1 /*
2 * Copyright (c) 2001, 2010, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
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23 */
24
25 # include "incls/_precompiled.incl"
26 # include "incls/_concurrentMarkSweepGeneration.cpp.incl"
27
28 // statics
29 CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL;
30 bool CMSCollector::_full_gc_requested = false;
31
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
89
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 }
100
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 };
109
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 };
126
127
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 };
137
138 //////////////////////////////////////////////////////////////////
139 // Concurrent Mark-Sweep Generation /////////////////////////////
140 //////////////////////////////////////////////////////////////////
141
142 NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;)
143
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;
150
151 // Constructor.
152 CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) {
153 promo.setSpace(cfls);
154 }
155 };
156
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)(CollectedHeap::min_fill_size()))),
163 _debug_collection_type(Concurrent_collection_type)
164 {
165 HeapWord* bottom = (HeapWord*) _virtual_space.low();
166 HeapWord* end = (HeapWord*) _virtual_space.high();
167
168 _direct_allocated_words = 0;
169 NOT_PRODUCT(
170 _numObjectsPromoted = 0;
171 _numWordsPromoted = 0;
172 _numObjectsAllocated = 0;
173 _numWordsAllocated = 0;
174 )
175
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;
185
186 _gc_stats = new CMSGCStats();
187
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(UseCompressedOops ||
194 junk->prev_addr() == (void*)(oop(junk)->klass_addr()),
195 "Offset of FreeChunk::_prev within FreeChunk must match"
196 " that of OopDesc::_klass within OopDesc");
197 )
198 if (CollectedHeap::use_parallel_gc_threads()) {
199 typedef CMSParGCThreadState* CMSParGCThreadStatePtr;
200 _par_gc_thread_states =
201 NEW_C_HEAP_ARRAY(CMSParGCThreadStatePtr, ParallelGCThreads);
202 if (_par_gc_thread_states == NULL) {
203 vm_exit_during_initialization("Could not allocate par gc structs");
204 }
205 for (uint i = 0; i < ParallelGCThreads; i++) {
206 _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace());
207 if (_par_gc_thread_states[i] == NULL) {
208 vm_exit_during_initialization("Could not allocate par gc structs");
209 }
210 }
211 } else {
212 _par_gc_thread_states = NULL;
213 }
214 _incremental_collection_failed = false;
215 // The "dilatation_factor" is the expansion that can occur on
216 // account of the fact that the minimum object size in the CMS
217 // generation may be larger than that in, say, a contiguous young
218 // generation.
219 // Ideally, in the calculation below, we'd compute the dilatation
220 // factor as: MinChunkSize/(promoting_gen's min object size)
221 // Since we do not have such a general query interface for the
222 // promoting generation, we'll instead just use the mimimum
223 // object size (which today is a header's worth of space);
224 // note that all arithmetic is in units of HeapWords.
225 assert(MinChunkSize >= CollectedHeap::min_fill_size(), "just checking");
226 assert(_dilatation_factor >= 1.0, "from previous assert");
227 }
228
229
230 // The field "_initiating_occupancy" represents the occupancy percentage
231 // at which we trigger a new collection cycle. Unless explicitly specified
232 // via CMSInitiating[Perm]OccupancyFraction (argument "io" below), it
233 // is calculated by:
234 //
235 // Let "f" be MinHeapFreeRatio in
236 //
237 // _intiating_occupancy = 100-f +
238 // f * (CMSTrigger[Perm]Ratio/100)
239 // where CMSTrigger[Perm]Ratio is the argument "tr" below.
240 //
241 // That is, if we assume the heap is at its desired maximum occupancy at the
242 // end of a collection, we let CMSTrigger[Perm]Ratio of the (purported) free
243 // space be allocated before initiating a new collection cycle.
244 //
245 void ConcurrentMarkSweepGeneration::init_initiating_occupancy(intx io, intx tr) {
246 assert(io <= 100 && tr >= 0 && tr <= 100, "Check the arguments");
247 if (io >= 0) {
248 _initiating_occupancy = (double)io / 100.0;
249 } else {
250 _initiating_occupancy = ((100 - MinHeapFreeRatio) +
251 (double)(tr * MinHeapFreeRatio) / 100.0)
252 / 100.0;
253 }
254 }
255
256 void ConcurrentMarkSweepGeneration::ref_processor_init() {
257 assert(collector() != NULL, "no collector");
258 collector()->ref_processor_init();
259 }
260
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);
273
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 }
282
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 }
293
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 }
302
303
304 void ConcurrentMarkSweepGeneration::initialize_performance_counters() {
305
306 const char* gen_name = "old";
307
308 // Generation Counters - generation 1, 1 subspace
309 _gen_counters = new GenerationCounters(gen_name, 1, 1, &_virtual_space);
310
311 _space_counters = new GSpaceCounters(gen_name, 0,
312 _virtual_space.reserved_size(),
313 this, _gen_counters);
314 }
315
316 CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha):
317 _cms_gen(cms_gen)
318 {
319 assert(alpha <= 100, "bad value");
320 _saved_alpha = alpha;
321
322 // Initialize the alphas to the bootstrap value of 100.
323 _gc0_alpha = _cms_alpha = 100;
324
325 _cms_begin_time.update();
326 _cms_end_time.update();
327
328 _gc0_duration = 0.0;
329 _gc0_period = 0.0;
330 _gc0_promoted = 0;
331
332 _cms_duration = 0.0;
333 _cms_period = 0.0;
334 _cms_allocated = 0;
335
336 _cms_used_at_gc0_begin = 0;
337 _cms_used_at_gc0_end = 0;
338 _allow_duty_cycle_reduction = false;
339 _valid_bits = 0;
340 _icms_duty_cycle = CMSIncrementalDutyCycle;
341 }
342
343 double CMSStats::cms_free_adjustment_factor(size_t free) const {
344 // TBD: CR 6909490
345 return 1.0;
346 }
347
348 void CMSStats::adjust_cms_free_adjustment_factor(bool fail, size_t free) {
349 }
350
351 // If promotion failure handling is on use
352 // the padded average size of the promotion for each
353 // young generation collection.
354 double CMSStats::time_until_cms_gen_full() const {
355 size_t cms_free = _cms_gen->cmsSpace()->free();
356 GenCollectedHeap* gch = GenCollectedHeap::heap();
357 size_t expected_promotion = gch->get_gen(0)->capacity();
358 if (HandlePromotionFailure) {
359 expected_promotion = MIN2(
360 (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average(),
361 expected_promotion);
362 }
363 if (cms_free > expected_promotion) {
364 // Start a cms collection if there isn't enough space to promote
365 // for the next minor collection. Use the padded average as
366 // a safety factor.
367 cms_free -= expected_promotion;
368
369 // Adjust by the safety factor.
370 double cms_free_dbl = (double)cms_free;
371 double cms_adjustment = (100.0 - CMSIncrementalSafetyFactor)/100.0;
372 // Apply a further correction factor which tries to adjust
373 // for recent occurance of concurrent mode failures.
374 cms_adjustment = cms_adjustment * cms_free_adjustment_factor(cms_free);
375 cms_free_dbl = cms_free_dbl * cms_adjustment;
376
377 if (PrintGCDetails && Verbose) {
378 gclog_or_tty->print_cr("CMSStats::time_until_cms_gen_full: cms_free "
379 SIZE_FORMAT " expected_promotion " SIZE_FORMAT,
380 cms_free, expected_promotion);
381 gclog_or_tty->print_cr(" cms_free_dbl %f cms_consumption_rate %f",
382 cms_free_dbl, cms_consumption_rate() + 1.0);
383 }
384 // Add 1 in case the consumption rate goes to zero.
385 return cms_free_dbl / (cms_consumption_rate() + 1.0);
386 }
387 return 0.0;
388 }
389
390 // Compare the duration of the cms collection to the
391 // time remaining before the cms generation is empty.
392 // Note that the time from the start of the cms collection
393 // to the start of the cms sweep (less than the total
394 // duration of the cms collection) can be used. This
395 // has been tried and some applications experienced
396 // promotion failures early in execution. This was
397 // possibly because the averages were not accurate
398 // enough at the beginning.
399 double CMSStats::time_until_cms_start() const {
400 // We add "gc0_period" to the "work" calculation
401 // below because this query is done (mostly) at the
402 // end of a scavenge, so we need to conservatively
403 // account for that much possible delay
404 // in the query so as to avoid concurrent mode failures
405 // due to starting the collection just a wee bit too
406 // late.
407 double work = cms_duration() + gc0_period();
408 double deadline = time_until_cms_gen_full();
409 // If a concurrent mode failure occurred recently, we want to be
410 // more conservative and halve our expected time_until_cms_gen_full()
411 if (work > deadline) {
412 if (Verbose && PrintGCDetails) {
413 gclog_or_tty->print(
414 " CMSCollector: collect because of anticipated promotion "
415 "before full %3.7f + %3.7f > %3.7f ", cms_duration(),
416 gc0_period(), time_until_cms_gen_full());
417 }
418 return 0.0;
419 }
420 return work - deadline;
421 }
422
423 // Return a duty cycle based on old_duty_cycle and new_duty_cycle, limiting the
424 // amount of change to prevent wild oscillation.
425 unsigned int CMSStats::icms_damped_duty_cycle(unsigned int old_duty_cycle,
426 unsigned int new_duty_cycle) {
427 assert(old_duty_cycle <= 100, "bad input value");
428 assert(new_duty_cycle <= 100, "bad input value");
429
430 // Note: use subtraction with caution since it may underflow (values are
431 // unsigned). Addition is safe since we're in the range 0-100.
432 unsigned int damped_duty_cycle = new_duty_cycle;
433 if (new_duty_cycle < old_duty_cycle) {
434 const unsigned int largest_delta = MAX2(old_duty_cycle / 4, 5U);
435 if (new_duty_cycle + largest_delta < old_duty_cycle) {
436 damped_duty_cycle = old_duty_cycle - largest_delta;
437 }
438 } else if (new_duty_cycle > old_duty_cycle) {
439 const unsigned int largest_delta = MAX2(old_duty_cycle / 4, 15U);
440 if (new_duty_cycle > old_duty_cycle + largest_delta) {
441 damped_duty_cycle = MIN2(old_duty_cycle + largest_delta, 100U);
442 }
443 }
444 assert(damped_duty_cycle <= 100, "invalid duty cycle computed");
445
446 if (CMSTraceIncrementalPacing) {
447 gclog_or_tty->print(" [icms_damped_duty_cycle(%d,%d) = %d] ",
448 old_duty_cycle, new_duty_cycle, damped_duty_cycle);
449 }
450 return damped_duty_cycle;
451 }
452
453 unsigned int CMSStats::icms_update_duty_cycle_impl() {
454 assert(CMSIncrementalPacing && valid(),
455 "should be handled in icms_update_duty_cycle()");
456
457 double cms_time_so_far = cms_timer().seconds();
458 double scaled_duration = cms_duration_per_mb() * _cms_used_at_gc0_end / M;
459 double scaled_duration_remaining = fabsd(scaled_duration - cms_time_so_far);
460
461 // Avoid division by 0.
462 double time_until_full = MAX2(time_until_cms_gen_full(), 0.01);
463 double duty_cycle_dbl = 100.0 * scaled_duration_remaining / time_until_full;
464
465 unsigned int new_duty_cycle = MIN2((unsigned int)duty_cycle_dbl, 100U);
466 if (new_duty_cycle > _icms_duty_cycle) {
467 // Avoid very small duty cycles (1 or 2); 0 is allowed.
468 if (new_duty_cycle > 2) {
469 _icms_duty_cycle = icms_damped_duty_cycle(_icms_duty_cycle,
470 new_duty_cycle);
471 }
472 } else if (_allow_duty_cycle_reduction) {
473 // The duty cycle is reduced only once per cms cycle (see record_cms_end()).
474 new_duty_cycle = icms_damped_duty_cycle(_icms_duty_cycle, new_duty_cycle);
475 // Respect the minimum duty cycle.
476 unsigned int min_duty_cycle = (unsigned int)CMSIncrementalDutyCycleMin;
477 _icms_duty_cycle = MAX2(new_duty_cycle, min_duty_cycle);
478 }
479
480 if (PrintGCDetails || CMSTraceIncrementalPacing) {
481 gclog_or_tty->print(" icms_dc=%d ", _icms_duty_cycle);
482 }
483
484 _allow_duty_cycle_reduction = false;
485 return _icms_duty_cycle;
486 }
487
488 #ifndef PRODUCT
489 void CMSStats::print_on(outputStream *st) const {
490 st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha);
491 st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo=" SIZE_FORMAT,
492 gc0_duration(), gc0_period(), gc0_promoted());
493 st->print(",cms_dur=%g,cms_dur_per_mb=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT,
494 cms_duration(), cms_duration_per_mb(),
495 cms_period(), cms_allocated());
496 st->print(",cms_since_beg=%g,cms_since_end=%g",
497 cms_time_since_begin(), cms_time_since_end());
498 st->print(",cms_used_beg=" SIZE_FORMAT ",cms_used_end=" SIZE_FORMAT,
499 _cms_used_at_gc0_begin, _cms_used_at_gc0_end);
500 if (CMSIncrementalMode) {
501 st->print(",dc=%d", icms_duty_cycle());
502 }
503
504 if (valid()) {
505 st->print(",promo_rate=%g,cms_alloc_rate=%g",
506 promotion_rate(), cms_allocation_rate());
507 st->print(",cms_consumption_rate=%g,time_until_full=%g",
508 cms_consumption_rate(), time_until_cms_gen_full());
509 }
510 st->print(" ");
511 }
512 #endif // #ifndef PRODUCT
513
514 CMSCollector::CollectorState CMSCollector::_collectorState =
515 CMSCollector::Idling;
516 bool CMSCollector::_foregroundGCIsActive = false;
517 bool CMSCollector::_foregroundGCShouldWait = false;
518
519 CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
520 ConcurrentMarkSweepGeneration* permGen,
521 CardTableRS* ct,
522 ConcurrentMarkSweepPolicy* cp):
523 _cmsGen(cmsGen),
524 _permGen(permGen),
525 _ct(ct),
526 _ref_processor(NULL), // will be set later
527 _conc_workers(NULL), // may be set later
528 _abort_preclean(false),
529 _start_sampling(false),
530 _between_prologue_and_epilogue(false),
531 _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"),
532 _perm_gen_verify_bit_map(0, -1 /* no mutex */, "No_lock"),
533 _modUnionTable((CardTableModRefBS::card_shift - LogHeapWordSize),
534 -1 /* lock-free */, "No_lock" /* dummy */),
535 _modUnionClosure(&_modUnionTable),
536 _modUnionClosurePar(&_modUnionTable),
537 // Adjust my span to cover old (cms) gen and perm gen
538 _span(cmsGen->reserved()._union(permGen->reserved())),
539 // Construct the is_alive_closure with _span & markBitMap
540 _is_alive_closure(_span, &_markBitMap),
541 _restart_addr(NULL),
542 _overflow_list(NULL),
543 _stats(cmsGen),
544 _eden_chunk_array(NULL), // may be set in ctor body
545 _eden_chunk_capacity(0), // -- ditto --
546 _eden_chunk_index(0), // -- ditto --
547 _survivor_plab_array(NULL), // -- ditto --
548 _survivor_chunk_array(NULL), // -- ditto --
549 _survivor_chunk_capacity(0), // -- ditto --
550 _survivor_chunk_index(0), // -- ditto --
551 _ser_pmc_preclean_ovflw(0),
552 _ser_kac_preclean_ovflw(0),
553 _ser_pmc_remark_ovflw(0),
554 _par_pmc_remark_ovflw(0),
555 _ser_kac_ovflw(0),
556 _par_kac_ovflw(0),
557 #ifndef PRODUCT
558 _num_par_pushes(0),
559 #endif
560 _collection_count_start(0),
561 _verifying(false),
562 _icms_start_limit(NULL),
563 _icms_stop_limit(NULL),
564 _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"),
565 _completed_initialization(false),
566 _collector_policy(cp),
567 _should_unload_classes(false),
568 _concurrent_cycles_since_last_unload(0),
569 _roots_scanning_options(0),
570 _inter_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
571 _intra_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding)
572 {
573 if (ExplicitGCInvokesConcurrentAndUnloadsClasses) {
574 ExplicitGCInvokesConcurrent = true;
575 }
576 // Now expand the span and allocate the collection support structures
577 // (MUT, marking bit map etc.) to cover both generations subject to
578 // collection.
579
580 // First check that _permGen is adjacent to _cmsGen and above it.
581 assert( _cmsGen->reserved().word_size() > 0
582 && _permGen->reserved().word_size() > 0,
583 "generations should not be of zero size");
584 assert(_cmsGen->reserved().intersection(_permGen->reserved()).is_empty(),
585 "_cmsGen and _permGen should not overlap");
586 assert(_cmsGen->reserved().end() == _permGen->reserved().start(),
587 "_cmsGen->end() different from _permGen->start()");
588
589 // For use by dirty card to oop closures.
590 _cmsGen->cmsSpace()->set_collector(this);
591 _permGen->cmsSpace()->set_collector(this);
592
593 // Allocate MUT and marking bit map
594 {
595 MutexLockerEx x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag);
596 if (!_markBitMap.allocate(_span)) {
597 warning("Failed to allocate CMS Bit Map");
598 return;
599 }
600 assert(_markBitMap.covers(_span), "_markBitMap inconsistency?");
601 }
602 {
603 _modUnionTable.allocate(_span);
604 assert(_modUnionTable.covers(_span), "_modUnionTable inconsistency?");
605 }
606
607 if (!_markStack.allocate(MarkStackSize)) {
608 warning("Failed to allocate CMS Marking Stack");
609 return;
610 }
611 if (!_revisitStack.allocate(CMSRevisitStackSize)) {
612 warning("Failed to allocate CMS Revisit Stack");
613 return;
614 }
615
616 // Support for multi-threaded concurrent phases
617 if (CollectedHeap::use_parallel_gc_threads() && CMSConcurrentMTEnabled) {
618 if (FLAG_IS_DEFAULT(ConcGCThreads)) {
619 // just for now
620 FLAG_SET_DEFAULT(ConcGCThreads, (ParallelGCThreads + 3)/4);
621 }
622 if (ConcGCThreads > 1) {
623 _conc_workers = new YieldingFlexibleWorkGang("Parallel CMS Threads",
624 ConcGCThreads, true);
625 if (_conc_workers == NULL) {
626 warning("GC/CMS: _conc_workers allocation failure: "
627 "forcing -CMSConcurrentMTEnabled");
628 CMSConcurrentMTEnabled = false;
629 } else {
630 _conc_workers->initialize_workers();
631 }
632 } else {
633 CMSConcurrentMTEnabled = false;
634 }
635 }
636 if (!CMSConcurrentMTEnabled) {
637 ConcGCThreads = 0;
638 } else {
639 // Turn off CMSCleanOnEnter optimization temporarily for
640 // the MT case where it's not fixed yet; see 6178663.
641 CMSCleanOnEnter = false;
642 }
643 assert((_conc_workers != NULL) == (ConcGCThreads > 1),
644 "Inconsistency");
645
646 // Parallel task queues; these are shared for the
647 // concurrent and stop-world phases of CMS, but
648 // are not shared with parallel scavenge (ParNew).
649 {
650 uint i;
651 uint num_queues = (uint) MAX2(ParallelGCThreads, ConcGCThreads);
652
653 if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled
654 || ParallelRefProcEnabled)
655 && num_queues > 0) {
656 _task_queues = new OopTaskQueueSet(num_queues);
657 if (_task_queues == NULL) {
658 warning("task_queues allocation failure.");
659 return;
660 }
661 _hash_seed = NEW_C_HEAP_ARRAY(int, num_queues);
662 if (_hash_seed == NULL) {
663 warning("_hash_seed array allocation failure");
664 return;
665 }
666
667 typedef Padded<OopTaskQueue> PaddedOopTaskQueue;
668 for (i = 0; i < num_queues; i++) {
669 PaddedOopTaskQueue *q = new PaddedOopTaskQueue();
670 if (q == NULL) {
671 warning("work_queue allocation failure.");
672 return;
673 }
674 _task_queues->register_queue(i, q);
675 }
676 for (i = 0; i < num_queues; i++) {
677 _task_queues->queue(i)->initialize();
678 _hash_seed[i] = 17; // copied from ParNew
679 }
680 }
681 }
682
683 _cmsGen ->init_initiating_occupancy(CMSInitiatingOccupancyFraction, CMSTriggerRatio);
684 _permGen->init_initiating_occupancy(CMSInitiatingPermOccupancyFraction, CMSTriggerPermRatio);
685
686 // Clip CMSBootstrapOccupancy between 0 and 100.
687 _bootstrap_occupancy = ((double)MIN2((uintx)100, MAX2((uintx)0, CMSBootstrapOccupancy)))
688 /(double)100;
689
690 _full_gcs_since_conc_gc = 0;
691
692 // Now tell CMS generations the identity of their collector
693 ConcurrentMarkSweepGeneration::set_collector(this);
694
695 // Create & start a CMS thread for this CMS collector
696 _cmsThread = ConcurrentMarkSweepThread::start(this);
697 assert(cmsThread() != NULL, "CMS Thread should have been created");
698 assert(cmsThread()->collector() == this,
699 "CMS Thread should refer to this gen");
700 assert(CGC_lock != NULL, "Where's the CGC_lock?");
701
702 // Support for parallelizing young gen rescan
703 GenCollectedHeap* gch = GenCollectedHeap::heap();
704 _young_gen = gch->prev_gen(_cmsGen);
705 if (gch->supports_inline_contig_alloc()) {
706 _top_addr = gch->top_addr();
707 _end_addr = gch->end_addr();
708 assert(_young_gen != NULL, "no _young_gen");
709 _eden_chunk_index = 0;
710 _eden_chunk_capacity = (_young_gen->max_capacity()+CMSSamplingGrain)/CMSSamplingGrain;
711 _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity);
712 if (_eden_chunk_array == NULL) {
713 _eden_chunk_capacity = 0;
714 warning("GC/CMS: _eden_chunk_array allocation failure");
715 }
716 }
717 assert(_eden_chunk_array != NULL || _eden_chunk_capacity == 0, "Error");
718
719 // Support for parallelizing survivor space rescan
720 if (CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) {
721 const size_t max_plab_samples =
722 ((DefNewGeneration*)_young_gen)->max_survivor_size()/MinTLABSize;
723
724 _survivor_plab_array = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads);
725 _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, 2*max_plab_samples);
726 _cursor = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads);
727 if (_survivor_plab_array == NULL || _survivor_chunk_array == NULL
728 || _cursor == NULL) {
729 warning("Failed to allocate survivor plab/chunk array");
730 if (_survivor_plab_array != NULL) {
731 FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array);
732 _survivor_plab_array = NULL;
733 }
734 if (_survivor_chunk_array != NULL) {
735 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array);
736 _survivor_chunk_array = NULL;
737 }
738 if (_cursor != NULL) {
739 FREE_C_HEAP_ARRAY(size_t, _cursor);
740 _cursor = NULL;
741 }
742 } else {
743 _survivor_chunk_capacity = 2*max_plab_samples;
744 for (uint i = 0; i < ParallelGCThreads; i++) {
745 HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples);
746 if (vec == NULL) {
747 warning("Failed to allocate survivor plab array");
748 for (int j = i; j > 0; j--) {
749 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_plab_array[j-1].array());
750 }
751 FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array);
752 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array);
753 _survivor_plab_array = NULL;
754 _survivor_chunk_array = NULL;
755 _survivor_chunk_capacity = 0;
756 break;
757 } else {
758 ChunkArray* cur =
759 ::new (&_survivor_plab_array[i]) ChunkArray(vec,
760 max_plab_samples);
761 assert(cur->end() == 0, "Should be 0");
762 assert(cur->array() == vec, "Should be vec");
763 assert(cur->capacity() == max_plab_samples, "Error");
764 }
765 }
766 }
767 }
768 assert( ( _survivor_plab_array != NULL
769 && _survivor_chunk_array != NULL)
770 || ( _survivor_chunk_capacity == 0
771 && _survivor_chunk_index == 0),
772 "Error");
773
774 // Choose what strong roots should be scanned depending on verification options
775 // and perm gen collection mode.
776 if (!CMSClassUnloadingEnabled) {
777 // If class unloading is disabled we want to include all classes into the root set.
778 add_root_scanning_option(SharedHeap::SO_AllClasses);
779 } else {
780 add_root_scanning_option(SharedHeap::SO_SystemClasses);
781 }
782
783 NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;)
784 _gc_counters = new CollectorCounters("CMS", 1);
785 _completed_initialization = true;
786 _inter_sweep_timer.start(); // start of time
787 #ifdef SPARC
788 // Issue a stern warning, but allow use for experimentation and debugging.
789 if (VM_Version::is_sun4v() && UseMemSetInBOT) {
790 assert(!FLAG_IS_DEFAULT(UseMemSetInBOT), "Error");
791 warning("Experimental flag -XX:+UseMemSetInBOT is known to cause instability"
792 " on sun4v; please understand that you are using at your own risk!");
793 }
794 #endif
795 }
796
797 const char* ConcurrentMarkSweepGeneration::name() const {
798 return "concurrent mark-sweep generation";
799 }
800 void ConcurrentMarkSweepGeneration::update_counters() {
801 if (UsePerfData) {
802 _space_counters->update_all();
803 _gen_counters->update_all();
804 }
805 }
806
807 // this is an optimized version of update_counters(). it takes the
808 // used value as a parameter rather than computing it.
809 //
810 void ConcurrentMarkSweepGeneration::update_counters(size_t used) {
811 if (UsePerfData) {
812 _space_counters->update_used(used);
813 _space_counters->update_capacity();
814 _gen_counters->update_all();
815 }
816 }
817
818 void ConcurrentMarkSweepGeneration::print() const {
819 Generation::print();
820 cmsSpace()->print();
821 }
822
823 #ifndef PRODUCT
824 void ConcurrentMarkSweepGeneration::print_statistics() {
825 cmsSpace()->printFLCensus(0);
826 }
827 #endif
828
829 void ConcurrentMarkSweepGeneration::printOccupancy(const char *s) {
830 GenCollectedHeap* gch = GenCollectedHeap::heap();
831 if (PrintGCDetails) {
832 if (Verbose) {
833 gclog_or_tty->print(" [%d %s-%s: "SIZE_FORMAT"("SIZE_FORMAT")]",
834 level(), short_name(), s, used(), capacity());
835 } else {
836 gclog_or_tty->print(" [%d %s-%s: "SIZE_FORMAT"K("SIZE_FORMAT"K)]",
837 level(), short_name(), s, used() / K, capacity() / K);
838 }
839 }
840 if (Verbose) {
841 gclog_or_tty->print(" "SIZE_FORMAT"("SIZE_FORMAT")",
842 gch->used(), gch->capacity());
843 } else {
844 gclog_or_tty->print(" "SIZE_FORMAT"K("SIZE_FORMAT"K)",
845 gch->used() / K, gch->capacity() / K);
846 }
847 }
848
849 size_t
850 ConcurrentMarkSweepGeneration::contiguous_available() const {
851 // dld proposes an improvement in precision here. If the committed
852 // part of the space ends in a free block we should add that to
853 // uncommitted size in the calculation below. Will make this
854 // change later, staying with the approximation below for the
855 // time being. -- ysr.
856 return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc());
857 }
858
859 size_t
860 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const {
861 return _cmsSpace->max_alloc_in_words() * HeapWordSize;
862 }
863
864 size_t ConcurrentMarkSweepGeneration::max_available() const {
865 return free() + _virtual_space.uncommitted_size();
866 }
867
868 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(
869 size_t max_promotion_in_bytes,
870 bool younger_handles_promotion_failure) const {
871
872 // This is the most conservative test. Full promotion is
873 // guaranteed if this is used. The multiplicative factor is to
874 // account for the worst case "dilatation".
875 double adjusted_max_promo_bytes = _dilatation_factor * max_promotion_in_bytes;
876 if (adjusted_max_promo_bytes > (double)max_uintx) { // larger than size_t
877 adjusted_max_promo_bytes = (double)max_uintx;
878 }
879 bool result = (max_contiguous_available() >= (size_t)adjusted_max_promo_bytes);
880
881 if (younger_handles_promotion_failure && !result) {
882 // Full promotion is not guaranteed because fragmentation
883 // of the cms generation can prevent the full promotion.
884 result = (max_available() >= (size_t)adjusted_max_promo_bytes);
885
886 if (!result) {
887 // With promotion failure handling the test for the ability
888 // to support the promotion does not have to be guaranteed.
889 // Use an average of the amount promoted.
890 result = max_available() >= (size_t)
891 gc_stats()->avg_promoted()->padded_average();
892 if (PrintGC && Verbose && result) {
893 gclog_or_tty->print_cr(
894 "\nConcurrentMarkSweepGeneration::promotion_attempt_is_safe"
895 " max_available: " SIZE_FORMAT
896 " avg_promoted: " SIZE_FORMAT,
897 max_available(), (size_t)
898 gc_stats()->avg_promoted()->padded_average());
899 }
900 } else {
901 if (PrintGC && Verbose) {
902 gclog_or_tty->print_cr(
903 "\nConcurrentMarkSweepGeneration::promotion_attempt_is_safe"
904 " max_available: " SIZE_FORMAT
905 " adj_max_promo_bytes: " SIZE_FORMAT,
906 max_available(), (size_t)adjusted_max_promo_bytes);
907 }
908 }
909 } else {
910 if (PrintGC && Verbose) {
911 gclog_or_tty->print_cr(
912 "\nConcurrentMarkSweepGeneration::promotion_attempt_is_safe"
913 " contiguous_available: " SIZE_FORMAT
914 " adj_max_promo_bytes: " SIZE_FORMAT,
915 max_contiguous_available(), (size_t)adjusted_max_promo_bytes);
916 }
917 }
918 return result;
919 }
920
921 // At a promotion failure dump information on block layout in heap
922 // (cms old generation).
923 void ConcurrentMarkSweepGeneration::promotion_failure_occurred() {
924 if (CMSDumpAtPromotionFailure) {
925 cmsSpace()->dump_at_safepoint_with_locks(collector(), gclog_or_tty);
926 }
927 }
928
929 CompactibleSpace*
930 ConcurrentMarkSweepGeneration::first_compaction_space() const {
931 return _cmsSpace;
932 }
933
934 void ConcurrentMarkSweepGeneration::reset_after_compaction() {
935 // Clear the promotion information. These pointers can be adjusted
936 // along with all the other pointers into the heap but
937 // compaction is expected to be a rare event with
938 // a heap using cms so don't do it without seeing the need.
939 if (CollectedHeap::use_parallel_gc_threads()) {
940 for (uint i = 0; i < ParallelGCThreads; i++) {
941 _par_gc_thread_states[i]->promo.reset();
942 }
943 }
944 }
945
946 void ConcurrentMarkSweepGeneration::space_iterate(SpaceClosure* blk, bool usedOnly) {
947 blk->do_space(_cmsSpace);
948 }
949
950 void ConcurrentMarkSweepGeneration::compute_new_size() {
951 assert_locked_or_safepoint(Heap_lock);
952
953 // If incremental collection failed, we just want to expand
954 // to the limit.
955 if (incremental_collection_failed()) {
956 clear_incremental_collection_failed();
957 grow_to_reserved();
958 return;
959 }
960
961 size_t expand_bytes = 0;
962 double free_percentage = ((double) free()) / capacity();
963 double desired_free_percentage = (double) MinHeapFreeRatio / 100;
964 double maximum_free_percentage = (double) MaxHeapFreeRatio / 100;
965
966 // compute expansion delta needed for reaching desired free percentage
967 if (free_percentage < desired_free_percentage) {
968 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
969 assert(desired_capacity >= capacity(), "invalid expansion size");
970 expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes);
971 }
972 if (expand_bytes > 0) {
973 if (PrintGCDetails && Verbose) {
974 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
975 gclog_or_tty->print_cr("\nFrom compute_new_size: ");
976 gclog_or_tty->print_cr(" Free fraction %f", free_percentage);
977 gclog_or_tty->print_cr(" Desired free fraction %f",
978 desired_free_percentage);
979 gclog_or_tty->print_cr(" Maximum free fraction %f",
980 maximum_free_percentage);
981 gclog_or_tty->print_cr(" Capactiy "SIZE_FORMAT, capacity()/1000);
982 gclog_or_tty->print_cr(" Desired capacity "SIZE_FORMAT,
983 desired_capacity/1000);
984 int prev_level = level() - 1;
985 if (prev_level >= 0) {
986 size_t prev_size = 0;
987 GenCollectedHeap* gch = GenCollectedHeap::heap();
988 Generation* prev_gen = gch->_gens[prev_level];
989 prev_size = prev_gen->capacity();
990 gclog_or_tty->print_cr(" Younger gen size "SIZE_FORMAT,
991 prev_size/1000);
992 }
993 gclog_or_tty->print_cr(" unsafe_max_alloc_nogc "SIZE_FORMAT,
994 unsafe_max_alloc_nogc()/1000);
995 gclog_or_tty->print_cr(" contiguous available "SIZE_FORMAT,
996 contiguous_available()/1000);
997 gclog_or_tty->print_cr(" Expand by "SIZE_FORMAT" (bytes)",
998 expand_bytes);
999 }
1000 // safe if expansion fails
1001 expand(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio);
1002 if (PrintGCDetails && Verbose) {
1003 gclog_or_tty->print_cr(" Expanded free fraction %f",
1004 ((double) free()) / capacity());
1005 }
1006 }
1007 }
1008
1009 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const {
1010 return cmsSpace()->freelistLock();
1011 }
1012
1013 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size,
1014 bool tlab) {
1015 CMSSynchronousYieldRequest yr;
1016 MutexLockerEx x(freelistLock(),
1017 Mutex::_no_safepoint_check_flag);
1018 return have_lock_and_allocate(size, tlab);
1019 }
1020
1021 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size,
1022 bool tlab /* ignored */) {
1023 assert_lock_strong(freelistLock());
1024 size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size);
1025 HeapWord* res = cmsSpace()->allocate(adjustedSize);
1026 // Allocate the object live (grey) if the background collector has
1027 // started marking. This is necessary because the marker may
1028 // have passed this address and consequently this object will
1029 // not otherwise be greyed and would be incorrectly swept up.
1030 // Note that if this object contains references, the writing
1031 // of those references will dirty the card containing this object
1032 // allowing the object to be blackened (and its references scanned)
1033 // either during a preclean phase or at the final checkpoint.
1034 if (res != NULL) {
1035 // We may block here with an uninitialized object with
1036 // its mark-bit or P-bits not yet set. Such objects need
1037 // to be safely navigable by block_start().
1038 assert(oop(res)->klass_or_null() == NULL, "Object should be uninitialized here.");
1039 assert(!((FreeChunk*)res)->isFree(), "Error, block will look free but show wrong size");
1040 collector()->direct_allocated(res, adjustedSize);
1041 _direct_allocated_words += adjustedSize;
1042 // allocation counters
1043 NOT_PRODUCT(
1044 _numObjectsAllocated++;
1045 _numWordsAllocated += (int)adjustedSize;
1046 )
1047 }
1048 return res;
1049 }
1050
1051 // In the case of direct allocation by mutators in a generation that
1052 // is being concurrently collected, the object must be allocated
1053 // live (grey) if the background collector has started marking.
1054 // This is necessary because the marker may
1055 // have passed this address and consequently this object will
1056 // not otherwise be greyed and would be incorrectly swept up.
1057 // Note that if this object contains references, the writing
1058 // of those references will dirty the card containing this object
1059 // allowing the object to be blackened (and its references scanned)
1060 // either during a preclean phase or at the final checkpoint.
1061 void CMSCollector::direct_allocated(HeapWord* start, size_t size) {
1062 assert(_markBitMap.covers(start, size), "Out of bounds");
1063 if (_collectorState >= Marking) {
1064 MutexLockerEx y(_markBitMap.lock(),
1065 Mutex::_no_safepoint_check_flag);
1066 // [see comments preceding SweepClosure::do_blk() below for details]
1067 // 1. need to mark the object as live so it isn't collected
1068 // 2. need to mark the 2nd bit to indicate the object may be uninitialized
1069 // 3. need to mark the end of the object so marking, precleaning or sweeping
1070 // can skip over uninitialized or unparsable objects. An allocated
1071 // object is considered uninitialized for our purposes as long as
1072 // its klass word is NULL. (Unparsable objects are those which are
1073 // initialized in the sense just described, but whose sizes can still
1074 // not be correctly determined. Note that the class of unparsable objects
1075 // can only occur in the perm gen. All old gen objects are parsable
1076 // as soon as they are initialized.)
1077 _markBitMap.mark(start); // object is live
1078 _markBitMap.mark(start + 1); // object is potentially uninitialized?
1079 _markBitMap.mark(start + size - 1);
1080 // mark end of object
1081 }
1082 // check that oop looks uninitialized
1083 assert(oop(start)->klass_or_null() == NULL, "_klass should be NULL");
1084 }
1085
1086 void CMSCollector::promoted(bool par, HeapWord* start,
1087 bool is_obj_array, size_t obj_size) {
1088 assert(_markBitMap.covers(start), "Out of bounds");
1089 // See comment in direct_allocated() about when objects should
1090 // be allocated live.
1091 if (_collectorState >= Marking) {
1092 // we already hold the marking bit map lock, taken in
1093 // the prologue
1094 if (par) {
1095 _markBitMap.par_mark(start);
1096 } else {
1097 _markBitMap.mark(start);
1098 }
1099 // We don't need to mark the object as uninitialized (as
1100 // in direct_allocated above) because this is being done with the
1101 // world stopped and the object will be initialized by the
1102 // time the marking, precleaning or sweeping get to look at it.
1103 // But see the code for copying objects into the CMS generation,
1104 // where we need to ensure that concurrent readers of the
1105 // block offset table are able to safely navigate a block that
1106 // is in flux from being free to being allocated (and in
1107 // transition while being copied into) and subsequently
1108 // becoming a bona-fide object when the copy/promotion is complete.
1109 assert(SafepointSynchronize::is_at_safepoint(),
1110 "expect promotion only at safepoints");
1111
1112 if (_collectorState < Sweeping) {
1113 // Mark the appropriate cards in the modUnionTable, so that
1114 // this object gets scanned before the sweep. If this is
1115 // not done, CMS generation references in the object might
1116 // not get marked.
1117 // For the case of arrays, which are otherwise precisely
1118 // marked, we need to dirty the entire array, not just its head.
1119 if (is_obj_array) {
1120 // The [par_]mark_range() method expects mr.end() below to
1121 // be aligned to the granularity of a bit's representation
1122 // in the heap. In the case of the MUT below, that's a
1123 // card size.
1124 MemRegion mr(start,
1125 (HeapWord*)round_to((intptr_t)(start + obj_size),
1126 CardTableModRefBS::card_size /* bytes */));
1127 if (par) {
1128 _modUnionTable.par_mark_range(mr);
1129 } else {
1130 _modUnionTable.mark_range(mr);
1131 }
1132 } else { // not an obj array; we can just mark the head
1133 if (par) {
1134 _modUnionTable.par_mark(start);
1135 } else {
1136 _modUnionTable.mark(start);
1137 }
1138 }
1139 }
1140 }
1141 }
1142
1143 static inline size_t percent_of_space(Space* space, HeapWord* addr)
1144 {
1145 size_t delta = pointer_delta(addr, space->bottom());
1146 return (size_t)(delta * 100.0 / (space->capacity() / HeapWordSize));
1147 }
1148
1149 void CMSCollector::icms_update_allocation_limits()
1150 {
1151 Generation* gen0 = GenCollectedHeap::heap()->get_gen(0);
1152 EdenSpace* eden = gen0->as_DefNewGeneration()->eden();
1153
1154 const unsigned int duty_cycle = stats().icms_update_duty_cycle();
1155 if (CMSTraceIncrementalPacing) {
1156 stats().print();
1157 }
1158
1159 assert(duty_cycle <= 100, "invalid duty cycle");
1160 if (duty_cycle != 0) {
1161 // The duty_cycle is a percentage between 0 and 100; convert to words and
1162 // then compute the offset from the endpoints of the space.
1163 size_t free_words = eden->free() / HeapWordSize;
1164 double free_words_dbl = (double)free_words;
1165 size_t duty_cycle_words = (size_t)(free_words_dbl * duty_cycle / 100.0);
1166 size_t offset_words = (free_words - duty_cycle_words) / 2;
1167
1168 _icms_start_limit = eden->top() + offset_words;
1169 _icms_stop_limit = eden->end() - offset_words;
1170
1171 // The limits may be adjusted (shifted to the right) by
1172 // CMSIncrementalOffset, to allow the application more mutator time after a
1173 // young gen gc (when all mutators were stopped) and before CMS starts and
1174 // takes away one or more cpus.
1175 if (CMSIncrementalOffset != 0) {
1176 double adjustment_dbl = free_words_dbl * CMSIncrementalOffset / 100.0;
1177 size_t adjustment = (size_t)adjustment_dbl;
1178 HeapWord* tmp_stop = _icms_stop_limit + adjustment;
1179 if (tmp_stop > _icms_stop_limit && tmp_stop < eden->end()) {
1180 _icms_start_limit += adjustment;
1181 _icms_stop_limit = tmp_stop;
1182 }
1183 }
1184 }
1185 if (duty_cycle == 0 || (_icms_start_limit == _icms_stop_limit)) {
1186 _icms_start_limit = _icms_stop_limit = eden->end();
1187 }
1188
1189 // Install the new start limit.
1190 eden->set_soft_end(_icms_start_limit);
1191
1192 if (CMSTraceIncrementalMode) {
1193 gclog_or_tty->print(" icms alloc limits: "
1194 PTR_FORMAT "," PTR_FORMAT
1195 " (" SIZE_FORMAT "%%," SIZE_FORMAT "%%) ",
1196 _icms_start_limit, _icms_stop_limit,
1197 percent_of_space(eden, _icms_start_limit),
1198 percent_of_space(eden, _icms_stop_limit));
1199 if (Verbose) {
1200 gclog_or_tty->print("eden: ");
1201 eden->print_on(gclog_or_tty);
1202 }
1203 }
1204 }
1205
1206 // Any changes here should try to maintain the invariant
1207 // that if this method is called with _icms_start_limit
1208 // and _icms_stop_limit both NULL, then it should return NULL
1209 // and not notify the icms thread.
1210 HeapWord*
1211 CMSCollector::allocation_limit_reached(Space* space, HeapWord* top,
1212 size_t word_size)
1213 {
1214 // A start_limit equal to end() means the duty cycle is 0, so treat that as a
1215 // nop.
1216 if (CMSIncrementalMode && _icms_start_limit != space->end()) {
1217 if (top <= _icms_start_limit) {
1218 if (CMSTraceIncrementalMode) {
1219 space->print_on(gclog_or_tty);
1220 gclog_or_tty->stamp();
1221 gclog_or_tty->print_cr(" start limit top=" PTR_FORMAT
1222 ", new limit=" PTR_FORMAT
1223 " (" SIZE_FORMAT "%%)",
1224 top, _icms_stop_limit,
1225 percent_of_space(space, _icms_stop_limit));
1226 }
1227 ConcurrentMarkSweepThread::start_icms();
1228 assert(top < _icms_stop_limit, "Tautology");
1229 if (word_size < pointer_delta(_icms_stop_limit, top)) {
1230 return _icms_stop_limit;
1231 }
1232
1233 // The allocation will cross both the _start and _stop limits, so do the
1234 // stop notification also and return end().
1235 if (CMSTraceIncrementalMode) {
1236 space->print_on(gclog_or_tty);
1237 gclog_or_tty->stamp();
1238 gclog_or_tty->print_cr(" +stop limit top=" PTR_FORMAT
1239 ", new limit=" PTR_FORMAT
1240 " (" SIZE_FORMAT "%%)",
1241 top, space->end(),
1242 percent_of_space(space, space->end()));
1243 }
1244 ConcurrentMarkSweepThread::stop_icms();
1245 return space->end();
1246 }
1247
1248 if (top <= _icms_stop_limit) {
1249 if (CMSTraceIncrementalMode) {
1250 space->print_on(gclog_or_tty);
1251 gclog_or_tty->stamp();
1252 gclog_or_tty->print_cr(" stop limit top=" PTR_FORMAT
1253 ", new limit=" PTR_FORMAT
1254 " (" SIZE_FORMAT "%%)",
1255 top, space->end(),
1256 percent_of_space(space, space->end()));
1257 }
1258 ConcurrentMarkSweepThread::stop_icms();
1259 return space->end();
1260 }
1261
1262 if (CMSTraceIncrementalMode) {
1263 space->print_on(gclog_or_tty);
1264 gclog_or_tty->stamp();
1265 gclog_or_tty->print_cr(" end limit top=" PTR_FORMAT
1266 ", new limit=" PTR_FORMAT,
1267 top, NULL);
1268 }
1269 }
1270
1271 return NULL;
1272 }
1273
1274 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size) {
1275 assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
1276 // allocate, copy and if necessary update promoinfo --
1277 // delegate to underlying space.
1278 assert_lock_strong(freelistLock());
1279
1280 #ifndef PRODUCT
1281 if (Universe::heap()->promotion_should_fail()) {
1282 return NULL;
1283 }
1284 #endif // #ifndef PRODUCT
1285
1286 oop res = _cmsSpace->promote(obj, obj_size);
1287 if (res == NULL) {
1288 // expand and retry
1289 size_t s = _cmsSpace->expansionSpaceRequired(obj_size); // HeapWords
1290 expand(s*HeapWordSize, MinHeapDeltaBytes,
1291 CMSExpansionCause::_satisfy_promotion);
1292 // Since there's currently no next generation, we don't try to promote
1293 // into a more senior generation.
1294 assert(next_gen() == NULL, "assumption, based upon which no attempt "
1295 "is made to pass on a possibly failing "
1296 "promotion to next generation");
1297 res = _cmsSpace->promote(obj, obj_size);
1298 }
1299 if (res != NULL) {
1300 // See comment in allocate() about when objects should
1301 // be allocated live.
1302 assert(obj->is_oop(), "Will dereference klass pointer below");
1303 collector()->promoted(false, // Not parallel
1304 (HeapWord*)res, obj->is_objArray(), obj_size);
1305 // promotion counters
1306 NOT_PRODUCT(
1307 _numObjectsPromoted++;
1308 _numWordsPromoted +=
1309 (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size()));
1310 )
1311 }
1312 return res;
1313 }
1314
1315
1316 HeapWord*
1317 ConcurrentMarkSweepGeneration::allocation_limit_reached(Space* space,
1318 HeapWord* top,
1319 size_t word_sz)
1320 {
1321 return collector()->allocation_limit_reached(space, top, word_sz);
1322 }
1323
1324 // IMPORTANT: Notes on object size recognition in CMS.
1325 // ---------------------------------------------------
1326 // A block of storage in the CMS generation is always in
1327 // one of three states. A free block (FREE), an allocated
1328 // object (OBJECT) whose size() method reports the correct size,
1329 // and an intermediate state (TRANSIENT) in which its size cannot
1330 // be accurately determined.
1331 // STATE IDENTIFICATION: (32 bit and 64 bit w/o COOPS)
1332 // -----------------------------------------------------
1333 // FREE: klass_word & 1 == 1; mark_word holds block size
1334 //
1335 // OBJECT: klass_word installed; klass_word != 0 && klass_word & 1 == 0;
1336 // obj->size() computes correct size
1337 // [Perm Gen objects needs to be "parsable" before they can be navigated]
1338 //
1339 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1340 //
1341 // STATE IDENTIFICATION: (64 bit+COOPS)
1342 // ------------------------------------
1343 // FREE: mark_word & CMS_FREE_BIT == 1; mark_word & ~CMS_FREE_BIT gives block_size
1344 //
1345 // OBJECT: klass_word installed; klass_word != 0;
1346 // obj->size() computes correct size
1347 // [Perm Gen comment above continues to hold]
1348 //
1349 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1350 //
1351 //
1352 // STATE TRANSITION DIAGRAM
1353 //
1354 // mut / parnew mut / parnew
1355 // FREE --------------------> TRANSIENT ---------------------> OBJECT --|
1356 // ^ |
1357 // |------------------------ DEAD <------------------------------------|
1358 // sweep mut
1359 //
1360 // While a block is in TRANSIENT state its size cannot be determined
1361 // so readers will either need to come back later or stall until
1362 // the size can be determined. Note that for the case of direct
1363 // allocation, P-bits, when available, may be used to determine the
1364 // size of an object that may not yet have been initialized.
1365
1366 // Things to support parallel young-gen collection.
1367 oop
1368 ConcurrentMarkSweepGeneration::par_promote(int thread_num,
1369 oop old, markOop m,
1370 size_t word_sz) {
1371 #ifndef PRODUCT
1372 if (Universe::heap()->promotion_should_fail()) {
1373 return NULL;
1374 }
1375 #endif // #ifndef PRODUCT
1376
1377 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1378 PromotionInfo* promoInfo = &ps->promo;
1379 // if we are tracking promotions, then first ensure space for
1380 // promotion (including spooling space for saving header if necessary).
1381 // then allocate and copy, then track promoted info if needed.
1382 // When tracking (see PromotionInfo::track()), the mark word may
1383 // be displaced and in this case restoration of the mark word
1384 // occurs in the (oop_since_save_marks_)iterate phase.
1385 if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) {
1386 // Out of space for allocating spooling buffers;
1387 // try expanding and allocating spooling buffers.
1388 if (!expand_and_ensure_spooling_space(promoInfo)) {
1389 return NULL;
1390 }
1391 }
1392 assert(promoInfo->has_spooling_space(), "Control point invariant");
1393 const size_t alloc_sz = CompactibleFreeListSpace::adjustObjectSize(word_sz);
1394 HeapWord* obj_ptr = ps->lab.alloc(alloc_sz);
1395 if (obj_ptr == NULL) {
1396 obj_ptr = expand_and_par_lab_allocate(ps, alloc_sz);
1397 if (obj_ptr == NULL) {
1398 return NULL;
1399 }
1400 }
1401 oop obj = oop(obj_ptr);
1402 OrderAccess::storestore();
1403 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1404 assert(!((FreeChunk*)obj_ptr)->isFree(), "Error, block will look free but show wrong size");
1405 // IMPORTANT: See note on object initialization for CMS above.
1406 // Otherwise, copy the object. Here we must be careful to insert the
1407 // klass pointer last, since this marks the block as an allocated object.
1408 // Except with compressed oops it's the mark word.
1409 HeapWord* old_ptr = (HeapWord*)old;
1410 // Restore the mark word copied above.
1411 obj->set_mark(m);
1412 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1413 assert(!((FreeChunk*)obj_ptr)->isFree(), "Error, block will look free but show wrong size");
1414 OrderAccess::storestore();
1415
1416 if (UseCompressedOops) {
1417 // Copy gap missed by (aligned) header size calculation below
1418 obj->set_klass_gap(old->klass_gap());
1419 }
1420 if (word_sz > (size_t)oopDesc::header_size()) {
1421 Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1422 obj_ptr + oopDesc::header_size(),
1423 word_sz - oopDesc::header_size());
1424 }
1425
1426 // Now we can track the promoted object, if necessary. We take care
1427 // to delay the transition from uninitialized to full object
1428 // (i.e., insertion of klass pointer) until after, so that it
1429 // atomically becomes a promoted object.
1430 if (promoInfo->tracking()) {
1431 promoInfo->track((PromotedObject*)obj, old->klass());
1432 }
1433 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1434 assert(!((FreeChunk*)obj_ptr)->isFree(), "Error, block will look free but show wrong size");
1435 assert(old->is_oop(), "Will use and dereference old klass ptr below");
1436
1437 // Finally, install the klass pointer (this should be volatile).
1438 OrderAccess::storestore();
1439 obj->set_klass(old->klass());
1440 // We should now be able to calculate the right size for this object
1441 assert(obj->is_oop() && obj->size() == (int)word_sz, "Error, incorrect size computed for promoted object");
1442
1443 collector()->promoted(true, // parallel
1444 obj_ptr, old->is_objArray(), word_sz);
1445
1446 NOT_PRODUCT(
1447 Atomic::inc_ptr(&_numObjectsPromoted);
1448 Atomic::add_ptr(alloc_sz, &_numWordsPromoted);
1449 )
1450
1451 return obj;
1452 }
1453
1454 void
1455 ConcurrentMarkSweepGeneration::
1456 par_promote_alloc_undo(int thread_num,
1457 HeapWord* obj, size_t word_sz) {
1458 // CMS does not support promotion undo.
1459 ShouldNotReachHere();
1460 }
1461
1462 void
1463 ConcurrentMarkSweepGeneration::
1464 par_promote_alloc_done(int thread_num) {
1465 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1466 ps->lab.retire(thread_num);
1467 }
1468
1469 void
1470 ConcurrentMarkSweepGeneration::
1471 par_oop_since_save_marks_iterate_done(int thread_num) {
1472 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1473 ParScanWithoutBarrierClosure* dummy_cl = NULL;
1474 ps->promo.promoted_oops_iterate_nv(dummy_cl);
1475 }
1476
1477 // XXXPERM
1478 bool ConcurrentMarkSweepGeneration::should_collect(bool full,
1479 size_t size,
1480 bool tlab)
1481 {
1482 // We allow a STW collection only if a full
1483 // collection was requested.
1484 return full || should_allocate(size, tlab); // FIX ME !!!
1485 // This and promotion failure handling are connected at the
1486 // hip and should be fixed by untying them.
1487 }
1488
1489 bool CMSCollector::shouldConcurrentCollect() {
1490 if (_full_gc_requested) {
1491 if (Verbose && PrintGCDetails) {
1492 gclog_or_tty->print_cr("CMSCollector: collect because of explicit "
1493 " gc request (or gc_locker)");
1494 }
1495 return true;
1496 }
1497
1498 // For debugging purposes, change the type of collection.
1499 // If the rotation is not on the concurrent collection
1500 // type, don't start a concurrent collection.
1501 NOT_PRODUCT(
1502 if (RotateCMSCollectionTypes &&
1503 (_cmsGen->debug_collection_type() !=
1504 ConcurrentMarkSweepGeneration::Concurrent_collection_type)) {
1505 assert(_cmsGen->debug_collection_type() !=
1506 ConcurrentMarkSweepGeneration::Unknown_collection_type,
1507 "Bad cms collection type");
1508 return false;
1509 }
1510 )
1511
1512 FreelistLocker x(this);
1513 // ------------------------------------------------------------------
1514 // Print out lots of information which affects the initiation of
1515 // a collection.
1516 if (PrintCMSInitiationStatistics && stats().valid()) {
1517 gclog_or_tty->print("CMSCollector shouldConcurrentCollect: ");
1518 gclog_or_tty->stamp();
1519 gclog_or_tty->print_cr("");
1520 stats().print_on(gclog_or_tty);
1521 gclog_or_tty->print_cr("time_until_cms_gen_full %3.7f",
1522 stats().time_until_cms_gen_full());
1523 gclog_or_tty->print_cr("free="SIZE_FORMAT, _cmsGen->free());
1524 gclog_or_tty->print_cr("contiguous_available="SIZE_FORMAT,
1525 _cmsGen->contiguous_available());
1526 gclog_or_tty->print_cr("promotion_rate=%g", stats().promotion_rate());
1527 gclog_or_tty->print_cr("cms_allocation_rate=%g", stats().cms_allocation_rate());
1528 gclog_or_tty->print_cr("occupancy=%3.7f", _cmsGen->occupancy());
1529 gclog_or_tty->print_cr("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy());
1530 gclog_or_tty->print_cr("initiatingPermOccupancy=%3.7f", _permGen->initiating_occupancy());
1531 }
1532 // ------------------------------------------------------------------
1533
1534 // If the estimated time to complete a cms collection (cms_duration())
1535 // is less than the estimated time remaining until the cms generation
1536 // is full, start a collection.
1537 if (!UseCMSInitiatingOccupancyOnly) {
1538 if (stats().valid()) {
1539 if (stats().time_until_cms_start() == 0.0) {
1540 return true;
1541 }
1542 } else {
1543 // We want to conservatively collect somewhat early in order
1544 // to try and "bootstrap" our CMS/promotion statistics;
1545 // this branch will not fire after the first successful CMS
1546 // collection because the stats should then be valid.
1547 if (_cmsGen->occupancy() >= _bootstrap_occupancy) {
1548 if (Verbose && PrintGCDetails) {
1549 gclog_or_tty->print_cr(
1550 " CMSCollector: collect for bootstrapping statistics:"
1551 " occupancy = %f, boot occupancy = %f", _cmsGen->occupancy(),
1552 _bootstrap_occupancy);
1553 }
1554 return true;
1555 }
1556 }
1557 }
1558
1559 // Otherwise, we start a collection cycle if either the perm gen or
1560 // old gen want a collection cycle started. Each may use
1561 // an appropriate criterion for making this decision.
1562 // XXX We need to make sure that the gen expansion
1563 // criterion dovetails well with this. XXX NEED TO FIX THIS
1564 if (_cmsGen->should_concurrent_collect()) {
1565 if (Verbose && PrintGCDetails) {
1566 gclog_or_tty->print_cr("CMS old gen initiated");
1567 }
1568 return true;
1569 }
1570
1571 // We start a collection if we believe an incremental collection may fail;
1572 // this is not likely to be productive in practice because it's probably too
1573 // late anyway.
1574 GenCollectedHeap* gch = GenCollectedHeap::heap();
1575 assert(gch->collector_policy()->is_two_generation_policy(),
1576 "You may want to check the correctness of the following");
1577 if (gch->incremental_collection_will_fail()) {
1578 if (PrintGCDetails && Verbose) {
1579 gclog_or_tty->print("CMSCollector: collect because incremental collection will fail ");
1580 }
1581 return true;
1582 }
1583
1584 if (CMSClassUnloadingEnabled && _permGen->should_concurrent_collect()) {
1585 bool res = update_should_unload_classes();
1586 if (res) {
1587 if (Verbose && PrintGCDetails) {
1588 gclog_or_tty->print_cr("CMS perm gen initiated");
1589 }
1590 return true;
1591 }
1592 }
1593 return false;
1594 }
1595
1596 // Clear _expansion_cause fields of constituent generations
1597 void CMSCollector::clear_expansion_cause() {
1598 _cmsGen->clear_expansion_cause();
1599 _permGen->clear_expansion_cause();
1600 }
1601
1602 // We should be conservative in starting a collection cycle. To
1603 // start too eagerly runs the risk of collecting too often in the
1604 // extreme. To collect too rarely falls back on full collections,
1605 // which works, even if not optimum in terms of concurrent work.
1606 // As a work around for too eagerly collecting, use the flag
1607 // UseCMSInitiatingOccupancyOnly. This also has the advantage of
1608 // giving the user an easily understandable way of controlling the
1609 // collections.
1610 // We want to start a new collection cycle if any of the following
1611 // conditions hold:
1612 // . our current occupancy exceeds the configured initiating occupancy
1613 // for this generation, or
1614 // . we recently needed to expand this space and have not, since that
1615 // expansion, done a collection of this generation, or
1616 // . the underlying space believes that it may be a good idea to initiate
1617 // a concurrent collection (this may be based on criteria such as the
1618 // following: the space uses linear allocation and linear allocation is
1619 // going to fail, or there is believed to be excessive fragmentation in
1620 // the generation, etc... or ...
1621 // [.(currently done by CMSCollector::shouldConcurrentCollect() only for
1622 // the case of the old generation, not the perm generation; see CR 6543076):
1623 // we may be approaching a point at which allocation requests may fail because
1624 // we will be out of sufficient free space given allocation rate estimates.]
1625 bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const {
1626
1627 assert_lock_strong(freelistLock());
1628 if (occupancy() > initiating_occupancy()) {
1629 if (PrintGCDetails && Verbose) {
1630 gclog_or_tty->print(" %s: collect because of occupancy %f / %f ",
1631 short_name(), occupancy(), initiating_occupancy());
1632 }
1633 return true;
1634 }
1635 if (UseCMSInitiatingOccupancyOnly) {
1636 return false;
1637 }
1638 if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) {
1639 if (PrintGCDetails && Verbose) {
1640 gclog_or_tty->print(" %s: collect because expanded for allocation ",
1641 short_name());
1642 }
1643 return true;
1644 }
1645 if (_cmsSpace->should_concurrent_collect()) {
1646 if (PrintGCDetails && Verbose) {
1647 gclog_or_tty->print(" %s: collect because cmsSpace says so ",
1648 short_name());
1649 }
1650 return true;
1651 }
1652 return false;
1653 }
1654
1655 void ConcurrentMarkSweepGeneration::collect(bool full,
1656 bool clear_all_soft_refs,
1657 size_t size,
1658 bool tlab)
1659 {
1660 collector()->collect(full, clear_all_soft_refs, size, tlab);
1661 }
1662
1663 void CMSCollector::collect(bool full,
1664 bool clear_all_soft_refs,
1665 size_t size,
1666 bool tlab)
1667 {
1668 if (!UseCMSCollectionPassing && _collectorState > Idling) {
1669 // For debugging purposes skip the collection if the state
1670 // is not currently idle
1671 if (TraceCMSState) {
1672 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " skipped full:%d CMS state %d",
1673 Thread::current(), full, _collectorState);
1674 }
1675 return;
1676 }
1677
1678 // The following "if" branch is present for defensive reasons.
1679 // In the current uses of this interface, it can be replaced with:
1680 // assert(!GC_locker.is_active(), "Can't be called otherwise");
1681 // But I am not placing that assert here to allow future
1682 // generality in invoking this interface.
1683 if (GC_locker::is_active()) {
1684 // A consistency test for GC_locker
1685 assert(GC_locker::needs_gc(), "Should have been set already");
1686 // Skip this foreground collection, instead
1687 // expanding the heap if necessary.
1688 // Need the free list locks for the call to free() in compute_new_size()
1689 compute_new_size();
1690 return;
1691 }
1692 acquire_control_and_collect(full, clear_all_soft_refs);
1693 _full_gcs_since_conc_gc++;
1694
1695 }
1696
1697 void CMSCollector::request_full_gc(unsigned int full_gc_count) {
1698 GenCollectedHeap* gch = GenCollectedHeap::heap();
1699 unsigned int gc_count = gch->total_full_collections();
1700 if (gc_count == full_gc_count) {
1701 MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag);
1702 _full_gc_requested = true;
1703 CGC_lock->notify(); // nudge CMS thread
1704 }
1705 }
1706
1707
1708 // The foreground and background collectors need to coordinate in order
1709 // to make sure that they do not mutually interfere with CMS collections.
1710 // When a background collection is active,
1711 // the foreground collector may need to take over (preempt) and
1712 // synchronously complete an ongoing collection. Depending on the
1713 // frequency of the background collections and the heap usage
1714 // of the application, this preemption can be seldom or frequent.
1715 // There are only certain
1716 // points in the background collection that the "collection-baton"
1717 // can be passed to the foreground collector.
1718 //
1719 // The foreground collector will wait for the baton before
1720 // starting any part of the collection. The foreground collector
1721 // will only wait at one location.
1722 //
1723 // The background collector will yield the baton before starting a new
1724 // phase of the collection (e.g., before initial marking, marking from roots,
1725 // precleaning, final re-mark, sweep etc.) This is normally done at the head
1726 // of the loop which switches the phases. The background collector does some
1727 // of the phases (initial mark, final re-mark) with the world stopped.
1728 // Because of locking involved in stopping the world,
1729 // the foreground collector should not block waiting for the background
1730 // collector when it is doing a stop-the-world phase. The background
1731 // collector will yield the baton at an additional point just before
1732 // it enters a stop-the-world phase. Once the world is stopped, the
1733 // background collector checks the phase of the collection. If the
1734 // phase has not changed, it proceeds with the collection. If the
1735 // phase has changed, it skips that phase of the collection. See
1736 // the comments on the use of the Heap_lock in collect_in_background().
1737 //
1738 // Variable used in baton passing.
1739 // _foregroundGCIsActive - Set to true by the foreground collector when
1740 // it wants the baton. The foreground clears it when it has finished
1741 // the collection.
1742 // _foregroundGCShouldWait - Set to true by the background collector
1743 // when it is running. The foreground collector waits while
1744 // _foregroundGCShouldWait is true.
1745 // CGC_lock - monitor used to protect access to the above variables
1746 // and to notify the foreground and background collectors.
1747 // _collectorState - current state of the CMS collection.
1748 //
1749 // The foreground collector
1750 // acquires the CGC_lock
1751 // sets _foregroundGCIsActive
1752 // waits on the CGC_lock for _foregroundGCShouldWait to be false
1753 // various locks acquired in preparation for the collection
1754 // are released so as not to block the background collector
1755 // that is in the midst of a collection
1756 // proceeds with the collection
1757 // clears _foregroundGCIsActive
1758 // returns
1759 //
1760 // The background collector in a loop iterating on the phases of the
1761 // collection
1762 // acquires the CGC_lock
1763 // sets _foregroundGCShouldWait
1764 // if _foregroundGCIsActive is set
1765 // clears _foregroundGCShouldWait, notifies _CGC_lock
1766 // waits on _CGC_lock for _foregroundGCIsActive to become false
1767 // and exits the loop.
1768 // otherwise
1769 // proceed with that phase of the collection
1770 // if the phase is a stop-the-world phase,
1771 // yield the baton once more just before enqueueing
1772 // the stop-world CMS operation (executed by the VM thread).
1773 // returns after all phases of the collection are done
1774 //
1775
1776 void CMSCollector::acquire_control_and_collect(bool full,
1777 bool clear_all_soft_refs) {
1778 assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
1779 assert(!Thread::current()->is_ConcurrentGC_thread(),
1780 "shouldn't try to acquire control from self!");
1781
1782 // Start the protocol for acquiring control of the
1783 // collection from the background collector (aka CMS thread).
1784 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1785 "VM thread should have CMS token");
1786 // Remember the possibly interrupted state of an ongoing
1787 // concurrent collection
1788 CollectorState first_state = _collectorState;
1789
1790 // Signal to a possibly ongoing concurrent collection that
1791 // we want to do a foreground collection.
1792 _foregroundGCIsActive = true;
1793
1794 // Disable incremental mode during a foreground collection.
1795 ICMSDisabler icms_disabler;
1796
1797 // release locks and wait for a notify from the background collector
1798 // releasing the locks in only necessary for phases which
1799 // do yields to improve the granularity of the collection.
1800 assert_lock_strong(bitMapLock());
1801 // We need to lock the Free list lock for the space that we are
1802 // currently collecting.
1803 assert(haveFreelistLocks(), "Must be holding free list locks");
1804 bitMapLock()->unlock();
1805 releaseFreelistLocks();
1806 {
1807 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1808 if (_foregroundGCShouldWait) {
1809 // We are going to be waiting for action for the CMS thread;
1810 // it had better not be gone (for instance at shutdown)!
1811 assert(ConcurrentMarkSweepThread::cmst() != NULL,
1812 "CMS thread must be running");
1813 // Wait here until the background collector gives us the go-ahead
1814 ConcurrentMarkSweepThread::clear_CMS_flag(
1815 ConcurrentMarkSweepThread::CMS_vm_has_token); // release token
1816 // Get a possibly blocked CMS thread going:
1817 // Note that we set _foregroundGCIsActive true above,
1818 // without protection of the CGC_lock.
1819 CGC_lock->notify();
1820 assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(),
1821 "Possible deadlock");
1822 while (_foregroundGCShouldWait) {
1823 // wait for notification
1824 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1825 // Possibility of delay/starvation here, since CMS token does
1826 // not know to give priority to VM thread? Actually, i think
1827 // there wouldn't be any delay/starvation, but the proof of
1828 // that "fact" (?) appears non-trivial. XXX 20011219YSR
1829 }
1830 ConcurrentMarkSweepThread::set_CMS_flag(
1831 ConcurrentMarkSweepThread::CMS_vm_has_token);
1832 }
1833 }
1834 // The CMS_token is already held. Get back the other locks.
1835 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1836 "VM thread should have CMS token");
1837 getFreelistLocks();
1838 bitMapLock()->lock_without_safepoint_check();
1839 if (TraceCMSState) {
1840 gclog_or_tty->print_cr("CMS foreground collector has asked for control "
1841 INTPTR_FORMAT " with first state %d", Thread::current(), first_state);
1842 gclog_or_tty->print_cr(" gets control with state %d", _collectorState);
1843 }
1844
1845 // Check if we need to do a compaction, or if not, whether
1846 // we need to start the mark-sweep from scratch.
1847 bool should_compact = false;
1848 bool should_start_over = false;
1849 decide_foreground_collection_type(clear_all_soft_refs,
1850 &should_compact, &should_start_over);
1851
1852 NOT_PRODUCT(
1853 if (RotateCMSCollectionTypes) {
1854 if (_cmsGen->debug_collection_type() ==
1855 ConcurrentMarkSweepGeneration::MSC_foreground_collection_type) {
1856 should_compact = true;
1857 } else if (_cmsGen->debug_collection_type() ==
1858 ConcurrentMarkSweepGeneration::MS_foreground_collection_type) {
1859 should_compact = false;
1860 }
1861 }
1862 )
1863
1864 if (PrintGCDetails && first_state > Idling) {
1865 GCCause::Cause cause = GenCollectedHeap::heap()->gc_cause();
1866 if (GCCause::is_user_requested_gc(cause) ||
1867 GCCause::is_serviceability_requested_gc(cause)) {
1868 gclog_or_tty->print(" (concurrent mode interrupted)");
1869 } else {
1870 gclog_or_tty->print(" (concurrent mode failure)");
1871 }
1872 }
1873
1874 if (should_compact) {
1875 // If the collection is being acquired from the background
1876 // collector, there may be references on the discovered
1877 // references lists that have NULL referents (being those
1878 // that were concurrently cleared by a mutator) or
1879 // that are no longer active (having been enqueued concurrently
1880 // by the mutator).
1881 // Scrub the list of those references because Mark-Sweep-Compact
1882 // code assumes referents are not NULL and that all discovered
1883 // Reference objects are active.
1884 ref_processor()->clean_up_discovered_references();
1885
1886 do_compaction_work(clear_all_soft_refs);
1887
1888 // Has the GC time limit been exceeded?
1889 DefNewGeneration* young_gen = _young_gen->as_DefNewGeneration();
1890 size_t max_eden_size = young_gen->max_capacity() -
1891 young_gen->to()->capacity() -
1892 young_gen->from()->capacity();
1893 GenCollectedHeap* gch = GenCollectedHeap::heap();
1894 GCCause::Cause gc_cause = gch->gc_cause();
1895 size_policy()->check_gc_overhead_limit(_young_gen->used(),
1896 young_gen->eden()->used(),
1897 _cmsGen->max_capacity(),
1898 max_eden_size,
1899 full,
1900 gc_cause,
1901 gch->collector_policy());
1902 } else {
1903 do_mark_sweep_work(clear_all_soft_refs, first_state,
1904 should_start_over);
1905 }
1906 // Reset the expansion cause, now that we just completed
1907 // a collection cycle.
1908 clear_expansion_cause();
1909 _foregroundGCIsActive = false;
1910 return;
1911 }
1912
1913 // Resize the perm generation and the tenured generation
1914 // after obtaining the free list locks for the
1915 // two generations.
1916 void CMSCollector::compute_new_size() {
1917 assert_locked_or_safepoint(Heap_lock);
1918 FreelistLocker z(this);
1919 _permGen->compute_new_size();
1920 _cmsGen->compute_new_size();
1921 }
1922
1923 // A work method used by foreground collection to determine
1924 // what type of collection (compacting or not, continuing or fresh)
1925 // it should do.
1926 // NOTE: the intent is to make UseCMSCompactAtFullCollection
1927 // and CMSCompactWhenClearAllSoftRefs the default in the future
1928 // and do away with the flags after a suitable period.
1929 void CMSCollector::decide_foreground_collection_type(
1930 bool clear_all_soft_refs, bool* should_compact,
1931 bool* should_start_over) {
1932 // Normally, we'll compact only if the UseCMSCompactAtFullCollection
1933 // flag is set, and we have either requested a System.gc() or
1934 // the number of full gc's since the last concurrent cycle
1935 // has exceeded the threshold set by CMSFullGCsBeforeCompaction,
1936 // or if an incremental collection has failed
1937 GenCollectedHeap* gch = GenCollectedHeap::heap();
1938 assert(gch->collector_policy()->is_two_generation_policy(),
1939 "You may want to check the correctness of the following");
1940 // Inform cms gen if this was due to partial collection failing.
1941 // The CMS gen may use this fact to determine its expansion policy.
1942 if (gch->incremental_collection_will_fail()) {
1943 assert(!_cmsGen->incremental_collection_failed(),
1944 "Should have been noticed, reacted to and cleared");
1945 _cmsGen->set_incremental_collection_failed();
1946 }
1947 *should_compact =
1948 UseCMSCompactAtFullCollection &&
1949 ((_full_gcs_since_conc_gc >= CMSFullGCsBeforeCompaction) ||
1950 GCCause::is_user_requested_gc(gch->gc_cause()) ||
1951 gch->incremental_collection_will_fail());
1952 *should_start_over = false;
1953 if (clear_all_soft_refs && !*should_compact) {
1954 // We are about to do a last ditch collection attempt
1955 // so it would normally make sense to do a compaction
1956 // to reclaim as much space as possible.
1957 if (CMSCompactWhenClearAllSoftRefs) {
1958 // Default: The rationale is that in this case either
1959 // we are past the final marking phase, in which case
1960 // we'd have to start over, or so little has been done
1961 // that there's little point in saving that work. Compaction
1962 // appears to be the sensible choice in either case.
1963 *should_compact = true;
1964 } else {
1965 // We have been asked to clear all soft refs, but not to
1966 // compact. Make sure that we aren't past the final checkpoint
1967 // phase, for that is where we process soft refs. If we are already
1968 // past that phase, we'll need to redo the refs discovery phase and
1969 // if necessary clear soft refs that weren't previously
1970 // cleared. We do so by remembering the phase in which
1971 // we came in, and if we are past the refs processing
1972 // phase, we'll choose to just redo the mark-sweep
1973 // collection from scratch.
1974 if (_collectorState > FinalMarking) {
1975 // We are past the refs processing phase;
1976 // start over and do a fresh synchronous CMS cycle
1977 _collectorState = Resetting; // skip to reset to start new cycle
1978 reset(false /* == !asynch */);
1979 *should_start_over = true;
1980 } // else we can continue a possibly ongoing current cycle
1981 }
1982 }
1983 }
1984
1985 // A work method used by the foreground collector to do
1986 // a mark-sweep-compact.
1987 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) {
1988 GenCollectedHeap* gch = GenCollectedHeap::heap();
1989 TraceTime t("CMS:MSC ", PrintGCDetails && Verbose, true, gclog_or_tty);
1990 if (PrintGC && Verbose && !(GCCause::is_user_requested_gc(gch->gc_cause()))) {
1991 gclog_or_tty->print_cr("Compact ConcurrentMarkSweepGeneration after %d "
1992 "collections passed to foreground collector", _full_gcs_since_conc_gc);
1993 }
1994
1995 // Sample collection interval time and reset for collection pause.
1996 if (UseAdaptiveSizePolicy) {
1997 size_policy()->msc_collection_begin();
1998 }
1999
2000 // Temporarily widen the span of the weak reference processing to
2001 // the entire heap.
2002 MemRegion new_span(GenCollectedHeap::heap()->reserved_region());
2003 ReferenceProcessorSpanMutator x(ref_processor(), new_span);
2004
2005 // Temporarily, clear the "is_alive_non_header" field of the
2006 // reference processor.
2007 ReferenceProcessorIsAliveMutator y(ref_processor(), NULL);
2008
2009 // Temporarily make reference _processing_ single threaded (non-MT).
2010 ReferenceProcessorMTProcMutator z(ref_processor(), false);
2011
2012 // Temporarily make refs discovery atomic
2013 ReferenceProcessorAtomicMutator w(ref_processor(), true);
2014
2015 ref_processor()->set_enqueuing_is_done(false);
2016 ref_processor()->enable_discovery();
2017 ref_processor()->setup_policy(clear_all_soft_refs);
2018 // If an asynchronous collection finishes, the _modUnionTable is
2019 // all clear. If we are assuming the collection from an asynchronous
2020 // collection, clear the _modUnionTable.
2021 assert(_collectorState != Idling || _modUnionTable.isAllClear(),
2022 "_modUnionTable should be clear if the baton was not passed");
2023 _modUnionTable.clear_all();
2024
2025 // We must adjust the allocation statistics being maintained
2026 // in the free list space. We do so by reading and clearing
2027 // the sweep timer and updating the block flux rate estimates below.
2028 assert(!_intra_sweep_timer.is_active(), "_intra_sweep_timer should be inactive");
2029 if (_inter_sweep_timer.is_active()) {
2030 _inter_sweep_timer.stop();
2031 // Note that we do not use this sample to update the _inter_sweep_estimate.
2032 _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
2033 _inter_sweep_estimate.padded_average(),
2034 _intra_sweep_estimate.padded_average());
2035 }
2036
2037 {
2038 TraceCMSMemoryManagerStats();
2039 }
2040 GenMarkSweep::invoke_at_safepoint(_cmsGen->level(),
2041 ref_processor(), clear_all_soft_refs);
2042 #ifdef ASSERT
2043 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
2044 size_t free_size = cms_space->free();
2045 assert(free_size ==
2046 pointer_delta(cms_space->end(), cms_space->compaction_top())
2047 * HeapWordSize,
2048 "All the free space should be compacted into one chunk at top");
2049 assert(cms_space->dictionary()->totalChunkSize(
2050 debug_only(cms_space->freelistLock())) == 0 ||
2051 cms_space->totalSizeInIndexedFreeLists() == 0,
2052 "All the free space should be in a single chunk");
2053 size_t num = cms_space->totalCount();
2054 assert((free_size == 0 && num == 0) ||
2055 (free_size > 0 && (num == 1 || num == 2)),
2056 "There should be at most 2 free chunks after compaction");
2057 #endif // ASSERT
2058 _collectorState = Resetting;
2059 assert(_restart_addr == NULL,
2060 "Should have been NULL'd before baton was passed");
2061 reset(false /* == !asynch */);
2062 _cmsGen->reset_after_compaction();
2063 _concurrent_cycles_since_last_unload = 0;
2064
2065 if (verifying() && !should_unload_classes()) {
2066 perm_gen_verify_bit_map()->clear_all();
2067 }
2068
2069 // Clear any data recorded in the PLAB chunk arrays.
2070 if (_survivor_plab_array != NULL) {
2071 reset_survivor_plab_arrays();
2072 }
2073
2074 // Adjust the per-size allocation stats for the next epoch.
2075 _cmsGen->cmsSpace()->endSweepFLCensus(sweep_count() /* fake */);
2076 // Restart the "inter sweep timer" for the next epoch.
2077 _inter_sweep_timer.reset();
2078 _inter_sweep_timer.start();
2079
2080 // Sample collection pause time and reset for collection interval.
2081 if (UseAdaptiveSizePolicy) {
2082 size_policy()->msc_collection_end(gch->gc_cause());
2083 }
2084
2085 // For a mark-sweep-compact, compute_new_size() will be called
2086 // in the heap's do_collection() method.
2087 }
2088
2089 // A work method used by the foreground collector to do
2090 // a mark-sweep, after taking over from a possibly on-going
2091 // concurrent mark-sweep collection.
2092 void CMSCollector::do_mark_sweep_work(bool clear_all_soft_refs,
2093 CollectorState first_state, bool should_start_over) {
2094 if (PrintGC && Verbose) {
2095 gclog_or_tty->print_cr("Pass concurrent collection to foreground "
2096 "collector with count %d",
2097 _full_gcs_since_conc_gc);
2098 }
2099 switch (_collectorState) {
2100 case Idling:
2101 if (first_state == Idling || should_start_over) {
2102 // The background GC was not active, or should
2103 // restarted from scratch; start the cycle.
2104 _collectorState = InitialMarking;
2105 }
2106 // If first_state was not Idling, then a background GC
2107 // was in progress and has now finished. No need to do it
2108 // again. Leave the state as Idling.
2109 break;
2110 case Precleaning:
2111 // In the foreground case don't do the precleaning since
2112 // it is not done concurrently and there is extra work
2113 // required.
2114 _collectorState = FinalMarking;
2115 }
2116 if (PrintGCDetails &&
2117 (_collectorState > Idling ||
2118 !GCCause::is_user_requested_gc(GenCollectedHeap::heap()->gc_cause()))) {
2119 gclog_or_tty->print(" (concurrent mode failure)");
2120 }
2121 collect_in_foreground(clear_all_soft_refs);
2122
2123 // For a mark-sweep, compute_new_size() will be called
2124 // in the heap's do_collection() method.
2125 }
2126
2127
2128 void CMSCollector::getFreelistLocks() const {
2129 // Get locks for all free lists in all generations that this
2130 // collector is responsible for
2131 _cmsGen->freelistLock()->lock_without_safepoint_check();
2132 _permGen->freelistLock()->lock_without_safepoint_check();
2133 }
2134
2135 void CMSCollector::releaseFreelistLocks() const {
2136 // Release locks for all free lists in all generations that this
2137 // collector is responsible for
2138 _cmsGen->freelistLock()->unlock();
2139 _permGen->freelistLock()->unlock();
2140 }
2141
2142 bool CMSCollector::haveFreelistLocks() const {
2143 // Check locks for all free lists in all generations that this
2144 // collector is responsible for
2145 assert_lock_strong(_cmsGen->freelistLock());
2146 assert_lock_strong(_permGen->freelistLock());
2147 PRODUCT_ONLY(ShouldNotReachHere());
2148 return true;
2149 }
2150
2151 // A utility class that is used by the CMS collector to
2152 // temporarily "release" the foreground collector from its
2153 // usual obligation to wait for the background collector to
2154 // complete an ongoing phase before proceeding.
2155 class ReleaseForegroundGC: public StackObj {
2156 private:
2157 CMSCollector* _c;
2158 public:
2159 ReleaseForegroundGC(CMSCollector* c) : _c(c) {
2160 assert(_c->_foregroundGCShouldWait, "Else should not need to call");
2161 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2162 // allow a potentially blocked foreground collector to proceed
2163 _c->_foregroundGCShouldWait = false;
2164 if (_c->_foregroundGCIsActive) {
2165 CGC_lock->notify();
2166 }
2167 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2168 "Possible deadlock");
2169 }
2170
2171 ~ReleaseForegroundGC() {
2172 assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?");
2173 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2174 _c->_foregroundGCShouldWait = true;
2175 }
2176 };
2177
2178 // There are separate collect_in_background and collect_in_foreground because of
2179 // the different locking requirements of the background collector and the
2180 // foreground collector. There was originally an attempt to share
2181 // one "collect" method between the background collector and the foreground
2182 // collector but the if-then-else required made it cleaner to have
2183 // separate methods.
2184 void CMSCollector::collect_in_background(bool clear_all_soft_refs) {
2185 assert(Thread::current()->is_ConcurrentGC_thread(),
2186 "A CMS asynchronous collection is only allowed on a CMS thread.");
2187
2188 GenCollectedHeap* gch = GenCollectedHeap::heap();
2189 {
2190 bool safepoint_check = Mutex::_no_safepoint_check_flag;
2191 MutexLockerEx hl(Heap_lock, safepoint_check);
2192 FreelistLocker fll(this);
2193 MutexLockerEx x(CGC_lock, safepoint_check);
2194 if (_foregroundGCIsActive || !UseAsyncConcMarkSweepGC) {
2195 // The foreground collector is active or we're
2196 // not using asynchronous collections. Skip this
2197 // background collection.
2198 assert(!_foregroundGCShouldWait, "Should be clear");
2199 return;
2200 } else {
2201 assert(_collectorState == Idling, "Should be idling before start.");
2202 _collectorState = InitialMarking;
2203 // Reset the expansion cause, now that we are about to begin
2204 // a new cycle.
2205 clear_expansion_cause();
2206 }
2207 // Decide if we want to enable class unloading as part of the
2208 // ensuing concurrent GC cycle.
2209 update_should_unload_classes();
2210 _full_gc_requested = false; // acks all outstanding full gc requests
2211 // Signal that we are about to start a collection
2212 gch->increment_total_full_collections(); // ... starting a collection cycle
2213 _collection_count_start = gch->total_full_collections();
2214 }
2215
2216 // Used for PrintGC
2217 size_t prev_used;
2218 if (PrintGC && Verbose) {
2219 prev_used = _cmsGen->used(); // XXXPERM
2220 }
2221
2222 // The change of the collection state is normally done at this level;
2223 // the exceptions are phases that are executed while the world is
2224 // stopped. For those phases the change of state is done while the
2225 // world is stopped. For baton passing purposes this allows the
2226 // background collector to finish the phase and change state atomically.
2227 // The foreground collector cannot wait on a phase that is done
2228 // while the world is stopped because the foreground collector already
2229 // has the world stopped and would deadlock.
2230 while (_collectorState != Idling) {
2231 if (TraceCMSState) {
2232 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
2233 Thread::current(), _collectorState);
2234 }
2235 // The foreground collector
2236 // holds the Heap_lock throughout its collection.
2237 // holds the CMS token (but not the lock)
2238 // except while it is waiting for the background collector to yield.
2239 //
2240 // The foreground collector should be blocked (not for long)
2241 // if the background collector is about to start a phase
2242 // executed with world stopped. If the background
2243 // collector has already started such a phase, the
2244 // foreground collector is blocked waiting for the
2245 // Heap_lock. The stop-world phases (InitialMarking and FinalMarking)
2246 // are executed in the VM thread.
2247 //
2248 // The locking order is
2249 // PendingListLock (PLL) -- if applicable (FinalMarking)
2250 // Heap_lock (both this & PLL locked in VM_CMS_Operation::prologue())
2251 // CMS token (claimed in
2252 // stop_world_and_do() -->
2253 // safepoint_synchronize() -->
2254 // CMSThread::synchronize())
2255
2256 {
2257 // Check if the FG collector wants us to yield.
2258 CMSTokenSync x(true); // is cms thread
2259 if (waitForForegroundGC()) {
2260 // We yielded to a foreground GC, nothing more to be
2261 // done this round.
2262 assert(_foregroundGCShouldWait == false, "We set it to false in "
2263 "waitForForegroundGC()");
2264 if (TraceCMSState) {
2265 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2266 " exiting collection CMS state %d",
2267 Thread::current(), _collectorState);
2268 }
2269 return;
2270 } else {
2271 // The background collector can run but check to see if the
2272 // foreground collector has done a collection while the
2273 // background collector was waiting to get the CGC_lock
2274 // above. If yes, break so that _foregroundGCShouldWait
2275 // is cleared before returning.
2276 if (_collectorState == Idling) {
2277 break;
2278 }
2279 }
2280 }
2281
2282 assert(_foregroundGCShouldWait, "Foreground collector, if active, "
2283 "should be waiting");
2284
2285 switch (_collectorState) {
2286 case InitialMarking:
2287 {
2288 ReleaseForegroundGC x(this);
2289 stats().record_cms_begin();
2290
2291 VM_CMS_Initial_Mark initial_mark_op(this);
2292 VMThread::execute(&initial_mark_op);
2293 }
2294 // The collector state may be any legal state at this point
2295 // since the background collector may have yielded to the
2296 // foreground collector.
2297 break;
2298 case Marking:
2299 // initial marking in checkpointRootsInitialWork has been completed
2300 if (markFromRoots(true)) { // we were successful
2301 assert(_collectorState == Precleaning, "Collector state should "
2302 "have changed");
2303 } else {
2304 assert(_foregroundGCIsActive, "Internal state inconsistency");
2305 }
2306 break;
2307 case Precleaning:
2308 if (UseAdaptiveSizePolicy) {
2309 size_policy()->concurrent_precleaning_begin();
2310 }
2311 // marking from roots in markFromRoots has been completed
2312 preclean();
2313 if (UseAdaptiveSizePolicy) {
2314 size_policy()->concurrent_precleaning_end();
2315 }
2316 assert(_collectorState == AbortablePreclean ||
2317 _collectorState == FinalMarking,
2318 "Collector state should have changed");
2319 break;
2320 case AbortablePreclean:
2321 if (UseAdaptiveSizePolicy) {
2322 size_policy()->concurrent_phases_resume();
2323 }
2324 abortable_preclean();
2325 if (UseAdaptiveSizePolicy) {
2326 size_policy()->concurrent_precleaning_end();
2327 }
2328 assert(_collectorState == FinalMarking, "Collector state should "
2329 "have changed");
2330 break;
2331 case FinalMarking:
2332 {
2333 ReleaseForegroundGC x(this);
2334
2335 VM_CMS_Final_Remark final_remark_op(this);
2336 VMThread::execute(&final_remark_op);
2337 }
2338 assert(_foregroundGCShouldWait, "block post-condition");
2339 break;
2340 case Sweeping:
2341 if (UseAdaptiveSizePolicy) {
2342 size_policy()->concurrent_sweeping_begin();
2343 }
2344 // final marking in checkpointRootsFinal has been completed
2345 sweep(true);
2346 assert(_collectorState == Resizing, "Collector state change "
2347 "to Resizing must be done under the free_list_lock");
2348 _full_gcs_since_conc_gc = 0;
2349
2350 // Stop the timers for adaptive size policy for the concurrent phases
2351 if (UseAdaptiveSizePolicy) {
2352 size_policy()->concurrent_sweeping_end();
2353 size_policy()->concurrent_phases_end(gch->gc_cause(),
2354 gch->prev_gen(_cmsGen)->capacity(),
2355 _cmsGen->free());
2356 }
2357
2358 case Resizing: {
2359 // Sweeping has been completed...
2360 // At this point the background collection has completed.
2361 // Don't move the call to compute_new_size() down
2362 // into code that might be executed if the background
2363 // collection was preempted.
2364 {
2365 ReleaseForegroundGC x(this); // unblock FG collection
2366 MutexLockerEx y(Heap_lock, Mutex::_no_safepoint_check_flag);
2367 CMSTokenSync z(true); // not strictly needed.
2368 if (_collectorState == Resizing) {
2369 compute_new_size();
2370 _collectorState = Resetting;
2371 } else {
2372 assert(_collectorState == Idling, "The state should only change"
2373 " because the foreground collector has finished the collection");
2374 }
2375 }
2376 break;
2377 }
2378 case Resetting:
2379 // CMS heap resizing has been completed
2380 reset(true);
2381 assert(_collectorState == Idling, "Collector state should "
2382 "have changed");
2383 stats().record_cms_end();
2384 // Don't move the concurrent_phases_end() and compute_new_size()
2385 // calls to here because a preempted background collection
2386 // has it's state set to "Resetting".
2387 break;
2388 case Idling:
2389 default:
2390 ShouldNotReachHere();
2391 break;
2392 }
2393 if (TraceCMSState) {
2394 gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d",
2395 Thread::current(), _collectorState);
2396 }
2397 assert(_foregroundGCShouldWait, "block post-condition");
2398 }
2399
2400 // Should this be in gc_epilogue?
2401 collector_policy()->counters()->update_counters();
2402
2403 {
2404 // Clear _foregroundGCShouldWait and, in the event that the
2405 // foreground collector is waiting, notify it, before
2406 // returning.
2407 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2408 _foregroundGCShouldWait = false;
2409 if (_foregroundGCIsActive) {
2410 CGC_lock->notify();
2411 }
2412 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2413 "Possible deadlock");
2414 }
2415 if (TraceCMSState) {
2416 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2417 " exiting collection CMS state %d",
2418 Thread::current(), _collectorState);
2419 }
2420 if (PrintGC && Verbose) {
2421 _cmsGen->print_heap_change(prev_used);
2422 }
2423 }
2424
2425 void CMSCollector::collect_in_foreground(bool clear_all_soft_refs) {
2426 assert(_foregroundGCIsActive && !_foregroundGCShouldWait,
2427 "Foreground collector should be waiting, not executing");
2428 assert(Thread::current()->is_VM_thread(), "A foreground collection"
2429 "may only be done by the VM Thread with the world stopped");
2430 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
2431 "VM thread should have CMS token");
2432
2433 NOT_PRODUCT(TraceTime t("CMS:MS (foreground) ", PrintGCDetails && Verbose,
2434 true, gclog_or_tty);)
2435 if (UseAdaptiveSizePolicy) {
2436 size_policy()->ms_collection_begin();
2437 }
2438 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact);
2439
2440 HandleMark hm; // Discard invalid handles created during verification
2441
2442 if (VerifyBeforeGC &&
2443 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2444 Universe::verify(true);
2445 }
2446
2447 // Snapshot the soft reference policy to be used in this collection cycle.
2448 ref_processor()->setup_policy(clear_all_soft_refs);
2449
2450 bool init_mark_was_synchronous = false; // until proven otherwise
2451 while (_collectorState != Idling) {
2452 if (TraceCMSState) {
2453 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
2454 Thread::current(), _collectorState);
2455 }
2456 switch (_collectorState) {
2457 case InitialMarking:
2458 init_mark_was_synchronous = true; // fact to be exploited in re-mark
2459 checkpointRootsInitial(false);
2460 assert(_collectorState == Marking, "Collector state should have changed"
2461 " within checkpointRootsInitial()");
2462 break;
2463 case Marking:
2464 // initial marking in checkpointRootsInitialWork has been completed
2465 if (VerifyDuringGC &&
2466 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2467 gclog_or_tty->print("Verify before initial mark: ");
2468 Universe::verify(true);
2469 }
2470 {
2471 bool res = markFromRoots(false);
2472 assert(res && _collectorState == FinalMarking, "Collector state should "
2473 "have changed");
2474 break;
2475 }
2476 case FinalMarking:
2477 if (VerifyDuringGC &&
2478 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2479 gclog_or_tty->print("Verify before re-mark: ");
2480 Universe::verify(true);
2481 }
2482 checkpointRootsFinal(false, clear_all_soft_refs,
2483 init_mark_was_synchronous);
2484 assert(_collectorState == Sweeping, "Collector state should not "
2485 "have changed within checkpointRootsFinal()");
2486 break;
2487 case Sweeping:
2488 // final marking in checkpointRootsFinal has been completed
2489 if (VerifyDuringGC &&
2490 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2491 gclog_or_tty->print("Verify before sweep: ");
2492 Universe::verify(true);
2493 }
2494 sweep(false);
2495 assert(_collectorState == Resizing, "Incorrect state");
2496 break;
2497 case Resizing: {
2498 // Sweeping has been completed; the actual resize in this case
2499 // is done separately; nothing to be done in this state.
2500 _collectorState = Resetting;
2501 break;
2502 }
2503 case Resetting:
2504 // The heap has been resized.
2505 if (VerifyDuringGC &&
2506 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2507 gclog_or_tty->print("Verify before reset: ");
2508 Universe::verify(true);
2509 }
2510 reset(false);
2511 assert(_collectorState == Idling, "Collector state should "
2512 "have changed");
2513 break;
2514 case Precleaning:
2515 case AbortablePreclean:
2516 // Elide the preclean phase
2517 _collectorState = FinalMarking;
2518 break;
2519 default:
2520 ShouldNotReachHere();
2521 }
2522 if (TraceCMSState) {
2523 gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d",
2524 Thread::current(), _collectorState);
2525 }
2526 }
2527
2528 if (UseAdaptiveSizePolicy) {
2529 GenCollectedHeap* gch = GenCollectedHeap::heap();
2530 size_policy()->ms_collection_end(gch->gc_cause());
2531 }
2532
2533 if (VerifyAfterGC &&
2534 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2535 Universe::verify(true);
2536 }
2537 if (TraceCMSState) {
2538 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2539 " exiting collection CMS state %d",
2540 Thread::current(), _collectorState);
2541 }
2542 }
2543
2544 bool CMSCollector::waitForForegroundGC() {
2545 bool res = false;
2546 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2547 "CMS thread should have CMS token");
2548 // Block the foreground collector until the
2549 // background collectors decides whether to
2550 // yield.
2551 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2552 _foregroundGCShouldWait = true;
2553 if (_foregroundGCIsActive) {
2554 // The background collector yields to the
2555 // foreground collector and returns a value
2556 // indicating that it has yielded. The foreground
2557 // collector can proceed.
2558 res = true;
2559 _foregroundGCShouldWait = false;
2560 ConcurrentMarkSweepThread::clear_CMS_flag(
2561 ConcurrentMarkSweepThread::CMS_cms_has_token);
2562 ConcurrentMarkSweepThread::set_CMS_flag(
2563 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2564 // Get a possibly blocked foreground thread going
2565 CGC_lock->notify();
2566 if (TraceCMSState) {
2567 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d",
2568 Thread::current(), _collectorState);
2569 }
2570 while (_foregroundGCIsActive) {
2571 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
2572 }
2573 ConcurrentMarkSweepThread::set_CMS_flag(
2574 ConcurrentMarkSweepThread::CMS_cms_has_token);
2575 ConcurrentMarkSweepThread::clear_CMS_flag(
2576 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2577 }
2578 if (TraceCMSState) {
2579 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d",
2580 Thread::current(), _collectorState);
2581 }
2582 return res;
2583 }
2584
2585 // Because of the need to lock the free lists and other structures in
2586 // the collector, common to all the generations that the collector is
2587 // collecting, we need the gc_prologues of individual CMS generations
2588 // delegate to their collector. It may have been simpler had the
2589 // current infrastructure allowed one to call a prologue on a
2590 // collector. In the absence of that we have the generation's
2591 // prologue delegate to the collector, which delegates back
2592 // some "local" work to a worker method in the individual generations
2593 // that it's responsible for collecting, while itself doing any
2594 // work common to all generations it's responsible for. A similar
2595 // comment applies to the gc_epilogue()'s.
2596 // The role of the varaible _between_prologue_and_epilogue is to
2597 // enforce the invocation protocol.
2598 void CMSCollector::gc_prologue(bool full) {
2599 // Call gc_prologue_work() for each CMSGen and PermGen that
2600 // we are responsible for.
2601
2602 // The following locking discipline assumes that we are only called
2603 // when the world is stopped.
2604 assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption");
2605
2606 // The CMSCollector prologue must call the gc_prologues for the
2607 // "generations" (including PermGen if any) that it's responsible
2608 // for.
2609
2610 assert( Thread::current()->is_VM_thread()
2611 || ( CMSScavengeBeforeRemark
2612 && Thread::current()->is_ConcurrentGC_thread()),
2613 "Incorrect thread type for prologue execution");
2614
2615 if (_between_prologue_and_epilogue) {
2616 // We have already been invoked; this is a gc_prologue delegation
2617 // from yet another CMS generation that we are responsible for, just
2618 // ignore it since all relevant work has already been done.
2619 return;
2620 }
2621
2622 // set a bit saying prologue has been called; cleared in epilogue
2623 _between_prologue_and_epilogue = true;
2624 // Claim locks for common data structures, then call gc_prologue_work()
2625 // for each CMSGen and PermGen that we are responsible for.
2626
2627 getFreelistLocks(); // gets free list locks on constituent spaces
2628 bitMapLock()->lock_without_safepoint_check();
2629
2630 // Should call gc_prologue_work() for all cms gens we are responsible for
2631 bool registerClosure = _collectorState >= Marking
2632 && _collectorState < Sweeping;
2633 ModUnionClosure* muc = CollectedHeap::use_parallel_gc_threads() ?
2634 &_modUnionClosurePar
2635 : &_modUnionClosure;
2636 _cmsGen->gc_prologue_work(full, registerClosure, muc);
2637 _permGen->gc_prologue_work(full, registerClosure, muc);
2638
2639 if (!full) {
2640 stats().record_gc0_begin();
2641 }
2642 }
2643
2644 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) {
2645 // Delegate to CMScollector which knows how to coordinate between
2646 // this and any other CMS generations that it is responsible for
2647 // collecting.
2648 collector()->gc_prologue(full);
2649 }
2650
2651 // This is a "private" interface for use by this generation's CMSCollector.
2652 // Not to be called directly by any other entity (for instance,
2653 // GenCollectedHeap, which calls the "public" gc_prologue method above).
2654 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full,
2655 bool registerClosure, ModUnionClosure* modUnionClosure) {
2656 assert(!incremental_collection_failed(), "Shouldn't be set yet");
2657 assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL,
2658 "Should be NULL");
2659 if (registerClosure) {
2660 cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure);
2661 }
2662 cmsSpace()->gc_prologue();
2663 // Clear stat counters
2664 NOT_PRODUCT(
2665 assert(_numObjectsPromoted == 0, "check");
2666 assert(_numWordsPromoted == 0, "check");
2667 if (Verbose && PrintGC) {
2668 gclog_or_tty->print("Allocated "SIZE_FORMAT" objects, "
2669 SIZE_FORMAT" bytes concurrently",
2670 _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord));
2671 }
2672 _numObjectsAllocated = 0;
2673 _numWordsAllocated = 0;
2674 )
2675 }
2676
2677 void CMSCollector::gc_epilogue(bool full) {
2678 // The following locking discipline assumes that we are only called
2679 // when the world is stopped.
2680 assert(SafepointSynchronize::is_at_safepoint(),
2681 "world is stopped assumption");
2682
2683 // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks
2684 // if linear allocation blocks need to be appropriately marked to allow the
2685 // the blocks to be parsable. We also check here whether we need to nudge the
2686 // CMS collector thread to start a new cycle (if it's not already active).
2687 assert( Thread::current()->is_VM_thread()
2688 || ( CMSScavengeBeforeRemark
2689 && Thread::current()->is_ConcurrentGC_thread()),
2690 "Incorrect thread type for epilogue execution");
2691
2692 if (!_between_prologue_and_epilogue) {
2693 // We have already been invoked; this is a gc_epilogue delegation
2694 // from yet another CMS generation that we are responsible for, just
2695 // ignore it since all relevant work has already been done.
2696 return;
2697 }
2698 assert(haveFreelistLocks(), "must have freelist locks");
2699 assert_lock_strong(bitMapLock());
2700
2701 _cmsGen->gc_epilogue_work(full);
2702 _permGen->gc_epilogue_work(full);
2703
2704 if (_collectorState == AbortablePreclean || _collectorState == Precleaning) {
2705 // in case sampling was not already enabled, enable it
2706 _start_sampling = true;
2707 }
2708 // reset _eden_chunk_array so sampling starts afresh
2709 _eden_chunk_index = 0;
2710
2711 size_t cms_used = _cmsGen->cmsSpace()->used();
2712 size_t perm_used = _permGen->cmsSpace()->used();
2713
2714 // update performance counters - this uses a special version of
2715 // update_counters() that allows the utilization to be passed as a
2716 // parameter, avoiding multiple calls to used().
2717 //
2718 _cmsGen->update_counters(cms_used);
2719 _permGen->update_counters(perm_used);
2720
2721 if (CMSIncrementalMode) {
2722 icms_update_allocation_limits();
2723 }
2724
2725 bitMapLock()->unlock();
2726 releaseFreelistLocks();
2727
2728 _between_prologue_and_epilogue = false; // ready for next cycle
2729 }
2730
2731 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) {
2732 collector()->gc_epilogue(full);
2733
2734 // Also reset promotion tracking in par gc thread states.
2735 if (CollectedHeap::use_parallel_gc_threads()) {
2736 for (uint i = 0; i < ParallelGCThreads; i++) {
2737 _par_gc_thread_states[i]->promo.stopTrackingPromotions(i);
2738 }
2739 }
2740 }
2741
2742 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2743 assert(!incremental_collection_failed(), "Should have been cleared");
2744 cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2745 cmsSpace()->gc_epilogue();
2746 // Print stat counters
2747 NOT_PRODUCT(
2748 assert(_numObjectsAllocated == 0, "check");
2749 assert(_numWordsAllocated == 0, "check");
2750 if (Verbose && PrintGC) {
2751 gclog_or_tty->print("Promoted "SIZE_FORMAT" objects, "
2752 SIZE_FORMAT" bytes",
2753 _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2754 }
2755 _numObjectsPromoted = 0;
2756 _numWordsPromoted = 0;
2757 )
2758
2759 if (PrintGC && Verbose) {
2760 // Call down the chain in contiguous_available needs the freelistLock
2761 // so print this out before releasing the freeListLock.
2762 gclog_or_tty->print(" Contiguous available "SIZE_FORMAT" bytes ",
2763 contiguous_available());
2764 }
2765 }
2766
2767 #ifndef PRODUCT
2768 bool CMSCollector::have_cms_token() {
2769 Thread* thr = Thread::current();
2770 if (thr->is_VM_thread()) {
2771 return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2772 } else if (thr->is_ConcurrentGC_thread()) {
2773 return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2774 } else if (thr->is_GC_task_thread()) {
2775 return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2776 ParGCRareEvent_lock->owned_by_self();
2777 }
2778 return false;
2779 }
2780 #endif
2781
2782 // Check reachability of the given heap address in CMS generation,
2783 // treating all other generations as roots.
2784 bool CMSCollector::is_cms_reachable(HeapWord* addr) {
2785 // We could "guarantee" below, rather than assert, but i'll
2786 // leave these as "asserts" so that an adventurous debugger
2787 // could try this in the product build provided some subset of
2788 // the conditions were met, provided they were intersted in the
2789 // results and knew that the computation below wouldn't interfere
2790 // with other concurrent computations mutating the structures
2791 // being read or written.
2792 assert(SafepointSynchronize::is_at_safepoint(),
2793 "Else mutations in object graph will make answer suspect");
2794 assert(have_cms_token(), "Should hold cms token");
2795 assert(haveFreelistLocks(), "must hold free list locks");
2796 assert_lock_strong(bitMapLock());
2797
2798 // Clear the marking bit map array before starting, but, just
2799 // for kicks, first report if the given address is already marked
2800 gclog_or_tty->print_cr("Start: Address 0x%x is%s marked", addr,
2801 _markBitMap.isMarked(addr) ? "" : " not");
2802
2803 if (verify_after_remark()) {
2804 MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2805 bool result = verification_mark_bm()->isMarked(addr);
2806 gclog_or_tty->print_cr("TransitiveMark: Address 0x%x %s marked", addr,
2807 result ? "IS" : "is NOT");
2808 return result;
2809 } else {
2810 gclog_or_tty->print_cr("Could not compute result");
2811 return false;
2812 }
2813 }
2814
2815 ////////////////////////////////////////////////////////
2816 // CMS Verification Support
2817 ////////////////////////////////////////////////////////
2818 // Following the remark phase, the following invariant
2819 // should hold -- each object in the CMS heap which is
2820 // marked in markBitMap() should be marked in the verification_mark_bm().
2821
2822 class VerifyMarkedClosure: public BitMapClosure {
2823 CMSBitMap* _marks;
2824 bool _failed;
2825
2826 public:
2827 VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2828
2829 bool do_bit(size_t offset) {
2830 HeapWord* addr = _marks->offsetToHeapWord(offset);
2831 if (!_marks->isMarked(addr)) {
2832 oop(addr)->print_on(gclog_or_tty);
2833 gclog_or_tty->print_cr(" ("INTPTR_FORMAT" should have been marked)", addr);
2834 _failed = true;
2835 }
2836 return true;
2837 }
2838
2839 bool failed() { return _failed; }
2840 };
2841
2842 bool CMSCollector::verify_after_remark() {
2843 gclog_or_tty->print(" [Verifying CMS Marking... ");
2844 MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2845 static bool init = false;
2846
2847 assert(SafepointSynchronize::is_at_safepoint(),
2848 "Else mutations in object graph will make answer suspect");
2849 assert(have_cms_token(),
2850 "Else there may be mutual interference in use of "
2851 " verification data structures");
2852 assert(_collectorState > Marking && _collectorState <= Sweeping,
2853 "Else marking info checked here may be obsolete");
2854 assert(haveFreelistLocks(), "must hold free list locks");
2855 assert_lock_strong(bitMapLock());
2856
2857
2858 // Allocate marking bit map if not already allocated
2859 if (!init) { // first time
2860 if (!verification_mark_bm()->allocate(_span)) {
2861 return false;
2862 }
2863 init = true;
2864 }
2865
2866 assert(verification_mark_stack()->isEmpty(), "Should be empty");
2867
2868 // Turn off refs discovery -- so we will be tracing through refs.
2869 // This is as intended, because by this time
2870 // GC must already have cleared any refs that need to be cleared,
2871 // and traced those that need to be marked; moreover,
2872 // the marking done here is not going to intefere in any
2873 // way with the marking information used by GC.
2874 NoRefDiscovery no_discovery(ref_processor());
2875
2876 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
2877
2878 // Clear any marks from a previous round
2879 verification_mark_bm()->clear_all();
2880 assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
2881 verify_work_stacks_empty();
2882
2883 GenCollectedHeap* gch = GenCollectedHeap::heap();
2884 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
2885 // Update the saved marks which may affect the root scans.
2886 gch->save_marks();
2887
2888 if (CMSRemarkVerifyVariant == 1) {
2889 // In this first variant of verification, we complete
2890 // all marking, then check if the new marks-verctor is
2891 // a subset of the CMS marks-vector.
2892 verify_after_remark_work_1();
2893 } else if (CMSRemarkVerifyVariant == 2) {
2894 // In this second variant of verification, we flag an error
2895 // (i.e. an object reachable in the new marks-vector not reachable
2896 // in the CMS marks-vector) immediately, also indicating the
2897 // identify of an object (A) that references the unmarked object (B) --
2898 // presumably, a mutation to A failed to be picked up by preclean/remark?
2899 verify_after_remark_work_2();
2900 } else {
2901 warning("Unrecognized value %d for CMSRemarkVerifyVariant",
2902 CMSRemarkVerifyVariant);
2903 }
2904 gclog_or_tty->print(" done] ");
2905 return true;
2906 }
2907
2908 void CMSCollector::verify_after_remark_work_1() {
2909 ResourceMark rm;
2910 HandleMark hm;
2911 GenCollectedHeap* gch = GenCollectedHeap::heap();
2912
2913 // Mark from roots one level into CMS
2914 MarkRefsIntoClosure notOlder(_span, verification_mark_bm());
2915 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2916
2917 gch->gen_process_strong_roots(_cmsGen->level(),
2918 true, // younger gens are roots
2919 true, // activate StrongRootsScope
2920 true, // collecting perm gen
2921 SharedHeap::ScanningOption(roots_scanning_options()),
2922 ¬Older,
2923 true, // walk code active on stacks
2924 NULL);
2925
2926 // Now mark from the roots
2927 assert(_revisitStack.isEmpty(), "Should be empty");
2928 MarkFromRootsClosure markFromRootsClosure(this, _span,
2929 verification_mark_bm(), verification_mark_stack(), &_revisitStack,
2930 false /* don't yield */, true /* verifying */);
2931 assert(_restart_addr == NULL, "Expected pre-condition");
2932 verification_mark_bm()->iterate(&markFromRootsClosure);
2933 while (_restart_addr != NULL) {
2934 // Deal with stack overflow: by restarting at the indicated
2935 // address.
2936 HeapWord* ra = _restart_addr;
2937 markFromRootsClosure.reset(ra);
2938 _restart_addr = NULL;
2939 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2940 }
2941 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2942 verify_work_stacks_empty();
2943 // Should reset the revisit stack above, since no class tree
2944 // surgery is forthcoming.
2945 _revisitStack.reset(); // throwing away all contents
2946
2947 // Marking completed -- now verify that each bit marked in
2948 // verification_mark_bm() is also marked in markBitMap(); flag all
2949 // errors by printing corresponding objects.
2950 VerifyMarkedClosure vcl(markBitMap());
2951 verification_mark_bm()->iterate(&vcl);
2952 if (vcl.failed()) {
2953 gclog_or_tty->print("Verification failed");
2954 Universe::heap()->print_on(gclog_or_tty);
2955 fatal("CMS: failed marking verification after remark");
2956 }
2957 }
2958
2959 void CMSCollector::verify_after_remark_work_2() {
2960 ResourceMark rm;
2961 HandleMark hm;
2962 GenCollectedHeap* gch = GenCollectedHeap::heap();
2963
2964 // Mark from roots one level into CMS
2965 MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
2966 markBitMap());
2967 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2968 gch->gen_process_strong_roots(_cmsGen->level(),
2969 true, // younger gens are roots
2970 true, // activate StrongRootsScope
2971 true, // collecting perm gen
2972 SharedHeap::ScanningOption(roots_scanning_options()),
2973 ¬Older,
2974 true, // walk code active on stacks
2975 NULL);
2976
2977 // Now mark from the roots
2978 assert(_revisitStack.isEmpty(), "Should be empty");
2979 MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
2980 verification_mark_bm(), markBitMap(), verification_mark_stack());
2981 assert(_restart_addr == NULL, "Expected pre-condition");
2982 verification_mark_bm()->iterate(&markFromRootsClosure);
2983 while (_restart_addr != NULL) {
2984 // Deal with stack overflow: by restarting at the indicated
2985 // address.
2986 HeapWord* ra = _restart_addr;
2987 markFromRootsClosure.reset(ra);
2988 _restart_addr = NULL;
2989 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2990 }
2991 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2992 verify_work_stacks_empty();
2993 // Should reset the revisit stack above, since no class tree
2994 // surgery is forthcoming.
2995 _revisitStack.reset(); // throwing away all contents
2996
2997 // Marking completed -- now verify that each bit marked in
2998 // verification_mark_bm() is also marked in markBitMap(); flag all
2999 // errors by printing corresponding objects.
3000 VerifyMarkedClosure vcl(markBitMap());
3001 verification_mark_bm()->iterate(&vcl);
3002 assert(!vcl.failed(), "Else verification above should not have succeeded");
3003 }
3004
3005 void ConcurrentMarkSweepGeneration::save_marks() {
3006 // delegate to CMS space
3007 cmsSpace()->save_marks();
3008 for (uint i = 0; i < ParallelGCThreads; i++) {
3009 _par_gc_thread_states[i]->promo.startTrackingPromotions();
3010 }
3011 }
3012
3013 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
3014 return cmsSpace()->no_allocs_since_save_marks();
3015 }
3016
3017 #define CMS_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix) \
3018 \
3019 void ConcurrentMarkSweepGeneration:: \
3020 oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) { \
3021 cl->set_generation(this); \
3022 cmsSpace()->oop_since_save_marks_iterate##nv_suffix(cl); \
3023 cl->reset_generation(); \
3024 save_marks(); \
3025 }
3026
3027 ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DEFN)
3028
3029 void
3030 ConcurrentMarkSweepGeneration::object_iterate_since_last_GC(ObjectClosure* blk)
3031 {
3032 // Not currently implemented; need to do the following. -- ysr.
3033 // dld -- I think that is used for some sort of allocation profiler. So it
3034 // really means the objects allocated by the mutator since the last
3035 // GC. We could potentially implement this cheaply by recording only
3036 // the direct allocations in a side data structure.
3037 //
3038 // I think we probably ought not to be required to support these
3039 // iterations at any arbitrary point; I think there ought to be some
3040 // call to enable/disable allocation profiling in a generation/space,
3041 // and the iterator ought to return the objects allocated in the
3042 // gen/space since the enable call, or the last iterator call (which
3043 // will probably be at a GC.) That way, for gens like CM&S that would
3044 // require some extra data structure to support this, we only pay the
3045 // cost when it's in use...
3046 cmsSpace()->object_iterate_since_last_GC(blk);
3047 }
3048
3049 void
3050 ConcurrentMarkSweepGeneration::younger_refs_iterate(OopsInGenClosure* cl) {
3051 cl->set_generation(this);
3052 younger_refs_in_space_iterate(_cmsSpace, cl);
3053 cl->reset_generation();
3054 }
3055
3056 void
3057 ConcurrentMarkSweepGeneration::oop_iterate(MemRegion mr, OopClosure* cl) {
3058 if (freelistLock()->owned_by_self()) {
3059 Generation::oop_iterate(mr, cl);
3060 } else {
3061 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3062 Generation::oop_iterate(mr, cl);
3063 }
3064 }
3065
3066 void
3067 ConcurrentMarkSweepGeneration::oop_iterate(OopClosure* cl) {
3068 if (freelistLock()->owned_by_self()) {
3069 Generation::oop_iterate(cl);
3070 } else {
3071 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3072 Generation::oop_iterate(cl);
3073 }
3074 }
3075
3076 void
3077 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
3078 if (freelistLock()->owned_by_self()) {
3079 Generation::object_iterate(cl);
3080 } else {
3081 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3082 Generation::object_iterate(cl);
3083 }
3084 }
3085
3086 void
3087 ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) {
3088 if (freelistLock()->owned_by_self()) {
3089 Generation::safe_object_iterate(cl);
3090 } else {
3091 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3092 Generation::safe_object_iterate(cl);
3093 }
3094 }
3095
3096 void
3097 ConcurrentMarkSweepGeneration::pre_adjust_pointers() {
3098 }
3099
3100 void
3101 ConcurrentMarkSweepGeneration::post_compact() {
3102 }
3103
3104 void
3105 ConcurrentMarkSweepGeneration::prepare_for_verify() {
3106 // Fix the linear allocation blocks to look like free blocks.
3107
3108 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
3109 // are not called when the heap is verified during universe initialization and
3110 // at vm shutdown.
3111 if (freelistLock()->owned_by_self()) {
3112 cmsSpace()->prepare_for_verify();
3113 } else {
3114 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
3115 cmsSpace()->prepare_for_verify();
3116 }
3117 }
3118
3119 void
3120 ConcurrentMarkSweepGeneration::verify(bool allow_dirty /* ignored */) {
3121 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
3122 // are not called when the heap is verified during universe initialization and
3123 // at vm shutdown.
3124 if (freelistLock()->owned_by_self()) {
3125 cmsSpace()->verify(false /* ignored */);
3126 } else {
3127 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
3128 cmsSpace()->verify(false /* ignored */);
3129 }
3130 }
3131
3132 void CMSCollector::verify(bool allow_dirty /* ignored */) {
3133 _cmsGen->verify(allow_dirty);
3134 _permGen->verify(allow_dirty);
3135 }
3136
3137 #ifndef PRODUCT
3138 bool CMSCollector::overflow_list_is_empty() const {
3139 assert(_num_par_pushes >= 0, "Inconsistency");
3140 if (_overflow_list == NULL) {
3141 assert(_num_par_pushes == 0, "Inconsistency");
3142 }
3143 return _overflow_list == NULL;
3144 }
3145
3146 // The methods verify_work_stacks_empty() and verify_overflow_empty()
3147 // merely consolidate assertion checks that appear to occur together frequently.
3148 void CMSCollector::verify_work_stacks_empty() const {
3149 assert(_markStack.isEmpty(), "Marking stack should be empty");
3150 assert(overflow_list_is_empty(), "Overflow list should be empty");
3151 }
3152
3153 void CMSCollector::verify_overflow_empty() const {
3154 assert(overflow_list_is_empty(), "Overflow list should be empty");
3155 assert(no_preserved_marks(), "No preserved marks");
3156 }
3157 #endif // PRODUCT
3158
3159 // Decide if we want to enable class unloading as part of the
3160 // ensuing concurrent GC cycle. We will collect the perm gen and
3161 // unload classes if it's the case that:
3162 // (1) an explicit gc request has been made and the flag
3163 // ExplicitGCInvokesConcurrentAndUnloadsClasses is set, OR
3164 // (2) (a) class unloading is enabled at the command line, and
3165 // (b) (i) perm gen threshold has been crossed, or
3166 // (ii) old gen is getting really full, or
3167 // (iii) the previous N CMS collections did not collect the
3168 // perm gen
3169 // NOTE: Provided there is no change in the state of the heap between
3170 // calls to this method, it should have idempotent results. Moreover,
3171 // its results should be monotonically increasing (i.e. going from 0 to 1,
3172 // but not 1 to 0) between successive calls between which the heap was
3173 // not collected. For the implementation below, it must thus rely on
3174 // the property that concurrent_cycles_since_last_unload()
3175 // will not decrease unless a collection cycle happened and that
3176 // _permGen->should_concurrent_collect() and _cmsGen->is_too_full() are
3177 // themselves also monotonic in that sense. See check_monotonicity()
3178 // below.
3179 bool CMSCollector::update_should_unload_classes() {
3180 _should_unload_classes = false;
3181 // Condition 1 above
3182 if (_full_gc_requested && ExplicitGCInvokesConcurrentAndUnloadsClasses) {
3183 _should_unload_classes = true;
3184 } else if (CMSClassUnloadingEnabled) { // Condition 2.a above
3185 // Disjuncts 2.b.(i,ii,iii) above
3186 _should_unload_classes = (concurrent_cycles_since_last_unload() >=
3187 CMSClassUnloadingMaxInterval)
3188 || _permGen->should_concurrent_collect()
3189 || _cmsGen->is_too_full();
3190 }
3191 return _should_unload_classes;
3192 }
3193
3194 bool ConcurrentMarkSweepGeneration::is_too_full() const {
3195 bool res = should_concurrent_collect();
3196 res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
3197 return res;
3198 }
3199
3200 void CMSCollector::setup_cms_unloading_and_verification_state() {
3201 const bool should_verify = VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
3202 || VerifyBeforeExit;
3203 const int rso = SharedHeap::SO_Symbols | SharedHeap::SO_Strings
3204 | SharedHeap::SO_CodeCache;
3205
3206 if (should_unload_classes()) { // Should unload classes this cycle
3207 remove_root_scanning_option(rso); // Shrink the root set appropriately
3208 set_verifying(should_verify); // Set verification state for this cycle
3209 return; // Nothing else needs to be done at this time
3210 }
3211
3212 // Not unloading classes this cycle
3213 assert(!should_unload_classes(), "Inconsitency!");
3214 if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
3215 // We were not verifying, or we _were_ unloading classes in the last cycle,
3216 // AND some verification options are enabled this cycle; in this case,
3217 // we must make sure that the deadness map is allocated if not already so,
3218 // and cleared (if already allocated previously --
3219 // CMSBitMap::sizeInBits() is used to determine if it's allocated).
3220 if (perm_gen_verify_bit_map()->sizeInBits() == 0) {
3221 if (!perm_gen_verify_bit_map()->allocate(_permGen->reserved())) {
3222 warning("Failed to allocate permanent generation verification CMS Bit Map;\n"
3223 "permanent generation verification disabled");
3224 return; // Note that we leave verification disabled, so we'll retry this
3225 // allocation next cycle. We _could_ remember this failure
3226 // and skip further attempts and permanently disable verification
3227 // attempts if that is considered more desirable.
3228 }
3229 assert(perm_gen_verify_bit_map()->covers(_permGen->reserved()),
3230 "_perm_gen_ver_bit_map inconsistency?");
3231 } else {
3232 perm_gen_verify_bit_map()->clear_all();
3233 }
3234 // Include symbols, strings and code cache elements to prevent their resurrection.
3235 add_root_scanning_option(rso);
3236 set_verifying(true);
3237 } else if (verifying() && !should_verify) {
3238 // We were verifying, but some verification flags got disabled.
3239 set_verifying(false);
3240 // Exclude symbols, strings and code cache elements from root scanning to
3241 // reduce IM and RM pauses.
3242 remove_root_scanning_option(rso);
3243 }
3244 }
3245
3246
3247 #ifndef PRODUCT
3248 HeapWord* CMSCollector::block_start(const void* p) const {
3249 const HeapWord* addr = (HeapWord*)p;
3250 if (_span.contains(p)) {
3251 if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
3252 return _cmsGen->cmsSpace()->block_start(p);
3253 } else {
3254 assert(_permGen->cmsSpace()->is_in_reserved(addr),
3255 "Inconsistent _span?");
3256 return _permGen->cmsSpace()->block_start(p);
3257 }
3258 }
3259 return NULL;
3260 }
3261 #endif
3262
3263 HeapWord*
3264 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
3265 bool tlab,
3266 bool parallel) {
3267 CMSSynchronousYieldRequest yr;
3268 assert(!tlab, "Can't deal with TLAB allocation");
3269 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3270 expand(word_size*HeapWordSize, MinHeapDeltaBytes,
3271 CMSExpansionCause::_satisfy_allocation);
3272 if (GCExpandToAllocateDelayMillis > 0) {
3273 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3274 }
3275 return have_lock_and_allocate(word_size, tlab);
3276 }
3277
3278 // YSR: All of this generation expansion/shrinking stuff is an exact copy of
3279 // OneContigSpaceCardGeneration, which makes me wonder if we should move this
3280 // to CardGeneration and share it...
3281 bool ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes) {
3282 return CardGeneration::expand(bytes, expand_bytes);
3283 }
3284
3285 void ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes,
3286 CMSExpansionCause::Cause cause)
3287 {
3288
3289 bool success = expand(bytes, expand_bytes);
3290
3291 // remember why we expanded; this information is used
3292 // by shouldConcurrentCollect() when making decisions on whether to start
3293 // a new CMS cycle.
3294 if (success) {
3295 set_expansion_cause(cause);
3296 if (PrintGCDetails && Verbose) {
3297 gclog_or_tty->print_cr("Expanded CMS gen for %s",
3298 CMSExpansionCause::to_string(cause));
3299 }
3300 }
3301 }
3302
3303 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
3304 HeapWord* res = NULL;
3305 MutexLocker x(ParGCRareEvent_lock);
3306 while (true) {
3307 // Expansion by some other thread might make alloc OK now:
3308 res = ps->lab.alloc(word_sz);
3309 if (res != NULL) return res;
3310 // If there's not enough expansion space available, give up.
3311 if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
3312 return NULL;
3313 }
3314 // Otherwise, we try expansion.
3315 expand(word_sz*HeapWordSize, MinHeapDeltaBytes,
3316 CMSExpansionCause::_allocate_par_lab);
3317 // Now go around the loop and try alloc again;
3318 // A competing par_promote might beat us to the expansion space,
3319 // so we may go around the loop again if promotion fails agaion.
3320 if (GCExpandToAllocateDelayMillis > 0) {
3321 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3322 }
3323 }
3324 }
3325
3326
3327 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
3328 PromotionInfo* promo) {
3329 MutexLocker x(ParGCRareEvent_lock);
3330 size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
3331 while (true) {
3332 // Expansion by some other thread might make alloc OK now:
3333 if (promo->ensure_spooling_space()) {
3334 assert(promo->has_spooling_space(),
3335 "Post-condition of successful ensure_spooling_space()");
3336 return true;
3337 }
3338 // If there's not enough expansion space available, give up.
3339 if (_virtual_space.uncommitted_size() < refill_size_bytes) {
3340 return false;
3341 }
3342 // Otherwise, we try expansion.
3343 expand(refill_size_bytes, MinHeapDeltaBytes,
3344 CMSExpansionCause::_allocate_par_spooling_space);
3345 // Now go around the loop and try alloc again;
3346 // A competing allocation might beat us to the expansion space,
3347 // so we may go around the loop again if allocation fails again.
3348 if (GCExpandToAllocateDelayMillis > 0) {
3349 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3350 }
3351 }
3352 }
3353
3354
3355
3356 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
3357 assert_locked_or_safepoint(Heap_lock);
3358 size_t size = ReservedSpace::page_align_size_down(bytes);
3359 if (size > 0) {
3360 shrink_by(size);
3361 }
3362 }
3363
3364 bool ConcurrentMarkSweepGeneration::grow_by(size_t bytes) {
3365 assert_locked_or_safepoint(Heap_lock);
3366 bool result = _virtual_space.expand_by(bytes);
3367 if (result) {
3368 HeapWord* old_end = _cmsSpace->end();
3369 size_t new_word_size =
3370 heap_word_size(_virtual_space.committed_size());
3371 MemRegion mr(_cmsSpace->bottom(), new_word_size);
3372 _bts->resize(new_word_size); // resize the block offset shared array
3373 Universe::heap()->barrier_set()->resize_covered_region(mr);
3374 // Hmmmm... why doesn't CFLS::set_end verify locking?
3375 // This is quite ugly; FIX ME XXX
3376 _cmsSpace->assert_locked(freelistLock());
3377 _cmsSpace->set_end((HeapWord*)_virtual_space.high());
3378
3379 // update the space and generation capacity counters
3380 if (UsePerfData) {
3381 _space_counters->update_capacity();
3382 _gen_counters->update_all();
3383 }
3384
3385 if (Verbose && PrintGC) {
3386 size_t new_mem_size = _virtual_space.committed_size();
3387 size_t old_mem_size = new_mem_size - bytes;
3388 gclog_or_tty->print_cr("Expanding %s from %ldK by %ldK to %ldK",
3389 name(), old_mem_size/K, bytes/K, new_mem_size/K);
3390 }
3391 }
3392 return result;
3393 }
3394
3395 bool ConcurrentMarkSweepGeneration::grow_to_reserved() {
3396 assert_locked_or_safepoint(Heap_lock);
3397 bool success = true;
3398 const size_t remaining_bytes = _virtual_space.uncommitted_size();
3399 if (remaining_bytes > 0) {
3400 success = grow_by(remaining_bytes);
3401 DEBUG_ONLY(if (!success) warning("grow to reserved failed");)
3402 }
3403 return success;
3404 }
3405
3406 void ConcurrentMarkSweepGeneration::shrink_by(size_t bytes) {
3407 assert_locked_or_safepoint(Heap_lock);
3408 assert_lock_strong(freelistLock());
3409 // XXX Fix when compaction is implemented.
3410 warning("Shrinking of CMS not yet implemented");
3411 return;
3412 }
3413
3414
3415 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
3416 // phases.
3417 class CMSPhaseAccounting: public StackObj {
3418 public:
3419 CMSPhaseAccounting(CMSCollector *collector,
3420 const char *phase,
3421 bool print_cr = true);
3422 ~CMSPhaseAccounting();
3423
3424 private:
3425 CMSCollector *_collector;
3426 const char *_phase;
3427 elapsedTimer _wallclock;
3428 bool _print_cr;
3429
3430 public:
3431 // Not MT-safe; so do not pass around these StackObj's
3432 // where they may be accessed by other threads.
3433 jlong wallclock_millis() {
3434 assert(_wallclock.is_active(), "Wall clock should not stop");
3435 _wallclock.stop(); // to record time
3436 jlong ret = _wallclock.milliseconds();
3437 _wallclock.start(); // restart
3438 return ret;
3439 }
3440 };
3441
3442 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
3443 const char *phase,
3444 bool print_cr) :
3445 _collector(collector), _phase(phase), _print_cr(print_cr) {
3446
3447 if (PrintCMSStatistics != 0) {
3448 _collector->resetYields();
3449 }
3450 if (PrintGCDetails && PrintGCTimeStamps) {
3451 gclog_or_tty->date_stamp(PrintGCDateStamps);
3452 gclog_or_tty->stamp();
3453 gclog_or_tty->print_cr(": [%s-concurrent-%s-start]",
3454 _collector->cmsGen()->short_name(), _phase);
3455 }
3456 _collector->resetTimer();
3457 _wallclock.start();
3458 _collector->startTimer();
3459 }
3460
3461 CMSPhaseAccounting::~CMSPhaseAccounting() {
3462 assert(_wallclock.is_active(), "Wall clock should not have stopped");
3463 _collector->stopTimer();
3464 _wallclock.stop();
3465 if (PrintGCDetails) {
3466 gclog_or_tty->date_stamp(PrintGCDateStamps);
3467 if (PrintGCTimeStamps) {
3468 gclog_or_tty->stamp();
3469 gclog_or_tty->print(": ");
3470 }
3471 gclog_or_tty->print("[%s-concurrent-%s: %3.3f/%3.3f secs]",
3472 _collector->cmsGen()->short_name(),
3473 _phase, _collector->timerValue(), _wallclock.seconds());
3474 if (_print_cr) {
3475 gclog_or_tty->print_cr("");
3476 }
3477 if (PrintCMSStatistics != 0) {
3478 gclog_or_tty->print_cr(" (CMS-concurrent-%s yielded %d times)", _phase,
3479 _collector->yields());
3480 }
3481 }
3482 }
3483
3484 // CMS work
3485
3486 // Checkpoint the roots into this generation from outside
3487 // this generation. [Note this initial checkpoint need only
3488 // be approximate -- we'll do a catch up phase subsequently.]
3489 void CMSCollector::checkpointRootsInitial(bool asynch) {
3490 assert(_collectorState == InitialMarking, "Wrong collector state");
3491 check_correct_thread_executing();
3492 TraceCMSMemoryManagerStats tms(_collectorState);
3493 ReferenceProcessor* rp = ref_processor();
3494 SpecializationStats::clear();
3495 assert(_restart_addr == NULL, "Control point invariant");
3496 if (asynch) {
3497 // acquire locks for subsequent manipulations
3498 MutexLockerEx x(bitMapLock(),
3499 Mutex::_no_safepoint_check_flag);
3500 checkpointRootsInitialWork(asynch);
3501 rp->verify_no_references_recorded();
3502 rp->enable_discovery(); // enable ("weak") refs discovery
3503 _collectorState = Marking;
3504 } else {
3505 // (Weak) Refs discovery: this is controlled from genCollectedHeap::do_collection
3506 // which recognizes if we are a CMS generation, and doesn't try to turn on
3507 // discovery; verify that they aren't meddling.
3508 assert(!rp->discovery_is_atomic(),
3509 "incorrect setting of discovery predicate");
3510 assert(!rp->discovery_enabled(), "genCollectedHeap shouldn't control "
3511 "ref discovery for this generation kind");
3512 // already have locks
3513 checkpointRootsInitialWork(asynch);
3514 rp->enable_discovery(); // now enable ("weak") refs discovery
3515 _collectorState = Marking;
3516 }
3517 SpecializationStats::print();
3518 }
3519
3520 void CMSCollector::checkpointRootsInitialWork(bool asynch) {
3521 assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
3522 assert(_collectorState == InitialMarking, "just checking");
3523
3524 // If there has not been a GC[n-1] since last GC[n] cycle completed,
3525 // precede our marking with a collection of all
3526 // younger generations to keep floating garbage to a minimum.
3527 // XXX: we won't do this for now -- it's an optimization to be done later.
3528
3529 // already have locks
3530 assert_lock_strong(bitMapLock());
3531 assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
3532
3533 // Setup the verification and class unloading state for this
3534 // CMS collection cycle.
3535 setup_cms_unloading_and_verification_state();
3536
3537 NOT_PRODUCT(TraceTime t("\ncheckpointRootsInitialWork",
3538 PrintGCDetails && Verbose, true, gclog_or_tty);)
3539 if (UseAdaptiveSizePolicy) {
3540 size_policy()->checkpoint_roots_initial_begin();
3541 }
3542
3543 // Reset all the PLAB chunk arrays if necessary.
3544 if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
3545 reset_survivor_plab_arrays();
3546 }
3547
3548 ResourceMark rm;
3549 HandleMark hm;
3550
3551 FalseClosure falseClosure;
3552 // In the case of a synchronous collection, we will elide the
3553 // remark step, so it's important to catch all the nmethod oops
3554 // in this step.
3555 // The final 'true' flag to gen_process_strong_roots will ensure this.
3556 // If 'async' is true, we can relax the nmethod tracing.
3557 MarkRefsIntoClosure notOlder(_span, &_markBitMap);
3558 GenCollectedHeap* gch = GenCollectedHeap::heap();
3559
3560 verify_work_stacks_empty();
3561 verify_overflow_empty();
3562
3563 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
3564 // Update the saved marks which may affect the root scans.
3565 gch->save_marks();
3566
3567 // weak reference processing has not started yet.
3568 ref_processor()->set_enqueuing_is_done(false);
3569
3570 {
3571 // This is not needed. DEBUG_ONLY(RememberKlassesChecker imx(true);)
3572 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
3573 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3574 gch->gen_process_strong_roots(_cmsGen->level(),
3575 true, // younger gens are roots
3576 true, // activate StrongRootsScope
3577 true, // collecting perm gen
3578 SharedHeap::ScanningOption(roots_scanning_options()),
3579 ¬Older,
3580 true, // walk all of code cache if (so & SO_CodeCache)
3581 NULL);
3582 }
3583
3584 // Clear mod-union table; it will be dirtied in the prologue of
3585 // CMS generation per each younger generation collection.
3586
3587 assert(_modUnionTable.isAllClear(),
3588 "Was cleared in most recent final checkpoint phase"
3589 " or no bits are set in the gc_prologue before the start of the next "
3590 "subsequent marking phase.");
3591
3592 // Temporarily disabled, since pre/post-consumption closures don't
3593 // care about precleaned cards
3594 #if 0
3595 {
3596 MemRegion mr = MemRegion((HeapWord*)_virtual_space.low(),
3597 (HeapWord*)_virtual_space.high());
3598 _ct->ct_bs()->preclean_dirty_cards(mr);
3599 }
3600 #endif
3601
3602 // Save the end of the used_region of the constituent generations
3603 // to be used to limit the extent of sweep in each generation.
3604 save_sweep_limits();
3605 if (UseAdaptiveSizePolicy) {
3606 size_policy()->checkpoint_roots_initial_end(gch->gc_cause());
3607 }
3608 verify_overflow_empty();
3609 }
3610
3611 bool CMSCollector::markFromRoots(bool asynch) {
3612 // we might be tempted to assert that:
3613 // assert(asynch == !SafepointSynchronize::is_at_safepoint(),
3614 // "inconsistent argument?");
3615 // However that wouldn't be right, because it's possible that
3616 // a safepoint is indeed in progress as a younger generation
3617 // stop-the-world GC happens even as we mark in this generation.
3618 assert(_collectorState == Marking, "inconsistent state?");
3619 check_correct_thread_executing();
3620 verify_overflow_empty();
3621
3622 bool res;
3623 if (asynch) {
3624
3625 // Start the timers for adaptive size policy for the concurrent phases
3626 // Do it here so that the foreground MS can use the concurrent
3627 // timer since a foreground MS might has the sweep done concurrently
3628 // or STW.
3629 if (UseAdaptiveSizePolicy) {
3630 size_policy()->concurrent_marking_begin();
3631 }
3632
3633 // Weak ref discovery note: We may be discovering weak
3634 // refs in this generation concurrent (but interleaved) with
3635 // weak ref discovery by a younger generation collector.
3636
3637 CMSTokenSyncWithLocks ts(true, bitMapLock());
3638 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3639 CMSPhaseAccounting pa(this, "mark", !PrintGCDetails);
3640 res = markFromRootsWork(asynch);
3641 if (res) {
3642 _collectorState = Precleaning;
3643 } else { // We failed and a foreground collection wants to take over
3644 assert(_foregroundGCIsActive, "internal state inconsistency");
3645 assert(_restart_addr == NULL, "foreground will restart from scratch");
3646 if (PrintGCDetails) {
3647 gclog_or_tty->print_cr("bailing out to foreground collection");
3648 }
3649 }
3650 if (UseAdaptiveSizePolicy) {
3651 size_policy()->concurrent_marking_end();
3652 }
3653 } else {
3654 assert(SafepointSynchronize::is_at_safepoint(),
3655 "inconsistent with asynch == false");
3656 if (UseAdaptiveSizePolicy) {
3657 size_policy()->ms_collection_marking_begin();
3658 }
3659 // already have locks
3660 res = markFromRootsWork(asynch);
3661 _collectorState = FinalMarking;
3662 if (UseAdaptiveSizePolicy) {
3663 GenCollectedHeap* gch = GenCollectedHeap::heap();
3664 size_policy()->ms_collection_marking_end(gch->gc_cause());
3665 }
3666 }
3667 verify_overflow_empty();
3668 return res;
3669 }
3670
3671 bool CMSCollector::markFromRootsWork(bool asynch) {
3672 // iterate over marked bits in bit map, doing a full scan and mark
3673 // from these roots using the following algorithm:
3674 // . if oop is to the right of the current scan pointer,
3675 // mark corresponding bit (we'll process it later)
3676 // . else (oop is to left of current scan pointer)
3677 // push oop on marking stack
3678 // . drain the marking stack
3679
3680 // Note that when we do a marking step we need to hold the
3681 // bit map lock -- recall that direct allocation (by mutators)
3682 // and promotion (by younger generation collectors) is also
3683 // marking the bit map. [the so-called allocate live policy.]
3684 // Because the implementation of bit map marking is not
3685 // robust wrt simultaneous marking of bits in the same word,
3686 // we need to make sure that there is no such interference
3687 // between concurrent such updates.
3688
3689 // already have locks
3690 assert_lock_strong(bitMapLock());
3691
3692 // Clear the revisit stack, just in case there are any
3693 // obsolete contents from a short-circuited previous CMS cycle.
3694 _revisitStack.reset();
3695 verify_work_stacks_empty();
3696 verify_overflow_empty();
3697 assert(_revisitStack.isEmpty(), "tabula rasa");
3698 DEBUG_ONLY(RememberKlassesChecker cmx(should_unload_classes());)
3699 bool result = false;
3700 if (CMSConcurrentMTEnabled && ConcGCThreads > 0) {
3701 result = do_marking_mt(asynch);
3702 } else {
3703 result = do_marking_st(asynch);
3704 }
3705 return result;
3706 }
3707
3708 // Forward decl
3709 class CMSConcMarkingTask;
3710
3711 class CMSConcMarkingTerminator: public ParallelTaskTerminator {
3712 CMSCollector* _collector;
3713 CMSConcMarkingTask* _task;
3714 public:
3715 virtual void yield();
3716
3717 // "n_threads" is the number of threads to be terminated.
3718 // "queue_set" is a set of work queues of other threads.
3719 // "collector" is the CMS collector associated with this task terminator.
3720 // "yield" indicates whether we need the gang as a whole to yield.
3721 CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
3722 ParallelTaskTerminator(n_threads, queue_set),
3723 _collector(collector) { }
3724
3725 void set_task(CMSConcMarkingTask* task) {
3726 _task = task;
3727 }
3728 };
3729
3730 class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator {
3731 CMSConcMarkingTask* _task;
3732 public:
3733 bool should_exit_termination();
3734 void set_task(CMSConcMarkingTask* task) {
3735 _task = task;
3736 }
3737 };
3738
3739 // MT Concurrent Marking Task
3740 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3741 CMSCollector* _collector;
3742 int _n_workers; // requested/desired # workers
3743 bool _asynch;
3744 bool _result;
3745 CompactibleFreeListSpace* _cms_space;
3746 CompactibleFreeListSpace* _perm_space;
3747 char _pad_front[64]; // padding to ...
3748 HeapWord* _global_finger; // ... avoid sharing cache line
3749 char _pad_back[64];
3750 HeapWord* _restart_addr;
3751
3752 // Exposed here for yielding support
3753 Mutex* const _bit_map_lock;
3754
3755 // The per thread work queues, available here for stealing
3756 OopTaskQueueSet* _task_queues;
3757
3758 // Termination (and yielding) support
3759 CMSConcMarkingTerminator _term;
3760 CMSConcMarkingTerminatorTerminator _term_term;
3761
3762 public:
3763 CMSConcMarkingTask(CMSCollector* collector,
3764 CompactibleFreeListSpace* cms_space,
3765 CompactibleFreeListSpace* perm_space,
3766 bool asynch,
3767 YieldingFlexibleWorkGang* workers,
3768 OopTaskQueueSet* task_queues):
3769 YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3770 _collector(collector),
3771 _cms_space(cms_space),
3772 _perm_space(perm_space),
3773 _asynch(asynch), _n_workers(0), _result(true),
3774 _task_queues(task_queues),
3775 _term(_n_workers, task_queues, _collector),
3776 _bit_map_lock(collector->bitMapLock())
3777 {
3778 _requested_size = _n_workers;
3779 _term.set_task(this);
3780 _term_term.set_task(this);
3781 assert(_cms_space->bottom() < _perm_space->bottom(),
3782 "Finger incorrectly initialized below");
3783 _restart_addr = _global_finger = _cms_space->bottom();
3784 }
3785
3786
3787 OopTaskQueueSet* task_queues() { return _task_queues; }
3788
3789 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3790
3791 HeapWord** global_finger_addr() { return &_global_finger; }
3792
3793 CMSConcMarkingTerminator* terminator() { return &_term; }
3794
3795 virtual void set_for_termination(int active_workers) {
3796 terminator()->reset_for_reuse(active_workers);
3797 }
3798
3799 void work(int i);
3800 bool should_yield() {
3801 return ConcurrentMarkSweepThread::should_yield()
3802 && !_collector->foregroundGCIsActive()
3803 && _asynch;
3804 }
3805
3806 virtual void coordinator_yield(); // stuff done by coordinator
3807 bool result() { return _result; }
3808
3809 void reset(HeapWord* ra) {
3810 assert(_global_finger >= _cms_space->end(), "Postcondition of ::work(i)");
3811 assert(_global_finger >= _perm_space->end(), "Postcondition of ::work(i)");
3812 assert(ra < _perm_space->end(), "ra too large");
3813 _restart_addr = _global_finger = ra;
3814 _term.reset_for_reuse();
3815 }
3816
3817 static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3818 OopTaskQueue* work_q);
3819
3820 private:
3821 void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3822 void do_work_steal(int i);
3823 void bump_global_finger(HeapWord* f);
3824 };
3825
3826 bool CMSConcMarkingTerminatorTerminator::should_exit_termination() {
3827 assert(_task != NULL, "Error");
3828 return _task->yielding();
3829 // Note that we do not need the disjunct || _task->should_yield() above
3830 // because we want terminating threads to yield only if the task
3831 // is already in the midst of yielding, which happens only after at least one
3832 // thread has yielded.
3833 }
3834
3835 void CMSConcMarkingTerminator::yield() {
3836 if (_task->should_yield()) {
3837 _task->yield();
3838 } else {
3839 ParallelTaskTerminator::yield();
3840 }
3841 }
3842
3843 ////////////////////////////////////////////////////////////////
3844 // Concurrent Marking Algorithm Sketch
3845 ////////////////////////////////////////////////////////////////
3846 // Until all tasks exhausted (both spaces):
3847 // -- claim next available chunk
3848 // -- bump global finger via CAS
3849 // -- find first object that starts in this chunk
3850 // and start scanning bitmap from that position
3851 // -- scan marked objects for oops
3852 // -- CAS-mark target, and if successful:
3853 // . if target oop is above global finger (volatile read)
3854 // nothing to do
3855 // . if target oop is in chunk and above local finger
3856 // then nothing to do
3857 // . else push on work-queue
3858 // -- Deal with possible overflow issues:
3859 // . local work-queue overflow causes stuff to be pushed on
3860 // global (common) overflow queue
3861 // . always first empty local work queue
3862 // . then get a batch of oops from global work queue if any
3863 // . then do work stealing
3864 // -- When all tasks claimed (both spaces)
3865 // and local work queue empty,
3866 // then in a loop do:
3867 // . check global overflow stack; steal a batch of oops and trace
3868 // . try to steal from other threads oif GOS is empty
3869 // . if neither is available, offer termination
3870 // -- Terminate and return result
3871 //
3872 void CMSConcMarkingTask::work(int i) {
3873 elapsedTimer _timer;
3874 ResourceMark rm;
3875 HandleMark hm;
3876
3877 DEBUG_ONLY(_collector->verify_overflow_empty();)
3878
3879 // Before we begin work, our work queue should be empty
3880 assert(work_queue(i)->size() == 0, "Expected to be empty");
3881 // Scan the bitmap covering _cms_space, tracing through grey objects.
3882 _timer.start();
3883 do_scan_and_mark(i, _cms_space);
3884 _timer.stop();
3885 if (PrintCMSStatistics != 0) {
3886 gclog_or_tty->print_cr("Finished cms space scanning in %dth thread: %3.3f sec",
3887 i, _timer.seconds()); // XXX: need xxx/xxx type of notation, two timers
3888 }
3889
3890 // ... do the same for the _perm_space
3891 _timer.reset();
3892 _timer.start();
3893 do_scan_and_mark(i, _perm_space);
3894 _timer.stop();
3895 if (PrintCMSStatistics != 0) {
3896 gclog_or_tty->print_cr("Finished perm space scanning in %dth thread: %3.3f sec",
3897 i, _timer.seconds()); // XXX: need xxx/xxx type of notation, two timers
3898 }
3899
3900 // ... do work stealing
3901 _timer.reset();
3902 _timer.start();
3903 do_work_steal(i);
3904 _timer.stop();
3905 if (PrintCMSStatistics != 0) {
3906 gclog_or_tty->print_cr("Finished work stealing in %dth thread: %3.3f sec",
3907 i, _timer.seconds()); // XXX: need xxx/xxx type of notation, two timers
3908 }
3909 assert(_collector->_markStack.isEmpty(), "Should have been emptied");
3910 assert(work_queue(i)->size() == 0, "Should have been emptied");
3911 // Note that under the current task protocol, the
3912 // following assertion is true even of the spaces
3913 // expanded since the completion of the concurrent
3914 // marking. XXX This will likely change under a strict
3915 // ABORT semantics.
3916 assert(_global_finger > _cms_space->end() &&
3917 _global_finger >= _perm_space->end(),
3918 "All tasks have been completed");
3919 DEBUG_ONLY(_collector->verify_overflow_empty();)
3920 }
3921
3922 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
3923 HeapWord* read = _global_finger;
3924 HeapWord* cur = read;
3925 while (f > read) {
3926 cur = read;
3927 read = (HeapWord*) Atomic::cmpxchg_ptr(f, &_global_finger, cur);
3928 if (cur == read) {
3929 // our cas succeeded
3930 assert(_global_finger >= f, "protocol consistency");
3931 break;
3932 }
3933 }
3934 }
3935
3936 // This is really inefficient, and should be redone by
3937 // using (not yet available) block-read and -write interfaces to the
3938 // stack and the work_queue. XXX FIX ME !!!
3939 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3940 OopTaskQueue* work_q) {
3941 // Fast lock-free check
3942 if (ovflw_stk->length() == 0) {
3943 return false;
3944 }
3945 assert(work_q->size() == 0, "Shouldn't steal");
3946 MutexLockerEx ml(ovflw_stk->par_lock(),
3947 Mutex::_no_safepoint_check_flag);
3948 // Grab up to 1/4 the size of the work queue
3949 size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
3950 (size_t)ParGCDesiredObjsFromOverflowList);
3951 num = MIN2(num, ovflw_stk->length());
3952 for (int i = (int) num; i > 0; i--) {
3953 oop cur = ovflw_stk->pop();
3954 assert(cur != NULL, "Counted wrong?");
3955 work_q->push(cur);
3956 }
3957 return num > 0;
3958 }
3959
3960 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
3961 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
3962 int n_tasks = pst->n_tasks();
3963 // We allow that there may be no tasks to do here because
3964 // we are restarting after a stack overflow.
3965 assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
3966 int nth_task = 0;
3967
3968 HeapWord* aligned_start = sp->bottom();
3969 if (sp->used_region().contains(_restart_addr)) {
3970 // Align down to a card boundary for the start of 0th task
3971 // for this space.
3972 aligned_start =
3973 (HeapWord*)align_size_down((uintptr_t)_restart_addr,
3974 CardTableModRefBS::card_size);
3975 }
3976
3977 size_t chunk_size = sp->marking_task_size();
3978 while (!pst->is_task_claimed(/* reference */ nth_task)) {
3979 // Having claimed the nth task in this space,
3980 // compute the chunk that it corresponds to:
3981 MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
3982 aligned_start + (nth_task+1)*chunk_size);
3983 // Try and bump the global finger via a CAS;
3984 // note that we need to do the global finger bump
3985 // _before_ taking the intersection below, because
3986 // the task corresponding to that region will be
3987 // deemed done even if the used_region() expands
3988 // because of allocation -- as it almost certainly will
3989 // during start-up while the threads yield in the
3990 // closure below.
3991 HeapWord* finger = span.end();
3992 bump_global_finger(finger); // atomically
3993 // There are null tasks here corresponding to chunks
3994 // beyond the "top" address of the space.
3995 span = span.intersection(sp->used_region());
3996 if (!span.is_empty()) { // Non-null task
3997 HeapWord* prev_obj;
3998 assert(!span.contains(_restart_addr) || nth_task == 0,
3999 "Inconsistency");
4000 if (nth_task == 0) {
4001 // For the 0th task, we'll not need to compute a block_start.
4002 if (span.contains(_restart_addr)) {
4003 // In the case of a restart because of stack overflow,
4004 // we might additionally skip a chunk prefix.
4005 prev_obj = _restart_addr;
4006 } else {
4007 prev_obj = span.start();
4008 }
4009 } else {
4010 // We want to skip the first object because
4011 // the protocol is to scan any object in its entirety
4012 // that _starts_ in this span; a fortiori, any
4013 // object starting in an earlier span is scanned
4014 // as part of an earlier claimed task.
4015 // Below we use the "careful" version of block_start
4016 // so we do not try to navigate uninitialized objects.
4017 prev_obj = sp->block_start_careful(span.start());
4018 // Below we use a variant of block_size that uses the
4019 // Printezis bits to avoid waiting for allocated
4020 // objects to become initialized/parsable.
4021 while (prev_obj < span.start()) {
4022 size_t sz = sp->block_size_no_stall(prev_obj, _collector);
4023 if (sz > 0) {
4024 prev_obj += sz;
4025 } else {
4026 // In this case we may end up doing a bit of redundant
4027 // scanning, but that appears unavoidable, short of
4028 // locking the free list locks; see bug 6324141.
4029 break;
4030 }
4031 }
4032 }
4033 if (prev_obj < span.end()) {
4034 MemRegion my_span = MemRegion(prev_obj, span.end());
4035 // Do the marking work within a non-empty span --
4036 // the last argument to the constructor indicates whether the
4037 // iteration should be incremental with periodic yields.
4038 Par_MarkFromRootsClosure cl(this, _collector, my_span,
4039 &_collector->_markBitMap,
4040 work_queue(i),
4041 &_collector->_markStack,
4042 &_collector->_revisitStack,
4043 _asynch);
4044 _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
4045 } // else nothing to do for this task
4046 } // else nothing to do for this task
4047 }
4048 // We'd be tempted to assert here that since there are no
4049 // more tasks left to claim in this space, the global_finger
4050 // must exceed space->top() and a fortiori space->end(). However,
4051 // that would not quite be correct because the bumping of
4052 // global_finger occurs strictly after the claiming of a task,
4053 // so by the time we reach here the global finger may not yet
4054 // have been bumped up by the thread that claimed the last
4055 // task.
4056 pst->all_tasks_completed();
4057 }
4058
4059 class Par_ConcMarkingClosure: public Par_KlassRememberingOopClosure {
4060 private:
4061 CMSConcMarkingTask* _task;
4062 MemRegion _span;
4063 CMSBitMap* _bit_map;
4064 CMSMarkStack* _overflow_stack;
4065 OopTaskQueue* _work_queue;
4066 protected:
4067 DO_OOP_WORK_DEFN
4068 public:
4069 Par_ConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue,
4070 CMSBitMap* bit_map, CMSMarkStack* overflow_stack,
4071 CMSMarkStack* revisit_stack):
4072 Par_KlassRememberingOopClosure(collector, NULL, revisit_stack),
4073 _task(task),
4074 _span(collector->_span),
4075 _work_queue(work_queue),
4076 _bit_map(bit_map),
4077 _overflow_stack(overflow_stack)
4078 { }
4079 virtual void do_oop(oop* p);
4080 virtual void do_oop(narrowOop* p);
4081 void trim_queue(size_t max);
4082 void handle_stack_overflow(HeapWord* lost);
4083 void do_yield_check() {
4084 if (_task->should_yield()) {
4085 _task->yield();
4086 }
4087 }
4088 };
4089
4090 // Grey object scanning during work stealing phase --
4091 // the salient assumption here is that any references
4092 // that are in these stolen objects being scanned must
4093 // already have been initialized (else they would not have
4094 // been published), so we do not need to check for
4095 // uninitialized objects before pushing here.
4096 void Par_ConcMarkingClosure::do_oop(oop obj) {
4097 assert(obj->is_oop_or_null(true), "expected an oop or NULL");
4098 HeapWord* addr = (HeapWord*)obj;
4099 // Check if oop points into the CMS generation
4100 // and is not marked
4101 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
4102 // a white object ...
4103 // If we manage to "claim" the object, by being the
4104 // first thread to mark it, then we push it on our
4105 // marking stack
4106 if (_bit_map->par_mark(addr)) { // ... now grey
4107 // push on work queue (grey set)
4108 bool simulate_overflow = false;
4109 NOT_PRODUCT(
4110 if (CMSMarkStackOverflowALot &&
4111 _collector->simulate_overflow()) {
4112 // simulate a stack overflow
4113 simulate_overflow = true;
4114 }
4115 )
4116 if (simulate_overflow ||
4117 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
4118 // stack overflow
4119 if (PrintCMSStatistics != 0) {
4120 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
4121 SIZE_FORMAT, _overflow_stack->capacity());
4122 }
4123 // We cannot assert that the overflow stack is full because
4124 // it may have been emptied since.
4125 assert(simulate_overflow ||
4126 _work_queue->size() == _work_queue->max_elems(),
4127 "Else push should have succeeded");
4128 handle_stack_overflow(addr);
4129 }
4130 } // Else, some other thread got there first
4131 do_yield_check();
4132 }
4133 }
4134
4135 void Par_ConcMarkingClosure::do_oop(oop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
4136 void Par_ConcMarkingClosure::do_oop(narrowOop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
4137
4138 void Par_ConcMarkingClosure::trim_queue(size_t max) {
4139 while (_work_queue->size() > max) {
4140 oop new_oop;
4141 if (_work_queue->pop_local(new_oop)) {
4142 assert(new_oop->is_oop(), "Should be an oop");
4143 assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
4144 assert(_span.contains((HeapWord*)new_oop), "Not in span");
4145 assert(new_oop->is_parsable(), "Should be parsable");
4146 new_oop->oop_iterate(this); // do_oop() above
4147 do_yield_check();
4148 }
4149 }
4150 }
4151
4152 // Upon stack overflow, we discard (part of) the stack,
4153 // remembering the least address amongst those discarded
4154 // in CMSCollector's _restart_address.
4155 void Par_ConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
4156 // We need to do this under a mutex to prevent other
4157 // workers from interfering with the work done below.
4158 MutexLockerEx ml(_overflow_stack->par_lock(),
4159 Mutex::_no_safepoint_check_flag);
4160 // Remember the least grey address discarded
4161 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
4162 _collector->lower_restart_addr(ra);
4163 _overflow_stack->reset(); // discard stack contents
4164 _overflow_stack->expand(); // expand the stack if possible
4165 }
4166
4167
4168 void CMSConcMarkingTask::do_work_steal(int i) {
4169 OopTaskQueue* work_q = work_queue(i);
4170 oop obj_to_scan;
4171 CMSBitMap* bm = &(_collector->_markBitMap);
4172 CMSMarkStack* ovflw = &(_collector->_markStack);
4173 CMSMarkStack* revisit = &(_collector->_revisitStack);
4174 int* seed = _collector->hash_seed(i);
4175 Par_ConcMarkingClosure cl(_collector, this, work_q, bm, ovflw, revisit);
4176 while (true) {
4177 cl.trim_queue(0);
4178 assert(work_q->size() == 0, "Should have been emptied above");
4179 if (get_work_from_overflow_stack(ovflw, work_q)) {
4180 // Can't assert below because the work obtained from the
4181 // overflow stack may already have been stolen from us.
4182 // assert(work_q->size() > 0, "Work from overflow stack");
4183 continue;
4184 } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
4185 assert(obj_to_scan->is_oop(), "Should be an oop");
4186 assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
4187 obj_to_scan->oop_iterate(&cl);
4188 } else if (terminator()->offer_termination(&_term_term)) {
4189 assert(work_q->size() == 0, "Impossible!");
4190 break;
4191 } else if (yielding() || should_yield()) {
4192 yield();
4193 }
4194 }
4195 }
4196
4197 // This is run by the CMS (coordinator) thread.
4198 void CMSConcMarkingTask::coordinator_yield() {
4199 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
4200 "CMS thread should hold CMS token");
4201 DEBUG_ONLY(RememberKlassesChecker mux(false);)
4202 // First give up the locks, then yield, then re-lock
4203 // We should probably use a constructor/destructor idiom to
4204 // do this unlock/lock or modify the MutexUnlocker class to
4205 // serve our purpose. XXX
4206 assert_lock_strong(_bit_map_lock);
4207 _bit_map_lock->unlock();
4208 ConcurrentMarkSweepThread::desynchronize(true);
4209 ConcurrentMarkSweepThread::acknowledge_yield_request();
4210 _collector->stopTimer();
4211 if (PrintCMSStatistics != 0) {
4212 _collector->incrementYields();
4213 }
4214 _collector->icms_wait();
4215
4216 // It is possible for whichever thread initiated the yield request
4217 // not to get a chance to wake up and take the bitmap lock between
4218 // this thread releasing it and reacquiring it. So, while the
4219 // should_yield() flag is on, let's sleep for a bit to give the
4220 // other thread a chance to wake up. The limit imposed on the number
4221 // of iterations is defensive, to avoid any unforseen circumstances
4222 // putting us into an infinite loop. Since it's always been this
4223 // (coordinator_yield()) method that was observed to cause the
4224 // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
4225 // which is by default non-zero. For the other seven methods that
4226 // also perform the yield operation, as are using a different
4227 // parameter (CMSYieldSleepCount) which is by default zero. This way we
4228 // can enable the sleeping for those methods too, if necessary.
4229 // See 6442774.
4230 //
4231 // We really need to reconsider the synchronization between the GC
4232 // thread and the yield-requesting threads in the future and we
4233 // should really use wait/notify, which is the recommended
4234 // way of doing this type of interaction. Additionally, we should
4235 // consolidate the eight methods that do the yield operation and they
4236 // are almost identical into one for better maintenability and
4237 // readability. See 6445193.
4238 //
4239 // Tony 2006.06.29
4240 for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
4241 ConcurrentMarkSweepThread::should_yield() &&
4242 !CMSCollector::foregroundGCIsActive(); ++i) {
4243 os::sleep(Thread::current(), 1, false);
4244 ConcurrentMarkSweepThread::acknowledge_yield_request();
4245 }
4246
4247 ConcurrentMarkSweepThread::synchronize(true);
4248 _bit_map_lock->lock_without_safepoint_check();
4249 _collector->startTimer();
4250 }
4251
4252 bool CMSCollector::do_marking_mt(bool asynch) {
4253 assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition");
4254 // In the future this would be determined ergonomically, based
4255 // on #cpu's, # active mutator threads (and load), and mutation rate.
4256 int num_workers = ConcGCThreads;
4257
4258 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
4259 CompactibleFreeListSpace* perm_space = _permGen->cmsSpace();
4260
4261 CMSConcMarkingTask tsk(this,
4262 cms_space,
4263 perm_space,
4264 asynch,
4265 conc_workers(),
4266 task_queues());
4267
4268 // Since the actual number of workers we get may be different
4269 // from the number we requested above, do we need to do anything different
4270 // below? In particular, may be we need to subclass the SequantialSubTasksDone
4271 // class?? XXX
4272 cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
4273 perm_space->initialize_sequential_subtasks_for_marking(num_workers);
4274
4275 // Refs discovery is already non-atomic.
4276 assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
4277 // Mutate the Refs discovery so it is MT during the
4278 // multi-threaded marking phase.
4279 ReferenceProcessorMTMutator mt(ref_processor(), num_workers > 1);
4280 DEBUG_ONLY(RememberKlassesChecker cmx(should_unload_classes());)
4281 conc_workers()->start_task(&tsk);
4282 while (tsk.yielded()) {
4283 tsk.coordinator_yield();
4284 conc_workers()->continue_task(&tsk);
4285 }
4286 // If the task was aborted, _restart_addr will be non-NULL
4287 assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
4288 while (_restart_addr != NULL) {
4289 // XXX For now we do not make use of ABORTED state and have not
4290 // yet implemented the right abort semantics (even in the original
4291 // single-threaded CMS case). That needs some more investigation
4292 // and is deferred for now; see CR# TBF. 07252005YSR. XXX
4293 assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
4294 // If _restart_addr is non-NULL, a marking stack overflow
4295 // occurred; we need to do a fresh marking iteration from the
4296 // indicated restart address.
4297 if (_foregroundGCIsActive && asynch) {
4298 // We may be running into repeated stack overflows, having
4299 // reached the limit of the stack size, while making very
4300 // slow forward progress. It may be best to bail out and
4301 // let the foreground collector do its job.
4302 // Clear _restart_addr, so that foreground GC
4303 // works from scratch. This avoids the headache of
4304 // a "rescan" which would otherwise be needed because
4305 // of the dirty mod union table & card table.
4306 _restart_addr = NULL;
4307 return false;
4308 }
4309 // Adjust the task to restart from _restart_addr
4310 tsk.reset(_restart_addr);
4311 cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
4312 _restart_addr);
4313 perm_space->initialize_sequential_subtasks_for_marking(num_workers,
4314 _restart_addr);
4315 _restart_addr = NULL;
4316 // Get the workers going again
4317 conc_workers()->start_task(&tsk);
4318 while (tsk.yielded()) {
4319 tsk.coordinator_yield();
4320 conc_workers()->continue_task(&tsk);
4321 }
4322 }
4323 assert(tsk.completed(), "Inconsistency");
4324 assert(tsk.result() == true, "Inconsistency");
4325 return true;
4326 }
4327
4328 bool CMSCollector::do_marking_st(bool asynch) {
4329 ResourceMark rm;
4330 HandleMark hm;
4331
4332 MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
4333 &_markStack, &_revisitStack, CMSYield && asynch);
4334 // the last argument to iterate indicates whether the iteration
4335 // should be incremental with periodic yields.
4336 _markBitMap.iterate(&markFromRootsClosure);
4337 // If _restart_addr is non-NULL, a marking stack overflow
4338 // occurred; we need to do a fresh iteration from the
4339 // indicated restart address.
4340 while (_restart_addr != NULL) {
4341 if (_foregroundGCIsActive && asynch) {
4342 // We may be running into repeated stack overflows, having
4343 // reached the limit of the stack size, while making very
4344 // slow forward progress. It may be best to bail out and
4345 // let the foreground collector do its job.
4346 // Clear _restart_addr, so that foreground GC
4347 // works from scratch. This avoids the headache of
4348 // a "rescan" which would otherwise be needed because
4349 // of the dirty mod union table & card table.
4350 _restart_addr = NULL;
4351 return false; // indicating failure to complete marking
4352 }
4353 // Deal with stack overflow:
4354 // we restart marking from _restart_addr
4355 HeapWord* ra = _restart_addr;
4356 markFromRootsClosure.reset(ra);
4357 _restart_addr = NULL;
4358 _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
4359 }
4360 return true;
4361 }
4362
4363 void CMSCollector::preclean() {
4364 check_correct_thread_executing();
4365 assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
4366 verify_work_stacks_empty();
4367 verify_overflow_empty();
4368 _abort_preclean = false;
4369 if (CMSPrecleaningEnabled) {
4370 // Precleaning is currently not MT but the reference processor
4371 // may be set for MT. Disable it temporarily here.
4372 ReferenceProcessor* rp = ref_processor();
4373 ReferenceProcessorMTProcMutator z(rp, false);
4374 _eden_chunk_index = 0;
4375 size_t used = get_eden_used();
4376 size_t capacity = get_eden_capacity();
4377 // Don't start sampling unless we will get sufficiently
4378 // many samples.
4379 if (used < (capacity/(CMSScheduleRemarkSamplingRatio * 100)
4380 * CMSScheduleRemarkEdenPenetration)) {
4381 _start_sampling = true;
4382 } else {
4383 _start_sampling = false;
4384 }
4385 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
4386 CMSPhaseAccounting pa(this, "preclean", !PrintGCDetails);
4387 preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
4388 }
4389 CMSTokenSync x(true); // is cms thread
4390 if (CMSPrecleaningEnabled) {
4391 sample_eden();
4392 _collectorState = AbortablePreclean;
4393 } else {
4394 _collectorState = FinalMarking;
4395 }
4396 verify_work_stacks_empty();
4397 verify_overflow_empty();
4398 }
4399
4400 // Try and schedule the remark such that young gen
4401 // occupancy is CMSScheduleRemarkEdenPenetration %.
4402 void CMSCollector::abortable_preclean() {
4403 check_correct_thread_executing();
4404 assert(CMSPrecleaningEnabled, "Inconsistent control state");
4405 assert(_collectorState == AbortablePreclean, "Inconsistent control state");
4406
4407 // If Eden's current occupancy is below this threshold,
4408 // immediately schedule the remark; else preclean
4409 // past the next scavenge in an effort to
4410 // schedule the pause as described avove. By choosing
4411 // CMSScheduleRemarkEdenSizeThreshold >= max eden size
4412 // we will never do an actual abortable preclean cycle.
4413 if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
4414 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
4415 CMSPhaseAccounting pa(this, "abortable-preclean", !PrintGCDetails);
4416 // We need more smarts in the abortable preclean
4417 // loop below to deal with cases where allocation
4418 // in young gen is very very slow, and our precleaning
4419 // is running a losing race against a horde of
4420 // mutators intent on flooding us with CMS updates
4421 // (dirty cards).
4422 // One, admittedly dumb, strategy is to give up
4423 // after a certain number of abortable precleaning loops
4424 // or after a certain maximum time. We want to make
4425 // this smarter in the next iteration.
4426 // XXX FIX ME!!! YSR
4427 size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
4428 while (!(should_abort_preclean() ||
4429 ConcurrentMarkSweepThread::should_terminate())) {
4430 workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
4431 cumworkdone += workdone;
4432 loops++;
4433 // Voluntarily terminate abortable preclean phase if we have
4434 // been at it for too long.
4435 if ((CMSMaxAbortablePrecleanLoops != 0) &&
4436 loops >= CMSMaxAbortablePrecleanLoops) {
4437 if (PrintGCDetails) {
4438 gclog_or_tty->print(" CMS: abort preclean due to loops ");
4439 }
4440 break;
4441 }
4442 if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
4443 if (PrintGCDetails) {
4444 gclog_or_tty->print(" CMS: abort preclean due to time ");
4445 }
4446 break;
4447 }
4448 // If we are doing little work each iteration, we should
4449 // take a short break.
4450 if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
4451 // Sleep for some time, waiting for work to accumulate
4452 stopTimer();
4453 cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
4454 startTimer();
4455 waited++;
4456 }
4457 }
4458 if (PrintCMSStatistics > 0) {
4459 gclog_or_tty->print(" [%d iterations, %d waits, %d cards)] ",
4460 loops, waited, cumworkdone);
4461 }
4462 }
4463 CMSTokenSync x(true); // is cms thread
4464 if (_collectorState != Idling) {
4465 assert(_collectorState == AbortablePreclean,
4466 "Spontaneous state transition?");
4467 _collectorState = FinalMarking;
4468 } // Else, a foreground collection completed this CMS cycle.
4469 return;
4470 }
4471
4472 // Respond to an Eden sampling opportunity
4473 void CMSCollector::sample_eden() {
4474 // Make sure a young gc cannot sneak in between our
4475 // reading and recording of a sample.
4476 assert(Thread::current()->is_ConcurrentGC_thread(),
4477 "Only the cms thread may collect Eden samples");
4478 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
4479 "Should collect samples while holding CMS token");
4480 if (!_start_sampling) {
4481 return;
4482 }
4483 if (_eden_chunk_array) {
4484 if (_eden_chunk_index < _eden_chunk_capacity) {
4485 _eden_chunk_array[_eden_chunk_index] = *_top_addr; // take sample
4486 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4487 "Unexpected state of Eden");
4488 // We'd like to check that what we just sampled is an oop-start address;
4489 // however, we cannot do that here since the object may not yet have been
4490 // initialized. So we'll instead do the check when we _use_ this sample
4491 // later.
4492 if (_eden_chunk_index == 0 ||
4493 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4494 _eden_chunk_array[_eden_chunk_index-1])
4495 >= CMSSamplingGrain)) {
4496 _eden_chunk_index++; // commit sample
4497 }
4498 }
4499 }
4500 if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
4501 size_t used = get_eden_used();
4502 size_t capacity = get_eden_capacity();
4503 assert(used <= capacity, "Unexpected state of Eden");
4504 if (used > (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
4505 _abort_preclean = true;
4506 }
4507 }
4508 }
4509
4510
4511 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
4512 assert(_collectorState == Precleaning ||
4513 _collectorState == AbortablePreclean, "incorrect state");
4514 ResourceMark rm;
4515 HandleMark hm;
4516 // Do one pass of scrubbing the discovered reference lists
4517 // to remove any reference objects with strongly-reachable
4518 // referents.
4519 if (clean_refs) {
4520 ReferenceProcessor* rp = ref_processor();
4521 CMSPrecleanRefsYieldClosure yield_cl(this);
4522 assert(rp->span().equals(_span), "Spans should be equal");
4523 CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
4524 &_markStack, &_revisitStack,
4525 true /* preclean */);
4526 CMSDrainMarkingStackClosure complete_trace(this,
4527 _span, &_markBitMap, &_markStack,
4528 &keep_alive, true /* preclean */);
4529
4530 // We don't want this step to interfere with a young
4531 // collection because we don't want to take CPU
4532 // or memory bandwidth away from the young GC threads
4533 // (which may be as many as there are CPUs).
4534 // Note that we don't need to protect ourselves from
4535 // interference with mutators because they can't
4536 // manipulate the discovered reference lists nor affect
4537 // the computed reachability of the referents, the
4538 // only properties manipulated by the precleaning
4539 // of these reference lists.
4540 stopTimer();
4541 CMSTokenSyncWithLocks x(true /* is cms thread */,
4542 bitMapLock());
4543 startTimer();
4544 sample_eden();
4545
4546 // The following will yield to allow foreground
4547 // collection to proceed promptly. XXX YSR:
4548 // The code in this method may need further
4549 // tweaking for better performance and some restructuring
4550 // for cleaner interfaces.
4551 rp->preclean_discovered_references(
4552 rp->is_alive_non_header(), &keep_alive, &complete_trace,
4553 &yield_cl, should_unload_classes());
4554 }
4555
4556 if (clean_survivor) { // preclean the active survivor space(s)
4557 assert(_young_gen->kind() == Generation::DefNew ||
4558 _young_gen->kind() == Generation::ParNew ||
4559 _young_gen->kind() == Generation::ASParNew,
4560 "incorrect type for cast");
4561 DefNewGeneration* dng = (DefNewGeneration*)_young_gen;
4562 PushAndMarkClosure pam_cl(this, _span, ref_processor(),
4563 &_markBitMap, &_modUnionTable,
4564 &_markStack, &_revisitStack,
4565 true /* precleaning phase */);
4566 stopTimer();
4567 CMSTokenSyncWithLocks ts(true /* is cms thread */,
4568 bitMapLock());
4569 startTimer();
4570 unsigned int before_count =
4571 GenCollectedHeap::heap()->total_collections();
4572 SurvivorSpacePrecleanClosure
4573 sss_cl(this, _span, &_markBitMap, &_markStack,
4574 &pam_cl, before_count, CMSYield);
4575 DEBUG_ONLY(RememberKlassesChecker mx(should_unload_classes());)
4576 dng->from()->object_iterate_careful(&sss_cl);
4577 dng->to()->object_iterate_careful(&sss_cl);
4578 }
4579 MarkRefsIntoAndScanClosure
4580 mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
4581 &_markStack, &_revisitStack, this, CMSYield,
4582 true /* precleaning phase */);
4583 // CAUTION: The following closure has persistent state that may need to
4584 // be reset upon a decrease in the sequence of addresses it
4585 // processes.
4586 ScanMarkedObjectsAgainCarefullyClosure
4587 smoac_cl(this, _span,
4588 &_markBitMap, &_markStack, &_revisitStack, &mrias_cl, CMSYield);
4589
4590 // Preclean dirty cards in ModUnionTable and CardTable using
4591 // appropriate convergence criterion;
4592 // repeat CMSPrecleanIter times unless we find that
4593 // we are losing.
4594 assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
4595 assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
4596 "Bad convergence multiplier");
4597 assert(CMSPrecleanThreshold >= 100,
4598 "Unreasonably low CMSPrecleanThreshold");
4599
4600 size_t numIter, cumNumCards, lastNumCards, curNumCards;
4601 for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
4602 numIter < CMSPrecleanIter;
4603 numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
4604 curNumCards = preclean_mod_union_table(_cmsGen, &smoac_cl);
4605 if (CMSPermGenPrecleaningEnabled) {
4606 curNumCards += preclean_mod_union_table(_permGen, &smoac_cl);
4607 }
4608 if (Verbose && PrintGCDetails) {
4609 gclog_or_tty->print(" (modUnionTable: %d cards)", curNumCards);
4610 }
4611 // Either there are very few dirty cards, so re-mark
4612 // pause will be small anyway, or our pre-cleaning isn't
4613 // that much faster than the rate at which cards are being
4614 // dirtied, so we might as well stop and re-mark since
4615 // precleaning won't improve our re-mark time by much.
4616 if (curNumCards <= CMSPrecleanThreshold ||
4617 (numIter > 0 &&
4618 (curNumCards * CMSPrecleanDenominator >
4619 lastNumCards * CMSPrecleanNumerator))) {
4620 numIter++;
4621 cumNumCards += curNumCards;
4622 break;
4623 }
4624 }
4625 curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
4626 if (CMSPermGenPrecleaningEnabled) {
4627 curNumCards += preclean_card_table(_permGen, &smoac_cl);
4628 }
4629 cumNumCards += curNumCards;
4630 if (PrintGCDetails && PrintCMSStatistics != 0) {
4631 gclog_or_tty->print_cr(" (cardTable: %d cards, re-scanned %d cards, %d iterations)",
4632 curNumCards, cumNumCards, numIter);
4633 }
4634 return cumNumCards; // as a measure of useful work done
4635 }
4636
4637 // PRECLEANING NOTES:
4638 // Precleaning involves:
4639 // . reading the bits of the modUnionTable and clearing the set bits.
4640 // . For the cards corresponding to the set bits, we scan the
4641 // objects on those cards. This means we need the free_list_lock
4642 // so that we can safely iterate over the CMS space when scanning
4643 // for oops.
4644 // . When we scan the objects, we'll be both reading and setting
4645 // marks in the marking bit map, so we'll need the marking bit map.
4646 // . For protecting _collector_state transitions, we take the CGC_lock.
4647 // Note that any races in the reading of of card table entries by the
4648 // CMS thread on the one hand and the clearing of those entries by the
4649 // VM thread or the setting of those entries by the mutator threads on the
4650 // other are quite benign. However, for efficiency it makes sense to keep
4651 // the VM thread from racing with the CMS thread while the latter is
4652 // dirty card info to the modUnionTable. We therefore also use the
4653 // CGC_lock to protect the reading of the card table and the mod union
4654 // table by the CM thread.
4655 // . We run concurrently with mutator updates, so scanning
4656 // needs to be done carefully -- we should not try to scan
4657 // potentially uninitialized objects.
4658 //
4659 // Locking strategy: While holding the CGC_lock, we scan over and
4660 // reset a maximal dirty range of the mod union / card tables, then lock
4661 // the free_list_lock and bitmap lock to do a full marking, then
4662 // release these locks; and repeat the cycle. This allows for a
4663 // certain amount of fairness in the sharing of these locks between
4664 // the CMS collector on the one hand, and the VM thread and the
4665 // mutators on the other.
4666
4667 // NOTE: preclean_mod_union_table() and preclean_card_table()
4668 // further below are largely identical; if you need to modify
4669 // one of these methods, please check the other method too.
4670
4671 size_t CMSCollector::preclean_mod_union_table(
4672 ConcurrentMarkSweepGeneration* gen,
4673 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4674 verify_work_stacks_empty();
4675 verify_overflow_empty();
4676
4677 // Turn off checking for this method but turn it back on
4678 // selectively. There are yield points in this method
4679 // but it is difficult to turn the checking off just around
4680 // the yield points. It is simpler to selectively turn
4681 // it on.
4682 DEBUG_ONLY(RememberKlassesChecker mux(false);)
4683
4684 // strategy: starting with the first card, accumulate contiguous
4685 // ranges of dirty cards; clear these cards, then scan the region
4686 // covered by these cards.
4687
4688 // Since all of the MUT is committed ahead, we can just use
4689 // that, in case the generations expand while we are precleaning.
4690 // It might also be fine to just use the committed part of the
4691 // generation, but we might potentially miss cards when the
4692 // generation is rapidly expanding while we are in the midst
4693 // of precleaning.
4694 HeapWord* startAddr = gen->reserved().start();
4695 HeapWord* endAddr = gen->reserved().end();
4696
4697 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4698
4699 size_t numDirtyCards, cumNumDirtyCards;
4700 HeapWord *nextAddr, *lastAddr;
4701 for (cumNumDirtyCards = numDirtyCards = 0,
4702 nextAddr = lastAddr = startAddr;
4703 nextAddr < endAddr;
4704 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4705
4706 ResourceMark rm;
4707 HandleMark hm;
4708
4709 MemRegion dirtyRegion;
4710 {
4711 stopTimer();
4712 // Potential yield point
4713 CMSTokenSync ts(true);
4714 startTimer();
4715 sample_eden();
4716 // Get dirty region starting at nextOffset (inclusive),
4717 // simultaneously clearing it.
4718 dirtyRegion =
4719 _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
4720 assert(dirtyRegion.start() >= nextAddr,
4721 "returned region inconsistent?");
4722 }
4723 // Remember where the next search should begin.
4724 // The returned region (if non-empty) is a right open interval,
4725 // so lastOffset is obtained from the right end of that
4726 // interval.
4727 lastAddr = dirtyRegion.end();
4728 // Should do something more transparent and less hacky XXX
4729 numDirtyCards =
4730 _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
4731
4732 // We'll scan the cards in the dirty region (with periodic
4733 // yields for foreground GC as needed).
4734 if (!dirtyRegion.is_empty()) {
4735 assert(numDirtyCards > 0, "consistency check");
4736 HeapWord* stop_point = NULL;
4737 stopTimer();
4738 // Potential yield point
4739 CMSTokenSyncWithLocks ts(true, gen->freelistLock(),
4740 bitMapLock());
4741 startTimer();
4742 {
4743 verify_work_stacks_empty();
4744 verify_overflow_empty();
4745 sample_eden();
4746 DEBUG_ONLY(RememberKlassesChecker mx(should_unload_classes());)
4747 stop_point =
4748 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4749 }
4750 if (stop_point != NULL) {
4751 // The careful iteration stopped early either because it found an
4752 // uninitialized object, or because we were in the midst of an
4753 // "abortable preclean", which should now be aborted. Redirty
4754 // the bits corresponding to the partially-scanned or unscanned
4755 // cards. We'll either restart at the next block boundary or
4756 // abort the preclean.
4757 assert((CMSPermGenPrecleaningEnabled && (gen == _permGen)) ||
4758 (_collectorState == AbortablePreclean && should_abort_preclean()),
4759 "Unparsable objects should only be in perm gen.");
4760 _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
4761 if (should_abort_preclean()) {
4762 break; // out of preclean loop
4763 } else {
4764 // Compute the next address at which preclean should pick up;
4765 // might need bitMapLock in order to read P-bits.
4766 lastAddr = next_card_start_after_block(stop_point);
4767 }
4768 }
4769 } else {
4770 assert(lastAddr == endAddr, "consistency check");
4771 assert(numDirtyCards == 0, "consistency check");
4772 break;
4773 }
4774 }
4775 verify_work_stacks_empty();
4776 verify_overflow_empty();
4777 return cumNumDirtyCards;
4778 }
4779
4780 // NOTE: preclean_mod_union_table() above and preclean_card_table()
4781 // below are largely identical; if you need to modify
4782 // one of these methods, please check the other method too.
4783
4784 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* gen,
4785 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4786 // strategy: it's similar to precleamModUnionTable above, in that
4787 // we accumulate contiguous ranges of dirty cards, mark these cards
4788 // precleaned, then scan the region covered by these cards.
4789 HeapWord* endAddr = (HeapWord*)(gen->_virtual_space.high());
4790 HeapWord* startAddr = (HeapWord*)(gen->_virtual_space.low());
4791
4792 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4793
4794 size_t numDirtyCards, cumNumDirtyCards;
4795 HeapWord *lastAddr, *nextAddr;
4796
4797 for (cumNumDirtyCards = numDirtyCards = 0,
4798 nextAddr = lastAddr = startAddr;
4799 nextAddr < endAddr;
4800 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4801
4802 ResourceMark rm;
4803 HandleMark hm;
4804
4805 MemRegion dirtyRegion;
4806 {
4807 // See comments in "Precleaning notes" above on why we
4808 // do this locking. XXX Could the locking overheads be
4809 // too high when dirty cards are sparse? [I don't think so.]
4810 stopTimer();
4811 CMSTokenSync x(true); // is cms thread
4812 startTimer();
4813 sample_eden();
4814 // Get and clear dirty region from card table
4815 dirtyRegion = _ct->ct_bs()->dirty_card_range_after_reset(
4816 MemRegion(nextAddr, endAddr),
4817 true,
4818 CardTableModRefBS::precleaned_card_val());
4819
4820 assert(dirtyRegion.start() >= nextAddr,
4821 "returned region inconsistent?");
4822 }
4823 lastAddr = dirtyRegion.end();
4824 numDirtyCards =
4825 dirtyRegion.word_size()/CardTableModRefBS::card_size_in_words;
4826
4827 if (!dirtyRegion.is_empty()) {
4828 stopTimer();
4829 CMSTokenSyncWithLocks ts(true, gen->freelistLock(), bitMapLock());
4830 startTimer();
4831 sample_eden();
4832 verify_work_stacks_empty();
4833 verify_overflow_empty();
4834 DEBUG_ONLY(RememberKlassesChecker mx(should_unload_classes());)
4835 HeapWord* stop_point =
4836 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4837 if (stop_point != NULL) {
4838 // The careful iteration stopped early because it found an
4839 // uninitialized object. Redirty the bits corresponding to the
4840 // partially-scanned or unscanned cards, and start again at the
4841 // next block boundary.
4842 assert(CMSPermGenPrecleaningEnabled ||
4843 (_collectorState == AbortablePreclean && should_abort_preclean()),
4844 "Unparsable objects should only be in perm gen.");
4845 _ct->ct_bs()->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4846 if (should_abort_preclean()) {
4847 break; // out of preclean loop
4848 } else {
4849 // Compute the next address at which preclean should pick up.
4850 lastAddr = next_card_start_after_block(stop_point);
4851 }
4852 }
4853 } else {
4854 break;
4855 }
4856 }
4857 verify_work_stacks_empty();
4858 verify_overflow_empty();
4859 return cumNumDirtyCards;
4860 }
4861
4862 void CMSCollector::checkpointRootsFinal(bool asynch,
4863 bool clear_all_soft_refs, bool init_mark_was_synchronous) {
4864 assert(_collectorState == FinalMarking, "incorrect state transition?");
4865 check_correct_thread_executing();
4866 // world is stopped at this checkpoint
4867 assert(SafepointSynchronize::is_at_safepoint(),
4868 "world should be stopped");
4869 TraceCMSMemoryManagerStats tms(_collectorState);
4870 verify_work_stacks_empty();
4871 verify_overflow_empty();
4872
4873 SpecializationStats::clear();
4874 if (PrintGCDetails) {
4875 gclog_or_tty->print("[YG occupancy: "SIZE_FORMAT" K ("SIZE_FORMAT" K)]",
4876 _young_gen->used() / K,
4877 _young_gen->capacity() / K);
4878 }
4879 if (asynch) {
4880 if (CMSScavengeBeforeRemark) {
4881 GenCollectedHeap* gch = GenCollectedHeap::heap();
4882 // Temporarily set flag to false, GCH->do_collection will
4883 // expect it to be false and set to true
4884 FlagSetting fl(gch->_is_gc_active, false);
4885 NOT_PRODUCT(TraceTime t("Scavenge-Before-Remark",
4886 PrintGCDetails && Verbose, true, gclog_or_tty);)
4887 int level = _cmsGen->level() - 1;
4888 if (level >= 0) {
4889 gch->do_collection(true, // full (i.e. force, see below)
4890 false, // !clear_all_soft_refs
4891 0, // size
4892 false, // is_tlab
4893 level // max_level
4894 );
4895 }
4896 }
4897 FreelistLocker x(this);
4898 MutexLockerEx y(bitMapLock(),
4899 Mutex::_no_safepoint_check_flag);
4900 assert(!init_mark_was_synchronous, "but that's impossible!");
4901 checkpointRootsFinalWork(asynch, clear_all_soft_refs, false);
4902 } else {
4903 // already have all the locks
4904 checkpointRootsFinalWork(asynch, clear_all_soft_refs,
4905 init_mark_was_synchronous);
4906 }
4907 verify_work_stacks_empty();
4908 verify_overflow_empty();
4909 SpecializationStats::print();
4910 }
4911
4912 void CMSCollector::checkpointRootsFinalWork(bool asynch,
4913 bool clear_all_soft_refs, bool init_mark_was_synchronous) {
4914
4915 NOT_PRODUCT(TraceTime tr("checkpointRootsFinalWork", PrintGCDetails, false, gclog_or_tty);)
4916
4917 assert(haveFreelistLocks(), "must have free list locks");
4918 assert_lock_strong(bitMapLock());
4919
4920 if (UseAdaptiveSizePolicy) {
4921 size_policy()->checkpoint_roots_final_begin();
4922 }
4923
4924 ResourceMark rm;
4925 HandleMark hm;
4926
4927 GenCollectedHeap* gch = GenCollectedHeap::heap();
4928
4929 if (should_unload_classes()) {
4930 CodeCache::gc_prologue();
4931 }
4932 assert(haveFreelistLocks(), "must have free list locks");
4933 assert_lock_strong(bitMapLock());
4934
4935 DEBUG_ONLY(RememberKlassesChecker fmx(should_unload_classes());)
4936 if (!init_mark_was_synchronous) {
4937 // We might assume that we need not fill TLAB's when
4938 // CMSScavengeBeforeRemark is set, because we may have just done
4939 // a scavenge which would have filled all TLAB's -- and besides
4940 // Eden would be empty. This however may not always be the case --
4941 // for instance although we asked for a scavenge, it may not have
4942 // happened because of a JNI critical section. We probably need
4943 // a policy for deciding whether we can in that case wait until
4944 // the critical section releases and then do the remark following
4945 // the scavenge, and skip it here. In the absence of that policy,
4946 // or of an indication of whether the scavenge did indeed occur,
4947 // we cannot rely on TLAB's having been filled and must do
4948 // so here just in case a scavenge did not happen.
4949 gch->ensure_parsability(false); // fill TLAB's, but no need to retire them
4950 // Update the saved marks which may affect the root scans.
4951 gch->save_marks();
4952
4953 {
4954 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
4955
4956 // Note on the role of the mod union table:
4957 // Since the marker in "markFromRoots" marks concurrently with
4958 // mutators, it is possible for some reachable objects not to have been
4959 // scanned. For instance, an only reference to an object A was
4960 // placed in object B after the marker scanned B. Unless B is rescanned,
4961 // A would be collected. Such updates to references in marked objects
4962 // are detected via the mod union table which is the set of all cards
4963 // dirtied since the first checkpoint in this GC cycle and prior to
4964 // the most recent young generation GC, minus those cleaned up by the
4965 // concurrent precleaning.
4966 if (CMSParallelRemarkEnabled && CollectedHeap::use_parallel_gc_threads()) {
4967 TraceTime t("Rescan (parallel) ", PrintGCDetails, false, gclog_or_tty);
4968 do_remark_parallel();
4969 } else {
4970 TraceTime t("Rescan (non-parallel) ", PrintGCDetails, false,
4971 gclog_or_tty);
4972 do_remark_non_parallel();
4973 }
4974 }
4975 } else {
4976 assert(!asynch, "Can't have init_mark_was_synchronous in asynch mode");
4977 // The initial mark was stop-world, so there's no rescanning to
4978 // do; go straight on to the next step below.
4979 }
4980 verify_work_stacks_empty();
4981 verify_overflow_empty();
4982
4983 {
4984 NOT_PRODUCT(TraceTime ts("refProcessingWork", PrintGCDetails, false, gclog_or_tty);)
4985 refProcessingWork(asynch, clear_all_soft_refs);
4986 }
4987 verify_work_stacks_empty();
4988 verify_overflow_empty();
4989
4990 if (should_unload_classes()) {
4991 CodeCache::gc_epilogue();
4992 }
4993
4994 // If we encountered any (marking stack / work queue) overflow
4995 // events during the current CMS cycle, take appropriate
4996 // remedial measures, where possible, so as to try and avoid
4997 // recurrence of that condition.
4998 assert(_markStack.isEmpty(), "No grey objects");
4999 size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
5000 _ser_kac_ovflw + _ser_kac_preclean_ovflw;
5001 if (ser_ovflw > 0) {
5002 if (PrintCMSStatistics != 0) {
5003 gclog_or_tty->print_cr("Marking stack overflow (benign) "
5004 "(pmc_pc="SIZE_FORMAT", pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT
5005 ", kac_preclean="SIZE_FORMAT")",
5006 _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw,
5007 _ser_kac_ovflw, _ser_kac_preclean_ovflw);
5008 }
5009 _markStack.expand();
5010 _ser_pmc_remark_ovflw = 0;
5011 _ser_pmc_preclean_ovflw = 0;
5012 _ser_kac_preclean_ovflw = 0;
5013 _ser_kac_ovflw = 0;
5014 }
5015 if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
5016 if (PrintCMSStatistics != 0) {
5017 gclog_or_tty->print_cr("Work queue overflow (benign) "
5018 "(pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT")",
5019 _par_pmc_remark_ovflw, _par_kac_ovflw);
5020 }
5021 _par_pmc_remark_ovflw = 0;
5022 _par_kac_ovflw = 0;
5023 }
5024 if (PrintCMSStatistics != 0) {
5025 if (_markStack._hit_limit > 0) {
5026 gclog_or_tty->print_cr(" (benign) Hit max stack size limit ("SIZE_FORMAT")",
5027 _markStack._hit_limit);
5028 }
5029 if (_markStack._failed_double > 0) {
5030 gclog_or_tty->print_cr(" (benign) Failed stack doubling ("SIZE_FORMAT"),"
5031 " current capacity "SIZE_FORMAT,
5032 _markStack._failed_double,
5033 _markStack.capacity());
5034 }
5035 }
5036 _markStack._hit_limit = 0;
5037 _markStack._failed_double = 0;
5038
5039 // Check that all the klasses have been checked
5040 assert(_revisitStack.isEmpty(), "Not all klasses revisited");
5041
5042 if ((VerifyAfterGC || VerifyDuringGC) &&
5043 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5044 verify_after_remark();
5045 }
5046
5047 // Change under the freelistLocks.
5048 _collectorState = Sweeping;
5049 // Call isAllClear() under bitMapLock
5050 assert(_modUnionTable.isAllClear(), "Should be clear by end of the"
5051 " final marking");
5052 if (UseAdaptiveSizePolicy) {
5053 size_policy()->checkpoint_roots_final_end(gch->gc_cause());
5054 }
5055 }
5056
5057 // Parallel remark task
5058 class CMSParRemarkTask: public AbstractGangTask {
5059 CMSCollector* _collector;
5060 int _n_workers;
5061 CompactibleFreeListSpace* _cms_space;
5062 CompactibleFreeListSpace* _perm_space;
5063
5064 // The per-thread work queues, available here for stealing.
5065 OopTaskQueueSet* _task_queues;
5066 ParallelTaskTerminator _term;
5067
5068 public:
5069 CMSParRemarkTask(CMSCollector* collector,
5070 CompactibleFreeListSpace* cms_space,
5071 CompactibleFreeListSpace* perm_space,
5072 int n_workers, FlexibleWorkGang* workers,
5073 OopTaskQueueSet* task_queues):
5074 AbstractGangTask("Rescan roots and grey objects in parallel"),
5075 _collector(collector),
5076 _cms_space(cms_space), _perm_space(perm_space),
5077 _n_workers(n_workers),
5078 _task_queues(task_queues),
5079 _term(n_workers, task_queues) { }
5080
5081 OopTaskQueueSet* task_queues() { return _task_queues; }
5082
5083 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5084
5085 ParallelTaskTerminator* terminator() { return &_term; }
5086 int n_workers() { return _n_workers; }
5087
5088 void work(int i);
5089
5090 private:
5091 // Work method in support of parallel rescan ... of young gen spaces
5092 void do_young_space_rescan(int i, Par_MarkRefsIntoAndScanClosure* cl,
5093 ContiguousSpace* space,
5094 HeapWord** chunk_array, size_t chunk_top);
5095
5096 // ... of dirty cards in old space
5097 void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
5098 Par_MarkRefsIntoAndScanClosure* cl);
5099
5100 // ... work stealing for the above
5101 void do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl, int* seed);
5102 };
5103
5104 // work_queue(i) is passed to the closure
5105 // Par_MarkRefsIntoAndScanClosure. The "i" parameter
5106 // also is passed to do_dirty_card_rescan_tasks() and to
5107 // do_work_steal() to select the i-th task_queue.
5108
5109 void CMSParRemarkTask::work(int i) {
5110 elapsedTimer _timer;
5111 ResourceMark rm;
5112 HandleMark hm;
5113
5114 // ---------- rescan from roots --------------
5115 _timer.start();
5116 GenCollectedHeap* gch = GenCollectedHeap::heap();
5117 Par_MarkRefsIntoAndScanClosure par_mrias_cl(_collector,
5118 _collector->_span, _collector->ref_processor(),
5119 &(_collector->_markBitMap),
5120 work_queue(i), &(_collector->_revisitStack));
5121
5122 // Rescan young gen roots first since these are likely
5123 // coarsely partitioned and may, on that account, constitute
5124 // the critical path; thus, it's best to start off that
5125 // work first.
5126 // ---------- young gen roots --------------
5127 {
5128 DefNewGeneration* dng = _collector->_young_gen->as_DefNewGeneration();
5129 EdenSpace* eden_space = dng->eden();
5130 ContiguousSpace* from_space = dng->from();
5131 ContiguousSpace* to_space = dng->to();
5132
5133 HeapWord** eca = _collector->_eden_chunk_array;
5134 size_t ect = _collector->_eden_chunk_index;
5135 HeapWord** sca = _collector->_survivor_chunk_array;
5136 size_t sct = _collector->_survivor_chunk_index;
5137
5138 assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
5139 assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
5140
5141 do_young_space_rescan(i, &par_mrias_cl, to_space, NULL, 0);
5142 do_young_space_rescan(i, &par_mrias_cl, from_space, sca, sct);
5143 do_young_space_rescan(i, &par_mrias_cl, eden_space, eca, ect);
5144
5145 _timer.stop();
5146 if (PrintCMSStatistics != 0) {
5147 gclog_or_tty->print_cr(
5148 "Finished young gen rescan work in %dth thread: %3.3f sec",
5149 i, _timer.seconds());
5150 }
5151 }
5152
5153 // ---------- remaining roots --------------
5154 _timer.reset();
5155 _timer.start();
5156 gch->gen_process_strong_roots(_collector->_cmsGen->level(),
5157 false, // yg was scanned above
5158 false, // this is parallel code
5159 true, // collecting perm gen
5160 SharedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
5161 &par_mrias_cl,
5162 true, // walk all of code cache if (so & SO_CodeCache)
5163 NULL);
5164 assert(_collector->should_unload_classes()
5165 || (_collector->CMSCollector::roots_scanning_options() & SharedHeap::SO_CodeCache),
5166 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5167 _timer.stop();
5168 if (PrintCMSStatistics != 0) {
5169 gclog_or_tty->print_cr(
5170 "Finished remaining root rescan work in %dth thread: %3.3f sec",
5171 i, _timer.seconds());
5172 }
5173
5174 // ---------- rescan dirty cards ------------
5175 _timer.reset();
5176 _timer.start();
5177
5178 // Do the rescan tasks for each of the two spaces
5179 // (cms_space and perm_space) in turn.
5180 // "i" is passed to select the "i-th" task_queue
5181 do_dirty_card_rescan_tasks(_cms_space, i, &par_mrias_cl);
5182 do_dirty_card_rescan_tasks(_perm_space, i, &par_mrias_cl);
5183 _timer.stop();
5184 if (PrintCMSStatistics != 0) {
5185 gclog_or_tty->print_cr(
5186 "Finished dirty card rescan work in %dth thread: %3.3f sec",
5187 i, _timer.seconds());
5188 }
5189
5190 // ---------- steal work from other threads ...
5191 // ---------- ... and drain overflow list.
5192 _timer.reset();
5193 _timer.start();
5194 do_work_steal(i, &par_mrias_cl, _collector->hash_seed(i));
5195 _timer.stop();
5196 if (PrintCMSStatistics != 0) {
5197 gclog_or_tty->print_cr(
5198 "Finished work stealing in %dth thread: %3.3f sec",
5199 i, _timer.seconds());
5200 }
5201 }
5202
5203 // Note that parameter "i" is not used.
5204 void
5205 CMSParRemarkTask::do_young_space_rescan(int i,
5206 Par_MarkRefsIntoAndScanClosure* cl, ContiguousSpace* space,
5207 HeapWord** chunk_array, size_t chunk_top) {
5208 // Until all tasks completed:
5209 // . claim an unclaimed task
5210 // . compute region boundaries corresponding to task claimed
5211 // using chunk_array
5212 // . par_oop_iterate(cl) over that region
5213
5214 ResourceMark rm;
5215 HandleMark hm;
5216
5217 SequentialSubTasksDone* pst = space->par_seq_tasks();
5218 assert(pst->valid(), "Uninitialized use?");
5219
5220 int nth_task = 0;
5221 int n_tasks = pst->n_tasks();
5222
5223 HeapWord *start, *end;
5224 while (!pst->is_task_claimed(/* reference */ nth_task)) {
5225 // We claimed task # nth_task; compute its boundaries.
5226 if (chunk_top == 0) { // no samples were taken
5227 assert(nth_task == 0 && n_tasks == 1, "Can have only 1 EdenSpace task");
5228 start = space->bottom();
5229 end = space->top();
5230 } else if (nth_task == 0) {
5231 start = space->bottom();
5232 end = chunk_array[nth_task];
5233 } else if (nth_task < (jint)chunk_top) {
5234 assert(nth_task >= 1, "Control point invariant");
5235 start = chunk_array[nth_task - 1];
5236 end = chunk_array[nth_task];
5237 } else {
5238 assert(nth_task == (jint)chunk_top, "Control point invariant");
5239 start = chunk_array[chunk_top - 1];
5240 end = space->top();
5241 }
5242 MemRegion mr(start, end);
5243 // Verify that mr is in space
5244 assert(mr.is_empty() || space->used_region().contains(mr),
5245 "Should be in space");
5246 // Verify that "start" is an object boundary
5247 assert(mr.is_empty() || oop(mr.start())->is_oop(),
5248 "Should be an oop");
5249 space->par_oop_iterate(mr, cl);
5250 }
5251 pst->all_tasks_completed();
5252 }
5253
5254 void
5255 CMSParRemarkTask::do_dirty_card_rescan_tasks(
5256 CompactibleFreeListSpace* sp, int i,
5257 Par_MarkRefsIntoAndScanClosure* cl) {
5258 // Until all tasks completed:
5259 // . claim an unclaimed task
5260 // . compute region boundaries corresponding to task claimed
5261 // . transfer dirty bits ct->mut for that region
5262 // . apply rescanclosure to dirty mut bits for that region
5263
5264 ResourceMark rm;
5265 HandleMark hm;
5266
5267 OopTaskQueue* work_q = work_queue(i);
5268 ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
5269 // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
5270 // CAUTION: This closure has state that persists across calls to
5271 // the work method dirty_range_iterate_clear() in that it has
5272 // imbedded in it a (subtype of) UpwardsObjectClosure. The
5273 // use of that state in the imbedded UpwardsObjectClosure instance
5274 // assumes that the cards are always iterated (even if in parallel
5275 // by several threads) in monotonically increasing order per each
5276 // thread. This is true of the implementation below which picks
5277 // card ranges (chunks) in monotonically increasing order globally
5278 // and, a-fortiori, in monotonically increasing order per thread
5279 // (the latter order being a subsequence of the former).
5280 // If the work code below is ever reorganized into a more chaotic
5281 // work-partitioning form than the current "sequential tasks"
5282 // paradigm, the use of that persistent state will have to be
5283 // revisited and modified appropriately. See also related
5284 // bug 4756801 work on which should examine this code to make
5285 // sure that the changes there do not run counter to the
5286 // assumptions made here and necessary for correctness and
5287 // efficiency. Note also that this code might yield inefficient
5288 // behaviour in the case of very large objects that span one or
5289 // more work chunks. Such objects would potentially be scanned
5290 // several times redundantly. Work on 4756801 should try and
5291 // address that performance anomaly if at all possible. XXX
5292 MemRegion full_span = _collector->_span;
5293 CMSBitMap* bm = &(_collector->_markBitMap); // shared
5294 CMSMarkStack* rs = &(_collector->_revisitStack); // shared
5295 MarkFromDirtyCardsClosure
5296 greyRescanClosure(_collector, full_span, // entire span of interest
5297 sp, bm, work_q, rs, cl);
5298
5299 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
5300 assert(pst->valid(), "Uninitialized use?");
5301 int nth_task = 0;
5302 const int alignment = CardTableModRefBS::card_size * BitsPerWord;
5303 MemRegion span = sp->used_region();
5304 HeapWord* start_addr = span.start();
5305 HeapWord* end_addr = (HeapWord*)round_to((intptr_t)span.end(),
5306 alignment);
5307 const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
5308 assert((HeapWord*)round_to((intptr_t)start_addr, alignment) ==
5309 start_addr, "Check alignment");
5310 assert((size_t)round_to((intptr_t)chunk_size, alignment) ==
5311 chunk_size, "Check alignment");
5312
5313 while (!pst->is_task_claimed(/* reference */ nth_task)) {
5314 // Having claimed the nth_task, compute corresponding mem-region,
5315 // which is a-fortiori aligned correctly (i.e. at a MUT bopundary).
5316 // The alignment restriction ensures that we do not need any
5317 // synchronization with other gang-workers while setting or
5318 // clearing bits in thus chunk of the MUT.
5319 MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
5320 start_addr + (nth_task+1)*chunk_size);
5321 // The last chunk's end might be way beyond end of the
5322 // used region. In that case pull back appropriately.
5323 if (this_span.end() > end_addr) {
5324 this_span.set_end(end_addr);
5325 assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
5326 }
5327 // Iterate over the dirty cards covering this chunk, marking them
5328 // precleaned, and setting the corresponding bits in the mod union
5329 // table. Since we have been careful to partition at Card and MUT-word
5330 // boundaries no synchronization is needed between parallel threads.
5331 _collector->_ct->ct_bs()->dirty_card_iterate(this_span,
5332 &modUnionClosure);
5333
5334 // Having transferred these marks into the modUnionTable,
5335 // rescan the marked objects on the dirty cards in the modUnionTable.
5336 // Even if this is at a synchronous collection, the initial marking
5337 // may have been done during an asynchronous collection so there
5338 // may be dirty bits in the mod-union table.
5339 _collector->_modUnionTable.dirty_range_iterate_clear(
5340 this_span, &greyRescanClosure);
5341 _collector->_modUnionTable.verifyNoOneBitsInRange(
5342 this_span.start(),
5343 this_span.end());
5344 }
5345 pst->all_tasks_completed(); // declare that i am done
5346 }
5347
5348 // . see if we can share work_queues with ParNew? XXX
5349 void
5350 CMSParRemarkTask::do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl,
5351 int* seed) {
5352 OopTaskQueue* work_q = work_queue(i);
5353 NOT_PRODUCT(int num_steals = 0;)
5354 oop obj_to_scan;
5355 CMSBitMap* bm = &(_collector->_markBitMap);
5356
5357 while (true) {
5358 // Completely finish any left over work from (an) earlier round(s)
5359 cl->trim_queue(0);
5360 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5361 (size_t)ParGCDesiredObjsFromOverflowList);
5362 // Now check if there's any work in the overflow list
5363 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5364 // only affects the number of attempts made to get work from the
5365 // overflow list and does not affect the number of workers. Just
5366 // pass ParallelGCThreads so this behavior is unchanged.
5367 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5368 work_q,
5369 ParallelGCThreads)) {
5370 // found something in global overflow list;
5371 // not yet ready to go stealing work from others.
5372 // We'd like to assert(work_q->size() != 0, ...)
5373 // because we just took work from the overflow list,
5374 // but of course we can't since all of that could have
5375 // been already stolen from us.
5376 // "He giveth and He taketh away."
5377 continue;
5378 }
5379 // Verify that we have no work before we resort to stealing
5380 assert(work_q->size() == 0, "Have work, shouldn't steal");
5381 // Try to steal from other queues that have work
5382 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5383 NOT_PRODUCT(num_steals++;)
5384 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5385 assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5386 // Do scanning work
5387 obj_to_scan->oop_iterate(cl);
5388 // Loop around, finish this work, and try to steal some more
5389 } else if (terminator()->offer_termination()) {
5390 break; // nirvana from the infinite cycle
5391 }
5392 }
5393 NOT_PRODUCT(
5394 if (PrintCMSStatistics != 0) {
5395 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5396 }
5397 )
5398 assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
5399 "Else our work is not yet done");
5400 }
5401
5402 // Return a thread-local PLAB recording array, as appropriate.
5403 void* CMSCollector::get_data_recorder(int thr_num) {
5404 if (_survivor_plab_array != NULL &&
5405 (CMSPLABRecordAlways ||
5406 (_collectorState > Marking && _collectorState < FinalMarking))) {
5407 assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
5408 ChunkArray* ca = &_survivor_plab_array[thr_num];
5409 ca->reset(); // clear it so that fresh data is recorded
5410 return (void*) ca;
5411 } else {
5412 return NULL;
5413 }
5414 }
5415
5416 // Reset all the thread-local PLAB recording arrays
5417 void CMSCollector::reset_survivor_plab_arrays() {
5418 for (uint i = 0; i < ParallelGCThreads; i++) {
5419 _survivor_plab_array[i].reset();
5420 }
5421 }
5422
5423 // Merge the per-thread plab arrays into the global survivor chunk
5424 // array which will provide the partitioning of the survivor space
5425 // for CMS rescan.
5426 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv,
5427 int no_of_gc_threads) {
5428 assert(_survivor_plab_array != NULL, "Error");
5429 assert(_survivor_chunk_array != NULL, "Error");
5430 assert(_collectorState == FinalMarking, "Error");
5431 for (int j = 0; j < no_of_gc_threads; j++) {
5432 _cursor[j] = 0;
5433 }
5434 HeapWord* top = surv->top();
5435 size_t i;
5436 for (i = 0; i < _survivor_chunk_capacity; i++) { // all sca entries
5437 HeapWord* min_val = top; // Higher than any PLAB address
5438 uint min_tid = 0; // position of min_val this round
5439 for (int j = 0; j < no_of_gc_threads; j++) {
5440 ChunkArray* cur_sca = &_survivor_plab_array[j];
5441 if (_cursor[j] == cur_sca->end()) {
5442 continue;
5443 }
5444 assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
5445 HeapWord* cur_val = cur_sca->nth(_cursor[j]);
5446 assert(surv->used_region().contains(cur_val), "Out of bounds value");
5447 if (cur_val < min_val) {
5448 min_tid = j;
5449 min_val = cur_val;
5450 } else {
5451 assert(cur_val < top, "All recorded addresses should be less");
5452 }
5453 }
5454 // At this point min_val and min_tid are respectively
5455 // the least address in _survivor_plab_array[j]->nth(_cursor[j])
5456 // and the thread (j) that witnesses that address.
5457 // We record this address in the _survivor_chunk_array[i]
5458 // and increment _cursor[min_tid] prior to the next round i.
5459 if (min_val == top) {
5460 break;
5461 }
5462 _survivor_chunk_array[i] = min_val;
5463 _cursor[min_tid]++;
5464 }
5465 // We are all done; record the size of the _survivor_chunk_array
5466 _survivor_chunk_index = i; // exclusive: [0, i)
5467 if (PrintCMSStatistics > 0) {
5468 gclog_or_tty->print(" (Survivor:" SIZE_FORMAT "chunks) ", i);
5469 }
5470 // Verify that we used up all the recorded entries
5471 #ifdef ASSERT
5472 size_t total = 0;
5473 for (int j = 0; j < no_of_gc_threads; j++) {
5474 assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
5475 total += _cursor[j];
5476 }
5477 assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
5478 // Check that the merged array is in sorted order
5479 if (total > 0) {
5480 for (size_t i = 0; i < total - 1; i++) {
5481 if (PrintCMSStatistics > 0) {
5482 gclog_or_tty->print(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
5483 i, _survivor_chunk_array[i]);
5484 }
5485 assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
5486 "Not sorted");
5487 }
5488 }
5489 #endif // ASSERT
5490 }
5491
5492 // Set up the space's par_seq_tasks structure for work claiming
5493 // for parallel rescan of young gen.
5494 // See ParRescanTask where this is currently used.
5495 void
5496 CMSCollector::
5497 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
5498 assert(n_threads > 0, "Unexpected n_threads argument");
5499 DefNewGeneration* dng = (DefNewGeneration*)_young_gen;
5500
5501 // Eden space
5502 {
5503 SequentialSubTasksDone* pst = dng->eden()->par_seq_tasks();
5504 assert(!pst->valid(), "Clobbering existing data?");
5505 // Each valid entry in [0, _eden_chunk_index) represents a task.
5506 size_t n_tasks = _eden_chunk_index + 1;
5507 assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
5508 // Sets the condition for completion of the subtask (how many threads
5509 // need to finish in order to be done).
5510 pst->set_n_threads(n_threads);
5511 pst->set_n_tasks((int)n_tasks);
5512 }
5513
5514 // Merge the survivor plab arrays into _survivor_chunk_array
5515 if (_survivor_plab_array != NULL) {
5516 merge_survivor_plab_arrays(dng->from(), n_threads);
5517 } else {
5518 assert(_survivor_chunk_index == 0, "Error");
5519 }
5520
5521 // To space
5522 {
5523 SequentialSubTasksDone* pst = dng->to()->par_seq_tasks();
5524 assert(!pst->valid(), "Clobbering existing data?");
5525 // Sets the condition for completion of the subtask (how many threads
5526 // need to finish in order to be done).
5527 pst->set_n_threads(n_threads);
5528 pst->set_n_tasks(1);
5529 assert(pst->valid(), "Error");
5530 }
5531
5532 // From space
5533 {
5534 SequentialSubTasksDone* pst = dng->from()->par_seq_tasks();
5535 assert(!pst->valid(), "Clobbering existing data?");
5536 size_t n_tasks = _survivor_chunk_index + 1;
5537 assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
5538 // Sets the condition for completion of the subtask (how many threads
5539 // need to finish in order to be done).
5540 pst->set_n_threads(n_threads);
5541 pst->set_n_tasks((int)n_tasks);
5542 assert(pst->valid(), "Error");
5543 }
5544 }
5545
5546 // Parallel version of remark
5547 void CMSCollector::do_remark_parallel() {
5548 GenCollectedHeap* gch = GenCollectedHeap::heap();
5549 FlexibleWorkGang* workers = gch->workers();
5550 assert(workers != NULL, "Need parallel worker threads.");
5551 int n_workers = workers->total_workers();
5552 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
5553 CompactibleFreeListSpace* perm_space = _permGen->cmsSpace();
5554
5555 CMSParRemarkTask tsk(this,
5556 cms_space, perm_space,
5557 n_workers, workers, task_queues());
5558
5559 // Set up for parallel process_strong_roots work.
5560 gch->set_par_threads(n_workers);
5561 // We won't be iterating over the cards in the card table updating
5562 // the younger_gen cards, so we shouldn't call the following else
5563 // the verification code as well as subsequent younger_refs_iterate
5564 // code would get confused. XXX
5565 // gch->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
5566
5567 // The young gen rescan work will not be done as part of
5568 // process_strong_roots (which currently doesn't knw how to
5569 // parallelize such a scan), but rather will be broken up into
5570 // a set of parallel tasks (via the sampling that the [abortable]
5571 // preclean phase did of EdenSpace, plus the [two] tasks of
5572 // scanning the [two] survivor spaces. Further fine-grain
5573 // parallelization of the scanning of the survivor spaces
5574 // themselves, and of precleaning of the younger gen itself
5575 // is deferred to the future.
5576 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
5577
5578 // The dirty card rescan work is broken up into a "sequence"
5579 // of parallel tasks (per constituent space) that are dynamically
5580 // claimed by the parallel threads.
5581 cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
5582 perm_space->initialize_sequential_subtasks_for_rescan(n_workers);
5583
5584 // It turns out that even when we're using 1 thread, doing the work in a
5585 // separate thread causes wide variance in run times. We can't help this
5586 // in the multi-threaded case, but we special-case n=1 here to get
5587 // repeatable measurements of the 1-thread overhead of the parallel code.
5588 if (n_workers > 1) {
5589 // Make refs discovery MT-safe
5590 ReferenceProcessorMTMutator mt(ref_processor(), true);
5591 GenCollectedHeap::StrongRootsScope srs(gch);
5592 workers->run_task(&tsk);
5593 } else {
5594 GenCollectedHeap::StrongRootsScope srs(gch);
5595 tsk.work(0);
5596 }
5597 gch->set_par_threads(0); // 0 ==> non-parallel.
5598 // restore, single-threaded for now, any preserved marks
5599 // as a result of work_q overflow
5600 restore_preserved_marks_if_any();
5601 }
5602
5603 // Non-parallel version of remark
5604 void CMSCollector::do_remark_non_parallel() {
5605 ResourceMark rm;
5606 HandleMark hm;
5607 GenCollectedHeap* gch = GenCollectedHeap::heap();
5608 MarkRefsIntoAndScanClosure
5609 mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
5610 &_markStack, &_revisitStack, this,
5611 false /* should_yield */, false /* not precleaning */);
5612 MarkFromDirtyCardsClosure
5613 markFromDirtyCardsClosure(this, _span,
5614 NULL, // space is set further below
5615 &_markBitMap, &_markStack, &_revisitStack,
5616 &mrias_cl);
5617 {
5618 TraceTime t("grey object rescan", PrintGCDetails, false, gclog_or_tty);
5619 // Iterate over the dirty cards, setting the corresponding bits in the
5620 // mod union table.
5621 {
5622 ModUnionClosure modUnionClosure(&_modUnionTable);
5623 _ct->ct_bs()->dirty_card_iterate(
5624 _cmsGen->used_region(),
5625 &modUnionClosure);
5626 _ct->ct_bs()->dirty_card_iterate(
5627 _permGen->used_region(),
5628 &modUnionClosure);
5629 }
5630 // Having transferred these marks into the modUnionTable, we just need
5631 // to rescan the marked objects on the dirty cards in the modUnionTable.
5632 // The initial marking may have been done during an asynchronous
5633 // collection so there may be dirty bits in the mod-union table.
5634 const int alignment =
5635 CardTableModRefBS::card_size * BitsPerWord;
5636 {
5637 // ... First handle dirty cards in CMS gen
5638 markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
5639 MemRegion ur = _cmsGen->used_region();
5640 HeapWord* lb = ur.start();
5641 HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
5642 MemRegion cms_span(lb, ub);
5643 _modUnionTable.dirty_range_iterate_clear(cms_span,
5644 &markFromDirtyCardsClosure);
5645 verify_work_stacks_empty();
5646 if (PrintCMSStatistics != 0) {
5647 gclog_or_tty->print(" (re-scanned "SIZE_FORMAT" dirty cards in cms gen) ",
5648 markFromDirtyCardsClosure.num_dirty_cards());
5649 }
5650 }
5651 {
5652 // .. and then repeat for dirty cards in perm gen
5653 markFromDirtyCardsClosure.set_space(_permGen->cmsSpace());
5654 MemRegion ur = _permGen->used_region();
5655 HeapWord* lb = ur.start();
5656 HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
5657 MemRegion perm_span(lb, ub);
5658 _modUnionTable.dirty_range_iterate_clear(perm_span,
5659 &markFromDirtyCardsClosure);
5660 verify_work_stacks_empty();
5661 if (PrintCMSStatistics != 0) {
5662 gclog_or_tty->print(" (re-scanned "SIZE_FORMAT" dirty cards in perm gen) ",
5663 markFromDirtyCardsClosure.num_dirty_cards());
5664 }
5665 }
5666 }
5667 if (VerifyDuringGC &&
5668 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5669 HandleMark hm; // Discard invalid handles created during verification
5670 Universe::verify(true);
5671 }
5672 {
5673 TraceTime t("root rescan", PrintGCDetails, false, gclog_or_tty);
5674
5675 verify_work_stacks_empty();
5676
5677 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
5678 GenCollectedHeap::StrongRootsScope srs(gch);
5679 gch->gen_process_strong_roots(_cmsGen->level(),
5680 true, // younger gens as roots
5681 false, // use the local StrongRootsScope
5682 true, // collecting perm gen
5683 SharedHeap::ScanningOption(roots_scanning_options()),
5684 &mrias_cl,
5685 true, // walk code active on stacks
5686 NULL);
5687 assert(should_unload_classes()
5688 || (roots_scanning_options() & SharedHeap::SO_CodeCache),
5689 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5690 }
5691 verify_work_stacks_empty();
5692 // Restore evacuated mark words, if any, used for overflow list links
5693 if (!CMSOverflowEarlyRestoration) {
5694 restore_preserved_marks_if_any();
5695 }
5696 verify_overflow_empty();
5697 }
5698
5699 ////////////////////////////////////////////////////////
5700 // Parallel Reference Processing Task Proxy Class
5701 ////////////////////////////////////////////////////////
5702 class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues {
5703 typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
5704 CMSCollector* _collector;
5705 CMSBitMap* _mark_bit_map;
5706 const MemRegion _span;
5707 ProcessTask& _task;
5708
5709 public:
5710 CMSRefProcTaskProxy(ProcessTask& task,
5711 CMSCollector* collector,
5712 const MemRegion& span,
5713 CMSBitMap* mark_bit_map,
5714 AbstractWorkGang* workers,
5715 OopTaskQueueSet* task_queues):
5716 AbstractGangTaskWOopQueues("Process referents by policy in parallel",
5717 task_queues),
5718 _task(task),
5719 _collector(collector), _span(span), _mark_bit_map(mark_bit_map)
5720 {
5721 assert(_collector->_span.equals(_span) && !_span.is_empty(),
5722 "Inconsistency in _span");
5723 }
5724
5725 OopTaskQueueSet* task_queues() { return queues(); }
5726
5727 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5728
5729 void do_work_steal(int i,
5730 CMSParDrainMarkingStackClosure* drain,
5731 CMSParKeepAliveClosure* keep_alive,
5732 int* seed);
5733
5734 virtual void work(int i);
5735 };
5736
5737 void CMSRefProcTaskProxy::work(int i) {
5738 assert(_collector->_span.equals(_span), "Inconsistency in _span");
5739 CMSParKeepAliveClosure par_keep_alive(_collector, _span,
5740 _mark_bit_map,
5741 &_collector->_revisitStack,
5742 work_queue(i));
5743 CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
5744 _mark_bit_map,
5745 &_collector->_revisitStack,
5746 work_queue(i));
5747 CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
5748 _task.work(i, is_alive_closure, par_keep_alive, par_drain_stack);
5749 if (_task.marks_oops_alive()) {
5750 do_work_steal(i, &par_drain_stack, &par_keep_alive,
5751 _collector->hash_seed(i));
5752 }
5753 assert(work_queue(i)->size() == 0, "work_queue should be empty");
5754 assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
5755 }
5756
5757 class CMSRefEnqueueTaskProxy: public AbstractGangTask {
5758 typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
5759 EnqueueTask& _task;
5760
5761 public:
5762 CMSRefEnqueueTaskProxy(EnqueueTask& task)
5763 : AbstractGangTask("Enqueue reference objects in parallel"),
5764 _task(task)
5765 { }
5766
5767 virtual void work(int i)
5768 {
5769 _task.work(i);
5770 }
5771 };
5772
5773 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
5774 MemRegion span, CMSBitMap* bit_map, CMSMarkStack* revisit_stack,
5775 OopTaskQueue* work_queue):
5776 Par_KlassRememberingOopClosure(collector, NULL, revisit_stack),
5777 _span(span),
5778 _bit_map(bit_map),
5779 _work_queue(work_queue),
5780 _mark_and_push(collector, span, bit_map, revisit_stack, work_queue),
5781 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
5782 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads)))
5783 { }
5784
5785 // . see if we can share work_queues with ParNew? XXX
5786 void CMSRefProcTaskProxy::do_work_steal(int i,
5787 CMSParDrainMarkingStackClosure* drain,
5788 CMSParKeepAliveClosure* keep_alive,
5789 int* seed) {
5790 OopTaskQueue* work_q = work_queue(i);
5791 NOT_PRODUCT(int num_steals = 0;)
5792 oop obj_to_scan;
5793
5794 while (true) {
5795 // Completely finish any left over work from (an) earlier round(s)
5796 drain->trim_queue(0);
5797 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5798 (size_t)ParGCDesiredObjsFromOverflowList);
5799 // Now check if there's any work in the overflow list
5800 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5801 // only affects the number of attempts made to get work from the
5802 // overflow list and does not affect the number of workers. Just
5803 // pass ParallelGCThreads so this behavior is unchanged.
5804 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5805 work_q,
5806 ParallelGCThreads)) {
5807 // Found something in global overflow list;
5808 // not yet ready to go stealing work from others.
5809 // We'd like to assert(work_q->size() != 0, ...)
5810 // because we just took work from the overflow list,
5811 // but of course we can't, since all of that might have
5812 // been already stolen from us.
5813 continue;
5814 }
5815 // Verify that we have no work before we resort to stealing
5816 assert(work_q->size() == 0, "Have work, shouldn't steal");
5817 // Try to steal from other queues that have work
5818 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5819 NOT_PRODUCT(num_steals++;)
5820 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5821 assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5822 // Do scanning work
5823 obj_to_scan->oop_iterate(keep_alive);
5824 // Loop around, finish this work, and try to steal some more
5825 } else if (terminator()->offer_termination()) {
5826 break; // nirvana from the infinite cycle
5827 }
5828 }
5829 NOT_PRODUCT(
5830 if (PrintCMSStatistics != 0) {
5831 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5832 }
5833 )
5834 }
5835
5836 void CMSRefProcTaskExecutor::execute(ProcessTask& task)
5837 {
5838 GenCollectedHeap* gch = GenCollectedHeap::heap();
5839 FlexibleWorkGang* workers = gch->workers();
5840 assert(workers != NULL, "Need parallel worker threads.");
5841 CMSRefProcTaskProxy rp_task(task, &_collector,
5842 _collector.ref_processor()->span(),
5843 _collector.markBitMap(),
5844 workers, _collector.task_queues());
5845 workers->run_task(&rp_task);
5846 }
5847
5848 void CMSRefProcTaskExecutor::execute(EnqueueTask& task)
5849 {
5850
5851 GenCollectedHeap* gch = GenCollectedHeap::heap();
5852 FlexibleWorkGang* workers = gch->workers();
5853 assert(workers != NULL, "Need parallel worker threads.");
5854 CMSRefEnqueueTaskProxy enq_task(task);
5855 workers->run_task(&enq_task);
5856 }
5857
5858 void CMSCollector::refProcessingWork(bool asynch, bool clear_all_soft_refs) {
5859
5860 ResourceMark rm;
5861 HandleMark hm;
5862
5863 ReferenceProcessor* rp = ref_processor();
5864 assert(rp->span().equals(_span), "Spans should be equal");
5865 assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
5866 // Process weak references.
5867 rp->setup_policy(clear_all_soft_refs);
5868 verify_work_stacks_empty();
5869
5870 CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
5871 &_markStack, &_revisitStack,
5872 false /* !preclean */);
5873 CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
5874 _span, &_markBitMap, &_markStack,
5875 &cmsKeepAliveClosure, false /* !preclean */);
5876 {
5877 TraceTime t("weak refs processing", PrintGCDetails, false, gclog_or_tty);
5878 if (rp->processing_is_mt()) {
5879 // Set the degree of MT here. If the discovery is done MT, there
5880 // may have been a different number of threads doing the discovery
5881 // and a different number of discovered lists may have Ref objects.
5882 // That is OK as long as the Reference lists are balanced (see
5883 // balance_all_queues() and balance_queues()).
5884
5885
5886 rp->set_mt_degree(ParallelGCThreads);
5887 CMSRefProcTaskExecutor task_executor(*this);
5888 rp->process_discovered_references(&_is_alive_closure,
5889 &cmsKeepAliveClosure,
5890 &cmsDrainMarkingStackClosure,
5891 &task_executor);
5892 } else {
5893 rp->process_discovered_references(&_is_alive_closure,
5894 &cmsKeepAliveClosure,
5895 &cmsDrainMarkingStackClosure,
5896 NULL);
5897 }
5898 verify_work_stacks_empty();
5899 }
5900
5901 if (should_unload_classes()) {
5902 {
5903 TraceTime t("class unloading", PrintGCDetails, false, gclog_or_tty);
5904
5905 // Follow SystemDictionary roots and unload classes
5906 bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure);
5907
5908 // Follow CodeCache roots and unload any methods marked for unloading
5909 CodeCache::do_unloading(&_is_alive_closure,
5910 &cmsKeepAliveClosure,
5911 purged_class);
5912
5913 cmsDrainMarkingStackClosure.do_void();
5914 verify_work_stacks_empty();
5915
5916 // Update subklass/sibling/implementor links in KlassKlass descendants
5917 assert(!_revisitStack.isEmpty(), "revisit stack should not be empty");
5918 oop k;
5919 while ((k = _revisitStack.pop()) != NULL) {
5920 ((Klass*)(oopDesc*)k)->follow_weak_klass_links(
5921 &_is_alive_closure,
5922 &cmsKeepAliveClosure);
5923 }
5924 assert(!ClassUnloading ||
5925 (_markStack.isEmpty() && overflow_list_is_empty()),
5926 "Should not have found new reachable objects");
5927 assert(_revisitStack.isEmpty(), "revisit stack should have been drained");
5928 cmsDrainMarkingStackClosure.do_void();
5929 verify_work_stacks_empty();
5930 }
5931
5932 {
5933 TraceTime t("scrub symbol & string tables", PrintGCDetails, false, gclog_or_tty);
5934 // Now clean up stale oops in SymbolTable and StringTable
5935 SymbolTable::unlink(&_is_alive_closure);
5936 StringTable::unlink(&_is_alive_closure);
5937 }
5938 }
5939
5940 verify_work_stacks_empty();
5941 // Restore any preserved marks as a result of mark stack or
5942 // work queue overflow
5943 restore_preserved_marks_if_any(); // done single-threaded for now
5944
5945 rp->set_enqueuing_is_done(true);
5946 if (rp->processing_is_mt()) {
5947 rp->balance_all_queues();
5948 CMSRefProcTaskExecutor task_executor(*this);
5949 rp->enqueue_discovered_references(&task_executor);
5950 } else {
5951 rp->enqueue_discovered_references(NULL);
5952 }
5953 rp->verify_no_references_recorded();
5954 assert(!rp->discovery_enabled(), "should have been disabled");
5955
5956 // JVMTI object tagging is based on JNI weak refs. If any of these
5957 // refs were cleared then JVMTI needs to update its maps and
5958 // maybe post ObjectFrees to agents.
5959 JvmtiExport::cms_ref_processing_epilogue();
5960 }
5961
5962 #ifndef PRODUCT
5963 void CMSCollector::check_correct_thread_executing() {
5964 Thread* t = Thread::current();
5965 // Only the VM thread or the CMS thread should be here.
5966 assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
5967 "Unexpected thread type");
5968 // If this is the vm thread, the foreground process
5969 // should not be waiting. Note that _foregroundGCIsActive is
5970 // true while the foreground collector is waiting.
5971 if (_foregroundGCShouldWait) {
5972 // We cannot be the VM thread
5973 assert(t->is_ConcurrentGC_thread(),
5974 "Should be CMS thread");
5975 } else {
5976 // We can be the CMS thread only if we are in a stop-world
5977 // phase of CMS collection.
5978 if (t->is_ConcurrentGC_thread()) {
5979 assert(_collectorState == InitialMarking ||
5980 _collectorState == FinalMarking,
5981 "Should be a stop-world phase");
5982 // The CMS thread should be holding the CMS_token.
5983 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5984 "Potential interference with concurrently "
5985 "executing VM thread");
5986 }
5987 }
5988 }
5989 #endif
5990
5991 void CMSCollector::sweep(bool asynch) {
5992 assert(_collectorState == Sweeping, "just checking");
5993 check_correct_thread_executing();
5994 verify_work_stacks_empty();
5995 verify_overflow_empty();
5996 increment_sweep_count();
5997 TraceCMSMemoryManagerStats tms(_collectorState);
5998
5999 _inter_sweep_timer.stop();
6000 _inter_sweep_estimate.sample(_inter_sweep_timer.seconds());
6001 size_policy()->avg_cms_free_at_sweep()->sample(_cmsGen->free());
6002
6003 // PermGen verification support: If perm gen sweeping is disabled in
6004 // this cycle, we preserve the perm gen object "deadness" information
6005 // in the perm_gen_verify_bit_map. In order to do that we traverse
6006 // all blocks in perm gen and mark all dead objects.
6007 if (verifying() && !should_unload_classes()) {
6008 assert(perm_gen_verify_bit_map()->sizeInBits() != 0,
6009 "Should have already been allocated");
6010 MarkDeadObjectsClosure mdo(this, _permGen->cmsSpace(),
6011 markBitMap(), perm_gen_verify_bit_map());
6012 if (asynch) {
6013 CMSTokenSyncWithLocks ts(true, _permGen->freelistLock(),
6014 bitMapLock());
6015 _permGen->cmsSpace()->blk_iterate(&mdo);
6016 } else {
6017 // In the case of synchronous sweep, we already have
6018 // the requisite locks/tokens.
6019 _permGen->cmsSpace()->blk_iterate(&mdo);
6020 }
6021 }
6022
6023 assert(!_intra_sweep_timer.is_active(), "Should not be active");
6024 _intra_sweep_timer.reset();
6025 _intra_sweep_timer.start();
6026 if (asynch) {
6027 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6028 CMSPhaseAccounting pa(this, "sweep", !PrintGCDetails);
6029 // First sweep the old gen then the perm gen
6030 {
6031 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
6032 bitMapLock());
6033 sweepWork(_cmsGen, asynch);
6034 }
6035
6036 // Now repeat for perm gen
6037 if (should_unload_classes()) {
6038 CMSTokenSyncWithLocks ts(true, _permGen->freelistLock(),
6039 bitMapLock());
6040 sweepWork(_permGen, asynch);
6041 }
6042
6043 // Update Universe::_heap_*_at_gc figures.
6044 // We need all the free list locks to make the abstract state
6045 // transition from Sweeping to Resetting. See detailed note
6046 // further below.
6047 {
6048 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
6049 _permGen->freelistLock());
6050 // Update heap occupancy information which is used as
6051 // input to soft ref clearing policy at the next gc.
6052 Universe::update_heap_info_at_gc();
6053 _collectorState = Resizing;
6054 }
6055 } else {
6056 // already have needed locks
6057 sweepWork(_cmsGen, asynch);
6058
6059 if (should_unload_classes()) {
6060 sweepWork(_permGen, asynch);
6061 }
6062 // Update heap occupancy information which is used as
6063 // input to soft ref clearing policy at the next gc.
6064 Universe::update_heap_info_at_gc();
6065 _collectorState = Resizing;
6066 }
6067 verify_work_stacks_empty();
6068 verify_overflow_empty();
6069
6070 _intra_sweep_timer.stop();
6071 _intra_sweep_estimate.sample(_intra_sweep_timer.seconds());
6072
6073 _inter_sweep_timer.reset();
6074 _inter_sweep_timer.start();
6075
6076 update_time_of_last_gc(os::javaTimeMillis());
6077
6078 // NOTE on abstract state transitions:
6079 // Mutators allocate-live and/or mark the mod-union table dirty
6080 // based on the state of the collection. The former is done in
6081 // the interval [Marking, Sweeping] and the latter in the interval
6082 // [Marking, Sweeping). Thus the transitions into the Marking state
6083 // and out of the Sweeping state must be synchronously visible
6084 // globally to the mutators.
6085 // The transition into the Marking state happens with the world
6086 // stopped so the mutators will globally see it. Sweeping is
6087 // done asynchronously by the background collector so the transition
6088 // from the Sweeping state to the Resizing state must be done
6089 // under the freelistLock (as is the check for whether to
6090 // allocate-live and whether to dirty the mod-union table).
6091 assert(_collectorState == Resizing, "Change of collector state to"
6092 " Resizing must be done under the freelistLocks (plural)");
6093
6094 // Now that sweeping has been completed, if the GCH's
6095 // incremental_collection_will_fail flag is set, clear it,
6096 // thus inviting a younger gen collection to promote into
6097 // this generation. If such a promotion may still fail,
6098 // the flag will be set again when a young collection is
6099 // attempted.
6100 // I think the incremental_collection_will_fail flag's use
6101 // is specific to a 2 generation collection policy, so i'll
6102 // assert that that's the configuration we are operating within.
6103 // The use of the flag can and should be generalized appropriately
6104 // in the future to deal with a general n-generation system.
6105
6106 GenCollectedHeap* gch = GenCollectedHeap::heap();
6107 assert(gch->collector_policy()->is_two_generation_policy(),
6108 "Resetting of incremental_collection_will_fail flag"
6109 " may be incorrect otherwise");
6110 gch->clear_incremental_collection_will_fail();
6111 gch->update_full_collections_completed(_collection_count_start);
6112 }
6113
6114 // FIX ME!!! Looks like this belongs in CFLSpace, with
6115 // CMSGen merely delegating to it.
6116 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
6117 double nearLargestPercent = FLSLargestBlockCoalesceProximity;
6118 HeapWord* minAddr = _cmsSpace->bottom();
6119 HeapWord* largestAddr =
6120 (HeapWord*) _cmsSpace->dictionary()->findLargestDict();
6121 if (largestAddr == NULL) {
6122 // The dictionary appears to be empty. In this case
6123 // try to coalesce at the end of the heap.
6124 largestAddr = _cmsSpace->end();
6125 }
6126 size_t largestOffset = pointer_delta(largestAddr, minAddr);
6127 size_t nearLargestOffset =
6128 (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
6129 if (PrintFLSStatistics != 0) {
6130 gclog_or_tty->print_cr(
6131 "CMS: Large Block: " PTR_FORMAT ";"
6132 " Proximity: " PTR_FORMAT " -> " PTR_FORMAT,
6133 largestAddr,
6134 _cmsSpace->nearLargestChunk(), minAddr + nearLargestOffset);
6135 }
6136 _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
6137 }
6138
6139 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
6140 return addr >= _cmsSpace->nearLargestChunk();
6141 }
6142
6143 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
6144 return _cmsSpace->find_chunk_at_end();
6145 }
6146
6147 void ConcurrentMarkSweepGeneration::update_gc_stats(int current_level,
6148 bool full) {
6149 // The next lower level has been collected. Gather any statistics
6150 // that are of interest at this point.
6151 if (!full && (current_level + 1) == level()) {
6152 // Gather statistics on the young generation collection.
6153 collector()->stats().record_gc0_end(used());
6154 }
6155 }
6156
6157 CMSAdaptiveSizePolicy* ConcurrentMarkSweepGeneration::size_policy() {
6158 GenCollectedHeap* gch = GenCollectedHeap::heap();
6159 assert(gch->kind() == CollectedHeap::GenCollectedHeap,
6160 "Wrong type of heap");
6161 CMSAdaptiveSizePolicy* sp = (CMSAdaptiveSizePolicy*)
6162 gch->gen_policy()->size_policy();
6163 assert(sp->is_gc_cms_adaptive_size_policy(),
6164 "Wrong type of size policy");
6165 return sp;
6166 }
6167
6168 void ConcurrentMarkSweepGeneration::rotate_debug_collection_type() {
6169 if (PrintGCDetails && Verbose) {
6170 gclog_or_tty->print("Rotate from %d ", _debug_collection_type);
6171 }
6172 _debug_collection_type = (CollectionTypes) (_debug_collection_type + 1);
6173 _debug_collection_type =
6174 (CollectionTypes) (_debug_collection_type % Unknown_collection_type);
6175 if (PrintGCDetails && Verbose) {
6176 gclog_or_tty->print_cr("to %d ", _debug_collection_type);
6177 }
6178 }
6179
6180 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* gen,
6181 bool asynch) {
6182 // We iterate over the space(s) underlying this generation,
6183 // checking the mark bit map to see if the bits corresponding
6184 // to specific blocks are marked or not. Blocks that are
6185 // marked are live and are not swept up. All remaining blocks
6186 // are swept up, with coalescing on-the-fly as we sweep up
6187 // contiguous free and/or garbage blocks:
6188 // We need to ensure that the sweeper synchronizes with allocators
6189 // and stop-the-world collectors. In particular, the following
6190 // locks are used:
6191 // . CMS token: if this is held, a stop the world collection cannot occur
6192 // . freelistLock: if this is held no allocation can occur from this
6193 // generation by another thread
6194 // . bitMapLock: if this is held, no other thread can access or update
6195 //
6196
6197 // Note that we need to hold the freelistLock if we use
6198 // block iterate below; else the iterator might go awry if
6199 // a mutator (or promotion) causes block contents to change
6200 // (for instance if the allocator divvies up a block).
6201 // If we hold the free list lock, for all practical purposes
6202 // young generation GC's can't occur (they'll usually need to
6203 // promote), so we might as well prevent all young generation
6204 // GC's while we do a sweeping step. For the same reason, we might
6205 // as well take the bit map lock for the entire duration
6206
6207 // check that we hold the requisite locks
6208 assert(have_cms_token(), "Should hold cms token");
6209 assert( (asynch && ConcurrentMarkSweepThread::cms_thread_has_cms_token())
6210 || (!asynch && ConcurrentMarkSweepThread::vm_thread_has_cms_token()),
6211 "Should possess CMS token to sweep");
6212 assert_lock_strong(gen->freelistLock());
6213 assert_lock_strong(bitMapLock());
6214
6215 assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context");
6216 assert(_intra_sweep_timer.is_active(), "Was switched on in an outer context");
6217 gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
6218 _inter_sweep_estimate.padded_average(),
6219 _intra_sweep_estimate.padded_average());
6220 gen->setNearLargestChunk();
6221
6222 {
6223 SweepClosure sweepClosure(this, gen, &_markBitMap,
6224 CMSYield && asynch);
6225 gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
6226 // We need to free-up/coalesce garbage/blocks from a
6227 // co-terminal free run. This is done in the SweepClosure
6228 // destructor; so, do not remove this scope, else the
6229 // end-of-sweep-census below will be off by a little bit.
6230 }
6231 gen->cmsSpace()->sweep_completed();
6232 gen->cmsSpace()->endSweepFLCensus(sweep_count());
6233 if (should_unload_classes()) { // unloaded classes this cycle,
6234 _concurrent_cycles_since_last_unload = 0; // ... reset count
6235 } else { // did not unload classes,
6236 _concurrent_cycles_since_last_unload++; // ... increment count
6237 }
6238 }
6239
6240 // Reset CMS data structures (for now just the marking bit map)
6241 // preparatory for the next cycle.
6242 void CMSCollector::reset(bool asynch) {
6243 GenCollectedHeap* gch = GenCollectedHeap::heap();
6244 CMSAdaptiveSizePolicy* sp = size_policy();
6245 AdaptiveSizePolicyOutput(sp, gch->total_collections());
6246 if (asynch) {
6247 CMSTokenSyncWithLocks ts(true, bitMapLock());
6248
6249 // If the state is not "Resetting", the foreground thread
6250 // has done a collection and the resetting.
6251 if (_collectorState != Resetting) {
6252 assert(_collectorState == Idling, "The state should only change"
6253 " because the foreground collector has finished the collection");
6254 return;
6255 }
6256
6257 // Clear the mark bitmap (no grey objects to start with)
6258 // for the next cycle.
6259 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6260 CMSPhaseAccounting cmspa(this, "reset", !PrintGCDetails);
6261
6262 HeapWord* curAddr = _markBitMap.startWord();
6263 while (curAddr < _markBitMap.endWord()) {
6264 size_t remaining = pointer_delta(_markBitMap.endWord(), curAddr);
6265 MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
6266 _markBitMap.clear_large_range(chunk);
6267 if (ConcurrentMarkSweepThread::should_yield() &&
6268 !foregroundGCIsActive() &&
6269 CMSYield) {
6270 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6271 "CMS thread should hold CMS token");
6272 assert_lock_strong(bitMapLock());
6273 bitMapLock()->unlock();
6274 ConcurrentMarkSweepThread::desynchronize(true);
6275 ConcurrentMarkSweepThread::acknowledge_yield_request();
6276 stopTimer();
6277 if (PrintCMSStatistics != 0) {
6278 incrementYields();
6279 }
6280 icms_wait();
6281
6282 // See the comment in coordinator_yield()
6283 for (unsigned i = 0; i < CMSYieldSleepCount &&
6284 ConcurrentMarkSweepThread::should_yield() &&
6285 !CMSCollector::foregroundGCIsActive(); ++i) {
6286 os::sleep(Thread::current(), 1, false);
6287 ConcurrentMarkSweepThread::acknowledge_yield_request();
6288 }
6289
6290 ConcurrentMarkSweepThread::synchronize(true);
6291 bitMapLock()->lock_without_safepoint_check();
6292 startTimer();
6293 }
6294 curAddr = chunk.end();
6295 }
6296 // A successful mostly concurrent collection has been done.
6297 // Because only the full (i.e., concurrent mode failure) collections
6298 // are being measured for gc overhead limits, clean the "near" flag
6299 // and count.
6300 sp->reset_gc_overhead_limit_count();
6301 _collectorState = Idling;
6302 } else {
6303 // already have the lock
6304 assert(_collectorState == Resetting, "just checking");
6305 assert_lock_strong(bitMapLock());
6306 _markBitMap.clear_all();
6307 _collectorState = Idling;
6308 }
6309
6310 // Stop incremental mode after a cycle completes, so that any future cycles
6311 // are triggered by allocation.
6312 stop_icms();
6313
6314 NOT_PRODUCT(
6315 if (RotateCMSCollectionTypes) {
6316 _cmsGen->rotate_debug_collection_type();
6317 }
6318 )
6319 }
6320
6321 void CMSCollector::do_CMS_operation(CMS_op_type op) {
6322 gclog_or_tty->date_stamp(PrintGC && PrintGCDateStamps);
6323 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6324 TraceTime t("GC", PrintGC, !PrintGCDetails, gclog_or_tty);
6325 TraceCollectorStats tcs(counters());
6326
6327 switch (op) {
6328 case CMS_op_checkpointRootsInitial: {
6329 checkpointRootsInitial(true); // asynch
6330 if (PrintGC) {
6331 _cmsGen->printOccupancy("initial-mark");
6332 }
6333 break;
6334 }
6335 case CMS_op_checkpointRootsFinal: {
6336 checkpointRootsFinal(true, // asynch
6337 false, // !clear_all_soft_refs
6338 false); // !init_mark_was_synchronous
6339 if (PrintGC) {
6340 _cmsGen->printOccupancy("remark");
6341 }
6342 break;
6343 }
6344 default:
6345 fatal("No such CMS_op");
6346 }
6347 }
6348
6349 #ifndef PRODUCT
6350 size_t const CMSCollector::skip_header_HeapWords() {
6351 return FreeChunk::header_size();
6352 }
6353
6354 // Try and collect here conditions that should hold when
6355 // CMS thread is exiting. The idea is that the foreground GC
6356 // thread should not be blocked if it wants to terminate
6357 // the CMS thread and yet continue to run the VM for a while
6358 // after that.
6359 void CMSCollector::verify_ok_to_terminate() const {
6360 assert(Thread::current()->is_ConcurrentGC_thread(),
6361 "should be called by CMS thread");
6362 assert(!_foregroundGCShouldWait, "should be false");
6363 // We could check here that all the various low-level locks
6364 // are not held by the CMS thread, but that is overkill; see
6365 // also CMSThread::verify_ok_to_terminate() where the CGC_lock
6366 // is checked.
6367 }
6368 #endif
6369
6370 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
6371 assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
6372 "missing Printezis mark?");
6373 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
6374 size_t size = pointer_delta(nextOneAddr + 1, addr);
6375 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6376 "alignment problem");
6377 assert(size >= 3, "Necessary for Printezis marks to work");
6378 return size;
6379 }
6380
6381 // A variant of the above (block_size_using_printezis_bits()) except
6382 // that we return 0 if the P-bits are not yet set.
6383 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
6384 if (_markBitMap.isMarked(addr)) {
6385 assert(_markBitMap.isMarked(addr + 1), "Missing Printezis bit?");
6386 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
6387 size_t size = pointer_delta(nextOneAddr + 1, addr);
6388 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6389 "alignment problem");
6390 assert(size >= 3, "Necessary for Printezis marks to work");
6391 return size;
6392 } else {
6393 assert(!_markBitMap.isMarked(addr + 1), "Bit map inconsistency?");
6394 return 0;
6395 }
6396 }
6397
6398 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
6399 size_t sz = 0;
6400 oop p = (oop)addr;
6401 if (p->klass_or_null() != NULL && p->is_parsable()) {
6402 sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
6403 } else {
6404 sz = block_size_using_printezis_bits(addr);
6405 }
6406 assert(sz > 0, "size must be nonzero");
6407 HeapWord* next_block = addr + sz;
6408 HeapWord* next_card = (HeapWord*)round_to((uintptr_t)next_block,
6409 CardTableModRefBS::card_size);
6410 assert(round_down((uintptr_t)addr, CardTableModRefBS::card_size) <
6411 round_down((uintptr_t)next_card, CardTableModRefBS::card_size),
6412 "must be different cards");
6413 return next_card;
6414 }
6415
6416
6417 // CMS Bit Map Wrapper /////////////////////////////////////////
6418
6419 // Construct a CMS bit map infrastructure, but don't create the
6420 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
6421 // further below.
6422 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
6423 _bm(),
6424 _shifter(shifter),
6425 _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true) : NULL)
6426 {
6427 _bmStartWord = 0;
6428 _bmWordSize = 0;
6429 }
6430
6431 bool CMSBitMap::allocate(MemRegion mr) {
6432 _bmStartWord = mr.start();
6433 _bmWordSize = mr.word_size();
6434 ReservedSpace brs(ReservedSpace::allocation_align_size_up(
6435 (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
6436 if (!brs.is_reserved()) {
6437 warning("CMS bit map allocation failure");
6438 return false;
6439 }
6440 // For now we'll just commit all of the bit map up fromt.
6441 // Later on we'll try to be more parsimonious with swap.
6442 if (!_virtual_space.initialize(brs, brs.size())) {
6443 warning("CMS bit map backing store failure");
6444 return false;
6445 }
6446 assert(_virtual_space.committed_size() == brs.size(),
6447 "didn't reserve backing store for all of CMS bit map?");
6448 _bm.set_map((BitMap::bm_word_t*)_virtual_space.low());
6449 assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
6450 _bmWordSize, "inconsistency in bit map sizing");
6451 _bm.set_size(_bmWordSize >> _shifter);
6452
6453 // bm.clear(); // can we rely on getting zero'd memory? verify below
6454 assert(isAllClear(),
6455 "Expected zero'd memory from ReservedSpace constructor");
6456 assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
6457 "consistency check");
6458 return true;
6459 }
6460
6461 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
6462 HeapWord *next_addr, *end_addr, *last_addr;
6463 assert_locked();
6464 assert(covers(mr), "out-of-range error");
6465 // XXX assert that start and end are appropriately aligned
6466 for (next_addr = mr.start(), end_addr = mr.end();
6467 next_addr < end_addr; next_addr = last_addr) {
6468 MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
6469 last_addr = dirty_region.end();
6470 if (!dirty_region.is_empty()) {
6471 cl->do_MemRegion(dirty_region);
6472 } else {
6473 assert(last_addr == end_addr, "program logic");
6474 return;
6475 }
6476 }
6477 }
6478
6479 #ifndef PRODUCT
6480 void CMSBitMap::assert_locked() const {
6481 CMSLockVerifier::assert_locked(lock());
6482 }
6483
6484 bool CMSBitMap::covers(MemRegion mr) const {
6485 // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
6486 assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
6487 "size inconsistency");
6488 return (mr.start() >= _bmStartWord) &&
6489 (mr.end() <= endWord());
6490 }
6491
6492 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
6493 return (start >= _bmStartWord && (start + size) <= endWord());
6494 }
6495
6496 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
6497 // verify that there are no 1 bits in the interval [left, right)
6498 FalseBitMapClosure falseBitMapClosure;
6499 iterate(&falseBitMapClosure, left, right);
6500 }
6501
6502 void CMSBitMap::region_invariant(MemRegion mr)
6503 {
6504 assert_locked();
6505 // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
6506 assert(!mr.is_empty(), "unexpected empty region");
6507 assert(covers(mr), "mr should be covered by bit map");
6508 // convert address range into offset range
6509 size_t start_ofs = heapWordToOffset(mr.start());
6510 // Make sure that end() is appropriately aligned
6511 assert(mr.end() == (HeapWord*)round_to((intptr_t)mr.end(),
6512 (1 << (_shifter+LogHeapWordSize))),
6513 "Misaligned mr.end()");
6514 size_t end_ofs = heapWordToOffset(mr.end());
6515 assert(end_ofs > start_ofs, "Should mark at least one bit");
6516 }
6517
6518 #endif
6519
6520 bool CMSMarkStack::allocate(size_t size) {
6521 // allocate a stack of the requisite depth
6522 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6523 size * sizeof(oop)));
6524 if (!rs.is_reserved()) {
6525 warning("CMSMarkStack allocation failure");
6526 return false;
6527 }
6528 if (!_virtual_space.initialize(rs, rs.size())) {
6529 warning("CMSMarkStack backing store failure");
6530 return false;
6531 }
6532 assert(_virtual_space.committed_size() == rs.size(),
6533 "didn't reserve backing store for all of CMS stack?");
6534 _base = (oop*)(_virtual_space.low());
6535 _index = 0;
6536 _capacity = size;
6537 NOT_PRODUCT(_max_depth = 0);
6538 return true;
6539 }
6540
6541 // XXX FIX ME !!! In the MT case we come in here holding a
6542 // leaf lock. For printing we need to take a further lock
6543 // which has lower rank. We need to recallibrate the two
6544 // lock-ranks involved in order to be able to rpint the
6545 // messages below. (Or defer the printing to the caller.
6546 // For now we take the expedient path of just disabling the
6547 // messages for the problematic case.)
6548 void CMSMarkStack::expand() {
6549 assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted");
6550 if (_capacity == MarkStackSizeMax) {
6551 if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6552 // We print a warning message only once per CMS cycle.
6553 gclog_or_tty->print_cr(" (benign) Hit CMSMarkStack max size limit");
6554 }
6555 return;
6556 }
6557 // Double capacity if possible
6558 size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax);
6559 // Do not give up existing stack until we have managed to
6560 // get the double capacity that we desired.
6561 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6562 new_capacity * sizeof(oop)));
6563 if (rs.is_reserved()) {
6564 // Release the backing store associated with old stack
6565 _virtual_space.release();
6566 // Reinitialize virtual space for new stack
6567 if (!_virtual_space.initialize(rs, rs.size())) {
6568 fatal("Not enough swap for expanded marking stack");
6569 }
6570 _base = (oop*)(_virtual_space.low());
6571 _index = 0;
6572 _capacity = new_capacity;
6573 } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6574 // Failed to double capacity, continue;
6575 // we print a detail message only once per CMS cycle.
6576 gclog_or_tty->print(" (benign) Failed to expand marking stack from "SIZE_FORMAT"K to "
6577 SIZE_FORMAT"K",
6578 _capacity / K, new_capacity / K);
6579 }
6580 }
6581
6582
6583 // Closures
6584 // XXX: there seems to be a lot of code duplication here;
6585 // should refactor and consolidate common code.
6586
6587 // This closure is used to mark refs into the CMS generation in
6588 // the CMS bit map. Called at the first checkpoint. This closure
6589 // assumes that we do not need to re-mark dirty cards; if the CMS
6590 // generation on which this is used is not an oldest (modulo perm gen)
6591 // generation then this will lose younger_gen cards!
6592
6593 MarkRefsIntoClosure::MarkRefsIntoClosure(
6594 MemRegion span, CMSBitMap* bitMap):
6595 _span(span),
6596 _bitMap(bitMap)
6597 {
6598 assert(_ref_processor == NULL, "deliberately left NULL");
6599 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6600 }
6601
6602 void MarkRefsIntoClosure::do_oop(oop obj) {
6603 // if p points into _span, then mark corresponding bit in _markBitMap
6604 assert(obj->is_oop(), "expected an oop");
6605 HeapWord* addr = (HeapWord*)obj;
6606 if (_span.contains(addr)) {
6607 // this should be made more efficient
6608 _bitMap->mark(addr);
6609 }
6610 }
6611
6612 void MarkRefsIntoClosure::do_oop(oop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6613 void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6614
6615 // A variant of the above, used for CMS marking verification.
6616 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
6617 MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm):
6618 _span(span),
6619 _verification_bm(verification_bm),
6620 _cms_bm(cms_bm)
6621 {
6622 assert(_ref_processor == NULL, "deliberately left NULL");
6623 assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
6624 }
6625
6626 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
6627 // if p points into _span, then mark corresponding bit in _markBitMap
6628 assert(obj->is_oop(), "expected an oop");
6629 HeapWord* addr = (HeapWord*)obj;
6630 if (_span.contains(addr)) {
6631 _verification_bm->mark(addr);
6632 if (!_cms_bm->isMarked(addr)) {
6633 oop(addr)->print();
6634 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)", addr);
6635 fatal("... aborting");
6636 }
6637 }
6638 }
6639
6640 void MarkRefsIntoVerifyClosure::do_oop(oop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6641 void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6642
6643 //////////////////////////////////////////////////
6644 // MarkRefsIntoAndScanClosure
6645 //////////////////////////////////////////////////
6646
6647 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
6648 ReferenceProcessor* rp,
6649 CMSBitMap* bit_map,
6650 CMSBitMap* mod_union_table,
6651 CMSMarkStack* mark_stack,
6652 CMSMarkStack* revisit_stack,
6653 CMSCollector* collector,
6654 bool should_yield,
6655 bool concurrent_precleaning):
6656 _collector(collector),
6657 _span(span),
6658 _bit_map(bit_map),
6659 _mark_stack(mark_stack),
6660 _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table,
6661 mark_stack, revisit_stack, concurrent_precleaning),
6662 _yield(should_yield),
6663 _concurrent_precleaning(concurrent_precleaning),
6664 _freelistLock(NULL)
6665 {
6666 _ref_processor = rp;
6667 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6668 }
6669
6670 // This closure is used to mark refs into the CMS generation at the
6671 // second (final) checkpoint, and to scan and transitively follow
6672 // the unmarked oops. It is also used during the concurrent precleaning
6673 // phase while scanning objects on dirty cards in the CMS generation.
6674 // The marks are made in the marking bit map and the marking stack is
6675 // used for keeping the (newly) grey objects during the scan.
6676 // The parallel version (Par_...) appears further below.
6677 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6678 if (obj != NULL) {
6679 assert(obj->is_oop(), "expected an oop");
6680 HeapWord* addr = (HeapWord*)obj;
6681 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6682 assert(_collector->overflow_list_is_empty(),
6683 "overflow list should be empty");
6684 if (_span.contains(addr) &&
6685 !_bit_map->isMarked(addr)) {
6686 // mark bit map (object is now grey)
6687 _bit_map->mark(addr);
6688 // push on marking stack (stack should be empty), and drain the
6689 // stack by applying this closure to the oops in the oops popped
6690 // from the stack (i.e. blacken the grey objects)
6691 bool res = _mark_stack->push(obj);
6692 assert(res, "Should have space to push on empty stack");
6693 do {
6694 oop new_oop = _mark_stack->pop();
6695 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6696 assert(new_oop->is_parsable(), "Found unparsable oop");
6697 assert(_bit_map->isMarked((HeapWord*)new_oop),
6698 "only grey objects on this stack");
6699 // iterate over the oops in this oop, marking and pushing
6700 // the ones in CMS heap (i.e. in _span).
6701 new_oop->oop_iterate(&_pushAndMarkClosure);
6702 // check if it's time to yield
6703 do_yield_check();
6704 } while (!_mark_stack->isEmpty() ||
6705 (!_concurrent_precleaning && take_from_overflow_list()));
6706 // if marking stack is empty, and we are not doing this
6707 // during precleaning, then check the overflow list
6708 }
6709 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6710 assert(_collector->overflow_list_is_empty(),
6711 "overflow list was drained above");
6712 // We could restore evacuated mark words, if any, used for
6713 // overflow list links here because the overflow list is
6714 // provably empty here. That would reduce the maximum
6715 // size requirements for preserved_{oop,mark}_stack.
6716 // But we'll just postpone it until we are all done
6717 // so we can just stream through.
6718 if (!_concurrent_precleaning && CMSOverflowEarlyRestoration) {
6719 _collector->restore_preserved_marks_if_any();
6720 assert(_collector->no_preserved_marks(), "No preserved marks");
6721 }
6722 assert(!CMSOverflowEarlyRestoration || _collector->no_preserved_marks(),
6723 "All preserved marks should have been restored above");
6724 }
6725 }
6726
6727 void MarkRefsIntoAndScanClosure::do_oop(oop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6728 void MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6729
6730 void MarkRefsIntoAndScanClosure::do_yield_work() {
6731 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6732 "CMS thread should hold CMS token");
6733 assert_lock_strong(_freelistLock);
6734 assert_lock_strong(_bit_map->lock());
6735 // relinquish the free_list_lock and bitMaplock()
6736 DEBUG_ONLY(RememberKlassesChecker mux(false);)
6737 _bit_map->lock()->unlock();
6738 _freelistLock->unlock();
6739 ConcurrentMarkSweepThread::desynchronize(true);
6740 ConcurrentMarkSweepThread::acknowledge_yield_request();
6741 _collector->stopTimer();
6742 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
6743 if (PrintCMSStatistics != 0) {
6744 _collector->incrementYields();
6745 }
6746 _collector->icms_wait();
6747
6748 // See the comment in coordinator_yield()
6749 for (unsigned i = 0;
6750 i < CMSYieldSleepCount &&
6751 ConcurrentMarkSweepThread::should_yield() &&
6752 !CMSCollector::foregroundGCIsActive();
6753 ++i) {
6754 os::sleep(Thread::current(), 1, false);
6755 ConcurrentMarkSweepThread::acknowledge_yield_request();
6756 }
6757
6758 ConcurrentMarkSweepThread::synchronize(true);
6759 _freelistLock->lock_without_safepoint_check();
6760 _bit_map->lock()->lock_without_safepoint_check();
6761 _collector->startTimer();
6762 }
6763
6764 ///////////////////////////////////////////////////////////
6765 // Par_MarkRefsIntoAndScanClosure: a parallel version of
6766 // MarkRefsIntoAndScanClosure
6767 ///////////////////////////////////////////////////////////
6768 Par_MarkRefsIntoAndScanClosure::Par_MarkRefsIntoAndScanClosure(
6769 CMSCollector* collector, MemRegion span, ReferenceProcessor* rp,
6770 CMSBitMap* bit_map, OopTaskQueue* work_queue, CMSMarkStack* revisit_stack):
6771 _span(span),
6772 _bit_map(bit_map),
6773 _work_queue(work_queue),
6774 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
6775 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads))),
6776 _par_pushAndMarkClosure(collector, span, rp, bit_map, work_queue,
6777 revisit_stack)
6778 {
6779 _ref_processor = rp;
6780 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6781 }
6782
6783 // This closure is used to mark refs into the CMS generation at the
6784 // second (final) checkpoint, and to scan and transitively follow
6785 // the unmarked oops. The marks are made in the marking bit map and
6786 // the work_queue is used for keeping the (newly) grey objects during
6787 // the scan phase whence they are also available for stealing by parallel
6788 // threads. Since the marking bit map is shared, updates are
6789 // synchronized (via CAS).
6790 void Par_MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6791 if (obj != NULL) {
6792 // Ignore mark word because this could be an already marked oop
6793 // that may be chained at the end of the overflow list.
6794 assert(obj->is_oop(true), "expected an oop");
6795 HeapWord* addr = (HeapWord*)obj;
6796 if (_span.contains(addr) &&
6797 !_bit_map->isMarked(addr)) {
6798 // mark bit map (object will become grey):
6799 // It is possible for several threads to be
6800 // trying to "claim" this object concurrently;
6801 // the unique thread that succeeds in marking the
6802 // object first will do the subsequent push on
6803 // to the work queue (or overflow list).
6804 if (_bit_map->par_mark(addr)) {
6805 // push on work_queue (which may not be empty), and trim the
6806 // queue to an appropriate length by applying this closure to
6807 // the oops in the oops popped from the stack (i.e. blacken the
6808 // grey objects)
6809 bool res = _work_queue->push(obj);
6810 assert(res, "Low water mark should be less than capacity?");
6811 trim_queue(_low_water_mark);
6812 } // Else, another thread claimed the object
6813 }
6814 }
6815 }
6816
6817 void Par_MarkRefsIntoAndScanClosure::do_oop(oop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6818 void Par_MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6819
6820 // This closure is used to rescan the marked objects on the dirty cards
6821 // in the mod union table and the card table proper.
6822 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
6823 oop p, MemRegion mr) {
6824
6825 size_t size = 0;
6826 HeapWord* addr = (HeapWord*)p;
6827 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6828 assert(_span.contains(addr), "we are scanning the CMS generation");
6829 // check if it's time to yield
6830 if (do_yield_check()) {
6831 // We yielded for some foreground stop-world work,
6832 // and we have been asked to abort this ongoing preclean cycle.
6833 return 0;
6834 }
6835 if (_bitMap->isMarked(addr)) {
6836 // it's marked; is it potentially uninitialized?
6837 if (p->klass_or_null() != NULL) {
6838 // If is_conc_safe is false, the object may be undergoing
6839 // change by the VM outside a safepoint. Don't try to
6840 // scan it, but rather leave it for the remark phase.
6841 if (CMSPermGenPrecleaningEnabled &&
6842 (!p->is_conc_safe() || !p->is_parsable())) {
6843 // Signal precleaning to redirty the card since
6844 // the klass pointer is already installed.
6845 assert(size == 0, "Initial value");
6846 } else {
6847 assert(p->is_parsable(), "must be parsable.");
6848 // an initialized object; ignore mark word in verification below
6849 // since we are running concurrent with mutators
6850 assert(p->is_oop(true), "should be an oop");
6851 if (p->is_objArray()) {
6852 // objArrays are precisely marked; restrict scanning
6853 // to dirty cards only.
6854 size = CompactibleFreeListSpace::adjustObjectSize(
6855 p->oop_iterate(_scanningClosure, mr));
6856 } else {
6857 // A non-array may have been imprecisely marked; we need
6858 // to scan object in its entirety.
6859 size = CompactibleFreeListSpace::adjustObjectSize(
6860 p->oop_iterate(_scanningClosure));
6861 }
6862 #ifdef DEBUG
6863 size_t direct_size =
6864 CompactibleFreeListSpace::adjustObjectSize(p->size());
6865 assert(size == direct_size, "Inconsistency in size");
6866 assert(size >= 3, "Necessary for Printezis marks to work");
6867 if (!_bitMap->isMarked(addr+1)) {
6868 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size);
6869 } else {
6870 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size-1);
6871 assert(_bitMap->isMarked(addr+size-1),
6872 "inconsistent Printezis mark");
6873 }
6874 #endif // DEBUG
6875 }
6876 } else {
6877 // an unitialized object
6878 assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
6879 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
6880 size = pointer_delta(nextOneAddr + 1, addr);
6881 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6882 "alignment problem");
6883 // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
6884 // will dirty the card when the klass pointer is installed in the
6885 // object (signalling the completion of initialization).
6886 }
6887 } else {
6888 // Either a not yet marked object or an uninitialized object
6889 if (p->klass_or_null() == NULL || !p->is_parsable()) {
6890 // An uninitialized object, skip to the next card, since
6891 // we may not be able to read its P-bits yet.
6892 assert(size == 0, "Initial value");
6893 } else {
6894 // An object not (yet) reached by marking: we merely need to
6895 // compute its size so as to go look at the next block.
6896 assert(p->is_oop(true), "should be an oop");
6897 size = CompactibleFreeListSpace::adjustObjectSize(p->size());
6898 }
6899 }
6900 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6901 return size;
6902 }
6903
6904 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
6905 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6906 "CMS thread should hold CMS token");
6907 assert_lock_strong(_freelistLock);
6908 assert_lock_strong(_bitMap->lock());
6909 DEBUG_ONLY(RememberKlassesChecker mux(false);)
6910 // relinquish the free_list_lock and bitMaplock()
6911 _bitMap->lock()->unlock();
6912 _freelistLock->unlock();
6913 ConcurrentMarkSweepThread::desynchronize(true);
6914 ConcurrentMarkSweepThread::acknowledge_yield_request();
6915 _collector->stopTimer();
6916 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
6917 if (PrintCMSStatistics != 0) {
6918 _collector->incrementYields();
6919 }
6920 _collector->icms_wait();
6921
6922 // See the comment in coordinator_yield()
6923 for (unsigned i = 0; i < CMSYieldSleepCount &&
6924 ConcurrentMarkSweepThread::should_yield() &&
6925 !CMSCollector::foregroundGCIsActive(); ++i) {
6926 os::sleep(Thread::current(), 1, false);
6927 ConcurrentMarkSweepThread::acknowledge_yield_request();
6928 }
6929
6930 ConcurrentMarkSweepThread::synchronize(true);
6931 _freelistLock->lock_without_safepoint_check();
6932 _bitMap->lock()->lock_without_safepoint_check();
6933 _collector->startTimer();
6934 }
6935
6936
6937 //////////////////////////////////////////////////////////////////
6938 // SurvivorSpacePrecleanClosure
6939 //////////////////////////////////////////////////////////////////
6940 // This (single-threaded) closure is used to preclean the oops in
6941 // the survivor spaces.
6942 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
6943
6944 HeapWord* addr = (HeapWord*)p;
6945 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6946 assert(!_span.contains(addr), "we are scanning the survivor spaces");
6947 assert(p->klass_or_null() != NULL, "object should be initializd");
6948 assert(p->is_parsable(), "must be parsable.");
6949 // an initialized object; ignore mark word in verification below
6950 // since we are running concurrent with mutators
6951 assert(p->is_oop(true), "should be an oop");
6952 // Note that we do not yield while we iterate over
6953 // the interior oops of p, pushing the relevant ones
6954 // on our marking stack.
6955 size_t size = p->oop_iterate(_scanning_closure);
6956 do_yield_check();
6957 // Observe that below, we do not abandon the preclean
6958 // phase as soon as we should; rather we empty the
6959 // marking stack before returning. This is to satisfy
6960 // some existing assertions. In general, it may be a
6961 // good idea to abort immediately and complete the marking
6962 // from the grey objects at a later time.
6963 while (!_mark_stack->isEmpty()) {
6964 oop new_oop = _mark_stack->pop();
6965 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6966 assert(new_oop->is_parsable(), "Found unparsable oop");
6967 assert(_bit_map->isMarked((HeapWord*)new_oop),
6968 "only grey objects on this stack");
6969 // iterate over the oops in this oop, marking and pushing
6970 // the ones in CMS heap (i.e. in _span).
6971 new_oop->oop_iterate(_scanning_closure);
6972 // check if it's time to yield
6973 do_yield_check();
6974 }
6975 unsigned int after_count =
6976 GenCollectedHeap::heap()->total_collections();
6977 bool abort = (_before_count != after_count) ||
6978 _collector->should_abort_preclean();
6979 return abort ? 0 : size;
6980 }
6981
6982 void SurvivorSpacePrecleanClosure::do_yield_work() {
6983 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6984 "CMS thread should hold CMS token");
6985 assert_lock_strong(_bit_map->lock());
6986 DEBUG_ONLY(RememberKlassesChecker smx(false);)
6987 // Relinquish the bit map lock
6988 _bit_map->lock()->unlock();
6989 ConcurrentMarkSweepThread::desynchronize(true);
6990 ConcurrentMarkSweepThread::acknowledge_yield_request();
6991 _collector->stopTimer();
6992 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
6993 if (PrintCMSStatistics != 0) {
6994 _collector->incrementYields();
6995 }
6996 _collector->icms_wait();
6997
6998 // See the comment in coordinator_yield()
6999 for (unsigned i = 0; i < CMSYieldSleepCount &&
7000 ConcurrentMarkSweepThread::should_yield() &&
7001 !CMSCollector::foregroundGCIsActive(); ++i) {
7002 os::sleep(Thread::current(), 1, false);
7003 ConcurrentMarkSweepThread::acknowledge_yield_request();
7004 }
7005
7006 ConcurrentMarkSweepThread::synchronize(true);
7007 _bit_map->lock()->lock_without_safepoint_check();
7008 _collector->startTimer();
7009 }
7010
7011 // This closure is used to rescan the marked objects on the dirty cards
7012 // in the mod union table and the card table proper. In the parallel
7013 // case, although the bitMap is shared, we do a single read so the
7014 // isMarked() query is "safe".
7015 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
7016 // Ignore mark word because we are running concurrent with mutators
7017 assert(p->is_oop_or_null(true), "expected an oop or null");
7018 HeapWord* addr = (HeapWord*)p;
7019 assert(_span.contains(addr), "we are scanning the CMS generation");
7020 bool is_obj_array = false;
7021 #ifdef DEBUG
7022 if (!_parallel) {
7023 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
7024 assert(_collector->overflow_list_is_empty(),
7025 "overflow list should be empty");
7026
7027 }
7028 #endif // DEBUG
7029 if (_bit_map->isMarked(addr)) {
7030 // Obj arrays are precisely marked, non-arrays are not;
7031 // so we scan objArrays precisely and non-arrays in their
7032 // entirety.
7033 if (p->is_objArray()) {
7034 is_obj_array = true;
7035 if (_parallel) {
7036 p->oop_iterate(_par_scan_closure, mr);
7037 } else {
7038 p->oop_iterate(_scan_closure, mr);
7039 }
7040 } else {
7041 if (_parallel) {
7042 p->oop_iterate(_par_scan_closure);
7043 } else {
7044 p->oop_iterate(_scan_closure);
7045 }
7046 }
7047 }
7048 #ifdef DEBUG
7049 if (!_parallel) {
7050 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
7051 assert(_collector->overflow_list_is_empty(),
7052 "overflow list should be empty");
7053
7054 }
7055 #endif // DEBUG
7056 return is_obj_array;
7057 }
7058
7059 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
7060 MemRegion span,
7061 CMSBitMap* bitMap, CMSMarkStack* markStack,
7062 CMSMarkStack* revisitStack,
7063 bool should_yield, bool verifying):
7064 _collector(collector),
7065 _span(span),
7066 _bitMap(bitMap),
7067 _mut(&collector->_modUnionTable),
7068 _markStack(markStack),
7069 _revisitStack(revisitStack),
7070 _yield(should_yield),
7071 _skipBits(0)
7072 {
7073 assert(_markStack->isEmpty(), "stack should be empty");
7074 _finger = _bitMap->startWord();
7075 _threshold = _finger;
7076 assert(_collector->_restart_addr == NULL, "Sanity check");
7077 assert(_span.contains(_finger), "Out of bounds _finger?");
7078 DEBUG_ONLY(_verifying = verifying;)
7079 }
7080
7081 void MarkFromRootsClosure::reset(HeapWord* addr) {
7082 assert(_markStack->isEmpty(), "would cause duplicates on stack");
7083 assert(_span.contains(addr), "Out of bounds _finger?");
7084 _finger = addr;
7085 _threshold = (HeapWord*)round_to(
7086 (intptr_t)_finger, CardTableModRefBS::card_size);
7087 }
7088
7089 // Should revisit to see if this should be restructured for
7090 // greater efficiency.
7091 bool MarkFromRootsClosure::do_bit(size_t offset) {
7092 if (_skipBits > 0) {
7093 _skipBits--;
7094 return true;
7095 }
7096 // convert offset into a HeapWord*
7097 HeapWord* addr = _bitMap->startWord() + offset;
7098 assert(_bitMap->endWord() && addr < _bitMap->endWord(),
7099 "address out of range");
7100 assert(_bitMap->isMarked(addr), "tautology");
7101 if (_bitMap->isMarked(addr+1)) {
7102 // this is an allocated but not yet initialized object
7103 assert(_skipBits == 0, "tautology");
7104 _skipBits = 2; // skip next two marked bits ("Printezis-marks")
7105 oop p = oop(addr);
7106 if (p->klass_or_null() == NULL || !p->is_parsable()) {
7107 DEBUG_ONLY(if (!_verifying) {)
7108 // We re-dirty the cards on which this object lies and increase
7109 // the _threshold so that we'll come back to scan this object
7110 // during the preclean or remark phase. (CMSCleanOnEnter)
7111 if (CMSCleanOnEnter) {
7112 size_t sz = _collector->block_size_using_printezis_bits(addr);
7113 HeapWord* end_card_addr = (HeapWord*)round_to(
7114 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7115 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7116 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7117 // Bump _threshold to end_card_addr; note that
7118 // _threshold cannot possibly exceed end_card_addr, anyhow.
7119 // This prevents future clearing of the card as the scan proceeds
7120 // to the right.
7121 assert(_threshold <= end_card_addr,
7122 "Because we are just scanning into this object");
7123 if (_threshold < end_card_addr) {
7124 _threshold = end_card_addr;
7125 }
7126 if (p->klass_or_null() != NULL) {
7127 // Redirty the range of cards...
7128 _mut->mark_range(redirty_range);
7129 } // ...else the setting of klass will dirty the card anyway.
7130 }
7131 DEBUG_ONLY(})
7132 return true;
7133 }
7134 }
7135 scanOopsInOop(addr);
7136 return true;
7137 }
7138
7139 // We take a break if we've been at this for a while,
7140 // so as to avoid monopolizing the locks involved.
7141 void MarkFromRootsClosure::do_yield_work() {
7142 // First give up the locks, then yield, then re-lock
7143 // We should probably use a constructor/destructor idiom to
7144 // do this unlock/lock or modify the MutexUnlocker class to
7145 // serve our purpose. XXX
7146 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7147 "CMS thread should hold CMS token");
7148 assert_lock_strong(_bitMap->lock());
7149 DEBUG_ONLY(RememberKlassesChecker mux(false);)
7150 _bitMap->lock()->unlock();
7151 ConcurrentMarkSweepThread::desynchronize(true);
7152 ConcurrentMarkSweepThread::acknowledge_yield_request();
7153 _collector->stopTimer();
7154 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7155 if (PrintCMSStatistics != 0) {
7156 _collector->incrementYields();
7157 }
7158 _collector->icms_wait();
7159
7160 // See the comment in coordinator_yield()
7161 for (unsigned i = 0; i < CMSYieldSleepCount &&
7162 ConcurrentMarkSweepThread::should_yield() &&
7163 !CMSCollector::foregroundGCIsActive(); ++i) {
7164 os::sleep(Thread::current(), 1, false);
7165 ConcurrentMarkSweepThread::acknowledge_yield_request();
7166 }
7167
7168 ConcurrentMarkSweepThread::synchronize(true);
7169 _bitMap->lock()->lock_without_safepoint_check();
7170 _collector->startTimer();
7171 }
7172
7173 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
7174 assert(_bitMap->isMarked(ptr), "expected bit to be set");
7175 assert(_markStack->isEmpty(),
7176 "should drain stack to limit stack usage");
7177 // convert ptr to an oop preparatory to scanning
7178 oop obj = oop(ptr);
7179 // Ignore mark word in verification below, since we
7180 // may be running concurrent with mutators.
7181 assert(obj->is_oop(true), "should be an oop");
7182 assert(_finger <= ptr, "_finger runneth ahead");
7183 // advance the finger to right end of this object
7184 _finger = ptr + obj->size();
7185 assert(_finger > ptr, "we just incremented it above");
7186 // On large heaps, it may take us some time to get through
7187 // the marking phase (especially if running iCMS). During
7188 // this time it's possible that a lot of mutations have
7189 // accumulated in the card table and the mod union table --
7190 // these mutation records are redundant until we have
7191 // actually traced into the corresponding card.
7192 // Here, we check whether advancing the finger would make
7193 // us cross into a new card, and if so clear corresponding
7194 // cards in the MUT (preclean them in the card-table in the
7195 // future).
7196
7197 DEBUG_ONLY(if (!_verifying) {)
7198 // The clean-on-enter optimization is disabled by default,
7199 // until we fix 6178663.
7200 if (CMSCleanOnEnter && (_finger > _threshold)) {
7201 // [_threshold, _finger) represents the interval
7202 // of cards to be cleared in MUT (or precleaned in card table).
7203 // The set of cards to be cleared is all those that overlap
7204 // with the interval [_threshold, _finger); note that
7205 // _threshold is always kept card-aligned but _finger isn't
7206 // always card-aligned.
7207 HeapWord* old_threshold = _threshold;
7208 assert(old_threshold == (HeapWord*)round_to(
7209 (intptr_t)old_threshold, CardTableModRefBS::card_size),
7210 "_threshold should always be card-aligned");
7211 _threshold = (HeapWord*)round_to(
7212 (intptr_t)_finger, CardTableModRefBS::card_size);
7213 MemRegion mr(old_threshold, _threshold);
7214 assert(!mr.is_empty(), "Control point invariant");
7215 assert(_span.contains(mr), "Should clear within span");
7216 // XXX When _finger crosses from old gen into perm gen
7217 // we may be doing unnecessary cleaning; do better in the
7218 // future by detecting that condition and clearing fewer
7219 // MUT/CT entries.
7220 _mut->clear_range(mr);
7221 }
7222 DEBUG_ONLY(})
7223 // Note: the finger doesn't advance while we drain
7224 // the stack below.
7225 PushOrMarkClosure pushOrMarkClosure(_collector,
7226 _span, _bitMap, _markStack,
7227 _revisitStack,
7228 _finger, this);
7229 bool res = _markStack->push(obj);
7230 assert(res, "Empty non-zero size stack should have space for single push");
7231 while (!_markStack->isEmpty()) {
7232 oop new_oop = _markStack->pop();
7233 // Skip verifying header mark word below because we are
7234 // running concurrent with mutators.
7235 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
7236 // now scan this oop's oops
7237 new_oop->oop_iterate(&pushOrMarkClosure);
7238 do_yield_check();
7239 }
7240 assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
7241 }
7242
7243 Par_MarkFromRootsClosure::Par_MarkFromRootsClosure(CMSConcMarkingTask* task,
7244 CMSCollector* collector, MemRegion span,
7245 CMSBitMap* bit_map,
7246 OopTaskQueue* work_queue,
7247 CMSMarkStack* overflow_stack,
7248 CMSMarkStack* revisit_stack,
7249 bool should_yield):
7250 _collector(collector),
7251 _whole_span(collector->_span),
7252 _span(span),
7253 _bit_map(bit_map),
7254 _mut(&collector->_modUnionTable),
7255 _work_queue(work_queue),
7256 _overflow_stack(overflow_stack),
7257 _revisit_stack(revisit_stack),
7258 _yield(should_yield),
7259 _skip_bits(0),
7260 _task(task)
7261 {
7262 assert(_work_queue->size() == 0, "work_queue should be empty");
7263 _finger = span.start();
7264 _threshold = _finger; // XXX Defer clear-on-enter optimization for now
7265 assert(_span.contains(_finger), "Out of bounds _finger?");
7266 }
7267
7268 // Should revisit to see if this should be restructured for
7269 // greater efficiency.
7270 bool Par_MarkFromRootsClosure::do_bit(size_t offset) {
7271 if (_skip_bits > 0) {
7272 _skip_bits--;
7273 return true;
7274 }
7275 // convert offset into a HeapWord*
7276 HeapWord* addr = _bit_map->startWord() + offset;
7277 assert(_bit_map->endWord() && addr < _bit_map->endWord(),
7278 "address out of range");
7279 assert(_bit_map->isMarked(addr), "tautology");
7280 if (_bit_map->isMarked(addr+1)) {
7281 // this is an allocated object that might not yet be initialized
7282 assert(_skip_bits == 0, "tautology");
7283 _skip_bits = 2; // skip next two marked bits ("Printezis-marks")
7284 oop p = oop(addr);
7285 if (p->klass_or_null() == NULL || !p->is_parsable()) {
7286 // in the case of Clean-on-Enter optimization, redirty card
7287 // and avoid clearing card by increasing the threshold.
7288 return true;
7289 }
7290 }
7291 scan_oops_in_oop(addr);
7292 return true;
7293 }
7294
7295 void Par_MarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
7296 assert(_bit_map->isMarked(ptr), "expected bit to be set");
7297 // Should we assert that our work queue is empty or
7298 // below some drain limit?
7299 assert(_work_queue->size() == 0,
7300 "should drain stack to limit stack usage");
7301 // convert ptr to an oop preparatory to scanning
7302 oop obj = oop(ptr);
7303 // Ignore mark word in verification below, since we
7304 // may be running concurrent with mutators.
7305 assert(obj->is_oop(true), "should be an oop");
7306 assert(_finger <= ptr, "_finger runneth ahead");
7307 // advance the finger to right end of this object
7308 _finger = ptr + obj->size();
7309 assert(_finger > ptr, "we just incremented it above");
7310 // On large heaps, it may take us some time to get through
7311 // the marking phase (especially if running iCMS). During
7312 // this time it's possible that a lot of mutations have
7313 // accumulated in the card table and the mod union table --
7314 // these mutation records are redundant until we have
7315 // actually traced into the corresponding card.
7316 // Here, we check whether advancing the finger would make
7317 // us cross into a new card, and if so clear corresponding
7318 // cards in the MUT (preclean them in the card-table in the
7319 // future).
7320
7321 // The clean-on-enter optimization is disabled by default,
7322 // until we fix 6178663.
7323 if (CMSCleanOnEnter && (_finger > _threshold)) {
7324 // [_threshold, _finger) represents the interval
7325 // of cards to be cleared in MUT (or precleaned in card table).
7326 // The set of cards to be cleared is all those that overlap
7327 // with the interval [_threshold, _finger); note that
7328 // _threshold is always kept card-aligned but _finger isn't
7329 // always card-aligned.
7330 HeapWord* old_threshold = _threshold;
7331 assert(old_threshold == (HeapWord*)round_to(
7332 (intptr_t)old_threshold, CardTableModRefBS::card_size),
7333 "_threshold should always be card-aligned");
7334 _threshold = (HeapWord*)round_to(
7335 (intptr_t)_finger, CardTableModRefBS::card_size);
7336 MemRegion mr(old_threshold, _threshold);
7337 assert(!mr.is_empty(), "Control point invariant");
7338 assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
7339 // XXX When _finger crosses from old gen into perm gen
7340 // we may be doing unnecessary cleaning; do better in the
7341 // future by detecting that condition and clearing fewer
7342 // MUT/CT entries.
7343 _mut->clear_range(mr);
7344 }
7345
7346 // Note: the local finger doesn't advance while we drain
7347 // the stack below, but the global finger sure can and will.
7348 HeapWord** gfa = _task->global_finger_addr();
7349 Par_PushOrMarkClosure pushOrMarkClosure(_collector,
7350 _span, _bit_map,
7351 _work_queue,
7352 _overflow_stack,
7353 _revisit_stack,
7354 _finger,
7355 gfa, this);
7356 bool res = _work_queue->push(obj); // overflow could occur here
7357 assert(res, "Will hold once we use workqueues");
7358 while (true) {
7359 oop new_oop;
7360 if (!_work_queue->pop_local(new_oop)) {
7361 // We emptied our work_queue; check if there's stuff that can
7362 // be gotten from the overflow stack.
7363 if (CMSConcMarkingTask::get_work_from_overflow_stack(
7364 _overflow_stack, _work_queue)) {
7365 do_yield_check();
7366 continue;
7367 } else { // done
7368 break;
7369 }
7370 }
7371 // Skip verifying header mark word below because we are
7372 // running concurrent with mutators.
7373 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
7374 // now scan this oop's oops
7375 new_oop->oop_iterate(&pushOrMarkClosure);
7376 do_yield_check();
7377 }
7378 assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
7379 }
7380
7381 // Yield in response to a request from VM Thread or
7382 // from mutators.
7383 void Par_MarkFromRootsClosure::do_yield_work() {
7384 assert(_task != NULL, "sanity");
7385 _task->yield();
7386 }
7387
7388 // A variant of the above used for verifying CMS marking work.
7389 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
7390 MemRegion span,
7391 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
7392 CMSMarkStack* mark_stack):
7393 _collector(collector),
7394 _span(span),
7395 _verification_bm(verification_bm),
7396 _cms_bm(cms_bm),
7397 _mark_stack(mark_stack),
7398 _pam_verify_closure(collector, span, verification_bm, cms_bm,
7399 mark_stack)
7400 {
7401 assert(_mark_stack->isEmpty(), "stack should be empty");
7402 _finger = _verification_bm->startWord();
7403 assert(_collector->_restart_addr == NULL, "Sanity check");
7404 assert(_span.contains(_finger), "Out of bounds _finger?");
7405 }
7406
7407 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
7408 assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
7409 assert(_span.contains(addr), "Out of bounds _finger?");
7410 _finger = addr;
7411 }
7412
7413 // Should revisit to see if this should be restructured for
7414 // greater efficiency.
7415 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
7416 // convert offset into a HeapWord*
7417 HeapWord* addr = _verification_bm->startWord() + offset;
7418 assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
7419 "address out of range");
7420 assert(_verification_bm->isMarked(addr), "tautology");
7421 assert(_cms_bm->isMarked(addr), "tautology");
7422
7423 assert(_mark_stack->isEmpty(),
7424 "should drain stack to limit stack usage");
7425 // convert addr to an oop preparatory to scanning
7426 oop obj = oop(addr);
7427 assert(obj->is_oop(), "should be an oop");
7428 assert(_finger <= addr, "_finger runneth ahead");
7429 // advance the finger to right end of this object
7430 _finger = addr + obj->size();
7431 assert(_finger > addr, "we just incremented it above");
7432 // Note: the finger doesn't advance while we drain
7433 // the stack below.
7434 bool res = _mark_stack->push(obj);
7435 assert(res, "Empty non-zero size stack should have space for single push");
7436 while (!_mark_stack->isEmpty()) {
7437 oop new_oop = _mark_stack->pop();
7438 assert(new_oop->is_oop(), "Oops! expected to pop an oop");
7439 // now scan this oop's oops
7440 new_oop->oop_iterate(&_pam_verify_closure);
7441 }
7442 assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
7443 return true;
7444 }
7445
7446 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
7447 CMSCollector* collector, MemRegion span,
7448 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
7449 CMSMarkStack* mark_stack):
7450 OopClosure(collector->ref_processor()),
7451 _collector(collector),
7452 _span(span),
7453 _verification_bm(verification_bm),
7454 _cms_bm(cms_bm),
7455 _mark_stack(mark_stack)
7456 { }
7457
7458 void PushAndMarkVerifyClosure::do_oop(oop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
7459 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
7460
7461 // Upon stack overflow, we discard (part of) the stack,
7462 // remembering the least address amongst those discarded
7463 // in CMSCollector's _restart_address.
7464 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
7465 // Remember the least grey address discarded
7466 HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
7467 _collector->lower_restart_addr(ra);
7468 _mark_stack->reset(); // discard stack contents
7469 _mark_stack->expand(); // expand the stack if possible
7470 }
7471
7472 void PushAndMarkVerifyClosure::do_oop(oop obj) {
7473 assert(obj->is_oop_or_null(), "expected an oop or NULL");
7474 HeapWord* addr = (HeapWord*)obj;
7475 if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
7476 // Oop lies in _span and isn't yet grey or black
7477 _verification_bm->mark(addr); // now grey
7478 if (!_cms_bm->isMarked(addr)) {
7479 oop(addr)->print();
7480 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)",
7481 addr);
7482 fatal("... aborting");
7483 }
7484
7485 if (!_mark_stack->push(obj)) { // stack overflow
7486 if (PrintCMSStatistics != 0) {
7487 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7488 SIZE_FORMAT, _mark_stack->capacity());
7489 }
7490 assert(_mark_stack->isFull(), "Else push should have succeeded");
7491 handle_stack_overflow(addr);
7492 }
7493 // anything including and to the right of _finger
7494 // will be scanned as we iterate over the remainder of the
7495 // bit map
7496 }
7497 }
7498
7499 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
7500 MemRegion span,
7501 CMSBitMap* bitMap, CMSMarkStack* markStack,
7502 CMSMarkStack* revisitStack,
7503 HeapWord* finger, MarkFromRootsClosure* parent) :
7504 KlassRememberingOopClosure(collector, collector->ref_processor(), revisitStack),
7505 _span(span),
7506 _bitMap(bitMap),
7507 _markStack(markStack),
7508 _finger(finger),
7509 _parent(parent)
7510 { }
7511
7512 Par_PushOrMarkClosure::Par_PushOrMarkClosure(CMSCollector* collector,
7513 MemRegion span,
7514 CMSBitMap* bit_map,
7515 OopTaskQueue* work_queue,
7516 CMSMarkStack* overflow_stack,
7517 CMSMarkStack* revisit_stack,
7518 HeapWord* finger,
7519 HeapWord** global_finger_addr,
7520 Par_MarkFromRootsClosure* parent) :
7521 Par_KlassRememberingOopClosure(collector,
7522 collector->ref_processor(),
7523 revisit_stack),
7524 _whole_span(collector->_span),
7525 _span(span),
7526 _bit_map(bit_map),
7527 _work_queue(work_queue),
7528 _overflow_stack(overflow_stack),
7529 _finger(finger),
7530 _global_finger_addr(global_finger_addr),
7531 _parent(parent)
7532 { }
7533
7534 // Assumes thread-safe access by callers, who are
7535 // responsible for mutual exclusion.
7536 void CMSCollector::lower_restart_addr(HeapWord* low) {
7537 assert(_span.contains(low), "Out of bounds addr");
7538 if (_restart_addr == NULL) {
7539 _restart_addr = low;
7540 } else {
7541 _restart_addr = MIN2(_restart_addr, low);
7542 }
7543 }
7544
7545 // Upon stack overflow, we discard (part of) the stack,
7546 // remembering the least address amongst those discarded
7547 // in CMSCollector's _restart_address.
7548 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7549 // Remember the least grey address discarded
7550 HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
7551 _collector->lower_restart_addr(ra);
7552 _markStack->reset(); // discard stack contents
7553 _markStack->expand(); // expand the stack if possible
7554 }
7555
7556 // Upon stack overflow, we discard (part of) the stack,
7557 // remembering the least address amongst those discarded
7558 // in CMSCollector's _restart_address.
7559 void Par_PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7560 // We need to do this under a mutex to prevent other
7561 // workers from interfering with the work done below.
7562 MutexLockerEx ml(_overflow_stack->par_lock(),
7563 Mutex::_no_safepoint_check_flag);
7564 // Remember the least grey address discarded
7565 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
7566 _collector->lower_restart_addr(ra);
7567 _overflow_stack->reset(); // discard stack contents
7568 _overflow_stack->expand(); // expand the stack if possible
7569 }
7570
7571 void PushOrMarkClosure::do_oop(oop obj) {
7572 // Ignore mark word because we are running concurrent with mutators.
7573 assert(obj->is_oop_or_null(true), "expected an oop or NULL");
7574 HeapWord* addr = (HeapWord*)obj;
7575 if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
7576 // Oop lies in _span and isn't yet grey or black
7577 _bitMap->mark(addr); // now grey
7578 if (addr < _finger) {
7579 // the bit map iteration has already either passed, or
7580 // sampled, this bit in the bit map; we'll need to
7581 // use the marking stack to scan this oop's oops.
7582 bool simulate_overflow = false;
7583 NOT_PRODUCT(
7584 if (CMSMarkStackOverflowALot &&
7585 _collector->simulate_overflow()) {
7586 // simulate a stack overflow
7587 simulate_overflow = true;
7588 }
7589 )
7590 if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
7591 if (PrintCMSStatistics != 0) {
7592 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7593 SIZE_FORMAT, _markStack->capacity());
7594 }
7595 assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
7596 handle_stack_overflow(addr);
7597 }
7598 }
7599 // anything including and to the right of _finger
7600 // will be scanned as we iterate over the remainder of the
7601 // bit map
7602 do_yield_check();
7603 }
7604 }
7605
7606 void PushOrMarkClosure::do_oop(oop* p) { PushOrMarkClosure::do_oop_work(p); }
7607 void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); }
7608
7609 void Par_PushOrMarkClosure::do_oop(oop obj) {
7610 // Ignore mark word because we are running concurrent with mutators.
7611 assert(obj->is_oop_or_null(true), "expected an oop or NULL");
7612 HeapWord* addr = (HeapWord*)obj;
7613 if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
7614 // Oop lies in _span and isn't yet grey or black
7615 // We read the global_finger (volatile read) strictly after marking oop
7616 bool res = _bit_map->par_mark(addr); // now grey
7617 volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
7618 // Should we push this marked oop on our stack?
7619 // -- if someone else marked it, nothing to do
7620 // -- if target oop is above global finger nothing to do
7621 // -- if target oop is in chunk and above local finger
7622 // then nothing to do
7623 // -- else push on work queue
7624 if ( !res // someone else marked it, they will deal with it
7625 || (addr >= *gfa) // will be scanned in a later task
7626 || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
7627 return;
7628 }
7629 // the bit map iteration has already either passed, or
7630 // sampled, this bit in the bit map; we'll need to
7631 // use the marking stack to scan this oop's oops.
7632 bool simulate_overflow = false;
7633 NOT_PRODUCT(
7634 if (CMSMarkStackOverflowALot &&
7635 _collector->simulate_overflow()) {
7636 // simulate a stack overflow
7637 simulate_overflow = true;
7638 }
7639 )
7640 if (simulate_overflow ||
7641 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
7642 // stack overflow
7643 if (PrintCMSStatistics != 0) {
7644 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7645 SIZE_FORMAT, _overflow_stack->capacity());
7646 }
7647 // We cannot assert that the overflow stack is full because
7648 // it may have been emptied since.
7649 assert(simulate_overflow ||
7650 _work_queue->size() == _work_queue->max_elems(),
7651 "Else push should have succeeded");
7652 handle_stack_overflow(addr);
7653 }
7654 do_yield_check();
7655 }
7656 }
7657
7658 void Par_PushOrMarkClosure::do_oop(oop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7659 void Par_PushOrMarkClosure::do_oop(narrowOop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7660
7661 KlassRememberingOopClosure::KlassRememberingOopClosure(CMSCollector* collector,
7662 ReferenceProcessor* rp,
7663 CMSMarkStack* revisit_stack) :
7664 OopClosure(rp),
7665 _collector(collector),
7666 _revisit_stack(revisit_stack),
7667 _should_remember_klasses(collector->should_unload_classes()) {}
7668
7669 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
7670 MemRegion span,
7671 ReferenceProcessor* rp,
7672 CMSBitMap* bit_map,
7673 CMSBitMap* mod_union_table,
7674 CMSMarkStack* mark_stack,
7675 CMSMarkStack* revisit_stack,
7676 bool concurrent_precleaning):
7677 KlassRememberingOopClosure(collector, rp, revisit_stack),
7678 _span(span),
7679 _bit_map(bit_map),
7680 _mod_union_table(mod_union_table),
7681 _mark_stack(mark_stack),
7682 _concurrent_precleaning(concurrent_precleaning)
7683 {
7684 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7685 }
7686
7687 // Grey object rescan during pre-cleaning and second checkpoint phases --
7688 // the non-parallel version (the parallel version appears further below.)
7689 void PushAndMarkClosure::do_oop(oop obj) {
7690 // Ignore mark word verification. If during concurrent precleaning,
7691 // the object monitor may be locked. If during the checkpoint
7692 // phases, the object may already have been reached by a different
7693 // path and may be at the end of the global overflow list (so
7694 // the mark word may be NULL).
7695 assert(obj->is_oop_or_null(true /* ignore mark word */),
7696 "expected an oop or NULL");
7697 HeapWord* addr = (HeapWord*)obj;
7698 // Check if oop points into the CMS generation
7699 // and is not marked
7700 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7701 // a white object ...
7702 _bit_map->mark(addr); // ... now grey
7703 // push on the marking stack (grey set)
7704 bool simulate_overflow = false;
7705 NOT_PRODUCT(
7706 if (CMSMarkStackOverflowALot &&
7707 _collector->simulate_overflow()) {
7708 // simulate a stack overflow
7709 simulate_overflow = true;
7710 }
7711 )
7712 if (simulate_overflow || !_mark_stack->push(obj)) {
7713 if (_concurrent_precleaning) {
7714 // During precleaning we can just dirty the appropriate card(s)
7715 // in the mod union table, thus ensuring that the object remains
7716 // in the grey set and continue. In the case of object arrays
7717 // we need to dirty all of the cards that the object spans,
7718 // since the rescan of object arrays will be limited to the
7719 // dirty cards.
7720 // Note that no one can be intefering with us in this action
7721 // of dirtying the mod union table, so no locking or atomics
7722 // are required.
7723 if (obj->is_objArray()) {
7724 size_t sz = obj->size();
7725 HeapWord* end_card_addr = (HeapWord*)round_to(
7726 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7727 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7728 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7729 _mod_union_table->mark_range(redirty_range);
7730 } else {
7731 _mod_union_table->mark(addr);
7732 }
7733 _collector->_ser_pmc_preclean_ovflw++;
7734 } else {
7735 // During the remark phase, we need to remember this oop
7736 // in the overflow list.
7737 _collector->push_on_overflow_list(obj);
7738 _collector->_ser_pmc_remark_ovflw++;
7739 }
7740 }
7741 }
7742 }
7743
7744 Par_PushAndMarkClosure::Par_PushAndMarkClosure(CMSCollector* collector,
7745 MemRegion span,
7746 ReferenceProcessor* rp,
7747 CMSBitMap* bit_map,
7748 OopTaskQueue* work_queue,
7749 CMSMarkStack* revisit_stack):
7750 Par_KlassRememberingOopClosure(collector, rp, revisit_stack),
7751 _span(span),
7752 _bit_map(bit_map),
7753 _work_queue(work_queue)
7754 {
7755 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7756 }
7757
7758 void PushAndMarkClosure::do_oop(oop* p) { PushAndMarkClosure::do_oop_work(p); }
7759 void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); }
7760
7761 // Grey object rescan during second checkpoint phase --
7762 // the parallel version.
7763 void Par_PushAndMarkClosure::do_oop(oop obj) {
7764 // In the assert below, we ignore the mark word because
7765 // this oop may point to an already visited object that is
7766 // on the overflow stack (in which case the mark word has
7767 // been hijacked for chaining into the overflow stack --
7768 // if this is the last object in the overflow stack then
7769 // its mark word will be NULL). Because this object may
7770 // have been subsequently popped off the global overflow
7771 // stack, and the mark word possibly restored to the prototypical
7772 // value, by the time we get to examined this failing assert in
7773 // the debugger, is_oop_or_null(false) may subsequently start
7774 // to hold.
7775 assert(obj->is_oop_or_null(true),
7776 "expected an oop or NULL");
7777 HeapWord* addr = (HeapWord*)obj;
7778 // Check if oop points into the CMS generation
7779 // and is not marked
7780 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7781 // a white object ...
7782 // If we manage to "claim" the object, by being the
7783 // first thread to mark it, then we push it on our
7784 // marking stack
7785 if (_bit_map->par_mark(addr)) { // ... now grey
7786 // push on work queue (grey set)
7787 bool simulate_overflow = false;
7788 NOT_PRODUCT(
7789 if (CMSMarkStackOverflowALot &&
7790 _collector->par_simulate_overflow()) {
7791 // simulate a stack overflow
7792 simulate_overflow = true;
7793 }
7794 )
7795 if (simulate_overflow || !_work_queue->push(obj)) {
7796 _collector->par_push_on_overflow_list(obj);
7797 _collector->_par_pmc_remark_ovflw++; // imprecise OK: no need to CAS
7798 }
7799 } // Else, some other thread got there first
7800 }
7801 }
7802
7803 void Par_PushAndMarkClosure::do_oop(oop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7804 void Par_PushAndMarkClosure::do_oop(narrowOop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7805
7806 void PushAndMarkClosure::remember_mdo(DataLayout* v) {
7807 // TBD
7808 }
7809
7810 void Par_PushAndMarkClosure::remember_mdo(DataLayout* v) {
7811 // TBD
7812 }
7813
7814 void CMSPrecleanRefsYieldClosure::do_yield_work() {
7815 DEBUG_ONLY(RememberKlassesChecker mux(false);)
7816 Mutex* bml = _collector->bitMapLock();
7817 assert_lock_strong(bml);
7818 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7819 "CMS thread should hold CMS token");
7820
7821 bml->unlock();
7822 ConcurrentMarkSweepThread::desynchronize(true);
7823
7824 ConcurrentMarkSweepThread::acknowledge_yield_request();
7825
7826 _collector->stopTimer();
7827 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7828 if (PrintCMSStatistics != 0) {
7829 _collector->incrementYields();
7830 }
7831 _collector->icms_wait();
7832
7833 // See the comment in coordinator_yield()
7834 for (unsigned i = 0; i < CMSYieldSleepCount &&
7835 ConcurrentMarkSweepThread::should_yield() &&
7836 !CMSCollector::foregroundGCIsActive(); ++i) {
7837 os::sleep(Thread::current(), 1, false);
7838 ConcurrentMarkSweepThread::acknowledge_yield_request();
7839 }
7840
7841 ConcurrentMarkSweepThread::synchronize(true);
7842 bml->lock();
7843
7844 _collector->startTimer();
7845 }
7846
7847 bool CMSPrecleanRefsYieldClosure::should_return() {
7848 if (ConcurrentMarkSweepThread::should_yield()) {
7849 do_yield_work();
7850 }
7851 return _collector->foregroundGCIsActive();
7852 }
7853
7854 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
7855 assert(((size_t)mr.start())%CardTableModRefBS::card_size_in_words == 0,
7856 "mr should be aligned to start at a card boundary");
7857 // We'd like to assert:
7858 // assert(mr.word_size()%CardTableModRefBS::card_size_in_words == 0,
7859 // "mr should be a range of cards");
7860 // However, that would be too strong in one case -- the last
7861 // partition ends at _unallocated_block which, in general, can be
7862 // an arbitrary boundary, not necessarily card aligned.
7863 if (PrintCMSStatistics != 0) {
7864 _num_dirty_cards +=
7865 mr.word_size()/CardTableModRefBS::card_size_in_words;
7866 }
7867 _space->object_iterate_mem(mr, &_scan_cl);
7868 }
7869
7870 SweepClosure::SweepClosure(CMSCollector* collector,
7871 ConcurrentMarkSweepGeneration* g,
7872 CMSBitMap* bitMap, bool should_yield) :
7873 _collector(collector),
7874 _g(g),
7875 _sp(g->cmsSpace()),
7876 _limit(_sp->sweep_limit()),
7877 _freelistLock(_sp->freelistLock()),
7878 _bitMap(bitMap),
7879 _yield(should_yield),
7880 _inFreeRange(false), // No free range at beginning of sweep
7881 _freeRangeInFreeLists(false), // No free range at beginning of sweep
7882 _lastFreeRangeCoalesced(false),
7883 _freeFinger(g->used_region().start())
7884 {
7885 NOT_PRODUCT(
7886 _numObjectsFreed = 0;
7887 _numWordsFreed = 0;
7888 _numObjectsLive = 0;
7889 _numWordsLive = 0;
7890 _numObjectsAlreadyFree = 0;
7891 _numWordsAlreadyFree = 0;
7892 _last_fc = NULL;
7893
7894 _sp->initializeIndexedFreeListArrayReturnedBytes();
7895 _sp->dictionary()->initializeDictReturnedBytes();
7896 )
7897 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7898 "sweep _limit out of bounds");
7899 if (CMSTraceSweeper) {
7900 gclog_or_tty->print("\n====================\nStarting new sweep\n");
7901 }
7902 }
7903
7904 // We need this destructor to reclaim any space at the end
7905 // of the space, which do_blk below may not have added back to
7906 // the free lists. [basically dealing with the "fringe effect"]
7907 SweepClosure::~SweepClosure() {
7908 assert_lock_strong(_freelistLock);
7909 // this should be treated as the end of a free run if any
7910 // The current free range should be returned to the free lists
7911 // as one coalesced chunk.
7912 if (inFreeRange()) {
7913 flushCurFreeChunk(freeFinger(),
7914 pointer_delta(_limit, freeFinger()));
7915 assert(freeFinger() < _limit, "the finger pointeth off base");
7916 if (CMSTraceSweeper) {
7917 gclog_or_tty->print("destructor:");
7918 gclog_or_tty->print("Sweep:put_free_blk 0x%x ("SIZE_FORMAT") "
7919 "[coalesced:"SIZE_FORMAT"]\n",
7920 freeFinger(), pointer_delta(_limit, freeFinger()),
7921 lastFreeRangeCoalesced());
7922 }
7923 }
7924 NOT_PRODUCT(
7925 if (Verbose && PrintGC) {
7926 gclog_or_tty->print("Collected "SIZE_FORMAT" objects, "
7927 SIZE_FORMAT " bytes",
7928 _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
7929 gclog_or_tty->print_cr("\nLive "SIZE_FORMAT" objects, "
7930 SIZE_FORMAT" bytes "
7931 "Already free "SIZE_FORMAT" objects, "SIZE_FORMAT" bytes",
7932 _numObjectsLive, _numWordsLive*sizeof(HeapWord),
7933 _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
7934 size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree) *
7935 sizeof(HeapWord);
7936 gclog_or_tty->print_cr("Total sweep: "SIZE_FORMAT" bytes", totalBytes);
7937
7938 if (PrintCMSStatistics && CMSVerifyReturnedBytes) {
7939 size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
7940 size_t dictReturnedBytes = _sp->dictionary()->sumDictReturnedBytes();
7941 size_t returnedBytes = indexListReturnedBytes + dictReturnedBytes;
7942 gclog_or_tty->print("Returned "SIZE_FORMAT" bytes", returnedBytes);
7943 gclog_or_tty->print(" Indexed List Returned "SIZE_FORMAT" bytes",
7944 indexListReturnedBytes);
7945 gclog_or_tty->print_cr(" Dictionary Returned "SIZE_FORMAT" bytes",
7946 dictReturnedBytes);
7947 }
7948 }
7949 )
7950 // Now, in debug mode, just null out the sweep_limit
7951 NOT_PRODUCT(_sp->clear_sweep_limit();)
7952 if (CMSTraceSweeper) {
7953 gclog_or_tty->print("end of sweep\n================\n");
7954 }
7955 }
7956
7957 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
7958 bool freeRangeInFreeLists) {
7959 if (CMSTraceSweeper) {
7960 gclog_or_tty->print("---- Start free range 0x%x with free block [%d] (%d)\n",
7961 freeFinger, _sp->block_size(freeFinger),
7962 freeRangeInFreeLists);
7963 }
7964 assert(!inFreeRange(), "Trampling existing free range");
7965 set_inFreeRange(true);
7966 set_lastFreeRangeCoalesced(false);
7967
7968 set_freeFinger(freeFinger);
7969 set_freeRangeInFreeLists(freeRangeInFreeLists);
7970 if (CMSTestInFreeList) {
7971 if (freeRangeInFreeLists) {
7972 FreeChunk* fc = (FreeChunk*) freeFinger;
7973 assert(fc->isFree(), "A chunk on the free list should be free.");
7974 assert(fc->size() > 0, "Free range should have a size");
7975 assert(_sp->verifyChunkInFreeLists(fc), "Chunk is not in free lists");
7976 }
7977 }
7978 }
7979
7980 // Note that the sweeper runs concurrently with mutators. Thus,
7981 // it is possible for direct allocation in this generation to happen
7982 // in the middle of the sweep. Note that the sweeper also coalesces
7983 // contiguous free blocks. Thus, unless the sweeper and the allocator
7984 // synchronize appropriately freshly allocated blocks may get swept up.
7985 // This is accomplished by the sweeper locking the free lists while
7986 // it is sweeping. Thus blocks that are determined to be free are
7987 // indeed free. There is however one additional complication:
7988 // blocks that have been allocated since the final checkpoint and
7989 // mark, will not have been marked and so would be treated as
7990 // unreachable and swept up. To prevent this, the allocator marks
7991 // the bit map when allocating during the sweep phase. This leads,
7992 // however, to a further complication -- objects may have been allocated
7993 // but not yet initialized -- in the sense that the header isn't yet
7994 // installed. The sweeper can not then determine the size of the block
7995 // in order to skip over it. To deal with this case, we use a technique
7996 // (due to Printezis) to encode such uninitialized block sizes in the
7997 // bit map. Since the bit map uses a bit per every HeapWord, but the
7998 // CMS generation has a minimum object size of 3 HeapWords, it follows
7999 // that "normal marks" won't be adjacent in the bit map (there will
8000 // always be at least two 0 bits between successive 1 bits). We make use
8001 // of these "unused" bits to represent uninitialized blocks -- the bit
8002 // corresponding to the start of the uninitialized object and the next
8003 // bit are both set. Finally, a 1 bit marks the end of the object that
8004 // started with the two consecutive 1 bits to indicate its potentially
8005 // uninitialized state.
8006
8007 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
8008 FreeChunk* fc = (FreeChunk*)addr;
8009 size_t res;
8010
8011 // Check if we are done sweeping. Below we check "addr >= _limit" rather
8012 // than "addr == _limit" because although _limit was a block boundary when
8013 // we started the sweep, it may no longer be one because heap expansion
8014 // may have caused us to coalesce the block ending at the address _limit
8015 // with a newly expanded chunk (this happens when _limit was set to the
8016 // previous _end of the space), so we may have stepped past _limit; see CR 6977970.
8017 if (addr >= _limit) { // we have swept up to or past the limit, do nothing more
8018 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
8019 "sweep _limit out of bounds");
8020 assert(addr < _sp->end(), "addr out of bounds");
8021 // help the closure application finish
8022 return pointer_delta(_sp->end(), addr);
8023 }
8024 assert(addr < _limit, "sweep invariant");
8025
8026 // check if we should yield
8027 do_yield_check(addr);
8028 if (fc->isFree()) {
8029 // Chunk that is already free
8030 res = fc->size();
8031 doAlreadyFreeChunk(fc);
8032 debug_only(_sp->verifyFreeLists());
8033 assert(res == fc->size(), "Don't expect the size to change");
8034 NOT_PRODUCT(
8035 _numObjectsAlreadyFree++;
8036 _numWordsAlreadyFree += res;
8037 )
8038 NOT_PRODUCT(_last_fc = fc;)
8039 } else if (!_bitMap->isMarked(addr)) {
8040 // Chunk is fresh garbage
8041 res = doGarbageChunk(fc);
8042 debug_only(_sp->verifyFreeLists());
8043 NOT_PRODUCT(
8044 _numObjectsFreed++;
8045 _numWordsFreed += res;
8046 )
8047 } else {
8048 // Chunk that is alive.
8049 res = doLiveChunk(fc);
8050 debug_only(_sp->verifyFreeLists());
8051 NOT_PRODUCT(
8052 _numObjectsLive++;
8053 _numWordsLive += res;
8054 )
8055 }
8056 return res;
8057 }
8058
8059 // For the smart allocation, record following
8060 // split deaths - a free chunk is removed from its free list because
8061 // it is being split into two or more chunks.
8062 // split birth - a free chunk is being added to its free list because
8063 // a larger free chunk has been split and resulted in this free chunk.
8064 // coal death - a free chunk is being removed from its free list because
8065 // it is being coalesced into a large free chunk.
8066 // coal birth - a free chunk is being added to its free list because
8067 // it was created when two or more free chunks where coalesced into
8068 // this free chunk.
8069 //
8070 // These statistics are used to determine the desired number of free
8071 // chunks of a given size. The desired number is chosen to be relative
8072 // to the end of a CMS sweep. The desired number at the end of a sweep
8073 // is the
8074 // count-at-end-of-previous-sweep (an amount that was enough)
8075 // - count-at-beginning-of-current-sweep (the excess)
8076 // + split-births (gains in this size during interval)
8077 // - split-deaths (demands on this size during interval)
8078 // where the interval is from the end of one sweep to the end of the
8079 // next.
8080 //
8081 // When sweeping the sweeper maintains an accumulated chunk which is
8082 // the chunk that is made up of chunks that have been coalesced. That
8083 // will be termed the left-hand chunk. A new chunk of garbage that
8084 // is being considered for coalescing will be referred to as the
8085 // right-hand chunk.
8086 //
8087 // When making a decision on whether to coalesce a right-hand chunk with
8088 // the current left-hand chunk, the current count vs. the desired count
8089 // of the left-hand chunk is considered. Also if the right-hand chunk
8090 // is near the large chunk at the end of the heap (see
8091 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
8092 // left-hand chunk is coalesced.
8093 //
8094 // When making a decision about whether to split a chunk, the desired count
8095 // vs. the current count of the candidate to be split is also considered.
8096 // If the candidate is underpopulated (currently fewer chunks than desired)
8097 // a chunk of an overpopulated (currently more chunks than desired) size may
8098 // be chosen. The "hint" associated with a free list, if non-null, points
8099 // to a free list which may be overpopulated.
8100 //
8101
8102 void SweepClosure::doAlreadyFreeChunk(FreeChunk* fc) {
8103 size_t size = fc->size();
8104 // Chunks that cannot be coalesced are not in the
8105 // free lists.
8106 if (CMSTestInFreeList && !fc->cantCoalesce()) {
8107 assert(_sp->verifyChunkInFreeLists(fc),
8108 "free chunk should be in free lists");
8109 }
8110 // a chunk that is already free, should not have been
8111 // marked in the bit map
8112 HeapWord* addr = (HeapWord*) fc;
8113 assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
8114 // Verify that the bit map has no bits marked between
8115 // addr and purported end of this block.
8116 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8117
8118 // Some chunks cannot be coalesced in under any circumstances.
8119 // See the definition of cantCoalesce().
8120 if (!fc->cantCoalesce()) {
8121 // This chunk can potentially be coalesced.
8122 if (_sp->adaptive_freelists()) {
8123 // All the work is done in
8124 doPostIsFreeOrGarbageChunk(fc, size);
8125 } else { // Not adaptive free lists
8126 // this is a free chunk that can potentially be coalesced by the sweeper;
8127 if (!inFreeRange()) {
8128 // if the next chunk is a free block that can't be coalesced
8129 // it doesn't make sense to remove this chunk from the free lists
8130 FreeChunk* nextChunk = (FreeChunk*)(addr + size);
8131 assert((HeapWord*)nextChunk <= _limit, "sweep invariant");
8132 if ((HeapWord*)nextChunk < _limit && // there's a next chunk...
8133 nextChunk->isFree() && // which is free...
8134 nextChunk->cantCoalesce()) { // ... but cant be coalesced
8135 // nothing to do
8136 } else {
8137 // Potentially the start of a new free range:
8138 // Don't eagerly remove it from the free lists.
8139 // No need to remove it if it will just be put
8140 // back again. (Also from a pragmatic point of view
8141 // if it is a free block in a region that is beyond
8142 // any allocated blocks, an assertion will fail)
8143 // Remember the start of a free run.
8144 initialize_free_range(addr, true);
8145 // end - can coalesce with next chunk
8146 }
8147 } else {
8148 // the midst of a free range, we are coalescing
8149 debug_only(record_free_block_coalesced(fc);)
8150 if (CMSTraceSweeper) {
8151 gclog_or_tty->print(" -- pick up free block 0x%x (%d)\n", fc, size);
8152 }
8153 // remove it from the free lists
8154 _sp->removeFreeChunkFromFreeLists(fc);
8155 set_lastFreeRangeCoalesced(true);
8156 // If the chunk is being coalesced and the current free range is
8157 // in the free lists, remove the current free range so that it
8158 // will be returned to the free lists in its entirety - all
8159 // the coalesced pieces included.
8160 if (freeRangeInFreeLists()) {
8161 FreeChunk* ffc = (FreeChunk*) freeFinger();
8162 assert(ffc->size() == pointer_delta(addr, freeFinger()),
8163 "Size of free range is inconsistent with chunk size.");
8164 if (CMSTestInFreeList) {
8165 assert(_sp->verifyChunkInFreeLists(ffc),
8166 "free range is not in free lists");
8167 }
8168 _sp->removeFreeChunkFromFreeLists(ffc);
8169 set_freeRangeInFreeLists(false);
8170 }
8171 }
8172 }
8173 } else {
8174 // Code path common to both original and adaptive free lists.
8175
8176 // cant coalesce with previous block; this should be treated
8177 // as the end of a free run if any
8178 if (inFreeRange()) {
8179 // we kicked some butt; time to pick up the garbage
8180 assert(freeFinger() < addr, "the finger pointeth off base");
8181 flushCurFreeChunk(freeFinger(), pointer_delta(addr, freeFinger()));
8182 }
8183 // else, nothing to do, just continue
8184 }
8185 }
8186
8187 size_t SweepClosure::doGarbageChunk(FreeChunk* fc) {
8188 // This is a chunk of garbage. It is not in any free list.
8189 // Add it to a free list or let it possibly be coalesced into
8190 // a larger chunk.
8191 HeapWord* addr = (HeapWord*) fc;
8192 size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
8193
8194 if (_sp->adaptive_freelists()) {
8195 // Verify that the bit map has no bits marked between
8196 // addr and purported end of just dead object.
8197 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8198
8199 doPostIsFreeOrGarbageChunk(fc, size);
8200 } else {
8201 if (!inFreeRange()) {
8202 // start of a new free range
8203 assert(size > 0, "A free range should have a size");
8204 initialize_free_range(addr, false);
8205
8206 } else {
8207 // this will be swept up when we hit the end of the
8208 // free range
8209 if (CMSTraceSweeper) {
8210 gclog_or_tty->print(" -- pick up garbage 0x%x (%d) \n", fc, size);
8211 }
8212 // If the chunk is being coalesced and the current free range is
8213 // in the free lists, remove the current free range so that it
8214 // will be returned to the free lists in its entirety - all
8215 // the coalesced pieces included.
8216 if (freeRangeInFreeLists()) {
8217 FreeChunk* ffc = (FreeChunk*)freeFinger();
8218 assert(ffc->size() == pointer_delta(addr, freeFinger()),
8219 "Size of free range is inconsistent with chunk size.");
8220 if (CMSTestInFreeList) {
8221 assert(_sp->verifyChunkInFreeLists(ffc),
8222 "free range is not in free lists");
8223 }
8224 _sp->removeFreeChunkFromFreeLists(ffc);
8225 set_freeRangeInFreeLists(false);
8226 }
8227 set_lastFreeRangeCoalesced(true);
8228 }
8229 // this will be swept up when we hit the end of the free range
8230
8231 // Verify that the bit map has no bits marked between
8232 // addr and purported end of just dead object.
8233 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8234 }
8235 return size;
8236 }
8237
8238 size_t SweepClosure::doLiveChunk(FreeChunk* fc) {
8239 HeapWord* addr = (HeapWord*) fc;
8240 // The sweeper has just found a live object. Return any accumulated
8241 // left hand chunk to the free lists.
8242 if (inFreeRange()) {
8243 if (_sp->adaptive_freelists()) {
8244 flushCurFreeChunk(freeFinger(),
8245 pointer_delta(addr, freeFinger()));
8246 } else { // not adaptive freelists
8247 set_inFreeRange(false);
8248 // Add the free range back to the free list if it is not already
8249 // there.
8250 if (!freeRangeInFreeLists()) {
8251 assert(freeFinger() < addr, "the finger pointeth off base");
8252 if (CMSTraceSweeper) {
8253 gclog_or_tty->print("Sweep:put_free_blk 0x%x (%d) "
8254 "[coalesced:%d]\n",
8255 freeFinger(), pointer_delta(addr, freeFinger()),
8256 lastFreeRangeCoalesced());
8257 }
8258 _sp->addChunkAndRepairOffsetTable(freeFinger(),
8259 pointer_delta(addr, freeFinger()), lastFreeRangeCoalesced());
8260 }
8261 }
8262 }
8263
8264 // Common code path for original and adaptive free lists.
8265
8266 // this object is live: we'd normally expect this to be
8267 // an oop, and like to assert the following:
8268 // assert(oop(addr)->is_oop(), "live block should be an oop");
8269 // However, as we commented above, this may be an object whose
8270 // header hasn't yet been initialized.
8271 size_t size;
8272 assert(_bitMap->isMarked(addr), "Tautology for this control point");
8273 if (_bitMap->isMarked(addr + 1)) {
8274 // Determine the size from the bit map, rather than trying to
8275 // compute it from the object header.
8276 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
8277 size = pointer_delta(nextOneAddr + 1, addr);
8278 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
8279 "alignment problem");
8280
8281 #ifdef DEBUG
8282 if (oop(addr)->klass_or_null() != NULL &&
8283 ( !_collector->should_unload_classes()
8284 || (oop(addr)->is_parsable()) &&
8285 oop(addr)->is_conc_safe())) {
8286 // Ignore mark word because we are running concurrent with mutators
8287 assert(oop(addr)->is_oop(true), "live block should be an oop");
8288 // is_conc_safe is checked before performing this assertion
8289 // because an object that is not is_conc_safe may yet have
8290 // the return from size() correct.
8291 assert(size ==
8292 CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
8293 "P-mark and computed size do not agree");
8294 }
8295 #endif
8296
8297 } else {
8298 // This should be an initialized object that's alive.
8299 assert(oop(addr)->klass_or_null() != NULL &&
8300 (!_collector->should_unload_classes()
8301 || oop(addr)->is_parsable()),
8302 "Should be an initialized object");
8303 // Note that there are objects used during class redefinition
8304 // (e.g., merge_cp in VM_RedefineClasses::merge_cp_and_rewrite()
8305 // which are discarded with their is_conc_safe state still
8306 // false. These object may be floating garbage so may be
8307 // seen here. If they are floating garbage their size
8308 // should be attainable from their klass. Do not that
8309 // is_conc_safe() is true for oop(addr).
8310 // Ignore mark word because we are running concurrent with mutators
8311 assert(oop(addr)->is_oop(true), "live block should be an oop");
8312 // Verify that the bit map has no bits marked between
8313 // addr and purported end of this block.
8314 size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
8315 assert(size >= 3, "Necessary for Printezis marks to work");
8316 assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
8317 DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
8318 }
8319 return size;
8320 }
8321
8322 void SweepClosure::doPostIsFreeOrGarbageChunk(FreeChunk* fc,
8323 size_t chunkSize) {
8324 // doPostIsFreeOrGarbageChunk() should only be called in the smart allocation
8325 // scheme.
8326 bool fcInFreeLists = fc->isFree();
8327 assert(_sp->adaptive_freelists(), "Should only be used in this case.");
8328 assert((HeapWord*)fc <= _limit, "sweep invariant");
8329 if (CMSTestInFreeList && fcInFreeLists) {
8330 assert(_sp->verifyChunkInFreeLists(fc),
8331 "free chunk is not in free lists");
8332 }
8333
8334
8335 if (CMSTraceSweeper) {
8336 gclog_or_tty->print_cr(" -- pick up another chunk at 0x%x (%d)", fc, chunkSize);
8337 }
8338
8339 HeapWord* addr = (HeapWord*) fc;
8340
8341 bool coalesce;
8342 size_t left = pointer_delta(addr, freeFinger());
8343 size_t right = chunkSize;
8344 switch (FLSCoalescePolicy) {
8345 // numeric value forms a coalition aggressiveness metric
8346 case 0: { // never coalesce
8347 coalesce = false;
8348 break;
8349 }
8350 case 1: { // coalesce if left & right chunks on overpopulated lists
8351 coalesce = _sp->coalOverPopulated(left) &&
8352 _sp->coalOverPopulated(right);
8353 break;
8354 }
8355 case 2: { // coalesce if left chunk on overpopulated list (default)
8356 coalesce = _sp->coalOverPopulated(left);
8357 break;
8358 }
8359 case 3: { // coalesce if left OR right chunk on overpopulated list
8360 coalesce = _sp->coalOverPopulated(left) ||
8361 _sp->coalOverPopulated(right);
8362 break;
8363 }
8364 case 4: { // always coalesce
8365 coalesce = true;
8366 break;
8367 }
8368 default:
8369 ShouldNotReachHere();
8370 }
8371
8372 // Should the current free range be coalesced?
8373 // If the chunk is in a free range and either we decided to coalesce above
8374 // or the chunk is near the large block at the end of the heap
8375 // (isNearLargestChunk() returns true), then coalesce this chunk.
8376 bool doCoalesce = inFreeRange() &&
8377 (coalesce || _g->isNearLargestChunk((HeapWord*)fc));
8378 if (doCoalesce) {
8379 // Coalesce the current free range on the left with the new
8380 // chunk on the right. If either is on a free list,
8381 // it must be removed from the list and stashed in the closure.
8382 if (freeRangeInFreeLists()) {
8383 FreeChunk* ffc = (FreeChunk*)freeFinger();
8384 assert(ffc->size() == pointer_delta(addr, freeFinger()),
8385 "Size of free range is inconsistent with chunk size.");
8386 if (CMSTestInFreeList) {
8387 assert(_sp->verifyChunkInFreeLists(ffc),
8388 "Chunk is not in free lists");
8389 }
8390 _sp->coalDeath(ffc->size());
8391 _sp->removeFreeChunkFromFreeLists(ffc);
8392 set_freeRangeInFreeLists(false);
8393 }
8394 if (fcInFreeLists) {
8395 _sp->coalDeath(chunkSize);
8396 assert(fc->size() == chunkSize,
8397 "The chunk has the wrong size or is not in the free lists");
8398 _sp->removeFreeChunkFromFreeLists(fc);
8399 }
8400 set_lastFreeRangeCoalesced(true);
8401 } else { // not in a free range and/or should not coalesce
8402 // Return the current free range and start a new one.
8403 if (inFreeRange()) {
8404 // In a free range but cannot coalesce with the right hand chunk.
8405 // Put the current free range into the free lists.
8406 flushCurFreeChunk(freeFinger(),
8407 pointer_delta(addr, freeFinger()));
8408 }
8409 // Set up for new free range. Pass along whether the right hand
8410 // chunk is in the free lists.
8411 initialize_free_range((HeapWord*)fc, fcInFreeLists);
8412 }
8413 }
8414 void SweepClosure::flushCurFreeChunk(HeapWord* chunk, size_t size) {
8415 assert(inFreeRange(), "Should only be called if currently in a free range.");
8416 assert(size > 0,
8417 "A zero sized chunk cannot be added to the free lists.");
8418 if (!freeRangeInFreeLists()) {
8419 if(CMSTestInFreeList) {
8420 FreeChunk* fc = (FreeChunk*) chunk;
8421 fc->setSize(size);
8422 assert(!_sp->verifyChunkInFreeLists(fc),
8423 "chunk should not be in free lists yet");
8424 }
8425 if (CMSTraceSweeper) {
8426 gclog_or_tty->print_cr(" -- add free block 0x%x (%d) to free lists",
8427 chunk, size);
8428 }
8429 // A new free range is going to be starting. The current
8430 // free range has not been added to the free lists yet or
8431 // was removed so add it back.
8432 // If the current free range was coalesced, then the death
8433 // of the free range was recorded. Record a birth now.
8434 if (lastFreeRangeCoalesced()) {
8435 _sp->coalBirth(size);
8436 }
8437 _sp->addChunkAndRepairOffsetTable(chunk, size,
8438 lastFreeRangeCoalesced());
8439 }
8440 set_inFreeRange(false);
8441 set_freeRangeInFreeLists(false);
8442 }
8443
8444 // We take a break if we've been at this for a while,
8445 // so as to avoid monopolizing the locks involved.
8446 void SweepClosure::do_yield_work(HeapWord* addr) {
8447 // Return current free chunk being used for coalescing (if any)
8448 // to the appropriate freelist. After yielding, the next
8449 // free block encountered will start a coalescing range of
8450 // free blocks. If the next free block is adjacent to the
8451 // chunk just flushed, they will need to wait for the next
8452 // sweep to be coalesced.
8453 if (inFreeRange()) {
8454 flushCurFreeChunk(freeFinger(), pointer_delta(addr, freeFinger()));
8455 }
8456
8457 // First give up the locks, then yield, then re-lock.
8458 // We should probably use a constructor/destructor idiom to
8459 // do this unlock/lock or modify the MutexUnlocker class to
8460 // serve our purpose. XXX
8461 assert_lock_strong(_bitMap->lock());
8462 assert_lock_strong(_freelistLock);
8463 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
8464 "CMS thread should hold CMS token");
8465 _bitMap->lock()->unlock();
8466 _freelistLock->unlock();
8467 ConcurrentMarkSweepThread::desynchronize(true);
8468 ConcurrentMarkSweepThread::acknowledge_yield_request();
8469 _collector->stopTimer();
8470 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
8471 if (PrintCMSStatistics != 0) {
8472 _collector->incrementYields();
8473 }
8474 _collector->icms_wait();
8475
8476 // See the comment in coordinator_yield()
8477 for (unsigned i = 0; i < CMSYieldSleepCount &&
8478 ConcurrentMarkSweepThread::should_yield() &&
8479 !CMSCollector::foregroundGCIsActive(); ++i) {
8480 os::sleep(Thread::current(), 1, false);
8481 ConcurrentMarkSweepThread::acknowledge_yield_request();
8482 }
8483
8484 ConcurrentMarkSweepThread::synchronize(true);
8485 _freelistLock->lock();
8486 _bitMap->lock()->lock_without_safepoint_check();
8487 _collector->startTimer();
8488 }
8489
8490 #ifndef PRODUCT
8491 // This is actually very useful in a product build if it can
8492 // be called from the debugger. Compile it into the product
8493 // as needed.
8494 bool debug_verifyChunkInFreeLists(FreeChunk* fc) {
8495 return debug_cms_space->verifyChunkInFreeLists(fc);
8496 }
8497
8498 void SweepClosure::record_free_block_coalesced(FreeChunk* fc) const {
8499 if (CMSTraceSweeper) {
8500 gclog_or_tty->print("Sweep:coal_free_blk 0x%x (%d)\n", fc, fc->size());
8501 }
8502 }
8503 #endif
8504
8505 // CMSIsAliveClosure
8506 bool CMSIsAliveClosure::do_object_b(oop obj) {
8507 HeapWord* addr = (HeapWord*)obj;
8508 return addr != NULL &&
8509 (!_span.contains(addr) || _bit_map->isMarked(addr));
8510 }
8511
8512 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector,
8513 MemRegion span,
8514 CMSBitMap* bit_map, CMSMarkStack* mark_stack,
8515 CMSMarkStack* revisit_stack, bool cpc):
8516 KlassRememberingOopClosure(collector, NULL, revisit_stack),
8517 _span(span),
8518 _bit_map(bit_map),
8519 _mark_stack(mark_stack),
8520 _concurrent_precleaning(cpc) {
8521 assert(!_span.is_empty(), "Empty span could spell trouble");
8522 }
8523
8524
8525 // CMSKeepAliveClosure: the serial version
8526 void CMSKeepAliveClosure::do_oop(oop obj) {
8527 HeapWord* addr = (HeapWord*)obj;
8528 if (_span.contains(addr) &&
8529 !_bit_map->isMarked(addr)) {
8530 _bit_map->mark(addr);
8531 bool simulate_overflow = false;
8532 NOT_PRODUCT(
8533 if (CMSMarkStackOverflowALot &&
8534 _collector->simulate_overflow()) {
8535 // simulate a stack overflow
8536 simulate_overflow = true;
8537 }
8538 )
8539 if (simulate_overflow || !_mark_stack->push(obj)) {
8540 if (_concurrent_precleaning) {
8541 // We dirty the overflown object and let the remark
8542 // phase deal with it.
8543 assert(_collector->overflow_list_is_empty(), "Error");
8544 // In the case of object arrays, we need to dirty all of
8545 // the cards that the object spans. No locking or atomics
8546 // are needed since no one else can be mutating the mod union
8547 // table.
8548 if (obj->is_objArray()) {
8549 size_t sz = obj->size();
8550 HeapWord* end_card_addr =
8551 (HeapWord*)round_to((intptr_t)(addr+sz), CardTableModRefBS::card_size);
8552 MemRegion redirty_range = MemRegion(addr, end_card_addr);
8553 assert(!redirty_range.is_empty(), "Arithmetical tautology");
8554 _collector->_modUnionTable.mark_range(redirty_range);
8555 } else {
8556 _collector->_modUnionTable.mark(addr);
8557 }
8558 _collector->_ser_kac_preclean_ovflw++;
8559 } else {
8560 _collector->push_on_overflow_list(obj);
8561 _collector->_ser_kac_ovflw++;
8562 }
8563 }
8564 }
8565 }
8566
8567 void CMSKeepAliveClosure::do_oop(oop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8568 void CMSKeepAliveClosure::do_oop(narrowOop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8569
8570 // CMSParKeepAliveClosure: a parallel version of the above.
8571 // The work queues are private to each closure (thread),
8572 // but (may be) available for stealing by other threads.
8573 void CMSParKeepAliveClosure::do_oop(oop obj) {
8574 HeapWord* addr = (HeapWord*)obj;
8575 if (_span.contains(addr) &&
8576 !_bit_map->isMarked(addr)) {
8577 // In general, during recursive tracing, several threads
8578 // may be concurrently getting here; the first one to
8579 // "tag" it, claims it.
8580 if (_bit_map->par_mark(addr)) {
8581 bool res = _work_queue->push(obj);
8582 assert(res, "Low water mark should be much less than capacity");
8583 // Do a recursive trim in the hope that this will keep
8584 // stack usage lower, but leave some oops for potential stealers
8585 trim_queue(_low_water_mark);
8586 } // Else, another thread got there first
8587 }
8588 }
8589
8590 void CMSParKeepAliveClosure::do_oop(oop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8591 void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8592
8593 void CMSParKeepAliveClosure::trim_queue(uint max) {
8594 while (_work_queue->size() > max) {
8595 oop new_oop;
8596 if (_work_queue->pop_local(new_oop)) {
8597 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
8598 assert(_bit_map->isMarked((HeapWord*)new_oop),
8599 "no white objects on this stack!");
8600 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8601 // iterate over the oops in this oop, marking and pushing
8602 // the ones in CMS heap (i.e. in _span).
8603 new_oop->oop_iterate(&_mark_and_push);
8604 }
8605 }
8606 }
8607
8608 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
8609 CMSCollector* collector,
8610 MemRegion span, CMSBitMap* bit_map,
8611 CMSMarkStack* revisit_stack,
8612 OopTaskQueue* work_queue):
8613 Par_KlassRememberingOopClosure(collector, NULL, revisit_stack),
8614 _span(span),
8615 _bit_map(bit_map),
8616 _work_queue(work_queue) { }
8617
8618 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
8619 HeapWord* addr = (HeapWord*)obj;
8620 if (_span.contains(addr) &&
8621 !_bit_map->isMarked(addr)) {
8622 if (_bit_map->par_mark(addr)) {
8623 bool simulate_overflow = false;
8624 NOT_PRODUCT(
8625 if (CMSMarkStackOverflowALot &&
8626 _collector->par_simulate_overflow()) {
8627 // simulate a stack overflow
8628 simulate_overflow = true;
8629 }
8630 )
8631 if (simulate_overflow || !_work_queue->push(obj)) {
8632 _collector->par_push_on_overflow_list(obj);
8633 _collector->_par_kac_ovflw++;
8634 }
8635 } // Else another thread got there already
8636 }
8637 }
8638
8639 void CMSInnerParMarkAndPushClosure::do_oop(oop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8640 void CMSInnerParMarkAndPushClosure::do_oop(narrowOop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8641
8642 //////////////////////////////////////////////////////////////////
8643 // CMSExpansionCause /////////////////////////////
8644 //////////////////////////////////////////////////////////////////
8645 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
8646 switch (cause) {
8647 case _no_expansion:
8648 return "No expansion";
8649 case _satisfy_free_ratio:
8650 return "Free ratio";
8651 case _satisfy_promotion:
8652 return "Satisfy promotion";
8653 case _satisfy_allocation:
8654 return "allocation";
8655 case _allocate_par_lab:
8656 return "Par LAB";
8657 case _allocate_par_spooling_space:
8658 return "Par Spooling Space";
8659 case _adaptive_size_policy:
8660 return "Ergonomics";
8661 default:
8662 return "unknown";
8663 }
8664 }
8665
8666 void CMSDrainMarkingStackClosure::do_void() {
8667 // the max number to take from overflow list at a time
8668 const size_t num = _mark_stack->capacity()/4;
8669 assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
8670 "Overflow list should be NULL during concurrent phases");
8671 while (!_mark_stack->isEmpty() ||
8672 // if stack is empty, check the overflow list
8673 _collector->take_from_overflow_list(num, _mark_stack)) {
8674 oop obj = _mark_stack->pop();
8675 HeapWord* addr = (HeapWord*)obj;
8676 assert(_span.contains(addr), "Should be within span");
8677 assert(_bit_map->isMarked(addr), "Should be marked");
8678 assert(obj->is_oop(), "Should be an oop");
8679 obj->oop_iterate(_keep_alive);
8680 }
8681 }
8682
8683 void CMSParDrainMarkingStackClosure::do_void() {
8684 // drain queue
8685 trim_queue(0);
8686 }
8687
8688 // Trim our work_queue so its length is below max at return
8689 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
8690 while (_work_queue->size() > max) {
8691 oop new_oop;
8692 if (_work_queue->pop_local(new_oop)) {
8693 assert(new_oop->is_oop(), "Expected an oop");
8694 assert(_bit_map->isMarked((HeapWord*)new_oop),
8695 "no white objects on this stack!");
8696 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8697 // iterate over the oops in this oop, marking and pushing
8698 // the ones in CMS heap (i.e. in _span).
8699 new_oop->oop_iterate(&_mark_and_push);
8700 }
8701 }
8702 }
8703
8704 ////////////////////////////////////////////////////////////////////
8705 // Support for Marking Stack Overflow list handling and related code
8706 ////////////////////////////////////////////////////////////////////
8707 // Much of the following code is similar in shape and spirit to the
8708 // code used in ParNewGC. We should try and share that code
8709 // as much as possible in the future.
8710
8711 #ifndef PRODUCT
8712 // Debugging support for CMSStackOverflowALot
8713
8714 // It's OK to call this multi-threaded; the worst thing
8715 // that can happen is that we'll get a bunch of closely
8716 // spaced simulated oveflows, but that's OK, in fact
8717 // probably good as it would exercise the overflow code
8718 // under contention.
8719 bool CMSCollector::simulate_overflow() {
8720 if (_overflow_counter-- <= 0) { // just being defensive
8721 _overflow_counter = CMSMarkStackOverflowInterval;
8722 return true;
8723 } else {
8724 return false;
8725 }
8726 }
8727
8728 bool CMSCollector::par_simulate_overflow() {
8729 return simulate_overflow();
8730 }
8731 #endif
8732
8733 // Single-threaded
8734 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
8735 assert(stack->isEmpty(), "Expected precondition");
8736 assert(stack->capacity() > num, "Shouldn't bite more than can chew");
8737 size_t i = num;
8738 oop cur = _overflow_list;
8739 const markOop proto = markOopDesc::prototype();
8740 NOT_PRODUCT(ssize_t n = 0;)
8741 for (oop next; i > 0 && cur != NULL; cur = next, i--) {
8742 next = oop(cur->mark());
8743 cur->set_mark(proto); // until proven otherwise
8744 assert(cur->is_oop(), "Should be an oop");
8745 bool res = stack->push(cur);
8746 assert(res, "Bit off more than can chew?");
8747 NOT_PRODUCT(n++;)
8748 }
8749 _overflow_list = cur;
8750 #ifndef PRODUCT
8751 assert(_num_par_pushes >= n, "Too many pops?");
8752 _num_par_pushes -=n;
8753 #endif
8754 return !stack->isEmpty();
8755 }
8756
8757 #define BUSY (oop(0x1aff1aff))
8758 // (MT-safe) Get a prefix of at most "num" from the list.
8759 // The overflow list is chained through the mark word of
8760 // each object in the list. We fetch the entire list,
8761 // break off a prefix of the right size and return the
8762 // remainder. If other threads try to take objects from
8763 // the overflow list at that time, they will wait for
8764 // some time to see if data becomes available. If (and
8765 // only if) another thread places one or more object(s)
8766 // on the global list before we have returned the suffix
8767 // to the global list, we will walk down our local list
8768 // to find its end and append the global list to
8769 // our suffix before returning it. This suffix walk can
8770 // prove to be expensive (quadratic in the amount of traffic)
8771 // when there are many objects in the overflow list and
8772 // there is much producer-consumer contention on the list.
8773 // *NOTE*: The overflow list manipulation code here and
8774 // in ParNewGeneration:: are very similar in shape,
8775 // except that in the ParNew case we use the old (from/eden)
8776 // copy of the object to thread the list via its klass word.
8777 // Because of the common code, if you make any changes in
8778 // the code below, please check the ParNew version to see if
8779 // similar changes might be needed.
8780 // CR 6797058 has been filed to consolidate the common code.
8781 bool CMSCollector::par_take_from_overflow_list(size_t num,
8782 OopTaskQueue* work_q,
8783 int no_of_gc_threads) {
8784 assert(work_q->size() == 0, "First empty local work queue");
8785 assert(num < work_q->max_elems(), "Can't bite more than we can chew");
8786 if (_overflow_list == NULL) {
8787 return false;
8788 }
8789 // Grab the entire list; we'll put back a suffix
8790 oop prefix = (oop)Atomic::xchg_ptr(BUSY, &_overflow_list);
8791 Thread* tid = Thread::current();
8792 // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was
8793 // set to ParallelGCThreads.
8794 size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads;
8795 size_t sleep_time_millis = MAX2((size_t)1, num/100);
8796 // If the list is busy, we spin for a short while,
8797 // sleeping between attempts to get the list.
8798 for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) {
8799 os::sleep(tid, sleep_time_millis, false);
8800 if (_overflow_list == NULL) {
8801 // Nothing left to take
8802 return false;
8803 } else if (_overflow_list != BUSY) {
8804 // Try and grab the prefix
8805 prefix = (oop)Atomic::xchg_ptr(BUSY, &_overflow_list);
8806 }
8807 }
8808 // If the list was found to be empty, or we spun long
8809 // enough, we give up and return empty-handed. If we leave
8810 // the list in the BUSY state below, it must be the case that
8811 // some other thread holds the overflow list and will set it
8812 // to a non-BUSY state in the future.
8813 if (prefix == NULL || prefix == BUSY) {
8814 // Nothing to take or waited long enough
8815 if (prefix == NULL) {
8816 // Write back the NULL in case we overwrote it with BUSY above
8817 // and it is still the same value.
8818 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8819 }
8820 return false;
8821 }
8822 assert(prefix != NULL && prefix != BUSY, "Error");
8823 size_t i = num;
8824 oop cur = prefix;
8825 // Walk down the first "num" objects, unless we reach the end.
8826 for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--);
8827 if (cur->mark() == NULL) {
8828 // We have "num" or fewer elements in the list, so there
8829 // is nothing to return to the global list.
8830 // Write back the NULL in lieu of the BUSY we wrote
8831 // above, if it is still the same value.
8832 if (_overflow_list == BUSY) {
8833 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8834 }
8835 } else {
8836 // Chop off the suffix and rerturn it to the global list.
8837 assert(cur->mark() != BUSY, "Error");
8838 oop suffix_head = cur->mark(); // suffix will be put back on global list
8839 cur->set_mark(NULL); // break off suffix
8840 // It's possible that the list is still in the empty(busy) state
8841 // we left it in a short while ago; in that case we may be
8842 // able to place back the suffix without incurring the cost
8843 // of a walk down the list.
8844 oop observed_overflow_list = _overflow_list;
8845 oop cur_overflow_list = observed_overflow_list;
8846 bool attached = false;
8847 while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
8848 observed_overflow_list =
8849 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
8850 if (cur_overflow_list == observed_overflow_list) {
8851 attached = true;
8852 break;
8853 } else cur_overflow_list = observed_overflow_list;
8854 }
8855 if (!attached) {
8856 // Too bad, someone else sneaked in (at least) an element; we'll need
8857 // to do a splice. Find tail of suffix so we can prepend suffix to global
8858 // list.
8859 for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark()));
8860 oop suffix_tail = cur;
8861 assert(suffix_tail != NULL && suffix_tail->mark() == NULL,
8862 "Tautology");
8863 observed_overflow_list = _overflow_list;
8864 do {
8865 cur_overflow_list = observed_overflow_list;
8866 if (cur_overflow_list != BUSY) {
8867 // Do the splice ...
8868 suffix_tail->set_mark(markOop(cur_overflow_list));
8869 } else { // cur_overflow_list == BUSY
8870 suffix_tail->set_mark(NULL);
8871 }
8872 // ... and try to place spliced list back on overflow_list ...
8873 observed_overflow_list =
8874 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
8875 } while (cur_overflow_list != observed_overflow_list);
8876 // ... until we have succeeded in doing so.
8877 }
8878 }
8879
8880 // Push the prefix elements on work_q
8881 assert(prefix != NULL, "control point invariant");
8882 const markOop proto = markOopDesc::prototype();
8883 oop next;
8884 NOT_PRODUCT(ssize_t n = 0;)
8885 for (cur = prefix; cur != NULL; cur = next) {
8886 next = oop(cur->mark());
8887 cur->set_mark(proto); // until proven otherwise
8888 assert(cur->is_oop(), "Should be an oop");
8889 bool res = work_q->push(cur);
8890 assert(res, "Bit off more than we can chew?");
8891 NOT_PRODUCT(n++;)
8892 }
8893 #ifndef PRODUCT
8894 assert(_num_par_pushes >= n, "Too many pops?");
8895 Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
8896 #endif
8897 return true;
8898 }
8899
8900 // Single-threaded
8901 void CMSCollector::push_on_overflow_list(oop p) {
8902 NOT_PRODUCT(_num_par_pushes++;)
8903 assert(p->is_oop(), "Not an oop");
8904 preserve_mark_if_necessary(p);
8905 p->set_mark((markOop)_overflow_list);
8906 _overflow_list = p;
8907 }
8908
8909 // Multi-threaded; use CAS to prepend to overflow list
8910 void CMSCollector::par_push_on_overflow_list(oop p) {
8911 NOT_PRODUCT(Atomic::inc_ptr(&_num_par_pushes);)
8912 assert(p->is_oop(), "Not an oop");
8913 par_preserve_mark_if_necessary(p);
8914 oop observed_overflow_list = _overflow_list;
8915 oop cur_overflow_list;
8916 do {
8917 cur_overflow_list = observed_overflow_list;
8918 if (cur_overflow_list != BUSY) {
8919 p->set_mark(markOop(cur_overflow_list));
8920 } else {
8921 p->set_mark(NULL);
8922 }
8923 observed_overflow_list =
8924 (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list);
8925 } while (cur_overflow_list != observed_overflow_list);
8926 }
8927 #undef BUSY
8928
8929 // Single threaded
8930 // General Note on GrowableArray: pushes may silently fail
8931 // because we are (temporarily) out of C-heap for expanding
8932 // the stack. The problem is quite ubiquitous and affects
8933 // a lot of code in the JVM. The prudent thing for GrowableArray
8934 // to do (for now) is to exit with an error. However, that may
8935 // be too draconian in some cases because the caller may be
8936 // able to recover without much harm. For such cases, we
8937 // should probably introduce a "soft_push" method which returns
8938 // an indication of success or failure with the assumption that
8939 // the caller may be able to recover from a failure; code in
8940 // the VM can then be changed, incrementally, to deal with such
8941 // failures where possible, thus, incrementally hardening the VM
8942 // in such low resource situations.
8943 void CMSCollector::preserve_mark_work(oop p, markOop m) {
8944 _preserved_oop_stack.push(p);
8945 _preserved_mark_stack.push(m);
8946 assert(m == p->mark(), "Mark word changed");
8947 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8948 "bijection");
8949 }
8950
8951 // Single threaded
8952 void CMSCollector::preserve_mark_if_necessary(oop p) {
8953 markOop m = p->mark();
8954 if (m->must_be_preserved(p)) {
8955 preserve_mark_work(p, m);
8956 }
8957 }
8958
8959 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
8960 markOop m = p->mark();
8961 if (m->must_be_preserved(p)) {
8962 MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
8963 // Even though we read the mark word without holding
8964 // the lock, we are assured that it will not change
8965 // because we "own" this oop, so no other thread can
8966 // be trying to push it on the overflow list; see
8967 // the assertion in preserve_mark_work() that checks
8968 // that m == p->mark().
8969 preserve_mark_work(p, m);
8970 }
8971 }
8972
8973 // We should be able to do this multi-threaded,
8974 // a chunk of stack being a task (this is
8975 // correct because each oop only ever appears
8976 // once in the overflow list. However, it's
8977 // not very easy to completely overlap this with
8978 // other operations, so will generally not be done
8979 // until all work's been completed. Because we
8980 // expect the preserved oop stack (set) to be small,
8981 // it's probably fine to do this single-threaded.
8982 // We can explore cleverer concurrent/overlapped/parallel
8983 // processing of preserved marks if we feel the
8984 // need for this in the future. Stack overflow should
8985 // be so rare in practice and, when it happens, its
8986 // effect on performance so great that this will
8987 // likely just be in the noise anyway.
8988 void CMSCollector::restore_preserved_marks_if_any() {
8989 assert(SafepointSynchronize::is_at_safepoint(),
8990 "world should be stopped");
8991 assert(Thread::current()->is_ConcurrentGC_thread() ||
8992 Thread::current()->is_VM_thread(),
8993 "should be single-threaded");
8994 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8995 "bijection");
8996
8997 while (!_preserved_oop_stack.is_empty()) {
8998 oop p = _preserved_oop_stack.pop();
8999 assert(p->is_oop(), "Should be an oop");
9000 assert(_span.contains(p), "oop should be in _span");
9001 assert(p->mark() == markOopDesc::prototype(),
9002 "Set when taken from overflow list");
9003 markOop m = _preserved_mark_stack.pop();
9004 p->set_mark(m);
9005 }
9006 assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(),
9007 "stacks were cleared above");
9008 }
9009
9010 #ifndef PRODUCT
9011 bool CMSCollector::no_preserved_marks() const {
9012 return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty();
9013 }
9014 #endif
9015
9016 CMSAdaptiveSizePolicy* ASConcurrentMarkSweepGeneration::cms_size_policy() const
9017 {
9018 GenCollectedHeap* gch = (GenCollectedHeap*) GenCollectedHeap::heap();
9019 CMSAdaptiveSizePolicy* size_policy =
9020 (CMSAdaptiveSizePolicy*) gch->gen_policy()->size_policy();
9021 assert(size_policy->is_gc_cms_adaptive_size_policy(),
9022 "Wrong type for size policy");
9023 return size_policy;
9024 }
9025
9026 void ASConcurrentMarkSweepGeneration::resize(size_t cur_promo_size,
9027 size_t desired_promo_size) {
9028 if (cur_promo_size < desired_promo_size) {
9029 size_t expand_bytes = desired_promo_size - cur_promo_size;
9030 if (PrintAdaptiveSizePolicy && Verbose) {
9031 gclog_or_tty->print_cr(" ASConcurrentMarkSweepGeneration::resize "
9032 "Expanding tenured generation by " SIZE_FORMAT " (bytes)",
9033 expand_bytes);
9034 }
9035 expand(expand_bytes,
9036 MinHeapDeltaBytes,
9037 CMSExpansionCause::_adaptive_size_policy);
9038 } else if (desired_promo_size < cur_promo_size) {
9039 size_t shrink_bytes = cur_promo_size - desired_promo_size;
9040 if (PrintAdaptiveSizePolicy && Verbose) {
9041 gclog_or_tty->print_cr(" ASConcurrentMarkSweepGeneration::resize "
9042 "Shrinking tenured generation by " SIZE_FORMAT " (bytes)",
9043 shrink_bytes);
9044 }
9045 shrink(shrink_bytes);
9046 }
9047 }
9048
9049 CMSGCAdaptivePolicyCounters* ASConcurrentMarkSweepGeneration::gc_adaptive_policy_counters() {
9050 GenCollectedHeap* gch = GenCollectedHeap::heap();
9051 CMSGCAdaptivePolicyCounters* counters =
9052 (CMSGCAdaptivePolicyCounters*) gch->collector_policy()->counters();
9053 assert(counters->kind() == GCPolicyCounters::CMSGCAdaptivePolicyCountersKind,
9054 "Wrong kind of counters");
9055 return counters;
9056 }
9057
9058
9059 void ASConcurrentMarkSweepGeneration::update_counters() {
9060 if (UsePerfData) {
9061 _space_counters->update_all();
9062 _gen_counters->update_all();
9063 CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
9064 GenCollectedHeap* gch = GenCollectedHeap::heap();
9065 CMSGCStats* gc_stats_l = (CMSGCStats*) gc_stats();
9066 assert(gc_stats_l->kind() == GCStats::CMSGCStatsKind,
9067 "Wrong gc statistics type");
9068 counters->update_counters(gc_stats_l);
9069 }
9070 }
9071
9072 void ASConcurrentMarkSweepGeneration::update_counters(size_t used) {
9073 if (UsePerfData) {
9074 _space_counters->update_used(used);
9075 _space_counters->update_capacity();
9076 _gen_counters->update_all();
9077
9078 CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
9079 GenCollectedHeap* gch = GenCollectedHeap::heap();
9080 CMSGCStats* gc_stats_l = (CMSGCStats*) gc_stats();
9081 assert(gc_stats_l->kind() == GCStats::CMSGCStatsKind,
9082 "Wrong gc statistics type");
9083 counters->update_counters(gc_stats_l);
9084 }
9085 }
9086
9087 // The desired expansion delta is computed so that:
9088 // . desired free percentage or greater is used
9089 void ASConcurrentMarkSweepGeneration::compute_new_size() {
9090 assert_locked_or_safepoint(Heap_lock);
9091
9092 GenCollectedHeap* gch = (GenCollectedHeap*) GenCollectedHeap::heap();
9093
9094 // If incremental collection failed, we just want to expand
9095 // to the limit.
9096 if (incremental_collection_failed()) {
9097 clear_incremental_collection_failed();
9098 grow_to_reserved();
9099 return;
9100 }
9101
9102 assert(UseAdaptiveSizePolicy, "Should be using adaptive sizing");
9103
9104 assert(gch->kind() == CollectedHeap::GenCollectedHeap,
9105 "Wrong type of heap");
9106 int prev_level = level() - 1;
9107 assert(prev_level >= 0, "The cms generation is the lowest generation");
9108 Generation* prev_gen = gch->get_gen(prev_level);
9109 assert(prev_gen->kind() == Generation::ASParNew,
9110 "Wrong type of young generation");
9111 ParNewGeneration* younger_gen = (ParNewGeneration*) prev_gen;
9112 size_t cur_eden = younger_gen->eden()->capacity();
9113 CMSAdaptiveSizePolicy* size_policy = cms_size_policy();
9114 size_t cur_promo = free();
9115 size_policy->compute_tenured_generation_free_space(cur_promo,
9116 max_available(),
9117 cur_eden);
9118 resize(cur_promo, size_policy->promo_size());
9119
9120 // Record the new size of the space in the cms generation
9121 // that is available for promotions. This is temporary.
9122 // It should be the desired promo size.
9123 size_policy->avg_cms_promo()->sample(free());
9124 size_policy->avg_old_live()->sample(used());
9125
9126 if (UsePerfData) {
9127 CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
9128 counters->update_cms_capacity_counter(capacity());
9129 }
9130 }
9131
9132 void ASConcurrentMarkSweepGeneration::shrink_by(size_t desired_bytes) {
9133 assert_locked_or_safepoint(Heap_lock);
9134 assert_lock_strong(freelistLock());
9135 HeapWord* old_end = _cmsSpace->end();
9136 HeapWord* unallocated_start = _cmsSpace->unallocated_block();
9137 assert(old_end >= unallocated_start, "Miscalculation of unallocated_start");
9138 FreeChunk* chunk_at_end = find_chunk_at_end();
9139 if (chunk_at_end == NULL) {
9140 // No room to shrink
9141 if (PrintGCDetails && Verbose) {
9142 gclog_or_tty->print_cr("No room to shrink: old_end "
9143 PTR_FORMAT " unallocated_start " PTR_FORMAT
9144 " chunk_at_end " PTR_FORMAT,
9145 old_end, unallocated_start, chunk_at_end);
9146 }
9147 return;
9148 } else {
9149
9150 // Find the chunk at the end of the space and determine
9151 // how much it can be shrunk.
9152 size_t shrinkable_size_in_bytes = chunk_at_end->size();
9153 size_t aligned_shrinkable_size_in_bytes =
9154 align_size_down(shrinkable_size_in_bytes, os::vm_page_size());
9155 assert(unallocated_start <= chunk_at_end->end(),
9156 "Inconsistent chunk at end of space");
9157 size_t bytes = MIN2(desired_bytes, aligned_shrinkable_size_in_bytes);
9158 size_t word_size_before = heap_word_size(_virtual_space.committed_size());
9159
9160 // Shrink the underlying space
9161 _virtual_space.shrink_by(bytes);
9162 if (PrintGCDetails && Verbose) {
9163 gclog_or_tty->print_cr("ConcurrentMarkSweepGeneration::shrink_by:"
9164 " desired_bytes " SIZE_FORMAT
9165 " shrinkable_size_in_bytes " SIZE_FORMAT
9166 " aligned_shrinkable_size_in_bytes " SIZE_FORMAT
9167 " bytes " SIZE_FORMAT,
9168 desired_bytes, shrinkable_size_in_bytes,
9169 aligned_shrinkable_size_in_bytes, bytes);
9170 gclog_or_tty->print_cr(" old_end " SIZE_FORMAT
9171 " unallocated_start " SIZE_FORMAT,
9172 old_end, unallocated_start);
9173 }
9174
9175 // If the space did shrink (shrinking is not guaranteed),
9176 // shrink the chunk at the end by the appropriate amount.
9177 if (((HeapWord*)_virtual_space.high()) < old_end) {
9178 size_t new_word_size =
9179 heap_word_size(_virtual_space.committed_size());
9180
9181 // Have to remove the chunk from the dictionary because it is changing
9182 // size and might be someplace elsewhere in the dictionary.
9183
9184 // Get the chunk at end, shrink it, and put it
9185 // back.
9186 _cmsSpace->removeChunkFromDictionary(chunk_at_end);
9187 size_t word_size_change = word_size_before - new_word_size;
9188 size_t chunk_at_end_old_size = chunk_at_end->size();
9189 assert(chunk_at_end_old_size >= word_size_change,
9190 "Shrink is too large");
9191 chunk_at_end->setSize(chunk_at_end_old_size -
9192 word_size_change);
9193 _cmsSpace->freed((HeapWord*) chunk_at_end->end(),
9194 word_size_change);
9195
9196 _cmsSpace->returnChunkToDictionary(chunk_at_end);
9197
9198 MemRegion mr(_cmsSpace->bottom(), new_word_size);
9199 _bts->resize(new_word_size); // resize the block offset shared array
9200 Universe::heap()->barrier_set()->resize_covered_region(mr);
9201 _cmsSpace->assert_locked();
9202 _cmsSpace->set_end((HeapWord*)_virtual_space.high());
9203
9204 NOT_PRODUCT(_cmsSpace->dictionary()->verify());
9205
9206 // update the space and generation capacity counters
9207 if (UsePerfData) {
9208 _space_counters->update_capacity();
9209 _gen_counters->update_all();
9210 }
9211
9212 if (Verbose && PrintGCDetails) {
9213 size_t new_mem_size = _virtual_space.committed_size();
9214 size_t old_mem_size = new_mem_size + bytes;
9215 gclog_or_tty->print_cr("Shrinking %s from %ldK by %ldK to %ldK",
9216 name(), old_mem_size/K, bytes/K, new_mem_size/K);
9217 }
9218 }
9219
9220 assert(_cmsSpace->unallocated_block() <= _cmsSpace->end(),
9221 "Inconsistency at end of space");
9222 assert(chunk_at_end->end() == _cmsSpace->end(),
9223 "Shrinking is inconsistent");
9224 return;
9225 }
9226 }
9227
9228 // Transfer some number of overflown objects to usual marking
9229 // stack. Return true if some objects were transferred.
9230 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
9231 size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,
9232 (size_t)ParGCDesiredObjsFromOverflowList);
9233
9234 bool res = _collector->take_from_overflow_list(num, _mark_stack);
9235 assert(_collector->overflow_list_is_empty() || res,
9236 "If list is not empty, we should have taken something");
9237 assert(!res || !_mark_stack->isEmpty(),
9238 "If we took something, it should now be on our stack");
9239 return res;
9240 }
9241
9242 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
9243 size_t res = _sp->block_size_no_stall(addr, _collector);
9244 assert(res != 0, "Should always be able to compute a size");
9245 if (_sp->block_is_obj(addr)) {
9246 if (_live_bit_map->isMarked(addr)) {
9247 // It can't have been dead in a previous cycle
9248 guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
9249 } else {
9250 _dead_bit_map->mark(addr); // mark the dead object
9251 }
9252 }
9253 return res;
9254 }
9255
9256 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase): TraceMemoryManagerStats() {
9257
9258 switch (phase) {
9259 case CMSCollector::InitialMarking:
9260 initialize(true /* fullGC */ ,
9261 true /* recordGCBeginTime */,
9262 true /* recordPreGCUsage */,
9263 false /* recordPeakUsage */,
9264 false /* recordPostGCusage */,
9265 true /* recordAccumulatedGCTime */,
9266 false /* recordGCEndTime */,
9267 false /* countCollection */ );
9268 break;
9269
9270 case CMSCollector::FinalMarking:
9271 initialize(true /* fullGC */ ,
9272 false /* recordGCBeginTime */,
9273 false /* recordPreGCUsage */,
9274 false /* recordPeakUsage */,
9275 false /* recordPostGCusage */,
9276 true /* recordAccumulatedGCTime */,
9277 false /* recordGCEndTime */,
9278 false /* countCollection */ );
9279 break;
9280
9281 case CMSCollector::Sweeping:
9282 initialize(true /* fullGC */ ,
9283 false /* recordGCBeginTime */,
9284 false /* recordPreGCUsage */,
9285 true /* recordPeakUsage */,
9286 true /* recordPostGCusage */,
9287 false /* recordAccumulatedGCTime */,
9288 true /* recordGCEndTime */,
9289 true /* countCollection */ );
9290 break;
9291
9292 default:
9293 ShouldNotReachHere();
9294 }
9295 }
9296
9297 // when bailing out of cms in concurrent mode failure
9298 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(): TraceMemoryManagerStats() {
9299 initialize(true /* fullGC */ ,
9300 true /* recordGCBeginTime */,
9301 true /* recordPreGCUsage */,
9302 true /* recordPeakUsage */,
9303 true /* recordPostGCusage */,
9304 true /* recordAccumulatedGCTime */,
9305 true /* recordGCEndTime */,
9306 true /* countCollection */ );
9307 }