1 /*
2 * Copyright (c) 2001, 2015, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include "precompiled.hpp"
26 #include "classfile/classLoaderData.hpp"
27 #include "classfile/stringTable.hpp"
28 #include "classfile/systemDictionary.hpp"
29 #include "code/codeCache.hpp"
30 #include "gc/cms/cmsCollectorPolicy.hpp"
31 #include "gc/cms/cmsOopClosures.inline.hpp"
32 #include "gc/cms/compactibleFreeListSpace.hpp"
33 #include "gc/cms/concurrentMarkSweepGeneration.inline.hpp"
34 #include "gc/cms/concurrentMarkSweepThread.hpp"
35 #include "gc/cms/parNewGeneration.hpp"
36 #include "gc/cms/vmCMSOperations.hpp"
37 #include "gc/serial/genMarkSweep.hpp"
38 #include "gc/serial/tenuredGeneration.hpp"
39 #include "gc/shared/adaptiveSizePolicy.hpp"
40 #include "gc/shared/cardGeneration.inline.hpp"
41 #include "gc/shared/cardTableRS.hpp"
42 #include "gc/shared/collectedHeap.inline.hpp"
43 #include "gc/shared/collectorCounters.hpp"
44 #include "gc/shared/collectorPolicy.hpp"
45 #include "gc/shared/gcLocker.inline.hpp"
46 #include "gc/shared/gcPolicyCounters.hpp"
47 #include "gc/shared/gcTimer.hpp"
48 #include "gc/shared/gcTrace.hpp"
49 #include "gc/shared/gcTraceTime.hpp"
50 #include "gc/shared/genCollectedHeap.hpp"
51 #include "gc/shared/genOopClosures.inline.hpp"
52 #include "gc/shared/isGCActiveMark.hpp"
53 #include "gc/shared/referencePolicy.hpp"
54 #include "gc/shared/strongRootsScope.hpp"
55 #include "gc/shared/taskqueue.inline.hpp"
56 #include "memory/allocation.hpp"
57 #include "memory/iterator.inline.hpp"
58 #include "memory/padded.hpp"
59 #include "memory/resourceArea.hpp"
60 #include "oops/oop.inline.hpp"
61 #include "prims/jvmtiExport.hpp"
62 #include "runtime/atomic.inline.hpp"
63 #include "runtime/globals_extension.hpp"
64 #include "runtime/handles.inline.hpp"
65 #include "runtime/java.hpp"
66 #include "runtime/orderAccess.inline.hpp"
67 #include "runtime/vmThread.hpp"
68 #include "services/memoryService.hpp"
69 #include "services/runtimeService.hpp"
70 #include "utilities/stack.inline.hpp"
71
72 // statics
73 CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL;
74 bool CMSCollector::_full_gc_requested = false;
75 GCCause::Cause CMSCollector::_full_gc_cause = GCCause::_no_gc;
76
77 //////////////////////////////////////////////////////////////////
78 // In support of CMS/VM thread synchronization
79 //////////////////////////////////////////////////////////////////
80 // We split use of the CGC_lock into 2 "levels".
81 // The low-level locking is of the usual CGC_lock monitor. We introduce
82 // a higher level "token" (hereafter "CMS token") built on top of the
83 // low level monitor (hereafter "CGC lock").
84 // The token-passing protocol gives priority to the VM thread. The
85 // CMS-lock doesn't provide any fairness guarantees, but clients
86 // should ensure that it is only held for very short, bounded
87 // durations.
88 //
89 // When either of the CMS thread or the VM thread is involved in
90 // collection operations during which it does not want the other
91 // thread to interfere, it obtains the CMS token.
92 //
93 // If either thread tries to get the token while the other has
94 // it, that thread waits. However, if the VM thread and CMS thread
95 // both want the token, then the VM thread gets priority while the
96 // CMS thread waits. This ensures, for instance, that the "concurrent"
97 // phases of the CMS thread's work do not block out the VM thread
98 // for long periods of time as the CMS thread continues to hog
99 // the token. (See bug 4616232).
100 //
101 // The baton-passing functions are, however, controlled by the
102 // flags _foregroundGCShouldWait and _foregroundGCIsActive,
103 // and here the low-level CMS lock, not the high level token,
104 // ensures mutual exclusion.
105 //
106 // Two important conditions that we have to satisfy:
107 // 1. if a thread does a low-level wait on the CMS lock, then it
108 // relinquishes the CMS token if it were holding that token
109 // when it acquired the low-level CMS lock.
110 // 2. any low-level notifications on the low-level lock
111 // should only be sent when a thread has relinquished the token.
112 //
113 // In the absence of either property, we'd have potential deadlock.
114 //
115 // We protect each of the CMS (concurrent and sequential) phases
116 // with the CMS _token_, not the CMS _lock_.
117 //
118 // The only code protected by CMS lock is the token acquisition code
119 // itself, see ConcurrentMarkSweepThread::[de]synchronize(), and the
120 // baton-passing code.
121 //
122 // Unfortunately, i couldn't come up with a good abstraction to factor and
123 // hide the naked CGC_lock manipulation in the baton-passing code
124 // further below. That's something we should try to do. Also, the proof
125 // of correctness of this 2-level locking scheme is far from obvious,
126 // and potentially quite slippery. We have an uneasy suspicion, for instance,
127 // that there may be a theoretical possibility of delay/starvation in the
128 // low-level lock/wait/notify scheme used for the baton-passing because of
129 // potential interference with the priority scheme embodied in the
130 // CMS-token-passing protocol. See related comments at a CGC_lock->wait()
131 // invocation further below and marked with "XXX 20011219YSR".
132 // Indeed, as we note elsewhere, this may become yet more slippery
133 // in the presence of multiple CMS and/or multiple VM threads. XXX
134
135 class CMSTokenSync: public StackObj {
136 private:
137 bool _is_cms_thread;
138 public:
139 CMSTokenSync(bool is_cms_thread):
140 _is_cms_thread(is_cms_thread) {
141 assert(is_cms_thread == Thread::current()->is_ConcurrentGC_thread(),
142 "Incorrect argument to constructor");
143 ConcurrentMarkSweepThread::synchronize(_is_cms_thread);
144 }
145
146 ~CMSTokenSync() {
147 assert(_is_cms_thread ?
148 ConcurrentMarkSweepThread::cms_thread_has_cms_token() :
149 ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
150 "Incorrect state");
151 ConcurrentMarkSweepThread::desynchronize(_is_cms_thread);
152 }
153 };
154
155 // Convenience class that does a CMSTokenSync, and then acquires
156 // upto three locks.
157 class CMSTokenSyncWithLocks: public CMSTokenSync {
158 private:
159 // Note: locks are acquired in textual declaration order
160 // and released in the opposite order
161 MutexLockerEx _locker1, _locker2, _locker3;
162 public:
163 CMSTokenSyncWithLocks(bool is_cms_thread, Mutex* mutex1,
164 Mutex* mutex2 = NULL, Mutex* mutex3 = NULL):
165 CMSTokenSync(is_cms_thread),
166 _locker1(mutex1, Mutex::_no_safepoint_check_flag),
167 _locker2(mutex2, Mutex::_no_safepoint_check_flag),
168 _locker3(mutex3, Mutex::_no_safepoint_check_flag)
169 { }
170 };
171
172
173 //////////////////////////////////////////////////////////////////
174 // Concurrent Mark-Sweep Generation /////////////////////////////
175 //////////////////////////////////////////////////////////////////
176
177 NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;)
178
179 // This struct contains per-thread things necessary to support parallel
180 // young-gen collection.
181 class CMSParGCThreadState: public CHeapObj<mtGC> {
182 public:
183 CFLS_LAB lab;
184 PromotionInfo promo;
185
186 // Constructor.
187 CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) {
188 promo.setSpace(cfls);
189 }
190 };
191
192 ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration(
193 ReservedSpace rs, size_t initial_byte_size, CardTableRS* ct) :
194 CardGeneration(rs, initial_byte_size, ct),
195 _dilatation_factor(((double)MinChunkSize)/((double)(CollectedHeap::min_fill_size()))),
196 _did_compact(false)
197 {
198 HeapWord* bottom = (HeapWord*) _virtual_space.low();
199 HeapWord* end = (HeapWord*) _virtual_space.high();
200
201 _direct_allocated_words = 0;
202 NOT_PRODUCT(
203 _numObjectsPromoted = 0;
204 _numWordsPromoted = 0;
205 _numObjectsAllocated = 0;
206 _numWordsAllocated = 0;
207 )
208
209 _cmsSpace = new CompactibleFreeListSpace(_bts, MemRegion(bottom, end));
210 NOT_PRODUCT(debug_cms_space = _cmsSpace;)
211 _cmsSpace->_old_gen = this;
212
213 _gc_stats = new CMSGCStats();
214
215 // Verify the assumption that FreeChunk::_prev and OopDesc::_klass
216 // offsets match. The ability to tell free chunks from objects
217 // depends on this property.
218 debug_only(
219 FreeChunk* junk = NULL;
220 assert(UseCompressedClassPointers ||
221 junk->prev_addr() == (void*)(oop(junk)->klass_addr()),
222 "Offset of FreeChunk::_prev within FreeChunk must match"
223 " that of OopDesc::_klass within OopDesc");
224 )
225
226 _par_gc_thread_states = NEW_C_HEAP_ARRAY(CMSParGCThreadState*, ParallelGCThreads, mtGC);
227 for (uint i = 0; i < ParallelGCThreads; i++) {
228 _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace());
229 }
230
231 _incremental_collection_failed = false;
232 // The "dilatation_factor" is the expansion that can occur on
233 // account of the fact that the minimum object size in the CMS
234 // generation may be larger than that in, say, a contiguous young
235 // generation.
236 // Ideally, in the calculation below, we'd compute the dilatation
237 // factor as: MinChunkSize/(promoting_gen's min object size)
238 // Since we do not have such a general query interface for the
239 // promoting generation, we'll instead just use the minimum
240 // object size (which today is a header's worth of space);
241 // note that all arithmetic is in units of HeapWords.
242 assert(MinChunkSize >= CollectedHeap::min_fill_size(), "just checking");
243 assert(_dilatation_factor >= 1.0, "from previous assert");
244 }
245
246
247 // The field "_initiating_occupancy" represents the occupancy percentage
248 // at which we trigger a new collection cycle. Unless explicitly specified
249 // via CMSInitiatingOccupancyFraction (argument "io" below), it
250 // is calculated by:
251 //
252 // Let "f" be MinHeapFreeRatio in
253 //
254 // _initiating_occupancy = 100-f +
255 // f * (CMSTriggerRatio/100)
256 // where CMSTriggerRatio is the argument "tr" below.
257 //
258 // That is, if we assume the heap is at its desired maximum occupancy at the
259 // end of a collection, we let CMSTriggerRatio of the (purported) free
260 // space be allocated before initiating a new collection cycle.
261 //
262 void ConcurrentMarkSweepGeneration::init_initiating_occupancy(intx io, uintx tr) {
263 assert(io <= 100 && tr <= 100, "Check the arguments");
264 if (io >= 0) {
265 _initiating_occupancy = (double)io / 100.0;
266 } else {
267 _initiating_occupancy = ((100 - MinHeapFreeRatio) +
268 (double)(tr * MinHeapFreeRatio) / 100.0)
269 / 100.0;
270 }
271 }
272
273 void ConcurrentMarkSweepGeneration::ref_processor_init() {
274 assert(collector() != NULL, "no collector");
275 collector()->ref_processor_init();
276 }
277
278 void CMSCollector::ref_processor_init() {
279 if (_ref_processor == NULL) {
280 // Allocate and initialize a reference processor
281 _ref_processor =
282 new ReferenceProcessor(_span, // span
283 (ParallelGCThreads > 1) && ParallelRefProcEnabled, // mt processing
284 ParallelGCThreads, // mt processing degree
285 _cmsGen->refs_discovery_is_mt(), // mt discovery
286 MAX2(ConcGCThreads, ParallelGCThreads), // mt discovery degree
287 _cmsGen->refs_discovery_is_atomic(), // discovery is not atomic
288 &_is_alive_closure); // closure for liveness info
289 // Initialize the _ref_processor field of CMSGen
290 _cmsGen->set_ref_processor(_ref_processor);
291
292 }
293 }
294
295 AdaptiveSizePolicy* CMSCollector::size_policy() {
296 GenCollectedHeap* gch = GenCollectedHeap::heap();
297 return gch->gen_policy()->size_policy();
298 }
299
300 void ConcurrentMarkSweepGeneration::initialize_performance_counters() {
301
302 const char* gen_name = "old";
303 GenCollectorPolicy* gcp = GenCollectedHeap::heap()->gen_policy();
304 // Generation Counters - generation 1, 1 subspace
305 _gen_counters = new GenerationCounters(gen_name, 1, 1,
306 gcp->min_old_size(), gcp->max_old_size(), &_virtual_space);
307
308 _space_counters = new GSpaceCounters(gen_name, 0,
309 _virtual_space.reserved_size(),
310 this, _gen_counters);
311 }
312
313 CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha):
314 _cms_gen(cms_gen)
315 {
316 assert(alpha <= 100, "bad value");
317 _saved_alpha = alpha;
318
319 // Initialize the alphas to the bootstrap value of 100.
320 _gc0_alpha = _cms_alpha = 100;
321
322 _cms_begin_time.update();
323 _cms_end_time.update();
324
325 _gc0_duration = 0.0;
326 _gc0_period = 0.0;
327 _gc0_promoted = 0;
328
329 _cms_duration = 0.0;
330 _cms_period = 0.0;
331 _cms_allocated = 0;
332
333 _cms_used_at_gc0_begin = 0;
334 _cms_used_at_gc0_end = 0;
335 _allow_duty_cycle_reduction = false;
336 _valid_bits = 0;
337 }
338
339 double CMSStats::cms_free_adjustment_factor(size_t free) const {
340 // TBD: CR 6909490
341 return 1.0;
342 }
343
344 void CMSStats::adjust_cms_free_adjustment_factor(bool fail, size_t free) {
345 }
346
347 // If promotion failure handling is on use
348 // the padded average size of the promotion for each
349 // young generation collection.
350 double CMSStats::time_until_cms_gen_full() const {
351 size_t cms_free = _cms_gen->cmsSpace()->free();
352 GenCollectedHeap* gch = GenCollectedHeap::heap();
353 size_t expected_promotion = MIN2(gch->young_gen()->capacity(),
354 (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average());
355 if (cms_free > expected_promotion) {
356 // Start a cms collection if there isn't enough space to promote
357 // for the next young collection. Use the padded average as
358 // a safety factor.
359 cms_free -= expected_promotion;
360
361 // Adjust by the safety factor.
362 double cms_free_dbl = (double)cms_free;
363 double cms_adjustment = (100.0 - CMSIncrementalSafetyFactor) / 100.0;
364 // Apply a further correction factor which tries to adjust
365 // for recent occurance of concurrent mode failures.
366 cms_adjustment = cms_adjustment * cms_free_adjustment_factor(cms_free);
367 cms_free_dbl = cms_free_dbl * cms_adjustment;
368
369 if (PrintGCDetails && Verbose) {
370 gclog_or_tty->print_cr("CMSStats::time_until_cms_gen_full: cms_free "
371 SIZE_FORMAT " expected_promotion " SIZE_FORMAT,
372 cms_free, expected_promotion);
373 gclog_or_tty->print_cr(" cms_free_dbl %f cms_consumption_rate %f",
374 cms_free_dbl, cms_consumption_rate() + 1.0);
375 }
376 // Add 1 in case the consumption rate goes to zero.
377 return cms_free_dbl / (cms_consumption_rate() + 1.0);
378 }
379 return 0.0;
380 }
381
382 // Compare the duration of the cms collection to the
383 // time remaining before the cms generation is empty.
384 // Note that the time from the start of the cms collection
385 // to the start of the cms sweep (less than the total
386 // duration of the cms collection) can be used. This
387 // has been tried and some applications experienced
388 // promotion failures early in execution. This was
389 // possibly because the averages were not accurate
390 // enough at the beginning.
391 double CMSStats::time_until_cms_start() const {
392 // We add "gc0_period" to the "work" calculation
393 // below because this query is done (mostly) at the
394 // end of a scavenge, so we need to conservatively
395 // account for that much possible delay
396 // in the query so as to avoid concurrent mode failures
397 // due to starting the collection just a wee bit too
398 // late.
399 double work = cms_duration() + gc0_period();
400 double deadline = time_until_cms_gen_full();
401 // If a concurrent mode failure occurred recently, we want to be
402 // more conservative and halve our expected time_until_cms_gen_full()
403 if (work > deadline) {
404 if (Verbose && PrintGCDetails) {
405 gclog_or_tty->print(
406 " CMSCollector: collect because of anticipated promotion "
407 "before full %3.7f + %3.7f > %3.7f ", cms_duration(),
408 gc0_period(), time_until_cms_gen_full());
409 }
410 return 0.0;
411 }
412 return work - deadline;
413 }
414
415 #ifndef PRODUCT
416 void CMSStats::print_on(outputStream *st) const {
417 st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha);
418 st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo=" SIZE_FORMAT,
419 gc0_duration(), gc0_period(), gc0_promoted());
420 st->print(",cms_dur=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT,
421 cms_duration(), cms_period(), cms_allocated());
422 st->print(",cms_since_beg=%g,cms_since_end=%g",
423 cms_time_since_begin(), cms_time_since_end());
424 st->print(",cms_used_beg=" SIZE_FORMAT ",cms_used_end=" SIZE_FORMAT,
425 _cms_used_at_gc0_begin, _cms_used_at_gc0_end);
426
427 if (valid()) {
428 st->print(",promo_rate=%g,cms_alloc_rate=%g",
429 promotion_rate(), cms_allocation_rate());
430 st->print(",cms_consumption_rate=%g,time_until_full=%g",
431 cms_consumption_rate(), time_until_cms_gen_full());
432 }
433 st->print(" ");
434 }
435 #endif // #ifndef PRODUCT
436
437 CMSCollector::CollectorState CMSCollector::_collectorState =
438 CMSCollector::Idling;
439 bool CMSCollector::_foregroundGCIsActive = false;
440 bool CMSCollector::_foregroundGCShouldWait = false;
441
442 CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
443 CardTableRS* ct,
444 ConcurrentMarkSweepPolicy* cp):
445 _cmsGen(cmsGen),
446 _ct(ct),
447 _ref_processor(NULL), // will be set later
448 _conc_workers(NULL), // may be set later
449 _abort_preclean(false),
450 _start_sampling(false),
451 _between_prologue_and_epilogue(false),
452 _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"),
453 _modUnionTable((CardTableModRefBS::card_shift - LogHeapWordSize),
454 -1 /* lock-free */, "No_lock" /* dummy */),
455 _modUnionClosurePar(&_modUnionTable),
456 // Adjust my span to cover old (cms) gen
457 _span(cmsGen->reserved()),
458 // Construct the is_alive_closure with _span & markBitMap
459 _is_alive_closure(_span, &_markBitMap),
460 _restart_addr(NULL),
461 _overflow_list(NULL),
462 _stats(cmsGen),
463 _eden_chunk_lock(new Mutex(Mutex::leaf + 1, "CMS_eden_chunk_lock", true,
464 //verify that this lock should be acquired with safepoint check.
465 Monitor::_safepoint_check_sometimes)),
466 _eden_chunk_array(NULL), // may be set in ctor body
467 _eden_chunk_capacity(0), // -- ditto --
468 _eden_chunk_index(0), // -- ditto --
469 _survivor_plab_array(NULL), // -- ditto --
470 _survivor_chunk_array(NULL), // -- ditto --
471 _survivor_chunk_capacity(0), // -- ditto --
472 _survivor_chunk_index(0), // -- ditto --
473 _ser_pmc_preclean_ovflw(0),
474 _ser_kac_preclean_ovflw(0),
475 _ser_pmc_remark_ovflw(0),
476 _par_pmc_remark_ovflw(0),
477 _ser_kac_ovflw(0),
478 _par_kac_ovflw(0),
479 #ifndef PRODUCT
480 _num_par_pushes(0),
481 #endif
482 _collection_count_start(0),
483 _verifying(false),
484 _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"),
485 _completed_initialization(false),
486 _collector_policy(cp),
487 _should_unload_classes(CMSClassUnloadingEnabled),
488 _concurrent_cycles_since_last_unload(0),
489 _roots_scanning_options(GenCollectedHeap::SO_None),
490 _inter_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
491 _intra_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
492 _gc_tracer_cm(new (ResourceObj::C_HEAP, mtGC) CMSTracer()),
493 _gc_timer_cm(new (ResourceObj::C_HEAP, mtGC) ConcurrentGCTimer()),
494 _cms_start_registered(false)
495 {
496 if (ExplicitGCInvokesConcurrentAndUnloadsClasses) {
497 ExplicitGCInvokesConcurrent = true;
498 }
499 // Now expand the span and allocate the collection support structures
500 // (MUT, marking bit map etc.) to cover both generations subject to
501 // collection.
502
503 // For use by dirty card to oop closures.
504 _cmsGen->cmsSpace()->set_collector(this);
505
506 // Allocate MUT and marking bit map
507 {
508 MutexLockerEx x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag);
509 if (!_markBitMap.allocate(_span)) {
510 warning("Failed to allocate CMS Bit Map");
511 return;
512 }
513 assert(_markBitMap.covers(_span), "_markBitMap inconsistency?");
514 }
515 {
516 _modUnionTable.allocate(_span);
517 assert(_modUnionTable.covers(_span), "_modUnionTable inconsistency?");
518 }
519
520 if (!_markStack.allocate(MarkStackSize)) {
521 warning("Failed to allocate CMS Marking Stack");
522 return;
523 }
524
525 // Support for multi-threaded concurrent phases
526 if (CMSConcurrentMTEnabled) {
527 if (FLAG_IS_DEFAULT(ConcGCThreads)) {
528 // just for now
529 FLAG_SET_DEFAULT(ConcGCThreads, (ParallelGCThreads + 3) / 4);
530 }
531 if (ConcGCThreads > 1) {
532 _conc_workers = new YieldingFlexibleWorkGang("CMS Thread",
533 ConcGCThreads, true);
534 if (_conc_workers == NULL) {
535 warning("GC/CMS: _conc_workers allocation failure: "
536 "forcing -CMSConcurrentMTEnabled");
537 CMSConcurrentMTEnabled = false;
538 } else {
539 _conc_workers->initialize_workers();
540 }
541 } else {
542 CMSConcurrentMTEnabled = false;
543 }
544 }
545 if (!CMSConcurrentMTEnabled) {
546 ConcGCThreads = 0;
547 } else {
548 // Turn off CMSCleanOnEnter optimization temporarily for
549 // the MT case where it's not fixed yet; see 6178663.
550 CMSCleanOnEnter = false;
551 }
552 assert((_conc_workers != NULL) == (ConcGCThreads > 1),
553 "Inconsistency");
554
555 // Parallel task queues; these are shared for the
556 // concurrent and stop-world phases of CMS, but
557 // are not shared with parallel scavenge (ParNew).
558 {
559 uint i;
560 uint num_queues = MAX2(ParallelGCThreads, ConcGCThreads);
561
562 if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled
563 || ParallelRefProcEnabled)
564 && num_queues > 0) {
565 _task_queues = new OopTaskQueueSet(num_queues);
566 if (_task_queues == NULL) {
567 warning("task_queues allocation failure.");
568 return;
569 }
570 _hash_seed = NEW_C_HEAP_ARRAY(int, num_queues, mtGC);
571 typedef Padded<OopTaskQueue> PaddedOopTaskQueue;
572 for (i = 0; i < num_queues; i++) {
573 PaddedOopTaskQueue *q = new PaddedOopTaskQueue();
574 if (q == NULL) {
575 warning("work_queue allocation failure.");
576 return;
577 }
578 _task_queues->register_queue(i, q);
579 }
580 for (i = 0; i < num_queues; i++) {
581 _task_queues->queue(i)->initialize();
582 _hash_seed[i] = 17; // copied from ParNew
583 }
584 }
585 }
586
587 _cmsGen ->init_initiating_occupancy(CMSInitiatingOccupancyFraction, CMSTriggerRatio);
588
589 // Clip CMSBootstrapOccupancy between 0 and 100.
590 _bootstrap_occupancy = CMSBootstrapOccupancy / 100.0;
591
592 // Now tell CMS generations the identity of their collector
593 ConcurrentMarkSweepGeneration::set_collector(this);
594
595 // Create & start a CMS thread for this CMS collector
596 _cmsThread = ConcurrentMarkSweepThread::start(this);
597 assert(cmsThread() != NULL, "CMS Thread should have been created");
598 assert(cmsThread()->collector() == this,
599 "CMS Thread should refer to this gen");
600 assert(CGC_lock != NULL, "Where's the CGC_lock?");
601
602 // Support for parallelizing young gen rescan
603 GenCollectedHeap* gch = GenCollectedHeap::heap();
604 assert(gch->young_gen()->kind() == Generation::ParNew, "CMS can only be used with ParNew");
605 _young_gen = (ParNewGeneration*)gch->young_gen();
606 if (gch->supports_inline_contig_alloc()) {
607 _top_addr = gch->top_addr();
608 _end_addr = gch->end_addr();
609 assert(_young_gen != NULL, "no _young_gen");
610 _eden_chunk_index = 0;
611 _eden_chunk_capacity = (_young_gen->max_capacity() + CMSSamplingGrain) / CMSSamplingGrain;
612 _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity, mtGC);
613 }
614
615 // Support for parallelizing survivor space rescan
616 if ((CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) || CMSParallelInitialMarkEnabled) {
617 const size_t max_plab_samples =
618 _young_gen->max_survivor_size() / (PLAB::min_size() * HeapWordSize);
619
620 _survivor_plab_array = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads, mtGC);
621 _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
622 _cursor = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads, mtGC);
623 _survivor_chunk_capacity = max_plab_samples;
624 for (uint i = 0; i < ParallelGCThreads; i++) {
625 HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
626 ChunkArray* cur = ::new (&_survivor_plab_array[i]) ChunkArray(vec, max_plab_samples);
627 assert(cur->end() == 0, "Should be 0");
628 assert(cur->array() == vec, "Should be vec");
629 assert(cur->capacity() == max_plab_samples, "Error");
630 }
631 }
632
633 NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;)
634 _gc_counters = new CollectorCounters("CMS", 1);
635 _completed_initialization = true;
636 _inter_sweep_timer.start(); // start of time
637 }
638
639 const char* ConcurrentMarkSweepGeneration::name() const {
640 return "concurrent mark-sweep generation";
641 }
642 void ConcurrentMarkSweepGeneration::update_counters() {
643 if (UsePerfData) {
644 _space_counters->update_all();
645 _gen_counters->update_all();
646 }
647 }
648
649 // this is an optimized version of update_counters(). it takes the
650 // used value as a parameter rather than computing it.
651 //
652 void ConcurrentMarkSweepGeneration::update_counters(size_t used) {
653 if (UsePerfData) {
654 _space_counters->update_used(used);
655 _space_counters->update_capacity();
656 _gen_counters->update_all();
657 }
658 }
659
660 void ConcurrentMarkSweepGeneration::print() const {
661 Generation::print();
662 cmsSpace()->print();
663 }
664
665 #ifndef PRODUCT
666 void ConcurrentMarkSweepGeneration::print_statistics() {
667 cmsSpace()->printFLCensus(0);
668 }
669 #endif
670
671 void ConcurrentMarkSweepGeneration::printOccupancy(const char *s) {
672 GenCollectedHeap* gch = GenCollectedHeap::heap();
673 if (PrintGCDetails) {
674 // I didn't want to change the logging when removing the level concept,
675 // but I guess this logging could say "old" or something instead of "1".
676 assert(gch->is_old_gen(this),
677 "The CMS generation should be the old generation");
678 uint level = 1;
679 if (Verbose) {
680 gclog_or_tty->print("[%u %s-%s: " SIZE_FORMAT "(" SIZE_FORMAT ")]",
681 level, short_name(), s, used(), capacity());
682 } else {
683 gclog_or_tty->print("[%u %s-%s: " SIZE_FORMAT "K(" SIZE_FORMAT "K)]",
684 level, short_name(), s, used() / K, capacity() / K);
685 }
686 }
687 if (Verbose) {
688 gclog_or_tty->print(" " SIZE_FORMAT "(" SIZE_FORMAT ")",
689 gch->used(), gch->capacity());
690 } else {
691 gclog_or_tty->print(" " SIZE_FORMAT "K(" SIZE_FORMAT "K)",
692 gch->used() / K, gch->capacity() / K);
693 }
694 }
695
696 size_t
697 ConcurrentMarkSweepGeneration::contiguous_available() const {
698 // dld proposes an improvement in precision here. If the committed
699 // part of the space ends in a free block we should add that to
700 // uncommitted size in the calculation below. Will make this
701 // change later, staying with the approximation below for the
702 // time being. -- ysr.
703 return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc());
704 }
705
706 size_t
707 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const {
708 return _cmsSpace->max_alloc_in_words() * HeapWordSize;
709 }
710
711 size_t ConcurrentMarkSweepGeneration::max_available() const {
712 return free() + _virtual_space.uncommitted_size();
713 }
714
715 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(size_t max_promotion_in_bytes) const {
716 size_t available = max_available();
717 size_t av_promo = (size_t)gc_stats()->avg_promoted()->padded_average();
718 bool res = (available >= av_promo) || (available >= max_promotion_in_bytes);
719 if (Verbose && PrintGCDetails) {
720 gclog_or_tty->print_cr(
721 "CMS: promo attempt is%s safe: available(" SIZE_FORMAT ") %s av_promo(" SIZE_FORMAT "),"
722 "max_promo(" SIZE_FORMAT ")",
723 res? "":" not", available, res? ">=":"<",
724 av_promo, max_promotion_in_bytes);
725 }
726 return res;
727 }
728
729 // At a promotion failure dump information on block layout in heap
730 // (cms old generation).
731 void ConcurrentMarkSweepGeneration::promotion_failure_occurred() {
732 if (CMSDumpAtPromotionFailure) {
733 cmsSpace()->dump_at_safepoint_with_locks(collector(), gclog_or_tty);
734 }
735 }
736
737 void ConcurrentMarkSweepGeneration::reset_after_compaction() {
738 // Clear the promotion information. These pointers can be adjusted
739 // along with all the other pointers into the heap but
740 // compaction is expected to be a rare event with
741 // a heap using cms so don't do it without seeing the need.
742 for (uint i = 0; i < ParallelGCThreads; i++) {
743 _par_gc_thread_states[i]->promo.reset();
744 }
745 }
746
747 void ConcurrentMarkSweepGeneration::compute_new_size() {
748 assert_locked_or_safepoint(Heap_lock);
749
750 // If incremental collection failed, we just want to expand
751 // to the limit.
752 if (incremental_collection_failed()) {
753 clear_incremental_collection_failed();
754 grow_to_reserved();
755 return;
756 }
757
758 // The heap has been compacted but not reset yet.
759 // Any metric such as free() or used() will be incorrect.
760
761 CardGeneration::compute_new_size();
762
763 // Reset again after a possible resizing
764 if (did_compact()) {
765 cmsSpace()->reset_after_compaction();
766 }
767 }
768
769 void ConcurrentMarkSweepGeneration::compute_new_size_free_list() {
770 assert_locked_or_safepoint(Heap_lock);
771
772 // If incremental collection failed, we just want to expand
773 // to the limit.
774 if (incremental_collection_failed()) {
775 clear_incremental_collection_failed();
776 grow_to_reserved();
777 return;
778 }
779
780 double free_percentage = ((double) free()) / capacity();
781 double desired_free_percentage = (double) MinHeapFreeRatio / 100;
782 double maximum_free_percentage = (double) MaxHeapFreeRatio / 100;
783
784 // compute expansion delta needed for reaching desired free percentage
785 if (free_percentage < desired_free_percentage) {
786 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
787 assert(desired_capacity >= capacity(), "invalid expansion size");
788 size_t expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes);
789 if (PrintGCDetails && Verbose) {
790 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
791 gclog_or_tty->print_cr("\nFrom compute_new_size: ");
792 gclog_or_tty->print_cr(" Free fraction %f", free_percentage);
793 gclog_or_tty->print_cr(" Desired free fraction %f", desired_free_percentage);
794 gclog_or_tty->print_cr(" Maximum free fraction %f", maximum_free_percentage);
795 gclog_or_tty->print_cr(" Capacity " SIZE_FORMAT, capacity() / 1000);
796 gclog_or_tty->print_cr(" Desired capacity " SIZE_FORMAT, desired_capacity / 1000);
797 GenCollectedHeap* gch = GenCollectedHeap::heap();
798 assert(gch->is_old_gen(this), "The CMS generation should always be the old generation");
799 size_t young_size = gch->young_gen()->capacity();
800 gclog_or_tty->print_cr(" Young gen size " SIZE_FORMAT, young_size / 1000);
801 gclog_or_tty->print_cr(" unsafe_max_alloc_nogc " SIZE_FORMAT, unsafe_max_alloc_nogc() / 1000);
802 gclog_or_tty->print_cr(" contiguous available " SIZE_FORMAT, contiguous_available() / 1000);
803 gclog_or_tty->print_cr(" Expand by " SIZE_FORMAT " (bytes)", expand_bytes);
804 }
805 // safe if expansion fails
806 expand_for_gc_cause(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio);
807 if (PrintGCDetails && Verbose) {
808 gclog_or_tty->print_cr(" Expanded free fraction %f", ((double) free()) / capacity());
809 }
810 } else {
811 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
812 assert(desired_capacity <= capacity(), "invalid expansion size");
813 size_t shrink_bytes = capacity() - desired_capacity;
814 // Don't shrink unless the delta is greater than the minimum shrink we want
815 if (shrink_bytes >= MinHeapDeltaBytes) {
816 shrink_free_list_by(shrink_bytes);
817 }
818 }
819 }
820
821 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const {
822 return cmsSpace()->freelistLock();
823 }
824
825 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size, bool tlab) {
826 CMSSynchronousYieldRequest yr;
827 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
828 return have_lock_and_allocate(size, tlab);
829 }
830
831 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size,
832 bool tlab /* ignored */) {
833 assert_lock_strong(freelistLock());
834 size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size);
835 HeapWord* res = cmsSpace()->allocate(adjustedSize);
836 // Allocate the object live (grey) if the background collector has
837 // started marking. This is necessary because the marker may
838 // have passed this address and consequently this object will
839 // not otherwise be greyed and would be incorrectly swept up.
840 // Note that if this object contains references, the writing
841 // of those references will dirty the card containing this object
842 // allowing the object to be blackened (and its references scanned)
843 // either during a preclean phase or at the final checkpoint.
844 if (res != NULL) {
845 // We may block here with an uninitialized object with
846 // its mark-bit or P-bits not yet set. Such objects need
847 // to be safely navigable by block_start().
848 assert(oop(res)->klass_or_null() == NULL, "Object should be uninitialized here.");
849 assert(!((FreeChunk*)res)->is_free(), "Error, block will look free but show wrong size");
850 collector()->direct_allocated(res, adjustedSize);
851 _direct_allocated_words += adjustedSize;
852 // allocation counters
853 NOT_PRODUCT(
854 _numObjectsAllocated++;
855 _numWordsAllocated += (int)adjustedSize;
856 )
857 }
858 return res;
859 }
860
861 // In the case of direct allocation by mutators in a generation that
862 // is being concurrently collected, the object must be allocated
863 // live (grey) if the background collector has started marking.
864 // This is necessary because the marker may
865 // have passed this address and consequently this object will
866 // not otherwise be greyed and would be incorrectly swept up.
867 // Note that if this object contains references, the writing
868 // of those references will dirty the card containing this object
869 // allowing the object to be blackened (and its references scanned)
870 // either during a preclean phase or at the final checkpoint.
871 void CMSCollector::direct_allocated(HeapWord* start, size_t size) {
872 assert(_markBitMap.covers(start, size), "Out of bounds");
873 if (_collectorState >= Marking) {
874 MutexLockerEx y(_markBitMap.lock(),
875 Mutex::_no_safepoint_check_flag);
876 // [see comments preceding SweepClosure::do_blk() below for details]
877 //
878 // Can the P-bits be deleted now? JJJ
879 //
880 // 1. need to mark the object as live so it isn't collected
881 // 2. need to mark the 2nd bit to indicate the object may be uninitialized
882 // 3. need to mark the end of the object so marking, precleaning or sweeping
883 // can skip over uninitialized or unparsable objects. An allocated
884 // object is considered uninitialized for our purposes as long as
885 // its klass word is NULL. All old gen objects are parsable
886 // as soon as they are initialized.)
887 _markBitMap.mark(start); // object is live
888 _markBitMap.mark(start + 1); // object is potentially uninitialized?
889 _markBitMap.mark(start + size - 1);
890 // mark end of object
891 }
892 // check that oop looks uninitialized
893 assert(oop(start)->klass_or_null() == NULL, "_klass should be NULL");
894 }
895
896 void CMSCollector::promoted(bool par, HeapWord* start,
897 bool is_obj_array, size_t obj_size) {
898 assert(_markBitMap.covers(start), "Out of bounds");
899 // See comment in direct_allocated() about when objects should
900 // be allocated live.
901 if (_collectorState >= Marking) {
902 // we already hold the marking bit map lock, taken in
903 // the prologue
904 if (par) {
905 _markBitMap.par_mark(start);
906 } else {
907 _markBitMap.mark(start);
908 }
909 // We don't need to mark the object as uninitialized (as
910 // in direct_allocated above) because this is being done with the
911 // world stopped and the object will be initialized by the
912 // time the marking, precleaning or sweeping get to look at it.
913 // But see the code for copying objects into the CMS generation,
914 // where we need to ensure that concurrent readers of the
915 // block offset table are able to safely navigate a block that
916 // is in flux from being free to being allocated (and in
917 // transition while being copied into) and subsequently
918 // becoming a bona-fide object when the copy/promotion is complete.
919 assert(SafepointSynchronize::is_at_safepoint(),
920 "expect promotion only at safepoints");
921
922 if (_collectorState < Sweeping) {
923 // Mark the appropriate cards in the modUnionTable, so that
924 // this object gets scanned before the sweep. If this is
925 // not done, CMS generation references in the object might
926 // not get marked.
927 // For the case of arrays, which are otherwise precisely
928 // marked, we need to dirty the entire array, not just its head.
929 if (is_obj_array) {
930 // The [par_]mark_range() method expects mr.end() below to
931 // be aligned to the granularity of a bit's representation
932 // in the heap. In the case of the MUT below, that's a
933 // card size.
934 MemRegion mr(start,
935 (HeapWord*)round_to((intptr_t)(start + obj_size),
936 CardTableModRefBS::card_size /* bytes */));
937 if (par) {
938 _modUnionTable.par_mark_range(mr);
939 } else {
940 _modUnionTable.mark_range(mr);
941 }
942 } else { // not an obj array; we can just mark the head
943 if (par) {
944 _modUnionTable.par_mark(start);
945 } else {
946 _modUnionTable.mark(start);
947 }
948 }
949 }
950 }
951 }
952
953 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size) {
954 assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
955 // allocate, copy and if necessary update promoinfo --
956 // delegate to underlying space.
957 assert_lock_strong(freelistLock());
958
959 #ifndef PRODUCT
960 if (GenCollectedHeap::heap()->promotion_should_fail()) {
961 return NULL;
962 }
963 #endif // #ifndef PRODUCT
964
965 oop res = _cmsSpace->promote(obj, obj_size);
966 if (res == NULL) {
967 // expand and retry
968 size_t s = _cmsSpace->expansionSpaceRequired(obj_size); // HeapWords
969 expand_for_gc_cause(s*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_promotion);
970 // Since this is the old generation, we don't try to promote
971 // into a more senior generation.
972 res = _cmsSpace->promote(obj, obj_size);
973 }
974 if (res != NULL) {
975 // See comment in allocate() about when objects should
976 // be allocated live.
977 assert(obj->is_oop(), "Will dereference klass pointer below");
978 collector()->promoted(false, // Not parallel
979 (HeapWord*)res, obj->is_objArray(), obj_size);
980 // promotion counters
981 NOT_PRODUCT(
982 _numObjectsPromoted++;
983 _numWordsPromoted +=
984 (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size()));
985 )
986 }
987 return res;
988 }
989
990
991 // IMPORTANT: Notes on object size recognition in CMS.
992 // ---------------------------------------------------
993 // A block of storage in the CMS generation is always in
994 // one of three states. A free block (FREE), an allocated
995 // object (OBJECT) whose size() method reports the correct size,
996 // and an intermediate state (TRANSIENT) in which its size cannot
997 // be accurately determined.
998 // STATE IDENTIFICATION: (32 bit and 64 bit w/o COOPS)
999 // -----------------------------------------------------
1000 // FREE: klass_word & 1 == 1; mark_word holds block size
1001 //
1002 // OBJECT: klass_word installed; klass_word != 0 && klass_word & 1 == 0;
1003 // obj->size() computes correct size
1004 //
1005 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1006 //
1007 // STATE IDENTIFICATION: (64 bit+COOPS)
1008 // ------------------------------------
1009 // FREE: mark_word & CMS_FREE_BIT == 1; mark_word & ~CMS_FREE_BIT gives block_size
1010 //
1011 // OBJECT: klass_word installed; klass_word != 0;
1012 // obj->size() computes correct size
1013 //
1014 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1015 //
1016 //
1017 // STATE TRANSITION DIAGRAM
1018 //
1019 // mut / parnew mut / parnew
1020 // FREE --------------------> TRANSIENT ---------------------> OBJECT --|
1021 // ^ |
1022 // |------------------------ DEAD <------------------------------------|
1023 // sweep mut
1024 //
1025 // While a block is in TRANSIENT state its size cannot be determined
1026 // so readers will either need to come back later or stall until
1027 // the size can be determined. Note that for the case of direct
1028 // allocation, P-bits, when available, may be used to determine the
1029 // size of an object that may not yet have been initialized.
1030
1031 // Things to support parallel young-gen collection.
1032 oop
1033 ConcurrentMarkSweepGeneration::par_promote(int thread_num,
1034 oop old, markOop m,
1035 size_t word_sz) {
1036 #ifndef PRODUCT
1037 if (GenCollectedHeap::heap()->promotion_should_fail()) {
1038 return NULL;
1039 }
1040 #endif // #ifndef PRODUCT
1041
1042 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1043 PromotionInfo* promoInfo = &ps->promo;
1044 // if we are tracking promotions, then first ensure space for
1045 // promotion (including spooling space for saving header if necessary).
1046 // then allocate and copy, then track promoted info if needed.
1047 // When tracking (see PromotionInfo::track()), the mark word may
1048 // be displaced and in this case restoration of the mark word
1049 // occurs in the (oop_since_save_marks_)iterate phase.
1050 if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) {
1051 // Out of space for allocating spooling buffers;
1052 // try expanding and allocating spooling buffers.
1053 if (!expand_and_ensure_spooling_space(promoInfo)) {
1054 return NULL;
1055 }
1056 }
1057 assert(promoInfo->has_spooling_space(), "Control point invariant");
1058 const size_t alloc_sz = CompactibleFreeListSpace::adjustObjectSize(word_sz);
1059 HeapWord* obj_ptr = ps->lab.alloc(alloc_sz);
1060 if (obj_ptr == NULL) {
1061 obj_ptr = expand_and_par_lab_allocate(ps, alloc_sz);
1062 if (obj_ptr == NULL) {
1063 return NULL;
1064 }
1065 }
1066 oop obj = oop(obj_ptr);
1067 OrderAccess::storestore();
1068 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1069 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1070 // IMPORTANT: See note on object initialization for CMS above.
1071 // Otherwise, copy the object. Here we must be careful to insert the
1072 // klass pointer last, since this marks the block as an allocated object.
1073 // Except with compressed oops it's the mark word.
1074 HeapWord* old_ptr = (HeapWord*)old;
1075 // Restore the mark word copied above.
1076 obj->set_mark(m);
1077 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1078 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1079 OrderAccess::storestore();
1080
1081 if (UseCompressedClassPointers) {
1082 // Copy gap missed by (aligned) header size calculation below
1083 obj->set_klass_gap(old->klass_gap());
1084 }
1085 if (word_sz > (size_t)oopDesc::header_size()) {
1086 Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1087 obj_ptr + oopDesc::header_size(),
1088 word_sz - oopDesc::header_size());
1089 }
1090
1091 // Now we can track the promoted object, if necessary. We take care
1092 // to delay the transition from uninitialized to full object
1093 // (i.e., insertion of klass pointer) until after, so that it
1094 // atomically becomes a promoted object.
1095 if (promoInfo->tracking()) {
1096 promoInfo->track((PromotedObject*)obj, old->klass());
1097 }
1098 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1099 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1100 assert(old->is_oop(), "Will use and dereference old klass ptr below");
1101
1102 // Finally, install the klass pointer (this should be volatile).
1103 OrderAccess::storestore();
1104 obj->set_klass(old->klass());
1105 // We should now be able to calculate the right size for this object
1106 assert(obj->is_oop() && obj->size() == (int)word_sz, "Error, incorrect size computed for promoted object");
1107
1108 collector()->promoted(true, // parallel
1109 obj_ptr, old->is_objArray(), word_sz);
1110
1111 NOT_PRODUCT(
1112 Atomic::inc_ptr(&_numObjectsPromoted);
1113 Atomic::add_ptr(alloc_sz, &_numWordsPromoted);
1114 )
1115
1116 return obj;
1117 }
1118
1119 void
1120 ConcurrentMarkSweepGeneration::
1121 par_promote_alloc_done(int thread_num) {
1122 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1123 ps->lab.retire(thread_num);
1124 }
1125
1126 void
1127 ConcurrentMarkSweepGeneration::
1128 par_oop_since_save_marks_iterate_done(int thread_num) {
1129 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1130 ParScanWithoutBarrierClosure* dummy_cl = NULL;
1131 ps->promo.promoted_oops_iterate_nv(dummy_cl);
1132 }
1133
1134 bool ConcurrentMarkSweepGeneration::should_collect(bool full,
1135 size_t size,
1136 bool tlab)
1137 {
1138 // We allow a STW collection only if a full
1139 // collection was requested.
1140 return full || should_allocate(size, tlab); // FIX ME !!!
1141 // This and promotion failure handling are connected at the
1142 // hip and should be fixed by untying them.
1143 }
1144
1145 bool CMSCollector::shouldConcurrentCollect() {
1146 if (_full_gc_requested) {
1147 if (Verbose && PrintGCDetails) {
1148 gclog_or_tty->print_cr("CMSCollector: collect because of explicit "
1149 " gc request (or gc_locker)");
1150 }
1151 return true;
1152 }
1153
1154 FreelistLocker x(this);
1155 // ------------------------------------------------------------------
1156 // Print out lots of information which affects the initiation of
1157 // a collection.
1158 if (PrintCMSInitiationStatistics && stats().valid()) {
1159 gclog_or_tty->print("CMSCollector shouldConcurrentCollect: ");
1160 gclog_or_tty->stamp();
1161 gclog_or_tty->cr();
1162 stats().print_on(gclog_or_tty);
1163 gclog_or_tty->print_cr("time_until_cms_gen_full %3.7f",
1164 stats().time_until_cms_gen_full());
1165 gclog_or_tty->print_cr("free=" SIZE_FORMAT, _cmsGen->free());
1166 gclog_or_tty->print_cr("contiguous_available=" SIZE_FORMAT,
1167 _cmsGen->contiguous_available());
1168 gclog_or_tty->print_cr("promotion_rate=%g", stats().promotion_rate());
1169 gclog_or_tty->print_cr("cms_allocation_rate=%g", stats().cms_allocation_rate());
1170 gclog_or_tty->print_cr("occupancy=%3.7f", _cmsGen->occupancy());
1171 gclog_or_tty->print_cr("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy());
1172 gclog_or_tty->print_cr("cms_time_since_begin=%3.7f", stats().cms_time_since_begin());
1173 gclog_or_tty->print_cr("cms_time_since_end=%3.7f", stats().cms_time_since_end());
1174 gclog_or_tty->print_cr("metadata initialized %d",
1175 MetaspaceGC::should_concurrent_collect());
1176 }
1177 // ------------------------------------------------------------------
1178
1179 // If the estimated time to complete a cms collection (cms_duration())
1180 // is less than the estimated time remaining until the cms generation
1181 // is full, start a collection.
1182 if (!UseCMSInitiatingOccupancyOnly) {
1183 if (stats().valid()) {
1184 if (stats().time_until_cms_start() == 0.0) {
1185 return true;
1186 }
1187 } else {
1188 // We want to conservatively collect somewhat early in order
1189 // to try and "bootstrap" our CMS/promotion statistics;
1190 // this branch will not fire after the first successful CMS
1191 // collection because the stats should then be valid.
1192 if (_cmsGen->occupancy() >= _bootstrap_occupancy) {
1193 if (Verbose && PrintGCDetails) {
1194 gclog_or_tty->print_cr(
1195 " CMSCollector: collect for bootstrapping statistics:"
1196 " occupancy = %f, boot occupancy = %f", _cmsGen->occupancy(),
1197 _bootstrap_occupancy);
1198 }
1199 return true;
1200 }
1201 }
1202 }
1203
1204 // Otherwise, we start a collection cycle if
1205 // old gen want a collection cycle started. Each may use
1206 // an appropriate criterion for making this decision.
1207 // XXX We need to make sure that the gen expansion
1208 // criterion dovetails well with this. XXX NEED TO FIX THIS
1209 if (_cmsGen->should_concurrent_collect()) {
1210 if (Verbose && PrintGCDetails) {
1211 gclog_or_tty->print_cr("CMS old gen initiated");
1212 }
1213 return true;
1214 }
1215
1216 // We start a collection if we believe an incremental collection may fail;
1217 // this is not likely to be productive in practice because it's probably too
1218 // late anyway.
1219 GenCollectedHeap* gch = GenCollectedHeap::heap();
1220 assert(gch->collector_policy()->is_generation_policy(),
1221 "You may want to check the correctness of the following");
1222 if (gch->incremental_collection_will_fail(true /* consult_young */)) {
1223 if (Verbose && PrintGCDetails) {
1224 gclog_or_tty->print("CMSCollector: collect because incremental collection will fail ");
1225 }
1226 return true;
1227 }
1228
1229 if (MetaspaceGC::should_concurrent_collect()) {
1230 if (Verbose && PrintGCDetails) {
1231 gclog_or_tty->print("CMSCollector: collect for metadata allocation ");
1232 }
1233 return true;
1234 }
1235
1236 // CMSTriggerInterval starts a CMS cycle if enough time has passed.
1237 if (CMSTriggerInterval >= 0) {
1238 if (CMSTriggerInterval == 0) {
1239 // Trigger always
1240 return true;
1241 }
1242
1243 // Check the CMS time since begin (we do not check the stats validity
1244 // as we want to be able to trigger the first CMS cycle as well)
1245 if (stats().cms_time_since_begin() >= (CMSTriggerInterval / ((double) MILLIUNITS))) {
1246 if (Verbose && PrintGCDetails) {
1247 if (stats().valid()) {
1248 gclog_or_tty->print_cr("CMSCollector: collect because of trigger interval (time since last begin %3.7f secs)",
1249 stats().cms_time_since_begin());
1250 } else {
1251 gclog_or_tty->print_cr("CMSCollector: collect because of trigger interval (first collection)");
1252 }
1253 }
1254 return true;
1255 }
1256 }
1257
1258 return false;
1259 }
1260
1261 void CMSCollector::set_did_compact(bool v) { _cmsGen->set_did_compact(v); }
1262
1263 // Clear _expansion_cause fields of constituent generations
1264 void CMSCollector::clear_expansion_cause() {
1265 _cmsGen->clear_expansion_cause();
1266 }
1267
1268 // We should be conservative in starting a collection cycle. To
1269 // start too eagerly runs the risk of collecting too often in the
1270 // extreme. To collect too rarely falls back on full collections,
1271 // which works, even if not optimum in terms of concurrent work.
1272 // As a work around for too eagerly collecting, use the flag
1273 // UseCMSInitiatingOccupancyOnly. This also has the advantage of
1274 // giving the user an easily understandable way of controlling the
1275 // collections.
1276 // We want to start a new collection cycle if any of the following
1277 // conditions hold:
1278 // . our current occupancy exceeds the configured initiating occupancy
1279 // for this generation, or
1280 // . we recently needed to expand this space and have not, since that
1281 // expansion, done a collection of this generation, or
1282 // . the underlying space believes that it may be a good idea to initiate
1283 // a concurrent collection (this may be based on criteria such as the
1284 // following: the space uses linear allocation and linear allocation is
1285 // going to fail, or there is believed to be excessive fragmentation in
1286 // the generation, etc... or ...
1287 // [.(currently done by CMSCollector::shouldConcurrentCollect() only for
1288 // the case of the old generation; see CR 6543076):
1289 // we may be approaching a point at which allocation requests may fail because
1290 // we will be out of sufficient free space given allocation rate estimates.]
1291 bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const {
1292
1293 assert_lock_strong(freelistLock());
1294 if (occupancy() > initiating_occupancy()) {
1295 if (PrintGCDetails && Verbose) {
1296 gclog_or_tty->print(" %s: collect because of occupancy %f / %f ",
1297 short_name(), occupancy(), initiating_occupancy());
1298 }
1299 return true;
1300 }
1301 if (UseCMSInitiatingOccupancyOnly) {
1302 return false;
1303 }
1304 if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) {
1305 if (PrintGCDetails && Verbose) {
1306 gclog_or_tty->print(" %s: collect because expanded for allocation ",
1307 short_name());
1308 }
1309 return true;
1310 }
1311 return false;
1312 }
1313
1314 void ConcurrentMarkSweepGeneration::collect(bool full,
1315 bool clear_all_soft_refs,
1316 size_t size,
1317 bool tlab)
1318 {
1319 collector()->collect(full, clear_all_soft_refs, size, tlab);
1320 }
1321
1322 void CMSCollector::collect(bool full,
1323 bool clear_all_soft_refs,
1324 size_t size,
1325 bool tlab)
1326 {
1327 // The following "if" branch is present for defensive reasons.
1328 // In the current uses of this interface, it can be replaced with:
1329 // assert(!GC_locker.is_active(), "Can't be called otherwise");
1330 // But I am not placing that assert here to allow future
1331 // generality in invoking this interface.
1332 if (GC_locker::is_active()) {
1333 // A consistency test for GC_locker
1334 assert(GC_locker::needs_gc(), "Should have been set already");
1335 // Skip this foreground collection, instead
1336 // expanding the heap if necessary.
1337 // Need the free list locks for the call to free() in compute_new_size()
1338 compute_new_size();
1339 return;
1340 }
1341 acquire_control_and_collect(full, clear_all_soft_refs);
1342 }
1343
1344 void CMSCollector::request_full_gc(unsigned int full_gc_count, GCCause::Cause cause) {
1345 GenCollectedHeap* gch = GenCollectedHeap::heap();
1346 unsigned int gc_count = gch->total_full_collections();
1347 if (gc_count == full_gc_count) {
1348 MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag);
1349 _full_gc_requested = true;
1350 _full_gc_cause = cause;
1351 CGC_lock->notify(); // nudge CMS thread
1352 } else {
1353 assert(gc_count > full_gc_count, "Error: causal loop");
1354 }
1355 }
1356
1357 bool CMSCollector::is_external_interruption() {
1358 GCCause::Cause cause = GenCollectedHeap::heap()->gc_cause();
1359 return GCCause::is_user_requested_gc(cause) ||
1360 GCCause::is_serviceability_requested_gc(cause);
1361 }
1362
1363 void CMSCollector::report_concurrent_mode_interruption() {
1364 if (is_external_interruption()) {
1365 if (PrintGCDetails) {
1366 gclog_or_tty->print(" (concurrent mode interrupted)");
1367 }
1368 } else {
1369 if (PrintGCDetails) {
1370 gclog_or_tty->print(" (concurrent mode failure)");
1371 }
1372 _gc_tracer_cm->report_concurrent_mode_failure();
1373 }
1374 }
1375
1376
1377 // The foreground and background collectors need to coordinate in order
1378 // to make sure that they do not mutually interfere with CMS collections.
1379 // When a background collection is active,
1380 // the foreground collector may need to take over (preempt) and
1381 // synchronously complete an ongoing collection. Depending on the
1382 // frequency of the background collections and the heap usage
1383 // of the application, this preemption can be seldom or frequent.
1384 // There are only certain
1385 // points in the background collection that the "collection-baton"
1386 // can be passed to the foreground collector.
1387 //
1388 // The foreground collector will wait for the baton before
1389 // starting any part of the collection. The foreground collector
1390 // will only wait at one location.
1391 //
1392 // The background collector will yield the baton before starting a new
1393 // phase of the collection (e.g., before initial marking, marking from roots,
1394 // precleaning, final re-mark, sweep etc.) This is normally done at the head
1395 // of the loop which switches the phases. The background collector does some
1396 // of the phases (initial mark, final re-mark) with the world stopped.
1397 // Because of locking involved in stopping the world,
1398 // the foreground collector should not block waiting for the background
1399 // collector when it is doing a stop-the-world phase. The background
1400 // collector will yield the baton at an additional point just before
1401 // it enters a stop-the-world phase. Once the world is stopped, the
1402 // background collector checks the phase of the collection. If the
1403 // phase has not changed, it proceeds with the collection. If the
1404 // phase has changed, it skips that phase of the collection. See
1405 // the comments on the use of the Heap_lock in collect_in_background().
1406 //
1407 // Variable used in baton passing.
1408 // _foregroundGCIsActive - Set to true by the foreground collector when
1409 // it wants the baton. The foreground clears it when it has finished
1410 // the collection.
1411 // _foregroundGCShouldWait - Set to true by the background collector
1412 // when it is running. The foreground collector waits while
1413 // _foregroundGCShouldWait is true.
1414 // CGC_lock - monitor used to protect access to the above variables
1415 // and to notify the foreground and background collectors.
1416 // _collectorState - current state of the CMS collection.
1417 //
1418 // The foreground collector
1419 // acquires the CGC_lock
1420 // sets _foregroundGCIsActive
1421 // waits on the CGC_lock for _foregroundGCShouldWait to be false
1422 // various locks acquired in preparation for the collection
1423 // are released so as not to block the background collector
1424 // that is in the midst of a collection
1425 // proceeds with the collection
1426 // clears _foregroundGCIsActive
1427 // returns
1428 //
1429 // The background collector in a loop iterating on the phases of the
1430 // collection
1431 // acquires the CGC_lock
1432 // sets _foregroundGCShouldWait
1433 // if _foregroundGCIsActive is set
1434 // clears _foregroundGCShouldWait, notifies _CGC_lock
1435 // waits on _CGC_lock for _foregroundGCIsActive to become false
1436 // and exits the loop.
1437 // otherwise
1438 // proceed with that phase of the collection
1439 // if the phase is a stop-the-world phase,
1440 // yield the baton once more just before enqueueing
1441 // the stop-world CMS operation (executed by the VM thread).
1442 // returns after all phases of the collection are done
1443 //
1444
1445 void CMSCollector::acquire_control_and_collect(bool full,
1446 bool clear_all_soft_refs) {
1447 assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
1448 assert(!Thread::current()->is_ConcurrentGC_thread(),
1449 "shouldn't try to acquire control from self!");
1450
1451 // Start the protocol for acquiring control of the
1452 // collection from the background collector (aka CMS thread).
1453 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1454 "VM thread should have CMS token");
1455 // Remember the possibly interrupted state of an ongoing
1456 // concurrent collection
1457 CollectorState first_state = _collectorState;
1458
1459 // Signal to a possibly ongoing concurrent collection that
1460 // we want to do a foreground collection.
1461 _foregroundGCIsActive = true;
1462
1463 // release locks and wait for a notify from the background collector
1464 // releasing the locks in only necessary for phases which
1465 // do yields to improve the granularity of the collection.
1466 assert_lock_strong(bitMapLock());
1467 // We need to lock the Free list lock for the space that we are
1468 // currently collecting.
1469 assert(haveFreelistLocks(), "Must be holding free list locks");
1470 bitMapLock()->unlock();
1471 releaseFreelistLocks();
1472 {
1473 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1474 if (_foregroundGCShouldWait) {
1475 // We are going to be waiting for action for the CMS thread;
1476 // it had better not be gone (for instance at shutdown)!
1477 assert(ConcurrentMarkSweepThread::cmst() != NULL,
1478 "CMS thread must be running");
1479 // Wait here until the background collector gives us the go-ahead
1480 ConcurrentMarkSweepThread::clear_CMS_flag(
1481 ConcurrentMarkSweepThread::CMS_vm_has_token); // release token
1482 // Get a possibly blocked CMS thread going:
1483 // Note that we set _foregroundGCIsActive true above,
1484 // without protection of the CGC_lock.
1485 CGC_lock->notify();
1486 assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(),
1487 "Possible deadlock");
1488 while (_foregroundGCShouldWait) {
1489 // wait for notification
1490 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1491 // Possibility of delay/starvation here, since CMS token does
1492 // not know to give priority to VM thread? Actually, i think
1493 // there wouldn't be any delay/starvation, but the proof of
1494 // that "fact" (?) appears non-trivial. XXX 20011219YSR
1495 }
1496 ConcurrentMarkSweepThread::set_CMS_flag(
1497 ConcurrentMarkSweepThread::CMS_vm_has_token);
1498 }
1499 }
1500 // The CMS_token is already held. Get back the other locks.
1501 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1502 "VM thread should have CMS token");
1503 getFreelistLocks();
1504 bitMapLock()->lock_without_safepoint_check();
1505 if (TraceCMSState) {
1506 gclog_or_tty->print_cr("CMS foreground collector has asked for control "
1507 INTPTR_FORMAT " with first state %d", p2i(Thread::current()), first_state);
1508 gclog_or_tty->print_cr(" gets control with state %d", _collectorState);
1509 }
1510
1511 // Inform cms gen if this was due to partial collection failing.
1512 // The CMS gen may use this fact to determine its expansion policy.
1513 GenCollectedHeap* gch = GenCollectedHeap::heap();
1514 if (gch->incremental_collection_will_fail(false /* don't consult_young */)) {
1515 assert(!_cmsGen->incremental_collection_failed(),
1516 "Should have been noticed, reacted to and cleared");
1517 _cmsGen->set_incremental_collection_failed();
1518 }
1519
1520 if (first_state > Idling) {
1521 report_concurrent_mode_interruption();
1522 }
1523
1524 set_did_compact(true);
1525
1526 // If the collection is being acquired from the background
1527 // collector, there may be references on the discovered
1528 // references lists. Abandon those references, since some
1529 // of them may have become unreachable after concurrent
1530 // discovery; the STW compacting collector will redo discovery
1531 // more precisely, without being subject to floating garbage.
1532 // Leaving otherwise unreachable references in the discovered
1533 // lists would require special handling.
1534 ref_processor()->disable_discovery();
1535 ref_processor()->abandon_partial_discovery();
1536 ref_processor()->verify_no_references_recorded();
1537
1538 if (first_state > Idling) {
1539 save_heap_summary();
1540 }
1541
1542 do_compaction_work(clear_all_soft_refs);
1543
1544 // Has the GC time limit been exceeded?
1545 size_t max_eden_size = _young_gen->max_eden_size();
1546 GCCause::Cause gc_cause = gch->gc_cause();
1547 size_policy()->check_gc_overhead_limit(_young_gen->used(),
1548 _young_gen->eden()->used(),
1549 _cmsGen->max_capacity(),
1550 max_eden_size,
1551 full,
1552 gc_cause,
1553 gch->collector_policy());
1554
1555 // Reset the expansion cause, now that we just completed
1556 // a collection cycle.
1557 clear_expansion_cause();
1558 _foregroundGCIsActive = false;
1559 return;
1560 }
1561
1562 // Resize the tenured generation
1563 // after obtaining the free list locks for the
1564 // two generations.
1565 void CMSCollector::compute_new_size() {
1566 assert_locked_or_safepoint(Heap_lock);
1567 FreelistLocker z(this);
1568 MetaspaceGC::compute_new_size();
1569 _cmsGen->compute_new_size_free_list();
1570 }
1571
1572 // A work method used by the foreground collector to do
1573 // a mark-sweep-compact.
1574 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) {
1575 GenCollectedHeap* gch = GenCollectedHeap::heap();
1576
1577 STWGCTimer* gc_timer = GenMarkSweep::gc_timer();
1578 gc_timer->register_gc_start();
1579
1580 SerialOldTracer* gc_tracer = GenMarkSweep::gc_tracer();
1581 gc_tracer->report_gc_start(gch->gc_cause(), gc_timer->gc_start());
1582
1583 GCTraceTime t("CMS:MSC ", PrintGCDetails && Verbose, true, NULL);
1584
1585 // Temporarily widen the span of the weak reference processing to
1586 // the entire heap.
1587 MemRegion new_span(GenCollectedHeap::heap()->reserved_region());
1588 ReferenceProcessorSpanMutator rp_mut_span(ref_processor(), new_span);
1589 // Temporarily, clear the "is_alive_non_header" field of the
1590 // reference processor.
1591 ReferenceProcessorIsAliveMutator rp_mut_closure(ref_processor(), NULL);
1592 // Temporarily make reference _processing_ single threaded (non-MT).
1593 ReferenceProcessorMTProcMutator rp_mut_mt_processing(ref_processor(), false);
1594 // Temporarily make refs discovery atomic
1595 ReferenceProcessorAtomicMutator rp_mut_atomic(ref_processor(), true);
1596 // Temporarily make reference _discovery_ single threaded (non-MT)
1597 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
1598
1599 ref_processor()->set_enqueuing_is_done(false);
1600 ref_processor()->enable_discovery();
1601 ref_processor()->setup_policy(clear_all_soft_refs);
1602 // If an asynchronous collection finishes, the _modUnionTable is
1603 // all clear. If we are assuming the collection from an asynchronous
1604 // collection, clear the _modUnionTable.
1605 assert(_collectorState != Idling || _modUnionTable.isAllClear(),
1606 "_modUnionTable should be clear if the baton was not passed");
1607 _modUnionTable.clear_all();
1608 assert(_collectorState != Idling || _ct->klass_rem_set()->mod_union_is_clear(),
1609 "mod union for klasses should be clear if the baton was passed");
1610 _ct->klass_rem_set()->clear_mod_union();
1611
1612 // We must adjust the allocation statistics being maintained
1613 // in the free list space. We do so by reading and clearing
1614 // the sweep timer and updating the block flux rate estimates below.
1615 assert(!_intra_sweep_timer.is_active(), "_intra_sweep_timer should be inactive");
1616 if (_inter_sweep_timer.is_active()) {
1617 _inter_sweep_timer.stop();
1618 // Note that we do not use this sample to update the _inter_sweep_estimate.
1619 _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
1620 _inter_sweep_estimate.padded_average(),
1621 _intra_sweep_estimate.padded_average());
1622 }
1623
1624 GenMarkSweep::invoke_at_safepoint(ref_processor(), clear_all_soft_refs);
1625 #ifdef ASSERT
1626 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
1627 size_t free_size = cms_space->free();
1628 assert(free_size ==
1629 pointer_delta(cms_space->end(), cms_space->compaction_top())
1630 * HeapWordSize,
1631 "All the free space should be compacted into one chunk at top");
1632 assert(cms_space->dictionary()->total_chunk_size(
1633 debug_only(cms_space->freelistLock())) == 0 ||
1634 cms_space->totalSizeInIndexedFreeLists() == 0,
1635 "All the free space should be in a single chunk");
1636 size_t num = cms_space->totalCount();
1637 assert((free_size == 0 && num == 0) ||
1638 (free_size > 0 && (num == 1 || num == 2)),
1639 "There should be at most 2 free chunks after compaction");
1640 #endif // ASSERT
1641 _collectorState = Resetting;
1642 assert(_restart_addr == NULL,
1643 "Should have been NULL'd before baton was passed");
1644 reset_stw();
1645 _cmsGen->reset_after_compaction();
1646 _concurrent_cycles_since_last_unload = 0;
1647
1648 // Clear any data recorded in the PLAB chunk arrays.
1649 if (_survivor_plab_array != NULL) {
1650 reset_survivor_plab_arrays();
1651 }
1652
1653 // Adjust the per-size allocation stats for the next epoch.
1654 _cmsGen->cmsSpace()->endSweepFLCensus(sweep_count() /* fake */);
1655 // Restart the "inter sweep timer" for the next epoch.
1656 _inter_sweep_timer.reset();
1657 _inter_sweep_timer.start();
1658
1659 gc_timer->register_gc_end();
1660
1661 gc_tracer->report_gc_end(gc_timer->gc_end(), gc_timer->time_partitions());
1662
1663 // For a mark-sweep-compact, compute_new_size() will be called
1664 // in the heap's do_collection() method.
1665 }
1666
1667 void CMSCollector::print_eden_and_survivor_chunk_arrays() {
1668 ContiguousSpace* eden_space = _young_gen->eden();
1669 ContiguousSpace* from_space = _young_gen->from();
1670 ContiguousSpace* to_space = _young_gen->to();
1671 // Eden
1672 if (_eden_chunk_array != NULL) {
1673 gclog_or_tty->print_cr("eden " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1674 p2i(eden_space->bottom()), p2i(eden_space->top()),
1675 p2i(eden_space->end()), eden_space->capacity());
1676 gclog_or_tty->print_cr("_eden_chunk_index=" SIZE_FORMAT ", "
1677 "_eden_chunk_capacity=" SIZE_FORMAT,
1678 _eden_chunk_index, _eden_chunk_capacity);
1679 for (size_t i = 0; i < _eden_chunk_index; i++) {
1680 gclog_or_tty->print_cr("_eden_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT,
1681 i, p2i(_eden_chunk_array[i]));
1682 }
1683 }
1684 // Survivor
1685 if (_survivor_chunk_array != NULL) {
1686 gclog_or_tty->print_cr("survivor " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1687 p2i(from_space->bottom()), p2i(from_space->top()),
1688 p2i(from_space->end()), from_space->capacity());
1689 gclog_or_tty->print_cr("_survivor_chunk_index=" SIZE_FORMAT ", "
1690 "_survivor_chunk_capacity=" SIZE_FORMAT,
1691 _survivor_chunk_index, _survivor_chunk_capacity);
1692 for (size_t i = 0; i < _survivor_chunk_index; i++) {
1693 gclog_or_tty->print_cr("_survivor_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT,
1694 i, p2i(_survivor_chunk_array[i]));
1695 }
1696 }
1697 }
1698
1699 void CMSCollector::getFreelistLocks() const {
1700 // Get locks for all free lists in all generations that this
1701 // collector is responsible for
1702 _cmsGen->freelistLock()->lock_without_safepoint_check();
1703 }
1704
1705 void CMSCollector::releaseFreelistLocks() const {
1706 // Release locks for all free lists in all generations that this
1707 // collector is responsible for
1708 _cmsGen->freelistLock()->unlock();
1709 }
1710
1711 bool CMSCollector::haveFreelistLocks() const {
1712 // Check locks for all free lists in all generations that this
1713 // collector is responsible for
1714 assert_lock_strong(_cmsGen->freelistLock());
1715 PRODUCT_ONLY(ShouldNotReachHere());
1716 return true;
1717 }
1718
1719 // A utility class that is used by the CMS collector to
1720 // temporarily "release" the foreground collector from its
1721 // usual obligation to wait for the background collector to
1722 // complete an ongoing phase before proceeding.
1723 class ReleaseForegroundGC: public StackObj {
1724 private:
1725 CMSCollector* _c;
1726 public:
1727 ReleaseForegroundGC(CMSCollector* c) : _c(c) {
1728 assert(_c->_foregroundGCShouldWait, "Else should not need to call");
1729 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1730 // allow a potentially blocked foreground collector to proceed
1731 _c->_foregroundGCShouldWait = false;
1732 if (_c->_foregroundGCIsActive) {
1733 CGC_lock->notify();
1734 }
1735 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1736 "Possible deadlock");
1737 }
1738
1739 ~ReleaseForegroundGC() {
1740 assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?");
1741 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1742 _c->_foregroundGCShouldWait = true;
1743 }
1744 };
1745
1746 void CMSCollector::collect_in_background(GCCause::Cause cause) {
1747 assert(Thread::current()->is_ConcurrentGC_thread(),
1748 "A CMS asynchronous collection is only allowed on a CMS thread.");
1749
1750 GenCollectedHeap* gch = GenCollectedHeap::heap();
1751 {
1752 bool safepoint_check = Mutex::_no_safepoint_check_flag;
1753 MutexLockerEx hl(Heap_lock, safepoint_check);
1754 FreelistLocker fll(this);
1755 MutexLockerEx x(CGC_lock, safepoint_check);
1756 if (_foregroundGCIsActive) {
1757 // The foreground collector is. Skip this
1758 // background collection.
1759 assert(!_foregroundGCShouldWait, "Should be clear");
1760 return;
1761 } else {
1762 assert(_collectorState == Idling, "Should be idling before start.");
1763 _collectorState = InitialMarking;
1764 register_gc_start(cause);
1765 // Reset the expansion cause, now that we are about to begin
1766 // a new cycle.
1767 clear_expansion_cause();
1768
1769 // Clear the MetaspaceGC flag since a concurrent collection
1770 // is starting but also clear it after the collection.
1771 MetaspaceGC::set_should_concurrent_collect(false);
1772 }
1773 // Decide if we want to enable class unloading as part of the
1774 // ensuing concurrent GC cycle.
1775 update_should_unload_classes();
1776 _full_gc_requested = false; // acks all outstanding full gc requests
1777 _full_gc_cause = GCCause::_no_gc;
1778 // Signal that we are about to start a collection
1779 gch->increment_total_full_collections(); // ... starting a collection cycle
1780 _collection_count_start = gch->total_full_collections();
1781 }
1782
1783 // Used for PrintGC
1784 size_t prev_used = 0;
1785 if (PrintGC && Verbose) {
1786 prev_used = _cmsGen->used();
1787 }
1788
1789 // The change of the collection state is normally done at this level;
1790 // the exceptions are phases that are executed while the world is
1791 // stopped. For those phases the change of state is done while the
1792 // world is stopped. For baton passing purposes this allows the
1793 // background collector to finish the phase and change state atomically.
1794 // The foreground collector cannot wait on a phase that is done
1795 // while the world is stopped because the foreground collector already
1796 // has the world stopped and would deadlock.
1797 while (_collectorState != Idling) {
1798 if (TraceCMSState) {
1799 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
1800 p2i(Thread::current()), _collectorState);
1801 }
1802 // The foreground collector
1803 // holds the Heap_lock throughout its collection.
1804 // holds the CMS token (but not the lock)
1805 // except while it is waiting for the background collector to yield.
1806 //
1807 // The foreground collector should be blocked (not for long)
1808 // if the background collector is about to start a phase
1809 // executed with world stopped. If the background
1810 // collector has already started such a phase, the
1811 // foreground collector is blocked waiting for the
1812 // Heap_lock. The stop-world phases (InitialMarking and FinalMarking)
1813 // are executed in the VM thread.
1814 //
1815 // The locking order is
1816 // PendingListLock (PLL) -- if applicable (FinalMarking)
1817 // Heap_lock (both this & PLL locked in VM_CMS_Operation::prologue())
1818 // CMS token (claimed in
1819 // stop_world_and_do() -->
1820 // safepoint_synchronize() -->
1821 // CMSThread::synchronize())
1822
1823 {
1824 // Check if the FG collector wants us to yield.
1825 CMSTokenSync x(true); // is cms thread
1826 if (waitForForegroundGC()) {
1827 // We yielded to a foreground GC, nothing more to be
1828 // done this round.
1829 assert(_foregroundGCShouldWait == false, "We set it to false in "
1830 "waitForForegroundGC()");
1831 if (TraceCMSState) {
1832 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
1833 " exiting collection CMS state %d",
1834 p2i(Thread::current()), _collectorState);
1835 }
1836 return;
1837 } else {
1838 // The background collector can run but check to see if the
1839 // foreground collector has done a collection while the
1840 // background collector was waiting to get the CGC_lock
1841 // above. If yes, break so that _foregroundGCShouldWait
1842 // is cleared before returning.
1843 if (_collectorState == Idling) {
1844 break;
1845 }
1846 }
1847 }
1848
1849 assert(_foregroundGCShouldWait, "Foreground collector, if active, "
1850 "should be waiting");
1851
1852 switch (_collectorState) {
1853 case InitialMarking:
1854 {
1855 ReleaseForegroundGC x(this);
1856 stats().record_cms_begin();
1857 VM_CMS_Initial_Mark initial_mark_op(this);
1858 VMThread::execute(&initial_mark_op);
1859 }
1860 // The collector state may be any legal state at this point
1861 // since the background collector may have yielded to the
1862 // foreground collector.
1863 break;
1864 case Marking:
1865 // initial marking in checkpointRootsInitialWork has been completed
1866 if (markFromRoots()) { // we were successful
1867 assert(_collectorState == Precleaning, "Collector state should "
1868 "have changed");
1869 } else {
1870 assert(_foregroundGCIsActive, "Internal state inconsistency");
1871 }
1872 break;
1873 case Precleaning:
1874 // marking from roots in markFromRoots has been completed
1875 preclean();
1876 assert(_collectorState == AbortablePreclean ||
1877 _collectorState == FinalMarking,
1878 "Collector state should have changed");
1879 break;
1880 case AbortablePreclean:
1881 abortable_preclean();
1882 assert(_collectorState == FinalMarking, "Collector state should "
1883 "have changed");
1884 break;
1885 case FinalMarking:
1886 {
1887 ReleaseForegroundGC x(this);
1888
1889 VM_CMS_Final_Remark final_remark_op(this);
1890 VMThread::execute(&final_remark_op);
1891 }
1892 assert(_foregroundGCShouldWait, "block post-condition");
1893 break;
1894 case Sweeping:
1895 // final marking in checkpointRootsFinal has been completed
1896 sweep();
1897 assert(_collectorState == Resizing, "Collector state change "
1898 "to Resizing must be done under the free_list_lock");
1899
1900 case Resizing: {
1901 // Sweeping has been completed...
1902 // At this point the background collection has completed.
1903 // Don't move the call to compute_new_size() down
1904 // into code that might be executed if the background
1905 // collection was preempted.
1906 {
1907 ReleaseForegroundGC x(this); // unblock FG collection
1908 MutexLockerEx y(Heap_lock, Mutex::_no_safepoint_check_flag);
1909 CMSTokenSync z(true); // not strictly needed.
1910 if (_collectorState == Resizing) {
1911 compute_new_size();
1912 save_heap_summary();
1913 _collectorState = Resetting;
1914 } else {
1915 assert(_collectorState == Idling, "The state should only change"
1916 " because the foreground collector has finished the collection");
1917 }
1918 }
1919 break;
1920 }
1921 case Resetting:
1922 // CMS heap resizing has been completed
1923 reset_concurrent();
1924 assert(_collectorState == Idling, "Collector state should "
1925 "have changed");
1926
1927 MetaspaceGC::set_should_concurrent_collect(false);
1928
1929 stats().record_cms_end();
1930 // Don't move the concurrent_phases_end() and compute_new_size()
1931 // calls to here because a preempted background collection
1932 // has it's state set to "Resetting".
1933 break;
1934 case Idling:
1935 default:
1936 ShouldNotReachHere();
1937 break;
1938 }
1939 if (TraceCMSState) {
1940 gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d",
1941 p2i(Thread::current()), _collectorState);
1942 }
1943 assert(_foregroundGCShouldWait, "block post-condition");
1944 }
1945
1946 // Should this be in gc_epilogue?
1947 collector_policy()->counters()->update_counters();
1948
1949 {
1950 // Clear _foregroundGCShouldWait and, in the event that the
1951 // foreground collector is waiting, notify it, before
1952 // returning.
1953 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1954 _foregroundGCShouldWait = false;
1955 if (_foregroundGCIsActive) {
1956 CGC_lock->notify();
1957 }
1958 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1959 "Possible deadlock");
1960 }
1961 if (TraceCMSState) {
1962 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
1963 " exiting collection CMS state %d",
1964 p2i(Thread::current()), _collectorState);
1965 }
1966 if (PrintGC && Verbose) {
1967 _cmsGen->print_heap_change(prev_used);
1968 }
1969 }
1970
1971 void CMSCollector::register_gc_start(GCCause::Cause cause) {
1972 _cms_start_registered = true;
1973 _gc_timer_cm->register_gc_start();
1974 _gc_tracer_cm->report_gc_start(cause, _gc_timer_cm->gc_start());
1975 }
1976
1977 void CMSCollector::register_gc_end() {
1978 if (_cms_start_registered) {
1979 report_heap_summary(GCWhen::AfterGC);
1980
1981 _gc_timer_cm->register_gc_end();
1982 _gc_tracer_cm->report_gc_end(_gc_timer_cm->gc_end(), _gc_timer_cm->time_partitions());
1983 _cms_start_registered = false;
1984 }
1985 }
1986
1987 void CMSCollector::save_heap_summary() {
1988 GenCollectedHeap* gch = GenCollectedHeap::heap();
1989 _last_heap_summary = gch->create_heap_summary();
1990 _last_metaspace_summary = gch->create_metaspace_summary();
1991 }
1992
1993 void CMSCollector::report_heap_summary(GCWhen::Type when) {
1994 _gc_tracer_cm->report_gc_heap_summary(when, _last_heap_summary);
1995 _gc_tracer_cm->report_metaspace_summary(when, _last_metaspace_summary);
1996 }
1997
1998 bool CMSCollector::waitForForegroundGC() {
1999 bool res = false;
2000 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2001 "CMS thread should have CMS token");
2002 // Block the foreground collector until the
2003 // background collectors decides whether to
2004 // yield.
2005 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2006 _foregroundGCShouldWait = true;
2007 if (_foregroundGCIsActive) {
2008 // The background collector yields to the
2009 // foreground collector and returns a value
2010 // indicating that it has yielded. The foreground
2011 // collector can proceed.
2012 res = true;
2013 _foregroundGCShouldWait = false;
2014 ConcurrentMarkSweepThread::clear_CMS_flag(
2015 ConcurrentMarkSweepThread::CMS_cms_has_token);
2016 ConcurrentMarkSweepThread::set_CMS_flag(
2017 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2018 // Get a possibly blocked foreground thread going
2019 CGC_lock->notify();
2020 if (TraceCMSState) {
2021 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d",
2022 p2i(Thread::current()), _collectorState);
2023 }
2024 while (_foregroundGCIsActive) {
2025 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
2026 }
2027 ConcurrentMarkSweepThread::set_CMS_flag(
2028 ConcurrentMarkSweepThread::CMS_cms_has_token);
2029 ConcurrentMarkSweepThread::clear_CMS_flag(
2030 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2031 }
2032 if (TraceCMSState) {
2033 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d",
2034 p2i(Thread::current()), _collectorState);
2035 }
2036 return res;
2037 }
2038
2039 // Because of the need to lock the free lists and other structures in
2040 // the collector, common to all the generations that the collector is
2041 // collecting, we need the gc_prologues of individual CMS generations
2042 // delegate to their collector. It may have been simpler had the
2043 // current infrastructure allowed one to call a prologue on a
2044 // collector. In the absence of that we have the generation's
2045 // prologue delegate to the collector, which delegates back
2046 // some "local" work to a worker method in the individual generations
2047 // that it's responsible for collecting, while itself doing any
2048 // work common to all generations it's responsible for. A similar
2049 // comment applies to the gc_epilogue()'s.
2050 // The role of the variable _between_prologue_and_epilogue is to
2051 // enforce the invocation protocol.
2052 void CMSCollector::gc_prologue(bool full) {
2053 // Call gc_prologue_work() for the CMSGen
2054 // we are responsible for.
2055
2056 // The following locking discipline assumes that we are only called
2057 // when the world is stopped.
2058 assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption");
2059
2060 // The CMSCollector prologue must call the gc_prologues for the
2061 // "generations" that it's responsible
2062 // for.
2063
2064 assert( Thread::current()->is_VM_thread()
2065 || ( CMSScavengeBeforeRemark
2066 && Thread::current()->is_ConcurrentGC_thread()),
2067 "Incorrect thread type for prologue execution");
2068
2069 if (_between_prologue_and_epilogue) {
2070 // We have already been invoked; this is a gc_prologue delegation
2071 // from yet another CMS generation that we are responsible for, just
2072 // ignore it since all relevant work has already been done.
2073 return;
2074 }
2075
2076 // set a bit saying prologue has been called; cleared in epilogue
2077 _between_prologue_and_epilogue = true;
2078 // Claim locks for common data structures, then call gc_prologue_work()
2079 // for each CMSGen.
2080
2081 getFreelistLocks(); // gets free list locks on constituent spaces
2082 bitMapLock()->lock_without_safepoint_check();
2083
2084 // Should call gc_prologue_work() for all cms gens we are responsible for
2085 bool duringMarking = _collectorState >= Marking
2086 && _collectorState < Sweeping;
2087
2088 // The young collections clear the modified oops state, which tells if
2089 // there are any modified oops in the class. The remark phase also needs
2090 // that information. Tell the young collection to save the union of all
2091 // modified klasses.
2092 if (duringMarking) {
2093 _ct->klass_rem_set()->set_accumulate_modified_oops(true);
2094 }
2095
2096 bool registerClosure = duringMarking;
2097
2098 _cmsGen->gc_prologue_work(full, registerClosure, &_modUnionClosurePar);
2099
2100 if (!full) {
2101 stats().record_gc0_begin();
2102 }
2103 }
2104
2105 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) {
2106
2107 _capacity_at_prologue = capacity();
2108 _used_at_prologue = used();
2109
2110 // Delegate to CMScollector which knows how to coordinate between
2111 // this and any other CMS generations that it is responsible for
2112 // collecting.
2113 collector()->gc_prologue(full);
2114 }
2115
2116 // This is a "private" interface for use by this generation's CMSCollector.
2117 // Not to be called directly by any other entity (for instance,
2118 // GenCollectedHeap, which calls the "public" gc_prologue method above).
2119 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full,
2120 bool registerClosure, ModUnionClosure* modUnionClosure) {
2121 assert(!incremental_collection_failed(), "Shouldn't be set yet");
2122 assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL,
2123 "Should be NULL");
2124 if (registerClosure) {
2125 cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure);
2126 }
2127 cmsSpace()->gc_prologue();
2128 // Clear stat counters
2129 NOT_PRODUCT(
2130 assert(_numObjectsPromoted == 0, "check");
2131 assert(_numWordsPromoted == 0, "check");
2132 if (Verbose && PrintGC) {
2133 gclog_or_tty->print("Allocated " SIZE_FORMAT " objects, "
2134 SIZE_FORMAT " bytes concurrently",
2135 _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord));
2136 }
2137 _numObjectsAllocated = 0;
2138 _numWordsAllocated = 0;
2139 )
2140 }
2141
2142 void CMSCollector::gc_epilogue(bool full) {
2143 // The following locking discipline assumes that we are only called
2144 // when the world is stopped.
2145 assert(SafepointSynchronize::is_at_safepoint(),
2146 "world is stopped assumption");
2147
2148 // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks
2149 // if linear allocation blocks need to be appropriately marked to allow the
2150 // the blocks to be parsable. We also check here whether we need to nudge the
2151 // CMS collector thread to start a new cycle (if it's not already active).
2152 assert( Thread::current()->is_VM_thread()
2153 || ( CMSScavengeBeforeRemark
2154 && Thread::current()->is_ConcurrentGC_thread()),
2155 "Incorrect thread type for epilogue execution");
2156
2157 if (!_between_prologue_and_epilogue) {
2158 // We have already been invoked; this is a gc_epilogue delegation
2159 // from yet another CMS generation that we are responsible for, just
2160 // ignore it since all relevant work has already been done.
2161 return;
2162 }
2163 assert(haveFreelistLocks(), "must have freelist locks");
2164 assert_lock_strong(bitMapLock());
2165
2166 _ct->klass_rem_set()->set_accumulate_modified_oops(false);
2167
2168 _cmsGen->gc_epilogue_work(full);
2169
2170 if (_collectorState == AbortablePreclean || _collectorState == Precleaning) {
2171 // in case sampling was not already enabled, enable it
2172 _start_sampling = true;
2173 }
2174 // reset _eden_chunk_array so sampling starts afresh
2175 _eden_chunk_index = 0;
2176
2177 size_t cms_used = _cmsGen->cmsSpace()->used();
2178
2179 // update performance counters - this uses a special version of
2180 // update_counters() that allows the utilization to be passed as a
2181 // parameter, avoiding multiple calls to used().
2182 //
2183 _cmsGen->update_counters(cms_used);
2184
2185 bitMapLock()->unlock();
2186 releaseFreelistLocks();
2187
2188 if (!CleanChunkPoolAsync) {
2189 Chunk::clean_chunk_pool();
2190 }
2191
2192 set_did_compact(false);
2193 _between_prologue_and_epilogue = false; // ready for next cycle
2194 }
2195
2196 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) {
2197 collector()->gc_epilogue(full);
2198
2199 // Also reset promotion tracking in par gc thread states.
2200 for (uint i = 0; i < ParallelGCThreads; i++) {
2201 _par_gc_thread_states[i]->promo.stopTrackingPromotions(i);
2202 }
2203 }
2204
2205 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2206 assert(!incremental_collection_failed(), "Should have been cleared");
2207 cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2208 cmsSpace()->gc_epilogue();
2209 // Print stat counters
2210 NOT_PRODUCT(
2211 assert(_numObjectsAllocated == 0, "check");
2212 assert(_numWordsAllocated == 0, "check");
2213 if (Verbose && PrintGC) {
2214 gclog_or_tty->print("Promoted " SIZE_FORMAT " objects, "
2215 SIZE_FORMAT " bytes",
2216 _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2217 }
2218 _numObjectsPromoted = 0;
2219 _numWordsPromoted = 0;
2220 )
2221
2222 if (PrintGC && Verbose) {
2223 // Call down the chain in contiguous_available needs the freelistLock
2224 // so print this out before releasing the freeListLock.
2225 gclog_or_tty->print(" Contiguous available " SIZE_FORMAT " bytes ",
2226 contiguous_available());
2227 }
2228 }
2229
2230 #ifndef PRODUCT
2231 bool CMSCollector::have_cms_token() {
2232 Thread* thr = Thread::current();
2233 if (thr->is_VM_thread()) {
2234 return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2235 } else if (thr->is_ConcurrentGC_thread()) {
2236 return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2237 } else if (thr->is_GC_task_thread()) {
2238 return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2239 ParGCRareEvent_lock->owned_by_self();
2240 }
2241 return false;
2242 }
2243
2244 // Check reachability of the given heap address in CMS generation,
2245 // treating all other generations as roots.
2246 bool CMSCollector::is_cms_reachable(HeapWord* addr) {
2247 // We could "guarantee" below, rather than assert, but I'll
2248 // leave these as "asserts" so that an adventurous debugger
2249 // could try this in the product build provided some subset of
2250 // the conditions were met, provided they were interested in the
2251 // results and knew that the computation below wouldn't interfere
2252 // with other concurrent computations mutating the structures
2253 // being read or written.
2254 assert(SafepointSynchronize::is_at_safepoint(),
2255 "Else mutations in object graph will make answer suspect");
2256 assert(have_cms_token(), "Should hold cms token");
2257 assert(haveFreelistLocks(), "must hold free list locks");
2258 assert_lock_strong(bitMapLock());
2259
2260 // Clear the marking bit map array before starting, but, just
2261 // for kicks, first report if the given address is already marked
2262 tty->print_cr("Start: Address " PTR_FORMAT " is%s marked", p2i(addr),
2263 _markBitMap.isMarked(addr) ? "" : " not");
2264
2265 if (verify_after_remark()) {
2266 MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2267 bool result = verification_mark_bm()->isMarked(addr);
2268 tty->print_cr("TransitiveMark: Address " PTR_FORMAT " %s marked", p2i(addr),
2269 result ? "IS" : "is NOT");
2270 return result;
2271 } else {
2272 tty->print_cr("Could not compute result");
2273 return false;
2274 }
2275 }
2276 #endif
2277
2278 void
2279 CMSCollector::print_on_error(outputStream* st) {
2280 CMSCollector* collector = ConcurrentMarkSweepGeneration::_collector;
2281 if (collector != NULL) {
2282 CMSBitMap* bitmap = &collector->_markBitMap;
2283 st->print_cr("Marking Bits: (CMSBitMap*) " PTR_FORMAT, p2i(bitmap));
2284 bitmap->print_on_error(st, " Bits: ");
2285
2286 st->cr();
2287
2288 CMSBitMap* mut_bitmap = &collector->_modUnionTable;
2289 st->print_cr("Mod Union Table: (CMSBitMap*) " PTR_FORMAT, p2i(mut_bitmap));
2290 mut_bitmap->print_on_error(st, " Bits: ");
2291 }
2292 }
2293
2294 ////////////////////////////////////////////////////////
2295 // CMS Verification Support
2296 ////////////////////////////////////////////////////////
2297 // Following the remark phase, the following invariant
2298 // should hold -- each object in the CMS heap which is
2299 // marked in markBitMap() should be marked in the verification_mark_bm().
2300
2301 class VerifyMarkedClosure: public BitMapClosure {
2302 CMSBitMap* _marks;
2303 bool _failed;
2304
2305 public:
2306 VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2307
2308 bool do_bit(size_t offset) {
2309 HeapWord* addr = _marks->offsetToHeapWord(offset);
2310 if (!_marks->isMarked(addr)) {
2311 oop(addr)->print_on(gclog_or_tty);
2312 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
2313 _failed = true;
2314 }
2315 return true;
2316 }
2317
2318 bool failed() { return _failed; }
2319 };
2320
2321 bool CMSCollector::verify_after_remark(bool silent) {
2322 if (!silent) gclog_or_tty->print(" [Verifying CMS Marking... ");
2323 MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2324 static bool init = false;
2325
2326 assert(SafepointSynchronize::is_at_safepoint(),
2327 "Else mutations in object graph will make answer suspect");
2328 assert(have_cms_token(),
2329 "Else there may be mutual interference in use of "
2330 " verification data structures");
2331 assert(_collectorState > Marking && _collectorState <= Sweeping,
2332 "Else marking info checked here may be obsolete");
2333 assert(haveFreelistLocks(), "must hold free list locks");
2334 assert_lock_strong(bitMapLock());
2335
2336
2337 // Allocate marking bit map if not already allocated
2338 if (!init) { // first time
2339 if (!verification_mark_bm()->allocate(_span)) {
2340 return false;
2341 }
2342 init = true;
2343 }
2344
2345 assert(verification_mark_stack()->isEmpty(), "Should be empty");
2346
2347 // Turn off refs discovery -- so we will be tracing through refs.
2348 // This is as intended, because by this time
2349 // GC must already have cleared any refs that need to be cleared,
2350 // and traced those that need to be marked; moreover,
2351 // the marking done here is not going to interfere in any
2352 // way with the marking information used by GC.
2353 NoRefDiscovery no_discovery(ref_processor());
2354
2355 #if defined(COMPILER2) || INCLUDE_JVMCI
2356 DerivedPointerTableDeactivate dpt_deact;
2357 #endif
2358
2359 // Clear any marks from a previous round
2360 verification_mark_bm()->clear_all();
2361 assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
2362 verify_work_stacks_empty();
2363
2364 GenCollectedHeap* gch = GenCollectedHeap::heap();
2365 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
2366 // Update the saved marks which may affect the root scans.
2367 gch->save_marks();
2368
2369 if (CMSRemarkVerifyVariant == 1) {
2370 // In this first variant of verification, we complete
2371 // all marking, then check if the new marks-vector is
2372 // a subset of the CMS marks-vector.
2373 verify_after_remark_work_1();
2374 } else if (CMSRemarkVerifyVariant == 2) {
2375 // In this second variant of verification, we flag an error
2376 // (i.e. an object reachable in the new marks-vector not reachable
2377 // in the CMS marks-vector) immediately, also indicating the
2378 // identify of an object (A) that references the unmarked object (B) --
2379 // presumably, a mutation to A failed to be picked up by preclean/remark?
2380 verify_after_remark_work_2();
2381 } else {
2382 warning("Unrecognized value " UINTX_FORMAT " for CMSRemarkVerifyVariant",
2383 CMSRemarkVerifyVariant);
2384 }
2385 if (!silent) gclog_or_tty->print(" done] ");
2386 return true;
2387 }
2388
2389 void CMSCollector::verify_after_remark_work_1() {
2390 ResourceMark rm;
2391 HandleMark hm;
2392 GenCollectedHeap* gch = GenCollectedHeap::heap();
2393
2394 // Get a clear set of claim bits for the roots processing to work with.
2395 ClassLoaderDataGraph::clear_claimed_marks();
2396
2397 // Mark from roots one level into CMS
2398 MarkRefsIntoClosure notOlder(_span, verification_mark_bm());
2399 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2400
2401 {
2402 StrongRootsScope srs(1);
2403
2404 gch->gen_process_roots(&srs,
2405 GenCollectedHeap::OldGen,
2406 true, // young gen as roots
2407 GenCollectedHeap::ScanningOption(roots_scanning_options()),
2408 should_unload_classes(),
2409 ¬Older,
2410 NULL,
2411 NULL);
2412 }
2413
2414 // Now mark from the roots
2415 MarkFromRootsClosure markFromRootsClosure(this, _span,
2416 verification_mark_bm(), verification_mark_stack(),
2417 false /* don't yield */, true /* verifying */);
2418 assert(_restart_addr == NULL, "Expected pre-condition");
2419 verification_mark_bm()->iterate(&markFromRootsClosure);
2420 while (_restart_addr != NULL) {
2421 // Deal with stack overflow: by restarting at the indicated
2422 // address.
2423 HeapWord* ra = _restart_addr;
2424 markFromRootsClosure.reset(ra);
2425 _restart_addr = NULL;
2426 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2427 }
2428 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2429 verify_work_stacks_empty();
2430
2431 // Marking completed -- now verify that each bit marked in
2432 // verification_mark_bm() is also marked in markBitMap(); flag all
2433 // errors by printing corresponding objects.
2434 VerifyMarkedClosure vcl(markBitMap());
2435 verification_mark_bm()->iterate(&vcl);
2436 if (vcl.failed()) {
2437 gclog_or_tty->print("Verification failed");
2438 gch->print_on(gclog_or_tty);
2439 fatal("CMS: failed marking verification after remark");
2440 }
2441 }
2442
2443 class VerifyKlassOopsKlassClosure : public KlassClosure {
2444 class VerifyKlassOopsClosure : public OopClosure {
2445 CMSBitMap* _bitmap;
2446 public:
2447 VerifyKlassOopsClosure(CMSBitMap* bitmap) : _bitmap(bitmap) { }
2448 void do_oop(oop* p) { guarantee(*p == NULL || _bitmap->isMarked((HeapWord*) *p), "Should be marked"); }
2449 void do_oop(narrowOop* p) { ShouldNotReachHere(); }
2450 } _oop_closure;
2451 public:
2452 VerifyKlassOopsKlassClosure(CMSBitMap* bitmap) : _oop_closure(bitmap) {}
2453 void do_klass(Klass* k) {
2454 k->oops_do(&_oop_closure);
2455 }
2456 };
2457
2458 void CMSCollector::verify_after_remark_work_2() {
2459 ResourceMark rm;
2460 HandleMark hm;
2461 GenCollectedHeap* gch = GenCollectedHeap::heap();
2462
2463 // Get a clear set of claim bits for the roots processing to work with.
2464 ClassLoaderDataGraph::clear_claimed_marks();
2465
2466 // Mark from roots one level into CMS
2467 MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
2468 markBitMap());
2469 CLDToOopClosure cld_closure(¬Older, true);
2470
2471 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2472
2473 {
2474 StrongRootsScope srs(1);
2475
2476 gch->gen_process_roots(&srs,
2477 GenCollectedHeap::OldGen,
2478 true, // young gen as roots
2479 GenCollectedHeap::ScanningOption(roots_scanning_options()),
2480 should_unload_classes(),
2481 ¬Older,
2482 NULL,
2483 &cld_closure);
2484 }
2485
2486 // Now mark from the roots
2487 MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
2488 verification_mark_bm(), markBitMap(), verification_mark_stack());
2489 assert(_restart_addr == NULL, "Expected pre-condition");
2490 verification_mark_bm()->iterate(&markFromRootsClosure);
2491 while (_restart_addr != NULL) {
2492 // Deal with stack overflow: by restarting at the indicated
2493 // address.
2494 HeapWord* ra = _restart_addr;
2495 markFromRootsClosure.reset(ra);
2496 _restart_addr = NULL;
2497 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2498 }
2499 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2500 verify_work_stacks_empty();
2501
2502 VerifyKlassOopsKlassClosure verify_klass_oops(verification_mark_bm());
2503 ClassLoaderDataGraph::classes_do(&verify_klass_oops);
2504
2505 // Marking completed -- now verify that each bit marked in
2506 // verification_mark_bm() is also marked in markBitMap(); flag all
2507 // errors by printing corresponding objects.
2508 VerifyMarkedClosure vcl(markBitMap());
2509 verification_mark_bm()->iterate(&vcl);
2510 assert(!vcl.failed(), "Else verification above should not have succeeded");
2511 }
2512
2513 void ConcurrentMarkSweepGeneration::save_marks() {
2514 // delegate to CMS space
2515 cmsSpace()->save_marks();
2516 for (uint i = 0; i < ParallelGCThreads; i++) {
2517 _par_gc_thread_states[i]->promo.startTrackingPromotions();
2518 }
2519 }
2520
2521 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
2522 return cmsSpace()->no_allocs_since_save_marks();
2523 }
2524
2525 #define CMS_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix) \
2526 \
2527 void ConcurrentMarkSweepGeneration:: \
2528 oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) { \
2529 cl->set_generation(this); \
2530 cmsSpace()->oop_since_save_marks_iterate##nv_suffix(cl); \
2531 cl->reset_generation(); \
2532 save_marks(); \
2533 }
2534
2535 ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DEFN)
2536
2537 void
2538 ConcurrentMarkSweepGeneration::oop_iterate(ExtendedOopClosure* cl) {
2539 if (freelistLock()->owned_by_self()) {
2540 Generation::oop_iterate(cl);
2541 } else {
2542 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2543 Generation::oop_iterate(cl);
2544 }
2545 }
2546
2547 void
2548 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
2549 if (freelistLock()->owned_by_self()) {
2550 Generation::object_iterate(cl);
2551 } else {
2552 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2553 Generation::object_iterate(cl);
2554 }
2555 }
2556
2557 void
2558 ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) {
2559 if (freelistLock()->owned_by_self()) {
2560 Generation::safe_object_iterate(cl);
2561 } else {
2562 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2563 Generation::safe_object_iterate(cl);
2564 }
2565 }
2566
2567 void
2568 ConcurrentMarkSweepGeneration::post_compact() {
2569 }
2570
2571 void
2572 ConcurrentMarkSweepGeneration::prepare_for_verify() {
2573 // Fix the linear allocation blocks to look like free blocks.
2574
2575 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2576 // are not called when the heap is verified during universe initialization and
2577 // at vm shutdown.
2578 if (freelistLock()->owned_by_self()) {
2579 cmsSpace()->prepare_for_verify();
2580 } else {
2581 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2582 cmsSpace()->prepare_for_verify();
2583 }
2584 }
2585
2586 void
2587 ConcurrentMarkSweepGeneration::verify() {
2588 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2589 // are not called when the heap is verified during universe initialization and
2590 // at vm shutdown.
2591 if (freelistLock()->owned_by_self()) {
2592 cmsSpace()->verify();
2593 } else {
2594 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2595 cmsSpace()->verify();
2596 }
2597 }
2598
2599 void CMSCollector::verify() {
2600 _cmsGen->verify();
2601 }
2602
2603 #ifndef PRODUCT
2604 bool CMSCollector::overflow_list_is_empty() const {
2605 assert(_num_par_pushes >= 0, "Inconsistency");
2606 if (_overflow_list == NULL) {
2607 assert(_num_par_pushes == 0, "Inconsistency");
2608 }
2609 return _overflow_list == NULL;
2610 }
2611
2612 // The methods verify_work_stacks_empty() and verify_overflow_empty()
2613 // merely consolidate assertion checks that appear to occur together frequently.
2614 void CMSCollector::verify_work_stacks_empty() const {
2615 assert(_markStack.isEmpty(), "Marking stack should be empty");
2616 assert(overflow_list_is_empty(), "Overflow list should be empty");
2617 }
2618
2619 void CMSCollector::verify_overflow_empty() const {
2620 assert(overflow_list_is_empty(), "Overflow list should be empty");
2621 assert(no_preserved_marks(), "No preserved marks");
2622 }
2623 #endif // PRODUCT
2624
2625 // Decide if we want to enable class unloading as part of the
2626 // ensuing concurrent GC cycle. We will collect and
2627 // unload classes if it's the case that:
2628 // (1) an explicit gc request has been made and the flag
2629 // ExplicitGCInvokesConcurrentAndUnloadsClasses is set, OR
2630 // (2) (a) class unloading is enabled at the command line, and
2631 // (b) old gen is getting really full
2632 // NOTE: Provided there is no change in the state of the heap between
2633 // calls to this method, it should have idempotent results. Moreover,
2634 // its results should be monotonically increasing (i.e. going from 0 to 1,
2635 // but not 1 to 0) between successive calls between which the heap was
2636 // not collected. For the implementation below, it must thus rely on
2637 // the property that concurrent_cycles_since_last_unload()
2638 // will not decrease unless a collection cycle happened and that
2639 // _cmsGen->is_too_full() are
2640 // themselves also monotonic in that sense. See check_monotonicity()
2641 // below.
2642 void CMSCollector::update_should_unload_classes() {
2643 _should_unload_classes = false;
2644 // Condition 1 above
2645 if (_full_gc_requested && ExplicitGCInvokesConcurrentAndUnloadsClasses) {
2646 _should_unload_classes = true;
2647 } else if (CMSClassUnloadingEnabled) { // Condition 2.a above
2648 // Disjuncts 2.b.(i,ii,iii) above
2649 _should_unload_classes = (concurrent_cycles_since_last_unload() >=
2650 CMSClassUnloadingMaxInterval)
2651 || _cmsGen->is_too_full();
2652 }
2653 }
2654
2655 bool ConcurrentMarkSweepGeneration::is_too_full() const {
2656 bool res = should_concurrent_collect();
2657 res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
2658 return res;
2659 }
2660
2661 void CMSCollector::setup_cms_unloading_and_verification_state() {
2662 const bool should_verify = VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
2663 || VerifyBeforeExit;
2664 const int rso = GenCollectedHeap::SO_AllCodeCache;
2665
2666 // We set the proper root for this CMS cycle here.
2667 if (should_unload_classes()) { // Should unload classes this cycle
2668 remove_root_scanning_option(rso); // Shrink the root set appropriately
2669 set_verifying(should_verify); // Set verification state for this cycle
2670 return; // Nothing else needs to be done at this time
2671 }
2672
2673 // Not unloading classes this cycle
2674 assert(!should_unload_classes(), "Inconsistency!");
2675
2676 // If we are not unloading classes then add SO_AllCodeCache to root
2677 // scanning options.
2678 add_root_scanning_option(rso);
2679
2680 if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
2681 set_verifying(true);
2682 } else if (verifying() && !should_verify) {
2683 // We were verifying, but some verification flags got disabled.
2684 set_verifying(false);
2685 // Exclude symbols, strings and code cache elements from root scanning to
2686 // reduce IM and RM pauses.
2687 remove_root_scanning_option(rso);
2688 }
2689 }
2690
2691
2692 #ifndef PRODUCT
2693 HeapWord* CMSCollector::block_start(const void* p) const {
2694 const HeapWord* addr = (HeapWord*)p;
2695 if (_span.contains(p)) {
2696 if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
2697 return _cmsGen->cmsSpace()->block_start(p);
2698 }
2699 }
2700 return NULL;
2701 }
2702 #endif
2703
2704 HeapWord*
2705 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
2706 bool tlab,
2707 bool parallel) {
2708 CMSSynchronousYieldRequest yr;
2709 assert(!tlab, "Can't deal with TLAB allocation");
2710 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2711 expand_for_gc_cause(word_size*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_allocation);
2712 if (GCExpandToAllocateDelayMillis > 0) {
2713 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2714 }
2715 return have_lock_and_allocate(word_size, tlab);
2716 }
2717
2718 void ConcurrentMarkSweepGeneration::expand_for_gc_cause(
2719 size_t bytes,
2720 size_t expand_bytes,
2721 CMSExpansionCause::Cause cause)
2722 {
2723
2724 bool success = expand(bytes, expand_bytes);
2725
2726 // remember why we expanded; this information is used
2727 // by shouldConcurrentCollect() when making decisions on whether to start
2728 // a new CMS cycle.
2729 if (success) {
2730 set_expansion_cause(cause);
2731 if (PrintGCDetails && Verbose) {
2732 gclog_or_tty->print_cr("Expanded CMS gen for %s",
2733 CMSExpansionCause::to_string(cause));
2734 }
2735 }
2736 }
2737
2738 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
2739 HeapWord* res = NULL;
2740 MutexLocker x(ParGCRareEvent_lock);
2741 while (true) {
2742 // Expansion by some other thread might make alloc OK now:
2743 res = ps->lab.alloc(word_sz);
2744 if (res != NULL) return res;
2745 // If there's not enough expansion space available, give up.
2746 if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
2747 return NULL;
2748 }
2749 // Otherwise, we try expansion.
2750 expand_for_gc_cause(word_sz*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_lab);
2751 // Now go around the loop and try alloc again;
2752 // A competing par_promote might beat us to the expansion space,
2753 // so we may go around the loop again if promotion fails again.
2754 if (GCExpandToAllocateDelayMillis > 0) {
2755 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2756 }
2757 }
2758 }
2759
2760
2761 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
2762 PromotionInfo* promo) {
2763 MutexLocker x(ParGCRareEvent_lock);
2764 size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
2765 while (true) {
2766 // Expansion by some other thread might make alloc OK now:
2767 if (promo->ensure_spooling_space()) {
2768 assert(promo->has_spooling_space(),
2769 "Post-condition of successful ensure_spooling_space()");
2770 return true;
2771 }
2772 // If there's not enough expansion space available, give up.
2773 if (_virtual_space.uncommitted_size() < refill_size_bytes) {
2774 return false;
2775 }
2776 // Otherwise, we try expansion.
2777 expand_for_gc_cause(refill_size_bytes, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_spooling_space);
2778 // Now go around the loop and try alloc again;
2779 // A competing allocation might beat us to the expansion space,
2780 // so we may go around the loop again if allocation fails again.
2781 if (GCExpandToAllocateDelayMillis > 0) {
2782 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2783 }
2784 }
2785 }
2786
2787 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
2788 // Only shrink if a compaction was done so that all the free space
2789 // in the generation is in a contiguous block at the end.
2790 if (did_compact()) {
2791 CardGeneration::shrink(bytes);
2792 }
2793 }
2794
2795 void ConcurrentMarkSweepGeneration::assert_correct_size_change_locking() {
2796 assert_locked_or_safepoint(Heap_lock);
2797 }
2798
2799 void ConcurrentMarkSweepGeneration::shrink_free_list_by(size_t bytes) {
2800 assert_locked_or_safepoint(Heap_lock);
2801 assert_lock_strong(freelistLock());
2802 if (PrintGCDetails && Verbose) {
2803 warning("Shrinking of CMS not yet implemented");
2804 }
2805 return;
2806 }
2807
2808
2809 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
2810 // phases.
2811 class CMSPhaseAccounting: public StackObj {
2812 public:
2813 CMSPhaseAccounting(CMSCollector *collector,
2814 const char *phase,
2815 bool print_cr = true);
2816 ~CMSPhaseAccounting();
2817
2818 private:
2819 CMSCollector *_collector;
2820 const char *_phase;
2821 elapsedTimer _wallclock;
2822 bool _print_cr;
2823
2824 public:
2825 // Not MT-safe; so do not pass around these StackObj's
2826 // where they may be accessed by other threads.
2827 jlong wallclock_millis() {
2828 assert(_wallclock.is_active(), "Wall clock should not stop");
2829 _wallclock.stop(); // to record time
2830 jlong ret = _wallclock.milliseconds();
2831 _wallclock.start(); // restart
2832 return ret;
2833 }
2834 };
2835
2836 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
2837 const char *phase,
2838 bool print_cr) :
2839 _collector(collector), _phase(phase), _print_cr(print_cr) {
2840
2841 if (PrintCMSStatistics != 0) {
2842 _collector->resetYields();
2843 }
2844 if (PrintGCDetails) {
2845 gclog_or_tty->gclog_stamp();
2846 gclog_or_tty->print_cr("[%s-concurrent-%s-start]",
2847 _collector->cmsGen()->short_name(), _phase);
2848 }
2849 _collector->resetTimer();
2850 _wallclock.start();
2851 _collector->startTimer();
2852 }
2853
2854 CMSPhaseAccounting::~CMSPhaseAccounting() {
2855 assert(_wallclock.is_active(), "Wall clock should not have stopped");
2856 _collector->stopTimer();
2857 _wallclock.stop();
2858 if (PrintGCDetails) {
2859 gclog_or_tty->gclog_stamp();
2860 gclog_or_tty->print("[%s-concurrent-%s: %3.3f/%3.3f secs]",
2861 _collector->cmsGen()->short_name(),
2862 _phase, _collector->timerValue(), _wallclock.seconds());
2863 if (_print_cr) {
2864 gclog_or_tty->cr();
2865 }
2866 if (PrintCMSStatistics != 0) {
2867 gclog_or_tty->print_cr(" (CMS-concurrent-%s yielded %d times)", _phase,
2868 _collector->yields());
2869 }
2870 }
2871 }
2872
2873 // CMS work
2874
2875 // The common parts of CMSParInitialMarkTask and CMSParRemarkTask.
2876 class CMSParMarkTask : public AbstractGangTask {
2877 protected:
2878 CMSCollector* _collector;
2879 uint _n_workers;
2880 CMSParMarkTask(const char* name, CMSCollector* collector, uint n_workers) :
2881 AbstractGangTask(name),
2882 _collector(collector),
2883 _n_workers(n_workers) {}
2884 // Work method in support of parallel rescan ... of young gen spaces
2885 void do_young_space_rescan(uint worker_id, OopsInGenClosure* cl,
2886 ContiguousSpace* space,
2887 HeapWord** chunk_array, size_t chunk_top);
2888 void work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl);
2889 };
2890
2891 // Parallel initial mark task
2892 class CMSParInitialMarkTask: public CMSParMarkTask {
2893 StrongRootsScope* _strong_roots_scope;
2894 public:
2895 CMSParInitialMarkTask(CMSCollector* collector, StrongRootsScope* strong_roots_scope, uint n_workers) :
2896 CMSParMarkTask("Scan roots and young gen for initial mark in parallel", collector, n_workers),
2897 _strong_roots_scope(strong_roots_scope) {}
2898 void work(uint worker_id);
2899 };
2900
2901 // Checkpoint the roots into this generation from outside
2902 // this generation. [Note this initial checkpoint need only
2903 // be approximate -- we'll do a catch up phase subsequently.]
2904 void CMSCollector::checkpointRootsInitial() {
2905 assert(_collectorState == InitialMarking, "Wrong collector state");
2906 check_correct_thread_executing();
2907 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
2908
2909 save_heap_summary();
2910 report_heap_summary(GCWhen::BeforeGC);
2911
2912 ReferenceProcessor* rp = ref_processor();
2913 assert(_restart_addr == NULL, "Control point invariant");
2914 {
2915 // acquire locks for subsequent manipulations
2916 MutexLockerEx x(bitMapLock(),
2917 Mutex::_no_safepoint_check_flag);
2918 checkpointRootsInitialWork();
2919 // enable ("weak") refs discovery
2920 rp->enable_discovery();
2921 _collectorState = Marking;
2922 }
2923 }
2924
2925 void CMSCollector::checkpointRootsInitialWork() {
2926 assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
2927 assert(_collectorState == InitialMarking, "just checking");
2928
2929 // Already have locks.
2930 assert_lock_strong(bitMapLock());
2931 assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
2932
2933 // Setup the verification and class unloading state for this
2934 // CMS collection cycle.
2935 setup_cms_unloading_and_verification_state();
2936
2937 NOT_PRODUCT(GCTraceTime t("\ncheckpointRootsInitialWork",
2938 PrintGCDetails && Verbose, true, _gc_timer_cm);)
2939
2940 // Reset all the PLAB chunk arrays if necessary.
2941 if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
2942 reset_survivor_plab_arrays();
2943 }
2944
2945 ResourceMark rm;
2946 HandleMark hm;
2947
2948 MarkRefsIntoClosure notOlder(_span, &_markBitMap);
2949 GenCollectedHeap* gch = GenCollectedHeap::heap();
2950
2951 verify_work_stacks_empty();
2952 verify_overflow_empty();
2953
2954 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
2955 // Update the saved marks which may affect the root scans.
2956 gch->save_marks();
2957
2958 // weak reference processing has not started yet.
2959 ref_processor()->set_enqueuing_is_done(false);
2960
2961 // Need to remember all newly created CLDs,
2962 // so that we can guarantee that the remark finds them.
2963 ClassLoaderDataGraph::remember_new_clds(true);
2964
2965 // Whenever a CLD is found, it will be claimed before proceeding to mark
2966 // the klasses. The claimed marks need to be cleared before marking starts.
2967 ClassLoaderDataGraph::clear_claimed_marks();
2968
2969 if (CMSPrintEdenSurvivorChunks) {
2970 print_eden_and_survivor_chunk_arrays();
2971 }
2972
2973 {
2974 #if defined(COMPILER2) || INCLUDE_JVMCI
2975 DerivedPointerTableDeactivate dpt_deact;
2976 #endif
2977 if (CMSParallelInitialMarkEnabled) {
2978 // The parallel version.
2979 WorkGang* workers = gch->workers();
2980 assert(workers != NULL, "Need parallel worker threads.");
2981 uint n_workers = workers->active_workers();
2982
2983 StrongRootsScope srs(n_workers);
2984
2985 CMSParInitialMarkTask tsk(this, &srs, n_workers);
2986 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
2987 if (n_workers > 1) {
2988 workers->run_task(&tsk);
2989 } else {
2990 tsk.work(0);
2991 }
2992 } else {
2993 // The serial version.
2994 CLDToOopClosure cld_closure(¬Older, true);
2995 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2996
2997 StrongRootsScope srs(1);
2998
2999 gch->gen_process_roots(&srs,
3000 GenCollectedHeap::OldGen,
3001 true, // young gen as roots
3002 GenCollectedHeap::ScanningOption(roots_scanning_options()),
3003 should_unload_classes(),
3004 ¬Older,
3005 NULL,
3006 &cld_closure);
3007 }
3008 }
3009
3010 // Clear mod-union table; it will be dirtied in the prologue of
3011 // CMS generation per each young generation collection.
3012
3013 assert(_modUnionTable.isAllClear(),
3014 "Was cleared in most recent final checkpoint phase"
3015 " or no bits are set in the gc_prologue before the start of the next "
3016 "subsequent marking phase.");
3017
3018 assert(_ct->klass_rem_set()->mod_union_is_clear(), "Must be");
3019
3020 // Save the end of the used_region of the constituent generations
3021 // to be used to limit the extent of sweep in each generation.
3022 save_sweep_limits();
3023 verify_overflow_empty();
3024 }
3025
3026 bool CMSCollector::markFromRoots() {
3027 // we might be tempted to assert that:
3028 // assert(!SafepointSynchronize::is_at_safepoint(),
3029 // "inconsistent argument?");
3030 // However that wouldn't be right, because it's possible that
3031 // a safepoint is indeed in progress as a young generation
3032 // stop-the-world GC happens even as we mark in this generation.
3033 assert(_collectorState == Marking, "inconsistent state?");
3034 check_correct_thread_executing();
3035 verify_overflow_empty();
3036
3037 // Weak ref discovery note: We may be discovering weak
3038 // refs in this generation concurrent (but interleaved) with
3039 // weak ref discovery by the young generation collector.
3040
3041 CMSTokenSyncWithLocks ts(true, bitMapLock());
3042 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3043 CMSPhaseAccounting pa(this, "mark", !PrintGCDetails);
3044 bool res = markFromRootsWork();
3045 if (res) {
3046 _collectorState = Precleaning;
3047 } else { // We failed and a foreground collection wants to take over
3048 assert(_foregroundGCIsActive, "internal state inconsistency");
3049 assert(_restart_addr == NULL, "foreground will restart from scratch");
3050 if (PrintGCDetails) {
3051 gclog_or_tty->print_cr("bailing out to foreground collection");
3052 }
3053 }
3054 verify_overflow_empty();
3055 return res;
3056 }
3057
3058 bool CMSCollector::markFromRootsWork() {
3059 // iterate over marked bits in bit map, doing a full scan and mark
3060 // from these roots using the following algorithm:
3061 // . if oop is to the right of the current scan pointer,
3062 // mark corresponding bit (we'll process it later)
3063 // . else (oop is to left of current scan pointer)
3064 // push oop on marking stack
3065 // . drain the marking stack
3066
3067 // Note that when we do a marking step we need to hold the
3068 // bit map lock -- recall that direct allocation (by mutators)
3069 // and promotion (by the young generation collector) is also
3070 // marking the bit map. [the so-called allocate live policy.]
3071 // Because the implementation of bit map marking is not
3072 // robust wrt simultaneous marking of bits in the same word,
3073 // we need to make sure that there is no such interference
3074 // between concurrent such updates.
3075
3076 // already have locks
3077 assert_lock_strong(bitMapLock());
3078
3079 verify_work_stacks_empty();
3080 verify_overflow_empty();
3081 bool result = false;
3082 if (CMSConcurrentMTEnabled && ConcGCThreads > 0) {
3083 result = do_marking_mt();
3084 } else {
3085 result = do_marking_st();
3086 }
3087 return result;
3088 }
3089
3090 // Forward decl
3091 class CMSConcMarkingTask;
3092
3093 class CMSConcMarkingTerminator: public ParallelTaskTerminator {
3094 CMSCollector* _collector;
3095 CMSConcMarkingTask* _task;
3096 public:
3097 virtual void yield();
3098
3099 // "n_threads" is the number of threads to be terminated.
3100 // "queue_set" is a set of work queues of other threads.
3101 // "collector" is the CMS collector associated with this task terminator.
3102 // "yield" indicates whether we need the gang as a whole to yield.
3103 CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
3104 ParallelTaskTerminator(n_threads, queue_set),
3105 _collector(collector) { }
3106
3107 void set_task(CMSConcMarkingTask* task) {
3108 _task = task;
3109 }
3110 };
3111
3112 class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator {
3113 CMSConcMarkingTask* _task;
3114 public:
3115 bool should_exit_termination();
3116 void set_task(CMSConcMarkingTask* task) {
3117 _task = task;
3118 }
3119 };
3120
3121 // MT Concurrent Marking Task
3122 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3123 CMSCollector* _collector;
3124 uint _n_workers; // requested/desired # workers
3125 bool _result;
3126 CompactibleFreeListSpace* _cms_space;
3127 char _pad_front[64]; // padding to ...
3128 HeapWord* _global_finger; // ... avoid sharing cache line
3129 char _pad_back[64];
3130 HeapWord* _restart_addr;
3131
3132 // Exposed here for yielding support
3133 Mutex* const _bit_map_lock;
3134
3135 // The per thread work queues, available here for stealing
3136 OopTaskQueueSet* _task_queues;
3137
3138 // Termination (and yielding) support
3139 CMSConcMarkingTerminator _term;
3140 CMSConcMarkingTerminatorTerminator _term_term;
3141
3142 public:
3143 CMSConcMarkingTask(CMSCollector* collector,
3144 CompactibleFreeListSpace* cms_space,
3145 YieldingFlexibleWorkGang* workers,
3146 OopTaskQueueSet* task_queues):
3147 YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3148 _collector(collector),
3149 _cms_space(cms_space),
3150 _n_workers(0), _result(true),
3151 _task_queues(task_queues),
3152 _term(_n_workers, task_queues, _collector),
3153 _bit_map_lock(collector->bitMapLock())
3154 {
3155 _requested_size = _n_workers;
3156 _term.set_task(this);
3157 _term_term.set_task(this);
3158 _restart_addr = _global_finger = _cms_space->bottom();
3159 }
3160
3161
3162 OopTaskQueueSet* task_queues() { return _task_queues; }
3163
3164 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3165
3166 HeapWord** global_finger_addr() { return &_global_finger; }
3167
3168 CMSConcMarkingTerminator* terminator() { return &_term; }
3169
3170 virtual void set_for_termination(uint active_workers) {
3171 terminator()->reset_for_reuse(active_workers);
3172 }
3173
3174 void work(uint worker_id);
3175 bool should_yield() {
3176 return ConcurrentMarkSweepThread::should_yield()
3177 && !_collector->foregroundGCIsActive();
3178 }
3179
3180 virtual void coordinator_yield(); // stuff done by coordinator
3181 bool result() { return _result; }
3182
3183 void reset(HeapWord* ra) {
3184 assert(_global_finger >= _cms_space->end(), "Postcondition of ::work(i)");
3185 _restart_addr = _global_finger = ra;
3186 _term.reset_for_reuse();
3187 }
3188
3189 static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3190 OopTaskQueue* work_q);
3191
3192 private:
3193 void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3194 void do_work_steal(int i);
3195 void bump_global_finger(HeapWord* f);
3196 };
3197
3198 bool CMSConcMarkingTerminatorTerminator::should_exit_termination() {
3199 assert(_task != NULL, "Error");
3200 return _task->yielding();
3201 // Note that we do not need the disjunct || _task->should_yield() above
3202 // because we want terminating threads to yield only if the task
3203 // is already in the midst of yielding, which happens only after at least one
3204 // thread has yielded.
3205 }
3206
3207 void CMSConcMarkingTerminator::yield() {
3208 if (_task->should_yield()) {
3209 _task->yield();
3210 } else {
3211 ParallelTaskTerminator::yield();
3212 }
3213 }
3214
3215 ////////////////////////////////////////////////////////////////
3216 // Concurrent Marking Algorithm Sketch
3217 ////////////////////////////////////////////////////////////////
3218 // Until all tasks exhausted (both spaces):
3219 // -- claim next available chunk
3220 // -- bump global finger via CAS
3221 // -- find first object that starts in this chunk
3222 // and start scanning bitmap from that position
3223 // -- scan marked objects for oops
3224 // -- CAS-mark target, and if successful:
3225 // . if target oop is above global finger (volatile read)
3226 // nothing to do
3227 // . if target oop is in chunk and above local finger
3228 // then nothing to do
3229 // . else push on work-queue
3230 // -- Deal with possible overflow issues:
3231 // . local work-queue overflow causes stuff to be pushed on
3232 // global (common) overflow queue
3233 // . always first empty local work queue
3234 // . then get a batch of oops from global work queue if any
3235 // . then do work stealing
3236 // -- When all tasks claimed (both spaces)
3237 // and local work queue empty,
3238 // then in a loop do:
3239 // . check global overflow stack; steal a batch of oops and trace
3240 // . try to steal from other threads oif GOS is empty
3241 // . if neither is available, offer termination
3242 // -- Terminate and return result
3243 //
3244 void CMSConcMarkingTask::work(uint worker_id) {
3245 elapsedTimer _timer;
3246 ResourceMark rm;
3247 HandleMark hm;
3248
3249 DEBUG_ONLY(_collector->verify_overflow_empty();)
3250
3251 // Before we begin work, our work queue should be empty
3252 assert(work_queue(worker_id)->size() == 0, "Expected to be empty");
3253 // Scan the bitmap covering _cms_space, tracing through grey objects.
3254 _timer.start();
3255 do_scan_and_mark(worker_id, _cms_space);
3256 _timer.stop();
3257 if (PrintCMSStatistics != 0) {
3258 gclog_or_tty->print_cr("Finished cms space scanning in %dth thread: %3.3f sec",
3259 worker_id, _timer.seconds());
3260 // XXX: need xxx/xxx type of notation, two timers
3261 }
3262
3263 // ... do work stealing
3264 _timer.reset();
3265 _timer.start();
3266 do_work_steal(worker_id);
3267 _timer.stop();
3268 if (PrintCMSStatistics != 0) {
3269 gclog_or_tty->print_cr("Finished work stealing in %dth thread: %3.3f sec",
3270 worker_id, _timer.seconds());
3271 // XXX: need xxx/xxx type of notation, two timers
3272 }
3273 assert(_collector->_markStack.isEmpty(), "Should have been emptied");
3274 assert(work_queue(worker_id)->size() == 0, "Should have been emptied");
3275 // Note that under the current task protocol, the
3276 // following assertion is true even of the spaces
3277 // expanded since the completion of the concurrent
3278 // marking. XXX This will likely change under a strict
3279 // ABORT semantics.
3280 // After perm removal the comparison was changed to
3281 // greater than or equal to from strictly greater than.
3282 // Before perm removal the highest address sweep would
3283 // have been at the end of perm gen but now is at the
3284 // end of the tenured gen.
3285 assert(_global_finger >= _cms_space->end(),
3286 "All tasks have been completed");
3287 DEBUG_ONLY(_collector->verify_overflow_empty();)
3288 }
3289
3290 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
3291 HeapWord* read = _global_finger;
3292 HeapWord* cur = read;
3293 while (f > read) {
3294 cur = read;
3295 read = (HeapWord*) Atomic::cmpxchg_ptr(f, &_global_finger, cur);
3296 if (cur == read) {
3297 // our cas succeeded
3298 assert(_global_finger >= f, "protocol consistency");
3299 break;
3300 }
3301 }
3302 }
3303
3304 // This is really inefficient, and should be redone by
3305 // using (not yet available) block-read and -write interfaces to the
3306 // stack and the work_queue. XXX FIX ME !!!
3307 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3308 OopTaskQueue* work_q) {
3309 // Fast lock-free check
3310 if (ovflw_stk->length() == 0) {
3311 return false;
3312 }
3313 assert(work_q->size() == 0, "Shouldn't steal");
3314 MutexLockerEx ml(ovflw_stk->par_lock(),
3315 Mutex::_no_safepoint_check_flag);
3316 // Grab up to 1/4 the size of the work queue
3317 size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
3318 (size_t)ParGCDesiredObjsFromOverflowList);
3319 num = MIN2(num, ovflw_stk->length());
3320 for (int i = (int) num; i > 0; i--) {
3321 oop cur = ovflw_stk->pop();
3322 assert(cur != NULL, "Counted wrong?");
3323 work_q->push(cur);
3324 }
3325 return num > 0;
3326 }
3327
3328 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
3329 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
3330 int n_tasks = pst->n_tasks();
3331 // We allow that there may be no tasks to do here because
3332 // we are restarting after a stack overflow.
3333 assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
3334 uint nth_task = 0;
3335
3336 HeapWord* aligned_start = sp->bottom();
3337 if (sp->used_region().contains(_restart_addr)) {
3338 // Align down to a card boundary for the start of 0th task
3339 // for this space.
3340 aligned_start =
3341 (HeapWord*)align_size_down((uintptr_t)_restart_addr,
3342 CardTableModRefBS::card_size);
3343 }
3344
3345 size_t chunk_size = sp->marking_task_size();
3346 while (!pst->is_task_claimed(/* reference */ nth_task)) {
3347 // Having claimed the nth task in this space,
3348 // compute the chunk that it corresponds to:
3349 MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
3350 aligned_start + (nth_task+1)*chunk_size);
3351 // Try and bump the global finger via a CAS;
3352 // note that we need to do the global finger bump
3353 // _before_ taking the intersection below, because
3354 // the task corresponding to that region will be
3355 // deemed done even if the used_region() expands
3356 // because of allocation -- as it almost certainly will
3357 // during start-up while the threads yield in the
3358 // closure below.
3359 HeapWord* finger = span.end();
3360 bump_global_finger(finger); // atomically
3361 // There are null tasks here corresponding to chunks
3362 // beyond the "top" address of the space.
3363 span = span.intersection(sp->used_region());
3364 if (!span.is_empty()) { // Non-null task
3365 HeapWord* prev_obj;
3366 assert(!span.contains(_restart_addr) || nth_task == 0,
3367 "Inconsistency");
3368 if (nth_task == 0) {
3369 // For the 0th task, we'll not need to compute a block_start.
3370 if (span.contains(_restart_addr)) {
3371 // In the case of a restart because of stack overflow,
3372 // we might additionally skip a chunk prefix.
3373 prev_obj = _restart_addr;
3374 } else {
3375 prev_obj = span.start();
3376 }
3377 } else {
3378 // We want to skip the first object because
3379 // the protocol is to scan any object in its entirety
3380 // that _starts_ in this span; a fortiori, any
3381 // object starting in an earlier span is scanned
3382 // as part of an earlier claimed task.
3383 // Below we use the "careful" version of block_start
3384 // so we do not try to navigate uninitialized objects.
3385 prev_obj = sp->block_start_careful(span.start());
3386 // Below we use a variant of block_size that uses the
3387 // Printezis bits to avoid waiting for allocated
3388 // objects to become initialized/parsable.
3389 while (prev_obj < span.start()) {
3390 size_t sz = sp->block_size_no_stall(prev_obj, _collector);
3391 if (sz > 0) {
3392 prev_obj += sz;
3393 } else {
3394 // In this case we may end up doing a bit of redundant
3395 // scanning, but that appears unavoidable, short of
3396 // locking the free list locks; see bug 6324141.
3397 break;
3398 }
3399 }
3400 }
3401 if (prev_obj < span.end()) {
3402 MemRegion my_span = MemRegion(prev_obj, span.end());
3403 // Do the marking work within a non-empty span --
3404 // the last argument to the constructor indicates whether the
3405 // iteration should be incremental with periodic yields.
3406 Par_MarkFromRootsClosure cl(this, _collector, my_span,
3407 &_collector->_markBitMap,
3408 work_queue(i),
3409 &_collector->_markStack);
3410 _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
3411 } // else nothing to do for this task
3412 } // else nothing to do for this task
3413 }
3414 // We'd be tempted to assert here that since there are no
3415 // more tasks left to claim in this space, the global_finger
3416 // must exceed space->top() and a fortiori space->end(). However,
3417 // that would not quite be correct because the bumping of
3418 // global_finger occurs strictly after the claiming of a task,
3419 // so by the time we reach here the global finger may not yet
3420 // have been bumped up by the thread that claimed the last
3421 // task.
3422 pst->all_tasks_completed();
3423 }
3424
3425 class Par_ConcMarkingClosure: public MetadataAwareOopClosure {
3426 private:
3427 CMSCollector* _collector;
3428 CMSConcMarkingTask* _task;
3429 MemRegion _span;
3430 CMSBitMap* _bit_map;
3431 CMSMarkStack* _overflow_stack;
3432 OopTaskQueue* _work_queue;
3433 protected:
3434 DO_OOP_WORK_DEFN
3435 public:
3436 Par_ConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue,
3437 CMSBitMap* bit_map, CMSMarkStack* overflow_stack):
3438 MetadataAwareOopClosure(collector->ref_processor()),
3439 _collector(collector),
3440 _task(task),
3441 _span(collector->_span),
3442 _work_queue(work_queue),
3443 _bit_map(bit_map),
3444 _overflow_stack(overflow_stack)
3445 { }
3446 virtual void do_oop(oop* p);
3447 virtual void do_oop(narrowOop* p);
3448
3449 void trim_queue(size_t max);
3450 void handle_stack_overflow(HeapWord* lost);
3451 void do_yield_check() {
3452 if (_task->should_yield()) {
3453 _task->yield();
3454 }
3455 }
3456 };
3457
3458 // Grey object scanning during work stealing phase --
3459 // the salient assumption here is that any references
3460 // that are in these stolen objects being scanned must
3461 // already have been initialized (else they would not have
3462 // been published), so we do not need to check for
3463 // uninitialized objects before pushing here.
3464 void Par_ConcMarkingClosure::do_oop(oop obj) {
3465 assert(obj->is_oop_or_null(true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
3466 HeapWord* addr = (HeapWord*)obj;
3467 // Check if oop points into the CMS generation
3468 // and is not marked
3469 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
3470 // a white object ...
3471 // If we manage to "claim" the object, by being the
3472 // first thread to mark it, then we push it on our
3473 // marking stack
3474 if (_bit_map->par_mark(addr)) { // ... now grey
3475 // push on work queue (grey set)
3476 bool simulate_overflow = false;
3477 NOT_PRODUCT(
3478 if (CMSMarkStackOverflowALot &&
3479 _collector->simulate_overflow()) {
3480 // simulate a stack overflow
3481 simulate_overflow = true;
3482 }
3483 )
3484 if (simulate_overflow ||
3485 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
3486 // stack overflow
3487 if (PrintCMSStatistics != 0) {
3488 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
3489 SIZE_FORMAT, _overflow_stack->capacity());
3490 }
3491 // We cannot assert that the overflow stack is full because
3492 // it may have been emptied since.
3493 assert(simulate_overflow ||
3494 _work_queue->size() == _work_queue->max_elems(),
3495 "Else push should have succeeded");
3496 handle_stack_overflow(addr);
3497 }
3498 } // Else, some other thread got there first
3499 do_yield_check();
3500 }
3501 }
3502
3503 void Par_ConcMarkingClosure::do_oop(oop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
3504 void Par_ConcMarkingClosure::do_oop(narrowOop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
3505
3506 void Par_ConcMarkingClosure::trim_queue(size_t max) {
3507 while (_work_queue->size() > max) {
3508 oop new_oop;
3509 if (_work_queue->pop_local(new_oop)) {
3510 assert(new_oop->is_oop(), "Should be an oop");
3511 assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
3512 assert(_span.contains((HeapWord*)new_oop), "Not in span");
3513 new_oop->oop_iterate(this); // do_oop() above
3514 do_yield_check();
3515 }
3516 }
3517 }
3518
3519 // Upon stack overflow, we discard (part of) the stack,
3520 // remembering the least address amongst those discarded
3521 // in CMSCollector's _restart_address.
3522 void Par_ConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
3523 // We need to do this under a mutex to prevent other
3524 // workers from interfering with the work done below.
3525 MutexLockerEx ml(_overflow_stack->par_lock(),
3526 Mutex::_no_safepoint_check_flag);
3527 // Remember the least grey address discarded
3528 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
3529 _collector->lower_restart_addr(ra);
3530 _overflow_stack->reset(); // discard stack contents
3531 _overflow_stack->expand(); // expand the stack if possible
3532 }
3533
3534
3535 void CMSConcMarkingTask::do_work_steal(int i) {
3536 OopTaskQueue* work_q = work_queue(i);
3537 oop obj_to_scan;
3538 CMSBitMap* bm = &(_collector->_markBitMap);
3539 CMSMarkStack* ovflw = &(_collector->_markStack);
3540 int* seed = _collector->hash_seed(i);
3541 Par_ConcMarkingClosure cl(_collector, this, work_q, bm, ovflw);
3542 while (true) {
3543 cl.trim_queue(0);
3544 assert(work_q->size() == 0, "Should have been emptied above");
3545 if (get_work_from_overflow_stack(ovflw, work_q)) {
3546 // Can't assert below because the work obtained from the
3547 // overflow stack may already have been stolen from us.
3548 // assert(work_q->size() > 0, "Work from overflow stack");
3549 continue;
3550 } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
3551 assert(obj_to_scan->is_oop(), "Should be an oop");
3552 assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
3553 obj_to_scan->oop_iterate(&cl);
3554 } else if (terminator()->offer_termination(&_term_term)) {
3555 assert(work_q->size() == 0, "Impossible!");
3556 break;
3557 } else if (yielding() || should_yield()) {
3558 yield();
3559 }
3560 }
3561 }
3562
3563 // This is run by the CMS (coordinator) thread.
3564 void CMSConcMarkingTask::coordinator_yield() {
3565 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3566 "CMS thread should hold CMS token");
3567 // First give up the locks, then yield, then re-lock
3568 // We should probably use a constructor/destructor idiom to
3569 // do this unlock/lock or modify the MutexUnlocker class to
3570 // serve our purpose. XXX
3571 assert_lock_strong(_bit_map_lock);
3572 _bit_map_lock->unlock();
3573 ConcurrentMarkSweepThread::desynchronize(true);
3574 _collector->stopTimer();
3575 if (PrintCMSStatistics != 0) {
3576 _collector->incrementYields();
3577 }
3578
3579 // It is possible for whichever thread initiated the yield request
3580 // not to get a chance to wake up and take the bitmap lock between
3581 // this thread releasing it and reacquiring it. So, while the
3582 // should_yield() flag is on, let's sleep for a bit to give the
3583 // other thread a chance to wake up. The limit imposed on the number
3584 // of iterations is defensive, to avoid any unforseen circumstances
3585 // putting us into an infinite loop. Since it's always been this
3586 // (coordinator_yield()) method that was observed to cause the
3587 // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
3588 // which is by default non-zero. For the other seven methods that
3589 // also perform the yield operation, as are using a different
3590 // parameter (CMSYieldSleepCount) which is by default zero. This way we
3591 // can enable the sleeping for those methods too, if necessary.
3592 // See 6442774.
3593 //
3594 // We really need to reconsider the synchronization between the GC
3595 // thread and the yield-requesting threads in the future and we
3596 // should really use wait/notify, which is the recommended
3597 // way of doing this type of interaction. Additionally, we should
3598 // consolidate the eight methods that do the yield operation and they
3599 // are almost identical into one for better maintainability and
3600 // readability. See 6445193.
3601 //
3602 // Tony 2006.06.29
3603 for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
3604 ConcurrentMarkSweepThread::should_yield() &&
3605 !CMSCollector::foregroundGCIsActive(); ++i) {
3606 os::sleep(Thread::current(), 1, false);
3607 }
3608
3609 ConcurrentMarkSweepThread::synchronize(true);
3610 _bit_map_lock->lock_without_safepoint_check();
3611 _collector->startTimer();
3612 }
3613
3614 bool CMSCollector::do_marking_mt() {
3615 assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition");
3616 uint num_workers = AdaptiveSizePolicy::calc_active_conc_workers(conc_workers()->total_workers(),
3617 conc_workers()->active_workers(),
3618 Threads::number_of_non_daemon_threads());
3619 conc_workers()->set_active_workers(num_workers);
3620
3621 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
3622
3623 CMSConcMarkingTask tsk(this,
3624 cms_space,
3625 conc_workers(),
3626 task_queues());
3627
3628 // Since the actual number of workers we get may be different
3629 // from the number we requested above, do we need to do anything different
3630 // below? In particular, may be we need to subclass the SequantialSubTasksDone
3631 // class?? XXX
3632 cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
3633
3634 // Refs discovery is already non-atomic.
3635 assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
3636 assert(ref_processor()->discovery_is_mt(), "Discovery should be MT");
3637 conc_workers()->start_task(&tsk);
3638 while (tsk.yielded()) {
3639 tsk.coordinator_yield();
3640 conc_workers()->continue_task(&tsk);
3641 }
3642 // If the task was aborted, _restart_addr will be non-NULL
3643 assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
3644 while (_restart_addr != NULL) {
3645 // XXX For now we do not make use of ABORTED state and have not
3646 // yet implemented the right abort semantics (even in the original
3647 // single-threaded CMS case). That needs some more investigation
3648 // and is deferred for now; see CR# TBF. 07252005YSR. XXX
3649 assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
3650 // If _restart_addr is non-NULL, a marking stack overflow
3651 // occurred; we need to do a fresh marking iteration from the
3652 // indicated restart address.
3653 if (_foregroundGCIsActive) {
3654 // We may be running into repeated stack overflows, having
3655 // reached the limit of the stack size, while making very
3656 // slow forward progress. It may be best to bail out and
3657 // let the foreground collector do its job.
3658 // Clear _restart_addr, so that foreground GC
3659 // works from scratch. This avoids the headache of
3660 // a "rescan" which would otherwise be needed because
3661 // of the dirty mod union table & card table.
3662 _restart_addr = NULL;
3663 return false;
3664 }
3665 // Adjust the task to restart from _restart_addr
3666 tsk.reset(_restart_addr);
3667 cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
3668 _restart_addr);
3669 _restart_addr = NULL;
3670 // Get the workers going again
3671 conc_workers()->start_task(&tsk);
3672 while (tsk.yielded()) {
3673 tsk.coordinator_yield();
3674 conc_workers()->continue_task(&tsk);
3675 }
3676 }
3677 assert(tsk.completed(), "Inconsistency");
3678 assert(tsk.result() == true, "Inconsistency");
3679 return true;
3680 }
3681
3682 bool CMSCollector::do_marking_st() {
3683 ResourceMark rm;
3684 HandleMark hm;
3685
3686 // Temporarily make refs discovery single threaded (non-MT)
3687 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
3688 MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
3689 &_markStack, CMSYield);
3690 // the last argument to iterate indicates whether the iteration
3691 // should be incremental with periodic yields.
3692 _markBitMap.iterate(&markFromRootsClosure);
3693 // If _restart_addr is non-NULL, a marking stack overflow
3694 // occurred; we need to do a fresh iteration from the
3695 // indicated restart address.
3696 while (_restart_addr != NULL) {
3697 if (_foregroundGCIsActive) {
3698 // We may be running into repeated stack overflows, having
3699 // reached the limit of the stack size, while making very
3700 // slow forward progress. It may be best to bail out and
3701 // let the foreground collector do its job.
3702 // Clear _restart_addr, so that foreground GC
3703 // works from scratch. This avoids the headache of
3704 // a "rescan" which would otherwise be needed because
3705 // of the dirty mod union table & card table.
3706 _restart_addr = NULL;
3707 return false; // indicating failure to complete marking
3708 }
3709 // Deal with stack overflow:
3710 // we restart marking from _restart_addr
3711 HeapWord* ra = _restart_addr;
3712 markFromRootsClosure.reset(ra);
3713 _restart_addr = NULL;
3714 _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
3715 }
3716 return true;
3717 }
3718
3719 void CMSCollector::preclean() {
3720 check_correct_thread_executing();
3721 assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
3722 verify_work_stacks_empty();
3723 verify_overflow_empty();
3724 _abort_preclean = false;
3725 if (CMSPrecleaningEnabled) {
3726 if (!CMSEdenChunksRecordAlways) {
3727 _eden_chunk_index = 0;
3728 }
3729 size_t used = get_eden_used();
3730 size_t capacity = get_eden_capacity();
3731 // Don't start sampling unless we will get sufficiently
3732 // many samples.
3733 if (used < (capacity/(CMSScheduleRemarkSamplingRatio * 100)
3734 * CMSScheduleRemarkEdenPenetration)) {
3735 _start_sampling = true;
3736 } else {
3737 _start_sampling = false;
3738 }
3739 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3740 CMSPhaseAccounting pa(this, "preclean", !PrintGCDetails);
3741 preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
3742 }
3743 CMSTokenSync x(true); // is cms thread
3744 if (CMSPrecleaningEnabled) {
3745 sample_eden();
3746 _collectorState = AbortablePreclean;
3747 } else {
3748 _collectorState = FinalMarking;
3749 }
3750 verify_work_stacks_empty();
3751 verify_overflow_empty();
3752 }
3753
3754 // Try and schedule the remark such that young gen
3755 // occupancy is CMSScheduleRemarkEdenPenetration %.
3756 void CMSCollector::abortable_preclean() {
3757 check_correct_thread_executing();
3758 assert(CMSPrecleaningEnabled, "Inconsistent control state");
3759 assert(_collectorState == AbortablePreclean, "Inconsistent control state");
3760
3761 // If Eden's current occupancy is below this threshold,
3762 // immediately schedule the remark; else preclean
3763 // past the next scavenge in an effort to
3764 // schedule the pause as described above. By choosing
3765 // CMSScheduleRemarkEdenSizeThreshold >= max eden size
3766 // we will never do an actual abortable preclean cycle.
3767 if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
3768 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3769 CMSPhaseAccounting pa(this, "abortable-preclean", !PrintGCDetails);
3770 // We need more smarts in the abortable preclean
3771 // loop below to deal with cases where allocation
3772 // in young gen is very very slow, and our precleaning
3773 // is running a losing race against a horde of
3774 // mutators intent on flooding us with CMS updates
3775 // (dirty cards).
3776 // One, admittedly dumb, strategy is to give up
3777 // after a certain number of abortable precleaning loops
3778 // or after a certain maximum time. We want to make
3779 // this smarter in the next iteration.
3780 // XXX FIX ME!!! YSR
3781 size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
3782 while (!(should_abort_preclean() ||
3783 ConcurrentMarkSweepThread::should_terminate())) {
3784 workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
3785 cumworkdone += workdone;
3786 loops++;
3787 // Voluntarily terminate abortable preclean phase if we have
3788 // been at it for too long.
3789 if ((CMSMaxAbortablePrecleanLoops != 0) &&
3790 loops >= CMSMaxAbortablePrecleanLoops) {
3791 if (PrintGCDetails) {
3792 gclog_or_tty->print(" CMS: abort preclean due to loops ");
3793 }
3794 break;
3795 }
3796 if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
3797 if (PrintGCDetails) {
3798 gclog_or_tty->print(" CMS: abort preclean due to time ");
3799 }
3800 break;
3801 }
3802 // If we are doing little work each iteration, we should
3803 // take a short break.
3804 if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
3805 // Sleep for some time, waiting for work to accumulate
3806 stopTimer();
3807 cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
3808 startTimer();
3809 waited++;
3810 }
3811 }
3812 if (PrintCMSStatistics > 0) {
3813 gclog_or_tty->print(" [" SIZE_FORMAT " iterations, " SIZE_FORMAT " waits, " SIZE_FORMAT " cards)] ",
3814 loops, waited, cumworkdone);
3815 }
3816 }
3817 CMSTokenSync x(true); // is cms thread
3818 if (_collectorState != Idling) {
3819 assert(_collectorState == AbortablePreclean,
3820 "Spontaneous state transition?");
3821 _collectorState = FinalMarking;
3822 } // Else, a foreground collection completed this CMS cycle.
3823 return;
3824 }
3825
3826 // Respond to an Eden sampling opportunity
3827 void CMSCollector::sample_eden() {
3828 // Make sure a young gc cannot sneak in between our
3829 // reading and recording of a sample.
3830 assert(Thread::current()->is_ConcurrentGC_thread(),
3831 "Only the cms thread may collect Eden samples");
3832 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3833 "Should collect samples while holding CMS token");
3834 if (!_start_sampling) {
3835 return;
3836 }
3837 // When CMSEdenChunksRecordAlways is true, the eden chunk array
3838 // is populated by the young generation.
3839 if (_eden_chunk_array != NULL && !CMSEdenChunksRecordAlways) {
3840 if (_eden_chunk_index < _eden_chunk_capacity) {
3841 _eden_chunk_array[_eden_chunk_index] = *_top_addr; // take sample
3842 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
3843 "Unexpected state of Eden");
3844 // We'd like to check that what we just sampled is an oop-start address;
3845 // however, we cannot do that here since the object may not yet have been
3846 // initialized. So we'll instead do the check when we _use_ this sample
3847 // later.
3848 if (_eden_chunk_index == 0 ||
3849 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
3850 _eden_chunk_array[_eden_chunk_index-1])
3851 >= CMSSamplingGrain)) {
3852 _eden_chunk_index++; // commit sample
3853 }
3854 }
3855 }
3856 if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
3857 size_t used = get_eden_used();
3858 size_t capacity = get_eden_capacity();
3859 assert(used <= capacity, "Unexpected state of Eden");
3860 if (used > (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
3861 _abort_preclean = true;
3862 }
3863 }
3864 }
3865
3866
3867 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
3868 assert(_collectorState == Precleaning ||
3869 _collectorState == AbortablePreclean, "incorrect state");
3870 ResourceMark rm;
3871 HandleMark hm;
3872
3873 // Precleaning is currently not MT but the reference processor
3874 // may be set for MT. Disable it temporarily here.
3875 ReferenceProcessor* rp = ref_processor();
3876 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false);
3877
3878 // Do one pass of scrubbing the discovered reference lists
3879 // to remove any reference objects with strongly-reachable
3880 // referents.
3881 if (clean_refs) {
3882 CMSPrecleanRefsYieldClosure yield_cl(this);
3883 assert(rp->span().equals(_span), "Spans should be equal");
3884 CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
3885 &_markStack, true /* preclean */);
3886 CMSDrainMarkingStackClosure complete_trace(this,
3887 _span, &_markBitMap, &_markStack,
3888 &keep_alive, true /* preclean */);
3889
3890 // We don't want this step to interfere with a young
3891 // collection because we don't want to take CPU
3892 // or memory bandwidth away from the young GC threads
3893 // (which may be as many as there are CPUs).
3894 // Note that we don't need to protect ourselves from
3895 // interference with mutators because they can't
3896 // manipulate the discovered reference lists nor affect
3897 // the computed reachability of the referents, the
3898 // only properties manipulated by the precleaning
3899 // of these reference lists.
3900 stopTimer();
3901 CMSTokenSyncWithLocks x(true /* is cms thread */,
3902 bitMapLock());
3903 startTimer();
3904 sample_eden();
3905
3906 // The following will yield to allow foreground
3907 // collection to proceed promptly. XXX YSR:
3908 // The code in this method may need further
3909 // tweaking for better performance and some restructuring
3910 // for cleaner interfaces.
3911 GCTimer *gc_timer = NULL; // Currently not tracing concurrent phases
3912 rp->preclean_discovered_references(
3913 rp->is_alive_non_header(), &keep_alive, &complete_trace, &yield_cl,
3914 gc_timer);
3915 }
3916
3917 if (clean_survivor) { // preclean the active survivor space(s)
3918 PushAndMarkClosure pam_cl(this, _span, ref_processor(),
3919 &_markBitMap, &_modUnionTable,
3920 &_markStack, true /* precleaning phase */);
3921 stopTimer();
3922 CMSTokenSyncWithLocks ts(true /* is cms thread */,
3923 bitMapLock());
3924 startTimer();
3925 unsigned int before_count =
3926 GenCollectedHeap::heap()->total_collections();
3927 SurvivorSpacePrecleanClosure
3928 sss_cl(this, _span, &_markBitMap, &_markStack,
3929 &pam_cl, before_count, CMSYield);
3930 _young_gen->from()->object_iterate_careful(&sss_cl);
3931 _young_gen->to()->object_iterate_careful(&sss_cl);
3932 }
3933 MarkRefsIntoAndScanClosure
3934 mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
3935 &_markStack, this, CMSYield,
3936 true /* precleaning phase */);
3937 // CAUTION: The following closure has persistent state that may need to
3938 // be reset upon a decrease in the sequence of addresses it
3939 // processes.
3940 ScanMarkedObjectsAgainCarefullyClosure
3941 smoac_cl(this, _span,
3942 &_markBitMap, &_markStack, &mrias_cl, CMSYield);
3943
3944 // Preclean dirty cards in ModUnionTable and CardTable using
3945 // appropriate convergence criterion;
3946 // repeat CMSPrecleanIter times unless we find that
3947 // we are losing.
3948 assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
3949 assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
3950 "Bad convergence multiplier");
3951 assert(CMSPrecleanThreshold >= 100,
3952 "Unreasonably low CMSPrecleanThreshold");
3953
3954 size_t numIter, cumNumCards, lastNumCards, curNumCards;
3955 for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
3956 numIter < CMSPrecleanIter;
3957 numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
3958 curNumCards = preclean_mod_union_table(_cmsGen, &smoac_cl);
3959 if (Verbose && PrintGCDetails) {
3960 gclog_or_tty->print(" (modUnionTable: " SIZE_FORMAT " cards)", curNumCards);
3961 }
3962 // Either there are very few dirty cards, so re-mark
3963 // pause will be small anyway, or our pre-cleaning isn't
3964 // that much faster than the rate at which cards are being
3965 // dirtied, so we might as well stop and re-mark since
3966 // precleaning won't improve our re-mark time by much.
3967 if (curNumCards <= CMSPrecleanThreshold ||
3968 (numIter > 0 &&
3969 (curNumCards * CMSPrecleanDenominator >
3970 lastNumCards * CMSPrecleanNumerator))) {
3971 numIter++;
3972 cumNumCards += curNumCards;
3973 break;
3974 }
3975 }
3976
3977 preclean_klasses(&mrias_cl, _cmsGen->freelistLock());
3978
3979 curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
3980 cumNumCards += curNumCards;
3981 if (PrintGCDetails && PrintCMSStatistics != 0) {
3982 gclog_or_tty->print_cr(" (cardTable: " SIZE_FORMAT " cards, re-scanned " SIZE_FORMAT " cards, " SIZE_FORMAT " iterations)",
3983 curNumCards, cumNumCards, numIter);
3984 }
3985 return cumNumCards; // as a measure of useful work done
3986 }
3987
3988 // PRECLEANING NOTES:
3989 // Precleaning involves:
3990 // . reading the bits of the modUnionTable and clearing the set bits.
3991 // . For the cards corresponding to the set bits, we scan the
3992 // objects on those cards. This means we need the free_list_lock
3993 // so that we can safely iterate over the CMS space when scanning
3994 // for oops.
3995 // . When we scan the objects, we'll be both reading and setting
3996 // marks in the marking bit map, so we'll need the marking bit map.
3997 // . For protecting _collector_state transitions, we take the CGC_lock.
3998 // Note that any races in the reading of of card table entries by the
3999 // CMS thread on the one hand and the clearing of those entries by the
4000 // VM thread or the setting of those entries by the mutator threads on the
4001 // other are quite benign. However, for efficiency it makes sense to keep
4002 // the VM thread from racing with the CMS thread while the latter is
4003 // dirty card info to the modUnionTable. We therefore also use the
4004 // CGC_lock to protect the reading of the card table and the mod union
4005 // table by the CM thread.
4006 // . We run concurrently with mutator updates, so scanning
4007 // needs to be done carefully -- we should not try to scan
4008 // potentially uninitialized objects.
4009 //
4010 // Locking strategy: While holding the CGC_lock, we scan over and
4011 // reset a maximal dirty range of the mod union / card tables, then lock
4012 // the free_list_lock and bitmap lock to do a full marking, then
4013 // release these locks; and repeat the cycle. This allows for a
4014 // certain amount of fairness in the sharing of these locks between
4015 // the CMS collector on the one hand, and the VM thread and the
4016 // mutators on the other.
4017
4018 // NOTE: preclean_mod_union_table() and preclean_card_table()
4019 // further below are largely identical; if you need to modify
4020 // one of these methods, please check the other method too.
4021
4022 size_t CMSCollector::preclean_mod_union_table(
4023 ConcurrentMarkSweepGeneration* old_gen,
4024 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4025 verify_work_stacks_empty();
4026 verify_overflow_empty();
4027
4028 // strategy: starting with the first card, accumulate contiguous
4029 // ranges of dirty cards; clear these cards, then scan the region
4030 // covered by these cards.
4031
4032 // Since all of the MUT is committed ahead, we can just use
4033 // that, in case the generations expand while we are precleaning.
4034 // It might also be fine to just use the committed part of the
4035 // generation, but we might potentially miss cards when the
4036 // generation is rapidly expanding while we are in the midst
4037 // of precleaning.
4038 HeapWord* startAddr = old_gen->reserved().start();
4039 HeapWord* endAddr = old_gen->reserved().end();
4040
4041 cl->setFreelistLock(old_gen->freelistLock()); // needed for yielding
4042
4043 size_t numDirtyCards, cumNumDirtyCards;
4044 HeapWord *nextAddr, *lastAddr;
4045 for (cumNumDirtyCards = numDirtyCards = 0,
4046 nextAddr = lastAddr = startAddr;
4047 nextAddr < endAddr;
4048 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4049
4050 ResourceMark rm;
4051 HandleMark hm;
4052
4053 MemRegion dirtyRegion;
4054 {
4055 stopTimer();
4056 // Potential yield point
4057 CMSTokenSync ts(true);
4058 startTimer();
4059 sample_eden();
4060 // Get dirty region starting at nextOffset (inclusive),
4061 // simultaneously clearing it.
4062 dirtyRegion =
4063 _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
4064 assert(dirtyRegion.start() >= nextAddr,
4065 "returned region inconsistent?");
4066 }
4067 // Remember where the next search should begin.
4068 // The returned region (if non-empty) is a right open interval,
4069 // so lastOffset is obtained from the right end of that
4070 // interval.
4071 lastAddr = dirtyRegion.end();
4072 // Should do something more transparent and less hacky XXX
4073 numDirtyCards =
4074 _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
4075
4076 // We'll scan the cards in the dirty region (with periodic
4077 // yields for foreground GC as needed).
4078 if (!dirtyRegion.is_empty()) {
4079 assert(numDirtyCards > 0, "consistency check");
4080 HeapWord* stop_point = NULL;
4081 stopTimer();
4082 // Potential yield point
4083 CMSTokenSyncWithLocks ts(true, old_gen->freelistLock(),
4084 bitMapLock());
4085 startTimer();
4086 {
4087 verify_work_stacks_empty();
4088 verify_overflow_empty();
4089 sample_eden();
4090 stop_point =
4091 old_gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4092 }
4093 if (stop_point != NULL) {
4094 // The careful iteration stopped early either because it found an
4095 // uninitialized object, or because we were in the midst of an
4096 // "abortable preclean", which should now be aborted. Redirty
4097 // the bits corresponding to the partially-scanned or unscanned
4098 // cards. We'll either restart at the next block boundary or
4099 // abort the preclean.
4100 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4101 "Should only be AbortablePreclean.");
4102 _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
4103 if (should_abort_preclean()) {
4104 break; // out of preclean loop
4105 } else {
4106 // Compute the next address at which preclean should pick up;
4107 // might need bitMapLock in order to read P-bits.
4108 lastAddr = next_card_start_after_block(stop_point);
4109 }
4110 }
4111 } else {
4112 assert(lastAddr == endAddr, "consistency check");
4113 assert(numDirtyCards == 0, "consistency check");
4114 break;
4115 }
4116 }
4117 verify_work_stacks_empty();
4118 verify_overflow_empty();
4119 return cumNumDirtyCards;
4120 }
4121
4122 // NOTE: preclean_mod_union_table() above and preclean_card_table()
4123 // below are largely identical; if you need to modify
4124 // one of these methods, please check the other method too.
4125
4126 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* old_gen,
4127 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4128 // strategy: it's similar to precleamModUnionTable above, in that
4129 // we accumulate contiguous ranges of dirty cards, mark these cards
4130 // precleaned, then scan the region covered by these cards.
4131 HeapWord* endAddr = (HeapWord*)(old_gen->_virtual_space.high());
4132 HeapWord* startAddr = (HeapWord*)(old_gen->_virtual_space.low());
4133
4134 cl->setFreelistLock(old_gen->freelistLock()); // needed for yielding
4135
4136 size_t numDirtyCards, cumNumDirtyCards;
4137 HeapWord *lastAddr, *nextAddr;
4138
4139 for (cumNumDirtyCards = numDirtyCards = 0,
4140 nextAddr = lastAddr = startAddr;
4141 nextAddr < endAddr;
4142 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4143
4144 ResourceMark rm;
4145 HandleMark hm;
4146
4147 MemRegion dirtyRegion;
4148 {
4149 // See comments in "Precleaning notes" above on why we
4150 // do this locking. XXX Could the locking overheads be
4151 // too high when dirty cards are sparse? [I don't think so.]
4152 stopTimer();
4153 CMSTokenSync x(true); // is cms thread
4154 startTimer();
4155 sample_eden();
4156 // Get and clear dirty region from card table
4157 dirtyRegion = _ct->ct_bs()->dirty_card_range_after_reset(
4158 MemRegion(nextAddr, endAddr),
4159 true,
4160 CardTableModRefBS::precleaned_card_val());
4161
4162 assert(dirtyRegion.start() >= nextAddr,
4163 "returned region inconsistent?");
4164 }
4165 lastAddr = dirtyRegion.end();
4166 numDirtyCards =
4167 dirtyRegion.word_size()/CardTableModRefBS::card_size_in_words;
4168
4169 if (!dirtyRegion.is_empty()) {
4170 stopTimer();
4171 CMSTokenSyncWithLocks ts(true, old_gen->freelistLock(), bitMapLock());
4172 startTimer();
4173 sample_eden();
4174 verify_work_stacks_empty();
4175 verify_overflow_empty();
4176 HeapWord* stop_point =
4177 old_gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4178 if (stop_point != NULL) {
4179 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4180 "Should only be AbortablePreclean.");
4181 _ct->ct_bs()->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4182 if (should_abort_preclean()) {
4183 break; // out of preclean loop
4184 } else {
4185 // Compute the next address at which preclean should pick up.
4186 lastAddr = next_card_start_after_block(stop_point);
4187 }
4188 }
4189 } else {
4190 break;
4191 }
4192 }
4193 verify_work_stacks_empty();
4194 verify_overflow_empty();
4195 return cumNumDirtyCards;
4196 }
4197
4198 class PrecleanKlassClosure : public KlassClosure {
4199 KlassToOopClosure _cm_klass_closure;
4200 public:
4201 PrecleanKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4202 void do_klass(Klass* k) {
4203 if (k->has_accumulated_modified_oops()) {
4204 k->clear_accumulated_modified_oops();
4205
4206 _cm_klass_closure.do_klass(k);
4207 }
4208 }
4209 };
4210
4211 // The freelist lock is needed to prevent asserts, is it really needed?
4212 void CMSCollector::preclean_klasses(MarkRefsIntoAndScanClosure* cl, Mutex* freelistLock) {
4213
4214 cl->set_freelistLock(freelistLock);
4215
4216 CMSTokenSyncWithLocks ts(true, freelistLock, bitMapLock());
4217
4218 // SSS: Add equivalent to ScanMarkedObjectsAgainCarefullyClosure::do_yield_check and should_abort_preclean?
4219 // SSS: We should probably check if precleaning should be aborted, at suitable intervals?
4220 PrecleanKlassClosure preclean_klass_closure(cl);
4221 ClassLoaderDataGraph::classes_do(&preclean_klass_closure);
4222
4223 verify_work_stacks_empty();
4224 verify_overflow_empty();
4225 }
4226
4227 void CMSCollector::checkpointRootsFinal() {
4228 assert(_collectorState == FinalMarking, "incorrect state transition?");
4229 check_correct_thread_executing();
4230 // world is stopped at this checkpoint
4231 assert(SafepointSynchronize::is_at_safepoint(),
4232 "world should be stopped");
4233 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
4234
4235 verify_work_stacks_empty();
4236 verify_overflow_empty();
4237
4238 if (PrintGCDetails) {
4239 gclog_or_tty->print("[YG occupancy: " SIZE_FORMAT " K (" SIZE_FORMAT " K)]",
4240 _young_gen->used() / K,
4241 _young_gen->capacity() / K);
4242 }
4243 {
4244 if (CMSScavengeBeforeRemark) {
4245 GenCollectedHeap* gch = GenCollectedHeap::heap();
4246 // Temporarily set flag to false, GCH->do_collection will
4247 // expect it to be false and set to true
4248 FlagSetting fl(gch->_is_gc_active, false);
4249 NOT_PRODUCT(GCTraceTime t("Scavenge-Before-Remark",
4250 PrintGCDetails && Verbose, true, _gc_timer_cm);)
4251 gch->do_collection(true, // full (i.e. force, see below)
4252 false, // !clear_all_soft_refs
4253 0, // size
4254 false, // is_tlab
4255 GenCollectedHeap::YoungGen // type
4256 );
4257 }
4258 FreelistLocker x(this);
4259 MutexLockerEx y(bitMapLock(),
4260 Mutex::_no_safepoint_check_flag);
4261 checkpointRootsFinalWork();
4262 }
4263 verify_work_stacks_empty();
4264 verify_overflow_empty();
4265 }
4266
4267 void CMSCollector::checkpointRootsFinalWork() {
4268 NOT_PRODUCT(GCTraceTime tr("checkpointRootsFinalWork", PrintGCDetails, false, _gc_timer_cm);)
4269
4270 assert(haveFreelistLocks(), "must have free list locks");
4271 assert_lock_strong(bitMapLock());
4272
4273 ResourceMark rm;
4274 HandleMark hm;
4275
4276 GenCollectedHeap* gch = GenCollectedHeap::heap();
4277
4278 if (should_unload_classes()) {
4279 CodeCache::gc_prologue();
4280 }
4281 assert(haveFreelistLocks(), "must have free list locks");
4282 assert_lock_strong(bitMapLock());
4283
4284 // We might assume that we need not fill TLAB's when
4285 // CMSScavengeBeforeRemark is set, because we may have just done
4286 // a scavenge which would have filled all TLAB's -- and besides
4287 // Eden would be empty. This however may not always be the case --
4288 // for instance although we asked for a scavenge, it may not have
4289 // happened because of a JNI critical section. We probably need
4290 // a policy for deciding whether we can in that case wait until
4291 // the critical section releases and then do the remark following
4292 // the scavenge, and skip it here. In the absence of that policy,
4293 // or of an indication of whether the scavenge did indeed occur,
4294 // we cannot rely on TLAB's having been filled and must do
4295 // so here just in case a scavenge did not happen.
4296 gch->ensure_parsability(false); // fill TLAB's, but no need to retire them
4297 // Update the saved marks which may affect the root scans.
4298 gch->save_marks();
4299
4300 if (CMSPrintEdenSurvivorChunks) {
4301 print_eden_and_survivor_chunk_arrays();
4302 }
4303
4304 {
4305 #if defined(COMPILER2) || INCLUDE_JVMCI
4306 DerivedPointerTableDeactivate dpt_deact;
4307 #endif
4308
4309 // Note on the role of the mod union table:
4310 // Since the marker in "markFromRoots" marks concurrently with
4311 // mutators, it is possible for some reachable objects not to have been
4312 // scanned. For instance, an only reference to an object A was
4313 // placed in object B after the marker scanned B. Unless B is rescanned,
4314 // A would be collected. Such updates to references in marked objects
4315 // are detected via the mod union table which is the set of all cards
4316 // dirtied since the first checkpoint in this GC cycle and prior to
4317 // the most recent young generation GC, minus those cleaned up by the
4318 // concurrent precleaning.
4319 if (CMSParallelRemarkEnabled) {
4320 GCTraceTime t("Rescan (parallel) ", PrintGCDetails, false, _gc_timer_cm);
4321 do_remark_parallel();
4322 } else {
4323 GCTraceTime t("Rescan (non-parallel) ", PrintGCDetails, false, _gc_timer_cm);
4324 do_remark_non_parallel();
4325 }
4326 }
4327 verify_work_stacks_empty();
4328 verify_overflow_empty();
4329
4330 {
4331 NOT_PRODUCT(GCTraceTime ts("refProcessingWork", PrintGCDetails, false, _gc_timer_cm);)
4332 refProcessingWork();
4333 }
4334 verify_work_stacks_empty();
4335 verify_overflow_empty();
4336
4337 if (should_unload_classes()) {
4338 CodeCache::gc_epilogue();
4339 }
4340 JvmtiExport::gc_epilogue();
4341
4342 // If we encountered any (marking stack / work queue) overflow
4343 // events during the current CMS cycle, take appropriate
4344 // remedial measures, where possible, so as to try and avoid
4345 // recurrence of that condition.
4346 assert(_markStack.isEmpty(), "No grey objects");
4347 size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
4348 _ser_kac_ovflw + _ser_kac_preclean_ovflw;
4349 if (ser_ovflw > 0) {
4350 if (PrintCMSStatistics != 0) {
4351 gclog_or_tty->print_cr("Marking stack overflow (benign) "
4352 "(pmc_pc=" SIZE_FORMAT ", pmc_rm=" SIZE_FORMAT ", kac=" SIZE_FORMAT
4353 ", kac_preclean=" SIZE_FORMAT ")",
4354 _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw,
4355 _ser_kac_ovflw, _ser_kac_preclean_ovflw);
4356 }
4357 _markStack.expand();
4358 _ser_pmc_remark_ovflw = 0;
4359 _ser_pmc_preclean_ovflw = 0;
4360 _ser_kac_preclean_ovflw = 0;
4361 _ser_kac_ovflw = 0;
4362 }
4363 if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
4364 if (PrintCMSStatistics != 0) {
4365 gclog_or_tty->print_cr("Work queue overflow (benign) "
4366 "(pmc_rm=" SIZE_FORMAT ", kac=" SIZE_FORMAT ")",
4367 _par_pmc_remark_ovflw, _par_kac_ovflw);
4368 }
4369 _par_pmc_remark_ovflw = 0;
4370 _par_kac_ovflw = 0;
4371 }
4372 if (PrintCMSStatistics != 0) {
4373 if (_markStack._hit_limit > 0) {
4374 gclog_or_tty->print_cr(" (benign) Hit max stack size limit (" SIZE_FORMAT ")",
4375 _markStack._hit_limit);
4376 }
4377 if (_markStack._failed_double > 0) {
4378 gclog_or_tty->print_cr(" (benign) Failed stack doubling (" SIZE_FORMAT "),"
4379 " current capacity " SIZE_FORMAT,
4380 _markStack._failed_double,
4381 _markStack.capacity());
4382 }
4383 }
4384 _markStack._hit_limit = 0;
4385 _markStack._failed_double = 0;
4386
4387 if ((VerifyAfterGC || VerifyDuringGC) &&
4388 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
4389 verify_after_remark();
4390 }
4391
4392 _gc_tracer_cm->report_object_count_after_gc(&_is_alive_closure);
4393
4394 // Change under the freelistLocks.
4395 _collectorState = Sweeping;
4396 // Call isAllClear() under bitMapLock
4397 assert(_modUnionTable.isAllClear(),
4398 "Should be clear by end of the final marking");
4399 assert(_ct->klass_rem_set()->mod_union_is_clear(),
4400 "Should be clear by end of the final marking");
4401 }
4402
4403 void CMSParInitialMarkTask::work(uint worker_id) {
4404 elapsedTimer _timer;
4405 ResourceMark rm;
4406 HandleMark hm;
4407
4408 // ---------- scan from roots --------------
4409 _timer.start();
4410 GenCollectedHeap* gch = GenCollectedHeap::heap();
4411 Par_MarkRefsIntoClosure par_mri_cl(_collector->_span, &(_collector->_markBitMap));
4412
4413 // ---------- young gen roots --------------
4414 {
4415 work_on_young_gen_roots(worker_id, &par_mri_cl);
4416 _timer.stop();
4417 if (PrintCMSStatistics != 0) {
4418 gclog_or_tty->print_cr(
4419 "Finished young gen initial mark scan work in %dth thread: %3.3f sec",
4420 worker_id, _timer.seconds());
4421 }
4422 }
4423
4424 // ---------- remaining roots --------------
4425 _timer.reset();
4426 _timer.start();
4427
4428 CLDToOopClosure cld_closure(&par_mri_cl, true);
4429
4430 gch->gen_process_roots(_strong_roots_scope,
4431 GenCollectedHeap::OldGen,
4432 false, // yg was scanned above
4433 GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4434 _collector->should_unload_classes(),
4435 &par_mri_cl,
4436 NULL,
4437 &cld_closure);
4438 assert(_collector->should_unload_classes()
4439 || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4440 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4441 _timer.stop();
4442 if (PrintCMSStatistics != 0) {
4443 gclog_or_tty->print_cr(
4444 "Finished remaining root initial mark scan work in %dth thread: %3.3f sec",
4445 worker_id, _timer.seconds());
4446 }
4447 }
4448
4449 // Parallel remark task
4450 class CMSParRemarkTask: public CMSParMarkTask {
4451 CompactibleFreeListSpace* _cms_space;
4452
4453 // The per-thread work queues, available here for stealing.
4454 OopTaskQueueSet* _task_queues;
4455 ParallelTaskTerminator _term;
4456 StrongRootsScope* _strong_roots_scope;
4457
4458 public:
4459 // A value of 0 passed to n_workers will cause the number of
4460 // workers to be taken from the active workers in the work gang.
4461 CMSParRemarkTask(CMSCollector* collector,
4462 CompactibleFreeListSpace* cms_space,
4463 uint n_workers, WorkGang* workers,
4464 OopTaskQueueSet* task_queues,
4465 StrongRootsScope* strong_roots_scope):
4466 CMSParMarkTask("Rescan roots and grey objects in parallel",
4467 collector, n_workers),
4468 _cms_space(cms_space),
4469 _task_queues(task_queues),
4470 _term(n_workers, task_queues),
4471 _strong_roots_scope(strong_roots_scope) { }
4472
4473 OopTaskQueueSet* task_queues() { return _task_queues; }
4474
4475 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
4476
4477 ParallelTaskTerminator* terminator() { return &_term; }
4478 uint n_workers() { return _n_workers; }
4479
4480 void work(uint worker_id);
4481
4482 private:
4483 // ... of dirty cards in old space
4484 void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
4485 Par_MarkRefsIntoAndScanClosure* cl);
4486
4487 // ... work stealing for the above
4488 void do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl, int* seed);
4489 };
4490
4491 class RemarkKlassClosure : public KlassClosure {
4492 KlassToOopClosure _cm_klass_closure;
4493 public:
4494 RemarkKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4495 void do_klass(Klass* k) {
4496 // Check if we have modified any oops in the Klass during the concurrent marking.
4497 if (k->has_accumulated_modified_oops()) {
4498 k->clear_accumulated_modified_oops();
4499
4500 // We could have transfered the current modified marks to the accumulated marks,
4501 // like we do with the Card Table to Mod Union Table. But it's not really necessary.
4502 } else if (k->has_modified_oops()) {
4503 // Don't clear anything, this info is needed by the next young collection.
4504 } else {
4505 // No modified oops in the Klass.
4506 return;
4507 }
4508
4509 // The klass has modified fields, need to scan the klass.
4510 _cm_klass_closure.do_klass(k);
4511 }
4512 };
4513
4514 void CMSParMarkTask::work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl) {
4515 ParNewGeneration* young_gen = _collector->_young_gen;
4516 ContiguousSpace* eden_space = young_gen->eden();
4517 ContiguousSpace* from_space = young_gen->from();
4518 ContiguousSpace* to_space = young_gen->to();
4519
4520 HeapWord** eca = _collector->_eden_chunk_array;
4521 size_t ect = _collector->_eden_chunk_index;
4522 HeapWord** sca = _collector->_survivor_chunk_array;
4523 size_t sct = _collector->_survivor_chunk_index;
4524
4525 assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
4526 assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
4527
4528 do_young_space_rescan(worker_id, cl, to_space, NULL, 0);
4529 do_young_space_rescan(worker_id, cl, from_space, sca, sct);
4530 do_young_space_rescan(worker_id, cl, eden_space, eca, ect);
4531 }
4532
4533 // work_queue(i) is passed to the closure
4534 // Par_MarkRefsIntoAndScanClosure. The "i" parameter
4535 // also is passed to do_dirty_card_rescan_tasks() and to
4536 // do_work_steal() to select the i-th task_queue.
4537
4538 void CMSParRemarkTask::work(uint worker_id) {
4539 elapsedTimer _timer;
4540 ResourceMark rm;
4541 HandleMark hm;
4542
4543 // ---------- rescan from roots --------------
4544 _timer.start();
4545 GenCollectedHeap* gch = GenCollectedHeap::heap();
4546 Par_MarkRefsIntoAndScanClosure par_mrias_cl(_collector,
4547 _collector->_span, _collector->ref_processor(),
4548 &(_collector->_markBitMap),
4549 work_queue(worker_id));
4550
4551 // Rescan young gen roots first since these are likely
4552 // coarsely partitioned and may, on that account, constitute
4553 // the critical path; thus, it's best to start off that
4554 // work first.
4555 // ---------- young gen roots --------------
4556 {
4557 work_on_young_gen_roots(worker_id, &par_mrias_cl);
4558 _timer.stop();
4559 if (PrintCMSStatistics != 0) {
4560 gclog_or_tty->print_cr(
4561 "Finished young gen rescan work in %dth thread: %3.3f sec",
4562 worker_id, _timer.seconds());
4563 }
4564 }
4565
4566 // ---------- remaining roots --------------
4567 _timer.reset();
4568 _timer.start();
4569 gch->gen_process_roots(_strong_roots_scope,
4570 GenCollectedHeap::OldGen,
4571 false, // yg was scanned above
4572 GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4573 _collector->should_unload_classes(),
4574 &par_mrias_cl,
4575 NULL,
4576 NULL); // The dirty klasses will be handled below
4577
4578 assert(_collector->should_unload_classes()
4579 || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4580 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4581 _timer.stop();
4582 if (PrintCMSStatistics != 0) {
4583 gclog_or_tty->print_cr(
4584 "Finished remaining root rescan work in %dth thread: %3.3f sec",
4585 worker_id, _timer.seconds());
4586 }
4587
4588 // ---------- unhandled CLD scanning ----------
4589 if (worker_id == 0) { // Single threaded at the moment.
4590 _timer.reset();
4591 _timer.start();
4592
4593 // Scan all new class loader data objects and new dependencies that were
4594 // introduced during concurrent marking.
4595 ResourceMark rm;
4596 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
4597 for (int i = 0; i < array->length(); i++) {
4598 par_mrias_cl.do_cld_nv(array->at(i));
4599 }
4600
4601 // We don't need to keep track of new CLDs anymore.
4602 ClassLoaderDataGraph::remember_new_clds(false);
4603
4604 _timer.stop();
4605 if (PrintCMSStatistics != 0) {
4606 gclog_or_tty->print_cr(
4607 "Finished unhandled CLD scanning work in %dth thread: %3.3f sec",
4608 worker_id, _timer.seconds());
4609 }
4610 }
4611
4612 // ---------- dirty klass scanning ----------
4613 if (worker_id == 0) { // Single threaded at the moment.
4614 _timer.reset();
4615 _timer.start();
4616
4617 // Scan all classes that was dirtied during the concurrent marking phase.
4618 RemarkKlassClosure remark_klass_closure(&par_mrias_cl);
4619 ClassLoaderDataGraph::classes_do(&remark_klass_closure);
4620
4621 _timer.stop();
4622 if (PrintCMSStatistics != 0) {
4623 gclog_or_tty->print_cr(
4624 "Finished dirty klass scanning work in %dth thread: %3.3f sec",
4625 worker_id, _timer.seconds());
4626 }
4627 }
4628
4629 // We might have added oops to ClassLoaderData::_handles during the
4630 // concurrent marking phase. These oops point to newly allocated objects
4631 // that are guaranteed to be kept alive. Either by the direct allocation
4632 // code, or when the young collector processes the roots. Hence,
4633 // we don't have to revisit the _handles block during the remark phase.
4634
4635 // ---------- rescan dirty cards ------------
4636 _timer.reset();
4637 _timer.start();
4638
4639 // Do the rescan tasks for each of the two spaces
4640 // (cms_space) in turn.
4641 // "worker_id" is passed to select the task_queue for "worker_id"
4642 do_dirty_card_rescan_tasks(_cms_space, worker_id, &par_mrias_cl);
4643 _timer.stop();
4644 if (PrintCMSStatistics != 0) {
4645 gclog_or_tty->print_cr(
4646 "Finished dirty card rescan work in %dth thread: %3.3f sec",
4647 worker_id, _timer.seconds());
4648 }
4649
4650 // ---------- steal work from other threads ...
4651 // ---------- ... and drain overflow list.
4652 _timer.reset();
4653 _timer.start();
4654 do_work_steal(worker_id, &par_mrias_cl, _collector->hash_seed(worker_id));
4655 _timer.stop();
4656 if (PrintCMSStatistics != 0) {
4657 gclog_or_tty->print_cr(
4658 "Finished work stealing in %dth thread: %3.3f sec",
4659 worker_id, _timer.seconds());
4660 }
4661 }
4662
4663 // Note that parameter "i" is not used.
4664 void
4665 CMSParMarkTask::do_young_space_rescan(uint worker_id,
4666 OopsInGenClosure* cl, ContiguousSpace* space,
4667 HeapWord** chunk_array, size_t chunk_top) {
4668 // Until all tasks completed:
4669 // . claim an unclaimed task
4670 // . compute region boundaries corresponding to task claimed
4671 // using chunk_array
4672 // . par_oop_iterate(cl) over that region
4673
4674 ResourceMark rm;
4675 HandleMark hm;
4676
4677 SequentialSubTasksDone* pst = space->par_seq_tasks();
4678
4679 uint nth_task = 0;
4680 uint n_tasks = pst->n_tasks();
4681
4682 if (n_tasks > 0) {
4683 assert(pst->valid(), "Uninitialized use?");
4684 HeapWord *start, *end;
4685 while (!pst->is_task_claimed(/* reference */ nth_task)) {
4686 // We claimed task # nth_task; compute its boundaries.
4687 if (chunk_top == 0) { // no samples were taken
4688 assert(nth_task == 0 && n_tasks == 1, "Can have only 1 eden task");
4689 start = space->bottom();
4690 end = space->top();
4691 } else if (nth_task == 0) {
4692 start = space->bottom();
4693 end = chunk_array[nth_task];
4694 } else if (nth_task < (uint)chunk_top) {
4695 assert(nth_task >= 1, "Control point invariant");
4696 start = chunk_array[nth_task - 1];
4697 end = chunk_array[nth_task];
4698 } else {
4699 assert(nth_task == (uint)chunk_top, "Control point invariant");
4700 start = chunk_array[chunk_top - 1];
4701 end = space->top();
4702 }
4703 MemRegion mr(start, end);
4704 // Verify that mr is in space
4705 assert(mr.is_empty() || space->used_region().contains(mr),
4706 "Should be in space");
4707 // Verify that "start" is an object boundary
4708 assert(mr.is_empty() || oop(mr.start())->is_oop(),
4709 "Should be an oop");
4710 space->par_oop_iterate(mr, cl);
4711 }
4712 pst->all_tasks_completed();
4713 }
4714 }
4715
4716 void
4717 CMSParRemarkTask::do_dirty_card_rescan_tasks(
4718 CompactibleFreeListSpace* sp, int i,
4719 Par_MarkRefsIntoAndScanClosure* cl) {
4720 // Until all tasks completed:
4721 // . claim an unclaimed task
4722 // . compute region boundaries corresponding to task claimed
4723 // . transfer dirty bits ct->mut for that region
4724 // . apply rescanclosure to dirty mut bits for that region
4725
4726 ResourceMark rm;
4727 HandleMark hm;
4728
4729 OopTaskQueue* work_q = work_queue(i);
4730 ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
4731 // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
4732 // CAUTION: This closure has state that persists across calls to
4733 // the work method dirty_range_iterate_clear() in that it has
4734 // embedded in it a (subtype of) UpwardsObjectClosure. The
4735 // use of that state in the embedded UpwardsObjectClosure instance
4736 // assumes that the cards are always iterated (even if in parallel
4737 // by several threads) in monotonically increasing order per each
4738 // thread. This is true of the implementation below which picks
4739 // card ranges (chunks) in monotonically increasing order globally
4740 // and, a-fortiori, in monotonically increasing order per thread
4741 // (the latter order being a subsequence of the former).
4742 // If the work code below is ever reorganized into a more chaotic
4743 // work-partitioning form than the current "sequential tasks"
4744 // paradigm, the use of that persistent state will have to be
4745 // revisited and modified appropriately. See also related
4746 // bug 4756801 work on which should examine this code to make
4747 // sure that the changes there do not run counter to the
4748 // assumptions made here and necessary for correctness and
4749 // efficiency. Note also that this code might yield inefficient
4750 // behavior in the case of very large objects that span one or
4751 // more work chunks. Such objects would potentially be scanned
4752 // several times redundantly. Work on 4756801 should try and
4753 // address that performance anomaly if at all possible. XXX
4754 MemRegion full_span = _collector->_span;
4755 CMSBitMap* bm = &(_collector->_markBitMap); // shared
4756 MarkFromDirtyCardsClosure
4757 greyRescanClosure(_collector, full_span, // entire span of interest
4758 sp, bm, work_q, cl);
4759
4760 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
4761 assert(pst->valid(), "Uninitialized use?");
4762 uint nth_task = 0;
4763 const int alignment = CardTableModRefBS::card_size * BitsPerWord;
4764 MemRegion span = sp->used_region();
4765 HeapWord* start_addr = span.start();
4766 HeapWord* end_addr = (HeapWord*)round_to((intptr_t)span.end(),
4767 alignment);
4768 const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
4769 assert((HeapWord*)round_to((intptr_t)start_addr, alignment) ==
4770 start_addr, "Check alignment");
4771 assert((size_t)round_to((intptr_t)chunk_size, alignment) ==
4772 chunk_size, "Check alignment");
4773
4774 while (!pst->is_task_claimed(/* reference */ nth_task)) {
4775 // Having claimed the nth_task, compute corresponding mem-region,
4776 // which is a-fortiori aligned correctly (i.e. at a MUT boundary).
4777 // The alignment restriction ensures that we do not need any
4778 // synchronization with other gang-workers while setting or
4779 // clearing bits in thus chunk of the MUT.
4780 MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
4781 start_addr + (nth_task+1)*chunk_size);
4782 // The last chunk's end might be way beyond end of the
4783 // used region. In that case pull back appropriately.
4784 if (this_span.end() > end_addr) {
4785 this_span.set_end(end_addr);
4786 assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
4787 }
4788 // Iterate over the dirty cards covering this chunk, marking them
4789 // precleaned, and setting the corresponding bits in the mod union
4790 // table. Since we have been careful to partition at Card and MUT-word
4791 // boundaries no synchronization is needed between parallel threads.
4792 _collector->_ct->ct_bs()->dirty_card_iterate(this_span,
4793 &modUnionClosure);
4794
4795 // Having transferred these marks into the modUnionTable,
4796 // rescan the marked objects on the dirty cards in the modUnionTable.
4797 // Even if this is at a synchronous collection, the initial marking
4798 // may have been done during an asynchronous collection so there
4799 // may be dirty bits in the mod-union table.
4800 _collector->_modUnionTable.dirty_range_iterate_clear(
4801 this_span, &greyRescanClosure);
4802 _collector->_modUnionTable.verifyNoOneBitsInRange(
4803 this_span.start(),
4804 this_span.end());
4805 }
4806 pst->all_tasks_completed(); // declare that i am done
4807 }
4808
4809 // . see if we can share work_queues with ParNew? XXX
4810 void
4811 CMSParRemarkTask::do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl,
4812 int* seed) {
4813 OopTaskQueue* work_q = work_queue(i);
4814 NOT_PRODUCT(int num_steals = 0;)
4815 oop obj_to_scan;
4816 CMSBitMap* bm = &(_collector->_markBitMap);
4817
4818 while (true) {
4819 // Completely finish any left over work from (an) earlier round(s)
4820 cl->trim_queue(0);
4821 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
4822 (size_t)ParGCDesiredObjsFromOverflowList);
4823 // Now check if there's any work in the overflow list
4824 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
4825 // only affects the number of attempts made to get work from the
4826 // overflow list and does not affect the number of workers. Just
4827 // pass ParallelGCThreads so this behavior is unchanged.
4828 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
4829 work_q,
4830 ParallelGCThreads)) {
4831 // found something in global overflow list;
4832 // not yet ready to go stealing work from others.
4833 // We'd like to assert(work_q->size() != 0, ...)
4834 // because we just took work from the overflow list,
4835 // but of course we can't since all of that could have
4836 // been already stolen from us.
4837 // "He giveth and He taketh away."
4838 continue;
4839 }
4840 // Verify that we have no work before we resort to stealing
4841 assert(work_q->size() == 0, "Have work, shouldn't steal");
4842 // Try to steal from other queues that have work
4843 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
4844 NOT_PRODUCT(num_steals++;)
4845 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
4846 assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
4847 // Do scanning work
4848 obj_to_scan->oop_iterate(cl);
4849 // Loop around, finish this work, and try to steal some more
4850 } else if (terminator()->offer_termination()) {
4851 break; // nirvana from the infinite cycle
4852 }
4853 }
4854 NOT_PRODUCT(
4855 if (PrintCMSStatistics != 0) {
4856 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
4857 }
4858 )
4859 assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
4860 "Else our work is not yet done");
4861 }
4862
4863 // Record object boundaries in _eden_chunk_array by sampling the eden
4864 // top in the slow-path eden object allocation code path and record
4865 // the boundaries, if CMSEdenChunksRecordAlways is true. If
4866 // CMSEdenChunksRecordAlways is false, we use the other asynchronous
4867 // sampling in sample_eden() that activates during the part of the
4868 // preclean phase.
4869 void CMSCollector::sample_eden_chunk() {
4870 if (CMSEdenChunksRecordAlways && _eden_chunk_array != NULL) {
4871 if (_eden_chunk_lock->try_lock()) {
4872 // Record a sample. This is the critical section. The contents
4873 // of the _eden_chunk_array have to be non-decreasing in the
4874 // address order.
4875 _eden_chunk_array[_eden_chunk_index] = *_top_addr;
4876 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4877 "Unexpected state of Eden");
4878 if (_eden_chunk_index == 0 ||
4879 ((_eden_chunk_array[_eden_chunk_index] > _eden_chunk_array[_eden_chunk_index-1]) &&
4880 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4881 _eden_chunk_array[_eden_chunk_index-1]) >= CMSSamplingGrain))) {
4882 _eden_chunk_index++; // commit sample
4883 }
4884 _eden_chunk_lock->unlock();
4885 }
4886 }
4887 }
4888
4889 // Return a thread-local PLAB recording array, as appropriate.
4890 void* CMSCollector::get_data_recorder(int thr_num) {
4891 if (_survivor_plab_array != NULL &&
4892 (CMSPLABRecordAlways ||
4893 (_collectorState > Marking && _collectorState < FinalMarking))) {
4894 assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
4895 ChunkArray* ca = &_survivor_plab_array[thr_num];
4896 ca->reset(); // clear it so that fresh data is recorded
4897 return (void*) ca;
4898 } else {
4899 return NULL;
4900 }
4901 }
4902
4903 // Reset all the thread-local PLAB recording arrays
4904 void CMSCollector::reset_survivor_plab_arrays() {
4905 for (uint i = 0; i < ParallelGCThreads; i++) {
4906 _survivor_plab_array[i].reset();
4907 }
4908 }
4909
4910 // Merge the per-thread plab arrays into the global survivor chunk
4911 // array which will provide the partitioning of the survivor space
4912 // for CMS initial scan and rescan.
4913 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv,
4914 int no_of_gc_threads) {
4915 assert(_survivor_plab_array != NULL, "Error");
4916 assert(_survivor_chunk_array != NULL, "Error");
4917 assert(_collectorState == FinalMarking ||
4918 (CMSParallelInitialMarkEnabled && _collectorState == InitialMarking), "Error");
4919 for (int j = 0; j < no_of_gc_threads; j++) {
4920 _cursor[j] = 0;
4921 }
4922 HeapWord* top = surv->top();
4923 size_t i;
4924 for (i = 0; i < _survivor_chunk_capacity; i++) { // all sca entries
4925 HeapWord* min_val = top; // Higher than any PLAB address
4926 uint min_tid = 0; // position of min_val this round
4927 for (int j = 0; j < no_of_gc_threads; j++) {
4928 ChunkArray* cur_sca = &_survivor_plab_array[j];
4929 if (_cursor[j] == cur_sca->end()) {
4930 continue;
4931 }
4932 assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
4933 HeapWord* cur_val = cur_sca->nth(_cursor[j]);
4934 assert(surv->used_region().contains(cur_val), "Out of bounds value");
4935 if (cur_val < min_val) {
4936 min_tid = j;
4937 min_val = cur_val;
4938 } else {
4939 assert(cur_val < top, "All recorded addresses should be less");
4940 }
4941 }
4942 // At this point min_val and min_tid are respectively
4943 // the least address in _survivor_plab_array[j]->nth(_cursor[j])
4944 // and the thread (j) that witnesses that address.
4945 // We record this address in the _survivor_chunk_array[i]
4946 // and increment _cursor[min_tid] prior to the next round i.
4947 if (min_val == top) {
4948 break;
4949 }
4950 _survivor_chunk_array[i] = min_val;
4951 _cursor[min_tid]++;
4952 }
4953 // We are all done; record the size of the _survivor_chunk_array
4954 _survivor_chunk_index = i; // exclusive: [0, i)
4955 if (PrintCMSStatistics > 0) {
4956 gclog_or_tty->print(" (Survivor:" SIZE_FORMAT "chunks) ", i);
4957 }
4958 // Verify that we used up all the recorded entries
4959 #ifdef ASSERT
4960 size_t total = 0;
4961 for (int j = 0; j < no_of_gc_threads; j++) {
4962 assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
4963 total += _cursor[j];
4964 }
4965 assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
4966 // Check that the merged array is in sorted order
4967 if (total > 0) {
4968 for (size_t i = 0; i < total - 1; i++) {
4969 if (PrintCMSStatistics > 0) {
4970 gclog_or_tty->print(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
4971 i, p2i(_survivor_chunk_array[i]));
4972 }
4973 assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
4974 "Not sorted");
4975 }
4976 }
4977 #endif // ASSERT
4978 }
4979
4980 // Set up the space's par_seq_tasks structure for work claiming
4981 // for parallel initial scan and rescan of young gen.
4982 // See ParRescanTask where this is currently used.
4983 void
4984 CMSCollector::
4985 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
4986 assert(n_threads > 0, "Unexpected n_threads argument");
4987
4988 // Eden space
4989 if (!_young_gen->eden()->is_empty()) {
4990 SequentialSubTasksDone* pst = _young_gen->eden()->par_seq_tasks();
4991 assert(!pst->valid(), "Clobbering existing data?");
4992 // Each valid entry in [0, _eden_chunk_index) represents a task.
4993 size_t n_tasks = _eden_chunk_index + 1;
4994 assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
4995 // Sets the condition for completion of the subtask (how many threads
4996 // need to finish in order to be done).
4997 pst->set_n_threads(n_threads);
4998 pst->set_n_tasks((int)n_tasks);
4999 }
5000
5001 // Merge the survivor plab arrays into _survivor_chunk_array
5002 if (_survivor_plab_array != NULL) {
5003 merge_survivor_plab_arrays(_young_gen->from(), n_threads);
5004 } else {
5005 assert(_survivor_chunk_index == 0, "Error");
5006 }
5007
5008 // To space
5009 {
5010 SequentialSubTasksDone* pst = _young_gen->to()->par_seq_tasks();
5011 assert(!pst->valid(), "Clobbering existing data?");
5012 // Sets the condition for completion of the subtask (how many threads
5013 // need to finish in order to be done).
5014 pst->set_n_threads(n_threads);
5015 pst->set_n_tasks(1);
5016 assert(pst->valid(), "Error");
5017 }
5018
5019 // From space
5020 {
5021 SequentialSubTasksDone* pst = _young_gen->from()->par_seq_tasks();
5022 assert(!pst->valid(), "Clobbering existing data?");
5023 size_t n_tasks = _survivor_chunk_index + 1;
5024 assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
5025 // Sets the condition for completion of the subtask (how many threads
5026 // need to finish in order to be done).
5027 pst->set_n_threads(n_threads);
5028 pst->set_n_tasks((int)n_tasks);
5029 assert(pst->valid(), "Error");
5030 }
5031 }
5032
5033 // Parallel version of remark
5034 void CMSCollector::do_remark_parallel() {
5035 GenCollectedHeap* gch = GenCollectedHeap::heap();
5036 WorkGang* workers = gch->workers();
5037 assert(workers != NULL, "Need parallel worker threads.");
5038 // Choose to use the number of GC workers most recently set
5039 // into "active_workers".
5040 uint n_workers = workers->active_workers();
5041
5042 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
5043
5044 StrongRootsScope srs(n_workers);
5045
5046 CMSParRemarkTask tsk(this, cms_space, n_workers, workers, task_queues(), &srs);
5047
5048 // We won't be iterating over the cards in the card table updating
5049 // the younger_gen cards, so we shouldn't call the following else
5050 // the verification code as well as subsequent younger_refs_iterate
5051 // code would get confused. XXX
5052 // gch->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
5053
5054 // The young gen rescan work will not be done as part of
5055 // process_roots (which currently doesn't know how to
5056 // parallelize such a scan), but rather will be broken up into
5057 // a set of parallel tasks (via the sampling that the [abortable]
5058 // preclean phase did of eden, plus the [two] tasks of
5059 // scanning the [two] survivor spaces. Further fine-grain
5060 // parallelization of the scanning of the survivor spaces
5061 // themselves, and of precleaning of the young gen itself
5062 // is deferred to the future.
5063 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
5064
5065 // The dirty card rescan work is broken up into a "sequence"
5066 // of parallel tasks (per constituent space) that are dynamically
5067 // claimed by the parallel threads.
5068 cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
5069
5070 // It turns out that even when we're using 1 thread, doing the work in a
5071 // separate thread causes wide variance in run times. We can't help this
5072 // in the multi-threaded case, but we special-case n=1 here to get
5073 // repeatable measurements of the 1-thread overhead of the parallel code.
5074 if (n_workers > 1) {
5075 // Make refs discovery MT-safe, if it isn't already: it may not
5076 // necessarily be so, since it's possible that we are doing
5077 // ST marking.
5078 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), true);
5079 workers->run_task(&tsk);
5080 } else {
5081 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5082 tsk.work(0);
5083 }
5084
5085 // restore, single-threaded for now, any preserved marks
5086 // as a result of work_q overflow
5087 restore_preserved_marks_if_any();
5088 }
5089
5090 // Non-parallel version of remark
5091 void CMSCollector::do_remark_non_parallel() {
5092 ResourceMark rm;
5093 HandleMark hm;
5094 GenCollectedHeap* gch = GenCollectedHeap::heap();
5095 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5096
5097 MarkRefsIntoAndScanClosure
5098 mrias_cl(_span, ref_processor(), &_markBitMap, NULL /* not precleaning */,
5099 &_markStack, this,
5100 false /* should_yield */, false /* not precleaning */);
5101 MarkFromDirtyCardsClosure
5102 markFromDirtyCardsClosure(this, _span,
5103 NULL, // space is set further below
5104 &_markBitMap, &_markStack, &mrias_cl);
5105 {
5106 GCTraceTime t("grey object rescan", PrintGCDetails, false, _gc_timer_cm);
5107 // Iterate over the dirty cards, setting the corresponding bits in the
5108 // mod union table.
5109 {
5110 ModUnionClosure modUnionClosure(&_modUnionTable);
5111 _ct->ct_bs()->dirty_card_iterate(
5112 _cmsGen->used_region(),
5113 &modUnionClosure);
5114 }
5115 // Having transferred these marks into the modUnionTable, we just need
5116 // to rescan the marked objects on the dirty cards in the modUnionTable.
5117 // The initial marking may have been done during an asynchronous
5118 // collection so there may be dirty bits in the mod-union table.
5119 const int alignment =
5120 CardTableModRefBS::card_size * BitsPerWord;
5121 {
5122 // ... First handle dirty cards in CMS gen
5123 markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
5124 MemRegion ur = _cmsGen->used_region();
5125 HeapWord* lb = ur.start();
5126 HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
5127 MemRegion cms_span(lb, ub);
5128 _modUnionTable.dirty_range_iterate_clear(cms_span,
5129 &markFromDirtyCardsClosure);
5130 verify_work_stacks_empty();
5131 if (PrintCMSStatistics != 0) {
5132 gclog_or_tty->print(" (re-scanned " SIZE_FORMAT " dirty cards in cms gen) ",
5133 markFromDirtyCardsClosure.num_dirty_cards());
5134 }
5135 }
5136 }
5137 if (VerifyDuringGC &&
5138 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5139 HandleMark hm; // Discard invalid handles created during verification
5140 Universe::verify();
5141 }
5142 {
5143 GCTraceTime t("root rescan", PrintGCDetails, false, _gc_timer_cm);
5144
5145 verify_work_stacks_empty();
5146
5147 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
5148 StrongRootsScope srs(1);
5149
5150 gch->gen_process_roots(&srs,
5151 GenCollectedHeap::OldGen,
5152 true, // young gen as roots
5153 GenCollectedHeap::ScanningOption(roots_scanning_options()),
5154 should_unload_classes(),
5155 &mrias_cl,
5156 NULL,
5157 NULL); // The dirty klasses will be handled below
5158
5159 assert(should_unload_classes()
5160 || (roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
5161 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5162 }
5163
5164 {
5165 GCTraceTime t("visit unhandled CLDs", PrintGCDetails, false, _gc_timer_cm);
5166
5167 verify_work_stacks_empty();
5168
5169 // Scan all class loader data objects that might have been introduced
5170 // during concurrent marking.
5171 ResourceMark rm;
5172 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
5173 for (int i = 0; i < array->length(); i++) {
5174 mrias_cl.do_cld_nv(array->at(i));
5175 }
5176
5177 // We don't need to keep track of new CLDs anymore.
5178 ClassLoaderDataGraph::remember_new_clds(false);
5179
5180 verify_work_stacks_empty();
5181 }
5182
5183 {
5184 GCTraceTime t("dirty klass scan", PrintGCDetails, false, _gc_timer_cm);
5185
5186 verify_work_stacks_empty();
5187
5188 RemarkKlassClosure remark_klass_closure(&mrias_cl);
5189 ClassLoaderDataGraph::classes_do(&remark_klass_closure);
5190
5191 verify_work_stacks_empty();
5192 }
5193
5194 // We might have added oops to ClassLoaderData::_handles during the
5195 // concurrent marking phase. These oops point to newly allocated objects
5196 // that are guaranteed to be kept alive. Either by the direct allocation
5197 // code, or when the young collector processes the roots. Hence,
5198 // we don't have to revisit the _handles block during the remark phase.
5199
5200 verify_work_stacks_empty();
5201 // Restore evacuated mark words, if any, used for overflow list links
5202 restore_preserved_marks_if_any();
5203
5204 verify_overflow_empty();
5205 }
5206
5207 ////////////////////////////////////////////////////////
5208 // Parallel Reference Processing Task Proxy Class
5209 ////////////////////////////////////////////////////////
5210 class AbstractGangTaskWOopQueues : public AbstractGangTask {
5211 OopTaskQueueSet* _queues;
5212 ParallelTaskTerminator _terminator;
5213 public:
5214 AbstractGangTaskWOopQueues(const char* name, OopTaskQueueSet* queues, uint n_threads) :
5215 AbstractGangTask(name), _queues(queues), _terminator(n_threads, _queues) {}
5216 ParallelTaskTerminator* terminator() { return &_terminator; }
5217 OopTaskQueueSet* queues() { return _queues; }
5218 };
5219
5220 class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues {
5221 typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
5222 CMSCollector* _collector;
5223 CMSBitMap* _mark_bit_map;
5224 const MemRegion _span;
5225 ProcessTask& _task;
5226
5227 public:
5228 CMSRefProcTaskProxy(ProcessTask& task,
5229 CMSCollector* collector,
5230 const MemRegion& span,
5231 CMSBitMap* mark_bit_map,
5232 AbstractWorkGang* workers,
5233 OopTaskQueueSet* task_queues):
5234 AbstractGangTaskWOopQueues("Process referents by policy in parallel",
5235 task_queues,
5236 workers->active_workers()),
5237 _task(task),
5238 _collector(collector), _span(span), _mark_bit_map(mark_bit_map)
5239 {
5240 assert(_collector->_span.equals(_span) && !_span.is_empty(),
5241 "Inconsistency in _span");
5242 }
5243
5244 OopTaskQueueSet* task_queues() { return queues(); }
5245
5246 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5247
5248 void do_work_steal(int i,
5249 CMSParDrainMarkingStackClosure* drain,
5250 CMSParKeepAliveClosure* keep_alive,
5251 int* seed);
5252
5253 virtual void work(uint worker_id);
5254 };
5255
5256 void CMSRefProcTaskProxy::work(uint worker_id) {
5257 ResourceMark rm;
5258 HandleMark hm;
5259 assert(_collector->_span.equals(_span), "Inconsistency in _span");
5260 CMSParKeepAliveClosure par_keep_alive(_collector, _span,
5261 _mark_bit_map,
5262 work_queue(worker_id));
5263 CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
5264 _mark_bit_map,
5265 work_queue(worker_id));
5266 CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
5267 _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack);
5268 if (_task.marks_oops_alive()) {
5269 do_work_steal(worker_id, &par_drain_stack, &par_keep_alive,
5270 _collector->hash_seed(worker_id));
5271 }
5272 assert(work_queue(worker_id)->size() == 0, "work_queue should be empty");
5273 assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
5274 }
5275
5276 class CMSRefEnqueueTaskProxy: public AbstractGangTask {
5277 typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
5278 EnqueueTask& _task;
5279
5280 public:
5281 CMSRefEnqueueTaskProxy(EnqueueTask& task)
5282 : AbstractGangTask("Enqueue reference objects in parallel"),
5283 _task(task)
5284 { }
5285
5286 virtual void work(uint worker_id)
5287 {
5288 _task.work(worker_id);
5289 }
5290 };
5291
5292 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
5293 MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue):
5294 _span(span),
5295 _bit_map(bit_map),
5296 _work_queue(work_queue),
5297 _mark_and_push(collector, span, bit_map, work_queue),
5298 _low_water_mark(MIN2((work_queue->max_elems()/4),
5299 ((uint)CMSWorkQueueDrainThreshold * ParallelGCThreads)))
5300 { }
5301
5302 // . see if we can share work_queues with ParNew? XXX
5303 void CMSRefProcTaskProxy::do_work_steal(int i,
5304 CMSParDrainMarkingStackClosure* drain,
5305 CMSParKeepAliveClosure* keep_alive,
5306 int* seed) {
5307 OopTaskQueue* work_q = work_queue(i);
5308 NOT_PRODUCT(int num_steals = 0;)
5309 oop obj_to_scan;
5310
5311 while (true) {
5312 // Completely finish any left over work from (an) earlier round(s)
5313 drain->trim_queue(0);
5314 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5315 (size_t)ParGCDesiredObjsFromOverflowList);
5316 // Now check if there's any work in the overflow list
5317 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5318 // only affects the number of attempts made to get work from the
5319 // overflow list and does not affect the number of workers. Just
5320 // pass ParallelGCThreads so this behavior is unchanged.
5321 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5322 work_q,
5323 ParallelGCThreads)) {
5324 // Found something in global overflow list;
5325 // not yet ready to go stealing work from others.
5326 // We'd like to assert(work_q->size() != 0, ...)
5327 // because we just took work from the overflow list,
5328 // but of course we can't, since all of that might have
5329 // been already stolen from us.
5330 continue;
5331 }
5332 // Verify that we have no work before we resort to stealing
5333 assert(work_q->size() == 0, "Have work, shouldn't steal");
5334 // Try to steal from other queues that have work
5335 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5336 NOT_PRODUCT(num_steals++;)
5337 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5338 assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5339 // Do scanning work
5340 obj_to_scan->oop_iterate(keep_alive);
5341 // Loop around, finish this work, and try to steal some more
5342 } else if (terminator()->offer_termination()) {
5343 break; // nirvana from the infinite cycle
5344 }
5345 }
5346 NOT_PRODUCT(
5347 if (PrintCMSStatistics != 0) {
5348 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5349 }
5350 )
5351 }
5352
5353 void CMSRefProcTaskExecutor::execute(ProcessTask& task)
5354 {
5355 GenCollectedHeap* gch = GenCollectedHeap::heap();
5356 WorkGang* workers = gch->workers();
5357 assert(workers != NULL, "Need parallel worker threads.");
5358 CMSRefProcTaskProxy rp_task(task, &_collector,
5359 _collector.ref_processor()->span(),
5360 _collector.markBitMap(),
5361 workers, _collector.task_queues());
5362 workers->run_task(&rp_task);
5363 }
5364
5365 void CMSRefProcTaskExecutor::execute(EnqueueTask& task)
5366 {
5367
5368 GenCollectedHeap* gch = GenCollectedHeap::heap();
5369 WorkGang* workers = gch->workers();
5370 assert(workers != NULL, "Need parallel worker threads.");
5371 CMSRefEnqueueTaskProxy enq_task(task);
5372 workers->run_task(&enq_task);
5373 }
5374
5375 void CMSCollector::refProcessingWork() {
5376 ResourceMark rm;
5377 HandleMark hm;
5378
5379 ReferenceProcessor* rp = ref_processor();
5380 assert(rp->span().equals(_span), "Spans should be equal");
5381 assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
5382 // Process weak references.
5383 rp->setup_policy(false);
5384 verify_work_stacks_empty();
5385
5386 CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
5387 &_markStack, false /* !preclean */);
5388 CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
5389 _span, &_markBitMap, &_markStack,
5390 &cmsKeepAliveClosure, false /* !preclean */);
5391 {
5392 GCTraceTime t("weak refs processing", PrintGCDetails, false, _gc_timer_cm);
5393
5394 ReferenceProcessorStats stats;
5395 if (rp->processing_is_mt()) {
5396 // Set the degree of MT here. If the discovery is done MT, there
5397 // may have been a different number of threads doing the discovery
5398 // and a different number of discovered lists may have Ref objects.
5399 // That is OK as long as the Reference lists are balanced (see
5400 // balance_all_queues() and balance_queues()).
5401 GenCollectedHeap* gch = GenCollectedHeap::heap();
5402 uint active_workers = ParallelGCThreads;
5403 WorkGang* workers = gch->workers();
5404 if (workers != NULL) {
5405 active_workers = workers->active_workers();
5406 // The expectation is that active_workers will have already
5407 // been set to a reasonable value. If it has not been set,
5408 // investigate.
5409 assert(active_workers > 0, "Should have been set during scavenge");
5410 }
5411 rp->set_active_mt_degree(active_workers);
5412 CMSRefProcTaskExecutor task_executor(*this);
5413 stats = rp->process_discovered_references(&_is_alive_closure,
5414 &cmsKeepAliveClosure,
5415 &cmsDrainMarkingStackClosure,
5416 &task_executor,
5417 _gc_timer_cm);
5418 } else {
5419 stats = rp->process_discovered_references(&_is_alive_closure,
5420 &cmsKeepAliveClosure,
5421 &cmsDrainMarkingStackClosure,
5422 NULL,
5423 _gc_timer_cm);
5424 }
5425 _gc_tracer_cm->report_gc_reference_stats(stats);
5426
5427 }
5428
5429 // This is the point where the entire marking should have completed.
5430 verify_work_stacks_empty();
5431
5432 if (should_unload_classes()) {
5433 {
5434 GCTraceTime t("class unloading", PrintGCDetails, false, _gc_timer_cm);
5435
5436 // Unload classes and purge the SystemDictionary.
5437 bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure);
5438
5439 // Unload nmethods.
5440 CodeCache::do_unloading(&_is_alive_closure, purged_class);
5441
5442 // Prune dead klasses from subklass/sibling/implementor lists.
5443 Klass::clean_weak_klass_links(&_is_alive_closure);
5444 }
5445
5446 {
5447 GCTraceTime t("scrub symbol table", PrintGCDetails, false, _gc_timer_cm);
5448 // Clean up unreferenced symbols in symbol table.
5449 SymbolTable::unlink();
5450 }
5451
5452 {
5453 GCTraceTime t("scrub string table", PrintGCDetails, false, _gc_timer_cm);
5454 // Delete entries for dead interned strings.
5455 StringTable::unlink(&_is_alive_closure);
5456 }
5457 }
5458
5459
5460 // Restore any preserved marks as a result of mark stack or
5461 // work queue overflow
5462 restore_preserved_marks_if_any(); // done single-threaded for now
5463
5464 rp->set_enqueuing_is_done(true);
5465 if (rp->processing_is_mt()) {
5466 rp->balance_all_queues();
5467 CMSRefProcTaskExecutor task_executor(*this);
5468 rp->enqueue_discovered_references(&task_executor);
5469 } else {
5470 rp->enqueue_discovered_references(NULL);
5471 }
5472 rp->verify_no_references_recorded();
5473 assert(!rp->discovery_enabled(), "should have been disabled");
5474 }
5475
5476 #ifndef PRODUCT
5477 void CMSCollector::check_correct_thread_executing() {
5478 Thread* t = Thread::current();
5479 // Only the VM thread or the CMS thread should be here.
5480 assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
5481 "Unexpected thread type");
5482 // If this is the vm thread, the foreground process
5483 // should not be waiting. Note that _foregroundGCIsActive is
5484 // true while the foreground collector is waiting.
5485 if (_foregroundGCShouldWait) {
5486 // We cannot be the VM thread
5487 assert(t->is_ConcurrentGC_thread(),
5488 "Should be CMS thread");
5489 } else {
5490 // We can be the CMS thread only if we are in a stop-world
5491 // phase of CMS collection.
5492 if (t->is_ConcurrentGC_thread()) {
5493 assert(_collectorState == InitialMarking ||
5494 _collectorState == FinalMarking,
5495 "Should be a stop-world phase");
5496 // The CMS thread should be holding the CMS_token.
5497 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5498 "Potential interference with concurrently "
5499 "executing VM thread");
5500 }
5501 }
5502 }
5503 #endif
5504
5505 void CMSCollector::sweep() {
5506 assert(_collectorState == Sweeping, "just checking");
5507 check_correct_thread_executing();
5508 verify_work_stacks_empty();
5509 verify_overflow_empty();
5510 increment_sweep_count();
5511 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
5512
5513 _inter_sweep_timer.stop();
5514 _inter_sweep_estimate.sample(_inter_sweep_timer.seconds());
5515
5516 assert(!_intra_sweep_timer.is_active(), "Should not be active");
5517 _intra_sweep_timer.reset();
5518 _intra_sweep_timer.start();
5519 {
5520 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
5521 CMSPhaseAccounting pa(this, "sweep", !PrintGCDetails);
5522 // First sweep the old gen
5523 {
5524 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
5525 bitMapLock());
5526 sweepWork(_cmsGen);
5527 }
5528
5529 // Update Universe::_heap_*_at_gc figures.
5530 // We need all the free list locks to make the abstract state
5531 // transition from Sweeping to Resetting. See detailed note
5532 // further below.
5533 {
5534 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock());
5535 // Update heap occupancy information which is used as
5536 // input to soft ref clearing policy at the next gc.
5537 Universe::update_heap_info_at_gc();
5538 _collectorState = Resizing;
5539 }
5540 }
5541 verify_work_stacks_empty();
5542 verify_overflow_empty();
5543
5544 if (should_unload_classes()) {
5545 // Delay purge to the beginning of the next safepoint. Metaspace::contains
5546 // requires that the virtual spaces are stable and not deleted.
5547 ClassLoaderDataGraph::set_should_purge(true);
5548 }
5549
5550 _intra_sweep_timer.stop();
5551 _intra_sweep_estimate.sample(_intra_sweep_timer.seconds());
5552
5553 _inter_sweep_timer.reset();
5554 _inter_sweep_timer.start();
5555
5556 // We need to use a monotonically non-decreasing time in ms
5557 // or we will see time-warp warnings and os::javaTimeMillis()
5558 // does not guarantee monotonicity.
5559 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
5560 update_time_of_last_gc(now);
5561
5562 // NOTE on abstract state transitions:
5563 // Mutators allocate-live and/or mark the mod-union table dirty
5564 // based on the state of the collection. The former is done in
5565 // the interval [Marking, Sweeping] and the latter in the interval
5566 // [Marking, Sweeping). Thus the transitions into the Marking state
5567 // and out of the Sweeping state must be synchronously visible
5568 // globally to the mutators.
5569 // The transition into the Marking state happens with the world
5570 // stopped so the mutators will globally see it. Sweeping is
5571 // done asynchronously by the background collector so the transition
5572 // from the Sweeping state to the Resizing state must be done
5573 // under the freelistLock (as is the check for whether to
5574 // allocate-live and whether to dirty the mod-union table).
5575 assert(_collectorState == Resizing, "Change of collector state to"
5576 " Resizing must be done under the freelistLocks (plural)");
5577
5578 // Now that sweeping has been completed, we clear
5579 // the incremental_collection_failed flag,
5580 // thus inviting a younger gen collection to promote into
5581 // this generation. If such a promotion may still fail,
5582 // the flag will be set again when a young collection is
5583 // attempted.
5584 GenCollectedHeap* gch = GenCollectedHeap::heap();
5585 gch->clear_incremental_collection_failed(); // Worth retrying as fresh space may have been freed up
5586 gch->update_full_collections_completed(_collection_count_start);
5587 }
5588
5589 // FIX ME!!! Looks like this belongs in CFLSpace, with
5590 // CMSGen merely delegating to it.
5591 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
5592 double nearLargestPercent = FLSLargestBlockCoalesceProximity;
5593 HeapWord* minAddr = _cmsSpace->bottom();
5594 HeapWord* largestAddr =
5595 (HeapWord*) _cmsSpace->dictionary()->find_largest_dict();
5596 if (largestAddr == NULL) {
5597 // The dictionary appears to be empty. In this case
5598 // try to coalesce at the end of the heap.
5599 largestAddr = _cmsSpace->end();
5600 }
5601 size_t largestOffset = pointer_delta(largestAddr, minAddr);
5602 size_t nearLargestOffset =
5603 (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
5604 if (PrintFLSStatistics != 0) {
5605 gclog_or_tty->print_cr(
5606 "CMS: Large Block: " PTR_FORMAT ";"
5607 " Proximity: " PTR_FORMAT " -> " PTR_FORMAT,
5608 p2i(largestAddr),
5609 p2i(_cmsSpace->nearLargestChunk()), p2i(minAddr + nearLargestOffset));
5610 }
5611 _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
5612 }
5613
5614 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
5615 return addr >= _cmsSpace->nearLargestChunk();
5616 }
5617
5618 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
5619 return _cmsSpace->find_chunk_at_end();
5620 }
5621
5622 void ConcurrentMarkSweepGeneration::update_gc_stats(Generation* current_generation,
5623 bool full) {
5624 // If the young generation has been collected, gather any statistics
5625 // that are of interest at this point.
5626 bool current_is_young = GenCollectedHeap::heap()->is_young_gen(current_generation);
5627 if (!full && current_is_young) {
5628 // Gather statistics on the young generation collection.
5629 collector()->stats().record_gc0_end(used());
5630 }
5631 }
5632
5633 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* old_gen) {
5634 // We iterate over the space(s) underlying this generation,
5635 // checking the mark bit map to see if the bits corresponding
5636 // to specific blocks are marked or not. Blocks that are
5637 // marked are live and are not swept up. All remaining blocks
5638 // are swept up, with coalescing on-the-fly as we sweep up
5639 // contiguous free and/or garbage blocks:
5640 // We need to ensure that the sweeper synchronizes with allocators
5641 // and stop-the-world collectors. In particular, the following
5642 // locks are used:
5643 // . CMS token: if this is held, a stop the world collection cannot occur
5644 // . freelistLock: if this is held no allocation can occur from this
5645 // generation by another thread
5646 // . bitMapLock: if this is held, no other thread can access or update
5647 //
5648
5649 // Note that we need to hold the freelistLock if we use
5650 // block iterate below; else the iterator might go awry if
5651 // a mutator (or promotion) causes block contents to change
5652 // (for instance if the allocator divvies up a block).
5653 // If we hold the free list lock, for all practical purposes
5654 // young generation GC's can't occur (they'll usually need to
5655 // promote), so we might as well prevent all young generation
5656 // GC's while we do a sweeping step. For the same reason, we might
5657 // as well take the bit map lock for the entire duration
5658
5659 // check that we hold the requisite locks
5660 assert(have_cms_token(), "Should hold cms token");
5661 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), "Should possess CMS token to sweep");
5662 assert_lock_strong(old_gen->freelistLock());
5663 assert_lock_strong(bitMapLock());
5664
5665 assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context");
5666 assert(_intra_sweep_timer.is_active(), "Was switched on in an outer context");
5667 old_gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
5668 _inter_sweep_estimate.padded_average(),
5669 _intra_sweep_estimate.padded_average());
5670 old_gen->setNearLargestChunk();
5671
5672 {
5673 SweepClosure sweepClosure(this, old_gen, &_markBitMap, CMSYield);
5674 old_gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
5675 // We need to free-up/coalesce garbage/blocks from a
5676 // co-terminal free run. This is done in the SweepClosure
5677 // destructor; so, do not remove this scope, else the
5678 // end-of-sweep-census below will be off by a little bit.
5679 }
5680 old_gen->cmsSpace()->sweep_completed();
5681 old_gen->cmsSpace()->endSweepFLCensus(sweep_count());
5682 if (should_unload_classes()) { // unloaded classes this cycle,
5683 _concurrent_cycles_since_last_unload = 0; // ... reset count
5684 } else { // did not unload classes,
5685 _concurrent_cycles_since_last_unload++; // ... increment count
5686 }
5687 }
5688
5689 // Reset CMS data structures (for now just the marking bit map)
5690 // preparatory for the next cycle.
5691 void CMSCollector::reset_concurrent() {
5692 CMSTokenSyncWithLocks ts(true, bitMapLock());
5693
5694 // If the state is not "Resetting", the foreground thread
5695 // has done a collection and the resetting.
5696 if (_collectorState != Resetting) {
5697 assert(_collectorState == Idling, "The state should only change"
5698 " because the foreground collector has finished the collection");
5699 return;
5700 }
5701
5702 // Clear the mark bitmap (no grey objects to start with)
5703 // for the next cycle.
5704 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
5705 CMSPhaseAccounting cmspa(this, "reset", !PrintGCDetails);
5706
5707 HeapWord* curAddr = _markBitMap.startWord();
5708 while (curAddr < _markBitMap.endWord()) {
5709 size_t remaining = pointer_delta(_markBitMap.endWord(), curAddr);
5710 MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
5711 _markBitMap.clear_large_range(chunk);
5712 if (ConcurrentMarkSweepThread::should_yield() &&
5713 !foregroundGCIsActive() &&
5714 CMSYield) {
5715 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5716 "CMS thread should hold CMS token");
5717 assert_lock_strong(bitMapLock());
5718 bitMapLock()->unlock();
5719 ConcurrentMarkSweepThread::desynchronize(true);
5720 stopTimer();
5721 if (PrintCMSStatistics != 0) {
5722 incrementYields();
5723 }
5724
5725 // See the comment in coordinator_yield()
5726 for (unsigned i = 0; i < CMSYieldSleepCount &&
5727 ConcurrentMarkSweepThread::should_yield() &&
5728 !CMSCollector::foregroundGCIsActive(); ++i) {
5729 os::sleep(Thread::current(), 1, false);
5730 }
5731
5732 ConcurrentMarkSweepThread::synchronize(true);
5733 bitMapLock()->lock_without_safepoint_check();
5734 startTimer();
5735 }
5736 curAddr = chunk.end();
5737 }
5738 // A successful mostly concurrent collection has been done.
5739 // Because only the full (i.e., concurrent mode failure) collections
5740 // are being measured for gc overhead limits, clean the "near" flag
5741 // and count.
5742 size_policy()->reset_gc_overhead_limit_count();
5743 _collectorState = Idling;
5744
5745 register_gc_end();
5746 }
5747
5748 // Same as above but for STW paths
5749 void CMSCollector::reset_stw() {
5750 // already have the lock
5751 assert(_collectorState == Resetting, "just checking");
5752 assert_lock_strong(bitMapLock());
5753 GCIdMarkAndRestore gc_id_mark(_cmsThread->gc_id());
5754 _markBitMap.clear_all();
5755 _collectorState = Idling;
5756 register_gc_end();
5757 }
5758
5759 void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) {
5760 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
5761 GCTraceTime t(GCCauseString("GC", gc_cause), PrintGC, !PrintGCDetails, NULL);
5762 TraceCollectorStats tcs(counters());
5763
5764 switch (op) {
5765 case CMS_op_checkpointRootsInitial: {
5766 SvcGCMarker sgcm(SvcGCMarker::OTHER);
5767 checkpointRootsInitial();
5768 if (PrintGC) {
5769 _cmsGen->printOccupancy("initial-mark");
5770 }
5771 break;
5772 }
5773 case CMS_op_checkpointRootsFinal: {
5774 SvcGCMarker sgcm(SvcGCMarker::OTHER);
5775 checkpointRootsFinal();
5776 if (PrintGC) {
5777 _cmsGen->printOccupancy("remark");
5778 }
5779 break;
5780 }
5781 default:
5782 fatal("No such CMS_op");
5783 }
5784 }
5785
5786 #ifndef PRODUCT
5787 size_t const CMSCollector::skip_header_HeapWords() {
5788 return FreeChunk::header_size();
5789 }
5790
5791 // Try and collect here conditions that should hold when
5792 // CMS thread is exiting. The idea is that the foreground GC
5793 // thread should not be blocked if it wants to terminate
5794 // the CMS thread and yet continue to run the VM for a while
5795 // after that.
5796 void CMSCollector::verify_ok_to_terminate() const {
5797 assert(Thread::current()->is_ConcurrentGC_thread(),
5798 "should be called by CMS thread");
5799 assert(!_foregroundGCShouldWait, "should be false");
5800 // We could check here that all the various low-level locks
5801 // are not held by the CMS thread, but that is overkill; see
5802 // also CMSThread::verify_ok_to_terminate() where the CGC_lock
5803 // is checked.
5804 }
5805 #endif
5806
5807 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
5808 assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
5809 "missing Printezis mark?");
5810 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5811 size_t size = pointer_delta(nextOneAddr + 1, addr);
5812 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5813 "alignment problem");
5814 assert(size >= 3, "Necessary for Printezis marks to work");
5815 return size;
5816 }
5817
5818 // A variant of the above (block_size_using_printezis_bits()) except
5819 // that we return 0 if the P-bits are not yet set.
5820 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
5821 if (_markBitMap.isMarked(addr + 1)) {
5822 assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects");
5823 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5824 size_t size = pointer_delta(nextOneAddr + 1, addr);
5825 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5826 "alignment problem");
5827 assert(size >= 3, "Necessary for Printezis marks to work");
5828 return size;
5829 }
5830 return 0;
5831 }
5832
5833 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
5834 size_t sz = 0;
5835 oop p = (oop)addr;
5836 if (p->klass_or_null() != NULL) {
5837 sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
5838 } else {
5839 sz = block_size_using_printezis_bits(addr);
5840 }
5841 assert(sz > 0, "size must be nonzero");
5842 HeapWord* next_block = addr + sz;
5843 HeapWord* next_card = (HeapWord*)round_to((uintptr_t)next_block,
5844 CardTableModRefBS::card_size);
5845 assert(round_down((uintptr_t)addr, CardTableModRefBS::card_size) <
5846 round_down((uintptr_t)next_card, CardTableModRefBS::card_size),
5847 "must be different cards");
5848 return next_card;
5849 }
5850
5851
5852 // CMS Bit Map Wrapper /////////////////////////////////////////
5853
5854 // Construct a CMS bit map infrastructure, but don't create the
5855 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
5856 // further below.
5857 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
5858 _bm(),
5859 _shifter(shifter),
5860 _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true,
5861 Monitor::_safepoint_check_sometimes) : NULL)
5862 {
5863 _bmStartWord = 0;
5864 _bmWordSize = 0;
5865 }
5866
5867 bool CMSBitMap::allocate(MemRegion mr) {
5868 _bmStartWord = mr.start();
5869 _bmWordSize = mr.word_size();
5870 ReservedSpace brs(ReservedSpace::allocation_align_size_up(
5871 (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
5872 if (!brs.is_reserved()) {
5873 warning("CMS bit map allocation failure");
5874 return false;
5875 }
5876 // For now we'll just commit all of the bit map up front.
5877 // Later on we'll try to be more parsimonious with swap.
5878 if (!_virtual_space.initialize(brs, brs.size())) {
5879 warning("CMS bit map backing store failure");
5880 return false;
5881 }
5882 assert(_virtual_space.committed_size() == brs.size(),
5883 "didn't reserve backing store for all of CMS bit map?");
5884 _bm.set_map((BitMap::bm_word_t*)_virtual_space.low());
5885 assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
5886 _bmWordSize, "inconsistency in bit map sizing");
5887 _bm.set_size(_bmWordSize >> _shifter);
5888
5889 // bm.clear(); // can we rely on getting zero'd memory? verify below
5890 assert(isAllClear(),
5891 "Expected zero'd memory from ReservedSpace constructor");
5892 assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
5893 "consistency check");
5894 return true;
5895 }
5896
5897 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
5898 HeapWord *next_addr, *end_addr, *last_addr;
5899 assert_locked();
5900 assert(covers(mr), "out-of-range error");
5901 // XXX assert that start and end are appropriately aligned
5902 for (next_addr = mr.start(), end_addr = mr.end();
5903 next_addr < end_addr; next_addr = last_addr) {
5904 MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
5905 last_addr = dirty_region.end();
5906 if (!dirty_region.is_empty()) {
5907 cl->do_MemRegion(dirty_region);
5908 } else {
5909 assert(last_addr == end_addr, "program logic");
5910 return;
5911 }
5912 }
5913 }
5914
5915 void CMSBitMap::print_on_error(outputStream* st, const char* prefix) const {
5916 _bm.print_on_error(st, prefix);
5917 }
5918
5919 #ifndef PRODUCT
5920 void CMSBitMap::assert_locked() const {
5921 CMSLockVerifier::assert_locked(lock());
5922 }
5923
5924 bool CMSBitMap::covers(MemRegion mr) const {
5925 // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
5926 assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
5927 "size inconsistency");
5928 return (mr.start() >= _bmStartWord) &&
5929 (mr.end() <= endWord());
5930 }
5931
5932 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
5933 return (start >= _bmStartWord && (start + size) <= endWord());
5934 }
5935
5936 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
5937 // verify that there are no 1 bits in the interval [left, right)
5938 FalseBitMapClosure falseBitMapClosure;
5939 iterate(&falseBitMapClosure, left, right);
5940 }
5941
5942 void CMSBitMap::region_invariant(MemRegion mr)
5943 {
5944 assert_locked();
5945 // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
5946 assert(!mr.is_empty(), "unexpected empty region");
5947 assert(covers(mr), "mr should be covered by bit map");
5948 // convert address range into offset range
5949 size_t start_ofs = heapWordToOffset(mr.start());
5950 // Make sure that end() is appropriately aligned
5951 assert(mr.end() == (HeapWord*)round_to((intptr_t)mr.end(),
5952 (1 << (_shifter+LogHeapWordSize))),
5953 "Misaligned mr.end()");
5954 size_t end_ofs = heapWordToOffset(mr.end());
5955 assert(end_ofs > start_ofs, "Should mark at least one bit");
5956 }
5957
5958 #endif
5959
5960 bool CMSMarkStack::allocate(size_t size) {
5961 // allocate a stack of the requisite depth
5962 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
5963 size * sizeof(oop)));
5964 if (!rs.is_reserved()) {
5965 warning("CMSMarkStack allocation failure");
5966 return false;
5967 }
5968 if (!_virtual_space.initialize(rs, rs.size())) {
5969 warning("CMSMarkStack backing store failure");
5970 return false;
5971 }
5972 assert(_virtual_space.committed_size() == rs.size(),
5973 "didn't reserve backing store for all of CMS stack?");
5974 _base = (oop*)(_virtual_space.low());
5975 _index = 0;
5976 _capacity = size;
5977 NOT_PRODUCT(_max_depth = 0);
5978 return true;
5979 }
5980
5981 // XXX FIX ME !!! In the MT case we come in here holding a
5982 // leaf lock. For printing we need to take a further lock
5983 // which has lower rank. We need to recalibrate the two
5984 // lock-ranks involved in order to be able to print the
5985 // messages below. (Or defer the printing to the caller.
5986 // For now we take the expedient path of just disabling the
5987 // messages for the problematic case.)
5988 void CMSMarkStack::expand() {
5989 assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted");
5990 if (_capacity == MarkStackSizeMax) {
5991 if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
5992 // We print a warning message only once per CMS cycle.
5993 gclog_or_tty->print_cr(" (benign) Hit CMSMarkStack max size limit");
5994 }
5995 return;
5996 }
5997 // Double capacity if possible
5998 size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax);
5999 // Do not give up existing stack until we have managed to
6000 // get the double capacity that we desired.
6001 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6002 new_capacity * sizeof(oop)));
6003 if (rs.is_reserved()) {
6004 // Release the backing store associated with old stack
6005 _virtual_space.release();
6006 // Reinitialize virtual space for new stack
6007 if (!_virtual_space.initialize(rs, rs.size())) {
6008 fatal("Not enough swap for expanded marking stack");
6009 }
6010 _base = (oop*)(_virtual_space.low());
6011 _index = 0;
6012 _capacity = new_capacity;
6013 } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6014 // Failed to double capacity, continue;
6015 // we print a detail message only once per CMS cycle.
6016 gclog_or_tty->print(" (benign) Failed to expand marking stack from " SIZE_FORMAT "K to "
6017 SIZE_FORMAT "K",
6018 _capacity / K, new_capacity / K);
6019 }
6020 }
6021
6022
6023 // Closures
6024 // XXX: there seems to be a lot of code duplication here;
6025 // should refactor and consolidate common code.
6026
6027 // This closure is used to mark refs into the CMS generation in
6028 // the CMS bit map. Called at the first checkpoint. This closure
6029 // assumes that we do not need to re-mark dirty cards; if the CMS
6030 // generation on which this is used is not an oldest
6031 // generation then this will lose younger_gen cards!
6032
6033 MarkRefsIntoClosure::MarkRefsIntoClosure(
6034 MemRegion span, CMSBitMap* bitMap):
6035 _span(span),
6036 _bitMap(bitMap)
6037 {
6038 assert(ref_processor() == NULL, "deliberately left NULL");
6039 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6040 }
6041
6042 void MarkRefsIntoClosure::do_oop(oop obj) {
6043 // if p points into _span, then mark corresponding bit in _markBitMap
6044 assert(obj->is_oop(), "expected an oop");
6045 HeapWord* addr = (HeapWord*)obj;
6046 if (_span.contains(addr)) {
6047 // this should be made more efficient
6048 _bitMap->mark(addr);
6049 }
6050 }
6051
6052 void MarkRefsIntoClosure::do_oop(oop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6053 void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6054
6055 Par_MarkRefsIntoClosure::Par_MarkRefsIntoClosure(
6056 MemRegion span, CMSBitMap* bitMap):
6057 _span(span),
6058 _bitMap(bitMap)
6059 {
6060 assert(ref_processor() == NULL, "deliberately left NULL");
6061 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6062 }
6063
6064 void Par_MarkRefsIntoClosure::do_oop(oop obj) {
6065 // if p points into _span, then mark corresponding bit in _markBitMap
6066 assert(obj->is_oop(), "expected an oop");
6067 HeapWord* addr = (HeapWord*)obj;
6068 if (_span.contains(addr)) {
6069 // this should be made more efficient
6070 _bitMap->par_mark(addr);
6071 }
6072 }
6073
6074 void Par_MarkRefsIntoClosure::do_oop(oop* p) { Par_MarkRefsIntoClosure::do_oop_work(p); }
6075 void Par_MarkRefsIntoClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoClosure::do_oop_work(p); }
6076
6077 // A variant of the above, used for CMS marking verification.
6078 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
6079 MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm):
6080 _span(span),
6081 _verification_bm(verification_bm),
6082 _cms_bm(cms_bm)
6083 {
6084 assert(ref_processor() == NULL, "deliberately left NULL");
6085 assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
6086 }
6087
6088 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
6089 // if p points into _span, then mark corresponding bit in _markBitMap
6090 assert(obj->is_oop(), "expected an oop");
6091 HeapWord* addr = (HeapWord*)obj;
6092 if (_span.contains(addr)) {
6093 _verification_bm->mark(addr);
6094 if (!_cms_bm->isMarked(addr)) {
6095 oop(addr)->print();
6096 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
6097 fatal("... aborting");
6098 }
6099 }
6100 }
6101
6102 void MarkRefsIntoVerifyClosure::do_oop(oop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6103 void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6104
6105 //////////////////////////////////////////////////
6106 // MarkRefsIntoAndScanClosure
6107 //////////////////////////////////////////////////
6108
6109 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
6110 ReferenceProcessor* rp,
6111 CMSBitMap* bit_map,
6112 CMSBitMap* mod_union_table,
6113 CMSMarkStack* mark_stack,
6114 CMSCollector* collector,
6115 bool should_yield,
6116 bool concurrent_precleaning):
6117 _collector(collector),
6118 _span(span),
6119 _bit_map(bit_map),
6120 _mark_stack(mark_stack),
6121 _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table,
6122 mark_stack, concurrent_precleaning),
6123 _yield(should_yield),
6124 _concurrent_precleaning(concurrent_precleaning),
6125 _freelistLock(NULL)
6126 {
6127 // FIXME: Should initialize in base class constructor.
6128 assert(rp != NULL, "ref_processor shouldn't be NULL");
6129 set_ref_processor_internal(rp);
6130 }
6131
6132 // This closure is used to mark refs into the CMS generation at the
6133 // second (final) checkpoint, and to scan and transitively follow
6134 // the unmarked oops. It is also used during the concurrent precleaning
6135 // phase while scanning objects on dirty cards in the CMS generation.
6136 // The marks are made in the marking bit map and the marking stack is
6137 // used for keeping the (newly) grey objects during the scan.
6138 // The parallel version (Par_...) appears further below.
6139 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6140 if (obj != NULL) {
6141 assert(obj->is_oop(), "expected an oop");
6142 HeapWord* addr = (HeapWord*)obj;
6143 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6144 assert(_collector->overflow_list_is_empty(),
6145 "overflow list should be empty");
6146 if (_span.contains(addr) &&
6147 !_bit_map->isMarked(addr)) {
6148 // mark bit map (object is now grey)
6149 _bit_map->mark(addr);
6150 // push on marking stack (stack should be empty), and drain the
6151 // stack by applying this closure to the oops in the oops popped
6152 // from the stack (i.e. blacken the grey objects)
6153 bool res = _mark_stack->push(obj);
6154 assert(res, "Should have space to push on empty stack");
6155 do {
6156 oop new_oop = _mark_stack->pop();
6157 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6158 assert(_bit_map->isMarked((HeapWord*)new_oop),
6159 "only grey objects on this stack");
6160 // iterate over the oops in this oop, marking and pushing
6161 // the ones in CMS heap (i.e. in _span).
6162 new_oop->oop_iterate(&_pushAndMarkClosure);
6163 // check if it's time to yield
6164 do_yield_check();
6165 } while (!_mark_stack->isEmpty() ||
6166 (!_concurrent_precleaning && take_from_overflow_list()));
6167 // if marking stack is empty, and we are not doing this
6168 // during precleaning, then check the overflow list
6169 }
6170 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6171 assert(_collector->overflow_list_is_empty(),
6172 "overflow list was drained above");
6173
6174 assert(_collector->no_preserved_marks(),
6175 "All preserved marks should have been restored above");
6176 }
6177 }
6178
6179 void MarkRefsIntoAndScanClosure::do_oop(oop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6180 void MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6181
6182 void MarkRefsIntoAndScanClosure::do_yield_work() {
6183 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6184 "CMS thread should hold CMS token");
6185 assert_lock_strong(_freelistLock);
6186 assert_lock_strong(_bit_map->lock());
6187 // relinquish the free_list_lock and bitMaplock()
6188 _bit_map->lock()->unlock();
6189 _freelistLock->unlock();
6190 ConcurrentMarkSweepThread::desynchronize(true);
6191 _collector->stopTimer();
6192 if (PrintCMSStatistics != 0) {
6193 _collector->incrementYields();
6194 }
6195
6196 // See the comment in coordinator_yield()
6197 for (unsigned i = 0;
6198 i < CMSYieldSleepCount &&
6199 ConcurrentMarkSweepThread::should_yield() &&
6200 !CMSCollector::foregroundGCIsActive();
6201 ++i) {
6202 os::sleep(Thread::current(), 1, false);
6203 }
6204
6205 ConcurrentMarkSweepThread::synchronize(true);
6206 _freelistLock->lock_without_safepoint_check();
6207 _bit_map->lock()->lock_without_safepoint_check();
6208 _collector->startTimer();
6209 }
6210
6211 ///////////////////////////////////////////////////////////
6212 // Par_MarkRefsIntoAndScanClosure: a parallel version of
6213 // MarkRefsIntoAndScanClosure
6214 ///////////////////////////////////////////////////////////
6215 Par_MarkRefsIntoAndScanClosure::Par_MarkRefsIntoAndScanClosure(
6216 CMSCollector* collector, MemRegion span, ReferenceProcessor* rp,
6217 CMSBitMap* bit_map, OopTaskQueue* work_queue):
6218 _span(span),
6219 _bit_map(bit_map),
6220 _work_queue(work_queue),
6221 _low_water_mark(MIN2((work_queue->max_elems()/4),
6222 ((uint)CMSWorkQueueDrainThreshold * ParallelGCThreads))),
6223 _par_pushAndMarkClosure(collector, span, rp, bit_map, work_queue)
6224 {
6225 // FIXME: Should initialize in base class constructor.
6226 assert(rp != NULL, "ref_processor shouldn't be NULL");
6227 set_ref_processor_internal(rp);
6228 }
6229
6230 // This closure is used to mark refs into the CMS generation at the
6231 // second (final) checkpoint, and to scan and transitively follow
6232 // the unmarked oops. The marks are made in the marking bit map and
6233 // the work_queue is used for keeping the (newly) grey objects during
6234 // the scan phase whence they are also available for stealing by parallel
6235 // threads. Since the marking bit map is shared, updates are
6236 // synchronized (via CAS).
6237 void Par_MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6238 if (obj != NULL) {
6239 // Ignore mark word because this could be an already marked oop
6240 // that may be chained at the end of the overflow list.
6241 assert(obj->is_oop(true), "expected an oop");
6242 HeapWord* addr = (HeapWord*)obj;
6243 if (_span.contains(addr) &&
6244 !_bit_map->isMarked(addr)) {
6245 // mark bit map (object will become grey):
6246 // It is possible for several threads to be
6247 // trying to "claim" this object concurrently;
6248 // the unique thread that succeeds in marking the
6249 // object first will do the subsequent push on
6250 // to the work queue (or overflow list).
6251 if (_bit_map->par_mark(addr)) {
6252 // push on work_queue (which may not be empty), and trim the
6253 // queue to an appropriate length by applying this closure to
6254 // the oops in the oops popped from the stack (i.e. blacken the
6255 // grey objects)
6256 bool res = _work_queue->push(obj);
6257 assert(res, "Low water mark should be less than capacity?");
6258 trim_queue(_low_water_mark);
6259 } // Else, another thread claimed the object
6260 }
6261 }
6262 }
6263
6264 void Par_MarkRefsIntoAndScanClosure::do_oop(oop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6265 void Par_MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6266
6267 // This closure is used to rescan the marked objects on the dirty cards
6268 // in the mod union table and the card table proper.
6269 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
6270 oop p, MemRegion mr) {
6271
6272 size_t size = 0;
6273 HeapWord* addr = (HeapWord*)p;
6274 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6275 assert(_span.contains(addr), "we are scanning the CMS generation");
6276 // check if it's time to yield
6277 if (do_yield_check()) {
6278 // We yielded for some foreground stop-world work,
6279 // and we have been asked to abort this ongoing preclean cycle.
6280 return 0;
6281 }
6282 if (_bitMap->isMarked(addr)) {
6283 // it's marked; is it potentially uninitialized?
6284 if (p->klass_or_null() != NULL) {
6285 // an initialized object; ignore mark word in verification below
6286 // since we are running concurrent with mutators
6287 assert(p->is_oop(true), "should be an oop");
6288 if (p->is_objArray()) {
6289 // objArrays are precisely marked; restrict scanning
6290 // to dirty cards only.
6291 size = CompactibleFreeListSpace::adjustObjectSize(
6292 p->oop_iterate_size(_scanningClosure, mr));
6293 } else {
6294 // A non-array may have been imprecisely marked; we need
6295 // to scan object in its entirety.
6296 size = CompactibleFreeListSpace::adjustObjectSize(
6297 p->oop_iterate_size(_scanningClosure));
6298 }
6299 #ifdef ASSERT
6300 size_t direct_size =
6301 CompactibleFreeListSpace::adjustObjectSize(p->size());
6302 assert(size == direct_size, "Inconsistency in size");
6303 assert(size >= 3, "Necessary for Printezis marks to work");
6304 if (!_bitMap->isMarked(addr+1)) {
6305 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size);
6306 } else {
6307 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size-1);
6308 assert(_bitMap->isMarked(addr+size-1),
6309 "inconsistent Printezis mark");
6310 }
6311 #endif // ASSERT
6312 } else {
6313 // An uninitialized object.
6314 assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
6315 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
6316 size = pointer_delta(nextOneAddr + 1, addr);
6317 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6318 "alignment problem");
6319 // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
6320 // will dirty the card when the klass pointer is installed in the
6321 // object (signaling the completion of initialization).
6322 }
6323 } else {
6324 // Either a not yet marked object or an uninitialized object
6325 if (p->klass_or_null() == NULL) {
6326 // An uninitialized object, skip to the next card, since
6327 // we may not be able to read its P-bits yet.
6328 assert(size == 0, "Initial value");
6329 } else {
6330 // An object not (yet) reached by marking: we merely need to
6331 // compute its size so as to go look at the next block.
6332 assert(p->is_oop(true), "should be an oop");
6333 size = CompactibleFreeListSpace::adjustObjectSize(p->size());
6334 }
6335 }
6336 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6337 return size;
6338 }
6339
6340 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
6341 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6342 "CMS thread should hold CMS token");
6343 assert_lock_strong(_freelistLock);
6344 assert_lock_strong(_bitMap->lock());
6345 // relinquish the free_list_lock and bitMaplock()
6346 _bitMap->lock()->unlock();
6347 _freelistLock->unlock();
6348 ConcurrentMarkSweepThread::desynchronize(true);
6349 _collector->stopTimer();
6350 if (PrintCMSStatistics != 0) {
6351 _collector->incrementYields();
6352 }
6353
6354 // See the comment in coordinator_yield()
6355 for (unsigned i = 0; i < CMSYieldSleepCount &&
6356 ConcurrentMarkSweepThread::should_yield() &&
6357 !CMSCollector::foregroundGCIsActive(); ++i) {
6358 os::sleep(Thread::current(), 1, false);
6359 }
6360
6361 ConcurrentMarkSweepThread::synchronize(true);
6362 _freelistLock->lock_without_safepoint_check();
6363 _bitMap->lock()->lock_without_safepoint_check();
6364 _collector->startTimer();
6365 }
6366
6367
6368 //////////////////////////////////////////////////////////////////
6369 // SurvivorSpacePrecleanClosure
6370 //////////////////////////////////////////////////////////////////
6371 // This (single-threaded) closure is used to preclean the oops in
6372 // the survivor spaces.
6373 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
6374
6375 HeapWord* addr = (HeapWord*)p;
6376 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6377 assert(!_span.contains(addr), "we are scanning the survivor spaces");
6378 assert(p->klass_or_null() != NULL, "object should be initialized");
6379 // an initialized object; ignore mark word in verification below
6380 // since we are running concurrent with mutators
6381 assert(p->is_oop(true), "should be an oop");
6382 // Note that we do not yield while we iterate over
6383 // the interior oops of p, pushing the relevant ones
6384 // on our marking stack.
6385 size_t size = p->oop_iterate_size(_scanning_closure);
6386 do_yield_check();
6387 // Observe that below, we do not abandon the preclean
6388 // phase as soon as we should; rather we empty the
6389 // marking stack before returning. This is to satisfy
6390 // some existing assertions. In general, it may be a
6391 // good idea to abort immediately and complete the marking
6392 // from the grey objects at a later time.
6393 while (!_mark_stack->isEmpty()) {
6394 oop new_oop = _mark_stack->pop();
6395 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6396 assert(_bit_map->isMarked((HeapWord*)new_oop),
6397 "only grey objects on this stack");
6398 // iterate over the oops in this oop, marking and pushing
6399 // the ones in CMS heap (i.e. in _span).
6400 new_oop->oop_iterate(_scanning_closure);
6401 // check if it's time to yield
6402 do_yield_check();
6403 }
6404 unsigned int after_count =
6405 GenCollectedHeap::heap()->total_collections();
6406 bool abort = (_before_count != after_count) ||
6407 _collector->should_abort_preclean();
6408 return abort ? 0 : size;
6409 }
6410
6411 void SurvivorSpacePrecleanClosure::do_yield_work() {
6412 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6413 "CMS thread should hold CMS token");
6414 assert_lock_strong(_bit_map->lock());
6415 // Relinquish the bit map lock
6416 _bit_map->lock()->unlock();
6417 ConcurrentMarkSweepThread::desynchronize(true);
6418 _collector->stopTimer();
6419 if (PrintCMSStatistics != 0) {
6420 _collector->incrementYields();
6421 }
6422
6423 // See the comment in coordinator_yield()
6424 for (unsigned i = 0; i < CMSYieldSleepCount &&
6425 ConcurrentMarkSweepThread::should_yield() &&
6426 !CMSCollector::foregroundGCIsActive(); ++i) {
6427 os::sleep(Thread::current(), 1, false);
6428 }
6429
6430 ConcurrentMarkSweepThread::synchronize(true);
6431 _bit_map->lock()->lock_without_safepoint_check();
6432 _collector->startTimer();
6433 }
6434
6435 // This closure is used to rescan the marked objects on the dirty cards
6436 // in the mod union table and the card table proper. In the parallel
6437 // case, although the bitMap is shared, we do a single read so the
6438 // isMarked() query is "safe".
6439 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
6440 // Ignore mark word because we are running concurrent with mutators
6441 assert(p->is_oop_or_null(true), "Expected an oop or NULL at " PTR_FORMAT, p2i(p));
6442 HeapWord* addr = (HeapWord*)p;
6443 assert(_span.contains(addr), "we are scanning the CMS generation");
6444 bool is_obj_array = false;
6445 #ifdef ASSERT
6446 if (!_parallel) {
6447 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6448 assert(_collector->overflow_list_is_empty(),
6449 "overflow list should be empty");
6450
6451 }
6452 #endif // ASSERT
6453 if (_bit_map->isMarked(addr)) {
6454 // Obj arrays are precisely marked, non-arrays are not;
6455 // so we scan objArrays precisely and non-arrays in their
6456 // entirety.
6457 if (p->is_objArray()) {
6458 is_obj_array = true;
6459 if (_parallel) {
6460 p->oop_iterate(_par_scan_closure, mr);
6461 } else {
6462 p->oop_iterate(_scan_closure, mr);
6463 }
6464 } else {
6465 if (_parallel) {
6466 p->oop_iterate(_par_scan_closure);
6467 } else {
6468 p->oop_iterate(_scan_closure);
6469 }
6470 }
6471 }
6472 #ifdef ASSERT
6473 if (!_parallel) {
6474 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6475 assert(_collector->overflow_list_is_empty(),
6476 "overflow list should be empty");
6477
6478 }
6479 #endif // ASSERT
6480 return is_obj_array;
6481 }
6482
6483 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
6484 MemRegion span,
6485 CMSBitMap* bitMap, CMSMarkStack* markStack,
6486 bool should_yield, bool verifying):
6487 _collector(collector),
6488 _span(span),
6489 _bitMap(bitMap),
6490 _mut(&collector->_modUnionTable),
6491 _markStack(markStack),
6492 _yield(should_yield),
6493 _skipBits(0)
6494 {
6495 assert(_markStack->isEmpty(), "stack should be empty");
6496 _finger = _bitMap->startWord();
6497 _threshold = _finger;
6498 assert(_collector->_restart_addr == NULL, "Sanity check");
6499 assert(_span.contains(_finger), "Out of bounds _finger?");
6500 DEBUG_ONLY(_verifying = verifying;)
6501 }
6502
6503 void MarkFromRootsClosure::reset(HeapWord* addr) {
6504 assert(_markStack->isEmpty(), "would cause duplicates on stack");
6505 assert(_span.contains(addr), "Out of bounds _finger?");
6506 _finger = addr;
6507 _threshold = (HeapWord*)round_to(
6508 (intptr_t)_finger, CardTableModRefBS::card_size);
6509 }
6510
6511 // Should revisit to see if this should be restructured for
6512 // greater efficiency.
6513 bool MarkFromRootsClosure::do_bit(size_t offset) {
6514 if (_skipBits > 0) {
6515 _skipBits--;
6516 return true;
6517 }
6518 // convert offset into a HeapWord*
6519 HeapWord* addr = _bitMap->startWord() + offset;
6520 assert(_bitMap->endWord() && addr < _bitMap->endWord(),
6521 "address out of range");
6522 assert(_bitMap->isMarked(addr), "tautology");
6523 if (_bitMap->isMarked(addr+1)) {
6524 // this is an allocated but not yet initialized object
6525 assert(_skipBits == 0, "tautology");
6526 _skipBits = 2; // skip next two marked bits ("Printezis-marks")
6527 oop p = oop(addr);
6528 if (p->klass_or_null() == NULL) {
6529 DEBUG_ONLY(if (!_verifying) {)
6530 // We re-dirty the cards on which this object lies and increase
6531 // the _threshold so that we'll come back to scan this object
6532 // during the preclean or remark phase. (CMSCleanOnEnter)
6533 if (CMSCleanOnEnter) {
6534 size_t sz = _collector->block_size_using_printezis_bits(addr);
6535 HeapWord* end_card_addr = (HeapWord*)round_to(
6536 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
6537 MemRegion redirty_range = MemRegion(addr, end_card_addr);
6538 assert(!redirty_range.is_empty(), "Arithmetical tautology");
6539 // Bump _threshold to end_card_addr; note that
6540 // _threshold cannot possibly exceed end_card_addr, anyhow.
6541 // This prevents future clearing of the card as the scan proceeds
6542 // to the right.
6543 assert(_threshold <= end_card_addr,
6544 "Because we are just scanning into this object");
6545 if (_threshold < end_card_addr) {
6546 _threshold = end_card_addr;
6547 }
6548 if (p->klass_or_null() != NULL) {
6549 // Redirty the range of cards...
6550 _mut->mark_range(redirty_range);
6551 } // ...else the setting of klass will dirty the card anyway.
6552 }
6553 DEBUG_ONLY(})
6554 return true;
6555 }
6556 }
6557 scanOopsInOop(addr);
6558 return true;
6559 }
6560
6561 // We take a break if we've been at this for a while,
6562 // so as to avoid monopolizing the locks involved.
6563 void MarkFromRootsClosure::do_yield_work() {
6564 // First give up the locks, then yield, then re-lock
6565 // We should probably use a constructor/destructor idiom to
6566 // do this unlock/lock or modify the MutexUnlocker class to
6567 // serve our purpose. XXX
6568 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6569 "CMS thread should hold CMS token");
6570 assert_lock_strong(_bitMap->lock());
6571 _bitMap->lock()->unlock();
6572 ConcurrentMarkSweepThread::desynchronize(true);
6573 _collector->stopTimer();
6574 if (PrintCMSStatistics != 0) {
6575 _collector->incrementYields();
6576 }
6577
6578 // See the comment in coordinator_yield()
6579 for (unsigned i = 0; i < CMSYieldSleepCount &&
6580 ConcurrentMarkSweepThread::should_yield() &&
6581 !CMSCollector::foregroundGCIsActive(); ++i) {
6582 os::sleep(Thread::current(), 1, false);
6583 }
6584
6585 ConcurrentMarkSweepThread::synchronize(true);
6586 _bitMap->lock()->lock_without_safepoint_check();
6587 _collector->startTimer();
6588 }
6589
6590 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
6591 assert(_bitMap->isMarked(ptr), "expected bit to be set");
6592 assert(_markStack->isEmpty(),
6593 "should drain stack to limit stack usage");
6594 // convert ptr to an oop preparatory to scanning
6595 oop obj = oop(ptr);
6596 // Ignore mark word in verification below, since we
6597 // may be running concurrent with mutators.
6598 assert(obj->is_oop(true), "should be an oop");
6599 assert(_finger <= ptr, "_finger runneth ahead");
6600 // advance the finger to right end of this object
6601 _finger = ptr + obj->size();
6602 assert(_finger > ptr, "we just incremented it above");
6603 // On large heaps, it may take us some time to get through
6604 // the marking phase. During
6605 // this time it's possible that a lot of mutations have
6606 // accumulated in the card table and the mod union table --
6607 // these mutation records are redundant until we have
6608 // actually traced into the corresponding card.
6609 // Here, we check whether advancing the finger would make
6610 // us cross into a new card, and if so clear corresponding
6611 // cards in the MUT (preclean them in the card-table in the
6612 // future).
6613
6614 DEBUG_ONLY(if (!_verifying) {)
6615 // The clean-on-enter optimization is disabled by default,
6616 // until we fix 6178663.
6617 if (CMSCleanOnEnter && (_finger > _threshold)) {
6618 // [_threshold, _finger) represents the interval
6619 // of cards to be cleared in MUT (or precleaned in card table).
6620 // The set of cards to be cleared is all those that overlap
6621 // with the interval [_threshold, _finger); note that
6622 // _threshold is always kept card-aligned but _finger isn't
6623 // always card-aligned.
6624 HeapWord* old_threshold = _threshold;
6625 assert(old_threshold == (HeapWord*)round_to(
6626 (intptr_t)old_threshold, CardTableModRefBS::card_size),
6627 "_threshold should always be card-aligned");
6628 _threshold = (HeapWord*)round_to(
6629 (intptr_t)_finger, CardTableModRefBS::card_size);
6630 MemRegion mr(old_threshold, _threshold);
6631 assert(!mr.is_empty(), "Control point invariant");
6632 assert(_span.contains(mr), "Should clear within span");
6633 _mut->clear_range(mr);
6634 }
6635 DEBUG_ONLY(})
6636 // Note: the finger doesn't advance while we drain
6637 // the stack below.
6638 PushOrMarkClosure pushOrMarkClosure(_collector,
6639 _span, _bitMap, _markStack,
6640 _finger, this);
6641 bool res = _markStack->push(obj);
6642 assert(res, "Empty non-zero size stack should have space for single push");
6643 while (!_markStack->isEmpty()) {
6644 oop new_oop = _markStack->pop();
6645 // Skip verifying header mark word below because we are
6646 // running concurrent with mutators.
6647 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
6648 // now scan this oop's oops
6649 new_oop->oop_iterate(&pushOrMarkClosure);
6650 do_yield_check();
6651 }
6652 assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
6653 }
6654
6655 Par_MarkFromRootsClosure::Par_MarkFromRootsClosure(CMSConcMarkingTask* task,
6656 CMSCollector* collector, MemRegion span,
6657 CMSBitMap* bit_map,
6658 OopTaskQueue* work_queue,
6659 CMSMarkStack* overflow_stack):
6660 _collector(collector),
6661 _whole_span(collector->_span),
6662 _span(span),
6663 _bit_map(bit_map),
6664 _mut(&collector->_modUnionTable),
6665 _work_queue(work_queue),
6666 _overflow_stack(overflow_stack),
6667 _skip_bits(0),
6668 _task(task)
6669 {
6670 assert(_work_queue->size() == 0, "work_queue should be empty");
6671 _finger = span.start();
6672 _threshold = _finger; // XXX Defer clear-on-enter optimization for now
6673 assert(_span.contains(_finger), "Out of bounds _finger?");
6674 }
6675
6676 // Should revisit to see if this should be restructured for
6677 // greater efficiency.
6678 bool Par_MarkFromRootsClosure::do_bit(size_t offset) {
6679 if (_skip_bits > 0) {
6680 _skip_bits--;
6681 return true;
6682 }
6683 // convert offset into a HeapWord*
6684 HeapWord* addr = _bit_map->startWord() + offset;
6685 assert(_bit_map->endWord() && addr < _bit_map->endWord(),
6686 "address out of range");
6687 assert(_bit_map->isMarked(addr), "tautology");
6688 if (_bit_map->isMarked(addr+1)) {
6689 // this is an allocated object that might not yet be initialized
6690 assert(_skip_bits == 0, "tautology");
6691 _skip_bits = 2; // skip next two marked bits ("Printezis-marks")
6692 oop p = oop(addr);
6693 if (p->klass_or_null() == NULL) {
6694 // in the case of Clean-on-Enter optimization, redirty card
6695 // and avoid clearing card by increasing the threshold.
6696 return true;
6697 }
6698 }
6699 scan_oops_in_oop(addr);
6700 return true;
6701 }
6702
6703 void Par_MarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
6704 assert(_bit_map->isMarked(ptr), "expected bit to be set");
6705 // Should we assert that our work queue is empty or
6706 // below some drain limit?
6707 assert(_work_queue->size() == 0,
6708 "should drain stack to limit stack usage");
6709 // convert ptr to an oop preparatory to scanning
6710 oop obj = oop(ptr);
6711 // Ignore mark word in verification below, since we
6712 // may be running concurrent with mutators.
6713 assert(obj->is_oop(true), "should be an oop");
6714 assert(_finger <= ptr, "_finger runneth ahead");
6715 // advance the finger to right end of this object
6716 _finger = ptr + obj->size();
6717 assert(_finger > ptr, "we just incremented it above");
6718 // On large heaps, it may take us some time to get through
6719 // the marking phase. During
6720 // this time it's possible that a lot of mutations have
6721 // accumulated in the card table and the mod union table --
6722 // these mutation records are redundant until we have
6723 // actually traced into the corresponding card.
6724 // Here, we check whether advancing the finger would make
6725 // us cross into a new card, and if so clear corresponding
6726 // cards in the MUT (preclean them in the card-table in the
6727 // future).
6728
6729 // The clean-on-enter optimization is disabled by default,
6730 // until we fix 6178663.
6731 if (CMSCleanOnEnter && (_finger > _threshold)) {
6732 // [_threshold, _finger) represents the interval
6733 // of cards to be cleared in MUT (or precleaned in card table).
6734 // The set of cards to be cleared is all those that overlap
6735 // with the interval [_threshold, _finger); note that
6736 // _threshold is always kept card-aligned but _finger isn't
6737 // always card-aligned.
6738 HeapWord* old_threshold = _threshold;
6739 assert(old_threshold == (HeapWord*)round_to(
6740 (intptr_t)old_threshold, CardTableModRefBS::card_size),
6741 "_threshold should always be card-aligned");
6742 _threshold = (HeapWord*)round_to(
6743 (intptr_t)_finger, CardTableModRefBS::card_size);
6744 MemRegion mr(old_threshold, _threshold);
6745 assert(!mr.is_empty(), "Control point invariant");
6746 assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
6747 _mut->clear_range(mr);
6748 }
6749
6750 // Note: the local finger doesn't advance while we drain
6751 // the stack below, but the global finger sure can and will.
6752 HeapWord** gfa = _task->global_finger_addr();
6753 Par_PushOrMarkClosure pushOrMarkClosure(_collector,
6754 _span, _bit_map,
6755 _work_queue,
6756 _overflow_stack,
6757 _finger,
6758 gfa, this);
6759 bool res = _work_queue->push(obj); // overflow could occur here
6760 assert(res, "Will hold once we use workqueues");
6761 while (true) {
6762 oop new_oop;
6763 if (!_work_queue->pop_local(new_oop)) {
6764 // We emptied our work_queue; check if there's stuff that can
6765 // be gotten from the overflow stack.
6766 if (CMSConcMarkingTask::get_work_from_overflow_stack(
6767 _overflow_stack, _work_queue)) {
6768 do_yield_check();
6769 continue;
6770 } else { // done
6771 break;
6772 }
6773 }
6774 // Skip verifying header mark word below because we are
6775 // running concurrent with mutators.
6776 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
6777 // now scan this oop's oops
6778 new_oop->oop_iterate(&pushOrMarkClosure);
6779 do_yield_check();
6780 }
6781 assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
6782 }
6783
6784 // Yield in response to a request from VM Thread or
6785 // from mutators.
6786 void Par_MarkFromRootsClosure::do_yield_work() {
6787 assert(_task != NULL, "sanity");
6788 _task->yield();
6789 }
6790
6791 // A variant of the above used for verifying CMS marking work.
6792 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
6793 MemRegion span,
6794 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6795 CMSMarkStack* mark_stack):
6796 _collector(collector),
6797 _span(span),
6798 _verification_bm(verification_bm),
6799 _cms_bm(cms_bm),
6800 _mark_stack(mark_stack),
6801 _pam_verify_closure(collector, span, verification_bm, cms_bm,
6802 mark_stack)
6803 {
6804 assert(_mark_stack->isEmpty(), "stack should be empty");
6805 _finger = _verification_bm->startWord();
6806 assert(_collector->_restart_addr == NULL, "Sanity check");
6807 assert(_span.contains(_finger), "Out of bounds _finger?");
6808 }
6809
6810 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
6811 assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
6812 assert(_span.contains(addr), "Out of bounds _finger?");
6813 _finger = addr;
6814 }
6815
6816 // Should revisit to see if this should be restructured for
6817 // greater efficiency.
6818 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
6819 // convert offset into a HeapWord*
6820 HeapWord* addr = _verification_bm->startWord() + offset;
6821 assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
6822 "address out of range");
6823 assert(_verification_bm->isMarked(addr), "tautology");
6824 assert(_cms_bm->isMarked(addr), "tautology");
6825
6826 assert(_mark_stack->isEmpty(),
6827 "should drain stack to limit stack usage");
6828 // convert addr to an oop preparatory to scanning
6829 oop obj = oop(addr);
6830 assert(obj->is_oop(), "should be an oop");
6831 assert(_finger <= addr, "_finger runneth ahead");
6832 // advance the finger to right end of this object
6833 _finger = addr + obj->size();
6834 assert(_finger > addr, "we just incremented it above");
6835 // Note: the finger doesn't advance while we drain
6836 // the stack below.
6837 bool res = _mark_stack->push(obj);
6838 assert(res, "Empty non-zero size stack should have space for single push");
6839 while (!_mark_stack->isEmpty()) {
6840 oop new_oop = _mark_stack->pop();
6841 assert(new_oop->is_oop(), "Oops! expected to pop an oop");
6842 // now scan this oop's oops
6843 new_oop->oop_iterate(&_pam_verify_closure);
6844 }
6845 assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
6846 return true;
6847 }
6848
6849 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
6850 CMSCollector* collector, MemRegion span,
6851 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6852 CMSMarkStack* mark_stack):
6853 MetadataAwareOopClosure(collector->ref_processor()),
6854 _collector(collector),
6855 _span(span),
6856 _verification_bm(verification_bm),
6857 _cms_bm(cms_bm),
6858 _mark_stack(mark_stack)
6859 { }
6860
6861 void PushAndMarkVerifyClosure::do_oop(oop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
6862 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
6863
6864 // Upon stack overflow, we discard (part of) the stack,
6865 // remembering the least address amongst those discarded
6866 // in CMSCollector's _restart_address.
6867 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
6868 // Remember the least grey address discarded
6869 HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
6870 _collector->lower_restart_addr(ra);
6871 _mark_stack->reset(); // discard stack contents
6872 _mark_stack->expand(); // expand the stack if possible
6873 }
6874
6875 void PushAndMarkVerifyClosure::do_oop(oop obj) {
6876 assert(obj->is_oop_or_null(), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6877 HeapWord* addr = (HeapWord*)obj;
6878 if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
6879 // Oop lies in _span and isn't yet grey or black
6880 _verification_bm->mark(addr); // now grey
6881 if (!_cms_bm->isMarked(addr)) {
6882 oop(addr)->print();
6883 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)",
6884 p2i(addr));
6885 fatal("... aborting");
6886 }
6887
6888 if (!_mark_stack->push(obj)) { // stack overflow
6889 if (PrintCMSStatistics != 0) {
6890 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
6891 SIZE_FORMAT, _mark_stack->capacity());
6892 }
6893 assert(_mark_stack->isFull(), "Else push should have succeeded");
6894 handle_stack_overflow(addr);
6895 }
6896 // anything including and to the right of _finger
6897 // will be scanned as we iterate over the remainder of the
6898 // bit map
6899 }
6900 }
6901
6902 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
6903 MemRegion span,
6904 CMSBitMap* bitMap, CMSMarkStack* markStack,
6905 HeapWord* finger, MarkFromRootsClosure* parent) :
6906 MetadataAwareOopClosure(collector->ref_processor()),
6907 _collector(collector),
6908 _span(span),
6909 _bitMap(bitMap),
6910 _markStack(markStack),
6911 _finger(finger),
6912 _parent(parent)
6913 { }
6914
6915 Par_PushOrMarkClosure::Par_PushOrMarkClosure(CMSCollector* collector,
6916 MemRegion span,
6917 CMSBitMap* bit_map,
6918 OopTaskQueue* work_queue,
6919 CMSMarkStack* overflow_stack,
6920 HeapWord* finger,
6921 HeapWord** global_finger_addr,
6922 Par_MarkFromRootsClosure* parent) :
6923 MetadataAwareOopClosure(collector->ref_processor()),
6924 _collector(collector),
6925 _whole_span(collector->_span),
6926 _span(span),
6927 _bit_map(bit_map),
6928 _work_queue(work_queue),
6929 _overflow_stack(overflow_stack),
6930 _finger(finger),
6931 _global_finger_addr(global_finger_addr),
6932 _parent(parent)
6933 { }
6934
6935 // Assumes thread-safe access by callers, who are
6936 // responsible for mutual exclusion.
6937 void CMSCollector::lower_restart_addr(HeapWord* low) {
6938 assert(_span.contains(low), "Out of bounds addr");
6939 if (_restart_addr == NULL) {
6940 _restart_addr = low;
6941 } else {
6942 _restart_addr = MIN2(_restart_addr, low);
6943 }
6944 }
6945
6946 // Upon stack overflow, we discard (part of) the stack,
6947 // remembering the least address amongst those discarded
6948 // in CMSCollector's _restart_address.
6949 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
6950 // Remember the least grey address discarded
6951 HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
6952 _collector->lower_restart_addr(ra);
6953 _markStack->reset(); // discard stack contents
6954 _markStack->expand(); // expand the stack if possible
6955 }
6956
6957 // Upon stack overflow, we discard (part of) the stack,
6958 // remembering the least address amongst those discarded
6959 // in CMSCollector's _restart_address.
6960 void Par_PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
6961 // We need to do this under a mutex to prevent other
6962 // workers from interfering with the work done below.
6963 MutexLockerEx ml(_overflow_stack->par_lock(),
6964 Mutex::_no_safepoint_check_flag);
6965 // Remember the least grey address discarded
6966 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
6967 _collector->lower_restart_addr(ra);
6968 _overflow_stack->reset(); // discard stack contents
6969 _overflow_stack->expand(); // expand the stack if possible
6970 }
6971
6972 void PushOrMarkClosure::do_oop(oop obj) {
6973 // Ignore mark word because we are running concurrent with mutators.
6974 assert(obj->is_oop_or_null(true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6975 HeapWord* addr = (HeapWord*)obj;
6976 if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
6977 // Oop lies in _span and isn't yet grey or black
6978 _bitMap->mark(addr); // now grey
6979 if (addr < _finger) {
6980 // the bit map iteration has already either passed, or
6981 // sampled, this bit in the bit map; we'll need to
6982 // use the marking stack to scan this oop's oops.
6983 bool simulate_overflow = false;
6984 NOT_PRODUCT(
6985 if (CMSMarkStackOverflowALot &&
6986 _collector->simulate_overflow()) {
6987 // simulate a stack overflow
6988 simulate_overflow = true;
6989 }
6990 )
6991 if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
6992 if (PrintCMSStatistics != 0) {
6993 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
6994 SIZE_FORMAT, _markStack->capacity());
6995 }
6996 assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
6997 handle_stack_overflow(addr);
6998 }
6999 }
7000 // anything including and to the right of _finger
7001 // will be scanned as we iterate over the remainder of the
7002 // bit map
7003 do_yield_check();
7004 }
7005 }
7006
7007 void PushOrMarkClosure::do_oop(oop* p) { PushOrMarkClosure::do_oop_work(p); }
7008 void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); }
7009
7010 void Par_PushOrMarkClosure::do_oop(oop obj) {
7011 // Ignore mark word because we are running concurrent with mutators.
7012 assert(obj->is_oop_or_null(true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
7013 HeapWord* addr = (HeapWord*)obj;
7014 if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
7015 // Oop lies in _span and isn't yet grey or black
7016 // We read the global_finger (volatile read) strictly after marking oop
7017 bool res = _bit_map->par_mark(addr); // now grey
7018 volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
7019 // Should we push this marked oop on our stack?
7020 // -- if someone else marked it, nothing to do
7021 // -- if target oop is above global finger nothing to do
7022 // -- if target oop is in chunk and above local finger
7023 // then nothing to do
7024 // -- else push on work queue
7025 if ( !res // someone else marked it, they will deal with it
7026 || (addr >= *gfa) // will be scanned in a later task
7027 || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
7028 return;
7029 }
7030 // the bit map iteration has already either passed, or
7031 // sampled, this bit in the bit map; we'll need to
7032 // use the marking stack to scan this oop's oops.
7033 bool simulate_overflow = false;
7034 NOT_PRODUCT(
7035 if (CMSMarkStackOverflowALot &&
7036 _collector->simulate_overflow()) {
7037 // simulate a stack overflow
7038 simulate_overflow = true;
7039 }
7040 )
7041 if (simulate_overflow ||
7042 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
7043 // stack overflow
7044 if (PrintCMSStatistics != 0) {
7045 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7046 SIZE_FORMAT, _overflow_stack->capacity());
7047 }
7048 // We cannot assert that the overflow stack is full because
7049 // it may have been emptied since.
7050 assert(simulate_overflow ||
7051 _work_queue->size() == _work_queue->max_elems(),
7052 "Else push should have succeeded");
7053 handle_stack_overflow(addr);
7054 }
7055 do_yield_check();
7056 }
7057 }
7058
7059 void Par_PushOrMarkClosure::do_oop(oop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7060 void Par_PushOrMarkClosure::do_oop(narrowOop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7061
7062 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
7063 MemRegion span,
7064 ReferenceProcessor* rp,
7065 CMSBitMap* bit_map,
7066 CMSBitMap* mod_union_table,
7067 CMSMarkStack* mark_stack,
7068 bool concurrent_precleaning):
7069 MetadataAwareOopClosure(rp),
7070 _collector(collector),
7071 _span(span),
7072 _bit_map(bit_map),
7073 _mod_union_table(mod_union_table),
7074 _mark_stack(mark_stack),
7075 _concurrent_precleaning(concurrent_precleaning)
7076 {
7077 assert(ref_processor() != NULL, "ref_processor shouldn't be NULL");
7078 }
7079
7080 // Grey object rescan during pre-cleaning and second checkpoint phases --
7081 // the non-parallel version (the parallel version appears further below.)
7082 void PushAndMarkClosure::do_oop(oop obj) {
7083 // Ignore mark word verification. If during concurrent precleaning,
7084 // the object monitor may be locked. If during the checkpoint
7085 // phases, the object may already have been reached by a different
7086 // path and may be at the end of the global overflow list (so
7087 // the mark word may be NULL).
7088 assert(obj->is_oop_or_null(true /* ignore mark word */),
7089 "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
7090 HeapWord* addr = (HeapWord*)obj;
7091 // Check if oop points into the CMS generation
7092 // and is not marked
7093 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7094 // a white object ...
7095 _bit_map->mark(addr); // ... now grey
7096 // push on the marking stack (grey set)
7097 bool simulate_overflow = false;
7098 NOT_PRODUCT(
7099 if (CMSMarkStackOverflowALot &&
7100 _collector->simulate_overflow()) {
7101 // simulate a stack overflow
7102 simulate_overflow = true;
7103 }
7104 )
7105 if (simulate_overflow || !_mark_stack->push(obj)) {
7106 if (_concurrent_precleaning) {
7107 // During precleaning we can just dirty the appropriate card(s)
7108 // in the mod union table, thus ensuring that the object remains
7109 // in the grey set and continue. In the case of object arrays
7110 // we need to dirty all of the cards that the object spans,
7111 // since the rescan of object arrays will be limited to the
7112 // dirty cards.
7113 // Note that no one can be interfering with us in this action
7114 // of dirtying the mod union table, so no locking or atomics
7115 // are required.
7116 if (obj->is_objArray()) {
7117 size_t sz = obj->size();
7118 HeapWord* end_card_addr = (HeapWord*)round_to(
7119 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7120 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7121 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7122 _mod_union_table->mark_range(redirty_range);
7123 } else {
7124 _mod_union_table->mark(addr);
7125 }
7126 _collector->_ser_pmc_preclean_ovflw++;
7127 } else {
7128 // During the remark phase, we need to remember this oop
7129 // in the overflow list.
7130 _collector->push_on_overflow_list(obj);
7131 _collector->_ser_pmc_remark_ovflw++;
7132 }
7133 }
7134 }
7135 }
7136
7137 Par_PushAndMarkClosure::Par_PushAndMarkClosure(CMSCollector* collector,
7138 MemRegion span,
7139 ReferenceProcessor* rp,
7140 CMSBitMap* bit_map,
7141 OopTaskQueue* work_queue):
7142 MetadataAwareOopClosure(rp),
7143 _collector(collector),
7144 _span(span),
7145 _bit_map(bit_map),
7146 _work_queue(work_queue)
7147 {
7148 assert(ref_processor() != NULL, "ref_processor shouldn't be NULL");
7149 }
7150
7151 void PushAndMarkClosure::do_oop(oop* p) { PushAndMarkClosure::do_oop_work(p); }
7152 void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); }
7153
7154 // Grey object rescan during second checkpoint phase --
7155 // the parallel version.
7156 void Par_PushAndMarkClosure::do_oop(oop obj) {
7157 // In the assert below, we ignore the mark word because
7158 // this oop may point to an already visited object that is
7159 // on the overflow stack (in which case the mark word has
7160 // been hijacked for chaining into the overflow stack --
7161 // if this is the last object in the overflow stack then
7162 // its mark word will be NULL). Because this object may
7163 // have been subsequently popped off the global overflow
7164 // stack, and the mark word possibly restored to the prototypical
7165 // value, by the time we get to examined this failing assert in
7166 // the debugger, is_oop_or_null(false) may subsequently start
7167 // to hold.
7168 assert(obj->is_oop_or_null(true),
7169 "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
7170 HeapWord* addr = (HeapWord*)obj;
7171 // Check if oop points into the CMS generation
7172 // and is not marked
7173 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7174 // a white object ...
7175 // If we manage to "claim" the object, by being the
7176 // first thread to mark it, then we push it on our
7177 // marking stack
7178 if (_bit_map->par_mark(addr)) { // ... now grey
7179 // push on work queue (grey set)
7180 bool simulate_overflow = false;
7181 NOT_PRODUCT(
7182 if (CMSMarkStackOverflowALot &&
7183 _collector->par_simulate_overflow()) {
7184 // simulate a stack overflow
7185 simulate_overflow = true;
7186 }
7187 )
7188 if (simulate_overflow || !_work_queue->push(obj)) {
7189 _collector->par_push_on_overflow_list(obj);
7190 _collector->_par_pmc_remark_ovflw++; // imprecise OK: no need to CAS
7191 }
7192 } // Else, some other thread got there first
7193 }
7194 }
7195
7196 void Par_PushAndMarkClosure::do_oop(oop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7197 void Par_PushAndMarkClosure::do_oop(narrowOop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7198
7199 void CMSPrecleanRefsYieldClosure::do_yield_work() {
7200 Mutex* bml = _collector->bitMapLock();
7201 assert_lock_strong(bml);
7202 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7203 "CMS thread should hold CMS token");
7204
7205 bml->unlock();
7206 ConcurrentMarkSweepThread::desynchronize(true);
7207
7208 _collector->stopTimer();
7209 if (PrintCMSStatistics != 0) {
7210 _collector->incrementYields();
7211 }
7212
7213 // See the comment in coordinator_yield()
7214 for (unsigned i = 0; i < CMSYieldSleepCount &&
7215 ConcurrentMarkSweepThread::should_yield() &&
7216 !CMSCollector::foregroundGCIsActive(); ++i) {
7217 os::sleep(Thread::current(), 1, false);
7218 }
7219
7220 ConcurrentMarkSweepThread::synchronize(true);
7221 bml->lock();
7222
7223 _collector->startTimer();
7224 }
7225
7226 bool CMSPrecleanRefsYieldClosure::should_return() {
7227 if (ConcurrentMarkSweepThread::should_yield()) {
7228 do_yield_work();
7229 }
7230 return _collector->foregroundGCIsActive();
7231 }
7232
7233 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
7234 assert(((size_t)mr.start())%CardTableModRefBS::card_size_in_words == 0,
7235 "mr should be aligned to start at a card boundary");
7236 // We'd like to assert:
7237 // assert(mr.word_size()%CardTableModRefBS::card_size_in_words == 0,
7238 // "mr should be a range of cards");
7239 // However, that would be too strong in one case -- the last
7240 // partition ends at _unallocated_block which, in general, can be
7241 // an arbitrary boundary, not necessarily card aligned.
7242 if (PrintCMSStatistics != 0) {
7243 _num_dirty_cards +=
7244 mr.word_size()/CardTableModRefBS::card_size_in_words;
7245 }
7246 _space->object_iterate_mem(mr, &_scan_cl);
7247 }
7248
7249 SweepClosure::SweepClosure(CMSCollector* collector,
7250 ConcurrentMarkSweepGeneration* g,
7251 CMSBitMap* bitMap, bool should_yield) :
7252 _collector(collector),
7253 _g(g),
7254 _sp(g->cmsSpace()),
7255 _limit(_sp->sweep_limit()),
7256 _freelistLock(_sp->freelistLock()),
7257 _bitMap(bitMap),
7258 _yield(should_yield),
7259 _inFreeRange(false), // No free range at beginning of sweep
7260 _freeRangeInFreeLists(false), // No free range at beginning of sweep
7261 _lastFreeRangeCoalesced(false),
7262 _freeFinger(g->used_region().start())
7263 {
7264 NOT_PRODUCT(
7265 _numObjectsFreed = 0;
7266 _numWordsFreed = 0;
7267 _numObjectsLive = 0;
7268 _numWordsLive = 0;
7269 _numObjectsAlreadyFree = 0;
7270 _numWordsAlreadyFree = 0;
7271 _last_fc = NULL;
7272
7273 _sp->initializeIndexedFreeListArrayReturnedBytes();
7274 _sp->dictionary()->initialize_dict_returned_bytes();
7275 )
7276 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7277 "sweep _limit out of bounds");
7278 if (CMSTraceSweeper) {
7279 gclog_or_tty->print_cr("\n====================\nStarting new sweep with limit " PTR_FORMAT,
7280 p2i(_limit));
7281 }
7282 }
7283
7284 void SweepClosure::print_on(outputStream* st) const {
7285 tty->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")",
7286 p2i(_sp->bottom()), p2i(_sp->end()));
7287 tty->print_cr("_limit = " PTR_FORMAT, p2i(_limit));
7288 tty->print_cr("_freeFinger = " PTR_FORMAT, p2i(_freeFinger));
7289 NOT_PRODUCT(tty->print_cr("_last_fc = " PTR_FORMAT, p2i(_last_fc));)
7290 tty->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d",
7291 _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced);
7292 }
7293
7294 #ifndef PRODUCT
7295 // Assertion checking only: no useful work in product mode --
7296 // however, if any of the flags below become product flags,
7297 // you may need to review this code to see if it needs to be
7298 // enabled in product mode.
7299 SweepClosure::~SweepClosure() {
7300 assert_lock_strong(_freelistLock);
7301 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7302 "sweep _limit out of bounds");
7303 if (inFreeRange()) {
7304 warning("inFreeRange() should have been reset; dumping state of SweepClosure");
7305 print();
7306 ShouldNotReachHere();
7307 }
7308 if (Verbose && PrintGC) {
7309 gclog_or_tty->print("Collected " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
7310 _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
7311 gclog_or_tty->print_cr("\nLive " SIZE_FORMAT " objects, "
7312 SIZE_FORMAT " bytes "
7313 "Already free " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
7314 _numObjectsLive, _numWordsLive*sizeof(HeapWord),
7315 _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
7316 size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree)
7317 * sizeof(HeapWord);
7318 gclog_or_tty->print_cr("Total sweep: " SIZE_FORMAT " bytes", totalBytes);
7319
7320 if (PrintCMSStatistics && CMSVerifyReturnedBytes) {
7321 size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
7322 size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes();
7323 size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes;
7324 gclog_or_tty->print("Returned " SIZE_FORMAT " bytes", returned_bytes);
7325 gclog_or_tty->print(" Indexed List Returned " SIZE_FORMAT " bytes",
7326 indexListReturnedBytes);
7327 gclog_or_tty->print_cr(" Dictionary Returned " SIZE_FORMAT " bytes",
7328 dict_returned_bytes);
7329 }
7330 }
7331 if (CMSTraceSweeper) {
7332 gclog_or_tty->print_cr("end of sweep with _limit = " PTR_FORMAT "\n================",
7333 p2i(_limit));
7334 }
7335 }
7336 #endif // PRODUCT
7337
7338 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
7339 bool freeRangeInFreeLists) {
7340 if (CMSTraceSweeper) {
7341 gclog_or_tty->print("---- Start free range at " PTR_FORMAT " with free block (%d)\n",
7342 p2i(freeFinger), freeRangeInFreeLists);
7343 }
7344 assert(!inFreeRange(), "Trampling existing free range");
7345 set_inFreeRange(true);
7346 set_lastFreeRangeCoalesced(false);
7347
7348 set_freeFinger(freeFinger);
7349 set_freeRangeInFreeLists(freeRangeInFreeLists);
7350 if (CMSTestInFreeList) {
7351 if (freeRangeInFreeLists) {
7352 FreeChunk* fc = (FreeChunk*) freeFinger;
7353 assert(fc->is_free(), "A chunk on the free list should be free.");
7354 assert(fc->size() > 0, "Free range should have a size");
7355 assert(_sp->verify_chunk_in_free_list(fc), "Chunk is not in free lists");
7356 }
7357 }
7358 }
7359
7360 // Note that the sweeper runs concurrently with mutators. Thus,
7361 // it is possible for direct allocation in this generation to happen
7362 // in the middle of the sweep. Note that the sweeper also coalesces
7363 // contiguous free blocks. Thus, unless the sweeper and the allocator
7364 // synchronize appropriately freshly allocated blocks may get swept up.
7365 // This is accomplished by the sweeper locking the free lists while
7366 // it is sweeping. Thus blocks that are determined to be free are
7367 // indeed free. There is however one additional complication:
7368 // blocks that have been allocated since the final checkpoint and
7369 // mark, will not have been marked and so would be treated as
7370 // unreachable and swept up. To prevent this, the allocator marks
7371 // the bit map when allocating during the sweep phase. This leads,
7372 // however, to a further complication -- objects may have been allocated
7373 // but not yet initialized -- in the sense that the header isn't yet
7374 // installed. The sweeper can not then determine the size of the block
7375 // in order to skip over it. To deal with this case, we use a technique
7376 // (due to Printezis) to encode such uninitialized block sizes in the
7377 // bit map. Since the bit map uses a bit per every HeapWord, but the
7378 // CMS generation has a minimum object size of 3 HeapWords, it follows
7379 // that "normal marks" won't be adjacent in the bit map (there will
7380 // always be at least two 0 bits between successive 1 bits). We make use
7381 // of these "unused" bits to represent uninitialized blocks -- the bit
7382 // corresponding to the start of the uninitialized object and the next
7383 // bit are both set. Finally, a 1 bit marks the end of the object that
7384 // started with the two consecutive 1 bits to indicate its potentially
7385 // uninitialized state.
7386
7387 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
7388 FreeChunk* fc = (FreeChunk*)addr;
7389 size_t res;
7390
7391 // Check if we are done sweeping. Below we check "addr >= _limit" rather
7392 // than "addr == _limit" because although _limit was a block boundary when
7393 // we started the sweep, it may no longer be one because heap expansion
7394 // may have caused us to coalesce the block ending at the address _limit
7395 // with a newly expanded chunk (this happens when _limit was set to the
7396 // previous _end of the space), so we may have stepped past _limit:
7397 // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740.
7398 if (addr >= _limit) { // we have swept up to or past the limit: finish up
7399 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7400 "sweep _limit out of bounds");
7401 assert(addr < _sp->end(), "addr out of bounds");
7402 // Flush any free range we might be holding as a single
7403 // coalesced chunk to the appropriate free list.
7404 if (inFreeRange()) {
7405 assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit,
7406 "freeFinger() " PTR_FORMAT " is out-of-bounds", p2i(freeFinger()));
7407 flush_cur_free_chunk(freeFinger(),
7408 pointer_delta(addr, freeFinger()));
7409 if (CMSTraceSweeper) {
7410 gclog_or_tty->print("Sweep: last chunk: ");
7411 gclog_or_tty->print("put_free_blk " PTR_FORMAT " (" SIZE_FORMAT ") "
7412 "[coalesced:%d]\n",
7413 p2i(freeFinger()), pointer_delta(addr, freeFinger()),
7414 lastFreeRangeCoalesced() ? 1 : 0);
7415 }
7416 }
7417
7418 // help the iterator loop finish
7419 return pointer_delta(_sp->end(), addr);
7420 }
7421
7422 assert(addr < _limit, "sweep invariant");
7423 // check if we should yield
7424 do_yield_check(addr);
7425 if (fc->is_free()) {
7426 // Chunk that is already free
7427 res = fc->size();
7428 do_already_free_chunk(fc);
7429 debug_only(_sp->verifyFreeLists());
7430 // If we flush the chunk at hand in lookahead_and_flush()
7431 // and it's coalesced with a preceding chunk, then the
7432 // process of "mangling" the payload of the coalesced block
7433 // will cause erasure of the size information from the
7434 // (erstwhile) header of all the coalesced blocks but the
7435 // first, so the first disjunct in the assert will not hold
7436 // in that specific case (in which case the second disjunct
7437 // will hold).
7438 assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit,
7439 "Otherwise the size info doesn't change at this step");
7440 NOT_PRODUCT(
7441 _numObjectsAlreadyFree++;
7442 _numWordsAlreadyFree += res;
7443 )
7444 NOT_PRODUCT(_last_fc = fc;)
7445 } else if (!_bitMap->isMarked(addr)) {
7446 // Chunk is fresh garbage
7447 res = do_garbage_chunk(fc);
7448 debug_only(_sp->verifyFreeLists());
7449 NOT_PRODUCT(
7450 _numObjectsFreed++;
7451 _numWordsFreed += res;
7452 )
7453 } else {
7454 // Chunk that is alive.
7455 res = do_live_chunk(fc);
7456 debug_only(_sp->verifyFreeLists());
7457 NOT_PRODUCT(
7458 _numObjectsLive++;
7459 _numWordsLive += res;
7460 )
7461 }
7462 return res;
7463 }
7464
7465 // For the smart allocation, record following
7466 // split deaths - a free chunk is removed from its free list because
7467 // it is being split into two or more chunks.
7468 // split birth - a free chunk is being added to its free list because
7469 // a larger free chunk has been split and resulted in this free chunk.
7470 // coal death - a free chunk is being removed from its free list because
7471 // it is being coalesced into a large free chunk.
7472 // coal birth - a free chunk is being added to its free list because
7473 // it was created when two or more free chunks where coalesced into
7474 // this free chunk.
7475 //
7476 // These statistics are used to determine the desired number of free
7477 // chunks of a given size. The desired number is chosen to be relative
7478 // to the end of a CMS sweep. The desired number at the end of a sweep
7479 // is the
7480 // count-at-end-of-previous-sweep (an amount that was enough)
7481 // - count-at-beginning-of-current-sweep (the excess)
7482 // + split-births (gains in this size during interval)
7483 // - split-deaths (demands on this size during interval)
7484 // where the interval is from the end of one sweep to the end of the
7485 // next.
7486 //
7487 // When sweeping the sweeper maintains an accumulated chunk which is
7488 // the chunk that is made up of chunks that have been coalesced. That
7489 // will be termed the left-hand chunk. A new chunk of garbage that
7490 // is being considered for coalescing will be referred to as the
7491 // right-hand chunk.
7492 //
7493 // When making a decision on whether to coalesce a right-hand chunk with
7494 // the current left-hand chunk, the current count vs. the desired count
7495 // of the left-hand chunk is considered. Also if the right-hand chunk
7496 // is near the large chunk at the end of the heap (see
7497 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
7498 // left-hand chunk is coalesced.
7499 //
7500 // When making a decision about whether to split a chunk, the desired count
7501 // vs. the current count of the candidate to be split is also considered.
7502 // If the candidate is underpopulated (currently fewer chunks than desired)
7503 // a chunk of an overpopulated (currently more chunks than desired) size may
7504 // be chosen. The "hint" associated with a free list, if non-null, points
7505 // to a free list which may be overpopulated.
7506 //
7507
7508 void SweepClosure::do_already_free_chunk(FreeChunk* fc) {
7509 const size_t size = fc->size();
7510 // Chunks that cannot be coalesced are not in the
7511 // free lists.
7512 if (CMSTestInFreeList && !fc->cantCoalesce()) {
7513 assert(_sp->verify_chunk_in_free_list(fc),
7514 "free chunk should be in free lists");
7515 }
7516 // a chunk that is already free, should not have been
7517 // marked in the bit map
7518 HeapWord* const addr = (HeapWord*) fc;
7519 assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
7520 // Verify that the bit map has no bits marked between
7521 // addr and purported end of this block.
7522 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7523
7524 // Some chunks cannot be coalesced under any circumstances.
7525 // See the definition of cantCoalesce().
7526 if (!fc->cantCoalesce()) {
7527 // This chunk can potentially be coalesced.
7528 // All the work is done in
7529 do_post_free_or_garbage_chunk(fc, size);
7530 // Note that if the chunk is not coalescable (the else arm
7531 // below), we unconditionally flush, without needing to do
7532 // a "lookahead," as we do below.
7533 if (inFreeRange()) lookahead_and_flush(fc, size);
7534 } else {
7535 // Code path common to both original and adaptive free lists.
7536
7537 // cant coalesce with previous block; this should be treated
7538 // as the end of a free run if any
7539 if (inFreeRange()) {
7540 // we kicked some butt; time to pick up the garbage
7541 assert(freeFinger() < addr, "freeFinger points too high");
7542 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7543 }
7544 // else, nothing to do, just continue
7545 }
7546 }
7547
7548 size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) {
7549 // This is a chunk of garbage. It is not in any free list.
7550 // Add it to a free list or let it possibly be coalesced into
7551 // a larger chunk.
7552 HeapWord* const addr = (HeapWord*) fc;
7553 const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7554
7555 // Verify that the bit map has no bits marked between
7556 // addr and purported end of just dead object.
7557 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7558 do_post_free_or_garbage_chunk(fc, size);
7559
7560 assert(_limit >= addr + size,
7561 "A freshly garbage chunk can't possibly straddle over _limit");
7562 if (inFreeRange()) lookahead_and_flush(fc, size);
7563 return size;
7564 }
7565
7566 size_t SweepClosure::do_live_chunk(FreeChunk* fc) {
7567 HeapWord* addr = (HeapWord*) fc;
7568 // The sweeper has just found a live object. Return any accumulated
7569 // left hand chunk to the free lists.
7570 if (inFreeRange()) {
7571 assert(freeFinger() < addr, "freeFinger points too high");
7572 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7573 }
7574
7575 // This object is live: we'd normally expect this to be
7576 // an oop, and like to assert the following:
7577 // assert(oop(addr)->is_oop(), "live block should be an oop");
7578 // However, as we commented above, this may be an object whose
7579 // header hasn't yet been initialized.
7580 size_t size;
7581 assert(_bitMap->isMarked(addr), "Tautology for this control point");
7582 if (_bitMap->isMarked(addr + 1)) {
7583 // Determine the size from the bit map, rather than trying to
7584 // compute it from the object header.
7585 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
7586 size = pointer_delta(nextOneAddr + 1, addr);
7587 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
7588 "alignment problem");
7589
7590 #ifdef ASSERT
7591 if (oop(addr)->klass_or_null() != NULL) {
7592 // Ignore mark word because we are running concurrent with mutators
7593 assert(oop(addr)->is_oop(true), "live block should be an oop");
7594 assert(size ==
7595 CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
7596 "P-mark and computed size do not agree");
7597 }
7598 #endif
7599
7600 } else {
7601 // This should be an initialized object that's alive.
7602 assert(oop(addr)->klass_or_null() != NULL,
7603 "Should be an initialized object");
7604 // Ignore mark word because we are running concurrent with mutators
7605 assert(oop(addr)->is_oop(true), "live block should be an oop");
7606 // Verify that the bit map has no bits marked between
7607 // addr and purported end of this block.
7608 size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7609 assert(size >= 3, "Necessary for Printezis marks to work");
7610 assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
7611 DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
7612 }
7613 return size;
7614 }
7615
7616 void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc,
7617 size_t chunkSize) {
7618 // do_post_free_or_garbage_chunk() should only be called in the case
7619 // of the adaptive free list allocator.
7620 const bool fcInFreeLists = fc->is_free();
7621 assert((HeapWord*)fc <= _limit, "sweep invariant");
7622 if (CMSTestInFreeList && fcInFreeLists) {
7623 assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists");
7624 }
7625
7626 if (CMSTraceSweeper) {
7627 gclog_or_tty->print_cr(" -- pick up another chunk at " PTR_FORMAT " (" SIZE_FORMAT ")", p2i(fc), chunkSize);
7628 }
7629
7630 HeapWord* const fc_addr = (HeapWord*) fc;
7631
7632 bool coalesce = false;
7633 const size_t left = pointer_delta(fc_addr, freeFinger());
7634 const size_t right = chunkSize;
7635 switch (FLSCoalescePolicy) {
7636 // numeric value forms a coalition aggressiveness metric
7637 case 0: { // never coalesce
7638 coalesce = false;
7639 break;
7640 }
7641 case 1: { // coalesce if left & right chunks on overpopulated lists
7642 coalesce = _sp->coalOverPopulated(left) &&
7643 _sp->coalOverPopulated(right);
7644 break;
7645 }
7646 case 2: { // coalesce if left chunk on overpopulated list (default)
7647 coalesce = _sp->coalOverPopulated(left);
7648 break;
7649 }
7650 case 3: { // coalesce if left OR right chunk on overpopulated list
7651 coalesce = _sp->coalOverPopulated(left) ||
7652 _sp->coalOverPopulated(right);
7653 break;
7654 }
7655 case 4: { // always coalesce
7656 coalesce = true;
7657 break;
7658 }
7659 default:
7660 ShouldNotReachHere();
7661 }
7662
7663 // Should the current free range be coalesced?
7664 // If the chunk is in a free range and either we decided to coalesce above
7665 // or the chunk is near the large block at the end of the heap
7666 // (isNearLargestChunk() returns true), then coalesce this chunk.
7667 const bool doCoalesce = inFreeRange()
7668 && (coalesce || _g->isNearLargestChunk(fc_addr));
7669 if (doCoalesce) {
7670 // Coalesce the current free range on the left with the new
7671 // chunk on the right. If either is on a free list,
7672 // it must be removed from the list and stashed in the closure.
7673 if (freeRangeInFreeLists()) {
7674 FreeChunk* const ffc = (FreeChunk*)freeFinger();
7675 assert(ffc->size() == pointer_delta(fc_addr, freeFinger()),
7676 "Size of free range is inconsistent with chunk size.");
7677 if (CMSTestInFreeList) {
7678 assert(_sp->verify_chunk_in_free_list(ffc),
7679 "Chunk is not in free lists");
7680 }
7681 _sp->coalDeath(ffc->size());
7682 _sp->removeFreeChunkFromFreeLists(ffc);
7683 set_freeRangeInFreeLists(false);
7684 }
7685 if (fcInFreeLists) {
7686 _sp->coalDeath(chunkSize);
7687 assert(fc->size() == chunkSize,
7688 "The chunk has the wrong size or is not in the free lists");
7689 _sp->removeFreeChunkFromFreeLists(fc);
7690 }
7691 set_lastFreeRangeCoalesced(true);
7692 print_free_block_coalesced(fc);
7693 } else { // not in a free range and/or should not coalesce
7694 // Return the current free range and start a new one.
7695 if (inFreeRange()) {
7696 // In a free range but cannot coalesce with the right hand chunk.
7697 // Put the current free range into the free lists.
7698 flush_cur_free_chunk(freeFinger(),
7699 pointer_delta(fc_addr, freeFinger()));
7700 }
7701 // Set up for new free range. Pass along whether the right hand
7702 // chunk is in the free lists.
7703 initialize_free_range((HeapWord*)fc, fcInFreeLists);
7704 }
7705 }
7706
7707 // Lookahead flush:
7708 // If we are tracking a free range, and this is the last chunk that
7709 // we'll look at because its end crosses past _limit, we'll preemptively
7710 // flush it along with any free range we may be holding on to. Note that
7711 // this can be the case only for an already free or freshly garbage
7712 // chunk. If this block is an object, it can never straddle
7713 // over _limit. The "straddling" occurs when _limit is set at
7714 // the previous end of the space when this cycle started, and
7715 // a subsequent heap expansion caused the previously co-terminal
7716 // free block to be coalesced with the newly expanded portion,
7717 // thus rendering _limit a non-block-boundary making it dangerous
7718 // for the sweeper to step over and examine.
7719 void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) {
7720 assert(inFreeRange(), "Should only be called if currently in a free range.");
7721 HeapWord* const eob = ((HeapWord*)fc) + chunk_size;
7722 assert(_sp->used_region().contains(eob - 1),
7723 "eob = " PTR_FORMAT " eob-1 = " PTR_FORMAT " _limit = " PTR_FORMAT
7724 " out of bounds wrt _sp = [" PTR_FORMAT "," PTR_FORMAT ")"
7725 " when examining fc = " PTR_FORMAT "(" SIZE_FORMAT ")",
7726 p2i(eob), p2i(eob-1), p2i(_limit), p2i(_sp->bottom()), p2i(_sp->end()), p2i(fc), chunk_size);
7727 if (eob >= _limit) {
7728 assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit");
7729 if (CMSTraceSweeper) {
7730 gclog_or_tty->print_cr("_limit " PTR_FORMAT " reached or crossed by block "
7731 "[" PTR_FORMAT "," PTR_FORMAT ") in space "
7732 "[" PTR_FORMAT "," PTR_FORMAT ")",
7733 p2i(_limit), p2i(fc), p2i(eob), p2i(_sp->bottom()), p2i(_sp->end()));
7734 }
7735 // Return the storage we are tracking back into the free lists.
7736 if (CMSTraceSweeper) {
7737 gclog_or_tty->print_cr("Flushing ... ");
7738 }
7739 assert(freeFinger() < eob, "Error");
7740 flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger()));
7741 }
7742 }
7743
7744 void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) {
7745 assert(inFreeRange(), "Should only be called if currently in a free range.");
7746 assert(size > 0,
7747 "A zero sized chunk cannot be added to the free lists.");
7748 if (!freeRangeInFreeLists()) {
7749 if (CMSTestInFreeList) {
7750 FreeChunk* fc = (FreeChunk*) chunk;
7751 fc->set_size(size);
7752 assert(!_sp->verify_chunk_in_free_list(fc),
7753 "chunk should not be in free lists yet");
7754 }
7755 if (CMSTraceSweeper) {
7756 gclog_or_tty->print_cr(" -- add free block " PTR_FORMAT " (" SIZE_FORMAT ") to free lists",
7757 p2i(chunk), size);
7758 }
7759 // A new free range is going to be starting. The current
7760 // free range has not been added to the free lists yet or
7761 // was removed so add it back.
7762 // If the current free range was coalesced, then the death
7763 // of the free range was recorded. Record a birth now.
7764 if (lastFreeRangeCoalesced()) {
7765 _sp->coalBirth(size);
7766 }
7767 _sp->addChunkAndRepairOffsetTable(chunk, size,
7768 lastFreeRangeCoalesced());
7769 } else if (CMSTraceSweeper) {
7770 gclog_or_tty->print_cr("Already in free list: nothing to flush");
7771 }
7772 set_inFreeRange(false);
7773 set_freeRangeInFreeLists(false);
7774 }
7775
7776 // We take a break if we've been at this for a while,
7777 // so as to avoid monopolizing the locks involved.
7778 void SweepClosure::do_yield_work(HeapWord* addr) {
7779 // Return current free chunk being used for coalescing (if any)
7780 // to the appropriate freelist. After yielding, the next
7781 // free block encountered will start a coalescing range of
7782 // free blocks. If the next free block is adjacent to the
7783 // chunk just flushed, they will need to wait for the next
7784 // sweep to be coalesced.
7785 if (inFreeRange()) {
7786 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7787 }
7788
7789 // First give up the locks, then yield, then re-lock.
7790 // We should probably use a constructor/destructor idiom to
7791 // do this unlock/lock or modify the MutexUnlocker class to
7792 // serve our purpose. XXX
7793 assert_lock_strong(_bitMap->lock());
7794 assert_lock_strong(_freelistLock);
7795 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7796 "CMS thread should hold CMS token");
7797 _bitMap->lock()->unlock();
7798 _freelistLock->unlock();
7799 ConcurrentMarkSweepThread::desynchronize(true);
7800 _collector->stopTimer();
7801 if (PrintCMSStatistics != 0) {
7802 _collector->incrementYields();
7803 }
7804
7805 // See the comment in coordinator_yield()
7806 for (unsigned i = 0; i < CMSYieldSleepCount &&
7807 ConcurrentMarkSweepThread::should_yield() &&
7808 !CMSCollector::foregroundGCIsActive(); ++i) {
7809 os::sleep(Thread::current(), 1, false);
7810 }
7811
7812 ConcurrentMarkSweepThread::synchronize(true);
7813 _freelistLock->lock();
7814 _bitMap->lock()->lock_without_safepoint_check();
7815 _collector->startTimer();
7816 }
7817
7818 #ifndef PRODUCT
7819 // This is actually very useful in a product build if it can
7820 // be called from the debugger. Compile it into the product
7821 // as needed.
7822 bool debug_verify_chunk_in_free_list(FreeChunk* fc) {
7823 return debug_cms_space->verify_chunk_in_free_list(fc);
7824 }
7825 #endif
7826
7827 void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const {
7828 if (CMSTraceSweeper) {
7829 gclog_or_tty->print_cr("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")",
7830 p2i(fc), fc->size());
7831 }
7832 }
7833
7834 // CMSIsAliveClosure
7835 bool CMSIsAliveClosure::do_object_b(oop obj) {
7836 HeapWord* addr = (HeapWord*)obj;
7837 return addr != NULL &&
7838 (!_span.contains(addr) || _bit_map->isMarked(addr));
7839 }
7840
7841
7842 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector,
7843 MemRegion span,
7844 CMSBitMap* bit_map, CMSMarkStack* mark_stack,
7845 bool cpc):
7846 _collector(collector),
7847 _span(span),
7848 _bit_map(bit_map),
7849 _mark_stack(mark_stack),
7850 _concurrent_precleaning(cpc) {
7851 assert(!_span.is_empty(), "Empty span could spell trouble");
7852 }
7853
7854
7855 // CMSKeepAliveClosure: the serial version
7856 void CMSKeepAliveClosure::do_oop(oop obj) {
7857 HeapWord* addr = (HeapWord*)obj;
7858 if (_span.contains(addr) &&
7859 !_bit_map->isMarked(addr)) {
7860 _bit_map->mark(addr);
7861 bool simulate_overflow = false;
7862 NOT_PRODUCT(
7863 if (CMSMarkStackOverflowALot &&
7864 _collector->simulate_overflow()) {
7865 // simulate a stack overflow
7866 simulate_overflow = true;
7867 }
7868 )
7869 if (simulate_overflow || !_mark_stack->push(obj)) {
7870 if (_concurrent_precleaning) {
7871 // We dirty the overflown object and let the remark
7872 // phase deal with it.
7873 assert(_collector->overflow_list_is_empty(), "Error");
7874 // In the case of object arrays, we need to dirty all of
7875 // the cards that the object spans. No locking or atomics
7876 // are needed since no one else can be mutating the mod union
7877 // table.
7878 if (obj->is_objArray()) {
7879 size_t sz = obj->size();
7880 HeapWord* end_card_addr =
7881 (HeapWord*)round_to((intptr_t)(addr+sz), CardTableModRefBS::card_size);
7882 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7883 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7884 _collector->_modUnionTable.mark_range(redirty_range);
7885 } else {
7886 _collector->_modUnionTable.mark(addr);
7887 }
7888 _collector->_ser_kac_preclean_ovflw++;
7889 } else {
7890 _collector->push_on_overflow_list(obj);
7891 _collector->_ser_kac_ovflw++;
7892 }
7893 }
7894 }
7895 }
7896
7897 void CMSKeepAliveClosure::do_oop(oop* p) { CMSKeepAliveClosure::do_oop_work(p); }
7898 void CMSKeepAliveClosure::do_oop(narrowOop* p) { CMSKeepAliveClosure::do_oop_work(p); }
7899
7900 // CMSParKeepAliveClosure: a parallel version of the above.
7901 // The work queues are private to each closure (thread),
7902 // but (may be) available for stealing by other threads.
7903 void CMSParKeepAliveClosure::do_oop(oop obj) {
7904 HeapWord* addr = (HeapWord*)obj;
7905 if (_span.contains(addr) &&
7906 !_bit_map->isMarked(addr)) {
7907 // In general, during recursive tracing, several threads
7908 // may be concurrently getting here; the first one to
7909 // "tag" it, claims it.
7910 if (_bit_map->par_mark(addr)) {
7911 bool res = _work_queue->push(obj);
7912 assert(res, "Low water mark should be much less than capacity");
7913 // Do a recursive trim in the hope that this will keep
7914 // stack usage lower, but leave some oops for potential stealers
7915 trim_queue(_low_water_mark);
7916 } // Else, another thread got there first
7917 }
7918 }
7919
7920 void CMSParKeepAliveClosure::do_oop(oop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
7921 void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
7922
7923 void CMSParKeepAliveClosure::trim_queue(uint max) {
7924 while (_work_queue->size() > max) {
7925 oop new_oop;
7926 if (_work_queue->pop_local(new_oop)) {
7927 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
7928 assert(_bit_map->isMarked((HeapWord*)new_oop),
7929 "no white objects on this stack!");
7930 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
7931 // iterate over the oops in this oop, marking and pushing
7932 // the ones in CMS heap (i.e. in _span).
7933 new_oop->oop_iterate(&_mark_and_push);
7934 }
7935 }
7936 }
7937
7938 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
7939 CMSCollector* collector,
7940 MemRegion span, CMSBitMap* bit_map,
7941 OopTaskQueue* work_queue):
7942 _collector(collector),
7943 _span(span),
7944 _bit_map(bit_map),
7945 _work_queue(work_queue) { }
7946
7947 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
7948 HeapWord* addr = (HeapWord*)obj;
7949 if (_span.contains(addr) &&
7950 !_bit_map->isMarked(addr)) {
7951 if (_bit_map->par_mark(addr)) {
7952 bool simulate_overflow = false;
7953 NOT_PRODUCT(
7954 if (CMSMarkStackOverflowALot &&
7955 _collector->par_simulate_overflow()) {
7956 // simulate a stack overflow
7957 simulate_overflow = true;
7958 }
7959 )
7960 if (simulate_overflow || !_work_queue->push(obj)) {
7961 _collector->par_push_on_overflow_list(obj);
7962 _collector->_par_kac_ovflw++;
7963 }
7964 } // Else another thread got there already
7965 }
7966 }
7967
7968 void CMSInnerParMarkAndPushClosure::do_oop(oop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
7969 void CMSInnerParMarkAndPushClosure::do_oop(narrowOop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
7970
7971 //////////////////////////////////////////////////////////////////
7972 // CMSExpansionCause /////////////////////////////
7973 //////////////////////////////////////////////////////////////////
7974 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
7975 switch (cause) {
7976 case _no_expansion:
7977 return "No expansion";
7978 case _satisfy_free_ratio:
7979 return "Free ratio";
7980 case _satisfy_promotion:
7981 return "Satisfy promotion";
7982 case _satisfy_allocation:
7983 return "allocation";
7984 case _allocate_par_lab:
7985 return "Par LAB";
7986 case _allocate_par_spooling_space:
7987 return "Par Spooling Space";
7988 case _adaptive_size_policy:
7989 return "Ergonomics";
7990 default:
7991 return "unknown";
7992 }
7993 }
7994
7995 void CMSDrainMarkingStackClosure::do_void() {
7996 // the max number to take from overflow list at a time
7997 const size_t num = _mark_stack->capacity()/4;
7998 assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
7999 "Overflow list should be NULL during concurrent phases");
8000 while (!_mark_stack->isEmpty() ||
8001 // if stack is empty, check the overflow list
8002 _collector->take_from_overflow_list(num, _mark_stack)) {
8003 oop obj = _mark_stack->pop();
8004 HeapWord* addr = (HeapWord*)obj;
8005 assert(_span.contains(addr), "Should be within span");
8006 assert(_bit_map->isMarked(addr), "Should be marked");
8007 assert(obj->is_oop(), "Should be an oop");
8008 obj->oop_iterate(_keep_alive);
8009 }
8010 }
8011
8012 void CMSParDrainMarkingStackClosure::do_void() {
8013 // drain queue
8014 trim_queue(0);
8015 }
8016
8017 // Trim our work_queue so its length is below max at return
8018 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
8019 while (_work_queue->size() > max) {
8020 oop new_oop;
8021 if (_work_queue->pop_local(new_oop)) {
8022 assert(new_oop->is_oop(), "Expected an oop");
8023 assert(_bit_map->isMarked((HeapWord*)new_oop),
8024 "no white objects on this stack!");
8025 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8026 // iterate over the oops in this oop, marking and pushing
8027 // the ones in CMS heap (i.e. in _span).
8028 new_oop->oop_iterate(&_mark_and_push);
8029 }
8030 }
8031 }
8032
8033 ////////////////////////////////////////////////////////////////////
8034 // Support for Marking Stack Overflow list handling and related code
8035 ////////////////////////////////////////////////////////////////////
8036 // Much of the following code is similar in shape and spirit to the
8037 // code used in ParNewGC. We should try and share that code
8038 // as much as possible in the future.
8039
8040 #ifndef PRODUCT
8041 // Debugging support for CMSStackOverflowALot
8042
8043 // It's OK to call this multi-threaded; the worst thing
8044 // that can happen is that we'll get a bunch of closely
8045 // spaced simulated overflows, but that's OK, in fact
8046 // probably good as it would exercise the overflow code
8047 // under contention.
8048 bool CMSCollector::simulate_overflow() {
8049 if (_overflow_counter-- <= 0) { // just being defensive
8050 _overflow_counter = CMSMarkStackOverflowInterval;
8051 return true;
8052 } else {
8053 return false;
8054 }
8055 }
8056
8057 bool CMSCollector::par_simulate_overflow() {
8058 return simulate_overflow();
8059 }
8060 #endif
8061
8062 // Single-threaded
8063 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
8064 assert(stack->isEmpty(), "Expected precondition");
8065 assert(stack->capacity() > num, "Shouldn't bite more than can chew");
8066 size_t i = num;
8067 oop cur = _overflow_list;
8068 const markOop proto = markOopDesc::prototype();
8069 NOT_PRODUCT(ssize_t n = 0;)
8070 for (oop next; i > 0 && cur != NULL; cur = next, i--) {
8071 next = oop(cur->mark());
8072 cur->set_mark(proto); // until proven otherwise
8073 assert(cur->is_oop(), "Should be an oop");
8074 bool res = stack->push(cur);
8075 assert(res, "Bit off more than can chew?");
8076 NOT_PRODUCT(n++;)
8077 }
8078 _overflow_list = cur;
8079 #ifndef PRODUCT
8080 assert(_num_par_pushes >= n, "Too many pops?");
8081 _num_par_pushes -=n;
8082 #endif
8083 return !stack->isEmpty();
8084 }
8085
8086 #define BUSY (cast_to_oop<intptr_t>(0x1aff1aff))
8087 // (MT-safe) Get a prefix of at most "num" from the list.
8088 // The overflow list is chained through the mark word of
8089 // each object in the list. We fetch the entire list,
8090 // break off a prefix of the right size and return the
8091 // remainder. If other threads try to take objects from
8092 // the overflow list at that time, they will wait for
8093 // some time to see if data becomes available. If (and
8094 // only if) another thread places one or more object(s)
8095 // on the global list before we have returned the suffix
8096 // to the global list, we will walk down our local list
8097 // to find its end and append the global list to
8098 // our suffix before returning it. This suffix walk can
8099 // prove to be expensive (quadratic in the amount of traffic)
8100 // when there are many objects in the overflow list and
8101 // there is much producer-consumer contention on the list.
8102 // *NOTE*: The overflow list manipulation code here and
8103 // in ParNewGeneration:: are very similar in shape,
8104 // except that in the ParNew case we use the old (from/eden)
8105 // copy of the object to thread the list via its klass word.
8106 // Because of the common code, if you make any changes in
8107 // the code below, please check the ParNew version to see if
8108 // similar changes might be needed.
8109 // CR 6797058 has been filed to consolidate the common code.
8110 bool CMSCollector::par_take_from_overflow_list(size_t num,
8111 OopTaskQueue* work_q,
8112 int no_of_gc_threads) {
8113 assert(work_q->size() == 0, "First empty local work queue");
8114 assert(num < work_q->max_elems(), "Can't bite more than we can chew");
8115 if (_overflow_list == NULL) {
8116 return false;
8117 }
8118 // Grab the entire list; we'll put back a suffix
8119 oop prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
8120 Thread* tid = Thread::current();
8121 // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was
8122 // set to ParallelGCThreads.
8123 size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads;
8124 size_t sleep_time_millis = MAX2((size_t)1, num/100);
8125 // If the list is busy, we spin for a short while,
8126 // sleeping between attempts to get the list.
8127 for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) {
8128 os::sleep(tid, sleep_time_millis, false);
8129 if (_overflow_list == NULL) {
8130 // Nothing left to take
8131 return false;
8132 } else if (_overflow_list != BUSY) {
8133 // Try and grab the prefix
8134 prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
8135 }
8136 }
8137 // If the list was found to be empty, or we spun long
8138 // enough, we give up and return empty-handed. If we leave
8139 // the list in the BUSY state below, it must be the case that
8140 // some other thread holds the overflow list and will set it
8141 // to a non-BUSY state in the future.
8142 if (prefix == NULL || prefix == BUSY) {
8143 // Nothing to take or waited long enough
8144 if (prefix == NULL) {
8145 // Write back the NULL in case we overwrote it with BUSY above
8146 // and it is still the same value.
8147 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8148 }
8149 return false;
8150 }
8151 assert(prefix != NULL && prefix != BUSY, "Error");
8152 size_t i = num;
8153 oop cur = prefix;
8154 // Walk down the first "num" objects, unless we reach the end.
8155 for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--);
8156 if (cur->mark() == NULL) {
8157 // We have "num" or fewer elements in the list, so there
8158 // is nothing to return to the global list.
8159 // Write back the NULL in lieu of the BUSY we wrote
8160 // above, if it is still the same value.
8161 if (_overflow_list == BUSY) {
8162 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8163 }
8164 } else {
8165 // Chop off the suffix and return it to the global list.
8166 assert(cur->mark() != BUSY, "Error");
8167 oop suffix_head = cur->mark(); // suffix will be put back on global list
8168 cur->set_mark(NULL); // break off suffix
8169 // It's possible that the list is still in the empty(busy) state
8170 // we left it in a short while ago; in that case we may be
8171 // able to place back the suffix without incurring the cost
8172 // of a walk down the list.
8173 oop observed_overflow_list = _overflow_list;
8174 oop cur_overflow_list = observed_overflow_list;
8175 bool attached = false;
8176 while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
8177 observed_overflow_list =
8178 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
8179 if (cur_overflow_list == observed_overflow_list) {
8180 attached = true;
8181 break;
8182 } else cur_overflow_list = observed_overflow_list;
8183 }
8184 if (!attached) {
8185 // Too bad, someone else sneaked in (at least) an element; we'll need
8186 // to do a splice. Find tail of suffix so we can prepend suffix to global
8187 // list.
8188 for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark()));
8189 oop suffix_tail = cur;
8190 assert(suffix_tail != NULL && suffix_tail->mark() == NULL,
8191 "Tautology");
8192 observed_overflow_list = _overflow_list;
8193 do {
8194 cur_overflow_list = observed_overflow_list;
8195 if (cur_overflow_list != BUSY) {
8196 // Do the splice ...
8197 suffix_tail->set_mark(markOop(cur_overflow_list));
8198 } else { // cur_overflow_list == BUSY
8199 suffix_tail->set_mark(NULL);
8200 }
8201 // ... and try to place spliced list back on overflow_list ...
8202 observed_overflow_list =
8203 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
8204 } while (cur_overflow_list != observed_overflow_list);
8205 // ... until we have succeeded in doing so.
8206 }
8207 }
8208
8209 // Push the prefix elements on work_q
8210 assert(prefix != NULL, "control point invariant");
8211 const markOop proto = markOopDesc::prototype();
8212 oop next;
8213 NOT_PRODUCT(ssize_t n = 0;)
8214 for (cur = prefix; cur != NULL; cur = next) {
8215 next = oop(cur->mark());
8216 cur->set_mark(proto); // until proven otherwise
8217 assert(cur->is_oop(), "Should be an oop");
8218 bool res = work_q->push(cur);
8219 assert(res, "Bit off more than we can chew?");
8220 NOT_PRODUCT(n++;)
8221 }
8222 #ifndef PRODUCT
8223 assert(_num_par_pushes >= n, "Too many pops?");
8224 Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
8225 #endif
8226 return true;
8227 }
8228
8229 // Single-threaded
8230 void CMSCollector::push_on_overflow_list(oop p) {
8231 NOT_PRODUCT(_num_par_pushes++;)
8232 assert(p->is_oop(), "Not an oop");
8233 preserve_mark_if_necessary(p);
8234 p->set_mark((markOop)_overflow_list);
8235 _overflow_list = p;
8236 }
8237
8238 // Multi-threaded; use CAS to prepend to overflow list
8239 void CMSCollector::par_push_on_overflow_list(oop p) {
8240 NOT_PRODUCT(Atomic::inc_ptr(&_num_par_pushes);)
8241 assert(p->is_oop(), "Not an oop");
8242 par_preserve_mark_if_necessary(p);
8243 oop observed_overflow_list = _overflow_list;
8244 oop cur_overflow_list;
8245 do {
8246 cur_overflow_list = observed_overflow_list;
8247 if (cur_overflow_list != BUSY) {
8248 p->set_mark(markOop(cur_overflow_list));
8249 } else {
8250 p->set_mark(NULL);
8251 }
8252 observed_overflow_list =
8253 (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list);
8254 } while (cur_overflow_list != observed_overflow_list);
8255 }
8256 #undef BUSY
8257
8258 // Single threaded
8259 // General Note on GrowableArray: pushes may silently fail
8260 // because we are (temporarily) out of C-heap for expanding
8261 // the stack. The problem is quite ubiquitous and affects
8262 // a lot of code in the JVM. The prudent thing for GrowableArray
8263 // to do (for now) is to exit with an error. However, that may
8264 // be too draconian in some cases because the caller may be
8265 // able to recover without much harm. For such cases, we
8266 // should probably introduce a "soft_push" method which returns
8267 // an indication of success or failure with the assumption that
8268 // the caller may be able to recover from a failure; code in
8269 // the VM can then be changed, incrementally, to deal with such
8270 // failures where possible, thus, incrementally hardening the VM
8271 // in such low resource situations.
8272 void CMSCollector::preserve_mark_work(oop p, markOop m) {
8273 _preserved_oop_stack.push(p);
8274 _preserved_mark_stack.push(m);
8275 assert(m == p->mark(), "Mark word changed");
8276 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8277 "bijection");
8278 }
8279
8280 // Single threaded
8281 void CMSCollector::preserve_mark_if_necessary(oop p) {
8282 markOop m = p->mark();
8283 if (m->must_be_preserved(p)) {
8284 preserve_mark_work(p, m);
8285 }
8286 }
8287
8288 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
8289 markOop m = p->mark();
8290 if (m->must_be_preserved(p)) {
8291 MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
8292 // Even though we read the mark word without holding
8293 // the lock, we are assured that it will not change
8294 // because we "own" this oop, so no other thread can
8295 // be trying to push it on the overflow list; see
8296 // the assertion in preserve_mark_work() that checks
8297 // that m == p->mark().
8298 preserve_mark_work(p, m);
8299 }
8300 }
8301
8302 // We should be able to do this multi-threaded,
8303 // a chunk of stack being a task (this is
8304 // correct because each oop only ever appears
8305 // once in the overflow list. However, it's
8306 // not very easy to completely overlap this with
8307 // other operations, so will generally not be done
8308 // until all work's been completed. Because we
8309 // expect the preserved oop stack (set) to be small,
8310 // it's probably fine to do this single-threaded.
8311 // We can explore cleverer concurrent/overlapped/parallel
8312 // processing of preserved marks if we feel the
8313 // need for this in the future. Stack overflow should
8314 // be so rare in practice and, when it happens, its
8315 // effect on performance so great that this will
8316 // likely just be in the noise anyway.
8317 void CMSCollector::restore_preserved_marks_if_any() {
8318 assert(SafepointSynchronize::is_at_safepoint(),
8319 "world should be stopped");
8320 assert(Thread::current()->is_ConcurrentGC_thread() ||
8321 Thread::current()->is_VM_thread(),
8322 "should be single-threaded");
8323 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8324 "bijection");
8325
8326 while (!_preserved_oop_stack.is_empty()) {
8327 oop p = _preserved_oop_stack.pop();
8328 assert(p->is_oop(), "Should be an oop");
8329 assert(_span.contains(p), "oop should be in _span");
8330 assert(p->mark() == markOopDesc::prototype(),
8331 "Set when taken from overflow list");
8332 markOop m = _preserved_mark_stack.pop();
8333 p->set_mark(m);
8334 }
8335 assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(),
8336 "stacks were cleared above");
8337 }
8338
8339 #ifndef PRODUCT
8340 bool CMSCollector::no_preserved_marks() const {
8341 return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty();
8342 }
8343 #endif
8344
8345 // Transfer some number of overflown objects to usual marking
8346 // stack. Return true if some objects were transferred.
8347 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
8348 size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,
8349 (size_t)ParGCDesiredObjsFromOverflowList);
8350
8351 bool res = _collector->take_from_overflow_list(num, _mark_stack);
8352 assert(_collector->overflow_list_is_empty() || res,
8353 "If list is not empty, we should have taken something");
8354 assert(!res || !_mark_stack->isEmpty(),
8355 "If we took something, it should now be on our stack");
8356 return res;
8357 }
8358
8359 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
8360 size_t res = _sp->block_size_no_stall(addr, _collector);
8361 if (_sp->block_is_obj(addr)) {
8362 if (_live_bit_map->isMarked(addr)) {
8363 // It can't have been dead in a previous cycle
8364 guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
8365 } else {
8366 _dead_bit_map->mark(addr); // mark the dead object
8367 }
8368 }
8369 // Could be 0, if the block size could not be computed without stalling.
8370 return res;
8371 }
8372
8373 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() {
8374
8375 switch (phase) {
8376 case CMSCollector::InitialMarking:
8377 initialize(true /* fullGC */ ,
8378 cause /* cause of the GC */,
8379 true /* recordGCBeginTime */,
8380 true /* recordPreGCUsage */,
8381 false /* recordPeakUsage */,
8382 false /* recordPostGCusage */,
8383 true /* recordAccumulatedGCTime */,
8384 false /* recordGCEndTime */,
8385 false /* countCollection */ );
8386 break;
8387
8388 case CMSCollector::FinalMarking:
8389 initialize(true /* fullGC */ ,
8390 cause /* cause of the GC */,
8391 false /* recordGCBeginTime */,
8392 false /* recordPreGCUsage */,
8393 false /* recordPeakUsage */,
8394 false /* recordPostGCusage */,
8395 true /* recordAccumulatedGCTime */,
8396 false /* recordGCEndTime */,
8397 false /* countCollection */ );
8398 break;
8399
8400 case CMSCollector::Sweeping:
8401 initialize(true /* fullGC */ ,
8402 cause /* cause of the GC */,
8403 false /* recordGCBeginTime */,
8404 false /* recordPreGCUsage */,
8405 true /* recordPeakUsage */,
8406 true /* recordPostGCusage */,
8407 false /* recordAccumulatedGCTime */,
8408 true /* recordGCEndTime */,
8409 true /* countCollection */ );
8410 break;
8411
8412 default:
8413 ShouldNotReachHere();
8414 }
8415 }