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