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/referencePolicy.hpp"
54 #include "memory/resourceArea.hpp"
55 #include "memory/tenuredGeneration.hpp"
56 #include "oops/oop.inline.hpp"
57 #include "prims/jvmtiExport.hpp"
58 #include "runtime/globals_extension.hpp"
59 #include "runtime/handles.inline.hpp"
60 #include "runtime/java.hpp"
61 #include "runtime/vmThread.hpp"
62 #include "services/memoryService.hpp"
63 #include "services/runtimeService.hpp"
64
65 // statics
66 CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL;
67 bool CMSCollector::_full_gc_requested = false;
68 GCCause::Cause CMSCollector::_full_gc_cause = GCCause::_no_gc;
69
70 //////////////////////////////////////////////////////////////////
71 // In support of CMS/VM thread synchronization
72 //////////////////////////////////////////////////////////////////
73 // We split use of the CGC_lock into 2 "levels".
74 // The low-level locking is of the usual CGC_lock monitor. We introduce
75 // a higher level "token" (hereafter "CMS token") built on top of the
76 // low level monitor (hereafter "CGC lock").
77 // The token-passing protocol gives priority to the VM thread. The
78 // CMS-lock doesn't provide any fairness guarantees, but clients
79 // should ensure that it is only held for very short, bounded
80 // durations.
81 //
82 // When either of the CMS thread or the VM thread is involved in
83 // collection operations during which it does not want the other
84 // thread to interfere, it obtains the CMS token.
85 //
86 // If either thread tries to get the token while the other has
87 // it, that thread waits. However, if the VM thread and CMS thread
88 // both want the token, then the VM thread gets priority while the
89 // CMS thread waits. This ensures, for instance, that the "concurrent"
90 // phases of the CMS thread's work do not block out the VM thread
91 // for long periods of time as the CMS thread continues to hog
92 // the token. (See bug 4616232).
93 //
94 // The baton-passing functions are, however, controlled by the
95 // flags _foregroundGCShouldWait and _foregroundGCIsActive,
96 // and here the low-level CMS lock, not the high level token,
97 // ensures mutual exclusion.
98 //
99 // Two important conditions that we have to satisfy:
100 // 1. if a thread does a low-level wait on the CMS lock, then it
101 // relinquishes the CMS token if it were holding that token
102 // when it acquired the low-level CMS lock.
103 // 2. any low-level notifications on the low-level lock
104 // should only be sent when a thread has relinquished the token.
105 //
106 // In the absence of either property, we'd have potential deadlock.
107 //
108 // We protect each of the CMS (concurrent and sequential) phases
109 // with the CMS _token_, not the CMS _lock_.
110 //
111 // The only code protected by CMS lock is the token acquisition code
112 // itself, see ConcurrentMarkSweepThread::[de]synchronize(), and the
113 // baton-passing code.
114 //
115 // Unfortunately, i couldn't come up with a good abstraction to factor and
116 // hide the naked CGC_lock manipulation in the baton-passing code
117 // further below. That's something we should try to do. Also, the proof
118 // of correctness of this 2-level locking scheme is far from obvious,
119 // and potentially quite slippery. We have an uneasy supsicion, for instance,
120 // that there may be a theoretical possibility of delay/starvation in the
121 // low-level lock/wait/notify scheme used for the baton-passing because of
122 // potential intereference with the priority scheme embodied in the
123 // CMS-token-passing protocol. See related comments at a CGC_lock->wait()
124 // invocation further below and marked with "XXX 20011219YSR".
125 // Indeed, as we note elsewhere, this may become yet more slippery
126 // in the presence of multiple CMS and/or multiple VM threads. XXX
127
128 class CMSTokenSync: public StackObj {
129 private:
130 bool _is_cms_thread;
131 public:
132 CMSTokenSync(bool is_cms_thread):
133 _is_cms_thread(is_cms_thread) {
134 assert(is_cms_thread == Thread::current()->is_ConcurrentGC_thread(),
135 "Incorrect argument to constructor");
136 ConcurrentMarkSweepThread::synchronize(_is_cms_thread);
137 }
138
139 ~CMSTokenSync() {
140 assert(_is_cms_thread ?
141 ConcurrentMarkSweepThread::cms_thread_has_cms_token() :
142 ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
143 "Incorrect state");
144 ConcurrentMarkSweepThread::desynchronize(_is_cms_thread);
145 }
146 };
147
148 // Convenience class that does a CMSTokenSync, and then acquires
149 // upto three locks.
150 class CMSTokenSyncWithLocks: public CMSTokenSync {
151 private:
152 // Note: locks are acquired in textual declaration order
153 // and released in the opposite order
154 MutexLockerEx _locker1, _locker2, _locker3;
155 public:
156 CMSTokenSyncWithLocks(bool is_cms_thread, Mutex* mutex1,
157 Mutex* mutex2 = NULL, Mutex* mutex3 = NULL):
158 CMSTokenSync(is_cms_thread),
159 _locker1(mutex1, Mutex::_no_safepoint_check_flag),
160 _locker2(mutex2, Mutex::_no_safepoint_check_flag),
161 _locker3(mutex3, Mutex::_no_safepoint_check_flag)
162 { }
163 };
164
165
166 // Wrapper class to temporarily disable icms during a foreground cms collection.
167 class ICMSDisabler: public StackObj {
168 public:
169 // The ctor disables icms and wakes up the thread so it notices the change;
170 // the dtor re-enables icms. Note that the CMSCollector methods will check
171 // CMSIncrementalMode.
172 ICMSDisabler() { CMSCollector::disable_icms(); CMSCollector::start_icms(); }
173 ~ICMSDisabler() { CMSCollector::enable_icms(); }
174 };
175
176 //////////////////////////////////////////////////////////////////
177 // Concurrent Mark-Sweep Generation /////////////////////////////
178 //////////////////////////////////////////////////////////////////
179
180 NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;)
181
182 // This struct contains per-thread things necessary to support parallel
183 // young-gen collection.
184 class CMSParGCThreadState: public CHeapObj<mtGC> {
185 public:
186 CFLS_LAB lab;
187 PromotionInfo promo;
188
189 // Constructor.
190 CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) {
191 promo.setSpace(cfls);
192 }
193 };
194
195 ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration(
196 ReservedSpace rs, size_t initial_byte_size, int level,
197 CardTableRS* ct, bool use_adaptive_freelists,
198 FreeBlockDictionary<FreeChunk>::DictionaryChoice dictionaryChoice) :
199 CardGeneration(rs, initial_byte_size, level, ct),
200 _dilatation_factor(((double)MinChunkSize)/((double)(CollectedHeap::min_fill_size()))),
201 _debug_collection_type(Concurrent_collection_type),
202 _did_compact(false)
203 {
204 HeapWord* bottom = (HeapWord*) _virtual_space.low();
205 HeapWord* end = (HeapWord*) _virtual_space.high();
206
207 _direct_allocated_words = 0;
208 NOT_PRODUCT(
209 _numObjectsPromoted = 0;
210 _numWordsPromoted = 0;
211 _numObjectsAllocated = 0;
212 _numWordsAllocated = 0;
213 )
214
215 _cmsSpace = new CompactibleFreeListSpace(_bts, MemRegion(bottom, end),
216 use_adaptive_freelists,
217 dictionaryChoice);
218 NOT_PRODUCT(debug_cms_space = _cmsSpace;)
219 if (_cmsSpace == NULL) {
220 vm_exit_during_initialization(
221 "CompactibleFreeListSpace allocation failure");
222 }
223 _cmsSpace->_gen = this;
224
225 _gc_stats = new CMSGCStats();
226
227 // Verify the assumption that FreeChunk::_prev and OopDesc::_klass
228 // offsets match. The ability to tell free chunks from objects
229 // depends on this property.
230 debug_only(
231 FreeChunk* junk = NULL;
232 assert(UseCompressedKlassPointers ||
233 junk->prev_addr() == (void*)(oop(junk)->klass_addr()),
234 "Offset of FreeChunk::_prev within FreeChunk must match"
235 " that of OopDesc::_klass within OopDesc");
236 )
237 if (CollectedHeap::use_parallel_gc_threads()) {
238 typedef CMSParGCThreadState* CMSParGCThreadStatePtr;
239 _par_gc_thread_states =
240 NEW_C_HEAP_ARRAY(CMSParGCThreadStatePtr, ParallelGCThreads, mtGC);
241 if (_par_gc_thread_states == NULL) {
242 vm_exit_during_initialization("Could not allocate par gc structs");
243 }
244 for (uint i = 0; i < ParallelGCThreads; i++) {
245 _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace());
246 if (_par_gc_thread_states[i] == NULL) {
247 vm_exit_during_initialization("Could not allocate par gc structs");
248 }
249 }
250 } else {
251 _par_gc_thread_states = NULL;
252 }
253 _incremental_collection_failed = false;
254 // The "dilatation_factor" is the expansion that can occur on
255 // account of the fact that the minimum object size in the CMS
256 // generation may be larger than that in, say, a contiguous young
257 // generation.
258 // Ideally, in the calculation below, we'd compute the dilatation
259 // factor as: MinChunkSize/(promoting_gen's min object size)
260 // Since we do not have such a general query interface for the
261 // promoting generation, we'll instead just use the mimimum
262 // object size (which today is a header's worth of space);
263 // note that all arithmetic is in units of HeapWords.
264 assert(MinChunkSize >= CollectedHeap::min_fill_size(), "just checking");
265 assert(_dilatation_factor >= 1.0, "from previous assert");
266 }
267
268
269 // The field "_initiating_occupancy" represents the occupancy percentage
270 // at which we trigger a new collection cycle. Unless explicitly specified
271 // via CMSInitiatingOccupancyFraction (argument "io" below), it
272 // is calculated by:
273 //
274 // Let "f" be MinHeapFreeRatio in
275 //
276 // _intiating_occupancy = 100-f +
277 // f * (CMSTriggerRatio/100)
278 // where CMSTriggerRatio is the argument "tr" below.
279 //
280 // That is, if we assume the heap is at its desired maximum occupancy at the
281 // end of a collection, we let CMSTriggerRatio of the (purported) free
282 // space be allocated before initiating a new collection cycle.
283 //
284 void ConcurrentMarkSweepGeneration::init_initiating_occupancy(intx io, uintx tr) {
285 assert(io <= 100 && tr <= 100, "Check the arguments");
286 if (io >= 0) {
287 _initiating_occupancy = (double)io / 100.0;
288 } else {
289 _initiating_occupancy = ((100 - MinHeapFreeRatio) +
290 (double)(tr * MinHeapFreeRatio) / 100.0)
291 / 100.0;
292 }
293 }
294
295 void ConcurrentMarkSweepGeneration::ref_processor_init() {
296 assert(collector() != NULL, "no collector");
297 collector()->ref_processor_init();
298 }
299
300 void CMSCollector::ref_processor_init() {
301 if (_ref_processor == NULL) {
302 // Allocate and initialize a reference processor
303 _ref_processor =
304 new ReferenceProcessor(_span, // span
305 (ParallelGCThreads > 1) && ParallelRefProcEnabled, // mt processing
306 (int) ParallelGCThreads, // mt processing degree
307 _cmsGen->refs_discovery_is_mt(), // mt discovery
308 (int) MAX2(ConcGCThreads, ParallelGCThreads), // mt discovery degree
309 _cmsGen->refs_discovery_is_atomic(), // discovery is not atomic
310 &_is_alive_closure, // closure for liveness info
311 false); // next field updates do not need write barrier
312 // Initialize the _ref_processor field of CMSGen
313 _cmsGen->set_ref_processor(_ref_processor);
314
315 }
316 }
317
318 CMSAdaptiveSizePolicy* CMSCollector::size_policy() {
319 GenCollectedHeap* gch = GenCollectedHeap::heap();
320 assert(gch->kind() == CollectedHeap::GenCollectedHeap,
321 "Wrong type of heap");
322 CMSAdaptiveSizePolicy* sp = (CMSAdaptiveSizePolicy*)
323 gch->gen_policy()->size_policy();
324 assert(sp->is_gc_cms_adaptive_size_policy(),
325 "Wrong type of size policy");
326 return sp;
327 }
328
329 CMSGCAdaptivePolicyCounters* CMSCollector::gc_adaptive_policy_counters() {
330 CMSGCAdaptivePolicyCounters* results =
331 (CMSGCAdaptivePolicyCounters*) collector_policy()->counters();
332 assert(
333 results->kind() == GCPolicyCounters::CMSGCAdaptivePolicyCountersKind,
334 "Wrong gc policy counter kind");
335 return results;
336 }
337
338
339 void ConcurrentMarkSweepGeneration::initialize_performance_counters() {
340
341 const char* gen_name = "old";
342
343 // Generation Counters - generation 1, 1 subspace
344 _gen_counters = new GenerationCounters(gen_name, 1, 1, &_virtual_space);
345
346 _space_counters = new GSpaceCounters(gen_name, 0,
347 _virtual_space.reserved_size(),
348 this, _gen_counters);
349 }
350
351 CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha):
352 _cms_gen(cms_gen)
353 {
354 assert(alpha <= 100, "bad value");
355 _saved_alpha = alpha;
356
357 // Initialize the alphas to the bootstrap value of 100.
358 _gc0_alpha = _cms_alpha = 100;
359
360 _cms_begin_time.update();
361 _cms_end_time.update();
362
363 _gc0_duration = 0.0;
364 _gc0_period = 0.0;
365 _gc0_promoted = 0;
366
367 _cms_duration = 0.0;
368 _cms_period = 0.0;
369 _cms_allocated = 0;
370
371 _cms_used_at_gc0_begin = 0;
372 _cms_used_at_gc0_end = 0;
373 _allow_duty_cycle_reduction = false;
374 _valid_bits = 0;
375 _icms_duty_cycle = CMSIncrementalDutyCycle;
376 }
377
378 double CMSStats::cms_free_adjustment_factor(size_t free) const {
379 // TBD: CR 6909490
380 return 1.0;
381 }
382
383 void CMSStats::adjust_cms_free_adjustment_factor(bool fail, size_t free) {
384 }
385
386 // If promotion failure handling is on use
387 // the padded average size of the promotion for each
388 // young generation collection.
389 double CMSStats::time_until_cms_gen_full() const {
390 size_t cms_free = _cms_gen->cmsSpace()->free();
391 GenCollectedHeap* gch = GenCollectedHeap::heap();
392 size_t expected_promotion = MIN2(gch->get_gen(0)->capacity(),
393 (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average());
394 if (cms_free > expected_promotion) {
395 // Start a cms collection if there isn't enough space to promote
396 // for the next minor collection. Use the padded average as
397 // a safety factor.
398 cms_free -= expected_promotion;
399
400 // Adjust by the safety factor.
401 double cms_free_dbl = (double)cms_free;
402 double cms_adjustment = (100.0 - CMSIncrementalSafetyFactor)/100.0;
403 // Apply a further correction factor which tries to adjust
404 // for recent occurance of concurrent mode failures.
405 cms_adjustment = cms_adjustment * cms_free_adjustment_factor(cms_free);
406 cms_free_dbl = cms_free_dbl * cms_adjustment;
407
408 if (PrintGCDetails && Verbose) {
409 gclog_or_tty->print_cr("CMSStats::time_until_cms_gen_full: cms_free "
410 SIZE_FORMAT " expected_promotion " SIZE_FORMAT,
411 cms_free, expected_promotion);
412 gclog_or_tty->print_cr(" cms_free_dbl %f cms_consumption_rate %f",
413 cms_free_dbl, cms_consumption_rate() + 1.0);
414 }
415 // Add 1 in case the consumption rate goes to zero.
416 return cms_free_dbl / (cms_consumption_rate() + 1.0);
417 }
418 return 0.0;
419 }
420
421 // Compare the duration of the cms collection to the
422 // time remaining before the cms generation is empty.
423 // Note that the time from the start of the cms collection
424 // to the start of the cms sweep (less than the total
425 // duration of the cms collection) can be used. This
426 // has been tried and some applications experienced
427 // promotion failures early in execution. This was
428 // possibly because the averages were not accurate
429 // enough at the beginning.
430 double CMSStats::time_until_cms_start() const {
431 // We add "gc0_period" to the "work" calculation
432 // below because this query is done (mostly) at the
433 // end of a scavenge, so we need to conservatively
434 // account for that much possible delay
435 // in the query so as to avoid concurrent mode failures
436 // due to starting the collection just a wee bit too
437 // late.
438 double work = cms_duration() + gc0_period();
439 double deadline = time_until_cms_gen_full();
440 // If a concurrent mode failure occurred recently, we want to be
441 // more conservative and halve our expected time_until_cms_gen_full()
442 if (work > deadline) {
443 if (Verbose && PrintGCDetails) {
444 gclog_or_tty->print(
445 " CMSCollector: collect because of anticipated promotion "
446 "before full %3.7f + %3.7f > %3.7f ", cms_duration(),
447 gc0_period(), time_until_cms_gen_full());
448 }
449 return 0.0;
450 }
451 return work - deadline;
452 }
453
454 // Return a duty cycle based on old_duty_cycle and new_duty_cycle, limiting the
455 // amount of change to prevent wild oscillation.
456 unsigned int CMSStats::icms_damped_duty_cycle(unsigned int old_duty_cycle,
457 unsigned int new_duty_cycle) {
458 assert(old_duty_cycle <= 100, "bad input value");
459 assert(new_duty_cycle <= 100, "bad input value");
460
461 // Note: use subtraction with caution since it may underflow (values are
462 // unsigned). Addition is safe since we're in the range 0-100.
463 unsigned int damped_duty_cycle = new_duty_cycle;
464 if (new_duty_cycle < old_duty_cycle) {
465 const unsigned int largest_delta = MAX2(old_duty_cycle / 4, 5U);
466 if (new_duty_cycle + largest_delta < old_duty_cycle) {
467 damped_duty_cycle = old_duty_cycle - largest_delta;
468 }
469 } else if (new_duty_cycle > old_duty_cycle) {
470 const unsigned int largest_delta = MAX2(old_duty_cycle / 4, 15U);
471 if (new_duty_cycle > old_duty_cycle + largest_delta) {
472 damped_duty_cycle = MIN2(old_duty_cycle + largest_delta, 100U);
473 }
474 }
475 assert(damped_duty_cycle <= 100, "invalid duty cycle computed");
476
477 if (CMSTraceIncrementalPacing) {
478 gclog_or_tty->print(" [icms_damped_duty_cycle(%d,%d) = %d] ",
479 old_duty_cycle, new_duty_cycle, damped_duty_cycle);
480 }
481 return damped_duty_cycle;
482 }
483
484 unsigned int CMSStats::icms_update_duty_cycle_impl() {
485 assert(CMSIncrementalPacing && valid(),
486 "should be handled in icms_update_duty_cycle()");
487
488 double cms_time_so_far = cms_timer().seconds();
489 double scaled_duration = cms_duration_per_mb() * _cms_used_at_gc0_end / M;
490 double scaled_duration_remaining = fabsd(scaled_duration - cms_time_so_far);
491
492 // Avoid division by 0.
493 double time_until_full = MAX2(time_until_cms_gen_full(), 0.01);
494 double duty_cycle_dbl = 100.0 * scaled_duration_remaining / time_until_full;
495
496 unsigned int new_duty_cycle = MIN2((unsigned int)duty_cycle_dbl, 100U);
497 if (new_duty_cycle > _icms_duty_cycle) {
498 // Avoid very small duty cycles (1 or 2); 0 is allowed.
499 if (new_duty_cycle > 2) {
500 _icms_duty_cycle = icms_damped_duty_cycle(_icms_duty_cycle,
501 new_duty_cycle);
502 }
503 } else if (_allow_duty_cycle_reduction) {
504 // The duty cycle is reduced only once per cms cycle (see record_cms_end()).
505 new_duty_cycle = icms_damped_duty_cycle(_icms_duty_cycle, new_duty_cycle);
506 // Respect the minimum duty cycle.
507 unsigned int min_duty_cycle = (unsigned int)CMSIncrementalDutyCycleMin;
508 _icms_duty_cycle = MAX2(new_duty_cycle, min_duty_cycle);
509 }
510
511 if (PrintGCDetails || CMSTraceIncrementalPacing) {
512 gclog_or_tty->print(" icms_dc=%d ", _icms_duty_cycle);
513 }
514
515 _allow_duty_cycle_reduction = false;
516 return _icms_duty_cycle;
517 }
518
519 #ifndef PRODUCT
520 void CMSStats::print_on(outputStream *st) const {
521 st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha);
522 st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo=" SIZE_FORMAT,
523 gc0_duration(), gc0_period(), gc0_promoted());
524 st->print(",cms_dur=%g,cms_dur_per_mb=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT,
525 cms_duration(), cms_duration_per_mb(),
526 cms_period(), cms_allocated());
527 st->print(",cms_since_beg=%g,cms_since_end=%g",
528 cms_time_since_begin(), cms_time_since_end());
529 st->print(",cms_used_beg=" SIZE_FORMAT ",cms_used_end=" SIZE_FORMAT,
530 _cms_used_at_gc0_begin, _cms_used_at_gc0_end);
531 if (CMSIncrementalMode) {
532 st->print(",dc=%d", icms_duty_cycle());
533 }
534
535 if (valid()) {
536 st->print(",promo_rate=%g,cms_alloc_rate=%g",
537 promotion_rate(), cms_allocation_rate());
538 st->print(",cms_consumption_rate=%g,time_until_full=%g",
539 cms_consumption_rate(), time_until_cms_gen_full());
540 }
541 st->print(" ");
542 }
543 #endif // #ifndef PRODUCT
544
545 CMSCollector::CollectorState CMSCollector::_collectorState =
546 CMSCollector::Idling;
547 bool CMSCollector::_foregroundGCIsActive = false;
548 bool CMSCollector::_foregroundGCShouldWait = false;
549
550 CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
551 CardTableRS* ct,
552 ConcurrentMarkSweepPolicy* cp):
553 _cmsGen(cmsGen),
554 _ct(ct),
555 _ref_processor(NULL), // will be set later
556 _conc_workers(NULL), // may be set later
557 _abort_preclean(false),
558 _start_sampling(false),
559 _between_prologue_and_epilogue(false),
560 _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"),
561 _modUnionTable((CardTableModRefBS::card_shift - LogHeapWordSize),
562 -1 /* lock-free */, "No_lock" /* dummy */),
563 _modUnionClosure(&_modUnionTable),
564 _modUnionClosurePar(&_modUnionTable),
565 // Adjust my span to cover old (cms) gen
566 _span(cmsGen->reserved()),
567 // Construct the is_alive_closure with _span & markBitMap
568 _is_alive_closure(_span, &_markBitMap),
569 _restart_addr(NULL),
570 _overflow_list(NULL),
571 _stats(cmsGen),
572 _eden_chunk_lock(new Mutex(Mutex::leaf + 1, "CMS_eden_chunk_lock", true)),
573 _eden_chunk_array(NULL), // may be set in ctor body
574 _eden_chunk_capacity(0), // -- ditto --
575 _eden_chunk_index(0), // -- ditto --
576 _survivor_plab_array(NULL), // -- ditto --
577 _survivor_chunk_array(NULL), // -- ditto --
578 _survivor_chunk_capacity(0), // -- ditto --
579 _survivor_chunk_index(0), // -- ditto --
580 _ser_pmc_preclean_ovflw(0),
581 _ser_kac_preclean_ovflw(0),
582 _ser_pmc_remark_ovflw(0),
583 _par_pmc_remark_ovflw(0),
584 _ser_kac_ovflw(0),
585 _par_kac_ovflw(0),
586 #ifndef PRODUCT
587 _num_par_pushes(0),
588 #endif
589 _collection_count_start(0),
590 _verifying(false),
591 _icms_start_limit(NULL),
592 _icms_stop_limit(NULL),
593 _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"),
594 _completed_initialization(false),
595 _collector_policy(cp),
596 _should_unload_classes(false),
597 _concurrent_cycles_since_last_unload(0),
598 _roots_scanning_options(0),
599 _inter_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
600 _intra_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
601 _gc_tracer_cm(new (ResourceObj::C_HEAP, mtGC) CMSTracer()),
602 _gc_timer_cm(new (ResourceObj::C_HEAP, mtGC) ConcurrentGCTimer()),
603 _cms_start_registered(false)
604 {
605 if (ExplicitGCInvokesConcurrentAndUnloadsClasses) {
606 ExplicitGCInvokesConcurrent = true;
607 }
608 // Now expand the span and allocate the collection support structures
609 // (MUT, marking bit map etc.) to cover both generations subject to
610 // collection.
611
612 // For use by dirty card to oop closures.
613 _cmsGen->cmsSpace()->set_collector(this);
614
615 // Allocate MUT and marking bit map
616 {
617 MutexLockerEx x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag);
618 if (!_markBitMap.allocate(_span)) {
619 warning("Failed to allocate CMS Bit Map");
620 return;
621 }
622 assert(_markBitMap.covers(_span), "_markBitMap inconsistency?");
623 }
624 {
625 _modUnionTable.allocate(_span);
626 assert(_modUnionTable.covers(_span), "_modUnionTable inconsistency?");
627 }
628
629 if (!_markStack.allocate(MarkStackSize)) {
630 warning("Failed to allocate CMS Marking Stack");
631 return;
632 }
633
634 // Support for multi-threaded concurrent phases
635 if (CMSConcurrentMTEnabled) {
636 if (FLAG_IS_DEFAULT(ConcGCThreads)) {
637 // just for now
638 FLAG_SET_DEFAULT(ConcGCThreads, (ParallelGCThreads + 3)/4);
639 }
640 if (ConcGCThreads > 1) {
641 _conc_workers = new YieldingFlexibleWorkGang("Parallel CMS Threads",
642 ConcGCThreads, true);
643 if (_conc_workers == NULL) {
644 warning("GC/CMS: _conc_workers allocation failure: "
645 "forcing -CMSConcurrentMTEnabled");
646 CMSConcurrentMTEnabled = false;
647 } else {
648 _conc_workers->initialize_workers();
649 }
650 } else {
651 CMSConcurrentMTEnabled = false;
652 }
653 }
654 if (!CMSConcurrentMTEnabled) {
655 ConcGCThreads = 0;
656 } else {
657 // Turn off CMSCleanOnEnter optimization temporarily for
658 // the MT case where it's not fixed yet; see 6178663.
659 CMSCleanOnEnter = false;
660 }
661 assert((_conc_workers != NULL) == (ConcGCThreads > 1),
662 "Inconsistency");
663
664 // Parallel task queues; these are shared for the
665 // concurrent and stop-world phases of CMS, but
666 // are not shared with parallel scavenge (ParNew).
667 {
668 uint i;
669 uint num_queues = (uint) MAX2(ParallelGCThreads, ConcGCThreads);
670
671 if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled
672 || ParallelRefProcEnabled)
673 && num_queues > 0) {
674 _task_queues = new OopTaskQueueSet(num_queues);
675 if (_task_queues == NULL) {
676 warning("task_queues allocation failure.");
677 return;
678 }
679 _hash_seed = NEW_C_HEAP_ARRAY(int, num_queues, mtGC);
680 if (_hash_seed == NULL) {
681 warning("_hash_seed array allocation failure");
682 return;
683 }
684
685 typedef Padded<OopTaskQueue> PaddedOopTaskQueue;
686 for (i = 0; i < num_queues; i++) {
687 PaddedOopTaskQueue *q = new PaddedOopTaskQueue();
688 if (q == NULL) {
689 warning("work_queue allocation failure.");
690 return;
691 }
692 _task_queues->register_queue(i, q);
693 }
694 for (i = 0; i < num_queues; i++) {
695 _task_queues->queue(i)->initialize();
696 _hash_seed[i] = 17; // copied from ParNew
697 }
698 }
699 }
700
701 _cmsGen ->init_initiating_occupancy(CMSInitiatingOccupancyFraction, CMSTriggerRatio);
702
703 // Clip CMSBootstrapOccupancy between 0 and 100.
704 _bootstrap_occupancy = ((double)CMSBootstrapOccupancy)/(double)100;
705
706 _full_gcs_since_conc_gc = 0;
707
708 // Now tell CMS generations the identity of their collector
709 ConcurrentMarkSweepGeneration::set_collector(this);
710
711 // Create & start a CMS thread for this CMS collector
712 _cmsThread = ConcurrentMarkSweepThread::start(this);
713 assert(cmsThread() != NULL, "CMS Thread should have been created");
714 assert(cmsThread()->collector() == this,
715 "CMS Thread should refer to this gen");
716 assert(CGC_lock != NULL, "Where's the CGC_lock?");
717
718 // Support for parallelizing young gen rescan
719 GenCollectedHeap* gch = GenCollectedHeap::heap();
720 _young_gen = gch->prev_gen(_cmsGen);
721 if (gch->supports_inline_contig_alloc()) {
722 _top_addr = gch->top_addr();
723 _end_addr = gch->end_addr();
724 assert(_young_gen != NULL, "no _young_gen");
725 _eden_chunk_index = 0;
726 _eden_chunk_capacity = (_young_gen->max_capacity()+CMSSamplingGrain)/CMSSamplingGrain;
727 _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity, mtGC);
728 if (_eden_chunk_array == NULL) {
729 _eden_chunk_capacity = 0;
730 warning("GC/CMS: _eden_chunk_array allocation failure");
731 }
732 }
733 assert(_eden_chunk_array != NULL || _eden_chunk_capacity == 0, "Error");
734
735 // Support for parallelizing survivor space rescan
736 if (CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) {
737 const size_t max_plab_samples =
738 ((DefNewGeneration*)_young_gen)->max_survivor_size()/MinTLABSize;
739
740 _survivor_plab_array = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads, mtGC);
741 _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, 2*max_plab_samples, mtGC);
742 _cursor = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads, mtGC);
743 if (_survivor_plab_array == NULL || _survivor_chunk_array == NULL
744 || _cursor == NULL) {
745 warning("Failed to allocate survivor plab/chunk array");
746 if (_survivor_plab_array != NULL) {
747 FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array, mtGC);
748 _survivor_plab_array = NULL;
749 }
750 if (_survivor_chunk_array != NULL) {
751 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array, mtGC);
752 _survivor_chunk_array = NULL;
753 }
754 if (_cursor != NULL) {
755 FREE_C_HEAP_ARRAY(size_t, _cursor, mtGC);
756 _cursor = NULL;
757 }
758 } else {
759 _survivor_chunk_capacity = 2*max_plab_samples;
760 for (uint i = 0; i < ParallelGCThreads; i++) {
761 HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
762 if (vec == NULL) {
763 warning("Failed to allocate survivor plab array");
764 for (int j = i; j > 0; j--) {
765 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_plab_array[j-1].array(), mtGC);
766 }
767 FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array, mtGC);
768 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array, mtGC);
769 _survivor_plab_array = NULL;
770 _survivor_chunk_array = NULL;
771 _survivor_chunk_capacity = 0;
772 break;
773 } else {
774 ChunkArray* cur =
775 ::new (&_survivor_plab_array[i]) ChunkArray(vec,
776 max_plab_samples);
777 assert(cur->end() == 0, "Should be 0");
778 assert(cur->array() == vec, "Should be vec");
779 assert(cur->capacity() == max_plab_samples, "Error");
780 }
781 }
782 }
783 }
784 assert( ( _survivor_plab_array != NULL
785 && _survivor_chunk_array != NULL)
786 || ( _survivor_chunk_capacity == 0
787 && _survivor_chunk_index == 0),
788 "Error");
789
790 // Choose what strong roots should be scanned depending on verification options
791 if (!CMSClassUnloadingEnabled) {
792 // If class unloading is disabled we want to include all classes into the root set.
793 add_root_scanning_option(SharedHeap::SO_AllClasses);
794 } else {
795 add_root_scanning_option(SharedHeap::SO_SystemClasses);
796 }
797
798 NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;)
799 _gc_counters = new CollectorCounters("CMS", 1);
800 _completed_initialization = true;
801 _inter_sweep_timer.start(); // start of time
802 }
803
804 const char* ConcurrentMarkSweepGeneration::name() const {
805 return "concurrent mark-sweep generation";
806 }
807 void ConcurrentMarkSweepGeneration::update_counters() {
808 if (UsePerfData) {
809 _space_counters->update_all();
810 _gen_counters->update_all();
811 }
812 }
813
814 // this is an optimized version of update_counters(). it takes the
815 // used value as a parameter rather than computing it.
816 //
817 void ConcurrentMarkSweepGeneration::update_counters(size_t used) {
818 if (UsePerfData) {
819 _space_counters->update_used(used);
820 _space_counters->update_capacity();
821 _gen_counters->update_all();
822 }
823 }
824
825 void ConcurrentMarkSweepGeneration::print() const {
826 Generation::print();
827 cmsSpace()->print();
828 }
829
830 #ifndef PRODUCT
831 void ConcurrentMarkSweepGeneration::print_statistics() {
832 cmsSpace()->printFLCensus(0);
833 }
834 #endif
835
836 void ConcurrentMarkSweepGeneration::printOccupancy(const char *s) {
837 GenCollectedHeap* gch = GenCollectedHeap::heap();
838 if (PrintGCDetails) {
839 if (Verbose) {
840 gclog_or_tty->print("[%d %s-%s: "SIZE_FORMAT"("SIZE_FORMAT")]",
841 level(), short_name(), s, used(), capacity());
842 } else {
843 gclog_or_tty->print("[%d %s-%s: "SIZE_FORMAT"K("SIZE_FORMAT"K)]",
844 level(), short_name(), s, used() / K, capacity() / K);
845 }
846 }
847 if (Verbose) {
848 gclog_or_tty->print(" "SIZE_FORMAT"("SIZE_FORMAT")",
849 gch->used(), gch->capacity());
850 } else {
851 gclog_or_tty->print(" "SIZE_FORMAT"K("SIZE_FORMAT"K)",
852 gch->used() / K, gch->capacity() / K);
853 }
854 }
855
856 size_t
857 ConcurrentMarkSweepGeneration::contiguous_available() const {
858 // dld proposes an improvement in precision here. If the committed
859 // part of the space ends in a free block we should add that to
860 // uncommitted size in the calculation below. Will make this
861 // change later, staying with the approximation below for the
862 // time being. -- ysr.
863 return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc());
864 }
865
866 size_t
867 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const {
868 return _cmsSpace->max_alloc_in_words() * HeapWordSize;
869 }
870
871 size_t ConcurrentMarkSweepGeneration::max_available() const {
872 return free() + _virtual_space.uncommitted_size();
873 }
874
875 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(size_t max_promotion_in_bytes) const {
876 size_t available = max_available();
877 size_t av_promo = (size_t)gc_stats()->avg_promoted()->padded_average();
878 bool res = (available >= av_promo) || (available >= max_promotion_in_bytes);
879 if (Verbose && PrintGCDetails) {
880 gclog_or_tty->print_cr(
881 "CMS: promo attempt is%s safe: available("SIZE_FORMAT") %s av_promo("SIZE_FORMAT"),"
882 "max_promo("SIZE_FORMAT")",
883 res? "":" not", available, res? ">=":"<",
884 av_promo, max_promotion_in_bytes);
885 }
886 return res;
887 }
888
889 // At a promotion failure dump information on block layout in heap
890 // (cms old generation).
891 void ConcurrentMarkSweepGeneration::promotion_failure_occurred() {
892 if (CMSDumpAtPromotionFailure) {
893 cmsSpace()->dump_at_safepoint_with_locks(collector(), gclog_or_tty);
894 }
895 }
896
897 CompactibleSpace*
898 ConcurrentMarkSweepGeneration::first_compaction_space() const {
899 return _cmsSpace;
900 }
901
902 void ConcurrentMarkSweepGeneration::reset_after_compaction() {
903 // Clear the promotion information. These pointers can be adjusted
904 // along with all the other pointers into the heap but
905 // compaction is expected to be a rare event with
906 // a heap using cms so don't do it without seeing the need.
907 if (CollectedHeap::use_parallel_gc_threads()) {
908 for (uint i = 0; i < ParallelGCThreads; i++) {
909 _par_gc_thread_states[i]->promo.reset();
910 }
911 }
912 }
913
914 void ConcurrentMarkSweepGeneration::space_iterate(SpaceClosure* blk, bool usedOnly) {
915 blk->do_space(_cmsSpace);
916 }
917
918 void ConcurrentMarkSweepGeneration::compute_new_size() {
919 assert_locked_or_safepoint(Heap_lock);
920
921 // If incremental collection failed, we just want to expand
922 // to the limit.
923 if (incremental_collection_failed()) {
924 clear_incremental_collection_failed();
925 grow_to_reserved();
926 return;
927 }
928
929 // The heap has been compacted but not reset yet.
930 // Any metric such as free() or used() will be incorrect.
931
932 CardGeneration::compute_new_size();
933
934 // Reset again after a possible resizing
935 if (did_compact()) {
936 cmsSpace()->reset_after_compaction();
937 }
938 }
939
940 void ConcurrentMarkSweepGeneration::compute_new_size_free_list() {
941 assert_locked_or_safepoint(Heap_lock);
942
943 // If incremental collection failed, we just want to expand
944 // to the limit.
945 if (incremental_collection_failed()) {
946 clear_incremental_collection_failed();
947 grow_to_reserved();
948 return;
949 }
950
951 double free_percentage = ((double) free()) / capacity();
952 double desired_free_percentage = (double) MinHeapFreeRatio / 100;
953 double maximum_free_percentage = (double) MaxHeapFreeRatio / 100;
954
955 // compute expansion delta needed for reaching desired free percentage
956 if (free_percentage < desired_free_percentage) {
957 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
958 assert(desired_capacity >= capacity(), "invalid expansion size");
959 size_t expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes);
960 if (PrintGCDetails && Verbose) {
961 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
962 gclog_or_tty->print_cr("\nFrom compute_new_size: ");
963 gclog_or_tty->print_cr(" Free fraction %f", free_percentage);
964 gclog_or_tty->print_cr(" Desired free fraction %f",
965 desired_free_percentage);
966 gclog_or_tty->print_cr(" Maximum free fraction %f",
967 maximum_free_percentage);
968 gclog_or_tty->print_cr(" Capactiy "SIZE_FORMAT, capacity()/1000);
969 gclog_or_tty->print_cr(" Desired capacity "SIZE_FORMAT,
970 desired_capacity/1000);
971 int prev_level = level() - 1;
972 if (prev_level >= 0) {
973 size_t prev_size = 0;
974 GenCollectedHeap* gch = GenCollectedHeap::heap();
975 Generation* prev_gen = gch->_gens[prev_level];
976 prev_size = prev_gen->capacity();
977 gclog_or_tty->print_cr(" Younger gen size "SIZE_FORMAT,
978 prev_size/1000);
979 }
980 gclog_or_tty->print_cr(" unsafe_max_alloc_nogc "SIZE_FORMAT,
981 unsafe_max_alloc_nogc()/1000);
982 gclog_or_tty->print_cr(" contiguous available "SIZE_FORMAT,
983 contiguous_available()/1000);
984 gclog_or_tty->print_cr(" Expand by "SIZE_FORMAT" (bytes)",
985 expand_bytes);
986 }
987 // safe if expansion fails
988 expand(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio);
989 if (PrintGCDetails && Verbose) {
990 gclog_or_tty->print_cr(" Expanded free fraction %f",
991 ((double) free()) / capacity());
992 }
993 } else {
994 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
995 assert(desired_capacity <= capacity(), "invalid expansion size");
996 size_t shrink_bytes = capacity() - desired_capacity;
997 // Don't shrink unless the delta is greater than the minimum shrink we want
998 if (shrink_bytes >= MinHeapDeltaBytes) {
999 shrink_free_list_by(shrink_bytes);
1000 }
1001 }
1002 }
1003
1004 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const {
1005 return cmsSpace()->freelistLock();
1006 }
1007
1008 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size,
1009 bool tlab) {
1010 CMSSynchronousYieldRequest yr;
1011 MutexLockerEx x(freelistLock(),
1012 Mutex::_no_safepoint_check_flag);
1013 return have_lock_and_allocate(size, tlab);
1014 }
1015
1016 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size,
1017 bool tlab /* ignored */) {
1018 assert_lock_strong(freelistLock());
1019 size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size);
1020 HeapWord* res = cmsSpace()->allocate(adjustedSize);
1021 // Allocate the object live (grey) if the background collector has
1022 // started marking. This is necessary because the marker may
1023 // have passed this address and consequently this object will
1024 // not otherwise be greyed and would be incorrectly swept up.
1025 // Note that if this object contains references, the writing
1026 // of those references will dirty the card containing this object
1027 // allowing the object to be blackened (and its references scanned)
1028 // either during a preclean phase or at the final checkpoint.
1029 if (res != NULL) {
1030 // We may block here with an uninitialized object with
1031 // its mark-bit or P-bits not yet set. Such objects need
1032 // to be safely navigable by block_start().
1033 assert(oop(res)->klass_or_null() == NULL, "Object should be uninitialized here.");
1034 assert(!((FreeChunk*)res)->is_free(), "Error, block will look free but show wrong size");
1035 collector()->direct_allocated(res, adjustedSize);
1036 _direct_allocated_words += adjustedSize;
1037 // allocation counters
1038 NOT_PRODUCT(
1039 _numObjectsAllocated++;
1040 _numWordsAllocated += (int)adjustedSize;
1041 )
1042 }
1043 return res;
1044 }
1045
1046 // In the case of direct allocation by mutators in a generation that
1047 // is being concurrently collected, the object must be allocated
1048 // live (grey) if the background collector has started marking.
1049 // This is necessary because the marker may
1050 // have passed this address and consequently this object will
1051 // not otherwise be greyed and would be incorrectly swept up.
1052 // Note that if this object contains references, the writing
1053 // of those references will dirty the card containing this object
1054 // allowing the object to be blackened (and its references scanned)
1055 // either during a preclean phase or at the final checkpoint.
1056 void CMSCollector::direct_allocated(HeapWord* start, size_t size) {
1057 assert(_markBitMap.covers(start, size), "Out of bounds");
1058 if (_collectorState >= Marking) {
1059 MutexLockerEx y(_markBitMap.lock(),
1060 Mutex::_no_safepoint_check_flag);
1061 // [see comments preceding SweepClosure::do_blk() below for details]
1062 //
1063 // Can the P-bits be deleted now? JJJ
1064 //
1065 // 1. need to mark the object as live so it isn't collected
1066 // 2. need to mark the 2nd bit to indicate the object may be uninitialized
1067 // 3. need to mark the end of the object so marking, precleaning or sweeping
1068 // can skip over uninitialized or unparsable objects. An allocated
1069 // object is considered uninitialized for our purposes as long as
1070 // its klass word is NULL. All old gen objects are parsable
1071 // as soon as they are initialized.)
1072 _markBitMap.mark(start); // object is live
1073 _markBitMap.mark(start + 1); // object is potentially uninitialized?
1074 _markBitMap.mark(start + size - 1);
1075 // mark end of object
1076 }
1077 // check that oop looks uninitialized
1078 assert(oop(start)->klass_or_null() == NULL, "_klass should be NULL");
1079 }
1080
1081 void CMSCollector::promoted(bool par, HeapWord* start,
1082 bool is_obj_array, size_t obj_size) {
1083 assert(_markBitMap.covers(start), "Out of bounds");
1084 // See comment in direct_allocated() about when objects should
1085 // be allocated live.
1086 if (_collectorState >= Marking) {
1087 // we already hold the marking bit map lock, taken in
1088 // the prologue
1089 if (par) {
1090 _markBitMap.par_mark(start);
1091 } else {
1092 _markBitMap.mark(start);
1093 }
1094 // We don't need to mark the object as uninitialized (as
1095 // in direct_allocated above) because this is being done with the
1096 // world stopped and the object will be initialized by the
1097 // time the marking, precleaning or sweeping get to look at it.
1098 // But see the code for copying objects into the CMS generation,
1099 // where we need to ensure that concurrent readers of the
1100 // block offset table are able to safely navigate a block that
1101 // is in flux from being free to being allocated (and in
1102 // transition while being copied into) and subsequently
1103 // becoming a bona-fide object when the copy/promotion is complete.
1104 assert(SafepointSynchronize::is_at_safepoint(),
1105 "expect promotion only at safepoints");
1106
1107 if (_collectorState < Sweeping) {
1108 // Mark the appropriate cards in the modUnionTable, so that
1109 // this object gets scanned before the sweep. If this is
1110 // not done, CMS generation references in the object might
1111 // not get marked.
1112 // For the case of arrays, which are otherwise precisely
1113 // marked, we need to dirty the entire array, not just its head.
1114 if (is_obj_array) {
1115 // The [par_]mark_range() method expects mr.end() below to
1116 // be aligned to the granularity of a bit's representation
1117 // in the heap. In the case of the MUT below, that's a
1118 // card size.
1119 MemRegion mr(start,
1120 (HeapWord*)round_to((intptr_t)(start + obj_size),
1121 CardTableModRefBS::card_size /* bytes */));
1122 if (par) {
1123 _modUnionTable.par_mark_range(mr);
1124 } else {
1125 _modUnionTable.mark_range(mr);
1126 }
1127 } else { // not an obj array; we can just mark the head
1128 if (par) {
1129 _modUnionTable.par_mark(start);
1130 } else {
1131 _modUnionTable.mark(start);
1132 }
1133 }
1134 }
1135 }
1136 }
1137
1138 static inline size_t percent_of_space(Space* space, HeapWord* addr)
1139 {
1140 size_t delta = pointer_delta(addr, space->bottom());
1141 return (size_t)(delta * 100.0 / (space->capacity() / HeapWordSize));
1142 }
1143
1144 void CMSCollector::icms_update_allocation_limits()
1145 {
1146 Generation* gen0 = GenCollectedHeap::heap()->get_gen(0);
1147 EdenSpace* eden = gen0->as_DefNewGeneration()->eden();
1148
1149 const unsigned int duty_cycle = stats().icms_update_duty_cycle();
1150 if (CMSTraceIncrementalPacing) {
1151 stats().print();
1152 }
1153
1154 assert(duty_cycle <= 100, "invalid duty cycle");
1155 if (duty_cycle != 0) {
1156 // The duty_cycle is a percentage between 0 and 100; convert to words and
1157 // then compute the offset from the endpoints of the space.
1158 size_t free_words = eden->free() / HeapWordSize;
1159 double free_words_dbl = (double)free_words;
1160 size_t duty_cycle_words = (size_t)(free_words_dbl * duty_cycle / 100.0);
1161 size_t offset_words = (free_words - duty_cycle_words) / 2;
1162
1163 _icms_start_limit = eden->top() + offset_words;
1164 _icms_stop_limit = eden->end() - offset_words;
1165
1166 // The limits may be adjusted (shifted to the right) by
1167 // CMSIncrementalOffset, to allow the application more mutator time after a
1168 // young gen gc (when all mutators were stopped) and before CMS starts and
1169 // takes away one or more cpus.
1170 if (CMSIncrementalOffset != 0) {
1171 double adjustment_dbl = free_words_dbl * CMSIncrementalOffset / 100.0;
1172 size_t adjustment = (size_t)adjustment_dbl;
1173 HeapWord* tmp_stop = _icms_stop_limit + adjustment;
1174 if (tmp_stop > _icms_stop_limit && tmp_stop < eden->end()) {
1175 _icms_start_limit += adjustment;
1176 _icms_stop_limit = tmp_stop;
1177 }
1178 }
1179 }
1180 if (duty_cycle == 0 || (_icms_start_limit == _icms_stop_limit)) {
1181 _icms_start_limit = _icms_stop_limit = eden->end();
1182 }
1183
1184 // Install the new start limit.
1185 eden->set_soft_end(_icms_start_limit);
1186
1187 if (CMSTraceIncrementalMode) {
1188 gclog_or_tty->print(" icms alloc limits: "
1189 PTR_FORMAT "," PTR_FORMAT
1190 " (" SIZE_FORMAT "%%," SIZE_FORMAT "%%) ",
1191 _icms_start_limit, _icms_stop_limit,
1192 percent_of_space(eden, _icms_start_limit),
1193 percent_of_space(eden, _icms_stop_limit));
1194 if (Verbose) {
1195 gclog_or_tty->print("eden: ");
1196 eden->print_on(gclog_or_tty);
1197 }
1198 }
1199 }
1200
1201 // Any changes here should try to maintain the invariant
1202 // that if this method is called with _icms_start_limit
1203 // and _icms_stop_limit both NULL, then it should return NULL
1204 // and not notify the icms thread.
1205 HeapWord*
1206 CMSCollector::allocation_limit_reached(Space* space, HeapWord* top,
1207 size_t word_size)
1208 {
1209 // A start_limit equal to end() means the duty cycle is 0, so treat that as a
1210 // nop.
1211 if (CMSIncrementalMode && _icms_start_limit != space->end()) {
1212 if (top <= _icms_start_limit) {
1213 if (CMSTraceIncrementalMode) {
1214 space->print_on(gclog_or_tty);
1215 gclog_or_tty->stamp();
1216 gclog_or_tty->print_cr(" start limit top=" PTR_FORMAT
1217 ", new limit=" PTR_FORMAT
1218 " (" SIZE_FORMAT "%%)",
1219 top, _icms_stop_limit,
1220 percent_of_space(space, _icms_stop_limit));
1221 }
1222 ConcurrentMarkSweepThread::start_icms();
1223 assert(top < _icms_stop_limit, "Tautology");
1224 if (word_size < pointer_delta(_icms_stop_limit, top)) {
1225 return _icms_stop_limit;
1226 }
1227
1228 // The allocation will cross both the _start and _stop limits, so do the
1229 // stop notification also and return end().
1230 if (CMSTraceIncrementalMode) {
1231 space->print_on(gclog_or_tty);
1232 gclog_or_tty->stamp();
1233 gclog_or_tty->print_cr(" +stop limit top=" PTR_FORMAT
1234 ", new limit=" PTR_FORMAT
1235 " (" SIZE_FORMAT "%%)",
1236 top, space->end(),
1237 percent_of_space(space, space->end()));
1238 }
1239 ConcurrentMarkSweepThread::stop_icms();
1240 return space->end();
1241 }
1242
1243 if (top <= _icms_stop_limit) {
1244 if (CMSTraceIncrementalMode) {
1245 space->print_on(gclog_or_tty);
1246 gclog_or_tty->stamp();
1247 gclog_or_tty->print_cr(" stop limit top=" PTR_FORMAT
1248 ", new limit=" PTR_FORMAT
1249 " (" SIZE_FORMAT "%%)",
1250 top, space->end(),
1251 percent_of_space(space, space->end()));
1252 }
1253 ConcurrentMarkSweepThread::stop_icms();
1254 return space->end();
1255 }
1256
1257 if (CMSTraceIncrementalMode) {
1258 space->print_on(gclog_or_tty);
1259 gclog_or_tty->stamp();
1260 gclog_or_tty->print_cr(" end limit top=" PTR_FORMAT
1261 ", new limit=" PTR_FORMAT,
1262 top, NULL);
1263 }
1264 }
1265
1266 return NULL;
1267 }
1268
1269 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size) {
1270 assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
1271 // allocate, copy and if necessary update promoinfo --
1272 // delegate to underlying space.
1273 assert_lock_strong(freelistLock());
1274
1275 #ifndef PRODUCT
1276 if (Universe::heap()->promotion_should_fail()) {
1277 return NULL;
1278 }
1279 #endif // #ifndef PRODUCT
1280
1281 oop res = _cmsSpace->promote(obj, obj_size);
1282 if (res == NULL) {
1283 // expand and retry
1284 size_t s = _cmsSpace->expansionSpaceRequired(obj_size); // HeapWords
1285 expand(s*HeapWordSize, MinHeapDeltaBytes,
1286 CMSExpansionCause::_satisfy_promotion);
1287 // Since there's currently no next generation, we don't try to promote
1288 // into a more senior generation.
1289 assert(next_gen() == NULL, "assumption, based upon which no attempt "
1290 "is made to pass on a possibly failing "
1291 "promotion to next generation");
1292 res = _cmsSpace->promote(obj, obj_size);
1293 }
1294 if (res != NULL) {
1295 // See comment in allocate() about when objects should
1296 // be allocated live.
1297 assert(obj->is_oop(), "Will dereference klass pointer below");
1298 collector()->promoted(false, // Not parallel
1299 (HeapWord*)res, obj->is_objArray(), obj_size);
1300 // promotion counters
1301 NOT_PRODUCT(
1302 _numObjectsPromoted++;
1303 _numWordsPromoted +=
1304 (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size()));
1305 )
1306 }
1307 return res;
1308 }
1309
1310
1311 HeapWord*
1312 ConcurrentMarkSweepGeneration::allocation_limit_reached(Space* space,
1313 HeapWord* top,
1314 size_t word_sz)
1315 {
1316 return collector()->allocation_limit_reached(space, top, word_sz);
1317 }
1318
1319 // IMPORTANT: Notes on object size recognition in CMS.
1320 // ---------------------------------------------------
1321 // A block of storage in the CMS generation is always in
1322 // one of three states. A free block (FREE), an allocated
1323 // object (OBJECT) whose size() method reports the correct size,
1324 // and an intermediate state (TRANSIENT) in which its size cannot
1325 // be accurately determined.
1326 // STATE IDENTIFICATION: (32 bit and 64 bit w/o COOPS)
1327 // -----------------------------------------------------
1328 // FREE: klass_word & 1 == 1; mark_word holds block size
1329 //
1330 // OBJECT: klass_word installed; klass_word != 0 && klass_word & 1 == 0;
1331 // obj->size() computes correct size
1332 //
1333 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1334 //
1335 // STATE IDENTIFICATION: (64 bit+COOPS)
1336 // ------------------------------------
1337 // FREE: mark_word & CMS_FREE_BIT == 1; mark_word & ~CMS_FREE_BIT gives block_size
1338 //
1339 // OBJECT: klass_word installed; klass_word != 0;
1340 // obj->size() computes correct size
1341 //
1342 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1343 //
1344 //
1345 // STATE TRANSITION DIAGRAM
1346 //
1347 // mut / parnew mut / parnew
1348 // FREE --------------------> TRANSIENT ---------------------> OBJECT --|
1349 // ^ |
1350 // |------------------------ DEAD <------------------------------------|
1351 // sweep mut
1352 //
1353 // While a block is in TRANSIENT state its size cannot be determined
1354 // so readers will either need to come back later or stall until
1355 // the size can be determined. Note that for the case of direct
1356 // allocation, P-bits, when available, may be used to determine the
1357 // size of an object that may not yet have been initialized.
1358
1359 // Things to support parallel young-gen collection.
1360 oop
1361 ConcurrentMarkSweepGeneration::par_promote(int thread_num,
1362 oop old, markOop m,
1363 size_t word_sz) {
1364 #ifndef PRODUCT
1365 if (Universe::heap()->promotion_should_fail()) {
1366 return NULL;
1367 }
1368 #endif // #ifndef PRODUCT
1369
1370 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1371 PromotionInfo* promoInfo = &ps->promo;
1372 // if we are tracking promotions, then first ensure space for
1373 // promotion (including spooling space for saving header if necessary).
1374 // then allocate and copy, then track promoted info if needed.
1375 // When tracking (see PromotionInfo::track()), the mark word may
1376 // be displaced and in this case restoration of the mark word
1377 // occurs in the (oop_since_save_marks_)iterate phase.
1378 if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) {
1379 // Out of space for allocating spooling buffers;
1380 // try expanding and allocating spooling buffers.
1381 if (!expand_and_ensure_spooling_space(promoInfo)) {
1382 return NULL;
1383 }
1384 }
1385 assert(promoInfo->has_spooling_space(), "Control point invariant");
1386 const size_t alloc_sz = CompactibleFreeListSpace::adjustObjectSize(word_sz);
1387 HeapWord* obj_ptr = ps->lab.alloc(alloc_sz);
1388 if (obj_ptr == NULL) {
1389 obj_ptr = expand_and_par_lab_allocate(ps, alloc_sz);
1390 if (obj_ptr == NULL) {
1391 return NULL;
1392 }
1393 }
1394 oop obj = oop(obj_ptr);
1395 OrderAccess::storestore();
1396 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1397 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1398 // IMPORTANT: See note on object initialization for CMS above.
1399 // Otherwise, copy the object. Here we must be careful to insert the
1400 // klass pointer last, since this marks the block as an allocated object.
1401 // Except with compressed oops it's the mark word.
1402 HeapWord* old_ptr = (HeapWord*)old;
1403 // Restore the mark word copied above.
1404 obj->set_mark(m);
1405 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1406 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1407 OrderAccess::storestore();
1408
1409 if (UseCompressedKlassPointers) {
1410 // Copy gap missed by (aligned) header size calculation below
1411 obj->set_klass_gap(old->klass_gap());
1412 }
1413 if (word_sz > (size_t)oopDesc::header_size()) {
1414 Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1415 obj_ptr + oopDesc::header_size(),
1416 word_sz - oopDesc::header_size());
1417 }
1418
1419 // Now we can track the promoted object, if necessary. We take care
1420 // to delay the transition from uninitialized to full object
1421 // (i.e., insertion of klass pointer) until after, so that it
1422 // atomically becomes a promoted object.
1423 if (promoInfo->tracking()) {
1424 promoInfo->track((PromotedObject*)obj, old->klass());
1425 }
1426 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1427 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1428 assert(old->is_oop(), "Will use and dereference old klass ptr below");
1429
1430 // Finally, install the klass pointer (this should be volatile).
1431 OrderAccess::storestore();
1432 obj->set_klass(old->klass());
1433 // We should now be able to calculate the right size for this object
1434 assert(obj->is_oop() && obj->size() == (int)word_sz, "Error, incorrect size computed for promoted object");
1435
1436 collector()->promoted(true, // parallel
1437 obj_ptr, old->is_objArray(), word_sz);
1438
1439 NOT_PRODUCT(
1440 Atomic::inc_ptr(&_numObjectsPromoted);
1441 Atomic::add_ptr(alloc_sz, &_numWordsPromoted);
1442 )
1443
1444 return obj;
1445 }
1446
1447 void
1448 ConcurrentMarkSweepGeneration::
1449 par_promote_alloc_undo(int thread_num,
1450 HeapWord* obj, size_t word_sz) {
1451 // CMS does not support promotion undo.
1452 ShouldNotReachHere();
1453 }
1454
1455 void
1456 ConcurrentMarkSweepGeneration::
1457 par_promote_alloc_done(int thread_num) {
1458 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1459 ps->lab.retire(thread_num);
1460 }
1461
1462 void
1463 ConcurrentMarkSweepGeneration::
1464 par_oop_since_save_marks_iterate_done(int thread_num) {
1465 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1466 ParScanWithoutBarrierClosure* dummy_cl = NULL;
1467 ps->promo.promoted_oops_iterate_nv(dummy_cl);
1468 }
1469
1470 bool ConcurrentMarkSweepGeneration::should_collect(bool full,
1471 size_t size,
1472 bool tlab)
1473 {
1474 // We allow a STW collection only if a full
1475 // collection was requested.
1476 return full || should_allocate(size, tlab); // FIX ME !!!
1477 // This and promotion failure handling are connected at the
1478 // hip and should be fixed by untying them.
1479 }
1480
1481 bool CMSCollector::shouldConcurrentCollect() {
1482 if (_full_gc_requested) {
1483 if (Verbose && PrintGCDetails) {
1484 gclog_or_tty->print_cr("CMSCollector: collect because of explicit "
1485 " gc request (or gc_locker)");
1486 }
1487 return true;
1488 }
1489
1490 // For debugging purposes, change the type of collection.
1491 // If the rotation is not on the concurrent collection
1492 // type, don't start a concurrent collection.
1493 NOT_PRODUCT(
1494 if (RotateCMSCollectionTypes &&
1495 (_cmsGen->debug_collection_type() !=
1496 ConcurrentMarkSweepGeneration::Concurrent_collection_type)) {
1497 assert(_cmsGen->debug_collection_type() !=
1498 ConcurrentMarkSweepGeneration::Unknown_collection_type,
1499 "Bad cms collection type");
1500 return false;
1501 }
1502 )
1503
1504 FreelistLocker x(this);
1505 // ------------------------------------------------------------------
1506 // Print out lots of information which affects the initiation of
1507 // a collection.
1508 if (PrintCMSInitiationStatistics && stats().valid()) {
1509 gclog_or_tty->print("CMSCollector shouldConcurrentCollect: ");
1510 gclog_or_tty->stamp();
1511 gclog_or_tty->print_cr("");
1512 stats().print_on(gclog_or_tty);
1513 gclog_or_tty->print_cr("time_until_cms_gen_full %3.7f",
1514 stats().time_until_cms_gen_full());
1515 gclog_or_tty->print_cr("free="SIZE_FORMAT, _cmsGen->free());
1516 gclog_or_tty->print_cr("contiguous_available="SIZE_FORMAT,
1517 _cmsGen->contiguous_available());
1518 gclog_or_tty->print_cr("promotion_rate=%g", stats().promotion_rate());
1519 gclog_or_tty->print_cr("cms_allocation_rate=%g", stats().cms_allocation_rate());
1520 gclog_or_tty->print_cr("occupancy=%3.7f", _cmsGen->occupancy());
1521 gclog_or_tty->print_cr("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy());
1522 gclog_or_tty->print_cr("metadata initialized %d",
1523 MetaspaceGC::should_concurrent_collect());
1524 }
1525 // ------------------------------------------------------------------
1526
1527 // If the estimated time to complete a cms collection (cms_duration())
1528 // is less than the estimated time remaining until the cms generation
1529 // is full, start a collection.
1530 if (!UseCMSInitiatingOccupancyOnly) {
1531 if (stats().valid()) {
1532 if (stats().time_until_cms_start() == 0.0) {
1533 return true;
1534 }
1535 } else {
1536 // We want to conservatively collect somewhat early in order
1537 // to try and "bootstrap" our CMS/promotion statistics;
1538 // this branch will not fire after the first successful CMS
1539 // collection because the stats should then be valid.
1540 if (_cmsGen->occupancy() >= _bootstrap_occupancy) {
1541 if (Verbose && PrintGCDetails) {
1542 gclog_or_tty->print_cr(
1543 " CMSCollector: collect for bootstrapping statistics:"
1544 " occupancy = %f, boot occupancy = %f", _cmsGen->occupancy(),
1545 _bootstrap_occupancy);
1546 }
1547 return true;
1548 }
1549 }
1550 }
1551
1552 // Otherwise, we start a collection cycle if
1553 // old gen want a collection cycle started. Each may use
1554 // an appropriate criterion for making this decision.
1555 // XXX We need to make sure that the gen expansion
1556 // criterion dovetails well with this. XXX NEED TO FIX THIS
1557 if (_cmsGen->should_concurrent_collect()) {
1558 if (Verbose && PrintGCDetails) {
1559 gclog_or_tty->print_cr("CMS old gen initiated");
1560 }
1561 return true;
1562 }
1563
1564 // We start a collection if we believe an incremental collection may fail;
1565 // this is not likely to be productive in practice because it's probably too
1566 // late anyway.
1567 GenCollectedHeap* gch = GenCollectedHeap::heap();
1568 assert(gch->collector_policy()->is_two_generation_policy(),
1569 "You may want to check the correctness of the following");
1570 if (gch->incremental_collection_will_fail(true /* consult_young */)) {
1571 if (Verbose && PrintGCDetails) {
1572 gclog_or_tty->print("CMSCollector: collect because incremental collection will fail ");
1573 }
1574 return true;
1575 }
1576
1577 if (MetaspaceGC::should_concurrent_collect()) {
1578 if (Verbose && PrintGCDetails) {
1579 gclog_or_tty->print("CMSCollector: collect for metadata allocation ");
1580 }
1581 return true;
1582 }
1583
1584 return false;
1585 }
1586
1587 void CMSCollector::set_did_compact(bool v) { _cmsGen->set_did_compact(v); }
1588
1589 // Clear _expansion_cause fields of constituent generations
1590 void CMSCollector::clear_expansion_cause() {
1591 _cmsGen->clear_expansion_cause();
1592 }
1593
1594 // We should be conservative in starting a collection cycle. To
1595 // start too eagerly runs the risk of collecting too often in the
1596 // extreme. To collect too rarely falls back on full collections,
1597 // which works, even if not optimum in terms of concurrent work.
1598 // As a work around for too eagerly collecting, use the flag
1599 // UseCMSInitiatingOccupancyOnly. This also has the advantage of
1600 // giving the user an easily understandable way of controlling the
1601 // collections.
1602 // We want to start a new collection cycle if any of the following
1603 // conditions hold:
1604 // . our current occupancy exceeds the configured initiating occupancy
1605 // for this generation, or
1606 // . we recently needed to expand this space and have not, since that
1607 // expansion, done a collection of this generation, or
1608 // . the underlying space believes that it may be a good idea to initiate
1609 // a concurrent collection (this may be based on criteria such as the
1610 // following: the space uses linear allocation and linear allocation is
1611 // going to fail, or there is believed to be excessive fragmentation in
1612 // the generation, etc... or ...
1613 // [.(currently done by CMSCollector::shouldConcurrentCollect() only for
1614 // the case of the old generation; see CR 6543076):
1615 // we may be approaching a point at which allocation requests may fail because
1616 // we will be out of sufficient free space given allocation rate estimates.]
1617 bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const {
1618
1619 assert_lock_strong(freelistLock());
1620 if (occupancy() > initiating_occupancy()) {
1621 if (PrintGCDetails && Verbose) {
1622 gclog_or_tty->print(" %s: collect because of occupancy %f / %f ",
1623 short_name(), occupancy(), initiating_occupancy());
1624 }
1625 return true;
1626 }
1627 if (UseCMSInitiatingOccupancyOnly) {
1628 return false;
1629 }
1630 if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) {
1631 if (PrintGCDetails && Verbose) {
1632 gclog_or_tty->print(" %s: collect because expanded for allocation ",
1633 short_name());
1634 }
1635 return true;
1636 }
1637 if (_cmsSpace->should_concurrent_collect()) {
1638 if (PrintGCDetails && Verbose) {
1639 gclog_or_tty->print(" %s: collect because cmsSpace says so ",
1640 short_name());
1641 }
1642 return true;
1643 }
1644 return false;
1645 }
1646
1647 void ConcurrentMarkSweepGeneration::collect(bool full,
1648 bool clear_all_soft_refs,
1649 size_t size,
1650 bool tlab)
1651 {
1652 collector()->collect(full, clear_all_soft_refs, size, tlab);
1653 }
1654
1655 void CMSCollector::collect(bool full,
1656 bool clear_all_soft_refs,
1657 size_t size,
1658 bool tlab)
1659 {
1660 if (!UseCMSCollectionPassing && _collectorState > Idling) {
1661 // For debugging purposes skip the collection if the state
1662 // is not currently idle
1663 if (TraceCMSState) {
1664 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " skipped full:%d CMS state %d",
1665 Thread::current(), full, _collectorState);
1666 }
1667 return;
1668 }
1669
1670 // The following "if" branch is present for defensive reasons.
1671 // In the current uses of this interface, it can be replaced with:
1672 // assert(!GC_locker.is_active(), "Can't be called otherwise");
1673 // But I am not placing that assert here to allow future
1674 // generality in invoking this interface.
1675 if (GC_locker::is_active()) {
1676 // A consistency test for GC_locker
1677 assert(GC_locker::needs_gc(), "Should have been set already");
1678 // Skip this foreground collection, instead
1679 // expanding the heap if necessary.
1680 // Need the free list locks for the call to free() in compute_new_size()
1681 compute_new_size();
1682 return;
1683 }
1684 acquire_control_and_collect(full, clear_all_soft_refs);
1685 _full_gcs_since_conc_gc++;
1686 }
1687
1688 void CMSCollector::request_full_gc(unsigned int full_gc_count, GCCause::Cause cause) {
1689 GenCollectedHeap* gch = GenCollectedHeap::heap();
1690 unsigned int gc_count = gch->total_full_collections();
1691 if (gc_count == full_gc_count) {
1692 MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag);
1693 _full_gc_requested = true;
1694 _full_gc_cause = cause;
1695 CGC_lock->notify(); // nudge CMS thread
1696 } else {
1697 assert(gc_count > full_gc_count, "Error: causal loop");
1698 }
1699 }
1700
1701 bool CMSCollector::is_external_interruption() {
1702 GCCause::Cause cause = GenCollectedHeap::heap()->gc_cause();
1703 return GCCause::is_user_requested_gc(cause) ||
1704 GCCause::is_serviceability_requested_gc(cause);
1705 }
1706
1707 void CMSCollector::report_concurrent_mode_interruption() {
1708 if (is_external_interruption()) {
1709 if (PrintGCDetails) {
1710 gclog_or_tty->print(" (concurrent mode interrupted)");
1711 }
1712 } else {
1713 if (PrintGCDetails) {
1714 gclog_or_tty->print(" (concurrent mode failure)");
1715 }
1716 _gc_tracer_cm->report_concurrent_mode_failure();
1717 }
1718 }
1719
1720
1721 // The foreground and background collectors need to coordinate in order
1722 // to make sure that they do not mutually interfere with CMS collections.
1723 // When a background collection is active,
1724 // the foreground collector may need to take over (preempt) and
1725 // synchronously complete an ongoing collection. Depending on the
1726 // frequency of the background collections and the heap usage
1727 // of the application, this preemption can be seldom or frequent.
1728 // There are only certain
1729 // points in the background collection that the "collection-baton"
1730 // can be passed to the foreground collector.
1731 //
1732 // The foreground collector will wait for the baton before
1733 // starting any part of the collection. The foreground collector
1734 // will only wait at one location.
1735 //
1736 // The background collector will yield the baton before starting a new
1737 // phase of the collection (e.g., before initial marking, marking from roots,
1738 // precleaning, final re-mark, sweep etc.) This is normally done at the head
1739 // of the loop which switches the phases. The background collector does some
1740 // of the phases (initial mark, final re-mark) with the world stopped.
1741 // Because of locking involved in stopping the world,
1742 // the foreground collector should not block waiting for the background
1743 // collector when it is doing a stop-the-world phase. The background
1744 // collector will yield the baton at an additional point just before
1745 // it enters a stop-the-world phase. Once the world is stopped, the
1746 // background collector checks the phase of the collection. If the
1747 // phase has not changed, it proceeds with the collection. If the
1748 // phase has changed, it skips that phase of the collection. See
1749 // the comments on the use of the Heap_lock in collect_in_background().
1750 //
1751 // Variable used in baton passing.
1752 // _foregroundGCIsActive - Set to true by the foreground collector when
1753 // it wants the baton. The foreground clears it when it has finished
1754 // the collection.
1755 // _foregroundGCShouldWait - Set to true by the background collector
1756 // when it is running. The foreground collector waits while
1757 // _foregroundGCShouldWait is true.
1758 // CGC_lock - monitor used to protect access to the above variables
1759 // and to notify the foreground and background collectors.
1760 // _collectorState - current state of the CMS collection.
1761 //
1762 // The foreground collector
1763 // acquires the CGC_lock
1764 // sets _foregroundGCIsActive
1765 // waits on the CGC_lock for _foregroundGCShouldWait to be false
1766 // various locks acquired in preparation for the collection
1767 // are released so as not to block the background collector
1768 // that is in the midst of a collection
1769 // proceeds with the collection
1770 // clears _foregroundGCIsActive
1771 // returns
1772 //
1773 // The background collector in a loop iterating on the phases of the
1774 // collection
1775 // acquires the CGC_lock
1776 // sets _foregroundGCShouldWait
1777 // if _foregroundGCIsActive is set
1778 // clears _foregroundGCShouldWait, notifies _CGC_lock
1779 // waits on _CGC_lock for _foregroundGCIsActive to become false
1780 // and exits the loop.
1781 // otherwise
1782 // proceed with that phase of the collection
1783 // if the phase is a stop-the-world phase,
1784 // yield the baton once more just before enqueueing
1785 // the stop-world CMS operation (executed by the VM thread).
1786 // returns after all phases of the collection are done
1787 //
1788
1789 void CMSCollector::acquire_control_and_collect(bool full,
1790 bool clear_all_soft_refs) {
1791 assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
1792 assert(!Thread::current()->is_ConcurrentGC_thread(),
1793 "shouldn't try to acquire control from self!");
1794
1795 // Start the protocol for acquiring control of the
1796 // collection from the background collector (aka CMS thread).
1797 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1798 "VM thread should have CMS token");
1799 // Remember the possibly interrupted state of an ongoing
1800 // concurrent collection
1801 CollectorState first_state = _collectorState;
1802
1803 // Signal to a possibly ongoing concurrent collection that
1804 // we want to do a foreground collection.
1805 _foregroundGCIsActive = true;
1806
1807 // Disable incremental mode during a foreground collection.
1808 ICMSDisabler icms_disabler;
1809
1810 // release locks and wait for a notify from the background collector
1811 // releasing the locks in only necessary for phases which
1812 // do yields to improve the granularity of the collection.
1813 assert_lock_strong(bitMapLock());
1814 // We need to lock the Free list lock for the space that we are
1815 // currently collecting.
1816 assert(haveFreelistLocks(), "Must be holding free list locks");
1817 bitMapLock()->unlock();
1818 releaseFreelistLocks();
1819 {
1820 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1821 if (_foregroundGCShouldWait) {
1822 // We are going to be waiting for action for the CMS thread;
1823 // it had better not be gone (for instance at shutdown)!
1824 assert(ConcurrentMarkSweepThread::cmst() != NULL,
1825 "CMS thread must be running");
1826 // Wait here until the background collector gives us the go-ahead
1827 ConcurrentMarkSweepThread::clear_CMS_flag(
1828 ConcurrentMarkSweepThread::CMS_vm_has_token); // release token
1829 // Get a possibly blocked CMS thread going:
1830 // Note that we set _foregroundGCIsActive true above,
1831 // without protection of the CGC_lock.
1832 CGC_lock->notify();
1833 assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(),
1834 "Possible deadlock");
1835 while (_foregroundGCShouldWait) {
1836 // wait for notification
1837 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1838 // Possibility of delay/starvation here, since CMS token does
1839 // not know to give priority to VM thread? Actually, i think
1840 // there wouldn't be any delay/starvation, but the proof of
1841 // that "fact" (?) appears non-trivial. XXX 20011219YSR
1842 }
1843 ConcurrentMarkSweepThread::set_CMS_flag(
1844 ConcurrentMarkSweepThread::CMS_vm_has_token);
1845 }
1846 }
1847 // The CMS_token is already held. Get back the other locks.
1848 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1849 "VM thread should have CMS token");
1850 getFreelistLocks();
1851 bitMapLock()->lock_without_safepoint_check();
1852 if (TraceCMSState) {
1853 gclog_or_tty->print_cr("CMS foreground collector has asked for control "
1854 INTPTR_FORMAT " with first state %d", Thread::current(), first_state);
1855 gclog_or_tty->print_cr(" gets control with state %d", _collectorState);
1856 }
1857
1858 // Check if we need to do a compaction, or if not, whether
1859 // we need to start the mark-sweep from scratch.
1860 bool should_compact = false;
1861 bool should_start_over = false;
1862 decide_foreground_collection_type(clear_all_soft_refs,
1863 &should_compact, &should_start_over);
1864
1865 NOT_PRODUCT(
1866 if (RotateCMSCollectionTypes) {
1867 if (_cmsGen->debug_collection_type() ==
1868 ConcurrentMarkSweepGeneration::MSC_foreground_collection_type) {
1869 should_compact = true;
1870 } else if (_cmsGen->debug_collection_type() ==
1871 ConcurrentMarkSweepGeneration::MS_foreground_collection_type) {
1872 should_compact = false;
1873 }
1874 }
1875 )
1876
1877 if (first_state > Idling) {
1878 report_concurrent_mode_interruption();
1879 }
1880
1881 set_did_compact(should_compact);
1882 if (should_compact) {
1883 // If the collection is being acquired from the background
1884 // collector, there may be references on the discovered
1885 // references lists that have NULL referents (being those
1886 // that were concurrently cleared by a mutator) or
1887 // that are no longer active (having been enqueued concurrently
1888 // by the mutator).
1889 // Scrub the list of those references because Mark-Sweep-Compact
1890 // code assumes referents are not NULL and that all discovered
1891 // Reference objects are active.
1892 ref_processor()->clean_up_discovered_references();
1893
1894 if (first_state > Idling) {
1895 save_heap_summary();
1896 }
1897
1898 do_compaction_work(clear_all_soft_refs);
1899
1900 // Has the GC time limit been exceeded?
1901 DefNewGeneration* young_gen = _young_gen->as_DefNewGeneration();
1902 size_t max_eden_size = young_gen->max_capacity() -
1903 young_gen->to()->capacity() -
1904 young_gen->from()->capacity();
1905 GenCollectedHeap* gch = GenCollectedHeap::heap();
1906 GCCause::Cause gc_cause = gch->gc_cause();
1907 size_policy()->check_gc_overhead_limit(_young_gen->used(),
1908 young_gen->eden()->used(),
1909 _cmsGen->max_capacity(),
1910 max_eden_size,
1911 full,
1912 gc_cause,
1913 gch->collector_policy());
1914 } else {
1915 do_mark_sweep_work(clear_all_soft_refs, first_state,
1916 should_start_over);
1917 }
1918 // Reset the expansion cause, now that we just completed
1919 // a collection cycle.
1920 clear_expansion_cause();
1921 _foregroundGCIsActive = false;
1922 return;
1923 }
1924
1925 // Resize the tenured generation
1926 // after obtaining the free list locks for the
1927 // two generations.
1928 void CMSCollector::compute_new_size() {
1929 assert_locked_or_safepoint(Heap_lock);
1930 FreelistLocker z(this);
1931 MetaspaceGC::compute_new_size();
1932 _cmsGen->compute_new_size_free_list();
1933 }
1934
1935 // A work method used by foreground collection to determine
1936 // what type of collection (compacting or not, continuing or fresh)
1937 // it should do.
1938 // NOTE: the intent is to make UseCMSCompactAtFullCollection
1939 // and CMSCompactWhenClearAllSoftRefs the default in the future
1940 // and do away with the flags after a suitable period.
1941 void CMSCollector::decide_foreground_collection_type(
1942 bool clear_all_soft_refs, bool* should_compact,
1943 bool* should_start_over) {
1944 // Normally, we'll compact only if the UseCMSCompactAtFullCollection
1945 // flag is set, and we have either requested a System.gc() or
1946 // the number of full gc's since the last concurrent cycle
1947 // has exceeded the threshold set by CMSFullGCsBeforeCompaction,
1948 // or if an incremental collection has failed
1949 GenCollectedHeap* gch = GenCollectedHeap::heap();
1950 assert(gch->collector_policy()->is_two_generation_policy(),
1951 "You may want to check the correctness of the following");
1952 // Inform cms gen if this was due to partial collection failing.
1953 // The CMS gen may use this fact to determine its expansion policy.
1954 if (gch->incremental_collection_will_fail(false /* don't consult_young */)) {
1955 assert(!_cmsGen->incremental_collection_failed(),
1956 "Should have been noticed, reacted to and cleared");
1957 _cmsGen->set_incremental_collection_failed();
1958 }
1959 *should_compact =
1960 UseCMSCompactAtFullCollection &&
1961 ((_full_gcs_since_conc_gc >= CMSFullGCsBeforeCompaction) ||
1962 GCCause::is_user_requested_gc(gch->gc_cause()) ||
1963 gch->incremental_collection_will_fail(true /* consult_young */));
1964 *should_start_over = false;
1965 if (clear_all_soft_refs && !*should_compact) {
1966 // We are about to do a last ditch collection attempt
1967 // so it would normally make sense to do a compaction
1968 // to reclaim as much space as possible.
1969 if (CMSCompactWhenClearAllSoftRefs) {
1970 // Default: The rationale is that in this case either
1971 // we are past the final marking phase, in which case
1972 // we'd have to start over, or so little has been done
1973 // that there's little point in saving that work. Compaction
1974 // appears to be the sensible choice in either case.
1975 *should_compact = true;
1976 } else {
1977 // We have been asked to clear all soft refs, but not to
1978 // compact. Make sure that we aren't past the final checkpoint
1979 // phase, for that is where we process soft refs. If we are already
1980 // past that phase, we'll need to redo the refs discovery phase and
1981 // if necessary clear soft refs that weren't previously
1982 // cleared. We do so by remembering the phase in which
1983 // we came in, and if we are past the refs processing
1984 // phase, we'll choose to just redo the mark-sweep
1985 // collection from scratch.
1986 if (_collectorState > FinalMarking) {
1987 // We are past the refs processing phase;
1988 // start over and do a fresh synchronous CMS cycle
1989 _collectorState = Resetting; // skip to reset to start new cycle
1990 reset(false /* == !asynch */);
1991 *should_start_over = true;
1992 } // else we can continue a possibly ongoing current cycle
1993 }
1994 }
1995 }
1996
1997 // A work method used by the foreground collector to do
1998 // a mark-sweep-compact.
1999 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) {
2000 GenCollectedHeap* gch = GenCollectedHeap::heap();
2001
2002 STWGCTimer* gc_timer = GenMarkSweep::gc_timer();
2003 gc_timer->register_gc_start(os::elapsed_counter());
2004
2005 SerialOldTracer* gc_tracer = GenMarkSweep::gc_tracer();
2006 gc_tracer->report_gc_start(gch->gc_cause(), gc_timer->gc_start());
2007
2008 GCTraceTime t("CMS:MSC ", PrintGCDetails && Verbose, true, NULL);
2009 if (PrintGC && Verbose && !(GCCause::is_user_requested_gc(gch->gc_cause()))) {
2010 gclog_or_tty->print_cr("Compact ConcurrentMarkSweepGeneration after %d "
2011 "collections passed to foreground collector", _full_gcs_since_conc_gc);
2012 }
2013
2014 // Sample collection interval time and reset for collection pause.
2015 if (UseAdaptiveSizePolicy) {
2016 size_policy()->msc_collection_begin();
2017 }
2018
2019 // Temporarily widen the span of the weak reference processing to
2020 // the entire heap.
2021 MemRegion new_span(GenCollectedHeap::heap()->reserved_region());
2022 ReferenceProcessorSpanMutator rp_mut_span(ref_processor(), new_span);
2023 // Temporarily, clear the "is_alive_non_header" field of the
2024 // reference processor.
2025 ReferenceProcessorIsAliveMutator rp_mut_closure(ref_processor(), NULL);
2026 // Temporarily make reference _processing_ single threaded (non-MT).
2027 ReferenceProcessorMTProcMutator rp_mut_mt_processing(ref_processor(), false);
2028 // Temporarily make refs discovery atomic
2029 ReferenceProcessorAtomicMutator rp_mut_atomic(ref_processor(), true);
2030 // Temporarily make reference _discovery_ single threaded (non-MT)
2031 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
2032
2033 ref_processor()->set_enqueuing_is_done(false);
2034 ref_processor()->enable_discovery(false /*verify_disabled*/, false /*check_no_refs*/);
2035 ref_processor()->setup_policy(clear_all_soft_refs);
2036 // If an asynchronous collection finishes, the _modUnionTable is
2037 // all clear. If we are assuming the collection from an asynchronous
2038 // collection, clear the _modUnionTable.
2039 assert(_collectorState != Idling || _modUnionTable.isAllClear(),
2040 "_modUnionTable should be clear if the baton was not passed");
2041 _modUnionTable.clear_all();
2042 assert(_collectorState != Idling || _ct->klass_rem_set()->mod_union_is_clear(),
2043 "mod union for klasses should be clear if the baton was passed");
2044 _ct->klass_rem_set()->clear_mod_union();
2045
2046 // We must adjust the allocation statistics being maintained
2047 // in the free list space. We do so by reading and clearing
2048 // the sweep timer and updating the block flux rate estimates below.
2049 assert(!_intra_sweep_timer.is_active(), "_intra_sweep_timer should be inactive");
2050 if (_inter_sweep_timer.is_active()) {
2051 _inter_sweep_timer.stop();
2052 // Note that we do not use this sample to update the _inter_sweep_estimate.
2053 _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
2054 _inter_sweep_estimate.padded_average(),
2055 _intra_sweep_estimate.padded_average());
2056 }
2057
2058 GenMarkSweep::invoke_at_safepoint(_cmsGen->level(),
2059 ref_processor(), clear_all_soft_refs);
2060 #ifdef ASSERT
2061 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
2062 size_t free_size = cms_space->free();
2063 assert(free_size ==
2064 pointer_delta(cms_space->end(), cms_space->compaction_top())
2065 * HeapWordSize,
2066 "All the free space should be compacted into one chunk at top");
2067 assert(cms_space->dictionary()->total_chunk_size(
2068 debug_only(cms_space->freelistLock())) == 0 ||
2069 cms_space->totalSizeInIndexedFreeLists() == 0,
2070 "All the free space should be in a single chunk");
2071 size_t num = cms_space->totalCount();
2072 assert((free_size == 0 && num == 0) ||
2073 (free_size > 0 && (num == 1 || num == 2)),
2074 "There should be at most 2 free chunks after compaction");
2075 #endif // ASSERT
2076 _collectorState = Resetting;
2077 assert(_restart_addr == NULL,
2078 "Should have been NULL'd before baton was passed");
2079 reset(false /* == !asynch */);
2080 _cmsGen->reset_after_compaction();
2081 _concurrent_cycles_since_last_unload = 0;
2082
2083 // Clear any data recorded in the PLAB chunk arrays.
2084 if (_survivor_plab_array != NULL) {
2085 reset_survivor_plab_arrays();
2086 }
2087
2088 // Adjust the per-size allocation stats for the next epoch.
2089 _cmsGen->cmsSpace()->endSweepFLCensus(sweep_count() /* fake */);
2090 // Restart the "inter sweep timer" for the next epoch.
2091 _inter_sweep_timer.reset();
2092 _inter_sweep_timer.start();
2093
2094 // Sample collection pause time and reset for collection interval.
2095 if (UseAdaptiveSizePolicy) {
2096 size_policy()->msc_collection_end(gch->gc_cause());
2097 }
2098
2099 gc_timer->register_gc_end(os::elapsed_counter());
2100
2101 gc_tracer->report_gc_end(gc_timer->gc_end(), gc_timer->time_partitions());
2102
2103 // For a mark-sweep-compact, compute_new_size() will be called
2104 // in the heap's do_collection() method.
2105 }
2106
2107 // A work method used by the foreground collector to do
2108 // a mark-sweep, after taking over from a possibly on-going
2109 // concurrent mark-sweep collection.
2110 void CMSCollector::do_mark_sweep_work(bool clear_all_soft_refs,
2111 CollectorState first_state, bool should_start_over) {
2112 if (PrintGC && Verbose) {
2113 gclog_or_tty->print_cr("Pass concurrent collection to foreground "
2114 "collector with count %d",
2115 _full_gcs_since_conc_gc);
2116 }
2117 switch (_collectorState) {
2118 case Idling:
2119 if (first_state == Idling || should_start_over) {
2120 // The background GC was not active, or should
2121 // restarted from scratch; start the cycle.
2122 _collectorState = InitialMarking;
2123 }
2124 // If first_state was not Idling, then a background GC
2125 // was in progress and has now finished. No need to do it
2126 // again. Leave the state as Idling.
2127 break;
2128 case Precleaning:
2129 // In the foreground case don't do the precleaning since
2130 // it is not done concurrently and there is extra work
2131 // required.
2132 _collectorState = FinalMarking;
2133 }
2134 collect_in_foreground(clear_all_soft_refs, GenCollectedHeap::heap()->gc_cause());
2135
2136 // For a mark-sweep, compute_new_size() will be called
2137 // in the heap's do_collection() method.
2138 }
2139
2140
2141 void CMSCollector::print_eden_and_survivor_chunk_arrays() {
2142 DefNewGeneration* dng = _young_gen->as_DefNewGeneration();
2143 EdenSpace* eden_space = dng->eden();
2144 ContiguousSpace* from_space = dng->from();
2145 ContiguousSpace* to_space = dng->to();
2146 // Eden
2147 if (_eden_chunk_array != NULL) {
2148 gclog_or_tty->print_cr("eden " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
2149 eden_space->bottom(), eden_space->top(),
2150 eden_space->end(), eden_space->capacity());
2151 gclog_or_tty->print_cr("_eden_chunk_index=" SIZE_FORMAT ", "
2152 "_eden_chunk_capacity=" SIZE_FORMAT,
2153 _eden_chunk_index, _eden_chunk_capacity);
2154 for (size_t i = 0; i < _eden_chunk_index; i++) {
2155 gclog_or_tty->print_cr("_eden_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT,
2156 i, _eden_chunk_array[i]);
2157 }
2158 }
2159 // Survivor
2160 if (_survivor_chunk_array != NULL) {
2161 gclog_or_tty->print_cr("survivor " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
2162 from_space->bottom(), from_space->top(),
2163 from_space->end(), from_space->capacity());
2164 gclog_or_tty->print_cr("_survivor_chunk_index=" SIZE_FORMAT ", "
2165 "_survivor_chunk_capacity=" SIZE_FORMAT,
2166 _survivor_chunk_index, _survivor_chunk_capacity);
2167 for (size_t i = 0; i < _survivor_chunk_index; i++) {
2168 gclog_or_tty->print_cr("_survivor_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT,
2169 i, _survivor_chunk_array[i]);
2170 }
2171 }
2172 }
2173
2174 void CMSCollector::getFreelistLocks() const {
2175 // Get locks for all free lists in all generations that this
2176 // collector is responsible for
2177 _cmsGen->freelistLock()->lock_without_safepoint_check();
2178 }
2179
2180 void CMSCollector::releaseFreelistLocks() const {
2181 // Release locks for all free lists in all generations that this
2182 // collector is responsible for
2183 _cmsGen->freelistLock()->unlock();
2184 }
2185
2186 bool CMSCollector::haveFreelistLocks() const {
2187 // Check locks for all free lists in all generations that this
2188 // collector is responsible for
2189 assert_lock_strong(_cmsGen->freelistLock());
2190 PRODUCT_ONLY(ShouldNotReachHere());
2191 return true;
2192 }
2193
2194 // A utility class that is used by the CMS collector to
2195 // temporarily "release" the foreground collector from its
2196 // usual obligation to wait for the background collector to
2197 // complete an ongoing phase before proceeding.
2198 class ReleaseForegroundGC: public StackObj {
2199 private:
2200 CMSCollector* _c;
2201 public:
2202 ReleaseForegroundGC(CMSCollector* c) : _c(c) {
2203 assert(_c->_foregroundGCShouldWait, "Else should not need to call");
2204 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2205 // allow a potentially blocked foreground collector to proceed
2206 _c->_foregroundGCShouldWait = false;
2207 if (_c->_foregroundGCIsActive) {
2208 CGC_lock->notify();
2209 }
2210 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2211 "Possible deadlock");
2212 }
2213
2214 ~ReleaseForegroundGC() {
2215 assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?");
2216 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2217 _c->_foregroundGCShouldWait = true;
2218 }
2219 };
2220
2221 // There are separate collect_in_background and collect_in_foreground because of
2222 // the different locking requirements of the background collector and the
2223 // foreground collector. There was originally an attempt to share
2224 // one "collect" method between the background collector and the foreground
2225 // collector but the if-then-else required made it cleaner to have
2226 // separate methods.
2227 void CMSCollector::collect_in_background(bool clear_all_soft_refs, GCCause::Cause cause) {
2228 assert(Thread::current()->is_ConcurrentGC_thread(),
2229 "A CMS asynchronous collection is only allowed on a CMS thread.");
2230
2231 GenCollectedHeap* gch = GenCollectedHeap::heap();
2232 {
2233 bool safepoint_check = Mutex::_no_safepoint_check_flag;
2234 MutexLockerEx hl(Heap_lock, safepoint_check);
2235 FreelistLocker fll(this);
2236 MutexLockerEx x(CGC_lock, safepoint_check);
2237 if (_foregroundGCIsActive || !UseAsyncConcMarkSweepGC) {
2238 // The foreground collector is active or we're
2239 // not using asynchronous collections. Skip this
2240 // background collection.
2241 assert(!_foregroundGCShouldWait, "Should be clear");
2242 return;
2243 } else {
2244 assert(_collectorState == Idling, "Should be idling before start.");
2245 _collectorState = InitialMarking;
2246 register_gc_start(cause);
2247 // Reset the expansion cause, now that we are about to begin
2248 // a new cycle.
2249 clear_expansion_cause();
2250
2251 // Clear the MetaspaceGC flag since a concurrent collection
2252 // is starting but also clear it after the collection.
2253 MetaspaceGC::set_should_concurrent_collect(false);
2254 }
2255 // Decide if we want to enable class unloading as part of the
2256 // ensuing concurrent GC cycle.
2257 update_should_unload_classes();
2258 _full_gc_requested = false; // acks all outstanding full gc requests
2259 _full_gc_cause = GCCause::_no_gc;
2260 // Signal that we are about to start a collection
2261 gch->increment_total_full_collections(); // ... starting a collection cycle
2262 _collection_count_start = gch->total_full_collections();
2263 }
2264
2265 // Used for PrintGC
2266 size_t prev_used;
2267 if (PrintGC && Verbose) {
2268 prev_used = _cmsGen->used(); // XXXPERM
2269 }
2270
2271 // The change of the collection state is normally done at this level;
2272 // the exceptions are phases that are executed while the world is
2273 // stopped. For those phases the change of state is done while the
2274 // world is stopped. For baton passing purposes this allows the
2275 // background collector to finish the phase and change state atomically.
2276 // The foreground collector cannot wait on a phase that is done
2277 // while the world is stopped because the foreground collector already
2278 // has the world stopped and would deadlock.
2279 while (_collectorState != Idling) {
2280 if (TraceCMSState) {
2281 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
2282 Thread::current(), _collectorState);
2283 }
2284 // The foreground collector
2285 // holds the Heap_lock throughout its collection.
2286 // holds the CMS token (but not the lock)
2287 // except while it is waiting for the background collector to yield.
2288 //
2289 // The foreground collector should be blocked (not for long)
2290 // if the background collector is about to start a phase
2291 // executed with world stopped. If the background
2292 // collector has already started such a phase, the
2293 // foreground collector is blocked waiting for the
2294 // Heap_lock. The stop-world phases (InitialMarking and FinalMarking)
2295 // are executed in the VM thread.
2296 //
2297 // The locking order is
2298 // PendingListLock (PLL) -- if applicable (FinalMarking)
2299 // Heap_lock (both this & PLL locked in VM_CMS_Operation::prologue())
2300 // CMS token (claimed in
2301 // stop_world_and_do() -->
2302 // safepoint_synchronize() -->
2303 // CMSThread::synchronize())
2304
2305 {
2306 // Check if the FG collector wants us to yield.
2307 CMSTokenSync x(true); // is cms thread
2308 if (waitForForegroundGC()) {
2309 // We yielded to a foreground GC, nothing more to be
2310 // done this round.
2311 assert(_foregroundGCShouldWait == false, "We set it to false in "
2312 "waitForForegroundGC()");
2313 if (TraceCMSState) {
2314 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2315 " exiting collection CMS state %d",
2316 Thread::current(), _collectorState);
2317 }
2318 return;
2319 } else {
2320 // The background collector can run but check to see if the
2321 // foreground collector has done a collection while the
2322 // background collector was waiting to get the CGC_lock
2323 // above. If yes, break so that _foregroundGCShouldWait
2324 // is cleared before returning.
2325 if (_collectorState == Idling) {
2326 break;
2327 }
2328 }
2329 }
2330
2331 assert(_foregroundGCShouldWait, "Foreground collector, if active, "
2332 "should be waiting");
2333
2334 switch (_collectorState) {
2335 case InitialMarking:
2336 {
2337 ReleaseForegroundGC x(this);
2338 stats().record_cms_begin();
2339 VM_CMS_Initial_Mark initial_mark_op(this);
2340 VMThread::execute(&initial_mark_op);
2341 }
2342 // The collector state may be any legal state at this point
2343 // since the background collector may have yielded to the
2344 // foreground collector.
2345 break;
2346 case Marking:
2347 // initial marking in checkpointRootsInitialWork has been completed
2348 if (markFromRoots(true)) { // we were successful
2349 assert(_collectorState == Precleaning, "Collector state should "
2350 "have changed");
2351 } else {
2352 assert(_foregroundGCIsActive, "Internal state inconsistency");
2353 }
2354 break;
2355 case Precleaning:
2356 if (UseAdaptiveSizePolicy) {
2357 size_policy()->concurrent_precleaning_begin();
2358 }
2359 // marking from roots in markFromRoots has been completed
2360 preclean();
2361 if (UseAdaptiveSizePolicy) {
2362 size_policy()->concurrent_precleaning_end();
2363 }
2364 assert(_collectorState == AbortablePreclean ||
2365 _collectorState == FinalMarking,
2366 "Collector state should have changed");
2367 break;
2368 case AbortablePreclean:
2369 if (UseAdaptiveSizePolicy) {
2370 size_policy()->concurrent_phases_resume();
2371 }
2372 abortable_preclean();
2373 if (UseAdaptiveSizePolicy) {
2374 size_policy()->concurrent_precleaning_end();
2375 }
2376 assert(_collectorState == FinalMarking, "Collector state should "
2377 "have changed");
2378 break;
2379 case FinalMarking:
2380 {
2381 ReleaseForegroundGC x(this);
2382
2383 VM_CMS_Final_Remark final_remark_op(this);
2384 VMThread::execute(&final_remark_op);
2385 }
2386 assert(_foregroundGCShouldWait, "block post-condition");
2387 break;
2388 case Sweeping:
2389 if (UseAdaptiveSizePolicy) {
2390 size_policy()->concurrent_sweeping_begin();
2391 }
2392 // final marking in checkpointRootsFinal has been completed
2393 sweep(true);
2394 assert(_collectorState == Resizing, "Collector state change "
2395 "to Resizing must be done under the free_list_lock");
2396 _full_gcs_since_conc_gc = 0;
2397
2398 // Stop the timers for adaptive size policy for the concurrent phases
2399 if (UseAdaptiveSizePolicy) {
2400 size_policy()->concurrent_sweeping_end();
2401 size_policy()->concurrent_phases_end(gch->gc_cause(),
2402 gch->prev_gen(_cmsGen)->capacity(),
2403 _cmsGen->free());
2404 }
2405
2406 case Resizing: {
2407 // Sweeping has been completed...
2408 // At this point the background collection has completed.
2409 // Don't move the call to compute_new_size() down
2410 // into code that might be executed if the background
2411 // collection was preempted.
2412 {
2413 ReleaseForegroundGC x(this); // unblock FG collection
2414 MutexLockerEx y(Heap_lock, Mutex::_no_safepoint_check_flag);
2415 CMSTokenSync z(true); // not strictly needed.
2416 if (_collectorState == Resizing) {
2417 compute_new_size();
2418 save_heap_summary();
2419 _collectorState = Resetting;
2420 } else {
2421 assert(_collectorState == Idling, "The state should only change"
2422 " because the foreground collector has finished the collection");
2423 }
2424 }
2425 break;
2426 }
2427 case Resetting:
2428 // CMS heap resizing has been completed
2429 reset(true);
2430 assert(_collectorState == Idling, "Collector state should "
2431 "have changed");
2432
2433 MetaspaceGC::set_should_concurrent_collect(false);
2434
2435 stats().record_cms_end();
2436 // Don't move the concurrent_phases_end() and compute_new_size()
2437 // calls to here because a preempted background collection
2438 // has it's state set to "Resetting".
2439 break;
2440 case Idling:
2441 default:
2442 ShouldNotReachHere();
2443 break;
2444 }
2445 if (TraceCMSState) {
2446 gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d",
2447 Thread::current(), _collectorState);
2448 }
2449 assert(_foregroundGCShouldWait, "block post-condition");
2450 }
2451
2452 // Should this be in gc_epilogue?
2453 collector_policy()->counters()->update_counters();
2454
2455 {
2456 // Clear _foregroundGCShouldWait and, in the event that the
2457 // foreground collector is waiting, notify it, before
2458 // returning.
2459 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2460 _foregroundGCShouldWait = false;
2461 if (_foregroundGCIsActive) {
2462 CGC_lock->notify();
2463 }
2464 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2465 "Possible deadlock");
2466 }
2467 if (TraceCMSState) {
2468 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2469 " exiting collection CMS state %d",
2470 Thread::current(), _collectorState);
2471 }
2472 if (PrintGC && Verbose) {
2473 _cmsGen->print_heap_change(prev_used);
2474 }
2475 }
2476
2477 void CMSCollector::register_foreground_gc_start(GCCause::Cause cause) {
2478 if (!_cms_start_registered) {
2479 register_gc_start(cause);
2480 }
2481 }
2482
2483 void CMSCollector::register_gc_start(GCCause::Cause cause) {
2484 _cms_start_registered = true;
2485 _gc_timer_cm->register_gc_start(os::elapsed_counter());
2486 _gc_tracer_cm->report_gc_start(cause, _gc_timer_cm->gc_start());
2487 }
2488
2489 void CMSCollector::register_gc_end() {
2490 if (_cms_start_registered) {
2491 report_heap_summary(GCWhen::AfterGC);
2492
2493 _gc_timer_cm->register_gc_end(os::elapsed_counter());
2494 _gc_tracer_cm->report_gc_end(_gc_timer_cm->gc_end(), _gc_timer_cm->time_partitions());
2495 _cms_start_registered = false;
2496 }
2497 }
2498
2499 void CMSCollector::save_heap_summary() {
2500 GenCollectedHeap* gch = GenCollectedHeap::heap();
2501 _last_heap_summary = gch->create_heap_summary();
2502 _last_metaspace_summary = gch->create_metaspace_summary();
2503 }
2504
2505 void CMSCollector::report_heap_summary(GCWhen::Type when) {
2506 _gc_tracer_cm->report_gc_heap_summary(when, _last_heap_summary, _last_metaspace_summary);
2507 }
2508
2509 void CMSCollector::collect_in_foreground(bool clear_all_soft_refs, GCCause::Cause cause) {
2510 assert(_foregroundGCIsActive && !_foregroundGCShouldWait,
2511 "Foreground collector should be waiting, not executing");
2512 assert(Thread::current()->is_VM_thread(), "A foreground collection"
2513 "may only be done by the VM Thread with the world stopped");
2514 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
2515 "VM thread should have CMS token");
2516
2517 NOT_PRODUCT(GCTraceTime t("CMS:MS (foreground) ", PrintGCDetails && Verbose,
2518 true, NULL);)
2519 if (UseAdaptiveSizePolicy) {
2520 size_policy()->ms_collection_begin();
2521 }
2522 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact);
2523
2524 HandleMark hm; // Discard invalid handles created during verification
2525
2526 if (VerifyBeforeGC &&
2527 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2528 Universe::verify();
2529 }
2530
2531 // Snapshot the soft reference policy to be used in this collection cycle.
2532 ref_processor()->setup_policy(clear_all_soft_refs);
2533
2534 bool init_mark_was_synchronous = false; // until proven otherwise
2535 while (_collectorState != Idling) {
2536 if (TraceCMSState) {
2537 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
2538 Thread::current(), _collectorState);
2539 }
2540 switch (_collectorState) {
2541 case InitialMarking:
2542 register_foreground_gc_start(cause);
2543 init_mark_was_synchronous = true; // fact to be exploited in re-mark
2544 checkpointRootsInitial(false);
2545 assert(_collectorState == Marking, "Collector state should have changed"
2546 " within checkpointRootsInitial()");
2547 break;
2548 case Marking:
2549 // initial marking in checkpointRootsInitialWork has been completed
2550 if (VerifyDuringGC &&
2551 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2552 Universe::verify("Verify before initial mark: ");
2553 }
2554 {
2555 bool res = markFromRoots(false);
2556 assert(res && _collectorState == FinalMarking, "Collector state should "
2557 "have changed");
2558 break;
2559 }
2560 case FinalMarking:
2561 if (VerifyDuringGC &&
2562 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2563 Universe::verify("Verify before re-mark: ");
2564 }
2565 checkpointRootsFinal(false, clear_all_soft_refs,
2566 init_mark_was_synchronous);
2567 assert(_collectorState == Sweeping, "Collector state should not "
2568 "have changed within checkpointRootsFinal()");
2569 break;
2570 case Sweeping:
2571 // final marking in checkpointRootsFinal has been completed
2572 if (VerifyDuringGC &&
2573 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2574 Universe::verify("Verify before sweep: ");
2575 }
2576 sweep(false);
2577 assert(_collectorState == Resizing, "Incorrect state");
2578 break;
2579 case Resizing: {
2580 // Sweeping has been completed; the actual resize in this case
2581 // is done separately; nothing to be done in this state.
2582 _collectorState = Resetting;
2583 break;
2584 }
2585 case Resetting:
2586 // The heap has been resized.
2587 if (VerifyDuringGC &&
2588 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2589 Universe::verify("Verify before reset: ");
2590 }
2591 save_heap_summary();
2592 reset(false);
2593 assert(_collectorState == Idling, "Collector state should "
2594 "have changed");
2595 break;
2596 case Precleaning:
2597 case AbortablePreclean:
2598 // Elide the preclean phase
2599 _collectorState = FinalMarking;
2600 break;
2601 default:
2602 ShouldNotReachHere();
2603 }
2604 if (TraceCMSState) {
2605 gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d",
2606 Thread::current(), _collectorState);
2607 }
2608 }
2609
2610 if (UseAdaptiveSizePolicy) {
2611 GenCollectedHeap* gch = GenCollectedHeap::heap();
2612 size_policy()->ms_collection_end(gch->gc_cause());
2613 }
2614
2615 if (VerifyAfterGC &&
2616 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2617 Universe::verify();
2618 }
2619 if (TraceCMSState) {
2620 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2621 " exiting collection CMS state %d",
2622 Thread::current(), _collectorState);
2623 }
2624 }
2625
2626 bool CMSCollector::waitForForegroundGC() {
2627 bool res = false;
2628 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2629 "CMS thread should have CMS token");
2630 // Block the foreground collector until the
2631 // background collectors decides whether to
2632 // yield.
2633 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2634 _foregroundGCShouldWait = true;
2635 if (_foregroundGCIsActive) {
2636 // The background collector yields to the
2637 // foreground collector and returns a value
2638 // indicating that it has yielded. The foreground
2639 // collector can proceed.
2640 res = true;
2641 _foregroundGCShouldWait = false;
2642 ConcurrentMarkSweepThread::clear_CMS_flag(
2643 ConcurrentMarkSweepThread::CMS_cms_has_token);
2644 ConcurrentMarkSweepThread::set_CMS_flag(
2645 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2646 // Get a possibly blocked foreground thread going
2647 CGC_lock->notify();
2648 if (TraceCMSState) {
2649 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d",
2650 Thread::current(), _collectorState);
2651 }
2652 while (_foregroundGCIsActive) {
2653 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
2654 }
2655 ConcurrentMarkSweepThread::set_CMS_flag(
2656 ConcurrentMarkSweepThread::CMS_cms_has_token);
2657 ConcurrentMarkSweepThread::clear_CMS_flag(
2658 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2659 }
2660 if (TraceCMSState) {
2661 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d",
2662 Thread::current(), _collectorState);
2663 }
2664 return res;
2665 }
2666
2667 // Because of the need to lock the free lists and other structures in
2668 // the collector, common to all the generations that the collector is
2669 // collecting, we need the gc_prologues of individual CMS generations
2670 // delegate to their collector. It may have been simpler had the
2671 // current infrastructure allowed one to call a prologue on a
2672 // collector. In the absence of that we have the generation's
2673 // prologue delegate to the collector, which delegates back
2674 // some "local" work to a worker method in the individual generations
2675 // that it's responsible for collecting, while itself doing any
2676 // work common to all generations it's responsible for. A similar
2677 // comment applies to the gc_epilogue()'s.
2678 // The role of the varaible _between_prologue_and_epilogue is to
2679 // enforce the invocation protocol.
2680 void CMSCollector::gc_prologue(bool full) {
2681 // Call gc_prologue_work() for the CMSGen
2682 // we are responsible for.
2683
2684 // The following locking discipline assumes that we are only called
2685 // when the world is stopped.
2686 assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption");
2687
2688 // The CMSCollector prologue must call the gc_prologues for the
2689 // "generations" that it's responsible
2690 // for.
2691
2692 assert( Thread::current()->is_VM_thread()
2693 || ( CMSScavengeBeforeRemark
2694 && Thread::current()->is_ConcurrentGC_thread()),
2695 "Incorrect thread type for prologue execution");
2696
2697 if (_between_prologue_and_epilogue) {
2698 // We have already been invoked; this is a gc_prologue delegation
2699 // from yet another CMS generation that we are responsible for, just
2700 // ignore it since all relevant work has already been done.
2701 return;
2702 }
2703
2704 // set a bit saying prologue has been called; cleared in epilogue
2705 _between_prologue_and_epilogue = true;
2706 // Claim locks for common data structures, then call gc_prologue_work()
2707 // for each CMSGen.
2708
2709 getFreelistLocks(); // gets free list locks on constituent spaces
2710 bitMapLock()->lock_without_safepoint_check();
2711
2712 // Should call gc_prologue_work() for all cms gens we are responsible for
2713 bool duringMarking = _collectorState >= Marking
2714 && _collectorState < Sweeping;
2715
2716 // The young collections clear the modified oops state, which tells if
2717 // there are any modified oops in the class. The remark phase also needs
2718 // that information. Tell the young collection to save the union of all
2719 // modified klasses.
2720 if (duringMarking) {
2721 _ct->klass_rem_set()->set_accumulate_modified_oops(true);
2722 }
2723
2724 bool registerClosure = duringMarking;
2725
2726 ModUnionClosure* muc = CollectedHeap::use_parallel_gc_threads() ?
2727 &_modUnionClosurePar
2728 : &_modUnionClosure;
2729 _cmsGen->gc_prologue_work(full, registerClosure, muc);
2730
2731 if (!full) {
2732 stats().record_gc0_begin();
2733 }
2734 }
2735
2736 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) {
2737
2738 _capacity_at_prologue = capacity();
2739 _used_at_prologue = used();
2740
2741 // Delegate to CMScollector which knows how to coordinate between
2742 // this and any other CMS generations that it is responsible for
2743 // collecting.
2744 collector()->gc_prologue(full);
2745 }
2746
2747 // This is a "private" interface for use by this generation's CMSCollector.
2748 // Not to be called directly by any other entity (for instance,
2749 // GenCollectedHeap, which calls the "public" gc_prologue method above).
2750 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full,
2751 bool registerClosure, ModUnionClosure* modUnionClosure) {
2752 assert(!incremental_collection_failed(), "Shouldn't be set yet");
2753 assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL,
2754 "Should be NULL");
2755 if (registerClosure) {
2756 cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure);
2757 }
2758 cmsSpace()->gc_prologue();
2759 // Clear stat counters
2760 NOT_PRODUCT(
2761 assert(_numObjectsPromoted == 0, "check");
2762 assert(_numWordsPromoted == 0, "check");
2763 if (Verbose && PrintGC) {
2764 gclog_or_tty->print("Allocated "SIZE_FORMAT" objects, "
2765 SIZE_FORMAT" bytes concurrently",
2766 _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord));
2767 }
2768 _numObjectsAllocated = 0;
2769 _numWordsAllocated = 0;
2770 )
2771 }
2772
2773 void CMSCollector::gc_epilogue(bool full) {
2774 // The following locking discipline assumes that we are only called
2775 // when the world is stopped.
2776 assert(SafepointSynchronize::is_at_safepoint(),
2777 "world is stopped assumption");
2778
2779 // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks
2780 // if linear allocation blocks need to be appropriately marked to allow the
2781 // the blocks to be parsable. We also check here whether we need to nudge the
2782 // CMS collector thread to start a new cycle (if it's not already active).
2783 assert( Thread::current()->is_VM_thread()
2784 || ( CMSScavengeBeforeRemark
2785 && Thread::current()->is_ConcurrentGC_thread()),
2786 "Incorrect thread type for epilogue execution");
2787
2788 if (!_between_prologue_and_epilogue) {
2789 // We have already been invoked; this is a gc_epilogue delegation
2790 // from yet another CMS generation that we are responsible for, just
2791 // ignore it since all relevant work has already been done.
2792 return;
2793 }
2794 assert(haveFreelistLocks(), "must have freelist locks");
2795 assert_lock_strong(bitMapLock());
2796
2797 _ct->klass_rem_set()->set_accumulate_modified_oops(false);
2798
2799 _cmsGen->gc_epilogue_work(full);
2800
2801 if (_collectorState == AbortablePreclean || _collectorState == Precleaning) {
2802 // in case sampling was not already enabled, enable it
2803 _start_sampling = true;
2804 }
2805 // reset _eden_chunk_array so sampling starts afresh
2806 _eden_chunk_index = 0;
2807
2808 size_t cms_used = _cmsGen->cmsSpace()->used();
2809
2810 // update performance counters - this uses a special version of
2811 // update_counters() that allows the utilization to be passed as a
2812 // parameter, avoiding multiple calls to used().
2813 //
2814 _cmsGen->update_counters(cms_used);
2815
2816 if (CMSIncrementalMode) {
2817 icms_update_allocation_limits();
2818 }
2819
2820 bitMapLock()->unlock();
2821 releaseFreelistLocks();
2822
2823 if (!CleanChunkPoolAsync) {
2824 Chunk::clean_chunk_pool();
2825 }
2826
2827 set_did_compact(false);
2828 _between_prologue_and_epilogue = false; // ready for next cycle
2829 }
2830
2831 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) {
2832 collector()->gc_epilogue(full);
2833
2834 // Also reset promotion tracking in par gc thread states.
2835 if (CollectedHeap::use_parallel_gc_threads()) {
2836 for (uint i = 0; i < ParallelGCThreads; i++) {
2837 _par_gc_thread_states[i]->promo.stopTrackingPromotions(i);
2838 }
2839 }
2840 }
2841
2842 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2843 assert(!incremental_collection_failed(), "Should have been cleared");
2844 cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2845 cmsSpace()->gc_epilogue();
2846 // Print stat counters
2847 NOT_PRODUCT(
2848 assert(_numObjectsAllocated == 0, "check");
2849 assert(_numWordsAllocated == 0, "check");
2850 if (Verbose && PrintGC) {
2851 gclog_or_tty->print("Promoted "SIZE_FORMAT" objects, "
2852 SIZE_FORMAT" bytes",
2853 _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2854 }
2855 _numObjectsPromoted = 0;
2856 _numWordsPromoted = 0;
2857 )
2858
2859 if (PrintGC && Verbose) {
2860 // Call down the chain in contiguous_available needs the freelistLock
2861 // so print this out before releasing the freeListLock.
2862 gclog_or_tty->print(" Contiguous available "SIZE_FORMAT" bytes ",
2863 contiguous_available());
2864 }
2865 }
2866
2867 #ifndef PRODUCT
2868 bool CMSCollector::have_cms_token() {
2869 Thread* thr = Thread::current();
2870 if (thr->is_VM_thread()) {
2871 return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2872 } else if (thr->is_ConcurrentGC_thread()) {
2873 return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2874 } else if (thr->is_GC_task_thread()) {
2875 return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2876 ParGCRareEvent_lock->owned_by_self();
2877 }
2878 return false;
2879 }
2880 #endif
2881
2882 // Check reachability of the given heap address in CMS generation,
2883 // treating all other generations as roots.
2884 bool CMSCollector::is_cms_reachable(HeapWord* addr) {
2885 // We could "guarantee" below, rather than assert, but i'll
2886 // leave these as "asserts" so that an adventurous debugger
2887 // could try this in the product build provided some subset of
2888 // the conditions were met, provided they were intersted in the
2889 // results and knew that the computation below wouldn't interfere
2890 // with other concurrent computations mutating the structures
2891 // being read or written.
2892 assert(SafepointSynchronize::is_at_safepoint(),
2893 "Else mutations in object graph will make answer suspect");
2894 assert(have_cms_token(), "Should hold cms token");
2895 assert(haveFreelistLocks(), "must hold free list locks");
2896 assert_lock_strong(bitMapLock());
2897
2898 // Clear the marking bit map array before starting, but, just
2899 // for kicks, first report if the given address is already marked
2900 gclog_or_tty->print_cr("Start: Address 0x%x is%s marked", addr,
2901 _markBitMap.isMarked(addr) ? "" : " not");
2902
2903 if (verify_after_remark()) {
2904 MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2905 bool result = verification_mark_bm()->isMarked(addr);
2906 gclog_or_tty->print_cr("TransitiveMark: Address 0x%x %s marked", addr,
2907 result ? "IS" : "is NOT");
2908 return result;
2909 } else {
2910 gclog_or_tty->print_cr("Could not compute result");
2911 return false;
2912 }
2913 }
2914
2915
2916 void
2917 CMSCollector::print_on_error(outputStream* st) {
2918 CMSCollector* collector = ConcurrentMarkSweepGeneration::_collector;
2919 if (collector != NULL) {
2920 CMSBitMap* bitmap = &collector->_markBitMap;
2921 st->print_cr("Marking Bits: (CMSBitMap*) " PTR_FORMAT, bitmap);
2922 bitmap->print_on_error(st, " Bits: ");
2923
2924 st->cr();
2925
2926 CMSBitMap* mut_bitmap = &collector->_modUnionTable;
2927 st->print_cr("Mod Union Table: (CMSBitMap*) " PTR_FORMAT, mut_bitmap);
2928 mut_bitmap->print_on_error(st, " Bits: ");
2929 }
2930 }
2931
2932 ////////////////////////////////////////////////////////
2933 // CMS Verification Support
2934 ////////////////////////////////////////////////////////
2935 // Following the remark phase, the following invariant
2936 // should hold -- each object in the CMS heap which is
2937 // marked in markBitMap() should be marked in the verification_mark_bm().
2938
2939 class VerifyMarkedClosure: public BitMapClosure {
2940 CMSBitMap* _marks;
2941 bool _failed;
2942
2943 public:
2944 VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2945
2946 bool do_bit(size_t offset) {
2947 HeapWord* addr = _marks->offsetToHeapWord(offset);
2948 if (!_marks->isMarked(addr)) {
2949 oop(addr)->print_on(gclog_or_tty);
2950 gclog_or_tty->print_cr(" ("INTPTR_FORMAT" should have been marked)", addr);
2951 _failed = true;
2952 }
2953 return true;
2954 }
2955
2956 bool failed() { return _failed; }
2957 };
2958
2959 bool CMSCollector::verify_after_remark(bool silent) {
2960 if (!silent) gclog_or_tty->print(" [Verifying CMS Marking... ");
2961 MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2962 static bool init = false;
2963
2964 assert(SafepointSynchronize::is_at_safepoint(),
2965 "Else mutations in object graph will make answer suspect");
2966 assert(have_cms_token(),
2967 "Else there may be mutual interference in use of "
2968 " verification data structures");
2969 assert(_collectorState > Marking && _collectorState <= Sweeping,
2970 "Else marking info checked here may be obsolete");
2971 assert(haveFreelistLocks(), "must hold free list locks");
2972 assert_lock_strong(bitMapLock());
2973
2974
2975 // Allocate marking bit map if not already allocated
2976 if (!init) { // first time
2977 if (!verification_mark_bm()->allocate(_span)) {
2978 return false;
2979 }
2980 init = true;
2981 }
2982
2983 assert(verification_mark_stack()->isEmpty(), "Should be empty");
2984
2985 // Turn off refs discovery -- so we will be tracing through refs.
2986 // This is as intended, because by this time
2987 // GC must already have cleared any refs that need to be cleared,
2988 // and traced those that need to be marked; moreover,
2989 // the marking done here is not going to intefere in any
2990 // way with the marking information used by GC.
2991 NoRefDiscovery no_discovery(ref_processor());
2992
2993 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
2994
2995 // Clear any marks from a previous round
2996 verification_mark_bm()->clear_all();
2997 assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
2998 verify_work_stacks_empty();
2999
3000 GenCollectedHeap* gch = GenCollectedHeap::heap();
3001 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
3002 // Update the saved marks which may affect the root scans.
3003 gch->save_marks();
3004
3005 if (CMSRemarkVerifyVariant == 1) {
3006 // In this first variant of verification, we complete
3007 // all marking, then check if the new marks-verctor is
3008 // a subset of the CMS marks-vector.
3009 verify_after_remark_work_1();
3010 } else if (CMSRemarkVerifyVariant == 2) {
3011 // In this second variant of verification, we flag an error
3012 // (i.e. an object reachable in the new marks-vector not reachable
3013 // in the CMS marks-vector) immediately, also indicating the
3014 // identify of an object (A) that references the unmarked object (B) --
3015 // presumably, a mutation to A failed to be picked up by preclean/remark?
3016 verify_after_remark_work_2();
3017 } else {
3018 warning("Unrecognized value %d for CMSRemarkVerifyVariant",
3019 CMSRemarkVerifyVariant);
3020 }
3021 if (!silent) gclog_or_tty->print(" done] ");
3022 return true;
3023 }
3024
3025 void CMSCollector::verify_after_remark_work_1() {
3026 ResourceMark rm;
3027 HandleMark hm;
3028 GenCollectedHeap* gch = GenCollectedHeap::heap();
3029
3030 // Get a clear set of claim bits for the strong roots processing to work with.
3031 ClassLoaderDataGraph::clear_claimed_marks();
3032
3033 // Mark from roots one level into CMS
3034 MarkRefsIntoClosure notOlder(_span, verification_mark_bm());
3035 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3036
3037 gch->gen_process_strong_roots(_cmsGen->level(),
3038 true, // younger gens are roots
3039 true, // activate StrongRootsScope
3040 false, // not scavenging
3041 SharedHeap::ScanningOption(roots_scanning_options()),
3042 ¬Older,
3043 true, // walk code active on stacks
3044 NULL,
3045 NULL); // SSS: Provide correct closure
3046
3047 // Now mark from the roots
3048 MarkFromRootsClosure markFromRootsClosure(this, _span,
3049 verification_mark_bm(), verification_mark_stack(),
3050 false /* don't yield */, true /* verifying */);
3051 assert(_restart_addr == NULL, "Expected pre-condition");
3052 verification_mark_bm()->iterate(&markFromRootsClosure);
3053 while (_restart_addr != NULL) {
3054 // Deal with stack overflow: by restarting at the indicated
3055 // address.
3056 HeapWord* ra = _restart_addr;
3057 markFromRootsClosure.reset(ra);
3058 _restart_addr = NULL;
3059 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
3060 }
3061 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
3062 verify_work_stacks_empty();
3063
3064 // Marking completed -- now verify that each bit marked in
3065 // verification_mark_bm() is also marked in markBitMap(); flag all
3066 // errors by printing corresponding objects.
3067 VerifyMarkedClosure vcl(markBitMap());
3068 verification_mark_bm()->iterate(&vcl);
3069 if (vcl.failed()) {
3070 gclog_or_tty->print("Verification failed");
3071 Universe::heap()->print_on(gclog_or_tty);
3072 fatal("CMS: failed marking verification after remark");
3073 }
3074 }
3075
3076 class VerifyKlassOopsKlassClosure : public KlassClosure {
3077 class VerifyKlassOopsClosure : public OopClosure {
3078 CMSBitMap* _bitmap;
3079 public:
3080 VerifyKlassOopsClosure(CMSBitMap* bitmap) : _bitmap(bitmap) { }
3081 void do_oop(oop* p) { guarantee(*p == NULL || _bitmap->isMarked((HeapWord*) *p), "Should be marked"); }
3082 void do_oop(narrowOop* p) { ShouldNotReachHere(); }
3083 } _oop_closure;
3084 public:
3085 VerifyKlassOopsKlassClosure(CMSBitMap* bitmap) : _oop_closure(bitmap) {}
3086 void do_klass(Klass* k) {
3087 k->oops_do(&_oop_closure);
3088 }
3089 };
3090
3091 void CMSCollector::verify_after_remark_work_2() {
3092 ResourceMark rm;
3093 HandleMark hm;
3094 GenCollectedHeap* gch = GenCollectedHeap::heap();
3095
3096 // Get a clear set of claim bits for the strong roots processing to work with.
3097 ClassLoaderDataGraph::clear_claimed_marks();
3098
3099 // Mark from roots one level into CMS
3100 MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
3101 markBitMap());
3102 CMKlassClosure klass_closure(¬Older);
3103
3104 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3105 gch->gen_process_strong_roots(_cmsGen->level(),
3106 true, // younger gens are roots
3107 true, // activate StrongRootsScope
3108 false, // not scavenging
3109 SharedHeap::ScanningOption(roots_scanning_options()),
3110 ¬Older,
3111 true, // walk code active on stacks
3112 NULL,
3113 &klass_closure);
3114
3115 // Now mark from the roots
3116 MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
3117 verification_mark_bm(), markBitMap(), verification_mark_stack());
3118 assert(_restart_addr == NULL, "Expected pre-condition");
3119 verification_mark_bm()->iterate(&markFromRootsClosure);
3120 while (_restart_addr != NULL) {
3121 // Deal with stack overflow: by restarting at the indicated
3122 // address.
3123 HeapWord* ra = _restart_addr;
3124 markFromRootsClosure.reset(ra);
3125 _restart_addr = NULL;
3126 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
3127 }
3128 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
3129 verify_work_stacks_empty();
3130
3131 VerifyKlassOopsKlassClosure verify_klass_oops(verification_mark_bm());
3132 ClassLoaderDataGraph::classes_do(&verify_klass_oops);
3133
3134 // Marking completed -- now verify that each bit marked in
3135 // verification_mark_bm() is also marked in markBitMap(); flag all
3136 // errors by printing corresponding objects.
3137 VerifyMarkedClosure vcl(markBitMap());
3138 verification_mark_bm()->iterate(&vcl);
3139 assert(!vcl.failed(), "Else verification above should not have succeeded");
3140 }
3141
3142 void ConcurrentMarkSweepGeneration::save_marks() {
3143 // delegate to CMS space
3144 cmsSpace()->save_marks();
3145 for (uint i = 0; i < ParallelGCThreads; i++) {
3146 _par_gc_thread_states[i]->promo.startTrackingPromotions();
3147 }
3148 }
3149
3150 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
3151 return cmsSpace()->no_allocs_since_save_marks();
3152 }
3153
3154 #define CMS_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix) \
3155 \
3156 void ConcurrentMarkSweepGeneration:: \
3157 oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) { \
3158 cl->set_generation(this); \
3159 cmsSpace()->oop_since_save_marks_iterate##nv_suffix(cl); \
3160 cl->reset_generation(); \
3161 save_marks(); \
3162 }
3163
3164 ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DEFN)
3165
3166 void
3167 ConcurrentMarkSweepGeneration::object_iterate_since_last_GC(ObjectClosure* blk)
3168 {
3169 // Not currently implemented; need to do the following. -- ysr.
3170 // dld -- I think that is used for some sort of allocation profiler. So it
3171 // really means the objects allocated by the mutator since the last
3172 // GC. We could potentially implement this cheaply by recording only
3173 // the direct allocations in a side data structure.
3174 //
3175 // I think we probably ought not to be required to support these
3176 // iterations at any arbitrary point; I think there ought to be some
3177 // call to enable/disable allocation profiling in a generation/space,
3178 // and the iterator ought to return the objects allocated in the
3179 // gen/space since the enable call, or the last iterator call (which
3180 // will probably be at a GC.) That way, for gens like CM&S that would
3181 // require some extra data structure to support this, we only pay the
3182 // cost when it's in use...
3183 cmsSpace()->object_iterate_since_last_GC(blk);
3184 }
3185
3186 void
3187 ConcurrentMarkSweepGeneration::younger_refs_iterate(OopsInGenClosure* cl) {
3188 cl->set_generation(this);
3189 younger_refs_in_space_iterate(_cmsSpace, cl);
3190 cl->reset_generation();
3191 }
3192
3193 void
3194 ConcurrentMarkSweepGeneration::oop_iterate(MemRegion mr, ExtendedOopClosure* cl) {
3195 if (freelistLock()->owned_by_self()) {
3196 Generation::oop_iterate(mr, cl);
3197 } else {
3198 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3199 Generation::oop_iterate(mr, cl);
3200 }
3201 }
3202
3203 void
3204 ConcurrentMarkSweepGeneration::oop_iterate(ExtendedOopClosure* cl) {
3205 if (freelistLock()->owned_by_self()) {
3206 Generation::oop_iterate(cl);
3207 } else {
3208 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3209 Generation::oop_iterate(cl);
3210 }
3211 }
3212
3213 void
3214 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
3215 if (freelistLock()->owned_by_self()) {
3216 Generation::object_iterate(cl);
3217 } else {
3218 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3219 Generation::object_iterate(cl);
3220 }
3221 }
3222
3223 void
3224 ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) {
3225 if (freelistLock()->owned_by_self()) {
3226 Generation::safe_object_iterate(cl);
3227 } else {
3228 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3229 Generation::safe_object_iterate(cl);
3230 }
3231 }
3232
3233 void
3234 ConcurrentMarkSweepGeneration::post_compact() {
3235 }
3236
3237 void
3238 ConcurrentMarkSweepGeneration::prepare_for_verify() {
3239 // Fix the linear allocation blocks to look like free blocks.
3240
3241 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
3242 // are not called when the heap is verified during universe initialization and
3243 // at vm shutdown.
3244 if (freelistLock()->owned_by_self()) {
3245 cmsSpace()->prepare_for_verify();
3246 } else {
3247 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
3248 cmsSpace()->prepare_for_verify();
3249 }
3250 }
3251
3252 void
3253 ConcurrentMarkSweepGeneration::verify() {
3254 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
3255 // are not called when the heap is verified during universe initialization and
3256 // at vm shutdown.
3257 if (freelistLock()->owned_by_self()) {
3258 cmsSpace()->verify();
3259 } else {
3260 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
3261 cmsSpace()->verify();
3262 }
3263 }
3264
3265 void CMSCollector::verify() {
3266 _cmsGen->verify();
3267 }
3268
3269 #ifndef PRODUCT
3270 bool CMSCollector::overflow_list_is_empty() const {
3271 assert(_num_par_pushes >= 0, "Inconsistency");
3272 if (_overflow_list == NULL) {
3273 assert(_num_par_pushes == 0, "Inconsistency");
3274 }
3275 return _overflow_list == NULL;
3276 }
3277
3278 // The methods verify_work_stacks_empty() and verify_overflow_empty()
3279 // merely consolidate assertion checks that appear to occur together frequently.
3280 void CMSCollector::verify_work_stacks_empty() const {
3281 assert(_markStack.isEmpty(), "Marking stack should be empty");
3282 assert(overflow_list_is_empty(), "Overflow list should be empty");
3283 }
3284
3285 void CMSCollector::verify_overflow_empty() const {
3286 assert(overflow_list_is_empty(), "Overflow list should be empty");
3287 assert(no_preserved_marks(), "No preserved marks");
3288 }
3289 #endif // PRODUCT
3290
3291 // Decide if we want to enable class unloading as part of the
3292 // ensuing concurrent GC cycle. We will collect and
3293 // unload classes if it's the case that:
3294 // (1) an explicit gc request has been made and the flag
3295 // ExplicitGCInvokesConcurrentAndUnloadsClasses is set, OR
3296 // (2) (a) class unloading is enabled at the command line, and
3297 // (b) old gen is getting really full
3298 // NOTE: Provided there is no change in the state of the heap between
3299 // calls to this method, it should have idempotent results. Moreover,
3300 // its results should be monotonically increasing (i.e. going from 0 to 1,
3301 // but not 1 to 0) between successive calls between which the heap was
3302 // not collected. For the implementation below, it must thus rely on
3303 // the property that concurrent_cycles_since_last_unload()
3304 // will not decrease unless a collection cycle happened and that
3305 // _cmsGen->is_too_full() are
3306 // themselves also monotonic in that sense. See check_monotonicity()
3307 // below.
3308 void CMSCollector::update_should_unload_classes() {
3309 _should_unload_classes = false;
3310 // Condition 1 above
3311 if (_full_gc_requested && ExplicitGCInvokesConcurrentAndUnloadsClasses) {
3312 _should_unload_classes = true;
3313 } else if (CMSClassUnloadingEnabled) { // Condition 2.a above
3314 // Disjuncts 2.b.(i,ii,iii) above
3315 _should_unload_classes = (concurrent_cycles_since_last_unload() >=
3316 CMSClassUnloadingMaxInterval)
3317 || _cmsGen->is_too_full();
3318 }
3319 }
3320
3321 bool ConcurrentMarkSweepGeneration::is_too_full() const {
3322 bool res = should_concurrent_collect();
3323 res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
3324 return res;
3325 }
3326
3327 void CMSCollector::setup_cms_unloading_and_verification_state() {
3328 const bool should_verify = VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
3329 || VerifyBeforeExit;
3330 const int rso = SharedHeap::SO_Strings | SharedHeap::SO_CodeCache;
3331
3332 if (should_unload_classes()) { // Should unload classes this cycle
3333 remove_root_scanning_option(rso); // Shrink the root set appropriately
3334 set_verifying(should_verify); // Set verification state for this cycle
3335 return; // Nothing else needs to be done at this time
3336 }
3337
3338 // Not unloading classes this cycle
3339 assert(!should_unload_classes(), "Inconsitency!");
3340 if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
3341 // Include symbols, strings and code cache elements to prevent their resurrection.
3342 add_root_scanning_option(rso);
3343 set_verifying(true);
3344 } else if (verifying() && !should_verify) {
3345 // We were verifying, but some verification flags got disabled.
3346 set_verifying(false);
3347 // Exclude symbols, strings and code cache elements from root scanning to
3348 // reduce IM and RM pauses.
3349 remove_root_scanning_option(rso);
3350 }
3351 }
3352
3353
3354 #ifndef PRODUCT
3355 HeapWord* CMSCollector::block_start(const void* p) const {
3356 const HeapWord* addr = (HeapWord*)p;
3357 if (_span.contains(p)) {
3358 if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
3359 return _cmsGen->cmsSpace()->block_start(p);
3360 }
3361 }
3362 return NULL;
3363 }
3364 #endif
3365
3366 HeapWord*
3367 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
3368 bool tlab,
3369 bool parallel) {
3370 CMSSynchronousYieldRequest yr;
3371 assert(!tlab, "Can't deal with TLAB allocation");
3372 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3373 expand(word_size*HeapWordSize, MinHeapDeltaBytes,
3374 CMSExpansionCause::_satisfy_allocation);
3375 if (GCExpandToAllocateDelayMillis > 0) {
3376 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3377 }
3378 return have_lock_and_allocate(word_size, tlab);
3379 }
3380
3381 // YSR: All of this generation expansion/shrinking stuff is an exact copy of
3382 // OneContigSpaceCardGeneration, which makes me wonder if we should move this
3383 // to CardGeneration and share it...
3384 bool ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes) {
3385 return CardGeneration::expand(bytes, expand_bytes);
3386 }
3387
3388 void ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes,
3389 CMSExpansionCause::Cause cause)
3390 {
3391
3392 bool success = expand(bytes, expand_bytes);
3393
3394 // remember why we expanded; this information is used
3395 // by shouldConcurrentCollect() when making decisions on whether to start
3396 // a new CMS cycle.
3397 if (success) {
3398 set_expansion_cause(cause);
3399 if (PrintGCDetails && Verbose) {
3400 gclog_or_tty->print_cr("Expanded CMS gen for %s",
3401 CMSExpansionCause::to_string(cause));
3402 }
3403 }
3404 }
3405
3406 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
3407 HeapWord* res = NULL;
3408 MutexLocker x(ParGCRareEvent_lock);
3409 while (true) {
3410 // Expansion by some other thread might make alloc OK now:
3411 res = ps->lab.alloc(word_sz);
3412 if (res != NULL) return res;
3413 // If there's not enough expansion space available, give up.
3414 if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
3415 return NULL;
3416 }
3417 // Otherwise, we try expansion.
3418 expand(word_sz*HeapWordSize, MinHeapDeltaBytes,
3419 CMSExpansionCause::_allocate_par_lab);
3420 // Now go around the loop and try alloc again;
3421 // A competing par_promote might beat us to the expansion space,
3422 // so we may go around the loop again if promotion fails agaion.
3423 if (GCExpandToAllocateDelayMillis > 0) {
3424 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3425 }
3426 }
3427 }
3428
3429
3430 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
3431 PromotionInfo* promo) {
3432 MutexLocker x(ParGCRareEvent_lock);
3433 size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
3434 while (true) {
3435 // Expansion by some other thread might make alloc OK now:
3436 if (promo->ensure_spooling_space()) {
3437 assert(promo->has_spooling_space(),
3438 "Post-condition of successful ensure_spooling_space()");
3439 return true;
3440 }
3441 // If there's not enough expansion space available, give up.
3442 if (_virtual_space.uncommitted_size() < refill_size_bytes) {
3443 return false;
3444 }
3445 // Otherwise, we try expansion.
3446 expand(refill_size_bytes, MinHeapDeltaBytes,
3447 CMSExpansionCause::_allocate_par_spooling_space);
3448 // Now go around the loop and try alloc again;
3449 // A competing allocation might beat us to the expansion space,
3450 // so we may go around the loop again if allocation fails again.
3451 if (GCExpandToAllocateDelayMillis > 0) {
3452 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3453 }
3454 }
3455 }
3456
3457
3458 void ConcurrentMarkSweepGeneration::shrink_by(size_t bytes) {
3459 assert_locked_or_safepoint(ExpandHeap_lock);
3460 // Shrink committed space
3461 _virtual_space.shrink_by(bytes);
3462 // Shrink space; this also shrinks the space's BOT
3463 _cmsSpace->set_end((HeapWord*) _virtual_space.high());
3464 size_t new_word_size = heap_word_size(_cmsSpace->capacity());
3465 // Shrink the shared block offset array
3466 _bts->resize(new_word_size);
3467 MemRegion mr(_cmsSpace->bottom(), new_word_size);
3468 // Shrink the card table
3469 Universe::heap()->barrier_set()->resize_covered_region(mr);
3470
3471 if (Verbose && PrintGC) {
3472 size_t new_mem_size = _virtual_space.committed_size();
3473 size_t old_mem_size = new_mem_size + bytes;
3474 gclog_or_tty->print_cr("Shrinking %s from " SIZE_FORMAT "K to " SIZE_FORMAT "K",
3475 name(), old_mem_size/K, new_mem_size/K);
3476 }
3477 }
3478
3479 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
3480 assert_locked_or_safepoint(Heap_lock);
3481 size_t size = ReservedSpace::page_align_size_down(bytes);
3482 if (size > 0) {
3483 shrink_by(size);
3484 }
3485 }
3486
3487 bool ConcurrentMarkSweepGeneration::grow_by(size_t bytes) {
3488 assert_locked_or_safepoint(Heap_lock);
3489 bool result = _virtual_space.expand_by(bytes);
3490 if (result) {
3491 size_t new_word_size =
3492 heap_word_size(_virtual_space.committed_size());
3493 MemRegion mr(_cmsSpace->bottom(), new_word_size);
3494 _bts->resize(new_word_size); // resize the block offset shared array
3495 Universe::heap()->barrier_set()->resize_covered_region(mr);
3496 // Hmmmm... why doesn't CFLS::set_end verify locking?
3497 // This is quite ugly; FIX ME XXX
3498 _cmsSpace->assert_locked(freelistLock());
3499 _cmsSpace->set_end((HeapWord*)_virtual_space.high());
3500
3501 // update the space and generation capacity counters
3502 if (UsePerfData) {
3503 _space_counters->update_capacity();
3504 _gen_counters->update_all();
3505 }
3506
3507 if (Verbose && PrintGC) {
3508 size_t new_mem_size = _virtual_space.committed_size();
3509 size_t old_mem_size = new_mem_size - bytes;
3510 gclog_or_tty->print_cr("Expanding %s from " SIZE_FORMAT "K by " SIZE_FORMAT "K to " SIZE_FORMAT "K",
3511 name(), old_mem_size/K, bytes/K, new_mem_size/K);
3512 }
3513 }
3514 return result;
3515 }
3516
3517 bool ConcurrentMarkSweepGeneration::grow_to_reserved() {
3518 assert_locked_or_safepoint(Heap_lock);
3519 bool success = true;
3520 const size_t remaining_bytes = _virtual_space.uncommitted_size();
3521 if (remaining_bytes > 0) {
3522 success = grow_by(remaining_bytes);
3523 DEBUG_ONLY(if (!success) warning("grow to reserved failed");)
3524 }
3525 return success;
3526 }
3527
3528 void ConcurrentMarkSweepGeneration::shrink_free_list_by(size_t bytes) {
3529 assert_locked_or_safepoint(Heap_lock);
3530 assert_lock_strong(freelistLock());
3531 if (PrintGCDetails && Verbose) {
3532 warning("Shrinking of CMS not yet implemented");
3533 }
3534 return;
3535 }
3536
3537
3538 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
3539 // phases.
3540 class CMSPhaseAccounting: public StackObj {
3541 public:
3542 CMSPhaseAccounting(CMSCollector *collector,
3543 const char *phase,
3544 bool print_cr = true);
3545 ~CMSPhaseAccounting();
3546
3547 private:
3548 CMSCollector *_collector;
3549 const char *_phase;
3550 elapsedTimer _wallclock;
3551 bool _print_cr;
3552
3553 public:
3554 // Not MT-safe; so do not pass around these StackObj's
3555 // where they may be accessed by other threads.
3556 jlong wallclock_millis() {
3557 assert(_wallclock.is_active(), "Wall clock should not stop");
3558 _wallclock.stop(); // to record time
3559 jlong ret = _wallclock.milliseconds();
3560 _wallclock.start(); // restart
3561 return ret;
3562 }
3563 };
3564
3565 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
3566 const char *phase,
3567 bool print_cr) :
3568 _collector(collector), _phase(phase), _print_cr(print_cr) {
3569
3570 if (PrintCMSStatistics != 0) {
3571 _collector->resetYields();
3572 }
3573 if (PrintGCDetails) {
3574 gclog_or_tty->date_stamp(PrintGCDateStamps);
3575 gclog_or_tty->stamp(PrintGCTimeStamps);
3576 gclog_or_tty->print_cr("[%s-concurrent-%s-start]",
3577 _collector->cmsGen()->short_name(), _phase);
3578 }
3579 _collector->resetTimer();
3580 _wallclock.start();
3581 _collector->startTimer();
3582 }
3583
3584 CMSPhaseAccounting::~CMSPhaseAccounting() {
3585 assert(_wallclock.is_active(), "Wall clock should not have stopped");
3586 _collector->stopTimer();
3587 _wallclock.stop();
3588 if (PrintGCDetails) {
3589 gclog_or_tty->date_stamp(PrintGCDateStamps);
3590 gclog_or_tty->stamp(PrintGCTimeStamps);
3591 gclog_or_tty->print("[%s-concurrent-%s: %3.3f/%3.3f secs]",
3592 _collector->cmsGen()->short_name(),
3593 _phase, _collector->timerValue(), _wallclock.seconds());
3594 if (_print_cr) {
3595 gclog_or_tty->print_cr("");
3596 }
3597 if (PrintCMSStatistics != 0) {
3598 gclog_or_tty->print_cr(" (CMS-concurrent-%s yielded %d times)", _phase,
3599 _collector->yields());
3600 }
3601 }
3602 }
3603
3604 // CMS work
3605
3606 // Checkpoint the roots into this generation from outside
3607 // this generation. [Note this initial checkpoint need only
3608 // be approximate -- we'll do a catch up phase subsequently.]
3609 void CMSCollector::checkpointRootsInitial(bool asynch) {
3610 assert(_collectorState == InitialMarking, "Wrong collector state");
3611 check_correct_thread_executing();
3612 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
3613
3614 save_heap_summary();
3615 report_heap_summary(GCWhen::BeforeGC);
3616
3617 ReferenceProcessor* rp = ref_processor();
3618 SpecializationStats::clear();
3619 assert(_restart_addr == NULL, "Control point invariant");
3620 if (asynch) {
3621 // acquire locks for subsequent manipulations
3622 MutexLockerEx x(bitMapLock(),
3623 Mutex::_no_safepoint_check_flag);
3624 checkpointRootsInitialWork(asynch);
3625 // enable ("weak") refs discovery
3626 rp->enable_discovery(true /*verify_disabled*/, true /*check_no_refs*/);
3627 _collectorState = Marking;
3628 } else {
3629 // (Weak) Refs discovery: this is controlled from genCollectedHeap::do_collection
3630 // which recognizes if we are a CMS generation, and doesn't try to turn on
3631 // discovery; verify that they aren't meddling.
3632 assert(!rp->discovery_is_atomic(),
3633 "incorrect setting of discovery predicate");
3634 assert(!rp->discovery_enabled(), "genCollectedHeap shouldn't control "
3635 "ref discovery for this generation kind");
3636 // already have locks
3637 checkpointRootsInitialWork(asynch);
3638 // now enable ("weak") refs discovery
3639 rp->enable_discovery(true /*verify_disabled*/, false /*verify_no_refs*/);
3640 _collectorState = Marking;
3641 }
3642 SpecializationStats::print();
3643 }
3644
3645 void CMSCollector::checkpointRootsInitialWork(bool asynch) {
3646 assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
3647 assert(_collectorState == InitialMarking, "just checking");
3648
3649 // If there has not been a GC[n-1] since last GC[n] cycle completed,
3650 // precede our marking with a collection of all
3651 // younger generations to keep floating garbage to a minimum.
3652 // XXX: we won't do this for now -- it's an optimization to be done later.
3653
3654 // already have locks
3655 assert_lock_strong(bitMapLock());
3656 assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
3657
3658 // Setup the verification and class unloading state for this
3659 // CMS collection cycle.
3660 setup_cms_unloading_and_verification_state();
3661
3662 NOT_PRODUCT(GCTraceTime t("\ncheckpointRootsInitialWork",
3663 PrintGCDetails && Verbose, true, _gc_timer_cm);)
3664 if (UseAdaptiveSizePolicy) {
3665 size_policy()->checkpoint_roots_initial_begin();
3666 }
3667
3668 // Reset all the PLAB chunk arrays if necessary.
3669 if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
3670 reset_survivor_plab_arrays();
3671 }
3672
3673 ResourceMark rm;
3674 HandleMark hm;
3675
3676 FalseClosure falseClosure;
3677 // In the case of a synchronous collection, we will elide the
3678 // remark step, so it's important to catch all the nmethod oops
3679 // in this step.
3680 // The final 'true' flag to gen_process_strong_roots will ensure this.
3681 // If 'async' is true, we can relax the nmethod tracing.
3682 MarkRefsIntoClosure notOlder(_span, &_markBitMap);
3683 GenCollectedHeap* gch = GenCollectedHeap::heap();
3684
3685 verify_work_stacks_empty();
3686 verify_overflow_empty();
3687
3688 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
3689 // Update the saved marks which may affect the root scans.
3690 gch->save_marks();
3691
3692 // weak reference processing has not started yet.
3693 ref_processor()->set_enqueuing_is_done(false);
3694
3695 // Need to remember all newly created CLDs,
3696 // so that we can guarantee that the remark finds them.
3697 ClassLoaderDataGraph::remember_new_clds(true);
3698
3699 // Whenever a CLD is found, it will be claimed before proceeding to mark
3700 // the klasses. The claimed marks need to be cleared before marking starts.
3701 ClassLoaderDataGraph::clear_claimed_marks();
3702
3703 if (CMSPrintEdenSurvivorChunks) {
3704 print_eden_and_survivor_chunk_arrays();
3705 }
3706
3707 CMKlassClosure klass_closure(¬Older);
3708 {
3709 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
3710 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3711 gch->gen_process_strong_roots(_cmsGen->level(),
3712 true, // younger gens are roots
3713 true, // activate StrongRootsScope
3714 false, // not scavenging
3715 SharedHeap::ScanningOption(roots_scanning_options()),
3716 ¬Older,
3717 true, // walk all of code cache if (so & SO_CodeCache)
3718 NULL,
3719 &klass_closure);
3720 }
3721
3722 // Clear mod-union table; it will be dirtied in the prologue of
3723 // CMS generation per each younger generation collection.
3724
3725 assert(_modUnionTable.isAllClear(),
3726 "Was cleared in most recent final checkpoint phase"
3727 " or no bits are set in the gc_prologue before the start of the next "
3728 "subsequent marking phase.");
3729
3730 assert(_ct->klass_rem_set()->mod_union_is_clear(), "Must be");
3731
3732 // Save the end of the used_region of the constituent generations
3733 // to be used to limit the extent of sweep in each generation.
3734 save_sweep_limits();
3735 if (UseAdaptiveSizePolicy) {
3736 size_policy()->checkpoint_roots_initial_end(gch->gc_cause());
3737 }
3738 verify_overflow_empty();
3739 }
3740
3741 bool CMSCollector::markFromRoots(bool asynch) {
3742 // we might be tempted to assert that:
3743 // assert(asynch == !SafepointSynchronize::is_at_safepoint(),
3744 // "inconsistent argument?");
3745 // However that wouldn't be right, because it's possible that
3746 // a safepoint is indeed in progress as a younger generation
3747 // stop-the-world GC happens even as we mark in this generation.
3748 assert(_collectorState == Marking, "inconsistent state?");
3749 check_correct_thread_executing();
3750 verify_overflow_empty();
3751
3752 bool res;
3753 if (asynch) {
3754
3755 // Start the timers for adaptive size policy for the concurrent phases
3756 // Do it here so that the foreground MS can use the concurrent
3757 // timer since a foreground MS might has the sweep done concurrently
3758 // or STW.
3759 if (UseAdaptiveSizePolicy) {
3760 size_policy()->concurrent_marking_begin();
3761 }
3762
3763 // Weak ref discovery note: We may be discovering weak
3764 // refs in this generation concurrent (but interleaved) with
3765 // weak ref discovery by a younger generation collector.
3766
3767 CMSTokenSyncWithLocks ts(true, bitMapLock());
3768 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3769 CMSPhaseAccounting pa(this, "mark", !PrintGCDetails);
3770 res = markFromRootsWork(asynch);
3771 if (res) {
3772 _collectorState = Precleaning;
3773 } else { // We failed and a foreground collection wants to take over
3774 assert(_foregroundGCIsActive, "internal state inconsistency");
3775 assert(_restart_addr == NULL, "foreground will restart from scratch");
3776 if (PrintGCDetails) {
3777 gclog_or_tty->print_cr("bailing out to foreground collection");
3778 }
3779 }
3780 if (UseAdaptiveSizePolicy) {
3781 size_policy()->concurrent_marking_end();
3782 }
3783 } else {
3784 assert(SafepointSynchronize::is_at_safepoint(),
3785 "inconsistent with asynch == false");
3786 if (UseAdaptiveSizePolicy) {
3787 size_policy()->ms_collection_marking_begin();
3788 }
3789 // already have locks
3790 res = markFromRootsWork(asynch);
3791 _collectorState = FinalMarking;
3792 if (UseAdaptiveSizePolicy) {
3793 GenCollectedHeap* gch = GenCollectedHeap::heap();
3794 size_policy()->ms_collection_marking_end(gch->gc_cause());
3795 }
3796 }
3797 verify_overflow_empty();
3798 return res;
3799 }
3800
3801 bool CMSCollector::markFromRootsWork(bool asynch) {
3802 // iterate over marked bits in bit map, doing a full scan and mark
3803 // from these roots using the following algorithm:
3804 // . if oop is to the right of the current scan pointer,
3805 // mark corresponding bit (we'll process it later)
3806 // . else (oop is to left of current scan pointer)
3807 // push oop on marking stack
3808 // . drain the marking stack
3809
3810 // Note that when we do a marking step we need to hold the
3811 // bit map lock -- recall that direct allocation (by mutators)
3812 // and promotion (by younger generation collectors) is also
3813 // marking the bit map. [the so-called allocate live policy.]
3814 // Because the implementation of bit map marking is not
3815 // robust wrt simultaneous marking of bits in the same word,
3816 // we need to make sure that there is no such interference
3817 // between concurrent such updates.
3818
3819 // already have locks
3820 assert_lock_strong(bitMapLock());
3821
3822 verify_work_stacks_empty();
3823 verify_overflow_empty();
3824 bool result = false;
3825 if (CMSConcurrentMTEnabled && ConcGCThreads > 0) {
3826 result = do_marking_mt(asynch);
3827 } else {
3828 result = do_marking_st(asynch);
3829 }
3830 return result;
3831 }
3832
3833 // Forward decl
3834 class CMSConcMarkingTask;
3835
3836 class CMSConcMarkingTerminator: public ParallelTaskTerminator {
3837 CMSCollector* _collector;
3838 CMSConcMarkingTask* _task;
3839 public:
3840 virtual void yield();
3841
3842 // "n_threads" is the number of threads to be terminated.
3843 // "queue_set" is a set of work queues of other threads.
3844 // "collector" is the CMS collector associated with this task terminator.
3845 // "yield" indicates whether we need the gang as a whole to yield.
3846 CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
3847 ParallelTaskTerminator(n_threads, queue_set),
3848 _collector(collector) { }
3849
3850 void set_task(CMSConcMarkingTask* task) {
3851 _task = task;
3852 }
3853 };
3854
3855 class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator {
3856 CMSConcMarkingTask* _task;
3857 public:
3858 bool should_exit_termination();
3859 void set_task(CMSConcMarkingTask* task) {
3860 _task = task;
3861 }
3862 };
3863
3864 // MT Concurrent Marking Task
3865 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3866 CMSCollector* _collector;
3867 int _n_workers; // requested/desired # workers
3868 bool _asynch;
3869 bool _result;
3870 CompactibleFreeListSpace* _cms_space;
3871 char _pad_front[64]; // padding to ...
3872 HeapWord* _global_finger; // ... avoid sharing cache line
3873 char _pad_back[64];
3874 HeapWord* _restart_addr;
3875
3876 // Exposed here for yielding support
3877 Mutex* const _bit_map_lock;
3878
3879 // The per thread work queues, available here for stealing
3880 OopTaskQueueSet* _task_queues;
3881
3882 // Termination (and yielding) support
3883 CMSConcMarkingTerminator _term;
3884 CMSConcMarkingTerminatorTerminator _term_term;
3885
3886 public:
3887 CMSConcMarkingTask(CMSCollector* collector,
3888 CompactibleFreeListSpace* cms_space,
3889 bool asynch,
3890 YieldingFlexibleWorkGang* workers,
3891 OopTaskQueueSet* task_queues):
3892 YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3893 _collector(collector),
3894 _cms_space(cms_space),
3895 _asynch(asynch), _n_workers(0), _result(true),
3896 _task_queues(task_queues),
3897 _term(_n_workers, task_queues, _collector),
3898 _bit_map_lock(collector->bitMapLock())
3899 {
3900 _requested_size = _n_workers;
3901 _term.set_task(this);
3902 _term_term.set_task(this);
3903 _restart_addr = _global_finger = _cms_space->bottom();
3904 }
3905
3906
3907 OopTaskQueueSet* task_queues() { return _task_queues; }
3908
3909 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3910
3911 HeapWord** global_finger_addr() { return &_global_finger; }
3912
3913 CMSConcMarkingTerminator* terminator() { return &_term; }
3914
3915 virtual void set_for_termination(int active_workers) {
3916 terminator()->reset_for_reuse(active_workers);
3917 }
3918
3919 void work(uint worker_id);
3920 bool should_yield() {
3921 return ConcurrentMarkSweepThread::should_yield()
3922 && !_collector->foregroundGCIsActive()
3923 && _asynch;
3924 }
3925
3926 virtual void coordinator_yield(); // stuff done by coordinator
3927 bool result() { return _result; }
3928
3929 void reset(HeapWord* ra) {
3930 assert(_global_finger >= _cms_space->end(), "Postcondition of ::work(i)");
3931 _restart_addr = _global_finger = ra;
3932 _term.reset_for_reuse();
3933 }
3934
3935 static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3936 OopTaskQueue* work_q);
3937
3938 private:
3939 void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3940 void do_work_steal(int i);
3941 void bump_global_finger(HeapWord* f);
3942 };
3943
3944 bool CMSConcMarkingTerminatorTerminator::should_exit_termination() {
3945 assert(_task != NULL, "Error");
3946 return _task->yielding();
3947 // Note that we do not need the disjunct || _task->should_yield() above
3948 // because we want terminating threads to yield only if the task
3949 // is already in the midst of yielding, which happens only after at least one
3950 // thread has yielded.
3951 }
3952
3953 void CMSConcMarkingTerminator::yield() {
3954 if (_task->should_yield()) {
3955 _task->yield();
3956 } else {
3957 ParallelTaskTerminator::yield();
3958 }
3959 }
3960
3961 ////////////////////////////////////////////////////////////////
3962 // Concurrent Marking Algorithm Sketch
3963 ////////////////////////////////////////////////////////////////
3964 // Until all tasks exhausted (both spaces):
3965 // -- claim next available chunk
3966 // -- bump global finger via CAS
3967 // -- find first object that starts in this chunk
3968 // and start scanning bitmap from that position
3969 // -- scan marked objects for oops
3970 // -- CAS-mark target, and if successful:
3971 // . if target oop is above global finger (volatile read)
3972 // nothing to do
3973 // . if target oop is in chunk and above local finger
3974 // then nothing to do
3975 // . else push on work-queue
3976 // -- Deal with possible overflow issues:
3977 // . local work-queue overflow causes stuff to be pushed on
3978 // global (common) overflow queue
3979 // . always first empty local work queue
3980 // . then get a batch of oops from global work queue if any
3981 // . then do work stealing
3982 // -- When all tasks claimed (both spaces)
3983 // and local work queue empty,
3984 // then in a loop do:
3985 // . check global overflow stack; steal a batch of oops and trace
3986 // . try to steal from other threads oif GOS is empty
3987 // . if neither is available, offer termination
3988 // -- Terminate and return result
3989 //
3990 void CMSConcMarkingTask::work(uint worker_id) {
3991 elapsedTimer _timer;
3992 ResourceMark rm;
3993 HandleMark hm;
3994
3995 DEBUG_ONLY(_collector->verify_overflow_empty();)
3996
3997 // Before we begin work, our work queue should be empty
3998 assert(work_queue(worker_id)->size() == 0, "Expected to be empty");
3999 // Scan the bitmap covering _cms_space, tracing through grey objects.
4000 _timer.start();
4001 do_scan_and_mark(worker_id, _cms_space);
4002 _timer.stop();
4003 if (PrintCMSStatistics != 0) {
4004 gclog_or_tty->print_cr("Finished cms space scanning in %dth thread: %3.3f sec",
4005 worker_id, _timer.seconds());
4006 // XXX: need xxx/xxx type of notation, two timers
4007 }
4008
4009 // ... do work stealing
4010 _timer.reset();
4011 _timer.start();
4012 do_work_steal(worker_id);
4013 _timer.stop();
4014 if (PrintCMSStatistics != 0) {
4015 gclog_or_tty->print_cr("Finished work stealing in %dth thread: %3.3f sec",
4016 worker_id, _timer.seconds());
4017 // XXX: need xxx/xxx type of notation, two timers
4018 }
4019 assert(_collector->_markStack.isEmpty(), "Should have been emptied");
4020 assert(work_queue(worker_id)->size() == 0, "Should have been emptied");
4021 // Note that under the current task protocol, the
4022 // following assertion is true even of the spaces
4023 // expanded since the completion of the concurrent
4024 // marking. XXX This will likely change under a strict
4025 // ABORT semantics.
4026 // After perm removal the comparison was changed to
4027 // greater than or equal to from strictly greater than.
4028 // Before perm removal the highest address sweep would
4029 // have been at the end of perm gen but now is at the
4030 // end of the tenured gen.
4031 assert(_global_finger >= _cms_space->end(),
4032 "All tasks have been completed");
4033 DEBUG_ONLY(_collector->verify_overflow_empty();)
4034 }
4035
4036 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
4037 HeapWord* read = _global_finger;
4038 HeapWord* cur = read;
4039 while (f > read) {
4040 cur = read;
4041 read = (HeapWord*) Atomic::cmpxchg_ptr(f, &_global_finger, cur);
4042 if (cur == read) {
4043 // our cas succeeded
4044 assert(_global_finger >= f, "protocol consistency");
4045 break;
4046 }
4047 }
4048 }
4049
4050 // This is really inefficient, and should be redone by
4051 // using (not yet available) block-read and -write interfaces to the
4052 // stack and the work_queue. XXX FIX ME !!!
4053 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
4054 OopTaskQueue* work_q) {
4055 // Fast lock-free check
4056 if (ovflw_stk->length() == 0) {
4057 return false;
4058 }
4059 assert(work_q->size() == 0, "Shouldn't steal");
4060 MutexLockerEx ml(ovflw_stk->par_lock(),
4061 Mutex::_no_safepoint_check_flag);
4062 // Grab up to 1/4 the size of the work queue
4063 size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
4064 (size_t)ParGCDesiredObjsFromOverflowList);
4065 num = MIN2(num, ovflw_stk->length());
4066 for (int i = (int) num; i > 0; i--) {
4067 oop cur = ovflw_stk->pop();
4068 assert(cur != NULL, "Counted wrong?");
4069 work_q->push(cur);
4070 }
4071 return num > 0;
4072 }
4073
4074 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
4075 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
4076 int n_tasks = pst->n_tasks();
4077 // We allow that there may be no tasks to do here because
4078 // we are restarting after a stack overflow.
4079 assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
4080 uint nth_task = 0;
4081
4082 HeapWord* aligned_start = sp->bottom();
4083 if (sp->used_region().contains(_restart_addr)) {
4084 // Align down to a card boundary for the start of 0th task
4085 // for this space.
4086 aligned_start =
4087 (HeapWord*)align_size_down((uintptr_t)_restart_addr,
4088 CardTableModRefBS::card_size);
4089 }
4090
4091 size_t chunk_size = sp->marking_task_size();
4092 while (!pst->is_task_claimed(/* reference */ nth_task)) {
4093 // Having claimed the nth task in this space,
4094 // compute the chunk that it corresponds to:
4095 MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
4096 aligned_start + (nth_task+1)*chunk_size);
4097 // Try and bump the global finger via a CAS;
4098 // note that we need to do the global finger bump
4099 // _before_ taking the intersection below, because
4100 // the task corresponding to that region will be
4101 // deemed done even if the used_region() expands
4102 // because of allocation -- as it almost certainly will
4103 // during start-up while the threads yield in the
4104 // closure below.
4105 HeapWord* finger = span.end();
4106 bump_global_finger(finger); // atomically
4107 // There are null tasks here corresponding to chunks
4108 // beyond the "top" address of the space.
4109 span = span.intersection(sp->used_region());
4110 if (!span.is_empty()) { // Non-null task
4111 HeapWord* prev_obj;
4112 assert(!span.contains(_restart_addr) || nth_task == 0,
4113 "Inconsistency");
4114 if (nth_task == 0) {
4115 // For the 0th task, we'll not need to compute a block_start.
4116 if (span.contains(_restart_addr)) {
4117 // In the case of a restart because of stack overflow,
4118 // we might additionally skip a chunk prefix.
4119 prev_obj = _restart_addr;
4120 } else {
4121 prev_obj = span.start();
4122 }
4123 } else {
4124 // We want to skip the first object because
4125 // the protocol is to scan any object in its entirety
4126 // that _starts_ in this span; a fortiori, any
4127 // object starting in an earlier span is scanned
4128 // as part of an earlier claimed task.
4129 // Below we use the "careful" version of block_start
4130 // so we do not try to navigate uninitialized objects.
4131 prev_obj = sp->block_start_careful(span.start());
4132 // Below we use a variant of block_size that uses the
4133 // Printezis bits to avoid waiting for allocated
4134 // objects to become initialized/parsable.
4135 while (prev_obj < span.start()) {
4136 size_t sz = sp->block_size_no_stall(prev_obj, _collector);
4137 if (sz > 0) {
4138 prev_obj += sz;
4139 } else {
4140 // In this case we may end up doing a bit of redundant
4141 // scanning, but that appears unavoidable, short of
4142 // locking the free list locks; see bug 6324141.
4143 break;
4144 }
4145 }
4146 }
4147 if (prev_obj < span.end()) {
4148 MemRegion my_span = MemRegion(prev_obj, span.end());
4149 // Do the marking work within a non-empty span --
4150 // the last argument to the constructor indicates whether the
4151 // iteration should be incremental with periodic yields.
4152 Par_MarkFromRootsClosure cl(this, _collector, my_span,
4153 &_collector->_markBitMap,
4154 work_queue(i),
4155 &_collector->_markStack,
4156 _asynch);
4157 _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
4158 } // else nothing to do for this task
4159 } // else nothing to do for this task
4160 }
4161 // We'd be tempted to assert here that since there are no
4162 // more tasks left to claim in this space, the global_finger
4163 // must exceed space->top() and a fortiori space->end(). However,
4164 // that would not quite be correct because the bumping of
4165 // global_finger occurs strictly after the claiming of a task,
4166 // so by the time we reach here the global finger may not yet
4167 // have been bumped up by the thread that claimed the last
4168 // task.
4169 pst->all_tasks_completed();
4170 }
4171
4172 class Par_ConcMarkingClosure: public CMSOopClosure {
4173 private:
4174 CMSCollector* _collector;
4175 CMSConcMarkingTask* _task;
4176 MemRegion _span;
4177 CMSBitMap* _bit_map;
4178 CMSMarkStack* _overflow_stack;
4179 OopTaskQueue* _work_queue;
4180 protected:
4181 DO_OOP_WORK_DEFN
4182 public:
4183 Par_ConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue,
4184 CMSBitMap* bit_map, CMSMarkStack* overflow_stack):
4185 CMSOopClosure(collector->ref_processor()),
4186 _collector(collector),
4187 _task(task),
4188 _span(collector->_span),
4189 _work_queue(work_queue),
4190 _bit_map(bit_map),
4191 _overflow_stack(overflow_stack)
4192 { }
4193 virtual void do_oop(oop* p);
4194 virtual void do_oop(narrowOop* p);
4195
4196 void trim_queue(size_t max);
4197 void handle_stack_overflow(HeapWord* lost);
4198 void do_yield_check() {
4199 if (_task->should_yield()) {
4200 _task->yield();
4201 }
4202 }
4203 };
4204
4205 // Grey object scanning during work stealing phase --
4206 // the salient assumption here is that any references
4207 // that are in these stolen objects being scanned must
4208 // already have been initialized (else they would not have
4209 // been published), so we do not need to check for
4210 // uninitialized objects before pushing here.
4211 void Par_ConcMarkingClosure::do_oop(oop obj) {
4212 assert(obj->is_oop_or_null(true), "expected an oop or NULL");
4213 HeapWord* addr = (HeapWord*)obj;
4214 // Check if oop points into the CMS generation
4215 // and is not marked
4216 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
4217 // a white object ...
4218 // If we manage to "claim" the object, by being the
4219 // first thread to mark it, then we push it on our
4220 // marking stack
4221 if (_bit_map->par_mark(addr)) { // ... now grey
4222 // push on work queue (grey set)
4223 bool simulate_overflow = false;
4224 NOT_PRODUCT(
4225 if (CMSMarkStackOverflowALot &&
4226 _collector->simulate_overflow()) {
4227 // simulate a stack overflow
4228 simulate_overflow = true;
4229 }
4230 )
4231 if (simulate_overflow ||
4232 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
4233 // stack overflow
4234 if (PrintCMSStatistics != 0) {
4235 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
4236 SIZE_FORMAT, _overflow_stack->capacity());
4237 }
4238 // We cannot assert that the overflow stack is full because
4239 // it may have been emptied since.
4240 assert(simulate_overflow ||
4241 _work_queue->size() == _work_queue->max_elems(),
4242 "Else push should have succeeded");
4243 handle_stack_overflow(addr);
4244 }
4245 } // Else, some other thread got there first
4246 do_yield_check();
4247 }
4248 }
4249
4250 void Par_ConcMarkingClosure::do_oop(oop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
4251 void Par_ConcMarkingClosure::do_oop(narrowOop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
4252
4253 void Par_ConcMarkingClosure::trim_queue(size_t max) {
4254 while (_work_queue->size() > max) {
4255 oop new_oop;
4256 if (_work_queue->pop_local(new_oop)) {
4257 assert(new_oop->is_oop(), "Should be an oop");
4258 assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
4259 assert(_span.contains((HeapWord*)new_oop), "Not in span");
4260 new_oop->oop_iterate(this); // do_oop() above
4261 do_yield_check();
4262 }
4263 }
4264 }
4265
4266 // Upon stack overflow, we discard (part of) the stack,
4267 // remembering the least address amongst those discarded
4268 // in CMSCollector's _restart_address.
4269 void Par_ConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
4270 // We need to do this under a mutex to prevent other
4271 // workers from interfering with the work done below.
4272 MutexLockerEx ml(_overflow_stack->par_lock(),
4273 Mutex::_no_safepoint_check_flag);
4274 // Remember the least grey address discarded
4275 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
4276 _collector->lower_restart_addr(ra);
4277 _overflow_stack->reset(); // discard stack contents
4278 _overflow_stack->expand(); // expand the stack if possible
4279 }
4280
4281
4282 void CMSConcMarkingTask::do_work_steal(int i) {
4283 OopTaskQueue* work_q = work_queue(i);
4284 oop obj_to_scan;
4285 CMSBitMap* bm = &(_collector->_markBitMap);
4286 CMSMarkStack* ovflw = &(_collector->_markStack);
4287 int* seed = _collector->hash_seed(i);
4288 Par_ConcMarkingClosure cl(_collector, this, work_q, bm, ovflw);
4289 while (true) {
4290 cl.trim_queue(0);
4291 assert(work_q->size() == 0, "Should have been emptied above");
4292 if (get_work_from_overflow_stack(ovflw, work_q)) {
4293 // Can't assert below because the work obtained from the
4294 // overflow stack may already have been stolen from us.
4295 // assert(work_q->size() > 0, "Work from overflow stack");
4296 continue;
4297 } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
4298 assert(obj_to_scan->is_oop(), "Should be an oop");
4299 assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
4300 obj_to_scan->oop_iterate(&cl);
4301 } else if (terminator()->offer_termination(&_term_term)) {
4302 assert(work_q->size() == 0, "Impossible!");
4303 break;
4304 } else if (yielding() || should_yield()) {
4305 yield();
4306 }
4307 }
4308 }
4309
4310 // This is run by the CMS (coordinator) thread.
4311 void CMSConcMarkingTask::coordinator_yield() {
4312 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
4313 "CMS thread should hold CMS token");
4314 // First give up the locks, then yield, then re-lock
4315 // We should probably use a constructor/destructor idiom to
4316 // do this unlock/lock or modify the MutexUnlocker class to
4317 // serve our purpose. XXX
4318 assert_lock_strong(_bit_map_lock);
4319 _bit_map_lock->unlock();
4320 ConcurrentMarkSweepThread::desynchronize(true);
4321 ConcurrentMarkSweepThread::acknowledge_yield_request();
4322 _collector->stopTimer();
4323 if (PrintCMSStatistics != 0) {
4324 _collector->incrementYields();
4325 }
4326 _collector->icms_wait();
4327
4328 // It is possible for whichever thread initiated the yield request
4329 // not to get a chance to wake up and take the bitmap lock between
4330 // this thread releasing it and reacquiring it. So, while the
4331 // should_yield() flag is on, let's sleep for a bit to give the
4332 // other thread a chance to wake up. The limit imposed on the number
4333 // of iterations is defensive, to avoid any unforseen circumstances
4334 // putting us into an infinite loop. Since it's always been this
4335 // (coordinator_yield()) method that was observed to cause the
4336 // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
4337 // which is by default non-zero. For the other seven methods that
4338 // also perform the yield operation, as are using a different
4339 // parameter (CMSYieldSleepCount) which is by default zero. This way we
4340 // can enable the sleeping for those methods too, if necessary.
4341 // See 6442774.
4342 //
4343 // We really need to reconsider the synchronization between the GC
4344 // thread and the yield-requesting threads in the future and we
4345 // should really use wait/notify, which is the recommended
4346 // way of doing this type of interaction. Additionally, we should
4347 // consolidate the eight methods that do the yield operation and they
4348 // are almost identical into one for better maintenability and
4349 // readability. See 6445193.
4350 //
4351 // Tony 2006.06.29
4352 for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
4353 ConcurrentMarkSweepThread::should_yield() &&
4354 !CMSCollector::foregroundGCIsActive(); ++i) {
4355 os::sleep(Thread::current(), 1, false);
4356 ConcurrentMarkSweepThread::acknowledge_yield_request();
4357 }
4358
4359 ConcurrentMarkSweepThread::synchronize(true);
4360 _bit_map_lock->lock_without_safepoint_check();
4361 _collector->startTimer();
4362 }
4363
4364 bool CMSCollector::do_marking_mt(bool asynch) {
4365 assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition");
4366 int num_workers = AdaptiveSizePolicy::calc_active_conc_workers(
4367 conc_workers()->total_workers(),
4368 conc_workers()->active_workers(),
4369 Threads::number_of_non_daemon_threads());
4370 conc_workers()->set_active_workers(num_workers);
4371
4372 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
4373
4374 CMSConcMarkingTask tsk(this,
4375 cms_space,
4376 asynch,
4377 conc_workers(),
4378 task_queues());
4379
4380 // Since the actual number of workers we get may be different
4381 // from the number we requested above, do we need to do anything different
4382 // below? In particular, may be we need to subclass the SequantialSubTasksDone
4383 // class?? XXX
4384 cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
4385
4386 // Refs discovery is already non-atomic.
4387 assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
4388 assert(ref_processor()->discovery_is_mt(), "Discovery should be MT");
4389 conc_workers()->start_task(&tsk);
4390 while (tsk.yielded()) {
4391 tsk.coordinator_yield();
4392 conc_workers()->continue_task(&tsk);
4393 }
4394 // If the task was aborted, _restart_addr will be non-NULL
4395 assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
4396 while (_restart_addr != NULL) {
4397 // XXX For now we do not make use of ABORTED state and have not
4398 // yet implemented the right abort semantics (even in the original
4399 // single-threaded CMS case). That needs some more investigation
4400 // and is deferred for now; see CR# TBF. 07252005YSR. XXX
4401 assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
4402 // If _restart_addr is non-NULL, a marking stack overflow
4403 // occurred; we need to do a fresh marking iteration from the
4404 // indicated restart address.
4405 if (_foregroundGCIsActive && asynch) {
4406 // We may be running into repeated stack overflows, having
4407 // reached the limit of the stack size, while making very
4408 // slow forward progress. It may be best to bail out and
4409 // let the foreground collector do its job.
4410 // Clear _restart_addr, so that foreground GC
4411 // works from scratch. This avoids the headache of
4412 // a "rescan" which would otherwise be needed because
4413 // of the dirty mod union table & card table.
4414 _restart_addr = NULL;
4415 return false;
4416 }
4417 // Adjust the task to restart from _restart_addr
4418 tsk.reset(_restart_addr);
4419 cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
4420 _restart_addr);
4421 _restart_addr = NULL;
4422 // Get the workers going again
4423 conc_workers()->start_task(&tsk);
4424 while (tsk.yielded()) {
4425 tsk.coordinator_yield();
4426 conc_workers()->continue_task(&tsk);
4427 }
4428 }
4429 assert(tsk.completed(), "Inconsistency");
4430 assert(tsk.result() == true, "Inconsistency");
4431 return true;
4432 }
4433
4434 bool CMSCollector::do_marking_st(bool asynch) {
4435 ResourceMark rm;
4436 HandleMark hm;
4437
4438 // Temporarily make refs discovery single threaded (non-MT)
4439 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
4440 MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
4441 &_markStack, CMSYield && asynch);
4442 // the last argument to iterate indicates whether the iteration
4443 // should be incremental with periodic yields.
4444 _markBitMap.iterate(&markFromRootsClosure);
4445 // If _restart_addr is non-NULL, a marking stack overflow
4446 // occurred; we need to do a fresh iteration from the
4447 // indicated restart address.
4448 while (_restart_addr != NULL) {
4449 if (_foregroundGCIsActive && asynch) {
4450 // We may be running into repeated stack overflows, having
4451 // reached the limit of the stack size, while making very
4452 // slow forward progress. It may be best to bail out and
4453 // let the foreground collector do its job.
4454 // Clear _restart_addr, so that foreground GC
4455 // works from scratch. This avoids the headache of
4456 // a "rescan" which would otherwise be needed because
4457 // of the dirty mod union table & card table.
4458 _restart_addr = NULL;
4459 return false; // indicating failure to complete marking
4460 }
4461 // Deal with stack overflow:
4462 // we restart marking from _restart_addr
4463 HeapWord* ra = _restart_addr;
4464 markFromRootsClosure.reset(ra);
4465 _restart_addr = NULL;
4466 _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
4467 }
4468 return true;
4469 }
4470
4471 void CMSCollector::preclean() {
4472 check_correct_thread_executing();
4473 assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
4474 verify_work_stacks_empty();
4475 verify_overflow_empty();
4476 _abort_preclean = false;
4477 if (CMSPrecleaningEnabled) {
4478 if (!CMSEdenChunksRecordAlways) {
4479 _eden_chunk_index = 0;
4480 }
4481 size_t used = get_eden_used();
4482 size_t capacity = get_eden_capacity();
4483 // Don't start sampling unless we will get sufficiently
4484 // many samples.
4485 if (used < (capacity/(CMSScheduleRemarkSamplingRatio * 100)
4486 * CMSScheduleRemarkEdenPenetration)) {
4487 _start_sampling = true;
4488 } else {
4489 _start_sampling = false;
4490 }
4491 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
4492 CMSPhaseAccounting pa(this, "preclean", !PrintGCDetails);
4493 preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
4494 }
4495 CMSTokenSync x(true); // is cms thread
4496 if (CMSPrecleaningEnabled) {
4497 sample_eden();
4498 _collectorState = AbortablePreclean;
4499 } else {
4500 _collectorState = FinalMarking;
4501 }
4502 verify_work_stacks_empty();
4503 verify_overflow_empty();
4504 }
4505
4506 // Try and schedule the remark such that young gen
4507 // occupancy is CMSScheduleRemarkEdenPenetration %.
4508 void CMSCollector::abortable_preclean() {
4509 check_correct_thread_executing();
4510 assert(CMSPrecleaningEnabled, "Inconsistent control state");
4511 assert(_collectorState == AbortablePreclean, "Inconsistent control state");
4512
4513 // If Eden's current occupancy is below this threshold,
4514 // immediately schedule the remark; else preclean
4515 // past the next scavenge in an effort to
4516 // schedule the pause as described avove. By choosing
4517 // CMSScheduleRemarkEdenSizeThreshold >= max eden size
4518 // we will never do an actual abortable preclean cycle.
4519 if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
4520 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
4521 CMSPhaseAccounting pa(this, "abortable-preclean", !PrintGCDetails);
4522 // We need more smarts in the abortable preclean
4523 // loop below to deal with cases where allocation
4524 // in young gen is very very slow, and our precleaning
4525 // is running a losing race against a horde of
4526 // mutators intent on flooding us with CMS updates
4527 // (dirty cards).
4528 // One, admittedly dumb, strategy is to give up
4529 // after a certain number of abortable precleaning loops
4530 // or after a certain maximum time. We want to make
4531 // this smarter in the next iteration.
4532 // XXX FIX ME!!! YSR
4533 size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
4534 while (!(should_abort_preclean() ||
4535 ConcurrentMarkSweepThread::should_terminate())) {
4536 workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
4537 cumworkdone += workdone;
4538 loops++;
4539 // Voluntarily terminate abortable preclean phase if we have
4540 // been at it for too long.
4541 if ((CMSMaxAbortablePrecleanLoops != 0) &&
4542 loops >= CMSMaxAbortablePrecleanLoops) {
4543 if (PrintGCDetails) {
4544 gclog_or_tty->print(" CMS: abort preclean due to loops ");
4545 }
4546 break;
4547 }
4548 if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
4549 if (PrintGCDetails) {
4550 gclog_or_tty->print(" CMS: abort preclean due to time ");
4551 }
4552 break;
4553 }
4554 // If we are doing little work each iteration, we should
4555 // take a short break.
4556 if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
4557 // Sleep for some time, waiting for work to accumulate
4558 stopTimer();
4559 cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
4560 startTimer();
4561 waited++;
4562 }
4563 }
4564 if (PrintCMSStatistics > 0) {
4565 gclog_or_tty->print(" [%d iterations, %d waits, %d cards)] ",
4566 loops, waited, cumworkdone);
4567 }
4568 }
4569 CMSTokenSync x(true); // is cms thread
4570 if (_collectorState != Idling) {
4571 assert(_collectorState == AbortablePreclean,
4572 "Spontaneous state transition?");
4573 _collectorState = FinalMarking;
4574 } // Else, a foreground collection completed this CMS cycle.
4575 return;
4576 }
4577
4578 // Respond to an Eden sampling opportunity
4579 void CMSCollector::sample_eden() {
4580 // Make sure a young gc cannot sneak in between our
4581 // reading and recording of a sample.
4582 assert(Thread::current()->is_ConcurrentGC_thread(),
4583 "Only the cms thread may collect Eden samples");
4584 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
4585 "Should collect samples while holding CMS token");
4586 if (!_start_sampling) {
4587 return;
4588 }
4589 // When CMSEdenChunksRecordAlways is true, the eden chunk array
4590 // is populated by the young generation.
4591 if (_eden_chunk_array != NULL && !CMSEdenChunksRecordAlways) {
4592 if (_eden_chunk_index < _eden_chunk_capacity) {
4593 _eden_chunk_array[_eden_chunk_index] = *_top_addr; // take sample
4594 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4595 "Unexpected state of Eden");
4596 // We'd like to check that what we just sampled is an oop-start address;
4597 // however, we cannot do that here since the object may not yet have been
4598 // initialized. So we'll instead do the check when we _use_ this sample
4599 // later.
4600 if (_eden_chunk_index == 0 ||
4601 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4602 _eden_chunk_array[_eden_chunk_index-1])
4603 >= CMSSamplingGrain)) {
4604 _eden_chunk_index++; // commit sample
4605 }
4606 }
4607 }
4608 if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
4609 size_t used = get_eden_used();
4610 size_t capacity = get_eden_capacity();
4611 assert(used <= capacity, "Unexpected state of Eden");
4612 if (used > (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
4613 _abort_preclean = true;
4614 }
4615 }
4616 }
4617
4618
4619 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
4620 assert(_collectorState == Precleaning ||
4621 _collectorState == AbortablePreclean, "incorrect state");
4622 ResourceMark rm;
4623 HandleMark hm;
4624
4625 // Precleaning is currently not MT but the reference processor
4626 // may be set for MT. Disable it temporarily here.
4627 ReferenceProcessor* rp = ref_processor();
4628 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false);
4629
4630 // Do one pass of scrubbing the discovered reference lists
4631 // to remove any reference objects with strongly-reachable
4632 // referents.
4633 if (clean_refs) {
4634 CMSPrecleanRefsYieldClosure yield_cl(this);
4635 assert(rp->span().equals(_span), "Spans should be equal");
4636 CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
4637 &_markStack, true /* preclean */);
4638 CMSDrainMarkingStackClosure complete_trace(this,
4639 _span, &_markBitMap, &_markStack,
4640 &keep_alive, true /* preclean */);
4641
4642 // We don't want this step to interfere with a young
4643 // collection because we don't want to take CPU
4644 // or memory bandwidth away from the young GC threads
4645 // (which may be as many as there are CPUs).
4646 // Note that we don't need to protect ourselves from
4647 // interference with mutators because they can't
4648 // manipulate the discovered reference lists nor affect
4649 // the computed reachability of the referents, the
4650 // only properties manipulated by the precleaning
4651 // of these reference lists.
4652 stopTimer();
4653 CMSTokenSyncWithLocks x(true /* is cms thread */,
4654 bitMapLock());
4655 startTimer();
4656 sample_eden();
4657
4658 // The following will yield to allow foreground
4659 // collection to proceed promptly. XXX YSR:
4660 // The code in this method may need further
4661 // tweaking for better performance and some restructuring
4662 // for cleaner interfaces.
4663 GCTimer *gc_timer = NULL; // Currently not tracing concurrent phases
4664 rp->preclean_discovered_references(
4665 rp->is_alive_non_header(), &keep_alive, &complete_trace, &yield_cl,
4666 gc_timer);
4667 }
4668
4669 if (clean_survivor) { // preclean the active survivor space(s)
4670 assert(_young_gen->kind() == Generation::DefNew ||
4671 _young_gen->kind() == Generation::ParNew ||
4672 _young_gen->kind() == Generation::ASParNew,
4673 "incorrect type for cast");
4674 DefNewGeneration* dng = (DefNewGeneration*)_young_gen;
4675 PushAndMarkClosure pam_cl(this, _span, ref_processor(),
4676 &_markBitMap, &_modUnionTable,
4677 &_markStack, true /* precleaning phase */);
4678 stopTimer();
4679 CMSTokenSyncWithLocks ts(true /* is cms thread */,
4680 bitMapLock());
4681 startTimer();
4682 unsigned int before_count =
4683 GenCollectedHeap::heap()->total_collections();
4684 SurvivorSpacePrecleanClosure
4685 sss_cl(this, _span, &_markBitMap, &_markStack,
4686 &pam_cl, before_count, CMSYield);
4687 dng->from()->object_iterate_careful(&sss_cl);
4688 dng->to()->object_iterate_careful(&sss_cl);
4689 }
4690 MarkRefsIntoAndScanClosure
4691 mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
4692 &_markStack, this, CMSYield,
4693 true /* precleaning phase */);
4694 // CAUTION: The following closure has persistent state that may need to
4695 // be reset upon a decrease in the sequence of addresses it
4696 // processes.
4697 ScanMarkedObjectsAgainCarefullyClosure
4698 smoac_cl(this, _span,
4699 &_markBitMap, &_markStack, &mrias_cl, CMSYield);
4700
4701 // Preclean dirty cards in ModUnionTable and CardTable using
4702 // appropriate convergence criterion;
4703 // repeat CMSPrecleanIter times unless we find that
4704 // we are losing.
4705 assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
4706 assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
4707 "Bad convergence multiplier");
4708 assert(CMSPrecleanThreshold >= 100,
4709 "Unreasonably low CMSPrecleanThreshold");
4710
4711 size_t numIter, cumNumCards, lastNumCards, curNumCards;
4712 for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
4713 numIter < CMSPrecleanIter;
4714 numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
4715 curNumCards = preclean_mod_union_table(_cmsGen, &smoac_cl);
4716 if (Verbose && PrintGCDetails) {
4717 gclog_or_tty->print(" (modUnionTable: %d cards)", curNumCards);
4718 }
4719 // Either there are very few dirty cards, so re-mark
4720 // pause will be small anyway, or our pre-cleaning isn't
4721 // that much faster than the rate at which cards are being
4722 // dirtied, so we might as well stop and re-mark since
4723 // precleaning won't improve our re-mark time by much.
4724 if (curNumCards <= CMSPrecleanThreshold ||
4725 (numIter > 0 &&
4726 (curNumCards * CMSPrecleanDenominator >
4727 lastNumCards * CMSPrecleanNumerator))) {
4728 numIter++;
4729 cumNumCards += curNumCards;
4730 break;
4731 }
4732 }
4733
4734 preclean_klasses(&mrias_cl, _cmsGen->freelistLock());
4735
4736 curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
4737 cumNumCards += curNumCards;
4738 if (PrintGCDetails && PrintCMSStatistics != 0) {
4739 gclog_or_tty->print_cr(" (cardTable: %d cards, re-scanned %d cards, %d iterations)",
4740 curNumCards, cumNumCards, numIter);
4741 }
4742 return cumNumCards; // as a measure of useful work done
4743 }
4744
4745 // PRECLEANING NOTES:
4746 // Precleaning involves:
4747 // . reading the bits of the modUnionTable and clearing the set bits.
4748 // . For the cards corresponding to the set bits, we scan the
4749 // objects on those cards. This means we need the free_list_lock
4750 // so that we can safely iterate over the CMS space when scanning
4751 // for oops.
4752 // . When we scan the objects, we'll be both reading and setting
4753 // marks in the marking bit map, so we'll need the marking bit map.
4754 // . For protecting _collector_state transitions, we take the CGC_lock.
4755 // Note that any races in the reading of of card table entries by the
4756 // CMS thread on the one hand and the clearing of those entries by the
4757 // VM thread or the setting of those entries by the mutator threads on the
4758 // other are quite benign. However, for efficiency it makes sense to keep
4759 // the VM thread from racing with the CMS thread while the latter is
4760 // dirty card info to the modUnionTable. We therefore also use the
4761 // CGC_lock to protect the reading of the card table and the mod union
4762 // table by the CM thread.
4763 // . We run concurrently with mutator updates, so scanning
4764 // needs to be done carefully -- we should not try to scan
4765 // potentially uninitialized objects.
4766 //
4767 // Locking strategy: While holding the CGC_lock, we scan over and
4768 // reset a maximal dirty range of the mod union / card tables, then lock
4769 // the free_list_lock and bitmap lock to do a full marking, then
4770 // release these locks; and repeat the cycle. This allows for a
4771 // certain amount of fairness in the sharing of these locks between
4772 // the CMS collector on the one hand, and the VM thread and the
4773 // mutators on the other.
4774
4775 // NOTE: preclean_mod_union_table() and preclean_card_table()
4776 // further below are largely identical; if you need to modify
4777 // one of these methods, please check the other method too.
4778
4779 size_t CMSCollector::preclean_mod_union_table(
4780 ConcurrentMarkSweepGeneration* gen,
4781 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4782 verify_work_stacks_empty();
4783 verify_overflow_empty();
4784
4785 // strategy: starting with the first card, accumulate contiguous
4786 // ranges of dirty cards; clear these cards, then scan the region
4787 // covered by these cards.
4788
4789 // Since all of the MUT is committed ahead, we can just use
4790 // that, in case the generations expand while we are precleaning.
4791 // It might also be fine to just use the committed part of the
4792 // generation, but we might potentially miss cards when the
4793 // generation is rapidly expanding while we are in the midst
4794 // of precleaning.
4795 HeapWord* startAddr = gen->reserved().start();
4796 HeapWord* endAddr = gen->reserved().end();
4797
4798 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4799
4800 size_t numDirtyCards, cumNumDirtyCards;
4801 HeapWord *nextAddr, *lastAddr;
4802 for (cumNumDirtyCards = numDirtyCards = 0,
4803 nextAddr = lastAddr = startAddr;
4804 nextAddr < endAddr;
4805 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4806
4807 ResourceMark rm;
4808 HandleMark hm;
4809
4810 MemRegion dirtyRegion;
4811 {
4812 stopTimer();
4813 // Potential yield point
4814 CMSTokenSync ts(true);
4815 startTimer();
4816 sample_eden();
4817 // Get dirty region starting at nextOffset (inclusive),
4818 // simultaneously clearing it.
4819 dirtyRegion =
4820 _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
4821 assert(dirtyRegion.start() >= nextAddr,
4822 "returned region inconsistent?");
4823 }
4824 // Remember where the next search should begin.
4825 // The returned region (if non-empty) is a right open interval,
4826 // so lastOffset is obtained from the right end of that
4827 // interval.
4828 lastAddr = dirtyRegion.end();
4829 // Should do something more transparent and less hacky XXX
4830 numDirtyCards =
4831 _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
4832
4833 // We'll scan the cards in the dirty region (with periodic
4834 // yields for foreground GC as needed).
4835 if (!dirtyRegion.is_empty()) {
4836 assert(numDirtyCards > 0, "consistency check");
4837 HeapWord* stop_point = NULL;
4838 stopTimer();
4839 // Potential yield point
4840 CMSTokenSyncWithLocks ts(true, gen->freelistLock(),
4841 bitMapLock());
4842 startTimer();
4843 {
4844 verify_work_stacks_empty();
4845 verify_overflow_empty();
4846 sample_eden();
4847 stop_point =
4848 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4849 }
4850 if (stop_point != NULL) {
4851 // The careful iteration stopped early either because it found an
4852 // uninitialized object, or because we were in the midst of an
4853 // "abortable preclean", which should now be aborted. Redirty
4854 // the bits corresponding to the partially-scanned or unscanned
4855 // cards. We'll either restart at the next block boundary or
4856 // abort the preclean.
4857 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4858 "Should only be AbortablePreclean.");
4859 _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
4860 if (should_abort_preclean()) {
4861 break; // out of preclean loop
4862 } else {
4863 // Compute the next address at which preclean should pick up;
4864 // might need bitMapLock in order to read P-bits.
4865 lastAddr = next_card_start_after_block(stop_point);
4866 }
4867 }
4868 } else {
4869 assert(lastAddr == endAddr, "consistency check");
4870 assert(numDirtyCards == 0, "consistency check");
4871 break;
4872 }
4873 }
4874 verify_work_stacks_empty();
4875 verify_overflow_empty();
4876 return cumNumDirtyCards;
4877 }
4878
4879 // NOTE: preclean_mod_union_table() above and preclean_card_table()
4880 // below are largely identical; if you need to modify
4881 // one of these methods, please check the other method too.
4882
4883 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* gen,
4884 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4885 // strategy: it's similar to precleamModUnionTable above, in that
4886 // we accumulate contiguous ranges of dirty cards, mark these cards
4887 // precleaned, then scan the region covered by these cards.
4888 HeapWord* endAddr = (HeapWord*)(gen->_virtual_space.high());
4889 HeapWord* startAddr = (HeapWord*)(gen->_virtual_space.low());
4890
4891 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4892
4893 size_t numDirtyCards, cumNumDirtyCards;
4894 HeapWord *lastAddr, *nextAddr;
4895
4896 for (cumNumDirtyCards = numDirtyCards = 0,
4897 nextAddr = lastAddr = startAddr;
4898 nextAddr < endAddr;
4899 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4900
4901 ResourceMark rm;
4902 HandleMark hm;
4903
4904 MemRegion dirtyRegion;
4905 {
4906 // See comments in "Precleaning notes" above on why we
4907 // do this locking. XXX Could the locking overheads be
4908 // too high when dirty cards are sparse? [I don't think so.]
4909 stopTimer();
4910 CMSTokenSync x(true); // is cms thread
4911 startTimer();
4912 sample_eden();
4913 // Get and clear dirty region from card table
4914 dirtyRegion = _ct->ct_bs()->dirty_card_range_after_reset(
4915 MemRegion(nextAddr, endAddr),
4916 true,
4917 CardTableModRefBS::precleaned_card_val());
4918
4919 assert(dirtyRegion.start() >= nextAddr,
4920 "returned region inconsistent?");
4921 }
4922 lastAddr = dirtyRegion.end();
4923 numDirtyCards =
4924 dirtyRegion.word_size()/CardTableModRefBS::card_size_in_words;
4925
4926 if (!dirtyRegion.is_empty()) {
4927 stopTimer();
4928 CMSTokenSyncWithLocks ts(true, gen->freelistLock(), bitMapLock());
4929 startTimer();
4930 sample_eden();
4931 verify_work_stacks_empty();
4932 verify_overflow_empty();
4933 HeapWord* stop_point =
4934 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4935 if (stop_point != NULL) {
4936 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4937 "Should only be AbortablePreclean.");
4938 _ct->ct_bs()->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4939 if (should_abort_preclean()) {
4940 break; // out of preclean loop
4941 } else {
4942 // Compute the next address at which preclean should pick up.
4943 lastAddr = next_card_start_after_block(stop_point);
4944 }
4945 }
4946 } else {
4947 break;
4948 }
4949 }
4950 verify_work_stacks_empty();
4951 verify_overflow_empty();
4952 return cumNumDirtyCards;
4953 }
4954
4955 class PrecleanKlassClosure : public KlassClosure {
4956 CMKlassClosure _cm_klass_closure;
4957 public:
4958 PrecleanKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4959 void do_klass(Klass* k) {
4960 if (k->has_accumulated_modified_oops()) {
4961 k->clear_accumulated_modified_oops();
4962
4963 _cm_klass_closure.do_klass(k);
4964 }
4965 }
4966 };
4967
4968 // The freelist lock is needed to prevent asserts, is it really needed?
4969 void CMSCollector::preclean_klasses(MarkRefsIntoAndScanClosure* cl, Mutex* freelistLock) {
4970
4971 cl->set_freelistLock(freelistLock);
4972
4973 CMSTokenSyncWithLocks ts(true, freelistLock, bitMapLock());
4974
4975 // SSS: Add equivalent to ScanMarkedObjectsAgainCarefullyClosure::do_yield_check and should_abort_preclean?
4976 // SSS: We should probably check if precleaning should be aborted, at suitable intervals?
4977 PrecleanKlassClosure preclean_klass_closure(cl);
4978 ClassLoaderDataGraph::classes_do(&preclean_klass_closure);
4979
4980 verify_work_stacks_empty();
4981 verify_overflow_empty();
4982 }
4983
4984 void CMSCollector::checkpointRootsFinal(bool asynch,
4985 bool clear_all_soft_refs, bool init_mark_was_synchronous) {
4986 assert(_collectorState == FinalMarking, "incorrect state transition?");
4987 check_correct_thread_executing();
4988 // world is stopped at this checkpoint
4989 assert(SafepointSynchronize::is_at_safepoint(),
4990 "world should be stopped");
4991 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
4992
4993 verify_work_stacks_empty();
4994 verify_overflow_empty();
4995
4996 SpecializationStats::clear();
4997 if (PrintGCDetails) {
4998 gclog_or_tty->print("[YG occupancy: "SIZE_FORMAT" K ("SIZE_FORMAT" K)]",
4999 _young_gen->used() / K,
5000 _young_gen->capacity() / K);
5001 }
5002 if (asynch) {
5003 if (CMSScavengeBeforeRemark) {
5004 GenCollectedHeap* gch = GenCollectedHeap::heap();
5005 // Temporarily set flag to false, GCH->do_collection will
5006 // expect it to be false and set to true
5007 FlagSetting fl(gch->_is_gc_active, false);
5008 NOT_PRODUCT(GCTraceTime t("Scavenge-Before-Remark",
5009 PrintGCDetails && Verbose, true, _gc_timer_cm);)
5010 int level = _cmsGen->level() - 1;
5011 if (level >= 0) {
5012 gch->do_collection(true, // full (i.e. force, see below)
5013 false, // !clear_all_soft_refs
5014 0, // size
5015 false, // is_tlab
5016 level // max_level
5017 );
5018 }
5019 }
5020 FreelistLocker x(this);
5021 MutexLockerEx y(bitMapLock(),
5022 Mutex::_no_safepoint_check_flag);
5023 assert(!init_mark_was_synchronous, "but that's impossible!");
5024 checkpointRootsFinalWork(asynch, clear_all_soft_refs, false);
5025 } else {
5026 // already have all the locks
5027 checkpointRootsFinalWork(asynch, clear_all_soft_refs,
5028 init_mark_was_synchronous);
5029 }
5030 verify_work_stacks_empty();
5031 verify_overflow_empty();
5032 SpecializationStats::print();
5033 }
5034
5035 void CMSCollector::checkpointRootsFinalWork(bool asynch,
5036 bool clear_all_soft_refs, bool init_mark_was_synchronous) {
5037
5038 NOT_PRODUCT(GCTraceTime tr("checkpointRootsFinalWork", PrintGCDetails, false, _gc_timer_cm);)
5039
5040 assert(haveFreelistLocks(), "must have free list locks");
5041 assert_lock_strong(bitMapLock());
5042
5043 if (UseAdaptiveSizePolicy) {
5044 size_policy()->checkpoint_roots_final_begin();
5045 }
5046
5047 ResourceMark rm;
5048 HandleMark hm;
5049
5050 GenCollectedHeap* gch = GenCollectedHeap::heap();
5051
5052 if (should_unload_classes()) {
5053 CodeCache::gc_prologue();
5054 }
5055 assert(haveFreelistLocks(), "must have free list locks");
5056 assert_lock_strong(bitMapLock());
5057
5058 if (!init_mark_was_synchronous) {
5059 // We might assume that we need not fill TLAB's when
5060 // CMSScavengeBeforeRemark is set, because we may have just done
5061 // a scavenge which would have filled all TLAB's -- and besides
5062 // Eden would be empty. This however may not always be the case --
5063 // for instance although we asked for a scavenge, it may not have
5064 // happened because of a JNI critical section. We probably need
5065 // a policy for deciding whether we can in that case wait until
5066 // the critical section releases and then do the remark following
5067 // the scavenge, and skip it here. In the absence of that policy,
5068 // or of an indication of whether the scavenge did indeed occur,
5069 // we cannot rely on TLAB's having been filled and must do
5070 // so here just in case a scavenge did not happen.
5071 gch->ensure_parsability(false); // fill TLAB's, but no need to retire them
5072 // Update the saved marks which may affect the root scans.
5073 gch->save_marks();
5074
5075 if (CMSPrintEdenSurvivorChunks) {
5076 print_eden_and_survivor_chunk_arrays();
5077 }
5078
5079 {
5080 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
5081
5082 // Note on the role of the mod union table:
5083 // Since the marker in "markFromRoots" marks concurrently with
5084 // mutators, it is possible for some reachable objects not to have been
5085 // scanned. For instance, an only reference to an object A was
5086 // placed in object B after the marker scanned B. Unless B is rescanned,
5087 // A would be collected. Such updates to references in marked objects
5088 // are detected via the mod union table which is the set of all cards
5089 // dirtied since the first checkpoint in this GC cycle and prior to
5090 // the most recent young generation GC, minus those cleaned up by the
5091 // concurrent precleaning.
5092 if (CMSParallelRemarkEnabled && CollectedHeap::use_parallel_gc_threads()) {
5093 GCTraceTime t("Rescan (parallel) ", PrintGCDetails, false, _gc_timer_cm);
5094 do_remark_parallel();
5095 } else {
5096 GCTraceTime t("Rescan (non-parallel) ", PrintGCDetails, false,
5097 _gc_timer_cm);
5098 do_remark_non_parallel();
5099 }
5100 }
5101 } else {
5102 assert(!asynch, "Can't have init_mark_was_synchronous in asynch mode");
5103 // The initial mark was stop-world, so there's no rescanning to
5104 // do; go straight on to the next step below.
5105 }
5106 verify_work_stacks_empty();
5107 verify_overflow_empty();
5108
5109 {
5110 NOT_PRODUCT(GCTraceTime ts("refProcessingWork", PrintGCDetails, false, _gc_timer_cm);)
5111 refProcessingWork(asynch, clear_all_soft_refs);
5112 }
5113 verify_work_stacks_empty();
5114 verify_overflow_empty();
5115
5116 if (should_unload_classes()) {
5117 CodeCache::gc_epilogue();
5118 }
5119 JvmtiExport::gc_epilogue();
5120
5121 // If we encountered any (marking stack / work queue) overflow
5122 // events during the current CMS cycle, take appropriate
5123 // remedial measures, where possible, so as to try and avoid
5124 // recurrence of that condition.
5125 assert(_markStack.isEmpty(), "No grey objects");
5126 size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
5127 _ser_kac_ovflw + _ser_kac_preclean_ovflw;
5128 if (ser_ovflw > 0) {
5129 if (PrintCMSStatistics != 0) {
5130 gclog_or_tty->print_cr("Marking stack overflow (benign) "
5131 "(pmc_pc="SIZE_FORMAT", pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT
5132 ", kac_preclean="SIZE_FORMAT")",
5133 _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw,
5134 _ser_kac_ovflw, _ser_kac_preclean_ovflw);
5135 }
5136 _markStack.expand();
5137 _ser_pmc_remark_ovflw = 0;
5138 _ser_pmc_preclean_ovflw = 0;
5139 _ser_kac_preclean_ovflw = 0;
5140 _ser_kac_ovflw = 0;
5141 }
5142 if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
5143 if (PrintCMSStatistics != 0) {
5144 gclog_or_tty->print_cr("Work queue overflow (benign) "
5145 "(pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT")",
5146 _par_pmc_remark_ovflw, _par_kac_ovflw);
5147 }
5148 _par_pmc_remark_ovflw = 0;
5149 _par_kac_ovflw = 0;
5150 }
5151 if (PrintCMSStatistics != 0) {
5152 if (_markStack._hit_limit > 0) {
5153 gclog_or_tty->print_cr(" (benign) Hit max stack size limit ("SIZE_FORMAT")",
5154 _markStack._hit_limit);
5155 }
5156 if (_markStack._failed_double > 0) {
5157 gclog_or_tty->print_cr(" (benign) Failed stack doubling ("SIZE_FORMAT"),"
5158 " current capacity "SIZE_FORMAT,
5159 _markStack._failed_double,
5160 _markStack.capacity());
5161 }
5162 }
5163 _markStack._hit_limit = 0;
5164 _markStack._failed_double = 0;
5165
5166 if ((VerifyAfterGC || VerifyDuringGC) &&
5167 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5168 verify_after_remark();
5169 }
5170
5171 _gc_tracer_cm->report_object_count_after_gc(&_is_alive_closure);
5172
5173 // Change under the freelistLocks.
5174 _collectorState = Sweeping;
5175 // Call isAllClear() under bitMapLock
5176 assert(_modUnionTable.isAllClear(),
5177 "Should be clear by end of the final marking");
5178 assert(_ct->klass_rem_set()->mod_union_is_clear(),
5179 "Should be clear by end of the final marking");
5180 if (UseAdaptiveSizePolicy) {
5181 size_policy()->checkpoint_roots_final_end(gch->gc_cause());
5182 }
5183 }
5184
5185 // Parallel remark task
5186 class CMSParRemarkTask: public AbstractGangTask {
5187 CMSCollector* _collector;
5188 int _n_workers;
5189 CompactibleFreeListSpace* _cms_space;
5190
5191 // The per-thread work queues, available here for stealing.
5192 OopTaskQueueSet* _task_queues;
5193 ParallelTaskTerminator _term;
5194
5195 public:
5196 // A value of 0 passed to n_workers will cause the number of
5197 // workers to be taken from the active workers in the work gang.
5198 CMSParRemarkTask(CMSCollector* collector,
5199 CompactibleFreeListSpace* cms_space,
5200 int n_workers, FlexibleWorkGang* workers,
5201 OopTaskQueueSet* task_queues):
5202 AbstractGangTask("Rescan roots and grey objects in parallel"),
5203 _collector(collector),
5204 _cms_space(cms_space),
5205 _n_workers(n_workers),
5206 _task_queues(task_queues),
5207 _term(n_workers, task_queues) { }
5208
5209 OopTaskQueueSet* task_queues() { return _task_queues; }
5210
5211 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5212
5213 ParallelTaskTerminator* terminator() { return &_term; }
5214 int n_workers() { return _n_workers; }
5215
5216 void work(uint worker_id);
5217
5218 private:
5219 // Work method in support of parallel rescan ... of young gen spaces
5220 void do_young_space_rescan(int i, Par_MarkRefsIntoAndScanClosure* cl,
5221 ContiguousSpace* space,
5222 HeapWord** chunk_array, size_t chunk_top);
5223
5224 // ... of dirty cards in old space
5225 void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
5226 Par_MarkRefsIntoAndScanClosure* cl);
5227
5228 // ... work stealing for the above
5229 void do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl, int* seed);
5230 };
5231
5232 class RemarkKlassClosure : public KlassClosure {
5233 CMKlassClosure _cm_klass_closure;
5234 public:
5235 RemarkKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
5236 void do_klass(Klass* k) {
5237 // Check if we have modified any oops in the Klass during the concurrent marking.
5238 if (k->has_accumulated_modified_oops()) {
5239 k->clear_accumulated_modified_oops();
5240
5241 // We could have transfered the current modified marks to the accumulated marks,
5242 // like we do with the Card Table to Mod Union Table. But it's not really necessary.
5243 } else if (k->has_modified_oops()) {
5244 // Don't clear anything, this info is needed by the next young collection.
5245 } else {
5246 // No modified oops in the Klass.
5247 return;
5248 }
5249
5250 // The klass has modified fields, need to scan the klass.
5251 _cm_klass_closure.do_klass(k);
5252 }
5253 };
5254
5255 // work_queue(i) is passed to the closure
5256 // Par_MarkRefsIntoAndScanClosure. The "i" parameter
5257 // also is passed to do_dirty_card_rescan_tasks() and to
5258 // do_work_steal() to select the i-th task_queue.
5259
5260 void CMSParRemarkTask::work(uint worker_id) {
5261 elapsedTimer _timer;
5262 ResourceMark rm;
5263 HandleMark hm;
5264
5265 // ---------- rescan from roots --------------
5266 _timer.start();
5267 GenCollectedHeap* gch = GenCollectedHeap::heap();
5268 Par_MarkRefsIntoAndScanClosure par_mrias_cl(_collector,
5269 _collector->_span, _collector->ref_processor(),
5270 &(_collector->_markBitMap),
5271 work_queue(worker_id));
5272
5273 // Rescan young gen roots first since these are likely
5274 // coarsely partitioned and may, on that account, constitute
5275 // the critical path; thus, it's best to start off that
5276 // work first.
5277 // ---------- young gen roots --------------
5278 {
5279 DefNewGeneration* dng = _collector->_young_gen->as_DefNewGeneration();
5280 EdenSpace* eden_space = dng->eden();
5281 ContiguousSpace* from_space = dng->from();
5282 ContiguousSpace* to_space = dng->to();
5283
5284 HeapWord** eca = _collector->_eden_chunk_array;
5285 size_t ect = _collector->_eden_chunk_index;
5286 HeapWord** sca = _collector->_survivor_chunk_array;
5287 size_t sct = _collector->_survivor_chunk_index;
5288
5289 assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
5290 assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
5291
5292 do_young_space_rescan(worker_id, &par_mrias_cl, to_space, NULL, 0);
5293 do_young_space_rescan(worker_id, &par_mrias_cl, from_space, sca, sct);
5294 do_young_space_rescan(worker_id, &par_mrias_cl, eden_space, eca, ect);
5295
5296 _timer.stop();
5297 if (PrintCMSStatistics != 0) {
5298 gclog_or_tty->print_cr(
5299 "Finished young gen rescan work in %dth thread: %3.3f sec",
5300 worker_id, _timer.seconds());
5301 }
5302 }
5303
5304 // ---------- remaining roots --------------
5305 _timer.reset();
5306 _timer.start();
5307 gch->gen_process_strong_roots(_collector->_cmsGen->level(),
5308 false, // yg was scanned above
5309 false, // this is parallel code
5310 false, // not scavenging
5311 SharedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
5312 &par_mrias_cl,
5313 true, // walk all of code cache if (so & SO_CodeCache)
5314 NULL,
5315 NULL); // The dirty klasses will be handled below
5316 assert(_collector->should_unload_classes()
5317 || (_collector->CMSCollector::roots_scanning_options() & SharedHeap::SO_CodeCache),
5318 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5319 _timer.stop();
5320 if (PrintCMSStatistics != 0) {
5321 gclog_or_tty->print_cr(
5322 "Finished remaining root rescan work in %dth thread: %3.3f sec",
5323 worker_id, _timer.seconds());
5324 }
5325
5326 // ---------- unhandled CLD scanning ----------
5327 if (worker_id == 0) { // Single threaded at the moment.
5328 _timer.reset();
5329 _timer.start();
5330
5331 // Scan all new class loader data objects and new dependencies that were
5332 // introduced during concurrent marking.
5333 ResourceMark rm;
5334 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
5335 for (int i = 0; i < array->length(); i++) {
5336 par_mrias_cl.do_class_loader_data(array->at(i));
5337 }
5338
5339 // We don't need to keep track of new CLDs anymore.
5340 ClassLoaderDataGraph::remember_new_clds(false);
5341
5342 _timer.stop();
5343 if (PrintCMSStatistics != 0) {
5344 gclog_or_tty->print_cr(
5345 "Finished unhandled CLD scanning work in %dth thread: %3.3f sec",
5346 worker_id, _timer.seconds());
5347 }
5348 }
5349
5350 // ---------- dirty klass scanning ----------
5351 if (worker_id == 0) { // Single threaded at the moment.
5352 _timer.reset();
5353 _timer.start();
5354
5355 // Scan all classes that was dirtied during the concurrent marking phase.
5356 RemarkKlassClosure remark_klass_closure(&par_mrias_cl);
5357 ClassLoaderDataGraph::classes_do(&remark_klass_closure);
5358
5359 _timer.stop();
5360 if (PrintCMSStatistics != 0) {
5361 gclog_or_tty->print_cr(
5362 "Finished dirty klass scanning work in %dth thread: %3.3f sec",
5363 worker_id, _timer.seconds());
5364 }
5365 }
5366
5367 // We might have added oops to ClassLoaderData::_handles during the
5368 // concurrent marking phase. These oops point to newly allocated objects
5369 // that are guaranteed to be kept alive. Either by the direct allocation
5370 // code, or when the young collector processes the strong roots. Hence,
5371 // we don't have to revisit the _handles block during the remark phase.
5372
5373 // ---------- rescan dirty cards ------------
5374 _timer.reset();
5375 _timer.start();
5376
5377 // Do the rescan tasks for each of the two spaces
5378 // (cms_space) in turn.
5379 // "worker_id" is passed to select the task_queue for "worker_id"
5380 do_dirty_card_rescan_tasks(_cms_space, worker_id, &par_mrias_cl);
5381 _timer.stop();
5382 if (PrintCMSStatistics != 0) {
5383 gclog_or_tty->print_cr(
5384 "Finished dirty card rescan work in %dth thread: %3.3f sec",
5385 worker_id, _timer.seconds());
5386 }
5387
5388 // ---------- steal work from other threads ...
5389 // ---------- ... and drain overflow list.
5390 _timer.reset();
5391 _timer.start();
5392 do_work_steal(worker_id, &par_mrias_cl, _collector->hash_seed(worker_id));
5393 _timer.stop();
5394 if (PrintCMSStatistics != 0) {
5395 gclog_or_tty->print_cr(
5396 "Finished work stealing in %dth thread: %3.3f sec",
5397 worker_id, _timer.seconds());
5398 }
5399 }
5400
5401 // Note that parameter "i" is not used.
5402 void
5403 CMSParRemarkTask::do_young_space_rescan(int i,
5404 Par_MarkRefsIntoAndScanClosure* cl, ContiguousSpace* space,
5405 HeapWord** chunk_array, size_t chunk_top) {
5406 // Until all tasks completed:
5407 // . claim an unclaimed task
5408 // . compute region boundaries corresponding to task claimed
5409 // using chunk_array
5410 // . par_oop_iterate(cl) over that region
5411
5412 ResourceMark rm;
5413 HandleMark hm;
5414
5415 SequentialSubTasksDone* pst = space->par_seq_tasks();
5416 assert(pst->valid(), "Uninitialized use?");
5417
5418 uint nth_task = 0;
5419 uint n_tasks = pst->n_tasks();
5420
5421 HeapWord *start, *end;
5422 while (!pst->is_task_claimed(/* reference */ nth_task)) {
5423 // We claimed task # nth_task; compute its boundaries.
5424 if (chunk_top == 0) { // no samples were taken
5425 assert(nth_task == 0 && n_tasks == 1, "Can have only 1 EdenSpace task");
5426 start = space->bottom();
5427 end = space->top();
5428 } else if (nth_task == 0) {
5429 start = space->bottom();
5430 end = chunk_array[nth_task];
5431 } else if (nth_task < (uint)chunk_top) {
5432 assert(nth_task >= 1, "Control point invariant");
5433 start = chunk_array[nth_task - 1];
5434 end = chunk_array[nth_task];
5435 } else {
5436 assert(nth_task == (uint)chunk_top, "Control point invariant");
5437 start = chunk_array[chunk_top - 1];
5438 end = space->top();
5439 }
5440 MemRegion mr(start, end);
5441 // Verify that mr is in space
5442 assert(mr.is_empty() || space->used_region().contains(mr),
5443 "Should be in space");
5444 // Verify that "start" is an object boundary
5445 assert(mr.is_empty() || oop(mr.start())->is_oop(),
5446 "Should be an oop");
5447 space->par_oop_iterate(mr, cl);
5448 }
5449 pst->all_tasks_completed();
5450 }
5451
5452 void
5453 CMSParRemarkTask::do_dirty_card_rescan_tasks(
5454 CompactibleFreeListSpace* sp, int i,
5455 Par_MarkRefsIntoAndScanClosure* cl) {
5456 // Until all tasks completed:
5457 // . claim an unclaimed task
5458 // . compute region boundaries corresponding to task claimed
5459 // . transfer dirty bits ct->mut for that region
5460 // . apply rescanclosure to dirty mut bits for that region
5461
5462 ResourceMark rm;
5463 HandleMark hm;
5464
5465 OopTaskQueue* work_q = work_queue(i);
5466 ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
5467 // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
5468 // CAUTION: This closure has state that persists across calls to
5469 // the work method dirty_range_iterate_clear() in that it has
5470 // imbedded in it a (subtype of) UpwardsObjectClosure. The
5471 // use of that state in the imbedded UpwardsObjectClosure instance
5472 // assumes that the cards are always iterated (even if in parallel
5473 // by several threads) in monotonically increasing order per each
5474 // thread. This is true of the implementation below which picks
5475 // card ranges (chunks) in monotonically increasing order globally
5476 // and, a-fortiori, in monotonically increasing order per thread
5477 // (the latter order being a subsequence of the former).
5478 // If the work code below is ever reorganized into a more chaotic
5479 // work-partitioning form than the current "sequential tasks"
5480 // paradigm, the use of that persistent state will have to be
5481 // revisited and modified appropriately. See also related
5482 // bug 4756801 work on which should examine this code to make
5483 // sure that the changes there do not run counter to the
5484 // assumptions made here and necessary for correctness and
5485 // efficiency. Note also that this code might yield inefficient
5486 // behaviour in the case of very large objects that span one or
5487 // more work chunks. Such objects would potentially be scanned
5488 // several times redundantly. Work on 4756801 should try and
5489 // address that performance anomaly if at all possible. XXX
5490 MemRegion full_span = _collector->_span;
5491 CMSBitMap* bm = &(_collector->_markBitMap); // shared
5492 MarkFromDirtyCardsClosure
5493 greyRescanClosure(_collector, full_span, // entire span of interest
5494 sp, bm, work_q, cl);
5495
5496 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
5497 assert(pst->valid(), "Uninitialized use?");
5498 uint nth_task = 0;
5499 const int alignment = CardTableModRefBS::card_size * BitsPerWord;
5500 MemRegion span = sp->used_region();
5501 HeapWord* start_addr = span.start();
5502 HeapWord* end_addr = (HeapWord*)round_to((intptr_t)span.end(),
5503 alignment);
5504 const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
5505 assert((HeapWord*)round_to((intptr_t)start_addr, alignment) ==
5506 start_addr, "Check alignment");
5507 assert((size_t)round_to((intptr_t)chunk_size, alignment) ==
5508 chunk_size, "Check alignment");
5509
5510 while (!pst->is_task_claimed(/* reference */ nth_task)) {
5511 // Having claimed the nth_task, compute corresponding mem-region,
5512 // which is a-fortiori aligned correctly (i.e. at a MUT bopundary).
5513 // The alignment restriction ensures that we do not need any
5514 // synchronization with other gang-workers while setting or
5515 // clearing bits in thus chunk of the MUT.
5516 MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
5517 start_addr + (nth_task+1)*chunk_size);
5518 // The last chunk's end might be way beyond end of the
5519 // used region. In that case pull back appropriately.
5520 if (this_span.end() > end_addr) {
5521 this_span.set_end(end_addr);
5522 assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
5523 }
5524 // Iterate over the dirty cards covering this chunk, marking them
5525 // precleaned, and setting the corresponding bits in the mod union
5526 // table. Since we have been careful to partition at Card and MUT-word
5527 // boundaries no synchronization is needed between parallel threads.
5528 _collector->_ct->ct_bs()->dirty_card_iterate(this_span,
5529 &modUnionClosure);
5530
5531 // Having transferred these marks into the modUnionTable,
5532 // rescan the marked objects on the dirty cards in the modUnionTable.
5533 // Even if this is at a synchronous collection, the initial marking
5534 // may have been done during an asynchronous collection so there
5535 // may be dirty bits in the mod-union table.
5536 _collector->_modUnionTable.dirty_range_iterate_clear(
5537 this_span, &greyRescanClosure);
5538 _collector->_modUnionTable.verifyNoOneBitsInRange(
5539 this_span.start(),
5540 this_span.end());
5541 }
5542 pst->all_tasks_completed(); // declare that i am done
5543 }
5544
5545 // . see if we can share work_queues with ParNew? XXX
5546 void
5547 CMSParRemarkTask::do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl,
5548 int* seed) {
5549 OopTaskQueue* work_q = work_queue(i);
5550 NOT_PRODUCT(int num_steals = 0;)
5551 oop obj_to_scan;
5552 CMSBitMap* bm = &(_collector->_markBitMap);
5553
5554 while (true) {
5555 // Completely finish any left over work from (an) earlier round(s)
5556 cl->trim_queue(0);
5557 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5558 (size_t)ParGCDesiredObjsFromOverflowList);
5559 // Now check if there's any work in the overflow list
5560 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5561 // only affects the number of attempts made to get work from the
5562 // overflow list and does not affect the number of workers. Just
5563 // pass ParallelGCThreads so this behavior is unchanged.
5564 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5565 work_q,
5566 ParallelGCThreads)) {
5567 // found something in global overflow list;
5568 // not yet ready to go stealing work from others.
5569 // We'd like to assert(work_q->size() != 0, ...)
5570 // because we just took work from the overflow list,
5571 // but of course we can't since all of that could have
5572 // been already stolen from us.
5573 // "He giveth and He taketh away."
5574 continue;
5575 }
5576 // Verify that we have no work before we resort to stealing
5577 assert(work_q->size() == 0, "Have work, shouldn't steal");
5578 // Try to steal from other queues that have work
5579 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5580 NOT_PRODUCT(num_steals++;)
5581 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5582 assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5583 // Do scanning work
5584 obj_to_scan->oop_iterate(cl);
5585 // Loop around, finish this work, and try to steal some more
5586 } else if (terminator()->offer_termination()) {
5587 break; // nirvana from the infinite cycle
5588 }
5589 }
5590 NOT_PRODUCT(
5591 if (PrintCMSStatistics != 0) {
5592 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5593 }
5594 )
5595 assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
5596 "Else our work is not yet done");
5597 }
5598
5599 // Record object boundaries in _eden_chunk_array by sampling the eden
5600 // top in the slow-path eden object allocation code path and record
5601 // the boundaries, if CMSEdenChunksRecordAlways is true. If
5602 // CMSEdenChunksRecordAlways is false, we use the other asynchronous
5603 // sampling in sample_eden() that activates during the part of the
5604 // preclean phase.
5605 void CMSCollector::sample_eden_chunk() {
5606 if (CMSEdenChunksRecordAlways && _eden_chunk_array != NULL) {
5607 if (_eden_chunk_lock->try_lock()) {
5608 // Record a sample. This is the critical section. The contents
5609 // of the _eden_chunk_array have to be non-decreasing in the
5610 // address order.
5611 _eden_chunk_array[_eden_chunk_index] = *_top_addr;
5612 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
5613 "Unexpected state of Eden");
5614 if (_eden_chunk_index == 0 ||
5615 ((_eden_chunk_array[_eden_chunk_index] > _eden_chunk_array[_eden_chunk_index-1]) &&
5616 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
5617 _eden_chunk_array[_eden_chunk_index-1]) >= CMSSamplingGrain))) {
5618 _eden_chunk_index++; // commit sample
5619 }
5620 _eden_chunk_lock->unlock();
5621 }
5622 }
5623 }
5624
5625 // Return a thread-local PLAB recording array, as appropriate.
5626 void* CMSCollector::get_data_recorder(int thr_num) {
5627 if (_survivor_plab_array != NULL &&
5628 (CMSPLABRecordAlways ||
5629 (_collectorState > Marking && _collectorState < FinalMarking))) {
5630 assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
5631 ChunkArray* ca = &_survivor_plab_array[thr_num];
5632 ca->reset(); // clear it so that fresh data is recorded
5633 return (void*) ca;
5634 } else {
5635 return NULL;
5636 }
5637 }
5638
5639 // Reset all the thread-local PLAB recording arrays
5640 void CMSCollector::reset_survivor_plab_arrays() {
5641 for (uint i = 0; i < ParallelGCThreads; i++) {
5642 _survivor_plab_array[i].reset();
5643 }
5644 }
5645
5646 // Merge the per-thread plab arrays into the global survivor chunk
5647 // array which will provide the partitioning of the survivor space
5648 // for CMS rescan.
5649 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv,
5650 int no_of_gc_threads) {
5651 assert(_survivor_plab_array != NULL, "Error");
5652 assert(_survivor_chunk_array != NULL, "Error");
5653 assert(_collectorState == FinalMarking, "Error");
5654 for (int j = 0; j < no_of_gc_threads; j++) {
5655 _cursor[j] = 0;
5656 }
5657 HeapWord* top = surv->top();
5658 size_t i;
5659 for (i = 0; i < _survivor_chunk_capacity; i++) { // all sca entries
5660 HeapWord* min_val = top; // Higher than any PLAB address
5661 uint min_tid = 0; // position of min_val this round
5662 for (int j = 0; j < no_of_gc_threads; j++) {
5663 ChunkArray* cur_sca = &_survivor_plab_array[j];
5664 if (_cursor[j] == cur_sca->end()) {
5665 continue;
5666 }
5667 assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
5668 HeapWord* cur_val = cur_sca->nth(_cursor[j]);
5669 assert(surv->used_region().contains(cur_val), "Out of bounds value");
5670 if (cur_val < min_val) {
5671 min_tid = j;
5672 min_val = cur_val;
5673 } else {
5674 assert(cur_val < top, "All recorded addresses should be less");
5675 }
5676 }
5677 // At this point min_val and min_tid are respectively
5678 // the least address in _survivor_plab_array[j]->nth(_cursor[j])
5679 // and the thread (j) that witnesses that address.
5680 // We record this address in the _survivor_chunk_array[i]
5681 // and increment _cursor[min_tid] prior to the next round i.
5682 if (min_val == top) {
5683 break;
5684 }
5685 _survivor_chunk_array[i] = min_val;
5686 _cursor[min_tid]++;
5687 }
5688 // We are all done; record the size of the _survivor_chunk_array
5689 _survivor_chunk_index = i; // exclusive: [0, i)
5690 if (PrintCMSStatistics > 0) {
5691 gclog_or_tty->print(" (Survivor:" SIZE_FORMAT "chunks) ", i);
5692 }
5693 // Verify that we used up all the recorded entries
5694 #ifdef ASSERT
5695 size_t total = 0;
5696 for (int j = 0; j < no_of_gc_threads; j++) {
5697 assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
5698 total += _cursor[j];
5699 }
5700 assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
5701 // Check that the merged array is in sorted order
5702 if (total > 0) {
5703 for (size_t i = 0; i < total - 1; i++) {
5704 if (PrintCMSStatistics > 0) {
5705 gclog_or_tty->print(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
5706 i, _survivor_chunk_array[i]);
5707 }
5708 assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
5709 "Not sorted");
5710 }
5711 }
5712 #endif // ASSERT
5713 }
5714
5715 // Set up the space's par_seq_tasks structure for work claiming
5716 // for parallel rescan of young gen.
5717 // See ParRescanTask where this is currently used.
5718 void
5719 CMSCollector::
5720 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
5721 assert(n_threads > 0, "Unexpected n_threads argument");
5722 DefNewGeneration* dng = (DefNewGeneration*)_young_gen;
5723
5724 // Eden space
5725 {
5726 SequentialSubTasksDone* pst = dng->eden()->par_seq_tasks();
5727 assert(!pst->valid(), "Clobbering existing data?");
5728 // Each valid entry in [0, _eden_chunk_index) represents a task.
5729 size_t n_tasks = _eden_chunk_index + 1;
5730 assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
5731 // Sets the condition for completion of the subtask (how many threads
5732 // need to finish in order to be done).
5733 pst->set_n_threads(n_threads);
5734 pst->set_n_tasks((int)n_tasks);
5735 }
5736
5737 // Merge the survivor plab arrays into _survivor_chunk_array
5738 if (_survivor_plab_array != NULL) {
5739 merge_survivor_plab_arrays(dng->from(), n_threads);
5740 } else {
5741 assert(_survivor_chunk_index == 0, "Error");
5742 }
5743
5744 // To space
5745 {
5746 SequentialSubTasksDone* pst = dng->to()->par_seq_tasks();
5747 assert(!pst->valid(), "Clobbering existing data?");
5748 // Sets the condition for completion of the subtask (how many threads
5749 // need to finish in order to be done).
5750 pst->set_n_threads(n_threads);
5751 pst->set_n_tasks(1);
5752 assert(pst->valid(), "Error");
5753 }
5754
5755 // From space
5756 {
5757 SequentialSubTasksDone* pst = dng->from()->par_seq_tasks();
5758 assert(!pst->valid(), "Clobbering existing data?");
5759 size_t n_tasks = _survivor_chunk_index + 1;
5760 assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
5761 // Sets the condition for completion of the subtask (how many threads
5762 // need to finish in order to be done).
5763 pst->set_n_threads(n_threads);
5764 pst->set_n_tasks((int)n_tasks);
5765 assert(pst->valid(), "Error");
5766 }
5767 }
5768
5769 // Parallel version of remark
5770 void CMSCollector::do_remark_parallel() {
5771 GenCollectedHeap* gch = GenCollectedHeap::heap();
5772 FlexibleWorkGang* workers = gch->workers();
5773 assert(workers != NULL, "Need parallel worker threads.");
5774 // Choose to use the number of GC workers most recently set
5775 // into "active_workers". If active_workers is not set, set it
5776 // to ParallelGCThreads.
5777 int n_workers = workers->active_workers();
5778 if (n_workers == 0) {
5779 assert(n_workers > 0, "Should have been set during scavenge");
5780 n_workers = ParallelGCThreads;
5781 workers->set_active_workers(n_workers);
5782 }
5783 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
5784
5785 CMSParRemarkTask tsk(this,
5786 cms_space,
5787 n_workers, workers, task_queues());
5788
5789 // Set up for parallel process_strong_roots work.
5790 gch->set_par_threads(n_workers);
5791 // We won't be iterating over the cards in the card table updating
5792 // the younger_gen cards, so we shouldn't call the following else
5793 // the verification code as well as subsequent younger_refs_iterate
5794 // code would get confused. XXX
5795 // gch->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
5796
5797 // The young gen rescan work will not be done as part of
5798 // process_strong_roots (which currently doesn't knw how to
5799 // parallelize such a scan), but rather will be broken up into
5800 // a set of parallel tasks (via the sampling that the [abortable]
5801 // preclean phase did of EdenSpace, plus the [two] tasks of
5802 // scanning the [two] survivor spaces. Further fine-grain
5803 // parallelization of the scanning of the survivor spaces
5804 // themselves, and of precleaning of the younger gen itself
5805 // is deferred to the future.
5806 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
5807
5808 // The dirty card rescan work is broken up into a "sequence"
5809 // of parallel tasks (per constituent space) that are dynamically
5810 // claimed by the parallel threads.
5811 cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
5812
5813 // It turns out that even when we're using 1 thread, doing the work in a
5814 // separate thread causes wide variance in run times. We can't help this
5815 // in the multi-threaded case, but we special-case n=1 here to get
5816 // repeatable measurements of the 1-thread overhead of the parallel code.
5817 if (n_workers > 1) {
5818 // Make refs discovery MT-safe, if it isn't already: it may not
5819 // necessarily be so, since it's possible that we are doing
5820 // ST marking.
5821 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), true);
5822 GenCollectedHeap::StrongRootsScope srs(gch);
5823 workers->run_task(&tsk);
5824 } else {
5825 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5826 GenCollectedHeap::StrongRootsScope srs(gch);
5827 tsk.work(0);
5828 }
5829
5830 gch->set_par_threads(0); // 0 ==> non-parallel.
5831 // restore, single-threaded for now, any preserved marks
5832 // as a result of work_q overflow
5833 restore_preserved_marks_if_any();
5834 }
5835
5836 // Non-parallel version of remark
5837 void CMSCollector::do_remark_non_parallel() {
5838 ResourceMark rm;
5839 HandleMark hm;
5840 GenCollectedHeap* gch = GenCollectedHeap::heap();
5841 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5842
5843 MarkRefsIntoAndScanClosure
5844 mrias_cl(_span, ref_processor(), &_markBitMap, NULL /* not precleaning */,
5845 &_markStack, this,
5846 false /* should_yield */, false /* not precleaning */);
5847 MarkFromDirtyCardsClosure
5848 markFromDirtyCardsClosure(this, _span,
5849 NULL, // space is set further below
5850 &_markBitMap, &_markStack, &mrias_cl);
5851 {
5852 GCTraceTime t("grey object rescan", PrintGCDetails, false, _gc_timer_cm);
5853 // Iterate over the dirty cards, setting the corresponding bits in the
5854 // mod union table.
5855 {
5856 ModUnionClosure modUnionClosure(&_modUnionTable);
5857 _ct->ct_bs()->dirty_card_iterate(
5858 _cmsGen->used_region(),
5859 &modUnionClosure);
5860 }
5861 // Having transferred these marks into the modUnionTable, we just need
5862 // to rescan the marked objects on the dirty cards in the modUnionTable.
5863 // The initial marking may have been done during an asynchronous
5864 // collection so there may be dirty bits in the mod-union table.
5865 const int alignment =
5866 CardTableModRefBS::card_size * BitsPerWord;
5867 {
5868 // ... First handle dirty cards in CMS gen
5869 markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
5870 MemRegion ur = _cmsGen->used_region();
5871 HeapWord* lb = ur.start();
5872 HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
5873 MemRegion cms_span(lb, ub);
5874 _modUnionTable.dirty_range_iterate_clear(cms_span,
5875 &markFromDirtyCardsClosure);
5876 verify_work_stacks_empty();
5877 if (PrintCMSStatistics != 0) {
5878 gclog_or_tty->print(" (re-scanned "SIZE_FORMAT" dirty cards in cms gen) ",
5879 markFromDirtyCardsClosure.num_dirty_cards());
5880 }
5881 }
5882 }
5883 if (VerifyDuringGC &&
5884 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5885 HandleMark hm; // Discard invalid handles created during verification
5886 Universe::verify();
5887 }
5888 {
5889 GCTraceTime t("root rescan", PrintGCDetails, false, _gc_timer_cm);
5890
5891 verify_work_stacks_empty();
5892
5893 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
5894 GenCollectedHeap::StrongRootsScope srs(gch);
5895 gch->gen_process_strong_roots(_cmsGen->level(),
5896 true, // younger gens as roots
5897 false, // use the local StrongRootsScope
5898 false, // not scavenging
5899 SharedHeap::ScanningOption(roots_scanning_options()),
5900 &mrias_cl,
5901 true, // walk code active on stacks
5902 NULL,
5903 NULL); // The dirty klasses will be handled below
5904
5905 assert(should_unload_classes()
5906 || (roots_scanning_options() & SharedHeap::SO_CodeCache),
5907 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5908 }
5909
5910 {
5911 GCTraceTime t("visit unhandled CLDs", PrintGCDetails, false, _gc_timer_cm);
5912
5913 verify_work_stacks_empty();
5914
5915 // Scan all class loader data objects that might have been introduced
5916 // during concurrent marking.
5917 ResourceMark rm;
5918 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
5919 for (int i = 0; i < array->length(); i++) {
5920 mrias_cl.do_class_loader_data(array->at(i));
5921 }
5922
5923 // We don't need to keep track of new CLDs anymore.
5924 ClassLoaderDataGraph::remember_new_clds(false);
5925
5926 verify_work_stacks_empty();
5927 }
5928
5929 {
5930 GCTraceTime t("dirty klass scan", PrintGCDetails, false, _gc_timer_cm);
5931
5932 verify_work_stacks_empty();
5933
5934 RemarkKlassClosure remark_klass_closure(&mrias_cl);
5935 ClassLoaderDataGraph::classes_do(&remark_klass_closure);
5936
5937 verify_work_stacks_empty();
5938 }
5939
5940 // We might have added oops to ClassLoaderData::_handles during the
5941 // concurrent marking phase. These oops point to newly allocated objects
5942 // that are guaranteed to be kept alive. Either by the direct allocation
5943 // code, or when the young collector processes the strong roots. Hence,
5944 // we don't have to revisit the _handles block during the remark phase.
5945
5946 verify_work_stacks_empty();
5947 // Restore evacuated mark words, if any, used for overflow list links
5948 if (!CMSOverflowEarlyRestoration) {
5949 restore_preserved_marks_if_any();
5950 }
5951 verify_overflow_empty();
5952 }
5953
5954 ////////////////////////////////////////////////////////
5955 // Parallel Reference Processing Task Proxy Class
5956 ////////////////////////////////////////////////////////
5957 class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues {
5958 typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
5959 CMSCollector* _collector;
5960 CMSBitMap* _mark_bit_map;
5961 const MemRegion _span;
5962 ProcessTask& _task;
5963
5964 public:
5965 CMSRefProcTaskProxy(ProcessTask& task,
5966 CMSCollector* collector,
5967 const MemRegion& span,
5968 CMSBitMap* mark_bit_map,
5969 AbstractWorkGang* workers,
5970 OopTaskQueueSet* task_queues):
5971 // XXX Should superclass AGTWOQ also know about AWG since it knows
5972 // about the task_queues used by the AWG? Then it could initialize
5973 // the terminator() object. See 6984287. The set_for_termination()
5974 // below is a temporary band-aid for the regression in 6984287.
5975 AbstractGangTaskWOopQueues("Process referents by policy in parallel",
5976 task_queues),
5977 _task(task),
5978 _collector(collector), _span(span), _mark_bit_map(mark_bit_map)
5979 {
5980 assert(_collector->_span.equals(_span) && !_span.is_empty(),
5981 "Inconsistency in _span");
5982 set_for_termination(workers->active_workers());
5983 }
5984
5985 OopTaskQueueSet* task_queues() { return queues(); }
5986
5987 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5988
5989 void do_work_steal(int i,
5990 CMSParDrainMarkingStackClosure* drain,
5991 CMSParKeepAliveClosure* keep_alive,
5992 int* seed);
5993
5994 virtual void work(uint worker_id);
5995 };
5996
5997 void CMSRefProcTaskProxy::work(uint worker_id) {
5998 assert(_collector->_span.equals(_span), "Inconsistency in _span");
5999 CMSParKeepAliveClosure par_keep_alive(_collector, _span,
6000 _mark_bit_map,
6001 work_queue(worker_id));
6002 CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
6003 _mark_bit_map,
6004 work_queue(worker_id));
6005 CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
6006 _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack);
6007 if (_task.marks_oops_alive()) {
6008 do_work_steal(worker_id, &par_drain_stack, &par_keep_alive,
6009 _collector->hash_seed(worker_id));
6010 }
6011 assert(work_queue(worker_id)->size() == 0, "work_queue should be empty");
6012 assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
6013 }
6014
6015 class CMSRefEnqueueTaskProxy: public AbstractGangTask {
6016 typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
6017 EnqueueTask& _task;
6018
6019 public:
6020 CMSRefEnqueueTaskProxy(EnqueueTask& task)
6021 : AbstractGangTask("Enqueue reference objects in parallel"),
6022 _task(task)
6023 { }
6024
6025 virtual void work(uint worker_id)
6026 {
6027 _task.work(worker_id);
6028 }
6029 };
6030
6031 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
6032 MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue):
6033 _span(span),
6034 _bit_map(bit_map),
6035 _work_queue(work_queue),
6036 _mark_and_push(collector, span, bit_map, work_queue),
6037 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
6038 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads)))
6039 { }
6040
6041 // . see if we can share work_queues with ParNew? XXX
6042 void CMSRefProcTaskProxy::do_work_steal(int i,
6043 CMSParDrainMarkingStackClosure* drain,
6044 CMSParKeepAliveClosure* keep_alive,
6045 int* seed) {
6046 OopTaskQueue* work_q = work_queue(i);
6047 NOT_PRODUCT(int num_steals = 0;)
6048 oop obj_to_scan;
6049
6050 while (true) {
6051 // Completely finish any left over work from (an) earlier round(s)
6052 drain->trim_queue(0);
6053 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
6054 (size_t)ParGCDesiredObjsFromOverflowList);
6055 // Now check if there's any work in the overflow list
6056 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
6057 // only affects the number of attempts made to get work from the
6058 // overflow list and does not affect the number of workers. Just
6059 // pass ParallelGCThreads so this behavior is unchanged.
6060 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
6061 work_q,
6062 ParallelGCThreads)) {
6063 // Found something in global overflow list;
6064 // not yet ready to go stealing work from others.
6065 // We'd like to assert(work_q->size() != 0, ...)
6066 // because we just took work from the overflow list,
6067 // but of course we can't, since all of that might have
6068 // been already stolen from us.
6069 continue;
6070 }
6071 // Verify that we have no work before we resort to stealing
6072 assert(work_q->size() == 0, "Have work, shouldn't steal");
6073 // Try to steal from other queues that have work
6074 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
6075 NOT_PRODUCT(num_steals++;)
6076 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
6077 assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
6078 // Do scanning work
6079 obj_to_scan->oop_iterate(keep_alive);
6080 // Loop around, finish this work, and try to steal some more
6081 } else if (terminator()->offer_termination()) {
6082 break; // nirvana from the infinite cycle
6083 }
6084 }
6085 NOT_PRODUCT(
6086 if (PrintCMSStatistics != 0) {
6087 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
6088 }
6089 )
6090 }
6091
6092 void CMSRefProcTaskExecutor::execute(ProcessTask& task)
6093 {
6094 GenCollectedHeap* gch = GenCollectedHeap::heap();
6095 FlexibleWorkGang* workers = gch->workers();
6096 assert(workers != NULL, "Need parallel worker threads.");
6097 CMSRefProcTaskProxy rp_task(task, &_collector,
6098 _collector.ref_processor()->span(),
6099 _collector.markBitMap(),
6100 workers, _collector.task_queues());
6101 workers->run_task(&rp_task);
6102 }
6103
6104 void CMSRefProcTaskExecutor::execute(EnqueueTask& task)
6105 {
6106
6107 GenCollectedHeap* gch = GenCollectedHeap::heap();
6108 FlexibleWorkGang* workers = gch->workers();
6109 assert(workers != NULL, "Need parallel worker threads.");
6110 CMSRefEnqueueTaskProxy enq_task(task);
6111 workers->run_task(&enq_task);
6112 }
6113
6114 void CMSCollector::refProcessingWork(bool asynch, bool clear_all_soft_refs) {
6115
6116 ResourceMark rm;
6117 HandleMark hm;
6118
6119 ReferenceProcessor* rp = ref_processor();
6120 assert(rp->span().equals(_span), "Spans should be equal");
6121 assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
6122 // Process weak references.
6123 rp->setup_policy(clear_all_soft_refs);
6124 verify_work_stacks_empty();
6125
6126 CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
6127 &_markStack, false /* !preclean */);
6128 CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
6129 _span, &_markBitMap, &_markStack,
6130 &cmsKeepAliveClosure, false /* !preclean */);
6131 {
6132 GCTraceTime t("weak refs processing", PrintGCDetails, false, _gc_timer_cm);
6133
6134 ReferenceProcessorStats stats;
6135 if (rp->processing_is_mt()) {
6136 // Set the degree of MT here. If the discovery is done MT, there
6137 // may have been a different number of threads doing the discovery
6138 // and a different number of discovered lists may have Ref objects.
6139 // That is OK as long as the Reference lists are balanced (see
6140 // balance_all_queues() and balance_queues()).
6141 GenCollectedHeap* gch = GenCollectedHeap::heap();
6142 int active_workers = ParallelGCThreads;
6143 FlexibleWorkGang* workers = gch->workers();
6144 if (workers != NULL) {
6145 active_workers = workers->active_workers();
6146 // The expectation is that active_workers will have already
6147 // been set to a reasonable value. If it has not been set,
6148 // investigate.
6149 assert(active_workers > 0, "Should have been set during scavenge");
6150 }
6151 rp->set_active_mt_degree(active_workers);
6152 CMSRefProcTaskExecutor task_executor(*this);
6153 stats = rp->process_discovered_references(&_is_alive_closure,
6154 &cmsKeepAliveClosure,
6155 &cmsDrainMarkingStackClosure,
6156 &task_executor,
6157 _gc_timer_cm);
6158 } else {
6159 stats = rp->process_discovered_references(&_is_alive_closure,
6160 &cmsKeepAliveClosure,
6161 &cmsDrainMarkingStackClosure,
6162 NULL,
6163 _gc_timer_cm);
6164 }
6165 _gc_tracer_cm->report_gc_reference_stats(stats);
6166
6167 }
6168
6169 // This is the point where the entire marking should have completed.
6170 verify_work_stacks_empty();
6171
6172 if (should_unload_classes()) {
6173 {
6174 GCTraceTime t("class unloading", PrintGCDetails, false, _gc_timer_cm);
6175
6176 // Unload classes and purge the SystemDictionary.
6177 bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure);
6178
6179 // Unload nmethods.
6180 CodeCache::do_unloading(&_is_alive_closure, purged_class);
6181
6182 // Prune dead klasses from subklass/sibling/implementor lists.
6183 Klass::clean_weak_klass_links(&_is_alive_closure);
6184 }
6185
6186 {
6187 GCTraceTime t("scrub symbol table", PrintGCDetails, false, _gc_timer_cm);
6188 // Clean up unreferenced symbols in symbol table.
6189 SymbolTable::unlink();
6190 }
6191 }
6192
6193 // CMS doesn't use the StringTable as hard roots when class unloading is turned off.
6194 // Need to check if we really scanned the StringTable.
6195 if ((roots_scanning_options() & SharedHeap::SO_Strings) == 0) {
6196 GCTraceTime t("scrub string table", PrintGCDetails, false, _gc_timer_cm);
6197 // Delete entries for dead interned strings.
6198 StringTable::unlink(&_is_alive_closure);
6199 }
6200
6201 // Restore any preserved marks as a result of mark stack or
6202 // work queue overflow
6203 restore_preserved_marks_if_any(); // done single-threaded for now
6204
6205 rp->set_enqueuing_is_done(true);
6206 if (rp->processing_is_mt()) {
6207 rp->balance_all_queues();
6208 CMSRefProcTaskExecutor task_executor(*this);
6209 rp->enqueue_discovered_references(&task_executor);
6210 } else {
6211 rp->enqueue_discovered_references(NULL);
6212 }
6213 rp->verify_no_references_recorded();
6214 assert(!rp->discovery_enabled(), "should have been disabled");
6215 }
6216
6217 #ifndef PRODUCT
6218 void CMSCollector::check_correct_thread_executing() {
6219 Thread* t = Thread::current();
6220 // Only the VM thread or the CMS thread should be here.
6221 assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
6222 "Unexpected thread type");
6223 // If this is the vm thread, the foreground process
6224 // should not be waiting. Note that _foregroundGCIsActive is
6225 // true while the foreground collector is waiting.
6226 if (_foregroundGCShouldWait) {
6227 // We cannot be the VM thread
6228 assert(t->is_ConcurrentGC_thread(),
6229 "Should be CMS thread");
6230 } else {
6231 // We can be the CMS thread only if we are in a stop-world
6232 // phase of CMS collection.
6233 if (t->is_ConcurrentGC_thread()) {
6234 assert(_collectorState == InitialMarking ||
6235 _collectorState == FinalMarking,
6236 "Should be a stop-world phase");
6237 // The CMS thread should be holding the CMS_token.
6238 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6239 "Potential interference with concurrently "
6240 "executing VM thread");
6241 }
6242 }
6243 }
6244 #endif
6245
6246 void CMSCollector::sweep(bool asynch) {
6247 assert(_collectorState == Sweeping, "just checking");
6248 check_correct_thread_executing();
6249 verify_work_stacks_empty();
6250 verify_overflow_empty();
6251 increment_sweep_count();
6252 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
6253
6254 _inter_sweep_timer.stop();
6255 _inter_sweep_estimate.sample(_inter_sweep_timer.seconds());
6256 size_policy()->avg_cms_free_at_sweep()->sample(_cmsGen->free());
6257
6258 assert(!_intra_sweep_timer.is_active(), "Should not be active");
6259 _intra_sweep_timer.reset();
6260 _intra_sweep_timer.start();
6261 if (asynch) {
6262 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6263 CMSPhaseAccounting pa(this, "sweep", !PrintGCDetails);
6264 // First sweep the old gen
6265 {
6266 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
6267 bitMapLock());
6268 sweepWork(_cmsGen, asynch);
6269 }
6270
6271 // Update Universe::_heap_*_at_gc figures.
6272 // We need all the free list locks to make the abstract state
6273 // transition from Sweeping to Resetting. See detailed note
6274 // further below.
6275 {
6276 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock());
6277 // Update heap occupancy information which is used as
6278 // input to soft ref clearing policy at the next gc.
6279 Universe::update_heap_info_at_gc();
6280 _collectorState = Resizing;
6281 }
6282 } else {
6283 // already have needed locks
6284 sweepWork(_cmsGen, asynch);
6285 // Update heap occupancy information which is used as
6286 // input to soft ref clearing policy at the next gc.
6287 Universe::update_heap_info_at_gc();
6288 _collectorState = Resizing;
6289 }
6290 verify_work_stacks_empty();
6291 verify_overflow_empty();
6292
6293 if (should_unload_classes()) {
6294 ClassLoaderDataGraph::purge();
6295 }
6296
6297 _intra_sweep_timer.stop();
6298 _intra_sweep_estimate.sample(_intra_sweep_timer.seconds());
6299
6300 _inter_sweep_timer.reset();
6301 _inter_sweep_timer.start();
6302
6303 // We need to use a monotonically non-deccreasing time in ms
6304 // or we will see time-warp warnings and os::javaTimeMillis()
6305 // does not guarantee monotonicity.
6306 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
6307 update_time_of_last_gc(now);
6308
6309 // NOTE on abstract state transitions:
6310 // Mutators allocate-live and/or mark the mod-union table dirty
6311 // based on the state of the collection. The former is done in
6312 // the interval [Marking, Sweeping] and the latter in the interval
6313 // [Marking, Sweeping). Thus the transitions into the Marking state
6314 // and out of the Sweeping state must be synchronously visible
6315 // globally to the mutators.
6316 // The transition into the Marking state happens with the world
6317 // stopped so the mutators will globally see it. Sweeping is
6318 // done asynchronously by the background collector so the transition
6319 // from the Sweeping state to the Resizing state must be done
6320 // under the freelistLock (as is the check for whether to
6321 // allocate-live and whether to dirty the mod-union table).
6322 assert(_collectorState == Resizing, "Change of collector state to"
6323 " Resizing must be done under the freelistLocks (plural)");
6324
6325 // Now that sweeping has been completed, we clear
6326 // the incremental_collection_failed flag,
6327 // thus inviting a younger gen collection to promote into
6328 // this generation. If such a promotion may still fail,
6329 // the flag will be set again when a young collection is
6330 // attempted.
6331 GenCollectedHeap* gch = GenCollectedHeap::heap();
6332 gch->clear_incremental_collection_failed(); // Worth retrying as fresh space may have been freed up
6333 gch->update_full_collections_completed(_collection_count_start);
6334 }
6335
6336 // FIX ME!!! Looks like this belongs in CFLSpace, with
6337 // CMSGen merely delegating to it.
6338 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
6339 double nearLargestPercent = FLSLargestBlockCoalesceProximity;
6340 HeapWord* minAddr = _cmsSpace->bottom();
6341 HeapWord* largestAddr =
6342 (HeapWord*) _cmsSpace->dictionary()->find_largest_dict();
6343 if (largestAddr == NULL) {
6344 // The dictionary appears to be empty. In this case
6345 // try to coalesce at the end of the heap.
6346 largestAddr = _cmsSpace->end();
6347 }
6348 size_t largestOffset = pointer_delta(largestAddr, minAddr);
6349 size_t nearLargestOffset =
6350 (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
6351 if (PrintFLSStatistics != 0) {
6352 gclog_or_tty->print_cr(
6353 "CMS: Large Block: " PTR_FORMAT ";"
6354 " Proximity: " PTR_FORMAT " -> " PTR_FORMAT,
6355 largestAddr,
6356 _cmsSpace->nearLargestChunk(), minAddr + nearLargestOffset);
6357 }
6358 _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
6359 }
6360
6361 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
6362 return addr >= _cmsSpace->nearLargestChunk();
6363 }
6364
6365 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
6366 return _cmsSpace->find_chunk_at_end();
6367 }
6368
6369 void ConcurrentMarkSweepGeneration::update_gc_stats(int current_level,
6370 bool full) {
6371 // The next lower level has been collected. Gather any statistics
6372 // that are of interest at this point.
6373 if (!full && (current_level + 1) == level()) {
6374 // Gather statistics on the young generation collection.
6375 collector()->stats().record_gc0_end(used());
6376 }
6377 }
6378
6379 CMSAdaptiveSizePolicy* ConcurrentMarkSweepGeneration::size_policy() {
6380 GenCollectedHeap* gch = GenCollectedHeap::heap();
6381 assert(gch->kind() == CollectedHeap::GenCollectedHeap,
6382 "Wrong type of heap");
6383 CMSAdaptiveSizePolicy* sp = (CMSAdaptiveSizePolicy*)
6384 gch->gen_policy()->size_policy();
6385 assert(sp->is_gc_cms_adaptive_size_policy(),
6386 "Wrong type of size policy");
6387 return sp;
6388 }
6389
6390 void ConcurrentMarkSweepGeneration::rotate_debug_collection_type() {
6391 if (PrintGCDetails && Verbose) {
6392 gclog_or_tty->print("Rotate from %d ", _debug_collection_type);
6393 }
6394 _debug_collection_type = (CollectionTypes) (_debug_collection_type + 1);
6395 _debug_collection_type =
6396 (CollectionTypes) (_debug_collection_type % Unknown_collection_type);
6397 if (PrintGCDetails && Verbose) {
6398 gclog_or_tty->print_cr("to %d ", _debug_collection_type);
6399 }
6400 }
6401
6402 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* gen,
6403 bool asynch) {
6404 // We iterate over the space(s) underlying this generation,
6405 // checking the mark bit map to see if the bits corresponding
6406 // to specific blocks are marked or not. Blocks that are
6407 // marked are live and are not swept up. All remaining blocks
6408 // are swept up, with coalescing on-the-fly as we sweep up
6409 // contiguous free and/or garbage blocks:
6410 // We need to ensure that the sweeper synchronizes with allocators
6411 // and stop-the-world collectors. In particular, the following
6412 // locks are used:
6413 // . CMS token: if this is held, a stop the world collection cannot occur
6414 // . freelistLock: if this is held no allocation can occur from this
6415 // generation by another thread
6416 // . bitMapLock: if this is held, no other thread can access or update
6417 //
6418
6419 // Note that we need to hold the freelistLock if we use
6420 // block iterate below; else the iterator might go awry if
6421 // a mutator (or promotion) causes block contents to change
6422 // (for instance if the allocator divvies up a block).
6423 // If we hold the free list lock, for all practical purposes
6424 // young generation GC's can't occur (they'll usually need to
6425 // promote), so we might as well prevent all young generation
6426 // GC's while we do a sweeping step. For the same reason, we might
6427 // as well take the bit map lock for the entire duration
6428
6429 // check that we hold the requisite locks
6430 assert(have_cms_token(), "Should hold cms token");
6431 assert( (asynch && ConcurrentMarkSweepThread::cms_thread_has_cms_token())
6432 || (!asynch && ConcurrentMarkSweepThread::vm_thread_has_cms_token()),
6433 "Should possess CMS token to sweep");
6434 assert_lock_strong(gen->freelistLock());
6435 assert_lock_strong(bitMapLock());
6436
6437 assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context");
6438 assert(_intra_sweep_timer.is_active(), "Was switched on in an outer context");
6439 gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
6440 _inter_sweep_estimate.padded_average(),
6441 _intra_sweep_estimate.padded_average());
6442 gen->setNearLargestChunk();
6443
6444 {
6445 SweepClosure sweepClosure(this, gen, &_markBitMap,
6446 CMSYield && asynch);
6447 gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
6448 // We need to free-up/coalesce garbage/blocks from a
6449 // co-terminal free run. This is done in the SweepClosure
6450 // destructor; so, do not remove this scope, else the
6451 // end-of-sweep-census below will be off by a little bit.
6452 }
6453 gen->cmsSpace()->sweep_completed();
6454 gen->cmsSpace()->endSweepFLCensus(sweep_count());
6455 if (should_unload_classes()) { // unloaded classes this cycle,
6456 _concurrent_cycles_since_last_unload = 0; // ... reset count
6457 } else { // did not unload classes,
6458 _concurrent_cycles_since_last_unload++; // ... increment count
6459 }
6460 }
6461
6462 // Reset CMS data structures (for now just the marking bit map)
6463 // preparatory for the next cycle.
6464 void CMSCollector::reset(bool asynch) {
6465 GenCollectedHeap* gch = GenCollectedHeap::heap();
6466 CMSAdaptiveSizePolicy* sp = size_policy();
6467 AdaptiveSizePolicyOutput(sp, gch->total_collections());
6468 if (asynch) {
6469 CMSTokenSyncWithLocks ts(true, bitMapLock());
6470
6471 // If the state is not "Resetting", the foreground thread
6472 // has done a collection and the resetting.
6473 if (_collectorState != Resetting) {
6474 assert(_collectorState == Idling, "The state should only change"
6475 " because the foreground collector has finished the collection");
6476 return;
6477 }
6478
6479 // Clear the mark bitmap (no grey objects to start with)
6480 // for the next cycle.
6481 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6482 CMSPhaseAccounting cmspa(this, "reset", !PrintGCDetails);
6483
6484 HeapWord* curAddr = _markBitMap.startWord();
6485 while (curAddr < _markBitMap.endWord()) {
6486 size_t remaining = pointer_delta(_markBitMap.endWord(), curAddr);
6487 MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
6488 _markBitMap.clear_large_range(chunk);
6489 if (ConcurrentMarkSweepThread::should_yield() &&
6490 !foregroundGCIsActive() &&
6491 CMSYield) {
6492 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6493 "CMS thread should hold CMS token");
6494 assert_lock_strong(bitMapLock());
6495 bitMapLock()->unlock();
6496 ConcurrentMarkSweepThread::desynchronize(true);
6497 ConcurrentMarkSweepThread::acknowledge_yield_request();
6498 stopTimer();
6499 if (PrintCMSStatistics != 0) {
6500 incrementYields();
6501 }
6502 icms_wait();
6503
6504 // See the comment in coordinator_yield()
6505 for (unsigned i = 0; i < CMSYieldSleepCount &&
6506 ConcurrentMarkSweepThread::should_yield() &&
6507 !CMSCollector::foregroundGCIsActive(); ++i) {
6508 os::sleep(Thread::current(), 1, false);
6509 ConcurrentMarkSweepThread::acknowledge_yield_request();
6510 }
6511
6512 ConcurrentMarkSweepThread::synchronize(true);
6513 bitMapLock()->lock_without_safepoint_check();
6514 startTimer();
6515 }
6516 curAddr = chunk.end();
6517 }
6518 // A successful mostly concurrent collection has been done.
6519 // Because only the full (i.e., concurrent mode failure) collections
6520 // are being measured for gc overhead limits, clean the "near" flag
6521 // and count.
6522 sp->reset_gc_overhead_limit_count();
6523 _collectorState = Idling;
6524 } else {
6525 // already have the lock
6526 assert(_collectorState == Resetting, "just checking");
6527 assert_lock_strong(bitMapLock());
6528 _markBitMap.clear_all();
6529 _collectorState = Idling;
6530 }
6531
6532 // Stop incremental mode after a cycle completes, so that any future cycles
6533 // are triggered by allocation.
6534 stop_icms();
6535
6536 NOT_PRODUCT(
6537 if (RotateCMSCollectionTypes) {
6538 _cmsGen->rotate_debug_collection_type();
6539 }
6540 )
6541
6542 register_gc_end();
6543 }
6544
6545 void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) {
6546 gclog_or_tty->date_stamp(PrintGC && PrintGCDateStamps);
6547 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6548 GCTraceTime t(GCCauseString("GC", gc_cause), PrintGC, !PrintGCDetails, NULL);
6549 TraceCollectorStats tcs(counters());
6550
6551 switch (op) {
6552 case CMS_op_checkpointRootsInitial: {
6553 SvcGCMarker sgcm(SvcGCMarker::OTHER);
6554 checkpointRootsInitial(true); // asynch
6555 if (PrintGC) {
6556 _cmsGen->printOccupancy("initial-mark");
6557 }
6558 break;
6559 }
6560 case CMS_op_checkpointRootsFinal: {
6561 SvcGCMarker sgcm(SvcGCMarker::OTHER);
6562 checkpointRootsFinal(true, // asynch
6563 false, // !clear_all_soft_refs
6564 false); // !init_mark_was_synchronous
6565 if (PrintGC) {
6566 _cmsGen->printOccupancy("remark");
6567 }
6568 break;
6569 }
6570 default:
6571 fatal("No such CMS_op");
6572 }
6573 }
6574
6575 #ifndef PRODUCT
6576 size_t const CMSCollector::skip_header_HeapWords() {
6577 return FreeChunk::header_size();
6578 }
6579
6580 // Try and collect here conditions that should hold when
6581 // CMS thread is exiting. The idea is that the foreground GC
6582 // thread should not be blocked if it wants to terminate
6583 // the CMS thread and yet continue to run the VM for a while
6584 // after that.
6585 void CMSCollector::verify_ok_to_terminate() const {
6586 assert(Thread::current()->is_ConcurrentGC_thread(),
6587 "should be called by CMS thread");
6588 assert(!_foregroundGCShouldWait, "should be false");
6589 // We could check here that all the various low-level locks
6590 // are not held by the CMS thread, but that is overkill; see
6591 // also CMSThread::verify_ok_to_terminate() where the CGC_lock
6592 // is checked.
6593 }
6594 #endif
6595
6596 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
6597 assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
6598 "missing Printezis mark?");
6599 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
6600 size_t size = pointer_delta(nextOneAddr + 1, addr);
6601 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6602 "alignment problem");
6603 assert(size >= 3, "Necessary for Printezis marks to work");
6604 return size;
6605 }
6606
6607 // A variant of the above (block_size_using_printezis_bits()) except
6608 // that we return 0 if the P-bits are not yet set.
6609 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
6610 if (_markBitMap.isMarked(addr + 1)) {
6611 assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects");
6612 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
6613 size_t size = pointer_delta(nextOneAddr + 1, addr);
6614 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6615 "alignment problem");
6616 assert(size >= 3, "Necessary for Printezis marks to work");
6617 return size;
6618 }
6619 return 0;
6620 }
6621
6622 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
6623 size_t sz = 0;
6624 oop p = (oop)addr;
6625 if (p->klass_or_null() != NULL) {
6626 sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
6627 } else {
6628 sz = block_size_using_printezis_bits(addr);
6629 }
6630 assert(sz > 0, "size must be nonzero");
6631 HeapWord* next_block = addr + sz;
6632 HeapWord* next_card = (HeapWord*)round_to((uintptr_t)next_block,
6633 CardTableModRefBS::card_size);
6634 assert(round_down((uintptr_t)addr, CardTableModRefBS::card_size) <
6635 round_down((uintptr_t)next_card, CardTableModRefBS::card_size),
6636 "must be different cards");
6637 return next_card;
6638 }
6639
6640
6641 // CMS Bit Map Wrapper /////////////////////////////////////////
6642
6643 // Construct a CMS bit map infrastructure, but don't create the
6644 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
6645 // further below.
6646 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
6647 _bm(),
6648 _shifter(shifter),
6649 _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true) : NULL)
6650 {
6651 _bmStartWord = 0;
6652 _bmWordSize = 0;
6653 }
6654
6655 bool CMSBitMap::allocate(MemRegion mr) {
6656 _bmStartWord = mr.start();
6657 _bmWordSize = mr.word_size();
6658 ReservedSpace brs(ReservedSpace::allocation_align_size_up(
6659 (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
6660 if (!brs.is_reserved()) {
6661 warning("CMS bit map allocation failure");
6662 return false;
6663 }
6664 // For now we'll just commit all of the bit map up fromt.
6665 // Later on we'll try to be more parsimonious with swap.
6666 if (!_virtual_space.initialize(brs, brs.size())) {
6667 warning("CMS bit map backing store failure");
6668 return false;
6669 }
6670 assert(_virtual_space.committed_size() == brs.size(),
6671 "didn't reserve backing store for all of CMS bit map?");
6672 _bm.set_map((BitMap::bm_word_t*)_virtual_space.low());
6673 assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
6674 _bmWordSize, "inconsistency in bit map sizing");
6675 _bm.set_size(_bmWordSize >> _shifter);
6676
6677 // bm.clear(); // can we rely on getting zero'd memory? verify below
6678 assert(isAllClear(),
6679 "Expected zero'd memory from ReservedSpace constructor");
6680 assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
6681 "consistency check");
6682 return true;
6683 }
6684
6685 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
6686 HeapWord *next_addr, *end_addr, *last_addr;
6687 assert_locked();
6688 assert(covers(mr), "out-of-range error");
6689 // XXX assert that start and end are appropriately aligned
6690 for (next_addr = mr.start(), end_addr = mr.end();
6691 next_addr < end_addr; next_addr = last_addr) {
6692 MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
6693 last_addr = dirty_region.end();
6694 if (!dirty_region.is_empty()) {
6695 cl->do_MemRegion(dirty_region);
6696 } else {
6697 assert(last_addr == end_addr, "program logic");
6698 return;
6699 }
6700 }
6701 }
6702
6703 void CMSBitMap::print_on_error(outputStream* st, const char* prefix) const {
6704 _bm.print_on_error(st, prefix);
6705 }
6706
6707 #ifndef PRODUCT
6708 void CMSBitMap::assert_locked() const {
6709 CMSLockVerifier::assert_locked(lock());
6710 }
6711
6712 bool CMSBitMap::covers(MemRegion mr) const {
6713 // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
6714 assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
6715 "size inconsistency");
6716 return (mr.start() >= _bmStartWord) &&
6717 (mr.end() <= endWord());
6718 }
6719
6720 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
6721 return (start >= _bmStartWord && (start + size) <= endWord());
6722 }
6723
6724 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
6725 // verify that there are no 1 bits in the interval [left, right)
6726 FalseBitMapClosure falseBitMapClosure;
6727 iterate(&falseBitMapClosure, left, right);
6728 }
6729
6730 void CMSBitMap::region_invariant(MemRegion mr)
6731 {
6732 assert_locked();
6733 // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
6734 assert(!mr.is_empty(), "unexpected empty region");
6735 assert(covers(mr), "mr should be covered by bit map");
6736 // convert address range into offset range
6737 size_t start_ofs = heapWordToOffset(mr.start());
6738 // Make sure that end() is appropriately aligned
6739 assert(mr.end() == (HeapWord*)round_to((intptr_t)mr.end(),
6740 (1 << (_shifter+LogHeapWordSize))),
6741 "Misaligned mr.end()");
6742 size_t end_ofs = heapWordToOffset(mr.end());
6743 assert(end_ofs > start_ofs, "Should mark at least one bit");
6744 }
6745
6746 #endif
6747
6748 bool CMSMarkStack::allocate(size_t size) {
6749 // allocate a stack of the requisite depth
6750 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6751 size * sizeof(oop)));
6752 if (!rs.is_reserved()) {
6753 warning("CMSMarkStack allocation failure");
6754 return false;
6755 }
6756 if (!_virtual_space.initialize(rs, rs.size())) {
6757 warning("CMSMarkStack backing store failure");
6758 return false;
6759 }
6760 assert(_virtual_space.committed_size() == rs.size(),
6761 "didn't reserve backing store for all of CMS stack?");
6762 _base = (oop*)(_virtual_space.low());
6763 _index = 0;
6764 _capacity = size;
6765 NOT_PRODUCT(_max_depth = 0);
6766 return true;
6767 }
6768
6769 // XXX FIX ME !!! In the MT case we come in here holding a
6770 // leaf lock. For printing we need to take a further lock
6771 // which has lower rank. We need to recallibrate the two
6772 // lock-ranks involved in order to be able to rpint the
6773 // messages below. (Or defer the printing to the caller.
6774 // For now we take the expedient path of just disabling the
6775 // messages for the problematic case.)
6776 void CMSMarkStack::expand() {
6777 assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted");
6778 if (_capacity == MarkStackSizeMax) {
6779 if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6780 // We print a warning message only once per CMS cycle.
6781 gclog_or_tty->print_cr(" (benign) Hit CMSMarkStack max size limit");
6782 }
6783 return;
6784 }
6785 // Double capacity if possible
6786 size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax);
6787 // Do not give up existing stack until we have managed to
6788 // get the double capacity that we desired.
6789 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6790 new_capacity * sizeof(oop)));
6791 if (rs.is_reserved()) {
6792 // Release the backing store associated with old stack
6793 _virtual_space.release();
6794 // Reinitialize virtual space for new stack
6795 if (!_virtual_space.initialize(rs, rs.size())) {
6796 fatal("Not enough swap for expanded marking stack");
6797 }
6798 _base = (oop*)(_virtual_space.low());
6799 _index = 0;
6800 _capacity = new_capacity;
6801 } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6802 // Failed to double capacity, continue;
6803 // we print a detail message only once per CMS cycle.
6804 gclog_or_tty->print(" (benign) Failed to expand marking stack from "SIZE_FORMAT"K to "
6805 SIZE_FORMAT"K",
6806 _capacity / K, new_capacity / K);
6807 }
6808 }
6809
6810
6811 // Closures
6812 // XXX: there seems to be a lot of code duplication here;
6813 // should refactor and consolidate common code.
6814
6815 // This closure is used to mark refs into the CMS generation in
6816 // the CMS bit map. Called at the first checkpoint. This closure
6817 // assumes that we do not need to re-mark dirty cards; if the CMS
6818 // generation on which this is used is not an oldest
6819 // generation then this will lose younger_gen cards!
6820
6821 MarkRefsIntoClosure::MarkRefsIntoClosure(
6822 MemRegion span, CMSBitMap* bitMap):
6823 _span(span),
6824 _bitMap(bitMap)
6825 {
6826 assert(_ref_processor == NULL, "deliberately left NULL");
6827 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6828 }
6829
6830 void MarkRefsIntoClosure::do_oop(oop obj) {
6831 // if p points into _span, then mark corresponding bit in _markBitMap
6832 assert(obj->is_oop(), "expected an oop");
6833 HeapWord* addr = (HeapWord*)obj;
6834 if (_span.contains(addr)) {
6835 // this should be made more efficient
6836 _bitMap->mark(addr);
6837 }
6838 }
6839
6840 void MarkRefsIntoClosure::do_oop(oop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6841 void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6842
6843 // A variant of the above, used for CMS marking verification.
6844 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
6845 MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm):
6846 _span(span),
6847 _verification_bm(verification_bm),
6848 _cms_bm(cms_bm)
6849 {
6850 assert(_ref_processor == NULL, "deliberately left NULL");
6851 assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
6852 }
6853
6854 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
6855 // if p points into _span, then mark corresponding bit in _markBitMap
6856 assert(obj->is_oop(), "expected an oop");
6857 HeapWord* addr = (HeapWord*)obj;
6858 if (_span.contains(addr)) {
6859 _verification_bm->mark(addr);
6860 if (!_cms_bm->isMarked(addr)) {
6861 oop(addr)->print();
6862 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)", addr);
6863 fatal("... aborting");
6864 }
6865 }
6866 }
6867
6868 void MarkRefsIntoVerifyClosure::do_oop(oop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6869 void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6870
6871 //////////////////////////////////////////////////
6872 // MarkRefsIntoAndScanClosure
6873 //////////////////////////////////////////////////
6874
6875 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
6876 ReferenceProcessor* rp,
6877 CMSBitMap* bit_map,
6878 CMSBitMap* mod_union_table,
6879 CMSMarkStack* mark_stack,
6880 CMSCollector* collector,
6881 bool should_yield,
6882 bool concurrent_precleaning):
6883 _collector(collector),
6884 _span(span),
6885 _bit_map(bit_map),
6886 _mark_stack(mark_stack),
6887 _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table,
6888 mark_stack, concurrent_precleaning),
6889 _yield(should_yield),
6890 _concurrent_precleaning(concurrent_precleaning),
6891 _freelistLock(NULL)
6892 {
6893 _ref_processor = rp;
6894 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6895 }
6896
6897 // This closure is used to mark refs into the CMS generation at the
6898 // second (final) checkpoint, and to scan and transitively follow
6899 // the unmarked oops. It is also used during the concurrent precleaning
6900 // phase while scanning objects on dirty cards in the CMS generation.
6901 // The marks are made in the marking bit map and the marking stack is
6902 // used for keeping the (newly) grey objects during the scan.
6903 // The parallel version (Par_...) appears further below.
6904 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6905 if (obj != NULL) {
6906 assert(obj->is_oop(), "expected an oop");
6907 HeapWord* addr = (HeapWord*)obj;
6908 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6909 assert(_collector->overflow_list_is_empty(),
6910 "overflow list should be empty");
6911 if (_span.contains(addr) &&
6912 !_bit_map->isMarked(addr)) {
6913 // mark bit map (object is now grey)
6914 _bit_map->mark(addr);
6915 // push on marking stack (stack should be empty), and drain the
6916 // stack by applying this closure to the oops in the oops popped
6917 // from the stack (i.e. blacken the grey objects)
6918 bool res = _mark_stack->push(obj);
6919 assert(res, "Should have space to push on empty stack");
6920 do {
6921 oop new_oop = _mark_stack->pop();
6922 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6923 assert(_bit_map->isMarked((HeapWord*)new_oop),
6924 "only grey objects on this stack");
6925 // iterate over the oops in this oop, marking and pushing
6926 // the ones in CMS heap (i.e. in _span).
6927 new_oop->oop_iterate(&_pushAndMarkClosure);
6928 // check if it's time to yield
6929 do_yield_check();
6930 } while (!_mark_stack->isEmpty() ||
6931 (!_concurrent_precleaning && take_from_overflow_list()));
6932 // if marking stack is empty, and we are not doing this
6933 // during precleaning, then check the overflow list
6934 }
6935 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6936 assert(_collector->overflow_list_is_empty(),
6937 "overflow list was drained above");
6938 // We could restore evacuated mark words, if any, used for
6939 // overflow list links here because the overflow list is
6940 // provably empty here. That would reduce the maximum
6941 // size requirements for preserved_{oop,mark}_stack.
6942 // But we'll just postpone it until we are all done
6943 // so we can just stream through.
6944 if (!_concurrent_precleaning && CMSOverflowEarlyRestoration) {
6945 _collector->restore_preserved_marks_if_any();
6946 assert(_collector->no_preserved_marks(), "No preserved marks");
6947 }
6948 assert(!CMSOverflowEarlyRestoration || _collector->no_preserved_marks(),
6949 "All preserved marks should have been restored above");
6950 }
6951 }
6952
6953 void MarkRefsIntoAndScanClosure::do_oop(oop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6954 void MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6955
6956 void MarkRefsIntoAndScanClosure::do_yield_work() {
6957 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6958 "CMS thread should hold CMS token");
6959 assert_lock_strong(_freelistLock);
6960 assert_lock_strong(_bit_map->lock());
6961 // relinquish the free_list_lock and bitMaplock()
6962 _bit_map->lock()->unlock();
6963 _freelistLock->unlock();
6964 ConcurrentMarkSweepThread::desynchronize(true);
6965 ConcurrentMarkSweepThread::acknowledge_yield_request();
6966 _collector->stopTimer();
6967 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
6968 if (PrintCMSStatistics != 0) {
6969 _collector->incrementYields();
6970 }
6971 _collector->icms_wait();
6972
6973 // See the comment in coordinator_yield()
6974 for (unsigned i = 0;
6975 i < CMSYieldSleepCount &&
6976 ConcurrentMarkSweepThread::should_yield() &&
6977 !CMSCollector::foregroundGCIsActive();
6978 ++i) {
6979 os::sleep(Thread::current(), 1, false);
6980 ConcurrentMarkSweepThread::acknowledge_yield_request();
6981 }
6982
6983 ConcurrentMarkSweepThread::synchronize(true);
6984 _freelistLock->lock_without_safepoint_check();
6985 _bit_map->lock()->lock_without_safepoint_check();
6986 _collector->startTimer();
6987 }
6988
6989 ///////////////////////////////////////////////////////////
6990 // Par_MarkRefsIntoAndScanClosure: a parallel version of
6991 // MarkRefsIntoAndScanClosure
6992 ///////////////////////////////////////////////////////////
6993 Par_MarkRefsIntoAndScanClosure::Par_MarkRefsIntoAndScanClosure(
6994 CMSCollector* collector, MemRegion span, ReferenceProcessor* rp,
6995 CMSBitMap* bit_map, OopTaskQueue* work_queue):
6996 _span(span),
6997 _bit_map(bit_map),
6998 _work_queue(work_queue),
6999 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
7000 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads))),
7001 _par_pushAndMarkClosure(collector, span, rp, bit_map, work_queue)
7002 {
7003 _ref_processor = rp;
7004 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7005 }
7006
7007 // This closure is used to mark refs into the CMS generation at the
7008 // second (final) checkpoint, and to scan and transitively follow
7009 // the unmarked oops. The marks are made in the marking bit map and
7010 // the work_queue is used for keeping the (newly) grey objects during
7011 // the scan phase whence they are also available for stealing by parallel
7012 // threads. Since the marking bit map is shared, updates are
7013 // synchronized (via CAS).
7014 void Par_MarkRefsIntoAndScanClosure::do_oop(oop obj) {
7015 if (obj != NULL) {
7016 // Ignore mark word because this could be an already marked oop
7017 // that may be chained at the end of the overflow list.
7018 assert(obj->is_oop(true), "expected an oop");
7019 HeapWord* addr = (HeapWord*)obj;
7020 if (_span.contains(addr) &&
7021 !_bit_map->isMarked(addr)) {
7022 // mark bit map (object will become grey):
7023 // It is possible for several threads to be
7024 // trying to "claim" this object concurrently;
7025 // the unique thread that succeeds in marking the
7026 // object first will do the subsequent push on
7027 // to the work queue (or overflow list).
7028 if (_bit_map->par_mark(addr)) {
7029 // push on work_queue (which may not be empty), and trim the
7030 // queue to an appropriate length by applying this closure to
7031 // the oops in the oops popped from the stack (i.e. blacken the
7032 // grey objects)
7033 bool res = _work_queue->push(obj);
7034 assert(res, "Low water mark should be less than capacity?");
7035 trim_queue(_low_water_mark);
7036 } // Else, another thread claimed the object
7037 }
7038 }
7039 }
7040
7041 void Par_MarkRefsIntoAndScanClosure::do_oop(oop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
7042 void Par_MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
7043
7044 // This closure is used to rescan the marked objects on the dirty cards
7045 // in the mod union table and the card table proper.
7046 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
7047 oop p, MemRegion mr) {
7048
7049 size_t size = 0;
7050 HeapWord* addr = (HeapWord*)p;
7051 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
7052 assert(_span.contains(addr), "we are scanning the CMS generation");
7053 // check if it's time to yield
7054 if (do_yield_check()) {
7055 // We yielded for some foreground stop-world work,
7056 // and we have been asked to abort this ongoing preclean cycle.
7057 return 0;
7058 }
7059 if (_bitMap->isMarked(addr)) {
7060 // it's marked; is it potentially uninitialized?
7061 if (p->klass_or_null() != NULL) {
7062 // an initialized object; ignore mark word in verification below
7063 // since we are running concurrent with mutators
7064 assert(p->is_oop(true), "should be an oop");
7065 if (p->is_objArray()) {
7066 // objArrays are precisely marked; restrict scanning
7067 // to dirty cards only.
7068 size = CompactibleFreeListSpace::adjustObjectSize(
7069 p->oop_iterate(_scanningClosure, mr));
7070 } else {
7071 // A non-array may have been imprecisely marked; we need
7072 // to scan object in its entirety.
7073 size = CompactibleFreeListSpace::adjustObjectSize(
7074 p->oop_iterate(_scanningClosure));
7075 }
7076 #ifdef ASSERT
7077 size_t direct_size =
7078 CompactibleFreeListSpace::adjustObjectSize(p->size());
7079 assert(size == direct_size, "Inconsistency in size");
7080 assert(size >= 3, "Necessary for Printezis marks to work");
7081 if (!_bitMap->isMarked(addr+1)) {
7082 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size);
7083 } else {
7084 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size-1);
7085 assert(_bitMap->isMarked(addr+size-1),
7086 "inconsistent Printezis mark");
7087 }
7088 #endif // ASSERT
7089 } else {
7090 // an unitialized object
7091 assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
7092 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
7093 size = pointer_delta(nextOneAddr + 1, addr);
7094 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
7095 "alignment problem");
7096 // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
7097 // will dirty the card when the klass pointer is installed in the
7098 // object (signalling the completion of initialization).
7099 }
7100 } else {
7101 // Either a not yet marked object or an uninitialized object
7102 if (p->klass_or_null() == NULL) {
7103 // An uninitialized object, skip to the next card, since
7104 // we may not be able to read its P-bits yet.
7105 assert(size == 0, "Initial value");
7106 } else {
7107 // An object not (yet) reached by marking: we merely need to
7108 // compute its size so as to go look at the next block.
7109 assert(p->is_oop(true), "should be an oop");
7110 size = CompactibleFreeListSpace::adjustObjectSize(p->size());
7111 }
7112 }
7113 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
7114 return size;
7115 }
7116
7117 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
7118 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7119 "CMS thread should hold CMS token");
7120 assert_lock_strong(_freelistLock);
7121 assert_lock_strong(_bitMap->lock());
7122 // relinquish the free_list_lock and bitMaplock()
7123 _bitMap->lock()->unlock();
7124 _freelistLock->unlock();
7125 ConcurrentMarkSweepThread::desynchronize(true);
7126 ConcurrentMarkSweepThread::acknowledge_yield_request();
7127 _collector->stopTimer();
7128 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7129 if (PrintCMSStatistics != 0) {
7130 _collector->incrementYields();
7131 }
7132 _collector->icms_wait();
7133
7134 // See the comment in coordinator_yield()
7135 for (unsigned i = 0; i < CMSYieldSleepCount &&
7136 ConcurrentMarkSweepThread::should_yield() &&
7137 !CMSCollector::foregroundGCIsActive(); ++i) {
7138 os::sleep(Thread::current(), 1, false);
7139 ConcurrentMarkSweepThread::acknowledge_yield_request();
7140 }
7141
7142 ConcurrentMarkSweepThread::synchronize(true);
7143 _freelistLock->lock_without_safepoint_check();
7144 _bitMap->lock()->lock_without_safepoint_check();
7145 _collector->startTimer();
7146 }
7147
7148
7149 //////////////////////////////////////////////////////////////////
7150 // SurvivorSpacePrecleanClosure
7151 //////////////////////////////////////////////////////////////////
7152 // This (single-threaded) closure is used to preclean the oops in
7153 // the survivor spaces.
7154 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
7155
7156 HeapWord* addr = (HeapWord*)p;
7157 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
7158 assert(!_span.contains(addr), "we are scanning the survivor spaces");
7159 assert(p->klass_or_null() != NULL, "object should be initializd");
7160 // an initialized object; ignore mark word in verification below
7161 // since we are running concurrent with mutators
7162 assert(p->is_oop(true), "should be an oop");
7163 // Note that we do not yield while we iterate over
7164 // the interior oops of p, pushing the relevant ones
7165 // on our marking stack.
7166 size_t size = p->oop_iterate(_scanning_closure);
7167 do_yield_check();
7168 // Observe that below, we do not abandon the preclean
7169 // phase as soon as we should; rather we empty the
7170 // marking stack before returning. This is to satisfy
7171 // some existing assertions. In general, it may be a
7172 // good idea to abort immediately and complete the marking
7173 // from the grey objects at a later time.
7174 while (!_mark_stack->isEmpty()) {
7175 oop new_oop = _mark_stack->pop();
7176 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
7177 assert(_bit_map->isMarked((HeapWord*)new_oop),
7178 "only grey objects on this stack");
7179 // iterate over the oops in this oop, marking and pushing
7180 // the ones in CMS heap (i.e. in _span).
7181 new_oop->oop_iterate(_scanning_closure);
7182 // check if it's time to yield
7183 do_yield_check();
7184 }
7185 unsigned int after_count =
7186 GenCollectedHeap::heap()->total_collections();
7187 bool abort = (_before_count != after_count) ||
7188 _collector->should_abort_preclean();
7189 return abort ? 0 : size;
7190 }
7191
7192 void SurvivorSpacePrecleanClosure::do_yield_work() {
7193 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7194 "CMS thread should hold CMS token");
7195 assert_lock_strong(_bit_map->lock());
7196 // Relinquish the bit map lock
7197 _bit_map->lock()->unlock();
7198 ConcurrentMarkSweepThread::desynchronize(true);
7199 ConcurrentMarkSweepThread::acknowledge_yield_request();
7200 _collector->stopTimer();
7201 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7202 if (PrintCMSStatistics != 0) {
7203 _collector->incrementYields();
7204 }
7205 _collector->icms_wait();
7206
7207 // See the comment in coordinator_yield()
7208 for (unsigned i = 0; i < CMSYieldSleepCount &&
7209 ConcurrentMarkSweepThread::should_yield() &&
7210 !CMSCollector::foregroundGCIsActive(); ++i) {
7211 os::sleep(Thread::current(), 1, false);
7212 ConcurrentMarkSweepThread::acknowledge_yield_request();
7213 }
7214
7215 ConcurrentMarkSweepThread::synchronize(true);
7216 _bit_map->lock()->lock_without_safepoint_check();
7217 _collector->startTimer();
7218 }
7219
7220 // This closure is used to rescan the marked objects on the dirty cards
7221 // in the mod union table and the card table proper. In the parallel
7222 // case, although the bitMap is shared, we do a single read so the
7223 // isMarked() query is "safe".
7224 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
7225 // Ignore mark word because we are running concurrent with mutators
7226 assert(p->is_oop_or_null(true), "expected an oop or null");
7227 HeapWord* addr = (HeapWord*)p;
7228 assert(_span.contains(addr), "we are scanning the CMS generation");
7229 bool is_obj_array = false;
7230 #ifdef ASSERT
7231 if (!_parallel) {
7232 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
7233 assert(_collector->overflow_list_is_empty(),
7234 "overflow list should be empty");
7235
7236 }
7237 #endif // ASSERT
7238 if (_bit_map->isMarked(addr)) {
7239 // Obj arrays are precisely marked, non-arrays are not;
7240 // so we scan objArrays precisely and non-arrays in their
7241 // entirety.
7242 if (p->is_objArray()) {
7243 is_obj_array = true;
7244 if (_parallel) {
7245 p->oop_iterate(_par_scan_closure, mr);
7246 } else {
7247 p->oop_iterate(_scan_closure, mr);
7248 }
7249 } else {
7250 if (_parallel) {
7251 p->oop_iterate(_par_scan_closure);
7252 } else {
7253 p->oop_iterate(_scan_closure);
7254 }
7255 }
7256 }
7257 #ifdef ASSERT
7258 if (!_parallel) {
7259 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
7260 assert(_collector->overflow_list_is_empty(),
7261 "overflow list should be empty");
7262
7263 }
7264 #endif // ASSERT
7265 return is_obj_array;
7266 }
7267
7268 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
7269 MemRegion span,
7270 CMSBitMap* bitMap, CMSMarkStack* markStack,
7271 bool should_yield, bool verifying):
7272 _collector(collector),
7273 _span(span),
7274 _bitMap(bitMap),
7275 _mut(&collector->_modUnionTable),
7276 _markStack(markStack),
7277 _yield(should_yield),
7278 _skipBits(0)
7279 {
7280 assert(_markStack->isEmpty(), "stack should be empty");
7281 _finger = _bitMap->startWord();
7282 _threshold = _finger;
7283 assert(_collector->_restart_addr == NULL, "Sanity check");
7284 assert(_span.contains(_finger), "Out of bounds _finger?");
7285 DEBUG_ONLY(_verifying = verifying;)
7286 }
7287
7288 void MarkFromRootsClosure::reset(HeapWord* addr) {
7289 assert(_markStack->isEmpty(), "would cause duplicates on stack");
7290 assert(_span.contains(addr), "Out of bounds _finger?");
7291 _finger = addr;
7292 _threshold = (HeapWord*)round_to(
7293 (intptr_t)_finger, CardTableModRefBS::card_size);
7294 }
7295
7296 // Should revisit to see if this should be restructured for
7297 // greater efficiency.
7298 bool MarkFromRootsClosure::do_bit(size_t offset) {
7299 if (_skipBits > 0) {
7300 _skipBits--;
7301 return true;
7302 }
7303 // convert offset into a HeapWord*
7304 HeapWord* addr = _bitMap->startWord() + offset;
7305 assert(_bitMap->endWord() && addr < _bitMap->endWord(),
7306 "address out of range");
7307 assert(_bitMap->isMarked(addr), "tautology");
7308 if (_bitMap->isMarked(addr+1)) {
7309 // this is an allocated but not yet initialized object
7310 assert(_skipBits == 0, "tautology");
7311 _skipBits = 2; // skip next two marked bits ("Printezis-marks")
7312 oop p = oop(addr);
7313 if (p->klass_or_null() == NULL) {
7314 DEBUG_ONLY(if (!_verifying) {)
7315 // We re-dirty the cards on which this object lies and increase
7316 // the _threshold so that we'll come back to scan this object
7317 // during the preclean or remark phase. (CMSCleanOnEnter)
7318 if (CMSCleanOnEnter) {
7319 size_t sz = _collector->block_size_using_printezis_bits(addr);
7320 HeapWord* end_card_addr = (HeapWord*)round_to(
7321 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7322 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7323 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7324 // Bump _threshold to end_card_addr; note that
7325 // _threshold cannot possibly exceed end_card_addr, anyhow.
7326 // This prevents future clearing of the card as the scan proceeds
7327 // to the right.
7328 assert(_threshold <= end_card_addr,
7329 "Because we are just scanning into this object");
7330 if (_threshold < end_card_addr) {
7331 _threshold = end_card_addr;
7332 }
7333 if (p->klass_or_null() != NULL) {
7334 // Redirty the range of cards...
7335 _mut->mark_range(redirty_range);
7336 } // ...else the setting of klass will dirty the card anyway.
7337 }
7338 DEBUG_ONLY(})
7339 return true;
7340 }
7341 }
7342 scanOopsInOop(addr);
7343 return true;
7344 }
7345
7346 // We take a break if we've been at this for a while,
7347 // so as to avoid monopolizing the locks involved.
7348 void MarkFromRootsClosure::do_yield_work() {
7349 // First give up the locks, then yield, then re-lock
7350 // We should probably use a constructor/destructor idiom to
7351 // do this unlock/lock or modify the MutexUnlocker class to
7352 // serve our purpose. XXX
7353 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7354 "CMS thread should hold CMS token");
7355 assert_lock_strong(_bitMap->lock());
7356 _bitMap->lock()->unlock();
7357 ConcurrentMarkSweepThread::desynchronize(true);
7358 ConcurrentMarkSweepThread::acknowledge_yield_request();
7359 _collector->stopTimer();
7360 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7361 if (PrintCMSStatistics != 0) {
7362 _collector->incrementYields();
7363 }
7364 _collector->icms_wait();
7365
7366 // See the comment in coordinator_yield()
7367 for (unsigned i = 0; i < CMSYieldSleepCount &&
7368 ConcurrentMarkSweepThread::should_yield() &&
7369 !CMSCollector::foregroundGCIsActive(); ++i) {
7370 os::sleep(Thread::current(), 1, false);
7371 ConcurrentMarkSweepThread::acknowledge_yield_request();
7372 }
7373
7374 ConcurrentMarkSweepThread::synchronize(true);
7375 _bitMap->lock()->lock_without_safepoint_check();
7376 _collector->startTimer();
7377 }
7378
7379 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
7380 assert(_bitMap->isMarked(ptr), "expected bit to be set");
7381 assert(_markStack->isEmpty(),
7382 "should drain stack to limit stack usage");
7383 // convert ptr to an oop preparatory to scanning
7384 oop obj = oop(ptr);
7385 // Ignore mark word in verification below, since we
7386 // may be running concurrent with mutators.
7387 assert(obj->is_oop(true), "should be an oop");
7388 assert(_finger <= ptr, "_finger runneth ahead");
7389 // advance the finger to right end of this object
7390 _finger = ptr + obj->size();
7391 assert(_finger > ptr, "we just incremented it above");
7392 // On large heaps, it may take us some time to get through
7393 // the marking phase (especially if running iCMS). During
7394 // this time it's possible that a lot of mutations have
7395 // accumulated in the card table and the mod union table --
7396 // these mutation records are redundant until we have
7397 // actually traced into the corresponding card.
7398 // Here, we check whether advancing the finger would make
7399 // us cross into a new card, and if so clear corresponding
7400 // cards in the MUT (preclean them in the card-table in the
7401 // future).
7402
7403 DEBUG_ONLY(if (!_verifying) {)
7404 // The clean-on-enter optimization is disabled by default,
7405 // until we fix 6178663.
7406 if (CMSCleanOnEnter && (_finger > _threshold)) {
7407 // [_threshold, _finger) represents the interval
7408 // of cards to be cleared in MUT (or precleaned in card table).
7409 // The set of cards to be cleared is all those that overlap
7410 // with the interval [_threshold, _finger); note that
7411 // _threshold is always kept card-aligned but _finger isn't
7412 // always card-aligned.
7413 HeapWord* old_threshold = _threshold;
7414 assert(old_threshold == (HeapWord*)round_to(
7415 (intptr_t)old_threshold, CardTableModRefBS::card_size),
7416 "_threshold should always be card-aligned");
7417 _threshold = (HeapWord*)round_to(
7418 (intptr_t)_finger, CardTableModRefBS::card_size);
7419 MemRegion mr(old_threshold, _threshold);
7420 assert(!mr.is_empty(), "Control point invariant");
7421 assert(_span.contains(mr), "Should clear within span");
7422 _mut->clear_range(mr);
7423 }
7424 DEBUG_ONLY(})
7425 // Note: the finger doesn't advance while we drain
7426 // the stack below.
7427 PushOrMarkClosure pushOrMarkClosure(_collector,
7428 _span, _bitMap, _markStack,
7429 _finger, this);
7430 bool res = _markStack->push(obj);
7431 assert(res, "Empty non-zero size stack should have space for single push");
7432 while (!_markStack->isEmpty()) {
7433 oop new_oop = _markStack->pop();
7434 // Skip verifying header mark word below because we are
7435 // running concurrent with mutators.
7436 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
7437 // now scan this oop's oops
7438 new_oop->oop_iterate(&pushOrMarkClosure);
7439 do_yield_check();
7440 }
7441 assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
7442 }
7443
7444 Par_MarkFromRootsClosure::Par_MarkFromRootsClosure(CMSConcMarkingTask* task,
7445 CMSCollector* collector, MemRegion span,
7446 CMSBitMap* bit_map,
7447 OopTaskQueue* work_queue,
7448 CMSMarkStack* overflow_stack,
7449 bool should_yield):
7450 _collector(collector),
7451 _whole_span(collector->_span),
7452 _span(span),
7453 _bit_map(bit_map),
7454 _mut(&collector->_modUnionTable),
7455 _work_queue(work_queue),
7456 _overflow_stack(overflow_stack),
7457 _yield(should_yield),
7458 _skip_bits(0),
7459 _task(task)
7460 {
7461 assert(_work_queue->size() == 0, "work_queue should be empty");
7462 _finger = span.start();
7463 _threshold = _finger; // XXX Defer clear-on-enter optimization for now
7464 assert(_span.contains(_finger), "Out of bounds _finger?");
7465 }
7466
7467 // Should revisit to see if this should be restructured for
7468 // greater efficiency.
7469 bool Par_MarkFromRootsClosure::do_bit(size_t offset) {
7470 if (_skip_bits > 0) {
7471 _skip_bits--;
7472 return true;
7473 }
7474 // convert offset into a HeapWord*
7475 HeapWord* addr = _bit_map->startWord() + offset;
7476 assert(_bit_map->endWord() && addr < _bit_map->endWord(),
7477 "address out of range");
7478 assert(_bit_map->isMarked(addr), "tautology");
7479 if (_bit_map->isMarked(addr+1)) {
7480 // this is an allocated object that might not yet be initialized
7481 assert(_skip_bits == 0, "tautology");
7482 _skip_bits = 2; // skip next two marked bits ("Printezis-marks")
7483 oop p = oop(addr);
7484 if (p->klass_or_null() == NULL) {
7485 // in the case of Clean-on-Enter optimization, redirty card
7486 // and avoid clearing card by increasing the threshold.
7487 return true;
7488 }
7489 }
7490 scan_oops_in_oop(addr);
7491 return true;
7492 }
7493
7494 void Par_MarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
7495 assert(_bit_map->isMarked(ptr), "expected bit to be set");
7496 // Should we assert that our work queue is empty or
7497 // below some drain limit?
7498 assert(_work_queue->size() == 0,
7499 "should drain stack to limit stack usage");
7500 // convert ptr to an oop preparatory to scanning
7501 oop obj = oop(ptr);
7502 // Ignore mark word in verification below, since we
7503 // may be running concurrent with mutators.
7504 assert(obj->is_oop(true), "should be an oop");
7505 assert(_finger <= ptr, "_finger runneth ahead");
7506 // advance the finger to right end of this object
7507 _finger = ptr + obj->size();
7508 assert(_finger > ptr, "we just incremented it above");
7509 // On large heaps, it may take us some time to get through
7510 // the marking phase (especially if running iCMS). During
7511 // this time it's possible that a lot of mutations have
7512 // accumulated in the card table and the mod union table --
7513 // these mutation records are redundant until we have
7514 // actually traced into the corresponding card.
7515 // Here, we check whether advancing the finger would make
7516 // us cross into a new card, and if so clear corresponding
7517 // cards in the MUT (preclean them in the card-table in the
7518 // future).
7519
7520 // The clean-on-enter optimization is disabled by default,
7521 // until we fix 6178663.
7522 if (CMSCleanOnEnter && (_finger > _threshold)) {
7523 // [_threshold, _finger) represents the interval
7524 // of cards to be cleared in MUT (or precleaned in card table).
7525 // The set of cards to be cleared is all those that overlap
7526 // with the interval [_threshold, _finger); note that
7527 // _threshold is always kept card-aligned but _finger isn't
7528 // always card-aligned.
7529 HeapWord* old_threshold = _threshold;
7530 assert(old_threshold == (HeapWord*)round_to(
7531 (intptr_t)old_threshold, CardTableModRefBS::card_size),
7532 "_threshold should always be card-aligned");
7533 _threshold = (HeapWord*)round_to(
7534 (intptr_t)_finger, CardTableModRefBS::card_size);
7535 MemRegion mr(old_threshold, _threshold);
7536 assert(!mr.is_empty(), "Control point invariant");
7537 assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
7538 _mut->clear_range(mr);
7539 }
7540
7541 // Note: the local finger doesn't advance while we drain
7542 // the stack below, but the global finger sure can and will.
7543 HeapWord** gfa = _task->global_finger_addr();
7544 Par_PushOrMarkClosure pushOrMarkClosure(_collector,
7545 _span, _bit_map,
7546 _work_queue,
7547 _overflow_stack,
7548 _finger,
7549 gfa, this);
7550 bool res = _work_queue->push(obj); // overflow could occur here
7551 assert(res, "Will hold once we use workqueues");
7552 while (true) {
7553 oop new_oop;
7554 if (!_work_queue->pop_local(new_oop)) {
7555 // We emptied our work_queue; check if there's stuff that can
7556 // be gotten from the overflow stack.
7557 if (CMSConcMarkingTask::get_work_from_overflow_stack(
7558 _overflow_stack, _work_queue)) {
7559 do_yield_check();
7560 continue;
7561 } else { // done
7562 break;
7563 }
7564 }
7565 // Skip verifying header mark word below because we are
7566 // running concurrent with mutators.
7567 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
7568 // now scan this oop's oops
7569 new_oop->oop_iterate(&pushOrMarkClosure);
7570 do_yield_check();
7571 }
7572 assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
7573 }
7574
7575 // Yield in response to a request from VM Thread or
7576 // from mutators.
7577 void Par_MarkFromRootsClosure::do_yield_work() {
7578 assert(_task != NULL, "sanity");
7579 _task->yield();
7580 }
7581
7582 // A variant of the above used for verifying CMS marking work.
7583 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
7584 MemRegion span,
7585 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
7586 CMSMarkStack* mark_stack):
7587 _collector(collector),
7588 _span(span),
7589 _verification_bm(verification_bm),
7590 _cms_bm(cms_bm),
7591 _mark_stack(mark_stack),
7592 _pam_verify_closure(collector, span, verification_bm, cms_bm,
7593 mark_stack)
7594 {
7595 assert(_mark_stack->isEmpty(), "stack should be empty");
7596 _finger = _verification_bm->startWord();
7597 assert(_collector->_restart_addr == NULL, "Sanity check");
7598 assert(_span.contains(_finger), "Out of bounds _finger?");
7599 }
7600
7601 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
7602 assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
7603 assert(_span.contains(addr), "Out of bounds _finger?");
7604 _finger = addr;
7605 }
7606
7607 // Should revisit to see if this should be restructured for
7608 // greater efficiency.
7609 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
7610 // convert offset into a HeapWord*
7611 HeapWord* addr = _verification_bm->startWord() + offset;
7612 assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
7613 "address out of range");
7614 assert(_verification_bm->isMarked(addr), "tautology");
7615 assert(_cms_bm->isMarked(addr), "tautology");
7616
7617 assert(_mark_stack->isEmpty(),
7618 "should drain stack to limit stack usage");
7619 // convert addr to an oop preparatory to scanning
7620 oop obj = oop(addr);
7621 assert(obj->is_oop(), "should be an oop");
7622 assert(_finger <= addr, "_finger runneth ahead");
7623 // advance the finger to right end of this object
7624 _finger = addr + obj->size();
7625 assert(_finger > addr, "we just incremented it above");
7626 // Note: the finger doesn't advance while we drain
7627 // the stack below.
7628 bool res = _mark_stack->push(obj);
7629 assert(res, "Empty non-zero size stack should have space for single push");
7630 while (!_mark_stack->isEmpty()) {
7631 oop new_oop = _mark_stack->pop();
7632 assert(new_oop->is_oop(), "Oops! expected to pop an oop");
7633 // now scan this oop's oops
7634 new_oop->oop_iterate(&_pam_verify_closure);
7635 }
7636 assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
7637 return true;
7638 }
7639
7640 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
7641 CMSCollector* collector, MemRegion span,
7642 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
7643 CMSMarkStack* mark_stack):
7644 CMSOopClosure(collector->ref_processor()),
7645 _collector(collector),
7646 _span(span),
7647 _verification_bm(verification_bm),
7648 _cms_bm(cms_bm),
7649 _mark_stack(mark_stack)
7650 { }
7651
7652 void PushAndMarkVerifyClosure::do_oop(oop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
7653 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
7654
7655 // Upon stack overflow, we discard (part of) the stack,
7656 // remembering the least address amongst those discarded
7657 // in CMSCollector's _restart_address.
7658 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
7659 // Remember the least grey address discarded
7660 HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
7661 _collector->lower_restart_addr(ra);
7662 _mark_stack->reset(); // discard stack contents
7663 _mark_stack->expand(); // expand the stack if possible
7664 }
7665
7666 void PushAndMarkVerifyClosure::do_oop(oop obj) {
7667 assert(obj->is_oop_or_null(), "expected an oop or NULL");
7668 HeapWord* addr = (HeapWord*)obj;
7669 if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
7670 // Oop lies in _span and isn't yet grey or black
7671 _verification_bm->mark(addr); // now grey
7672 if (!_cms_bm->isMarked(addr)) {
7673 oop(addr)->print();
7674 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)",
7675 addr);
7676 fatal("... aborting");
7677 }
7678
7679 if (!_mark_stack->push(obj)) { // stack overflow
7680 if (PrintCMSStatistics != 0) {
7681 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7682 SIZE_FORMAT, _mark_stack->capacity());
7683 }
7684 assert(_mark_stack->isFull(), "Else push should have succeeded");
7685 handle_stack_overflow(addr);
7686 }
7687 // anything including and to the right of _finger
7688 // will be scanned as we iterate over the remainder of the
7689 // bit map
7690 }
7691 }
7692
7693 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
7694 MemRegion span,
7695 CMSBitMap* bitMap, CMSMarkStack* markStack,
7696 HeapWord* finger, MarkFromRootsClosure* parent) :
7697 CMSOopClosure(collector->ref_processor()),
7698 _collector(collector),
7699 _span(span),
7700 _bitMap(bitMap),
7701 _markStack(markStack),
7702 _finger(finger),
7703 _parent(parent)
7704 { }
7705
7706 Par_PushOrMarkClosure::Par_PushOrMarkClosure(CMSCollector* collector,
7707 MemRegion span,
7708 CMSBitMap* bit_map,
7709 OopTaskQueue* work_queue,
7710 CMSMarkStack* overflow_stack,
7711 HeapWord* finger,
7712 HeapWord** global_finger_addr,
7713 Par_MarkFromRootsClosure* parent) :
7714 CMSOopClosure(collector->ref_processor()),
7715 _collector(collector),
7716 _whole_span(collector->_span),
7717 _span(span),
7718 _bit_map(bit_map),
7719 _work_queue(work_queue),
7720 _overflow_stack(overflow_stack),
7721 _finger(finger),
7722 _global_finger_addr(global_finger_addr),
7723 _parent(parent)
7724 { }
7725
7726 // Assumes thread-safe access by callers, who are
7727 // responsible for mutual exclusion.
7728 void CMSCollector::lower_restart_addr(HeapWord* low) {
7729 assert(_span.contains(low), "Out of bounds addr");
7730 if (_restart_addr == NULL) {
7731 _restart_addr = low;
7732 } else {
7733 _restart_addr = MIN2(_restart_addr, low);
7734 }
7735 }
7736
7737 // Upon stack overflow, we discard (part of) the stack,
7738 // remembering the least address amongst those discarded
7739 // in CMSCollector's _restart_address.
7740 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7741 // Remember the least grey address discarded
7742 HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
7743 _collector->lower_restart_addr(ra);
7744 _markStack->reset(); // discard stack contents
7745 _markStack->expand(); // expand the stack if possible
7746 }
7747
7748 // Upon stack overflow, we discard (part of) the stack,
7749 // remembering the least address amongst those discarded
7750 // in CMSCollector's _restart_address.
7751 void Par_PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7752 // We need to do this under a mutex to prevent other
7753 // workers from interfering with the work done below.
7754 MutexLockerEx ml(_overflow_stack->par_lock(),
7755 Mutex::_no_safepoint_check_flag);
7756 // Remember the least grey address discarded
7757 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
7758 _collector->lower_restart_addr(ra);
7759 _overflow_stack->reset(); // discard stack contents
7760 _overflow_stack->expand(); // expand the stack if possible
7761 }
7762
7763 void CMKlassClosure::do_klass(Klass* k) {
7764 assert(_oop_closure != NULL, "Not initialized?");
7765 k->oops_do(_oop_closure);
7766 }
7767
7768 void PushOrMarkClosure::do_oop(oop obj) {
7769 // Ignore mark word because we are running concurrent with mutators.
7770 assert(obj->is_oop_or_null(true), "expected an oop or NULL");
7771 HeapWord* addr = (HeapWord*)obj;
7772 if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
7773 // Oop lies in _span and isn't yet grey or black
7774 _bitMap->mark(addr); // now grey
7775 if (addr < _finger) {
7776 // the bit map iteration has already either passed, or
7777 // sampled, this bit in the bit map; we'll need to
7778 // use the marking stack to scan this oop's oops.
7779 bool simulate_overflow = false;
7780 NOT_PRODUCT(
7781 if (CMSMarkStackOverflowALot &&
7782 _collector->simulate_overflow()) {
7783 // simulate a stack overflow
7784 simulate_overflow = true;
7785 }
7786 )
7787 if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
7788 if (PrintCMSStatistics != 0) {
7789 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7790 SIZE_FORMAT, _markStack->capacity());
7791 }
7792 assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
7793 handle_stack_overflow(addr);
7794 }
7795 }
7796 // anything including and to the right of _finger
7797 // will be scanned as we iterate over the remainder of the
7798 // bit map
7799 do_yield_check();
7800 }
7801 }
7802
7803 void PushOrMarkClosure::do_oop(oop* p) { PushOrMarkClosure::do_oop_work(p); }
7804 void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); }
7805
7806 void Par_PushOrMarkClosure::do_oop(oop obj) {
7807 // Ignore mark word because we are running concurrent with mutators.
7808 assert(obj->is_oop_or_null(true), "expected an oop or NULL");
7809 HeapWord* addr = (HeapWord*)obj;
7810 if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
7811 // Oop lies in _span and isn't yet grey or black
7812 // We read the global_finger (volatile read) strictly after marking oop
7813 bool res = _bit_map->par_mark(addr); // now grey
7814 volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
7815 // Should we push this marked oop on our stack?
7816 // -- if someone else marked it, nothing to do
7817 // -- if target oop is above global finger nothing to do
7818 // -- if target oop is in chunk and above local finger
7819 // then nothing to do
7820 // -- else push on work queue
7821 if ( !res // someone else marked it, they will deal with it
7822 || (addr >= *gfa) // will be scanned in a later task
7823 || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
7824 return;
7825 }
7826 // the bit map iteration has already either passed, or
7827 // sampled, this bit in the bit map; we'll need to
7828 // use the marking stack to scan this oop's oops.
7829 bool simulate_overflow = false;
7830 NOT_PRODUCT(
7831 if (CMSMarkStackOverflowALot &&
7832 _collector->simulate_overflow()) {
7833 // simulate a stack overflow
7834 simulate_overflow = true;
7835 }
7836 )
7837 if (simulate_overflow ||
7838 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
7839 // stack overflow
7840 if (PrintCMSStatistics != 0) {
7841 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7842 SIZE_FORMAT, _overflow_stack->capacity());
7843 }
7844 // We cannot assert that the overflow stack is full because
7845 // it may have been emptied since.
7846 assert(simulate_overflow ||
7847 _work_queue->size() == _work_queue->max_elems(),
7848 "Else push should have succeeded");
7849 handle_stack_overflow(addr);
7850 }
7851 do_yield_check();
7852 }
7853 }
7854
7855 void Par_PushOrMarkClosure::do_oop(oop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7856 void Par_PushOrMarkClosure::do_oop(narrowOop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7857
7858 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
7859 MemRegion span,
7860 ReferenceProcessor* rp,
7861 CMSBitMap* bit_map,
7862 CMSBitMap* mod_union_table,
7863 CMSMarkStack* mark_stack,
7864 bool concurrent_precleaning):
7865 CMSOopClosure(rp),
7866 _collector(collector),
7867 _span(span),
7868 _bit_map(bit_map),
7869 _mod_union_table(mod_union_table),
7870 _mark_stack(mark_stack),
7871 _concurrent_precleaning(concurrent_precleaning)
7872 {
7873 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7874 }
7875
7876 // Grey object rescan during pre-cleaning and second checkpoint phases --
7877 // the non-parallel version (the parallel version appears further below.)
7878 void PushAndMarkClosure::do_oop(oop obj) {
7879 // Ignore mark word verification. If during concurrent precleaning,
7880 // the object monitor may be locked. If during the checkpoint
7881 // phases, the object may already have been reached by a different
7882 // path and may be at the end of the global overflow list (so
7883 // the mark word may be NULL).
7884 assert(obj->is_oop_or_null(true /* ignore mark word */),
7885 "expected an oop or NULL");
7886 HeapWord* addr = (HeapWord*)obj;
7887 // Check if oop points into the CMS generation
7888 // and is not marked
7889 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7890 // a white object ...
7891 _bit_map->mark(addr); // ... now grey
7892 // push on the marking stack (grey set)
7893 bool simulate_overflow = false;
7894 NOT_PRODUCT(
7895 if (CMSMarkStackOverflowALot &&
7896 _collector->simulate_overflow()) {
7897 // simulate a stack overflow
7898 simulate_overflow = true;
7899 }
7900 )
7901 if (simulate_overflow || !_mark_stack->push(obj)) {
7902 if (_concurrent_precleaning) {
7903 // During precleaning we can just dirty the appropriate card(s)
7904 // in the mod union table, thus ensuring that the object remains
7905 // in the grey set and continue. In the case of object arrays
7906 // we need to dirty all of the cards that the object spans,
7907 // since the rescan of object arrays will be limited to the
7908 // dirty cards.
7909 // Note that no one can be intefering with us in this action
7910 // of dirtying the mod union table, so no locking or atomics
7911 // are required.
7912 if (obj->is_objArray()) {
7913 size_t sz = obj->size();
7914 HeapWord* end_card_addr = (HeapWord*)round_to(
7915 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7916 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7917 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7918 _mod_union_table->mark_range(redirty_range);
7919 } else {
7920 _mod_union_table->mark(addr);
7921 }
7922 _collector->_ser_pmc_preclean_ovflw++;
7923 } else {
7924 // During the remark phase, we need to remember this oop
7925 // in the overflow list.
7926 _collector->push_on_overflow_list(obj);
7927 _collector->_ser_pmc_remark_ovflw++;
7928 }
7929 }
7930 }
7931 }
7932
7933 Par_PushAndMarkClosure::Par_PushAndMarkClosure(CMSCollector* collector,
7934 MemRegion span,
7935 ReferenceProcessor* rp,
7936 CMSBitMap* bit_map,
7937 OopTaskQueue* work_queue):
7938 CMSOopClosure(rp),
7939 _collector(collector),
7940 _span(span),
7941 _bit_map(bit_map),
7942 _work_queue(work_queue)
7943 {
7944 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7945 }
7946
7947 void PushAndMarkClosure::do_oop(oop* p) { PushAndMarkClosure::do_oop_work(p); }
7948 void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); }
7949
7950 // Grey object rescan during second checkpoint phase --
7951 // the parallel version.
7952 void Par_PushAndMarkClosure::do_oop(oop obj) {
7953 // In the assert below, we ignore the mark word because
7954 // this oop may point to an already visited object that is
7955 // on the overflow stack (in which case the mark word has
7956 // been hijacked for chaining into the overflow stack --
7957 // if this is the last object in the overflow stack then
7958 // its mark word will be NULL). Because this object may
7959 // have been subsequently popped off the global overflow
7960 // stack, and the mark word possibly restored to the prototypical
7961 // value, by the time we get to examined this failing assert in
7962 // the debugger, is_oop_or_null(false) may subsequently start
7963 // to hold.
7964 assert(obj->is_oop_or_null(true),
7965 "expected an oop or NULL");
7966 HeapWord* addr = (HeapWord*)obj;
7967 // Check if oop points into the CMS generation
7968 // and is not marked
7969 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7970 // a white object ...
7971 // If we manage to "claim" the object, by being the
7972 // first thread to mark it, then we push it on our
7973 // marking stack
7974 if (_bit_map->par_mark(addr)) { // ... now grey
7975 // push on work queue (grey set)
7976 bool simulate_overflow = false;
7977 NOT_PRODUCT(
7978 if (CMSMarkStackOverflowALot &&
7979 _collector->par_simulate_overflow()) {
7980 // simulate a stack overflow
7981 simulate_overflow = true;
7982 }
7983 )
7984 if (simulate_overflow || !_work_queue->push(obj)) {
7985 _collector->par_push_on_overflow_list(obj);
7986 _collector->_par_pmc_remark_ovflw++; // imprecise OK: no need to CAS
7987 }
7988 } // Else, some other thread got there first
7989 }
7990 }
7991
7992 void Par_PushAndMarkClosure::do_oop(oop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7993 void Par_PushAndMarkClosure::do_oop(narrowOop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7994
7995 void CMSPrecleanRefsYieldClosure::do_yield_work() {
7996 Mutex* bml = _collector->bitMapLock();
7997 assert_lock_strong(bml);
7998 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7999 "CMS thread should hold CMS token");
8000
8001 bml->unlock();
8002 ConcurrentMarkSweepThread::desynchronize(true);
8003
8004 ConcurrentMarkSweepThread::acknowledge_yield_request();
8005
8006 _collector->stopTimer();
8007 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
8008 if (PrintCMSStatistics != 0) {
8009 _collector->incrementYields();
8010 }
8011 _collector->icms_wait();
8012
8013 // See the comment in coordinator_yield()
8014 for (unsigned i = 0; i < CMSYieldSleepCount &&
8015 ConcurrentMarkSweepThread::should_yield() &&
8016 !CMSCollector::foregroundGCIsActive(); ++i) {
8017 os::sleep(Thread::current(), 1, false);
8018 ConcurrentMarkSweepThread::acknowledge_yield_request();
8019 }
8020
8021 ConcurrentMarkSweepThread::synchronize(true);
8022 bml->lock();
8023
8024 _collector->startTimer();
8025 }
8026
8027 bool CMSPrecleanRefsYieldClosure::should_return() {
8028 if (ConcurrentMarkSweepThread::should_yield()) {
8029 do_yield_work();
8030 }
8031 return _collector->foregroundGCIsActive();
8032 }
8033
8034 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
8035 assert(((size_t)mr.start())%CardTableModRefBS::card_size_in_words == 0,
8036 "mr should be aligned to start at a card boundary");
8037 // We'd like to assert:
8038 // assert(mr.word_size()%CardTableModRefBS::card_size_in_words == 0,
8039 // "mr should be a range of cards");
8040 // However, that would be too strong in one case -- the last
8041 // partition ends at _unallocated_block which, in general, can be
8042 // an arbitrary boundary, not necessarily card aligned.
8043 if (PrintCMSStatistics != 0) {
8044 _num_dirty_cards +=
8045 mr.word_size()/CardTableModRefBS::card_size_in_words;
8046 }
8047 _space->object_iterate_mem(mr, &_scan_cl);
8048 }
8049
8050 SweepClosure::SweepClosure(CMSCollector* collector,
8051 ConcurrentMarkSweepGeneration* g,
8052 CMSBitMap* bitMap, bool should_yield) :
8053 _collector(collector),
8054 _g(g),
8055 _sp(g->cmsSpace()),
8056 _limit(_sp->sweep_limit()),
8057 _freelistLock(_sp->freelistLock()),
8058 _bitMap(bitMap),
8059 _yield(should_yield),
8060 _inFreeRange(false), // No free range at beginning of sweep
8061 _freeRangeInFreeLists(false), // No free range at beginning of sweep
8062 _lastFreeRangeCoalesced(false),
8063 _freeFinger(g->used_region().start())
8064 {
8065 NOT_PRODUCT(
8066 _numObjectsFreed = 0;
8067 _numWordsFreed = 0;
8068 _numObjectsLive = 0;
8069 _numWordsLive = 0;
8070 _numObjectsAlreadyFree = 0;
8071 _numWordsAlreadyFree = 0;
8072 _last_fc = NULL;
8073
8074 _sp->initializeIndexedFreeListArrayReturnedBytes();
8075 _sp->dictionary()->initialize_dict_returned_bytes();
8076 )
8077 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
8078 "sweep _limit out of bounds");
8079 if (CMSTraceSweeper) {
8080 gclog_or_tty->print_cr("\n====================\nStarting new sweep with limit " PTR_FORMAT,
8081 _limit);
8082 }
8083 }
8084
8085 void SweepClosure::print_on(outputStream* st) const {
8086 tty->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")",
8087 _sp->bottom(), _sp->end());
8088 tty->print_cr("_limit = " PTR_FORMAT, _limit);
8089 tty->print_cr("_freeFinger = " PTR_FORMAT, _freeFinger);
8090 NOT_PRODUCT(tty->print_cr("_last_fc = " PTR_FORMAT, _last_fc);)
8091 tty->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d",
8092 _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced);
8093 }
8094
8095 #ifndef PRODUCT
8096 // Assertion checking only: no useful work in product mode --
8097 // however, if any of the flags below become product flags,
8098 // you may need to review this code to see if it needs to be
8099 // enabled in product mode.
8100 SweepClosure::~SweepClosure() {
8101 assert_lock_strong(_freelistLock);
8102 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
8103 "sweep _limit out of bounds");
8104 if (inFreeRange()) {
8105 warning("inFreeRange() should have been reset; dumping state of SweepClosure");
8106 print();
8107 ShouldNotReachHere();
8108 }
8109 if (Verbose && PrintGC) {
8110 gclog_or_tty->print("Collected "SIZE_FORMAT" objects, " SIZE_FORMAT " bytes",
8111 _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
8112 gclog_or_tty->print_cr("\nLive "SIZE_FORMAT" objects, "
8113 SIZE_FORMAT" bytes "
8114 "Already free "SIZE_FORMAT" objects, "SIZE_FORMAT" bytes",
8115 _numObjectsLive, _numWordsLive*sizeof(HeapWord),
8116 _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
8117 size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree)
8118 * sizeof(HeapWord);
8119 gclog_or_tty->print_cr("Total sweep: "SIZE_FORMAT" bytes", totalBytes);
8120
8121 if (PrintCMSStatistics && CMSVerifyReturnedBytes) {
8122 size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
8123 size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes();
8124 size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes;
8125 gclog_or_tty->print("Returned "SIZE_FORMAT" bytes", returned_bytes);
8126 gclog_or_tty->print(" Indexed List Returned "SIZE_FORMAT" bytes",
8127 indexListReturnedBytes);
8128 gclog_or_tty->print_cr(" Dictionary Returned "SIZE_FORMAT" bytes",
8129 dict_returned_bytes);
8130 }
8131 }
8132 if (CMSTraceSweeper) {
8133 gclog_or_tty->print_cr("end of sweep with _limit = " PTR_FORMAT "\n================",
8134 _limit);
8135 }
8136 }
8137 #endif // PRODUCT
8138
8139 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
8140 bool freeRangeInFreeLists) {
8141 if (CMSTraceSweeper) {
8142 gclog_or_tty->print("---- Start free range at 0x%x with free block (%d)\n",
8143 freeFinger, freeRangeInFreeLists);
8144 }
8145 assert(!inFreeRange(), "Trampling existing free range");
8146 set_inFreeRange(true);
8147 set_lastFreeRangeCoalesced(false);
8148
8149 set_freeFinger(freeFinger);
8150 set_freeRangeInFreeLists(freeRangeInFreeLists);
8151 if (CMSTestInFreeList) {
8152 if (freeRangeInFreeLists) {
8153 FreeChunk* fc = (FreeChunk*) freeFinger;
8154 assert(fc->is_free(), "A chunk on the free list should be free.");
8155 assert(fc->size() > 0, "Free range should have a size");
8156 assert(_sp->verify_chunk_in_free_list(fc), "Chunk is not in free lists");
8157 }
8158 }
8159 }
8160
8161 // Note that the sweeper runs concurrently with mutators. Thus,
8162 // it is possible for direct allocation in this generation to happen
8163 // in the middle of the sweep. Note that the sweeper also coalesces
8164 // contiguous free blocks. Thus, unless the sweeper and the allocator
8165 // synchronize appropriately freshly allocated blocks may get swept up.
8166 // This is accomplished by the sweeper locking the free lists while
8167 // it is sweeping. Thus blocks that are determined to be free are
8168 // indeed free. There is however one additional complication:
8169 // blocks that have been allocated since the final checkpoint and
8170 // mark, will not have been marked and so would be treated as
8171 // unreachable and swept up. To prevent this, the allocator marks
8172 // the bit map when allocating during the sweep phase. This leads,
8173 // however, to a further complication -- objects may have been allocated
8174 // but not yet initialized -- in the sense that the header isn't yet
8175 // installed. The sweeper can not then determine the size of the block
8176 // in order to skip over it. To deal with this case, we use a technique
8177 // (due to Printezis) to encode such uninitialized block sizes in the
8178 // bit map. Since the bit map uses a bit per every HeapWord, but the
8179 // CMS generation has a minimum object size of 3 HeapWords, it follows
8180 // that "normal marks" won't be adjacent in the bit map (there will
8181 // always be at least two 0 bits between successive 1 bits). We make use
8182 // of these "unused" bits to represent uninitialized blocks -- the bit
8183 // corresponding to the start of the uninitialized object and the next
8184 // bit are both set. Finally, a 1 bit marks the end of the object that
8185 // started with the two consecutive 1 bits to indicate its potentially
8186 // uninitialized state.
8187
8188 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
8189 FreeChunk* fc = (FreeChunk*)addr;
8190 size_t res;
8191
8192 // Check if we are done sweeping. Below we check "addr >= _limit" rather
8193 // than "addr == _limit" because although _limit was a block boundary when
8194 // we started the sweep, it may no longer be one because heap expansion
8195 // may have caused us to coalesce the block ending at the address _limit
8196 // with a newly expanded chunk (this happens when _limit was set to the
8197 // previous _end of the space), so we may have stepped past _limit:
8198 // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740.
8199 if (addr >= _limit) { // we have swept up to or past the limit: finish up
8200 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
8201 "sweep _limit out of bounds");
8202 assert(addr < _sp->end(), "addr out of bounds");
8203 // Flush any free range we might be holding as a single
8204 // coalesced chunk to the appropriate free list.
8205 if (inFreeRange()) {
8206 assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit,
8207 err_msg("freeFinger() " PTR_FORMAT" is out-of-bounds", freeFinger()));
8208 flush_cur_free_chunk(freeFinger(),
8209 pointer_delta(addr, freeFinger()));
8210 if (CMSTraceSweeper) {
8211 gclog_or_tty->print("Sweep: last chunk: ");
8212 gclog_or_tty->print("put_free_blk 0x%x ("SIZE_FORMAT") "
8213 "[coalesced:"SIZE_FORMAT"]\n",
8214 freeFinger(), pointer_delta(addr, freeFinger()),
8215 lastFreeRangeCoalesced());
8216 }
8217 }
8218
8219 // help the iterator loop finish
8220 return pointer_delta(_sp->end(), addr);
8221 }
8222
8223 assert(addr < _limit, "sweep invariant");
8224 // check if we should yield
8225 do_yield_check(addr);
8226 if (fc->is_free()) {
8227 // Chunk that is already free
8228 res = fc->size();
8229 do_already_free_chunk(fc);
8230 debug_only(_sp->verifyFreeLists());
8231 // If we flush the chunk at hand in lookahead_and_flush()
8232 // and it's coalesced with a preceding chunk, then the
8233 // process of "mangling" the payload of the coalesced block
8234 // will cause erasure of the size information from the
8235 // (erstwhile) header of all the coalesced blocks but the
8236 // first, so the first disjunct in the assert will not hold
8237 // in that specific case (in which case the second disjunct
8238 // will hold).
8239 assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit,
8240 "Otherwise the size info doesn't change at this step");
8241 NOT_PRODUCT(
8242 _numObjectsAlreadyFree++;
8243 _numWordsAlreadyFree += res;
8244 )
8245 NOT_PRODUCT(_last_fc = fc;)
8246 } else if (!_bitMap->isMarked(addr)) {
8247 // Chunk is fresh garbage
8248 res = do_garbage_chunk(fc);
8249 debug_only(_sp->verifyFreeLists());
8250 NOT_PRODUCT(
8251 _numObjectsFreed++;
8252 _numWordsFreed += res;
8253 )
8254 } else {
8255 // Chunk that is alive.
8256 res = do_live_chunk(fc);
8257 debug_only(_sp->verifyFreeLists());
8258 NOT_PRODUCT(
8259 _numObjectsLive++;
8260 _numWordsLive += res;
8261 )
8262 }
8263 return res;
8264 }
8265
8266 // For the smart allocation, record following
8267 // split deaths - a free chunk is removed from its free list because
8268 // it is being split into two or more chunks.
8269 // split birth - a free chunk is being added to its free list because
8270 // a larger free chunk has been split and resulted in this free chunk.
8271 // coal death - a free chunk is being removed from its free list because
8272 // it is being coalesced into a large free chunk.
8273 // coal birth - a free chunk is being added to its free list because
8274 // it was created when two or more free chunks where coalesced into
8275 // this free chunk.
8276 //
8277 // These statistics are used to determine the desired number of free
8278 // chunks of a given size. The desired number is chosen to be relative
8279 // to the end of a CMS sweep. The desired number at the end of a sweep
8280 // is the
8281 // count-at-end-of-previous-sweep (an amount that was enough)
8282 // - count-at-beginning-of-current-sweep (the excess)
8283 // + split-births (gains in this size during interval)
8284 // - split-deaths (demands on this size during interval)
8285 // where the interval is from the end of one sweep to the end of the
8286 // next.
8287 //
8288 // When sweeping the sweeper maintains an accumulated chunk which is
8289 // the chunk that is made up of chunks that have been coalesced. That
8290 // will be termed the left-hand chunk. A new chunk of garbage that
8291 // is being considered for coalescing will be referred to as the
8292 // right-hand chunk.
8293 //
8294 // When making a decision on whether to coalesce a right-hand chunk with
8295 // the current left-hand chunk, the current count vs. the desired count
8296 // of the left-hand chunk is considered. Also if the right-hand chunk
8297 // is near the large chunk at the end of the heap (see
8298 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
8299 // left-hand chunk is coalesced.
8300 //
8301 // When making a decision about whether to split a chunk, the desired count
8302 // vs. the current count of the candidate to be split is also considered.
8303 // If the candidate is underpopulated (currently fewer chunks than desired)
8304 // a chunk of an overpopulated (currently more chunks than desired) size may
8305 // be chosen. The "hint" associated with a free list, if non-null, points
8306 // to a free list which may be overpopulated.
8307 //
8308
8309 void SweepClosure::do_already_free_chunk(FreeChunk* fc) {
8310 const size_t size = fc->size();
8311 // Chunks that cannot be coalesced are not in the
8312 // free lists.
8313 if (CMSTestInFreeList && !fc->cantCoalesce()) {
8314 assert(_sp->verify_chunk_in_free_list(fc),
8315 "free chunk should be in free lists");
8316 }
8317 // a chunk that is already free, should not have been
8318 // marked in the bit map
8319 HeapWord* const addr = (HeapWord*) fc;
8320 assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
8321 // Verify that the bit map has no bits marked between
8322 // addr and purported end of this block.
8323 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8324
8325 // Some chunks cannot be coalesced under any circumstances.
8326 // See the definition of cantCoalesce().
8327 if (!fc->cantCoalesce()) {
8328 // This chunk can potentially be coalesced.
8329 if (_sp->adaptive_freelists()) {
8330 // All the work is done in
8331 do_post_free_or_garbage_chunk(fc, size);
8332 } else { // Not adaptive free lists
8333 // this is a free chunk that can potentially be coalesced by the sweeper;
8334 if (!inFreeRange()) {
8335 // if the next chunk is a free block that can't be coalesced
8336 // it doesn't make sense to remove this chunk from the free lists
8337 FreeChunk* nextChunk = (FreeChunk*)(addr + size);
8338 assert((HeapWord*)nextChunk <= _sp->end(), "Chunk size out of bounds?");
8339 if ((HeapWord*)nextChunk < _sp->end() && // There is another free chunk to the right ...
8340 nextChunk->is_free() && // ... which is free...
8341 nextChunk->cantCoalesce()) { // ... but can't be coalesced
8342 // nothing to do
8343 } else {
8344 // Potentially the start of a new free range:
8345 // Don't eagerly remove it from the free lists.
8346 // No need to remove it if it will just be put
8347 // back again. (Also from a pragmatic point of view
8348 // if it is a free block in a region that is beyond
8349 // any allocated blocks, an assertion will fail)
8350 // Remember the start of a free run.
8351 initialize_free_range(addr, true);
8352 // end - can coalesce with next chunk
8353 }
8354 } else {
8355 // the midst of a free range, we are coalescing
8356 print_free_block_coalesced(fc);
8357 if (CMSTraceSweeper) {
8358 gclog_or_tty->print(" -- pick up free block 0x%x (%d)\n", fc, size);
8359 }
8360 // remove it from the free lists
8361 _sp->removeFreeChunkFromFreeLists(fc);
8362 set_lastFreeRangeCoalesced(true);
8363 // If the chunk is being coalesced and the current free range is
8364 // in the free lists, remove the current free range so that it
8365 // will be returned to the free lists in its entirety - all
8366 // the coalesced pieces included.
8367 if (freeRangeInFreeLists()) {
8368 FreeChunk* ffc = (FreeChunk*) freeFinger();
8369 assert(ffc->size() == pointer_delta(addr, freeFinger()),
8370 "Size of free range is inconsistent with chunk size.");
8371 if (CMSTestInFreeList) {
8372 assert(_sp->verify_chunk_in_free_list(ffc),
8373 "free range is not in free lists");
8374 }
8375 _sp->removeFreeChunkFromFreeLists(ffc);
8376 set_freeRangeInFreeLists(false);
8377 }
8378 }
8379 }
8380 // Note that if the chunk is not coalescable (the else arm
8381 // below), we unconditionally flush, without needing to do
8382 // a "lookahead," as we do below.
8383 if (inFreeRange()) lookahead_and_flush(fc, size);
8384 } else {
8385 // Code path common to both original and adaptive free lists.
8386
8387 // cant coalesce with previous block; this should be treated
8388 // as the end of a free run if any
8389 if (inFreeRange()) {
8390 // we kicked some butt; time to pick up the garbage
8391 assert(freeFinger() < addr, "freeFinger points too high");
8392 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8393 }
8394 // else, nothing to do, just continue
8395 }
8396 }
8397
8398 size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) {
8399 // This is a chunk of garbage. It is not in any free list.
8400 // Add it to a free list or let it possibly be coalesced into
8401 // a larger chunk.
8402 HeapWord* const addr = (HeapWord*) fc;
8403 const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
8404
8405 if (_sp->adaptive_freelists()) {
8406 // Verify that the bit map has no bits marked between
8407 // addr and purported end of just dead object.
8408 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8409
8410 do_post_free_or_garbage_chunk(fc, size);
8411 } else {
8412 if (!inFreeRange()) {
8413 // start of a new free range
8414 assert(size > 0, "A free range should have a size");
8415 initialize_free_range(addr, false);
8416 } else {
8417 // this will be swept up when we hit the end of the
8418 // free range
8419 if (CMSTraceSweeper) {
8420 gclog_or_tty->print(" -- pick up garbage 0x%x (%d) \n", fc, size);
8421 }
8422 // If the chunk is being coalesced and the current free range is
8423 // in the free lists, remove the current free range so that it
8424 // will be returned to the free lists in its entirety - all
8425 // the coalesced pieces included.
8426 if (freeRangeInFreeLists()) {
8427 FreeChunk* ffc = (FreeChunk*)freeFinger();
8428 assert(ffc->size() == pointer_delta(addr, freeFinger()),
8429 "Size of free range is inconsistent with chunk size.");
8430 if (CMSTestInFreeList) {
8431 assert(_sp->verify_chunk_in_free_list(ffc),
8432 "free range is not in free lists");
8433 }
8434 _sp->removeFreeChunkFromFreeLists(ffc);
8435 set_freeRangeInFreeLists(false);
8436 }
8437 set_lastFreeRangeCoalesced(true);
8438 }
8439 // this will be swept up when we hit the end of the free range
8440
8441 // Verify that the bit map has no bits marked between
8442 // addr and purported end of just dead object.
8443 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8444 }
8445 assert(_limit >= addr + size,
8446 "A freshly garbage chunk can't possibly straddle over _limit");
8447 if (inFreeRange()) lookahead_and_flush(fc, size);
8448 return size;
8449 }
8450
8451 size_t SweepClosure::do_live_chunk(FreeChunk* fc) {
8452 HeapWord* addr = (HeapWord*) fc;
8453 // The sweeper has just found a live object. Return any accumulated
8454 // left hand chunk to the free lists.
8455 if (inFreeRange()) {
8456 assert(freeFinger() < addr, "freeFinger points too high");
8457 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8458 }
8459
8460 // This object is live: we'd normally expect this to be
8461 // an oop, and like to assert the following:
8462 // assert(oop(addr)->is_oop(), "live block should be an oop");
8463 // However, as we commented above, this may be an object whose
8464 // header hasn't yet been initialized.
8465 size_t size;
8466 assert(_bitMap->isMarked(addr), "Tautology for this control point");
8467 if (_bitMap->isMarked(addr + 1)) {
8468 // Determine the size from the bit map, rather than trying to
8469 // compute it from the object header.
8470 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
8471 size = pointer_delta(nextOneAddr + 1, addr);
8472 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
8473 "alignment problem");
8474
8475 #ifdef ASSERT
8476 if (oop(addr)->klass_or_null() != NULL) {
8477 // Ignore mark word because we are running concurrent with mutators
8478 assert(oop(addr)->is_oop(true), "live block should be an oop");
8479 assert(size ==
8480 CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
8481 "P-mark and computed size do not agree");
8482 }
8483 #endif
8484
8485 } else {
8486 // This should be an initialized object that's alive.
8487 assert(oop(addr)->klass_or_null() != NULL,
8488 "Should be an initialized object");
8489 // Ignore mark word because we are running concurrent with mutators
8490 assert(oop(addr)->is_oop(true), "live block should be an oop");
8491 // Verify that the bit map has no bits marked between
8492 // addr and purported end of this block.
8493 size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
8494 assert(size >= 3, "Necessary for Printezis marks to work");
8495 assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
8496 DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
8497 }
8498 return size;
8499 }
8500
8501 void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc,
8502 size_t chunkSize) {
8503 // do_post_free_or_garbage_chunk() should only be called in the case
8504 // of the adaptive free list allocator.
8505 const bool fcInFreeLists = fc->is_free();
8506 assert(_sp->adaptive_freelists(), "Should only be used in this case.");
8507 assert((HeapWord*)fc <= _limit, "sweep invariant");
8508 if (CMSTestInFreeList && fcInFreeLists) {
8509 assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists");
8510 }
8511
8512 if (CMSTraceSweeper) {
8513 gclog_or_tty->print_cr(" -- pick up another chunk at 0x%x (%d)", fc, chunkSize);
8514 }
8515
8516 HeapWord* const fc_addr = (HeapWord*) fc;
8517
8518 bool coalesce;
8519 const size_t left = pointer_delta(fc_addr, freeFinger());
8520 const size_t right = chunkSize;
8521 switch (FLSCoalescePolicy) {
8522 // numeric value forms a coalition aggressiveness metric
8523 case 0: { // never coalesce
8524 coalesce = false;
8525 break;
8526 }
8527 case 1: { // coalesce if left & right chunks on overpopulated lists
8528 coalesce = _sp->coalOverPopulated(left) &&
8529 _sp->coalOverPopulated(right);
8530 break;
8531 }
8532 case 2: { // coalesce if left chunk on overpopulated list (default)
8533 coalesce = _sp->coalOverPopulated(left);
8534 break;
8535 }
8536 case 3: { // coalesce if left OR right chunk on overpopulated list
8537 coalesce = _sp->coalOverPopulated(left) ||
8538 _sp->coalOverPopulated(right);
8539 break;
8540 }
8541 case 4: { // always coalesce
8542 coalesce = true;
8543 break;
8544 }
8545 default:
8546 ShouldNotReachHere();
8547 }
8548
8549 // Should the current free range be coalesced?
8550 // If the chunk is in a free range and either we decided to coalesce above
8551 // or the chunk is near the large block at the end of the heap
8552 // (isNearLargestChunk() returns true), then coalesce this chunk.
8553 const bool doCoalesce = inFreeRange()
8554 && (coalesce || _g->isNearLargestChunk(fc_addr));
8555 if (doCoalesce) {
8556 // Coalesce the current free range on the left with the new
8557 // chunk on the right. If either is on a free list,
8558 // it must be removed from the list and stashed in the closure.
8559 if (freeRangeInFreeLists()) {
8560 FreeChunk* const ffc = (FreeChunk*)freeFinger();
8561 assert(ffc->size() == pointer_delta(fc_addr, freeFinger()),
8562 "Size of free range is inconsistent with chunk size.");
8563 if (CMSTestInFreeList) {
8564 assert(_sp->verify_chunk_in_free_list(ffc),
8565 "Chunk is not in free lists");
8566 }
8567 _sp->coalDeath(ffc->size());
8568 _sp->removeFreeChunkFromFreeLists(ffc);
8569 set_freeRangeInFreeLists(false);
8570 }
8571 if (fcInFreeLists) {
8572 _sp->coalDeath(chunkSize);
8573 assert(fc->size() == chunkSize,
8574 "The chunk has the wrong size or is not in the free lists");
8575 _sp->removeFreeChunkFromFreeLists(fc);
8576 }
8577 set_lastFreeRangeCoalesced(true);
8578 print_free_block_coalesced(fc);
8579 } else { // not in a free range and/or should not coalesce
8580 // Return the current free range and start a new one.
8581 if (inFreeRange()) {
8582 // In a free range but cannot coalesce with the right hand chunk.
8583 // Put the current free range into the free lists.
8584 flush_cur_free_chunk(freeFinger(),
8585 pointer_delta(fc_addr, freeFinger()));
8586 }
8587 // Set up for new free range. Pass along whether the right hand
8588 // chunk is in the free lists.
8589 initialize_free_range((HeapWord*)fc, fcInFreeLists);
8590 }
8591 }
8592
8593 // Lookahead flush:
8594 // If we are tracking a free range, and this is the last chunk that
8595 // we'll look at because its end crosses past _limit, we'll preemptively
8596 // flush it along with any free range we may be holding on to. Note that
8597 // this can be the case only for an already free or freshly garbage
8598 // chunk. If this block is an object, it can never straddle
8599 // over _limit. The "straddling" occurs when _limit is set at
8600 // the previous end of the space when this cycle started, and
8601 // a subsequent heap expansion caused the previously co-terminal
8602 // free block to be coalesced with the newly expanded portion,
8603 // thus rendering _limit a non-block-boundary making it dangerous
8604 // for the sweeper to step over and examine.
8605 void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) {
8606 assert(inFreeRange(), "Should only be called if currently in a free range.");
8607 HeapWord* const eob = ((HeapWord*)fc) + chunk_size;
8608 assert(_sp->used_region().contains(eob - 1),
8609 err_msg("eob = " PTR_FORMAT " out of bounds wrt _sp = [" PTR_FORMAT "," PTR_FORMAT ")"
8610 " when examining fc = " PTR_FORMAT "(" SIZE_FORMAT ")",
8611 _limit, _sp->bottom(), _sp->end(), fc, chunk_size));
8612 if (eob >= _limit) {
8613 assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit");
8614 if (CMSTraceSweeper) {
8615 gclog_or_tty->print_cr("_limit " PTR_FORMAT " reached or crossed by block "
8616 "[" PTR_FORMAT "," PTR_FORMAT ") in space "
8617 "[" PTR_FORMAT "," PTR_FORMAT ")",
8618 _limit, fc, eob, _sp->bottom(), _sp->end());
8619 }
8620 // Return the storage we are tracking back into the free lists.
8621 if (CMSTraceSweeper) {
8622 gclog_or_tty->print_cr("Flushing ... ");
8623 }
8624 assert(freeFinger() < eob, "Error");
8625 flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger()));
8626 }
8627 }
8628
8629 void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) {
8630 assert(inFreeRange(), "Should only be called if currently in a free range.");
8631 assert(size > 0,
8632 "A zero sized chunk cannot be added to the free lists.");
8633 if (!freeRangeInFreeLists()) {
8634 if (CMSTestInFreeList) {
8635 FreeChunk* fc = (FreeChunk*) chunk;
8636 fc->set_size(size);
8637 assert(!_sp->verify_chunk_in_free_list(fc),
8638 "chunk should not be in free lists yet");
8639 }
8640 if (CMSTraceSweeper) {
8641 gclog_or_tty->print_cr(" -- add free block 0x%x (%d) to free lists",
8642 chunk, size);
8643 }
8644 // A new free range is going to be starting. The current
8645 // free range has not been added to the free lists yet or
8646 // was removed so add it back.
8647 // If the current free range was coalesced, then the death
8648 // of the free range was recorded. Record a birth now.
8649 if (lastFreeRangeCoalesced()) {
8650 _sp->coalBirth(size);
8651 }
8652 _sp->addChunkAndRepairOffsetTable(chunk, size,
8653 lastFreeRangeCoalesced());
8654 } else if (CMSTraceSweeper) {
8655 gclog_or_tty->print_cr("Already in free list: nothing to flush");
8656 }
8657 set_inFreeRange(false);
8658 set_freeRangeInFreeLists(false);
8659 }
8660
8661 // We take a break if we've been at this for a while,
8662 // so as to avoid monopolizing the locks involved.
8663 void SweepClosure::do_yield_work(HeapWord* addr) {
8664 // Return current free chunk being used for coalescing (if any)
8665 // to the appropriate freelist. After yielding, the next
8666 // free block encountered will start a coalescing range of
8667 // free blocks. If the next free block is adjacent to the
8668 // chunk just flushed, they will need to wait for the next
8669 // sweep to be coalesced.
8670 if (inFreeRange()) {
8671 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8672 }
8673
8674 // First give up the locks, then yield, then re-lock.
8675 // We should probably use a constructor/destructor idiom to
8676 // do this unlock/lock or modify the MutexUnlocker class to
8677 // serve our purpose. XXX
8678 assert_lock_strong(_bitMap->lock());
8679 assert_lock_strong(_freelistLock);
8680 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
8681 "CMS thread should hold CMS token");
8682 _bitMap->lock()->unlock();
8683 _freelistLock->unlock();
8684 ConcurrentMarkSweepThread::desynchronize(true);
8685 ConcurrentMarkSweepThread::acknowledge_yield_request();
8686 _collector->stopTimer();
8687 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
8688 if (PrintCMSStatistics != 0) {
8689 _collector->incrementYields();
8690 }
8691 _collector->icms_wait();
8692
8693 // See the comment in coordinator_yield()
8694 for (unsigned i = 0; i < CMSYieldSleepCount &&
8695 ConcurrentMarkSweepThread::should_yield() &&
8696 !CMSCollector::foregroundGCIsActive(); ++i) {
8697 os::sleep(Thread::current(), 1, false);
8698 ConcurrentMarkSweepThread::acknowledge_yield_request();
8699 }
8700
8701 ConcurrentMarkSweepThread::synchronize(true);
8702 _freelistLock->lock();
8703 _bitMap->lock()->lock_without_safepoint_check();
8704 _collector->startTimer();
8705 }
8706
8707 #ifndef PRODUCT
8708 // This is actually very useful in a product build if it can
8709 // be called from the debugger. Compile it into the product
8710 // as needed.
8711 bool debug_verify_chunk_in_free_list(FreeChunk* fc) {
8712 return debug_cms_space->verify_chunk_in_free_list(fc);
8713 }
8714 #endif
8715
8716 void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const {
8717 if (CMSTraceSweeper) {
8718 gclog_or_tty->print_cr("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")",
8719 fc, fc->size());
8720 }
8721 }
8722
8723 // CMSIsAliveClosure
8724 bool CMSIsAliveClosure::do_object_b(oop obj) {
8725 HeapWord* addr = (HeapWord*)obj;
8726 return addr != NULL &&
8727 (!_span.contains(addr) || _bit_map->isMarked(addr));
8728 }
8729
8730
8731 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector,
8732 MemRegion span,
8733 CMSBitMap* bit_map, CMSMarkStack* mark_stack,
8734 bool cpc):
8735 _collector(collector),
8736 _span(span),
8737 _bit_map(bit_map),
8738 _mark_stack(mark_stack),
8739 _concurrent_precleaning(cpc) {
8740 assert(!_span.is_empty(), "Empty span could spell trouble");
8741 }
8742
8743
8744 // CMSKeepAliveClosure: the serial version
8745 void CMSKeepAliveClosure::do_oop(oop obj) {
8746 HeapWord* addr = (HeapWord*)obj;
8747 if (_span.contains(addr) &&
8748 !_bit_map->isMarked(addr)) {
8749 _bit_map->mark(addr);
8750 bool simulate_overflow = false;
8751 NOT_PRODUCT(
8752 if (CMSMarkStackOverflowALot &&
8753 _collector->simulate_overflow()) {
8754 // simulate a stack overflow
8755 simulate_overflow = true;
8756 }
8757 )
8758 if (simulate_overflow || !_mark_stack->push(obj)) {
8759 if (_concurrent_precleaning) {
8760 // We dirty the overflown object and let the remark
8761 // phase deal with it.
8762 assert(_collector->overflow_list_is_empty(), "Error");
8763 // In the case of object arrays, we need to dirty all of
8764 // the cards that the object spans. No locking or atomics
8765 // are needed since no one else can be mutating the mod union
8766 // table.
8767 if (obj->is_objArray()) {
8768 size_t sz = obj->size();
8769 HeapWord* end_card_addr =
8770 (HeapWord*)round_to((intptr_t)(addr+sz), CardTableModRefBS::card_size);
8771 MemRegion redirty_range = MemRegion(addr, end_card_addr);
8772 assert(!redirty_range.is_empty(), "Arithmetical tautology");
8773 _collector->_modUnionTable.mark_range(redirty_range);
8774 } else {
8775 _collector->_modUnionTable.mark(addr);
8776 }
8777 _collector->_ser_kac_preclean_ovflw++;
8778 } else {
8779 _collector->push_on_overflow_list(obj);
8780 _collector->_ser_kac_ovflw++;
8781 }
8782 }
8783 }
8784 }
8785
8786 void CMSKeepAliveClosure::do_oop(oop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8787 void CMSKeepAliveClosure::do_oop(narrowOop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8788
8789 // CMSParKeepAliveClosure: a parallel version of the above.
8790 // The work queues are private to each closure (thread),
8791 // but (may be) available for stealing by other threads.
8792 void CMSParKeepAliveClosure::do_oop(oop obj) {
8793 HeapWord* addr = (HeapWord*)obj;
8794 if (_span.contains(addr) &&
8795 !_bit_map->isMarked(addr)) {
8796 // In general, during recursive tracing, several threads
8797 // may be concurrently getting here; the first one to
8798 // "tag" it, claims it.
8799 if (_bit_map->par_mark(addr)) {
8800 bool res = _work_queue->push(obj);
8801 assert(res, "Low water mark should be much less than capacity");
8802 // Do a recursive trim in the hope that this will keep
8803 // stack usage lower, but leave some oops for potential stealers
8804 trim_queue(_low_water_mark);
8805 } // Else, another thread got there first
8806 }
8807 }
8808
8809 void CMSParKeepAliveClosure::do_oop(oop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8810 void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8811
8812 void CMSParKeepAliveClosure::trim_queue(uint max) {
8813 while (_work_queue->size() > max) {
8814 oop new_oop;
8815 if (_work_queue->pop_local(new_oop)) {
8816 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
8817 assert(_bit_map->isMarked((HeapWord*)new_oop),
8818 "no white objects on this stack!");
8819 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8820 // iterate over the oops in this oop, marking and pushing
8821 // the ones in CMS heap (i.e. in _span).
8822 new_oop->oop_iterate(&_mark_and_push);
8823 }
8824 }
8825 }
8826
8827 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
8828 CMSCollector* collector,
8829 MemRegion span, CMSBitMap* bit_map,
8830 OopTaskQueue* work_queue):
8831 _collector(collector),
8832 _span(span),
8833 _bit_map(bit_map),
8834 _work_queue(work_queue) { }
8835
8836 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
8837 HeapWord* addr = (HeapWord*)obj;
8838 if (_span.contains(addr) &&
8839 !_bit_map->isMarked(addr)) {
8840 if (_bit_map->par_mark(addr)) {
8841 bool simulate_overflow = false;
8842 NOT_PRODUCT(
8843 if (CMSMarkStackOverflowALot &&
8844 _collector->par_simulate_overflow()) {
8845 // simulate a stack overflow
8846 simulate_overflow = true;
8847 }
8848 )
8849 if (simulate_overflow || !_work_queue->push(obj)) {
8850 _collector->par_push_on_overflow_list(obj);
8851 _collector->_par_kac_ovflw++;
8852 }
8853 } // Else another thread got there already
8854 }
8855 }
8856
8857 void CMSInnerParMarkAndPushClosure::do_oop(oop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8858 void CMSInnerParMarkAndPushClosure::do_oop(narrowOop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8859
8860 //////////////////////////////////////////////////////////////////
8861 // CMSExpansionCause /////////////////////////////
8862 //////////////////////////////////////////////////////////////////
8863 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
8864 switch (cause) {
8865 case _no_expansion:
8866 return "No expansion";
8867 case _satisfy_free_ratio:
8868 return "Free ratio";
8869 case _satisfy_promotion:
8870 return "Satisfy promotion";
8871 case _satisfy_allocation:
8872 return "allocation";
8873 case _allocate_par_lab:
8874 return "Par LAB";
8875 case _allocate_par_spooling_space:
8876 return "Par Spooling Space";
8877 case _adaptive_size_policy:
8878 return "Ergonomics";
8879 default:
8880 return "unknown";
8881 }
8882 }
8883
8884 void CMSDrainMarkingStackClosure::do_void() {
8885 // the max number to take from overflow list at a time
8886 const size_t num = _mark_stack->capacity()/4;
8887 assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
8888 "Overflow list should be NULL during concurrent phases");
8889 while (!_mark_stack->isEmpty() ||
8890 // if stack is empty, check the overflow list
8891 _collector->take_from_overflow_list(num, _mark_stack)) {
8892 oop obj = _mark_stack->pop();
8893 HeapWord* addr = (HeapWord*)obj;
8894 assert(_span.contains(addr), "Should be within span");
8895 assert(_bit_map->isMarked(addr), "Should be marked");
8896 assert(obj->is_oop(), "Should be an oop");
8897 obj->oop_iterate(_keep_alive);
8898 }
8899 }
8900
8901 void CMSParDrainMarkingStackClosure::do_void() {
8902 // drain queue
8903 trim_queue(0);
8904 }
8905
8906 // Trim our work_queue so its length is below max at return
8907 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
8908 while (_work_queue->size() > max) {
8909 oop new_oop;
8910 if (_work_queue->pop_local(new_oop)) {
8911 assert(new_oop->is_oop(), "Expected an oop");
8912 assert(_bit_map->isMarked((HeapWord*)new_oop),
8913 "no white objects on this stack!");
8914 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8915 // iterate over the oops in this oop, marking and pushing
8916 // the ones in CMS heap (i.e. in _span).
8917 new_oop->oop_iterate(&_mark_and_push);
8918 }
8919 }
8920 }
8921
8922 ////////////////////////////////////////////////////////////////////
8923 // Support for Marking Stack Overflow list handling and related code
8924 ////////////////////////////////////////////////////////////////////
8925 // Much of the following code is similar in shape and spirit to the
8926 // code used in ParNewGC. We should try and share that code
8927 // as much as possible in the future.
8928
8929 #ifndef PRODUCT
8930 // Debugging support for CMSStackOverflowALot
8931
8932 // It's OK to call this multi-threaded; the worst thing
8933 // that can happen is that we'll get a bunch of closely
8934 // spaced simulated oveflows, but that's OK, in fact
8935 // probably good as it would exercise the overflow code
8936 // under contention.
8937 bool CMSCollector::simulate_overflow() {
8938 if (_overflow_counter-- <= 0) { // just being defensive
8939 _overflow_counter = CMSMarkStackOverflowInterval;
8940 return true;
8941 } else {
8942 return false;
8943 }
8944 }
8945
8946 bool CMSCollector::par_simulate_overflow() {
8947 return simulate_overflow();
8948 }
8949 #endif
8950
8951 // Single-threaded
8952 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
8953 assert(stack->isEmpty(), "Expected precondition");
8954 assert(stack->capacity() > num, "Shouldn't bite more than can chew");
8955 size_t i = num;
8956 oop cur = _overflow_list;
8957 const markOop proto = markOopDesc::prototype();
8958 NOT_PRODUCT(ssize_t n = 0;)
8959 for (oop next; i > 0 && cur != NULL; cur = next, i--) {
8960 next = oop(cur->mark());
8961 cur->set_mark(proto); // until proven otherwise
8962 assert(cur->is_oop(), "Should be an oop");
8963 bool res = stack->push(cur);
8964 assert(res, "Bit off more than can chew?");
8965 NOT_PRODUCT(n++;)
8966 }
8967 _overflow_list = cur;
8968 #ifndef PRODUCT
8969 assert(_num_par_pushes >= n, "Too many pops?");
8970 _num_par_pushes -=n;
8971 #endif
8972 return !stack->isEmpty();
8973 }
8974
8975 #define BUSY (oop(0x1aff1aff))
8976 // (MT-safe) Get a prefix of at most "num" from the list.
8977 // The overflow list is chained through the mark word of
8978 // each object in the list. We fetch the entire list,
8979 // break off a prefix of the right size and return the
8980 // remainder. If other threads try to take objects from
8981 // the overflow list at that time, they will wait for
8982 // some time to see if data becomes available. If (and
8983 // only if) another thread places one or more object(s)
8984 // on the global list before we have returned the suffix
8985 // to the global list, we will walk down our local list
8986 // to find its end and append the global list to
8987 // our suffix before returning it. This suffix walk can
8988 // prove to be expensive (quadratic in the amount of traffic)
8989 // when there are many objects in the overflow list and
8990 // there is much producer-consumer contention on the list.
8991 // *NOTE*: The overflow list manipulation code here and
8992 // in ParNewGeneration:: are very similar in shape,
8993 // except that in the ParNew case we use the old (from/eden)
8994 // copy of the object to thread the list via its klass word.
8995 // Because of the common code, if you make any changes in
8996 // the code below, please check the ParNew version to see if
8997 // similar changes might be needed.
8998 // CR 6797058 has been filed to consolidate the common code.
8999 bool CMSCollector::par_take_from_overflow_list(size_t num,
9000 OopTaskQueue* work_q,
9001 int no_of_gc_threads) {
9002 assert(work_q->size() == 0, "First empty local work queue");
9003 assert(num < work_q->max_elems(), "Can't bite more than we can chew");
9004 if (_overflow_list == NULL) {
9005 return false;
9006 }
9007 // Grab the entire list; we'll put back a suffix
9008 oop prefix = (oop)Atomic::xchg_ptr(BUSY, &_overflow_list);
9009 Thread* tid = Thread::current();
9010 // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was
9011 // set to ParallelGCThreads.
9012 size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads;
9013 size_t sleep_time_millis = MAX2((size_t)1, num/100);
9014 // If the list is busy, we spin for a short while,
9015 // sleeping between attempts to get the list.
9016 for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) {
9017 os::sleep(tid, sleep_time_millis, false);
9018 if (_overflow_list == NULL) {
9019 // Nothing left to take
9020 return false;
9021 } else if (_overflow_list != BUSY) {
9022 // Try and grab the prefix
9023 prefix = (oop)Atomic::xchg_ptr(BUSY, &_overflow_list);
9024 }
9025 }
9026 // If the list was found to be empty, or we spun long
9027 // enough, we give up and return empty-handed. If we leave
9028 // the list in the BUSY state below, it must be the case that
9029 // some other thread holds the overflow list and will set it
9030 // to a non-BUSY state in the future.
9031 if (prefix == NULL || prefix == BUSY) {
9032 // Nothing to take or waited long enough
9033 if (prefix == NULL) {
9034 // Write back the NULL in case we overwrote it with BUSY above
9035 // and it is still the same value.
9036 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
9037 }
9038 return false;
9039 }
9040 assert(prefix != NULL && prefix != BUSY, "Error");
9041 size_t i = num;
9042 oop cur = prefix;
9043 // Walk down the first "num" objects, unless we reach the end.
9044 for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--);
9045 if (cur->mark() == NULL) {
9046 // We have "num" or fewer elements in the list, so there
9047 // is nothing to return to the global list.
9048 // Write back the NULL in lieu of the BUSY we wrote
9049 // above, if it is still the same value.
9050 if (_overflow_list == BUSY) {
9051 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
9052 }
9053 } else {
9054 // Chop off the suffix and rerturn it to the global list.
9055 assert(cur->mark() != BUSY, "Error");
9056 oop suffix_head = cur->mark(); // suffix will be put back on global list
9057 cur->set_mark(NULL); // break off suffix
9058 // It's possible that the list is still in the empty(busy) state
9059 // we left it in a short while ago; in that case we may be
9060 // able to place back the suffix without incurring the cost
9061 // of a walk down the list.
9062 oop observed_overflow_list = _overflow_list;
9063 oop cur_overflow_list = observed_overflow_list;
9064 bool attached = false;
9065 while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
9066 observed_overflow_list =
9067 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
9068 if (cur_overflow_list == observed_overflow_list) {
9069 attached = true;
9070 break;
9071 } else cur_overflow_list = observed_overflow_list;
9072 }
9073 if (!attached) {
9074 // Too bad, someone else sneaked in (at least) an element; we'll need
9075 // to do a splice. Find tail of suffix so we can prepend suffix to global
9076 // list.
9077 for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark()));
9078 oop suffix_tail = cur;
9079 assert(suffix_tail != NULL && suffix_tail->mark() == NULL,
9080 "Tautology");
9081 observed_overflow_list = _overflow_list;
9082 do {
9083 cur_overflow_list = observed_overflow_list;
9084 if (cur_overflow_list != BUSY) {
9085 // Do the splice ...
9086 suffix_tail->set_mark(markOop(cur_overflow_list));
9087 } else { // cur_overflow_list == BUSY
9088 suffix_tail->set_mark(NULL);
9089 }
9090 // ... and try to place spliced list back on overflow_list ...
9091 observed_overflow_list =
9092 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
9093 } while (cur_overflow_list != observed_overflow_list);
9094 // ... until we have succeeded in doing so.
9095 }
9096 }
9097
9098 // Push the prefix elements on work_q
9099 assert(prefix != NULL, "control point invariant");
9100 const markOop proto = markOopDesc::prototype();
9101 oop next;
9102 NOT_PRODUCT(ssize_t n = 0;)
9103 for (cur = prefix; cur != NULL; cur = next) {
9104 next = oop(cur->mark());
9105 cur->set_mark(proto); // until proven otherwise
9106 assert(cur->is_oop(), "Should be an oop");
9107 bool res = work_q->push(cur);
9108 assert(res, "Bit off more than we can chew?");
9109 NOT_PRODUCT(n++;)
9110 }
9111 #ifndef PRODUCT
9112 assert(_num_par_pushes >= n, "Too many pops?");
9113 Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
9114 #endif
9115 return true;
9116 }
9117
9118 // Single-threaded
9119 void CMSCollector::push_on_overflow_list(oop p) {
9120 NOT_PRODUCT(_num_par_pushes++;)
9121 assert(p->is_oop(), "Not an oop");
9122 preserve_mark_if_necessary(p);
9123 p->set_mark((markOop)_overflow_list);
9124 _overflow_list = p;
9125 }
9126
9127 // Multi-threaded; use CAS to prepend to overflow list
9128 void CMSCollector::par_push_on_overflow_list(oop p) {
9129 NOT_PRODUCT(Atomic::inc_ptr(&_num_par_pushes);)
9130 assert(p->is_oop(), "Not an oop");
9131 par_preserve_mark_if_necessary(p);
9132 oop observed_overflow_list = _overflow_list;
9133 oop cur_overflow_list;
9134 do {
9135 cur_overflow_list = observed_overflow_list;
9136 if (cur_overflow_list != BUSY) {
9137 p->set_mark(markOop(cur_overflow_list));
9138 } else {
9139 p->set_mark(NULL);
9140 }
9141 observed_overflow_list =
9142 (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list);
9143 } while (cur_overflow_list != observed_overflow_list);
9144 }
9145 #undef BUSY
9146
9147 // Single threaded
9148 // General Note on GrowableArray: pushes may silently fail
9149 // because we are (temporarily) out of C-heap for expanding
9150 // the stack. The problem is quite ubiquitous and affects
9151 // a lot of code in the JVM. The prudent thing for GrowableArray
9152 // to do (for now) is to exit with an error. However, that may
9153 // be too draconian in some cases because the caller may be
9154 // able to recover without much harm. For such cases, we
9155 // should probably introduce a "soft_push" method which returns
9156 // an indication of success or failure with the assumption that
9157 // the caller may be able to recover from a failure; code in
9158 // the VM can then be changed, incrementally, to deal with such
9159 // failures where possible, thus, incrementally hardening the VM
9160 // in such low resource situations.
9161 void CMSCollector::preserve_mark_work(oop p, markOop m) {
9162 _preserved_oop_stack.push(p);
9163 _preserved_mark_stack.push(m);
9164 assert(m == p->mark(), "Mark word changed");
9165 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
9166 "bijection");
9167 }
9168
9169 // Single threaded
9170 void CMSCollector::preserve_mark_if_necessary(oop p) {
9171 markOop m = p->mark();
9172 if (m->must_be_preserved(p)) {
9173 preserve_mark_work(p, m);
9174 }
9175 }
9176
9177 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
9178 markOop m = p->mark();
9179 if (m->must_be_preserved(p)) {
9180 MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
9181 // Even though we read the mark word without holding
9182 // the lock, we are assured that it will not change
9183 // because we "own" this oop, so no other thread can
9184 // be trying to push it on the overflow list; see
9185 // the assertion in preserve_mark_work() that checks
9186 // that m == p->mark().
9187 preserve_mark_work(p, m);
9188 }
9189 }
9190
9191 // We should be able to do this multi-threaded,
9192 // a chunk of stack being a task (this is
9193 // correct because each oop only ever appears
9194 // once in the overflow list. However, it's
9195 // not very easy to completely overlap this with
9196 // other operations, so will generally not be done
9197 // until all work's been completed. Because we
9198 // expect the preserved oop stack (set) to be small,
9199 // it's probably fine to do this single-threaded.
9200 // We can explore cleverer concurrent/overlapped/parallel
9201 // processing of preserved marks if we feel the
9202 // need for this in the future. Stack overflow should
9203 // be so rare in practice and, when it happens, its
9204 // effect on performance so great that this will
9205 // likely just be in the noise anyway.
9206 void CMSCollector::restore_preserved_marks_if_any() {
9207 assert(SafepointSynchronize::is_at_safepoint(),
9208 "world should be stopped");
9209 assert(Thread::current()->is_ConcurrentGC_thread() ||
9210 Thread::current()->is_VM_thread(),
9211 "should be single-threaded");
9212 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
9213 "bijection");
9214
9215 while (!_preserved_oop_stack.is_empty()) {
9216 oop p = _preserved_oop_stack.pop();
9217 assert(p->is_oop(), "Should be an oop");
9218 assert(_span.contains(p), "oop should be in _span");
9219 assert(p->mark() == markOopDesc::prototype(),
9220 "Set when taken from overflow list");
9221 markOop m = _preserved_mark_stack.pop();
9222 p->set_mark(m);
9223 }
9224 assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(),
9225 "stacks were cleared above");
9226 }
9227
9228 #ifndef PRODUCT
9229 bool CMSCollector::no_preserved_marks() const {
9230 return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty();
9231 }
9232 #endif
9233
9234 CMSAdaptiveSizePolicy* ASConcurrentMarkSweepGeneration::cms_size_policy() const
9235 {
9236 GenCollectedHeap* gch = (GenCollectedHeap*) GenCollectedHeap::heap();
9237 CMSAdaptiveSizePolicy* size_policy =
9238 (CMSAdaptiveSizePolicy*) gch->gen_policy()->size_policy();
9239 assert(size_policy->is_gc_cms_adaptive_size_policy(),
9240 "Wrong type for size policy");
9241 return size_policy;
9242 }
9243
9244 void ASConcurrentMarkSweepGeneration::resize(size_t cur_promo_size,
9245 size_t desired_promo_size) {
9246 if (cur_promo_size < desired_promo_size) {
9247 size_t expand_bytes = desired_promo_size - cur_promo_size;
9248 if (PrintAdaptiveSizePolicy && Verbose) {
9249 gclog_or_tty->print_cr(" ASConcurrentMarkSweepGeneration::resize "
9250 "Expanding tenured generation by " SIZE_FORMAT " (bytes)",
9251 expand_bytes);
9252 }
9253 expand(expand_bytes,
9254 MinHeapDeltaBytes,
9255 CMSExpansionCause::_adaptive_size_policy);
9256 } else if (desired_promo_size < cur_promo_size) {
9257 size_t shrink_bytes = cur_promo_size - desired_promo_size;
9258 if (PrintAdaptiveSizePolicy && Verbose) {
9259 gclog_or_tty->print_cr(" ASConcurrentMarkSweepGeneration::resize "
9260 "Shrinking tenured generation by " SIZE_FORMAT " (bytes)",
9261 shrink_bytes);
9262 }
9263 shrink(shrink_bytes);
9264 }
9265 }
9266
9267 CMSGCAdaptivePolicyCounters* ASConcurrentMarkSweepGeneration::gc_adaptive_policy_counters() {
9268 GenCollectedHeap* gch = GenCollectedHeap::heap();
9269 CMSGCAdaptivePolicyCounters* counters =
9270 (CMSGCAdaptivePolicyCounters*) gch->collector_policy()->counters();
9271 assert(counters->kind() == GCPolicyCounters::CMSGCAdaptivePolicyCountersKind,
9272 "Wrong kind of counters");
9273 return counters;
9274 }
9275
9276
9277 void ASConcurrentMarkSweepGeneration::update_counters() {
9278 if (UsePerfData) {
9279 _space_counters->update_all();
9280 _gen_counters->update_all();
9281 CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
9282 GenCollectedHeap* gch = GenCollectedHeap::heap();
9283 CMSGCStats* gc_stats_l = (CMSGCStats*) gc_stats();
9284 assert(gc_stats_l->kind() == GCStats::CMSGCStatsKind,
9285 "Wrong gc statistics type");
9286 counters->update_counters(gc_stats_l);
9287 }
9288 }
9289
9290 void ASConcurrentMarkSweepGeneration::update_counters(size_t used) {
9291 if (UsePerfData) {
9292 _space_counters->update_used(used);
9293 _space_counters->update_capacity();
9294 _gen_counters->update_all();
9295
9296 CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
9297 GenCollectedHeap* gch = GenCollectedHeap::heap();
9298 CMSGCStats* gc_stats_l = (CMSGCStats*) gc_stats();
9299 assert(gc_stats_l->kind() == GCStats::CMSGCStatsKind,
9300 "Wrong gc statistics type");
9301 counters->update_counters(gc_stats_l);
9302 }
9303 }
9304
9305 void ASConcurrentMarkSweepGeneration::shrink_by(size_t desired_bytes) {
9306 assert_locked_or_safepoint(Heap_lock);
9307 assert_lock_strong(freelistLock());
9308 HeapWord* old_end = _cmsSpace->end();
9309 HeapWord* unallocated_start = _cmsSpace->unallocated_block();
9310 assert(old_end >= unallocated_start, "Miscalculation of unallocated_start");
9311 FreeChunk* chunk_at_end = find_chunk_at_end();
9312 if (chunk_at_end == NULL) {
9313 // No room to shrink
9314 if (PrintGCDetails && Verbose) {
9315 gclog_or_tty->print_cr("No room to shrink: old_end "
9316 PTR_FORMAT " unallocated_start " PTR_FORMAT
9317 " chunk_at_end " PTR_FORMAT,
9318 old_end, unallocated_start, chunk_at_end);
9319 }
9320 return;
9321 } else {
9322
9323 // Find the chunk at the end of the space and determine
9324 // how much it can be shrunk.
9325 size_t shrinkable_size_in_bytes = chunk_at_end->size();
9326 size_t aligned_shrinkable_size_in_bytes =
9327 align_size_down(shrinkable_size_in_bytes, os::vm_page_size());
9328 assert(unallocated_start <= (HeapWord*) chunk_at_end->end(),
9329 "Inconsistent chunk at end of space");
9330 size_t bytes = MIN2(desired_bytes, aligned_shrinkable_size_in_bytes);
9331 size_t word_size_before = heap_word_size(_virtual_space.committed_size());
9332
9333 // Shrink the underlying space
9334 _virtual_space.shrink_by(bytes);
9335 if (PrintGCDetails && Verbose) {
9336 gclog_or_tty->print_cr("ConcurrentMarkSweepGeneration::shrink_by:"
9337 " desired_bytes " SIZE_FORMAT
9338 " shrinkable_size_in_bytes " SIZE_FORMAT
9339 " aligned_shrinkable_size_in_bytes " SIZE_FORMAT
9340 " bytes " SIZE_FORMAT,
9341 desired_bytes, shrinkable_size_in_bytes,
9342 aligned_shrinkable_size_in_bytes, bytes);
9343 gclog_or_tty->print_cr(" old_end " SIZE_FORMAT
9344 " unallocated_start " SIZE_FORMAT,
9345 old_end, unallocated_start);
9346 }
9347
9348 // If the space did shrink (shrinking is not guaranteed),
9349 // shrink the chunk at the end by the appropriate amount.
9350 if (((HeapWord*)_virtual_space.high()) < old_end) {
9351 size_t new_word_size =
9352 heap_word_size(_virtual_space.committed_size());
9353
9354 // Have to remove the chunk from the dictionary because it is changing
9355 // size and might be someplace elsewhere in the dictionary.
9356
9357 // Get the chunk at end, shrink it, and put it
9358 // back.
9359 _cmsSpace->removeChunkFromDictionary(chunk_at_end);
9360 size_t word_size_change = word_size_before - new_word_size;
9361 size_t chunk_at_end_old_size = chunk_at_end->size();
9362 assert(chunk_at_end_old_size >= word_size_change,
9363 "Shrink is too large");
9364 chunk_at_end->set_size(chunk_at_end_old_size -
9365 word_size_change);
9366 _cmsSpace->freed((HeapWord*) chunk_at_end->end(),
9367 word_size_change);
9368
9369 _cmsSpace->returnChunkToDictionary(chunk_at_end);
9370
9371 MemRegion mr(_cmsSpace->bottom(), new_word_size);
9372 _bts->resize(new_word_size); // resize the block offset shared array
9373 Universe::heap()->barrier_set()->resize_covered_region(mr);
9374 _cmsSpace->assert_locked();
9375 _cmsSpace->set_end((HeapWord*)_virtual_space.high());
9376
9377 NOT_PRODUCT(_cmsSpace->dictionary()->verify());
9378
9379 // update the space and generation capacity counters
9380 if (UsePerfData) {
9381 _space_counters->update_capacity();
9382 _gen_counters->update_all();
9383 }
9384
9385 if (Verbose && PrintGCDetails) {
9386 size_t new_mem_size = _virtual_space.committed_size();
9387 size_t old_mem_size = new_mem_size + bytes;
9388 gclog_or_tty->print_cr("Shrinking %s from " SIZE_FORMAT "K by " SIZE_FORMAT "K to " SIZE_FORMAT "K",
9389 name(), old_mem_size/K, bytes/K, new_mem_size/K);
9390 }
9391 }
9392
9393 assert(_cmsSpace->unallocated_block() <= _cmsSpace->end(),
9394 "Inconsistency at end of space");
9395 assert(chunk_at_end->end() == (uintptr_t*) _cmsSpace->end(),
9396 "Shrinking is inconsistent");
9397 return;
9398 }
9399 }
9400
9401 // Transfer some number of overflown objects to usual marking
9402 // stack. Return true if some objects were transferred.
9403 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
9404 size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,
9405 (size_t)ParGCDesiredObjsFromOverflowList);
9406
9407 bool res = _collector->take_from_overflow_list(num, _mark_stack);
9408 assert(_collector->overflow_list_is_empty() || res,
9409 "If list is not empty, we should have taken something");
9410 assert(!res || !_mark_stack->isEmpty(),
9411 "If we took something, it should now be on our stack");
9412 return res;
9413 }
9414
9415 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
9416 size_t res = _sp->block_size_no_stall(addr, _collector);
9417 if (_sp->block_is_obj(addr)) {
9418 if (_live_bit_map->isMarked(addr)) {
9419 // It can't have been dead in a previous cycle
9420 guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
9421 } else {
9422 _dead_bit_map->mark(addr); // mark the dead object
9423 }
9424 }
9425 // Could be 0, if the block size could not be computed without stalling.
9426 return res;
9427 }
9428
9429 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() {
9430
9431 switch (phase) {
9432 case CMSCollector::InitialMarking:
9433 initialize(true /* fullGC */ ,
9434 cause /* cause of the GC */,
9435 true /* recordGCBeginTime */,
9436 true /* recordPreGCUsage */,
9437 false /* recordPeakUsage */,
9438 false /* recordPostGCusage */,
9439 true /* recordAccumulatedGCTime */,
9440 false /* recordGCEndTime */,
9441 false /* countCollection */ );
9442 break;
9443
9444 case CMSCollector::FinalMarking:
9445 initialize(true /* fullGC */ ,
9446 cause /* cause of the GC */,
9447 false /* recordGCBeginTime */,
9448 false /* recordPreGCUsage */,
9449 false /* recordPeakUsage */,
9450 false /* recordPostGCusage */,
9451 true /* recordAccumulatedGCTime */,
9452 false /* recordGCEndTime */,
9453 false /* countCollection */ );
9454 break;
9455
9456 case CMSCollector::Sweeping:
9457 initialize(true /* fullGC */ ,
9458 cause /* cause of the GC */,
9459 false /* recordGCBeginTime */,
9460 false /* recordPreGCUsage */,
9461 true /* recordPeakUsage */,
9462 true /* recordPostGCusage */,
9463 false /* recordAccumulatedGCTime */,
9464 true /* recordGCEndTime */,
9465 true /* countCollection */ );
9466 break;
9467
9468 default:
9469 ShouldNotReachHere();
9470 }
9471 }