1 /*
2 * Copyright (c) 2001, 2015, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include "precompiled.hpp"
26 #include "classfile/classLoaderData.hpp"
27 #include "classfile/stringTable.hpp"
28 #include "classfile/systemDictionary.hpp"
29 #include "code/codeCache.hpp"
30 #include "gc_implementation/shared/adaptiveSizePolicy.hpp"
31 #include "gc_implementation/concurrentMarkSweep/cmsCollectorPolicy.hpp"
32 #include "gc_implementation/concurrentMarkSweep/cmsOopClosures.inline.hpp"
33 #include "gc_implementation/concurrentMarkSweep/compactibleFreeListSpace.hpp"
34 #include "gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.inline.hpp"
35 #include "gc_implementation/concurrentMarkSweep/concurrentMarkSweepThread.hpp"
36 #include "gc_implementation/concurrentMarkSweep/vmCMSOperations.hpp"
37 #include "gc_implementation/parNew/parNewGeneration.hpp"
38 #include "gc_implementation/shared/collectorCounters.hpp"
39 #include "gc_implementation/shared/gcTimer.hpp"
40 #include "gc_implementation/shared/gcTrace.hpp"
41 #include "gc_implementation/shared/gcTraceTime.hpp"
42 #include "gc_implementation/shared/isGCActiveMark.hpp"
43 #include "gc_interface/collectedHeap.inline.hpp"
44 #include "memory/allocation.hpp"
45 #include "memory/cardGeneration.inline.hpp"
46 #include "memory/cardTableRS.hpp"
47 #include "memory/collectorPolicy.hpp"
48 #include "memory/gcLocker.inline.hpp"
49 #include "memory/genCollectedHeap.hpp"
50 #include "memory/genMarkSweep.hpp"
51 #include "memory/genOopClosures.inline.hpp"
52 #include "memory/iterator.inline.hpp"
53 #include "memory/padded.hpp"
54 #include "memory/referencePolicy.hpp"
55 #include "memory/resourceArea.hpp"
56 #include "memory/tenuredGeneration.hpp"
57 #include "oops/oop.inline.hpp"
58 #include "prims/jvmtiExport.hpp"
59 #include "runtime/atomic.inline.hpp"
60 #include "runtime/globals_extension.hpp"
61 #include "runtime/handles.inline.hpp"
62 #include "runtime/java.hpp"
63 #include "runtime/orderAccess.inline.hpp"
64 #include "runtime/vmThread.hpp"
65 #include "services/memoryService.hpp"
66 #include "services/runtimeService.hpp"
67
68 // statics
69 CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL;
70 bool CMSCollector::_full_gc_requested = false;
71 GCCause::Cause CMSCollector::_full_gc_cause = GCCause::_no_gc;
72
73 //////////////////////////////////////////////////////////////////
74 // In support of CMS/VM thread synchronization
75 //////////////////////////////////////////////////////////////////
76 // We split use of the CGC_lock into 2 "levels".
77 // The low-level locking is of the usual CGC_lock monitor. We introduce
78 // a higher level "token" (hereafter "CMS token") built on top of the
79 // low level monitor (hereafter "CGC lock").
80 // The token-passing protocol gives priority to the VM thread. The
81 // CMS-lock doesn't provide any fairness guarantees, but clients
82 // should ensure that it is only held for very short, bounded
83 // durations.
84 //
85 // When either of the CMS thread or the VM thread is involved in
86 // collection operations during which it does not want the other
87 // thread to interfere, it obtains the CMS token.
88 //
89 // If either thread tries to get the token while the other has
90 // it, that thread waits. However, if the VM thread and CMS thread
91 // both want the token, then the VM thread gets priority while the
92 // CMS thread waits. This ensures, for instance, that the "concurrent"
93 // phases of the CMS thread's work do not block out the VM thread
94 // for long periods of time as the CMS thread continues to hog
95 // the token. (See bug 4616232).
96 //
97 // The baton-passing functions are, however, controlled by the
98 // flags _foregroundGCShouldWait and _foregroundGCIsActive,
99 // and here the low-level CMS lock, not the high level token,
100 // ensures mutual exclusion.
101 //
102 // Two important conditions that we have to satisfy:
103 // 1. if a thread does a low-level wait on the CMS lock, then it
104 // relinquishes the CMS token if it were holding that token
105 // when it acquired the low-level CMS lock.
106 // 2. any low-level notifications on the low-level lock
107 // should only be sent when a thread has relinquished the token.
108 //
109 // In the absence of either property, we'd have potential deadlock.
110 //
111 // We protect each of the CMS (concurrent and sequential) phases
112 // with the CMS _token_, not the CMS _lock_.
113 //
114 // The only code protected by CMS lock is the token acquisition code
115 // itself, see ConcurrentMarkSweepThread::[de]synchronize(), and the
116 // baton-passing code.
117 //
118 // Unfortunately, i couldn't come up with a good abstraction to factor and
119 // hide the naked CGC_lock manipulation in the baton-passing code
120 // further below. That's something we should try to do. Also, the proof
121 // of correctness of this 2-level locking scheme is far from obvious,
122 // and potentially quite slippery. We have an uneasy suspicion, for instance,
123 // that there may be a theoretical possibility of delay/starvation in the
124 // low-level lock/wait/notify scheme used for the baton-passing because of
125 // potential interference with the priority scheme embodied in the
126 // CMS-token-passing protocol. See related comments at a CGC_lock->wait()
127 // invocation further below and marked with "XXX 20011219YSR".
128 // Indeed, as we note elsewhere, this may become yet more slippery
129 // in the presence of multiple CMS and/or multiple VM threads. XXX
130
131 class CMSTokenSync: public StackObj {
132 private:
133 bool _is_cms_thread;
134 public:
135 CMSTokenSync(bool is_cms_thread):
136 _is_cms_thread(is_cms_thread) {
137 assert(is_cms_thread == Thread::current()->is_ConcurrentGC_thread(),
138 "Incorrect argument to constructor");
139 ConcurrentMarkSweepThread::synchronize(_is_cms_thread);
140 }
141
142 ~CMSTokenSync() {
143 assert(_is_cms_thread ?
144 ConcurrentMarkSweepThread::cms_thread_has_cms_token() :
145 ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
146 "Incorrect state");
147 ConcurrentMarkSweepThread::desynchronize(_is_cms_thread);
148 }
149 };
150
151 // Convenience class that does a CMSTokenSync, and then acquires
152 // upto three locks.
153 class CMSTokenSyncWithLocks: public CMSTokenSync {
154 private:
155 // Note: locks are acquired in textual declaration order
156 // and released in the opposite order
157 MutexLockerEx _locker1, _locker2, _locker3;
158 public:
159 CMSTokenSyncWithLocks(bool is_cms_thread, Mutex* mutex1,
160 Mutex* mutex2 = NULL, Mutex* mutex3 = NULL):
161 CMSTokenSync(is_cms_thread),
162 _locker1(mutex1, Mutex::_no_safepoint_check_flag),
163 _locker2(mutex2, Mutex::_no_safepoint_check_flag),
164 _locker3(mutex3, Mutex::_no_safepoint_check_flag)
165 { }
166 };
167
168
169 //////////////////////////////////////////////////////////////////
170 // Concurrent Mark-Sweep Generation /////////////////////////////
171 //////////////////////////////////////////////////////////////////
172
173 NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;)
174
175 // This struct contains per-thread things necessary to support parallel
176 // young-gen collection.
177 class CMSParGCThreadState: public CHeapObj<mtGC> {
178 public:
179 CFLS_LAB lab;
180 PromotionInfo promo;
181
182 // Constructor.
183 CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) {
184 promo.setSpace(cfls);
185 }
186 };
187
188 ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration(
189 ReservedSpace rs, size_t initial_byte_size, int level,
190 CardTableRS* ct, bool use_adaptive_freelists,
191 FreeBlockDictionary<FreeChunk>::DictionaryChoice dictionaryChoice) :
192 CardGeneration(rs, initial_byte_size, level, ct),
193 _dilatation_factor(((double)MinChunkSize)/((double)(CollectedHeap::min_fill_size()))),
194 _did_compact(false)
195 {
196 HeapWord* bottom = (HeapWord*) _virtual_space.low();
197 HeapWord* end = (HeapWord*) _virtual_space.high();
198
199 _direct_allocated_words = 0;
200 NOT_PRODUCT(
201 _numObjectsPromoted = 0;
202 _numWordsPromoted = 0;
203 _numObjectsAllocated = 0;
204 _numWordsAllocated = 0;
205 )
206
207 _cmsSpace = new CompactibleFreeListSpace(_bts, MemRegion(bottom, end),
208 use_adaptive_freelists,
209 dictionaryChoice);
210 NOT_PRODUCT(debug_cms_space = _cmsSpace;)
211 if (_cmsSpace == NULL) {
212 vm_exit_during_initialization(
213 "CompactibleFreeListSpace allocation failure");
214 }
215 _cmsSpace->_gen = this;
216
217 _gc_stats = new CMSGCStats();
218
219 // Verify the assumption that FreeChunk::_prev and OopDesc::_klass
220 // offsets match. The ability to tell free chunks from objects
221 // depends on this property.
222 debug_only(
223 FreeChunk* junk = NULL;
224 assert(UseCompressedClassPointers ||
225 junk->prev_addr() == (void*)(oop(junk)->klass_addr()),
226 "Offset of FreeChunk::_prev within FreeChunk must match"
227 " that of OopDesc::_klass within OopDesc");
228 )
229 if (CollectedHeap::use_parallel_gc_threads()) {
230 typedef CMSParGCThreadState* CMSParGCThreadStatePtr;
231 _par_gc_thread_states =
232 NEW_C_HEAP_ARRAY(CMSParGCThreadStatePtr, ParallelGCThreads, mtGC);
233 if (_par_gc_thread_states == NULL) {
234 vm_exit_during_initialization("Could not allocate par gc structs");
235 }
236 for (uint i = 0; i < ParallelGCThreads; i++) {
237 _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace());
238 if (_par_gc_thread_states[i] == NULL) {
239 vm_exit_during_initialization("Could not allocate par gc structs");
240 }
241 }
242 } else {
243 _par_gc_thread_states = NULL;
244 }
245 _incremental_collection_failed = false;
246 // The "dilatation_factor" is the expansion that can occur on
247 // account of the fact that the minimum object size in the CMS
248 // generation may be larger than that in, say, a contiguous young
249 // generation.
250 // Ideally, in the calculation below, we'd compute the dilatation
251 // factor as: MinChunkSize/(promoting_gen's min object size)
252 // Since we do not have such a general query interface for the
253 // promoting generation, we'll instead just use the minimum
254 // object size (which today is a header's worth of space);
255 // note that all arithmetic is in units of HeapWords.
256 assert(MinChunkSize >= CollectedHeap::min_fill_size(), "just checking");
257 assert(_dilatation_factor >= 1.0, "from previous assert");
258 }
259
260
261 // The field "_initiating_occupancy" represents the occupancy percentage
262 // at which we trigger a new collection cycle. Unless explicitly specified
263 // via CMSInitiatingOccupancyFraction (argument "io" below), it
264 // is calculated by:
265 //
266 // Let "f" be MinHeapFreeRatio in
267 //
268 // _initiating_occupancy = 100-f +
269 // f * (CMSTriggerRatio/100)
270 // where CMSTriggerRatio is the argument "tr" below.
271 //
272 // That is, if we assume the heap is at its desired maximum occupancy at the
273 // end of a collection, we let CMSTriggerRatio of the (purported) free
274 // space be allocated before initiating a new collection cycle.
275 //
276 void ConcurrentMarkSweepGeneration::init_initiating_occupancy(intx io, uintx tr) {
277 assert(io <= 100 && tr <= 100, "Check the arguments");
278 if (io >= 0) {
279 _initiating_occupancy = (double)io / 100.0;
280 } else {
281 _initiating_occupancy = ((100 - MinHeapFreeRatio) +
282 (double)(tr * MinHeapFreeRatio) / 100.0)
283 / 100.0;
284 }
285 }
286
287 void ConcurrentMarkSweepGeneration::ref_processor_init() {
288 assert(collector() != NULL, "no collector");
289 collector()->ref_processor_init();
290 }
291
292 void CMSCollector::ref_processor_init() {
293 if (_ref_processor == NULL) {
294 // Allocate and initialize a reference processor
295 _ref_processor =
296 new ReferenceProcessor(_span, // span
297 (ParallelGCThreads > 1) && ParallelRefProcEnabled, // mt processing
298 (int) ParallelGCThreads, // mt processing degree
299 _cmsGen->refs_discovery_is_mt(), // mt discovery
300 (int) MAX2(ConcGCThreads, ParallelGCThreads), // mt discovery degree
301 _cmsGen->refs_discovery_is_atomic(), // discovery is not atomic
302 &_is_alive_closure); // closure for liveness info
303 // Initialize the _ref_processor field of CMSGen
304 _cmsGen->set_ref_processor(_ref_processor);
305
306 }
307 }
308
309 AdaptiveSizePolicy* CMSCollector::size_policy() {
310 GenCollectedHeap* gch = GenCollectedHeap::heap();
311 assert(gch->kind() == CollectedHeap::GenCollectedHeap,
312 "Wrong type of heap");
313 return gch->gen_policy()->size_policy();
314 }
315
316 void ConcurrentMarkSweepGeneration::initialize_performance_counters() {
317
318 const char* gen_name = "old";
319 GenCollectorPolicy* gcp = (GenCollectorPolicy*) GenCollectedHeap::heap()->collector_policy();
320
321 // Generation Counters - generation 1, 1 subspace
322 _gen_counters = new GenerationCounters(gen_name, 1, 1,
323 gcp->min_old_size(), gcp->max_old_size(), &_virtual_space);
324
325 _space_counters = new GSpaceCounters(gen_name, 0,
326 _virtual_space.reserved_size(),
327 this, _gen_counters);
328 }
329
330 CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha):
331 _cms_gen(cms_gen)
332 {
333 assert(alpha <= 100, "bad value");
334 _saved_alpha = alpha;
335
336 // Initialize the alphas to the bootstrap value of 100.
337 _gc0_alpha = _cms_alpha = 100;
338
339 _cms_begin_time.update();
340 _cms_end_time.update();
341
342 _gc0_duration = 0.0;
343 _gc0_period = 0.0;
344 _gc0_promoted = 0;
345
346 _cms_duration = 0.0;
347 _cms_period = 0.0;
348 _cms_allocated = 0;
349
350 _cms_used_at_gc0_begin = 0;
351 _cms_used_at_gc0_end = 0;
352 _allow_duty_cycle_reduction = false;
353 _valid_bits = 0;
354 }
355
356 double CMSStats::cms_free_adjustment_factor(size_t free) const {
357 // TBD: CR 6909490
358 return 1.0;
359 }
360
361 void CMSStats::adjust_cms_free_adjustment_factor(bool fail, size_t free) {
362 }
363
364 // If promotion failure handling is on use
365 // the padded average size of the promotion for each
366 // young generation collection.
367 double CMSStats::time_until_cms_gen_full() const {
368 size_t cms_free = _cms_gen->cmsSpace()->free();
369 GenCollectedHeap* gch = GenCollectedHeap::heap();
370 size_t expected_promotion = MIN2(gch->young_gen()->capacity(),
371 (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average());
372 if (cms_free > expected_promotion) {
373 // Start a cms collection if there isn't enough space to promote
374 // for the next minor collection. Use the padded average as
375 // a safety factor.
376 cms_free -= expected_promotion;
377
378 // Adjust by the safety factor.
379 double cms_free_dbl = (double)cms_free;
380 double cms_adjustment = (100.0 - CMSIncrementalSafetyFactor)/100.0;
381 // Apply a further correction factor which tries to adjust
382 // for recent occurance of concurrent mode failures.
383 cms_adjustment = cms_adjustment * cms_free_adjustment_factor(cms_free);
384 cms_free_dbl = cms_free_dbl * cms_adjustment;
385
386 if (PrintGCDetails && Verbose) {
387 gclog_or_tty->print_cr("CMSStats::time_until_cms_gen_full: cms_free "
388 SIZE_FORMAT " expected_promotion " SIZE_FORMAT,
389 cms_free, expected_promotion);
390 gclog_or_tty->print_cr(" cms_free_dbl %f cms_consumption_rate %f",
391 cms_free_dbl, cms_consumption_rate() + 1.0);
392 }
393 // Add 1 in case the consumption rate goes to zero.
394 return cms_free_dbl / (cms_consumption_rate() + 1.0);
395 }
396 return 0.0;
397 }
398
399 // Compare the duration of the cms collection to the
400 // time remaining before the cms generation is empty.
401 // Note that the time from the start of the cms collection
402 // to the start of the cms sweep (less than the total
403 // duration of the cms collection) can be used. This
404 // has been tried and some applications experienced
405 // promotion failures early in execution. This was
406 // possibly because the averages were not accurate
407 // enough at the beginning.
408 double CMSStats::time_until_cms_start() const {
409 // We add "gc0_period" to the "work" calculation
410 // below because this query is done (mostly) at the
411 // end of a scavenge, so we need to conservatively
412 // account for that much possible delay
413 // in the query so as to avoid concurrent mode failures
414 // due to starting the collection just a wee bit too
415 // late.
416 double work = cms_duration() + gc0_period();
417 double deadline = time_until_cms_gen_full();
418 // If a concurrent mode failure occurred recently, we want to be
419 // more conservative and halve our expected time_until_cms_gen_full()
420 if (work > deadline) {
421 if (Verbose && PrintGCDetails) {
422 gclog_or_tty->print(
423 " CMSCollector: collect because of anticipated promotion "
424 "before full %3.7f + %3.7f > %3.7f ", cms_duration(),
425 gc0_period(), time_until_cms_gen_full());
426 }
427 return 0.0;
428 }
429 return work - deadline;
430 }
431
432 #ifndef PRODUCT
433 void CMSStats::print_on(outputStream *st) const {
434 st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha);
435 st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo=" SIZE_FORMAT,
436 gc0_duration(), gc0_period(), gc0_promoted());
437 st->print(",cms_dur=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT,
438 cms_duration(), cms_period(), cms_allocated());
439 st->print(",cms_since_beg=%g,cms_since_end=%g",
440 cms_time_since_begin(), cms_time_since_end());
441 st->print(",cms_used_beg=" SIZE_FORMAT ",cms_used_end=" SIZE_FORMAT,
442 _cms_used_at_gc0_begin, _cms_used_at_gc0_end);
443
444 if (valid()) {
445 st->print(",promo_rate=%g,cms_alloc_rate=%g",
446 promotion_rate(), cms_allocation_rate());
447 st->print(",cms_consumption_rate=%g,time_until_full=%g",
448 cms_consumption_rate(), time_until_cms_gen_full());
449 }
450 st->print(" ");
451 }
452 #endif // #ifndef PRODUCT
453
454 CMSCollector::CollectorState CMSCollector::_collectorState =
455 CMSCollector::Idling;
456 bool CMSCollector::_foregroundGCIsActive = false;
457 bool CMSCollector::_foregroundGCShouldWait = false;
458
459 CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
460 CardTableRS* ct,
461 ConcurrentMarkSweepPolicy* cp):
462 _cmsGen(cmsGen),
463 _ct(ct),
464 _ref_processor(NULL), // will be set later
465 _conc_workers(NULL), // may be set later
466 _abort_preclean(false),
467 _start_sampling(false),
468 _between_prologue_and_epilogue(false),
469 _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"),
470 _modUnionTable((CardTableModRefBS::card_shift - LogHeapWordSize),
471 -1 /* lock-free */, "No_lock" /* dummy */),
472 _modUnionClosure(&_modUnionTable),
473 _modUnionClosurePar(&_modUnionTable),
474 // Adjust my span to cover old (cms) gen
475 _span(cmsGen->reserved()),
476 // Construct the is_alive_closure with _span & markBitMap
477 _is_alive_closure(_span, &_markBitMap),
478 _restart_addr(NULL),
479 _overflow_list(NULL),
480 _stats(cmsGen),
481 _eden_chunk_lock(new Mutex(Mutex::leaf + 1, "CMS_eden_chunk_lock", true,
482 //verify that this lock should be acquired with safepoint check.
483 Monitor::_safepoint_check_sometimes)),
484 _eden_chunk_array(NULL), // may be set in ctor body
485 _eden_chunk_capacity(0), // -- ditto --
486 _eden_chunk_index(0), // -- ditto --
487 _survivor_plab_array(NULL), // -- ditto --
488 _survivor_chunk_array(NULL), // -- ditto --
489 _survivor_chunk_capacity(0), // -- ditto --
490 _survivor_chunk_index(0), // -- ditto --
491 _ser_pmc_preclean_ovflw(0),
492 _ser_kac_preclean_ovflw(0),
493 _ser_pmc_remark_ovflw(0),
494 _par_pmc_remark_ovflw(0),
495 _ser_kac_ovflw(0),
496 _par_kac_ovflw(0),
497 #ifndef PRODUCT
498 _num_par_pushes(0),
499 #endif
500 _collection_count_start(0),
501 _verifying(false),
502 _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"),
503 _completed_initialization(false),
504 _collector_policy(cp),
505 _should_unload_classes(CMSClassUnloadingEnabled),
506 _concurrent_cycles_since_last_unload(0),
507 _roots_scanning_options(GenCollectedHeap::SO_None),
508 _inter_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
509 _intra_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
510 _gc_tracer_cm(new (ResourceObj::C_HEAP, mtGC) CMSTracer()),
511 _gc_timer_cm(new (ResourceObj::C_HEAP, mtGC) ConcurrentGCTimer()),
512 _cms_start_registered(false)
513 {
514 if (ExplicitGCInvokesConcurrentAndUnloadsClasses) {
515 ExplicitGCInvokesConcurrent = true;
516 }
517 // Now expand the span and allocate the collection support structures
518 // (MUT, marking bit map etc.) to cover both generations subject to
519 // collection.
520
521 // For use by dirty card to oop closures.
522 _cmsGen->cmsSpace()->set_collector(this);
523
524 // Allocate MUT and marking bit map
525 {
526 MutexLockerEx x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag);
527 if (!_markBitMap.allocate(_span)) {
528 warning("Failed to allocate CMS Bit Map");
529 return;
530 }
531 assert(_markBitMap.covers(_span), "_markBitMap inconsistency?");
532 }
533 {
534 _modUnionTable.allocate(_span);
535 assert(_modUnionTable.covers(_span), "_modUnionTable inconsistency?");
536 }
537
538 if (!_markStack.allocate(MarkStackSize)) {
539 warning("Failed to allocate CMS Marking Stack");
540 return;
541 }
542
543 // Support for multi-threaded concurrent phases
544 if (CMSConcurrentMTEnabled) {
545 if (FLAG_IS_DEFAULT(ConcGCThreads)) {
546 // just for now
547 FLAG_SET_DEFAULT(ConcGCThreads, (ParallelGCThreads + 3)/4);
548 }
549 if (ConcGCThreads > 1) {
550 _conc_workers = new YieldingFlexibleWorkGang("CMS Thread",
551 ConcGCThreads, true);
552 if (_conc_workers == NULL) {
553 warning("GC/CMS: _conc_workers allocation failure: "
554 "forcing -CMSConcurrentMTEnabled");
555 CMSConcurrentMTEnabled = false;
556 } else {
557 _conc_workers->initialize_workers();
558 }
559 } else {
560 CMSConcurrentMTEnabled = false;
561 }
562 }
563 if (!CMSConcurrentMTEnabled) {
564 ConcGCThreads = 0;
565 } else {
566 // Turn off CMSCleanOnEnter optimization temporarily for
567 // the MT case where it's not fixed yet; see 6178663.
568 CMSCleanOnEnter = false;
569 }
570 assert((_conc_workers != NULL) == (ConcGCThreads > 1),
571 "Inconsistency");
572
573 // Parallel task queues; these are shared for the
574 // concurrent and stop-world phases of CMS, but
575 // are not shared with parallel scavenge (ParNew).
576 {
577 uint i;
578 uint num_queues = (uint) MAX2(ParallelGCThreads, ConcGCThreads);
579
580 if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled
581 || ParallelRefProcEnabled)
582 && num_queues > 0) {
583 _task_queues = new OopTaskQueueSet(num_queues);
584 if (_task_queues == NULL) {
585 warning("task_queues allocation failure.");
586 return;
587 }
588 _hash_seed = NEW_C_HEAP_ARRAY(int, num_queues, mtGC);
589 if (_hash_seed == NULL) {
590 warning("_hash_seed array allocation failure");
591 return;
592 }
593
594 typedef Padded<OopTaskQueue> PaddedOopTaskQueue;
595 for (i = 0; i < num_queues; i++) {
596 PaddedOopTaskQueue *q = new PaddedOopTaskQueue();
597 if (q == NULL) {
598 warning("work_queue allocation failure.");
599 return;
600 }
601 _task_queues->register_queue(i, q);
602 }
603 for (i = 0; i < num_queues; i++) {
604 _task_queues->queue(i)->initialize();
605 _hash_seed[i] = 17; // copied from ParNew
606 }
607 }
608 }
609
610 _cmsGen ->init_initiating_occupancy(CMSInitiatingOccupancyFraction, CMSTriggerRatio);
611
612 // Clip CMSBootstrapOccupancy between 0 and 100.
613 _bootstrap_occupancy = ((double)CMSBootstrapOccupancy)/(double)100;
614
615 // Now tell CMS generations the identity of their collector
616 ConcurrentMarkSweepGeneration::set_collector(this);
617
618 // Create & start a CMS thread for this CMS collector
619 _cmsThread = ConcurrentMarkSweepThread::start(this);
620 assert(cmsThread() != NULL, "CMS Thread should have been created");
621 assert(cmsThread()->collector() == this,
622 "CMS Thread should refer to this gen");
623 assert(CGC_lock != NULL, "Where's the CGC_lock?");
624
625 // Support for parallelizing young gen rescan
626 GenCollectedHeap* gch = GenCollectedHeap::heap();
627 assert(gch->young_gen()->kind() == Generation::ParNew, "CMS can only be used with ParNew");
628 _young_gen = (ParNewGeneration*)gch->young_gen();
629 if (gch->supports_inline_contig_alloc()) {
630 _top_addr = gch->top_addr();
631 _end_addr = gch->end_addr();
632 assert(_young_gen != NULL, "no _young_gen");
633 _eden_chunk_index = 0;
634 _eden_chunk_capacity = (_young_gen->max_capacity()+CMSSamplingGrain)/CMSSamplingGrain;
635 _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity, mtGC);
636 if (_eden_chunk_array == NULL) {
637 _eden_chunk_capacity = 0;
638 warning("GC/CMS: _eden_chunk_array allocation failure");
639 }
640 }
641 assert(_eden_chunk_array != NULL || _eden_chunk_capacity == 0, "Error");
642
643 // Support for parallelizing survivor space rescan
644 if ((CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) || CMSParallelInitialMarkEnabled) {
645 const size_t max_plab_samples =
646 ((DefNewGeneration*)_young_gen)->max_survivor_size() / plab_sample_minimum_size();
647
648 _survivor_plab_array = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads, mtGC);
649 _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, 2*max_plab_samples, mtGC);
650 _cursor = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads, mtGC);
651 if (_survivor_plab_array == NULL || _survivor_chunk_array == NULL
652 || _cursor == NULL) {
653 warning("Failed to allocate survivor plab/chunk array");
654 if (_survivor_plab_array != NULL) {
655 FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array);
656 _survivor_plab_array = NULL;
657 }
658 if (_survivor_chunk_array != NULL) {
659 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array);
660 _survivor_chunk_array = NULL;
661 }
662 if (_cursor != NULL) {
663 FREE_C_HEAP_ARRAY(size_t, _cursor);
664 _cursor = NULL;
665 }
666 } else {
667 _survivor_chunk_capacity = 2*max_plab_samples;
668 for (uint i = 0; i < ParallelGCThreads; i++) {
669 HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
670 if (vec == NULL) {
671 warning("Failed to allocate survivor plab array");
672 for (int j = i; j > 0; j--) {
673 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_plab_array[j-1].array());
674 }
675 FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array);
676 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array);
677 _survivor_plab_array = NULL;
678 _survivor_chunk_array = NULL;
679 _survivor_chunk_capacity = 0;
680 break;
681 } else {
682 ChunkArray* cur =
683 ::new (&_survivor_plab_array[i]) ChunkArray(vec,
684 max_plab_samples);
685 assert(cur->end() == 0, "Should be 0");
686 assert(cur->array() == vec, "Should be vec");
687 assert(cur->capacity() == max_plab_samples, "Error");
688 }
689 }
690 }
691 }
692 assert( ( _survivor_plab_array != NULL
693 && _survivor_chunk_array != NULL)
694 || ( _survivor_chunk_capacity == 0
695 && _survivor_chunk_index == 0),
696 "Error");
697
698 NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;)
699 _gc_counters = new CollectorCounters("CMS", 1);
700 _completed_initialization = true;
701 _inter_sweep_timer.start(); // start of time
702 }
703
704 size_t CMSCollector::plab_sample_minimum_size() {
705 // The default value of MinTLABSize is 2k, but there is
706 // no way to get the default value if the flag has been overridden.
707 return MAX2(ThreadLocalAllocBuffer::min_size() * HeapWordSize, 2 * K);
708 }
709
710 const char* ConcurrentMarkSweepGeneration::name() const {
711 return "concurrent mark-sweep generation";
712 }
713 void ConcurrentMarkSweepGeneration::update_counters() {
714 if (UsePerfData) {
715 _space_counters->update_all();
716 _gen_counters->update_all();
717 }
718 }
719
720 // this is an optimized version of update_counters(). it takes the
721 // used value as a parameter rather than computing it.
722 //
723 void ConcurrentMarkSweepGeneration::update_counters(size_t used) {
724 if (UsePerfData) {
725 _space_counters->update_used(used);
726 _space_counters->update_capacity();
727 _gen_counters->update_all();
728 }
729 }
730
731 void ConcurrentMarkSweepGeneration::print() const {
732 Generation::print();
733 cmsSpace()->print();
734 }
735
736 #ifndef PRODUCT
737 void ConcurrentMarkSweepGeneration::print_statistics() {
738 cmsSpace()->printFLCensus(0);
739 }
740 #endif
741
742 void ConcurrentMarkSweepGeneration::printOccupancy(const char *s) {
743 GenCollectedHeap* gch = GenCollectedHeap::heap();
744 if (PrintGCDetails) {
745 if (Verbose) {
746 gclog_or_tty->print("[%d %s-%s: "SIZE_FORMAT"("SIZE_FORMAT")]",
747 level(), short_name(), s, used(), capacity());
748 } else {
749 gclog_or_tty->print("[%d %s-%s: "SIZE_FORMAT"K("SIZE_FORMAT"K)]",
750 level(), short_name(), s, used() / K, capacity() / K);
751 }
752 }
753 if (Verbose) {
754 gclog_or_tty->print(" "SIZE_FORMAT"("SIZE_FORMAT")",
755 gch->used(), gch->capacity());
756 } else {
757 gclog_or_tty->print(" "SIZE_FORMAT"K("SIZE_FORMAT"K)",
758 gch->used() / K, gch->capacity() / K);
759 }
760 }
761
762 size_t
763 ConcurrentMarkSweepGeneration::contiguous_available() const {
764 // dld proposes an improvement in precision here. If the committed
765 // part of the space ends in a free block we should add that to
766 // uncommitted size in the calculation below. Will make this
767 // change later, staying with the approximation below for the
768 // time being. -- ysr.
769 return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc());
770 }
771
772 size_t
773 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const {
774 return _cmsSpace->max_alloc_in_words() * HeapWordSize;
775 }
776
777 size_t ConcurrentMarkSweepGeneration::max_available() const {
778 return free() + _virtual_space.uncommitted_size();
779 }
780
781 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(size_t max_promotion_in_bytes) const {
782 size_t available = max_available();
783 size_t av_promo = (size_t)gc_stats()->avg_promoted()->padded_average();
784 bool res = (available >= av_promo) || (available >= max_promotion_in_bytes);
785 if (Verbose && PrintGCDetails) {
786 gclog_or_tty->print_cr(
787 "CMS: promo attempt is%s safe: available("SIZE_FORMAT") %s av_promo("SIZE_FORMAT"),"
788 "max_promo("SIZE_FORMAT")",
789 res? "":" not", available, res? ">=":"<",
790 av_promo, max_promotion_in_bytes);
791 }
792 return res;
793 }
794
795 // At a promotion failure dump information on block layout in heap
796 // (cms old generation).
797 void ConcurrentMarkSweepGeneration::promotion_failure_occurred() {
798 if (CMSDumpAtPromotionFailure) {
799 cmsSpace()->dump_at_safepoint_with_locks(collector(), gclog_or_tty);
800 }
801 }
802
803 void ConcurrentMarkSweepGeneration::reset_after_compaction() {
804 // Clear the promotion information. These pointers can be adjusted
805 // along with all the other pointers into the heap but
806 // compaction is expected to be a rare event with
807 // a heap using cms so don't do it without seeing the need.
808 for (uint i = 0; i < ParallelGCThreads; i++) {
809 _par_gc_thread_states[i]->promo.reset();
810 }
811 }
812
813 void ConcurrentMarkSweepGeneration::compute_new_size() {
814 assert_locked_or_safepoint(Heap_lock);
815
816 // If incremental collection failed, we just want to expand
817 // to the limit.
818 if (incremental_collection_failed()) {
819 clear_incremental_collection_failed();
820 grow_to_reserved();
821 return;
822 }
823
824 // The heap has been compacted but not reset yet.
825 // Any metric such as free() or used() will be incorrect.
826
827 CardGeneration::compute_new_size();
828
829 // Reset again after a possible resizing
830 if (did_compact()) {
831 cmsSpace()->reset_after_compaction();
832 }
833 }
834
835 void ConcurrentMarkSweepGeneration::compute_new_size_free_list() {
836 assert_locked_or_safepoint(Heap_lock);
837
838 // If incremental collection failed, we just want to expand
839 // to the limit.
840 if (incremental_collection_failed()) {
841 clear_incremental_collection_failed();
842 grow_to_reserved();
843 return;
844 }
845
846 double free_percentage = ((double) free()) / capacity();
847 double desired_free_percentage = (double) MinHeapFreeRatio / 100;
848 double maximum_free_percentage = (double) MaxHeapFreeRatio / 100;
849
850 // compute expansion delta needed for reaching desired free percentage
851 if (free_percentage < desired_free_percentage) {
852 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
853 assert(desired_capacity >= capacity(), "invalid expansion size");
854 size_t expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes);
855 if (PrintGCDetails && Verbose) {
856 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
857 gclog_or_tty->print_cr("\nFrom compute_new_size: ");
858 gclog_or_tty->print_cr(" Free fraction %f", free_percentage);
859 gclog_or_tty->print_cr(" Desired free fraction %f",
860 desired_free_percentage);
861 gclog_or_tty->print_cr(" Maximum free fraction %f",
862 maximum_free_percentage);
863 gclog_or_tty->print_cr(" Capacity "SIZE_FORMAT, capacity()/1000);
864 gclog_or_tty->print_cr(" Desired capacity "SIZE_FORMAT,
865 desired_capacity/1000);
866 int prev_level = level() - 1;
867 if (prev_level >= 0) {
868 size_t prev_size = 0;
869 GenCollectedHeap* gch = GenCollectedHeap::heap();
870 Generation* prev_gen = gch->young_gen();
871 prev_size = prev_gen->capacity();
872 gclog_or_tty->print_cr(" Younger gen size "SIZE_FORMAT,
873 prev_size/1000);
874 }
875 gclog_or_tty->print_cr(" unsafe_max_alloc_nogc "SIZE_FORMAT,
876 unsafe_max_alloc_nogc()/1000);
877 gclog_or_tty->print_cr(" contiguous available "SIZE_FORMAT,
878 contiguous_available()/1000);
879 gclog_or_tty->print_cr(" Expand by "SIZE_FORMAT" (bytes)",
880 expand_bytes);
881 }
882 // safe if expansion fails
883 expand_for_gc_cause(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio);
884 if (PrintGCDetails && Verbose) {
885 gclog_or_tty->print_cr(" Expanded free fraction %f",
886 ((double) free()) / capacity());
887 }
888 } else {
889 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
890 assert(desired_capacity <= capacity(), "invalid expansion size");
891 size_t shrink_bytes = capacity() - desired_capacity;
892 // Don't shrink unless the delta is greater than the minimum shrink we want
893 if (shrink_bytes >= MinHeapDeltaBytes) {
894 shrink_free_list_by(shrink_bytes);
895 }
896 }
897 }
898
899 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const {
900 return cmsSpace()->freelistLock();
901 }
902
903 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size,
904 bool tlab) {
905 CMSSynchronousYieldRequest yr;
906 MutexLockerEx x(freelistLock(),
907 Mutex::_no_safepoint_check_flag);
908 return have_lock_and_allocate(size, tlab);
909 }
910
911 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size,
912 bool tlab /* ignored */) {
913 assert_lock_strong(freelistLock());
914 size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size);
915 HeapWord* res = cmsSpace()->allocate(adjustedSize);
916 // Allocate the object live (grey) if the background collector has
917 // started marking. This is necessary because the marker may
918 // have passed this address and consequently this object will
919 // not otherwise be greyed and would be incorrectly swept up.
920 // Note that if this object contains references, the writing
921 // of those references will dirty the card containing this object
922 // allowing the object to be blackened (and its references scanned)
923 // either during a preclean phase or at the final checkpoint.
924 if (res != NULL) {
925 // We may block here with an uninitialized object with
926 // its mark-bit or P-bits not yet set. Such objects need
927 // to be safely navigable by block_start().
928 assert(oop(res)->klass_or_null() == NULL, "Object should be uninitialized here.");
929 assert(!((FreeChunk*)res)->is_free(), "Error, block will look free but show wrong size");
930 collector()->direct_allocated(res, adjustedSize);
931 _direct_allocated_words += adjustedSize;
932 // allocation counters
933 NOT_PRODUCT(
934 _numObjectsAllocated++;
935 _numWordsAllocated += (int)adjustedSize;
936 )
937 }
938 return res;
939 }
940
941 // In the case of direct allocation by mutators in a generation that
942 // is being concurrently collected, the object must be allocated
943 // live (grey) if the background collector has started marking.
944 // This is necessary because the marker may
945 // have passed this address and consequently this object will
946 // not otherwise be greyed and would be incorrectly swept up.
947 // Note that if this object contains references, the writing
948 // of those references will dirty the card containing this object
949 // allowing the object to be blackened (and its references scanned)
950 // either during a preclean phase or at the final checkpoint.
951 void CMSCollector::direct_allocated(HeapWord* start, size_t size) {
952 assert(_markBitMap.covers(start, size), "Out of bounds");
953 if (_collectorState >= Marking) {
954 MutexLockerEx y(_markBitMap.lock(),
955 Mutex::_no_safepoint_check_flag);
956 // [see comments preceding SweepClosure::do_blk() below for details]
957 //
958 // Can the P-bits be deleted now? JJJ
959 //
960 // 1. need to mark the object as live so it isn't collected
961 // 2. need to mark the 2nd bit to indicate the object may be uninitialized
962 // 3. need to mark the end of the object so marking, precleaning or sweeping
963 // can skip over uninitialized or unparsable objects. An allocated
964 // object is considered uninitialized for our purposes as long as
965 // its klass word is NULL. All old gen objects are parsable
966 // as soon as they are initialized.)
967 _markBitMap.mark(start); // object is live
968 _markBitMap.mark(start + 1); // object is potentially uninitialized?
969 _markBitMap.mark(start + size - 1);
970 // mark end of object
971 }
972 // check that oop looks uninitialized
973 assert(oop(start)->klass_or_null() == NULL, "_klass should be NULL");
974 }
975
976 void CMSCollector::promoted(bool par, HeapWord* start,
977 bool is_obj_array, size_t obj_size) {
978 assert(_markBitMap.covers(start), "Out of bounds");
979 // See comment in direct_allocated() about when objects should
980 // be allocated live.
981 if (_collectorState >= Marking) {
982 // we already hold the marking bit map lock, taken in
983 // the prologue
984 if (par) {
985 _markBitMap.par_mark(start);
986 } else {
987 _markBitMap.mark(start);
988 }
989 // We don't need to mark the object as uninitialized (as
990 // in direct_allocated above) because this is being done with the
991 // world stopped and the object will be initialized by the
992 // time the marking, precleaning or sweeping get to look at it.
993 // But see the code for copying objects into the CMS generation,
994 // where we need to ensure that concurrent readers of the
995 // block offset table are able to safely navigate a block that
996 // is in flux from being free to being allocated (and in
997 // transition while being copied into) and subsequently
998 // becoming a bona-fide object when the copy/promotion is complete.
999 assert(SafepointSynchronize::is_at_safepoint(),
1000 "expect promotion only at safepoints");
1001
1002 if (_collectorState < Sweeping) {
1003 // Mark the appropriate cards in the modUnionTable, so that
1004 // this object gets scanned before the sweep. If this is
1005 // not done, CMS generation references in the object might
1006 // not get marked.
1007 // For the case of arrays, which are otherwise precisely
1008 // marked, we need to dirty the entire array, not just its head.
1009 if (is_obj_array) {
1010 // The [par_]mark_range() method expects mr.end() below to
1011 // be aligned to the granularity of a bit's representation
1012 // in the heap. In the case of the MUT below, that's a
1013 // card size.
1014 MemRegion mr(start,
1015 (HeapWord*)round_to((intptr_t)(start + obj_size),
1016 CardTableModRefBS::card_size /* bytes */));
1017 if (par) {
1018 _modUnionTable.par_mark_range(mr);
1019 } else {
1020 _modUnionTable.mark_range(mr);
1021 }
1022 } else { // not an obj array; we can just mark the head
1023 if (par) {
1024 _modUnionTable.par_mark(start);
1025 } else {
1026 _modUnionTable.mark(start);
1027 }
1028 }
1029 }
1030 }
1031 }
1032
1033 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size) {
1034 assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
1035 // allocate, copy and if necessary update promoinfo --
1036 // delegate to underlying space.
1037 assert_lock_strong(freelistLock());
1038
1039 #ifndef PRODUCT
1040 if (Universe::heap()->promotion_should_fail()) {
1041 return NULL;
1042 }
1043 #endif // #ifndef PRODUCT
1044
1045 oop res = _cmsSpace->promote(obj, obj_size);
1046 if (res == NULL) {
1047 // expand and retry
1048 size_t s = _cmsSpace->expansionSpaceRequired(obj_size); // HeapWords
1049 expand_for_gc_cause(s*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_promotion);
1050 // Since this is the old generation, we don't try to promote
1051 // into a more senior generation.
1052 res = _cmsSpace->promote(obj, obj_size);
1053 }
1054 if (res != NULL) {
1055 // See comment in allocate() about when objects should
1056 // be allocated live.
1057 assert(obj->is_oop(), "Will dereference klass pointer below");
1058 collector()->promoted(false, // Not parallel
1059 (HeapWord*)res, obj->is_objArray(), obj_size);
1060 // promotion counters
1061 NOT_PRODUCT(
1062 _numObjectsPromoted++;
1063 _numWordsPromoted +=
1064 (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size()));
1065 )
1066 }
1067 return res;
1068 }
1069
1070
1071 // IMPORTANT: Notes on object size recognition in CMS.
1072 // ---------------------------------------------------
1073 // A block of storage in the CMS generation is always in
1074 // one of three states. A free block (FREE), an allocated
1075 // object (OBJECT) whose size() method reports the correct size,
1076 // and an intermediate state (TRANSIENT) in which its size cannot
1077 // be accurately determined.
1078 // STATE IDENTIFICATION: (32 bit and 64 bit w/o COOPS)
1079 // -----------------------------------------------------
1080 // FREE: klass_word & 1 == 1; mark_word holds block size
1081 //
1082 // OBJECT: klass_word installed; klass_word != 0 && klass_word & 1 == 0;
1083 // obj->size() computes correct size
1084 //
1085 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1086 //
1087 // STATE IDENTIFICATION: (64 bit+COOPS)
1088 // ------------------------------------
1089 // FREE: mark_word & CMS_FREE_BIT == 1; mark_word & ~CMS_FREE_BIT gives block_size
1090 //
1091 // OBJECT: klass_word installed; klass_word != 0;
1092 // obj->size() computes correct size
1093 //
1094 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1095 //
1096 //
1097 // STATE TRANSITION DIAGRAM
1098 //
1099 // mut / parnew mut / parnew
1100 // FREE --------------------> TRANSIENT ---------------------> OBJECT --|
1101 // ^ |
1102 // |------------------------ DEAD <------------------------------------|
1103 // sweep mut
1104 //
1105 // While a block is in TRANSIENT state its size cannot be determined
1106 // so readers will either need to come back later or stall until
1107 // the size can be determined. Note that for the case of direct
1108 // allocation, P-bits, when available, may be used to determine the
1109 // size of an object that may not yet have been initialized.
1110
1111 // Things to support parallel young-gen collection.
1112 oop
1113 ConcurrentMarkSweepGeneration::par_promote(int thread_num,
1114 oop old, markOop m,
1115 size_t word_sz) {
1116 #ifndef PRODUCT
1117 if (Universe::heap()->promotion_should_fail()) {
1118 return NULL;
1119 }
1120 #endif // #ifndef PRODUCT
1121
1122 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1123 PromotionInfo* promoInfo = &ps->promo;
1124 // if we are tracking promotions, then first ensure space for
1125 // promotion (including spooling space for saving header if necessary).
1126 // then allocate and copy, then track promoted info if needed.
1127 // When tracking (see PromotionInfo::track()), the mark word may
1128 // be displaced and in this case restoration of the mark word
1129 // occurs in the (oop_since_save_marks_)iterate phase.
1130 if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) {
1131 // Out of space for allocating spooling buffers;
1132 // try expanding and allocating spooling buffers.
1133 if (!expand_and_ensure_spooling_space(promoInfo)) {
1134 return NULL;
1135 }
1136 }
1137 assert(promoInfo->has_spooling_space(), "Control point invariant");
1138 const size_t alloc_sz = CompactibleFreeListSpace::adjustObjectSize(word_sz);
1139 HeapWord* obj_ptr = ps->lab.alloc(alloc_sz);
1140 if (obj_ptr == NULL) {
1141 obj_ptr = expand_and_par_lab_allocate(ps, alloc_sz);
1142 if (obj_ptr == NULL) {
1143 return NULL;
1144 }
1145 }
1146 oop obj = oop(obj_ptr);
1147 OrderAccess::storestore();
1148 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1149 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1150 // IMPORTANT: See note on object initialization for CMS above.
1151 // Otherwise, copy the object. Here we must be careful to insert the
1152 // klass pointer last, since this marks the block as an allocated object.
1153 // Except with compressed oops it's the mark word.
1154 HeapWord* old_ptr = (HeapWord*)old;
1155 // Restore the mark word copied above.
1156 obj->set_mark(m);
1157 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1158 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1159 OrderAccess::storestore();
1160
1161 if (UseCompressedClassPointers) {
1162 // Copy gap missed by (aligned) header size calculation below
1163 obj->set_klass_gap(old->klass_gap());
1164 }
1165 if (word_sz > (size_t)oopDesc::header_size()) {
1166 Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1167 obj_ptr + oopDesc::header_size(),
1168 word_sz - oopDesc::header_size());
1169 }
1170
1171 // Now we can track the promoted object, if necessary. We take care
1172 // to delay the transition from uninitialized to full object
1173 // (i.e., insertion of klass pointer) until after, so that it
1174 // atomically becomes a promoted object.
1175 if (promoInfo->tracking()) {
1176 promoInfo->track((PromotedObject*)obj, old->klass());
1177 }
1178 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1179 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1180 assert(old->is_oop(), "Will use and dereference old klass ptr below");
1181
1182 // Finally, install the klass pointer (this should be volatile).
1183 OrderAccess::storestore();
1184 obj->set_klass(old->klass());
1185 // We should now be able to calculate the right size for this object
1186 assert(obj->is_oop() && obj->size() == (int)word_sz, "Error, incorrect size computed for promoted object");
1187
1188 collector()->promoted(true, // parallel
1189 obj_ptr, old->is_objArray(), word_sz);
1190
1191 NOT_PRODUCT(
1192 Atomic::inc_ptr(&_numObjectsPromoted);
1193 Atomic::add_ptr(alloc_sz, &_numWordsPromoted);
1194 )
1195
1196 return obj;
1197 }
1198
1199 void
1200 ConcurrentMarkSweepGeneration::
1201 par_promote_alloc_done(int thread_num) {
1202 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1203 ps->lab.retire(thread_num);
1204 }
1205
1206 void
1207 ConcurrentMarkSweepGeneration::
1208 par_oop_since_save_marks_iterate_done(int thread_num) {
1209 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1210 ParScanWithoutBarrierClosure* dummy_cl = NULL;
1211 ps->promo.promoted_oops_iterate_nv(dummy_cl);
1212 }
1213
1214 bool ConcurrentMarkSweepGeneration::should_collect(bool full,
1215 size_t size,
1216 bool tlab)
1217 {
1218 // We allow a STW collection only if a full
1219 // collection was requested.
1220 return full || should_allocate(size, tlab); // FIX ME !!!
1221 // This and promotion failure handling are connected at the
1222 // hip and should be fixed by untying them.
1223 }
1224
1225 bool CMSCollector::shouldConcurrentCollect() {
1226 if (_full_gc_requested) {
1227 if (Verbose && PrintGCDetails) {
1228 gclog_or_tty->print_cr("CMSCollector: collect because of explicit "
1229 " gc request (or gc_locker)");
1230 }
1231 return true;
1232 }
1233
1234 FreelistLocker x(this);
1235 // ------------------------------------------------------------------
1236 // Print out lots of information which affects the initiation of
1237 // a collection.
1238 if (PrintCMSInitiationStatistics && stats().valid()) {
1239 gclog_or_tty->print("CMSCollector shouldConcurrentCollect: ");
1240 gclog_or_tty->stamp();
1241 gclog_or_tty->cr();
1242 stats().print_on(gclog_or_tty);
1243 gclog_or_tty->print_cr("time_until_cms_gen_full %3.7f",
1244 stats().time_until_cms_gen_full());
1245 gclog_or_tty->print_cr("free="SIZE_FORMAT, _cmsGen->free());
1246 gclog_or_tty->print_cr("contiguous_available="SIZE_FORMAT,
1247 _cmsGen->contiguous_available());
1248 gclog_or_tty->print_cr("promotion_rate=%g", stats().promotion_rate());
1249 gclog_or_tty->print_cr("cms_allocation_rate=%g", stats().cms_allocation_rate());
1250 gclog_or_tty->print_cr("occupancy=%3.7f", _cmsGen->occupancy());
1251 gclog_or_tty->print_cr("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy());
1252 gclog_or_tty->print_cr("cms_time_since_begin=%3.7f", stats().cms_time_since_begin());
1253 gclog_or_tty->print_cr("cms_time_since_end=%3.7f", stats().cms_time_since_end());
1254 gclog_or_tty->print_cr("metadata initialized %d",
1255 MetaspaceGC::should_concurrent_collect());
1256 }
1257 // ------------------------------------------------------------------
1258
1259 // If the estimated time to complete a cms collection (cms_duration())
1260 // is less than the estimated time remaining until the cms generation
1261 // is full, start a collection.
1262 if (!UseCMSInitiatingOccupancyOnly) {
1263 if (stats().valid()) {
1264 if (stats().time_until_cms_start() == 0.0) {
1265 return true;
1266 }
1267 } else {
1268 // We want to conservatively collect somewhat early in order
1269 // to try and "bootstrap" our CMS/promotion statistics;
1270 // this branch will not fire after the first successful CMS
1271 // collection because the stats should then be valid.
1272 if (_cmsGen->occupancy() >= _bootstrap_occupancy) {
1273 if (Verbose && PrintGCDetails) {
1274 gclog_or_tty->print_cr(
1275 " CMSCollector: collect for bootstrapping statistics:"
1276 " occupancy = %f, boot occupancy = %f", _cmsGen->occupancy(),
1277 _bootstrap_occupancy);
1278 }
1279 return true;
1280 }
1281 }
1282 }
1283
1284 // Otherwise, we start a collection cycle if
1285 // old gen want a collection cycle started. Each may use
1286 // an appropriate criterion for making this decision.
1287 // XXX We need to make sure that the gen expansion
1288 // criterion dovetails well with this. XXX NEED TO FIX THIS
1289 if (_cmsGen->should_concurrent_collect()) {
1290 if (Verbose && PrintGCDetails) {
1291 gclog_or_tty->print_cr("CMS old gen initiated");
1292 }
1293 return true;
1294 }
1295
1296 // We start a collection if we believe an incremental collection may fail;
1297 // this is not likely to be productive in practice because it's probably too
1298 // late anyway.
1299 GenCollectedHeap* gch = GenCollectedHeap::heap();
1300 assert(gch->collector_policy()->is_generation_policy(),
1301 "You may want to check the correctness of the following");
1302 if (gch->incremental_collection_will_fail(true /* consult_young */)) {
1303 if (Verbose && PrintGCDetails) {
1304 gclog_or_tty->print("CMSCollector: collect because incremental collection will fail ");
1305 }
1306 return true;
1307 }
1308
1309 if (MetaspaceGC::should_concurrent_collect()) {
1310 if (Verbose && PrintGCDetails) {
1311 gclog_or_tty->print("CMSCollector: collect for metadata allocation ");
1312 }
1313 return true;
1314 }
1315
1316 // CMSTriggerInterval starts a CMS cycle if enough time has passed.
1317 if (CMSTriggerInterval >= 0) {
1318 if (CMSTriggerInterval == 0) {
1319 // Trigger always
1320 return true;
1321 }
1322
1323 // Check the CMS time since begin (we do not check the stats validity
1324 // as we want to be able to trigger the first CMS cycle as well)
1325 if (stats().cms_time_since_begin() >= (CMSTriggerInterval / ((double) MILLIUNITS))) {
1326 if (Verbose && PrintGCDetails) {
1327 if (stats().valid()) {
1328 gclog_or_tty->print_cr("CMSCollector: collect because of trigger interval (time since last begin %3.7f secs)",
1329 stats().cms_time_since_begin());
1330 } else {
1331 gclog_or_tty->print_cr("CMSCollector: collect because of trigger interval (first collection)");
1332 }
1333 }
1334 return true;
1335 }
1336 }
1337
1338 return false;
1339 }
1340
1341 void CMSCollector::set_did_compact(bool v) { _cmsGen->set_did_compact(v); }
1342
1343 // Clear _expansion_cause fields of constituent generations
1344 void CMSCollector::clear_expansion_cause() {
1345 _cmsGen->clear_expansion_cause();
1346 }
1347
1348 // We should be conservative in starting a collection cycle. To
1349 // start too eagerly runs the risk of collecting too often in the
1350 // extreme. To collect too rarely falls back on full collections,
1351 // which works, even if not optimum in terms of concurrent work.
1352 // As a work around for too eagerly collecting, use the flag
1353 // UseCMSInitiatingOccupancyOnly. This also has the advantage of
1354 // giving the user an easily understandable way of controlling the
1355 // collections.
1356 // We want to start a new collection cycle if any of the following
1357 // conditions hold:
1358 // . our current occupancy exceeds the configured initiating occupancy
1359 // for this generation, or
1360 // . we recently needed to expand this space and have not, since that
1361 // expansion, done a collection of this generation, or
1362 // . the underlying space believes that it may be a good idea to initiate
1363 // a concurrent collection (this may be based on criteria such as the
1364 // following: the space uses linear allocation and linear allocation is
1365 // going to fail, or there is believed to be excessive fragmentation in
1366 // the generation, etc... or ...
1367 // [.(currently done by CMSCollector::shouldConcurrentCollect() only for
1368 // the case of the old generation; see CR 6543076):
1369 // we may be approaching a point at which allocation requests may fail because
1370 // we will be out of sufficient free space given allocation rate estimates.]
1371 bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const {
1372
1373 assert_lock_strong(freelistLock());
1374 if (occupancy() > initiating_occupancy()) {
1375 if (PrintGCDetails && Verbose) {
1376 gclog_or_tty->print(" %s: collect because of occupancy %f / %f ",
1377 short_name(), occupancy(), initiating_occupancy());
1378 }
1379 return true;
1380 }
1381 if (UseCMSInitiatingOccupancyOnly) {
1382 return false;
1383 }
1384 if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) {
1385 if (PrintGCDetails && Verbose) {
1386 gclog_or_tty->print(" %s: collect because expanded for allocation ",
1387 short_name());
1388 }
1389 return true;
1390 }
1391 if (_cmsSpace->should_concurrent_collect()) {
1392 if (PrintGCDetails && Verbose) {
1393 gclog_or_tty->print(" %s: collect because cmsSpace says so ",
1394 short_name());
1395 }
1396 return true;
1397 }
1398 return false;
1399 }
1400
1401 void ConcurrentMarkSweepGeneration::collect(bool full,
1402 bool clear_all_soft_refs,
1403 size_t size,
1404 bool tlab)
1405 {
1406 collector()->collect(full, clear_all_soft_refs, size, tlab);
1407 }
1408
1409 void CMSCollector::collect(bool full,
1410 bool clear_all_soft_refs,
1411 size_t size,
1412 bool tlab)
1413 {
1414 // The following "if" branch is present for defensive reasons.
1415 // In the current uses of this interface, it can be replaced with:
1416 // assert(!GC_locker.is_active(), "Can't be called otherwise");
1417 // But I am not placing that assert here to allow future
1418 // generality in invoking this interface.
1419 if (GC_locker::is_active()) {
1420 // A consistency test for GC_locker
1421 assert(GC_locker::needs_gc(), "Should have been set already");
1422 // Skip this foreground collection, instead
1423 // expanding the heap if necessary.
1424 // Need the free list locks for the call to free() in compute_new_size()
1425 compute_new_size();
1426 return;
1427 }
1428 acquire_control_and_collect(full, clear_all_soft_refs);
1429 }
1430
1431 void CMSCollector::request_full_gc(unsigned int full_gc_count, GCCause::Cause cause) {
1432 GenCollectedHeap* gch = GenCollectedHeap::heap();
1433 unsigned int gc_count = gch->total_full_collections();
1434 if (gc_count == full_gc_count) {
1435 MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag);
1436 _full_gc_requested = true;
1437 _full_gc_cause = cause;
1438 CGC_lock->notify(); // nudge CMS thread
1439 } else {
1440 assert(gc_count > full_gc_count, "Error: causal loop");
1441 }
1442 }
1443
1444 bool CMSCollector::is_external_interruption() {
1445 GCCause::Cause cause = GenCollectedHeap::heap()->gc_cause();
1446 return GCCause::is_user_requested_gc(cause) ||
1447 GCCause::is_serviceability_requested_gc(cause);
1448 }
1449
1450 void CMSCollector::report_concurrent_mode_interruption() {
1451 if (is_external_interruption()) {
1452 if (PrintGCDetails) {
1453 gclog_or_tty->print(" (concurrent mode interrupted)");
1454 }
1455 } else {
1456 if (PrintGCDetails) {
1457 gclog_or_tty->print(" (concurrent mode failure)");
1458 }
1459 _gc_tracer_cm->report_concurrent_mode_failure();
1460 }
1461 }
1462
1463
1464 // The foreground and background collectors need to coordinate in order
1465 // to make sure that they do not mutually interfere with CMS collections.
1466 // When a background collection is active,
1467 // the foreground collector may need to take over (preempt) and
1468 // synchronously complete an ongoing collection. Depending on the
1469 // frequency of the background collections and the heap usage
1470 // of the application, this preemption can be seldom or frequent.
1471 // There are only certain
1472 // points in the background collection that the "collection-baton"
1473 // can be passed to the foreground collector.
1474 //
1475 // The foreground collector will wait for the baton before
1476 // starting any part of the collection. The foreground collector
1477 // will only wait at one location.
1478 //
1479 // The background collector will yield the baton before starting a new
1480 // phase of the collection (e.g., before initial marking, marking from roots,
1481 // precleaning, final re-mark, sweep etc.) This is normally done at the head
1482 // of the loop which switches the phases. The background collector does some
1483 // of the phases (initial mark, final re-mark) with the world stopped.
1484 // Because of locking involved in stopping the world,
1485 // the foreground collector should not block waiting for the background
1486 // collector when it is doing a stop-the-world phase. The background
1487 // collector will yield the baton at an additional point just before
1488 // it enters a stop-the-world phase. Once the world is stopped, the
1489 // background collector checks the phase of the collection. If the
1490 // phase has not changed, it proceeds with the collection. If the
1491 // phase has changed, it skips that phase of the collection. See
1492 // the comments on the use of the Heap_lock in collect_in_background().
1493 //
1494 // Variable used in baton passing.
1495 // _foregroundGCIsActive - Set to true by the foreground collector when
1496 // it wants the baton. The foreground clears it when it has finished
1497 // the collection.
1498 // _foregroundGCShouldWait - Set to true by the background collector
1499 // when it is running. The foreground collector waits while
1500 // _foregroundGCShouldWait is true.
1501 // CGC_lock - monitor used to protect access to the above variables
1502 // and to notify the foreground and background collectors.
1503 // _collectorState - current state of the CMS collection.
1504 //
1505 // The foreground collector
1506 // acquires the CGC_lock
1507 // sets _foregroundGCIsActive
1508 // waits on the CGC_lock for _foregroundGCShouldWait to be false
1509 // various locks acquired in preparation for the collection
1510 // are released so as not to block the background collector
1511 // that is in the midst of a collection
1512 // proceeds with the collection
1513 // clears _foregroundGCIsActive
1514 // returns
1515 //
1516 // The background collector in a loop iterating on the phases of the
1517 // collection
1518 // acquires the CGC_lock
1519 // sets _foregroundGCShouldWait
1520 // if _foregroundGCIsActive is set
1521 // clears _foregroundGCShouldWait, notifies _CGC_lock
1522 // waits on _CGC_lock for _foregroundGCIsActive to become false
1523 // and exits the loop.
1524 // otherwise
1525 // proceed with that phase of the collection
1526 // if the phase is a stop-the-world phase,
1527 // yield the baton once more just before enqueueing
1528 // the stop-world CMS operation (executed by the VM thread).
1529 // returns after all phases of the collection are done
1530 //
1531
1532 void CMSCollector::acquire_control_and_collect(bool full,
1533 bool clear_all_soft_refs) {
1534 assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
1535 assert(!Thread::current()->is_ConcurrentGC_thread(),
1536 "shouldn't try to acquire control from self!");
1537
1538 // Start the protocol for acquiring control of the
1539 // collection from the background collector (aka CMS thread).
1540 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1541 "VM thread should have CMS token");
1542 // Remember the possibly interrupted state of an ongoing
1543 // concurrent collection
1544 CollectorState first_state = _collectorState;
1545
1546 // Signal to a possibly ongoing concurrent collection that
1547 // we want to do a foreground collection.
1548 _foregroundGCIsActive = true;
1549
1550 // release locks and wait for a notify from the background collector
1551 // releasing the locks in only necessary for phases which
1552 // do yields to improve the granularity of the collection.
1553 assert_lock_strong(bitMapLock());
1554 // We need to lock the Free list lock for the space that we are
1555 // currently collecting.
1556 assert(haveFreelistLocks(), "Must be holding free list locks");
1557 bitMapLock()->unlock();
1558 releaseFreelistLocks();
1559 {
1560 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1561 if (_foregroundGCShouldWait) {
1562 // We are going to be waiting for action for the CMS thread;
1563 // it had better not be gone (for instance at shutdown)!
1564 assert(ConcurrentMarkSweepThread::cmst() != NULL,
1565 "CMS thread must be running");
1566 // Wait here until the background collector gives us the go-ahead
1567 ConcurrentMarkSweepThread::clear_CMS_flag(
1568 ConcurrentMarkSweepThread::CMS_vm_has_token); // release token
1569 // Get a possibly blocked CMS thread going:
1570 // Note that we set _foregroundGCIsActive true above,
1571 // without protection of the CGC_lock.
1572 CGC_lock->notify();
1573 assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(),
1574 "Possible deadlock");
1575 while (_foregroundGCShouldWait) {
1576 // wait for notification
1577 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1578 // Possibility of delay/starvation here, since CMS token does
1579 // not know to give priority to VM thread? Actually, i think
1580 // there wouldn't be any delay/starvation, but the proof of
1581 // that "fact" (?) appears non-trivial. XXX 20011219YSR
1582 }
1583 ConcurrentMarkSweepThread::set_CMS_flag(
1584 ConcurrentMarkSweepThread::CMS_vm_has_token);
1585 }
1586 }
1587 // The CMS_token is already held. Get back the other locks.
1588 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1589 "VM thread should have CMS token");
1590 getFreelistLocks();
1591 bitMapLock()->lock_without_safepoint_check();
1592 if (TraceCMSState) {
1593 gclog_or_tty->print_cr("CMS foreground collector has asked for control "
1594 INTPTR_FORMAT " with first state %d", p2i(Thread::current()), first_state);
1595 gclog_or_tty->print_cr(" gets control with state %d", _collectorState);
1596 }
1597
1598 // Inform cms gen if this was due to partial collection failing.
1599 // The CMS gen may use this fact to determine its expansion policy.
1600 GenCollectedHeap* gch = GenCollectedHeap::heap();
1601 if (gch->incremental_collection_will_fail(false /* don't consult_young */)) {
1602 assert(!_cmsGen->incremental_collection_failed(),
1603 "Should have been noticed, reacted to and cleared");
1604 _cmsGen->set_incremental_collection_failed();
1605 }
1606
1607 if (first_state > Idling) {
1608 report_concurrent_mode_interruption();
1609 }
1610
1611 set_did_compact(true);
1612
1613 // If the collection is being acquired from the background
1614 // collector, there may be references on the discovered
1615 // references lists. Abandon those references, since some
1616 // of them may have become unreachable after concurrent
1617 // discovery; the STW compacting collector will redo discovery
1618 // more precisely, without being subject to floating garbage.
1619 // Leaving otherwise unreachable references in the discovered
1620 // lists would require special handling.
1621 ref_processor()->disable_discovery();
1622 ref_processor()->abandon_partial_discovery();
1623 ref_processor()->verify_no_references_recorded();
1624
1625 if (first_state > Idling) {
1626 save_heap_summary();
1627 }
1628
1629 do_compaction_work(clear_all_soft_refs);
1630
1631 // Has the GC time limit been exceeded?
1632 size_t max_eden_size = _young_gen->max_capacity() -
1633 _young_gen->to()->capacity() -
1634 _young_gen->from()->capacity();
1635 GCCause::Cause gc_cause = gch->gc_cause();
1636 size_policy()->check_gc_overhead_limit(_young_gen->used(),
1637 _young_gen->eden()->used(),
1638 _cmsGen->max_capacity(),
1639 max_eden_size,
1640 full,
1641 gc_cause,
1642 gch->collector_policy());
1643
1644 // Reset the expansion cause, now that we just completed
1645 // a collection cycle.
1646 clear_expansion_cause();
1647 _foregroundGCIsActive = false;
1648 return;
1649 }
1650
1651 // Resize the tenured generation
1652 // after obtaining the free list locks for the
1653 // two generations.
1654 void CMSCollector::compute_new_size() {
1655 assert_locked_or_safepoint(Heap_lock);
1656 FreelistLocker z(this);
1657 MetaspaceGC::compute_new_size();
1658 _cmsGen->compute_new_size_free_list();
1659 }
1660
1661 // A work method used by the foreground collector to do
1662 // a mark-sweep-compact.
1663 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) {
1664 GenCollectedHeap* gch = GenCollectedHeap::heap();
1665
1666 STWGCTimer* gc_timer = GenMarkSweep::gc_timer();
1667 gc_timer->register_gc_start();
1668
1669 SerialOldTracer* gc_tracer = GenMarkSweep::gc_tracer();
1670 gc_tracer->report_gc_start(gch->gc_cause(), gc_timer->gc_start());
1671
1672 GCTraceTime t("CMS:MSC ", PrintGCDetails && Verbose, true, NULL, gc_tracer->gc_id());
1673
1674 // Temporarily widen the span of the weak reference processing to
1675 // the entire heap.
1676 MemRegion new_span(GenCollectedHeap::heap()->reserved_region());
1677 ReferenceProcessorSpanMutator rp_mut_span(ref_processor(), new_span);
1678 // Temporarily, clear the "is_alive_non_header" field of the
1679 // reference processor.
1680 ReferenceProcessorIsAliveMutator rp_mut_closure(ref_processor(), NULL);
1681 // Temporarily make reference _processing_ single threaded (non-MT).
1682 ReferenceProcessorMTProcMutator rp_mut_mt_processing(ref_processor(), false);
1683 // Temporarily make refs discovery atomic
1684 ReferenceProcessorAtomicMutator rp_mut_atomic(ref_processor(), true);
1685 // Temporarily make reference _discovery_ single threaded (non-MT)
1686 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
1687
1688 ref_processor()->set_enqueuing_is_done(false);
1689 ref_processor()->enable_discovery();
1690 ref_processor()->setup_policy(clear_all_soft_refs);
1691 // If an asynchronous collection finishes, the _modUnionTable is
1692 // all clear. If we are assuming the collection from an asynchronous
1693 // collection, clear the _modUnionTable.
1694 assert(_collectorState != Idling || _modUnionTable.isAllClear(),
1695 "_modUnionTable should be clear if the baton was not passed");
1696 _modUnionTable.clear_all();
1697 assert(_collectorState != Idling || _ct->klass_rem_set()->mod_union_is_clear(),
1698 "mod union for klasses should be clear if the baton was passed");
1699 _ct->klass_rem_set()->clear_mod_union();
1700
1701 // We must adjust the allocation statistics being maintained
1702 // in the free list space. We do so by reading and clearing
1703 // the sweep timer and updating the block flux rate estimates below.
1704 assert(!_intra_sweep_timer.is_active(), "_intra_sweep_timer should be inactive");
1705 if (_inter_sweep_timer.is_active()) {
1706 _inter_sweep_timer.stop();
1707 // Note that we do not use this sample to update the _inter_sweep_estimate.
1708 _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
1709 _inter_sweep_estimate.padded_average(),
1710 _intra_sweep_estimate.padded_average());
1711 }
1712
1713 GenMarkSweep::invoke_at_safepoint(_cmsGen->level(),
1714 ref_processor(), clear_all_soft_refs);
1715 #ifdef ASSERT
1716 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
1717 size_t free_size = cms_space->free();
1718 assert(free_size ==
1719 pointer_delta(cms_space->end(), cms_space->compaction_top())
1720 * HeapWordSize,
1721 "All the free space should be compacted into one chunk at top");
1722 assert(cms_space->dictionary()->total_chunk_size(
1723 debug_only(cms_space->freelistLock())) == 0 ||
1724 cms_space->totalSizeInIndexedFreeLists() == 0,
1725 "All the free space should be in a single chunk");
1726 size_t num = cms_space->totalCount();
1727 assert((free_size == 0 && num == 0) ||
1728 (free_size > 0 && (num == 1 || num == 2)),
1729 "There should be at most 2 free chunks after compaction");
1730 #endif // ASSERT
1731 _collectorState = Resetting;
1732 assert(_restart_addr == NULL,
1733 "Should have been NULL'd before baton was passed");
1734 reset(false /* == !concurrent */);
1735 _cmsGen->reset_after_compaction();
1736 _concurrent_cycles_since_last_unload = 0;
1737
1738 // Clear any data recorded in the PLAB chunk arrays.
1739 if (_survivor_plab_array != NULL) {
1740 reset_survivor_plab_arrays();
1741 }
1742
1743 // Adjust the per-size allocation stats for the next epoch.
1744 _cmsGen->cmsSpace()->endSweepFLCensus(sweep_count() /* fake */);
1745 // Restart the "inter sweep timer" for the next epoch.
1746 _inter_sweep_timer.reset();
1747 _inter_sweep_timer.start();
1748
1749 gc_timer->register_gc_end();
1750
1751 gc_tracer->report_gc_end(gc_timer->gc_end(), gc_timer->time_partitions());
1752
1753 // For a mark-sweep-compact, compute_new_size() will be called
1754 // in the heap's do_collection() method.
1755 }
1756
1757 void CMSCollector::print_eden_and_survivor_chunk_arrays() {
1758 ContiguousSpace* eden_space = _young_gen->eden();
1759 ContiguousSpace* from_space = _young_gen->from();
1760 ContiguousSpace* to_space = _young_gen->to();
1761 // Eden
1762 if (_eden_chunk_array != NULL) {
1763 gclog_or_tty->print_cr("eden " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1764 p2i(eden_space->bottom()), p2i(eden_space->top()),
1765 p2i(eden_space->end()), eden_space->capacity());
1766 gclog_or_tty->print_cr("_eden_chunk_index=" SIZE_FORMAT ", "
1767 "_eden_chunk_capacity=" SIZE_FORMAT,
1768 _eden_chunk_index, _eden_chunk_capacity);
1769 for (size_t i = 0; i < _eden_chunk_index; i++) {
1770 gclog_or_tty->print_cr("_eden_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT,
1771 i, p2i(_eden_chunk_array[i]));
1772 }
1773 }
1774 // Survivor
1775 if (_survivor_chunk_array != NULL) {
1776 gclog_or_tty->print_cr("survivor " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1777 p2i(from_space->bottom()), p2i(from_space->top()),
1778 p2i(from_space->end()), from_space->capacity());
1779 gclog_or_tty->print_cr("_survivor_chunk_index=" SIZE_FORMAT ", "
1780 "_survivor_chunk_capacity=" SIZE_FORMAT,
1781 _survivor_chunk_index, _survivor_chunk_capacity);
1782 for (size_t i = 0; i < _survivor_chunk_index; i++) {
1783 gclog_or_tty->print_cr("_survivor_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT,
1784 i, p2i(_survivor_chunk_array[i]));
1785 }
1786 }
1787 }
1788
1789 void CMSCollector::getFreelistLocks() const {
1790 // Get locks for all free lists in all generations that this
1791 // collector is responsible for
1792 _cmsGen->freelistLock()->lock_without_safepoint_check();
1793 }
1794
1795 void CMSCollector::releaseFreelistLocks() const {
1796 // Release locks for all free lists in all generations that this
1797 // collector is responsible for
1798 _cmsGen->freelistLock()->unlock();
1799 }
1800
1801 bool CMSCollector::haveFreelistLocks() const {
1802 // Check locks for all free lists in all generations that this
1803 // collector is responsible for
1804 assert_lock_strong(_cmsGen->freelistLock());
1805 PRODUCT_ONLY(ShouldNotReachHere());
1806 return true;
1807 }
1808
1809 // A utility class that is used by the CMS collector to
1810 // temporarily "release" the foreground collector from its
1811 // usual obligation to wait for the background collector to
1812 // complete an ongoing phase before proceeding.
1813 class ReleaseForegroundGC: public StackObj {
1814 private:
1815 CMSCollector* _c;
1816 public:
1817 ReleaseForegroundGC(CMSCollector* c) : _c(c) {
1818 assert(_c->_foregroundGCShouldWait, "Else should not need to call");
1819 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1820 // allow a potentially blocked foreground collector to proceed
1821 _c->_foregroundGCShouldWait = false;
1822 if (_c->_foregroundGCIsActive) {
1823 CGC_lock->notify();
1824 }
1825 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1826 "Possible deadlock");
1827 }
1828
1829 ~ReleaseForegroundGC() {
1830 assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?");
1831 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1832 _c->_foregroundGCShouldWait = true;
1833 }
1834 };
1835
1836 void CMSCollector::collect_in_background(GCCause::Cause cause) {
1837 assert(Thread::current()->is_ConcurrentGC_thread(),
1838 "A CMS asynchronous collection is only allowed on a CMS thread.");
1839
1840 GenCollectedHeap* gch = GenCollectedHeap::heap();
1841 {
1842 bool safepoint_check = Mutex::_no_safepoint_check_flag;
1843 MutexLockerEx hl(Heap_lock, safepoint_check);
1844 FreelistLocker fll(this);
1845 MutexLockerEx x(CGC_lock, safepoint_check);
1846 if (_foregroundGCIsActive || !UseAsyncConcMarkSweepGC) {
1847 // The foreground collector is active or we're
1848 // not using asynchronous collections. Skip this
1849 // background collection.
1850 assert(!_foregroundGCShouldWait, "Should be clear");
1851 return;
1852 } else {
1853 assert(_collectorState == Idling, "Should be idling before start.");
1854 _collectorState = InitialMarking;
1855 register_gc_start(cause);
1856 // Reset the expansion cause, now that we are about to begin
1857 // a new cycle.
1858 clear_expansion_cause();
1859
1860 // Clear the MetaspaceGC flag since a concurrent collection
1861 // is starting but also clear it after the collection.
1862 MetaspaceGC::set_should_concurrent_collect(false);
1863 }
1864 // Decide if we want to enable class unloading as part of the
1865 // ensuing concurrent GC cycle.
1866 update_should_unload_classes();
1867 _full_gc_requested = false; // acks all outstanding full gc requests
1868 _full_gc_cause = GCCause::_no_gc;
1869 // Signal that we are about to start a collection
1870 gch->increment_total_full_collections(); // ... starting a collection cycle
1871 _collection_count_start = gch->total_full_collections();
1872 }
1873
1874 // Used for PrintGC
1875 size_t prev_used;
1876 if (PrintGC && Verbose) {
1877 prev_used = _cmsGen->used();
1878 }
1879
1880 // The change of the collection state is normally done at this level;
1881 // the exceptions are phases that are executed while the world is
1882 // stopped. For those phases the change of state is done while the
1883 // world is stopped. For baton passing purposes this allows the
1884 // background collector to finish the phase and change state atomically.
1885 // The foreground collector cannot wait on a phase that is done
1886 // while the world is stopped because the foreground collector already
1887 // has the world stopped and would deadlock.
1888 while (_collectorState != Idling) {
1889 if (TraceCMSState) {
1890 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
1891 p2i(Thread::current()), _collectorState);
1892 }
1893 // The foreground collector
1894 // holds the Heap_lock throughout its collection.
1895 // holds the CMS token (but not the lock)
1896 // except while it is waiting for the background collector to yield.
1897 //
1898 // The foreground collector should be blocked (not for long)
1899 // if the background collector is about to start a phase
1900 // executed with world stopped. If the background
1901 // collector has already started such a phase, the
1902 // foreground collector is blocked waiting for the
1903 // Heap_lock. The stop-world phases (InitialMarking and FinalMarking)
1904 // are executed in the VM thread.
1905 //
1906 // The locking order is
1907 // PendingListLock (PLL) -- if applicable (FinalMarking)
1908 // Heap_lock (both this & PLL locked in VM_CMS_Operation::prologue())
1909 // CMS token (claimed in
1910 // stop_world_and_do() -->
1911 // safepoint_synchronize() -->
1912 // CMSThread::synchronize())
1913
1914 {
1915 // Check if the FG collector wants us to yield.
1916 CMSTokenSync x(true); // is cms thread
1917 if (waitForForegroundGC()) {
1918 // We yielded to a foreground GC, nothing more to be
1919 // done this round.
1920 assert(_foregroundGCShouldWait == false, "We set it to false in "
1921 "waitForForegroundGC()");
1922 if (TraceCMSState) {
1923 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
1924 " exiting collection CMS state %d",
1925 p2i(Thread::current()), _collectorState);
1926 }
1927 return;
1928 } else {
1929 // The background collector can run but check to see if the
1930 // foreground collector has done a collection while the
1931 // background collector was waiting to get the CGC_lock
1932 // above. If yes, break so that _foregroundGCShouldWait
1933 // is cleared before returning.
1934 if (_collectorState == Idling) {
1935 break;
1936 }
1937 }
1938 }
1939
1940 assert(_foregroundGCShouldWait, "Foreground collector, if active, "
1941 "should be waiting");
1942
1943 switch (_collectorState) {
1944 case InitialMarking:
1945 {
1946 ReleaseForegroundGC x(this);
1947 stats().record_cms_begin();
1948 VM_CMS_Initial_Mark initial_mark_op(this);
1949 VMThread::execute(&initial_mark_op);
1950 }
1951 // The collector state may be any legal state at this point
1952 // since the background collector may have yielded to the
1953 // foreground collector.
1954 break;
1955 case Marking:
1956 // initial marking in checkpointRootsInitialWork has been completed
1957 if (markFromRoots()) { // we were successful
1958 assert(_collectorState == Precleaning, "Collector state should "
1959 "have changed");
1960 } else {
1961 assert(_foregroundGCIsActive, "Internal state inconsistency");
1962 }
1963 break;
1964 case Precleaning:
1965 // marking from roots in markFromRoots has been completed
1966 preclean();
1967 assert(_collectorState == AbortablePreclean ||
1968 _collectorState == FinalMarking,
1969 "Collector state should have changed");
1970 break;
1971 case AbortablePreclean:
1972 abortable_preclean();
1973 assert(_collectorState == FinalMarking, "Collector state should "
1974 "have changed");
1975 break;
1976 case FinalMarking:
1977 {
1978 ReleaseForegroundGC x(this);
1979
1980 VM_CMS_Final_Remark final_remark_op(this);
1981 VMThread::execute(&final_remark_op);
1982 }
1983 assert(_foregroundGCShouldWait, "block post-condition");
1984 break;
1985 case Sweeping:
1986 // final marking in checkpointRootsFinal has been completed
1987 sweep();
1988 assert(_collectorState == Resizing, "Collector state change "
1989 "to Resizing must be done under the free_list_lock");
1990
1991 case Resizing: {
1992 // Sweeping has been completed...
1993 // At this point the background collection has completed.
1994 // Don't move the call to compute_new_size() down
1995 // into code that might be executed if the background
1996 // collection was preempted.
1997 {
1998 ReleaseForegroundGC x(this); // unblock FG collection
1999 MutexLockerEx y(Heap_lock, Mutex::_no_safepoint_check_flag);
2000 CMSTokenSync z(true); // not strictly needed.
2001 if (_collectorState == Resizing) {
2002 compute_new_size();
2003 save_heap_summary();
2004 _collectorState = Resetting;
2005 } else {
2006 assert(_collectorState == Idling, "The state should only change"
2007 " because the foreground collector has finished the collection");
2008 }
2009 }
2010 break;
2011 }
2012 case Resetting:
2013 // CMS heap resizing has been completed
2014 reset(true);
2015 assert(_collectorState == Idling, "Collector state should "
2016 "have changed");
2017
2018 MetaspaceGC::set_should_concurrent_collect(false);
2019
2020 stats().record_cms_end();
2021 // Don't move the concurrent_phases_end() and compute_new_size()
2022 // calls to here because a preempted background collection
2023 // has it's state set to "Resetting".
2024 break;
2025 case Idling:
2026 default:
2027 ShouldNotReachHere();
2028 break;
2029 }
2030 if (TraceCMSState) {
2031 gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d",
2032 p2i(Thread::current()), _collectorState);
2033 }
2034 assert(_foregroundGCShouldWait, "block post-condition");
2035 }
2036
2037 // Should this be in gc_epilogue?
2038 collector_policy()->counters()->update_counters();
2039
2040 {
2041 // Clear _foregroundGCShouldWait and, in the event that the
2042 // foreground collector is waiting, notify it, before
2043 // returning.
2044 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2045 _foregroundGCShouldWait = false;
2046 if (_foregroundGCIsActive) {
2047 CGC_lock->notify();
2048 }
2049 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2050 "Possible deadlock");
2051 }
2052 if (TraceCMSState) {
2053 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2054 " exiting collection CMS state %d",
2055 p2i(Thread::current()), _collectorState);
2056 }
2057 if (PrintGC && Verbose) {
2058 _cmsGen->print_heap_change(prev_used);
2059 }
2060 }
2061
2062 void CMSCollector::register_gc_start(GCCause::Cause cause) {
2063 _cms_start_registered = true;
2064 _gc_timer_cm->register_gc_start();
2065 _gc_tracer_cm->report_gc_start(cause, _gc_timer_cm->gc_start());
2066 }
2067
2068 void CMSCollector::register_gc_end() {
2069 if (_cms_start_registered) {
2070 report_heap_summary(GCWhen::AfterGC);
2071
2072 _gc_timer_cm->register_gc_end();
2073 _gc_tracer_cm->report_gc_end(_gc_timer_cm->gc_end(), _gc_timer_cm->time_partitions());
2074 _cms_start_registered = false;
2075 }
2076 }
2077
2078 void CMSCollector::save_heap_summary() {
2079 GenCollectedHeap* gch = GenCollectedHeap::heap();
2080 _last_heap_summary = gch->create_heap_summary();
2081 _last_metaspace_summary = gch->create_metaspace_summary();
2082 }
2083
2084 void CMSCollector::report_heap_summary(GCWhen::Type when) {
2085 _gc_tracer_cm->report_gc_heap_summary(when, _last_heap_summary);
2086 _gc_tracer_cm->report_metaspace_summary(when, _last_metaspace_summary);
2087 }
2088
2089 bool CMSCollector::waitForForegroundGC() {
2090 bool res = false;
2091 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2092 "CMS thread should have CMS token");
2093 // Block the foreground collector until the
2094 // background collectors decides whether to
2095 // yield.
2096 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2097 _foregroundGCShouldWait = true;
2098 if (_foregroundGCIsActive) {
2099 // The background collector yields to the
2100 // foreground collector and returns a value
2101 // indicating that it has yielded. The foreground
2102 // collector can proceed.
2103 res = true;
2104 _foregroundGCShouldWait = false;
2105 ConcurrentMarkSweepThread::clear_CMS_flag(
2106 ConcurrentMarkSweepThread::CMS_cms_has_token);
2107 ConcurrentMarkSweepThread::set_CMS_flag(
2108 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2109 // Get a possibly blocked foreground thread going
2110 CGC_lock->notify();
2111 if (TraceCMSState) {
2112 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d",
2113 p2i(Thread::current()), _collectorState);
2114 }
2115 while (_foregroundGCIsActive) {
2116 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
2117 }
2118 ConcurrentMarkSweepThread::set_CMS_flag(
2119 ConcurrentMarkSweepThread::CMS_cms_has_token);
2120 ConcurrentMarkSweepThread::clear_CMS_flag(
2121 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2122 }
2123 if (TraceCMSState) {
2124 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d",
2125 p2i(Thread::current()), _collectorState);
2126 }
2127 return res;
2128 }
2129
2130 // Because of the need to lock the free lists and other structures in
2131 // the collector, common to all the generations that the collector is
2132 // collecting, we need the gc_prologues of individual CMS generations
2133 // delegate to their collector. It may have been simpler had the
2134 // current infrastructure allowed one to call a prologue on a
2135 // collector. In the absence of that we have the generation's
2136 // prologue delegate to the collector, which delegates back
2137 // some "local" work to a worker method in the individual generations
2138 // that it's responsible for collecting, while itself doing any
2139 // work common to all generations it's responsible for. A similar
2140 // comment applies to the gc_epilogue()'s.
2141 // The role of the variable _between_prologue_and_epilogue is to
2142 // enforce the invocation protocol.
2143 void CMSCollector::gc_prologue(bool full) {
2144 // Call gc_prologue_work() for the CMSGen
2145 // we are responsible for.
2146
2147 // The following locking discipline assumes that we are only called
2148 // when the world is stopped.
2149 assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption");
2150
2151 // The CMSCollector prologue must call the gc_prologues for the
2152 // "generations" that it's responsible
2153 // for.
2154
2155 assert( Thread::current()->is_VM_thread()
2156 || ( CMSScavengeBeforeRemark
2157 && Thread::current()->is_ConcurrentGC_thread()),
2158 "Incorrect thread type for prologue execution");
2159
2160 if (_between_prologue_and_epilogue) {
2161 // We have already been invoked; this is a gc_prologue delegation
2162 // from yet another CMS generation that we are responsible for, just
2163 // ignore it since all relevant work has already been done.
2164 return;
2165 }
2166
2167 // set a bit saying prologue has been called; cleared in epilogue
2168 _between_prologue_and_epilogue = true;
2169 // Claim locks for common data structures, then call gc_prologue_work()
2170 // for each CMSGen.
2171
2172 getFreelistLocks(); // gets free list locks on constituent spaces
2173 bitMapLock()->lock_without_safepoint_check();
2174
2175 // Should call gc_prologue_work() for all cms gens we are responsible for
2176 bool duringMarking = _collectorState >= Marking
2177 && _collectorState < Sweeping;
2178
2179 // The young collections clear the modified oops state, which tells if
2180 // there are any modified oops in the class. The remark phase also needs
2181 // that information. Tell the young collection to save the union of all
2182 // modified klasses.
2183 if (duringMarking) {
2184 _ct->klass_rem_set()->set_accumulate_modified_oops(true);
2185 }
2186
2187 bool registerClosure = duringMarking;
2188
2189 ModUnionClosure* muc = CollectedHeap::use_parallel_gc_threads() ?
2190 &_modUnionClosurePar
2191 : &_modUnionClosure;
2192 _cmsGen->gc_prologue_work(full, registerClosure, muc);
2193
2194 if (!full) {
2195 stats().record_gc0_begin();
2196 }
2197 }
2198
2199 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) {
2200
2201 _capacity_at_prologue = capacity();
2202 _used_at_prologue = used();
2203
2204 // Delegate to CMScollector which knows how to coordinate between
2205 // this and any other CMS generations that it is responsible for
2206 // collecting.
2207 collector()->gc_prologue(full);
2208 }
2209
2210 // This is a "private" interface for use by this generation's CMSCollector.
2211 // Not to be called directly by any other entity (for instance,
2212 // GenCollectedHeap, which calls the "public" gc_prologue method above).
2213 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full,
2214 bool registerClosure, ModUnionClosure* modUnionClosure) {
2215 assert(!incremental_collection_failed(), "Shouldn't be set yet");
2216 assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL,
2217 "Should be NULL");
2218 if (registerClosure) {
2219 cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure);
2220 }
2221 cmsSpace()->gc_prologue();
2222 // Clear stat counters
2223 NOT_PRODUCT(
2224 assert(_numObjectsPromoted == 0, "check");
2225 assert(_numWordsPromoted == 0, "check");
2226 if (Verbose && PrintGC) {
2227 gclog_or_tty->print("Allocated "SIZE_FORMAT" objects, "
2228 SIZE_FORMAT" bytes concurrently",
2229 _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord));
2230 }
2231 _numObjectsAllocated = 0;
2232 _numWordsAllocated = 0;
2233 )
2234 }
2235
2236 void CMSCollector::gc_epilogue(bool full) {
2237 // The following locking discipline assumes that we are only called
2238 // when the world is stopped.
2239 assert(SafepointSynchronize::is_at_safepoint(),
2240 "world is stopped assumption");
2241
2242 // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks
2243 // if linear allocation blocks need to be appropriately marked to allow the
2244 // the blocks to be parsable. We also check here whether we need to nudge the
2245 // CMS collector thread to start a new cycle (if it's not already active).
2246 assert( Thread::current()->is_VM_thread()
2247 || ( CMSScavengeBeforeRemark
2248 && Thread::current()->is_ConcurrentGC_thread()),
2249 "Incorrect thread type for epilogue execution");
2250
2251 if (!_between_prologue_and_epilogue) {
2252 // We have already been invoked; this is a gc_epilogue delegation
2253 // from yet another CMS generation that we are responsible for, just
2254 // ignore it since all relevant work has already been done.
2255 return;
2256 }
2257 assert(haveFreelistLocks(), "must have freelist locks");
2258 assert_lock_strong(bitMapLock());
2259
2260 _ct->klass_rem_set()->set_accumulate_modified_oops(false);
2261
2262 _cmsGen->gc_epilogue_work(full);
2263
2264 if (_collectorState == AbortablePreclean || _collectorState == Precleaning) {
2265 // in case sampling was not already enabled, enable it
2266 _start_sampling = true;
2267 }
2268 // reset _eden_chunk_array so sampling starts afresh
2269 _eden_chunk_index = 0;
2270
2271 size_t cms_used = _cmsGen->cmsSpace()->used();
2272
2273 // update performance counters - this uses a special version of
2274 // update_counters() that allows the utilization to be passed as a
2275 // parameter, avoiding multiple calls to used().
2276 //
2277 _cmsGen->update_counters(cms_used);
2278
2279 bitMapLock()->unlock();
2280 releaseFreelistLocks();
2281
2282 if (!CleanChunkPoolAsync) {
2283 Chunk::clean_chunk_pool();
2284 }
2285
2286 set_did_compact(false);
2287 _between_prologue_and_epilogue = false; // ready for next cycle
2288 }
2289
2290 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) {
2291 collector()->gc_epilogue(full);
2292
2293 // Also reset promotion tracking in par gc thread states.
2294 for (uint i = 0; i < ParallelGCThreads; i++) {
2295 _par_gc_thread_states[i]->promo.stopTrackingPromotions(i);
2296 }
2297 }
2298
2299 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2300 assert(!incremental_collection_failed(), "Should have been cleared");
2301 cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2302 cmsSpace()->gc_epilogue();
2303 // Print stat counters
2304 NOT_PRODUCT(
2305 assert(_numObjectsAllocated == 0, "check");
2306 assert(_numWordsAllocated == 0, "check");
2307 if (Verbose && PrintGC) {
2308 gclog_or_tty->print("Promoted "SIZE_FORMAT" objects, "
2309 SIZE_FORMAT" bytes",
2310 _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2311 }
2312 _numObjectsPromoted = 0;
2313 _numWordsPromoted = 0;
2314 )
2315
2316 if (PrintGC && Verbose) {
2317 // Call down the chain in contiguous_available needs the freelistLock
2318 // so print this out before releasing the freeListLock.
2319 gclog_or_tty->print(" Contiguous available "SIZE_FORMAT" bytes ",
2320 contiguous_available());
2321 }
2322 }
2323
2324 #ifndef PRODUCT
2325 bool CMSCollector::have_cms_token() {
2326 Thread* thr = Thread::current();
2327 if (thr->is_VM_thread()) {
2328 return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2329 } else if (thr->is_ConcurrentGC_thread()) {
2330 return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2331 } else if (thr->is_GC_task_thread()) {
2332 return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2333 ParGCRareEvent_lock->owned_by_self();
2334 }
2335 return false;
2336 }
2337 #endif
2338
2339 // Check reachability of the given heap address in CMS generation,
2340 // treating all other generations as roots.
2341 bool CMSCollector::is_cms_reachable(HeapWord* addr) {
2342 // We could "guarantee" below, rather than assert, but I'll
2343 // leave these as "asserts" so that an adventurous debugger
2344 // could try this in the product build provided some subset of
2345 // the conditions were met, provided they were interested in the
2346 // results and knew that the computation below wouldn't interfere
2347 // with other concurrent computations mutating the structures
2348 // being read or written.
2349 assert(SafepointSynchronize::is_at_safepoint(),
2350 "Else mutations in object graph will make answer suspect");
2351 assert(have_cms_token(), "Should hold cms token");
2352 assert(haveFreelistLocks(), "must hold free list locks");
2353 assert_lock_strong(bitMapLock());
2354
2355 // Clear the marking bit map array before starting, but, just
2356 // for kicks, first report if the given address is already marked
2357 gclog_or_tty->print_cr("Start: Address " PTR_FORMAT " is%s marked", p2i(addr),
2358 _markBitMap.isMarked(addr) ? "" : " not");
2359
2360 if (verify_after_remark()) {
2361 MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2362 bool result = verification_mark_bm()->isMarked(addr);
2363 gclog_or_tty->print_cr("TransitiveMark: Address " PTR_FORMAT " %s marked", p2i(addr),
2364 result ? "IS" : "is NOT");
2365 return result;
2366 } else {
2367 gclog_or_tty->print_cr("Could not compute result");
2368 return false;
2369 }
2370 }
2371
2372
2373 void
2374 CMSCollector::print_on_error(outputStream* st) {
2375 CMSCollector* collector = ConcurrentMarkSweepGeneration::_collector;
2376 if (collector != NULL) {
2377 CMSBitMap* bitmap = &collector->_markBitMap;
2378 st->print_cr("Marking Bits: (CMSBitMap*) " PTR_FORMAT, p2i(bitmap));
2379 bitmap->print_on_error(st, " Bits: ");
2380
2381 st->cr();
2382
2383 CMSBitMap* mut_bitmap = &collector->_modUnionTable;
2384 st->print_cr("Mod Union Table: (CMSBitMap*) " PTR_FORMAT, p2i(mut_bitmap));
2385 mut_bitmap->print_on_error(st, " Bits: ");
2386 }
2387 }
2388
2389 ////////////////////////////////////////////////////////
2390 // CMS Verification Support
2391 ////////////////////////////////////////////////////////
2392 // Following the remark phase, the following invariant
2393 // should hold -- each object in the CMS heap which is
2394 // marked in markBitMap() should be marked in the verification_mark_bm().
2395
2396 class VerifyMarkedClosure: public BitMapClosure {
2397 CMSBitMap* _marks;
2398 bool _failed;
2399
2400 public:
2401 VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2402
2403 bool do_bit(size_t offset) {
2404 HeapWord* addr = _marks->offsetToHeapWord(offset);
2405 if (!_marks->isMarked(addr)) {
2406 oop(addr)->print_on(gclog_or_tty);
2407 gclog_or_tty->print_cr(" ("INTPTR_FORMAT" should have been marked)", p2i(addr));
2408 _failed = true;
2409 }
2410 return true;
2411 }
2412
2413 bool failed() { return _failed; }
2414 };
2415
2416 bool CMSCollector::verify_after_remark(bool silent) {
2417 if (!silent) gclog_or_tty->print(" [Verifying CMS Marking... ");
2418 MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2419 static bool init = false;
2420
2421 assert(SafepointSynchronize::is_at_safepoint(),
2422 "Else mutations in object graph will make answer suspect");
2423 assert(have_cms_token(),
2424 "Else there may be mutual interference in use of "
2425 " verification data structures");
2426 assert(_collectorState > Marking && _collectorState <= Sweeping,
2427 "Else marking info checked here may be obsolete");
2428 assert(haveFreelistLocks(), "must hold free list locks");
2429 assert_lock_strong(bitMapLock());
2430
2431
2432 // Allocate marking bit map if not already allocated
2433 if (!init) { // first time
2434 if (!verification_mark_bm()->allocate(_span)) {
2435 return false;
2436 }
2437 init = true;
2438 }
2439
2440 assert(verification_mark_stack()->isEmpty(), "Should be empty");
2441
2442 // Turn off refs discovery -- so we will be tracing through refs.
2443 // This is as intended, because by this time
2444 // GC must already have cleared any refs that need to be cleared,
2445 // and traced those that need to be marked; moreover,
2446 // the marking done here is not going to interfere in any
2447 // way with the marking information used by GC.
2448 NoRefDiscovery no_discovery(ref_processor());
2449
2450 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
2451
2452 // Clear any marks from a previous round
2453 verification_mark_bm()->clear_all();
2454 assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
2455 verify_work_stacks_empty();
2456
2457 GenCollectedHeap* gch = GenCollectedHeap::heap();
2458 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
2459 // Update the saved marks which may affect the root scans.
2460 gch->save_marks();
2461
2462 if (CMSRemarkVerifyVariant == 1) {
2463 // In this first variant of verification, we complete
2464 // all marking, then check if the new marks-vector is
2465 // a subset of the CMS marks-vector.
2466 verify_after_remark_work_1();
2467 } else if (CMSRemarkVerifyVariant == 2) {
2468 // In this second variant of verification, we flag an error
2469 // (i.e. an object reachable in the new marks-vector not reachable
2470 // in the CMS marks-vector) immediately, also indicating the
2471 // identify of an object (A) that references the unmarked object (B) --
2472 // presumably, a mutation to A failed to be picked up by preclean/remark?
2473 verify_after_remark_work_2();
2474 } else {
2475 warning("Unrecognized value " UINTX_FORMAT " for CMSRemarkVerifyVariant",
2476 CMSRemarkVerifyVariant);
2477 }
2478 if (!silent) gclog_or_tty->print(" done] ");
2479 return true;
2480 }
2481
2482 void CMSCollector::verify_after_remark_work_1() {
2483 ResourceMark rm;
2484 HandleMark hm;
2485 GenCollectedHeap* gch = GenCollectedHeap::heap();
2486
2487 // Get a clear set of claim bits for the roots processing to work with.
2488 ClassLoaderDataGraph::clear_claimed_marks();
2489
2490 // Mark from roots one level into CMS
2491 MarkRefsIntoClosure notOlder(_span, verification_mark_bm());
2492 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2493
2494 gch->gen_process_roots(_cmsGen->level(),
2495 true, // younger gens are roots
2496 true, // activate StrongRootsScope
2497 GenCollectedHeap::ScanningOption(roots_scanning_options()),
2498 should_unload_classes(),
2499 ¬Older,
2500 NULL,
2501 NULL); // SSS: Provide correct closure
2502
2503 // Now mark from the roots
2504 MarkFromRootsClosure markFromRootsClosure(this, _span,
2505 verification_mark_bm(), verification_mark_stack(),
2506 false /* don't yield */, true /* verifying */);
2507 assert(_restart_addr == NULL, "Expected pre-condition");
2508 verification_mark_bm()->iterate(&markFromRootsClosure);
2509 while (_restart_addr != NULL) {
2510 // Deal with stack overflow: by restarting at the indicated
2511 // address.
2512 HeapWord* ra = _restart_addr;
2513 markFromRootsClosure.reset(ra);
2514 _restart_addr = NULL;
2515 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2516 }
2517 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2518 verify_work_stacks_empty();
2519
2520 // Marking completed -- now verify that each bit marked in
2521 // verification_mark_bm() is also marked in markBitMap(); flag all
2522 // errors by printing corresponding objects.
2523 VerifyMarkedClosure vcl(markBitMap());
2524 verification_mark_bm()->iterate(&vcl);
2525 if (vcl.failed()) {
2526 gclog_or_tty->print("Verification failed");
2527 Universe::heap()->print_on(gclog_or_tty);
2528 fatal("CMS: failed marking verification after remark");
2529 }
2530 }
2531
2532 class VerifyKlassOopsKlassClosure : public KlassClosure {
2533 class VerifyKlassOopsClosure : public OopClosure {
2534 CMSBitMap* _bitmap;
2535 public:
2536 VerifyKlassOopsClosure(CMSBitMap* bitmap) : _bitmap(bitmap) { }
2537 void do_oop(oop* p) { guarantee(*p == NULL || _bitmap->isMarked((HeapWord*) *p), "Should be marked"); }
2538 void do_oop(narrowOop* p) { ShouldNotReachHere(); }
2539 } _oop_closure;
2540 public:
2541 VerifyKlassOopsKlassClosure(CMSBitMap* bitmap) : _oop_closure(bitmap) {}
2542 void do_klass(Klass* k) {
2543 k->oops_do(&_oop_closure);
2544 }
2545 };
2546
2547 void CMSCollector::verify_after_remark_work_2() {
2548 ResourceMark rm;
2549 HandleMark hm;
2550 GenCollectedHeap* gch = GenCollectedHeap::heap();
2551
2552 // Get a clear set of claim bits for the roots processing to work with.
2553 ClassLoaderDataGraph::clear_claimed_marks();
2554
2555 // Mark from roots one level into CMS
2556 MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
2557 markBitMap());
2558 CLDToOopClosure cld_closure(¬Older, true);
2559
2560 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2561
2562 gch->gen_process_roots(_cmsGen->level(),
2563 true, // younger gens are roots
2564 true, // activate StrongRootsScope
2565 GenCollectedHeap::ScanningOption(roots_scanning_options()),
2566 should_unload_classes(),
2567 ¬Older,
2568 NULL,
2569 &cld_closure);
2570
2571 // Now mark from the roots
2572 MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
2573 verification_mark_bm(), markBitMap(), verification_mark_stack());
2574 assert(_restart_addr == NULL, "Expected pre-condition");
2575 verification_mark_bm()->iterate(&markFromRootsClosure);
2576 while (_restart_addr != NULL) {
2577 // Deal with stack overflow: by restarting at the indicated
2578 // address.
2579 HeapWord* ra = _restart_addr;
2580 markFromRootsClosure.reset(ra);
2581 _restart_addr = NULL;
2582 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2583 }
2584 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2585 verify_work_stacks_empty();
2586
2587 VerifyKlassOopsKlassClosure verify_klass_oops(verification_mark_bm());
2588 ClassLoaderDataGraph::classes_do(&verify_klass_oops);
2589
2590 // Marking completed -- now verify that each bit marked in
2591 // verification_mark_bm() is also marked in markBitMap(); flag all
2592 // errors by printing corresponding objects.
2593 VerifyMarkedClosure vcl(markBitMap());
2594 verification_mark_bm()->iterate(&vcl);
2595 assert(!vcl.failed(), "Else verification above should not have succeeded");
2596 }
2597
2598 void ConcurrentMarkSweepGeneration::save_marks() {
2599 // delegate to CMS space
2600 cmsSpace()->save_marks();
2601 for (uint i = 0; i < ParallelGCThreads; i++) {
2602 _par_gc_thread_states[i]->promo.startTrackingPromotions();
2603 }
2604 }
2605
2606 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
2607 return cmsSpace()->no_allocs_since_save_marks();
2608 }
2609
2610 #define CMS_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix) \
2611 \
2612 void ConcurrentMarkSweepGeneration:: \
2613 oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) { \
2614 cl->set_generation(this); \
2615 cmsSpace()->oop_since_save_marks_iterate##nv_suffix(cl); \
2616 cl->reset_generation(); \
2617 save_marks(); \
2618 }
2619
2620 ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DEFN)
2621
2622 void
2623 ConcurrentMarkSweepGeneration::oop_iterate(ExtendedOopClosure* cl) {
2624 if (freelistLock()->owned_by_self()) {
2625 Generation::oop_iterate(cl);
2626 } else {
2627 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2628 Generation::oop_iterate(cl);
2629 }
2630 }
2631
2632 void
2633 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
2634 if (freelistLock()->owned_by_self()) {
2635 Generation::object_iterate(cl);
2636 } else {
2637 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2638 Generation::object_iterate(cl);
2639 }
2640 }
2641
2642 void
2643 ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) {
2644 if (freelistLock()->owned_by_self()) {
2645 Generation::safe_object_iterate(cl);
2646 } else {
2647 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2648 Generation::safe_object_iterate(cl);
2649 }
2650 }
2651
2652 void
2653 ConcurrentMarkSweepGeneration::post_compact() {
2654 }
2655
2656 void
2657 ConcurrentMarkSweepGeneration::prepare_for_verify() {
2658 // Fix the linear allocation blocks to look like free blocks.
2659
2660 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2661 // are not called when the heap is verified during universe initialization and
2662 // at vm shutdown.
2663 if (freelistLock()->owned_by_self()) {
2664 cmsSpace()->prepare_for_verify();
2665 } else {
2666 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2667 cmsSpace()->prepare_for_verify();
2668 }
2669 }
2670
2671 void
2672 ConcurrentMarkSweepGeneration::verify() {
2673 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2674 // are not called when the heap is verified during universe initialization and
2675 // at vm shutdown.
2676 if (freelistLock()->owned_by_self()) {
2677 cmsSpace()->verify();
2678 } else {
2679 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2680 cmsSpace()->verify();
2681 }
2682 }
2683
2684 void CMSCollector::verify() {
2685 _cmsGen->verify();
2686 }
2687
2688 #ifndef PRODUCT
2689 bool CMSCollector::overflow_list_is_empty() const {
2690 assert(_num_par_pushes >= 0, "Inconsistency");
2691 if (_overflow_list == NULL) {
2692 assert(_num_par_pushes == 0, "Inconsistency");
2693 }
2694 return _overflow_list == NULL;
2695 }
2696
2697 // The methods verify_work_stacks_empty() and verify_overflow_empty()
2698 // merely consolidate assertion checks that appear to occur together frequently.
2699 void CMSCollector::verify_work_stacks_empty() const {
2700 assert(_markStack.isEmpty(), "Marking stack should be empty");
2701 assert(overflow_list_is_empty(), "Overflow list should be empty");
2702 }
2703
2704 void CMSCollector::verify_overflow_empty() const {
2705 assert(overflow_list_is_empty(), "Overflow list should be empty");
2706 assert(no_preserved_marks(), "No preserved marks");
2707 }
2708 #endif // PRODUCT
2709
2710 // Decide if we want to enable class unloading as part of the
2711 // ensuing concurrent GC cycle. We will collect and
2712 // unload classes if it's the case that:
2713 // (1) an explicit gc request has been made and the flag
2714 // ExplicitGCInvokesConcurrentAndUnloadsClasses is set, OR
2715 // (2) (a) class unloading is enabled at the command line, and
2716 // (b) old gen is getting really full
2717 // NOTE: Provided there is no change in the state of the heap between
2718 // calls to this method, it should have idempotent results. Moreover,
2719 // its results should be monotonically increasing (i.e. going from 0 to 1,
2720 // but not 1 to 0) between successive calls between which the heap was
2721 // not collected. For the implementation below, it must thus rely on
2722 // the property that concurrent_cycles_since_last_unload()
2723 // will not decrease unless a collection cycle happened and that
2724 // _cmsGen->is_too_full() are
2725 // themselves also monotonic in that sense. See check_monotonicity()
2726 // below.
2727 void CMSCollector::update_should_unload_classes() {
2728 _should_unload_classes = false;
2729 // Condition 1 above
2730 if (_full_gc_requested && ExplicitGCInvokesConcurrentAndUnloadsClasses) {
2731 _should_unload_classes = true;
2732 } else if (CMSClassUnloadingEnabled) { // Condition 2.a above
2733 // Disjuncts 2.b.(i,ii,iii) above
2734 _should_unload_classes = (concurrent_cycles_since_last_unload() >=
2735 CMSClassUnloadingMaxInterval)
2736 || _cmsGen->is_too_full();
2737 }
2738 }
2739
2740 bool ConcurrentMarkSweepGeneration::is_too_full() const {
2741 bool res = should_concurrent_collect();
2742 res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
2743 return res;
2744 }
2745
2746 void CMSCollector::setup_cms_unloading_and_verification_state() {
2747 const bool should_verify = VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
2748 || VerifyBeforeExit;
2749 const int rso = GenCollectedHeap::SO_AllCodeCache;
2750
2751 // We set the proper root for this CMS cycle here.
2752 if (should_unload_classes()) { // Should unload classes this cycle
2753 remove_root_scanning_option(rso); // Shrink the root set appropriately
2754 set_verifying(should_verify); // Set verification state for this cycle
2755 return; // Nothing else needs to be done at this time
2756 }
2757
2758 // Not unloading classes this cycle
2759 assert(!should_unload_classes(), "Inconsistency!");
2760
2761 if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
2762 // Include symbols, strings and code cache elements to prevent their resurrection.
2763 add_root_scanning_option(rso);
2764 set_verifying(true);
2765 } else if (verifying() && !should_verify) {
2766 // We were verifying, but some verification flags got disabled.
2767 set_verifying(false);
2768 // Exclude symbols, strings and code cache elements from root scanning to
2769 // reduce IM and RM pauses.
2770 remove_root_scanning_option(rso);
2771 }
2772 }
2773
2774
2775 #ifndef PRODUCT
2776 HeapWord* CMSCollector::block_start(const void* p) const {
2777 const HeapWord* addr = (HeapWord*)p;
2778 if (_span.contains(p)) {
2779 if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
2780 return _cmsGen->cmsSpace()->block_start(p);
2781 }
2782 }
2783 return NULL;
2784 }
2785 #endif
2786
2787 HeapWord*
2788 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
2789 bool tlab,
2790 bool parallel) {
2791 CMSSynchronousYieldRequest yr;
2792 assert(!tlab, "Can't deal with TLAB allocation");
2793 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2794 expand_for_gc_cause(word_size*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_allocation);
2795 if (GCExpandToAllocateDelayMillis > 0) {
2796 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2797 }
2798 return have_lock_and_allocate(word_size, tlab);
2799 }
2800
2801 void ConcurrentMarkSweepGeneration::expand_for_gc_cause(
2802 size_t bytes,
2803 size_t expand_bytes,
2804 CMSExpansionCause::Cause cause)
2805 {
2806
2807 bool success = expand(bytes, expand_bytes);
2808
2809 // remember why we expanded; this information is used
2810 // by shouldConcurrentCollect() when making decisions on whether to start
2811 // a new CMS cycle.
2812 if (success) {
2813 set_expansion_cause(cause);
2814 if (PrintGCDetails && Verbose) {
2815 gclog_or_tty->print_cr("Expanded CMS gen for %s",
2816 CMSExpansionCause::to_string(cause));
2817 }
2818 }
2819 }
2820
2821 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
2822 HeapWord* res = NULL;
2823 MutexLocker x(ParGCRareEvent_lock);
2824 while (true) {
2825 // Expansion by some other thread might make alloc OK now:
2826 res = ps->lab.alloc(word_sz);
2827 if (res != NULL) return res;
2828 // If there's not enough expansion space available, give up.
2829 if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
2830 return NULL;
2831 }
2832 // Otherwise, we try expansion.
2833 expand_for_gc_cause(word_sz*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_lab);
2834 // Now go around the loop and try alloc again;
2835 // A competing par_promote might beat us to the expansion space,
2836 // so we may go around the loop again if promotion fails again.
2837 if (GCExpandToAllocateDelayMillis > 0) {
2838 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2839 }
2840 }
2841 }
2842
2843
2844 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
2845 PromotionInfo* promo) {
2846 MutexLocker x(ParGCRareEvent_lock);
2847 size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
2848 while (true) {
2849 // Expansion by some other thread might make alloc OK now:
2850 if (promo->ensure_spooling_space()) {
2851 assert(promo->has_spooling_space(),
2852 "Post-condition of successful ensure_spooling_space()");
2853 return true;
2854 }
2855 // If there's not enough expansion space available, give up.
2856 if (_virtual_space.uncommitted_size() < refill_size_bytes) {
2857 return false;
2858 }
2859 // Otherwise, we try expansion.
2860 expand_for_gc_cause(refill_size_bytes, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_spooling_space);
2861 // Now go around the loop and try alloc again;
2862 // A competing allocation might beat us to the expansion space,
2863 // so we may go around the loop again if allocation fails again.
2864 if (GCExpandToAllocateDelayMillis > 0) {
2865 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2866 }
2867 }
2868 }
2869
2870 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
2871 // Only shrink if a compaction was done so that all the free space
2872 // in the generation is in a contiguous block at the end.
2873 if (did_compact()) {
2874 CardGeneration::shrink(bytes);
2875 }
2876 }
2877
2878 void ConcurrentMarkSweepGeneration::assert_correct_size_change_locking() {
2879 assert_locked_or_safepoint(Heap_lock);
2880 }
2881
2882 void ConcurrentMarkSweepGeneration::shrink_free_list_by(size_t bytes) {
2883 assert_locked_or_safepoint(Heap_lock);
2884 assert_lock_strong(freelistLock());
2885 if (PrintGCDetails && Verbose) {
2886 warning("Shrinking of CMS not yet implemented");
2887 }
2888 return;
2889 }
2890
2891
2892 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
2893 // phases.
2894 class CMSPhaseAccounting: public StackObj {
2895 public:
2896 CMSPhaseAccounting(CMSCollector *collector,
2897 const char *phase,
2898 const GCId gc_id,
2899 bool print_cr = true);
2900 ~CMSPhaseAccounting();
2901
2902 private:
2903 CMSCollector *_collector;
2904 const char *_phase;
2905 elapsedTimer _wallclock;
2906 bool _print_cr;
2907 const GCId _gc_id;
2908
2909 public:
2910 // Not MT-safe; so do not pass around these StackObj's
2911 // where they may be accessed by other threads.
2912 jlong wallclock_millis() {
2913 assert(_wallclock.is_active(), "Wall clock should not stop");
2914 _wallclock.stop(); // to record time
2915 jlong ret = _wallclock.milliseconds();
2916 _wallclock.start(); // restart
2917 return ret;
2918 }
2919 };
2920
2921 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
2922 const char *phase,
2923 const GCId gc_id,
2924 bool print_cr) :
2925 _collector(collector), _phase(phase), _print_cr(print_cr), _gc_id(gc_id) {
2926
2927 if (PrintCMSStatistics != 0) {
2928 _collector->resetYields();
2929 }
2930 if (PrintGCDetails) {
2931 gclog_or_tty->gclog_stamp(_gc_id);
2932 gclog_or_tty->print_cr("[%s-concurrent-%s-start]",
2933 _collector->cmsGen()->short_name(), _phase);
2934 }
2935 _collector->resetTimer();
2936 _wallclock.start();
2937 _collector->startTimer();
2938 }
2939
2940 CMSPhaseAccounting::~CMSPhaseAccounting() {
2941 assert(_wallclock.is_active(), "Wall clock should not have stopped");
2942 _collector->stopTimer();
2943 _wallclock.stop();
2944 if (PrintGCDetails) {
2945 gclog_or_tty->gclog_stamp(_gc_id);
2946 gclog_or_tty->print("[%s-concurrent-%s: %3.3f/%3.3f secs]",
2947 _collector->cmsGen()->short_name(),
2948 _phase, _collector->timerValue(), _wallclock.seconds());
2949 if (_print_cr) {
2950 gclog_or_tty->cr();
2951 }
2952 if (PrintCMSStatistics != 0) {
2953 gclog_or_tty->print_cr(" (CMS-concurrent-%s yielded %d times)", _phase,
2954 _collector->yields());
2955 }
2956 }
2957 }
2958
2959 // CMS work
2960
2961 // The common parts of CMSParInitialMarkTask and CMSParRemarkTask.
2962 class CMSParMarkTask : public AbstractGangTask {
2963 protected:
2964 CMSCollector* _collector;
2965 int _n_workers;
2966 CMSParMarkTask(const char* name, CMSCollector* collector, int n_workers) :
2967 AbstractGangTask(name),
2968 _collector(collector),
2969 _n_workers(n_workers) {}
2970 // Work method in support of parallel rescan ... of young gen spaces
2971 void do_young_space_rescan(uint worker_id, OopsInGenClosure* cl,
2972 ContiguousSpace* space,
2973 HeapWord** chunk_array, size_t chunk_top);
2974 void work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl);
2975 };
2976
2977 // Parallel initial mark task
2978 class CMSParInitialMarkTask: public CMSParMarkTask {
2979 public:
2980 CMSParInitialMarkTask(CMSCollector* collector, int n_workers) :
2981 CMSParMarkTask("Scan roots and young gen for initial mark in parallel",
2982 collector, n_workers) {}
2983 void work(uint worker_id);
2984 };
2985
2986 // Checkpoint the roots into this generation from outside
2987 // this generation. [Note this initial checkpoint need only
2988 // be approximate -- we'll do a catch up phase subsequently.]
2989 void CMSCollector::checkpointRootsInitial() {
2990 assert(_collectorState == InitialMarking, "Wrong collector state");
2991 check_correct_thread_executing();
2992 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
2993
2994 save_heap_summary();
2995 report_heap_summary(GCWhen::BeforeGC);
2996
2997 ReferenceProcessor* rp = ref_processor();
2998 assert(_restart_addr == NULL, "Control point invariant");
2999 {
3000 // acquire locks for subsequent manipulations
3001 MutexLockerEx x(bitMapLock(),
3002 Mutex::_no_safepoint_check_flag);
3003 checkpointRootsInitialWork();
3004 // enable ("weak") refs discovery
3005 rp->enable_discovery();
3006 _collectorState = Marking;
3007 }
3008 }
3009
3010 void CMSCollector::checkpointRootsInitialWork() {
3011 assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
3012 assert(_collectorState == InitialMarking, "just checking");
3013
3014 // If there has not been a GC[n-1] since last GC[n] cycle completed,
3015 // precede our marking with a collection of all
3016 // younger generations to keep floating garbage to a minimum.
3017 // XXX: we won't do this for now -- it's an optimization to be done later.
3018
3019 // already have locks
3020 assert_lock_strong(bitMapLock());
3021 assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
3022
3023 // Setup the verification and class unloading state for this
3024 // CMS collection cycle.
3025 setup_cms_unloading_and_verification_state();
3026
3027 NOT_PRODUCT(GCTraceTime t("\ncheckpointRootsInitialWork",
3028 PrintGCDetails && Verbose, true, _gc_timer_cm, _gc_tracer_cm->gc_id());)
3029
3030 // Reset all the PLAB chunk arrays if necessary.
3031 if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
3032 reset_survivor_plab_arrays();
3033 }
3034
3035 ResourceMark rm;
3036 HandleMark hm;
3037
3038 MarkRefsIntoClosure notOlder(_span, &_markBitMap);
3039 GenCollectedHeap* gch = GenCollectedHeap::heap();
3040
3041 verify_work_stacks_empty();
3042 verify_overflow_empty();
3043
3044 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
3045 // Update the saved marks which may affect the root scans.
3046 gch->save_marks();
3047
3048 // weak reference processing has not started yet.
3049 ref_processor()->set_enqueuing_is_done(false);
3050
3051 // Need to remember all newly created CLDs,
3052 // so that we can guarantee that the remark finds them.
3053 ClassLoaderDataGraph::remember_new_clds(true);
3054
3055 // Whenever a CLD is found, it will be claimed before proceeding to mark
3056 // the klasses. The claimed marks need to be cleared before marking starts.
3057 ClassLoaderDataGraph::clear_claimed_marks();
3058
3059 if (CMSPrintEdenSurvivorChunks) {
3060 print_eden_and_survivor_chunk_arrays();
3061 }
3062
3063 {
3064 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
3065 if (CMSParallelInitialMarkEnabled && CollectedHeap::use_parallel_gc_threads()) {
3066 // The parallel version.
3067 FlexibleWorkGang* workers = gch->workers();
3068 assert(workers != NULL, "Need parallel worker threads.");
3069 int n_workers = workers->active_workers();
3070 CMSParInitialMarkTask tsk(this, n_workers);
3071 gch->set_par_threads(n_workers);
3072 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
3073 if (n_workers > 1) {
3074 GenCollectedHeap::StrongRootsScope srs;
3075 workers->run_task(&tsk);
3076 } else {
3077 GenCollectedHeap::StrongRootsScope srs;
3078 tsk.work(0);
3079 }
3080 gch->set_par_threads(0);
3081 } else {
3082 // The serial version.
3083 CLDToOopClosure cld_closure(¬Older, true);
3084 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3085 gch->gen_process_roots(_cmsGen->level(),
3086 true, // younger gens are roots
3087 true, // activate StrongRootsScope
3088 GenCollectedHeap::ScanningOption(roots_scanning_options()),
3089 should_unload_classes(),
3090 ¬Older,
3091 NULL,
3092 &cld_closure);
3093 }
3094 }
3095
3096 // Clear mod-union table; it will be dirtied in the prologue of
3097 // CMS generation per each younger generation collection.
3098
3099 assert(_modUnionTable.isAllClear(),
3100 "Was cleared in most recent final checkpoint phase"
3101 " or no bits are set in the gc_prologue before the start of the next "
3102 "subsequent marking phase.");
3103
3104 assert(_ct->klass_rem_set()->mod_union_is_clear(), "Must be");
3105
3106 // Save the end of the used_region of the constituent generations
3107 // to be used to limit the extent of sweep in each generation.
3108 save_sweep_limits();
3109 verify_overflow_empty();
3110 }
3111
3112 bool CMSCollector::markFromRoots() {
3113 // we might be tempted to assert that:
3114 // assert(!SafepointSynchronize::is_at_safepoint(),
3115 // "inconsistent argument?");
3116 // However that wouldn't be right, because it's possible that
3117 // a safepoint is indeed in progress as a younger generation
3118 // stop-the-world GC happens even as we mark in this generation.
3119 assert(_collectorState == Marking, "inconsistent state?");
3120 check_correct_thread_executing();
3121 verify_overflow_empty();
3122
3123 // Weak ref discovery note: We may be discovering weak
3124 // refs in this generation concurrent (but interleaved) with
3125 // weak ref discovery by a younger generation collector.
3126
3127 CMSTokenSyncWithLocks ts(true, bitMapLock());
3128 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3129 CMSPhaseAccounting pa(this, "mark", _gc_tracer_cm->gc_id(), !PrintGCDetails);
3130 bool res = markFromRootsWork();
3131 if (res) {
3132 _collectorState = Precleaning;
3133 } else { // We failed and a foreground collection wants to take over
3134 assert(_foregroundGCIsActive, "internal state inconsistency");
3135 assert(_restart_addr == NULL, "foreground will restart from scratch");
3136 if (PrintGCDetails) {
3137 gclog_or_tty->print_cr("bailing out to foreground collection");
3138 }
3139 }
3140 verify_overflow_empty();
3141 return res;
3142 }
3143
3144 bool CMSCollector::markFromRootsWork() {
3145 // iterate over marked bits in bit map, doing a full scan and mark
3146 // from these roots using the following algorithm:
3147 // . if oop is to the right of the current scan pointer,
3148 // mark corresponding bit (we'll process it later)
3149 // . else (oop is to left of current scan pointer)
3150 // push oop on marking stack
3151 // . drain the marking stack
3152
3153 // Note that when we do a marking step we need to hold the
3154 // bit map lock -- recall that direct allocation (by mutators)
3155 // and promotion (by younger generation collectors) is also
3156 // marking the bit map. [the so-called allocate live policy.]
3157 // Because the implementation of bit map marking is not
3158 // robust wrt simultaneous marking of bits in the same word,
3159 // we need to make sure that there is no such interference
3160 // between concurrent such updates.
3161
3162 // already have locks
3163 assert_lock_strong(bitMapLock());
3164
3165 verify_work_stacks_empty();
3166 verify_overflow_empty();
3167 bool result = false;
3168 if (CMSConcurrentMTEnabled && ConcGCThreads > 0) {
3169 result = do_marking_mt();
3170 } else {
3171 result = do_marking_st();
3172 }
3173 return result;
3174 }
3175
3176 // Forward decl
3177 class CMSConcMarkingTask;
3178
3179 class CMSConcMarkingTerminator: public ParallelTaskTerminator {
3180 CMSCollector* _collector;
3181 CMSConcMarkingTask* _task;
3182 public:
3183 virtual void yield();
3184
3185 // "n_threads" is the number of threads to be terminated.
3186 // "queue_set" is a set of work queues of other threads.
3187 // "collector" is the CMS collector associated with this task terminator.
3188 // "yield" indicates whether we need the gang as a whole to yield.
3189 CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
3190 ParallelTaskTerminator(n_threads, queue_set),
3191 _collector(collector) { }
3192
3193 void set_task(CMSConcMarkingTask* task) {
3194 _task = task;
3195 }
3196 };
3197
3198 class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator {
3199 CMSConcMarkingTask* _task;
3200 public:
3201 bool should_exit_termination();
3202 void set_task(CMSConcMarkingTask* task) {
3203 _task = task;
3204 }
3205 };
3206
3207 // MT Concurrent Marking Task
3208 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3209 CMSCollector* _collector;
3210 int _n_workers; // requested/desired # workers
3211 bool _result;
3212 CompactibleFreeListSpace* _cms_space;
3213 char _pad_front[64]; // padding to ...
3214 HeapWord* _global_finger; // ... avoid sharing cache line
3215 char _pad_back[64];
3216 HeapWord* _restart_addr;
3217
3218 // Exposed here for yielding support
3219 Mutex* const _bit_map_lock;
3220
3221 // The per thread work queues, available here for stealing
3222 OopTaskQueueSet* _task_queues;
3223
3224 // Termination (and yielding) support
3225 CMSConcMarkingTerminator _term;
3226 CMSConcMarkingTerminatorTerminator _term_term;
3227
3228 public:
3229 CMSConcMarkingTask(CMSCollector* collector,
3230 CompactibleFreeListSpace* cms_space,
3231 YieldingFlexibleWorkGang* workers,
3232 OopTaskQueueSet* task_queues):
3233 YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3234 _collector(collector),
3235 _cms_space(cms_space),
3236 _n_workers(0), _result(true),
3237 _task_queues(task_queues),
3238 _term(_n_workers, task_queues, _collector),
3239 _bit_map_lock(collector->bitMapLock())
3240 {
3241 _requested_size = _n_workers;
3242 _term.set_task(this);
3243 _term_term.set_task(this);
3244 _restart_addr = _global_finger = _cms_space->bottom();
3245 }
3246
3247
3248 OopTaskQueueSet* task_queues() { return _task_queues; }
3249
3250 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3251
3252 HeapWord** global_finger_addr() { return &_global_finger; }
3253
3254 CMSConcMarkingTerminator* terminator() { return &_term; }
3255
3256 virtual void set_for_termination(int active_workers) {
3257 terminator()->reset_for_reuse(active_workers);
3258 }
3259
3260 void work(uint worker_id);
3261 bool should_yield() {
3262 return ConcurrentMarkSweepThread::should_yield()
3263 && !_collector->foregroundGCIsActive();
3264 }
3265
3266 virtual void coordinator_yield(); // stuff done by coordinator
3267 bool result() { return _result; }
3268
3269 void reset(HeapWord* ra) {
3270 assert(_global_finger >= _cms_space->end(), "Postcondition of ::work(i)");
3271 _restart_addr = _global_finger = ra;
3272 _term.reset_for_reuse();
3273 }
3274
3275 static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3276 OopTaskQueue* work_q);
3277
3278 private:
3279 void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3280 void do_work_steal(int i);
3281 void bump_global_finger(HeapWord* f);
3282 };
3283
3284 bool CMSConcMarkingTerminatorTerminator::should_exit_termination() {
3285 assert(_task != NULL, "Error");
3286 return _task->yielding();
3287 // Note that we do not need the disjunct || _task->should_yield() above
3288 // because we want terminating threads to yield only if the task
3289 // is already in the midst of yielding, which happens only after at least one
3290 // thread has yielded.
3291 }
3292
3293 void CMSConcMarkingTerminator::yield() {
3294 if (_task->should_yield()) {
3295 _task->yield();
3296 } else {
3297 ParallelTaskTerminator::yield();
3298 }
3299 }
3300
3301 ////////////////////////////////////////////////////////////////
3302 // Concurrent Marking Algorithm Sketch
3303 ////////////////////////////////////////////////////////////////
3304 // Until all tasks exhausted (both spaces):
3305 // -- claim next available chunk
3306 // -- bump global finger via CAS
3307 // -- find first object that starts in this chunk
3308 // and start scanning bitmap from that position
3309 // -- scan marked objects for oops
3310 // -- CAS-mark target, and if successful:
3311 // . if target oop is above global finger (volatile read)
3312 // nothing to do
3313 // . if target oop is in chunk and above local finger
3314 // then nothing to do
3315 // . else push on work-queue
3316 // -- Deal with possible overflow issues:
3317 // . local work-queue overflow causes stuff to be pushed on
3318 // global (common) overflow queue
3319 // . always first empty local work queue
3320 // . then get a batch of oops from global work queue if any
3321 // . then do work stealing
3322 // -- When all tasks claimed (both spaces)
3323 // and local work queue empty,
3324 // then in a loop do:
3325 // . check global overflow stack; steal a batch of oops and trace
3326 // . try to steal from other threads oif GOS is empty
3327 // . if neither is available, offer termination
3328 // -- Terminate and return result
3329 //
3330 void CMSConcMarkingTask::work(uint worker_id) {
3331 elapsedTimer _timer;
3332 ResourceMark rm;
3333 HandleMark hm;
3334
3335 DEBUG_ONLY(_collector->verify_overflow_empty();)
3336
3337 // Before we begin work, our work queue should be empty
3338 assert(work_queue(worker_id)->size() == 0, "Expected to be empty");
3339 // Scan the bitmap covering _cms_space, tracing through grey objects.
3340 _timer.start();
3341 do_scan_and_mark(worker_id, _cms_space);
3342 _timer.stop();
3343 if (PrintCMSStatistics != 0) {
3344 gclog_or_tty->print_cr("Finished cms space scanning in %dth thread: %3.3f sec",
3345 worker_id, _timer.seconds());
3346 // XXX: need xxx/xxx type of notation, two timers
3347 }
3348
3349 // ... do work stealing
3350 _timer.reset();
3351 _timer.start();
3352 do_work_steal(worker_id);
3353 _timer.stop();
3354 if (PrintCMSStatistics != 0) {
3355 gclog_or_tty->print_cr("Finished work stealing in %dth thread: %3.3f sec",
3356 worker_id, _timer.seconds());
3357 // XXX: need xxx/xxx type of notation, two timers
3358 }
3359 assert(_collector->_markStack.isEmpty(), "Should have been emptied");
3360 assert(work_queue(worker_id)->size() == 0, "Should have been emptied");
3361 // Note that under the current task protocol, the
3362 // following assertion is true even of the spaces
3363 // expanded since the completion of the concurrent
3364 // marking. XXX This will likely change under a strict
3365 // ABORT semantics.
3366 // After perm removal the comparison was changed to
3367 // greater than or equal to from strictly greater than.
3368 // Before perm removal the highest address sweep would
3369 // have been at the end of perm gen but now is at the
3370 // end of the tenured gen.
3371 assert(_global_finger >= _cms_space->end(),
3372 "All tasks have been completed");
3373 DEBUG_ONLY(_collector->verify_overflow_empty();)
3374 }
3375
3376 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
3377 HeapWord* read = _global_finger;
3378 HeapWord* cur = read;
3379 while (f > read) {
3380 cur = read;
3381 read = (HeapWord*) Atomic::cmpxchg_ptr(f, &_global_finger, cur);
3382 if (cur == read) {
3383 // our cas succeeded
3384 assert(_global_finger >= f, "protocol consistency");
3385 break;
3386 }
3387 }
3388 }
3389
3390 // This is really inefficient, and should be redone by
3391 // using (not yet available) block-read and -write interfaces to the
3392 // stack and the work_queue. XXX FIX ME !!!
3393 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3394 OopTaskQueue* work_q) {
3395 // Fast lock-free check
3396 if (ovflw_stk->length() == 0) {
3397 return false;
3398 }
3399 assert(work_q->size() == 0, "Shouldn't steal");
3400 MutexLockerEx ml(ovflw_stk->par_lock(),
3401 Mutex::_no_safepoint_check_flag);
3402 // Grab up to 1/4 the size of the work queue
3403 size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
3404 (size_t)ParGCDesiredObjsFromOverflowList);
3405 num = MIN2(num, ovflw_stk->length());
3406 for (int i = (int) num; i > 0; i--) {
3407 oop cur = ovflw_stk->pop();
3408 assert(cur != NULL, "Counted wrong?");
3409 work_q->push(cur);
3410 }
3411 return num > 0;
3412 }
3413
3414 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
3415 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
3416 int n_tasks = pst->n_tasks();
3417 // We allow that there may be no tasks to do here because
3418 // we are restarting after a stack overflow.
3419 assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
3420 uint nth_task = 0;
3421
3422 HeapWord* aligned_start = sp->bottom();
3423 if (sp->used_region().contains(_restart_addr)) {
3424 // Align down to a card boundary for the start of 0th task
3425 // for this space.
3426 aligned_start =
3427 (HeapWord*)align_size_down((uintptr_t)_restart_addr,
3428 CardTableModRefBS::card_size);
3429 }
3430
3431 size_t chunk_size = sp->marking_task_size();
3432 while (!pst->is_task_claimed(/* reference */ nth_task)) {
3433 // Having claimed the nth task in this space,
3434 // compute the chunk that it corresponds to:
3435 MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
3436 aligned_start + (nth_task+1)*chunk_size);
3437 // Try and bump the global finger via a CAS;
3438 // note that we need to do the global finger bump
3439 // _before_ taking the intersection below, because
3440 // the task corresponding to that region will be
3441 // deemed done even if the used_region() expands
3442 // because of allocation -- as it almost certainly will
3443 // during start-up while the threads yield in the
3444 // closure below.
3445 HeapWord* finger = span.end();
3446 bump_global_finger(finger); // atomically
3447 // There are null tasks here corresponding to chunks
3448 // beyond the "top" address of the space.
3449 span = span.intersection(sp->used_region());
3450 if (!span.is_empty()) { // Non-null task
3451 HeapWord* prev_obj;
3452 assert(!span.contains(_restart_addr) || nth_task == 0,
3453 "Inconsistency");
3454 if (nth_task == 0) {
3455 // For the 0th task, we'll not need to compute a block_start.
3456 if (span.contains(_restart_addr)) {
3457 // In the case of a restart because of stack overflow,
3458 // we might additionally skip a chunk prefix.
3459 prev_obj = _restart_addr;
3460 } else {
3461 prev_obj = span.start();
3462 }
3463 } else {
3464 // We want to skip the first object because
3465 // the protocol is to scan any object in its entirety
3466 // that _starts_ in this span; a fortiori, any
3467 // object starting in an earlier span is scanned
3468 // as part of an earlier claimed task.
3469 // Below we use the "careful" version of block_start
3470 // so we do not try to navigate uninitialized objects.
3471 prev_obj = sp->block_start_careful(span.start());
3472 // Below we use a variant of block_size that uses the
3473 // Printezis bits to avoid waiting for allocated
3474 // objects to become initialized/parsable.
3475 while (prev_obj < span.start()) {
3476 size_t sz = sp->block_size_no_stall(prev_obj, _collector);
3477 if (sz > 0) {
3478 prev_obj += sz;
3479 } else {
3480 // In this case we may end up doing a bit of redundant
3481 // scanning, but that appears unavoidable, short of
3482 // locking the free list locks; see bug 6324141.
3483 break;
3484 }
3485 }
3486 }
3487 if (prev_obj < span.end()) {
3488 MemRegion my_span = MemRegion(prev_obj, span.end());
3489 // Do the marking work within a non-empty span --
3490 // the last argument to the constructor indicates whether the
3491 // iteration should be incremental with periodic yields.
3492 Par_MarkFromRootsClosure cl(this, _collector, my_span,
3493 &_collector->_markBitMap,
3494 work_queue(i),
3495 &_collector->_markStack);
3496 _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
3497 } // else nothing to do for this task
3498 } // else nothing to do for this task
3499 }
3500 // We'd be tempted to assert here that since there are no
3501 // more tasks left to claim in this space, the global_finger
3502 // must exceed space->top() and a fortiori space->end(). However,
3503 // that would not quite be correct because the bumping of
3504 // global_finger occurs strictly after the claiming of a task,
3505 // so by the time we reach here the global finger may not yet
3506 // have been bumped up by the thread that claimed the last
3507 // task.
3508 pst->all_tasks_completed();
3509 }
3510
3511 class Par_ConcMarkingClosure: public MetadataAwareOopClosure {
3512 private:
3513 CMSCollector* _collector;
3514 CMSConcMarkingTask* _task;
3515 MemRegion _span;
3516 CMSBitMap* _bit_map;
3517 CMSMarkStack* _overflow_stack;
3518 OopTaskQueue* _work_queue;
3519 protected:
3520 DO_OOP_WORK_DEFN
3521 public:
3522 Par_ConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue,
3523 CMSBitMap* bit_map, CMSMarkStack* overflow_stack):
3524 MetadataAwareOopClosure(collector->ref_processor()),
3525 _collector(collector),
3526 _task(task),
3527 _span(collector->_span),
3528 _work_queue(work_queue),
3529 _bit_map(bit_map),
3530 _overflow_stack(overflow_stack)
3531 { }
3532 virtual void do_oop(oop* p);
3533 virtual void do_oop(narrowOop* p);
3534
3535 void trim_queue(size_t max);
3536 void handle_stack_overflow(HeapWord* lost);
3537 void do_yield_check() {
3538 if (_task->should_yield()) {
3539 _task->yield();
3540 }
3541 }
3542 };
3543
3544 // Grey object scanning during work stealing phase --
3545 // the salient assumption here is that any references
3546 // that are in these stolen objects being scanned must
3547 // already have been initialized (else they would not have
3548 // been published), so we do not need to check for
3549 // uninitialized objects before pushing here.
3550 void Par_ConcMarkingClosure::do_oop(oop obj) {
3551 assert(obj->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
3552 HeapWord* addr = (HeapWord*)obj;
3553 // Check if oop points into the CMS generation
3554 // and is not marked
3555 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
3556 // a white object ...
3557 // If we manage to "claim" the object, by being the
3558 // first thread to mark it, then we push it on our
3559 // marking stack
3560 if (_bit_map->par_mark(addr)) { // ... now grey
3561 // push on work queue (grey set)
3562 bool simulate_overflow = false;
3563 NOT_PRODUCT(
3564 if (CMSMarkStackOverflowALot &&
3565 _collector->simulate_overflow()) {
3566 // simulate a stack overflow
3567 simulate_overflow = true;
3568 }
3569 )
3570 if (simulate_overflow ||
3571 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
3572 // stack overflow
3573 if (PrintCMSStatistics != 0) {
3574 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
3575 SIZE_FORMAT, _overflow_stack->capacity());
3576 }
3577 // We cannot assert that the overflow stack is full because
3578 // it may have been emptied since.
3579 assert(simulate_overflow ||
3580 _work_queue->size() == _work_queue->max_elems(),
3581 "Else push should have succeeded");
3582 handle_stack_overflow(addr);
3583 }
3584 } // Else, some other thread got there first
3585 do_yield_check();
3586 }
3587 }
3588
3589 void Par_ConcMarkingClosure::do_oop(oop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
3590 void Par_ConcMarkingClosure::do_oop(narrowOop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
3591
3592 void Par_ConcMarkingClosure::trim_queue(size_t max) {
3593 while (_work_queue->size() > max) {
3594 oop new_oop;
3595 if (_work_queue->pop_local(new_oop)) {
3596 assert(new_oop->is_oop(), "Should be an oop");
3597 assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
3598 assert(_span.contains((HeapWord*)new_oop), "Not in span");
3599 new_oop->oop_iterate(this); // do_oop() above
3600 do_yield_check();
3601 }
3602 }
3603 }
3604
3605 // Upon stack overflow, we discard (part of) the stack,
3606 // remembering the least address amongst those discarded
3607 // in CMSCollector's _restart_address.
3608 void Par_ConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
3609 // We need to do this under a mutex to prevent other
3610 // workers from interfering with the work done below.
3611 MutexLockerEx ml(_overflow_stack->par_lock(),
3612 Mutex::_no_safepoint_check_flag);
3613 // Remember the least grey address discarded
3614 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
3615 _collector->lower_restart_addr(ra);
3616 _overflow_stack->reset(); // discard stack contents
3617 _overflow_stack->expand(); // expand the stack if possible
3618 }
3619
3620
3621 void CMSConcMarkingTask::do_work_steal(int i) {
3622 OopTaskQueue* work_q = work_queue(i);
3623 oop obj_to_scan;
3624 CMSBitMap* bm = &(_collector->_markBitMap);
3625 CMSMarkStack* ovflw = &(_collector->_markStack);
3626 int* seed = _collector->hash_seed(i);
3627 Par_ConcMarkingClosure cl(_collector, this, work_q, bm, ovflw);
3628 while (true) {
3629 cl.trim_queue(0);
3630 assert(work_q->size() == 0, "Should have been emptied above");
3631 if (get_work_from_overflow_stack(ovflw, work_q)) {
3632 // Can't assert below because the work obtained from the
3633 // overflow stack may already have been stolen from us.
3634 // assert(work_q->size() > 0, "Work from overflow stack");
3635 continue;
3636 } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
3637 assert(obj_to_scan->is_oop(), "Should be an oop");
3638 assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
3639 obj_to_scan->oop_iterate(&cl);
3640 } else if (terminator()->offer_termination(&_term_term)) {
3641 assert(work_q->size() == 0, "Impossible!");
3642 break;
3643 } else if (yielding() || should_yield()) {
3644 yield();
3645 }
3646 }
3647 }
3648
3649 // This is run by the CMS (coordinator) thread.
3650 void CMSConcMarkingTask::coordinator_yield() {
3651 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3652 "CMS thread should hold CMS token");
3653 // First give up the locks, then yield, then re-lock
3654 // We should probably use a constructor/destructor idiom to
3655 // do this unlock/lock or modify the MutexUnlocker class to
3656 // serve our purpose. XXX
3657 assert_lock_strong(_bit_map_lock);
3658 _bit_map_lock->unlock();
3659 ConcurrentMarkSweepThread::desynchronize(true);
3660 _collector->stopTimer();
3661 if (PrintCMSStatistics != 0) {
3662 _collector->incrementYields();
3663 }
3664
3665 // It is possible for whichever thread initiated the yield request
3666 // not to get a chance to wake up and take the bitmap lock between
3667 // this thread releasing it and reacquiring it. So, while the
3668 // should_yield() flag is on, let's sleep for a bit to give the
3669 // other thread a chance to wake up. The limit imposed on the number
3670 // of iterations is defensive, to avoid any unforseen circumstances
3671 // putting us into an infinite loop. Since it's always been this
3672 // (coordinator_yield()) method that was observed to cause the
3673 // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
3674 // which is by default non-zero. For the other seven methods that
3675 // also perform the yield operation, as are using a different
3676 // parameter (CMSYieldSleepCount) which is by default zero. This way we
3677 // can enable the sleeping for those methods too, if necessary.
3678 // See 6442774.
3679 //
3680 // We really need to reconsider the synchronization between the GC
3681 // thread and the yield-requesting threads in the future and we
3682 // should really use wait/notify, which is the recommended
3683 // way of doing this type of interaction. Additionally, we should
3684 // consolidate the eight methods that do the yield operation and they
3685 // are almost identical into one for better maintainability and
3686 // readability. See 6445193.
3687 //
3688 // Tony 2006.06.29
3689 for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
3690 ConcurrentMarkSweepThread::should_yield() &&
3691 !CMSCollector::foregroundGCIsActive(); ++i) {
3692 os::sleep(Thread::current(), 1, false);
3693 }
3694
3695 ConcurrentMarkSweepThread::synchronize(true);
3696 _bit_map_lock->lock_without_safepoint_check();
3697 _collector->startTimer();
3698 }
3699
3700 bool CMSCollector::do_marking_mt() {
3701 assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition");
3702 int num_workers = AdaptiveSizePolicy::calc_active_conc_workers(
3703 conc_workers()->total_workers(),
3704 conc_workers()->active_workers(),
3705 Threads::number_of_non_daemon_threads());
3706 conc_workers()->set_active_workers(num_workers);
3707
3708 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
3709
3710 CMSConcMarkingTask tsk(this,
3711 cms_space,
3712 conc_workers(),
3713 task_queues());
3714
3715 // Since the actual number of workers we get may be different
3716 // from the number we requested above, do we need to do anything different
3717 // below? In particular, may be we need to subclass the SequantialSubTasksDone
3718 // class?? XXX
3719 cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
3720
3721 // Refs discovery is already non-atomic.
3722 assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
3723 assert(ref_processor()->discovery_is_mt(), "Discovery should be MT");
3724 conc_workers()->start_task(&tsk);
3725 while (tsk.yielded()) {
3726 tsk.coordinator_yield();
3727 conc_workers()->continue_task(&tsk);
3728 }
3729 // If the task was aborted, _restart_addr will be non-NULL
3730 assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
3731 while (_restart_addr != NULL) {
3732 // XXX For now we do not make use of ABORTED state and have not
3733 // yet implemented the right abort semantics (even in the original
3734 // single-threaded CMS case). That needs some more investigation
3735 // and is deferred for now; see CR# TBF. 07252005YSR. XXX
3736 assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
3737 // If _restart_addr is non-NULL, a marking stack overflow
3738 // occurred; we need to do a fresh marking iteration from the
3739 // indicated restart address.
3740 if (_foregroundGCIsActive) {
3741 // We may be running into repeated stack overflows, having
3742 // reached the limit of the stack size, while making very
3743 // slow forward progress. It may be best to bail out and
3744 // let the foreground collector do its job.
3745 // Clear _restart_addr, so that foreground GC
3746 // works from scratch. This avoids the headache of
3747 // a "rescan" which would otherwise be needed because
3748 // of the dirty mod union table & card table.
3749 _restart_addr = NULL;
3750 return false;
3751 }
3752 // Adjust the task to restart from _restart_addr
3753 tsk.reset(_restart_addr);
3754 cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
3755 _restart_addr);
3756 _restart_addr = NULL;
3757 // Get the workers going again
3758 conc_workers()->start_task(&tsk);
3759 while (tsk.yielded()) {
3760 tsk.coordinator_yield();
3761 conc_workers()->continue_task(&tsk);
3762 }
3763 }
3764 assert(tsk.completed(), "Inconsistency");
3765 assert(tsk.result() == true, "Inconsistency");
3766 return true;
3767 }
3768
3769 bool CMSCollector::do_marking_st() {
3770 ResourceMark rm;
3771 HandleMark hm;
3772
3773 // Temporarily make refs discovery single threaded (non-MT)
3774 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
3775 MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
3776 &_markStack, CMSYield);
3777 // the last argument to iterate indicates whether the iteration
3778 // should be incremental with periodic yields.
3779 _markBitMap.iterate(&markFromRootsClosure);
3780 // If _restart_addr is non-NULL, a marking stack overflow
3781 // occurred; we need to do a fresh iteration from the
3782 // indicated restart address.
3783 while (_restart_addr != NULL) {
3784 if (_foregroundGCIsActive) {
3785 // We may be running into repeated stack overflows, having
3786 // reached the limit of the stack size, while making very
3787 // slow forward progress. It may be best to bail out and
3788 // let the foreground collector do its job.
3789 // Clear _restart_addr, so that foreground GC
3790 // works from scratch. This avoids the headache of
3791 // a "rescan" which would otherwise be needed because
3792 // of the dirty mod union table & card table.
3793 _restart_addr = NULL;
3794 return false; // indicating failure to complete marking
3795 }
3796 // Deal with stack overflow:
3797 // we restart marking from _restart_addr
3798 HeapWord* ra = _restart_addr;
3799 markFromRootsClosure.reset(ra);
3800 _restart_addr = NULL;
3801 _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
3802 }
3803 return true;
3804 }
3805
3806 void CMSCollector::preclean() {
3807 check_correct_thread_executing();
3808 assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
3809 verify_work_stacks_empty();
3810 verify_overflow_empty();
3811 _abort_preclean = false;
3812 if (CMSPrecleaningEnabled) {
3813 if (!CMSEdenChunksRecordAlways) {
3814 _eden_chunk_index = 0;
3815 }
3816 size_t used = get_eden_used();
3817 size_t capacity = get_eden_capacity();
3818 // Don't start sampling unless we will get sufficiently
3819 // many samples.
3820 if (used < (capacity/(CMSScheduleRemarkSamplingRatio * 100)
3821 * CMSScheduleRemarkEdenPenetration)) {
3822 _start_sampling = true;
3823 } else {
3824 _start_sampling = false;
3825 }
3826 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3827 CMSPhaseAccounting pa(this, "preclean", _gc_tracer_cm->gc_id(), !PrintGCDetails);
3828 preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
3829 }
3830 CMSTokenSync x(true); // is cms thread
3831 if (CMSPrecleaningEnabled) {
3832 sample_eden();
3833 _collectorState = AbortablePreclean;
3834 } else {
3835 _collectorState = FinalMarking;
3836 }
3837 verify_work_stacks_empty();
3838 verify_overflow_empty();
3839 }
3840
3841 // Try and schedule the remark such that young gen
3842 // occupancy is CMSScheduleRemarkEdenPenetration %.
3843 void CMSCollector::abortable_preclean() {
3844 check_correct_thread_executing();
3845 assert(CMSPrecleaningEnabled, "Inconsistent control state");
3846 assert(_collectorState == AbortablePreclean, "Inconsistent control state");
3847
3848 // If Eden's current occupancy is below this threshold,
3849 // immediately schedule the remark; else preclean
3850 // past the next scavenge in an effort to
3851 // schedule the pause as described above. By choosing
3852 // CMSScheduleRemarkEdenSizeThreshold >= max eden size
3853 // we will never do an actual abortable preclean cycle.
3854 if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
3855 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3856 CMSPhaseAccounting pa(this, "abortable-preclean", _gc_tracer_cm->gc_id(), !PrintGCDetails);
3857 // We need more smarts in the abortable preclean
3858 // loop below to deal with cases where allocation
3859 // in young gen is very very slow, and our precleaning
3860 // is running a losing race against a horde of
3861 // mutators intent on flooding us with CMS updates
3862 // (dirty cards).
3863 // One, admittedly dumb, strategy is to give up
3864 // after a certain number of abortable precleaning loops
3865 // or after a certain maximum time. We want to make
3866 // this smarter in the next iteration.
3867 // XXX FIX ME!!! YSR
3868 size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
3869 while (!(should_abort_preclean() ||
3870 ConcurrentMarkSweepThread::should_terminate())) {
3871 workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
3872 cumworkdone += workdone;
3873 loops++;
3874 // Voluntarily terminate abortable preclean phase if we have
3875 // been at it for too long.
3876 if ((CMSMaxAbortablePrecleanLoops != 0) &&
3877 loops >= CMSMaxAbortablePrecleanLoops) {
3878 if (PrintGCDetails) {
3879 gclog_or_tty->print(" CMS: abort preclean due to loops ");
3880 }
3881 break;
3882 }
3883 if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
3884 if (PrintGCDetails) {
3885 gclog_or_tty->print(" CMS: abort preclean due to time ");
3886 }
3887 break;
3888 }
3889 // If we are doing little work each iteration, we should
3890 // take a short break.
3891 if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
3892 // Sleep for some time, waiting for work to accumulate
3893 stopTimer();
3894 cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
3895 startTimer();
3896 waited++;
3897 }
3898 }
3899 if (PrintCMSStatistics > 0) {
3900 gclog_or_tty->print(" [" SIZE_FORMAT " iterations, " SIZE_FORMAT " waits, " SIZE_FORMAT " cards)] ",
3901 loops, waited, cumworkdone);
3902 }
3903 }
3904 CMSTokenSync x(true); // is cms thread
3905 if (_collectorState != Idling) {
3906 assert(_collectorState == AbortablePreclean,
3907 "Spontaneous state transition?");
3908 _collectorState = FinalMarking;
3909 } // Else, a foreground collection completed this CMS cycle.
3910 return;
3911 }
3912
3913 // Respond to an Eden sampling opportunity
3914 void CMSCollector::sample_eden() {
3915 // Make sure a young gc cannot sneak in between our
3916 // reading and recording of a sample.
3917 assert(Thread::current()->is_ConcurrentGC_thread(),
3918 "Only the cms thread may collect Eden samples");
3919 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3920 "Should collect samples while holding CMS token");
3921 if (!_start_sampling) {
3922 return;
3923 }
3924 // When CMSEdenChunksRecordAlways is true, the eden chunk array
3925 // is populated by the young generation.
3926 if (_eden_chunk_array != NULL && !CMSEdenChunksRecordAlways) {
3927 if (_eden_chunk_index < _eden_chunk_capacity) {
3928 _eden_chunk_array[_eden_chunk_index] = *_top_addr; // take sample
3929 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
3930 "Unexpected state of Eden");
3931 // We'd like to check that what we just sampled is an oop-start address;
3932 // however, we cannot do that here since the object may not yet have been
3933 // initialized. So we'll instead do the check when we _use_ this sample
3934 // later.
3935 if (_eden_chunk_index == 0 ||
3936 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
3937 _eden_chunk_array[_eden_chunk_index-1])
3938 >= CMSSamplingGrain)) {
3939 _eden_chunk_index++; // commit sample
3940 }
3941 }
3942 }
3943 if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
3944 size_t used = get_eden_used();
3945 size_t capacity = get_eden_capacity();
3946 assert(used <= capacity, "Unexpected state of Eden");
3947 if (used > (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
3948 _abort_preclean = true;
3949 }
3950 }
3951 }
3952
3953
3954 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
3955 assert(_collectorState == Precleaning ||
3956 _collectorState == AbortablePreclean, "incorrect state");
3957 ResourceMark rm;
3958 HandleMark hm;
3959
3960 // Precleaning is currently not MT but the reference processor
3961 // may be set for MT. Disable it temporarily here.
3962 ReferenceProcessor* rp = ref_processor();
3963 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false);
3964
3965 // Do one pass of scrubbing the discovered reference lists
3966 // to remove any reference objects with strongly-reachable
3967 // referents.
3968 if (clean_refs) {
3969 CMSPrecleanRefsYieldClosure yield_cl(this);
3970 assert(rp->span().equals(_span), "Spans should be equal");
3971 CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
3972 &_markStack, true /* preclean */);
3973 CMSDrainMarkingStackClosure complete_trace(this,
3974 _span, &_markBitMap, &_markStack,
3975 &keep_alive, true /* preclean */);
3976
3977 // We don't want this step to interfere with a young
3978 // collection because we don't want to take CPU
3979 // or memory bandwidth away from the young GC threads
3980 // (which may be as many as there are CPUs).
3981 // Note that we don't need to protect ourselves from
3982 // interference with mutators because they can't
3983 // manipulate the discovered reference lists nor affect
3984 // the computed reachability of the referents, the
3985 // only properties manipulated by the precleaning
3986 // of these reference lists.
3987 stopTimer();
3988 CMSTokenSyncWithLocks x(true /* is cms thread */,
3989 bitMapLock());
3990 startTimer();
3991 sample_eden();
3992
3993 // The following will yield to allow foreground
3994 // collection to proceed promptly. XXX YSR:
3995 // The code in this method may need further
3996 // tweaking for better performance and some restructuring
3997 // for cleaner interfaces.
3998 GCTimer *gc_timer = NULL; // Currently not tracing concurrent phases
3999 rp->preclean_discovered_references(
4000 rp->is_alive_non_header(), &keep_alive, &complete_trace, &yield_cl,
4001 gc_timer, _gc_tracer_cm->gc_id());
4002 }
4003
4004 if (clean_survivor) { // preclean the active survivor space(s)
4005 PushAndMarkClosure pam_cl(this, _span, ref_processor(),
4006 &_markBitMap, &_modUnionTable,
4007 &_markStack, true /* precleaning phase */);
4008 stopTimer();
4009 CMSTokenSyncWithLocks ts(true /* is cms thread */,
4010 bitMapLock());
4011 startTimer();
4012 unsigned int before_count =
4013 GenCollectedHeap::heap()->total_collections();
4014 SurvivorSpacePrecleanClosure
4015 sss_cl(this, _span, &_markBitMap, &_markStack,
4016 &pam_cl, before_count, CMSYield);
4017 _young_gen->from()->object_iterate_careful(&sss_cl);
4018 _young_gen->to()->object_iterate_careful(&sss_cl);
4019 }
4020 MarkRefsIntoAndScanClosure
4021 mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
4022 &_markStack, this, CMSYield,
4023 true /* precleaning phase */);
4024 // CAUTION: The following closure has persistent state that may need to
4025 // be reset upon a decrease in the sequence of addresses it
4026 // processes.
4027 ScanMarkedObjectsAgainCarefullyClosure
4028 smoac_cl(this, _span,
4029 &_markBitMap, &_markStack, &mrias_cl, CMSYield);
4030
4031 // Preclean dirty cards in ModUnionTable and CardTable using
4032 // appropriate convergence criterion;
4033 // repeat CMSPrecleanIter times unless we find that
4034 // we are losing.
4035 assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
4036 assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
4037 "Bad convergence multiplier");
4038 assert(CMSPrecleanThreshold >= 100,
4039 "Unreasonably low CMSPrecleanThreshold");
4040
4041 size_t numIter, cumNumCards, lastNumCards, curNumCards;
4042 for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
4043 numIter < CMSPrecleanIter;
4044 numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
4045 curNumCards = preclean_mod_union_table(_cmsGen, &smoac_cl);
4046 if (Verbose && PrintGCDetails) {
4047 gclog_or_tty->print(" (modUnionTable: " SIZE_FORMAT " cards)", curNumCards);
4048 }
4049 // Either there are very few dirty cards, so re-mark
4050 // pause will be small anyway, or our pre-cleaning isn't
4051 // that much faster than the rate at which cards are being
4052 // dirtied, so we might as well stop and re-mark since
4053 // precleaning won't improve our re-mark time by much.
4054 if (curNumCards <= CMSPrecleanThreshold ||
4055 (numIter > 0 &&
4056 (curNumCards * CMSPrecleanDenominator >
4057 lastNumCards * CMSPrecleanNumerator))) {
4058 numIter++;
4059 cumNumCards += curNumCards;
4060 break;
4061 }
4062 }
4063
4064 preclean_klasses(&mrias_cl, _cmsGen->freelistLock());
4065
4066 curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
4067 cumNumCards += curNumCards;
4068 if (PrintGCDetails && PrintCMSStatistics != 0) {
4069 gclog_or_tty->print_cr(" (cardTable: " SIZE_FORMAT " cards, re-scanned " SIZE_FORMAT " cards, " SIZE_FORMAT " iterations)",
4070 curNumCards, cumNumCards, numIter);
4071 }
4072 return cumNumCards; // as a measure of useful work done
4073 }
4074
4075 // PRECLEANING NOTES:
4076 // Precleaning involves:
4077 // . reading the bits of the modUnionTable and clearing the set bits.
4078 // . For the cards corresponding to the set bits, we scan the
4079 // objects on those cards. This means we need the free_list_lock
4080 // so that we can safely iterate over the CMS space when scanning
4081 // for oops.
4082 // . When we scan the objects, we'll be both reading and setting
4083 // marks in the marking bit map, so we'll need the marking bit map.
4084 // . For protecting _collector_state transitions, we take the CGC_lock.
4085 // Note that any races in the reading of of card table entries by the
4086 // CMS thread on the one hand and the clearing of those entries by the
4087 // VM thread or the setting of those entries by the mutator threads on the
4088 // other are quite benign. However, for efficiency it makes sense to keep
4089 // the VM thread from racing with the CMS thread while the latter is
4090 // dirty card info to the modUnionTable. We therefore also use the
4091 // CGC_lock to protect the reading of the card table and the mod union
4092 // table by the CM thread.
4093 // . We run concurrently with mutator updates, so scanning
4094 // needs to be done carefully -- we should not try to scan
4095 // potentially uninitialized objects.
4096 //
4097 // Locking strategy: While holding the CGC_lock, we scan over and
4098 // reset a maximal dirty range of the mod union / card tables, then lock
4099 // the free_list_lock and bitmap lock to do a full marking, then
4100 // release these locks; and repeat the cycle. This allows for a
4101 // certain amount of fairness in the sharing of these locks between
4102 // the CMS collector on the one hand, and the VM thread and the
4103 // mutators on the other.
4104
4105 // NOTE: preclean_mod_union_table() and preclean_card_table()
4106 // further below are largely identical; if you need to modify
4107 // one of these methods, please check the other method too.
4108
4109 size_t CMSCollector::preclean_mod_union_table(
4110 ConcurrentMarkSweepGeneration* gen,
4111 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4112 verify_work_stacks_empty();
4113 verify_overflow_empty();
4114
4115 // strategy: starting with the first card, accumulate contiguous
4116 // ranges of dirty cards; clear these cards, then scan the region
4117 // covered by these cards.
4118
4119 // Since all of the MUT is committed ahead, we can just use
4120 // that, in case the generations expand while we are precleaning.
4121 // It might also be fine to just use the committed part of the
4122 // generation, but we might potentially miss cards when the
4123 // generation is rapidly expanding while we are in the midst
4124 // of precleaning.
4125 HeapWord* startAddr = gen->reserved().start();
4126 HeapWord* endAddr = gen->reserved().end();
4127
4128 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4129
4130 size_t numDirtyCards, cumNumDirtyCards;
4131 HeapWord *nextAddr, *lastAddr;
4132 for (cumNumDirtyCards = numDirtyCards = 0,
4133 nextAddr = lastAddr = startAddr;
4134 nextAddr < endAddr;
4135 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4136
4137 ResourceMark rm;
4138 HandleMark hm;
4139
4140 MemRegion dirtyRegion;
4141 {
4142 stopTimer();
4143 // Potential yield point
4144 CMSTokenSync ts(true);
4145 startTimer();
4146 sample_eden();
4147 // Get dirty region starting at nextOffset (inclusive),
4148 // simultaneously clearing it.
4149 dirtyRegion =
4150 _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
4151 assert(dirtyRegion.start() >= nextAddr,
4152 "returned region inconsistent?");
4153 }
4154 // Remember where the next search should begin.
4155 // The returned region (if non-empty) is a right open interval,
4156 // so lastOffset is obtained from the right end of that
4157 // interval.
4158 lastAddr = dirtyRegion.end();
4159 // Should do something more transparent and less hacky XXX
4160 numDirtyCards =
4161 _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
4162
4163 // We'll scan the cards in the dirty region (with periodic
4164 // yields for foreground GC as needed).
4165 if (!dirtyRegion.is_empty()) {
4166 assert(numDirtyCards > 0, "consistency check");
4167 HeapWord* stop_point = NULL;
4168 stopTimer();
4169 // Potential yield point
4170 CMSTokenSyncWithLocks ts(true, gen->freelistLock(),
4171 bitMapLock());
4172 startTimer();
4173 {
4174 verify_work_stacks_empty();
4175 verify_overflow_empty();
4176 sample_eden();
4177 stop_point =
4178 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4179 }
4180 if (stop_point != NULL) {
4181 // The careful iteration stopped early either because it found an
4182 // uninitialized object, or because we were in the midst of an
4183 // "abortable preclean", which should now be aborted. Redirty
4184 // the bits corresponding to the partially-scanned or unscanned
4185 // cards. We'll either restart at the next block boundary or
4186 // abort the preclean.
4187 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4188 "Should only be AbortablePreclean.");
4189 _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
4190 if (should_abort_preclean()) {
4191 break; // out of preclean loop
4192 } else {
4193 // Compute the next address at which preclean should pick up;
4194 // might need bitMapLock in order to read P-bits.
4195 lastAddr = next_card_start_after_block(stop_point);
4196 }
4197 }
4198 } else {
4199 assert(lastAddr == endAddr, "consistency check");
4200 assert(numDirtyCards == 0, "consistency check");
4201 break;
4202 }
4203 }
4204 verify_work_stacks_empty();
4205 verify_overflow_empty();
4206 return cumNumDirtyCards;
4207 }
4208
4209 // NOTE: preclean_mod_union_table() above and preclean_card_table()
4210 // below are largely identical; if you need to modify
4211 // one of these methods, please check the other method too.
4212
4213 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* gen,
4214 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4215 // strategy: it's similar to precleamModUnionTable above, in that
4216 // we accumulate contiguous ranges of dirty cards, mark these cards
4217 // precleaned, then scan the region covered by these cards.
4218 HeapWord* endAddr = (HeapWord*)(gen->_virtual_space.high());
4219 HeapWord* startAddr = (HeapWord*)(gen->_virtual_space.low());
4220
4221 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4222
4223 size_t numDirtyCards, cumNumDirtyCards;
4224 HeapWord *lastAddr, *nextAddr;
4225
4226 for (cumNumDirtyCards = numDirtyCards = 0,
4227 nextAddr = lastAddr = startAddr;
4228 nextAddr < endAddr;
4229 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4230
4231 ResourceMark rm;
4232 HandleMark hm;
4233
4234 MemRegion dirtyRegion;
4235 {
4236 // See comments in "Precleaning notes" above on why we
4237 // do this locking. XXX Could the locking overheads be
4238 // too high when dirty cards are sparse? [I don't think so.]
4239 stopTimer();
4240 CMSTokenSync x(true); // is cms thread
4241 startTimer();
4242 sample_eden();
4243 // Get and clear dirty region from card table
4244 dirtyRegion = _ct->ct_bs()->dirty_card_range_after_reset(
4245 MemRegion(nextAddr, endAddr),
4246 true,
4247 CardTableModRefBS::precleaned_card_val());
4248
4249 assert(dirtyRegion.start() >= nextAddr,
4250 "returned region inconsistent?");
4251 }
4252 lastAddr = dirtyRegion.end();
4253 numDirtyCards =
4254 dirtyRegion.word_size()/CardTableModRefBS::card_size_in_words;
4255
4256 if (!dirtyRegion.is_empty()) {
4257 stopTimer();
4258 CMSTokenSyncWithLocks ts(true, gen->freelistLock(), bitMapLock());
4259 startTimer();
4260 sample_eden();
4261 verify_work_stacks_empty();
4262 verify_overflow_empty();
4263 HeapWord* stop_point =
4264 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4265 if (stop_point != NULL) {
4266 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4267 "Should only be AbortablePreclean.");
4268 _ct->ct_bs()->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4269 if (should_abort_preclean()) {
4270 break; // out of preclean loop
4271 } else {
4272 // Compute the next address at which preclean should pick up.
4273 lastAddr = next_card_start_after_block(stop_point);
4274 }
4275 }
4276 } else {
4277 break;
4278 }
4279 }
4280 verify_work_stacks_empty();
4281 verify_overflow_empty();
4282 return cumNumDirtyCards;
4283 }
4284
4285 class PrecleanKlassClosure : public KlassClosure {
4286 KlassToOopClosure _cm_klass_closure;
4287 public:
4288 PrecleanKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4289 void do_klass(Klass* k) {
4290 if (k->has_accumulated_modified_oops()) {
4291 k->clear_accumulated_modified_oops();
4292
4293 _cm_klass_closure.do_klass(k);
4294 }
4295 }
4296 };
4297
4298 // The freelist lock is needed to prevent asserts, is it really needed?
4299 void CMSCollector::preclean_klasses(MarkRefsIntoAndScanClosure* cl, Mutex* freelistLock) {
4300
4301 cl->set_freelistLock(freelistLock);
4302
4303 CMSTokenSyncWithLocks ts(true, freelistLock, bitMapLock());
4304
4305 // SSS: Add equivalent to ScanMarkedObjectsAgainCarefullyClosure::do_yield_check and should_abort_preclean?
4306 // SSS: We should probably check if precleaning should be aborted, at suitable intervals?
4307 PrecleanKlassClosure preclean_klass_closure(cl);
4308 ClassLoaderDataGraph::classes_do(&preclean_klass_closure);
4309
4310 verify_work_stacks_empty();
4311 verify_overflow_empty();
4312 }
4313
4314 void CMSCollector::checkpointRootsFinal() {
4315 assert(_collectorState == FinalMarking, "incorrect state transition?");
4316 check_correct_thread_executing();
4317 // world is stopped at this checkpoint
4318 assert(SafepointSynchronize::is_at_safepoint(),
4319 "world should be stopped");
4320 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
4321
4322 verify_work_stacks_empty();
4323 verify_overflow_empty();
4324
4325 if (PrintGCDetails) {
4326 gclog_or_tty->print("[YG occupancy: "SIZE_FORMAT" K ("SIZE_FORMAT" K)]",
4327 _young_gen->used() / K,
4328 _young_gen->capacity() / K);
4329 }
4330 {
4331 if (CMSScavengeBeforeRemark) {
4332 GenCollectedHeap* gch = GenCollectedHeap::heap();
4333 // Temporarily set flag to false, GCH->do_collection will
4334 // expect it to be false and set to true
4335 FlagSetting fl(gch->_is_gc_active, false);
4336 NOT_PRODUCT(GCTraceTime t("Scavenge-Before-Remark",
4337 PrintGCDetails && Verbose, true, _gc_timer_cm, _gc_tracer_cm->gc_id());)
4338 int level = _cmsGen->level() - 1;
4339 if (level >= 0) {
4340 gch->do_collection(true, // full (i.e. force, see below)
4341 false, // !clear_all_soft_refs
4342 0, // size
4343 false, // is_tlab
4344 level // max_level
4345 );
4346 }
4347 }
4348 FreelistLocker x(this);
4349 MutexLockerEx y(bitMapLock(),
4350 Mutex::_no_safepoint_check_flag);
4351 checkpointRootsFinalWork();
4352 }
4353 verify_work_stacks_empty();
4354 verify_overflow_empty();
4355 }
4356
4357 void CMSCollector::checkpointRootsFinalWork() {
4358 NOT_PRODUCT(GCTraceTime tr("checkpointRootsFinalWork", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());)
4359
4360 assert(haveFreelistLocks(), "must have free list locks");
4361 assert_lock_strong(bitMapLock());
4362
4363 ResourceMark rm;
4364 HandleMark hm;
4365
4366 GenCollectedHeap* gch = GenCollectedHeap::heap();
4367
4368 if (should_unload_classes()) {
4369 CodeCache::gc_prologue();
4370 }
4371 assert(haveFreelistLocks(), "must have free list locks");
4372 assert_lock_strong(bitMapLock());
4373
4374 // We might assume that we need not fill TLAB's when
4375 // CMSScavengeBeforeRemark is set, because we may have just done
4376 // a scavenge which would have filled all TLAB's -- and besides
4377 // Eden would be empty. This however may not always be the case --
4378 // for instance although we asked for a scavenge, it may not have
4379 // happened because of a JNI critical section. We probably need
4380 // a policy for deciding whether we can in that case wait until
4381 // the critical section releases and then do the remark following
4382 // the scavenge, and skip it here. In the absence of that policy,
4383 // or of an indication of whether the scavenge did indeed occur,
4384 // we cannot rely on TLAB's having been filled and must do
4385 // so here just in case a scavenge did not happen.
4386 gch->ensure_parsability(false); // fill TLAB's, but no need to retire them
4387 // Update the saved marks which may affect the root scans.
4388 gch->save_marks();
4389
4390 if (CMSPrintEdenSurvivorChunks) {
4391 print_eden_and_survivor_chunk_arrays();
4392 }
4393
4394 {
4395 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
4396
4397 // Note on the role of the mod union table:
4398 // Since the marker in "markFromRoots" marks concurrently with
4399 // mutators, it is possible for some reachable objects not to have been
4400 // scanned. For instance, an only reference to an object A was
4401 // placed in object B after the marker scanned B. Unless B is rescanned,
4402 // A would be collected. Such updates to references in marked objects
4403 // are detected via the mod union table which is the set of all cards
4404 // dirtied since the first checkpoint in this GC cycle and prior to
4405 // the most recent young generation GC, minus those cleaned up by the
4406 // concurrent precleaning.
4407 if (CMSParallelRemarkEnabled && CollectedHeap::use_parallel_gc_threads()) {
4408 GCTraceTime t("Rescan (parallel) ", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
4409 do_remark_parallel();
4410 } else {
4411 GCTraceTime t("Rescan (non-parallel) ", PrintGCDetails, false,
4412 _gc_timer_cm, _gc_tracer_cm->gc_id());
4413 do_remark_non_parallel();
4414 }
4415 }
4416 verify_work_stacks_empty();
4417 verify_overflow_empty();
4418
4419 {
4420 NOT_PRODUCT(GCTraceTime ts("refProcessingWork", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());)
4421 refProcessingWork();
4422 }
4423 verify_work_stacks_empty();
4424 verify_overflow_empty();
4425
4426 if (should_unload_classes()) {
4427 CodeCache::gc_epilogue();
4428 }
4429 JvmtiExport::gc_epilogue();
4430
4431 // If we encountered any (marking stack / work queue) overflow
4432 // events during the current CMS cycle, take appropriate
4433 // remedial measures, where possible, so as to try and avoid
4434 // recurrence of that condition.
4435 assert(_markStack.isEmpty(), "No grey objects");
4436 size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
4437 _ser_kac_ovflw + _ser_kac_preclean_ovflw;
4438 if (ser_ovflw > 0) {
4439 if (PrintCMSStatistics != 0) {
4440 gclog_or_tty->print_cr("Marking stack overflow (benign) "
4441 "(pmc_pc="SIZE_FORMAT", pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT
4442 ", kac_preclean="SIZE_FORMAT")",
4443 _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw,
4444 _ser_kac_ovflw, _ser_kac_preclean_ovflw);
4445 }
4446 _markStack.expand();
4447 _ser_pmc_remark_ovflw = 0;
4448 _ser_pmc_preclean_ovflw = 0;
4449 _ser_kac_preclean_ovflw = 0;
4450 _ser_kac_ovflw = 0;
4451 }
4452 if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
4453 if (PrintCMSStatistics != 0) {
4454 gclog_or_tty->print_cr("Work queue overflow (benign) "
4455 "(pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT")",
4456 _par_pmc_remark_ovflw, _par_kac_ovflw);
4457 }
4458 _par_pmc_remark_ovflw = 0;
4459 _par_kac_ovflw = 0;
4460 }
4461 if (PrintCMSStatistics != 0) {
4462 if (_markStack._hit_limit > 0) {
4463 gclog_or_tty->print_cr(" (benign) Hit max stack size limit ("SIZE_FORMAT")",
4464 _markStack._hit_limit);
4465 }
4466 if (_markStack._failed_double > 0) {
4467 gclog_or_tty->print_cr(" (benign) Failed stack doubling ("SIZE_FORMAT"),"
4468 " current capacity "SIZE_FORMAT,
4469 _markStack._failed_double,
4470 _markStack.capacity());
4471 }
4472 }
4473 _markStack._hit_limit = 0;
4474 _markStack._failed_double = 0;
4475
4476 if ((VerifyAfterGC || VerifyDuringGC) &&
4477 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
4478 verify_after_remark();
4479 }
4480
4481 _gc_tracer_cm->report_object_count_after_gc(&_is_alive_closure);
4482
4483 // Change under the freelistLocks.
4484 _collectorState = Sweeping;
4485 // Call isAllClear() under bitMapLock
4486 assert(_modUnionTable.isAllClear(),
4487 "Should be clear by end of the final marking");
4488 assert(_ct->klass_rem_set()->mod_union_is_clear(),
4489 "Should be clear by end of the final marking");
4490 }
4491
4492 void CMSParInitialMarkTask::work(uint worker_id) {
4493 elapsedTimer _timer;
4494 ResourceMark rm;
4495 HandleMark hm;
4496
4497 // ---------- scan from roots --------------
4498 _timer.start();
4499 GenCollectedHeap* gch = GenCollectedHeap::heap();
4500 Par_MarkRefsIntoClosure par_mri_cl(_collector->_span, &(_collector->_markBitMap));
4501
4502 // ---------- young gen roots --------------
4503 {
4504 work_on_young_gen_roots(worker_id, &par_mri_cl);
4505 _timer.stop();
4506 if (PrintCMSStatistics != 0) {
4507 gclog_or_tty->print_cr(
4508 "Finished young gen initial mark scan work in %dth thread: %3.3f sec",
4509 worker_id, _timer.seconds());
4510 }
4511 }
4512
4513 // ---------- remaining roots --------------
4514 _timer.reset();
4515 _timer.start();
4516
4517 CLDToOopClosure cld_closure(&par_mri_cl, true);
4518
4519 gch->gen_process_roots(_collector->_cmsGen->level(),
4520 false, // yg was scanned above
4521 false, // this is parallel code
4522 GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4523 _collector->should_unload_classes(),
4524 &par_mri_cl,
4525 NULL,
4526 &cld_closure);
4527 assert(_collector->should_unload_classes()
4528 || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4529 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4530 _timer.stop();
4531 if (PrintCMSStatistics != 0) {
4532 gclog_or_tty->print_cr(
4533 "Finished remaining root initial mark scan work in %dth thread: %3.3f sec",
4534 worker_id, _timer.seconds());
4535 }
4536 }
4537
4538 // Parallel remark task
4539 class CMSParRemarkTask: public CMSParMarkTask {
4540 CompactibleFreeListSpace* _cms_space;
4541
4542 // The per-thread work queues, available here for stealing.
4543 OopTaskQueueSet* _task_queues;
4544 ParallelTaskTerminator _term;
4545
4546 public:
4547 // A value of 0 passed to n_workers will cause the number of
4548 // workers to be taken from the active workers in the work gang.
4549 CMSParRemarkTask(CMSCollector* collector,
4550 CompactibleFreeListSpace* cms_space,
4551 int n_workers, FlexibleWorkGang* workers,
4552 OopTaskQueueSet* task_queues):
4553 CMSParMarkTask("Rescan roots and grey objects in parallel",
4554 collector, n_workers),
4555 _cms_space(cms_space),
4556 _task_queues(task_queues),
4557 _term(n_workers, task_queues) { }
4558
4559 OopTaskQueueSet* task_queues() { return _task_queues; }
4560
4561 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
4562
4563 ParallelTaskTerminator* terminator() { return &_term; }
4564 int n_workers() { return _n_workers; }
4565
4566 void work(uint worker_id);
4567
4568 private:
4569 // ... of dirty cards in old space
4570 void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
4571 Par_MarkRefsIntoAndScanClosure* cl);
4572
4573 // ... work stealing for the above
4574 void do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl, int* seed);
4575 };
4576
4577 class RemarkKlassClosure : public KlassClosure {
4578 KlassToOopClosure _cm_klass_closure;
4579 public:
4580 RemarkKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4581 void do_klass(Klass* k) {
4582 // Check if we have modified any oops in the Klass during the concurrent marking.
4583 if (k->has_accumulated_modified_oops()) {
4584 k->clear_accumulated_modified_oops();
4585
4586 // We could have transfered the current modified marks to the accumulated marks,
4587 // like we do with the Card Table to Mod Union Table. But it's not really necessary.
4588 } else if (k->has_modified_oops()) {
4589 // Don't clear anything, this info is needed by the next young collection.
4590 } else {
4591 // No modified oops in the Klass.
4592 return;
4593 }
4594
4595 // The klass has modified fields, need to scan the klass.
4596 _cm_klass_closure.do_klass(k);
4597 }
4598 };
4599
4600 void CMSParMarkTask::work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl) {
4601 ParNewGeneration* young_gen = _collector->_young_gen;
4602 ContiguousSpace* eden_space = young_gen->eden();
4603 ContiguousSpace* from_space = young_gen->from();
4604 ContiguousSpace* to_space = young_gen->to();
4605
4606 HeapWord** eca = _collector->_eden_chunk_array;
4607 size_t ect = _collector->_eden_chunk_index;
4608 HeapWord** sca = _collector->_survivor_chunk_array;
4609 size_t sct = _collector->_survivor_chunk_index;
4610
4611 assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
4612 assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
4613
4614 do_young_space_rescan(worker_id, cl, to_space, NULL, 0);
4615 do_young_space_rescan(worker_id, cl, from_space, sca, sct);
4616 do_young_space_rescan(worker_id, cl, eden_space, eca, ect);
4617 }
4618
4619 // work_queue(i) is passed to the closure
4620 // Par_MarkRefsIntoAndScanClosure. The "i" parameter
4621 // also is passed to do_dirty_card_rescan_tasks() and to
4622 // do_work_steal() to select the i-th task_queue.
4623
4624 void CMSParRemarkTask::work(uint worker_id) {
4625 elapsedTimer _timer;
4626 ResourceMark rm;
4627 HandleMark hm;
4628
4629 // ---------- rescan from roots --------------
4630 _timer.start();
4631 GenCollectedHeap* gch = GenCollectedHeap::heap();
4632 Par_MarkRefsIntoAndScanClosure par_mrias_cl(_collector,
4633 _collector->_span, _collector->ref_processor(),
4634 &(_collector->_markBitMap),
4635 work_queue(worker_id));
4636
4637 // Rescan young gen roots first since these are likely
4638 // coarsely partitioned and may, on that account, constitute
4639 // the critical path; thus, it's best to start off that
4640 // work first.
4641 // ---------- young gen roots --------------
4642 {
4643 work_on_young_gen_roots(worker_id, &par_mrias_cl);
4644 _timer.stop();
4645 if (PrintCMSStatistics != 0) {
4646 gclog_or_tty->print_cr(
4647 "Finished young gen rescan work in %dth thread: %3.3f sec",
4648 worker_id, _timer.seconds());
4649 }
4650 }
4651
4652 // ---------- remaining roots --------------
4653 _timer.reset();
4654 _timer.start();
4655 gch->gen_process_roots(_collector->_cmsGen->level(),
4656 false, // yg was scanned above
4657 false, // this is parallel code
4658 GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4659 _collector->should_unload_classes(),
4660 &par_mrias_cl,
4661 NULL,
4662 NULL); // The dirty klasses will be handled below
4663
4664 assert(_collector->should_unload_classes()
4665 || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4666 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4667 _timer.stop();
4668 if (PrintCMSStatistics != 0) {
4669 gclog_or_tty->print_cr(
4670 "Finished remaining root rescan work in %dth thread: %3.3f sec",
4671 worker_id, _timer.seconds());
4672 }
4673
4674 // ---------- unhandled CLD scanning ----------
4675 if (worker_id == 0) { // Single threaded at the moment.
4676 _timer.reset();
4677 _timer.start();
4678
4679 // Scan all new class loader data objects and new dependencies that were
4680 // introduced during concurrent marking.
4681 ResourceMark rm;
4682 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
4683 for (int i = 0; i < array->length(); i++) {
4684 par_mrias_cl.do_class_loader_data(array->at(i));
4685 }
4686
4687 // We don't need to keep track of new CLDs anymore.
4688 ClassLoaderDataGraph::remember_new_clds(false);
4689
4690 _timer.stop();
4691 if (PrintCMSStatistics != 0) {
4692 gclog_or_tty->print_cr(
4693 "Finished unhandled CLD scanning work in %dth thread: %3.3f sec",
4694 worker_id, _timer.seconds());
4695 }
4696 }
4697
4698 // ---------- dirty klass scanning ----------
4699 if (worker_id == 0) { // Single threaded at the moment.
4700 _timer.reset();
4701 _timer.start();
4702
4703 // Scan all classes that was dirtied during the concurrent marking phase.
4704 RemarkKlassClosure remark_klass_closure(&par_mrias_cl);
4705 ClassLoaderDataGraph::classes_do(&remark_klass_closure);
4706
4707 _timer.stop();
4708 if (PrintCMSStatistics != 0) {
4709 gclog_or_tty->print_cr(
4710 "Finished dirty klass scanning work in %dth thread: %3.3f sec",
4711 worker_id, _timer.seconds());
4712 }
4713 }
4714
4715 // We might have added oops to ClassLoaderData::_handles during the
4716 // concurrent marking phase. These oops point to newly allocated objects
4717 // that are guaranteed to be kept alive. Either by the direct allocation
4718 // code, or when the young collector processes the roots. Hence,
4719 // we don't have to revisit the _handles block during the remark phase.
4720
4721 // ---------- rescan dirty cards ------------
4722 _timer.reset();
4723 _timer.start();
4724
4725 // Do the rescan tasks for each of the two spaces
4726 // (cms_space) in turn.
4727 // "worker_id" is passed to select the task_queue for "worker_id"
4728 do_dirty_card_rescan_tasks(_cms_space, worker_id, &par_mrias_cl);
4729 _timer.stop();
4730 if (PrintCMSStatistics != 0) {
4731 gclog_or_tty->print_cr(
4732 "Finished dirty card rescan work in %dth thread: %3.3f sec",
4733 worker_id, _timer.seconds());
4734 }
4735
4736 // ---------- steal work from other threads ...
4737 // ---------- ... and drain overflow list.
4738 _timer.reset();
4739 _timer.start();
4740 do_work_steal(worker_id, &par_mrias_cl, _collector->hash_seed(worker_id));
4741 _timer.stop();
4742 if (PrintCMSStatistics != 0) {
4743 gclog_or_tty->print_cr(
4744 "Finished work stealing in %dth thread: %3.3f sec",
4745 worker_id, _timer.seconds());
4746 }
4747 }
4748
4749 // Note that parameter "i" is not used.
4750 void
4751 CMSParMarkTask::do_young_space_rescan(uint worker_id,
4752 OopsInGenClosure* cl, ContiguousSpace* space,
4753 HeapWord** chunk_array, size_t chunk_top) {
4754 // Until all tasks completed:
4755 // . claim an unclaimed task
4756 // . compute region boundaries corresponding to task claimed
4757 // using chunk_array
4758 // . par_oop_iterate(cl) over that region
4759
4760 ResourceMark rm;
4761 HandleMark hm;
4762
4763 SequentialSubTasksDone* pst = space->par_seq_tasks();
4764
4765 uint nth_task = 0;
4766 uint n_tasks = pst->n_tasks();
4767
4768 if (n_tasks > 0) {
4769 assert(pst->valid(), "Uninitialized use?");
4770 HeapWord *start, *end;
4771 while (!pst->is_task_claimed(/* reference */ nth_task)) {
4772 // We claimed task # nth_task; compute its boundaries.
4773 if (chunk_top == 0) { // no samples were taken
4774 assert(nth_task == 0 && n_tasks == 1, "Can have only 1 eden task");
4775 start = space->bottom();
4776 end = space->top();
4777 } else if (nth_task == 0) {
4778 start = space->bottom();
4779 end = chunk_array[nth_task];
4780 } else if (nth_task < (uint)chunk_top) {
4781 assert(nth_task >= 1, "Control point invariant");
4782 start = chunk_array[nth_task - 1];
4783 end = chunk_array[nth_task];
4784 } else {
4785 assert(nth_task == (uint)chunk_top, "Control point invariant");
4786 start = chunk_array[chunk_top - 1];
4787 end = space->top();
4788 }
4789 MemRegion mr(start, end);
4790 // Verify that mr is in space
4791 assert(mr.is_empty() || space->used_region().contains(mr),
4792 "Should be in space");
4793 // Verify that "start" is an object boundary
4794 assert(mr.is_empty() || oop(mr.start())->is_oop(),
4795 "Should be an oop");
4796 space->par_oop_iterate(mr, cl);
4797 }
4798 pst->all_tasks_completed();
4799 }
4800 }
4801
4802 void
4803 CMSParRemarkTask::do_dirty_card_rescan_tasks(
4804 CompactibleFreeListSpace* sp, int i,
4805 Par_MarkRefsIntoAndScanClosure* cl) {
4806 // Until all tasks completed:
4807 // . claim an unclaimed task
4808 // . compute region boundaries corresponding to task claimed
4809 // . transfer dirty bits ct->mut for that region
4810 // . apply rescanclosure to dirty mut bits for that region
4811
4812 ResourceMark rm;
4813 HandleMark hm;
4814
4815 OopTaskQueue* work_q = work_queue(i);
4816 ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
4817 // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
4818 // CAUTION: This closure has state that persists across calls to
4819 // the work method dirty_range_iterate_clear() in that it has
4820 // embedded in it a (subtype of) UpwardsObjectClosure. The
4821 // use of that state in the embedded UpwardsObjectClosure instance
4822 // assumes that the cards are always iterated (even if in parallel
4823 // by several threads) in monotonically increasing order per each
4824 // thread. This is true of the implementation below which picks
4825 // card ranges (chunks) in monotonically increasing order globally
4826 // and, a-fortiori, in monotonically increasing order per thread
4827 // (the latter order being a subsequence of the former).
4828 // If the work code below is ever reorganized into a more chaotic
4829 // work-partitioning form than the current "sequential tasks"
4830 // paradigm, the use of that persistent state will have to be
4831 // revisited and modified appropriately. See also related
4832 // bug 4756801 work on which should examine this code to make
4833 // sure that the changes there do not run counter to the
4834 // assumptions made here and necessary for correctness and
4835 // efficiency. Note also that this code might yield inefficient
4836 // behavior in the case of very large objects that span one or
4837 // more work chunks. Such objects would potentially be scanned
4838 // several times redundantly. Work on 4756801 should try and
4839 // address that performance anomaly if at all possible. XXX
4840 MemRegion full_span = _collector->_span;
4841 CMSBitMap* bm = &(_collector->_markBitMap); // shared
4842 MarkFromDirtyCardsClosure
4843 greyRescanClosure(_collector, full_span, // entire span of interest
4844 sp, bm, work_q, cl);
4845
4846 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
4847 assert(pst->valid(), "Uninitialized use?");
4848 uint nth_task = 0;
4849 const int alignment = CardTableModRefBS::card_size * BitsPerWord;
4850 MemRegion span = sp->used_region();
4851 HeapWord* start_addr = span.start();
4852 HeapWord* end_addr = (HeapWord*)round_to((intptr_t)span.end(),
4853 alignment);
4854 const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
4855 assert((HeapWord*)round_to((intptr_t)start_addr, alignment) ==
4856 start_addr, "Check alignment");
4857 assert((size_t)round_to((intptr_t)chunk_size, alignment) ==
4858 chunk_size, "Check alignment");
4859
4860 while (!pst->is_task_claimed(/* reference */ nth_task)) {
4861 // Having claimed the nth_task, compute corresponding mem-region,
4862 // which is a-fortiori aligned correctly (i.e. at a MUT boundary).
4863 // The alignment restriction ensures that we do not need any
4864 // synchronization with other gang-workers while setting or
4865 // clearing bits in thus chunk of the MUT.
4866 MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
4867 start_addr + (nth_task+1)*chunk_size);
4868 // The last chunk's end might be way beyond end of the
4869 // used region. In that case pull back appropriately.
4870 if (this_span.end() > end_addr) {
4871 this_span.set_end(end_addr);
4872 assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
4873 }
4874 // Iterate over the dirty cards covering this chunk, marking them
4875 // precleaned, and setting the corresponding bits in the mod union
4876 // table. Since we have been careful to partition at Card and MUT-word
4877 // boundaries no synchronization is needed between parallel threads.
4878 _collector->_ct->ct_bs()->dirty_card_iterate(this_span,
4879 &modUnionClosure);
4880
4881 // Having transferred these marks into the modUnionTable,
4882 // rescan the marked objects on the dirty cards in the modUnionTable.
4883 // Even if this is at a synchronous collection, the initial marking
4884 // may have been done during an asynchronous collection so there
4885 // may be dirty bits in the mod-union table.
4886 _collector->_modUnionTable.dirty_range_iterate_clear(
4887 this_span, &greyRescanClosure);
4888 _collector->_modUnionTable.verifyNoOneBitsInRange(
4889 this_span.start(),
4890 this_span.end());
4891 }
4892 pst->all_tasks_completed(); // declare that i am done
4893 }
4894
4895 // . see if we can share work_queues with ParNew? XXX
4896 void
4897 CMSParRemarkTask::do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl,
4898 int* seed) {
4899 OopTaskQueue* work_q = work_queue(i);
4900 NOT_PRODUCT(int num_steals = 0;)
4901 oop obj_to_scan;
4902 CMSBitMap* bm = &(_collector->_markBitMap);
4903
4904 while (true) {
4905 // Completely finish any left over work from (an) earlier round(s)
4906 cl->trim_queue(0);
4907 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
4908 (size_t)ParGCDesiredObjsFromOverflowList);
4909 // Now check if there's any work in the overflow list
4910 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
4911 // only affects the number of attempts made to get work from the
4912 // overflow list and does not affect the number of workers. Just
4913 // pass ParallelGCThreads so this behavior is unchanged.
4914 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
4915 work_q,
4916 ParallelGCThreads)) {
4917 // found something in global overflow list;
4918 // not yet ready to go stealing work from others.
4919 // We'd like to assert(work_q->size() != 0, ...)
4920 // because we just took work from the overflow list,
4921 // but of course we can't since all of that could have
4922 // been already stolen from us.
4923 // "He giveth and He taketh away."
4924 continue;
4925 }
4926 // Verify that we have no work before we resort to stealing
4927 assert(work_q->size() == 0, "Have work, shouldn't steal");
4928 // Try to steal from other queues that have work
4929 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
4930 NOT_PRODUCT(num_steals++;)
4931 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
4932 assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
4933 // Do scanning work
4934 obj_to_scan->oop_iterate(cl);
4935 // Loop around, finish this work, and try to steal some more
4936 } else if (terminator()->offer_termination()) {
4937 break; // nirvana from the infinite cycle
4938 }
4939 }
4940 NOT_PRODUCT(
4941 if (PrintCMSStatistics != 0) {
4942 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
4943 }
4944 )
4945 assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
4946 "Else our work is not yet done");
4947 }
4948
4949 // Record object boundaries in _eden_chunk_array by sampling the eden
4950 // top in the slow-path eden object allocation code path and record
4951 // the boundaries, if CMSEdenChunksRecordAlways is true. If
4952 // CMSEdenChunksRecordAlways is false, we use the other asynchronous
4953 // sampling in sample_eden() that activates during the part of the
4954 // preclean phase.
4955 void CMSCollector::sample_eden_chunk() {
4956 if (CMSEdenChunksRecordAlways && _eden_chunk_array != NULL) {
4957 if (_eden_chunk_lock->try_lock()) {
4958 // Record a sample. This is the critical section. The contents
4959 // of the _eden_chunk_array have to be non-decreasing in the
4960 // address order.
4961 _eden_chunk_array[_eden_chunk_index] = *_top_addr;
4962 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4963 "Unexpected state of Eden");
4964 if (_eden_chunk_index == 0 ||
4965 ((_eden_chunk_array[_eden_chunk_index] > _eden_chunk_array[_eden_chunk_index-1]) &&
4966 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4967 _eden_chunk_array[_eden_chunk_index-1]) >= CMSSamplingGrain))) {
4968 _eden_chunk_index++; // commit sample
4969 }
4970 _eden_chunk_lock->unlock();
4971 }
4972 }
4973 }
4974
4975 // Return a thread-local PLAB recording array, as appropriate.
4976 void* CMSCollector::get_data_recorder(int thr_num) {
4977 if (_survivor_plab_array != NULL &&
4978 (CMSPLABRecordAlways ||
4979 (_collectorState > Marking && _collectorState < FinalMarking))) {
4980 assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
4981 ChunkArray* ca = &_survivor_plab_array[thr_num];
4982 ca->reset(); // clear it so that fresh data is recorded
4983 return (void*) ca;
4984 } else {
4985 return NULL;
4986 }
4987 }
4988
4989 // Reset all the thread-local PLAB recording arrays
4990 void CMSCollector::reset_survivor_plab_arrays() {
4991 for (uint i = 0; i < ParallelGCThreads; i++) {
4992 _survivor_plab_array[i].reset();
4993 }
4994 }
4995
4996 // Merge the per-thread plab arrays into the global survivor chunk
4997 // array which will provide the partitioning of the survivor space
4998 // for CMS initial scan and rescan.
4999 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv,
5000 int no_of_gc_threads) {
5001 assert(_survivor_plab_array != NULL, "Error");
5002 assert(_survivor_chunk_array != NULL, "Error");
5003 assert(_collectorState == FinalMarking ||
5004 (CMSParallelInitialMarkEnabled && _collectorState == InitialMarking), "Error");
5005 for (int j = 0; j < no_of_gc_threads; j++) {
5006 _cursor[j] = 0;
5007 }
5008 HeapWord* top = surv->top();
5009 size_t i;
5010 for (i = 0; i < _survivor_chunk_capacity; i++) { // all sca entries
5011 HeapWord* min_val = top; // Higher than any PLAB address
5012 uint min_tid = 0; // position of min_val this round
5013 for (int j = 0; j < no_of_gc_threads; j++) {
5014 ChunkArray* cur_sca = &_survivor_plab_array[j];
5015 if (_cursor[j] == cur_sca->end()) {
5016 continue;
5017 }
5018 assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
5019 HeapWord* cur_val = cur_sca->nth(_cursor[j]);
5020 assert(surv->used_region().contains(cur_val), "Out of bounds value");
5021 if (cur_val < min_val) {
5022 min_tid = j;
5023 min_val = cur_val;
5024 } else {
5025 assert(cur_val < top, "All recorded addresses should be less");
5026 }
5027 }
5028 // At this point min_val and min_tid are respectively
5029 // the least address in _survivor_plab_array[j]->nth(_cursor[j])
5030 // and the thread (j) that witnesses that address.
5031 // We record this address in the _survivor_chunk_array[i]
5032 // and increment _cursor[min_tid] prior to the next round i.
5033 if (min_val == top) {
5034 break;
5035 }
5036 _survivor_chunk_array[i] = min_val;
5037 _cursor[min_tid]++;
5038 }
5039 // We are all done; record the size of the _survivor_chunk_array
5040 _survivor_chunk_index = i; // exclusive: [0, i)
5041 if (PrintCMSStatistics > 0) {
5042 gclog_or_tty->print(" (Survivor:" SIZE_FORMAT "chunks) ", i);
5043 }
5044 // Verify that we used up all the recorded entries
5045 #ifdef ASSERT
5046 size_t total = 0;
5047 for (int j = 0; j < no_of_gc_threads; j++) {
5048 assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
5049 total += _cursor[j];
5050 }
5051 assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
5052 // Check that the merged array is in sorted order
5053 if (total > 0) {
5054 for (size_t i = 0; i < total - 1; i++) {
5055 if (PrintCMSStatistics > 0) {
5056 gclog_or_tty->print(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
5057 i, p2i(_survivor_chunk_array[i]));
5058 }
5059 assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
5060 "Not sorted");
5061 }
5062 }
5063 #endif // ASSERT
5064 }
5065
5066 // Set up the space's par_seq_tasks structure for work claiming
5067 // for parallel initial scan and rescan of young gen.
5068 // See ParRescanTask where this is currently used.
5069 void
5070 CMSCollector::
5071 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
5072 assert(n_threads > 0, "Unexpected n_threads argument");
5073
5074 // Eden space
5075 if (!_young_gen->eden()->is_empty()) {
5076 SequentialSubTasksDone* pst = _young_gen->eden()->par_seq_tasks();
5077 assert(!pst->valid(), "Clobbering existing data?");
5078 // Each valid entry in [0, _eden_chunk_index) represents a task.
5079 size_t n_tasks = _eden_chunk_index + 1;
5080 assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
5081 // Sets the condition for completion of the subtask (how many threads
5082 // need to finish in order to be done).
5083 pst->set_n_threads(n_threads);
5084 pst->set_n_tasks((int)n_tasks);
5085 }
5086
5087 // Merge the survivor plab arrays into _survivor_chunk_array
5088 if (_survivor_plab_array != NULL) {
5089 merge_survivor_plab_arrays(_young_gen->from(), n_threads);
5090 } else {
5091 assert(_survivor_chunk_index == 0, "Error");
5092 }
5093
5094 // To space
5095 {
5096 SequentialSubTasksDone* pst = _young_gen->to()->par_seq_tasks();
5097 assert(!pst->valid(), "Clobbering existing data?");
5098 // Sets the condition for completion of the subtask (how many threads
5099 // need to finish in order to be done).
5100 pst->set_n_threads(n_threads);
5101 pst->set_n_tasks(1);
5102 assert(pst->valid(), "Error");
5103 }
5104
5105 // From space
5106 {
5107 SequentialSubTasksDone* pst = _young_gen->from()->par_seq_tasks();
5108 assert(!pst->valid(), "Clobbering existing data?");
5109 size_t n_tasks = _survivor_chunk_index + 1;
5110 assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
5111 // Sets the condition for completion of the subtask (how many threads
5112 // need to finish in order to be done).
5113 pst->set_n_threads(n_threads);
5114 pst->set_n_tasks((int)n_tasks);
5115 assert(pst->valid(), "Error");
5116 }
5117 }
5118
5119 // Parallel version of remark
5120 void CMSCollector::do_remark_parallel() {
5121 GenCollectedHeap* gch = GenCollectedHeap::heap();
5122 FlexibleWorkGang* workers = gch->workers();
5123 assert(workers != NULL, "Need parallel worker threads.");
5124 // Choose to use the number of GC workers most recently set
5125 // into "active_workers". If active_workers is not set, set it
5126 // to ParallelGCThreads.
5127 int n_workers = workers->active_workers();
5128 if (n_workers == 0) {
5129 assert(n_workers > 0, "Should have been set during scavenge");
5130 n_workers = ParallelGCThreads;
5131 workers->set_active_workers(n_workers);
5132 }
5133 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
5134
5135 CMSParRemarkTask tsk(this,
5136 cms_space,
5137 n_workers, workers, task_queues());
5138
5139 // Set up for parallel process_roots work.
5140 gch->set_par_threads(n_workers);
5141 // We won't be iterating over the cards in the card table updating
5142 // the younger_gen cards, so we shouldn't call the following else
5143 // the verification code as well as subsequent younger_refs_iterate
5144 // code would get confused. XXX
5145 // gch->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
5146
5147 // The young gen rescan work will not be done as part of
5148 // process_roots (which currently doesn't know how to
5149 // parallelize such a scan), but rather will be broken up into
5150 // a set of parallel tasks (via the sampling that the [abortable]
5151 // preclean phase did of eden, plus the [two] tasks of
5152 // scanning the [two] survivor spaces. Further fine-grain
5153 // parallelization of the scanning of the survivor spaces
5154 // themselves, and of precleaning of the younger gen itself
5155 // is deferred to the future.
5156 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
5157
5158 // The dirty card rescan work is broken up into a "sequence"
5159 // of parallel tasks (per constituent space) that are dynamically
5160 // claimed by the parallel threads.
5161 cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
5162
5163 // It turns out that even when we're using 1 thread, doing the work in a
5164 // separate thread causes wide variance in run times. We can't help this
5165 // in the multi-threaded case, but we special-case n=1 here to get
5166 // repeatable measurements of the 1-thread overhead of the parallel code.
5167 if (n_workers > 1) {
5168 // Make refs discovery MT-safe, if it isn't already: it may not
5169 // necessarily be so, since it's possible that we are doing
5170 // ST marking.
5171 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), true);
5172 GenCollectedHeap::StrongRootsScope srs;
5173 workers->run_task(&tsk);
5174 } else {
5175 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5176 GenCollectedHeap::StrongRootsScope srs;
5177 tsk.work(0);
5178 }
5179
5180 gch->set_par_threads(0); // 0 ==> non-parallel.
5181 // restore, single-threaded for now, any preserved marks
5182 // as a result of work_q overflow
5183 restore_preserved_marks_if_any();
5184 }
5185
5186 // Non-parallel version of remark
5187 void CMSCollector::do_remark_non_parallel() {
5188 ResourceMark rm;
5189 HandleMark hm;
5190 GenCollectedHeap* gch = GenCollectedHeap::heap();
5191 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5192
5193 MarkRefsIntoAndScanClosure
5194 mrias_cl(_span, ref_processor(), &_markBitMap, NULL /* not precleaning */,
5195 &_markStack, this,
5196 false /* should_yield */, false /* not precleaning */);
5197 MarkFromDirtyCardsClosure
5198 markFromDirtyCardsClosure(this, _span,
5199 NULL, // space is set further below
5200 &_markBitMap, &_markStack, &mrias_cl);
5201 {
5202 GCTraceTime t("grey object rescan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5203 // Iterate over the dirty cards, setting the corresponding bits in the
5204 // mod union table.
5205 {
5206 ModUnionClosure modUnionClosure(&_modUnionTable);
5207 _ct->ct_bs()->dirty_card_iterate(
5208 _cmsGen->used_region(),
5209 &modUnionClosure);
5210 }
5211 // Having transferred these marks into the modUnionTable, we just need
5212 // to rescan the marked objects on the dirty cards in the modUnionTable.
5213 // The initial marking may have been done during an asynchronous
5214 // collection so there may be dirty bits in the mod-union table.
5215 const int alignment =
5216 CardTableModRefBS::card_size * BitsPerWord;
5217 {
5218 // ... First handle dirty cards in CMS gen
5219 markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
5220 MemRegion ur = _cmsGen->used_region();
5221 HeapWord* lb = ur.start();
5222 HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
5223 MemRegion cms_span(lb, ub);
5224 _modUnionTable.dirty_range_iterate_clear(cms_span,
5225 &markFromDirtyCardsClosure);
5226 verify_work_stacks_empty();
5227 if (PrintCMSStatistics != 0) {
5228 gclog_or_tty->print(" (re-scanned "SIZE_FORMAT" dirty cards in cms gen) ",
5229 markFromDirtyCardsClosure.num_dirty_cards());
5230 }
5231 }
5232 }
5233 if (VerifyDuringGC &&
5234 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5235 HandleMark hm; // Discard invalid handles created during verification
5236 Universe::verify();
5237 }
5238 {
5239 GCTraceTime t("root rescan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5240
5241 verify_work_stacks_empty();
5242
5243 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
5244 GenCollectedHeap::StrongRootsScope srs;
5245
5246 gch->gen_process_roots(_cmsGen->level(),
5247 true, // younger gens as roots
5248 false, // use the local StrongRootsScope
5249 GenCollectedHeap::ScanningOption(roots_scanning_options()),
5250 should_unload_classes(),
5251 &mrias_cl,
5252 NULL,
5253 NULL); // The dirty klasses will be handled below
5254
5255 assert(should_unload_classes()
5256 || (roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
5257 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5258 }
5259
5260 {
5261 GCTraceTime t("visit unhandled CLDs", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5262
5263 verify_work_stacks_empty();
5264
5265 // Scan all class loader data objects that might have been introduced
5266 // during concurrent marking.
5267 ResourceMark rm;
5268 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
5269 for (int i = 0; i < array->length(); i++) {
5270 mrias_cl.do_class_loader_data(array->at(i));
5271 }
5272
5273 // We don't need to keep track of new CLDs anymore.
5274 ClassLoaderDataGraph::remember_new_clds(false);
5275
5276 verify_work_stacks_empty();
5277 }
5278
5279 {
5280 GCTraceTime t("dirty klass scan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5281
5282 verify_work_stacks_empty();
5283
5284 RemarkKlassClosure remark_klass_closure(&mrias_cl);
5285 ClassLoaderDataGraph::classes_do(&remark_klass_closure);
5286
5287 verify_work_stacks_empty();
5288 }
5289
5290 // We might have added oops to ClassLoaderData::_handles during the
5291 // concurrent marking phase. These oops point to newly allocated objects
5292 // that are guaranteed to be kept alive. Either by the direct allocation
5293 // code, or when the young collector processes the roots. Hence,
5294 // we don't have to revisit the _handles block during the remark phase.
5295
5296 verify_work_stacks_empty();
5297 // Restore evacuated mark words, if any, used for overflow list links
5298 if (!CMSOverflowEarlyRestoration) {
5299 restore_preserved_marks_if_any();
5300 }
5301 verify_overflow_empty();
5302 }
5303
5304 ////////////////////////////////////////////////////////
5305 // Parallel Reference Processing Task Proxy Class
5306 ////////////////////////////////////////////////////////
5307 class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues {
5308 typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
5309 CMSCollector* _collector;
5310 CMSBitMap* _mark_bit_map;
5311 const MemRegion _span;
5312 ProcessTask& _task;
5313
5314 public:
5315 CMSRefProcTaskProxy(ProcessTask& task,
5316 CMSCollector* collector,
5317 const MemRegion& span,
5318 CMSBitMap* mark_bit_map,
5319 AbstractWorkGang* workers,
5320 OopTaskQueueSet* task_queues):
5321 // XXX Should superclass AGTWOQ also know about AWG since it knows
5322 // about the task_queues used by the AWG? Then it could initialize
5323 // the terminator() object. See 6984287. The set_for_termination()
5324 // below is a temporary band-aid for the regression in 6984287.
5325 AbstractGangTaskWOopQueues("Process referents by policy in parallel",
5326 task_queues),
5327 _task(task),
5328 _collector(collector), _span(span), _mark_bit_map(mark_bit_map)
5329 {
5330 assert(_collector->_span.equals(_span) && !_span.is_empty(),
5331 "Inconsistency in _span");
5332 set_for_termination(workers->active_workers());
5333 }
5334
5335 OopTaskQueueSet* task_queues() { return queues(); }
5336
5337 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5338
5339 void do_work_steal(int i,
5340 CMSParDrainMarkingStackClosure* drain,
5341 CMSParKeepAliveClosure* keep_alive,
5342 int* seed);
5343
5344 virtual void work(uint worker_id);
5345 };
5346
5347 void CMSRefProcTaskProxy::work(uint worker_id) {
5348 ResourceMark rm;
5349 HandleMark hm;
5350 assert(_collector->_span.equals(_span), "Inconsistency in _span");
5351 CMSParKeepAliveClosure par_keep_alive(_collector, _span,
5352 _mark_bit_map,
5353 work_queue(worker_id));
5354 CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
5355 _mark_bit_map,
5356 work_queue(worker_id));
5357 CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
5358 _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack);
5359 if (_task.marks_oops_alive()) {
5360 do_work_steal(worker_id, &par_drain_stack, &par_keep_alive,
5361 _collector->hash_seed(worker_id));
5362 }
5363 assert(work_queue(worker_id)->size() == 0, "work_queue should be empty");
5364 assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
5365 }
5366
5367 class CMSRefEnqueueTaskProxy: public AbstractGangTask {
5368 typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
5369 EnqueueTask& _task;
5370
5371 public:
5372 CMSRefEnqueueTaskProxy(EnqueueTask& task)
5373 : AbstractGangTask("Enqueue reference objects in parallel"),
5374 _task(task)
5375 { }
5376
5377 virtual void work(uint worker_id)
5378 {
5379 _task.work(worker_id);
5380 }
5381 };
5382
5383 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
5384 MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue):
5385 _span(span),
5386 _bit_map(bit_map),
5387 _work_queue(work_queue),
5388 _mark_and_push(collector, span, bit_map, work_queue),
5389 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
5390 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads)))
5391 { }
5392
5393 // . see if we can share work_queues with ParNew? XXX
5394 void CMSRefProcTaskProxy::do_work_steal(int i,
5395 CMSParDrainMarkingStackClosure* drain,
5396 CMSParKeepAliveClosure* keep_alive,
5397 int* seed) {
5398 OopTaskQueue* work_q = work_queue(i);
5399 NOT_PRODUCT(int num_steals = 0;)
5400 oop obj_to_scan;
5401
5402 while (true) {
5403 // Completely finish any left over work from (an) earlier round(s)
5404 drain->trim_queue(0);
5405 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5406 (size_t)ParGCDesiredObjsFromOverflowList);
5407 // Now check if there's any work in the overflow list
5408 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5409 // only affects the number of attempts made to get work from the
5410 // overflow list and does not affect the number of workers. Just
5411 // pass ParallelGCThreads so this behavior is unchanged.
5412 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5413 work_q,
5414 ParallelGCThreads)) {
5415 // Found something in global overflow list;
5416 // not yet ready to go stealing work from others.
5417 // We'd like to assert(work_q->size() != 0, ...)
5418 // because we just took work from the overflow list,
5419 // but of course we can't, since all of that might have
5420 // been already stolen from us.
5421 continue;
5422 }
5423 // Verify that we have no work before we resort to stealing
5424 assert(work_q->size() == 0, "Have work, shouldn't steal");
5425 // Try to steal from other queues that have work
5426 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5427 NOT_PRODUCT(num_steals++;)
5428 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5429 assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5430 // Do scanning work
5431 obj_to_scan->oop_iterate(keep_alive);
5432 // Loop around, finish this work, and try to steal some more
5433 } else if (terminator()->offer_termination()) {
5434 break; // nirvana from the infinite cycle
5435 }
5436 }
5437 NOT_PRODUCT(
5438 if (PrintCMSStatistics != 0) {
5439 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5440 }
5441 )
5442 }
5443
5444 void CMSRefProcTaskExecutor::execute(ProcessTask& task)
5445 {
5446 GenCollectedHeap* gch = GenCollectedHeap::heap();
5447 FlexibleWorkGang* workers = gch->workers();
5448 assert(workers != NULL, "Need parallel worker threads.");
5449 CMSRefProcTaskProxy rp_task(task, &_collector,
5450 _collector.ref_processor()->span(),
5451 _collector.markBitMap(),
5452 workers, _collector.task_queues());
5453 workers->run_task(&rp_task);
5454 }
5455
5456 void CMSRefProcTaskExecutor::execute(EnqueueTask& task)
5457 {
5458
5459 GenCollectedHeap* gch = GenCollectedHeap::heap();
5460 FlexibleWorkGang* workers = gch->workers();
5461 assert(workers != NULL, "Need parallel worker threads.");
5462 CMSRefEnqueueTaskProxy enq_task(task);
5463 workers->run_task(&enq_task);
5464 }
5465
5466 void CMSCollector::refProcessingWork() {
5467 ResourceMark rm;
5468 HandleMark hm;
5469
5470 ReferenceProcessor* rp = ref_processor();
5471 assert(rp->span().equals(_span), "Spans should be equal");
5472 assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
5473 // Process weak references.
5474 rp->setup_policy(false);
5475 verify_work_stacks_empty();
5476
5477 CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
5478 &_markStack, false /* !preclean */);
5479 CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
5480 _span, &_markBitMap, &_markStack,
5481 &cmsKeepAliveClosure, false /* !preclean */);
5482 {
5483 GCTraceTime t("weak refs processing", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5484
5485 ReferenceProcessorStats stats;
5486 if (rp->processing_is_mt()) {
5487 // Set the degree of MT here. If the discovery is done MT, there
5488 // may have been a different number of threads doing the discovery
5489 // and a different number of discovered lists may have Ref objects.
5490 // That is OK as long as the Reference lists are balanced (see
5491 // balance_all_queues() and balance_queues()).
5492 GenCollectedHeap* gch = GenCollectedHeap::heap();
5493 int active_workers = ParallelGCThreads;
5494 FlexibleWorkGang* workers = gch->workers();
5495 if (workers != NULL) {
5496 active_workers = workers->active_workers();
5497 // The expectation is that active_workers will have already
5498 // been set to a reasonable value. If it has not been set,
5499 // investigate.
5500 assert(active_workers > 0, "Should have been set during scavenge");
5501 }
5502 rp->set_active_mt_degree(active_workers);
5503 CMSRefProcTaskExecutor task_executor(*this);
5504 stats = rp->process_discovered_references(&_is_alive_closure,
5505 &cmsKeepAliveClosure,
5506 &cmsDrainMarkingStackClosure,
5507 &task_executor,
5508 _gc_timer_cm,
5509 _gc_tracer_cm->gc_id());
5510 } else {
5511 stats = rp->process_discovered_references(&_is_alive_closure,
5512 &cmsKeepAliveClosure,
5513 &cmsDrainMarkingStackClosure,
5514 NULL,
5515 _gc_timer_cm,
5516 _gc_tracer_cm->gc_id());
5517 }
5518 _gc_tracer_cm->report_gc_reference_stats(stats);
5519
5520 }
5521
5522 // This is the point where the entire marking should have completed.
5523 verify_work_stacks_empty();
5524
5525 if (should_unload_classes()) {
5526 {
5527 GCTraceTime t("class unloading", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5528
5529 // Unload classes and purge the SystemDictionary.
5530 bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure);
5531
5532 // Unload nmethods.
5533 CodeCache::do_unloading(&_is_alive_closure, purged_class);
5534
5535 // Prune dead klasses from subklass/sibling/implementor lists.
5536 Klass::clean_weak_klass_links(&_is_alive_closure);
5537 }
5538
5539 {
5540 GCTraceTime t("scrub symbol table", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5541 // Clean up unreferenced symbols in symbol table.
5542 SymbolTable::unlink();
5543 }
5544
5545 {
5546 GCTraceTime t("scrub string table", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5547 // Delete entries for dead interned strings.
5548 StringTable::unlink(&_is_alive_closure);
5549 }
5550 }
5551
5552
5553 // Restore any preserved marks as a result of mark stack or
5554 // work queue overflow
5555 restore_preserved_marks_if_any(); // done single-threaded for now
5556
5557 rp->set_enqueuing_is_done(true);
5558 if (rp->processing_is_mt()) {
5559 rp->balance_all_queues();
5560 CMSRefProcTaskExecutor task_executor(*this);
5561 rp->enqueue_discovered_references(&task_executor);
5562 } else {
5563 rp->enqueue_discovered_references(NULL);
5564 }
5565 rp->verify_no_references_recorded();
5566 assert(!rp->discovery_enabled(), "should have been disabled");
5567 }
5568
5569 #ifndef PRODUCT
5570 void CMSCollector::check_correct_thread_executing() {
5571 Thread* t = Thread::current();
5572 // Only the VM thread or the CMS thread should be here.
5573 assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
5574 "Unexpected thread type");
5575 // If this is the vm thread, the foreground process
5576 // should not be waiting. Note that _foregroundGCIsActive is
5577 // true while the foreground collector is waiting.
5578 if (_foregroundGCShouldWait) {
5579 // We cannot be the VM thread
5580 assert(t->is_ConcurrentGC_thread(),
5581 "Should be CMS thread");
5582 } else {
5583 // We can be the CMS thread only if we are in a stop-world
5584 // phase of CMS collection.
5585 if (t->is_ConcurrentGC_thread()) {
5586 assert(_collectorState == InitialMarking ||
5587 _collectorState == FinalMarking,
5588 "Should be a stop-world phase");
5589 // The CMS thread should be holding the CMS_token.
5590 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5591 "Potential interference with concurrently "
5592 "executing VM thread");
5593 }
5594 }
5595 }
5596 #endif
5597
5598 void CMSCollector::sweep() {
5599 assert(_collectorState == Sweeping, "just checking");
5600 check_correct_thread_executing();
5601 verify_work_stacks_empty();
5602 verify_overflow_empty();
5603 increment_sweep_count();
5604 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
5605
5606 _inter_sweep_timer.stop();
5607 _inter_sweep_estimate.sample(_inter_sweep_timer.seconds());
5608
5609 assert(!_intra_sweep_timer.is_active(), "Should not be active");
5610 _intra_sweep_timer.reset();
5611 _intra_sweep_timer.start();
5612 {
5613 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
5614 CMSPhaseAccounting pa(this, "sweep", _gc_tracer_cm->gc_id(), !PrintGCDetails);
5615 // First sweep the old gen
5616 {
5617 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
5618 bitMapLock());
5619 sweepWork(_cmsGen);
5620 }
5621
5622 // Update Universe::_heap_*_at_gc figures.
5623 // We need all the free list locks to make the abstract state
5624 // transition from Sweeping to Resetting. See detailed note
5625 // further below.
5626 {
5627 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock());
5628 // Update heap occupancy information which is used as
5629 // input to soft ref clearing policy at the next gc.
5630 Universe::update_heap_info_at_gc();
5631 _collectorState = Resizing;
5632 }
5633 }
5634 verify_work_stacks_empty();
5635 verify_overflow_empty();
5636
5637 if (should_unload_classes()) {
5638 // Delay purge to the beginning of the next safepoint. Metaspace::contains
5639 // requires that the virtual spaces are stable and not deleted.
5640 ClassLoaderDataGraph::set_should_purge(true);
5641 }
5642
5643 _intra_sweep_timer.stop();
5644 _intra_sweep_estimate.sample(_intra_sweep_timer.seconds());
5645
5646 _inter_sweep_timer.reset();
5647 _inter_sweep_timer.start();
5648
5649 // We need to use a monotonically non-decreasing time in ms
5650 // or we will see time-warp warnings and os::javaTimeMillis()
5651 // does not guarantee monotonicity.
5652 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
5653 update_time_of_last_gc(now);
5654
5655 // NOTE on abstract state transitions:
5656 // Mutators allocate-live and/or mark the mod-union table dirty
5657 // based on the state of the collection. The former is done in
5658 // the interval [Marking, Sweeping] and the latter in the interval
5659 // [Marking, Sweeping). Thus the transitions into the Marking state
5660 // and out of the Sweeping state must be synchronously visible
5661 // globally to the mutators.
5662 // The transition into the Marking state happens with the world
5663 // stopped so the mutators will globally see it. Sweeping is
5664 // done asynchronously by the background collector so the transition
5665 // from the Sweeping state to the Resizing state must be done
5666 // under the freelistLock (as is the check for whether to
5667 // allocate-live and whether to dirty the mod-union table).
5668 assert(_collectorState == Resizing, "Change of collector state to"
5669 " Resizing must be done under the freelistLocks (plural)");
5670
5671 // Now that sweeping has been completed, we clear
5672 // the incremental_collection_failed flag,
5673 // thus inviting a younger gen collection to promote into
5674 // this generation. If such a promotion may still fail,
5675 // the flag will be set again when a young collection is
5676 // attempted.
5677 GenCollectedHeap* gch = GenCollectedHeap::heap();
5678 gch->clear_incremental_collection_failed(); // Worth retrying as fresh space may have been freed up
5679 gch->update_full_collections_completed(_collection_count_start);
5680 }
5681
5682 // FIX ME!!! Looks like this belongs in CFLSpace, with
5683 // CMSGen merely delegating to it.
5684 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
5685 double nearLargestPercent = FLSLargestBlockCoalesceProximity;
5686 HeapWord* minAddr = _cmsSpace->bottom();
5687 HeapWord* largestAddr =
5688 (HeapWord*) _cmsSpace->dictionary()->find_largest_dict();
5689 if (largestAddr == NULL) {
5690 // The dictionary appears to be empty. In this case
5691 // try to coalesce at the end of the heap.
5692 largestAddr = _cmsSpace->end();
5693 }
5694 size_t largestOffset = pointer_delta(largestAddr, minAddr);
5695 size_t nearLargestOffset =
5696 (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
5697 if (PrintFLSStatistics != 0) {
5698 gclog_or_tty->print_cr(
5699 "CMS: Large Block: " PTR_FORMAT ";"
5700 " Proximity: " PTR_FORMAT " -> " PTR_FORMAT,
5701 p2i(largestAddr),
5702 p2i(_cmsSpace->nearLargestChunk()), p2i(minAddr + nearLargestOffset));
5703 }
5704 _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
5705 }
5706
5707 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
5708 return addr >= _cmsSpace->nearLargestChunk();
5709 }
5710
5711 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
5712 return _cmsSpace->find_chunk_at_end();
5713 }
5714
5715 void ConcurrentMarkSweepGeneration::update_gc_stats(int current_level,
5716 bool full) {
5717 // The next lower level has been collected. Gather any statistics
5718 // that are of interest at this point.
5719 if (!full && (current_level + 1) == level()) {
5720 // Gather statistics on the young generation collection.
5721 collector()->stats().record_gc0_end(used());
5722 }
5723 }
5724
5725 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* gen) {
5726 // We iterate over the space(s) underlying this generation,
5727 // checking the mark bit map to see if the bits corresponding
5728 // to specific blocks are marked or not. Blocks that are
5729 // marked are live and are not swept up. All remaining blocks
5730 // are swept up, with coalescing on-the-fly as we sweep up
5731 // contiguous free and/or garbage blocks:
5732 // We need to ensure that the sweeper synchronizes with allocators
5733 // and stop-the-world collectors. In particular, the following
5734 // locks are used:
5735 // . CMS token: if this is held, a stop the world collection cannot occur
5736 // . freelistLock: if this is held no allocation can occur from this
5737 // generation by another thread
5738 // . bitMapLock: if this is held, no other thread can access or update
5739 //
5740
5741 // Note that we need to hold the freelistLock if we use
5742 // block iterate below; else the iterator might go awry if
5743 // a mutator (or promotion) causes block contents to change
5744 // (for instance if the allocator divvies up a block).
5745 // If we hold the free list lock, for all practical purposes
5746 // young generation GC's can't occur (they'll usually need to
5747 // promote), so we might as well prevent all young generation
5748 // GC's while we do a sweeping step. For the same reason, we might
5749 // as well take the bit map lock for the entire duration
5750
5751 // check that we hold the requisite locks
5752 assert(have_cms_token(), "Should hold cms token");
5753 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), "Should possess CMS token to sweep");
5754 assert_lock_strong(gen->freelistLock());
5755 assert_lock_strong(bitMapLock());
5756
5757 assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context");
5758 assert(_intra_sweep_timer.is_active(), "Was switched on in an outer context");
5759 gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
5760 _inter_sweep_estimate.padded_average(),
5761 _intra_sweep_estimate.padded_average());
5762 gen->setNearLargestChunk();
5763
5764 {
5765 SweepClosure sweepClosure(this, gen, &_markBitMap, CMSYield);
5766 gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
5767 // We need to free-up/coalesce garbage/blocks from a
5768 // co-terminal free run. This is done in the SweepClosure
5769 // destructor; so, do not remove this scope, else the
5770 // end-of-sweep-census below will be off by a little bit.
5771 }
5772 gen->cmsSpace()->sweep_completed();
5773 gen->cmsSpace()->endSweepFLCensus(sweep_count());
5774 if (should_unload_classes()) { // unloaded classes this cycle,
5775 _concurrent_cycles_since_last_unload = 0; // ... reset count
5776 } else { // did not unload classes,
5777 _concurrent_cycles_since_last_unload++; // ... increment count
5778 }
5779 }
5780
5781 // Reset CMS data structures (for now just the marking bit map)
5782 // preparatory for the next cycle.
5783 void CMSCollector::reset(bool concurrent) {
5784 if (concurrent) {
5785 CMSTokenSyncWithLocks ts(true, bitMapLock());
5786
5787 // If the state is not "Resetting", the foreground thread
5788 // has done a collection and the resetting.
5789 if (_collectorState != Resetting) {
5790 assert(_collectorState == Idling, "The state should only change"
5791 " because the foreground collector has finished the collection");
5792 return;
5793 }
5794
5795 // Clear the mark bitmap (no grey objects to start with)
5796 // for the next cycle.
5797 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
5798 CMSPhaseAccounting cmspa(this, "reset", _gc_tracer_cm->gc_id(), !PrintGCDetails);
5799
5800 HeapWord* curAddr = _markBitMap.startWord();
5801 while (curAddr < _markBitMap.endWord()) {
5802 size_t remaining = pointer_delta(_markBitMap.endWord(), curAddr);
5803 MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
5804 _markBitMap.clear_large_range(chunk);
5805 if (ConcurrentMarkSweepThread::should_yield() &&
5806 !foregroundGCIsActive() &&
5807 CMSYield) {
5808 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5809 "CMS thread should hold CMS token");
5810 assert_lock_strong(bitMapLock());
5811 bitMapLock()->unlock();
5812 ConcurrentMarkSweepThread::desynchronize(true);
5813 stopTimer();
5814 if (PrintCMSStatistics != 0) {
5815 incrementYields();
5816 }
5817
5818 // See the comment in coordinator_yield()
5819 for (unsigned i = 0; i < CMSYieldSleepCount &&
5820 ConcurrentMarkSweepThread::should_yield() &&
5821 !CMSCollector::foregroundGCIsActive(); ++i) {
5822 os::sleep(Thread::current(), 1, false);
5823 }
5824
5825 ConcurrentMarkSweepThread::synchronize(true);
5826 bitMapLock()->lock_without_safepoint_check();
5827 startTimer();
5828 }
5829 curAddr = chunk.end();
5830 }
5831 // A successful mostly concurrent collection has been done.
5832 // Because only the full (i.e., concurrent mode failure) collections
5833 // are being measured for gc overhead limits, clean the "near" flag
5834 // and count.
5835 size_policy()->reset_gc_overhead_limit_count();
5836 _collectorState = Idling;
5837 } else {
5838 // already have the lock
5839 assert(_collectorState == Resetting, "just checking");
5840 assert_lock_strong(bitMapLock());
5841 _markBitMap.clear_all();
5842 _collectorState = Idling;
5843 }
5844
5845 register_gc_end();
5846 }
5847
5848 void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) {
5849 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
5850 GCTraceTime t(GCCauseString("GC", gc_cause), PrintGC, !PrintGCDetails, NULL, _gc_tracer_cm->gc_id());
5851 TraceCollectorStats tcs(counters());
5852
5853 switch (op) {
5854 case CMS_op_checkpointRootsInitial: {
5855 SvcGCMarker sgcm(SvcGCMarker::OTHER);
5856 checkpointRootsInitial();
5857 if (PrintGC) {
5858 _cmsGen->printOccupancy("initial-mark");
5859 }
5860 break;
5861 }
5862 case CMS_op_checkpointRootsFinal: {
5863 SvcGCMarker sgcm(SvcGCMarker::OTHER);
5864 checkpointRootsFinal();
5865 if (PrintGC) {
5866 _cmsGen->printOccupancy("remark");
5867 }
5868 break;
5869 }
5870 default:
5871 fatal("No such CMS_op");
5872 }
5873 }
5874
5875 #ifndef PRODUCT
5876 size_t const CMSCollector::skip_header_HeapWords() {
5877 return FreeChunk::header_size();
5878 }
5879
5880 // Try and collect here conditions that should hold when
5881 // CMS thread is exiting. The idea is that the foreground GC
5882 // thread should not be blocked if it wants to terminate
5883 // the CMS thread and yet continue to run the VM for a while
5884 // after that.
5885 void CMSCollector::verify_ok_to_terminate() const {
5886 assert(Thread::current()->is_ConcurrentGC_thread(),
5887 "should be called by CMS thread");
5888 assert(!_foregroundGCShouldWait, "should be false");
5889 // We could check here that all the various low-level locks
5890 // are not held by the CMS thread, but that is overkill; see
5891 // also CMSThread::verify_ok_to_terminate() where the CGC_lock
5892 // is checked.
5893 }
5894 #endif
5895
5896 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
5897 assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
5898 "missing Printezis mark?");
5899 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5900 size_t size = pointer_delta(nextOneAddr + 1, addr);
5901 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5902 "alignment problem");
5903 assert(size >= 3, "Necessary for Printezis marks to work");
5904 return size;
5905 }
5906
5907 // A variant of the above (block_size_using_printezis_bits()) except
5908 // that we return 0 if the P-bits are not yet set.
5909 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
5910 if (_markBitMap.isMarked(addr + 1)) {
5911 assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects");
5912 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5913 size_t size = pointer_delta(nextOneAddr + 1, addr);
5914 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5915 "alignment problem");
5916 assert(size >= 3, "Necessary for Printezis marks to work");
5917 return size;
5918 }
5919 return 0;
5920 }
5921
5922 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
5923 size_t sz = 0;
5924 oop p = (oop)addr;
5925 if (p->klass_or_null() != NULL) {
5926 sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
5927 } else {
5928 sz = block_size_using_printezis_bits(addr);
5929 }
5930 assert(sz > 0, "size must be nonzero");
5931 HeapWord* next_block = addr + sz;
5932 HeapWord* next_card = (HeapWord*)round_to((uintptr_t)next_block,
5933 CardTableModRefBS::card_size);
5934 assert(round_down((uintptr_t)addr, CardTableModRefBS::card_size) <
5935 round_down((uintptr_t)next_card, CardTableModRefBS::card_size),
5936 "must be different cards");
5937 return next_card;
5938 }
5939
5940
5941 // CMS Bit Map Wrapper /////////////////////////////////////////
5942
5943 // Construct a CMS bit map infrastructure, but don't create the
5944 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
5945 // further below.
5946 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
5947 _bm(),
5948 _shifter(shifter),
5949 _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true,
5950 Monitor::_safepoint_check_sometimes) : NULL)
5951 {
5952 _bmStartWord = 0;
5953 _bmWordSize = 0;
5954 }
5955
5956 bool CMSBitMap::allocate(MemRegion mr) {
5957 _bmStartWord = mr.start();
5958 _bmWordSize = mr.word_size();
5959 ReservedSpace brs(ReservedSpace::allocation_align_size_up(
5960 (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
5961 if (!brs.is_reserved()) {
5962 warning("CMS bit map allocation failure");
5963 return false;
5964 }
5965 // For now we'll just commit all of the bit map up front.
5966 // Later on we'll try to be more parsimonious with swap.
5967 if (!_virtual_space.initialize(brs, brs.size())) {
5968 warning("CMS bit map backing store failure");
5969 return false;
5970 }
5971 assert(_virtual_space.committed_size() == brs.size(),
5972 "didn't reserve backing store for all of CMS bit map?");
5973 _bm.set_map((BitMap::bm_word_t*)_virtual_space.low());
5974 assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
5975 _bmWordSize, "inconsistency in bit map sizing");
5976 _bm.set_size(_bmWordSize >> _shifter);
5977
5978 // bm.clear(); // can we rely on getting zero'd memory? verify below
5979 assert(isAllClear(),
5980 "Expected zero'd memory from ReservedSpace constructor");
5981 assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
5982 "consistency check");
5983 return true;
5984 }
5985
5986 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
5987 HeapWord *next_addr, *end_addr, *last_addr;
5988 assert_locked();
5989 assert(covers(mr), "out-of-range error");
5990 // XXX assert that start and end are appropriately aligned
5991 for (next_addr = mr.start(), end_addr = mr.end();
5992 next_addr < end_addr; next_addr = last_addr) {
5993 MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
5994 last_addr = dirty_region.end();
5995 if (!dirty_region.is_empty()) {
5996 cl->do_MemRegion(dirty_region);
5997 } else {
5998 assert(last_addr == end_addr, "program logic");
5999 return;
6000 }
6001 }
6002 }
6003
6004 void CMSBitMap::print_on_error(outputStream* st, const char* prefix) const {
6005 _bm.print_on_error(st, prefix);
6006 }
6007
6008 #ifndef PRODUCT
6009 void CMSBitMap::assert_locked() const {
6010 CMSLockVerifier::assert_locked(lock());
6011 }
6012
6013 bool CMSBitMap::covers(MemRegion mr) const {
6014 // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
6015 assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
6016 "size inconsistency");
6017 return (mr.start() >= _bmStartWord) &&
6018 (mr.end() <= endWord());
6019 }
6020
6021 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
6022 return (start >= _bmStartWord && (start + size) <= endWord());
6023 }
6024
6025 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
6026 // verify that there are no 1 bits in the interval [left, right)
6027 FalseBitMapClosure falseBitMapClosure;
6028 iterate(&falseBitMapClosure, left, right);
6029 }
6030
6031 void CMSBitMap::region_invariant(MemRegion mr)
6032 {
6033 assert_locked();
6034 // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
6035 assert(!mr.is_empty(), "unexpected empty region");
6036 assert(covers(mr), "mr should be covered by bit map");
6037 // convert address range into offset range
6038 size_t start_ofs = heapWordToOffset(mr.start());
6039 // Make sure that end() is appropriately aligned
6040 assert(mr.end() == (HeapWord*)round_to((intptr_t)mr.end(),
6041 (1 << (_shifter+LogHeapWordSize))),
6042 "Misaligned mr.end()");
6043 size_t end_ofs = heapWordToOffset(mr.end());
6044 assert(end_ofs > start_ofs, "Should mark at least one bit");
6045 }
6046
6047 #endif
6048
6049 bool CMSMarkStack::allocate(size_t size) {
6050 // allocate a stack of the requisite depth
6051 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6052 size * sizeof(oop)));
6053 if (!rs.is_reserved()) {
6054 warning("CMSMarkStack allocation failure");
6055 return false;
6056 }
6057 if (!_virtual_space.initialize(rs, rs.size())) {
6058 warning("CMSMarkStack backing store failure");
6059 return false;
6060 }
6061 assert(_virtual_space.committed_size() == rs.size(),
6062 "didn't reserve backing store for all of CMS stack?");
6063 _base = (oop*)(_virtual_space.low());
6064 _index = 0;
6065 _capacity = size;
6066 NOT_PRODUCT(_max_depth = 0);
6067 return true;
6068 }
6069
6070 // XXX FIX ME !!! In the MT case we come in here holding a
6071 // leaf lock. For printing we need to take a further lock
6072 // which has lower rank. We need to recalibrate the two
6073 // lock-ranks involved in order to be able to print the
6074 // messages below. (Or defer the printing to the caller.
6075 // For now we take the expedient path of just disabling the
6076 // messages for the problematic case.)
6077 void CMSMarkStack::expand() {
6078 assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted");
6079 if (_capacity == MarkStackSizeMax) {
6080 if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6081 // We print a warning message only once per CMS cycle.
6082 gclog_or_tty->print_cr(" (benign) Hit CMSMarkStack max size limit");
6083 }
6084 return;
6085 }
6086 // Double capacity if possible
6087 size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax);
6088 // Do not give up existing stack until we have managed to
6089 // get the double capacity that we desired.
6090 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6091 new_capacity * sizeof(oop)));
6092 if (rs.is_reserved()) {
6093 // Release the backing store associated with old stack
6094 _virtual_space.release();
6095 // Reinitialize virtual space for new stack
6096 if (!_virtual_space.initialize(rs, rs.size())) {
6097 fatal("Not enough swap for expanded marking stack");
6098 }
6099 _base = (oop*)(_virtual_space.low());
6100 _index = 0;
6101 _capacity = new_capacity;
6102 } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6103 // Failed to double capacity, continue;
6104 // we print a detail message only once per CMS cycle.
6105 gclog_or_tty->print(" (benign) Failed to expand marking stack from "SIZE_FORMAT"K to "
6106 SIZE_FORMAT"K",
6107 _capacity / K, new_capacity / K);
6108 }
6109 }
6110
6111
6112 // Closures
6113 // XXX: there seems to be a lot of code duplication here;
6114 // should refactor and consolidate common code.
6115
6116 // This closure is used to mark refs into the CMS generation in
6117 // the CMS bit map. Called at the first checkpoint. This closure
6118 // assumes that we do not need to re-mark dirty cards; if the CMS
6119 // generation on which this is used is not an oldest
6120 // generation then this will lose younger_gen cards!
6121
6122 MarkRefsIntoClosure::MarkRefsIntoClosure(
6123 MemRegion span, CMSBitMap* bitMap):
6124 _span(span),
6125 _bitMap(bitMap)
6126 {
6127 assert(_ref_processor == NULL, "deliberately left NULL");
6128 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6129 }
6130
6131 void MarkRefsIntoClosure::do_oop(oop obj) {
6132 // if p points into _span, then mark corresponding bit in _markBitMap
6133 assert(obj->is_oop(), "expected an oop");
6134 HeapWord* addr = (HeapWord*)obj;
6135 if (_span.contains(addr)) {
6136 // this should be made more efficient
6137 _bitMap->mark(addr);
6138 }
6139 }
6140
6141 void MarkRefsIntoClosure::do_oop(oop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6142 void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6143
6144 Par_MarkRefsIntoClosure::Par_MarkRefsIntoClosure(
6145 MemRegion span, CMSBitMap* bitMap):
6146 _span(span),
6147 _bitMap(bitMap)
6148 {
6149 assert(_ref_processor == NULL, "deliberately left NULL");
6150 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6151 }
6152
6153 void Par_MarkRefsIntoClosure::do_oop(oop obj) {
6154 // if p points into _span, then mark corresponding bit in _markBitMap
6155 assert(obj->is_oop(), "expected an oop");
6156 HeapWord* addr = (HeapWord*)obj;
6157 if (_span.contains(addr)) {
6158 // this should be made more efficient
6159 _bitMap->par_mark(addr);
6160 }
6161 }
6162
6163 void Par_MarkRefsIntoClosure::do_oop(oop* p) { Par_MarkRefsIntoClosure::do_oop_work(p); }
6164 void Par_MarkRefsIntoClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoClosure::do_oop_work(p); }
6165
6166 // A variant of the above, used for CMS marking verification.
6167 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
6168 MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm):
6169 _span(span),
6170 _verification_bm(verification_bm),
6171 _cms_bm(cms_bm)
6172 {
6173 assert(_ref_processor == NULL, "deliberately left NULL");
6174 assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
6175 }
6176
6177 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
6178 // if p points into _span, then mark corresponding bit in _markBitMap
6179 assert(obj->is_oop(), "expected an oop");
6180 HeapWord* addr = (HeapWord*)obj;
6181 if (_span.contains(addr)) {
6182 _verification_bm->mark(addr);
6183 if (!_cms_bm->isMarked(addr)) {
6184 oop(addr)->print();
6185 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
6186 fatal("... aborting");
6187 }
6188 }
6189 }
6190
6191 void MarkRefsIntoVerifyClosure::do_oop(oop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6192 void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6193
6194 //////////////////////////////////////////////////
6195 // MarkRefsIntoAndScanClosure
6196 //////////////////////////////////////////////////
6197
6198 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
6199 ReferenceProcessor* rp,
6200 CMSBitMap* bit_map,
6201 CMSBitMap* mod_union_table,
6202 CMSMarkStack* mark_stack,
6203 CMSCollector* collector,
6204 bool should_yield,
6205 bool concurrent_precleaning):
6206 _collector(collector),
6207 _span(span),
6208 _bit_map(bit_map),
6209 _mark_stack(mark_stack),
6210 _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table,
6211 mark_stack, concurrent_precleaning),
6212 _yield(should_yield),
6213 _concurrent_precleaning(concurrent_precleaning),
6214 _freelistLock(NULL)
6215 {
6216 _ref_processor = rp;
6217 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6218 }
6219
6220 // This closure is used to mark refs into the CMS generation at the
6221 // second (final) checkpoint, and to scan and transitively follow
6222 // the unmarked oops. It is also used during the concurrent precleaning
6223 // phase while scanning objects on dirty cards in the CMS generation.
6224 // The marks are made in the marking bit map and the marking stack is
6225 // used for keeping the (newly) grey objects during the scan.
6226 // The parallel version (Par_...) appears further below.
6227 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6228 if (obj != NULL) {
6229 assert(obj->is_oop(), "expected an oop");
6230 HeapWord* addr = (HeapWord*)obj;
6231 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6232 assert(_collector->overflow_list_is_empty(),
6233 "overflow list should be empty");
6234 if (_span.contains(addr) &&
6235 !_bit_map->isMarked(addr)) {
6236 // mark bit map (object is now grey)
6237 _bit_map->mark(addr);
6238 // push on marking stack (stack should be empty), and drain the
6239 // stack by applying this closure to the oops in the oops popped
6240 // from the stack (i.e. blacken the grey objects)
6241 bool res = _mark_stack->push(obj);
6242 assert(res, "Should have space to push on empty stack");
6243 do {
6244 oop new_oop = _mark_stack->pop();
6245 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6246 assert(_bit_map->isMarked((HeapWord*)new_oop),
6247 "only grey objects on this stack");
6248 // iterate over the oops in this oop, marking and pushing
6249 // the ones in CMS heap (i.e. in _span).
6250 new_oop->oop_iterate(&_pushAndMarkClosure);
6251 // check if it's time to yield
6252 do_yield_check();
6253 } while (!_mark_stack->isEmpty() ||
6254 (!_concurrent_precleaning && take_from_overflow_list()));
6255 // if marking stack is empty, and we are not doing this
6256 // during precleaning, then check the overflow list
6257 }
6258 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6259 assert(_collector->overflow_list_is_empty(),
6260 "overflow list was drained above");
6261 // We could restore evacuated mark words, if any, used for
6262 // overflow list links here because the overflow list is
6263 // provably empty here. That would reduce the maximum
6264 // size requirements for preserved_{oop,mark}_stack.
6265 // But we'll just postpone it until we are all done
6266 // so we can just stream through.
6267 if (!_concurrent_precleaning && CMSOverflowEarlyRestoration) {
6268 _collector->restore_preserved_marks_if_any();
6269 assert(_collector->no_preserved_marks(), "No preserved marks");
6270 }
6271 assert(!CMSOverflowEarlyRestoration || _collector->no_preserved_marks(),
6272 "All preserved marks should have been restored above");
6273 }
6274 }
6275
6276 void MarkRefsIntoAndScanClosure::do_oop(oop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6277 void MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6278
6279 void MarkRefsIntoAndScanClosure::do_yield_work() {
6280 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6281 "CMS thread should hold CMS token");
6282 assert_lock_strong(_freelistLock);
6283 assert_lock_strong(_bit_map->lock());
6284 // relinquish the free_list_lock and bitMaplock()
6285 _bit_map->lock()->unlock();
6286 _freelistLock->unlock();
6287 ConcurrentMarkSweepThread::desynchronize(true);
6288 _collector->stopTimer();
6289 if (PrintCMSStatistics != 0) {
6290 _collector->incrementYields();
6291 }
6292
6293 // See the comment in coordinator_yield()
6294 for (unsigned i = 0;
6295 i < CMSYieldSleepCount &&
6296 ConcurrentMarkSweepThread::should_yield() &&
6297 !CMSCollector::foregroundGCIsActive();
6298 ++i) {
6299 os::sleep(Thread::current(), 1, false);
6300 }
6301
6302 ConcurrentMarkSweepThread::synchronize(true);
6303 _freelistLock->lock_without_safepoint_check();
6304 _bit_map->lock()->lock_without_safepoint_check();
6305 _collector->startTimer();
6306 }
6307
6308 ///////////////////////////////////////////////////////////
6309 // Par_MarkRefsIntoAndScanClosure: a parallel version of
6310 // MarkRefsIntoAndScanClosure
6311 ///////////////////////////////////////////////////////////
6312 Par_MarkRefsIntoAndScanClosure::Par_MarkRefsIntoAndScanClosure(
6313 CMSCollector* collector, MemRegion span, ReferenceProcessor* rp,
6314 CMSBitMap* bit_map, OopTaskQueue* work_queue):
6315 _span(span),
6316 _bit_map(bit_map),
6317 _work_queue(work_queue),
6318 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
6319 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads))),
6320 _par_pushAndMarkClosure(collector, span, rp, bit_map, work_queue)
6321 {
6322 _ref_processor = rp;
6323 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6324 }
6325
6326 // This closure is used to mark refs into the CMS generation at the
6327 // second (final) checkpoint, and to scan and transitively follow
6328 // the unmarked oops. The marks are made in the marking bit map and
6329 // the work_queue is used for keeping the (newly) grey objects during
6330 // the scan phase whence they are also available for stealing by parallel
6331 // threads. Since the marking bit map is shared, updates are
6332 // synchronized (via CAS).
6333 void Par_MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6334 if (obj != NULL) {
6335 // Ignore mark word because this could be an already marked oop
6336 // that may be chained at the end of the overflow list.
6337 assert(obj->is_oop(true), "expected an oop");
6338 HeapWord* addr = (HeapWord*)obj;
6339 if (_span.contains(addr) &&
6340 !_bit_map->isMarked(addr)) {
6341 // mark bit map (object will become grey):
6342 // It is possible for several threads to be
6343 // trying to "claim" this object concurrently;
6344 // the unique thread that succeeds in marking the
6345 // object first will do the subsequent push on
6346 // to the work queue (or overflow list).
6347 if (_bit_map->par_mark(addr)) {
6348 // push on work_queue (which may not be empty), and trim the
6349 // queue to an appropriate length by applying this closure to
6350 // the oops in the oops popped from the stack (i.e. blacken the
6351 // grey objects)
6352 bool res = _work_queue->push(obj);
6353 assert(res, "Low water mark should be less than capacity?");
6354 trim_queue(_low_water_mark);
6355 } // Else, another thread claimed the object
6356 }
6357 }
6358 }
6359
6360 void Par_MarkRefsIntoAndScanClosure::do_oop(oop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6361 void Par_MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6362
6363 // This closure is used to rescan the marked objects on the dirty cards
6364 // in the mod union table and the card table proper.
6365 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
6366 oop p, MemRegion mr) {
6367
6368 size_t size = 0;
6369 HeapWord* addr = (HeapWord*)p;
6370 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6371 assert(_span.contains(addr), "we are scanning the CMS generation");
6372 // check if it's time to yield
6373 if (do_yield_check()) {
6374 // We yielded for some foreground stop-world work,
6375 // and we have been asked to abort this ongoing preclean cycle.
6376 return 0;
6377 }
6378 if (_bitMap->isMarked(addr)) {
6379 // it's marked; is it potentially uninitialized?
6380 if (p->klass_or_null() != NULL) {
6381 // an initialized object; ignore mark word in verification below
6382 // since we are running concurrent with mutators
6383 assert(p->is_oop(true), "should be an oop");
6384 if (p->is_objArray()) {
6385 // objArrays are precisely marked; restrict scanning
6386 // to dirty cards only.
6387 size = CompactibleFreeListSpace::adjustObjectSize(
6388 p->oop_iterate(_scanningClosure, mr));
6389 } else {
6390 // A non-array may have been imprecisely marked; we need
6391 // to scan object in its entirety.
6392 size = CompactibleFreeListSpace::adjustObjectSize(
6393 p->oop_iterate(_scanningClosure));
6394 }
6395 #ifdef ASSERT
6396 size_t direct_size =
6397 CompactibleFreeListSpace::adjustObjectSize(p->size());
6398 assert(size == direct_size, "Inconsistency in size");
6399 assert(size >= 3, "Necessary for Printezis marks to work");
6400 if (!_bitMap->isMarked(addr+1)) {
6401 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size);
6402 } else {
6403 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size-1);
6404 assert(_bitMap->isMarked(addr+size-1),
6405 "inconsistent Printezis mark");
6406 }
6407 #endif // ASSERT
6408 } else {
6409 // An uninitialized object.
6410 assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
6411 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
6412 size = pointer_delta(nextOneAddr + 1, addr);
6413 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6414 "alignment problem");
6415 // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
6416 // will dirty the card when the klass pointer is installed in the
6417 // object (signaling the completion of initialization).
6418 }
6419 } else {
6420 // Either a not yet marked object or an uninitialized object
6421 if (p->klass_or_null() == NULL) {
6422 // An uninitialized object, skip to the next card, since
6423 // we may not be able to read its P-bits yet.
6424 assert(size == 0, "Initial value");
6425 } else {
6426 // An object not (yet) reached by marking: we merely need to
6427 // compute its size so as to go look at the next block.
6428 assert(p->is_oop(true), "should be an oop");
6429 size = CompactibleFreeListSpace::adjustObjectSize(p->size());
6430 }
6431 }
6432 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6433 return size;
6434 }
6435
6436 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
6437 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6438 "CMS thread should hold CMS token");
6439 assert_lock_strong(_freelistLock);
6440 assert_lock_strong(_bitMap->lock());
6441 // relinquish the free_list_lock and bitMaplock()
6442 _bitMap->lock()->unlock();
6443 _freelistLock->unlock();
6444 ConcurrentMarkSweepThread::desynchronize(true);
6445 _collector->stopTimer();
6446 if (PrintCMSStatistics != 0) {
6447 _collector->incrementYields();
6448 }
6449
6450 // See the comment in coordinator_yield()
6451 for (unsigned i = 0; i < CMSYieldSleepCount &&
6452 ConcurrentMarkSweepThread::should_yield() &&
6453 !CMSCollector::foregroundGCIsActive(); ++i) {
6454 os::sleep(Thread::current(), 1, false);
6455 }
6456
6457 ConcurrentMarkSweepThread::synchronize(true);
6458 _freelistLock->lock_without_safepoint_check();
6459 _bitMap->lock()->lock_without_safepoint_check();
6460 _collector->startTimer();
6461 }
6462
6463
6464 //////////////////////////////////////////////////////////////////
6465 // SurvivorSpacePrecleanClosure
6466 //////////////////////////////////////////////////////////////////
6467 // This (single-threaded) closure is used to preclean the oops in
6468 // the survivor spaces.
6469 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
6470
6471 HeapWord* addr = (HeapWord*)p;
6472 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6473 assert(!_span.contains(addr), "we are scanning the survivor spaces");
6474 assert(p->klass_or_null() != NULL, "object should be initialized");
6475 // an initialized object; ignore mark word in verification below
6476 // since we are running concurrent with mutators
6477 assert(p->is_oop(true), "should be an oop");
6478 // Note that we do not yield while we iterate over
6479 // the interior oops of p, pushing the relevant ones
6480 // on our marking stack.
6481 size_t size = p->oop_iterate(_scanning_closure);
6482 do_yield_check();
6483 // Observe that below, we do not abandon the preclean
6484 // phase as soon as we should; rather we empty the
6485 // marking stack before returning. This is to satisfy
6486 // some existing assertions. In general, it may be a
6487 // good idea to abort immediately and complete the marking
6488 // from the grey objects at a later time.
6489 while (!_mark_stack->isEmpty()) {
6490 oop new_oop = _mark_stack->pop();
6491 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6492 assert(_bit_map->isMarked((HeapWord*)new_oop),
6493 "only grey objects on this stack");
6494 // iterate over the oops in this oop, marking and pushing
6495 // the ones in CMS heap (i.e. in _span).
6496 new_oop->oop_iterate(_scanning_closure);
6497 // check if it's time to yield
6498 do_yield_check();
6499 }
6500 unsigned int after_count =
6501 GenCollectedHeap::heap()->total_collections();
6502 bool abort = (_before_count != after_count) ||
6503 _collector->should_abort_preclean();
6504 return abort ? 0 : size;
6505 }
6506
6507 void SurvivorSpacePrecleanClosure::do_yield_work() {
6508 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6509 "CMS thread should hold CMS token");
6510 assert_lock_strong(_bit_map->lock());
6511 // Relinquish the bit map lock
6512 _bit_map->lock()->unlock();
6513 ConcurrentMarkSweepThread::desynchronize(true);
6514 _collector->stopTimer();
6515 if (PrintCMSStatistics != 0) {
6516 _collector->incrementYields();
6517 }
6518
6519 // See the comment in coordinator_yield()
6520 for (unsigned i = 0; i < CMSYieldSleepCount &&
6521 ConcurrentMarkSweepThread::should_yield() &&
6522 !CMSCollector::foregroundGCIsActive(); ++i) {
6523 os::sleep(Thread::current(), 1, false);
6524 }
6525
6526 ConcurrentMarkSweepThread::synchronize(true);
6527 _bit_map->lock()->lock_without_safepoint_check();
6528 _collector->startTimer();
6529 }
6530
6531 // This closure is used to rescan the marked objects on the dirty cards
6532 // in the mod union table and the card table proper. In the parallel
6533 // case, although the bitMap is shared, we do a single read so the
6534 // isMarked() query is "safe".
6535 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
6536 // Ignore mark word because we are running concurrent with mutators
6537 assert(p->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(p)));
6538 HeapWord* addr = (HeapWord*)p;
6539 assert(_span.contains(addr), "we are scanning the CMS generation");
6540 bool is_obj_array = false;
6541 #ifdef ASSERT
6542 if (!_parallel) {
6543 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6544 assert(_collector->overflow_list_is_empty(),
6545 "overflow list should be empty");
6546
6547 }
6548 #endif // ASSERT
6549 if (_bit_map->isMarked(addr)) {
6550 // Obj arrays are precisely marked, non-arrays are not;
6551 // so we scan objArrays precisely and non-arrays in their
6552 // entirety.
6553 if (p->is_objArray()) {
6554 is_obj_array = true;
6555 if (_parallel) {
6556 p->oop_iterate(_par_scan_closure, mr);
6557 } else {
6558 p->oop_iterate(_scan_closure, mr);
6559 }
6560 } else {
6561 if (_parallel) {
6562 p->oop_iterate(_par_scan_closure);
6563 } else {
6564 p->oop_iterate(_scan_closure);
6565 }
6566 }
6567 }
6568 #ifdef ASSERT
6569 if (!_parallel) {
6570 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6571 assert(_collector->overflow_list_is_empty(),
6572 "overflow list should be empty");
6573
6574 }
6575 #endif // ASSERT
6576 return is_obj_array;
6577 }
6578
6579 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
6580 MemRegion span,
6581 CMSBitMap* bitMap, CMSMarkStack* markStack,
6582 bool should_yield, bool verifying):
6583 _collector(collector),
6584 _span(span),
6585 _bitMap(bitMap),
6586 _mut(&collector->_modUnionTable),
6587 _markStack(markStack),
6588 _yield(should_yield),
6589 _skipBits(0)
6590 {
6591 assert(_markStack->isEmpty(), "stack should be empty");
6592 _finger = _bitMap->startWord();
6593 _threshold = _finger;
6594 assert(_collector->_restart_addr == NULL, "Sanity check");
6595 assert(_span.contains(_finger), "Out of bounds _finger?");
6596 DEBUG_ONLY(_verifying = verifying;)
6597 }
6598
6599 void MarkFromRootsClosure::reset(HeapWord* addr) {
6600 assert(_markStack->isEmpty(), "would cause duplicates on stack");
6601 assert(_span.contains(addr), "Out of bounds _finger?");
6602 _finger = addr;
6603 _threshold = (HeapWord*)round_to(
6604 (intptr_t)_finger, CardTableModRefBS::card_size);
6605 }
6606
6607 // Should revisit to see if this should be restructured for
6608 // greater efficiency.
6609 bool MarkFromRootsClosure::do_bit(size_t offset) {
6610 if (_skipBits > 0) {
6611 _skipBits--;
6612 return true;
6613 }
6614 // convert offset into a HeapWord*
6615 HeapWord* addr = _bitMap->startWord() + offset;
6616 assert(_bitMap->endWord() && addr < _bitMap->endWord(),
6617 "address out of range");
6618 assert(_bitMap->isMarked(addr), "tautology");
6619 if (_bitMap->isMarked(addr+1)) {
6620 // this is an allocated but not yet initialized object
6621 assert(_skipBits == 0, "tautology");
6622 _skipBits = 2; // skip next two marked bits ("Printezis-marks")
6623 oop p = oop(addr);
6624 if (p->klass_or_null() == NULL) {
6625 DEBUG_ONLY(if (!_verifying) {)
6626 // We re-dirty the cards on which this object lies and increase
6627 // the _threshold so that we'll come back to scan this object
6628 // during the preclean or remark phase. (CMSCleanOnEnter)
6629 if (CMSCleanOnEnter) {
6630 size_t sz = _collector->block_size_using_printezis_bits(addr);
6631 HeapWord* end_card_addr = (HeapWord*)round_to(
6632 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
6633 MemRegion redirty_range = MemRegion(addr, end_card_addr);
6634 assert(!redirty_range.is_empty(), "Arithmetical tautology");
6635 // Bump _threshold to end_card_addr; note that
6636 // _threshold cannot possibly exceed end_card_addr, anyhow.
6637 // This prevents future clearing of the card as the scan proceeds
6638 // to the right.
6639 assert(_threshold <= end_card_addr,
6640 "Because we are just scanning into this object");
6641 if (_threshold < end_card_addr) {
6642 _threshold = end_card_addr;
6643 }
6644 if (p->klass_or_null() != NULL) {
6645 // Redirty the range of cards...
6646 _mut->mark_range(redirty_range);
6647 } // ...else the setting of klass will dirty the card anyway.
6648 }
6649 DEBUG_ONLY(})
6650 return true;
6651 }
6652 }
6653 scanOopsInOop(addr);
6654 return true;
6655 }
6656
6657 // We take a break if we've been at this for a while,
6658 // so as to avoid monopolizing the locks involved.
6659 void MarkFromRootsClosure::do_yield_work() {
6660 // First give up the locks, then yield, then re-lock
6661 // We should probably use a constructor/destructor idiom to
6662 // do this unlock/lock or modify the MutexUnlocker class to
6663 // serve our purpose. XXX
6664 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6665 "CMS thread should hold CMS token");
6666 assert_lock_strong(_bitMap->lock());
6667 _bitMap->lock()->unlock();
6668 ConcurrentMarkSweepThread::desynchronize(true);
6669 _collector->stopTimer();
6670 if (PrintCMSStatistics != 0) {
6671 _collector->incrementYields();
6672 }
6673
6674 // See the comment in coordinator_yield()
6675 for (unsigned i = 0; i < CMSYieldSleepCount &&
6676 ConcurrentMarkSweepThread::should_yield() &&
6677 !CMSCollector::foregroundGCIsActive(); ++i) {
6678 os::sleep(Thread::current(), 1, false);
6679 }
6680
6681 ConcurrentMarkSweepThread::synchronize(true);
6682 _bitMap->lock()->lock_without_safepoint_check();
6683 _collector->startTimer();
6684 }
6685
6686 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
6687 assert(_bitMap->isMarked(ptr), "expected bit to be set");
6688 assert(_markStack->isEmpty(),
6689 "should drain stack to limit stack usage");
6690 // convert ptr to an oop preparatory to scanning
6691 oop obj = oop(ptr);
6692 // Ignore mark word in verification below, since we
6693 // may be running concurrent with mutators.
6694 assert(obj->is_oop(true), "should be an oop");
6695 assert(_finger <= ptr, "_finger runneth ahead");
6696 // advance the finger to right end of this object
6697 _finger = ptr + obj->size();
6698 assert(_finger > ptr, "we just incremented it above");
6699 // On large heaps, it may take us some time to get through
6700 // the marking phase. During
6701 // this time it's possible that a lot of mutations have
6702 // accumulated in the card table and the mod union table --
6703 // these mutation records are redundant until we have
6704 // actually traced into the corresponding card.
6705 // Here, we check whether advancing the finger would make
6706 // us cross into a new card, and if so clear corresponding
6707 // cards in the MUT (preclean them in the card-table in the
6708 // future).
6709
6710 DEBUG_ONLY(if (!_verifying) {)
6711 // The clean-on-enter optimization is disabled by default,
6712 // until we fix 6178663.
6713 if (CMSCleanOnEnter && (_finger > _threshold)) {
6714 // [_threshold, _finger) represents the interval
6715 // of cards to be cleared in MUT (or precleaned in card table).
6716 // The set of cards to be cleared is all those that overlap
6717 // with the interval [_threshold, _finger); note that
6718 // _threshold is always kept card-aligned but _finger isn't
6719 // always card-aligned.
6720 HeapWord* old_threshold = _threshold;
6721 assert(old_threshold == (HeapWord*)round_to(
6722 (intptr_t)old_threshold, CardTableModRefBS::card_size),
6723 "_threshold should always be card-aligned");
6724 _threshold = (HeapWord*)round_to(
6725 (intptr_t)_finger, CardTableModRefBS::card_size);
6726 MemRegion mr(old_threshold, _threshold);
6727 assert(!mr.is_empty(), "Control point invariant");
6728 assert(_span.contains(mr), "Should clear within span");
6729 _mut->clear_range(mr);
6730 }
6731 DEBUG_ONLY(})
6732 // Note: the finger doesn't advance while we drain
6733 // the stack below.
6734 PushOrMarkClosure pushOrMarkClosure(_collector,
6735 _span, _bitMap, _markStack,
6736 _finger, this);
6737 bool res = _markStack->push(obj);
6738 assert(res, "Empty non-zero size stack should have space for single push");
6739 while (!_markStack->isEmpty()) {
6740 oop new_oop = _markStack->pop();
6741 // Skip verifying header mark word below because we are
6742 // running concurrent with mutators.
6743 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
6744 // now scan this oop's oops
6745 new_oop->oop_iterate(&pushOrMarkClosure);
6746 do_yield_check();
6747 }
6748 assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
6749 }
6750
6751 Par_MarkFromRootsClosure::Par_MarkFromRootsClosure(CMSConcMarkingTask* task,
6752 CMSCollector* collector, MemRegion span,
6753 CMSBitMap* bit_map,
6754 OopTaskQueue* work_queue,
6755 CMSMarkStack* overflow_stack):
6756 _collector(collector),
6757 _whole_span(collector->_span),
6758 _span(span),
6759 _bit_map(bit_map),
6760 _mut(&collector->_modUnionTable),
6761 _work_queue(work_queue),
6762 _overflow_stack(overflow_stack),
6763 _skip_bits(0),
6764 _task(task)
6765 {
6766 assert(_work_queue->size() == 0, "work_queue should be empty");
6767 _finger = span.start();
6768 _threshold = _finger; // XXX Defer clear-on-enter optimization for now
6769 assert(_span.contains(_finger), "Out of bounds _finger?");
6770 }
6771
6772 // Should revisit to see if this should be restructured for
6773 // greater efficiency.
6774 bool Par_MarkFromRootsClosure::do_bit(size_t offset) {
6775 if (_skip_bits > 0) {
6776 _skip_bits--;
6777 return true;
6778 }
6779 // convert offset into a HeapWord*
6780 HeapWord* addr = _bit_map->startWord() + offset;
6781 assert(_bit_map->endWord() && addr < _bit_map->endWord(),
6782 "address out of range");
6783 assert(_bit_map->isMarked(addr), "tautology");
6784 if (_bit_map->isMarked(addr+1)) {
6785 // this is an allocated object that might not yet be initialized
6786 assert(_skip_bits == 0, "tautology");
6787 _skip_bits = 2; // skip next two marked bits ("Printezis-marks")
6788 oop p = oop(addr);
6789 if (p->klass_or_null() == NULL) {
6790 // in the case of Clean-on-Enter optimization, redirty card
6791 // and avoid clearing card by increasing the threshold.
6792 return true;
6793 }
6794 }
6795 scan_oops_in_oop(addr);
6796 return true;
6797 }
6798
6799 void Par_MarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
6800 assert(_bit_map->isMarked(ptr), "expected bit to be set");
6801 // Should we assert that our work queue is empty or
6802 // below some drain limit?
6803 assert(_work_queue->size() == 0,
6804 "should drain stack to limit stack usage");
6805 // convert ptr to an oop preparatory to scanning
6806 oop obj = oop(ptr);
6807 // Ignore mark word in verification below, since we
6808 // may be running concurrent with mutators.
6809 assert(obj->is_oop(true), "should be an oop");
6810 assert(_finger <= ptr, "_finger runneth ahead");
6811 // advance the finger to right end of this object
6812 _finger = ptr + obj->size();
6813 assert(_finger > ptr, "we just incremented it above");
6814 // On large heaps, it may take us some time to get through
6815 // the marking phase. During
6816 // this time it's possible that a lot of mutations have
6817 // accumulated in the card table and the mod union table --
6818 // these mutation records are redundant until we have
6819 // actually traced into the corresponding card.
6820 // Here, we check whether advancing the finger would make
6821 // us cross into a new card, and if so clear corresponding
6822 // cards in the MUT (preclean them in the card-table in the
6823 // future).
6824
6825 // The clean-on-enter optimization is disabled by default,
6826 // until we fix 6178663.
6827 if (CMSCleanOnEnter && (_finger > _threshold)) {
6828 // [_threshold, _finger) represents the interval
6829 // of cards to be cleared in MUT (or precleaned in card table).
6830 // The set of cards to be cleared is all those that overlap
6831 // with the interval [_threshold, _finger); note that
6832 // _threshold is always kept card-aligned but _finger isn't
6833 // always card-aligned.
6834 HeapWord* old_threshold = _threshold;
6835 assert(old_threshold == (HeapWord*)round_to(
6836 (intptr_t)old_threshold, CardTableModRefBS::card_size),
6837 "_threshold should always be card-aligned");
6838 _threshold = (HeapWord*)round_to(
6839 (intptr_t)_finger, CardTableModRefBS::card_size);
6840 MemRegion mr(old_threshold, _threshold);
6841 assert(!mr.is_empty(), "Control point invariant");
6842 assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
6843 _mut->clear_range(mr);
6844 }
6845
6846 // Note: the local finger doesn't advance while we drain
6847 // the stack below, but the global finger sure can and will.
6848 HeapWord** gfa = _task->global_finger_addr();
6849 Par_PushOrMarkClosure pushOrMarkClosure(_collector,
6850 _span, _bit_map,
6851 _work_queue,
6852 _overflow_stack,
6853 _finger,
6854 gfa, this);
6855 bool res = _work_queue->push(obj); // overflow could occur here
6856 assert(res, "Will hold once we use workqueues");
6857 while (true) {
6858 oop new_oop;
6859 if (!_work_queue->pop_local(new_oop)) {
6860 // We emptied our work_queue; check if there's stuff that can
6861 // be gotten from the overflow stack.
6862 if (CMSConcMarkingTask::get_work_from_overflow_stack(
6863 _overflow_stack, _work_queue)) {
6864 do_yield_check();
6865 continue;
6866 } else { // done
6867 break;
6868 }
6869 }
6870 // Skip verifying header mark word below because we are
6871 // running concurrent with mutators.
6872 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
6873 // now scan this oop's oops
6874 new_oop->oop_iterate(&pushOrMarkClosure);
6875 do_yield_check();
6876 }
6877 assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
6878 }
6879
6880 // Yield in response to a request from VM Thread or
6881 // from mutators.
6882 void Par_MarkFromRootsClosure::do_yield_work() {
6883 assert(_task != NULL, "sanity");
6884 _task->yield();
6885 }
6886
6887 // A variant of the above used for verifying CMS marking work.
6888 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
6889 MemRegion span,
6890 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6891 CMSMarkStack* mark_stack):
6892 _collector(collector),
6893 _span(span),
6894 _verification_bm(verification_bm),
6895 _cms_bm(cms_bm),
6896 _mark_stack(mark_stack),
6897 _pam_verify_closure(collector, span, verification_bm, cms_bm,
6898 mark_stack)
6899 {
6900 assert(_mark_stack->isEmpty(), "stack should be empty");
6901 _finger = _verification_bm->startWord();
6902 assert(_collector->_restart_addr == NULL, "Sanity check");
6903 assert(_span.contains(_finger), "Out of bounds _finger?");
6904 }
6905
6906 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
6907 assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
6908 assert(_span.contains(addr), "Out of bounds _finger?");
6909 _finger = addr;
6910 }
6911
6912 // Should revisit to see if this should be restructured for
6913 // greater efficiency.
6914 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
6915 // convert offset into a HeapWord*
6916 HeapWord* addr = _verification_bm->startWord() + offset;
6917 assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
6918 "address out of range");
6919 assert(_verification_bm->isMarked(addr), "tautology");
6920 assert(_cms_bm->isMarked(addr), "tautology");
6921
6922 assert(_mark_stack->isEmpty(),
6923 "should drain stack to limit stack usage");
6924 // convert addr to an oop preparatory to scanning
6925 oop obj = oop(addr);
6926 assert(obj->is_oop(), "should be an oop");
6927 assert(_finger <= addr, "_finger runneth ahead");
6928 // advance the finger to right end of this object
6929 _finger = addr + obj->size();
6930 assert(_finger > addr, "we just incremented it above");
6931 // Note: the finger doesn't advance while we drain
6932 // the stack below.
6933 bool res = _mark_stack->push(obj);
6934 assert(res, "Empty non-zero size stack should have space for single push");
6935 while (!_mark_stack->isEmpty()) {
6936 oop new_oop = _mark_stack->pop();
6937 assert(new_oop->is_oop(), "Oops! expected to pop an oop");
6938 // now scan this oop's oops
6939 new_oop->oop_iterate(&_pam_verify_closure);
6940 }
6941 assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
6942 return true;
6943 }
6944
6945 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
6946 CMSCollector* collector, MemRegion span,
6947 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6948 CMSMarkStack* mark_stack):
6949 MetadataAwareOopClosure(collector->ref_processor()),
6950 _collector(collector),
6951 _span(span),
6952 _verification_bm(verification_bm),
6953 _cms_bm(cms_bm),
6954 _mark_stack(mark_stack)
6955 { }
6956
6957 void PushAndMarkVerifyClosure::do_oop(oop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
6958 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
6959
6960 // Upon stack overflow, we discard (part of) the stack,
6961 // remembering the least address amongst those discarded
6962 // in CMSCollector's _restart_address.
6963 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
6964 // Remember the least grey address discarded
6965 HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
6966 _collector->lower_restart_addr(ra);
6967 _mark_stack->reset(); // discard stack contents
6968 _mark_stack->expand(); // expand the stack if possible
6969 }
6970
6971 void PushAndMarkVerifyClosure::do_oop(oop obj) {
6972 assert(obj->is_oop_or_null(), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
6973 HeapWord* addr = (HeapWord*)obj;
6974 if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
6975 // Oop lies in _span and isn't yet grey or black
6976 _verification_bm->mark(addr); // now grey
6977 if (!_cms_bm->isMarked(addr)) {
6978 oop(addr)->print();
6979 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)",
6980 p2i(addr));
6981 fatal("... aborting");
6982 }
6983
6984 if (!_mark_stack->push(obj)) { // stack overflow
6985 if (PrintCMSStatistics != 0) {
6986 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
6987 SIZE_FORMAT, _mark_stack->capacity());
6988 }
6989 assert(_mark_stack->isFull(), "Else push should have succeeded");
6990 handle_stack_overflow(addr);
6991 }
6992 // anything including and to the right of _finger
6993 // will be scanned as we iterate over the remainder of the
6994 // bit map
6995 }
6996 }
6997
6998 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
6999 MemRegion span,
7000 CMSBitMap* bitMap, CMSMarkStack* markStack,
7001 HeapWord* finger, MarkFromRootsClosure* parent) :
7002 MetadataAwareOopClosure(collector->ref_processor()),
7003 _collector(collector),
7004 _span(span),
7005 _bitMap(bitMap),
7006 _markStack(markStack),
7007 _finger(finger),
7008 _parent(parent)
7009 { }
7010
7011 Par_PushOrMarkClosure::Par_PushOrMarkClosure(CMSCollector* collector,
7012 MemRegion span,
7013 CMSBitMap* bit_map,
7014 OopTaskQueue* work_queue,
7015 CMSMarkStack* overflow_stack,
7016 HeapWord* finger,
7017 HeapWord** global_finger_addr,
7018 Par_MarkFromRootsClosure* parent) :
7019 MetadataAwareOopClosure(collector->ref_processor()),
7020 _collector(collector),
7021 _whole_span(collector->_span),
7022 _span(span),
7023 _bit_map(bit_map),
7024 _work_queue(work_queue),
7025 _overflow_stack(overflow_stack),
7026 _finger(finger),
7027 _global_finger_addr(global_finger_addr),
7028 _parent(parent)
7029 { }
7030
7031 // Assumes thread-safe access by callers, who are
7032 // responsible for mutual exclusion.
7033 void CMSCollector::lower_restart_addr(HeapWord* low) {
7034 assert(_span.contains(low), "Out of bounds addr");
7035 if (_restart_addr == NULL) {
7036 _restart_addr = low;
7037 } else {
7038 _restart_addr = MIN2(_restart_addr, low);
7039 }
7040 }
7041
7042 // Upon stack overflow, we discard (part of) the stack,
7043 // remembering the least address amongst those discarded
7044 // in CMSCollector's _restart_address.
7045 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7046 // Remember the least grey address discarded
7047 HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
7048 _collector->lower_restart_addr(ra);
7049 _markStack->reset(); // discard stack contents
7050 _markStack->expand(); // expand the stack if possible
7051 }
7052
7053 // Upon stack overflow, we discard (part of) the stack,
7054 // remembering the least address amongst those discarded
7055 // in CMSCollector's _restart_address.
7056 void Par_PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7057 // We need to do this under a mutex to prevent other
7058 // workers from interfering with the work done below.
7059 MutexLockerEx ml(_overflow_stack->par_lock(),
7060 Mutex::_no_safepoint_check_flag);
7061 // Remember the least grey address discarded
7062 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
7063 _collector->lower_restart_addr(ra);
7064 _overflow_stack->reset(); // discard stack contents
7065 _overflow_stack->expand(); // expand the stack if possible
7066 }
7067
7068 void PushOrMarkClosure::do_oop(oop obj) {
7069 // Ignore mark word because we are running concurrent with mutators.
7070 assert(obj->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7071 HeapWord* addr = (HeapWord*)obj;
7072 if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
7073 // Oop lies in _span and isn't yet grey or black
7074 _bitMap->mark(addr); // now grey
7075 if (addr < _finger) {
7076 // the bit map iteration has already either passed, or
7077 // sampled, this bit in the bit map; we'll need to
7078 // use the marking stack to scan this oop's oops.
7079 bool simulate_overflow = false;
7080 NOT_PRODUCT(
7081 if (CMSMarkStackOverflowALot &&
7082 _collector->simulate_overflow()) {
7083 // simulate a stack overflow
7084 simulate_overflow = true;
7085 }
7086 )
7087 if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
7088 if (PrintCMSStatistics != 0) {
7089 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7090 SIZE_FORMAT, _markStack->capacity());
7091 }
7092 assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
7093 handle_stack_overflow(addr);
7094 }
7095 }
7096 // anything including and to the right of _finger
7097 // will be scanned as we iterate over the remainder of the
7098 // bit map
7099 do_yield_check();
7100 }
7101 }
7102
7103 void PushOrMarkClosure::do_oop(oop* p) { PushOrMarkClosure::do_oop_work(p); }
7104 void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); }
7105
7106 void Par_PushOrMarkClosure::do_oop(oop obj) {
7107 // Ignore mark word because we are running concurrent with mutators.
7108 assert(obj->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7109 HeapWord* addr = (HeapWord*)obj;
7110 if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
7111 // Oop lies in _span and isn't yet grey or black
7112 // We read the global_finger (volatile read) strictly after marking oop
7113 bool res = _bit_map->par_mark(addr); // now grey
7114 volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
7115 // Should we push this marked oop on our stack?
7116 // -- if someone else marked it, nothing to do
7117 // -- if target oop is above global finger nothing to do
7118 // -- if target oop is in chunk and above local finger
7119 // then nothing to do
7120 // -- else push on work queue
7121 if ( !res // someone else marked it, they will deal with it
7122 || (addr >= *gfa) // will be scanned in a later task
7123 || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
7124 return;
7125 }
7126 // the bit map iteration has already either passed, or
7127 // sampled, this bit in the bit map; we'll need to
7128 // use the marking stack to scan this oop's oops.
7129 bool simulate_overflow = false;
7130 NOT_PRODUCT(
7131 if (CMSMarkStackOverflowALot &&
7132 _collector->simulate_overflow()) {
7133 // simulate a stack overflow
7134 simulate_overflow = true;
7135 }
7136 )
7137 if (simulate_overflow ||
7138 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
7139 // stack overflow
7140 if (PrintCMSStatistics != 0) {
7141 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7142 SIZE_FORMAT, _overflow_stack->capacity());
7143 }
7144 // We cannot assert that the overflow stack is full because
7145 // it may have been emptied since.
7146 assert(simulate_overflow ||
7147 _work_queue->size() == _work_queue->max_elems(),
7148 "Else push should have succeeded");
7149 handle_stack_overflow(addr);
7150 }
7151 do_yield_check();
7152 }
7153 }
7154
7155 void Par_PushOrMarkClosure::do_oop(oop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7156 void Par_PushOrMarkClosure::do_oop(narrowOop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7157
7158 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
7159 MemRegion span,
7160 ReferenceProcessor* rp,
7161 CMSBitMap* bit_map,
7162 CMSBitMap* mod_union_table,
7163 CMSMarkStack* mark_stack,
7164 bool concurrent_precleaning):
7165 MetadataAwareOopClosure(rp),
7166 _collector(collector),
7167 _span(span),
7168 _bit_map(bit_map),
7169 _mod_union_table(mod_union_table),
7170 _mark_stack(mark_stack),
7171 _concurrent_precleaning(concurrent_precleaning)
7172 {
7173 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7174 }
7175
7176 // Grey object rescan during pre-cleaning and second checkpoint phases --
7177 // the non-parallel version (the parallel version appears further below.)
7178 void PushAndMarkClosure::do_oop(oop obj) {
7179 // Ignore mark word verification. If during concurrent precleaning,
7180 // the object monitor may be locked. If during the checkpoint
7181 // phases, the object may already have been reached by a different
7182 // path and may be at the end of the global overflow list (so
7183 // the mark word may be NULL).
7184 assert(obj->is_oop_or_null(true /* ignore mark word */),
7185 err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7186 HeapWord* addr = (HeapWord*)obj;
7187 // Check if oop points into the CMS generation
7188 // and is not marked
7189 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7190 // a white object ...
7191 _bit_map->mark(addr); // ... now grey
7192 // push on the marking stack (grey set)
7193 bool simulate_overflow = false;
7194 NOT_PRODUCT(
7195 if (CMSMarkStackOverflowALot &&
7196 _collector->simulate_overflow()) {
7197 // simulate a stack overflow
7198 simulate_overflow = true;
7199 }
7200 )
7201 if (simulate_overflow || !_mark_stack->push(obj)) {
7202 if (_concurrent_precleaning) {
7203 // During precleaning we can just dirty the appropriate card(s)
7204 // in the mod union table, thus ensuring that the object remains
7205 // in the grey set and continue. In the case of object arrays
7206 // we need to dirty all of the cards that the object spans,
7207 // since the rescan of object arrays will be limited to the
7208 // dirty cards.
7209 // Note that no one can be interfering with us in this action
7210 // of dirtying the mod union table, so no locking or atomics
7211 // are required.
7212 if (obj->is_objArray()) {
7213 size_t sz = obj->size();
7214 HeapWord* end_card_addr = (HeapWord*)round_to(
7215 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7216 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7217 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7218 _mod_union_table->mark_range(redirty_range);
7219 } else {
7220 _mod_union_table->mark(addr);
7221 }
7222 _collector->_ser_pmc_preclean_ovflw++;
7223 } else {
7224 // During the remark phase, we need to remember this oop
7225 // in the overflow list.
7226 _collector->push_on_overflow_list(obj);
7227 _collector->_ser_pmc_remark_ovflw++;
7228 }
7229 }
7230 }
7231 }
7232
7233 Par_PushAndMarkClosure::Par_PushAndMarkClosure(CMSCollector* collector,
7234 MemRegion span,
7235 ReferenceProcessor* rp,
7236 CMSBitMap* bit_map,
7237 OopTaskQueue* work_queue):
7238 MetadataAwareOopClosure(rp),
7239 _collector(collector),
7240 _span(span),
7241 _bit_map(bit_map),
7242 _work_queue(work_queue)
7243 {
7244 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7245 }
7246
7247 void PushAndMarkClosure::do_oop(oop* p) { PushAndMarkClosure::do_oop_work(p); }
7248 void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); }
7249
7250 // Grey object rescan during second checkpoint phase --
7251 // the parallel version.
7252 void Par_PushAndMarkClosure::do_oop(oop obj) {
7253 // In the assert below, we ignore the mark word because
7254 // this oop may point to an already visited object that is
7255 // on the overflow stack (in which case the mark word has
7256 // been hijacked for chaining into the overflow stack --
7257 // if this is the last object in the overflow stack then
7258 // its mark word will be NULL). Because this object may
7259 // have been subsequently popped off the global overflow
7260 // stack, and the mark word possibly restored to the prototypical
7261 // value, by the time we get to examined this failing assert in
7262 // the debugger, is_oop_or_null(false) may subsequently start
7263 // to hold.
7264 assert(obj->is_oop_or_null(true),
7265 err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7266 HeapWord* addr = (HeapWord*)obj;
7267 // Check if oop points into the CMS generation
7268 // and is not marked
7269 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7270 // a white object ...
7271 // If we manage to "claim" the object, by being the
7272 // first thread to mark it, then we push it on our
7273 // marking stack
7274 if (_bit_map->par_mark(addr)) { // ... now grey
7275 // push on work queue (grey set)
7276 bool simulate_overflow = false;
7277 NOT_PRODUCT(
7278 if (CMSMarkStackOverflowALot &&
7279 _collector->par_simulate_overflow()) {
7280 // simulate a stack overflow
7281 simulate_overflow = true;
7282 }
7283 )
7284 if (simulate_overflow || !_work_queue->push(obj)) {
7285 _collector->par_push_on_overflow_list(obj);
7286 _collector->_par_pmc_remark_ovflw++; // imprecise OK: no need to CAS
7287 }
7288 } // Else, some other thread got there first
7289 }
7290 }
7291
7292 void Par_PushAndMarkClosure::do_oop(oop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7293 void Par_PushAndMarkClosure::do_oop(narrowOop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7294
7295 void CMSPrecleanRefsYieldClosure::do_yield_work() {
7296 Mutex* bml = _collector->bitMapLock();
7297 assert_lock_strong(bml);
7298 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7299 "CMS thread should hold CMS token");
7300
7301 bml->unlock();
7302 ConcurrentMarkSweepThread::desynchronize(true);
7303
7304 _collector->stopTimer();
7305 if (PrintCMSStatistics != 0) {
7306 _collector->incrementYields();
7307 }
7308
7309 // See the comment in coordinator_yield()
7310 for (unsigned i = 0; i < CMSYieldSleepCount &&
7311 ConcurrentMarkSweepThread::should_yield() &&
7312 !CMSCollector::foregroundGCIsActive(); ++i) {
7313 os::sleep(Thread::current(), 1, false);
7314 }
7315
7316 ConcurrentMarkSweepThread::synchronize(true);
7317 bml->lock();
7318
7319 _collector->startTimer();
7320 }
7321
7322 bool CMSPrecleanRefsYieldClosure::should_return() {
7323 if (ConcurrentMarkSweepThread::should_yield()) {
7324 do_yield_work();
7325 }
7326 return _collector->foregroundGCIsActive();
7327 }
7328
7329 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
7330 assert(((size_t)mr.start())%CardTableModRefBS::card_size_in_words == 0,
7331 "mr should be aligned to start at a card boundary");
7332 // We'd like to assert:
7333 // assert(mr.word_size()%CardTableModRefBS::card_size_in_words == 0,
7334 // "mr should be a range of cards");
7335 // However, that would be too strong in one case -- the last
7336 // partition ends at _unallocated_block which, in general, can be
7337 // an arbitrary boundary, not necessarily card aligned.
7338 if (PrintCMSStatistics != 0) {
7339 _num_dirty_cards +=
7340 mr.word_size()/CardTableModRefBS::card_size_in_words;
7341 }
7342 _space->object_iterate_mem(mr, &_scan_cl);
7343 }
7344
7345 SweepClosure::SweepClosure(CMSCollector* collector,
7346 ConcurrentMarkSweepGeneration* g,
7347 CMSBitMap* bitMap, bool should_yield) :
7348 _collector(collector),
7349 _g(g),
7350 _sp(g->cmsSpace()),
7351 _limit(_sp->sweep_limit()),
7352 _freelistLock(_sp->freelistLock()),
7353 _bitMap(bitMap),
7354 _yield(should_yield),
7355 _inFreeRange(false), // No free range at beginning of sweep
7356 _freeRangeInFreeLists(false), // No free range at beginning of sweep
7357 _lastFreeRangeCoalesced(false),
7358 _freeFinger(g->used_region().start())
7359 {
7360 NOT_PRODUCT(
7361 _numObjectsFreed = 0;
7362 _numWordsFreed = 0;
7363 _numObjectsLive = 0;
7364 _numWordsLive = 0;
7365 _numObjectsAlreadyFree = 0;
7366 _numWordsAlreadyFree = 0;
7367 _last_fc = NULL;
7368
7369 _sp->initializeIndexedFreeListArrayReturnedBytes();
7370 _sp->dictionary()->initialize_dict_returned_bytes();
7371 )
7372 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7373 "sweep _limit out of bounds");
7374 if (CMSTraceSweeper) {
7375 gclog_or_tty->print_cr("\n====================\nStarting new sweep with limit " PTR_FORMAT,
7376 p2i(_limit));
7377 }
7378 }
7379
7380 void SweepClosure::print_on(outputStream* st) const {
7381 tty->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")",
7382 p2i(_sp->bottom()), p2i(_sp->end()));
7383 tty->print_cr("_limit = " PTR_FORMAT, p2i(_limit));
7384 tty->print_cr("_freeFinger = " PTR_FORMAT, p2i(_freeFinger));
7385 NOT_PRODUCT(tty->print_cr("_last_fc = " PTR_FORMAT, p2i(_last_fc));)
7386 tty->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d",
7387 _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced);
7388 }
7389
7390 #ifndef PRODUCT
7391 // Assertion checking only: no useful work in product mode --
7392 // however, if any of the flags below become product flags,
7393 // you may need to review this code to see if it needs to be
7394 // enabled in product mode.
7395 SweepClosure::~SweepClosure() {
7396 assert_lock_strong(_freelistLock);
7397 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7398 "sweep _limit out of bounds");
7399 if (inFreeRange()) {
7400 warning("inFreeRange() should have been reset; dumping state of SweepClosure");
7401 print();
7402 ShouldNotReachHere();
7403 }
7404 if (Verbose && PrintGC) {
7405 gclog_or_tty->print("Collected "SIZE_FORMAT" objects, " SIZE_FORMAT " bytes",
7406 _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
7407 gclog_or_tty->print_cr("\nLive "SIZE_FORMAT" objects, "
7408 SIZE_FORMAT" bytes "
7409 "Already free "SIZE_FORMAT" objects, "SIZE_FORMAT" bytes",
7410 _numObjectsLive, _numWordsLive*sizeof(HeapWord),
7411 _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
7412 size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree)
7413 * sizeof(HeapWord);
7414 gclog_or_tty->print_cr("Total sweep: "SIZE_FORMAT" bytes", totalBytes);
7415
7416 if (PrintCMSStatistics && CMSVerifyReturnedBytes) {
7417 size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
7418 size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes();
7419 size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes;
7420 gclog_or_tty->print("Returned "SIZE_FORMAT" bytes", returned_bytes);
7421 gclog_or_tty->print(" Indexed List Returned "SIZE_FORMAT" bytes",
7422 indexListReturnedBytes);
7423 gclog_or_tty->print_cr(" Dictionary Returned "SIZE_FORMAT" bytes",
7424 dict_returned_bytes);
7425 }
7426 }
7427 if (CMSTraceSweeper) {
7428 gclog_or_tty->print_cr("end of sweep with _limit = " PTR_FORMAT "\n================",
7429 p2i(_limit));
7430 }
7431 }
7432 #endif // PRODUCT
7433
7434 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
7435 bool freeRangeInFreeLists) {
7436 if (CMSTraceSweeper) {
7437 gclog_or_tty->print("---- Start free range at " PTR_FORMAT " with free block (%d)\n",
7438 p2i(freeFinger), freeRangeInFreeLists);
7439 }
7440 assert(!inFreeRange(), "Trampling existing free range");
7441 set_inFreeRange(true);
7442 set_lastFreeRangeCoalesced(false);
7443
7444 set_freeFinger(freeFinger);
7445 set_freeRangeInFreeLists(freeRangeInFreeLists);
7446 if (CMSTestInFreeList) {
7447 if (freeRangeInFreeLists) {
7448 FreeChunk* fc = (FreeChunk*) freeFinger;
7449 assert(fc->is_free(), "A chunk on the free list should be free.");
7450 assert(fc->size() > 0, "Free range should have a size");
7451 assert(_sp->verify_chunk_in_free_list(fc), "Chunk is not in free lists");
7452 }
7453 }
7454 }
7455
7456 // Note that the sweeper runs concurrently with mutators. Thus,
7457 // it is possible for direct allocation in this generation to happen
7458 // in the middle of the sweep. Note that the sweeper also coalesces
7459 // contiguous free blocks. Thus, unless the sweeper and the allocator
7460 // synchronize appropriately freshly allocated blocks may get swept up.
7461 // This is accomplished by the sweeper locking the free lists while
7462 // it is sweeping. Thus blocks that are determined to be free are
7463 // indeed free. There is however one additional complication:
7464 // blocks that have been allocated since the final checkpoint and
7465 // mark, will not have been marked and so would be treated as
7466 // unreachable and swept up. To prevent this, the allocator marks
7467 // the bit map when allocating during the sweep phase. This leads,
7468 // however, to a further complication -- objects may have been allocated
7469 // but not yet initialized -- in the sense that the header isn't yet
7470 // installed. The sweeper can not then determine the size of the block
7471 // in order to skip over it. To deal with this case, we use a technique
7472 // (due to Printezis) to encode such uninitialized block sizes in the
7473 // bit map. Since the bit map uses a bit per every HeapWord, but the
7474 // CMS generation has a minimum object size of 3 HeapWords, it follows
7475 // that "normal marks" won't be adjacent in the bit map (there will
7476 // always be at least two 0 bits between successive 1 bits). We make use
7477 // of these "unused" bits to represent uninitialized blocks -- the bit
7478 // corresponding to the start of the uninitialized object and the next
7479 // bit are both set. Finally, a 1 bit marks the end of the object that
7480 // started with the two consecutive 1 bits to indicate its potentially
7481 // uninitialized state.
7482
7483 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
7484 FreeChunk* fc = (FreeChunk*)addr;
7485 size_t res;
7486
7487 // Check if we are done sweeping. Below we check "addr >= _limit" rather
7488 // than "addr == _limit" because although _limit was a block boundary when
7489 // we started the sweep, it may no longer be one because heap expansion
7490 // may have caused us to coalesce the block ending at the address _limit
7491 // with a newly expanded chunk (this happens when _limit was set to the
7492 // previous _end of the space), so we may have stepped past _limit:
7493 // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740.
7494 if (addr >= _limit) { // we have swept up to or past the limit: finish up
7495 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7496 "sweep _limit out of bounds");
7497 assert(addr < _sp->end(), "addr out of bounds");
7498 // Flush any free range we might be holding as a single
7499 // coalesced chunk to the appropriate free list.
7500 if (inFreeRange()) {
7501 assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit,
7502 err_msg("freeFinger() " PTR_FORMAT" is out-of-bounds", p2i(freeFinger())));
7503 flush_cur_free_chunk(freeFinger(),
7504 pointer_delta(addr, freeFinger()));
7505 if (CMSTraceSweeper) {
7506 gclog_or_tty->print("Sweep: last chunk: ");
7507 gclog_or_tty->print("put_free_blk " PTR_FORMAT " ("SIZE_FORMAT") "
7508 "[coalesced:%d]\n",
7509 p2i(freeFinger()), pointer_delta(addr, freeFinger()),
7510 lastFreeRangeCoalesced() ? 1 : 0);
7511 }
7512 }
7513
7514 // help the iterator loop finish
7515 return pointer_delta(_sp->end(), addr);
7516 }
7517
7518 assert(addr < _limit, "sweep invariant");
7519 // check if we should yield
7520 do_yield_check(addr);
7521 if (fc->is_free()) {
7522 // Chunk that is already free
7523 res = fc->size();
7524 do_already_free_chunk(fc);
7525 debug_only(_sp->verifyFreeLists());
7526 // If we flush the chunk at hand in lookahead_and_flush()
7527 // and it's coalesced with a preceding chunk, then the
7528 // process of "mangling" the payload of the coalesced block
7529 // will cause erasure of the size information from the
7530 // (erstwhile) header of all the coalesced blocks but the
7531 // first, so the first disjunct in the assert will not hold
7532 // in that specific case (in which case the second disjunct
7533 // will hold).
7534 assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit,
7535 "Otherwise the size info doesn't change at this step");
7536 NOT_PRODUCT(
7537 _numObjectsAlreadyFree++;
7538 _numWordsAlreadyFree += res;
7539 )
7540 NOT_PRODUCT(_last_fc = fc;)
7541 } else if (!_bitMap->isMarked(addr)) {
7542 // Chunk is fresh garbage
7543 res = do_garbage_chunk(fc);
7544 debug_only(_sp->verifyFreeLists());
7545 NOT_PRODUCT(
7546 _numObjectsFreed++;
7547 _numWordsFreed += res;
7548 )
7549 } else {
7550 // Chunk that is alive.
7551 res = do_live_chunk(fc);
7552 debug_only(_sp->verifyFreeLists());
7553 NOT_PRODUCT(
7554 _numObjectsLive++;
7555 _numWordsLive += res;
7556 )
7557 }
7558 return res;
7559 }
7560
7561 // For the smart allocation, record following
7562 // split deaths - a free chunk is removed from its free list because
7563 // it is being split into two or more chunks.
7564 // split birth - a free chunk is being added to its free list because
7565 // a larger free chunk has been split and resulted in this free chunk.
7566 // coal death - a free chunk is being removed from its free list because
7567 // it is being coalesced into a large free chunk.
7568 // coal birth - a free chunk is being added to its free list because
7569 // it was created when two or more free chunks where coalesced into
7570 // this free chunk.
7571 //
7572 // These statistics are used to determine the desired number of free
7573 // chunks of a given size. The desired number is chosen to be relative
7574 // to the end of a CMS sweep. The desired number at the end of a sweep
7575 // is the
7576 // count-at-end-of-previous-sweep (an amount that was enough)
7577 // - count-at-beginning-of-current-sweep (the excess)
7578 // + split-births (gains in this size during interval)
7579 // - split-deaths (demands on this size during interval)
7580 // where the interval is from the end of one sweep to the end of the
7581 // next.
7582 //
7583 // When sweeping the sweeper maintains an accumulated chunk which is
7584 // the chunk that is made up of chunks that have been coalesced. That
7585 // will be termed the left-hand chunk. A new chunk of garbage that
7586 // is being considered for coalescing will be referred to as the
7587 // right-hand chunk.
7588 //
7589 // When making a decision on whether to coalesce a right-hand chunk with
7590 // the current left-hand chunk, the current count vs. the desired count
7591 // of the left-hand chunk is considered. Also if the right-hand chunk
7592 // is near the large chunk at the end of the heap (see
7593 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
7594 // left-hand chunk is coalesced.
7595 //
7596 // When making a decision about whether to split a chunk, the desired count
7597 // vs. the current count of the candidate to be split is also considered.
7598 // If the candidate is underpopulated (currently fewer chunks than desired)
7599 // a chunk of an overpopulated (currently more chunks than desired) size may
7600 // be chosen. The "hint" associated with a free list, if non-null, points
7601 // to a free list which may be overpopulated.
7602 //
7603
7604 void SweepClosure::do_already_free_chunk(FreeChunk* fc) {
7605 const size_t size = fc->size();
7606 // Chunks that cannot be coalesced are not in the
7607 // free lists.
7608 if (CMSTestInFreeList && !fc->cantCoalesce()) {
7609 assert(_sp->verify_chunk_in_free_list(fc),
7610 "free chunk should be in free lists");
7611 }
7612 // a chunk that is already free, should not have been
7613 // marked in the bit map
7614 HeapWord* const addr = (HeapWord*) fc;
7615 assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
7616 // Verify that the bit map has no bits marked between
7617 // addr and purported end of this block.
7618 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7619
7620 // Some chunks cannot be coalesced under any circumstances.
7621 // See the definition of cantCoalesce().
7622 if (!fc->cantCoalesce()) {
7623 // This chunk can potentially be coalesced.
7624 if (_sp->adaptive_freelists()) {
7625 // All the work is done in
7626 do_post_free_or_garbage_chunk(fc, size);
7627 } else { // Not adaptive free lists
7628 // this is a free chunk that can potentially be coalesced by the sweeper;
7629 if (!inFreeRange()) {
7630 // if the next chunk is a free block that can't be coalesced
7631 // it doesn't make sense to remove this chunk from the free lists
7632 FreeChunk* nextChunk = (FreeChunk*)(addr + size);
7633 assert((HeapWord*)nextChunk <= _sp->end(), "Chunk size out of bounds?");
7634 if ((HeapWord*)nextChunk < _sp->end() && // There is another free chunk to the right ...
7635 nextChunk->is_free() && // ... which is free...
7636 nextChunk->cantCoalesce()) { // ... but can't be coalesced
7637 // nothing to do
7638 } else {
7639 // Potentially the start of a new free range:
7640 // Don't eagerly remove it from the free lists.
7641 // No need to remove it if it will just be put
7642 // back again. (Also from a pragmatic point of view
7643 // if it is a free block in a region that is beyond
7644 // any allocated blocks, an assertion will fail)
7645 // Remember the start of a free run.
7646 initialize_free_range(addr, true);
7647 // end - can coalesce with next chunk
7648 }
7649 } else {
7650 // the midst of a free range, we are coalescing
7651 print_free_block_coalesced(fc);
7652 if (CMSTraceSweeper) {
7653 gclog_or_tty->print(" -- pick up free block " PTR_FORMAT " (" SIZE_FORMAT ")\n", p2i(fc), size);
7654 }
7655 // remove it from the free lists
7656 _sp->removeFreeChunkFromFreeLists(fc);
7657 set_lastFreeRangeCoalesced(true);
7658 // If the chunk is being coalesced and the current free range is
7659 // in the free lists, remove the current free range so that it
7660 // will be returned to the free lists in its entirety - all
7661 // the coalesced pieces included.
7662 if (freeRangeInFreeLists()) {
7663 FreeChunk* ffc = (FreeChunk*) freeFinger();
7664 assert(ffc->size() == pointer_delta(addr, freeFinger()),
7665 "Size of free range is inconsistent with chunk size.");
7666 if (CMSTestInFreeList) {
7667 assert(_sp->verify_chunk_in_free_list(ffc),
7668 "free range is not in free lists");
7669 }
7670 _sp->removeFreeChunkFromFreeLists(ffc);
7671 set_freeRangeInFreeLists(false);
7672 }
7673 }
7674 }
7675 // Note that if the chunk is not coalescable (the else arm
7676 // below), we unconditionally flush, without needing to do
7677 // a "lookahead," as we do below.
7678 if (inFreeRange()) lookahead_and_flush(fc, size);
7679 } else {
7680 // Code path common to both original and adaptive free lists.
7681
7682 // cant coalesce with previous block; this should be treated
7683 // as the end of a free run if any
7684 if (inFreeRange()) {
7685 // we kicked some butt; time to pick up the garbage
7686 assert(freeFinger() < addr, "freeFinger points too high");
7687 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7688 }
7689 // else, nothing to do, just continue
7690 }
7691 }
7692
7693 size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) {
7694 // This is a chunk of garbage. It is not in any free list.
7695 // Add it to a free list or let it possibly be coalesced into
7696 // a larger chunk.
7697 HeapWord* const addr = (HeapWord*) fc;
7698 const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7699
7700 if (_sp->adaptive_freelists()) {
7701 // Verify that the bit map has no bits marked between
7702 // addr and purported end of just dead object.
7703 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7704
7705 do_post_free_or_garbage_chunk(fc, size);
7706 } else {
7707 if (!inFreeRange()) {
7708 // start of a new free range
7709 assert(size > 0, "A free range should have a size");
7710 initialize_free_range(addr, false);
7711 } else {
7712 // this will be swept up when we hit the end of the
7713 // free range
7714 if (CMSTraceSweeper) {
7715 gclog_or_tty->print(" -- pick up garbage " PTR_FORMAT " (" SIZE_FORMAT ")\n", p2i(fc), size);
7716 }
7717 // If the chunk is being coalesced and the current free range is
7718 // in the free lists, remove the current free range so that it
7719 // will be returned to the free lists in its entirety - all
7720 // the coalesced pieces included.
7721 if (freeRangeInFreeLists()) {
7722 FreeChunk* ffc = (FreeChunk*)freeFinger();
7723 assert(ffc->size() == pointer_delta(addr, freeFinger()),
7724 "Size of free range is inconsistent with chunk size.");
7725 if (CMSTestInFreeList) {
7726 assert(_sp->verify_chunk_in_free_list(ffc),
7727 "free range is not in free lists");
7728 }
7729 _sp->removeFreeChunkFromFreeLists(ffc);
7730 set_freeRangeInFreeLists(false);
7731 }
7732 set_lastFreeRangeCoalesced(true);
7733 }
7734 // this will be swept up when we hit the end of the free range
7735
7736 // Verify that the bit map has no bits marked between
7737 // addr and purported end of just dead object.
7738 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7739 }
7740 assert(_limit >= addr + size,
7741 "A freshly garbage chunk can't possibly straddle over _limit");
7742 if (inFreeRange()) lookahead_and_flush(fc, size);
7743 return size;
7744 }
7745
7746 size_t SweepClosure::do_live_chunk(FreeChunk* fc) {
7747 HeapWord* addr = (HeapWord*) fc;
7748 // The sweeper has just found a live object. Return any accumulated
7749 // left hand chunk to the free lists.
7750 if (inFreeRange()) {
7751 assert(freeFinger() < addr, "freeFinger points too high");
7752 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7753 }
7754
7755 // This object is live: we'd normally expect this to be
7756 // an oop, and like to assert the following:
7757 // assert(oop(addr)->is_oop(), "live block should be an oop");
7758 // However, as we commented above, this may be an object whose
7759 // header hasn't yet been initialized.
7760 size_t size;
7761 assert(_bitMap->isMarked(addr), "Tautology for this control point");
7762 if (_bitMap->isMarked(addr + 1)) {
7763 // Determine the size from the bit map, rather than trying to
7764 // compute it from the object header.
7765 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
7766 size = pointer_delta(nextOneAddr + 1, addr);
7767 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
7768 "alignment problem");
7769
7770 #ifdef ASSERT
7771 if (oop(addr)->klass_or_null() != NULL) {
7772 // Ignore mark word because we are running concurrent with mutators
7773 assert(oop(addr)->is_oop(true), "live block should be an oop");
7774 assert(size ==
7775 CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
7776 "P-mark and computed size do not agree");
7777 }
7778 #endif
7779
7780 } else {
7781 // This should be an initialized object that's alive.
7782 assert(oop(addr)->klass_or_null() != NULL,
7783 "Should be an initialized object");
7784 // Ignore mark word because we are running concurrent with mutators
7785 assert(oop(addr)->is_oop(true), "live block should be an oop");
7786 // Verify that the bit map has no bits marked between
7787 // addr and purported end of this block.
7788 size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7789 assert(size >= 3, "Necessary for Printezis marks to work");
7790 assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
7791 DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
7792 }
7793 return size;
7794 }
7795
7796 void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc,
7797 size_t chunkSize) {
7798 // do_post_free_or_garbage_chunk() should only be called in the case
7799 // of the adaptive free list allocator.
7800 const bool fcInFreeLists = fc->is_free();
7801 assert(_sp->adaptive_freelists(), "Should only be used in this case.");
7802 assert((HeapWord*)fc <= _limit, "sweep invariant");
7803 if (CMSTestInFreeList && fcInFreeLists) {
7804 assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists");
7805 }
7806
7807 if (CMSTraceSweeper) {
7808 gclog_or_tty->print_cr(" -- pick up another chunk at " PTR_FORMAT " (" SIZE_FORMAT ")", p2i(fc), chunkSize);
7809 }
7810
7811 HeapWord* const fc_addr = (HeapWord*) fc;
7812
7813 bool coalesce;
7814 const size_t left = pointer_delta(fc_addr, freeFinger());
7815 const size_t right = chunkSize;
7816 switch (FLSCoalescePolicy) {
7817 // numeric value forms a coalition aggressiveness metric
7818 case 0: { // never coalesce
7819 coalesce = false;
7820 break;
7821 }
7822 case 1: { // coalesce if left & right chunks on overpopulated lists
7823 coalesce = _sp->coalOverPopulated(left) &&
7824 _sp->coalOverPopulated(right);
7825 break;
7826 }
7827 case 2: { // coalesce if left chunk on overpopulated list (default)
7828 coalesce = _sp->coalOverPopulated(left);
7829 break;
7830 }
7831 case 3: { // coalesce if left OR right chunk on overpopulated list
7832 coalesce = _sp->coalOverPopulated(left) ||
7833 _sp->coalOverPopulated(right);
7834 break;
7835 }
7836 case 4: { // always coalesce
7837 coalesce = true;
7838 break;
7839 }
7840 default:
7841 ShouldNotReachHere();
7842 }
7843
7844 // Should the current free range be coalesced?
7845 // If the chunk is in a free range and either we decided to coalesce above
7846 // or the chunk is near the large block at the end of the heap
7847 // (isNearLargestChunk() returns true), then coalesce this chunk.
7848 const bool doCoalesce = inFreeRange()
7849 && (coalesce || _g->isNearLargestChunk(fc_addr));
7850 if (doCoalesce) {
7851 // Coalesce the current free range on the left with the new
7852 // chunk on the right. If either is on a free list,
7853 // it must be removed from the list and stashed in the closure.
7854 if (freeRangeInFreeLists()) {
7855 FreeChunk* const ffc = (FreeChunk*)freeFinger();
7856 assert(ffc->size() == pointer_delta(fc_addr, freeFinger()),
7857 "Size of free range is inconsistent with chunk size.");
7858 if (CMSTestInFreeList) {
7859 assert(_sp->verify_chunk_in_free_list(ffc),
7860 "Chunk is not in free lists");
7861 }
7862 _sp->coalDeath(ffc->size());
7863 _sp->removeFreeChunkFromFreeLists(ffc);
7864 set_freeRangeInFreeLists(false);
7865 }
7866 if (fcInFreeLists) {
7867 _sp->coalDeath(chunkSize);
7868 assert(fc->size() == chunkSize,
7869 "The chunk has the wrong size or is not in the free lists");
7870 _sp->removeFreeChunkFromFreeLists(fc);
7871 }
7872 set_lastFreeRangeCoalesced(true);
7873 print_free_block_coalesced(fc);
7874 } else { // not in a free range and/or should not coalesce
7875 // Return the current free range and start a new one.
7876 if (inFreeRange()) {
7877 // In a free range but cannot coalesce with the right hand chunk.
7878 // Put the current free range into the free lists.
7879 flush_cur_free_chunk(freeFinger(),
7880 pointer_delta(fc_addr, freeFinger()));
7881 }
7882 // Set up for new free range. Pass along whether the right hand
7883 // chunk is in the free lists.
7884 initialize_free_range((HeapWord*)fc, fcInFreeLists);
7885 }
7886 }
7887
7888 // Lookahead flush:
7889 // If we are tracking a free range, and this is the last chunk that
7890 // we'll look at because its end crosses past _limit, we'll preemptively
7891 // flush it along with any free range we may be holding on to. Note that
7892 // this can be the case only for an already free or freshly garbage
7893 // chunk. If this block is an object, it can never straddle
7894 // over _limit. The "straddling" occurs when _limit is set at
7895 // the previous end of the space when this cycle started, and
7896 // a subsequent heap expansion caused the previously co-terminal
7897 // free block to be coalesced with the newly expanded portion,
7898 // thus rendering _limit a non-block-boundary making it dangerous
7899 // for the sweeper to step over and examine.
7900 void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) {
7901 assert(inFreeRange(), "Should only be called if currently in a free range.");
7902 HeapWord* const eob = ((HeapWord*)fc) + chunk_size;
7903 assert(_sp->used_region().contains(eob - 1),
7904 err_msg("eob = " PTR_FORMAT " eob-1 = " PTR_FORMAT " _limit = " PTR_FORMAT
7905 " out of bounds wrt _sp = [" PTR_FORMAT "," PTR_FORMAT ")"
7906 " when examining fc = " PTR_FORMAT "(" SIZE_FORMAT ")",
7907 p2i(eob), p2i(eob-1), p2i(_limit), p2i(_sp->bottom()), p2i(_sp->end()), p2i(fc), chunk_size));
7908 if (eob >= _limit) {
7909 assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit");
7910 if (CMSTraceSweeper) {
7911 gclog_or_tty->print_cr("_limit " PTR_FORMAT " reached or crossed by block "
7912 "[" PTR_FORMAT "," PTR_FORMAT ") in space "
7913 "[" PTR_FORMAT "," PTR_FORMAT ")",
7914 p2i(_limit), p2i(fc), p2i(eob), p2i(_sp->bottom()), p2i(_sp->end()));
7915 }
7916 // Return the storage we are tracking back into the free lists.
7917 if (CMSTraceSweeper) {
7918 gclog_or_tty->print_cr("Flushing ... ");
7919 }
7920 assert(freeFinger() < eob, "Error");
7921 flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger()));
7922 }
7923 }
7924
7925 void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) {
7926 assert(inFreeRange(), "Should only be called if currently in a free range.");
7927 assert(size > 0,
7928 "A zero sized chunk cannot be added to the free lists.");
7929 if (!freeRangeInFreeLists()) {
7930 if (CMSTestInFreeList) {
7931 FreeChunk* fc = (FreeChunk*) chunk;
7932 fc->set_size(size);
7933 assert(!_sp->verify_chunk_in_free_list(fc),
7934 "chunk should not be in free lists yet");
7935 }
7936 if (CMSTraceSweeper) {
7937 gclog_or_tty->print_cr(" -- add free block " PTR_FORMAT " (" SIZE_FORMAT ") to free lists",
7938 p2i(chunk), size);
7939 }
7940 // A new free range is going to be starting. The current
7941 // free range has not been added to the free lists yet or
7942 // was removed so add it back.
7943 // If the current free range was coalesced, then the death
7944 // of the free range was recorded. Record a birth now.
7945 if (lastFreeRangeCoalesced()) {
7946 _sp->coalBirth(size);
7947 }
7948 _sp->addChunkAndRepairOffsetTable(chunk, size,
7949 lastFreeRangeCoalesced());
7950 } else if (CMSTraceSweeper) {
7951 gclog_or_tty->print_cr("Already in free list: nothing to flush");
7952 }
7953 set_inFreeRange(false);
7954 set_freeRangeInFreeLists(false);
7955 }
7956
7957 // We take a break if we've been at this for a while,
7958 // so as to avoid monopolizing the locks involved.
7959 void SweepClosure::do_yield_work(HeapWord* addr) {
7960 // Return current free chunk being used for coalescing (if any)
7961 // to the appropriate freelist. After yielding, the next
7962 // free block encountered will start a coalescing range of
7963 // free blocks. If the next free block is adjacent to the
7964 // chunk just flushed, they will need to wait for the next
7965 // sweep to be coalesced.
7966 if (inFreeRange()) {
7967 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7968 }
7969
7970 // First give up the locks, then yield, then re-lock.
7971 // We should probably use a constructor/destructor idiom to
7972 // do this unlock/lock or modify the MutexUnlocker class to
7973 // serve our purpose. XXX
7974 assert_lock_strong(_bitMap->lock());
7975 assert_lock_strong(_freelistLock);
7976 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7977 "CMS thread should hold CMS token");
7978 _bitMap->lock()->unlock();
7979 _freelistLock->unlock();
7980 ConcurrentMarkSweepThread::desynchronize(true);
7981 _collector->stopTimer();
7982 if (PrintCMSStatistics != 0) {
7983 _collector->incrementYields();
7984 }
7985
7986 // See the comment in coordinator_yield()
7987 for (unsigned i = 0; i < CMSYieldSleepCount &&
7988 ConcurrentMarkSweepThread::should_yield() &&
7989 !CMSCollector::foregroundGCIsActive(); ++i) {
7990 os::sleep(Thread::current(), 1, false);
7991 }
7992
7993 ConcurrentMarkSweepThread::synchronize(true);
7994 _freelistLock->lock();
7995 _bitMap->lock()->lock_without_safepoint_check();
7996 _collector->startTimer();
7997 }
7998
7999 #ifndef PRODUCT
8000 // This is actually very useful in a product build if it can
8001 // be called from the debugger. Compile it into the product
8002 // as needed.
8003 bool debug_verify_chunk_in_free_list(FreeChunk* fc) {
8004 return debug_cms_space->verify_chunk_in_free_list(fc);
8005 }
8006 #endif
8007
8008 void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const {
8009 if (CMSTraceSweeper) {
8010 gclog_or_tty->print_cr("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")",
8011 p2i(fc), fc->size());
8012 }
8013 }
8014
8015 // CMSIsAliveClosure
8016 bool CMSIsAliveClosure::do_object_b(oop obj) {
8017 HeapWord* addr = (HeapWord*)obj;
8018 return addr != NULL &&
8019 (!_span.contains(addr) || _bit_map->isMarked(addr));
8020 }
8021
8022
8023 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector,
8024 MemRegion span,
8025 CMSBitMap* bit_map, CMSMarkStack* mark_stack,
8026 bool cpc):
8027 _collector(collector),
8028 _span(span),
8029 _bit_map(bit_map),
8030 _mark_stack(mark_stack),
8031 _concurrent_precleaning(cpc) {
8032 assert(!_span.is_empty(), "Empty span could spell trouble");
8033 }
8034
8035
8036 // CMSKeepAliveClosure: the serial version
8037 void CMSKeepAliveClosure::do_oop(oop obj) {
8038 HeapWord* addr = (HeapWord*)obj;
8039 if (_span.contains(addr) &&
8040 !_bit_map->isMarked(addr)) {
8041 _bit_map->mark(addr);
8042 bool simulate_overflow = false;
8043 NOT_PRODUCT(
8044 if (CMSMarkStackOverflowALot &&
8045 _collector->simulate_overflow()) {
8046 // simulate a stack overflow
8047 simulate_overflow = true;
8048 }
8049 )
8050 if (simulate_overflow || !_mark_stack->push(obj)) {
8051 if (_concurrent_precleaning) {
8052 // We dirty the overflown object and let the remark
8053 // phase deal with it.
8054 assert(_collector->overflow_list_is_empty(), "Error");
8055 // In the case of object arrays, we need to dirty all of
8056 // the cards that the object spans. No locking or atomics
8057 // are needed since no one else can be mutating the mod union
8058 // table.
8059 if (obj->is_objArray()) {
8060 size_t sz = obj->size();
8061 HeapWord* end_card_addr =
8062 (HeapWord*)round_to((intptr_t)(addr+sz), CardTableModRefBS::card_size);
8063 MemRegion redirty_range = MemRegion(addr, end_card_addr);
8064 assert(!redirty_range.is_empty(), "Arithmetical tautology");
8065 _collector->_modUnionTable.mark_range(redirty_range);
8066 } else {
8067 _collector->_modUnionTable.mark(addr);
8068 }
8069 _collector->_ser_kac_preclean_ovflw++;
8070 } else {
8071 _collector->push_on_overflow_list(obj);
8072 _collector->_ser_kac_ovflw++;
8073 }
8074 }
8075 }
8076 }
8077
8078 void CMSKeepAliveClosure::do_oop(oop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8079 void CMSKeepAliveClosure::do_oop(narrowOop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8080
8081 // CMSParKeepAliveClosure: a parallel version of the above.
8082 // The work queues are private to each closure (thread),
8083 // but (may be) available for stealing by other threads.
8084 void CMSParKeepAliveClosure::do_oop(oop obj) {
8085 HeapWord* addr = (HeapWord*)obj;
8086 if (_span.contains(addr) &&
8087 !_bit_map->isMarked(addr)) {
8088 // In general, during recursive tracing, several threads
8089 // may be concurrently getting here; the first one to
8090 // "tag" it, claims it.
8091 if (_bit_map->par_mark(addr)) {
8092 bool res = _work_queue->push(obj);
8093 assert(res, "Low water mark should be much less than capacity");
8094 // Do a recursive trim in the hope that this will keep
8095 // stack usage lower, but leave some oops for potential stealers
8096 trim_queue(_low_water_mark);
8097 } // Else, another thread got there first
8098 }
8099 }
8100
8101 void CMSParKeepAliveClosure::do_oop(oop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8102 void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8103
8104 void CMSParKeepAliveClosure::trim_queue(uint max) {
8105 while (_work_queue->size() > max) {
8106 oop new_oop;
8107 if (_work_queue->pop_local(new_oop)) {
8108 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
8109 assert(_bit_map->isMarked((HeapWord*)new_oop),
8110 "no white objects on this stack!");
8111 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8112 // iterate over the oops in this oop, marking and pushing
8113 // the ones in CMS heap (i.e. in _span).
8114 new_oop->oop_iterate(&_mark_and_push);
8115 }
8116 }
8117 }
8118
8119 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
8120 CMSCollector* collector,
8121 MemRegion span, CMSBitMap* bit_map,
8122 OopTaskQueue* work_queue):
8123 _collector(collector),
8124 _span(span),
8125 _bit_map(bit_map),
8126 _work_queue(work_queue) { }
8127
8128 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
8129 HeapWord* addr = (HeapWord*)obj;
8130 if (_span.contains(addr) &&
8131 !_bit_map->isMarked(addr)) {
8132 if (_bit_map->par_mark(addr)) {
8133 bool simulate_overflow = false;
8134 NOT_PRODUCT(
8135 if (CMSMarkStackOverflowALot &&
8136 _collector->par_simulate_overflow()) {
8137 // simulate a stack overflow
8138 simulate_overflow = true;
8139 }
8140 )
8141 if (simulate_overflow || !_work_queue->push(obj)) {
8142 _collector->par_push_on_overflow_list(obj);
8143 _collector->_par_kac_ovflw++;
8144 }
8145 } // Else another thread got there already
8146 }
8147 }
8148
8149 void CMSInnerParMarkAndPushClosure::do_oop(oop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8150 void CMSInnerParMarkAndPushClosure::do_oop(narrowOop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8151
8152 //////////////////////////////////////////////////////////////////
8153 // CMSExpansionCause /////////////////////////////
8154 //////////////////////////////////////////////////////////////////
8155 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
8156 switch (cause) {
8157 case _no_expansion:
8158 return "No expansion";
8159 case _satisfy_free_ratio:
8160 return "Free ratio";
8161 case _satisfy_promotion:
8162 return "Satisfy promotion";
8163 case _satisfy_allocation:
8164 return "allocation";
8165 case _allocate_par_lab:
8166 return "Par LAB";
8167 case _allocate_par_spooling_space:
8168 return "Par Spooling Space";
8169 case _adaptive_size_policy:
8170 return "Ergonomics";
8171 default:
8172 return "unknown";
8173 }
8174 }
8175
8176 void CMSDrainMarkingStackClosure::do_void() {
8177 // the max number to take from overflow list at a time
8178 const size_t num = _mark_stack->capacity()/4;
8179 assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
8180 "Overflow list should be NULL during concurrent phases");
8181 while (!_mark_stack->isEmpty() ||
8182 // if stack is empty, check the overflow list
8183 _collector->take_from_overflow_list(num, _mark_stack)) {
8184 oop obj = _mark_stack->pop();
8185 HeapWord* addr = (HeapWord*)obj;
8186 assert(_span.contains(addr), "Should be within span");
8187 assert(_bit_map->isMarked(addr), "Should be marked");
8188 assert(obj->is_oop(), "Should be an oop");
8189 obj->oop_iterate(_keep_alive);
8190 }
8191 }
8192
8193 void CMSParDrainMarkingStackClosure::do_void() {
8194 // drain queue
8195 trim_queue(0);
8196 }
8197
8198 // Trim our work_queue so its length is below max at return
8199 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
8200 while (_work_queue->size() > max) {
8201 oop new_oop;
8202 if (_work_queue->pop_local(new_oop)) {
8203 assert(new_oop->is_oop(), "Expected an oop");
8204 assert(_bit_map->isMarked((HeapWord*)new_oop),
8205 "no white objects on this stack!");
8206 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8207 // iterate over the oops in this oop, marking and pushing
8208 // the ones in CMS heap (i.e. in _span).
8209 new_oop->oop_iterate(&_mark_and_push);
8210 }
8211 }
8212 }
8213
8214 ////////////////////////////////////////////////////////////////////
8215 // Support for Marking Stack Overflow list handling and related code
8216 ////////////////////////////////////////////////////////////////////
8217 // Much of the following code is similar in shape and spirit to the
8218 // code used in ParNewGC. We should try and share that code
8219 // as much as possible in the future.
8220
8221 #ifndef PRODUCT
8222 // Debugging support for CMSStackOverflowALot
8223
8224 // It's OK to call this multi-threaded; the worst thing
8225 // that can happen is that we'll get a bunch of closely
8226 // spaced simulated overflows, but that's OK, in fact
8227 // probably good as it would exercise the overflow code
8228 // under contention.
8229 bool CMSCollector::simulate_overflow() {
8230 if (_overflow_counter-- <= 0) { // just being defensive
8231 _overflow_counter = CMSMarkStackOverflowInterval;
8232 return true;
8233 } else {
8234 return false;
8235 }
8236 }
8237
8238 bool CMSCollector::par_simulate_overflow() {
8239 return simulate_overflow();
8240 }
8241 #endif
8242
8243 // Single-threaded
8244 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
8245 assert(stack->isEmpty(), "Expected precondition");
8246 assert(stack->capacity() > num, "Shouldn't bite more than can chew");
8247 size_t i = num;
8248 oop cur = _overflow_list;
8249 const markOop proto = markOopDesc::prototype();
8250 NOT_PRODUCT(ssize_t n = 0;)
8251 for (oop next; i > 0 && cur != NULL; cur = next, i--) {
8252 next = oop(cur->mark());
8253 cur->set_mark(proto); // until proven otherwise
8254 assert(cur->is_oop(), "Should be an oop");
8255 bool res = stack->push(cur);
8256 assert(res, "Bit off more than can chew?");
8257 NOT_PRODUCT(n++;)
8258 }
8259 _overflow_list = cur;
8260 #ifndef PRODUCT
8261 assert(_num_par_pushes >= n, "Too many pops?");
8262 _num_par_pushes -=n;
8263 #endif
8264 return !stack->isEmpty();
8265 }
8266
8267 #define BUSY (cast_to_oop<intptr_t>(0x1aff1aff))
8268 // (MT-safe) Get a prefix of at most "num" from the list.
8269 // The overflow list is chained through the mark word of
8270 // each object in the list. We fetch the entire list,
8271 // break off a prefix of the right size and return the
8272 // remainder. If other threads try to take objects from
8273 // the overflow list at that time, they will wait for
8274 // some time to see if data becomes available. If (and
8275 // only if) another thread places one or more object(s)
8276 // on the global list before we have returned the suffix
8277 // to the global list, we will walk down our local list
8278 // to find its end and append the global list to
8279 // our suffix before returning it. This suffix walk can
8280 // prove to be expensive (quadratic in the amount of traffic)
8281 // when there are many objects in the overflow list and
8282 // there is much producer-consumer contention on the list.
8283 // *NOTE*: The overflow list manipulation code here and
8284 // in ParNewGeneration:: are very similar in shape,
8285 // except that in the ParNew case we use the old (from/eden)
8286 // copy of the object to thread the list via its klass word.
8287 // Because of the common code, if you make any changes in
8288 // the code below, please check the ParNew version to see if
8289 // similar changes might be needed.
8290 // CR 6797058 has been filed to consolidate the common code.
8291 bool CMSCollector::par_take_from_overflow_list(size_t num,
8292 OopTaskQueue* work_q,
8293 int no_of_gc_threads) {
8294 assert(work_q->size() == 0, "First empty local work queue");
8295 assert(num < work_q->max_elems(), "Can't bite more than we can chew");
8296 if (_overflow_list == NULL) {
8297 return false;
8298 }
8299 // Grab the entire list; we'll put back a suffix
8300 oop prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
8301 Thread* tid = Thread::current();
8302 // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was
8303 // set to ParallelGCThreads.
8304 size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads;
8305 size_t sleep_time_millis = MAX2((size_t)1, num/100);
8306 // If the list is busy, we spin for a short while,
8307 // sleeping between attempts to get the list.
8308 for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) {
8309 os::sleep(tid, sleep_time_millis, false);
8310 if (_overflow_list == NULL) {
8311 // Nothing left to take
8312 return false;
8313 } else if (_overflow_list != BUSY) {
8314 // Try and grab the prefix
8315 prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
8316 }
8317 }
8318 // If the list was found to be empty, or we spun long
8319 // enough, we give up and return empty-handed. If we leave
8320 // the list in the BUSY state below, it must be the case that
8321 // some other thread holds the overflow list and will set it
8322 // to a non-BUSY state in the future.
8323 if (prefix == NULL || prefix == BUSY) {
8324 // Nothing to take or waited long enough
8325 if (prefix == NULL) {
8326 // Write back the NULL in case we overwrote it with BUSY above
8327 // and it is still the same value.
8328 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8329 }
8330 return false;
8331 }
8332 assert(prefix != NULL && prefix != BUSY, "Error");
8333 size_t i = num;
8334 oop cur = prefix;
8335 // Walk down the first "num" objects, unless we reach the end.
8336 for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--);
8337 if (cur->mark() == NULL) {
8338 // We have "num" or fewer elements in the list, so there
8339 // is nothing to return to the global list.
8340 // Write back the NULL in lieu of the BUSY we wrote
8341 // above, if it is still the same value.
8342 if (_overflow_list == BUSY) {
8343 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8344 }
8345 } else {
8346 // Chop off the suffix and return it to the global list.
8347 assert(cur->mark() != BUSY, "Error");
8348 oop suffix_head = cur->mark(); // suffix will be put back on global list
8349 cur->set_mark(NULL); // break off suffix
8350 // It's possible that the list is still in the empty(busy) state
8351 // we left it in a short while ago; in that case we may be
8352 // able to place back the suffix without incurring the cost
8353 // of a walk down the list.
8354 oop observed_overflow_list = _overflow_list;
8355 oop cur_overflow_list = observed_overflow_list;
8356 bool attached = false;
8357 while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
8358 observed_overflow_list =
8359 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
8360 if (cur_overflow_list == observed_overflow_list) {
8361 attached = true;
8362 break;
8363 } else cur_overflow_list = observed_overflow_list;
8364 }
8365 if (!attached) {
8366 // Too bad, someone else sneaked in (at least) an element; we'll need
8367 // to do a splice. Find tail of suffix so we can prepend suffix to global
8368 // list.
8369 for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark()));
8370 oop suffix_tail = cur;
8371 assert(suffix_tail != NULL && suffix_tail->mark() == NULL,
8372 "Tautology");
8373 observed_overflow_list = _overflow_list;
8374 do {
8375 cur_overflow_list = observed_overflow_list;
8376 if (cur_overflow_list != BUSY) {
8377 // Do the splice ...
8378 suffix_tail->set_mark(markOop(cur_overflow_list));
8379 } else { // cur_overflow_list == BUSY
8380 suffix_tail->set_mark(NULL);
8381 }
8382 // ... and try to place spliced list back on overflow_list ...
8383 observed_overflow_list =
8384 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
8385 } while (cur_overflow_list != observed_overflow_list);
8386 // ... until we have succeeded in doing so.
8387 }
8388 }
8389
8390 // Push the prefix elements on work_q
8391 assert(prefix != NULL, "control point invariant");
8392 const markOop proto = markOopDesc::prototype();
8393 oop next;
8394 NOT_PRODUCT(ssize_t n = 0;)
8395 for (cur = prefix; cur != NULL; cur = next) {
8396 next = oop(cur->mark());
8397 cur->set_mark(proto); // until proven otherwise
8398 assert(cur->is_oop(), "Should be an oop");
8399 bool res = work_q->push(cur);
8400 assert(res, "Bit off more than we can chew?");
8401 NOT_PRODUCT(n++;)
8402 }
8403 #ifndef PRODUCT
8404 assert(_num_par_pushes >= n, "Too many pops?");
8405 Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
8406 #endif
8407 return true;
8408 }
8409
8410 // Single-threaded
8411 void CMSCollector::push_on_overflow_list(oop p) {
8412 NOT_PRODUCT(_num_par_pushes++;)
8413 assert(p->is_oop(), "Not an oop");
8414 preserve_mark_if_necessary(p);
8415 p->set_mark((markOop)_overflow_list);
8416 _overflow_list = p;
8417 }
8418
8419 // Multi-threaded; use CAS to prepend to overflow list
8420 void CMSCollector::par_push_on_overflow_list(oop p) {
8421 NOT_PRODUCT(Atomic::inc_ptr(&_num_par_pushes);)
8422 assert(p->is_oop(), "Not an oop");
8423 par_preserve_mark_if_necessary(p);
8424 oop observed_overflow_list = _overflow_list;
8425 oop cur_overflow_list;
8426 do {
8427 cur_overflow_list = observed_overflow_list;
8428 if (cur_overflow_list != BUSY) {
8429 p->set_mark(markOop(cur_overflow_list));
8430 } else {
8431 p->set_mark(NULL);
8432 }
8433 observed_overflow_list =
8434 (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list);
8435 } while (cur_overflow_list != observed_overflow_list);
8436 }
8437 #undef BUSY
8438
8439 // Single threaded
8440 // General Note on GrowableArray: pushes may silently fail
8441 // because we are (temporarily) out of C-heap for expanding
8442 // the stack. The problem is quite ubiquitous and affects
8443 // a lot of code in the JVM. The prudent thing for GrowableArray
8444 // to do (for now) is to exit with an error. However, that may
8445 // be too draconian in some cases because the caller may be
8446 // able to recover without much harm. For such cases, we
8447 // should probably introduce a "soft_push" method which returns
8448 // an indication of success or failure with the assumption that
8449 // the caller may be able to recover from a failure; code in
8450 // the VM can then be changed, incrementally, to deal with such
8451 // failures where possible, thus, incrementally hardening the VM
8452 // in such low resource situations.
8453 void CMSCollector::preserve_mark_work(oop p, markOop m) {
8454 _preserved_oop_stack.push(p);
8455 _preserved_mark_stack.push(m);
8456 assert(m == p->mark(), "Mark word changed");
8457 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8458 "bijection");
8459 }
8460
8461 // Single threaded
8462 void CMSCollector::preserve_mark_if_necessary(oop p) {
8463 markOop m = p->mark();
8464 if (m->must_be_preserved(p)) {
8465 preserve_mark_work(p, m);
8466 }
8467 }
8468
8469 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
8470 markOop m = p->mark();
8471 if (m->must_be_preserved(p)) {
8472 MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
8473 // Even though we read the mark word without holding
8474 // the lock, we are assured that it will not change
8475 // because we "own" this oop, so no other thread can
8476 // be trying to push it on the overflow list; see
8477 // the assertion in preserve_mark_work() that checks
8478 // that m == p->mark().
8479 preserve_mark_work(p, m);
8480 }
8481 }
8482
8483 // We should be able to do this multi-threaded,
8484 // a chunk of stack being a task (this is
8485 // correct because each oop only ever appears
8486 // once in the overflow list. However, it's
8487 // not very easy to completely overlap this with
8488 // other operations, so will generally not be done
8489 // until all work's been completed. Because we
8490 // expect the preserved oop stack (set) to be small,
8491 // it's probably fine to do this single-threaded.
8492 // We can explore cleverer concurrent/overlapped/parallel
8493 // processing of preserved marks if we feel the
8494 // need for this in the future. Stack overflow should
8495 // be so rare in practice and, when it happens, its
8496 // effect on performance so great that this will
8497 // likely just be in the noise anyway.
8498 void CMSCollector::restore_preserved_marks_if_any() {
8499 assert(SafepointSynchronize::is_at_safepoint(),
8500 "world should be stopped");
8501 assert(Thread::current()->is_ConcurrentGC_thread() ||
8502 Thread::current()->is_VM_thread(),
8503 "should be single-threaded");
8504 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8505 "bijection");
8506
8507 while (!_preserved_oop_stack.is_empty()) {
8508 oop p = _preserved_oop_stack.pop();
8509 assert(p->is_oop(), "Should be an oop");
8510 assert(_span.contains(p), "oop should be in _span");
8511 assert(p->mark() == markOopDesc::prototype(),
8512 "Set when taken from overflow list");
8513 markOop m = _preserved_mark_stack.pop();
8514 p->set_mark(m);
8515 }
8516 assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(),
8517 "stacks were cleared above");
8518 }
8519
8520 #ifndef PRODUCT
8521 bool CMSCollector::no_preserved_marks() const {
8522 return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty();
8523 }
8524 #endif
8525
8526 // Transfer some number of overflown objects to usual marking
8527 // stack. Return true if some objects were transferred.
8528 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
8529 size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,
8530 (size_t)ParGCDesiredObjsFromOverflowList);
8531
8532 bool res = _collector->take_from_overflow_list(num, _mark_stack);
8533 assert(_collector->overflow_list_is_empty() || res,
8534 "If list is not empty, we should have taken something");
8535 assert(!res || !_mark_stack->isEmpty(),
8536 "If we took something, it should now be on our stack");
8537 return res;
8538 }
8539
8540 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
8541 size_t res = _sp->block_size_no_stall(addr, _collector);
8542 if (_sp->block_is_obj(addr)) {
8543 if (_live_bit_map->isMarked(addr)) {
8544 // It can't have been dead in a previous cycle
8545 guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
8546 } else {
8547 _dead_bit_map->mark(addr); // mark the dead object
8548 }
8549 }
8550 // Could be 0, if the block size could not be computed without stalling.
8551 return res;
8552 }
8553
8554 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() {
8555
8556 switch (phase) {
8557 case CMSCollector::InitialMarking:
8558 initialize(true /* fullGC */ ,
8559 cause /* cause of the GC */,
8560 true /* recordGCBeginTime */,
8561 true /* recordPreGCUsage */,
8562 false /* recordPeakUsage */,
8563 false /* recordPostGCusage */,
8564 true /* recordAccumulatedGCTime */,
8565 false /* recordGCEndTime */,
8566 false /* countCollection */ );
8567 break;
8568
8569 case CMSCollector::FinalMarking:
8570 initialize(true /* fullGC */ ,
8571 cause /* cause of the GC */,
8572 false /* recordGCBeginTime */,
8573 false /* recordPreGCUsage */,
8574 false /* recordPeakUsage */,
8575 false /* recordPostGCusage */,
8576 true /* recordAccumulatedGCTime */,
8577 false /* recordGCEndTime */,
8578 false /* countCollection */ );
8579 break;
8580
8581 case CMSCollector::Sweeping:
8582 initialize(true /* fullGC */ ,
8583 cause /* cause of the GC */,
8584 false /* recordGCBeginTime */,
8585 false /* recordPreGCUsage */,
8586 true /* recordPeakUsage */,
8587 true /* recordPostGCusage */,
8588 false /* recordAccumulatedGCTime */,
8589 true /* recordGCEndTime */,
8590 true /* countCollection */ );
8591 break;
8592
8593 default:
8594 ShouldNotReachHere();
8595 }
8596 }