1 /*
2 * Copyright (c) 2001, 2013, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include "precompiled.hpp"
26 #include "classfile/classLoaderData.hpp"
27 #include "classfile/symbolTable.hpp"
28 #include "classfile/systemDictionary.hpp"
29 #include "code/codeCache.hpp"
30 #include "gc_implementation/concurrentMarkSweep/cmsAdaptiveSizePolicy.hpp"
31 #include "gc_implementation/concurrentMarkSweep/cmsCollectorPolicy.hpp"
32 #include "gc_implementation/concurrentMarkSweep/cmsGCAdaptivePolicyCounters.hpp"
33 #include "gc_implementation/concurrentMarkSweep/cmsOopClosures.inline.hpp"
34 #include "gc_implementation/concurrentMarkSweep/compactibleFreeListSpace.hpp"
35 #include "gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.inline.hpp"
36 #include "gc_implementation/concurrentMarkSweep/concurrentMarkSweepThread.hpp"
37 #include "gc_implementation/concurrentMarkSweep/vmCMSOperations.hpp"
38 #include "gc_implementation/parNew/parNewGeneration.hpp"
39 #include "gc_implementation/shared/collectorCounters.hpp"
40 #include "gc_implementation/shared/gcTimer.hpp"
41 #include "gc_implementation/shared/gcTrace.hpp"
42 #include "gc_implementation/shared/gcTraceTime.hpp"
43 #include "gc_implementation/shared/isGCActiveMark.hpp"
44 #include "gc_interface/collectedHeap.inline.hpp"
45 #include "memory/allocation.hpp"
46 #include "memory/cardTableRS.hpp"
47 #include "memory/collectorPolicy.hpp"
48 #include "memory/gcLocker.inline.hpp"
49 #include "memory/genCollectedHeap.hpp"
50 #include "memory/genMarkSweep.hpp"
51 #include "memory/genOopClosures.inline.hpp"
52 #include "memory/iterator.hpp"
53 #include "memory/padded.hpp"
54 #include "memory/referencePolicy.hpp"
55 #include "memory/resourceArea.hpp"
56 #include "memory/tenuredGeneration.hpp"
57 #include "oops/oop.inline.hpp"
58 #include "prims/jvmtiExport.hpp"
59 #include "runtime/globals_extension.hpp"
60 #include "runtime/handles.inline.hpp"
61 #include "runtime/java.hpp"
62 #include "runtime/vmThread.hpp"
63 #include "services/memoryService.hpp"
64 #include "services/runtimeService.hpp"
65
66 // statics
67 CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL;
68 bool CMSCollector::_full_gc_requested = false;
69 GCCause::Cause CMSCollector::_full_gc_cause = GCCause::_no_gc;
70
71 //////////////////////////////////////////////////////////////////
72 // In support of CMS/VM thread synchronization
73 //////////////////////////////////////////////////////////////////
74 // We split use of the CGC_lock into 2 "levels".
75 // The low-level locking is of the usual CGC_lock monitor. We introduce
76 // a higher level "token" (hereafter "CMS token") built on top of the
77 // low level monitor (hereafter "CGC lock").
78 // The token-passing protocol gives priority to the VM thread. The
79 // CMS-lock doesn't provide any fairness guarantees, but clients
80 // should ensure that it is only held for very short, bounded
81 // durations.
82 //
83 // When either of the CMS thread or the VM thread is involved in
84 // collection operations during which it does not want the other
85 // thread to interfere, it obtains the CMS token.
86 //
87 // If either thread tries to get the token while the other has
88 // it, that thread waits. However, if the VM thread and CMS thread
89 // both want the token, then the VM thread gets priority while the
90 // CMS thread waits. This ensures, for instance, that the "concurrent"
91 // phases of the CMS thread's work do not block out the VM thread
92 // for long periods of time as the CMS thread continues to hog
93 // the token. (See bug 4616232).
94 //
95 // The baton-passing functions are, however, controlled by the
96 // flags _foregroundGCShouldWait and _foregroundGCIsActive,
97 // and here the low-level CMS lock, not the high level token,
98 // ensures mutual exclusion.
99 //
100 // Two important conditions that we have to satisfy:
101 // 1. if a thread does a low-level wait on the CMS lock, then it
102 // relinquishes the CMS token if it were holding that token
103 // when it acquired the low-level CMS lock.
104 // 2. any low-level notifications on the low-level lock
105 // should only be sent when a thread has relinquished the token.
106 //
107 // In the absence of either property, we'd have potential deadlock.
108 //
109 // We protect each of the CMS (concurrent and sequential) phases
110 // with the CMS _token_, not the CMS _lock_.
111 //
112 // The only code protected by CMS lock is the token acquisition code
113 // itself, see ConcurrentMarkSweepThread::[de]synchronize(), and the
114 // baton-passing code.
115 //
116 // Unfortunately, i couldn't come up with a good abstraction to factor and
117 // hide the naked CGC_lock manipulation in the baton-passing code
118 // further below. That's something we should try to do. Also, the proof
119 // of correctness of this 2-level locking scheme is far from obvious,
120 // and potentially quite slippery. We have an uneasy suspicion, for instance,
121 // that there may be a theoretical possibility of delay/starvation in the
122 // low-level lock/wait/notify scheme used for the baton-passing because of
123 // potential interference with the priority scheme embodied in the
124 // CMS-token-passing protocol. See related comments at a CGC_lock->wait()
125 // invocation further below and marked with "XXX 20011219YSR".
126 // Indeed, as we note elsewhere, this may become yet more slippery
127 // in the presence of multiple CMS and/or multiple VM threads. XXX
128
129 class CMSTokenSync: public StackObj {
130 private:
131 bool _is_cms_thread;
132 public:
133 CMSTokenSync(bool is_cms_thread):
134 _is_cms_thread(is_cms_thread) {
135 assert(is_cms_thread == Thread::current()->is_ConcurrentGC_thread(),
136 "Incorrect argument to constructor");
137 ConcurrentMarkSweepThread::synchronize(_is_cms_thread);
138 }
139
140 ~CMSTokenSync() {
141 assert(_is_cms_thread ?
142 ConcurrentMarkSweepThread::cms_thread_has_cms_token() :
143 ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
144 "Incorrect state");
145 ConcurrentMarkSweepThread::desynchronize(_is_cms_thread);
146 }
147 };
148
149 // Convenience class that does a CMSTokenSync, and then acquires
150 // upto three locks.
151 class CMSTokenSyncWithLocks: public CMSTokenSync {
152 private:
153 // Note: locks are acquired in textual declaration order
154 // and released in the opposite order
155 MutexLockerEx _locker1, _locker2, _locker3;
156 public:
157 CMSTokenSyncWithLocks(bool is_cms_thread, Mutex* mutex1,
158 Mutex* mutex2 = NULL, Mutex* mutex3 = NULL):
159 CMSTokenSync(is_cms_thread),
160 _locker1(mutex1, Mutex::_no_safepoint_check_flag),
161 _locker2(mutex2, Mutex::_no_safepoint_check_flag),
162 _locker3(mutex3, Mutex::_no_safepoint_check_flag)
163 { }
164 };
165
166
167 // Wrapper class to temporarily disable icms during a foreground cms collection.
168 class ICMSDisabler: public StackObj {
169 public:
170 // The ctor disables icms and wakes up the thread so it notices the change;
171 // the dtor re-enables icms. Note that the CMSCollector methods will check
172 // CMSIncrementalMode.
173 ICMSDisabler() { CMSCollector::disable_icms(); CMSCollector::start_icms(); }
174 ~ICMSDisabler() { CMSCollector::enable_icms(); }
175 };
176
177 //////////////////////////////////////////////////////////////////
178 // Concurrent Mark-Sweep Generation /////////////////////////////
179 //////////////////////////////////////////////////////////////////
180
181 NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;)
182
183 // This struct contains per-thread things necessary to support parallel
184 // young-gen collection.
185 class CMSParGCThreadState: public CHeapObj<mtGC> {
186 public:
187 CFLS_LAB lab;
188 PromotionInfo promo;
189
190 // Constructor.
191 CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) {
192 promo.setSpace(cfls);
193 }
194 };
195
196 ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration(
197 ReservedSpace rs, size_t initial_byte_size, int level,
198 CardTableRS* ct, bool use_adaptive_freelists,
199 FreeBlockDictionary<FreeChunk>::DictionaryChoice dictionaryChoice) :
200 CardGeneration(rs, initial_byte_size, level, ct),
201 _dilatation_factor(((double)MinChunkSize)/((double)(CollectedHeap::min_fill_size()))),
202 _debug_collection_type(Concurrent_collection_type),
203 _did_compact(false)
204 {
205 HeapWord* bottom = (HeapWord*) _virtual_space.low();
206 HeapWord* end = (HeapWord*) _virtual_space.high();
207
208 _direct_allocated_words = 0;
209 NOT_PRODUCT(
210 _numObjectsPromoted = 0;
211 _numWordsPromoted = 0;
212 _numObjectsAllocated = 0;
213 _numWordsAllocated = 0;
214 )
215
216 _cmsSpace = new CompactibleFreeListSpace(_bts, MemRegion(bottom, end),
217 use_adaptive_freelists,
218 dictionaryChoice);
219 NOT_PRODUCT(debug_cms_space = _cmsSpace;)
220 if (_cmsSpace == NULL) {
221 vm_exit_during_initialization(
222 "CompactibleFreeListSpace allocation failure");
223 }
224 _cmsSpace->_gen = this;
225
226 _gc_stats = new CMSGCStats();
227
228 // Verify the assumption that FreeChunk::_prev and OopDesc::_klass
229 // offsets match. The ability to tell free chunks from objects
230 // depends on this property.
231 debug_only(
232 FreeChunk* junk = NULL;
233 assert(UseCompressedClassPointers ||
234 junk->prev_addr() == (void*)(oop(junk)->klass_addr()),
235 "Offset of FreeChunk::_prev within FreeChunk must match"
236 " that of OopDesc::_klass within OopDesc");
237 )
238 if (CollectedHeap::use_parallel_gc_threads()) {
239 typedef CMSParGCThreadState* CMSParGCThreadStatePtr;
240 _par_gc_thread_states =
241 NEW_C_HEAP_ARRAY(CMSParGCThreadStatePtr, ParallelGCThreads, mtGC);
242 if (_par_gc_thread_states == NULL) {
243 vm_exit_during_initialization("Could not allocate par gc structs");
244 }
245 for (uint i = 0; i < ParallelGCThreads; i++) {
246 _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace());
247 if (_par_gc_thread_states[i] == NULL) {
248 vm_exit_during_initialization("Could not allocate par gc structs");
249 }
250 }
251 } else {
252 _par_gc_thread_states = NULL;
253 }
254 _incremental_collection_failed = false;
255 // The "dilatation_factor" is the expansion that can occur on
256 // account of the fact that the minimum object size in the CMS
257 // generation may be larger than that in, say, a contiguous young
258 // generation.
259 // Ideally, in the calculation below, we'd compute the dilatation
260 // factor as: MinChunkSize/(promoting_gen's min object size)
261 // Since we do not have such a general query interface for the
262 // promoting generation, we'll instead just use the minimum
263 // object size (which today is a header's worth of space);
264 // note that all arithmetic is in units of HeapWords.
265 assert(MinChunkSize >= CollectedHeap::min_fill_size(), "just checking");
266 assert(_dilatation_factor >= 1.0, "from previous assert");
267 }
268
269
270 // The field "_initiating_occupancy" represents the occupancy percentage
271 // at which we trigger a new collection cycle. Unless explicitly specified
272 // via CMSInitiatingOccupancyFraction (argument "io" below), it
273 // is calculated by:
274 //
275 // Let "f" be MinHeapFreeRatio in
276 //
277 // _initiating_occupancy = 100-f +
278 // f * (CMSTriggerRatio/100)
279 // where CMSTriggerRatio is the argument "tr" below.
280 //
281 // That is, if we assume the heap is at its desired maximum occupancy at the
282 // end of a collection, we let CMSTriggerRatio of the (purported) free
283 // space be allocated before initiating a new collection cycle.
284 //
285 void ConcurrentMarkSweepGeneration::init_initiating_occupancy(intx io, uintx tr) {
286 assert(io <= 100 && tr <= 100, "Check the arguments");
287 if (io >= 0) {
288 _initiating_occupancy = (double)io / 100.0;
289 } else {
290 _initiating_occupancy = ((100 - MinHeapFreeRatio) +
291 (double)(tr * MinHeapFreeRatio) / 100.0)
292 / 100.0;
293 }
294 }
295
296 void ConcurrentMarkSweepGeneration::ref_processor_init() {
297 assert(collector() != NULL, "no collector");
298 collector()->ref_processor_init();
299 }
300
301 void CMSCollector::ref_processor_init() {
302 if (_ref_processor == NULL) {
303 // Allocate and initialize a reference processor
304 _ref_processor =
305 new ReferenceProcessor(_span, // span
306 (ParallelGCThreads > 1) && ParallelRefProcEnabled, // mt processing
307 (int) ParallelGCThreads, // mt processing degree
308 _cmsGen->refs_discovery_is_mt(), // mt discovery
309 (int) MAX2(ConcGCThreads, ParallelGCThreads), // mt discovery degree
310 _cmsGen->refs_discovery_is_atomic(), // discovery is not atomic
311 &_is_alive_closure, // closure for liveness info
312 false); // next field updates do not need write barrier
313 // Initialize the _ref_processor field of CMSGen
314 _cmsGen->set_ref_processor(_ref_processor);
315
316 }
317 }
318
319 CMSAdaptiveSizePolicy* CMSCollector::size_policy() {
320 GenCollectedHeap* gch = GenCollectedHeap::heap();
321 assert(gch->kind() == CollectedHeap::GenCollectedHeap,
322 "Wrong type of heap");
323 CMSAdaptiveSizePolicy* sp = (CMSAdaptiveSizePolicy*)
324 gch->gen_policy()->size_policy();
325 assert(sp->is_gc_cms_adaptive_size_policy(),
326 "Wrong type of size policy");
327 return sp;
328 }
329
330 CMSGCAdaptivePolicyCounters* CMSCollector::gc_adaptive_policy_counters() {
331 CMSGCAdaptivePolicyCounters* results =
332 (CMSGCAdaptivePolicyCounters*) collector_policy()->counters();
333 assert(
334 results->kind() == GCPolicyCounters::CMSGCAdaptivePolicyCountersKind,
335 "Wrong gc policy counter kind");
336 return results;
337 }
338
339
340 void ConcurrentMarkSweepGeneration::initialize_performance_counters() {
341
342 const char* gen_name = "old";
343
344 // Generation Counters - generation 1, 1 subspace
345 _gen_counters = new GenerationCounters(gen_name, 1, 1, &_virtual_space);
346
347 _space_counters = new GSpaceCounters(gen_name, 0,
348 _virtual_space.reserved_size(),
349 this, _gen_counters);
350 }
351
352 CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha):
353 _cms_gen(cms_gen)
354 {
355 assert(alpha <= 100, "bad value");
356 _saved_alpha = alpha;
357
358 // Initialize the alphas to the bootstrap value of 100.
359 _gc0_alpha = _cms_alpha = 100;
360
361 _cms_begin_time.update();
362 _cms_end_time.update();
363
364 _gc0_duration = 0.0;
365 _gc0_period = 0.0;
366 _gc0_promoted = 0;
367
368 _cms_duration = 0.0;
369 _cms_period = 0.0;
370 _cms_allocated = 0;
371
372 _cms_used_at_gc0_begin = 0;
373 _cms_used_at_gc0_end = 0;
374 _allow_duty_cycle_reduction = false;
375 _valid_bits = 0;
376 _icms_duty_cycle = CMSIncrementalDutyCycle;
377 }
378
379 double CMSStats::cms_free_adjustment_factor(size_t free) const {
380 // TBD: CR 6909490
381 return 1.0;
382 }
383
384 void CMSStats::adjust_cms_free_adjustment_factor(bool fail, size_t free) {
385 }
386
387 // If promotion failure handling is on use
388 // the padded average size of the promotion for each
389 // young generation collection.
390 double CMSStats::time_until_cms_gen_full() const {
391 size_t cms_free = _cms_gen->cmsSpace()->free();
392 GenCollectedHeap* gch = GenCollectedHeap::heap();
393 size_t expected_promotion = MIN2(gch->get_gen(0)->capacity(),
394 (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average());
395 if (cms_free > expected_promotion) {
396 // Start a cms collection if there isn't enough space to promote
397 // for the next minor collection. Use the padded average as
398 // a safety factor.
399 cms_free -= expected_promotion;
400
401 // Adjust by the safety factor.
402 double cms_free_dbl = (double)cms_free;
403 double cms_adjustment = (100.0 - CMSIncrementalSafetyFactor)/100.0;
404 // Apply a further correction factor which tries to adjust
405 // for recent occurance of concurrent mode failures.
406 cms_adjustment = cms_adjustment * cms_free_adjustment_factor(cms_free);
407 cms_free_dbl = cms_free_dbl * cms_adjustment;
408
409 if (PrintGCDetails && Verbose) {
410 gclog_or_tty->print_cr("CMSStats::time_until_cms_gen_full: cms_free "
411 SIZE_FORMAT " expected_promotion " SIZE_FORMAT,
412 cms_free, expected_promotion);
413 gclog_or_tty->print_cr(" cms_free_dbl %f cms_consumption_rate %f",
414 cms_free_dbl, cms_consumption_rate() + 1.0);
415 }
416 // Add 1 in case the consumption rate goes to zero.
417 return cms_free_dbl / (cms_consumption_rate() + 1.0);
418 }
419 return 0.0;
420 }
421
422 // Compare the duration of the cms collection to the
423 // time remaining before the cms generation is empty.
424 // Note that the time from the start of the cms collection
425 // to the start of the cms sweep (less than the total
426 // duration of the cms collection) can be used. This
427 // has been tried and some applications experienced
428 // promotion failures early in execution. This was
429 // possibly because the averages were not accurate
430 // enough at the beginning.
431 double CMSStats::time_until_cms_start() const {
432 // We add "gc0_period" to the "work" calculation
433 // below because this query is done (mostly) at the
434 // end of a scavenge, so we need to conservatively
435 // account for that much possible delay
436 // in the query so as to avoid concurrent mode failures
437 // due to starting the collection just a wee bit too
438 // late.
439 double work = cms_duration() + gc0_period();
440 double deadline = time_until_cms_gen_full();
441 // If a concurrent mode failure occurred recently, we want to be
442 // more conservative and halve our expected time_until_cms_gen_full()
443 if (work > deadline) {
444 if (Verbose && PrintGCDetails) {
445 gclog_or_tty->print(
446 " CMSCollector: collect because of anticipated promotion "
447 "before full %3.7f + %3.7f > %3.7f ", cms_duration(),
448 gc0_period(), time_until_cms_gen_full());
449 }
450 return 0.0;
451 }
452 return work - deadline;
453 }
454
455 // Return a duty cycle based on old_duty_cycle and new_duty_cycle, limiting the
456 // amount of change to prevent wild oscillation.
457 unsigned int CMSStats::icms_damped_duty_cycle(unsigned int old_duty_cycle,
458 unsigned int new_duty_cycle) {
459 assert(old_duty_cycle <= 100, "bad input value");
460 assert(new_duty_cycle <= 100, "bad input value");
461
462 // Note: use subtraction with caution since it may underflow (values are
463 // unsigned). Addition is safe since we're in the range 0-100.
464 unsigned int damped_duty_cycle = new_duty_cycle;
465 if (new_duty_cycle < old_duty_cycle) {
466 const unsigned int largest_delta = MAX2(old_duty_cycle / 4, 5U);
467 if (new_duty_cycle + largest_delta < old_duty_cycle) {
468 damped_duty_cycle = old_duty_cycle - largest_delta;
469 }
470 } else if (new_duty_cycle > old_duty_cycle) {
471 const unsigned int largest_delta = MAX2(old_duty_cycle / 4, 15U);
472 if (new_duty_cycle > old_duty_cycle + largest_delta) {
473 damped_duty_cycle = MIN2(old_duty_cycle + largest_delta, 100U);
474 }
475 }
476 assert(damped_duty_cycle <= 100, "invalid duty cycle computed");
477
478 if (CMSTraceIncrementalPacing) {
479 gclog_or_tty->print(" [icms_damped_duty_cycle(%d,%d) = %d] ",
480 old_duty_cycle, new_duty_cycle, damped_duty_cycle);
481 }
482 return damped_duty_cycle;
483 }
484
485 unsigned int CMSStats::icms_update_duty_cycle_impl() {
486 assert(CMSIncrementalPacing && valid(),
487 "should be handled in icms_update_duty_cycle()");
488
489 double cms_time_so_far = cms_timer().seconds();
490 double scaled_duration = cms_duration_per_mb() * _cms_used_at_gc0_end / M;
491 double scaled_duration_remaining = fabsd(scaled_duration - cms_time_so_far);
492
493 // Avoid division by 0.
494 double time_until_full = MAX2(time_until_cms_gen_full(), 0.01);
495 double duty_cycle_dbl = 100.0 * scaled_duration_remaining / time_until_full;
496
497 unsigned int new_duty_cycle = MIN2((unsigned int)duty_cycle_dbl, 100U);
498 if (new_duty_cycle > _icms_duty_cycle) {
499 // Avoid very small duty cycles (1 or 2); 0 is allowed.
500 if (new_duty_cycle > 2) {
501 _icms_duty_cycle = icms_damped_duty_cycle(_icms_duty_cycle,
502 new_duty_cycle);
503 }
504 } else if (_allow_duty_cycle_reduction) {
505 // The duty cycle is reduced only once per cms cycle (see record_cms_end()).
506 new_duty_cycle = icms_damped_duty_cycle(_icms_duty_cycle, new_duty_cycle);
507 // Respect the minimum duty cycle.
508 unsigned int min_duty_cycle = (unsigned int)CMSIncrementalDutyCycleMin;
509 _icms_duty_cycle = MAX2(new_duty_cycle, min_duty_cycle);
510 }
511
512 if (PrintGCDetails || CMSTraceIncrementalPacing) {
513 gclog_or_tty->print(" icms_dc=%d ", _icms_duty_cycle);
514 }
515
516 _allow_duty_cycle_reduction = false;
517 return _icms_duty_cycle;
518 }
519
520 #ifndef PRODUCT
521 void CMSStats::print_on(outputStream *st) const {
522 st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha);
523 st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo=" SIZE_FORMAT,
524 gc0_duration(), gc0_period(), gc0_promoted());
525 st->print(",cms_dur=%g,cms_dur_per_mb=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT,
526 cms_duration(), cms_duration_per_mb(),
527 cms_period(), cms_allocated());
528 st->print(",cms_since_beg=%g,cms_since_end=%g",
529 cms_time_since_begin(), cms_time_since_end());
530 st->print(",cms_used_beg=" SIZE_FORMAT ",cms_used_end=" SIZE_FORMAT,
531 _cms_used_at_gc0_begin, _cms_used_at_gc0_end);
532 if (CMSIncrementalMode) {
533 st->print(",dc=%d", icms_duty_cycle());
534 }
535
536 if (valid()) {
537 st->print(",promo_rate=%g,cms_alloc_rate=%g",
538 promotion_rate(), cms_allocation_rate());
539 st->print(",cms_consumption_rate=%g,time_until_full=%g",
540 cms_consumption_rate(), time_until_cms_gen_full());
541 }
542 st->print(" ");
543 }
544 #endif // #ifndef PRODUCT
545
546 CMSCollector::CollectorState CMSCollector::_collectorState =
547 CMSCollector::Idling;
548 bool CMSCollector::_foregroundGCIsActive = false;
549 bool CMSCollector::_foregroundGCShouldWait = false;
550
551 CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
552 CardTableRS* ct,
553 ConcurrentMarkSweepPolicy* cp):
554 _cmsGen(cmsGen),
555 _ct(ct),
556 _ref_processor(NULL), // will be set later
557 _conc_workers(NULL), // may be set later
558 _abort_preclean(false),
559 _start_sampling(false),
560 _between_prologue_and_epilogue(false),
561 _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"),
562 _modUnionTable((CardTableModRefBS::card_shift - LogHeapWordSize),
563 -1 /* lock-free */, "No_lock" /* dummy */),
564 _modUnionClosure(&_modUnionTable),
565 _modUnionClosurePar(&_modUnionTable),
566 // Adjust my span to cover old (cms) gen
567 _span(cmsGen->reserved()),
568 // Construct the is_alive_closure with _span & markBitMap
569 _is_alive_closure(_span, &_markBitMap),
570 _restart_addr(NULL),
571 _overflow_list(NULL),
572 _stats(cmsGen),
573 _eden_chunk_lock(new Mutex(Mutex::leaf + 1, "CMS_eden_chunk_lock", true)),
574 _eden_chunk_array(NULL), // may be set in ctor body
575 _eden_chunk_capacity(0), // -- ditto --
576 _eden_chunk_index(0), // -- ditto --
577 _survivor_plab_array(NULL), // -- ditto --
578 _survivor_chunk_array(NULL), // -- ditto --
579 _survivor_chunk_capacity(0), // -- ditto --
580 _survivor_chunk_index(0), // -- ditto --
581 _ser_pmc_preclean_ovflw(0),
582 _ser_kac_preclean_ovflw(0),
583 _ser_pmc_remark_ovflw(0),
584 _par_pmc_remark_ovflw(0),
585 _ser_kac_ovflw(0),
586 _par_kac_ovflw(0),
587 #ifndef PRODUCT
588 _num_par_pushes(0),
589 #endif
590 _collection_count_start(0),
591 _verifying(false),
592 _icms_start_limit(NULL),
593 _icms_stop_limit(NULL),
594 _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"),
595 _completed_initialization(false),
596 _collector_policy(cp),
597 _should_unload_classes(CMSClassUnloadingEnabled),
598 _concurrent_cycles_since_last_unload(0),
599 _roots_scanning_options(SharedHeap::SO_None),
600 _inter_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
601 _intra_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
602 _gc_tracer_cm(new (ResourceObj::C_HEAP, mtGC) CMSTracer()),
603 _gc_timer_cm(new (ResourceObj::C_HEAP, mtGC) ConcurrentGCTimer()),
604 _cms_start_registered(false)
605 {
606 if (ExplicitGCInvokesConcurrentAndUnloadsClasses) {
607 ExplicitGCInvokesConcurrent = true;
608 }
609 // Now expand the span and allocate the collection support structures
610 // (MUT, marking bit map etc.) to cover both generations subject to
611 // collection.
612
613 // For use by dirty card to oop closures.
614 _cmsGen->cmsSpace()->set_collector(this);
615
616 // Allocate MUT and marking bit map
617 {
618 MutexLockerEx x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag);
619 if (!_markBitMap.allocate(_span)) {
620 warning("Failed to allocate CMS Bit Map");
621 return;
622 }
623 assert(_markBitMap.covers(_span), "_markBitMap inconsistency?");
624 }
625 {
626 _modUnionTable.allocate(_span);
627 assert(_modUnionTable.covers(_span), "_modUnionTable inconsistency?");
628 }
629
630 if (!_markStack.allocate(MarkStackSize)) {
631 warning("Failed to allocate CMS Marking Stack");
632 return;
633 }
634
635 // Support for multi-threaded concurrent phases
636 if (CMSConcurrentMTEnabled) {
637 if (FLAG_IS_DEFAULT(ConcGCThreads)) {
638 // just for now
639 FLAG_SET_DEFAULT(ConcGCThreads, (ParallelGCThreads + 3)/4);
640 }
641 if (ConcGCThreads > 1) {
642 _conc_workers = new YieldingFlexibleWorkGang("Parallel CMS Threads",
643 ConcGCThreads, true);
644 if (_conc_workers == NULL) {
645 warning("GC/CMS: _conc_workers allocation failure: "
646 "forcing -CMSConcurrentMTEnabled");
647 CMSConcurrentMTEnabled = false;
648 } else {
649 _conc_workers->initialize_workers();
650 }
651 } else {
652 CMSConcurrentMTEnabled = false;
653 }
654 }
655 if (!CMSConcurrentMTEnabled) {
656 ConcGCThreads = 0;
657 } else {
658 // Turn off CMSCleanOnEnter optimization temporarily for
659 // the MT case where it's not fixed yet; see 6178663.
660 CMSCleanOnEnter = false;
661 }
662 assert((_conc_workers != NULL) == (ConcGCThreads > 1),
663 "Inconsistency");
664
665 // Parallel task queues; these are shared for the
666 // concurrent and stop-world phases of CMS, but
667 // are not shared with parallel scavenge (ParNew).
668 {
669 uint i;
670 uint num_queues = (uint) MAX2(ParallelGCThreads, ConcGCThreads);
671
672 if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled
673 || ParallelRefProcEnabled)
674 && num_queues > 0) {
675 _task_queues = new OopTaskQueueSet(num_queues);
676 if (_task_queues == NULL) {
677 warning("task_queues allocation failure.");
678 return;
679 }
680 _hash_seed = NEW_C_HEAP_ARRAY(int, num_queues, mtGC);
681 if (_hash_seed == NULL) {
682 warning("_hash_seed array allocation failure");
683 return;
684 }
685
686 typedef Padded<OopTaskQueue> PaddedOopTaskQueue;
687 for (i = 0; i < num_queues; i++) {
688 PaddedOopTaskQueue *q = new PaddedOopTaskQueue();
689 if (q == NULL) {
690 warning("work_queue allocation failure.");
691 return;
692 }
693 _task_queues->register_queue(i, q);
694 }
695 for (i = 0; i < num_queues; i++) {
696 _task_queues->queue(i)->initialize();
697 _hash_seed[i] = 17; // copied from ParNew
698 }
699 }
700 }
701
702 _cmsGen ->init_initiating_occupancy(CMSInitiatingOccupancyFraction, CMSTriggerRatio);
703
704 // Clip CMSBootstrapOccupancy between 0 and 100.
705 _bootstrap_occupancy = ((double)CMSBootstrapOccupancy)/(double)100;
706
707 _full_gcs_since_conc_gc = 0;
708
709 // Now tell CMS generations the identity of their collector
710 ConcurrentMarkSweepGeneration::set_collector(this);
711
712 // Create & start a CMS thread for this CMS collector
713 _cmsThread = ConcurrentMarkSweepThread::start(this);
714 assert(cmsThread() != NULL, "CMS Thread should have been created");
715 assert(cmsThread()->collector() == this,
716 "CMS Thread should refer to this gen");
717 assert(CGC_lock != NULL, "Where's the CGC_lock?");
718
719 // Support for parallelizing young gen rescan
720 GenCollectedHeap* gch = GenCollectedHeap::heap();
721 _young_gen = gch->prev_gen(_cmsGen);
722 if (gch->supports_inline_contig_alloc()) {
723 _top_addr = gch->top_addr();
724 _end_addr = gch->end_addr();
725 assert(_young_gen != NULL, "no _young_gen");
726 _eden_chunk_index = 0;
727 _eden_chunk_capacity = (_young_gen->max_capacity()+CMSSamplingGrain)/CMSSamplingGrain;
728 _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity, mtGC);
729 if (_eden_chunk_array == NULL) {
730 _eden_chunk_capacity = 0;
731 warning("GC/CMS: _eden_chunk_array allocation failure");
732 }
733 }
734 assert(_eden_chunk_array != NULL || _eden_chunk_capacity == 0, "Error");
735
736 // Support for parallelizing survivor space rescan
737 if ((CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) || CMSParallelInitialMarkEnabled) {
738 const size_t max_plab_samples =
739 ((DefNewGeneration*)_young_gen)->max_survivor_size()/MinTLABSize;
740
741 _survivor_plab_array = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads, mtGC);
742 _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, 2*max_plab_samples, mtGC);
743 _cursor = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads, mtGC);
744 if (_survivor_plab_array == NULL || _survivor_chunk_array == NULL
745 || _cursor == NULL) {
746 warning("Failed to allocate survivor plab/chunk array");
747 if (_survivor_plab_array != NULL) {
748 FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array, mtGC);
749 _survivor_plab_array = NULL;
750 }
751 if (_survivor_chunk_array != NULL) {
752 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array, mtGC);
753 _survivor_chunk_array = NULL;
754 }
755 if (_cursor != NULL) {
756 FREE_C_HEAP_ARRAY(size_t, _cursor, mtGC);
757 _cursor = NULL;
758 }
759 } else {
760 _survivor_chunk_capacity = 2*max_plab_samples;
761 for (uint i = 0; i < ParallelGCThreads; i++) {
762 HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
763 if (vec == NULL) {
764 warning("Failed to allocate survivor plab array");
765 for (int j = i; j > 0; j--) {
766 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_plab_array[j-1].array(), mtGC);
767 }
768 FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array, mtGC);
769 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array, mtGC);
770 _survivor_plab_array = NULL;
771 _survivor_chunk_array = NULL;
772 _survivor_chunk_capacity = 0;
773 break;
774 } else {
775 ChunkArray* cur =
776 ::new (&_survivor_plab_array[i]) ChunkArray(vec,
777 max_plab_samples);
778 assert(cur->end() == 0, "Should be 0");
779 assert(cur->array() == vec, "Should be vec");
780 assert(cur->capacity() == max_plab_samples, "Error");
781 }
782 }
783 }
784 }
785 assert( ( _survivor_plab_array != NULL
786 && _survivor_chunk_array != NULL)
787 || ( _survivor_chunk_capacity == 0
788 && _survivor_chunk_index == 0),
789 "Error");
790
791 NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;)
792 _gc_counters = new CollectorCounters("CMS", 1);
793 _completed_initialization = true;
794 _inter_sweep_timer.start(); // start of time
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(size_t max_promotion_in_bytes) const {
869 size_t available = max_available();
870 size_t av_promo = (size_t)gc_stats()->avg_promoted()->padded_average();
871 bool res = (available >= av_promo) || (available >= max_promotion_in_bytes);
872 if (Verbose && PrintGCDetails) {
873 gclog_or_tty->print_cr(
874 "CMS: promo attempt is%s safe: available("SIZE_FORMAT") %s av_promo("SIZE_FORMAT"),"
875 "max_promo("SIZE_FORMAT")",
876 res? "":" not", available, res? ">=":"<",
877 av_promo, max_promotion_in_bytes);
878 }
879 return res;
880 }
881
882 // At a promotion failure dump information on block layout in heap
883 // (cms old generation).
884 void ConcurrentMarkSweepGeneration::promotion_failure_occurred() {
885 if (CMSDumpAtPromotionFailure) {
886 cmsSpace()->dump_at_safepoint_with_locks(collector(), gclog_or_tty);
887 }
888 }
889
890 CompactibleSpace*
891 ConcurrentMarkSweepGeneration::first_compaction_space() const {
892 return _cmsSpace;
893 }
894
895 void ConcurrentMarkSweepGeneration::reset_after_compaction() {
896 // Clear the promotion information. These pointers can be adjusted
897 // along with all the other pointers into the heap but
898 // compaction is expected to be a rare event with
899 // a heap using cms so don't do it without seeing the need.
900 if (CollectedHeap::use_parallel_gc_threads()) {
901 for (uint i = 0; i < ParallelGCThreads; i++) {
902 _par_gc_thread_states[i]->promo.reset();
903 }
904 }
905 }
906
907 void ConcurrentMarkSweepGeneration::space_iterate(SpaceClosure* blk, bool usedOnly) {
908 blk->do_space(_cmsSpace);
909 }
910
911 void ConcurrentMarkSweepGeneration::compute_new_size() {
912 assert_locked_or_safepoint(Heap_lock);
913
914 // If incremental collection failed, we just want to expand
915 // to the limit.
916 if (incremental_collection_failed()) {
917 clear_incremental_collection_failed();
918 grow_to_reserved();
919 return;
920 }
921
922 // The heap has been compacted but not reset yet.
923 // Any metric such as free() or used() will be incorrect.
924
925 CardGeneration::compute_new_size();
926
927 // Reset again after a possible resizing
928 if (did_compact()) {
929 cmsSpace()->reset_after_compaction();
930 }
931 }
932
933 void ConcurrentMarkSweepGeneration::compute_new_size_free_list() {
934 assert_locked_or_safepoint(Heap_lock);
935
936 // If incremental collection failed, we just want to expand
937 // to the limit.
938 if (incremental_collection_failed()) {
939 clear_incremental_collection_failed();
940 grow_to_reserved();
941 return;
942 }
943
944 double free_percentage = ((double) free()) / capacity();
945 double desired_free_percentage = (double) MinHeapFreeRatio / 100;
946 double maximum_free_percentage = (double) MaxHeapFreeRatio / 100;
947
948 // compute expansion delta needed for reaching desired free percentage
949 if (free_percentage < desired_free_percentage) {
950 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
951 assert(desired_capacity >= capacity(), "invalid expansion size");
952 size_t expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes);
953 if (PrintGCDetails && Verbose) {
954 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
955 gclog_or_tty->print_cr("\nFrom compute_new_size: ");
956 gclog_or_tty->print_cr(" Free fraction %f", free_percentage);
957 gclog_or_tty->print_cr(" Desired free fraction %f",
958 desired_free_percentage);
959 gclog_or_tty->print_cr(" Maximum free fraction %f",
960 maximum_free_percentage);
961 gclog_or_tty->print_cr(" Capactiy "SIZE_FORMAT, capacity()/1000);
962 gclog_or_tty->print_cr(" Desired capacity "SIZE_FORMAT,
963 desired_capacity/1000);
964 int prev_level = level() - 1;
965 if (prev_level >= 0) {
966 size_t prev_size = 0;
967 GenCollectedHeap* gch = GenCollectedHeap::heap();
968 Generation* prev_gen = gch->_gens[prev_level];
969 prev_size = prev_gen->capacity();
970 gclog_or_tty->print_cr(" Younger gen size "SIZE_FORMAT,
971 prev_size/1000);
972 }
973 gclog_or_tty->print_cr(" unsafe_max_alloc_nogc "SIZE_FORMAT,
974 unsafe_max_alloc_nogc()/1000);
975 gclog_or_tty->print_cr(" contiguous available "SIZE_FORMAT,
976 contiguous_available()/1000);
977 gclog_or_tty->print_cr(" Expand by "SIZE_FORMAT" (bytes)",
978 expand_bytes);
979 }
980 // safe if expansion fails
981 expand(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio);
982 if (PrintGCDetails && Verbose) {
983 gclog_or_tty->print_cr(" Expanded free fraction %f",
984 ((double) free()) / capacity());
985 }
986 } else {
987 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
988 assert(desired_capacity <= capacity(), "invalid expansion size");
989 size_t shrink_bytes = capacity() - desired_capacity;
990 // Don't shrink unless the delta is greater than the minimum shrink we want
991 if (shrink_bytes >= MinHeapDeltaBytes) {
992 shrink_free_list_by(shrink_bytes);
993 }
994 }
995 }
996
997 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const {
998 return cmsSpace()->freelistLock();
999 }
1000
1001 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size,
1002 bool tlab) {
1003 CMSSynchronousYieldRequest yr;
1004 MutexLockerEx x(freelistLock(),
1005 Mutex::_no_safepoint_check_flag);
1006 return have_lock_and_allocate(size, tlab);
1007 }
1008
1009 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size,
1010 bool tlab /* ignored */) {
1011 assert_lock_strong(freelistLock());
1012 size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size);
1013 HeapWord* res = cmsSpace()->allocate(adjustedSize);
1014 // Allocate the object live (grey) if the background collector has
1015 // started marking. This is necessary because the marker may
1016 // have passed this address and consequently this object will
1017 // not otherwise be greyed and would be incorrectly swept up.
1018 // Note that if this object contains references, the writing
1019 // of those references will dirty the card containing this object
1020 // allowing the object to be blackened (and its references scanned)
1021 // either during a preclean phase or at the final checkpoint.
1022 if (res != NULL) {
1023 // We may block here with an uninitialized object with
1024 // its mark-bit or P-bits not yet set. Such objects need
1025 // to be safely navigable by block_start().
1026 assert(oop(res)->klass_or_null() == NULL, "Object should be uninitialized here.");
1027 assert(!((FreeChunk*)res)->is_free(), "Error, block will look free but show wrong size");
1028 collector()->direct_allocated(res, adjustedSize);
1029 _direct_allocated_words += adjustedSize;
1030 // allocation counters
1031 NOT_PRODUCT(
1032 _numObjectsAllocated++;
1033 _numWordsAllocated += (int)adjustedSize;
1034 )
1035 }
1036 return res;
1037 }
1038
1039 // In the case of direct allocation by mutators in a generation that
1040 // is being concurrently collected, the object must be allocated
1041 // live (grey) if the background collector has started marking.
1042 // This is necessary because the marker may
1043 // have passed this address and consequently this object will
1044 // not otherwise be greyed and would be incorrectly swept up.
1045 // Note that if this object contains references, the writing
1046 // of those references will dirty the card containing this object
1047 // allowing the object to be blackened (and its references scanned)
1048 // either during a preclean phase or at the final checkpoint.
1049 void CMSCollector::direct_allocated(HeapWord* start, size_t size) {
1050 assert(_markBitMap.covers(start, size), "Out of bounds");
1051 if (_collectorState >= Marking) {
1052 MutexLockerEx y(_markBitMap.lock(),
1053 Mutex::_no_safepoint_check_flag);
1054 // [see comments preceding SweepClosure::do_blk() below for details]
1055 //
1056 // Can the P-bits be deleted now? JJJ
1057 //
1058 // 1. need to mark the object as live so it isn't collected
1059 // 2. need to mark the 2nd bit to indicate the object may be uninitialized
1060 // 3. need to mark the end of the object so marking, precleaning or sweeping
1061 // can skip over uninitialized or unparsable objects. An allocated
1062 // object is considered uninitialized for our purposes as long as
1063 // its klass word is NULL. All old gen objects are parsable
1064 // as soon as they are initialized.)
1065 _markBitMap.mark(start); // object is live
1066 _markBitMap.mark(start + 1); // object is potentially uninitialized?
1067 _markBitMap.mark(start + size - 1);
1068 // mark end of object
1069 }
1070 // check that oop looks uninitialized
1071 assert(oop(start)->klass_or_null() == NULL, "_klass should be NULL");
1072 }
1073
1074 void CMSCollector::promoted(bool par, HeapWord* start,
1075 bool is_obj_array, size_t obj_size) {
1076 assert(_markBitMap.covers(start), "Out of bounds");
1077 // See comment in direct_allocated() about when objects should
1078 // be allocated live.
1079 if (_collectorState >= Marking) {
1080 // we already hold the marking bit map lock, taken in
1081 // the prologue
1082 if (par) {
1083 _markBitMap.par_mark(start);
1084 } else {
1085 _markBitMap.mark(start);
1086 }
1087 // We don't need to mark the object as uninitialized (as
1088 // in direct_allocated above) because this is being done with the
1089 // world stopped and the object will be initialized by the
1090 // time the marking, precleaning or sweeping get to look at it.
1091 // But see the code for copying objects into the CMS generation,
1092 // where we need to ensure that concurrent readers of the
1093 // block offset table are able to safely navigate a block that
1094 // is in flux from being free to being allocated (and in
1095 // transition while being copied into) and subsequently
1096 // becoming a bona-fide object when the copy/promotion is complete.
1097 assert(SafepointSynchronize::is_at_safepoint(),
1098 "expect promotion only at safepoints");
1099
1100 if (_collectorState < Sweeping) {
1101 // Mark the appropriate cards in the modUnionTable, so that
1102 // this object gets scanned before the sweep. If this is
1103 // not done, CMS generation references in the object might
1104 // not get marked.
1105 // For the case of arrays, which are otherwise precisely
1106 // marked, we need to dirty the entire array, not just its head.
1107 if (is_obj_array) {
1108 // The [par_]mark_range() method expects mr.end() below to
1109 // be aligned to the granularity of a bit's representation
1110 // in the heap. In the case of the MUT below, that's a
1111 // card size.
1112 MemRegion mr(start,
1113 (HeapWord*)round_to((intptr_t)(start + obj_size),
1114 CardTableModRefBS::card_size /* bytes */));
1115 if (par) {
1116 _modUnionTable.par_mark_range(mr);
1117 } else {
1118 _modUnionTable.mark_range(mr);
1119 }
1120 } else { // not an obj array; we can just mark the head
1121 if (par) {
1122 _modUnionTable.par_mark(start);
1123 } else {
1124 _modUnionTable.mark(start);
1125 }
1126 }
1127 }
1128 }
1129 }
1130
1131 static inline size_t percent_of_space(Space* space, HeapWord* addr)
1132 {
1133 size_t delta = pointer_delta(addr, space->bottom());
1134 return (size_t)(delta * 100.0 / (space->capacity() / HeapWordSize));
1135 }
1136
1137 void CMSCollector::icms_update_allocation_limits()
1138 {
1139 Generation* gen0 = GenCollectedHeap::heap()->get_gen(0);
1140 EdenSpace* eden = gen0->as_DefNewGeneration()->eden();
1141
1142 const unsigned int duty_cycle = stats().icms_update_duty_cycle();
1143 if (CMSTraceIncrementalPacing) {
1144 stats().print();
1145 }
1146
1147 assert(duty_cycle <= 100, "invalid duty cycle");
1148 if (duty_cycle != 0) {
1149 // The duty_cycle is a percentage between 0 and 100; convert to words and
1150 // then compute the offset from the endpoints of the space.
1151 size_t free_words = eden->free() / HeapWordSize;
1152 double free_words_dbl = (double)free_words;
1153 size_t duty_cycle_words = (size_t)(free_words_dbl * duty_cycle / 100.0);
1154 size_t offset_words = (free_words - duty_cycle_words) / 2;
1155
1156 _icms_start_limit = eden->top() + offset_words;
1157 _icms_stop_limit = eden->end() - offset_words;
1158
1159 // The limits may be adjusted (shifted to the right) by
1160 // CMSIncrementalOffset, to allow the application more mutator time after a
1161 // young gen gc (when all mutators were stopped) and before CMS starts and
1162 // takes away one or more cpus.
1163 if (CMSIncrementalOffset != 0) {
1164 double adjustment_dbl = free_words_dbl * CMSIncrementalOffset / 100.0;
1165 size_t adjustment = (size_t)adjustment_dbl;
1166 HeapWord* tmp_stop = _icms_stop_limit + adjustment;
1167 if (tmp_stop > _icms_stop_limit && tmp_stop < eden->end()) {
1168 _icms_start_limit += adjustment;
1169 _icms_stop_limit = tmp_stop;
1170 }
1171 }
1172 }
1173 if (duty_cycle == 0 || (_icms_start_limit == _icms_stop_limit)) {
1174 _icms_start_limit = _icms_stop_limit = eden->end();
1175 }
1176
1177 // Install the new start limit.
1178 eden->set_soft_end(_icms_start_limit);
1179
1180 if (CMSTraceIncrementalMode) {
1181 gclog_or_tty->print(" icms alloc limits: "
1182 PTR_FORMAT "," PTR_FORMAT
1183 " (" SIZE_FORMAT "%%," SIZE_FORMAT "%%) ",
1184 _icms_start_limit, _icms_stop_limit,
1185 percent_of_space(eden, _icms_start_limit),
1186 percent_of_space(eden, _icms_stop_limit));
1187 if (Verbose) {
1188 gclog_or_tty->print("eden: ");
1189 eden->print_on(gclog_or_tty);
1190 }
1191 }
1192 }
1193
1194 // Any changes here should try to maintain the invariant
1195 // that if this method is called with _icms_start_limit
1196 // and _icms_stop_limit both NULL, then it should return NULL
1197 // and not notify the icms thread.
1198 HeapWord*
1199 CMSCollector::allocation_limit_reached(Space* space, HeapWord* top,
1200 size_t word_size)
1201 {
1202 // A start_limit equal to end() means the duty cycle is 0, so treat that as a
1203 // nop.
1204 if (CMSIncrementalMode && _icms_start_limit != space->end()) {
1205 if (top <= _icms_start_limit) {
1206 if (CMSTraceIncrementalMode) {
1207 space->print_on(gclog_or_tty);
1208 gclog_or_tty->stamp();
1209 gclog_or_tty->print_cr(" start limit top=" PTR_FORMAT
1210 ", new limit=" PTR_FORMAT
1211 " (" SIZE_FORMAT "%%)",
1212 top, _icms_stop_limit,
1213 percent_of_space(space, _icms_stop_limit));
1214 }
1215 ConcurrentMarkSweepThread::start_icms();
1216 assert(top < _icms_stop_limit, "Tautology");
1217 if (word_size < pointer_delta(_icms_stop_limit, top)) {
1218 return _icms_stop_limit;
1219 }
1220
1221 // The allocation will cross both the _start and _stop limits, so do the
1222 // stop notification also and return end().
1223 if (CMSTraceIncrementalMode) {
1224 space->print_on(gclog_or_tty);
1225 gclog_or_tty->stamp();
1226 gclog_or_tty->print_cr(" +stop limit top=" PTR_FORMAT
1227 ", new limit=" PTR_FORMAT
1228 " (" SIZE_FORMAT "%%)",
1229 top, space->end(),
1230 percent_of_space(space, space->end()));
1231 }
1232 ConcurrentMarkSweepThread::stop_icms();
1233 return space->end();
1234 }
1235
1236 if (top <= _icms_stop_limit) {
1237 if (CMSTraceIncrementalMode) {
1238 space->print_on(gclog_or_tty);
1239 gclog_or_tty->stamp();
1240 gclog_or_tty->print_cr(" stop limit top=" PTR_FORMAT
1241 ", new limit=" PTR_FORMAT
1242 " (" SIZE_FORMAT "%%)",
1243 top, space->end(),
1244 percent_of_space(space, space->end()));
1245 }
1246 ConcurrentMarkSweepThread::stop_icms();
1247 return space->end();
1248 }
1249
1250 if (CMSTraceIncrementalMode) {
1251 space->print_on(gclog_or_tty);
1252 gclog_or_tty->stamp();
1253 gclog_or_tty->print_cr(" end limit top=" PTR_FORMAT
1254 ", new limit=" PTR_FORMAT,
1255 top, NULL);
1256 }
1257 }
1258
1259 return NULL;
1260 }
1261
1262 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size) {
1263 assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
1264 // allocate, copy and if necessary update promoinfo --
1265 // delegate to underlying space.
1266 assert_lock_strong(freelistLock());
1267
1268 #ifndef PRODUCT
1269 if (Universe::heap()->promotion_should_fail()) {
1270 return NULL;
1271 }
1272 #endif // #ifndef PRODUCT
1273
1274 oop res = _cmsSpace->promote(obj, obj_size);
1275 if (res == NULL) {
1276 // expand and retry
1277 size_t s = _cmsSpace->expansionSpaceRequired(obj_size); // HeapWords
1278 expand(s*HeapWordSize, MinHeapDeltaBytes,
1279 CMSExpansionCause::_satisfy_promotion);
1280 // Since there's currently no next generation, we don't try to promote
1281 // into a more senior generation.
1282 assert(next_gen() == NULL, "assumption, based upon which no attempt "
1283 "is made to pass on a possibly failing "
1284 "promotion to next generation");
1285 res = _cmsSpace->promote(obj, obj_size);
1286 }
1287 if (res != NULL) {
1288 // See comment in allocate() about when objects should
1289 // be allocated live.
1290 assert(obj->is_oop(), "Will dereference klass pointer below");
1291 collector()->promoted(false, // Not parallel
1292 (HeapWord*)res, obj->is_objArray(), obj_size);
1293 // promotion counters
1294 NOT_PRODUCT(
1295 _numObjectsPromoted++;
1296 _numWordsPromoted +=
1297 (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size()));
1298 )
1299 }
1300 return res;
1301 }
1302
1303
1304 HeapWord*
1305 ConcurrentMarkSweepGeneration::allocation_limit_reached(Space* space,
1306 HeapWord* top,
1307 size_t word_sz)
1308 {
1309 return collector()->allocation_limit_reached(space, top, word_sz);
1310 }
1311
1312 // IMPORTANT: Notes on object size recognition in CMS.
1313 // ---------------------------------------------------
1314 // A block of storage in the CMS generation is always in
1315 // one of three states. A free block (FREE), an allocated
1316 // object (OBJECT) whose size() method reports the correct size,
1317 // and an intermediate state (TRANSIENT) in which its size cannot
1318 // be accurately determined.
1319 // STATE IDENTIFICATION: (32 bit and 64 bit w/o COOPS)
1320 // -----------------------------------------------------
1321 // FREE: klass_word & 1 == 1; mark_word holds block size
1322 //
1323 // OBJECT: klass_word installed; klass_word != 0 && klass_word & 1 == 0;
1324 // obj->size() computes correct size
1325 //
1326 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1327 //
1328 // STATE IDENTIFICATION: (64 bit+COOPS)
1329 // ------------------------------------
1330 // FREE: mark_word & CMS_FREE_BIT == 1; mark_word & ~CMS_FREE_BIT gives block_size
1331 //
1332 // OBJECT: klass_word installed; klass_word != 0;
1333 // obj->size() computes correct size
1334 //
1335 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1336 //
1337 //
1338 // STATE TRANSITION DIAGRAM
1339 //
1340 // mut / parnew mut / parnew
1341 // FREE --------------------> TRANSIENT ---------------------> OBJECT --|
1342 // ^ |
1343 // |------------------------ DEAD <------------------------------------|
1344 // sweep mut
1345 //
1346 // While a block is in TRANSIENT state its size cannot be determined
1347 // so readers will either need to come back later or stall until
1348 // the size can be determined. Note that for the case of direct
1349 // allocation, P-bits, when available, may be used to determine the
1350 // size of an object that may not yet have been initialized.
1351
1352 // Things to support parallel young-gen collection.
1353 oop
1354 ConcurrentMarkSweepGeneration::par_promote(int thread_num,
1355 oop old, markOop m,
1356 size_t word_sz) {
1357 #ifndef PRODUCT
1358 if (Universe::heap()->promotion_should_fail()) {
1359 return NULL;
1360 }
1361 #endif // #ifndef PRODUCT
1362
1363 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1364 PromotionInfo* promoInfo = &ps->promo;
1365 // if we are tracking promotions, then first ensure space for
1366 // promotion (including spooling space for saving header if necessary).
1367 // then allocate and copy, then track promoted info if needed.
1368 // When tracking (see PromotionInfo::track()), the mark word may
1369 // be displaced and in this case restoration of the mark word
1370 // occurs in the (oop_since_save_marks_)iterate phase.
1371 if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) {
1372 // Out of space for allocating spooling buffers;
1373 // try expanding and allocating spooling buffers.
1374 if (!expand_and_ensure_spooling_space(promoInfo)) {
1375 return NULL;
1376 }
1377 }
1378 assert(promoInfo->has_spooling_space(), "Control point invariant");
1379 const size_t alloc_sz = CompactibleFreeListSpace::adjustObjectSize(word_sz);
1380 HeapWord* obj_ptr = ps->lab.alloc(alloc_sz);
1381 if (obj_ptr == NULL) {
1382 obj_ptr = expand_and_par_lab_allocate(ps, alloc_sz);
1383 if (obj_ptr == NULL) {
1384 return NULL;
1385 }
1386 }
1387 oop obj = oop(obj_ptr);
1388 OrderAccess::storestore();
1389 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1390 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1391 // IMPORTANT: See note on object initialization for CMS above.
1392 // Otherwise, copy the object. Here we must be careful to insert the
1393 // klass pointer last, since this marks the block as an allocated object.
1394 // Except with compressed oops it's the mark word.
1395 HeapWord* old_ptr = (HeapWord*)old;
1396 // Restore the mark word copied above.
1397 obj->set_mark(m);
1398 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1399 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1400 OrderAccess::storestore();
1401
1402 if (UseCompressedClassPointers) {
1403 // Copy gap missed by (aligned) header size calculation below
1404 obj->set_klass_gap(old->klass_gap());
1405 }
1406 if (word_sz > (size_t)oopDesc::header_size()) {
1407 Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1408 obj_ptr + oopDesc::header_size(),
1409 word_sz - oopDesc::header_size());
1410 }
1411
1412 // Now we can track the promoted object, if necessary. We take care
1413 // to delay the transition from uninitialized to full object
1414 // (i.e., insertion of klass pointer) until after, so that it
1415 // atomically becomes a promoted object.
1416 if (promoInfo->tracking()) {
1417 promoInfo->track((PromotedObject*)obj, old->klass());
1418 }
1419 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1420 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1421 assert(old->is_oop(), "Will use and dereference old klass ptr below");
1422
1423 // Finally, install the klass pointer (this should be volatile).
1424 OrderAccess::storestore();
1425 obj->set_klass(old->klass());
1426 // We should now be able to calculate the right size for this object
1427 assert(obj->is_oop() && obj->size() == (int)word_sz, "Error, incorrect size computed for promoted object");
1428
1429 collector()->promoted(true, // parallel
1430 obj_ptr, old->is_objArray(), word_sz);
1431
1432 NOT_PRODUCT(
1433 Atomic::inc_ptr(&_numObjectsPromoted);
1434 Atomic::add_ptr(alloc_sz, &_numWordsPromoted);
1435 )
1436
1437 return obj;
1438 }
1439
1440 void
1441 ConcurrentMarkSweepGeneration::
1442 par_promote_alloc_undo(int thread_num,
1443 HeapWord* obj, size_t word_sz) {
1444 // CMS does not support promotion undo.
1445 ShouldNotReachHere();
1446 }
1447
1448 void
1449 ConcurrentMarkSweepGeneration::
1450 par_promote_alloc_done(int thread_num) {
1451 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1452 ps->lab.retire(thread_num);
1453 }
1454
1455 void
1456 ConcurrentMarkSweepGeneration::
1457 par_oop_since_save_marks_iterate_done(int thread_num) {
1458 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1459 ParScanWithoutBarrierClosure* dummy_cl = NULL;
1460 ps->promo.promoted_oops_iterate_nv(dummy_cl);
1461 }
1462
1463 bool ConcurrentMarkSweepGeneration::should_collect(bool full,
1464 size_t size,
1465 bool tlab)
1466 {
1467 // We allow a STW collection only if a full
1468 // collection was requested.
1469 return full || should_allocate(size, tlab); // FIX ME !!!
1470 // This and promotion failure handling are connected at the
1471 // hip and should be fixed by untying them.
1472 }
1473
1474 bool CMSCollector::shouldConcurrentCollect() {
1475 if (_full_gc_requested) {
1476 if (Verbose && PrintGCDetails) {
1477 gclog_or_tty->print_cr("CMSCollector: collect because of explicit "
1478 " gc request (or gc_locker)");
1479 }
1480 return true;
1481 }
1482
1483 // For debugging purposes, change the type of collection.
1484 // If the rotation is not on the concurrent collection
1485 // type, don't start a concurrent collection.
1486 NOT_PRODUCT(
1487 if (RotateCMSCollectionTypes &&
1488 (_cmsGen->debug_collection_type() !=
1489 ConcurrentMarkSweepGeneration::Concurrent_collection_type)) {
1490 assert(_cmsGen->debug_collection_type() !=
1491 ConcurrentMarkSweepGeneration::Unknown_collection_type,
1492 "Bad cms collection type");
1493 return false;
1494 }
1495 )
1496
1497 FreelistLocker x(this);
1498 // ------------------------------------------------------------------
1499 // Print out lots of information which affects the initiation of
1500 // a collection.
1501 if (PrintCMSInitiationStatistics && stats().valid()) {
1502 gclog_or_tty->print("CMSCollector shouldConcurrentCollect: ");
1503 gclog_or_tty->stamp();
1504 gclog_or_tty->print_cr("");
1505 stats().print_on(gclog_or_tty);
1506 gclog_or_tty->print_cr("time_until_cms_gen_full %3.7f",
1507 stats().time_until_cms_gen_full());
1508 gclog_or_tty->print_cr("free="SIZE_FORMAT, _cmsGen->free());
1509 gclog_or_tty->print_cr("contiguous_available="SIZE_FORMAT,
1510 _cmsGen->contiguous_available());
1511 gclog_or_tty->print_cr("promotion_rate=%g", stats().promotion_rate());
1512 gclog_or_tty->print_cr("cms_allocation_rate=%g", stats().cms_allocation_rate());
1513 gclog_or_tty->print_cr("occupancy=%3.7f", _cmsGen->occupancy());
1514 gclog_or_tty->print_cr("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy());
1515 gclog_or_tty->print_cr("metadata initialized %d",
1516 MetaspaceGC::should_concurrent_collect());
1517 }
1518 // ------------------------------------------------------------------
1519
1520 // If the estimated time to complete a cms collection (cms_duration())
1521 // is less than the estimated time remaining until the cms generation
1522 // is full, start a collection.
1523 if (!UseCMSInitiatingOccupancyOnly) {
1524 if (stats().valid()) {
1525 if (stats().time_until_cms_start() == 0.0) {
1526 return true;
1527 }
1528 } else {
1529 // We want to conservatively collect somewhat early in order
1530 // to try and "bootstrap" our CMS/promotion statistics;
1531 // this branch will not fire after the first successful CMS
1532 // collection because the stats should then be valid.
1533 if (_cmsGen->occupancy() >= _bootstrap_occupancy) {
1534 if (Verbose && PrintGCDetails) {
1535 gclog_or_tty->print_cr(
1536 " CMSCollector: collect for bootstrapping statistics:"
1537 " occupancy = %f, boot occupancy = %f", _cmsGen->occupancy(),
1538 _bootstrap_occupancy);
1539 }
1540 return true;
1541 }
1542 }
1543 }
1544
1545 // Otherwise, we start a collection cycle if
1546 // old gen want a collection cycle started. Each may use
1547 // an appropriate criterion for making this decision.
1548 // XXX We need to make sure that the gen expansion
1549 // criterion dovetails well with this. XXX NEED TO FIX THIS
1550 if (_cmsGen->should_concurrent_collect()) {
1551 if (Verbose && PrintGCDetails) {
1552 gclog_or_tty->print_cr("CMS old gen initiated");
1553 }
1554 return true;
1555 }
1556
1557 // We start a collection if we believe an incremental collection may fail;
1558 // this is not likely to be productive in practice because it's probably too
1559 // late anyway.
1560 GenCollectedHeap* gch = GenCollectedHeap::heap();
1561 assert(gch->collector_policy()->is_two_generation_policy(),
1562 "You may want to check the correctness of the following");
1563 if (gch->incremental_collection_will_fail(true /* consult_young */)) {
1564 if (Verbose && PrintGCDetails) {
1565 gclog_or_tty->print("CMSCollector: collect because incremental collection will fail ");
1566 }
1567 return true;
1568 }
1569
1570 if (MetaspaceGC::should_concurrent_collect()) {
1571 if (Verbose && PrintGCDetails) {
1572 gclog_or_tty->print("CMSCollector: collect for metadata allocation ");
1573 }
1574 return true;
1575 }
1576
1577 return false;
1578 }
1579
1580 void CMSCollector::set_did_compact(bool v) { _cmsGen->set_did_compact(v); }
1581
1582 // Clear _expansion_cause fields of constituent generations
1583 void CMSCollector::clear_expansion_cause() {
1584 _cmsGen->clear_expansion_cause();
1585 }
1586
1587 // We should be conservative in starting a collection cycle. To
1588 // start too eagerly runs the risk of collecting too often in the
1589 // extreme. To collect too rarely falls back on full collections,
1590 // which works, even if not optimum in terms of concurrent work.
1591 // As a work around for too eagerly collecting, use the flag
1592 // UseCMSInitiatingOccupancyOnly. This also has the advantage of
1593 // giving the user an easily understandable way of controlling the
1594 // collections.
1595 // We want to start a new collection cycle if any of the following
1596 // conditions hold:
1597 // . our current occupancy exceeds the configured initiating occupancy
1598 // for this generation, or
1599 // . we recently needed to expand this space and have not, since that
1600 // expansion, done a collection of this generation, or
1601 // . the underlying space believes that it may be a good idea to initiate
1602 // a concurrent collection (this may be based on criteria such as the
1603 // following: the space uses linear allocation and linear allocation is
1604 // going to fail, or there is believed to be excessive fragmentation in
1605 // the generation, etc... or ...
1606 // [.(currently done by CMSCollector::shouldConcurrentCollect() only for
1607 // the case of the old generation; see CR 6543076):
1608 // we may be approaching a point at which allocation requests may fail because
1609 // we will be out of sufficient free space given allocation rate estimates.]
1610 bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const {
1611
1612 assert_lock_strong(freelistLock());
1613 if (occupancy() > initiating_occupancy()) {
1614 if (PrintGCDetails && Verbose) {
1615 gclog_or_tty->print(" %s: collect because of occupancy %f / %f ",
1616 short_name(), occupancy(), initiating_occupancy());
1617 }
1618 return true;
1619 }
1620 if (UseCMSInitiatingOccupancyOnly) {
1621 return false;
1622 }
1623 if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) {
1624 if (PrintGCDetails && Verbose) {
1625 gclog_or_tty->print(" %s: collect because expanded for allocation ",
1626 short_name());
1627 }
1628 return true;
1629 }
1630 if (_cmsSpace->should_concurrent_collect()) {
1631 if (PrintGCDetails && Verbose) {
1632 gclog_or_tty->print(" %s: collect because cmsSpace says so ",
1633 short_name());
1634 }
1635 return true;
1636 }
1637 return false;
1638 }
1639
1640 void ConcurrentMarkSweepGeneration::collect(bool full,
1641 bool clear_all_soft_refs,
1642 size_t size,
1643 bool tlab)
1644 {
1645 collector()->collect(full, clear_all_soft_refs, size, tlab);
1646 }
1647
1648 void CMSCollector::collect(bool full,
1649 bool clear_all_soft_refs,
1650 size_t size,
1651 bool tlab)
1652 {
1653 if (!UseCMSCollectionPassing && _collectorState > Idling) {
1654 // For debugging purposes skip the collection if the state
1655 // is not currently idle
1656 if (TraceCMSState) {
1657 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " skipped full:%d CMS state %d",
1658 Thread::current(), full, _collectorState);
1659 }
1660 return;
1661 }
1662
1663 // The following "if" branch is present for defensive reasons.
1664 // In the current uses of this interface, it can be replaced with:
1665 // assert(!GC_locker.is_active(), "Can't be called otherwise");
1666 // But I am not placing that assert here to allow future
1667 // generality in invoking this interface.
1668 if (GC_locker::is_active()) {
1669 // A consistency test for GC_locker
1670 assert(GC_locker::needs_gc(), "Should have been set already");
1671 // Skip this foreground collection, instead
1672 // expanding the heap if necessary.
1673 // Need the free list locks for the call to free() in compute_new_size()
1674 compute_new_size();
1675 return;
1676 }
1677 acquire_control_and_collect(full, clear_all_soft_refs);
1678 _full_gcs_since_conc_gc++;
1679 }
1680
1681 void CMSCollector::request_full_gc(unsigned int full_gc_count, GCCause::Cause cause) {
1682 GenCollectedHeap* gch = GenCollectedHeap::heap();
1683 unsigned int gc_count = gch->total_full_collections();
1684 if (gc_count == full_gc_count) {
1685 MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag);
1686 _full_gc_requested = true;
1687 _full_gc_cause = cause;
1688 CGC_lock->notify(); // nudge CMS thread
1689 } else {
1690 assert(gc_count > full_gc_count, "Error: causal loop");
1691 }
1692 }
1693
1694 bool CMSCollector::is_external_interruption() {
1695 GCCause::Cause cause = GenCollectedHeap::heap()->gc_cause();
1696 return GCCause::is_user_requested_gc(cause) ||
1697 GCCause::is_serviceability_requested_gc(cause);
1698 }
1699
1700 void CMSCollector::report_concurrent_mode_interruption() {
1701 if (is_external_interruption()) {
1702 if (PrintGCDetails) {
1703 gclog_or_tty->print(" (concurrent mode interrupted)");
1704 }
1705 } else {
1706 if (PrintGCDetails) {
1707 gclog_or_tty->print(" (concurrent mode failure)");
1708 }
1709 _gc_tracer_cm->report_concurrent_mode_failure();
1710 }
1711 }
1712
1713
1714 // The foreground and background collectors need to coordinate in order
1715 // to make sure that they do not mutually interfere with CMS collections.
1716 // When a background collection is active,
1717 // the foreground collector may need to take over (preempt) and
1718 // synchronously complete an ongoing collection. Depending on the
1719 // frequency of the background collections and the heap usage
1720 // of the application, this preemption can be seldom or frequent.
1721 // There are only certain
1722 // points in the background collection that the "collection-baton"
1723 // can be passed to the foreground collector.
1724 //
1725 // The foreground collector will wait for the baton before
1726 // starting any part of the collection. The foreground collector
1727 // will only wait at one location.
1728 //
1729 // The background collector will yield the baton before starting a new
1730 // phase of the collection (e.g., before initial marking, marking from roots,
1731 // precleaning, final re-mark, sweep etc.) This is normally done at the head
1732 // of the loop which switches the phases. The background collector does some
1733 // of the phases (initial mark, final re-mark) with the world stopped.
1734 // Because of locking involved in stopping the world,
1735 // the foreground collector should not block waiting for the background
1736 // collector when it is doing a stop-the-world phase. The background
1737 // collector will yield the baton at an additional point just before
1738 // it enters a stop-the-world phase. Once the world is stopped, the
1739 // background collector checks the phase of the collection. If the
1740 // phase has not changed, it proceeds with the collection. If the
1741 // phase has changed, it skips that phase of the collection. See
1742 // the comments on the use of the Heap_lock in collect_in_background().
1743 //
1744 // Variable used in baton passing.
1745 // _foregroundGCIsActive - Set to true by the foreground collector when
1746 // it wants the baton. The foreground clears it when it has finished
1747 // the collection.
1748 // _foregroundGCShouldWait - Set to true by the background collector
1749 // when it is running. The foreground collector waits while
1750 // _foregroundGCShouldWait is true.
1751 // CGC_lock - monitor used to protect access to the above variables
1752 // and to notify the foreground and background collectors.
1753 // _collectorState - current state of the CMS collection.
1754 //
1755 // The foreground collector
1756 // acquires the CGC_lock
1757 // sets _foregroundGCIsActive
1758 // waits on the CGC_lock for _foregroundGCShouldWait to be false
1759 // various locks acquired in preparation for the collection
1760 // are released so as not to block the background collector
1761 // that is in the midst of a collection
1762 // proceeds with the collection
1763 // clears _foregroundGCIsActive
1764 // returns
1765 //
1766 // The background collector in a loop iterating on the phases of the
1767 // collection
1768 // acquires the CGC_lock
1769 // sets _foregroundGCShouldWait
1770 // if _foregroundGCIsActive is set
1771 // clears _foregroundGCShouldWait, notifies _CGC_lock
1772 // waits on _CGC_lock for _foregroundGCIsActive to become false
1773 // and exits the loop.
1774 // otherwise
1775 // proceed with that phase of the collection
1776 // if the phase is a stop-the-world phase,
1777 // yield the baton once more just before enqueueing
1778 // the stop-world CMS operation (executed by the VM thread).
1779 // returns after all phases of the collection are done
1780 //
1781
1782 void CMSCollector::acquire_control_and_collect(bool full,
1783 bool clear_all_soft_refs) {
1784 assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
1785 assert(!Thread::current()->is_ConcurrentGC_thread(),
1786 "shouldn't try to acquire control from self!");
1787
1788 // Start the protocol for acquiring control of the
1789 // collection from the background collector (aka CMS thread).
1790 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1791 "VM thread should have CMS token");
1792 // Remember the possibly interrupted state of an ongoing
1793 // concurrent collection
1794 CollectorState first_state = _collectorState;
1795
1796 // Signal to a possibly ongoing concurrent collection that
1797 // we want to do a foreground collection.
1798 _foregroundGCIsActive = true;
1799
1800 // Disable incremental mode during a foreground collection.
1801 ICMSDisabler icms_disabler;
1802
1803 // release locks and wait for a notify from the background collector
1804 // releasing the locks in only necessary for phases which
1805 // do yields to improve the granularity of the collection.
1806 assert_lock_strong(bitMapLock());
1807 // We need to lock the Free list lock for the space that we are
1808 // currently collecting.
1809 assert(haveFreelistLocks(), "Must be holding free list locks");
1810 bitMapLock()->unlock();
1811 releaseFreelistLocks();
1812 {
1813 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1814 if (_foregroundGCShouldWait) {
1815 // We are going to be waiting for action for the CMS thread;
1816 // it had better not be gone (for instance at shutdown)!
1817 assert(ConcurrentMarkSweepThread::cmst() != NULL,
1818 "CMS thread must be running");
1819 // Wait here until the background collector gives us the go-ahead
1820 ConcurrentMarkSweepThread::clear_CMS_flag(
1821 ConcurrentMarkSweepThread::CMS_vm_has_token); // release token
1822 // Get a possibly blocked CMS thread going:
1823 // Note that we set _foregroundGCIsActive true above,
1824 // without protection of the CGC_lock.
1825 CGC_lock->notify();
1826 assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(),
1827 "Possible deadlock");
1828 while (_foregroundGCShouldWait) {
1829 // wait for notification
1830 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1831 // Possibility of delay/starvation here, since CMS token does
1832 // not know to give priority to VM thread? Actually, i think
1833 // there wouldn't be any delay/starvation, but the proof of
1834 // that "fact" (?) appears non-trivial. XXX 20011219YSR
1835 }
1836 ConcurrentMarkSweepThread::set_CMS_flag(
1837 ConcurrentMarkSweepThread::CMS_vm_has_token);
1838 }
1839 }
1840 // The CMS_token is already held. Get back the other locks.
1841 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1842 "VM thread should have CMS token");
1843 getFreelistLocks();
1844 bitMapLock()->lock_without_safepoint_check();
1845 if (TraceCMSState) {
1846 gclog_or_tty->print_cr("CMS foreground collector has asked for control "
1847 INTPTR_FORMAT " with first state %d", Thread::current(), first_state);
1848 gclog_or_tty->print_cr(" gets control with state %d", _collectorState);
1849 }
1850
1851 // Check if we need to do a compaction, or if not, whether
1852 // we need to start the mark-sweep from scratch.
1853 bool should_compact = false;
1854 bool should_start_over = false;
1855 decide_foreground_collection_type(clear_all_soft_refs,
1856 &should_compact, &should_start_over);
1857
1858 NOT_PRODUCT(
1859 if (RotateCMSCollectionTypes) {
1860 if (_cmsGen->debug_collection_type() ==
1861 ConcurrentMarkSweepGeneration::MSC_foreground_collection_type) {
1862 should_compact = true;
1863 } else if (_cmsGen->debug_collection_type() ==
1864 ConcurrentMarkSweepGeneration::MS_foreground_collection_type) {
1865 should_compact = false;
1866 }
1867 }
1868 )
1869
1870 if (first_state > Idling) {
1871 report_concurrent_mode_interruption();
1872 }
1873
1874 set_did_compact(should_compact);
1875 if (should_compact) {
1876 // If the collection is being acquired from the background
1877 // collector, there may be references on the discovered
1878 // references lists that have NULL referents (being those
1879 // that were concurrently cleared by a mutator) or
1880 // that are no longer active (having been enqueued concurrently
1881 // by the mutator).
1882 // Scrub the list of those references because Mark-Sweep-Compact
1883 // code assumes referents are not NULL and that all discovered
1884 // Reference objects are active.
1885 ref_processor()->clean_up_discovered_references();
1886
1887 if (first_state > Idling) {
1888 save_heap_summary();
1889 }
1890
1891 do_compaction_work(clear_all_soft_refs);
1892
1893 // Has the GC time limit been exceeded?
1894 DefNewGeneration* young_gen = _young_gen->as_DefNewGeneration();
1895 size_t max_eden_size = young_gen->max_capacity() -
1896 young_gen->to()->capacity() -
1897 young_gen->from()->capacity();
1898 GenCollectedHeap* gch = GenCollectedHeap::heap();
1899 GCCause::Cause gc_cause = gch->gc_cause();
1900 size_policy()->check_gc_overhead_limit(_young_gen->used(),
1901 young_gen->eden()->used(),
1902 _cmsGen->max_capacity(),
1903 max_eden_size,
1904 full,
1905 gc_cause,
1906 gch->collector_policy());
1907 } else {
1908 do_mark_sweep_work(clear_all_soft_refs, first_state,
1909 should_start_over);
1910 }
1911 // Reset the expansion cause, now that we just completed
1912 // a collection cycle.
1913 clear_expansion_cause();
1914 _foregroundGCIsActive = false;
1915 return;
1916 }
1917
1918 // Resize the tenured generation
1919 // after obtaining the free list locks for the
1920 // two generations.
1921 void CMSCollector::compute_new_size() {
1922 assert_locked_or_safepoint(Heap_lock);
1923 FreelistLocker z(this);
1924 MetaspaceGC::compute_new_size();
1925 _cmsGen->compute_new_size_free_list();
1926 }
1927
1928 // A work method used by foreground collection to determine
1929 // what type of collection (compacting or not, continuing or fresh)
1930 // it should do.
1931 // NOTE: the intent is to make UseCMSCompactAtFullCollection
1932 // and CMSCompactWhenClearAllSoftRefs the default in the future
1933 // and do away with the flags after a suitable period.
1934 void CMSCollector::decide_foreground_collection_type(
1935 bool clear_all_soft_refs, bool* should_compact,
1936 bool* should_start_over) {
1937 // Normally, we'll compact only if the UseCMSCompactAtFullCollection
1938 // flag is set, and we have either requested a System.gc() or
1939 // the number of full gc's since the last concurrent cycle
1940 // has exceeded the threshold set by CMSFullGCsBeforeCompaction,
1941 // or if an incremental collection has failed
1942 GenCollectedHeap* gch = GenCollectedHeap::heap();
1943 assert(gch->collector_policy()->is_two_generation_policy(),
1944 "You may want to check the correctness of the following");
1945 // Inform cms gen if this was due to partial collection failing.
1946 // The CMS gen may use this fact to determine its expansion policy.
1947 if (gch->incremental_collection_will_fail(false /* don't consult_young */)) {
1948 assert(!_cmsGen->incremental_collection_failed(),
1949 "Should have been noticed, reacted to and cleared");
1950 _cmsGen->set_incremental_collection_failed();
1951 }
1952 *should_compact =
1953 UseCMSCompactAtFullCollection &&
1954 ((_full_gcs_since_conc_gc >= CMSFullGCsBeforeCompaction) ||
1955 GCCause::is_user_requested_gc(gch->gc_cause()) ||
1956 gch->incremental_collection_will_fail(true /* consult_young */));
1957 *should_start_over = false;
1958 if (clear_all_soft_refs && !*should_compact) {
1959 // We are about to do a last ditch collection attempt
1960 // so it would normally make sense to do a compaction
1961 // to reclaim as much space as possible.
1962 if (CMSCompactWhenClearAllSoftRefs) {
1963 // Default: The rationale is that in this case either
1964 // we are past the final marking phase, in which case
1965 // we'd have to start over, or so little has been done
1966 // that there's little point in saving that work. Compaction
1967 // appears to be the sensible choice in either case.
1968 *should_compact = true;
1969 } else {
1970 // We have been asked to clear all soft refs, but not to
1971 // compact. Make sure that we aren't past the final checkpoint
1972 // phase, for that is where we process soft refs. If we are already
1973 // past that phase, we'll need to redo the refs discovery phase and
1974 // if necessary clear soft refs that weren't previously
1975 // cleared. We do so by remembering the phase in which
1976 // we came in, and if we are past the refs processing
1977 // phase, we'll choose to just redo the mark-sweep
1978 // collection from scratch.
1979 if (_collectorState > FinalMarking) {
1980 // We are past the refs processing phase;
1981 // start over and do a fresh synchronous CMS cycle
1982 _collectorState = Resetting; // skip to reset to start new cycle
1983 reset(false /* == !asynch */);
1984 *should_start_over = true;
1985 } // else we can continue a possibly ongoing current cycle
1986 }
1987 }
1988 }
1989
1990 // A work method used by the foreground collector to do
1991 // a mark-sweep-compact.
1992 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) {
1993 GenCollectedHeap* gch = GenCollectedHeap::heap();
1994
1995 STWGCTimer* gc_timer = GenMarkSweep::gc_timer();
1996 gc_timer->register_gc_start();
1997
1998 SerialOldTracer* gc_tracer = GenMarkSweep::gc_tracer();
1999 gc_tracer->report_gc_start(gch->gc_cause(), gc_timer->gc_start());
2000
2001 GCTraceTime t("CMS:MSC ", PrintGCDetails && Verbose, true, NULL);
2002 if (PrintGC && Verbose && !(GCCause::is_user_requested_gc(gch->gc_cause()))) {
2003 gclog_or_tty->print_cr("Compact ConcurrentMarkSweepGeneration after %d "
2004 "collections passed to foreground collector", _full_gcs_since_conc_gc);
2005 }
2006
2007 // Sample collection interval time and reset for collection pause.
2008 if (UseAdaptiveSizePolicy) {
2009 size_policy()->msc_collection_begin();
2010 }
2011
2012 // Temporarily widen the span of the weak reference processing to
2013 // the entire heap.
2014 MemRegion new_span(GenCollectedHeap::heap()->reserved_region());
2015 ReferenceProcessorSpanMutator rp_mut_span(ref_processor(), new_span);
2016 // Temporarily, clear the "is_alive_non_header" field of the
2017 // reference processor.
2018 ReferenceProcessorIsAliveMutator rp_mut_closure(ref_processor(), NULL);
2019 // Temporarily make reference _processing_ single threaded (non-MT).
2020 ReferenceProcessorMTProcMutator rp_mut_mt_processing(ref_processor(), false);
2021 // Temporarily make refs discovery atomic
2022 ReferenceProcessorAtomicMutator rp_mut_atomic(ref_processor(), true);
2023 // Temporarily make reference _discovery_ single threaded (non-MT)
2024 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
2025
2026 ref_processor()->set_enqueuing_is_done(false);
2027 ref_processor()->enable_discovery(false /*verify_disabled*/, false /*check_no_refs*/);
2028 ref_processor()->setup_policy(clear_all_soft_refs);
2029 // If an asynchronous collection finishes, the _modUnionTable is
2030 // all clear. If we are assuming the collection from an asynchronous
2031 // collection, clear the _modUnionTable.
2032 assert(_collectorState != Idling || _modUnionTable.isAllClear(),
2033 "_modUnionTable should be clear if the baton was not passed");
2034 _modUnionTable.clear_all();
2035 assert(_collectorState != Idling || _ct->klass_rem_set()->mod_union_is_clear(),
2036 "mod union for klasses should be clear if the baton was passed");
2037 _ct->klass_rem_set()->clear_mod_union();
2038
2039 // We must adjust the allocation statistics being maintained
2040 // in the free list space. We do so by reading and clearing
2041 // the sweep timer and updating the block flux rate estimates below.
2042 assert(!_intra_sweep_timer.is_active(), "_intra_sweep_timer should be inactive");
2043 if (_inter_sweep_timer.is_active()) {
2044 _inter_sweep_timer.stop();
2045 // Note that we do not use this sample to update the _inter_sweep_estimate.
2046 _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
2047 _inter_sweep_estimate.padded_average(),
2048 _intra_sweep_estimate.padded_average());
2049 }
2050
2051 GenMarkSweep::invoke_at_safepoint(_cmsGen->level(),
2052 ref_processor(), clear_all_soft_refs);
2053 #ifdef ASSERT
2054 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
2055 size_t free_size = cms_space->free();
2056 assert(free_size ==
2057 pointer_delta(cms_space->end(), cms_space->compaction_top())
2058 * HeapWordSize,
2059 "All the free space should be compacted into one chunk at top");
2060 assert(cms_space->dictionary()->total_chunk_size(
2061 debug_only(cms_space->freelistLock())) == 0 ||
2062 cms_space->totalSizeInIndexedFreeLists() == 0,
2063 "All the free space should be in a single chunk");
2064 size_t num = cms_space->totalCount();
2065 assert((free_size == 0 && num == 0) ||
2066 (free_size > 0 && (num == 1 || num == 2)),
2067 "There should be at most 2 free chunks after compaction");
2068 #endif // ASSERT
2069 _collectorState = Resetting;
2070 assert(_restart_addr == NULL,
2071 "Should have been NULL'd before baton was passed");
2072 reset(false /* == !asynch */);
2073 _cmsGen->reset_after_compaction();
2074 _concurrent_cycles_since_last_unload = 0;
2075
2076 // Clear any data recorded in the PLAB chunk arrays.
2077 if (_survivor_plab_array != NULL) {
2078 reset_survivor_plab_arrays();
2079 }
2080
2081 // Adjust the per-size allocation stats for the next epoch.
2082 _cmsGen->cmsSpace()->endSweepFLCensus(sweep_count() /* fake */);
2083 // Restart the "inter sweep timer" for the next epoch.
2084 _inter_sweep_timer.reset();
2085 _inter_sweep_timer.start();
2086
2087 // Sample collection pause time and reset for collection interval.
2088 if (UseAdaptiveSizePolicy) {
2089 size_policy()->msc_collection_end(gch->gc_cause());
2090 }
2091
2092 gc_timer->register_gc_end();
2093
2094 gc_tracer->report_gc_end(gc_timer->gc_end(), gc_timer->time_partitions());
2095
2096 // For a mark-sweep-compact, compute_new_size() will be called
2097 // in the heap's do_collection() method.
2098 }
2099
2100 // A work method used by the foreground collector to do
2101 // a mark-sweep, after taking over from a possibly on-going
2102 // concurrent mark-sweep collection.
2103 void CMSCollector::do_mark_sweep_work(bool clear_all_soft_refs,
2104 CollectorState first_state, bool should_start_over) {
2105 if (PrintGC && Verbose) {
2106 gclog_or_tty->print_cr("Pass concurrent collection to foreground "
2107 "collector with count %d",
2108 _full_gcs_since_conc_gc);
2109 }
2110 switch (_collectorState) {
2111 case Idling:
2112 if (first_state == Idling || should_start_over) {
2113 // The background GC was not active, or should
2114 // restarted from scratch; start the cycle.
2115 _collectorState = InitialMarking;
2116 }
2117 // If first_state was not Idling, then a background GC
2118 // was in progress and has now finished. No need to do it
2119 // again. Leave the state as Idling.
2120 break;
2121 case Precleaning:
2122 // In the foreground case don't do the precleaning since
2123 // it is not done concurrently and there is extra work
2124 // required.
2125 _collectorState = FinalMarking;
2126 }
2127 collect_in_foreground(clear_all_soft_refs, GenCollectedHeap::heap()->gc_cause());
2128
2129 // For a mark-sweep, compute_new_size() will be called
2130 // in the heap's do_collection() method.
2131 }
2132
2133
2134 void CMSCollector::print_eden_and_survivor_chunk_arrays() {
2135 DefNewGeneration* dng = _young_gen->as_DefNewGeneration();
2136 EdenSpace* eden_space = dng->eden();
2137 ContiguousSpace* from_space = dng->from();
2138 ContiguousSpace* to_space = dng->to();
2139 // Eden
2140 if (_eden_chunk_array != NULL) {
2141 gclog_or_tty->print_cr("eden " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
2142 eden_space->bottom(), eden_space->top(),
2143 eden_space->end(), eden_space->capacity());
2144 gclog_or_tty->print_cr("_eden_chunk_index=" SIZE_FORMAT ", "
2145 "_eden_chunk_capacity=" SIZE_FORMAT,
2146 _eden_chunk_index, _eden_chunk_capacity);
2147 for (size_t i = 0; i < _eden_chunk_index; i++) {
2148 gclog_or_tty->print_cr("_eden_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT,
2149 i, _eden_chunk_array[i]);
2150 }
2151 }
2152 // Survivor
2153 if (_survivor_chunk_array != NULL) {
2154 gclog_or_tty->print_cr("survivor " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
2155 from_space->bottom(), from_space->top(),
2156 from_space->end(), from_space->capacity());
2157 gclog_or_tty->print_cr("_survivor_chunk_index=" SIZE_FORMAT ", "
2158 "_survivor_chunk_capacity=" SIZE_FORMAT,
2159 _survivor_chunk_index, _survivor_chunk_capacity);
2160 for (size_t i = 0; i < _survivor_chunk_index; i++) {
2161 gclog_or_tty->print_cr("_survivor_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT,
2162 i, _survivor_chunk_array[i]);
2163 }
2164 }
2165 }
2166
2167 void CMSCollector::getFreelistLocks() const {
2168 // Get locks for all free lists in all generations that this
2169 // collector is responsible for
2170 _cmsGen->freelistLock()->lock_without_safepoint_check();
2171 }
2172
2173 void CMSCollector::releaseFreelistLocks() const {
2174 // Release locks for all free lists in all generations that this
2175 // collector is responsible for
2176 _cmsGen->freelistLock()->unlock();
2177 }
2178
2179 bool CMSCollector::haveFreelistLocks() const {
2180 // Check locks for all free lists in all generations that this
2181 // collector is responsible for
2182 assert_lock_strong(_cmsGen->freelistLock());
2183 PRODUCT_ONLY(ShouldNotReachHere());
2184 return true;
2185 }
2186
2187 // A utility class that is used by the CMS collector to
2188 // temporarily "release" the foreground collector from its
2189 // usual obligation to wait for the background collector to
2190 // complete an ongoing phase before proceeding.
2191 class ReleaseForegroundGC: public StackObj {
2192 private:
2193 CMSCollector* _c;
2194 public:
2195 ReleaseForegroundGC(CMSCollector* c) : _c(c) {
2196 assert(_c->_foregroundGCShouldWait, "Else should not need to call");
2197 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2198 // allow a potentially blocked foreground collector to proceed
2199 _c->_foregroundGCShouldWait = false;
2200 if (_c->_foregroundGCIsActive) {
2201 CGC_lock->notify();
2202 }
2203 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2204 "Possible deadlock");
2205 }
2206
2207 ~ReleaseForegroundGC() {
2208 assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?");
2209 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2210 _c->_foregroundGCShouldWait = true;
2211 }
2212 };
2213
2214 // There are separate collect_in_background and collect_in_foreground because of
2215 // the different locking requirements of the background collector and the
2216 // foreground collector. There was originally an attempt to share
2217 // one "collect" method between the background collector and the foreground
2218 // collector but the if-then-else required made it cleaner to have
2219 // separate methods.
2220 void CMSCollector::collect_in_background(bool clear_all_soft_refs, GCCause::Cause cause) {
2221 assert(Thread::current()->is_ConcurrentGC_thread(),
2222 "A CMS asynchronous collection is only allowed on a CMS thread.");
2223
2224 GenCollectedHeap* gch = GenCollectedHeap::heap();
2225 {
2226 bool safepoint_check = Mutex::_no_safepoint_check_flag;
2227 MutexLockerEx hl(Heap_lock, safepoint_check);
2228 FreelistLocker fll(this);
2229 MutexLockerEx x(CGC_lock, safepoint_check);
2230 if (_foregroundGCIsActive || !UseAsyncConcMarkSweepGC) {
2231 // The foreground collector is active or we're
2232 // not using asynchronous collections. Skip this
2233 // background collection.
2234 assert(!_foregroundGCShouldWait, "Should be clear");
2235 return;
2236 } else {
2237 assert(_collectorState == Idling, "Should be idling before start.");
2238 _collectorState = InitialMarking;
2239 register_gc_start(cause);
2240 // Reset the expansion cause, now that we are about to begin
2241 // a new cycle.
2242 clear_expansion_cause();
2243
2244 // Clear the MetaspaceGC flag since a concurrent collection
2245 // is starting but also clear it after the collection.
2246 MetaspaceGC::set_should_concurrent_collect(false);
2247 }
2248 // Decide if we want to enable class unloading as part of the
2249 // ensuing concurrent GC cycle.
2250 update_should_unload_classes();
2251 _full_gc_requested = false; // acks all outstanding full gc requests
2252 _full_gc_cause = GCCause::_no_gc;
2253 // Signal that we are about to start a collection
2254 gch->increment_total_full_collections(); // ... starting a collection cycle
2255 _collection_count_start = gch->total_full_collections();
2256 }
2257
2258 // Used for PrintGC
2259 size_t prev_used;
2260 if (PrintGC && Verbose) {
2261 prev_used = _cmsGen->used(); // XXXPERM
2262 }
2263
2264 // The change of the collection state is normally done at this level;
2265 // the exceptions are phases that are executed while the world is
2266 // stopped. For those phases the change of state is done while the
2267 // world is stopped. For baton passing purposes this allows the
2268 // background collector to finish the phase and change state atomically.
2269 // The foreground collector cannot wait on a phase that is done
2270 // while the world is stopped because the foreground collector already
2271 // has the world stopped and would deadlock.
2272 while (_collectorState != Idling) {
2273 if (TraceCMSState) {
2274 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
2275 Thread::current(), _collectorState);
2276 }
2277 // The foreground collector
2278 // holds the Heap_lock throughout its collection.
2279 // holds the CMS token (but not the lock)
2280 // except while it is waiting for the background collector to yield.
2281 //
2282 // The foreground collector should be blocked (not for long)
2283 // if the background collector is about to start a phase
2284 // executed with world stopped. If the background
2285 // collector has already started such a phase, the
2286 // foreground collector is blocked waiting for the
2287 // Heap_lock. The stop-world phases (InitialMarking and FinalMarking)
2288 // are executed in the VM thread.
2289 //
2290 // The locking order is
2291 // PendingListLock (PLL) -- if applicable (FinalMarking)
2292 // Heap_lock (both this & PLL locked in VM_CMS_Operation::prologue())
2293 // CMS token (claimed in
2294 // stop_world_and_do() -->
2295 // safepoint_synchronize() -->
2296 // CMSThread::synchronize())
2297
2298 {
2299 // Check if the FG collector wants us to yield.
2300 CMSTokenSync x(true); // is cms thread
2301 if (waitForForegroundGC()) {
2302 // We yielded to a foreground GC, nothing more to be
2303 // done this round.
2304 assert(_foregroundGCShouldWait == false, "We set it to false in "
2305 "waitForForegroundGC()");
2306 if (TraceCMSState) {
2307 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2308 " exiting collection CMS state %d",
2309 Thread::current(), _collectorState);
2310 }
2311 return;
2312 } else {
2313 // The background collector can run but check to see if the
2314 // foreground collector has done a collection while the
2315 // background collector was waiting to get the CGC_lock
2316 // above. If yes, break so that _foregroundGCShouldWait
2317 // is cleared before returning.
2318 if (_collectorState == Idling) {
2319 break;
2320 }
2321 }
2322 }
2323
2324 assert(_foregroundGCShouldWait, "Foreground collector, if active, "
2325 "should be waiting");
2326
2327 switch (_collectorState) {
2328 case InitialMarking:
2329 {
2330 ReleaseForegroundGC x(this);
2331 stats().record_cms_begin();
2332 VM_CMS_Initial_Mark initial_mark_op(this);
2333 VMThread::execute(&initial_mark_op);
2334 }
2335 // The collector state may be any legal state at this point
2336 // since the background collector may have yielded to the
2337 // foreground collector.
2338 break;
2339 case Marking:
2340 // initial marking in checkpointRootsInitialWork has been completed
2341 if (markFromRoots(true)) { // we were successful
2342 assert(_collectorState == Precleaning, "Collector state should "
2343 "have changed");
2344 } else {
2345 assert(_foregroundGCIsActive, "Internal state inconsistency");
2346 }
2347 break;
2348 case Precleaning:
2349 if (UseAdaptiveSizePolicy) {
2350 size_policy()->concurrent_precleaning_begin();
2351 }
2352 // marking from roots in markFromRoots has been completed
2353 preclean();
2354 if (UseAdaptiveSizePolicy) {
2355 size_policy()->concurrent_precleaning_end();
2356 }
2357 assert(_collectorState == AbortablePreclean ||
2358 _collectorState == FinalMarking,
2359 "Collector state should have changed");
2360 break;
2361 case AbortablePreclean:
2362 if (UseAdaptiveSizePolicy) {
2363 size_policy()->concurrent_phases_resume();
2364 }
2365 abortable_preclean();
2366 if (UseAdaptiveSizePolicy) {
2367 size_policy()->concurrent_precleaning_end();
2368 }
2369 assert(_collectorState == FinalMarking, "Collector state should "
2370 "have changed");
2371 break;
2372 case FinalMarking:
2373 {
2374 ReleaseForegroundGC x(this);
2375
2376 VM_CMS_Final_Remark final_remark_op(this);
2377 VMThread::execute(&final_remark_op);
2378 }
2379 assert(_foregroundGCShouldWait, "block post-condition");
2380 break;
2381 case Sweeping:
2382 if (UseAdaptiveSizePolicy) {
2383 size_policy()->concurrent_sweeping_begin();
2384 }
2385 // final marking in checkpointRootsFinal has been completed
2386 sweep(true);
2387 assert(_collectorState == Resizing, "Collector state change "
2388 "to Resizing must be done under the free_list_lock");
2389 _full_gcs_since_conc_gc = 0;
2390
2391 // Stop the timers for adaptive size policy for the concurrent phases
2392 if (UseAdaptiveSizePolicy) {
2393 size_policy()->concurrent_sweeping_end();
2394 size_policy()->concurrent_phases_end(gch->gc_cause(),
2395 gch->prev_gen(_cmsGen)->capacity(),
2396 _cmsGen->free());
2397 }
2398
2399 case Resizing: {
2400 // Sweeping has been completed...
2401 // At this point the background collection has completed.
2402 // Don't move the call to compute_new_size() down
2403 // into code that might be executed if the background
2404 // collection was preempted.
2405 {
2406 ReleaseForegroundGC x(this); // unblock FG collection
2407 MutexLockerEx y(Heap_lock, Mutex::_no_safepoint_check_flag);
2408 CMSTokenSync z(true); // not strictly needed.
2409 if (_collectorState == Resizing) {
2410 compute_new_size();
2411 save_heap_summary();
2412 _collectorState = Resetting;
2413 } else {
2414 assert(_collectorState == Idling, "The state should only change"
2415 " because the foreground collector has finished the collection");
2416 }
2417 }
2418 break;
2419 }
2420 case Resetting:
2421 // CMS heap resizing has been completed
2422 reset(true);
2423 assert(_collectorState == Idling, "Collector state should "
2424 "have changed");
2425
2426 MetaspaceGC::set_should_concurrent_collect(false);
2427
2428 stats().record_cms_end();
2429 // Don't move the concurrent_phases_end() and compute_new_size()
2430 // calls to here because a preempted background collection
2431 // has it's state set to "Resetting".
2432 break;
2433 case Idling:
2434 default:
2435 ShouldNotReachHere();
2436 break;
2437 }
2438 if (TraceCMSState) {
2439 gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d",
2440 Thread::current(), _collectorState);
2441 }
2442 assert(_foregroundGCShouldWait, "block post-condition");
2443 }
2444
2445 // Should this be in gc_epilogue?
2446 collector_policy()->counters()->update_counters();
2447
2448 {
2449 // Clear _foregroundGCShouldWait and, in the event that the
2450 // foreground collector is waiting, notify it, before
2451 // returning.
2452 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2453 _foregroundGCShouldWait = false;
2454 if (_foregroundGCIsActive) {
2455 CGC_lock->notify();
2456 }
2457 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2458 "Possible deadlock");
2459 }
2460 if (TraceCMSState) {
2461 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2462 " exiting collection CMS state %d",
2463 Thread::current(), _collectorState);
2464 }
2465 if (PrintGC && Verbose) {
2466 _cmsGen->print_heap_change(prev_used);
2467 }
2468 }
2469
2470 void CMSCollector::register_foreground_gc_start(GCCause::Cause cause) {
2471 if (!_cms_start_registered) {
2472 register_gc_start(cause);
2473 }
2474 }
2475
2476 void CMSCollector::register_gc_start(GCCause::Cause cause) {
2477 _cms_start_registered = true;
2478 _gc_timer_cm->register_gc_start();
2479 _gc_tracer_cm->report_gc_start(cause, _gc_timer_cm->gc_start());
2480 }
2481
2482 void CMSCollector::register_gc_end() {
2483 if (_cms_start_registered) {
2484 report_heap_summary(GCWhen::AfterGC);
2485
2486 _gc_timer_cm->register_gc_end();
2487 _gc_tracer_cm->report_gc_end(_gc_timer_cm->gc_end(), _gc_timer_cm->time_partitions());
2488 _cms_start_registered = false;
2489 }
2490 }
2491
2492 void CMSCollector::save_heap_summary() {
2493 GenCollectedHeap* gch = GenCollectedHeap::heap();
2494 _last_heap_summary = gch->create_heap_summary();
2495 _last_metaspace_summary = gch->create_metaspace_summary();
2496 }
2497
2498 void CMSCollector::report_heap_summary(GCWhen::Type when) {
2499 _gc_tracer_cm->report_gc_heap_summary(when, _last_heap_summary, _last_metaspace_summary);
2500 }
2501
2502 void CMSCollector::collect_in_foreground(bool clear_all_soft_refs, GCCause::Cause cause) {
2503 assert(_foregroundGCIsActive && !_foregroundGCShouldWait,
2504 "Foreground collector should be waiting, not executing");
2505 assert(Thread::current()->is_VM_thread(), "A foreground collection"
2506 "may only be done by the VM Thread with the world stopped");
2507 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
2508 "VM thread should have CMS token");
2509
2510 NOT_PRODUCT(GCTraceTime t("CMS:MS (foreground) ", PrintGCDetails && Verbose,
2511 true, NULL);)
2512 if (UseAdaptiveSizePolicy) {
2513 size_policy()->ms_collection_begin();
2514 }
2515 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact);
2516
2517 HandleMark hm; // Discard invalid handles created during verification
2518
2519 if (VerifyBeforeGC &&
2520 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2521 Universe::verify();
2522 }
2523
2524 // Snapshot the soft reference policy to be used in this collection cycle.
2525 ref_processor()->setup_policy(clear_all_soft_refs);
2526
2527 // Decide if class unloading should be done
2528 update_should_unload_classes();
2529
2530 bool init_mark_was_synchronous = false; // until proven otherwise
2531 while (_collectorState != Idling) {
2532 if (TraceCMSState) {
2533 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
2534 Thread::current(), _collectorState);
2535 }
2536 switch (_collectorState) {
2537 case InitialMarking:
2538 register_foreground_gc_start(cause);
2539 init_mark_was_synchronous = true; // fact to be exploited in re-mark
2540 checkpointRootsInitial(false);
2541 assert(_collectorState == Marking, "Collector state should have changed"
2542 " within checkpointRootsInitial()");
2543 break;
2544 case Marking:
2545 // initial marking in checkpointRootsInitialWork has been completed
2546 if (VerifyDuringGC &&
2547 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2548 Universe::verify("Verify before initial mark: ");
2549 }
2550 {
2551 bool res = markFromRoots(false);
2552 assert(res && _collectorState == FinalMarking, "Collector state should "
2553 "have changed");
2554 break;
2555 }
2556 case FinalMarking:
2557 if (VerifyDuringGC &&
2558 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2559 Universe::verify("Verify before re-mark: ");
2560 }
2561 checkpointRootsFinal(false, clear_all_soft_refs,
2562 init_mark_was_synchronous);
2563 assert(_collectorState == Sweeping, "Collector state should not "
2564 "have changed within checkpointRootsFinal()");
2565 break;
2566 case Sweeping:
2567 // final marking in checkpointRootsFinal has been completed
2568 if (VerifyDuringGC &&
2569 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2570 Universe::verify("Verify before sweep: ");
2571 }
2572 sweep(false);
2573 assert(_collectorState == Resizing, "Incorrect state");
2574 break;
2575 case Resizing: {
2576 // Sweeping has been completed; the actual resize in this case
2577 // is done separately; nothing to be done in this state.
2578 _collectorState = Resetting;
2579 break;
2580 }
2581 case Resetting:
2582 // The heap has been resized.
2583 if (VerifyDuringGC &&
2584 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2585 Universe::verify("Verify before reset: ");
2586 }
2587 save_heap_summary();
2588 reset(false);
2589 assert(_collectorState == Idling, "Collector state should "
2590 "have changed");
2591 break;
2592 case Precleaning:
2593 case AbortablePreclean:
2594 // Elide the preclean phase
2595 _collectorState = FinalMarking;
2596 break;
2597 default:
2598 ShouldNotReachHere();
2599 }
2600 if (TraceCMSState) {
2601 gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d",
2602 Thread::current(), _collectorState);
2603 }
2604 }
2605
2606 if (UseAdaptiveSizePolicy) {
2607 GenCollectedHeap* gch = GenCollectedHeap::heap();
2608 size_policy()->ms_collection_end(gch->gc_cause());
2609 }
2610
2611 if (VerifyAfterGC &&
2612 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2613 Universe::verify();
2614 }
2615 if (TraceCMSState) {
2616 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2617 " exiting collection CMS state %d",
2618 Thread::current(), _collectorState);
2619 }
2620 }
2621
2622 bool CMSCollector::waitForForegroundGC() {
2623 bool res = false;
2624 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2625 "CMS thread should have CMS token");
2626 // Block the foreground collector until the
2627 // background collectors decides whether to
2628 // yield.
2629 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2630 _foregroundGCShouldWait = true;
2631 if (_foregroundGCIsActive) {
2632 // The background collector yields to the
2633 // foreground collector and returns a value
2634 // indicating that it has yielded. The foreground
2635 // collector can proceed.
2636 res = true;
2637 _foregroundGCShouldWait = false;
2638 ConcurrentMarkSweepThread::clear_CMS_flag(
2639 ConcurrentMarkSweepThread::CMS_cms_has_token);
2640 ConcurrentMarkSweepThread::set_CMS_flag(
2641 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2642 // Get a possibly blocked foreground thread going
2643 CGC_lock->notify();
2644 if (TraceCMSState) {
2645 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d",
2646 Thread::current(), _collectorState);
2647 }
2648 while (_foregroundGCIsActive) {
2649 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
2650 }
2651 ConcurrentMarkSweepThread::set_CMS_flag(
2652 ConcurrentMarkSweepThread::CMS_cms_has_token);
2653 ConcurrentMarkSweepThread::clear_CMS_flag(
2654 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2655 }
2656 if (TraceCMSState) {
2657 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d",
2658 Thread::current(), _collectorState);
2659 }
2660 return res;
2661 }
2662
2663 // Because of the need to lock the free lists and other structures in
2664 // the collector, common to all the generations that the collector is
2665 // collecting, we need the gc_prologues of individual CMS generations
2666 // delegate to their collector. It may have been simpler had the
2667 // current infrastructure allowed one to call a prologue on a
2668 // collector. In the absence of that we have the generation's
2669 // prologue delegate to the collector, which delegates back
2670 // some "local" work to a worker method in the individual generations
2671 // that it's responsible for collecting, while itself doing any
2672 // work common to all generations it's responsible for. A similar
2673 // comment applies to the gc_epilogue()'s.
2674 // The role of the variable _between_prologue_and_epilogue is to
2675 // enforce the invocation protocol.
2676 void CMSCollector::gc_prologue(bool full) {
2677 // Call gc_prologue_work() for the CMSGen
2678 // we are responsible for.
2679
2680 // The following locking discipline assumes that we are only called
2681 // when the world is stopped.
2682 assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption");
2683
2684 // The CMSCollector prologue must call the gc_prologues for the
2685 // "generations" that it's responsible
2686 // for.
2687
2688 assert( Thread::current()->is_VM_thread()
2689 || ( CMSScavengeBeforeRemark
2690 && Thread::current()->is_ConcurrentGC_thread()),
2691 "Incorrect thread type for prologue execution");
2692
2693 if (_between_prologue_and_epilogue) {
2694 // We have already been invoked; this is a gc_prologue delegation
2695 // from yet another CMS generation that we are responsible for, just
2696 // ignore it since all relevant work has already been done.
2697 return;
2698 }
2699
2700 // set a bit saying prologue has been called; cleared in epilogue
2701 _between_prologue_and_epilogue = true;
2702 // Claim locks for common data structures, then call gc_prologue_work()
2703 // for each CMSGen.
2704
2705 getFreelistLocks(); // gets free list locks on constituent spaces
2706 bitMapLock()->lock_without_safepoint_check();
2707
2708 // Should call gc_prologue_work() for all cms gens we are responsible for
2709 bool duringMarking = _collectorState >= Marking
2710 && _collectorState < Sweeping;
2711
2712 // The young collections clear the modified oops state, which tells if
2713 // there are any modified oops in the class. The remark phase also needs
2714 // that information. Tell the young collection to save the union of all
2715 // modified klasses.
2716 if (duringMarking) {
2717 _ct->klass_rem_set()->set_accumulate_modified_oops(true);
2718 }
2719
2720 bool registerClosure = duringMarking;
2721
2722 ModUnionClosure* muc = CollectedHeap::use_parallel_gc_threads() ?
2723 &_modUnionClosurePar
2724 : &_modUnionClosure;
2725 _cmsGen->gc_prologue_work(full, registerClosure, muc);
2726
2727 if (!full) {
2728 stats().record_gc0_begin();
2729 }
2730 }
2731
2732 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) {
2733
2734 _capacity_at_prologue = capacity();
2735 _used_at_prologue = used();
2736
2737 // Delegate to CMScollector which knows how to coordinate between
2738 // this and any other CMS generations that it is responsible for
2739 // collecting.
2740 collector()->gc_prologue(full);
2741 }
2742
2743 // This is a "private" interface for use by this generation's CMSCollector.
2744 // Not to be called directly by any other entity (for instance,
2745 // GenCollectedHeap, which calls the "public" gc_prologue method above).
2746 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full,
2747 bool registerClosure, ModUnionClosure* modUnionClosure) {
2748 assert(!incremental_collection_failed(), "Shouldn't be set yet");
2749 assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL,
2750 "Should be NULL");
2751 if (registerClosure) {
2752 cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure);
2753 }
2754 cmsSpace()->gc_prologue();
2755 // Clear stat counters
2756 NOT_PRODUCT(
2757 assert(_numObjectsPromoted == 0, "check");
2758 assert(_numWordsPromoted == 0, "check");
2759 if (Verbose && PrintGC) {
2760 gclog_or_tty->print("Allocated "SIZE_FORMAT" objects, "
2761 SIZE_FORMAT" bytes concurrently",
2762 _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord));
2763 }
2764 _numObjectsAllocated = 0;
2765 _numWordsAllocated = 0;
2766 )
2767 }
2768
2769 void CMSCollector::gc_epilogue(bool full) {
2770 // The following locking discipline assumes that we are only called
2771 // when the world is stopped.
2772 assert(SafepointSynchronize::is_at_safepoint(),
2773 "world is stopped assumption");
2774
2775 // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks
2776 // if linear allocation blocks need to be appropriately marked to allow the
2777 // the blocks to be parsable. We also check here whether we need to nudge the
2778 // CMS collector thread to start a new cycle (if it's not already active).
2779 assert( Thread::current()->is_VM_thread()
2780 || ( CMSScavengeBeforeRemark
2781 && Thread::current()->is_ConcurrentGC_thread()),
2782 "Incorrect thread type for epilogue execution");
2783
2784 if (!_between_prologue_and_epilogue) {
2785 // We have already been invoked; this is a gc_epilogue delegation
2786 // from yet another CMS generation that we are responsible for, just
2787 // ignore it since all relevant work has already been done.
2788 return;
2789 }
2790 assert(haveFreelistLocks(), "must have freelist locks");
2791 assert_lock_strong(bitMapLock());
2792
2793 _ct->klass_rem_set()->set_accumulate_modified_oops(false);
2794
2795 _cmsGen->gc_epilogue_work(full);
2796
2797 if (_collectorState == AbortablePreclean || _collectorState == Precleaning) {
2798 // in case sampling was not already enabled, enable it
2799 _start_sampling = true;
2800 }
2801 // reset _eden_chunk_array so sampling starts afresh
2802 _eden_chunk_index = 0;
2803
2804 size_t cms_used = _cmsGen->cmsSpace()->used();
2805
2806 // update performance counters - this uses a special version of
2807 // update_counters() that allows the utilization to be passed as a
2808 // parameter, avoiding multiple calls to used().
2809 //
2810 _cmsGen->update_counters(cms_used);
2811
2812 if (CMSIncrementalMode) {
2813 icms_update_allocation_limits();
2814 }
2815
2816 bitMapLock()->unlock();
2817 releaseFreelistLocks();
2818
2819 if (!CleanChunkPoolAsync) {
2820 Chunk::clean_chunk_pool();
2821 }
2822
2823 set_did_compact(false);
2824 _between_prologue_and_epilogue = false; // ready for next cycle
2825 }
2826
2827 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) {
2828 collector()->gc_epilogue(full);
2829
2830 // Also reset promotion tracking in par gc thread states.
2831 if (CollectedHeap::use_parallel_gc_threads()) {
2832 for (uint i = 0; i < ParallelGCThreads; i++) {
2833 _par_gc_thread_states[i]->promo.stopTrackingPromotions(i);
2834 }
2835 }
2836 }
2837
2838 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2839 assert(!incremental_collection_failed(), "Should have been cleared");
2840 cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2841 cmsSpace()->gc_epilogue();
2842 // Print stat counters
2843 NOT_PRODUCT(
2844 assert(_numObjectsAllocated == 0, "check");
2845 assert(_numWordsAllocated == 0, "check");
2846 if (Verbose && PrintGC) {
2847 gclog_or_tty->print("Promoted "SIZE_FORMAT" objects, "
2848 SIZE_FORMAT" bytes",
2849 _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2850 }
2851 _numObjectsPromoted = 0;
2852 _numWordsPromoted = 0;
2853 )
2854
2855 if (PrintGC && Verbose) {
2856 // Call down the chain in contiguous_available needs the freelistLock
2857 // so print this out before releasing the freeListLock.
2858 gclog_or_tty->print(" Contiguous available "SIZE_FORMAT" bytes ",
2859 contiguous_available());
2860 }
2861 }
2862
2863 #ifndef PRODUCT
2864 bool CMSCollector::have_cms_token() {
2865 Thread* thr = Thread::current();
2866 if (thr->is_VM_thread()) {
2867 return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2868 } else if (thr->is_ConcurrentGC_thread()) {
2869 return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2870 } else if (thr->is_GC_task_thread()) {
2871 return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2872 ParGCRareEvent_lock->owned_by_self();
2873 }
2874 return false;
2875 }
2876 #endif
2877
2878 // Check reachability of the given heap address in CMS generation,
2879 // treating all other generations as roots.
2880 bool CMSCollector::is_cms_reachable(HeapWord* addr) {
2881 // We could "guarantee" below, rather than assert, but I'll
2882 // leave these as "asserts" so that an adventurous debugger
2883 // could try this in the product build provided some subset of
2884 // the conditions were met, provided they were interested in the
2885 // results and knew that the computation below wouldn't interfere
2886 // with other concurrent computations mutating the structures
2887 // being read or written.
2888 assert(SafepointSynchronize::is_at_safepoint(),
2889 "Else mutations in object graph will make answer suspect");
2890 assert(have_cms_token(), "Should hold cms token");
2891 assert(haveFreelistLocks(), "must hold free list locks");
2892 assert_lock_strong(bitMapLock());
2893
2894 // Clear the marking bit map array before starting, but, just
2895 // for kicks, first report if the given address is already marked
2896 gclog_or_tty->print_cr("Start: Address 0x%x is%s marked", addr,
2897 _markBitMap.isMarked(addr) ? "" : " not");
2898
2899 if (verify_after_remark()) {
2900 MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2901 bool result = verification_mark_bm()->isMarked(addr);
2902 gclog_or_tty->print_cr("TransitiveMark: Address 0x%x %s marked", addr,
2903 result ? "IS" : "is NOT");
2904 return result;
2905 } else {
2906 gclog_or_tty->print_cr("Could not compute result");
2907 return false;
2908 }
2909 }
2910
2911
2912 void
2913 CMSCollector::print_on_error(outputStream* st) {
2914 CMSCollector* collector = ConcurrentMarkSweepGeneration::_collector;
2915 if (collector != NULL) {
2916 CMSBitMap* bitmap = &collector->_markBitMap;
2917 st->print_cr("Marking Bits: (CMSBitMap*) " PTR_FORMAT, bitmap);
2918 bitmap->print_on_error(st, " Bits: ");
2919
2920 st->cr();
2921
2922 CMSBitMap* mut_bitmap = &collector->_modUnionTable;
2923 st->print_cr("Mod Union Table: (CMSBitMap*) " PTR_FORMAT, mut_bitmap);
2924 mut_bitmap->print_on_error(st, " Bits: ");
2925 }
2926 }
2927
2928 ////////////////////////////////////////////////////////
2929 // CMS Verification Support
2930 ////////////////////////////////////////////////////////
2931 // Following the remark phase, the following invariant
2932 // should hold -- each object in the CMS heap which is
2933 // marked in markBitMap() should be marked in the verification_mark_bm().
2934
2935 class VerifyMarkedClosure: public BitMapClosure {
2936 CMSBitMap* _marks;
2937 bool _failed;
2938
2939 public:
2940 VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2941
2942 bool do_bit(size_t offset) {
2943 HeapWord* addr = _marks->offsetToHeapWord(offset);
2944 if (!_marks->isMarked(addr)) {
2945 oop(addr)->print_on(gclog_or_tty);
2946 gclog_or_tty->print_cr(" ("INTPTR_FORMAT" should have been marked)", addr);
2947 _failed = true;
2948 }
2949 return true;
2950 }
2951
2952 bool failed() { return _failed; }
2953 };
2954
2955 bool CMSCollector::verify_after_remark(bool silent) {
2956 if (!silent) gclog_or_tty->print(" [Verifying CMS Marking... ");
2957 MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2958 static bool init = false;
2959
2960 assert(SafepointSynchronize::is_at_safepoint(),
2961 "Else mutations in object graph will make answer suspect");
2962 assert(have_cms_token(),
2963 "Else there may be mutual interference in use of "
2964 " verification data structures");
2965 assert(_collectorState > Marking && _collectorState <= Sweeping,
2966 "Else marking info checked here may be obsolete");
2967 assert(haveFreelistLocks(), "must hold free list locks");
2968 assert_lock_strong(bitMapLock());
2969
2970
2971 // Allocate marking bit map if not already allocated
2972 if (!init) { // first time
2973 if (!verification_mark_bm()->allocate(_span)) {
2974 return false;
2975 }
2976 init = true;
2977 }
2978
2979 assert(verification_mark_stack()->isEmpty(), "Should be empty");
2980
2981 // Turn off refs discovery -- so we will be tracing through refs.
2982 // This is as intended, because by this time
2983 // GC must already have cleared any refs that need to be cleared,
2984 // and traced those that need to be marked; moreover,
2985 // the marking done here is not going to interfere in any
2986 // way with the marking information used by GC.
2987 NoRefDiscovery no_discovery(ref_processor());
2988
2989 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
2990
2991 // Clear any marks from a previous round
2992 verification_mark_bm()->clear_all();
2993 assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
2994 verify_work_stacks_empty();
2995
2996 GenCollectedHeap* gch = GenCollectedHeap::heap();
2997 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
2998 // Update the saved marks which may affect the root scans.
2999 gch->save_marks();
3000
3001 if (CMSRemarkVerifyVariant == 1) {
3002 // In this first variant of verification, we complete
3003 // all marking, then check if the new marks-vector is
3004 // a subset of the CMS marks-vector.
3005 verify_after_remark_work_1();
3006 } else if (CMSRemarkVerifyVariant == 2) {
3007 // In this second variant of verification, we flag an error
3008 // (i.e. an object reachable in the new marks-vector not reachable
3009 // in the CMS marks-vector) immediately, also indicating the
3010 // identify of an object (A) that references the unmarked object (B) --
3011 // presumably, a mutation to A failed to be picked up by preclean/remark?
3012 verify_after_remark_work_2();
3013 } else {
3014 warning("Unrecognized value %d for CMSRemarkVerifyVariant",
3015 CMSRemarkVerifyVariant);
3016 }
3017 if (!silent) gclog_or_tty->print(" done] ");
3018 return true;
3019 }
3020
3021 void CMSCollector::verify_after_remark_work_1() {
3022 ResourceMark rm;
3023 HandleMark hm;
3024 GenCollectedHeap* gch = GenCollectedHeap::heap();
3025
3026 // Get a clear set of claim bits for the strong roots processing to work with.
3027 ClassLoaderDataGraph::clear_claimed_marks();
3028
3029 // Mark from roots one level into CMS
3030 MarkRefsIntoClosure notOlder(_span, verification_mark_bm());
3031 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3032
3033 gch->gen_process_strong_roots(_cmsGen->level(),
3034 true, // younger gens are roots
3035 true, // activate StrongRootsScope
3036 SharedHeap::ScanningOption(roots_scanning_options()),
3037 ¬Older,
3038 true, // walk code active on stacks
3039 NULL,
3040 NULL); // SSS: Provide correct closure
3041
3042 // Now mark from the roots
3043 MarkFromRootsClosure markFromRootsClosure(this, _span,
3044 verification_mark_bm(), verification_mark_stack(),
3045 false /* don't yield */, true /* verifying */);
3046 assert(_restart_addr == NULL, "Expected pre-condition");
3047 verification_mark_bm()->iterate(&markFromRootsClosure);
3048 while (_restart_addr != NULL) {
3049 // Deal with stack overflow: by restarting at the indicated
3050 // address.
3051 HeapWord* ra = _restart_addr;
3052 markFromRootsClosure.reset(ra);
3053 _restart_addr = NULL;
3054 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
3055 }
3056 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
3057 verify_work_stacks_empty();
3058
3059 // Marking completed -- now verify that each bit marked in
3060 // verification_mark_bm() is also marked in markBitMap(); flag all
3061 // errors by printing corresponding objects.
3062 VerifyMarkedClosure vcl(markBitMap());
3063 verification_mark_bm()->iterate(&vcl);
3064 if (vcl.failed()) {
3065 gclog_or_tty->print("Verification failed");
3066 Universe::heap()->print_on(gclog_or_tty);
3067 fatal("CMS: failed marking verification after remark");
3068 }
3069 }
3070
3071 class VerifyKlassOopsKlassClosure : public KlassClosure {
3072 class VerifyKlassOopsClosure : public OopClosure {
3073 CMSBitMap* _bitmap;
3074 public:
3075 VerifyKlassOopsClosure(CMSBitMap* bitmap) : _bitmap(bitmap) { }
3076 void do_oop(oop* p) { guarantee(*p == NULL || _bitmap->isMarked((HeapWord*) *p), "Should be marked"); }
3077 void do_oop(narrowOop* p) { ShouldNotReachHere(); }
3078 } _oop_closure;
3079 public:
3080 VerifyKlassOopsKlassClosure(CMSBitMap* bitmap) : _oop_closure(bitmap) {}
3081 void do_klass(Klass* k) {
3082 k->oops_do(&_oop_closure);
3083 }
3084 };
3085
3086 void CMSCollector::verify_after_remark_work_2() {
3087 ResourceMark rm;
3088 HandleMark hm;
3089 GenCollectedHeap* gch = GenCollectedHeap::heap();
3090
3091 // Get a clear set of claim bits for the strong roots processing to work with.
3092 ClassLoaderDataGraph::clear_claimed_marks();
3093
3094 // Mark from roots one level into CMS
3095 MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
3096 markBitMap());
3097 CMKlassClosure klass_closure(¬Older);
3098
3099 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3100 gch->gen_process_strong_roots(_cmsGen->level(),
3101 true, // younger gens are roots
3102 true, // activate StrongRootsScope
3103 SharedHeap::ScanningOption(roots_scanning_options()),
3104 ¬Older,
3105 true, // walk code active on stacks
3106 NULL,
3107 &klass_closure);
3108
3109 // Now mark from the roots
3110 MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
3111 verification_mark_bm(), markBitMap(), verification_mark_stack());
3112 assert(_restart_addr == NULL, "Expected pre-condition");
3113 verification_mark_bm()->iterate(&markFromRootsClosure);
3114 while (_restart_addr != NULL) {
3115 // Deal with stack overflow: by restarting at the indicated
3116 // address.
3117 HeapWord* ra = _restart_addr;
3118 markFromRootsClosure.reset(ra);
3119 _restart_addr = NULL;
3120 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
3121 }
3122 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
3123 verify_work_stacks_empty();
3124
3125 VerifyKlassOopsKlassClosure verify_klass_oops(verification_mark_bm());
3126 ClassLoaderDataGraph::classes_do(&verify_klass_oops);
3127
3128 // Marking completed -- now verify that each bit marked in
3129 // verification_mark_bm() is also marked in markBitMap(); flag all
3130 // errors by printing corresponding objects.
3131 VerifyMarkedClosure vcl(markBitMap());
3132 verification_mark_bm()->iterate(&vcl);
3133 assert(!vcl.failed(), "Else verification above should not have succeeded");
3134 }
3135
3136 void ConcurrentMarkSweepGeneration::save_marks() {
3137 // delegate to CMS space
3138 cmsSpace()->save_marks();
3139 for (uint i = 0; i < ParallelGCThreads; i++) {
3140 _par_gc_thread_states[i]->promo.startTrackingPromotions();
3141 }
3142 }
3143
3144 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
3145 return cmsSpace()->no_allocs_since_save_marks();
3146 }
3147
3148 #define CMS_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix) \
3149 \
3150 void ConcurrentMarkSweepGeneration:: \
3151 oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) { \
3152 cl->set_generation(this); \
3153 cmsSpace()->oop_since_save_marks_iterate##nv_suffix(cl); \
3154 cl->reset_generation(); \
3155 save_marks(); \
3156 }
3157
3158 ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DEFN)
3159
3160 void
3161 ConcurrentMarkSweepGeneration::younger_refs_iterate(OopsInGenClosure* cl) {
3162 cl->set_generation(this);
3163 younger_refs_in_space_iterate(_cmsSpace, cl);
3164 cl->reset_generation();
3165 }
3166
3167 void
3168 ConcurrentMarkSweepGeneration::oop_iterate(MemRegion mr, ExtendedOopClosure* cl) {
3169 if (freelistLock()->owned_by_self()) {
3170 Generation::oop_iterate(mr, cl);
3171 } else {
3172 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3173 Generation::oop_iterate(mr, cl);
3174 }
3175 }
3176
3177 void
3178 ConcurrentMarkSweepGeneration::oop_iterate(ExtendedOopClosure* cl) {
3179 if (freelistLock()->owned_by_self()) {
3180 Generation::oop_iterate(cl);
3181 } else {
3182 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3183 Generation::oop_iterate(cl);
3184 }
3185 }
3186
3187 void
3188 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
3189 if (freelistLock()->owned_by_self()) {
3190 Generation::object_iterate(cl);
3191 } else {
3192 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3193 Generation::object_iterate(cl);
3194 }
3195 }
3196
3197 void
3198 ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) {
3199 if (freelistLock()->owned_by_self()) {
3200 Generation::safe_object_iterate(cl);
3201 } else {
3202 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3203 Generation::safe_object_iterate(cl);
3204 }
3205 }
3206
3207 void
3208 ConcurrentMarkSweepGeneration::post_compact() {
3209 }
3210
3211 void
3212 ConcurrentMarkSweepGeneration::prepare_for_verify() {
3213 // Fix the linear allocation blocks to look like free blocks.
3214
3215 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
3216 // are not called when the heap is verified during universe initialization and
3217 // at vm shutdown.
3218 if (freelistLock()->owned_by_self()) {
3219 cmsSpace()->prepare_for_verify();
3220 } else {
3221 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
3222 cmsSpace()->prepare_for_verify();
3223 }
3224 }
3225
3226 void
3227 ConcurrentMarkSweepGeneration::verify() {
3228 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
3229 // are not called when the heap is verified during universe initialization and
3230 // at vm shutdown.
3231 if (freelistLock()->owned_by_self()) {
3232 cmsSpace()->verify();
3233 } else {
3234 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
3235 cmsSpace()->verify();
3236 }
3237 }
3238
3239 void CMSCollector::verify() {
3240 _cmsGen->verify();
3241 }
3242
3243 #ifndef PRODUCT
3244 bool CMSCollector::overflow_list_is_empty() const {
3245 assert(_num_par_pushes >= 0, "Inconsistency");
3246 if (_overflow_list == NULL) {
3247 assert(_num_par_pushes == 0, "Inconsistency");
3248 }
3249 return _overflow_list == NULL;
3250 }
3251
3252 // The methods verify_work_stacks_empty() and verify_overflow_empty()
3253 // merely consolidate assertion checks that appear to occur together frequently.
3254 void CMSCollector::verify_work_stacks_empty() const {
3255 assert(_markStack.isEmpty(), "Marking stack should be empty");
3256 assert(overflow_list_is_empty(), "Overflow list should be empty");
3257 }
3258
3259 void CMSCollector::verify_overflow_empty() const {
3260 assert(overflow_list_is_empty(), "Overflow list should be empty");
3261 assert(no_preserved_marks(), "No preserved marks");
3262 }
3263 #endif // PRODUCT
3264
3265 // Decide if we want to enable class unloading as part of the
3266 // ensuing concurrent GC cycle. We will collect and
3267 // unload classes if it's the case that:
3268 // (1) an explicit gc request has been made and the flag
3269 // ExplicitGCInvokesConcurrentAndUnloadsClasses is set, OR
3270 // (2) (a) class unloading is enabled at the command line, and
3271 // (b) old gen is getting really full
3272 // NOTE: Provided there is no change in the state of the heap between
3273 // calls to this method, it should have idempotent results. Moreover,
3274 // its results should be monotonically increasing (i.e. going from 0 to 1,
3275 // but not 1 to 0) between successive calls between which the heap was
3276 // not collected. For the implementation below, it must thus rely on
3277 // the property that concurrent_cycles_since_last_unload()
3278 // will not decrease unless a collection cycle happened and that
3279 // _cmsGen->is_too_full() are
3280 // themselves also monotonic in that sense. See check_monotonicity()
3281 // below.
3282 void CMSCollector::update_should_unload_classes() {
3283 _should_unload_classes = false;
3284 // Condition 1 above
3285 if (_full_gc_requested && ExplicitGCInvokesConcurrentAndUnloadsClasses) {
3286 _should_unload_classes = true;
3287 } else if (CMSClassUnloadingEnabled) { // Condition 2.a above
3288 // Disjuncts 2.b.(i,ii,iii) above
3289 _should_unload_classes = (concurrent_cycles_since_last_unload() >=
3290 CMSClassUnloadingMaxInterval)
3291 || _cmsGen->is_too_full();
3292 }
3293 }
3294
3295 bool ConcurrentMarkSweepGeneration::is_too_full() const {
3296 bool res = should_concurrent_collect();
3297 res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
3298 return res;
3299 }
3300
3301 void CMSCollector::setup_cms_unloading_and_verification_state() {
3302 const bool should_verify = VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
3303 || VerifyBeforeExit;
3304 const int rso = SharedHeap::SO_Strings | SharedHeap::SO_AllCodeCache;
3305
3306 // We set the proper root for this CMS cycle here.
3307 if (should_unload_classes()) { // Should unload classes this cycle
3308 remove_root_scanning_option(SharedHeap::SO_AllClasses);
3309 add_root_scanning_option(SharedHeap::SO_SystemClasses);
3310 remove_root_scanning_option(rso); // Shrink the root set appropriately
3311 set_verifying(should_verify); // Set verification state for this cycle
3312 return; // Nothing else needs to be done at this time
3313 }
3314
3315 // Not unloading classes this cycle
3316 assert(!should_unload_classes(), "Inconsitency!");
3317 remove_root_scanning_option(SharedHeap::SO_SystemClasses);
3318 add_root_scanning_option(SharedHeap::SO_AllClasses);
3319
3320 if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
3321 // Include symbols, strings and code cache elements to prevent their resurrection.
3322 add_root_scanning_option(rso);
3323 set_verifying(true);
3324 } else if (verifying() && !should_verify) {
3325 // We were verifying, but some verification flags got disabled.
3326 set_verifying(false);
3327 // Exclude symbols, strings and code cache elements from root scanning to
3328 // reduce IM and RM pauses.
3329 remove_root_scanning_option(rso);
3330 }
3331 }
3332
3333
3334 #ifndef PRODUCT
3335 HeapWord* CMSCollector::block_start(const void* p) const {
3336 const HeapWord* addr = (HeapWord*)p;
3337 if (_span.contains(p)) {
3338 if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
3339 return _cmsGen->cmsSpace()->block_start(p);
3340 }
3341 }
3342 return NULL;
3343 }
3344 #endif
3345
3346 HeapWord*
3347 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
3348 bool tlab,
3349 bool parallel) {
3350 CMSSynchronousYieldRequest yr;
3351 assert(!tlab, "Can't deal with TLAB allocation");
3352 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3353 expand(word_size*HeapWordSize, MinHeapDeltaBytes,
3354 CMSExpansionCause::_satisfy_allocation);
3355 if (GCExpandToAllocateDelayMillis > 0) {
3356 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3357 }
3358 return have_lock_and_allocate(word_size, tlab);
3359 }
3360
3361 // YSR: All of this generation expansion/shrinking stuff is an exact copy of
3362 // OneContigSpaceCardGeneration, which makes me wonder if we should move this
3363 // to CardGeneration and share it...
3364 bool ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes) {
3365 return CardGeneration::expand(bytes, expand_bytes);
3366 }
3367
3368 void ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes,
3369 CMSExpansionCause::Cause cause)
3370 {
3371
3372 bool success = expand(bytes, expand_bytes);
3373
3374 // remember why we expanded; this information is used
3375 // by shouldConcurrentCollect() when making decisions on whether to start
3376 // a new CMS cycle.
3377 if (success) {
3378 set_expansion_cause(cause);
3379 if (PrintGCDetails && Verbose) {
3380 gclog_or_tty->print_cr("Expanded CMS gen for %s",
3381 CMSExpansionCause::to_string(cause));
3382 }
3383 }
3384 }
3385
3386 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
3387 HeapWord* res = NULL;
3388 MutexLocker x(ParGCRareEvent_lock);
3389 while (true) {
3390 // Expansion by some other thread might make alloc OK now:
3391 res = ps->lab.alloc(word_sz);
3392 if (res != NULL) return res;
3393 // If there's not enough expansion space available, give up.
3394 if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
3395 return NULL;
3396 }
3397 // Otherwise, we try expansion.
3398 expand(word_sz*HeapWordSize, MinHeapDeltaBytes,
3399 CMSExpansionCause::_allocate_par_lab);
3400 // Now go around the loop and try alloc again;
3401 // A competing par_promote might beat us to the expansion space,
3402 // so we may go around the loop again if promotion fails again.
3403 if (GCExpandToAllocateDelayMillis > 0) {
3404 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3405 }
3406 }
3407 }
3408
3409
3410 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
3411 PromotionInfo* promo) {
3412 MutexLocker x(ParGCRareEvent_lock);
3413 size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
3414 while (true) {
3415 // Expansion by some other thread might make alloc OK now:
3416 if (promo->ensure_spooling_space()) {
3417 assert(promo->has_spooling_space(),
3418 "Post-condition of successful ensure_spooling_space()");
3419 return true;
3420 }
3421 // If there's not enough expansion space available, give up.
3422 if (_virtual_space.uncommitted_size() < refill_size_bytes) {
3423 return false;
3424 }
3425 // Otherwise, we try expansion.
3426 expand(refill_size_bytes, MinHeapDeltaBytes,
3427 CMSExpansionCause::_allocate_par_spooling_space);
3428 // Now go around the loop and try alloc again;
3429 // A competing allocation might beat us to the expansion space,
3430 // so we may go around the loop again if allocation fails again.
3431 if (GCExpandToAllocateDelayMillis > 0) {
3432 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3433 }
3434 }
3435 }
3436
3437
3438 void ConcurrentMarkSweepGeneration::shrink_by(size_t bytes) {
3439 assert_locked_or_safepoint(ExpandHeap_lock);
3440 // Shrink committed space
3441 _virtual_space.shrink_by(bytes);
3442 // Shrink space; this also shrinks the space's BOT
3443 _cmsSpace->set_end((HeapWord*) _virtual_space.high());
3444 size_t new_word_size = heap_word_size(_cmsSpace->capacity());
3445 // Shrink the shared block offset array
3446 _bts->resize(new_word_size);
3447 MemRegion mr(_cmsSpace->bottom(), new_word_size);
3448 // Shrink the card table
3449 Universe::heap()->barrier_set()->resize_covered_region(mr);
3450
3451 if (Verbose && PrintGC) {
3452 size_t new_mem_size = _virtual_space.committed_size();
3453 size_t old_mem_size = new_mem_size + bytes;
3454 gclog_or_tty->print_cr("Shrinking %s from " SIZE_FORMAT "K to " SIZE_FORMAT "K",
3455 name(), old_mem_size/K, new_mem_size/K);
3456 }
3457 }
3458
3459 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
3460 assert_locked_or_safepoint(Heap_lock);
3461 size_t size = ReservedSpace::page_align_size_down(bytes);
3462 // Only shrink if a compaction was done so that all the free space
3463 // in the generation is in a contiguous block at the end.
3464 if (size > 0 && did_compact()) {
3465 shrink_by(size);
3466 }
3467 }
3468
3469 bool ConcurrentMarkSweepGeneration::grow_by(size_t bytes) {
3470 assert_locked_or_safepoint(Heap_lock);
3471 bool result = _virtual_space.expand_by(bytes);
3472 if (result) {
3473 size_t new_word_size =
3474 heap_word_size(_virtual_space.committed_size());
3475 MemRegion mr(_cmsSpace->bottom(), new_word_size);
3476 _bts->resize(new_word_size); // resize the block offset shared array
3477 Universe::heap()->barrier_set()->resize_covered_region(mr);
3478 // Hmmmm... why doesn't CFLS::set_end verify locking?
3479 // This is quite ugly; FIX ME XXX
3480 _cmsSpace->assert_locked(freelistLock());
3481 _cmsSpace->set_end((HeapWord*)_virtual_space.high());
3482
3483 // update the space and generation capacity counters
3484 if (UsePerfData) {
3485 _space_counters->update_capacity();
3486 _gen_counters->update_all();
3487 }
3488
3489 if (Verbose && PrintGC) {
3490 size_t new_mem_size = _virtual_space.committed_size();
3491 size_t old_mem_size = new_mem_size - bytes;
3492 gclog_or_tty->print_cr("Expanding %s from " SIZE_FORMAT "K by " SIZE_FORMAT "K to " SIZE_FORMAT "K",
3493 name(), old_mem_size/K, bytes/K, new_mem_size/K);
3494 }
3495 }
3496 return result;
3497 }
3498
3499 bool ConcurrentMarkSweepGeneration::grow_to_reserved() {
3500 assert_locked_or_safepoint(Heap_lock);
3501 bool success = true;
3502 const size_t remaining_bytes = _virtual_space.uncommitted_size();
3503 if (remaining_bytes > 0) {
3504 success = grow_by(remaining_bytes);
3505 DEBUG_ONLY(if (!success) warning("grow to reserved failed");)
3506 }
3507 return success;
3508 }
3509
3510 void ConcurrentMarkSweepGeneration::shrink_free_list_by(size_t bytes) {
3511 assert_locked_or_safepoint(Heap_lock);
3512 assert_lock_strong(freelistLock());
3513 if (PrintGCDetails && Verbose) {
3514 warning("Shrinking of CMS not yet implemented");
3515 }
3516 return;
3517 }
3518
3519
3520 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
3521 // phases.
3522 class CMSPhaseAccounting: public StackObj {
3523 public:
3524 CMSPhaseAccounting(CMSCollector *collector,
3525 const char *phase,
3526 bool print_cr = true);
3527 ~CMSPhaseAccounting();
3528
3529 private:
3530 CMSCollector *_collector;
3531 const char *_phase;
3532 elapsedTimer _wallclock;
3533 bool _print_cr;
3534
3535 public:
3536 // Not MT-safe; so do not pass around these StackObj's
3537 // where they may be accessed by other threads.
3538 jlong wallclock_millis() {
3539 assert(_wallclock.is_active(), "Wall clock should not stop");
3540 _wallclock.stop(); // to record time
3541 jlong ret = _wallclock.milliseconds();
3542 _wallclock.start(); // restart
3543 return ret;
3544 }
3545 };
3546
3547 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
3548 const char *phase,
3549 bool print_cr) :
3550 _collector(collector), _phase(phase), _print_cr(print_cr) {
3551
3552 if (PrintCMSStatistics != 0) {
3553 _collector->resetYields();
3554 }
3555 if (PrintGCDetails) {
3556 gclog_or_tty->date_stamp(PrintGCDateStamps);
3557 gclog_or_tty->stamp(PrintGCTimeStamps);
3558 gclog_or_tty->print_cr("[%s-concurrent-%s-start]",
3559 _collector->cmsGen()->short_name(), _phase);
3560 }
3561 _collector->resetTimer();
3562 _wallclock.start();
3563 _collector->startTimer();
3564 }
3565
3566 CMSPhaseAccounting::~CMSPhaseAccounting() {
3567 assert(_wallclock.is_active(), "Wall clock should not have stopped");
3568 _collector->stopTimer();
3569 _wallclock.stop();
3570 if (PrintGCDetails) {
3571 gclog_or_tty->date_stamp(PrintGCDateStamps);
3572 gclog_or_tty->stamp(PrintGCTimeStamps);
3573 gclog_or_tty->print("[%s-concurrent-%s: %3.3f/%3.3f secs]",
3574 _collector->cmsGen()->short_name(),
3575 _phase, _collector->timerValue(), _wallclock.seconds());
3576 if (_print_cr) {
3577 gclog_or_tty->print_cr("");
3578 }
3579 if (PrintCMSStatistics != 0) {
3580 gclog_or_tty->print_cr(" (CMS-concurrent-%s yielded %d times)", _phase,
3581 _collector->yields());
3582 }
3583 }
3584 }
3585
3586 // CMS work
3587
3588 // The common parts of CMSParInitialMarkTask and CMSParRemarkTask.
3589 class CMSParMarkTask : public AbstractGangTask {
3590 protected:
3591 CMSCollector* _collector;
3592 int _n_workers;
3593 CMSParMarkTask(const char* name, CMSCollector* collector, int n_workers) :
3594 AbstractGangTask(name),
3595 _collector(collector),
3596 _n_workers(n_workers) {}
3597 // Work method in support of parallel rescan ... of young gen spaces
3598 void do_young_space_rescan(uint worker_id, OopsInGenClosure* cl,
3599 ContiguousSpace* space,
3600 HeapWord** chunk_array, size_t chunk_top);
3601 void work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl);
3602 };
3603
3604 // Parallel initial mark task
3605 class CMSParInitialMarkTask: public CMSParMarkTask {
3606 public:
3607 CMSParInitialMarkTask(CMSCollector* collector, int n_workers) :
3608 CMSParMarkTask("Scan roots and young gen for initial mark in parallel",
3609 collector, n_workers) {}
3610 void work(uint worker_id);
3611 };
3612
3613 // Checkpoint the roots into this generation from outside
3614 // this generation. [Note this initial checkpoint need only
3615 // be approximate -- we'll do a catch up phase subsequently.]
3616 void CMSCollector::checkpointRootsInitial(bool asynch) {
3617 assert(_collectorState == InitialMarking, "Wrong collector state");
3618 check_correct_thread_executing();
3619 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
3620
3621 save_heap_summary();
3622 report_heap_summary(GCWhen::BeforeGC);
3623
3624 ReferenceProcessor* rp = ref_processor();
3625 SpecializationStats::clear();
3626 assert(_restart_addr == NULL, "Control point invariant");
3627 if (asynch) {
3628 // acquire locks for subsequent manipulations
3629 MutexLockerEx x(bitMapLock(),
3630 Mutex::_no_safepoint_check_flag);
3631 checkpointRootsInitialWork(asynch);
3632 // enable ("weak") refs discovery
3633 rp->enable_discovery(true /*verify_disabled*/, true /*check_no_refs*/);
3634 _collectorState = Marking;
3635 } else {
3636 // (Weak) Refs discovery: this is controlled from genCollectedHeap::do_collection
3637 // which recognizes if we are a CMS generation, and doesn't try to turn on
3638 // discovery; verify that they aren't meddling.
3639 assert(!rp->discovery_is_atomic(),
3640 "incorrect setting of discovery predicate");
3641 assert(!rp->discovery_enabled(), "genCollectedHeap shouldn't control "
3642 "ref discovery for this generation kind");
3643 // already have locks
3644 checkpointRootsInitialWork(asynch);
3645 // now enable ("weak") refs discovery
3646 rp->enable_discovery(true /*verify_disabled*/, false /*verify_no_refs*/);
3647 _collectorState = Marking;
3648 }
3649 SpecializationStats::print();
3650 }
3651
3652 void CMSCollector::checkpointRootsInitialWork(bool asynch) {
3653 assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
3654 assert(_collectorState == InitialMarking, "just checking");
3655
3656 // If there has not been a GC[n-1] since last GC[n] cycle completed,
3657 // precede our marking with a collection of all
3658 // younger generations to keep floating garbage to a minimum.
3659 // XXX: we won't do this for now -- it's an optimization to be done later.
3660
3661 // already have locks
3662 assert_lock_strong(bitMapLock());
3663 assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
3664
3665 // Setup the verification and class unloading state for this
3666 // CMS collection cycle.
3667 setup_cms_unloading_and_verification_state();
3668
3669 NOT_PRODUCT(GCTraceTime t("\ncheckpointRootsInitialWork",
3670 PrintGCDetails && Verbose, true, _gc_timer_cm);)
3671 if (UseAdaptiveSizePolicy) {
3672 size_policy()->checkpoint_roots_initial_begin();
3673 }
3674
3675 // Reset all the PLAB chunk arrays if necessary.
3676 if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
3677 reset_survivor_plab_arrays();
3678 }
3679
3680 ResourceMark rm;
3681 HandleMark hm;
3682
3683 FalseClosure falseClosure;
3684 // In the case of a synchronous collection, we will elide the
3685 // remark step, so it's important to catch all the nmethod oops
3686 // in this step.
3687 // The final 'true' flag to gen_process_strong_roots will ensure this.
3688 // If 'async' is true, we can relax the nmethod tracing.
3689 MarkRefsIntoClosure notOlder(_span, &_markBitMap);
3690 GenCollectedHeap* gch = GenCollectedHeap::heap();
3691
3692 verify_work_stacks_empty();
3693 verify_overflow_empty();
3694
3695 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
3696 // Update the saved marks which may affect the root scans.
3697 gch->save_marks();
3698
3699 // weak reference processing has not started yet.
3700 ref_processor()->set_enqueuing_is_done(false);
3701
3702 // Need to remember all newly created CLDs,
3703 // so that we can guarantee that the remark finds them.
3704 ClassLoaderDataGraph::remember_new_clds(true);
3705
3706 // Whenever a CLD is found, it will be claimed before proceeding to mark
3707 // the klasses. The claimed marks need to be cleared before marking starts.
3708 ClassLoaderDataGraph::clear_claimed_marks();
3709
3710 if (CMSPrintEdenSurvivorChunks) {
3711 print_eden_and_survivor_chunk_arrays();
3712 }
3713
3714 {
3715 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
3716 if (CMSParallelInitialMarkEnabled && CollectedHeap::use_parallel_gc_threads()) {
3717 // The parallel version.
3718 FlexibleWorkGang* workers = gch->workers();
3719 assert(workers != NULL, "Need parallel worker threads.");
3720 int n_workers = workers->active_workers();
3721 CMSParInitialMarkTask tsk(this, n_workers);
3722 gch->set_par_threads(n_workers);
3723 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
3724 if (n_workers > 1) {
3725 GenCollectedHeap::StrongRootsScope srs(gch);
3726 workers->run_task(&tsk);
3727 } else {
3728 GenCollectedHeap::StrongRootsScope srs(gch);
3729 tsk.work(0);
3730 }
3731 gch->set_par_threads(0);
3732 } else {
3733 // The serial version.
3734 CMKlassClosure klass_closure(¬Older);
3735 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3736 gch->gen_process_strong_roots(_cmsGen->level(),
3737 true, // younger gens are roots
3738 true, // activate StrongRootsScope
3739 SharedHeap::ScanningOption(roots_scanning_options()),
3740 ¬Older,
3741 true, // walk all of code cache if (so & SO_AllCodeCache)
3742 NULL,
3743 &klass_closure);
3744 }
3745 }
3746
3747 // Clear mod-union table; it will be dirtied in the prologue of
3748 // CMS generation per each younger generation collection.
3749
3750 assert(_modUnionTable.isAllClear(),
3751 "Was cleared in most recent final checkpoint phase"
3752 " or no bits are set in the gc_prologue before the start of the next "
3753 "subsequent marking phase.");
3754
3755 assert(_ct->klass_rem_set()->mod_union_is_clear(), "Must be");
3756
3757 // Save the end of the used_region of the constituent generations
3758 // to be used to limit the extent of sweep in each generation.
3759 save_sweep_limits();
3760 if (UseAdaptiveSizePolicy) {
3761 size_policy()->checkpoint_roots_initial_end(gch->gc_cause());
3762 }
3763 verify_overflow_empty();
3764 }
3765
3766 bool CMSCollector::markFromRoots(bool asynch) {
3767 // we might be tempted to assert that:
3768 // assert(asynch == !SafepointSynchronize::is_at_safepoint(),
3769 // "inconsistent argument?");
3770 // However that wouldn't be right, because it's possible that
3771 // a safepoint is indeed in progress as a younger generation
3772 // stop-the-world GC happens even as we mark in this generation.
3773 assert(_collectorState == Marking, "inconsistent state?");
3774 check_correct_thread_executing();
3775 verify_overflow_empty();
3776
3777 bool res;
3778 if (asynch) {
3779
3780 // Start the timers for adaptive size policy for the concurrent phases
3781 // Do it here so that the foreground MS can use the concurrent
3782 // timer since a foreground MS might has the sweep done concurrently
3783 // or STW.
3784 if (UseAdaptiveSizePolicy) {
3785 size_policy()->concurrent_marking_begin();
3786 }
3787
3788 // Weak ref discovery note: We may be discovering weak
3789 // refs in this generation concurrent (but interleaved) with
3790 // weak ref discovery by a younger generation collector.
3791
3792 CMSTokenSyncWithLocks ts(true, bitMapLock());
3793 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3794 CMSPhaseAccounting pa(this, "mark", !PrintGCDetails);
3795 res = markFromRootsWork(asynch);
3796 if (res) {
3797 _collectorState = Precleaning;
3798 } else { // We failed and a foreground collection wants to take over
3799 assert(_foregroundGCIsActive, "internal state inconsistency");
3800 assert(_restart_addr == NULL, "foreground will restart from scratch");
3801 if (PrintGCDetails) {
3802 gclog_or_tty->print_cr("bailing out to foreground collection");
3803 }
3804 }
3805 if (UseAdaptiveSizePolicy) {
3806 size_policy()->concurrent_marking_end();
3807 }
3808 } else {
3809 assert(SafepointSynchronize::is_at_safepoint(),
3810 "inconsistent with asynch == false");
3811 if (UseAdaptiveSizePolicy) {
3812 size_policy()->ms_collection_marking_begin();
3813 }
3814 // already have locks
3815 res = markFromRootsWork(asynch);
3816 _collectorState = FinalMarking;
3817 if (UseAdaptiveSizePolicy) {
3818 GenCollectedHeap* gch = GenCollectedHeap::heap();
3819 size_policy()->ms_collection_marking_end(gch->gc_cause());
3820 }
3821 }
3822 verify_overflow_empty();
3823 return res;
3824 }
3825
3826 bool CMSCollector::markFromRootsWork(bool asynch) {
3827 // iterate over marked bits in bit map, doing a full scan and mark
3828 // from these roots using the following algorithm:
3829 // . if oop is to the right of the current scan pointer,
3830 // mark corresponding bit (we'll process it later)
3831 // . else (oop is to left of current scan pointer)
3832 // push oop on marking stack
3833 // . drain the marking stack
3834
3835 // Note that when we do a marking step we need to hold the
3836 // bit map lock -- recall that direct allocation (by mutators)
3837 // and promotion (by younger generation collectors) is also
3838 // marking the bit map. [the so-called allocate live policy.]
3839 // Because the implementation of bit map marking is not
3840 // robust wrt simultaneous marking of bits in the same word,
3841 // we need to make sure that there is no such interference
3842 // between concurrent such updates.
3843
3844 // already have locks
3845 assert_lock_strong(bitMapLock());
3846
3847 verify_work_stacks_empty();
3848 verify_overflow_empty();
3849 bool result = false;
3850 if (CMSConcurrentMTEnabled && ConcGCThreads > 0) {
3851 result = do_marking_mt(asynch);
3852 } else {
3853 result = do_marking_st(asynch);
3854 }
3855 return result;
3856 }
3857
3858 // Forward decl
3859 class CMSConcMarkingTask;
3860
3861 class CMSConcMarkingTerminator: public ParallelTaskTerminator {
3862 CMSCollector* _collector;
3863 CMSConcMarkingTask* _task;
3864 public:
3865 virtual void yield();
3866
3867 // "n_threads" is the number of threads to be terminated.
3868 // "queue_set" is a set of work queues of other threads.
3869 // "collector" is the CMS collector associated with this task terminator.
3870 // "yield" indicates whether we need the gang as a whole to yield.
3871 CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
3872 ParallelTaskTerminator(n_threads, queue_set),
3873 _collector(collector) { }
3874
3875 void set_task(CMSConcMarkingTask* task) {
3876 _task = task;
3877 }
3878 };
3879
3880 class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator {
3881 CMSConcMarkingTask* _task;
3882 public:
3883 bool should_exit_termination();
3884 void set_task(CMSConcMarkingTask* task) {
3885 _task = task;
3886 }
3887 };
3888
3889 // MT Concurrent Marking Task
3890 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3891 CMSCollector* _collector;
3892 int _n_workers; // requested/desired # workers
3893 bool _asynch;
3894 bool _result;
3895 CompactibleFreeListSpace* _cms_space;
3896 char _pad_front[64]; // padding to ...
3897 HeapWord* _global_finger; // ... avoid sharing cache line
3898 char _pad_back[64];
3899 HeapWord* _restart_addr;
3900
3901 // Exposed here for yielding support
3902 Mutex* const _bit_map_lock;
3903
3904 // The per thread work queues, available here for stealing
3905 OopTaskQueueSet* _task_queues;
3906
3907 // Termination (and yielding) support
3908 CMSConcMarkingTerminator _term;
3909 CMSConcMarkingTerminatorTerminator _term_term;
3910
3911 public:
3912 CMSConcMarkingTask(CMSCollector* collector,
3913 CompactibleFreeListSpace* cms_space,
3914 bool asynch,
3915 YieldingFlexibleWorkGang* workers,
3916 OopTaskQueueSet* task_queues):
3917 YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3918 _collector(collector),
3919 _cms_space(cms_space),
3920 _asynch(asynch), _n_workers(0), _result(true),
3921 _task_queues(task_queues),
3922 _term(_n_workers, task_queues, _collector),
3923 _bit_map_lock(collector->bitMapLock())
3924 {
3925 _requested_size = _n_workers;
3926 _term.set_task(this);
3927 _term_term.set_task(this);
3928 _restart_addr = _global_finger = _cms_space->bottom();
3929 }
3930
3931
3932 OopTaskQueueSet* task_queues() { return _task_queues; }
3933
3934 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3935
3936 HeapWord** global_finger_addr() { return &_global_finger; }
3937
3938 CMSConcMarkingTerminator* terminator() { return &_term; }
3939
3940 virtual void set_for_termination(int active_workers) {
3941 terminator()->reset_for_reuse(active_workers);
3942 }
3943
3944 void work(uint worker_id);
3945 bool should_yield() {
3946 return ConcurrentMarkSweepThread::should_yield()
3947 && !_collector->foregroundGCIsActive()
3948 && _asynch;
3949 }
3950
3951 virtual void coordinator_yield(); // stuff done by coordinator
3952 bool result() { return _result; }
3953
3954 void reset(HeapWord* ra) {
3955 assert(_global_finger >= _cms_space->end(), "Postcondition of ::work(i)");
3956 _restart_addr = _global_finger = ra;
3957 _term.reset_for_reuse();
3958 }
3959
3960 static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3961 OopTaskQueue* work_q);
3962
3963 private:
3964 void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3965 void do_work_steal(int i);
3966 void bump_global_finger(HeapWord* f);
3967 };
3968
3969 bool CMSConcMarkingTerminatorTerminator::should_exit_termination() {
3970 assert(_task != NULL, "Error");
3971 return _task->yielding();
3972 // Note that we do not need the disjunct || _task->should_yield() above
3973 // because we want terminating threads to yield only if the task
3974 // is already in the midst of yielding, which happens only after at least one
3975 // thread has yielded.
3976 }
3977
3978 void CMSConcMarkingTerminator::yield() {
3979 if (_task->should_yield()) {
3980 _task->yield();
3981 } else {
3982 ParallelTaskTerminator::yield();
3983 }
3984 }
3985
3986 ////////////////////////////////////////////////////////////////
3987 // Concurrent Marking Algorithm Sketch
3988 ////////////////////////////////////////////////////////////////
3989 // Until all tasks exhausted (both spaces):
3990 // -- claim next available chunk
3991 // -- bump global finger via CAS
3992 // -- find first object that starts in this chunk
3993 // and start scanning bitmap from that position
3994 // -- scan marked objects for oops
3995 // -- CAS-mark target, and if successful:
3996 // . if target oop is above global finger (volatile read)
3997 // nothing to do
3998 // . if target oop is in chunk and above local finger
3999 // then nothing to do
4000 // . else push on work-queue
4001 // -- Deal with possible overflow issues:
4002 // . local work-queue overflow causes stuff to be pushed on
4003 // global (common) overflow queue
4004 // . always first empty local work queue
4005 // . then get a batch of oops from global work queue if any
4006 // . then do work stealing
4007 // -- When all tasks claimed (both spaces)
4008 // and local work queue empty,
4009 // then in a loop do:
4010 // . check global overflow stack; steal a batch of oops and trace
4011 // . try to steal from other threads oif GOS is empty
4012 // . if neither is available, offer termination
4013 // -- Terminate and return result
4014 //
4015 void CMSConcMarkingTask::work(uint worker_id) {
4016 elapsedTimer _timer;
4017 ResourceMark rm;
4018 HandleMark hm;
4019
4020 DEBUG_ONLY(_collector->verify_overflow_empty();)
4021
4022 // Before we begin work, our work queue should be empty
4023 assert(work_queue(worker_id)->size() == 0, "Expected to be empty");
4024 // Scan the bitmap covering _cms_space, tracing through grey objects.
4025 _timer.start();
4026 do_scan_and_mark(worker_id, _cms_space);
4027 _timer.stop();
4028 if (PrintCMSStatistics != 0) {
4029 gclog_or_tty->print_cr("Finished cms space scanning in %dth thread: %3.3f sec",
4030 worker_id, _timer.seconds());
4031 // XXX: need xxx/xxx type of notation, two timers
4032 }
4033
4034 // ... do work stealing
4035 _timer.reset();
4036 _timer.start();
4037 do_work_steal(worker_id);
4038 _timer.stop();
4039 if (PrintCMSStatistics != 0) {
4040 gclog_or_tty->print_cr("Finished work stealing in %dth thread: %3.3f sec",
4041 worker_id, _timer.seconds());
4042 // XXX: need xxx/xxx type of notation, two timers
4043 }
4044 assert(_collector->_markStack.isEmpty(), "Should have been emptied");
4045 assert(work_queue(worker_id)->size() == 0, "Should have been emptied");
4046 // Note that under the current task protocol, the
4047 // following assertion is true even of the spaces
4048 // expanded since the completion of the concurrent
4049 // marking. XXX This will likely change under a strict
4050 // ABORT semantics.
4051 // After perm removal the comparison was changed to
4052 // greater than or equal to from strictly greater than.
4053 // Before perm removal the highest address sweep would
4054 // have been at the end of perm gen but now is at the
4055 // end of the tenured gen.
4056 assert(_global_finger >= _cms_space->end(),
4057 "All tasks have been completed");
4058 DEBUG_ONLY(_collector->verify_overflow_empty();)
4059 }
4060
4061 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
4062 HeapWord* read = _global_finger;
4063 HeapWord* cur = read;
4064 while (f > read) {
4065 cur = read;
4066 read = (HeapWord*) Atomic::cmpxchg_ptr(f, &_global_finger, cur);
4067 if (cur == read) {
4068 // our cas succeeded
4069 assert(_global_finger >= f, "protocol consistency");
4070 break;
4071 }
4072 }
4073 }
4074
4075 // This is really inefficient, and should be redone by
4076 // using (not yet available) block-read and -write interfaces to the
4077 // stack and the work_queue. XXX FIX ME !!!
4078 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
4079 OopTaskQueue* work_q) {
4080 // Fast lock-free check
4081 if (ovflw_stk->length() == 0) {
4082 return false;
4083 }
4084 assert(work_q->size() == 0, "Shouldn't steal");
4085 MutexLockerEx ml(ovflw_stk->par_lock(),
4086 Mutex::_no_safepoint_check_flag);
4087 // Grab up to 1/4 the size of the work queue
4088 size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
4089 (size_t)ParGCDesiredObjsFromOverflowList);
4090 num = MIN2(num, ovflw_stk->length());
4091 for (int i = (int) num; i > 0; i--) {
4092 oop cur = ovflw_stk->pop();
4093 assert(cur != NULL, "Counted wrong?");
4094 work_q->push(cur);
4095 }
4096 return num > 0;
4097 }
4098
4099 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
4100 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
4101 int n_tasks = pst->n_tasks();
4102 // We allow that there may be no tasks to do here because
4103 // we are restarting after a stack overflow.
4104 assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
4105 uint nth_task = 0;
4106
4107 HeapWord* aligned_start = sp->bottom();
4108 if (sp->used_region().contains(_restart_addr)) {
4109 // Align down to a card boundary for the start of 0th task
4110 // for this space.
4111 aligned_start =
4112 (HeapWord*)align_size_down((uintptr_t)_restart_addr,
4113 CardTableModRefBS::card_size);
4114 }
4115
4116 size_t chunk_size = sp->marking_task_size();
4117 while (!pst->is_task_claimed(/* reference */ nth_task)) {
4118 // Having claimed the nth task in this space,
4119 // compute the chunk that it corresponds to:
4120 MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
4121 aligned_start + (nth_task+1)*chunk_size);
4122 // Try and bump the global finger via a CAS;
4123 // note that we need to do the global finger bump
4124 // _before_ taking the intersection below, because
4125 // the task corresponding to that region will be
4126 // deemed done even if the used_region() expands
4127 // because of allocation -- as it almost certainly will
4128 // during start-up while the threads yield in the
4129 // closure below.
4130 HeapWord* finger = span.end();
4131 bump_global_finger(finger); // atomically
4132 // There are null tasks here corresponding to chunks
4133 // beyond the "top" address of the space.
4134 span = span.intersection(sp->used_region());
4135 if (!span.is_empty()) { // Non-null task
4136 HeapWord* prev_obj;
4137 assert(!span.contains(_restart_addr) || nth_task == 0,
4138 "Inconsistency");
4139 if (nth_task == 0) {
4140 // For the 0th task, we'll not need to compute a block_start.
4141 if (span.contains(_restart_addr)) {
4142 // In the case of a restart because of stack overflow,
4143 // we might additionally skip a chunk prefix.
4144 prev_obj = _restart_addr;
4145 } else {
4146 prev_obj = span.start();
4147 }
4148 } else {
4149 // We want to skip the first object because
4150 // the protocol is to scan any object in its entirety
4151 // that _starts_ in this span; a fortiori, any
4152 // object starting in an earlier span is scanned
4153 // as part of an earlier claimed task.
4154 // Below we use the "careful" version of block_start
4155 // so we do not try to navigate uninitialized objects.
4156 prev_obj = sp->block_start_careful(span.start());
4157 // Below we use a variant of block_size that uses the
4158 // Printezis bits to avoid waiting for allocated
4159 // objects to become initialized/parsable.
4160 while (prev_obj < span.start()) {
4161 size_t sz = sp->block_size_no_stall(prev_obj, _collector);
4162 if (sz > 0) {
4163 prev_obj += sz;
4164 } else {
4165 // In this case we may end up doing a bit of redundant
4166 // scanning, but that appears unavoidable, short of
4167 // locking the free list locks; see bug 6324141.
4168 break;
4169 }
4170 }
4171 }
4172 if (prev_obj < span.end()) {
4173 MemRegion my_span = MemRegion(prev_obj, span.end());
4174 // Do the marking work within a non-empty span --
4175 // the last argument to the constructor indicates whether the
4176 // iteration should be incremental with periodic yields.
4177 Par_MarkFromRootsClosure cl(this, _collector, my_span,
4178 &_collector->_markBitMap,
4179 work_queue(i),
4180 &_collector->_markStack,
4181 _asynch);
4182 _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
4183 } // else nothing to do for this task
4184 } // else nothing to do for this task
4185 }
4186 // We'd be tempted to assert here that since there are no
4187 // more tasks left to claim in this space, the global_finger
4188 // must exceed space->top() and a fortiori space->end(). However,
4189 // that would not quite be correct because the bumping of
4190 // global_finger occurs strictly after the claiming of a task,
4191 // so by the time we reach here the global finger may not yet
4192 // have been bumped up by the thread that claimed the last
4193 // task.
4194 pst->all_tasks_completed();
4195 }
4196
4197 class Par_ConcMarkingClosure: public CMSOopClosure {
4198 private:
4199 CMSCollector* _collector;
4200 CMSConcMarkingTask* _task;
4201 MemRegion _span;
4202 CMSBitMap* _bit_map;
4203 CMSMarkStack* _overflow_stack;
4204 OopTaskQueue* _work_queue;
4205 protected:
4206 DO_OOP_WORK_DEFN
4207 public:
4208 Par_ConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue,
4209 CMSBitMap* bit_map, CMSMarkStack* overflow_stack):
4210 CMSOopClosure(collector->ref_processor()),
4211 _collector(collector),
4212 _task(task),
4213 _span(collector->_span),
4214 _work_queue(work_queue),
4215 _bit_map(bit_map),
4216 _overflow_stack(overflow_stack)
4217 { }
4218 virtual void do_oop(oop* p);
4219 virtual void do_oop(narrowOop* p);
4220
4221 void trim_queue(size_t max);
4222 void handle_stack_overflow(HeapWord* lost);
4223 void do_yield_check() {
4224 if (_task->should_yield()) {
4225 _task->yield();
4226 }
4227 }
4228 };
4229
4230 // Grey object scanning during work stealing phase --
4231 // the salient assumption here is that any references
4232 // that are in these stolen objects being scanned must
4233 // already have been initialized (else they would not have
4234 // been published), so we do not need to check for
4235 // uninitialized objects before pushing here.
4236 void Par_ConcMarkingClosure::do_oop(oop obj) {
4237 assert(obj->is_oop_or_null(true), "expected an oop or NULL");
4238 HeapWord* addr = (HeapWord*)obj;
4239 // Check if oop points into the CMS generation
4240 // and is not marked
4241 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
4242 // a white object ...
4243 // If we manage to "claim" the object, by being the
4244 // first thread to mark it, then we push it on our
4245 // marking stack
4246 if (_bit_map->par_mark(addr)) { // ... now grey
4247 // push on work queue (grey set)
4248 bool simulate_overflow = false;
4249 NOT_PRODUCT(
4250 if (CMSMarkStackOverflowALot &&
4251 _collector->simulate_overflow()) {
4252 // simulate a stack overflow
4253 simulate_overflow = true;
4254 }
4255 )
4256 if (simulate_overflow ||
4257 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
4258 // stack overflow
4259 if (PrintCMSStatistics != 0) {
4260 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
4261 SIZE_FORMAT, _overflow_stack->capacity());
4262 }
4263 // We cannot assert that the overflow stack is full because
4264 // it may have been emptied since.
4265 assert(simulate_overflow ||
4266 _work_queue->size() == _work_queue->max_elems(),
4267 "Else push should have succeeded");
4268 handle_stack_overflow(addr);
4269 }
4270 } // Else, some other thread got there first
4271 do_yield_check();
4272 }
4273 }
4274
4275 void Par_ConcMarkingClosure::do_oop(oop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
4276 void Par_ConcMarkingClosure::do_oop(narrowOop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
4277
4278 void Par_ConcMarkingClosure::trim_queue(size_t max) {
4279 while (_work_queue->size() > max) {
4280 oop new_oop;
4281 if (_work_queue->pop_local(new_oop)) {
4282 assert(new_oop->is_oop(), "Should be an oop");
4283 assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
4284 assert(_span.contains((HeapWord*)new_oop), "Not in span");
4285 new_oop->oop_iterate(this); // do_oop() above
4286 do_yield_check();
4287 }
4288 }
4289 }
4290
4291 // Upon stack overflow, we discard (part of) the stack,
4292 // remembering the least address amongst those discarded
4293 // in CMSCollector's _restart_address.
4294 void Par_ConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
4295 // We need to do this under a mutex to prevent other
4296 // workers from interfering with the work done below.
4297 MutexLockerEx ml(_overflow_stack->par_lock(),
4298 Mutex::_no_safepoint_check_flag);
4299 // Remember the least grey address discarded
4300 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
4301 _collector->lower_restart_addr(ra);
4302 _overflow_stack->reset(); // discard stack contents
4303 _overflow_stack->expand(); // expand the stack if possible
4304 }
4305
4306
4307 void CMSConcMarkingTask::do_work_steal(int i) {
4308 OopTaskQueue* work_q = work_queue(i);
4309 oop obj_to_scan;
4310 CMSBitMap* bm = &(_collector->_markBitMap);
4311 CMSMarkStack* ovflw = &(_collector->_markStack);
4312 int* seed = _collector->hash_seed(i);
4313 Par_ConcMarkingClosure cl(_collector, this, work_q, bm, ovflw);
4314 while (true) {
4315 cl.trim_queue(0);
4316 assert(work_q->size() == 0, "Should have been emptied above");
4317 if (get_work_from_overflow_stack(ovflw, work_q)) {
4318 // Can't assert below because the work obtained from the
4319 // overflow stack may already have been stolen from us.
4320 // assert(work_q->size() > 0, "Work from overflow stack");
4321 continue;
4322 } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
4323 assert(obj_to_scan->is_oop(), "Should be an oop");
4324 assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
4325 obj_to_scan->oop_iterate(&cl);
4326 } else if (terminator()->offer_termination(&_term_term)) {
4327 assert(work_q->size() == 0, "Impossible!");
4328 break;
4329 } else if (yielding() || should_yield()) {
4330 yield();
4331 }
4332 }
4333 }
4334
4335 // This is run by the CMS (coordinator) thread.
4336 void CMSConcMarkingTask::coordinator_yield() {
4337 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
4338 "CMS thread should hold CMS token");
4339 // First give up the locks, then yield, then re-lock
4340 // We should probably use a constructor/destructor idiom to
4341 // do this unlock/lock or modify the MutexUnlocker class to
4342 // serve our purpose. XXX
4343 assert_lock_strong(_bit_map_lock);
4344 _bit_map_lock->unlock();
4345 ConcurrentMarkSweepThread::desynchronize(true);
4346 ConcurrentMarkSweepThread::acknowledge_yield_request();
4347 _collector->stopTimer();
4348 if (PrintCMSStatistics != 0) {
4349 _collector->incrementYields();
4350 }
4351 _collector->icms_wait();
4352
4353 // It is possible for whichever thread initiated the yield request
4354 // not to get a chance to wake up and take the bitmap lock between
4355 // this thread releasing it and reacquiring it. So, while the
4356 // should_yield() flag is on, let's sleep for a bit to give the
4357 // other thread a chance to wake up. The limit imposed on the number
4358 // of iterations is defensive, to avoid any unforseen circumstances
4359 // putting us into an infinite loop. Since it's always been this
4360 // (coordinator_yield()) method that was observed to cause the
4361 // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
4362 // which is by default non-zero. For the other seven methods that
4363 // also perform the yield operation, as are using a different
4364 // parameter (CMSYieldSleepCount) which is by default zero. This way we
4365 // can enable the sleeping for those methods too, if necessary.
4366 // See 6442774.
4367 //
4368 // We really need to reconsider the synchronization between the GC
4369 // thread and the yield-requesting threads in the future and we
4370 // should really use wait/notify, which is the recommended
4371 // way of doing this type of interaction. Additionally, we should
4372 // consolidate the eight methods that do the yield operation and they
4373 // are almost identical into one for better maintainability and
4374 // readability. See 6445193.
4375 //
4376 // Tony 2006.06.29
4377 for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
4378 ConcurrentMarkSweepThread::should_yield() &&
4379 !CMSCollector::foregroundGCIsActive(); ++i) {
4380 os::sleep(Thread::current(), 1, false);
4381 ConcurrentMarkSweepThread::acknowledge_yield_request();
4382 }
4383
4384 ConcurrentMarkSweepThread::synchronize(true);
4385 _bit_map_lock->lock_without_safepoint_check();
4386 _collector->startTimer();
4387 }
4388
4389 bool CMSCollector::do_marking_mt(bool asynch) {
4390 assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition");
4391 int num_workers = AdaptiveSizePolicy::calc_active_conc_workers(
4392 conc_workers()->total_workers(),
4393 conc_workers()->active_workers(),
4394 Threads::number_of_non_daemon_threads());
4395 conc_workers()->set_active_workers(num_workers);
4396
4397 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
4398
4399 CMSConcMarkingTask tsk(this,
4400 cms_space,
4401 asynch,
4402 conc_workers(),
4403 task_queues());
4404
4405 // Since the actual number of workers we get may be different
4406 // from the number we requested above, do we need to do anything different
4407 // below? In particular, may be we need to subclass the SequantialSubTasksDone
4408 // class?? XXX
4409 cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
4410
4411 // Refs discovery is already non-atomic.
4412 assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
4413 assert(ref_processor()->discovery_is_mt(), "Discovery should be MT");
4414 conc_workers()->start_task(&tsk);
4415 while (tsk.yielded()) {
4416 tsk.coordinator_yield();
4417 conc_workers()->continue_task(&tsk);
4418 }
4419 // If the task was aborted, _restart_addr will be non-NULL
4420 assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
4421 while (_restart_addr != NULL) {
4422 // XXX For now we do not make use of ABORTED state and have not
4423 // yet implemented the right abort semantics (even in the original
4424 // single-threaded CMS case). That needs some more investigation
4425 // and is deferred for now; see CR# TBF. 07252005YSR. XXX
4426 assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
4427 // If _restart_addr is non-NULL, a marking stack overflow
4428 // occurred; we need to do a fresh marking iteration from the
4429 // indicated restart address.
4430 if (_foregroundGCIsActive && asynch) {
4431 // We may be running into repeated stack overflows, having
4432 // reached the limit of the stack size, while making very
4433 // slow forward progress. It may be best to bail out and
4434 // let the foreground collector do its job.
4435 // Clear _restart_addr, so that foreground GC
4436 // works from scratch. This avoids the headache of
4437 // a "rescan" which would otherwise be needed because
4438 // of the dirty mod union table & card table.
4439 _restart_addr = NULL;
4440 return false;
4441 }
4442 // Adjust the task to restart from _restart_addr
4443 tsk.reset(_restart_addr);
4444 cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
4445 _restart_addr);
4446 _restart_addr = NULL;
4447 // Get the workers going again
4448 conc_workers()->start_task(&tsk);
4449 while (tsk.yielded()) {
4450 tsk.coordinator_yield();
4451 conc_workers()->continue_task(&tsk);
4452 }
4453 }
4454 assert(tsk.completed(), "Inconsistency");
4455 assert(tsk.result() == true, "Inconsistency");
4456 return true;
4457 }
4458
4459 bool CMSCollector::do_marking_st(bool asynch) {
4460 ResourceMark rm;
4461 HandleMark hm;
4462
4463 // Temporarily make refs discovery single threaded (non-MT)
4464 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
4465 MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
4466 &_markStack, CMSYield && asynch);
4467 // the last argument to iterate indicates whether the iteration
4468 // should be incremental with periodic yields.
4469 _markBitMap.iterate(&markFromRootsClosure);
4470 // If _restart_addr is non-NULL, a marking stack overflow
4471 // occurred; we need to do a fresh iteration from the
4472 // indicated restart address.
4473 while (_restart_addr != NULL) {
4474 if (_foregroundGCIsActive && asynch) {
4475 // We may be running into repeated stack overflows, having
4476 // reached the limit of the stack size, while making very
4477 // slow forward progress. It may be best to bail out and
4478 // let the foreground collector do its job.
4479 // Clear _restart_addr, so that foreground GC
4480 // works from scratch. This avoids the headache of
4481 // a "rescan" which would otherwise be needed because
4482 // of the dirty mod union table & card table.
4483 _restart_addr = NULL;
4484 return false; // indicating failure to complete marking
4485 }
4486 // Deal with stack overflow:
4487 // we restart marking from _restart_addr
4488 HeapWord* ra = _restart_addr;
4489 markFromRootsClosure.reset(ra);
4490 _restart_addr = NULL;
4491 _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
4492 }
4493 return true;
4494 }
4495
4496 void CMSCollector::preclean() {
4497 check_correct_thread_executing();
4498 assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
4499 verify_work_stacks_empty();
4500 verify_overflow_empty();
4501 _abort_preclean = false;
4502 if (CMSPrecleaningEnabled) {
4503 if (!CMSEdenChunksRecordAlways) {
4504 _eden_chunk_index = 0;
4505 }
4506 size_t used = get_eden_used();
4507 size_t capacity = get_eden_capacity();
4508 // Don't start sampling unless we will get sufficiently
4509 // many samples.
4510 if (used < (capacity/(CMSScheduleRemarkSamplingRatio * 100)
4511 * CMSScheduleRemarkEdenPenetration)) {
4512 _start_sampling = true;
4513 } else {
4514 _start_sampling = false;
4515 }
4516 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
4517 CMSPhaseAccounting pa(this, "preclean", !PrintGCDetails);
4518 preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
4519 }
4520 CMSTokenSync x(true); // is cms thread
4521 if (CMSPrecleaningEnabled) {
4522 sample_eden();
4523 _collectorState = AbortablePreclean;
4524 } else {
4525 _collectorState = FinalMarking;
4526 }
4527 verify_work_stacks_empty();
4528 verify_overflow_empty();
4529 }
4530
4531 // Try and schedule the remark such that young gen
4532 // occupancy is CMSScheduleRemarkEdenPenetration %.
4533 void CMSCollector::abortable_preclean() {
4534 check_correct_thread_executing();
4535 assert(CMSPrecleaningEnabled, "Inconsistent control state");
4536 assert(_collectorState == AbortablePreclean, "Inconsistent control state");
4537
4538 // If Eden's current occupancy is below this threshold,
4539 // immediately schedule the remark; else preclean
4540 // past the next scavenge in an effort to
4541 // schedule the pause as described above. By choosing
4542 // CMSScheduleRemarkEdenSizeThreshold >= max eden size
4543 // we will never do an actual abortable preclean cycle.
4544 if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
4545 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
4546 CMSPhaseAccounting pa(this, "abortable-preclean", !PrintGCDetails);
4547 // We need more smarts in the abortable preclean
4548 // loop below to deal with cases where allocation
4549 // in young gen is very very slow, and our precleaning
4550 // is running a losing race against a horde of
4551 // mutators intent on flooding us with CMS updates
4552 // (dirty cards).
4553 // One, admittedly dumb, strategy is to give up
4554 // after a certain number of abortable precleaning loops
4555 // or after a certain maximum time. We want to make
4556 // this smarter in the next iteration.
4557 // XXX FIX ME!!! YSR
4558 size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
4559 while (!(should_abort_preclean() ||
4560 ConcurrentMarkSweepThread::should_terminate())) {
4561 workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
4562 cumworkdone += workdone;
4563 loops++;
4564 // Voluntarily terminate abortable preclean phase if we have
4565 // been at it for too long.
4566 if ((CMSMaxAbortablePrecleanLoops != 0) &&
4567 loops >= CMSMaxAbortablePrecleanLoops) {
4568 if (PrintGCDetails) {
4569 gclog_or_tty->print(" CMS: abort preclean due to loops ");
4570 }
4571 break;
4572 }
4573 if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
4574 if (PrintGCDetails) {
4575 gclog_or_tty->print(" CMS: abort preclean due to time ");
4576 }
4577 break;
4578 }
4579 // If we are doing little work each iteration, we should
4580 // take a short break.
4581 if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
4582 // Sleep for some time, waiting for work to accumulate
4583 stopTimer();
4584 cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
4585 startTimer();
4586 waited++;
4587 }
4588 }
4589 if (PrintCMSStatistics > 0) {
4590 gclog_or_tty->print(" [%d iterations, %d waits, %d cards)] ",
4591 loops, waited, cumworkdone);
4592 }
4593 }
4594 CMSTokenSync x(true); // is cms thread
4595 if (_collectorState != Idling) {
4596 assert(_collectorState == AbortablePreclean,
4597 "Spontaneous state transition?");
4598 _collectorState = FinalMarking;
4599 } // Else, a foreground collection completed this CMS cycle.
4600 return;
4601 }
4602
4603 // Respond to an Eden sampling opportunity
4604 void CMSCollector::sample_eden() {
4605 // Make sure a young gc cannot sneak in between our
4606 // reading and recording of a sample.
4607 assert(Thread::current()->is_ConcurrentGC_thread(),
4608 "Only the cms thread may collect Eden samples");
4609 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
4610 "Should collect samples while holding CMS token");
4611 if (!_start_sampling) {
4612 return;
4613 }
4614 // When CMSEdenChunksRecordAlways is true, the eden chunk array
4615 // is populated by the young generation.
4616 if (_eden_chunk_array != NULL && !CMSEdenChunksRecordAlways) {
4617 if (_eden_chunk_index < _eden_chunk_capacity) {
4618 _eden_chunk_array[_eden_chunk_index] = *_top_addr; // take sample
4619 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4620 "Unexpected state of Eden");
4621 // We'd like to check that what we just sampled is an oop-start address;
4622 // however, we cannot do that here since the object may not yet have been
4623 // initialized. So we'll instead do the check when we _use_ this sample
4624 // later.
4625 if (_eden_chunk_index == 0 ||
4626 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4627 _eden_chunk_array[_eden_chunk_index-1])
4628 >= CMSSamplingGrain)) {
4629 _eden_chunk_index++; // commit sample
4630 }
4631 }
4632 }
4633 if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
4634 size_t used = get_eden_used();
4635 size_t capacity = get_eden_capacity();
4636 assert(used <= capacity, "Unexpected state of Eden");
4637 if (used > (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
4638 _abort_preclean = true;
4639 }
4640 }
4641 }
4642
4643
4644 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
4645 assert(_collectorState == Precleaning ||
4646 _collectorState == AbortablePreclean, "incorrect state");
4647 ResourceMark rm;
4648 HandleMark hm;
4649
4650 // Precleaning is currently not MT but the reference processor
4651 // may be set for MT. Disable it temporarily here.
4652 ReferenceProcessor* rp = ref_processor();
4653 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false);
4654
4655 // Do one pass of scrubbing the discovered reference lists
4656 // to remove any reference objects with strongly-reachable
4657 // referents.
4658 if (clean_refs) {
4659 CMSPrecleanRefsYieldClosure yield_cl(this);
4660 assert(rp->span().equals(_span), "Spans should be equal");
4661 CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
4662 &_markStack, true /* preclean */);
4663 CMSDrainMarkingStackClosure complete_trace(this,
4664 _span, &_markBitMap, &_markStack,
4665 &keep_alive, true /* preclean */);
4666
4667 // We don't want this step to interfere with a young
4668 // collection because we don't want to take CPU
4669 // or memory bandwidth away from the young GC threads
4670 // (which may be as many as there are CPUs).
4671 // Note that we don't need to protect ourselves from
4672 // interference with mutators because they can't
4673 // manipulate the discovered reference lists nor affect
4674 // the computed reachability of the referents, the
4675 // only properties manipulated by the precleaning
4676 // of these reference lists.
4677 stopTimer();
4678 CMSTokenSyncWithLocks x(true /* is cms thread */,
4679 bitMapLock());
4680 startTimer();
4681 sample_eden();
4682
4683 // The following will yield to allow foreground
4684 // collection to proceed promptly. XXX YSR:
4685 // The code in this method may need further
4686 // tweaking for better performance and some restructuring
4687 // for cleaner interfaces.
4688 GCTimer *gc_timer = NULL; // Currently not tracing concurrent phases
4689 rp->preclean_discovered_references(
4690 rp->is_alive_non_header(), &keep_alive, &complete_trace, &yield_cl,
4691 gc_timer);
4692 }
4693
4694 if (clean_survivor) { // preclean the active survivor space(s)
4695 assert(_young_gen->kind() == Generation::DefNew ||
4696 _young_gen->kind() == Generation::ParNew ||
4697 _young_gen->kind() == Generation::ASParNew,
4698 "incorrect type for cast");
4699 DefNewGeneration* dng = (DefNewGeneration*)_young_gen;
4700 PushAndMarkClosure pam_cl(this, _span, ref_processor(),
4701 &_markBitMap, &_modUnionTable,
4702 &_markStack, true /* precleaning phase */);
4703 stopTimer();
4704 CMSTokenSyncWithLocks ts(true /* is cms thread */,
4705 bitMapLock());
4706 startTimer();
4707 unsigned int before_count =
4708 GenCollectedHeap::heap()->total_collections();
4709 SurvivorSpacePrecleanClosure
4710 sss_cl(this, _span, &_markBitMap, &_markStack,
4711 &pam_cl, before_count, CMSYield);
4712 dng->from()->object_iterate_careful(&sss_cl);
4713 dng->to()->object_iterate_careful(&sss_cl);
4714 }
4715 MarkRefsIntoAndScanClosure
4716 mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
4717 &_markStack, this, CMSYield,
4718 true /* precleaning phase */);
4719 // CAUTION: The following closure has persistent state that may need to
4720 // be reset upon a decrease in the sequence of addresses it
4721 // processes.
4722 ScanMarkedObjectsAgainCarefullyClosure
4723 smoac_cl(this, _span,
4724 &_markBitMap, &_markStack, &mrias_cl, CMSYield);
4725
4726 // Preclean dirty cards in ModUnionTable and CardTable using
4727 // appropriate convergence criterion;
4728 // repeat CMSPrecleanIter times unless we find that
4729 // we are losing.
4730 assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
4731 assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
4732 "Bad convergence multiplier");
4733 assert(CMSPrecleanThreshold >= 100,
4734 "Unreasonably low CMSPrecleanThreshold");
4735
4736 size_t numIter, cumNumCards, lastNumCards, curNumCards;
4737 for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
4738 numIter < CMSPrecleanIter;
4739 numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
4740 curNumCards = preclean_mod_union_table(_cmsGen, &smoac_cl);
4741 if (Verbose && PrintGCDetails) {
4742 gclog_or_tty->print(" (modUnionTable: %d cards)", curNumCards);
4743 }
4744 // Either there are very few dirty cards, so re-mark
4745 // pause will be small anyway, or our pre-cleaning isn't
4746 // that much faster than the rate at which cards are being
4747 // dirtied, so we might as well stop and re-mark since
4748 // precleaning won't improve our re-mark time by much.
4749 if (curNumCards <= CMSPrecleanThreshold ||
4750 (numIter > 0 &&
4751 (curNumCards * CMSPrecleanDenominator >
4752 lastNumCards * CMSPrecleanNumerator))) {
4753 numIter++;
4754 cumNumCards += curNumCards;
4755 break;
4756 }
4757 }
4758
4759 preclean_klasses(&mrias_cl, _cmsGen->freelistLock());
4760
4761 curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
4762 cumNumCards += curNumCards;
4763 if (PrintGCDetails && PrintCMSStatistics != 0) {
4764 gclog_or_tty->print_cr(" (cardTable: %d cards, re-scanned %d cards, %d iterations)",
4765 curNumCards, cumNumCards, numIter);
4766 }
4767 return cumNumCards; // as a measure of useful work done
4768 }
4769
4770 // PRECLEANING NOTES:
4771 // Precleaning involves:
4772 // . reading the bits of the modUnionTable and clearing the set bits.
4773 // . For the cards corresponding to the set bits, we scan the
4774 // objects on those cards. This means we need the free_list_lock
4775 // so that we can safely iterate over the CMS space when scanning
4776 // for oops.
4777 // . When we scan the objects, we'll be both reading and setting
4778 // marks in the marking bit map, so we'll need the marking bit map.
4779 // . For protecting _collector_state transitions, we take the CGC_lock.
4780 // Note that any races in the reading of of card table entries by the
4781 // CMS thread on the one hand and the clearing of those entries by the
4782 // VM thread or the setting of those entries by the mutator threads on the
4783 // other are quite benign. However, for efficiency it makes sense to keep
4784 // the VM thread from racing with the CMS thread while the latter is
4785 // dirty card info to the modUnionTable. We therefore also use the
4786 // CGC_lock to protect the reading of the card table and the mod union
4787 // table by the CM thread.
4788 // . We run concurrently with mutator updates, so scanning
4789 // needs to be done carefully -- we should not try to scan
4790 // potentially uninitialized objects.
4791 //
4792 // Locking strategy: While holding the CGC_lock, we scan over and
4793 // reset a maximal dirty range of the mod union / card tables, then lock
4794 // the free_list_lock and bitmap lock to do a full marking, then
4795 // release these locks; and repeat the cycle. This allows for a
4796 // certain amount of fairness in the sharing of these locks between
4797 // the CMS collector on the one hand, and the VM thread and the
4798 // mutators on the other.
4799
4800 // NOTE: preclean_mod_union_table() and preclean_card_table()
4801 // further below are largely identical; if you need to modify
4802 // one of these methods, please check the other method too.
4803
4804 size_t CMSCollector::preclean_mod_union_table(
4805 ConcurrentMarkSweepGeneration* gen,
4806 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4807 verify_work_stacks_empty();
4808 verify_overflow_empty();
4809
4810 // strategy: starting with the first card, accumulate contiguous
4811 // ranges of dirty cards; clear these cards, then scan the region
4812 // covered by these cards.
4813
4814 // Since all of the MUT is committed ahead, we can just use
4815 // that, in case the generations expand while we are precleaning.
4816 // It might also be fine to just use the committed part of the
4817 // generation, but we might potentially miss cards when the
4818 // generation is rapidly expanding while we are in the midst
4819 // of precleaning.
4820 HeapWord* startAddr = gen->reserved().start();
4821 HeapWord* endAddr = gen->reserved().end();
4822
4823 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4824
4825 size_t numDirtyCards, cumNumDirtyCards;
4826 HeapWord *nextAddr, *lastAddr;
4827 for (cumNumDirtyCards = numDirtyCards = 0,
4828 nextAddr = lastAddr = startAddr;
4829 nextAddr < endAddr;
4830 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4831
4832 ResourceMark rm;
4833 HandleMark hm;
4834
4835 MemRegion dirtyRegion;
4836 {
4837 stopTimer();
4838 // Potential yield point
4839 CMSTokenSync ts(true);
4840 startTimer();
4841 sample_eden();
4842 // Get dirty region starting at nextOffset (inclusive),
4843 // simultaneously clearing it.
4844 dirtyRegion =
4845 _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
4846 assert(dirtyRegion.start() >= nextAddr,
4847 "returned region inconsistent?");
4848 }
4849 // Remember where the next search should begin.
4850 // The returned region (if non-empty) is a right open interval,
4851 // so lastOffset is obtained from the right end of that
4852 // interval.
4853 lastAddr = dirtyRegion.end();
4854 // Should do something more transparent and less hacky XXX
4855 numDirtyCards =
4856 _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
4857
4858 // We'll scan the cards in the dirty region (with periodic
4859 // yields for foreground GC as needed).
4860 if (!dirtyRegion.is_empty()) {
4861 assert(numDirtyCards > 0, "consistency check");
4862 HeapWord* stop_point = NULL;
4863 stopTimer();
4864 // Potential yield point
4865 CMSTokenSyncWithLocks ts(true, gen->freelistLock(),
4866 bitMapLock());
4867 startTimer();
4868 {
4869 verify_work_stacks_empty();
4870 verify_overflow_empty();
4871 sample_eden();
4872 stop_point =
4873 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4874 }
4875 if (stop_point != NULL) {
4876 // The careful iteration stopped early either because it found an
4877 // uninitialized object, or because we were in the midst of an
4878 // "abortable preclean", which should now be aborted. Redirty
4879 // the bits corresponding to the partially-scanned or unscanned
4880 // cards. We'll either restart at the next block boundary or
4881 // abort the preclean.
4882 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4883 "Should only be AbortablePreclean.");
4884 _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
4885 if (should_abort_preclean()) {
4886 break; // out of preclean loop
4887 } else {
4888 // Compute the next address at which preclean should pick up;
4889 // might need bitMapLock in order to read P-bits.
4890 lastAddr = next_card_start_after_block(stop_point);
4891 }
4892 }
4893 } else {
4894 assert(lastAddr == endAddr, "consistency check");
4895 assert(numDirtyCards == 0, "consistency check");
4896 break;
4897 }
4898 }
4899 verify_work_stacks_empty();
4900 verify_overflow_empty();
4901 return cumNumDirtyCards;
4902 }
4903
4904 // NOTE: preclean_mod_union_table() above and preclean_card_table()
4905 // below are largely identical; if you need to modify
4906 // one of these methods, please check the other method too.
4907
4908 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* gen,
4909 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4910 // strategy: it's similar to precleamModUnionTable above, in that
4911 // we accumulate contiguous ranges of dirty cards, mark these cards
4912 // precleaned, then scan the region covered by these cards.
4913 HeapWord* endAddr = (HeapWord*)(gen->_virtual_space.high());
4914 HeapWord* startAddr = (HeapWord*)(gen->_virtual_space.low());
4915
4916 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4917
4918 size_t numDirtyCards, cumNumDirtyCards;
4919 HeapWord *lastAddr, *nextAddr;
4920
4921 for (cumNumDirtyCards = numDirtyCards = 0,
4922 nextAddr = lastAddr = startAddr;
4923 nextAddr < endAddr;
4924 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4925
4926 ResourceMark rm;
4927 HandleMark hm;
4928
4929 MemRegion dirtyRegion;
4930 {
4931 // See comments in "Precleaning notes" above on why we
4932 // do this locking. XXX Could the locking overheads be
4933 // too high when dirty cards are sparse? [I don't think so.]
4934 stopTimer();
4935 CMSTokenSync x(true); // is cms thread
4936 startTimer();
4937 sample_eden();
4938 // Get and clear dirty region from card table
4939 dirtyRegion = _ct->ct_bs()->dirty_card_range_after_reset(
4940 MemRegion(nextAddr, endAddr),
4941 true,
4942 CardTableModRefBS::precleaned_card_val());
4943
4944 assert(dirtyRegion.start() >= nextAddr,
4945 "returned region inconsistent?");
4946 }
4947 lastAddr = dirtyRegion.end();
4948 numDirtyCards =
4949 dirtyRegion.word_size()/CardTableModRefBS::card_size_in_words;
4950
4951 if (!dirtyRegion.is_empty()) {
4952 stopTimer();
4953 CMSTokenSyncWithLocks ts(true, gen->freelistLock(), bitMapLock());
4954 startTimer();
4955 sample_eden();
4956 verify_work_stacks_empty();
4957 verify_overflow_empty();
4958 HeapWord* stop_point =
4959 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4960 if (stop_point != NULL) {
4961 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4962 "Should only be AbortablePreclean.");
4963 _ct->ct_bs()->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4964 if (should_abort_preclean()) {
4965 break; // out of preclean loop
4966 } else {
4967 // Compute the next address at which preclean should pick up.
4968 lastAddr = next_card_start_after_block(stop_point);
4969 }
4970 }
4971 } else {
4972 break;
4973 }
4974 }
4975 verify_work_stacks_empty();
4976 verify_overflow_empty();
4977 return cumNumDirtyCards;
4978 }
4979
4980 class PrecleanKlassClosure : public KlassClosure {
4981 CMKlassClosure _cm_klass_closure;
4982 public:
4983 PrecleanKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4984 void do_klass(Klass* k) {
4985 if (k->has_accumulated_modified_oops()) {
4986 k->clear_accumulated_modified_oops();
4987
4988 _cm_klass_closure.do_klass(k);
4989 }
4990 }
4991 };
4992
4993 // The freelist lock is needed to prevent asserts, is it really needed?
4994 void CMSCollector::preclean_klasses(MarkRefsIntoAndScanClosure* cl, Mutex* freelistLock) {
4995
4996 cl->set_freelistLock(freelistLock);
4997
4998 CMSTokenSyncWithLocks ts(true, freelistLock, bitMapLock());
4999
5000 // SSS: Add equivalent to ScanMarkedObjectsAgainCarefullyClosure::do_yield_check and should_abort_preclean?
5001 // SSS: We should probably check if precleaning should be aborted, at suitable intervals?
5002 PrecleanKlassClosure preclean_klass_closure(cl);
5003 ClassLoaderDataGraph::classes_do(&preclean_klass_closure);
5004
5005 verify_work_stacks_empty();
5006 verify_overflow_empty();
5007 }
5008
5009 void CMSCollector::checkpointRootsFinal(bool asynch,
5010 bool clear_all_soft_refs, bool init_mark_was_synchronous) {
5011 assert(_collectorState == FinalMarking, "incorrect state transition?");
5012 check_correct_thread_executing();
5013 // world is stopped at this checkpoint
5014 assert(SafepointSynchronize::is_at_safepoint(),
5015 "world should be stopped");
5016 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
5017
5018 verify_work_stacks_empty();
5019 verify_overflow_empty();
5020
5021 SpecializationStats::clear();
5022 if (PrintGCDetails) {
5023 gclog_or_tty->print("[YG occupancy: "SIZE_FORMAT" K ("SIZE_FORMAT" K)]",
5024 _young_gen->used() / K,
5025 _young_gen->capacity() / K);
5026 }
5027 if (asynch) {
5028 if (CMSScavengeBeforeRemark) {
5029 GenCollectedHeap* gch = GenCollectedHeap::heap();
5030 // Temporarily set flag to false, GCH->do_collection will
5031 // expect it to be false and set to true
5032 FlagSetting fl(gch->_is_gc_active, false);
5033 NOT_PRODUCT(GCTraceTime t("Scavenge-Before-Remark",
5034 PrintGCDetails && Verbose, true, _gc_timer_cm);)
5035 int level = _cmsGen->level() - 1;
5036 if (level >= 0) {
5037 gch->do_collection(true, // full (i.e. force, see below)
5038 false, // !clear_all_soft_refs
5039 0, // size
5040 false, // is_tlab
5041 level // max_level
5042 );
5043 }
5044 }
5045 FreelistLocker x(this);
5046 MutexLockerEx y(bitMapLock(),
5047 Mutex::_no_safepoint_check_flag);
5048 assert(!init_mark_was_synchronous, "but that's impossible!");
5049 checkpointRootsFinalWork(asynch, clear_all_soft_refs, false);
5050 } else {
5051 // already have all the locks
5052 checkpointRootsFinalWork(asynch, clear_all_soft_refs,
5053 init_mark_was_synchronous);
5054 }
5055 verify_work_stacks_empty();
5056 verify_overflow_empty();
5057 SpecializationStats::print();
5058 }
5059
5060 void CMSCollector::checkpointRootsFinalWork(bool asynch,
5061 bool clear_all_soft_refs, bool init_mark_was_synchronous) {
5062
5063 NOT_PRODUCT(GCTraceTime tr("checkpointRootsFinalWork", PrintGCDetails, false, _gc_timer_cm);)
5064
5065 assert(haveFreelistLocks(), "must have free list locks");
5066 assert_lock_strong(bitMapLock());
5067
5068 if (UseAdaptiveSizePolicy) {
5069 size_policy()->checkpoint_roots_final_begin();
5070 }
5071
5072 ResourceMark rm;
5073 HandleMark hm;
5074
5075 GenCollectedHeap* gch = GenCollectedHeap::heap();
5076
5077 if (should_unload_classes()) {
5078 CodeCache::gc_prologue();
5079 }
5080 assert(haveFreelistLocks(), "must have free list locks");
5081 assert_lock_strong(bitMapLock());
5082
5083 if (!init_mark_was_synchronous) {
5084 // We might assume that we need not fill TLAB's when
5085 // CMSScavengeBeforeRemark is set, because we may have just done
5086 // a scavenge which would have filled all TLAB's -- and besides
5087 // Eden would be empty. This however may not always be the case --
5088 // for instance although we asked for a scavenge, it may not have
5089 // happened because of a JNI critical section. We probably need
5090 // a policy for deciding whether we can in that case wait until
5091 // the critical section releases and then do the remark following
5092 // the scavenge, and skip it here. In the absence of that policy,
5093 // or of an indication of whether the scavenge did indeed occur,
5094 // we cannot rely on TLAB's having been filled and must do
5095 // so here just in case a scavenge did not happen.
5096 gch->ensure_parsability(false); // fill TLAB's, but no need to retire them
5097 // Update the saved marks which may affect the root scans.
5098 gch->save_marks();
5099
5100 if (CMSPrintEdenSurvivorChunks) {
5101 print_eden_and_survivor_chunk_arrays();
5102 }
5103
5104 {
5105 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
5106
5107 // Note on the role of the mod union table:
5108 // Since the marker in "markFromRoots" marks concurrently with
5109 // mutators, it is possible for some reachable objects not to have been
5110 // scanned. For instance, an only reference to an object A was
5111 // placed in object B after the marker scanned B. Unless B is rescanned,
5112 // A would be collected. Such updates to references in marked objects
5113 // are detected via the mod union table which is the set of all cards
5114 // dirtied since the first checkpoint in this GC cycle and prior to
5115 // the most recent young generation GC, minus those cleaned up by the
5116 // concurrent precleaning.
5117 if (CMSParallelRemarkEnabled && CollectedHeap::use_parallel_gc_threads()) {
5118 GCTraceTime t("Rescan (parallel) ", PrintGCDetails, false, _gc_timer_cm);
5119 do_remark_parallel();
5120 } else {
5121 GCTraceTime t("Rescan (non-parallel) ", PrintGCDetails, false,
5122 _gc_timer_cm);
5123 do_remark_non_parallel();
5124 }
5125 }
5126 } else {
5127 assert(!asynch, "Can't have init_mark_was_synchronous in asynch mode");
5128 // The initial mark was stop-world, so there's no rescanning to
5129 // do; go straight on to the next step below.
5130 }
5131 verify_work_stacks_empty();
5132 verify_overflow_empty();
5133
5134 {
5135 NOT_PRODUCT(GCTraceTime ts("refProcessingWork", PrintGCDetails, false, _gc_timer_cm);)
5136 refProcessingWork(asynch, clear_all_soft_refs);
5137 }
5138 verify_work_stacks_empty();
5139 verify_overflow_empty();
5140
5141 if (should_unload_classes()) {
5142 CodeCache::gc_epilogue();
5143 }
5144 JvmtiExport::gc_epilogue();
5145
5146 // If we encountered any (marking stack / work queue) overflow
5147 // events during the current CMS cycle, take appropriate
5148 // remedial measures, where possible, so as to try and avoid
5149 // recurrence of that condition.
5150 assert(_markStack.isEmpty(), "No grey objects");
5151 size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
5152 _ser_kac_ovflw + _ser_kac_preclean_ovflw;
5153 if (ser_ovflw > 0) {
5154 if (PrintCMSStatistics != 0) {
5155 gclog_or_tty->print_cr("Marking stack overflow (benign) "
5156 "(pmc_pc="SIZE_FORMAT", pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT
5157 ", kac_preclean="SIZE_FORMAT")",
5158 _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw,
5159 _ser_kac_ovflw, _ser_kac_preclean_ovflw);
5160 }
5161 _markStack.expand();
5162 _ser_pmc_remark_ovflw = 0;
5163 _ser_pmc_preclean_ovflw = 0;
5164 _ser_kac_preclean_ovflw = 0;
5165 _ser_kac_ovflw = 0;
5166 }
5167 if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
5168 if (PrintCMSStatistics != 0) {
5169 gclog_or_tty->print_cr("Work queue overflow (benign) "
5170 "(pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT")",
5171 _par_pmc_remark_ovflw, _par_kac_ovflw);
5172 }
5173 _par_pmc_remark_ovflw = 0;
5174 _par_kac_ovflw = 0;
5175 }
5176 if (PrintCMSStatistics != 0) {
5177 if (_markStack._hit_limit > 0) {
5178 gclog_or_tty->print_cr(" (benign) Hit max stack size limit ("SIZE_FORMAT")",
5179 _markStack._hit_limit);
5180 }
5181 if (_markStack._failed_double > 0) {
5182 gclog_or_tty->print_cr(" (benign) Failed stack doubling ("SIZE_FORMAT"),"
5183 " current capacity "SIZE_FORMAT,
5184 _markStack._failed_double,
5185 _markStack.capacity());
5186 }
5187 }
5188 _markStack._hit_limit = 0;
5189 _markStack._failed_double = 0;
5190
5191 if ((VerifyAfterGC || VerifyDuringGC) &&
5192 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5193 verify_after_remark();
5194 }
5195
5196 _gc_tracer_cm->report_object_count_after_gc(&_is_alive_closure);
5197
5198 // Change under the freelistLocks.
5199 _collectorState = Sweeping;
5200 // Call isAllClear() under bitMapLock
5201 assert(_modUnionTable.isAllClear(),
5202 "Should be clear by end of the final marking");
5203 assert(_ct->klass_rem_set()->mod_union_is_clear(),
5204 "Should be clear by end of the final marking");
5205 if (UseAdaptiveSizePolicy) {
5206 size_policy()->checkpoint_roots_final_end(gch->gc_cause());
5207 }
5208 }
5209
5210 void CMSParInitialMarkTask::work(uint worker_id) {
5211 elapsedTimer _timer;
5212 ResourceMark rm;
5213 HandleMark hm;
5214
5215 // ---------- scan from roots --------------
5216 _timer.start();
5217 GenCollectedHeap* gch = GenCollectedHeap::heap();
5218 Par_MarkRefsIntoClosure par_mri_cl(_collector->_span, &(_collector->_markBitMap));
5219 CMKlassClosure klass_closure(&par_mri_cl);
5220
5221 // ---------- young gen roots --------------
5222 {
5223 work_on_young_gen_roots(worker_id, &par_mri_cl);
5224 _timer.stop();
5225 if (PrintCMSStatistics != 0) {
5226 gclog_or_tty->print_cr(
5227 "Finished young gen initial mark scan work in %dth thread: %3.3f sec",
5228 worker_id, _timer.seconds());
5229 }
5230 }
5231
5232 // ---------- remaining roots --------------
5233 _timer.reset();
5234 _timer.start();
5235 gch->gen_process_strong_roots(_collector->_cmsGen->level(),
5236 false, // yg was scanned above
5237 false, // this is parallel code
5238 SharedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
5239 &par_mri_cl,
5240 true, // walk all of code cache if (so & SO_AllCodeCache)
5241 NULL,
5242 &klass_closure);
5243 assert(_collector->should_unload_classes()
5244 || (_collector->CMSCollector::roots_scanning_options() & SharedHeap::SO_AllCodeCache),
5245 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5246 _timer.stop();
5247 if (PrintCMSStatistics != 0) {
5248 gclog_or_tty->print_cr(
5249 "Finished remaining root initial mark scan work in %dth thread: %3.3f sec",
5250 worker_id, _timer.seconds());
5251 }
5252 }
5253
5254 // Parallel remark task
5255 class CMSParRemarkTask: public CMSParMarkTask {
5256 CompactibleFreeListSpace* _cms_space;
5257
5258 // The per-thread work queues, available here for stealing.
5259 OopTaskQueueSet* _task_queues;
5260 ParallelTaskTerminator _term;
5261
5262 public:
5263 // A value of 0 passed to n_workers will cause the number of
5264 // workers to be taken from the active workers in the work gang.
5265 CMSParRemarkTask(CMSCollector* collector,
5266 CompactibleFreeListSpace* cms_space,
5267 int n_workers, FlexibleWorkGang* workers,
5268 OopTaskQueueSet* task_queues):
5269 CMSParMarkTask("Rescan roots and grey objects in parallel",
5270 collector, n_workers),
5271 _cms_space(cms_space),
5272 _task_queues(task_queues),
5273 _term(n_workers, task_queues) { }
5274
5275 OopTaskQueueSet* task_queues() { return _task_queues; }
5276
5277 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5278
5279 ParallelTaskTerminator* terminator() { return &_term; }
5280 int n_workers() { return _n_workers; }
5281
5282 void work(uint worker_id);
5283
5284 private:
5285 // ... of dirty cards in old space
5286 void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
5287 Par_MarkRefsIntoAndScanClosure* cl);
5288
5289 // ... work stealing for the above
5290 void do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl, int* seed);
5291 };
5292
5293 class RemarkKlassClosure : public KlassClosure {
5294 CMKlassClosure _cm_klass_closure;
5295 public:
5296 RemarkKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
5297 void do_klass(Klass* k) {
5298 // Check if we have modified any oops in the Klass during the concurrent marking.
5299 if (k->has_accumulated_modified_oops()) {
5300 k->clear_accumulated_modified_oops();
5301
5302 // We could have transfered the current modified marks to the accumulated marks,
5303 // like we do with the Card Table to Mod Union Table. But it's not really necessary.
5304 } else if (k->has_modified_oops()) {
5305 // Don't clear anything, this info is needed by the next young collection.
5306 } else {
5307 // No modified oops in the Klass.
5308 return;
5309 }
5310
5311 // The klass has modified fields, need to scan the klass.
5312 _cm_klass_closure.do_klass(k);
5313 }
5314 };
5315
5316 void CMSParMarkTask::work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl) {
5317 DefNewGeneration* dng = _collector->_young_gen->as_DefNewGeneration();
5318 EdenSpace* eden_space = dng->eden();
5319 ContiguousSpace* from_space = dng->from();
5320 ContiguousSpace* to_space = dng->to();
5321
5322 HeapWord** eca = _collector->_eden_chunk_array;
5323 size_t ect = _collector->_eden_chunk_index;
5324 HeapWord** sca = _collector->_survivor_chunk_array;
5325 size_t sct = _collector->_survivor_chunk_index;
5326
5327 assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
5328 assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
5329
5330 do_young_space_rescan(worker_id, cl, to_space, NULL, 0);
5331 do_young_space_rescan(worker_id, cl, from_space, sca, sct);
5332 do_young_space_rescan(worker_id, cl, eden_space, eca, ect);
5333 }
5334
5335 // work_queue(i) is passed to the closure
5336 // Par_MarkRefsIntoAndScanClosure. The "i" parameter
5337 // also is passed to do_dirty_card_rescan_tasks() and to
5338 // do_work_steal() to select the i-th task_queue.
5339
5340 void CMSParRemarkTask::work(uint worker_id) {
5341 elapsedTimer _timer;
5342 ResourceMark rm;
5343 HandleMark hm;
5344
5345 // ---------- rescan from roots --------------
5346 _timer.start();
5347 GenCollectedHeap* gch = GenCollectedHeap::heap();
5348 Par_MarkRefsIntoAndScanClosure par_mrias_cl(_collector,
5349 _collector->_span, _collector->ref_processor(),
5350 &(_collector->_markBitMap),
5351 work_queue(worker_id));
5352
5353 // Rescan young gen roots first since these are likely
5354 // coarsely partitioned and may, on that account, constitute
5355 // the critical path; thus, it's best to start off that
5356 // work first.
5357 // ---------- young gen roots --------------
5358 {
5359 work_on_young_gen_roots(worker_id, &par_mrias_cl);
5360 _timer.stop();
5361 if (PrintCMSStatistics != 0) {
5362 gclog_or_tty->print_cr(
5363 "Finished young gen rescan work in %dth thread: %3.3f sec",
5364 worker_id, _timer.seconds());
5365 }
5366 }
5367
5368 // ---------- remaining roots --------------
5369 _timer.reset();
5370 _timer.start();
5371 gch->gen_process_strong_roots(_collector->_cmsGen->level(),
5372 false, // yg was scanned above
5373 false, // this is parallel code
5374 SharedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
5375 &par_mrias_cl,
5376 true, // walk all of code cache if (so & SO_AllCodeCache)
5377 NULL,
5378 NULL); // The dirty klasses will be handled below
5379 assert(_collector->should_unload_classes()
5380 || (_collector->CMSCollector::roots_scanning_options() & SharedHeap::SO_AllCodeCache),
5381 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5382 _timer.stop();
5383 if (PrintCMSStatistics != 0) {
5384 gclog_or_tty->print_cr(
5385 "Finished remaining root rescan work in %dth thread: %3.3f sec",
5386 worker_id, _timer.seconds());
5387 }
5388
5389 // ---------- unhandled CLD scanning ----------
5390 if (worker_id == 0) { // Single threaded at the moment.
5391 _timer.reset();
5392 _timer.start();
5393
5394 // Scan all new class loader data objects and new dependencies that were
5395 // introduced during concurrent marking.
5396 ResourceMark rm;
5397 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
5398 for (int i = 0; i < array->length(); i++) {
5399 par_mrias_cl.do_class_loader_data(array->at(i));
5400 }
5401
5402 // We don't need to keep track of new CLDs anymore.
5403 ClassLoaderDataGraph::remember_new_clds(false);
5404
5405 _timer.stop();
5406 if (PrintCMSStatistics != 0) {
5407 gclog_or_tty->print_cr(
5408 "Finished unhandled CLD scanning work in %dth thread: %3.3f sec",
5409 worker_id, _timer.seconds());
5410 }
5411 }
5412
5413 // ---------- dirty klass scanning ----------
5414 if (worker_id == 0) { // Single threaded at the moment.
5415 _timer.reset();
5416 _timer.start();
5417
5418 // Scan all classes that was dirtied during the concurrent marking phase.
5419 RemarkKlassClosure remark_klass_closure(&par_mrias_cl);
5420 ClassLoaderDataGraph::classes_do(&remark_klass_closure);
5421
5422 _timer.stop();
5423 if (PrintCMSStatistics != 0) {
5424 gclog_or_tty->print_cr(
5425 "Finished dirty klass scanning work in %dth thread: %3.3f sec",
5426 worker_id, _timer.seconds());
5427 }
5428 }
5429
5430 // We might have added oops to ClassLoaderData::_handles during the
5431 // concurrent marking phase. These oops point to newly allocated objects
5432 // that are guaranteed to be kept alive. Either by the direct allocation
5433 // code, or when the young collector processes the strong roots. Hence,
5434 // we don't have to revisit the _handles block during the remark phase.
5435
5436 // ---------- rescan dirty cards ------------
5437 _timer.reset();
5438 _timer.start();
5439
5440 // Do the rescan tasks for each of the two spaces
5441 // (cms_space) in turn.
5442 // "worker_id" is passed to select the task_queue for "worker_id"
5443 do_dirty_card_rescan_tasks(_cms_space, worker_id, &par_mrias_cl);
5444 _timer.stop();
5445 if (PrintCMSStatistics != 0) {
5446 gclog_or_tty->print_cr(
5447 "Finished dirty card rescan work in %dth thread: %3.3f sec",
5448 worker_id, _timer.seconds());
5449 }
5450
5451 // ---------- steal work from other threads ...
5452 // ---------- ... and drain overflow list.
5453 _timer.reset();
5454 _timer.start();
5455 do_work_steal(worker_id, &par_mrias_cl, _collector->hash_seed(worker_id));
5456 _timer.stop();
5457 if (PrintCMSStatistics != 0) {
5458 gclog_or_tty->print_cr(
5459 "Finished work stealing in %dth thread: %3.3f sec",
5460 worker_id, _timer.seconds());
5461 }
5462 }
5463
5464 // Note that parameter "i" is not used.
5465 void
5466 CMSParMarkTask::do_young_space_rescan(uint worker_id,
5467 OopsInGenClosure* cl, ContiguousSpace* space,
5468 HeapWord** chunk_array, size_t chunk_top) {
5469 // Until all tasks completed:
5470 // . claim an unclaimed task
5471 // . compute region boundaries corresponding to task claimed
5472 // using chunk_array
5473 // . par_oop_iterate(cl) over that region
5474
5475 ResourceMark rm;
5476 HandleMark hm;
5477
5478 SequentialSubTasksDone* pst = space->par_seq_tasks();
5479
5480 uint nth_task = 0;
5481 uint n_tasks = pst->n_tasks();
5482
5483 if (n_tasks > 0) {
5484 assert(pst->valid(), "Uninitialized use?");
5485 HeapWord *start, *end;
5486 while (!pst->is_task_claimed(/* reference */ nth_task)) {
5487 // We claimed task # nth_task; compute its boundaries.
5488 if (chunk_top == 0) { // no samples were taken
5489 assert(nth_task == 0 && n_tasks == 1, "Can have only 1 EdenSpace task");
5490 start = space->bottom();
5491 end = space->top();
5492 } else if (nth_task == 0) {
5493 start = space->bottom();
5494 end = chunk_array[nth_task];
5495 } else if (nth_task < (uint)chunk_top) {
5496 assert(nth_task >= 1, "Control point invariant");
5497 start = chunk_array[nth_task - 1];
5498 end = chunk_array[nth_task];
5499 } else {
5500 assert(nth_task == (uint)chunk_top, "Control point invariant");
5501 start = chunk_array[chunk_top - 1];
5502 end = space->top();
5503 }
5504 MemRegion mr(start, end);
5505 // Verify that mr is in space
5506 assert(mr.is_empty() || space->used_region().contains(mr),
5507 "Should be in space");
5508 // Verify that "start" is an object boundary
5509 assert(mr.is_empty() || oop(mr.start())->is_oop(),
5510 "Should be an oop");
5511 space->par_oop_iterate(mr, cl);
5512 }
5513 pst->all_tasks_completed();
5514 }
5515 }
5516
5517 void
5518 CMSParRemarkTask::do_dirty_card_rescan_tasks(
5519 CompactibleFreeListSpace* sp, int i,
5520 Par_MarkRefsIntoAndScanClosure* cl) {
5521 // Until all tasks completed:
5522 // . claim an unclaimed task
5523 // . compute region boundaries corresponding to task claimed
5524 // . transfer dirty bits ct->mut for that region
5525 // . apply rescanclosure to dirty mut bits for that region
5526
5527 ResourceMark rm;
5528 HandleMark hm;
5529
5530 OopTaskQueue* work_q = work_queue(i);
5531 ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
5532 // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
5533 // CAUTION: This closure has state that persists across calls to
5534 // the work method dirty_range_iterate_clear() in that it has
5535 // embedded in it a (subtype of) UpwardsObjectClosure. The
5536 // use of that state in the embedded UpwardsObjectClosure instance
5537 // assumes that the cards are always iterated (even if in parallel
5538 // by several threads) in monotonically increasing order per each
5539 // thread. This is true of the implementation below which picks
5540 // card ranges (chunks) in monotonically increasing order globally
5541 // and, a-fortiori, in monotonically increasing order per thread
5542 // (the latter order being a subsequence of the former).
5543 // If the work code below is ever reorganized into a more chaotic
5544 // work-partitioning form than the current "sequential tasks"
5545 // paradigm, the use of that persistent state will have to be
5546 // revisited and modified appropriately. See also related
5547 // bug 4756801 work on which should examine this code to make
5548 // sure that the changes there do not run counter to the
5549 // assumptions made here and necessary for correctness and
5550 // efficiency. Note also that this code might yield inefficient
5551 // behavior in the case of very large objects that span one or
5552 // more work chunks. Such objects would potentially be scanned
5553 // several times redundantly. Work on 4756801 should try and
5554 // address that performance anomaly if at all possible. XXX
5555 MemRegion full_span = _collector->_span;
5556 CMSBitMap* bm = &(_collector->_markBitMap); // shared
5557 MarkFromDirtyCardsClosure
5558 greyRescanClosure(_collector, full_span, // entire span of interest
5559 sp, bm, work_q, cl);
5560
5561 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
5562 assert(pst->valid(), "Uninitialized use?");
5563 uint nth_task = 0;
5564 const int alignment = CardTableModRefBS::card_size * BitsPerWord;
5565 MemRegion span = sp->used_region();
5566 HeapWord* start_addr = span.start();
5567 HeapWord* end_addr = (HeapWord*)round_to((intptr_t)span.end(),
5568 alignment);
5569 const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
5570 assert((HeapWord*)round_to((intptr_t)start_addr, alignment) ==
5571 start_addr, "Check alignment");
5572 assert((size_t)round_to((intptr_t)chunk_size, alignment) ==
5573 chunk_size, "Check alignment");
5574
5575 while (!pst->is_task_claimed(/* reference */ nth_task)) {
5576 // Having claimed the nth_task, compute corresponding mem-region,
5577 // which is a-fortiori aligned correctly (i.e. at a MUT boundary).
5578 // The alignment restriction ensures that we do not need any
5579 // synchronization with other gang-workers while setting or
5580 // clearing bits in thus chunk of the MUT.
5581 MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
5582 start_addr + (nth_task+1)*chunk_size);
5583 // The last chunk's end might be way beyond end of the
5584 // used region. In that case pull back appropriately.
5585 if (this_span.end() > end_addr) {
5586 this_span.set_end(end_addr);
5587 assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
5588 }
5589 // Iterate over the dirty cards covering this chunk, marking them
5590 // precleaned, and setting the corresponding bits in the mod union
5591 // table. Since we have been careful to partition at Card and MUT-word
5592 // boundaries no synchronization is needed between parallel threads.
5593 _collector->_ct->ct_bs()->dirty_card_iterate(this_span,
5594 &modUnionClosure);
5595
5596 // Having transferred these marks into the modUnionTable,
5597 // rescan the marked objects on the dirty cards in the modUnionTable.
5598 // Even if this is at a synchronous collection, the initial marking
5599 // may have been done during an asynchronous collection so there
5600 // may be dirty bits in the mod-union table.
5601 _collector->_modUnionTable.dirty_range_iterate_clear(
5602 this_span, &greyRescanClosure);
5603 _collector->_modUnionTable.verifyNoOneBitsInRange(
5604 this_span.start(),
5605 this_span.end());
5606 }
5607 pst->all_tasks_completed(); // declare that i am done
5608 }
5609
5610 // . see if we can share work_queues with ParNew? XXX
5611 void
5612 CMSParRemarkTask::do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl,
5613 int* seed) {
5614 OopTaskQueue* work_q = work_queue(i);
5615 NOT_PRODUCT(int num_steals = 0;)
5616 oop obj_to_scan;
5617 CMSBitMap* bm = &(_collector->_markBitMap);
5618
5619 while (true) {
5620 // Completely finish any left over work from (an) earlier round(s)
5621 cl->trim_queue(0);
5622 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5623 (size_t)ParGCDesiredObjsFromOverflowList);
5624 // Now check if there's any work in the overflow list
5625 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5626 // only affects the number of attempts made to get work from the
5627 // overflow list and does not affect the number of workers. Just
5628 // pass ParallelGCThreads so this behavior is unchanged.
5629 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5630 work_q,
5631 ParallelGCThreads)) {
5632 // found something in global overflow list;
5633 // not yet ready to go stealing work from others.
5634 // We'd like to assert(work_q->size() != 0, ...)
5635 // because we just took work from the overflow list,
5636 // but of course we can't since all of that could have
5637 // been already stolen from us.
5638 // "He giveth and He taketh away."
5639 continue;
5640 }
5641 // Verify that we have no work before we resort to stealing
5642 assert(work_q->size() == 0, "Have work, shouldn't steal");
5643 // Try to steal from other queues that have work
5644 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5645 NOT_PRODUCT(num_steals++;)
5646 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5647 assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5648 // Do scanning work
5649 obj_to_scan->oop_iterate(cl);
5650 // Loop around, finish this work, and try to steal some more
5651 } else if (terminator()->offer_termination()) {
5652 break; // nirvana from the infinite cycle
5653 }
5654 }
5655 NOT_PRODUCT(
5656 if (PrintCMSStatistics != 0) {
5657 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5658 }
5659 )
5660 assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
5661 "Else our work is not yet done");
5662 }
5663
5664 // Record object boundaries in _eden_chunk_array by sampling the eden
5665 // top in the slow-path eden object allocation code path and record
5666 // the boundaries, if CMSEdenChunksRecordAlways is true. If
5667 // CMSEdenChunksRecordAlways is false, we use the other asynchronous
5668 // sampling in sample_eden() that activates during the part of the
5669 // preclean phase.
5670 void CMSCollector::sample_eden_chunk() {
5671 if (CMSEdenChunksRecordAlways && _eden_chunk_array != NULL) {
5672 if (_eden_chunk_lock->try_lock()) {
5673 // Record a sample. This is the critical section. The contents
5674 // of the _eden_chunk_array have to be non-decreasing in the
5675 // address order.
5676 _eden_chunk_array[_eden_chunk_index] = *_top_addr;
5677 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
5678 "Unexpected state of Eden");
5679 if (_eden_chunk_index == 0 ||
5680 ((_eden_chunk_array[_eden_chunk_index] > _eden_chunk_array[_eden_chunk_index-1]) &&
5681 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
5682 _eden_chunk_array[_eden_chunk_index-1]) >= CMSSamplingGrain))) {
5683 _eden_chunk_index++; // commit sample
5684 }
5685 _eden_chunk_lock->unlock();
5686 }
5687 }
5688 }
5689
5690 // Return a thread-local PLAB recording array, as appropriate.
5691 void* CMSCollector::get_data_recorder(int thr_num) {
5692 if (_survivor_plab_array != NULL &&
5693 (CMSPLABRecordAlways ||
5694 (_collectorState > Marking && _collectorState < FinalMarking))) {
5695 assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
5696 ChunkArray* ca = &_survivor_plab_array[thr_num];
5697 ca->reset(); // clear it so that fresh data is recorded
5698 return (void*) ca;
5699 } else {
5700 return NULL;
5701 }
5702 }
5703
5704 // Reset all the thread-local PLAB recording arrays
5705 void CMSCollector::reset_survivor_plab_arrays() {
5706 for (uint i = 0; i < ParallelGCThreads; i++) {
5707 _survivor_plab_array[i].reset();
5708 }
5709 }
5710
5711 // Merge the per-thread plab arrays into the global survivor chunk
5712 // array which will provide the partitioning of the survivor space
5713 // for CMS initial scan and rescan.
5714 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv,
5715 int no_of_gc_threads) {
5716 assert(_survivor_plab_array != NULL, "Error");
5717 assert(_survivor_chunk_array != NULL, "Error");
5718 assert(_collectorState == FinalMarking ||
5719 (CMSParallelInitialMarkEnabled && _collectorState == InitialMarking), "Error");
5720 for (int j = 0; j < no_of_gc_threads; j++) {
5721 _cursor[j] = 0;
5722 }
5723 HeapWord* top = surv->top();
5724 size_t i;
5725 for (i = 0; i < _survivor_chunk_capacity; i++) { // all sca entries
5726 HeapWord* min_val = top; // Higher than any PLAB address
5727 uint min_tid = 0; // position of min_val this round
5728 for (int j = 0; j < no_of_gc_threads; j++) {
5729 ChunkArray* cur_sca = &_survivor_plab_array[j];
5730 if (_cursor[j] == cur_sca->end()) {
5731 continue;
5732 }
5733 assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
5734 HeapWord* cur_val = cur_sca->nth(_cursor[j]);
5735 assert(surv->used_region().contains(cur_val), "Out of bounds value");
5736 if (cur_val < min_val) {
5737 min_tid = j;
5738 min_val = cur_val;
5739 } else {
5740 assert(cur_val < top, "All recorded addresses should be less");
5741 }
5742 }
5743 // At this point min_val and min_tid are respectively
5744 // the least address in _survivor_plab_array[j]->nth(_cursor[j])
5745 // and the thread (j) that witnesses that address.
5746 // We record this address in the _survivor_chunk_array[i]
5747 // and increment _cursor[min_tid] prior to the next round i.
5748 if (min_val == top) {
5749 break;
5750 }
5751 _survivor_chunk_array[i] = min_val;
5752 _cursor[min_tid]++;
5753 }
5754 // We are all done; record the size of the _survivor_chunk_array
5755 _survivor_chunk_index = i; // exclusive: [0, i)
5756 if (PrintCMSStatistics > 0) {
5757 gclog_or_tty->print(" (Survivor:" SIZE_FORMAT "chunks) ", i);
5758 }
5759 // Verify that we used up all the recorded entries
5760 #ifdef ASSERT
5761 size_t total = 0;
5762 for (int j = 0; j < no_of_gc_threads; j++) {
5763 assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
5764 total += _cursor[j];
5765 }
5766 assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
5767 // Check that the merged array is in sorted order
5768 if (total > 0) {
5769 for (size_t i = 0; i < total - 1; i++) {
5770 if (PrintCMSStatistics > 0) {
5771 gclog_or_tty->print(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
5772 i, _survivor_chunk_array[i]);
5773 }
5774 assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
5775 "Not sorted");
5776 }
5777 }
5778 #endif // ASSERT
5779 }
5780
5781 // Set up the space's par_seq_tasks structure for work claiming
5782 // for parallel initial scan and rescan of young gen.
5783 // See ParRescanTask where this is currently used.
5784 void
5785 CMSCollector::
5786 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
5787 assert(n_threads > 0, "Unexpected n_threads argument");
5788 DefNewGeneration* dng = (DefNewGeneration*)_young_gen;
5789
5790 // Eden space
5791 if (!dng->eden()->is_empty()) {
5792 SequentialSubTasksDone* pst = dng->eden()->par_seq_tasks();
5793 assert(!pst->valid(), "Clobbering existing data?");
5794 // Each valid entry in [0, _eden_chunk_index) represents a task.
5795 size_t n_tasks = _eden_chunk_index + 1;
5796 assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
5797 // Sets the condition for completion of the subtask (how many threads
5798 // need to finish in order to be done).
5799 pst->set_n_threads(n_threads);
5800 pst->set_n_tasks((int)n_tasks);
5801 }
5802
5803 // Merge the survivor plab arrays into _survivor_chunk_array
5804 if (_survivor_plab_array != NULL) {
5805 merge_survivor_plab_arrays(dng->from(), n_threads);
5806 } else {
5807 assert(_survivor_chunk_index == 0, "Error");
5808 }
5809
5810 // To space
5811 {
5812 SequentialSubTasksDone* pst = dng->to()->par_seq_tasks();
5813 assert(!pst->valid(), "Clobbering existing data?");
5814 // Sets the condition for completion of the subtask (how many threads
5815 // need to finish in order to be done).
5816 pst->set_n_threads(n_threads);
5817 pst->set_n_tasks(1);
5818 assert(pst->valid(), "Error");
5819 }
5820
5821 // From space
5822 {
5823 SequentialSubTasksDone* pst = dng->from()->par_seq_tasks();
5824 assert(!pst->valid(), "Clobbering existing data?");
5825 size_t n_tasks = _survivor_chunk_index + 1;
5826 assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
5827 // Sets the condition for completion of the subtask (how many threads
5828 // need to finish in order to be done).
5829 pst->set_n_threads(n_threads);
5830 pst->set_n_tasks((int)n_tasks);
5831 assert(pst->valid(), "Error");
5832 }
5833 }
5834
5835 // Parallel version of remark
5836 void CMSCollector::do_remark_parallel() {
5837 GenCollectedHeap* gch = GenCollectedHeap::heap();
5838 FlexibleWorkGang* workers = gch->workers();
5839 assert(workers != NULL, "Need parallel worker threads.");
5840 // Choose to use the number of GC workers most recently set
5841 // into "active_workers". If active_workers is not set, set it
5842 // to ParallelGCThreads.
5843 int n_workers = workers->active_workers();
5844 if (n_workers == 0) {
5845 assert(n_workers > 0, "Should have been set during scavenge");
5846 n_workers = ParallelGCThreads;
5847 workers->set_active_workers(n_workers);
5848 }
5849 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
5850
5851 CMSParRemarkTask tsk(this,
5852 cms_space,
5853 n_workers, workers, task_queues());
5854
5855 // Set up for parallel process_strong_roots work.
5856 gch->set_par_threads(n_workers);
5857 // We won't be iterating over the cards in the card table updating
5858 // the younger_gen cards, so we shouldn't call the following else
5859 // the verification code as well as subsequent younger_refs_iterate
5860 // code would get confused. XXX
5861 // gch->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
5862
5863 // The young gen rescan work will not be done as part of
5864 // process_strong_roots (which currently doesn't knw how to
5865 // parallelize such a scan), but rather will be broken up into
5866 // a set of parallel tasks (via the sampling that the [abortable]
5867 // preclean phase did of EdenSpace, plus the [two] tasks of
5868 // scanning the [two] survivor spaces. Further fine-grain
5869 // parallelization of the scanning of the survivor spaces
5870 // themselves, and of precleaning of the younger gen itself
5871 // is deferred to the future.
5872 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
5873
5874 // The dirty card rescan work is broken up into a "sequence"
5875 // of parallel tasks (per constituent space) that are dynamically
5876 // claimed by the parallel threads.
5877 cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
5878
5879 // It turns out that even when we're using 1 thread, doing the work in a
5880 // separate thread causes wide variance in run times. We can't help this
5881 // in the multi-threaded case, but we special-case n=1 here to get
5882 // repeatable measurements of the 1-thread overhead of the parallel code.
5883 if (n_workers > 1) {
5884 // Make refs discovery MT-safe, if it isn't already: it may not
5885 // necessarily be so, since it's possible that we are doing
5886 // ST marking.
5887 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), true);
5888 GenCollectedHeap::StrongRootsScope srs(gch);
5889 workers->run_task(&tsk);
5890 } else {
5891 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5892 GenCollectedHeap::StrongRootsScope srs(gch);
5893 tsk.work(0);
5894 }
5895
5896 gch->set_par_threads(0); // 0 ==> non-parallel.
5897 // restore, single-threaded for now, any preserved marks
5898 // as a result of work_q overflow
5899 restore_preserved_marks_if_any();
5900 }
5901
5902 // Non-parallel version of remark
5903 void CMSCollector::do_remark_non_parallel() {
5904 ResourceMark rm;
5905 HandleMark hm;
5906 GenCollectedHeap* gch = GenCollectedHeap::heap();
5907 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5908
5909 MarkRefsIntoAndScanClosure
5910 mrias_cl(_span, ref_processor(), &_markBitMap, NULL /* not precleaning */,
5911 &_markStack, this,
5912 false /* should_yield */, false /* not precleaning */);
5913 MarkFromDirtyCardsClosure
5914 markFromDirtyCardsClosure(this, _span,
5915 NULL, // space is set further below
5916 &_markBitMap, &_markStack, &mrias_cl);
5917 {
5918 GCTraceTime t("grey object rescan", PrintGCDetails, false, _gc_timer_cm);
5919 // Iterate over the dirty cards, setting the corresponding bits in the
5920 // mod union table.
5921 {
5922 ModUnionClosure modUnionClosure(&_modUnionTable);
5923 _ct->ct_bs()->dirty_card_iterate(
5924 _cmsGen->used_region(),
5925 &modUnionClosure);
5926 }
5927 // Having transferred these marks into the modUnionTable, we just need
5928 // to rescan the marked objects on the dirty cards in the modUnionTable.
5929 // The initial marking may have been done during an asynchronous
5930 // collection so there may be dirty bits in the mod-union table.
5931 const int alignment =
5932 CardTableModRefBS::card_size * BitsPerWord;
5933 {
5934 // ... First handle dirty cards in CMS gen
5935 markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
5936 MemRegion ur = _cmsGen->used_region();
5937 HeapWord* lb = ur.start();
5938 HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
5939 MemRegion cms_span(lb, ub);
5940 _modUnionTable.dirty_range_iterate_clear(cms_span,
5941 &markFromDirtyCardsClosure);
5942 verify_work_stacks_empty();
5943 if (PrintCMSStatistics != 0) {
5944 gclog_or_tty->print(" (re-scanned "SIZE_FORMAT" dirty cards in cms gen) ",
5945 markFromDirtyCardsClosure.num_dirty_cards());
5946 }
5947 }
5948 }
5949 if (VerifyDuringGC &&
5950 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5951 HandleMark hm; // Discard invalid handles created during verification
5952 Universe::verify();
5953 }
5954 {
5955 GCTraceTime t("root rescan", PrintGCDetails, false, _gc_timer_cm);
5956
5957 verify_work_stacks_empty();
5958
5959 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
5960 GenCollectedHeap::StrongRootsScope srs(gch);
5961 gch->gen_process_strong_roots(_cmsGen->level(),
5962 true, // younger gens as roots
5963 false, // use the local StrongRootsScope
5964 SharedHeap::ScanningOption(roots_scanning_options()),
5965 &mrias_cl,
5966 true, // walk code active on stacks
5967 NULL,
5968 NULL); // The dirty klasses will be handled below
5969
5970 assert(should_unload_classes()
5971 || (roots_scanning_options() & SharedHeap::SO_AllCodeCache),
5972 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5973 }
5974
5975 {
5976 GCTraceTime t("visit unhandled CLDs", PrintGCDetails, false, _gc_timer_cm);
5977
5978 verify_work_stacks_empty();
5979
5980 // Scan all class loader data objects that might have been introduced
5981 // during concurrent marking.
5982 ResourceMark rm;
5983 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
5984 for (int i = 0; i < array->length(); i++) {
5985 mrias_cl.do_class_loader_data(array->at(i));
5986 }
5987
5988 // We don't need to keep track of new CLDs anymore.
5989 ClassLoaderDataGraph::remember_new_clds(false);
5990
5991 verify_work_stacks_empty();
5992 }
5993
5994 {
5995 GCTraceTime t("dirty klass scan", PrintGCDetails, false, _gc_timer_cm);
5996
5997 verify_work_stacks_empty();
5998
5999 RemarkKlassClosure remark_klass_closure(&mrias_cl);
6000 ClassLoaderDataGraph::classes_do(&remark_klass_closure);
6001
6002 verify_work_stacks_empty();
6003 }
6004
6005 // We might have added oops to ClassLoaderData::_handles during the
6006 // concurrent marking phase. These oops point to newly allocated objects
6007 // that are guaranteed to be kept alive. Either by the direct allocation
6008 // code, or when the young collector processes the strong roots. Hence,
6009 // we don't have to revisit the _handles block during the remark phase.
6010
6011 verify_work_stacks_empty();
6012 // Restore evacuated mark words, if any, used for overflow list links
6013 if (!CMSOverflowEarlyRestoration) {
6014 restore_preserved_marks_if_any();
6015 }
6016 verify_overflow_empty();
6017 }
6018
6019 ////////////////////////////////////////////////////////
6020 // Parallel Reference Processing Task Proxy Class
6021 ////////////////////////////////////////////////////////
6022 class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues {
6023 typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
6024 CMSCollector* _collector;
6025 CMSBitMap* _mark_bit_map;
6026 const MemRegion _span;
6027 ProcessTask& _task;
6028
6029 public:
6030 CMSRefProcTaskProxy(ProcessTask& task,
6031 CMSCollector* collector,
6032 const MemRegion& span,
6033 CMSBitMap* mark_bit_map,
6034 AbstractWorkGang* workers,
6035 OopTaskQueueSet* task_queues):
6036 // XXX Should superclass AGTWOQ also know about AWG since it knows
6037 // about the task_queues used by the AWG? Then it could initialize
6038 // the terminator() object. See 6984287. The set_for_termination()
6039 // below is a temporary band-aid for the regression in 6984287.
6040 AbstractGangTaskWOopQueues("Process referents by policy in parallel",
6041 task_queues),
6042 _task(task),
6043 _collector(collector), _span(span), _mark_bit_map(mark_bit_map)
6044 {
6045 assert(_collector->_span.equals(_span) && !_span.is_empty(),
6046 "Inconsistency in _span");
6047 set_for_termination(workers->active_workers());
6048 }
6049
6050 OopTaskQueueSet* task_queues() { return queues(); }
6051
6052 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
6053
6054 void do_work_steal(int i,
6055 CMSParDrainMarkingStackClosure* drain,
6056 CMSParKeepAliveClosure* keep_alive,
6057 int* seed);
6058
6059 virtual void work(uint worker_id);
6060 };
6061
6062 void CMSRefProcTaskProxy::work(uint worker_id) {
6063 assert(_collector->_span.equals(_span), "Inconsistency in _span");
6064 CMSParKeepAliveClosure par_keep_alive(_collector, _span,
6065 _mark_bit_map,
6066 work_queue(worker_id));
6067 CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
6068 _mark_bit_map,
6069 work_queue(worker_id));
6070 CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
6071 _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack);
6072 if (_task.marks_oops_alive()) {
6073 do_work_steal(worker_id, &par_drain_stack, &par_keep_alive,
6074 _collector->hash_seed(worker_id));
6075 }
6076 assert(work_queue(worker_id)->size() == 0, "work_queue should be empty");
6077 assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
6078 }
6079
6080 class CMSRefEnqueueTaskProxy: public AbstractGangTask {
6081 typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
6082 EnqueueTask& _task;
6083
6084 public:
6085 CMSRefEnqueueTaskProxy(EnqueueTask& task)
6086 : AbstractGangTask("Enqueue reference objects in parallel"),
6087 _task(task)
6088 { }
6089
6090 virtual void work(uint worker_id)
6091 {
6092 _task.work(worker_id);
6093 }
6094 };
6095
6096 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
6097 MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue):
6098 _span(span),
6099 _bit_map(bit_map),
6100 _work_queue(work_queue),
6101 _mark_and_push(collector, span, bit_map, work_queue),
6102 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
6103 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads)))
6104 { }
6105
6106 // . see if we can share work_queues with ParNew? XXX
6107 void CMSRefProcTaskProxy::do_work_steal(int i,
6108 CMSParDrainMarkingStackClosure* drain,
6109 CMSParKeepAliveClosure* keep_alive,
6110 int* seed) {
6111 OopTaskQueue* work_q = work_queue(i);
6112 NOT_PRODUCT(int num_steals = 0;)
6113 oop obj_to_scan;
6114
6115 while (true) {
6116 // Completely finish any left over work from (an) earlier round(s)
6117 drain->trim_queue(0);
6118 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
6119 (size_t)ParGCDesiredObjsFromOverflowList);
6120 // Now check if there's any work in the overflow list
6121 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
6122 // only affects the number of attempts made to get work from the
6123 // overflow list and does not affect the number of workers. Just
6124 // pass ParallelGCThreads so this behavior is unchanged.
6125 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
6126 work_q,
6127 ParallelGCThreads)) {
6128 // Found something in global overflow list;
6129 // not yet ready to go stealing work from others.
6130 // We'd like to assert(work_q->size() != 0, ...)
6131 // because we just took work from the overflow list,
6132 // but of course we can't, since all of that might have
6133 // been already stolen from us.
6134 continue;
6135 }
6136 // Verify that we have no work before we resort to stealing
6137 assert(work_q->size() == 0, "Have work, shouldn't steal");
6138 // Try to steal from other queues that have work
6139 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
6140 NOT_PRODUCT(num_steals++;)
6141 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
6142 assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
6143 // Do scanning work
6144 obj_to_scan->oop_iterate(keep_alive);
6145 // Loop around, finish this work, and try to steal some more
6146 } else if (terminator()->offer_termination()) {
6147 break; // nirvana from the infinite cycle
6148 }
6149 }
6150 NOT_PRODUCT(
6151 if (PrintCMSStatistics != 0) {
6152 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
6153 }
6154 )
6155 }
6156
6157 void CMSRefProcTaskExecutor::execute(ProcessTask& task)
6158 {
6159 GenCollectedHeap* gch = GenCollectedHeap::heap();
6160 FlexibleWorkGang* workers = gch->workers();
6161 assert(workers != NULL, "Need parallel worker threads.");
6162 CMSRefProcTaskProxy rp_task(task, &_collector,
6163 _collector.ref_processor()->span(),
6164 _collector.markBitMap(),
6165 workers, _collector.task_queues());
6166 workers->run_task(&rp_task);
6167 }
6168
6169 void CMSRefProcTaskExecutor::execute(EnqueueTask& task)
6170 {
6171
6172 GenCollectedHeap* gch = GenCollectedHeap::heap();
6173 FlexibleWorkGang* workers = gch->workers();
6174 assert(workers != NULL, "Need parallel worker threads.");
6175 CMSRefEnqueueTaskProxy enq_task(task);
6176 workers->run_task(&enq_task);
6177 }
6178
6179 void CMSCollector::refProcessingWork(bool asynch, bool clear_all_soft_refs) {
6180
6181 ResourceMark rm;
6182 HandleMark hm;
6183
6184 ReferenceProcessor* rp = ref_processor();
6185 assert(rp->span().equals(_span), "Spans should be equal");
6186 assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
6187 // Process weak references.
6188 rp->setup_policy(clear_all_soft_refs);
6189 verify_work_stacks_empty();
6190
6191 CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
6192 &_markStack, false /* !preclean */);
6193 CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
6194 _span, &_markBitMap, &_markStack,
6195 &cmsKeepAliveClosure, false /* !preclean */);
6196 {
6197 GCTraceTime t("weak refs processing", PrintGCDetails, false, _gc_timer_cm);
6198
6199 ReferenceProcessorStats stats;
6200 if (rp->processing_is_mt()) {
6201 // Set the degree of MT here. If the discovery is done MT, there
6202 // may have been a different number of threads doing the discovery
6203 // and a different number of discovered lists may have Ref objects.
6204 // That is OK as long as the Reference lists are balanced (see
6205 // balance_all_queues() and balance_queues()).
6206 GenCollectedHeap* gch = GenCollectedHeap::heap();
6207 int active_workers = ParallelGCThreads;
6208 FlexibleWorkGang* workers = gch->workers();
6209 if (workers != NULL) {
6210 active_workers = workers->active_workers();
6211 // The expectation is that active_workers will have already
6212 // been set to a reasonable value. If it has not been set,
6213 // investigate.
6214 assert(active_workers > 0, "Should have been set during scavenge");
6215 }
6216 rp->set_active_mt_degree(active_workers);
6217 CMSRefProcTaskExecutor task_executor(*this);
6218 stats = rp->process_discovered_references(&_is_alive_closure,
6219 &cmsKeepAliveClosure,
6220 &cmsDrainMarkingStackClosure,
6221 &task_executor,
6222 _gc_timer_cm);
6223 } else {
6224 stats = rp->process_discovered_references(&_is_alive_closure,
6225 &cmsKeepAliveClosure,
6226 &cmsDrainMarkingStackClosure,
6227 NULL,
6228 _gc_timer_cm);
6229 }
6230 _gc_tracer_cm->report_gc_reference_stats(stats);
6231
6232 }
6233
6234 // This is the point where the entire marking should have completed.
6235 verify_work_stacks_empty();
6236
6237 if (should_unload_classes()) {
6238 {
6239 GCTraceTime t("class unloading", PrintGCDetails, false, _gc_timer_cm);
6240
6241 // Unload classes and purge the SystemDictionary.
6242 bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure);
6243
6244 // Unload nmethods.
6245 CodeCache::do_unloading(&_is_alive_closure, purged_class);
6246
6247 // Prune dead klasses from subklass/sibling/implementor lists.
6248 Klass::clean_weak_klass_links(&_is_alive_closure);
6249 }
6250
6251 {
6252 GCTraceTime t("scrub symbol table", PrintGCDetails, false, _gc_timer_cm);
6253 // Clean up unreferenced symbols in symbol table.
6254 SymbolTable::unlink();
6255 }
6256 }
6257
6258 // CMS doesn't use the StringTable as hard roots when class unloading is turned off.
6259 // Need to check if we really scanned the StringTable.
6260 if ((roots_scanning_options() & SharedHeap::SO_Strings) == 0) {
6261 GCTraceTime t("scrub string table", PrintGCDetails, false, _gc_timer_cm);
6262 // Delete entries for dead interned strings.
6263 StringTable::unlink(&_is_alive_closure);
6264 }
6265
6266 // Restore any preserved marks as a result of mark stack or
6267 // work queue overflow
6268 restore_preserved_marks_if_any(); // done single-threaded for now
6269
6270 rp->set_enqueuing_is_done(true);
6271 if (rp->processing_is_mt()) {
6272 rp->balance_all_queues();
6273 CMSRefProcTaskExecutor task_executor(*this);
6274 rp->enqueue_discovered_references(&task_executor);
6275 } else {
6276 rp->enqueue_discovered_references(NULL);
6277 }
6278 rp->verify_no_references_recorded();
6279 assert(!rp->discovery_enabled(), "should have been disabled");
6280 }
6281
6282 #ifndef PRODUCT
6283 void CMSCollector::check_correct_thread_executing() {
6284 Thread* t = Thread::current();
6285 // Only the VM thread or the CMS thread should be here.
6286 assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
6287 "Unexpected thread type");
6288 // If this is the vm thread, the foreground process
6289 // should not be waiting. Note that _foregroundGCIsActive is
6290 // true while the foreground collector is waiting.
6291 if (_foregroundGCShouldWait) {
6292 // We cannot be the VM thread
6293 assert(t->is_ConcurrentGC_thread(),
6294 "Should be CMS thread");
6295 } else {
6296 // We can be the CMS thread only if we are in a stop-world
6297 // phase of CMS collection.
6298 if (t->is_ConcurrentGC_thread()) {
6299 assert(_collectorState == InitialMarking ||
6300 _collectorState == FinalMarking,
6301 "Should be a stop-world phase");
6302 // The CMS thread should be holding the CMS_token.
6303 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6304 "Potential interference with concurrently "
6305 "executing VM thread");
6306 }
6307 }
6308 }
6309 #endif
6310
6311 void CMSCollector::sweep(bool asynch) {
6312 assert(_collectorState == Sweeping, "just checking");
6313 check_correct_thread_executing();
6314 verify_work_stacks_empty();
6315 verify_overflow_empty();
6316 increment_sweep_count();
6317 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
6318
6319 _inter_sweep_timer.stop();
6320 _inter_sweep_estimate.sample(_inter_sweep_timer.seconds());
6321 size_policy()->avg_cms_free_at_sweep()->sample(_cmsGen->free());
6322
6323 assert(!_intra_sweep_timer.is_active(), "Should not be active");
6324 _intra_sweep_timer.reset();
6325 _intra_sweep_timer.start();
6326 if (asynch) {
6327 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6328 CMSPhaseAccounting pa(this, "sweep", !PrintGCDetails);
6329 // First sweep the old gen
6330 {
6331 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
6332 bitMapLock());
6333 sweepWork(_cmsGen, asynch);
6334 }
6335
6336 // Update Universe::_heap_*_at_gc figures.
6337 // We need all the free list locks to make the abstract state
6338 // transition from Sweeping to Resetting. See detailed note
6339 // further below.
6340 {
6341 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock());
6342 // Update heap occupancy information which is used as
6343 // input to soft ref clearing policy at the next gc.
6344 Universe::update_heap_info_at_gc();
6345 _collectorState = Resizing;
6346 }
6347 } else {
6348 // already have needed locks
6349 sweepWork(_cmsGen, asynch);
6350 // Update heap occupancy information which is used as
6351 // input to soft ref clearing policy at the next gc.
6352 Universe::update_heap_info_at_gc();
6353 _collectorState = Resizing;
6354 }
6355 verify_work_stacks_empty();
6356 verify_overflow_empty();
6357
6358 if (should_unload_classes()) {
6359 ClassLoaderDataGraph::purge();
6360 }
6361
6362 _intra_sweep_timer.stop();
6363 _intra_sweep_estimate.sample(_intra_sweep_timer.seconds());
6364
6365 _inter_sweep_timer.reset();
6366 _inter_sweep_timer.start();
6367
6368 // We need to use a monotonically non-decreasing time in ms
6369 // or we will see time-warp warnings and os::javaTimeMillis()
6370 // does not guarantee monotonicity.
6371 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
6372 update_time_of_last_gc(now);
6373
6374 // NOTE on abstract state transitions:
6375 // Mutators allocate-live and/or mark the mod-union table dirty
6376 // based on the state of the collection. The former is done in
6377 // the interval [Marking, Sweeping] and the latter in the interval
6378 // [Marking, Sweeping). Thus the transitions into the Marking state
6379 // and out of the Sweeping state must be synchronously visible
6380 // globally to the mutators.
6381 // The transition into the Marking state happens with the world
6382 // stopped so the mutators will globally see it. Sweeping is
6383 // done asynchronously by the background collector so the transition
6384 // from the Sweeping state to the Resizing state must be done
6385 // under the freelistLock (as is the check for whether to
6386 // allocate-live and whether to dirty the mod-union table).
6387 assert(_collectorState == Resizing, "Change of collector state to"
6388 " Resizing must be done under the freelistLocks (plural)");
6389
6390 // Now that sweeping has been completed, we clear
6391 // the incremental_collection_failed flag,
6392 // thus inviting a younger gen collection to promote into
6393 // this generation. If such a promotion may still fail,
6394 // the flag will be set again when a young collection is
6395 // attempted.
6396 GenCollectedHeap* gch = GenCollectedHeap::heap();
6397 gch->clear_incremental_collection_failed(); // Worth retrying as fresh space may have been freed up
6398 gch->update_full_collections_completed(_collection_count_start);
6399 }
6400
6401 // FIX ME!!! Looks like this belongs in CFLSpace, with
6402 // CMSGen merely delegating to it.
6403 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
6404 double nearLargestPercent = FLSLargestBlockCoalesceProximity;
6405 HeapWord* minAddr = _cmsSpace->bottom();
6406 HeapWord* largestAddr =
6407 (HeapWord*) _cmsSpace->dictionary()->find_largest_dict();
6408 if (largestAddr == NULL) {
6409 // The dictionary appears to be empty. In this case
6410 // try to coalesce at the end of the heap.
6411 largestAddr = _cmsSpace->end();
6412 }
6413 size_t largestOffset = pointer_delta(largestAddr, minAddr);
6414 size_t nearLargestOffset =
6415 (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
6416 if (PrintFLSStatistics != 0) {
6417 gclog_or_tty->print_cr(
6418 "CMS: Large Block: " PTR_FORMAT ";"
6419 " Proximity: " PTR_FORMAT " -> " PTR_FORMAT,
6420 largestAddr,
6421 _cmsSpace->nearLargestChunk(), minAddr + nearLargestOffset);
6422 }
6423 _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
6424 }
6425
6426 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
6427 return addr >= _cmsSpace->nearLargestChunk();
6428 }
6429
6430 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
6431 return _cmsSpace->find_chunk_at_end();
6432 }
6433
6434 void ConcurrentMarkSweepGeneration::update_gc_stats(int current_level,
6435 bool full) {
6436 // The next lower level has been collected. Gather any statistics
6437 // that are of interest at this point.
6438 if (!full && (current_level + 1) == level()) {
6439 // Gather statistics on the young generation collection.
6440 collector()->stats().record_gc0_end(used());
6441 }
6442 }
6443
6444 CMSAdaptiveSizePolicy* ConcurrentMarkSweepGeneration::size_policy() {
6445 GenCollectedHeap* gch = GenCollectedHeap::heap();
6446 assert(gch->kind() == CollectedHeap::GenCollectedHeap,
6447 "Wrong type of heap");
6448 CMSAdaptiveSizePolicy* sp = (CMSAdaptiveSizePolicy*)
6449 gch->gen_policy()->size_policy();
6450 assert(sp->is_gc_cms_adaptive_size_policy(),
6451 "Wrong type of size policy");
6452 return sp;
6453 }
6454
6455 void ConcurrentMarkSweepGeneration::rotate_debug_collection_type() {
6456 if (PrintGCDetails && Verbose) {
6457 gclog_or_tty->print("Rotate from %d ", _debug_collection_type);
6458 }
6459 _debug_collection_type = (CollectionTypes) (_debug_collection_type + 1);
6460 _debug_collection_type =
6461 (CollectionTypes) (_debug_collection_type % Unknown_collection_type);
6462 if (PrintGCDetails && Verbose) {
6463 gclog_or_tty->print_cr("to %d ", _debug_collection_type);
6464 }
6465 }
6466
6467 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* gen,
6468 bool asynch) {
6469 // We iterate over the space(s) underlying this generation,
6470 // checking the mark bit map to see if the bits corresponding
6471 // to specific blocks are marked or not. Blocks that are
6472 // marked are live and are not swept up. All remaining blocks
6473 // are swept up, with coalescing on-the-fly as we sweep up
6474 // contiguous free and/or garbage blocks:
6475 // We need to ensure that the sweeper synchronizes with allocators
6476 // and stop-the-world collectors. In particular, the following
6477 // locks are used:
6478 // . CMS token: if this is held, a stop the world collection cannot occur
6479 // . freelistLock: if this is held no allocation can occur from this
6480 // generation by another thread
6481 // . bitMapLock: if this is held, no other thread can access or update
6482 //
6483
6484 // Note that we need to hold the freelistLock if we use
6485 // block iterate below; else the iterator might go awry if
6486 // a mutator (or promotion) causes block contents to change
6487 // (for instance if the allocator divvies up a block).
6488 // If we hold the free list lock, for all practical purposes
6489 // young generation GC's can't occur (they'll usually need to
6490 // promote), so we might as well prevent all young generation
6491 // GC's while we do a sweeping step. For the same reason, we might
6492 // as well take the bit map lock for the entire duration
6493
6494 // check that we hold the requisite locks
6495 assert(have_cms_token(), "Should hold cms token");
6496 assert( (asynch && ConcurrentMarkSweepThread::cms_thread_has_cms_token())
6497 || (!asynch && ConcurrentMarkSweepThread::vm_thread_has_cms_token()),
6498 "Should possess CMS token to sweep");
6499 assert_lock_strong(gen->freelistLock());
6500 assert_lock_strong(bitMapLock());
6501
6502 assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context");
6503 assert(_intra_sweep_timer.is_active(), "Was switched on in an outer context");
6504 gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
6505 _inter_sweep_estimate.padded_average(),
6506 _intra_sweep_estimate.padded_average());
6507 gen->setNearLargestChunk();
6508
6509 {
6510 SweepClosure sweepClosure(this, gen, &_markBitMap,
6511 CMSYield && asynch);
6512 gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
6513 // We need to free-up/coalesce garbage/blocks from a
6514 // co-terminal free run. This is done in the SweepClosure
6515 // destructor; so, do not remove this scope, else the
6516 // end-of-sweep-census below will be off by a little bit.
6517 }
6518 gen->cmsSpace()->sweep_completed();
6519 gen->cmsSpace()->endSweepFLCensus(sweep_count());
6520 if (should_unload_classes()) { // unloaded classes this cycle,
6521 _concurrent_cycles_since_last_unload = 0; // ... reset count
6522 } else { // did not unload classes,
6523 _concurrent_cycles_since_last_unload++; // ... increment count
6524 }
6525 }
6526
6527 // Reset CMS data structures (for now just the marking bit map)
6528 // preparatory for the next cycle.
6529 void CMSCollector::reset(bool asynch) {
6530 GenCollectedHeap* gch = GenCollectedHeap::heap();
6531 CMSAdaptiveSizePolicy* sp = size_policy();
6532 AdaptiveSizePolicyOutput(sp, gch->total_collections());
6533 if (asynch) {
6534 CMSTokenSyncWithLocks ts(true, bitMapLock());
6535
6536 // If the state is not "Resetting", the foreground thread
6537 // has done a collection and the resetting.
6538 if (_collectorState != Resetting) {
6539 assert(_collectorState == Idling, "The state should only change"
6540 " because the foreground collector has finished the collection");
6541 return;
6542 }
6543
6544 // Clear the mark bitmap (no grey objects to start with)
6545 // for the next cycle.
6546 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6547 CMSPhaseAccounting cmspa(this, "reset", !PrintGCDetails);
6548
6549 HeapWord* curAddr = _markBitMap.startWord();
6550 while (curAddr < _markBitMap.endWord()) {
6551 size_t remaining = pointer_delta(_markBitMap.endWord(), curAddr);
6552 MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
6553 _markBitMap.clear_large_range(chunk);
6554 if (ConcurrentMarkSweepThread::should_yield() &&
6555 !foregroundGCIsActive() &&
6556 CMSYield) {
6557 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6558 "CMS thread should hold CMS token");
6559 assert_lock_strong(bitMapLock());
6560 bitMapLock()->unlock();
6561 ConcurrentMarkSweepThread::desynchronize(true);
6562 ConcurrentMarkSweepThread::acknowledge_yield_request();
6563 stopTimer();
6564 if (PrintCMSStatistics != 0) {
6565 incrementYields();
6566 }
6567 icms_wait();
6568
6569 // See the comment in coordinator_yield()
6570 for (unsigned i = 0; i < CMSYieldSleepCount &&
6571 ConcurrentMarkSweepThread::should_yield() &&
6572 !CMSCollector::foregroundGCIsActive(); ++i) {
6573 os::sleep(Thread::current(), 1, false);
6574 ConcurrentMarkSweepThread::acknowledge_yield_request();
6575 }
6576
6577 ConcurrentMarkSweepThread::synchronize(true);
6578 bitMapLock()->lock_without_safepoint_check();
6579 startTimer();
6580 }
6581 curAddr = chunk.end();
6582 }
6583 // A successful mostly concurrent collection has been done.
6584 // Because only the full (i.e., concurrent mode failure) collections
6585 // are being measured for gc overhead limits, clean the "near" flag
6586 // and count.
6587 sp->reset_gc_overhead_limit_count();
6588 _collectorState = Idling;
6589 } else {
6590 // already have the lock
6591 assert(_collectorState == Resetting, "just checking");
6592 assert_lock_strong(bitMapLock());
6593 _markBitMap.clear_all();
6594 _collectorState = Idling;
6595 }
6596
6597 // Stop incremental mode after a cycle completes, so that any future cycles
6598 // are triggered by allocation.
6599 stop_icms();
6600
6601 NOT_PRODUCT(
6602 if (RotateCMSCollectionTypes) {
6603 _cmsGen->rotate_debug_collection_type();
6604 }
6605 )
6606
6607 register_gc_end();
6608 }
6609
6610 void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) {
6611 gclog_or_tty->date_stamp(PrintGC && PrintGCDateStamps);
6612 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6613 GCTraceTime t(GCCauseString("GC", gc_cause), PrintGC, !PrintGCDetails, NULL);
6614 TraceCollectorStats tcs(counters());
6615
6616 switch (op) {
6617 case CMS_op_checkpointRootsInitial: {
6618 SvcGCMarker sgcm(SvcGCMarker::OTHER);
6619 checkpointRootsInitial(true); // asynch
6620 if (PrintGC) {
6621 _cmsGen->printOccupancy("initial-mark");
6622 }
6623 break;
6624 }
6625 case CMS_op_checkpointRootsFinal: {
6626 SvcGCMarker sgcm(SvcGCMarker::OTHER);
6627 checkpointRootsFinal(true, // asynch
6628 false, // !clear_all_soft_refs
6629 false); // !init_mark_was_synchronous
6630 if (PrintGC) {
6631 _cmsGen->printOccupancy("remark");
6632 }
6633 break;
6634 }
6635 default:
6636 fatal("No such CMS_op");
6637 }
6638 }
6639
6640 #ifndef PRODUCT
6641 size_t const CMSCollector::skip_header_HeapWords() {
6642 return FreeChunk::header_size();
6643 }
6644
6645 // Try and collect here conditions that should hold when
6646 // CMS thread is exiting. The idea is that the foreground GC
6647 // thread should not be blocked if it wants to terminate
6648 // the CMS thread and yet continue to run the VM for a while
6649 // after that.
6650 void CMSCollector::verify_ok_to_terminate() const {
6651 assert(Thread::current()->is_ConcurrentGC_thread(),
6652 "should be called by CMS thread");
6653 assert(!_foregroundGCShouldWait, "should be false");
6654 // We could check here that all the various low-level locks
6655 // are not held by the CMS thread, but that is overkill; see
6656 // also CMSThread::verify_ok_to_terminate() where the CGC_lock
6657 // is checked.
6658 }
6659 #endif
6660
6661 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
6662 assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
6663 "missing Printezis mark?");
6664 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
6665 size_t size = pointer_delta(nextOneAddr + 1, addr);
6666 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6667 "alignment problem");
6668 assert(size >= 3, "Necessary for Printezis marks to work");
6669 return size;
6670 }
6671
6672 // A variant of the above (block_size_using_printezis_bits()) except
6673 // that we return 0 if the P-bits are not yet set.
6674 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
6675 if (_markBitMap.isMarked(addr + 1)) {
6676 assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects");
6677 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
6678 size_t size = pointer_delta(nextOneAddr + 1, addr);
6679 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6680 "alignment problem");
6681 assert(size >= 3, "Necessary for Printezis marks to work");
6682 return size;
6683 }
6684 return 0;
6685 }
6686
6687 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
6688 size_t sz = 0;
6689 oop p = (oop)addr;
6690 if (p->klass_or_null() != NULL) {
6691 sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
6692 } else {
6693 sz = block_size_using_printezis_bits(addr);
6694 }
6695 assert(sz > 0, "size must be nonzero");
6696 HeapWord* next_block = addr + sz;
6697 HeapWord* next_card = (HeapWord*)round_to((uintptr_t)next_block,
6698 CardTableModRefBS::card_size);
6699 assert(round_down((uintptr_t)addr, CardTableModRefBS::card_size) <
6700 round_down((uintptr_t)next_card, CardTableModRefBS::card_size),
6701 "must be different cards");
6702 return next_card;
6703 }
6704
6705
6706 // CMS Bit Map Wrapper /////////////////////////////////////////
6707
6708 // Construct a CMS bit map infrastructure, but don't create the
6709 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
6710 // further below.
6711 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
6712 _bm(),
6713 _shifter(shifter),
6714 _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true) : NULL)
6715 {
6716 _bmStartWord = 0;
6717 _bmWordSize = 0;
6718 }
6719
6720 bool CMSBitMap::allocate(MemRegion mr) {
6721 _bmStartWord = mr.start();
6722 _bmWordSize = mr.word_size();
6723 ReservedSpace brs(ReservedSpace::allocation_align_size_up(
6724 (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
6725 if (!brs.is_reserved()) {
6726 warning("CMS bit map allocation failure");
6727 return false;
6728 }
6729 // For now we'll just commit all of the bit map up front.
6730 // Later on we'll try to be more parsimonious with swap.
6731 if (!_virtual_space.initialize(brs, brs.size())) {
6732 warning("CMS bit map backing store failure");
6733 return false;
6734 }
6735 assert(_virtual_space.committed_size() == brs.size(),
6736 "didn't reserve backing store for all of CMS bit map?");
6737 _bm.set_map((BitMap::bm_word_t*)_virtual_space.low());
6738 assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
6739 _bmWordSize, "inconsistency in bit map sizing");
6740 _bm.set_size(_bmWordSize >> _shifter);
6741
6742 // bm.clear(); // can we rely on getting zero'd memory? verify below
6743 assert(isAllClear(),
6744 "Expected zero'd memory from ReservedSpace constructor");
6745 assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
6746 "consistency check");
6747 return true;
6748 }
6749
6750 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
6751 HeapWord *next_addr, *end_addr, *last_addr;
6752 assert_locked();
6753 assert(covers(mr), "out-of-range error");
6754 // XXX assert that start and end are appropriately aligned
6755 for (next_addr = mr.start(), end_addr = mr.end();
6756 next_addr < end_addr; next_addr = last_addr) {
6757 MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
6758 last_addr = dirty_region.end();
6759 if (!dirty_region.is_empty()) {
6760 cl->do_MemRegion(dirty_region);
6761 } else {
6762 assert(last_addr == end_addr, "program logic");
6763 return;
6764 }
6765 }
6766 }
6767
6768 void CMSBitMap::print_on_error(outputStream* st, const char* prefix) const {
6769 _bm.print_on_error(st, prefix);
6770 }
6771
6772 #ifndef PRODUCT
6773 void CMSBitMap::assert_locked() const {
6774 CMSLockVerifier::assert_locked(lock());
6775 }
6776
6777 bool CMSBitMap::covers(MemRegion mr) const {
6778 // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
6779 assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
6780 "size inconsistency");
6781 return (mr.start() >= _bmStartWord) &&
6782 (mr.end() <= endWord());
6783 }
6784
6785 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
6786 return (start >= _bmStartWord && (start + size) <= endWord());
6787 }
6788
6789 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
6790 // verify that there are no 1 bits in the interval [left, right)
6791 FalseBitMapClosure falseBitMapClosure;
6792 iterate(&falseBitMapClosure, left, right);
6793 }
6794
6795 void CMSBitMap::region_invariant(MemRegion mr)
6796 {
6797 assert_locked();
6798 // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
6799 assert(!mr.is_empty(), "unexpected empty region");
6800 assert(covers(mr), "mr should be covered by bit map");
6801 // convert address range into offset range
6802 size_t start_ofs = heapWordToOffset(mr.start());
6803 // Make sure that end() is appropriately aligned
6804 assert(mr.end() == (HeapWord*)round_to((intptr_t)mr.end(),
6805 (1 << (_shifter+LogHeapWordSize))),
6806 "Misaligned mr.end()");
6807 size_t end_ofs = heapWordToOffset(mr.end());
6808 assert(end_ofs > start_ofs, "Should mark at least one bit");
6809 }
6810
6811 #endif
6812
6813 bool CMSMarkStack::allocate(size_t size) {
6814 // allocate a stack of the requisite depth
6815 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6816 size * sizeof(oop)));
6817 if (!rs.is_reserved()) {
6818 warning("CMSMarkStack allocation failure");
6819 return false;
6820 }
6821 if (!_virtual_space.initialize(rs, rs.size())) {
6822 warning("CMSMarkStack backing store failure");
6823 return false;
6824 }
6825 assert(_virtual_space.committed_size() == rs.size(),
6826 "didn't reserve backing store for all of CMS stack?");
6827 _base = (oop*)(_virtual_space.low());
6828 _index = 0;
6829 _capacity = size;
6830 NOT_PRODUCT(_max_depth = 0);
6831 return true;
6832 }
6833
6834 // XXX FIX ME !!! In the MT case we come in here holding a
6835 // leaf lock. For printing we need to take a further lock
6836 // which has lower rank. We need to recalibrate the two
6837 // lock-ranks involved in order to be able to print the
6838 // messages below. (Or defer the printing to the caller.
6839 // For now we take the expedient path of just disabling the
6840 // messages for the problematic case.)
6841 void CMSMarkStack::expand() {
6842 assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted");
6843 if (_capacity == MarkStackSizeMax) {
6844 if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6845 // We print a warning message only once per CMS cycle.
6846 gclog_or_tty->print_cr(" (benign) Hit CMSMarkStack max size limit");
6847 }
6848 return;
6849 }
6850 // Double capacity if possible
6851 size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax);
6852 // Do not give up existing stack until we have managed to
6853 // get the double capacity that we desired.
6854 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6855 new_capacity * sizeof(oop)));
6856 if (rs.is_reserved()) {
6857 // Release the backing store associated with old stack
6858 _virtual_space.release();
6859 // Reinitialize virtual space for new stack
6860 if (!_virtual_space.initialize(rs, rs.size())) {
6861 fatal("Not enough swap for expanded marking stack");
6862 }
6863 _base = (oop*)(_virtual_space.low());
6864 _index = 0;
6865 _capacity = new_capacity;
6866 } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6867 // Failed to double capacity, continue;
6868 // we print a detail message only once per CMS cycle.
6869 gclog_or_tty->print(" (benign) Failed to expand marking stack from "SIZE_FORMAT"K to "
6870 SIZE_FORMAT"K",
6871 _capacity / K, new_capacity / K);
6872 }
6873 }
6874
6875
6876 // Closures
6877 // XXX: there seems to be a lot of code duplication here;
6878 // should refactor and consolidate common code.
6879
6880 // This closure is used to mark refs into the CMS generation in
6881 // the CMS bit map. Called at the first checkpoint. This closure
6882 // assumes that we do not need to re-mark dirty cards; if the CMS
6883 // generation on which this is used is not an oldest
6884 // generation then this will lose younger_gen cards!
6885
6886 MarkRefsIntoClosure::MarkRefsIntoClosure(
6887 MemRegion span, CMSBitMap* bitMap):
6888 _span(span),
6889 _bitMap(bitMap)
6890 {
6891 assert(_ref_processor == NULL, "deliberately left NULL");
6892 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6893 }
6894
6895 void MarkRefsIntoClosure::do_oop(oop obj) {
6896 // if p points into _span, then mark corresponding bit in _markBitMap
6897 assert(obj->is_oop(), "expected an oop");
6898 HeapWord* addr = (HeapWord*)obj;
6899 if (_span.contains(addr)) {
6900 // this should be made more efficient
6901 _bitMap->mark(addr);
6902 }
6903 }
6904
6905 void MarkRefsIntoClosure::do_oop(oop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6906 void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6907
6908 Par_MarkRefsIntoClosure::Par_MarkRefsIntoClosure(
6909 MemRegion span, CMSBitMap* bitMap):
6910 _span(span),
6911 _bitMap(bitMap)
6912 {
6913 assert(_ref_processor == NULL, "deliberately left NULL");
6914 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6915 }
6916
6917 void Par_MarkRefsIntoClosure::do_oop(oop obj) {
6918 // if p points into _span, then mark corresponding bit in _markBitMap
6919 assert(obj->is_oop(), "expected an oop");
6920 HeapWord* addr = (HeapWord*)obj;
6921 if (_span.contains(addr)) {
6922 // this should be made more efficient
6923 _bitMap->par_mark(addr);
6924 }
6925 }
6926
6927 void Par_MarkRefsIntoClosure::do_oop(oop* p) { Par_MarkRefsIntoClosure::do_oop_work(p); }
6928 void Par_MarkRefsIntoClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoClosure::do_oop_work(p); }
6929
6930 // A variant of the above, used for CMS marking verification.
6931 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
6932 MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm):
6933 _span(span),
6934 _verification_bm(verification_bm),
6935 _cms_bm(cms_bm)
6936 {
6937 assert(_ref_processor == NULL, "deliberately left NULL");
6938 assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
6939 }
6940
6941 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
6942 // if p points into _span, then mark corresponding bit in _markBitMap
6943 assert(obj->is_oop(), "expected an oop");
6944 HeapWord* addr = (HeapWord*)obj;
6945 if (_span.contains(addr)) {
6946 _verification_bm->mark(addr);
6947 if (!_cms_bm->isMarked(addr)) {
6948 oop(addr)->print();
6949 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)", addr);
6950 fatal("... aborting");
6951 }
6952 }
6953 }
6954
6955 void MarkRefsIntoVerifyClosure::do_oop(oop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6956 void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6957
6958 //////////////////////////////////////////////////
6959 // MarkRefsIntoAndScanClosure
6960 //////////////////////////////////////////////////
6961
6962 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
6963 ReferenceProcessor* rp,
6964 CMSBitMap* bit_map,
6965 CMSBitMap* mod_union_table,
6966 CMSMarkStack* mark_stack,
6967 CMSCollector* collector,
6968 bool should_yield,
6969 bool concurrent_precleaning):
6970 _collector(collector),
6971 _span(span),
6972 _bit_map(bit_map),
6973 _mark_stack(mark_stack),
6974 _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table,
6975 mark_stack, concurrent_precleaning),
6976 _yield(should_yield),
6977 _concurrent_precleaning(concurrent_precleaning),
6978 _freelistLock(NULL)
6979 {
6980 _ref_processor = rp;
6981 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6982 }
6983
6984 // This closure is used to mark refs into the CMS generation at the
6985 // second (final) checkpoint, and to scan and transitively follow
6986 // the unmarked oops. It is also used during the concurrent precleaning
6987 // phase while scanning objects on dirty cards in the CMS generation.
6988 // The marks are made in the marking bit map and the marking stack is
6989 // used for keeping the (newly) grey objects during the scan.
6990 // The parallel version (Par_...) appears further below.
6991 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6992 if (obj != NULL) {
6993 assert(obj->is_oop(), "expected an oop");
6994 HeapWord* addr = (HeapWord*)obj;
6995 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6996 assert(_collector->overflow_list_is_empty(),
6997 "overflow list should be empty");
6998 if (_span.contains(addr) &&
6999 !_bit_map->isMarked(addr)) {
7000 // mark bit map (object is now grey)
7001 _bit_map->mark(addr);
7002 // push on marking stack (stack should be empty), and drain the
7003 // stack by applying this closure to the oops in the oops popped
7004 // from the stack (i.e. blacken the grey objects)
7005 bool res = _mark_stack->push(obj);
7006 assert(res, "Should have space to push on empty stack");
7007 do {
7008 oop new_oop = _mark_stack->pop();
7009 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
7010 assert(_bit_map->isMarked((HeapWord*)new_oop),
7011 "only grey objects on this stack");
7012 // iterate over the oops in this oop, marking and pushing
7013 // the ones in CMS heap (i.e. in _span).
7014 new_oop->oop_iterate(&_pushAndMarkClosure);
7015 // check if it's time to yield
7016 do_yield_check();
7017 } while (!_mark_stack->isEmpty() ||
7018 (!_concurrent_precleaning && take_from_overflow_list()));
7019 // if marking stack is empty, and we are not doing this
7020 // during precleaning, then check the overflow list
7021 }
7022 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
7023 assert(_collector->overflow_list_is_empty(),
7024 "overflow list was drained above");
7025 // We could restore evacuated mark words, if any, used for
7026 // overflow list links here because the overflow list is
7027 // provably empty here. That would reduce the maximum
7028 // size requirements for preserved_{oop,mark}_stack.
7029 // But we'll just postpone it until we are all done
7030 // so we can just stream through.
7031 if (!_concurrent_precleaning && CMSOverflowEarlyRestoration) {
7032 _collector->restore_preserved_marks_if_any();
7033 assert(_collector->no_preserved_marks(), "No preserved marks");
7034 }
7035 assert(!CMSOverflowEarlyRestoration || _collector->no_preserved_marks(),
7036 "All preserved marks should have been restored above");
7037 }
7038 }
7039
7040 void MarkRefsIntoAndScanClosure::do_oop(oop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
7041 void MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
7042
7043 void MarkRefsIntoAndScanClosure::do_yield_work() {
7044 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7045 "CMS thread should hold CMS token");
7046 assert_lock_strong(_freelistLock);
7047 assert_lock_strong(_bit_map->lock());
7048 // relinquish the free_list_lock and bitMaplock()
7049 _bit_map->lock()->unlock();
7050 _freelistLock->unlock();
7051 ConcurrentMarkSweepThread::desynchronize(true);
7052 ConcurrentMarkSweepThread::acknowledge_yield_request();
7053 _collector->stopTimer();
7054 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7055 if (PrintCMSStatistics != 0) {
7056 _collector->incrementYields();
7057 }
7058 _collector->icms_wait();
7059
7060 // See the comment in coordinator_yield()
7061 for (unsigned i = 0;
7062 i < CMSYieldSleepCount &&
7063 ConcurrentMarkSweepThread::should_yield() &&
7064 !CMSCollector::foregroundGCIsActive();
7065 ++i) {
7066 os::sleep(Thread::current(), 1, false);
7067 ConcurrentMarkSweepThread::acknowledge_yield_request();
7068 }
7069
7070 ConcurrentMarkSweepThread::synchronize(true);
7071 _freelistLock->lock_without_safepoint_check();
7072 _bit_map->lock()->lock_without_safepoint_check();
7073 _collector->startTimer();
7074 }
7075
7076 ///////////////////////////////////////////////////////////
7077 // Par_MarkRefsIntoAndScanClosure: a parallel version of
7078 // MarkRefsIntoAndScanClosure
7079 ///////////////////////////////////////////////////////////
7080 Par_MarkRefsIntoAndScanClosure::Par_MarkRefsIntoAndScanClosure(
7081 CMSCollector* collector, MemRegion span, ReferenceProcessor* rp,
7082 CMSBitMap* bit_map, OopTaskQueue* work_queue):
7083 _span(span),
7084 _bit_map(bit_map),
7085 _work_queue(work_queue),
7086 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
7087 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads))),
7088 _par_pushAndMarkClosure(collector, span, rp, bit_map, work_queue)
7089 {
7090 _ref_processor = rp;
7091 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7092 }
7093
7094 // This closure is used to mark refs into the CMS generation at the
7095 // second (final) checkpoint, and to scan and transitively follow
7096 // the unmarked oops. The marks are made in the marking bit map and
7097 // the work_queue is used for keeping the (newly) grey objects during
7098 // the scan phase whence they are also available for stealing by parallel
7099 // threads. Since the marking bit map is shared, updates are
7100 // synchronized (via CAS).
7101 void Par_MarkRefsIntoAndScanClosure::do_oop(oop obj) {
7102 if (obj != NULL) {
7103 // Ignore mark word because this could be an already marked oop
7104 // that may be chained at the end of the overflow list.
7105 assert(obj->is_oop(true), "expected an oop");
7106 HeapWord* addr = (HeapWord*)obj;
7107 if (_span.contains(addr) &&
7108 !_bit_map->isMarked(addr)) {
7109 // mark bit map (object will become grey):
7110 // It is possible for several threads to be
7111 // trying to "claim" this object concurrently;
7112 // the unique thread that succeeds in marking the
7113 // object first will do the subsequent push on
7114 // to the work queue (or overflow list).
7115 if (_bit_map->par_mark(addr)) {
7116 // push on work_queue (which may not be empty), and trim the
7117 // queue to an appropriate length by applying this closure to
7118 // the oops in the oops popped from the stack (i.e. blacken the
7119 // grey objects)
7120 bool res = _work_queue->push(obj);
7121 assert(res, "Low water mark should be less than capacity?");
7122 trim_queue(_low_water_mark);
7123 } // Else, another thread claimed the object
7124 }
7125 }
7126 }
7127
7128 void Par_MarkRefsIntoAndScanClosure::do_oop(oop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
7129 void Par_MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
7130
7131 // This closure is used to rescan the marked objects on the dirty cards
7132 // in the mod union table and the card table proper.
7133 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
7134 oop p, MemRegion mr) {
7135
7136 size_t size = 0;
7137 HeapWord* addr = (HeapWord*)p;
7138 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
7139 assert(_span.contains(addr), "we are scanning the CMS generation");
7140 // check if it's time to yield
7141 if (do_yield_check()) {
7142 // We yielded for some foreground stop-world work,
7143 // and we have been asked to abort this ongoing preclean cycle.
7144 return 0;
7145 }
7146 if (_bitMap->isMarked(addr)) {
7147 // it's marked; is it potentially uninitialized?
7148 if (p->klass_or_null() != NULL) {
7149 // an initialized object; ignore mark word in verification below
7150 // since we are running concurrent with mutators
7151 assert(p->is_oop(true), "should be an oop");
7152 if (p->is_objArray()) {
7153 // objArrays are precisely marked; restrict scanning
7154 // to dirty cards only.
7155 size = CompactibleFreeListSpace::adjustObjectSize(
7156 p->oop_iterate(_scanningClosure, mr));
7157 } else {
7158 // A non-array may have been imprecisely marked; we need
7159 // to scan object in its entirety.
7160 size = CompactibleFreeListSpace::adjustObjectSize(
7161 p->oop_iterate(_scanningClosure));
7162 }
7163 #ifdef ASSERT
7164 size_t direct_size =
7165 CompactibleFreeListSpace::adjustObjectSize(p->size());
7166 assert(size == direct_size, "Inconsistency in size");
7167 assert(size >= 3, "Necessary for Printezis marks to work");
7168 if (!_bitMap->isMarked(addr+1)) {
7169 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size);
7170 } else {
7171 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size-1);
7172 assert(_bitMap->isMarked(addr+size-1),
7173 "inconsistent Printezis mark");
7174 }
7175 #endif // ASSERT
7176 } else {
7177 // An uninitialized object.
7178 assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
7179 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
7180 size = pointer_delta(nextOneAddr + 1, addr);
7181 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
7182 "alignment problem");
7183 // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
7184 // will dirty the card when the klass pointer is installed in the
7185 // object (signaling the completion of initialization).
7186 }
7187 } else {
7188 // Either a not yet marked object or an uninitialized object
7189 if (p->klass_or_null() == NULL) {
7190 // An uninitialized object, skip to the next card, since
7191 // we may not be able to read its P-bits yet.
7192 assert(size == 0, "Initial value");
7193 } else {
7194 // An object not (yet) reached by marking: we merely need to
7195 // compute its size so as to go look at the next block.
7196 assert(p->is_oop(true), "should be an oop");
7197 size = CompactibleFreeListSpace::adjustObjectSize(p->size());
7198 }
7199 }
7200 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
7201 return size;
7202 }
7203
7204 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
7205 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7206 "CMS thread should hold CMS token");
7207 assert_lock_strong(_freelistLock);
7208 assert_lock_strong(_bitMap->lock());
7209 // relinquish the free_list_lock and bitMaplock()
7210 _bitMap->lock()->unlock();
7211 _freelistLock->unlock();
7212 ConcurrentMarkSweepThread::desynchronize(true);
7213 ConcurrentMarkSweepThread::acknowledge_yield_request();
7214 _collector->stopTimer();
7215 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7216 if (PrintCMSStatistics != 0) {
7217 _collector->incrementYields();
7218 }
7219 _collector->icms_wait();
7220
7221 // See the comment in coordinator_yield()
7222 for (unsigned i = 0; i < CMSYieldSleepCount &&
7223 ConcurrentMarkSweepThread::should_yield() &&
7224 !CMSCollector::foregroundGCIsActive(); ++i) {
7225 os::sleep(Thread::current(), 1, false);
7226 ConcurrentMarkSweepThread::acknowledge_yield_request();
7227 }
7228
7229 ConcurrentMarkSweepThread::synchronize(true);
7230 _freelistLock->lock_without_safepoint_check();
7231 _bitMap->lock()->lock_without_safepoint_check();
7232 _collector->startTimer();
7233 }
7234
7235
7236 //////////////////////////////////////////////////////////////////
7237 // SurvivorSpacePrecleanClosure
7238 //////////////////////////////////////////////////////////////////
7239 // This (single-threaded) closure is used to preclean the oops in
7240 // the survivor spaces.
7241 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
7242
7243 HeapWord* addr = (HeapWord*)p;
7244 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
7245 assert(!_span.contains(addr), "we are scanning the survivor spaces");
7246 assert(p->klass_or_null() != NULL, "object should be initializd");
7247 // an initialized object; ignore mark word in verification below
7248 // since we are running concurrent with mutators
7249 assert(p->is_oop(true), "should be an oop");
7250 // Note that we do not yield while we iterate over
7251 // the interior oops of p, pushing the relevant ones
7252 // on our marking stack.
7253 size_t size = p->oop_iterate(_scanning_closure);
7254 do_yield_check();
7255 // Observe that below, we do not abandon the preclean
7256 // phase as soon as we should; rather we empty the
7257 // marking stack before returning. This is to satisfy
7258 // some existing assertions. In general, it may be a
7259 // good idea to abort immediately and complete the marking
7260 // from the grey objects at a later time.
7261 while (!_mark_stack->isEmpty()) {
7262 oop new_oop = _mark_stack->pop();
7263 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
7264 assert(_bit_map->isMarked((HeapWord*)new_oop),
7265 "only grey objects on this stack");
7266 // iterate over the oops in this oop, marking and pushing
7267 // the ones in CMS heap (i.e. in _span).
7268 new_oop->oop_iterate(_scanning_closure);
7269 // check if it's time to yield
7270 do_yield_check();
7271 }
7272 unsigned int after_count =
7273 GenCollectedHeap::heap()->total_collections();
7274 bool abort = (_before_count != after_count) ||
7275 _collector->should_abort_preclean();
7276 return abort ? 0 : size;
7277 }
7278
7279 void SurvivorSpacePrecleanClosure::do_yield_work() {
7280 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7281 "CMS thread should hold CMS token");
7282 assert_lock_strong(_bit_map->lock());
7283 // Relinquish the bit map lock
7284 _bit_map->lock()->unlock();
7285 ConcurrentMarkSweepThread::desynchronize(true);
7286 ConcurrentMarkSweepThread::acknowledge_yield_request();
7287 _collector->stopTimer();
7288 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7289 if (PrintCMSStatistics != 0) {
7290 _collector->incrementYields();
7291 }
7292 _collector->icms_wait();
7293
7294 // See the comment in coordinator_yield()
7295 for (unsigned i = 0; i < CMSYieldSleepCount &&
7296 ConcurrentMarkSweepThread::should_yield() &&
7297 !CMSCollector::foregroundGCIsActive(); ++i) {
7298 os::sleep(Thread::current(), 1, false);
7299 ConcurrentMarkSweepThread::acknowledge_yield_request();
7300 }
7301
7302 ConcurrentMarkSweepThread::synchronize(true);
7303 _bit_map->lock()->lock_without_safepoint_check();
7304 _collector->startTimer();
7305 }
7306
7307 // This closure is used to rescan the marked objects on the dirty cards
7308 // in the mod union table and the card table proper. In the parallel
7309 // case, although the bitMap is shared, we do a single read so the
7310 // isMarked() query is "safe".
7311 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
7312 // Ignore mark word because we are running concurrent with mutators
7313 assert(p->is_oop_or_null(true), "expected an oop or null");
7314 HeapWord* addr = (HeapWord*)p;
7315 assert(_span.contains(addr), "we are scanning the CMS generation");
7316 bool is_obj_array = false;
7317 #ifdef ASSERT
7318 if (!_parallel) {
7319 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
7320 assert(_collector->overflow_list_is_empty(),
7321 "overflow list should be empty");
7322
7323 }
7324 #endif // ASSERT
7325 if (_bit_map->isMarked(addr)) {
7326 // Obj arrays are precisely marked, non-arrays are not;
7327 // so we scan objArrays precisely and non-arrays in their
7328 // entirety.
7329 if (p->is_objArray()) {
7330 is_obj_array = true;
7331 if (_parallel) {
7332 p->oop_iterate(_par_scan_closure, mr);
7333 } else {
7334 p->oop_iterate(_scan_closure, mr);
7335 }
7336 } else {
7337 if (_parallel) {
7338 p->oop_iterate(_par_scan_closure);
7339 } else {
7340 p->oop_iterate(_scan_closure);
7341 }
7342 }
7343 }
7344 #ifdef ASSERT
7345 if (!_parallel) {
7346 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
7347 assert(_collector->overflow_list_is_empty(),
7348 "overflow list should be empty");
7349
7350 }
7351 #endif // ASSERT
7352 return is_obj_array;
7353 }
7354
7355 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
7356 MemRegion span,
7357 CMSBitMap* bitMap, CMSMarkStack* markStack,
7358 bool should_yield, bool verifying):
7359 _collector(collector),
7360 _span(span),
7361 _bitMap(bitMap),
7362 _mut(&collector->_modUnionTable),
7363 _markStack(markStack),
7364 _yield(should_yield),
7365 _skipBits(0)
7366 {
7367 assert(_markStack->isEmpty(), "stack should be empty");
7368 _finger = _bitMap->startWord();
7369 _threshold = _finger;
7370 assert(_collector->_restart_addr == NULL, "Sanity check");
7371 assert(_span.contains(_finger), "Out of bounds _finger?");
7372 DEBUG_ONLY(_verifying = verifying;)
7373 }
7374
7375 void MarkFromRootsClosure::reset(HeapWord* addr) {
7376 assert(_markStack->isEmpty(), "would cause duplicates on stack");
7377 assert(_span.contains(addr), "Out of bounds _finger?");
7378 _finger = addr;
7379 _threshold = (HeapWord*)round_to(
7380 (intptr_t)_finger, CardTableModRefBS::card_size);
7381 }
7382
7383 // Should revisit to see if this should be restructured for
7384 // greater efficiency.
7385 bool MarkFromRootsClosure::do_bit(size_t offset) {
7386 if (_skipBits > 0) {
7387 _skipBits--;
7388 return true;
7389 }
7390 // convert offset into a HeapWord*
7391 HeapWord* addr = _bitMap->startWord() + offset;
7392 assert(_bitMap->endWord() && addr < _bitMap->endWord(),
7393 "address out of range");
7394 assert(_bitMap->isMarked(addr), "tautology");
7395 if (_bitMap->isMarked(addr+1)) {
7396 // this is an allocated but not yet initialized object
7397 assert(_skipBits == 0, "tautology");
7398 _skipBits = 2; // skip next two marked bits ("Printezis-marks")
7399 oop p = oop(addr);
7400 if (p->klass_or_null() == NULL) {
7401 DEBUG_ONLY(if (!_verifying) {)
7402 // We re-dirty the cards on which this object lies and increase
7403 // the _threshold so that we'll come back to scan this object
7404 // during the preclean or remark phase. (CMSCleanOnEnter)
7405 if (CMSCleanOnEnter) {
7406 size_t sz = _collector->block_size_using_printezis_bits(addr);
7407 HeapWord* end_card_addr = (HeapWord*)round_to(
7408 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7409 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7410 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7411 // Bump _threshold to end_card_addr; note that
7412 // _threshold cannot possibly exceed end_card_addr, anyhow.
7413 // This prevents future clearing of the card as the scan proceeds
7414 // to the right.
7415 assert(_threshold <= end_card_addr,
7416 "Because we are just scanning into this object");
7417 if (_threshold < end_card_addr) {
7418 _threshold = end_card_addr;
7419 }
7420 if (p->klass_or_null() != NULL) {
7421 // Redirty the range of cards...
7422 _mut->mark_range(redirty_range);
7423 } // ...else the setting of klass will dirty the card anyway.
7424 }
7425 DEBUG_ONLY(})
7426 return true;
7427 }
7428 }
7429 scanOopsInOop(addr);
7430 return true;
7431 }
7432
7433 // We take a break if we've been at this for a while,
7434 // so as to avoid monopolizing the locks involved.
7435 void MarkFromRootsClosure::do_yield_work() {
7436 // First give up the locks, then yield, then re-lock
7437 // We should probably use a constructor/destructor idiom to
7438 // do this unlock/lock or modify the MutexUnlocker class to
7439 // serve our purpose. XXX
7440 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7441 "CMS thread should hold CMS token");
7442 assert_lock_strong(_bitMap->lock());
7443 _bitMap->lock()->unlock();
7444 ConcurrentMarkSweepThread::desynchronize(true);
7445 ConcurrentMarkSweepThread::acknowledge_yield_request();
7446 _collector->stopTimer();
7447 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7448 if (PrintCMSStatistics != 0) {
7449 _collector->incrementYields();
7450 }
7451 _collector->icms_wait();
7452
7453 // See the comment in coordinator_yield()
7454 for (unsigned i = 0; i < CMSYieldSleepCount &&
7455 ConcurrentMarkSweepThread::should_yield() &&
7456 !CMSCollector::foregroundGCIsActive(); ++i) {
7457 os::sleep(Thread::current(), 1, false);
7458 ConcurrentMarkSweepThread::acknowledge_yield_request();
7459 }
7460
7461 ConcurrentMarkSweepThread::synchronize(true);
7462 _bitMap->lock()->lock_without_safepoint_check();
7463 _collector->startTimer();
7464 }
7465
7466 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
7467 assert(_bitMap->isMarked(ptr), "expected bit to be set");
7468 assert(_markStack->isEmpty(),
7469 "should drain stack to limit stack usage");
7470 // convert ptr to an oop preparatory to scanning
7471 oop obj = oop(ptr);
7472 // Ignore mark word in verification below, since we
7473 // may be running concurrent with mutators.
7474 assert(obj->is_oop(true), "should be an oop");
7475 assert(_finger <= ptr, "_finger runneth ahead");
7476 // advance the finger to right end of this object
7477 _finger = ptr + obj->size();
7478 assert(_finger > ptr, "we just incremented it above");
7479 // On large heaps, it may take us some time to get through
7480 // the marking phase (especially if running iCMS). During
7481 // this time it's possible that a lot of mutations have
7482 // accumulated in the card table and the mod union table --
7483 // these mutation records are redundant until we have
7484 // actually traced into the corresponding card.
7485 // Here, we check whether advancing the finger would make
7486 // us cross into a new card, and if so clear corresponding
7487 // cards in the MUT (preclean them in the card-table in the
7488 // future).
7489
7490 DEBUG_ONLY(if (!_verifying) {)
7491 // The clean-on-enter optimization is disabled by default,
7492 // until we fix 6178663.
7493 if (CMSCleanOnEnter && (_finger > _threshold)) {
7494 // [_threshold, _finger) represents the interval
7495 // of cards to be cleared in MUT (or precleaned in card table).
7496 // The set of cards to be cleared is all those that overlap
7497 // with the interval [_threshold, _finger); note that
7498 // _threshold is always kept card-aligned but _finger isn't
7499 // always card-aligned.
7500 HeapWord* old_threshold = _threshold;
7501 assert(old_threshold == (HeapWord*)round_to(
7502 (intptr_t)old_threshold, CardTableModRefBS::card_size),
7503 "_threshold should always be card-aligned");
7504 _threshold = (HeapWord*)round_to(
7505 (intptr_t)_finger, CardTableModRefBS::card_size);
7506 MemRegion mr(old_threshold, _threshold);
7507 assert(!mr.is_empty(), "Control point invariant");
7508 assert(_span.contains(mr), "Should clear within span");
7509 _mut->clear_range(mr);
7510 }
7511 DEBUG_ONLY(})
7512 // Note: the finger doesn't advance while we drain
7513 // the stack below.
7514 PushOrMarkClosure pushOrMarkClosure(_collector,
7515 _span, _bitMap, _markStack,
7516 _finger, this);
7517 bool res = _markStack->push(obj);
7518 assert(res, "Empty non-zero size stack should have space for single push");
7519 while (!_markStack->isEmpty()) {
7520 oop new_oop = _markStack->pop();
7521 // Skip verifying header mark word below because we are
7522 // running concurrent with mutators.
7523 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
7524 // now scan this oop's oops
7525 new_oop->oop_iterate(&pushOrMarkClosure);
7526 do_yield_check();
7527 }
7528 assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
7529 }
7530
7531 Par_MarkFromRootsClosure::Par_MarkFromRootsClosure(CMSConcMarkingTask* task,
7532 CMSCollector* collector, MemRegion span,
7533 CMSBitMap* bit_map,
7534 OopTaskQueue* work_queue,
7535 CMSMarkStack* overflow_stack,
7536 bool should_yield):
7537 _collector(collector),
7538 _whole_span(collector->_span),
7539 _span(span),
7540 _bit_map(bit_map),
7541 _mut(&collector->_modUnionTable),
7542 _work_queue(work_queue),
7543 _overflow_stack(overflow_stack),
7544 _yield(should_yield),
7545 _skip_bits(0),
7546 _task(task)
7547 {
7548 assert(_work_queue->size() == 0, "work_queue should be empty");
7549 _finger = span.start();
7550 _threshold = _finger; // XXX Defer clear-on-enter optimization for now
7551 assert(_span.contains(_finger), "Out of bounds _finger?");
7552 }
7553
7554 // Should revisit to see if this should be restructured for
7555 // greater efficiency.
7556 bool Par_MarkFromRootsClosure::do_bit(size_t offset) {
7557 if (_skip_bits > 0) {
7558 _skip_bits--;
7559 return true;
7560 }
7561 // convert offset into a HeapWord*
7562 HeapWord* addr = _bit_map->startWord() + offset;
7563 assert(_bit_map->endWord() && addr < _bit_map->endWord(),
7564 "address out of range");
7565 assert(_bit_map->isMarked(addr), "tautology");
7566 if (_bit_map->isMarked(addr+1)) {
7567 // this is an allocated object that might not yet be initialized
7568 assert(_skip_bits == 0, "tautology");
7569 _skip_bits = 2; // skip next two marked bits ("Printezis-marks")
7570 oop p = oop(addr);
7571 if (p->klass_or_null() == NULL) {
7572 // in the case of Clean-on-Enter optimization, redirty card
7573 // and avoid clearing card by increasing the threshold.
7574 return true;
7575 }
7576 }
7577 scan_oops_in_oop(addr);
7578 return true;
7579 }
7580
7581 void Par_MarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
7582 assert(_bit_map->isMarked(ptr), "expected bit to be set");
7583 // Should we assert that our work queue is empty or
7584 // below some drain limit?
7585 assert(_work_queue->size() == 0,
7586 "should drain stack to limit stack usage");
7587 // convert ptr to an oop preparatory to scanning
7588 oop obj = oop(ptr);
7589 // Ignore mark word in verification below, since we
7590 // may be running concurrent with mutators.
7591 assert(obj->is_oop(true), "should be an oop");
7592 assert(_finger <= ptr, "_finger runneth ahead");
7593 // advance the finger to right end of this object
7594 _finger = ptr + obj->size();
7595 assert(_finger > ptr, "we just incremented it above");
7596 // On large heaps, it may take us some time to get through
7597 // the marking phase (especially if running iCMS). During
7598 // this time it's possible that a lot of mutations have
7599 // accumulated in the card table and the mod union table --
7600 // these mutation records are redundant until we have
7601 // actually traced into the corresponding card.
7602 // Here, we check whether advancing the finger would make
7603 // us cross into a new card, and if so clear corresponding
7604 // cards in the MUT (preclean them in the card-table in the
7605 // future).
7606
7607 // The clean-on-enter optimization is disabled by default,
7608 // until we fix 6178663.
7609 if (CMSCleanOnEnter && (_finger > _threshold)) {
7610 // [_threshold, _finger) represents the interval
7611 // of cards to be cleared in MUT (or precleaned in card table).
7612 // The set of cards to be cleared is all those that overlap
7613 // with the interval [_threshold, _finger); note that
7614 // _threshold is always kept card-aligned but _finger isn't
7615 // always card-aligned.
7616 HeapWord* old_threshold = _threshold;
7617 assert(old_threshold == (HeapWord*)round_to(
7618 (intptr_t)old_threshold, CardTableModRefBS::card_size),
7619 "_threshold should always be card-aligned");
7620 _threshold = (HeapWord*)round_to(
7621 (intptr_t)_finger, CardTableModRefBS::card_size);
7622 MemRegion mr(old_threshold, _threshold);
7623 assert(!mr.is_empty(), "Control point invariant");
7624 assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
7625 _mut->clear_range(mr);
7626 }
7627
7628 // Note: the local finger doesn't advance while we drain
7629 // the stack below, but the global finger sure can and will.
7630 HeapWord** gfa = _task->global_finger_addr();
7631 Par_PushOrMarkClosure pushOrMarkClosure(_collector,
7632 _span, _bit_map,
7633 _work_queue,
7634 _overflow_stack,
7635 _finger,
7636 gfa, this);
7637 bool res = _work_queue->push(obj); // overflow could occur here
7638 assert(res, "Will hold once we use workqueues");
7639 while (true) {
7640 oop new_oop;
7641 if (!_work_queue->pop_local(new_oop)) {
7642 // We emptied our work_queue; check if there's stuff that can
7643 // be gotten from the overflow stack.
7644 if (CMSConcMarkingTask::get_work_from_overflow_stack(
7645 _overflow_stack, _work_queue)) {
7646 do_yield_check();
7647 continue;
7648 } else { // done
7649 break;
7650 }
7651 }
7652 // Skip verifying header mark word below because we are
7653 // running concurrent with mutators.
7654 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
7655 // now scan this oop's oops
7656 new_oop->oop_iterate(&pushOrMarkClosure);
7657 do_yield_check();
7658 }
7659 assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
7660 }
7661
7662 // Yield in response to a request from VM Thread or
7663 // from mutators.
7664 void Par_MarkFromRootsClosure::do_yield_work() {
7665 assert(_task != NULL, "sanity");
7666 _task->yield();
7667 }
7668
7669 // A variant of the above used for verifying CMS marking work.
7670 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
7671 MemRegion span,
7672 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
7673 CMSMarkStack* mark_stack):
7674 _collector(collector),
7675 _span(span),
7676 _verification_bm(verification_bm),
7677 _cms_bm(cms_bm),
7678 _mark_stack(mark_stack),
7679 _pam_verify_closure(collector, span, verification_bm, cms_bm,
7680 mark_stack)
7681 {
7682 assert(_mark_stack->isEmpty(), "stack should be empty");
7683 _finger = _verification_bm->startWord();
7684 assert(_collector->_restart_addr == NULL, "Sanity check");
7685 assert(_span.contains(_finger), "Out of bounds _finger?");
7686 }
7687
7688 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
7689 assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
7690 assert(_span.contains(addr), "Out of bounds _finger?");
7691 _finger = addr;
7692 }
7693
7694 // Should revisit to see if this should be restructured for
7695 // greater efficiency.
7696 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
7697 // convert offset into a HeapWord*
7698 HeapWord* addr = _verification_bm->startWord() + offset;
7699 assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
7700 "address out of range");
7701 assert(_verification_bm->isMarked(addr), "tautology");
7702 assert(_cms_bm->isMarked(addr), "tautology");
7703
7704 assert(_mark_stack->isEmpty(),
7705 "should drain stack to limit stack usage");
7706 // convert addr to an oop preparatory to scanning
7707 oop obj = oop(addr);
7708 assert(obj->is_oop(), "should be an oop");
7709 assert(_finger <= addr, "_finger runneth ahead");
7710 // advance the finger to right end of this object
7711 _finger = addr + obj->size();
7712 assert(_finger > addr, "we just incremented it above");
7713 // Note: the finger doesn't advance while we drain
7714 // the stack below.
7715 bool res = _mark_stack->push(obj);
7716 assert(res, "Empty non-zero size stack should have space for single push");
7717 while (!_mark_stack->isEmpty()) {
7718 oop new_oop = _mark_stack->pop();
7719 assert(new_oop->is_oop(), "Oops! expected to pop an oop");
7720 // now scan this oop's oops
7721 new_oop->oop_iterate(&_pam_verify_closure);
7722 }
7723 assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
7724 return true;
7725 }
7726
7727 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
7728 CMSCollector* collector, MemRegion span,
7729 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
7730 CMSMarkStack* mark_stack):
7731 CMSOopClosure(collector->ref_processor()),
7732 _collector(collector),
7733 _span(span),
7734 _verification_bm(verification_bm),
7735 _cms_bm(cms_bm),
7736 _mark_stack(mark_stack)
7737 { }
7738
7739 void PushAndMarkVerifyClosure::do_oop(oop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
7740 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
7741
7742 // Upon stack overflow, we discard (part of) the stack,
7743 // remembering the least address amongst those discarded
7744 // in CMSCollector's _restart_address.
7745 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
7746 // Remember the least grey address discarded
7747 HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
7748 _collector->lower_restart_addr(ra);
7749 _mark_stack->reset(); // discard stack contents
7750 _mark_stack->expand(); // expand the stack if possible
7751 }
7752
7753 void PushAndMarkVerifyClosure::do_oop(oop obj) {
7754 assert(obj->is_oop_or_null(), "expected an oop or NULL");
7755 HeapWord* addr = (HeapWord*)obj;
7756 if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
7757 // Oop lies in _span and isn't yet grey or black
7758 _verification_bm->mark(addr); // now grey
7759 if (!_cms_bm->isMarked(addr)) {
7760 oop(addr)->print();
7761 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)",
7762 addr);
7763 fatal("... aborting");
7764 }
7765
7766 if (!_mark_stack->push(obj)) { // stack overflow
7767 if (PrintCMSStatistics != 0) {
7768 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7769 SIZE_FORMAT, _mark_stack->capacity());
7770 }
7771 assert(_mark_stack->isFull(), "Else push should have succeeded");
7772 handle_stack_overflow(addr);
7773 }
7774 // anything including and to the right of _finger
7775 // will be scanned as we iterate over the remainder of the
7776 // bit map
7777 }
7778 }
7779
7780 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
7781 MemRegion span,
7782 CMSBitMap* bitMap, CMSMarkStack* markStack,
7783 HeapWord* finger, MarkFromRootsClosure* parent) :
7784 CMSOopClosure(collector->ref_processor()),
7785 _collector(collector),
7786 _span(span),
7787 _bitMap(bitMap),
7788 _markStack(markStack),
7789 _finger(finger),
7790 _parent(parent)
7791 { }
7792
7793 Par_PushOrMarkClosure::Par_PushOrMarkClosure(CMSCollector* collector,
7794 MemRegion span,
7795 CMSBitMap* bit_map,
7796 OopTaskQueue* work_queue,
7797 CMSMarkStack* overflow_stack,
7798 HeapWord* finger,
7799 HeapWord** global_finger_addr,
7800 Par_MarkFromRootsClosure* parent) :
7801 CMSOopClosure(collector->ref_processor()),
7802 _collector(collector),
7803 _whole_span(collector->_span),
7804 _span(span),
7805 _bit_map(bit_map),
7806 _work_queue(work_queue),
7807 _overflow_stack(overflow_stack),
7808 _finger(finger),
7809 _global_finger_addr(global_finger_addr),
7810 _parent(parent)
7811 { }
7812
7813 // Assumes thread-safe access by callers, who are
7814 // responsible for mutual exclusion.
7815 void CMSCollector::lower_restart_addr(HeapWord* low) {
7816 assert(_span.contains(low), "Out of bounds addr");
7817 if (_restart_addr == NULL) {
7818 _restart_addr = low;
7819 } else {
7820 _restart_addr = MIN2(_restart_addr, low);
7821 }
7822 }
7823
7824 // Upon stack overflow, we discard (part of) the stack,
7825 // remembering the least address amongst those discarded
7826 // in CMSCollector's _restart_address.
7827 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7828 // Remember the least grey address discarded
7829 HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
7830 _collector->lower_restart_addr(ra);
7831 _markStack->reset(); // discard stack contents
7832 _markStack->expand(); // expand the stack if possible
7833 }
7834
7835 // Upon stack overflow, we discard (part of) the stack,
7836 // remembering the least address amongst those discarded
7837 // in CMSCollector's _restart_address.
7838 void Par_PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7839 // We need to do this under a mutex to prevent other
7840 // workers from interfering with the work done below.
7841 MutexLockerEx ml(_overflow_stack->par_lock(),
7842 Mutex::_no_safepoint_check_flag);
7843 // Remember the least grey address discarded
7844 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
7845 _collector->lower_restart_addr(ra);
7846 _overflow_stack->reset(); // discard stack contents
7847 _overflow_stack->expand(); // expand the stack if possible
7848 }
7849
7850 void CMKlassClosure::do_klass(Klass* k) {
7851 assert(_oop_closure != NULL, "Not initialized?");
7852 k->oops_do(_oop_closure);
7853 }
7854
7855 void PushOrMarkClosure::do_oop(oop obj) {
7856 // Ignore mark word because we are running concurrent with mutators.
7857 assert(obj->is_oop_or_null(true), "expected an oop or NULL");
7858 HeapWord* addr = (HeapWord*)obj;
7859 if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
7860 // Oop lies in _span and isn't yet grey or black
7861 _bitMap->mark(addr); // now grey
7862 if (addr < _finger) {
7863 // the bit map iteration has already either passed, or
7864 // sampled, this bit in the bit map; we'll need to
7865 // use the marking stack to scan this oop's oops.
7866 bool simulate_overflow = false;
7867 NOT_PRODUCT(
7868 if (CMSMarkStackOverflowALot &&
7869 _collector->simulate_overflow()) {
7870 // simulate a stack overflow
7871 simulate_overflow = true;
7872 }
7873 )
7874 if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
7875 if (PrintCMSStatistics != 0) {
7876 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7877 SIZE_FORMAT, _markStack->capacity());
7878 }
7879 assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
7880 handle_stack_overflow(addr);
7881 }
7882 }
7883 // anything including and to the right of _finger
7884 // will be scanned as we iterate over the remainder of the
7885 // bit map
7886 do_yield_check();
7887 }
7888 }
7889
7890 void PushOrMarkClosure::do_oop(oop* p) { PushOrMarkClosure::do_oop_work(p); }
7891 void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); }
7892
7893 void Par_PushOrMarkClosure::do_oop(oop obj) {
7894 // Ignore mark word because we are running concurrent with mutators.
7895 assert(obj->is_oop_or_null(true), "expected an oop or NULL");
7896 HeapWord* addr = (HeapWord*)obj;
7897 if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
7898 // Oop lies in _span and isn't yet grey or black
7899 // We read the global_finger (volatile read) strictly after marking oop
7900 bool res = _bit_map->par_mark(addr); // now grey
7901 volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
7902 // Should we push this marked oop on our stack?
7903 // -- if someone else marked it, nothing to do
7904 // -- if target oop is above global finger nothing to do
7905 // -- if target oop is in chunk and above local finger
7906 // then nothing to do
7907 // -- else push on work queue
7908 if ( !res // someone else marked it, they will deal with it
7909 || (addr >= *gfa) // will be scanned in a later task
7910 || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
7911 return;
7912 }
7913 // the bit map iteration has already either passed, or
7914 // sampled, this bit in the bit map; we'll need to
7915 // use the marking stack to scan this oop's oops.
7916 bool simulate_overflow = false;
7917 NOT_PRODUCT(
7918 if (CMSMarkStackOverflowALot &&
7919 _collector->simulate_overflow()) {
7920 // simulate a stack overflow
7921 simulate_overflow = true;
7922 }
7923 )
7924 if (simulate_overflow ||
7925 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
7926 // stack overflow
7927 if (PrintCMSStatistics != 0) {
7928 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7929 SIZE_FORMAT, _overflow_stack->capacity());
7930 }
7931 // We cannot assert that the overflow stack is full because
7932 // it may have been emptied since.
7933 assert(simulate_overflow ||
7934 _work_queue->size() == _work_queue->max_elems(),
7935 "Else push should have succeeded");
7936 handle_stack_overflow(addr);
7937 }
7938 do_yield_check();
7939 }
7940 }
7941
7942 void Par_PushOrMarkClosure::do_oop(oop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7943 void Par_PushOrMarkClosure::do_oop(narrowOop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7944
7945 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
7946 MemRegion span,
7947 ReferenceProcessor* rp,
7948 CMSBitMap* bit_map,
7949 CMSBitMap* mod_union_table,
7950 CMSMarkStack* mark_stack,
7951 bool concurrent_precleaning):
7952 CMSOopClosure(rp),
7953 _collector(collector),
7954 _span(span),
7955 _bit_map(bit_map),
7956 _mod_union_table(mod_union_table),
7957 _mark_stack(mark_stack),
7958 _concurrent_precleaning(concurrent_precleaning)
7959 {
7960 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7961 }
7962
7963 // Grey object rescan during pre-cleaning and second checkpoint phases --
7964 // the non-parallel version (the parallel version appears further below.)
7965 void PushAndMarkClosure::do_oop(oop obj) {
7966 // Ignore mark word verification. If during concurrent precleaning,
7967 // the object monitor may be locked. If during the checkpoint
7968 // phases, the object may already have been reached by a different
7969 // path and may be at the end of the global overflow list (so
7970 // the mark word may be NULL).
7971 assert(obj->is_oop_or_null(true /* ignore mark word */),
7972 "expected an oop or NULL");
7973 HeapWord* addr = (HeapWord*)obj;
7974 // Check if oop points into the CMS generation
7975 // and is not marked
7976 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7977 // a white object ...
7978 _bit_map->mark(addr); // ... now grey
7979 // push on the marking stack (grey set)
7980 bool simulate_overflow = false;
7981 NOT_PRODUCT(
7982 if (CMSMarkStackOverflowALot &&
7983 _collector->simulate_overflow()) {
7984 // simulate a stack overflow
7985 simulate_overflow = true;
7986 }
7987 )
7988 if (simulate_overflow || !_mark_stack->push(obj)) {
7989 if (_concurrent_precleaning) {
7990 // During precleaning we can just dirty the appropriate card(s)
7991 // in the mod union table, thus ensuring that the object remains
7992 // in the grey set and continue. In the case of object arrays
7993 // we need to dirty all of the cards that the object spans,
7994 // since the rescan of object arrays will be limited to the
7995 // dirty cards.
7996 // Note that no one can be interfering with us in this action
7997 // of dirtying the mod union table, so no locking or atomics
7998 // are required.
7999 if (obj->is_objArray()) {
8000 size_t sz = obj->size();
8001 HeapWord* end_card_addr = (HeapWord*)round_to(
8002 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
8003 MemRegion redirty_range = MemRegion(addr, end_card_addr);
8004 assert(!redirty_range.is_empty(), "Arithmetical tautology");
8005 _mod_union_table->mark_range(redirty_range);
8006 } else {
8007 _mod_union_table->mark(addr);
8008 }
8009 _collector->_ser_pmc_preclean_ovflw++;
8010 } else {
8011 // During the remark phase, we need to remember this oop
8012 // in the overflow list.
8013 _collector->push_on_overflow_list(obj);
8014 _collector->_ser_pmc_remark_ovflw++;
8015 }
8016 }
8017 }
8018 }
8019
8020 Par_PushAndMarkClosure::Par_PushAndMarkClosure(CMSCollector* collector,
8021 MemRegion span,
8022 ReferenceProcessor* rp,
8023 CMSBitMap* bit_map,
8024 OopTaskQueue* work_queue):
8025 CMSOopClosure(rp),
8026 _collector(collector),
8027 _span(span),
8028 _bit_map(bit_map),
8029 _work_queue(work_queue)
8030 {
8031 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
8032 }
8033
8034 void PushAndMarkClosure::do_oop(oop* p) { PushAndMarkClosure::do_oop_work(p); }
8035 void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); }
8036
8037 // Grey object rescan during second checkpoint phase --
8038 // the parallel version.
8039 void Par_PushAndMarkClosure::do_oop(oop obj) {
8040 // In the assert below, we ignore the mark word because
8041 // this oop may point to an already visited object that is
8042 // on the overflow stack (in which case the mark word has
8043 // been hijacked for chaining into the overflow stack --
8044 // if this is the last object in the overflow stack then
8045 // its mark word will be NULL). Because this object may
8046 // have been subsequently popped off the global overflow
8047 // stack, and the mark word possibly restored to the prototypical
8048 // value, by the time we get to examined this failing assert in
8049 // the debugger, is_oop_or_null(false) may subsequently start
8050 // to hold.
8051 assert(obj->is_oop_or_null(true),
8052 "expected an oop or NULL");
8053 HeapWord* addr = (HeapWord*)obj;
8054 // Check if oop points into the CMS generation
8055 // and is not marked
8056 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
8057 // a white object ...
8058 // If we manage to "claim" the object, by being the
8059 // first thread to mark it, then we push it on our
8060 // marking stack
8061 if (_bit_map->par_mark(addr)) { // ... now grey
8062 // push on work queue (grey set)
8063 bool simulate_overflow = false;
8064 NOT_PRODUCT(
8065 if (CMSMarkStackOverflowALot &&
8066 _collector->par_simulate_overflow()) {
8067 // simulate a stack overflow
8068 simulate_overflow = true;
8069 }
8070 )
8071 if (simulate_overflow || !_work_queue->push(obj)) {
8072 _collector->par_push_on_overflow_list(obj);
8073 _collector->_par_pmc_remark_ovflw++; // imprecise OK: no need to CAS
8074 }
8075 } // Else, some other thread got there first
8076 }
8077 }
8078
8079 void Par_PushAndMarkClosure::do_oop(oop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
8080 void Par_PushAndMarkClosure::do_oop(narrowOop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
8081
8082 void CMSPrecleanRefsYieldClosure::do_yield_work() {
8083 Mutex* bml = _collector->bitMapLock();
8084 assert_lock_strong(bml);
8085 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
8086 "CMS thread should hold CMS token");
8087
8088 bml->unlock();
8089 ConcurrentMarkSweepThread::desynchronize(true);
8090
8091 ConcurrentMarkSweepThread::acknowledge_yield_request();
8092
8093 _collector->stopTimer();
8094 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
8095 if (PrintCMSStatistics != 0) {
8096 _collector->incrementYields();
8097 }
8098 _collector->icms_wait();
8099
8100 // See the comment in coordinator_yield()
8101 for (unsigned i = 0; i < CMSYieldSleepCount &&
8102 ConcurrentMarkSweepThread::should_yield() &&
8103 !CMSCollector::foregroundGCIsActive(); ++i) {
8104 os::sleep(Thread::current(), 1, false);
8105 ConcurrentMarkSweepThread::acknowledge_yield_request();
8106 }
8107
8108 ConcurrentMarkSweepThread::synchronize(true);
8109 bml->lock();
8110
8111 _collector->startTimer();
8112 }
8113
8114 bool CMSPrecleanRefsYieldClosure::should_return() {
8115 if (ConcurrentMarkSweepThread::should_yield()) {
8116 do_yield_work();
8117 }
8118 return _collector->foregroundGCIsActive();
8119 }
8120
8121 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
8122 assert(((size_t)mr.start())%CardTableModRefBS::card_size_in_words == 0,
8123 "mr should be aligned to start at a card boundary");
8124 // We'd like to assert:
8125 // assert(mr.word_size()%CardTableModRefBS::card_size_in_words == 0,
8126 // "mr should be a range of cards");
8127 // However, that would be too strong in one case -- the last
8128 // partition ends at _unallocated_block which, in general, can be
8129 // an arbitrary boundary, not necessarily card aligned.
8130 if (PrintCMSStatistics != 0) {
8131 _num_dirty_cards +=
8132 mr.word_size()/CardTableModRefBS::card_size_in_words;
8133 }
8134 _space->object_iterate_mem(mr, &_scan_cl);
8135 }
8136
8137 SweepClosure::SweepClosure(CMSCollector* collector,
8138 ConcurrentMarkSweepGeneration* g,
8139 CMSBitMap* bitMap, bool should_yield) :
8140 _collector(collector),
8141 _g(g),
8142 _sp(g->cmsSpace()),
8143 _limit(_sp->sweep_limit()),
8144 _freelistLock(_sp->freelistLock()),
8145 _bitMap(bitMap),
8146 _yield(should_yield),
8147 _inFreeRange(false), // No free range at beginning of sweep
8148 _freeRangeInFreeLists(false), // No free range at beginning of sweep
8149 _lastFreeRangeCoalesced(false),
8150 _freeFinger(g->used_region().start())
8151 {
8152 NOT_PRODUCT(
8153 _numObjectsFreed = 0;
8154 _numWordsFreed = 0;
8155 _numObjectsLive = 0;
8156 _numWordsLive = 0;
8157 _numObjectsAlreadyFree = 0;
8158 _numWordsAlreadyFree = 0;
8159 _last_fc = NULL;
8160
8161 _sp->initializeIndexedFreeListArrayReturnedBytes();
8162 _sp->dictionary()->initialize_dict_returned_bytes();
8163 )
8164 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
8165 "sweep _limit out of bounds");
8166 if (CMSTraceSweeper) {
8167 gclog_or_tty->print_cr("\n====================\nStarting new sweep with limit " PTR_FORMAT,
8168 _limit);
8169 }
8170 }
8171
8172 void SweepClosure::print_on(outputStream* st) const {
8173 tty->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")",
8174 _sp->bottom(), _sp->end());
8175 tty->print_cr("_limit = " PTR_FORMAT, _limit);
8176 tty->print_cr("_freeFinger = " PTR_FORMAT, _freeFinger);
8177 NOT_PRODUCT(tty->print_cr("_last_fc = " PTR_FORMAT, _last_fc);)
8178 tty->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d",
8179 _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced);
8180 }
8181
8182 #ifndef PRODUCT
8183 // Assertion checking only: no useful work in product mode --
8184 // however, if any of the flags below become product flags,
8185 // you may need to review this code to see if it needs to be
8186 // enabled in product mode.
8187 SweepClosure::~SweepClosure() {
8188 assert_lock_strong(_freelistLock);
8189 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
8190 "sweep _limit out of bounds");
8191 if (inFreeRange()) {
8192 warning("inFreeRange() should have been reset; dumping state of SweepClosure");
8193 print();
8194 ShouldNotReachHere();
8195 }
8196 if (Verbose && PrintGC) {
8197 gclog_or_tty->print("Collected "SIZE_FORMAT" objects, " SIZE_FORMAT " bytes",
8198 _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
8199 gclog_or_tty->print_cr("\nLive "SIZE_FORMAT" objects, "
8200 SIZE_FORMAT" bytes "
8201 "Already free "SIZE_FORMAT" objects, "SIZE_FORMAT" bytes",
8202 _numObjectsLive, _numWordsLive*sizeof(HeapWord),
8203 _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
8204 size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree)
8205 * sizeof(HeapWord);
8206 gclog_or_tty->print_cr("Total sweep: "SIZE_FORMAT" bytes", totalBytes);
8207
8208 if (PrintCMSStatistics && CMSVerifyReturnedBytes) {
8209 size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
8210 size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes();
8211 size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes;
8212 gclog_or_tty->print("Returned "SIZE_FORMAT" bytes", returned_bytes);
8213 gclog_or_tty->print(" Indexed List Returned "SIZE_FORMAT" bytes",
8214 indexListReturnedBytes);
8215 gclog_or_tty->print_cr(" Dictionary Returned "SIZE_FORMAT" bytes",
8216 dict_returned_bytes);
8217 }
8218 }
8219 if (CMSTraceSweeper) {
8220 gclog_or_tty->print_cr("end of sweep with _limit = " PTR_FORMAT "\n================",
8221 _limit);
8222 }
8223 }
8224 #endif // PRODUCT
8225
8226 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
8227 bool freeRangeInFreeLists) {
8228 if (CMSTraceSweeper) {
8229 gclog_or_tty->print("---- Start free range at 0x%x with free block (%d)\n",
8230 freeFinger, freeRangeInFreeLists);
8231 }
8232 assert(!inFreeRange(), "Trampling existing free range");
8233 set_inFreeRange(true);
8234 set_lastFreeRangeCoalesced(false);
8235
8236 set_freeFinger(freeFinger);
8237 set_freeRangeInFreeLists(freeRangeInFreeLists);
8238 if (CMSTestInFreeList) {
8239 if (freeRangeInFreeLists) {
8240 FreeChunk* fc = (FreeChunk*) freeFinger;
8241 assert(fc->is_free(), "A chunk on the free list should be free.");
8242 assert(fc->size() > 0, "Free range should have a size");
8243 assert(_sp->verify_chunk_in_free_list(fc), "Chunk is not in free lists");
8244 }
8245 }
8246 }
8247
8248 // Note that the sweeper runs concurrently with mutators. Thus,
8249 // it is possible for direct allocation in this generation to happen
8250 // in the middle of the sweep. Note that the sweeper also coalesces
8251 // contiguous free blocks. Thus, unless the sweeper and the allocator
8252 // synchronize appropriately freshly allocated blocks may get swept up.
8253 // This is accomplished by the sweeper locking the free lists while
8254 // it is sweeping. Thus blocks that are determined to be free are
8255 // indeed free. There is however one additional complication:
8256 // blocks that have been allocated since the final checkpoint and
8257 // mark, will not have been marked and so would be treated as
8258 // unreachable and swept up. To prevent this, the allocator marks
8259 // the bit map when allocating during the sweep phase. This leads,
8260 // however, to a further complication -- objects may have been allocated
8261 // but not yet initialized -- in the sense that the header isn't yet
8262 // installed. The sweeper can not then determine the size of the block
8263 // in order to skip over it. To deal with this case, we use a technique
8264 // (due to Printezis) to encode such uninitialized block sizes in the
8265 // bit map. Since the bit map uses a bit per every HeapWord, but the
8266 // CMS generation has a minimum object size of 3 HeapWords, it follows
8267 // that "normal marks" won't be adjacent in the bit map (there will
8268 // always be at least two 0 bits between successive 1 bits). We make use
8269 // of these "unused" bits to represent uninitialized blocks -- the bit
8270 // corresponding to the start of the uninitialized object and the next
8271 // bit are both set. Finally, a 1 bit marks the end of the object that
8272 // started with the two consecutive 1 bits to indicate its potentially
8273 // uninitialized state.
8274
8275 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
8276 FreeChunk* fc = (FreeChunk*)addr;
8277 size_t res;
8278
8279 // Check if we are done sweeping. Below we check "addr >= _limit" rather
8280 // than "addr == _limit" because although _limit was a block boundary when
8281 // we started the sweep, it may no longer be one because heap expansion
8282 // may have caused us to coalesce the block ending at the address _limit
8283 // with a newly expanded chunk (this happens when _limit was set to the
8284 // previous _end of the space), so we may have stepped past _limit:
8285 // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740.
8286 if (addr >= _limit) { // we have swept up to or past the limit: finish up
8287 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
8288 "sweep _limit out of bounds");
8289 assert(addr < _sp->end(), "addr out of bounds");
8290 // Flush any free range we might be holding as a single
8291 // coalesced chunk to the appropriate free list.
8292 if (inFreeRange()) {
8293 assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit,
8294 err_msg("freeFinger() " PTR_FORMAT" is out-of-bounds", freeFinger()));
8295 flush_cur_free_chunk(freeFinger(),
8296 pointer_delta(addr, freeFinger()));
8297 if (CMSTraceSweeper) {
8298 gclog_or_tty->print("Sweep: last chunk: ");
8299 gclog_or_tty->print("put_free_blk 0x%x ("SIZE_FORMAT") "
8300 "[coalesced:"SIZE_FORMAT"]\n",
8301 freeFinger(), pointer_delta(addr, freeFinger()),
8302 lastFreeRangeCoalesced());
8303 }
8304 }
8305
8306 // help the iterator loop finish
8307 return pointer_delta(_sp->end(), addr);
8308 }
8309
8310 assert(addr < _limit, "sweep invariant");
8311 // check if we should yield
8312 do_yield_check(addr);
8313 if (fc->is_free()) {
8314 // Chunk that is already free
8315 res = fc->size();
8316 do_already_free_chunk(fc);
8317 debug_only(_sp->verifyFreeLists());
8318 // If we flush the chunk at hand in lookahead_and_flush()
8319 // and it's coalesced with a preceding chunk, then the
8320 // process of "mangling" the payload of the coalesced block
8321 // will cause erasure of the size information from the
8322 // (erstwhile) header of all the coalesced blocks but the
8323 // first, so the first disjunct in the assert will not hold
8324 // in that specific case (in which case the second disjunct
8325 // will hold).
8326 assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit,
8327 "Otherwise the size info doesn't change at this step");
8328 NOT_PRODUCT(
8329 _numObjectsAlreadyFree++;
8330 _numWordsAlreadyFree += res;
8331 )
8332 NOT_PRODUCT(_last_fc = fc;)
8333 } else if (!_bitMap->isMarked(addr)) {
8334 // Chunk is fresh garbage
8335 res = do_garbage_chunk(fc);
8336 debug_only(_sp->verifyFreeLists());
8337 NOT_PRODUCT(
8338 _numObjectsFreed++;
8339 _numWordsFreed += res;
8340 )
8341 } else {
8342 // Chunk that is alive.
8343 res = do_live_chunk(fc);
8344 debug_only(_sp->verifyFreeLists());
8345 NOT_PRODUCT(
8346 _numObjectsLive++;
8347 _numWordsLive += res;
8348 )
8349 }
8350 return res;
8351 }
8352
8353 // For the smart allocation, record following
8354 // split deaths - a free chunk is removed from its free list because
8355 // it is being split into two or more chunks.
8356 // split birth - a free chunk is being added to its free list because
8357 // a larger free chunk has been split and resulted in this free chunk.
8358 // coal death - a free chunk is being removed from its free list because
8359 // it is being coalesced into a large free chunk.
8360 // coal birth - a free chunk is being added to its free list because
8361 // it was created when two or more free chunks where coalesced into
8362 // this free chunk.
8363 //
8364 // These statistics are used to determine the desired number of free
8365 // chunks of a given size. The desired number is chosen to be relative
8366 // to the end of a CMS sweep. The desired number at the end of a sweep
8367 // is the
8368 // count-at-end-of-previous-sweep (an amount that was enough)
8369 // - count-at-beginning-of-current-sweep (the excess)
8370 // + split-births (gains in this size during interval)
8371 // - split-deaths (demands on this size during interval)
8372 // where the interval is from the end of one sweep to the end of the
8373 // next.
8374 //
8375 // When sweeping the sweeper maintains an accumulated chunk which is
8376 // the chunk that is made up of chunks that have been coalesced. That
8377 // will be termed the left-hand chunk. A new chunk of garbage that
8378 // is being considered for coalescing will be referred to as the
8379 // right-hand chunk.
8380 //
8381 // When making a decision on whether to coalesce a right-hand chunk with
8382 // the current left-hand chunk, the current count vs. the desired count
8383 // of the left-hand chunk is considered. Also if the right-hand chunk
8384 // is near the large chunk at the end of the heap (see
8385 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
8386 // left-hand chunk is coalesced.
8387 //
8388 // When making a decision about whether to split a chunk, the desired count
8389 // vs. the current count of the candidate to be split is also considered.
8390 // If the candidate is underpopulated (currently fewer chunks than desired)
8391 // a chunk of an overpopulated (currently more chunks than desired) size may
8392 // be chosen. The "hint" associated with a free list, if non-null, points
8393 // to a free list which may be overpopulated.
8394 //
8395
8396 void SweepClosure::do_already_free_chunk(FreeChunk* fc) {
8397 const size_t size = fc->size();
8398 // Chunks that cannot be coalesced are not in the
8399 // free lists.
8400 if (CMSTestInFreeList && !fc->cantCoalesce()) {
8401 assert(_sp->verify_chunk_in_free_list(fc),
8402 "free chunk should be in free lists");
8403 }
8404 // a chunk that is already free, should not have been
8405 // marked in the bit map
8406 HeapWord* const addr = (HeapWord*) fc;
8407 assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
8408 // Verify that the bit map has no bits marked between
8409 // addr and purported end of this block.
8410 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8411
8412 // Some chunks cannot be coalesced under any circumstances.
8413 // See the definition of cantCoalesce().
8414 if (!fc->cantCoalesce()) {
8415 // This chunk can potentially be coalesced.
8416 if (_sp->adaptive_freelists()) {
8417 // All the work is done in
8418 do_post_free_or_garbage_chunk(fc, size);
8419 } else { // Not adaptive free lists
8420 // this is a free chunk that can potentially be coalesced by the sweeper;
8421 if (!inFreeRange()) {
8422 // if the next chunk is a free block that can't be coalesced
8423 // it doesn't make sense to remove this chunk from the free lists
8424 FreeChunk* nextChunk = (FreeChunk*)(addr + size);
8425 assert((HeapWord*)nextChunk <= _sp->end(), "Chunk size out of bounds?");
8426 if ((HeapWord*)nextChunk < _sp->end() && // There is another free chunk to the right ...
8427 nextChunk->is_free() && // ... which is free...
8428 nextChunk->cantCoalesce()) { // ... but can't be coalesced
8429 // nothing to do
8430 } else {
8431 // Potentially the start of a new free range:
8432 // Don't eagerly remove it from the free lists.
8433 // No need to remove it if it will just be put
8434 // back again. (Also from a pragmatic point of view
8435 // if it is a free block in a region that is beyond
8436 // any allocated blocks, an assertion will fail)
8437 // Remember the start of a free run.
8438 initialize_free_range(addr, true);
8439 // end - can coalesce with next chunk
8440 }
8441 } else {
8442 // the midst of a free range, we are coalescing
8443 print_free_block_coalesced(fc);
8444 if (CMSTraceSweeper) {
8445 gclog_or_tty->print(" -- pick up free block 0x%x (%d)\n", fc, size);
8446 }
8447 // remove it from the free lists
8448 _sp->removeFreeChunkFromFreeLists(fc);
8449 set_lastFreeRangeCoalesced(true);
8450 // If the chunk is being coalesced and the current free range is
8451 // in the free lists, remove the current free range so that it
8452 // will be returned to the free lists in its entirety - all
8453 // the coalesced pieces included.
8454 if (freeRangeInFreeLists()) {
8455 FreeChunk* ffc = (FreeChunk*) freeFinger();
8456 assert(ffc->size() == pointer_delta(addr, freeFinger()),
8457 "Size of free range is inconsistent with chunk size.");
8458 if (CMSTestInFreeList) {
8459 assert(_sp->verify_chunk_in_free_list(ffc),
8460 "free range is not in free lists");
8461 }
8462 _sp->removeFreeChunkFromFreeLists(ffc);
8463 set_freeRangeInFreeLists(false);
8464 }
8465 }
8466 }
8467 // Note that if the chunk is not coalescable (the else arm
8468 // below), we unconditionally flush, without needing to do
8469 // a "lookahead," as we do below.
8470 if (inFreeRange()) lookahead_and_flush(fc, size);
8471 } else {
8472 // Code path common to both original and adaptive free lists.
8473
8474 // cant coalesce with previous block; this should be treated
8475 // as the end of a free run if any
8476 if (inFreeRange()) {
8477 // we kicked some butt; time to pick up the garbage
8478 assert(freeFinger() < addr, "freeFinger points too high");
8479 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8480 }
8481 // else, nothing to do, just continue
8482 }
8483 }
8484
8485 size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) {
8486 // This is a chunk of garbage. It is not in any free list.
8487 // Add it to a free list or let it possibly be coalesced into
8488 // a larger chunk.
8489 HeapWord* const addr = (HeapWord*) fc;
8490 const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
8491
8492 if (_sp->adaptive_freelists()) {
8493 // Verify that the bit map has no bits marked between
8494 // addr and purported end of just dead object.
8495 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8496
8497 do_post_free_or_garbage_chunk(fc, size);
8498 } else {
8499 if (!inFreeRange()) {
8500 // start of a new free range
8501 assert(size > 0, "A free range should have a size");
8502 initialize_free_range(addr, false);
8503 } else {
8504 // this will be swept up when we hit the end of the
8505 // free range
8506 if (CMSTraceSweeper) {
8507 gclog_or_tty->print(" -- pick up garbage 0x%x (%d) \n", fc, size);
8508 }
8509 // If the chunk is being coalesced and the current free range is
8510 // in the free lists, remove the current free range so that it
8511 // will be returned to the free lists in its entirety - all
8512 // the coalesced pieces included.
8513 if (freeRangeInFreeLists()) {
8514 FreeChunk* ffc = (FreeChunk*)freeFinger();
8515 assert(ffc->size() == pointer_delta(addr, freeFinger()),
8516 "Size of free range is inconsistent with chunk size.");
8517 if (CMSTestInFreeList) {
8518 assert(_sp->verify_chunk_in_free_list(ffc),
8519 "free range is not in free lists");
8520 }
8521 _sp->removeFreeChunkFromFreeLists(ffc);
8522 set_freeRangeInFreeLists(false);
8523 }
8524 set_lastFreeRangeCoalesced(true);
8525 }
8526 // this will be swept up when we hit the end of the free range
8527
8528 // Verify that the bit map has no bits marked between
8529 // addr and purported end of just dead object.
8530 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8531 }
8532 assert(_limit >= addr + size,
8533 "A freshly garbage chunk can't possibly straddle over _limit");
8534 if (inFreeRange()) lookahead_and_flush(fc, size);
8535 return size;
8536 }
8537
8538 size_t SweepClosure::do_live_chunk(FreeChunk* fc) {
8539 HeapWord* addr = (HeapWord*) fc;
8540 // The sweeper has just found a live object. Return any accumulated
8541 // left hand chunk to the free lists.
8542 if (inFreeRange()) {
8543 assert(freeFinger() < addr, "freeFinger points too high");
8544 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8545 }
8546
8547 // This object is live: we'd normally expect this to be
8548 // an oop, and like to assert the following:
8549 // assert(oop(addr)->is_oop(), "live block should be an oop");
8550 // However, as we commented above, this may be an object whose
8551 // header hasn't yet been initialized.
8552 size_t size;
8553 assert(_bitMap->isMarked(addr), "Tautology for this control point");
8554 if (_bitMap->isMarked(addr + 1)) {
8555 // Determine the size from the bit map, rather than trying to
8556 // compute it from the object header.
8557 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
8558 size = pointer_delta(nextOneAddr + 1, addr);
8559 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
8560 "alignment problem");
8561
8562 #ifdef ASSERT
8563 if (oop(addr)->klass_or_null() != NULL) {
8564 // Ignore mark word because we are running concurrent with mutators
8565 assert(oop(addr)->is_oop(true), "live block should be an oop");
8566 assert(size ==
8567 CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
8568 "P-mark and computed size do not agree");
8569 }
8570 #endif
8571
8572 } else {
8573 // This should be an initialized object that's alive.
8574 assert(oop(addr)->klass_or_null() != NULL,
8575 "Should be an initialized object");
8576 // Ignore mark word because we are running concurrent with mutators
8577 assert(oop(addr)->is_oop(true), "live block should be an oop");
8578 // Verify that the bit map has no bits marked between
8579 // addr and purported end of this block.
8580 size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
8581 assert(size >= 3, "Necessary for Printezis marks to work");
8582 assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
8583 DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
8584 }
8585 return size;
8586 }
8587
8588 void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc,
8589 size_t chunkSize) {
8590 // do_post_free_or_garbage_chunk() should only be called in the case
8591 // of the adaptive free list allocator.
8592 const bool fcInFreeLists = fc->is_free();
8593 assert(_sp->adaptive_freelists(), "Should only be used in this case.");
8594 assert((HeapWord*)fc <= _limit, "sweep invariant");
8595 if (CMSTestInFreeList && fcInFreeLists) {
8596 assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists");
8597 }
8598
8599 if (CMSTraceSweeper) {
8600 gclog_or_tty->print_cr(" -- pick up another chunk at 0x%x (%d)", fc, chunkSize);
8601 }
8602
8603 HeapWord* const fc_addr = (HeapWord*) fc;
8604
8605 bool coalesce;
8606 const size_t left = pointer_delta(fc_addr, freeFinger());
8607 const size_t right = chunkSize;
8608 switch (FLSCoalescePolicy) {
8609 // numeric value forms a coalition aggressiveness metric
8610 case 0: { // never coalesce
8611 coalesce = false;
8612 break;
8613 }
8614 case 1: { // coalesce if left & right chunks on overpopulated lists
8615 coalesce = _sp->coalOverPopulated(left) &&
8616 _sp->coalOverPopulated(right);
8617 break;
8618 }
8619 case 2: { // coalesce if left chunk on overpopulated list (default)
8620 coalesce = _sp->coalOverPopulated(left);
8621 break;
8622 }
8623 case 3: { // coalesce if left OR right chunk on overpopulated list
8624 coalesce = _sp->coalOverPopulated(left) ||
8625 _sp->coalOverPopulated(right);
8626 break;
8627 }
8628 case 4: { // always coalesce
8629 coalesce = true;
8630 break;
8631 }
8632 default:
8633 ShouldNotReachHere();
8634 }
8635
8636 // Should the current free range be coalesced?
8637 // If the chunk is in a free range and either we decided to coalesce above
8638 // or the chunk is near the large block at the end of the heap
8639 // (isNearLargestChunk() returns true), then coalesce this chunk.
8640 const bool doCoalesce = inFreeRange()
8641 && (coalesce || _g->isNearLargestChunk(fc_addr));
8642 if (doCoalesce) {
8643 // Coalesce the current free range on the left with the new
8644 // chunk on the right. If either is on a free list,
8645 // it must be removed from the list and stashed in the closure.
8646 if (freeRangeInFreeLists()) {
8647 FreeChunk* const ffc = (FreeChunk*)freeFinger();
8648 assert(ffc->size() == pointer_delta(fc_addr, freeFinger()),
8649 "Size of free range is inconsistent with chunk size.");
8650 if (CMSTestInFreeList) {
8651 assert(_sp->verify_chunk_in_free_list(ffc),
8652 "Chunk is not in free lists");
8653 }
8654 _sp->coalDeath(ffc->size());
8655 _sp->removeFreeChunkFromFreeLists(ffc);
8656 set_freeRangeInFreeLists(false);
8657 }
8658 if (fcInFreeLists) {
8659 _sp->coalDeath(chunkSize);
8660 assert(fc->size() == chunkSize,
8661 "The chunk has the wrong size or is not in the free lists");
8662 _sp->removeFreeChunkFromFreeLists(fc);
8663 }
8664 set_lastFreeRangeCoalesced(true);
8665 print_free_block_coalesced(fc);
8666 } else { // not in a free range and/or should not coalesce
8667 // Return the current free range and start a new one.
8668 if (inFreeRange()) {
8669 // In a free range but cannot coalesce with the right hand chunk.
8670 // Put the current free range into the free lists.
8671 flush_cur_free_chunk(freeFinger(),
8672 pointer_delta(fc_addr, freeFinger()));
8673 }
8674 // Set up for new free range. Pass along whether the right hand
8675 // chunk is in the free lists.
8676 initialize_free_range((HeapWord*)fc, fcInFreeLists);
8677 }
8678 }
8679
8680 // Lookahead flush:
8681 // If we are tracking a free range, and this is the last chunk that
8682 // we'll look at because its end crosses past _limit, we'll preemptively
8683 // flush it along with any free range we may be holding on to. Note that
8684 // this can be the case only for an already free or freshly garbage
8685 // chunk. If this block is an object, it can never straddle
8686 // over _limit. The "straddling" occurs when _limit is set at
8687 // the previous end of the space when this cycle started, and
8688 // a subsequent heap expansion caused the previously co-terminal
8689 // free block to be coalesced with the newly expanded portion,
8690 // thus rendering _limit a non-block-boundary making it dangerous
8691 // for the sweeper to step over and examine.
8692 void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) {
8693 assert(inFreeRange(), "Should only be called if currently in a free range.");
8694 HeapWord* const eob = ((HeapWord*)fc) + chunk_size;
8695 assert(_sp->used_region().contains(eob - 1),
8696 err_msg("eob = " PTR_FORMAT " eob-1 = " PTR_FORMAT " _limit = " PTR_FORMAT
8697 " out of bounds wrt _sp = [" PTR_FORMAT "," PTR_FORMAT ")"
8698 " when examining fc = " PTR_FORMAT "(" SIZE_FORMAT ")",
8699 eob, eob-1, _limit, _sp->bottom(), _sp->end(), fc, chunk_size));
8700 if (eob >= _limit) {
8701 assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit");
8702 if (CMSTraceSweeper) {
8703 gclog_or_tty->print_cr("_limit " PTR_FORMAT " reached or crossed by block "
8704 "[" PTR_FORMAT "," PTR_FORMAT ") in space "
8705 "[" PTR_FORMAT "," PTR_FORMAT ")",
8706 _limit, fc, eob, _sp->bottom(), _sp->end());
8707 }
8708 // Return the storage we are tracking back into the free lists.
8709 if (CMSTraceSweeper) {
8710 gclog_or_tty->print_cr("Flushing ... ");
8711 }
8712 assert(freeFinger() < eob, "Error");
8713 flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger()));
8714 }
8715 }
8716
8717 void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) {
8718 assert(inFreeRange(), "Should only be called if currently in a free range.");
8719 assert(size > 0,
8720 "A zero sized chunk cannot be added to the free lists.");
8721 if (!freeRangeInFreeLists()) {
8722 if (CMSTestInFreeList) {
8723 FreeChunk* fc = (FreeChunk*) chunk;
8724 fc->set_size(size);
8725 assert(!_sp->verify_chunk_in_free_list(fc),
8726 "chunk should not be in free lists yet");
8727 }
8728 if (CMSTraceSweeper) {
8729 gclog_or_tty->print_cr(" -- add free block 0x%x (%d) to free lists",
8730 chunk, size);
8731 }
8732 // A new free range is going to be starting. The current
8733 // free range has not been added to the free lists yet or
8734 // was removed so add it back.
8735 // If the current free range was coalesced, then the death
8736 // of the free range was recorded. Record a birth now.
8737 if (lastFreeRangeCoalesced()) {
8738 _sp->coalBirth(size);
8739 }
8740 _sp->addChunkAndRepairOffsetTable(chunk, size,
8741 lastFreeRangeCoalesced());
8742 } else if (CMSTraceSweeper) {
8743 gclog_or_tty->print_cr("Already in free list: nothing to flush");
8744 }
8745 set_inFreeRange(false);
8746 set_freeRangeInFreeLists(false);
8747 }
8748
8749 // We take a break if we've been at this for a while,
8750 // so as to avoid monopolizing the locks involved.
8751 void SweepClosure::do_yield_work(HeapWord* addr) {
8752 // Return current free chunk being used for coalescing (if any)
8753 // to the appropriate freelist. After yielding, the next
8754 // free block encountered will start a coalescing range of
8755 // free blocks. If the next free block is adjacent to the
8756 // chunk just flushed, they will need to wait for the next
8757 // sweep to be coalesced.
8758 if (inFreeRange()) {
8759 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8760 }
8761
8762 // First give up the locks, then yield, then re-lock.
8763 // We should probably use a constructor/destructor idiom to
8764 // do this unlock/lock or modify the MutexUnlocker class to
8765 // serve our purpose. XXX
8766 assert_lock_strong(_bitMap->lock());
8767 assert_lock_strong(_freelistLock);
8768 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
8769 "CMS thread should hold CMS token");
8770 _bitMap->lock()->unlock();
8771 _freelistLock->unlock();
8772 ConcurrentMarkSweepThread::desynchronize(true);
8773 ConcurrentMarkSweepThread::acknowledge_yield_request();
8774 _collector->stopTimer();
8775 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
8776 if (PrintCMSStatistics != 0) {
8777 _collector->incrementYields();
8778 }
8779 _collector->icms_wait();
8780
8781 // See the comment in coordinator_yield()
8782 for (unsigned i = 0; i < CMSYieldSleepCount &&
8783 ConcurrentMarkSweepThread::should_yield() &&
8784 !CMSCollector::foregroundGCIsActive(); ++i) {
8785 os::sleep(Thread::current(), 1, false);
8786 ConcurrentMarkSweepThread::acknowledge_yield_request();
8787 }
8788
8789 ConcurrentMarkSweepThread::synchronize(true);
8790 _freelistLock->lock();
8791 _bitMap->lock()->lock_without_safepoint_check();
8792 _collector->startTimer();
8793 }
8794
8795 #ifndef PRODUCT
8796 // This is actually very useful in a product build if it can
8797 // be called from the debugger. Compile it into the product
8798 // as needed.
8799 bool debug_verify_chunk_in_free_list(FreeChunk* fc) {
8800 return debug_cms_space->verify_chunk_in_free_list(fc);
8801 }
8802 #endif
8803
8804 void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const {
8805 if (CMSTraceSweeper) {
8806 gclog_or_tty->print_cr("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")",
8807 fc, fc->size());
8808 }
8809 }
8810
8811 // CMSIsAliveClosure
8812 bool CMSIsAliveClosure::do_object_b(oop obj) {
8813 HeapWord* addr = (HeapWord*)obj;
8814 return addr != NULL &&
8815 (!_span.contains(addr) || _bit_map->isMarked(addr));
8816 }
8817
8818
8819 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector,
8820 MemRegion span,
8821 CMSBitMap* bit_map, CMSMarkStack* mark_stack,
8822 bool cpc):
8823 _collector(collector),
8824 _span(span),
8825 _bit_map(bit_map),
8826 _mark_stack(mark_stack),
8827 _concurrent_precleaning(cpc) {
8828 assert(!_span.is_empty(), "Empty span could spell trouble");
8829 }
8830
8831
8832 // CMSKeepAliveClosure: the serial version
8833 void CMSKeepAliveClosure::do_oop(oop obj) {
8834 HeapWord* addr = (HeapWord*)obj;
8835 if (_span.contains(addr) &&
8836 !_bit_map->isMarked(addr)) {
8837 _bit_map->mark(addr);
8838 bool simulate_overflow = false;
8839 NOT_PRODUCT(
8840 if (CMSMarkStackOverflowALot &&
8841 _collector->simulate_overflow()) {
8842 // simulate a stack overflow
8843 simulate_overflow = true;
8844 }
8845 )
8846 if (simulate_overflow || !_mark_stack->push(obj)) {
8847 if (_concurrent_precleaning) {
8848 // We dirty the overflown object and let the remark
8849 // phase deal with it.
8850 assert(_collector->overflow_list_is_empty(), "Error");
8851 // In the case of object arrays, we need to dirty all of
8852 // the cards that the object spans. No locking or atomics
8853 // are needed since no one else can be mutating the mod union
8854 // table.
8855 if (obj->is_objArray()) {
8856 size_t sz = obj->size();
8857 HeapWord* end_card_addr =
8858 (HeapWord*)round_to((intptr_t)(addr+sz), CardTableModRefBS::card_size);
8859 MemRegion redirty_range = MemRegion(addr, end_card_addr);
8860 assert(!redirty_range.is_empty(), "Arithmetical tautology");
8861 _collector->_modUnionTable.mark_range(redirty_range);
8862 } else {
8863 _collector->_modUnionTable.mark(addr);
8864 }
8865 _collector->_ser_kac_preclean_ovflw++;
8866 } else {
8867 _collector->push_on_overflow_list(obj);
8868 _collector->_ser_kac_ovflw++;
8869 }
8870 }
8871 }
8872 }
8873
8874 void CMSKeepAliveClosure::do_oop(oop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8875 void CMSKeepAliveClosure::do_oop(narrowOop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8876
8877 // CMSParKeepAliveClosure: a parallel version of the above.
8878 // The work queues are private to each closure (thread),
8879 // but (may be) available for stealing by other threads.
8880 void CMSParKeepAliveClosure::do_oop(oop obj) {
8881 HeapWord* addr = (HeapWord*)obj;
8882 if (_span.contains(addr) &&
8883 !_bit_map->isMarked(addr)) {
8884 // In general, during recursive tracing, several threads
8885 // may be concurrently getting here; the first one to
8886 // "tag" it, claims it.
8887 if (_bit_map->par_mark(addr)) {
8888 bool res = _work_queue->push(obj);
8889 assert(res, "Low water mark should be much less than capacity");
8890 // Do a recursive trim in the hope that this will keep
8891 // stack usage lower, but leave some oops for potential stealers
8892 trim_queue(_low_water_mark);
8893 } // Else, another thread got there first
8894 }
8895 }
8896
8897 void CMSParKeepAliveClosure::do_oop(oop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8898 void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8899
8900 void CMSParKeepAliveClosure::trim_queue(uint max) {
8901 while (_work_queue->size() > max) {
8902 oop new_oop;
8903 if (_work_queue->pop_local(new_oop)) {
8904 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
8905 assert(_bit_map->isMarked((HeapWord*)new_oop),
8906 "no white objects on this stack!");
8907 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8908 // iterate over the oops in this oop, marking and pushing
8909 // the ones in CMS heap (i.e. in _span).
8910 new_oop->oop_iterate(&_mark_and_push);
8911 }
8912 }
8913 }
8914
8915 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
8916 CMSCollector* collector,
8917 MemRegion span, CMSBitMap* bit_map,
8918 OopTaskQueue* work_queue):
8919 _collector(collector),
8920 _span(span),
8921 _bit_map(bit_map),
8922 _work_queue(work_queue) { }
8923
8924 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
8925 HeapWord* addr = (HeapWord*)obj;
8926 if (_span.contains(addr) &&
8927 !_bit_map->isMarked(addr)) {
8928 if (_bit_map->par_mark(addr)) {
8929 bool simulate_overflow = false;
8930 NOT_PRODUCT(
8931 if (CMSMarkStackOverflowALot &&
8932 _collector->par_simulate_overflow()) {
8933 // simulate a stack overflow
8934 simulate_overflow = true;
8935 }
8936 )
8937 if (simulate_overflow || !_work_queue->push(obj)) {
8938 _collector->par_push_on_overflow_list(obj);
8939 _collector->_par_kac_ovflw++;
8940 }
8941 } // Else another thread got there already
8942 }
8943 }
8944
8945 void CMSInnerParMarkAndPushClosure::do_oop(oop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8946 void CMSInnerParMarkAndPushClosure::do_oop(narrowOop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8947
8948 //////////////////////////////////////////////////////////////////
8949 // CMSExpansionCause /////////////////////////////
8950 //////////////////////////////////////////////////////////////////
8951 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
8952 switch (cause) {
8953 case _no_expansion:
8954 return "No expansion";
8955 case _satisfy_free_ratio:
8956 return "Free ratio";
8957 case _satisfy_promotion:
8958 return "Satisfy promotion";
8959 case _satisfy_allocation:
8960 return "allocation";
8961 case _allocate_par_lab:
8962 return "Par LAB";
8963 case _allocate_par_spooling_space:
8964 return "Par Spooling Space";
8965 case _adaptive_size_policy:
8966 return "Ergonomics";
8967 default:
8968 return "unknown";
8969 }
8970 }
8971
8972 void CMSDrainMarkingStackClosure::do_void() {
8973 // the max number to take from overflow list at a time
8974 const size_t num = _mark_stack->capacity()/4;
8975 assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
8976 "Overflow list should be NULL during concurrent phases");
8977 while (!_mark_stack->isEmpty() ||
8978 // if stack is empty, check the overflow list
8979 _collector->take_from_overflow_list(num, _mark_stack)) {
8980 oop obj = _mark_stack->pop();
8981 HeapWord* addr = (HeapWord*)obj;
8982 assert(_span.contains(addr), "Should be within span");
8983 assert(_bit_map->isMarked(addr), "Should be marked");
8984 assert(obj->is_oop(), "Should be an oop");
8985 obj->oop_iterate(_keep_alive);
8986 }
8987 }
8988
8989 void CMSParDrainMarkingStackClosure::do_void() {
8990 // drain queue
8991 trim_queue(0);
8992 }
8993
8994 // Trim our work_queue so its length is below max at return
8995 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
8996 while (_work_queue->size() > max) {
8997 oop new_oop;
8998 if (_work_queue->pop_local(new_oop)) {
8999 assert(new_oop->is_oop(), "Expected an oop");
9000 assert(_bit_map->isMarked((HeapWord*)new_oop),
9001 "no white objects on this stack!");
9002 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
9003 // iterate over the oops in this oop, marking and pushing
9004 // the ones in CMS heap (i.e. in _span).
9005 new_oop->oop_iterate(&_mark_and_push);
9006 }
9007 }
9008 }
9009
9010 ////////////////////////////////////////////////////////////////////
9011 // Support for Marking Stack Overflow list handling and related code
9012 ////////////////////////////////////////////////////////////////////
9013 // Much of the following code is similar in shape and spirit to the
9014 // code used in ParNewGC. We should try and share that code
9015 // as much as possible in the future.
9016
9017 #ifndef PRODUCT
9018 // Debugging support for CMSStackOverflowALot
9019
9020 // It's OK to call this multi-threaded; the worst thing
9021 // that can happen is that we'll get a bunch of closely
9022 // spaced simulated overflows, but that's OK, in fact
9023 // probably good as it would exercise the overflow code
9024 // under contention.
9025 bool CMSCollector::simulate_overflow() {
9026 if (_overflow_counter-- <= 0) { // just being defensive
9027 _overflow_counter = CMSMarkStackOverflowInterval;
9028 return true;
9029 } else {
9030 return false;
9031 }
9032 }
9033
9034 bool CMSCollector::par_simulate_overflow() {
9035 return simulate_overflow();
9036 }
9037 #endif
9038
9039 // Single-threaded
9040 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
9041 assert(stack->isEmpty(), "Expected precondition");
9042 assert(stack->capacity() > num, "Shouldn't bite more than can chew");
9043 size_t i = num;
9044 oop cur = _overflow_list;
9045 const markOop proto = markOopDesc::prototype();
9046 NOT_PRODUCT(ssize_t n = 0;)
9047 for (oop next; i > 0 && cur != NULL; cur = next, i--) {
9048 next = oop(cur->mark());
9049 cur->set_mark(proto); // until proven otherwise
9050 assert(cur->is_oop(), "Should be an oop");
9051 bool res = stack->push(cur);
9052 assert(res, "Bit off more than can chew?");
9053 NOT_PRODUCT(n++;)
9054 }
9055 _overflow_list = cur;
9056 #ifndef PRODUCT
9057 assert(_num_par_pushes >= n, "Too many pops?");
9058 _num_par_pushes -=n;
9059 #endif
9060 return !stack->isEmpty();
9061 }
9062
9063 #define BUSY (cast_to_oop<intptr_t>(0x1aff1aff))
9064 // (MT-safe) Get a prefix of at most "num" from the list.
9065 // The overflow list is chained through the mark word of
9066 // each object in the list. We fetch the entire list,
9067 // break off a prefix of the right size and return the
9068 // remainder. If other threads try to take objects from
9069 // the overflow list at that time, they will wait for
9070 // some time to see if data becomes available. If (and
9071 // only if) another thread places one or more object(s)
9072 // on the global list before we have returned the suffix
9073 // to the global list, we will walk down our local list
9074 // to find its end and append the global list to
9075 // our suffix before returning it. This suffix walk can
9076 // prove to be expensive (quadratic in the amount of traffic)
9077 // when there are many objects in the overflow list and
9078 // there is much producer-consumer contention on the list.
9079 // *NOTE*: The overflow list manipulation code here and
9080 // in ParNewGeneration:: are very similar in shape,
9081 // except that in the ParNew case we use the old (from/eden)
9082 // copy of the object to thread the list via its klass word.
9083 // Because of the common code, if you make any changes in
9084 // the code below, please check the ParNew version to see if
9085 // similar changes might be needed.
9086 // CR 6797058 has been filed to consolidate the common code.
9087 bool CMSCollector::par_take_from_overflow_list(size_t num,
9088 OopTaskQueue* work_q,
9089 int no_of_gc_threads) {
9090 assert(work_q->size() == 0, "First empty local work queue");
9091 assert(num < work_q->max_elems(), "Can't bite more than we can chew");
9092 if (_overflow_list == NULL) {
9093 return false;
9094 }
9095 // Grab the entire list; we'll put back a suffix
9096 oop prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
9097 Thread* tid = Thread::current();
9098 // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was
9099 // set to ParallelGCThreads.
9100 size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads;
9101 size_t sleep_time_millis = MAX2((size_t)1, num/100);
9102 // If the list is busy, we spin for a short while,
9103 // sleeping between attempts to get the list.
9104 for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) {
9105 os::sleep(tid, sleep_time_millis, false);
9106 if (_overflow_list == NULL) {
9107 // Nothing left to take
9108 return false;
9109 } else if (_overflow_list != BUSY) {
9110 // Try and grab the prefix
9111 prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
9112 }
9113 }
9114 // If the list was found to be empty, or we spun long
9115 // enough, we give up and return empty-handed. If we leave
9116 // the list in the BUSY state below, it must be the case that
9117 // some other thread holds the overflow list and will set it
9118 // to a non-BUSY state in the future.
9119 if (prefix == NULL || prefix == BUSY) {
9120 // Nothing to take or waited long enough
9121 if (prefix == NULL) {
9122 // Write back the NULL in case we overwrote it with BUSY above
9123 // and it is still the same value.
9124 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
9125 }
9126 return false;
9127 }
9128 assert(prefix != NULL && prefix != BUSY, "Error");
9129 size_t i = num;
9130 oop cur = prefix;
9131 // Walk down the first "num" objects, unless we reach the end.
9132 for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--);
9133 if (cur->mark() == NULL) {
9134 // We have "num" or fewer elements in the list, so there
9135 // is nothing to return to the global list.
9136 // Write back the NULL in lieu of the BUSY we wrote
9137 // above, if it is still the same value.
9138 if (_overflow_list == BUSY) {
9139 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
9140 }
9141 } else {
9142 // Chop off the suffix and return it to the global list.
9143 assert(cur->mark() != BUSY, "Error");
9144 oop suffix_head = cur->mark(); // suffix will be put back on global list
9145 cur->set_mark(NULL); // break off suffix
9146 // It's possible that the list is still in the empty(busy) state
9147 // we left it in a short while ago; in that case we may be
9148 // able to place back the suffix without incurring the cost
9149 // of a walk down the list.
9150 oop observed_overflow_list = _overflow_list;
9151 oop cur_overflow_list = observed_overflow_list;
9152 bool attached = false;
9153 while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
9154 observed_overflow_list =
9155 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
9156 if (cur_overflow_list == observed_overflow_list) {
9157 attached = true;
9158 break;
9159 } else cur_overflow_list = observed_overflow_list;
9160 }
9161 if (!attached) {
9162 // Too bad, someone else sneaked in (at least) an element; we'll need
9163 // to do a splice. Find tail of suffix so we can prepend suffix to global
9164 // list.
9165 for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark()));
9166 oop suffix_tail = cur;
9167 assert(suffix_tail != NULL && suffix_tail->mark() == NULL,
9168 "Tautology");
9169 observed_overflow_list = _overflow_list;
9170 do {
9171 cur_overflow_list = observed_overflow_list;
9172 if (cur_overflow_list != BUSY) {
9173 // Do the splice ...
9174 suffix_tail->set_mark(markOop(cur_overflow_list));
9175 } else { // cur_overflow_list == BUSY
9176 suffix_tail->set_mark(NULL);
9177 }
9178 // ... and try to place spliced list back on overflow_list ...
9179 observed_overflow_list =
9180 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
9181 } while (cur_overflow_list != observed_overflow_list);
9182 // ... until we have succeeded in doing so.
9183 }
9184 }
9185
9186 // Push the prefix elements on work_q
9187 assert(prefix != NULL, "control point invariant");
9188 const markOop proto = markOopDesc::prototype();
9189 oop next;
9190 NOT_PRODUCT(ssize_t n = 0;)
9191 for (cur = prefix; cur != NULL; cur = next) {
9192 next = oop(cur->mark());
9193 cur->set_mark(proto); // until proven otherwise
9194 assert(cur->is_oop(), "Should be an oop");
9195 bool res = work_q->push(cur);
9196 assert(res, "Bit off more than we can chew?");
9197 NOT_PRODUCT(n++;)
9198 }
9199 #ifndef PRODUCT
9200 assert(_num_par_pushes >= n, "Too many pops?");
9201 Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
9202 #endif
9203 return true;
9204 }
9205
9206 // Single-threaded
9207 void CMSCollector::push_on_overflow_list(oop p) {
9208 NOT_PRODUCT(_num_par_pushes++;)
9209 assert(p->is_oop(), "Not an oop");
9210 preserve_mark_if_necessary(p);
9211 p->set_mark((markOop)_overflow_list);
9212 _overflow_list = p;
9213 }
9214
9215 // Multi-threaded; use CAS to prepend to overflow list
9216 void CMSCollector::par_push_on_overflow_list(oop p) {
9217 NOT_PRODUCT(Atomic::inc_ptr(&_num_par_pushes);)
9218 assert(p->is_oop(), "Not an oop");
9219 par_preserve_mark_if_necessary(p);
9220 oop observed_overflow_list = _overflow_list;
9221 oop cur_overflow_list;
9222 do {
9223 cur_overflow_list = observed_overflow_list;
9224 if (cur_overflow_list != BUSY) {
9225 p->set_mark(markOop(cur_overflow_list));
9226 } else {
9227 p->set_mark(NULL);
9228 }
9229 observed_overflow_list =
9230 (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list);
9231 } while (cur_overflow_list != observed_overflow_list);
9232 }
9233 #undef BUSY
9234
9235 // Single threaded
9236 // General Note on GrowableArray: pushes may silently fail
9237 // because we are (temporarily) out of C-heap for expanding
9238 // the stack. The problem is quite ubiquitous and affects
9239 // a lot of code in the JVM. The prudent thing for GrowableArray
9240 // to do (for now) is to exit with an error. However, that may
9241 // be too draconian in some cases because the caller may be
9242 // able to recover without much harm. For such cases, we
9243 // should probably introduce a "soft_push" method which returns
9244 // an indication of success or failure with the assumption that
9245 // the caller may be able to recover from a failure; code in
9246 // the VM can then be changed, incrementally, to deal with such
9247 // failures where possible, thus, incrementally hardening the VM
9248 // in such low resource situations.
9249 void CMSCollector::preserve_mark_work(oop p, markOop m) {
9250 _preserved_oop_stack.push(p);
9251 _preserved_mark_stack.push(m);
9252 assert(m == p->mark(), "Mark word changed");
9253 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
9254 "bijection");
9255 }
9256
9257 // Single threaded
9258 void CMSCollector::preserve_mark_if_necessary(oop p) {
9259 markOop m = p->mark();
9260 if (m->must_be_preserved(p)) {
9261 preserve_mark_work(p, m);
9262 }
9263 }
9264
9265 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
9266 markOop m = p->mark();
9267 if (m->must_be_preserved(p)) {
9268 MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
9269 // Even though we read the mark word without holding
9270 // the lock, we are assured that it will not change
9271 // because we "own" this oop, so no other thread can
9272 // be trying to push it on the overflow list; see
9273 // the assertion in preserve_mark_work() that checks
9274 // that m == p->mark().
9275 preserve_mark_work(p, m);
9276 }
9277 }
9278
9279 // We should be able to do this multi-threaded,
9280 // a chunk of stack being a task (this is
9281 // correct because each oop only ever appears
9282 // once in the overflow list. However, it's
9283 // not very easy to completely overlap this with
9284 // other operations, so will generally not be done
9285 // until all work's been completed. Because we
9286 // expect the preserved oop stack (set) to be small,
9287 // it's probably fine to do this single-threaded.
9288 // We can explore cleverer concurrent/overlapped/parallel
9289 // processing of preserved marks if we feel the
9290 // need for this in the future. Stack overflow should
9291 // be so rare in practice and, when it happens, its
9292 // effect on performance so great that this will
9293 // likely just be in the noise anyway.
9294 void CMSCollector::restore_preserved_marks_if_any() {
9295 assert(SafepointSynchronize::is_at_safepoint(),
9296 "world should be stopped");
9297 assert(Thread::current()->is_ConcurrentGC_thread() ||
9298 Thread::current()->is_VM_thread(),
9299 "should be single-threaded");
9300 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
9301 "bijection");
9302
9303 while (!_preserved_oop_stack.is_empty()) {
9304 oop p = _preserved_oop_stack.pop();
9305 assert(p->is_oop(), "Should be an oop");
9306 assert(_span.contains(p), "oop should be in _span");
9307 assert(p->mark() == markOopDesc::prototype(),
9308 "Set when taken from overflow list");
9309 markOop m = _preserved_mark_stack.pop();
9310 p->set_mark(m);
9311 }
9312 assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(),
9313 "stacks were cleared above");
9314 }
9315
9316 #ifndef PRODUCT
9317 bool CMSCollector::no_preserved_marks() const {
9318 return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty();
9319 }
9320 #endif
9321
9322 CMSAdaptiveSizePolicy* ASConcurrentMarkSweepGeneration::cms_size_policy() const
9323 {
9324 GenCollectedHeap* gch = (GenCollectedHeap*) GenCollectedHeap::heap();
9325 CMSAdaptiveSizePolicy* size_policy =
9326 (CMSAdaptiveSizePolicy*) gch->gen_policy()->size_policy();
9327 assert(size_policy->is_gc_cms_adaptive_size_policy(),
9328 "Wrong type for size policy");
9329 return size_policy;
9330 }
9331
9332 void ASConcurrentMarkSweepGeneration::resize(size_t cur_promo_size,
9333 size_t desired_promo_size) {
9334 if (cur_promo_size < desired_promo_size) {
9335 size_t expand_bytes = desired_promo_size - cur_promo_size;
9336 if (PrintAdaptiveSizePolicy && Verbose) {
9337 gclog_or_tty->print_cr(" ASConcurrentMarkSweepGeneration::resize "
9338 "Expanding tenured generation by " SIZE_FORMAT " (bytes)",
9339 expand_bytes);
9340 }
9341 expand(expand_bytes,
9342 MinHeapDeltaBytes,
9343 CMSExpansionCause::_adaptive_size_policy);
9344 } else if (desired_promo_size < cur_promo_size) {
9345 size_t shrink_bytes = cur_promo_size - desired_promo_size;
9346 if (PrintAdaptiveSizePolicy && Verbose) {
9347 gclog_or_tty->print_cr(" ASConcurrentMarkSweepGeneration::resize "
9348 "Shrinking tenured generation by " SIZE_FORMAT " (bytes)",
9349 shrink_bytes);
9350 }
9351 shrink(shrink_bytes);
9352 }
9353 }
9354
9355 CMSGCAdaptivePolicyCounters* ASConcurrentMarkSweepGeneration::gc_adaptive_policy_counters() {
9356 GenCollectedHeap* gch = GenCollectedHeap::heap();
9357 CMSGCAdaptivePolicyCounters* counters =
9358 (CMSGCAdaptivePolicyCounters*) gch->collector_policy()->counters();
9359 assert(counters->kind() == GCPolicyCounters::CMSGCAdaptivePolicyCountersKind,
9360 "Wrong kind of counters");
9361 return counters;
9362 }
9363
9364
9365 void ASConcurrentMarkSweepGeneration::update_counters() {
9366 if (UsePerfData) {
9367 _space_counters->update_all();
9368 _gen_counters->update_all();
9369 CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
9370 GenCollectedHeap* gch = GenCollectedHeap::heap();
9371 CMSGCStats* gc_stats_l = (CMSGCStats*) gc_stats();
9372 assert(gc_stats_l->kind() == GCStats::CMSGCStatsKind,
9373 "Wrong gc statistics type");
9374 counters->update_counters(gc_stats_l);
9375 }
9376 }
9377
9378 void ASConcurrentMarkSweepGeneration::update_counters(size_t used) {
9379 if (UsePerfData) {
9380 _space_counters->update_used(used);
9381 _space_counters->update_capacity();
9382 _gen_counters->update_all();
9383
9384 CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
9385 GenCollectedHeap* gch = GenCollectedHeap::heap();
9386 CMSGCStats* gc_stats_l = (CMSGCStats*) gc_stats();
9387 assert(gc_stats_l->kind() == GCStats::CMSGCStatsKind,
9388 "Wrong gc statistics type");
9389 counters->update_counters(gc_stats_l);
9390 }
9391 }
9392
9393 void ASConcurrentMarkSweepGeneration::shrink_by(size_t desired_bytes) {
9394 assert_locked_or_safepoint(Heap_lock);
9395 assert_lock_strong(freelistLock());
9396 HeapWord* old_end = _cmsSpace->end();
9397 HeapWord* unallocated_start = _cmsSpace->unallocated_block();
9398 assert(old_end >= unallocated_start, "Miscalculation of unallocated_start");
9399 FreeChunk* chunk_at_end = find_chunk_at_end();
9400 if (chunk_at_end == NULL) {
9401 // No room to shrink
9402 if (PrintGCDetails && Verbose) {
9403 gclog_or_tty->print_cr("No room to shrink: old_end "
9404 PTR_FORMAT " unallocated_start " PTR_FORMAT
9405 " chunk_at_end " PTR_FORMAT,
9406 old_end, unallocated_start, chunk_at_end);
9407 }
9408 return;
9409 } else {
9410
9411 // Find the chunk at the end of the space and determine
9412 // how much it can be shrunk.
9413 size_t shrinkable_size_in_bytes = chunk_at_end->size();
9414 size_t aligned_shrinkable_size_in_bytes =
9415 align_size_down(shrinkable_size_in_bytes, os::vm_page_size());
9416 assert(unallocated_start <= (HeapWord*) chunk_at_end->end(),
9417 "Inconsistent chunk at end of space");
9418 size_t bytes = MIN2(desired_bytes, aligned_shrinkable_size_in_bytes);
9419 size_t word_size_before = heap_word_size(_virtual_space.committed_size());
9420
9421 // Shrink the underlying space
9422 _virtual_space.shrink_by(bytes);
9423 if (PrintGCDetails && Verbose) {
9424 gclog_or_tty->print_cr("ConcurrentMarkSweepGeneration::shrink_by:"
9425 " desired_bytes " SIZE_FORMAT
9426 " shrinkable_size_in_bytes " SIZE_FORMAT
9427 " aligned_shrinkable_size_in_bytes " SIZE_FORMAT
9428 " bytes " SIZE_FORMAT,
9429 desired_bytes, shrinkable_size_in_bytes,
9430 aligned_shrinkable_size_in_bytes, bytes);
9431 gclog_or_tty->print_cr(" old_end " SIZE_FORMAT
9432 " unallocated_start " SIZE_FORMAT,
9433 old_end, unallocated_start);
9434 }
9435
9436 // If the space did shrink (shrinking is not guaranteed),
9437 // shrink the chunk at the end by the appropriate amount.
9438 if (((HeapWord*)_virtual_space.high()) < old_end) {
9439 size_t new_word_size =
9440 heap_word_size(_virtual_space.committed_size());
9441
9442 // Have to remove the chunk from the dictionary because it is changing
9443 // size and might be someplace elsewhere in the dictionary.
9444
9445 // Get the chunk at end, shrink it, and put it
9446 // back.
9447 _cmsSpace->removeChunkFromDictionary(chunk_at_end);
9448 size_t word_size_change = word_size_before - new_word_size;
9449 size_t chunk_at_end_old_size = chunk_at_end->size();
9450 assert(chunk_at_end_old_size >= word_size_change,
9451 "Shrink is too large");
9452 chunk_at_end->set_size(chunk_at_end_old_size -
9453 word_size_change);
9454 _cmsSpace->freed((HeapWord*) chunk_at_end->end(),
9455 word_size_change);
9456
9457 _cmsSpace->returnChunkToDictionary(chunk_at_end);
9458
9459 MemRegion mr(_cmsSpace->bottom(), new_word_size);
9460 _bts->resize(new_word_size); // resize the block offset shared array
9461 Universe::heap()->barrier_set()->resize_covered_region(mr);
9462 _cmsSpace->assert_locked();
9463 _cmsSpace->set_end((HeapWord*)_virtual_space.high());
9464
9465 NOT_PRODUCT(_cmsSpace->dictionary()->verify());
9466
9467 // update the space and generation capacity counters
9468 if (UsePerfData) {
9469 _space_counters->update_capacity();
9470 _gen_counters->update_all();
9471 }
9472
9473 if (Verbose && PrintGCDetails) {
9474 size_t new_mem_size = _virtual_space.committed_size();
9475 size_t old_mem_size = new_mem_size + bytes;
9476 gclog_or_tty->print_cr("Shrinking %s from " SIZE_FORMAT "K by " SIZE_FORMAT "K to " SIZE_FORMAT "K",
9477 name(), old_mem_size/K, bytes/K, new_mem_size/K);
9478 }
9479 }
9480
9481 assert(_cmsSpace->unallocated_block() <= _cmsSpace->end(),
9482 "Inconsistency at end of space");
9483 assert(chunk_at_end->end() == (uintptr_t*) _cmsSpace->end(),
9484 "Shrinking is inconsistent");
9485 return;
9486 }
9487 }
9488 // Transfer some number of overflown objects to usual marking
9489 // stack. Return true if some objects were transferred.
9490 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
9491 size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,
9492 (size_t)ParGCDesiredObjsFromOverflowList);
9493
9494 bool res = _collector->take_from_overflow_list(num, _mark_stack);
9495 assert(_collector->overflow_list_is_empty() || res,
9496 "If list is not empty, we should have taken something");
9497 assert(!res || !_mark_stack->isEmpty(),
9498 "If we took something, it should now be on our stack");
9499 return res;
9500 }
9501
9502 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
9503 size_t res = _sp->block_size_no_stall(addr, _collector);
9504 if (_sp->block_is_obj(addr)) {
9505 if (_live_bit_map->isMarked(addr)) {
9506 // It can't have been dead in a previous cycle
9507 guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
9508 } else {
9509 _dead_bit_map->mark(addr); // mark the dead object
9510 }
9511 }
9512 // Could be 0, if the block size could not be computed without stalling.
9513 return res;
9514 }
9515
9516 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() {
9517
9518 switch (phase) {
9519 case CMSCollector::InitialMarking:
9520 initialize(true /* fullGC */ ,
9521 cause /* cause of the GC */,
9522 true /* recordGCBeginTime */,
9523 true /* recordPreGCUsage */,
9524 false /* recordPeakUsage */,
9525 false /* recordPostGCusage */,
9526 true /* recordAccumulatedGCTime */,
9527 false /* recordGCEndTime */,
9528 false /* countCollection */ );
9529 break;
9530
9531 case CMSCollector::FinalMarking:
9532 initialize(true /* fullGC */ ,
9533 cause /* cause of the GC */,
9534 false /* recordGCBeginTime */,
9535 false /* recordPreGCUsage */,
9536 false /* recordPeakUsage */,
9537 false /* recordPostGCusage */,
9538 true /* recordAccumulatedGCTime */,
9539 false /* recordGCEndTime */,
9540 false /* countCollection */ );
9541 break;
9542
9543 case CMSCollector::Sweeping:
9544 initialize(true /* fullGC */ ,
9545 cause /* cause of the GC */,
9546 false /* recordGCBeginTime */,
9547 false /* recordPreGCUsage */,
9548 true /* recordPeakUsage */,
9549 true /* recordPostGCusage */,
9550 false /* recordAccumulatedGCTime */,
9551 true /* recordGCEndTime */,
9552 true /* countCollection */ );
9553 break;
9554
9555 default:
9556 ShouldNotReachHere();
9557 }
9558 }