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