   oop cur_overflow_list;
8765   do {
8766     cur_overflow_list = observed_overflow_list;
8767     if (cur_overflow_list != BUSY) {
8768       p->set_mark(markOop(cur_overflow_list));
8769     } else {
8770       p->set_mark(NULL);
8771     }
8772     observed_overflow_list =
8773       (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list);
8774   } while (cur_overflow_list != observed_overflow_list);
8775 }
8776 #undef BUSY
8777 
8778 // Single threaded
8779 // General Note on GrowableArray: pushes may silently fail
8780 // because we are (temporarily) out of C-heap for expanding
8781 // the stack. The problem is quite ubiquitous and affects
8782 // a lot of code in the JVM. The prudent thing for GrowableArray
8783 // to do (for now) is to exit with an error. However, that may
8784 // be too draconian in some cases because the caller may be
8785 // able to recover without much harm. For such cases, we
8786 // should probably introduce a "soft_push" method which returns
8787 // an indication of success or failure with the assumption that
8788 // the caller may be able to recover from a failure; code in
8789 // the VM can then be changed, incrementally, to deal with such
8790 // failures where possible, thus, incrementally hardening the VM
8791 // in such low resource situations.
8792 void CMSCollector::preserve_mark_work(oop p, markOop m) {
8793   if (_preserved_oop_stack == NULL) {
8794     assert(_preserved_mark_stack == NULL,
8795            "bijection with preserved_oop_stack");
8796     // Allocate the stacks
8797     _preserved_oop_stack  = new (ResourceObj::C_HEAP)
8798       GrowableArray<oop>(PreserveMarkStackSize, true);
8799     _preserved_mark_stack = new (ResourceObj::C_HEAP)
8800       GrowableArray<markOop>(PreserveMarkStackSize, true);
8801     if (_preserved_oop_stack == NULL || _preserved_mark_stack == NULL) {
8802       vm_exit_out_of_memory(2* PreserveMarkStackSize * sizeof(oop) /* punt */,
8803                             "Preserved Mark/Oop Stack for CMS (C-heap)");
8804     }
8805   }
8806   _preserved_oop_stack->push(p);
8807   _preserved_mark_stack->push(m);
8808   assert(m == p->mark(), "Mark word changed");
8809   assert(_preserved_oop_stack->length() == _preserved_mark_stack->length(),
8810          "bijection");
8811 }
8812 
8813 // Single threaded
8814 void CMSCollector::preserve_mark_if_necessary(oop p) {
8815   markOop m = p->mark();
8816   if (m->must_be_preserved(p)) {
8817     preserve_mark_work(p, m);
8818   }
8819 }
8820 
8821 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
8822   markOop m = p->mark();
8823   if (m->must_be_preserved(p)) {
8824     MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
8825     // Even though we read the mark word without holding
8826     // the lock, we are assured that it will not change
8827     // because we "own" this oop, so no other thread can
8828     // be trying to push it on the overflow list; see
8829     // the assertion in preserve_mark_work() that checks
8830     // that m == p->mark().
8831     preserve_mark_work(p, m);
8832   }
8833 }
8834 
8835 // We should be able to do this multi-threaded,
8836 // a chunk of stack being a task (this is
8837 // correct because each oop only ever appears
8838 // once in the overflow list. However, it's
8839 // not very easy to completely overlap this with
8840 // other operations, so will generally not be done
8841 // until all work's been completed. Because we
8842 // expect the preserved oop stack (set) to be small,
8843 // it's probably fine to do this single-threaded.
8844 // We can explore cleverer concurrent/overlapped/parallel
8845 // processing of preserved marks if we feel the
8846 // need for this in the future. Stack overflow should
8847 // be so rare in practice and, when it happens, its
8848 // effect on performance so great that this will
8849 // likely just be in the noise anyway.
8850 void CMSCollector::restore_preserved_marks_if_any() {
8851   if (_preserved_oop_stack == NULL) {
8852     assert(_preserved_mark_stack == NULL,
8853            "bijection with preserved_oop_stack");
8854     return;
8855   }
8856 
8857   assert(SafepointSynchronize::is_at_safepoint(),
8858          "world should be stopped");
8859   assert(Thread::current()->is_ConcurrentGC_thread() ||
8860          Thread::current()->is_VM_thread(),
8861          "should be single-threaded");
8862 
8863   int length = _preserved_oop_stack->length();
8864   assert(_preserved_mark_stack->length() == length, "bijection");
8865   for (int i = 0; i < length; i++) {
8866     oop p = _preserved_oop_stack->at(i);
8867     assert(p->is_oop(), "Should be an oop");
8868     assert(_span.contains(p), "oop should be in _span");
8869     assert(p->mark() == markOopDesc::prototype(),
8870            "Set when taken from overflow list");
8871     markOop m = _preserved_mark_stack->at(i);
8872     p->set_mark(m);
8873   }
8874   _preserved_mark_stack->clear();
8875   _preserved_oop_stack->clear();
8876   assert(_preserved_mark_stack->is_empty() &&
8877          _preserved_oop_stack->is_empty(),
8878          "stacks were cleared above");
8879 }
8880 
8881 #ifndef PRODUCT
8882 bool CMSCollector::no_preserved_marks() const {
8883   return (   (   _preserved_mark_stack == NULL
8884               && _preserved_oop_stack == NULL)
8885           || (   _preserved_mark_stack->is_empty()
8886               && _preserved_oop_stack->is_empty()));
8887 }
8888 #endif
8889 
8890 CMSAdaptiveSizePolicy* ASConcurrentMarkSweepGeneration::cms_size_policy() const
8891 {
8892   GenCollectedHeap* gch = (GenCollectedHeap*) GenCollectedHeap::heap();
8893   CMSAdaptiveSizePolicy* size_policy =
8894     (CMSAdaptiveSizePolicy*) gch->gen_policy()->size_policy();
8895   assert(size_policy->is_gc_cms_adaptive_size_policy(),
8896     "Wrong type for size policy");
8897   return size_policy;
8898 }
8899 
8900 void ASConcurrentMarkSweepGeneration::resize(size_t cur_promo_size,
8901                                            size_t desired_promo_size) {
8902   if (cur_promo_size < desired_promo_size) {
8903     size_t expand_bytes = desired_promo_size - cur_promo_size;
8904     if (PrintAdaptiveSizePolicy && Verbose) {
8905       gclog_or_tty->print_cr(" ASConcurrentMarkSweepGeneration::resize "
8906         "Expanding tenured generation by " SIZE_FORMAT " (bytes)",
8907         expand_bytes);
8908     }
8909     expand(expand_bytes,
8910            MinHeapDeltaBytes,
8911            CMSExpansionCause::_adaptive_size_policy);
8912   } else if (desired_promo_size < cur_promo_size) {
8913     size_t shrink_bytes = cur_promo_size - desired_promo_size;
8914     if (PrintAdaptiveSizePolicy && Verbose) {
8915       gclog_or_tty->print_cr(" ASConcurrentMarkSweepGeneration::resize "
8916         "Shrinking tenured generation by " SIZE_FORMAT " (bytes)",
8917         shrink_bytes);
8918     }
8919     shrink(shrink_bytes);
8920   }
8921 }
8922 
8923 CMSGCAdaptivePolicyCounters* ASConcurrentMarkSweepGeneration::gc_adaptive_policy_counters() {
8924   GenCollectedHeap* gch = GenCollectedHeap::heap();
8925   CMSGCAdaptivePolicyCounters* counters =
8926     (CMSGCAdaptivePolicyCounters*) gch->collector_policy()->counters();
8927   assert(counters->kind() == GCPolicyCounters::CMSGCAdaptivePolicyCountersKind,
8928     "Wrong kind of counters");
8929   return counters;
8930 }
8931 
8932 
8933 void ASConcurrentMarkSweepGeneration::update_counters() {
8934   if (UsePerfData) {
8935     _space_counters->update_all();
8936     _gen_counters->update_all();
8937     CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
8938     GenCollectedHeap* gch = GenCollectedHeap::heap();
8939     CMSGCStats* gc_stats_l = (CMSGCStats*) gc_stats();
8940     assert(gc_stats_l->kind() == GCStats::CMSGCStatsKind,
8941       "Wrong gc statistics type");
8942     counters->update_counters(gc_stats_l);
8943   }
8944 }
8945 
8946 void ASConcurrentMarkSweepGeneration::update_counters(size_t used) {
8947   if (UsePerfData) {
8948     _space_counters->update_used(used);
8949     _space_counters->update_capacity();
8950     _gen_counters->update_all();
8951 
8952     CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
8953     GenCollectedHeap* gch = GenCollectedHeap::heap();
8954     CMSGCStats* gc_stats_l = (CMSGCStats*) gc_stats();
8955     assert(gc_stats_l->kind() == GCStats::CMSGCStatsKind,
8956       "Wrong gc statistics type");
8957     counters->update_counters(gc_stats_l);
8958   }
8959 }
8960 
8961 // The desired expansion delta is computed so that:
8962 // . desired free percentage or greater is used
8963 void ASConcurrentMarkSweepGeneration::compute_new_size() {
8964   assert_locked_or_safepoint(Heap_lock);
8965 
8966   GenCollectedHeap* gch = (GenCollectedHeap*) GenCollectedHeap::heap();
8967 
8968   // If incremental collection failed, we just want to expand
8969   // to the limit.
8970   if (incremental_collection_failed()) {
8971     clear_incremental_collection_failed();
8972     grow_to_reserved();
8973     return;
8974   }
8975 
8976   assert(UseAdaptiveSizePolicy, "Should be using adaptive sizing");
8977 
8978   assert(gch->kind() == CollectedHeap::GenCollectedHeap,
8979     "Wrong type of heap");
8980   int prev_level = level() - 1;
8981   assert(prev_level >= 0, "The cms generation is the lowest generation");
8982   Generation* prev_gen = gch->get_gen(prev_level);
8983   assert(prev_gen->kind() == Generation::ASParNew,
8984     "Wrong type of young generation");
8985   ParNewGeneration* younger_gen = (ParNewGeneration*) prev_gen;
8986   size_t cur_eden = younger_gen->eden()->capacity();
8987   CMSAdaptiveSizePolicy* size_policy = cms_size_policy();
8988   size_t cur_promo = free();
8989   size_policy->compute_tenured_generation_free_space(cur_promo,
8990                                                        max_available(),
8991                                                        cur_eden);
8992   resize(cur_promo, size_policy->promo_size());
8993 
8994   // Record the new size of the space in the cms generation
8995   // that is available for promotions.  This is temporary.
8996   // It should be the desired promo size.
8997   size_policy->avg_cms_promo()->sample(free());
8998   size_policy->avg_old_live()->sample(used());
8999 
9000   if (UsePerfData) {
9001     CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
9002     counters->update_cms_capacity_counter(capacity());
9003   }
9004 }
9005 
9006 void ASConcurrentMarkSweepGeneration::shrink_by(size_t desired_bytes) {
9007   assert_locked_or_safepoint(Heap_lock);
9008   assert_lock_strong(freelistLock());
9009   HeapWord* old_end = _cmsSpace->end();
9010   HeapWord* unallocated_start = _cmsSpace->unallocated_block();
9011   assert(old_end >= unallocated_start, "Miscalculation of unallocated_start");
9012   FreeChunk* chunk_at_end = find_chunk_at_end();
9013   if (chunk_at_end == NULL) {
9014     // No room to shrink
9015     if (PrintGCDetails && Verbose) {
9016       gclog_or_tty->print_cr("No room to shrink: old_end  "
9017         PTR_FORMAT "  unallocated_start  " PTR_FORMAT
9018         " chunk_at_end  " PTR_FORMAT,
9019         old_end, unallocated_start, chunk_at_end);
9020     }
9021     return;
9022   } else {
9023 
9024     // Find the chunk at the end of the space and determine
9025     // how much it can be shrunk.
9026     size_t shrinkable_size_in_bytes = chunk_at_end->size();
9027     size_t aligned_shrinkable_size_in_bytes =
9028       align_size_down(shrinkable_size_in_bytes, os::vm_page_size());
9029     assert(unallocated_start <= chunk_at_end->end(),
9030       "Inconsistent chunk at end of space");
9031     size_t bytes = MIN2(desired_bytes, aligned_shrinkable_size_in_bytes);
9032     size_t word_size_before = heap_word_size(_virtual_space.committed_size());
9033 
9034     // Shrink the underlying space
9035     _virtual_space.shrink_by(bytes);
9036     if (PrintGCDetails && Verbose) {
9037       gclog_or_tty->print_cr("ConcurrentMarkSweepGeneration::shrink_by:"
9038         " desired_bytes " SIZE_FORMAT
9039         " shrinkable_size_in_bytes " SIZE_FORMAT
9040         " aligned_shrinkable_size_in_bytes " SIZE_FORMAT
9041         "  bytes  " SIZE_FORMAT,
9042         desired_bytes, shrinkable_size_in_bytes,
9043         aligned_shrinkable_size_in_bytes, bytes);
9044       gclog_or_tty->print_cr("          old_end  " SIZE_FORMAT
9045         "  unallocated_start  " SIZE_FORMAT,
9046         old_end, unallocated_start);
9047     }
9048 
9049     // If the space did shrink (shrinking is not guaranteed),
9050     // shrink the chunk at the end by the appropriate amount.
9051     if (((HeapWord*)_virtual_space.high()) < old_end) {
9052       size_t new_word_size =
9053         heap_word_size(_virtual_space.committed_size());
9054 
9055       // Have to remove the chunk from the dictionary because it is changing
9056       // size and might be someplace elsewhere in the dictionary.
9057 
9058       // Get the chunk at end, shrink it, and put it
9059       // back.
9060       _cmsSpace->removeChunkFromDictionary(chunk_at_end);
9061       size_t word_size_change = word_size_before - new_word_size;
9062       size_t chunk_at_end_old_size = chunk_at_end->size();
9063       assert(chunk_at_end_old_size >= word_size_change,
9064         "Shrink is too large");
9065       chunk_at_end->setSize(chunk_at_end_old_size -
9066                           word_size_change);
9067       _cmsSpace->freed((HeapWord*) chunk_at_end->end(),
9068         word_size_change);
9069 
9070       _cmsSpace->returnChunkToDictionary(chunk_at_end);
9071 
9072       MemRegion mr(_cmsSpace->bottom(), new_word_size);
9073       _bts->resize(new_word_size);  // resize the block offset shared array
9074       Universe::heap()->barrier_set()->resize_covered_region(mr);
9075       _cmsSpace->assert_locked();
9076       _cmsSpace->set_end((HeapWord*)_virtual_space.high());
9077 
9078       NOT_PRODUCT(_cmsSpace->dictionary()->verify());
9079 
9080       // update the space and generation capacity counters
9081       if (UsePerfData) {
9082         _space_counters->update_capacity();
9083         _gen_counters->update_all();
9084       }
9085 
9086       if (Verbose && PrintGCDetails) {
9087         size_t new_mem_size = _virtual_space.committed_size();
9088         size_t old_mem_size = new_mem_size + bytes;
9089         gclog_or_tty->print_cr("Shrinking %s from %ldK by %ldK to %ldK",
9090                       name(), old_mem_size/K, bytes/K, new_mem_size/K);
9091       }
9092     }
9093 
9094     assert(_cmsSpace->unallocated_block() <= _cmsSpace->end(),
9095       "Inconsistency at end of space");
9096     assert(chunk_at_end->end() == _cmsSpace->end(),
9097       "Shrinking is inconsistent");
9098     return;
9099   }
9100 }
9101 
9102 // Transfer some number of overflown objects to usual marking
9103 // stack. Return true if some objects were transferred.
9104 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
9105   size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,
9106                     (size_t)ParGCDesiredObjsFromOverflowList);
9107 
9108   bool res = _collector->take_from_overflow_list(num, _mark_stack);
9109   assert(_collector->overflow_list_is_empty() || res,
9110          "If list is not empty, we should have taken something");
9111   assert(!res || !_mark_stack->isEmpty(),
9112          "If we took something, it should now be on our stack");
9113   return res;
9114 }
9115 
9116 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
9117   size_t res = _sp->block_size_no_stall(addr, _collector);
9118   assert(res != 0, "Should always be able to compute a size");
9119   if (_sp->block_is_obj(addr)) {
9120     if (_live_bit_map->isMarked(addr)) {
9121       // It can't have been dead in a previous cycle
9122       guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
9123     } else {
9124       _dead_bit_map->mark(addr);      // mark the dead object
9125     }
9126   }
9127   return res;
9128 }






















































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