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/cardGeneration.inline.hpp"
46 #include "memory/cardTableRS.hpp"
47 #include "memory/collectorPolicy.hpp"
48 #include "memory/gcLocker.inline.hpp"
49 #include "memory/genCollectedHeap.hpp"
50 #include "memory/genMarkSweep.hpp"
51 #include "memory/genOopClosures.inline.hpp"
52 #include "memory/iterator.inline.hpp"
53 #include "memory/padded.hpp"
54 #include "memory/referencePolicy.hpp"
55 #include "memory/resourceArea.hpp"
56 #include "memory/tenuredGeneration.hpp"
57 #include "oops/oop.inline.hpp"
58 #include "prims/jvmtiExport.hpp"
59 #include "runtime/atomic.inline.hpp"
60 #include "runtime/globals_extension.hpp"
61 #include "runtime/handles.inline.hpp"
62 #include "runtime/java.hpp"
63 #include "runtime/orderAccess.inline.hpp"
64 #include "runtime/vmThread.hpp"
65 #include "services/memoryService.hpp"
66 #include "services/runtimeService.hpp"
67
68 PRAGMA_FORMAT_MUTE_WARNINGS_FOR_GCC
69
70 // statics
71 CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL;
72 bool CMSCollector::_full_gc_requested = false;
73 GCCause::Cause CMSCollector::_full_gc_cause = GCCause::_no_gc;
74
75 //////////////////////////////////////////////////////////////////
76 // In support of CMS/VM thread synchronization
77 //////////////////////////////////////////////////////////////////
78 // We split use of the CGC_lock into 2 "levels".
79 // The low-level locking is of the usual CGC_lock monitor. We introduce
80 // a higher level "token" (hereafter "CMS token") built on top of the
81 // low level monitor (hereafter "CGC lock").
82 // The token-passing protocol gives priority to the VM thread. The
83 // CMS-lock doesn't provide any fairness guarantees, but clients
84 // should ensure that it is only held for very short, bounded
85 // durations.
86 //
87 // When either of the CMS thread or the VM thread is involved in
88 // collection operations during which it does not want the other
89 // thread to interfere, it obtains the CMS token.
90 //
91 // If either thread tries to get the token while the other has
92 // it, that thread waits. However, if the VM thread and CMS thread
93 // both want the token, then the VM thread gets priority while the
94 // CMS thread waits. This ensures, for instance, that the "concurrent"
95 // phases of the CMS thread's work do not block out the VM thread
96 // for long periods of time as the CMS thread continues to hog
97 // the token. (See bug 4616232).
98 //
99 // The baton-passing functions are, however, controlled by the
100 // flags _foregroundGCShouldWait and _foregroundGCIsActive,
101 // and here the low-level CMS lock, not the high level token,
102 // ensures mutual exclusion.
103 //
104 // Two important conditions that we have to satisfy:
105 // 1. if a thread does a low-level wait on the CMS lock, then it
106 // relinquishes the CMS token if it were holding that token
107 // when it acquired the low-level CMS lock.
108 // 2. any low-level notifications on the low-level lock
109 // should only be sent when a thread has relinquished the token.
110 //
111 // In the absence of either property, we'd have potential deadlock.
112 //
113 // We protect each of the CMS (concurrent and sequential) phases
114 // with the CMS _token_, not the CMS _lock_.
115 //
116 // The only code protected by CMS lock is the token acquisition code
117 // itself, see ConcurrentMarkSweepThread::[de]synchronize(), and the
118 // baton-passing code.
119 //
120 // Unfortunately, i couldn't come up with a good abstraction to factor and
121 // hide the naked CGC_lock manipulation in the baton-passing code
122 // further below. That's something we should try to do. Also, the proof
123 // of correctness of this 2-level locking scheme is far from obvious,
124 // and potentially quite slippery. We have an uneasy suspicion, for instance,
125 // that there may be a theoretical possibility of delay/starvation in the
126 // low-level lock/wait/notify scheme used for the baton-passing because of
127 // potential interference with the priority scheme embodied in the
128 // CMS-token-passing protocol. See related comments at a CGC_lock->wait()
129 // invocation further below and marked with "XXX 20011219YSR".
130 // Indeed, as we note elsewhere, this may become yet more slippery
131 // in the presence of multiple CMS and/or multiple VM threads. XXX
132
133 class CMSTokenSync: public StackObj {
134 private:
135 bool _is_cms_thread;
136 public:
137 CMSTokenSync(bool is_cms_thread):
138 _is_cms_thread(is_cms_thread) {
139 assert(is_cms_thread == Thread::current()->is_ConcurrentGC_thread(),
140 "Incorrect argument to constructor");
141 ConcurrentMarkSweepThread::synchronize(_is_cms_thread);
142 }
143
144 ~CMSTokenSync() {
145 assert(_is_cms_thread ?
146 ConcurrentMarkSweepThread::cms_thread_has_cms_token() :
147 ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
148 "Incorrect state");
149 ConcurrentMarkSweepThread::desynchronize(_is_cms_thread);
150 }
151 };
152
153 // Convenience class that does a CMSTokenSync, and then acquires
154 // upto three locks.
155 class CMSTokenSyncWithLocks: public CMSTokenSync {
156 private:
157 // Note: locks are acquired in textual declaration order
158 // and released in the opposite order
159 MutexLockerEx _locker1, _locker2, _locker3;
160 public:
161 CMSTokenSyncWithLocks(bool is_cms_thread, Mutex* mutex1,
162 Mutex* mutex2 = NULL, Mutex* mutex3 = NULL):
163 CMSTokenSync(is_cms_thread),
164 _locker1(mutex1, Mutex::_no_safepoint_check_flag),
165 _locker2(mutex2, Mutex::_no_safepoint_check_flag),
166 _locker3(mutex3, Mutex::_no_safepoint_check_flag)
167 { }
168 };
169
170
171 //////////////////////////////////////////////////////////////////
172 // Concurrent Mark-Sweep Generation /////////////////////////////
173 //////////////////////////////////////////////////////////////////
174
175 NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;)
176
177 // This struct contains per-thread things necessary to support parallel
178 // young-gen collection.
179 class CMSParGCThreadState: public CHeapObj<mtGC> {
180 public:
181 CFLS_LAB lab;
182 PromotionInfo promo;
183
184 // Constructor.
185 CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) {
186 promo.setSpace(cfls);
187 }
188 };
189
190 ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration(
191 ReservedSpace rs, size_t initial_byte_size, int level,
192 CardTableRS* ct, bool use_adaptive_freelists,
193 FreeBlockDictionary<FreeChunk>::DictionaryChoice dictionaryChoice) :
194 CardGeneration(rs, initial_byte_size, level, ct),
195 _dilatation_factor(((double)MinChunkSize)/((double)(CollectedHeap::min_fill_size()))),
196 _did_compact(false)
197 {
198 HeapWord* bottom = (HeapWord*) _virtual_space.low();
199 HeapWord* end = (HeapWord*) _virtual_space.high();
200
201 _direct_allocated_words = 0;
202 NOT_PRODUCT(
203 _numObjectsPromoted = 0;
204 _numWordsPromoted = 0;
205 _numObjectsAllocated = 0;
206 _numWordsAllocated = 0;
207 )
208
209 _cmsSpace = new CompactibleFreeListSpace(_bts, MemRegion(bottom, end),
210 use_adaptive_freelists,
211 dictionaryChoice);
212 NOT_PRODUCT(debug_cms_space = _cmsSpace;)
213 if (_cmsSpace == NULL) {
214 vm_exit_during_initialization(
215 "CompactibleFreeListSpace allocation failure");
216 }
217 _cmsSpace->_gen = this;
218
219 _gc_stats = new CMSGCStats();
220
221 // Verify the assumption that FreeChunk::_prev and OopDesc::_klass
222 // offsets match. The ability to tell free chunks from objects
223 // depends on this property.
224 debug_only(
225 FreeChunk* junk = NULL;
226 assert(UseCompressedClassPointers ||
227 junk->prev_addr() == (void*)(oop(junk)->klass_addr()),
228 "Offset of FreeChunk::_prev within FreeChunk must match"
229 " that of OopDesc::_klass within OopDesc");
230 )
231 if (CollectedHeap::use_parallel_gc_threads()) {
232 typedef CMSParGCThreadState* CMSParGCThreadStatePtr;
233 _par_gc_thread_states =
234 NEW_C_HEAP_ARRAY(CMSParGCThreadStatePtr, ParallelGCThreads, mtGC);
235 if (_par_gc_thread_states == NULL) {
236 vm_exit_during_initialization("Could not allocate par gc structs");
237 }
238 for (uint i = 0; i < ParallelGCThreads; i++) {
239 _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace());
240 if (_par_gc_thread_states[i] == NULL) {
241 vm_exit_during_initialization("Could not allocate par gc structs");
242 }
243 }
244 } else {
245 _par_gc_thread_states = NULL;
246 }
247 _incremental_collection_failed = false;
248 // The "dilatation_factor" is the expansion that can occur on
249 // account of the fact that the minimum object size in the CMS
250 // generation may be larger than that in, say, a contiguous young
251 // generation.
252 // Ideally, in the calculation below, we'd compute the dilatation
253 // factor as: MinChunkSize/(promoting_gen's min object size)
254 // Since we do not have such a general query interface for the
255 // promoting generation, we'll instead just use the minimum
256 // object size (which today is a header's worth of space);
257 // note that all arithmetic is in units of HeapWords.
258 assert(MinChunkSize >= CollectedHeap::min_fill_size(), "just checking");
259 assert(_dilatation_factor >= 1.0, "from previous assert");
260 }
261
262
263 // The field "_initiating_occupancy" represents the occupancy percentage
264 // at which we trigger a new collection cycle. Unless explicitly specified
265 // via CMSInitiatingOccupancyFraction (argument "io" below), it
266 // is calculated by:
267 //
268 // Let "f" be MinHeapFreeRatio in
269 //
270 // _initiating_occupancy = 100-f +
271 // f * (CMSTriggerRatio/100)
272 // where CMSTriggerRatio is the argument "tr" below.
273 //
274 // That is, if we assume the heap is at its desired maximum occupancy at the
275 // end of a collection, we let CMSTriggerRatio of the (purported) free
276 // space be allocated before initiating a new collection cycle.
277 //
278 void ConcurrentMarkSweepGeneration::init_initiating_occupancy(intx io, uintx tr) {
279 assert(io <= 100 && tr <= 100, "Check the arguments");
280 if (io >= 0) {
281 _initiating_occupancy = (double)io / 100.0;
282 } else {
283 _initiating_occupancy = ((100 - MinHeapFreeRatio) +
284 (double)(tr * MinHeapFreeRatio) / 100.0)
285 / 100.0;
286 }
287 }
288
289 void ConcurrentMarkSweepGeneration::ref_processor_init() {
290 assert(collector() != NULL, "no collector");
291 collector()->ref_processor_init();
292 }
293
294 void CMSCollector::ref_processor_init() {
295 if (_ref_processor == NULL) {
296 // Allocate and initialize a reference processor
297 _ref_processor =
298 new ReferenceProcessor(_span, // span
299 (ParallelGCThreads > 1) && ParallelRefProcEnabled, // mt processing
300 (int) ParallelGCThreads, // mt processing degree
301 _cmsGen->refs_discovery_is_mt(), // mt discovery
302 (int) MAX2(ConcGCThreads, ParallelGCThreads), // mt discovery degree
303 _cmsGen->refs_discovery_is_atomic(), // discovery is not atomic
304 &_is_alive_closure); // closure for liveness info
305 // Initialize the _ref_processor field of CMSGen
306 _cmsGen->set_ref_processor(_ref_processor);
307
308 }
309 }
310
311 AdaptiveSizePolicy* CMSCollector::size_policy() {
312 GenCollectedHeap* gch = GenCollectedHeap::heap();
313 assert(gch->kind() == CollectedHeap::GenCollectedHeap,
314 "Wrong type of heap");
315 return gch->gen_policy()->size_policy();
316 }
317
318 void ConcurrentMarkSweepGeneration::initialize_performance_counters() {
319
320 const char* gen_name = "old";
321 GenCollectorPolicy* gcp = (GenCollectorPolicy*) GenCollectedHeap::heap()->collector_policy();
322
323 // Generation Counters - generation 1, 1 subspace
324 _gen_counters = new GenerationCounters(gen_name, 1, 1,
325 gcp->min_old_size(), gcp->max_old_size(), &_virtual_space);
326
327 _space_counters = new GSpaceCounters(gen_name, 0,
328 _virtual_space.reserved_size(),
329 this, _gen_counters);
330 }
331
332 CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha):
333 _cms_gen(cms_gen)
334 {
335 assert(alpha <= 100, "bad value");
336 _saved_alpha = alpha;
337
338 // Initialize the alphas to the bootstrap value of 100.
339 _gc0_alpha = _cms_alpha = 100;
340
341 _cms_begin_time.update();
342 _cms_end_time.update();
343
344 _gc0_duration = 0.0;
345 _gc0_period = 0.0;
346 _gc0_promoted = 0;
347
348 _cms_duration = 0.0;
349 _cms_period = 0.0;
350 _cms_allocated = 0;
351
352 _cms_used_at_gc0_begin = 0;
353 _cms_used_at_gc0_end = 0;
354 _allow_duty_cycle_reduction = false;
355 _valid_bits = 0;
356 }
357
358 double CMSStats::cms_free_adjustment_factor(size_t free) const {
359 // TBD: CR 6909490
360 return 1.0;
361 }
362
363 void CMSStats::adjust_cms_free_adjustment_factor(bool fail, size_t free) {
364 }
365
366 // If promotion failure handling is on use
367 // the padded average size of the promotion for each
368 // young generation collection.
369 double CMSStats::time_until_cms_gen_full() const {
370 size_t cms_free = _cms_gen->cmsSpace()->free();
371 GenCollectedHeap* gch = GenCollectedHeap::heap();
372 size_t expected_promotion = MIN2(gch->get_gen(0)->capacity(),
373 (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average());
374 if (cms_free > expected_promotion) {
375 // Start a cms collection if there isn't enough space to promote
376 // for the next minor collection. Use the padded average as
377 // a safety factor.
378 cms_free -= expected_promotion;
379
380 // Adjust by the safety factor.
381 double cms_free_dbl = (double)cms_free;
382 double cms_adjustment = (100.0 - CMSIncrementalSafetyFactor)/100.0;
383 // Apply a further correction factor which tries to adjust
384 // for recent occurance of concurrent mode failures.
385 cms_adjustment = cms_adjustment * cms_free_adjustment_factor(cms_free);
386 cms_free_dbl = cms_free_dbl * cms_adjustment;
387
388 if (PrintGCDetails && Verbose) {
389 gclog_or_tty->print_cr("CMSStats::time_until_cms_gen_full: cms_free "
390 SIZE_FORMAT " expected_promotion " SIZE_FORMAT,
391 cms_free, expected_promotion);
392 gclog_or_tty->print_cr(" cms_free_dbl %f cms_consumption_rate %f",
393 cms_free_dbl, cms_consumption_rate() + 1.0);
394 }
395 // Add 1 in case the consumption rate goes to zero.
396 return cms_free_dbl / (cms_consumption_rate() + 1.0);
397 }
398 return 0.0;
399 }
400
401 // Compare the duration of the cms collection to the
402 // time remaining before the cms generation is empty.
403 // Note that the time from the start of the cms collection
404 // to the start of the cms sweep (less than the total
405 // duration of the cms collection) can be used. This
406 // has been tried and some applications experienced
407 // promotion failures early in execution. This was
408 // possibly because the averages were not accurate
409 // enough at the beginning.
410 double CMSStats::time_until_cms_start() const {
411 // We add "gc0_period" to the "work" calculation
412 // below because this query is done (mostly) at the
413 // end of a scavenge, so we need to conservatively
414 // account for that much possible delay
415 // in the query so as to avoid concurrent mode failures
416 // due to starting the collection just a wee bit too
417 // late.
418 double work = cms_duration() + gc0_period();
419 double deadline = time_until_cms_gen_full();
420 // If a concurrent mode failure occurred recently, we want to be
421 // more conservative and halve our expected time_until_cms_gen_full()
422 if (work > deadline) {
423 if (Verbose && PrintGCDetails) {
424 gclog_or_tty->print(
425 " CMSCollector: collect because of anticipated promotion "
426 "before full %3.7f + %3.7f > %3.7f ", cms_duration(),
427 gc0_period(), time_until_cms_gen_full());
428 }
429 return 0.0;
430 }
431 return work - deadline;
432 }
433
434 #ifndef PRODUCT
435 void CMSStats::print_on(outputStream *st) const {
436 st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha);
437 st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo=" SIZE_FORMAT,
438 gc0_duration(), gc0_period(), gc0_promoted());
439 st->print(",cms_dur=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT,
440 cms_duration(), cms_period(), cms_allocated());
441 st->print(",cms_since_beg=%g,cms_since_end=%g",
442 cms_time_since_begin(), cms_time_since_end());
443 st->print(",cms_used_beg=" SIZE_FORMAT ",cms_used_end=" SIZE_FORMAT,
444 _cms_used_at_gc0_begin, _cms_used_at_gc0_end);
445
446 if (valid()) {
447 st->print(",promo_rate=%g,cms_alloc_rate=%g",
448 promotion_rate(), cms_allocation_rate());
449 st->print(",cms_consumption_rate=%g,time_until_full=%g",
450 cms_consumption_rate(), time_until_cms_gen_full());
451 }
452 st->print(" ");
453 }
454 #endif // #ifndef PRODUCT
455
456 CMSCollector::CollectorState CMSCollector::_collectorState =
457 CMSCollector::Idling;
458 bool CMSCollector::_foregroundGCIsActive = false;
459 bool CMSCollector::_foregroundGCShouldWait = false;
460
461 CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
462 CardTableRS* ct,
463 ConcurrentMarkSweepPolicy* cp):
464 _cmsGen(cmsGen),
465 _ct(ct),
466 _ref_processor(NULL), // will be set later
467 _conc_workers(NULL), // may be set later
468 _abort_preclean(false),
469 _start_sampling(false),
470 _between_prologue_and_epilogue(false),
471 _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"),
472 _modUnionTable((CardTableModRefBS::card_shift - LogHeapWordSize),
473 -1 /* lock-free */, "No_lock" /* dummy */),
474 _modUnionClosure(&_modUnionTable),
475 _modUnionClosurePar(&_modUnionTable),
476 // Adjust my span to cover old (cms) gen
477 _span(cmsGen->reserved()),
478 // Construct the is_alive_closure with _span & markBitMap
479 _is_alive_closure(_span, &_markBitMap),
480 _restart_addr(NULL),
481 _overflow_list(NULL),
482 _stats(cmsGen),
483 _eden_chunk_lock(new Mutex(Mutex::leaf + 1, "CMS_eden_chunk_lock", true,
484 //verify that this lock should be acquired with safepoint check.
485 Monitor::_safepoint_check_sometimes)),
486 _eden_chunk_array(NULL), // may be set in ctor body
487 _eden_chunk_capacity(0), // -- ditto --
488 _eden_chunk_index(0), // -- ditto --
489 _survivor_plab_array(NULL), // -- ditto --
490 _survivor_chunk_array(NULL), // -- ditto --
491 _survivor_chunk_capacity(0), // -- ditto --
492 _survivor_chunk_index(0), // -- ditto --
493 _ser_pmc_preclean_ovflw(0),
494 _ser_kac_preclean_ovflw(0),
495 _ser_pmc_remark_ovflw(0),
496 _par_pmc_remark_ovflw(0),
497 _ser_kac_ovflw(0),
498 _par_kac_ovflw(0),
499 #ifndef PRODUCT
500 _num_par_pushes(0),
501 #endif
502 _collection_count_start(0),
503 _verifying(false),
504 _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"),
505 _completed_initialization(false),
506 _collector_policy(cp),
507 _should_unload_classes(CMSClassUnloadingEnabled),
508 _concurrent_cycles_since_last_unload(0),
509 _roots_scanning_options(SharedHeap::SO_None),
510 _inter_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
511 _intra_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
512 _gc_tracer_cm(new (ResourceObj::C_HEAP, mtGC) CMSTracer()),
513 _gc_timer_cm(new (ResourceObj::C_HEAP, mtGC) ConcurrentGCTimer()),
514 _cms_start_registered(false)
515 {
516 if (ExplicitGCInvokesConcurrentAndUnloadsClasses) {
517 ExplicitGCInvokesConcurrent = true;
518 }
519 // Now expand the span and allocate the collection support structures
520 // (MUT, marking bit map etc.) to cover both generations subject to
521 // collection.
522
523 // For use by dirty card to oop closures.
524 _cmsGen->cmsSpace()->set_collector(this);
525
526 // Allocate MUT and marking bit map
527 {
528 MutexLockerEx x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag);
529 if (!_markBitMap.allocate(_span)) {
530 warning("Failed to allocate CMS Bit Map");
531 return;
532 }
533 assert(_markBitMap.covers(_span), "_markBitMap inconsistency?");
534 }
535 {
536 _modUnionTable.allocate(_span);
537 assert(_modUnionTable.covers(_span), "_modUnionTable inconsistency?");
538 }
539
540 if (!_markStack.allocate(MarkStackSize)) {
541 warning("Failed to allocate CMS Marking Stack");
542 return;
543 }
544
545 // Support for multi-threaded concurrent phases
546 if (CMSConcurrentMTEnabled) {
547 if (FLAG_IS_DEFAULT(ConcGCThreads)) {
548 // just for now
549 FLAG_SET_DEFAULT(ConcGCThreads, (ParallelGCThreads + 3)/4);
550 }
551 if (ConcGCThreads > 1) {
552 _conc_workers = new YieldingFlexibleWorkGang("Parallel CMS Threads",
553 ConcGCThreads, true);
554 if (_conc_workers == NULL) {
555 warning("GC/CMS: _conc_workers allocation failure: "
556 "forcing -CMSConcurrentMTEnabled");
557 CMSConcurrentMTEnabled = false;
558 } else {
559 _conc_workers->initialize_workers();
560 }
561 } else {
562 CMSConcurrentMTEnabled = false;
563 }
564 }
565 if (!CMSConcurrentMTEnabled) {
566 ConcGCThreads = 0;
567 } else {
568 // Turn off CMSCleanOnEnter optimization temporarily for
569 // the MT case where it's not fixed yet; see 6178663.
570 CMSCleanOnEnter = false;
571 }
572 assert((_conc_workers != NULL) == (ConcGCThreads > 1),
573 "Inconsistency");
574
575 // Parallel task queues; these are shared for the
576 // concurrent and stop-world phases of CMS, but
577 // are not shared with parallel scavenge (ParNew).
578 {
579 uint i;
580 uint num_queues = (uint) MAX2(ParallelGCThreads, ConcGCThreads);
581
582 if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled
583 || ParallelRefProcEnabled)
584 && num_queues > 0) {
585 _task_queues = new OopTaskQueueSet(num_queues);
586 if (_task_queues == NULL) {
587 warning("task_queues allocation failure.");
588 return;
589 }
590 _hash_seed = NEW_C_HEAP_ARRAY(int, num_queues, mtGC);
591 if (_hash_seed == NULL) {
592 warning("_hash_seed array allocation failure");
593 return;
594 }
595
596 typedef Padded<OopTaskQueue> PaddedOopTaskQueue;
597 for (i = 0; i < num_queues; i++) {
598 PaddedOopTaskQueue *q = new PaddedOopTaskQueue();
599 if (q == NULL) {
600 warning("work_queue allocation failure.");
601 return;
602 }
603 _task_queues->register_queue(i, q);
604 }
605 for (i = 0; i < num_queues; i++) {
606 _task_queues->queue(i)->initialize();
607 _hash_seed[i] = 17; // copied from ParNew
608 }
609 }
610 }
611
612 _cmsGen ->init_initiating_occupancy(CMSInitiatingOccupancyFraction, CMSTriggerRatio);
613
614 // Clip CMSBootstrapOccupancy between 0 and 100.
615 _bootstrap_occupancy = ((double)CMSBootstrapOccupancy)/(double)100;
616
617 // Now tell CMS generations the identity of their collector
618 ConcurrentMarkSweepGeneration::set_collector(this);
619
620 // Create & start a CMS thread for this CMS collector
621 _cmsThread = ConcurrentMarkSweepThread::start(this);
622 assert(cmsThread() != NULL, "CMS Thread should have been created");
623 assert(cmsThread()->collector() == this,
624 "CMS Thread should refer to this gen");
625 assert(CGC_lock != NULL, "Where's the CGC_lock?");
626
627 // Support for parallelizing young gen rescan
628 GenCollectedHeap* gch = GenCollectedHeap::heap();
629 assert(gch->prev_gen(_cmsGen)->kind() == Generation::ParNew, "CMS can only be used with ParNew");
630 _young_gen = (ParNewGeneration*)gch->prev_gen(_cmsGen);
631 if (gch->supports_inline_contig_alloc()) {
632 _top_addr = gch->top_addr();
633 _end_addr = gch->end_addr();
634 assert(_young_gen != NULL, "no _young_gen");
635 _eden_chunk_index = 0;
636 _eden_chunk_capacity = (_young_gen->max_capacity()+CMSSamplingGrain)/CMSSamplingGrain;
637 _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity, mtGC);
638 if (_eden_chunk_array == NULL) {
639 _eden_chunk_capacity = 0;
640 warning("GC/CMS: _eden_chunk_array allocation failure");
641 }
642 }
643 assert(_eden_chunk_array != NULL || _eden_chunk_capacity == 0, "Error");
644
645 // Support for parallelizing survivor space rescan
646 if ((CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) || CMSParallelInitialMarkEnabled) {
647 const size_t max_plab_samples =
648 ((DefNewGeneration*)_young_gen)->max_survivor_size() / plab_sample_minimum_size();
649
650 _survivor_plab_array = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads, mtGC);
651 _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, 2*max_plab_samples, mtGC);
652 _cursor = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads, mtGC);
653 if (_survivor_plab_array == NULL || _survivor_chunk_array == NULL
654 || _cursor == NULL) {
655 warning("Failed to allocate survivor plab/chunk array");
656 if (_survivor_plab_array != NULL) {
657 FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array);
658 _survivor_plab_array = NULL;
659 }
660 if (_survivor_chunk_array != NULL) {
661 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array);
662 _survivor_chunk_array = NULL;
663 }
664 if (_cursor != NULL) {
665 FREE_C_HEAP_ARRAY(size_t, _cursor);
666 _cursor = NULL;
667 }
668 } else {
669 _survivor_chunk_capacity = 2*max_plab_samples;
670 for (uint i = 0; i < ParallelGCThreads; i++) {
671 HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
672 if (vec == NULL) {
673 warning("Failed to allocate survivor plab array");
674 for (int j = i; j > 0; j--) {
675 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_plab_array[j-1].array());
676 }
677 FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array);
678 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array);
679 _survivor_plab_array = NULL;
680 _survivor_chunk_array = NULL;
681 _survivor_chunk_capacity = 0;
682 break;
683 } else {
684 ChunkArray* cur =
685 ::new (&_survivor_plab_array[i]) ChunkArray(vec,
686 max_plab_samples);
687 assert(cur->end() == 0, "Should be 0");
688 assert(cur->array() == vec, "Should be vec");
689 assert(cur->capacity() == max_plab_samples, "Error");
690 }
691 }
692 }
693 }
694 assert( ( _survivor_plab_array != NULL
695 && _survivor_chunk_array != NULL)
696 || ( _survivor_chunk_capacity == 0
697 && _survivor_chunk_index == 0),
698 "Error");
699
700 NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;)
701 _gc_counters = new CollectorCounters("CMS", 1);
702 _completed_initialization = true;
703 _inter_sweep_timer.start(); // start of time
704 }
705
706 size_t CMSCollector::plab_sample_minimum_size() {
707 // The default value of MinTLABSize is 2k, but there is
708 // no way to get the default value if the flag has been overridden.
709 return MAX2(ThreadLocalAllocBuffer::min_size() * HeapWordSize, 2 * K);
710 }
711
712 const char* ConcurrentMarkSweepGeneration::name() const {
713 return "concurrent mark-sweep generation";
714 }
715 void ConcurrentMarkSweepGeneration::update_counters() {
716 if (UsePerfData) {
717 _space_counters->update_all();
718 _gen_counters->update_all();
719 }
720 }
721
722 // this is an optimized version of update_counters(). it takes the
723 // used value as a parameter rather than computing it.
724 //
725 void ConcurrentMarkSweepGeneration::update_counters(size_t used) {
726 if (UsePerfData) {
727 _space_counters->update_used(used);
728 _space_counters->update_capacity();
729 _gen_counters->update_all();
730 }
731 }
732
733 void ConcurrentMarkSweepGeneration::print() const {
734 Generation::print();
735 cmsSpace()->print();
736 }
737
738 #ifndef PRODUCT
739 void ConcurrentMarkSweepGeneration::print_statistics() {
740 cmsSpace()->printFLCensus(0);
741 }
742 #endif
743
744 void ConcurrentMarkSweepGeneration::printOccupancy(const char *s) {
745 GenCollectedHeap* gch = GenCollectedHeap::heap();
746 if (PrintGCDetails) {
747 if (Verbose) {
748 gclog_or_tty->print("[%d %s-%s: "SIZE_FORMAT"("SIZE_FORMAT")]",
749 level(), short_name(), s, used(), capacity());
750 } else {
751 gclog_or_tty->print("[%d %s-%s: "SIZE_FORMAT"K("SIZE_FORMAT"K)]",
752 level(), short_name(), s, used() / K, capacity() / K);
753 }
754 }
755 if (Verbose) {
756 gclog_or_tty->print(" "SIZE_FORMAT"("SIZE_FORMAT")",
757 gch->used(), gch->capacity());
758 } else {
759 gclog_or_tty->print(" "SIZE_FORMAT"K("SIZE_FORMAT"K)",
760 gch->used() / K, gch->capacity() / K);
761 }
762 }
763
764 size_t
765 ConcurrentMarkSweepGeneration::contiguous_available() const {
766 // dld proposes an improvement in precision here. If the committed
767 // part of the space ends in a free block we should add that to
768 // uncommitted size in the calculation below. Will make this
769 // change later, staying with the approximation below for the
770 // time being. -- ysr.
771 return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc());
772 }
773
774 size_t
775 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const {
776 return _cmsSpace->max_alloc_in_words() * HeapWordSize;
777 }
778
779 size_t ConcurrentMarkSweepGeneration::max_available() const {
780 return free() + _virtual_space.uncommitted_size();
781 }
782
783 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(size_t max_promotion_in_bytes) const {
784 size_t available = max_available();
785 size_t av_promo = (size_t)gc_stats()->avg_promoted()->padded_average();
786 bool res = (available >= av_promo) || (available >= max_promotion_in_bytes);
787 if (Verbose && PrintGCDetails) {
788 gclog_or_tty->print_cr(
789 "CMS: promo attempt is%s safe: available("SIZE_FORMAT") %s av_promo("SIZE_FORMAT"),"
790 "max_promo("SIZE_FORMAT")",
791 res? "":" not", available, res? ">=":"<",
792 av_promo, max_promotion_in_bytes);
793 }
794 return res;
795 }
796
797 // At a promotion failure dump information on block layout in heap
798 // (cms old generation).
799 void ConcurrentMarkSweepGeneration::promotion_failure_occurred() {
800 if (CMSDumpAtPromotionFailure) {
801 cmsSpace()->dump_at_safepoint_with_locks(collector(), gclog_or_tty);
802 }
803 }
804
805 void ConcurrentMarkSweepGeneration::reset_after_compaction() {
806 // Clear the promotion information. These pointers can be adjusted
807 // along with all the other pointers into the heap but
808 // compaction is expected to be a rare event with
809 // a heap using cms so don't do it without seeing the need.
810 for (uint i = 0; i < ParallelGCThreads; i++) {
811 _par_gc_thread_states[i]->promo.reset();
812 }
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_for_gc_cause(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_for_gc_cause(s*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_promotion);
1052 // Since there's currently no next generation, we don't try to promote
1053 // into a more senior generation.
1054 assert(next_gen() == NULL, "assumption, based upon which no attempt "
1055 "is made to pass on a possibly failing "
1056 "promotion to next generation");
1057 res = _cmsSpace->promote(obj, obj_size);
1058 }
1059 if (res != NULL) {
1060 // See comment in allocate() about when objects should
1061 // be allocated live.
1062 assert(obj->is_oop(), "Will dereference klass pointer below");
1063 collector()->promoted(false, // Not parallel
1064 (HeapWord*)res, obj->is_objArray(), obj_size);
1065 // promotion counters
1066 NOT_PRODUCT(
1067 _numObjectsPromoted++;
1068 _numWordsPromoted +=
1069 (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size()));
1070 )
1071 }
1072 return res;
1073 }
1074
1075
1076 // IMPORTANT: Notes on object size recognition in CMS.
1077 // ---------------------------------------------------
1078 // A block of storage in the CMS generation is always in
1079 // one of three states. A free block (FREE), an allocated
1080 // object (OBJECT) whose size() method reports the correct size,
1081 // and an intermediate state (TRANSIENT) in which its size cannot
1082 // be accurately determined.
1083 // STATE IDENTIFICATION: (32 bit and 64 bit w/o COOPS)
1084 // -----------------------------------------------------
1085 // FREE: klass_word & 1 == 1; mark_word holds block size
1086 //
1087 // OBJECT: klass_word installed; klass_word != 0 && klass_word & 1 == 0;
1088 // obj->size() computes correct size
1089 //
1090 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1091 //
1092 // STATE IDENTIFICATION: (64 bit+COOPS)
1093 // ------------------------------------
1094 // FREE: mark_word & CMS_FREE_BIT == 1; mark_word & ~CMS_FREE_BIT gives block_size
1095 //
1096 // OBJECT: klass_word installed; klass_word != 0;
1097 // obj->size() computes correct size
1098 //
1099 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1100 //
1101 //
1102 // STATE TRANSITION DIAGRAM
1103 //
1104 // mut / parnew mut / parnew
1105 // FREE --------------------> TRANSIENT ---------------------> OBJECT --|
1106 // ^ |
1107 // |------------------------ DEAD <------------------------------------|
1108 // sweep mut
1109 //
1110 // While a block is in TRANSIENT state its size cannot be determined
1111 // so readers will either need to come back later or stall until
1112 // the size can be determined. Note that for the case of direct
1113 // allocation, P-bits, when available, may be used to determine the
1114 // size of an object that may not yet have been initialized.
1115
1116 // Things to support parallel young-gen collection.
1117 oop
1118 ConcurrentMarkSweepGeneration::par_promote(int thread_num,
1119 oop old, markOop m,
1120 size_t word_sz) {
1121 #ifndef PRODUCT
1122 if (Universe::heap()->promotion_should_fail()) {
1123 return NULL;
1124 }
1125 #endif // #ifndef PRODUCT
1126
1127 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1128 PromotionInfo* promoInfo = &ps->promo;
1129 // if we are tracking promotions, then first ensure space for
1130 // promotion (including spooling space for saving header if necessary).
1131 // then allocate and copy, then track promoted info if needed.
1132 // When tracking (see PromotionInfo::track()), the mark word may
1133 // be displaced and in this case restoration of the mark word
1134 // occurs in the (oop_since_save_marks_)iterate phase.
1135 if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) {
1136 // Out of space for allocating spooling buffers;
1137 // try expanding and allocating spooling buffers.
1138 if (!expand_and_ensure_spooling_space(promoInfo)) {
1139 return NULL;
1140 }
1141 }
1142 assert(promoInfo->has_spooling_space(), "Control point invariant");
1143 const size_t alloc_sz = CompactibleFreeListSpace::adjustObjectSize(word_sz);
1144 HeapWord* obj_ptr = ps->lab.alloc(alloc_sz);
1145 if (obj_ptr == NULL) {
1146 obj_ptr = expand_and_par_lab_allocate(ps, alloc_sz);
1147 if (obj_ptr == NULL) {
1148 return NULL;
1149 }
1150 }
1151 oop obj = oop(obj_ptr);
1152 OrderAccess::storestore();
1153 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1154 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1155 // IMPORTANT: See note on object initialization for CMS above.
1156 // Otherwise, copy the object. Here we must be careful to insert the
1157 // klass pointer last, since this marks the block as an allocated object.
1158 // Except with compressed oops it's the mark word.
1159 HeapWord* old_ptr = (HeapWord*)old;
1160 // Restore the mark word copied above.
1161 obj->set_mark(m);
1162 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1163 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1164 OrderAccess::storestore();
1165
1166 if (UseCompressedClassPointers) {
1167 // Copy gap missed by (aligned) header size calculation below
1168 obj->set_klass_gap(old->klass_gap());
1169 }
1170 if (word_sz > (size_t)oopDesc::header_size()) {
1171 Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1172 obj_ptr + oopDesc::header_size(),
1173 word_sz - oopDesc::header_size());
1174 }
1175
1176 // Now we can track the promoted object, if necessary. We take care
1177 // to delay the transition from uninitialized to full object
1178 // (i.e., insertion of klass pointer) until after, so that it
1179 // atomically becomes a promoted object.
1180 if (promoInfo->tracking()) {
1181 promoInfo->track((PromotedObject*)obj, old->klass());
1182 }
1183 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1184 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1185 assert(old->is_oop(), "Will use and dereference old klass ptr below");
1186
1187 // Finally, install the klass pointer (this should be volatile).
1188 OrderAccess::storestore();
1189 obj->set_klass(old->klass());
1190 // We should now be able to calculate the right size for this object
1191 assert(obj->is_oop() && obj->size() == (int)word_sz, "Error, incorrect size computed for promoted object");
1192
1193 collector()->promoted(true, // parallel
1194 obj_ptr, old->is_objArray(), word_sz);
1195
1196 NOT_PRODUCT(
1197 Atomic::inc_ptr(&_numObjectsPromoted);
1198 Atomic::add_ptr(alloc_sz, &_numWordsPromoted);
1199 )
1200
1201 return obj;
1202 }
1203
1204 void
1205 ConcurrentMarkSweepGeneration::
1206 par_promote_alloc_done(int thread_num) {
1207 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1208 ps->lab.retire(thread_num);
1209 }
1210
1211 void
1212 ConcurrentMarkSweepGeneration::
1213 par_oop_since_save_marks_iterate_done(int thread_num) {
1214 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1215 ParScanWithoutBarrierClosure* dummy_cl = NULL;
1216 ps->promo.promoted_oops_iterate_nv(dummy_cl);
1217 }
1218
1219 bool ConcurrentMarkSweepGeneration::should_collect(bool full,
1220 size_t size,
1221 bool tlab)
1222 {
1223 // We allow a STW collection only if a full
1224 // collection was requested.
1225 return full || should_allocate(size, tlab); // FIX ME !!!
1226 // This and promotion failure handling are connected at the
1227 // hip and should be fixed by untying them.
1228 }
1229
1230 bool CMSCollector::shouldConcurrentCollect() {
1231 if (_full_gc_requested) {
1232 if (Verbose && PrintGCDetails) {
1233 gclog_or_tty->print_cr("CMSCollector: collect because of explicit "
1234 " gc request (or gc_locker)");
1235 }
1236 return true;
1237 }
1238
1239 FreelistLocker x(this);
1240 // ------------------------------------------------------------------
1241 // Print out lots of information which affects the initiation of
1242 // a collection.
1243 if (PrintCMSInitiationStatistics && stats().valid()) {
1244 gclog_or_tty->print("CMSCollector shouldConcurrentCollect: ");
1245 gclog_or_tty->stamp();
1246 gclog_or_tty->cr();
1247 stats().print_on(gclog_or_tty);
1248 gclog_or_tty->print_cr("time_until_cms_gen_full %3.7f",
1249 stats().time_until_cms_gen_full());
1250 gclog_or_tty->print_cr("free="SIZE_FORMAT, _cmsGen->free());
1251 gclog_or_tty->print_cr("contiguous_available="SIZE_FORMAT,
1252 _cmsGen->contiguous_available());
1253 gclog_or_tty->print_cr("promotion_rate=%g", stats().promotion_rate());
1254 gclog_or_tty->print_cr("cms_allocation_rate=%g", stats().cms_allocation_rate());
1255 gclog_or_tty->print_cr("occupancy=%3.7f", _cmsGen->occupancy());
1256 gclog_or_tty->print_cr("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy());
1257 gclog_or_tty->print_cr("cms_time_since_begin=%3.7f", stats().cms_time_since_begin());
1258 gclog_or_tty->print_cr("cms_time_since_end=%3.7f", stats().cms_time_since_end());
1259 gclog_or_tty->print_cr("metadata initialized %d",
1260 MetaspaceGC::should_concurrent_collect());
1261 }
1262 // ------------------------------------------------------------------
1263
1264 // If the estimated time to complete a cms collection (cms_duration())
1265 // is less than the estimated time remaining until the cms generation
1266 // is full, start a collection.
1267 if (!UseCMSInitiatingOccupancyOnly) {
1268 if (stats().valid()) {
1269 if (stats().time_until_cms_start() == 0.0) {
1270 return true;
1271 }
1272 } else {
1273 // We want to conservatively collect somewhat early in order
1274 // to try and "bootstrap" our CMS/promotion statistics;
1275 // this branch will not fire after the first successful CMS
1276 // collection because the stats should then be valid.
1277 if (_cmsGen->occupancy() >= _bootstrap_occupancy) {
1278 if (Verbose && PrintGCDetails) {
1279 gclog_or_tty->print_cr(
1280 " CMSCollector: collect for bootstrapping statistics:"
1281 " occupancy = %f, boot occupancy = %f", _cmsGen->occupancy(),
1282 _bootstrap_occupancy);
1283 }
1284 return true;
1285 }
1286 }
1287 }
1288
1289 // Otherwise, we start a collection cycle if
1290 // old gen want a collection cycle started. Each may use
1291 // an appropriate criterion for making this decision.
1292 // XXX We need to make sure that the gen expansion
1293 // criterion dovetails well with this. XXX NEED TO FIX THIS
1294 if (_cmsGen->should_concurrent_collect()) {
1295 if (Verbose && PrintGCDetails) {
1296 gclog_or_tty->print_cr("CMS old gen initiated");
1297 }
1298 return true;
1299 }
1300
1301 // We start a collection if we believe an incremental collection may fail;
1302 // this is not likely to be productive in practice because it's probably too
1303 // late anyway.
1304 GenCollectedHeap* gch = GenCollectedHeap::heap();
1305 assert(gch->collector_policy()->is_generation_policy(),
1306 "You may want to check the correctness of the following");
1307 if (gch->incremental_collection_will_fail(true /* consult_young */)) {
1308 if (Verbose && PrintGCDetails) {
1309 gclog_or_tty->print("CMSCollector: collect because incremental collection will fail ");
1310 }
1311 return true;
1312 }
1313
1314 if (MetaspaceGC::should_concurrent_collect()) {
1315 if (Verbose && PrintGCDetails) {
1316 gclog_or_tty->print("CMSCollector: collect for metadata allocation ");
1317 }
1318 return true;
1319 }
1320
1321 // CMSTriggerInterval starts a CMS cycle if enough time has passed.
1322 if (CMSTriggerInterval >= 0) {
1323 if (CMSTriggerInterval == 0) {
1324 // Trigger always
1325 return true;
1326 }
1327
1328 // Check the CMS time since begin (we do not check the stats validity
1329 // as we want to be able to trigger the first CMS cycle as well)
1330 if (stats().cms_time_since_begin() >= (CMSTriggerInterval / ((double) MILLIUNITS))) {
1331 if (Verbose && PrintGCDetails) {
1332 if (stats().valid()) {
1333 gclog_or_tty->print_cr("CMSCollector: collect because of trigger interval (time since last begin %3.7f secs)",
1334 stats().cms_time_since_begin());
1335 } else {
1336 gclog_or_tty->print_cr("CMSCollector: collect because of trigger interval (first collection)");
1337 }
1338 }
1339 return true;
1340 }
1341 }
1342
1343 return false;
1344 }
1345
1346 void CMSCollector::set_did_compact(bool v) { _cmsGen->set_did_compact(v); }
1347
1348 // Clear _expansion_cause fields of constituent generations
1349 void CMSCollector::clear_expansion_cause() {
1350 _cmsGen->clear_expansion_cause();
1351 }
1352
1353 // We should be conservative in starting a collection cycle. To
1354 // start too eagerly runs the risk of collecting too often in the
1355 // extreme. To collect too rarely falls back on full collections,
1356 // which works, even if not optimum in terms of concurrent work.
1357 // As a work around for too eagerly collecting, use the flag
1358 // UseCMSInitiatingOccupancyOnly. This also has the advantage of
1359 // giving the user an easily understandable way of controlling the
1360 // collections.
1361 // We want to start a new collection cycle if any of the following
1362 // conditions hold:
1363 // . our current occupancy exceeds the configured initiating occupancy
1364 // for this generation, or
1365 // . we recently needed to expand this space and have not, since that
1366 // expansion, done a collection of this generation, or
1367 // . the underlying space believes that it may be a good idea to initiate
1368 // a concurrent collection (this may be based on criteria such as the
1369 // following: the space uses linear allocation and linear allocation is
1370 // going to fail, or there is believed to be excessive fragmentation in
1371 // the generation, etc... or ...
1372 // [.(currently done by CMSCollector::shouldConcurrentCollect() only for
1373 // the case of the old generation; see CR 6543076):
1374 // we may be approaching a point at which allocation requests may fail because
1375 // we will be out of sufficient free space given allocation rate estimates.]
1376 bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const {
1377
1378 assert_lock_strong(freelistLock());
1379 if (occupancy() > initiating_occupancy()) {
1380 if (PrintGCDetails && Verbose) {
1381 gclog_or_tty->print(" %s: collect because of occupancy %f / %f ",
1382 short_name(), occupancy(), initiating_occupancy());
1383 }
1384 return true;
1385 }
1386 if (UseCMSInitiatingOccupancyOnly) {
1387 return false;
1388 }
1389 if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) {
1390 if (PrintGCDetails && Verbose) {
1391 gclog_or_tty->print(" %s: collect because expanded for allocation ",
1392 short_name());
1393 }
1394 return true;
1395 }
1396 if (_cmsSpace->should_concurrent_collect()) {
1397 if (PrintGCDetails && Verbose) {
1398 gclog_or_tty->print(" %s: collect because cmsSpace says so ",
1399 short_name());
1400 }
1401 return true;
1402 }
1403 return false;
1404 }
1405
1406 void ConcurrentMarkSweepGeneration::collect(bool full,
1407 bool clear_all_soft_refs,
1408 size_t size,
1409 bool tlab)
1410 {
1411 collector()->collect(full, clear_all_soft_refs, size, tlab);
1412 }
1413
1414 void CMSCollector::collect(bool full,
1415 bool clear_all_soft_refs,
1416 size_t size,
1417 bool tlab)
1418 {
1419 // The following "if" branch is present for defensive reasons.
1420 // In the current uses of this interface, it can be replaced with:
1421 // assert(!GC_locker.is_active(), "Can't be called otherwise");
1422 // But I am not placing that assert here to allow future
1423 // generality in invoking this interface.
1424 if (GC_locker::is_active()) {
1425 // A consistency test for GC_locker
1426 assert(GC_locker::needs_gc(), "Should have been set already");
1427 // Skip this foreground collection, instead
1428 // expanding the heap if necessary.
1429 // Need the free list locks for the call to free() in compute_new_size()
1430 compute_new_size();
1431 return;
1432 }
1433 acquire_control_and_collect(full, clear_all_soft_refs);
1434 }
1435
1436 void CMSCollector::request_full_gc(unsigned int full_gc_count, GCCause::Cause cause) {
1437 GenCollectedHeap* gch = GenCollectedHeap::heap();
1438 unsigned int gc_count = gch->total_full_collections();
1439 if (gc_count == full_gc_count) {
1440 MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag);
1441 _full_gc_requested = true;
1442 _full_gc_cause = cause;
1443 CGC_lock->notify(); // nudge CMS thread
1444 } else {
1445 assert(gc_count > full_gc_count, "Error: causal loop");
1446 }
1447 }
1448
1449 bool CMSCollector::is_external_interruption() {
1450 GCCause::Cause cause = GenCollectedHeap::heap()->gc_cause();
1451 return GCCause::is_user_requested_gc(cause) ||
1452 GCCause::is_serviceability_requested_gc(cause);
1453 }
1454
1455 void CMSCollector::report_concurrent_mode_interruption() {
1456 if (is_external_interruption()) {
1457 if (PrintGCDetails) {
1458 gclog_or_tty->print(" (concurrent mode interrupted)");
1459 }
1460 } else {
1461 if (PrintGCDetails) {
1462 gclog_or_tty->print(" (concurrent mode failure)");
1463 }
1464 _gc_tracer_cm->report_concurrent_mode_failure();
1465 }
1466 }
1467
1468
1469 // The foreground and background collectors need to coordinate in order
1470 // to make sure that they do not mutually interfere with CMS collections.
1471 // When a background collection is active,
1472 // the foreground collector may need to take over (preempt) and
1473 // synchronously complete an ongoing collection. Depending on the
1474 // frequency of the background collections and the heap usage
1475 // of the application, this preemption can be seldom or frequent.
1476 // There are only certain
1477 // points in the background collection that the "collection-baton"
1478 // can be passed to the foreground collector.
1479 //
1480 // The foreground collector will wait for the baton before
1481 // starting any part of the collection. The foreground collector
1482 // will only wait at one location.
1483 //
1484 // The background collector will yield the baton before starting a new
1485 // phase of the collection (e.g., before initial marking, marking from roots,
1486 // precleaning, final re-mark, sweep etc.) This is normally done at the head
1487 // of the loop which switches the phases. The background collector does some
1488 // of the phases (initial mark, final re-mark) with the world stopped.
1489 // Because of locking involved in stopping the world,
1490 // the foreground collector should not block waiting for the background
1491 // collector when it is doing a stop-the-world phase. The background
1492 // collector will yield the baton at an additional point just before
1493 // it enters a stop-the-world phase. Once the world is stopped, the
1494 // background collector checks the phase of the collection. If the
1495 // phase has not changed, it proceeds with the collection. If the
1496 // phase has changed, it skips that phase of the collection. See
1497 // the comments on the use of the Heap_lock in collect_in_background().
1498 //
1499 // Variable used in baton passing.
1500 // _foregroundGCIsActive - Set to true by the foreground collector when
1501 // it wants the baton. The foreground clears it when it has finished
1502 // the collection.
1503 // _foregroundGCShouldWait - Set to true by the background collector
1504 // when it is running. The foreground collector waits while
1505 // _foregroundGCShouldWait is true.
1506 // CGC_lock - monitor used to protect access to the above variables
1507 // and to notify the foreground and background collectors.
1508 // _collectorState - current state of the CMS collection.
1509 //
1510 // The foreground collector
1511 // acquires the CGC_lock
1512 // sets _foregroundGCIsActive
1513 // waits on the CGC_lock for _foregroundGCShouldWait to be false
1514 // various locks acquired in preparation for the collection
1515 // are released so as not to block the background collector
1516 // that is in the midst of a collection
1517 // proceeds with the collection
1518 // clears _foregroundGCIsActive
1519 // returns
1520 //
1521 // The background collector in a loop iterating on the phases of the
1522 // collection
1523 // acquires the CGC_lock
1524 // sets _foregroundGCShouldWait
1525 // if _foregroundGCIsActive is set
1526 // clears _foregroundGCShouldWait, notifies _CGC_lock
1527 // waits on _CGC_lock for _foregroundGCIsActive to become false
1528 // and exits the loop.
1529 // otherwise
1530 // proceed with that phase of the collection
1531 // if the phase is a stop-the-world phase,
1532 // yield the baton once more just before enqueueing
1533 // the stop-world CMS operation (executed by the VM thread).
1534 // returns after all phases of the collection are done
1535 //
1536
1537 void CMSCollector::acquire_control_and_collect(bool full,
1538 bool clear_all_soft_refs) {
1539 assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
1540 assert(!Thread::current()->is_ConcurrentGC_thread(),
1541 "shouldn't try to acquire control from self!");
1542
1543 // Start the protocol for acquiring control of the
1544 // collection from the background collector (aka CMS thread).
1545 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1546 "VM thread should have CMS token");
1547 // Remember the possibly interrupted state of an ongoing
1548 // concurrent collection
1549 CollectorState first_state = _collectorState;
1550
1551 // Signal to a possibly ongoing concurrent collection that
1552 // we want to do a foreground collection.
1553 _foregroundGCIsActive = true;
1554
1555 // release locks and wait for a notify from the background collector
1556 // releasing the locks in only necessary for phases which
1557 // do yields to improve the granularity of the collection.
1558 assert_lock_strong(bitMapLock());
1559 // We need to lock the Free list lock for the space that we are
1560 // currently collecting.
1561 assert(haveFreelistLocks(), "Must be holding free list locks");
1562 bitMapLock()->unlock();
1563 releaseFreelistLocks();
1564 {
1565 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1566 if (_foregroundGCShouldWait) {
1567 // We are going to be waiting for action for the CMS thread;
1568 // it had better not be gone (for instance at shutdown)!
1569 assert(ConcurrentMarkSweepThread::cmst() != NULL,
1570 "CMS thread must be running");
1571 // Wait here until the background collector gives us the go-ahead
1572 ConcurrentMarkSweepThread::clear_CMS_flag(
1573 ConcurrentMarkSweepThread::CMS_vm_has_token); // release token
1574 // Get a possibly blocked CMS thread going:
1575 // Note that we set _foregroundGCIsActive true above,
1576 // without protection of the CGC_lock.
1577 CGC_lock->notify();
1578 assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(),
1579 "Possible deadlock");
1580 while (_foregroundGCShouldWait) {
1581 // wait for notification
1582 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1583 // Possibility of delay/starvation here, since CMS token does
1584 // not know to give priority to VM thread? Actually, i think
1585 // there wouldn't be any delay/starvation, but the proof of
1586 // that "fact" (?) appears non-trivial. XXX 20011219YSR
1587 }
1588 ConcurrentMarkSweepThread::set_CMS_flag(
1589 ConcurrentMarkSweepThread::CMS_vm_has_token);
1590 }
1591 }
1592 // The CMS_token is already held. Get back the other locks.
1593 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1594 "VM thread should have CMS token");
1595 getFreelistLocks();
1596 bitMapLock()->lock_without_safepoint_check();
1597 if (TraceCMSState) {
1598 gclog_or_tty->print_cr("CMS foreground collector has asked for control "
1599 INTPTR_FORMAT " with first state %d", Thread::current(), first_state);
1600 gclog_or_tty->print_cr(" gets control with state %d", _collectorState);
1601 }
1602
1603 // Inform cms gen if this was due to partial collection failing.
1604 // The CMS gen may use this fact to determine its expansion policy.
1605 GenCollectedHeap* gch = GenCollectedHeap::heap();
1606 if (gch->incremental_collection_will_fail(false /* don't consult_young */)) {
1607 assert(!_cmsGen->incremental_collection_failed(),
1608 "Should have been noticed, reacted to and cleared");
1609 _cmsGen->set_incremental_collection_failed();
1610 }
1611
1612 if (first_state > Idling) {
1613 report_concurrent_mode_interruption();
1614 }
1615
1616 set_did_compact(true);
1617
1618 // If the collection is being acquired from the background
1619 // collector, there may be references on the discovered
1620 // references lists. Abandon those references, since some
1621 // of them may have become unreachable after concurrent
1622 // discovery; the STW compacting collector will redo discovery
1623 // more precisely, without being subject to floating garbage.
1624 // Leaving otherwise unreachable references in the discovered
1625 // lists would require special handling.
1626 ref_processor()->disable_discovery();
1627 ref_processor()->abandon_partial_discovery();
1628 ref_processor()->verify_no_references_recorded();
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();
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::oop_iterate(ExtendedOopClosure* cl) {
2629 if (freelistLock()->owned_by_self()) {
2630 Generation::oop_iterate(cl);
2631 } else {
2632 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2633 Generation::oop_iterate(cl);
2634 }
2635 }
2636
2637 void
2638 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
2639 if (freelistLock()->owned_by_self()) {
2640 Generation::object_iterate(cl);
2641 } else {
2642 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2643 Generation::object_iterate(cl);
2644 }
2645 }
2646
2647 void
2648 ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) {
2649 if (freelistLock()->owned_by_self()) {
2650 Generation::safe_object_iterate(cl);
2651 } else {
2652 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2653 Generation::safe_object_iterate(cl);
2654 }
2655 }
2656
2657 void
2658 ConcurrentMarkSweepGeneration::post_compact() {
2659 }
2660
2661 void
2662 ConcurrentMarkSweepGeneration::prepare_for_verify() {
2663 // Fix the linear allocation blocks to look like free blocks.
2664
2665 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2666 // are not called when the heap is verified during universe initialization and
2667 // at vm shutdown.
2668 if (freelistLock()->owned_by_self()) {
2669 cmsSpace()->prepare_for_verify();
2670 } else {
2671 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2672 cmsSpace()->prepare_for_verify();
2673 }
2674 }
2675
2676 void
2677 ConcurrentMarkSweepGeneration::verify() {
2678 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2679 // are not called when the heap is verified during universe initialization and
2680 // at vm shutdown.
2681 if (freelistLock()->owned_by_self()) {
2682 cmsSpace()->verify();
2683 } else {
2684 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2685 cmsSpace()->verify();
2686 }
2687 }
2688
2689 void CMSCollector::verify() {
2690 _cmsGen->verify();
2691 }
2692
2693 #ifndef PRODUCT
2694 bool CMSCollector::overflow_list_is_empty() const {
2695 assert(_num_par_pushes >= 0, "Inconsistency");
2696 if (_overflow_list == NULL) {
2697 assert(_num_par_pushes == 0, "Inconsistency");
2698 }
2699 return _overflow_list == NULL;
2700 }
2701
2702 // The methods verify_work_stacks_empty() and verify_overflow_empty()
2703 // merely consolidate assertion checks that appear to occur together frequently.
2704 void CMSCollector::verify_work_stacks_empty() const {
2705 assert(_markStack.isEmpty(), "Marking stack should be empty");
2706 assert(overflow_list_is_empty(), "Overflow list should be empty");
2707 }
2708
2709 void CMSCollector::verify_overflow_empty() const {
2710 assert(overflow_list_is_empty(), "Overflow list should be empty");
2711 assert(no_preserved_marks(), "No preserved marks");
2712 }
2713 #endif // PRODUCT
2714
2715 // Decide if we want to enable class unloading as part of the
2716 // ensuing concurrent GC cycle. We will collect and
2717 // unload classes if it's the case that:
2718 // (1) an explicit gc request has been made and the flag
2719 // ExplicitGCInvokesConcurrentAndUnloadsClasses is set, OR
2720 // (2) (a) class unloading is enabled at the command line, and
2721 // (b) old gen is getting really full
2722 // NOTE: Provided there is no change in the state of the heap between
2723 // calls to this method, it should have idempotent results. Moreover,
2724 // its results should be monotonically increasing (i.e. going from 0 to 1,
2725 // but not 1 to 0) between successive calls between which the heap was
2726 // not collected. For the implementation below, it must thus rely on
2727 // the property that concurrent_cycles_since_last_unload()
2728 // will not decrease unless a collection cycle happened and that
2729 // _cmsGen->is_too_full() are
2730 // themselves also monotonic in that sense. See check_monotonicity()
2731 // below.
2732 void CMSCollector::update_should_unload_classes() {
2733 _should_unload_classes = false;
2734 // Condition 1 above
2735 if (_full_gc_requested && ExplicitGCInvokesConcurrentAndUnloadsClasses) {
2736 _should_unload_classes = true;
2737 } else if (CMSClassUnloadingEnabled) { // Condition 2.a above
2738 // Disjuncts 2.b.(i,ii,iii) above
2739 _should_unload_classes = (concurrent_cycles_since_last_unload() >=
2740 CMSClassUnloadingMaxInterval)
2741 || _cmsGen->is_too_full();
2742 }
2743 }
2744
2745 bool ConcurrentMarkSweepGeneration::is_too_full() const {
2746 bool res = should_concurrent_collect();
2747 res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
2748 return res;
2749 }
2750
2751 void CMSCollector::setup_cms_unloading_and_verification_state() {
2752 const bool should_verify = VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
2753 || VerifyBeforeExit;
2754 const int rso = SharedHeap::SO_AllCodeCache;
2755
2756 // We set the proper root for this CMS cycle here.
2757 if (should_unload_classes()) { // Should unload classes this cycle
2758 remove_root_scanning_option(rso); // Shrink the root set appropriately
2759 set_verifying(should_verify); // Set verification state for this cycle
2760 return; // Nothing else needs to be done at this time
2761 }
2762
2763 // Not unloading classes this cycle
2764 assert(!should_unload_classes(), "Inconsistency!");
2765
2766 if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
2767 // Include symbols, strings and code cache elements to prevent their resurrection.
2768 add_root_scanning_option(rso);
2769 set_verifying(true);
2770 } else if (verifying() && !should_verify) {
2771 // We were verifying, but some verification flags got disabled.
2772 set_verifying(false);
2773 // Exclude symbols, strings and code cache elements from root scanning to
2774 // reduce IM and RM pauses.
2775 remove_root_scanning_option(rso);
2776 }
2777 }
2778
2779
2780 #ifndef PRODUCT
2781 HeapWord* CMSCollector::block_start(const void* p) const {
2782 const HeapWord* addr = (HeapWord*)p;
2783 if (_span.contains(p)) {
2784 if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
2785 return _cmsGen->cmsSpace()->block_start(p);
2786 }
2787 }
2788 return NULL;
2789 }
2790 #endif
2791
2792 HeapWord*
2793 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
2794 bool tlab,
2795 bool parallel) {
2796 CMSSynchronousYieldRequest yr;
2797 assert(!tlab, "Can't deal with TLAB allocation");
2798 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2799 expand_for_gc_cause(word_size*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_allocation);
2800 if (GCExpandToAllocateDelayMillis > 0) {
2801 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2802 }
2803 return have_lock_and_allocate(word_size, tlab);
2804 }
2805
2806 void ConcurrentMarkSweepGeneration::expand_for_gc_cause(
2807 size_t bytes,
2808 size_t expand_bytes,
2809 CMSExpansionCause::Cause cause)
2810 {
2811
2812 bool success = expand(bytes, expand_bytes);
2813
2814 // remember why we expanded; this information is used
2815 // by shouldConcurrentCollect() when making decisions on whether to start
2816 // a new CMS cycle.
2817 if (success) {
2818 set_expansion_cause(cause);
2819 if (PrintGCDetails && Verbose) {
2820 gclog_or_tty->print_cr("Expanded CMS gen for %s",
2821 CMSExpansionCause::to_string(cause));
2822 }
2823 }
2824 }
2825
2826 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
2827 HeapWord* res = NULL;
2828 MutexLocker x(ParGCRareEvent_lock);
2829 while (true) {
2830 // Expansion by some other thread might make alloc OK now:
2831 res = ps->lab.alloc(word_sz);
2832 if (res != NULL) return res;
2833 // If there's not enough expansion space available, give up.
2834 if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
2835 return NULL;
2836 }
2837 // Otherwise, we try expansion.
2838 expand_for_gc_cause(word_sz*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_lab);
2839 // Now go around the loop and try alloc again;
2840 // A competing par_promote might beat us to the expansion space,
2841 // so we may go around the loop again if promotion fails again.
2842 if (GCExpandToAllocateDelayMillis > 0) {
2843 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2844 }
2845 }
2846 }
2847
2848
2849 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
2850 PromotionInfo* promo) {
2851 MutexLocker x(ParGCRareEvent_lock);
2852 size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
2853 while (true) {
2854 // Expansion by some other thread might make alloc OK now:
2855 if (promo->ensure_spooling_space()) {
2856 assert(promo->has_spooling_space(),
2857 "Post-condition of successful ensure_spooling_space()");
2858 return true;
2859 }
2860 // If there's not enough expansion space available, give up.
2861 if (_virtual_space.uncommitted_size() < refill_size_bytes) {
2862 return false;
2863 }
2864 // Otherwise, we try expansion.
2865 expand_for_gc_cause(refill_size_bytes, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_spooling_space);
2866 // Now go around the loop and try alloc again;
2867 // A competing allocation might beat us to the expansion space,
2868 // so we may go around the loop again if allocation fails again.
2869 if (GCExpandToAllocateDelayMillis > 0) {
2870 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2871 }
2872 }
2873 }
2874
2875 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
2876 // Only shrink if a compaction was done so that all the free space
2877 // in the generation is in a contiguous block at the end.
2878 if (did_compact()) {
2879 CardGeneration::shrink(bytes);
2880 }
2881 }
2882
2883 void ConcurrentMarkSweepGeneration::assert_correct_size_change_locking() {
2884 assert_locked_or_safepoint(Heap_lock);
2885 }
2886
2887 void ConcurrentMarkSweepGeneration::shrink_free_list_by(size_t bytes) {
2888 assert_locked_or_safepoint(Heap_lock);
2889 assert_lock_strong(freelistLock());
2890 if (PrintGCDetails && Verbose) {
2891 warning("Shrinking of CMS not yet implemented");
2892 }
2893 return;
2894 }
2895
2896
2897 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
2898 // phases.
2899 class CMSPhaseAccounting: public StackObj {
2900 public:
2901 CMSPhaseAccounting(CMSCollector *collector,
2902 const char *phase,
2903 const GCId gc_id,
2904 bool print_cr = true);
2905 ~CMSPhaseAccounting();
2906
2907 private:
2908 CMSCollector *_collector;
2909 const char *_phase;
2910 elapsedTimer _wallclock;
2911 bool _print_cr;
2912 const GCId _gc_id;
2913
2914 public:
2915 // Not MT-safe; so do not pass around these StackObj's
2916 // where they may be accessed by other threads.
2917 jlong wallclock_millis() {
2918 assert(_wallclock.is_active(), "Wall clock should not stop");
2919 _wallclock.stop(); // to record time
2920 jlong ret = _wallclock.milliseconds();
2921 _wallclock.start(); // restart
2922 return ret;
2923 }
2924 };
2925
2926 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
2927 const char *phase,
2928 const GCId gc_id,
2929 bool print_cr) :
2930 _collector(collector), _phase(phase), _print_cr(print_cr), _gc_id(gc_id) {
2931
2932 if (PrintCMSStatistics != 0) {
2933 _collector->resetYields();
2934 }
2935 if (PrintGCDetails) {
2936 gclog_or_tty->gclog_stamp(_gc_id);
2937 gclog_or_tty->print_cr("[%s-concurrent-%s-start]",
2938 _collector->cmsGen()->short_name(), _phase);
2939 }
2940 _collector->resetTimer();
2941 _wallclock.start();
2942 _collector->startTimer();
2943 }
2944
2945 CMSPhaseAccounting::~CMSPhaseAccounting() {
2946 assert(_wallclock.is_active(), "Wall clock should not have stopped");
2947 _collector->stopTimer();
2948 _wallclock.stop();
2949 if (PrintGCDetails) {
2950 gclog_or_tty->gclog_stamp(_gc_id);
2951 gclog_or_tty->print("[%s-concurrent-%s: %3.3f/%3.3f secs]",
2952 _collector->cmsGen()->short_name(),
2953 _phase, _collector->timerValue(), _wallclock.seconds());
2954 if (_print_cr) {
2955 gclog_or_tty->cr();
2956 }
2957 if (PrintCMSStatistics != 0) {
2958 gclog_or_tty->print_cr(" (CMS-concurrent-%s yielded %d times)", _phase,
2959 _collector->yields());
2960 }
2961 }
2962 }
2963
2964 // CMS work
2965
2966 // The common parts of CMSParInitialMarkTask and CMSParRemarkTask.
2967 class CMSParMarkTask : public AbstractGangTask {
2968 protected:
2969 CMSCollector* _collector;
2970 int _n_workers;
2971 CMSParMarkTask(const char* name, CMSCollector* collector, int n_workers) :
2972 AbstractGangTask(name),
2973 _collector(collector),
2974 _n_workers(n_workers) {}
2975 // Work method in support of parallel rescan ... of young gen spaces
2976 void do_young_space_rescan(uint worker_id, OopsInGenClosure* cl,
2977 ContiguousSpace* space,
2978 HeapWord** chunk_array, size_t chunk_top);
2979 void work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl);
2980 };
2981
2982 // Parallel initial mark task
2983 class CMSParInitialMarkTask: public CMSParMarkTask {
2984 public:
2985 CMSParInitialMarkTask(CMSCollector* collector, int n_workers) :
2986 CMSParMarkTask("Scan roots and young gen for initial mark in parallel",
2987 collector, n_workers) {}
2988 void work(uint worker_id);
2989 };
2990
2991 // Checkpoint the roots into this generation from outside
2992 // this generation. [Note this initial checkpoint need only
2993 // be approximate -- we'll do a catch up phase subsequently.]
2994 void CMSCollector::checkpointRootsInitial() {
2995 assert(_collectorState == InitialMarking, "Wrong collector state");
2996 check_correct_thread_executing();
2997 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
2998
2999 save_heap_summary();
3000 report_heap_summary(GCWhen::BeforeGC);
3001
3002 ReferenceProcessor* rp = ref_processor();
3003 SpecializationStats::clear();
3004 assert(_restart_addr == NULL, "Control point invariant");
3005 {
3006 // acquire locks for subsequent manipulations
3007 MutexLockerEx x(bitMapLock(),
3008 Mutex::_no_safepoint_check_flag);
3009 checkpointRootsInitialWork();
3010 // enable ("weak") refs discovery
3011 rp->enable_discovery();
3012 _collectorState = Marking;
3013 }
3014 SpecializationStats::print();
3015 }
3016
3017 void CMSCollector::checkpointRootsInitialWork() {
3018 assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
3019 assert(_collectorState == InitialMarking, "just checking");
3020
3021 // If there has not been a GC[n-1] since last GC[n] cycle completed,
3022 // precede our marking with a collection of all
3023 // younger generations to keep floating garbage to a minimum.
3024 // XXX: we won't do this for now -- it's an optimization to be done later.
3025
3026 // already have locks
3027 assert_lock_strong(bitMapLock());
3028 assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
3029
3030 // Setup the verification and class unloading state for this
3031 // CMS collection cycle.
3032 setup_cms_unloading_and_verification_state();
3033
3034 NOT_PRODUCT(GCTraceTime t("\ncheckpointRootsInitialWork",
3035 PrintGCDetails && Verbose, true, _gc_timer_cm, _gc_tracer_cm->gc_id());)
3036
3037 // Reset all the PLAB chunk arrays if necessary.
3038 if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
3039 reset_survivor_plab_arrays();
3040 }
3041
3042 ResourceMark rm;
3043 HandleMark hm;
3044
3045 MarkRefsIntoClosure notOlder(_span, &_markBitMap);
3046 GenCollectedHeap* gch = GenCollectedHeap::heap();
3047
3048 verify_work_stacks_empty();
3049 verify_overflow_empty();
3050
3051 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
3052 // Update the saved marks which may affect the root scans.
3053 gch->save_marks();
3054
3055 // weak reference processing has not started yet.
3056 ref_processor()->set_enqueuing_is_done(false);
3057
3058 // Need to remember all newly created CLDs,
3059 // so that we can guarantee that the remark finds them.
3060 ClassLoaderDataGraph::remember_new_clds(true);
3061
3062 // Whenever a CLD is found, it will be claimed before proceeding to mark
3063 // the klasses. The claimed marks need to be cleared before marking starts.
3064 ClassLoaderDataGraph::clear_claimed_marks();
3065
3066 if (CMSPrintEdenSurvivorChunks) {
3067 print_eden_and_survivor_chunk_arrays();
3068 }
3069
3070 {
3071 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
3072 if (CMSParallelInitialMarkEnabled && CollectedHeap::use_parallel_gc_threads()) {
3073 // The parallel version.
3074 FlexibleWorkGang* workers = gch->workers();
3075 assert(workers != NULL, "Need parallel worker threads.");
3076 int n_workers = workers->active_workers();
3077 CMSParInitialMarkTask tsk(this, n_workers);
3078 gch->set_par_threads(n_workers);
3079 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
3080 if (n_workers > 1) {
3081 GenCollectedHeap::StrongRootsScope srs(gch);
3082 workers->run_task(&tsk);
3083 } else {
3084 GenCollectedHeap::StrongRootsScope srs(gch);
3085 tsk.work(0);
3086 }
3087 gch->set_par_threads(0);
3088 } else {
3089 // The serial version.
3090 CLDToOopClosure cld_closure(¬Older, true);
3091 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3092 gch->gen_process_roots(_cmsGen->level(),
3093 true, // younger gens are roots
3094 true, // activate StrongRootsScope
3095 SharedHeap::ScanningOption(roots_scanning_options()),
3096 should_unload_classes(),
3097 ¬Older,
3098 NULL,
3099 &cld_closure);
3100 }
3101 }
3102
3103 // Clear mod-union table; it will be dirtied in the prologue of
3104 // CMS generation per each younger generation collection.
3105
3106 assert(_modUnionTable.isAllClear(),
3107 "Was cleared in most recent final checkpoint phase"
3108 " or no bits are set in the gc_prologue before the start of the next "
3109 "subsequent marking phase.");
3110
3111 assert(_ct->klass_rem_set()->mod_union_is_clear(), "Must be");
3112
3113 // Save the end of the used_region of the constituent generations
3114 // to be used to limit the extent of sweep in each generation.
3115 save_sweep_limits();
3116 verify_overflow_empty();
3117 }
3118
3119 bool CMSCollector::markFromRoots() {
3120 // we might be tempted to assert that:
3121 // assert(!SafepointSynchronize::is_at_safepoint(),
3122 // "inconsistent argument?");
3123 // However that wouldn't be right, because it's possible that
3124 // a safepoint is indeed in progress as a younger generation
3125 // stop-the-world GC happens even as we mark in this generation.
3126 assert(_collectorState == Marking, "inconsistent state?");
3127 check_correct_thread_executing();
3128 verify_overflow_empty();
3129
3130 // Weak ref discovery note: We may be discovering weak
3131 // refs in this generation concurrent (but interleaved) with
3132 // weak ref discovery by a younger generation collector.
3133
3134 CMSTokenSyncWithLocks ts(true, bitMapLock());
3135 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3136 CMSPhaseAccounting pa(this, "mark", _gc_tracer_cm->gc_id(), !PrintGCDetails);
3137 bool res = markFromRootsWork();
3138 if (res) {
3139 _collectorState = Precleaning;
3140 } else { // We failed and a foreground collection wants to take over
3141 assert(_foregroundGCIsActive, "internal state inconsistency");
3142 assert(_restart_addr == NULL, "foreground will restart from scratch");
3143 if (PrintGCDetails) {
3144 gclog_or_tty->print_cr("bailing out to foreground collection");
3145 }
3146 }
3147 verify_overflow_empty();
3148 return res;
3149 }
3150
3151 bool CMSCollector::markFromRootsWork() {
3152 // iterate over marked bits in bit map, doing a full scan and mark
3153 // from these roots using the following algorithm:
3154 // . if oop is to the right of the current scan pointer,
3155 // mark corresponding bit (we'll process it later)
3156 // . else (oop is to left of current scan pointer)
3157 // push oop on marking stack
3158 // . drain the marking stack
3159
3160 // Note that when we do a marking step we need to hold the
3161 // bit map lock -- recall that direct allocation (by mutators)
3162 // and promotion (by younger generation collectors) is also
3163 // marking the bit map. [the so-called allocate live policy.]
3164 // Because the implementation of bit map marking is not
3165 // robust wrt simultaneous marking of bits in the same word,
3166 // we need to make sure that there is no such interference
3167 // between concurrent such updates.
3168
3169 // already have locks
3170 assert_lock_strong(bitMapLock());
3171
3172 verify_work_stacks_empty();
3173 verify_overflow_empty();
3174 bool result = false;
3175 if (CMSConcurrentMTEnabled && ConcGCThreads > 0) {
3176 result = do_marking_mt();
3177 } else {
3178 result = do_marking_st();
3179 }
3180 return result;
3181 }
3182
3183 // Forward decl
3184 class CMSConcMarkingTask;
3185
3186 class CMSConcMarkingTerminator: public ParallelTaskTerminator {
3187 CMSCollector* _collector;
3188 CMSConcMarkingTask* _task;
3189 public:
3190 virtual void yield();
3191
3192 // "n_threads" is the number of threads to be terminated.
3193 // "queue_set" is a set of work queues of other threads.
3194 // "collector" is the CMS collector associated with this task terminator.
3195 // "yield" indicates whether we need the gang as a whole to yield.
3196 CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
3197 ParallelTaskTerminator(n_threads, queue_set),
3198 _collector(collector) { }
3199
3200 void set_task(CMSConcMarkingTask* task) {
3201 _task = task;
3202 }
3203 };
3204
3205 class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator {
3206 CMSConcMarkingTask* _task;
3207 public:
3208 bool should_exit_termination();
3209 void set_task(CMSConcMarkingTask* task) {
3210 _task = task;
3211 }
3212 };
3213
3214 // MT Concurrent Marking Task
3215 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3216 CMSCollector* _collector;
3217 int _n_workers; // requested/desired # workers
3218 bool _result;
3219 CompactibleFreeListSpace* _cms_space;
3220 char _pad_front[64]; // padding to ...
3221 HeapWord* _global_finger; // ... avoid sharing cache line
3222 char _pad_back[64];
3223 HeapWord* _restart_addr;
3224
3225 // Exposed here for yielding support
3226 Mutex* const _bit_map_lock;
3227
3228 // The per thread work queues, available here for stealing
3229 OopTaskQueueSet* _task_queues;
3230
3231 // Termination (and yielding) support
3232 CMSConcMarkingTerminator _term;
3233 CMSConcMarkingTerminatorTerminator _term_term;
3234
3235 public:
3236 CMSConcMarkingTask(CMSCollector* collector,
3237 CompactibleFreeListSpace* cms_space,
3238 YieldingFlexibleWorkGang* workers,
3239 OopTaskQueueSet* task_queues):
3240 YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3241 _collector(collector),
3242 _cms_space(cms_space),
3243 _n_workers(0), _result(true),
3244 _task_queues(task_queues),
3245 _term(_n_workers, task_queues, _collector),
3246 _bit_map_lock(collector->bitMapLock())
3247 {
3248 _requested_size = _n_workers;
3249 _term.set_task(this);
3250 _term_term.set_task(this);
3251 _restart_addr = _global_finger = _cms_space->bottom();
3252 }
3253
3254
3255 OopTaskQueueSet* task_queues() { return _task_queues; }
3256
3257 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3258
3259 HeapWord** global_finger_addr() { return &_global_finger; }
3260
3261 CMSConcMarkingTerminator* terminator() { return &_term; }
3262
3263 virtual void set_for_termination(int active_workers) {
3264 terminator()->reset_for_reuse(active_workers);
3265 }
3266
3267 void work(uint worker_id);
3268 bool should_yield() {
3269 return ConcurrentMarkSweepThread::should_yield()
3270 && !_collector->foregroundGCIsActive();
3271 }
3272
3273 virtual void coordinator_yield(); // stuff done by coordinator
3274 bool result() { return _result; }
3275
3276 void reset(HeapWord* ra) {
3277 assert(_global_finger >= _cms_space->end(), "Postcondition of ::work(i)");
3278 _restart_addr = _global_finger = ra;
3279 _term.reset_for_reuse();
3280 }
3281
3282 static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3283 OopTaskQueue* work_q);
3284
3285 private:
3286 void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3287 void do_work_steal(int i);
3288 void bump_global_finger(HeapWord* f);
3289 };
3290
3291 bool CMSConcMarkingTerminatorTerminator::should_exit_termination() {
3292 assert(_task != NULL, "Error");
3293 return _task->yielding();
3294 // Note that we do not need the disjunct || _task->should_yield() above
3295 // because we want terminating threads to yield only if the task
3296 // is already in the midst of yielding, which happens only after at least one
3297 // thread has yielded.
3298 }
3299
3300 void CMSConcMarkingTerminator::yield() {
3301 if (_task->should_yield()) {
3302 _task->yield();
3303 } else {
3304 ParallelTaskTerminator::yield();
3305 }
3306 }
3307
3308 ////////////////////////////////////////////////////////////////
3309 // Concurrent Marking Algorithm Sketch
3310 ////////////////////////////////////////////////////////////////
3311 // Until all tasks exhausted (both spaces):
3312 // -- claim next available chunk
3313 // -- bump global finger via CAS
3314 // -- find first object that starts in this chunk
3315 // and start scanning bitmap from that position
3316 // -- scan marked objects for oops
3317 // -- CAS-mark target, and if successful:
3318 // . if target oop is above global finger (volatile read)
3319 // nothing to do
3320 // . if target oop is in chunk and above local finger
3321 // then nothing to do
3322 // . else push on work-queue
3323 // -- Deal with possible overflow issues:
3324 // . local work-queue overflow causes stuff to be pushed on
3325 // global (common) overflow queue
3326 // . always first empty local work queue
3327 // . then get a batch of oops from global work queue if any
3328 // . then do work stealing
3329 // -- When all tasks claimed (both spaces)
3330 // and local work queue empty,
3331 // then in a loop do:
3332 // . check global overflow stack; steal a batch of oops and trace
3333 // . try to steal from other threads oif GOS is empty
3334 // . if neither is available, offer termination
3335 // -- Terminate and return result
3336 //
3337 void CMSConcMarkingTask::work(uint worker_id) {
3338 elapsedTimer _timer;
3339 ResourceMark rm;
3340 HandleMark hm;
3341
3342 DEBUG_ONLY(_collector->verify_overflow_empty();)
3343
3344 // Before we begin work, our work queue should be empty
3345 assert(work_queue(worker_id)->size() == 0, "Expected to be empty");
3346 // Scan the bitmap covering _cms_space, tracing through grey objects.
3347 _timer.start();
3348 do_scan_and_mark(worker_id, _cms_space);
3349 _timer.stop();
3350 if (PrintCMSStatistics != 0) {
3351 gclog_or_tty->print_cr("Finished cms space scanning in %dth thread: %3.3f sec",
3352 worker_id, _timer.seconds());
3353 // XXX: need xxx/xxx type of notation, two timers
3354 }
3355
3356 // ... do work stealing
3357 _timer.reset();
3358 _timer.start();
3359 do_work_steal(worker_id);
3360 _timer.stop();
3361 if (PrintCMSStatistics != 0) {
3362 gclog_or_tty->print_cr("Finished work stealing in %dth thread: %3.3f sec",
3363 worker_id, _timer.seconds());
3364 // XXX: need xxx/xxx type of notation, two timers
3365 }
3366 assert(_collector->_markStack.isEmpty(), "Should have been emptied");
3367 assert(work_queue(worker_id)->size() == 0, "Should have been emptied");
3368 // Note that under the current task protocol, the
3369 // following assertion is true even of the spaces
3370 // expanded since the completion of the concurrent
3371 // marking. XXX This will likely change under a strict
3372 // ABORT semantics.
3373 // After perm removal the comparison was changed to
3374 // greater than or equal to from strictly greater than.
3375 // Before perm removal the highest address sweep would
3376 // have been at the end of perm gen but now is at the
3377 // end of the tenured gen.
3378 assert(_global_finger >= _cms_space->end(),
3379 "All tasks have been completed");
3380 DEBUG_ONLY(_collector->verify_overflow_empty();)
3381 }
3382
3383 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
3384 HeapWord* read = _global_finger;
3385 HeapWord* cur = read;
3386 while (f > read) {
3387 cur = read;
3388 read = (HeapWord*) Atomic::cmpxchg_ptr(f, &_global_finger, cur);
3389 if (cur == read) {
3390 // our cas succeeded
3391 assert(_global_finger >= f, "protocol consistency");
3392 break;
3393 }
3394 }
3395 }
3396
3397 // This is really inefficient, and should be redone by
3398 // using (not yet available) block-read and -write interfaces to the
3399 // stack and the work_queue. XXX FIX ME !!!
3400 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3401 OopTaskQueue* work_q) {
3402 // Fast lock-free check
3403 if (ovflw_stk->length() == 0) {
3404 return false;
3405 }
3406 assert(work_q->size() == 0, "Shouldn't steal");
3407 MutexLockerEx ml(ovflw_stk->par_lock(),
3408 Mutex::_no_safepoint_check_flag);
3409 // Grab up to 1/4 the size of the work queue
3410 size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
3411 (size_t)ParGCDesiredObjsFromOverflowList);
3412 num = MIN2(num, ovflw_stk->length());
3413 for (int i = (int) num; i > 0; i--) {
3414 oop cur = ovflw_stk->pop();
3415 assert(cur != NULL, "Counted wrong?");
3416 work_q->push(cur);
3417 }
3418 return num > 0;
3419 }
3420
3421 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
3422 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
3423 int n_tasks = pst->n_tasks();
3424 // We allow that there may be no tasks to do here because
3425 // we are restarting after a stack overflow.
3426 assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
3427 uint nth_task = 0;
3428
3429 HeapWord* aligned_start = sp->bottom();
3430 if (sp->used_region().contains(_restart_addr)) {
3431 // Align down to a card boundary for the start of 0th task
3432 // for this space.
3433 aligned_start =
3434 (HeapWord*)align_size_down((uintptr_t)_restart_addr,
3435 CardTableModRefBS::card_size);
3436 }
3437
3438 size_t chunk_size = sp->marking_task_size();
3439 while (!pst->is_task_claimed(/* reference */ nth_task)) {
3440 // Having claimed the nth task in this space,
3441 // compute the chunk that it corresponds to:
3442 MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
3443 aligned_start + (nth_task+1)*chunk_size);
3444 // Try and bump the global finger via a CAS;
3445 // note that we need to do the global finger bump
3446 // _before_ taking the intersection below, because
3447 // the task corresponding to that region will be
3448 // deemed done even if the used_region() expands
3449 // because of allocation -- as it almost certainly will
3450 // during start-up while the threads yield in the
3451 // closure below.
3452 HeapWord* finger = span.end();
3453 bump_global_finger(finger); // atomically
3454 // There are null tasks here corresponding to chunks
3455 // beyond the "top" address of the space.
3456 span = span.intersection(sp->used_region());
3457 if (!span.is_empty()) { // Non-null task
3458 HeapWord* prev_obj;
3459 assert(!span.contains(_restart_addr) || nth_task == 0,
3460 "Inconsistency");
3461 if (nth_task == 0) {
3462 // For the 0th task, we'll not need to compute a block_start.
3463 if (span.contains(_restart_addr)) {
3464 // In the case of a restart because of stack overflow,
3465 // we might additionally skip a chunk prefix.
3466 prev_obj = _restart_addr;
3467 } else {
3468 prev_obj = span.start();
3469 }
3470 } else {
3471 // We want to skip the first object because
3472 // the protocol is to scan any object in its entirety
3473 // that _starts_ in this span; a fortiori, any
3474 // object starting in an earlier span is scanned
3475 // as part of an earlier claimed task.
3476 // Below we use the "careful" version of block_start
3477 // so we do not try to navigate uninitialized objects.
3478 prev_obj = sp->block_start_careful(span.start());
3479 // Below we use a variant of block_size that uses the
3480 // Printezis bits to avoid waiting for allocated
3481 // objects to become initialized/parsable.
3482 while (prev_obj < span.start()) {
3483 size_t sz = sp->block_size_no_stall(prev_obj, _collector);
3484 if (sz > 0) {
3485 prev_obj += sz;
3486 } else {
3487 // In this case we may end up doing a bit of redundant
3488 // scanning, but that appears unavoidable, short of
3489 // locking the free list locks; see bug 6324141.
3490 break;
3491 }
3492 }
3493 }
3494 if (prev_obj < span.end()) {
3495 MemRegion my_span = MemRegion(prev_obj, span.end());
3496 // Do the marking work within a non-empty span --
3497 // the last argument to the constructor indicates whether the
3498 // iteration should be incremental with periodic yields.
3499 Par_MarkFromRootsClosure cl(this, _collector, my_span,
3500 &_collector->_markBitMap,
3501 work_queue(i),
3502 &_collector->_markStack);
3503 _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
3504 } // else nothing to do for this task
3505 } // else nothing to do for this task
3506 }
3507 // We'd be tempted to assert here that since there are no
3508 // more tasks left to claim in this space, the global_finger
3509 // must exceed space->top() and a fortiori space->end(). However,
3510 // that would not quite be correct because the bumping of
3511 // global_finger occurs strictly after the claiming of a task,
3512 // so by the time we reach here the global finger may not yet
3513 // have been bumped up by the thread that claimed the last
3514 // task.
3515 pst->all_tasks_completed();
3516 }
3517
3518 class Par_ConcMarkingClosure: public MetadataAwareOopClosure {
3519 private:
3520 CMSCollector* _collector;
3521 CMSConcMarkingTask* _task;
3522 MemRegion _span;
3523 CMSBitMap* _bit_map;
3524 CMSMarkStack* _overflow_stack;
3525 OopTaskQueue* _work_queue;
3526 protected:
3527 DO_OOP_WORK_DEFN
3528 public:
3529 Par_ConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue,
3530 CMSBitMap* bit_map, CMSMarkStack* overflow_stack):
3531 MetadataAwareOopClosure(collector->ref_processor()),
3532 _collector(collector),
3533 _task(task),
3534 _span(collector->_span),
3535 _work_queue(work_queue),
3536 _bit_map(bit_map),
3537 _overflow_stack(overflow_stack)
3538 { }
3539 virtual void do_oop(oop* p);
3540 virtual void do_oop(narrowOop* p);
3541
3542 void trim_queue(size_t max);
3543 void handle_stack_overflow(HeapWord* lost);
3544 void do_yield_check() {
3545 if (_task->should_yield()) {
3546 _task->yield();
3547 }
3548 }
3549 };
3550
3551 // Grey object scanning during work stealing phase --
3552 // the salient assumption here is that any references
3553 // that are in these stolen objects being scanned must
3554 // already have been initialized (else they would not have
3555 // been published), so we do not need to check for
3556 // uninitialized objects before pushing here.
3557 void Par_ConcMarkingClosure::do_oop(oop obj) {
3558 assert(obj->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
3559 HeapWord* addr = (HeapWord*)obj;
3560 // Check if oop points into the CMS generation
3561 // and is not marked
3562 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
3563 // a white object ...
3564 // If we manage to "claim" the object, by being the
3565 // first thread to mark it, then we push it on our
3566 // marking stack
3567 if (_bit_map->par_mark(addr)) { // ... now grey
3568 // push on work queue (grey set)
3569 bool simulate_overflow = false;
3570 NOT_PRODUCT(
3571 if (CMSMarkStackOverflowALot &&
3572 _collector->simulate_overflow()) {
3573 // simulate a stack overflow
3574 simulate_overflow = true;
3575 }
3576 )
3577 if (simulate_overflow ||
3578 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
3579 // stack overflow
3580 if (PrintCMSStatistics != 0) {
3581 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
3582 SIZE_FORMAT, _overflow_stack->capacity());
3583 }
3584 // We cannot assert that the overflow stack is full because
3585 // it may have been emptied since.
3586 assert(simulate_overflow ||
3587 _work_queue->size() == _work_queue->max_elems(),
3588 "Else push should have succeeded");
3589 handle_stack_overflow(addr);
3590 }
3591 } // Else, some other thread got there first
3592 do_yield_check();
3593 }
3594 }
3595
3596 void Par_ConcMarkingClosure::do_oop(oop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
3597 void Par_ConcMarkingClosure::do_oop(narrowOop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
3598
3599 void Par_ConcMarkingClosure::trim_queue(size_t max) {
3600 while (_work_queue->size() > max) {
3601 oop new_oop;
3602 if (_work_queue->pop_local(new_oop)) {
3603 assert(new_oop->is_oop(), "Should be an oop");
3604 assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
3605 assert(_span.contains((HeapWord*)new_oop), "Not in span");
3606 new_oop->oop_iterate(this); // do_oop() above
3607 do_yield_check();
3608 }
3609 }
3610 }
3611
3612 // Upon stack overflow, we discard (part of) the stack,
3613 // remembering the least address amongst those discarded
3614 // in CMSCollector's _restart_address.
3615 void Par_ConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
3616 // We need to do this under a mutex to prevent other
3617 // workers from interfering with the work done below.
3618 MutexLockerEx ml(_overflow_stack->par_lock(),
3619 Mutex::_no_safepoint_check_flag);
3620 // Remember the least grey address discarded
3621 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
3622 _collector->lower_restart_addr(ra);
3623 _overflow_stack->reset(); // discard stack contents
3624 _overflow_stack->expand(); // expand the stack if possible
3625 }
3626
3627
3628 void CMSConcMarkingTask::do_work_steal(int i) {
3629 OopTaskQueue* work_q = work_queue(i);
3630 oop obj_to_scan;
3631 CMSBitMap* bm = &(_collector->_markBitMap);
3632 CMSMarkStack* ovflw = &(_collector->_markStack);
3633 int* seed = _collector->hash_seed(i);
3634 Par_ConcMarkingClosure cl(_collector, this, work_q, bm, ovflw);
3635 while (true) {
3636 cl.trim_queue(0);
3637 assert(work_q->size() == 0, "Should have been emptied above");
3638 if (get_work_from_overflow_stack(ovflw, work_q)) {
3639 // Can't assert below because the work obtained from the
3640 // overflow stack may already have been stolen from us.
3641 // assert(work_q->size() > 0, "Work from overflow stack");
3642 continue;
3643 } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
3644 assert(obj_to_scan->is_oop(), "Should be an oop");
3645 assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
3646 obj_to_scan->oop_iterate(&cl);
3647 } else if (terminator()->offer_termination(&_term_term)) {
3648 assert(work_q->size() == 0, "Impossible!");
3649 break;
3650 } else if (yielding() || should_yield()) {
3651 yield();
3652 }
3653 }
3654 }
3655
3656 // This is run by the CMS (coordinator) thread.
3657 void CMSConcMarkingTask::coordinator_yield() {
3658 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3659 "CMS thread should hold CMS token");
3660 // First give up the locks, then yield, then re-lock
3661 // We should probably use a constructor/destructor idiom to
3662 // do this unlock/lock or modify the MutexUnlocker class to
3663 // serve our purpose. XXX
3664 assert_lock_strong(_bit_map_lock);
3665 _bit_map_lock->unlock();
3666 ConcurrentMarkSweepThread::desynchronize(true);
3667 _collector->stopTimer();
3668 if (PrintCMSStatistics != 0) {
3669 _collector->incrementYields();
3670 }
3671
3672 // It is possible for whichever thread initiated the yield request
3673 // not to get a chance to wake up and take the bitmap lock between
3674 // this thread releasing it and reacquiring it. So, while the
3675 // should_yield() flag is on, let's sleep for a bit to give the
3676 // other thread a chance to wake up. The limit imposed on the number
3677 // of iterations is defensive, to avoid any unforseen circumstances
3678 // putting us into an infinite loop. Since it's always been this
3679 // (coordinator_yield()) method that was observed to cause the
3680 // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
3681 // which is by default non-zero. For the other seven methods that
3682 // also perform the yield operation, as are using a different
3683 // parameter (CMSYieldSleepCount) which is by default zero. This way we
3684 // can enable the sleeping for those methods too, if necessary.
3685 // See 6442774.
3686 //
3687 // We really need to reconsider the synchronization between the GC
3688 // thread and the yield-requesting threads in the future and we
3689 // should really use wait/notify, which is the recommended
3690 // way of doing this type of interaction. Additionally, we should
3691 // consolidate the eight methods that do the yield operation and they
3692 // are almost identical into one for better maintainability and
3693 // readability. See 6445193.
3694 //
3695 // Tony 2006.06.29
3696 for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
3697 ConcurrentMarkSweepThread::should_yield() &&
3698 !CMSCollector::foregroundGCIsActive(); ++i) {
3699 os::sleep(Thread::current(), 1, false);
3700 }
3701
3702 ConcurrentMarkSweepThread::synchronize(true);
3703 _bit_map_lock->lock_without_safepoint_check();
3704 _collector->startTimer();
3705 }
3706
3707 bool CMSCollector::do_marking_mt() {
3708 assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition");
3709 int num_workers = AdaptiveSizePolicy::calc_active_conc_workers(
3710 conc_workers()->total_workers(),
3711 conc_workers()->active_workers(),
3712 Threads::number_of_non_daemon_threads());
3713 conc_workers()->set_active_workers(num_workers);
3714
3715 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
3716
3717 CMSConcMarkingTask tsk(this,
3718 cms_space,
3719 conc_workers(),
3720 task_queues());
3721
3722 // Since the actual number of workers we get may be different
3723 // from the number we requested above, do we need to do anything different
3724 // below? In particular, may be we need to subclass the SequantialSubTasksDone
3725 // class?? XXX
3726 cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
3727
3728 // Refs discovery is already non-atomic.
3729 assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
3730 assert(ref_processor()->discovery_is_mt(), "Discovery should be MT");
3731 conc_workers()->start_task(&tsk);
3732 while (tsk.yielded()) {
3733 tsk.coordinator_yield();
3734 conc_workers()->continue_task(&tsk);
3735 }
3736 // If the task was aborted, _restart_addr will be non-NULL
3737 assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
3738 while (_restart_addr != NULL) {
3739 // XXX For now we do not make use of ABORTED state and have not
3740 // yet implemented the right abort semantics (even in the original
3741 // single-threaded CMS case). That needs some more investigation
3742 // and is deferred for now; see CR# TBF. 07252005YSR. XXX
3743 assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
3744 // If _restart_addr is non-NULL, a marking stack overflow
3745 // occurred; we need to do a fresh marking iteration from the
3746 // indicated restart address.
3747 if (_foregroundGCIsActive) {
3748 // We may be running into repeated stack overflows, having
3749 // reached the limit of the stack size, while making very
3750 // slow forward progress. It may be best to bail out and
3751 // let the foreground collector do its job.
3752 // Clear _restart_addr, so that foreground GC
3753 // works from scratch. This avoids the headache of
3754 // a "rescan" which would otherwise be needed because
3755 // of the dirty mod union table & card table.
3756 _restart_addr = NULL;
3757 return false;
3758 }
3759 // Adjust the task to restart from _restart_addr
3760 tsk.reset(_restart_addr);
3761 cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
3762 _restart_addr);
3763 _restart_addr = NULL;
3764 // Get the workers going again
3765 conc_workers()->start_task(&tsk);
3766 while (tsk.yielded()) {
3767 tsk.coordinator_yield();
3768 conc_workers()->continue_task(&tsk);
3769 }
3770 }
3771 assert(tsk.completed(), "Inconsistency");
3772 assert(tsk.result() == true, "Inconsistency");
3773 return true;
3774 }
3775
3776 bool CMSCollector::do_marking_st() {
3777 ResourceMark rm;
3778 HandleMark hm;
3779
3780 // Temporarily make refs discovery single threaded (non-MT)
3781 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
3782 MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
3783 &_markStack, CMSYield);
3784 // the last argument to iterate indicates whether the iteration
3785 // should be incremental with periodic yields.
3786 _markBitMap.iterate(&markFromRootsClosure);
3787 // If _restart_addr is non-NULL, a marking stack overflow
3788 // occurred; we need to do a fresh iteration from the
3789 // indicated restart address.
3790 while (_restart_addr != NULL) {
3791 if (_foregroundGCIsActive) {
3792 // We may be running into repeated stack overflows, having
3793 // reached the limit of the stack size, while making very
3794 // slow forward progress. It may be best to bail out and
3795 // let the foreground collector do its job.
3796 // Clear _restart_addr, so that foreground GC
3797 // works from scratch. This avoids the headache of
3798 // a "rescan" which would otherwise be needed because
3799 // of the dirty mod union table & card table.
3800 _restart_addr = NULL;
3801 return false; // indicating failure to complete marking
3802 }
3803 // Deal with stack overflow:
3804 // we restart marking from _restart_addr
3805 HeapWord* ra = _restart_addr;
3806 markFromRootsClosure.reset(ra);
3807 _restart_addr = NULL;
3808 _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
3809 }
3810 return true;
3811 }
3812
3813 void CMSCollector::preclean() {
3814 check_correct_thread_executing();
3815 assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
3816 verify_work_stacks_empty();
3817 verify_overflow_empty();
3818 _abort_preclean = false;
3819 if (CMSPrecleaningEnabled) {
3820 if (!CMSEdenChunksRecordAlways) {
3821 _eden_chunk_index = 0;
3822 }
3823 size_t used = get_eden_used();
3824 size_t capacity = get_eden_capacity();
3825 // Don't start sampling unless we will get sufficiently
3826 // many samples.
3827 if (used < (capacity/(CMSScheduleRemarkSamplingRatio * 100)
3828 * CMSScheduleRemarkEdenPenetration)) {
3829 _start_sampling = true;
3830 } else {
3831 _start_sampling = false;
3832 }
3833 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3834 CMSPhaseAccounting pa(this, "preclean", _gc_tracer_cm->gc_id(), !PrintGCDetails);
3835 preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
3836 }
3837 CMSTokenSync x(true); // is cms thread
3838 if (CMSPrecleaningEnabled) {
3839 sample_eden();
3840 _collectorState = AbortablePreclean;
3841 } else {
3842 _collectorState = FinalMarking;
3843 }
3844 verify_work_stacks_empty();
3845 verify_overflow_empty();
3846 }
3847
3848 // Try and schedule the remark such that young gen
3849 // occupancy is CMSScheduleRemarkEdenPenetration %.
3850 void CMSCollector::abortable_preclean() {
3851 check_correct_thread_executing();
3852 assert(CMSPrecleaningEnabled, "Inconsistent control state");
3853 assert(_collectorState == AbortablePreclean, "Inconsistent control state");
3854
3855 // If Eden's current occupancy is below this threshold,
3856 // immediately schedule the remark; else preclean
3857 // past the next scavenge in an effort to
3858 // schedule the pause as described above. By choosing
3859 // CMSScheduleRemarkEdenSizeThreshold >= max eden size
3860 // we will never do an actual abortable preclean cycle.
3861 if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
3862 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3863 CMSPhaseAccounting pa(this, "abortable-preclean", _gc_tracer_cm->gc_id(), !PrintGCDetails);
3864 // We need more smarts in the abortable preclean
3865 // loop below to deal with cases where allocation
3866 // in young gen is very very slow, and our precleaning
3867 // is running a losing race against a horde of
3868 // mutators intent on flooding us with CMS updates
3869 // (dirty cards).
3870 // One, admittedly dumb, strategy is to give up
3871 // after a certain number of abortable precleaning loops
3872 // or after a certain maximum time. We want to make
3873 // this smarter in the next iteration.
3874 // XXX FIX ME!!! YSR
3875 size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
3876 while (!(should_abort_preclean() ||
3877 ConcurrentMarkSweepThread::should_terminate())) {
3878 workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
3879 cumworkdone += workdone;
3880 loops++;
3881 // Voluntarily terminate abortable preclean phase if we have
3882 // been at it for too long.
3883 if ((CMSMaxAbortablePrecleanLoops != 0) &&
3884 loops >= CMSMaxAbortablePrecleanLoops) {
3885 if (PrintGCDetails) {
3886 gclog_or_tty->print(" CMS: abort preclean due to loops ");
3887 }
3888 break;
3889 }
3890 if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
3891 if (PrintGCDetails) {
3892 gclog_or_tty->print(" CMS: abort preclean due to time ");
3893 }
3894 break;
3895 }
3896 // If we are doing little work each iteration, we should
3897 // take a short break.
3898 if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
3899 // Sleep for some time, waiting for work to accumulate
3900 stopTimer();
3901 cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
3902 startTimer();
3903 waited++;
3904 }
3905 }
3906 if (PrintCMSStatistics > 0) {
3907 gclog_or_tty->print(" [" SIZE_FORMAT " iterations, " SIZE_FORMAT " waits, " SIZE_FORMAT " cards)] ",
3908 loops, waited, cumworkdone);
3909 }
3910 }
3911 CMSTokenSync x(true); // is cms thread
3912 if (_collectorState != Idling) {
3913 assert(_collectorState == AbortablePreclean,
3914 "Spontaneous state transition?");
3915 _collectorState = FinalMarking;
3916 } // Else, a foreground collection completed this CMS cycle.
3917 return;
3918 }
3919
3920 // Respond to an Eden sampling opportunity
3921 void CMSCollector::sample_eden() {
3922 // Make sure a young gc cannot sneak in between our
3923 // reading and recording of a sample.
3924 assert(Thread::current()->is_ConcurrentGC_thread(),
3925 "Only the cms thread may collect Eden samples");
3926 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3927 "Should collect samples while holding CMS token");
3928 if (!_start_sampling) {
3929 return;
3930 }
3931 // When CMSEdenChunksRecordAlways is true, the eden chunk array
3932 // is populated by the young generation.
3933 if (_eden_chunk_array != NULL && !CMSEdenChunksRecordAlways) {
3934 if (_eden_chunk_index < _eden_chunk_capacity) {
3935 _eden_chunk_array[_eden_chunk_index] = *_top_addr; // take sample
3936 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
3937 "Unexpected state of Eden");
3938 // We'd like to check that what we just sampled is an oop-start address;
3939 // however, we cannot do that here since the object may not yet have been
3940 // initialized. So we'll instead do the check when we _use_ this sample
3941 // later.
3942 if (_eden_chunk_index == 0 ||
3943 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
3944 _eden_chunk_array[_eden_chunk_index-1])
3945 >= CMSSamplingGrain)) {
3946 _eden_chunk_index++; // commit sample
3947 }
3948 }
3949 }
3950 if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
3951 size_t used = get_eden_used();
3952 size_t capacity = get_eden_capacity();
3953 assert(used <= capacity, "Unexpected state of Eden");
3954 if (used > (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
3955 _abort_preclean = true;
3956 }
3957 }
3958 }
3959
3960
3961 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
3962 assert(_collectorState == Precleaning ||
3963 _collectorState == AbortablePreclean, "incorrect state");
3964 ResourceMark rm;
3965 HandleMark hm;
3966
3967 // Precleaning is currently not MT but the reference processor
3968 // may be set for MT. Disable it temporarily here.
3969 ReferenceProcessor* rp = ref_processor();
3970 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false);
3971
3972 // Do one pass of scrubbing the discovered reference lists
3973 // to remove any reference objects with strongly-reachable
3974 // referents.
3975 if (clean_refs) {
3976 CMSPrecleanRefsYieldClosure yield_cl(this);
3977 assert(rp->span().equals(_span), "Spans should be equal");
3978 CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
3979 &_markStack, true /* preclean */);
3980 CMSDrainMarkingStackClosure complete_trace(this,
3981 _span, &_markBitMap, &_markStack,
3982 &keep_alive, true /* preclean */);
3983
3984 // We don't want this step to interfere with a young
3985 // collection because we don't want to take CPU
3986 // or memory bandwidth away from the young GC threads
3987 // (which may be as many as there are CPUs).
3988 // Note that we don't need to protect ourselves from
3989 // interference with mutators because they can't
3990 // manipulate the discovered reference lists nor affect
3991 // the computed reachability of the referents, the
3992 // only properties manipulated by the precleaning
3993 // of these reference lists.
3994 stopTimer();
3995 CMSTokenSyncWithLocks x(true /* is cms thread */,
3996 bitMapLock());
3997 startTimer();
3998 sample_eden();
3999
4000 // The following will yield to allow foreground
4001 // collection to proceed promptly. XXX YSR:
4002 // The code in this method may need further
4003 // tweaking for better performance and some restructuring
4004 // for cleaner interfaces.
4005 GCTimer *gc_timer = NULL; // Currently not tracing concurrent phases
4006 rp->preclean_discovered_references(
4007 rp->is_alive_non_header(), &keep_alive, &complete_trace, &yield_cl,
4008 gc_timer, _gc_tracer_cm->gc_id());
4009 }
4010
4011 if (clean_survivor) { // preclean the active survivor space(s)
4012 PushAndMarkClosure pam_cl(this, _span, ref_processor(),
4013 &_markBitMap, &_modUnionTable,
4014 &_markStack, true /* precleaning phase */);
4015 stopTimer();
4016 CMSTokenSyncWithLocks ts(true /* is cms thread */,
4017 bitMapLock());
4018 startTimer();
4019 unsigned int before_count =
4020 GenCollectedHeap::heap()->total_collections();
4021 SurvivorSpacePrecleanClosure
4022 sss_cl(this, _span, &_markBitMap, &_markStack,
4023 &pam_cl, before_count, CMSYield);
4024 _young_gen->from()->object_iterate_careful(&sss_cl);
4025 _young_gen->to()->object_iterate_careful(&sss_cl);
4026 }
4027 MarkRefsIntoAndScanClosure
4028 mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
4029 &_markStack, this, CMSYield,
4030 true /* precleaning phase */);
4031 // CAUTION: The following closure has persistent state that may need to
4032 // be reset upon a decrease in the sequence of addresses it
4033 // processes.
4034 ScanMarkedObjectsAgainCarefullyClosure
4035 smoac_cl(this, _span,
4036 &_markBitMap, &_markStack, &mrias_cl, CMSYield);
4037
4038 // Preclean dirty cards in ModUnionTable and CardTable using
4039 // appropriate convergence criterion;
4040 // repeat CMSPrecleanIter times unless we find that
4041 // we are losing.
4042 assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
4043 assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
4044 "Bad convergence multiplier");
4045 assert(CMSPrecleanThreshold >= 100,
4046 "Unreasonably low CMSPrecleanThreshold");
4047
4048 size_t numIter, cumNumCards, lastNumCards, curNumCards;
4049 for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
4050 numIter < CMSPrecleanIter;
4051 numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
4052 curNumCards = preclean_mod_union_table(_cmsGen, &smoac_cl);
4053 if (Verbose && PrintGCDetails) {
4054 gclog_or_tty->print(" (modUnionTable: " SIZE_FORMAT " cards)", curNumCards);
4055 }
4056 // Either there are very few dirty cards, so re-mark
4057 // pause will be small anyway, or our pre-cleaning isn't
4058 // that much faster than the rate at which cards are being
4059 // dirtied, so we might as well stop and re-mark since
4060 // precleaning won't improve our re-mark time by much.
4061 if (curNumCards <= CMSPrecleanThreshold ||
4062 (numIter > 0 &&
4063 (curNumCards * CMSPrecleanDenominator >
4064 lastNumCards * CMSPrecleanNumerator))) {
4065 numIter++;
4066 cumNumCards += curNumCards;
4067 break;
4068 }
4069 }
4070
4071 preclean_klasses(&mrias_cl, _cmsGen->freelistLock());
4072
4073 curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
4074 cumNumCards += curNumCards;
4075 if (PrintGCDetails && PrintCMSStatistics != 0) {
4076 gclog_or_tty->print_cr(" (cardTable: " SIZE_FORMAT " cards, re-scanned " SIZE_FORMAT " cards, " SIZE_FORMAT " iterations)",
4077 curNumCards, cumNumCards, numIter);
4078 }
4079 return cumNumCards; // as a measure of useful work done
4080 }
4081
4082 // PRECLEANING NOTES:
4083 // Precleaning involves:
4084 // . reading the bits of the modUnionTable and clearing the set bits.
4085 // . For the cards corresponding to the set bits, we scan the
4086 // objects on those cards. This means we need the free_list_lock
4087 // so that we can safely iterate over the CMS space when scanning
4088 // for oops.
4089 // . When we scan the objects, we'll be both reading and setting
4090 // marks in the marking bit map, so we'll need the marking bit map.
4091 // . For protecting _collector_state transitions, we take the CGC_lock.
4092 // Note that any races in the reading of of card table entries by the
4093 // CMS thread on the one hand and the clearing of those entries by the
4094 // VM thread or the setting of those entries by the mutator threads on the
4095 // other are quite benign. However, for efficiency it makes sense to keep
4096 // the VM thread from racing with the CMS thread while the latter is
4097 // dirty card info to the modUnionTable. We therefore also use the
4098 // CGC_lock to protect the reading of the card table and the mod union
4099 // table by the CM thread.
4100 // . We run concurrently with mutator updates, so scanning
4101 // needs to be done carefully -- we should not try to scan
4102 // potentially uninitialized objects.
4103 //
4104 // Locking strategy: While holding the CGC_lock, we scan over and
4105 // reset a maximal dirty range of the mod union / card tables, then lock
4106 // the free_list_lock and bitmap lock to do a full marking, then
4107 // release these locks; and repeat the cycle. This allows for a
4108 // certain amount of fairness in the sharing of these locks between
4109 // the CMS collector on the one hand, and the VM thread and the
4110 // mutators on the other.
4111
4112 // NOTE: preclean_mod_union_table() and preclean_card_table()
4113 // further below are largely identical; if you need to modify
4114 // one of these methods, please check the other method too.
4115
4116 size_t CMSCollector::preclean_mod_union_table(
4117 ConcurrentMarkSweepGeneration* gen,
4118 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4119 verify_work_stacks_empty();
4120 verify_overflow_empty();
4121
4122 // strategy: starting with the first card, accumulate contiguous
4123 // ranges of dirty cards; clear these cards, then scan the region
4124 // covered by these cards.
4125
4126 // Since all of the MUT is committed ahead, we can just use
4127 // that, in case the generations expand while we are precleaning.
4128 // It might also be fine to just use the committed part of the
4129 // generation, but we might potentially miss cards when the
4130 // generation is rapidly expanding while we are in the midst
4131 // of precleaning.
4132 HeapWord* startAddr = gen->reserved().start();
4133 HeapWord* endAddr = gen->reserved().end();
4134
4135 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4136
4137 size_t numDirtyCards, cumNumDirtyCards;
4138 HeapWord *nextAddr, *lastAddr;
4139 for (cumNumDirtyCards = numDirtyCards = 0,
4140 nextAddr = lastAddr = startAddr;
4141 nextAddr < endAddr;
4142 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4143
4144 ResourceMark rm;
4145 HandleMark hm;
4146
4147 MemRegion dirtyRegion;
4148 {
4149 stopTimer();
4150 // Potential yield point
4151 CMSTokenSync ts(true);
4152 startTimer();
4153 sample_eden();
4154 // Get dirty region starting at nextOffset (inclusive),
4155 // simultaneously clearing it.
4156 dirtyRegion =
4157 _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
4158 assert(dirtyRegion.start() >= nextAddr,
4159 "returned region inconsistent?");
4160 }
4161 // Remember where the next search should begin.
4162 // The returned region (if non-empty) is a right open interval,
4163 // so lastOffset is obtained from the right end of that
4164 // interval.
4165 lastAddr = dirtyRegion.end();
4166 // Should do something more transparent and less hacky XXX
4167 numDirtyCards =
4168 _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
4169
4170 // We'll scan the cards in the dirty region (with periodic
4171 // yields for foreground GC as needed).
4172 if (!dirtyRegion.is_empty()) {
4173 assert(numDirtyCards > 0, "consistency check");
4174 HeapWord* stop_point = NULL;
4175 stopTimer();
4176 // Potential yield point
4177 CMSTokenSyncWithLocks ts(true, gen->freelistLock(),
4178 bitMapLock());
4179 startTimer();
4180 {
4181 verify_work_stacks_empty();
4182 verify_overflow_empty();
4183 sample_eden();
4184 stop_point =
4185 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4186 }
4187 if (stop_point != NULL) {
4188 // The careful iteration stopped early either because it found an
4189 // uninitialized object, or because we were in the midst of an
4190 // "abortable preclean", which should now be aborted. Redirty
4191 // the bits corresponding to the partially-scanned or unscanned
4192 // cards. We'll either restart at the next block boundary or
4193 // abort the preclean.
4194 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4195 "Should only be AbortablePreclean.");
4196 _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
4197 if (should_abort_preclean()) {
4198 break; // out of preclean loop
4199 } else {
4200 // Compute the next address at which preclean should pick up;
4201 // might need bitMapLock in order to read P-bits.
4202 lastAddr = next_card_start_after_block(stop_point);
4203 }
4204 }
4205 } else {
4206 assert(lastAddr == endAddr, "consistency check");
4207 assert(numDirtyCards == 0, "consistency check");
4208 break;
4209 }
4210 }
4211 verify_work_stacks_empty();
4212 verify_overflow_empty();
4213 return cumNumDirtyCards;
4214 }
4215
4216 // NOTE: preclean_mod_union_table() above and preclean_card_table()
4217 // below are largely identical; if you need to modify
4218 // one of these methods, please check the other method too.
4219
4220 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* gen,
4221 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4222 // strategy: it's similar to precleamModUnionTable above, in that
4223 // we accumulate contiguous ranges of dirty cards, mark these cards
4224 // precleaned, then scan the region covered by these cards.
4225 HeapWord* endAddr = (HeapWord*)(gen->_virtual_space.high());
4226 HeapWord* startAddr = (HeapWord*)(gen->_virtual_space.low());
4227
4228 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4229
4230 size_t numDirtyCards, cumNumDirtyCards;
4231 HeapWord *lastAddr, *nextAddr;
4232
4233 for (cumNumDirtyCards = numDirtyCards = 0,
4234 nextAddr = lastAddr = startAddr;
4235 nextAddr < endAddr;
4236 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4237
4238 ResourceMark rm;
4239 HandleMark hm;
4240
4241 MemRegion dirtyRegion;
4242 {
4243 // See comments in "Precleaning notes" above on why we
4244 // do this locking. XXX Could the locking overheads be
4245 // too high when dirty cards are sparse? [I don't think so.]
4246 stopTimer();
4247 CMSTokenSync x(true); // is cms thread
4248 startTimer();
4249 sample_eden();
4250 // Get and clear dirty region from card table
4251 dirtyRegion = _ct->ct_bs()->dirty_card_range_after_reset(
4252 MemRegion(nextAddr, endAddr),
4253 true,
4254 CardTableModRefBS::precleaned_card_val());
4255
4256 assert(dirtyRegion.start() >= nextAddr,
4257 "returned region inconsistent?");
4258 }
4259 lastAddr = dirtyRegion.end();
4260 numDirtyCards =
4261 dirtyRegion.word_size()/CardTableModRefBS::card_size_in_words;
4262
4263 if (!dirtyRegion.is_empty()) {
4264 stopTimer();
4265 CMSTokenSyncWithLocks ts(true, gen->freelistLock(), bitMapLock());
4266 startTimer();
4267 sample_eden();
4268 verify_work_stacks_empty();
4269 verify_overflow_empty();
4270 HeapWord* stop_point =
4271 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4272 if (stop_point != NULL) {
4273 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4274 "Should only be AbortablePreclean.");
4275 _ct->ct_bs()->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4276 if (should_abort_preclean()) {
4277 break; // out of preclean loop
4278 } else {
4279 // Compute the next address at which preclean should pick up.
4280 lastAddr = next_card_start_after_block(stop_point);
4281 }
4282 }
4283 } else {
4284 break;
4285 }
4286 }
4287 verify_work_stacks_empty();
4288 verify_overflow_empty();
4289 return cumNumDirtyCards;
4290 }
4291
4292 class PrecleanKlassClosure : public KlassClosure {
4293 KlassToOopClosure _cm_klass_closure;
4294 public:
4295 PrecleanKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4296 void do_klass(Klass* k) {
4297 if (k->has_accumulated_modified_oops()) {
4298 k->clear_accumulated_modified_oops();
4299
4300 _cm_klass_closure.do_klass(k);
4301 }
4302 }
4303 };
4304
4305 // The freelist lock is needed to prevent asserts, is it really needed?
4306 void CMSCollector::preclean_klasses(MarkRefsIntoAndScanClosure* cl, Mutex* freelistLock) {
4307
4308 cl->set_freelistLock(freelistLock);
4309
4310 CMSTokenSyncWithLocks ts(true, freelistLock, bitMapLock());
4311
4312 // SSS: Add equivalent to ScanMarkedObjectsAgainCarefullyClosure::do_yield_check and should_abort_preclean?
4313 // SSS: We should probably check if precleaning should be aborted, at suitable intervals?
4314 PrecleanKlassClosure preclean_klass_closure(cl);
4315 ClassLoaderDataGraph::classes_do(&preclean_klass_closure);
4316
4317 verify_work_stacks_empty();
4318 verify_overflow_empty();
4319 }
4320
4321 void CMSCollector::checkpointRootsFinal() {
4322 assert(_collectorState == FinalMarking, "incorrect state transition?");
4323 check_correct_thread_executing();
4324 // world is stopped at this checkpoint
4325 assert(SafepointSynchronize::is_at_safepoint(),
4326 "world should be stopped");
4327 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
4328
4329 verify_work_stacks_empty();
4330 verify_overflow_empty();
4331
4332 SpecializationStats::clear();
4333 if (PrintGCDetails) {
4334 gclog_or_tty->print("[YG occupancy: "SIZE_FORMAT" K ("SIZE_FORMAT" K)]",
4335 _young_gen->used() / K,
4336 _young_gen->capacity() / K);
4337 }
4338 {
4339 if (CMSScavengeBeforeRemark) {
4340 GenCollectedHeap* gch = GenCollectedHeap::heap();
4341 // Temporarily set flag to false, GCH->do_collection will
4342 // expect it to be false and set to true
4343 FlagSetting fl(gch->_is_gc_active, false);
4344 NOT_PRODUCT(GCTraceTime t("Scavenge-Before-Remark",
4345 PrintGCDetails && Verbose, true, _gc_timer_cm, _gc_tracer_cm->gc_id());)
4346 int level = _cmsGen->level() - 1;
4347 if (level >= 0) {
4348 gch->do_collection(true, // full (i.e. force, see below)
4349 false, // !clear_all_soft_refs
4350 0, // size
4351 false, // is_tlab
4352 level // max_level
4353 );
4354 }
4355 }
4356 FreelistLocker x(this);
4357 MutexLockerEx y(bitMapLock(),
4358 Mutex::_no_safepoint_check_flag);
4359 checkpointRootsFinalWork();
4360 }
4361 verify_work_stacks_empty();
4362 verify_overflow_empty();
4363 SpecializationStats::print();
4364 }
4365
4366 void CMSCollector::checkpointRootsFinalWork() {
4367 NOT_PRODUCT(GCTraceTime tr("checkpointRootsFinalWork", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());)
4368
4369 assert(haveFreelistLocks(), "must have free list locks");
4370 assert_lock_strong(bitMapLock());
4371
4372 ResourceMark rm;
4373 HandleMark hm;
4374
4375 GenCollectedHeap* gch = GenCollectedHeap::heap();
4376
4377 if (should_unload_classes()) {
4378 CodeCache::gc_prologue();
4379 }
4380 assert(haveFreelistLocks(), "must have free list locks");
4381 assert_lock_strong(bitMapLock());
4382
4383 // We might assume that we need not fill TLAB's when
4384 // CMSScavengeBeforeRemark is set, because we may have just done
4385 // a scavenge which would have filled all TLAB's -- and besides
4386 // Eden would be empty. This however may not always be the case --
4387 // for instance although we asked for a scavenge, it may not have
4388 // happened because of a JNI critical section. We probably need
4389 // a policy for deciding whether we can in that case wait until
4390 // the critical section releases and then do the remark following
4391 // the scavenge, and skip it here. In the absence of that policy,
4392 // or of an indication of whether the scavenge did indeed occur,
4393 // we cannot rely on TLAB's having been filled and must do
4394 // so here just in case a scavenge did not happen.
4395 gch->ensure_parsability(false); // fill TLAB's, but no need to retire them
4396 // Update the saved marks which may affect the root scans.
4397 gch->save_marks();
4398
4399 if (CMSPrintEdenSurvivorChunks) {
4400 print_eden_and_survivor_chunk_arrays();
4401 }
4402
4403 {
4404 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
4405
4406 // Note on the role of the mod union table:
4407 // Since the marker in "markFromRoots" marks concurrently with
4408 // mutators, it is possible for some reachable objects not to have been
4409 // scanned. For instance, an only reference to an object A was
4410 // placed in object B after the marker scanned B. Unless B is rescanned,
4411 // A would be collected. Such updates to references in marked objects
4412 // are detected via the mod union table which is the set of all cards
4413 // dirtied since the first checkpoint in this GC cycle and prior to
4414 // the most recent young generation GC, minus those cleaned up by the
4415 // concurrent precleaning.
4416 if (CMSParallelRemarkEnabled && CollectedHeap::use_parallel_gc_threads()) {
4417 GCTraceTime t("Rescan (parallel) ", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
4418 do_remark_parallel();
4419 } else {
4420 GCTraceTime t("Rescan (non-parallel) ", PrintGCDetails, false,
4421 _gc_timer_cm, _gc_tracer_cm->gc_id());
4422 do_remark_non_parallel();
4423 }
4424 }
4425 verify_work_stacks_empty();
4426 verify_overflow_empty();
4427
4428 {
4429 NOT_PRODUCT(GCTraceTime ts("refProcessingWork", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());)
4430 refProcessingWork();
4431 }
4432 verify_work_stacks_empty();
4433 verify_overflow_empty();
4434
4435 if (should_unload_classes()) {
4436 CodeCache::gc_epilogue();
4437 }
4438 JvmtiExport::gc_epilogue();
4439
4440 // If we encountered any (marking stack / work queue) overflow
4441 // events during the current CMS cycle, take appropriate
4442 // remedial measures, where possible, so as to try and avoid
4443 // recurrence of that condition.
4444 assert(_markStack.isEmpty(), "No grey objects");
4445 size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
4446 _ser_kac_ovflw + _ser_kac_preclean_ovflw;
4447 if (ser_ovflw > 0) {
4448 if (PrintCMSStatistics != 0) {
4449 gclog_or_tty->print_cr("Marking stack overflow (benign) "
4450 "(pmc_pc="SIZE_FORMAT", pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT
4451 ", kac_preclean="SIZE_FORMAT")",
4452 _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw,
4453 _ser_kac_ovflw, _ser_kac_preclean_ovflw);
4454 }
4455 _markStack.expand();
4456 _ser_pmc_remark_ovflw = 0;
4457 _ser_pmc_preclean_ovflw = 0;
4458 _ser_kac_preclean_ovflw = 0;
4459 _ser_kac_ovflw = 0;
4460 }
4461 if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
4462 if (PrintCMSStatistics != 0) {
4463 gclog_or_tty->print_cr("Work queue overflow (benign) "
4464 "(pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT")",
4465 _par_pmc_remark_ovflw, _par_kac_ovflw);
4466 }
4467 _par_pmc_remark_ovflw = 0;
4468 _par_kac_ovflw = 0;
4469 }
4470 if (PrintCMSStatistics != 0) {
4471 if (_markStack._hit_limit > 0) {
4472 gclog_or_tty->print_cr(" (benign) Hit max stack size limit ("SIZE_FORMAT")",
4473 _markStack._hit_limit);
4474 }
4475 if (_markStack._failed_double > 0) {
4476 gclog_or_tty->print_cr(" (benign) Failed stack doubling ("SIZE_FORMAT"),"
4477 " current capacity "SIZE_FORMAT,
4478 _markStack._failed_double,
4479 _markStack.capacity());
4480 }
4481 }
4482 _markStack._hit_limit = 0;
4483 _markStack._failed_double = 0;
4484
4485 if ((VerifyAfterGC || VerifyDuringGC) &&
4486 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
4487 verify_after_remark();
4488 }
4489
4490 _gc_tracer_cm->report_object_count_after_gc(&_is_alive_closure);
4491
4492 // Change under the freelistLocks.
4493 _collectorState = Sweeping;
4494 // Call isAllClear() under bitMapLock
4495 assert(_modUnionTable.isAllClear(),
4496 "Should be clear by end of the final marking");
4497 assert(_ct->klass_rem_set()->mod_union_is_clear(),
4498 "Should be clear by end of the final marking");
4499 }
4500
4501 void CMSParInitialMarkTask::work(uint worker_id) {
4502 elapsedTimer _timer;
4503 ResourceMark rm;
4504 HandleMark hm;
4505
4506 // ---------- scan from roots --------------
4507 _timer.start();
4508 GenCollectedHeap* gch = GenCollectedHeap::heap();
4509 Par_MarkRefsIntoClosure par_mri_cl(_collector->_span, &(_collector->_markBitMap));
4510
4511 // ---------- young gen roots --------------
4512 {
4513 work_on_young_gen_roots(worker_id, &par_mri_cl);
4514 _timer.stop();
4515 if (PrintCMSStatistics != 0) {
4516 gclog_or_tty->print_cr(
4517 "Finished young gen initial mark scan work in %dth thread: %3.3f sec",
4518 worker_id, _timer.seconds());
4519 }
4520 }
4521
4522 // ---------- remaining roots --------------
4523 _timer.reset();
4524 _timer.start();
4525
4526 CLDToOopClosure cld_closure(&par_mri_cl, true);
4527
4528 gch->gen_process_roots(_collector->_cmsGen->level(),
4529 false, // yg was scanned above
4530 false, // this is parallel code
4531 SharedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4532 _collector->should_unload_classes(),
4533 &par_mri_cl,
4534 NULL,
4535 &cld_closure);
4536 assert(_collector->should_unload_classes()
4537 || (_collector->CMSCollector::roots_scanning_options() & SharedHeap::SO_AllCodeCache),
4538 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4539 _timer.stop();
4540 if (PrintCMSStatistics != 0) {
4541 gclog_or_tty->print_cr(
4542 "Finished remaining root initial mark scan work in %dth thread: %3.3f sec",
4543 worker_id, _timer.seconds());
4544 }
4545 }
4546
4547 // Parallel remark task
4548 class CMSParRemarkTask: public CMSParMarkTask {
4549 CompactibleFreeListSpace* _cms_space;
4550
4551 // The per-thread work queues, available here for stealing.
4552 OopTaskQueueSet* _task_queues;
4553 ParallelTaskTerminator _term;
4554
4555 public:
4556 // A value of 0 passed to n_workers will cause the number of
4557 // workers to be taken from the active workers in the work gang.
4558 CMSParRemarkTask(CMSCollector* collector,
4559 CompactibleFreeListSpace* cms_space,
4560 int n_workers, FlexibleWorkGang* workers,
4561 OopTaskQueueSet* task_queues):
4562 CMSParMarkTask("Rescan roots and grey objects in parallel",
4563 collector, n_workers),
4564 _cms_space(cms_space),
4565 _task_queues(task_queues),
4566 _term(n_workers, task_queues) { }
4567
4568 OopTaskQueueSet* task_queues() { return _task_queues; }
4569
4570 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
4571
4572 ParallelTaskTerminator* terminator() { return &_term; }
4573 int n_workers() { return _n_workers; }
4574
4575 void work(uint worker_id);
4576
4577 private:
4578 // ... of dirty cards in old space
4579 void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
4580 Par_MarkRefsIntoAndScanClosure* cl);
4581
4582 // ... work stealing for the above
4583 void do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl, int* seed);
4584 };
4585
4586 class RemarkKlassClosure : public KlassClosure {
4587 KlassToOopClosure _cm_klass_closure;
4588 public:
4589 RemarkKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4590 void do_klass(Klass* k) {
4591 // Check if we have modified any oops in the Klass during the concurrent marking.
4592 if (k->has_accumulated_modified_oops()) {
4593 k->clear_accumulated_modified_oops();
4594
4595 // We could have transfered the current modified marks to the accumulated marks,
4596 // like we do with the Card Table to Mod Union Table. But it's not really necessary.
4597 } else if (k->has_modified_oops()) {
4598 // Don't clear anything, this info is needed by the next young collection.
4599 } else {
4600 // No modified oops in the Klass.
4601 return;
4602 }
4603
4604 // The klass has modified fields, need to scan the klass.
4605 _cm_klass_closure.do_klass(k);
4606 }
4607 };
4608
4609 void CMSParMarkTask::work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl) {
4610 ParNewGeneration* young_gen = _collector->_young_gen;
4611 ContiguousSpace* eden_space = young_gen->eden();
4612 ContiguousSpace* from_space = young_gen->from();
4613 ContiguousSpace* to_space = young_gen->to();
4614
4615 HeapWord** eca = _collector->_eden_chunk_array;
4616 size_t ect = _collector->_eden_chunk_index;
4617 HeapWord** sca = _collector->_survivor_chunk_array;
4618 size_t sct = _collector->_survivor_chunk_index;
4619
4620 assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
4621 assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
4622
4623 do_young_space_rescan(worker_id, cl, to_space, NULL, 0);
4624 do_young_space_rescan(worker_id, cl, from_space, sca, sct);
4625 do_young_space_rescan(worker_id, cl, eden_space, eca, ect);
4626 }
4627
4628 // work_queue(i) is passed to the closure
4629 // Par_MarkRefsIntoAndScanClosure. The "i" parameter
4630 // also is passed to do_dirty_card_rescan_tasks() and to
4631 // do_work_steal() to select the i-th task_queue.
4632
4633 void CMSParRemarkTask::work(uint worker_id) {
4634 elapsedTimer _timer;
4635 ResourceMark rm;
4636 HandleMark hm;
4637
4638 // ---------- rescan from roots --------------
4639 _timer.start();
4640 GenCollectedHeap* gch = GenCollectedHeap::heap();
4641 Par_MarkRefsIntoAndScanClosure par_mrias_cl(_collector,
4642 _collector->_span, _collector->ref_processor(),
4643 &(_collector->_markBitMap),
4644 work_queue(worker_id));
4645
4646 // Rescan young gen roots first since these are likely
4647 // coarsely partitioned and may, on that account, constitute
4648 // the critical path; thus, it's best to start off that
4649 // work first.
4650 // ---------- young gen roots --------------
4651 {
4652 work_on_young_gen_roots(worker_id, &par_mrias_cl);
4653 _timer.stop();
4654 if (PrintCMSStatistics != 0) {
4655 gclog_or_tty->print_cr(
4656 "Finished young gen rescan work in %dth thread: %3.3f sec",
4657 worker_id, _timer.seconds());
4658 }
4659 }
4660
4661 // ---------- remaining roots --------------
4662 _timer.reset();
4663 _timer.start();
4664 gch->gen_process_roots(_collector->_cmsGen->level(),
4665 false, // yg was scanned above
4666 false, // this is parallel code
4667 SharedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4668 _collector->should_unload_classes(),
4669 &par_mrias_cl,
4670 NULL,
4671 NULL); // The dirty klasses will be handled below
4672
4673 assert(_collector->should_unload_classes()
4674 || (_collector->CMSCollector::roots_scanning_options() & SharedHeap::SO_AllCodeCache),
4675 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4676 _timer.stop();
4677 if (PrintCMSStatistics != 0) {
4678 gclog_or_tty->print_cr(
4679 "Finished remaining root rescan work in %dth thread: %3.3f sec",
4680 worker_id, _timer.seconds());
4681 }
4682
4683 // ---------- unhandled CLD scanning ----------
4684 if (worker_id == 0) { // Single threaded at the moment.
4685 _timer.reset();
4686 _timer.start();
4687
4688 // Scan all new class loader data objects and new dependencies that were
4689 // introduced during concurrent marking.
4690 ResourceMark rm;
4691 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
4692 for (int i = 0; i < array->length(); i++) {
4693 par_mrias_cl.do_class_loader_data(array->at(i));
4694 }
4695
4696 // We don't need to keep track of new CLDs anymore.
4697 ClassLoaderDataGraph::remember_new_clds(false);
4698
4699 _timer.stop();
4700 if (PrintCMSStatistics != 0) {
4701 gclog_or_tty->print_cr(
4702 "Finished unhandled CLD scanning work in %dth thread: %3.3f sec",
4703 worker_id, _timer.seconds());
4704 }
4705 }
4706
4707 // ---------- dirty klass scanning ----------
4708 if (worker_id == 0) { // Single threaded at the moment.
4709 _timer.reset();
4710 _timer.start();
4711
4712 // Scan all classes that was dirtied during the concurrent marking phase.
4713 RemarkKlassClosure remark_klass_closure(&par_mrias_cl);
4714 ClassLoaderDataGraph::classes_do(&remark_klass_closure);
4715
4716 _timer.stop();
4717 if (PrintCMSStatistics != 0) {
4718 gclog_or_tty->print_cr(
4719 "Finished dirty klass scanning work in %dth thread: %3.3f sec",
4720 worker_id, _timer.seconds());
4721 }
4722 }
4723
4724 // We might have added oops to ClassLoaderData::_handles during the
4725 // concurrent marking phase. These oops point to newly allocated objects
4726 // that are guaranteed to be kept alive. Either by the direct allocation
4727 // code, or when the young collector processes the roots. Hence,
4728 // we don't have to revisit the _handles block during the remark phase.
4729
4730 // ---------- rescan dirty cards ------------
4731 _timer.reset();
4732 _timer.start();
4733
4734 // Do the rescan tasks for each of the two spaces
4735 // (cms_space) in turn.
4736 // "worker_id" is passed to select the task_queue for "worker_id"
4737 do_dirty_card_rescan_tasks(_cms_space, worker_id, &par_mrias_cl);
4738 _timer.stop();
4739 if (PrintCMSStatistics != 0) {
4740 gclog_or_tty->print_cr(
4741 "Finished dirty card rescan work in %dth thread: %3.3f sec",
4742 worker_id, _timer.seconds());
4743 }
4744
4745 // ---------- steal work from other threads ...
4746 // ---------- ... and drain overflow list.
4747 _timer.reset();
4748 _timer.start();
4749 do_work_steal(worker_id, &par_mrias_cl, _collector->hash_seed(worker_id));
4750 _timer.stop();
4751 if (PrintCMSStatistics != 0) {
4752 gclog_or_tty->print_cr(
4753 "Finished work stealing in %dth thread: %3.3f sec",
4754 worker_id, _timer.seconds());
4755 }
4756 }
4757
4758 // Note that parameter "i" is not used.
4759 void
4760 CMSParMarkTask::do_young_space_rescan(uint worker_id,
4761 OopsInGenClosure* cl, ContiguousSpace* space,
4762 HeapWord** chunk_array, size_t chunk_top) {
4763 // Until all tasks completed:
4764 // . claim an unclaimed task
4765 // . compute region boundaries corresponding to task claimed
4766 // using chunk_array
4767 // . par_oop_iterate(cl) over that region
4768
4769 ResourceMark rm;
4770 HandleMark hm;
4771
4772 SequentialSubTasksDone* pst = space->par_seq_tasks();
4773
4774 uint nth_task = 0;
4775 uint n_tasks = pst->n_tasks();
4776
4777 if (n_tasks > 0) {
4778 assert(pst->valid(), "Uninitialized use?");
4779 HeapWord *start, *end;
4780 while (!pst->is_task_claimed(/* reference */ nth_task)) {
4781 // We claimed task # nth_task; compute its boundaries.
4782 if (chunk_top == 0) { // no samples were taken
4783 assert(nth_task == 0 && n_tasks == 1, "Can have only 1 eden task");
4784 start = space->bottom();
4785 end = space->top();
4786 } else if (nth_task == 0) {
4787 start = space->bottom();
4788 end = chunk_array[nth_task];
4789 } else if (nth_task < (uint)chunk_top) {
4790 assert(nth_task >= 1, "Control point invariant");
4791 start = chunk_array[nth_task - 1];
4792 end = chunk_array[nth_task];
4793 } else {
4794 assert(nth_task == (uint)chunk_top, "Control point invariant");
4795 start = chunk_array[chunk_top - 1];
4796 end = space->top();
4797 }
4798 MemRegion mr(start, end);
4799 // Verify that mr is in space
4800 assert(mr.is_empty() || space->used_region().contains(mr),
4801 "Should be in space");
4802 // Verify that "start" is an object boundary
4803 assert(mr.is_empty() || oop(mr.start())->is_oop(),
4804 "Should be an oop");
4805 space->par_oop_iterate(mr, cl);
4806 }
4807 pst->all_tasks_completed();
4808 }
4809 }
4810
4811 void
4812 CMSParRemarkTask::do_dirty_card_rescan_tasks(
4813 CompactibleFreeListSpace* sp, int i,
4814 Par_MarkRefsIntoAndScanClosure* cl) {
4815 // Until all tasks completed:
4816 // . claim an unclaimed task
4817 // . compute region boundaries corresponding to task claimed
4818 // . transfer dirty bits ct->mut for that region
4819 // . apply rescanclosure to dirty mut bits for that region
4820
4821 ResourceMark rm;
4822 HandleMark hm;
4823
4824 OopTaskQueue* work_q = work_queue(i);
4825 ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
4826 // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
4827 // CAUTION: This closure has state that persists across calls to
4828 // the work method dirty_range_iterate_clear() in that it has
4829 // embedded in it a (subtype of) UpwardsObjectClosure. The
4830 // use of that state in the embedded UpwardsObjectClosure instance
4831 // assumes that the cards are always iterated (even if in parallel
4832 // by several threads) in monotonically increasing order per each
4833 // thread. This is true of the implementation below which picks
4834 // card ranges (chunks) in monotonically increasing order globally
4835 // and, a-fortiori, in monotonically increasing order per thread
4836 // (the latter order being a subsequence of the former).
4837 // If the work code below is ever reorganized into a more chaotic
4838 // work-partitioning form than the current "sequential tasks"
4839 // paradigm, the use of that persistent state will have to be
4840 // revisited and modified appropriately. See also related
4841 // bug 4756801 work on which should examine this code to make
4842 // sure that the changes there do not run counter to the
4843 // assumptions made here and necessary for correctness and
4844 // efficiency. Note also that this code might yield inefficient
4845 // behavior in the case of very large objects that span one or
4846 // more work chunks. Such objects would potentially be scanned
4847 // several times redundantly. Work on 4756801 should try and
4848 // address that performance anomaly if at all possible. XXX
4849 MemRegion full_span = _collector->_span;
4850 CMSBitMap* bm = &(_collector->_markBitMap); // shared
4851 MarkFromDirtyCardsClosure
4852 greyRescanClosure(_collector, full_span, // entire span of interest
4853 sp, bm, work_q, cl);
4854
4855 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
4856 assert(pst->valid(), "Uninitialized use?");
4857 uint nth_task = 0;
4858 const int alignment = CardTableModRefBS::card_size * BitsPerWord;
4859 MemRegion span = sp->used_region();
4860 HeapWord* start_addr = span.start();
4861 HeapWord* end_addr = (HeapWord*)round_to((intptr_t)span.end(),
4862 alignment);
4863 const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
4864 assert((HeapWord*)round_to((intptr_t)start_addr, alignment) ==
4865 start_addr, "Check alignment");
4866 assert((size_t)round_to((intptr_t)chunk_size, alignment) ==
4867 chunk_size, "Check alignment");
4868
4869 while (!pst->is_task_claimed(/* reference */ nth_task)) {
4870 // Having claimed the nth_task, compute corresponding mem-region,
4871 // which is a-fortiori aligned correctly (i.e. at a MUT boundary).
4872 // The alignment restriction ensures that we do not need any
4873 // synchronization with other gang-workers while setting or
4874 // clearing bits in thus chunk of the MUT.
4875 MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
4876 start_addr + (nth_task+1)*chunk_size);
4877 // The last chunk's end might be way beyond end of the
4878 // used region. In that case pull back appropriately.
4879 if (this_span.end() > end_addr) {
4880 this_span.set_end(end_addr);
4881 assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
4882 }
4883 // Iterate over the dirty cards covering this chunk, marking them
4884 // precleaned, and setting the corresponding bits in the mod union
4885 // table. Since we have been careful to partition at Card and MUT-word
4886 // boundaries no synchronization is needed between parallel threads.
4887 _collector->_ct->ct_bs()->dirty_card_iterate(this_span,
4888 &modUnionClosure);
4889
4890 // Having transferred these marks into the modUnionTable,
4891 // rescan the marked objects on the dirty cards in the modUnionTable.
4892 // Even if this is at a synchronous collection, the initial marking
4893 // may have been done during an asynchronous collection so there
4894 // may be dirty bits in the mod-union table.
4895 _collector->_modUnionTable.dirty_range_iterate_clear(
4896 this_span, &greyRescanClosure);
4897 _collector->_modUnionTable.verifyNoOneBitsInRange(
4898 this_span.start(),
4899 this_span.end());
4900 }
4901 pst->all_tasks_completed(); // declare that i am done
4902 }
4903
4904 // . see if we can share work_queues with ParNew? XXX
4905 void
4906 CMSParRemarkTask::do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl,
4907 int* seed) {
4908 OopTaskQueue* work_q = work_queue(i);
4909 NOT_PRODUCT(int num_steals = 0;)
4910 oop obj_to_scan;
4911 CMSBitMap* bm = &(_collector->_markBitMap);
4912
4913 while (true) {
4914 // Completely finish any left over work from (an) earlier round(s)
4915 cl->trim_queue(0);
4916 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
4917 (size_t)ParGCDesiredObjsFromOverflowList);
4918 // Now check if there's any work in the overflow list
4919 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
4920 // only affects the number of attempts made to get work from the
4921 // overflow list and does not affect the number of workers. Just
4922 // pass ParallelGCThreads so this behavior is unchanged.
4923 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
4924 work_q,
4925 ParallelGCThreads)) {
4926 // found something in global overflow list;
4927 // not yet ready to go stealing work from others.
4928 // We'd like to assert(work_q->size() != 0, ...)
4929 // because we just took work from the overflow list,
4930 // but of course we can't since all of that could have
4931 // been already stolen from us.
4932 // "He giveth and He taketh away."
4933 continue;
4934 }
4935 // Verify that we have no work before we resort to stealing
4936 assert(work_q->size() == 0, "Have work, shouldn't steal");
4937 // Try to steal from other queues that have work
4938 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
4939 NOT_PRODUCT(num_steals++;)
4940 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
4941 assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
4942 // Do scanning work
4943 obj_to_scan->oop_iterate(cl);
4944 // Loop around, finish this work, and try to steal some more
4945 } else if (terminator()->offer_termination()) {
4946 break; // nirvana from the infinite cycle
4947 }
4948 }
4949 NOT_PRODUCT(
4950 if (PrintCMSStatistics != 0) {
4951 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
4952 }
4953 )
4954 assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
4955 "Else our work is not yet done");
4956 }
4957
4958 // Record object boundaries in _eden_chunk_array by sampling the eden
4959 // top in the slow-path eden object allocation code path and record
4960 // the boundaries, if CMSEdenChunksRecordAlways is true. If
4961 // CMSEdenChunksRecordAlways is false, we use the other asynchronous
4962 // sampling in sample_eden() that activates during the part of the
4963 // preclean phase.
4964 void CMSCollector::sample_eden_chunk() {
4965 if (CMSEdenChunksRecordAlways && _eden_chunk_array != NULL) {
4966 if (_eden_chunk_lock->try_lock()) {
4967 // Record a sample. This is the critical section. The contents
4968 // of the _eden_chunk_array have to be non-decreasing in the
4969 // address order.
4970 _eden_chunk_array[_eden_chunk_index] = *_top_addr;
4971 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4972 "Unexpected state of Eden");
4973 if (_eden_chunk_index == 0 ||
4974 ((_eden_chunk_array[_eden_chunk_index] > _eden_chunk_array[_eden_chunk_index-1]) &&
4975 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4976 _eden_chunk_array[_eden_chunk_index-1]) >= CMSSamplingGrain))) {
4977 _eden_chunk_index++; // commit sample
4978 }
4979 _eden_chunk_lock->unlock();
4980 }
4981 }
4982 }
4983
4984 // Return a thread-local PLAB recording array, as appropriate.
4985 void* CMSCollector::get_data_recorder(int thr_num) {
4986 if (_survivor_plab_array != NULL &&
4987 (CMSPLABRecordAlways ||
4988 (_collectorState > Marking && _collectorState < FinalMarking))) {
4989 assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
4990 ChunkArray* ca = &_survivor_plab_array[thr_num];
4991 ca->reset(); // clear it so that fresh data is recorded
4992 return (void*) ca;
4993 } else {
4994 return NULL;
4995 }
4996 }
4997
4998 // Reset all the thread-local PLAB recording arrays
4999 void CMSCollector::reset_survivor_plab_arrays() {
5000 for (uint i = 0; i < ParallelGCThreads; i++) {
5001 _survivor_plab_array[i].reset();
5002 }
5003 }
5004
5005 // Merge the per-thread plab arrays into the global survivor chunk
5006 // array which will provide the partitioning of the survivor space
5007 // for CMS initial scan and rescan.
5008 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv,
5009 int no_of_gc_threads) {
5010 assert(_survivor_plab_array != NULL, "Error");
5011 assert(_survivor_chunk_array != NULL, "Error");
5012 assert(_collectorState == FinalMarking ||
5013 (CMSParallelInitialMarkEnabled && _collectorState == InitialMarking), "Error");
5014 for (int j = 0; j < no_of_gc_threads; j++) {
5015 _cursor[j] = 0;
5016 }
5017 HeapWord* top = surv->top();
5018 size_t i;
5019 for (i = 0; i < _survivor_chunk_capacity; i++) { // all sca entries
5020 HeapWord* min_val = top; // Higher than any PLAB address
5021 uint min_tid = 0; // position of min_val this round
5022 for (int j = 0; j < no_of_gc_threads; j++) {
5023 ChunkArray* cur_sca = &_survivor_plab_array[j];
5024 if (_cursor[j] == cur_sca->end()) {
5025 continue;
5026 }
5027 assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
5028 HeapWord* cur_val = cur_sca->nth(_cursor[j]);
5029 assert(surv->used_region().contains(cur_val), "Out of bounds value");
5030 if (cur_val < min_val) {
5031 min_tid = j;
5032 min_val = cur_val;
5033 } else {
5034 assert(cur_val < top, "All recorded addresses should be less");
5035 }
5036 }
5037 // At this point min_val and min_tid are respectively
5038 // the least address in _survivor_plab_array[j]->nth(_cursor[j])
5039 // and the thread (j) that witnesses that address.
5040 // We record this address in the _survivor_chunk_array[i]
5041 // and increment _cursor[min_tid] prior to the next round i.
5042 if (min_val == top) {
5043 break;
5044 }
5045 _survivor_chunk_array[i] = min_val;
5046 _cursor[min_tid]++;
5047 }
5048 // We are all done; record the size of the _survivor_chunk_array
5049 _survivor_chunk_index = i; // exclusive: [0, i)
5050 if (PrintCMSStatistics > 0) {
5051 gclog_or_tty->print(" (Survivor:" SIZE_FORMAT "chunks) ", i);
5052 }
5053 // Verify that we used up all the recorded entries
5054 #ifdef ASSERT
5055 size_t total = 0;
5056 for (int j = 0; j < no_of_gc_threads; j++) {
5057 assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
5058 total += _cursor[j];
5059 }
5060 assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
5061 // Check that the merged array is in sorted order
5062 if (total > 0) {
5063 for (size_t i = 0; i < total - 1; i++) {
5064 if (PrintCMSStatistics > 0) {
5065 gclog_or_tty->print(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
5066 i, _survivor_chunk_array[i]);
5067 }
5068 assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
5069 "Not sorted");
5070 }
5071 }
5072 #endif // ASSERT
5073 }
5074
5075 // Set up the space's par_seq_tasks structure for work claiming
5076 // for parallel initial scan and rescan of young gen.
5077 // See ParRescanTask where this is currently used.
5078 void
5079 CMSCollector::
5080 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
5081 assert(n_threads > 0, "Unexpected n_threads argument");
5082
5083 // Eden space
5084 if (!_young_gen->eden()->is_empty()) {
5085 SequentialSubTasksDone* pst = _young_gen->eden()->par_seq_tasks();
5086 assert(!pst->valid(), "Clobbering existing data?");
5087 // Each valid entry in [0, _eden_chunk_index) represents a task.
5088 size_t n_tasks = _eden_chunk_index + 1;
5089 assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
5090 // Sets the condition for completion of the subtask (how many threads
5091 // need to finish in order to be done).
5092 pst->set_n_threads(n_threads);
5093 pst->set_n_tasks((int)n_tasks);
5094 }
5095
5096 // Merge the survivor plab arrays into _survivor_chunk_array
5097 if (_survivor_plab_array != NULL) {
5098 merge_survivor_plab_arrays(_young_gen->from(), n_threads);
5099 } else {
5100 assert(_survivor_chunk_index == 0, "Error");
5101 }
5102
5103 // To space
5104 {
5105 SequentialSubTasksDone* pst = _young_gen->to()->par_seq_tasks();
5106 assert(!pst->valid(), "Clobbering existing data?");
5107 // Sets the condition for completion of the subtask (how many threads
5108 // need to finish in order to be done).
5109 pst->set_n_threads(n_threads);
5110 pst->set_n_tasks(1);
5111 assert(pst->valid(), "Error");
5112 }
5113
5114 // From space
5115 {
5116 SequentialSubTasksDone* pst = _young_gen->from()->par_seq_tasks();
5117 assert(!pst->valid(), "Clobbering existing data?");
5118 size_t n_tasks = _survivor_chunk_index + 1;
5119 assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
5120 // Sets the condition for completion of the subtask (how many threads
5121 // need to finish in order to be done).
5122 pst->set_n_threads(n_threads);
5123 pst->set_n_tasks((int)n_tasks);
5124 assert(pst->valid(), "Error");
5125 }
5126 }
5127
5128 // Parallel version of remark
5129 void CMSCollector::do_remark_parallel() {
5130 GenCollectedHeap* gch = GenCollectedHeap::heap();
5131 FlexibleWorkGang* workers = gch->workers();
5132 assert(workers != NULL, "Need parallel worker threads.");
5133 // Choose to use the number of GC workers most recently set
5134 // into "active_workers". If active_workers is not set, set it
5135 // to ParallelGCThreads.
5136 int n_workers = workers->active_workers();
5137 if (n_workers == 0) {
5138 assert(n_workers > 0, "Should have been set during scavenge");
5139 n_workers = ParallelGCThreads;
5140 workers->set_active_workers(n_workers);
5141 }
5142 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
5143
5144 CMSParRemarkTask tsk(this,
5145 cms_space,
5146 n_workers, workers, task_queues());
5147
5148 // Set up for parallel process_roots work.
5149 gch->set_par_threads(n_workers);
5150 // We won't be iterating over the cards in the card table updating
5151 // the younger_gen cards, so we shouldn't call the following else
5152 // the verification code as well as subsequent younger_refs_iterate
5153 // code would get confused. XXX
5154 // gch->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
5155
5156 // The young gen rescan work will not be done as part of
5157 // process_roots (which currently doesn't know how to
5158 // parallelize such a scan), but rather will be broken up into
5159 // a set of parallel tasks (via the sampling that the [abortable]
5160 // preclean phase did of eden, plus the [two] tasks of
5161 // scanning the [two] survivor spaces. Further fine-grain
5162 // parallelization of the scanning of the survivor spaces
5163 // themselves, and of precleaning of the younger gen itself
5164 // is deferred to the future.
5165 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
5166
5167 // The dirty card rescan work is broken up into a "sequence"
5168 // of parallel tasks (per constituent space) that are dynamically
5169 // claimed by the parallel threads.
5170 cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
5171
5172 // It turns out that even when we're using 1 thread, doing the work in a
5173 // separate thread causes wide variance in run times. We can't help this
5174 // in the multi-threaded case, but we special-case n=1 here to get
5175 // repeatable measurements of the 1-thread overhead of the parallel code.
5176 if (n_workers > 1) {
5177 // Make refs discovery MT-safe, if it isn't already: it may not
5178 // necessarily be so, since it's possible that we are doing
5179 // ST marking.
5180 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), true);
5181 GenCollectedHeap::StrongRootsScope srs(gch);
5182 workers->run_task(&tsk);
5183 } else {
5184 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5185 GenCollectedHeap::StrongRootsScope srs(gch);
5186 tsk.work(0);
5187 }
5188
5189 gch->set_par_threads(0); // 0 ==> non-parallel.
5190 // restore, single-threaded for now, any preserved marks
5191 // as a result of work_q overflow
5192 restore_preserved_marks_if_any();
5193 }
5194
5195 // Non-parallel version of remark
5196 void CMSCollector::do_remark_non_parallel() {
5197 ResourceMark rm;
5198 HandleMark hm;
5199 GenCollectedHeap* gch = GenCollectedHeap::heap();
5200 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5201
5202 MarkRefsIntoAndScanClosure
5203 mrias_cl(_span, ref_processor(), &_markBitMap, NULL /* not precleaning */,
5204 &_markStack, this,
5205 false /* should_yield */, false /* not precleaning */);
5206 MarkFromDirtyCardsClosure
5207 markFromDirtyCardsClosure(this, _span,
5208 NULL, // space is set further below
5209 &_markBitMap, &_markStack, &mrias_cl);
5210 {
5211 GCTraceTime t("grey object rescan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5212 // Iterate over the dirty cards, setting the corresponding bits in the
5213 // mod union table.
5214 {
5215 ModUnionClosure modUnionClosure(&_modUnionTable);
5216 _ct->ct_bs()->dirty_card_iterate(
5217 _cmsGen->used_region(),
5218 &modUnionClosure);
5219 }
5220 // Having transferred these marks into the modUnionTable, we just need
5221 // to rescan the marked objects on the dirty cards in the modUnionTable.
5222 // The initial marking may have been done during an asynchronous
5223 // collection so there may be dirty bits in the mod-union table.
5224 const int alignment =
5225 CardTableModRefBS::card_size * BitsPerWord;
5226 {
5227 // ... First handle dirty cards in CMS gen
5228 markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
5229 MemRegion ur = _cmsGen->used_region();
5230 HeapWord* lb = ur.start();
5231 HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
5232 MemRegion cms_span(lb, ub);
5233 _modUnionTable.dirty_range_iterate_clear(cms_span,
5234 &markFromDirtyCardsClosure);
5235 verify_work_stacks_empty();
5236 if (PrintCMSStatistics != 0) {
5237 gclog_or_tty->print(" (re-scanned "SIZE_FORMAT" dirty cards in cms gen) ",
5238 markFromDirtyCardsClosure.num_dirty_cards());
5239 }
5240 }
5241 }
5242 if (VerifyDuringGC &&
5243 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5244 HandleMark hm; // Discard invalid handles created during verification
5245 Universe::verify();
5246 }
5247 {
5248 GCTraceTime t("root rescan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5249
5250 verify_work_stacks_empty();
5251
5252 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
5253 GenCollectedHeap::StrongRootsScope srs(gch);
5254
5255 gch->gen_process_roots(_cmsGen->level(),
5256 true, // younger gens as roots
5257 false, // use the local StrongRootsScope
5258 SharedHeap::ScanningOption(roots_scanning_options()),
5259 should_unload_classes(),
5260 &mrias_cl,
5261 NULL,
5262 NULL); // The dirty klasses will be handled below
5263
5264 assert(should_unload_classes()
5265 || (roots_scanning_options() & SharedHeap::SO_AllCodeCache),
5266 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5267 }
5268
5269 {
5270 GCTraceTime t("visit unhandled CLDs", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5271
5272 verify_work_stacks_empty();
5273
5274 // Scan all class loader data objects that might have been introduced
5275 // during concurrent marking.
5276 ResourceMark rm;
5277 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
5278 for (int i = 0; i < array->length(); i++) {
5279 mrias_cl.do_class_loader_data(array->at(i));
5280 }
5281
5282 // We don't need to keep track of new CLDs anymore.
5283 ClassLoaderDataGraph::remember_new_clds(false);
5284
5285 verify_work_stacks_empty();
5286 }
5287
5288 {
5289 GCTraceTime t("dirty klass scan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5290
5291 verify_work_stacks_empty();
5292
5293 RemarkKlassClosure remark_klass_closure(&mrias_cl);
5294 ClassLoaderDataGraph::classes_do(&remark_klass_closure);
5295
5296 verify_work_stacks_empty();
5297 }
5298
5299 // We might have added oops to ClassLoaderData::_handles during the
5300 // concurrent marking phase. These oops point to newly allocated objects
5301 // that are guaranteed to be kept alive. Either by the direct allocation
5302 // code, or when the young collector processes the roots. Hence,
5303 // we don't have to revisit the _handles block during the remark phase.
5304
5305 verify_work_stacks_empty();
5306 // Restore evacuated mark words, if any, used for overflow list links
5307 if (!CMSOverflowEarlyRestoration) {
5308 restore_preserved_marks_if_any();
5309 }
5310 verify_overflow_empty();
5311 }
5312
5313 ////////////////////////////////////////////////////////
5314 // Parallel Reference Processing Task Proxy Class
5315 ////////////////////////////////////////////////////////
5316 class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues {
5317 typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
5318 CMSCollector* _collector;
5319 CMSBitMap* _mark_bit_map;
5320 const MemRegion _span;
5321 ProcessTask& _task;
5322
5323 public:
5324 CMSRefProcTaskProxy(ProcessTask& task,
5325 CMSCollector* collector,
5326 const MemRegion& span,
5327 CMSBitMap* mark_bit_map,
5328 AbstractWorkGang* workers,
5329 OopTaskQueueSet* task_queues):
5330 // XXX Should superclass AGTWOQ also know about AWG since it knows
5331 // about the task_queues used by the AWG? Then it could initialize
5332 // the terminator() object. See 6984287. The set_for_termination()
5333 // below is a temporary band-aid for the regression in 6984287.
5334 AbstractGangTaskWOopQueues("Process referents by policy in parallel",
5335 task_queues),
5336 _task(task),
5337 _collector(collector), _span(span), _mark_bit_map(mark_bit_map)
5338 {
5339 assert(_collector->_span.equals(_span) && !_span.is_empty(),
5340 "Inconsistency in _span");
5341 set_for_termination(workers->active_workers());
5342 }
5343
5344 OopTaskQueueSet* task_queues() { return queues(); }
5345
5346 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5347
5348 void do_work_steal(int i,
5349 CMSParDrainMarkingStackClosure* drain,
5350 CMSParKeepAliveClosure* keep_alive,
5351 int* seed);
5352
5353 virtual void work(uint worker_id);
5354 };
5355
5356 void CMSRefProcTaskProxy::work(uint worker_id) {
5357 ResourceMark rm;
5358 HandleMark hm;
5359 assert(_collector->_span.equals(_span), "Inconsistency in _span");
5360 CMSParKeepAliveClosure par_keep_alive(_collector, _span,
5361 _mark_bit_map,
5362 work_queue(worker_id));
5363 CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
5364 _mark_bit_map,
5365 work_queue(worker_id));
5366 CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
5367 _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack);
5368 if (_task.marks_oops_alive()) {
5369 do_work_steal(worker_id, &par_drain_stack, &par_keep_alive,
5370 _collector->hash_seed(worker_id));
5371 }
5372 assert(work_queue(worker_id)->size() == 0, "work_queue should be empty");
5373 assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
5374 }
5375
5376 class CMSRefEnqueueTaskProxy: public AbstractGangTask {
5377 typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
5378 EnqueueTask& _task;
5379
5380 public:
5381 CMSRefEnqueueTaskProxy(EnqueueTask& task)
5382 : AbstractGangTask("Enqueue reference objects in parallel"),
5383 _task(task)
5384 { }
5385
5386 virtual void work(uint worker_id)
5387 {
5388 _task.work(worker_id);
5389 }
5390 };
5391
5392 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
5393 MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue):
5394 _span(span),
5395 _bit_map(bit_map),
5396 _work_queue(work_queue),
5397 _mark_and_push(collector, span, bit_map, work_queue),
5398 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
5399 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads)))
5400 { }
5401
5402 // . see if we can share work_queues with ParNew? XXX
5403 void CMSRefProcTaskProxy::do_work_steal(int i,
5404 CMSParDrainMarkingStackClosure* drain,
5405 CMSParKeepAliveClosure* keep_alive,
5406 int* seed) {
5407 OopTaskQueue* work_q = work_queue(i);
5408 NOT_PRODUCT(int num_steals = 0;)
5409 oop obj_to_scan;
5410
5411 while (true) {
5412 // Completely finish any left over work from (an) earlier round(s)
5413 drain->trim_queue(0);
5414 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5415 (size_t)ParGCDesiredObjsFromOverflowList);
5416 // Now check if there's any work in the overflow list
5417 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5418 // only affects the number of attempts made to get work from the
5419 // overflow list and does not affect the number of workers. Just
5420 // pass ParallelGCThreads so this behavior is unchanged.
5421 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5422 work_q,
5423 ParallelGCThreads)) {
5424 // Found something in global overflow list;
5425 // not yet ready to go stealing work from others.
5426 // We'd like to assert(work_q->size() != 0, ...)
5427 // because we just took work from the overflow list,
5428 // but of course we can't, since all of that might have
5429 // been already stolen from us.
5430 continue;
5431 }
5432 // Verify that we have no work before we resort to stealing
5433 assert(work_q->size() == 0, "Have work, shouldn't steal");
5434 // Try to steal from other queues that have work
5435 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5436 NOT_PRODUCT(num_steals++;)
5437 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5438 assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5439 // Do scanning work
5440 obj_to_scan->oop_iterate(keep_alive);
5441 // Loop around, finish this work, and try to steal some more
5442 } else if (terminator()->offer_termination()) {
5443 break; // nirvana from the infinite cycle
5444 }
5445 }
5446 NOT_PRODUCT(
5447 if (PrintCMSStatistics != 0) {
5448 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5449 }
5450 )
5451 }
5452
5453 void CMSRefProcTaskExecutor::execute(ProcessTask& task)
5454 {
5455 GenCollectedHeap* gch = GenCollectedHeap::heap();
5456 FlexibleWorkGang* workers = gch->workers();
5457 assert(workers != NULL, "Need parallel worker threads.");
5458 CMSRefProcTaskProxy rp_task(task, &_collector,
5459 _collector.ref_processor()->span(),
5460 _collector.markBitMap(),
5461 workers, _collector.task_queues());
5462 workers->run_task(&rp_task);
5463 }
5464
5465 void CMSRefProcTaskExecutor::execute(EnqueueTask& task)
5466 {
5467
5468 GenCollectedHeap* gch = GenCollectedHeap::heap();
5469 FlexibleWorkGang* workers = gch->workers();
5470 assert(workers != NULL, "Need parallel worker threads.");
5471 CMSRefEnqueueTaskProxy enq_task(task);
5472 workers->run_task(&enq_task);
5473 }
5474
5475 void CMSCollector::refProcessingWork() {
5476 ResourceMark rm;
5477 HandleMark hm;
5478
5479 ReferenceProcessor* rp = ref_processor();
5480 assert(rp->span().equals(_span), "Spans should be equal");
5481 assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
5482 // Process weak references.
5483 rp->setup_policy(false);
5484 verify_work_stacks_empty();
5485
5486 CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
5487 &_markStack, false /* !preclean */);
5488 CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
5489 _span, &_markBitMap, &_markStack,
5490 &cmsKeepAliveClosure, false /* !preclean */);
5491 {
5492 GCTraceTime t("weak refs processing", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5493
5494 ReferenceProcessorStats stats;
5495 if (rp->processing_is_mt()) {
5496 // Set the degree of MT here. If the discovery is done MT, there
5497 // may have been a different number of threads doing the discovery
5498 // and a different number of discovered lists may have Ref objects.
5499 // That is OK as long as the Reference lists are balanced (see
5500 // balance_all_queues() and balance_queues()).
5501 GenCollectedHeap* gch = GenCollectedHeap::heap();
5502 int active_workers = ParallelGCThreads;
5503 FlexibleWorkGang* workers = gch->workers();
5504 if (workers != NULL) {
5505 active_workers = workers->active_workers();
5506 // The expectation is that active_workers will have already
5507 // been set to a reasonable value. If it has not been set,
5508 // investigate.
5509 assert(active_workers > 0, "Should have been set during scavenge");
5510 }
5511 rp->set_active_mt_degree(active_workers);
5512 CMSRefProcTaskExecutor task_executor(*this);
5513 stats = rp->process_discovered_references(&_is_alive_closure,
5514 &cmsKeepAliveClosure,
5515 &cmsDrainMarkingStackClosure,
5516 &task_executor,
5517 _gc_timer_cm,
5518 _gc_tracer_cm->gc_id());
5519 } else {
5520 stats = rp->process_discovered_references(&_is_alive_closure,
5521 &cmsKeepAliveClosure,
5522 &cmsDrainMarkingStackClosure,
5523 NULL,
5524 _gc_timer_cm,
5525 _gc_tracer_cm->gc_id());
5526 }
5527 _gc_tracer_cm->report_gc_reference_stats(stats);
5528
5529 }
5530
5531 // This is the point where the entire marking should have completed.
5532 verify_work_stacks_empty();
5533
5534 if (should_unload_classes()) {
5535 {
5536 GCTraceTime t("class unloading", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5537
5538 // Unload classes and purge the SystemDictionary.
5539 bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure);
5540
5541 // Unload nmethods.
5542 CodeCache::do_unloading(&_is_alive_closure, purged_class);
5543
5544 // Prune dead klasses from subklass/sibling/implementor lists.
5545 Klass::clean_weak_klass_links(&_is_alive_closure);
5546 }
5547
5548 {
5549 GCTraceTime t("scrub symbol table", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5550 // Clean up unreferenced symbols in symbol table.
5551 SymbolTable::unlink();
5552 }
5553
5554 {
5555 GCTraceTime t("scrub string table", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5556 // Delete entries for dead interned strings.
5557 StringTable::unlink(&_is_alive_closure);
5558 }
5559 }
5560
5561
5562 // Restore any preserved marks as a result of mark stack or
5563 // work queue overflow
5564 restore_preserved_marks_if_any(); // done single-threaded for now
5565
5566 rp->set_enqueuing_is_done(true);
5567 if (rp->processing_is_mt()) {
5568 rp->balance_all_queues();
5569 CMSRefProcTaskExecutor task_executor(*this);
5570 rp->enqueue_discovered_references(&task_executor);
5571 } else {
5572 rp->enqueue_discovered_references(NULL);
5573 }
5574 rp->verify_no_references_recorded();
5575 assert(!rp->discovery_enabled(), "should have been disabled");
5576 }
5577
5578 #ifndef PRODUCT
5579 void CMSCollector::check_correct_thread_executing() {
5580 Thread* t = Thread::current();
5581 // Only the VM thread or the CMS thread should be here.
5582 assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
5583 "Unexpected thread type");
5584 // If this is the vm thread, the foreground process
5585 // should not be waiting. Note that _foregroundGCIsActive is
5586 // true while the foreground collector is waiting.
5587 if (_foregroundGCShouldWait) {
5588 // We cannot be the VM thread
5589 assert(t->is_ConcurrentGC_thread(),
5590 "Should be CMS thread");
5591 } else {
5592 // We can be the CMS thread only if we are in a stop-world
5593 // phase of CMS collection.
5594 if (t->is_ConcurrentGC_thread()) {
5595 assert(_collectorState == InitialMarking ||
5596 _collectorState == FinalMarking,
5597 "Should be a stop-world phase");
5598 // The CMS thread should be holding the CMS_token.
5599 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5600 "Potential interference with concurrently "
5601 "executing VM thread");
5602 }
5603 }
5604 }
5605 #endif
5606
5607 void CMSCollector::sweep() {
5608 assert(_collectorState == Sweeping, "just checking");
5609 check_correct_thread_executing();
5610 verify_work_stacks_empty();
5611 verify_overflow_empty();
5612 increment_sweep_count();
5613 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
5614
5615 _inter_sweep_timer.stop();
5616 _inter_sweep_estimate.sample(_inter_sweep_timer.seconds());
5617
5618 assert(!_intra_sweep_timer.is_active(), "Should not be active");
5619 _intra_sweep_timer.reset();
5620 _intra_sweep_timer.start();
5621 {
5622 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
5623 CMSPhaseAccounting pa(this, "sweep", _gc_tracer_cm->gc_id(), !PrintGCDetails);
5624 // First sweep the old gen
5625 {
5626 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
5627 bitMapLock());
5628 sweepWork(_cmsGen);
5629 }
5630
5631 // Update Universe::_heap_*_at_gc figures.
5632 // We need all the free list locks to make the abstract state
5633 // transition from Sweeping to Resetting. See detailed note
5634 // further below.
5635 {
5636 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock());
5637 // Update heap occupancy information which is used as
5638 // input to soft ref clearing policy at the next gc.
5639 Universe::update_heap_info_at_gc();
5640 _collectorState = Resizing;
5641 }
5642 }
5643 verify_work_stacks_empty();
5644 verify_overflow_empty();
5645
5646 if (should_unload_classes()) {
5647 // Delay purge to the beginning of the next safepoint. Metaspace::contains
5648 // requires that the virtual spaces are stable and not deleted.
5649 ClassLoaderDataGraph::set_should_purge(true);
5650 }
5651
5652 _intra_sweep_timer.stop();
5653 _intra_sweep_estimate.sample(_intra_sweep_timer.seconds());
5654
5655 _inter_sweep_timer.reset();
5656 _inter_sweep_timer.start();
5657
5658 // We need to use a monotonically non-decreasing time in ms
5659 // or we will see time-warp warnings and os::javaTimeMillis()
5660 // does not guarantee monotonicity.
5661 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
5662 update_time_of_last_gc(now);
5663
5664 // NOTE on abstract state transitions:
5665 // Mutators allocate-live and/or mark the mod-union table dirty
5666 // based on the state of the collection. The former is done in
5667 // the interval [Marking, Sweeping] and the latter in the interval
5668 // [Marking, Sweeping). Thus the transitions into the Marking state
5669 // and out of the Sweeping state must be synchronously visible
5670 // globally to the mutators.
5671 // The transition into the Marking state happens with the world
5672 // stopped so the mutators will globally see it. Sweeping is
5673 // done asynchronously by the background collector so the transition
5674 // from the Sweeping state to the Resizing state must be done
5675 // under the freelistLock (as is the check for whether to
5676 // allocate-live and whether to dirty the mod-union table).
5677 assert(_collectorState == Resizing, "Change of collector state to"
5678 " Resizing must be done under the freelistLocks (plural)");
5679
5680 // Now that sweeping has been completed, we clear
5681 // the incremental_collection_failed flag,
5682 // thus inviting a younger gen collection to promote into
5683 // this generation. If such a promotion may still fail,
5684 // the flag will be set again when a young collection is
5685 // attempted.
5686 GenCollectedHeap* gch = GenCollectedHeap::heap();
5687 gch->clear_incremental_collection_failed(); // Worth retrying as fresh space may have been freed up
5688 gch->update_full_collections_completed(_collection_count_start);
5689 }
5690
5691 // FIX ME!!! Looks like this belongs in CFLSpace, with
5692 // CMSGen merely delegating to it.
5693 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
5694 double nearLargestPercent = FLSLargestBlockCoalesceProximity;
5695 HeapWord* minAddr = _cmsSpace->bottom();
5696 HeapWord* largestAddr =
5697 (HeapWord*) _cmsSpace->dictionary()->find_largest_dict();
5698 if (largestAddr == NULL) {
5699 // The dictionary appears to be empty. In this case
5700 // try to coalesce at the end of the heap.
5701 largestAddr = _cmsSpace->end();
5702 }
5703 size_t largestOffset = pointer_delta(largestAddr, minAddr);
5704 size_t nearLargestOffset =
5705 (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
5706 if (PrintFLSStatistics != 0) {
5707 gclog_or_tty->print_cr(
5708 "CMS: Large Block: " PTR_FORMAT ";"
5709 " Proximity: " PTR_FORMAT " -> " PTR_FORMAT,
5710 largestAddr,
5711 _cmsSpace->nearLargestChunk(), minAddr + nearLargestOffset);
5712 }
5713 _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
5714 }
5715
5716 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
5717 return addr >= _cmsSpace->nearLargestChunk();
5718 }
5719
5720 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
5721 return _cmsSpace->find_chunk_at_end();
5722 }
5723
5724 void ConcurrentMarkSweepGeneration::update_gc_stats(int current_level,
5725 bool full) {
5726 // The next lower level has been collected. Gather any statistics
5727 // that are of interest at this point.
5728 if (!full && (current_level + 1) == level()) {
5729 // Gather statistics on the young generation collection.
5730 collector()->stats().record_gc0_end(used());
5731 }
5732 }
5733
5734 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* gen) {
5735 // We iterate over the space(s) underlying this generation,
5736 // checking the mark bit map to see if the bits corresponding
5737 // to specific blocks are marked or not. Blocks that are
5738 // marked are live and are not swept up. All remaining blocks
5739 // are swept up, with coalescing on-the-fly as we sweep up
5740 // contiguous free and/or garbage blocks:
5741 // We need to ensure that the sweeper synchronizes with allocators
5742 // and stop-the-world collectors. In particular, the following
5743 // locks are used:
5744 // . CMS token: if this is held, a stop the world collection cannot occur
5745 // . freelistLock: if this is held no allocation can occur from this
5746 // generation by another thread
5747 // . bitMapLock: if this is held, no other thread can access or update
5748 //
5749
5750 // Note that we need to hold the freelistLock if we use
5751 // block iterate below; else the iterator might go awry if
5752 // a mutator (or promotion) causes block contents to change
5753 // (for instance if the allocator divvies up a block).
5754 // If we hold the free list lock, for all practical purposes
5755 // young generation GC's can't occur (they'll usually need to
5756 // promote), so we might as well prevent all young generation
5757 // GC's while we do a sweeping step. For the same reason, we might
5758 // as well take the bit map lock for the entire duration
5759
5760 // check that we hold the requisite locks
5761 assert(have_cms_token(), "Should hold cms token");
5762 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), "Should possess CMS token to sweep");
5763 assert_lock_strong(gen->freelistLock());
5764 assert_lock_strong(bitMapLock());
5765
5766 assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context");
5767 assert(_intra_sweep_timer.is_active(), "Was switched on in an outer context");
5768 gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
5769 _inter_sweep_estimate.padded_average(),
5770 _intra_sweep_estimate.padded_average());
5771 gen->setNearLargestChunk();
5772
5773 {
5774 SweepClosure sweepClosure(this, gen, &_markBitMap, CMSYield);
5775 gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
5776 // We need to free-up/coalesce garbage/blocks from a
5777 // co-terminal free run. This is done in the SweepClosure
5778 // destructor; so, do not remove this scope, else the
5779 // end-of-sweep-census below will be off by a little bit.
5780 }
5781 gen->cmsSpace()->sweep_completed();
5782 gen->cmsSpace()->endSweepFLCensus(sweep_count());
5783 if (should_unload_classes()) { // unloaded classes this cycle,
5784 _concurrent_cycles_since_last_unload = 0; // ... reset count
5785 } else { // did not unload classes,
5786 _concurrent_cycles_since_last_unload++; // ... increment count
5787 }
5788 }
5789
5790 // Reset CMS data structures (for now just the marking bit map)
5791 // preparatory for the next cycle.
5792 void CMSCollector::reset(bool concurrent) {
5793 if (concurrent) {
5794 CMSTokenSyncWithLocks ts(true, bitMapLock());
5795
5796 // If the state is not "Resetting", the foreground thread
5797 // has done a collection and the resetting.
5798 if (_collectorState != Resetting) {
5799 assert(_collectorState == Idling, "The state should only change"
5800 " because the foreground collector has finished the collection");
5801 return;
5802 }
5803
5804 // Clear the mark bitmap (no grey objects to start with)
5805 // for the next cycle.
5806 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
5807 CMSPhaseAccounting cmspa(this, "reset", _gc_tracer_cm->gc_id(), !PrintGCDetails);
5808
5809 HeapWord* curAddr = _markBitMap.startWord();
5810 while (curAddr < _markBitMap.endWord()) {
5811 size_t remaining = pointer_delta(_markBitMap.endWord(), curAddr);
5812 MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
5813 _markBitMap.clear_large_range(chunk);
5814 if (ConcurrentMarkSweepThread::should_yield() &&
5815 !foregroundGCIsActive() &&
5816 CMSYield) {
5817 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5818 "CMS thread should hold CMS token");
5819 assert_lock_strong(bitMapLock());
5820 bitMapLock()->unlock();
5821 ConcurrentMarkSweepThread::desynchronize(true);
5822 stopTimer();
5823 if (PrintCMSStatistics != 0) {
5824 incrementYields();
5825 }
5826
5827 // See the comment in coordinator_yield()
5828 for (unsigned i = 0; i < CMSYieldSleepCount &&
5829 ConcurrentMarkSweepThread::should_yield() &&
5830 !CMSCollector::foregroundGCIsActive(); ++i) {
5831 os::sleep(Thread::current(), 1, false);
5832 }
5833
5834 ConcurrentMarkSweepThread::synchronize(true);
5835 bitMapLock()->lock_without_safepoint_check();
5836 startTimer();
5837 }
5838 curAddr = chunk.end();
5839 }
5840 // A successful mostly concurrent collection has been done.
5841 // Because only the full (i.e., concurrent mode failure) collections
5842 // are being measured for gc overhead limits, clean the "near" flag
5843 // and count.
5844 size_policy()->reset_gc_overhead_limit_count();
5845 _collectorState = Idling;
5846 } else {
5847 // already have the lock
5848 assert(_collectorState == Resetting, "just checking");
5849 assert_lock_strong(bitMapLock());
5850 _markBitMap.clear_all();
5851 _collectorState = Idling;
5852 }
5853
5854 register_gc_end();
5855 }
5856
5857 void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) {
5858 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
5859 GCTraceTime t(GCCauseString("GC", gc_cause), PrintGC, !PrintGCDetails, NULL, _gc_tracer_cm->gc_id());
5860 TraceCollectorStats tcs(counters());
5861
5862 switch (op) {
5863 case CMS_op_checkpointRootsInitial: {
5864 SvcGCMarker sgcm(SvcGCMarker::OTHER);
5865 checkpointRootsInitial();
5866 if (PrintGC) {
5867 _cmsGen->printOccupancy("initial-mark");
5868 }
5869 break;
5870 }
5871 case CMS_op_checkpointRootsFinal: {
5872 SvcGCMarker sgcm(SvcGCMarker::OTHER);
5873 checkpointRootsFinal();
5874 if (PrintGC) {
5875 _cmsGen->printOccupancy("remark");
5876 }
5877 break;
5878 }
5879 default:
5880 fatal("No such CMS_op");
5881 }
5882 }
5883
5884 #ifndef PRODUCT
5885 size_t const CMSCollector::skip_header_HeapWords() {
5886 return FreeChunk::header_size();
5887 }
5888
5889 // Try and collect here conditions that should hold when
5890 // CMS thread is exiting. The idea is that the foreground GC
5891 // thread should not be blocked if it wants to terminate
5892 // the CMS thread and yet continue to run the VM for a while
5893 // after that.
5894 void CMSCollector::verify_ok_to_terminate() const {
5895 assert(Thread::current()->is_ConcurrentGC_thread(),
5896 "should be called by CMS thread");
5897 assert(!_foregroundGCShouldWait, "should be false");
5898 // We could check here that all the various low-level locks
5899 // are not held by the CMS thread, but that is overkill; see
5900 // also CMSThread::verify_ok_to_terminate() where the CGC_lock
5901 // is checked.
5902 }
5903 #endif
5904
5905 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
5906 assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
5907 "missing Printezis mark?");
5908 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5909 size_t size = pointer_delta(nextOneAddr + 1, addr);
5910 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5911 "alignment problem");
5912 assert(size >= 3, "Necessary for Printezis marks to work");
5913 return size;
5914 }
5915
5916 // A variant of the above (block_size_using_printezis_bits()) except
5917 // that we return 0 if the P-bits are not yet set.
5918 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
5919 if (_markBitMap.isMarked(addr + 1)) {
5920 assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects");
5921 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5922 size_t size = pointer_delta(nextOneAddr + 1, addr);
5923 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5924 "alignment problem");
5925 assert(size >= 3, "Necessary for Printezis marks to work");
5926 return size;
5927 }
5928 return 0;
5929 }
5930
5931 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
5932 size_t sz = 0;
5933 oop p = (oop)addr;
5934 if (p->klass_or_null() != NULL) {
5935 sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
5936 } else {
5937 sz = block_size_using_printezis_bits(addr);
5938 }
5939 assert(sz > 0, "size must be nonzero");
5940 HeapWord* next_block = addr + sz;
5941 HeapWord* next_card = (HeapWord*)round_to((uintptr_t)next_block,
5942 CardTableModRefBS::card_size);
5943 assert(round_down((uintptr_t)addr, CardTableModRefBS::card_size) <
5944 round_down((uintptr_t)next_card, CardTableModRefBS::card_size),
5945 "must be different cards");
5946 return next_card;
5947 }
5948
5949
5950 // CMS Bit Map Wrapper /////////////////////////////////////////
5951
5952 // Construct a CMS bit map infrastructure, but don't create the
5953 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
5954 // further below.
5955 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
5956 _bm(),
5957 _shifter(shifter),
5958 _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true,
5959 Monitor::_safepoint_check_sometimes) : NULL)
5960 {
5961 _bmStartWord = 0;
5962 _bmWordSize = 0;
5963 }
5964
5965 bool CMSBitMap::allocate(MemRegion mr) {
5966 _bmStartWord = mr.start();
5967 _bmWordSize = mr.word_size();
5968 ReservedSpace brs(ReservedSpace::allocation_align_size_up(
5969 (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
5970 if (!brs.is_reserved()) {
5971 warning("CMS bit map allocation failure");
5972 return false;
5973 }
5974 // For now we'll just commit all of the bit map up front.
5975 // Later on we'll try to be more parsimonious with swap.
5976 if (!_virtual_space.initialize(brs, brs.size())) {
5977 warning("CMS bit map backing store failure");
5978 return false;
5979 }
5980 assert(_virtual_space.committed_size() == brs.size(),
5981 "didn't reserve backing store for all of CMS bit map?");
5982 _bm.set_map((BitMap::bm_word_t*)_virtual_space.low());
5983 assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
5984 _bmWordSize, "inconsistency in bit map sizing");
5985 _bm.set_size(_bmWordSize >> _shifter);
5986
5987 // bm.clear(); // can we rely on getting zero'd memory? verify below
5988 assert(isAllClear(),
5989 "Expected zero'd memory from ReservedSpace constructor");
5990 assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
5991 "consistency check");
5992 return true;
5993 }
5994
5995 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
5996 HeapWord *next_addr, *end_addr, *last_addr;
5997 assert_locked();
5998 assert(covers(mr), "out-of-range error");
5999 // XXX assert that start and end are appropriately aligned
6000 for (next_addr = mr.start(), end_addr = mr.end();
6001 next_addr < end_addr; next_addr = last_addr) {
6002 MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
6003 last_addr = dirty_region.end();
6004 if (!dirty_region.is_empty()) {
6005 cl->do_MemRegion(dirty_region);
6006 } else {
6007 assert(last_addr == end_addr, "program logic");
6008 return;
6009 }
6010 }
6011 }
6012
6013 void CMSBitMap::print_on_error(outputStream* st, const char* prefix) const {
6014 _bm.print_on_error(st, prefix);
6015 }
6016
6017 #ifndef PRODUCT
6018 void CMSBitMap::assert_locked() const {
6019 CMSLockVerifier::assert_locked(lock());
6020 }
6021
6022 bool CMSBitMap::covers(MemRegion mr) const {
6023 // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
6024 assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
6025 "size inconsistency");
6026 return (mr.start() >= _bmStartWord) &&
6027 (mr.end() <= endWord());
6028 }
6029
6030 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
6031 return (start >= _bmStartWord && (start + size) <= endWord());
6032 }
6033
6034 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
6035 // verify that there are no 1 bits in the interval [left, right)
6036 FalseBitMapClosure falseBitMapClosure;
6037 iterate(&falseBitMapClosure, left, right);
6038 }
6039
6040 void CMSBitMap::region_invariant(MemRegion mr)
6041 {
6042 assert_locked();
6043 // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
6044 assert(!mr.is_empty(), "unexpected empty region");
6045 assert(covers(mr), "mr should be covered by bit map");
6046 // convert address range into offset range
6047 size_t start_ofs = heapWordToOffset(mr.start());
6048 // Make sure that end() is appropriately aligned
6049 assert(mr.end() == (HeapWord*)round_to((intptr_t)mr.end(),
6050 (1 << (_shifter+LogHeapWordSize))),
6051 "Misaligned mr.end()");
6052 size_t end_ofs = heapWordToOffset(mr.end());
6053 assert(end_ofs > start_ofs, "Should mark at least one bit");
6054 }
6055
6056 #endif
6057
6058 bool CMSMarkStack::allocate(size_t size) {
6059 // allocate a stack of the requisite depth
6060 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6061 size * sizeof(oop)));
6062 if (!rs.is_reserved()) {
6063 warning("CMSMarkStack allocation failure");
6064 return false;
6065 }
6066 if (!_virtual_space.initialize(rs, rs.size())) {
6067 warning("CMSMarkStack backing store failure");
6068 return false;
6069 }
6070 assert(_virtual_space.committed_size() == rs.size(),
6071 "didn't reserve backing store for all of CMS stack?");
6072 _base = (oop*)(_virtual_space.low());
6073 _index = 0;
6074 _capacity = size;
6075 NOT_PRODUCT(_max_depth = 0);
6076 return true;
6077 }
6078
6079 // XXX FIX ME !!! In the MT case we come in here holding a
6080 // leaf lock. For printing we need to take a further lock
6081 // which has lower rank. We need to recalibrate the two
6082 // lock-ranks involved in order to be able to print the
6083 // messages below. (Or defer the printing to the caller.
6084 // For now we take the expedient path of just disabling the
6085 // messages for the problematic case.)
6086 void CMSMarkStack::expand() {
6087 assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted");
6088 if (_capacity == MarkStackSizeMax) {
6089 if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6090 // We print a warning message only once per CMS cycle.
6091 gclog_or_tty->print_cr(" (benign) Hit CMSMarkStack max size limit");
6092 }
6093 return;
6094 }
6095 // Double capacity if possible
6096 size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax);
6097 // Do not give up existing stack until we have managed to
6098 // get the double capacity that we desired.
6099 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6100 new_capacity * sizeof(oop)));
6101 if (rs.is_reserved()) {
6102 // Release the backing store associated with old stack
6103 _virtual_space.release();
6104 // Reinitialize virtual space for new stack
6105 if (!_virtual_space.initialize(rs, rs.size())) {
6106 fatal("Not enough swap for expanded marking stack");
6107 }
6108 _base = (oop*)(_virtual_space.low());
6109 _index = 0;
6110 _capacity = new_capacity;
6111 } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6112 // Failed to double capacity, continue;
6113 // we print a detail message only once per CMS cycle.
6114 gclog_or_tty->print(" (benign) Failed to expand marking stack from "SIZE_FORMAT"K to "
6115 SIZE_FORMAT"K",
6116 _capacity / K, new_capacity / K);
6117 }
6118 }
6119
6120
6121 // Closures
6122 // XXX: there seems to be a lot of code duplication here;
6123 // should refactor and consolidate common code.
6124
6125 // This closure is used to mark refs into the CMS generation in
6126 // the CMS bit map. Called at the first checkpoint. This closure
6127 // assumes that we do not need to re-mark dirty cards; if the CMS
6128 // generation on which this is used is not an oldest
6129 // generation then this will lose younger_gen cards!
6130
6131 MarkRefsIntoClosure::MarkRefsIntoClosure(
6132 MemRegion span, CMSBitMap* bitMap):
6133 _span(span),
6134 _bitMap(bitMap)
6135 {
6136 assert(_ref_processor == NULL, "deliberately left NULL");
6137 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6138 }
6139
6140 void MarkRefsIntoClosure::do_oop(oop obj) {
6141 // if p points into _span, then mark corresponding bit in _markBitMap
6142 assert(obj->is_oop(), "expected an oop");
6143 HeapWord* addr = (HeapWord*)obj;
6144 if (_span.contains(addr)) {
6145 // this should be made more efficient
6146 _bitMap->mark(addr);
6147 }
6148 }
6149
6150 void MarkRefsIntoClosure::do_oop(oop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6151 void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6152
6153 Par_MarkRefsIntoClosure::Par_MarkRefsIntoClosure(
6154 MemRegion span, CMSBitMap* bitMap):
6155 _span(span),
6156 _bitMap(bitMap)
6157 {
6158 assert(_ref_processor == NULL, "deliberately left NULL");
6159 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6160 }
6161
6162 void Par_MarkRefsIntoClosure::do_oop(oop obj) {
6163 // if p points into _span, then mark corresponding bit in _markBitMap
6164 assert(obj->is_oop(), "expected an oop");
6165 HeapWord* addr = (HeapWord*)obj;
6166 if (_span.contains(addr)) {
6167 // this should be made more efficient
6168 _bitMap->par_mark(addr);
6169 }
6170 }
6171
6172 void Par_MarkRefsIntoClosure::do_oop(oop* p) { Par_MarkRefsIntoClosure::do_oop_work(p); }
6173 void Par_MarkRefsIntoClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoClosure::do_oop_work(p); }
6174
6175 // A variant of the above, used for CMS marking verification.
6176 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
6177 MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm):
6178 _span(span),
6179 _verification_bm(verification_bm),
6180 _cms_bm(cms_bm)
6181 {
6182 assert(_ref_processor == NULL, "deliberately left NULL");
6183 assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
6184 }
6185
6186 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
6187 // if p points into _span, then mark corresponding bit in _markBitMap
6188 assert(obj->is_oop(), "expected an oop");
6189 HeapWord* addr = (HeapWord*)obj;
6190 if (_span.contains(addr)) {
6191 _verification_bm->mark(addr);
6192 if (!_cms_bm->isMarked(addr)) {
6193 oop(addr)->print();
6194 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)", addr);
6195 fatal("... aborting");
6196 }
6197 }
6198 }
6199
6200 void MarkRefsIntoVerifyClosure::do_oop(oop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6201 void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6202
6203 //////////////////////////////////////////////////
6204 // MarkRefsIntoAndScanClosure
6205 //////////////////////////////////////////////////
6206
6207 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
6208 ReferenceProcessor* rp,
6209 CMSBitMap* bit_map,
6210 CMSBitMap* mod_union_table,
6211 CMSMarkStack* mark_stack,
6212 CMSCollector* collector,
6213 bool should_yield,
6214 bool concurrent_precleaning):
6215 _collector(collector),
6216 _span(span),
6217 _bit_map(bit_map),
6218 _mark_stack(mark_stack),
6219 _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table,
6220 mark_stack, concurrent_precleaning),
6221 _yield(should_yield),
6222 _concurrent_precleaning(concurrent_precleaning),
6223 _freelistLock(NULL)
6224 {
6225 _ref_processor = rp;
6226 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6227 }
6228
6229 // This closure is used to mark refs into the CMS generation at the
6230 // second (final) checkpoint, and to scan and transitively follow
6231 // the unmarked oops. It is also used during the concurrent precleaning
6232 // phase while scanning objects on dirty cards in the CMS generation.
6233 // The marks are made in the marking bit map and the marking stack is
6234 // used for keeping the (newly) grey objects during the scan.
6235 // The parallel version (Par_...) appears further below.
6236 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6237 if (obj != NULL) {
6238 assert(obj->is_oop(), "expected an oop");
6239 HeapWord* addr = (HeapWord*)obj;
6240 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6241 assert(_collector->overflow_list_is_empty(),
6242 "overflow list should be empty");
6243 if (_span.contains(addr) &&
6244 !_bit_map->isMarked(addr)) {
6245 // mark bit map (object is now grey)
6246 _bit_map->mark(addr);
6247 // push on marking stack (stack should be empty), and drain the
6248 // stack by applying this closure to the oops in the oops popped
6249 // from the stack (i.e. blacken the grey objects)
6250 bool res = _mark_stack->push(obj);
6251 assert(res, "Should have space to push on empty stack");
6252 do {
6253 oop new_oop = _mark_stack->pop();
6254 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6255 assert(_bit_map->isMarked((HeapWord*)new_oop),
6256 "only grey objects on this stack");
6257 // iterate over the oops in this oop, marking and pushing
6258 // the ones in CMS heap (i.e. in _span).
6259 new_oop->oop_iterate(&_pushAndMarkClosure);
6260 // check if it's time to yield
6261 do_yield_check();
6262 } while (!_mark_stack->isEmpty() ||
6263 (!_concurrent_precleaning && take_from_overflow_list()));
6264 // if marking stack is empty, and we are not doing this
6265 // during precleaning, then check the overflow list
6266 }
6267 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6268 assert(_collector->overflow_list_is_empty(),
6269 "overflow list was drained above");
6270 // We could restore evacuated mark words, if any, used for
6271 // overflow list links here because the overflow list is
6272 // provably empty here. That would reduce the maximum
6273 // size requirements for preserved_{oop,mark}_stack.
6274 // But we'll just postpone it until we are all done
6275 // so we can just stream through.
6276 if (!_concurrent_precleaning && CMSOverflowEarlyRestoration) {
6277 _collector->restore_preserved_marks_if_any();
6278 assert(_collector->no_preserved_marks(), "No preserved marks");
6279 }
6280 assert(!CMSOverflowEarlyRestoration || _collector->no_preserved_marks(),
6281 "All preserved marks should have been restored above");
6282 }
6283 }
6284
6285 void MarkRefsIntoAndScanClosure::do_oop(oop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6286 void MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6287
6288 void MarkRefsIntoAndScanClosure::do_yield_work() {
6289 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6290 "CMS thread should hold CMS token");
6291 assert_lock_strong(_freelistLock);
6292 assert_lock_strong(_bit_map->lock());
6293 // relinquish the free_list_lock and bitMaplock()
6294 _bit_map->lock()->unlock();
6295 _freelistLock->unlock();
6296 ConcurrentMarkSweepThread::desynchronize(true);
6297 _collector->stopTimer();
6298 if (PrintCMSStatistics != 0) {
6299 _collector->incrementYields();
6300 }
6301
6302 // See the comment in coordinator_yield()
6303 for (unsigned i = 0;
6304 i < CMSYieldSleepCount &&
6305 ConcurrentMarkSweepThread::should_yield() &&
6306 !CMSCollector::foregroundGCIsActive();
6307 ++i) {
6308 os::sleep(Thread::current(), 1, false);
6309 }
6310
6311 ConcurrentMarkSweepThread::synchronize(true);
6312 _freelistLock->lock_without_safepoint_check();
6313 _bit_map->lock()->lock_without_safepoint_check();
6314 _collector->startTimer();
6315 }
6316
6317 ///////////////////////////////////////////////////////////
6318 // Par_MarkRefsIntoAndScanClosure: a parallel version of
6319 // MarkRefsIntoAndScanClosure
6320 ///////////////////////////////////////////////////////////
6321 Par_MarkRefsIntoAndScanClosure::Par_MarkRefsIntoAndScanClosure(
6322 CMSCollector* collector, MemRegion span, ReferenceProcessor* rp,
6323 CMSBitMap* bit_map, OopTaskQueue* work_queue):
6324 _span(span),
6325 _bit_map(bit_map),
6326 _work_queue(work_queue),
6327 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
6328 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads))),
6329 _par_pushAndMarkClosure(collector, span, rp, bit_map, work_queue)
6330 {
6331 _ref_processor = rp;
6332 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6333 }
6334
6335 // This closure is used to mark refs into the CMS generation at the
6336 // second (final) checkpoint, and to scan and transitively follow
6337 // the unmarked oops. The marks are made in the marking bit map and
6338 // the work_queue is used for keeping the (newly) grey objects during
6339 // the scan phase whence they are also available for stealing by parallel
6340 // threads. Since the marking bit map is shared, updates are
6341 // synchronized (via CAS).
6342 void Par_MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6343 if (obj != NULL) {
6344 // Ignore mark word because this could be an already marked oop
6345 // that may be chained at the end of the overflow list.
6346 assert(obj->is_oop(true), "expected an oop");
6347 HeapWord* addr = (HeapWord*)obj;
6348 if (_span.contains(addr) &&
6349 !_bit_map->isMarked(addr)) {
6350 // mark bit map (object will become grey):
6351 // It is possible for several threads to be
6352 // trying to "claim" this object concurrently;
6353 // the unique thread that succeeds in marking the
6354 // object first will do the subsequent push on
6355 // to the work queue (or overflow list).
6356 if (_bit_map->par_mark(addr)) {
6357 // push on work_queue (which may not be empty), and trim the
6358 // queue to an appropriate length by applying this closure to
6359 // the oops in the oops popped from the stack (i.e. blacken the
6360 // grey objects)
6361 bool res = _work_queue->push(obj);
6362 assert(res, "Low water mark should be less than capacity?");
6363 trim_queue(_low_water_mark);
6364 } // Else, another thread claimed the object
6365 }
6366 }
6367 }
6368
6369 void Par_MarkRefsIntoAndScanClosure::do_oop(oop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6370 void Par_MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6371
6372 // This closure is used to rescan the marked objects on the dirty cards
6373 // in the mod union table and the card table proper.
6374 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
6375 oop p, MemRegion mr) {
6376
6377 size_t size = 0;
6378 HeapWord* addr = (HeapWord*)p;
6379 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6380 assert(_span.contains(addr), "we are scanning the CMS generation");
6381 // check if it's time to yield
6382 if (do_yield_check()) {
6383 // We yielded for some foreground stop-world work,
6384 // and we have been asked to abort this ongoing preclean cycle.
6385 return 0;
6386 }
6387 if (_bitMap->isMarked(addr)) {
6388 // it's marked; is it potentially uninitialized?
6389 if (p->klass_or_null() != NULL) {
6390 // an initialized object; ignore mark word in verification below
6391 // since we are running concurrent with mutators
6392 assert(p->is_oop(true), "should be an oop");
6393 if (p->is_objArray()) {
6394 // objArrays are precisely marked; restrict scanning
6395 // to dirty cards only.
6396 size = CompactibleFreeListSpace::adjustObjectSize(
6397 p->oop_iterate(_scanningClosure, mr));
6398 } else {
6399 // A non-array may have been imprecisely marked; we need
6400 // to scan object in its entirety.
6401 size = CompactibleFreeListSpace::adjustObjectSize(
6402 p->oop_iterate(_scanningClosure));
6403 }
6404 #ifdef ASSERT
6405 size_t direct_size =
6406 CompactibleFreeListSpace::adjustObjectSize(p->size());
6407 assert(size == direct_size, "Inconsistency in size");
6408 assert(size >= 3, "Necessary for Printezis marks to work");
6409 if (!_bitMap->isMarked(addr+1)) {
6410 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size);
6411 } else {
6412 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size-1);
6413 assert(_bitMap->isMarked(addr+size-1),
6414 "inconsistent Printezis mark");
6415 }
6416 #endif // ASSERT
6417 } else {
6418 // An uninitialized object.
6419 assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
6420 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
6421 size = pointer_delta(nextOneAddr + 1, addr);
6422 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6423 "alignment problem");
6424 // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
6425 // will dirty the card when the klass pointer is installed in the
6426 // object (signaling the completion of initialization).
6427 }
6428 } else {
6429 // Either a not yet marked object or an uninitialized object
6430 if (p->klass_or_null() == NULL) {
6431 // An uninitialized object, skip to the next card, since
6432 // we may not be able to read its P-bits yet.
6433 assert(size == 0, "Initial value");
6434 } else {
6435 // An object not (yet) reached by marking: we merely need to
6436 // compute its size so as to go look at the next block.
6437 assert(p->is_oop(true), "should be an oop");
6438 size = CompactibleFreeListSpace::adjustObjectSize(p->size());
6439 }
6440 }
6441 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6442 return size;
6443 }
6444
6445 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
6446 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6447 "CMS thread should hold CMS token");
6448 assert_lock_strong(_freelistLock);
6449 assert_lock_strong(_bitMap->lock());
6450 // relinquish the free_list_lock and bitMaplock()
6451 _bitMap->lock()->unlock();
6452 _freelistLock->unlock();
6453 ConcurrentMarkSweepThread::desynchronize(true);
6454 _collector->stopTimer();
6455 if (PrintCMSStatistics != 0) {
6456 _collector->incrementYields();
6457 }
6458
6459 // See the comment in coordinator_yield()
6460 for (unsigned i = 0; i < CMSYieldSleepCount &&
6461 ConcurrentMarkSweepThread::should_yield() &&
6462 !CMSCollector::foregroundGCIsActive(); ++i) {
6463 os::sleep(Thread::current(), 1, false);
6464 }
6465
6466 ConcurrentMarkSweepThread::synchronize(true);
6467 _freelistLock->lock_without_safepoint_check();
6468 _bitMap->lock()->lock_without_safepoint_check();
6469 _collector->startTimer();
6470 }
6471
6472
6473 //////////////////////////////////////////////////////////////////
6474 // SurvivorSpacePrecleanClosure
6475 //////////////////////////////////////////////////////////////////
6476 // This (single-threaded) closure is used to preclean the oops in
6477 // the survivor spaces.
6478 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
6479
6480 HeapWord* addr = (HeapWord*)p;
6481 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6482 assert(!_span.contains(addr), "we are scanning the survivor spaces");
6483 assert(p->klass_or_null() != NULL, "object should be initialized");
6484 // an initialized object; ignore mark word in verification below
6485 // since we are running concurrent with mutators
6486 assert(p->is_oop(true), "should be an oop");
6487 // Note that we do not yield while we iterate over
6488 // the interior oops of p, pushing the relevant ones
6489 // on our marking stack.
6490 size_t size = p->oop_iterate(_scanning_closure);
6491 do_yield_check();
6492 // Observe that below, we do not abandon the preclean
6493 // phase as soon as we should; rather we empty the
6494 // marking stack before returning. This is to satisfy
6495 // some existing assertions. In general, it may be a
6496 // good idea to abort immediately and complete the marking
6497 // from the grey objects at a later time.
6498 while (!_mark_stack->isEmpty()) {
6499 oop new_oop = _mark_stack->pop();
6500 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6501 assert(_bit_map->isMarked((HeapWord*)new_oop),
6502 "only grey objects on this stack");
6503 // iterate over the oops in this oop, marking and pushing
6504 // the ones in CMS heap (i.e. in _span).
6505 new_oop->oop_iterate(_scanning_closure);
6506 // check if it's time to yield
6507 do_yield_check();
6508 }
6509 unsigned int after_count =
6510 GenCollectedHeap::heap()->total_collections();
6511 bool abort = (_before_count != after_count) ||
6512 _collector->should_abort_preclean();
6513 return abort ? 0 : size;
6514 }
6515
6516 void SurvivorSpacePrecleanClosure::do_yield_work() {
6517 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6518 "CMS thread should hold CMS token");
6519 assert_lock_strong(_bit_map->lock());
6520 // Relinquish the bit map lock
6521 _bit_map->lock()->unlock();
6522 ConcurrentMarkSweepThread::desynchronize(true);
6523 _collector->stopTimer();
6524 if (PrintCMSStatistics != 0) {
6525 _collector->incrementYields();
6526 }
6527
6528 // See the comment in coordinator_yield()
6529 for (unsigned i = 0; i < CMSYieldSleepCount &&
6530 ConcurrentMarkSweepThread::should_yield() &&
6531 !CMSCollector::foregroundGCIsActive(); ++i) {
6532 os::sleep(Thread::current(), 1, false);
6533 }
6534
6535 ConcurrentMarkSweepThread::synchronize(true);
6536 _bit_map->lock()->lock_without_safepoint_check();
6537 _collector->startTimer();
6538 }
6539
6540 // This closure is used to rescan the marked objects on the dirty cards
6541 // in the mod union table and the card table proper. In the parallel
6542 // case, although the bitMap is shared, we do a single read so the
6543 // isMarked() query is "safe".
6544 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
6545 // Ignore mark word because we are running concurrent with mutators
6546 assert(p->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(p)));
6547 HeapWord* addr = (HeapWord*)p;
6548 assert(_span.contains(addr), "we are scanning the CMS generation");
6549 bool is_obj_array = false;
6550 #ifdef ASSERT
6551 if (!_parallel) {
6552 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6553 assert(_collector->overflow_list_is_empty(),
6554 "overflow list should be empty");
6555
6556 }
6557 #endif // ASSERT
6558 if (_bit_map->isMarked(addr)) {
6559 // Obj arrays are precisely marked, non-arrays are not;
6560 // so we scan objArrays precisely and non-arrays in their
6561 // entirety.
6562 if (p->is_objArray()) {
6563 is_obj_array = true;
6564 if (_parallel) {
6565 p->oop_iterate(_par_scan_closure, mr);
6566 } else {
6567 p->oop_iterate(_scan_closure, mr);
6568 }
6569 } else {
6570 if (_parallel) {
6571 p->oop_iterate(_par_scan_closure);
6572 } else {
6573 p->oop_iterate(_scan_closure);
6574 }
6575 }
6576 }
6577 #ifdef ASSERT
6578 if (!_parallel) {
6579 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6580 assert(_collector->overflow_list_is_empty(),
6581 "overflow list should be empty");
6582
6583 }
6584 #endif // ASSERT
6585 return is_obj_array;
6586 }
6587
6588 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
6589 MemRegion span,
6590 CMSBitMap* bitMap, CMSMarkStack* markStack,
6591 bool should_yield, bool verifying):
6592 _collector(collector),
6593 _span(span),
6594 _bitMap(bitMap),
6595 _mut(&collector->_modUnionTable),
6596 _markStack(markStack),
6597 _yield(should_yield),
6598 _skipBits(0)
6599 {
6600 assert(_markStack->isEmpty(), "stack should be empty");
6601 _finger = _bitMap->startWord();
6602 _threshold = _finger;
6603 assert(_collector->_restart_addr == NULL, "Sanity check");
6604 assert(_span.contains(_finger), "Out of bounds _finger?");
6605 DEBUG_ONLY(_verifying = verifying;)
6606 }
6607
6608 void MarkFromRootsClosure::reset(HeapWord* addr) {
6609 assert(_markStack->isEmpty(), "would cause duplicates on stack");
6610 assert(_span.contains(addr), "Out of bounds _finger?");
6611 _finger = addr;
6612 _threshold = (HeapWord*)round_to(
6613 (intptr_t)_finger, CardTableModRefBS::card_size);
6614 }
6615
6616 // Should revisit to see if this should be restructured for
6617 // greater efficiency.
6618 bool MarkFromRootsClosure::do_bit(size_t offset) {
6619 if (_skipBits > 0) {
6620 _skipBits--;
6621 return true;
6622 }
6623 // convert offset into a HeapWord*
6624 HeapWord* addr = _bitMap->startWord() + offset;
6625 assert(_bitMap->endWord() && addr < _bitMap->endWord(),
6626 "address out of range");
6627 assert(_bitMap->isMarked(addr), "tautology");
6628 if (_bitMap->isMarked(addr+1)) {
6629 // this is an allocated but not yet initialized object
6630 assert(_skipBits == 0, "tautology");
6631 _skipBits = 2; // skip next two marked bits ("Printezis-marks")
6632 oop p = oop(addr);
6633 if (p->klass_or_null() == NULL) {
6634 DEBUG_ONLY(if (!_verifying) {)
6635 // We re-dirty the cards on which this object lies and increase
6636 // the _threshold so that we'll come back to scan this object
6637 // during the preclean or remark phase. (CMSCleanOnEnter)
6638 if (CMSCleanOnEnter) {
6639 size_t sz = _collector->block_size_using_printezis_bits(addr);
6640 HeapWord* end_card_addr = (HeapWord*)round_to(
6641 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
6642 MemRegion redirty_range = MemRegion(addr, end_card_addr);
6643 assert(!redirty_range.is_empty(), "Arithmetical tautology");
6644 // Bump _threshold to end_card_addr; note that
6645 // _threshold cannot possibly exceed end_card_addr, anyhow.
6646 // This prevents future clearing of the card as the scan proceeds
6647 // to the right.
6648 assert(_threshold <= end_card_addr,
6649 "Because we are just scanning into this object");
6650 if (_threshold < end_card_addr) {
6651 _threshold = end_card_addr;
6652 }
6653 if (p->klass_or_null() != NULL) {
6654 // Redirty the range of cards...
6655 _mut->mark_range(redirty_range);
6656 } // ...else the setting of klass will dirty the card anyway.
6657 }
6658 DEBUG_ONLY(})
6659 return true;
6660 }
6661 }
6662 scanOopsInOop(addr);
6663 return true;
6664 }
6665
6666 // We take a break if we've been at this for a while,
6667 // so as to avoid monopolizing the locks involved.
6668 void MarkFromRootsClosure::do_yield_work() {
6669 // First give up the locks, then yield, then re-lock
6670 // We should probably use a constructor/destructor idiom to
6671 // do this unlock/lock or modify the MutexUnlocker class to
6672 // serve our purpose. XXX
6673 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6674 "CMS thread should hold CMS token");
6675 assert_lock_strong(_bitMap->lock());
6676 _bitMap->lock()->unlock();
6677 ConcurrentMarkSweepThread::desynchronize(true);
6678 _collector->stopTimer();
6679 if (PrintCMSStatistics != 0) {
6680 _collector->incrementYields();
6681 }
6682
6683 // See the comment in coordinator_yield()
6684 for (unsigned i = 0; i < CMSYieldSleepCount &&
6685 ConcurrentMarkSweepThread::should_yield() &&
6686 !CMSCollector::foregroundGCIsActive(); ++i) {
6687 os::sleep(Thread::current(), 1, false);
6688 }
6689
6690 ConcurrentMarkSweepThread::synchronize(true);
6691 _bitMap->lock()->lock_without_safepoint_check();
6692 _collector->startTimer();
6693 }
6694
6695 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
6696 assert(_bitMap->isMarked(ptr), "expected bit to be set");
6697 assert(_markStack->isEmpty(),
6698 "should drain stack to limit stack usage");
6699 // convert ptr to an oop preparatory to scanning
6700 oop obj = oop(ptr);
6701 // Ignore mark word in verification below, since we
6702 // may be running concurrent with mutators.
6703 assert(obj->is_oop(true), "should be an oop");
6704 assert(_finger <= ptr, "_finger runneth ahead");
6705 // advance the finger to right end of this object
6706 _finger = ptr + obj->size();
6707 assert(_finger > ptr, "we just incremented it above");
6708 // On large heaps, it may take us some time to get through
6709 // the marking phase. During
6710 // this time it's possible that a lot of mutations have
6711 // accumulated in the card table and the mod union table --
6712 // these mutation records are redundant until we have
6713 // actually traced into the corresponding card.
6714 // Here, we check whether advancing the finger would make
6715 // us cross into a new card, and if so clear corresponding
6716 // cards in the MUT (preclean them in the card-table in the
6717 // future).
6718
6719 DEBUG_ONLY(if (!_verifying) {)
6720 // The clean-on-enter optimization is disabled by default,
6721 // until we fix 6178663.
6722 if (CMSCleanOnEnter && (_finger > _threshold)) {
6723 // [_threshold, _finger) represents the interval
6724 // of cards to be cleared in MUT (or precleaned in card table).
6725 // The set of cards to be cleared is all those that overlap
6726 // with the interval [_threshold, _finger); note that
6727 // _threshold is always kept card-aligned but _finger isn't
6728 // always card-aligned.
6729 HeapWord* old_threshold = _threshold;
6730 assert(old_threshold == (HeapWord*)round_to(
6731 (intptr_t)old_threshold, CardTableModRefBS::card_size),
6732 "_threshold should always be card-aligned");
6733 _threshold = (HeapWord*)round_to(
6734 (intptr_t)_finger, CardTableModRefBS::card_size);
6735 MemRegion mr(old_threshold, _threshold);
6736 assert(!mr.is_empty(), "Control point invariant");
6737 assert(_span.contains(mr), "Should clear within span");
6738 _mut->clear_range(mr);
6739 }
6740 DEBUG_ONLY(})
6741 // Note: the finger doesn't advance while we drain
6742 // the stack below.
6743 PushOrMarkClosure pushOrMarkClosure(_collector,
6744 _span, _bitMap, _markStack,
6745 _finger, this);
6746 bool res = _markStack->push(obj);
6747 assert(res, "Empty non-zero size stack should have space for single push");
6748 while (!_markStack->isEmpty()) {
6749 oop new_oop = _markStack->pop();
6750 // Skip verifying header mark word below because we are
6751 // running concurrent with mutators.
6752 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
6753 // now scan this oop's oops
6754 new_oop->oop_iterate(&pushOrMarkClosure);
6755 do_yield_check();
6756 }
6757 assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
6758 }
6759
6760 Par_MarkFromRootsClosure::Par_MarkFromRootsClosure(CMSConcMarkingTask* task,
6761 CMSCollector* collector, MemRegion span,
6762 CMSBitMap* bit_map,
6763 OopTaskQueue* work_queue,
6764 CMSMarkStack* overflow_stack):
6765 _collector(collector),
6766 _whole_span(collector->_span),
6767 _span(span),
6768 _bit_map(bit_map),
6769 _mut(&collector->_modUnionTable),
6770 _work_queue(work_queue),
6771 _overflow_stack(overflow_stack),
6772 _skip_bits(0),
6773 _task(task)
6774 {
6775 assert(_work_queue->size() == 0, "work_queue should be empty");
6776 _finger = span.start();
6777 _threshold = _finger; // XXX Defer clear-on-enter optimization for now
6778 assert(_span.contains(_finger), "Out of bounds _finger?");
6779 }
6780
6781 // Should revisit to see if this should be restructured for
6782 // greater efficiency.
6783 bool Par_MarkFromRootsClosure::do_bit(size_t offset) {
6784 if (_skip_bits > 0) {
6785 _skip_bits--;
6786 return true;
6787 }
6788 // convert offset into a HeapWord*
6789 HeapWord* addr = _bit_map->startWord() + offset;
6790 assert(_bit_map->endWord() && addr < _bit_map->endWord(),
6791 "address out of range");
6792 assert(_bit_map->isMarked(addr), "tautology");
6793 if (_bit_map->isMarked(addr+1)) {
6794 // this is an allocated object that might not yet be initialized
6795 assert(_skip_bits == 0, "tautology");
6796 _skip_bits = 2; // skip next two marked bits ("Printezis-marks")
6797 oop p = oop(addr);
6798 if (p->klass_or_null() == NULL) {
6799 // in the case of Clean-on-Enter optimization, redirty card
6800 // and avoid clearing card by increasing the threshold.
6801 return true;
6802 }
6803 }
6804 scan_oops_in_oop(addr);
6805 return true;
6806 }
6807
6808 void Par_MarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
6809 assert(_bit_map->isMarked(ptr), "expected bit to be set");
6810 // Should we assert that our work queue is empty or
6811 // below some drain limit?
6812 assert(_work_queue->size() == 0,
6813 "should drain stack to limit stack usage");
6814 // convert ptr to an oop preparatory to scanning
6815 oop obj = oop(ptr);
6816 // Ignore mark word in verification below, since we
6817 // may be running concurrent with mutators.
6818 assert(obj->is_oop(true), "should be an oop");
6819 assert(_finger <= ptr, "_finger runneth ahead");
6820 // advance the finger to right end of this object
6821 _finger = ptr + obj->size();
6822 assert(_finger > ptr, "we just incremented it above");
6823 // On large heaps, it may take us some time to get through
6824 // the marking phase. During
6825 // this time it's possible that a lot of mutations have
6826 // accumulated in the card table and the mod union table --
6827 // these mutation records are redundant until we have
6828 // actually traced into the corresponding card.
6829 // Here, we check whether advancing the finger would make
6830 // us cross into a new card, and if so clear corresponding
6831 // cards in the MUT (preclean them in the card-table in the
6832 // future).
6833
6834 // The clean-on-enter optimization is disabled by default,
6835 // until we fix 6178663.
6836 if (CMSCleanOnEnter && (_finger > _threshold)) {
6837 // [_threshold, _finger) represents the interval
6838 // of cards to be cleared in MUT (or precleaned in card table).
6839 // The set of cards to be cleared is all those that overlap
6840 // with the interval [_threshold, _finger); note that
6841 // _threshold is always kept card-aligned but _finger isn't
6842 // always card-aligned.
6843 HeapWord* old_threshold = _threshold;
6844 assert(old_threshold == (HeapWord*)round_to(
6845 (intptr_t)old_threshold, CardTableModRefBS::card_size),
6846 "_threshold should always be card-aligned");
6847 _threshold = (HeapWord*)round_to(
6848 (intptr_t)_finger, CardTableModRefBS::card_size);
6849 MemRegion mr(old_threshold, _threshold);
6850 assert(!mr.is_empty(), "Control point invariant");
6851 assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
6852 _mut->clear_range(mr);
6853 }
6854
6855 // Note: the local finger doesn't advance while we drain
6856 // the stack below, but the global finger sure can and will.
6857 HeapWord** gfa = _task->global_finger_addr();
6858 Par_PushOrMarkClosure pushOrMarkClosure(_collector,
6859 _span, _bit_map,
6860 _work_queue,
6861 _overflow_stack,
6862 _finger,
6863 gfa, this);
6864 bool res = _work_queue->push(obj); // overflow could occur here
6865 assert(res, "Will hold once we use workqueues");
6866 while (true) {
6867 oop new_oop;
6868 if (!_work_queue->pop_local(new_oop)) {
6869 // We emptied our work_queue; check if there's stuff that can
6870 // be gotten from the overflow stack.
6871 if (CMSConcMarkingTask::get_work_from_overflow_stack(
6872 _overflow_stack, _work_queue)) {
6873 do_yield_check();
6874 continue;
6875 } else { // done
6876 break;
6877 }
6878 }
6879 // Skip verifying header mark word below because we are
6880 // running concurrent with mutators.
6881 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
6882 // now scan this oop's oops
6883 new_oop->oop_iterate(&pushOrMarkClosure);
6884 do_yield_check();
6885 }
6886 assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
6887 }
6888
6889 // Yield in response to a request from VM Thread or
6890 // from mutators.
6891 void Par_MarkFromRootsClosure::do_yield_work() {
6892 assert(_task != NULL, "sanity");
6893 _task->yield();
6894 }
6895
6896 // A variant of the above used for verifying CMS marking work.
6897 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
6898 MemRegion span,
6899 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6900 CMSMarkStack* mark_stack):
6901 _collector(collector),
6902 _span(span),
6903 _verification_bm(verification_bm),
6904 _cms_bm(cms_bm),
6905 _mark_stack(mark_stack),
6906 _pam_verify_closure(collector, span, verification_bm, cms_bm,
6907 mark_stack)
6908 {
6909 assert(_mark_stack->isEmpty(), "stack should be empty");
6910 _finger = _verification_bm->startWord();
6911 assert(_collector->_restart_addr == NULL, "Sanity check");
6912 assert(_span.contains(_finger), "Out of bounds _finger?");
6913 }
6914
6915 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
6916 assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
6917 assert(_span.contains(addr), "Out of bounds _finger?");
6918 _finger = addr;
6919 }
6920
6921 // Should revisit to see if this should be restructured for
6922 // greater efficiency.
6923 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
6924 // convert offset into a HeapWord*
6925 HeapWord* addr = _verification_bm->startWord() + offset;
6926 assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
6927 "address out of range");
6928 assert(_verification_bm->isMarked(addr), "tautology");
6929 assert(_cms_bm->isMarked(addr), "tautology");
6930
6931 assert(_mark_stack->isEmpty(),
6932 "should drain stack to limit stack usage");
6933 // convert addr to an oop preparatory to scanning
6934 oop obj = oop(addr);
6935 assert(obj->is_oop(), "should be an oop");
6936 assert(_finger <= addr, "_finger runneth ahead");
6937 // advance the finger to right end of this object
6938 _finger = addr + obj->size();
6939 assert(_finger > addr, "we just incremented it above");
6940 // Note: the finger doesn't advance while we drain
6941 // the stack below.
6942 bool res = _mark_stack->push(obj);
6943 assert(res, "Empty non-zero size stack should have space for single push");
6944 while (!_mark_stack->isEmpty()) {
6945 oop new_oop = _mark_stack->pop();
6946 assert(new_oop->is_oop(), "Oops! expected to pop an oop");
6947 // now scan this oop's oops
6948 new_oop->oop_iterate(&_pam_verify_closure);
6949 }
6950 assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
6951 return true;
6952 }
6953
6954 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
6955 CMSCollector* collector, MemRegion span,
6956 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6957 CMSMarkStack* mark_stack):
6958 MetadataAwareOopClosure(collector->ref_processor()),
6959 _collector(collector),
6960 _span(span),
6961 _verification_bm(verification_bm),
6962 _cms_bm(cms_bm),
6963 _mark_stack(mark_stack)
6964 { }
6965
6966 void PushAndMarkVerifyClosure::do_oop(oop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
6967 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
6968
6969 // Upon stack overflow, we discard (part of) the stack,
6970 // remembering the least address amongst those discarded
6971 // in CMSCollector's _restart_address.
6972 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
6973 // Remember the least grey address discarded
6974 HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
6975 _collector->lower_restart_addr(ra);
6976 _mark_stack->reset(); // discard stack contents
6977 _mark_stack->expand(); // expand the stack if possible
6978 }
6979
6980 void PushAndMarkVerifyClosure::do_oop(oop obj) {
6981 assert(obj->is_oop_or_null(), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
6982 HeapWord* addr = (HeapWord*)obj;
6983 if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
6984 // Oop lies in _span and isn't yet grey or black
6985 _verification_bm->mark(addr); // now grey
6986 if (!_cms_bm->isMarked(addr)) {
6987 oop(addr)->print();
6988 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)",
6989 addr);
6990 fatal("... aborting");
6991 }
6992
6993 if (!_mark_stack->push(obj)) { // stack overflow
6994 if (PrintCMSStatistics != 0) {
6995 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
6996 SIZE_FORMAT, _mark_stack->capacity());
6997 }
6998 assert(_mark_stack->isFull(), "Else push should have succeeded");
6999 handle_stack_overflow(addr);
7000 }
7001 // anything including and to the right of _finger
7002 // will be scanned as we iterate over the remainder of the
7003 // bit map
7004 }
7005 }
7006
7007 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
7008 MemRegion span,
7009 CMSBitMap* bitMap, CMSMarkStack* markStack,
7010 HeapWord* finger, MarkFromRootsClosure* parent) :
7011 MetadataAwareOopClosure(collector->ref_processor()),
7012 _collector(collector),
7013 _span(span),
7014 _bitMap(bitMap),
7015 _markStack(markStack),
7016 _finger(finger),
7017 _parent(parent)
7018 { }
7019
7020 Par_PushOrMarkClosure::Par_PushOrMarkClosure(CMSCollector* collector,
7021 MemRegion span,
7022 CMSBitMap* bit_map,
7023 OopTaskQueue* work_queue,
7024 CMSMarkStack* overflow_stack,
7025 HeapWord* finger,
7026 HeapWord** global_finger_addr,
7027 Par_MarkFromRootsClosure* parent) :
7028 MetadataAwareOopClosure(collector->ref_processor()),
7029 _collector(collector),
7030 _whole_span(collector->_span),
7031 _span(span),
7032 _bit_map(bit_map),
7033 _work_queue(work_queue),
7034 _overflow_stack(overflow_stack),
7035 _finger(finger),
7036 _global_finger_addr(global_finger_addr),
7037 _parent(parent)
7038 { }
7039
7040 // Assumes thread-safe access by callers, who are
7041 // responsible for mutual exclusion.
7042 void CMSCollector::lower_restart_addr(HeapWord* low) {
7043 assert(_span.contains(low), "Out of bounds addr");
7044 if (_restart_addr == NULL) {
7045 _restart_addr = low;
7046 } else {
7047 _restart_addr = MIN2(_restart_addr, low);
7048 }
7049 }
7050
7051 // Upon stack overflow, we discard (part of) the stack,
7052 // remembering the least address amongst those discarded
7053 // in CMSCollector's _restart_address.
7054 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7055 // Remember the least grey address discarded
7056 HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
7057 _collector->lower_restart_addr(ra);
7058 _markStack->reset(); // discard stack contents
7059 _markStack->expand(); // expand the stack if possible
7060 }
7061
7062 // Upon stack overflow, we discard (part of) the stack,
7063 // remembering the least address amongst those discarded
7064 // in CMSCollector's _restart_address.
7065 void Par_PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7066 // We need to do this under a mutex to prevent other
7067 // workers from interfering with the work done below.
7068 MutexLockerEx ml(_overflow_stack->par_lock(),
7069 Mutex::_no_safepoint_check_flag);
7070 // Remember the least grey address discarded
7071 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
7072 _collector->lower_restart_addr(ra);
7073 _overflow_stack->reset(); // discard stack contents
7074 _overflow_stack->expand(); // expand the stack if possible
7075 }
7076
7077 void PushOrMarkClosure::do_oop(oop obj) {
7078 // Ignore mark word because we are running concurrent with mutators.
7079 assert(obj->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7080 HeapWord* addr = (HeapWord*)obj;
7081 if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
7082 // Oop lies in _span and isn't yet grey or black
7083 _bitMap->mark(addr); // now grey
7084 if (addr < _finger) {
7085 // the bit map iteration has already either passed, or
7086 // sampled, this bit in the bit map; we'll need to
7087 // use the marking stack to scan this oop's oops.
7088 bool simulate_overflow = false;
7089 NOT_PRODUCT(
7090 if (CMSMarkStackOverflowALot &&
7091 _collector->simulate_overflow()) {
7092 // simulate a stack overflow
7093 simulate_overflow = true;
7094 }
7095 )
7096 if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
7097 if (PrintCMSStatistics != 0) {
7098 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7099 SIZE_FORMAT, _markStack->capacity());
7100 }
7101 assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
7102 handle_stack_overflow(addr);
7103 }
7104 }
7105 // anything including and to the right of _finger
7106 // will be scanned as we iterate over the remainder of the
7107 // bit map
7108 do_yield_check();
7109 }
7110 }
7111
7112 void PushOrMarkClosure::do_oop(oop* p) { PushOrMarkClosure::do_oop_work(p); }
7113 void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); }
7114
7115 void Par_PushOrMarkClosure::do_oop(oop obj) {
7116 // Ignore mark word because we are running concurrent with mutators.
7117 assert(obj->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7118 HeapWord* addr = (HeapWord*)obj;
7119 if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
7120 // Oop lies in _span and isn't yet grey or black
7121 // We read the global_finger (volatile read) strictly after marking oop
7122 bool res = _bit_map->par_mark(addr); // now grey
7123 volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
7124 // Should we push this marked oop on our stack?
7125 // -- if someone else marked it, nothing to do
7126 // -- if target oop is above global finger nothing to do
7127 // -- if target oop is in chunk and above local finger
7128 // then nothing to do
7129 // -- else push on work queue
7130 if ( !res // someone else marked it, they will deal with it
7131 || (addr >= *gfa) // will be scanned in a later task
7132 || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
7133 return;
7134 }
7135 // the bit map iteration has already either passed, or
7136 // sampled, this bit in the bit map; we'll need to
7137 // use the marking stack to scan this oop's oops.
7138 bool simulate_overflow = false;
7139 NOT_PRODUCT(
7140 if (CMSMarkStackOverflowALot &&
7141 _collector->simulate_overflow()) {
7142 // simulate a stack overflow
7143 simulate_overflow = true;
7144 }
7145 )
7146 if (simulate_overflow ||
7147 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
7148 // stack overflow
7149 if (PrintCMSStatistics != 0) {
7150 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7151 SIZE_FORMAT, _overflow_stack->capacity());
7152 }
7153 // We cannot assert that the overflow stack is full because
7154 // it may have been emptied since.
7155 assert(simulate_overflow ||
7156 _work_queue->size() == _work_queue->max_elems(),
7157 "Else push should have succeeded");
7158 handle_stack_overflow(addr);
7159 }
7160 do_yield_check();
7161 }
7162 }
7163
7164 void Par_PushOrMarkClosure::do_oop(oop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7165 void Par_PushOrMarkClosure::do_oop(narrowOop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7166
7167 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
7168 MemRegion span,
7169 ReferenceProcessor* rp,
7170 CMSBitMap* bit_map,
7171 CMSBitMap* mod_union_table,
7172 CMSMarkStack* mark_stack,
7173 bool concurrent_precleaning):
7174 MetadataAwareOopClosure(rp),
7175 _collector(collector),
7176 _span(span),
7177 _bit_map(bit_map),
7178 _mod_union_table(mod_union_table),
7179 _mark_stack(mark_stack),
7180 _concurrent_precleaning(concurrent_precleaning)
7181 {
7182 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7183 }
7184
7185 // Grey object rescan during pre-cleaning and second checkpoint phases --
7186 // the non-parallel version (the parallel version appears further below.)
7187 void PushAndMarkClosure::do_oop(oop obj) {
7188 // Ignore mark word verification. If during concurrent precleaning,
7189 // the object monitor may be locked. If during the checkpoint
7190 // phases, the object may already have been reached by a different
7191 // path and may be at the end of the global overflow list (so
7192 // the mark word may be NULL).
7193 assert(obj->is_oop_or_null(true /* ignore mark word */),
7194 err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7195 HeapWord* addr = (HeapWord*)obj;
7196 // Check if oop points into the CMS generation
7197 // and is not marked
7198 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7199 // a white object ...
7200 _bit_map->mark(addr); // ... now grey
7201 // push on the marking stack (grey set)
7202 bool simulate_overflow = false;
7203 NOT_PRODUCT(
7204 if (CMSMarkStackOverflowALot &&
7205 _collector->simulate_overflow()) {
7206 // simulate a stack overflow
7207 simulate_overflow = true;
7208 }
7209 )
7210 if (simulate_overflow || !_mark_stack->push(obj)) {
7211 if (_concurrent_precleaning) {
7212 // During precleaning we can just dirty the appropriate card(s)
7213 // in the mod union table, thus ensuring that the object remains
7214 // in the grey set and continue. In the case of object arrays
7215 // we need to dirty all of the cards that the object spans,
7216 // since the rescan of object arrays will be limited to the
7217 // dirty cards.
7218 // Note that no one can be interfering with us in this action
7219 // of dirtying the mod union table, so no locking or atomics
7220 // are required.
7221 if (obj->is_objArray()) {
7222 size_t sz = obj->size();
7223 HeapWord* end_card_addr = (HeapWord*)round_to(
7224 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7225 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7226 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7227 _mod_union_table->mark_range(redirty_range);
7228 } else {
7229 _mod_union_table->mark(addr);
7230 }
7231 _collector->_ser_pmc_preclean_ovflw++;
7232 } else {
7233 // During the remark phase, we need to remember this oop
7234 // in the overflow list.
7235 _collector->push_on_overflow_list(obj);
7236 _collector->_ser_pmc_remark_ovflw++;
7237 }
7238 }
7239 }
7240 }
7241
7242 Par_PushAndMarkClosure::Par_PushAndMarkClosure(CMSCollector* collector,
7243 MemRegion span,
7244 ReferenceProcessor* rp,
7245 CMSBitMap* bit_map,
7246 OopTaskQueue* work_queue):
7247 MetadataAwareOopClosure(rp),
7248 _collector(collector),
7249 _span(span),
7250 _bit_map(bit_map),
7251 _work_queue(work_queue)
7252 {
7253 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7254 }
7255
7256 void PushAndMarkClosure::do_oop(oop* p) { PushAndMarkClosure::do_oop_work(p); }
7257 void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); }
7258
7259 // Grey object rescan during second checkpoint phase --
7260 // the parallel version.
7261 void Par_PushAndMarkClosure::do_oop(oop obj) {
7262 // In the assert below, we ignore the mark word because
7263 // this oop may point to an already visited object that is
7264 // on the overflow stack (in which case the mark word has
7265 // been hijacked for chaining into the overflow stack --
7266 // if this is the last object in the overflow stack then
7267 // its mark word will be NULL). Because this object may
7268 // have been subsequently popped off the global overflow
7269 // stack, and the mark word possibly restored to the prototypical
7270 // value, by the time we get to examined this failing assert in
7271 // the debugger, is_oop_or_null(false) may subsequently start
7272 // to hold.
7273 assert(obj->is_oop_or_null(true),
7274 err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7275 HeapWord* addr = (HeapWord*)obj;
7276 // Check if oop points into the CMS generation
7277 // and is not marked
7278 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7279 // a white object ...
7280 // If we manage to "claim" the object, by being the
7281 // first thread to mark it, then we push it on our
7282 // marking stack
7283 if (_bit_map->par_mark(addr)) { // ... now grey
7284 // push on work queue (grey set)
7285 bool simulate_overflow = false;
7286 NOT_PRODUCT(
7287 if (CMSMarkStackOverflowALot &&
7288 _collector->par_simulate_overflow()) {
7289 // simulate a stack overflow
7290 simulate_overflow = true;
7291 }
7292 )
7293 if (simulate_overflow || !_work_queue->push(obj)) {
7294 _collector->par_push_on_overflow_list(obj);
7295 _collector->_par_pmc_remark_ovflw++; // imprecise OK: no need to CAS
7296 }
7297 } // Else, some other thread got there first
7298 }
7299 }
7300
7301 void Par_PushAndMarkClosure::do_oop(oop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7302 void Par_PushAndMarkClosure::do_oop(narrowOop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7303
7304 void CMSPrecleanRefsYieldClosure::do_yield_work() {
7305 Mutex* bml = _collector->bitMapLock();
7306 assert_lock_strong(bml);
7307 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7308 "CMS thread should hold CMS token");
7309
7310 bml->unlock();
7311 ConcurrentMarkSweepThread::desynchronize(true);
7312
7313 _collector->stopTimer();
7314 if (PrintCMSStatistics != 0) {
7315 _collector->incrementYields();
7316 }
7317
7318 // See the comment in coordinator_yield()
7319 for (unsigned i = 0; i < CMSYieldSleepCount &&
7320 ConcurrentMarkSweepThread::should_yield() &&
7321 !CMSCollector::foregroundGCIsActive(); ++i) {
7322 os::sleep(Thread::current(), 1, false);
7323 }
7324
7325 ConcurrentMarkSweepThread::synchronize(true);
7326 bml->lock();
7327
7328 _collector->startTimer();
7329 }
7330
7331 bool CMSPrecleanRefsYieldClosure::should_return() {
7332 if (ConcurrentMarkSweepThread::should_yield()) {
7333 do_yield_work();
7334 }
7335 return _collector->foregroundGCIsActive();
7336 }
7337
7338 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
7339 assert(((size_t)mr.start())%CardTableModRefBS::card_size_in_words == 0,
7340 "mr should be aligned to start at a card boundary");
7341 // We'd like to assert:
7342 // assert(mr.word_size()%CardTableModRefBS::card_size_in_words == 0,
7343 // "mr should be a range of cards");
7344 // However, that would be too strong in one case -- the last
7345 // partition ends at _unallocated_block which, in general, can be
7346 // an arbitrary boundary, not necessarily card aligned.
7347 if (PrintCMSStatistics != 0) {
7348 _num_dirty_cards +=
7349 mr.word_size()/CardTableModRefBS::card_size_in_words;
7350 }
7351 _space->object_iterate_mem(mr, &_scan_cl);
7352 }
7353
7354 SweepClosure::SweepClosure(CMSCollector* collector,
7355 ConcurrentMarkSweepGeneration* g,
7356 CMSBitMap* bitMap, bool should_yield) :
7357 _collector(collector),
7358 _g(g),
7359 _sp(g->cmsSpace()),
7360 _limit(_sp->sweep_limit()),
7361 _freelistLock(_sp->freelistLock()),
7362 _bitMap(bitMap),
7363 _yield(should_yield),
7364 _inFreeRange(false), // No free range at beginning of sweep
7365 _freeRangeInFreeLists(false), // No free range at beginning of sweep
7366 _lastFreeRangeCoalesced(false),
7367 _freeFinger(g->used_region().start())
7368 {
7369 NOT_PRODUCT(
7370 _numObjectsFreed = 0;
7371 _numWordsFreed = 0;
7372 _numObjectsLive = 0;
7373 _numWordsLive = 0;
7374 _numObjectsAlreadyFree = 0;
7375 _numWordsAlreadyFree = 0;
7376 _last_fc = NULL;
7377
7378 _sp->initializeIndexedFreeListArrayReturnedBytes();
7379 _sp->dictionary()->initialize_dict_returned_bytes();
7380 )
7381 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7382 "sweep _limit out of bounds");
7383 if (CMSTraceSweeper) {
7384 gclog_or_tty->print_cr("\n====================\nStarting new sweep with limit " PTR_FORMAT,
7385 _limit);
7386 }
7387 }
7388
7389 void SweepClosure::print_on(outputStream* st) const {
7390 tty->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")",
7391 _sp->bottom(), _sp->end());
7392 tty->print_cr("_limit = " PTR_FORMAT, _limit);
7393 tty->print_cr("_freeFinger = " PTR_FORMAT, _freeFinger);
7394 NOT_PRODUCT(tty->print_cr("_last_fc = " PTR_FORMAT, _last_fc);)
7395 tty->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d",
7396 _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced);
7397 }
7398
7399 #ifndef PRODUCT
7400 // Assertion checking only: no useful work in product mode --
7401 // however, if any of the flags below become product flags,
7402 // you may need to review this code to see if it needs to be
7403 // enabled in product mode.
7404 SweepClosure::~SweepClosure() {
7405 assert_lock_strong(_freelistLock);
7406 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7407 "sweep _limit out of bounds");
7408 if (inFreeRange()) {
7409 warning("inFreeRange() should have been reset; dumping state of SweepClosure");
7410 print();
7411 ShouldNotReachHere();
7412 }
7413 if (Verbose && PrintGC) {
7414 gclog_or_tty->print("Collected "SIZE_FORMAT" objects, " SIZE_FORMAT " bytes",
7415 _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
7416 gclog_or_tty->print_cr("\nLive "SIZE_FORMAT" objects, "
7417 SIZE_FORMAT" bytes "
7418 "Already free "SIZE_FORMAT" objects, "SIZE_FORMAT" bytes",
7419 _numObjectsLive, _numWordsLive*sizeof(HeapWord),
7420 _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
7421 size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree)
7422 * sizeof(HeapWord);
7423 gclog_or_tty->print_cr("Total sweep: "SIZE_FORMAT" bytes", totalBytes);
7424
7425 if (PrintCMSStatistics && CMSVerifyReturnedBytes) {
7426 size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
7427 size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes();
7428 size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes;
7429 gclog_or_tty->print("Returned "SIZE_FORMAT" bytes", returned_bytes);
7430 gclog_or_tty->print(" Indexed List Returned "SIZE_FORMAT" bytes",
7431 indexListReturnedBytes);
7432 gclog_or_tty->print_cr(" Dictionary Returned "SIZE_FORMAT" bytes",
7433 dict_returned_bytes);
7434 }
7435 }
7436 if (CMSTraceSweeper) {
7437 gclog_or_tty->print_cr("end of sweep with _limit = " PTR_FORMAT "\n================",
7438 _limit);
7439 }
7440 }
7441 #endif // PRODUCT
7442
7443 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
7444 bool freeRangeInFreeLists) {
7445 if (CMSTraceSweeper) {
7446 gclog_or_tty->print("---- Start free range at " PTR_FORMAT " with free block (%d)\n",
7447 freeFinger, freeRangeInFreeLists);
7448 }
7449 assert(!inFreeRange(), "Trampling existing free range");
7450 set_inFreeRange(true);
7451 set_lastFreeRangeCoalesced(false);
7452
7453 set_freeFinger(freeFinger);
7454 set_freeRangeInFreeLists(freeRangeInFreeLists);
7455 if (CMSTestInFreeList) {
7456 if (freeRangeInFreeLists) {
7457 FreeChunk* fc = (FreeChunk*) freeFinger;
7458 assert(fc->is_free(), "A chunk on the free list should be free.");
7459 assert(fc->size() > 0, "Free range should have a size");
7460 assert(_sp->verify_chunk_in_free_list(fc), "Chunk is not in free lists");
7461 }
7462 }
7463 }
7464
7465 // Note that the sweeper runs concurrently with mutators. Thus,
7466 // it is possible for direct allocation in this generation to happen
7467 // in the middle of the sweep. Note that the sweeper also coalesces
7468 // contiguous free blocks. Thus, unless the sweeper and the allocator
7469 // synchronize appropriately freshly allocated blocks may get swept up.
7470 // This is accomplished by the sweeper locking the free lists while
7471 // it is sweeping. Thus blocks that are determined to be free are
7472 // indeed free. There is however one additional complication:
7473 // blocks that have been allocated since the final checkpoint and
7474 // mark, will not have been marked and so would be treated as
7475 // unreachable and swept up. To prevent this, the allocator marks
7476 // the bit map when allocating during the sweep phase. This leads,
7477 // however, to a further complication -- objects may have been allocated
7478 // but not yet initialized -- in the sense that the header isn't yet
7479 // installed. The sweeper can not then determine the size of the block
7480 // in order to skip over it. To deal with this case, we use a technique
7481 // (due to Printezis) to encode such uninitialized block sizes in the
7482 // bit map. Since the bit map uses a bit per every HeapWord, but the
7483 // CMS generation has a minimum object size of 3 HeapWords, it follows
7484 // that "normal marks" won't be adjacent in the bit map (there will
7485 // always be at least two 0 bits between successive 1 bits). We make use
7486 // of these "unused" bits to represent uninitialized blocks -- the bit
7487 // corresponding to the start of the uninitialized object and the next
7488 // bit are both set. Finally, a 1 bit marks the end of the object that
7489 // started with the two consecutive 1 bits to indicate its potentially
7490 // uninitialized state.
7491
7492 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
7493 FreeChunk* fc = (FreeChunk*)addr;
7494 size_t res;
7495
7496 // Check if we are done sweeping. Below we check "addr >= _limit" rather
7497 // than "addr == _limit" because although _limit was a block boundary when
7498 // we started the sweep, it may no longer be one because heap expansion
7499 // may have caused us to coalesce the block ending at the address _limit
7500 // with a newly expanded chunk (this happens when _limit was set to the
7501 // previous _end of the space), so we may have stepped past _limit:
7502 // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740.
7503 if (addr >= _limit) { // we have swept up to or past the limit: finish up
7504 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7505 "sweep _limit out of bounds");
7506 assert(addr < _sp->end(), "addr out of bounds");
7507 // Flush any free range we might be holding as a single
7508 // coalesced chunk to the appropriate free list.
7509 if (inFreeRange()) {
7510 assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit,
7511 err_msg("freeFinger() " PTR_FORMAT" is out-of-bounds", freeFinger()));
7512 flush_cur_free_chunk(freeFinger(),
7513 pointer_delta(addr, freeFinger()));
7514 if (CMSTraceSweeper) {
7515 gclog_or_tty->print("Sweep: last chunk: ");
7516 gclog_or_tty->print("put_free_blk " PTR_FORMAT " ("SIZE_FORMAT") "
7517 "[coalesced:%d]\n",
7518 freeFinger(), pointer_delta(addr, freeFinger()),
7519 lastFreeRangeCoalesced() ? 1 : 0);
7520 }
7521 }
7522
7523 // help the iterator loop finish
7524 return pointer_delta(_sp->end(), addr);
7525 }
7526
7527 assert(addr < _limit, "sweep invariant");
7528 // check if we should yield
7529 do_yield_check(addr);
7530 if (fc->is_free()) {
7531 // Chunk that is already free
7532 res = fc->size();
7533 do_already_free_chunk(fc);
7534 debug_only(_sp->verifyFreeLists());
7535 // If we flush the chunk at hand in lookahead_and_flush()
7536 // and it's coalesced with a preceding chunk, then the
7537 // process of "mangling" the payload of the coalesced block
7538 // will cause erasure of the size information from the
7539 // (erstwhile) header of all the coalesced blocks but the
7540 // first, so the first disjunct in the assert will not hold
7541 // in that specific case (in which case the second disjunct
7542 // will hold).
7543 assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit,
7544 "Otherwise the size info doesn't change at this step");
7545 NOT_PRODUCT(
7546 _numObjectsAlreadyFree++;
7547 _numWordsAlreadyFree += res;
7548 )
7549 NOT_PRODUCT(_last_fc = fc;)
7550 } else if (!_bitMap->isMarked(addr)) {
7551 // Chunk is fresh garbage
7552 res = do_garbage_chunk(fc);
7553 debug_only(_sp->verifyFreeLists());
7554 NOT_PRODUCT(
7555 _numObjectsFreed++;
7556 _numWordsFreed += res;
7557 )
7558 } else {
7559 // Chunk that is alive.
7560 res = do_live_chunk(fc);
7561 debug_only(_sp->verifyFreeLists());
7562 NOT_PRODUCT(
7563 _numObjectsLive++;
7564 _numWordsLive += res;
7565 )
7566 }
7567 return res;
7568 }
7569
7570 // For the smart allocation, record following
7571 // split deaths - a free chunk is removed from its free list because
7572 // it is being split into two or more chunks.
7573 // split birth - a free chunk is being added to its free list because
7574 // a larger free chunk has been split and resulted in this free chunk.
7575 // coal death - a free chunk is being removed from its free list because
7576 // it is being coalesced into a large free chunk.
7577 // coal birth - a free chunk is being added to its free list because
7578 // it was created when two or more free chunks where coalesced into
7579 // this free chunk.
7580 //
7581 // These statistics are used to determine the desired number of free
7582 // chunks of a given size. The desired number is chosen to be relative
7583 // to the end of a CMS sweep. The desired number at the end of a sweep
7584 // is the
7585 // count-at-end-of-previous-sweep (an amount that was enough)
7586 // - count-at-beginning-of-current-sweep (the excess)
7587 // + split-births (gains in this size during interval)
7588 // - split-deaths (demands on this size during interval)
7589 // where the interval is from the end of one sweep to the end of the
7590 // next.
7591 //
7592 // When sweeping the sweeper maintains an accumulated chunk which is
7593 // the chunk that is made up of chunks that have been coalesced. That
7594 // will be termed the left-hand chunk. A new chunk of garbage that
7595 // is being considered for coalescing will be referred to as the
7596 // right-hand chunk.
7597 //
7598 // When making a decision on whether to coalesce a right-hand chunk with
7599 // the current left-hand chunk, the current count vs. the desired count
7600 // of the left-hand chunk is considered. Also if the right-hand chunk
7601 // is near the large chunk at the end of the heap (see
7602 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
7603 // left-hand chunk is coalesced.
7604 //
7605 // When making a decision about whether to split a chunk, the desired count
7606 // vs. the current count of the candidate to be split is also considered.
7607 // If the candidate is underpopulated (currently fewer chunks than desired)
7608 // a chunk of an overpopulated (currently more chunks than desired) size may
7609 // be chosen. The "hint" associated with a free list, if non-null, points
7610 // to a free list which may be overpopulated.
7611 //
7612
7613 void SweepClosure::do_already_free_chunk(FreeChunk* fc) {
7614 const size_t size = fc->size();
7615 // Chunks that cannot be coalesced are not in the
7616 // free lists.
7617 if (CMSTestInFreeList && !fc->cantCoalesce()) {
7618 assert(_sp->verify_chunk_in_free_list(fc),
7619 "free chunk should be in free lists");
7620 }
7621 // a chunk that is already free, should not have been
7622 // marked in the bit map
7623 HeapWord* const addr = (HeapWord*) fc;
7624 assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
7625 // Verify that the bit map has no bits marked between
7626 // addr and purported end of this block.
7627 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7628
7629 // Some chunks cannot be coalesced under any circumstances.
7630 // See the definition of cantCoalesce().
7631 if (!fc->cantCoalesce()) {
7632 // This chunk can potentially be coalesced.
7633 if (_sp->adaptive_freelists()) {
7634 // All the work is done in
7635 do_post_free_or_garbage_chunk(fc, size);
7636 } else { // Not adaptive free lists
7637 // this is a free chunk that can potentially be coalesced by the sweeper;
7638 if (!inFreeRange()) {
7639 // if the next chunk is a free block that can't be coalesced
7640 // it doesn't make sense to remove this chunk from the free lists
7641 FreeChunk* nextChunk = (FreeChunk*)(addr + size);
7642 assert((HeapWord*)nextChunk <= _sp->end(), "Chunk size out of bounds?");
7643 if ((HeapWord*)nextChunk < _sp->end() && // There is another free chunk to the right ...
7644 nextChunk->is_free() && // ... which is free...
7645 nextChunk->cantCoalesce()) { // ... but can't be coalesced
7646 // nothing to do
7647 } else {
7648 // Potentially the start of a new free range:
7649 // Don't eagerly remove it from the free lists.
7650 // No need to remove it if it will just be put
7651 // back again. (Also from a pragmatic point of view
7652 // if it is a free block in a region that is beyond
7653 // any allocated blocks, an assertion will fail)
7654 // Remember the start of a free run.
7655 initialize_free_range(addr, true);
7656 // end - can coalesce with next chunk
7657 }
7658 } else {
7659 // the midst of a free range, we are coalescing
7660 print_free_block_coalesced(fc);
7661 if (CMSTraceSweeper) {
7662 gclog_or_tty->print(" -- pick up free block " PTR_FORMAT " (" SIZE_FORMAT ")\n", fc, size);
7663 }
7664 // remove it from the free lists
7665 _sp->removeFreeChunkFromFreeLists(fc);
7666 set_lastFreeRangeCoalesced(true);
7667 // If the chunk is being coalesced and the current free range is
7668 // in the free lists, remove the current free range so that it
7669 // will be returned to the free lists in its entirety - all
7670 // the coalesced pieces included.
7671 if (freeRangeInFreeLists()) {
7672 FreeChunk* ffc = (FreeChunk*) freeFinger();
7673 assert(ffc->size() == pointer_delta(addr, freeFinger()),
7674 "Size of free range is inconsistent with chunk size.");
7675 if (CMSTestInFreeList) {
7676 assert(_sp->verify_chunk_in_free_list(ffc),
7677 "free range is not in free lists");
7678 }
7679 _sp->removeFreeChunkFromFreeLists(ffc);
7680 set_freeRangeInFreeLists(false);
7681 }
7682 }
7683 }
7684 // Note that if the chunk is not coalescable (the else arm
7685 // below), we unconditionally flush, without needing to do
7686 // a "lookahead," as we do below.
7687 if (inFreeRange()) lookahead_and_flush(fc, size);
7688 } else {
7689 // Code path common to both original and adaptive free lists.
7690
7691 // cant coalesce with previous block; this should be treated
7692 // as the end of a free run if any
7693 if (inFreeRange()) {
7694 // we kicked some butt; time to pick up the garbage
7695 assert(freeFinger() < addr, "freeFinger points too high");
7696 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7697 }
7698 // else, nothing to do, just continue
7699 }
7700 }
7701
7702 size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) {
7703 // This is a chunk of garbage. It is not in any free list.
7704 // Add it to a free list or let it possibly be coalesced into
7705 // a larger chunk.
7706 HeapWord* const addr = (HeapWord*) fc;
7707 const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7708
7709 if (_sp->adaptive_freelists()) {
7710 // Verify that the bit map has no bits marked between
7711 // addr and purported end of just dead object.
7712 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7713
7714 do_post_free_or_garbage_chunk(fc, size);
7715 } else {
7716 if (!inFreeRange()) {
7717 // start of a new free range
7718 assert(size > 0, "A free range should have a size");
7719 initialize_free_range(addr, false);
7720 } else {
7721 // this will be swept up when we hit the end of the
7722 // free range
7723 if (CMSTraceSweeper) {
7724 gclog_or_tty->print(" -- pick up garbage " PTR_FORMAT " (" SIZE_FORMAT ")\n", fc, size);
7725 }
7726 // If the chunk is being coalesced and the current free range is
7727 // in the free lists, remove the current free range so that it
7728 // will be returned to the free lists in its entirety - all
7729 // the coalesced pieces included.
7730 if (freeRangeInFreeLists()) {
7731 FreeChunk* ffc = (FreeChunk*)freeFinger();
7732 assert(ffc->size() == pointer_delta(addr, freeFinger()),
7733 "Size of free range is inconsistent with chunk size.");
7734 if (CMSTestInFreeList) {
7735 assert(_sp->verify_chunk_in_free_list(ffc),
7736 "free range is not in free lists");
7737 }
7738 _sp->removeFreeChunkFromFreeLists(ffc);
7739 set_freeRangeInFreeLists(false);
7740 }
7741 set_lastFreeRangeCoalesced(true);
7742 }
7743 // this will be swept up when we hit the end of the free range
7744
7745 // Verify that the bit map has no bits marked between
7746 // addr and purported end of just dead object.
7747 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7748 }
7749 assert(_limit >= addr + size,
7750 "A freshly garbage chunk can't possibly straddle over _limit");
7751 if (inFreeRange()) lookahead_and_flush(fc, size);
7752 return size;
7753 }
7754
7755 size_t SweepClosure::do_live_chunk(FreeChunk* fc) {
7756 HeapWord* addr = (HeapWord*) fc;
7757 // The sweeper has just found a live object. Return any accumulated
7758 // left hand chunk to the free lists.
7759 if (inFreeRange()) {
7760 assert(freeFinger() < addr, "freeFinger points too high");
7761 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7762 }
7763
7764 // This object is live: we'd normally expect this to be
7765 // an oop, and like to assert the following:
7766 // assert(oop(addr)->is_oop(), "live block should be an oop");
7767 // However, as we commented above, this may be an object whose
7768 // header hasn't yet been initialized.
7769 size_t size;
7770 assert(_bitMap->isMarked(addr), "Tautology for this control point");
7771 if (_bitMap->isMarked(addr + 1)) {
7772 // Determine the size from the bit map, rather than trying to
7773 // compute it from the object header.
7774 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
7775 size = pointer_delta(nextOneAddr + 1, addr);
7776 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
7777 "alignment problem");
7778
7779 #ifdef ASSERT
7780 if (oop(addr)->klass_or_null() != NULL) {
7781 // Ignore mark word because we are running concurrent with mutators
7782 assert(oop(addr)->is_oop(true), "live block should be an oop");
7783 assert(size ==
7784 CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
7785 "P-mark and computed size do not agree");
7786 }
7787 #endif
7788
7789 } else {
7790 // This should be an initialized object that's alive.
7791 assert(oop(addr)->klass_or_null() != NULL,
7792 "Should be an initialized object");
7793 // Ignore mark word because we are running concurrent with mutators
7794 assert(oop(addr)->is_oop(true), "live block should be an oop");
7795 // Verify that the bit map has no bits marked between
7796 // addr and purported end of this block.
7797 size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7798 assert(size >= 3, "Necessary for Printezis marks to work");
7799 assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
7800 DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
7801 }
7802 return size;
7803 }
7804
7805 void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc,
7806 size_t chunkSize) {
7807 // do_post_free_or_garbage_chunk() should only be called in the case
7808 // of the adaptive free list allocator.
7809 const bool fcInFreeLists = fc->is_free();
7810 assert(_sp->adaptive_freelists(), "Should only be used in this case.");
7811 assert((HeapWord*)fc <= _limit, "sweep invariant");
7812 if (CMSTestInFreeList && fcInFreeLists) {
7813 assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists");
7814 }
7815
7816 if (CMSTraceSweeper) {
7817 gclog_or_tty->print_cr(" -- pick up another chunk at " PTR_FORMAT " (" SIZE_FORMAT ")", fc, chunkSize);
7818 }
7819
7820 HeapWord* const fc_addr = (HeapWord*) fc;
7821
7822 bool coalesce;
7823 const size_t left = pointer_delta(fc_addr, freeFinger());
7824 const size_t right = chunkSize;
7825 switch (FLSCoalescePolicy) {
7826 // numeric value forms a coalition aggressiveness metric
7827 case 0: { // never coalesce
7828 coalesce = false;
7829 break;
7830 }
7831 case 1: { // coalesce if left & right chunks on overpopulated lists
7832 coalesce = _sp->coalOverPopulated(left) &&
7833 _sp->coalOverPopulated(right);
7834 break;
7835 }
7836 case 2: { // coalesce if left chunk on overpopulated list (default)
7837 coalesce = _sp->coalOverPopulated(left);
7838 break;
7839 }
7840 case 3: { // coalesce if left OR right chunk on overpopulated list
7841 coalesce = _sp->coalOverPopulated(left) ||
7842 _sp->coalOverPopulated(right);
7843 break;
7844 }
7845 case 4: { // always coalesce
7846 coalesce = true;
7847 break;
7848 }
7849 default:
7850 ShouldNotReachHere();
7851 }
7852
7853 // Should the current free range be coalesced?
7854 // If the chunk is in a free range and either we decided to coalesce above
7855 // or the chunk is near the large block at the end of the heap
7856 // (isNearLargestChunk() returns true), then coalesce this chunk.
7857 const bool doCoalesce = inFreeRange()
7858 && (coalesce || _g->isNearLargestChunk(fc_addr));
7859 if (doCoalesce) {
7860 // Coalesce the current free range on the left with the new
7861 // chunk on the right. If either is on a free list,
7862 // it must be removed from the list and stashed in the closure.
7863 if (freeRangeInFreeLists()) {
7864 FreeChunk* const ffc = (FreeChunk*)freeFinger();
7865 assert(ffc->size() == pointer_delta(fc_addr, freeFinger()),
7866 "Size of free range is inconsistent with chunk size.");
7867 if (CMSTestInFreeList) {
7868 assert(_sp->verify_chunk_in_free_list(ffc),
7869 "Chunk is not in free lists");
7870 }
7871 _sp->coalDeath(ffc->size());
7872 _sp->removeFreeChunkFromFreeLists(ffc);
7873 set_freeRangeInFreeLists(false);
7874 }
7875 if (fcInFreeLists) {
7876 _sp->coalDeath(chunkSize);
7877 assert(fc->size() == chunkSize,
7878 "The chunk has the wrong size or is not in the free lists");
7879 _sp->removeFreeChunkFromFreeLists(fc);
7880 }
7881 set_lastFreeRangeCoalesced(true);
7882 print_free_block_coalesced(fc);
7883 } else { // not in a free range and/or should not coalesce
7884 // Return the current free range and start a new one.
7885 if (inFreeRange()) {
7886 // In a free range but cannot coalesce with the right hand chunk.
7887 // Put the current free range into the free lists.
7888 flush_cur_free_chunk(freeFinger(),
7889 pointer_delta(fc_addr, freeFinger()));
7890 }
7891 // Set up for new free range. Pass along whether the right hand
7892 // chunk is in the free lists.
7893 initialize_free_range((HeapWord*)fc, fcInFreeLists);
7894 }
7895 }
7896
7897 // Lookahead flush:
7898 // If we are tracking a free range, and this is the last chunk that
7899 // we'll look at because its end crosses past _limit, we'll preemptively
7900 // flush it along with any free range we may be holding on to. Note that
7901 // this can be the case only for an already free or freshly garbage
7902 // chunk. If this block is an object, it can never straddle
7903 // over _limit. The "straddling" occurs when _limit is set at
7904 // the previous end of the space when this cycle started, and
7905 // a subsequent heap expansion caused the previously co-terminal
7906 // free block to be coalesced with the newly expanded portion,
7907 // thus rendering _limit a non-block-boundary making it dangerous
7908 // for the sweeper to step over and examine.
7909 void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) {
7910 assert(inFreeRange(), "Should only be called if currently in a free range.");
7911 HeapWord* const eob = ((HeapWord*)fc) + chunk_size;
7912 assert(_sp->used_region().contains(eob - 1),
7913 err_msg("eob = " PTR_FORMAT " eob-1 = " PTR_FORMAT " _limit = " PTR_FORMAT
7914 " out of bounds wrt _sp = [" PTR_FORMAT "," PTR_FORMAT ")"
7915 " when examining fc = " PTR_FORMAT "(" SIZE_FORMAT ")",
7916 eob, eob-1, _limit, _sp->bottom(), _sp->end(), fc, chunk_size));
7917 if (eob >= _limit) {
7918 assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit");
7919 if (CMSTraceSweeper) {
7920 gclog_or_tty->print_cr("_limit " PTR_FORMAT " reached or crossed by block "
7921 "[" PTR_FORMAT "," PTR_FORMAT ") in space "
7922 "[" PTR_FORMAT "," PTR_FORMAT ")",
7923 _limit, fc, eob, _sp->bottom(), _sp->end());
7924 }
7925 // Return the storage we are tracking back into the free lists.
7926 if (CMSTraceSweeper) {
7927 gclog_or_tty->print_cr("Flushing ... ");
7928 }
7929 assert(freeFinger() < eob, "Error");
7930 flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger()));
7931 }
7932 }
7933
7934 void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) {
7935 assert(inFreeRange(), "Should only be called if currently in a free range.");
7936 assert(size > 0,
7937 "A zero sized chunk cannot be added to the free lists.");
7938 if (!freeRangeInFreeLists()) {
7939 if (CMSTestInFreeList) {
7940 FreeChunk* fc = (FreeChunk*) chunk;
7941 fc->set_size(size);
7942 assert(!_sp->verify_chunk_in_free_list(fc),
7943 "chunk should not be in free lists yet");
7944 }
7945 if (CMSTraceSweeper) {
7946 gclog_or_tty->print_cr(" -- add free block " PTR_FORMAT " (" SIZE_FORMAT ") to free lists",
7947 chunk, size);
7948 }
7949 // A new free range is going to be starting. The current
7950 // free range has not been added to the free lists yet or
7951 // was removed so add it back.
7952 // If the current free range was coalesced, then the death
7953 // of the free range was recorded. Record a birth now.
7954 if (lastFreeRangeCoalesced()) {
7955 _sp->coalBirth(size);
7956 }
7957 _sp->addChunkAndRepairOffsetTable(chunk, size,
7958 lastFreeRangeCoalesced());
7959 } else if (CMSTraceSweeper) {
7960 gclog_or_tty->print_cr("Already in free list: nothing to flush");
7961 }
7962 set_inFreeRange(false);
7963 set_freeRangeInFreeLists(false);
7964 }
7965
7966 // We take a break if we've been at this for a while,
7967 // so as to avoid monopolizing the locks involved.
7968 void SweepClosure::do_yield_work(HeapWord* addr) {
7969 // Return current free chunk being used for coalescing (if any)
7970 // to the appropriate freelist. After yielding, the next
7971 // free block encountered will start a coalescing range of
7972 // free blocks. If the next free block is adjacent to the
7973 // chunk just flushed, they will need to wait for the next
7974 // sweep to be coalesced.
7975 if (inFreeRange()) {
7976 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7977 }
7978
7979 // First give up the locks, then yield, then re-lock.
7980 // We should probably use a constructor/destructor idiom to
7981 // do this unlock/lock or modify the MutexUnlocker class to
7982 // serve our purpose. XXX
7983 assert_lock_strong(_bitMap->lock());
7984 assert_lock_strong(_freelistLock);
7985 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7986 "CMS thread should hold CMS token");
7987 _bitMap->lock()->unlock();
7988 _freelistLock->unlock();
7989 ConcurrentMarkSweepThread::desynchronize(true);
7990 _collector->stopTimer();
7991 if (PrintCMSStatistics != 0) {
7992 _collector->incrementYields();
7993 }
7994
7995 // See the comment in coordinator_yield()
7996 for (unsigned i = 0; i < CMSYieldSleepCount &&
7997 ConcurrentMarkSweepThread::should_yield() &&
7998 !CMSCollector::foregroundGCIsActive(); ++i) {
7999 os::sleep(Thread::current(), 1, false);
8000 }
8001
8002 ConcurrentMarkSweepThread::synchronize(true);
8003 _freelistLock->lock();
8004 _bitMap->lock()->lock_without_safepoint_check();
8005 _collector->startTimer();
8006 }
8007
8008 #ifndef PRODUCT
8009 // This is actually very useful in a product build if it can
8010 // be called from the debugger. Compile it into the product
8011 // as needed.
8012 bool debug_verify_chunk_in_free_list(FreeChunk* fc) {
8013 return debug_cms_space->verify_chunk_in_free_list(fc);
8014 }
8015 #endif
8016
8017 void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const {
8018 if (CMSTraceSweeper) {
8019 gclog_or_tty->print_cr("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")",
8020 fc, fc->size());
8021 }
8022 }
8023
8024 // CMSIsAliveClosure
8025 bool CMSIsAliveClosure::do_object_b(oop obj) {
8026 HeapWord* addr = (HeapWord*)obj;
8027 return addr != NULL &&
8028 (!_span.contains(addr) || _bit_map->isMarked(addr));
8029 }
8030
8031
8032 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector,
8033 MemRegion span,
8034 CMSBitMap* bit_map, CMSMarkStack* mark_stack,
8035 bool cpc):
8036 _collector(collector),
8037 _span(span),
8038 _bit_map(bit_map),
8039 _mark_stack(mark_stack),
8040 _concurrent_precleaning(cpc) {
8041 assert(!_span.is_empty(), "Empty span could spell trouble");
8042 }
8043
8044
8045 // CMSKeepAliveClosure: the serial version
8046 void CMSKeepAliveClosure::do_oop(oop obj) {
8047 HeapWord* addr = (HeapWord*)obj;
8048 if (_span.contains(addr) &&
8049 !_bit_map->isMarked(addr)) {
8050 _bit_map->mark(addr);
8051 bool simulate_overflow = false;
8052 NOT_PRODUCT(
8053 if (CMSMarkStackOverflowALot &&
8054 _collector->simulate_overflow()) {
8055 // simulate a stack overflow
8056 simulate_overflow = true;
8057 }
8058 )
8059 if (simulate_overflow || !_mark_stack->push(obj)) {
8060 if (_concurrent_precleaning) {
8061 // We dirty the overflown object and let the remark
8062 // phase deal with it.
8063 assert(_collector->overflow_list_is_empty(), "Error");
8064 // In the case of object arrays, we need to dirty all of
8065 // the cards that the object spans. No locking or atomics
8066 // are needed since no one else can be mutating the mod union
8067 // table.
8068 if (obj->is_objArray()) {
8069 size_t sz = obj->size();
8070 HeapWord* end_card_addr =
8071 (HeapWord*)round_to((intptr_t)(addr+sz), CardTableModRefBS::card_size);
8072 MemRegion redirty_range = MemRegion(addr, end_card_addr);
8073 assert(!redirty_range.is_empty(), "Arithmetical tautology");
8074 _collector->_modUnionTable.mark_range(redirty_range);
8075 } else {
8076 _collector->_modUnionTable.mark(addr);
8077 }
8078 _collector->_ser_kac_preclean_ovflw++;
8079 } else {
8080 _collector->push_on_overflow_list(obj);
8081 _collector->_ser_kac_ovflw++;
8082 }
8083 }
8084 }
8085 }
8086
8087 void CMSKeepAliveClosure::do_oop(oop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8088 void CMSKeepAliveClosure::do_oop(narrowOop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8089
8090 // CMSParKeepAliveClosure: a parallel version of the above.
8091 // The work queues are private to each closure (thread),
8092 // but (may be) available for stealing by other threads.
8093 void CMSParKeepAliveClosure::do_oop(oop obj) {
8094 HeapWord* addr = (HeapWord*)obj;
8095 if (_span.contains(addr) &&
8096 !_bit_map->isMarked(addr)) {
8097 // In general, during recursive tracing, several threads
8098 // may be concurrently getting here; the first one to
8099 // "tag" it, claims it.
8100 if (_bit_map->par_mark(addr)) {
8101 bool res = _work_queue->push(obj);
8102 assert(res, "Low water mark should be much less than capacity");
8103 // Do a recursive trim in the hope that this will keep
8104 // stack usage lower, but leave some oops for potential stealers
8105 trim_queue(_low_water_mark);
8106 } // Else, another thread got there first
8107 }
8108 }
8109
8110 void CMSParKeepAliveClosure::do_oop(oop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8111 void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8112
8113 void CMSParKeepAliveClosure::trim_queue(uint max) {
8114 while (_work_queue->size() > max) {
8115 oop new_oop;
8116 if (_work_queue->pop_local(new_oop)) {
8117 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
8118 assert(_bit_map->isMarked((HeapWord*)new_oop),
8119 "no white objects on this stack!");
8120 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8121 // iterate over the oops in this oop, marking and pushing
8122 // the ones in CMS heap (i.e. in _span).
8123 new_oop->oop_iterate(&_mark_and_push);
8124 }
8125 }
8126 }
8127
8128 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
8129 CMSCollector* collector,
8130 MemRegion span, CMSBitMap* bit_map,
8131 OopTaskQueue* work_queue):
8132 _collector(collector),
8133 _span(span),
8134 _bit_map(bit_map),
8135 _work_queue(work_queue) { }
8136
8137 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
8138 HeapWord* addr = (HeapWord*)obj;
8139 if (_span.contains(addr) &&
8140 !_bit_map->isMarked(addr)) {
8141 if (_bit_map->par_mark(addr)) {
8142 bool simulate_overflow = false;
8143 NOT_PRODUCT(
8144 if (CMSMarkStackOverflowALot &&
8145 _collector->par_simulate_overflow()) {
8146 // simulate a stack overflow
8147 simulate_overflow = true;
8148 }
8149 )
8150 if (simulate_overflow || !_work_queue->push(obj)) {
8151 _collector->par_push_on_overflow_list(obj);
8152 _collector->_par_kac_ovflw++;
8153 }
8154 } // Else another thread got there already
8155 }
8156 }
8157
8158 void CMSInnerParMarkAndPushClosure::do_oop(oop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8159 void CMSInnerParMarkAndPushClosure::do_oop(narrowOop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8160
8161 //////////////////////////////////////////////////////////////////
8162 // CMSExpansionCause /////////////////////////////
8163 //////////////////////////////////////////////////////////////////
8164 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
8165 switch (cause) {
8166 case _no_expansion:
8167 return "No expansion";
8168 case _satisfy_free_ratio:
8169 return "Free ratio";
8170 case _satisfy_promotion:
8171 return "Satisfy promotion";
8172 case _satisfy_allocation:
8173 return "allocation";
8174 case _allocate_par_lab:
8175 return "Par LAB";
8176 case _allocate_par_spooling_space:
8177 return "Par Spooling Space";
8178 case _adaptive_size_policy:
8179 return "Ergonomics";
8180 default:
8181 return "unknown";
8182 }
8183 }
8184
8185 void CMSDrainMarkingStackClosure::do_void() {
8186 // the max number to take from overflow list at a time
8187 const size_t num = _mark_stack->capacity()/4;
8188 assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
8189 "Overflow list should be NULL during concurrent phases");
8190 while (!_mark_stack->isEmpty() ||
8191 // if stack is empty, check the overflow list
8192 _collector->take_from_overflow_list(num, _mark_stack)) {
8193 oop obj = _mark_stack->pop();
8194 HeapWord* addr = (HeapWord*)obj;
8195 assert(_span.contains(addr), "Should be within span");
8196 assert(_bit_map->isMarked(addr), "Should be marked");
8197 assert(obj->is_oop(), "Should be an oop");
8198 obj->oop_iterate(_keep_alive);
8199 }
8200 }
8201
8202 void CMSParDrainMarkingStackClosure::do_void() {
8203 // drain queue
8204 trim_queue(0);
8205 }
8206
8207 // Trim our work_queue so its length is below max at return
8208 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
8209 while (_work_queue->size() > max) {
8210 oop new_oop;
8211 if (_work_queue->pop_local(new_oop)) {
8212 assert(new_oop->is_oop(), "Expected an oop");
8213 assert(_bit_map->isMarked((HeapWord*)new_oop),
8214 "no white objects on this stack!");
8215 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8216 // iterate over the oops in this oop, marking and pushing
8217 // the ones in CMS heap (i.e. in _span).
8218 new_oop->oop_iterate(&_mark_and_push);
8219 }
8220 }
8221 }
8222
8223 ////////////////////////////////////////////////////////////////////
8224 // Support for Marking Stack Overflow list handling and related code
8225 ////////////////////////////////////////////////////////////////////
8226 // Much of the following code is similar in shape and spirit to the
8227 // code used in ParNewGC. We should try and share that code
8228 // as much as possible in the future.
8229
8230 #ifndef PRODUCT
8231 // Debugging support for CMSStackOverflowALot
8232
8233 // It's OK to call this multi-threaded; the worst thing
8234 // that can happen is that we'll get a bunch of closely
8235 // spaced simulated overflows, but that's OK, in fact
8236 // probably good as it would exercise the overflow code
8237 // under contention.
8238 bool CMSCollector::simulate_overflow() {
8239 if (_overflow_counter-- <= 0) { // just being defensive
8240 _overflow_counter = CMSMarkStackOverflowInterval;
8241 return true;
8242 } else {
8243 return false;
8244 }
8245 }
8246
8247 bool CMSCollector::par_simulate_overflow() {
8248 return simulate_overflow();
8249 }
8250 #endif
8251
8252 // Single-threaded
8253 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
8254 assert(stack->isEmpty(), "Expected precondition");
8255 assert(stack->capacity() > num, "Shouldn't bite more than can chew");
8256 size_t i = num;
8257 oop cur = _overflow_list;
8258 const markOop proto = markOopDesc::prototype();
8259 NOT_PRODUCT(ssize_t n = 0;)
8260 for (oop next; i > 0 && cur != NULL; cur = next, i--) {
8261 next = oop(cur->mark());
8262 cur->set_mark(proto); // until proven otherwise
8263 assert(cur->is_oop(), "Should be an oop");
8264 bool res = stack->push(cur);
8265 assert(res, "Bit off more than can chew?");
8266 NOT_PRODUCT(n++;)
8267 }
8268 _overflow_list = cur;
8269 #ifndef PRODUCT
8270 assert(_num_par_pushes >= n, "Too many pops?");
8271 _num_par_pushes -=n;
8272 #endif
8273 return !stack->isEmpty();
8274 }
8275
8276 #define BUSY (cast_to_oop<intptr_t>(0x1aff1aff))
8277 // (MT-safe) Get a prefix of at most "num" from the list.
8278 // The overflow list is chained through the mark word of
8279 // each object in the list. We fetch the entire list,
8280 // break off a prefix of the right size and return the
8281 // remainder. If other threads try to take objects from
8282 // the overflow list at that time, they will wait for
8283 // some time to see if data becomes available. If (and
8284 // only if) another thread places one or more object(s)
8285 // on the global list before we have returned the suffix
8286 // to the global list, we will walk down our local list
8287 // to find its end and append the global list to
8288 // our suffix before returning it. This suffix walk can
8289 // prove to be expensive (quadratic in the amount of traffic)
8290 // when there are many objects in the overflow list and
8291 // there is much producer-consumer contention on the list.
8292 // *NOTE*: The overflow list manipulation code here and
8293 // in ParNewGeneration:: are very similar in shape,
8294 // except that in the ParNew case we use the old (from/eden)
8295 // copy of the object to thread the list via its klass word.
8296 // Because of the common code, if you make any changes in
8297 // the code below, please check the ParNew version to see if
8298 // similar changes might be needed.
8299 // CR 6797058 has been filed to consolidate the common code.
8300 bool CMSCollector::par_take_from_overflow_list(size_t num,
8301 OopTaskQueue* work_q,
8302 int no_of_gc_threads) {
8303 assert(work_q->size() == 0, "First empty local work queue");
8304 assert(num < work_q->max_elems(), "Can't bite more than we can chew");
8305 if (_overflow_list == NULL) {
8306 return false;
8307 }
8308 // Grab the entire list; we'll put back a suffix
8309 oop prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
8310 Thread* tid = Thread::current();
8311 // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was
8312 // set to ParallelGCThreads.
8313 size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads;
8314 size_t sleep_time_millis = MAX2((size_t)1, num/100);
8315 // If the list is busy, we spin for a short while,
8316 // sleeping between attempts to get the list.
8317 for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) {
8318 os::sleep(tid, sleep_time_millis, false);
8319 if (_overflow_list == NULL) {
8320 // Nothing left to take
8321 return false;
8322 } else if (_overflow_list != BUSY) {
8323 // Try and grab the prefix
8324 prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
8325 }
8326 }
8327 // If the list was found to be empty, or we spun long
8328 // enough, we give up and return empty-handed. If we leave
8329 // the list in the BUSY state below, it must be the case that
8330 // some other thread holds the overflow list and will set it
8331 // to a non-BUSY state in the future.
8332 if (prefix == NULL || prefix == BUSY) {
8333 // Nothing to take or waited long enough
8334 if (prefix == NULL) {
8335 // Write back the NULL in case we overwrote it with BUSY above
8336 // and it is still the same value.
8337 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8338 }
8339 return false;
8340 }
8341 assert(prefix != NULL && prefix != BUSY, "Error");
8342 size_t i = num;
8343 oop cur = prefix;
8344 // Walk down the first "num" objects, unless we reach the end.
8345 for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--);
8346 if (cur->mark() == NULL) {
8347 // We have "num" or fewer elements in the list, so there
8348 // is nothing to return to the global list.
8349 // Write back the NULL in lieu of the BUSY we wrote
8350 // above, if it is still the same value.
8351 if (_overflow_list == BUSY) {
8352 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8353 }
8354 } else {
8355 // Chop off the suffix and return it to the global list.
8356 assert(cur->mark() != BUSY, "Error");
8357 oop suffix_head = cur->mark(); // suffix will be put back on global list
8358 cur->set_mark(NULL); // break off suffix
8359 // It's possible that the list is still in the empty(busy) state
8360 // we left it in a short while ago; in that case we may be
8361 // able to place back the suffix without incurring the cost
8362 // of a walk down the list.
8363 oop observed_overflow_list = _overflow_list;
8364 oop cur_overflow_list = observed_overflow_list;
8365 bool attached = false;
8366 while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
8367 observed_overflow_list =
8368 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
8369 if (cur_overflow_list == observed_overflow_list) {
8370 attached = true;
8371 break;
8372 } else cur_overflow_list = observed_overflow_list;
8373 }
8374 if (!attached) {
8375 // Too bad, someone else sneaked in (at least) an element; we'll need
8376 // to do a splice. Find tail of suffix so we can prepend suffix to global
8377 // list.
8378 for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark()));
8379 oop suffix_tail = cur;
8380 assert(suffix_tail != NULL && suffix_tail->mark() == NULL,
8381 "Tautology");
8382 observed_overflow_list = _overflow_list;
8383 do {
8384 cur_overflow_list = observed_overflow_list;
8385 if (cur_overflow_list != BUSY) {
8386 // Do the splice ...
8387 suffix_tail->set_mark(markOop(cur_overflow_list));
8388 } else { // cur_overflow_list == BUSY
8389 suffix_tail->set_mark(NULL);
8390 }
8391 // ... and try to place spliced list back on overflow_list ...
8392 observed_overflow_list =
8393 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
8394 } while (cur_overflow_list != observed_overflow_list);
8395 // ... until we have succeeded in doing so.
8396 }
8397 }
8398
8399 // Push the prefix elements on work_q
8400 assert(prefix != NULL, "control point invariant");
8401 const markOop proto = markOopDesc::prototype();
8402 oop next;
8403 NOT_PRODUCT(ssize_t n = 0;)
8404 for (cur = prefix; cur != NULL; cur = next) {
8405 next = oop(cur->mark());
8406 cur->set_mark(proto); // until proven otherwise
8407 assert(cur->is_oop(), "Should be an oop");
8408 bool res = work_q->push(cur);
8409 assert(res, "Bit off more than we can chew?");
8410 NOT_PRODUCT(n++;)
8411 }
8412 #ifndef PRODUCT
8413 assert(_num_par_pushes >= n, "Too many pops?");
8414 Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
8415 #endif
8416 return true;
8417 }
8418
8419 // Single-threaded
8420 void CMSCollector::push_on_overflow_list(oop p) {
8421 NOT_PRODUCT(_num_par_pushes++;)
8422 assert(p->is_oop(), "Not an oop");
8423 preserve_mark_if_necessary(p);
8424 p->set_mark((markOop)_overflow_list);
8425 _overflow_list = p;
8426 }
8427
8428 // Multi-threaded; use CAS to prepend to overflow list
8429 void CMSCollector::par_push_on_overflow_list(oop p) {
8430 NOT_PRODUCT(Atomic::inc_ptr(&_num_par_pushes);)
8431 assert(p->is_oop(), "Not an oop");
8432 par_preserve_mark_if_necessary(p);
8433 oop observed_overflow_list = _overflow_list;
8434 oop cur_overflow_list;
8435 do {
8436 cur_overflow_list = observed_overflow_list;
8437 if (cur_overflow_list != BUSY) {
8438 p->set_mark(markOop(cur_overflow_list));
8439 } else {
8440 p->set_mark(NULL);
8441 }
8442 observed_overflow_list =
8443 (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list);
8444 } while (cur_overflow_list != observed_overflow_list);
8445 }
8446 #undef BUSY
8447
8448 // Single threaded
8449 // General Note on GrowableArray: pushes may silently fail
8450 // because we are (temporarily) out of C-heap for expanding
8451 // the stack. The problem is quite ubiquitous and affects
8452 // a lot of code in the JVM. The prudent thing for GrowableArray
8453 // to do (for now) is to exit with an error. However, that may
8454 // be too draconian in some cases because the caller may be
8455 // able to recover without much harm. For such cases, we
8456 // should probably introduce a "soft_push" method which returns
8457 // an indication of success or failure with the assumption that
8458 // the caller may be able to recover from a failure; code in
8459 // the VM can then be changed, incrementally, to deal with such
8460 // failures where possible, thus, incrementally hardening the VM
8461 // in such low resource situations.
8462 void CMSCollector::preserve_mark_work(oop p, markOop m) {
8463 _preserved_oop_stack.push(p);
8464 _preserved_mark_stack.push(m);
8465 assert(m == p->mark(), "Mark word changed");
8466 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8467 "bijection");
8468 }
8469
8470 // Single threaded
8471 void CMSCollector::preserve_mark_if_necessary(oop p) {
8472 markOop m = p->mark();
8473 if (m->must_be_preserved(p)) {
8474 preserve_mark_work(p, m);
8475 }
8476 }
8477
8478 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
8479 markOop m = p->mark();
8480 if (m->must_be_preserved(p)) {
8481 MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
8482 // Even though we read the mark word without holding
8483 // the lock, we are assured that it will not change
8484 // because we "own" this oop, so no other thread can
8485 // be trying to push it on the overflow list; see
8486 // the assertion in preserve_mark_work() that checks
8487 // that m == p->mark().
8488 preserve_mark_work(p, m);
8489 }
8490 }
8491
8492 // We should be able to do this multi-threaded,
8493 // a chunk of stack being a task (this is
8494 // correct because each oop only ever appears
8495 // once in the overflow list. However, it's
8496 // not very easy to completely overlap this with
8497 // other operations, so will generally not be done
8498 // until all work's been completed. Because we
8499 // expect the preserved oop stack (set) to be small,
8500 // it's probably fine to do this single-threaded.
8501 // We can explore cleverer concurrent/overlapped/parallel
8502 // processing of preserved marks if we feel the
8503 // need for this in the future. Stack overflow should
8504 // be so rare in practice and, when it happens, its
8505 // effect on performance so great that this will
8506 // likely just be in the noise anyway.
8507 void CMSCollector::restore_preserved_marks_if_any() {
8508 assert(SafepointSynchronize::is_at_safepoint(),
8509 "world should be stopped");
8510 assert(Thread::current()->is_ConcurrentGC_thread() ||
8511 Thread::current()->is_VM_thread(),
8512 "should be single-threaded");
8513 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8514 "bijection");
8515
8516 while (!_preserved_oop_stack.is_empty()) {
8517 oop p = _preserved_oop_stack.pop();
8518 assert(p->is_oop(), "Should be an oop");
8519 assert(_span.contains(p), "oop should be in _span");
8520 assert(p->mark() == markOopDesc::prototype(),
8521 "Set when taken from overflow list");
8522 markOop m = _preserved_mark_stack.pop();
8523 p->set_mark(m);
8524 }
8525 assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(),
8526 "stacks were cleared above");
8527 }
8528
8529 #ifndef PRODUCT
8530 bool CMSCollector::no_preserved_marks() const {
8531 return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty();
8532 }
8533 #endif
8534
8535 // Transfer some number of overflown objects to usual marking
8536 // stack. Return true if some objects were transferred.
8537 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
8538 size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,
8539 (size_t)ParGCDesiredObjsFromOverflowList);
8540
8541 bool res = _collector->take_from_overflow_list(num, _mark_stack);
8542 assert(_collector->overflow_list_is_empty() || res,
8543 "If list is not empty, we should have taken something");
8544 assert(!res || !_mark_stack->isEmpty(),
8545 "If we took something, it should now be on our stack");
8546 return res;
8547 }
8548
8549 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
8550 size_t res = _sp->block_size_no_stall(addr, _collector);
8551 if (_sp->block_is_obj(addr)) {
8552 if (_live_bit_map->isMarked(addr)) {
8553 // It can't have been dead in a previous cycle
8554 guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
8555 } else {
8556 _dead_bit_map->mark(addr); // mark the dead object
8557 }
8558 }
8559 // Could be 0, if the block size could not be computed without stalling.
8560 return res;
8561 }
8562
8563 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() {
8564
8565 switch (phase) {
8566 case CMSCollector::InitialMarking:
8567 initialize(true /* fullGC */ ,
8568 cause /* cause of the GC */,
8569 true /* recordGCBeginTime */,
8570 true /* recordPreGCUsage */,
8571 false /* recordPeakUsage */,
8572 false /* recordPostGCusage */,
8573 true /* recordAccumulatedGCTime */,
8574 false /* recordGCEndTime */,
8575 false /* countCollection */ );
8576 break;
8577
8578 case CMSCollector::FinalMarking:
8579 initialize(true /* fullGC */ ,
8580 cause /* cause of the GC */,
8581 false /* recordGCBeginTime */,
8582 false /* recordPreGCUsage */,
8583 false /* recordPeakUsage */,
8584 false /* recordPostGCusage */,
8585 true /* recordAccumulatedGCTime */,
8586 false /* recordGCEndTime */,
8587 false /* countCollection */ );
8588 break;
8589
8590 case CMSCollector::Sweeping:
8591 initialize(true /* fullGC */ ,
8592 cause /* cause of the GC */,
8593 false /* recordGCBeginTime */,
8594 false /* recordPreGCUsage */,
8595 true /* recordPeakUsage */,
8596 true /* recordPostGCusage */,
8597 false /* recordAccumulatedGCTime */,
8598 true /* recordGCEndTime */,
8599 true /* countCollection */ );
8600 break;
8601
8602 default:
8603 ShouldNotReachHere();
8604 }
8605 }