1 /*
2 * Copyright (c) 2001, 2014, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include "precompiled.hpp"
26 #include "classfile/classLoaderData.hpp"
27 #include "classfile/stringTable.hpp"
28 #include "classfile/systemDictionary.hpp"
29 #include "code/codeCache.hpp"
30 #include "gc_implementation/shared/adaptiveSizePolicy.hpp"
31 #include "gc_implementation/concurrentMarkSweep/cmsCollectorPolicy.hpp"
32 #include "gc_implementation/concurrentMarkSweep/cmsOopClosures.inline.hpp"
33 #include "gc_implementation/concurrentMarkSweep/compactibleFreeListSpace.hpp"
34 #include "gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.inline.hpp"
35 #include "gc_implementation/concurrentMarkSweep/concurrentMarkSweepThread.hpp"
36 #include "gc_implementation/concurrentMarkSweep/vmCMSOperations.hpp"
37 #include "gc_implementation/parNew/parNewGeneration.hpp"
38 #include "gc_implementation/shared/collectorCounters.hpp"
39 #include "gc_implementation/shared/gcTimer.hpp"
40 #include "gc_implementation/shared/gcTrace.hpp"
41 #include "gc_implementation/shared/gcTraceTime.hpp"
42 #include "gc_implementation/shared/isGCActiveMark.hpp"
43 #include "gc_interface/collectedHeap.inline.hpp"
44 #include "memory/allocation.hpp"
45 #include "memory/cardTableRS.hpp"
46 #include "memory/collectorPolicy.hpp"
47 #include "memory/gcLocker.inline.hpp"
48 #include "memory/genCollectedHeap.hpp"
49 #include "memory/genMarkSweep.hpp"
50 #include "memory/genOopClosures.inline.hpp"
51 #include "memory/iterator.inline.hpp"
52 #include "memory/padded.hpp"
53 #include "memory/referencePolicy.hpp"
54 #include "memory/resourceArea.hpp"
55 #include "memory/tenuredGeneration.hpp"
56 #include "oops/oop.inline.hpp"
57 #include "prims/jvmtiExport.hpp"
58 #include "runtime/atomic.inline.hpp"
59 #include "runtime/globals_extension.hpp"
60 #include "runtime/handles.inline.hpp"
61 #include "runtime/java.hpp"
62 #include "runtime/orderAccess.inline.hpp"
63 #include "runtime/vmThread.hpp"
64 #include "services/memoryService.hpp"
65 #include "services/runtimeService.hpp"
66
67 PRAGMA_FORMAT_MUTE_WARNINGS_FOR_GCC
68
69 // statics
70 CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL;
71 bool CMSCollector::_full_gc_requested = false;
72 GCCause::Cause CMSCollector::_full_gc_cause = GCCause::_no_gc;
73
74 //////////////////////////////////////////////////////////////////
75 // In support of CMS/VM thread synchronization
76 //////////////////////////////////////////////////////////////////
77 // We split use of the CGC_lock into 2 "levels".
78 // The low-level locking is of the usual CGC_lock monitor. We introduce
79 // a higher level "token" (hereafter "CMS token") built on top of the
80 // low level monitor (hereafter "CGC lock").
81 // The token-passing protocol gives priority to the VM thread. The
82 // CMS-lock doesn't provide any fairness guarantees, but clients
83 // should ensure that it is only held for very short, bounded
84 // durations.
85 //
86 // When either of the CMS thread or the VM thread is involved in
87 // collection operations during which it does not want the other
88 // thread to interfere, it obtains the CMS token.
89 //
90 // If either thread tries to get the token while the other has
91 // it, that thread waits. However, if the VM thread and CMS thread
92 // both want the token, then the VM thread gets priority while the
93 // CMS thread waits. This ensures, for instance, that the "concurrent"
94 // phases of the CMS thread's work do not block out the VM thread
95 // for long periods of time as the CMS thread continues to hog
96 // the token. (See bug 4616232).
97 //
98 // The baton-passing functions are, however, controlled by the
99 // flags _foregroundGCShouldWait and _foregroundGCIsActive,
100 // and here the low-level CMS lock, not the high level token,
101 // ensures mutual exclusion.
102 //
103 // Two important conditions that we have to satisfy:
104 // 1. if a thread does a low-level wait on the CMS lock, then it
105 // relinquishes the CMS token if it were holding that token
106 // when it acquired the low-level CMS lock.
107 // 2. any low-level notifications on the low-level lock
108 // should only be sent when a thread has relinquished the token.
109 //
110 // In the absence of either property, we'd have potential deadlock.
111 //
112 // We protect each of the CMS (concurrent and sequential) phases
113 // with the CMS _token_, not the CMS _lock_.
114 //
115 // The only code protected by CMS lock is the token acquisition code
116 // itself, see ConcurrentMarkSweepThread::[de]synchronize(), and the
117 // baton-passing code.
118 //
119 // Unfortunately, i couldn't come up with a good abstraction to factor and
120 // hide the naked CGC_lock manipulation in the baton-passing code
121 // further below. That's something we should try to do. Also, the proof
122 // of correctness of this 2-level locking scheme is far from obvious,
123 // and potentially quite slippery. We have an uneasy suspicion, for instance,
124 // that there may be a theoretical possibility of delay/starvation in the
125 // low-level lock/wait/notify scheme used for the baton-passing because of
126 // potential interference with the priority scheme embodied in the
127 // CMS-token-passing protocol. See related comments at a CGC_lock->wait()
128 // invocation further below and marked with "XXX 20011219YSR".
129 // Indeed, as we note elsewhere, this may become yet more slippery
130 // in the presence of multiple CMS and/or multiple VM threads. XXX
131
132 class CMSTokenSync: public StackObj {
133 private:
134 bool _is_cms_thread;
135 public:
136 CMSTokenSync(bool is_cms_thread):
137 _is_cms_thread(is_cms_thread) {
138 assert(is_cms_thread == Thread::current()->is_ConcurrentGC_thread(),
139 "Incorrect argument to constructor");
140 ConcurrentMarkSweepThread::synchronize(_is_cms_thread);
141 }
142
143 ~CMSTokenSync() {
144 assert(_is_cms_thread ?
145 ConcurrentMarkSweepThread::cms_thread_has_cms_token() :
146 ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
147 "Incorrect state");
148 ConcurrentMarkSweepThread::desynchronize(_is_cms_thread);
149 }
150 };
151
152 // Convenience class that does a CMSTokenSync, and then acquires
153 // upto three locks.
154 class CMSTokenSyncWithLocks: public CMSTokenSync {
155 private:
156 // Note: locks are acquired in textual declaration order
157 // and released in the opposite order
158 MutexLockerEx _locker1, _locker2, _locker3;
159 public:
160 CMSTokenSyncWithLocks(bool is_cms_thread, Mutex* mutex1,
161 Mutex* mutex2 = NULL, Mutex* mutex3 = NULL):
162 CMSTokenSync(is_cms_thread),
163 _locker1(mutex1, Mutex::_no_safepoint_check_flag),
164 _locker2(mutex2, Mutex::_no_safepoint_check_flag),
165 _locker3(mutex3, Mutex::_no_safepoint_check_flag)
166 { }
167 };
168
169
170 //////////////////////////////////////////////////////////////////
171 // Concurrent Mark-Sweep Generation /////////////////////////////
172 //////////////////////////////////////////////////////////////////
173
174 NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;)
175
176 // This struct contains per-thread things necessary to support parallel
177 // young-gen collection.
178 class CMSParGCThreadState: public CHeapObj<mtGC> {
179 public:
180 CFLS_LAB lab;
181 PromotionInfo promo;
182
183 // Constructor.
184 CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) {
185 promo.setSpace(cfls);
186 }
187 };
188
189 ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration(
190 ReservedSpace rs, size_t initial_byte_size, int level,
191 CardTableRS* ct, bool use_adaptive_freelists,
192 FreeBlockDictionary<FreeChunk>::DictionaryChoice dictionaryChoice) :
193 CardGeneration(rs, initial_byte_size, level, ct),
194 _dilatation_factor(((double)MinChunkSize)/((double)(CollectedHeap::min_fill_size()))),
195 _did_compact(false)
196 {
197 HeapWord* bottom = (HeapWord*) _virtual_space.low();
198 HeapWord* end = (HeapWord*) _virtual_space.high();
199
200 _direct_allocated_words = 0;
201 NOT_PRODUCT(
202 _numObjectsPromoted = 0;
203 _numWordsPromoted = 0;
204 _numObjectsAllocated = 0;
205 _numWordsAllocated = 0;
206 )
207
208 _cmsSpace = new CompactibleFreeListSpace(_bts, MemRegion(bottom, end),
209 use_adaptive_freelists,
210 dictionaryChoice);
211 NOT_PRODUCT(debug_cms_space = _cmsSpace;)
212 if (_cmsSpace == NULL) {
213 vm_exit_during_initialization(
214 "CompactibleFreeListSpace allocation failure");
215 }
216 _cmsSpace->_gen = this;
217
218 _gc_stats = new CMSGCStats();
219
220 // Verify the assumption that FreeChunk::_prev and OopDesc::_klass
221 // offsets match. The ability to tell free chunks from objects
222 // depends on this property.
223 debug_only(
224 FreeChunk* junk = NULL;
225 assert(UseCompressedClassPointers ||
226 junk->prev_addr() == (void*)(oop(junk)->klass_addr()),
227 "Offset of FreeChunk::_prev within FreeChunk must match"
228 " that of OopDesc::_klass within OopDesc");
229 )
230 if (CollectedHeap::use_parallel_gc_threads()) {
231 typedef CMSParGCThreadState* CMSParGCThreadStatePtr;
232 _par_gc_thread_states =
233 NEW_C_HEAP_ARRAY(CMSParGCThreadStatePtr, ParallelGCThreads, mtGC);
234 if (_par_gc_thread_states == NULL) {
235 vm_exit_during_initialization("Could not allocate par gc structs");
236 }
237 for (uint i = 0; i < ParallelGCThreads; i++) {
238 _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace());
239 if (_par_gc_thread_states[i] == NULL) {
240 vm_exit_during_initialization("Could not allocate par gc structs");
241 }
242 }
243 } else {
244 _par_gc_thread_states = NULL;
245 }
246 _incremental_collection_failed = false;
247 // The "dilatation_factor" is the expansion that can occur on
248 // account of the fact that the minimum object size in the CMS
249 // generation may be larger than that in, say, a contiguous young
250 // generation.
251 // Ideally, in the calculation below, we'd compute the dilatation
252 // factor as: MinChunkSize/(promoting_gen's min object size)
253 // Since we do not have such a general query interface for the
254 // promoting generation, we'll instead just use the minimum
255 // object size (which today is a header's worth of space);
256 // note that all arithmetic is in units of HeapWords.
257 assert(MinChunkSize >= CollectedHeap::min_fill_size(), "just checking");
258 assert(_dilatation_factor >= 1.0, "from previous assert");
259 }
260
261
262 // The field "_initiating_occupancy" represents the occupancy percentage
263 // at which we trigger a new collection cycle. Unless explicitly specified
264 // via CMSInitiatingOccupancyFraction (argument "io" below), it
265 // is calculated by:
266 //
267 // Let "f" be MinHeapFreeRatio in
268 //
269 // _initiating_occupancy = 100-f +
270 // f * (CMSTriggerRatio/100)
271 // where CMSTriggerRatio is the argument "tr" below.
272 //
273 // That is, if we assume the heap is at its desired maximum occupancy at the
274 // end of a collection, we let CMSTriggerRatio of the (purported) free
275 // space be allocated before initiating a new collection cycle.
276 //
277 void ConcurrentMarkSweepGeneration::init_initiating_occupancy(intx io, uintx tr) {
278 assert(io <= 100 && tr <= 100, "Check the arguments");
279 if (io >= 0) {
280 _initiating_occupancy = (double)io / 100.0;
281 } else {
282 _initiating_occupancy = ((100 - MinHeapFreeRatio) +
283 (double)(tr * MinHeapFreeRatio) / 100.0)
284 / 100.0;
285 }
286 }
287
288 void ConcurrentMarkSweepGeneration::ref_processor_init() {
289 assert(collector() != NULL, "no collector");
290 collector()->ref_processor_init();
291 }
292
293 void CMSCollector::ref_processor_init() {
294 if (_ref_processor == NULL) {
295 // Allocate and initialize a reference processor
296 _ref_processor =
297 new ReferenceProcessor(_span, // span
298 (ParallelGCThreads > 1) && ParallelRefProcEnabled, // mt processing
299 (int) ParallelGCThreads, // mt processing degree
300 _cmsGen->refs_discovery_is_mt(), // mt discovery
301 (int) MAX2(ConcGCThreads, ParallelGCThreads), // mt discovery degree
302 _cmsGen->refs_discovery_is_atomic(), // discovery is not atomic
303 &_is_alive_closure); // closure for liveness info
304 // Initialize the _ref_processor field of CMSGen
305 _cmsGen->set_ref_processor(_ref_processor);
306
307 }
308 }
309
310 AdaptiveSizePolicy* CMSCollector::size_policy() {
311 GenCollectedHeap* gch = GenCollectedHeap::heap();
312 assert(gch->kind() == CollectedHeap::GenCollectedHeap,
313 "Wrong type of heap");
314 return gch->gen_policy()->size_policy();
315 }
316
317 void ConcurrentMarkSweepGeneration::initialize_performance_counters() {
318
319 const char* gen_name = "old";
320 GenCollectorPolicy* gcp = (GenCollectorPolicy*) GenCollectedHeap::heap()->collector_policy();
321
322 // Generation Counters - generation 1, 1 subspace
323 _gen_counters = new GenerationCounters(gen_name, 1, 1,
324 gcp->min_old_size(), gcp->max_old_size(), &_virtual_space);
325
326 _space_counters = new GSpaceCounters(gen_name, 0,
327 _virtual_space.reserved_size(),
328 this, _gen_counters);
329 }
330
331 CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha):
332 _cms_gen(cms_gen)
333 {
334 assert(alpha <= 100, "bad value");
335 _saved_alpha = alpha;
336
337 // Initialize the alphas to the bootstrap value of 100.
338 _gc0_alpha = _cms_alpha = 100;
339
340 _cms_begin_time.update();
341 _cms_end_time.update();
342
343 _gc0_duration = 0.0;
344 _gc0_period = 0.0;
345 _gc0_promoted = 0;
346
347 _cms_duration = 0.0;
348 _cms_period = 0.0;
349 _cms_allocated = 0;
350
351 _cms_used_at_gc0_begin = 0;
352 _cms_used_at_gc0_end = 0;
353 _allow_duty_cycle_reduction = false;
354 _valid_bits = 0;
355 }
356
357 double CMSStats::cms_free_adjustment_factor(size_t free) const {
358 // TBD: CR 6909490
359 return 1.0;
360 }
361
362 void CMSStats::adjust_cms_free_adjustment_factor(bool fail, size_t free) {
363 }
364
365 // If promotion failure handling is on use
366 // the padded average size of the promotion for each
367 // young generation collection.
368 double CMSStats::time_until_cms_gen_full() const {
369 size_t cms_free = _cms_gen->cmsSpace()->free();
370 GenCollectedHeap* gch = GenCollectedHeap::heap();
371 size_t expected_promotion = MIN2(gch->get_gen(0)->capacity(),
372 (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average());
373 if (cms_free > expected_promotion) {
374 // Start a cms collection if there isn't enough space to promote
375 // for the next minor collection. Use the padded average as
376 // a safety factor.
377 cms_free -= expected_promotion;
378
379 // Adjust by the safety factor.
380 double cms_free_dbl = (double)cms_free;
381 double cms_adjustment = (100.0 - CMSIncrementalSafetyFactor)/100.0;
382 // Apply a further correction factor which tries to adjust
383 // for recent occurance of concurrent mode failures.
384 cms_adjustment = cms_adjustment * cms_free_adjustment_factor(cms_free);
385 cms_free_dbl = cms_free_dbl * cms_adjustment;
386
387 if (PrintGCDetails && Verbose) {
388 gclog_or_tty->print_cr("CMSStats::time_until_cms_gen_full: cms_free "
389 SIZE_FORMAT " expected_promotion " SIZE_FORMAT,
390 cms_free, expected_promotion);
391 gclog_or_tty->print_cr(" cms_free_dbl %f cms_consumption_rate %f",
392 cms_free_dbl, cms_consumption_rate() + 1.0);
393 }
394 // Add 1 in case the consumption rate goes to zero.
395 return cms_free_dbl / (cms_consumption_rate() + 1.0);
396 }
397 return 0.0;
398 }
399
400 // Compare the duration of the cms collection to the
401 // time remaining before the cms generation is empty.
402 // Note that the time from the start of the cms collection
403 // to the start of the cms sweep (less than the total
404 // duration of the cms collection) can be used. This
405 // has been tried and some applications experienced
406 // promotion failures early in execution. This was
407 // possibly because the averages were not accurate
408 // enough at the beginning.
409 double CMSStats::time_until_cms_start() const {
410 // We add "gc0_period" to the "work" calculation
411 // below because this query is done (mostly) at the
412 // end of a scavenge, so we need to conservatively
413 // account for that much possible delay
414 // in the query so as to avoid concurrent mode failures
415 // due to starting the collection just a wee bit too
416 // late.
417 double work = cms_duration() + gc0_period();
418 double deadline = time_until_cms_gen_full();
419 // If a concurrent mode failure occurred recently, we want to be
420 // more conservative and halve our expected time_until_cms_gen_full()
421 if (work > deadline) {
422 if (Verbose && PrintGCDetails) {
423 gclog_or_tty->print(
424 " CMSCollector: collect because of anticipated promotion "
425 "before full %3.7f + %3.7f > %3.7f ", cms_duration(),
426 gc0_period(), time_until_cms_gen_full());
427 }
428 return 0.0;
429 }
430 return work - deadline;
431 }
432
433 #ifndef PRODUCT
434 void CMSStats::print_on(outputStream *st) const {
435 st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha);
436 st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo=" SIZE_FORMAT,
437 gc0_duration(), gc0_period(), gc0_promoted());
438 st->print(",cms_dur=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT,
439 cms_duration(), cms_period(), cms_allocated());
440 st->print(",cms_since_beg=%g,cms_since_end=%g",
441 cms_time_since_begin(), cms_time_since_end());
442 st->print(",cms_used_beg=" SIZE_FORMAT ",cms_used_end=" SIZE_FORMAT,
443 _cms_used_at_gc0_begin, _cms_used_at_gc0_end);
444
445 if (valid()) {
446 st->print(",promo_rate=%g,cms_alloc_rate=%g",
447 promotion_rate(), cms_allocation_rate());
448 st->print(",cms_consumption_rate=%g,time_until_full=%g",
449 cms_consumption_rate(), time_until_cms_gen_full());
450 }
451 st->print(" ");
452 }
453 #endif // #ifndef PRODUCT
454
455 CMSCollector::CollectorState CMSCollector::_collectorState =
456 CMSCollector::Idling;
457 bool CMSCollector::_foregroundGCIsActive = false;
458 bool CMSCollector::_foregroundGCShouldWait = false;
459
460 CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
461 CardTableRS* ct,
462 ConcurrentMarkSweepPolicy* cp):
463 _cmsGen(cmsGen),
464 _ct(ct),
465 _ref_processor(NULL), // will be set later
466 _conc_workers(NULL), // may be set later
467 _abort_preclean(false),
468 _start_sampling(false),
469 _between_prologue_and_epilogue(false),
470 _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"),
471 _modUnionTable((CardTableModRefBS::card_shift - LogHeapWordSize),
472 -1 /* lock-free */, "No_lock" /* dummy */),
473 _modUnionClosure(&_modUnionTable),
474 _modUnionClosurePar(&_modUnionTable),
475 // Adjust my span to cover old (cms) gen
476 _span(cmsGen->reserved()),
477 // Construct the is_alive_closure with _span & markBitMap
478 _is_alive_closure(_span, &_markBitMap),
479 _restart_addr(NULL),
480 _overflow_list(NULL),
481 _stats(cmsGen),
482 _eden_chunk_lock(new Mutex(Mutex::leaf + 1, "CMS_eden_chunk_lock", true)),
483 _eden_chunk_array(NULL), // may be set in ctor body
484 _eden_chunk_capacity(0), // -- ditto --
485 _eden_chunk_index(0), // -- ditto --
486 _survivor_plab_array(NULL), // -- ditto --
487 _survivor_chunk_array(NULL), // -- ditto --
488 _survivor_chunk_capacity(0), // -- ditto --
489 _survivor_chunk_index(0), // -- ditto --
490 _ser_pmc_preclean_ovflw(0),
491 _ser_kac_preclean_ovflw(0),
492 _ser_pmc_remark_ovflw(0),
493 _par_pmc_remark_ovflw(0),
494 _ser_kac_ovflw(0),
495 _par_kac_ovflw(0),
496 #ifndef PRODUCT
497 _num_par_pushes(0),
498 #endif
499 _collection_count_start(0),
500 _verifying(false),
501 _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"),
502 _completed_initialization(false),
503 _collector_policy(cp),
504 _should_unload_classes(CMSClassUnloadingEnabled),
505 _concurrent_cycles_since_last_unload(0),
506 _roots_scanning_options(SharedHeap::SO_None),
507 _inter_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
508 _intra_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
509 _gc_tracer_cm(new (ResourceObj::C_HEAP, mtGC) CMSTracer()),
510 _gc_timer_cm(new (ResourceObj::C_HEAP, mtGC) ConcurrentGCTimer()),
511 _cms_start_registered(false)
512 {
513 if (ExplicitGCInvokesConcurrentAndUnloadsClasses) {
514 ExplicitGCInvokesConcurrent = true;
515 }
516 // Now expand the span and allocate the collection support structures
517 // (MUT, marking bit map etc.) to cover both generations subject to
518 // collection.
519
520 // For use by dirty card to oop closures.
521 _cmsGen->cmsSpace()->set_collector(this);
522
523 // Allocate MUT and marking bit map
524 {
525 MutexLockerEx x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag);
526 if (!_markBitMap.allocate(_span)) {
527 warning("Failed to allocate CMS Bit Map");
528 return;
529 }
530 assert(_markBitMap.covers(_span), "_markBitMap inconsistency?");
531 }
532 {
533 _modUnionTable.allocate(_span);
534 assert(_modUnionTable.covers(_span), "_modUnionTable inconsistency?");
535 }
536
537 if (!_markStack.allocate(MarkStackSize)) {
538 warning("Failed to allocate CMS Marking Stack");
539 return;
540 }
541
542 // Support for multi-threaded concurrent phases
543 if (CMSConcurrentMTEnabled) {
544 if (FLAG_IS_DEFAULT(ConcGCThreads)) {
545 // just for now
546 FLAG_SET_DEFAULT(ConcGCThreads, (ParallelGCThreads + 3)/4);
547 }
548 if (ConcGCThreads > 1) {
549 _conc_workers = new YieldingFlexibleWorkGang("Parallel CMS Threads",
550 ConcGCThreads, true);
551 if (_conc_workers == NULL) {
552 warning("GC/CMS: _conc_workers allocation failure: "
553 "forcing -CMSConcurrentMTEnabled");
554 CMSConcurrentMTEnabled = false;
555 } else {
556 _conc_workers->initialize_workers();
557 }
558 } else {
559 CMSConcurrentMTEnabled = false;
560 }
561 }
562 if (!CMSConcurrentMTEnabled) {
563 ConcGCThreads = 0;
564 } else {
565 // Turn off CMSCleanOnEnter optimization temporarily for
566 // the MT case where it's not fixed yet; see 6178663.
567 CMSCleanOnEnter = false;
568 }
569 assert((_conc_workers != NULL) == (ConcGCThreads > 1),
570 "Inconsistency");
571
572 // Parallel task queues; these are shared for the
573 // concurrent and stop-world phases of CMS, but
574 // are not shared with parallel scavenge (ParNew).
575 {
576 uint i;
577 uint num_queues = (uint) MAX2(ParallelGCThreads, ConcGCThreads);
578
579 if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled
580 || ParallelRefProcEnabled)
581 && num_queues > 0) {
582 _task_queues = new OopTaskQueueSet(num_queues);
583 if (_task_queues == NULL) {
584 warning("task_queues allocation failure.");
585 return;
586 }
587 _hash_seed = NEW_C_HEAP_ARRAY(int, num_queues, mtGC);
588 if (_hash_seed == NULL) {
589 warning("_hash_seed array allocation failure");
590 return;
591 }
592
593 typedef Padded<OopTaskQueue> PaddedOopTaskQueue;
594 for (i = 0; i < num_queues; i++) {
595 PaddedOopTaskQueue *q = new PaddedOopTaskQueue();
596 if (q == NULL) {
597 warning("work_queue allocation failure.");
598 return;
599 }
600 _task_queues->register_queue(i, q);
601 }
602 for (i = 0; i < num_queues; i++) {
603 _task_queues->queue(i)->initialize();
604 _hash_seed[i] = 17; // copied from ParNew
605 }
606 }
607 }
608
609 _cmsGen ->init_initiating_occupancy(CMSInitiatingOccupancyFraction, CMSTriggerRatio);
610
611 // Clip CMSBootstrapOccupancy between 0 and 100.
612 _bootstrap_occupancy = ((double)CMSBootstrapOccupancy)/(double)100;
613
614 // Now tell CMS generations the identity of their collector
615 ConcurrentMarkSweepGeneration::set_collector(this);
616
617 // Create & start a CMS thread for this CMS collector
618 _cmsThread = ConcurrentMarkSweepThread::start(this);
619 assert(cmsThread() != NULL, "CMS Thread should have been created");
620 assert(cmsThread()->collector() == this,
621 "CMS Thread should refer to this gen");
622 assert(CGC_lock != NULL, "Where's the CGC_lock?");
623
624 // Support for parallelizing young gen rescan
625 GenCollectedHeap* gch = GenCollectedHeap::heap();
626 assert(gch->prev_gen(_cmsGen)->kind() == Generation::ParNew, "CMS can only be used with ParNew");
627 _young_gen = (ParNewGeneration*)gch->prev_gen(_cmsGen);
628 if (gch->supports_inline_contig_alloc()) {
629 _top_addr = gch->top_addr();
630 _end_addr = gch->end_addr();
631 assert(_young_gen != NULL, "no _young_gen");
632 _eden_chunk_index = 0;
633 _eden_chunk_capacity = (_young_gen->max_capacity()+CMSSamplingGrain)/CMSSamplingGrain;
634 _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity, mtGC);
635 if (_eden_chunk_array == NULL) {
636 _eden_chunk_capacity = 0;
637 warning("GC/CMS: _eden_chunk_array allocation failure");
638 }
639 }
640 assert(_eden_chunk_array != NULL || _eden_chunk_capacity == 0, "Error");
641
642 // Support for parallelizing survivor space rescan
643 if ((CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) || CMSParallelInitialMarkEnabled) {
644 const size_t max_plab_samples =
645 ((DefNewGeneration*)_young_gen)->max_survivor_size()/MinTLABSize;
646
647 _survivor_plab_array = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads, mtGC);
648 _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, 2*max_plab_samples, mtGC);
649 _cursor = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads, mtGC);
650 if (_survivor_plab_array == NULL || _survivor_chunk_array == NULL
651 || _cursor == NULL) {
652 warning("Failed to allocate survivor plab/chunk array");
653 if (_survivor_plab_array != NULL) {
654 FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array, mtGC);
655 _survivor_plab_array = NULL;
656 }
657 if (_survivor_chunk_array != NULL) {
658 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array, mtGC);
659 _survivor_chunk_array = NULL;
660 }
661 if (_cursor != NULL) {
662 FREE_C_HEAP_ARRAY(size_t, _cursor, mtGC);
663 _cursor = NULL;
664 }
665 } else {
666 _survivor_chunk_capacity = 2*max_plab_samples;
667 for (uint i = 0; i < ParallelGCThreads; i++) {
668 HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
669 if (vec == NULL) {
670 warning("Failed to allocate survivor plab array");
671 for (int j = i; j > 0; j--) {
672 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_plab_array[j-1].array(), mtGC);
673 }
674 FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array, mtGC);
675 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array, mtGC);
676 _survivor_plab_array = NULL;
677 _survivor_chunk_array = NULL;
678 _survivor_chunk_capacity = 0;
679 break;
680 } else {
681 ChunkArray* cur =
682 ::new (&_survivor_plab_array[i]) ChunkArray(vec,
683 max_plab_samples);
684 assert(cur->end() == 0, "Should be 0");
685 assert(cur->array() == vec, "Should be vec");
686 assert(cur->capacity() == max_plab_samples, "Error");
687 }
688 }
689 }
690 }
691 assert( ( _survivor_plab_array != NULL
692 && _survivor_chunk_array != NULL)
693 || ( _survivor_chunk_capacity == 0
694 && _survivor_chunk_index == 0),
695 "Error");
696
697 NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;)
698 _gc_counters = new CollectorCounters("CMS", 1);
699 _completed_initialization = true;
700 _inter_sweep_timer.start(); // start of time
701 }
702
703 const char* ConcurrentMarkSweepGeneration::name() const {
704 return "concurrent mark-sweep generation";
705 }
706 void ConcurrentMarkSweepGeneration::update_counters() {
707 if (UsePerfData) {
708 _space_counters->update_all();
709 _gen_counters->update_all();
710 }
711 }
712
713 // this is an optimized version of update_counters(). it takes the
714 // used value as a parameter rather than computing it.
715 //
716 void ConcurrentMarkSweepGeneration::update_counters(size_t used) {
717 if (UsePerfData) {
718 _space_counters->update_used(used);
719 _space_counters->update_capacity();
720 _gen_counters->update_all();
721 }
722 }
723
724 void ConcurrentMarkSweepGeneration::print() const {
725 Generation::print();
726 cmsSpace()->print();
727 }
728
729 #ifndef PRODUCT
730 void ConcurrentMarkSweepGeneration::print_statistics() {
731 cmsSpace()->printFLCensus(0);
732 }
733 #endif
734
735 void ConcurrentMarkSweepGeneration::printOccupancy(const char *s) {
736 GenCollectedHeap* gch = GenCollectedHeap::heap();
737 if (PrintGCDetails) {
738 if (Verbose) {
739 gclog_or_tty->print("[%d %s-%s: "SIZE_FORMAT"("SIZE_FORMAT")]",
740 level(), short_name(), s, used(), capacity());
741 } else {
742 gclog_or_tty->print("[%d %s-%s: "SIZE_FORMAT"K("SIZE_FORMAT"K)]",
743 level(), short_name(), s, used() / K, capacity() / K);
744 }
745 }
746 if (Verbose) {
747 gclog_or_tty->print(" "SIZE_FORMAT"("SIZE_FORMAT")",
748 gch->used(), gch->capacity());
749 } else {
750 gclog_or_tty->print(" "SIZE_FORMAT"K("SIZE_FORMAT"K)",
751 gch->used() / K, gch->capacity() / K);
752 }
753 }
754
755 size_t
756 ConcurrentMarkSweepGeneration::contiguous_available() const {
757 // dld proposes an improvement in precision here. If the committed
758 // part of the space ends in a free block we should add that to
759 // uncommitted size in the calculation below. Will make this
760 // change later, staying with the approximation below for the
761 // time being. -- ysr.
762 return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc());
763 }
764
765 size_t
766 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const {
767 return _cmsSpace->max_alloc_in_words() * HeapWordSize;
768 }
769
770 size_t ConcurrentMarkSweepGeneration::max_available() const {
771 return free() + _virtual_space.uncommitted_size();
772 }
773
774 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(size_t max_promotion_in_bytes) const {
775 size_t available = max_available();
776 size_t av_promo = (size_t)gc_stats()->avg_promoted()->padded_average();
777 bool res = (available >= av_promo) || (available >= max_promotion_in_bytes);
778 if (Verbose && PrintGCDetails) {
779 gclog_or_tty->print_cr(
780 "CMS: promo attempt is%s safe: available("SIZE_FORMAT") %s av_promo("SIZE_FORMAT"),"
781 "max_promo("SIZE_FORMAT")",
782 res? "":" not", available, res? ">=":"<",
783 av_promo, max_promotion_in_bytes);
784 }
785 return res;
786 }
787
788 // At a promotion failure dump information on block layout in heap
789 // (cms old generation).
790 void ConcurrentMarkSweepGeneration::promotion_failure_occurred() {
791 if (CMSDumpAtPromotionFailure) {
792 cmsSpace()->dump_at_safepoint_with_locks(collector(), gclog_or_tty);
793 }
794 }
795
796 CompactibleSpace*
797 ConcurrentMarkSweepGeneration::first_compaction_space() const {
798 return _cmsSpace;
799 }
800
801 void ConcurrentMarkSweepGeneration::reset_after_compaction() {
802 // Clear the promotion information. These pointers can be adjusted
803 // along with all the other pointers into the heap but
804 // compaction is expected to be a rare event with
805 // a heap using cms so don't do it without seeing the need.
806 for (uint i = 0; i < ParallelGCThreads; i++) {
807 _par_gc_thread_states[i]->promo.reset();
808 }
809 }
810
811 void ConcurrentMarkSweepGeneration::space_iterate(SpaceClosure* blk, bool usedOnly) {
812 blk->do_space(_cmsSpace);
813 }
814
815 void ConcurrentMarkSweepGeneration::compute_new_size() {
816 assert_locked_or_safepoint(Heap_lock);
817
818 // If incremental collection failed, we just want to expand
819 // to the limit.
820 if (incremental_collection_failed()) {
821 clear_incremental_collection_failed();
822 grow_to_reserved();
823 return;
824 }
825
826 // The heap has been compacted but not reset yet.
827 // Any metric such as free() or used() will be incorrect.
828
829 CardGeneration::compute_new_size();
830
831 // Reset again after a possible resizing
832 if (did_compact()) {
833 cmsSpace()->reset_after_compaction();
834 }
835 }
836
837 void ConcurrentMarkSweepGeneration::compute_new_size_free_list() {
838 assert_locked_or_safepoint(Heap_lock);
839
840 // If incremental collection failed, we just want to expand
841 // to the limit.
842 if (incremental_collection_failed()) {
843 clear_incremental_collection_failed();
844 grow_to_reserved();
845 return;
846 }
847
848 double free_percentage = ((double) free()) / capacity();
849 double desired_free_percentage = (double) MinHeapFreeRatio / 100;
850 double maximum_free_percentage = (double) MaxHeapFreeRatio / 100;
851
852 // compute expansion delta needed for reaching desired free percentage
853 if (free_percentage < desired_free_percentage) {
854 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
855 assert(desired_capacity >= capacity(), "invalid expansion size");
856 size_t expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes);
857 if (PrintGCDetails && Verbose) {
858 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
859 gclog_or_tty->print_cr("\nFrom compute_new_size: ");
860 gclog_or_tty->print_cr(" Free fraction %f", free_percentage);
861 gclog_or_tty->print_cr(" Desired free fraction %f",
862 desired_free_percentage);
863 gclog_or_tty->print_cr(" Maximum free fraction %f",
864 maximum_free_percentage);
865 gclog_or_tty->print_cr(" Capacity "SIZE_FORMAT, capacity()/1000);
866 gclog_or_tty->print_cr(" Desired capacity "SIZE_FORMAT,
867 desired_capacity/1000);
868 int prev_level = level() - 1;
869 if (prev_level >= 0) {
870 size_t prev_size = 0;
871 GenCollectedHeap* gch = GenCollectedHeap::heap();
872 Generation* prev_gen = gch->_gens[prev_level];
873 prev_size = prev_gen->capacity();
874 gclog_or_tty->print_cr(" Younger gen size "SIZE_FORMAT,
875 prev_size/1000);
876 }
877 gclog_or_tty->print_cr(" unsafe_max_alloc_nogc "SIZE_FORMAT,
878 unsafe_max_alloc_nogc()/1000);
879 gclog_or_tty->print_cr(" contiguous available "SIZE_FORMAT,
880 contiguous_available()/1000);
881 gclog_or_tty->print_cr(" Expand by "SIZE_FORMAT" (bytes)",
882 expand_bytes);
883 }
884 // safe if expansion fails
885 expand(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio);
886 if (PrintGCDetails && Verbose) {
887 gclog_or_tty->print_cr(" Expanded free fraction %f",
888 ((double) free()) / capacity());
889 }
890 } else {
891 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
892 assert(desired_capacity <= capacity(), "invalid expansion size");
893 size_t shrink_bytes = capacity() - desired_capacity;
894 // Don't shrink unless the delta is greater than the minimum shrink we want
895 if (shrink_bytes >= MinHeapDeltaBytes) {
896 shrink_free_list_by(shrink_bytes);
897 }
898 }
899 }
900
901 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const {
902 return cmsSpace()->freelistLock();
903 }
904
905 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size,
906 bool tlab) {
907 CMSSynchronousYieldRequest yr;
908 MutexLockerEx x(freelistLock(),
909 Mutex::_no_safepoint_check_flag);
910 return have_lock_and_allocate(size, tlab);
911 }
912
913 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size,
914 bool tlab /* ignored */) {
915 assert_lock_strong(freelistLock());
916 size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size);
917 HeapWord* res = cmsSpace()->allocate(adjustedSize);
918 // Allocate the object live (grey) if the background collector has
919 // started marking. This is necessary because the marker may
920 // have passed this address and consequently this object will
921 // not otherwise be greyed and would be incorrectly swept up.
922 // Note that if this object contains references, the writing
923 // of those references will dirty the card containing this object
924 // allowing the object to be blackened (and its references scanned)
925 // either during a preclean phase or at the final checkpoint.
926 if (res != NULL) {
927 // We may block here with an uninitialized object with
928 // its mark-bit or P-bits not yet set. Such objects need
929 // to be safely navigable by block_start().
930 assert(oop(res)->klass_or_null() == NULL, "Object should be uninitialized here.");
931 assert(!((FreeChunk*)res)->is_free(), "Error, block will look free but show wrong size");
932 collector()->direct_allocated(res, adjustedSize);
933 _direct_allocated_words += adjustedSize;
934 // allocation counters
935 NOT_PRODUCT(
936 _numObjectsAllocated++;
937 _numWordsAllocated += (int)adjustedSize;
938 )
939 }
940 return res;
941 }
942
943 // In the case of direct allocation by mutators in a generation that
944 // is being concurrently collected, the object must be allocated
945 // live (grey) if the background collector has started marking.
946 // This is necessary because the marker may
947 // have passed this address and consequently this object will
948 // not otherwise be greyed and would be incorrectly swept up.
949 // Note that if this object contains references, the writing
950 // of those references will dirty the card containing this object
951 // allowing the object to be blackened (and its references scanned)
952 // either during a preclean phase or at the final checkpoint.
953 void CMSCollector::direct_allocated(HeapWord* start, size_t size) {
954 assert(_markBitMap.covers(start, size), "Out of bounds");
955 if (_collectorState >= Marking) {
956 MutexLockerEx y(_markBitMap.lock(),
957 Mutex::_no_safepoint_check_flag);
958 // [see comments preceding SweepClosure::do_blk() below for details]
959 //
960 // Can the P-bits be deleted now? JJJ
961 //
962 // 1. need to mark the object as live so it isn't collected
963 // 2. need to mark the 2nd bit to indicate the object may be uninitialized
964 // 3. need to mark the end of the object so marking, precleaning or sweeping
965 // can skip over uninitialized or unparsable objects. An allocated
966 // object is considered uninitialized for our purposes as long as
967 // its klass word is NULL. All old gen objects are parsable
968 // as soon as they are initialized.)
969 _markBitMap.mark(start); // object is live
970 _markBitMap.mark(start + 1); // object is potentially uninitialized?
971 _markBitMap.mark(start + size - 1);
972 // mark end of object
973 }
974 // check that oop looks uninitialized
975 assert(oop(start)->klass_or_null() == NULL, "_klass should be NULL");
976 }
977
978 void CMSCollector::promoted(bool par, HeapWord* start,
979 bool is_obj_array, size_t obj_size) {
980 assert(_markBitMap.covers(start), "Out of bounds");
981 // See comment in direct_allocated() about when objects should
982 // be allocated live.
983 if (_collectorState >= Marking) {
984 // we already hold the marking bit map lock, taken in
985 // the prologue
986 if (par) {
987 _markBitMap.par_mark(start);
988 } else {
989 _markBitMap.mark(start);
990 }
991 // We don't need to mark the object as uninitialized (as
992 // in direct_allocated above) because this is being done with the
993 // world stopped and the object will be initialized by the
994 // time the marking, precleaning or sweeping get to look at it.
995 // But see the code for copying objects into the CMS generation,
996 // where we need to ensure that concurrent readers of the
997 // block offset table are able to safely navigate a block that
998 // is in flux from being free to being allocated (and in
999 // transition while being copied into) and subsequently
1000 // becoming a bona-fide object when the copy/promotion is complete.
1001 assert(SafepointSynchronize::is_at_safepoint(),
1002 "expect promotion only at safepoints");
1003
1004 if (_collectorState < Sweeping) {
1005 // Mark the appropriate cards in the modUnionTable, so that
1006 // this object gets scanned before the sweep. If this is
1007 // not done, CMS generation references in the object might
1008 // not get marked.
1009 // For the case of arrays, which are otherwise precisely
1010 // marked, we need to dirty the entire array, not just its head.
1011 if (is_obj_array) {
1012 // The [par_]mark_range() method expects mr.end() below to
1013 // be aligned to the granularity of a bit's representation
1014 // in the heap. In the case of the MUT below, that's a
1015 // card size.
1016 MemRegion mr(start,
1017 (HeapWord*)round_to((intptr_t)(start + obj_size),
1018 CardTableModRefBS::card_size /* bytes */));
1019 if (par) {
1020 _modUnionTable.par_mark_range(mr);
1021 } else {
1022 _modUnionTable.mark_range(mr);
1023 }
1024 } else { // not an obj array; we can just mark the head
1025 if (par) {
1026 _modUnionTable.par_mark(start);
1027 } else {
1028 _modUnionTable.mark(start);
1029 }
1030 }
1031 }
1032 }
1033 }
1034
1035 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size) {
1036 assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
1037 // allocate, copy and if necessary update promoinfo --
1038 // delegate to underlying space.
1039 assert_lock_strong(freelistLock());
1040
1041 #ifndef PRODUCT
1042 if (Universe::heap()->promotion_should_fail()) {
1043 return NULL;
1044 }
1045 #endif // #ifndef PRODUCT
1046
1047 oop res = _cmsSpace->promote(obj, obj_size);
1048 if (res == NULL) {
1049 // expand and retry
1050 size_t s = _cmsSpace->expansionSpaceRequired(obj_size); // HeapWords
1051 expand(s*HeapWordSize, MinHeapDeltaBytes,
1052 CMSExpansionCause::_satisfy_promotion);
1053 // Since there's currently no next generation, we don't try to promote
1054 // into a more senior generation.
1055 assert(next_gen() == NULL, "assumption, based upon which no attempt "
1056 "is made to pass on a possibly failing "
1057 "promotion to next generation");
1058 res = _cmsSpace->promote(obj, obj_size);
1059 }
1060 if (res != NULL) {
1061 // See comment in allocate() about when objects should
1062 // be allocated live.
1063 assert(obj->is_oop(), "Will dereference klass pointer below");
1064 collector()->promoted(false, // Not parallel
1065 (HeapWord*)res, obj->is_objArray(), obj_size);
1066 // promotion counters
1067 NOT_PRODUCT(
1068 _numObjectsPromoted++;
1069 _numWordsPromoted +=
1070 (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size()));
1071 )
1072 }
1073 return res;
1074 }
1075
1076
1077 // IMPORTANT: Notes on object size recognition in CMS.
1078 // ---------------------------------------------------
1079 // A block of storage in the CMS generation is always in
1080 // one of three states. A free block (FREE), an allocated
1081 // object (OBJECT) whose size() method reports the correct size,
1082 // and an intermediate state (TRANSIENT) in which its size cannot
1083 // be accurately determined.
1084 // STATE IDENTIFICATION: (32 bit and 64 bit w/o COOPS)
1085 // -----------------------------------------------------
1086 // FREE: klass_word & 1 == 1; mark_word holds block size
1087 //
1088 // OBJECT: klass_word installed; klass_word != 0 && klass_word & 1 == 0;
1089 // obj->size() computes correct size
1090 //
1091 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1092 //
1093 // STATE IDENTIFICATION: (64 bit+COOPS)
1094 // ------------------------------------
1095 // FREE: mark_word & CMS_FREE_BIT == 1; mark_word & ~CMS_FREE_BIT gives block_size
1096 //
1097 // OBJECT: klass_word installed; klass_word != 0;
1098 // obj->size() computes correct size
1099 //
1100 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1101 //
1102 //
1103 // STATE TRANSITION DIAGRAM
1104 //
1105 // mut / parnew mut / parnew
1106 // FREE --------------------> TRANSIENT ---------------------> OBJECT --|
1107 // ^ |
1108 // |------------------------ DEAD <------------------------------------|
1109 // sweep mut
1110 //
1111 // While a block is in TRANSIENT state its size cannot be determined
1112 // so readers will either need to come back later or stall until
1113 // the size can be determined. Note that for the case of direct
1114 // allocation, P-bits, when available, may be used to determine the
1115 // size of an object that may not yet have been initialized.
1116
1117 // Things to support parallel young-gen collection.
1118 oop
1119 ConcurrentMarkSweepGeneration::par_promote(int thread_num,
1120 oop old, markOop m,
1121 size_t word_sz) {
1122 #ifndef PRODUCT
1123 if (Universe::heap()->promotion_should_fail()) {
1124 return NULL;
1125 }
1126 #endif // #ifndef PRODUCT
1127
1128 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1129 PromotionInfo* promoInfo = &ps->promo;
1130 // if we are tracking promotions, then first ensure space for
1131 // promotion (including spooling space for saving header if necessary).
1132 // then allocate and copy, then track promoted info if needed.
1133 // When tracking (see PromotionInfo::track()), the mark word may
1134 // be displaced and in this case restoration of the mark word
1135 // occurs in the (oop_since_save_marks_)iterate phase.
1136 if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) {
1137 // Out of space for allocating spooling buffers;
1138 // try expanding and allocating spooling buffers.
1139 if (!expand_and_ensure_spooling_space(promoInfo)) {
1140 return NULL;
1141 }
1142 }
1143 assert(promoInfo->has_spooling_space(), "Control point invariant");
1144 const size_t alloc_sz = CompactibleFreeListSpace::adjustObjectSize(word_sz);
1145 HeapWord* obj_ptr = ps->lab.alloc(alloc_sz);
1146 if (obj_ptr == NULL) {
1147 obj_ptr = expand_and_par_lab_allocate(ps, alloc_sz);
1148 if (obj_ptr == NULL) {
1149 return NULL;
1150 }
1151 }
1152 oop obj = oop(obj_ptr);
1153 OrderAccess::storestore();
1154 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1155 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1156 // IMPORTANT: See note on object initialization for CMS above.
1157 // Otherwise, copy the object. Here we must be careful to insert the
1158 // klass pointer last, since this marks the block as an allocated object.
1159 // Except with compressed oops it's the mark word.
1160 HeapWord* old_ptr = (HeapWord*)old;
1161 // Restore the mark word copied above.
1162 obj->set_mark(m);
1163 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1164 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1165 OrderAccess::storestore();
1166
1167 if (UseCompressedClassPointers) {
1168 // Copy gap missed by (aligned) header size calculation below
1169 obj->set_klass_gap(old->klass_gap());
1170 }
1171 if (word_sz > (size_t)oopDesc::header_size()) {
1172 Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1173 obj_ptr + oopDesc::header_size(),
1174 word_sz - oopDesc::header_size());
1175 }
1176
1177 // Now we can track the promoted object, if necessary. We take care
1178 // to delay the transition from uninitialized to full object
1179 // (i.e., insertion of klass pointer) until after, so that it
1180 // atomically becomes a promoted object.
1181 if (promoInfo->tracking()) {
1182 promoInfo->track((PromotedObject*)obj, old->klass());
1183 }
1184 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1185 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1186 assert(old->is_oop(), "Will use and dereference old klass ptr below");
1187
1188 // Finally, install the klass pointer (this should be volatile).
1189 OrderAccess::storestore();
1190 obj->set_klass(old->klass());
1191 // We should now be able to calculate the right size for this object
1192 assert(obj->is_oop() && obj->size() == (int)word_sz, "Error, incorrect size computed for promoted object");
1193
1194 collector()->promoted(true, // parallel
1195 obj_ptr, old->is_objArray(), word_sz);
1196
1197 NOT_PRODUCT(
1198 Atomic::inc_ptr(&_numObjectsPromoted);
1199 Atomic::add_ptr(alloc_sz, &_numWordsPromoted);
1200 )
1201
1202 return obj;
1203 }
1204
1205 void
1206 ConcurrentMarkSweepGeneration::
1207 par_promote_alloc_done(int thread_num) {
1208 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1209 ps->lab.retire(thread_num);
1210 }
1211
1212 void
1213 ConcurrentMarkSweepGeneration::
1214 par_oop_since_save_marks_iterate_done(int thread_num) {
1215 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1216 ParScanWithoutBarrierClosure* dummy_cl = NULL;
1217 ps->promo.promoted_oops_iterate_nv(dummy_cl);
1218 }
1219
1220 bool ConcurrentMarkSweepGeneration::should_collect(bool full,
1221 size_t size,
1222 bool tlab)
1223 {
1224 // We allow a STW collection only if a full
1225 // collection was requested.
1226 return full || should_allocate(size, tlab); // FIX ME !!!
1227 // This and promotion failure handling are connected at the
1228 // hip and should be fixed by untying them.
1229 }
1230
1231 bool CMSCollector::shouldConcurrentCollect() {
1232 if (_full_gc_requested) {
1233 if (Verbose && PrintGCDetails) {
1234 gclog_or_tty->print_cr("CMSCollector: collect because of explicit "
1235 " gc request (or gc_locker)");
1236 }
1237 return true;
1238 }
1239
1240 FreelistLocker x(this);
1241 // ------------------------------------------------------------------
1242 // Print out lots of information which affects the initiation of
1243 // a collection.
1244 if (PrintCMSInitiationStatistics && stats().valid()) {
1245 gclog_or_tty->print("CMSCollector shouldConcurrentCollect: ");
1246 gclog_or_tty->stamp();
1247 gclog_or_tty->cr();
1248 stats().print_on(gclog_or_tty);
1249 gclog_or_tty->print_cr("time_until_cms_gen_full %3.7f",
1250 stats().time_until_cms_gen_full());
1251 gclog_or_tty->print_cr("free="SIZE_FORMAT, _cmsGen->free());
1252 gclog_or_tty->print_cr("contiguous_available="SIZE_FORMAT,
1253 _cmsGen->contiguous_available());
1254 gclog_or_tty->print_cr("promotion_rate=%g", stats().promotion_rate());
1255 gclog_or_tty->print_cr("cms_allocation_rate=%g", stats().cms_allocation_rate());
1256 gclog_or_tty->print_cr("occupancy=%3.7f", _cmsGen->occupancy());
1257 gclog_or_tty->print_cr("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy());
1258 gclog_or_tty->print_cr("cms_time_since_begin=%3.7f", stats().cms_time_since_begin());
1259 gclog_or_tty->print_cr("cms_time_since_end=%3.7f", stats().cms_time_since_end());
1260 gclog_or_tty->print_cr("metadata initialized %d",
1261 MetaspaceGC::should_concurrent_collect());
1262 }
1263 // ------------------------------------------------------------------
1264
1265 // If the estimated time to complete a cms collection (cms_duration())
1266 // is less than the estimated time remaining until the cms generation
1267 // is full, start a collection.
1268 if (!UseCMSInitiatingOccupancyOnly) {
1269 if (stats().valid()) {
1270 if (stats().time_until_cms_start() == 0.0) {
1271 return true;
1272 }
1273 } else {
1274 // We want to conservatively collect somewhat early in order
1275 // to try and "bootstrap" our CMS/promotion statistics;
1276 // this branch will not fire after the first successful CMS
1277 // collection because the stats should then be valid.
1278 if (_cmsGen->occupancy() >= _bootstrap_occupancy) {
1279 if (Verbose && PrintGCDetails) {
1280 gclog_or_tty->print_cr(
1281 " CMSCollector: collect for bootstrapping statistics:"
1282 " occupancy = %f, boot occupancy = %f", _cmsGen->occupancy(),
1283 _bootstrap_occupancy);
1284 }
1285 return true;
1286 }
1287 }
1288 }
1289
1290 // Otherwise, we start a collection cycle if
1291 // old gen want a collection cycle started. Each may use
1292 // an appropriate criterion for making this decision.
1293 // XXX We need to make sure that the gen expansion
1294 // criterion dovetails well with this. XXX NEED TO FIX THIS
1295 if (_cmsGen->should_concurrent_collect()) {
1296 if (Verbose && PrintGCDetails) {
1297 gclog_or_tty->print_cr("CMS old gen initiated");
1298 }
1299 return true;
1300 }
1301
1302 // We start a collection if we believe an incremental collection may fail;
1303 // this is not likely to be productive in practice because it's probably too
1304 // late anyway.
1305 GenCollectedHeap* gch = GenCollectedHeap::heap();
1306 assert(gch->collector_policy()->is_generation_policy(),
1307 "You may want to check the correctness of the following");
1308 if (gch->incremental_collection_will_fail(true /* consult_young */)) {
1309 if (Verbose && PrintGCDetails) {
1310 gclog_or_tty->print("CMSCollector: collect because incremental collection will fail ");
1311 }
1312 return true;
1313 }
1314
1315 if (MetaspaceGC::should_concurrent_collect()) {
1316 if (Verbose && PrintGCDetails) {
1317 gclog_or_tty->print("CMSCollector: collect for metadata allocation ");
1318 }
1319 return true;
1320 }
1321
1322 // CMSTriggerInterval starts a CMS cycle if enough time has passed.
1323 if (CMSTriggerInterval >= 0) {
1324 if (CMSTriggerInterval == 0) {
1325 // Trigger always
1326 return true;
1327 }
1328
1329 // Check the CMS time since begin (we do not check the stats validity
1330 // as we want to be able to trigger the first CMS cycle as well)
1331 if (stats().cms_time_since_begin() >= (CMSTriggerInterval / ((double) MILLIUNITS))) {
1332 if (Verbose && PrintGCDetails) {
1333 if (stats().valid()) {
1334 gclog_or_tty->print_cr("CMSCollector: collect because of trigger interval (time since last begin %3.7f secs)",
1335 stats().cms_time_since_begin());
1336 } else {
1337 gclog_or_tty->print_cr("CMSCollector: collect because of trigger interval (first collection)");
1338 }
1339 }
1340 return true;
1341 }
1342 }
1343
1344 return false;
1345 }
1346
1347 void CMSCollector::set_did_compact(bool v) { _cmsGen->set_did_compact(v); }
1348
1349 // Clear _expansion_cause fields of constituent generations
1350 void CMSCollector::clear_expansion_cause() {
1351 _cmsGen->clear_expansion_cause();
1352 }
1353
1354 // We should be conservative in starting a collection cycle. To
1355 // start too eagerly runs the risk of collecting too often in the
1356 // extreme. To collect too rarely falls back on full collections,
1357 // which works, even if not optimum in terms of concurrent work.
1358 // As a work around for too eagerly collecting, use the flag
1359 // UseCMSInitiatingOccupancyOnly. This also has the advantage of
1360 // giving the user an easily understandable way of controlling the
1361 // collections.
1362 // We want to start a new collection cycle if any of the following
1363 // conditions hold:
1364 // . our current occupancy exceeds the configured initiating occupancy
1365 // for this generation, or
1366 // . we recently needed to expand this space and have not, since that
1367 // expansion, done a collection of this generation, or
1368 // . the underlying space believes that it may be a good idea to initiate
1369 // a concurrent collection (this may be based on criteria such as the
1370 // following: the space uses linear allocation and linear allocation is
1371 // going to fail, or there is believed to be excessive fragmentation in
1372 // the generation, etc... or ...
1373 // [.(currently done by CMSCollector::shouldConcurrentCollect() only for
1374 // the case of the old generation; see CR 6543076):
1375 // we may be approaching a point at which allocation requests may fail because
1376 // we will be out of sufficient free space given allocation rate estimates.]
1377 bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const {
1378
1379 assert_lock_strong(freelistLock());
1380 if (occupancy() > initiating_occupancy()) {
1381 if (PrintGCDetails && Verbose) {
1382 gclog_or_tty->print(" %s: collect because of occupancy %f / %f ",
1383 short_name(), occupancy(), initiating_occupancy());
1384 }
1385 return true;
1386 }
1387 if (UseCMSInitiatingOccupancyOnly) {
1388 return false;
1389 }
1390 if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) {
1391 if (PrintGCDetails && Verbose) {
1392 gclog_or_tty->print(" %s: collect because expanded for allocation ",
1393 short_name());
1394 }
1395 return true;
1396 }
1397 if (_cmsSpace->should_concurrent_collect()) {
1398 if (PrintGCDetails && Verbose) {
1399 gclog_or_tty->print(" %s: collect because cmsSpace says so ",
1400 short_name());
1401 }
1402 return true;
1403 }
1404 return false;
1405 }
1406
1407 void ConcurrentMarkSweepGeneration::collect(bool full,
1408 bool clear_all_soft_refs,
1409 size_t size,
1410 bool tlab)
1411 {
1412 collector()->collect(full, clear_all_soft_refs, size, tlab);
1413 }
1414
1415 void CMSCollector::collect(bool full,
1416 bool clear_all_soft_refs,
1417 size_t size,
1418 bool tlab)
1419 {
1420 // The following "if" branch is present for defensive reasons.
1421 // In the current uses of this interface, it can be replaced with:
1422 // assert(!GC_locker.is_active(), "Can't be called otherwise");
1423 // But I am not placing that assert here to allow future
1424 // generality in invoking this interface.
1425 if (GC_locker::is_active()) {
1426 // A consistency test for GC_locker
1427 assert(GC_locker::needs_gc(), "Should have been set already");
1428 // Skip this foreground collection, instead
1429 // expanding the heap if necessary.
1430 // Need the free list locks for the call to free() in compute_new_size()
1431 compute_new_size();
1432 return;
1433 }
1434 acquire_control_and_collect(full, clear_all_soft_refs);
1435 }
1436
1437 void CMSCollector::request_full_gc(unsigned int full_gc_count, GCCause::Cause cause) {
1438 GenCollectedHeap* gch = GenCollectedHeap::heap();
1439 unsigned int gc_count = gch->total_full_collections();
1440 if (gc_count == full_gc_count) {
1441 MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag);
1442 _full_gc_requested = true;
1443 _full_gc_cause = cause;
1444 CGC_lock->notify(); // nudge CMS thread
1445 } else {
1446 assert(gc_count > full_gc_count, "Error: causal loop");
1447 }
1448 }
1449
1450 bool CMSCollector::is_external_interruption() {
1451 GCCause::Cause cause = GenCollectedHeap::heap()->gc_cause();
1452 return GCCause::is_user_requested_gc(cause) ||
1453 GCCause::is_serviceability_requested_gc(cause);
1454 }
1455
1456 void CMSCollector::report_concurrent_mode_interruption() {
1457 if (is_external_interruption()) {
1458 if (PrintGCDetails) {
1459 gclog_or_tty->print(" (concurrent mode interrupted)");
1460 }
1461 } else {
1462 if (PrintGCDetails) {
1463 gclog_or_tty->print(" (concurrent mode failure)");
1464 }
1465 _gc_tracer_cm->report_concurrent_mode_failure();
1466 }
1467 }
1468
1469
1470 // The foreground and background collectors need to coordinate in order
1471 // to make sure that they do not mutually interfere with CMS collections.
1472 // When a background collection is active,
1473 // the foreground collector may need to take over (preempt) and
1474 // synchronously complete an ongoing collection. Depending on the
1475 // frequency of the background collections and the heap usage
1476 // of the application, this preemption can be seldom or frequent.
1477 // There are only certain
1478 // points in the background collection that the "collection-baton"
1479 // can be passed to the foreground collector.
1480 //
1481 // The foreground collector will wait for the baton before
1482 // starting any part of the collection. The foreground collector
1483 // will only wait at one location.
1484 //
1485 // The background collector will yield the baton before starting a new
1486 // phase of the collection (e.g., before initial marking, marking from roots,
1487 // precleaning, final re-mark, sweep etc.) This is normally done at the head
1488 // of the loop which switches the phases. The background collector does some
1489 // of the phases (initial mark, final re-mark) with the world stopped.
1490 // Because of locking involved in stopping the world,
1491 // the foreground collector should not block waiting for the background
1492 // collector when it is doing a stop-the-world phase. The background
1493 // collector will yield the baton at an additional point just before
1494 // it enters a stop-the-world phase. Once the world is stopped, the
1495 // background collector checks the phase of the collection. If the
1496 // phase has not changed, it proceeds with the collection. If the
1497 // phase has changed, it skips that phase of the collection. See
1498 // the comments on the use of the Heap_lock in collect_in_background().
1499 //
1500 // Variable used in baton passing.
1501 // _foregroundGCIsActive - Set to true by the foreground collector when
1502 // it wants the baton. The foreground clears it when it has finished
1503 // the collection.
1504 // _foregroundGCShouldWait - Set to true by the background collector
1505 // when it is running. The foreground collector waits while
1506 // _foregroundGCShouldWait is true.
1507 // CGC_lock - monitor used to protect access to the above variables
1508 // and to notify the foreground and background collectors.
1509 // _collectorState - current state of the CMS collection.
1510 //
1511 // The foreground collector
1512 // acquires the CGC_lock
1513 // sets _foregroundGCIsActive
1514 // waits on the CGC_lock for _foregroundGCShouldWait to be false
1515 // various locks acquired in preparation for the collection
1516 // are released so as not to block the background collector
1517 // that is in the midst of a collection
1518 // proceeds with the collection
1519 // clears _foregroundGCIsActive
1520 // returns
1521 //
1522 // The background collector in a loop iterating on the phases of the
1523 // collection
1524 // acquires the CGC_lock
1525 // sets _foregroundGCShouldWait
1526 // if _foregroundGCIsActive is set
1527 // clears _foregroundGCShouldWait, notifies _CGC_lock
1528 // waits on _CGC_lock for _foregroundGCIsActive to become false
1529 // and exits the loop.
1530 // otherwise
1531 // proceed with that phase of the collection
1532 // if the phase is a stop-the-world phase,
1533 // yield the baton once more just before enqueueing
1534 // the stop-world CMS operation (executed by the VM thread).
1535 // returns after all phases of the collection are done
1536 //
1537
1538 void CMSCollector::acquire_control_and_collect(bool full,
1539 bool clear_all_soft_refs) {
1540 assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
1541 assert(!Thread::current()->is_ConcurrentGC_thread(),
1542 "shouldn't try to acquire control from self!");
1543
1544 // Start the protocol for acquiring control of the
1545 // collection from the background collector (aka CMS thread).
1546 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1547 "VM thread should have CMS token");
1548 // Remember the possibly interrupted state of an ongoing
1549 // concurrent collection
1550 CollectorState first_state = _collectorState;
1551
1552 // Signal to a possibly ongoing concurrent collection that
1553 // we want to do a foreground collection.
1554 _foregroundGCIsActive = true;
1555
1556 // release locks and wait for a notify from the background collector
1557 // releasing the locks in only necessary for phases which
1558 // do yields to improve the granularity of the collection.
1559 assert_lock_strong(bitMapLock());
1560 // We need to lock the Free list lock for the space that we are
1561 // currently collecting.
1562 assert(haveFreelistLocks(), "Must be holding free list locks");
1563 bitMapLock()->unlock();
1564 releaseFreelistLocks();
1565 {
1566 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1567 if (_foregroundGCShouldWait) {
1568 // We are going to be waiting for action for the CMS thread;
1569 // it had better not be gone (for instance at shutdown)!
1570 assert(ConcurrentMarkSweepThread::cmst() != NULL,
1571 "CMS thread must be running");
1572 // Wait here until the background collector gives us the go-ahead
1573 ConcurrentMarkSweepThread::clear_CMS_flag(
1574 ConcurrentMarkSweepThread::CMS_vm_has_token); // release token
1575 // Get a possibly blocked CMS thread going:
1576 // Note that we set _foregroundGCIsActive true above,
1577 // without protection of the CGC_lock.
1578 CGC_lock->notify();
1579 assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(),
1580 "Possible deadlock");
1581 while (_foregroundGCShouldWait) {
1582 // wait for notification
1583 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1584 // Possibility of delay/starvation here, since CMS token does
1585 // not know to give priority to VM thread? Actually, i think
1586 // there wouldn't be any delay/starvation, but the proof of
1587 // that "fact" (?) appears non-trivial. XXX 20011219YSR
1588 }
1589 ConcurrentMarkSweepThread::set_CMS_flag(
1590 ConcurrentMarkSweepThread::CMS_vm_has_token);
1591 }
1592 }
1593 // The CMS_token is already held. Get back the other locks.
1594 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1595 "VM thread should have CMS token");
1596 getFreelistLocks();
1597 bitMapLock()->lock_without_safepoint_check();
1598 if (TraceCMSState) {
1599 gclog_or_tty->print_cr("CMS foreground collector has asked for control "
1600 INTPTR_FORMAT " with first state %d", Thread::current(), first_state);
1601 gclog_or_tty->print_cr(" gets control with state %d", _collectorState);
1602 }
1603
1604 // Inform cms gen if this was due to partial collection failing.
1605 // The CMS gen may use this fact to determine its expansion policy.
1606 GenCollectedHeap* gch = GenCollectedHeap::heap();
1607 if (gch->incremental_collection_will_fail(false /* don't consult_young */)) {
1608 assert(!_cmsGen->incremental_collection_failed(),
1609 "Should have been noticed, reacted to and cleared");
1610 _cmsGen->set_incremental_collection_failed();
1611 }
1612
1613 if (first_state > Idling) {
1614 report_concurrent_mode_interruption();
1615 }
1616
1617 set_did_compact(true);
1618
1619 // If the collection is being acquired from the background
1620 // collector, there may be references on the discovered
1621 // references lists that have NULL referents (being those
1622 // that were concurrently cleared by a mutator) or
1623 // that are no longer active (having been enqueued concurrently
1624 // by the mutator).
1625 // Scrub the list of those references because Mark-Sweep-Compact
1626 // code assumes referents are not NULL and that all discovered
1627 // Reference objects are active.
1628 ref_processor()->clean_up_discovered_references();
1629
1630 if (first_state > Idling) {
1631 save_heap_summary();
1632 }
1633
1634 do_compaction_work(clear_all_soft_refs);
1635
1636 // Has the GC time limit been exceeded?
1637 size_t max_eden_size = _young_gen->max_capacity() -
1638 _young_gen->to()->capacity() -
1639 _young_gen->from()->capacity();
1640 GCCause::Cause gc_cause = gch->gc_cause();
1641 size_policy()->check_gc_overhead_limit(_young_gen->used(),
1642 _young_gen->eden()->used(),
1643 _cmsGen->max_capacity(),
1644 max_eden_size,
1645 full,
1646 gc_cause,
1647 gch->collector_policy());
1648
1649 // Reset the expansion cause, now that we just completed
1650 // a collection cycle.
1651 clear_expansion_cause();
1652 _foregroundGCIsActive = false;
1653 return;
1654 }
1655
1656 // Resize the tenured generation
1657 // after obtaining the free list locks for the
1658 // two generations.
1659 void CMSCollector::compute_new_size() {
1660 assert_locked_or_safepoint(Heap_lock);
1661 FreelistLocker z(this);
1662 MetaspaceGC::compute_new_size();
1663 _cmsGen->compute_new_size_free_list();
1664 }
1665
1666 // A work method used by the foreground collector to do
1667 // a mark-sweep-compact.
1668 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) {
1669 GenCollectedHeap* gch = GenCollectedHeap::heap();
1670
1671 STWGCTimer* gc_timer = GenMarkSweep::gc_timer();
1672 gc_timer->register_gc_start();
1673
1674 SerialOldTracer* gc_tracer = GenMarkSweep::gc_tracer();
1675 gc_tracer->report_gc_start(gch->gc_cause(), gc_timer->gc_start());
1676
1677 GCTraceTime t("CMS:MSC ", PrintGCDetails && Verbose, true, NULL, gc_tracer->gc_id());
1678
1679 // Temporarily widen the span of the weak reference processing to
1680 // the entire heap.
1681 MemRegion new_span(GenCollectedHeap::heap()->reserved_region());
1682 ReferenceProcessorSpanMutator rp_mut_span(ref_processor(), new_span);
1683 // Temporarily, clear the "is_alive_non_header" field of the
1684 // reference processor.
1685 ReferenceProcessorIsAliveMutator rp_mut_closure(ref_processor(), NULL);
1686 // Temporarily make reference _processing_ single threaded (non-MT).
1687 ReferenceProcessorMTProcMutator rp_mut_mt_processing(ref_processor(), false);
1688 // Temporarily make refs discovery atomic
1689 ReferenceProcessorAtomicMutator rp_mut_atomic(ref_processor(), true);
1690 // Temporarily make reference _discovery_ single threaded (non-MT)
1691 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
1692
1693 ref_processor()->set_enqueuing_is_done(false);
1694 ref_processor()->enable_discovery(false /*verify_disabled*/, false /*check_no_refs*/);
1695 ref_processor()->setup_policy(clear_all_soft_refs);
1696 // If an asynchronous collection finishes, the _modUnionTable is
1697 // all clear. If we are assuming the collection from an asynchronous
1698 // collection, clear the _modUnionTable.
1699 assert(_collectorState != Idling || _modUnionTable.isAllClear(),
1700 "_modUnionTable should be clear if the baton was not passed");
1701 _modUnionTable.clear_all();
1702 assert(_collectorState != Idling || _ct->klass_rem_set()->mod_union_is_clear(),
1703 "mod union for klasses should be clear if the baton was passed");
1704 _ct->klass_rem_set()->clear_mod_union();
1705
1706 // We must adjust the allocation statistics being maintained
1707 // in the free list space. We do so by reading and clearing
1708 // the sweep timer and updating the block flux rate estimates below.
1709 assert(!_intra_sweep_timer.is_active(), "_intra_sweep_timer should be inactive");
1710 if (_inter_sweep_timer.is_active()) {
1711 _inter_sweep_timer.stop();
1712 // Note that we do not use this sample to update the _inter_sweep_estimate.
1713 _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
1714 _inter_sweep_estimate.padded_average(),
1715 _intra_sweep_estimate.padded_average());
1716 }
1717
1718 GenMarkSweep::invoke_at_safepoint(_cmsGen->level(),
1719 ref_processor(), clear_all_soft_refs);
1720 #ifdef ASSERT
1721 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
1722 size_t free_size = cms_space->free();
1723 assert(free_size ==
1724 pointer_delta(cms_space->end(), cms_space->compaction_top())
1725 * HeapWordSize,
1726 "All the free space should be compacted into one chunk at top");
1727 assert(cms_space->dictionary()->total_chunk_size(
1728 debug_only(cms_space->freelistLock())) == 0 ||
1729 cms_space->totalSizeInIndexedFreeLists() == 0,
1730 "All the free space should be in a single chunk");
1731 size_t num = cms_space->totalCount();
1732 assert((free_size == 0 && num == 0) ||
1733 (free_size > 0 && (num == 1 || num == 2)),
1734 "There should be at most 2 free chunks after compaction");
1735 #endif // ASSERT
1736 _collectorState = Resetting;
1737 assert(_restart_addr == NULL,
1738 "Should have been NULL'd before baton was passed");
1739 reset(false /* == !concurrent */);
1740 _cmsGen->reset_after_compaction();
1741 _concurrent_cycles_since_last_unload = 0;
1742
1743 // Clear any data recorded in the PLAB chunk arrays.
1744 if (_survivor_plab_array != NULL) {
1745 reset_survivor_plab_arrays();
1746 }
1747
1748 // Adjust the per-size allocation stats for the next epoch.
1749 _cmsGen->cmsSpace()->endSweepFLCensus(sweep_count() /* fake */);
1750 // Restart the "inter sweep timer" for the next epoch.
1751 _inter_sweep_timer.reset();
1752 _inter_sweep_timer.start();
1753
1754 gc_timer->register_gc_end();
1755
1756 gc_tracer->report_gc_end(gc_timer->gc_end(), gc_timer->time_partitions());
1757
1758 // For a mark-sweep-compact, compute_new_size() will be called
1759 // in the heap's do_collection() method.
1760 }
1761
1762 void CMSCollector::print_eden_and_survivor_chunk_arrays() {
1763 ContiguousSpace* eden_space = _young_gen->eden();
1764 ContiguousSpace* from_space = _young_gen->from();
1765 ContiguousSpace* to_space = _young_gen->to();
1766 // Eden
1767 if (_eden_chunk_array != NULL) {
1768 gclog_or_tty->print_cr("eden " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1769 eden_space->bottom(), eden_space->top(),
1770 eden_space->end(), eden_space->capacity());
1771 gclog_or_tty->print_cr("_eden_chunk_index=" SIZE_FORMAT ", "
1772 "_eden_chunk_capacity=" SIZE_FORMAT,
1773 _eden_chunk_index, _eden_chunk_capacity);
1774 for (size_t i = 0; i < _eden_chunk_index; i++) {
1775 gclog_or_tty->print_cr("_eden_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT,
1776 i, _eden_chunk_array[i]);
1777 }
1778 }
1779 // Survivor
1780 if (_survivor_chunk_array != NULL) {
1781 gclog_or_tty->print_cr("survivor " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1782 from_space->bottom(), from_space->top(),
1783 from_space->end(), from_space->capacity());
1784 gclog_or_tty->print_cr("_survivor_chunk_index=" SIZE_FORMAT ", "
1785 "_survivor_chunk_capacity=" SIZE_FORMAT,
1786 _survivor_chunk_index, _survivor_chunk_capacity);
1787 for (size_t i = 0; i < _survivor_chunk_index; i++) {
1788 gclog_or_tty->print_cr("_survivor_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT,
1789 i, _survivor_chunk_array[i]);
1790 }
1791 }
1792 }
1793
1794 void CMSCollector::getFreelistLocks() const {
1795 // Get locks for all free lists in all generations that this
1796 // collector is responsible for
1797 _cmsGen->freelistLock()->lock_without_safepoint_check();
1798 }
1799
1800 void CMSCollector::releaseFreelistLocks() const {
1801 // Release locks for all free lists in all generations that this
1802 // collector is responsible for
1803 _cmsGen->freelistLock()->unlock();
1804 }
1805
1806 bool CMSCollector::haveFreelistLocks() const {
1807 // Check locks for all free lists in all generations that this
1808 // collector is responsible for
1809 assert_lock_strong(_cmsGen->freelistLock());
1810 PRODUCT_ONLY(ShouldNotReachHere());
1811 return true;
1812 }
1813
1814 // A utility class that is used by the CMS collector to
1815 // temporarily "release" the foreground collector from its
1816 // usual obligation to wait for the background collector to
1817 // complete an ongoing phase before proceeding.
1818 class ReleaseForegroundGC: public StackObj {
1819 private:
1820 CMSCollector* _c;
1821 public:
1822 ReleaseForegroundGC(CMSCollector* c) : _c(c) {
1823 assert(_c->_foregroundGCShouldWait, "Else should not need to call");
1824 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1825 // allow a potentially blocked foreground collector to proceed
1826 _c->_foregroundGCShouldWait = false;
1827 if (_c->_foregroundGCIsActive) {
1828 CGC_lock->notify();
1829 }
1830 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1831 "Possible deadlock");
1832 }
1833
1834 ~ReleaseForegroundGC() {
1835 assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?");
1836 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1837 _c->_foregroundGCShouldWait = true;
1838 }
1839 };
1840
1841 void CMSCollector::collect_in_background(GCCause::Cause cause) {
1842 assert(Thread::current()->is_ConcurrentGC_thread(),
1843 "A CMS asynchronous collection is only allowed on a CMS thread.");
1844
1845 GenCollectedHeap* gch = GenCollectedHeap::heap();
1846 {
1847 bool safepoint_check = Mutex::_no_safepoint_check_flag;
1848 MutexLockerEx hl(Heap_lock, safepoint_check);
1849 FreelistLocker fll(this);
1850 MutexLockerEx x(CGC_lock, safepoint_check);
1851 if (_foregroundGCIsActive || !UseAsyncConcMarkSweepGC) {
1852 // The foreground collector is active or we're
1853 // not using asynchronous collections. Skip this
1854 // background collection.
1855 assert(!_foregroundGCShouldWait, "Should be clear");
1856 return;
1857 } else {
1858 assert(_collectorState == Idling, "Should be idling before start.");
1859 _collectorState = InitialMarking;
1860 register_gc_start(cause);
1861 // Reset the expansion cause, now that we are about to begin
1862 // a new cycle.
1863 clear_expansion_cause();
1864
1865 // Clear the MetaspaceGC flag since a concurrent collection
1866 // is starting but also clear it after the collection.
1867 MetaspaceGC::set_should_concurrent_collect(false);
1868 }
1869 // Decide if we want to enable class unloading as part of the
1870 // ensuing concurrent GC cycle.
1871 update_should_unload_classes();
1872 _full_gc_requested = false; // acks all outstanding full gc requests
1873 _full_gc_cause = GCCause::_no_gc;
1874 // Signal that we are about to start a collection
1875 gch->increment_total_full_collections(); // ... starting a collection cycle
1876 _collection_count_start = gch->total_full_collections();
1877 }
1878
1879 // Used for PrintGC
1880 size_t prev_used;
1881 if (PrintGC && Verbose) {
1882 prev_used = _cmsGen->used();
1883 }
1884
1885 // The change of the collection state is normally done at this level;
1886 // the exceptions are phases that are executed while the world is
1887 // stopped. For those phases the change of state is done while the
1888 // world is stopped. For baton passing purposes this allows the
1889 // background collector to finish the phase and change state atomically.
1890 // The foreground collector cannot wait on a phase that is done
1891 // while the world is stopped because the foreground collector already
1892 // has the world stopped and would deadlock.
1893 while (_collectorState != Idling) {
1894 if (TraceCMSState) {
1895 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
1896 Thread::current(), _collectorState);
1897 }
1898 // The foreground collector
1899 // holds the Heap_lock throughout its collection.
1900 // holds the CMS token (but not the lock)
1901 // except while it is waiting for the background collector to yield.
1902 //
1903 // The foreground collector should be blocked (not for long)
1904 // if the background collector is about to start a phase
1905 // executed with world stopped. If the background
1906 // collector has already started such a phase, the
1907 // foreground collector is blocked waiting for the
1908 // Heap_lock. The stop-world phases (InitialMarking and FinalMarking)
1909 // are executed in the VM thread.
1910 //
1911 // The locking order is
1912 // PendingListLock (PLL) -- if applicable (FinalMarking)
1913 // Heap_lock (both this & PLL locked in VM_CMS_Operation::prologue())
1914 // CMS token (claimed in
1915 // stop_world_and_do() -->
1916 // safepoint_synchronize() -->
1917 // CMSThread::synchronize())
1918
1919 {
1920 // Check if the FG collector wants us to yield.
1921 CMSTokenSync x(true); // is cms thread
1922 if (waitForForegroundGC()) {
1923 // We yielded to a foreground GC, nothing more to be
1924 // done this round.
1925 assert(_foregroundGCShouldWait == false, "We set it to false in "
1926 "waitForForegroundGC()");
1927 if (TraceCMSState) {
1928 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
1929 " exiting collection CMS state %d",
1930 Thread::current(), _collectorState);
1931 }
1932 return;
1933 } else {
1934 // The background collector can run but check to see if the
1935 // foreground collector has done a collection while the
1936 // background collector was waiting to get the CGC_lock
1937 // above. If yes, break so that _foregroundGCShouldWait
1938 // is cleared before returning.
1939 if (_collectorState == Idling) {
1940 break;
1941 }
1942 }
1943 }
1944
1945 assert(_foregroundGCShouldWait, "Foreground collector, if active, "
1946 "should be waiting");
1947
1948 switch (_collectorState) {
1949 case InitialMarking:
1950 {
1951 ReleaseForegroundGC x(this);
1952 stats().record_cms_begin();
1953 VM_CMS_Initial_Mark initial_mark_op(this);
1954 VMThread::execute(&initial_mark_op);
1955 }
1956 // The collector state may be any legal state at this point
1957 // since the background collector may have yielded to the
1958 // foreground collector.
1959 break;
1960 case Marking:
1961 // initial marking in checkpointRootsInitialWork has been completed
1962 if (markFromRoots()) { // we were successful
1963 assert(_collectorState == Precleaning, "Collector state should "
1964 "have changed");
1965 } else {
1966 assert(_foregroundGCIsActive, "Internal state inconsistency");
1967 }
1968 break;
1969 case Precleaning:
1970 // marking from roots in markFromRoots has been completed
1971 preclean();
1972 assert(_collectorState == AbortablePreclean ||
1973 _collectorState == FinalMarking,
1974 "Collector state should have changed");
1975 break;
1976 case AbortablePreclean:
1977 abortable_preclean();
1978 assert(_collectorState == FinalMarking, "Collector state should "
1979 "have changed");
1980 break;
1981 case FinalMarking:
1982 {
1983 ReleaseForegroundGC x(this);
1984
1985 VM_CMS_Final_Remark final_remark_op(this);
1986 VMThread::execute(&final_remark_op);
1987 }
1988 assert(_foregroundGCShouldWait, "block post-condition");
1989 break;
1990 case Sweeping:
1991 // final marking in checkpointRootsFinal has been completed
1992 sweep();
1993 assert(_collectorState == Resizing, "Collector state change "
1994 "to Resizing must be done under the free_list_lock");
1995
1996 case Resizing: {
1997 // Sweeping has been completed...
1998 // At this point the background collection has completed.
1999 // Don't move the call to compute_new_size() down
2000 // into code that might be executed if the background
2001 // collection was preempted.
2002 {
2003 ReleaseForegroundGC x(this); // unblock FG collection
2004 MutexLockerEx y(Heap_lock, Mutex::_no_safepoint_check_flag);
2005 CMSTokenSync z(true); // not strictly needed.
2006 if (_collectorState == Resizing) {
2007 compute_new_size();
2008 save_heap_summary();
2009 _collectorState = Resetting;
2010 } else {
2011 assert(_collectorState == Idling, "The state should only change"
2012 " because the foreground collector has finished the collection");
2013 }
2014 }
2015 break;
2016 }
2017 case Resetting:
2018 // CMS heap resizing has been completed
2019 reset(true);
2020 assert(_collectorState == Idling, "Collector state should "
2021 "have changed");
2022
2023 MetaspaceGC::set_should_concurrent_collect(false);
2024
2025 stats().record_cms_end();
2026 // Don't move the concurrent_phases_end() and compute_new_size()
2027 // calls to here because a preempted background collection
2028 // has it's state set to "Resetting".
2029 break;
2030 case Idling:
2031 default:
2032 ShouldNotReachHere();
2033 break;
2034 }
2035 if (TraceCMSState) {
2036 gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d",
2037 Thread::current(), _collectorState);
2038 }
2039 assert(_foregroundGCShouldWait, "block post-condition");
2040 }
2041
2042 // Should this be in gc_epilogue?
2043 collector_policy()->counters()->update_counters();
2044
2045 {
2046 // Clear _foregroundGCShouldWait and, in the event that the
2047 // foreground collector is waiting, notify it, before
2048 // returning.
2049 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2050 _foregroundGCShouldWait = false;
2051 if (_foregroundGCIsActive) {
2052 CGC_lock->notify();
2053 }
2054 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2055 "Possible deadlock");
2056 }
2057 if (TraceCMSState) {
2058 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2059 " exiting collection CMS state %d",
2060 Thread::current(), _collectorState);
2061 }
2062 if (PrintGC && Verbose) {
2063 _cmsGen->print_heap_change(prev_used);
2064 }
2065 }
2066
2067 void CMSCollector::register_gc_start(GCCause::Cause cause) {
2068 _cms_start_registered = true;
2069 _gc_timer_cm->register_gc_start();
2070 _gc_tracer_cm->report_gc_start(cause, _gc_timer_cm->gc_start());
2071 }
2072
2073 void CMSCollector::register_gc_end() {
2074 if (_cms_start_registered) {
2075 report_heap_summary(GCWhen::AfterGC);
2076
2077 _gc_timer_cm->register_gc_end();
2078 _gc_tracer_cm->report_gc_end(_gc_timer_cm->gc_end(), _gc_timer_cm->time_partitions());
2079 _cms_start_registered = false;
2080 }
2081 }
2082
2083 void CMSCollector::save_heap_summary() {
2084 GenCollectedHeap* gch = GenCollectedHeap::heap();
2085 _last_heap_summary = gch->create_heap_summary();
2086 _last_metaspace_summary = gch->create_metaspace_summary();
2087 }
2088
2089 void CMSCollector::report_heap_summary(GCWhen::Type when) {
2090 _gc_tracer_cm->report_gc_heap_summary(when, _last_heap_summary);
2091 _gc_tracer_cm->report_metaspace_summary(when, _last_metaspace_summary);
2092 }
2093
2094 bool CMSCollector::waitForForegroundGC() {
2095 bool res = false;
2096 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2097 "CMS thread should have CMS token");
2098 // Block the foreground collector until the
2099 // background collectors decides whether to
2100 // yield.
2101 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2102 _foregroundGCShouldWait = true;
2103 if (_foregroundGCIsActive) {
2104 // The background collector yields to the
2105 // foreground collector and returns a value
2106 // indicating that it has yielded. The foreground
2107 // collector can proceed.
2108 res = true;
2109 _foregroundGCShouldWait = false;
2110 ConcurrentMarkSweepThread::clear_CMS_flag(
2111 ConcurrentMarkSweepThread::CMS_cms_has_token);
2112 ConcurrentMarkSweepThread::set_CMS_flag(
2113 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2114 // Get a possibly blocked foreground thread going
2115 CGC_lock->notify();
2116 if (TraceCMSState) {
2117 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d",
2118 Thread::current(), _collectorState);
2119 }
2120 while (_foregroundGCIsActive) {
2121 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
2122 }
2123 ConcurrentMarkSweepThread::set_CMS_flag(
2124 ConcurrentMarkSweepThread::CMS_cms_has_token);
2125 ConcurrentMarkSweepThread::clear_CMS_flag(
2126 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2127 }
2128 if (TraceCMSState) {
2129 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d",
2130 Thread::current(), _collectorState);
2131 }
2132 return res;
2133 }
2134
2135 // Because of the need to lock the free lists and other structures in
2136 // the collector, common to all the generations that the collector is
2137 // collecting, we need the gc_prologues of individual CMS generations
2138 // delegate to their collector. It may have been simpler had the
2139 // current infrastructure allowed one to call a prologue on a
2140 // collector. In the absence of that we have the generation's
2141 // prologue delegate to the collector, which delegates back
2142 // some "local" work to a worker method in the individual generations
2143 // that it's responsible for collecting, while itself doing any
2144 // work common to all generations it's responsible for. A similar
2145 // comment applies to the gc_epilogue()'s.
2146 // The role of the variable _between_prologue_and_epilogue is to
2147 // enforce the invocation protocol.
2148 void CMSCollector::gc_prologue(bool full) {
2149 // Call gc_prologue_work() for the CMSGen
2150 // we are responsible for.
2151
2152 // The following locking discipline assumes that we are only called
2153 // when the world is stopped.
2154 assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption");
2155
2156 // The CMSCollector prologue must call the gc_prologues for the
2157 // "generations" that it's responsible
2158 // for.
2159
2160 assert( Thread::current()->is_VM_thread()
2161 || ( CMSScavengeBeforeRemark
2162 && Thread::current()->is_ConcurrentGC_thread()),
2163 "Incorrect thread type for prologue execution");
2164
2165 if (_between_prologue_and_epilogue) {
2166 // We have already been invoked; this is a gc_prologue delegation
2167 // from yet another CMS generation that we are responsible for, just
2168 // ignore it since all relevant work has already been done.
2169 return;
2170 }
2171
2172 // set a bit saying prologue has been called; cleared in epilogue
2173 _between_prologue_and_epilogue = true;
2174 // Claim locks for common data structures, then call gc_prologue_work()
2175 // for each CMSGen.
2176
2177 getFreelistLocks(); // gets free list locks on constituent spaces
2178 bitMapLock()->lock_without_safepoint_check();
2179
2180 // Should call gc_prologue_work() for all cms gens we are responsible for
2181 bool duringMarking = _collectorState >= Marking
2182 && _collectorState < Sweeping;
2183
2184 // The young collections clear the modified oops state, which tells if
2185 // there are any modified oops in the class. The remark phase also needs
2186 // that information. Tell the young collection to save the union of all
2187 // modified klasses.
2188 if (duringMarking) {
2189 _ct->klass_rem_set()->set_accumulate_modified_oops(true);
2190 }
2191
2192 bool registerClosure = duringMarking;
2193
2194 ModUnionClosure* muc = CollectedHeap::use_parallel_gc_threads() ?
2195 &_modUnionClosurePar
2196 : &_modUnionClosure;
2197 _cmsGen->gc_prologue_work(full, registerClosure, muc);
2198
2199 if (!full) {
2200 stats().record_gc0_begin();
2201 }
2202 }
2203
2204 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) {
2205
2206 _capacity_at_prologue = capacity();
2207 _used_at_prologue = used();
2208
2209 // Delegate to CMScollector which knows how to coordinate between
2210 // this and any other CMS generations that it is responsible for
2211 // collecting.
2212 collector()->gc_prologue(full);
2213 }
2214
2215 // This is a "private" interface for use by this generation's CMSCollector.
2216 // Not to be called directly by any other entity (for instance,
2217 // GenCollectedHeap, which calls the "public" gc_prologue method above).
2218 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full,
2219 bool registerClosure, ModUnionClosure* modUnionClosure) {
2220 assert(!incremental_collection_failed(), "Shouldn't be set yet");
2221 assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL,
2222 "Should be NULL");
2223 if (registerClosure) {
2224 cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure);
2225 }
2226 cmsSpace()->gc_prologue();
2227 // Clear stat counters
2228 NOT_PRODUCT(
2229 assert(_numObjectsPromoted == 0, "check");
2230 assert(_numWordsPromoted == 0, "check");
2231 if (Verbose && PrintGC) {
2232 gclog_or_tty->print("Allocated "SIZE_FORMAT" objects, "
2233 SIZE_FORMAT" bytes concurrently",
2234 _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord));
2235 }
2236 _numObjectsAllocated = 0;
2237 _numWordsAllocated = 0;
2238 )
2239 }
2240
2241 void CMSCollector::gc_epilogue(bool full) {
2242 // The following locking discipline assumes that we are only called
2243 // when the world is stopped.
2244 assert(SafepointSynchronize::is_at_safepoint(),
2245 "world is stopped assumption");
2246
2247 // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks
2248 // if linear allocation blocks need to be appropriately marked to allow the
2249 // the blocks to be parsable. We also check here whether we need to nudge the
2250 // CMS collector thread to start a new cycle (if it's not already active).
2251 assert( Thread::current()->is_VM_thread()
2252 || ( CMSScavengeBeforeRemark
2253 && Thread::current()->is_ConcurrentGC_thread()),
2254 "Incorrect thread type for epilogue execution");
2255
2256 if (!_between_prologue_and_epilogue) {
2257 // We have already been invoked; this is a gc_epilogue delegation
2258 // from yet another CMS generation that we are responsible for, just
2259 // ignore it since all relevant work has already been done.
2260 return;
2261 }
2262 assert(haveFreelistLocks(), "must have freelist locks");
2263 assert_lock_strong(bitMapLock());
2264
2265 _ct->klass_rem_set()->set_accumulate_modified_oops(false);
2266
2267 _cmsGen->gc_epilogue_work(full);
2268
2269 if (_collectorState == AbortablePreclean || _collectorState == Precleaning) {
2270 // in case sampling was not already enabled, enable it
2271 _start_sampling = true;
2272 }
2273 // reset _eden_chunk_array so sampling starts afresh
2274 _eden_chunk_index = 0;
2275
2276 size_t cms_used = _cmsGen->cmsSpace()->used();
2277
2278 // update performance counters - this uses a special version of
2279 // update_counters() that allows the utilization to be passed as a
2280 // parameter, avoiding multiple calls to used().
2281 //
2282 _cmsGen->update_counters(cms_used);
2283
2284 bitMapLock()->unlock();
2285 releaseFreelistLocks();
2286
2287 if (!CleanChunkPoolAsync) {
2288 Chunk::clean_chunk_pool();
2289 }
2290
2291 set_did_compact(false);
2292 _between_prologue_and_epilogue = false; // ready for next cycle
2293 }
2294
2295 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) {
2296 collector()->gc_epilogue(full);
2297
2298 // Also reset promotion tracking in par gc thread states.
2299 for (uint i = 0; i < ParallelGCThreads; i++) {
2300 _par_gc_thread_states[i]->promo.stopTrackingPromotions(i);
2301 }
2302 }
2303
2304 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2305 assert(!incremental_collection_failed(), "Should have been cleared");
2306 cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2307 cmsSpace()->gc_epilogue();
2308 // Print stat counters
2309 NOT_PRODUCT(
2310 assert(_numObjectsAllocated == 0, "check");
2311 assert(_numWordsAllocated == 0, "check");
2312 if (Verbose && PrintGC) {
2313 gclog_or_tty->print("Promoted "SIZE_FORMAT" objects, "
2314 SIZE_FORMAT" bytes",
2315 _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2316 }
2317 _numObjectsPromoted = 0;
2318 _numWordsPromoted = 0;
2319 )
2320
2321 if (PrintGC && Verbose) {
2322 // Call down the chain in contiguous_available needs the freelistLock
2323 // so print this out before releasing the freeListLock.
2324 gclog_or_tty->print(" Contiguous available "SIZE_FORMAT" bytes ",
2325 contiguous_available());
2326 }
2327 }
2328
2329 #ifndef PRODUCT
2330 bool CMSCollector::have_cms_token() {
2331 Thread* thr = Thread::current();
2332 if (thr->is_VM_thread()) {
2333 return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2334 } else if (thr->is_ConcurrentGC_thread()) {
2335 return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2336 } else if (thr->is_GC_task_thread()) {
2337 return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2338 ParGCRareEvent_lock->owned_by_self();
2339 }
2340 return false;
2341 }
2342 #endif
2343
2344 // Check reachability of the given heap address in CMS generation,
2345 // treating all other generations as roots.
2346 bool CMSCollector::is_cms_reachable(HeapWord* addr) {
2347 // We could "guarantee" below, rather than assert, but I'll
2348 // leave these as "asserts" so that an adventurous debugger
2349 // could try this in the product build provided some subset of
2350 // the conditions were met, provided they were interested in the
2351 // results and knew that the computation below wouldn't interfere
2352 // with other concurrent computations mutating the structures
2353 // being read or written.
2354 assert(SafepointSynchronize::is_at_safepoint(),
2355 "Else mutations in object graph will make answer suspect");
2356 assert(have_cms_token(), "Should hold cms token");
2357 assert(haveFreelistLocks(), "must hold free list locks");
2358 assert_lock_strong(bitMapLock());
2359
2360 // Clear the marking bit map array before starting, but, just
2361 // for kicks, first report if the given address is already marked
2362 gclog_or_tty->print_cr("Start: Address " PTR_FORMAT " is%s marked", addr,
2363 _markBitMap.isMarked(addr) ? "" : " not");
2364
2365 if (verify_after_remark()) {
2366 MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2367 bool result = verification_mark_bm()->isMarked(addr);
2368 gclog_or_tty->print_cr("TransitiveMark: Address " PTR_FORMAT " %s marked", addr,
2369 result ? "IS" : "is NOT");
2370 return result;
2371 } else {
2372 gclog_or_tty->print_cr("Could not compute result");
2373 return false;
2374 }
2375 }
2376
2377
2378 void
2379 CMSCollector::print_on_error(outputStream* st) {
2380 CMSCollector* collector = ConcurrentMarkSweepGeneration::_collector;
2381 if (collector != NULL) {
2382 CMSBitMap* bitmap = &collector->_markBitMap;
2383 st->print_cr("Marking Bits: (CMSBitMap*) " PTR_FORMAT, bitmap);
2384 bitmap->print_on_error(st, " Bits: ");
2385
2386 st->cr();
2387
2388 CMSBitMap* mut_bitmap = &collector->_modUnionTable;
2389 st->print_cr("Mod Union Table: (CMSBitMap*) " PTR_FORMAT, mut_bitmap);
2390 mut_bitmap->print_on_error(st, " Bits: ");
2391 }
2392 }
2393
2394 ////////////////////////////////////////////////////////
2395 // CMS Verification Support
2396 ////////////////////////////////////////////////////////
2397 // Following the remark phase, the following invariant
2398 // should hold -- each object in the CMS heap which is
2399 // marked in markBitMap() should be marked in the verification_mark_bm().
2400
2401 class VerifyMarkedClosure: public BitMapClosure {
2402 CMSBitMap* _marks;
2403 bool _failed;
2404
2405 public:
2406 VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2407
2408 bool do_bit(size_t offset) {
2409 HeapWord* addr = _marks->offsetToHeapWord(offset);
2410 if (!_marks->isMarked(addr)) {
2411 oop(addr)->print_on(gclog_or_tty);
2412 gclog_or_tty->print_cr(" ("INTPTR_FORMAT" should have been marked)", addr);
2413 _failed = true;
2414 }
2415 return true;
2416 }
2417
2418 bool failed() { return _failed; }
2419 };
2420
2421 bool CMSCollector::verify_after_remark(bool silent) {
2422 if (!silent) gclog_or_tty->print(" [Verifying CMS Marking... ");
2423 MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2424 static bool init = false;
2425
2426 assert(SafepointSynchronize::is_at_safepoint(),
2427 "Else mutations in object graph will make answer suspect");
2428 assert(have_cms_token(),
2429 "Else there may be mutual interference in use of "
2430 " verification data structures");
2431 assert(_collectorState > Marking && _collectorState <= Sweeping,
2432 "Else marking info checked here may be obsolete");
2433 assert(haveFreelistLocks(), "must hold free list locks");
2434 assert_lock_strong(bitMapLock());
2435
2436
2437 // Allocate marking bit map if not already allocated
2438 if (!init) { // first time
2439 if (!verification_mark_bm()->allocate(_span)) {
2440 return false;
2441 }
2442 init = true;
2443 }
2444
2445 assert(verification_mark_stack()->isEmpty(), "Should be empty");
2446
2447 // Turn off refs discovery -- so we will be tracing through refs.
2448 // This is as intended, because by this time
2449 // GC must already have cleared any refs that need to be cleared,
2450 // and traced those that need to be marked; moreover,
2451 // the marking done here is not going to interfere in any
2452 // way with the marking information used by GC.
2453 NoRefDiscovery no_discovery(ref_processor());
2454
2455 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
2456
2457 // Clear any marks from a previous round
2458 verification_mark_bm()->clear_all();
2459 assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
2460 verify_work_stacks_empty();
2461
2462 GenCollectedHeap* gch = GenCollectedHeap::heap();
2463 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
2464 // Update the saved marks which may affect the root scans.
2465 gch->save_marks();
2466
2467 if (CMSRemarkVerifyVariant == 1) {
2468 // In this first variant of verification, we complete
2469 // all marking, then check if the new marks-vector is
2470 // a subset of the CMS marks-vector.
2471 verify_after_remark_work_1();
2472 } else if (CMSRemarkVerifyVariant == 2) {
2473 // In this second variant of verification, we flag an error
2474 // (i.e. an object reachable in the new marks-vector not reachable
2475 // in the CMS marks-vector) immediately, also indicating the
2476 // identify of an object (A) that references the unmarked object (B) --
2477 // presumably, a mutation to A failed to be picked up by preclean/remark?
2478 verify_after_remark_work_2();
2479 } else {
2480 warning("Unrecognized value %d for CMSRemarkVerifyVariant",
2481 CMSRemarkVerifyVariant);
2482 }
2483 if (!silent) gclog_or_tty->print(" done] ");
2484 return true;
2485 }
2486
2487 void CMSCollector::verify_after_remark_work_1() {
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 MarkRefsIntoClosure notOlder(_span, verification_mark_bm());
2497 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2498
2499 gch->gen_process_roots(_cmsGen->level(),
2500 true, // younger gens are roots
2501 true, // activate StrongRootsScope
2502 SharedHeap::ScanningOption(roots_scanning_options()),
2503 should_unload_classes(),
2504 ¬Older,
2505 NULL,
2506 NULL); // SSS: Provide correct closure
2507
2508 // Now mark from the roots
2509 MarkFromRootsClosure markFromRootsClosure(this, _span,
2510 verification_mark_bm(), verification_mark_stack(),
2511 false /* don't yield */, true /* verifying */);
2512 assert(_restart_addr == NULL, "Expected pre-condition");
2513 verification_mark_bm()->iterate(&markFromRootsClosure);
2514 while (_restart_addr != NULL) {
2515 // Deal with stack overflow: by restarting at the indicated
2516 // address.
2517 HeapWord* ra = _restart_addr;
2518 markFromRootsClosure.reset(ra);
2519 _restart_addr = NULL;
2520 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2521 }
2522 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2523 verify_work_stacks_empty();
2524
2525 // Marking completed -- now verify that each bit marked in
2526 // verification_mark_bm() is also marked in markBitMap(); flag all
2527 // errors by printing corresponding objects.
2528 VerifyMarkedClosure vcl(markBitMap());
2529 verification_mark_bm()->iterate(&vcl);
2530 if (vcl.failed()) {
2531 gclog_or_tty->print("Verification failed");
2532 Universe::heap()->print_on(gclog_or_tty);
2533 fatal("CMS: failed marking verification after remark");
2534 }
2535 }
2536
2537 class VerifyKlassOopsKlassClosure : public KlassClosure {
2538 class VerifyKlassOopsClosure : public OopClosure {
2539 CMSBitMap* _bitmap;
2540 public:
2541 VerifyKlassOopsClosure(CMSBitMap* bitmap) : _bitmap(bitmap) { }
2542 void do_oop(oop* p) { guarantee(*p == NULL || _bitmap->isMarked((HeapWord*) *p), "Should be marked"); }
2543 void do_oop(narrowOop* p) { ShouldNotReachHere(); }
2544 } _oop_closure;
2545 public:
2546 VerifyKlassOopsKlassClosure(CMSBitMap* bitmap) : _oop_closure(bitmap) {}
2547 void do_klass(Klass* k) {
2548 k->oops_do(&_oop_closure);
2549 }
2550 };
2551
2552 void CMSCollector::verify_after_remark_work_2() {
2553 ResourceMark rm;
2554 HandleMark hm;
2555 GenCollectedHeap* gch = GenCollectedHeap::heap();
2556
2557 // Get a clear set of claim bits for the roots processing to work with.
2558 ClassLoaderDataGraph::clear_claimed_marks();
2559
2560 // Mark from roots one level into CMS
2561 MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
2562 markBitMap());
2563 CLDToOopClosure cld_closure(¬Older, true);
2564
2565 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2566
2567 gch->gen_process_roots(_cmsGen->level(),
2568 true, // younger gens are roots
2569 true, // activate StrongRootsScope
2570 SharedHeap::ScanningOption(roots_scanning_options()),
2571 should_unload_classes(),
2572 ¬Older,
2573 NULL,
2574 &cld_closure);
2575
2576 // Now mark from the roots
2577 MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
2578 verification_mark_bm(), markBitMap(), verification_mark_stack());
2579 assert(_restart_addr == NULL, "Expected pre-condition");
2580 verification_mark_bm()->iterate(&markFromRootsClosure);
2581 while (_restart_addr != NULL) {
2582 // Deal with stack overflow: by restarting at the indicated
2583 // address.
2584 HeapWord* ra = _restart_addr;
2585 markFromRootsClosure.reset(ra);
2586 _restart_addr = NULL;
2587 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2588 }
2589 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2590 verify_work_stacks_empty();
2591
2592 VerifyKlassOopsKlassClosure verify_klass_oops(verification_mark_bm());
2593 ClassLoaderDataGraph::classes_do(&verify_klass_oops);
2594
2595 // Marking completed -- now verify that each bit marked in
2596 // verification_mark_bm() is also marked in markBitMap(); flag all
2597 // errors by printing corresponding objects.
2598 VerifyMarkedClosure vcl(markBitMap());
2599 verification_mark_bm()->iterate(&vcl);
2600 assert(!vcl.failed(), "Else verification above should not have succeeded");
2601 }
2602
2603 void ConcurrentMarkSweepGeneration::save_marks() {
2604 // delegate to CMS space
2605 cmsSpace()->save_marks();
2606 for (uint i = 0; i < ParallelGCThreads; i++) {
2607 _par_gc_thread_states[i]->promo.startTrackingPromotions();
2608 }
2609 }
2610
2611 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
2612 return cmsSpace()->no_allocs_since_save_marks();
2613 }
2614
2615 #define CMS_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix) \
2616 \
2617 void ConcurrentMarkSweepGeneration:: \
2618 oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) { \
2619 cl->set_generation(this); \
2620 cmsSpace()->oop_since_save_marks_iterate##nv_suffix(cl); \
2621 cl->reset_generation(); \
2622 save_marks(); \
2623 }
2624
2625 ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DEFN)
2626
2627 void
2628 ConcurrentMarkSweepGeneration::younger_refs_iterate(OopsInGenClosure* cl) {
2629 cl->set_generation(this);
2630 younger_refs_in_space_iterate(_cmsSpace, cl);
2631 cl->reset_generation();
2632 }
2633
2634 void
2635 ConcurrentMarkSweepGeneration::oop_iterate(ExtendedOopClosure* cl) {
2636 if (freelistLock()->owned_by_self()) {
2637 Generation::oop_iterate(cl);
2638 } else {
2639 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2640 Generation::oop_iterate(cl);
2641 }
2642 }
2643
2644 void
2645 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
2646 if (freelistLock()->owned_by_self()) {
2647 Generation::object_iterate(cl);
2648 } else {
2649 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2650 Generation::object_iterate(cl);
2651 }
2652 }
2653
2654 void
2655 ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) {
2656 if (freelistLock()->owned_by_self()) {
2657 Generation::safe_object_iterate(cl);
2658 } else {
2659 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2660 Generation::safe_object_iterate(cl);
2661 }
2662 }
2663
2664 void
2665 ConcurrentMarkSweepGeneration::post_compact() {
2666 }
2667
2668 void
2669 ConcurrentMarkSweepGeneration::prepare_for_verify() {
2670 // Fix the linear allocation blocks to look like free blocks.
2671
2672 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2673 // are not called when the heap is verified during universe initialization and
2674 // at vm shutdown.
2675 if (freelistLock()->owned_by_self()) {
2676 cmsSpace()->prepare_for_verify();
2677 } else {
2678 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2679 cmsSpace()->prepare_for_verify();
2680 }
2681 }
2682
2683 void
2684 ConcurrentMarkSweepGeneration::verify() {
2685 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2686 // are not called when the heap is verified during universe initialization and
2687 // at vm shutdown.
2688 if (freelistLock()->owned_by_self()) {
2689 cmsSpace()->verify();
2690 } else {
2691 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2692 cmsSpace()->verify();
2693 }
2694 }
2695
2696 void CMSCollector::verify() {
2697 _cmsGen->verify();
2698 }
2699
2700 #ifndef PRODUCT
2701 bool CMSCollector::overflow_list_is_empty() const {
2702 assert(_num_par_pushes >= 0, "Inconsistency");
2703 if (_overflow_list == NULL) {
2704 assert(_num_par_pushes == 0, "Inconsistency");
2705 }
2706 return _overflow_list == NULL;
2707 }
2708
2709 // The methods verify_work_stacks_empty() and verify_overflow_empty()
2710 // merely consolidate assertion checks that appear to occur together frequently.
2711 void CMSCollector::verify_work_stacks_empty() const {
2712 assert(_markStack.isEmpty(), "Marking stack should be empty");
2713 assert(overflow_list_is_empty(), "Overflow list should be empty");
2714 }
2715
2716 void CMSCollector::verify_overflow_empty() const {
2717 assert(overflow_list_is_empty(), "Overflow list should be empty");
2718 assert(no_preserved_marks(), "No preserved marks");
2719 }
2720 #endif // PRODUCT
2721
2722 // Decide if we want to enable class unloading as part of the
2723 // ensuing concurrent GC cycle. We will collect and
2724 // unload classes if it's the case that:
2725 // (1) an explicit gc request has been made and the flag
2726 // ExplicitGCInvokesConcurrentAndUnloadsClasses is set, OR
2727 // (2) (a) class unloading is enabled at the command line, and
2728 // (b) old gen is getting really full
2729 // NOTE: Provided there is no change in the state of the heap between
2730 // calls to this method, it should have idempotent results. Moreover,
2731 // its results should be monotonically increasing (i.e. going from 0 to 1,
2732 // but not 1 to 0) between successive calls between which the heap was
2733 // not collected. For the implementation below, it must thus rely on
2734 // the property that concurrent_cycles_since_last_unload()
2735 // will not decrease unless a collection cycle happened and that
2736 // _cmsGen->is_too_full() are
2737 // themselves also monotonic in that sense. See check_monotonicity()
2738 // below.
2739 void CMSCollector::update_should_unload_classes() {
2740 _should_unload_classes = false;
2741 // Condition 1 above
2742 if (_full_gc_requested && ExplicitGCInvokesConcurrentAndUnloadsClasses) {
2743 _should_unload_classes = true;
2744 } else if (CMSClassUnloadingEnabled) { // Condition 2.a above
2745 // Disjuncts 2.b.(i,ii,iii) above
2746 _should_unload_classes = (concurrent_cycles_since_last_unload() >=
2747 CMSClassUnloadingMaxInterval)
2748 || _cmsGen->is_too_full();
2749 }
2750 }
2751
2752 bool ConcurrentMarkSweepGeneration::is_too_full() const {
2753 bool res = should_concurrent_collect();
2754 res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
2755 return res;
2756 }
2757
2758 void CMSCollector::setup_cms_unloading_and_verification_state() {
2759 const bool should_verify = VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
2760 || VerifyBeforeExit;
2761 const int rso = SharedHeap::SO_AllCodeCache;
2762
2763 // We set the proper root for this CMS cycle here.
2764 if (should_unload_classes()) { // Should unload classes this cycle
2765 remove_root_scanning_option(rso); // Shrink the root set appropriately
2766 set_verifying(should_verify); // Set verification state for this cycle
2767 return; // Nothing else needs to be done at this time
2768 }
2769
2770 // Not unloading classes this cycle
2771 assert(!should_unload_classes(), "Inconsistency!");
2772
2773 if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
2774 // Include symbols, strings and code cache elements to prevent their resurrection.
2775 add_root_scanning_option(rso);
2776 set_verifying(true);
2777 } else if (verifying() && !should_verify) {
2778 // We were verifying, but some verification flags got disabled.
2779 set_verifying(false);
2780 // Exclude symbols, strings and code cache elements from root scanning to
2781 // reduce IM and RM pauses.
2782 remove_root_scanning_option(rso);
2783 }
2784 }
2785
2786
2787 #ifndef PRODUCT
2788 HeapWord* CMSCollector::block_start(const void* p) const {
2789 const HeapWord* addr = (HeapWord*)p;
2790 if (_span.contains(p)) {
2791 if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
2792 return _cmsGen->cmsSpace()->block_start(p);
2793 }
2794 }
2795 return NULL;
2796 }
2797 #endif
2798
2799 HeapWord*
2800 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
2801 bool tlab,
2802 bool parallel) {
2803 CMSSynchronousYieldRequest yr;
2804 assert(!tlab, "Can't deal with TLAB allocation");
2805 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2806 expand(word_size*HeapWordSize, MinHeapDeltaBytes,
2807 CMSExpansionCause::_satisfy_allocation);
2808 if (GCExpandToAllocateDelayMillis > 0) {
2809 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2810 }
2811 return have_lock_and_allocate(word_size, tlab);
2812 }
2813
2814 // YSR: All of this generation expansion/shrinking stuff is an exact copy of
2815 // TenuredGeneration, which makes me wonder if we should move this
2816 // to CardGeneration and share it...
2817 bool ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes) {
2818 return CardGeneration::expand(bytes, expand_bytes);
2819 }
2820
2821 void ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes,
2822 CMSExpansionCause::Cause cause)
2823 {
2824
2825 bool success = expand(bytes, expand_bytes);
2826
2827 // remember why we expanded; this information is used
2828 // by shouldConcurrentCollect() when making decisions on whether to start
2829 // a new CMS cycle.
2830 if (success) {
2831 set_expansion_cause(cause);
2832 if (PrintGCDetails && Verbose) {
2833 gclog_or_tty->print_cr("Expanded CMS gen for %s",
2834 CMSExpansionCause::to_string(cause));
2835 }
2836 }
2837 }
2838
2839 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
2840 HeapWord* res = NULL;
2841 MutexLocker x(ParGCRareEvent_lock);
2842 while (true) {
2843 // Expansion by some other thread might make alloc OK now:
2844 res = ps->lab.alloc(word_sz);
2845 if (res != NULL) return res;
2846 // If there's not enough expansion space available, give up.
2847 if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
2848 return NULL;
2849 }
2850 // Otherwise, we try expansion.
2851 expand(word_sz*HeapWordSize, MinHeapDeltaBytes,
2852 CMSExpansionCause::_allocate_par_lab);
2853 // Now go around the loop and try alloc again;
2854 // A competing par_promote might beat us to the expansion space,
2855 // so we may go around the loop again if promotion fails again.
2856 if (GCExpandToAllocateDelayMillis > 0) {
2857 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2858 }
2859 }
2860 }
2861
2862
2863 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
2864 PromotionInfo* promo) {
2865 MutexLocker x(ParGCRareEvent_lock);
2866 size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
2867 while (true) {
2868 // Expansion by some other thread might make alloc OK now:
2869 if (promo->ensure_spooling_space()) {
2870 assert(promo->has_spooling_space(),
2871 "Post-condition of successful ensure_spooling_space()");
2872 return true;
2873 }
2874 // If there's not enough expansion space available, give up.
2875 if (_virtual_space.uncommitted_size() < refill_size_bytes) {
2876 return false;
2877 }
2878 // Otherwise, we try expansion.
2879 expand(refill_size_bytes, MinHeapDeltaBytes,
2880 CMSExpansionCause::_allocate_par_spooling_space);
2881 // Now go around the loop and try alloc again;
2882 // A competing allocation might beat us to the expansion space,
2883 // so we may go around the loop again if allocation fails again.
2884 if (GCExpandToAllocateDelayMillis > 0) {
2885 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2886 }
2887 }
2888 }
2889
2890
2891 void ConcurrentMarkSweepGeneration::shrink_by(size_t bytes) {
2892 assert_locked_or_safepoint(ExpandHeap_lock);
2893 // Shrink committed space
2894 _virtual_space.shrink_by(bytes);
2895 // Shrink space; this also shrinks the space's BOT
2896 _cmsSpace->set_end((HeapWord*) _virtual_space.high());
2897 size_t new_word_size = heap_word_size(_cmsSpace->capacity());
2898 // Shrink the shared block offset array
2899 _bts->resize(new_word_size);
2900 MemRegion mr(_cmsSpace->bottom(), new_word_size);
2901 // Shrink the card table
2902 Universe::heap()->barrier_set()->resize_covered_region(mr);
2903
2904 if (Verbose && PrintGC) {
2905 size_t new_mem_size = _virtual_space.committed_size();
2906 size_t old_mem_size = new_mem_size + bytes;
2907 gclog_or_tty->print_cr("Shrinking %s from " SIZE_FORMAT "K to " SIZE_FORMAT "K",
2908 name(), old_mem_size/K, new_mem_size/K);
2909 }
2910 }
2911
2912 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
2913 assert_locked_or_safepoint(Heap_lock);
2914 size_t size = ReservedSpace::page_align_size_down(bytes);
2915 // Only shrink if a compaction was done so that all the free space
2916 // in the generation is in a contiguous block at the end.
2917 if (size > 0 && did_compact()) {
2918 shrink_by(size);
2919 }
2920 }
2921
2922 bool ConcurrentMarkSweepGeneration::grow_by(size_t bytes) {
2923 assert_locked_or_safepoint(Heap_lock);
2924 bool result = _virtual_space.expand_by(bytes);
2925 if (result) {
2926 size_t new_word_size =
2927 heap_word_size(_virtual_space.committed_size());
2928 MemRegion mr(_cmsSpace->bottom(), new_word_size);
2929 _bts->resize(new_word_size); // resize the block offset shared array
2930 Universe::heap()->barrier_set()->resize_covered_region(mr);
2931 // Hmmmm... why doesn't CFLS::set_end verify locking?
2932 // This is quite ugly; FIX ME XXX
2933 _cmsSpace->assert_locked(freelistLock());
2934 _cmsSpace->set_end((HeapWord*)_virtual_space.high());
2935
2936 // update the space and generation capacity counters
2937 if (UsePerfData) {
2938 _space_counters->update_capacity();
2939 _gen_counters->update_all();
2940 }
2941
2942 if (Verbose && PrintGC) {
2943 size_t new_mem_size = _virtual_space.committed_size();
2944 size_t old_mem_size = new_mem_size - bytes;
2945 gclog_or_tty->print_cr("Expanding %s from " SIZE_FORMAT "K by " SIZE_FORMAT "K to " SIZE_FORMAT "K",
2946 name(), old_mem_size/K, bytes/K, new_mem_size/K);
2947 }
2948 }
2949 return result;
2950 }
2951
2952 bool ConcurrentMarkSweepGeneration::grow_to_reserved() {
2953 assert_locked_or_safepoint(Heap_lock);
2954 bool success = true;
2955 const size_t remaining_bytes = _virtual_space.uncommitted_size();
2956 if (remaining_bytes > 0) {
2957 success = grow_by(remaining_bytes);
2958 DEBUG_ONLY(if (!success) warning("grow to reserved failed");)
2959 }
2960 return success;
2961 }
2962
2963 void ConcurrentMarkSweepGeneration::shrink_free_list_by(size_t bytes) {
2964 assert_locked_or_safepoint(Heap_lock);
2965 assert_lock_strong(freelistLock());
2966 if (PrintGCDetails && Verbose) {
2967 warning("Shrinking of CMS not yet implemented");
2968 }
2969 return;
2970 }
2971
2972
2973 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
2974 // phases.
2975 class CMSPhaseAccounting: public StackObj {
2976 public:
2977 CMSPhaseAccounting(CMSCollector *collector,
2978 const char *phase,
2979 const GCId gc_id,
2980 bool print_cr = true);
2981 ~CMSPhaseAccounting();
2982
2983 private:
2984 CMSCollector *_collector;
2985 const char *_phase;
2986 elapsedTimer _wallclock;
2987 bool _print_cr;
2988 const GCId _gc_id;
2989
2990 public:
2991 // Not MT-safe; so do not pass around these StackObj's
2992 // where they may be accessed by other threads.
2993 jlong wallclock_millis() {
2994 assert(_wallclock.is_active(), "Wall clock should not stop");
2995 _wallclock.stop(); // to record time
2996 jlong ret = _wallclock.milliseconds();
2997 _wallclock.start(); // restart
2998 return ret;
2999 }
3000 };
3001
3002 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
3003 const char *phase,
3004 const GCId gc_id,
3005 bool print_cr) :
3006 _collector(collector), _phase(phase), _print_cr(print_cr), _gc_id(gc_id) {
3007
3008 if (PrintCMSStatistics != 0) {
3009 _collector->resetYields();
3010 }
3011 if (PrintGCDetails) {
3012 gclog_or_tty->gclog_stamp(_gc_id);
3013 gclog_or_tty->print_cr("[%s-concurrent-%s-start]",
3014 _collector->cmsGen()->short_name(), _phase);
3015 }
3016 _collector->resetTimer();
3017 _wallclock.start();
3018 _collector->startTimer();
3019 }
3020
3021 CMSPhaseAccounting::~CMSPhaseAccounting() {
3022 assert(_wallclock.is_active(), "Wall clock should not have stopped");
3023 _collector->stopTimer();
3024 _wallclock.stop();
3025 if (PrintGCDetails) {
3026 gclog_or_tty->gclog_stamp(_gc_id);
3027 gclog_or_tty->print("[%s-concurrent-%s: %3.3f/%3.3f secs]",
3028 _collector->cmsGen()->short_name(),
3029 _phase, _collector->timerValue(), _wallclock.seconds());
3030 if (_print_cr) {
3031 gclog_or_tty->cr();
3032 }
3033 if (PrintCMSStatistics != 0) {
3034 gclog_or_tty->print_cr(" (CMS-concurrent-%s yielded %d times)", _phase,
3035 _collector->yields());
3036 }
3037 }
3038 }
3039
3040 // CMS work
3041
3042 // The common parts of CMSParInitialMarkTask and CMSParRemarkTask.
3043 class CMSParMarkTask : public AbstractGangTask {
3044 protected:
3045 CMSCollector* _collector;
3046 int _n_workers;
3047 CMSParMarkTask(const char* name, CMSCollector* collector, int n_workers) :
3048 AbstractGangTask(name),
3049 _collector(collector),
3050 _n_workers(n_workers) {}
3051 // Work method in support of parallel rescan ... of young gen spaces
3052 void do_young_space_rescan(uint worker_id, OopsInGenClosure* cl,
3053 ContiguousSpace* space,
3054 HeapWord** chunk_array, size_t chunk_top);
3055 void work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl);
3056 };
3057
3058 // Parallel initial mark task
3059 class CMSParInitialMarkTask: public CMSParMarkTask {
3060 public:
3061 CMSParInitialMarkTask(CMSCollector* collector, int n_workers) :
3062 CMSParMarkTask("Scan roots and young gen for initial mark in parallel",
3063 collector, n_workers) {}
3064 void work(uint worker_id);
3065 };
3066
3067 // Checkpoint the roots into this generation from outside
3068 // this generation. [Note this initial checkpoint need only
3069 // be approximate -- we'll do a catch up phase subsequently.]
3070 void CMSCollector::checkpointRootsInitial() {
3071 assert(_collectorState == InitialMarking, "Wrong collector state");
3072 check_correct_thread_executing();
3073 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
3074
3075 save_heap_summary();
3076 report_heap_summary(GCWhen::BeforeGC);
3077
3078 ReferenceProcessor* rp = ref_processor();
3079 SpecializationStats::clear();
3080 assert(_restart_addr == NULL, "Control point invariant");
3081 {
3082 // acquire locks for subsequent manipulations
3083 MutexLockerEx x(bitMapLock(),
3084 Mutex::_no_safepoint_check_flag);
3085 checkpointRootsInitialWork();
3086 // enable ("weak") refs discovery
3087 rp->enable_discovery(true /*verify_disabled*/, true /*check_no_refs*/);
3088 _collectorState = Marking;
3089 }
3090 SpecializationStats::print();
3091 }
3092
3093 void CMSCollector::checkpointRootsInitialWork() {
3094 assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
3095 assert(_collectorState == InitialMarking, "just checking");
3096
3097 // If there has not been a GC[n-1] since last GC[n] cycle completed,
3098 // precede our marking with a collection of all
3099 // younger generations to keep floating garbage to a minimum.
3100 // XXX: we won't do this for now -- it's an optimization to be done later.
3101
3102 // already have locks
3103 assert_lock_strong(bitMapLock());
3104 assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
3105
3106 // Setup the verification and class unloading state for this
3107 // CMS collection cycle.
3108 setup_cms_unloading_and_verification_state();
3109
3110 NOT_PRODUCT(GCTraceTime t("\ncheckpointRootsInitialWork",
3111 PrintGCDetails && Verbose, true, _gc_timer_cm, _gc_tracer_cm->gc_id());)
3112
3113 // Reset all the PLAB chunk arrays if necessary.
3114 if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
3115 reset_survivor_plab_arrays();
3116 }
3117
3118 ResourceMark rm;
3119 HandleMark hm;
3120
3121 MarkRefsIntoClosure notOlder(_span, &_markBitMap);
3122 GenCollectedHeap* gch = GenCollectedHeap::heap();
3123
3124 verify_work_stacks_empty();
3125 verify_overflow_empty();
3126
3127 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
3128 // Update the saved marks which may affect the root scans.
3129 gch->save_marks();
3130
3131 // weak reference processing has not started yet.
3132 ref_processor()->set_enqueuing_is_done(false);
3133
3134 // Need to remember all newly created CLDs,
3135 // so that we can guarantee that the remark finds them.
3136 ClassLoaderDataGraph::remember_new_clds(true);
3137
3138 // Whenever a CLD is found, it will be claimed before proceeding to mark
3139 // the klasses. The claimed marks need to be cleared before marking starts.
3140 ClassLoaderDataGraph::clear_claimed_marks();
3141
3142 if (CMSPrintEdenSurvivorChunks) {
3143 print_eden_and_survivor_chunk_arrays();
3144 }
3145
3146 {
3147 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
3148 if (CMSParallelInitialMarkEnabled && CollectedHeap::use_parallel_gc_threads()) {
3149 // The parallel version.
3150 FlexibleWorkGang* workers = gch->workers();
3151 assert(workers != NULL, "Need parallel worker threads.");
3152 int n_workers = workers->active_workers();
3153 CMSParInitialMarkTask tsk(this, n_workers);
3154 gch->set_par_threads(n_workers);
3155 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
3156 if (n_workers > 1) {
3157 GenCollectedHeap::StrongRootsScope srs(gch);
3158 workers->run_task(&tsk);
3159 } else {
3160 GenCollectedHeap::StrongRootsScope srs(gch);
3161 tsk.work(0);
3162 }
3163 gch->set_par_threads(0);
3164 } else {
3165 // The serial version.
3166 CLDToOopClosure cld_closure(¬Older, true);
3167 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3168 gch->gen_process_roots(_cmsGen->level(),
3169 true, // younger gens are roots
3170 true, // activate StrongRootsScope
3171 SharedHeap::ScanningOption(roots_scanning_options()),
3172 should_unload_classes(),
3173 ¬Older,
3174 NULL,
3175 &cld_closure);
3176 }
3177 }
3178
3179 // Clear mod-union table; it will be dirtied in the prologue of
3180 // CMS generation per each younger generation collection.
3181
3182 assert(_modUnionTable.isAllClear(),
3183 "Was cleared in most recent final checkpoint phase"
3184 " or no bits are set in the gc_prologue before the start of the next "
3185 "subsequent marking phase.");
3186
3187 assert(_ct->klass_rem_set()->mod_union_is_clear(), "Must be");
3188
3189 // Save the end of the used_region of the constituent generations
3190 // to be used to limit the extent of sweep in each generation.
3191 save_sweep_limits();
3192 verify_overflow_empty();
3193 }
3194
3195 bool CMSCollector::markFromRoots() {
3196 // we might be tempted to assert that:
3197 // assert(!SafepointSynchronize::is_at_safepoint(),
3198 // "inconsistent argument?");
3199 // However that wouldn't be right, because it's possible that
3200 // a safepoint is indeed in progress as a younger generation
3201 // stop-the-world GC happens even as we mark in this generation.
3202 assert(_collectorState == Marking, "inconsistent state?");
3203 check_correct_thread_executing();
3204 verify_overflow_empty();
3205
3206 // Weak ref discovery note: We may be discovering weak
3207 // refs in this generation concurrent (but interleaved) with
3208 // weak ref discovery by a younger generation collector.
3209
3210 CMSTokenSyncWithLocks ts(true, bitMapLock());
3211 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3212 CMSPhaseAccounting pa(this, "mark", _gc_tracer_cm->gc_id(), !PrintGCDetails);
3213 bool res = markFromRootsWork();
3214 if (res) {
3215 _collectorState = Precleaning;
3216 } else { // We failed and a foreground collection wants to take over
3217 assert(_foregroundGCIsActive, "internal state inconsistency");
3218 assert(_restart_addr == NULL, "foreground will restart from scratch");
3219 if (PrintGCDetails) {
3220 gclog_or_tty->print_cr("bailing out to foreground collection");
3221 }
3222 }
3223 verify_overflow_empty();
3224 return res;
3225 }
3226
3227 bool CMSCollector::markFromRootsWork() {
3228 // iterate over marked bits in bit map, doing a full scan and mark
3229 // from these roots using the following algorithm:
3230 // . if oop is to the right of the current scan pointer,
3231 // mark corresponding bit (we'll process it later)
3232 // . else (oop is to left of current scan pointer)
3233 // push oop on marking stack
3234 // . drain the marking stack
3235
3236 // Note that when we do a marking step we need to hold the
3237 // bit map lock -- recall that direct allocation (by mutators)
3238 // and promotion (by younger generation collectors) is also
3239 // marking the bit map. [the so-called allocate live policy.]
3240 // Because the implementation of bit map marking is not
3241 // robust wrt simultaneous marking of bits in the same word,
3242 // we need to make sure that there is no such interference
3243 // between concurrent such updates.
3244
3245 // already have locks
3246 assert_lock_strong(bitMapLock());
3247
3248 verify_work_stacks_empty();
3249 verify_overflow_empty();
3250 bool result = false;
3251 if (CMSConcurrentMTEnabled && ConcGCThreads > 0) {
3252 result = do_marking_mt();
3253 } else {
3254 result = do_marking_st();
3255 }
3256 return result;
3257 }
3258
3259 // Forward decl
3260 class CMSConcMarkingTask;
3261
3262 class CMSConcMarkingTerminator: public ParallelTaskTerminator {
3263 CMSCollector* _collector;
3264 CMSConcMarkingTask* _task;
3265 public:
3266 virtual void yield();
3267
3268 // "n_threads" is the number of threads to be terminated.
3269 // "queue_set" is a set of work queues of other threads.
3270 // "collector" is the CMS collector associated with this task terminator.
3271 // "yield" indicates whether we need the gang as a whole to yield.
3272 CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
3273 ParallelTaskTerminator(n_threads, queue_set),
3274 _collector(collector) { }
3275
3276 void set_task(CMSConcMarkingTask* task) {
3277 _task = task;
3278 }
3279 };
3280
3281 class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator {
3282 CMSConcMarkingTask* _task;
3283 public:
3284 bool should_exit_termination();
3285 void set_task(CMSConcMarkingTask* task) {
3286 _task = task;
3287 }
3288 };
3289
3290 // MT Concurrent Marking Task
3291 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3292 CMSCollector* _collector;
3293 int _n_workers; // requested/desired # workers
3294 bool _result;
3295 CompactibleFreeListSpace* _cms_space;
3296 char _pad_front[64]; // padding to ...
3297 HeapWord* _global_finger; // ... avoid sharing cache line
3298 char _pad_back[64];
3299 HeapWord* _restart_addr;
3300
3301 // Exposed here for yielding support
3302 Mutex* const _bit_map_lock;
3303
3304 // The per thread work queues, available here for stealing
3305 OopTaskQueueSet* _task_queues;
3306
3307 // Termination (and yielding) support
3308 CMSConcMarkingTerminator _term;
3309 CMSConcMarkingTerminatorTerminator _term_term;
3310
3311 public:
3312 CMSConcMarkingTask(CMSCollector* collector,
3313 CompactibleFreeListSpace* cms_space,
3314 YieldingFlexibleWorkGang* workers,
3315 OopTaskQueueSet* task_queues):
3316 YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3317 _collector(collector),
3318 _cms_space(cms_space),
3319 _n_workers(0), _result(true),
3320 _task_queues(task_queues),
3321 _term(_n_workers, task_queues, _collector),
3322 _bit_map_lock(collector->bitMapLock())
3323 {
3324 _requested_size = _n_workers;
3325 _term.set_task(this);
3326 _term_term.set_task(this);
3327 _restart_addr = _global_finger = _cms_space->bottom();
3328 }
3329
3330
3331 OopTaskQueueSet* task_queues() { return _task_queues; }
3332
3333 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3334
3335 HeapWord** global_finger_addr() { return &_global_finger; }
3336
3337 CMSConcMarkingTerminator* terminator() { return &_term; }
3338
3339 virtual void set_for_termination(int active_workers) {
3340 terminator()->reset_for_reuse(active_workers);
3341 }
3342
3343 void work(uint worker_id);
3344 bool should_yield() {
3345 return ConcurrentMarkSweepThread::should_yield()
3346 && !_collector->foregroundGCIsActive();
3347 }
3348
3349 virtual void coordinator_yield(); // stuff done by coordinator
3350 bool result() { return _result; }
3351
3352 void reset(HeapWord* ra) {
3353 assert(_global_finger >= _cms_space->end(), "Postcondition of ::work(i)");
3354 _restart_addr = _global_finger = ra;
3355 _term.reset_for_reuse();
3356 }
3357
3358 static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3359 OopTaskQueue* work_q);
3360
3361 private:
3362 void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3363 void do_work_steal(int i);
3364 void bump_global_finger(HeapWord* f);
3365 };
3366
3367 bool CMSConcMarkingTerminatorTerminator::should_exit_termination() {
3368 assert(_task != NULL, "Error");
3369 return _task->yielding();
3370 // Note that we do not need the disjunct || _task->should_yield() above
3371 // because we want terminating threads to yield only if the task
3372 // is already in the midst of yielding, which happens only after at least one
3373 // thread has yielded.
3374 }
3375
3376 void CMSConcMarkingTerminator::yield() {
3377 if (_task->should_yield()) {
3378 _task->yield();
3379 } else {
3380 ParallelTaskTerminator::yield();
3381 }
3382 }
3383
3384 ////////////////////////////////////////////////////////////////
3385 // Concurrent Marking Algorithm Sketch
3386 ////////////////////////////////////////////////////////////////
3387 // Until all tasks exhausted (both spaces):
3388 // -- claim next available chunk
3389 // -- bump global finger via CAS
3390 // -- find first object that starts in this chunk
3391 // and start scanning bitmap from that position
3392 // -- scan marked objects for oops
3393 // -- CAS-mark target, and if successful:
3394 // . if target oop is above global finger (volatile read)
3395 // nothing to do
3396 // . if target oop is in chunk and above local finger
3397 // then nothing to do
3398 // . else push on work-queue
3399 // -- Deal with possible overflow issues:
3400 // . local work-queue overflow causes stuff to be pushed on
3401 // global (common) overflow queue
3402 // . always first empty local work queue
3403 // . then get a batch of oops from global work queue if any
3404 // . then do work stealing
3405 // -- When all tasks claimed (both spaces)
3406 // and local work queue empty,
3407 // then in a loop do:
3408 // . check global overflow stack; steal a batch of oops and trace
3409 // . try to steal from other threads oif GOS is empty
3410 // . if neither is available, offer termination
3411 // -- Terminate and return result
3412 //
3413 void CMSConcMarkingTask::work(uint worker_id) {
3414 elapsedTimer _timer;
3415 ResourceMark rm;
3416 HandleMark hm;
3417
3418 DEBUG_ONLY(_collector->verify_overflow_empty();)
3419
3420 // Before we begin work, our work queue should be empty
3421 assert(work_queue(worker_id)->size() == 0, "Expected to be empty");
3422 // Scan the bitmap covering _cms_space, tracing through grey objects.
3423 _timer.start();
3424 do_scan_and_mark(worker_id, _cms_space);
3425 _timer.stop();
3426 if (PrintCMSStatistics != 0) {
3427 gclog_or_tty->print_cr("Finished cms space scanning in %dth thread: %3.3f sec",
3428 worker_id, _timer.seconds());
3429 // XXX: need xxx/xxx type of notation, two timers
3430 }
3431
3432 // ... do work stealing
3433 _timer.reset();
3434 _timer.start();
3435 do_work_steal(worker_id);
3436 _timer.stop();
3437 if (PrintCMSStatistics != 0) {
3438 gclog_or_tty->print_cr("Finished work stealing in %dth thread: %3.3f sec",
3439 worker_id, _timer.seconds());
3440 // XXX: need xxx/xxx type of notation, two timers
3441 }
3442 assert(_collector->_markStack.isEmpty(), "Should have been emptied");
3443 assert(work_queue(worker_id)->size() == 0, "Should have been emptied");
3444 // Note that under the current task protocol, the
3445 // following assertion is true even of the spaces
3446 // expanded since the completion of the concurrent
3447 // marking. XXX This will likely change under a strict
3448 // ABORT semantics.
3449 // After perm removal the comparison was changed to
3450 // greater than or equal to from strictly greater than.
3451 // Before perm removal the highest address sweep would
3452 // have been at the end of perm gen but now is at the
3453 // end of the tenured gen.
3454 assert(_global_finger >= _cms_space->end(),
3455 "All tasks have been completed");
3456 DEBUG_ONLY(_collector->verify_overflow_empty();)
3457 }
3458
3459 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
3460 HeapWord* read = _global_finger;
3461 HeapWord* cur = read;
3462 while (f > read) {
3463 cur = read;
3464 read = (HeapWord*) Atomic::cmpxchg_ptr(f, &_global_finger, cur);
3465 if (cur == read) {
3466 // our cas succeeded
3467 assert(_global_finger >= f, "protocol consistency");
3468 break;
3469 }
3470 }
3471 }
3472
3473 // This is really inefficient, and should be redone by
3474 // using (not yet available) block-read and -write interfaces to the
3475 // stack and the work_queue. XXX FIX ME !!!
3476 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3477 OopTaskQueue* work_q) {
3478 // Fast lock-free check
3479 if (ovflw_stk->length() == 0) {
3480 return false;
3481 }
3482 assert(work_q->size() == 0, "Shouldn't steal");
3483 MutexLockerEx ml(ovflw_stk->par_lock(),
3484 Mutex::_no_safepoint_check_flag);
3485 // Grab up to 1/4 the size of the work queue
3486 size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
3487 (size_t)ParGCDesiredObjsFromOverflowList);
3488 num = MIN2(num, ovflw_stk->length());
3489 for (int i = (int) num; i > 0; i--) {
3490 oop cur = ovflw_stk->pop();
3491 assert(cur != NULL, "Counted wrong?");
3492 work_q->push(cur);
3493 }
3494 return num > 0;
3495 }
3496
3497 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
3498 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
3499 int n_tasks = pst->n_tasks();
3500 // We allow that there may be no tasks to do here because
3501 // we are restarting after a stack overflow.
3502 assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
3503 uint nth_task = 0;
3504
3505 HeapWord* aligned_start = sp->bottom();
3506 if (sp->used_region().contains(_restart_addr)) {
3507 // Align down to a card boundary for the start of 0th task
3508 // for this space.
3509 aligned_start =
3510 (HeapWord*)align_size_down((uintptr_t)_restart_addr,
3511 CardTableModRefBS::card_size);
3512 }
3513
3514 size_t chunk_size = sp->marking_task_size();
3515 while (!pst->is_task_claimed(/* reference */ nth_task)) {
3516 // Having claimed the nth task in this space,
3517 // compute the chunk that it corresponds to:
3518 MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
3519 aligned_start + (nth_task+1)*chunk_size);
3520 // Try and bump the global finger via a CAS;
3521 // note that we need to do the global finger bump
3522 // _before_ taking the intersection below, because
3523 // the task corresponding to that region will be
3524 // deemed done even if the used_region() expands
3525 // because of allocation -- as it almost certainly will
3526 // during start-up while the threads yield in the
3527 // closure below.
3528 HeapWord* finger = span.end();
3529 bump_global_finger(finger); // atomically
3530 // There are null tasks here corresponding to chunks
3531 // beyond the "top" address of the space.
3532 span = span.intersection(sp->used_region());
3533 if (!span.is_empty()) { // Non-null task
3534 HeapWord* prev_obj;
3535 assert(!span.contains(_restart_addr) || nth_task == 0,
3536 "Inconsistency");
3537 if (nth_task == 0) {
3538 // For the 0th task, we'll not need to compute a block_start.
3539 if (span.contains(_restart_addr)) {
3540 // In the case of a restart because of stack overflow,
3541 // we might additionally skip a chunk prefix.
3542 prev_obj = _restart_addr;
3543 } else {
3544 prev_obj = span.start();
3545 }
3546 } else {
3547 // We want to skip the first object because
3548 // the protocol is to scan any object in its entirety
3549 // that _starts_ in this span; a fortiori, any
3550 // object starting in an earlier span is scanned
3551 // as part of an earlier claimed task.
3552 // Below we use the "careful" version of block_start
3553 // so we do not try to navigate uninitialized objects.
3554 prev_obj = sp->block_start_careful(span.start());
3555 // Below we use a variant of block_size that uses the
3556 // Printezis bits to avoid waiting for allocated
3557 // objects to become initialized/parsable.
3558 while (prev_obj < span.start()) {
3559 size_t sz = sp->block_size_no_stall(prev_obj, _collector);
3560 if (sz > 0) {
3561 prev_obj += sz;
3562 } else {
3563 // In this case we may end up doing a bit of redundant
3564 // scanning, but that appears unavoidable, short of
3565 // locking the free list locks; see bug 6324141.
3566 break;
3567 }
3568 }
3569 }
3570 if (prev_obj < span.end()) {
3571 MemRegion my_span = MemRegion(prev_obj, span.end());
3572 // Do the marking work within a non-empty span --
3573 // the last argument to the constructor indicates whether the
3574 // iteration should be incremental with periodic yields.
3575 Par_MarkFromRootsClosure cl(this, _collector, my_span,
3576 &_collector->_markBitMap,
3577 work_queue(i),
3578 &_collector->_markStack);
3579 _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
3580 } // else nothing to do for this task
3581 } // else nothing to do for this task
3582 }
3583 // We'd be tempted to assert here that since there are no
3584 // more tasks left to claim in this space, the global_finger
3585 // must exceed space->top() and a fortiori space->end(). However,
3586 // that would not quite be correct because the bumping of
3587 // global_finger occurs strictly after the claiming of a task,
3588 // so by the time we reach here the global finger may not yet
3589 // have been bumped up by the thread that claimed the last
3590 // task.
3591 pst->all_tasks_completed();
3592 }
3593
3594 class Par_ConcMarkingClosure: public MetadataAwareOopClosure {
3595 private:
3596 CMSCollector* _collector;
3597 CMSConcMarkingTask* _task;
3598 MemRegion _span;
3599 CMSBitMap* _bit_map;
3600 CMSMarkStack* _overflow_stack;
3601 OopTaskQueue* _work_queue;
3602 protected:
3603 DO_OOP_WORK_DEFN
3604 public:
3605 Par_ConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue,
3606 CMSBitMap* bit_map, CMSMarkStack* overflow_stack):
3607 MetadataAwareOopClosure(collector->ref_processor()),
3608 _collector(collector),
3609 _task(task),
3610 _span(collector->_span),
3611 _work_queue(work_queue),
3612 _bit_map(bit_map),
3613 _overflow_stack(overflow_stack)
3614 { }
3615 virtual void do_oop(oop* p);
3616 virtual void do_oop(narrowOop* p);
3617
3618 void trim_queue(size_t max);
3619 void handle_stack_overflow(HeapWord* lost);
3620 void do_yield_check() {
3621 if (_task->should_yield()) {
3622 _task->yield();
3623 }
3624 }
3625 };
3626
3627 // Grey object scanning during work stealing phase --
3628 // the salient assumption here is that any references
3629 // that are in these stolen objects being scanned must
3630 // already have been initialized (else they would not have
3631 // been published), so we do not need to check for
3632 // uninitialized objects before pushing here.
3633 void Par_ConcMarkingClosure::do_oop(oop obj) {
3634 assert(obj->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
3635 HeapWord* addr = (HeapWord*)obj;
3636 // Check if oop points into the CMS generation
3637 // and is not marked
3638 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
3639 // a white object ...
3640 // If we manage to "claim" the object, by being the
3641 // first thread to mark it, then we push it on our
3642 // marking stack
3643 if (_bit_map->par_mark(addr)) { // ... now grey
3644 // push on work queue (grey set)
3645 bool simulate_overflow = false;
3646 NOT_PRODUCT(
3647 if (CMSMarkStackOverflowALot &&
3648 _collector->simulate_overflow()) {
3649 // simulate a stack overflow
3650 simulate_overflow = true;
3651 }
3652 )
3653 if (simulate_overflow ||
3654 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
3655 // stack overflow
3656 if (PrintCMSStatistics != 0) {
3657 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
3658 SIZE_FORMAT, _overflow_stack->capacity());
3659 }
3660 // We cannot assert that the overflow stack is full because
3661 // it may have been emptied since.
3662 assert(simulate_overflow ||
3663 _work_queue->size() == _work_queue->max_elems(),
3664 "Else push should have succeeded");
3665 handle_stack_overflow(addr);
3666 }
3667 } // Else, some other thread got there first
3668 do_yield_check();
3669 }
3670 }
3671
3672 void Par_ConcMarkingClosure::do_oop(oop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
3673 void Par_ConcMarkingClosure::do_oop(narrowOop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
3674
3675 void Par_ConcMarkingClosure::trim_queue(size_t max) {
3676 while (_work_queue->size() > max) {
3677 oop new_oop;
3678 if (_work_queue->pop_local(new_oop)) {
3679 assert(new_oop->is_oop(), "Should be an oop");
3680 assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
3681 assert(_span.contains((HeapWord*)new_oop), "Not in span");
3682 new_oop->oop_iterate(this); // do_oop() above
3683 do_yield_check();
3684 }
3685 }
3686 }
3687
3688 // Upon stack overflow, we discard (part of) the stack,
3689 // remembering the least address amongst those discarded
3690 // in CMSCollector's _restart_address.
3691 void Par_ConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
3692 // We need to do this under a mutex to prevent other
3693 // workers from interfering with the work done below.
3694 MutexLockerEx ml(_overflow_stack->par_lock(),
3695 Mutex::_no_safepoint_check_flag);
3696 // Remember the least grey address discarded
3697 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
3698 _collector->lower_restart_addr(ra);
3699 _overflow_stack->reset(); // discard stack contents
3700 _overflow_stack->expand(); // expand the stack if possible
3701 }
3702
3703
3704 void CMSConcMarkingTask::do_work_steal(int i) {
3705 OopTaskQueue* work_q = work_queue(i);
3706 oop obj_to_scan;
3707 CMSBitMap* bm = &(_collector->_markBitMap);
3708 CMSMarkStack* ovflw = &(_collector->_markStack);
3709 int* seed = _collector->hash_seed(i);
3710 Par_ConcMarkingClosure cl(_collector, this, work_q, bm, ovflw);
3711 while (true) {
3712 cl.trim_queue(0);
3713 assert(work_q->size() == 0, "Should have been emptied above");
3714 if (get_work_from_overflow_stack(ovflw, work_q)) {
3715 // Can't assert below because the work obtained from the
3716 // overflow stack may already have been stolen from us.
3717 // assert(work_q->size() > 0, "Work from overflow stack");
3718 continue;
3719 } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
3720 assert(obj_to_scan->is_oop(), "Should be an oop");
3721 assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
3722 obj_to_scan->oop_iterate(&cl);
3723 } else if (terminator()->offer_termination(&_term_term)) {
3724 assert(work_q->size() == 0, "Impossible!");
3725 break;
3726 } else if (yielding() || should_yield()) {
3727 yield();
3728 }
3729 }
3730 }
3731
3732 // This is run by the CMS (coordinator) thread.
3733 void CMSConcMarkingTask::coordinator_yield() {
3734 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3735 "CMS thread should hold CMS token");
3736 // First give up the locks, then yield, then re-lock
3737 // We should probably use a constructor/destructor idiom to
3738 // do this unlock/lock or modify the MutexUnlocker class to
3739 // serve our purpose. XXX
3740 assert_lock_strong(_bit_map_lock);
3741 _bit_map_lock->unlock();
3742 ConcurrentMarkSweepThread::desynchronize(true);
3743 _collector->stopTimer();
3744 if (PrintCMSStatistics != 0) {
3745 _collector->incrementYields();
3746 }
3747
3748 // It is possible for whichever thread initiated the yield request
3749 // not to get a chance to wake up and take the bitmap lock between
3750 // this thread releasing it and reacquiring it. So, while the
3751 // should_yield() flag is on, let's sleep for a bit to give the
3752 // other thread a chance to wake up. The limit imposed on the number
3753 // of iterations is defensive, to avoid any unforseen circumstances
3754 // putting us into an infinite loop. Since it's always been this
3755 // (coordinator_yield()) method that was observed to cause the
3756 // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
3757 // which is by default non-zero. For the other seven methods that
3758 // also perform the yield operation, as are using a different
3759 // parameter (CMSYieldSleepCount) which is by default zero. This way we
3760 // can enable the sleeping for those methods too, if necessary.
3761 // See 6442774.
3762 //
3763 // We really need to reconsider the synchronization between the GC
3764 // thread and the yield-requesting threads in the future and we
3765 // should really use wait/notify, which is the recommended
3766 // way of doing this type of interaction. Additionally, we should
3767 // consolidate the eight methods that do the yield operation and they
3768 // are almost identical into one for better maintainability and
3769 // readability. See 6445193.
3770 //
3771 // Tony 2006.06.29
3772 for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
3773 ConcurrentMarkSweepThread::should_yield() &&
3774 !CMSCollector::foregroundGCIsActive(); ++i) {
3775 os::sleep(Thread::current(), 1, false);
3776 }
3777
3778 ConcurrentMarkSweepThread::synchronize(true);
3779 _bit_map_lock->lock_without_safepoint_check();
3780 _collector->startTimer();
3781 }
3782
3783 bool CMSCollector::do_marking_mt() {
3784 assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition");
3785 int num_workers = AdaptiveSizePolicy::calc_active_conc_workers(
3786 conc_workers()->total_workers(),
3787 conc_workers()->active_workers(),
3788 Threads::number_of_non_daemon_threads());
3789 conc_workers()->set_active_workers(num_workers);
3790
3791 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
3792
3793 CMSConcMarkingTask tsk(this,
3794 cms_space,
3795 conc_workers(),
3796 task_queues());
3797
3798 // Since the actual number of workers we get may be different
3799 // from the number we requested above, do we need to do anything different
3800 // below? In particular, may be we need to subclass the SequantialSubTasksDone
3801 // class?? XXX
3802 cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
3803
3804 // Refs discovery is already non-atomic.
3805 assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
3806 assert(ref_processor()->discovery_is_mt(), "Discovery should be MT");
3807 conc_workers()->start_task(&tsk);
3808 while (tsk.yielded()) {
3809 tsk.coordinator_yield();
3810 conc_workers()->continue_task(&tsk);
3811 }
3812 // If the task was aborted, _restart_addr will be non-NULL
3813 assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
3814 while (_restart_addr != NULL) {
3815 // XXX For now we do not make use of ABORTED state and have not
3816 // yet implemented the right abort semantics (even in the original
3817 // single-threaded CMS case). That needs some more investigation
3818 // and is deferred for now; see CR# TBF. 07252005YSR. XXX
3819 assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
3820 // If _restart_addr is non-NULL, a marking stack overflow
3821 // occurred; we need to do a fresh marking iteration from the
3822 // indicated restart address.
3823 if (_foregroundGCIsActive) {
3824 // We may be running into repeated stack overflows, having
3825 // reached the limit of the stack size, while making very
3826 // slow forward progress. It may be best to bail out and
3827 // let the foreground collector do its job.
3828 // Clear _restart_addr, so that foreground GC
3829 // works from scratch. This avoids the headache of
3830 // a "rescan" which would otherwise be needed because
3831 // of the dirty mod union table & card table.
3832 _restart_addr = NULL;
3833 return false;
3834 }
3835 // Adjust the task to restart from _restart_addr
3836 tsk.reset(_restart_addr);
3837 cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
3838 _restart_addr);
3839 _restart_addr = NULL;
3840 // Get the workers going again
3841 conc_workers()->start_task(&tsk);
3842 while (tsk.yielded()) {
3843 tsk.coordinator_yield();
3844 conc_workers()->continue_task(&tsk);
3845 }
3846 }
3847 assert(tsk.completed(), "Inconsistency");
3848 assert(tsk.result() == true, "Inconsistency");
3849 return true;
3850 }
3851
3852 bool CMSCollector::do_marking_st() {
3853 ResourceMark rm;
3854 HandleMark hm;
3855
3856 // Temporarily make refs discovery single threaded (non-MT)
3857 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
3858 MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
3859 &_markStack, CMSYield);
3860 // the last argument to iterate indicates whether the iteration
3861 // should be incremental with periodic yields.
3862 _markBitMap.iterate(&markFromRootsClosure);
3863 // If _restart_addr is non-NULL, a marking stack overflow
3864 // occurred; we need to do a fresh iteration from the
3865 // indicated restart address.
3866 while (_restart_addr != NULL) {
3867 if (_foregroundGCIsActive) {
3868 // We may be running into repeated stack overflows, having
3869 // reached the limit of the stack size, while making very
3870 // slow forward progress. It may be best to bail out and
3871 // let the foreground collector do its job.
3872 // Clear _restart_addr, so that foreground GC
3873 // works from scratch. This avoids the headache of
3874 // a "rescan" which would otherwise be needed because
3875 // of the dirty mod union table & card table.
3876 _restart_addr = NULL;
3877 return false; // indicating failure to complete marking
3878 }
3879 // Deal with stack overflow:
3880 // we restart marking from _restart_addr
3881 HeapWord* ra = _restart_addr;
3882 markFromRootsClosure.reset(ra);
3883 _restart_addr = NULL;
3884 _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
3885 }
3886 return true;
3887 }
3888
3889 void CMSCollector::preclean() {
3890 check_correct_thread_executing();
3891 assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
3892 verify_work_stacks_empty();
3893 verify_overflow_empty();
3894 _abort_preclean = false;
3895 if (CMSPrecleaningEnabled) {
3896 if (!CMSEdenChunksRecordAlways) {
3897 _eden_chunk_index = 0;
3898 }
3899 size_t used = get_eden_used();
3900 size_t capacity = get_eden_capacity();
3901 // Don't start sampling unless we will get sufficiently
3902 // many samples.
3903 if (used < (capacity/(CMSScheduleRemarkSamplingRatio * 100)
3904 * CMSScheduleRemarkEdenPenetration)) {
3905 _start_sampling = true;
3906 } else {
3907 _start_sampling = false;
3908 }
3909 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3910 CMSPhaseAccounting pa(this, "preclean", _gc_tracer_cm->gc_id(), !PrintGCDetails);
3911 preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
3912 }
3913 CMSTokenSync x(true); // is cms thread
3914 if (CMSPrecleaningEnabled) {
3915 sample_eden();
3916 _collectorState = AbortablePreclean;
3917 } else {
3918 _collectorState = FinalMarking;
3919 }
3920 verify_work_stacks_empty();
3921 verify_overflow_empty();
3922 }
3923
3924 // Try and schedule the remark such that young gen
3925 // occupancy is CMSScheduleRemarkEdenPenetration %.
3926 void CMSCollector::abortable_preclean() {
3927 check_correct_thread_executing();
3928 assert(CMSPrecleaningEnabled, "Inconsistent control state");
3929 assert(_collectorState == AbortablePreclean, "Inconsistent control state");
3930
3931 // If Eden's current occupancy is below this threshold,
3932 // immediately schedule the remark; else preclean
3933 // past the next scavenge in an effort to
3934 // schedule the pause as described above. By choosing
3935 // CMSScheduleRemarkEdenSizeThreshold >= max eden size
3936 // we will never do an actual abortable preclean cycle.
3937 if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
3938 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3939 CMSPhaseAccounting pa(this, "abortable-preclean", _gc_tracer_cm->gc_id(), !PrintGCDetails);
3940 // We need more smarts in the abortable preclean
3941 // loop below to deal with cases where allocation
3942 // in young gen is very very slow, and our precleaning
3943 // is running a losing race against a horde of
3944 // mutators intent on flooding us with CMS updates
3945 // (dirty cards).
3946 // One, admittedly dumb, strategy is to give up
3947 // after a certain number of abortable precleaning loops
3948 // or after a certain maximum time. We want to make
3949 // this smarter in the next iteration.
3950 // XXX FIX ME!!! YSR
3951 size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
3952 while (!(should_abort_preclean() ||
3953 ConcurrentMarkSweepThread::should_terminate())) {
3954 workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
3955 cumworkdone += workdone;
3956 loops++;
3957 // Voluntarily terminate abortable preclean phase if we have
3958 // been at it for too long.
3959 if ((CMSMaxAbortablePrecleanLoops != 0) &&
3960 loops >= CMSMaxAbortablePrecleanLoops) {
3961 if (PrintGCDetails) {
3962 gclog_or_tty->print(" CMS: abort preclean due to loops ");
3963 }
3964 break;
3965 }
3966 if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
3967 if (PrintGCDetails) {
3968 gclog_or_tty->print(" CMS: abort preclean due to time ");
3969 }
3970 break;
3971 }
3972 // If we are doing little work each iteration, we should
3973 // take a short break.
3974 if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
3975 // Sleep for some time, waiting for work to accumulate
3976 stopTimer();
3977 cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
3978 startTimer();
3979 waited++;
3980 }
3981 }
3982 if (PrintCMSStatistics > 0) {
3983 gclog_or_tty->print(" [" SIZE_FORMAT " iterations, " SIZE_FORMAT " waits, " SIZE_FORMAT " cards)] ",
3984 loops, waited, cumworkdone);
3985 }
3986 }
3987 CMSTokenSync x(true); // is cms thread
3988 if (_collectorState != Idling) {
3989 assert(_collectorState == AbortablePreclean,
3990 "Spontaneous state transition?");
3991 _collectorState = FinalMarking;
3992 } // Else, a foreground collection completed this CMS cycle.
3993 return;
3994 }
3995
3996 // Respond to an Eden sampling opportunity
3997 void CMSCollector::sample_eden() {
3998 // Make sure a young gc cannot sneak in between our
3999 // reading and recording of a sample.
4000 assert(Thread::current()->is_ConcurrentGC_thread(),
4001 "Only the cms thread may collect Eden samples");
4002 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
4003 "Should collect samples while holding CMS token");
4004 if (!_start_sampling) {
4005 return;
4006 }
4007 // When CMSEdenChunksRecordAlways is true, the eden chunk array
4008 // is populated by the young generation.
4009 if (_eden_chunk_array != NULL && !CMSEdenChunksRecordAlways) {
4010 if (_eden_chunk_index < _eden_chunk_capacity) {
4011 _eden_chunk_array[_eden_chunk_index] = *_top_addr; // take sample
4012 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4013 "Unexpected state of Eden");
4014 // We'd like to check that what we just sampled is an oop-start address;
4015 // however, we cannot do that here since the object may not yet have been
4016 // initialized. So we'll instead do the check when we _use_ this sample
4017 // later.
4018 if (_eden_chunk_index == 0 ||
4019 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4020 _eden_chunk_array[_eden_chunk_index-1])
4021 >= CMSSamplingGrain)) {
4022 _eden_chunk_index++; // commit sample
4023 }
4024 }
4025 }
4026 if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
4027 size_t used = get_eden_used();
4028 size_t capacity = get_eden_capacity();
4029 assert(used <= capacity, "Unexpected state of Eden");
4030 if (used > (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
4031 _abort_preclean = true;
4032 }
4033 }
4034 }
4035
4036
4037 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
4038 assert(_collectorState == Precleaning ||
4039 _collectorState == AbortablePreclean, "incorrect state");
4040 ResourceMark rm;
4041 HandleMark hm;
4042
4043 // Precleaning is currently not MT but the reference processor
4044 // may be set for MT. Disable it temporarily here.
4045 ReferenceProcessor* rp = ref_processor();
4046 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false);
4047
4048 // Do one pass of scrubbing the discovered reference lists
4049 // to remove any reference objects with strongly-reachable
4050 // referents.
4051 if (clean_refs) {
4052 CMSPrecleanRefsYieldClosure yield_cl(this);
4053 assert(rp->span().equals(_span), "Spans should be equal");
4054 CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
4055 &_markStack, true /* preclean */);
4056 CMSDrainMarkingStackClosure complete_trace(this,
4057 _span, &_markBitMap, &_markStack,
4058 &keep_alive, true /* preclean */);
4059
4060 // We don't want this step to interfere with a young
4061 // collection because we don't want to take CPU
4062 // or memory bandwidth away from the young GC threads
4063 // (which may be as many as there are CPUs).
4064 // Note that we don't need to protect ourselves from
4065 // interference with mutators because they can't
4066 // manipulate the discovered reference lists nor affect
4067 // the computed reachability of the referents, the
4068 // only properties manipulated by the precleaning
4069 // of these reference lists.
4070 stopTimer();
4071 CMSTokenSyncWithLocks x(true /* is cms thread */,
4072 bitMapLock());
4073 startTimer();
4074 sample_eden();
4075
4076 // The following will yield to allow foreground
4077 // collection to proceed promptly. XXX YSR:
4078 // The code in this method may need further
4079 // tweaking for better performance and some restructuring
4080 // for cleaner interfaces.
4081 GCTimer *gc_timer = NULL; // Currently not tracing concurrent phases
4082 rp->preclean_discovered_references(
4083 rp->is_alive_non_header(), &keep_alive, &complete_trace, &yield_cl,
4084 gc_timer, _gc_tracer_cm->gc_id());
4085 }
4086
4087 if (clean_survivor) { // preclean the active survivor space(s)
4088 PushAndMarkClosure pam_cl(this, _span, ref_processor(),
4089 &_markBitMap, &_modUnionTable,
4090 &_markStack, true /* precleaning phase */);
4091 stopTimer();
4092 CMSTokenSyncWithLocks ts(true /* is cms thread */,
4093 bitMapLock());
4094 startTimer();
4095 unsigned int before_count =
4096 GenCollectedHeap::heap()->total_collections();
4097 SurvivorSpacePrecleanClosure
4098 sss_cl(this, _span, &_markBitMap, &_markStack,
4099 &pam_cl, before_count, CMSYield);
4100 _young_gen->from()->object_iterate_careful(&sss_cl);
4101 _young_gen->to()->object_iterate_careful(&sss_cl);
4102 }
4103 MarkRefsIntoAndScanClosure
4104 mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
4105 &_markStack, this, CMSYield,
4106 true /* precleaning phase */);
4107 // CAUTION: The following closure has persistent state that may need to
4108 // be reset upon a decrease in the sequence of addresses it
4109 // processes.
4110 ScanMarkedObjectsAgainCarefullyClosure
4111 smoac_cl(this, _span,
4112 &_markBitMap, &_markStack, &mrias_cl, CMSYield);
4113
4114 // Preclean dirty cards in ModUnionTable and CardTable using
4115 // appropriate convergence criterion;
4116 // repeat CMSPrecleanIter times unless we find that
4117 // we are losing.
4118 assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
4119 assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
4120 "Bad convergence multiplier");
4121 assert(CMSPrecleanThreshold >= 100,
4122 "Unreasonably low CMSPrecleanThreshold");
4123
4124 size_t numIter, cumNumCards, lastNumCards, curNumCards;
4125 for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
4126 numIter < CMSPrecleanIter;
4127 numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
4128 curNumCards = preclean_mod_union_table(_cmsGen, &smoac_cl);
4129 if (Verbose && PrintGCDetails) {
4130 gclog_or_tty->print(" (modUnionTable: " SIZE_FORMAT " cards)", curNumCards);
4131 }
4132 // Either there are very few dirty cards, so re-mark
4133 // pause will be small anyway, or our pre-cleaning isn't
4134 // that much faster than the rate at which cards are being
4135 // dirtied, so we might as well stop and re-mark since
4136 // precleaning won't improve our re-mark time by much.
4137 if (curNumCards <= CMSPrecleanThreshold ||
4138 (numIter > 0 &&
4139 (curNumCards * CMSPrecleanDenominator >
4140 lastNumCards * CMSPrecleanNumerator))) {
4141 numIter++;
4142 cumNumCards += curNumCards;
4143 break;
4144 }
4145 }
4146
4147 preclean_klasses(&mrias_cl, _cmsGen->freelistLock());
4148
4149 curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
4150 cumNumCards += curNumCards;
4151 if (PrintGCDetails && PrintCMSStatistics != 0) {
4152 gclog_or_tty->print_cr(" (cardTable: " SIZE_FORMAT " cards, re-scanned " SIZE_FORMAT " cards, " SIZE_FORMAT " iterations)",
4153 curNumCards, cumNumCards, numIter);
4154 }
4155 return cumNumCards; // as a measure of useful work done
4156 }
4157
4158 // PRECLEANING NOTES:
4159 // Precleaning involves:
4160 // . reading the bits of the modUnionTable and clearing the set bits.
4161 // . For the cards corresponding to the set bits, we scan the
4162 // objects on those cards. This means we need the free_list_lock
4163 // so that we can safely iterate over the CMS space when scanning
4164 // for oops.
4165 // . When we scan the objects, we'll be both reading and setting
4166 // marks in the marking bit map, so we'll need the marking bit map.
4167 // . For protecting _collector_state transitions, we take the CGC_lock.
4168 // Note that any races in the reading of of card table entries by the
4169 // CMS thread on the one hand and the clearing of those entries by the
4170 // VM thread or the setting of those entries by the mutator threads on the
4171 // other are quite benign. However, for efficiency it makes sense to keep
4172 // the VM thread from racing with the CMS thread while the latter is
4173 // dirty card info to the modUnionTable. We therefore also use the
4174 // CGC_lock to protect the reading of the card table and the mod union
4175 // table by the CM thread.
4176 // . We run concurrently with mutator updates, so scanning
4177 // needs to be done carefully -- we should not try to scan
4178 // potentially uninitialized objects.
4179 //
4180 // Locking strategy: While holding the CGC_lock, we scan over and
4181 // reset a maximal dirty range of the mod union / card tables, then lock
4182 // the free_list_lock and bitmap lock to do a full marking, then
4183 // release these locks; and repeat the cycle. This allows for a
4184 // certain amount of fairness in the sharing of these locks between
4185 // the CMS collector on the one hand, and the VM thread and the
4186 // mutators on the other.
4187
4188 // NOTE: preclean_mod_union_table() and preclean_card_table()
4189 // further below are largely identical; if you need to modify
4190 // one of these methods, please check the other method too.
4191
4192 size_t CMSCollector::preclean_mod_union_table(
4193 ConcurrentMarkSweepGeneration* gen,
4194 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4195 verify_work_stacks_empty();
4196 verify_overflow_empty();
4197
4198 // strategy: starting with the first card, accumulate contiguous
4199 // ranges of dirty cards; clear these cards, then scan the region
4200 // covered by these cards.
4201
4202 // Since all of the MUT is committed ahead, we can just use
4203 // that, in case the generations expand while we are precleaning.
4204 // It might also be fine to just use the committed part of the
4205 // generation, but we might potentially miss cards when the
4206 // generation is rapidly expanding while we are in the midst
4207 // of precleaning.
4208 HeapWord* startAddr = gen->reserved().start();
4209 HeapWord* endAddr = gen->reserved().end();
4210
4211 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4212
4213 size_t numDirtyCards, cumNumDirtyCards;
4214 HeapWord *nextAddr, *lastAddr;
4215 for (cumNumDirtyCards = numDirtyCards = 0,
4216 nextAddr = lastAddr = startAddr;
4217 nextAddr < endAddr;
4218 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4219
4220 ResourceMark rm;
4221 HandleMark hm;
4222
4223 MemRegion dirtyRegion;
4224 {
4225 stopTimer();
4226 // Potential yield point
4227 CMSTokenSync ts(true);
4228 startTimer();
4229 sample_eden();
4230 // Get dirty region starting at nextOffset (inclusive),
4231 // simultaneously clearing it.
4232 dirtyRegion =
4233 _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
4234 assert(dirtyRegion.start() >= nextAddr,
4235 "returned region inconsistent?");
4236 }
4237 // Remember where the next search should begin.
4238 // The returned region (if non-empty) is a right open interval,
4239 // so lastOffset is obtained from the right end of that
4240 // interval.
4241 lastAddr = dirtyRegion.end();
4242 // Should do something more transparent and less hacky XXX
4243 numDirtyCards =
4244 _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
4245
4246 // We'll scan the cards in the dirty region (with periodic
4247 // yields for foreground GC as needed).
4248 if (!dirtyRegion.is_empty()) {
4249 assert(numDirtyCards > 0, "consistency check");
4250 HeapWord* stop_point = NULL;
4251 stopTimer();
4252 // Potential yield point
4253 CMSTokenSyncWithLocks ts(true, gen->freelistLock(),
4254 bitMapLock());
4255 startTimer();
4256 {
4257 verify_work_stacks_empty();
4258 verify_overflow_empty();
4259 sample_eden();
4260 stop_point =
4261 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4262 }
4263 if (stop_point != NULL) {
4264 // The careful iteration stopped early either because it found an
4265 // uninitialized object, or because we were in the midst of an
4266 // "abortable preclean", which should now be aborted. Redirty
4267 // the bits corresponding to the partially-scanned or unscanned
4268 // cards. We'll either restart at the next block boundary or
4269 // abort the preclean.
4270 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4271 "Should only be AbortablePreclean.");
4272 _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
4273 if (should_abort_preclean()) {
4274 break; // out of preclean loop
4275 } else {
4276 // Compute the next address at which preclean should pick up;
4277 // might need bitMapLock in order to read P-bits.
4278 lastAddr = next_card_start_after_block(stop_point);
4279 }
4280 }
4281 } else {
4282 assert(lastAddr == endAddr, "consistency check");
4283 assert(numDirtyCards == 0, "consistency check");
4284 break;
4285 }
4286 }
4287 verify_work_stacks_empty();
4288 verify_overflow_empty();
4289 return cumNumDirtyCards;
4290 }
4291
4292 // NOTE: preclean_mod_union_table() above and preclean_card_table()
4293 // below are largely identical; if you need to modify
4294 // one of these methods, please check the other method too.
4295
4296 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* gen,
4297 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4298 // strategy: it's similar to precleamModUnionTable above, in that
4299 // we accumulate contiguous ranges of dirty cards, mark these cards
4300 // precleaned, then scan the region covered by these cards.
4301 HeapWord* endAddr = (HeapWord*)(gen->_virtual_space.high());
4302 HeapWord* startAddr = (HeapWord*)(gen->_virtual_space.low());
4303
4304 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4305
4306 size_t numDirtyCards, cumNumDirtyCards;
4307 HeapWord *lastAddr, *nextAddr;
4308
4309 for (cumNumDirtyCards = numDirtyCards = 0,
4310 nextAddr = lastAddr = startAddr;
4311 nextAddr < endAddr;
4312 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4313
4314 ResourceMark rm;
4315 HandleMark hm;
4316
4317 MemRegion dirtyRegion;
4318 {
4319 // See comments in "Precleaning notes" above on why we
4320 // do this locking. XXX Could the locking overheads be
4321 // too high when dirty cards are sparse? [I don't think so.]
4322 stopTimer();
4323 CMSTokenSync x(true); // is cms thread
4324 startTimer();
4325 sample_eden();
4326 // Get and clear dirty region from card table
4327 dirtyRegion = _ct->ct_bs()->dirty_card_range_after_reset(
4328 MemRegion(nextAddr, endAddr),
4329 true,
4330 CardTableModRefBS::precleaned_card_val());
4331
4332 assert(dirtyRegion.start() >= nextAddr,
4333 "returned region inconsistent?");
4334 }
4335 lastAddr = dirtyRegion.end();
4336 numDirtyCards =
4337 dirtyRegion.word_size()/CardTableModRefBS::card_size_in_words;
4338
4339 if (!dirtyRegion.is_empty()) {
4340 stopTimer();
4341 CMSTokenSyncWithLocks ts(true, gen->freelistLock(), bitMapLock());
4342 startTimer();
4343 sample_eden();
4344 verify_work_stacks_empty();
4345 verify_overflow_empty();
4346 HeapWord* stop_point =
4347 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4348 if (stop_point != NULL) {
4349 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4350 "Should only be AbortablePreclean.");
4351 _ct->ct_bs()->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4352 if (should_abort_preclean()) {
4353 break; // out of preclean loop
4354 } else {
4355 // Compute the next address at which preclean should pick up.
4356 lastAddr = next_card_start_after_block(stop_point);
4357 }
4358 }
4359 } else {
4360 break;
4361 }
4362 }
4363 verify_work_stacks_empty();
4364 verify_overflow_empty();
4365 return cumNumDirtyCards;
4366 }
4367
4368 class PrecleanKlassClosure : public KlassClosure {
4369 KlassToOopClosure _cm_klass_closure;
4370 public:
4371 PrecleanKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4372 void do_klass(Klass* k) {
4373 if (k->has_accumulated_modified_oops()) {
4374 k->clear_accumulated_modified_oops();
4375
4376 _cm_klass_closure.do_klass(k);
4377 }
4378 }
4379 };
4380
4381 // The freelist lock is needed to prevent asserts, is it really needed?
4382 void CMSCollector::preclean_klasses(MarkRefsIntoAndScanClosure* cl, Mutex* freelistLock) {
4383
4384 cl->set_freelistLock(freelistLock);
4385
4386 CMSTokenSyncWithLocks ts(true, freelistLock, bitMapLock());
4387
4388 // SSS: Add equivalent to ScanMarkedObjectsAgainCarefullyClosure::do_yield_check and should_abort_preclean?
4389 // SSS: We should probably check if precleaning should be aborted, at suitable intervals?
4390 PrecleanKlassClosure preclean_klass_closure(cl);
4391 ClassLoaderDataGraph::classes_do(&preclean_klass_closure);
4392
4393 verify_work_stacks_empty();
4394 verify_overflow_empty();
4395 }
4396
4397 void CMSCollector::checkpointRootsFinal() {
4398 assert(_collectorState == FinalMarking, "incorrect state transition?");
4399 check_correct_thread_executing();
4400 // world is stopped at this checkpoint
4401 assert(SafepointSynchronize::is_at_safepoint(),
4402 "world should be stopped");
4403 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
4404
4405 verify_work_stacks_empty();
4406 verify_overflow_empty();
4407
4408 SpecializationStats::clear();
4409 if (PrintGCDetails) {
4410 gclog_or_tty->print("[YG occupancy: "SIZE_FORMAT" K ("SIZE_FORMAT" K)]",
4411 _young_gen->used() / K,
4412 _young_gen->capacity() / K);
4413 }
4414 {
4415 if (CMSScavengeBeforeRemark) {
4416 GenCollectedHeap* gch = GenCollectedHeap::heap();
4417 // Temporarily set flag to false, GCH->do_collection will
4418 // expect it to be false and set to true
4419 FlagSetting fl(gch->_is_gc_active, false);
4420 NOT_PRODUCT(GCTraceTime t("Scavenge-Before-Remark",
4421 PrintGCDetails && Verbose, true, _gc_timer_cm, _gc_tracer_cm->gc_id());)
4422 int level = _cmsGen->level() - 1;
4423 if (level >= 0) {
4424 gch->do_collection(true, // full (i.e. force, see below)
4425 false, // !clear_all_soft_refs
4426 0, // size
4427 false, // is_tlab
4428 level // max_level
4429 );
4430 }
4431 }
4432 FreelistLocker x(this);
4433 MutexLockerEx y(bitMapLock(),
4434 Mutex::_no_safepoint_check_flag);
4435 checkpointRootsFinalWork();
4436 }
4437 verify_work_stacks_empty();
4438 verify_overflow_empty();
4439 SpecializationStats::print();
4440 }
4441
4442 void CMSCollector::checkpointRootsFinalWork() {
4443 NOT_PRODUCT(GCTraceTime tr("checkpointRootsFinalWork", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());)
4444
4445 assert(haveFreelistLocks(), "must have free list locks");
4446 assert_lock_strong(bitMapLock());
4447
4448 ResourceMark rm;
4449 HandleMark hm;
4450
4451 GenCollectedHeap* gch = GenCollectedHeap::heap();
4452
4453 if (should_unload_classes()) {
4454 CodeCache::gc_prologue();
4455 }
4456 assert(haveFreelistLocks(), "must have free list locks");
4457 assert_lock_strong(bitMapLock());
4458
4459 // We might assume that we need not fill TLAB's when
4460 // CMSScavengeBeforeRemark is set, because we may have just done
4461 // a scavenge which would have filled all TLAB's -- and besides
4462 // Eden would be empty. This however may not always be the case --
4463 // for instance although we asked for a scavenge, it may not have
4464 // happened because of a JNI critical section. We probably need
4465 // a policy for deciding whether we can in that case wait until
4466 // the critical section releases and then do the remark following
4467 // the scavenge, and skip it here. In the absence of that policy,
4468 // or of an indication of whether the scavenge did indeed occur,
4469 // we cannot rely on TLAB's having been filled and must do
4470 // so here just in case a scavenge did not happen.
4471 gch->ensure_parsability(false); // fill TLAB's, but no need to retire them
4472 // Update the saved marks which may affect the root scans.
4473 gch->save_marks();
4474
4475 if (CMSPrintEdenSurvivorChunks) {
4476 print_eden_and_survivor_chunk_arrays();
4477 }
4478
4479 {
4480 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
4481
4482 // Note on the role of the mod union table:
4483 // Since the marker in "markFromRoots" marks concurrently with
4484 // mutators, it is possible for some reachable objects not to have been
4485 // scanned. For instance, an only reference to an object A was
4486 // placed in object B after the marker scanned B. Unless B is rescanned,
4487 // A would be collected. Such updates to references in marked objects
4488 // are detected via the mod union table which is the set of all cards
4489 // dirtied since the first checkpoint in this GC cycle and prior to
4490 // the most recent young generation GC, minus those cleaned up by the
4491 // concurrent precleaning.
4492 if (CMSParallelRemarkEnabled && CollectedHeap::use_parallel_gc_threads()) {
4493 GCTraceTime t("Rescan (parallel) ", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
4494 do_remark_parallel();
4495 } else {
4496 GCTraceTime t("Rescan (non-parallel) ", PrintGCDetails, false,
4497 _gc_timer_cm, _gc_tracer_cm->gc_id());
4498 do_remark_non_parallel();
4499 }
4500 }
4501 verify_work_stacks_empty();
4502 verify_overflow_empty();
4503
4504 {
4505 NOT_PRODUCT(GCTraceTime ts("refProcessingWork", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());)
4506 refProcessingWork();
4507 }
4508 verify_work_stacks_empty();
4509 verify_overflow_empty();
4510
4511 if (should_unload_classes()) {
4512 CodeCache::gc_epilogue();
4513 }
4514 JvmtiExport::gc_epilogue();
4515
4516 // If we encountered any (marking stack / work queue) overflow
4517 // events during the current CMS cycle, take appropriate
4518 // remedial measures, where possible, so as to try and avoid
4519 // recurrence of that condition.
4520 assert(_markStack.isEmpty(), "No grey objects");
4521 size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
4522 _ser_kac_ovflw + _ser_kac_preclean_ovflw;
4523 if (ser_ovflw > 0) {
4524 if (PrintCMSStatistics != 0) {
4525 gclog_or_tty->print_cr("Marking stack overflow (benign) "
4526 "(pmc_pc="SIZE_FORMAT", pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT
4527 ", kac_preclean="SIZE_FORMAT")",
4528 _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw,
4529 _ser_kac_ovflw, _ser_kac_preclean_ovflw);
4530 }
4531 _markStack.expand();
4532 _ser_pmc_remark_ovflw = 0;
4533 _ser_pmc_preclean_ovflw = 0;
4534 _ser_kac_preclean_ovflw = 0;
4535 _ser_kac_ovflw = 0;
4536 }
4537 if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
4538 if (PrintCMSStatistics != 0) {
4539 gclog_or_tty->print_cr("Work queue overflow (benign) "
4540 "(pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT")",
4541 _par_pmc_remark_ovflw, _par_kac_ovflw);
4542 }
4543 _par_pmc_remark_ovflw = 0;
4544 _par_kac_ovflw = 0;
4545 }
4546 if (PrintCMSStatistics != 0) {
4547 if (_markStack._hit_limit > 0) {
4548 gclog_or_tty->print_cr(" (benign) Hit max stack size limit ("SIZE_FORMAT")",
4549 _markStack._hit_limit);
4550 }
4551 if (_markStack._failed_double > 0) {
4552 gclog_or_tty->print_cr(" (benign) Failed stack doubling ("SIZE_FORMAT"),"
4553 " current capacity "SIZE_FORMAT,
4554 _markStack._failed_double,
4555 _markStack.capacity());
4556 }
4557 }
4558 _markStack._hit_limit = 0;
4559 _markStack._failed_double = 0;
4560
4561 if ((VerifyAfterGC || VerifyDuringGC) &&
4562 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
4563 verify_after_remark();
4564 }
4565
4566 _gc_tracer_cm->report_object_count_after_gc(&_is_alive_closure);
4567
4568 // Change under the freelistLocks.
4569 _collectorState = Sweeping;
4570 // Call isAllClear() under bitMapLock
4571 assert(_modUnionTable.isAllClear(),
4572 "Should be clear by end of the final marking");
4573 assert(_ct->klass_rem_set()->mod_union_is_clear(),
4574 "Should be clear by end of the final marking");
4575 }
4576
4577 void CMSParInitialMarkTask::work(uint worker_id) {
4578 elapsedTimer _timer;
4579 ResourceMark rm;
4580 HandleMark hm;
4581
4582 // ---------- scan from roots --------------
4583 _timer.start();
4584 GenCollectedHeap* gch = GenCollectedHeap::heap();
4585 Par_MarkRefsIntoClosure par_mri_cl(_collector->_span, &(_collector->_markBitMap));
4586
4587 // ---------- young gen roots --------------
4588 {
4589 work_on_young_gen_roots(worker_id, &par_mri_cl);
4590 _timer.stop();
4591 if (PrintCMSStatistics != 0) {
4592 gclog_or_tty->print_cr(
4593 "Finished young gen initial mark scan work in %dth thread: %3.3f sec",
4594 worker_id, _timer.seconds());
4595 }
4596 }
4597
4598 // ---------- remaining roots --------------
4599 _timer.reset();
4600 _timer.start();
4601
4602 CLDToOopClosure cld_closure(&par_mri_cl, true);
4603
4604 gch->gen_process_roots(_collector->_cmsGen->level(),
4605 false, // yg was scanned above
4606 false, // this is parallel code
4607 SharedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4608 _collector->should_unload_classes(),
4609 &par_mri_cl,
4610 NULL,
4611 &cld_closure);
4612 assert(_collector->should_unload_classes()
4613 || (_collector->CMSCollector::roots_scanning_options() & SharedHeap::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 initial mark scan work in %dth thread: %3.3f sec",
4619 worker_id, _timer.seconds());
4620 }
4621 }
4622
4623 // Parallel remark task
4624 class CMSParRemarkTask: public CMSParMarkTask {
4625 CompactibleFreeListSpace* _cms_space;
4626
4627 // The per-thread work queues, available here for stealing.
4628 OopTaskQueueSet* _task_queues;
4629 ParallelTaskTerminator _term;
4630
4631 public:
4632 // A value of 0 passed to n_workers will cause the number of
4633 // workers to be taken from the active workers in the work gang.
4634 CMSParRemarkTask(CMSCollector* collector,
4635 CompactibleFreeListSpace* cms_space,
4636 int n_workers, FlexibleWorkGang* workers,
4637 OopTaskQueueSet* task_queues):
4638 CMSParMarkTask("Rescan roots and grey objects in parallel",
4639 collector, n_workers),
4640 _cms_space(cms_space),
4641 _task_queues(task_queues),
4642 _term(n_workers, task_queues) { }
4643
4644 OopTaskQueueSet* task_queues() { return _task_queues; }
4645
4646 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
4647
4648 ParallelTaskTerminator* terminator() { return &_term; }
4649 int n_workers() { return _n_workers; }
4650
4651 void work(uint worker_id);
4652
4653 private:
4654 // ... of dirty cards in old space
4655 void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
4656 Par_MarkRefsIntoAndScanClosure* cl);
4657
4658 // ... work stealing for the above
4659 void do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl, int* seed);
4660 };
4661
4662 class RemarkKlassClosure : public KlassClosure {
4663 KlassToOopClosure _cm_klass_closure;
4664 public:
4665 RemarkKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4666 void do_klass(Klass* k) {
4667 // Check if we have modified any oops in the Klass during the concurrent marking.
4668 if (k->has_accumulated_modified_oops()) {
4669 k->clear_accumulated_modified_oops();
4670
4671 // We could have transfered the current modified marks to the accumulated marks,
4672 // like we do with the Card Table to Mod Union Table. But it's not really necessary.
4673 } else if (k->has_modified_oops()) {
4674 // Don't clear anything, this info is needed by the next young collection.
4675 } else {
4676 // No modified oops in the Klass.
4677 return;
4678 }
4679
4680 // The klass has modified fields, need to scan the klass.
4681 _cm_klass_closure.do_klass(k);
4682 }
4683 };
4684
4685 void CMSParMarkTask::work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl) {
4686 ParNewGeneration* young_gen = _collector->_young_gen;
4687 ContiguousSpace* eden_space = young_gen->eden();
4688 ContiguousSpace* from_space = young_gen->from();
4689 ContiguousSpace* to_space = young_gen->to();
4690
4691 HeapWord** eca = _collector->_eden_chunk_array;
4692 size_t ect = _collector->_eden_chunk_index;
4693 HeapWord** sca = _collector->_survivor_chunk_array;
4694 size_t sct = _collector->_survivor_chunk_index;
4695
4696 assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
4697 assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
4698
4699 do_young_space_rescan(worker_id, cl, to_space, NULL, 0);
4700 do_young_space_rescan(worker_id, cl, from_space, sca, sct);
4701 do_young_space_rescan(worker_id, cl, eden_space, eca, ect);
4702 }
4703
4704 // work_queue(i) is passed to the closure
4705 // Par_MarkRefsIntoAndScanClosure. The "i" parameter
4706 // also is passed to do_dirty_card_rescan_tasks() and to
4707 // do_work_steal() to select the i-th task_queue.
4708
4709 void CMSParRemarkTask::work(uint worker_id) {
4710 elapsedTimer _timer;
4711 ResourceMark rm;
4712 HandleMark hm;
4713
4714 // ---------- rescan from roots --------------
4715 _timer.start();
4716 GenCollectedHeap* gch = GenCollectedHeap::heap();
4717 Par_MarkRefsIntoAndScanClosure par_mrias_cl(_collector,
4718 _collector->_span, _collector->ref_processor(),
4719 &(_collector->_markBitMap),
4720 work_queue(worker_id));
4721
4722 // Rescan young gen roots first since these are likely
4723 // coarsely partitioned and may, on that account, constitute
4724 // the critical path; thus, it's best to start off that
4725 // work first.
4726 // ---------- young gen roots --------------
4727 {
4728 work_on_young_gen_roots(worker_id, &par_mrias_cl);
4729 _timer.stop();
4730 if (PrintCMSStatistics != 0) {
4731 gclog_or_tty->print_cr(
4732 "Finished young gen rescan work in %dth thread: %3.3f sec",
4733 worker_id, _timer.seconds());
4734 }
4735 }
4736
4737 // ---------- remaining roots --------------
4738 _timer.reset();
4739 _timer.start();
4740 gch->gen_process_roots(_collector->_cmsGen->level(),
4741 false, // yg was scanned above
4742 false, // this is parallel code
4743 SharedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4744 _collector->should_unload_classes(),
4745 &par_mrias_cl,
4746 NULL,
4747 NULL); // The dirty klasses will be handled below
4748
4749 assert(_collector->should_unload_classes()
4750 || (_collector->CMSCollector::roots_scanning_options() & SharedHeap::SO_AllCodeCache),
4751 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4752 _timer.stop();
4753 if (PrintCMSStatistics != 0) {
4754 gclog_or_tty->print_cr(
4755 "Finished remaining root rescan work in %dth thread: %3.3f sec",
4756 worker_id, _timer.seconds());
4757 }
4758
4759 // ---------- unhandled CLD scanning ----------
4760 if (worker_id == 0) { // Single threaded at the moment.
4761 _timer.reset();
4762 _timer.start();
4763
4764 // Scan all new class loader data objects and new dependencies that were
4765 // introduced during concurrent marking.
4766 ResourceMark rm;
4767 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
4768 for (int i = 0; i < array->length(); i++) {
4769 par_mrias_cl.do_class_loader_data(array->at(i));
4770 }
4771
4772 // We don't need to keep track of new CLDs anymore.
4773 ClassLoaderDataGraph::remember_new_clds(false);
4774
4775 _timer.stop();
4776 if (PrintCMSStatistics != 0) {
4777 gclog_or_tty->print_cr(
4778 "Finished unhandled CLD scanning work in %dth thread: %3.3f sec",
4779 worker_id, _timer.seconds());
4780 }
4781 }
4782
4783 // ---------- dirty klass scanning ----------
4784 if (worker_id == 0) { // Single threaded at the moment.
4785 _timer.reset();
4786 _timer.start();
4787
4788 // Scan all classes that was dirtied during the concurrent marking phase.
4789 RemarkKlassClosure remark_klass_closure(&par_mrias_cl);
4790 ClassLoaderDataGraph::classes_do(&remark_klass_closure);
4791
4792 _timer.stop();
4793 if (PrintCMSStatistics != 0) {
4794 gclog_or_tty->print_cr(
4795 "Finished dirty klass scanning work in %dth thread: %3.3f sec",
4796 worker_id, _timer.seconds());
4797 }
4798 }
4799
4800 // We might have added oops to ClassLoaderData::_handles during the
4801 // concurrent marking phase. These oops point to newly allocated objects
4802 // that are guaranteed to be kept alive. Either by the direct allocation
4803 // code, or when the young collector processes the roots. Hence,
4804 // we don't have to revisit the _handles block during the remark phase.
4805
4806 // ---------- rescan dirty cards ------------
4807 _timer.reset();
4808 _timer.start();
4809
4810 // Do the rescan tasks for each of the two spaces
4811 // (cms_space) in turn.
4812 // "worker_id" is passed to select the task_queue for "worker_id"
4813 do_dirty_card_rescan_tasks(_cms_space, worker_id, &par_mrias_cl);
4814 _timer.stop();
4815 if (PrintCMSStatistics != 0) {
4816 gclog_or_tty->print_cr(
4817 "Finished dirty card rescan work in %dth thread: %3.3f sec",
4818 worker_id, _timer.seconds());
4819 }
4820
4821 // ---------- steal work from other threads ...
4822 // ---------- ... and drain overflow list.
4823 _timer.reset();
4824 _timer.start();
4825 do_work_steal(worker_id, &par_mrias_cl, _collector->hash_seed(worker_id));
4826 _timer.stop();
4827 if (PrintCMSStatistics != 0) {
4828 gclog_or_tty->print_cr(
4829 "Finished work stealing in %dth thread: %3.3f sec",
4830 worker_id, _timer.seconds());
4831 }
4832 }
4833
4834 // Note that parameter "i" is not used.
4835 void
4836 CMSParMarkTask::do_young_space_rescan(uint worker_id,
4837 OopsInGenClosure* cl, ContiguousSpace* space,
4838 HeapWord** chunk_array, size_t chunk_top) {
4839 // Until all tasks completed:
4840 // . claim an unclaimed task
4841 // . compute region boundaries corresponding to task claimed
4842 // using chunk_array
4843 // . par_oop_iterate(cl) over that region
4844
4845 ResourceMark rm;
4846 HandleMark hm;
4847
4848 SequentialSubTasksDone* pst = space->par_seq_tasks();
4849
4850 uint nth_task = 0;
4851 uint n_tasks = pst->n_tasks();
4852
4853 if (n_tasks > 0) {
4854 assert(pst->valid(), "Uninitialized use?");
4855 HeapWord *start, *end;
4856 while (!pst->is_task_claimed(/* reference */ nth_task)) {
4857 // We claimed task # nth_task; compute its boundaries.
4858 if (chunk_top == 0) { // no samples were taken
4859 assert(nth_task == 0 && n_tasks == 1, "Can have only 1 eden task");
4860 start = space->bottom();
4861 end = space->top();
4862 } else if (nth_task == 0) {
4863 start = space->bottom();
4864 end = chunk_array[nth_task];
4865 } else if (nth_task < (uint)chunk_top) {
4866 assert(nth_task >= 1, "Control point invariant");
4867 start = chunk_array[nth_task - 1];
4868 end = chunk_array[nth_task];
4869 } else {
4870 assert(nth_task == (uint)chunk_top, "Control point invariant");
4871 start = chunk_array[chunk_top - 1];
4872 end = space->top();
4873 }
4874 MemRegion mr(start, end);
4875 // Verify that mr is in space
4876 assert(mr.is_empty() || space->used_region().contains(mr),
4877 "Should be in space");
4878 // Verify that "start" is an object boundary
4879 assert(mr.is_empty() || oop(mr.start())->is_oop(),
4880 "Should be an oop");
4881 space->par_oop_iterate(mr, cl);
4882 }
4883 pst->all_tasks_completed();
4884 }
4885 }
4886
4887 void
4888 CMSParRemarkTask::do_dirty_card_rescan_tasks(
4889 CompactibleFreeListSpace* sp, int i,
4890 Par_MarkRefsIntoAndScanClosure* cl) {
4891 // Until all tasks completed:
4892 // . claim an unclaimed task
4893 // . compute region boundaries corresponding to task claimed
4894 // . transfer dirty bits ct->mut for that region
4895 // . apply rescanclosure to dirty mut bits for that region
4896
4897 ResourceMark rm;
4898 HandleMark hm;
4899
4900 OopTaskQueue* work_q = work_queue(i);
4901 ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
4902 // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
4903 // CAUTION: This closure has state that persists across calls to
4904 // the work method dirty_range_iterate_clear() in that it has
4905 // embedded in it a (subtype of) UpwardsObjectClosure. The
4906 // use of that state in the embedded UpwardsObjectClosure instance
4907 // assumes that the cards are always iterated (even if in parallel
4908 // by several threads) in monotonically increasing order per each
4909 // thread. This is true of the implementation below which picks
4910 // card ranges (chunks) in monotonically increasing order globally
4911 // and, a-fortiori, in monotonically increasing order per thread
4912 // (the latter order being a subsequence of the former).
4913 // If the work code below is ever reorganized into a more chaotic
4914 // work-partitioning form than the current "sequential tasks"
4915 // paradigm, the use of that persistent state will have to be
4916 // revisited and modified appropriately. See also related
4917 // bug 4756801 work on which should examine this code to make
4918 // sure that the changes there do not run counter to the
4919 // assumptions made here and necessary for correctness and
4920 // efficiency. Note also that this code might yield inefficient
4921 // behavior in the case of very large objects that span one or
4922 // more work chunks. Such objects would potentially be scanned
4923 // several times redundantly. Work on 4756801 should try and
4924 // address that performance anomaly if at all possible. XXX
4925 MemRegion full_span = _collector->_span;
4926 CMSBitMap* bm = &(_collector->_markBitMap); // shared
4927 MarkFromDirtyCardsClosure
4928 greyRescanClosure(_collector, full_span, // entire span of interest
4929 sp, bm, work_q, cl);
4930
4931 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
4932 assert(pst->valid(), "Uninitialized use?");
4933 uint nth_task = 0;
4934 const int alignment = CardTableModRefBS::card_size * BitsPerWord;
4935 MemRegion span = sp->used_region();
4936 HeapWord* start_addr = span.start();
4937 HeapWord* end_addr = (HeapWord*)round_to((intptr_t)span.end(),
4938 alignment);
4939 const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
4940 assert((HeapWord*)round_to((intptr_t)start_addr, alignment) ==
4941 start_addr, "Check alignment");
4942 assert((size_t)round_to((intptr_t)chunk_size, alignment) ==
4943 chunk_size, "Check alignment");
4944
4945 while (!pst->is_task_claimed(/* reference */ nth_task)) {
4946 // Having claimed the nth_task, compute corresponding mem-region,
4947 // which is a-fortiori aligned correctly (i.e. at a MUT boundary).
4948 // The alignment restriction ensures that we do not need any
4949 // synchronization with other gang-workers while setting or
4950 // clearing bits in thus chunk of the MUT.
4951 MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
4952 start_addr + (nth_task+1)*chunk_size);
4953 // The last chunk's end might be way beyond end of the
4954 // used region. In that case pull back appropriately.
4955 if (this_span.end() > end_addr) {
4956 this_span.set_end(end_addr);
4957 assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
4958 }
4959 // Iterate over the dirty cards covering this chunk, marking them
4960 // precleaned, and setting the corresponding bits in the mod union
4961 // table. Since we have been careful to partition at Card and MUT-word
4962 // boundaries no synchronization is needed between parallel threads.
4963 _collector->_ct->ct_bs()->dirty_card_iterate(this_span,
4964 &modUnionClosure);
4965
4966 // Having transferred these marks into the modUnionTable,
4967 // rescan the marked objects on the dirty cards in the modUnionTable.
4968 // Even if this is at a synchronous collection, the initial marking
4969 // may have been done during an asynchronous collection so there
4970 // may be dirty bits in the mod-union table.
4971 _collector->_modUnionTable.dirty_range_iterate_clear(
4972 this_span, &greyRescanClosure);
4973 _collector->_modUnionTable.verifyNoOneBitsInRange(
4974 this_span.start(),
4975 this_span.end());
4976 }
4977 pst->all_tasks_completed(); // declare that i am done
4978 }
4979
4980 // . see if we can share work_queues with ParNew? XXX
4981 void
4982 CMSParRemarkTask::do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl,
4983 int* seed) {
4984 OopTaskQueue* work_q = work_queue(i);
4985 NOT_PRODUCT(int num_steals = 0;)
4986 oop obj_to_scan;
4987 CMSBitMap* bm = &(_collector->_markBitMap);
4988
4989 while (true) {
4990 // Completely finish any left over work from (an) earlier round(s)
4991 cl->trim_queue(0);
4992 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
4993 (size_t)ParGCDesiredObjsFromOverflowList);
4994 // Now check if there's any work in the overflow list
4995 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
4996 // only affects the number of attempts made to get work from the
4997 // overflow list and does not affect the number of workers. Just
4998 // pass ParallelGCThreads so this behavior is unchanged.
4999 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5000 work_q,
5001 ParallelGCThreads)) {
5002 // found something in global overflow list;
5003 // not yet ready to go stealing work from others.
5004 // We'd like to assert(work_q->size() != 0, ...)
5005 // because we just took work from the overflow list,
5006 // but of course we can't since all of that could have
5007 // been already stolen from us.
5008 // "He giveth and He taketh away."
5009 continue;
5010 }
5011 // Verify that we have no work before we resort to stealing
5012 assert(work_q->size() == 0, "Have work, shouldn't steal");
5013 // Try to steal from other queues that have work
5014 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5015 NOT_PRODUCT(num_steals++;)
5016 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5017 assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5018 // Do scanning work
5019 obj_to_scan->oop_iterate(cl);
5020 // Loop around, finish this work, and try to steal some more
5021 } else if (terminator()->offer_termination()) {
5022 break; // nirvana from the infinite cycle
5023 }
5024 }
5025 NOT_PRODUCT(
5026 if (PrintCMSStatistics != 0) {
5027 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5028 }
5029 )
5030 assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
5031 "Else our work is not yet done");
5032 }
5033
5034 // Record object boundaries in _eden_chunk_array by sampling the eden
5035 // top in the slow-path eden object allocation code path and record
5036 // the boundaries, if CMSEdenChunksRecordAlways is true. If
5037 // CMSEdenChunksRecordAlways is false, we use the other asynchronous
5038 // sampling in sample_eden() that activates during the part of the
5039 // preclean phase.
5040 void CMSCollector::sample_eden_chunk() {
5041 if (CMSEdenChunksRecordAlways && _eden_chunk_array != NULL) {
5042 if (_eden_chunk_lock->try_lock()) {
5043 // Record a sample. This is the critical section. The contents
5044 // of the _eden_chunk_array have to be non-decreasing in the
5045 // address order.
5046 _eden_chunk_array[_eden_chunk_index] = *_top_addr;
5047 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
5048 "Unexpected state of Eden");
5049 if (_eden_chunk_index == 0 ||
5050 ((_eden_chunk_array[_eden_chunk_index] > _eden_chunk_array[_eden_chunk_index-1]) &&
5051 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
5052 _eden_chunk_array[_eden_chunk_index-1]) >= CMSSamplingGrain))) {
5053 _eden_chunk_index++; // commit sample
5054 }
5055 _eden_chunk_lock->unlock();
5056 }
5057 }
5058 }
5059
5060 // Return a thread-local PLAB recording array, as appropriate.
5061 void* CMSCollector::get_data_recorder(int thr_num) {
5062 if (_survivor_plab_array != NULL &&
5063 (CMSPLABRecordAlways ||
5064 (_collectorState > Marking && _collectorState < FinalMarking))) {
5065 assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
5066 ChunkArray* ca = &_survivor_plab_array[thr_num];
5067 ca->reset(); // clear it so that fresh data is recorded
5068 return (void*) ca;
5069 } else {
5070 return NULL;
5071 }
5072 }
5073
5074 // Reset all the thread-local PLAB recording arrays
5075 void CMSCollector::reset_survivor_plab_arrays() {
5076 for (uint i = 0; i < ParallelGCThreads; i++) {
5077 _survivor_plab_array[i].reset();
5078 }
5079 }
5080
5081 // Merge the per-thread plab arrays into the global survivor chunk
5082 // array which will provide the partitioning of the survivor space
5083 // for CMS initial scan and rescan.
5084 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv,
5085 int no_of_gc_threads) {
5086 assert(_survivor_plab_array != NULL, "Error");
5087 assert(_survivor_chunk_array != NULL, "Error");
5088 assert(_collectorState == FinalMarking ||
5089 (CMSParallelInitialMarkEnabled && _collectorState == InitialMarking), "Error");
5090 for (int j = 0; j < no_of_gc_threads; j++) {
5091 _cursor[j] = 0;
5092 }
5093 HeapWord* top = surv->top();
5094 size_t i;
5095 for (i = 0; i < _survivor_chunk_capacity; i++) { // all sca entries
5096 HeapWord* min_val = top; // Higher than any PLAB address
5097 uint min_tid = 0; // position of min_val this round
5098 for (int j = 0; j < no_of_gc_threads; j++) {
5099 ChunkArray* cur_sca = &_survivor_plab_array[j];
5100 if (_cursor[j] == cur_sca->end()) {
5101 continue;
5102 }
5103 assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
5104 HeapWord* cur_val = cur_sca->nth(_cursor[j]);
5105 assert(surv->used_region().contains(cur_val), "Out of bounds value");
5106 if (cur_val < min_val) {
5107 min_tid = j;
5108 min_val = cur_val;
5109 } else {
5110 assert(cur_val < top, "All recorded addresses should be less");
5111 }
5112 }
5113 // At this point min_val and min_tid are respectively
5114 // the least address in _survivor_plab_array[j]->nth(_cursor[j])
5115 // and the thread (j) that witnesses that address.
5116 // We record this address in the _survivor_chunk_array[i]
5117 // and increment _cursor[min_tid] prior to the next round i.
5118 if (min_val == top) {
5119 break;
5120 }
5121 _survivor_chunk_array[i] = min_val;
5122 _cursor[min_tid]++;
5123 }
5124 // We are all done; record the size of the _survivor_chunk_array
5125 _survivor_chunk_index = i; // exclusive: [0, i)
5126 if (PrintCMSStatistics > 0) {
5127 gclog_or_tty->print(" (Survivor:" SIZE_FORMAT "chunks) ", i);
5128 }
5129 // Verify that we used up all the recorded entries
5130 #ifdef ASSERT
5131 size_t total = 0;
5132 for (int j = 0; j < no_of_gc_threads; j++) {
5133 assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
5134 total += _cursor[j];
5135 }
5136 assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
5137 // Check that the merged array is in sorted order
5138 if (total > 0) {
5139 for (size_t i = 0; i < total - 1; i++) {
5140 if (PrintCMSStatistics > 0) {
5141 gclog_or_tty->print(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
5142 i, _survivor_chunk_array[i]);
5143 }
5144 assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
5145 "Not sorted");
5146 }
5147 }
5148 #endif // ASSERT
5149 }
5150
5151 // Set up the space's par_seq_tasks structure for work claiming
5152 // for parallel initial scan and rescan of young gen.
5153 // See ParRescanTask where this is currently used.
5154 void
5155 CMSCollector::
5156 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
5157 assert(n_threads > 0, "Unexpected n_threads argument");
5158
5159 // Eden space
5160 if (!_young_gen->eden()->is_empty()) {
5161 SequentialSubTasksDone* pst = _young_gen->eden()->par_seq_tasks();
5162 assert(!pst->valid(), "Clobbering existing data?");
5163 // Each valid entry in [0, _eden_chunk_index) represents a task.
5164 size_t n_tasks = _eden_chunk_index + 1;
5165 assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
5166 // Sets the condition for completion of the subtask (how many threads
5167 // need to finish in order to be done).
5168 pst->set_n_threads(n_threads);
5169 pst->set_n_tasks((int)n_tasks);
5170 }
5171
5172 // Merge the survivor plab arrays into _survivor_chunk_array
5173 if (_survivor_plab_array != NULL) {
5174 merge_survivor_plab_arrays(_young_gen->from(), n_threads);
5175 } else {
5176 assert(_survivor_chunk_index == 0, "Error");
5177 }
5178
5179 // To space
5180 {
5181 SequentialSubTasksDone* pst = _young_gen->to()->par_seq_tasks();
5182 assert(!pst->valid(), "Clobbering existing data?");
5183 // Sets the condition for completion of the subtask (how many threads
5184 // need to finish in order to be done).
5185 pst->set_n_threads(n_threads);
5186 pst->set_n_tasks(1);
5187 assert(pst->valid(), "Error");
5188 }
5189
5190 // From space
5191 {
5192 SequentialSubTasksDone* pst = _young_gen->from()->par_seq_tasks();
5193 assert(!pst->valid(), "Clobbering existing data?");
5194 size_t n_tasks = _survivor_chunk_index + 1;
5195 assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
5196 // Sets the condition for completion of the subtask (how many threads
5197 // need to finish in order to be done).
5198 pst->set_n_threads(n_threads);
5199 pst->set_n_tasks((int)n_tasks);
5200 assert(pst->valid(), "Error");
5201 }
5202 }
5203
5204 // Parallel version of remark
5205 void CMSCollector::do_remark_parallel() {
5206 GenCollectedHeap* gch = GenCollectedHeap::heap();
5207 FlexibleWorkGang* workers = gch->workers();
5208 assert(workers != NULL, "Need parallel worker threads.");
5209 // Choose to use the number of GC workers most recently set
5210 // into "active_workers". If active_workers is not set, set it
5211 // to ParallelGCThreads.
5212 int n_workers = workers->active_workers();
5213 if (n_workers == 0) {
5214 assert(n_workers > 0, "Should have been set during scavenge");
5215 n_workers = ParallelGCThreads;
5216 workers->set_active_workers(n_workers);
5217 }
5218 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
5219
5220 CMSParRemarkTask tsk(this,
5221 cms_space,
5222 n_workers, workers, task_queues());
5223
5224 // Set up for parallel process_roots work.
5225 gch->set_par_threads(n_workers);
5226 // We won't be iterating over the cards in the card table updating
5227 // the younger_gen cards, so we shouldn't call the following else
5228 // the verification code as well as subsequent younger_refs_iterate
5229 // code would get confused. XXX
5230 // gch->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
5231
5232 // The young gen rescan work will not be done as part of
5233 // process_roots (which currently doesn't know how to
5234 // parallelize such a scan), but rather will be broken up into
5235 // a set of parallel tasks (via the sampling that the [abortable]
5236 // preclean phase did of eden, plus the [two] tasks of
5237 // scanning the [two] survivor spaces. Further fine-grain
5238 // parallelization of the scanning of the survivor spaces
5239 // themselves, and of precleaning of the younger gen itself
5240 // is deferred to the future.
5241 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
5242
5243 // The dirty card rescan work is broken up into a "sequence"
5244 // of parallel tasks (per constituent space) that are dynamically
5245 // claimed by the parallel threads.
5246 cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
5247
5248 // It turns out that even when we're using 1 thread, doing the work in a
5249 // separate thread causes wide variance in run times. We can't help this
5250 // in the multi-threaded case, but we special-case n=1 here to get
5251 // repeatable measurements of the 1-thread overhead of the parallel code.
5252 if (n_workers > 1) {
5253 // Make refs discovery MT-safe, if it isn't already: it may not
5254 // necessarily be so, since it's possible that we are doing
5255 // ST marking.
5256 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), true);
5257 GenCollectedHeap::StrongRootsScope srs(gch);
5258 workers->run_task(&tsk);
5259 } else {
5260 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5261 GenCollectedHeap::StrongRootsScope srs(gch);
5262 tsk.work(0);
5263 }
5264
5265 gch->set_par_threads(0); // 0 ==> non-parallel.
5266 // restore, single-threaded for now, any preserved marks
5267 // as a result of work_q overflow
5268 restore_preserved_marks_if_any();
5269 }
5270
5271 // Non-parallel version of remark
5272 void CMSCollector::do_remark_non_parallel() {
5273 ResourceMark rm;
5274 HandleMark hm;
5275 GenCollectedHeap* gch = GenCollectedHeap::heap();
5276 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5277
5278 MarkRefsIntoAndScanClosure
5279 mrias_cl(_span, ref_processor(), &_markBitMap, NULL /* not precleaning */,
5280 &_markStack, this,
5281 false /* should_yield */, false /* not precleaning */);
5282 MarkFromDirtyCardsClosure
5283 markFromDirtyCardsClosure(this, _span,
5284 NULL, // space is set further below
5285 &_markBitMap, &_markStack, &mrias_cl);
5286 {
5287 GCTraceTime t("grey object rescan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5288 // Iterate over the dirty cards, setting the corresponding bits in the
5289 // mod union table.
5290 {
5291 ModUnionClosure modUnionClosure(&_modUnionTable);
5292 _ct->ct_bs()->dirty_card_iterate(
5293 _cmsGen->used_region(),
5294 &modUnionClosure);
5295 }
5296 // Having transferred these marks into the modUnionTable, we just need
5297 // to rescan the marked objects on the dirty cards in the modUnionTable.
5298 // The initial marking may have been done during an asynchronous
5299 // collection so there may be dirty bits in the mod-union table.
5300 const int alignment =
5301 CardTableModRefBS::card_size * BitsPerWord;
5302 {
5303 // ... First handle dirty cards in CMS gen
5304 markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
5305 MemRegion ur = _cmsGen->used_region();
5306 HeapWord* lb = ur.start();
5307 HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
5308 MemRegion cms_span(lb, ub);
5309 _modUnionTable.dirty_range_iterate_clear(cms_span,
5310 &markFromDirtyCardsClosure);
5311 verify_work_stacks_empty();
5312 if (PrintCMSStatistics != 0) {
5313 gclog_or_tty->print(" (re-scanned "SIZE_FORMAT" dirty cards in cms gen) ",
5314 markFromDirtyCardsClosure.num_dirty_cards());
5315 }
5316 }
5317 }
5318 if (VerifyDuringGC &&
5319 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5320 HandleMark hm; // Discard invalid handles created during verification
5321 Universe::verify();
5322 }
5323 {
5324 GCTraceTime t("root rescan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5325
5326 verify_work_stacks_empty();
5327
5328 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
5329 GenCollectedHeap::StrongRootsScope srs(gch);
5330
5331 gch->gen_process_roots(_cmsGen->level(),
5332 true, // younger gens as roots
5333 false, // use the local StrongRootsScope
5334 SharedHeap::ScanningOption(roots_scanning_options()),
5335 should_unload_classes(),
5336 &mrias_cl,
5337 NULL,
5338 NULL); // The dirty klasses will be handled below
5339
5340 assert(should_unload_classes()
5341 || (roots_scanning_options() & SharedHeap::SO_AllCodeCache),
5342 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5343 }
5344
5345 {
5346 GCTraceTime t("visit unhandled CLDs", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5347
5348 verify_work_stacks_empty();
5349
5350 // Scan all class loader data objects that might have been introduced
5351 // during concurrent marking.
5352 ResourceMark rm;
5353 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
5354 for (int i = 0; i < array->length(); i++) {
5355 mrias_cl.do_class_loader_data(array->at(i));
5356 }
5357
5358 // We don't need to keep track of new CLDs anymore.
5359 ClassLoaderDataGraph::remember_new_clds(false);
5360
5361 verify_work_stacks_empty();
5362 }
5363
5364 {
5365 GCTraceTime t("dirty klass scan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5366
5367 verify_work_stacks_empty();
5368
5369 RemarkKlassClosure remark_klass_closure(&mrias_cl);
5370 ClassLoaderDataGraph::classes_do(&remark_klass_closure);
5371
5372 verify_work_stacks_empty();
5373 }
5374
5375 // We might have added oops to ClassLoaderData::_handles during the
5376 // concurrent marking phase. These oops point to newly allocated objects
5377 // that are guaranteed to be kept alive. Either by the direct allocation
5378 // code, or when the young collector processes the roots. Hence,
5379 // we don't have to revisit the _handles block during the remark phase.
5380
5381 verify_work_stacks_empty();
5382 // Restore evacuated mark words, if any, used for overflow list links
5383 if (!CMSOverflowEarlyRestoration) {
5384 restore_preserved_marks_if_any();
5385 }
5386 verify_overflow_empty();
5387 }
5388
5389 ////////////////////////////////////////////////////////
5390 // Parallel Reference Processing Task Proxy Class
5391 ////////////////////////////////////////////////////////
5392 class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues {
5393 typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
5394 CMSCollector* _collector;
5395 CMSBitMap* _mark_bit_map;
5396 const MemRegion _span;
5397 ProcessTask& _task;
5398
5399 public:
5400 CMSRefProcTaskProxy(ProcessTask& task,
5401 CMSCollector* collector,
5402 const MemRegion& span,
5403 CMSBitMap* mark_bit_map,
5404 AbstractWorkGang* workers,
5405 OopTaskQueueSet* task_queues):
5406 // XXX Should superclass AGTWOQ also know about AWG since it knows
5407 // about the task_queues used by the AWG? Then it could initialize
5408 // the terminator() object. See 6984287. The set_for_termination()
5409 // below is a temporary band-aid for the regression in 6984287.
5410 AbstractGangTaskWOopQueues("Process referents by policy in parallel",
5411 task_queues),
5412 _task(task),
5413 _collector(collector), _span(span), _mark_bit_map(mark_bit_map)
5414 {
5415 assert(_collector->_span.equals(_span) && !_span.is_empty(),
5416 "Inconsistency in _span");
5417 set_for_termination(workers->active_workers());
5418 }
5419
5420 OopTaskQueueSet* task_queues() { return queues(); }
5421
5422 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5423
5424 void do_work_steal(int i,
5425 CMSParDrainMarkingStackClosure* drain,
5426 CMSParKeepAliveClosure* keep_alive,
5427 int* seed);
5428
5429 virtual void work(uint worker_id);
5430 };
5431
5432 void CMSRefProcTaskProxy::work(uint worker_id) {
5433 ResourceMark rm;
5434 HandleMark hm;
5435 assert(_collector->_span.equals(_span), "Inconsistency in _span");
5436 CMSParKeepAliveClosure par_keep_alive(_collector, _span,
5437 _mark_bit_map,
5438 work_queue(worker_id));
5439 CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
5440 _mark_bit_map,
5441 work_queue(worker_id));
5442 CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
5443 _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack);
5444 if (_task.marks_oops_alive()) {
5445 do_work_steal(worker_id, &par_drain_stack, &par_keep_alive,
5446 _collector->hash_seed(worker_id));
5447 }
5448 assert(work_queue(worker_id)->size() == 0, "work_queue should be empty");
5449 assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
5450 }
5451
5452 class CMSRefEnqueueTaskProxy: public AbstractGangTask {
5453 typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
5454 EnqueueTask& _task;
5455
5456 public:
5457 CMSRefEnqueueTaskProxy(EnqueueTask& task)
5458 : AbstractGangTask("Enqueue reference objects in parallel"),
5459 _task(task)
5460 { }
5461
5462 virtual void work(uint worker_id)
5463 {
5464 _task.work(worker_id);
5465 }
5466 };
5467
5468 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
5469 MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue):
5470 _span(span),
5471 _bit_map(bit_map),
5472 _work_queue(work_queue),
5473 _mark_and_push(collector, span, bit_map, work_queue),
5474 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
5475 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads)))
5476 { }
5477
5478 // . see if we can share work_queues with ParNew? XXX
5479 void CMSRefProcTaskProxy::do_work_steal(int i,
5480 CMSParDrainMarkingStackClosure* drain,
5481 CMSParKeepAliveClosure* keep_alive,
5482 int* seed) {
5483 OopTaskQueue* work_q = work_queue(i);
5484 NOT_PRODUCT(int num_steals = 0;)
5485 oop obj_to_scan;
5486
5487 while (true) {
5488 // Completely finish any left over work from (an) earlier round(s)
5489 drain->trim_queue(0);
5490 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5491 (size_t)ParGCDesiredObjsFromOverflowList);
5492 // Now check if there's any work in the overflow list
5493 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5494 // only affects the number of attempts made to get work from the
5495 // overflow list and does not affect the number of workers. Just
5496 // pass ParallelGCThreads so this behavior is unchanged.
5497 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5498 work_q,
5499 ParallelGCThreads)) {
5500 // Found something in global overflow list;
5501 // not yet ready to go stealing work from others.
5502 // We'd like to assert(work_q->size() != 0, ...)
5503 // because we just took work from the overflow list,
5504 // but of course we can't, since all of that might have
5505 // been already stolen from us.
5506 continue;
5507 }
5508 // Verify that we have no work before we resort to stealing
5509 assert(work_q->size() == 0, "Have work, shouldn't steal");
5510 // Try to steal from other queues that have work
5511 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5512 NOT_PRODUCT(num_steals++;)
5513 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5514 assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5515 // Do scanning work
5516 obj_to_scan->oop_iterate(keep_alive);
5517 // Loop around, finish this work, and try to steal some more
5518 } else if (terminator()->offer_termination()) {
5519 break; // nirvana from the infinite cycle
5520 }
5521 }
5522 NOT_PRODUCT(
5523 if (PrintCMSStatistics != 0) {
5524 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5525 }
5526 )
5527 }
5528
5529 void CMSRefProcTaskExecutor::execute(ProcessTask& task)
5530 {
5531 GenCollectedHeap* gch = GenCollectedHeap::heap();
5532 FlexibleWorkGang* workers = gch->workers();
5533 assert(workers != NULL, "Need parallel worker threads.");
5534 CMSRefProcTaskProxy rp_task(task, &_collector,
5535 _collector.ref_processor()->span(),
5536 _collector.markBitMap(),
5537 workers, _collector.task_queues());
5538 workers->run_task(&rp_task);
5539 }
5540
5541 void CMSRefProcTaskExecutor::execute(EnqueueTask& task)
5542 {
5543
5544 GenCollectedHeap* gch = GenCollectedHeap::heap();
5545 FlexibleWorkGang* workers = gch->workers();
5546 assert(workers != NULL, "Need parallel worker threads.");
5547 CMSRefEnqueueTaskProxy enq_task(task);
5548 workers->run_task(&enq_task);
5549 }
5550
5551 void CMSCollector::refProcessingWork() {
5552 ResourceMark rm;
5553 HandleMark hm;
5554
5555 ReferenceProcessor* rp = ref_processor();
5556 assert(rp->span().equals(_span), "Spans should be equal");
5557 assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
5558 // Process weak references.
5559 rp->setup_policy(false);
5560 verify_work_stacks_empty();
5561
5562 CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
5563 &_markStack, false /* !preclean */);
5564 CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
5565 _span, &_markBitMap, &_markStack,
5566 &cmsKeepAliveClosure, false /* !preclean */);
5567 {
5568 GCTraceTime t("weak refs processing", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5569
5570 ReferenceProcessorStats stats;
5571 if (rp->processing_is_mt()) {
5572 // Set the degree of MT here. If the discovery is done MT, there
5573 // may have been a different number of threads doing the discovery
5574 // and a different number of discovered lists may have Ref objects.
5575 // That is OK as long as the Reference lists are balanced (see
5576 // balance_all_queues() and balance_queues()).
5577 GenCollectedHeap* gch = GenCollectedHeap::heap();
5578 int active_workers = ParallelGCThreads;
5579 FlexibleWorkGang* workers = gch->workers();
5580 if (workers != NULL) {
5581 active_workers = workers->active_workers();
5582 // The expectation is that active_workers will have already
5583 // been set to a reasonable value. If it has not been set,
5584 // investigate.
5585 assert(active_workers > 0, "Should have been set during scavenge");
5586 }
5587 rp->set_active_mt_degree(active_workers);
5588 CMSRefProcTaskExecutor task_executor(*this);
5589 stats = rp->process_discovered_references(&_is_alive_closure,
5590 &cmsKeepAliveClosure,
5591 &cmsDrainMarkingStackClosure,
5592 &task_executor,
5593 _gc_timer_cm,
5594 _gc_tracer_cm->gc_id());
5595 } else {
5596 stats = rp->process_discovered_references(&_is_alive_closure,
5597 &cmsKeepAliveClosure,
5598 &cmsDrainMarkingStackClosure,
5599 NULL,
5600 _gc_timer_cm,
5601 _gc_tracer_cm->gc_id());
5602 }
5603 _gc_tracer_cm->report_gc_reference_stats(stats);
5604
5605 }
5606
5607 // This is the point where the entire marking should have completed.
5608 verify_work_stacks_empty();
5609
5610 if (should_unload_classes()) {
5611 {
5612 GCTraceTime t("class unloading", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5613
5614 // Unload classes and purge the SystemDictionary.
5615 bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure);
5616
5617 // Unload nmethods.
5618 CodeCache::do_unloading(&_is_alive_closure, purged_class);
5619
5620 // Prune dead klasses from subklass/sibling/implementor lists.
5621 Klass::clean_weak_klass_links(&_is_alive_closure);
5622 }
5623
5624 {
5625 GCTraceTime t("scrub symbol table", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5626 // Clean up unreferenced symbols in symbol table.
5627 SymbolTable::unlink();
5628 }
5629
5630 {
5631 GCTraceTime t("scrub string table", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5632 // Delete entries for dead interned strings.
5633 StringTable::unlink(&_is_alive_closure);
5634 }
5635 }
5636
5637
5638 // Restore any preserved marks as a result of mark stack or
5639 // work queue overflow
5640 restore_preserved_marks_if_any(); // done single-threaded for now
5641
5642 rp->set_enqueuing_is_done(true);
5643 if (rp->processing_is_mt()) {
5644 rp->balance_all_queues();
5645 CMSRefProcTaskExecutor task_executor(*this);
5646 rp->enqueue_discovered_references(&task_executor);
5647 } else {
5648 rp->enqueue_discovered_references(NULL);
5649 }
5650 rp->verify_no_references_recorded();
5651 assert(!rp->discovery_enabled(), "should have been disabled");
5652 }
5653
5654 #ifndef PRODUCT
5655 void CMSCollector::check_correct_thread_executing() {
5656 Thread* t = Thread::current();
5657 // Only the VM thread or the CMS thread should be here.
5658 assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
5659 "Unexpected thread type");
5660 // If this is the vm thread, the foreground process
5661 // should not be waiting. Note that _foregroundGCIsActive is
5662 // true while the foreground collector is waiting.
5663 if (_foregroundGCShouldWait) {
5664 // We cannot be the VM thread
5665 assert(t->is_ConcurrentGC_thread(),
5666 "Should be CMS thread");
5667 } else {
5668 // We can be the CMS thread only if we are in a stop-world
5669 // phase of CMS collection.
5670 if (t->is_ConcurrentGC_thread()) {
5671 assert(_collectorState == InitialMarking ||
5672 _collectorState == FinalMarking,
5673 "Should be a stop-world phase");
5674 // The CMS thread should be holding the CMS_token.
5675 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5676 "Potential interference with concurrently "
5677 "executing VM thread");
5678 }
5679 }
5680 }
5681 #endif
5682
5683 void CMSCollector::sweep() {
5684 assert(_collectorState == Sweeping, "just checking");
5685 check_correct_thread_executing();
5686 verify_work_stacks_empty();
5687 verify_overflow_empty();
5688 increment_sweep_count();
5689 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
5690
5691 _inter_sweep_timer.stop();
5692 _inter_sweep_estimate.sample(_inter_sweep_timer.seconds());
5693
5694 assert(!_intra_sweep_timer.is_active(), "Should not be active");
5695 _intra_sweep_timer.reset();
5696 _intra_sweep_timer.start();
5697 {
5698 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
5699 CMSPhaseAccounting pa(this, "sweep", _gc_tracer_cm->gc_id(), !PrintGCDetails);
5700 // First sweep the old gen
5701 {
5702 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
5703 bitMapLock());
5704 sweepWork(_cmsGen);
5705 }
5706
5707 // Update Universe::_heap_*_at_gc figures.
5708 // We need all the free list locks to make the abstract state
5709 // transition from Sweeping to Resetting. See detailed note
5710 // further below.
5711 {
5712 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock());
5713 // Update heap occupancy information which is used as
5714 // input to soft ref clearing policy at the next gc.
5715 Universe::update_heap_info_at_gc();
5716 _collectorState = Resizing;
5717 }
5718 }
5719 verify_work_stacks_empty();
5720 verify_overflow_empty();
5721
5722 if (should_unload_classes()) {
5723 // Delay purge to the beginning of the next safepoint. Metaspace::contains
5724 // requires that the virtual spaces are stable and not deleted.
5725 ClassLoaderDataGraph::set_should_purge(true);
5726 }
5727
5728 _intra_sweep_timer.stop();
5729 _intra_sweep_estimate.sample(_intra_sweep_timer.seconds());
5730
5731 _inter_sweep_timer.reset();
5732 _inter_sweep_timer.start();
5733
5734 // We need to use a monotonically non-decreasing time in ms
5735 // or we will see time-warp warnings and os::javaTimeMillis()
5736 // does not guarantee monotonicity.
5737 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
5738 update_time_of_last_gc(now);
5739
5740 // NOTE on abstract state transitions:
5741 // Mutators allocate-live and/or mark the mod-union table dirty
5742 // based on the state of the collection. The former is done in
5743 // the interval [Marking, Sweeping] and the latter in the interval
5744 // [Marking, Sweeping). Thus the transitions into the Marking state
5745 // and out of the Sweeping state must be synchronously visible
5746 // globally to the mutators.
5747 // The transition into the Marking state happens with the world
5748 // stopped so the mutators will globally see it. Sweeping is
5749 // done asynchronously by the background collector so the transition
5750 // from the Sweeping state to the Resizing state must be done
5751 // under the freelistLock (as is the check for whether to
5752 // allocate-live and whether to dirty the mod-union table).
5753 assert(_collectorState == Resizing, "Change of collector state to"
5754 " Resizing must be done under the freelistLocks (plural)");
5755
5756 // Now that sweeping has been completed, we clear
5757 // the incremental_collection_failed flag,
5758 // thus inviting a younger gen collection to promote into
5759 // this generation. If such a promotion may still fail,
5760 // the flag will be set again when a young collection is
5761 // attempted.
5762 GenCollectedHeap* gch = GenCollectedHeap::heap();
5763 gch->clear_incremental_collection_failed(); // Worth retrying as fresh space may have been freed up
5764 gch->update_full_collections_completed(_collection_count_start);
5765 }
5766
5767 // FIX ME!!! Looks like this belongs in CFLSpace, with
5768 // CMSGen merely delegating to it.
5769 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
5770 double nearLargestPercent = FLSLargestBlockCoalesceProximity;
5771 HeapWord* minAddr = _cmsSpace->bottom();
5772 HeapWord* largestAddr =
5773 (HeapWord*) _cmsSpace->dictionary()->find_largest_dict();
5774 if (largestAddr == NULL) {
5775 // The dictionary appears to be empty. In this case
5776 // try to coalesce at the end of the heap.
5777 largestAddr = _cmsSpace->end();
5778 }
5779 size_t largestOffset = pointer_delta(largestAddr, minAddr);
5780 size_t nearLargestOffset =
5781 (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
5782 if (PrintFLSStatistics != 0) {
5783 gclog_or_tty->print_cr(
5784 "CMS: Large Block: " PTR_FORMAT ";"
5785 " Proximity: " PTR_FORMAT " -> " PTR_FORMAT,
5786 largestAddr,
5787 _cmsSpace->nearLargestChunk(), minAddr + nearLargestOffset);
5788 }
5789 _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
5790 }
5791
5792 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
5793 return addr >= _cmsSpace->nearLargestChunk();
5794 }
5795
5796 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
5797 return _cmsSpace->find_chunk_at_end();
5798 }
5799
5800 void ConcurrentMarkSweepGeneration::update_gc_stats(int current_level,
5801 bool full) {
5802 // The next lower level has been collected. Gather any statistics
5803 // that are of interest at this point.
5804 if (!full && (current_level + 1) == level()) {
5805 // Gather statistics on the young generation collection.
5806 collector()->stats().record_gc0_end(used());
5807 }
5808 }
5809
5810 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* gen) {
5811 // We iterate over the space(s) underlying this generation,
5812 // checking the mark bit map to see if the bits corresponding
5813 // to specific blocks are marked or not. Blocks that are
5814 // marked are live and are not swept up. All remaining blocks
5815 // are swept up, with coalescing on-the-fly as we sweep up
5816 // contiguous free and/or garbage blocks:
5817 // We need to ensure that the sweeper synchronizes with allocators
5818 // and stop-the-world collectors. In particular, the following
5819 // locks are used:
5820 // . CMS token: if this is held, a stop the world collection cannot occur
5821 // . freelistLock: if this is held no allocation can occur from this
5822 // generation by another thread
5823 // . bitMapLock: if this is held, no other thread can access or update
5824 //
5825
5826 // Note that we need to hold the freelistLock if we use
5827 // block iterate below; else the iterator might go awry if
5828 // a mutator (or promotion) causes block contents to change
5829 // (for instance if the allocator divvies up a block).
5830 // If we hold the free list lock, for all practical purposes
5831 // young generation GC's can't occur (they'll usually need to
5832 // promote), so we might as well prevent all young generation
5833 // GC's while we do a sweeping step. For the same reason, we might
5834 // as well take the bit map lock for the entire duration
5835
5836 // check that we hold the requisite locks
5837 assert(have_cms_token(), "Should hold cms token");
5838 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), "Should possess CMS token to sweep");
5839 assert_lock_strong(gen->freelistLock());
5840 assert_lock_strong(bitMapLock());
5841
5842 assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context");
5843 assert(_intra_sweep_timer.is_active(), "Was switched on in an outer context");
5844 gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
5845 _inter_sweep_estimate.padded_average(),
5846 _intra_sweep_estimate.padded_average());
5847 gen->setNearLargestChunk();
5848
5849 {
5850 SweepClosure sweepClosure(this, gen, &_markBitMap, CMSYield);
5851 gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
5852 // We need to free-up/coalesce garbage/blocks from a
5853 // co-terminal free run. This is done in the SweepClosure
5854 // destructor; so, do not remove this scope, else the
5855 // end-of-sweep-census below will be off by a little bit.
5856 }
5857 gen->cmsSpace()->sweep_completed();
5858 gen->cmsSpace()->endSweepFLCensus(sweep_count());
5859 if (should_unload_classes()) { // unloaded classes this cycle,
5860 _concurrent_cycles_since_last_unload = 0; // ... reset count
5861 } else { // did not unload classes,
5862 _concurrent_cycles_since_last_unload++; // ... increment count
5863 }
5864 }
5865
5866 // Reset CMS data structures (for now just the marking bit map)
5867 // preparatory for the next cycle.
5868 void CMSCollector::reset(bool concurrent) {
5869 if (concurrent) {
5870 CMSTokenSyncWithLocks ts(true, bitMapLock());
5871
5872 // If the state is not "Resetting", the foreground thread
5873 // has done a collection and the resetting.
5874 if (_collectorState != Resetting) {
5875 assert(_collectorState == Idling, "The state should only change"
5876 " because the foreground collector has finished the collection");
5877 return;
5878 }
5879
5880 // Clear the mark bitmap (no grey objects to start with)
5881 // for the next cycle.
5882 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
5883 CMSPhaseAccounting cmspa(this, "reset", _gc_tracer_cm->gc_id(), !PrintGCDetails);
5884
5885 HeapWord* curAddr = _markBitMap.startWord();
5886 while (curAddr < _markBitMap.endWord()) {
5887 size_t remaining = pointer_delta(_markBitMap.endWord(), curAddr);
5888 MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
5889 _markBitMap.clear_large_range(chunk);
5890 if (ConcurrentMarkSweepThread::should_yield() &&
5891 !foregroundGCIsActive() &&
5892 CMSYield) {
5893 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5894 "CMS thread should hold CMS token");
5895 assert_lock_strong(bitMapLock());
5896 bitMapLock()->unlock();
5897 ConcurrentMarkSweepThread::desynchronize(true);
5898 stopTimer();
5899 if (PrintCMSStatistics != 0) {
5900 incrementYields();
5901 }
5902
5903 // See the comment in coordinator_yield()
5904 for (unsigned i = 0; i < CMSYieldSleepCount &&
5905 ConcurrentMarkSweepThread::should_yield() &&
5906 !CMSCollector::foregroundGCIsActive(); ++i) {
5907 os::sleep(Thread::current(), 1, false);
5908 }
5909
5910 ConcurrentMarkSweepThread::synchronize(true);
5911 bitMapLock()->lock_without_safepoint_check();
5912 startTimer();
5913 }
5914 curAddr = chunk.end();
5915 }
5916 // A successful mostly concurrent collection has been done.
5917 // Because only the full (i.e., concurrent mode failure) collections
5918 // are being measured for gc overhead limits, clean the "near" flag
5919 // and count.
5920 size_policy()->reset_gc_overhead_limit_count();
5921 _collectorState = Idling;
5922 } else {
5923 // already have the lock
5924 assert(_collectorState == Resetting, "just checking");
5925 assert_lock_strong(bitMapLock());
5926 _markBitMap.clear_all();
5927 _collectorState = Idling;
5928 }
5929
5930 register_gc_end();
5931 }
5932
5933 void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) {
5934 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
5935 GCTraceTime t(GCCauseString("GC", gc_cause), PrintGC, !PrintGCDetails, NULL, _gc_tracer_cm->gc_id());
5936 TraceCollectorStats tcs(counters());
5937
5938 switch (op) {
5939 case CMS_op_checkpointRootsInitial: {
5940 SvcGCMarker sgcm(SvcGCMarker::OTHER);
5941 checkpointRootsInitial();
5942 if (PrintGC) {
5943 _cmsGen->printOccupancy("initial-mark");
5944 }
5945 break;
5946 }
5947 case CMS_op_checkpointRootsFinal: {
5948 SvcGCMarker sgcm(SvcGCMarker::OTHER);
5949 checkpointRootsFinal();
5950 if (PrintGC) {
5951 _cmsGen->printOccupancy("remark");
5952 }
5953 break;
5954 }
5955 default:
5956 fatal("No such CMS_op");
5957 }
5958 }
5959
5960 #ifndef PRODUCT
5961 size_t const CMSCollector::skip_header_HeapWords() {
5962 return FreeChunk::header_size();
5963 }
5964
5965 // Try and collect here conditions that should hold when
5966 // CMS thread is exiting. The idea is that the foreground GC
5967 // thread should not be blocked if it wants to terminate
5968 // the CMS thread and yet continue to run the VM for a while
5969 // after that.
5970 void CMSCollector::verify_ok_to_terminate() const {
5971 assert(Thread::current()->is_ConcurrentGC_thread(),
5972 "should be called by CMS thread");
5973 assert(!_foregroundGCShouldWait, "should be false");
5974 // We could check here that all the various low-level locks
5975 // are not held by the CMS thread, but that is overkill; see
5976 // also CMSThread::verify_ok_to_terminate() where the CGC_lock
5977 // is checked.
5978 }
5979 #endif
5980
5981 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
5982 assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
5983 "missing Printezis mark?");
5984 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5985 size_t size = pointer_delta(nextOneAddr + 1, addr);
5986 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5987 "alignment problem");
5988 assert(size >= 3, "Necessary for Printezis marks to work");
5989 return size;
5990 }
5991
5992 // A variant of the above (block_size_using_printezis_bits()) except
5993 // that we return 0 if the P-bits are not yet set.
5994 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
5995 if (_markBitMap.isMarked(addr + 1)) {
5996 assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects");
5997 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5998 size_t size = pointer_delta(nextOneAddr + 1, addr);
5999 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6000 "alignment problem");
6001 assert(size >= 3, "Necessary for Printezis marks to work");
6002 return size;
6003 }
6004 return 0;
6005 }
6006
6007 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
6008 size_t sz = 0;
6009 oop p = (oop)addr;
6010 if (p->klass_or_null() != NULL) {
6011 sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
6012 } else {
6013 sz = block_size_using_printezis_bits(addr);
6014 }
6015 assert(sz > 0, "size must be nonzero");
6016 HeapWord* next_block = addr + sz;
6017 HeapWord* next_card = (HeapWord*)round_to((uintptr_t)next_block,
6018 CardTableModRefBS::card_size);
6019 assert(round_down((uintptr_t)addr, CardTableModRefBS::card_size) <
6020 round_down((uintptr_t)next_card, CardTableModRefBS::card_size),
6021 "must be different cards");
6022 return next_card;
6023 }
6024
6025
6026 // CMS Bit Map Wrapper /////////////////////////////////////////
6027
6028 // Construct a CMS bit map infrastructure, but don't create the
6029 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
6030 // further below.
6031 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
6032 _bm(),
6033 _shifter(shifter),
6034 _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true) : NULL)
6035 {
6036 _bmStartWord = 0;
6037 _bmWordSize = 0;
6038 }
6039
6040 bool CMSBitMap::allocate(MemRegion mr) {
6041 _bmStartWord = mr.start();
6042 _bmWordSize = mr.word_size();
6043 ReservedSpace brs(ReservedSpace::allocation_align_size_up(
6044 (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
6045 if (!brs.is_reserved()) {
6046 warning("CMS bit map allocation failure");
6047 return false;
6048 }
6049 // For now we'll just commit all of the bit map up front.
6050 // Later on we'll try to be more parsimonious with swap.
6051 if (!_virtual_space.initialize(brs, brs.size())) {
6052 warning("CMS bit map backing store failure");
6053 return false;
6054 }
6055 assert(_virtual_space.committed_size() == brs.size(),
6056 "didn't reserve backing store for all of CMS bit map?");
6057 _bm.set_map((BitMap::bm_word_t*)_virtual_space.low());
6058 assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
6059 _bmWordSize, "inconsistency in bit map sizing");
6060 _bm.set_size(_bmWordSize >> _shifter);
6061
6062 // bm.clear(); // can we rely on getting zero'd memory? verify below
6063 assert(isAllClear(),
6064 "Expected zero'd memory from ReservedSpace constructor");
6065 assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
6066 "consistency check");
6067 return true;
6068 }
6069
6070 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
6071 HeapWord *next_addr, *end_addr, *last_addr;
6072 assert_locked();
6073 assert(covers(mr), "out-of-range error");
6074 // XXX assert that start and end are appropriately aligned
6075 for (next_addr = mr.start(), end_addr = mr.end();
6076 next_addr < end_addr; next_addr = last_addr) {
6077 MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
6078 last_addr = dirty_region.end();
6079 if (!dirty_region.is_empty()) {
6080 cl->do_MemRegion(dirty_region);
6081 } else {
6082 assert(last_addr == end_addr, "program logic");
6083 return;
6084 }
6085 }
6086 }
6087
6088 void CMSBitMap::print_on_error(outputStream* st, const char* prefix) const {
6089 _bm.print_on_error(st, prefix);
6090 }
6091
6092 #ifndef PRODUCT
6093 void CMSBitMap::assert_locked() const {
6094 CMSLockVerifier::assert_locked(lock());
6095 }
6096
6097 bool CMSBitMap::covers(MemRegion mr) const {
6098 // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
6099 assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
6100 "size inconsistency");
6101 return (mr.start() >= _bmStartWord) &&
6102 (mr.end() <= endWord());
6103 }
6104
6105 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
6106 return (start >= _bmStartWord && (start + size) <= endWord());
6107 }
6108
6109 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
6110 // verify that there are no 1 bits in the interval [left, right)
6111 FalseBitMapClosure falseBitMapClosure;
6112 iterate(&falseBitMapClosure, left, right);
6113 }
6114
6115 void CMSBitMap::region_invariant(MemRegion mr)
6116 {
6117 assert_locked();
6118 // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
6119 assert(!mr.is_empty(), "unexpected empty region");
6120 assert(covers(mr), "mr should be covered by bit map");
6121 // convert address range into offset range
6122 size_t start_ofs = heapWordToOffset(mr.start());
6123 // Make sure that end() is appropriately aligned
6124 assert(mr.end() == (HeapWord*)round_to((intptr_t)mr.end(),
6125 (1 << (_shifter+LogHeapWordSize))),
6126 "Misaligned mr.end()");
6127 size_t end_ofs = heapWordToOffset(mr.end());
6128 assert(end_ofs > start_ofs, "Should mark at least one bit");
6129 }
6130
6131 #endif
6132
6133 bool CMSMarkStack::allocate(size_t size) {
6134 // allocate a stack of the requisite depth
6135 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6136 size * sizeof(oop)));
6137 if (!rs.is_reserved()) {
6138 warning("CMSMarkStack allocation failure");
6139 return false;
6140 }
6141 if (!_virtual_space.initialize(rs, rs.size())) {
6142 warning("CMSMarkStack backing store failure");
6143 return false;
6144 }
6145 assert(_virtual_space.committed_size() == rs.size(),
6146 "didn't reserve backing store for all of CMS stack?");
6147 _base = (oop*)(_virtual_space.low());
6148 _index = 0;
6149 _capacity = size;
6150 NOT_PRODUCT(_max_depth = 0);
6151 return true;
6152 }
6153
6154 // XXX FIX ME !!! In the MT case we come in here holding a
6155 // leaf lock. For printing we need to take a further lock
6156 // which has lower rank. We need to recalibrate the two
6157 // lock-ranks involved in order to be able to print the
6158 // messages below. (Or defer the printing to the caller.
6159 // For now we take the expedient path of just disabling the
6160 // messages for the problematic case.)
6161 void CMSMarkStack::expand() {
6162 assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted");
6163 if (_capacity == MarkStackSizeMax) {
6164 if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6165 // We print a warning message only once per CMS cycle.
6166 gclog_or_tty->print_cr(" (benign) Hit CMSMarkStack max size limit");
6167 }
6168 return;
6169 }
6170 // Double capacity if possible
6171 size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax);
6172 // Do not give up existing stack until we have managed to
6173 // get the double capacity that we desired.
6174 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6175 new_capacity * sizeof(oop)));
6176 if (rs.is_reserved()) {
6177 // Release the backing store associated with old stack
6178 _virtual_space.release();
6179 // Reinitialize virtual space for new stack
6180 if (!_virtual_space.initialize(rs, rs.size())) {
6181 fatal("Not enough swap for expanded marking stack");
6182 }
6183 _base = (oop*)(_virtual_space.low());
6184 _index = 0;
6185 _capacity = new_capacity;
6186 } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6187 // Failed to double capacity, continue;
6188 // we print a detail message only once per CMS cycle.
6189 gclog_or_tty->print(" (benign) Failed to expand marking stack from "SIZE_FORMAT"K to "
6190 SIZE_FORMAT"K",
6191 _capacity / K, new_capacity / K);
6192 }
6193 }
6194
6195
6196 // Closures
6197 // XXX: there seems to be a lot of code duplication here;
6198 // should refactor and consolidate common code.
6199
6200 // This closure is used to mark refs into the CMS generation in
6201 // the CMS bit map. Called at the first checkpoint. This closure
6202 // assumes that we do not need to re-mark dirty cards; if the CMS
6203 // generation on which this is used is not an oldest
6204 // generation then this will lose younger_gen cards!
6205
6206 MarkRefsIntoClosure::MarkRefsIntoClosure(
6207 MemRegion span, CMSBitMap* bitMap):
6208 _span(span),
6209 _bitMap(bitMap)
6210 {
6211 assert(_ref_processor == NULL, "deliberately left NULL");
6212 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6213 }
6214
6215 void MarkRefsIntoClosure::do_oop(oop obj) {
6216 // if p points into _span, then mark corresponding bit in _markBitMap
6217 assert(obj->is_oop(), "expected an oop");
6218 HeapWord* addr = (HeapWord*)obj;
6219 if (_span.contains(addr)) {
6220 // this should be made more efficient
6221 _bitMap->mark(addr);
6222 }
6223 }
6224
6225 void MarkRefsIntoClosure::do_oop(oop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6226 void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6227
6228 Par_MarkRefsIntoClosure::Par_MarkRefsIntoClosure(
6229 MemRegion span, CMSBitMap* bitMap):
6230 _span(span),
6231 _bitMap(bitMap)
6232 {
6233 assert(_ref_processor == NULL, "deliberately left NULL");
6234 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6235 }
6236
6237 void Par_MarkRefsIntoClosure::do_oop(oop obj) {
6238 // if p points into _span, then mark corresponding bit in _markBitMap
6239 assert(obj->is_oop(), "expected an oop");
6240 HeapWord* addr = (HeapWord*)obj;
6241 if (_span.contains(addr)) {
6242 // this should be made more efficient
6243 _bitMap->par_mark(addr);
6244 }
6245 }
6246
6247 void Par_MarkRefsIntoClosure::do_oop(oop* p) { Par_MarkRefsIntoClosure::do_oop_work(p); }
6248 void Par_MarkRefsIntoClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoClosure::do_oop_work(p); }
6249
6250 // A variant of the above, used for CMS marking verification.
6251 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
6252 MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm):
6253 _span(span),
6254 _verification_bm(verification_bm),
6255 _cms_bm(cms_bm)
6256 {
6257 assert(_ref_processor == NULL, "deliberately left NULL");
6258 assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
6259 }
6260
6261 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
6262 // if p points into _span, then mark corresponding bit in _markBitMap
6263 assert(obj->is_oop(), "expected an oop");
6264 HeapWord* addr = (HeapWord*)obj;
6265 if (_span.contains(addr)) {
6266 _verification_bm->mark(addr);
6267 if (!_cms_bm->isMarked(addr)) {
6268 oop(addr)->print();
6269 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)", addr);
6270 fatal("... aborting");
6271 }
6272 }
6273 }
6274
6275 void MarkRefsIntoVerifyClosure::do_oop(oop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6276 void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6277
6278 //////////////////////////////////////////////////
6279 // MarkRefsIntoAndScanClosure
6280 //////////////////////////////////////////////////
6281
6282 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
6283 ReferenceProcessor* rp,
6284 CMSBitMap* bit_map,
6285 CMSBitMap* mod_union_table,
6286 CMSMarkStack* mark_stack,
6287 CMSCollector* collector,
6288 bool should_yield,
6289 bool concurrent_precleaning):
6290 _collector(collector),
6291 _span(span),
6292 _bit_map(bit_map),
6293 _mark_stack(mark_stack),
6294 _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table,
6295 mark_stack, concurrent_precleaning),
6296 _yield(should_yield),
6297 _concurrent_precleaning(concurrent_precleaning),
6298 _freelistLock(NULL)
6299 {
6300 _ref_processor = rp;
6301 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6302 }
6303
6304 // This closure is used to mark refs into the CMS generation at the
6305 // second (final) checkpoint, and to scan and transitively follow
6306 // the unmarked oops. It is also used during the concurrent precleaning
6307 // phase while scanning objects on dirty cards in the CMS generation.
6308 // The marks are made in the marking bit map and the marking stack is
6309 // used for keeping the (newly) grey objects during the scan.
6310 // The parallel version (Par_...) appears further below.
6311 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6312 if (obj != NULL) {
6313 assert(obj->is_oop(), "expected an oop");
6314 HeapWord* addr = (HeapWord*)obj;
6315 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6316 assert(_collector->overflow_list_is_empty(),
6317 "overflow list should be empty");
6318 if (_span.contains(addr) &&
6319 !_bit_map->isMarked(addr)) {
6320 // mark bit map (object is now grey)
6321 _bit_map->mark(addr);
6322 // push on marking stack (stack should be empty), and drain the
6323 // stack by applying this closure to the oops in the oops popped
6324 // from the stack (i.e. blacken the grey objects)
6325 bool res = _mark_stack->push(obj);
6326 assert(res, "Should have space to push on empty stack");
6327 do {
6328 oop new_oop = _mark_stack->pop();
6329 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6330 assert(_bit_map->isMarked((HeapWord*)new_oop),
6331 "only grey objects on this stack");
6332 // iterate over the oops in this oop, marking and pushing
6333 // the ones in CMS heap (i.e. in _span).
6334 new_oop->oop_iterate(&_pushAndMarkClosure);
6335 // check if it's time to yield
6336 do_yield_check();
6337 } while (!_mark_stack->isEmpty() ||
6338 (!_concurrent_precleaning && take_from_overflow_list()));
6339 // if marking stack is empty, and we are not doing this
6340 // during precleaning, then check the overflow list
6341 }
6342 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6343 assert(_collector->overflow_list_is_empty(),
6344 "overflow list was drained above");
6345 // We could restore evacuated mark words, if any, used for
6346 // overflow list links here because the overflow list is
6347 // provably empty here. That would reduce the maximum
6348 // size requirements for preserved_{oop,mark}_stack.
6349 // But we'll just postpone it until we are all done
6350 // so we can just stream through.
6351 if (!_concurrent_precleaning && CMSOverflowEarlyRestoration) {
6352 _collector->restore_preserved_marks_if_any();
6353 assert(_collector->no_preserved_marks(), "No preserved marks");
6354 }
6355 assert(!CMSOverflowEarlyRestoration || _collector->no_preserved_marks(),
6356 "All preserved marks should have been restored above");
6357 }
6358 }
6359
6360 void MarkRefsIntoAndScanClosure::do_oop(oop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6361 void MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6362
6363 void MarkRefsIntoAndScanClosure::do_yield_work() {
6364 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6365 "CMS thread should hold CMS token");
6366 assert_lock_strong(_freelistLock);
6367 assert_lock_strong(_bit_map->lock());
6368 // relinquish the free_list_lock and bitMaplock()
6369 _bit_map->lock()->unlock();
6370 _freelistLock->unlock();
6371 ConcurrentMarkSweepThread::desynchronize(true);
6372 _collector->stopTimer();
6373 if (PrintCMSStatistics != 0) {
6374 _collector->incrementYields();
6375 }
6376
6377 // See the comment in coordinator_yield()
6378 for (unsigned i = 0;
6379 i < CMSYieldSleepCount &&
6380 ConcurrentMarkSweepThread::should_yield() &&
6381 !CMSCollector::foregroundGCIsActive();
6382 ++i) {
6383 os::sleep(Thread::current(), 1, false);
6384 }
6385
6386 ConcurrentMarkSweepThread::synchronize(true);
6387 _freelistLock->lock_without_safepoint_check();
6388 _bit_map->lock()->lock_without_safepoint_check();
6389 _collector->startTimer();
6390 }
6391
6392 ///////////////////////////////////////////////////////////
6393 // Par_MarkRefsIntoAndScanClosure: a parallel version of
6394 // MarkRefsIntoAndScanClosure
6395 ///////////////////////////////////////////////////////////
6396 Par_MarkRefsIntoAndScanClosure::Par_MarkRefsIntoAndScanClosure(
6397 CMSCollector* collector, MemRegion span, ReferenceProcessor* rp,
6398 CMSBitMap* bit_map, OopTaskQueue* work_queue):
6399 _span(span),
6400 _bit_map(bit_map),
6401 _work_queue(work_queue),
6402 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
6403 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads))),
6404 _par_pushAndMarkClosure(collector, span, rp, bit_map, work_queue)
6405 {
6406 _ref_processor = rp;
6407 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6408 }
6409
6410 // This closure is used to mark refs into the CMS generation at the
6411 // second (final) checkpoint, and to scan and transitively follow
6412 // the unmarked oops. The marks are made in the marking bit map and
6413 // the work_queue is used for keeping the (newly) grey objects during
6414 // the scan phase whence they are also available for stealing by parallel
6415 // threads. Since the marking bit map is shared, updates are
6416 // synchronized (via CAS).
6417 void Par_MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6418 if (obj != NULL) {
6419 // Ignore mark word because this could be an already marked oop
6420 // that may be chained at the end of the overflow list.
6421 assert(obj->is_oop(true), "expected an oop");
6422 HeapWord* addr = (HeapWord*)obj;
6423 if (_span.contains(addr) &&
6424 !_bit_map->isMarked(addr)) {
6425 // mark bit map (object will become grey):
6426 // It is possible for several threads to be
6427 // trying to "claim" this object concurrently;
6428 // the unique thread that succeeds in marking the
6429 // object first will do the subsequent push on
6430 // to the work queue (or overflow list).
6431 if (_bit_map->par_mark(addr)) {
6432 // push on work_queue (which may not be empty), and trim the
6433 // queue to an appropriate length by applying this closure to
6434 // the oops in the oops popped from the stack (i.e. blacken the
6435 // grey objects)
6436 bool res = _work_queue->push(obj);
6437 assert(res, "Low water mark should be less than capacity?");
6438 trim_queue(_low_water_mark);
6439 } // Else, another thread claimed the object
6440 }
6441 }
6442 }
6443
6444 void Par_MarkRefsIntoAndScanClosure::do_oop(oop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6445 void Par_MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6446
6447 // This closure is used to rescan the marked objects on the dirty cards
6448 // in the mod union table and the card table proper.
6449 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
6450 oop p, MemRegion mr) {
6451
6452 size_t size = 0;
6453 HeapWord* addr = (HeapWord*)p;
6454 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6455 assert(_span.contains(addr), "we are scanning the CMS generation");
6456 // check if it's time to yield
6457 if (do_yield_check()) {
6458 // We yielded for some foreground stop-world work,
6459 // and we have been asked to abort this ongoing preclean cycle.
6460 return 0;
6461 }
6462 if (_bitMap->isMarked(addr)) {
6463 // it's marked; is it potentially uninitialized?
6464 if (p->klass_or_null() != NULL) {
6465 // an initialized object; ignore mark word in verification below
6466 // since we are running concurrent with mutators
6467 assert(p->is_oop(true), "should be an oop");
6468 if (p->is_objArray()) {
6469 // objArrays are precisely marked; restrict scanning
6470 // to dirty cards only.
6471 size = CompactibleFreeListSpace::adjustObjectSize(
6472 p->oop_iterate(_scanningClosure, mr));
6473 } else {
6474 // A non-array may have been imprecisely marked; we need
6475 // to scan object in its entirety.
6476 size = CompactibleFreeListSpace::adjustObjectSize(
6477 p->oop_iterate(_scanningClosure));
6478 }
6479 #ifdef ASSERT
6480 size_t direct_size =
6481 CompactibleFreeListSpace::adjustObjectSize(p->size());
6482 assert(size == direct_size, "Inconsistency in size");
6483 assert(size >= 3, "Necessary for Printezis marks to work");
6484 if (!_bitMap->isMarked(addr+1)) {
6485 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size);
6486 } else {
6487 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size-1);
6488 assert(_bitMap->isMarked(addr+size-1),
6489 "inconsistent Printezis mark");
6490 }
6491 #endif // ASSERT
6492 } else {
6493 // An uninitialized object.
6494 assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
6495 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
6496 size = pointer_delta(nextOneAddr + 1, addr);
6497 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6498 "alignment problem");
6499 // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
6500 // will dirty the card when the klass pointer is installed in the
6501 // object (signaling the completion of initialization).
6502 }
6503 } else {
6504 // Either a not yet marked object or an uninitialized object
6505 if (p->klass_or_null() == NULL) {
6506 // An uninitialized object, skip to the next card, since
6507 // we may not be able to read its P-bits yet.
6508 assert(size == 0, "Initial value");
6509 } else {
6510 // An object not (yet) reached by marking: we merely need to
6511 // compute its size so as to go look at the next block.
6512 assert(p->is_oop(true), "should be an oop");
6513 size = CompactibleFreeListSpace::adjustObjectSize(p->size());
6514 }
6515 }
6516 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6517 return size;
6518 }
6519
6520 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
6521 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6522 "CMS thread should hold CMS token");
6523 assert_lock_strong(_freelistLock);
6524 assert_lock_strong(_bitMap->lock());
6525 // relinquish the free_list_lock and bitMaplock()
6526 _bitMap->lock()->unlock();
6527 _freelistLock->unlock();
6528 ConcurrentMarkSweepThread::desynchronize(true);
6529 _collector->stopTimer();
6530 if (PrintCMSStatistics != 0) {
6531 _collector->incrementYields();
6532 }
6533
6534 // See the comment in coordinator_yield()
6535 for (unsigned i = 0; i < CMSYieldSleepCount &&
6536 ConcurrentMarkSweepThread::should_yield() &&
6537 !CMSCollector::foregroundGCIsActive(); ++i) {
6538 os::sleep(Thread::current(), 1, false);
6539 }
6540
6541 ConcurrentMarkSweepThread::synchronize(true);
6542 _freelistLock->lock_without_safepoint_check();
6543 _bitMap->lock()->lock_without_safepoint_check();
6544 _collector->startTimer();
6545 }
6546
6547
6548 //////////////////////////////////////////////////////////////////
6549 // SurvivorSpacePrecleanClosure
6550 //////////////////////////////////////////////////////////////////
6551 // This (single-threaded) closure is used to preclean the oops in
6552 // the survivor spaces.
6553 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
6554
6555 HeapWord* addr = (HeapWord*)p;
6556 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6557 assert(!_span.contains(addr), "we are scanning the survivor spaces");
6558 assert(p->klass_or_null() != NULL, "object should be initialized");
6559 // an initialized object; ignore mark word in verification below
6560 // since we are running concurrent with mutators
6561 assert(p->is_oop(true), "should be an oop");
6562 // Note that we do not yield while we iterate over
6563 // the interior oops of p, pushing the relevant ones
6564 // on our marking stack.
6565 size_t size = p->oop_iterate(_scanning_closure);
6566 do_yield_check();
6567 // Observe that below, we do not abandon the preclean
6568 // phase as soon as we should; rather we empty the
6569 // marking stack before returning. This is to satisfy
6570 // some existing assertions. In general, it may be a
6571 // good idea to abort immediately and complete the marking
6572 // from the grey objects at a later time.
6573 while (!_mark_stack->isEmpty()) {
6574 oop new_oop = _mark_stack->pop();
6575 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6576 assert(_bit_map->isMarked((HeapWord*)new_oop),
6577 "only grey objects on this stack");
6578 // iterate over the oops in this oop, marking and pushing
6579 // the ones in CMS heap (i.e. in _span).
6580 new_oop->oop_iterate(_scanning_closure);
6581 // check if it's time to yield
6582 do_yield_check();
6583 }
6584 unsigned int after_count =
6585 GenCollectedHeap::heap()->total_collections();
6586 bool abort = (_before_count != after_count) ||
6587 _collector->should_abort_preclean();
6588 return abort ? 0 : size;
6589 }
6590
6591 void SurvivorSpacePrecleanClosure::do_yield_work() {
6592 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6593 "CMS thread should hold CMS token");
6594 assert_lock_strong(_bit_map->lock());
6595 // Relinquish the bit map lock
6596 _bit_map->lock()->unlock();
6597 ConcurrentMarkSweepThread::desynchronize(true);
6598 _collector->stopTimer();
6599 if (PrintCMSStatistics != 0) {
6600 _collector->incrementYields();
6601 }
6602
6603 // See the comment in coordinator_yield()
6604 for (unsigned i = 0; i < CMSYieldSleepCount &&
6605 ConcurrentMarkSweepThread::should_yield() &&
6606 !CMSCollector::foregroundGCIsActive(); ++i) {
6607 os::sleep(Thread::current(), 1, false);
6608 }
6609
6610 ConcurrentMarkSweepThread::synchronize(true);
6611 _bit_map->lock()->lock_without_safepoint_check();
6612 _collector->startTimer();
6613 }
6614
6615 // This closure is used to rescan the marked objects on the dirty cards
6616 // in the mod union table and the card table proper. In the parallel
6617 // case, although the bitMap is shared, we do a single read so the
6618 // isMarked() query is "safe".
6619 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
6620 // Ignore mark word because we are running concurrent with mutators
6621 assert(p->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(p)));
6622 HeapWord* addr = (HeapWord*)p;
6623 assert(_span.contains(addr), "we are scanning the CMS generation");
6624 bool is_obj_array = false;
6625 #ifdef ASSERT
6626 if (!_parallel) {
6627 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6628 assert(_collector->overflow_list_is_empty(),
6629 "overflow list should be empty");
6630
6631 }
6632 #endif // ASSERT
6633 if (_bit_map->isMarked(addr)) {
6634 // Obj arrays are precisely marked, non-arrays are not;
6635 // so we scan objArrays precisely and non-arrays in their
6636 // entirety.
6637 if (p->is_objArray()) {
6638 is_obj_array = true;
6639 if (_parallel) {
6640 p->oop_iterate(_par_scan_closure, mr);
6641 } else {
6642 p->oop_iterate(_scan_closure, mr);
6643 }
6644 } else {
6645 if (_parallel) {
6646 p->oop_iterate(_par_scan_closure);
6647 } else {
6648 p->oop_iterate(_scan_closure);
6649 }
6650 }
6651 }
6652 #ifdef ASSERT
6653 if (!_parallel) {
6654 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6655 assert(_collector->overflow_list_is_empty(),
6656 "overflow list should be empty");
6657
6658 }
6659 #endif // ASSERT
6660 return is_obj_array;
6661 }
6662
6663 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
6664 MemRegion span,
6665 CMSBitMap* bitMap, CMSMarkStack* markStack,
6666 bool should_yield, bool verifying):
6667 _collector(collector),
6668 _span(span),
6669 _bitMap(bitMap),
6670 _mut(&collector->_modUnionTable),
6671 _markStack(markStack),
6672 _yield(should_yield),
6673 _skipBits(0)
6674 {
6675 assert(_markStack->isEmpty(), "stack should be empty");
6676 _finger = _bitMap->startWord();
6677 _threshold = _finger;
6678 assert(_collector->_restart_addr == NULL, "Sanity check");
6679 assert(_span.contains(_finger), "Out of bounds _finger?");
6680 DEBUG_ONLY(_verifying = verifying;)
6681 }
6682
6683 void MarkFromRootsClosure::reset(HeapWord* addr) {
6684 assert(_markStack->isEmpty(), "would cause duplicates on stack");
6685 assert(_span.contains(addr), "Out of bounds _finger?");
6686 _finger = addr;
6687 _threshold = (HeapWord*)round_to(
6688 (intptr_t)_finger, CardTableModRefBS::card_size);
6689 }
6690
6691 // Should revisit to see if this should be restructured for
6692 // greater efficiency.
6693 bool MarkFromRootsClosure::do_bit(size_t offset) {
6694 if (_skipBits > 0) {
6695 _skipBits--;
6696 return true;
6697 }
6698 // convert offset into a HeapWord*
6699 HeapWord* addr = _bitMap->startWord() + offset;
6700 assert(_bitMap->endWord() && addr < _bitMap->endWord(),
6701 "address out of range");
6702 assert(_bitMap->isMarked(addr), "tautology");
6703 if (_bitMap->isMarked(addr+1)) {
6704 // this is an allocated but not yet initialized object
6705 assert(_skipBits == 0, "tautology");
6706 _skipBits = 2; // skip next two marked bits ("Printezis-marks")
6707 oop p = oop(addr);
6708 if (p->klass_or_null() == NULL) {
6709 DEBUG_ONLY(if (!_verifying) {)
6710 // We re-dirty the cards on which this object lies and increase
6711 // the _threshold so that we'll come back to scan this object
6712 // during the preclean or remark phase. (CMSCleanOnEnter)
6713 if (CMSCleanOnEnter) {
6714 size_t sz = _collector->block_size_using_printezis_bits(addr);
6715 HeapWord* end_card_addr = (HeapWord*)round_to(
6716 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
6717 MemRegion redirty_range = MemRegion(addr, end_card_addr);
6718 assert(!redirty_range.is_empty(), "Arithmetical tautology");
6719 // Bump _threshold to end_card_addr; note that
6720 // _threshold cannot possibly exceed end_card_addr, anyhow.
6721 // This prevents future clearing of the card as the scan proceeds
6722 // to the right.
6723 assert(_threshold <= end_card_addr,
6724 "Because we are just scanning into this object");
6725 if (_threshold < end_card_addr) {
6726 _threshold = end_card_addr;
6727 }
6728 if (p->klass_or_null() != NULL) {
6729 // Redirty the range of cards...
6730 _mut->mark_range(redirty_range);
6731 } // ...else the setting of klass will dirty the card anyway.
6732 }
6733 DEBUG_ONLY(})
6734 return true;
6735 }
6736 }
6737 scanOopsInOop(addr);
6738 return true;
6739 }
6740
6741 // We take a break if we've been at this for a while,
6742 // so as to avoid monopolizing the locks involved.
6743 void MarkFromRootsClosure::do_yield_work() {
6744 // First give up the locks, then yield, then re-lock
6745 // We should probably use a constructor/destructor idiom to
6746 // do this unlock/lock or modify the MutexUnlocker class to
6747 // serve our purpose. XXX
6748 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6749 "CMS thread should hold CMS token");
6750 assert_lock_strong(_bitMap->lock());
6751 _bitMap->lock()->unlock();
6752 ConcurrentMarkSweepThread::desynchronize(true);
6753 _collector->stopTimer();
6754 if (PrintCMSStatistics != 0) {
6755 _collector->incrementYields();
6756 }
6757
6758 // See the comment in coordinator_yield()
6759 for (unsigned i = 0; i < CMSYieldSleepCount &&
6760 ConcurrentMarkSweepThread::should_yield() &&
6761 !CMSCollector::foregroundGCIsActive(); ++i) {
6762 os::sleep(Thread::current(), 1, false);
6763 }
6764
6765 ConcurrentMarkSweepThread::synchronize(true);
6766 _bitMap->lock()->lock_without_safepoint_check();
6767 _collector->startTimer();
6768 }
6769
6770 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
6771 assert(_bitMap->isMarked(ptr), "expected bit to be set");
6772 assert(_markStack->isEmpty(),
6773 "should drain stack to limit stack usage");
6774 // convert ptr to an oop preparatory to scanning
6775 oop obj = oop(ptr);
6776 // Ignore mark word in verification below, since we
6777 // may be running concurrent with mutators.
6778 assert(obj->is_oop(true), "should be an oop");
6779 assert(_finger <= ptr, "_finger runneth ahead");
6780 // advance the finger to right end of this object
6781 _finger = ptr + obj->size();
6782 assert(_finger > ptr, "we just incremented it above");
6783 // On large heaps, it may take us some time to get through
6784 // the marking phase. During
6785 // this time it's possible that a lot of mutations have
6786 // accumulated in the card table and the mod union table --
6787 // these mutation records are redundant until we have
6788 // actually traced into the corresponding card.
6789 // Here, we check whether advancing the finger would make
6790 // us cross into a new card, and if so clear corresponding
6791 // cards in the MUT (preclean them in the card-table in the
6792 // future).
6793
6794 DEBUG_ONLY(if (!_verifying) {)
6795 // The clean-on-enter optimization is disabled by default,
6796 // until we fix 6178663.
6797 if (CMSCleanOnEnter && (_finger > _threshold)) {
6798 // [_threshold, _finger) represents the interval
6799 // of cards to be cleared in MUT (or precleaned in card table).
6800 // The set of cards to be cleared is all those that overlap
6801 // with the interval [_threshold, _finger); note that
6802 // _threshold is always kept card-aligned but _finger isn't
6803 // always card-aligned.
6804 HeapWord* old_threshold = _threshold;
6805 assert(old_threshold == (HeapWord*)round_to(
6806 (intptr_t)old_threshold, CardTableModRefBS::card_size),
6807 "_threshold should always be card-aligned");
6808 _threshold = (HeapWord*)round_to(
6809 (intptr_t)_finger, CardTableModRefBS::card_size);
6810 MemRegion mr(old_threshold, _threshold);
6811 assert(!mr.is_empty(), "Control point invariant");
6812 assert(_span.contains(mr), "Should clear within span");
6813 _mut->clear_range(mr);
6814 }
6815 DEBUG_ONLY(})
6816 // Note: the finger doesn't advance while we drain
6817 // the stack below.
6818 PushOrMarkClosure pushOrMarkClosure(_collector,
6819 _span, _bitMap, _markStack,
6820 _finger, this);
6821 bool res = _markStack->push(obj);
6822 assert(res, "Empty non-zero size stack should have space for single push");
6823 while (!_markStack->isEmpty()) {
6824 oop new_oop = _markStack->pop();
6825 // Skip verifying header mark word below because we are
6826 // running concurrent with mutators.
6827 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
6828 // now scan this oop's oops
6829 new_oop->oop_iterate(&pushOrMarkClosure);
6830 do_yield_check();
6831 }
6832 assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
6833 }
6834
6835 Par_MarkFromRootsClosure::Par_MarkFromRootsClosure(CMSConcMarkingTask* task,
6836 CMSCollector* collector, MemRegion span,
6837 CMSBitMap* bit_map,
6838 OopTaskQueue* work_queue,
6839 CMSMarkStack* overflow_stack):
6840 _collector(collector),
6841 _whole_span(collector->_span),
6842 _span(span),
6843 _bit_map(bit_map),
6844 _mut(&collector->_modUnionTable),
6845 _work_queue(work_queue),
6846 _overflow_stack(overflow_stack),
6847 _skip_bits(0),
6848 _task(task)
6849 {
6850 assert(_work_queue->size() == 0, "work_queue should be empty");
6851 _finger = span.start();
6852 _threshold = _finger; // XXX Defer clear-on-enter optimization for now
6853 assert(_span.contains(_finger), "Out of bounds _finger?");
6854 }
6855
6856 // Should revisit to see if this should be restructured for
6857 // greater efficiency.
6858 bool Par_MarkFromRootsClosure::do_bit(size_t offset) {
6859 if (_skip_bits > 0) {
6860 _skip_bits--;
6861 return true;
6862 }
6863 // convert offset into a HeapWord*
6864 HeapWord* addr = _bit_map->startWord() + offset;
6865 assert(_bit_map->endWord() && addr < _bit_map->endWord(),
6866 "address out of range");
6867 assert(_bit_map->isMarked(addr), "tautology");
6868 if (_bit_map->isMarked(addr+1)) {
6869 // this is an allocated object that might not yet be initialized
6870 assert(_skip_bits == 0, "tautology");
6871 _skip_bits = 2; // skip next two marked bits ("Printezis-marks")
6872 oop p = oop(addr);
6873 if (p->klass_or_null() == NULL) {
6874 // in the case of Clean-on-Enter optimization, redirty card
6875 // and avoid clearing card by increasing the threshold.
6876 return true;
6877 }
6878 }
6879 scan_oops_in_oop(addr);
6880 return true;
6881 }
6882
6883 void Par_MarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
6884 assert(_bit_map->isMarked(ptr), "expected bit to be set");
6885 // Should we assert that our work queue is empty or
6886 // below some drain limit?
6887 assert(_work_queue->size() == 0,
6888 "should drain stack to limit stack usage");
6889 // convert ptr to an oop preparatory to scanning
6890 oop obj = oop(ptr);
6891 // Ignore mark word in verification below, since we
6892 // may be running concurrent with mutators.
6893 assert(obj->is_oop(true), "should be an oop");
6894 assert(_finger <= ptr, "_finger runneth ahead");
6895 // advance the finger to right end of this object
6896 _finger = ptr + obj->size();
6897 assert(_finger > ptr, "we just incremented it above");
6898 // On large heaps, it may take us some time to get through
6899 // the marking phase. During
6900 // this time it's possible that a lot of mutations have
6901 // accumulated in the card table and the mod union table --
6902 // these mutation records are redundant until we have
6903 // actually traced into the corresponding card.
6904 // Here, we check whether advancing the finger would make
6905 // us cross into a new card, and if so clear corresponding
6906 // cards in the MUT (preclean them in the card-table in the
6907 // future).
6908
6909 // The clean-on-enter optimization is disabled by default,
6910 // until we fix 6178663.
6911 if (CMSCleanOnEnter && (_finger > _threshold)) {
6912 // [_threshold, _finger) represents the interval
6913 // of cards to be cleared in MUT (or precleaned in card table).
6914 // The set of cards to be cleared is all those that overlap
6915 // with the interval [_threshold, _finger); note that
6916 // _threshold is always kept card-aligned but _finger isn't
6917 // always card-aligned.
6918 HeapWord* old_threshold = _threshold;
6919 assert(old_threshold == (HeapWord*)round_to(
6920 (intptr_t)old_threshold, CardTableModRefBS::card_size),
6921 "_threshold should always be card-aligned");
6922 _threshold = (HeapWord*)round_to(
6923 (intptr_t)_finger, CardTableModRefBS::card_size);
6924 MemRegion mr(old_threshold, _threshold);
6925 assert(!mr.is_empty(), "Control point invariant");
6926 assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
6927 _mut->clear_range(mr);
6928 }
6929
6930 // Note: the local finger doesn't advance while we drain
6931 // the stack below, but the global finger sure can and will.
6932 HeapWord** gfa = _task->global_finger_addr();
6933 Par_PushOrMarkClosure pushOrMarkClosure(_collector,
6934 _span, _bit_map,
6935 _work_queue,
6936 _overflow_stack,
6937 _finger,
6938 gfa, this);
6939 bool res = _work_queue->push(obj); // overflow could occur here
6940 assert(res, "Will hold once we use workqueues");
6941 while (true) {
6942 oop new_oop;
6943 if (!_work_queue->pop_local(new_oop)) {
6944 // We emptied our work_queue; check if there's stuff that can
6945 // be gotten from the overflow stack.
6946 if (CMSConcMarkingTask::get_work_from_overflow_stack(
6947 _overflow_stack, _work_queue)) {
6948 do_yield_check();
6949 continue;
6950 } else { // done
6951 break;
6952 }
6953 }
6954 // Skip verifying header mark word below because we are
6955 // running concurrent with mutators.
6956 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
6957 // now scan this oop's oops
6958 new_oop->oop_iterate(&pushOrMarkClosure);
6959 do_yield_check();
6960 }
6961 assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
6962 }
6963
6964 // Yield in response to a request from VM Thread or
6965 // from mutators.
6966 void Par_MarkFromRootsClosure::do_yield_work() {
6967 assert(_task != NULL, "sanity");
6968 _task->yield();
6969 }
6970
6971 // A variant of the above used for verifying CMS marking work.
6972 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
6973 MemRegion span,
6974 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6975 CMSMarkStack* mark_stack):
6976 _collector(collector),
6977 _span(span),
6978 _verification_bm(verification_bm),
6979 _cms_bm(cms_bm),
6980 _mark_stack(mark_stack),
6981 _pam_verify_closure(collector, span, verification_bm, cms_bm,
6982 mark_stack)
6983 {
6984 assert(_mark_stack->isEmpty(), "stack should be empty");
6985 _finger = _verification_bm->startWord();
6986 assert(_collector->_restart_addr == NULL, "Sanity check");
6987 assert(_span.contains(_finger), "Out of bounds _finger?");
6988 }
6989
6990 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
6991 assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
6992 assert(_span.contains(addr), "Out of bounds _finger?");
6993 _finger = addr;
6994 }
6995
6996 // Should revisit to see if this should be restructured for
6997 // greater efficiency.
6998 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
6999 // convert offset into a HeapWord*
7000 HeapWord* addr = _verification_bm->startWord() + offset;
7001 assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
7002 "address out of range");
7003 assert(_verification_bm->isMarked(addr), "tautology");
7004 assert(_cms_bm->isMarked(addr), "tautology");
7005
7006 assert(_mark_stack->isEmpty(),
7007 "should drain stack to limit stack usage");
7008 // convert addr to an oop preparatory to scanning
7009 oop obj = oop(addr);
7010 assert(obj->is_oop(), "should be an oop");
7011 assert(_finger <= addr, "_finger runneth ahead");
7012 // advance the finger to right end of this object
7013 _finger = addr + obj->size();
7014 assert(_finger > addr, "we just incremented it above");
7015 // Note: the finger doesn't advance while we drain
7016 // the stack below.
7017 bool res = _mark_stack->push(obj);
7018 assert(res, "Empty non-zero size stack should have space for single push");
7019 while (!_mark_stack->isEmpty()) {
7020 oop new_oop = _mark_stack->pop();
7021 assert(new_oop->is_oop(), "Oops! expected to pop an oop");
7022 // now scan this oop's oops
7023 new_oop->oop_iterate(&_pam_verify_closure);
7024 }
7025 assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
7026 return true;
7027 }
7028
7029 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
7030 CMSCollector* collector, MemRegion span,
7031 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
7032 CMSMarkStack* mark_stack):
7033 MetadataAwareOopClosure(collector->ref_processor()),
7034 _collector(collector),
7035 _span(span),
7036 _verification_bm(verification_bm),
7037 _cms_bm(cms_bm),
7038 _mark_stack(mark_stack)
7039 { }
7040
7041 void PushAndMarkVerifyClosure::do_oop(oop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
7042 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
7043
7044 // Upon stack overflow, we discard (part of) the stack,
7045 // remembering the least address amongst those discarded
7046 // in CMSCollector's _restart_address.
7047 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
7048 // Remember the least grey address discarded
7049 HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
7050 _collector->lower_restart_addr(ra);
7051 _mark_stack->reset(); // discard stack contents
7052 _mark_stack->expand(); // expand the stack if possible
7053 }
7054
7055 void PushAndMarkVerifyClosure::do_oop(oop obj) {
7056 assert(obj->is_oop_or_null(), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7057 HeapWord* addr = (HeapWord*)obj;
7058 if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
7059 // Oop lies in _span and isn't yet grey or black
7060 _verification_bm->mark(addr); // now grey
7061 if (!_cms_bm->isMarked(addr)) {
7062 oop(addr)->print();
7063 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)",
7064 addr);
7065 fatal("... aborting");
7066 }
7067
7068 if (!_mark_stack->push(obj)) { // stack overflow
7069 if (PrintCMSStatistics != 0) {
7070 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7071 SIZE_FORMAT, _mark_stack->capacity());
7072 }
7073 assert(_mark_stack->isFull(), "Else push should have succeeded");
7074 handle_stack_overflow(addr);
7075 }
7076 // anything including and to the right of _finger
7077 // will be scanned as we iterate over the remainder of the
7078 // bit map
7079 }
7080 }
7081
7082 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
7083 MemRegion span,
7084 CMSBitMap* bitMap, CMSMarkStack* markStack,
7085 HeapWord* finger, MarkFromRootsClosure* parent) :
7086 MetadataAwareOopClosure(collector->ref_processor()),
7087 _collector(collector),
7088 _span(span),
7089 _bitMap(bitMap),
7090 _markStack(markStack),
7091 _finger(finger),
7092 _parent(parent)
7093 { }
7094
7095 Par_PushOrMarkClosure::Par_PushOrMarkClosure(CMSCollector* collector,
7096 MemRegion span,
7097 CMSBitMap* bit_map,
7098 OopTaskQueue* work_queue,
7099 CMSMarkStack* overflow_stack,
7100 HeapWord* finger,
7101 HeapWord** global_finger_addr,
7102 Par_MarkFromRootsClosure* parent) :
7103 MetadataAwareOopClosure(collector->ref_processor()),
7104 _collector(collector),
7105 _whole_span(collector->_span),
7106 _span(span),
7107 _bit_map(bit_map),
7108 _work_queue(work_queue),
7109 _overflow_stack(overflow_stack),
7110 _finger(finger),
7111 _global_finger_addr(global_finger_addr),
7112 _parent(parent)
7113 { }
7114
7115 // Assumes thread-safe access by callers, who are
7116 // responsible for mutual exclusion.
7117 void CMSCollector::lower_restart_addr(HeapWord* low) {
7118 assert(_span.contains(low), "Out of bounds addr");
7119 if (_restart_addr == NULL) {
7120 _restart_addr = low;
7121 } else {
7122 _restart_addr = MIN2(_restart_addr, low);
7123 }
7124 }
7125
7126 // Upon stack overflow, we discard (part of) the stack,
7127 // remembering the least address amongst those discarded
7128 // in CMSCollector's _restart_address.
7129 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7130 // Remember the least grey address discarded
7131 HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
7132 _collector->lower_restart_addr(ra);
7133 _markStack->reset(); // discard stack contents
7134 _markStack->expand(); // expand the stack if possible
7135 }
7136
7137 // Upon stack overflow, we discard (part of) the stack,
7138 // remembering the least address amongst those discarded
7139 // in CMSCollector's _restart_address.
7140 void Par_PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7141 // We need to do this under a mutex to prevent other
7142 // workers from interfering with the work done below.
7143 MutexLockerEx ml(_overflow_stack->par_lock(),
7144 Mutex::_no_safepoint_check_flag);
7145 // Remember the least grey address discarded
7146 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
7147 _collector->lower_restart_addr(ra);
7148 _overflow_stack->reset(); // discard stack contents
7149 _overflow_stack->expand(); // expand the stack if possible
7150 }
7151
7152 void PushOrMarkClosure::do_oop(oop obj) {
7153 // Ignore mark word because we are running concurrent with mutators.
7154 assert(obj->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7155 HeapWord* addr = (HeapWord*)obj;
7156 if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
7157 // Oop lies in _span and isn't yet grey or black
7158 _bitMap->mark(addr); // now grey
7159 if (addr < _finger) {
7160 // the bit map iteration has already either passed, or
7161 // sampled, this bit in the bit map; we'll need to
7162 // use the marking stack to scan this oop's oops.
7163 bool simulate_overflow = false;
7164 NOT_PRODUCT(
7165 if (CMSMarkStackOverflowALot &&
7166 _collector->simulate_overflow()) {
7167 // simulate a stack overflow
7168 simulate_overflow = true;
7169 }
7170 )
7171 if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
7172 if (PrintCMSStatistics != 0) {
7173 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7174 SIZE_FORMAT, _markStack->capacity());
7175 }
7176 assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
7177 handle_stack_overflow(addr);
7178 }
7179 }
7180 // anything including and to the right of _finger
7181 // will be scanned as we iterate over the remainder of the
7182 // bit map
7183 do_yield_check();
7184 }
7185 }
7186
7187 void PushOrMarkClosure::do_oop(oop* p) { PushOrMarkClosure::do_oop_work(p); }
7188 void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); }
7189
7190 void Par_PushOrMarkClosure::do_oop(oop obj) {
7191 // Ignore mark word because we are running concurrent with mutators.
7192 assert(obj->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7193 HeapWord* addr = (HeapWord*)obj;
7194 if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
7195 // Oop lies in _span and isn't yet grey or black
7196 // We read the global_finger (volatile read) strictly after marking oop
7197 bool res = _bit_map->par_mark(addr); // now grey
7198 volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
7199 // Should we push this marked oop on our stack?
7200 // -- if someone else marked it, nothing to do
7201 // -- if target oop is above global finger nothing to do
7202 // -- if target oop is in chunk and above local finger
7203 // then nothing to do
7204 // -- else push on work queue
7205 if ( !res // someone else marked it, they will deal with it
7206 || (addr >= *gfa) // will be scanned in a later task
7207 || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
7208 return;
7209 }
7210 // the bit map iteration has already either passed, or
7211 // sampled, this bit in the bit map; we'll need to
7212 // use the marking stack to scan this oop's oops.
7213 bool simulate_overflow = false;
7214 NOT_PRODUCT(
7215 if (CMSMarkStackOverflowALot &&
7216 _collector->simulate_overflow()) {
7217 // simulate a stack overflow
7218 simulate_overflow = true;
7219 }
7220 )
7221 if (simulate_overflow ||
7222 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
7223 // stack overflow
7224 if (PrintCMSStatistics != 0) {
7225 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7226 SIZE_FORMAT, _overflow_stack->capacity());
7227 }
7228 // We cannot assert that the overflow stack is full because
7229 // it may have been emptied since.
7230 assert(simulate_overflow ||
7231 _work_queue->size() == _work_queue->max_elems(),
7232 "Else push should have succeeded");
7233 handle_stack_overflow(addr);
7234 }
7235 do_yield_check();
7236 }
7237 }
7238
7239 void Par_PushOrMarkClosure::do_oop(oop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7240 void Par_PushOrMarkClosure::do_oop(narrowOop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7241
7242 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
7243 MemRegion span,
7244 ReferenceProcessor* rp,
7245 CMSBitMap* bit_map,
7246 CMSBitMap* mod_union_table,
7247 CMSMarkStack* mark_stack,
7248 bool concurrent_precleaning):
7249 MetadataAwareOopClosure(rp),
7250 _collector(collector),
7251 _span(span),
7252 _bit_map(bit_map),
7253 _mod_union_table(mod_union_table),
7254 _mark_stack(mark_stack),
7255 _concurrent_precleaning(concurrent_precleaning)
7256 {
7257 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7258 }
7259
7260 // Grey object rescan during pre-cleaning and second checkpoint phases --
7261 // the non-parallel version (the parallel version appears further below.)
7262 void PushAndMarkClosure::do_oop(oop obj) {
7263 // Ignore mark word verification. If during concurrent precleaning,
7264 // the object monitor may be locked. If during the checkpoint
7265 // phases, the object may already have been reached by a different
7266 // path and may be at the end of the global overflow list (so
7267 // the mark word may be NULL).
7268 assert(obj->is_oop_or_null(true /* ignore mark word */),
7269 err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7270 HeapWord* addr = (HeapWord*)obj;
7271 // Check if oop points into the CMS generation
7272 // and is not marked
7273 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7274 // a white object ...
7275 _bit_map->mark(addr); // ... now grey
7276 // push on the marking stack (grey set)
7277 bool simulate_overflow = false;
7278 NOT_PRODUCT(
7279 if (CMSMarkStackOverflowALot &&
7280 _collector->simulate_overflow()) {
7281 // simulate a stack overflow
7282 simulate_overflow = true;
7283 }
7284 )
7285 if (simulate_overflow || !_mark_stack->push(obj)) {
7286 if (_concurrent_precleaning) {
7287 // During precleaning we can just dirty the appropriate card(s)
7288 // in the mod union table, thus ensuring that the object remains
7289 // in the grey set and continue. In the case of object arrays
7290 // we need to dirty all of the cards that the object spans,
7291 // since the rescan of object arrays will be limited to the
7292 // dirty cards.
7293 // Note that no one can be interfering with us in this action
7294 // of dirtying the mod union table, so no locking or atomics
7295 // are required.
7296 if (obj->is_objArray()) {
7297 size_t sz = obj->size();
7298 HeapWord* end_card_addr = (HeapWord*)round_to(
7299 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7300 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7301 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7302 _mod_union_table->mark_range(redirty_range);
7303 } else {
7304 _mod_union_table->mark(addr);
7305 }
7306 _collector->_ser_pmc_preclean_ovflw++;
7307 } else {
7308 // During the remark phase, we need to remember this oop
7309 // in the overflow list.
7310 _collector->push_on_overflow_list(obj);
7311 _collector->_ser_pmc_remark_ovflw++;
7312 }
7313 }
7314 }
7315 }
7316
7317 Par_PushAndMarkClosure::Par_PushAndMarkClosure(CMSCollector* collector,
7318 MemRegion span,
7319 ReferenceProcessor* rp,
7320 CMSBitMap* bit_map,
7321 OopTaskQueue* work_queue):
7322 MetadataAwareOopClosure(rp),
7323 _collector(collector),
7324 _span(span),
7325 _bit_map(bit_map),
7326 _work_queue(work_queue)
7327 {
7328 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7329 }
7330
7331 void PushAndMarkClosure::do_oop(oop* p) { PushAndMarkClosure::do_oop_work(p); }
7332 void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); }
7333
7334 // Grey object rescan during second checkpoint phase --
7335 // the parallel version.
7336 void Par_PushAndMarkClosure::do_oop(oop obj) {
7337 // In the assert below, we ignore the mark word because
7338 // this oop may point to an already visited object that is
7339 // on the overflow stack (in which case the mark word has
7340 // been hijacked for chaining into the overflow stack --
7341 // if this is the last object in the overflow stack then
7342 // its mark word will be NULL). Because this object may
7343 // have been subsequently popped off the global overflow
7344 // stack, and the mark word possibly restored to the prototypical
7345 // value, by the time we get to examined this failing assert in
7346 // the debugger, is_oop_or_null(false) may subsequently start
7347 // to hold.
7348 assert(obj->is_oop_or_null(true),
7349 err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7350 HeapWord* addr = (HeapWord*)obj;
7351 // Check if oop points into the CMS generation
7352 // and is not marked
7353 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7354 // a white object ...
7355 // If we manage to "claim" the object, by being the
7356 // first thread to mark it, then we push it on our
7357 // marking stack
7358 if (_bit_map->par_mark(addr)) { // ... now grey
7359 // push on work queue (grey set)
7360 bool simulate_overflow = false;
7361 NOT_PRODUCT(
7362 if (CMSMarkStackOverflowALot &&
7363 _collector->par_simulate_overflow()) {
7364 // simulate a stack overflow
7365 simulate_overflow = true;
7366 }
7367 )
7368 if (simulate_overflow || !_work_queue->push(obj)) {
7369 _collector->par_push_on_overflow_list(obj);
7370 _collector->_par_pmc_remark_ovflw++; // imprecise OK: no need to CAS
7371 }
7372 } // Else, some other thread got there first
7373 }
7374 }
7375
7376 void Par_PushAndMarkClosure::do_oop(oop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7377 void Par_PushAndMarkClosure::do_oop(narrowOop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7378
7379 void CMSPrecleanRefsYieldClosure::do_yield_work() {
7380 Mutex* bml = _collector->bitMapLock();
7381 assert_lock_strong(bml);
7382 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7383 "CMS thread should hold CMS token");
7384
7385 bml->unlock();
7386 ConcurrentMarkSweepThread::desynchronize(true);
7387
7388 _collector->stopTimer();
7389 if (PrintCMSStatistics != 0) {
7390 _collector->incrementYields();
7391 }
7392
7393 // See the comment in coordinator_yield()
7394 for (unsigned i = 0; i < CMSYieldSleepCount &&
7395 ConcurrentMarkSweepThread::should_yield() &&
7396 !CMSCollector::foregroundGCIsActive(); ++i) {
7397 os::sleep(Thread::current(), 1, false);
7398 }
7399
7400 ConcurrentMarkSweepThread::synchronize(true);
7401 bml->lock();
7402
7403 _collector->startTimer();
7404 }
7405
7406 bool CMSPrecleanRefsYieldClosure::should_return() {
7407 if (ConcurrentMarkSweepThread::should_yield()) {
7408 do_yield_work();
7409 }
7410 return _collector->foregroundGCIsActive();
7411 }
7412
7413 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
7414 assert(((size_t)mr.start())%CardTableModRefBS::card_size_in_words == 0,
7415 "mr should be aligned to start at a card boundary");
7416 // We'd like to assert:
7417 // assert(mr.word_size()%CardTableModRefBS::card_size_in_words == 0,
7418 // "mr should be a range of cards");
7419 // However, that would be too strong in one case -- the last
7420 // partition ends at _unallocated_block which, in general, can be
7421 // an arbitrary boundary, not necessarily card aligned.
7422 if (PrintCMSStatistics != 0) {
7423 _num_dirty_cards +=
7424 mr.word_size()/CardTableModRefBS::card_size_in_words;
7425 }
7426 _space->object_iterate_mem(mr, &_scan_cl);
7427 }
7428
7429 SweepClosure::SweepClosure(CMSCollector* collector,
7430 ConcurrentMarkSweepGeneration* g,
7431 CMSBitMap* bitMap, bool should_yield) :
7432 _collector(collector),
7433 _g(g),
7434 _sp(g->cmsSpace()),
7435 _limit(_sp->sweep_limit()),
7436 _freelistLock(_sp->freelistLock()),
7437 _bitMap(bitMap),
7438 _yield(should_yield),
7439 _inFreeRange(false), // No free range at beginning of sweep
7440 _freeRangeInFreeLists(false), // No free range at beginning of sweep
7441 _lastFreeRangeCoalesced(false),
7442 _freeFinger(g->used_region().start())
7443 {
7444 NOT_PRODUCT(
7445 _numObjectsFreed = 0;
7446 _numWordsFreed = 0;
7447 _numObjectsLive = 0;
7448 _numWordsLive = 0;
7449 _numObjectsAlreadyFree = 0;
7450 _numWordsAlreadyFree = 0;
7451 _last_fc = NULL;
7452
7453 _sp->initializeIndexedFreeListArrayReturnedBytes();
7454 _sp->dictionary()->initialize_dict_returned_bytes();
7455 )
7456 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7457 "sweep _limit out of bounds");
7458 if (CMSTraceSweeper) {
7459 gclog_or_tty->print_cr("\n====================\nStarting new sweep with limit " PTR_FORMAT,
7460 _limit);
7461 }
7462 }
7463
7464 void SweepClosure::print_on(outputStream* st) const {
7465 tty->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")",
7466 _sp->bottom(), _sp->end());
7467 tty->print_cr("_limit = " PTR_FORMAT, _limit);
7468 tty->print_cr("_freeFinger = " PTR_FORMAT, _freeFinger);
7469 NOT_PRODUCT(tty->print_cr("_last_fc = " PTR_FORMAT, _last_fc);)
7470 tty->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d",
7471 _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced);
7472 }
7473
7474 #ifndef PRODUCT
7475 // Assertion checking only: no useful work in product mode --
7476 // however, if any of the flags below become product flags,
7477 // you may need to review this code to see if it needs to be
7478 // enabled in product mode.
7479 SweepClosure::~SweepClosure() {
7480 assert_lock_strong(_freelistLock);
7481 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7482 "sweep _limit out of bounds");
7483 if (inFreeRange()) {
7484 warning("inFreeRange() should have been reset; dumping state of SweepClosure");
7485 print();
7486 ShouldNotReachHere();
7487 }
7488 if (Verbose && PrintGC) {
7489 gclog_or_tty->print("Collected "SIZE_FORMAT" objects, " SIZE_FORMAT " bytes",
7490 _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
7491 gclog_or_tty->print_cr("\nLive "SIZE_FORMAT" objects, "
7492 SIZE_FORMAT" bytes "
7493 "Already free "SIZE_FORMAT" objects, "SIZE_FORMAT" bytes",
7494 _numObjectsLive, _numWordsLive*sizeof(HeapWord),
7495 _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
7496 size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree)
7497 * sizeof(HeapWord);
7498 gclog_or_tty->print_cr("Total sweep: "SIZE_FORMAT" bytes", totalBytes);
7499
7500 if (PrintCMSStatistics && CMSVerifyReturnedBytes) {
7501 size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
7502 size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes();
7503 size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes;
7504 gclog_or_tty->print("Returned "SIZE_FORMAT" bytes", returned_bytes);
7505 gclog_or_tty->print(" Indexed List Returned "SIZE_FORMAT" bytes",
7506 indexListReturnedBytes);
7507 gclog_or_tty->print_cr(" Dictionary Returned "SIZE_FORMAT" bytes",
7508 dict_returned_bytes);
7509 }
7510 }
7511 if (CMSTraceSweeper) {
7512 gclog_or_tty->print_cr("end of sweep with _limit = " PTR_FORMAT "\n================",
7513 _limit);
7514 }
7515 }
7516 #endif // PRODUCT
7517
7518 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
7519 bool freeRangeInFreeLists) {
7520 if (CMSTraceSweeper) {
7521 gclog_or_tty->print("---- Start free range at " PTR_FORMAT " with free block (%d)\n",
7522 freeFinger, freeRangeInFreeLists);
7523 }
7524 assert(!inFreeRange(), "Trampling existing free range");
7525 set_inFreeRange(true);
7526 set_lastFreeRangeCoalesced(false);
7527
7528 set_freeFinger(freeFinger);
7529 set_freeRangeInFreeLists(freeRangeInFreeLists);
7530 if (CMSTestInFreeList) {
7531 if (freeRangeInFreeLists) {
7532 FreeChunk* fc = (FreeChunk*) freeFinger;
7533 assert(fc->is_free(), "A chunk on the free list should be free.");
7534 assert(fc->size() > 0, "Free range should have a size");
7535 assert(_sp->verify_chunk_in_free_list(fc), "Chunk is not in free lists");
7536 }
7537 }
7538 }
7539
7540 // Note that the sweeper runs concurrently with mutators. Thus,
7541 // it is possible for direct allocation in this generation to happen
7542 // in the middle of the sweep. Note that the sweeper also coalesces
7543 // contiguous free blocks. Thus, unless the sweeper and the allocator
7544 // synchronize appropriately freshly allocated blocks may get swept up.
7545 // This is accomplished by the sweeper locking the free lists while
7546 // it is sweeping. Thus blocks that are determined to be free are
7547 // indeed free. There is however one additional complication:
7548 // blocks that have been allocated since the final checkpoint and
7549 // mark, will not have been marked and so would be treated as
7550 // unreachable and swept up. To prevent this, the allocator marks
7551 // the bit map when allocating during the sweep phase. This leads,
7552 // however, to a further complication -- objects may have been allocated
7553 // but not yet initialized -- in the sense that the header isn't yet
7554 // installed. The sweeper can not then determine the size of the block
7555 // in order to skip over it. To deal with this case, we use a technique
7556 // (due to Printezis) to encode such uninitialized block sizes in the
7557 // bit map. Since the bit map uses a bit per every HeapWord, but the
7558 // CMS generation has a minimum object size of 3 HeapWords, it follows
7559 // that "normal marks" won't be adjacent in the bit map (there will
7560 // always be at least two 0 bits between successive 1 bits). We make use
7561 // of these "unused" bits to represent uninitialized blocks -- the bit
7562 // corresponding to the start of the uninitialized object and the next
7563 // bit are both set. Finally, a 1 bit marks the end of the object that
7564 // started with the two consecutive 1 bits to indicate its potentially
7565 // uninitialized state.
7566
7567 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
7568 FreeChunk* fc = (FreeChunk*)addr;
7569 size_t res;
7570
7571 // Check if we are done sweeping. Below we check "addr >= _limit" rather
7572 // than "addr == _limit" because although _limit was a block boundary when
7573 // we started the sweep, it may no longer be one because heap expansion
7574 // may have caused us to coalesce the block ending at the address _limit
7575 // with a newly expanded chunk (this happens when _limit was set to the
7576 // previous _end of the space), so we may have stepped past _limit:
7577 // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740.
7578 if (addr >= _limit) { // we have swept up to or past the limit: finish up
7579 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7580 "sweep _limit out of bounds");
7581 assert(addr < _sp->end(), "addr out of bounds");
7582 // Flush any free range we might be holding as a single
7583 // coalesced chunk to the appropriate free list.
7584 if (inFreeRange()) {
7585 assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit,
7586 err_msg("freeFinger() " PTR_FORMAT" is out-of-bounds", freeFinger()));
7587 flush_cur_free_chunk(freeFinger(),
7588 pointer_delta(addr, freeFinger()));
7589 if (CMSTraceSweeper) {
7590 gclog_or_tty->print("Sweep: last chunk: ");
7591 gclog_or_tty->print("put_free_blk " PTR_FORMAT " ("SIZE_FORMAT") "
7592 "[coalesced:%d]\n",
7593 freeFinger(), pointer_delta(addr, freeFinger()),
7594 lastFreeRangeCoalesced() ? 1 : 0);
7595 }
7596 }
7597
7598 // help the iterator loop finish
7599 return pointer_delta(_sp->end(), addr);
7600 }
7601
7602 assert(addr < _limit, "sweep invariant");
7603 // check if we should yield
7604 do_yield_check(addr);
7605 if (fc->is_free()) {
7606 // Chunk that is already free
7607 res = fc->size();
7608 do_already_free_chunk(fc);
7609 debug_only(_sp->verifyFreeLists());
7610 // If we flush the chunk at hand in lookahead_and_flush()
7611 // and it's coalesced with a preceding chunk, then the
7612 // process of "mangling" the payload of the coalesced block
7613 // will cause erasure of the size information from the
7614 // (erstwhile) header of all the coalesced blocks but the
7615 // first, so the first disjunct in the assert will not hold
7616 // in that specific case (in which case the second disjunct
7617 // will hold).
7618 assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit,
7619 "Otherwise the size info doesn't change at this step");
7620 NOT_PRODUCT(
7621 _numObjectsAlreadyFree++;
7622 _numWordsAlreadyFree += res;
7623 )
7624 NOT_PRODUCT(_last_fc = fc;)
7625 } else if (!_bitMap->isMarked(addr)) {
7626 // Chunk is fresh garbage
7627 res = do_garbage_chunk(fc);
7628 debug_only(_sp->verifyFreeLists());
7629 NOT_PRODUCT(
7630 _numObjectsFreed++;
7631 _numWordsFreed += res;
7632 )
7633 } else {
7634 // Chunk that is alive.
7635 res = do_live_chunk(fc);
7636 debug_only(_sp->verifyFreeLists());
7637 NOT_PRODUCT(
7638 _numObjectsLive++;
7639 _numWordsLive += res;
7640 )
7641 }
7642 return res;
7643 }
7644
7645 // For the smart allocation, record following
7646 // split deaths - a free chunk is removed from its free list because
7647 // it is being split into two or more chunks.
7648 // split birth - a free chunk is being added to its free list because
7649 // a larger free chunk has been split and resulted in this free chunk.
7650 // coal death - a free chunk is being removed from its free list because
7651 // it is being coalesced into a large free chunk.
7652 // coal birth - a free chunk is being added to its free list because
7653 // it was created when two or more free chunks where coalesced into
7654 // this free chunk.
7655 //
7656 // These statistics are used to determine the desired number of free
7657 // chunks of a given size. The desired number is chosen to be relative
7658 // to the end of a CMS sweep. The desired number at the end of a sweep
7659 // is the
7660 // count-at-end-of-previous-sweep (an amount that was enough)
7661 // - count-at-beginning-of-current-sweep (the excess)
7662 // + split-births (gains in this size during interval)
7663 // - split-deaths (demands on this size during interval)
7664 // where the interval is from the end of one sweep to the end of the
7665 // next.
7666 //
7667 // When sweeping the sweeper maintains an accumulated chunk which is
7668 // the chunk that is made up of chunks that have been coalesced. That
7669 // will be termed the left-hand chunk. A new chunk of garbage that
7670 // is being considered for coalescing will be referred to as the
7671 // right-hand chunk.
7672 //
7673 // When making a decision on whether to coalesce a right-hand chunk with
7674 // the current left-hand chunk, the current count vs. the desired count
7675 // of the left-hand chunk is considered. Also if the right-hand chunk
7676 // is near the large chunk at the end of the heap (see
7677 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
7678 // left-hand chunk is coalesced.
7679 //
7680 // When making a decision about whether to split a chunk, the desired count
7681 // vs. the current count of the candidate to be split is also considered.
7682 // If the candidate is underpopulated (currently fewer chunks than desired)
7683 // a chunk of an overpopulated (currently more chunks than desired) size may
7684 // be chosen. The "hint" associated with a free list, if non-null, points
7685 // to a free list which may be overpopulated.
7686 //
7687
7688 void SweepClosure::do_already_free_chunk(FreeChunk* fc) {
7689 const size_t size = fc->size();
7690 // Chunks that cannot be coalesced are not in the
7691 // free lists.
7692 if (CMSTestInFreeList && !fc->cantCoalesce()) {
7693 assert(_sp->verify_chunk_in_free_list(fc),
7694 "free chunk should be in free lists");
7695 }
7696 // a chunk that is already free, should not have been
7697 // marked in the bit map
7698 HeapWord* const addr = (HeapWord*) fc;
7699 assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
7700 // Verify that the bit map has no bits marked between
7701 // addr and purported end of this block.
7702 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7703
7704 // Some chunks cannot be coalesced under any circumstances.
7705 // See the definition of cantCoalesce().
7706 if (!fc->cantCoalesce()) {
7707 // This chunk can potentially be coalesced.
7708 if (_sp->adaptive_freelists()) {
7709 // All the work is done in
7710 do_post_free_or_garbage_chunk(fc, size);
7711 } else { // Not adaptive free lists
7712 // this is a free chunk that can potentially be coalesced by the sweeper;
7713 if (!inFreeRange()) {
7714 // if the next chunk is a free block that can't be coalesced
7715 // it doesn't make sense to remove this chunk from the free lists
7716 FreeChunk* nextChunk = (FreeChunk*)(addr + size);
7717 assert((HeapWord*)nextChunk <= _sp->end(), "Chunk size out of bounds?");
7718 if ((HeapWord*)nextChunk < _sp->end() && // There is another free chunk to the right ...
7719 nextChunk->is_free() && // ... which is free...
7720 nextChunk->cantCoalesce()) { // ... but can't be coalesced
7721 // nothing to do
7722 } else {
7723 // Potentially the start of a new free range:
7724 // Don't eagerly remove it from the free lists.
7725 // No need to remove it if it will just be put
7726 // back again. (Also from a pragmatic point of view
7727 // if it is a free block in a region that is beyond
7728 // any allocated blocks, an assertion will fail)
7729 // Remember the start of a free run.
7730 initialize_free_range(addr, true);
7731 // end - can coalesce with next chunk
7732 }
7733 } else {
7734 // the midst of a free range, we are coalescing
7735 print_free_block_coalesced(fc);
7736 if (CMSTraceSweeper) {
7737 gclog_or_tty->print(" -- pick up free block " PTR_FORMAT " (" SIZE_FORMAT ")\n", fc, size);
7738 }
7739 // remove it from the free lists
7740 _sp->removeFreeChunkFromFreeLists(fc);
7741 set_lastFreeRangeCoalesced(true);
7742 // If the chunk is being coalesced and the current free range is
7743 // in the free lists, remove the current free range so that it
7744 // will be returned to the free lists in its entirety - all
7745 // the coalesced pieces included.
7746 if (freeRangeInFreeLists()) {
7747 FreeChunk* ffc = (FreeChunk*) freeFinger();
7748 assert(ffc->size() == pointer_delta(addr, freeFinger()),
7749 "Size of free range is inconsistent with chunk size.");
7750 if (CMSTestInFreeList) {
7751 assert(_sp->verify_chunk_in_free_list(ffc),
7752 "free range is not in free lists");
7753 }
7754 _sp->removeFreeChunkFromFreeLists(ffc);
7755 set_freeRangeInFreeLists(false);
7756 }
7757 }
7758 }
7759 // Note that if the chunk is not coalescable (the else arm
7760 // below), we unconditionally flush, without needing to do
7761 // a "lookahead," as we do below.
7762 if (inFreeRange()) lookahead_and_flush(fc, size);
7763 } else {
7764 // Code path common to both original and adaptive free lists.
7765
7766 // cant coalesce with previous block; this should be treated
7767 // as the end of a free run if any
7768 if (inFreeRange()) {
7769 // we kicked some butt; time to pick up the garbage
7770 assert(freeFinger() < addr, "freeFinger points too high");
7771 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7772 }
7773 // else, nothing to do, just continue
7774 }
7775 }
7776
7777 size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) {
7778 // This is a chunk of garbage. It is not in any free list.
7779 // Add it to a free list or let it possibly be coalesced into
7780 // a larger chunk.
7781 HeapWord* const addr = (HeapWord*) fc;
7782 const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7783
7784 if (_sp->adaptive_freelists()) {
7785 // Verify that the bit map has no bits marked between
7786 // addr and purported end of just dead object.
7787 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7788
7789 do_post_free_or_garbage_chunk(fc, size);
7790 } else {
7791 if (!inFreeRange()) {
7792 // start of a new free range
7793 assert(size > 0, "A free range should have a size");
7794 initialize_free_range(addr, false);
7795 } else {
7796 // this will be swept up when we hit the end of the
7797 // free range
7798 if (CMSTraceSweeper) {
7799 gclog_or_tty->print(" -- pick up garbage " PTR_FORMAT " (" SIZE_FORMAT ")\n", fc, size);
7800 }
7801 // If the chunk is being coalesced and the current free range is
7802 // in the free lists, remove the current free range so that it
7803 // will be returned to the free lists in its entirety - all
7804 // the coalesced pieces included.
7805 if (freeRangeInFreeLists()) {
7806 FreeChunk* ffc = (FreeChunk*)freeFinger();
7807 assert(ffc->size() == pointer_delta(addr, freeFinger()),
7808 "Size of free range is inconsistent with chunk size.");
7809 if (CMSTestInFreeList) {
7810 assert(_sp->verify_chunk_in_free_list(ffc),
7811 "free range is not in free lists");
7812 }
7813 _sp->removeFreeChunkFromFreeLists(ffc);
7814 set_freeRangeInFreeLists(false);
7815 }
7816 set_lastFreeRangeCoalesced(true);
7817 }
7818 // this will be swept up when we hit the end of the free range
7819
7820 // Verify that the bit map has no bits marked between
7821 // addr and purported end of just dead object.
7822 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7823 }
7824 assert(_limit >= addr + size,
7825 "A freshly garbage chunk can't possibly straddle over _limit");
7826 if (inFreeRange()) lookahead_and_flush(fc, size);
7827 return size;
7828 }
7829
7830 size_t SweepClosure::do_live_chunk(FreeChunk* fc) {
7831 HeapWord* addr = (HeapWord*) fc;
7832 // The sweeper has just found a live object. Return any accumulated
7833 // left hand chunk to the free lists.
7834 if (inFreeRange()) {
7835 assert(freeFinger() < addr, "freeFinger points too high");
7836 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7837 }
7838
7839 // This object is live: we'd normally expect this to be
7840 // an oop, and like to assert the following:
7841 // assert(oop(addr)->is_oop(), "live block should be an oop");
7842 // However, as we commented above, this may be an object whose
7843 // header hasn't yet been initialized.
7844 size_t size;
7845 assert(_bitMap->isMarked(addr), "Tautology for this control point");
7846 if (_bitMap->isMarked(addr + 1)) {
7847 // Determine the size from the bit map, rather than trying to
7848 // compute it from the object header.
7849 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
7850 size = pointer_delta(nextOneAddr + 1, addr);
7851 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
7852 "alignment problem");
7853
7854 #ifdef ASSERT
7855 if (oop(addr)->klass_or_null() != NULL) {
7856 // Ignore mark word because we are running concurrent with mutators
7857 assert(oop(addr)->is_oop(true), "live block should be an oop");
7858 assert(size ==
7859 CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
7860 "P-mark and computed size do not agree");
7861 }
7862 #endif
7863
7864 } else {
7865 // This should be an initialized object that's alive.
7866 assert(oop(addr)->klass_or_null() != NULL,
7867 "Should be an initialized object");
7868 // Ignore mark word because we are running concurrent with mutators
7869 assert(oop(addr)->is_oop(true), "live block should be an oop");
7870 // Verify that the bit map has no bits marked between
7871 // addr and purported end of this block.
7872 size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7873 assert(size >= 3, "Necessary for Printezis marks to work");
7874 assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
7875 DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
7876 }
7877 return size;
7878 }
7879
7880 void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc,
7881 size_t chunkSize) {
7882 // do_post_free_or_garbage_chunk() should only be called in the case
7883 // of the adaptive free list allocator.
7884 const bool fcInFreeLists = fc->is_free();
7885 assert(_sp->adaptive_freelists(), "Should only be used in this case.");
7886 assert((HeapWord*)fc <= _limit, "sweep invariant");
7887 if (CMSTestInFreeList && fcInFreeLists) {
7888 assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists");
7889 }
7890
7891 if (CMSTraceSweeper) {
7892 gclog_or_tty->print_cr(" -- pick up another chunk at " PTR_FORMAT " (" SIZE_FORMAT ")", fc, chunkSize);
7893 }
7894
7895 HeapWord* const fc_addr = (HeapWord*) fc;
7896
7897 bool coalesce;
7898 const size_t left = pointer_delta(fc_addr, freeFinger());
7899 const size_t right = chunkSize;
7900 switch (FLSCoalescePolicy) {
7901 // numeric value forms a coalition aggressiveness metric
7902 case 0: { // never coalesce
7903 coalesce = false;
7904 break;
7905 }
7906 case 1: { // coalesce if left & right chunks on overpopulated lists
7907 coalesce = _sp->coalOverPopulated(left) &&
7908 _sp->coalOverPopulated(right);
7909 break;
7910 }
7911 case 2: { // coalesce if left chunk on overpopulated list (default)
7912 coalesce = _sp->coalOverPopulated(left);
7913 break;
7914 }
7915 case 3: { // coalesce if left OR right chunk on overpopulated list
7916 coalesce = _sp->coalOverPopulated(left) ||
7917 _sp->coalOverPopulated(right);
7918 break;
7919 }
7920 case 4: { // always coalesce
7921 coalesce = true;
7922 break;
7923 }
7924 default:
7925 ShouldNotReachHere();
7926 }
7927
7928 // Should the current free range be coalesced?
7929 // If the chunk is in a free range and either we decided to coalesce above
7930 // or the chunk is near the large block at the end of the heap
7931 // (isNearLargestChunk() returns true), then coalesce this chunk.
7932 const bool doCoalesce = inFreeRange()
7933 && (coalesce || _g->isNearLargestChunk(fc_addr));
7934 if (doCoalesce) {
7935 // Coalesce the current free range on the left with the new
7936 // chunk on the right. If either is on a free list,
7937 // it must be removed from the list and stashed in the closure.
7938 if (freeRangeInFreeLists()) {
7939 FreeChunk* const ffc = (FreeChunk*)freeFinger();
7940 assert(ffc->size() == pointer_delta(fc_addr, freeFinger()),
7941 "Size of free range is inconsistent with chunk size.");
7942 if (CMSTestInFreeList) {
7943 assert(_sp->verify_chunk_in_free_list(ffc),
7944 "Chunk is not in free lists");
7945 }
7946 _sp->coalDeath(ffc->size());
7947 _sp->removeFreeChunkFromFreeLists(ffc);
7948 set_freeRangeInFreeLists(false);
7949 }
7950 if (fcInFreeLists) {
7951 _sp->coalDeath(chunkSize);
7952 assert(fc->size() == chunkSize,
7953 "The chunk has the wrong size or is not in the free lists");
7954 _sp->removeFreeChunkFromFreeLists(fc);
7955 }
7956 set_lastFreeRangeCoalesced(true);
7957 print_free_block_coalesced(fc);
7958 } else { // not in a free range and/or should not coalesce
7959 // Return the current free range and start a new one.
7960 if (inFreeRange()) {
7961 // In a free range but cannot coalesce with the right hand chunk.
7962 // Put the current free range into the free lists.
7963 flush_cur_free_chunk(freeFinger(),
7964 pointer_delta(fc_addr, freeFinger()));
7965 }
7966 // Set up for new free range. Pass along whether the right hand
7967 // chunk is in the free lists.
7968 initialize_free_range((HeapWord*)fc, fcInFreeLists);
7969 }
7970 }
7971
7972 // Lookahead flush:
7973 // If we are tracking a free range, and this is the last chunk that
7974 // we'll look at because its end crosses past _limit, we'll preemptively
7975 // flush it along with any free range we may be holding on to. Note that
7976 // this can be the case only for an already free or freshly garbage
7977 // chunk. If this block is an object, it can never straddle
7978 // over _limit. The "straddling" occurs when _limit is set at
7979 // the previous end of the space when this cycle started, and
7980 // a subsequent heap expansion caused the previously co-terminal
7981 // free block to be coalesced with the newly expanded portion,
7982 // thus rendering _limit a non-block-boundary making it dangerous
7983 // for the sweeper to step over and examine.
7984 void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) {
7985 assert(inFreeRange(), "Should only be called if currently in a free range.");
7986 HeapWord* const eob = ((HeapWord*)fc) + chunk_size;
7987 assert(_sp->used_region().contains(eob - 1),
7988 err_msg("eob = " PTR_FORMAT " eob-1 = " PTR_FORMAT " _limit = " PTR_FORMAT
7989 " out of bounds wrt _sp = [" PTR_FORMAT "," PTR_FORMAT ")"
7990 " when examining fc = " PTR_FORMAT "(" SIZE_FORMAT ")",
7991 eob, eob-1, _limit, _sp->bottom(), _sp->end(), fc, chunk_size));
7992 if (eob >= _limit) {
7993 assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit");
7994 if (CMSTraceSweeper) {
7995 gclog_or_tty->print_cr("_limit " PTR_FORMAT " reached or crossed by block "
7996 "[" PTR_FORMAT "," PTR_FORMAT ") in space "
7997 "[" PTR_FORMAT "," PTR_FORMAT ")",
7998 _limit, fc, eob, _sp->bottom(), _sp->end());
7999 }
8000 // Return the storage we are tracking back into the free lists.
8001 if (CMSTraceSweeper) {
8002 gclog_or_tty->print_cr("Flushing ... ");
8003 }
8004 assert(freeFinger() < eob, "Error");
8005 flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger()));
8006 }
8007 }
8008
8009 void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) {
8010 assert(inFreeRange(), "Should only be called if currently in a free range.");
8011 assert(size > 0,
8012 "A zero sized chunk cannot be added to the free lists.");
8013 if (!freeRangeInFreeLists()) {
8014 if (CMSTestInFreeList) {
8015 FreeChunk* fc = (FreeChunk*) chunk;
8016 fc->set_size(size);
8017 assert(!_sp->verify_chunk_in_free_list(fc),
8018 "chunk should not be in free lists yet");
8019 }
8020 if (CMSTraceSweeper) {
8021 gclog_or_tty->print_cr(" -- add free block " PTR_FORMAT " (" SIZE_FORMAT ") to free lists",
8022 chunk, size);
8023 }
8024 // A new free range is going to be starting. The current
8025 // free range has not been added to the free lists yet or
8026 // was removed so add it back.
8027 // If the current free range was coalesced, then the death
8028 // of the free range was recorded. Record a birth now.
8029 if (lastFreeRangeCoalesced()) {
8030 _sp->coalBirth(size);
8031 }
8032 _sp->addChunkAndRepairOffsetTable(chunk, size,
8033 lastFreeRangeCoalesced());
8034 } else if (CMSTraceSweeper) {
8035 gclog_or_tty->print_cr("Already in free list: nothing to flush");
8036 }
8037 set_inFreeRange(false);
8038 set_freeRangeInFreeLists(false);
8039 }
8040
8041 // We take a break if we've been at this for a while,
8042 // so as to avoid monopolizing the locks involved.
8043 void SweepClosure::do_yield_work(HeapWord* addr) {
8044 // Return current free chunk being used for coalescing (if any)
8045 // to the appropriate freelist. After yielding, the next
8046 // free block encountered will start a coalescing range of
8047 // free blocks. If the next free block is adjacent to the
8048 // chunk just flushed, they will need to wait for the next
8049 // sweep to be coalesced.
8050 if (inFreeRange()) {
8051 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8052 }
8053
8054 // First give up the locks, then yield, then re-lock.
8055 // We should probably use a constructor/destructor idiom to
8056 // do this unlock/lock or modify the MutexUnlocker class to
8057 // serve our purpose. XXX
8058 assert_lock_strong(_bitMap->lock());
8059 assert_lock_strong(_freelistLock);
8060 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
8061 "CMS thread should hold CMS token");
8062 _bitMap->lock()->unlock();
8063 _freelistLock->unlock();
8064 ConcurrentMarkSweepThread::desynchronize(true);
8065 _collector->stopTimer();
8066 if (PrintCMSStatistics != 0) {
8067 _collector->incrementYields();
8068 }
8069
8070 // See the comment in coordinator_yield()
8071 for (unsigned i = 0; i < CMSYieldSleepCount &&
8072 ConcurrentMarkSweepThread::should_yield() &&
8073 !CMSCollector::foregroundGCIsActive(); ++i) {
8074 os::sleep(Thread::current(), 1, false);
8075 }
8076
8077 ConcurrentMarkSweepThread::synchronize(true);
8078 _freelistLock->lock();
8079 _bitMap->lock()->lock_without_safepoint_check();
8080 _collector->startTimer();
8081 }
8082
8083 #ifndef PRODUCT
8084 // This is actually very useful in a product build if it can
8085 // be called from the debugger. Compile it into the product
8086 // as needed.
8087 bool debug_verify_chunk_in_free_list(FreeChunk* fc) {
8088 return debug_cms_space->verify_chunk_in_free_list(fc);
8089 }
8090 #endif
8091
8092 void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const {
8093 if (CMSTraceSweeper) {
8094 gclog_or_tty->print_cr("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")",
8095 fc, fc->size());
8096 }
8097 }
8098
8099 // CMSIsAliveClosure
8100 bool CMSIsAliveClosure::do_object_b(oop obj) {
8101 HeapWord* addr = (HeapWord*)obj;
8102 return addr != NULL &&
8103 (!_span.contains(addr) || _bit_map->isMarked(addr));
8104 }
8105
8106
8107 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector,
8108 MemRegion span,
8109 CMSBitMap* bit_map, CMSMarkStack* mark_stack,
8110 bool cpc):
8111 _collector(collector),
8112 _span(span),
8113 _bit_map(bit_map),
8114 _mark_stack(mark_stack),
8115 _concurrent_precleaning(cpc) {
8116 assert(!_span.is_empty(), "Empty span could spell trouble");
8117 }
8118
8119
8120 // CMSKeepAliveClosure: the serial version
8121 void CMSKeepAliveClosure::do_oop(oop obj) {
8122 HeapWord* addr = (HeapWord*)obj;
8123 if (_span.contains(addr) &&
8124 !_bit_map->isMarked(addr)) {
8125 _bit_map->mark(addr);
8126 bool simulate_overflow = false;
8127 NOT_PRODUCT(
8128 if (CMSMarkStackOverflowALot &&
8129 _collector->simulate_overflow()) {
8130 // simulate a stack overflow
8131 simulate_overflow = true;
8132 }
8133 )
8134 if (simulate_overflow || !_mark_stack->push(obj)) {
8135 if (_concurrent_precleaning) {
8136 // We dirty the overflown object and let the remark
8137 // phase deal with it.
8138 assert(_collector->overflow_list_is_empty(), "Error");
8139 // In the case of object arrays, we need to dirty all of
8140 // the cards that the object spans. No locking or atomics
8141 // are needed since no one else can be mutating the mod union
8142 // table.
8143 if (obj->is_objArray()) {
8144 size_t sz = obj->size();
8145 HeapWord* end_card_addr =
8146 (HeapWord*)round_to((intptr_t)(addr+sz), CardTableModRefBS::card_size);
8147 MemRegion redirty_range = MemRegion(addr, end_card_addr);
8148 assert(!redirty_range.is_empty(), "Arithmetical tautology");
8149 _collector->_modUnionTable.mark_range(redirty_range);
8150 } else {
8151 _collector->_modUnionTable.mark(addr);
8152 }
8153 _collector->_ser_kac_preclean_ovflw++;
8154 } else {
8155 _collector->push_on_overflow_list(obj);
8156 _collector->_ser_kac_ovflw++;
8157 }
8158 }
8159 }
8160 }
8161
8162 void CMSKeepAliveClosure::do_oop(oop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8163 void CMSKeepAliveClosure::do_oop(narrowOop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8164
8165 // CMSParKeepAliveClosure: a parallel version of the above.
8166 // The work queues are private to each closure (thread),
8167 // but (may be) available for stealing by other threads.
8168 void CMSParKeepAliveClosure::do_oop(oop obj) {
8169 HeapWord* addr = (HeapWord*)obj;
8170 if (_span.contains(addr) &&
8171 !_bit_map->isMarked(addr)) {
8172 // In general, during recursive tracing, several threads
8173 // may be concurrently getting here; the first one to
8174 // "tag" it, claims it.
8175 if (_bit_map->par_mark(addr)) {
8176 bool res = _work_queue->push(obj);
8177 assert(res, "Low water mark should be much less than capacity");
8178 // Do a recursive trim in the hope that this will keep
8179 // stack usage lower, but leave some oops for potential stealers
8180 trim_queue(_low_water_mark);
8181 } // Else, another thread got there first
8182 }
8183 }
8184
8185 void CMSParKeepAliveClosure::do_oop(oop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8186 void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8187
8188 void CMSParKeepAliveClosure::trim_queue(uint max) {
8189 while (_work_queue->size() > max) {
8190 oop new_oop;
8191 if (_work_queue->pop_local(new_oop)) {
8192 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
8193 assert(_bit_map->isMarked((HeapWord*)new_oop),
8194 "no white objects on this stack!");
8195 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8196 // iterate over the oops in this oop, marking and pushing
8197 // the ones in CMS heap (i.e. in _span).
8198 new_oop->oop_iterate(&_mark_and_push);
8199 }
8200 }
8201 }
8202
8203 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
8204 CMSCollector* collector,
8205 MemRegion span, CMSBitMap* bit_map,
8206 OopTaskQueue* work_queue):
8207 _collector(collector),
8208 _span(span),
8209 _bit_map(bit_map),
8210 _work_queue(work_queue) { }
8211
8212 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
8213 HeapWord* addr = (HeapWord*)obj;
8214 if (_span.contains(addr) &&
8215 !_bit_map->isMarked(addr)) {
8216 if (_bit_map->par_mark(addr)) {
8217 bool simulate_overflow = false;
8218 NOT_PRODUCT(
8219 if (CMSMarkStackOverflowALot &&
8220 _collector->par_simulate_overflow()) {
8221 // simulate a stack overflow
8222 simulate_overflow = true;
8223 }
8224 )
8225 if (simulate_overflow || !_work_queue->push(obj)) {
8226 _collector->par_push_on_overflow_list(obj);
8227 _collector->_par_kac_ovflw++;
8228 }
8229 } // Else another thread got there already
8230 }
8231 }
8232
8233 void CMSInnerParMarkAndPushClosure::do_oop(oop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8234 void CMSInnerParMarkAndPushClosure::do_oop(narrowOop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8235
8236 //////////////////////////////////////////////////////////////////
8237 // CMSExpansionCause /////////////////////////////
8238 //////////////////////////////////////////////////////////////////
8239 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
8240 switch (cause) {
8241 case _no_expansion:
8242 return "No expansion";
8243 case _satisfy_free_ratio:
8244 return "Free ratio";
8245 case _satisfy_promotion:
8246 return "Satisfy promotion";
8247 case _satisfy_allocation:
8248 return "allocation";
8249 case _allocate_par_lab:
8250 return "Par LAB";
8251 case _allocate_par_spooling_space:
8252 return "Par Spooling Space";
8253 case _adaptive_size_policy:
8254 return "Ergonomics";
8255 default:
8256 return "unknown";
8257 }
8258 }
8259
8260 void CMSDrainMarkingStackClosure::do_void() {
8261 // the max number to take from overflow list at a time
8262 const size_t num = _mark_stack->capacity()/4;
8263 assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
8264 "Overflow list should be NULL during concurrent phases");
8265 while (!_mark_stack->isEmpty() ||
8266 // if stack is empty, check the overflow list
8267 _collector->take_from_overflow_list(num, _mark_stack)) {
8268 oop obj = _mark_stack->pop();
8269 HeapWord* addr = (HeapWord*)obj;
8270 assert(_span.contains(addr), "Should be within span");
8271 assert(_bit_map->isMarked(addr), "Should be marked");
8272 assert(obj->is_oop(), "Should be an oop");
8273 obj->oop_iterate(_keep_alive);
8274 }
8275 }
8276
8277 void CMSParDrainMarkingStackClosure::do_void() {
8278 // drain queue
8279 trim_queue(0);
8280 }
8281
8282 // Trim our work_queue so its length is below max at return
8283 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
8284 while (_work_queue->size() > max) {
8285 oop new_oop;
8286 if (_work_queue->pop_local(new_oop)) {
8287 assert(new_oop->is_oop(), "Expected an oop");
8288 assert(_bit_map->isMarked((HeapWord*)new_oop),
8289 "no white objects on this stack!");
8290 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8291 // iterate over the oops in this oop, marking and pushing
8292 // the ones in CMS heap (i.e. in _span).
8293 new_oop->oop_iterate(&_mark_and_push);
8294 }
8295 }
8296 }
8297
8298 ////////////////////////////////////////////////////////////////////
8299 // Support for Marking Stack Overflow list handling and related code
8300 ////////////////////////////////////////////////////////////////////
8301 // Much of the following code is similar in shape and spirit to the
8302 // code used in ParNewGC. We should try and share that code
8303 // as much as possible in the future.
8304
8305 #ifndef PRODUCT
8306 // Debugging support for CMSStackOverflowALot
8307
8308 // It's OK to call this multi-threaded; the worst thing
8309 // that can happen is that we'll get a bunch of closely
8310 // spaced simulated overflows, but that's OK, in fact
8311 // probably good as it would exercise the overflow code
8312 // under contention.
8313 bool CMSCollector::simulate_overflow() {
8314 if (_overflow_counter-- <= 0) { // just being defensive
8315 _overflow_counter = CMSMarkStackOverflowInterval;
8316 return true;
8317 } else {
8318 return false;
8319 }
8320 }
8321
8322 bool CMSCollector::par_simulate_overflow() {
8323 return simulate_overflow();
8324 }
8325 #endif
8326
8327 // Single-threaded
8328 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
8329 assert(stack->isEmpty(), "Expected precondition");
8330 assert(stack->capacity() > num, "Shouldn't bite more than can chew");
8331 size_t i = num;
8332 oop cur = _overflow_list;
8333 const markOop proto = markOopDesc::prototype();
8334 NOT_PRODUCT(ssize_t n = 0;)
8335 for (oop next; i > 0 && cur != NULL; cur = next, i--) {
8336 next = oop(cur->mark());
8337 cur->set_mark(proto); // until proven otherwise
8338 assert(cur->is_oop(), "Should be an oop");
8339 bool res = stack->push(cur);
8340 assert(res, "Bit off more than can chew?");
8341 NOT_PRODUCT(n++;)
8342 }
8343 _overflow_list = cur;
8344 #ifndef PRODUCT
8345 assert(_num_par_pushes >= n, "Too many pops?");
8346 _num_par_pushes -=n;
8347 #endif
8348 return !stack->isEmpty();
8349 }
8350
8351 #define BUSY (cast_to_oop<intptr_t>(0x1aff1aff))
8352 // (MT-safe) Get a prefix of at most "num" from the list.
8353 // The overflow list is chained through the mark word of
8354 // each object in the list. We fetch the entire list,
8355 // break off a prefix of the right size and return the
8356 // remainder. If other threads try to take objects from
8357 // the overflow list at that time, they will wait for
8358 // some time to see if data becomes available. If (and
8359 // only if) another thread places one or more object(s)
8360 // on the global list before we have returned the suffix
8361 // to the global list, we will walk down our local list
8362 // to find its end and append the global list to
8363 // our suffix before returning it. This suffix walk can
8364 // prove to be expensive (quadratic in the amount of traffic)
8365 // when there are many objects in the overflow list and
8366 // there is much producer-consumer contention on the list.
8367 // *NOTE*: The overflow list manipulation code here and
8368 // in ParNewGeneration:: are very similar in shape,
8369 // except that in the ParNew case we use the old (from/eden)
8370 // copy of the object to thread the list via its klass word.
8371 // Because of the common code, if you make any changes in
8372 // the code below, please check the ParNew version to see if
8373 // similar changes might be needed.
8374 // CR 6797058 has been filed to consolidate the common code.
8375 bool CMSCollector::par_take_from_overflow_list(size_t num,
8376 OopTaskQueue* work_q,
8377 int no_of_gc_threads) {
8378 assert(work_q->size() == 0, "First empty local work queue");
8379 assert(num < work_q->max_elems(), "Can't bite more than we can chew");
8380 if (_overflow_list == NULL) {
8381 return false;
8382 }
8383 // Grab the entire list; we'll put back a suffix
8384 oop prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
8385 Thread* tid = Thread::current();
8386 // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was
8387 // set to ParallelGCThreads.
8388 size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads;
8389 size_t sleep_time_millis = MAX2((size_t)1, num/100);
8390 // If the list is busy, we spin for a short while,
8391 // sleeping between attempts to get the list.
8392 for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) {
8393 os::sleep(tid, sleep_time_millis, false);
8394 if (_overflow_list == NULL) {
8395 // Nothing left to take
8396 return false;
8397 } else if (_overflow_list != BUSY) {
8398 // Try and grab the prefix
8399 prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
8400 }
8401 }
8402 // If the list was found to be empty, or we spun long
8403 // enough, we give up and return empty-handed. If we leave
8404 // the list in the BUSY state below, it must be the case that
8405 // some other thread holds the overflow list and will set it
8406 // to a non-BUSY state in the future.
8407 if (prefix == NULL || prefix == BUSY) {
8408 // Nothing to take or waited long enough
8409 if (prefix == NULL) {
8410 // Write back the NULL in case we overwrote it with BUSY above
8411 // and it is still the same value.
8412 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8413 }
8414 return false;
8415 }
8416 assert(prefix != NULL && prefix != BUSY, "Error");
8417 size_t i = num;
8418 oop cur = prefix;
8419 // Walk down the first "num" objects, unless we reach the end.
8420 for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--);
8421 if (cur->mark() == NULL) {
8422 // We have "num" or fewer elements in the list, so there
8423 // is nothing to return to the global list.
8424 // Write back the NULL in lieu of the BUSY we wrote
8425 // above, if it is still the same value.
8426 if (_overflow_list == BUSY) {
8427 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8428 }
8429 } else {
8430 // Chop off the suffix and return it to the global list.
8431 assert(cur->mark() != BUSY, "Error");
8432 oop suffix_head = cur->mark(); // suffix will be put back on global list
8433 cur->set_mark(NULL); // break off suffix
8434 // It's possible that the list is still in the empty(busy) state
8435 // we left it in a short while ago; in that case we may be
8436 // able to place back the suffix without incurring the cost
8437 // of a walk down the list.
8438 oop observed_overflow_list = _overflow_list;
8439 oop cur_overflow_list = observed_overflow_list;
8440 bool attached = false;
8441 while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
8442 observed_overflow_list =
8443 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
8444 if (cur_overflow_list == observed_overflow_list) {
8445 attached = true;
8446 break;
8447 } else cur_overflow_list = observed_overflow_list;
8448 }
8449 if (!attached) {
8450 // Too bad, someone else sneaked in (at least) an element; we'll need
8451 // to do a splice. Find tail of suffix so we can prepend suffix to global
8452 // list.
8453 for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark()));
8454 oop suffix_tail = cur;
8455 assert(suffix_tail != NULL && suffix_tail->mark() == NULL,
8456 "Tautology");
8457 observed_overflow_list = _overflow_list;
8458 do {
8459 cur_overflow_list = observed_overflow_list;
8460 if (cur_overflow_list != BUSY) {
8461 // Do the splice ...
8462 suffix_tail->set_mark(markOop(cur_overflow_list));
8463 } else { // cur_overflow_list == BUSY
8464 suffix_tail->set_mark(NULL);
8465 }
8466 // ... and try to place spliced list back on overflow_list ...
8467 observed_overflow_list =
8468 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
8469 } while (cur_overflow_list != observed_overflow_list);
8470 // ... until we have succeeded in doing so.
8471 }
8472 }
8473
8474 // Push the prefix elements on work_q
8475 assert(prefix != NULL, "control point invariant");
8476 const markOop proto = markOopDesc::prototype();
8477 oop next;
8478 NOT_PRODUCT(ssize_t n = 0;)
8479 for (cur = prefix; cur != NULL; cur = next) {
8480 next = oop(cur->mark());
8481 cur->set_mark(proto); // until proven otherwise
8482 assert(cur->is_oop(), "Should be an oop");
8483 bool res = work_q->push(cur);
8484 assert(res, "Bit off more than we can chew?");
8485 NOT_PRODUCT(n++;)
8486 }
8487 #ifndef PRODUCT
8488 assert(_num_par_pushes >= n, "Too many pops?");
8489 Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
8490 #endif
8491 return true;
8492 }
8493
8494 // Single-threaded
8495 void CMSCollector::push_on_overflow_list(oop p) {
8496 NOT_PRODUCT(_num_par_pushes++;)
8497 assert(p->is_oop(), "Not an oop");
8498 preserve_mark_if_necessary(p);
8499 p->set_mark((markOop)_overflow_list);
8500 _overflow_list = p;
8501 }
8502
8503 // Multi-threaded; use CAS to prepend to overflow list
8504 void CMSCollector::par_push_on_overflow_list(oop p) {
8505 NOT_PRODUCT(Atomic::inc_ptr(&_num_par_pushes);)
8506 assert(p->is_oop(), "Not an oop");
8507 par_preserve_mark_if_necessary(p);
8508 oop observed_overflow_list = _overflow_list;
8509 oop cur_overflow_list;
8510 do {
8511 cur_overflow_list = observed_overflow_list;
8512 if (cur_overflow_list != BUSY) {
8513 p->set_mark(markOop(cur_overflow_list));
8514 } else {
8515 p->set_mark(NULL);
8516 }
8517 observed_overflow_list =
8518 (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list);
8519 } while (cur_overflow_list != observed_overflow_list);
8520 }
8521 #undef BUSY
8522
8523 // Single threaded
8524 // General Note on GrowableArray: pushes may silently fail
8525 // because we are (temporarily) out of C-heap for expanding
8526 // the stack. The problem is quite ubiquitous and affects
8527 // a lot of code in the JVM. The prudent thing for GrowableArray
8528 // to do (for now) is to exit with an error. However, that may
8529 // be too draconian in some cases because the caller may be
8530 // able to recover without much harm. For such cases, we
8531 // should probably introduce a "soft_push" method which returns
8532 // an indication of success or failure with the assumption that
8533 // the caller may be able to recover from a failure; code in
8534 // the VM can then be changed, incrementally, to deal with such
8535 // failures where possible, thus, incrementally hardening the VM
8536 // in such low resource situations.
8537 void CMSCollector::preserve_mark_work(oop p, markOop m) {
8538 _preserved_oop_stack.push(p);
8539 _preserved_mark_stack.push(m);
8540 assert(m == p->mark(), "Mark word changed");
8541 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8542 "bijection");
8543 }
8544
8545 // Single threaded
8546 void CMSCollector::preserve_mark_if_necessary(oop p) {
8547 markOop m = p->mark();
8548 if (m->must_be_preserved(p)) {
8549 preserve_mark_work(p, m);
8550 }
8551 }
8552
8553 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
8554 markOop m = p->mark();
8555 if (m->must_be_preserved(p)) {
8556 MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
8557 // Even though we read the mark word without holding
8558 // the lock, we are assured that it will not change
8559 // because we "own" this oop, so no other thread can
8560 // be trying to push it on the overflow list; see
8561 // the assertion in preserve_mark_work() that checks
8562 // that m == p->mark().
8563 preserve_mark_work(p, m);
8564 }
8565 }
8566
8567 // We should be able to do this multi-threaded,
8568 // a chunk of stack being a task (this is
8569 // correct because each oop only ever appears
8570 // once in the overflow list. However, it's
8571 // not very easy to completely overlap this with
8572 // other operations, so will generally not be done
8573 // until all work's been completed. Because we
8574 // expect the preserved oop stack (set) to be small,
8575 // it's probably fine to do this single-threaded.
8576 // We can explore cleverer concurrent/overlapped/parallel
8577 // processing of preserved marks if we feel the
8578 // need for this in the future. Stack overflow should
8579 // be so rare in practice and, when it happens, its
8580 // effect on performance so great that this will
8581 // likely just be in the noise anyway.
8582 void CMSCollector::restore_preserved_marks_if_any() {
8583 assert(SafepointSynchronize::is_at_safepoint(),
8584 "world should be stopped");
8585 assert(Thread::current()->is_ConcurrentGC_thread() ||
8586 Thread::current()->is_VM_thread(),
8587 "should be single-threaded");
8588 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8589 "bijection");
8590
8591 while (!_preserved_oop_stack.is_empty()) {
8592 oop p = _preserved_oop_stack.pop();
8593 assert(p->is_oop(), "Should be an oop");
8594 assert(_span.contains(p), "oop should be in _span");
8595 assert(p->mark() == markOopDesc::prototype(),
8596 "Set when taken from overflow list");
8597 markOop m = _preserved_mark_stack.pop();
8598 p->set_mark(m);
8599 }
8600 assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(),
8601 "stacks were cleared above");
8602 }
8603
8604 #ifndef PRODUCT
8605 bool CMSCollector::no_preserved_marks() const {
8606 return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty();
8607 }
8608 #endif
8609
8610 // Transfer some number of overflown objects to usual marking
8611 // stack. Return true if some objects were transferred.
8612 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
8613 size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,
8614 (size_t)ParGCDesiredObjsFromOverflowList);
8615
8616 bool res = _collector->take_from_overflow_list(num, _mark_stack);
8617 assert(_collector->overflow_list_is_empty() || res,
8618 "If list is not empty, we should have taken something");
8619 assert(!res || !_mark_stack->isEmpty(),
8620 "If we took something, it should now be on our stack");
8621 return res;
8622 }
8623
8624 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
8625 size_t res = _sp->block_size_no_stall(addr, _collector);
8626 if (_sp->block_is_obj(addr)) {
8627 if (_live_bit_map->isMarked(addr)) {
8628 // It can't have been dead in a previous cycle
8629 guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
8630 } else {
8631 _dead_bit_map->mark(addr); // mark the dead object
8632 }
8633 }
8634 // Could be 0, if the block size could not be computed without stalling.
8635 return res;
8636 }
8637
8638 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() {
8639
8640 switch (phase) {
8641 case CMSCollector::InitialMarking:
8642 initialize(true /* fullGC */ ,
8643 cause /* cause of the GC */,
8644 true /* recordGCBeginTime */,
8645 true /* recordPreGCUsage */,
8646 false /* recordPeakUsage */,
8647 false /* recordPostGCusage */,
8648 true /* recordAccumulatedGCTime */,
8649 false /* recordGCEndTime */,
8650 false /* countCollection */ );
8651 break;
8652
8653 case CMSCollector::FinalMarking:
8654 initialize(true /* fullGC */ ,
8655 cause /* cause of the GC */,
8656 false /* recordGCBeginTime */,
8657 false /* recordPreGCUsage */,
8658 false /* recordPeakUsage */,
8659 false /* recordPostGCusage */,
8660 true /* recordAccumulatedGCTime */,
8661 false /* recordGCEndTime */,
8662 false /* countCollection */ );
8663 break;
8664
8665 case CMSCollector::Sweeping:
8666 initialize(true /* fullGC */ ,
8667 cause /* cause of the GC */,
8668 false /* recordGCBeginTime */,
8669 false /* recordPreGCUsage */,
8670 true /* recordPeakUsage */,
8671 true /* recordPostGCusage */,
8672 false /* recordAccumulatedGCTime */,
8673 true /* recordGCEndTime */,
8674 true /* countCollection */ );
8675 break;
8676
8677 default:
8678 ShouldNotReachHere();
8679 }
8680 }