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