Sun, 13 Apr 2008 17:43:42 -0400
6420645: Create a vm that uses compressed oops for up to 32gb heapsizes
Summary: Compressed oops in instances, arrays, and headers. Code contributors are coleenp, phh, never, swamyv
Reviewed-by: jmasa, kamg, acorn, tbell, kvn, rasbold
1 /*
2 * Copyright 2001-2007 Sun Microsystems, Inc. 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
20 * CA 95054 USA or visit www.sun.com if you need additional information or
21 * have any questions.
22 *
23 */
25 # include "incls/_precompiled.incl"
26 # include "incls/_concurrentMarkSweepGeneration.cpp.incl"
28 // statics
29 CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL;
30 bool CMSCollector::_full_gc_requested = false;
32 //////////////////////////////////////////////////////////////////
33 // In support of CMS/VM thread synchronization
34 //////////////////////////////////////////////////////////////////
35 // We split use of the CGC_lock into 2 "levels".
36 // The low-level locking is of the usual CGC_lock monitor. We introduce
37 // a higher level "token" (hereafter "CMS token") built on top of the
38 // low level monitor (hereafter "CGC lock").
39 // The token-passing protocol gives priority to the VM thread. The
40 // CMS-lock doesn't provide any fairness guarantees, but clients
41 // should ensure that it is only held for very short, bounded
42 // durations.
43 //
44 // When either of the CMS thread or the VM thread is involved in
45 // collection operations during which it does not want the other
46 // thread to interfere, it obtains the CMS token.
47 //
48 // If either thread tries to get the token while the other has
49 // it, that thread waits. However, if the VM thread and CMS thread
50 // both want the token, then the VM thread gets priority while the
51 // CMS thread waits. This ensures, for instance, that the "concurrent"
52 // phases of the CMS thread's work do not block out the VM thread
53 // for long periods of time as the CMS thread continues to hog
54 // the token. (See bug 4616232).
55 //
56 // The baton-passing functions are, however, controlled by the
57 // flags _foregroundGCShouldWait and _foregroundGCIsActive,
58 // and here the low-level CMS lock, not the high level token,
59 // ensures mutual exclusion.
60 //
61 // Two important conditions that we have to satisfy:
62 // 1. if a thread does a low-level wait on the CMS lock, then it
63 // relinquishes the CMS token if it were holding that token
64 // when it acquired the low-level CMS lock.
65 // 2. any low-level notifications on the low-level lock
66 // should only be sent when a thread has relinquished the token.
67 //
68 // In the absence of either property, we'd have potential deadlock.
69 //
70 // We protect each of the CMS (concurrent and sequential) phases
71 // with the CMS _token_, not the CMS _lock_.
72 //
73 // The only code protected by CMS lock is the token acquisition code
74 // itself, see ConcurrentMarkSweepThread::[de]synchronize(), and the
75 // baton-passing code.
76 //
77 // Unfortunately, i couldn't come up with a good abstraction to factor and
78 // hide the naked CGC_lock manipulation in the baton-passing code
79 // further below. That's something we should try to do. Also, the proof
80 // of correctness of this 2-level locking scheme is far from obvious,
81 // and potentially quite slippery. We have an uneasy supsicion, for instance,
82 // that there may be a theoretical possibility of delay/starvation in the
83 // low-level lock/wait/notify scheme used for the baton-passing because of
84 // potential intereference with the priority scheme embodied in the
85 // CMS-token-passing protocol. See related comments at a CGC_lock->wait()
86 // invocation further below and marked with "XXX 20011219YSR".
87 // Indeed, as we note elsewhere, this may become yet more slippery
88 // in the presence of multiple CMS and/or multiple VM threads. XXX
90 class CMSTokenSync: public StackObj {
91 private:
92 bool _is_cms_thread;
93 public:
94 CMSTokenSync(bool is_cms_thread):
95 _is_cms_thread(is_cms_thread) {
96 assert(is_cms_thread == Thread::current()->is_ConcurrentGC_thread(),
97 "Incorrect argument to constructor");
98 ConcurrentMarkSweepThread::synchronize(_is_cms_thread);
99 }
101 ~CMSTokenSync() {
102 assert(_is_cms_thread ?
103 ConcurrentMarkSweepThread::cms_thread_has_cms_token() :
104 ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
105 "Incorrect state");
106 ConcurrentMarkSweepThread::desynchronize(_is_cms_thread);
107 }
108 };
110 // Convenience class that does a CMSTokenSync, and then acquires
111 // upto three locks.
112 class CMSTokenSyncWithLocks: public CMSTokenSync {
113 private:
114 // Note: locks are acquired in textual declaration order
115 // and released in the opposite order
116 MutexLockerEx _locker1, _locker2, _locker3;
117 public:
118 CMSTokenSyncWithLocks(bool is_cms_thread, Mutex* mutex1,
119 Mutex* mutex2 = NULL, Mutex* mutex3 = NULL):
120 CMSTokenSync(is_cms_thread),
121 _locker1(mutex1, Mutex::_no_safepoint_check_flag),
122 _locker2(mutex2, Mutex::_no_safepoint_check_flag),
123 _locker3(mutex3, Mutex::_no_safepoint_check_flag)
124 { }
125 };
128 // Wrapper class to temporarily disable icms during a foreground cms collection.
129 class ICMSDisabler: public StackObj {
130 public:
131 // The ctor disables icms and wakes up the thread so it notices the change;
132 // the dtor re-enables icms. Note that the CMSCollector methods will check
133 // CMSIncrementalMode.
134 ICMSDisabler() { CMSCollector::disable_icms(); CMSCollector::start_icms(); }
135 ~ICMSDisabler() { CMSCollector::enable_icms(); }
136 };
138 //////////////////////////////////////////////////////////////////
139 // Concurrent Mark-Sweep Generation /////////////////////////////
140 //////////////////////////////////////////////////////////////////
142 NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;)
144 // This struct contains per-thread things necessary to support parallel
145 // young-gen collection.
146 class CMSParGCThreadState: public CHeapObj {
147 public:
148 CFLS_LAB lab;
149 PromotionInfo promo;
151 // Constructor.
152 CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) {
153 promo.setSpace(cfls);
154 }
155 };
157 ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration(
158 ReservedSpace rs, size_t initial_byte_size, int level,
159 CardTableRS* ct, bool use_adaptive_freelists,
160 FreeBlockDictionary::DictionaryChoice dictionaryChoice) :
161 CardGeneration(rs, initial_byte_size, level, ct),
162 _dilatation_factor(((double)MinChunkSize)/((double)(oopDesc::header_size()))),
163 _debug_collection_type(Concurrent_collection_type)
164 {
165 HeapWord* bottom = (HeapWord*) _virtual_space.low();
166 HeapWord* end = (HeapWord*) _virtual_space.high();
168 _direct_allocated_words = 0;
169 NOT_PRODUCT(
170 _numObjectsPromoted = 0;
171 _numWordsPromoted = 0;
172 _numObjectsAllocated = 0;
173 _numWordsAllocated = 0;
174 )
176 _cmsSpace = new CompactibleFreeListSpace(_bts, MemRegion(bottom, end),
177 use_adaptive_freelists,
178 dictionaryChoice);
179 NOT_PRODUCT(debug_cms_space = _cmsSpace;)
180 if (_cmsSpace == NULL) {
181 vm_exit_during_initialization(
182 "CompactibleFreeListSpace allocation failure");
183 }
184 _cmsSpace->_gen = this;
186 _gc_stats = new CMSGCStats();
188 // Verify the assumption that FreeChunk::_prev and OopDesc::_klass
189 // offsets match. The ability to tell free chunks from objects
190 // depends on this property.
191 debug_only(
192 FreeChunk* junk = NULL;
193 assert(junk->prev_addr() == (void*)(oop(junk)->klass_addr()),
194 "Offset of FreeChunk::_prev within FreeChunk must match"
195 " that of OopDesc::_klass within OopDesc");
196 )
197 if (ParallelGCThreads > 0) {
198 typedef CMSParGCThreadState* CMSParGCThreadStatePtr;
199 _par_gc_thread_states =
200 NEW_C_HEAP_ARRAY(CMSParGCThreadStatePtr, ParallelGCThreads);
201 if (_par_gc_thread_states == NULL) {
202 vm_exit_during_initialization("Could not allocate par gc structs");
203 }
204 for (uint i = 0; i < ParallelGCThreads; i++) {
205 _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace());
206 if (_par_gc_thread_states[i] == NULL) {
207 vm_exit_during_initialization("Could not allocate par gc structs");
208 }
209 }
210 } else {
211 _par_gc_thread_states = NULL;
212 }
213 _incremental_collection_failed = false;
214 // The "dilatation_factor" is the expansion that can occur on
215 // account of the fact that the minimum object size in the CMS
216 // generation may be larger than that in, say, a contiguous young
217 // generation.
218 // Ideally, in the calculation below, we'd compute the dilatation
219 // factor as: MinChunkSize/(promoting_gen's min object size)
220 // Since we do not have such a general query interface for the
221 // promoting generation, we'll instead just use the mimimum
222 // object size (which today is a header's worth of space);
223 // note that all arithmetic is in units of HeapWords.
224 assert(MinChunkSize >= oopDesc::header_size(), "just checking");
225 assert(_dilatation_factor >= 1.0, "from previous assert");
226 }
229 // The field "_initiating_occupancy" represents the occupancy percentage
230 // at which we trigger a new collection cycle. Unless explicitly specified
231 // via CMSInitiating[Perm]OccupancyFraction (argument "io" below), it
232 // is calculated by:
233 //
234 // Let "f" be MinHeapFreeRatio in
235 //
236 // _intiating_occupancy = 100-f +
237 // f * (CMSTrigger[Perm]Ratio/100)
238 // where CMSTrigger[Perm]Ratio is the argument "tr" below.
239 //
240 // That is, if we assume the heap is at its desired maximum occupancy at the
241 // end of a collection, we let CMSTrigger[Perm]Ratio of the (purported) free
242 // space be allocated before initiating a new collection cycle.
243 //
244 void ConcurrentMarkSweepGeneration::init_initiating_occupancy(intx io, intx tr) {
245 assert(io <= 100 && tr >= 0 && tr <= 100, "Check the arguments");
246 if (io >= 0) {
247 _initiating_occupancy = (double)io / 100.0;
248 } else {
249 _initiating_occupancy = ((100 - MinHeapFreeRatio) +
250 (double)(tr * MinHeapFreeRatio) / 100.0)
251 / 100.0;
252 }
253 }
256 void ConcurrentMarkSweepGeneration::ref_processor_init() {
257 assert(collector() != NULL, "no collector");
258 collector()->ref_processor_init();
259 }
261 void CMSCollector::ref_processor_init() {
262 if (_ref_processor == NULL) {
263 // Allocate and initialize a reference processor
264 _ref_processor = ReferenceProcessor::create_ref_processor(
265 _span, // span
266 _cmsGen->refs_discovery_is_atomic(), // atomic_discovery
267 _cmsGen->refs_discovery_is_mt(), // mt_discovery
268 &_is_alive_closure,
269 ParallelGCThreads,
270 ParallelRefProcEnabled);
271 // Initialize the _ref_processor field of CMSGen
272 _cmsGen->set_ref_processor(_ref_processor);
274 // Allocate a dummy ref processor for perm gen.
275 ReferenceProcessor* rp2 = new ReferenceProcessor();
276 if (rp2 == NULL) {
277 vm_exit_during_initialization("Could not allocate ReferenceProcessor object");
278 }
279 _permGen->set_ref_processor(rp2);
280 }
281 }
283 CMSAdaptiveSizePolicy* CMSCollector::size_policy() {
284 GenCollectedHeap* gch = GenCollectedHeap::heap();
285 assert(gch->kind() == CollectedHeap::GenCollectedHeap,
286 "Wrong type of heap");
287 CMSAdaptiveSizePolicy* sp = (CMSAdaptiveSizePolicy*)
288 gch->gen_policy()->size_policy();
289 assert(sp->is_gc_cms_adaptive_size_policy(),
290 "Wrong type of size policy");
291 return sp;
292 }
294 CMSGCAdaptivePolicyCounters* CMSCollector::gc_adaptive_policy_counters() {
295 CMSGCAdaptivePolicyCounters* results =
296 (CMSGCAdaptivePolicyCounters*) collector_policy()->counters();
297 assert(
298 results->kind() == GCPolicyCounters::CMSGCAdaptivePolicyCountersKind,
299 "Wrong gc policy counter kind");
300 return results;
301 }
304 void ConcurrentMarkSweepGeneration::initialize_performance_counters() {
306 const char* gen_name = "old";
308 // Generation Counters - generation 1, 1 subspace
309 _gen_counters = new GenerationCounters(gen_name, 1, 1, &_virtual_space);
311 _space_counters = new GSpaceCounters(gen_name, 0,
312 _virtual_space.reserved_size(),
313 this, _gen_counters);
314 }
316 CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha):
317 _cms_gen(cms_gen)
318 {
319 assert(alpha <= 100, "bad value");
320 _saved_alpha = alpha;
322 // Initialize the alphas to the bootstrap value of 100.
323 _gc0_alpha = _cms_alpha = 100;
325 _cms_begin_time.update();
326 _cms_end_time.update();
328 _gc0_duration = 0.0;
329 _gc0_period = 0.0;
330 _gc0_promoted = 0;
332 _cms_duration = 0.0;
333 _cms_period = 0.0;
334 _cms_allocated = 0;
336 _cms_used_at_gc0_begin = 0;
337 _cms_used_at_gc0_end = 0;
338 _allow_duty_cycle_reduction = false;
339 _valid_bits = 0;
340 _icms_duty_cycle = CMSIncrementalDutyCycle;
341 }
343 // If promotion failure handling is on use
344 // the padded average size of the promotion for each
345 // young generation collection.
346 double CMSStats::time_until_cms_gen_full() const {
347 size_t cms_free = _cms_gen->cmsSpace()->free();
348 GenCollectedHeap* gch = GenCollectedHeap::heap();
349 size_t expected_promotion = gch->get_gen(0)->capacity();
350 if (HandlePromotionFailure) {
351 expected_promotion = MIN2(
352 (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average(),
353 expected_promotion);
354 }
355 if (cms_free > expected_promotion) {
356 // Start a cms collection if there isn't enough space to promote
357 // for the next minor collection. Use the padded average as
358 // a safety factor.
359 cms_free -= expected_promotion;
361 // Adjust by the safety factor.
362 double cms_free_dbl = (double)cms_free;
363 cms_free_dbl = cms_free_dbl * (100.0 - CMSIncrementalSafetyFactor) / 100.0;
365 if (PrintGCDetails && Verbose) {
366 gclog_or_tty->print_cr("CMSStats::time_until_cms_gen_full: cms_free "
367 SIZE_FORMAT " expected_promotion " SIZE_FORMAT,
368 cms_free, expected_promotion);
369 gclog_or_tty->print_cr(" cms_free_dbl %f cms_consumption_rate %f",
370 cms_free_dbl, cms_consumption_rate() + 1.0);
371 }
372 // Add 1 in case the consumption rate goes to zero.
373 return cms_free_dbl / (cms_consumption_rate() + 1.0);
374 }
375 return 0.0;
376 }
378 // Compare the duration of the cms collection to the
379 // time remaining before the cms generation is empty.
380 // Note that the time from the start of the cms collection
381 // to the start of the cms sweep (less than the total
382 // duration of the cms collection) can be used. This
383 // has been tried and some applications experienced
384 // promotion failures early in execution. This was
385 // possibly because the averages were not accurate
386 // enough at the beginning.
387 double CMSStats::time_until_cms_start() const {
388 // We add "gc0_period" to the "work" calculation
389 // below because this query is done (mostly) at the
390 // end of a scavenge, so we need to conservatively
391 // account for that much possible delay
392 // in the query so as to avoid concurrent mode failures
393 // due to starting the collection just a wee bit too
394 // late.
395 double work = cms_duration() + gc0_period();
396 double deadline = time_until_cms_gen_full();
397 if (work > deadline) {
398 if (Verbose && PrintGCDetails) {
399 gclog_or_tty->print(
400 " CMSCollector: collect because of anticipated promotion "
401 "before full %3.7f + %3.7f > %3.7f ", cms_duration(),
402 gc0_period(), time_until_cms_gen_full());
403 }
404 return 0.0;
405 }
406 return work - deadline;
407 }
409 // Return a duty cycle based on old_duty_cycle and new_duty_cycle, limiting the
410 // amount of change to prevent wild oscillation.
411 unsigned int CMSStats::icms_damped_duty_cycle(unsigned int old_duty_cycle,
412 unsigned int new_duty_cycle) {
413 assert(old_duty_cycle <= 100, "bad input value");
414 assert(new_duty_cycle <= 100, "bad input value");
416 // Note: use subtraction with caution since it may underflow (values are
417 // unsigned). Addition is safe since we're in the range 0-100.
418 unsigned int damped_duty_cycle = new_duty_cycle;
419 if (new_duty_cycle < old_duty_cycle) {
420 const unsigned int largest_delta = MAX2(old_duty_cycle / 4, 5U);
421 if (new_duty_cycle + largest_delta < old_duty_cycle) {
422 damped_duty_cycle = old_duty_cycle - largest_delta;
423 }
424 } else if (new_duty_cycle > old_duty_cycle) {
425 const unsigned int largest_delta = MAX2(old_duty_cycle / 4, 15U);
426 if (new_duty_cycle > old_duty_cycle + largest_delta) {
427 damped_duty_cycle = MIN2(old_duty_cycle + largest_delta, 100U);
428 }
429 }
430 assert(damped_duty_cycle <= 100, "invalid duty cycle computed");
432 if (CMSTraceIncrementalPacing) {
433 gclog_or_tty->print(" [icms_damped_duty_cycle(%d,%d) = %d] ",
434 old_duty_cycle, new_duty_cycle, damped_duty_cycle);
435 }
436 return damped_duty_cycle;
437 }
439 unsigned int CMSStats::icms_update_duty_cycle_impl() {
440 assert(CMSIncrementalPacing && valid(),
441 "should be handled in icms_update_duty_cycle()");
443 double cms_time_so_far = cms_timer().seconds();
444 double scaled_duration = cms_duration_per_mb() * _cms_used_at_gc0_end / M;
445 double scaled_duration_remaining = fabsd(scaled_duration - cms_time_so_far);
447 // Avoid division by 0.
448 double time_until_full = MAX2(time_until_cms_gen_full(), 0.01);
449 double duty_cycle_dbl = 100.0 * scaled_duration_remaining / time_until_full;
451 unsigned int new_duty_cycle = MIN2((unsigned int)duty_cycle_dbl, 100U);
452 if (new_duty_cycle > _icms_duty_cycle) {
453 // Avoid very small duty cycles (1 or 2); 0 is allowed.
454 if (new_duty_cycle > 2) {
455 _icms_duty_cycle = icms_damped_duty_cycle(_icms_duty_cycle,
456 new_duty_cycle);
457 }
458 } else if (_allow_duty_cycle_reduction) {
459 // The duty cycle is reduced only once per cms cycle (see record_cms_end()).
460 new_duty_cycle = icms_damped_duty_cycle(_icms_duty_cycle, new_duty_cycle);
461 // Respect the minimum duty cycle.
462 unsigned int min_duty_cycle = (unsigned int)CMSIncrementalDutyCycleMin;
463 _icms_duty_cycle = MAX2(new_duty_cycle, min_duty_cycle);
464 }
466 if (PrintGCDetails || CMSTraceIncrementalPacing) {
467 gclog_or_tty->print(" icms_dc=%d ", _icms_duty_cycle);
468 }
470 _allow_duty_cycle_reduction = false;
471 return _icms_duty_cycle;
472 }
474 #ifndef PRODUCT
475 void CMSStats::print_on(outputStream *st) const {
476 st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha);
477 st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo=" SIZE_FORMAT,
478 gc0_duration(), gc0_period(), gc0_promoted());
479 st->print(",cms_dur=%g,cms_dur_per_mb=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT,
480 cms_duration(), cms_duration_per_mb(),
481 cms_period(), cms_allocated());
482 st->print(",cms_since_beg=%g,cms_since_end=%g",
483 cms_time_since_begin(), cms_time_since_end());
484 st->print(",cms_used_beg=" SIZE_FORMAT ",cms_used_end=" SIZE_FORMAT,
485 _cms_used_at_gc0_begin, _cms_used_at_gc0_end);
486 if (CMSIncrementalMode) {
487 st->print(",dc=%d", icms_duty_cycle());
488 }
490 if (valid()) {
491 st->print(",promo_rate=%g,cms_alloc_rate=%g",
492 promotion_rate(), cms_allocation_rate());
493 st->print(",cms_consumption_rate=%g,time_until_full=%g",
494 cms_consumption_rate(), time_until_cms_gen_full());
495 }
496 st->print(" ");
497 }
498 #endif // #ifndef PRODUCT
500 CMSCollector::CollectorState CMSCollector::_collectorState =
501 CMSCollector::Idling;
502 bool CMSCollector::_foregroundGCIsActive = false;
503 bool CMSCollector::_foregroundGCShouldWait = false;
505 CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
506 ConcurrentMarkSweepGeneration* permGen,
507 CardTableRS* ct,
508 ConcurrentMarkSweepPolicy* cp):
509 _cmsGen(cmsGen),
510 _permGen(permGen),
511 _ct(ct),
512 _ref_processor(NULL), // will be set later
513 _conc_workers(NULL), // may be set later
514 _abort_preclean(false),
515 _start_sampling(false),
516 _between_prologue_and_epilogue(false),
517 _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"),
518 _perm_gen_verify_bit_map(0, -1 /* no mutex */, "No_lock"),
519 _modUnionTable((CardTableModRefBS::card_shift - LogHeapWordSize),
520 -1 /* lock-free */, "No_lock" /* dummy */),
521 _modUnionClosure(&_modUnionTable),
522 _modUnionClosurePar(&_modUnionTable),
523 _is_alive_closure(&_markBitMap),
524 _restart_addr(NULL),
525 _overflow_list(NULL),
526 _preserved_oop_stack(NULL),
527 _preserved_mark_stack(NULL),
528 _stats(cmsGen),
529 _eden_chunk_array(NULL), // may be set in ctor body
530 _eden_chunk_capacity(0), // -- ditto --
531 _eden_chunk_index(0), // -- ditto --
532 _survivor_plab_array(NULL), // -- ditto --
533 _survivor_chunk_array(NULL), // -- ditto --
534 _survivor_chunk_capacity(0), // -- ditto --
535 _survivor_chunk_index(0), // -- ditto --
536 _ser_pmc_preclean_ovflw(0),
537 _ser_pmc_remark_ovflw(0),
538 _par_pmc_remark_ovflw(0),
539 _ser_kac_ovflw(0),
540 _par_kac_ovflw(0),
541 #ifndef PRODUCT
542 _num_par_pushes(0),
543 #endif
544 _collection_count_start(0),
545 _verifying(false),
546 _icms_start_limit(NULL),
547 _icms_stop_limit(NULL),
548 _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"),
549 _completed_initialization(false),
550 _collector_policy(cp),
551 _should_unload_classes(false),
552 _concurrent_cycles_since_last_unload(0),
553 _sweep_estimate(CMS_SweepWeight, CMS_SweepPadding)
554 {
555 if (ExplicitGCInvokesConcurrentAndUnloadsClasses) {
556 ExplicitGCInvokesConcurrent = true;
557 }
558 // Now expand the span and allocate the collection support structures
559 // (MUT, marking bit map etc.) to cover both generations subject to
560 // collection.
562 // First check that _permGen is adjacent to _cmsGen and above it.
563 assert( _cmsGen->reserved().word_size() > 0
564 && _permGen->reserved().word_size() > 0,
565 "generations should not be of zero size");
566 assert(_cmsGen->reserved().intersection(_permGen->reserved()).is_empty(),
567 "_cmsGen and _permGen should not overlap");
568 assert(_cmsGen->reserved().end() == _permGen->reserved().start(),
569 "_cmsGen->end() different from _permGen->start()");
571 // For use by dirty card to oop closures.
572 _cmsGen->cmsSpace()->set_collector(this);
573 _permGen->cmsSpace()->set_collector(this);
575 // Adjust my span to cover old (cms) gen and perm gen
576 _span = _cmsGen->reserved()._union(_permGen->reserved());
577 // Initialize the span of is_alive_closure
578 _is_alive_closure.set_span(_span);
580 // Allocate MUT and marking bit map
581 {
582 MutexLockerEx x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag);
583 if (!_markBitMap.allocate(_span)) {
584 warning("Failed to allocate CMS Bit Map");
585 return;
586 }
587 assert(_markBitMap.covers(_span), "_markBitMap inconsistency?");
588 }
589 {
590 _modUnionTable.allocate(_span);
591 assert(_modUnionTable.covers(_span), "_modUnionTable inconsistency?");
592 }
594 if (!_markStack.allocate(CMSMarkStackSize)) {
595 warning("Failed to allocate CMS Marking Stack");
596 return;
597 }
598 if (!_revisitStack.allocate(CMSRevisitStackSize)) {
599 warning("Failed to allocate CMS Revisit Stack");
600 return;
601 }
603 // Support for multi-threaded concurrent phases
604 if (ParallelGCThreads > 0 && CMSConcurrentMTEnabled) {
605 if (FLAG_IS_DEFAULT(ParallelCMSThreads)) {
606 // just for now
607 FLAG_SET_DEFAULT(ParallelCMSThreads, (ParallelGCThreads + 3)/4);
608 }
609 if (ParallelCMSThreads > 1) {
610 _conc_workers = new YieldingFlexibleWorkGang("Parallel CMS Threads",
611 ParallelCMSThreads, true);
612 if (_conc_workers == NULL) {
613 warning("GC/CMS: _conc_workers allocation failure: "
614 "forcing -CMSConcurrentMTEnabled");
615 CMSConcurrentMTEnabled = false;
616 }
617 } else {
618 CMSConcurrentMTEnabled = false;
619 }
620 }
621 if (!CMSConcurrentMTEnabled) {
622 ParallelCMSThreads = 0;
623 } else {
624 // Turn off CMSCleanOnEnter optimization temporarily for
625 // the MT case where it's not fixed yet; see 6178663.
626 CMSCleanOnEnter = false;
627 }
628 assert((_conc_workers != NULL) == (ParallelCMSThreads > 1),
629 "Inconsistency");
631 // Parallel task queues; these are shared for the
632 // concurrent and stop-world phases of CMS, but
633 // are not shared with parallel scavenge (ParNew).
634 {
635 uint i;
636 uint num_queues = (uint) MAX2(ParallelGCThreads, ParallelCMSThreads);
638 if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled
639 || ParallelRefProcEnabled)
640 && num_queues > 0) {
641 _task_queues = new OopTaskQueueSet(num_queues);
642 if (_task_queues == NULL) {
643 warning("task_queues allocation failure.");
644 return;
645 }
646 _hash_seed = NEW_C_HEAP_ARRAY(int, num_queues);
647 if (_hash_seed == NULL) {
648 warning("_hash_seed array allocation failure");
649 return;
650 }
652 // XXX use a global constant instead of 64!
653 typedef struct OopTaskQueuePadded {
654 OopTaskQueue work_queue;
655 char pad[64 - sizeof(OopTaskQueue)]; // prevent false sharing
656 } OopTaskQueuePadded;
658 for (i = 0; i < num_queues; i++) {
659 OopTaskQueuePadded *q_padded = new OopTaskQueuePadded();
660 if (q_padded == NULL) {
661 warning("work_queue allocation failure.");
662 return;
663 }
664 _task_queues->register_queue(i, &q_padded->work_queue);
665 }
666 for (i = 0; i < num_queues; i++) {
667 _task_queues->queue(i)->initialize();
668 _hash_seed[i] = 17; // copied from ParNew
669 }
670 }
671 }
673 _cmsGen ->init_initiating_occupancy(CMSInitiatingOccupancyFraction, CMSTriggerRatio);
674 _permGen->init_initiating_occupancy(CMSInitiatingPermOccupancyFraction, CMSTriggerPermRatio);
676 // Clip CMSBootstrapOccupancy between 0 and 100.
677 _bootstrap_occupancy = ((double)MIN2((uintx)100, MAX2((uintx)0, CMSBootstrapOccupancy)))
678 /(double)100;
680 _full_gcs_since_conc_gc = 0;
682 // Now tell CMS generations the identity of their collector
683 ConcurrentMarkSweepGeneration::set_collector(this);
685 // Create & start a CMS thread for this CMS collector
686 _cmsThread = ConcurrentMarkSweepThread::start(this);
687 assert(cmsThread() != NULL, "CMS Thread should have been created");
688 assert(cmsThread()->collector() == this,
689 "CMS Thread should refer to this gen");
690 assert(CGC_lock != NULL, "Where's the CGC_lock?");
692 // Support for parallelizing young gen rescan
693 GenCollectedHeap* gch = GenCollectedHeap::heap();
694 _young_gen = gch->prev_gen(_cmsGen);
695 if (gch->supports_inline_contig_alloc()) {
696 _top_addr = gch->top_addr();
697 _end_addr = gch->end_addr();
698 assert(_young_gen != NULL, "no _young_gen");
699 _eden_chunk_index = 0;
700 _eden_chunk_capacity = (_young_gen->max_capacity()+CMSSamplingGrain)/CMSSamplingGrain;
701 _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity);
702 if (_eden_chunk_array == NULL) {
703 _eden_chunk_capacity = 0;
704 warning("GC/CMS: _eden_chunk_array allocation failure");
705 }
706 }
707 assert(_eden_chunk_array != NULL || _eden_chunk_capacity == 0, "Error");
709 // Support for parallelizing survivor space rescan
710 if (CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) {
711 size_t max_plab_samples = MaxNewSize/((SurvivorRatio+2)*MinTLABSize);
712 _survivor_plab_array = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads);
713 _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, 2*max_plab_samples);
714 _cursor = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads);
715 if (_survivor_plab_array == NULL || _survivor_chunk_array == NULL
716 || _cursor == NULL) {
717 warning("Failed to allocate survivor plab/chunk array");
718 if (_survivor_plab_array != NULL) {
719 FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array);
720 _survivor_plab_array = NULL;
721 }
722 if (_survivor_chunk_array != NULL) {
723 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array);
724 _survivor_chunk_array = NULL;
725 }
726 if (_cursor != NULL) {
727 FREE_C_HEAP_ARRAY(size_t, _cursor);
728 _cursor = NULL;
729 }
730 } else {
731 _survivor_chunk_capacity = 2*max_plab_samples;
732 for (uint i = 0; i < ParallelGCThreads; i++) {
733 HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples);
734 if (vec == NULL) {
735 warning("Failed to allocate survivor plab array");
736 for (int j = i; j > 0; j--) {
737 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_plab_array[j-1].array());
738 }
739 FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array);
740 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array);
741 _survivor_plab_array = NULL;
742 _survivor_chunk_array = NULL;
743 _survivor_chunk_capacity = 0;
744 break;
745 } else {
746 ChunkArray* cur =
747 ::new (&_survivor_plab_array[i]) ChunkArray(vec,
748 max_plab_samples);
749 assert(cur->end() == 0, "Should be 0");
750 assert(cur->array() == vec, "Should be vec");
751 assert(cur->capacity() == max_plab_samples, "Error");
752 }
753 }
754 }
755 }
756 assert( ( _survivor_plab_array != NULL
757 && _survivor_chunk_array != NULL)
758 || ( _survivor_chunk_capacity == 0
759 && _survivor_chunk_index == 0),
760 "Error");
762 // Choose what strong roots should be scanned depending on verification options
763 // and perm gen collection mode.
764 if (!CMSClassUnloadingEnabled) {
765 // If class unloading is disabled we want to include all classes into the root set.
766 add_root_scanning_option(SharedHeap::SO_AllClasses);
767 } else {
768 add_root_scanning_option(SharedHeap::SO_SystemClasses);
769 }
771 NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;)
772 _gc_counters = new CollectorCounters("CMS", 1);
773 _completed_initialization = true;
774 _sweep_timer.start(); // start of time
775 }
777 const char* ConcurrentMarkSweepGeneration::name() const {
778 return "concurrent mark-sweep generation";
779 }
780 void ConcurrentMarkSweepGeneration::update_counters() {
781 if (UsePerfData) {
782 _space_counters->update_all();
783 _gen_counters->update_all();
784 }
785 }
787 // this is an optimized version of update_counters(). it takes the
788 // used value as a parameter rather than computing it.
789 //
790 void ConcurrentMarkSweepGeneration::update_counters(size_t used) {
791 if (UsePerfData) {
792 _space_counters->update_used(used);
793 _space_counters->update_capacity();
794 _gen_counters->update_all();
795 }
796 }
798 void ConcurrentMarkSweepGeneration::print() const {
799 Generation::print();
800 cmsSpace()->print();
801 }
803 #ifndef PRODUCT
804 void ConcurrentMarkSweepGeneration::print_statistics() {
805 cmsSpace()->printFLCensus(0);
806 }
807 #endif
809 void ConcurrentMarkSweepGeneration::printOccupancy(const char *s) {
810 GenCollectedHeap* gch = GenCollectedHeap::heap();
811 if (PrintGCDetails) {
812 if (Verbose) {
813 gclog_or_tty->print(" [%d %s-%s: "SIZE_FORMAT"("SIZE_FORMAT")]",
814 level(), short_name(), s, used(), capacity());
815 } else {
816 gclog_or_tty->print(" [%d %s-%s: "SIZE_FORMAT"K("SIZE_FORMAT"K)]",
817 level(), short_name(), s, used() / K, capacity() / K);
818 }
819 }
820 if (Verbose) {
821 gclog_or_tty->print(" "SIZE_FORMAT"("SIZE_FORMAT")",
822 gch->used(), gch->capacity());
823 } else {
824 gclog_or_tty->print(" "SIZE_FORMAT"K("SIZE_FORMAT"K)",
825 gch->used() / K, gch->capacity() / K);
826 }
827 }
829 size_t
830 ConcurrentMarkSweepGeneration::contiguous_available() const {
831 // dld proposes an improvement in precision here. If the committed
832 // part of the space ends in a free block we should add that to
833 // uncommitted size in the calculation below. Will make this
834 // change later, staying with the approximation below for the
835 // time being. -- ysr.
836 return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc());
837 }
839 size_t
840 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const {
841 return _cmsSpace->max_alloc_in_words() * HeapWordSize;
842 }
844 size_t ConcurrentMarkSweepGeneration::max_available() const {
845 return free() + _virtual_space.uncommitted_size();
846 }
848 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(
849 size_t max_promotion_in_bytes,
850 bool younger_handles_promotion_failure) const {
852 // This is the most conservative test. Full promotion is
853 // guaranteed if this is used. The multiplicative factor is to
854 // account for the worst case "dilatation".
855 double adjusted_max_promo_bytes = _dilatation_factor * max_promotion_in_bytes;
856 if (adjusted_max_promo_bytes > (double)max_uintx) { // larger than size_t
857 adjusted_max_promo_bytes = (double)max_uintx;
858 }
859 bool result = (max_contiguous_available() >= (size_t)adjusted_max_promo_bytes);
861 if (younger_handles_promotion_failure && !result) {
862 // Full promotion is not guaranteed because fragmentation
863 // of the cms generation can prevent the full promotion.
864 result = (max_available() >= (size_t)adjusted_max_promo_bytes);
866 if (!result) {
867 // With promotion failure handling the test for the ability
868 // to support the promotion does not have to be guaranteed.
869 // Use an average of the amount promoted.
870 result = max_available() >= (size_t)
871 gc_stats()->avg_promoted()->padded_average();
872 if (PrintGC && Verbose && result) {
873 gclog_or_tty->print_cr(
874 "\nConcurrentMarkSweepGeneration::promotion_attempt_is_safe"
875 " max_available: " SIZE_FORMAT
876 " avg_promoted: " SIZE_FORMAT,
877 max_available(), (size_t)
878 gc_stats()->avg_promoted()->padded_average());
879 }
880 } else {
881 if (PrintGC && Verbose) {
882 gclog_or_tty->print_cr(
883 "\nConcurrentMarkSweepGeneration::promotion_attempt_is_safe"
884 " max_available: " SIZE_FORMAT
885 " adj_max_promo_bytes: " SIZE_FORMAT,
886 max_available(), (size_t)adjusted_max_promo_bytes);
887 }
888 }
889 } else {
890 if (PrintGC && Verbose) {
891 gclog_or_tty->print_cr(
892 "\nConcurrentMarkSweepGeneration::promotion_attempt_is_safe"
893 " contiguous_available: " SIZE_FORMAT
894 " adj_max_promo_bytes: " SIZE_FORMAT,
895 max_contiguous_available(), (size_t)adjusted_max_promo_bytes);
896 }
897 }
898 return result;
899 }
901 CompactibleSpace*
902 ConcurrentMarkSweepGeneration::first_compaction_space() const {
903 return _cmsSpace;
904 }
906 void ConcurrentMarkSweepGeneration::reset_after_compaction() {
907 // Clear the promotion information. These pointers can be adjusted
908 // along with all the other pointers into the heap but
909 // compaction is expected to be a rare event with
910 // a heap using cms so don't do it without seeing the need.
911 if (ParallelGCThreads > 0) {
912 for (uint i = 0; i < ParallelGCThreads; i++) {
913 _par_gc_thread_states[i]->promo.reset();
914 }
915 }
916 }
918 void ConcurrentMarkSweepGeneration::space_iterate(SpaceClosure* blk, bool usedOnly) {
919 blk->do_space(_cmsSpace);
920 }
922 void ConcurrentMarkSweepGeneration::compute_new_size() {
923 assert_locked_or_safepoint(Heap_lock);
925 // If incremental collection failed, we just want to expand
926 // to the limit.
927 if (incremental_collection_failed()) {
928 clear_incremental_collection_failed();
929 grow_to_reserved();
930 return;
931 }
933 size_t expand_bytes = 0;
934 double free_percentage = ((double) free()) / capacity();
935 double desired_free_percentage = (double) MinHeapFreeRatio / 100;
936 double maximum_free_percentage = (double) MaxHeapFreeRatio / 100;
938 // compute expansion delta needed for reaching desired free percentage
939 if (free_percentage < desired_free_percentage) {
940 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
941 assert(desired_capacity >= capacity(), "invalid expansion size");
942 expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes);
943 }
944 if (expand_bytes > 0) {
945 if (PrintGCDetails && Verbose) {
946 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
947 gclog_or_tty->print_cr("\nFrom compute_new_size: ");
948 gclog_or_tty->print_cr(" Free fraction %f", free_percentage);
949 gclog_or_tty->print_cr(" Desired free fraction %f",
950 desired_free_percentage);
951 gclog_or_tty->print_cr(" Maximum free fraction %f",
952 maximum_free_percentage);
953 gclog_or_tty->print_cr(" Capactiy "SIZE_FORMAT, capacity()/1000);
954 gclog_or_tty->print_cr(" Desired capacity "SIZE_FORMAT,
955 desired_capacity/1000);
956 int prev_level = level() - 1;
957 if (prev_level >= 0) {
958 size_t prev_size = 0;
959 GenCollectedHeap* gch = GenCollectedHeap::heap();
960 Generation* prev_gen = gch->_gens[prev_level];
961 prev_size = prev_gen->capacity();
962 gclog_or_tty->print_cr(" Younger gen size "SIZE_FORMAT,
963 prev_size/1000);
964 }
965 gclog_or_tty->print_cr(" unsafe_max_alloc_nogc "SIZE_FORMAT,
966 unsafe_max_alloc_nogc()/1000);
967 gclog_or_tty->print_cr(" contiguous available "SIZE_FORMAT,
968 contiguous_available()/1000);
969 gclog_or_tty->print_cr(" Expand by "SIZE_FORMAT" (bytes)",
970 expand_bytes);
971 }
972 // safe if expansion fails
973 expand(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio);
974 if (PrintGCDetails && Verbose) {
975 gclog_or_tty->print_cr(" Expanded free fraction %f",
976 ((double) free()) / capacity());
977 }
978 }
979 }
981 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const {
982 return cmsSpace()->freelistLock();
983 }
985 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size,
986 bool tlab) {
987 CMSSynchronousYieldRequest yr;
988 MutexLockerEx x(freelistLock(),
989 Mutex::_no_safepoint_check_flag);
990 return have_lock_and_allocate(size, tlab);
991 }
993 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size,
994 bool tlab) {
995 assert_lock_strong(freelistLock());
996 size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size);
997 HeapWord* res = cmsSpace()->allocate(adjustedSize);
998 // Allocate the object live (grey) if the background collector has
999 // started marking. This is necessary because the marker may
1000 // have passed this address and consequently this object will
1001 // not otherwise be greyed and would be incorrectly swept up.
1002 // Note that if this object contains references, the writing
1003 // of those references will dirty the card containing this object
1004 // allowing the object to be blackened (and its references scanned)
1005 // either during a preclean phase or at the final checkpoint.
1006 if (res != NULL) {
1007 collector()->direct_allocated(res, adjustedSize);
1008 _direct_allocated_words += adjustedSize;
1009 // allocation counters
1010 NOT_PRODUCT(
1011 _numObjectsAllocated++;
1012 _numWordsAllocated += (int)adjustedSize;
1013 )
1014 }
1015 return res;
1016 }
1018 // In the case of direct allocation by mutators in a generation that
1019 // is being concurrently collected, the object must be allocated
1020 // live (grey) if the background collector has started marking.
1021 // This is necessary because the marker may
1022 // have passed this address and consequently this object will
1023 // not otherwise be greyed and would be incorrectly swept up.
1024 // Note that if this object contains references, the writing
1025 // of those references will dirty the card containing this object
1026 // allowing the object to be blackened (and its references scanned)
1027 // either during a preclean phase or at the final checkpoint.
1028 void CMSCollector::direct_allocated(HeapWord* start, size_t size) {
1029 assert(_markBitMap.covers(start, size), "Out of bounds");
1030 if (_collectorState >= Marking) {
1031 MutexLockerEx y(_markBitMap.lock(),
1032 Mutex::_no_safepoint_check_flag);
1033 // [see comments preceding SweepClosure::do_blk() below for details]
1034 // 1. need to mark the object as live so it isn't collected
1035 // 2. need to mark the 2nd bit to indicate the object may be uninitialized
1036 // 3. need to mark the end of the object so sweeper can skip over it
1037 // if it's uninitialized when the sweeper reaches it.
1038 _markBitMap.mark(start); // object is live
1039 _markBitMap.mark(start + 1); // object is potentially uninitialized?
1040 _markBitMap.mark(start + size - 1);
1041 // mark end of object
1042 }
1043 // check that oop looks uninitialized
1044 assert(oop(start)->klass() == NULL, "_klass should be NULL");
1045 }
1047 void CMSCollector::promoted(bool par, HeapWord* start,
1048 bool is_obj_array, size_t obj_size) {
1049 assert(_markBitMap.covers(start), "Out of bounds");
1050 // See comment in direct_allocated() about when objects should
1051 // be allocated live.
1052 if (_collectorState >= Marking) {
1053 // we already hold the marking bit map lock, taken in
1054 // the prologue
1055 if (par) {
1056 _markBitMap.par_mark(start);
1057 } else {
1058 _markBitMap.mark(start);
1059 }
1060 // We don't need to mark the object as uninitialized (as
1061 // in direct_allocated above) because this is being done with the
1062 // world stopped and the object will be initialized by the
1063 // time the sweeper gets to look at it.
1064 assert(SafepointSynchronize::is_at_safepoint(),
1065 "expect promotion only at safepoints");
1067 if (_collectorState < Sweeping) {
1068 // Mark the appropriate cards in the modUnionTable, so that
1069 // this object gets scanned before the sweep. If this is
1070 // not done, CMS generation references in the object might
1071 // not get marked.
1072 // For the case of arrays, which are otherwise precisely
1073 // marked, we need to dirty the entire array, not just its head.
1074 if (is_obj_array) {
1075 // The [par_]mark_range() method expects mr.end() below to
1076 // be aligned to the granularity of a bit's representation
1077 // in the heap. In the case of the MUT below, that's a
1078 // card size.
1079 MemRegion mr(start,
1080 (HeapWord*)round_to((intptr_t)(start + obj_size),
1081 CardTableModRefBS::card_size /* bytes */));
1082 if (par) {
1083 _modUnionTable.par_mark_range(mr);
1084 } else {
1085 _modUnionTable.mark_range(mr);
1086 }
1087 } else { // not an obj array; we can just mark the head
1088 if (par) {
1089 _modUnionTable.par_mark(start);
1090 } else {
1091 _modUnionTable.mark(start);
1092 }
1093 }
1094 }
1095 }
1096 }
1098 static inline size_t percent_of_space(Space* space, HeapWord* addr)
1099 {
1100 size_t delta = pointer_delta(addr, space->bottom());
1101 return (size_t)(delta * 100.0 / (space->capacity() / HeapWordSize));
1102 }
1104 void CMSCollector::icms_update_allocation_limits()
1105 {
1106 Generation* gen0 = GenCollectedHeap::heap()->get_gen(0);
1107 EdenSpace* eden = gen0->as_DefNewGeneration()->eden();
1109 const unsigned int duty_cycle = stats().icms_update_duty_cycle();
1110 if (CMSTraceIncrementalPacing) {
1111 stats().print();
1112 }
1114 assert(duty_cycle <= 100, "invalid duty cycle");
1115 if (duty_cycle != 0) {
1116 // The duty_cycle is a percentage between 0 and 100; convert to words and
1117 // then compute the offset from the endpoints of the space.
1118 size_t free_words = eden->free() / HeapWordSize;
1119 double free_words_dbl = (double)free_words;
1120 size_t duty_cycle_words = (size_t)(free_words_dbl * duty_cycle / 100.0);
1121 size_t offset_words = (free_words - duty_cycle_words) / 2;
1123 _icms_start_limit = eden->top() + offset_words;
1124 _icms_stop_limit = eden->end() - offset_words;
1126 // The limits may be adjusted (shifted to the right) by
1127 // CMSIncrementalOffset, to allow the application more mutator time after a
1128 // young gen gc (when all mutators were stopped) and before CMS starts and
1129 // takes away one or more cpus.
1130 if (CMSIncrementalOffset != 0) {
1131 double adjustment_dbl = free_words_dbl * CMSIncrementalOffset / 100.0;
1132 size_t adjustment = (size_t)adjustment_dbl;
1133 HeapWord* tmp_stop = _icms_stop_limit + adjustment;
1134 if (tmp_stop > _icms_stop_limit && tmp_stop < eden->end()) {
1135 _icms_start_limit += adjustment;
1136 _icms_stop_limit = tmp_stop;
1137 }
1138 }
1139 }
1140 if (duty_cycle == 0 || (_icms_start_limit == _icms_stop_limit)) {
1141 _icms_start_limit = _icms_stop_limit = eden->end();
1142 }
1144 // Install the new start limit.
1145 eden->set_soft_end(_icms_start_limit);
1147 if (CMSTraceIncrementalMode) {
1148 gclog_or_tty->print(" icms alloc limits: "
1149 PTR_FORMAT "," PTR_FORMAT
1150 " (" SIZE_FORMAT "%%," SIZE_FORMAT "%%) ",
1151 _icms_start_limit, _icms_stop_limit,
1152 percent_of_space(eden, _icms_start_limit),
1153 percent_of_space(eden, _icms_stop_limit));
1154 if (Verbose) {
1155 gclog_or_tty->print("eden: ");
1156 eden->print_on(gclog_or_tty);
1157 }
1158 }
1159 }
1161 // Any changes here should try to maintain the invariant
1162 // that if this method is called with _icms_start_limit
1163 // and _icms_stop_limit both NULL, then it should return NULL
1164 // and not notify the icms thread.
1165 HeapWord*
1166 CMSCollector::allocation_limit_reached(Space* space, HeapWord* top,
1167 size_t word_size)
1168 {
1169 // A start_limit equal to end() means the duty cycle is 0, so treat that as a
1170 // nop.
1171 if (CMSIncrementalMode && _icms_start_limit != space->end()) {
1172 if (top <= _icms_start_limit) {
1173 if (CMSTraceIncrementalMode) {
1174 space->print_on(gclog_or_tty);
1175 gclog_or_tty->stamp();
1176 gclog_or_tty->print_cr(" start limit top=" PTR_FORMAT
1177 ", new limit=" PTR_FORMAT
1178 " (" SIZE_FORMAT "%%)",
1179 top, _icms_stop_limit,
1180 percent_of_space(space, _icms_stop_limit));
1181 }
1182 ConcurrentMarkSweepThread::start_icms();
1183 assert(top < _icms_stop_limit, "Tautology");
1184 if (word_size < pointer_delta(_icms_stop_limit, top)) {
1185 return _icms_stop_limit;
1186 }
1188 // The allocation will cross both the _start and _stop limits, so do the
1189 // stop notification also and return end().
1190 if (CMSTraceIncrementalMode) {
1191 space->print_on(gclog_or_tty);
1192 gclog_or_tty->stamp();
1193 gclog_or_tty->print_cr(" +stop limit top=" PTR_FORMAT
1194 ", new limit=" PTR_FORMAT
1195 " (" SIZE_FORMAT "%%)",
1196 top, space->end(),
1197 percent_of_space(space, space->end()));
1198 }
1199 ConcurrentMarkSweepThread::stop_icms();
1200 return space->end();
1201 }
1203 if (top <= _icms_stop_limit) {
1204 if (CMSTraceIncrementalMode) {
1205 space->print_on(gclog_or_tty);
1206 gclog_or_tty->stamp();
1207 gclog_or_tty->print_cr(" stop limit top=" PTR_FORMAT
1208 ", new limit=" PTR_FORMAT
1209 " (" SIZE_FORMAT "%%)",
1210 top, space->end(),
1211 percent_of_space(space, space->end()));
1212 }
1213 ConcurrentMarkSweepThread::stop_icms();
1214 return space->end();
1215 }
1217 if (CMSTraceIncrementalMode) {
1218 space->print_on(gclog_or_tty);
1219 gclog_or_tty->stamp();
1220 gclog_or_tty->print_cr(" end limit top=" PTR_FORMAT
1221 ", new limit=" PTR_FORMAT,
1222 top, NULL);
1223 }
1224 }
1226 return NULL;
1227 }
1229 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size) {
1230 assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
1231 // allocate, copy and if necessary update promoinfo --
1232 // delegate to underlying space.
1233 assert_lock_strong(freelistLock());
1235 #ifndef PRODUCT
1236 if (Universe::heap()->promotion_should_fail()) {
1237 return NULL;
1238 }
1239 #endif // #ifndef PRODUCT
1241 oop res = _cmsSpace->promote(obj, obj_size);
1242 if (res == NULL) {
1243 // expand and retry
1244 size_t s = _cmsSpace->expansionSpaceRequired(obj_size); // HeapWords
1245 expand(s*HeapWordSize, MinHeapDeltaBytes,
1246 CMSExpansionCause::_satisfy_promotion);
1247 // Since there's currently no next generation, we don't try to promote
1248 // into a more senior generation.
1249 assert(next_gen() == NULL, "assumption, based upon which no attempt "
1250 "is made to pass on a possibly failing "
1251 "promotion to next generation");
1252 res = _cmsSpace->promote(obj, obj_size);
1253 }
1254 if (res != NULL) {
1255 // See comment in allocate() about when objects should
1256 // be allocated live.
1257 assert(obj->is_oop(), "Will dereference klass pointer below");
1258 collector()->promoted(false, // Not parallel
1259 (HeapWord*)res, obj->is_objArray(), obj_size);
1260 // promotion counters
1261 NOT_PRODUCT(
1262 _numObjectsPromoted++;
1263 _numWordsPromoted +=
1264 (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size()));
1265 )
1266 }
1267 return res;
1268 }
1271 HeapWord*
1272 ConcurrentMarkSweepGeneration::allocation_limit_reached(Space* space,
1273 HeapWord* top,
1274 size_t word_sz)
1275 {
1276 return collector()->allocation_limit_reached(space, top, word_sz);
1277 }
1279 // Things to support parallel young-gen collection.
1280 oop
1281 ConcurrentMarkSweepGeneration::par_promote(int thread_num,
1282 oop old, markOop m,
1283 size_t word_sz) {
1284 #ifndef PRODUCT
1285 if (Universe::heap()->promotion_should_fail()) {
1286 return NULL;
1287 }
1288 #endif // #ifndef PRODUCT
1290 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1291 PromotionInfo* promoInfo = &ps->promo;
1292 // if we are tracking promotions, then first ensure space for
1293 // promotion (including spooling space for saving header if necessary).
1294 // then allocate and copy, then track promoted info if needed.
1295 // When tracking (see PromotionInfo::track()), the mark word may
1296 // be displaced and in this case restoration of the mark word
1297 // occurs in the (oop_since_save_marks_)iterate phase.
1298 if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) {
1299 // Out of space for allocating spooling buffers;
1300 // try expanding and allocating spooling buffers.
1301 if (!expand_and_ensure_spooling_space(promoInfo)) {
1302 return NULL;
1303 }
1304 }
1305 assert(promoInfo->has_spooling_space(), "Control point invariant");
1306 HeapWord* obj_ptr = ps->lab.alloc(word_sz);
1307 if (obj_ptr == NULL) {
1308 obj_ptr = expand_and_par_lab_allocate(ps, word_sz);
1309 if (obj_ptr == NULL) {
1310 return NULL;
1311 }
1312 }
1313 oop obj = oop(obj_ptr);
1314 assert(obj->klass() == NULL, "Object should be uninitialized here.");
1315 // Otherwise, copy the object. Here we must be careful to insert the
1316 // klass pointer last, since this marks the block as an allocated object.
1317 HeapWord* old_ptr = (HeapWord*)old;
1318 if (word_sz > (size_t)oopDesc::header_size()) {
1319 Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1320 obj_ptr + oopDesc::header_size(),
1321 word_sz - oopDesc::header_size());
1322 }
1323 // Restore the mark word copied above.
1324 obj->set_mark(m);
1325 // Now we can track the promoted object, if necessary. We take care
1326 // To delay the transition from uninitialized to full object
1327 // (i.e., insertion of klass pointer) until after, so that it
1328 // atomically becomes a promoted object.
1329 if (promoInfo->tracking()) {
1330 promoInfo->track((PromotedObject*)obj, old->klass());
1331 }
1332 // Finally, install the klass pointer.
1333 obj->set_klass(old->klass());
1335 assert(old->is_oop(), "Will dereference klass ptr below");
1336 collector()->promoted(true, // parallel
1337 obj_ptr, old->is_objArray(), word_sz);
1339 NOT_PRODUCT(
1340 Atomic::inc(&_numObjectsPromoted);
1341 Atomic::add((jint)CompactibleFreeListSpace::adjustObjectSize(obj->size()),
1342 &_numWordsPromoted);
1343 )
1345 return obj;
1346 }
1348 void
1349 ConcurrentMarkSweepGeneration::
1350 par_promote_alloc_undo(int thread_num,
1351 HeapWord* obj, size_t word_sz) {
1352 // CMS does not support promotion undo.
1353 ShouldNotReachHere();
1354 }
1356 void
1357 ConcurrentMarkSweepGeneration::
1358 par_promote_alloc_done(int thread_num) {
1359 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1360 ps->lab.retire();
1361 #if CFLS_LAB_REFILL_STATS
1362 if (thread_num == 0) {
1363 _cmsSpace->print_par_alloc_stats();
1364 }
1365 #endif
1366 }
1368 void
1369 ConcurrentMarkSweepGeneration::
1370 par_oop_since_save_marks_iterate_done(int thread_num) {
1371 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1372 ParScanWithoutBarrierClosure* dummy_cl = NULL;
1373 ps->promo.promoted_oops_iterate_nv(dummy_cl);
1374 }
1376 // XXXPERM
1377 bool ConcurrentMarkSweepGeneration::should_collect(bool full,
1378 size_t size,
1379 bool tlab)
1380 {
1381 // We allow a STW collection only if a full
1382 // collection was requested.
1383 return full || should_allocate(size, tlab); // FIX ME !!!
1384 // This and promotion failure handling are connected at the
1385 // hip and should be fixed by untying them.
1386 }
1388 bool CMSCollector::shouldConcurrentCollect() {
1389 if (_full_gc_requested) {
1390 assert(ExplicitGCInvokesConcurrent, "Unexpected state");
1391 if (Verbose && PrintGCDetails) {
1392 gclog_or_tty->print_cr("CMSCollector: collect because of explicit "
1393 " gc request");
1394 }
1395 return true;
1396 }
1398 // For debugging purposes, change the type of collection.
1399 // If the rotation is not on the concurrent collection
1400 // type, don't start a concurrent collection.
1401 NOT_PRODUCT(
1402 if (RotateCMSCollectionTypes &&
1403 (_cmsGen->debug_collection_type() !=
1404 ConcurrentMarkSweepGeneration::Concurrent_collection_type)) {
1405 assert(_cmsGen->debug_collection_type() !=
1406 ConcurrentMarkSweepGeneration::Unknown_collection_type,
1407 "Bad cms collection type");
1408 return false;
1409 }
1410 )
1412 FreelistLocker x(this);
1413 // ------------------------------------------------------------------
1414 // Print out lots of information which affects the initiation of
1415 // a collection.
1416 if (PrintCMSInitiationStatistics && stats().valid()) {
1417 gclog_or_tty->print("CMSCollector shouldConcurrentCollect: ");
1418 gclog_or_tty->stamp();
1419 gclog_or_tty->print_cr("");
1420 stats().print_on(gclog_or_tty);
1421 gclog_or_tty->print_cr("time_until_cms_gen_full %3.7f",
1422 stats().time_until_cms_gen_full());
1423 gclog_or_tty->print_cr("free="SIZE_FORMAT, _cmsGen->free());
1424 gclog_or_tty->print_cr("contiguous_available="SIZE_FORMAT,
1425 _cmsGen->contiguous_available());
1426 gclog_or_tty->print_cr("promotion_rate=%g", stats().promotion_rate());
1427 gclog_or_tty->print_cr("cms_allocation_rate=%g", stats().cms_allocation_rate());
1428 gclog_or_tty->print_cr("occupancy=%3.7f", _cmsGen->occupancy());
1429 gclog_or_tty->print_cr("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy());
1430 gclog_or_tty->print_cr("initiatingPermOccupancy=%3.7f", _permGen->initiating_occupancy());
1431 }
1432 // ------------------------------------------------------------------
1434 // If the estimated time to complete a cms collection (cms_duration())
1435 // is less than the estimated time remaining until the cms generation
1436 // is full, start a collection.
1437 if (!UseCMSInitiatingOccupancyOnly) {
1438 if (stats().valid()) {
1439 if (stats().time_until_cms_start() == 0.0) {
1440 return true;
1441 }
1442 } else {
1443 // We want to conservatively collect somewhat early in order
1444 // to try and "bootstrap" our CMS/promotion statistics;
1445 // this branch will not fire after the first successful CMS
1446 // collection because the stats should then be valid.
1447 if (_cmsGen->occupancy() >= _bootstrap_occupancy) {
1448 if (Verbose && PrintGCDetails) {
1449 gclog_or_tty->print_cr(
1450 " CMSCollector: collect for bootstrapping statistics:"
1451 " occupancy = %f, boot occupancy = %f", _cmsGen->occupancy(),
1452 _bootstrap_occupancy);
1453 }
1454 return true;
1455 }
1456 }
1457 }
1459 // Otherwise, we start a collection cycle if either the perm gen or
1460 // old gen want a collection cycle started. Each may use
1461 // an appropriate criterion for making this decision.
1462 // XXX We need to make sure that the gen expansion
1463 // criterion dovetails well with this. XXX NEED TO FIX THIS
1464 if (_cmsGen->should_concurrent_collect()) {
1465 if (Verbose && PrintGCDetails) {
1466 gclog_or_tty->print_cr("CMS old gen initiated");
1467 }
1468 return true;
1469 }
1471 // We start a collection if we believe an incremental collection may fail;
1472 // this is not likely to be productive in practice because it's probably too
1473 // late anyway.
1474 GenCollectedHeap* gch = GenCollectedHeap::heap();
1475 assert(gch->collector_policy()->is_two_generation_policy(),
1476 "You may want to check the correctness of the following");
1477 if (gch->incremental_collection_will_fail()) {
1478 if (PrintGCDetails && Verbose) {
1479 gclog_or_tty->print("CMSCollector: collect because incremental collection will fail ");
1480 }
1481 return true;
1482 }
1484 if (CMSClassUnloadingEnabled && _permGen->should_concurrent_collect()) {
1485 bool res = update_should_unload_classes();
1486 if (res) {
1487 if (Verbose && PrintGCDetails) {
1488 gclog_or_tty->print_cr("CMS perm gen initiated");
1489 }
1490 return true;
1491 }
1492 }
1493 return false;
1494 }
1496 // Clear _expansion_cause fields of constituent generations
1497 void CMSCollector::clear_expansion_cause() {
1498 _cmsGen->clear_expansion_cause();
1499 _permGen->clear_expansion_cause();
1500 }
1502 // We should be conservative in starting a collection cycle. To
1503 // start too eagerly runs the risk of collecting too often in the
1504 // extreme. To collect too rarely falls back on full collections,
1505 // which works, even if not optimum in terms of concurrent work.
1506 // As a work around for too eagerly collecting, use the flag
1507 // UseCMSInitiatingOccupancyOnly. This also has the advantage of
1508 // giving the user an easily understandable way of controlling the
1509 // collections.
1510 // We want to start a new collection cycle if any of the following
1511 // conditions hold:
1512 // . our current occupancy exceeds the configured initiating occupancy
1513 // for this generation, or
1514 // . we recently needed to expand this space and have not, since that
1515 // expansion, done a collection of this generation, or
1516 // . the underlying space believes that it may be a good idea to initiate
1517 // a concurrent collection (this may be based on criteria such as the
1518 // following: the space uses linear allocation and linear allocation is
1519 // going to fail, or there is believed to be excessive fragmentation in
1520 // the generation, etc... or ...
1521 // [.(currently done by CMSCollector::shouldConcurrentCollect() only for
1522 // the case of the old generation, not the perm generation; see CR 6543076):
1523 // we may be approaching a point at which allocation requests may fail because
1524 // we will be out of sufficient free space given allocation rate estimates.]
1525 bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const {
1527 assert_lock_strong(freelistLock());
1528 if (occupancy() > initiating_occupancy()) {
1529 if (PrintGCDetails && Verbose) {
1530 gclog_or_tty->print(" %s: collect because of occupancy %f / %f ",
1531 short_name(), occupancy(), initiating_occupancy());
1532 }
1533 return true;
1534 }
1535 if (UseCMSInitiatingOccupancyOnly) {
1536 return false;
1537 }
1538 if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) {
1539 if (PrintGCDetails && Verbose) {
1540 gclog_or_tty->print(" %s: collect because expanded for allocation ",
1541 short_name());
1542 }
1543 return true;
1544 }
1545 if (_cmsSpace->should_concurrent_collect()) {
1546 if (PrintGCDetails && Verbose) {
1547 gclog_or_tty->print(" %s: collect because cmsSpace says so ",
1548 short_name());
1549 }
1550 return true;
1551 }
1552 return false;
1553 }
1555 void ConcurrentMarkSweepGeneration::collect(bool full,
1556 bool clear_all_soft_refs,
1557 size_t size,
1558 bool tlab)
1559 {
1560 collector()->collect(full, clear_all_soft_refs, size, tlab);
1561 }
1563 void CMSCollector::collect(bool full,
1564 bool clear_all_soft_refs,
1565 size_t size,
1566 bool tlab)
1567 {
1568 if (!UseCMSCollectionPassing && _collectorState > Idling) {
1569 // For debugging purposes skip the collection if the state
1570 // is not currently idle
1571 if (TraceCMSState) {
1572 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " skipped full:%d CMS state %d",
1573 Thread::current(), full, _collectorState);
1574 }
1575 return;
1576 }
1578 // The following "if" branch is present for defensive reasons.
1579 // In the current uses of this interface, it can be replaced with:
1580 // assert(!GC_locker.is_active(), "Can't be called otherwise");
1581 // But I am not placing that assert here to allow future
1582 // generality in invoking this interface.
1583 if (GC_locker::is_active()) {
1584 // A consistency test for GC_locker
1585 assert(GC_locker::needs_gc(), "Should have been set already");
1586 // Skip this foreground collection, instead
1587 // expanding the heap if necessary.
1588 // Need the free list locks for the call to free() in compute_new_size()
1589 compute_new_size();
1590 return;
1591 }
1592 acquire_control_and_collect(full, clear_all_soft_refs);
1593 _full_gcs_since_conc_gc++;
1595 }
1597 void CMSCollector::request_full_gc(unsigned int full_gc_count) {
1598 GenCollectedHeap* gch = GenCollectedHeap::heap();
1599 unsigned int gc_count = gch->total_full_collections();
1600 if (gc_count == full_gc_count) {
1601 MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag);
1602 _full_gc_requested = true;
1603 CGC_lock->notify(); // nudge CMS thread
1604 }
1605 }
1608 // The foreground and background collectors need to coordinate in order
1609 // to make sure that they do not mutually interfere with CMS collections.
1610 // When a background collection is active,
1611 // the foreground collector may need to take over (preempt) and
1612 // synchronously complete an ongoing collection. Depending on the
1613 // frequency of the background collections and the heap usage
1614 // of the application, this preemption can be seldom or frequent.
1615 // There are only certain
1616 // points in the background collection that the "collection-baton"
1617 // can be passed to the foreground collector.
1618 //
1619 // The foreground collector will wait for the baton before
1620 // starting any part of the collection. The foreground collector
1621 // will only wait at one location.
1622 //
1623 // The background collector will yield the baton before starting a new
1624 // phase of the collection (e.g., before initial marking, marking from roots,
1625 // precleaning, final re-mark, sweep etc.) This is normally done at the head
1626 // of the loop which switches the phases. The background collector does some
1627 // of the phases (initial mark, final re-mark) with the world stopped.
1628 // Because of locking involved in stopping the world,
1629 // the foreground collector should not block waiting for the background
1630 // collector when it is doing a stop-the-world phase. The background
1631 // collector will yield the baton at an additional point just before
1632 // it enters a stop-the-world phase. Once the world is stopped, the
1633 // background collector checks the phase of the collection. If the
1634 // phase has not changed, it proceeds with the collection. If the
1635 // phase has changed, it skips that phase of the collection. See
1636 // the comments on the use of the Heap_lock in collect_in_background().
1637 //
1638 // Variable used in baton passing.
1639 // _foregroundGCIsActive - Set to true by the foreground collector when
1640 // it wants the baton. The foreground clears it when it has finished
1641 // the collection.
1642 // _foregroundGCShouldWait - Set to true by the background collector
1643 // when it is running. The foreground collector waits while
1644 // _foregroundGCShouldWait is true.
1645 // CGC_lock - monitor used to protect access to the above variables
1646 // and to notify the foreground and background collectors.
1647 // _collectorState - current state of the CMS collection.
1648 //
1649 // The foreground collector
1650 // acquires the CGC_lock
1651 // sets _foregroundGCIsActive
1652 // waits on the CGC_lock for _foregroundGCShouldWait to be false
1653 // various locks acquired in preparation for the collection
1654 // are released so as not to block the background collector
1655 // that is in the midst of a collection
1656 // proceeds with the collection
1657 // clears _foregroundGCIsActive
1658 // returns
1659 //
1660 // The background collector in a loop iterating on the phases of the
1661 // collection
1662 // acquires the CGC_lock
1663 // sets _foregroundGCShouldWait
1664 // if _foregroundGCIsActive is set
1665 // clears _foregroundGCShouldWait, notifies _CGC_lock
1666 // waits on _CGC_lock for _foregroundGCIsActive to become false
1667 // and exits the loop.
1668 // otherwise
1669 // proceed with that phase of the collection
1670 // if the phase is a stop-the-world phase,
1671 // yield the baton once more just before enqueueing
1672 // the stop-world CMS operation (executed by the VM thread).
1673 // returns after all phases of the collection are done
1674 //
1676 void CMSCollector::acquire_control_and_collect(bool full,
1677 bool clear_all_soft_refs) {
1678 assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
1679 assert(!Thread::current()->is_ConcurrentGC_thread(),
1680 "shouldn't try to acquire control from self!");
1682 // Start the protocol for acquiring control of the
1683 // collection from the background collector (aka CMS thread).
1684 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1685 "VM thread should have CMS token");
1686 // Remember the possibly interrupted state of an ongoing
1687 // concurrent collection
1688 CollectorState first_state = _collectorState;
1690 // Signal to a possibly ongoing concurrent collection that
1691 // we want to do a foreground collection.
1692 _foregroundGCIsActive = true;
1694 // Disable incremental mode during a foreground collection.
1695 ICMSDisabler icms_disabler;
1697 // release locks and wait for a notify from the background collector
1698 // releasing the locks in only necessary for phases which
1699 // do yields to improve the granularity of the collection.
1700 assert_lock_strong(bitMapLock());
1701 // We need to lock the Free list lock for the space that we are
1702 // currently collecting.
1703 assert(haveFreelistLocks(), "Must be holding free list locks");
1704 bitMapLock()->unlock();
1705 releaseFreelistLocks();
1706 {
1707 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1708 if (_foregroundGCShouldWait) {
1709 // We are going to be waiting for action for the CMS thread;
1710 // it had better not be gone (for instance at shutdown)!
1711 assert(ConcurrentMarkSweepThread::cmst() != NULL,
1712 "CMS thread must be running");
1713 // Wait here until the background collector gives us the go-ahead
1714 ConcurrentMarkSweepThread::clear_CMS_flag(
1715 ConcurrentMarkSweepThread::CMS_vm_has_token); // release token
1716 // Get a possibly blocked CMS thread going:
1717 // Note that we set _foregroundGCIsActive true above,
1718 // without protection of the CGC_lock.
1719 CGC_lock->notify();
1720 assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(),
1721 "Possible deadlock");
1722 while (_foregroundGCShouldWait) {
1723 // wait for notification
1724 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1725 // Possibility of delay/starvation here, since CMS token does
1726 // not know to give priority to VM thread? Actually, i think
1727 // there wouldn't be any delay/starvation, but the proof of
1728 // that "fact" (?) appears non-trivial. XXX 20011219YSR
1729 }
1730 ConcurrentMarkSweepThread::set_CMS_flag(
1731 ConcurrentMarkSweepThread::CMS_vm_has_token);
1732 }
1733 }
1734 // The CMS_token is already held. Get back the other locks.
1735 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1736 "VM thread should have CMS token");
1737 getFreelistLocks();
1738 bitMapLock()->lock_without_safepoint_check();
1739 if (TraceCMSState) {
1740 gclog_or_tty->print_cr("CMS foreground collector has asked for control "
1741 INTPTR_FORMAT " with first state %d", Thread::current(), first_state);
1742 gclog_or_tty->print_cr(" gets control with state %d", _collectorState);
1743 }
1745 // Check if we need to do a compaction, or if not, whether
1746 // we need to start the mark-sweep from scratch.
1747 bool should_compact = false;
1748 bool should_start_over = false;
1749 decide_foreground_collection_type(clear_all_soft_refs,
1750 &should_compact, &should_start_over);
1752 NOT_PRODUCT(
1753 if (RotateCMSCollectionTypes) {
1754 if (_cmsGen->debug_collection_type() ==
1755 ConcurrentMarkSweepGeneration::MSC_foreground_collection_type) {
1756 should_compact = true;
1757 } else if (_cmsGen->debug_collection_type() ==
1758 ConcurrentMarkSweepGeneration::MS_foreground_collection_type) {
1759 should_compact = false;
1760 }
1761 }
1762 )
1764 if (PrintGCDetails && first_state > Idling) {
1765 GCCause::Cause cause = GenCollectedHeap::heap()->gc_cause();
1766 if (GCCause::is_user_requested_gc(cause) ||
1767 GCCause::is_serviceability_requested_gc(cause)) {
1768 gclog_or_tty->print(" (concurrent mode interrupted)");
1769 } else {
1770 gclog_or_tty->print(" (concurrent mode failure)");
1771 }
1772 }
1774 if (should_compact) {
1775 // If the collection is being acquired from the background
1776 // collector, there may be references on the discovered
1777 // references lists that have NULL referents (being those
1778 // that were concurrently cleared by a mutator) or
1779 // that are no longer active (having been enqueued concurrently
1780 // by the mutator).
1781 // Scrub the list of those references because Mark-Sweep-Compact
1782 // code assumes referents are not NULL and that all discovered
1783 // Reference objects are active.
1784 ref_processor()->clean_up_discovered_references();
1786 do_compaction_work(clear_all_soft_refs);
1788 // Has the GC time limit been exceeded?
1789 check_gc_time_limit();
1791 } else {
1792 do_mark_sweep_work(clear_all_soft_refs, first_state,
1793 should_start_over);
1794 }
1795 // Reset the expansion cause, now that we just completed
1796 // a collection cycle.
1797 clear_expansion_cause();
1798 _foregroundGCIsActive = false;
1799 return;
1800 }
1802 void CMSCollector::check_gc_time_limit() {
1804 // Ignore explicit GC's. Exiting here does not set the flag and
1805 // does not reset the count. Updating of the averages for system
1806 // GC's is still controlled by UseAdaptiveSizePolicyWithSystemGC.
1807 GCCause::Cause gc_cause = GenCollectedHeap::heap()->gc_cause();
1808 if (GCCause::is_user_requested_gc(gc_cause) ||
1809 GCCause::is_serviceability_requested_gc(gc_cause)) {
1810 return;
1811 }
1813 // Calculate the fraction of the CMS generation was freed during
1814 // the last collection.
1815 // Only consider the STW compacting cost for now.
1816 //
1817 // Note that the gc time limit test only works for the collections
1818 // of the young gen + tenured gen and not for collections of the
1819 // permanent gen. That is because the calculation of the space
1820 // freed by the collection is the free space in the young gen +
1821 // tenured gen.
1823 double fraction_free =
1824 ((double)_cmsGen->free())/((double)_cmsGen->max_capacity());
1825 if ((100.0 * size_policy()->compacting_gc_cost()) >
1826 ((double) GCTimeLimit) &&
1827 ((fraction_free * 100) < GCHeapFreeLimit)) {
1828 size_policy()->inc_gc_time_limit_count();
1829 if (UseGCOverheadLimit &&
1830 (size_policy()->gc_time_limit_count() >
1831 AdaptiveSizePolicyGCTimeLimitThreshold)) {
1832 size_policy()->set_gc_time_limit_exceeded(true);
1833 // Avoid consecutive OOM due to the gc time limit by resetting
1834 // the counter.
1835 size_policy()->reset_gc_time_limit_count();
1836 if (PrintGCDetails) {
1837 gclog_or_tty->print_cr(" GC is exceeding overhead limit "
1838 "of %d%%", GCTimeLimit);
1839 }
1840 } else {
1841 if (PrintGCDetails) {
1842 gclog_or_tty->print_cr(" GC would exceed overhead limit "
1843 "of %d%%", GCTimeLimit);
1844 }
1845 }
1846 } else {
1847 size_policy()->reset_gc_time_limit_count();
1848 }
1849 }
1851 // Resize the perm generation and the tenured generation
1852 // after obtaining the free list locks for the
1853 // two generations.
1854 void CMSCollector::compute_new_size() {
1855 assert_locked_or_safepoint(Heap_lock);
1856 FreelistLocker z(this);
1857 _permGen->compute_new_size();
1858 _cmsGen->compute_new_size();
1859 }
1861 // A work method used by foreground collection to determine
1862 // what type of collection (compacting or not, continuing or fresh)
1863 // it should do.
1864 // NOTE: the intent is to make UseCMSCompactAtFullCollection
1865 // and CMSCompactWhenClearAllSoftRefs the default in the future
1866 // and do away with the flags after a suitable period.
1867 void CMSCollector::decide_foreground_collection_type(
1868 bool clear_all_soft_refs, bool* should_compact,
1869 bool* should_start_over) {
1870 // Normally, we'll compact only if the UseCMSCompactAtFullCollection
1871 // flag is set, and we have either requested a System.gc() or
1872 // the number of full gc's since the last concurrent cycle
1873 // has exceeded the threshold set by CMSFullGCsBeforeCompaction,
1874 // or if an incremental collection has failed
1875 GenCollectedHeap* gch = GenCollectedHeap::heap();
1876 assert(gch->collector_policy()->is_two_generation_policy(),
1877 "You may want to check the correctness of the following");
1878 // Inform cms gen if this was due to partial collection failing.
1879 // The CMS gen may use this fact to determine its expansion policy.
1880 if (gch->incremental_collection_will_fail()) {
1881 assert(!_cmsGen->incremental_collection_failed(),
1882 "Should have been noticed, reacted to and cleared");
1883 _cmsGen->set_incremental_collection_failed();
1884 }
1885 *should_compact =
1886 UseCMSCompactAtFullCollection &&
1887 ((_full_gcs_since_conc_gc >= CMSFullGCsBeforeCompaction) ||
1888 GCCause::is_user_requested_gc(gch->gc_cause()) ||
1889 gch->incremental_collection_will_fail());
1890 *should_start_over = false;
1891 if (clear_all_soft_refs && !*should_compact) {
1892 // We are about to do a last ditch collection attempt
1893 // so it would normally make sense to do a compaction
1894 // to reclaim as much space as possible.
1895 if (CMSCompactWhenClearAllSoftRefs) {
1896 // Default: The rationale is that in this case either
1897 // we are past the final marking phase, in which case
1898 // we'd have to start over, or so little has been done
1899 // that there's little point in saving that work. Compaction
1900 // appears to be the sensible choice in either case.
1901 *should_compact = true;
1902 } else {
1903 // We have been asked to clear all soft refs, but not to
1904 // compact. Make sure that we aren't past the final checkpoint
1905 // phase, for that is where we process soft refs. If we are already
1906 // past that phase, we'll need to redo the refs discovery phase and
1907 // if necessary clear soft refs that weren't previously
1908 // cleared. We do so by remembering the phase in which
1909 // we came in, and if we are past the refs processing
1910 // phase, we'll choose to just redo the mark-sweep
1911 // collection from scratch.
1912 if (_collectorState > FinalMarking) {
1913 // We are past the refs processing phase;
1914 // start over and do a fresh synchronous CMS cycle
1915 _collectorState = Resetting; // skip to reset to start new cycle
1916 reset(false /* == !asynch */);
1917 *should_start_over = true;
1918 } // else we can continue a possibly ongoing current cycle
1919 }
1920 }
1921 }
1923 // A work method used by the foreground collector to do
1924 // a mark-sweep-compact.
1925 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) {
1926 GenCollectedHeap* gch = GenCollectedHeap::heap();
1927 TraceTime t("CMS:MSC ", PrintGCDetails && Verbose, true, gclog_or_tty);
1928 if (PrintGC && Verbose && !(GCCause::is_user_requested_gc(gch->gc_cause()))) {
1929 gclog_or_tty->print_cr("Compact ConcurrentMarkSweepGeneration after %d "
1930 "collections passed to foreground collector", _full_gcs_since_conc_gc);
1931 }
1933 // Sample collection interval time and reset for collection pause.
1934 if (UseAdaptiveSizePolicy) {
1935 size_policy()->msc_collection_begin();
1936 }
1938 // Temporarily widen the span of the weak reference processing to
1939 // the entire heap.
1940 MemRegion new_span(GenCollectedHeap::heap()->reserved_region());
1941 ReferenceProcessorSpanMutator x(ref_processor(), new_span);
1943 // Temporarily, clear the "is_alive_non_header" field of the
1944 // reference processor.
1945 ReferenceProcessorIsAliveMutator y(ref_processor(), NULL);
1947 // Temporarily make reference _processing_ single threaded (non-MT).
1948 ReferenceProcessorMTProcMutator z(ref_processor(), false);
1950 // Temporarily make refs discovery atomic
1951 ReferenceProcessorAtomicMutator w(ref_processor(), true);
1953 ref_processor()->set_enqueuing_is_done(false);
1954 ref_processor()->enable_discovery();
1955 // If an asynchronous collection finishes, the _modUnionTable is
1956 // all clear. If we are assuming the collection from an asynchronous
1957 // collection, clear the _modUnionTable.
1958 assert(_collectorState != Idling || _modUnionTable.isAllClear(),
1959 "_modUnionTable should be clear if the baton was not passed");
1960 _modUnionTable.clear_all();
1962 // We must adjust the allocation statistics being maintained
1963 // in the free list space. We do so by reading and clearing
1964 // the sweep timer and updating the block flux rate estimates below.
1965 assert(_sweep_timer.is_active(), "We should never see the timer inactive");
1966 _sweep_timer.stop();
1967 // Note that we do not use this sample to update the _sweep_estimate.
1968 _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_sweep_timer.seconds()),
1969 _sweep_estimate.padded_average());
1971 GenMarkSweep::invoke_at_safepoint(_cmsGen->level(),
1972 ref_processor(), clear_all_soft_refs);
1973 #ifdef ASSERT
1974 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
1975 size_t free_size = cms_space->free();
1976 assert(free_size ==
1977 pointer_delta(cms_space->end(), cms_space->compaction_top())
1978 * HeapWordSize,
1979 "All the free space should be compacted into one chunk at top");
1980 assert(cms_space->dictionary()->totalChunkSize(
1981 debug_only(cms_space->freelistLock())) == 0 ||
1982 cms_space->totalSizeInIndexedFreeLists() == 0,
1983 "All the free space should be in a single chunk");
1984 size_t num = cms_space->totalCount();
1985 assert((free_size == 0 && num == 0) ||
1986 (free_size > 0 && (num == 1 || num == 2)),
1987 "There should be at most 2 free chunks after compaction");
1988 #endif // ASSERT
1989 _collectorState = Resetting;
1990 assert(_restart_addr == NULL,
1991 "Should have been NULL'd before baton was passed");
1992 reset(false /* == !asynch */);
1993 _cmsGen->reset_after_compaction();
1994 _concurrent_cycles_since_last_unload = 0;
1996 if (verifying() && !should_unload_classes()) {
1997 perm_gen_verify_bit_map()->clear_all();
1998 }
2000 // Clear any data recorded in the PLAB chunk arrays.
2001 if (_survivor_plab_array != NULL) {
2002 reset_survivor_plab_arrays();
2003 }
2005 // Adjust the per-size allocation stats for the next epoch.
2006 _cmsGen->cmsSpace()->endSweepFLCensus(sweepCount() /* fake */);
2007 // Restart the "sweep timer" for next epoch.
2008 _sweep_timer.reset();
2009 _sweep_timer.start();
2011 // Sample collection pause time and reset for collection interval.
2012 if (UseAdaptiveSizePolicy) {
2013 size_policy()->msc_collection_end(gch->gc_cause());
2014 }
2016 // For a mark-sweep-compact, compute_new_size() will be called
2017 // in the heap's do_collection() method.
2018 }
2020 // A work method used by the foreground collector to do
2021 // a mark-sweep, after taking over from a possibly on-going
2022 // concurrent mark-sweep collection.
2023 void CMSCollector::do_mark_sweep_work(bool clear_all_soft_refs,
2024 CollectorState first_state, bool should_start_over) {
2025 if (PrintGC && Verbose) {
2026 gclog_or_tty->print_cr("Pass concurrent collection to foreground "
2027 "collector with count %d",
2028 _full_gcs_since_conc_gc);
2029 }
2030 switch (_collectorState) {
2031 case Idling:
2032 if (first_state == Idling || should_start_over) {
2033 // The background GC was not active, or should
2034 // restarted from scratch; start the cycle.
2035 _collectorState = InitialMarking;
2036 }
2037 // If first_state was not Idling, then a background GC
2038 // was in progress and has now finished. No need to do it
2039 // again. Leave the state as Idling.
2040 break;
2041 case Precleaning:
2042 // In the foreground case don't do the precleaning since
2043 // it is not done concurrently and there is extra work
2044 // required.
2045 _collectorState = FinalMarking;
2046 }
2047 if (PrintGCDetails &&
2048 (_collectorState > Idling ||
2049 !GCCause::is_user_requested_gc(GenCollectedHeap::heap()->gc_cause()))) {
2050 gclog_or_tty->print(" (concurrent mode failure)");
2051 }
2052 collect_in_foreground(clear_all_soft_refs);
2054 // For a mark-sweep, compute_new_size() will be called
2055 // in the heap's do_collection() method.
2056 }
2059 void CMSCollector::getFreelistLocks() const {
2060 // Get locks for all free lists in all generations that this
2061 // collector is responsible for
2062 _cmsGen->freelistLock()->lock_without_safepoint_check();
2063 _permGen->freelistLock()->lock_without_safepoint_check();
2064 }
2066 void CMSCollector::releaseFreelistLocks() const {
2067 // Release locks for all free lists in all generations that this
2068 // collector is responsible for
2069 _cmsGen->freelistLock()->unlock();
2070 _permGen->freelistLock()->unlock();
2071 }
2073 bool CMSCollector::haveFreelistLocks() const {
2074 // Check locks for all free lists in all generations that this
2075 // collector is responsible for
2076 assert_lock_strong(_cmsGen->freelistLock());
2077 assert_lock_strong(_permGen->freelistLock());
2078 PRODUCT_ONLY(ShouldNotReachHere());
2079 return true;
2080 }
2082 // A utility class that is used by the CMS collector to
2083 // temporarily "release" the foreground collector from its
2084 // usual obligation to wait for the background collector to
2085 // complete an ongoing phase before proceeding.
2086 class ReleaseForegroundGC: public StackObj {
2087 private:
2088 CMSCollector* _c;
2089 public:
2090 ReleaseForegroundGC(CMSCollector* c) : _c(c) {
2091 assert(_c->_foregroundGCShouldWait, "Else should not need to call");
2092 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2093 // allow a potentially blocked foreground collector to proceed
2094 _c->_foregroundGCShouldWait = false;
2095 if (_c->_foregroundGCIsActive) {
2096 CGC_lock->notify();
2097 }
2098 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2099 "Possible deadlock");
2100 }
2102 ~ReleaseForegroundGC() {
2103 assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?");
2104 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2105 _c->_foregroundGCShouldWait = true;
2106 }
2107 };
2109 // There are separate collect_in_background and collect_in_foreground because of
2110 // the different locking requirements of the background collector and the
2111 // foreground collector. There was originally an attempt to share
2112 // one "collect" method between the background collector and the foreground
2113 // collector but the if-then-else required made it cleaner to have
2114 // separate methods.
2115 void CMSCollector::collect_in_background(bool clear_all_soft_refs) {
2116 assert(Thread::current()->is_ConcurrentGC_thread(),
2117 "A CMS asynchronous collection is only allowed on a CMS thread.");
2119 GenCollectedHeap* gch = GenCollectedHeap::heap();
2120 {
2121 bool safepoint_check = Mutex::_no_safepoint_check_flag;
2122 MutexLockerEx hl(Heap_lock, safepoint_check);
2123 FreelistLocker fll(this);
2124 MutexLockerEx x(CGC_lock, safepoint_check);
2125 if (_foregroundGCIsActive || !UseAsyncConcMarkSweepGC) {
2126 // The foreground collector is active or we're
2127 // not using asynchronous collections. Skip this
2128 // background collection.
2129 assert(!_foregroundGCShouldWait, "Should be clear");
2130 return;
2131 } else {
2132 assert(_collectorState == Idling, "Should be idling before start.");
2133 _collectorState = InitialMarking;
2134 // Reset the expansion cause, now that we are about to begin
2135 // a new cycle.
2136 clear_expansion_cause();
2137 }
2138 // Decide if we want to enable class unloading as part of the
2139 // ensuing concurrent GC cycle.
2140 update_should_unload_classes();
2141 _full_gc_requested = false; // acks all outstanding full gc requests
2142 // Signal that we are about to start a collection
2143 gch->increment_total_full_collections(); // ... starting a collection cycle
2144 _collection_count_start = gch->total_full_collections();
2145 }
2147 // Used for PrintGC
2148 size_t prev_used;
2149 if (PrintGC && Verbose) {
2150 prev_used = _cmsGen->used(); // XXXPERM
2151 }
2153 // The change of the collection state is normally done at this level;
2154 // the exceptions are phases that are executed while the world is
2155 // stopped. For those phases the change of state is done while the
2156 // world is stopped. For baton passing purposes this allows the
2157 // background collector to finish the phase and change state atomically.
2158 // The foreground collector cannot wait on a phase that is done
2159 // while the world is stopped because the foreground collector already
2160 // has the world stopped and would deadlock.
2161 while (_collectorState != Idling) {
2162 if (TraceCMSState) {
2163 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
2164 Thread::current(), _collectorState);
2165 }
2166 // The foreground collector
2167 // holds the Heap_lock throughout its collection.
2168 // holds the CMS token (but not the lock)
2169 // except while it is waiting for the background collector to yield.
2170 //
2171 // The foreground collector should be blocked (not for long)
2172 // if the background collector is about to start a phase
2173 // executed with world stopped. If the background
2174 // collector has already started such a phase, the
2175 // foreground collector is blocked waiting for the
2176 // Heap_lock. The stop-world phases (InitialMarking and FinalMarking)
2177 // are executed in the VM thread.
2178 //
2179 // The locking order is
2180 // PendingListLock (PLL) -- if applicable (FinalMarking)
2181 // Heap_lock (both this & PLL locked in VM_CMS_Operation::prologue())
2182 // CMS token (claimed in
2183 // stop_world_and_do() -->
2184 // safepoint_synchronize() -->
2185 // CMSThread::synchronize())
2187 {
2188 // Check if the FG collector wants us to yield.
2189 CMSTokenSync x(true); // is cms thread
2190 if (waitForForegroundGC()) {
2191 // We yielded to a foreground GC, nothing more to be
2192 // done this round.
2193 assert(_foregroundGCShouldWait == false, "We set it to false in "
2194 "waitForForegroundGC()");
2195 if (TraceCMSState) {
2196 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2197 " exiting collection CMS state %d",
2198 Thread::current(), _collectorState);
2199 }
2200 return;
2201 } else {
2202 // The background collector can run but check to see if the
2203 // foreground collector has done a collection while the
2204 // background collector was waiting to get the CGC_lock
2205 // above. If yes, break so that _foregroundGCShouldWait
2206 // is cleared before returning.
2207 if (_collectorState == Idling) {
2208 break;
2209 }
2210 }
2211 }
2213 assert(_foregroundGCShouldWait, "Foreground collector, if active, "
2214 "should be waiting");
2216 switch (_collectorState) {
2217 case InitialMarking:
2218 {
2219 ReleaseForegroundGC x(this);
2220 stats().record_cms_begin();
2222 VM_CMS_Initial_Mark initial_mark_op(this);
2223 VMThread::execute(&initial_mark_op);
2224 }
2225 // The collector state may be any legal state at this point
2226 // since the background collector may have yielded to the
2227 // foreground collector.
2228 break;
2229 case Marking:
2230 // initial marking in checkpointRootsInitialWork has been completed
2231 if (markFromRoots(true)) { // we were successful
2232 assert(_collectorState == Precleaning, "Collector state should "
2233 "have changed");
2234 } else {
2235 assert(_foregroundGCIsActive, "Internal state inconsistency");
2236 }
2237 break;
2238 case Precleaning:
2239 if (UseAdaptiveSizePolicy) {
2240 size_policy()->concurrent_precleaning_begin();
2241 }
2242 // marking from roots in markFromRoots has been completed
2243 preclean();
2244 if (UseAdaptiveSizePolicy) {
2245 size_policy()->concurrent_precleaning_end();
2246 }
2247 assert(_collectorState == AbortablePreclean ||
2248 _collectorState == FinalMarking,
2249 "Collector state should have changed");
2250 break;
2251 case AbortablePreclean:
2252 if (UseAdaptiveSizePolicy) {
2253 size_policy()->concurrent_phases_resume();
2254 }
2255 abortable_preclean();
2256 if (UseAdaptiveSizePolicy) {
2257 size_policy()->concurrent_precleaning_end();
2258 }
2259 assert(_collectorState == FinalMarking, "Collector state should "
2260 "have changed");
2261 break;
2262 case FinalMarking:
2263 {
2264 ReleaseForegroundGC x(this);
2266 VM_CMS_Final_Remark final_remark_op(this);
2267 VMThread::execute(&final_remark_op);
2268 }
2269 assert(_foregroundGCShouldWait, "block post-condition");
2270 break;
2271 case Sweeping:
2272 if (UseAdaptiveSizePolicy) {
2273 size_policy()->concurrent_sweeping_begin();
2274 }
2275 // final marking in checkpointRootsFinal has been completed
2276 sweep(true);
2277 assert(_collectorState == Resizing, "Collector state change "
2278 "to Resizing must be done under the free_list_lock");
2279 _full_gcs_since_conc_gc = 0;
2281 // Stop the timers for adaptive size policy for the concurrent phases
2282 if (UseAdaptiveSizePolicy) {
2283 size_policy()->concurrent_sweeping_end();
2284 size_policy()->concurrent_phases_end(gch->gc_cause(),
2285 gch->prev_gen(_cmsGen)->capacity(),
2286 _cmsGen->free());
2287 }
2289 case Resizing: {
2290 // Sweeping has been completed...
2291 // At this point the background collection has completed.
2292 // Don't move the call to compute_new_size() down
2293 // into code that might be executed if the background
2294 // collection was preempted.
2295 {
2296 ReleaseForegroundGC x(this); // unblock FG collection
2297 MutexLockerEx y(Heap_lock, Mutex::_no_safepoint_check_flag);
2298 CMSTokenSync z(true); // not strictly needed.
2299 if (_collectorState == Resizing) {
2300 compute_new_size();
2301 _collectorState = Resetting;
2302 } else {
2303 assert(_collectorState == Idling, "The state should only change"
2304 " because the foreground collector has finished the collection");
2305 }
2306 }
2307 break;
2308 }
2309 case Resetting:
2310 // CMS heap resizing has been completed
2311 reset(true);
2312 assert(_collectorState == Idling, "Collector state should "
2313 "have changed");
2314 stats().record_cms_end();
2315 // Don't move the concurrent_phases_end() and compute_new_size()
2316 // calls to here because a preempted background collection
2317 // has it's state set to "Resetting".
2318 break;
2319 case Idling:
2320 default:
2321 ShouldNotReachHere();
2322 break;
2323 }
2324 if (TraceCMSState) {
2325 gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d",
2326 Thread::current(), _collectorState);
2327 }
2328 assert(_foregroundGCShouldWait, "block post-condition");
2329 }
2331 // Should this be in gc_epilogue?
2332 collector_policy()->counters()->update_counters();
2334 {
2335 // Clear _foregroundGCShouldWait and, in the event that the
2336 // foreground collector is waiting, notify it, before
2337 // returning.
2338 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2339 _foregroundGCShouldWait = false;
2340 if (_foregroundGCIsActive) {
2341 CGC_lock->notify();
2342 }
2343 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2344 "Possible deadlock");
2345 }
2346 if (TraceCMSState) {
2347 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2348 " exiting collection CMS state %d",
2349 Thread::current(), _collectorState);
2350 }
2351 if (PrintGC && Verbose) {
2352 _cmsGen->print_heap_change(prev_used);
2353 }
2354 }
2356 void CMSCollector::collect_in_foreground(bool clear_all_soft_refs) {
2357 assert(_foregroundGCIsActive && !_foregroundGCShouldWait,
2358 "Foreground collector should be waiting, not executing");
2359 assert(Thread::current()->is_VM_thread(), "A foreground collection"
2360 "may only be done by the VM Thread with the world stopped");
2361 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
2362 "VM thread should have CMS token");
2364 NOT_PRODUCT(TraceTime t("CMS:MS (foreground) ", PrintGCDetails && Verbose,
2365 true, gclog_or_tty);)
2366 if (UseAdaptiveSizePolicy) {
2367 size_policy()->ms_collection_begin();
2368 }
2369 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact);
2371 HandleMark hm; // Discard invalid handles created during verification
2373 if (VerifyBeforeGC &&
2374 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2375 Universe::verify(true);
2376 }
2378 bool init_mark_was_synchronous = false; // until proven otherwise
2379 while (_collectorState != Idling) {
2380 if (TraceCMSState) {
2381 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
2382 Thread::current(), _collectorState);
2383 }
2384 switch (_collectorState) {
2385 case InitialMarking:
2386 init_mark_was_synchronous = true; // fact to be exploited in re-mark
2387 checkpointRootsInitial(false);
2388 assert(_collectorState == Marking, "Collector state should have changed"
2389 " within checkpointRootsInitial()");
2390 break;
2391 case Marking:
2392 // initial marking in checkpointRootsInitialWork has been completed
2393 if (VerifyDuringGC &&
2394 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2395 gclog_or_tty->print("Verify before initial mark: ");
2396 Universe::verify(true);
2397 }
2398 {
2399 bool res = markFromRoots(false);
2400 assert(res && _collectorState == FinalMarking, "Collector state should "
2401 "have changed");
2402 break;
2403 }
2404 case FinalMarking:
2405 if (VerifyDuringGC &&
2406 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2407 gclog_or_tty->print("Verify before re-mark: ");
2408 Universe::verify(true);
2409 }
2410 checkpointRootsFinal(false, clear_all_soft_refs,
2411 init_mark_was_synchronous);
2412 assert(_collectorState == Sweeping, "Collector state should not "
2413 "have changed within checkpointRootsFinal()");
2414 break;
2415 case Sweeping:
2416 // final marking in checkpointRootsFinal has been completed
2417 if (VerifyDuringGC &&
2418 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2419 gclog_or_tty->print("Verify before sweep: ");
2420 Universe::verify(true);
2421 }
2422 sweep(false);
2423 assert(_collectorState == Resizing, "Incorrect state");
2424 break;
2425 case Resizing: {
2426 // Sweeping has been completed; the actual resize in this case
2427 // is done separately; nothing to be done in this state.
2428 _collectorState = Resetting;
2429 break;
2430 }
2431 case Resetting:
2432 // The heap has been resized.
2433 if (VerifyDuringGC &&
2434 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2435 gclog_or_tty->print("Verify before reset: ");
2436 Universe::verify(true);
2437 }
2438 reset(false);
2439 assert(_collectorState == Idling, "Collector state should "
2440 "have changed");
2441 break;
2442 case Precleaning:
2443 case AbortablePreclean:
2444 // Elide the preclean phase
2445 _collectorState = FinalMarking;
2446 break;
2447 default:
2448 ShouldNotReachHere();
2449 }
2450 if (TraceCMSState) {
2451 gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d",
2452 Thread::current(), _collectorState);
2453 }
2454 }
2456 if (UseAdaptiveSizePolicy) {
2457 GenCollectedHeap* gch = GenCollectedHeap::heap();
2458 size_policy()->ms_collection_end(gch->gc_cause());
2459 }
2461 if (VerifyAfterGC &&
2462 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2463 Universe::verify(true);
2464 }
2465 if (TraceCMSState) {
2466 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2467 " exiting collection CMS state %d",
2468 Thread::current(), _collectorState);
2469 }
2470 }
2472 bool CMSCollector::waitForForegroundGC() {
2473 bool res = false;
2474 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2475 "CMS thread should have CMS token");
2476 // Block the foreground collector until the
2477 // background collectors decides whether to
2478 // yield.
2479 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2480 _foregroundGCShouldWait = true;
2481 if (_foregroundGCIsActive) {
2482 // The background collector yields to the
2483 // foreground collector and returns a value
2484 // indicating that it has yielded. The foreground
2485 // collector can proceed.
2486 res = true;
2487 _foregroundGCShouldWait = false;
2488 ConcurrentMarkSweepThread::clear_CMS_flag(
2489 ConcurrentMarkSweepThread::CMS_cms_has_token);
2490 ConcurrentMarkSweepThread::set_CMS_flag(
2491 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2492 // Get a possibly blocked foreground thread going
2493 CGC_lock->notify();
2494 if (TraceCMSState) {
2495 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d",
2496 Thread::current(), _collectorState);
2497 }
2498 while (_foregroundGCIsActive) {
2499 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
2500 }
2501 ConcurrentMarkSweepThread::set_CMS_flag(
2502 ConcurrentMarkSweepThread::CMS_cms_has_token);
2503 ConcurrentMarkSweepThread::clear_CMS_flag(
2504 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2505 }
2506 if (TraceCMSState) {
2507 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d",
2508 Thread::current(), _collectorState);
2509 }
2510 return res;
2511 }
2513 // Because of the need to lock the free lists and other structures in
2514 // the collector, common to all the generations that the collector is
2515 // collecting, we need the gc_prologues of individual CMS generations
2516 // delegate to their collector. It may have been simpler had the
2517 // current infrastructure allowed one to call a prologue on a
2518 // collector. In the absence of that we have the generation's
2519 // prologue delegate to the collector, which delegates back
2520 // some "local" work to a worker method in the individual generations
2521 // that it's responsible for collecting, while itself doing any
2522 // work common to all generations it's responsible for. A similar
2523 // comment applies to the gc_epilogue()'s.
2524 // The role of the varaible _between_prologue_and_epilogue is to
2525 // enforce the invocation protocol.
2526 void CMSCollector::gc_prologue(bool full) {
2527 // Call gc_prologue_work() for each CMSGen and PermGen that
2528 // we are responsible for.
2530 // The following locking discipline assumes that we are only called
2531 // when the world is stopped.
2532 assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption");
2534 // The CMSCollector prologue must call the gc_prologues for the
2535 // "generations" (including PermGen if any) that it's responsible
2536 // for.
2538 assert( Thread::current()->is_VM_thread()
2539 || ( CMSScavengeBeforeRemark
2540 && Thread::current()->is_ConcurrentGC_thread()),
2541 "Incorrect thread type for prologue execution");
2543 if (_between_prologue_and_epilogue) {
2544 // We have already been invoked; this is a gc_prologue delegation
2545 // from yet another CMS generation that we are responsible for, just
2546 // ignore it since all relevant work has already been done.
2547 return;
2548 }
2550 // set a bit saying prologue has been called; cleared in epilogue
2551 _between_prologue_and_epilogue = true;
2552 // Claim locks for common data structures, then call gc_prologue_work()
2553 // for each CMSGen and PermGen that we are responsible for.
2555 getFreelistLocks(); // gets free list locks on constituent spaces
2556 bitMapLock()->lock_without_safepoint_check();
2558 // Should call gc_prologue_work() for all cms gens we are responsible for
2559 bool registerClosure = _collectorState >= Marking
2560 && _collectorState < Sweeping;
2561 ModUnionClosure* muc = ParallelGCThreads > 0 ? &_modUnionClosurePar
2562 : &_modUnionClosure;
2563 _cmsGen->gc_prologue_work(full, registerClosure, muc);
2564 _permGen->gc_prologue_work(full, registerClosure, muc);
2566 if (!full) {
2567 stats().record_gc0_begin();
2568 }
2569 }
2571 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) {
2572 // Delegate to CMScollector which knows how to coordinate between
2573 // this and any other CMS generations that it is responsible for
2574 // collecting.
2575 collector()->gc_prologue(full);
2576 }
2578 // This is a "private" interface for use by this generation's CMSCollector.
2579 // Not to be called directly by any other entity (for instance,
2580 // GenCollectedHeap, which calls the "public" gc_prologue method above).
2581 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full,
2582 bool registerClosure, ModUnionClosure* modUnionClosure) {
2583 assert(!incremental_collection_failed(), "Shouldn't be set yet");
2584 assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL,
2585 "Should be NULL");
2586 if (registerClosure) {
2587 cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure);
2588 }
2589 cmsSpace()->gc_prologue();
2590 // Clear stat counters
2591 NOT_PRODUCT(
2592 assert(_numObjectsPromoted == 0, "check");
2593 assert(_numWordsPromoted == 0, "check");
2594 if (Verbose && PrintGC) {
2595 gclog_or_tty->print("Allocated "SIZE_FORMAT" objects, "
2596 SIZE_FORMAT" bytes concurrently",
2597 _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord));
2598 }
2599 _numObjectsAllocated = 0;
2600 _numWordsAllocated = 0;
2601 )
2602 }
2604 void CMSCollector::gc_epilogue(bool full) {
2605 // The following locking discipline assumes that we are only called
2606 // when the world is stopped.
2607 assert(SafepointSynchronize::is_at_safepoint(),
2608 "world is stopped assumption");
2610 // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks
2611 // if linear allocation blocks need to be appropriately marked to allow the
2612 // the blocks to be parsable. We also check here whether we need to nudge the
2613 // CMS collector thread to start a new cycle (if it's not already active).
2614 assert( Thread::current()->is_VM_thread()
2615 || ( CMSScavengeBeforeRemark
2616 && Thread::current()->is_ConcurrentGC_thread()),
2617 "Incorrect thread type for epilogue execution");
2619 if (!_between_prologue_and_epilogue) {
2620 // We have already been invoked; this is a gc_epilogue delegation
2621 // from yet another CMS generation that we are responsible for, just
2622 // ignore it since all relevant work has already been done.
2623 return;
2624 }
2625 assert(haveFreelistLocks(), "must have freelist locks");
2626 assert_lock_strong(bitMapLock());
2628 _cmsGen->gc_epilogue_work(full);
2629 _permGen->gc_epilogue_work(full);
2631 if (_collectorState == AbortablePreclean || _collectorState == Precleaning) {
2632 // in case sampling was not already enabled, enable it
2633 _start_sampling = true;
2634 }
2635 // reset _eden_chunk_array so sampling starts afresh
2636 _eden_chunk_index = 0;
2638 size_t cms_used = _cmsGen->cmsSpace()->used();
2639 size_t perm_used = _permGen->cmsSpace()->used();
2641 // update performance counters - this uses a special version of
2642 // update_counters() that allows the utilization to be passed as a
2643 // parameter, avoiding multiple calls to used().
2644 //
2645 _cmsGen->update_counters(cms_used);
2646 _permGen->update_counters(perm_used);
2648 if (CMSIncrementalMode) {
2649 icms_update_allocation_limits();
2650 }
2652 bitMapLock()->unlock();
2653 releaseFreelistLocks();
2655 _between_prologue_and_epilogue = false; // ready for next cycle
2656 }
2658 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) {
2659 collector()->gc_epilogue(full);
2661 // Also reset promotion tracking in par gc thread states.
2662 if (ParallelGCThreads > 0) {
2663 for (uint i = 0; i < ParallelGCThreads; i++) {
2664 _par_gc_thread_states[i]->promo.stopTrackingPromotions();
2665 }
2666 }
2667 }
2669 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2670 assert(!incremental_collection_failed(), "Should have been cleared");
2671 cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2672 cmsSpace()->gc_epilogue();
2673 // Print stat counters
2674 NOT_PRODUCT(
2675 assert(_numObjectsAllocated == 0, "check");
2676 assert(_numWordsAllocated == 0, "check");
2677 if (Verbose && PrintGC) {
2678 gclog_or_tty->print("Promoted "SIZE_FORMAT" objects, "
2679 SIZE_FORMAT" bytes",
2680 _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2681 }
2682 _numObjectsPromoted = 0;
2683 _numWordsPromoted = 0;
2684 )
2686 if (PrintGC && Verbose) {
2687 // Call down the chain in contiguous_available needs the freelistLock
2688 // so print this out before releasing the freeListLock.
2689 gclog_or_tty->print(" Contiguous available "SIZE_FORMAT" bytes ",
2690 contiguous_available());
2691 }
2692 }
2694 #ifndef PRODUCT
2695 bool CMSCollector::have_cms_token() {
2696 Thread* thr = Thread::current();
2697 if (thr->is_VM_thread()) {
2698 return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2699 } else if (thr->is_ConcurrentGC_thread()) {
2700 return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2701 } else if (thr->is_GC_task_thread()) {
2702 return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2703 ParGCRareEvent_lock->owned_by_self();
2704 }
2705 return false;
2706 }
2707 #endif
2709 // Check reachability of the given heap address in CMS generation,
2710 // treating all other generations as roots.
2711 bool CMSCollector::is_cms_reachable(HeapWord* addr) {
2712 // We could "guarantee" below, rather than assert, but i'll
2713 // leave these as "asserts" so that an adventurous debugger
2714 // could try this in the product build provided some subset of
2715 // the conditions were met, provided they were intersted in the
2716 // results and knew that the computation below wouldn't interfere
2717 // with other concurrent computations mutating the structures
2718 // being read or written.
2719 assert(SafepointSynchronize::is_at_safepoint(),
2720 "Else mutations in object graph will make answer suspect");
2721 assert(have_cms_token(), "Should hold cms token");
2722 assert(haveFreelistLocks(), "must hold free list locks");
2723 assert_lock_strong(bitMapLock());
2725 // Clear the marking bit map array before starting, but, just
2726 // for kicks, first report if the given address is already marked
2727 gclog_or_tty->print_cr("Start: Address 0x%x is%s marked", addr,
2728 _markBitMap.isMarked(addr) ? "" : " not");
2730 if (verify_after_remark()) {
2731 MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2732 bool result = verification_mark_bm()->isMarked(addr);
2733 gclog_or_tty->print_cr("TransitiveMark: Address 0x%x %s marked", addr,
2734 result ? "IS" : "is NOT");
2735 return result;
2736 } else {
2737 gclog_or_tty->print_cr("Could not compute result");
2738 return false;
2739 }
2740 }
2742 ////////////////////////////////////////////////////////
2743 // CMS Verification Support
2744 ////////////////////////////////////////////////////////
2745 // Following the remark phase, the following invariant
2746 // should hold -- each object in the CMS heap which is
2747 // marked in markBitMap() should be marked in the verification_mark_bm().
2749 class VerifyMarkedClosure: public BitMapClosure {
2750 CMSBitMap* _marks;
2751 bool _failed;
2753 public:
2754 VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2756 void do_bit(size_t offset) {
2757 HeapWord* addr = _marks->offsetToHeapWord(offset);
2758 if (!_marks->isMarked(addr)) {
2759 oop(addr)->print();
2760 gclog_or_tty->print_cr(" ("INTPTR_FORMAT" should have been marked)", addr);
2761 _failed = true;
2762 }
2763 }
2765 bool failed() { return _failed; }
2766 };
2768 bool CMSCollector::verify_after_remark() {
2769 gclog_or_tty->print(" [Verifying CMS Marking... ");
2770 MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2771 static bool init = false;
2773 assert(SafepointSynchronize::is_at_safepoint(),
2774 "Else mutations in object graph will make answer suspect");
2775 assert(have_cms_token(),
2776 "Else there may be mutual interference in use of "
2777 " verification data structures");
2778 assert(_collectorState > Marking && _collectorState <= Sweeping,
2779 "Else marking info checked here may be obsolete");
2780 assert(haveFreelistLocks(), "must hold free list locks");
2781 assert_lock_strong(bitMapLock());
2784 // Allocate marking bit map if not already allocated
2785 if (!init) { // first time
2786 if (!verification_mark_bm()->allocate(_span)) {
2787 return false;
2788 }
2789 init = true;
2790 }
2792 assert(verification_mark_stack()->isEmpty(), "Should be empty");
2794 // Turn off refs discovery -- so we will be tracing through refs.
2795 // This is as intended, because by this time
2796 // GC must already have cleared any refs that need to be cleared,
2797 // and traced those that need to be marked; moreover,
2798 // the marking done here is not going to intefere in any
2799 // way with the marking information used by GC.
2800 NoRefDiscovery no_discovery(ref_processor());
2802 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
2804 // Clear any marks from a previous round
2805 verification_mark_bm()->clear_all();
2806 assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
2807 assert(overflow_list_is_empty(), "overflow list should be empty");
2809 GenCollectedHeap* gch = GenCollectedHeap::heap();
2810 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
2811 // Update the saved marks which may affect the root scans.
2812 gch->save_marks();
2814 if (CMSRemarkVerifyVariant == 1) {
2815 // In this first variant of verification, we complete
2816 // all marking, then check if the new marks-verctor is
2817 // a subset of the CMS marks-vector.
2818 verify_after_remark_work_1();
2819 } else if (CMSRemarkVerifyVariant == 2) {
2820 // In this second variant of verification, we flag an error
2821 // (i.e. an object reachable in the new marks-vector not reachable
2822 // in the CMS marks-vector) immediately, also indicating the
2823 // identify of an object (A) that references the unmarked object (B) --
2824 // presumably, a mutation to A failed to be picked up by preclean/remark?
2825 verify_after_remark_work_2();
2826 } else {
2827 warning("Unrecognized value %d for CMSRemarkVerifyVariant",
2828 CMSRemarkVerifyVariant);
2829 }
2830 gclog_or_tty->print(" done] ");
2831 return true;
2832 }
2834 void CMSCollector::verify_after_remark_work_1() {
2835 ResourceMark rm;
2836 HandleMark hm;
2837 GenCollectedHeap* gch = GenCollectedHeap::heap();
2839 // Mark from roots one level into CMS
2840 MarkRefsIntoClosure notOlder(_span, verification_mark_bm(), true /* nmethods */);
2841 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2843 gch->gen_process_strong_roots(_cmsGen->level(),
2844 true, // younger gens are roots
2845 true, // collecting perm gen
2846 SharedHeap::ScanningOption(roots_scanning_options()),
2847 NULL, ¬Older);
2849 // Now mark from the roots
2850 assert(_revisitStack.isEmpty(), "Should be empty");
2851 MarkFromRootsClosure markFromRootsClosure(this, _span,
2852 verification_mark_bm(), verification_mark_stack(), &_revisitStack,
2853 false /* don't yield */, true /* verifying */);
2854 assert(_restart_addr == NULL, "Expected pre-condition");
2855 verification_mark_bm()->iterate(&markFromRootsClosure);
2856 while (_restart_addr != NULL) {
2857 // Deal with stack overflow: by restarting at the indicated
2858 // address.
2859 HeapWord* ra = _restart_addr;
2860 markFromRootsClosure.reset(ra);
2861 _restart_addr = NULL;
2862 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2863 }
2864 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2865 verify_work_stacks_empty();
2866 // Should reset the revisit stack above, since no class tree
2867 // surgery is forthcoming.
2868 _revisitStack.reset(); // throwing away all contents
2870 // Marking completed -- now verify that each bit marked in
2871 // verification_mark_bm() is also marked in markBitMap(); flag all
2872 // errors by printing corresponding objects.
2873 VerifyMarkedClosure vcl(markBitMap());
2874 verification_mark_bm()->iterate(&vcl);
2875 if (vcl.failed()) {
2876 gclog_or_tty->print("Verification failed");
2877 Universe::heap()->print();
2878 fatal(" ... aborting");
2879 }
2880 }
2882 void CMSCollector::verify_after_remark_work_2() {
2883 ResourceMark rm;
2884 HandleMark hm;
2885 GenCollectedHeap* gch = GenCollectedHeap::heap();
2887 // Mark from roots one level into CMS
2888 MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
2889 markBitMap(), true /* nmethods */);
2890 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2891 gch->gen_process_strong_roots(_cmsGen->level(),
2892 true, // younger gens are roots
2893 true, // collecting perm gen
2894 SharedHeap::ScanningOption(roots_scanning_options()),
2895 NULL, ¬Older);
2897 // Now mark from the roots
2898 assert(_revisitStack.isEmpty(), "Should be empty");
2899 MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
2900 verification_mark_bm(), markBitMap(), verification_mark_stack());
2901 assert(_restart_addr == NULL, "Expected pre-condition");
2902 verification_mark_bm()->iterate(&markFromRootsClosure);
2903 while (_restart_addr != NULL) {
2904 // Deal with stack overflow: by restarting at the indicated
2905 // address.
2906 HeapWord* ra = _restart_addr;
2907 markFromRootsClosure.reset(ra);
2908 _restart_addr = NULL;
2909 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2910 }
2911 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2912 verify_work_stacks_empty();
2913 // Should reset the revisit stack above, since no class tree
2914 // surgery is forthcoming.
2915 _revisitStack.reset(); // throwing away all contents
2917 // Marking completed -- now verify that each bit marked in
2918 // verification_mark_bm() is also marked in markBitMap(); flag all
2919 // errors by printing corresponding objects.
2920 VerifyMarkedClosure vcl(markBitMap());
2921 verification_mark_bm()->iterate(&vcl);
2922 assert(!vcl.failed(), "Else verification above should not have succeeded");
2923 }
2925 void ConcurrentMarkSweepGeneration::save_marks() {
2926 // delegate to CMS space
2927 cmsSpace()->save_marks();
2928 for (uint i = 0; i < ParallelGCThreads; i++) {
2929 _par_gc_thread_states[i]->promo.startTrackingPromotions();
2930 }
2931 }
2933 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
2934 return cmsSpace()->no_allocs_since_save_marks();
2935 }
2937 #define CMS_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix) \
2938 \
2939 void ConcurrentMarkSweepGeneration:: \
2940 oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) { \
2941 cl->set_generation(this); \
2942 cmsSpace()->oop_since_save_marks_iterate##nv_suffix(cl); \
2943 cl->reset_generation(); \
2944 save_marks(); \
2945 }
2947 ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DEFN)
2949 void
2950 ConcurrentMarkSweepGeneration::object_iterate_since_last_GC(ObjectClosure* blk)
2951 {
2952 // Not currently implemented; need to do the following. -- ysr.
2953 // dld -- I think that is used for some sort of allocation profiler. So it
2954 // really means the objects allocated by the mutator since the last
2955 // GC. We could potentially implement this cheaply by recording only
2956 // the direct allocations in a side data structure.
2957 //
2958 // I think we probably ought not to be required to support these
2959 // iterations at any arbitrary point; I think there ought to be some
2960 // call to enable/disable allocation profiling in a generation/space,
2961 // and the iterator ought to return the objects allocated in the
2962 // gen/space since the enable call, or the last iterator call (which
2963 // will probably be at a GC.) That way, for gens like CM&S that would
2964 // require some extra data structure to support this, we only pay the
2965 // cost when it's in use...
2966 cmsSpace()->object_iterate_since_last_GC(blk);
2967 }
2969 void
2970 ConcurrentMarkSweepGeneration::younger_refs_iterate(OopsInGenClosure* cl) {
2971 cl->set_generation(this);
2972 younger_refs_in_space_iterate(_cmsSpace, cl);
2973 cl->reset_generation();
2974 }
2976 void
2977 ConcurrentMarkSweepGeneration::oop_iterate(MemRegion mr, OopClosure* cl) {
2978 if (freelistLock()->owned_by_self()) {
2979 Generation::oop_iterate(mr, cl);
2980 } else {
2981 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2982 Generation::oop_iterate(mr, cl);
2983 }
2984 }
2986 void
2987 ConcurrentMarkSweepGeneration::oop_iterate(OopClosure* cl) {
2988 if (freelistLock()->owned_by_self()) {
2989 Generation::oop_iterate(cl);
2990 } else {
2991 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2992 Generation::oop_iterate(cl);
2993 }
2994 }
2996 void
2997 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
2998 if (freelistLock()->owned_by_self()) {
2999 Generation::object_iterate(cl);
3000 } else {
3001 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3002 Generation::object_iterate(cl);
3003 }
3004 }
3006 void
3007 ConcurrentMarkSweepGeneration::pre_adjust_pointers() {
3008 }
3010 void
3011 ConcurrentMarkSweepGeneration::post_compact() {
3012 }
3014 void
3015 ConcurrentMarkSweepGeneration::prepare_for_verify() {
3016 // Fix the linear allocation blocks to look like free blocks.
3018 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
3019 // are not called when the heap is verified during universe initialization and
3020 // at vm shutdown.
3021 if (freelistLock()->owned_by_self()) {
3022 cmsSpace()->prepare_for_verify();
3023 } else {
3024 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
3025 cmsSpace()->prepare_for_verify();
3026 }
3027 }
3029 void
3030 ConcurrentMarkSweepGeneration::verify(bool allow_dirty /* ignored */) {
3031 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
3032 // are not called when the heap is verified during universe initialization and
3033 // at vm shutdown.
3034 if (freelistLock()->owned_by_self()) {
3035 cmsSpace()->verify(false /* ignored */);
3036 } else {
3037 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
3038 cmsSpace()->verify(false /* ignored */);
3039 }
3040 }
3042 void CMSCollector::verify(bool allow_dirty /* ignored */) {
3043 _cmsGen->verify(allow_dirty);
3044 _permGen->verify(allow_dirty);
3045 }
3047 #ifndef PRODUCT
3048 bool CMSCollector::overflow_list_is_empty() const {
3049 assert(_num_par_pushes >= 0, "Inconsistency");
3050 if (_overflow_list == NULL) {
3051 assert(_num_par_pushes == 0, "Inconsistency");
3052 }
3053 return _overflow_list == NULL;
3054 }
3056 // The methods verify_work_stacks_empty() and verify_overflow_empty()
3057 // merely consolidate assertion checks that appear to occur together frequently.
3058 void CMSCollector::verify_work_stacks_empty() const {
3059 assert(_markStack.isEmpty(), "Marking stack should be empty");
3060 assert(overflow_list_is_empty(), "Overflow list should be empty");
3061 }
3063 void CMSCollector::verify_overflow_empty() const {
3064 assert(overflow_list_is_empty(), "Overflow list should be empty");
3065 assert(no_preserved_marks(), "No preserved marks");
3066 }
3067 #endif // PRODUCT
3069 // Decide if we want to enable class unloading as part of the
3070 // ensuing concurrent GC cycle. We will collect the perm gen and
3071 // unload classes if it's the case that:
3072 // (1) an explicit gc request has been made and the flag
3073 // ExplicitGCInvokesConcurrentAndUnloadsClasses is set, OR
3074 // (2) (a) class unloading is enabled at the command line, and
3075 // (b) (i) perm gen threshold has been crossed, or
3076 // (ii) old gen is getting really full, or
3077 // (iii) the previous N CMS collections did not collect the
3078 // perm gen
3079 // NOTE: Provided there is no change in the state of the heap between
3080 // calls to this method, it should have idempotent results. Moreover,
3081 // its results should be monotonically increasing (i.e. going from 0 to 1,
3082 // but not 1 to 0) between successive calls between which the heap was
3083 // not collected. For the implementation below, it must thus rely on
3084 // the property that concurrent_cycles_since_last_unload()
3085 // will not decrease unless a collection cycle happened and that
3086 // _permGen->should_concurrent_collect() and _cmsGen->is_too_full() are
3087 // themselves also monotonic in that sense. See check_monotonicity()
3088 // below.
3089 bool CMSCollector::update_should_unload_classes() {
3090 _should_unload_classes = false;
3091 // Condition 1 above
3092 if (_full_gc_requested && ExplicitGCInvokesConcurrentAndUnloadsClasses) {
3093 _should_unload_classes = true;
3094 } else if (CMSClassUnloadingEnabled) { // Condition 2.a above
3095 // Disjuncts 2.b.(i,ii,iii) above
3096 _should_unload_classes = (concurrent_cycles_since_last_unload() >=
3097 CMSClassUnloadingMaxInterval)
3098 || _permGen->should_concurrent_collect()
3099 || _cmsGen->is_too_full();
3100 }
3101 return _should_unload_classes;
3102 }
3104 bool ConcurrentMarkSweepGeneration::is_too_full() const {
3105 bool res = should_concurrent_collect();
3106 res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
3107 return res;
3108 }
3110 void CMSCollector::setup_cms_unloading_and_verification_state() {
3111 const bool should_verify = VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
3112 || VerifyBeforeExit;
3113 const int rso = SharedHeap::SO_Symbols | SharedHeap::SO_Strings
3114 | SharedHeap::SO_CodeCache;
3116 if (should_unload_classes()) { // Should unload classes this cycle
3117 remove_root_scanning_option(rso); // Shrink the root set appropriately
3118 set_verifying(should_verify); // Set verification state for this cycle
3119 return; // Nothing else needs to be done at this time
3120 }
3122 // Not unloading classes this cycle
3123 assert(!should_unload_classes(), "Inconsitency!");
3124 if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
3125 // We were not verifying, or we _were_ unloading classes in the last cycle,
3126 // AND some verification options are enabled this cycle; in this case,
3127 // we must make sure that the deadness map is allocated if not already so,
3128 // and cleared (if already allocated previously --
3129 // CMSBitMap::sizeInBits() is used to determine if it's allocated).
3130 if (perm_gen_verify_bit_map()->sizeInBits() == 0) {
3131 if (!perm_gen_verify_bit_map()->allocate(_permGen->reserved())) {
3132 warning("Failed to allocate permanent generation verification CMS Bit Map;\n"
3133 "permanent generation verification disabled");
3134 return; // Note that we leave verification disabled, so we'll retry this
3135 // allocation next cycle. We _could_ remember this failure
3136 // and skip further attempts and permanently disable verification
3137 // attempts if that is considered more desirable.
3138 }
3139 assert(perm_gen_verify_bit_map()->covers(_permGen->reserved()),
3140 "_perm_gen_ver_bit_map inconsistency?");
3141 } else {
3142 perm_gen_verify_bit_map()->clear_all();
3143 }
3144 // Include symbols, strings and code cache elements to prevent their resurrection.
3145 add_root_scanning_option(rso);
3146 set_verifying(true);
3147 } else if (verifying() && !should_verify) {
3148 // We were verifying, but some verification flags got disabled.
3149 set_verifying(false);
3150 // Exclude symbols, strings and code cache elements from root scanning to
3151 // reduce IM and RM pauses.
3152 remove_root_scanning_option(rso);
3153 }
3154 }
3157 #ifndef PRODUCT
3158 HeapWord* CMSCollector::block_start(const void* p) const {
3159 const HeapWord* addr = (HeapWord*)p;
3160 if (_span.contains(p)) {
3161 if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
3162 return _cmsGen->cmsSpace()->block_start(p);
3163 } else {
3164 assert(_permGen->cmsSpace()->is_in_reserved(addr),
3165 "Inconsistent _span?");
3166 return _permGen->cmsSpace()->block_start(p);
3167 }
3168 }
3169 return NULL;
3170 }
3171 #endif
3173 HeapWord*
3174 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
3175 bool tlab,
3176 bool parallel) {
3177 assert(!tlab, "Can't deal with TLAB allocation");
3178 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3179 expand(word_size*HeapWordSize, MinHeapDeltaBytes,
3180 CMSExpansionCause::_satisfy_allocation);
3181 if (GCExpandToAllocateDelayMillis > 0) {
3182 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3183 }
3184 return have_lock_and_allocate(word_size, tlab);
3185 }
3187 // YSR: All of this generation expansion/shrinking stuff is an exact copy of
3188 // OneContigSpaceCardGeneration, which makes me wonder if we should move this
3189 // to CardGeneration and share it...
3190 void ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes,
3191 CMSExpansionCause::Cause cause)
3192 {
3193 assert_locked_or_safepoint(Heap_lock);
3195 size_t aligned_bytes = ReservedSpace::page_align_size_up(bytes);
3196 size_t aligned_expand_bytes = ReservedSpace::page_align_size_up(expand_bytes);
3197 bool success = false;
3198 if (aligned_expand_bytes > aligned_bytes) {
3199 success = grow_by(aligned_expand_bytes);
3200 }
3201 if (!success) {
3202 success = grow_by(aligned_bytes);
3203 }
3204 if (!success) {
3205 size_t remaining_bytes = _virtual_space.uncommitted_size();
3206 if (remaining_bytes > 0) {
3207 success = grow_by(remaining_bytes);
3208 }
3209 }
3210 if (GC_locker::is_active()) {
3211 if (PrintGC && Verbose) {
3212 gclog_or_tty->print_cr("Garbage collection disabled, expanded heap instead");
3213 }
3214 }
3215 // remember why we expanded; this information is used
3216 // by shouldConcurrentCollect() when making decisions on whether to start
3217 // a new CMS cycle.
3218 if (success) {
3219 set_expansion_cause(cause);
3220 if (PrintGCDetails && Verbose) {
3221 gclog_or_tty->print_cr("Expanded CMS gen for %s",
3222 CMSExpansionCause::to_string(cause));
3223 }
3224 }
3225 }
3227 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
3228 HeapWord* res = NULL;
3229 MutexLocker x(ParGCRareEvent_lock);
3230 while (true) {
3231 // Expansion by some other thread might make alloc OK now:
3232 res = ps->lab.alloc(word_sz);
3233 if (res != NULL) return res;
3234 // If there's not enough expansion space available, give up.
3235 if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
3236 return NULL;
3237 }
3238 // Otherwise, we try expansion.
3239 expand(word_sz*HeapWordSize, MinHeapDeltaBytes,
3240 CMSExpansionCause::_allocate_par_lab);
3241 // Now go around the loop and try alloc again;
3242 // A competing par_promote might beat us to the expansion space,
3243 // so we may go around the loop again if promotion fails agaion.
3244 if (GCExpandToAllocateDelayMillis > 0) {
3245 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3246 }
3247 }
3248 }
3251 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
3252 PromotionInfo* promo) {
3253 MutexLocker x(ParGCRareEvent_lock);
3254 size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
3255 while (true) {
3256 // Expansion by some other thread might make alloc OK now:
3257 if (promo->ensure_spooling_space()) {
3258 assert(promo->has_spooling_space(),
3259 "Post-condition of successful ensure_spooling_space()");
3260 return true;
3261 }
3262 // If there's not enough expansion space available, give up.
3263 if (_virtual_space.uncommitted_size() < refill_size_bytes) {
3264 return false;
3265 }
3266 // Otherwise, we try expansion.
3267 expand(refill_size_bytes, MinHeapDeltaBytes,
3268 CMSExpansionCause::_allocate_par_spooling_space);
3269 // Now go around the loop and try alloc again;
3270 // A competing allocation might beat us to the expansion space,
3271 // so we may go around the loop again if allocation fails again.
3272 if (GCExpandToAllocateDelayMillis > 0) {
3273 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3274 }
3275 }
3276 }
3280 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
3281 assert_locked_or_safepoint(Heap_lock);
3282 size_t size = ReservedSpace::page_align_size_down(bytes);
3283 if (size > 0) {
3284 shrink_by(size);
3285 }
3286 }
3288 bool ConcurrentMarkSweepGeneration::grow_by(size_t bytes) {
3289 assert_locked_or_safepoint(Heap_lock);
3290 bool result = _virtual_space.expand_by(bytes);
3291 if (result) {
3292 HeapWord* old_end = _cmsSpace->end();
3293 size_t new_word_size =
3294 heap_word_size(_virtual_space.committed_size());
3295 MemRegion mr(_cmsSpace->bottom(), new_word_size);
3296 _bts->resize(new_word_size); // resize the block offset shared array
3297 Universe::heap()->barrier_set()->resize_covered_region(mr);
3298 // Hmmmm... why doesn't CFLS::set_end verify locking?
3299 // This is quite ugly; FIX ME XXX
3300 _cmsSpace->assert_locked();
3301 _cmsSpace->set_end((HeapWord*)_virtual_space.high());
3303 // update the space and generation capacity counters
3304 if (UsePerfData) {
3305 _space_counters->update_capacity();
3306 _gen_counters->update_all();
3307 }
3309 if (Verbose && PrintGC) {
3310 size_t new_mem_size = _virtual_space.committed_size();
3311 size_t old_mem_size = new_mem_size - bytes;
3312 gclog_or_tty->print_cr("Expanding %s from %ldK by %ldK to %ldK",
3313 name(), old_mem_size/K, bytes/K, new_mem_size/K);
3314 }
3315 }
3316 return result;
3317 }
3319 bool ConcurrentMarkSweepGeneration::grow_to_reserved() {
3320 assert_locked_or_safepoint(Heap_lock);
3321 bool success = true;
3322 const size_t remaining_bytes = _virtual_space.uncommitted_size();
3323 if (remaining_bytes > 0) {
3324 success = grow_by(remaining_bytes);
3325 DEBUG_ONLY(if (!success) warning("grow to reserved failed");)
3326 }
3327 return success;
3328 }
3330 void ConcurrentMarkSweepGeneration::shrink_by(size_t bytes) {
3331 assert_locked_or_safepoint(Heap_lock);
3332 assert_lock_strong(freelistLock());
3333 // XXX Fix when compaction is implemented.
3334 warning("Shrinking of CMS not yet implemented");
3335 return;
3336 }
3339 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
3340 // phases.
3341 class CMSPhaseAccounting: public StackObj {
3342 public:
3343 CMSPhaseAccounting(CMSCollector *collector,
3344 const char *phase,
3345 bool print_cr = true);
3346 ~CMSPhaseAccounting();
3348 private:
3349 CMSCollector *_collector;
3350 const char *_phase;
3351 elapsedTimer _wallclock;
3352 bool _print_cr;
3354 public:
3355 // Not MT-safe; so do not pass around these StackObj's
3356 // where they may be accessed by other threads.
3357 jlong wallclock_millis() {
3358 assert(_wallclock.is_active(), "Wall clock should not stop");
3359 _wallclock.stop(); // to record time
3360 jlong ret = _wallclock.milliseconds();
3361 _wallclock.start(); // restart
3362 return ret;
3363 }
3364 };
3366 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
3367 const char *phase,
3368 bool print_cr) :
3369 _collector(collector), _phase(phase), _print_cr(print_cr) {
3371 if (PrintCMSStatistics != 0) {
3372 _collector->resetYields();
3373 }
3374 if (PrintGCDetails && PrintGCTimeStamps) {
3375 gclog_or_tty->date_stamp(PrintGCDateStamps);
3376 gclog_or_tty->stamp();
3377 gclog_or_tty->print_cr(": [%s-concurrent-%s-start]",
3378 _collector->cmsGen()->short_name(), _phase);
3379 }
3380 _collector->resetTimer();
3381 _wallclock.start();
3382 _collector->startTimer();
3383 }
3385 CMSPhaseAccounting::~CMSPhaseAccounting() {
3386 assert(_wallclock.is_active(), "Wall clock should not have stopped");
3387 _collector->stopTimer();
3388 _wallclock.stop();
3389 if (PrintGCDetails) {
3390 gclog_or_tty->date_stamp(PrintGCDateStamps);
3391 if (PrintGCTimeStamps) {
3392 gclog_or_tty->stamp();
3393 gclog_or_tty->print(": ");
3394 }
3395 gclog_or_tty->print("[%s-concurrent-%s: %3.3f/%3.3f secs]",
3396 _collector->cmsGen()->short_name(),
3397 _phase, _collector->timerValue(), _wallclock.seconds());
3398 if (_print_cr) {
3399 gclog_or_tty->print_cr("");
3400 }
3401 if (PrintCMSStatistics != 0) {
3402 gclog_or_tty->print_cr(" (CMS-concurrent-%s yielded %d times)", _phase,
3403 _collector->yields());
3404 }
3405 }
3406 }
3408 // CMS work
3410 // Checkpoint the roots into this generation from outside
3411 // this generation. [Note this initial checkpoint need only
3412 // be approximate -- we'll do a catch up phase subsequently.]
3413 void CMSCollector::checkpointRootsInitial(bool asynch) {
3414 assert(_collectorState == InitialMarking, "Wrong collector state");
3415 check_correct_thread_executing();
3416 ReferenceProcessor* rp = ref_processor();
3417 SpecializationStats::clear();
3418 assert(_restart_addr == NULL, "Control point invariant");
3419 if (asynch) {
3420 // acquire locks for subsequent manipulations
3421 MutexLockerEx x(bitMapLock(),
3422 Mutex::_no_safepoint_check_flag);
3423 checkpointRootsInitialWork(asynch);
3424 rp->verify_no_references_recorded();
3425 rp->enable_discovery(); // enable ("weak") refs discovery
3426 _collectorState = Marking;
3427 } else {
3428 // (Weak) Refs discovery: this is controlled from genCollectedHeap::do_collection
3429 // which recognizes if we are a CMS generation, and doesn't try to turn on
3430 // discovery; verify that they aren't meddling.
3431 assert(!rp->discovery_is_atomic(),
3432 "incorrect setting of discovery predicate");
3433 assert(!rp->discovery_enabled(), "genCollectedHeap shouldn't control "
3434 "ref discovery for this generation kind");
3435 // already have locks
3436 checkpointRootsInitialWork(asynch);
3437 rp->enable_discovery(); // now enable ("weak") refs discovery
3438 _collectorState = Marking;
3439 }
3440 SpecializationStats::print();
3441 }
3443 void CMSCollector::checkpointRootsInitialWork(bool asynch) {
3444 assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
3445 assert(_collectorState == InitialMarking, "just checking");
3447 // If there has not been a GC[n-1] since last GC[n] cycle completed,
3448 // precede our marking with a collection of all
3449 // younger generations to keep floating garbage to a minimum.
3450 // XXX: we won't do this for now -- it's an optimization to be done later.
3452 // already have locks
3453 assert_lock_strong(bitMapLock());
3454 assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
3456 // Setup the verification and class unloading state for this
3457 // CMS collection cycle.
3458 setup_cms_unloading_and_verification_state();
3460 NOT_PRODUCT(TraceTime t("\ncheckpointRootsInitialWork",
3461 PrintGCDetails && Verbose, true, gclog_or_tty);)
3462 if (UseAdaptiveSizePolicy) {
3463 size_policy()->checkpoint_roots_initial_begin();
3464 }
3466 // Reset all the PLAB chunk arrays if necessary.
3467 if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
3468 reset_survivor_plab_arrays();
3469 }
3471 ResourceMark rm;
3472 HandleMark hm;
3474 FalseClosure falseClosure;
3475 // In the case of a synchronous collection, we will elide the
3476 // remark step, so it's important to catch all the nmethod oops
3477 // in this step; hence the last argument to the constrcutor below.
3478 MarkRefsIntoClosure notOlder(_span, &_markBitMap, !asynch /* nmethods */);
3479 GenCollectedHeap* gch = GenCollectedHeap::heap();
3481 verify_work_stacks_empty();
3482 verify_overflow_empty();
3484 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
3485 // Update the saved marks which may affect the root scans.
3486 gch->save_marks();
3488 // weak reference processing has not started yet.
3489 ref_processor()->set_enqueuing_is_done(false);
3491 {
3492 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
3493 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3494 gch->gen_process_strong_roots(_cmsGen->level(),
3495 true, // younger gens are roots
3496 true, // collecting perm gen
3497 SharedHeap::ScanningOption(roots_scanning_options()),
3498 NULL, ¬Older);
3499 }
3501 // Clear mod-union table; it will be dirtied in the prologue of
3502 // CMS generation per each younger generation collection.
3504 assert(_modUnionTable.isAllClear(),
3505 "Was cleared in most recent final checkpoint phase"
3506 " or no bits are set in the gc_prologue before the start of the next "
3507 "subsequent marking phase.");
3509 // Temporarily disabled, since pre/post-consumption closures don't
3510 // care about precleaned cards
3511 #if 0
3512 {
3513 MemRegion mr = MemRegion((HeapWord*)_virtual_space.low(),
3514 (HeapWord*)_virtual_space.high());
3515 _ct->ct_bs()->preclean_dirty_cards(mr);
3516 }
3517 #endif
3519 // Save the end of the used_region of the constituent generations
3520 // to be used to limit the extent of sweep in each generation.
3521 save_sweep_limits();
3522 if (UseAdaptiveSizePolicy) {
3523 size_policy()->checkpoint_roots_initial_end(gch->gc_cause());
3524 }
3525 verify_overflow_empty();
3526 }
3528 bool CMSCollector::markFromRoots(bool asynch) {
3529 // we might be tempted to assert that:
3530 // assert(asynch == !SafepointSynchronize::is_at_safepoint(),
3531 // "inconsistent argument?");
3532 // However that wouldn't be right, because it's possible that
3533 // a safepoint is indeed in progress as a younger generation
3534 // stop-the-world GC happens even as we mark in this generation.
3535 assert(_collectorState == Marking, "inconsistent state?");
3536 check_correct_thread_executing();
3537 verify_overflow_empty();
3539 bool res;
3540 if (asynch) {
3542 // Start the timers for adaptive size policy for the concurrent phases
3543 // Do it here so that the foreground MS can use the concurrent
3544 // timer since a foreground MS might has the sweep done concurrently
3545 // or STW.
3546 if (UseAdaptiveSizePolicy) {
3547 size_policy()->concurrent_marking_begin();
3548 }
3550 // Weak ref discovery note: We may be discovering weak
3551 // refs in this generation concurrent (but interleaved) with
3552 // weak ref discovery by a younger generation collector.
3554 CMSTokenSyncWithLocks ts(true, bitMapLock());
3555 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3556 CMSPhaseAccounting pa(this, "mark", !PrintGCDetails);
3557 res = markFromRootsWork(asynch);
3558 if (res) {
3559 _collectorState = Precleaning;
3560 } else { // We failed and a foreground collection wants to take over
3561 assert(_foregroundGCIsActive, "internal state inconsistency");
3562 assert(_restart_addr == NULL, "foreground will restart from scratch");
3563 if (PrintGCDetails) {
3564 gclog_or_tty->print_cr("bailing out to foreground collection");
3565 }
3566 }
3567 if (UseAdaptiveSizePolicy) {
3568 size_policy()->concurrent_marking_end();
3569 }
3570 } else {
3571 assert(SafepointSynchronize::is_at_safepoint(),
3572 "inconsistent with asynch == false");
3573 if (UseAdaptiveSizePolicy) {
3574 size_policy()->ms_collection_marking_begin();
3575 }
3576 // already have locks
3577 res = markFromRootsWork(asynch);
3578 _collectorState = FinalMarking;
3579 if (UseAdaptiveSizePolicy) {
3580 GenCollectedHeap* gch = GenCollectedHeap::heap();
3581 size_policy()->ms_collection_marking_end(gch->gc_cause());
3582 }
3583 }
3584 verify_overflow_empty();
3585 return res;
3586 }
3588 bool CMSCollector::markFromRootsWork(bool asynch) {
3589 // iterate over marked bits in bit map, doing a full scan and mark
3590 // from these roots using the following algorithm:
3591 // . if oop is to the right of the current scan pointer,
3592 // mark corresponding bit (we'll process it later)
3593 // . else (oop is to left of current scan pointer)
3594 // push oop on marking stack
3595 // . drain the marking stack
3597 // Note that when we do a marking step we need to hold the
3598 // bit map lock -- recall that direct allocation (by mutators)
3599 // and promotion (by younger generation collectors) is also
3600 // marking the bit map. [the so-called allocate live policy.]
3601 // Because the implementation of bit map marking is not
3602 // robust wrt simultaneous marking of bits in the same word,
3603 // we need to make sure that there is no such interference
3604 // between concurrent such updates.
3606 // already have locks
3607 assert_lock_strong(bitMapLock());
3609 // Clear the revisit stack, just in case there are any
3610 // obsolete contents from a short-circuited previous CMS cycle.
3611 _revisitStack.reset();
3612 verify_work_stacks_empty();
3613 verify_overflow_empty();
3614 assert(_revisitStack.isEmpty(), "tabula rasa");
3616 bool result = false;
3617 if (CMSConcurrentMTEnabled && ParallelCMSThreads > 0) {
3618 result = do_marking_mt(asynch);
3619 } else {
3620 result = do_marking_st(asynch);
3621 }
3622 return result;
3623 }
3625 // Forward decl
3626 class CMSConcMarkingTask;
3628 class CMSConcMarkingTerminator: public ParallelTaskTerminator {
3629 CMSCollector* _collector;
3630 CMSConcMarkingTask* _task;
3631 bool _yield;
3632 protected:
3633 virtual void yield();
3634 public:
3635 // "n_threads" is the number of threads to be terminated.
3636 // "queue_set" is a set of work queues of other threads.
3637 // "collector" is the CMS collector associated with this task terminator.
3638 // "yield" indicates whether we need the gang as a whole to yield.
3639 CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set,
3640 CMSCollector* collector, bool yield) :
3641 ParallelTaskTerminator(n_threads, queue_set),
3642 _collector(collector),
3643 _yield(yield) { }
3645 void set_task(CMSConcMarkingTask* task) {
3646 _task = task;
3647 }
3648 };
3650 // MT Concurrent Marking Task
3651 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3652 CMSCollector* _collector;
3653 YieldingFlexibleWorkGang* _workers; // the whole gang
3654 int _n_workers; // requested/desired # workers
3655 bool _asynch;
3656 bool _result;
3657 CompactibleFreeListSpace* _cms_space;
3658 CompactibleFreeListSpace* _perm_space;
3659 HeapWord* _global_finger;
3661 // Exposed here for yielding support
3662 Mutex* const _bit_map_lock;
3664 // The per thread work queues, available here for stealing
3665 OopTaskQueueSet* _task_queues;
3666 CMSConcMarkingTerminator _term;
3668 public:
3669 CMSConcMarkingTask(CMSCollector* collector,
3670 CompactibleFreeListSpace* cms_space,
3671 CompactibleFreeListSpace* perm_space,
3672 bool asynch, int n_workers,
3673 YieldingFlexibleWorkGang* workers,
3674 OopTaskQueueSet* task_queues):
3675 YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3676 _collector(collector),
3677 _cms_space(cms_space),
3678 _perm_space(perm_space),
3679 _asynch(asynch), _n_workers(n_workers), _result(true),
3680 _workers(workers), _task_queues(task_queues),
3681 _term(n_workers, task_queues, _collector, asynch),
3682 _bit_map_lock(collector->bitMapLock())
3683 {
3684 assert(n_workers <= workers->total_workers(),
3685 "Else termination won't work correctly today"); // XXX FIX ME!
3686 _requested_size = n_workers;
3687 _term.set_task(this);
3688 assert(_cms_space->bottom() < _perm_space->bottom(),
3689 "Finger incorrectly initialized below");
3690 _global_finger = _cms_space->bottom();
3691 }
3694 OopTaskQueueSet* task_queues() { return _task_queues; }
3696 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3698 HeapWord** global_finger_addr() { return &_global_finger; }
3700 CMSConcMarkingTerminator* terminator() { return &_term; }
3702 void work(int i);
3704 virtual void coordinator_yield(); // stuff done by coordinator
3705 bool result() { return _result; }
3707 void reset(HeapWord* ra) {
3708 _term.reset_for_reuse();
3709 }
3711 static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3712 OopTaskQueue* work_q);
3714 private:
3715 void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3716 void do_work_steal(int i);
3717 void bump_global_finger(HeapWord* f);
3718 };
3720 void CMSConcMarkingTerminator::yield() {
3721 if (ConcurrentMarkSweepThread::should_yield() &&
3722 !_collector->foregroundGCIsActive() &&
3723 _yield) {
3724 _task->yield();
3725 } else {
3726 ParallelTaskTerminator::yield();
3727 }
3728 }
3730 ////////////////////////////////////////////////////////////////
3731 // Concurrent Marking Algorithm Sketch
3732 ////////////////////////////////////////////////////////////////
3733 // Until all tasks exhausted (both spaces):
3734 // -- claim next available chunk
3735 // -- bump global finger via CAS
3736 // -- find first object that starts in this chunk
3737 // and start scanning bitmap from that position
3738 // -- scan marked objects for oops
3739 // -- CAS-mark target, and if successful:
3740 // . if target oop is above global finger (volatile read)
3741 // nothing to do
3742 // . if target oop is in chunk and above local finger
3743 // then nothing to do
3744 // . else push on work-queue
3745 // -- Deal with possible overflow issues:
3746 // . local work-queue overflow causes stuff to be pushed on
3747 // global (common) overflow queue
3748 // . always first empty local work queue
3749 // . then get a batch of oops from global work queue if any
3750 // . then do work stealing
3751 // -- When all tasks claimed (both spaces)
3752 // and local work queue empty,
3753 // then in a loop do:
3754 // . check global overflow stack; steal a batch of oops and trace
3755 // . try to steal from other threads oif GOS is empty
3756 // . if neither is available, offer termination
3757 // -- Terminate and return result
3758 //
3759 void CMSConcMarkingTask::work(int i) {
3760 elapsedTimer _timer;
3761 ResourceMark rm;
3762 HandleMark hm;
3764 DEBUG_ONLY(_collector->verify_overflow_empty();)
3766 // Before we begin work, our work queue should be empty
3767 assert(work_queue(i)->size() == 0, "Expected to be empty");
3768 // Scan the bitmap covering _cms_space, tracing through grey objects.
3769 _timer.start();
3770 do_scan_and_mark(i, _cms_space);
3771 _timer.stop();
3772 if (PrintCMSStatistics != 0) {
3773 gclog_or_tty->print_cr("Finished cms space scanning in %dth thread: %3.3f sec",
3774 i, _timer.seconds()); // XXX: need xxx/xxx type of notation, two timers
3775 }
3777 // ... do the same for the _perm_space
3778 _timer.reset();
3779 _timer.start();
3780 do_scan_and_mark(i, _perm_space);
3781 _timer.stop();
3782 if (PrintCMSStatistics != 0) {
3783 gclog_or_tty->print_cr("Finished perm space scanning in %dth thread: %3.3f sec",
3784 i, _timer.seconds()); // XXX: need xxx/xxx type of notation, two timers
3785 }
3787 // ... do work stealing
3788 _timer.reset();
3789 _timer.start();
3790 do_work_steal(i);
3791 _timer.stop();
3792 if (PrintCMSStatistics != 0) {
3793 gclog_or_tty->print_cr("Finished work stealing in %dth thread: %3.3f sec",
3794 i, _timer.seconds()); // XXX: need xxx/xxx type of notation, two timers
3795 }
3796 assert(_collector->_markStack.isEmpty(), "Should have been emptied");
3797 assert(work_queue(i)->size() == 0, "Should have been emptied");
3798 // Note that under the current task protocol, the
3799 // following assertion is true even of the spaces
3800 // expanded since the completion of the concurrent
3801 // marking. XXX This will likely change under a strict
3802 // ABORT semantics.
3803 assert(_global_finger > _cms_space->end() &&
3804 _global_finger >= _perm_space->end(),
3805 "All tasks have been completed");
3806 DEBUG_ONLY(_collector->verify_overflow_empty();)
3807 }
3809 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
3810 HeapWord* read = _global_finger;
3811 HeapWord* cur = read;
3812 while (f > read) {
3813 cur = read;
3814 read = (HeapWord*) Atomic::cmpxchg_ptr(f, &_global_finger, cur);
3815 if (cur == read) {
3816 // our cas succeeded
3817 assert(_global_finger >= f, "protocol consistency");
3818 break;
3819 }
3820 }
3821 }
3823 // This is really inefficient, and should be redone by
3824 // using (not yet available) block-read and -write interfaces to the
3825 // stack and the work_queue. XXX FIX ME !!!
3826 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3827 OopTaskQueue* work_q) {
3828 // Fast lock-free check
3829 if (ovflw_stk->length() == 0) {
3830 return false;
3831 }
3832 assert(work_q->size() == 0, "Shouldn't steal");
3833 MutexLockerEx ml(ovflw_stk->par_lock(),
3834 Mutex::_no_safepoint_check_flag);
3835 // Grab up to 1/4 the size of the work queue
3836 size_t num = MIN2((size_t)work_q->max_elems()/4,
3837 (size_t)ParGCDesiredObjsFromOverflowList);
3838 num = MIN2(num, ovflw_stk->length());
3839 for (int i = (int) num; i > 0; i--) {
3840 oop cur = ovflw_stk->pop();
3841 assert(cur != NULL, "Counted wrong?");
3842 work_q->push(cur);
3843 }
3844 return num > 0;
3845 }
3847 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
3848 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
3849 int n_tasks = pst->n_tasks();
3850 // We allow that there may be no tasks to do here because
3851 // we are restarting after a stack overflow.
3852 assert(pst->valid() || n_tasks == 0, "Uninitializd use?");
3853 int nth_task = 0;
3855 HeapWord* start = sp->bottom();
3856 size_t chunk_size = sp->marking_task_size();
3857 while (!pst->is_task_claimed(/* reference */ nth_task)) {
3858 // Having claimed the nth task in this space,
3859 // compute the chunk that it corresponds to:
3860 MemRegion span = MemRegion(start + nth_task*chunk_size,
3861 start + (nth_task+1)*chunk_size);
3862 // Try and bump the global finger via a CAS;
3863 // note that we need to do the global finger bump
3864 // _before_ taking the intersection below, because
3865 // the task corresponding to that region will be
3866 // deemed done even if the used_region() expands
3867 // because of allocation -- as it almost certainly will
3868 // during start-up while the threads yield in the
3869 // closure below.
3870 HeapWord* finger = span.end();
3871 bump_global_finger(finger); // atomically
3872 // There are null tasks here corresponding to chunks
3873 // beyond the "top" address of the space.
3874 span = span.intersection(sp->used_region());
3875 if (!span.is_empty()) { // Non-null task
3876 // We want to skip the first object because
3877 // the protocol is to scan any object in its entirety
3878 // that _starts_ in this span; a fortiori, any
3879 // object starting in an earlier span is scanned
3880 // as part of an earlier claimed task.
3881 // Below we use the "careful" version of block_start
3882 // so we do not try to navigate uninitialized objects.
3883 HeapWord* prev_obj = sp->block_start_careful(span.start());
3884 // Below we use a variant of block_size that uses the
3885 // Printezis bits to avoid waiting for allocated
3886 // objects to become initialized/parsable.
3887 while (prev_obj < span.start()) {
3888 size_t sz = sp->block_size_no_stall(prev_obj, _collector);
3889 if (sz > 0) {
3890 prev_obj += sz;
3891 } else {
3892 // In this case we may end up doing a bit of redundant
3893 // scanning, but that appears unavoidable, short of
3894 // locking the free list locks; see bug 6324141.
3895 break;
3896 }
3897 }
3898 if (prev_obj < span.end()) {
3899 MemRegion my_span = MemRegion(prev_obj, span.end());
3900 // Do the marking work within a non-empty span --
3901 // the last argument to the constructor indicates whether the
3902 // iteration should be incremental with periodic yields.
3903 Par_MarkFromRootsClosure cl(this, _collector, my_span,
3904 &_collector->_markBitMap,
3905 work_queue(i),
3906 &_collector->_markStack,
3907 &_collector->_revisitStack,
3908 _asynch);
3909 _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
3910 } // else nothing to do for this task
3911 } // else nothing to do for this task
3912 }
3913 // We'd be tempted to assert here that since there are no
3914 // more tasks left to claim in this space, the global_finger
3915 // must exceed space->top() and a fortiori space->end(). However,
3916 // that would not quite be correct because the bumping of
3917 // global_finger occurs strictly after the claiming of a task,
3918 // so by the time we reach here the global finger may not yet
3919 // have been bumped up by the thread that claimed the last
3920 // task.
3921 pst->all_tasks_completed();
3922 }
3924 class Par_ConcMarkingClosure: public OopClosure {
3925 private:
3926 CMSCollector* _collector;
3927 MemRegion _span;
3928 CMSBitMap* _bit_map;
3929 CMSMarkStack* _overflow_stack;
3930 CMSMarkStack* _revisit_stack; // XXXXXX Check proper use
3931 OopTaskQueue* _work_queue;
3932 protected:
3933 DO_OOP_WORK_DEFN
3934 public:
3935 Par_ConcMarkingClosure(CMSCollector* collector, OopTaskQueue* work_queue,
3936 CMSBitMap* bit_map, CMSMarkStack* overflow_stack):
3937 _collector(collector),
3938 _span(_collector->_span),
3939 _work_queue(work_queue),
3940 _bit_map(bit_map),
3941 _overflow_stack(overflow_stack) { } // need to initialize revisit stack etc.
3942 virtual void do_oop(oop* p);
3943 virtual void do_oop(narrowOop* p);
3944 void trim_queue(size_t max);
3945 void handle_stack_overflow(HeapWord* lost);
3946 };
3948 // Grey object rescan during work stealing phase --
3949 // the salient assumption here is that stolen oops must
3950 // always be initialized, so we do not need to check for
3951 // uninitialized objects before scanning here.
3952 void Par_ConcMarkingClosure::do_oop(oop obj) {
3953 assert(obj->is_oop_or_null(), "expected an oop or NULL");
3954 HeapWord* addr = (HeapWord*)obj;
3955 // Check if oop points into the CMS generation
3956 // and is not marked
3957 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
3958 // a white object ...
3959 // If we manage to "claim" the object, by being the
3960 // first thread to mark it, then we push it on our
3961 // marking stack
3962 if (_bit_map->par_mark(addr)) { // ... now grey
3963 // push on work queue (grey set)
3964 bool simulate_overflow = false;
3965 NOT_PRODUCT(
3966 if (CMSMarkStackOverflowALot &&
3967 _collector->simulate_overflow()) {
3968 // simulate a stack overflow
3969 simulate_overflow = true;
3970 }
3971 )
3972 if (simulate_overflow ||
3973 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
3974 // stack overflow
3975 if (PrintCMSStatistics != 0) {
3976 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
3977 SIZE_FORMAT, _overflow_stack->capacity());
3978 }
3979 // We cannot assert that the overflow stack is full because
3980 // it may have been emptied since.
3981 assert(simulate_overflow ||
3982 _work_queue->size() == _work_queue->max_elems(),
3983 "Else push should have succeeded");
3984 handle_stack_overflow(addr);
3985 }
3986 } // Else, some other thread got there first
3987 }
3988 }
3990 void Par_ConcMarkingClosure::do_oop(oop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
3991 void Par_ConcMarkingClosure::do_oop(narrowOop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
3993 void Par_ConcMarkingClosure::trim_queue(size_t max) {
3994 while (_work_queue->size() > max) {
3995 oop new_oop;
3996 if (_work_queue->pop_local(new_oop)) {
3997 assert(new_oop->is_oop(), "Should be an oop");
3998 assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
3999 assert(_span.contains((HeapWord*)new_oop), "Not in span");
4000 assert(new_oop->is_parsable(), "Should be parsable");
4001 new_oop->oop_iterate(this); // do_oop() above
4002 }
4003 }
4004 }
4006 // Upon stack overflow, we discard (part of) the stack,
4007 // remembering the least address amongst those discarded
4008 // in CMSCollector's _restart_address.
4009 void Par_ConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
4010 // We need to do this under a mutex to prevent other
4011 // workers from interfering with the expansion below.
4012 MutexLockerEx ml(_overflow_stack->par_lock(),
4013 Mutex::_no_safepoint_check_flag);
4014 // Remember the least grey address discarded
4015 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
4016 _collector->lower_restart_addr(ra);
4017 _overflow_stack->reset(); // discard stack contents
4018 _overflow_stack->expand(); // expand the stack if possible
4019 }
4022 void CMSConcMarkingTask::do_work_steal(int i) {
4023 OopTaskQueue* work_q = work_queue(i);
4024 oop obj_to_scan;
4025 CMSBitMap* bm = &(_collector->_markBitMap);
4026 CMSMarkStack* ovflw = &(_collector->_markStack);
4027 int* seed = _collector->hash_seed(i);
4028 Par_ConcMarkingClosure cl(_collector, work_q, bm, ovflw);
4029 while (true) {
4030 cl.trim_queue(0);
4031 assert(work_q->size() == 0, "Should have been emptied above");
4032 if (get_work_from_overflow_stack(ovflw, work_q)) {
4033 // Can't assert below because the work obtained from the
4034 // overflow stack may already have been stolen from us.
4035 // assert(work_q->size() > 0, "Work from overflow stack");
4036 continue;
4037 } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
4038 assert(obj_to_scan->is_oop(), "Should be an oop");
4039 assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
4040 obj_to_scan->oop_iterate(&cl);
4041 } else if (terminator()->offer_termination()) {
4042 assert(work_q->size() == 0, "Impossible!");
4043 break;
4044 }
4045 }
4046 }
4048 // This is run by the CMS (coordinator) thread.
4049 void CMSConcMarkingTask::coordinator_yield() {
4050 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
4051 "CMS thread should hold CMS token");
4053 // First give up the locks, then yield, then re-lock
4054 // We should probably use a constructor/destructor idiom to
4055 // do this unlock/lock or modify the MutexUnlocker class to
4056 // serve our purpose. XXX
4057 assert_lock_strong(_bit_map_lock);
4058 _bit_map_lock->unlock();
4059 ConcurrentMarkSweepThread::desynchronize(true);
4060 ConcurrentMarkSweepThread::acknowledge_yield_request();
4061 _collector->stopTimer();
4062 if (PrintCMSStatistics != 0) {
4063 _collector->incrementYields();
4064 }
4065 _collector->icms_wait();
4067 // It is possible for whichever thread initiated the yield request
4068 // not to get a chance to wake up and take the bitmap lock between
4069 // this thread releasing it and reacquiring it. So, while the
4070 // should_yield() flag is on, let's sleep for a bit to give the
4071 // other thread a chance to wake up. The limit imposed on the number
4072 // of iterations is defensive, to avoid any unforseen circumstances
4073 // putting us into an infinite loop. Since it's always been this
4074 // (coordinator_yield()) method that was observed to cause the
4075 // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
4076 // which is by default non-zero. For the other seven methods that
4077 // also perform the yield operation, as are using a different
4078 // parameter (CMSYieldSleepCount) which is by default zero. This way we
4079 // can enable the sleeping for those methods too, if necessary.
4080 // See 6442774.
4081 //
4082 // We really need to reconsider the synchronization between the GC
4083 // thread and the yield-requesting threads in the future and we
4084 // should really use wait/notify, which is the recommended
4085 // way of doing this type of interaction. Additionally, we should
4086 // consolidate the eight methods that do the yield operation and they
4087 // are almost identical into one for better maintenability and
4088 // readability. See 6445193.
4089 //
4090 // Tony 2006.06.29
4091 for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
4092 ConcurrentMarkSweepThread::should_yield() &&
4093 !CMSCollector::foregroundGCIsActive(); ++i) {
4094 os::sleep(Thread::current(), 1, false);
4095 ConcurrentMarkSweepThread::acknowledge_yield_request();
4096 }
4098 ConcurrentMarkSweepThread::synchronize(true);
4099 _bit_map_lock->lock_without_safepoint_check();
4100 _collector->startTimer();
4101 }
4103 bool CMSCollector::do_marking_mt(bool asynch) {
4104 assert(ParallelCMSThreads > 0 && conc_workers() != NULL, "precondition");
4105 // In the future this would be determined ergonomically, based
4106 // on #cpu's, # active mutator threads (and load), and mutation rate.
4107 int num_workers = ParallelCMSThreads;
4109 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
4110 CompactibleFreeListSpace* perm_space = _permGen->cmsSpace();
4112 CMSConcMarkingTask tsk(this, cms_space, perm_space,
4113 asynch, num_workers /* number requested XXX */,
4114 conc_workers(), task_queues());
4116 // Since the actual number of workers we get may be different
4117 // from the number we requested above, do we need to do anything different
4118 // below? In particular, may be we need to subclass the SequantialSubTasksDone
4119 // class?? XXX
4120 cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
4121 perm_space->initialize_sequential_subtasks_for_marking(num_workers);
4123 // Refs discovery is already non-atomic.
4124 assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
4125 // Mutate the Refs discovery so it is MT during the
4126 // multi-threaded marking phase.
4127 ReferenceProcessorMTMutator mt(ref_processor(), num_workers > 1);
4129 conc_workers()->start_task(&tsk);
4130 while (tsk.yielded()) {
4131 tsk.coordinator_yield();
4132 conc_workers()->continue_task(&tsk);
4133 }
4134 // If the task was aborted, _restart_addr will be non-NULL
4135 assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
4136 while (_restart_addr != NULL) {
4137 // XXX For now we do not make use of ABORTED state and have not
4138 // yet implemented the right abort semantics (even in the original
4139 // single-threaded CMS case). That needs some more investigation
4140 // and is deferred for now; see CR# TBF. 07252005YSR. XXX
4141 assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
4142 // If _restart_addr is non-NULL, a marking stack overflow
4143 // occured; we need to do a fresh marking iteration from the
4144 // indicated restart address.
4145 if (_foregroundGCIsActive && asynch) {
4146 // We may be running into repeated stack overflows, having
4147 // reached the limit of the stack size, while making very
4148 // slow forward progress. It may be best to bail out and
4149 // let the foreground collector do its job.
4150 // Clear _restart_addr, so that foreground GC
4151 // works from scratch. This avoids the headache of
4152 // a "rescan" which would otherwise be needed because
4153 // of the dirty mod union table & card table.
4154 _restart_addr = NULL;
4155 return false;
4156 }
4157 // Adjust the task to restart from _restart_addr
4158 tsk.reset(_restart_addr);
4159 cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
4160 _restart_addr);
4161 perm_space->initialize_sequential_subtasks_for_marking(num_workers,
4162 _restart_addr);
4163 _restart_addr = NULL;
4164 // Get the workers going again
4165 conc_workers()->start_task(&tsk);
4166 while (tsk.yielded()) {
4167 tsk.coordinator_yield();
4168 conc_workers()->continue_task(&tsk);
4169 }
4170 }
4171 assert(tsk.completed(), "Inconsistency");
4172 assert(tsk.result() == true, "Inconsistency");
4173 return true;
4174 }
4176 bool CMSCollector::do_marking_st(bool asynch) {
4177 ResourceMark rm;
4178 HandleMark hm;
4180 MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
4181 &_markStack, &_revisitStack, CMSYield && asynch);
4182 // the last argument to iterate indicates whether the iteration
4183 // should be incremental with periodic yields.
4184 _markBitMap.iterate(&markFromRootsClosure);
4185 // If _restart_addr is non-NULL, a marking stack overflow
4186 // occured; we need to do a fresh iteration from the
4187 // indicated restart address.
4188 while (_restart_addr != NULL) {
4189 if (_foregroundGCIsActive && asynch) {
4190 // We may be running into repeated stack overflows, having
4191 // reached the limit of the stack size, while making very
4192 // slow forward progress. It may be best to bail out and
4193 // let the foreground collector do its job.
4194 // Clear _restart_addr, so that foreground GC
4195 // works from scratch. This avoids the headache of
4196 // a "rescan" which would otherwise be needed because
4197 // of the dirty mod union table & card table.
4198 _restart_addr = NULL;
4199 return false; // indicating failure to complete marking
4200 }
4201 // Deal with stack overflow:
4202 // we restart marking from _restart_addr
4203 HeapWord* ra = _restart_addr;
4204 markFromRootsClosure.reset(ra);
4205 _restart_addr = NULL;
4206 _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
4207 }
4208 return true;
4209 }
4211 void CMSCollector::preclean() {
4212 check_correct_thread_executing();
4213 assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
4214 verify_work_stacks_empty();
4215 verify_overflow_empty();
4216 _abort_preclean = false;
4217 if (CMSPrecleaningEnabled) {
4218 _eden_chunk_index = 0;
4219 size_t used = get_eden_used();
4220 size_t capacity = get_eden_capacity();
4221 // Don't start sampling unless we will get sufficiently
4222 // many samples.
4223 if (used < (capacity/(CMSScheduleRemarkSamplingRatio * 100)
4224 * CMSScheduleRemarkEdenPenetration)) {
4225 _start_sampling = true;
4226 } else {
4227 _start_sampling = false;
4228 }
4229 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
4230 CMSPhaseAccounting pa(this, "preclean", !PrintGCDetails);
4231 preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
4232 }
4233 CMSTokenSync x(true); // is cms thread
4234 if (CMSPrecleaningEnabled) {
4235 sample_eden();
4236 _collectorState = AbortablePreclean;
4237 } else {
4238 _collectorState = FinalMarking;
4239 }
4240 verify_work_stacks_empty();
4241 verify_overflow_empty();
4242 }
4244 // Try and schedule the remark such that young gen
4245 // occupancy is CMSScheduleRemarkEdenPenetration %.
4246 void CMSCollector::abortable_preclean() {
4247 check_correct_thread_executing();
4248 assert(CMSPrecleaningEnabled, "Inconsistent control state");
4249 assert(_collectorState == AbortablePreclean, "Inconsistent control state");
4251 // If Eden's current occupancy is below this threshold,
4252 // immediately schedule the remark; else preclean
4253 // past the next scavenge in an effort to
4254 // schedule the pause as described avove. By choosing
4255 // CMSScheduleRemarkEdenSizeThreshold >= max eden size
4256 // we will never do an actual abortable preclean cycle.
4257 if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
4258 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
4259 CMSPhaseAccounting pa(this, "abortable-preclean", !PrintGCDetails);
4260 // We need more smarts in the abortable preclean
4261 // loop below to deal with cases where allocation
4262 // in young gen is very very slow, and our precleaning
4263 // is running a losing race against a horde of
4264 // mutators intent on flooding us with CMS updates
4265 // (dirty cards).
4266 // One, admittedly dumb, strategy is to give up
4267 // after a certain number of abortable precleaning loops
4268 // or after a certain maximum time. We want to make
4269 // this smarter in the next iteration.
4270 // XXX FIX ME!!! YSR
4271 size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
4272 while (!(should_abort_preclean() ||
4273 ConcurrentMarkSweepThread::should_terminate())) {
4274 workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
4275 cumworkdone += workdone;
4276 loops++;
4277 // Voluntarily terminate abortable preclean phase if we have
4278 // been at it for too long.
4279 if ((CMSMaxAbortablePrecleanLoops != 0) &&
4280 loops >= CMSMaxAbortablePrecleanLoops) {
4281 if (PrintGCDetails) {
4282 gclog_or_tty->print(" CMS: abort preclean due to loops ");
4283 }
4284 break;
4285 }
4286 if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
4287 if (PrintGCDetails) {
4288 gclog_or_tty->print(" CMS: abort preclean due to time ");
4289 }
4290 break;
4291 }
4292 // If we are doing little work each iteration, we should
4293 // take a short break.
4294 if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
4295 // Sleep for some time, waiting for work to accumulate
4296 stopTimer();
4297 cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
4298 startTimer();
4299 waited++;
4300 }
4301 }
4302 if (PrintCMSStatistics > 0) {
4303 gclog_or_tty->print(" [%d iterations, %d waits, %d cards)] ",
4304 loops, waited, cumworkdone);
4305 }
4306 }
4307 CMSTokenSync x(true); // is cms thread
4308 if (_collectorState != Idling) {
4309 assert(_collectorState == AbortablePreclean,
4310 "Spontaneous state transition?");
4311 _collectorState = FinalMarking;
4312 } // Else, a foreground collection completed this CMS cycle.
4313 return;
4314 }
4316 // Respond to an Eden sampling opportunity
4317 void CMSCollector::sample_eden() {
4318 // Make sure a young gc cannot sneak in between our
4319 // reading and recording of a sample.
4320 assert(Thread::current()->is_ConcurrentGC_thread(),
4321 "Only the cms thread may collect Eden samples");
4322 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
4323 "Should collect samples while holding CMS token");
4324 if (!_start_sampling) {
4325 return;
4326 }
4327 if (_eden_chunk_array) {
4328 if (_eden_chunk_index < _eden_chunk_capacity) {
4329 _eden_chunk_array[_eden_chunk_index] = *_top_addr; // take sample
4330 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4331 "Unexpected state of Eden");
4332 // We'd like to check that what we just sampled is an oop-start address;
4333 // however, we cannot do that here since the object may not yet have been
4334 // initialized. So we'll instead do the check when we _use_ this sample
4335 // later.
4336 if (_eden_chunk_index == 0 ||
4337 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4338 _eden_chunk_array[_eden_chunk_index-1])
4339 >= CMSSamplingGrain)) {
4340 _eden_chunk_index++; // commit sample
4341 }
4342 }
4343 }
4344 if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
4345 size_t used = get_eden_used();
4346 size_t capacity = get_eden_capacity();
4347 assert(used <= capacity, "Unexpected state of Eden");
4348 if (used > (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
4349 _abort_preclean = true;
4350 }
4351 }
4352 }
4355 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
4356 assert(_collectorState == Precleaning ||
4357 _collectorState == AbortablePreclean, "incorrect state");
4358 ResourceMark rm;
4359 HandleMark hm;
4360 // Do one pass of scrubbing the discovered reference lists
4361 // to remove any reference objects with strongly-reachable
4362 // referents.
4363 if (clean_refs) {
4364 ReferenceProcessor* rp = ref_processor();
4365 CMSPrecleanRefsYieldClosure yield_cl(this);
4366 assert(rp->span().equals(_span), "Spans should be equal");
4367 CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
4368 &_markStack);
4369 CMSDrainMarkingStackClosure complete_trace(this,
4370 _span, &_markBitMap, &_markStack,
4371 &keep_alive);
4373 // We don't want this step to interfere with a young
4374 // collection because we don't want to take CPU
4375 // or memory bandwidth away from the young GC threads
4376 // (which may be as many as there are CPUs).
4377 // Note that we don't need to protect ourselves from
4378 // interference with mutators because they can't
4379 // manipulate the discovered reference lists nor affect
4380 // the computed reachability of the referents, the
4381 // only properties manipulated by the precleaning
4382 // of these reference lists.
4383 stopTimer();
4384 CMSTokenSyncWithLocks x(true /* is cms thread */,
4385 bitMapLock());
4386 startTimer();
4387 sample_eden();
4388 // The following will yield to allow foreground
4389 // collection to proceed promptly. XXX YSR:
4390 // The code in this method may need further
4391 // tweaking for better performance and some restructuring
4392 // for cleaner interfaces.
4393 rp->preclean_discovered_references(
4394 rp->is_alive_non_header(), &keep_alive, &complete_trace,
4395 &yield_cl);
4396 }
4398 if (clean_survivor) { // preclean the active survivor space(s)
4399 assert(_young_gen->kind() == Generation::DefNew ||
4400 _young_gen->kind() == Generation::ParNew ||
4401 _young_gen->kind() == Generation::ASParNew,
4402 "incorrect type for cast");
4403 DefNewGeneration* dng = (DefNewGeneration*)_young_gen;
4404 PushAndMarkClosure pam_cl(this, _span, ref_processor(),
4405 &_markBitMap, &_modUnionTable,
4406 &_markStack, &_revisitStack,
4407 true /* precleaning phase */);
4408 stopTimer();
4409 CMSTokenSyncWithLocks ts(true /* is cms thread */,
4410 bitMapLock());
4411 startTimer();
4412 unsigned int before_count =
4413 GenCollectedHeap::heap()->total_collections();
4414 SurvivorSpacePrecleanClosure
4415 sss_cl(this, _span, &_markBitMap, &_markStack,
4416 &pam_cl, before_count, CMSYield);
4417 dng->from()->object_iterate_careful(&sss_cl);
4418 dng->to()->object_iterate_careful(&sss_cl);
4419 }
4420 MarkRefsIntoAndScanClosure
4421 mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
4422 &_markStack, &_revisitStack, this, CMSYield,
4423 true /* precleaning phase */);
4424 // CAUTION: The following closure has persistent state that may need to
4425 // be reset upon a decrease in the sequence of addresses it
4426 // processes.
4427 ScanMarkedObjectsAgainCarefullyClosure
4428 smoac_cl(this, _span,
4429 &_markBitMap, &_markStack, &_revisitStack, &mrias_cl, CMSYield);
4431 // Preclean dirty cards in ModUnionTable and CardTable using
4432 // appropriate convergence criterion;
4433 // repeat CMSPrecleanIter times unless we find that
4434 // we are losing.
4435 assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
4436 assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
4437 "Bad convergence multiplier");
4438 assert(CMSPrecleanThreshold >= 100,
4439 "Unreasonably low CMSPrecleanThreshold");
4441 size_t numIter, cumNumCards, lastNumCards, curNumCards;
4442 for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
4443 numIter < CMSPrecleanIter;
4444 numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
4445 curNumCards = preclean_mod_union_table(_cmsGen, &smoac_cl);
4446 if (CMSPermGenPrecleaningEnabled) {
4447 curNumCards += preclean_mod_union_table(_permGen, &smoac_cl);
4448 }
4449 if (Verbose && PrintGCDetails) {
4450 gclog_or_tty->print(" (modUnionTable: %d cards)", curNumCards);
4451 }
4452 // Either there are very few dirty cards, so re-mark
4453 // pause will be small anyway, or our pre-cleaning isn't
4454 // that much faster than the rate at which cards are being
4455 // dirtied, so we might as well stop and re-mark since
4456 // precleaning won't improve our re-mark time by much.
4457 if (curNumCards <= CMSPrecleanThreshold ||
4458 (numIter > 0 &&
4459 (curNumCards * CMSPrecleanDenominator >
4460 lastNumCards * CMSPrecleanNumerator))) {
4461 numIter++;
4462 cumNumCards += curNumCards;
4463 break;
4464 }
4465 }
4466 curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
4467 if (CMSPermGenPrecleaningEnabled) {
4468 curNumCards += preclean_card_table(_permGen, &smoac_cl);
4469 }
4470 cumNumCards += curNumCards;
4471 if (PrintGCDetails && PrintCMSStatistics != 0) {
4472 gclog_or_tty->print_cr(" (cardTable: %d cards, re-scanned %d cards, %d iterations)",
4473 curNumCards, cumNumCards, numIter);
4474 }
4475 return cumNumCards; // as a measure of useful work done
4476 }
4478 // PRECLEANING NOTES:
4479 // Precleaning involves:
4480 // . reading the bits of the modUnionTable and clearing the set bits.
4481 // . For the cards corresponding to the set bits, we scan the
4482 // objects on those cards. This means we need the free_list_lock
4483 // so that we can safely iterate over the CMS space when scanning
4484 // for oops.
4485 // . When we scan the objects, we'll be both reading and setting
4486 // marks in the marking bit map, so we'll need the marking bit map.
4487 // . For protecting _collector_state transitions, we take the CGC_lock.
4488 // Note that any races in the reading of of card table entries by the
4489 // CMS thread on the one hand and the clearing of those entries by the
4490 // VM thread or the setting of those entries by the mutator threads on the
4491 // other are quite benign. However, for efficiency it makes sense to keep
4492 // the VM thread from racing with the CMS thread while the latter is
4493 // dirty card info to the modUnionTable. We therefore also use the
4494 // CGC_lock to protect the reading of the card table and the mod union
4495 // table by the CM thread.
4496 // . We run concurrently with mutator updates, so scanning
4497 // needs to be done carefully -- we should not try to scan
4498 // potentially uninitialized objects.
4499 //
4500 // Locking strategy: While holding the CGC_lock, we scan over and
4501 // reset a maximal dirty range of the mod union / card tables, then lock
4502 // the free_list_lock and bitmap lock to do a full marking, then
4503 // release these locks; and repeat the cycle. This allows for a
4504 // certain amount of fairness in the sharing of these locks between
4505 // the CMS collector on the one hand, and the VM thread and the
4506 // mutators on the other.
4508 // NOTE: preclean_mod_union_table() and preclean_card_table()
4509 // further below are largely identical; if you need to modify
4510 // one of these methods, please check the other method too.
4512 size_t CMSCollector::preclean_mod_union_table(
4513 ConcurrentMarkSweepGeneration* gen,
4514 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4515 verify_work_stacks_empty();
4516 verify_overflow_empty();
4518 // strategy: starting with the first card, accumulate contiguous
4519 // ranges of dirty cards; clear these cards, then scan the region
4520 // covered by these cards.
4522 // Since all of the MUT is committed ahead, we can just use
4523 // that, in case the generations expand while we are precleaning.
4524 // It might also be fine to just use the committed part of the
4525 // generation, but we might potentially miss cards when the
4526 // generation is rapidly expanding while we are in the midst
4527 // of precleaning.
4528 HeapWord* startAddr = gen->reserved().start();
4529 HeapWord* endAddr = gen->reserved().end();
4531 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4533 size_t numDirtyCards, cumNumDirtyCards;
4534 HeapWord *nextAddr, *lastAddr;
4535 for (cumNumDirtyCards = numDirtyCards = 0,
4536 nextAddr = lastAddr = startAddr;
4537 nextAddr < endAddr;
4538 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4540 ResourceMark rm;
4541 HandleMark hm;
4543 MemRegion dirtyRegion;
4544 {
4545 stopTimer();
4546 CMSTokenSync ts(true);
4547 startTimer();
4548 sample_eden();
4549 // Get dirty region starting at nextOffset (inclusive),
4550 // simultaneously clearing it.
4551 dirtyRegion =
4552 _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
4553 assert(dirtyRegion.start() >= nextAddr,
4554 "returned region inconsistent?");
4555 }
4556 // Remember where the next search should begin.
4557 // The returned region (if non-empty) is a right open interval,
4558 // so lastOffset is obtained from the right end of that
4559 // interval.
4560 lastAddr = dirtyRegion.end();
4561 // Should do something more transparent and less hacky XXX
4562 numDirtyCards =
4563 _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
4565 // We'll scan the cards in the dirty region (with periodic
4566 // yields for foreground GC as needed).
4567 if (!dirtyRegion.is_empty()) {
4568 assert(numDirtyCards > 0, "consistency check");
4569 HeapWord* stop_point = NULL;
4570 {
4571 stopTimer();
4572 CMSTokenSyncWithLocks ts(true, gen->freelistLock(),
4573 bitMapLock());
4574 startTimer();
4575 verify_work_stacks_empty();
4576 verify_overflow_empty();
4577 sample_eden();
4578 stop_point =
4579 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4580 }
4581 if (stop_point != NULL) {
4582 // The careful iteration stopped early either because it found an
4583 // uninitialized object, or because we were in the midst of an
4584 // "abortable preclean", which should now be aborted. Redirty
4585 // the bits corresponding to the partially-scanned or unscanned
4586 // cards. We'll either restart at the next block boundary or
4587 // abort the preclean.
4588 assert((CMSPermGenPrecleaningEnabled && (gen == _permGen)) ||
4589 (_collectorState == AbortablePreclean && should_abort_preclean()),
4590 "Unparsable objects should only be in perm gen.");
4592 stopTimer();
4593 CMSTokenSyncWithLocks ts(true, bitMapLock());
4594 startTimer();
4595 _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
4596 if (should_abort_preclean()) {
4597 break; // out of preclean loop
4598 } else {
4599 // Compute the next address at which preclean should pick up;
4600 // might need bitMapLock in order to read P-bits.
4601 lastAddr = next_card_start_after_block(stop_point);
4602 }
4603 }
4604 } else {
4605 assert(lastAddr == endAddr, "consistency check");
4606 assert(numDirtyCards == 0, "consistency check");
4607 break;
4608 }
4609 }
4610 verify_work_stacks_empty();
4611 verify_overflow_empty();
4612 return cumNumDirtyCards;
4613 }
4615 // NOTE: preclean_mod_union_table() above and preclean_card_table()
4616 // below are largely identical; if you need to modify
4617 // one of these methods, please check the other method too.
4619 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* gen,
4620 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4621 // strategy: it's similar to precleamModUnionTable above, in that
4622 // we accumulate contiguous ranges of dirty cards, mark these cards
4623 // precleaned, then scan the region covered by these cards.
4624 HeapWord* endAddr = (HeapWord*)(gen->_virtual_space.high());
4625 HeapWord* startAddr = (HeapWord*)(gen->_virtual_space.low());
4627 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4629 size_t numDirtyCards, cumNumDirtyCards;
4630 HeapWord *lastAddr, *nextAddr;
4632 for (cumNumDirtyCards = numDirtyCards = 0,
4633 nextAddr = lastAddr = startAddr;
4634 nextAddr < endAddr;
4635 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4637 ResourceMark rm;
4638 HandleMark hm;
4640 MemRegion dirtyRegion;
4641 {
4642 // See comments in "Precleaning notes" above on why we
4643 // do this locking. XXX Could the locking overheads be
4644 // too high when dirty cards are sparse? [I don't think so.]
4645 stopTimer();
4646 CMSTokenSync x(true); // is cms thread
4647 startTimer();
4648 sample_eden();
4649 // Get and clear dirty region from card table
4650 dirtyRegion = _ct->ct_bs()->dirty_card_range_after_preclean(
4651 MemRegion(nextAddr, endAddr));
4652 assert(dirtyRegion.start() >= nextAddr,
4653 "returned region inconsistent?");
4654 }
4655 lastAddr = dirtyRegion.end();
4656 numDirtyCards =
4657 dirtyRegion.word_size()/CardTableModRefBS::card_size_in_words;
4659 if (!dirtyRegion.is_empty()) {
4660 stopTimer();
4661 CMSTokenSyncWithLocks ts(true, gen->freelistLock(), bitMapLock());
4662 startTimer();
4663 sample_eden();
4664 verify_work_stacks_empty();
4665 verify_overflow_empty();
4666 HeapWord* stop_point =
4667 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4668 if (stop_point != NULL) {
4669 // The careful iteration stopped early because it found an
4670 // uninitialized object. Redirty the bits corresponding to the
4671 // partially-scanned or unscanned cards, and start again at the
4672 // next block boundary.
4673 assert(CMSPermGenPrecleaningEnabled ||
4674 (_collectorState == AbortablePreclean && should_abort_preclean()),
4675 "Unparsable objects should only be in perm gen.");
4676 _ct->ct_bs()->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4677 if (should_abort_preclean()) {
4678 break; // out of preclean loop
4679 } else {
4680 // Compute the next address at which preclean should pick up.
4681 lastAddr = next_card_start_after_block(stop_point);
4682 }
4683 }
4684 } else {
4685 break;
4686 }
4687 }
4688 verify_work_stacks_empty();
4689 verify_overflow_empty();
4690 return cumNumDirtyCards;
4691 }
4693 void CMSCollector::checkpointRootsFinal(bool asynch,
4694 bool clear_all_soft_refs, bool init_mark_was_synchronous) {
4695 assert(_collectorState == FinalMarking, "incorrect state transition?");
4696 check_correct_thread_executing();
4697 // world is stopped at this checkpoint
4698 assert(SafepointSynchronize::is_at_safepoint(),
4699 "world should be stopped");
4700 verify_work_stacks_empty();
4701 verify_overflow_empty();
4703 SpecializationStats::clear();
4704 if (PrintGCDetails) {
4705 gclog_or_tty->print("[YG occupancy: "SIZE_FORMAT" K ("SIZE_FORMAT" K)]",
4706 _young_gen->used() / K,
4707 _young_gen->capacity() / K);
4708 }
4709 if (asynch) {
4710 if (CMSScavengeBeforeRemark) {
4711 GenCollectedHeap* gch = GenCollectedHeap::heap();
4712 // Temporarily set flag to false, GCH->do_collection will
4713 // expect it to be false and set to true
4714 FlagSetting fl(gch->_is_gc_active, false);
4715 NOT_PRODUCT(TraceTime t("Scavenge-Before-Remark",
4716 PrintGCDetails && Verbose, true, gclog_or_tty);)
4717 int level = _cmsGen->level() - 1;
4718 if (level >= 0) {
4719 gch->do_collection(true, // full (i.e. force, see below)
4720 false, // !clear_all_soft_refs
4721 0, // size
4722 false, // is_tlab
4723 level // max_level
4724 );
4725 }
4726 }
4727 FreelistLocker x(this);
4728 MutexLockerEx y(bitMapLock(),
4729 Mutex::_no_safepoint_check_flag);
4730 assert(!init_mark_was_synchronous, "but that's impossible!");
4731 checkpointRootsFinalWork(asynch, clear_all_soft_refs, false);
4732 } else {
4733 // already have all the locks
4734 checkpointRootsFinalWork(asynch, clear_all_soft_refs,
4735 init_mark_was_synchronous);
4736 }
4737 verify_work_stacks_empty();
4738 verify_overflow_empty();
4739 SpecializationStats::print();
4740 }
4742 void CMSCollector::checkpointRootsFinalWork(bool asynch,
4743 bool clear_all_soft_refs, bool init_mark_was_synchronous) {
4745 NOT_PRODUCT(TraceTime tr("checkpointRootsFinalWork", PrintGCDetails, false, gclog_or_tty);)
4747 assert(haveFreelistLocks(), "must have free list locks");
4748 assert_lock_strong(bitMapLock());
4750 if (UseAdaptiveSizePolicy) {
4751 size_policy()->checkpoint_roots_final_begin();
4752 }
4754 ResourceMark rm;
4755 HandleMark hm;
4757 GenCollectedHeap* gch = GenCollectedHeap::heap();
4759 if (should_unload_classes()) {
4760 CodeCache::gc_prologue();
4761 }
4762 assert(haveFreelistLocks(), "must have free list locks");
4763 assert_lock_strong(bitMapLock());
4765 if (!init_mark_was_synchronous) {
4766 // We might assume that we need not fill TLAB's when
4767 // CMSScavengeBeforeRemark is set, because we may have just done
4768 // a scavenge which would have filled all TLAB's -- and besides
4769 // Eden would be empty. This however may not always be the case --
4770 // for instance although we asked for a scavenge, it may not have
4771 // happened because of a JNI critical section. We probably need
4772 // a policy for deciding whether we can in that case wait until
4773 // the critical section releases and then do the remark following
4774 // the scavenge, and skip it here. In the absence of that policy,
4775 // or of an indication of whether the scavenge did indeed occur,
4776 // we cannot rely on TLAB's having been filled and must do
4777 // so here just in case a scavenge did not happen.
4778 gch->ensure_parsability(false); // fill TLAB's, but no need to retire them
4779 // Update the saved marks which may affect the root scans.
4780 gch->save_marks();
4782 {
4783 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
4785 // Note on the role of the mod union table:
4786 // Since the marker in "markFromRoots" marks concurrently with
4787 // mutators, it is possible for some reachable objects not to have been
4788 // scanned. For instance, an only reference to an object A was
4789 // placed in object B after the marker scanned B. Unless B is rescanned,
4790 // A would be collected. Such updates to references in marked objects
4791 // are detected via the mod union table which is the set of all cards
4792 // dirtied since the first checkpoint in this GC cycle and prior to
4793 // the most recent young generation GC, minus those cleaned up by the
4794 // concurrent precleaning.
4795 if (CMSParallelRemarkEnabled && ParallelGCThreads > 0) {
4796 TraceTime t("Rescan (parallel) ", PrintGCDetails, false, gclog_or_tty);
4797 do_remark_parallel();
4798 } else {
4799 TraceTime t("Rescan (non-parallel) ", PrintGCDetails, false,
4800 gclog_or_tty);
4801 do_remark_non_parallel();
4802 }
4803 }
4804 } else {
4805 assert(!asynch, "Can't have init_mark_was_synchronous in asynch mode");
4806 // The initial mark was stop-world, so there's no rescanning to
4807 // do; go straight on to the next step below.
4808 }
4809 verify_work_stacks_empty();
4810 verify_overflow_empty();
4812 {
4813 NOT_PRODUCT(TraceTime ts("refProcessingWork", PrintGCDetails, false, gclog_or_tty);)
4814 refProcessingWork(asynch, clear_all_soft_refs);
4815 }
4816 verify_work_stacks_empty();
4817 verify_overflow_empty();
4819 if (should_unload_classes()) {
4820 CodeCache::gc_epilogue();
4821 }
4823 // If we encountered any (marking stack / work queue) overflow
4824 // events during the current CMS cycle, take appropriate
4825 // remedial measures, where possible, so as to try and avoid
4826 // recurrence of that condition.
4827 assert(_markStack.isEmpty(), "No grey objects");
4828 size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
4829 _ser_kac_ovflw;
4830 if (ser_ovflw > 0) {
4831 if (PrintCMSStatistics != 0) {
4832 gclog_or_tty->print_cr("Marking stack overflow (benign) "
4833 "(pmc_pc="SIZE_FORMAT", pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT")",
4834 _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw,
4835 _ser_kac_ovflw);
4836 }
4837 _markStack.expand();
4838 _ser_pmc_remark_ovflw = 0;
4839 _ser_pmc_preclean_ovflw = 0;
4840 _ser_kac_ovflw = 0;
4841 }
4842 if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
4843 if (PrintCMSStatistics != 0) {
4844 gclog_or_tty->print_cr("Work queue overflow (benign) "
4845 "(pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT")",
4846 _par_pmc_remark_ovflw, _par_kac_ovflw);
4847 }
4848 _par_pmc_remark_ovflw = 0;
4849 _par_kac_ovflw = 0;
4850 }
4851 if (PrintCMSStatistics != 0) {
4852 if (_markStack._hit_limit > 0) {
4853 gclog_or_tty->print_cr(" (benign) Hit max stack size limit ("SIZE_FORMAT")",
4854 _markStack._hit_limit);
4855 }
4856 if (_markStack._failed_double > 0) {
4857 gclog_or_tty->print_cr(" (benign) Failed stack doubling ("SIZE_FORMAT"),"
4858 " current capacity "SIZE_FORMAT,
4859 _markStack._failed_double,
4860 _markStack.capacity());
4861 }
4862 }
4863 _markStack._hit_limit = 0;
4864 _markStack._failed_double = 0;
4866 if ((VerifyAfterGC || VerifyDuringGC) &&
4867 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
4868 verify_after_remark();
4869 }
4871 // Change under the freelistLocks.
4872 _collectorState = Sweeping;
4873 // Call isAllClear() under bitMapLock
4874 assert(_modUnionTable.isAllClear(), "Should be clear by end of the"
4875 " final marking");
4876 if (UseAdaptiveSizePolicy) {
4877 size_policy()->checkpoint_roots_final_end(gch->gc_cause());
4878 }
4879 }
4881 // Parallel remark task
4882 class CMSParRemarkTask: public AbstractGangTask {
4883 CMSCollector* _collector;
4884 WorkGang* _workers;
4885 int _n_workers;
4886 CompactibleFreeListSpace* _cms_space;
4887 CompactibleFreeListSpace* _perm_space;
4889 // The per-thread work queues, available here for stealing.
4890 OopTaskQueueSet* _task_queues;
4891 ParallelTaskTerminator _term;
4893 public:
4894 CMSParRemarkTask(CMSCollector* collector,
4895 CompactibleFreeListSpace* cms_space,
4896 CompactibleFreeListSpace* perm_space,
4897 int n_workers, WorkGang* workers,
4898 OopTaskQueueSet* task_queues):
4899 AbstractGangTask("Rescan roots and grey objects in parallel"),
4900 _collector(collector),
4901 _cms_space(cms_space), _perm_space(perm_space),
4902 _n_workers(n_workers),
4903 _workers(workers),
4904 _task_queues(task_queues),
4905 _term(workers->total_workers(), task_queues) { }
4907 OopTaskQueueSet* task_queues() { return _task_queues; }
4909 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
4911 ParallelTaskTerminator* terminator() { return &_term; }
4913 void work(int i);
4915 private:
4916 // Work method in support of parallel rescan ... of young gen spaces
4917 void do_young_space_rescan(int i, Par_MarkRefsIntoAndScanClosure* cl,
4918 ContiguousSpace* space,
4919 HeapWord** chunk_array, size_t chunk_top);
4921 // ... of dirty cards in old space
4922 void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
4923 Par_MarkRefsIntoAndScanClosure* cl);
4925 // ... work stealing for the above
4926 void do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl, int* seed);
4927 };
4929 void CMSParRemarkTask::work(int i) {
4930 elapsedTimer _timer;
4931 ResourceMark rm;
4932 HandleMark hm;
4934 // ---------- rescan from roots --------------
4935 _timer.start();
4936 GenCollectedHeap* gch = GenCollectedHeap::heap();
4937 Par_MarkRefsIntoAndScanClosure par_mrias_cl(_collector,
4938 _collector->_span, _collector->ref_processor(),
4939 &(_collector->_markBitMap),
4940 work_queue(i), &(_collector->_revisitStack));
4942 // Rescan young gen roots first since these are likely
4943 // coarsely partitioned and may, on that account, constitute
4944 // the critical path; thus, it's best to start off that
4945 // work first.
4946 // ---------- young gen roots --------------
4947 {
4948 DefNewGeneration* dng = _collector->_young_gen->as_DefNewGeneration();
4949 EdenSpace* eden_space = dng->eden();
4950 ContiguousSpace* from_space = dng->from();
4951 ContiguousSpace* to_space = dng->to();
4953 HeapWord** eca = _collector->_eden_chunk_array;
4954 size_t ect = _collector->_eden_chunk_index;
4955 HeapWord** sca = _collector->_survivor_chunk_array;
4956 size_t sct = _collector->_survivor_chunk_index;
4958 assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
4959 assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
4961 do_young_space_rescan(i, &par_mrias_cl, to_space, NULL, 0);
4962 do_young_space_rescan(i, &par_mrias_cl, from_space, sca, sct);
4963 do_young_space_rescan(i, &par_mrias_cl, eden_space, eca, ect);
4965 _timer.stop();
4966 if (PrintCMSStatistics != 0) {
4967 gclog_or_tty->print_cr(
4968 "Finished young gen rescan work in %dth thread: %3.3f sec",
4969 i, _timer.seconds());
4970 }
4971 }
4973 // ---------- remaining roots --------------
4974 _timer.reset();
4975 _timer.start();
4976 gch->gen_process_strong_roots(_collector->_cmsGen->level(),
4977 false, // yg was scanned above
4978 true, // collecting perm gen
4979 SharedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4980 NULL, &par_mrias_cl);
4981 _timer.stop();
4982 if (PrintCMSStatistics != 0) {
4983 gclog_or_tty->print_cr(
4984 "Finished remaining root rescan work in %dth thread: %3.3f sec",
4985 i, _timer.seconds());
4986 }
4988 // ---------- rescan dirty cards ------------
4989 _timer.reset();
4990 _timer.start();
4992 // Do the rescan tasks for each of the two spaces
4993 // (cms_space and perm_space) in turn.
4994 do_dirty_card_rescan_tasks(_cms_space, i, &par_mrias_cl);
4995 do_dirty_card_rescan_tasks(_perm_space, i, &par_mrias_cl);
4996 _timer.stop();
4997 if (PrintCMSStatistics != 0) {
4998 gclog_or_tty->print_cr(
4999 "Finished dirty card rescan work in %dth thread: %3.3f sec",
5000 i, _timer.seconds());
5001 }
5003 // ---------- steal work from other threads ...
5004 // ---------- ... and drain overflow list.
5005 _timer.reset();
5006 _timer.start();
5007 do_work_steal(i, &par_mrias_cl, _collector->hash_seed(i));
5008 _timer.stop();
5009 if (PrintCMSStatistics != 0) {
5010 gclog_or_tty->print_cr(
5011 "Finished work stealing in %dth thread: %3.3f sec",
5012 i, _timer.seconds());
5013 }
5014 }
5016 void
5017 CMSParRemarkTask::do_young_space_rescan(int i,
5018 Par_MarkRefsIntoAndScanClosure* cl, ContiguousSpace* space,
5019 HeapWord** chunk_array, size_t chunk_top) {
5020 // Until all tasks completed:
5021 // . claim an unclaimed task
5022 // . compute region boundaries corresponding to task claimed
5023 // using chunk_array
5024 // . par_oop_iterate(cl) over that region
5026 ResourceMark rm;
5027 HandleMark hm;
5029 SequentialSubTasksDone* pst = space->par_seq_tasks();
5030 assert(pst->valid(), "Uninitialized use?");
5032 int nth_task = 0;
5033 int n_tasks = pst->n_tasks();
5035 HeapWord *start, *end;
5036 while (!pst->is_task_claimed(/* reference */ nth_task)) {
5037 // We claimed task # nth_task; compute its boundaries.
5038 if (chunk_top == 0) { // no samples were taken
5039 assert(nth_task == 0 && n_tasks == 1, "Can have only 1 EdenSpace task");
5040 start = space->bottom();
5041 end = space->top();
5042 } else if (nth_task == 0) {
5043 start = space->bottom();
5044 end = chunk_array[nth_task];
5045 } else if (nth_task < (jint)chunk_top) {
5046 assert(nth_task >= 1, "Control point invariant");
5047 start = chunk_array[nth_task - 1];
5048 end = chunk_array[nth_task];
5049 } else {
5050 assert(nth_task == (jint)chunk_top, "Control point invariant");
5051 start = chunk_array[chunk_top - 1];
5052 end = space->top();
5053 }
5054 MemRegion mr(start, end);
5055 // Verify that mr is in space
5056 assert(mr.is_empty() || space->used_region().contains(mr),
5057 "Should be in space");
5058 // Verify that "start" is an object boundary
5059 assert(mr.is_empty() || oop(mr.start())->is_oop(),
5060 "Should be an oop");
5061 space->par_oop_iterate(mr, cl);
5062 }
5063 pst->all_tasks_completed();
5064 }
5066 void
5067 CMSParRemarkTask::do_dirty_card_rescan_tasks(
5068 CompactibleFreeListSpace* sp, int i,
5069 Par_MarkRefsIntoAndScanClosure* cl) {
5070 // Until all tasks completed:
5071 // . claim an unclaimed task
5072 // . compute region boundaries corresponding to task claimed
5073 // . transfer dirty bits ct->mut for that region
5074 // . apply rescanclosure to dirty mut bits for that region
5076 ResourceMark rm;
5077 HandleMark hm;
5079 OopTaskQueue* work_q = work_queue(i);
5080 ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
5081 // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
5082 // CAUTION: This closure has state that persists across calls to
5083 // the work method dirty_range_iterate_clear() in that it has
5084 // imbedded in it a (subtype of) UpwardsObjectClosure. The
5085 // use of that state in the imbedded UpwardsObjectClosure instance
5086 // assumes that the cards are always iterated (even if in parallel
5087 // by several threads) in monotonically increasing order per each
5088 // thread. This is true of the implementation below which picks
5089 // card ranges (chunks) in monotonically increasing order globally
5090 // and, a-fortiori, in monotonically increasing order per thread
5091 // (the latter order being a subsequence of the former).
5092 // If the work code below is ever reorganized into a more chaotic
5093 // work-partitioning form than the current "sequential tasks"
5094 // paradigm, the use of that persistent state will have to be
5095 // revisited and modified appropriately. See also related
5096 // bug 4756801 work on which should examine this code to make
5097 // sure that the changes there do not run counter to the
5098 // assumptions made here and necessary for correctness and
5099 // efficiency. Note also that this code might yield inefficient
5100 // behaviour in the case of very large objects that span one or
5101 // more work chunks. Such objects would potentially be scanned
5102 // several times redundantly. Work on 4756801 should try and
5103 // address that performance anomaly if at all possible. XXX
5104 MemRegion full_span = _collector->_span;
5105 CMSBitMap* bm = &(_collector->_markBitMap); // shared
5106 CMSMarkStack* rs = &(_collector->_revisitStack); // shared
5107 MarkFromDirtyCardsClosure
5108 greyRescanClosure(_collector, full_span, // entire span of interest
5109 sp, bm, work_q, rs, cl);
5111 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
5112 assert(pst->valid(), "Uninitialized use?");
5113 int nth_task = 0;
5114 const int alignment = CardTableModRefBS::card_size * BitsPerWord;
5115 MemRegion span = sp->used_region();
5116 HeapWord* start_addr = span.start();
5117 HeapWord* end_addr = (HeapWord*)round_to((intptr_t)span.end(),
5118 alignment);
5119 const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
5120 assert((HeapWord*)round_to((intptr_t)start_addr, alignment) ==
5121 start_addr, "Check alignment");
5122 assert((size_t)round_to((intptr_t)chunk_size, alignment) ==
5123 chunk_size, "Check alignment");
5125 while (!pst->is_task_claimed(/* reference */ nth_task)) {
5126 // Having claimed the nth_task, compute corresponding mem-region,
5127 // which is a-fortiori aligned correctly (i.e. at a MUT bopundary).
5128 // The alignment restriction ensures that we do not need any
5129 // synchronization with other gang-workers while setting or
5130 // clearing bits in thus chunk of the MUT.
5131 MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
5132 start_addr + (nth_task+1)*chunk_size);
5133 // The last chunk's end might be way beyond end of the
5134 // used region. In that case pull back appropriately.
5135 if (this_span.end() > end_addr) {
5136 this_span.set_end(end_addr);
5137 assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
5138 }
5139 // Iterate over the dirty cards covering this chunk, marking them
5140 // precleaned, and setting the corresponding bits in the mod union
5141 // table. Since we have been careful to partition at Card and MUT-word
5142 // boundaries no synchronization is needed between parallel threads.
5143 _collector->_ct->ct_bs()->dirty_card_iterate(this_span,
5144 &modUnionClosure);
5146 // Having transferred these marks into the modUnionTable,
5147 // rescan the marked objects on the dirty cards in the modUnionTable.
5148 // Even if this is at a synchronous collection, the initial marking
5149 // may have been done during an asynchronous collection so there
5150 // may be dirty bits in the mod-union table.
5151 _collector->_modUnionTable.dirty_range_iterate_clear(
5152 this_span, &greyRescanClosure);
5153 _collector->_modUnionTable.verifyNoOneBitsInRange(
5154 this_span.start(),
5155 this_span.end());
5156 }
5157 pst->all_tasks_completed(); // declare that i am done
5158 }
5160 // . see if we can share work_queues with ParNew? XXX
5161 void
5162 CMSParRemarkTask::do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl,
5163 int* seed) {
5164 OopTaskQueue* work_q = work_queue(i);
5165 NOT_PRODUCT(int num_steals = 0;)
5166 oop obj_to_scan;
5167 CMSBitMap* bm = &(_collector->_markBitMap);
5168 size_t num_from_overflow_list =
5169 MIN2((size_t)work_q->max_elems()/4,
5170 (size_t)ParGCDesiredObjsFromOverflowList);
5172 while (true) {
5173 // Completely finish any left over work from (an) earlier round(s)
5174 cl->trim_queue(0);
5175 // Now check if there's any work in the overflow list
5176 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5177 work_q)) {
5178 // found something in global overflow list;
5179 // not yet ready to go stealing work from others.
5180 // We'd like to assert(work_q->size() != 0, ...)
5181 // because we just took work from the overflow list,
5182 // but of course we can't since all of that could have
5183 // been already stolen from us.
5184 // "He giveth and He taketh away."
5185 continue;
5186 }
5187 // Verify that we have no work before we resort to stealing
5188 assert(work_q->size() == 0, "Have work, shouldn't steal");
5189 // Try to steal from other queues that have work
5190 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5191 NOT_PRODUCT(num_steals++;)
5192 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5193 assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5194 // Do scanning work
5195 obj_to_scan->oop_iterate(cl);
5196 // Loop around, finish this work, and try to steal some more
5197 } else if (terminator()->offer_termination()) {
5198 break; // nirvana from the infinite cycle
5199 }
5200 }
5201 NOT_PRODUCT(
5202 if (PrintCMSStatistics != 0) {
5203 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5204 }
5205 )
5206 assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
5207 "Else our work is not yet done");
5208 }
5210 // Return a thread-local PLAB recording array, as appropriate.
5211 void* CMSCollector::get_data_recorder(int thr_num) {
5212 if (_survivor_plab_array != NULL &&
5213 (CMSPLABRecordAlways ||
5214 (_collectorState > Marking && _collectorState < FinalMarking))) {
5215 assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
5216 ChunkArray* ca = &_survivor_plab_array[thr_num];
5217 ca->reset(); // clear it so that fresh data is recorded
5218 return (void*) ca;
5219 } else {
5220 return NULL;
5221 }
5222 }
5224 // Reset all the thread-local PLAB recording arrays
5225 void CMSCollector::reset_survivor_plab_arrays() {
5226 for (uint i = 0; i < ParallelGCThreads; i++) {
5227 _survivor_plab_array[i].reset();
5228 }
5229 }
5231 // Merge the per-thread plab arrays into the global survivor chunk
5232 // array which will provide the partitioning of the survivor space
5233 // for CMS rescan.
5234 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv) {
5235 assert(_survivor_plab_array != NULL, "Error");
5236 assert(_survivor_chunk_array != NULL, "Error");
5237 assert(_collectorState == FinalMarking, "Error");
5238 for (uint j = 0; j < ParallelGCThreads; j++) {
5239 _cursor[j] = 0;
5240 }
5241 HeapWord* top = surv->top();
5242 size_t i;
5243 for (i = 0; i < _survivor_chunk_capacity; i++) { // all sca entries
5244 HeapWord* min_val = top; // Higher than any PLAB address
5245 uint min_tid = 0; // position of min_val this round
5246 for (uint j = 0; j < ParallelGCThreads; j++) {
5247 ChunkArray* cur_sca = &_survivor_plab_array[j];
5248 if (_cursor[j] == cur_sca->end()) {
5249 continue;
5250 }
5251 assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
5252 HeapWord* cur_val = cur_sca->nth(_cursor[j]);
5253 assert(surv->used_region().contains(cur_val), "Out of bounds value");
5254 if (cur_val < min_val) {
5255 min_tid = j;
5256 min_val = cur_val;
5257 } else {
5258 assert(cur_val < top, "All recorded addresses should be less");
5259 }
5260 }
5261 // At this point min_val and min_tid are respectively
5262 // the least address in _survivor_plab_array[j]->nth(_cursor[j])
5263 // and the thread (j) that witnesses that address.
5264 // We record this address in the _survivor_chunk_array[i]
5265 // and increment _cursor[min_tid] prior to the next round i.
5266 if (min_val == top) {
5267 break;
5268 }
5269 _survivor_chunk_array[i] = min_val;
5270 _cursor[min_tid]++;
5271 }
5272 // We are all done; record the size of the _survivor_chunk_array
5273 _survivor_chunk_index = i; // exclusive: [0, i)
5274 if (PrintCMSStatistics > 0) {
5275 gclog_or_tty->print(" (Survivor:" SIZE_FORMAT "chunks) ", i);
5276 }
5277 // Verify that we used up all the recorded entries
5278 #ifdef ASSERT
5279 size_t total = 0;
5280 for (uint j = 0; j < ParallelGCThreads; j++) {
5281 assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
5282 total += _cursor[j];
5283 }
5284 assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
5285 // Check that the merged array is in sorted order
5286 if (total > 0) {
5287 for (size_t i = 0; i < total - 1; i++) {
5288 if (PrintCMSStatistics > 0) {
5289 gclog_or_tty->print(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
5290 i, _survivor_chunk_array[i]);
5291 }
5292 assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
5293 "Not sorted");
5294 }
5295 }
5296 #endif // ASSERT
5297 }
5299 // Set up the space's par_seq_tasks structure for work claiming
5300 // for parallel rescan of young gen.
5301 // See ParRescanTask where this is currently used.
5302 void
5303 CMSCollector::
5304 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
5305 assert(n_threads > 0, "Unexpected n_threads argument");
5306 DefNewGeneration* dng = (DefNewGeneration*)_young_gen;
5308 // Eden space
5309 {
5310 SequentialSubTasksDone* pst = dng->eden()->par_seq_tasks();
5311 assert(!pst->valid(), "Clobbering existing data?");
5312 // Each valid entry in [0, _eden_chunk_index) represents a task.
5313 size_t n_tasks = _eden_chunk_index + 1;
5314 assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
5315 pst->set_par_threads(n_threads);
5316 pst->set_n_tasks((int)n_tasks);
5317 }
5319 // Merge the survivor plab arrays into _survivor_chunk_array
5320 if (_survivor_plab_array != NULL) {
5321 merge_survivor_plab_arrays(dng->from());
5322 } else {
5323 assert(_survivor_chunk_index == 0, "Error");
5324 }
5326 // To space
5327 {
5328 SequentialSubTasksDone* pst = dng->to()->par_seq_tasks();
5329 assert(!pst->valid(), "Clobbering existing data?");
5330 pst->set_par_threads(n_threads);
5331 pst->set_n_tasks(1);
5332 assert(pst->valid(), "Error");
5333 }
5335 // From space
5336 {
5337 SequentialSubTasksDone* pst = dng->from()->par_seq_tasks();
5338 assert(!pst->valid(), "Clobbering existing data?");
5339 size_t n_tasks = _survivor_chunk_index + 1;
5340 assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
5341 pst->set_par_threads(n_threads);
5342 pst->set_n_tasks((int)n_tasks);
5343 assert(pst->valid(), "Error");
5344 }
5345 }
5347 // Parallel version of remark
5348 void CMSCollector::do_remark_parallel() {
5349 GenCollectedHeap* gch = GenCollectedHeap::heap();
5350 WorkGang* workers = gch->workers();
5351 assert(workers != NULL, "Need parallel worker threads.");
5352 int n_workers = workers->total_workers();
5353 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
5354 CompactibleFreeListSpace* perm_space = _permGen->cmsSpace();
5356 CMSParRemarkTask tsk(this,
5357 cms_space, perm_space,
5358 n_workers, workers, task_queues());
5360 // Set up for parallel process_strong_roots work.
5361 gch->set_par_threads(n_workers);
5362 gch->change_strong_roots_parity();
5363 // We won't be iterating over the cards in the card table updating
5364 // the younger_gen cards, so we shouldn't call the following else
5365 // the verification code as well as subsequent younger_refs_iterate
5366 // code would get confused. XXX
5367 // gch->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
5369 // The young gen rescan work will not be done as part of
5370 // process_strong_roots (which currently doesn't knw how to
5371 // parallelize such a scan), but rather will be broken up into
5372 // a set of parallel tasks (via the sampling that the [abortable]
5373 // preclean phase did of EdenSpace, plus the [two] tasks of
5374 // scanning the [two] survivor spaces. Further fine-grain
5375 // parallelization of the scanning of the survivor spaces
5376 // themselves, and of precleaning of the younger gen itself
5377 // is deferred to the future.
5378 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
5380 // The dirty card rescan work is broken up into a "sequence"
5381 // of parallel tasks (per constituent space) that are dynamically
5382 // claimed by the parallel threads.
5383 cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
5384 perm_space->initialize_sequential_subtasks_for_rescan(n_workers);
5386 // It turns out that even when we're using 1 thread, doing the work in a
5387 // separate thread causes wide variance in run times. We can't help this
5388 // in the multi-threaded case, but we special-case n=1 here to get
5389 // repeatable measurements of the 1-thread overhead of the parallel code.
5390 if (n_workers > 1) {
5391 // Make refs discovery MT-safe
5392 ReferenceProcessorMTMutator mt(ref_processor(), true);
5393 workers->run_task(&tsk);
5394 } else {
5395 tsk.work(0);
5396 }
5397 gch->set_par_threads(0); // 0 ==> non-parallel.
5398 // restore, single-threaded for now, any preserved marks
5399 // as a result of work_q overflow
5400 restore_preserved_marks_if_any();
5401 }
5403 // Non-parallel version of remark
5404 void CMSCollector::do_remark_non_parallel() {
5405 ResourceMark rm;
5406 HandleMark hm;
5407 GenCollectedHeap* gch = GenCollectedHeap::heap();
5408 MarkRefsIntoAndScanClosure
5409 mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
5410 &_markStack, &_revisitStack, this,
5411 false /* should_yield */, false /* not precleaning */);
5412 MarkFromDirtyCardsClosure
5413 markFromDirtyCardsClosure(this, _span,
5414 NULL, // space is set further below
5415 &_markBitMap, &_markStack, &_revisitStack,
5416 &mrias_cl);
5417 {
5418 TraceTime t("grey object rescan", PrintGCDetails, false, gclog_or_tty);
5419 // Iterate over the dirty cards, marking them precleaned, and
5420 // setting the corresponding bits in the mod union table.
5421 {
5422 ModUnionClosure modUnionClosure(&_modUnionTable);
5423 _ct->ct_bs()->dirty_card_iterate(
5424 _cmsGen->used_region(),
5425 &modUnionClosure);
5426 _ct->ct_bs()->dirty_card_iterate(
5427 _permGen->used_region(),
5428 &modUnionClosure);
5429 }
5430 // Having transferred these marks into the modUnionTable, we just need
5431 // to rescan the marked objects on the dirty cards in the modUnionTable.
5432 // The initial marking may have been done during an asynchronous
5433 // collection so there may be dirty bits in the mod-union table.
5434 const int alignment =
5435 CardTableModRefBS::card_size * BitsPerWord;
5436 {
5437 // ... First handle dirty cards in CMS gen
5438 markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
5439 MemRegion ur = _cmsGen->used_region();
5440 HeapWord* lb = ur.start();
5441 HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
5442 MemRegion cms_span(lb, ub);
5443 _modUnionTable.dirty_range_iterate_clear(cms_span,
5444 &markFromDirtyCardsClosure);
5445 verify_work_stacks_empty();
5446 if (PrintCMSStatistics != 0) {
5447 gclog_or_tty->print(" (re-scanned "SIZE_FORMAT" dirty cards in cms gen) ",
5448 markFromDirtyCardsClosure.num_dirty_cards());
5449 }
5450 }
5451 {
5452 // .. and then repeat for dirty cards in perm gen
5453 markFromDirtyCardsClosure.set_space(_permGen->cmsSpace());
5454 MemRegion ur = _permGen->used_region();
5455 HeapWord* lb = ur.start();
5456 HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
5457 MemRegion perm_span(lb, ub);
5458 _modUnionTable.dirty_range_iterate_clear(perm_span,
5459 &markFromDirtyCardsClosure);
5460 verify_work_stacks_empty();
5461 if (PrintCMSStatistics != 0) {
5462 gclog_or_tty->print(" (re-scanned "SIZE_FORMAT" dirty cards in perm gen) ",
5463 markFromDirtyCardsClosure.num_dirty_cards());
5464 }
5465 }
5466 }
5467 if (VerifyDuringGC &&
5468 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5469 HandleMark hm; // Discard invalid handles created during verification
5470 Universe::verify(true);
5471 }
5472 {
5473 TraceTime t("root rescan", PrintGCDetails, false, gclog_or_tty);
5475 verify_work_stacks_empty();
5477 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
5478 gch->gen_process_strong_roots(_cmsGen->level(),
5479 true, // younger gens as roots
5480 true, // collecting perm gen
5481 SharedHeap::ScanningOption(roots_scanning_options()),
5482 NULL, &mrias_cl);
5483 }
5484 verify_work_stacks_empty();
5485 // Restore evacuated mark words, if any, used for overflow list links
5486 if (!CMSOverflowEarlyRestoration) {
5487 restore_preserved_marks_if_any();
5488 }
5489 verify_overflow_empty();
5490 }
5492 ////////////////////////////////////////////////////////
5493 // Parallel Reference Processing Task Proxy Class
5494 ////////////////////////////////////////////////////////
5495 class CMSRefProcTaskProxy: public AbstractGangTask {
5496 typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
5497 CMSCollector* _collector;
5498 CMSBitMap* _mark_bit_map;
5499 MemRegion _span;
5500 OopTaskQueueSet* _task_queues;
5501 ParallelTaskTerminator _term;
5502 ProcessTask& _task;
5504 public:
5505 CMSRefProcTaskProxy(ProcessTask& task,
5506 CMSCollector* collector,
5507 const MemRegion& span,
5508 CMSBitMap* mark_bit_map,
5509 int total_workers,
5510 OopTaskQueueSet* task_queues):
5511 AbstractGangTask("Process referents by policy in parallel"),
5512 _task(task),
5513 _collector(collector), _span(span), _mark_bit_map(mark_bit_map),
5514 _task_queues(task_queues),
5515 _term(total_workers, task_queues)
5516 { }
5518 OopTaskQueueSet* task_queues() { return _task_queues; }
5520 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5522 ParallelTaskTerminator* terminator() { return &_term; }
5524 void do_work_steal(int i,
5525 CMSParDrainMarkingStackClosure* drain,
5526 CMSParKeepAliveClosure* keep_alive,
5527 int* seed);
5529 virtual void work(int i);
5530 };
5532 void CMSRefProcTaskProxy::work(int i) {
5533 CMSParKeepAliveClosure par_keep_alive(_collector, _span,
5534 _mark_bit_map, work_queue(i));
5535 CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
5536 _mark_bit_map, work_queue(i));
5537 CMSIsAliveClosure is_alive_closure(_mark_bit_map);
5538 _task.work(i, is_alive_closure, par_keep_alive, par_drain_stack);
5539 if (_task.marks_oops_alive()) {
5540 do_work_steal(i, &par_drain_stack, &par_keep_alive,
5541 _collector->hash_seed(i));
5542 }
5543 assert(work_queue(i)->size() == 0, "work_queue should be empty");
5544 assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
5545 }
5547 class CMSRefEnqueueTaskProxy: public AbstractGangTask {
5548 typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
5549 EnqueueTask& _task;
5551 public:
5552 CMSRefEnqueueTaskProxy(EnqueueTask& task)
5553 : AbstractGangTask("Enqueue reference objects in parallel"),
5554 _task(task)
5555 { }
5557 virtual void work(int i)
5558 {
5559 _task.work(i);
5560 }
5561 };
5563 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
5564 MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue):
5565 _collector(collector),
5566 _span(span),
5567 _bit_map(bit_map),
5568 _work_queue(work_queue),
5569 _mark_and_push(collector, span, bit_map, work_queue),
5570 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
5571 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads)))
5572 { }
5574 // . see if we can share work_queues with ParNew? XXX
5575 void CMSRefProcTaskProxy::do_work_steal(int i,
5576 CMSParDrainMarkingStackClosure* drain,
5577 CMSParKeepAliveClosure* keep_alive,
5578 int* seed) {
5579 OopTaskQueue* work_q = work_queue(i);
5580 NOT_PRODUCT(int num_steals = 0;)
5581 oop obj_to_scan;
5582 size_t num_from_overflow_list =
5583 MIN2((size_t)work_q->max_elems()/4,
5584 (size_t)ParGCDesiredObjsFromOverflowList);
5586 while (true) {
5587 // Completely finish any left over work from (an) earlier round(s)
5588 drain->trim_queue(0);
5589 // Now check if there's any work in the overflow list
5590 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5591 work_q)) {
5592 // Found something in global overflow list;
5593 // not yet ready to go stealing work from others.
5594 // We'd like to assert(work_q->size() != 0, ...)
5595 // because we just took work from the overflow list,
5596 // but of course we can't, since all of that might have
5597 // been already stolen from us.
5598 continue;
5599 }
5600 // Verify that we have no work before we resort to stealing
5601 assert(work_q->size() == 0, "Have work, shouldn't steal");
5602 // Try to steal from other queues that have work
5603 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5604 NOT_PRODUCT(num_steals++;)
5605 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5606 assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5607 // Do scanning work
5608 obj_to_scan->oop_iterate(keep_alive);
5609 // Loop around, finish this work, and try to steal some more
5610 } else if (terminator()->offer_termination()) {
5611 break; // nirvana from the infinite cycle
5612 }
5613 }
5614 NOT_PRODUCT(
5615 if (PrintCMSStatistics != 0) {
5616 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5617 }
5618 )
5619 }
5621 void CMSRefProcTaskExecutor::execute(ProcessTask& task)
5622 {
5623 GenCollectedHeap* gch = GenCollectedHeap::heap();
5624 WorkGang* workers = gch->workers();
5625 assert(workers != NULL, "Need parallel worker threads.");
5626 int n_workers = workers->total_workers();
5627 CMSRefProcTaskProxy rp_task(task, &_collector,
5628 _collector.ref_processor()->span(),
5629 _collector.markBitMap(),
5630 n_workers, _collector.task_queues());
5631 workers->run_task(&rp_task);
5632 }
5634 void CMSRefProcTaskExecutor::execute(EnqueueTask& task)
5635 {
5637 GenCollectedHeap* gch = GenCollectedHeap::heap();
5638 WorkGang* workers = gch->workers();
5639 assert(workers != NULL, "Need parallel worker threads.");
5640 CMSRefEnqueueTaskProxy enq_task(task);
5641 workers->run_task(&enq_task);
5642 }
5644 void CMSCollector::refProcessingWork(bool asynch, bool clear_all_soft_refs) {
5646 ResourceMark rm;
5647 HandleMark hm;
5648 ReferencePolicy* soft_ref_policy;
5650 assert(!ref_processor()->enqueuing_is_done(), "Enqueuing should not be complete");
5651 // Process weak references.
5652 if (clear_all_soft_refs) {
5653 soft_ref_policy = new AlwaysClearPolicy();
5654 } else {
5655 #ifdef COMPILER2
5656 soft_ref_policy = new LRUMaxHeapPolicy();
5657 #else
5658 soft_ref_policy = new LRUCurrentHeapPolicy();
5659 #endif // COMPILER2
5660 }
5661 verify_work_stacks_empty();
5663 ReferenceProcessor* rp = ref_processor();
5664 assert(rp->span().equals(_span), "Spans should be equal");
5665 CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
5666 &_markStack);
5667 CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
5668 _span, &_markBitMap, &_markStack,
5669 &cmsKeepAliveClosure);
5670 {
5671 TraceTime t("weak refs processing", PrintGCDetails, false, gclog_or_tty);
5672 if (rp->processing_is_mt()) {
5673 CMSRefProcTaskExecutor task_executor(*this);
5674 rp->process_discovered_references(soft_ref_policy,
5675 &_is_alive_closure,
5676 &cmsKeepAliveClosure,
5677 &cmsDrainMarkingStackClosure,
5678 &task_executor);
5679 } else {
5680 rp->process_discovered_references(soft_ref_policy,
5681 &_is_alive_closure,
5682 &cmsKeepAliveClosure,
5683 &cmsDrainMarkingStackClosure,
5684 NULL);
5685 }
5686 verify_work_stacks_empty();
5687 }
5689 if (should_unload_classes()) {
5690 {
5691 TraceTime t("class unloading", PrintGCDetails, false, gclog_or_tty);
5693 // Follow SystemDictionary roots and unload classes
5694 bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure);
5696 // Follow CodeCache roots and unload any methods marked for unloading
5697 CodeCache::do_unloading(&_is_alive_closure,
5698 &cmsKeepAliveClosure,
5699 purged_class);
5701 cmsDrainMarkingStackClosure.do_void();
5702 verify_work_stacks_empty();
5704 // Update subklass/sibling/implementor links in KlassKlass descendants
5705 assert(!_revisitStack.isEmpty(), "revisit stack should not be empty");
5706 oop k;
5707 while ((k = _revisitStack.pop()) != NULL) {
5708 ((Klass*)(oopDesc*)k)->follow_weak_klass_links(
5709 &_is_alive_closure,
5710 &cmsKeepAliveClosure);
5711 }
5712 assert(!ClassUnloading ||
5713 (_markStack.isEmpty() && overflow_list_is_empty()),
5714 "Should not have found new reachable objects");
5715 assert(_revisitStack.isEmpty(), "revisit stack should have been drained");
5716 cmsDrainMarkingStackClosure.do_void();
5717 verify_work_stacks_empty();
5718 }
5720 {
5721 TraceTime t("scrub symbol & string tables", PrintGCDetails, false, gclog_or_tty);
5722 // Now clean up stale oops in SymbolTable and StringTable
5723 SymbolTable::unlink(&_is_alive_closure);
5724 StringTable::unlink(&_is_alive_closure);
5725 }
5726 }
5728 verify_work_stacks_empty();
5729 // Restore any preserved marks as a result of mark stack or
5730 // work queue overflow
5731 restore_preserved_marks_if_any(); // done single-threaded for now
5733 rp->set_enqueuing_is_done(true);
5734 if (rp->processing_is_mt()) {
5735 CMSRefProcTaskExecutor task_executor(*this);
5736 rp->enqueue_discovered_references(&task_executor);
5737 } else {
5738 rp->enqueue_discovered_references(NULL);
5739 }
5740 rp->verify_no_references_recorded();
5741 assert(!rp->discovery_enabled(), "should have been disabled");
5743 // JVMTI object tagging is based on JNI weak refs. If any of these
5744 // refs were cleared then JVMTI needs to update its maps and
5745 // maybe post ObjectFrees to agents.
5746 JvmtiExport::cms_ref_processing_epilogue();
5747 }
5749 #ifndef PRODUCT
5750 void CMSCollector::check_correct_thread_executing() {
5751 Thread* t = Thread::current();
5752 // Only the VM thread or the CMS thread should be here.
5753 assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
5754 "Unexpected thread type");
5755 // If this is the vm thread, the foreground process
5756 // should not be waiting. Note that _foregroundGCIsActive is
5757 // true while the foreground collector is waiting.
5758 if (_foregroundGCShouldWait) {
5759 // We cannot be the VM thread
5760 assert(t->is_ConcurrentGC_thread(),
5761 "Should be CMS thread");
5762 } else {
5763 // We can be the CMS thread only if we are in a stop-world
5764 // phase of CMS collection.
5765 if (t->is_ConcurrentGC_thread()) {
5766 assert(_collectorState == InitialMarking ||
5767 _collectorState == FinalMarking,
5768 "Should be a stop-world phase");
5769 // The CMS thread should be holding the CMS_token.
5770 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5771 "Potential interference with concurrently "
5772 "executing VM thread");
5773 }
5774 }
5775 }
5776 #endif
5778 void CMSCollector::sweep(bool asynch) {
5779 assert(_collectorState == Sweeping, "just checking");
5780 check_correct_thread_executing();
5781 verify_work_stacks_empty();
5782 verify_overflow_empty();
5783 incrementSweepCount();
5784 _sweep_timer.stop();
5785 _sweep_estimate.sample(_sweep_timer.seconds());
5786 size_policy()->avg_cms_free_at_sweep()->sample(_cmsGen->free());
5788 // PermGen verification support: If perm gen sweeping is disabled in
5789 // this cycle, we preserve the perm gen object "deadness" information
5790 // in the perm_gen_verify_bit_map. In order to do that we traverse
5791 // all blocks in perm gen and mark all dead objects.
5792 if (verifying() && !should_unload_classes()) {
5793 assert(perm_gen_verify_bit_map()->sizeInBits() != 0,
5794 "Should have already been allocated");
5795 MarkDeadObjectsClosure mdo(this, _permGen->cmsSpace(),
5796 markBitMap(), perm_gen_verify_bit_map());
5797 if (asynch) {
5798 CMSTokenSyncWithLocks ts(true, _permGen->freelistLock(),
5799 bitMapLock());
5800 _permGen->cmsSpace()->blk_iterate(&mdo);
5801 } else {
5802 // In the case of synchronous sweep, we already have
5803 // the requisite locks/tokens.
5804 _permGen->cmsSpace()->blk_iterate(&mdo);
5805 }
5806 }
5808 if (asynch) {
5809 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
5810 CMSPhaseAccounting pa(this, "sweep", !PrintGCDetails);
5811 // First sweep the old gen then the perm gen
5812 {
5813 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
5814 bitMapLock());
5815 sweepWork(_cmsGen, asynch);
5816 }
5818 // Now repeat for perm gen
5819 if (should_unload_classes()) {
5820 CMSTokenSyncWithLocks ts(true, _permGen->freelistLock(),
5821 bitMapLock());
5822 sweepWork(_permGen, asynch);
5823 }
5825 // Update Universe::_heap_*_at_gc figures.
5826 // We need all the free list locks to make the abstract state
5827 // transition from Sweeping to Resetting. See detailed note
5828 // further below.
5829 {
5830 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
5831 _permGen->freelistLock());
5832 // Update heap occupancy information which is used as
5833 // input to soft ref clearing policy at the next gc.
5834 Universe::update_heap_info_at_gc();
5835 _collectorState = Resizing;
5836 }
5837 } else {
5838 // already have needed locks
5839 sweepWork(_cmsGen, asynch);
5841 if (should_unload_classes()) {
5842 sweepWork(_permGen, asynch);
5843 }
5844 // Update heap occupancy information which is used as
5845 // input to soft ref clearing policy at the next gc.
5846 Universe::update_heap_info_at_gc();
5847 _collectorState = Resizing;
5848 }
5849 verify_work_stacks_empty();
5850 verify_overflow_empty();
5852 _sweep_timer.reset();
5853 _sweep_timer.start();
5855 update_time_of_last_gc(os::javaTimeMillis());
5857 // NOTE on abstract state transitions:
5858 // Mutators allocate-live and/or mark the mod-union table dirty
5859 // based on the state of the collection. The former is done in
5860 // the interval [Marking, Sweeping] and the latter in the interval
5861 // [Marking, Sweeping). Thus the transitions into the Marking state
5862 // and out of the Sweeping state must be synchronously visible
5863 // globally to the mutators.
5864 // The transition into the Marking state happens with the world
5865 // stopped so the mutators will globally see it. Sweeping is
5866 // done asynchronously by the background collector so the transition
5867 // from the Sweeping state to the Resizing state must be done
5868 // under the freelistLock (as is the check for whether to
5869 // allocate-live and whether to dirty the mod-union table).
5870 assert(_collectorState == Resizing, "Change of collector state to"
5871 " Resizing must be done under the freelistLocks (plural)");
5873 // Now that sweeping has been completed, if the GCH's
5874 // incremental_collection_will_fail flag is set, clear it,
5875 // thus inviting a younger gen collection to promote into
5876 // this generation. If such a promotion may still fail,
5877 // the flag will be set again when a young collection is
5878 // attempted.
5879 // I think the incremental_collection_will_fail flag's use
5880 // is specific to a 2 generation collection policy, so i'll
5881 // assert that that's the configuration we are operating within.
5882 // The use of the flag can and should be generalized appropriately
5883 // in the future to deal with a general n-generation system.
5885 GenCollectedHeap* gch = GenCollectedHeap::heap();
5886 assert(gch->collector_policy()->is_two_generation_policy(),
5887 "Resetting of incremental_collection_will_fail flag"
5888 " may be incorrect otherwise");
5889 gch->clear_incremental_collection_will_fail();
5890 gch->update_full_collections_completed(_collection_count_start);
5891 }
5893 // FIX ME!!! Looks like this belongs in CFLSpace, with
5894 // CMSGen merely delegating to it.
5895 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
5896 double nearLargestPercent = 0.999;
5897 HeapWord* minAddr = _cmsSpace->bottom();
5898 HeapWord* largestAddr =
5899 (HeapWord*) _cmsSpace->dictionary()->findLargestDict();
5900 if (largestAddr == 0) {
5901 // The dictionary appears to be empty. In this case
5902 // try to coalesce at the end of the heap.
5903 largestAddr = _cmsSpace->end();
5904 }
5905 size_t largestOffset = pointer_delta(largestAddr, minAddr);
5906 size_t nearLargestOffset =
5907 (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
5908 _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
5909 }
5911 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
5912 return addr >= _cmsSpace->nearLargestChunk();
5913 }
5915 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
5916 return _cmsSpace->find_chunk_at_end();
5917 }
5919 void ConcurrentMarkSweepGeneration::update_gc_stats(int current_level,
5920 bool full) {
5921 // The next lower level has been collected. Gather any statistics
5922 // that are of interest at this point.
5923 if (!full && (current_level + 1) == level()) {
5924 // Gather statistics on the young generation collection.
5925 collector()->stats().record_gc0_end(used());
5926 }
5927 }
5929 CMSAdaptiveSizePolicy* ConcurrentMarkSweepGeneration::size_policy() {
5930 GenCollectedHeap* gch = GenCollectedHeap::heap();
5931 assert(gch->kind() == CollectedHeap::GenCollectedHeap,
5932 "Wrong type of heap");
5933 CMSAdaptiveSizePolicy* sp = (CMSAdaptiveSizePolicy*)
5934 gch->gen_policy()->size_policy();
5935 assert(sp->is_gc_cms_adaptive_size_policy(),
5936 "Wrong type of size policy");
5937 return sp;
5938 }
5940 void ConcurrentMarkSweepGeneration::rotate_debug_collection_type() {
5941 if (PrintGCDetails && Verbose) {
5942 gclog_or_tty->print("Rotate from %d ", _debug_collection_type);
5943 }
5944 _debug_collection_type = (CollectionTypes) (_debug_collection_type + 1);
5945 _debug_collection_type =
5946 (CollectionTypes) (_debug_collection_type % Unknown_collection_type);
5947 if (PrintGCDetails && Verbose) {
5948 gclog_or_tty->print_cr("to %d ", _debug_collection_type);
5949 }
5950 }
5952 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* gen,
5953 bool asynch) {
5954 // We iterate over the space(s) underlying this generation,
5955 // checking the mark bit map to see if the bits corresponding
5956 // to specific blocks are marked or not. Blocks that are
5957 // marked are live and are not swept up. All remaining blocks
5958 // are swept up, with coalescing on-the-fly as we sweep up
5959 // contiguous free and/or garbage blocks:
5960 // We need to ensure that the sweeper synchronizes with allocators
5961 // and stop-the-world collectors. In particular, the following
5962 // locks are used:
5963 // . CMS token: if this is held, a stop the world collection cannot occur
5964 // . freelistLock: if this is held no allocation can occur from this
5965 // generation by another thread
5966 // . bitMapLock: if this is held, no other thread can access or update
5967 //
5969 // Note that we need to hold the freelistLock if we use
5970 // block iterate below; else the iterator might go awry if
5971 // a mutator (or promotion) causes block contents to change
5972 // (for instance if the allocator divvies up a block).
5973 // If we hold the free list lock, for all practical purposes
5974 // young generation GC's can't occur (they'll usually need to
5975 // promote), so we might as well prevent all young generation
5976 // GC's while we do a sweeping step. For the same reason, we might
5977 // as well take the bit map lock for the entire duration
5979 // check that we hold the requisite locks
5980 assert(have_cms_token(), "Should hold cms token");
5981 assert( (asynch && ConcurrentMarkSweepThread::cms_thread_has_cms_token())
5982 || (!asynch && ConcurrentMarkSweepThread::vm_thread_has_cms_token()),
5983 "Should possess CMS token to sweep");
5984 assert_lock_strong(gen->freelistLock());
5985 assert_lock_strong(bitMapLock());
5987 assert(!_sweep_timer.is_active(), "Was switched off in an outer context");
5988 gen->cmsSpace()->beginSweepFLCensus((float)(_sweep_timer.seconds()),
5989 _sweep_estimate.padded_average());
5990 gen->setNearLargestChunk();
5992 {
5993 SweepClosure sweepClosure(this, gen, &_markBitMap,
5994 CMSYield && asynch);
5995 gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
5996 // We need to free-up/coalesce garbage/blocks from a
5997 // co-terminal free run. This is done in the SweepClosure
5998 // destructor; so, do not remove this scope, else the
5999 // end-of-sweep-census below will be off by a little bit.
6000 }
6001 gen->cmsSpace()->sweep_completed();
6002 gen->cmsSpace()->endSweepFLCensus(sweepCount());
6003 if (should_unload_classes()) { // unloaded classes this cycle,
6004 _concurrent_cycles_since_last_unload = 0; // ... reset count
6005 } else { // did not unload classes,
6006 _concurrent_cycles_since_last_unload++; // ... increment count
6007 }
6008 }
6010 // Reset CMS data structures (for now just the marking bit map)
6011 // preparatory for the next cycle.
6012 void CMSCollector::reset(bool asynch) {
6013 GenCollectedHeap* gch = GenCollectedHeap::heap();
6014 CMSAdaptiveSizePolicy* sp = size_policy();
6015 AdaptiveSizePolicyOutput(sp, gch->total_collections());
6016 if (asynch) {
6017 CMSTokenSyncWithLocks ts(true, bitMapLock());
6019 // If the state is not "Resetting", the foreground thread
6020 // has done a collection and the resetting.
6021 if (_collectorState != Resetting) {
6022 assert(_collectorState == Idling, "The state should only change"
6023 " because the foreground collector has finished the collection");
6024 return;
6025 }
6027 // Clear the mark bitmap (no grey objects to start with)
6028 // for the next cycle.
6029 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6030 CMSPhaseAccounting cmspa(this, "reset", !PrintGCDetails);
6032 HeapWord* curAddr = _markBitMap.startWord();
6033 while (curAddr < _markBitMap.endWord()) {
6034 size_t remaining = pointer_delta(_markBitMap.endWord(), curAddr);
6035 MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
6036 _markBitMap.clear_large_range(chunk);
6037 if (ConcurrentMarkSweepThread::should_yield() &&
6038 !foregroundGCIsActive() &&
6039 CMSYield) {
6040 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6041 "CMS thread should hold CMS token");
6042 assert_lock_strong(bitMapLock());
6043 bitMapLock()->unlock();
6044 ConcurrentMarkSweepThread::desynchronize(true);
6045 ConcurrentMarkSweepThread::acknowledge_yield_request();
6046 stopTimer();
6047 if (PrintCMSStatistics != 0) {
6048 incrementYields();
6049 }
6050 icms_wait();
6052 // See the comment in coordinator_yield()
6053 for (unsigned i = 0; i < CMSYieldSleepCount &&
6054 ConcurrentMarkSweepThread::should_yield() &&
6055 !CMSCollector::foregroundGCIsActive(); ++i) {
6056 os::sleep(Thread::current(), 1, false);
6057 ConcurrentMarkSweepThread::acknowledge_yield_request();
6058 }
6060 ConcurrentMarkSweepThread::synchronize(true);
6061 bitMapLock()->lock_without_safepoint_check();
6062 startTimer();
6063 }
6064 curAddr = chunk.end();
6065 }
6066 _collectorState = Idling;
6067 } else {
6068 // already have the lock
6069 assert(_collectorState == Resetting, "just checking");
6070 assert_lock_strong(bitMapLock());
6071 _markBitMap.clear_all();
6072 _collectorState = Idling;
6073 }
6075 // Stop incremental mode after a cycle completes, so that any future cycles
6076 // are triggered by allocation.
6077 stop_icms();
6079 NOT_PRODUCT(
6080 if (RotateCMSCollectionTypes) {
6081 _cmsGen->rotate_debug_collection_type();
6082 }
6083 )
6084 }
6086 void CMSCollector::do_CMS_operation(CMS_op_type op) {
6087 gclog_or_tty->date_stamp(PrintGC && PrintGCDateStamps);
6088 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6089 TraceTime t("GC", PrintGC, !PrintGCDetails, gclog_or_tty);
6090 TraceCollectorStats tcs(counters());
6092 switch (op) {
6093 case CMS_op_checkpointRootsInitial: {
6094 checkpointRootsInitial(true); // asynch
6095 if (PrintGC) {
6096 _cmsGen->printOccupancy("initial-mark");
6097 }
6098 break;
6099 }
6100 case CMS_op_checkpointRootsFinal: {
6101 checkpointRootsFinal(true, // asynch
6102 false, // !clear_all_soft_refs
6103 false); // !init_mark_was_synchronous
6104 if (PrintGC) {
6105 _cmsGen->printOccupancy("remark");
6106 }
6107 break;
6108 }
6109 default:
6110 fatal("No such CMS_op");
6111 }
6112 }
6114 #ifndef PRODUCT
6115 size_t const CMSCollector::skip_header_HeapWords() {
6116 return FreeChunk::header_size();
6117 }
6119 // Try and collect here conditions that should hold when
6120 // CMS thread is exiting. The idea is that the foreground GC
6121 // thread should not be blocked if it wants to terminate
6122 // the CMS thread and yet continue to run the VM for a while
6123 // after that.
6124 void CMSCollector::verify_ok_to_terminate() const {
6125 assert(Thread::current()->is_ConcurrentGC_thread(),
6126 "should be called by CMS thread");
6127 assert(!_foregroundGCShouldWait, "should be false");
6128 // We could check here that all the various low-level locks
6129 // are not held by the CMS thread, but that is overkill; see
6130 // also CMSThread::verify_ok_to_terminate() where the CGC_lock
6131 // is checked.
6132 }
6133 #endif
6135 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
6136 assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
6137 "missing Printezis mark?");
6138 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
6139 size_t size = pointer_delta(nextOneAddr + 1, addr);
6140 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6141 "alignment problem");
6142 assert(size >= 3, "Necessary for Printezis marks to work");
6143 return size;
6144 }
6146 // A variant of the above (block_size_using_printezis_bits()) except
6147 // that we return 0 if the P-bits are not yet set.
6148 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
6149 if (_markBitMap.isMarked(addr)) {
6150 assert(_markBitMap.isMarked(addr + 1), "Missing Printezis bit?");
6151 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
6152 size_t size = pointer_delta(nextOneAddr + 1, addr);
6153 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6154 "alignment problem");
6155 assert(size >= 3, "Necessary for Printezis marks to work");
6156 return size;
6157 } else {
6158 assert(!_markBitMap.isMarked(addr + 1), "Bit map inconsistency?");
6159 return 0;
6160 }
6161 }
6163 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
6164 size_t sz = 0;
6165 oop p = (oop)addr;
6166 if (p->klass() != NULL && p->is_parsable()) {
6167 sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
6168 } else {
6169 sz = block_size_using_printezis_bits(addr);
6170 }
6171 assert(sz > 0, "size must be nonzero");
6172 HeapWord* next_block = addr + sz;
6173 HeapWord* next_card = (HeapWord*)round_to((uintptr_t)next_block,
6174 CardTableModRefBS::card_size);
6175 assert(round_down((uintptr_t)addr, CardTableModRefBS::card_size) <
6176 round_down((uintptr_t)next_card, CardTableModRefBS::card_size),
6177 "must be different cards");
6178 return next_card;
6179 }
6182 // CMS Bit Map Wrapper /////////////////////////////////////////
6184 // Construct a CMS bit map infrastructure, but don't create the
6185 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
6186 // further below.
6187 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
6188 _bm(NULL,0),
6189 _shifter(shifter),
6190 _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true) : NULL)
6191 {
6192 _bmStartWord = 0;
6193 _bmWordSize = 0;
6194 }
6196 bool CMSBitMap::allocate(MemRegion mr) {
6197 _bmStartWord = mr.start();
6198 _bmWordSize = mr.word_size();
6199 ReservedSpace brs(ReservedSpace::allocation_align_size_up(
6200 (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
6201 if (!brs.is_reserved()) {
6202 warning("CMS bit map allocation failure");
6203 return false;
6204 }
6205 // For now we'll just commit all of the bit map up fromt.
6206 // Later on we'll try to be more parsimonious with swap.
6207 if (!_virtual_space.initialize(brs, brs.size())) {
6208 warning("CMS bit map backing store failure");
6209 return false;
6210 }
6211 assert(_virtual_space.committed_size() == brs.size(),
6212 "didn't reserve backing store for all of CMS bit map?");
6213 _bm.set_map((uintptr_t*)_virtual_space.low());
6214 assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
6215 _bmWordSize, "inconsistency in bit map sizing");
6216 _bm.set_size(_bmWordSize >> _shifter);
6218 // bm.clear(); // can we rely on getting zero'd memory? verify below
6219 assert(isAllClear(),
6220 "Expected zero'd memory from ReservedSpace constructor");
6221 assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
6222 "consistency check");
6223 return true;
6224 }
6226 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
6227 HeapWord *next_addr, *end_addr, *last_addr;
6228 assert_locked();
6229 assert(covers(mr), "out-of-range error");
6230 // XXX assert that start and end are appropriately aligned
6231 for (next_addr = mr.start(), end_addr = mr.end();
6232 next_addr < end_addr; next_addr = last_addr) {
6233 MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
6234 last_addr = dirty_region.end();
6235 if (!dirty_region.is_empty()) {
6236 cl->do_MemRegion(dirty_region);
6237 } else {
6238 assert(last_addr == end_addr, "program logic");
6239 return;
6240 }
6241 }
6242 }
6244 #ifndef PRODUCT
6245 void CMSBitMap::assert_locked() const {
6246 CMSLockVerifier::assert_locked(lock());
6247 }
6249 bool CMSBitMap::covers(MemRegion mr) const {
6250 // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
6251 assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
6252 "size inconsistency");
6253 return (mr.start() >= _bmStartWord) &&
6254 (mr.end() <= endWord());
6255 }
6257 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
6258 return (start >= _bmStartWord && (start + size) <= endWord());
6259 }
6261 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
6262 // verify that there are no 1 bits in the interval [left, right)
6263 FalseBitMapClosure falseBitMapClosure;
6264 iterate(&falseBitMapClosure, left, right);
6265 }
6267 void CMSBitMap::region_invariant(MemRegion mr)
6268 {
6269 assert_locked();
6270 // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
6271 assert(!mr.is_empty(), "unexpected empty region");
6272 assert(covers(mr), "mr should be covered by bit map");
6273 // convert address range into offset range
6274 size_t start_ofs = heapWordToOffset(mr.start());
6275 // Make sure that end() is appropriately aligned
6276 assert(mr.end() == (HeapWord*)round_to((intptr_t)mr.end(),
6277 (1 << (_shifter+LogHeapWordSize))),
6278 "Misaligned mr.end()");
6279 size_t end_ofs = heapWordToOffset(mr.end());
6280 assert(end_ofs > start_ofs, "Should mark at least one bit");
6281 }
6283 #endif
6285 bool CMSMarkStack::allocate(size_t size) {
6286 // allocate a stack of the requisite depth
6287 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6288 size * sizeof(oop)));
6289 if (!rs.is_reserved()) {
6290 warning("CMSMarkStack allocation failure");
6291 return false;
6292 }
6293 if (!_virtual_space.initialize(rs, rs.size())) {
6294 warning("CMSMarkStack backing store failure");
6295 return false;
6296 }
6297 assert(_virtual_space.committed_size() == rs.size(),
6298 "didn't reserve backing store for all of CMS stack?");
6299 _base = (oop*)(_virtual_space.low());
6300 _index = 0;
6301 _capacity = size;
6302 NOT_PRODUCT(_max_depth = 0);
6303 return true;
6304 }
6306 // XXX FIX ME !!! In the MT case we come in here holding a
6307 // leaf lock. For printing we need to take a further lock
6308 // which has lower rank. We need to recallibrate the two
6309 // lock-ranks involved in order to be able to rpint the
6310 // messages below. (Or defer the printing to the caller.
6311 // For now we take the expedient path of just disabling the
6312 // messages for the problematic case.)
6313 void CMSMarkStack::expand() {
6314 assert(_capacity <= CMSMarkStackSizeMax, "stack bigger than permitted");
6315 if (_capacity == CMSMarkStackSizeMax) {
6316 if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6317 // We print a warning message only once per CMS cycle.
6318 gclog_or_tty->print_cr(" (benign) Hit CMSMarkStack max size limit");
6319 }
6320 return;
6321 }
6322 // Double capacity if possible
6323 size_t new_capacity = MIN2(_capacity*2, CMSMarkStackSizeMax);
6324 // Do not give up existing stack until we have managed to
6325 // get the double capacity that we desired.
6326 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6327 new_capacity * sizeof(oop)));
6328 if (rs.is_reserved()) {
6329 // Release the backing store associated with old stack
6330 _virtual_space.release();
6331 // Reinitialize virtual space for new stack
6332 if (!_virtual_space.initialize(rs, rs.size())) {
6333 fatal("Not enough swap for expanded marking stack");
6334 }
6335 _base = (oop*)(_virtual_space.low());
6336 _index = 0;
6337 _capacity = new_capacity;
6338 } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6339 // Failed to double capacity, continue;
6340 // we print a detail message only once per CMS cycle.
6341 gclog_or_tty->print(" (benign) Failed to expand marking stack from "SIZE_FORMAT"K to "
6342 SIZE_FORMAT"K",
6343 _capacity / K, new_capacity / K);
6344 }
6345 }
6348 // Closures
6349 // XXX: there seems to be a lot of code duplication here;
6350 // should refactor and consolidate common code.
6352 // This closure is used to mark refs into the CMS generation in
6353 // the CMS bit map. Called at the first checkpoint. This closure
6354 // assumes that we do not need to re-mark dirty cards; if the CMS
6355 // generation on which this is used is not an oldest (modulo perm gen)
6356 // generation then this will lose younger_gen cards!
6358 MarkRefsIntoClosure::MarkRefsIntoClosure(
6359 MemRegion span, CMSBitMap* bitMap, bool should_do_nmethods):
6360 _span(span),
6361 _bitMap(bitMap),
6362 _should_do_nmethods(should_do_nmethods)
6363 {
6364 assert(_ref_processor == NULL, "deliberately left NULL");
6365 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6366 }
6368 void MarkRefsIntoClosure::do_oop(oop obj) {
6369 // if p points into _span, then mark corresponding bit in _markBitMap
6370 assert(obj->is_oop(), "expected an oop");
6371 HeapWord* addr = (HeapWord*)obj;
6372 if (_span.contains(addr)) {
6373 // this should be made more efficient
6374 _bitMap->mark(addr);
6375 }
6376 }
6378 void MarkRefsIntoClosure::do_oop(oop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6379 void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6381 // A variant of the above, used for CMS marking verification.
6382 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
6383 MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6384 bool should_do_nmethods):
6385 _span(span),
6386 _verification_bm(verification_bm),
6387 _cms_bm(cms_bm),
6388 _should_do_nmethods(should_do_nmethods) {
6389 assert(_ref_processor == NULL, "deliberately left NULL");
6390 assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
6391 }
6393 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
6394 // if p points into _span, then mark corresponding bit in _markBitMap
6395 assert(obj->is_oop(), "expected an oop");
6396 HeapWord* addr = (HeapWord*)obj;
6397 if (_span.contains(addr)) {
6398 _verification_bm->mark(addr);
6399 if (!_cms_bm->isMarked(addr)) {
6400 oop(addr)->print();
6401 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)", addr);
6402 fatal("... aborting");
6403 }
6404 }
6405 }
6407 void MarkRefsIntoVerifyClosure::do_oop(oop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6408 void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6410 //////////////////////////////////////////////////
6411 // MarkRefsIntoAndScanClosure
6412 //////////////////////////////////////////////////
6414 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
6415 ReferenceProcessor* rp,
6416 CMSBitMap* bit_map,
6417 CMSBitMap* mod_union_table,
6418 CMSMarkStack* mark_stack,
6419 CMSMarkStack* revisit_stack,
6420 CMSCollector* collector,
6421 bool should_yield,
6422 bool concurrent_precleaning):
6423 _collector(collector),
6424 _span(span),
6425 _bit_map(bit_map),
6426 _mark_stack(mark_stack),
6427 _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table,
6428 mark_stack, revisit_stack, concurrent_precleaning),
6429 _yield(should_yield),
6430 _concurrent_precleaning(concurrent_precleaning),
6431 _freelistLock(NULL)
6432 {
6433 _ref_processor = rp;
6434 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6435 }
6437 // This closure is used to mark refs into the CMS generation at the
6438 // second (final) checkpoint, and to scan and transitively follow
6439 // the unmarked oops. It is also used during the concurrent precleaning
6440 // phase while scanning objects on dirty cards in the CMS generation.
6441 // The marks are made in the marking bit map and the marking stack is
6442 // used for keeping the (newly) grey objects during the scan.
6443 // The parallel version (Par_...) appears further below.
6444 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6445 if (obj != NULL) {
6446 assert(obj->is_oop(), "expected an oop");
6447 HeapWord* addr = (HeapWord*)obj;
6448 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6449 assert(_collector->overflow_list_is_empty(),
6450 "overflow list should be empty");
6451 if (_span.contains(addr) &&
6452 !_bit_map->isMarked(addr)) {
6453 // mark bit map (object is now grey)
6454 _bit_map->mark(addr);
6455 // push on marking stack (stack should be empty), and drain the
6456 // stack by applying this closure to the oops in the oops popped
6457 // from the stack (i.e. blacken the grey objects)
6458 bool res = _mark_stack->push(obj);
6459 assert(res, "Should have space to push on empty stack");
6460 do {
6461 oop new_oop = _mark_stack->pop();
6462 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6463 assert(new_oop->is_parsable(), "Found unparsable oop");
6464 assert(_bit_map->isMarked((HeapWord*)new_oop),
6465 "only grey objects on this stack");
6466 // iterate over the oops in this oop, marking and pushing
6467 // the ones in CMS heap (i.e. in _span).
6468 new_oop->oop_iterate(&_pushAndMarkClosure);
6469 // check if it's time to yield
6470 do_yield_check();
6471 } while (!_mark_stack->isEmpty() ||
6472 (!_concurrent_precleaning && take_from_overflow_list()));
6473 // if marking stack is empty, and we are not doing this
6474 // during precleaning, then check the overflow list
6475 }
6476 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6477 assert(_collector->overflow_list_is_empty(),
6478 "overflow list was drained above");
6479 // We could restore evacuated mark words, if any, used for
6480 // overflow list links here because the overflow list is
6481 // provably empty here. That would reduce the maximum
6482 // size requirements for preserved_{oop,mark}_stack.
6483 // But we'll just postpone it until we are all done
6484 // so we can just stream through.
6485 if (!_concurrent_precleaning && CMSOverflowEarlyRestoration) {
6486 _collector->restore_preserved_marks_if_any();
6487 assert(_collector->no_preserved_marks(), "No preserved marks");
6488 }
6489 assert(!CMSOverflowEarlyRestoration || _collector->no_preserved_marks(),
6490 "All preserved marks should have been restored above");
6491 }
6492 }
6494 void MarkRefsIntoAndScanClosure::do_oop(oop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6495 void MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6497 void MarkRefsIntoAndScanClosure::do_yield_work() {
6498 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6499 "CMS thread should hold CMS token");
6500 assert_lock_strong(_freelistLock);
6501 assert_lock_strong(_bit_map->lock());
6502 // relinquish the free_list_lock and bitMaplock()
6503 _bit_map->lock()->unlock();
6504 _freelistLock->unlock();
6505 ConcurrentMarkSweepThread::desynchronize(true);
6506 ConcurrentMarkSweepThread::acknowledge_yield_request();
6507 _collector->stopTimer();
6508 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
6509 if (PrintCMSStatistics != 0) {
6510 _collector->incrementYields();
6511 }
6512 _collector->icms_wait();
6514 // See the comment in coordinator_yield()
6515 for (unsigned i = 0;
6516 i < CMSYieldSleepCount &&
6517 ConcurrentMarkSweepThread::should_yield() &&
6518 !CMSCollector::foregroundGCIsActive();
6519 ++i) {
6520 os::sleep(Thread::current(), 1, false);
6521 ConcurrentMarkSweepThread::acknowledge_yield_request();
6522 }
6524 ConcurrentMarkSweepThread::synchronize(true);
6525 _freelistLock->lock_without_safepoint_check();
6526 _bit_map->lock()->lock_without_safepoint_check();
6527 _collector->startTimer();
6528 }
6530 ///////////////////////////////////////////////////////////
6531 // Par_MarkRefsIntoAndScanClosure: a parallel version of
6532 // MarkRefsIntoAndScanClosure
6533 ///////////////////////////////////////////////////////////
6534 Par_MarkRefsIntoAndScanClosure::Par_MarkRefsIntoAndScanClosure(
6535 CMSCollector* collector, MemRegion span, ReferenceProcessor* rp,
6536 CMSBitMap* bit_map, OopTaskQueue* work_queue, CMSMarkStack* revisit_stack):
6537 _span(span),
6538 _bit_map(bit_map),
6539 _work_queue(work_queue),
6540 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
6541 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads))),
6542 _par_pushAndMarkClosure(collector, span, rp, bit_map, work_queue,
6543 revisit_stack)
6544 {
6545 _ref_processor = rp;
6546 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6547 }
6549 // This closure is used to mark refs into the CMS generation at the
6550 // second (final) checkpoint, and to scan and transitively follow
6551 // the unmarked oops. The marks are made in the marking bit map and
6552 // the work_queue is used for keeping the (newly) grey objects during
6553 // the scan phase whence they are also available for stealing by parallel
6554 // threads. Since the marking bit map is shared, updates are
6555 // synchronized (via CAS).
6556 void Par_MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6557 if (obj != NULL) {
6558 // Ignore mark word because this could be an already marked oop
6559 // that may be chained at the end of the overflow list.
6560 assert(obj->is_oop(), "expected an oop");
6561 HeapWord* addr = (HeapWord*)obj;
6562 if (_span.contains(addr) &&
6563 !_bit_map->isMarked(addr)) {
6564 // mark bit map (object will become grey):
6565 // It is possible for several threads to be
6566 // trying to "claim" this object concurrently;
6567 // the unique thread that succeeds in marking the
6568 // object first will do the subsequent push on
6569 // to the work queue (or overflow list).
6570 if (_bit_map->par_mark(addr)) {
6571 // push on work_queue (which may not be empty), and trim the
6572 // queue to an appropriate length by applying this closure to
6573 // the oops in the oops popped from the stack (i.e. blacken the
6574 // grey objects)
6575 bool res = _work_queue->push(obj);
6576 assert(res, "Low water mark should be less than capacity?");
6577 trim_queue(_low_water_mark);
6578 } // Else, another thread claimed the object
6579 }
6580 }
6581 }
6583 void Par_MarkRefsIntoAndScanClosure::do_oop(oop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6584 void Par_MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6586 // This closure is used to rescan the marked objects on the dirty cards
6587 // in the mod union table and the card table proper.
6588 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
6589 oop p, MemRegion mr) {
6591 size_t size = 0;
6592 HeapWord* addr = (HeapWord*)p;
6593 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6594 assert(_span.contains(addr), "we are scanning the CMS generation");
6595 // check if it's time to yield
6596 if (do_yield_check()) {
6597 // We yielded for some foreground stop-world work,
6598 // and we have been asked to abort this ongoing preclean cycle.
6599 return 0;
6600 }
6601 if (_bitMap->isMarked(addr)) {
6602 // it's marked; is it potentially uninitialized?
6603 if (p->klass() != NULL) {
6604 if (CMSPermGenPrecleaningEnabled && !p->is_parsable()) {
6605 // Signal precleaning to redirty the card since
6606 // the klass pointer is already installed.
6607 assert(size == 0, "Initial value");
6608 } else {
6609 assert(p->is_parsable(), "must be parsable.");
6610 // an initialized object; ignore mark word in verification below
6611 // since we are running concurrent with mutators
6612 assert(p->is_oop(true), "should be an oop");
6613 if (p->is_objArray()) {
6614 // objArrays are precisely marked; restrict scanning
6615 // to dirty cards only.
6616 size = p->oop_iterate(_scanningClosure, mr);
6617 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6618 "adjustObjectSize should be the identity for array sizes, "
6619 "which are necessarily larger than minimum object size of "
6620 "two heap words");
6621 } else {
6622 // A non-array may have been imprecisely marked; we need
6623 // to scan object in its entirety.
6624 size = CompactibleFreeListSpace::adjustObjectSize(
6625 p->oop_iterate(_scanningClosure));
6626 }
6627 #ifdef DEBUG
6628 size_t direct_size =
6629 CompactibleFreeListSpace::adjustObjectSize(p->size());
6630 assert(size == direct_size, "Inconsistency in size");
6631 assert(size >= 3, "Necessary for Printezis marks to work");
6632 if (!_bitMap->isMarked(addr+1)) {
6633 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size);
6634 } else {
6635 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size-1);
6636 assert(_bitMap->isMarked(addr+size-1),
6637 "inconsistent Printezis mark");
6638 }
6639 #endif // DEBUG
6640 }
6641 } else {
6642 // an unitialized object
6643 assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
6644 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
6645 size = pointer_delta(nextOneAddr + 1, addr);
6646 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6647 "alignment problem");
6648 // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
6649 // will dirty the card when the klass pointer is installed in the
6650 // object (signalling the completion of initialization).
6651 }
6652 } else {
6653 // Either a not yet marked object or an uninitialized object
6654 if (p->klass() == NULL || !p->is_parsable()) {
6655 // An uninitialized object, skip to the next card, since
6656 // we may not be able to read its P-bits yet.
6657 assert(size == 0, "Initial value");
6658 } else {
6659 // An object not (yet) reached by marking: we merely need to
6660 // compute its size so as to go look at the next block.
6661 assert(p->is_oop(true), "should be an oop");
6662 size = CompactibleFreeListSpace::adjustObjectSize(p->size());
6663 }
6664 }
6665 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6666 return size;
6667 }
6669 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
6670 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6671 "CMS thread should hold CMS token");
6672 assert_lock_strong(_freelistLock);
6673 assert_lock_strong(_bitMap->lock());
6674 // relinquish the free_list_lock and bitMaplock()
6675 _bitMap->lock()->unlock();
6676 _freelistLock->unlock();
6677 ConcurrentMarkSweepThread::desynchronize(true);
6678 ConcurrentMarkSweepThread::acknowledge_yield_request();
6679 _collector->stopTimer();
6680 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
6681 if (PrintCMSStatistics != 0) {
6682 _collector->incrementYields();
6683 }
6684 _collector->icms_wait();
6686 // See the comment in coordinator_yield()
6687 for (unsigned i = 0; i < CMSYieldSleepCount &&
6688 ConcurrentMarkSweepThread::should_yield() &&
6689 !CMSCollector::foregroundGCIsActive(); ++i) {
6690 os::sleep(Thread::current(), 1, false);
6691 ConcurrentMarkSweepThread::acknowledge_yield_request();
6692 }
6694 ConcurrentMarkSweepThread::synchronize(true);
6695 _freelistLock->lock_without_safepoint_check();
6696 _bitMap->lock()->lock_without_safepoint_check();
6697 _collector->startTimer();
6698 }
6701 //////////////////////////////////////////////////////////////////
6702 // SurvivorSpacePrecleanClosure
6703 //////////////////////////////////////////////////////////////////
6704 // This (single-threaded) closure is used to preclean the oops in
6705 // the survivor spaces.
6706 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
6708 HeapWord* addr = (HeapWord*)p;
6709 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6710 assert(!_span.contains(addr), "we are scanning the survivor spaces");
6711 assert(p->klass() != NULL, "object should be initializd");
6712 assert(p->is_parsable(), "must be parsable.");
6713 // an initialized object; ignore mark word in verification below
6714 // since we are running concurrent with mutators
6715 assert(p->is_oop(true), "should be an oop");
6716 // Note that we do not yield while we iterate over
6717 // the interior oops of p, pushing the relevant ones
6718 // on our marking stack.
6719 size_t size = p->oop_iterate(_scanning_closure);
6720 do_yield_check();
6721 // Observe that below, we do not abandon the preclean
6722 // phase as soon as we should; rather we empty the
6723 // marking stack before returning. This is to satisfy
6724 // some existing assertions. In general, it may be a
6725 // good idea to abort immediately and complete the marking
6726 // from the grey objects at a later time.
6727 while (!_mark_stack->isEmpty()) {
6728 oop new_oop = _mark_stack->pop();
6729 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6730 assert(new_oop->is_parsable(), "Found unparsable oop");
6731 assert(_bit_map->isMarked((HeapWord*)new_oop),
6732 "only grey objects on this stack");
6733 // iterate over the oops in this oop, marking and pushing
6734 // the ones in CMS heap (i.e. in _span).
6735 new_oop->oop_iterate(_scanning_closure);
6736 // check if it's time to yield
6737 do_yield_check();
6738 }
6739 unsigned int after_count =
6740 GenCollectedHeap::heap()->total_collections();
6741 bool abort = (_before_count != after_count) ||
6742 _collector->should_abort_preclean();
6743 return abort ? 0 : size;
6744 }
6746 void SurvivorSpacePrecleanClosure::do_yield_work() {
6747 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6748 "CMS thread should hold CMS token");
6749 assert_lock_strong(_bit_map->lock());
6750 // Relinquish the bit map lock
6751 _bit_map->lock()->unlock();
6752 ConcurrentMarkSweepThread::desynchronize(true);
6753 ConcurrentMarkSweepThread::acknowledge_yield_request();
6754 _collector->stopTimer();
6755 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
6756 if (PrintCMSStatistics != 0) {
6757 _collector->incrementYields();
6758 }
6759 _collector->icms_wait();
6761 // See the comment in coordinator_yield()
6762 for (unsigned i = 0; i < CMSYieldSleepCount &&
6763 ConcurrentMarkSweepThread::should_yield() &&
6764 !CMSCollector::foregroundGCIsActive(); ++i) {
6765 os::sleep(Thread::current(), 1, false);
6766 ConcurrentMarkSweepThread::acknowledge_yield_request();
6767 }
6769 ConcurrentMarkSweepThread::synchronize(true);
6770 _bit_map->lock()->lock_without_safepoint_check();
6771 _collector->startTimer();
6772 }
6774 // This closure is used to rescan the marked objects on the dirty cards
6775 // in the mod union table and the card table proper. In the parallel
6776 // case, although the bitMap is shared, we do a single read so the
6777 // isMarked() query is "safe".
6778 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
6779 // Ignore mark word because we are running concurrent with mutators
6780 assert(p->is_oop_or_null(true), "expected an oop or null");
6781 HeapWord* addr = (HeapWord*)p;
6782 assert(_span.contains(addr), "we are scanning the CMS generation");
6783 bool is_obj_array = false;
6784 #ifdef DEBUG
6785 if (!_parallel) {
6786 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6787 assert(_collector->overflow_list_is_empty(),
6788 "overflow list should be empty");
6790 }
6791 #endif // DEBUG
6792 if (_bit_map->isMarked(addr)) {
6793 // Obj arrays are precisely marked, non-arrays are not;
6794 // so we scan objArrays precisely and non-arrays in their
6795 // entirety.
6796 if (p->is_objArray()) {
6797 is_obj_array = true;
6798 if (_parallel) {
6799 p->oop_iterate(_par_scan_closure, mr);
6800 } else {
6801 p->oop_iterate(_scan_closure, mr);
6802 }
6803 } else {
6804 if (_parallel) {
6805 p->oop_iterate(_par_scan_closure);
6806 } else {
6807 p->oop_iterate(_scan_closure);
6808 }
6809 }
6810 }
6811 #ifdef DEBUG
6812 if (!_parallel) {
6813 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6814 assert(_collector->overflow_list_is_empty(),
6815 "overflow list should be empty");
6817 }
6818 #endif // DEBUG
6819 return is_obj_array;
6820 }
6822 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
6823 MemRegion span,
6824 CMSBitMap* bitMap, CMSMarkStack* markStack,
6825 CMSMarkStack* revisitStack,
6826 bool should_yield, bool verifying):
6827 _collector(collector),
6828 _span(span),
6829 _bitMap(bitMap),
6830 _mut(&collector->_modUnionTable),
6831 _markStack(markStack),
6832 _revisitStack(revisitStack),
6833 _yield(should_yield),
6834 _skipBits(0)
6835 {
6836 assert(_markStack->isEmpty(), "stack should be empty");
6837 _finger = _bitMap->startWord();
6838 _threshold = _finger;
6839 assert(_collector->_restart_addr == NULL, "Sanity check");
6840 assert(_span.contains(_finger), "Out of bounds _finger?");
6841 DEBUG_ONLY(_verifying = verifying;)
6842 }
6844 void MarkFromRootsClosure::reset(HeapWord* addr) {
6845 assert(_markStack->isEmpty(), "would cause duplicates on stack");
6846 assert(_span.contains(addr), "Out of bounds _finger?");
6847 _finger = addr;
6848 _threshold = (HeapWord*)round_to(
6849 (intptr_t)_finger, CardTableModRefBS::card_size);
6850 }
6852 // Should revisit to see if this should be restructured for
6853 // greater efficiency.
6854 void MarkFromRootsClosure::do_bit(size_t offset) {
6855 if (_skipBits > 0) {
6856 _skipBits--;
6857 return;
6858 }
6859 // convert offset into a HeapWord*
6860 HeapWord* addr = _bitMap->startWord() + offset;
6861 assert(_bitMap->endWord() && addr < _bitMap->endWord(),
6862 "address out of range");
6863 assert(_bitMap->isMarked(addr), "tautology");
6864 if (_bitMap->isMarked(addr+1)) {
6865 // this is an allocated but not yet initialized object
6866 assert(_skipBits == 0, "tautology");
6867 _skipBits = 2; // skip next two marked bits ("Printezis-marks")
6868 oop p = oop(addr);
6869 if (p->klass() == NULL || !p->is_parsable()) {
6870 DEBUG_ONLY(if (!_verifying) {)
6871 // We re-dirty the cards on which this object lies and increase
6872 // the _threshold so that we'll come back to scan this object
6873 // during the preclean or remark phase. (CMSCleanOnEnter)
6874 if (CMSCleanOnEnter) {
6875 size_t sz = _collector->block_size_using_printezis_bits(addr);
6876 HeapWord* start_card_addr = (HeapWord*)round_down(
6877 (intptr_t)addr, CardTableModRefBS::card_size);
6878 HeapWord* end_card_addr = (HeapWord*)round_to(
6879 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
6880 MemRegion redirty_range = MemRegion(start_card_addr, end_card_addr);
6881 assert(!redirty_range.is_empty(), "Arithmetical tautology");
6882 // Bump _threshold to end_card_addr; note that
6883 // _threshold cannot possibly exceed end_card_addr, anyhow.
6884 // This prevents future clearing of the card as the scan proceeds
6885 // to the right.
6886 assert(_threshold <= end_card_addr,
6887 "Because we are just scanning into this object");
6888 if (_threshold < end_card_addr) {
6889 _threshold = end_card_addr;
6890 }
6891 if (p->klass() != NULL) {
6892 // Redirty the range of cards...
6893 _mut->mark_range(redirty_range);
6894 } // ...else the setting of klass will dirty the card anyway.
6895 }
6896 DEBUG_ONLY(})
6897 return;
6898 }
6899 }
6900 scanOopsInOop(addr);
6901 }
6903 // We take a break if we've been at this for a while,
6904 // so as to avoid monopolizing the locks involved.
6905 void MarkFromRootsClosure::do_yield_work() {
6906 // First give up the locks, then yield, then re-lock
6907 // We should probably use a constructor/destructor idiom to
6908 // do this unlock/lock or modify the MutexUnlocker class to
6909 // serve our purpose. XXX
6910 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6911 "CMS thread should hold CMS token");
6912 assert_lock_strong(_bitMap->lock());
6913 _bitMap->lock()->unlock();
6914 ConcurrentMarkSweepThread::desynchronize(true);
6915 ConcurrentMarkSweepThread::acknowledge_yield_request();
6916 _collector->stopTimer();
6917 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
6918 if (PrintCMSStatistics != 0) {
6919 _collector->incrementYields();
6920 }
6921 _collector->icms_wait();
6923 // See the comment in coordinator_yield()
6924 for (unsigned i = 0; i < CMSYieldSleepCount &&
6925 ConcurrentMarkSweepThread::should_yield() &&
6926 !CMSCollector::foregroundGCIsActive(); ++i) {
6927 os::sleep(Thread::current(), 1, false);
6928 ConcurrentMarkSweepThread::acknowledge_yield_request();
6929 }
6931 ConcurrentMarkSweepThread::synchronize(true);
6932 _bitMap->lock()->lock_without_safepoint_check();
6933 _collector->startTimer();
6934 }
6936 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
6937 assert(_bitMap->isMarked(ptr), "expected bit to be set");
6938 assert(_markStack->isEmpty(),
6939 "should drain stack to limit stack usage");
6940 // convert ptr to an oop preparatory to scanning
6941 oop obj = oop(ptr);
6942 // Ignore mark word in verification below, since we
6943 // may be running concurrent with mutators.
6944 assert(obj->is_oop(true), "should be an oop");
6945 assert(_finger <= ptr, "_finger runneth ahead");
6946 // advance the finger to right end of this object
6947 _finger = ptr + obj->size();
6948 assert(_finger > ptr, "we just incremented it above");
6949 // On large heaps, it may take us some time to get through
6950 // the marking phase (especially if running iCMS). During
6951 // this time it's possible that a lot of mutations have
6952 // accumulated in the card table and the mod union table --
6953 // these mutation records are redundant until we have
6954 // actually traced into the corresponding card.
6955 // Here, we check whether advancing the finger would make
6956 // us cross into a new card, and if so clear corresponding
6957 // cards in the MUT (preclean them in the card-table in the
6958 // future).
6960 DEBUG_ONLY(if (!_verifying) {)
6961 // The clean-on-enter optimization is disabled by default,
6962 // until we fix 6178663.
6963 if (CMSCleanOnEnter && (_finger > _threshold)) {
6964 // [_threshold, _finger) represents the interval
6965 // of cards to be cleared in MUT (or precleaned in card table).
6966 // The set of cards to be cleared is all those that overlap
6967 // with the interval [_threshold, _finger); note that
6968 // _threshold is always kept card-aligned but _finger isn't
6969 // always card-aligned.
6970 HeapWord* old_threshold = _threshold;
6971 assert(old_threshold == (HeapWord*)round_to(
6972 (intptr_t)old_threshold, CardTableModRefBS::card_size),
6973 "_threshold should always be card-aligned");
6974 _threshold = (HeapWord*)round_to(
6975 (intptr_t)_finger, CardTableModRefBS::card_size);
6976 MemRegion mr(old_threshold, _threshold);
6977 assert(!mr.is_empty(), "Control point invariant");
6978 assert(_span.contains(mr), "Should clear within span");
6979 // XXX When _finger crosses from old gen into perm gen
6980 // we may be doing unnecessary cleaning; do better in the
6981 // future by detecting that condition and clearing fewer
6982 // MUT/CT entries.
6983 _mut->clear_range(mr);
6984 }
6985 DEBUG_ONLY(})
6987 // Note: the finger doesn't advance while we drain
6988 // the stack below.
6989 PushOrMarkClosure pushOrMarkClosure(_collector,
6990 _span, _bitMap, _markStack,
6991 _revisitStack,
6992 _finger, this);
6993 bool res = _markStack->push(obj);
6994 assert(res, "Empty non-zero size stack should have space for single push");
6995 while (!_markStack->isEmpty()) {
6996 oop new_oop = _markStack->pop();
6997 // Skip verifying header mark word below because we are
6998 // running concurrent with mutators.
6999 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
7000 // now scan this oop's oops
7001 new_oop->oop_iterate(&pushOrMarkClosure);
7002 do_yield_check();
7003 }
7004 assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
7005 }
7007 Par_MarkFromRootsClosure::Par_MarkFromRootsClosure(CMSConcMarkingTask* task,
7008 CMSCollector* collector, MemRegion span,
7009 CMSBitMap* bit_map,
7010 OopTaskQueue* work_queue,
7011 CMSMarkStack* overflow_stack,
7012 CMSMarkStack* revisit_stack,
7013 bool should_yield):
7014 _collector(collector),
7015 _whole_span(collector->_span),
7016 _span(span),
7017 _bit_map(bit_map),
7018 _mut(&collector->_modUnionTable),
7019 _work_queue(work_queue),
7020 _overflow_stack(overflow_stack),
7021 _revisit_stack(revisit_stack),
7022 _yield(should_yield),
7023 _skip_bits(0),
7024 _task(task)
7025 {
7026 assert(_work_queue->size() == 0, "work_queue should be empty");
7027 _finger = span.start();
7028 _threshold = _finger; // XXX Defer clear-on-enter optimization for now
7029 assert(_span.contains(_finger), "Out of bounds _finger?");
7030 }
7032 // Should revisit to see if this should be restructured for
7033 // greater efficiency.
7034 void Par_MarkFromRootsClosure::do_bit(size_t offset) {
7035 if (_skip_bits > 0) {
7036 _skip_bits--;
7037 return;
7038 }
7039 // convert offset into a HeapWord*
7040 HeapWord* addr = _bit_map->startWord() + offset;
7041 assert(_bit_map->endWord() && addr < _bit_map->endWord(),
7042 "address out of range");
7043 assert(_bit_map->isMarked(addr), "tautology");
7044 if (_bit_map->isMarked(addr+1)) {
7045 // this is an allocated object that might not yet be initialized
7046 assert(_skip_bits == 0, "tautology");
7047 _skip_bits = 2; // skip next two marked bits ("Printezis-marks")
7048 oop p = oop(addr);
7049 if (p->klass() == NULL || !p->is_parsable()) {
7050 // in the case of Clean-on-Enter optimization, redirty card
7051 // and avoid clearing card by increasing the threshold.
7052 return;
7053 }
7054 }
7055 scan_oops_in_oop(addr);
7056 }
7058 void Par_MarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
7059 assert(_bit_map->isMarked(ptr), "expected bit to be set");
7060 // Should we assert that our work queue is empty or
7061 // below some drain limit?
7062 assert(_work_queue->size() == 0,
7063 "should drain stack to limit stack usage");
7064 // convert ptr to an oop preparatory to scanning
7065 oop obj = oop(ptr);
7066 // Ignore mark word in verification below, since we
7067 // may be running concurrent with mutators.
7068 assert(obj->is_oop(true), "should be an oop");
7069 assert(_finger <= ptr, "_finger runneth ahead");
7070 // advance the finger to right end of this object
7071 _finger = ptr + obj->size();
7072 assert(_finger > ptr, "we just incremented it above");
7073 // On large heaps, it may take us some time to get through
7074 // the marking phase (especially if running iCMS). During
7075 // this time it's possible that a lot of mutations have
7076 // accumulated in the card table and the mod union table --
7077 // these mutation records are redundant until we have
7078 // actually traced into the corresponding card.
7079 // Here, we check whether advancing the finger would make
7080 // us cross into a new card, and if so clear corresponding
7081 // cards in the MUT (preclean them in the card-table in the
7082 // future).
7084 // The clean-on-enter optimization is disabled by default,
7085 // until we fix 6178663.
7086 if (CMSCleanOnEnter && (_finger > _threshold)) {
7087 // [_threshold, _finger) represents the interval
7088 // of cards to be cleared in MUT (or precleaned in card table).
7089 // The set of cards to be cleared is all those that overlap
7090 // with the interval [_threshold, _finger); note that
7091 // _threshold is always kept card-aligned but _finger isn't
7092 // always card-aligned.
7093 HeapWord* old_threshold = _threshold;
7094 assert(old_threshold == (HeapWord*)round_to(
7095 (intptr_t)old_threshold, CardTableModRefBS::card_size),
7096 "_threshold should always be card-aligned");
7097 _threshold = (HeapWord*)round_to(
7098 (intptr_t)_finger, CardTableModRefBS::card_size);
7099 MemRegion mr(old_threshold, _threshold);
7100 assert(!mr.is_empty(), "Control point invariant");
7101 assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
7102 // XXX When _finger crosses from old gen into perm gen
7103 // we may be doing unnecessary cleaning; do better in the
7104 // future by detecting that condition and clearing fewer
7105 // MUT/CT entries.
7106 _mut->clear_range(mr);
7107 }
7109 // Note: the local finger doesn't advance while we drain
7110 // the stack below, but the global finger sure can and will.
7111 HeapWord** gfa = _task->global_finger_addr();
7112 Par_PushOrMarkClosure pushOrMarkClosure(_collector,
7113 _span, _bit_map,
7114 _work_queue,
7115 _overflow_stack,
7116 _revisit_stack,
7117 _finger,
7118 gfa, this);
7119 bool res = _work_queue->push(obj); // overflow could occur here
7120 assert(res, "Will hold once we use workqueues");
7121 while (true) {
7122 oop new_oop;
7123 if (!_work_queue->pop_local(new_oop)) {
7124 // We emptied our work_queue; check if there's stuff that can
7125 // be gotten from the overflow stack.
7126 if (CMSConcMarkingTask::get_work_from_overflow_stack(
7127 _overflow_stack, _work_queue)) {
7128 do_yield_check();
7129 continue;
7130 } else { // done
7131 break;
7132 }
7133 }
7134 // Skip verifying header mark word below because we are
7135 // running concurrent with mutators.
7136 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
7137 // now scan this oop's oops
7138 new_oop->oop_iterate(&pushOrMarkClosure);
7139 do_yield_check();
7140 }
7141 assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
7142 }
7144 // Yield in response to a request from VM Thread or
7145 // from mutators.
7146 void Par_MarkFromRootsClosure::do_yield_work() {
7147 assert(_task != NULL, "sanity");
7148 _task->yield();
7149 }
7151 // A variant of the above used for verifying CMS marking work.
7152 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
7153 MemRegion span,
7154 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
7155 CMSMarkStack* mark_stack):
7156 _collector(collector),
7157 _span(span),
7158 _verification_bm(verification_bm),
7159 _cms_bm(cms_bm),
7160 _mark_stack(mark_stack),
7161 _pam_verify_closure(collector, span, verification_bm, cms_bm,
7162 mark_stack)
7163 {
7164 assert(_mark_stack->isEmpty(), "stack should be empty");
7165 _finger = _verification_bm->startWord();
7166 assert(_collector->_restart_addr == NULL, "Sanity check");
7167 assert(_span.contains(_finger), "Out of bounds _finger?");
7168 }
7170 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
7171 assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
7172 assert(_span.contains(addr), "Out of bounds _finger?");
7173 _finger = addr;
7174 }
7176 // Should revisit to see if this should be restructured for
7177 // greater efficiency.
7178 void MarkFromRootsVerifyClosure::do_bit(size_t offset) {
7179 // convert offset into a HeapWord*
7180 HeapWord* addr = _verification_bm->startWord() + offset;
7181 assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
7182 "address out of range");
7183 assert(_verification_bm->isMarked(addr), "tautology");
7184 assert(_cms_bm->isMarked(addr), "tautology");
7186 assert(_mark_stack->isEmpty(),
7187 "should drain stack to limit stack usage");
7188 // convert addr to an oop preparatory to scanning
7189 oop obj = oop(addr);
7190 assert(obj->is_oop(), "should be an oop");
7191 assert(_finger <= addr, "_finger runneth ahead");
7192 // advance the finger to right end of this object
7193 _finger = addr + obj->size();
7194 assert(_finger > addr, "we just incremented it above");
7195 // Note: the finger doesn't advance while we drain
7196 // the stack below.
7197 bool res = _mark_stack->push(obj);
7198 assert(res, "Empty non-zero size stack should have space for single push");
7199 while (!_mark_stack->isEmpty()) {
7200 oop new_oop = _mark_stack->pop();
7201 assert(new_oop->is_oop(), "Oops! expected to pop an oop");
7202 // now scan this oop's oops
7203 new_oop->oop_iterate(&_pam_verify_closure);
7204 }
7205 assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
7206 }
7208 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
7209 CMSCollector* collector, MemRegion span,
7210 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
7211 CMSMarkStack* mark_stack):
7212 OopClosure(collector->ref_processor()),
7213 _collector(collector),
7214 _span(span),
7215 _verification_bm(verification_bm),
7216 _cms_bm(cms_bm),
7217 _mark_stack(mark_stack)
7218 { }
7220 void PushAndMarkVerifyClosure::do_oop(oop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
7221 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
7223 // Upon stack overflow, we discard (part of) the stack,
7224 // remembering the least address amongst those discarded
7225 // in CMSCollector's _restart_address.
7226 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
7227 // Remember the least grey address discarded
7228 HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
7229 _collector->lower_restart_addr(ra);
7230 _mark_stack->reset(); // discard stack contents
7231 _mark_stack->expand(); // expand the stack if possible
7232 }
7234 void PushAndMarkVerifyClosure::do_oop(oop obj) {
7235 assert(obj->is_oop_or_null(), "expected an oop or NULL");
7236 HeapWord* addr = (HeapWord*)obj;
7237 if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
7238 // Oop lies in _span and isn't yet grey or black
7239 _verification_bm->mark(addr); // now grey
7240 if (!_cms_bm->isMarked(addr)) {
7241 oop(addr)->print();
7242 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)",
7243 addr);
7244 fatal("... aborting");
7245 }
7247 if (!_mark_stack->push(obj)) { // stack overflow
7248 if (PrintCMSStatistics != 0) {
7249 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7250 SIZE_FORMAT, _mark_stack->capacity());
7251 }
7252 assert(_mark_stack->isFull(), "Else push should have succeeded");
7253 handle_stack_overflow(addr);
7254 }
7255 // anything including and to the right of _finger
7256 // will be scanned as we iterate over the remainder of the
7257 // bit map
7258 }
7259 }
7261 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
7262 MemRegion span,
7263 CMSBitMap* bitMap, CMSMarkStack* markStack,
7264 CMSMarkStack* revisitStack,
7265 HeapWord* finger, MarkFromRootsClosure* parent) :
7266 OopClosure(collector->ref_processor()),
7267 _collector(collector),
7268 _span(span),
7269 _bitMap(bitMap),
7270 _markStack(markStack),
7271 _revisitStack(revisitStack),
7272 _finger(finger),
7273 _parent(parent),
7274 _should_remember_klasses(collector->should_unload_classes())
7275 { }
7277 Par_PushOrMarkClosure::Par_PushOrMarkClosure(CMSCollector* collector,
7278 MemRegion span,
7279 CMSBitMap* bit_map,
7280 OopTaskQueue* work_queue,
7281 CMSMarkStack* overflow_stack,
7282 CMSMarkStack* revisit_stack,
7283 HeapWord* finger,
7284 HeapWord** global_finger_addr,
7285 Par_MarkFromRootsClosure* parent) :
7286 OopClosure(collector->ref_processor()),
7287 _collector(collector),
7288 _whole_span(collector->_span),
7289 _span(span),
7290 _bit_map(bit_map),
7291 _work_queue(work_queue),
7292 _overflow_stack(overflow_stack),
7293 _revisit_stack(revisit_stack),
7294 _finger(finger),
7295 _global_finger_addr(global_finger_addr),
7296 _parent(parent),
7297 _should_remember_klasses(collector->should_unload_classes())
7298 { }
7300 void CMSCollector::lower_restart_addr(HeapWord* low) {
7301 assert(_span.contains(low), "Out of bounds addr");
7302 if (_restart_addr == NULL) {
7303 _restart_addr = low;
7304 } else {
7305 _restart_addr = MIN2(_restart_addr, low);
7306 }
7307 }
7309 // Upon stack overflow, we discard (part of) the stack,
7310 // remembering the least address amongst those discarded
7311 // in CMSCollector's _restart_address.
7312 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7313 // Remember the least grey address discarded
7314 HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
7315 _collector->lower_restart_addr(ra);
7316 _markStack->reset(); // discard stack contents
7317 _markStack->expand(); // expand the stack if possible
7318 }
7320 // Upon stack overflow, we discard (part of) the stack,
7321 // remembering the least address amongst those discarded
7322 // in CMSCollector's _restart_address.
7323 void Par_PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7324 // We need to do this under a mutex to prevent other
7325 // workers from interfering with the expansion below.
7326 MutexLockerEx ml(_overflow_stack->par_lock(),
7327 Mutex::_no_safepoint_check_flag);
7328 // Remember the least grey address discarded
7329 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
7330 _collector->lower_restart_addr(ra);
7331 _overflow_stack->reset(); // discard stack contents
7332 _overflow_stack->expand(); // expand the stack if possible
7333 }
7335 void PushOrMarkClosure::do_oop(oop obj) {
7336 // Ignore mark word because we are running concurrent with mutators.
7337 assert(obj->is_oop_or_null(true), "expected an oop or NULL");
7338 HeapWord* addr = (HeapWord*)obj;
7339 if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
7340 // Oop lies in _span and isn't yet grey or black
7341 _bitMap->mark(addr); // now grey
7342 if (addr < _finger) {
7343 // the bit map iteration has already either passed, or
7344 // sampled, this bit in the bit map; we'll need to
7345 // use the marking stack to scan this oop's oops.
7346 bool simulate_overflow = false;
7347 NOT_PRODUCT(
7348 if (CMSMarkStackOverflowALot &&
7349 _collector->simulate_overflow()) {
7350 // simulate a stack overflow
7351 simulate_overflow = true;
7352 }
7353 )
7354 if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
7355 if (PrintCMSStatistics != 0) {
7356 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7357 SIZE_FORMAT, _markStack->capacity());
7358 }
7359 assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
7360 handle_stack_overflow(addr);
7361 }
7362 }
7363 // anything including and to the right of _finger
7364 // will be scanned as we iterate over the remainder of the
7365 // bit map
7366 do_yield_check();
7367 }
7368 }
7370 void PushOrMarkClosure::do_oop(oop* p) { PushOrMarkClosure::do_oop_work(p); }
7371 void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); }
7373 void Par_PushOrMarkClosure::do_oop(oop obj) {
7374 // Ignore mark word because we are running concurrent with mutators.
7375 assert(obj->is_oop_or_null(true), "expected an oop or NULL");
7376 HeapWord* addr = (HeapWord*)obj;
7377 if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
7378 // Oop lies in _span and isn't yet grey or black
7379 // We read the global_finger (volatile read) strictly after marking oop
7380 bool res = _bit_map->par_mark(addr); // now grey
7381 volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
7382 // Should we push this marked oop on our stack?
7383 // -- if someone else marked it, nothing to do
7384 // -- if target oop is above global finger nothing to do
7385 // -- if target oop is in chunk and above local finger
7386 // then nothing to do
7387 // -- else push on work queue
7388 if ( !res // someone else marked it, they will deal with it
7389 || (addr >= *gfa) // will be scanned in a later task
7390 || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
7391 return;
7392 }
7393 // the bit map iteration has already either passed, or
7394 // sampled, this bit in the bit map; we'll need to
7395 // use the marking stack to scan this oop's oops.
7396 bool simulate_overflow = false;
7397 NOT_PRODUCT(
7398 if (CMSMarkStackOverflowALot &&
7399 _collector->simulate_overflow()) {
7400 // simulate a stack overflow
7401 simulate_overflow = true;
7402 }
7403 )
7404 if (simulate_overflow ||
7405 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
7406 // stack overflow
7407 if (PrintCMSStatistics != 0) {
7408 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7409 SIZE_FORMAT, _overflow_stack->capacity());
7410 }
7411 // We cannot assert that the overflow stack is full because
7412 // it may have been emptied since.
7413 assert(simulate_overflow ||
7414 _work_queue->size() == _work_queue->max_elems(),
7415 "Else push should have succeeded");
7416 handle_stack_overflow(addr);
7417 }
7418 do_yield_check();
7419 }
7420 }
7422 void Par_PushOrMarkClosure::do_oop(oop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7423 void Par_PushOrMarkClosure::do_oop(narrowOop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7425 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
7426 MemRegion span,
7427 ReferenceProcessor* rp,
7428 CMSBitMap* bit_map,
7429 CMSBitMap* mod_union_table,
7430 CMSMarkStack* mark_stack,
7431 CMSMarkStack* revisit_stack,
7432 bool concurrent_precleaning):
7433 OopClosure(rp),
7434 _collector(collector),
7435 _span(span),
7436 _bit_map(bit_map),
7437 _mod_union_table(mod_union_table),
7438 _mark_stack(mark_stack),
7439 _revisit_stack(revisit_stack),
7440 _concurrent_precleaning(concurrent_precleaning),
7441 _should_remember_klasses(collector->should_unload_classes())
7442 {
7443 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7444 }
7446 // Grey object rescan during pre-cleaning and second checkpoint phases --
7447 // the non-parallel version (the parallel version appears further below.)
7448 void PushAndMarkClosure::do_oop(oop obj) {
7449 // If _concurrent_precleaning, ignore mark word verification
7450 assert(obj->is_oop_or_null(_concurrent_precleaning),
7451 "expected an oop or NULL");
7452 HeapWord* addr = (HeapWord*)obj;
7453 // Check if oop points into the CMS generation
7454 // and is not marked
7455 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7456 // a white object ...
7457 _bit_map->mark(addr); // ... now grey
7458 // push on the marking stack (grey set)
7459 bool simulate_overflow = false;
7460 NOT_PRODUCT(
7461 if (CMSMarkStackOverflowALot &&
7462 _collector->simulate_overflow()) {
7463 // simulate a stack overflow
7464 simulate_overflow = true;
7465 }
7466 )
7467 if (simulate_overflow || !_mark_stack->push(obj)) {
7468 if (_concurrent_precleaning) {
7469 // During precleaning we can just dirty the appropriate card
7470 // in the mod union table, thus ensuring that the object remains
7471 // in the grey set and continue. Note that no one can be intefering
7472 // with us in this action of dirtying the mod union table, so
7473 // no locking is required.
7474 _mod_union_table->mark(addr);
7475 _collector->_ser_pmc_preclean_ovflw++;
7476 } else {
7477 // During the remark phase, we need to remember this oop
7478 // in the overflow list.
7479 _collector->push_on_overflow_list(obj);
7480 _collector->_ser_pmc_remark_ovflw++;
7481 }
7482 }
7483 }
7484 }
7486 Par_PushAndMarkClosure::Par_PushAndMarkClosure(CMSCollector* collector,
7487 MemRegion span,
7488 ReferenceProcessor* rp,
7489 CMSBitMap* bit_map,
7490 OopTaskQueue* work_queue,
7491 CMSMarkStack* revisit_stack):
7492 OopClosure(rp),
7493 _collector(collector),
7494 _span(span),
7495 _bit_map(bit_map),
7496 _work_queue(work_queue),
7497 _revisit_stack(revisit_stack),
7498 _should_remember_klasses(collector->should_unload_classes())
7499 {
7500 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7501 }
7503 void PushAndMarkClosure::do_oop(oop* p) { PushAndMarkClosure::do_oop_work(p); }
7504 void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); }
7506 // Grey object rescan during second checkpoint phase --
7507 // the parallel version.
7508 void Par_PushAndMarkClosure::do_oop(oop obj) {
7509 // In the assert below, we ignore the mark word because
7510 // this oop may point to an already visited object that is
7511 // on the overflow stack (in which case the mark word has
7512 // been hijacked for chaining into the overflow stack --
7513 // if this is the last object in the overflow stack then
7514 // its mark word will be NULL). Because this object may
7515 // have been subsequently popped off the global overflow
7516 // stack, and the mark word possibly restored to the prototypical
7517 // value, by the time we get to examined this failing assert in
7518 // the debugger, is_oop_or_null(false) may subsequently start
7519 // to hold.
7520 assert(obj->is_oop_or_null(true),
7521 "expected an oop or NULL");
7522 HeapWord* addr = (HeapWord*)obj;
7523 // Check if oop points into the CMS generation
7524 // and is not marked
7525 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7526 // a white object ...
7527 // If we manage to "claim" the object, by being the
7528 // first thread to mark it, then we push it on our
7529 // marking stack
7530 if (_bit_map->par_mark(addr)) { // ... now grey
7531 // push on work queue (grey set)
7532 bool simulate_overflow = false;
7533 NOT_PRODUCT(
7534 if (CMSMarkStackOverflowALot &&
7535 _collector->par_simulate_overflow()) {
7536 // simulate a stack overflow
7537 simulate_overflow = true;
7538 }
7539 )
7540 if (simulate_overflow || !_work_queue->push(obj)) {
7541 _collector->par_push_on_overflow_list(obj);
7542 _collector->_par_pmc_remark_ovflw++; // imprecise OK: no need to CAS
7543 }
7544 } // Else, some other thread got there first
7545 }
7546 }
7548 void Par_PushAndMarkClosure::do_oop(oop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7549 void Par_PushAndMarkClosure::do_oop(narrowOop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7551 void PushAndMarkClosure::remember_klass(Klass* k) {
7552 if (!_revisit_stack->push(oop(k))) {
7553 fatal("Revisit stack overflowed in PushAndMarkClosure");
7554 }
7555 }
7557 void Par_PushAndMarkClosure::remember_klass(Klass* k) {
7558 if (!_revisit_stack->par_push(oop(k))) {
7559 fatal("Revist stack overflowed in Par_PushAndMarkClosure");
7560 }
7561 }
7563 void CMSPrecleanRefsYieldClosure::do_yield_work() {
7564 Mutex* bml = _collector->bitMapLock();
7565 assert_lock_strong(bml);
7566 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7567 "CMS thread should hold CMS token");
7569 bml->unlock();
7570 ConcurrentMarkSweepThread::desynchronize(true);
7572 ConcurrentMarkSweepThread::acknowledge_yield_request();
7574 _collector->stopTimer();
7575 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7576 if (PrintCMSStatistics != 0) {
7577 _collector->incrementYields();
7578 }
7579 _collector->icms_wait();
7581 // See the comment in coordinator_yield()
7582 for (unsigned i = 0; i < CMSYieldSleepCount &&
7583 ConcurrentMarkSweepThread::should_yield() &&
7584 !CMSCollector::foregroundGCIsActive(); ++i) {
7585 os::sleep(Thread::current(), 1, false);
7586 ConcurrentMarkSweepThread::acknowledge_yield_request();
7587 }
7589 ConcurrentMarkSweepThread::synchronize(true);
7590 bml->lock();
7592 _collector->startTimer();
7593 }
7595 bool CMSPrecleanRefsYieldClosure::should_return() {
7596 if (ConcurrentMarkSweepThread::should_yield()) {
7597 do_yield_work();
7598 }
7599 return _collector->foregroundGCIsActive();
7600 }
7602 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
7603 assert(((size_t)mr.start())%CardTableModRefBS::card_size_in_words == 0,
7604 "mr should be aligned to start at a card boundary");
7605 // We'd like to assert:
7606 // assert(mr.word_size()%CardTableModRefBS::card_size_in_words == 0,
7607 // "mr should be a range of cards");
7608 // However, that would be too strong in one case -- the last
7609 // partition ends at _unallocated_block which, in general, can be
7610 // an arbitrary boundary, not necessarily card aligned.
7611 if (PrintCMSStatistics != 0) {
7612 _num_dirty_cards +=
7613 mr.word_size()/CardTableModRefBS::card_size_in_words;
7614 }
7615 _space->object_iterate_mem(mr, &_scan_cl);
7616 }
7618 SweepClosure::SweepClosure(CMSCollector* collector,
7619 ConcurrentMarkSweepGeneration* g,
7620 CMSBitMap* bitMap, bool should_yield) :
7621 _collector(collector),
7622 _g(g),
7623 _sp(g->cmsSpace()),
7624 _limit(_sp->sweep_limit()),
7625 _freelistLock(_sp->freelistLock()),
7626 _bitMap(bitMap),
7627 _yield(should_yield),
7628 _inFreeRange(false), // No free range at beginning of sweep
7629 _freeRangeInFreeLists(false), // No free range at beginning of sweep
7630 _lastFreeRangeCoalesced(false),
7631 _freeFinger(g->used_region().start())
7632 {
7633 NOT_PRODUCT(
7634 _numObjectsFreed = 0;
7635 _numWordsFreed = 0;
7636 _numObjectsLive = 0;
7637 _numWordsLive = 0;
7638 _numObjectsAlreadyFree = 0;
7639 _numWordsAlreadyFree = 0;
7640 _last_fc = NULL;
7642 _sp->initializeIndexedFreeListArrayReturnedBytes();
7643 _sp->dictionary()->initializeDictReturnedBytes();
7644 )
7645 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7646 "sweep _limit out of bounds");
7647 if (CMSTraceSweeper) {
7648 gclog_or_tty->print("\n====================\nStarting new sweep\n");
7649 }
7650 }
7652 // We need this destructor to reclaim any space at the end
7653 // of the space, which do_blk below may not have added back to
7654 // the free lists. [basically dealing with the "fringe effect"]
7655 SweepClosure::~SweepClosure() {
7656 assert_lock_strong(_freelistLock);
7657 // this should be treated as the end of a free run if any
7658 // The current free range should be returned to the free lists
7659 // as one coalesced chunk.
7660 if (inFreeRange()) {
7661 flushCurFreeChunk(freeFinger(),
7662 pointer_delta(_limit, freeFinger()));
7663 assert(freeFinger() < _limit, "the finger pointeth off base");
7664 if (CMSTraceSweeper) {
7665 gclog_or_tty->print("destructor:");
7666 gclog_or_tty->print("Sweep:put_free_blk 0x%x ("SIZE_FORMAT") "
7667 "[coalesced:"SIZE_FORMAT"]\n",
7668 freeFinger(), pointer_delta(_limit, freeFinger()),
7669 lastFreeRangeCoalesced());
7670 }
7671 }
7672 NOT_PRODUCT(
7673 if (Verbose && PrintGC) {
7674 gclog_or_tty->print("Collected "SIZE_FORMAT" objects, "
7675 SIZE_FORMAT " bytes",
7676 _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
7677 gclog_or_tty->print_cr("\nLive "SIZE_FORMAT" objects, "
7678 SIZE_FORMAT" bytes "
7679 "Already free "SIZE_FORMAT" objects, "SIZE_FORMAT" bytes",
7680 _numObjectsLive, _numWordsLive*sizeof(HeapWord),
7681 _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
7682 size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree) *
7683 sizeof(HeapWord);
7684 gclog_or_tty->print_cr("Total sweep: "SIZE_FORMAT" bytes", totalBytes);
7686 if (PrintCMSStatistics && CMSVerifyReturnedBytes) {
7687 size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
7688 size_t dictReturnedBytes = _sp->dictionary()->sumDictReturnedBytes();
7689 size_t returnedBytes = indexListReturnedBytes + dictReturnedBytes;
7690 gclog_or_tty->print("Returned "SIZE_FORMAT" bytes", returnedBytes);
7691 gclog_or_tty->print(" Indexed List Returned "SIZE_FORMAT" bytes",
7692 indexListReturnedBytes);
7693 gclog_or_tty->print_cr(" Dictionary Returned "SIZE_FORMAT" bytes",
7694 dictReturnedBytes);
7695 }
7696 }
7697 )
7698 // Now, in debug mode, just null out the sweep_limit
7699 NOT_PRODUCT(_sp->clear_sweep_limit();)
7700 if (CMSTraceSweeper) {
7701 gclog_or_tty->print("end of sweep\n================\n");
7702 }
7703 }
7705 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
7706 bool freeRangeInFreeLists) {
7707 if (CMSTraceSweeper) {
7708 gclog_or_tty->print("---- Start free range 0x%x with free block [%d] (%d)\n",
7709 freeFinger, _sp->block_size(freeFinger),
7710 freeRangeInFreeLists);
7711 }
7712 assert(!inFreeRange(), "Trampling existing free range");
7713 set_inFreeRange(true);
7714 set_lastFreeRangeCoalesced(false);
7716 set_freeFinger(freeFinger);
7717 set_freeRangeInFreeLists(freeRangeInFreeLists);
7718 if (CMSTestInFreeList) {
7719 if (freeRangeInFreeLists) {
7720 FreeChunk* fc = (FreeChunk*) freeFinger;
7721 assert(fc->isFree(), "A chunk on the free list should be free.");
7722 assert(fc->size() > 0, "Free range should have a size");
7723 assert(_sp->verifyChunkInFreeLists(fc), "Chunk is not in free lists");
7724 }
7725 }
7726 }
7728 // Note that the sweeper runs concurrently with mutators. Thus,
7729 // it is possible for direct allocation in this generation to happen
7730 // in the middle of the sweep. Note that the sweeper also coalesces
7731 // contiguous free blocks. Thus, unless the sweeper and the allocator
7732 // synchronize appropriately freshly allocated blocks may get swept up.
7733 // This is accomplished by the sweeper locking the free lists while
7734 // it is sweeping. Thus blocks that are determined to be free are
7735 // indeed free. There is however one additional complication:
7736 // blocks that have been allocated since the final checkpoint and
7737 // mark, will not have been marked and so would be treated as
7738 // unreachable and swept up. To prevent this, the allocator marks
7739 // the bit map when allocating during the sweep phase. This leads,
7740 // however, to a further complication -- objects may have been allocated
7741 // but not yet initialized -- in the sense that the header isn't yet
7742 // installed. The sweeper can not then determine the size of the block
7743 // in order to skip over it. To deal with this case, we use a technique
7744 // (due to Printezis) to encode such uninitialized block sizes in the
7745 // bit map. Since the bit map uses a bit per every HeapWord, but the
7746 // CMS generation has a minimum object size of 3 HeapWords, it follows
7747 // that "normal marks" won't be adjacent in the bit map (there will
7748 // always be at least two 0 bits between successive 1 bits). We make use
7749 // of these "unused" bits to represent uninitialized blocks -- the bit
7750 // corresponding to the start of the uninitialized object and the next
7751 // bit are both set. Finally, a 1 bit marks the end of the object that
7752 // started with the two consecutive 1 bits to indicate its potentially
7753 // uninitialized state.
7755 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
7756 FreeChunk* fc = (FreeChunk*)addr;
7757 size_t res;
7759 // check if we are done sweepinrg
7760 if (addr == _limit) { // we have swept up to the limit, do nothing more
7761 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7762 "sweep _limit out of bounds");
7763 // help the closure application finish
7764 return pointer_delta(_sp->end(), _limit);
7765 }
7766 assert(addr <= _limit, "sweep invariant");
7768 // check if we should yield
7769 do_yield_check(addr);
7770 if (fc->isFree()) {
7771 // Chunk that is already free
7772 res = fc->size();
7773 doAlreadyFreeChunk(fc);
7774 debug_only(_sp->verifyFreeLists());
7775 assert(res == fc->size(), "Don't expect the size to change");
7776 NOT_PRODUCT(
7777 _numObjectsAlreadyFree++;
7778 _numWordsAlreadyFree += res;
7779 )
7780 NOT_PRODUCT(_last_fc = fc;)
7781 } else if (!_bitMap->isMarked(addr)) {
7782 // Chunk is fresh garbage
7783 res = doGarbageChunk(fc);
7784 debug_only(_sp->verifyFreeLists());
7785 NOT_PRODUCT(
7786 _numObjectsFreed++;
7787 _numWordsFreed += res;
7788 )
7789 } else {
7790 // Chunk that is alive.
7791 res = doLiveChunk(fc);
7792 debug_only(_sp->verifyFreeLists());
7793 NOT_PRODUCT(
7794 _numObjectsLive++;
7795 _numWordsLive += res;
7796 )
7797 }
7798 return res;
7799 }
7801 // For the smart allocation, record following
7802 // split deaths - a free chunk is removed from its free list because
7803 // it is being split into two or more chunks.
7804 // split birth - a free chunk is being added to its free list because
7805 // a larger free chunk has been split and resulted in this free chunk.
7806 // coal death - a free chunk is being removed from its free list because
7807 // it is being coalesced into a large free chunk.
7808 // coal birth - a free chunk is being added to its free list because
7809 // it was created when two or more free chunks where coalesced into
7810 // this free chunk.
7811 //
7812 // These statistics are used to determine the desired number of free
7813 // chunks of a given size. The desired number is chosen to be relative
7814 // to the end of a CMS sweep. The desired number at the end of a sweep
7815 // is the
7816 // count-at-end-of-previous-sweep (an amount that was enough)
7817 // - count-at-beginning-of-current-sweep (the excess)
7818 // + split-births (gains in this size during interval)
7819 // - split-deaths (demands on this size during interval)
7820 // where the interval is from the end of one sweep to the end of the
7821 // next.
7822 //
7823 // When sweeping the sweeper maintains an accumulated chunk which is
7824 // the chunk that is made up of chunks that have been coalesced. That
7825 // will be termed the left-hand chunk. A new chunk of garbage that
7826 // is being considered for coalescing will be referred to as the
7827 // right-hand chunk.
7828 //
7829 // When making a decision on whether to coalesce a right-hand chunk with
7830 // the current left-hand chunk, the current count vs. the desired count
7831 // of the left-hand chunk is considered. Also if the right-hand chunk
7832 // is near the large chunk at the end of the heap (see
7833 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
7834 // left-hand chunk is coalesced.
7835 //
7836 // When making a decision about whether to split a chunk, the desired count
7837 // vs. the current count of the candidate to be split is also considered.
7838 // If the candidate is underpopulated (currently fewer chunks than desired)
7839 // a chunk of an overpopulated (currently more chunks than desired) size may
7840 // be chosen. The "hint" associated with a free list, if non-null, points
7841 // to a free list which may be overpopulated.
7842 //
7844 void SweepClosure::doAlreadyFreeChunk(FreeChunk* fc) {
7845 size_t size = fc->size();
7846 // Chunks that cannot be coalesced are not in the
7847 // free lists.
7848 if (CMSTestInFreeList && !fc->cantCoalesce()) {
7849 assert(_sp->verifyChunkInFreeLists(fc),
7850 "free chunk should be in free lists");
7851 }
7852 // a chunk that is already free, should not have been
7853 // marked in the bit map
7854 HeapWord* addr = (HeapWord*) fc;
7855 assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
7856 // Verify that the bit map has no bits marked between
7857 // addr and purported end of this block.
7858 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7860 // Some chunks cannot be coalesced in under any circumstances.
7861 // See the definition of cantCoalesce().
7862 if (!fc->cantCoalesce()) {
7863 // This chunk can potentially be coalesced.
7864 if (_sp->adaptive_freelists()) {
7865 // All the work is done in
7866 doPostIsFreeOrGarbageChunk(fc, size);
7867 } else { // Not adaptive free lists
7868 // this is a free chunk that can potentially be coalesced by the sweeper;
7869 if (!inFreeRange()) {
7870 // if the next chunk is a free block that can't be coalesced
7871 // it doesn't make sense to remove this chunk from the free lists
7872 FreeChunk* nextChunk = (FreeChunk*)(addr + size);
7873 assert((HeapWord*)nextChunk <= _limit, "sweep invariant");
7874 if ((HeapWord*)nextChunk < _limit && // there's a next chunk...
7875 nextChunk->isFree() && // which is free...
7876 nextChunk->cantCoalesce()) { // ... but cant be coalesced
7877 // nothing to do
7878 } else {
7879 // Potentially the start of a new free range:
7880 // Don't eagerly remove it from the free lists.
7881 // No need to remove it if it will just be put
7882 // back again. (Also from a pragmatic point of view
7883 // if it is a free block in a region that is beyond
7884 // any allocated blocks, an assertion will fail)
7885 // Remember the start of a free run.
7886 initialize_free_range(addr, true);
7887 // end - can coalesce with next chunk
7888 }
7889 } else {
7890 // the midst of a free range, we are coalescing
7891 debug_only(record_free_block_coalesced(fc);)
7892 if (CMSTraceSweeper) {
7893 gclog_or_tty->print(" -- pick up free block 0x%x (%d)\n", fc, size);
7894 }
7895 // remove it from the free lists
7896 _sp->removeFreeChunkFromFreeLists(fc);
7897 set_lastFreeRangeCoalesced(true);
7898 // If the chunk is being coalesced and the current free range is
7899 // in the free lists, remove the current free range so that it
7900 // will be returned to the free lists in its entirety - all
7901 // the coalesced pieces included.
7902 if (freeRangeInFreeLists()) {
7903 FreeChunk* ffc = (FreeChunk*) freeFinger();
7904 assert(ffc->size() == pointer_delta(addr, freeFinger()),
7905 "Size of free range is inconsistent with chunk size.");
7906 if (CMSTestInFreeList) {
7907 assert(_sp->verifyChunkInFreeLists(ffc),
7908 "free range is not in free lists");
7909 }
7910 _sp->removeFreeChunkFromFreeLists(ffc);
7911 set_freeRangeInFreeLists(false);
7912 }
7913 }
7914 }
7915 } else {
7916 // Code path common to both original and adaptive free lists.
7918 // cant coalesce with previous block; this should be treated
7919 // as the end of a free run if any
7920 if (inFreeRange()) {
7921 // we kicked some butt; time to pick up the garbage
7922 assert(freeFinger() < addr, "the finger pointeth off base");
7923 flushCurFreeChunk(freeFinger(), pointer_delta(addr, freeFinger()));
7924 }
7925 // else, nothing to do, just continue
7926 }
7927 }
7929 size_t SweepClosure::doGarbageChunk(FreeChunk* fc) {
7930 // This is a chunk of garbage. It is not in any free list.
7931 // Add it to a free list or let it possibly be coalesced into
7932 // a larger chunk.
7933 HeapWord* addr = (HeapWord*) fc;
7934 size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7936 if (_sp->adaptive_freelists()) {
7937 // Verify that the bit map has no bits marked between
7938 // addr and purported end of just dead object.
7939 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7941 doPostIsFreeOrGarbageChunk(fc, size);
7942 } else {
7943 if (!inFreeRange()) {
7944 // start of a new free range
7945 assert(size > 0, "A free range should have a size");
7946 initialize_free_range(addr, false);
7948 } else {
7949 // this will be swept up when we hit the end of the
7950 // free range
7951 if (CMSTraceSweeper) {
7952 gclog_or_tty->print(" -- pick up garbage 0x%x (%d) \n", fc, size);
7953 }
7954 // If the chunk is being coalesced and the current free range is
7955 // in the free lists, remove the current free range so that it
7956 // will be returned to the free lists in its entirety - all
7957 // the coalesced pieces included.
7958 if (freeRangeInFreeLists()) {
7959 FreeChunk* ffc = (FreeChunk*)freeFinger();
7960 assert(ffc->size() == pointer_delta(addr, freeFinger()),
7961 "Size of free range is inconsistent with chunk size.");
7962 if (CMSTestInFreeList) {
7963 assert(_sp->verifyChunkInFreeLists(ffc),
7964 "free range is not in free lists");
7965 }
7966 _sp->removeFreeChunkFromFreeLists(ffc);
7967 set_freeRangeInFreeLists(false);
7968 }
7969 set_lastFreeRangeCoalesced(true);
7970 }
7971 // this will be swept up when we hit the end of the free range
7973 // Verify that the bit map has no bits marked between
7974 // addr and purported end of just dead object.
7975 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7976 }
7977 return size;
7978 }
7980 size_t SweepClosure::doLiveChunk(FreeChunk* fc) {
7981 HeapWord* addr = (HeapWord*) fc;
7982 // The sweeper has just found a live object. Return any accumulated
7983 // left hand chunk to the free lists.
7984 if (inFreeRange()) {
7985 if (_sp->adaptive_freelists()) {
7986 flushCurFreeChunk(freeFinger(),
7987 pointer_delta(addr, freeFinger()));
7988 } else { // not adaptive freelists
7989 set_inFreeRange(false);
7990 // Add the free range back to the free list if it is not already
7991 // there.
7992 if (!freeRangeInFreeLists()) {
7993 assert(freeFinger() < addr, "the finger pointeth off base");
7994 if (CMSTraceSweeper) {
7995 gclog_or_tty->print("Sweep:put_free_blk 0x%x (%d) "
7996 "[coalesced:%d]\n",
7997 freeFinger(), pointer_delta(addr, freeFinger()),
7998 lastFreeRangeCoalesced());
7999 }
8000 _sp->addChunkAndRepairOffsetTable(freeFinger(),
8001 pointer_delta(addr, freeFinger()), lastFreeRangeCoalesced());
8002 }
8003 }
8004 }
8006 // Common code path for original and adaptive free lists.
8008 // this object is live: we'd normally expect this to be
8009 // an oop, and like to assert the following:
8010 // assert(oop(addr)->is_oop(), "live block should be an oop");
8011 // However, as we commented above, this may be an object whose
8012 // header hasn't yet been initialized.
8013 size_t size;
8014 assert(_bitMap->isMarked(addr), "Tautology for this control point");
8015 if (_bitMap->isMarked(addr + 1)) {
8016 // Determine the size from the bit map, rather than trying to
8017 // compute it from the object header.
8018 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
8019 size = pointer_delta(nextOneAddr + 1, addr);
8020 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
8021 "alignment problem");
8023 #ifdef DEBUG
8024 if (oop(addr)->klass() != NULL &&
8025 ( !_collector->should_unload_classes()
8026 || oop(addr)->is_parsable())) {
8027 // Ignore mark word because we are running concurrent with mutators
8028 assert(oop(addr)->is_oop(true), "live block should be an oop");
8029 assert(size ==
8030 CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
8031 "P-mark and computed size do not agree");
8032 }
8033 #endif
8035 } else {
8036 // This should be an initialized object that's alive.
8037 assert(oop(addr)->klass() != NULL &&
8038 (!_collector->should_unload_classes()
8039 || oop(addr)->is_parsable()),
8040 "Should be an initialized object");
8041 // Ignore mark word because we are running concurrent with mutators
8042 assert(oop(addr)->is_oop(true), "live block should be an oop");
8043 // Verify that the bit map has no bits marked between
8044 // addr and purported end of this block.
8045 size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
8046 assert(size >= 3, "Necessary for Printezis marks to work");
8047 assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
8048 DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
8049 }
8050 return size;
8051 }
8053 void SweepClosure::doPostIsFreeOrGarbageChunk(FreeChunk* fc,
8054 size_t chunkSize) {
8055 // doPostIsFreeOrGarbageChunk() should only be called in the smart allocation
8056 // scheme.
8057 bool fcInFreeLists = fc->isFree();
8058 assert(_sp->adaptive_freelists(), "Should only be used in this case.");
8059 assert((HeapWord*)fc <= _limit, "sweep invariant");
8060 if (CMSTestInFreeList && fcInFreeLists) {
8061 assert(_sp->verifyChunkInFreeLists(fc),
8062 "free chunk is not in free lists");
8063 }
8066 if (CMSTraceSweeper) {
8067 gclog_or_tty->print_cr(" -- pick up another chunk at 0x%x (%d)", fc, chunkSize);
8068 }
8070 HeapWord* addr = (HeapWord*) fc;
8072 bool coalesce;
8073 size_t left = pointer_delta(addr, freeFinger());
8074 size_t right = chunkSize;
8075 switch (FLSCoalescePolicy) {
8076 // numeric value forms a coalition aggressiveness metric
8077 case 0: { // never coalesce
8078 coalesce = false;
8079 break;
8080 }
8081 case 1: { // coalesce if left & right chunks on overpopulated lists
8082 coalesce = _sp->coalOverPopulated(left) &&
8083 _sp->coalOverPopulated(right);
8084 break;
8085 }
8086 case 2: { // coalesce if left chunk on overpopulated list (default)
8087 coalesce = _sp->coalOverPopulated(left);
8088 break;
8089 }
8090 case 3: { // coalesce if left OR right chunk on overpopulated list
8091 coalesce = _sp->coalOverPopulated(left) ||
8092 _sp->coalOverPopulated(right);
8093 break;
8094 }
8095 case 4: { // always coalesce
8096 coalesce = true;
8097 break;
8098 }
8099 default:
8100 ShouldNotReachHere();
8101 }
8103 // Should the current free range be coalesced?
8104 // If the chunk is in a free range and either we decided to coalesce above
8105 // or the chunk is near the large block at the end of the heap
8106 // (isNearLargestChunk() returns true), then coalesce this chunk.
8107 bool doCoalesce = inFreeRange() &&
8108 (coalesce || _g->isNearLargestChunk((HeapWord*)fc));
8109 if (doCoalesce) {
8110 // Coalesce the current free range on the left with the new
8111 // chunk on the right. If either is on a free list,
8112 // it must be removed from the list and stashed in the closure.
8113 if (freeRangeInFreeLists()) {
8114 FreeChunk* ffc = (FreeChunk*)freeFinger();
8115 assert(ffc->size() == pointer_delta(addr, freeFinger()),
8116 "Size of free range is inconsistent with chunk size.");
8117 if (CMSTestInFreeList) {
8118 assert(_sp->verifyChunkInFreeLists(ffc),
8119 "Chunk is not in free lists");
8120 }
8121 _sp->coalDeath(ffc->size());
8122 _sp->removeFreeChunkFromFreeLists(ffc);
8123 set_freeRangeInFreeLists(false);
8124 }
8125 if (fcInFreeLists) {
8126 _sp->coalDeath(chunkSize);
8127 assert(fc->size() == chunkSize,
8128 "The chunk has the wrong size or is not in the free lists");
8129 _sp->removeFreeChunkFromFreeLists(fc);
8130 }
8131 set_lastFreeRangeCoalesced(true);
8132 } else { // not in a free range and/or should not coalesce
8133 // Return the current free range and start a new one.
8134 if (inFreeRange()) {
8135 // In a free range but cannot coalesce with the right hand chunk.
8136 // Put the current free range into the free lists.
8137 flushCurFreeChunk(freeFinger(),
8138 pointer_delta(addr, freeFinger()));
8139 }
8140 // Set up for new free range. Pass along whether the right hand
8141 // chunk is in the free lists.
8142 initialize_free_range((HeapWord*)fc, fcInFreeLists);
8143 }
8144 }
8145 void SweepClosure::flushCurFreeChunk(HeapWord* chunk, size_t size) {
8146 assert(inFreeRange(), "Should only be called if currently in a free range.");
8147 assert(size > 0,
8148 "A zero sized chunk cannot be added to the free lists.");
8149 if (!freeRangeInFreeLists()) {
8150 if(CMSTestInFreeList) {
8151 FreeChunk* fc = (FreeChunk*) chunk;
8152 fc->setSize(size);
8153 assert(!_sp->verifyChunkInFreeLists(fc),
8154 "chunk should not be in free lists yet");
8155 }
8156 if (CMSTraceSweeper) {
8157 gclog_or_tty->print_cr(" -- add free block 0x%x (%d) to free lists",
8158 chunk, size);
8159 }
8160 // A new free range is going to be starting. The current
8161 // free range has not been added to the free lists yet or
8162 // was removed so add it back.
8163 // If the current free range was coalesced, then the death
8164 // of the free range was recorded. Record a birth now.
8165 if (lastFreeRangeCoalesced()) {
8166 _sp->coalBirth(size);
8167 }
8168 _sp->addChunkAndRepairOffsetTable(chunk, size,
8169 lastFreeRangeCoalesced());
8170 }
8171 set_inFreeRange(false);
8172 set_freeRangeInFreeLists(false);
8173 }
8175 // We take a break if we've been at this for a while,
8176 // so as to avoid monopolizing the locks involved.
8177 void SweepClosure::do_yield_work(HeapWord* addr) {
8178 // Return current free chunk being used for coalescing (if any)
8179 // to the appropriate freelist. After yielding, the next
8180 // free block encountered will start a coalescing range of
8181 // free blocks. If the next free block is adjacent to the
8182 // chunk just flushed, they will need to wait for the next
8183 // sweep to be coalesced.
8184 if (inFreeRange()) {
8185 flushCurFreeChunk(freeFinger(), pointer_delta(addr, freeFinger()));
8186 }
8188 // First give up the locks, then yield, then re-lock.
8189 // We should probably use a constructor/destructor idiom to
8190 // do this unlock/lock or modify the MutexUnlocker class to
8191 // serve our purpose. XXX
8192 assert_lock_strong(_bitMap->lock());
8193 assert_lock_strong(_freelistLock);
8194 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
8195 "CMS thread should hold CMS token");
8196 _bitMap->lock()->unlock();
8197 _freelistLock->unlock();
8198 ConcurrentMarkSweepThread::desynchronize(true);
8199 ConcurrentMarkSweepThread::acknowledge_yield_request();
8200 _collector->stopTimer();
8201 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
8202 if (PrintCMSStatistics != 0) {
8203 _collector->incrementYields();
8204 }
8205 _collector->icms_wait();
8207 // See the comment in coordinator_yield()
8208 for (unsigned i = 0; i < CMSYieldSleepCount &&
8209 ConcurrentMarkSweepThread::should_yield() &&
8210 !CMSCollector::foregroundGCIsActive(); ++i) {
8211 os::sleep(Thread::current(), 1, false);
8212 ConcurrentMarkSweepThread::acknowledge_yield_request();
8213 }
8215 ConcurrentMarkSweepThread::synchronize(true);
8216 _freelistLock->lock();
8217 _bitMap->lock()->lock_without_safepoint_check();
8218 _collector->startTimer();
8219 }
8221 #ifndef PRODUCT
8222 // This is actually very useful in a product build if it can
8223 // be called from the debugger. Compile it into the product
8224 // as needed.
8225 bool debug_verifyChunkInFreeLists(FreeChunk* fc) {
8226 return debug_cms_space->verifyChunkInFreeLists(fc);
8227 }
8229 void SweepClosure::record_free_block_coalesced(FreeChunk* fc) const {
8230 if (CMSTraceSweeper) {
8231 gclog_or_tty->print("Sweep:coal_free_blk 0x%x (%d)\n", fc, fc->size());
8232 }
8233 }
8234 #endif
8236 // CMSIsAliveClosure
8237 bool CMSIsAliveClosure::do_object_b(oop obj) {
8238 HeapWord* addr = (HeapWord*)obj;
8239 return addr != NULL &&
8240 (!_span.contains(addr) || _bit_map->isMarked(addr));
8241 }
8243 // CMSKeepAliveClosure: the serial version
8244 void CMSKeepAliveClosure::do_oop(oop obj) {
8245 HeapWord* addr = (HeapWord*)obj;
8246 if (_span.contains(addr) &&
8247 !_bit_map->isMarked(addr)) {
8248 _bit_map->mark(addr);
8249 bool simulate_overflow = false;
8250 NOT_PRODUCT(
8251 if (CMSMarkStackOverflowALot &&
8252 _collector->simulate_overflow()) {
8253 // simulate a stack overflow
8254 simulate_overflow = true;
8255 }
8256 )
8257 if (simulate_overflow || !_mark_stack->push(obj)) {
8258 _collector->push_on_overflow_list(obj);
8259 _collector->_ser_kac_ovflw++;
8260 }
8261 }
8262 }
8264 void CMSKeepAliveClosure::do_oop(oop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8265 void CMSKeepAliveClosure::do_oop(narrowOop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8267 // CMSParKeepAliveClosure: a parallel version of the above.
8268 // The work queues are private to each closure (thread),
8269 // but (may be) available for stealing by other threads.
8270 void CMSParKeepAliveClosure::do_oop(oop obj) {
8271 HeapWord* addr = (HeapWord*)obj;
8272 if (_span.contains(addr) &&
8273 !_bit_map->isMarked(addr)) {
8274 // In general, during recursive tracing, several threads
8275 // may be concurrently getting here; the first one to
8276 // "tag" it, claims it.
8277 if (_bit_map->par_mark(addr)) {
8278 bool res = _work_queue->push(obj);
8279 assert(res, "Low water mark should be much less than capacity");
8280 // Do a recursive trim in the hope that this will keep
8281 // stack usage lower, but leave some oops for potential stealers
8282 trim_queue(_low_water_mark);
8283 } // Else, another thread got there first
8284 }
8285 }
8287 void CMSParKeepAliveClosure::do_oop(oop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8288 void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8290 void CMSParKeepAliveClosure::trim_queue(uint max) {
8291 while (_work_queue->size() > max) {
8292 oop new_oop;
8293 if (_work_queue->pop_local(new_oop)) {
8294 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
8295 assert(_bit_map->isMarked((HeapWord*)new_oop),
8296 "no white objects on this stack!");
8297 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8298 // iterate over the oops in this oop, marking and pushing
8299 // the ones in CMS heap (i.e. in _span).
8300 new_oop->oop_iterate(&_mark_and_push);
8301 }
8302 }
8303 }
8305 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
8306 HeapWord* addr = (HeapWord*)obj;
8307 if (_span.contains(addr) &&
8308 !_bit_map->isMarked(addr)) {
8309 if (_bit_map->par_mark(addr)) {
8310 bool simulate_overflow = false;
8311 NOT_PRODUCT(
8312 if (CMSMarkStackOverflowALot &&
8313 _collector->par_simulate_overflow()) {
8314 // simulate a stack overflow
8315 simulate_overflow = true;
8316 }
8317 )
8318 if (simulate_overflow || !_work_queue->push(obj)) {
8319 _collector->par_push_on_overflow_list(obj);
8320 _collector->_par_kac_ovflw++;
8321 }
8322 } // Else another thread got there already
8323 }
8324 }
8326 void CMSInnerParMarkAndPushClosure::do_oop(oop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8327 void CMSInnerParMarkAndPushClosure::do_oop(narrowOop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8329 //////////////////////////////////////////////////////////////////
8330 // CMSExpansionCause /////////////////////////////
8331 //////////////////////////////////////////////////////////////////
8332 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
8333 switch (cause) {
8334 case _no_expansion:
8335 return "No expansion";
8336 case _satisfy_free_ratio:
8337 return "Free ratio";
8338 case _satisfy_promotion:
8339 return "Satisfy promotion";
8340 case _satisfy_allocation:
8341 return "allocation";
8342 case _allocate_par_lab:
8343 return "Par LAB";
8344 case _allocate_par_spooling_space:
8345 return "Par Spooling Space";
8346 case _adaptive_size_policy:
8347 return "Ergonomics";
8348 default:
8349 return "unknown";
8350 }
8351 }
8353 void CMSDrainMarkingStackClosure::do_void() {
8354 // the max number to take from overflow list at a time
8355 const size_t num = _mark_stack->capacity()/4;
8356 while (!_mark_stack->isEmpty() ||
8357 // if stack is empty, check the overflow list
8358 _collector->take_from_overflow_list(num, _mark_stack)) {
8359 oop obj = _mark_stack->pop();
8360 HeapWord* addr = (HeapWord*)obj;
8361 assert(_span.contains(addr), "Should be within span");
8362 assert(_bit_map->isMarked(addr), "Should be marked");
8363 assert(obj->is_oop(), "Should be an oop");
8364 obj->oop_iterate(_keep_alive);
8365 }
8366 }
8368 void CMSParDrainMarkingStackClosure::do_void() {
8369 // drain queue
8370 trim_queue(0);
8371 }
8373 // Trim our work_queue so its length is below max at return
8374 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
8375 while (_work_queue->size() > max) {
8376 oop new_oop;
8377 if (_work_queue->pop_local(new_oop)) {
8378 assert(new_oop->is_oop(), "Expected an oop");
8379 assert(_bit_map->isMarked((HeapWord*)new_oop),
8380 "no white objects on this stack!");
8381 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8382 // iterate over the oops in this oop, marking and pushing
8383 // the ones in CMS heap (i.e. in _span).
8384 new_oop->oop_iterate(&_mark_and_push);
8385 }
8386 }
8387 }
8389 ////////////////////////////////////////////////////////////////////
8390 // Support for Marking Stack Overflow list handling and related code
8391 ////////////////////////////////////////////////////////////////////
8392 // Much of the following code is similar in shape and spirit to the
8393 // code used in ParNewGC. We should try and share that code
8394 // as much as possible in the future.
8396 #ifndef PRODUCT
8397 // Debugging support for CMSStackOverflowALot
8399 // It's OK to call this multi-threaded; the worst thing
8400 // that can happen is that we'll get a bunch of closely
8401 // spaced simulated oveflows, but that's OK, in fact
8402 // probably good as it would exercise the overflow code
8403 // under contention.
8404 bool CMSCollector::simulate_overflow() {
8405 if (_overflow_counter-- <= 0) { // just being defensive
8406 _overflow_counter = CMSMarkStackOverflowInterval;
8407 return true;
8408 } else {
8409 return false;
8410 }
8411 }
8413 bool CMSCollector::par_simulate_overflow() {
8414 return simulate_overflow();
8415 }
8416 #endif
8418 // Single-threaded
8419 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
8420 assert(stack->isEmpty(), "Expected precondition");
8421 assert(stack->capacity() > num, "Shouldn't bite more than can chew");
8422 size_t i = num;
8423 oop cur = _overflow_list;
8424 const markOop proto = markOopDesc::prototype();
8425 NOT_PRODUCT(size_t n = 0;)
8426 for (oop next; i > 0 && cur != NULL; cur = next, i--) {
8427 next = oop(cur->mark());
8428 cur->set_mark(proto); // until proven otherwise
8429 assert(cur->is_oop(), "Should be an oop");
8430 bool res = stack->push(cur);
8431 assert(res, "Bit off more than can chew?");
8432 NOT_PRODUCT(n++;)
8433 }
8434 _overflow_list = cur;
8435 #ifndef PRODUCT
8436 assert(_num_par_pushes >= n, "Too many pops?");
8437 _num_par_pushes -=n;
8438 #endif
8439 return !stack->isEmpty();
8440 }
8442 // Multi-threaded; use CAS to break off a prefix
8443 bool CMSCollector::par_take_from_overflow_list(size_t num,
8444 OopTaskQueue* work_q) {
8445 assert(work_q->size() == 0, "That's the current policy");
8446 assert(num < work_q->max_elems(), "Can't bite more than we can chew");
8447 if (_overflow_list == NULL) {
8448 return false;
8449 }
8450 // Grab the entire list; we'll put back a suffix
8451 oop prefix = (oop)Atomic::xchg_ptr(NULL, &_overflow_list);
8452 if (prefix == NULL) { // someone grabbed it before we did ...
8453 // ... we could spin for a short while, but for now we don't
8454 return false;
8455 }
8456 size_t i = num;
8457 oop cur = prefix;
8458 for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--);
8459 if (cur->mark() != NULL) {
8460 oop suffix_head = cur->mark(); // suffix will be put back on global list
8461 cur->set_mark(NULL); // break off suffix
8462 // Find tail of suffix so we can prepend suffix to global list
8463 for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark()));
8464 oop suffix_tail = cur;
8465 assert(suffix_tail != NULL && suffix_tail->mark() == NULL,
8466 "Tautology");
8467 oop observed_overflow_list = _overflow_list;
8468 do {
8469 cur = observed_overflow_list;
8470 suffix_tail->set_mark(markOop(cur));
8471 observed_overflow_list =
8472 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur);
8473 } while (cur != observed_overflow_list);
8474 }
8476 // Push the prefix elements on work_q
8477 assert(prefix != NULL, "control point invariant");
8478 const markOop proto = markOopDesc::prototype();
8479 oop next;
8480 NOT_PRODUCT(size_t n = 0;)
8481 for (cur = prefix; cur != NULL; cur = next) {
8482 next = oop(cur->mark());
8483 cur->set_mark(proto); // until proven otherwise
8484 assert(cur->is_oop(), "Should be an oop");
8485 bool res = work_q->push(cur);
8486 assert(res, "Bit off more than we can chew?");
8487 NOT_PRODUCT(n++;)
8488 }
8489 #ifndef PRODUCT
8490 assert(_num_par_pushes >= n, "Too many pops?");
8491 Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
8492 #endif
8493 return true;
8494 }
8496 // Single-threaded
8497 void CMSCollector::push_on_overflow_list(oop p) {
8498 NOT_PRODUCT(_num_par_pushes++;)
8499 assert(p->is_oop(), "Not an oop");
8500 preserve_mark_if_necessary(p);
8501 p->set_mark((markOop)_overflow_list);
8502 _overflow_list = p;
8503 }
8505 // Multi-threaded; use CAS to prepend to overflow list
8506 void CMSCollector::par_push_on_overflow_list(oop p) {
8507 NOT_PRODUCT(Atomic::inc_ptr(&_num_par_pushes);)
8508 assert(p->is_oop(), "Not an oop");
8509 par_preserve_mark_if_necessary(p);
8510 oop observed_overflow_list = _overflow_list;
8511 oop cur_overflow_list;
8512 do {
8513 cur_overflow_list = observed_overflow_list;
8514 p->set_mark(markOop(cur_overflow_list));
8515 observed_overflow_list =
8516 (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list);
8517 } while (cur_overflow_list != observed_overflow_list);
8518 }
8520 // Single threaded
8521 // General Note on GrowableArray: pushes may silently fail
8522 // because we are (temporarily) out of C-heap for expanding
8523 // the stack. The problem is quite ubiquitous and affects
8524 // a lot of code in the JVM. The prudent thing for GrowableArray
8525 // to do (for now) is to exit with an error. However, that may
8526 // be too draconian in some cases because the caller may be
8527 // able to recover without much harm. For suych cases, we
8528 // should probably introduce a "soft_push" method which returns
8529 // an indication of success or failure with the assumption that
8530 // the caller may be able to recover from a failure; code in
8531 // the VM can then be changed, incrementally, to deal with such
8532 // failures where possible, thus, incrementally hardening the VM
8533 // in such low resource situations.
8534 void CMSCollector::preserve_mark_work(oop p, markOop m) {
8535 int PreserveMarkStackSize = 128;
8537 if (_preserved_oop_stack == NULL) {
8538 assert(_preserved_mark_stack == NULL,
8539 "bijection with preserved_oop_stack");
8540 // Allocate the stacks
8541 _preserved_oop_stack = new (ResourceObj::C_HEAP)
8542 GrowableArray<oop>(PreserveMarkStackSize, true);
8543 _preserved_mark_stack = new (ResourceObj::C_HEAP)
8544 GrowableArray<markOop>(PreserveMarkStackSize, true);
8545 if (_preserved_oop_stack == NULL || _preserved_mark_stack == NULL) {
8546 vm_exit_out_of_memory(2* PreserveMarkStackSize * sizeof(oop) /* punt */,
8547 "Preserved Mark/Oop Stack for CMS (C-heap)");
8548 }
8549 }
8550 _preserved_oop_stack->push(p);
8551 _preserved_mark_stack->push(m);
8552 assert(m == p->mark(), "Mark word changed");
8553 assert(_preserved_oop_stack->length() == _preserved_mark_stack->length(),
8554 "bijection");
8555 }
8557 // Single threaded
8558 void CMSCollector::preserve_mark_if_necessary(oop p) {
8559 markOop m = p->mark();
8560 if (m->must_be_preserved(p)) {
8561 preserve_mark_work(p, m);
8562 }
8563 }
8565 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
8566 markOop m = p->mark();
8567 if (m->must_be_preserved(p)) {
8568 MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
8569 // Even though we read the mark word without holding
8570 // the lock, we are assured that it will not change
8571 // because we "own" this oop, so no other thread can
8572 // be trying to push it on the overflow list; see
8573 // the assertion in preserve_mark_work() that checks
8574 // that m == p->mark().
8575 preserve_mark_work(p, m);
8576 }
8577 }
8579 // We should be able to do this multi-threaded,
8580 // a chunk of stack being a task (this is
8581 // correct because each oop only ever appears
8582 // once in the overflow list. However, it's
8583 // not very easy to completely overlap this with
8584 // other operations, so will generally not be done
8585 // until all work's been completed. Because we
8586 // expect the preserved oop stack (set) to be small,
8587 // it's probably fine to do this single-threaded.
8588 // We can explore cleverer concurrent/overlapped/parallel
8589 // processing of preserved marks if we feel the
8590 // need for this in the future. Stack overflow should
8591 // be so rare in practice and, when it happens, its
8592 // effect on performance so great that this will
8593 // likely just be in the noise anyway.
8594 void CMSCollector::restore_preserved_marks_if_any() {
8595 if (_preserved_oop_stack == NULL) {
8596 assert(_preserved_mark_stack == NULL,
8597 "bijection with preserved_oop_stack");
8598 return;
8599 }
8601 assert(SafepointSynchronize::is_at_safepoint(),
8602 "world should be stopped");
8603 assert(Thread::current()->is_ConcurrentGC_thread() ||
8604 Thread::current()->is_VM_thread(),
8605 "should be single-threaded");
8607 int length = _preserved_oop_stack->length();
8608 assert(_preserved_mark_stack->length() == length, "bijection");
8609 for (int i = 0; i < length; i++) {
8610 oop p = _preserved_oop_stack->at(i);
8611 assert(p->is_oop(), "Should be an oop");
8612 assert(_span.contains(p), "oop should be in _span");
8613 assert(p->mark() == markOopDesc::prototype(),
8614 "Set when taken from overflow list");
8615 markOop m = _preserved_mark_stack->at(i);
8616 p->set_mark(m);
8617 }
8618 _preserved_mark_stack->clear();
8619 _preserved_oop_stack->clear();
8620 assert(_preserved_mark_stack->is_empty() &&
8621 _preserved_oop_stack->is_empty(),
8622 "stacks were cleared above");
8623 }
8625 #ifndef PRODUCT
8626 bool CMSCollector::no_preserved_marks() const {
8627 return ( ( _preserved_mark_stack == NULL
8628 && _preserved_oop_stack == NULL)
8629 || ( _preserved_mark_stack->is_empty()
8630 && _preserved_oop_stack->is_empty()));
8631 }
8632 #endif
8634 CMSAdaptiveSizePolicy* ASConcurrentMarkSweepGeneration::cms_size_policy() const
8635 {
8636 GenCollectedHeap* gch = (GenCollectedHeap*) GenCollectedHeap::heap();
8637 CMSAdaptiveSizePolicy* size_policy =
8638 (CMSAdaptiveSizePolicy*) gch->gen_policy()->size_policy();
8639 assert(size_policy->is_gc_cms_adaptive_size_policy(),
8640 "Wrong type for size policy");
8641 return size_policy;
8642 }
8644 void ASConcurrentMarkSweepGeneration::resize(size_t cur_promo_size,
8645 size_t desired_promo_size) {
8646 if (cur_promo_size < desired_promo_size) {
8647 size_t expand_bytes = desired_promo_size - cur_promo_size;
8648 if (PrintAdaptiveSizePolicy && Verbose) {
8649 gclog_or_tty->print_cr(" ASConcurrentMarkSweepGeneration::resize "
8650 "Expanding tenured generation by " SIZE_FORMAT " (bytes)",
8651 expand_bytes);
8652 }
8653 expand(expand_bytes,
8654 MinHeapDeltaBytes,
8655 CMSExpansionCause::_adaptive_size_policy);
8656 } else if (desired_promo_size < cur_promo_size) {
8657 size_t shrink_bytes = cur_promo_size - desired_promo_size;
8658 if (PrintAdaptiveSizePolicy && Verbose) {
8659 gclog_or_tty->print_cr(" ASConcurrentMarkSweepGeneration::resize "
8660 "Shrinking tenured generation by " SIZE_FORMAT " (bytes)",
8661 shrink_bytes);
8662 }
8663 shrink(shrink_bytes);
8664 }
8665 }
8667 CMSGCAdaptivePolicyCounters* ASConcurrentMarkSweepGeneration::gc_adaptive_policy_counters() {
8668 GenCollectedHeap* gch = GenCollectedHeap::heap();
8669 CMSGCAdaptivePolicyCounters* counters =
8670 (CMSGCAdaptivePolicyCounters*) gch->collector_policy()->counters();
8671 assert(counters->kind() == GCPolicyCounters::CMSGCAdaptivePolicyCountersKind,
8672 "Wrong kind of counters");
8673 return counters;
8674 }
8677 void ASConcurrentMarkSweepGeneration::update_counters() {
8678 if (UsePerfData) {
8679 _space_counters->update_all();
8680 _gen_counters->update_all();
8681 CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
8682 GenCollectedHeap* gch = GenCollectedHeap::heap();
8683 CMSGCStats* gc_stats_l = (CMSGCStats*) gc_stats();
8684 assert(gc_stats_l->kind() == GCStats::CMSGCStatsKind,
8685 "Wrong gc statistics type");
8686 counters->update_counters(gc_stats_l);
8687 }
8688 }
8690 void ASConcurrentMarkSweepGeneration::update_counters(size_t used) {
8691 if (UsePerfData) {
8692 _space_counters->update_used(used);
8693 _space_counters->update_capacity();
8694 _gen_counters->update_all();
8696 CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
8697 GenCollectedHeap* gch = GenCollectedHeap::heap();
8698 CMSGCStats* gc_stats_l = (CMSGCStats*) gc_stats();
8699 assert(gc_stats_l->kind() == GCStats::CMSGCStatsKind,
8700 "Wrong gc statistics type");
8701 counters->update_counters(gc_stats_l);
8702 }
8703 }
8705 // The desired expansion delta is computed so that:
8706 // . desired free percentage or greater is used
8707 void ASConcurrentMarkSweepGeneration::compute_new_size() {
8708 assert_locked_or_safepoint(Heap_lock);
8710 GenCollectedHeap* gch = (GenCollectedHeap*) GenCollectedHeap::heap();
8712 // If incremental collection failed, we just want to expand
8713 // to the limit.
8714 if (incremental_collection_failed()) {
8715 clear_incremental_collection_failed();
8716 grow_to_reserved();
8717 return;
8718 }
8720 assert(UseAdaptiveSizePolicy, "Should be using adaptive sizing");
8722 assert(gch->kind() == CollectedHeap::GenCollectedHeap,
8723 "Wrong type of heap");
8724 int prev_level = level() - 1;
8725 assert(prev_level >= 0, "The cms generation is the lowest generation");
8726 Generation* prev_gen = gch->get_gen(prev_level);
8727 assert(prev_gen->kind() == Generation::ASParNew,
8728 "Wrong type of young generation");
8729 ParNewGeneration* younger_gen = (ParNewGeneration*) prev_gen;
8730 size_t cur_eden = younger_gen->eden()->capacity();
8731 CMSAdaptiveSizePolicy* size_policy = cms_size_policy();
8732 size_t cur_promo = free();
8733 size_policy->compute_tenured_generation_free_space(cur_promo,
8734 max_available(),
8735 cur_eden);
8736 resize(cur_promo, size_policy->promo_size());
8738 // Record the new size of the space in the cms generation
8739 // that is available for promotions. This is temporary.
8740 // It should be the desired promo size.
8741 size_policy->avg_cms_promo()->sample(free());
8742 size_policy->avg_old_live()->sample(used());
8744 if (UsePerfData) {
8745 CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
8746 counters->update_cms_capacity_counter(capacity());
8747 }
8748 }
8750 void ASConcurrentMarkSweepGeneration::shrink_by(size_t desired_bytes) {
8751 assert_locked_or_safepoint(Heap_lock);
8752 assert_lock_strong(freelistLock());
8753 HeapWord* old_end = _cmsSpace->end();
8754 HeapWord* unallocated_start = _cmsSpace->unallocated_block();
8755 assert(old_end >= unallocated_start, "Miscalculation of unallocated_start");
8756 FreeChunk* chunk_at_end = find_chunk_at_end();
8757 if (chunk_at_end == NULL) {
8758 // No room to shrink
8759 if (PrintGCDetails && Verbose) {
8760 gclog_or_tty->print_cr("No room to shrink: old_end "
8761 PTR_FORMAT " unallocated_start " PTR_FORMAT
8762 " chunk_at_end " PTR_FORMAT,
8763 old_end, unallocated_start, chunk_at_end);
8764 }
8765 return;
8766 } else {
8768 // Find the chunk at the end of the space and determine
8769 // how much it can be shrunk.
8770 size_t shrinkable_size_in_bytes = chunk_at_end->size();
8771 size_t aligned_shrinkable_size_in_bytes =
8772 align_size_down(shrinkable_size_in_bytes, os::vm_page_size());
8773 assert(unallocated_start <= chunk_at_end->end(),
8774 "Inconsistent chunk at end of space");
8775 size_t bytes = MIN2(desired_bytes, aligned_shrinkable_size_in_bytes);
8776 size_t word_size_before = heap_word_size(_virtual_space.committed_size());
8778 // Shrink the underlying space
8779 _virtual_space.shrink_by(bytes);
8780 if (PrintGCDetails && Verbose) {
8781 gclog_or_tty->print_cr("ConcurrentMarkSweepGeneration::shrink_by:"
8782 " desired_bytes " SIZE_FORMAT
8783 " shrinkable_size_in_bytes " SIZE_FORMAT
8784 " aligned_shrinkable_size_in_bytes " SIZE_FORMAT
8785 " bytes " SIZE_FORMAT,
8786 desired_bytes, shrinkable_size_in_bytes,
8787 aligned_shrinkable_size_in_bytes, bytes);
8788 gclog_or_tty->print_cr(" old_end " SIZE_FORMAT
8789 " unallocated_start " SIZE_FORMAT,
8790 old_end, unallocated_start);
8791 }
8793 // If the space did shrink (shrinking is not guaranteed),
8794 // shrink the chunk at the end by the appropriate amount.
8795 if (((HeapWord*)_virtual_space.high()) < old_end) {
8796 size_t new_word_size =
8797 heap_word_size(_virtual_space.committed_size());
8799 // Have to remove the chunk from the dictionary because it is changing
8800 // size and might be someplace elsewhere in the dictionary.
8802 // Get the chunk at end, shrink it, and put it
8803 // back.
8804 _cmsSpace->removeChunkFromDictionary(chunk_at_end);
8805 size_t word_size_change = word_size_before - new_word_size;
8806 size_t chunk_at_end_old_size = chunk_at_end->size();
8807 assert(chunk_at_end_old_size >= word_size_change,
8808 "Shrink is too large");
8809 chunk_at_end->setSize(chunk_at_end_old_size -
8810 word_size_change);
8811 _cmsSpace->freed((HeapWord*) chunk_at_end->end(),
8812 word_size_change);
8814 _cmsSpace->returnChunkToDictionary(chunk_at_end);
8816 MemRegion mr(_cmsSpace->bottom(), new_word_size);
8817 _bts->resize(new_word_size); // resize the block offset shared array
8818 Universe::heap()->barrier_set()->resize_covered_region(mr);
8819 _cmsSpace->assert_locked();
8820 _cmsSpace->set_end((HeapWord*)_virtual_space.high());
8822 NOT_PRODUCT(_cmsSpace->dictionary()->verify());
8824 // update the space and generation capacity counters
8825 if (UsePerfData) {
8826 _space_counters->update_capacity();
8827 _gen_counters->update_all();
8828 }
8830 if (Verbose && PrintGCDetails) {
8831 size_t new_mem_size = _virtual_space.committed_size();
8832 size_t old_mem_size = new_mem_size + bytes;
8833 gclog_or_tty->print_cr("Shrinking %s from %ldK by %ldK to %ldK",
8834 name(), old_mem_size/K, bytes/K, new_mem_size/K);
8835 }
8836 }
8838 assert(_cmsSpace->unallocated_block() <= _cmsSpace->end(),
8839 "Inconsistency at end of space");
8840 assert(chunk_at_end->end() == _cmsSpace->end(),
8841 "Shrinking is inconsistent");
8842 return;
8843 }
8844 }
8846 // Transfer some number of overflown objects to usual marking
8847 // stack. Return true if some objects were transferred.
8848 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
8849 size_t num = MIN2((size_t)_mark_stack->capacity()/4,
8850 (size_t)ParGCDesiredObjsFromOverflowList);
8852 bool res = _collector->take_from_overflow_list(num, _mark_stack);
8853 assert(_collector->overflow_list_is_empty() || res,
8854 "If list is not empty, we should have taken something");
8855 assert(!res || !_mark_stack->isEmpty(),
8856 "If we took something, it should now be on our stack");
8857 return res;
8858 }
8860 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
8861 size_t res = _sp->block_size_no_stall(addr, _collector);
8862 assert(res != 0, "Should always be able to compute a size");
8863 if (_sp->block_is_obj(addr)) {
8864 if (_live_bit_map->isMarked(addr)) {
8865 // It can't have been dead in a previous cycle
8866 guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
8867 } else {
8868 _dead_bit_map->mark(addr); // mark the dead object
8869 }
8870 }
8871 return res;
8872 }