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