1 /*
2 * Copyright (c) 2001, 2014, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include "precompiled.hpp"
26 #include "classfile/classLoaderData.hpp"
27 #include "classfile/stringTable.hpp"
28 #include "classfile/systemDictionary.hpp"
29 #include "code/codeCache.hpp"
30 #include "gc_implementation/shared/adaptiveSizePolicy.hpp"
31 #include "gc_implementation/concurrentMarkSweep/cmsCollectorPolicy.hpp"
32 #include "gc_implementation/concurrentMarkSweep/cmsOopClosures.inline.hpp"
33 #include "gc_implementation/concurrentMarkSweep/compactibleFreeListSpace.hpp"
34 #include "gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.inline.hpp"
35 #include "gc_implementation/concurrentMarkSweep/concurrentMarkSweepThread.hpp"
36 #include "gc_implementation/concurrentMarkSweep/vmCMSOperations.hpp"
37 #include "gc_implementation/parNew/parNewGeneration.hpp"
38 #include "gc_implementation/shared/collectorCounters.hpp"
39 #include "gc_implementation/shared/gcTimer.hpp"
40 #include "gc_implementation/shared/gcTrace.hpp"
41 #include "gc_implementation/shared/gcTraceTime.hpp"
42 #include "gc_implementation/shared/isGCActiveMark.hpp"
43 #include "gc_interface/collectedHeap.inline.hpp"
44 #include "memory/allocation.hpp"
45 #include "memory/cardTableRS.hpp"
46 #include "memory/collectorPolicy.hpp"
47 #include "memory/gcLocker.inline.hpp"
48 #include "memory/genCollectedHeap.hpp"
49 #include "memory/genMarkSweep.hpp"
50 #include "memory/genOopClosures.inline.hpp"
51 #include "memory/iterator.inline.hpp"
52 #include "memory/padded.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/atomic.inline.hpp"
59 #include "runtime/globals_extension.hpp"
60 #include "runtime/handles.inline.hpp"
61 #include "runtime/java.hpp"
62 #include "runtime/orderAccess.inline.hpp"
63 #include "runtime/vmThread.hpp"
64 #include "services/memoryService.hpp"
65 #include "services/runtimeService.hpp"
66
67 PRAGMA_FORMAT_MUTE_WARNINGS_FOR_GCC
68
69 // statics
70 CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL;
71 bool CMSCollector::_full_gc_requested = false;
72 GCCause::Cause CMSCollector::_full_gc_cause = GCCause::_no_gc;
73
74 //////////////////////////////////////////////////////////////////
75 // In support of CMS/VM thread synchronization
76 //////////////////////////////////////////////////////////////////
77 // We split use of the CGC_lock into 2 "levels".
78 // The low-level locking is of the usual CGC_lock monitor. We introduce
79 // a higher level "token" (hereafter "CMS token") built on top of the
80 // low level monitor (hereafter "CGC lock").
81 // The token-passing protocol gives priority to the VM thread. The
82 // CMS-lock doesn't provide any fairness guarantees, but clients
83 // should ensure that it is only held for very short, bounded
84 // durations.
85 //
86 // When either of the CMS thread or the VM thread is involved in
87 // collection operations during which it does not want the other
88 // thread to interfere, it obtains the CMS token.
89 //
90 // If either thread tries to get the token while the other has
91 // it, that thread waits. However, if the VM thread and CMS thread
92 // both want the token, then the VM thread gets priority while the
93 // CMS thread waits. This ensures, for instance, that the "concurrent"
94 // phases of the CMS thread's work do not block out the VM thread
95 // for long periods of time as the CMS thread continues to hog
96 // the token. (See bug 4616232).
97 //
98 // The baton-passing functions are, however, controlled by the
99 // flags _foregroundGCShouldWait and _foregroundGCIsActive,
100 // and here the low-level CMS lock, not the high level token,
101 // ensures mutual exclusion.
102 //
103 // Two important conditions that we have to satisfy:
104 // 1. if a thread does a low-level wait on the CMS lock, then it
105 // relinquishes the CMS token if it were holding that token
106 // when it acquired the low-level CMS lock.
107 // 2. any low-level notifications on the low-level lock
108 // should only be sent when a thread has relinquished the token.
109 //
110 // In the absence of either property, we'd have potential deadlock.
111 //
112 // We protect each of the CMS (concurrent and sequential) phases
113 // with the CMS _token_, not the CMS _lock_.
114 //
115 // The only code protected by CMS lock is the token acquisition code
116 // itself, see ConcurrentMarkSweepThread::[de]synchronize(), and the
117 // baton-passing code.
118 //
119 // Unfortunately, i couldn't come up with a good abstraction to factor and
120 // hide the naked CGC_lock manipulation in the baton-passing code
121 // further below. That's something we should try to do. Also, the proof
122 // of correctness of this 2-level locking scheme is far from obvious,
123 // and potentially quite slippery. We have an uneasy suspicion, for instance,
124 // that there may be a theoretical possibility of delay/starvation in the
125 // low-level lock/wait/notify scheme used for the baton-passing because of
126 // potential interference with the priority scheme embodied in the
127 // CMS-token-passing protocol. See related comments at a CGC_lock->wait()
128 // invocation further below and marked with "XXX 20011219YSR".
129 // Indeed, as we note elsewhere, this may become yet more slippery
130 // in the presence of multiple CMS and/or multiple VM threads. XXX
131
132 class CMSTokenSync: public StackObj {
133 private:
134 bool _is_cms_thread;
135 public:
136 CMSTokenSync(bool is_cms_thread):
137 _is_cms_thread(is_cms_thread) {
138 assert(is_cms_thread == Thread::current()->is_ConcurrentGC_thread(),
139 "Incorrect argument to constructor");
140 ConcurrentMarkSweepThread::synchronize(_is_cms_thread);
141 }
142
143 ~CMSTokenSync() {
144 assert(_is_cms_thread ?
145 ConcurrentMarkSweepThread::cms_thread_has_cms_token() :
146 ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
147 "Incorrect state");
148 ConcurrentMarkSweepThread::desynchronize(_is_cms_thread);
149 }
150 };
151
152 // Convenience class that does a CMSTokenSync, and then acquires
153 // upto three locks.
154 class CMSTokenSyncWithLocks: public CMSTokenSync {
155 private:
156 // Note: locks are acquired in textual declaration order
157 // and released in the opposite order
158 MutexLockerEx _locker1, _locker2, _locker3;
159 public:
160 CMSTokenSyncWithLocks(bool is_cms_thread, Mutex* mutex1,
161 Mutex* mutex2 = NULL, Mutex* mutex3 = NULL):
162 CMSTokenSync(is_cms_thread),
163 _locker1(mutex1, Mutex::_no_safepoint_check_flag),
164 _locker2(mutex2, Mutex::_no_safepoint_check_flag),
165 _locker3(mutex3, Mutex::_no_safepoint_check_flag)
166 { }
167 };
168
169
170 // Wrapper class to temporarily disable icms during a foreground cms collection.
171 class ICMSDisabler: public StackObj {
172 public:
173 // The ctor disables icms and wakes up the thread so it notices the change;
174 // the dtor re-enables icms. Note that the CMSCollector methods will check
175 // CMSIncrementalMode.
176 ICMSDisabler() { CMSCollector::disable_icms(); CMSCollector::start_icms(); }
177 ~ICMSDisabler() { CMSCollector::enable_icms(); }
178 };
179
180 //////////////////////////////////////////////////////////////////
181 // Concurrent Mark-Sweep Generation /////////////////////////////
182 //////////////////////////////////////////////////////////////////
183
184 NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;)
185
186 // This struct contains per-thread things necessary to support parallel
187 // young-gen collection.
188 class CMSParGCThreadState: public CHeapObj<mtGC> {
189 public:
190 CFLS_LAB lab;
191 PromotionInfo promo;
192
193 // Constructor.
194 CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) {
195 promo.setSpace(cfls);
196 }
197 };
198
199 ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration(
200 ReservedSpace rs, size_t initial_byte_size, int level,
201 CardTableRS* ct, bool use_adaptive_freelists,
202 FreeBlockDictionary<FreeChunk>::DictionaryChoice dictionaryChoice) :
203 CardGeneration(rs, initial_byte_size, level, ct),
204 _dilatation_factor(((double)MinChunkSize)/((double)(CollectedHeap::min_fill_size()))),
205 _debug_collection_type(Concurrent_collection_type),
206 _did_compact(false)
207 {
208 HeapWord* bottom = (HeapWord*) _virtual_space.low();
209 HeapWord* end = (HeapWord*) _virtual_space.high();
210
211 _direct_allocated_words = 0;
212 NOT_PRODUCT(
213 _numObjectsPromoted = 0;
214 _numWordsPromoted = 0;
215 _numObjectsAllocated = 0;
216 _numWordsAllocated = 0;
217 )
218
219 _cmsSpace = new CompactibleFreeListSpace(_bts, MemRegion(bottom, end),
220 use_adaptive_freelists,
221 dictionaryChoice);
222 NOT_PRODUCT(debug_cms_space = _cmsSpace;)
223 if (_cmsSpace == NULL) {
224 vm_exit_during_initialization(
225 "CompactibleFreeListSpace allocation failure");
226 }
227 _cmsSpace->_gen = this;
228
229 _gc_stats = new CMSGCStats();
230
231 // Verify the assumption that FreeChunk::_prev and OopDesc::_klass
232 // offsets match. The ability to tell free chunks from objects
233 // depends on this property.
234 debug_only(
235 FreeChunk* junk = NULL;
236 assert(UseCompressedClassPointers ||
237 junk->prev_addr() == (void*)(oop(junk)->klass_addr()),
238 "Offset of FreeChunk::_prev within FreeChunk must match"
239 " that of OopDesc::_klass within OopDesc");
240 )
241 if (CollectedHeap::use_parallel_gc_threads()) {
242 typedef CMSParGCThreadState* CMSParGCThreadStatePtr;
243 _par_gc_thread_states =
244 NEW_C_HEAP_ARRAY(CMSParGCThreadStatePtr, ParallelGCThreads, mtGC);
245 if (_par_gc_thread_states == NULL) {
246 vm_exit_during_initialization("Could not allocate par gc structs");
247 }
248 for (uint i = 0; i < ParallelGCThreads; i++) {
249 _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace());
250 if (_par_gc_thread_states[i] == NULL) {
251 vm_exit_during_initialization("Could not allocate par gc structs");
252 }
253 }
254 } else {
255 _par_gc_thread_states = NULL;
256 }
257 _incremental_collection_failed = false;
258 // The "dilatation_factor" is the expansion that can occur on
259 // account of the fact that the minimum object size in the CMS
260 // generation may be larger than that in, say, a contiguous young
261 // generation.
262 // Ideally, in the calculation below, we'd compute the dilatation
263 // factor as: MinChunkSize/(promoting_gen's min object size)
264 // Since we do not have such a general query interface for the
265 // promoting generation, we'll instead just use the minimum
266 // object size (which today is a header's worth of space);
267 // note that all arithmetic is in units of HeapWords.
268 assert(MinChunkSize >= CollectedHeap::min_fill_size(), "just checking");
269 assert(_dilatation_factor >= 1.0, "from previous assert");
270 }
271
272
273 // The field "_initiating_occupancy" represents the occupancy percentage
274 // at which we trigger a new collection cycle. Unless explicitly specified
275 // via CMSInitiatingOccupancyFraction (argument "io" below), it
276 // is calculated by:
277 //
278 // Let "f" be MinHeapFreeRatio in
279 //
280 // _initiating_occupancy = 100-f +
281 // f * (CMSTriggerRatio/100)
282 // where CMSTriggerRatio is the argument "tr" below.
283 //
284 // That is, if we assume the heap is at its desired maximum occupancy at the
285 // end of a collection, we let CMSTriggerRatio of the (purported) free
286 // space be allocated before initiating a new collection cycle.
287 //
288 void ConcurrentMarkSweepGeneration::init_initiating_occupancy(intx io, uintx tr) {
289 assert(io <= 100 && tr <= 100, "Check the arguments");
290 if (io >= 0) {
291 _initiating_occupancy = (double)io / 100.0;
292 } else {
293 _initiating_occupancy = ((100 - MinHeapFreeRatio) +
294 (double)(tr * MinHeapFreeRatio) / 100.0)
295 / 100.0;
296 }
297 }
298
299 void ConcurrentMarkSweepGeneration::ref_processor_init() {
300 assert(collector() != NULL, "no collector");
301 collector()->ref_processor_init();
302 }
303
304 void CMSCollector::ref_processor_init() {
305 if (_ref_processor == NULL) {
306 // Allocate and initialize a reference processor
307 _ref_processor =
308 new ReferenceProcessor(_span, // span
309 (ParallelGCThreads > 1) && ParallelRefProcEnabled, // mt processing
310 (int) ParallelGCThreads, // mt processing degree
311 _cmsGen->refs_discovery_is_mt(), // mt discovery
312 (int) MAX2(ConcGCThreads, ParallelGCThreads), // mt discovery degree
313 _cmsGen->refs_discovery_is_atomic(), // discovery is not atomic
314 &_is_alive_closure); // closure for liveness info
315 // Initialize the _ref_processor field of CMSGen
316 _cmsGen->set_ref_processor(_ref_processor);
317
318 }
319 }
320
321 AdaptiveSizePolicy* CMSCollector::size_policy() {
322 GenCollectedHeap* gch = GenCollectedHeap::heap();
323 assert(gch->kind() == CollectedHeap::GenCollectedHeap,
324 "Wrong type of heap");
325 return gch->gen_policy()->size_policy();
326 }
327
328 void ConcurrentMarkSweepGeneration::initialize_performance_counters() {
329
330 const char* gen_name = "old";
331 GenCollectorPolicy* gcp = (GenCollectorPolicy*) GenCollectedHeap::heap()->collector_policy();
332
333 // Generation Counters - generation 1, 1 subspace
334 _gen_counters = new GenerationCounters(gen_name, 1, 1,
335 gcp->min_old_size(), gcp->max_old_size(), &_virtual_space);
336
337 _space_counters = new GSpaceCounters(gen_name, 0,
338 _virtual_space.reserved_size(),
339 this, _gen_counters);
340 }
341
342 CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha):
343 _cms_gen(cms_gen)
344 {
345 assert(alpha <= 100, "bad value");
346 _saved_alpha = alpha;
347
348 // Initialize the alphas to the bootstrap value of 100.
349 _gc0_alpha = _cms_alpha = 100;
350
351 _cms_begin_time.update();
352 _cms_end_time.update();
353
354 _gc0_duration = 0.0;
355 _gc0_period = 0.0;
356 _gc0_promoted = 0;
357
358 _cms_duration = 0.0;
359 _cms_period = 0.0;
360 _cms_allocated = 0;
361
362 _cms_used_at_gc0_begin = 0;
363 _cms_used_at_gc0_end = 0;
364 _allow_duty_cycle_reduction = false;
365 _valid_bits = 0;
366 _icms_duty_cycle = CMSIncrementalDutyCycle;
367 }
368
369 double CMSStats::cms_free_adjustment_factor(size_t free) const {
370 // TBD: CR 6909490
371 return 1.0;
372 }
373
374 void CMSStats::adjust_cms_free_adjustment_factor(bool fail, size_t free) {
375 }
376
377 // If promotion failure handling is on use
378 // the padded average size of the promotion for each
379 // young generation collection.
380 double CMSStats::time_until_cms_gen_full() const {
381 size_t cms_free = _cms_gen->cmsSpace()->free();
382 GenCollectedHeap* gch = GenCollectedHeap::heap();
383 size_t expected_promotion = MIN2(gch->get_gen(0)->capacity(),
384 (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average());
385 if (cms_free > expected_promotion) {
386 // Start a cms collection if there isn't enough space to promote
387 // for the next minor collection. Use the padded average as
388 // a safety factor.
389 cms_free -= expected_promotion;
390
391 // Adjust by the safety factor.
392 double cms_free_dbl = (double)cms_free;
393 double cms_adjustment = (100.0 - CMSIncrementalSafetyFactor)/100.0;
394 // Apply a further correction factor which tries to adjust
395 // for recent occurance of concurrent mode failures.
396 cms_adjustment = cms_adjustment * cms_free_adjustment_factor(cms_free);
397 cms_free_dbl = cms_free_dbl * cms_adjustment;
398
399 if (PrintGCDetails && Verbose) {
400 gclog_or_tty->print_cr("CMSStats::time_until_cms_gen_full: cms_free "
401 SIZE_FORMAT " expected_promotion " SIZE_FORMAT,
402 cms_free, expected_promotion);
403 gclog_or_tty->print_cr(" cms_free_dbl %f cms_consumption_rate %f",
404 cms_free_dbl, cms_consumption_rate() + 1.0);
405 }
406 // Add 1 in case the consumption rate goes to zero.
407 return cms_free_dbl / (cms_consumption_rate() + 1.0);
408 }
409 return 0.0;
410 }
411
412 // Compare the duration of the cms collection to the
413 // time remaining before the cms generation is empty.
414 // Note that the time from the start of the cms collection
415 // to the start of the cms sweep (less than the total
416 // duration of the cms collection) can be used. This
417 // has been tried and some applications experienced
418 // promotion failures early in execution. This was
419 // possibly because the averages were not accurate
420 // enough at the beginning.
421 double CMSStats::time_until_cms_start() const {
422 // We add "gc0_period" to the "work" calculation
423 // below because this query is done (mostly) at the
424 // end of a scavenge, so we need to conservatively
425 // account for that much possible delay
426 // in the query so as to avoid concurrent mode failures
427 // due to starting the collection just a wee bit too
428 // late.
429 double work = cms_duration() + gc0_period();
430 double deadline = time_until_cms_gen_full();
431 // If a concurrent mode failure occurred recently, we want to be
432 // more conservative and halve our expected time_until_cms_gen_full()
433 if (work > deadline) {
434 if (Verbose && PrintGCDetails) {
435 gclog_or_tty->print(
436 " CMSCollector: collect because of anticipated promotion "
437 "before full %3.7f + %3.7f > %3.7f ", cms_duration(),
438 gc0_period(), time_until_cms_gen_full());
439 }
440 return 0.0;
441 }
442 return work - deadline;
443 }
444
445 // Return a duty cycle based on old_duty_cycle and new_duty_cycle, limiting the
446 // amount of change to prevent wild oscillation.
447 unsigned int CMSStats::icms_damped_duty_cycle(unsigned int old_duty_cycle,
448 unsigned int new_duty_cycle) {
449 assert(old_duty_cycle <= 100, "bad input value");
450 assert(new_duty_cycle <= 100, "bad input value");
451
452 // Note: use subtraction with caution since it may underflow (values are
453 // unsigned). Addition is safe since we're in the range 0-100.
454 unsigned int damped_duty_cycle = new_duty_cycle;
455 if (new_duty_cycle < old_duty_cycle) {
456 const unsigned int largest_delta = MAX2(old_duty_cycle / 4, 5U);
457 if (new_duty_cycle + largest_delta < old_duty_cycle) {
458 damped_duty_cycle = old_duty_cycle - largest_delta;
459 }
460 } else if (new_duty_cycle > old_duty_cycle) {
461 const unsigned int largest_delta = MAX2(old_duty_cycle / 4, 15U);
462 if (new_duty_cycle > old_duty_cycle + largest_delta) {
463 damped_duty_cycle = MIN2(old_duty_cycle + largest_delta, 100U);
464 }
465 }
466 assert(damped_duty_cycle <= 100, "invalid duty cycle computed");
467
468 if (CMSTraceIncrementalPacing) {
469 gclog_or_tty->print(" [icms_damped_duty_cycle(%d,%d) = %d] ",
470 old_duty_cycle, new_duty_cycle, damped_duty_cycle);
471 }
472 return damped_duty_cycle;
473 }
474
475 unsigned int CMSStats::icms_update_duty_cycle_impl() {
476 assert(CMSIncrementalPacing && valid(),
477 "should be handled in icms_update_duty_cycle()");
478
479 double cms_time_so_far = cms_timer().seconds();
480 double scaled_duration = cms_duration_per_mb() * _cms_used_at_gc0_end / M;
481 double scaled_duration_remaining = fabsd(scaled_duration - cms_time_so_far);
482
483 // Avoid division by 0.
484 double time_until_full = MAX2(time_until_cms_gen_full(), 0.01);
485 double duty_cycle_dbl = 100.0 * scaled_duration_remaining / time_until_full;
486
487 unsigned int new_duty_cycle = MIN2((unsigned int)duty_cycle_dbl, 100U);
488 if (new_duty_cycle > _icms_duty_cycle) {
489 // Avoid very small duty cycles (1 or 2); 0 is allowed.
490 if (new_duty_cycle > 2) {
491 _icms_duty_cycle = icms_damped_duty_cycle(_icms_duty_cycle,
492 new_duty_cycle);
493 }
494 } else if (_allow_duty_cycle_reduction) {
495 // The duty cycle is reduced only once per cms cycle (see record_cms_end()).
496 new_duty_cycle = icms_damped_duty_cycle(_icms_duty_cycle, new_duty_cycle);
497 // Respect the minimum duty cycle.
498 unsigned int min_duty_cycle = (unsigned int)CMSIncrementalDutyCycleMin;
499 _icms_duty_cycle = MAX2(new_duty_cycle, min_duty_cycle);
500 }
501
502 if (PrintGCDetails || CMSTraceIncrementalPacing) {
503 gclog_or_tty->print(" icms_dc=%d ", _icms_duty_cycle);
504 }
505
506 _allow_duty_cycle_reduction = false;
507 return _icms_duty_cycle;
508 }
509
510 #ifndef PRODUCT
511 void CMSStats::print_on(outputStream *st) const {
512 st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha);
513 st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo=" SIZE_FORMAT,
514 gc0_duration(), gc0_period(), gc0_promoted());
515 st->print(",cms_dur=%g,cms_dur_per_mb=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT,
516 cms_duration(), cms_duration_per_mb(),
517 cms_period(), cms_allocated());
518 st->print(",cms_since_beg=%g,cms_since_end=%g",
519 cms_time_since_begin(), cms_time_since_end());
520 st->print(",cms_used_beg=" SIZE_FORMAT ",cms_used_end=" SIZE_FORMAT,
521 _cms_used_at_gc0_begin, _cms_used_at_gc0_end);
522 if (CMSIncrementalMode) {
523 st->print(",dc=%d", icms_duty_cycle());
524 }
525
526 if (valid()) {
527 st->print(",promo_rate=%g,cms_alloc_rate=%g",
528 promotion_rate(), cms_allocation_rate());
529 st->print(",cms_consumption_rate=%g,time_until_full=%g",
530 cms_consumption_rate(), time_until_cms_gen_full());
531 }
532 st->print(" ");
533 }
534 #endif // #ifndef PRODUCT
535
536 CMSCollector::CollectorState CMSCollector::_collectorState =
537 CMSCollector::Idling;
538 bool CMSCollector::_foregroundGCIsActive = false;
539 bool CMSCollector::_foregroundGCShouldWait = false;
540
541 CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
542 CardTableRS* ct,
543 ConcurrentMarkSweepPolicy* cp):
544 _cmsGen(cmsGen),
545 _ct(ct),
546 _ref_processor(NULL), // will be set later
547 _conc_workers(NULL), // may be set later
548 _abort_preclean(false),
549 _start_sampling(false),
550 _between_prologue_and_epilogue(false),
551 _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"),
552 _modUnionTable((CardTableModRefBS::card_shift - LogHeapWordSize),
553 -1 /* lock-free */, "No_lock" /* dummy */),
554 _modUnionClosure(&_modUnionTable),
555 _modUnionClosurePar(&_modUnionTable),
556 // Adjust my span to cover old (cms) gen
557 _span(cmsGen->reserved()),
558 // Construct the is_alive_closure with _span & markBitMap
559 _is_alive_closure(_span, &_markBitMap),
560 _restart_addr(NULL),
561 _overflow_list(NULL),
562 _stats(cmsGen),
563 _eden_chunk_lock(new Mutex(Mutex::leaf + 1, "CMS_eden_chunk_lock", true)),
564 _eden_chunk_array(NULL), // may be set in ctor body
565 _eden_chunk_capacity(0), // -- ditto --
566 _eden_chunk_index(0), // -- ditto --
567 _survivor_plab_array(NULL), // -- ditto --
568 _survivor_chunk_array(NULL), // -- ditto --
569 _survivor_chunk_capacity(0), // -- ditto --
570 _survivor_chunk_index(0), // -- ditto --
571 _ser_pmc_preclean_ovflw(0),
572 _ser_kac_preclean_ovflw(0),
573 _ser_pmc_remark_ovflw(0),
574 _par_pmc_remark_ovflw(0),
575 _ser_kac_ovflw(0),
576 _par_kac_ovflw(0),
577 #ifndef PRODUCT
578 _num_par_pushes(0),
579 #endif
580 _collection_count_start(0),
581 _verifying(false),
582 _icms_start_limit(NULL),
583 _icms_stop_limit(NULL),
584 _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"),
585 _completed_initialization(false),
586 _collector_policy(cp),
587 _should_unload_classes(CMSClassUnloadingEnabled),
588 _concurrent_cycles_since_last_unload(0),
589 _roots_scanning_options(SharedHeap::SO_None),
590 _inter_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
591 _intra_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
592 _gc_tracer_cm(new (ResourceObj::C_HEAP, mtGC) CMSTracer()),
593 _gc_timer_cm(new (ResourceObj::C_HEAP, mtGC) ConcurrentGCTimer()),
594 _cms_start_registered(false)
595 {
596 if (ExplicitGCInvokesConcurrentAndUnloadsClasses) {
597 ExplicitGCInvokesConcurrent = true;
598 }
599 // Now expand the span and allocate the collection support structures
600 // (MUT, marking bit map etc.) to cover both generations subject to
601 // collection.
602
603 // For use by dirty card to oop closures.
604 _cmsGen->cmsSpace()->set_collector(this);
605
606 // Allocate MUT and marking bit map
607 {
608 MutexLockerEx x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag);
609 if (!_markBitMap.allocate(_span)) {
610 warning("Failed to allocate CMS Bit Map");
611 return;
612 }
613 assert(_markBitMap.covers(_span), "_markBitMap inconsistency?");
614 }
615 {
616 _modUnionTable.allocate(_span);
617 assert(_modUnionTable.covers(_span), "_modUnionTable inconsistency?");
618 }
619
620 if (!_markStack.allocate(MarkStackSize)) {
621 warning("Failed to allocate CMS Marking Stack");
622 return;
623 }
624
625 // Support for multi-threaded concurrent phases
626 if (CMSConcurrentMTEnabled) {
627 if (FLAG_IS_DEFAULT(ConcGCThreads)) {
628 // just for now
629 FLAG_SET_DEFAULT(ConcGCThreads, (ParallelGCThreads + 3)/4);
630 }
631 if (ConcGCThreads > 1) {
632 _conc_workers = new YieldingFlexibleWorkGang("Parallel CMS Threads",
633 ConcGCThreads, true);
634 if (_conc_workers == NULL) {
635 warning("GC/CMS: _conc_workers allocation failure: "
636 "forcing -CMSConcurrentMTEnabled");
637 CMSConcurrentMTEnabled = false;
638 } else {
639 _conc_workers->initialize_workers();
640 }
641 } else {
642 CMSConcurrentMTEnabled = false;
643 }
644 }
645 if (!CMSConcurrentMTEnabled) {
646 ConcGCThreads = 0;
647 } else {
648 // Turn off CMSCleanOnEnter optimization temporarily for
649 // the MT case where it's not fixed yet; see 6178663.
650 CMSCleanOnEnter = false;
651 }
652 assert((_conc_workers != NULL) == (ConcGCThreads > 1),
653 "Inconsistency");
654
655 // Parallel task queues; these are shared for the
656 // concurrent and stop-world phases of CMS, but
657 // are not shared with parallel scavenge (ParNew).
658 {
659 uint i;
660 uint num_queues = (uint) MAX2(ParallelGCThreads, ConcGCThreads);
661
662 if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled
663 || ParallelRefProcEnabled)
664 && num_queues > 0) {
665 _task_queues = new OopTaskQueueSet(num_queues);
666 if (_task_queues == NULL) {
667 warning("task_queues allocation failure.");
668 return;
669 }
670 _hash_seed = NEW_C_HEAP_ARRAY(int, num_queues, mtGC);
671 if (_hash_seed == NULL) {
672 warning("_hash_seed array allocation failure");
673 return;
674 }
675
676 typedef Padded<OopTaskQueue> PaddedOopTaskQueue;
677 for (i = 0; i < num_queues; i++) {
678 PaddedOopTaskQueue *q = new PaddedOopTaskQueue();
679 if (q == NULL) {
680 warning("work_queue allocation failure.");
681 return;
682 }
683 _task_queues->register_queue(i, q);
684 }
685 for (i = 0; i < num_queues; i++) {
686 _task_queues->queue(i)->initialize();
687 _hash_seed[i] = 17; // copied from ParNew
688 }
689 }
690 }
691
692 _cmsGen ->init_initiating_occupancy(CMSInitiatingOccupancyFraction, CMSTriggerRatio);
693
694 // Clip CMSBootstrapOccupancy between 0 and 100.
695 _bootstrap_occupancy = ((double)CMSBootstrapOccupancy)/(double)100;
696
697 _full_gcs_since_conc_gc = 0;
698
699 // Now tell CMS generations the identity of their collector
700 ConcurrentMarkSweepGeneration::set_collector(this);
701
702 // Create & start a CMS thread for this CMS collector
703 _cmsThread = ConcurrentMarkSweepThread::start(this);
704 assert(cmsThread() != NULL, "CMS Thread should have been created");
705 assert(cmsThread()->collector() == this,
706 "CMS Thread should refer to this gen");
707 assert(CGC_lock != NULL, "Where's the CGC_lock?");
708
709 // Support for parallelizing young gen rescan
710 GenCollectedHeap* gch = GenCollectedHeap::heap();
711 _young_gen = gch->prev_gen(_cmsGen);
712 if (gch->supports_inline_contig_alloc()) {
713 _top_addr = gch->top_addr();
714 _end_addr = gch->end_addr();
715 assert(_young_gen != NULL, "no _young_gen");
716 _eden_chunk_index = 0;
717 _eden_chunk_capacity = (_young_gen->max_capacity()+CMSSamplingGrain)/CMSSamplingGrain;
718 _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity, mtGC);
719 if (_eden_chunk_array == NULL) {
720 _eden_chunk_capacity = 0;
721 warning("GC/CMS: _eden_chunk_array allocation failure");
722 }
723 }
724 assert(_eden_chunk_array != NULL || _eden_chunk_capacity == 0, "Error");
725
726 // Support for parallelizing survivor space rescan
727 if ((CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) || CMSParallelInitialMarkEnabled) {
728 const size_t max_plab_samples =
729 ((DefNewGeneration*)_young_gen)->max_survivor_size()/MinTLABSize;
730
731 _survivor_plab_array = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads, mtGC);
732 _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, 2*max_plab_samples, mtGC);
733 _cursor = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads, mtGC);
734 if (_survivor_plab_array == NULL || _survivor_chunk_array == NULL
735 || _cursor == NULL) {
736 warning("Failed to allocate survivor plab/chunk array");
737 if (_survivor_plab_array != NULL) {
738 FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array, mtGC);
739 _survivor_plab_array = NULL;
740 }
741 if (_survivor_chunk_array != NULL) {
742 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array, mtGC);
743 _survivor_chunk_array = NULL;
744 }
745 if (_cursor != NULL) {
746 FREE_C_HEAP_ARRAY(size_t, _cursor, mtGC);
747 _cursor = NULL;
748 }
749 } else {
750 _survivor_chunk_capacity = 2*max_plab_samples;
751 for (uint i = 0; i < ParallelGCThreads; i++) {
752 HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
753 if (vec == NULL) {
754 warning("Failed to allocate survivor plab array");
755 for (int j = i; j > 0; j--) {
756 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_plab_array[j-1].array(), mtGC);
757 }
758 FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array, mtGC);
759 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array, mtGC);
760 _survivor_plab_array = NULL;
761 _survivor_chunk_array = NULL;
762 _survivor_chunk_capacity = 0;
763 break;
764 } else {
765 ChunkArray* cur =
766 ::new (&_survivor_plab_array[i]) ChunkArray(vec,
767 max_plab_samples);
768 assert(cur->end() == 0, "Should be 0");
769 assert(cur->array() == vec, "Should be vec");
770 assert(cur->capacity() == max_plab_samples, "Error");
771 }
772 }
773 }
774 }
775 assert( ( _survivor_plab_array != NULL
776 && _survivor_chunk_array != NULL)
777 || ( _survivor_chunk_capacity == 0
778 && _survivor_chunk_index == 0),
779 "Error");
780
781 NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;)
782 _gc_counters = new CollectorCounters("CMS", 1);
783 _completed_initialization = true;
784 _inter_sweep_timer.start(); // start of time
785 }
786
787 const char* ConcurrentMarkSweepGeneration::name() const {
788 return "concurrent mark-sweep generation";
789 }
790 void ConcurrentMarkSweepGeneration::update_counters() {
791 if (UsePerfData) {
792 _space_counters->update_all();
793 _gen_counters->update_all();
794 }
795 }
796
797 // this is an optimized version of update_counters(). it takes the
798 // used value as a parameter rather than computing it.
799 //
800 void ConcurrentMarkSweepGeneration::update_counters(size_t used) {
801 if (UsePerfData) {
802 _space_counters->update_used(used);
803 _space_counters->update_capacity();
804 _gen_counters->update_all();
805 }
806 }
807
808 void ConcurrentMarkSweepGeneration::print() const {
809 Generation::print();
810 cmsSpace()->print();
811 }
812
813 #ifndef PRODUCT
814 void ConcurrentMarkSweepGeneration::print_statistics() {
815 cmsSpace()->printFLCensus(0);
816 }
817 #endif
818
819 void ConcurrentMarkSweepGeneration::printOccupancy(const char *s) {
820 GenCollectedHeap* gch = GenCollectedHeap::heap();
821 if (PrintGCDetails) {
822 if (Verbose) {
823 gclog_or_tty->print("[%d %s-%s: "SIZE_FORMAT"("SIZE_FORMAT")]",
824 level(), short_name(), s, used(), capacity());
825 } else {
826 gclog_or_tty->print("[%d %s-%s: "SIZE_FORMAT"K("SIZE_FORMAT"K)]",
827 level(), short_name(), s, used() / K, capacity() / K);
828 }
829 }
830 if (Verbose) {
831 gclog_or_tty->print(" "SIZE_FORMAT"("SIZE_FORMAT")",
832 gch->used(), gch->capacity());
833 } else {
834 gclog_or_tty->print(" "SIZE_FORMAT"K("SIZE_FORMAT"K)",
835 gch->used() / K, gch->capacity() / K);
836 }
837 }
838
839 size_t
840 ConcurrentMarkSweepGeneration::contiguous_available() const {
841 // dld proposes an improvement in precision here. If the committed
842 // part of the space ends in a free block we should add that to
843 // uncommitted size in the calculation below. Will make this
844 // change later, staying with the approximation below for the
845 // time being. -- ysr.
846 return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc());
847 }
848
849 size_t
850 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const {
851 return _cmsSpace->max_alloc_in_words() * HeapWordSize;
852 }
853
854 size_t ConcurrentMarkSweepGeneration::max_available() const {
855 return free() + _virtual_space.uncommitted_size();
856 }
857
858 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(size_t max_promotion_in_bytes) const {
859 size_t available = max_available();
860 size_t av_promo = (size_t)gc_stats()->avg_promoted()->padded_average();
861 bool res = (available >= av_promo) || (available >= max_promotion_in_bytes);
862 if (Verbose && PrintGCDetails) {
863 gclog_or_tty->print_cr(
864 "CMS: promo attempt is%s safe: available("SIZE_FORMAT") %s av_promo("SIZE_FORMAT"),"
865 "max_promo("SIZE_FORMAT")",
866 res? "":" not", available, res? ">=":"<",
867 av_promo, max_promotion_in_bytes);
868 }
869 return res;
870 }
871
872 // At a promotion failure dump information on block layout in heap
873 // (cms old generation).
874 void ConcurrentMarkSweepGeneration::promotion_failure_occurred() {
875 if (CMSDumpAtPromotionFailure) {
876 cmsSpace()->dump_at_safepoint_with_locks(collector(), gclog_or_tty);
877 }
878 }
879
880 CompactibleSpace*
881 ConcurrentMarkSweepGeneration::first_compaction_space() const {
882 return _cmsSpace;
883 }
884
885 void ConcurrentMarkSweepGeneration::reset_after_compaction() {
886 // Clear the promotion information. These pointers can be adjusted
887 // along with all the other pointers into the heap but
888 // compaction is expected to be a rare event with
889 // a heap using cms so don't do it without seeing the need.
890 if (CollectedHeap::use_parallel_gc_threads()) {
891 for (uint i = 0; i < ParallelGCThreads; i++) {
892 _par_gc_thread_states[i]->promo.reset();
893 }
894 }
895 }
896
897 void ConcurrentMarkSweepGeneration::space_iterate(SpaceClosure* blk, bool usedOnly) {
898 blk->do_space(_cmsSpace);
899 }
900
901 void ConcurrentMarkSweepGeneration::compute_new_size() {
902 assert_locked_or_safepoint(Heap_lock);
903
904 // If incremental collection failed, we just want to expand
905 // to the limit.
906 if (incremental_collection_failed()) {
907 clear_incremental_collection_failed();
908 grow_to_reserved();
909 return;
910 }
911
912 // The heap has been compacted but not reset yet.
913 // Any metric such as free() or used() will be incorrect.
914
915 CardGeneration::compute_new_size();
916
917 // Reset again after a possible resizing
918 if (did_compact()) {
919 cmsSpace()->reset_after_compaction();
920 }
921 }
922
923 void ConcurrentMarkSweepGeneration::compute_new_size_free_list() {
924 assert_locked_or_safepoint(Heap_lock);
925
926 // If incremental collection failed, we just want to expand
927 // to the limit.
928 if (incremental_collection_failed()) {
929 clear_incremental_collection_failed();
930 grow_to_reserved();
931 return;
932 }
933
934 double free_percentage = ((double) free()) / capacity();
935 double desired_free_percentage = (double) MinHeapFreeRatio / 100;
936 double maximum_free_percentage = (double) MaxHeapFreeRatio / 100;
937
938 // compute expansion delta needed for reaching desired free percentage
939 if (free_percentage < desired_free_percentage) {
940 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
941 assert(desired_capacity >= capacity(), "invalid expansion size");
942 size_t expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes);
943 if (PrintGCDetails && Verbose) {
944 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
945 gclog_or_tty->print_cr("\nFrom compute_new_size: ");
946 gclog_or_tty->print_cr(" Free fraction %f", free_percentage);
947 gclog_or_tty->print_cr(" Desired free fraction %f",
948 desired_free_percentage);
949 gclog_or_tty->print_cr(" Maximum free fraction %f",
950 maximum_free_percentage);
951 gclog_or_tty->print_cr(" Capacity "SIZE_FORMAT, capacity()/1000);
952 gclog_or_tty->print_cr(" Desired capacity "SIZE_FORMAT,
953 desired_capacity/1000);
954 int prev_level = level() - 1;
955 if (prev_level >= 0) {
956 size_t prev_size = 0;
957 GenCollectedHeap* gch = GenCollectedHeap::heap();
958 Generation* prev_gen = gch->_gens[prev_level];
959 prev_size = prev_gen->capacity();
960 gclog_or_tty->print_cr(" Younger gen size "SIZE_FORMAT,
961 prev_size/1000);
962 }
963 gclog_or_tty->print_cr(" unsafe_max_alloc_nogc "SIZE_FORMAT,
964 unsafe_max_alloc_nogc()/1000);
965 gclog_or_tty->print_cr(" contiguous available "SIZE_FORMAT,
966 contiguous_available()/1000);
967 gclog_or_tty->print_cr(" Expand by "SIZE_FORMAT" (bytes)",
968 expand_bytes);
969 }
970 // safe if expansion fails
971 expand(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio);
972 if (PrintGCDetails && Verbose) {
973 gclog_or_tty->print_cr(" Expanded free fraction %f",
974 ((double) free()) / capacity());
975 }
976 } else {
977 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
978 assert(desired_capacity <= capacity(), "invalid expansion size");
979 size_t shrink_bytes = capacity() - desired_capacity;
980 // Don't shrink unless the delta is greater than the minimum shrink we want
981 if (shrink_bytes >= MinHeapDeltaBytes) {
982 shrink_free_list_by(shrink_bytes);
983 }
984 }
985 }
986
987 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const {
988 return cmsSpace()->freelistLock();
989 }
990
991 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size,
992 bool tlab) {
993 CMSSynchronousYieldRequest yr;
994 MutexLockerEx x(freelistLock(),
995 Mutex::_no_safepoint_check_flag);
996 return have_lock_and_allocate(size, tlab);
997 }
998
999 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size,
1000 bool tlab /* ignored */) {
1001 assert_lock_strong(freelistLock());
1002 size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size);
1003 HeapWord* res = cmsSpace()->allocate(adjustedSize);
1004 // Allocate the object live (grey) if the background collector has
1005 // started marking. This is necessary because the marker may
1006 // have passed this address and consequently this object will
1007 // not otherwise be greyed and would be incorrectly swept up.
1008 // Note that if this object contains references, the writing
1009 // of those references will dirty the card containing this object
1010 // allowing the object to be blackened (and its references scanned)
1011 // either during a preclean phase or at the final checkpoint.
1012 if (res != NULL) {
1013 // We may block here with an uninitialized object with
1014 // its mark-bit or P-bits not yet set. Such objects need
1015 // to be safely navigable by block_start().
1016 assert(oop(res)->klass_or_null() == NULL, "Object should be uninitialized here.");
1017 assert(!((FreeChunk*)res)->is_free(), "Error, block will look free but show wrong size");
1018 collector()->direct_allocated(res, adjustedSize);
1019 _direct_allocated_words += adjustedSize;
1020 // allocation counters
1021 NOT_PRODUCT(
1022 _numObjectsAllocated++;
1023 _numWordsAllocated += (int)adjustedSize;
1024 )
1025 }
1026 return res;
1027 }
1028
1029 // In the case of direct allocation by mutators in a generation that
1030 // is being concurrently collected, the object must be allocated
1031 // live (grey) if the background collector has started marking.
1032 // This is necessary because the marker may
1033 // have passed this address and consequently this object will
1034 // not otherwise be greyed and would be incorrectly swept up.
1035 // Note that if this object contains references, the writing
1036 // of those references will dirty the card containing this object
1037 // allowing the object to be blackened (and its references scanned)
1038 // either during a preclean phase or at the final checkpoint.
1039 void CMSCollector::direct_allocated(HeapWord* start, size_t size) {
1040 assert(_markBitMap.covers(start, size), "Out of bounds");
1041 if (_collectorState >= Marking) {
1042 MutexLockerEx y(_markBitMap.lock(),
1043 Mutex::_no_safepoint_check_flag);
1044 // [see comments preceding SweepClosure::do_blk() below for details]
1045 //
1046 // Can the P-bits be deleted now? JJJ
1047 //
1048 // 1. need to mark the object as live so it isn't collected
1049 // 2. need to mark the 2nd bit to indicate the object may be uninitialized
1050 // 3. need to mark the end of the object so marking, precleaning or sweeping
1051 // can skip over uninitialized or unparsable objects. An allocated
1052 // object is considered uninitialized for our purposes as long as
1053 // its klass word is NULL. All old gen objects are parsable
1054 // as soon as they are initialized.)
1055 _markBitMap.mark(start); // object is live
1056 _markBitMap.mark(start + 1); // object is potentially uninitialized?
1057 _markBitMap.mark(start + size - 1);
1058 // mark end of object
1059 }
1060 // check that oop looks uninitialized
1061 assert(oop(start)->klass_or_null() == NULL, "_klass should be NULL");
1062 }
1063
1064 void CMSCollector::promoted(bool par, HeapWord* start,
1065 bool is_obj_array, size_t obj_size) {
1066 assert(_markBitMap.covers(start), "Out of bounds");
1067 // See comment in direct_allocated() about when objects should
1068 // be allocated live.
1069 if (_collectorState >= Marking) {
1070 // we already hold the marking bit map lock, taken in
1071 // the prologue
1072 if (par) {
1073 _markBitMap.par_mark(start);
1074 } else {
1075 _markBitMap.mark(start);
1076 }
1077 // We don't need to mark the object as uninitialized (as
1078 // in direct_allocated above) because this is being done with the
1079 // world stopped and the object will be initialized by the
1080 // time the marking, precleaning or sweeping get to look at it.
1081 // But see the code for copying objects into the CMS generation,
1082 // where we need to ensure that concurrent readers of the
1083 // block offset table are able to safely navigate a block that
1084 // is in flux from being free to being allocated (and in
1085 // transition while being copied into) and subsequently
1086 // becoming a bona-fide object when the copy/promotion is complete.
1087 assert(SafepointSynchronize::is_at_safepoint(),
1088 "expect promotion only at safepoints");
1089
1090 if (_collectorState < Sweeping) {
1091 // Mark the appropriate cards in the modUnionTable, so that
1092 // this object gets scanned before the sweep. If this is
1093 // not done, CMS generation references in the object might
1094 // not get marked.
1095 // For the case of arrays, which are otherwise precisely
1096 // marked, we need to dirty the entire array, not just its head.
1097 if (is_obj_array) {
1098 // The [par_]mark_range() method expects mr.end() below to
1099 // be aligned to the granularity of a bit's representation
1100 // in the heap. In the case of the MUT below, that's a
1101 // card size.
1102 MemRegion mr(start,
1103 (HeapWord*)round_to((intptr_t)(start + obj_size),
1104 CardTableModRefBS::card_size /* bytes */));
1105 if (par) {
1106 _modUnionTable.par_mark_range(mr);
1107 } else {
1108 _modUnionTable.mark_range(mr);
1109 }
1110 } else { // not an obj array; we can just mark the head
1111 if (par) {
1112 _modUnionTable.par_mark(start);
1113 } else {
1114 _modUnionTable.mark(start);
1115 }
1116 }
1117 }
1118 }
1119 }
1120
1121 static inline size_t percent_of_space(Space* space, HeapWord* addr)
1122 {
1123 size_t delta = pointer_delta(addr, space->bottom());
1124 return (size_t)(delta * 100.0 / (space->capacity() / HeapWordSize));
1125 }
1126
1127 void CMSCollector::icms_update_allocation_limits()
1128 {
1129 Generation* young = GenCollectedHeap::heap()->get_gen(0);
1130 EdenSpace* eden = young->as_DefNewGeneration()->eden();
1131
1132 const unsigned int duty_cycle = stats().icms_update_duty_cycle();
1133 if (CMSTraceIncrementalPacing) {
1134 stats().print();
1135 }
1136
1137 assert(duty_cycle <= 100, "invalid duty cycle");
1138 if (duty_cycle != 0) {
1139 // The duty_cycle is a percentage between 0 and 100; convert to words and
1140 // then compute the offset from the endpoints of the space.
1141 size_t free_words = eden->free() / HeapWordSize;
1142 double free_words_dbl = (double)free_words;
1143 size_t duty_cycle_words = (size_t)(free_words_dbl * duty_cycle / 100.0);
1144 size_t offset_words = (free_words - duty_cycle_words) / 2;
1145
1146 _icms_start_limit = eden->top() + offset_words;
1147 _icms_stop_limit = eden->end() - offset_words;
1148
1149 // The limits may be adjusted (shifted to the right) by
1150 // CMSIncrementalOffset, to allow the application more mutator time after a
1151 // young gen gc (when all mutators were stopped) and before CMS starts and
1152 // takes away one or more cpus.
1153 if (CMSIncrementalOffset != 0) {
1154 double adjustment_dbl = free_words_dbl * CMSIncrementalOffset / 100.0;
1155 size_t adjustment = (size_t)adjustment_dbl;
1156 HeapWord* tmp_stop = _icms_stop_limit + adjustment;
1157 if (tmp_stop > _icms_stop_limit && tmp_stop < eden->end()) {
1158 _icms_start_limit += adjustment;
1159 _icms_stop_limit = tmp_stop;
1160 }
1161 }
1162 }
1163 if (duty_cycle == 0 || (_icms_start_limit == _icms_stop_limit)) {
1164 _icms_start_limit = _icms_stop_limit = eden->end();
1165 }
1166
1167 // Install the new start limit.
1168 eden->set_soft_end(_icms_start_limit);
1169
1170 if (CMSTraceIncrementalMode) {
1171 gclog_or_tty->print(" icms alloc limits: "
1172 PTR_FORMAT "," PTR_FORMAT
1173 " (" SIZE_FORMAT "%%," SIZE_FORMAT "%%) ",
1174 p2i(_icms_start_limit), p2i(_icms_stop_limit),
1175 percent_of_space(eden, _icms_start_limit),
1176 percent_of_space(eden, _icms_stop_limit));
1177 if (Verbose) {
1178 gclog_or_tty->print("eden: ");
1179 eden->print_on(gclog_or_tty);
1180 }
1181 }
1182 }
1183
1184 // Any changes here should try to maintain the invariant
1185 // that if this method is called with _icms_start_limit
1186 // and _icms_stop_limit both NULL, then it should return NULL
1187 // and not notify the icms thread.
1188 HeapWord*
1189 CMSCollector::allocation_limit_reached(Space* space, HeapWord* top,
1190 size_t word_size)
1191 {
1192 // A start_limit equal to end() means the duty cycle is 0, so treat that as a
1193 // nop.
1194 if (CMSIncrementalMode && _icms_start_limit != space->end()) {
1195 if (top <= _icms_start_limit) {
1196 if (CMSTraceIncrementalMode) {
1197 space->print_on(gclog_or_tty);
1198 gclog_or_tty->stamp();
1199 gclog_or_tty->print_cr(" start limit top=" PTR_FORMAT
1200 ", new limit=" PTR_FORMAT
1201 " (" SIZE_FORMAT "%%)",
1202 p2i(top), p2i(_icms_stop_limit),
1203 percent_of_space(space, _icms_stop_limit));
1204 }
1205 ConcurrentMarkSweepThread::start_icms();
1206 assert(top < _icms_stop_limit, "Tautology");
1207 if (word_size < pointer_delta(_icms_stop_limit, top)) {
1208 return _icms_stop_limit;
1209 }
1210
1211 // The allocation will cross both the _start and _stop limits, so do the
1212 // stop notification also and return end().
1213 if (CMSTraceIncrementalMode) {
1214 space->print_on(gclog_or_tty);
1215 gclog_or_tty->stamp();
1216 gclog_or_tty->print_cr(" +stop limit top=" PTR_FORMAT
1217 ", new limit=" PTR_FORMAT
1218 " (" SIZE_FORMAT "%%)",
1219 p2i(top), p2i(space->end()),
1220 percent_of_space(space, space->end()));
1221 }
1222 ConcurrentMarkSweepThread::stop_icms();
1223 return space->end();
1224 }
1225
1226 if (top <= _icms_stop_limit) {
1227 if (CMSTraceIncrementalMode) {
1228 space->print_on(gclog_or_tty);
1229 gclog_or_tty->stamp();
1230 gclog_or_tty->print_cr(" stop limit top=" PTR_FORMAT
1231 ", new limit=" PTR_FORMAT
1232 " (" SIZE_FORMAT "%%)",
1233 top, space->end(),
1234 percent_of_space(space, space->end()));
1235 }
1236 ConcurrentMarkSweepThread::stop_icms();
1237 return space->end();
1238 }
1239
1240 if (CMSTraceIncrementalMode) {
1241 space->print_on(gclog_or_tty);
1242 gclog_or_tty->stamp();
1243 gclog_or_tty->print_cr(" end limit top=" PTR_FORMAT
1244 ", new limit=" PTR_FORMAT,
1245 top, NULL);
1246 }
1247 }
1248
1249 return NULL;
1250 }
1251
1252 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size) {
1253 assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
1254 // allocate, copy and if necessary update promoinfo --
1255 // delegate to underlying space.
1256 assert_lock_strong(freelistLock());
1257
1258 #ifndef PRODUCT
1259 if (Universe::heap()->promotion_should_fail()) {
1260 return NULL;
1261 }
1262 #endif // #ifndef PRODUCT
1263
1264 oop res = _cmsSpace->promote(obj, obj_size);
1265 if (res == NULL) {
1266 // expand and retry
1267 size_t s = _cmsSpace->expansionSpaceRequired(obj_size); // HeapWords
1268 expand(s*HeapWordSize, MinHeapDeltaBytes,
1269 CMSExpansionCause::_satisfy_promotion);
1270 // Since there's currently no next generation, we don't try to promote
1271 // into a more senior generation.
1272 assert(next_gen() == NULL, "assumption, based upon which no attempt "
1273 "is made to pass on a possibly failing "
1274 "promotion to next generation");
1275 res = _cmsSpace->promote(obj, obj_size);
1276 }
1277 if (res != NULL) {
1278 // See comment in allocate() about when objects should
1279 // be allocated live.
1280 assert(obj->is_oop(), "Will dereference klass pointer below");
1281 collector()->promoted(false, // Not parallel
1282 (HeapWord*)res, obj->is_objArray(), obj_size);
1283 // promotion counters
1284 NOT_PRODUCT(
1285 _numObjectsPromoted++;
1286 _numWordsPromoted +=
1287 (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size()));
1288 )
1289 }
1290 return res;
1291 }
1292
1293
1294 HeapWord*
1295 ConcurrentMarkSweepGeneration::allocation_limit_reached(Space* space,
1296 HeapWord* top,
1297 size_t word_sz)
1298 {
1299 return collector()->allocation_limit_reached(space, top, word_sz);
1300 }
1301
1302 // IMPORTANT: Notes on object size recognition in CMS.
1303 // ---------------------------------------------------
1304 // A block of storage in the CMS generation is always in
1305 // one of three states. A free block (FREE), an allocated
1306 // object (OBJECT) whose size() method reports the correct size,
1307 // and an intermediate state (TRANSIENT) in which its size cannot
1308 // be accurately determined.
1309 // STATE IDENTIFICATION: (32 bit and 64 bit w/o COOPS)
1310 // -----------------------------------------------------
1311 // FREE: klass_word & 1 == 1; mark_word holds block size
1312 //
1313 // OBJECT: klass_word installed; klass_word != 0 && klass_word & 1 == 0;
1314 // obj->size() computes correct size
1315 //
1316 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1317 //
1318 // STATE IDENTIFICATION: (64 bit+COOPS)
1319 // ------------------------------------
1320 // FREE: mark_word & CMS_FREE_BIT == 1; mark_word & ~CMS_FREE_BIT gives block_size
1321 //
1322 // OBJECT: klass_word installed; klass_word != 0;
1323 // obj->size() computes correct size
1324 //
1325 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1326 //
1327 //
1328 // STATE TRANSITION DIAGRAM
1329 //
1330 // mut / parnew mut / parnew
1331 // FREE --------------------> TRANSIENT ---------------------> OBJECT --|
1332 // ^ |
1333 // |------------------------ DEAD <------------------------------------|
1334 // sweep mut
1335 //
1336 // While a block is in TRANSIENT state its size cannot be determined
1337 // so readers will either need to come back later or stall until
1338 // the size can be determined. Note that for the case of direct
1339 // allocation, P-bits, when available, may be used to determine the
1340 // size of an object that may not yet have been initialized.
1341
1342 // Things to support parallel young-gen collection.
1343 oop
1344 ConcurrentMarkSweepGeneration::par_promote(int thread_num,
1345 oop old, markOop m,
1346 size_t word_sz) {
1347 #ifndef PRODUCT
1348 if (Universe::heap()->promotion_should_fail()) {
1349 return NULL;
1350 }
1351 #endif // #ifndef PRODUCT
1352
1353 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1354 PromotionInfo* promoInfo = &ps->promo;
1355 // if we are tracking promotions, then first ensure space for
1356 // promotion (including spooling space for saving header if necessary).
1357 // then allocate and copy, then track promoted info if needed.
1358 // When tracking (see PromotionInfo::track()), the mark word may
1359 // be displaced and in this case restoration of the mark word
1360 // occurs in the (oop_since_save_marks_)iterate phase.
1361 if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) {
1362 // Out of space for allocating spooling buffers;
1363 // try expanding and allocating spooling buffers.
1364 if (!expand_and_ensure_spooling_space(promoInfo)) {
1365 return NULL;
1366 }
1367 }
1368 assert(promoInfo->has_spooling_space(), "Control point invariant");
1369 const size_t alloc_sz = CompactibleFreeListSpace::adjustObjectSize(word_sz);
1370 HeapWord* obj_ptr = ps->lab.alloc(alloc_sz);
1371 if (obj_ptr == NULL) {
1372 obj_ptr = expand_and_par_lab_allocate(ps, alloc_sz);
1373 if (obj_ptr == NULL) {
1374 return NULL;
1375 }
1376 }
1377 oop obj = oop(obj_ptr);
1378 OrderAccess::storestore();
1379 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1380 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1381 // IMPORTANT: See note on object initialization for CMS above.
1382 // Otherwise, copy the object. Here we must be careful to insert the
1383 // klass pointer last, since this marks the block as an allocated object.
1384 // Except with compressed oops it's the mark word.
1385 HeapWord* old_ptr = (HeapWord*)old;
1386 // Restore the mark word copied above.
1387 obj->set_mark(m);
1388 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1389 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1390 OrderAccess::storestore();
1391
1392 if (UseCompressedClassPointers) {
1393 // Copy gap missed by (aligned) header size calculation below
1394 obj->set_klass_gap(old->klass_gap());
1395 }
1396 if (word_sz > (size_t)oopDesc::header_size()) {
1397 Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1398 obj_ptr + oopDesc::header_size(),
1399 word_sz - oopDesc::header_size());
1400 }
1401
1402 // Now we can track the promoted object, if necessary. We take care
1403 // to delay the transition from uninitialized to full object
1404 // (i.e., insertion of klass pointer) until after, so that it
1405 // atomically becomes a promoted object.
1406 if (promoInfo->tracking()) {
1407 promoInfo->track((PromotedObject*)obj, old->klass());
1408 }
1409 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1410 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1411 assert(old->is_oop(), "Will use and dereference old klass ptr below");
1412
1413 // Finally, install the klass pointer (this should be volatile).
1414 OrderAccess::storestore();
1415 obj->set_klass(old->klass());
1416 // We should now be able to calculate the right size for this object
1417 assert(obj->is_oop() && obj->size() == (int)word_sz, "Error, incorrect size computed for promoted object");
1418
1419 collector()->promoted(true, // parallel
1420 obj_ptr, old->is_objArray(), word_sz);
1421
1422 NOT_PRODUCT(
1423 Atomic::inc_ptr(&_numObjectsPromoted);
1424 Atomic::add_ptr(alloc_sz, &_numWordsPromoted);
1425 )
1426
1427 return obj;
1428 }
1429
1430 void
1431 ConcurrentMarkSweepGeneration::
1432 par_promote_alloc_undo(int thread_num,
1433 HeapWord* obj, size_t word_sz) {
1434 // CMS does not support promotion undo.
1435 ShouldNotReachHere();
1436 }
1437
1438 void
1439 ConcurrentMarkSweepGeneration::
1440 par_promote_alloc_done(int thread_num) {
1441 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1442 ps->lab.retire(thread_num);
1443 }
1444
1445 void
1446 ConcurrentMarkSweepGeneration::
1447 par_oop_since_save_marks_iterate_done(int thread_num) {
1448 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1449 ParScanWithoutBarrierClosure* dummy_cl = NULL;
1450 ps->promo.promoted_oops_iterate_nv(dummy_cl);
1451 }
1452
1453 bool ConcurrentMarkSweepGeneration::should_collect(bool full,
1454 size_t size,
1455 bool tlab)
1456 {
1457 // We allow a STW collection only if a full
1458 // collection was requested.
1459 return full || should_allocate(size, tlab); // FIX ME !!!
1460 // This and promotion failure handling are connected at the
1461 // hip and should be fixed by untying them.
1462 }
1463
1464 bool CMSCollector::shouldConcurrentCollect() {
1465 if (_full_gc_requested) {
1466 if (Verbose && PrintGCDetails) {
1467 gclog_or_tty->print_cr("CMSCollector: collect because of explicit "
1468 " gc request (or gc_locker)");
1469 }
1470 return true;
1471 }
1472
1473 // For debugging purposes, change the type of collection.
1474 // If the rotation is not on the concurrent collection
1475 // type, don't start a concurrent collection.
1476 NOT_PRODUCT(
1477 if (RotateCMSCollectionTypes &&
1478 (_cmsGen->debug_collection_type() !=
1479 ConcurrentMarkSweepGeneration::Concurrent_collection_type)) {
1480 assert(_cmsGen->debug_collection_type() !=
1481 ConcurrentMarkSweepGeneration::Unknown_collection_type,
1482 "Bad cms collection type");
1483 return false;
1484 }
1485 )
1486
1487 FreelistLocker x(this);
1488 // ------------------------------------------------------------------
1489 // Print out lots of information which affects the initiation of
1490 // a collection.
1491 if (PrintCMSInitiationStatistics && stats().valid()) {
1492 gclog_or_tty->print("CMSCollector shouldConcurrentCollect: ");
1493 gclog_or_tty->stamp();
1494 gclog_or_tty->cr();
1495 stats().print_on(gclog_or_tty);
1496 gclog_or_tty->print_cr("time_until_cms_gen_full %3.7f",
1497 stats().time_until_cms_gen_full());
1498 gclog_or_tty->print_cr("free="SIZE_FORMAT, _cmsGen->free());
1499 gclog_or_tty->print_cr("contiguous_available="SIZE_FORMAT,
1500 _cmsGen->contiguous_available());
1501 gclog_or_tty->print_cr("promotion_rate=%g", stats().promotion_rate());
1502 gclog_or_tty->print_cr("cms_allocation_rate=%g", stats().cms_allocation_rate());
1503 gclog_or_tty->print_cr("occupancy=%3.7f", _cmsGen->occupancy());
1504 gclog_or_tty->print_cr("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy());
1505 gclog_or_tty->print_cr("cms_time_since_begin=%3.7f", stats().cms_time_since_begin());
1506 gclog_or_tty->print_cr("cms_time_since_end=%3.7f", stats().cms_time_since_end());
1507 gclog_or_tty->print_cr("metadata initialized %d",
1508 MetaspaceGC::should_concurrent_collect());
1509 }
1510 // ------------------------------------------------------------------
1511
1512 // If the estimated time to complete a cms collection (cms_duration())
1513 // is less than the estimated time remaining until the cms generation
1514 // is full, start a collection.
1515 if (!UseCMSInitiatingOccupancyOnly) {
1516 if (stats().valid()) {
1517 if (stats().time_until_cms_start() == 0.0) {
1518 return true;
1519 }
1520 } else {
1521 // We want to conservatively collect somewhat early in order
1522 // to try and "bootstrap" our CMS/promotion statistics;
1523 // this branch will not fire after the first successful CMS
1524 // collection because the stats should then be valid.
1525 if (_cmsGen->occupancy() >= _bootstrap_occupancy) {
1526 if (Verbose && PrintGCDetails) {
1527 gclog_or_tty->print_cr(
1528 " CMSCollector: collect for bootstrapping statistics:"
1529 " occupancy = %f, boot occupancy = %f", _cmsGen->occupancy(),
1530 _bootstrap_occupancy);
1531 }
1532 return true;
1533 }
1534 }
1535 }
1536
1537 // Otherwise, we start a collection cycle if
1538 // old gen want a collection cycle started. Each may use
1539 // an appropriate criterion for making this decision.
1540 // XXX We need to make sure that the gen expansion
1541 // criterion dovetails well with this. XXX NEED TO FIX THIS
1542 if (_cmsGen->should_concurrent_collect()) {
1543 if (Verbose && PrintGCDetails) {
1544 gclog_or_tty->print_cr("CMS old gen initiated");
1545 }
1546 return true;
1547 }
1548
1549 // We start a collection if we believe an incremental collection may fail;
1550 // this is not likely to be productive in practice because it's probably too
1551 // late anyway.
1552 GenCollectedHeap* gch = GenCollectedHeap::heap();
1553 assert(gch->collector_policy()->is_generation_policy(),
1554 "You may want to check the correctness of the following");
1555 if (gch->incremental_collection_will_fail(true /* consult_young */)) {
1556 if (Verbose && PrintGCDetails) {
1557 gclog_or_tty->print("CMSCollector: collect because incremental collection will fail ");
1558 }
1559 return true;
1560 }
1561
1562 if (MetaspaceGC::should_concurrent_collect()) {
1563 if (Verbose && PrintGCDetails) {
1564 gclog_or_tty->print("CMSCollector: collect for metadata allocation ");
1565 }
1566 return true;
1567 }
1568
1569 // CMSTriggerInterval starts a CMS cycle if enough time has passed.
1570 if (CMSTriggerInterval >= 0) {
1571 if (CMSTriggerInterval == 0) {
1572 // Trigger always
1573 return true;
1574 }
1575
1576 // Check the CMS time since begin (we do not check the stats validity
1577 // as we want to be able to trigger the first CMS cycle as well)
1578 if (stats().cms_time_since_begin() >= (CMSTriggerInterval / ((double) MILLIUNITS))) {
1579 if (Verbose && PrintGCDetails) {
1580 if (stats().valid()) {
1581 gclog_or_tty->print_cr("CMSCollector: collect because of trigger interval (time since last begin %3.7f secs)",
1582 stats().cms_time_since_begin());
1583 } else {
1584 gclog_or_tty->print_cr("CMSCollector: collect because of trigger interval (first collection)");
1585 }
1586 }
1587 return true;
1588 }
1589 }
1590
1591 return false;
1592 }
1593
1594 void CMSCollector::set_did_compact(bool v) { _cmsGen->set_did_compact(v); }
1595
1596 // Clear _expansion_cause fields of constituent generations
1597 void CMSCollector::clear_expansion_cause() {
1598 _cmsGen->clear_expansion_cause();
1599 }
1600
1601 // We should be conservative in starting a collection cycle. To
1602 // start too eagerly runs the risk of collecting too often in the
1603 // extreme. To collect too rarely falls back on full collections,
1604 // which works, even if not optimum in terms of concurrent work.
1605 // As a work around for too eagerly collecting, use the flag
1606 // UseCMSInitiatingOccupancyOnly. This also has the advantage of
1607 // giving the user an easily understandable way of controlling the
1608 // collections.
1609 // We want to start a new collection cycle if any of the following
1610 // conditions hold:
1611 // . our current occupancy exceeds the configured initiating occupancy
1612 // for this generation, or
1613 // . we recently needed to expand this space and have not, since that
1614 // expansion, done a collection of this generation, or
1615 // . the underlying space believes that it may be a good idea to initiate
1616 // a concurrent collection (this may be based on criteria such as the
1617 // following: the space uses linear allocation and linear allocation is
1618 // going to fail, or there is believed to be excessive fragmentation in
1619 // the generation, etc... or ...
1620 // [.(currently done by CMSCollector::shouldConcurrentCollect() only for
1621 // the case of the old generation; see CR 6543076):
1622 // we may be approaching a point at which allocation requests may fail because
1623 // we will be out of sufficient free space given allocation rate estimates.]
1624 bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const {
1625
1626 assert_lock_strong(freelistLock());
1627 if (occupancy() > initiating_occupancy()) {
1628 if (PrintGCDetails && Verbose) {
1629 gclog_or_tty->print(" %s: collect because of occupancy %f / %f ",
1630 short_name(), occupancy(), initiating_occupancy());
1631 }
1632 return true;
1633 }
1634 if (UseCMSInitiatingOccupancyOnly) {
1635 return false;
1636 }
1637 if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) {
1638 if (PrintGCDetails && Verbose) {
1639 gclog_or_tty->print(" %s: collect because expanded for allocation ",
1640 short_name());
1641 }
1642 return true;
1643 }
1644 if (_cmsSpace->should_concurrent_collect()) {
1645 if (PrintGCDetails && Verbose) {
1646 gclog_or_tty->print(" %s: collect because cmsSpace says so ",
1647 short_name());
1648 }
1649 return true;
1650 }
1651 return false;
1652 }
1653
1654 void ConcurrentMarkSweepGeneration::collect(bool full,
1655 bool clear_all_soft_refs,
1656 size_t size,
1657 bool tlab)
1658 {
1659 collector()->collect(full, clear_all_soft_refs, size, tlab);
1660 }
1661
1662 void CMSCollector::collect(bool full,
1663 bool clear_all_soft_refs,
1664 size_t size,
1665 bool tlab)
1666 {
1667 if (!UseCMSCollectionPassing && _collectorState > Idling) {
1668 // For debugging purposes skip the collection if the state
1669 // is not currently idle
1670 if (TraceCMSState) {
1671 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " skipped full:%d CMS state %d",
1672 Thread::current(), full, _collectorState);
1673 }
1674 return;
1675 }
1676
1677 // The following "if" branch is present for defensive reasons.
1678 // In the current uses of this interface, it can be replaced with:
1679 // assert(!GC_locker.is_active(), "Can't be called otherwise");
1680 // But I am not placing that assert here to allow future
1681 // generality in invoking this interface.
1682 if (GC_locker::is_active()) {
1683 // A consistency test for GC_locker
1684 assert(GC_locker::needs_gc(), "Should have been set already");
1685 // Skip this foreground collection, instead
1686 // expanding the heap if necessary.
1687 // Need the free list locks for the call to free() in compute_new_size()
1688 compute_new_size();
1689 return;
1690 }
1691 acquire_control_and_collect(full, clear_all_soft_refs);
1692 _full_gcs_since_conc_gc++;
1693 }
1694
1695 void CMSCollector::request_full_gc(unsigned int full_gc_count, GCCause::Cause cause) {
1696 GenCollectedHeap* gch = GenCollectedHeap::heap();
1697 unsigned int gc_count = gch->total_full_collections();
1698 if (gc_count == full_gc_count) {
1699 MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag);
1700 _full_gc_requested = true;
1701 _full_gc_cause = cause;
1702 CGC_lock->notify(); // nudge CMS thread
1703 } else {
1704 assert(gc_count > full_gc_count, "Error: causal loop");
1705 }
1706 }
1707
1708 bool CMSCollector::is_external_interruption() {
1709 GCCause::Cause cause = GenCollectedHeap::heap()->gc_cause();
1710 return GCCause::is_user_requested_gc(cause) ||
1711 GCCause::is_serviceability_requested_gc(cause);
1712 }
1713
1714 void CMSCollector::report_concurrent_mode_interruption() {
1715 if (is_external_interruption()) {
1716 if (PrintGCDetails) {
1717 gclog_or_tty->print(" (concurrent mode interrupted)");
1718 }
1719 } else {
1720 if (PrintGCDetails) {
1721 gclog_or_tty->print(" (concurrent mode failure)");
1722 }
1723 _gc_tracer_cm->report_concurrent_mode_failure();
1724 }
1725 }
1726
1727
1728 // The foreground and background collectors need to coordinate in order
1729 // to make sure that they do not mutually interfere with CMS collections.
1730 // When a background collection is active,
1731 // the foreground collector may need to take over (preempt) and
1732 // synchronously complete an ongoing collection. Depending on the
1733 // frequency of the background collections and the heap usage
1734 // of the application, this preemption can be seldom or frequent.
1735 // There are only certain
1736 // points in the background collection that the "collection-baton"
1737 // can be passed to the foreground collector.
1738 //
1739 // The foreground collector will wait for the baton before
1740 // starting any part of the collection. The foreground collector
1741 // will only wait at one location.
1742 //
1743 // The background collector will yield the baton before starting a new
1744 // phase of the collection (e.g., before initial marking, marking from roots,
1745 // precleaning, final re-mark, sweep etc.) This is normally done at the head
1746 // of the loop which switches the phases. The background collector does some
1747 // of the phases (initial mark, final re-mark) with the world stopped.
1748 // Because of locking involved in stopping the world,
1749 // the foreground collector should not block waiting for the background
1750 // collector when it is doing a stop-the-world phase. The background
1751 // collector will yield the baton at an additional point just before
1752 // it enters a stop-the-world phase. Once the world is stopped, the
1753 // background collector checks the phase of the collection. If the
1754 // phase has not changed, it proceeds with the collection. If the
1755 // phase has changed, it skips that phase of the collection. See
1756 // the comments on the use of the Heap_lock in collect_in_background().
1757 //
1758 // Variable used in baton passing.
1759 // _foregroundGCIsActive - Set to true by the foreground collector when
1760 // it wants the baton. The foreground clears it when it has finished
1761 // the collection.
1762 // _foregroundGCShouldWait - Set to true by the background collector
1763 // when it is running. The foreground collector waits while
1764 // _foregroundGCShouldWait is true.
1765 // CGC_lock - monitor used to protect access to the above variables
1766 // and to notify the foreground and background collectors.
1767 // _collectorState - current state of the CMS collection.
1768 //
1769 // The foreground collector
1770 // acquires the CGC_lock
1771 // sets _foregroundGCIsActive
1772 // waits on the CGC_lock for _foregroundGCShouldWait to be false
1773 // various locks acquired in preparation for the collection
1774 // are released so as not to block the background collector
1775 // that is in the midst of a collection
1776 // proceeds with the collection
1777 // clears _foregroundGCIsActive
1778 // returns
1779 //
1780 // The background collector in a loop iterating on the phases of the
1781 // collection
1782 // acquires the CGC_lock
1783 // sets _foregroundGCShouldWait
1784 // if _foregroundGCIsActive is set
1785 // clears _foregroundGCShouldWait, notifies _CGC_lock
1786 // waits on _CGC_lock for _foregroundGCIsActive to become false
1787 // and exits the loop.
1788 // otherwise
1789 // proceed with that phase of the collection
1790 // if the phase is a stop-the-world phase,
1791 // yield the baton once more just before enqueueing
1792 // the stop-world CMS operation (executed by the VM thread).
1793 // returns after all phases of the collection are done
1794 //
1795
1796 void CMSCollector::acquire_control_and_collect(bool full,
1797 bool clear_all_soft_refs) {
1798 assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
1799 assert(!Thread::current()->is_ConcurrentGC_thread(),
1800 "shouldn't try to acquire control from self!");
1801
1802 // Start the protocol for acquiring control of the
1803 // collection from the background collector (aka CMS thread).
1804 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1805 "VM thread should have CMS token");
1806 // Remember the possibly interrupted state of an ongoing
1807 // concurrent collection
1808 CollectorState first_state = _collectorState;
1809
1810 // Signal to a possibly ongoing concurrent collection that
1811 // we want to do a foreground collection.
1812 _foregroundGCIsActive = true;
1813
1814 // Disable incremental mode during a foreground collection.
1815 ICMSDisabler icms_disabler;
1816
1817 // release locks and wait for a notify from the background collector
1818 // releasing the locks in only necessary for phases which
1819 // do yields to improve the granularity of the collection.
1820 assert_lock_strong(bitMapLock());
1821 // We need to lock the Free list lock for the space that we are
1822 // currently collecting.
1823 assert(haveFreelistLocks(), "Must be holding free list locks");
1824 bitMapLock()->unlock();
1825 releaseFreelistLocks();
1826 {
1827 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1828 if (_foregroundGCShouldWait) {
1829 // We are going to be waiting for action for the CMS thread;
1830 // it had better not be gone (for instance at shutdown)!
1831 assert(ConcurrentMarkSweepThread::cmst() != NULL,
1832 "CMS thread must be running");
1833 // Wait here until the background collector gives us the go-ahead
1834 ConcurrentMarkSweepThread::clear_CMS_flag(
1835 ConcurrentMarkSweepThread::CMS_vm_has_token); // release token
1836 // Get a possibly blocked CMS thread going:
1837 // Note that we set _foregroundGCIsActive true above,
1838 // without protection of the CGC_lock.
1839 CGC_lock->notify();
1840 assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(),
1841 "Possible deadlock");
1842 while (_foregroundGCShouldWait) {
1843 // wait for notification
1844 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1845 // Possibility of delay/starvation here, since CMS token does
1846 // not know to give priority to VM thread? Actually, i think
1847 // there wouldn't be any delay/starvation, but the proof of
1848 // that "fact" (?) appears non-trivial. XXX 20011219YSR
1849 }
1850 ConcurrentMarkSweepThread::set_CMS_flag(
1851 ConcurrentMarkSweepThread::CMS_vm_has_token);
1852 }
1853 }
1854 // The CMS_token is already held. Get back the other locks.
1855 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1856 "VM thread should have CMS token");
1857 getFreelistLocks();
1858 bitMapLock()->lock_without_safepoint_check();
1859 if (TraceCMSState) {
1860 gclog_or_tty->print_cr("CMS foreground collector has asked for control "
1861 INTPTR_FORMAT " with first state %d", Thread::current(), first_state);
1862 gclog_or_tty->print_cr(" gets control with state %d", _collectorState);
1863 }
1864
1865 // Check if we need to do a compaction, or if not, whether
1866 // we need to start the mark-sweep from scratch.
1867 bool should_compact = false;
1868 bool should_start_over = false;
1869 decide_foreground_collection_type(clear_all_soft_refs,
1870 &should_compact, &should_start_over);
1871
1872 NOT_PRODUCT(
1873 if (RotateCMSCollectionTypes) {
1874 if (_cmsGen->debug_collection_type() ==
1875 ConcurrentMarkSweepGeneration::MSC_foreground_collection_type) {
1876 should_compact = true;
1877 } else if (_cmsGen->debug_collection_type() ==
1878 ConcurrentMarkSweepGeneration::MS_foreground_collection_type) {
1879 should_compact = false;
1880 }
1881 }
1882 )
1883
1884 if (first_state > Idling) {
1885 report_concurrent_mode_interruption();
1886 }
1887
1888 set_did_compact(should_compact);
1889 if (should_compact) {
1890 // If the collection is being acquired from the background
1891 // collector, there may be references on the discovered
1892 // references lists that have NULL referents (being those
1893 // that were concurrently cleared by a mutator) or
1894 // that are no longer active (having been enqueued concurrently
1895 // by the mutator).
1896 // Scrub the list of those references because Mark-Sweep-Compact
1897 // code assumes referents are not NULL and that all discovered
1898 // Reference objects are active.
1899 ref_processor()->clean_up_discovered_references();
1900
1901 if (first_state > Idling) {
1902 save_heap_summary();
1903 }
1904
1905 do_compaction_work(clear_all_soft_refs);
1906
1907 // Has the GC time limit been exceeded?
1908 DefNewGeneration* young_gen = _young_gen->as_DefNewGeneration();
1909 size_t max_eden_size = young_gen->max_capacity() -
1910 young_gen->to()->capacity() -
1911 young_gen->from()->capacity();
1912 GenCollectedHeap* gch = GenCollectedHeap::heap();
1913 GCCause::Cause gc_cause = gch->gc_cause();
1914 size_policy()->check_gc_overhead_limit(_young_gen->used(),
1915 young_gen->eden()->used(),
1916 _cmsGen->max_capacity(),
1917 max_eden_size,
1918 full,
1919 gc_cause,
1920 gch->collector_policy());
1921 } else {
1922 do_mark_sweep_work(clear_all_soft_refs, first_state,
1923 should_start_over);
1924 }
1925 // Reset the expansion cause, now that we just completed
1926 // a collection cycle.
1927 clear_expansion_cause();
1928 _foregroundGCIsActive = false;
1929 return;
1930 }
1931
1932 // Resize the tenured generation
1933 // after obtaining the free list locks for the
1934 // two generations.
1935 void CMSCollector::compute_new_size() {
1936 assert_locked_or_safepoint(Heap_lock);
1937 FreelistLocker z(this);
1938 MetaspaceGC::compute_new_size();
1939 _cmsGen->compute_new_size_free_list();
1940 }
1941
1942 // A work method used by foreground collection to determine
1943 // what type of collection (compacting or not, continuing or fresh)
1944 // it should do.
1945 // NOTE: the intent is to make UseCMSCompactAtFullCollection
1946 // and CMSCompactWhenClearAllSoftRefs the default in the future
1947 // and do away with the flags after a suitable period.
1948 void CMSCollector::decide_foreground_collection_type(
1949 bool clear_all_soft_refs, bool* should_compact,
1950 bool* should_start_over) {
1951 // Normally, we'll compact only if the UseCMSCompactAtFullCollection
1952 // flag is set, and we have either requested a System.gc() or
1953 // the number of full gc's since the last concurrent cycle
1954 // has exceeded the threshold set by CMSFullGCsBeforeCompaction,
1955 // or if an incremental collection has failed
1956 GenCollectedHeap* gch = GenCollectedHeap::heap();
1957 assert(gch->collector_policy()->is_generation_policy(),
1958 "You may want to check the correctness of the following");
1959 // Inform cms gen if this was due to partial collection failing.
1960 // The CMS gen may use this fact to determine its expansion policy.
1961 if (gch->incremental_collection_will_fail(false /* don't consult_young */)) {
1962 assert(!_cmsGen->incremental_collection_failed(),
1963 "Should have been noticed, reacted to and cleared");
1964 _cmsGen->set_incremental_collection_failed();
1965 }
1966 *should_compact =
1967 UseCMSCompactAtFullCollection &&
1968 ((_full_gcs_since_conc_gc >= CMSFullGCsBeforeCompaction) ||
1969 GCCause::is_user_requested_gc(gch->gc_cause()) ||
1970 gch->incremental_collection_will_fail(true /* consult_young */));
1971 *should_start_over = false;
1972 if (clear_all_soft_refs && !*should_compact) {
1973 // We are about to do a last ditch collection attempt
1974 // so it would normally make sense to do a compaction
1975 // to reclaim as much space as possible.
1976 if (CMSCompactWhenClearAllSoftRefs) {
1977 // Default: The rationale is that in this case either
1978 // we are past the final marking phase, in which case
1979 // we'd have to start over, or so little has been done
1980 // that there's little point in saving that work. Compaction
1981 // appears to be the sensible choice in either case.
1982 *should_compact = true;
1983 } else {
1984 // We have been asked to clear all soft refs, but not to
1985 // compact. Make sure that we aren't past the final checkpoint
1986 // phase, for that is where we process soft refs. If we are already
1987 // past that phase, we'll need to redo the refs discovery phase and
1988 // if necessary clear soft refs that weren't previously
1989 // cleared. We do so by remembering the phase in which
1990 // we came in, and if we are past the refs processing
1991 // phase, we'll choose to just redo the mark-sweep
1992 // collection from scratch.
1993 if (_collectorState > FinalMarking) {
1994 // We are past the refs processing phase;
1995 // start over and do a fresh synchronous CMS cycle
1996 _collectorState = Resetting; // skip to reset to start new cycle
1997 reset(false /* == !asynch */);
1998 *should_start_over = true;
1999 } // else we can continue a possibly ongoing current cycle
2000 }
2001 }
2002 }
2003
2004 // A work method used by the foreground collector to do
2005 // a mark-sweep-compact.
2006 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) {
2007 GenCollectedHeap* gch = GenCollectedHeap::heap();
2008
2009 STWGCTimer* gc_timer = GenMarkSweep::gc_timer();
2010 gc_timer->register_gc_start();
2011
2012 SerialOldTracer* gc_tracer = GenMarkSweep::gc_tracer();
2013 gc_tracer->report_gc_start(gch->gc_cause(), gc_timer->gc_start());
2014
2015 GCTraceTime t("CMS:MSC ", PrintGCDetails && Verbose, true, NULL, gc_tracer->gc_id());
2016 if (PrintGC && Verbose && !(GCCause::is_user_requested_gc(gch->gc_cause()))) {
2017 gclog_or_tty->print_cr("Compact ConcurrentMarkSweepGeneration after %d "
2018 "collections passed to foreground collector", _full_gcs_since_conc_gc);
2019 }
2020
2021 // Temporarily widen the span of the weak reference processing to
2022 // the entire heap.
2023 MemRegion new_span(GenCollectedHeap::heap()->reserved_region());
2024 ReferenceProcessorSpanMutator rp_mut_span(ref_processor(), new_span);
2025 // Temporarily, clear the "is_alive_non_header" field of the
2026 // reference processor.
2027 ReferenceProcessorIsAliveMutator rp_mut_closure(ref_processor(), NULL);
2028 // Temporarily make reference _processing_ single threaded (non-MT).
2029 ReferenceProcessorMTProcMutator rp_mut_mt_processing(ref_processor(), false);
2030 // Temporarily make refs discovery atomic
2031 ReferenceProcessorAtomicMutator rp_mut_atomic(ref_processor(), true);
2032 // Temporarily make reference _discovery_ single threaded (non-MT)
2033 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
2034
2035 ref_processor()->set_enqueuing_is_done(false);
2036 ref_processor()->enable_discovery(false /*verify_disabled*/, false /*check_no_refs*/);
2037 ref_processor()->setup_policy(clear_all_soft_refs);
2038 // If an asynchronous collection finishes, the _modUnionTable is
2039 // all clear. If we are assuming the collection from an asynchronous
2040 // collection, clear the _modUnionTable.
2041 assert(_collectorState != Idling || _modUnionTable.isAllClear(),
2042 "_modUnionTable should be clear if the baton was not passed");
2043 _modUnionTable.clear_all();
2044 assert(_collectorState != Idling || _ct->klass_rem_set()->mod_union_is_clear(),
2045 "mod union for klasses should be clear if the baton was passed");
2046 _ct->klass_rem_set()->clear_mod_union();
2047
2048 // We must adjust the allocation statistics being maintained
2049 // in the free list space. We do so by reading and clearing
2050 // the sweep timer and updating the block flux rate estimates below.
2051 assert(!_intra_sweep_timer.is_active(), "_intra_sweep_timer should be inactive");
2052 if (_inter_sweep_timer.is_active()) {
2053 _inter_sweep_timer.stop();
2054 // Note that we do not use this sample to update the _inter_sweep_estimate.
2055 _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
2056 _inter_sweep_estimate.padded_average(),
2057 _intra_sweep_estimate.padded_average());
2058 }
2059
2060 GenMarkSweep::invoke_at_safepoint(_cmsGen->level(),
2061 ref_processor(), clear_all_soft_refs);
2062 #ifdef ASSERT
2063 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
2064 size_t free_size = cms_space->free();
2065 assert(free_size ==
2066 pointer_delta(cms_space->end(), cms_space->compaction_top())
2067 * HeapWordSize,
2068 "All the free space should be compacted into one chunk at top");
2069 assert(cms_space->dictionary()->total_chunk_size(
2070 debug_only(cms_space->freelistLock())) == 0 ||
2071 cms_space->totalSizeInIndexedFreeLists() == 0,
2072 "All the free space should be in a single chunk");
2073 size_t num = cms_space->totalCount();
2074 assert((free_size == 0 && num == 0) ||
2075 (free_size > 0 && (num == 1 || num == 2)),
2076 "There should be at most 2 free chunks after compaction");
2077 #endif // ASSERT
2078 _collectorState = Resetting;
2079 assert(_restart_addr == NULL,
2080 "Should have been NULL'd before baton was passed");
2081 reset(false /* == !asynch */);
2082 _cmsGen->reset_after_compaction();
2083 _concurrent_cycles_since_last_unload = 0;
2084
2085 // Clear any data recorded in the PLAB chunk arrays.
2086 if (_survivor_plab_array != NULL) {
2087 reset_survivor_plab_arrays();
2088 }
2089
2090 // Adjust the per-size allocation stats for the next epoch.
2091 _cmsGen->cmsSpace()->endSweepFLCensus(sweep_count() /* fake */);
2092 // Restart the "inter sweep timer" for the next epoch.
2093 _inter_sweep_timer.reset();
2094 _inter_sweep_timer.start();
2095
2096 gc_timer->register_gc_end();
2097
2098 gc_tracer->report_gc_end(gc_timer->gc_end(), gc_timer->time_partitions());
2099
2100 // For a mark-sweep-compact, compute_new_size() will be called
2101 // in the heap's do_collection() method.
2102 }
2103
2104 // A work method used by the foreground collector to do
2105 // a mark-sweep, after taking over from a possibly on-going
2106 // concurrent mark-sweep collection.
2107 void CMSCollector::do_mark_sweep_work(bool clear_all_soft_refs,
2108 CollectorState first_state, bool should_start_over) {
2109 if (PrintGC && Verbose) {
2110 gclog_or_tty->print_cr("Pass concurrent collection to foreground "
2111 "collector with count %d",
2112 _full_gcs_since_conc_gc);
2113 }
2114 switch (_collectorState) {
2115 case Idling:
2116 if (first_state == Idling || should_start_over) {
2117 // The background GC was not active, or should
2118 // restarted from scratch; start the cycle.
2119 _collectorState = InitialMarking;
2120 }
2121 // If first_state was not Idling, then a background GC
2122 // was in progress and has now finished. No need to do it
2123 // again. Leave the state as Idling.
2124 break;
2125 case Precleaning:
2126 // In the foreground case don't do the precleaning since
2127 // it is not done concurrently and there is extra work
2128 // required.
2129 _collectorState = FinalMarking;
2130 }
2131 collect_in_foreground(clear_all_soft_refs, GenCollectedHeap::heap()->gc_cause());
2132
2133 // For a mark-sweep, compute_new_size() will be called
2134 // in the heap's do_collection() method.
2135 }
2136
2137
2138 void CMSCollector::print_eden_and_survivor_chunk_arrays() {
2139 DefNewGeneration* dng = _young_gen->as_DefNewGeneration();
2140 EdenSpace* eden_space = dng->eden();
2141 ContiguousSpace* from_space = dng->from();
2142 ContiguousSpace* to_space = dng->to();
2143 // Eden
2144 if (_eden_chunk_array != NULL) {
2145 gclog_or_tty->print_cr("eden " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
2146 eden_space->bottom(), eden_space->top(),
2147 eden_space->end(), eden_space->capacity());
2148 gclog_or_tty->print_cr("_eden_chunk_index=" SIZE_FORMAT ", "
2149 "_eden_chunk_capacity=" SIZE_FORMAT,
2150 _eden_chunk_index, _eden_chunk_capacity);
2151 for (size_t i = 0; i < _eden_chunk_index; i++) {
2152 gclog_or_tty->print_cr("_eden_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT,
2153 i, _eden_chunk_array[i]);
2154 }
2155 }
2156 // Survivor
2157 if (_survivor_chunk_array != NULL) {
2158 gclog_or_tty->print_cr("survivor " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
2159 from_space->bottom(), from_space->top(),
2160 from_space->end(), from_space->capacity());
2161 gclog_or_tty->print_cr("_survivor_chunk_index=" SIZE_FORMAT ", "
2162 "_survivor_chunk_capacity=" SIZE_FORMAT,
2163 _survivor_chunk_index, _survivor_chunk_capacity);
2164 for (size_t i = 0; i < _survivor_chunk_index; i++) {
2165 gclog_or_tty->print_cr("_survivor_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT,
2166 i, _survivor_chunk_array[i]);
2167 }
2168 }
2169 }
2170
2171 void CMSCollector::getFreelistLocks() const {
2172 // Get locks for all free lists in all generations that this
2173 // collector is responsible for
2174 _cmsGen->freelistLock()->lock_without_safepoint_check();
2175 }
2176
2177 void CMSCollector::releaseFreelistLocks() const {
2178 // Release locks for all free lists in all generations that this
2179 // collector is responsible for
2180 _cmsGen->freelistLock()->unlock();
2181 }
2182
2183 bool CMSCollector::haveFreelistLocks() const {
2184 // Check locks for all free lists in all generations that this
2185 // collector is responsible for
2186 assert_lock_strong(_cmsGen->freelistLock());
2187 PRODUCT_ONLY(ShouldNotReachHere());
2188 return true;
2189 }
2190
2191 // A utility class that is used by the CMS collector to
2192 // temporarily "release" the foreground collector from its
2193 // usual obligation to wait for the background collector to
2194 // complete an ongoing phase before proceeding.
2195 class ReleaseForegroundGC: public StackObj {
2196 private:
2197 CMSCollector* _c;
2198 public:
2199 ReleaseForegroundGC(CMSCollector* c) : _c(c) {
2200 assert(_c->_foregroundGCShouldWait, "Else should not need to call");
2201 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2202 // allow a potentially blocked foreground collector to proceed
2203 _c->_foregroundGCShouldWait = false;
2204 if (_c->_foregroundGCIsActive) {
2205 CGC_lock->notify();
2206 }
2207 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2208 "Possible deadlock");
2209 }
2210
2211 ~ReleaseForegroundGC() {
2212 assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?");
2213 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2214 _c->_foregroundGCShouldWait = true;
2215 }
2216 };
2217
2218 // There are separate collect_in_background and collect_in_foreground because of
2219 // the different locking requirements of the background collector and the
2220 // foreground collector. There was originally an attempt to share
2221 // one "collect" method between the background collector and the foreground
2222 // collector but the if-then-else required made it cleaner to have
2223 // separate methods.
2224 void CMSCollector::collect_in_background(bool clear_all_soft_refs, GCCause::Cause cause) {
2225 assert(Thread::current()->is_ConcurrentGC_thread(),
2226 "A CMS asynchronous collection is only allowed on a CMS thread.");
2227
2228 GenCollectedHeap* gch = GenCollectedHeap::heap();
2229 {
2230 bool safepoint_check = Mutex::_no_safepoint_check_flag;
2231 MutexLockerEx hl(Heap_lock, safepoint_check);
2232 FreelistLocker fll(this);
2233 MutexLockerEx x(CGC_lock, safepoint_check);
2234 if (_foregroundGCIsActive || !UseAsyncConcMarkSweepGC) {
2235 // The foreground collector is active or we're
2236 // not using asynchronous collections. Skip this
2237 // background collection.
2238 assert(!_foregroundGCShouldWait, "Should be clear");
2239 return;
2240 } else {
2241 assert(_collectorState == Idling, "Should be idling before start.");
2242 _collectorState = InitialMarking;
2243 register_gc_start(cause);
2244 // Reset the expansion cause, now that we are about to begin
2245 // a new cycle.
2246 clear_expansion_cause();
2247
2248 // Clear the MetaspaceGC flag since a concurrent collection
2249 // is starting but also clear it after the collection.
2250 MetaspaceGC::set_should_concurrent_collect(false);
2251 }
2252 // Decide if we want to enable class unloading as part of the
2253 // ensuing concurrent GC cycle.
2254 update_should_unload_classes();
2255 _full_gc_requested = false; // acks all outstanding full gc requests
2256 _full_gc_cause = GCCause::_no_gc;
2257 // Signal that we are about to start a collection
2258 gch->increment_total_full_collections(); // ... starting a collection cycle
2259 _collection_count_start = gch->total_full_collections();
2260 }
2261
2262 // Used for PrintGC
2263 size_t prev_used;
2264 if (PrintGC && Verbose) {
2265 prev_used = _cmsGen->used(); // XXXPERM
2266 }
2267
2268 // The change of the collection state is normally done at this level;
2269 // the exceptions are phases that are executed while the world is
2270 // stopped. For those phases the change of state is done while the
2271 // world is stopped. For baton passing purposes this allows the
2272 // background collector to finish the phase and change state atomically.
2273 // The foreground collector cannot wait on a phase that is done
2274 // while the world is stopped because the foreground collector already
2275 // has the world stopped and would deadlock.
2276 while (_collectorState != Idling) {
2277 if (TraceCMSState) {
2278 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
2279 Thread::current(), _collectorState);
2280 }
2281 // The foreground collector
2282 // holds the Heap_lock throughout its collection.
2283 // holds the CMS token (but not the lock)
2284 // except while it is waiting for the background collector to yield.
2285 //
2286 // The foreground collector should be blocked (not for long)
2287 // if the background collector is about to start a phase
2288 // executed with world stopped. If the background
2289 // collector has already started such a phase, the
2290 // foreground collector is blocked waiting for the
2291 // Heap_lock. The stop-world phases (InitialMarking and FinalMarking)
2292 // are executed in the VM thread.
2293 //
2294 // The locking order is
2295 // PendingListLock (PLL) -- if applicable (FinalMarking)
2296 // Heap_lock (both this & PLL locked in VM_CMS_Operation::prologue())
2297 // CMS token (claimed in
2298 // stop_world_and_do() -->
2299 // safepoint_synchronize() -->
2300 // CMSThread::synchronize())
2301
2302 {
2303 // Check if the FG collector wants us to yield.
2304 CMSTokenSync x(true); // is cms thread
2305 if (waitForForegroundGC()) {
2306 // We yielded to a foreground GC, nothing more to be
2307 // done this round.
2308 assert(_foregroundGCShouldWait == false, "We set it to false in "
2309 "waitForForegroundGC()");
2310 if (TraceCMSState) {
2311 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2312 " exiting collection CMS state %d",
2313 Thread::current(), _collectorState);
2314 }
2315 return;
2316 } else {
2317 // The background collector can run but check to see if the
2318 // foreground collector has done a collection while the
2319 // background collector was waiting to get the CGC_lock
2320 // above. If yes, break so that _foregroundGCShouldWait
2321 // is cleared before returning.
2322 if (_collectorState == Idling) {
2323 break;
2324 }
2325 }
2326 }
2327
2328 assert(_foregroundGCShouldWait, "Foreground collector, if active, "
2329 "should be waiting");
2330
2331 switch (_collectorState) {
2332 case InitialMarking:
2333 {
2334 ReleaseForegroundGC x(this);
2335 stats().record_cms_begin();
2336 VM_CMS_Initial_Mark initial_mark_op(this);
2337 VMThread::execute(&initial_mark_op);
2338 }
2339 // The collector state may be any legal state at this point
2340 // since the background collector may have yielded to the
2341 // foreground collector.
2342 break;
2343 case Marking:
2344 // initial marking in checkpointRootsInitialWork has been completed
2345 if (markFromRoots(true)) { // we were successful
2346 assert(_collectorState == Precleaning, "Collector state should "
2347 "have changed");
2348 } else {
2349 assert(_foregroundGCIsActive, "Internal state inconsistency");
2350 }
2351 break;
2352 case Precleaning:
2353 // marking from roots in markFromRoots has been completed
2354 preclean();
2355 assert(_collectorState == AbortablePreclean ||
2356 _collectorState == FinalMarking,
2357 "Collector state should have changed");
2358 break;
2359 case AbortablePreclean:
2360 abortable_preclean();
2361 assert(_collectorState == FinalMarking, "Collector state should "
2362 "have changed");
2363 break;
2364 case FinalMarking:
2365 {
2366 ReleaseForegroundGC x(this);
2367
2368 VM_CMS_Final_Remark final_remark_op(this);
2369 VMThread::execute(&final_remark_op);
2370 }
2371 assert(_foregroundGCShouldWait, "block post-condition");
2372 break;
2373 case Sweeping:
2374 // final marking in checkpointRootsFinal has been completed
2375 sweep(true);
2376 assert(_collectorState == Resizing, "Collector state change "
2377 "to Resizing must be done under the free_list_lock");
2378 _full_gcs_since_conc_gc = 0;
2379
2380 case Resizing: {
2381 // Sweeping has been completed...
2382 // At this point the background collection has completed.
2383 // Don't move the call to compute_new_size() down
2384 // into code that might be executed if the background
2385 // collection was preempted.
2386 {
2387 ReleaseForegroundGC x(this); // unblock FG collection
2388 MutexLockerEx y(Heap_lock, Mutex::_no_safepoint_check_flag);
2389 CMSTokenSync z(true); // not strictly needed.
2390 if (_collectorState == Resizing) {
2391 compute_new_size();
2392 save_heap_summary();
2393 _collectorState = Resetting;
2394 } else {
2395 assert(_collectorState == Idling, "The state should only change"
2396 " because the foreground collector has finished the collection");
2397 }
2398 }
2399 break;
2400 }
2401 case Resetting:
2402 // CMS heap resizing has been completed
2403 reset(true);
2404 assert(_collectorState == Idling, "Collector state should "
2405 "have changed");
2406
2407 MetaspaceGC::set_should_concurrent_collect(false);
2408
2409 stats().record_cms_end();
2410 // Don't move the concurrent_phases_end() and compute_new_size()
2411 // calls to here because a preempted background collection
2412 // has it's state set to "Resetting".
2413 break;
2414 case Idling:
2415 default:
2416 ShouldNotReachHere();
2417 break;
2418 }
2419 if (TraceCMSState) {
2420 gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d",
2421 Thread::current(), _collectorState);
2422 }
2423 assert(_foregroundGCShouldWait, "block post-condition");
2424 }
2425
2426 // Should this be in gc_epilogue?
2427 collector_policy()->counters()->update_counters();
2428
2429 {
2430 // Clear _foregroundGCShouldWait and, in the event that the
2431 // foreground collector is waiting, notify it, before
2432 // returning.
2433 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2434 _foregroundGCShouldWait = false;
2435 if (_foregroundGCIsActive) {
2436 CGC_lock->notify();
2437 }
2438 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2439 "Possible deadlock");
2440 }
2441 if (TraceCMSState) {
2442 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2443 " exiting collection CMS state %d",
2444 Thread::current(), _collectorState);
2445 }
2446 if (PrintGC && Verbose) {
2447 _cmsGen->print_heap_change(prev_used);
2448 }
2449 }
2450
2451 void CMSCollector::register_foreground_gc_start(GCCause::Cause cause) {
2452 if (!_cms_start_registered) {
2453 register_gc_start(cause);
2454 }
2455 }
2456
2457 void CMSCollector::register_gc_start(GCCause::Cause cause) {
2458 _cms_start_registered = true;
2459 _gc_timer_cm->register_gc_start();
2460 _gc_tracer_cm->report_gc_start(cause, _gc_timer_cm->gc_start());
2461 }
2462
2463 void CMSCollector::register_gc_end() {
2464 if (_cms_start_registered) {
2465 report_heap_summary(GCWhen::AfterGC);
2466
2467 _gc_timer_cm->register_gc_end();
2468 _gc_tracer_cm->report_gc_end(_gc_timer_cm->gc_end(), _gc_timer_cm->time_partitions());
2469 _cms_start_registered = false;
2470 }
2471 }
2472
2473 void CMSCollector::save_heap_summary() {
2474 GenCollectedHeap* gch = GenCollectedHeap::heap();
2475 _last_heap_summary = gch->create_heap_summary();
2476 _last_metaspace_summary = gch->create_metaspace_summary();
2477 }
2478
2479 void CMSCollector::report_heap_summary(GCWhen::Type when) {
2480 _gc_tracer_cm->report_gc_heap_summary(when, _last_heap_summary);
2481 _gc_tracer_cm->report_metaspace_summary(when, _last_metaspace_summary);
2482 }
2483
2484 void CMSCollector::collect_in_foreground(bool clear_all_soft_refs, GCCause::Cause cause) {
2485 assert(_foregroundGCIsActive && !_foregroundGCShouldWait,
2486 "Foreground collector should be waiting, not executing");
2487 assert(Thread::current()->is_VM_thread(), "A foreground collection"
2488 "may only be done by the VM Thread with the world stopped");
2489 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
2490 "VM thread should have CMS token");
2491
2492 // The gc id is created in register_foreground_gc_start if this collection is synchronous
2493 const GCId gc_id = _collectorState == InitialMarking ? GCId::peek() : _gc_tracer_cm->gc_id();
2494 NOT_PRODUCT(GCTraceTime t("CMS:MS (foreground) ", PrintGCDetails && Verbose,
2495 true, NULL, gc_id);)
2496 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact);
2497
2498 HandleMark hm; // Discard invalid handles created during verification
2499
2500 if (VerifyBeforeGC &&
2501 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2502 Universe::verify();
2503 }
2504
2505 // Snapshot the soft reference policy to be used in this collection cycle.
2506 ref_processor()->setup_policy(clear_all_soft_refs);
2507
2508 // Decide if class unloading should be done
2509 update_should_unload_classes();
2510
2511 bool init_mark_was_synchronous = false; // until proven otherwise
2512 while (_collectorState != Idling) {
2513 if (TraceCMSState) {
2514 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
2515 Thread::current(), _collectorState);
2516 }
2517 switch (_collectorState) {
2518 case InitialMarking:
2519 register_foreground_gc_start(cause);
2520 init_mark_was_synchronous = true; // fact to be exploited in re-mark
2521 checkpointRootsInitial(false);
2522 assert(_collectorState == Marking, "Collector state should have changed"
2523 " within checkpointRootsInitial()");
2524 break;
2525 case Marking:
2526 // initial marking in checkpointRootsInitialWork has been completed
2527 if (VerifyDuringGC &&
2528 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2529 Universe::verify("Verify before initial mark: ");
2530 }
2531 {
2532 bool res = markFromRoots(false);
2533 assert(res && _collectorState == FinalMarking, "Collector state should "
2534 "have changed");
2535 break;
2536 }
2537 case FinalMarking:
2538 if (VerifyDuringGC &&
2539 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2540 Universe::verify("Verify before re-mark: ");
2541 }
2542 checkpointRootsFinal(false, clear_all_soft_refs,
2543 init_mark_was_synchronous);
2544 assert(_collectorState == Sweeping, "Collector state should not "
2545 "have changed within checkpointRootsFinal()");
2546 break;
2547 case Sweeping:
2548 // final marking in checkpointRootsFinal has been completed
2549 if (VerifyDuringGC &&
2550 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2551 Universe::verify("Verify before sweep: ");
2552 }
2553 sweep(false);
2554 assert(_collectorState == Resizing, "Incorrect state");
2555 break;
2556 case Resizing: {
2557 // Sweeping has been completed; the actual resize in this case
2558 // is done separately; nothing to be done in this state.
2559 _collectorState = Resetting;
2560 break;
2561 }
2562 case Resetting:
2563 // The heap has been resized.
2564 if (VerifyDuringGC &&
2565 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2566 Universe::verify("Verify before reset: ");
2567 }
2568 save_heap_summary();
2569 reset(false);
2570 assert(_collectorState == Idling, "Collector state should "
2571 "have changed");
2572 break;
2573 case Precleaning:
2574 case AbortablePreclean:
2575 // Elide the preclean phase
2576 _collectorState = FinalMarking;
2577 break;
2578 default:
2579 ShouldNotReachHere();
2580 }
2581 if (TraceCMSState) {
2582 gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d",
2583 Thread::current(), _collectorState);
2584 }
2585 }
2586
2587 if (VerifyAfterGC &&
2588 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2589 Universe::verify();
2590 }
2591 if (TraceCMSState) {
2592 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2593 " exiting collection CMS state %d",
2594 Thread::current(), _collectorState);
2595 }
2596 }
2597
2598 bool CMSCollector::waitForForegroundGC() {
2599 bool res = false;
2600 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2601 "CMS thread should have CMS token");
2602 // Block the foreground collector until the
2603 // background collectors decides whether to
2604 // yield.
2605 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2606 _foregroundGCShouldWait = true;
2607 if (_foregroundGCIsActive) {
2608 // The background collector yields to the
2609 // foreground collector and returns a value
2610 // indicating that it has yielded. The foreground
2611 // collector can proceed.
2612 res = true;
2613 _foregroundGCShouldWait = false;
2614 ConcurrentMarkSweepThread::clear_CMS_flag(
2615 ConcurrentMarkSweepThread::CMS_cms_has_token);
2616 ConcurrentMarkSweepThread::set_CMS_flag(
2617 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2618 // Get a possibly blocked foreground thread going
2619 CGC_lock->notify();
2620 if (TraceCMSState) {
2621 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d",
2622 Thread::current(), _collectorState);
2623 }
2624 while (_foregroundGCIsActive) {
2625 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
2626 }
2627 ConcurrentMarkSweepThread::set_CMS_flag(
2628 ConcurrentMarkSweepThread::CMS_cms_has_token);
2629 ConcurrentMarkSweepThread::clear_CMS_flag(
2630 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2631 }
2632 if (TraceCMSState) {
2633 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d",
2634 Thread::current(), _collectorState);
2635 }
2636 return res;
2637 }
2638
2639 // Because of the need to lock the free lists and other structures in
2640 // the collector, common to all the generations that the collector is
2641 // collecting, we need the gc_prologues of individual CMS generations
2642 // delegate to their collector. It may have been simpler had the
2643 // current infrastructure allowed one to call a prologue on a
2644 // collector. In the absence of that we have the generation's
2645 // prologue delegate to the collector, which delegates back
2646 // some "local" work to a worker method in the individual generations
2647 // that it's responsible for collecting, while itself doing any
2648 // work common to all generations it's responsible for. A similar
2649 // comment applies to the gc_epilogue()'s.
2650 // The role of the variable _between_prologue_and_epilogue is to
2651 // enforce the invocation protocol.
2652 void CMSCollector::gc_prologue(bool full) {
2653 // Call gc_prologue_work() for the CMSGen
2654 // we are responsible for.
2655
2656 // The following locking discipline assumes that we are only called
2657 // when the world is stopped.
2658 assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption");
2659
2660 // The CMSCollector prologue must call the gc_prologues for the
2661 // "generations" that it's responsible
2662 // for.
2663
2664 assert( Thread::current()->is_VM_thread()
2665 || ( CMSScavengeBeforeRemark
2666 && Thread::current()->is_ConcurrentGC_thread()),
2667 "Incorrect thread type for prologue execution");
2668
2669 if (_between_prologue_and_epilogue) {
2670 // We have already been invoked; this is a gc_prologue delegation
2671 // from yet another CMS generation that we are responsible for, just
2672 // ignore it since all relevant work has already been done.
2673 return;
2674 }
2675
2676 // set a bit saying prologue has been called; cleared in epilogue
2677 _between_prologue_and_epilogue = true;
2678 // Claim locks for common data structures, then call gc_prologue_work()
2679 // for each CMSGen.
2680
2681 getFreelistLocks(); // gets free list locks on constituent spaces
2682 bitMapLock()->lock_without_safepoint_check();
2683
2684 // Should call gc_prologue_work() for all cms gens we are responsible for
2685 bool duringMarking = _collectorState >= Marking
2686 && _collectorState < Sweeping;
2687
2688 // The young collections clear the modified oops state, which tells if
2689 // there are any modified oops in the class. The remark phase also needs
2690 // that information. Tell the young collection to save the union of all
2691 // modified klasses.
2692 if (duringMarking) {
2693 _ct->klass_rem_set()->set_accumulate_modified_oops(true);
2694 }
2695
2696 bool registerClosure = duringMarking;
2697
2698 ModUnionClosure* muc = CollectedHeap::use_parallel_gc_threads() ?
2699 &_modUnionClosurePar
2700 : &_modUnionClosure;
2701 _cmsGen->gc_prologue_work(full, registerClosure, muc);
2702
2703 if (!full) {
2704 stats().record_gc0_begin();
2705 }
2706 }
2707
2708 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) {
2709
2710 _capacity_at_prologue = capacity();
2711 _used_at_prologue = used();
2712
2713 // Delegate to CMScollector which knows how to coordinate between
2714 // this and any other CMS generations that it is responsible for
2715 // collecting.
2716 collector()->gc_prologue(full);
2717 }
2718
2719 // This is a "private" interface for use by this generation's CMSCollector.
2720 // Not to be called directly by any other entity (for instance,
2721 // GenCollectedHeap, which calls the "public" gc_prologue method above).
2722 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full,
2723 bool registerClosure, ModUnionClosure* modUnionClosure) {
2724 assert(!incremental_collection_failed(), "Shouldn't be set yet");
2725 assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL,
2726 "Should be NULL");
2727 if (registerClosure) {
2728 cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure);
2729 }
2730 cmsSpace()->gc_prologue();
2731 // Clear stat counters
2732 NOT_PRODUCT(
2733 assert(_numObjectsPromoted == 0, "check");
2734 assert(_numWordsPromoted == 0, "check");
2735 if (Verbose && PrintGC) {
2736 gclog_or_tty->print("Allocated "SIZE_FORMAT" objects, "
2737 SIZE_FORMAT" bytes concurrently",
2738 _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord));
2739 }
2740 _numObjectsAllocated = 0;
2741 _numWordsAllocated = 0;
2742 )
2743 }
2744
2745 void CMSCollector::gc_epilogue(bool full) {
2746 // The following locking discipline assumes that we are only called
2747 // when the world is stopped.
2748 assert(SafepointSynchronize::is_at_safepoint(),
2749 "world is stopped assumption");
2750
2751 // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks
2752 // if linear allocation blocks need to be appropriately marked to allow the
2753 // the blocks to be parsable. We also check here whether we need to nudge the
2754 // CMS collector thread to start a new cycle (if it's not already active).
2755 assert( Thread::current()->is_VM_thread()
2756 || ( CMSScavengeBeforeRemark
2757 && Thread::current()->is_ConcurrentGC_thread()),
2758 "Incorrect thread type for epilogue execution");
2759
2760 if (!_between_prologue_and_epilogue) {
2761 // We have already been invoked; this is a gc_epilogue delegation
2762 // from yet another CMS generation that we are responsible for, just
2763 // ignore it since all relevant work has already been done.
2764 return;
2765 }
2766 assert(haveFreelistLocks(), "must have freelist locks");
2767 assert_lock_strong(bitMapLock());
2768
2769 _ct->klass_rem_set()->set_accumulate_modified_oops(false);
2770
2771 _cmsGen->gc_epilogue_work(full);
2772
2773 if (_collectorState == AbortablePreclean || _collectorState == Precleaning) {
2774 // in case sampling was not already enabled, enable it
2775 _start_sampling = true;
2776 }
2777 // reset _eden_chunk_array so sampling starts afresh
2778 _eden_chunk_index = 0;
2779
2780 size_t cms_used = _cmsGen->cmsSpace()->used();
2781
2782 // update performance counters - this uses a special version of
2783 // update_counters() that allows the utilization to be passed as a
2784 // parameter, avoiding multiple calls to used().
2785 //
2786 _cmsGen->update_counters(cms_used);
2787
2788 if (CMSIncrementalMode) {
2789 icms_update_allocation_limits();
2790 }
2791
2792 bitMapLock()->unlock();
2793 releaseFreelistLocks();
2794
2795 if (!CleanChunkPoolAsync) {
2796 Chunk::clean_chunk_pool();
2797 }
2798
2799 set_did_compact(false);
2800 _between_prologue_and_epilogue = false; // ready for next cycle
2801 }
2802
2803 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) {
2804 collector()->gc_epilogue(full);
2805
2806 // Also reset promotion tracking in par gc thread states.
2807 if (CollectedHeap::use_parallel_gc_threads()) {
2808 for (uint i = 0; i < ParallelGCThreads; i++) {
2809 _par_gc_thread_states[i]->promo.stopTrackingPromotions(i);
2810 }
2811 }
2812 }
2813
2814 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2815 assert(!incremental_collection_failed(), "Should have been cleared");
2816 cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2817 cmsSpace()->gc_epilogue();
2818 // Print stat counters
2819 NOT_PRODUCT(
2820 assert(_numObjectsAllocated == 0, "check");
2821 assert(_numWordsAllocated == 0, "check");
2822 if (Verbose && PrintGC) {
2823 gclog_or_tty->print("Promoted "SIZE_FORMAT" objects, "
2824 SIZE_FORMAT" bytes",
2825 _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2826 }
2827 _numObjectsPromoted = 0;
2828 _numWordsPromoted = 0;
2829 )
2830
2831 if (PrintGC && Verbose) {
2832 // Call down the chain in contiguous_available needs the freelistLock
2833 // so print this out before releasing the freeListLock.
2834 gclog_or_tty->print(" Contiguous available "SIZE_FORMAT" bytes ",
2835 contiguous_available());
2836 }
2837 }
2838
2839 #ifndef PRODUCT
2840 bool CMSCollector::have_cms_token() {
2841 Thread* thr = Thread::current();
2842 if (thr->is_VM_thread()) {
2843 return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2844 } else if (thr->is_ConcurrentGC_thread()) {
2845 return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2846 } else if (thr->is_GC_task_thread()) {
2847 return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2848 ParGCRareEvent_lock->owned_by_self();
2849 }
2850 return false;
2851 }
2852 #endif
2853
2854 // Check reachability of the given heap address in CMS generation,
2855 // treating all other generations as roots.
2856 bool CMSCollector::is_cms_reachable(HeapWord* addr) {
2857 // We could "guarantee" below, rather than assert, but I'll
2858 // leave these as "asserts" so that an adventurous debugger
2859 // could try this in the product build provided some subset of
2860 // the conditions were met, provided they were interested in the
2861 // results and knew that the computation below wouldn't interfere
2862 // with other concurrent computations mutating the structures
2863 // being read or written.
2864 assert(SafepointSynchronize::is_at_safepoint(),
2865 "Else mutations in object graph will make answer suspect");
2866 assert(have_cms_token(), "Should hold cms token");
2867 assert(haveFreelistLocks(), "must hold free list locks");
2868 assert_lock_strong(bitMapLock());
2869
2870 // Clear the marking bit map array before starting, but, just
2871 // for kicks, first report if the given address is already marked
2872 gclog_or_tty->print_cr("Start: Address " PTR_FORMAT " is%s marked", addr,
2873 _markBitMap.isMarked(addr) ? "" : " not");
2874
2875 if (verify_after_remark()) {
2876 MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2877 bool result = verification_mark_bm()->isMarked(addr);
2878 gclog_or_tty->print_cr("TransitiveMark: Address " PTR_FORMAT " %s marked", addr,
2879 result ? "IS" : "is NOT");
2880 return result;
2881 } else {
2882 gclog_or_tty->print_cr("Could not compute result");
2883 return false;
2884 }
2885 }
2886
2887
2888 void
2889 CMSCollector::print_on_error(outputStream* st) {
2890 CMSCollector* collector = ConcurrentMarkSweepGeneration::_collector;
2891 if (collector != NULL) {
2892 CMSBitMap* bitmap = &collector->_markBitMap;
2893 st->print_cr("Marking Bits: (CMSBitMap*) " PTR_FORMAT, bitmap);
2894 bitmap->print_on_error(st, " Bits: ");
2895
2896 st->cr();
2897
2898 CMSBitMap* mut_bitmap = &collector->_modUnionTable;
2899 st->print_cr("Mod Union Table: (CMSBitMap*) " PTR_FORMAT, mut_bitmap);
2900 mut_bitmap->print_on_error(st, " Bits: ");
2901 }
2902 }
2903
2904 ////////////////////////////////////////////////////////
2905 // CMS Verification Support
2906 ////////////////////////////////////////////////////////
2907 // Following the remark phase, the following invariant
2908 // should hold -- each object in the CMS heap which is
2909 // marked in markBitMap() should be marked in the verification_mark_bm().
2910
2911 class VerifyMarkedClosure: public BitMapClosure {
2912 CMSBitMap* _marks;
2913 bool _failed;
2914
2915 public:
2916 VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2917
2918 bool do_bit(size_t offset) {
2919 HeapWord* addr = _marks->offsetToHeapWord(offset);
2920 if (!_marks->isMarked(addr)) {
2921 oop(addr)->print_on(gclog_or_tty);
2922 gclog_or_tty->print_cr(" ("INTPTR_FORMAT" should have been marked)", addr);
2923 _failed = true;
2924 }
2925 return true;
2926 }
2927
2928 bool failed() { return _failed; }
2929 };
2930
2931 bool CMSCollector::verify_after_remark(bool silent) {
2932 if (!silent) gclog_or_tty->print(" [Verifying CMS Marking... ");
2933 MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2934 static bool init = false;
2935
2936 assert(SafepointSynchronize::is_at_safepoint(),
2937 "Else mutations in object graph will make answer suspect");
2938 assert(have_cms_token(),
2939 "Else there may be mutual interference in use of "
2940 " verification data structures");
2941 assert(_collectorState > Marking && _collectorState <= Sweeping,
2942 "Else marking info checked here may be obsolete");
2943 assert(haveFreelistLocks(), "must hold free list locks");
2944 assert_lock_strong(bitMapLock());
2945
2946
2947 // Allocate marking bit map if not already allocated
2948 if (!init) { // first time
2949 if (!verification_mark_bm()->allocate(_span)) {
2950 return false;
2951 }
2952 init = true;
2953 }
2954
2955 assert(verification_mark_stack()->isEmpty(), "Should be empty");
2956
2957 // Turn off refs discovery -- so we will be tracing through refs.
2958 // This is as intended, because by this time
2959 // GC must already have cleared any refs that need to be cleared,
2960 // and traced those that need to be marked; moreover,
2961 // the marking done here is not going to interfere in any
2962 // way with the marking information used by GC.
2963 NoRefDiscovery no_discovery(ref_processor());
2964
2965 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
2966
2967 // Clear any marks from a previous round
2968 verification_mark_bm()->clear_all();
2969 assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
2970 verify_work_stacks_empty();
2971
2972 GenCollectedHeap* gch = GenCollectedHeap::heap();
2973 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
2974 // Update the saved marks which may affect the root scans.
2975 gch->save_marks();
2976
2977 if (CMSRemarkVerifyVariant == 1) {
2978 // In this first variant of verification, we complete
2979 // all marking, then check if the new marks-vector is
2980 // a subset of the CMS marks-vector.
2981 verify_after_remark_work_1();
2982 } else if (CMSRemarkVerifyVariant == 2) {
2983 // In this second variant of verification, we flag an error
2984 // (i.e. an object reachable in the new marks-vector not reachable
2985 // in the CMS marks-vector) immediately, also indicating the
2986 // identify of an object (A) that references the unmarked object (B) --
2987 // presumably, a mutation to A failed to be picked up by preclean/remark?
2988 verify_after_remark_work_2();
2989 } else {
2990 warning("Unrecognized value %d for CMSRemarkVerifyVariant",
2991 CMSRemarkVerifyVariant);
2992 }
2993 if (!silent) gclog_or_tty->print(" done] ");
2994 return true;
2995 }
2996
2997 void CMSCollector::verify_after_remark_work_1() {
2998 ResourceMark rm;
2999 HandleMark hm;
3000 GenCollectedHeap* gch = GenCollectedHeap::heap();
3001
3002 // Get a clear set of claim bits for the roots processing to work with.
3003 ClassLoaderDataGraph::clear_claimed_marks();
3004
3005 // Mark from roots one level into CMS
3006 MarkRefsIntoClosure notOlder(_span, verification_mark_bm());
3007 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3008
3009 gch->gen_process_roots(_cmsGen->level(),
3010 true, // younger gens are roots
3011 true, // activate StrongRootsScope
3012 SharedHeap::ScanningOption(roots_scanning_options()),
3013 should_unload_classes(),
3014 ¬Older,
3015 NULL,
3016 NULL); // SSS: Provide correct closure
3017
3018 // Now mark from the roots
3019 MarkFromRootsClosure markFromRootsClosure(this, _span,
3020 verification_mark_bm(), verification_mark_stack(),
3021 false /* don't yield */, true /* verifying */);
3022 assert(_restart_addr == NULL, "Expected pre-condition");
3023 verification_mark_bm()->iterate(&markFromRootsClosure);
3024 while (_restart_addr != NULL) {
3025 // Deal with stack overflow: by restarting at the indicated
3026 // address.
3027 HeapWord* ra = _restart_addr;
3028 markFromRootsClosure.reset(ra);
3029 _restart_addr = NULL;
3030 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
3031 }
3032 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
3033 verify_work_stacks_empty();
3034
3035 // Marking completed -- now verify that each bit marked in
3036 // verification_mark_bm() is also marked in markBitMap(); flag all
3037 // errors by printing corresponding objects.
3038 VerifyMarkedClosure vcl(markBitMap());
3039 verification_mark_bm()->iterate(&vcl);
3040 if (vcl.failed()) {
3041 gclog_or_tty->print("Verification failed");
3042 Universe::heap()->print_on(gclog_or_tty);
3043 fatal("CMS: failed marking verification after remark");
3044 }
3045 }
3046
3047 class VerifyKlassOopsKlassClosure : public KlassClosure {
3048 class VerifyKlassOopsClosure : public OopClosure {
3049 CMSBitMap* _bitmap;
3050 public:
3051 VerifyKlassOopsClosure(CMSBitMap* bitmap) : _bitmap(bitmap) { }
3052 void do_oop(oop* p) { guarantee(*p == NULL || _bitmap->isMarked((HeapWord*) *p), "Should be marked"); }
3053 void do_oop(narrowOop* p) { ShouldNotReachHere(); }
3054 } _oop_closure;
3055 public:
3056 VerifyKlassOopsKlassClosure(CMSBitMap* bitmap) : _oop_closure(bitmap) {}
3057 void do_klass(Klass* k) {
3058 k->oops_do(&_oop_closure);
3059 }
3060 };
3061
3062 void CMSCollector::verify_after_remark_work_2() {
3063 ResourceMark rm;
3064 HandleMark hm;
3065 GenCollectedHeap* gch = GenCollectedHeap::heap();
3066
3067 // Get a clear set of claim bits for the roots processing to work with.
3068 ClassLoaderDataGraph::clear_claimed_marks();
3069
3070 // Mark from roots one level into CMS
3071 MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
3072 markBitMap());
3073 CLDToOopClosure cld_closure(¬Older, true);
3074
3075 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3076
3077 gch->gen_process_roots(_cmsGen->level(),
3078 true, // younger gens are roots
3079 true, // activate StrongRootsScope
3080 SharedHeap::ScanningOption(roots_scanning_options()),
3081 should_unload_classes(),
3082 ¬Older,
3083 NULL,
3084 &cld_closure);
3085
3086 // Now mark from the roots
3087 MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
3088 verification_mark_bm(), markBitMap(), verification_mark_stack());
3089 assert(_restart_addr == NULL, "Expected pre-condition");
3090 verification_mark_bm()->iterate(&markFromRootsClosure);
3091 while (_restart_addr != NULL) {
3092 // Deal with stack overflow: by restarting at the indicated
3093 // address.
3094 HeapWord* ra = _restart_addr;
3095 markFromRootsClosure.reset(ra);
3096 _restart_addr = NULL;
3097 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
3098 }
3099 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
3100 verify_work_stacks_empty();
3101
3102 VerifyKlassOopsKlassClosure verify_klass_oops(verification_mark_bm());
3103 ClassLoaderDataGraph::classes_do(&verify_klass_oops);
3104
3105 // Marking completed -- now verify that each bit marked in
3106 // verification_mark_bm() is also marked in markBitMap(); flag all
3107 // errors by printing corresponding objects.
3108 VerifyMarkedClosure vcl(markBitMap());
3109 verification_mark_bm()->iterate(&vcl);
3110 assert(!vcl.failed(), "Else verification above should not have succeeded");
3111 }
3112
3113 void ConcurrentMarkSweepGeneration::save_marks() {
3114 // delegate to CMS space
3115 cmsSpace()->save_marks();
3116 for (uint i = 0; i < ParallelGCThreads; i++) {
3117 _par_gc_thread_states[i]->promo.startTrackingPromotions();
3118 }
3119 }
3120
3121 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
3122 return cmsSpace()->no_allocs_since_save_marks();
3123 }
3124
3125 #define CMS_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix) \
3126 \
3127 void ConcurrentMarkSweepGeneration:: \
3128 oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) { \
3129 cl->set_generation(this); \
3130 cmsSpace()->oop_since_save_marks_iterate##nv_suffix(cl); \
3131 cl->reset_generation(); \
3132 save_marks(); \
3133 }
3134
3135 ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DEFN)
3136
3137 void
3138 ConcurrentMarkSweepGeneration::younger_refs_iterate(OopsInGenClosure* cl) {
3139 cl->set_generation(this);
3140 younger_refs_in_space_iterate(_cmsSpace, cl);
3141 cl->reset_generation();
3142 }
3143
3144 void
3145 ConcurrentMarkSweepGeneration::oop_iterate(ExtendedOopClosure* cl) {
3146 if (freelistLock()->owned_by_self()) {
3147 Generation::oop_iterate(cl);
3148 } else {
3149 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3150 Generation::oop_iterate(cl);
3151 }
3152 }
3153
3154 void
3155 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
3156 if (freelistLock()->owned_by_self()) {
3157 Generation::object_iterate(cl);
3158 } else {
3159 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3160 Generation::object_iterate(cl);
3161 }
3162 }
3163
3164 void
3165 ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) {
3166 if (freelistLock()->owned_by_self()) {
3167 Generation::safe_object_iterate(cl);
3168 } else {
3169 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3170 Generation::safe_object_iterate(cl);
3171 }
3172 }
3173
3174 void
3175 ConcurrentMarkSweepGeneration::post_compact() {
3176 }
3177
3178 void
3179 ConcurrentMarkSweepGeneration::prepare_for_verify() {
3180 // Fix the linear allocation blocks to look like free blocks.
3181
3182 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
3183 // are not called when the heap is verified during universe initialization and
3184 // at vm shutdown.
3185 if (freelistLock()->owned_by_self()) {
3186 cmsSpace()->prepare_for_verify();
3187 } else {
3188 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
3189 cmsSpace()->prepare_for_verify();
3190 }
3191 }
3192
3193 void
3194 ConcurrentMarkSweepGeneration::verify() {
3195 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
3196 // are not called when the heap is verified during universe initialization and
3197 // at vm shutdown.
3198 if (freelistLock()->owned_by_self()) {
3199 cmsSpace()->verify();
3200 } else {
3201 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
3202 cmsSpace()->verify();
3203 }
3204 }
3205
3206 void CMSCollector::verify() {
3207 _cmsGen->verify();
3208 }
3209
3210 #ifndef PRODUCT
3211 bool CMSCollector::overflow_list_is_empty() const {
3212 assert(_num_par_pushes >= 0, "Inconsistency");
3213 if (_overflow_list == NULL) {
3214 assert(_num_par_pushes == 0, "Inconsistency");
3215 }
3216 return _overflow_list == NULL;
3217 }
3218
3219 // The methods verify_work_stacks_empty() and verify_overflow_empty()
3220 // merely consolidate assertion checks that appear to occur together frequently.
3221 void CMSCollector::verify_work_stacks_empty() const {
3222 assert(_markStack.isEmpty(), "Marking stack should be empty");
3223 assert(overflow_list_is_empty(), "Overflow list should be empty");
3224 }
3225
3226 void CMSCollector::verify_overflow_empty() const {
3227 assert(overflow_list_is_empty(), "Overflow list should be empty");
3228 assert(no_preserved_marks(), "No preserved marks");
3229 }
3230 #endif // PRODUCT
3231
3232 // Decide if we want to enable class unloading as part of the
3233 // ensuing concurrent GC cycle. We will collect and
3234 // unload classes if it's the case that:
3235 // (1) an explicit gc request has been made and the flag
3236 // ExplicitGCInvokesConcurrentAndUnloadsClasses is set, OR
3237 // (2) (a) class unloading is enabled at the command line, and
3238 // (b) old gen is getting really full
3239 // NOTE: Provided there is no change in the state of the heap between
3240 // calls to this method, it should have idempotent results. Moreover,
3241 // its results should be monotonically increasing (i.e. going from 0 to 1,
3242 // but not 1 to 0) between successive calls between which the heap was
3243 // not collected. For the implementation below, it must thus rely on
3244 // the property that concurrent_cycles_since_last_unload()
3245 // will not decrease unless a collection cycle happened and that
3246 // _cmsGen->is_too_full() are
3247 // themselves also monotonic in that sense. See check_monotonicity()
3248 // below.
3249 void CMSCollector::update_should_unload_classes() {
3250 _should_unload_classes = false;
3251 // Condition 1 above
3252 if (_full_gc_requested && ExplicitGCInvokesConcurrentAndUnloadsClasses) {
3253 _should_unload_classes = true;
3254 } else if (CMSClassUnloadingEnabled) { // Condition 2.a above
3255 // Disjuncts 2.b.(i,ii,iii) above
3256 _should_unload_classes = (concurrent_cycles_since_last_unload() >=
3257 CMSClassUnloadingMaxInterval)
3258 || _cmsGen->is_too_full();
3259 }
3260 }
3261
3262 bool ConcurrentMarkSweepGeneration::is_too_full() const {
3263 bool res = should_concurrent_collect();
3264 res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
3265 return res;
3266 }
3267
3268 void CMSCollector::setup_cms_unloading_and_verification_state() {
3269 const bool should_verify = VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
3270 || VerifyBeforeExit;
3271 const int rso = SharedHeap::SO_AllCodeCache;
3272
3273 // We set the proper root for this CMS cycle here.
3274 if (should_unload_classes()) { // Should unload classes this cycle
3275 remove_root_scanning_option(rso); // Shrink the root set appropriately
3276 set_verifying(should_verify); // Set verification state for this cycle
3277 return; // Nothing else needs to be done at this time
3278 }
3279
3280 // Not unloading classes this cycle
3281 assert(!should_unload_classes(), "Inconsistency!");
3282
3283 if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
3284 // Include symbols, strings and code cache elements to prevent their resurrection.
3285 add_root_scanning_option(rso);
3286 set_verifying(true);
3287 } else if (verifying() && !should_verify) {
3288 // We were verifying, but some verification flags got disabled.
3289 set_verifying(false);
3290 // Exclude symbols, strings and code cache elements from root scanning to
3291 // reduce IM and RM pauses.
3292 remove_root_scanning_option(rso);
3293 }
3294 }
3295
3296
3297 #ifndef PRODUCT
3298 HeapWord* CMSCollector::block_start(const void* p) const {
3299 const HeapWord* addr = (HeapWord*)p;
3300 if (_span.contains(p)) {
3301 if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
3302 return _cmsGen->cmsSpace()->block_start(p);
3303 }
3304 }
3305 return NULL;
3306 }
3307 #endif
3308
3309 HeapWord*
3310 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
3311 bool tlab,
3312 bool parallel) {
3313 CMSSynchronousYieldRequest yr;
3314 assert(!tlab, "Can't deal with TLAB allocation");
3315 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3316 expand(word_size*HeapWordSize, MinHeapDeltaBytes,
3317 CMSExpansionCause::_satisfy_allocation);
3318 if (GCExpandToAllocateDelayMillis > 0) {
3319 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3320 }
3321 return have_lock_and_allocate(word_size, tlab);
3322 }
3323
3324 // YSR: All of this generation expansion/shrinking stuff is an exact copy of
3325 // OneContigSpaceCardGeneration, which makes me wonder if we should move this
3326 // to CardGeneration and share it...
3327 bool ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes) {
3328 return CardGeneration::expand(bytes, expand_bytes);
3329 }
3330
3331 void ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes,
3332 CMSExpansionCause::Cause cause)
3333 {
3334
3335 bool success = expand(bytes, expand_bytes);
3336
3337 // remember why we expanded; this information is used
3338 // by shouldConcurrentCollect() when making decisions on whether to start
3339 // a new CMS cycle.
3340 if (success) {
3341 set_expansion_cause(cause);
3342 if (PrintGCDetails && Verbose) {
3343 gclog_or_tty->print_cr("Expanded CMS gen for %s",
3344 CMSExpansionCause::to_string(cause));
3345 }
3346 }
3347 }
3348
3349 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
3350 HeapWord* res = NULL;
3351 MutexLocker x(ParGCRareEvent_lock);
3352 while (true) {
3353 // Expansion by some other thread might make alloc OK now:
3354 res = ps->lab.alloc(word_sz);
3355 if (res != NULL) return res;
3356 // If there's not enough expansion space available, give up.
3357 if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
3358 return NULL;
3359 }
3360 // Otherwise, we try expansion.
3361 expand(word_sz*HeapWordSize, MinHeapDeltaBytes,
3362 CMSExpansionCause::_allocate_par_lab);
3363 // Now go around the loop and try alloc again;
3364 // A competing par_promote might beat us to the expansion space,
3365 // so we may go around the loop again if promotion fails again.
3366 if (GCExpandToAllocateDelayMillis > 0) {
3367 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3368 }
3369 }
3370 }
3371
3372
3373 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
3374 PromotionInfo* promo) {
3375 MutexLocker x(ParGCRareEvent_lock);
3376 size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
3377 while (true) {
3378 // Expansion by some other thread might make alloc OK now:
3379 if (promo->ensure_spooling_space()) {
3380 assert(promo->has_spooling_space(),
3381 "Post-condition of successful ensure_spooling_space()");
3382 return true;
3383 }
3384 // If there's not enough expansion space available, give up.
3385 if (_virtual_space.uncommitted_size() < refill_size_bytes) {
3386 return false;
3387 }
3388 // Otherwise, we try expansion.
3389 expand(refill_size_bytes, MinHeapDeltaBytes,
3390 CMSExpansionCause::_allocate_par_spooling_space);
3391 // Now go around the loop and try alloc again;
3392 // A competing allocation might beat us to the expansion space,
3393 // so we may go around the loop again if allocation fails again.
3394 if (GCExpandToAllocateDelayMillis > 0) {
3395 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3396 }
3397 }
3398 }
3399
3400
3401 void ConcurrentMarkSweepGeneration::shrink_by(size_t bytes) {
3402 assert_locked_or_safepoint(ExpandHeap_lock);
3403 // Shrink committed space
3404 _virtual_space.shrink_by(bytes);
3405 // Shrink space; this also shrinks the space's BOT
3406 _cmsSpace->set_end((HeapWord*) _virtual_space.high());
3407 size_t new_word_size = heap_word_size(_cmsSpace->capacity());
3408 // Shrink the shared block offset array
3409 _bts->resize(new_word_size);
3410 MemRegion mr(_cmsSpace->bottom(), new_word_size);
3411 // Shrink the card table
3412 Universe::heap()->barrier_set()->resize_covered_region(mr);
3413
3414 if (Verbose && PrintGC) {
3415 size_t new_mem_size = _virtual_space.committed_size();
3416 size_t old_mem_size = new_mem_size + bytes;
3417 gclog_or_tty->print_cr("Shrinking %s from " SIZE_FORMAT "K to " SIZE_FORMAT "K",
3418 name(), old_mem_size/K, new_mem_size/K);
3419 }
3420 }
3421
3422 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
3423 assert_locked_or_safepoint(Heap_lock);
3424 size_t size = ReservedSpace::page_align_size_down(bytes);
3425 // Only shrink if a compaction was done so that all the free space
3426 // in the generation is in a contiguous block at the end.
3427 if (size > 0 && did_compact()) {
3428 shrink_by(size);
3429 }
3430 }
3431
3432 bool ConcurrentMarkSweepGeneration::grow_by(size_t bytes) {
3433 assert_locked_or_safepoint(Heap_lock);
3434 bool result = _virtual_space.expand_by(bytes);
3435 if (result) {
3436 size_t new_word_size =
3437 heap_word_size(_virtual_space.committed_size());
3438 MemRegion mr(_cmsSpace->bottom(), new_word_size);
3439 _bts->resize(new_word_size); // resize the block offset shared array
3440 Universe::heap()->barrier_set()->resize_covered_region(mr);
3441 // Hmmmm... why doesn't CFLS::set_end verify locking?
3442 // This is quite ugly; FIX ME XXX
3443 _cmsSpace->assert_locked(freelistLock());
3444 _cmsSpace->set_end((HeapWord*)_virtual_space.high());
3445
3446 // update the space and generation capacity counters
3447 if (UsePerfData) {
3448 _space_counters->update_capacity();
3449 _gen_counters->update_all();
3450 }
3451
3452 if (Verbose && PrintGC) {
3453 size_t new_mem_size = _virtual_space.committed_size();
3454 size_t old_mem_size = new_mem_size - bytes;
3455 gclog_or_tty->print_cr("Expanding %s from " SIZE_FORMAT "K by " SIZE_FORMAT "K to " SIZE_FORMAT "K",
3456 name(), old_mem_size/K, bytes/K, new_mem_size/K);
3457 }
3458 }
3459 return result;
3460 }
3461
3462 bool ConcurrentMarkSweepGeneration::grow_to_reserved() {
3463 assert_locked_or_safepoint(Heap_lock);
3464 bool success = true;
3465 const size_t remaining_bytes = _virtual_space.uncommitted_size();
3466 if (remaining_bytes > 0) {
3467 success = grow_by(remaining_bytes);
3468 DEBUG_ONLY(if (!success) warning("grow to reserved failed");)
3469 }
3470 return success;
3471 }
3472
3473 void ConcurrentMarkSweepGeneration::shrink_free_list_by(size_t bytes) {
3474 assert_locked_or_safepoint(Heap_lock);
3475 assert_lock_strong(freelistLock());
3476 if (PrintGCDetails && Verbose) {
3477 warning("Shrinking of CMS not yet implemented");
3478 }
3479 return;
3480 }
3481
3482
3483 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
3484 // phases.
3485 class CMSPhaseAccounting: public StackObj {
3486 public:
3487 CMSPhaseAccounting(CMSCollector *collector,
3488 const char *phase,
3489 const GCId gc_id,
3490 bool print_cr = true);
3491 ~CMSPhaseAccounting();
3492
3493 private:
3494 CMSCollector *_collector;
3495 const char *_phase;
3496 elapsedTimer _wallclock;
3497 bool _print_cr;
3498 const GCId _gc_id;
3499
3500 public:
3501 // Not MT-safe; so do not pass around these StackObj's
3502 // where they may be accessed by other threads.
3503 jlong wallclock_millis() {
3504 assert(_wallclock.is_active(), "Wall clock should not stop");
3505 _wallclock.stop(); // to record time
3506 jlong ret = _wallclock.milliseconds();
3507 _wallclock.start(); // restart
3508 return ret;
3509 }
3510 };
3511
3512 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
3513 const char *phase,
3514 const GCId gc_id,
3515 bool print_cr) :
3516 _collector(collector), _phase(phase), _print_cr(print_cr), _gc_id(gc_id) {
3517
3518 if (PrintCMSStatistics != 0) {
3519 _collector->resetYields();
3520 }
3521 if (PrintGCDetails) {
3522 gclog_or_tty->gclog_stamp(_gc_id);
3523 gclog_or_tty->print_cr("[%s-concurrent-%s-start]",
3524 _collector->cmsGen()->short_name(), _phase);
3525 }
3526 _collector->resetTimer();
3527 _wallclock.start();
3528 _collector->startTimer();
3529 }
3530
3531 CMSPhaseAccounting::~CMSPhaseAccounting() {
3532 assert(_wallclock.is_active(), "Wall clock should not have stopped");
3533 _collector->stopTimer();
3534 _wallclock.stop();
3535 if (PrintGCDetails) {
3536 gclog_or_tty->gclog_stamp(_gc_id);
3537 gclog_or_tty->print("[%s-concurrent-%s: %3.3f/%3.3f secs]",
3538 _collector->cmsGen()->short_name(),
3539 _phase, _collector->timerValue(), _wallclock.seconds());
3540 if (_print_cr) {
3541 gclog_or_tty->cr();
3542 }
3543 if (PrintCMSStatistics != 0) {
3544 gclog_or_tty->print_cr(" (CMS-concurrent-%s yielded %d times)", _phase,
3545 _collector->yields());
3546 }
3547 }
3548 }
3549
3550 // CMS work
3551
3552 // The common parts of CMSParInitialMarkTask and CMSParRemarkTask.
3553 class CMSParMarkTask : public AbstractGangTask {
3554 protected:
3555 CMSCollector* _collector;
3556 int _n_workers;
3557 CMSParMarkTask(const char* name, CMSCollector* collector, int n_workers) :
3558 AbstractGangTask(name),
3559 _collector(collector),
3560 _n_workers(n_workers) {}
3561 // Work method in support of parallel rescan ... of young gen spaces
3562 void do_young_space_rescan(uint worker_id, OopsInGenClosure* cl,
3563 ContiguousSpace* space,
3564 HeapWord** chunk_array, size_t chunk_top);
3565 void work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl);
3566 };
3567
3568 // Parallel initial mark task
3569 class CMSParInitialMarkTask: public CMSParMarkTask {
3570 public:
3571 CMSParInitialMarkTask(CMSCollector* collector, int n_workers) :
3572 CMSParMarkTask("Scan roots and young gen for initial mark in parallel",
3573 collector, n_workers) {}
3574 void work(uint worker_id);
3575 };
3576
3577 // Checkpoint the roots into this generation from outside
3578 // this generation. [Note this initial checkpoint need only
3579 // be approximate -- we'll do a catch up phase subsequently.]
3580 void CMSCollector::checkpointRootsInitial(bool asynch) {
3581 assert(_collectorState == InitialMarking, "Wrong collector state");
3582 check_correct_thread_executing();
3583 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
3584
3585 save_heap_summary();
3586 report_heap_summary(GCWhen::BeforeGC);
3587
3588 ReferenceProcessor* rp = ref_processor();
3589 SpecializationStats::clear();
3590 assert(_restart_addr == NULL, "Control point invariant");
3591 if (asynch) {
3592 // acquire locks for subsequent manipulations
3593 MutexLockerEx x(bitMapLock(),
3594 Mutex::_no_safepoint_check_flag);
3595 checkpointRootsInitialWork(asynch);
3596 // enable ("weak") refs discovery
3597 rp->enable_discovery(true /*verify_disabled*/, true /*check_no_refs*/);
3598 _collectorState = Marking;
3599 } else {
3600 // (Weak) Refs discovery: this is controlled from genCollectedHeap::do_collection
3601 // which recognizes if we are a CMS generation, and doesn't try to turn on
3602 // discovery; verify that they aren't meddling.
3603 assert(!rp->discovery_is_atomic(),
3604 "incorrect setting of discovery predicate");
3605 assert(!rp->discovery_enabled(), "genCollectedHeap shouldn't control "
3606 "ref discovery for this generation kind");
3607 // already have locks
3608 checkpointRootsInitialWork(asynch);
3609 // now enable ("weak") refs discovery
3610 rp->enable_discovery(true /*verify_disabled*/, false /*verify_no_refs*/);
3611 _collectorState = Marking;
3612 }
3613 SpecializationStats::print();
3614 }
3615
3616 void CMSCollector::checkpointRootsInitialWork(bool asynch) {
3617 assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
3618 assert(_collectorState == InitialMarking, "just checking");
3619
3620 // If there has not been a GC[n-1] since last GC[n] cycle completed,
3621 // precede our marking with a collection of all
3622 // younger generations to keep floating garbage to a minimum.
3623 // XXX: we won't do this for now -- it's an optimization to be done later.
3624
3625 // already have locks
3626 assert_lock_strong(bitMapLock());
3627 assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
3628
3629 // Setup the verification and class unloading state for this
3630 // CMS collection cycle.
3631 setup_cms_unloading_and_verification_state();
3632
3633 NOT_PRODUCT(GCTraceTime t("\ncheckpointRootsInitialWork",
3634 PrintGCDetails && Verbose, true, _gc_timer_cm, _gc_tracer_cm->gc_id());)
3635
3636 // Reset all the PLAB chunk arrays if necessary.
3637 if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
3638 reset_survivor_plab_arrays();
3639 }
3640
3641 ResourceMark rm;
3642 HandleMark hm;
3643
3644 MarkRefsIntoClosure notOlder(_span, &_markBitMap);
3645 GenCollectedHeap* gch = GenCollectedHeap::heap();
3646
3647 verify_work_stacks_empty();
3648 verify_overflow_empty();
3649
3650 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
3651 // Update the saved marks which may affect the root scans.
3652 gch->save_marks();
3653
3654 // weak reference processing has not started yet.
3655 ref_processor()->set_enqueuing_is_done(false);
3656
3657 // Need to remember all newly created CLDs,
3658 // so that we can guarantee that the remark finds them.
3659 ClassLoaderDataGraph::remember_new_clds(true);
3660
3661 // Whenever a CLD is found, it will be claimed before proceeding to mark
3662 // the klasses. The claimed marks need to be cleared before marking starts.
3663 ClassLoaderDataGraph::clear_claimed_marks();
3664
3665 if (CMSPrintEdenSurvivorChunks) {
3666 print_eden_and_survivor_chunk_arrays();
3667 }
3668
3669 {
3670 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
3671 if (CMSParallelInitialMarkEnabled && CollectedHeap::use_parallel_gc_threads()) {
3672 // The parallel version.
3673 FlexibleWorkGang* workers = gch->workers();
3674 assert(workers != NULL, "Need parallel worker threads.");
3675 int n_workers = workers->active_workers();
3676 CMSParInitialMarkTask tsk(this, n_workers);
3677 gch->set_par_threads(n_workers);
3678 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
3679 if (n_workers > 1) {
3680 GenCollectedHeap::StrongRootsScope srs(gch);
3681 workers->run_task(&tsk);
3682 } else {
3683 GenCollectedHeap::StrongRootsScope srs(gch);
3684 tsk.work(0);
3685 }
3686 gch->set_par_threads(0);
3687 } else {
3688 // The serial version.
3689 CLDToOopClosure cld_closure(¬Older, true);
3690 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3691 gch->gen_process_roots(_cmsGen->level(),
3692 true, // younger gens are roots
3693 true, // activate StrongRootsScope
3694 SharedHeap::ScanningOption(roots_scanning_options()),
3695 should_unload_classes(),
3696 ¬Older,
3697 NULL,
3698 &cld_closure);
3699 }
3700 }
3701
3702 // Clear mod-union table; it will be dirtied in the prologue of
3703 // CMS generation per each younger generation collection.
3704
3705 assert(_modUnionTable.isAllClear(),
3706 "Was cleared in most recent final checkpoint phase"
3707 " or no bits are set in the gc_prologue before the start of the next "
3708 "subsequent marking phase.");
3709
3710 assert(_ct->klass_rem_set()->mod_union_is_clear(), "Must be");
3711
3712 // Save the end of the used_region of the constituent generations
3713 // to be used to limit the extent of sweep in each generation.
3714 save_sweep_limits();
3715 verify_overflow_empty();
3716 }
3717
3718 bool CMSCollector::markFromRoots(bool asynch) {
3719 // we might be tempted to assert that:
3720 // assert(asynch == !SafepointSynchronize::is_at_safepoint(),
3721 // "inconsistent argument?");
3722 // However that wouldn't be right, because it's possible that
3723 // a safepoint is indeed in progress as a younger generation
3724 // stop-the-world GC happens even as we mark in this generation.
3725 assert(_collectorState == Marking, "inconsistent state?");
3726 check_correct_thread_executing();
3727 verify_overflow_empty();
3728
3729 bool res;
3730 if (asynch) {
3731 // Weak ref discovery note: We may be discovering weak
3732 // refs in this generation concurrent (but interleaved) with
3733 // weak ref discovery by a younger generation collector.
3734
3735 CMSTokenSyncWithLocks ts(true, bitMapLock());
3736 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3737 CMSPhaseAccounting pa(this, "mark", _gc_tracer_cm->gc_id(), !PrintGCDetails);
3738 res = markFromRootsWork(asynch);
3739 if (res) {
3740 _collectorState = Precleaning;
3741 } else { // We failed and a foreground collection wants to take over
3742 assert(_foregroundGCIsActive, "internal state inconsistency");
3743 assert(_restart_addr == NULL, "foreground will restart from scratch");
3744 if (PrintGCDetails) {
3745 gclog_or_tty->print_cr("bailing out to foreground collection");
3746 }
3747 }
3748 } else {
3749 assert(SafepointSynchronize::is_at_safepoint(),
3750 "inconsistent with asynch == false");
3751 // already have locks
3752 res = markFromRootsWork(asynch);
3753 _collectorState = FinalMarking;
3754 }
3755 verify_overflow_empty();
3756 return res;
3757 }
3758
3759 bool CMSCollector::markFromRootsWork(bool asynch) {
3760 // iterate over marked bits in bit map, doing a full scan and mark
3761 // from these roots using the following algorithm:
3762 // . if oop is to the right of the current scan pointer,
3763 // mark corresponding bit (we'll process it later)
3764 // . else (oop is to left of current scan pointer)
3765 // push oop on marking stack
3766 // . drain the marking stack
3767
3768 // Note that when we do a marking step we need to hold the
3769 // bit map lock -- recall that direct allocation (by mutators)
3770 // and promotion (by younger generation collectors) is also
3771 // marking the bit map. [the so-called allocate live policy.]
3772 // Because the implementation of bit map marking is not
3773 // robust wrt simultaneous marking of bits in the same word,
3774 // we need to make sure that there is no such interference
3775 // between concurrent such updates.
3776
3777 // already have locks
3778 assert_lock_strong(bitMapLock());
3779
3780 verify_work_stacks_empty();
3781 verify_overflow_empty();
3782 bool result = false;
3783 if (CMSConcurrentMTEnabled && ConcGCThreads > 0) {
3784 result = do_marking_mt(asynch);
3785 } else {
3786 result = do_marking_st(asynch);
3787 }
3788 return result;
3789 }
3790
3791 // Forward decl
3792 class CMSConcMarkingTask;
3793
3794 class CMSConcMarkingTerminator: public ParallelTaskTerminator {
3795 CMSCollector* _collector;
3796 CMSConcMarkingTask* _task;
3797 public:
3798 virtual void yield();
3799
3800 // "n_threads" is the number of threads to be terminated.
3801 // "queue_set" is a set of work queues of other threads.
3802 // "collector" is the CMS collector associated with this task terminator.
3803 // "yield" indicates whether we need the gang as a whole to yield.
3804 CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
3805 ParallelTaskTerminator(n_threads, queue_set),
3806 _collector(collector) { }
3807
3808 void set_task(CMSConcMarkingTask* task) {
3809 _task = task;
3810 }
3811 };
3812
3813 class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator {
3814 CMSConcMarkingTask* _task;
3815 public:
3816 bool should_exit_termination();
3817 void set_task(CMSConcMarkingTask* task) {
3818 _task = task;
3819 }
3820 };
3821
3822 // MT Concurrent Marking Task
3823 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3824 CMSCollector* _collector;
3825 int _n_workers; // requested/desired # workers
3826 bool _asynch;
3827 bool _result;
3828 CompactibleFreeListSpace* _cms_space;
3829 char _pad_front[64]; // padding to ...
3830 HeapWord* _global_finger; // ... avoid sharing cache line
3831 char _pad_back[64];
3832 HeapWord* _restart_addr;
3833
3834 // Exposed here for yielding support
3835 Mutex* const _bit_map_lock;
3836
3837 // The per thread work queues, available here for stealing
3838 OopTaskQueueSet* _task_queues;
3839
3840 // Termination (and yielding) support
3841 CMSConcMarkingTerminator _term;
3842 CMSConcMarkingTerminatorTerminator _term_term;
3843
3844 public:
3845 CMSConcMarkingTask(CMSCollector* collector,
3846 CompactibleFreeListSpace* cms_space,
3847 bool asynch,
3848 YieldingFlexibleWorkGang* workers,
3849 OopTaskQueueSet* task_queues):
3850 YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3851 _collector(collector),
3852 _cms_space(cms_space),
3853 _asynch(asynch), _n_workers(0), _result(true),
3854 _task_queues(task_queues),
3855 _term(_n_workers, task_queues, _collector),
3856 _bit_map_lock(collector->bitMapLock())
3857 {
3858 _requested_size = _n_workers;
3859 _term.set_task(this);
3860 _term_term.set_task(this);
3861 _restart_addr = _global_finger = _cms_space->bottom();
3862 }
3863
3864
3865 OopTaskQueueSet* task_queues() { return _task_queues; }
3866
3867 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3868
3869 HeapWord** global_finger_addr() { return &_global_finger; }
3870
3871 CMSConcMarkingTerminator* terminator() { return &_term; }
3872
3873 virtual void set_for_termination(int active_workers) {
3874 terminator()->reset_for_reuse(active_workers);
3875 }
3876
3877 void work(uint worker_id);
3878 bool should_yield() {
3879 return ConcurrentMarkSweepThread::should_yield()
3880 && !_collector->foregroundGCIsActive()
3881 && _asynch;
3882 }
3883
3884 virtual void coordinator_yield(); // stuff done by coordinator
3885 bool result() { return _result; }
3886
3887 void reset(HeapWord* ra) {
3888 assert(_global_finger >= _cms_space->end(), "Postcondition of ::work(i)");
3889 _restart_addr = _global_finger = ra;
3890 _term.reset_for_reuse();
3891 }
3892
3893 static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3894 OopTaskQueue* work_q);
3895
3896 private:
3897 void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3898 void do_work_steal(int i);
3899 void bump_global_finger(HeapWord* f);
3900 };
3901
3902 bool CMSConcMarkingTerminatorTerminator::should_exit_termination() {
3903 assert(_task != NULL, "Error");
3904 return _task->yielding();
3905 // Note that we do not need the disjunct || _task->should_yield() above
3906 // because we want terminating threads to yield only if the task
3907 // is already in the midst of yielding, which happens only after at least one
3908 // thread has yielded.
3909 }
3910
3911 void CMSConcMarkingTerminator::yield() {
3912 if (_task->should_yield()) {
3913 _task->yield();
3914 } else {
3915 ParallelTaskTerminator::yield();
3916 }
3917 }
3918
3919 ////////////////////////////////////////////////////////////////
3920 // Concurrent Marking Algorithm Sketch
3921 ////////////////////////////////////////////////////////////////
3922 // Until all tasks exhausted (both spaces):
3923 // -- claim next available chunk
3924 // -- bump global finger via CAS
3925 // -- find first object that starts in this chunk
3926 // and start scanning bitmap from that position
3927 // -- scan marked objects for oops
3928 // -- CAS-mark target, and if successful:
3929 // . if target oop is above global finger (volatile read)
3930 // nothing to do
3931 // . if target oop is in chunk and above local finger
3932 // then nothing to do
3933 // . else push on work-queue
3934 // -- Deal with possible overflow issues:
3935 // . local work-queue overflow causes stuff to be pushed on
3936 // global (common) overflow queue
3937 // . always first empty local work queue
3938 // . then get a batch of oops from global work queue if any
3939 // . then do work stealing
3940 // -- When all tasks claimed (both spaces)
3941 // and local work queue empty,
3942 // then in a loop do:
3943 // . check global overflow stack; steal a batch of oops and trace
3944 // . try to steal from other threads oif GOS is empty
3945 // . if neither is available, offer termination
3946 // -- Terminate and return result
3947 //
3948 void CMSConcMarkingTask::work(uint worker_id) {
3949 elapsedTimer _timer;
3950 ResourceMark rm;
3951 HandleMark hm;
3952
3953 DEBUG_ONLY(_collector->verify_overflow_empty();)
3954
3955 // Before we begin work, our work queue should be empty
3956 assert(work_queue(worker_id)->size() == 0, "Expected to be empty");
3957 // Scan the bitmap covering _cms_space, tracing through grey objects.
3958 _timer.start();
3959 do_scan_and_mark(worker_id, _cms_space);
3960 _timer.stop();
3961 if (PrintCMSStatistics != 0) {
3962 gclog_or_tty->print_cr("Finished cms space scanning in %dth thread: %3.3f sec",
3963 worker_id, _timer.seconds());
3964 // XXX: need xxx/xxx type of notation, two timers
3965 }
3966
3967 // ... do work stealing
3968 _timer.reset();
3969 _timer.start();
3970 do_work_steal(worker_id);
3971 _timer.stop();
3972 if (PrintCMSStatistics != 0) {
3973 gclog_or_tty->print_cr("Finished work stealing in %dth thread: %3.3f sec",
3974 worker_id, _timer.seconds());
3975 // XXX: need xxx/xxx type of notation, two timers
3976 }
3977 assert(_collector->_markStack.isEmpty(), "Should have been emptied");
3978 assert(work_queue(worker_id)->size() == 0, "Should have been emptied");
3979 // Note that under the current task protocol, the
3980 // following assertion is true even of the spaces
3981 // expanded since the completion of the concurrent
3982 // marking. XXX This will likely change under a strict
3983 // ABORT semantics.
3984 // After perm removal the comparison was changed to
3985 // greater than or equal to from strictly greater than.
3986 // Before perm removal the highest address sweep would
3987 // have been at the end of perm gen but now is at the
3988 // end of the tenured gen.
3989 assert(_global_finger >= _cms_space->end(),
3990 "All tasks have been completed");
3991 DEBUG_ONLY(_collector->verify_overflow_empty();)
3992 }
3993
3994 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
3995 HeapWord* read = _global_finger;
3996 HeapWord* cur = read;
3997 while (f > read) {
3998 cur = read;
3999 read = (HeapWord*) Atomic::cmpxchg_ptr(f, &_global_finger, cur);
4000 if (cur == read) {
4001 // our cas succeeded
4002 assert(_global_finger >= f, "protocol consistency");
4003 break;
4004 }
4005 }
4006 }
4007
4008 // This is really inefficient, and should be redone by
4009 // using (not yet available) block-read and -write interfaces to the
4010 // stack and the work_queue. XXX FIX ME !!!
4011 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
4012 OopTaskQueue* work_q) {
4013 // Fast lock-free check
4014 if (ovflw_stk->length() == 0) {
4015 return false;
4016 }
4017 assert(work_q->size() == 0, "Shouldn't steal");
4018 MutexLockerEx ml(ovflw_stk->par_lock(),
4019 Mutex::_no_safepoint_check_flag);
4020 // Grab up to 1/4 the size of the work queue
4021 size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
4022 (size_t)ParGCDesiredObjsFromOverflowList);
4023 num = MIN2(num, ovflw_stk->length());
4024 for (int i = (int) num; i > 0; i--) {
4025 oop cur = ovflw_stk->pop();
4026 assert(cur != NULL, "Counted wrong?");
4027 work_q->push(cur);
4028 }
4029 return num > 0;
4030 }
4031
4032 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
4033 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
4034 int n_tasks = pst->n_tasks();
4035 // We allow that there may be no tasks to do here because
4036 // we are restarting after a stack overflow.
4037 assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
4038 uint nth_task = 0;
4039
4040 HeapWord* aligned_start = sp->bottom();
4041 if (sp->used_region().contains(_restart_addr)) {
4042 // Align down to a card boundary for the start of 0th task
4043 // for this space.
4044 aligned_start =
4045 (HeapWord*)align_size_down((uintptr_t)_restart_addr,
4046 CardTableModRefBS::card_size);
4047 }
4048
4049 size_t chunk_size = sp->marking_task_size();
4050 while (!pst->is_task_claimed(/* reference */ nth_task)) {
4051 // Having claimed the nth task in this space,
4052 // compute the chunk that it corresponds to:
4053 MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
4054 aligned_start + (nth_task+1)*chunk_size);
4055 // Try and bump the global finger via a CAS;
4056 // note that we need to do the global finger bump
4057 // _before_ taking the intersection below, because
4058 // the task corresponding to that region will be
4059 // deemed done even if the used_region() expands
4060 // because of allocation -- as it almost certainly will
4061 // during start-up while the threads yield in the
4062 // closure below.
4063 HeapWord* finger = span.end();
4064 bump_global_finger(finger); // atomically
4065 // There are null tasks here corresponding to chunks
4066 // beyond the "top" address of the space.
4067 span = span.intersection(sp->used_region());
4068 if (!span.is_empty()) { // Non-null task
4069 HeapWord* prev_obj;
4070 assert(!span.contains(_restart_addr) || nth_task == 0,
4071 "Inconsistency");
4072 if (nth_task == 0) {
4073 // For the 0th task, we'll not need to compute a block_start.
4074 if (span.contains(_restart_addr)) {
4075 // In the case of a restart because of stack overflow,
4076 // we might additionally skip a chunk prefix.
4077 prev_obj = _restart_addr;
4078 } else {
4079 prev_obj = span.start();
4080 }
4081 } else {
4082 // We want to skip the first object because
4083 // the protocol is to scan any object in its entirety
4084 // that _starts_ in this span; a fortiori, any
4085 // object starting in an earlier span is scanned
4086 // as part of an earlier claimed task.
4087 // Below we use the "careful" version of block_start
4088 // so we do not try to navigate uninitialized objects.
4089 prev_obj = sp->block_start_careful(span.start());
4090 // Below we use a variant of block_size that uses the
4091 // Printezis bits to avoid waiting for allocated
4092 // objects to become initialized/parsable.
4093 while (prev_obj < span.start()) {
4094 size_t sz = sp->block_size_no_stall(prev_obj, _collector);
4095 if (sz > 0) {
4096 prev_obj += sz;
4097 } else {
4098 // In this case we may end up doing a bit of redundant
4099 // scanning, but that appears unavoidable, short of
4100 // locking the free list locks; see bug 6324141.
4101 break;
4102 }
4103 }
4104 }
4105 if (prev_obj < span.end()) {
4106 MemRegion my_span = MemRegion(prev_obj, span.end());
4107 // Do the marking work within a non-empty span --
4108 // the last argument to the constructor indicates whether the
4109 // iteration should be incremental with periodic yields.
4110 Par_MarkFromRootsClosure cl(this, _collector, my_span,
4111 &_collector->_markBitMap,
4112 work_queue(i),
4113 &_collector->_markStack,
4114 _asynch);
4115 _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
4116 } // else nothing to do for this task
4117 } // else nothing to do for this task
4118 }
4119 // We'd be tempted to assert here that since there are no
4120 // more tasks left to claim in this space, the global_finger
4121 // must exceed space->top() and a fortiori space->end(). However,
4122 // that would not quite be correct because the bumping of
4123 // global_finger occurs strictly after the claiming of a task,
4124 // so by the time we reach here the global finger may not yet
4125 // have been bumped up by the thread that claimed the last
4126 // task.
4127 pst->all_tasks_completed();
4128 }
4129
4130 class Par_ConcMarkingClosure: public MetadataAwareOopClosure {
4131 private:
4132 CMSCollector* _collector;
4133 CMSConcMarkingTask* _task;
4134 MemRegion _span;
4135 CMSBitMap* _bit_map;
4136 CMSMarkStack* _overflow_stack;
4137 OopTaskQueue* _work_queue;
4138 protected:
4139 DO_OOP_WORK_DEFN
4140 public:
4141 Par_ConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue,
4142 CMSBitMap* bit_map, CMSMarkStack* overflow_stack):
4143 MetadataAwareOopClosure(collector->ref_processor()),
4144 _collector(collector),
4145 _task(task),
4146 _span(collector->_span),
4147 _work_queue(work_queue),
4148 _bit_map(bit_map),
4149 _overflow_stack(overflow_stack)
4150 { }
4151 virtual void do_oop(oop* p);
4152 virtual void do_oop(narrowOop* p);
4153
4154 void trim_queue(size_t max);
4155 void handle_stack_overflow(HeapWord* lost);
4156 void do_yield_check() {
4157 if (_task->should_yield()) {
4158 _task->yield();
4159 }
4160 }
4161 };
4162
4163 // Grey object scanning during work stealing phase --
4164 // the salient assumption here is that any references
4165 // that are in these stolen objects being scanned must
4166 // already have been initialized (else they would not have
4167 // been published), so we do not need to check for
4168 // uninitialized objects before pushing here.
4169 void Par_ConcMarkingClosure::do_oop(oop obj) {
4170 assert(obj->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
4171 HeapWord* addr = (HeapWord*)obj;
4172 // Check if oop points into the CMS generation
4173 // and is not marked
4174 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
4175 // a white object ...
4176 // If we manage to "claim" the object, by being the
4177 // first thread to mark it, then we push it on our
4178 // marking stack
4179 if (_bit_map->par_mark(addr)) { // ... now grey
4180 // push on work queue (grey set)
4181 bool simulate_overflow = false;
4182 NOT_PRODUCT(
4183 if (CMSMarkStackOverflowALot &&
4184 _collector->simulate_overflow()) {
4185 // simulate a stack overflow
4186 simulate_overflow = true;
4187 }
4188 )
4189 if (simulate_overflow ||
4190 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
4191 // stack overflow
4192 if (PrintCMSStatistics != 0) {
4193 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
4194 SIZE_FORMAT, _overflow_stack->capacity());
4195 }
4196 // We cannot assert that the overflow stack is full because
4197 // it may have been emptied since.
4198 assert(simulate_overflow ||
4199 _work_queue->size() == _work_queue->max_elems(),
4200 "Else push should have succeeded");
4201 handle_stack_overflow(addr);
4202 }
4203 } // Else, some other thread got there first
4204 do_yield_check();
4205 }
4206 }
4207
4208 void Par_ConcMarkingClosure::do_oop(oop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
4209 void Par_ConcMarkingClosure::do_oop(narrowOop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
4210
4211 void Par_ConcMarkingClosure::trim_queue(size_t max) {
4212 while (_work_queue->size() > max) {
4213 oop new_oop;
4214 if (_work_queue->pop_local(new_oop)) {
4215 assert(new_oop->is_oop(), "Should be an oop");
4216 assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
4217 assert(_span.contains((HeapWord*)new_oop), "Not in span");
4218 new_oop->oop_iterate(this); // do_oop() above
4219 do_yield_check();
4220 }
4221 }
4222 }
4223
4224 // Upon stack overflow, we discard (part of) the stack,
4225 // remembering the least address amongst those discarded
4226 // in CMSCollector's _restart_address.
4227 void Par_ConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
4228 // We need to do this under a mutex to prevent other
4229 // workers from interfering with the work done below.
4230 MutexLockerEx ml(_overflow_stack->par_lock(),
4231 Mutex::_no_safepoint_check_flag);
4232 // Remember the least grey address discarded
4233 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
4234 _collector->lower_restart_addr(ra);
4235 _overflow_stack->reset(); // discard stack contents
4236 _overflow_stack->expand(); // expand the stack if possible
4237 }
4238
4239
4240 void CMSConcMarkingTask::do_work_steal(int i) {
4241 OopTaskQueue* work_q = work_queue(i);
4242 oop obj_to_scan;
4243 CMSBitMap* bm = &(_collector->_markBitMap);
4244 CMSMarkStack* ovflw = &(_collector->_markStack);
4245 int* seed = _collector->hash_seed(i);
4246 Par_ConcMarkingClosure cl(_collector, this, work_q, bm, ovflw);
4247 while (true) {
4248 cl.trim_queue(0);
4249 assert(work_q->size() == 0, "Should have been emptied above");
4250 if (get_work_from_overflow_stack(ovflw, work_q)) {
4251 // Can't assert below because the work obtained from the
4252 // overflow stack may already have been stolen from us.
4253 // assert(work_q->size() > 0, "Work from overflow stack");
4254 continue;
4255 } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
4256 assert(obj_to_scan->is_oop(), "Should be an oop");
4257 assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
4258 obj_to_scan->oop_iterate(&cl);
4259 } else if (terminator()->offer_termination(&_term_term)) {
4260 assert(work_q->size() == 0, "Impossible!");
4261 break;
4262 } else if (yielding() || should_yield()) {
4263 yield();
4264 }
4265 }
4266 }
4267
4268 // This is run by the CMS (coordinator) thread.
4269 void CMSConcMarkingTask::coordinator_yield() {
4270 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
4271 "CMS thread should hold CMS token");
4272 // First give up the locks, then yield, then re-lock
4273 // We should probably use a constructor/destructor idiom to
4274 // do this unlock/lock or modify the MutexUnlocker class to
4275 // serve our purpose. XXX
4276 assert_lock_strong(_bit_map_lock);
4277 _bit_map_lock->unlock();
4278 ConcurrentMarkSweepThread::desynchronize(true);
4279 ConcurrentMarkSweepThread::acknowledge_yield_request();
4280 _collector->stopTimer();
4281 if (PrintCMSStatistics != 0) {
4282 _collector->incrementYields();
4283 }
4284 _collector->icms_wait();
4285
4286 // It is possible for whichever thread initiated the yield request
4287 // not to get a chance to wake up and take the bitmap lock between
4288 // this thread releasing it and reacquiring it. So, while the
4289 // should_yield() flag is on, let's sleep for a bit to give the
4290 // other thread a chance to wake up. The limit imposed on the number
4291 // of iterations is defensive, to avoid any unforseen circumstances
4292 // putting us into an infinite loop. Since it's always been this
4293 // (coordinator_yield()) method that was observed to cause the
4294 // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
4295 // which is by default non-zero. For the other seven methods that
4296 // also perform the yield operation, as are using a different
4297 // parameter (CMSYieldSleepCount) which is by default zero. This way we
4298 // can enable the sleeping for those methods too, if necessary.
4299 // See 6442774.
4300 //
4301 // We really need to reconsider the synchronization between the GC
4302 // thread and the yield-requesting threads in the future and we
4303 // should really use wait/notify, which is the recommended
4304 // way of doing this type of interaction. Additionally, we should
4305 // consolidate the eight methods that do the yield operation and they
4306 // are almost identical into one for better maintainability and
4307 // readability. See 6445193.
4308 //
4309 // Tony 2006.06.29
4310 for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
4311 ConcurrentMarkSweepThread::should_yield() &&
4312 !CMSCollector::foregroundGCIsActive(); ++i) {
4313 os::sleep(Thread::current(), 1, false);
4314 ConcurrentMarkSweepThread::acknowledge_yield_request();
4315 }
4316
4317 ConcurrentMarkSweepThread::synchronize(true);
4318 _bit_map_lock->lock_without_safepoint_check();
4319 _collector->startTimer();
4320 }
4321
4322 bool CMSCollector::do_marking_mt(bool asynch) {
4323 assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition");
4324 int num_workers = AdaptiveSizePolicy::calc_active_conc_workers(
4325 conc_workers()->total_workers(),
4326 conc_workers()->active_workers(),
4327 Threads::number_of_non_daemon_threads());
4328 conc_workers()->set_active_workers(num_workers);
4329
4330 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
4331
4332 CMSConcMarkingTask tsk(this,
4333 cms_space,
4334 asynch,
4335 conc_workers(),
4336 task_queues());
4337
4338 // Since the actual number of workers we get may be different
4339 // from the number we requested above, do we need to do anything different
4340 // below? In particular, may be we need to subclass the SequantialSubTasksDone
4341 // class?? XXX
4342 cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
4343
4344 // Refs discovery is already non-atomic.
4345 assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
4346 assert(ref_processor()->discovery_is_mt(), "Discovery should be MT");
4347 conc_workers()->start_task(&tsk);
4348 while (tsk.yielded()) {
4349 tsk.coordinator_yield();
4350 conc_workers()->continue_task(&tsk);
4351 }
4352 // If the task was aborted, _restart_addr will be non-NULL
4353 assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
4354 while (_restart_addr != NULL) {
4355 // XXX For now we do not make use of ABORTED state and have not
4356 // yet implemented the right abort semantics (even in the original
4357 // single-threaded CMS case). That needs some more investigation
4358 // and is deferred for now; see CR# TBF. 07252005YSR. XXX
4359 assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
4360 // If _restart_addr is non-NULL, a marking stack overflow
4361 // occurred; we need to do a fresh marking iteration from the
4362 // indicated restart address.
4363 if (_foregroundGCIsActive && asynch) {
4364 // We may be running into repeated stack overflows, having
4365 // reached the limit of the stack size, while making very
4366 // slow forward progress. It may be best to bail out and
4367 // let the foreground collector do its job.
4368 // Clear _restart_addr, so that foreground GC
4369 // works from scratch. This avoids the headache of
4370 // a "rescan" which would otherwise be needed because
4371 // of the dirty mod union table & card table.
4372 _restart_addr = NULL;
4373 return false;
4374 }
4375 // Adjust the task to restart from _restart_addr
4376 tsk.reset(_restart_addr);
4377 cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
4378 _restart_addr);
4379 _restart_addr = NULL;
4380 // Get the workers going again
4381 conc_workers()->start_task(&tsk);
4382 while (tsk.yielded()) {
4383 tsk.coordinator_yield();
4384 conc_workers()->continue_task(&tsk);
4385 }
4386 }
4387 assert(tsk.completed(), "Inconsistency");
4388 assert(tsk.result() == true, "Inconsistency");
4389 return true;
4390 }
4391
4392 bool CMSCollector::do_marking_st(bool asynch) {
4393 ResourceMark rm;
4394 HandleMark hm;
4395
4396 // Temporarily make refs discovery single threaded (non-MT)
4397 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
4398 MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
4399 &_markStack, CMSYield && asynch);
4400 // the last argument to iterate indicates whether the iteration
4401 // should be incremental with periodic yields.
4402 _markBitMap.iterate(&markFromRootsClosure);
4403 // If _restart_addr is non-NULL, a marking stack overflow
4404 // occurred; we need to do a fresh iteration from the
4405 // indicated restart address.
4406 while (_restart_addr != NULL) {
4407 if (_foregroundGCIsActive && asynch) {
4408 // We may be running into repeated stack overflows, having
4409 // reached the limit of the stack size, while making very
4410 // slow forward progress. It may be best to bail out and
4411 // let the foreground collector do its job.
4412 // Clear _restart_addr, so that foreground GC
4413 // works from scratch. This avoids the headache of
4414 // a "rescan" which would otherwise be needed because
4415 // of the dirty mod union table & card table.
4416 _restart_addr = NULL;
4417 return false; // indicating failure to complete marking
4418 }
4419 // Deal with stack overflow:
4420 // we restart marking from _restart_addr
4421 HeapWord* ra = _restart_addr;
4422 markFromRootsClosure.reset(ra);
4423 _restart_addr = NULL;
4424 _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
4425 }
4426 return true;
4427 }
4428
4429 void CMSCollector::preclean() {
4430 check_correct_thread_executing();
4431 assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
4432 verify_work_stacks_empty();
4433 verify_overflow_empty();
4434 _abort_preclean = false;
4435 if (CMSPrecleaningEnabled) {
4436 if (!CMSEdenChunksRecordAlways) {
4437 _eden_chunk_index = 0;
4438 }
4439 size_t used = get_eden_used();
4440 size_t capacity = get_eden_capacity();
4441 // Don't start sampling unless we will get sufficiently
4442 // many samples.
4443 if (used < (capacity/(CMSScheduleRemarkSamplingRatio * 100)
4444 * CMSScheduleRemarkEdenPenetration)) {
4445 _start_sampling = true;
4446 } else {
4447 _start_sampling = false;
4448 }
4449 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
4450 CMSPhaseAccounting pa(this, "preclean", _gc_tracer_cm->gc_id(), !PrintGCDetails);
4451 preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
4452 }
4453 CMSTokenSync x(true); // is cms thread
4454 if (CMSPrecleaningEnabled) {
4455 sample_eden();
4456 _collectorState = AbortablePreclean;
4457 } else {
4458 _collectorState = FinalMarking;
4459 }
4460 verify_work_stacks_empty();
4461 verify_overflow_empty();
4462 }
4463
4464 // Try and schedule the remark such that young gen
4465 // occupancy is CMSScheduleRemarkEdenPenetration %.
4466 void CMSCollector::abortable_preclean() {
4467 check_correct_thread_executing();
4468 assert(CMSPrecleaningEnabled, "Inconsistent control state");
4469 assert(_collectorState == AbortablePreclean, "Inconsistent control state");
4470
4471 // If Eden's current occupancy is below this threshold,
4472 // immediately schedule the remark; else preclean
4473 // past the next scavenge in an effort to
4474 // schedule the pause as described above. By choosing
4475 // CMSScheduleRemarkEdenSizeThreshold >= max eden size
4476 // we will never do an actual abortable preclean cycle.
4477 if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
4478 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
4479 CMSPhaseAccounting pa(this, "abortable-preclean", _gc_tracer_cm->gc_id(), !PrintGCDetails);
4480 // We need more smarts in the abortable preclean
4481 // loop below to deal with cases where allocation
4482 // in young gen is very very slow, and our precleaning
4483 // is running a losing race against a horde of
4484 // mutators intent on flooding us with CMS updates
4485 // (dirty cards).
4486 // One, admittedly dumb, strategy is to give up
4487 // after a certain number of abortable precleaning loops
4488 // or after a certain maximum time. We want to make
4489 // this smarter in the next iteration.
4490 // XXX FIX ME!!! YSR
4491 size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
4492 while (!(should_abort_preclean() ||
4493 ConcurrentMarkSweepThread::should_terminate())) {
4494 workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
4495 cumworkdone += workdone;
4496 loops++;
4497 // Voluntarily terminate abortable preclean phase if we have
4498 // been at it for too long.
4499 if ((CMSMaxAbortablePrecleanLoops != 0) &&
4500 loops >= CMSMaxAbortablePrecleanLoops) {
4501 if (PrintGCDetails) {
4502 gclog_or_tty->print(" CMS: abort preclean due to loops ");
4503 }
4504 break;
4505 }
4506 if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
4507 if (PrintGCDetails) {
4508 gclog_or_tty->print(" CMS: abort preclean due to time ");
4509 }
4510 break;
4511 }
4512 // If we are doing little work each iteration, we should
4513 // take a short break.
4514 if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
4515 // Sleep for some time, waiting for work to accumulate
4516 stopTimer();
4517 cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
4518 startTimer();
4519 waited++;
4520 }
4521 }
4522 if (PrintCMSStatistics > 0) {
4523 gclog_or_tty->print(" [" SIZE_FORMAT " iterations, " SIZE_FORMAT " waits, " SIZE_FORMAT " cards)] ",
4524 loops, waited, cumworkdone);
4525 }
4526 }
4527 CMSTokenSync x(true); // is cms thread
4528 if (_collectorState != Idling) {
4529 assert(_collectorState == AbortablePreclean,
4530 "Spontaneous state transition?");
4531 _collectorState = FinalMarking;
4532 } // Else, a foreground collection completed this CMS cycle.
4533 return;
4534 }
4535
4536 // Respond to an Eden sampling opportunity
4537 void CMSCollector::sample_eden() {
4538 // Make sure a young gc cannot sneak in between our
4539 // reading and recording of a sample.
4540 assert(Thread::current()->is_ConcurrentGC_thread(),
4541 "Only the cms thread may collect Eden samples");
4542 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
4543 "Should collect samples while holding CMS token");
4544 if (!_start_sampling) {
4545 return;
4546 }
4547 // When CMSEdenChunksRecordAlways is true, the eden chunk array
4548 // is populated by the young generation.
4549 if (_eden_chunk_array != NULL && !CMSEdenChunksRecordAlways) {
4550 if (_eden_chunk_index < _eden_chunk_capacity) {
4551 _eden_chunk_array[_eden_chunk_index] = *_top_addr; // take sample
4552 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4553 "Unexpected state of Eden");
4554 // We'd like to check that what we just sampled is an oop-start address;
4555 // however, we cannot do that here since the object may not yet have been
4556 // initialized. So we'll instead do the check when we _use_ this sample
4557 // later.
4558 if (_eden_chunk_index == 0 ||
4559 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4560 _eden_chunk_array[_eden_chunk_index-1])
4561 >= CMSSamplingGrain)) {
4562 _eden_chunk_index++; // commit sample
4563 }
4564 }
4565 }
4566 if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
4567 size_t used = get_eden_used();
4568 size_t capacity = get_eden_capacity();
4569 assert(used <= capacity, "Unexpected state of Eden");
4570 if (used > (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
4571 _abort_preclean = true;
4572 }
4573 }
4574 }
4575
4576
4577 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
4578 assert(_collectorState == Precleaning ||
4579 _collectorState == AbortablePreclean, "incorrect state");
4580 ResourceMark rm;
4581 HandleMark hm;
4582
4583 // Precleaning is currently not MT but the reference processor
4584 // may be set for MT. Disable it temporarily here.
4585 ReferenceProcessor* rp = ref_processor();
4586 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false);
4587
4588 // Do one pass of scrubbing the discovered reference lists
4589 // to remove any reference objects with strongly-reachable
4590 // referents.
4591 if (clean_refs) {
4592 CMSPrecleanRefsYieldClosure yield_cl(this);
4593 assert(rp->span().equals(_span), "Spans should be equal");
4594 CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
4595 &_markStack, true /* preclean */);
4596 CMSDrainMarkingStackClosure complete_trace(this,
4597 _span, &_markBitMap, &_markStack,
4598 &keep_alive, true /* preclean */);
4599
4600 // We don't want this step to interfere with a young
4601 // collection because we don't want to take CPU
4602 // or memory bandwidth away from the young GC threads
4603 // (which may be as many as there are CPUs).
4604 // Note that we don't need to protect ourselves from
4605 // interference with mutators because they can't
4606 // manipulate the discovered reference lists nor affect
4607 // the computed reachability of the referents, the
4608 // only properties manipulated by the precleaning
4609 // of these reference lists.
4610 stopTimer();
4611 CMSTokenSyncWithLocks x(true /* is cms thread */,
4612 bitMapLock());
4613 startTimer();
4614 sample_eden();
4615
4616 // The following will yield to allow foreground
4617 // collection to proceed promptly. XXX YSR:
4618 // The code in this method may need further
4619 // tweaking for better performance and some restructuring
4620 // for cleaner interfaces.
4621 GCTimer *gc_timer = NULL; // Currently not tracing concurrent phases
4622 rp->preclean_discovered_references(
4623 rp->is_alive_non_header(), &keep_alive, &complete_trace, &yield_cl,
4624 gc_timer, _gc_tracer_cm->gc_id());
4625 }
4626
4627 if (clean_survivor) { // preclean the active survivor space(s)
4628 assert(_young_gen->kind() == Generation::DefNew ||
4629 _young_gen->kind() == Generation::ParNew,
4630 "incorrect type for cast");
4631 DefNewGeneration* dng = (DefNewGeneration*)_young_gen;
4632 PushAndMarkClosure pam_cl(this, _span, ref_processor(),
4633 &_markBitMap, &_modUnionTable,
4634 &_markStack, true /* precleaning phase */);
4635 stopTimer();
4636 CMSTokenSyncWithLocks ts(true /* is cms thread */,
4637 bitMapLock());
4638 startTimer();
4639 unsigned int before_count =
4640 GenCollectedHeap::heap()->total_collections();
4641 SurvivorSpacePrecleanClosure
4642 sss_cl(this, _span, &_markBitMap, &_markStack,
4643 &pam_cl, before_count, CMSYield);
4644 dng->from()->object_iterate_careful(&sss_cl);
4645 dng->to()->object_iterate_careful(&sss_cl);
4646 }
4647 MarkRefsIntoAndScanClosure
4648 mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
4649 &_markStack, this, CMSYield,
4650 true /* precleaning phase */);
4651 // CAUTION: The following closure has persistent state that may need to
4652 // be reset upon a decrease in the sequence of addresses it
4653 // processes.
4654 ScanMarkedObjectsAgainCarefullyClosure
4655 smoac_cl(this, _span,
4656 &_markBitMap, &_markStack, &mrias_cl, CMSYield);
4657
4658 // Preclean dirty cards in ModUnionTable and CardTable using
4659 // appropriate convergence criterion;
4660 // repeat CMSPrecleanIter times unless we find that
4661 // we are losing.
4662 assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
4663 assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
4664 "Bad convergence multiplier");
4665 assert(CMSPrecleanThreshold >= 100,
4666 "Unreasonably low CMSPrecleanThreshold");
4667
4668 size_t numIter, cumNumCards, lastNumCards, curNumCards;
4669 for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
4670 numIter < CMSPrecleanIter;
4671 numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
4672 curNumCards = preclean_mod_union_table(_cmsGen, &smoac_cl);
4673 if (Verbose && PrintGCDetails) {
4674 gclog_or_tty->print(" (modUnionTable: " SIZE_FORMAT " cards)", curNumCards);
4675 }
4676 // Either there are very few dirty cards, so re-mark
4677 // pause will be small anyway, or our pre-cleaning isn't
4678 // that much faster than the rate at which cards are being
4679 // dirtied, so we might as well stop and re-mark since
4680 // precleaning won't improve our re-mark time by much.
4681 if (curNumCards <= CMSPrecleanThreshold ||
4682 (numIter > 0 &&
4683 (curNumCards * CMSPrecleanDenominator >
4684 lastNumCards * CMSPrecleanNumerator))) {
4685 numIter++;
4686 cumNumCards += curNumCards;
4687 break;
4688 }
4689 }
4690
4691 preclean_klasses(&mrias_cl, _cmsGen->freelistLock());
4692
4693 curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
4694 cumNumCards += curNumCards;
4695 if (PrintGCDetails && PrintCMSStatistics != 0) {
4696 gclog_or_tty->print_cr(" (cardTable: " SIZE_FORMAT " cards, re-scanned " SIZE_FORMAT " cards, " SIZE_FORMAT " iterations)",
4697 curNumCards, cumNumCards, numIter);
4698 }
4699 return cumNumCards; // as a measure of useful work done
4700 }
4701
4702 // PRECLEANING NOTES:
4703 // Precleaning involves:
4704 // . reading the bits of the modUnionTable and clearing the set bits.
4705 // . For the cards corresponding to the set bits, we scan the
4706 // objects on those cards. This means we need the free_list_lock
4707 // so that we can safely iterate over the CMS space when scanning
4708 // for oops.
4709 // . When we scan the objects, we'll be both reading and setting
4710 // marks in the marking bit map, so we'll need the marking bit map.
4711 // . For protecting _collector_state transitions, we take the CGC_lock.
4712 // Note that any races in the reading of of card table entries by the
4713 // CMS thread on the one hand and the clearing of those entries by the
4714 // VM thread or the setting of those entries by the mutator threads on the
4715 // other are quite benign. However, for efficiency it makes sense to keep
4716 // the VM thread from racing with the CMS thread while the latter is
4717 // dirty card info to the modUnionTable. We therefore also use the
4718 // CGC_lock to protect the reading of the card table and the mod union
4719 // table by the CM thread.
4720 // . We run concurrently with mutator updates, so scanning
4721 // needs to be done carefully -- we should not try to scan
4722 // potentially uninitialized objects.
4723 //
4724 // Locking strategy: While holding the CGC_lock, we scan over and
4725 // reset a maximal dirty range of the mod union / card tables, then lock
4726 // the free_list_lock and bitmap lock to do a full marking, then
4727 // release these locks; and repeat the cycle. This allows for a
4728 // certain amount of fairness in the sharing of these locks between
4729 // the CMS collector on the one hand, and the VM thread and the
4730 // mutators on the other.
4731
4732 // NOTE: preclean_mod_union_table() and preclean_card_table()
4733 // further below are largely identical; if you need to modify
4734 // one of these methods, please check the other method too.
4735
4736 size_t CMSCollector::preclean_mod_union_table(
4737 ConcurrentMarkSweepGeneration* gen,
4738 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4739 verify_work_stacks_empty();
4740 verify_overflow_empty();
4741
4742 // strategy: starting with the first card, accumulate contiguous
4743 // ranges of dirty cards; clear these cards, then scan the region
4744 // covered by these cards.
4745
4746 // Since all of the MUT is committed ahead, we can just use
4747 // that, in case the generations expand while we are precleaning.
4748 // It might also be fine to just use the committed part of the
4749 // generation, but we might potentially miss cards when the
4750 // generation is rapidly expanding while we are in the midst
4751 // of precleaning.
4752 HeapWord* startAddr = gen->reserved().start();
4753 HeapWord* endAddr = gen->reserved().end();
4754
4755 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4756
4757 size_t numDirtyCards, cumNumDirtyCards;
4758 HeapWord *nextAddr, *lastAddr;
4759 for (cumNumDirtyCards = numDirtyCards = 0,
4760 nextAddr = lastAddr = startAddr;
4761 nextAddr < endAddr;
4762 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4763
4764 ResourceMark rm;
4765 HandleMark hm;
4766
4767 MemRegion dirtyRegion;
4768 {
4769 stopTimer();
4770 // Potential yield point
4771 CMSTokenSync ts(true);
4772 startTimer();
4773 sample_eden();
4774 // Get dirty region starting at nextOffset (inclusive),
4775 // simultaneously clearing it.
4776 dirtyRegion =
4777 _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
4778 assert(dirtyRegion.start() >= nextAddr,
4779 "returned region inconsistent?");
4780 }
4781 // Remember where the next search should begin.
4782 // The returned region (if non-empty) is a right open interval,
4783 // so lastOffset is obtained from the right end of that
4784 // interval.
4785 lastAddr = dirtyRegion.end();
4786 // Should do something more transparent and less hacky XXX
4787 numDirtyCards =
4788 _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
4789
4790 // We'll scan the cards in the dirty region (with periodic
4791 // yields for foreground GC as needed).
4792 if (!dirtyRegion.is_empty()) {
4793 assert(numDirtyCards > 0, "consistency check");
4794 HeapWord* stop_point = NULL;
4795 stopTimer();
4796 // Potential yield point
4797 CMSTokenSyncWithLocks ts(true, gen->freelistLock(),
4798 bitMapLock());
4799 startTimer();
4800 {
4801 verify_work_stacks_empty();
4802 verify_overflow_empty();
4803 sample_eden();
4804 stop_point =
4805 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4806 }
4807 if (stop_point != NULL) {
4808 // The careful iteration stopped early either because it found an
4809 // uninitialized object, or because we were in the midst of an
4810 // "abortable preclean", which should now be aborted. Redirty
4811 // the bits corresponding to the partially-scanned or unscanned
4812 // cards. We'll either restart at the next block boundary or
4813 // abort the preclean.
4814 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4815 "Should only be AbortablePreclean.");
4816 _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
4817 if (should_abort_preclean()) {
4818 break; // out of preclean loop
4819 } else {
4820 // Compute the next address at which preclean should pick up;
4821 // might need bitMapLock in order to read P-bits.
4822 lastAddr = next_card_start_after_block(stop_point);
4823 }
4824 }
4825 } else {
4826 assert(lastAddr == endAddr, "consistency check");
4827 assert(numDirtyCards == 0, "consistency check");
4828 break;
4829 }
4830 }
4831 verify_work_stacks_empty();
4832 verify_overflow_empty();
4833 return cumNumDirtyCards;
4834 }
4835
4836 // NOTE: preclean_mod_union_table() above and preclean_card_table()
4837 // below are largely identical; if you need to modify
4838 // one of these methods, please check the other method too.
4839
4840 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* gen,
4841 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4842 // strategy: it's similar to precleamModUnionTable above, in that
4843 // we accumulate contiguous ranges of dirty cards, mark these cards
4844 // precleaned, then scan the region covered by these cards.
4845 HeapWord* endAddr = (HeapWord*)(gen->_virtual_space.high());
4846 HeapWord* startAddr = (HeapWord*)(gen->_virtual_space.low());
4847
4848 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4849
4850 size_t numDirtyCards, cumNumDirtyCards;
4851 HeapWord *lastAddr, *nextAddr;
4852
4853 for (cumNumDirtyCards = numDirtyCards = 0,
4854 nextAddr = lastAddr = startAddr;
4855 nextAddr < endAddr;
4856 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4857
4858 ResourceMark rm;
4859 HandleMark hm;
4860
4861 MemRegion dirtyRegion;
4862 {
4863 // See comments in "Precleaning notes" above on why we
4864 // do this locking. XXX Could the locking overheads be
4865 // too high when dirty cards are sparse? [I don't think so.]
4866 stopTimer();
4867 CMSTokenSync x(true); // is cms thread
4868 startTimer();
4869 sample_eden();
4870 // Get and clear dirty region from card table
4871 dirtyRegion = _ct->ct_bs()->dirty_card_range_after_reset(
4872 MemRegion(nextAddr, endAddr),
4873 true,
4874 CardTableModRefBS::precleaned_card_val());
4875
4876 assert(dirtyRegion.start() >= nextAddr,
4877 "returned region inconsistent?");
4878 }
4879 lastAddr = dirtyRegion.end();
4880 numDirtyCards =
4881 dirtyRegion.word_size()/CardTableModRefBS::card_size_in_words;
4882
4883 if (!dirtyRegion.is_empty()) {
4884 stopTimer();
4885 CMSTokenSyncWithLocks ts(true, gen->freelistLock(), bitMapLock());
4886 startTimer();
4887 sample_eden();
4888 verify_work_stacks_empty();
4889 verify_overflow_empty();
4890 HeapWord* stop_point =
4891 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4892 if (stop_point != NULL) {
4893 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4894 "Should only be AbortablePreclean.");
4895 _ct->ct_bs()->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4896 if (should_abort_preclean()) {
4897 break; // out of preclean loop
4898 } else {
4899 // Compute the next address at which preclean should pick up.
4900 lastAddr = next_card_start_after_block(stop_point);
4901 }
4902 }
4903 } else {
4904 break;
4905 }
4906 }
4907 verify_work_stacks_empty();
4908 verify_overflow_empty();
4909 return cumNumDirtyCards;
4910 }
4911
4912 class PrecleanKlassClosure : public KlassClosure {
4913 KlassToOopClosure _cm_klass_closure;
4914 public:
4915 PrecleanKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4916 void do_klass(Klass* k) {
4917 if (k->has_accumulated_modified_oops()) {
4918 k->clear_accumulated_modified_oops();
4919
4920 _cm_klass_closure.do_klass(k);
4921 }
4922 }
4923 };
4924
4925 // The freelist lock is needed to prevent asserts, is it really needed?
4926 void CMSCollector::preclean_klasses(MarkRefsIntoAndScanClosure* cl, Mutex* freelistLock) {
4927
4928 cl->set_freelistLock(freelistLock);
4929
4930 CMSTokenSyncWithLocks ts(true, freelistLock, bitMapLock());
4931
4932 // SSS: Add equivalent to ScanMarkedObjectsAgainCarefullyClosure::do_yield_check and should_abort_preclean?
4933 // SSS: We should probably check if precleaning should be aborted, at suitable intervals?
4934 PrecleanKlassClosure preclean_klass_closure(cl);
4935 ClassLoaderDataGraph::classes_do(&preclean_klass_closure);
4936
4937 verify_work_stacks_empty();
4938 verify_overflow_empty();
4939 }
4940
4941 void CMSCollector::checkpointRootsFinal(bool asynch,
4942 bool clear_all_soft_refs, bool init_mark_was_synchronous) {
4943 assert(_collectorState == FinalMarking, "incorrect state transition?");
4944 check_correct_thread_executing();
4945 // world is stopped at this checkpoint
4946 assert(SafepointSynchronize::is_at_safepoint(),
4947 "world should be stopped");
4948 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
4949
4950 verify_work_stacks_empty();
4951 verify_overflow_empty();
4952
4953 SpecializationStats::clear();
4954 if (PrintGCDetails) {
4955 gclog_or_tty->print("[YG occupancy: "SIZE_FORMAT" K ("SIZE_FORMAT" K)]",
4956 _young_gen->used() / K,
4957 _young_gen->capacity() / K);
4958 }
4959 if (asynch) {
4960 if (CMSScavengeBeforeRemark) {
4961 GenCollectedHeap* gch = GenCollectedHeap::heap();
4962 // Temporarily set flag to false, GCH->do_collection will
4963 // expect it to be false and set to true
4964 FlagSetting fl(gch->_is_gc_active, false);
4965 NOT_PRODUCT(GCTraceTime t("Scavenge-Before-Remark",
4966 PrintGCDetails && Verbose, true, _gc_timer_cm, _gc_tracer_cm->gc_id());)
4967 int level = _cmsGen->level() - 1;
4968 if (level >= 0) {
4969 gch->do_collection(true, // full (i.e. force, see below)
4970 false, // !clear_all_soft_refs
4971 0, // size
4972 false, // is_tlab
4973 level // max_level
4974 );
4975 }
4976 }
4977 FreelistLocker x(this);
4978 MutexLockerEx y(bitMapLock(),
4979 Mutex::_no_safepoint_check_flag);
4980 assert(!init_mark_was_synchronous, "but that's impossible!");
4981 checkpointRootsFinalWork(asynch, clear_all_soft_refs, false);
4982 } else {
4983 // already have all the locks
4984 checkpointRootsFinalWork(asynch, clear_all_soft_refs,
4985 init_mark_was_synchronous);
4986 }
4987 verify_work_stacks_empty();
4988 verify_overflow_empty();
4989 SpecializationStats::print();
4990 }
4991
4992 void CMSCollector::checkpointRootsFinalWork(bool asynch,
4993 bool clear_all_soft_refs, bool init_mark_was_synchronous) {
4994
4995 NOT_PRODUCT(GCTraceTime tr("checkpointRootsFinalWork", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());)
4996
4997 assert(haveFreelistLocks(), "must have free list locks");
4998 assert_lock_strong(bitMapLock());
4999
5000 ResourceMark rm;
5001 HandleMark hm;
5002
5003 GenCollectedHeap* gch = GenCollectedHeap::heap();
5004
5005 if (should_unload_classes()) {
5006 CodeCache::gc_prologue();
5007 }
5008 assert(haveFreelistLocks(), "must have free list locks");
5009 assert_lock_strong(bitMapLock());
5010
5011 if (!init_mark_was_synchronous) {
5012 // We might assume that we need not fill TLAB's when
5013 // CMSScavengeBeforeRemark is set, because we may have just done
5014 // a scavenge which would have filled all TLAB's -- and besides
5015 // Eden would be empty. This however may not always be the case --
5016 // for instance although we asked for a scavenge, it may not have
5017 // happened because of a JNI critical section. We probably need
5018 // a policy for deciding whether we can in that case wait until
5019 // the critical section releases and then do the remark following
5020 // the scavenge, and skip it here. In the absence of that policy,
5021 // or of an indication of whether the scavenge did indeed occur,
5022 // we cannot rely on TLAB's having been filled and must do
5023 // so here just in case a scavenge did not happen.
5024 gch->ensure_parsability(false); // fill TLAB's, but no need to retire them
5025 // Update the saved marks which may affect the root scans.
5026 gch->save_marks();
5027
5028 if (CMSPrintEdenSurvivorChunks) {
5029 print_eden_and_survivor_chunk_arrays();
5030 }
5031
5032 {
5033 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
5034
5035 // Note on the role of the mod union table:
5036 // Since the marker in "markFromRoots" marks concurrently with
5037 // mutators, it is possible for some reachable objects not to have been
5038 // scanned. For instance, an only reference to an object A was
5039 // placed in object B after the marker scanned B. Unless B is rescanned,
5040 // A would be collected. Such updates to references in marked objects
5041 // are detected via the mod union table which is the set of all cards
5042 // dirtied since the first checkpoint in this GC cycle and prior to
5043 // the most recent young generation GC, minus those cleaned up by the
5044 // concurrent precleaning.
5045 if (CMSParallelRemarkEnabled && CollectedHeap::use_parallel_gc_threads()) {
5046 GCTraceTime t("Rescan (parallel) ", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5047 do_remark_parallel();
5048 } else {
5049 GCTraceTime t("Rescan (non-parallel) ", PrintGCDetails, false,
5050 _gc_timer_cm, _gc_tracer_cm->gc_id());
5051 do_remark_non_parallel();
5052 }
5053 }
5054 } else {
5055 assert(!asynch, "Can't have init_mark_was_synchronous in asynch mode");
5056 // The initial mark was stop-world, so there's no rescanning to
5057 // do; go straight on to the next step below.
5058 }
5059 verify_work_stacks_empty();
5060 verify_overflow_empty();
5061
5062 {
5063 NOT_PRODUCT(GCTraceTime ts("refProcessingWork", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());)
5064 refProcessingWork(asynch, clear_all_soft_refs);
5065 }
5066 verify_work_stacks_empty();
5067 verify_overflow_empty();
5068
5069 if (should_unload_classes()) {
5070 CodeCache::gc_epilogue();
5071 }
5072 JvmtiExport::gc_epilogue();
5073
5074 // If we encountered any (marking stack / work queue) overflow
5075 // events during the current CMS cycle, take appropriate
5076 // remedial measures, where possible, so as to try and avoid
5077 // recurrence of that condition.
5078 assert(_markStack.isEmpty(), "No grey objects");
5079 size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
5080 _ser_kac_ovflw + _ser_kac_preclean_ovflw;
5081 if (ser_ovflw > 0) {
5082 if (PrintCMSStatistics != 0) {
5083 gclog_or_tty->print_cr("Marking stack overflow (benign) "
5084 "(pmc_pc="SIZE_FORMAT", pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT
5085 ", kac_preclean="SIZE_FORMAT")",
5086 _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw,
5087 _ser_kac_ovflw, _ser_kac_preclean_ovflw);
5088 }
5089 _markStack.expand();
5090 _ser_pmc_remark_ovflw = 0;
5091 _ser_pmc_preclean_ovflw = 0;
5092 _ser_kac_preclean_ovflw = 0;
5093 _ser_kac_ovflw = 0;
5094 }
5095 if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
5096 if (PrintCMSStatistics != 0) {
5097 gclog_or_tty->print_cr("Work queue overflow (benign) "
5098 "(pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT")",
5099 _par_pmc_remark_ovflw, _par_kac_ovflw);
5100 }
5101 _par_pmc_remark_ovflw = 0;
5102 _par_kac_ovflw = 0;
5103 }
5104 if (PrintCMSStatistics != 0) {
5105 if (_markStack._hit_limit > 0) {
5106 gclog_or_tty->print_cr(" (benign) Hit max stack size limit ("SIZE_FORMAT")",
5107 _markStack._hit_limit);
5108 }
5109 if (_markStack._failed_double > 0) {
5110 gclog_or_tty->print_cr(" (benign) Failed stack doubling ("SIZE_FORMAT"),"
5111 " current capacity "SIZE_FORMAT,
5112 _markStack._failed_double,
5113 _markStack.capacity());
5114 }
5115 }
5116 _markStack._hit_limit = 0;
5117 _markStack._failed_double = 0;
5118
5119 if ((VerifyAfterGC || VerifyDuringGC) &&
5120 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5121 verify_after_remark();
5122 }
5123
5124 _gc_tracer_cm->report_object_count_after_gc(&_is_alive_closure);
5125
5126 // Change under the freelistLocks.
5127 _collectorState = Sweeping;
5128 // Call isAllClear() under bitMapLock
5129 assert(_modUnionTable.isAllClear(),
5130 "Should be clear by end of the final marking");
5131 assert(_ct->klass_rem_set()->mod_union_is_clear(),
5132 "Should be clear by end of the final marking");
5133 }
5134
5135 void CMSParInitialMarkTask::work(uint worker_id) {
5136 elapsedTimer _timer;
5137 ResourceMark rm;
5138 HandleMark hm;
5139
5140 // ---------- scan from roots --------------
5141 _timer.start();
5142 GenCollectedHeap* gch = GenCollectedHeap::heap();
5143 Par_MarkRefsIntoClosure par_mri_cl(_collector->_span, &(_collector->_markBitMap));
5144
5145 // ---------- young gen roots --------------
5146 {
5147 work_on_young_gen_roots(worker_id, &par_mri_cl);
5148 _timer.stop();
5149 if (PrintCMSStatistics != 0) {
5150 gclog_or_tty->print_cr(
5151 "Finished young gen initial mark scan work in %dth thread: %3.3f sec",
5152 worker_id, _timer.seconds());
5153 }
5154 }
5155
5156 // ---------- remaining roots --------------
5157 _timer.reset();
5158 _timer.start();
5159
5160 CLDToOopClosure cld_closure(&par_mri_cl, true);
5161
5162 gch->gen_process_roots(_collector->_cmsGen->level(),
5163 false, // yg was scanned above
5164 false, // this is parallel code
5165 SharedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
5166 _collector->should_unload_classes(),
5167 &par_mri_cl,
5168 NULL,
5169 &cld_closure);
5170 assert(_collector->should_unload_classes()
5171 || (_collector->CMSCollector::roots_scanning_options() & SharedHeap::SO_AllCodeCache),
5172 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5173 _timer.stop();
5174 if (PrintCMSStatistics != 0) {
5175 gclog_or_tty->print_cr(
5176 "Finished remaining root initial mark scan work in %dth thread: %3.3f sec",
5177 worker_id, _timer.seconds());
5178 }
5179 }
5180
5181 // Parallel remark task
5182 class CMSParRemarkTask: public CMSParMarkTask {
5183 CompactibleFreeListSpace* _cms_space;
5184
5185 // The per-thread work queues, available here for stealing.
5186 OopTaskQueueSet* _task_queues;
5187 ParallelTaskTerminator _term;
5188
5189 public:
5190 // A value of 0 passed to n_workers will cause the number of
5191 // workers to be taken from the active workers in the work gang.
5192 CMSParRemarkTask(CMSCollector* collector,
5193 CompactibleFreeListSpace* cms_space,
5194 int n_workers, FlexibleWorkGang* workers,
5195 OopTaskQueueSet* task_queues):
5196 CMSParMarkTask("Rescan roots and grey objects in parallel",
5197 collector, n_workers),
5198 _cms_space(cms_space),
5199 _task_queues(task_queues),
5200 _term(n_workers, task_queues) { }
5201
5202 OopTaskQueueSet* task_queues() { return _task_queues; }
5203
5204 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5205
5206 ParallelTaskTerminator* terminator() { return &_term; }
5207 int n_workers() { return _n_workers; }
5208
5209 void work(uint worker_id);
5210
5211 private:
5212 // ... of dirty cards in old space
5213 void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
5214 Par_MarkRefsIntoAndScanClosure* cl);
5215
5216 // ... work stealing for the above
5217 void do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl, int* seed);
5218 };
5219
5220 class RemarkKlassClosure : public KlassClosure {
5221 KlassToOopClosure _cm_klass_closure;
5222 public:
5223 RemarkKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
5224 void do_klass(Klass* k) {
5225 // Check if we have modified any oops in the Klass during the concurrent marking.
5226 if (k->has_accumulated_modified_oops()) {
5227 k->clear_accumulated_modified_oops();
5228
5229 // We could have transfered the current modified marks to the accumulated marks,
5230 // like we do with the Card Table to Mod Union Table. But it's not really necessary.
5231 } else if (k->has_modified_oops()) {
5232 // Don't clear anything, this info is needed by the next young collection.
5233 } else {
5234 // No modified oops in the Klass.
5235 return;
5236 }
5237
5238 // The klass has modified fields, need to scan the klass.
5239 _cm_klass_closure.do_klass(k);
5240 }
5241 };
5242
5243 void CMSParMarkTask::work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl) {
5244 DefNewGeneration* dng = _collector->_young_gen->as_DefNewGeneration();
5245 EdenSpace* eden_space = dng->eden();
5246 ContiguousSpace* from_space = dng->from();
5247 ContiguousSpace* to_space = dng->to();
5248
5249 HeapWord** eca = _collector->_eden_chunk_array;
5250 size_t ect = _collector->_eden_chunk_index;
5251 HeapWord** sca = _collector->_survivor_chunk_array;
5252 size_t sct = _collector->_survivor_chunk_index;
5253
5254 assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
5255 assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
5256
5257 do_young_space_rescan(worker_id, cl, to_space, NULL, 0);
5258 do_young_space_rescan(worker_id, cl, from_space, sca, sct);
5259 do_young_space_rescan(worker_id, cl, eden_space, eca, ect);
5260 }
5261
5262 // work_queue(i) is passed to the closure
5263 // Par_MarkRefsIntoAndScanClosure. The "i" parameter
5264 // also is passed to do_dirty_card_rescan_tasks() and to
5265 // do_work_steal() to select the i-th task_queue.
5266
5267 void CMSParRemarkTask::work(uint worker_id) {
5268 elapsedTimer _timer;
5269 ResourceMark rm;
5270 HandleMark hm;
5271
5272 // ---------- rescan from roots --------------
5273 _timer.start();
5274 GenCollectedHeap* gch = GenCollectedHeap::heap();
5275 Par_MarkRefsIntoAndScanClosure par_mrias_cl(_collector,
5276 _collector->_span, _collector->ref_processor(),
5277 &(_collector->_markBitMap),
5278 work_queue(worker_id));
5279
5280 // Rescan young gen roots first since these are likely
5281 // coarsely partitioned and may, on that account, constitute
5282 // the critical path; thus, it's best to start off that
5283 // work first.
5284 // ---------- young gen roots --------------
5285 {
5286 work_on_young_gen_roots(worker_id, &par_mrias_cl);
5287 _timer.stop();
5288 if (PrintCMSStatistics != 0) {
5289 gclog_or_tty->print_cr(
5290 "Finished young gen rescan work in %dth thread: %3.3f sec",
5291 worker_id, _timer.seconds());
5292 }
5293 }
5294
5295 // ---------- remaining roots --------------
5296 _timer.reset();
5297 _timer.start();
5298 gch->gen_process_roots(_collector->_cmsGen->level(),
5299 false, // yg was scanned above
5300 false, // this is parallel code
5301 SharedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
5302 _collector->should_unload_classes(),
5303 &par_mrias_cl,
5304 NULL,
5305 NULL); // The dirty klasses will be handled below
5306
5307 assert(_collector->should_unload_classes()
5308 || (_collector->CMSCollector::roots_scanning_options() & SharedHeap::SO_AllCodeCache),
5309 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5310 _timer.stop();
5311 if (PrintCMSStatistics != 0) {
5312 gclog_or_tty->print_cr(
5313 "Finished remaining root rescan work in %dth thread: %3.3f sec",
5314 worker_id, _timer.seconds());
5315 }
5316
5317 // ---------- unhandled CLD scanning ----------
5318 if (worker_id == 0) { // Single threaded at the moment.
5319 _timer.reset();
5320 _timer.start();
5321
5322 // Scan all new class loader data objects and new dependencies that were
5323 // introduced during concurrent marking.
5324 ResourceMark rm;
5325 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
5326 for (int i = 0; i < array->length(); i++) {
5327 par_mrias_cl.do_class_loader_data(array->at(i));
5328 }
5329
5330 // We don't need to keep track of new CLDs anymore.
5331 ClassLoaderDataGraph::remember_new_clds(false);
5332
5333 _timer.stop();
5334 if (PrintCMSStatistics != 0) {
5335 gclog_or_tty->print_cr(
5336 "Finished unhandled CLD scanning work in %dth thread: %3.3f sec",
5337 worker_id, _timer.seconds());
5338 }
5339 }
5340
5341 // ---------- dirty klass scanning ----------
5342 if (worker_id == 0) { // Single threaded at the moment.
5343 _timer.reset();
5344 _timer.start();
5345
5346 // Scan all classes that was dirtied during the concurrent marking phase.
5347 RemarkKlassClosure remark_klass_closure(&par_mrias_cl);
5348 ClassLoaderDataGraph::classes_do(&remark_klass_closure);
5349
5350 _timer.stop();
5351 if (PrintCMSStatistics != 0) {
5352 gclog_or_tty->print_cr(
5353 "Finished dirty klass scanning work in %dth thread: %3.3f sec",
5354 worker_id, _timer.seconds());
5355 }
5356 }
5357
5358 // We might have added oops to ClassLoaderData::_handles during the
5359 // concurrent marking phase. These oops point to newly allocated objects
5360 // that are guaranteed to be kept alive. Either by the direct allocation
5361 // code, or when the young collector processes the roots. Hence,
5362 // we don't have to revisit the _handles block during the remark phase.
5363
5364 // ---------- rescan dirty cards ------------
5365 _timer.reset();
5366 _timer.start();
5367
5368 // Do the rescan tasks for each of the two spaces
5369 // (cms_space) in turn.
5370 // "worker_id" is passed to select the task_queue for "worker_id"
5371 do_dirty_card_rescan_tasks(_cms_space, worker_id, &par_mrias_cl);
5372 _timer.stop();
5373 if (PrintCMSStatistics != 0) {
5374 gclog_or_tty->print_cr(
5375 "Finished dirty card rescan work in %dth thread: %3.3f sec",
5376 worker_id, _timer.seconds());
5377 }
5378
5379 // ---------- steal work from other threads ...
5380 // ---------- ... and drain overflow list.
5381 _timer.reset();
5382 _timer.start();
5383 do_work_steal(worker_id, &par_mrias_cl, _collector->hash_seed(worker_id));
5384 _timer.stop();
5385 if (PrintCMSStatistics != 0) {
5386 gclog_or_tty->print_cr(
5387 "Finished work stealing in %dth thread: %3.3f sec",
5388 worker_id, _timer.seconds());
5389 }
5390 }
5391
5392 // Note that parameter "i" is not used.
5393 void
5394 CMSParMarkTask::do_young_space_rescan(uint worker_id,
5395 OopsInGenClosure* cl, ContiguousSpace* space,
5396 HeapWord** chunk_array, size_t chunk_top) {
5397 // Until all tasks completed:
5398 // . claim an unclaimed task
5399 // . compute region boundaries corresponding to task claimed
5400 // using chunk_array
5401 // . par_oop_iterate(cl) over that region
5402
5403 ResourceMark rm;
5404 HandleMark hm;
5405
5406 SequentialSubTasksDone* pst = space->par_seq_tasks();
5407
5408 uint nth_task = 0;
5409 uint n_tasks = pst->n_tasks();
5410
5411 if (n_tasks > 0) {
5412 assert(pst->valid(), "Uninitialized use?");
5413 HeapWord *start, *end;
5414 while (!pst->is_task_claimed(/* reference */ nth_task)) {
5415 // We claimed task # nth_task; compute its boundaries.
5416 if (chunk_top == 0) { // no samples were taken
5417 assert(nth_task == 0 && n_tasks == 1, "Can have only 1 EdenSpace task");
5418 start = space->bottom();
5419 end = space->top();
5420 } else if (nth_task == 0) {
5421 start = space->bottom();
5422 end = chunk_array[nth_task];
5423 } else if (nth_task < (uint)chunk_top) {
5424 assert(nth_task >= 1, "Control point invariant");
5425 start = chunk_array[nth_task - 1];
5426 end = chunk_array[nth_task];
5427 } else {
5428 assert(nth_task == (uint)chunk_top, "Control point invariant");
5429 start = chunk_array[chunk_top - 1];
5430 end = space->top();
5431 }
5432 MemRegion mr(start, end);
5433 // Verify that mr is in space
5434 assert(mr.is_empty() || space->used_region().contains(mr),
5435 "Should be in space");
5436 // Verify that "start" is an object boundary
5437 assert(mr.is_empty() || oop(mr.start())->is_oop(),
5438 "Should be an oop");
5439 space->par_oop_iterate(mr, cl);
5440 }
5441 pst->all_tasks_completed();
5442 }
5443 }
5444
5445 void
5446 CMSParRemarkTask::do_dirty_card_rescan_tasks(
5447 CompactibleFreeListSpace* sp, int i,
5448 Par_MarkRefsIntoAndScanClosure* cl) {
5449 // Until all tasks completed:
5450 // . claim an unclaimed task
5451 // . compute region boundaries corresponding to task claimed
5452 // . transfer dirty bits ct->mut for that region
5453 // . apply rescanclosure to dirty mut bits for that region
5454
5455 ResourceMark rm;
5456 HandleMark hm;
5457
5458 OopTaskQueue* work_q = work_queue(i);
5459 ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
5460 // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
5461 // CAUTION: This closure has state that persists across calls to
5462 // the work method dirty_range_iterate_clear() in that it has
5463 // embedded in it a (subtype of) UpwardsObjectClosure. The
5464 // use of that state in the embedded UpwardsObjectClosure instance
5465 // assumes that the cards are always iterated (even if in parallel
5466 // by several threads) in monotonically increasing order per each
5467 // thread. This is true of the implementation below which picks
5468 // card ranges (chunks) in monotonically increasing order globally
5469 // and, a-fortiori, in monotonically increasing order per thread
5470 // (the latter order being a subsequence of the former).
5471 // If the work code below is ever reorganized into a more chaotic
5472 // work-partitioning form than the current "sequential tasks"
5473 // paradigm, the use of that persistent state will have to be
5474 // revisited and modified appropriately. See also related
5475 // bug 4756801 work on which should examine this code to make
5476 // sure that the changes there do not run counter to the
5477 // assumptions made here and necessary for correctness and
5478 // efficiency. Note also that this code might yield inefficient
5479 // behavior in the case of very large objects that span one or
5480 // more work chunks. Such objects would potentially be scanned
5481 // several times redundantly. Work on 4756801 should try and
5482 // address that performance anomaly if at all possible. XXX
5483 MemRegion full_span = _collector->_span;
5484 CMSBitMap* bm = &(_collector->_markBitMap); // shared
5485 MarkFromDirtyCardsClosure
5486 greyRescanClosure(_collector, full_span, // entire span of interest
5487 sp, bm, work_q, cl);
5488
5489 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
5490 assert(pst->valid(), "Uninitialized use?");
5491 uint nth_task = 0;
5492 const int alignment = CardTableModRefBS::card_size * BitsPerWord;
5493 MemRegion span = sp->used_region();
5494 HeapWord* start_addr = span.start();
5495 HeapWord* end_addr = (HeapWord*)round_to((intptr_t)span.end(),
5496 alignment);
5497 const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
5498 assert((HeapWord*)round_to((intptr_t)start_addr, alignment) ==
5499 start_addr, "Check alignment");
5500 assert((size_t)round_to((intptr_t)chunk_size, alignment) ==
5501 chunk_size, "Check alignment");
5502
5503 while (!pst->is_task_claimed(/* reference */ nth_task)) {
5504 // Having claimed the nth_task, compute corresponding mem-region,
5505 // which is a-fortiori aligned correctly (i.e. at a MUT boundary).
5506 // The alignment restriction ensures that we do not need any
5507 // synchronization with other gang-workers while setting or
5508 // clearing bits in thus chunk of the MUT.
5509 MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
5510 start_addr + (nth_task+1)*chunk_size);
5511 // The last chunk's end might be way beyond end of the
5512 // used region. In that case pull back appropriately.
5513 if (this_span.end() > end_addr) {
5514 this_span.set_end(end_addr);
5515 assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
5516 }
5517 // Iterate over the dirty cards covering this chunk, marking them
5518 // precleaned, and setting the corresponding bits in the mod union
5519 // table. Since we have been careful to partition at Card and MUT-word
5520 // boundaries no synchronization is needed between parallel threads.
5521 _collector->_ct->ct_bs()->dirty_card_iterate(this_span,
5522 &modUnionClosure);
5523
5524 // Having transferred these marks into the modUnionTable,
5525 // rescan the marked objects on the dirty cards in the modUnionTable.
5526 // Even if this is at a synchronous collection, the initial marking
5527 // may have been done during an asynchronous collection so there
5528 // may be dirty bits in the mod-union table.
5529 _collector->_modUnionTable.dirty_range_iterate_clear(
5530 this_span, &greyRescanClosure);
5531 _collector->_modUnionTable.verifyNoOneBitsInRange(
5532 this_span.start(),
5533 this_span.end());
5534 }
5535 pst->all_tasks_completed(); // declare that i am done
5536 }
5537
5538 // . see if we can share work_queues with ParNew? XXX
5539 void
5540 CMSParRemarkTask::do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl,
5541 int* seed) {
5542 OopTaskQueue* work_q = work_queue(i);
5543 NOT_PRODUCT(int num_steals = 0;)
5544 oop obj_to_scan;
5545 CMSBitMap* bm = &(_collector->_markBitMap);
5546
5547 while (true) {
5548 // Completely finish any left over work from (an) earlier round(s)
5549 cl->trim_queue(0);
5550 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5551 (size_t)ParGCDesiredObjsFromOverflowList);
5552 // Now check if there's any work in the overflow list
5553 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5554 // only affects the number of attempts made to get work from the
5555 // overflow list and does not affect the number of workers. Just
5556 // pass ParallelGCThreads so this behavior is unchanged.
5557 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5558 work_q,
5559 ParallelGCThreads)) {
5560 // found something in global overflow list;
5561 // not yet ready to go stealing work from others.
5562 // We'd like to assert(work_q->size() != 0, ...)
5563 // because we just took work from the overflow list,
5564 // but of course we can't since all of that could have
5565 // been already stolen from us.
5566 // "He giveth and He taketh away."
5567 continue;
5568 }
5569 // Verify that we have no work before we resort to stealing
5570 assert(work_q->size() == 0, "Have work, shouldn't steal");
5571 // Try to steal from other queues that have work
5572 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5573 NOT_PRODUCT(num_steals++;)
5574 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5575 assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5576 // Do scanning work
5577 obj_to_scan->oop_iterate(cl);
5578 // Loop around, finish this work, and try to steal some more
5579 } else if (terminator()->offer_termination()) {
5580 break; // nirvana from the infinite cycle
5581 }
5582 }
5583 NOT_PRODUCT(
5584 if (PrintCMSStatistics != 0) {
5585 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5586 }
5587 )
5588 assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
5589 "Else our work is not yet done");
5590 }
5591
5592 // Record object boundaries in _eden_chunk_array by sampling the eden
5593 // top in the slow-path eden object allocation code path and record
5594 // the boundaries, if CMSEdenChunksRecordAlways is true. If
5595 // CMSEdenChunksRecordAlways is false, we use the other asynchronous
5596 // sampling in sample_eden() that activates during the part of the
5597 // preclean phase.
5598 void CMSCollector::sample_eden_chunk() {
5599 if (CMSEdenChunksRecordAlways && _eden_chunk_array != NULL) {
5600 if (_eden_chunk_lock->try_lock()) {
5601 // Record a sample. This is the critical section. The contents
5602 // of the _eden_chunk_array have to be non-decreasing in the
5603 // address order.
5604 _eden_chunk_array[_eden_chunk_index] = *_top_addr;
5605 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
5606 "Unexpected state of Eden");
5607 if (_eden_chunk_index == 0 ||
5608 ((_eden_chunk_array[_eden_chunk_index] > _eden_chunk_array[_eden_chunk_index-1]) &&
5609 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
5610 _eden_chunk_array[_eden_chunk_index-1]) >= CMSSamplingGrain))) {
5611 _eden_chunk_index++; // commit sample
5612 }
5613 _eden_chunk_lock->unlock();
5614 }
5615 }
5616 }
5617
5618 // Return a thread-local PLAB recording array, as appropriate.
5619 void* CMSCollector::get_data_recorder(int thr_num) {
5620 if (_survivor_plab_array != NULL &&
5621 (CMSPLABRecordAlways ||
5622 (_collectorState > Marking && _collectorState < FinalMarking))) {
5623 assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
5624 ChunkArray* ca = &_survivor_plab_array[thr_num];
5625 ca->reset(); // clear it so that fresh data is recorded
5626 return (void*) ca;
5627 } else {
5628 return NULL;
5629 }
5630 }
5631
5632 // Reset all the thread-local PLAB recording arrays
5633 void CMSCollector::reset_survivor_plab_arrays() {
5634 for (uint i = 0; i < ParallelGCThreads; i++) {
5635 _survivor_plab_array[i].reset();
5636 }
5637 }
5638
5639 // Merge the per-thread plab arrays into the global survivor chunk
5640 // array which will provide the partitioning of the survivor space
5641 // for CMS initial scan and rescan.
5642 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv,
5643 int no_of_gc_threads) {
5644 assert(_survivor_plab_array != NULL, "Error");
5645 assert(_survivor_chunk_array != NULL, "Error");
5646 assert(_collectorState == FinalMarking ||
5647 (CMSParallelInitialMarkEnabled && _collectorState == InitialMarking), "Error");
5648 for (int j = 0; j < no_of_gc_threads; j++) {
5649 _cursor[j] = 0;
5650 }
5651 HeapWord* top = surv->top();
5652 size_t i;
5653 for (i = 0; i < _survivor_chunk_capacity; i++) { // all sca entries
5654 HeapWord* min_val = top; // Higher than any PLAB address
5655 uint min_tid = 0; // position of min_val this round
5656 for (int j = 0; j < no_of_gc_threads; j++) {
5657 ChunkArray* cur_sca = &_survivor_plab_array[j];
5658 if (_cursor[j] == cur_sca->end()) {
5659 continue;
5660 }
5661 assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
5662 HeapWord* cur_val = cur_sca->nth(_cursor[j]);
5663 assert(surv->used_region().contains(cur_val), "Out of bounds value");
5664 if (cur_val < min_val) {
5665 min_tid = j;
5666 min_val = cur_val;
5667 } else {
5668 assert(cur_val < top, "All recorded addresses should be less");
5669 }
5670 }
5671 // At this point min_val and min_tid are respectively
5672 // the least address in _survivor_plab_array[j]->nth(_cursor[j])
5673 // and the thread (j) that witnesses that address.
5674 // We record this address in the _survivor_chunk_array[i]
5675 // and increment _cursor[min_tid] prior to the next round i.
5676 if (min_val == top) {
5677 break;
5678 }
5679 _survivor_chunk_array[i] = min_val;
5680 _cursor[min_tid]++;
5681 }
5682 // We are all done; record the size of the _survivor_chunk_array
5683 _survivor_chunk_index = i; // exclusive: [0, i)
5684 if (PrintCMSStatistics > 0) {
5685 gclog_or_tty->print(" (Survivor:" SIZE_FORMAT "chunks) ", i);
5686 }
5687 // Verify that we used up all the recorded entries
5688 #ifdef ASSERT
5689 size_t total = 0;
5690 for (int j = 0; j < no_of_gc_threads; j++) {
5691 assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
5692 total += _cursor[j];
5693 }
5694 assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
5695 // Check that the merged array is in sorted order
5696 if (total > 0) {
5697 for (size_t i = 0; i < total - 1; i++) {
5698 if (PrintCMSStatistics > 0) {
5699 gclog_or_tty->print(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
5700 i, _survivor_chunk_array[i]);
5701 }
5702 assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
5703 "Not sorted");
5704 }
5705 }
5706 #endif // ASSERT
5707 }
5708
5709 // Set up the space's par_seq_tasks structure for work claiming
5710 // for parallel initial scan and rescan of young gen.
5711 // See ParRescanTask where this is currently used.
5712 void
5713 CMSCollector::
5714 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
5715 assert(n_threads > 0, "Unexpected n_threads argument");
5716 DefNewGeneration* dng = (DefNewGeneration*)_young_gen;
5717
5718 // Eden space
5719 if (!dng->eden()->is_empty()) {
5720 SequentialSubTasksDone* pst = dng->eden()->par_seq_tasks();
5721 assert(!pst->valid(), "Clobbering existing data?");
5722 // Each valid entry in [0, _eden_chunk_index) represents a task.
5723 size_t n_tasks = _eden_chunk_index + 1;
5724 assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
5725 // Sets the condition for completion of the subtask (how many threads
5726 // need to finish in order to be done).
5727 pst->set_n_threads(n_threads);
5728 pst->set_n_tasks((int)n_tasks);
5729 }
5730
5731 // Merge the survivor plab arrays into _survivor_chunk_array
5732 if (_survivor_plab_array != NULL) {
5733 merge_survivor_plab_arrays(dng->from(), n_threads);
5734 } else {
5735 assert(_survivor_chunk_index == 0, "Error");
5736 }
5737
5738 // To space
5739 {
5740 SequentialSubTasksDone* pst = dng->to()->par_seq_tasks();
5741 assert(!pst->valid(), "Clobbering existing data?");
5742 // Sets the condition for completion of the subtask (how many threads
5743 // need to finish in order to be done).
5744 pst->set_n_threads(n_threads);
5745 pst->set_n_tasks(1);
5746 assert(pst->valid(), "Error");
5747 }
5748
5749 // From space
5750 {
5751 SequentialSubTasksDone* pst = dng->from()->par_seq_tasks();
5752 assert(!pst->valid(), "Clobbering existing data?");
5753 size_t n_tasks = _survivor_chunk_index + 1;
5754 assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
5755 // Sets the condition for completion of the subtask (how many threads
5756 // need to finish in order to be done).
5757 pst->set_n_threads(n_threads);
5758 pst->set_n_tasks((int)n_tasks);
5759 assert(pst->valid(), "Error");
5760 }
5761 }
5762
5763 // Parallel version of remark
5764 void CMSCollector::do_remark_parallel() {
5765 GenCollectedHeap* gch = GenCollectedHeap::heap();
5766 FlexibleWorkGang* workers = gch->workers();
5767 assert(workers != NULL, "Need parallel worker threads.");
5768 // Choose to use the number of GC workers most recently set
5769 // into "active_workers". If active_workers is not set, set it
5770 // to ParallelGCThreads.
5771 int n_workers = workers->active_workers();
5772 if (n_workers == 0) {
5773 assert(n_workers > 0, "Should have been set during scavenge");
5774 n_workers = ParallelGCThreads;
5775 workers->set_active_workers(n_workers);
5776 }
5777 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
5778
5779 CMSParRemarkTask tsk(this,
5780 cms_space,
5781 n_workers, workers, task_queues());
5782
5783 // Set up for parallel process_roots work.
5784 gch->set_par_threads(n_workers);
5785 // We won't be iterating over the cards in the card table updating
5786 // the younger_gen cards, so we shouldn't call the following else
5787 // the verification code as well as subsequent younger_refs_iterate
5788 // code would get confused. XXX
5789 // gch->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
5790
5791 // The young gen rescan work will not be done as part of
5792 // process_roots (which currently doesn't know how to
5793 // parallelize such a scan), but rather will be broken up into
5794 // a set of parallel tasks (via the sampling that the [abortable]
5795 // preclean phase did of EdenSpace, plus the [two] tasks of
5796 // scanning the [two] survivor spaces. Further fine-grain
5797 // parallelization of the scanning of the survivor spaces
5798 // themselves, and of precleaning of the younger gen itself
5799 // is deferred to the future.
5800 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
5801
5802 // The dirty card rescan work is broken up into a "sequence"
5803 // of parallel tasks (per constituent space) that are dynamically
5804 // claimed by the parallel threads.
5805 cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
5806
5807 // It turns out that even when we're using 1 thread, doing the work in a
5808 // separate thread causes wide variance in run times. We can't help this
5809 // in the multi-threaded case, but we special-case n=1 here to get
5810 // repeatable measurements of the 1-thread overhead of the parallel code.
5811 if (n_workers > 1) {
5812 // Make refs discovery MT-safe, if it isn't already: it may not
5813 // necessarily be so, since it's possible that we are doing
5814 // ST marking.
5815 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), true);
5816 GenCollectedHeap::StrongRootsScope srs(gch);
5817 workers->run_task(&tsk);
5818 } else {
5819 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5820 GenCollectedHeap::StrongRootsScope srs(gch);
5821 tsk.work(0);
5822 }
5823
5824 gch->set_par_threads(0); // 0 ==> non-parallel.
5825 // restore, single-threaded for now, any preserved marks
5826 // as a result of work_q overflow
5827 restore_preserved_marks_if_any();
5828 }
5829
5830 // Non-parallel version of remark
5831 void CMSCollector::do_remark_non_parallel() {
5832 ResourceMark rm;
5833 HandleMark hm;
5834 GenCollectedHeap* gch = GenCollectedHeap::heap();
5835 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5836
5837 MarkRefsIntoAndScanClosure
5838 mrias_cl(_span, ref_processor(), &_markBitMap, NULL /* not precleaning */,
5839 &_markStack, this,
5840 false /* should_yield */, false /* not precleaning */);
5841 MarkFromDirtyCardsClosure
5842 markFromDirtyCardsClosure(this, _span,
5843 NULL, // space is set further below
5844 &_markBitMap, &_markStack, &mrias_cl);
5845 {
5846 GCTraceTime t("grey object rescan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5847 // Iterate over the dirty cards, setting the corresponding bits in the
5848 // mod union table.
5849 {
5850 ModUnionClosure modUnionClosure(&_modUnionTable);
5851 _ct->ct_bs()->dirty_card_iterate(
5852 _cmsGen->used_region(),
5853 &modUnionClosure);
5854 }
5855 // Having transferred these marks into the modUnionTable, we just need
5856 // to rescan the marked objects on the dirty cards in the modUnionTable.
5857 // The initial marking may have been done during an asynchronous
5858 // collection so there may be dirty bits in the mod-union table.
5859 const int alignment =
5860 CardTableModRefBS::card_size * BitsPerWord;
5861 {
5862 // ... First handle dirty cards in CMS gen
5863 markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
5864 MemRegion ur = _cmsGen->used_region();
5865 HeapWord* lb = ur.start();
5866 HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
5867 MemRegion cms_span(lb, ub);
5868 _modUnionTable.dirty_range_iterate_clear(cms_span,
5869 &markFromDirtyCardsClosure);
5870 verify_work_stacks_empty();
5871 if (PrintCMSStatistics != 0) {
5872 gclog_or_tty->print(" (re-scanned "SIZE_FORMAT" dirty cards in cms gen) ",
5873 markFromDirtyCardsClosure.num_dirty_cards());
5874 }
5875 }
5876 }
5877 if (VerifyDuringGC &&
5878 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5879 HandleMark hm; // Discard invalid handles created during verification
5880 Universe::verify();
5881 }
5882 {
5883 GCTraceTime t("root rescan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5884
5885 verify_work_stacks_empty();
5886
5887 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
5888 GenCollectedHeap::StrongRootsScope srs(gch);
5889
5890 gch->gen_process_roots(_cmsGen->level(),
5891 true, // younger gens as roots
5892 false, // use the local StrongRootsScope
5893 SharedHeap::ScanningOption(roots_scanning_options()),
5894 should_unload_classes(),
5895 &mrias_cl,
5896 NULL,
5897 NULL); // The dirty klasses will be handled below
5898
5899 assert(should_unload_classes()
5900 || (roots_scanning_options() & SharedHeap::SO_AllCodeCache),
5901 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5902 }
5903
5904 {
5905 GCTraceTime t("visit unhandled CLDs", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5906
5907 verify_work_stacks_empty();
5908
5909 // Scan all class loader data objects that might have been introduced
5910 // during concurrent marking.
5911 ResourceMark rm;
5912 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
5913 for (int i = 0; i < array->length(); i++) {
5914 mrias_cl.do_class_loader_data(array->at(i));
5915 }
5916
5917 // We don't need to keep track of new CLDs anymore.
5918 ClassLoaderDataGraph::remember_new_clds(false);
5919
5920 verify_work_stacks_empty();
5921 }
5922
5923 {
5924 GCTraceTime t("dirty klass scan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5925
5926 verify_work_stacks_empty();
5927
5928 RemarkKlassClosure remark_klass_closure(&mrias_cl);
5929 ClassLoaderDataGraph::classes_do(&remark_klass_closure);
5930
5931 verify_work_stacks_empty();
5932 }
5933
5934 // We might have added oops to ClassLoaderData::_handles during the
5935 // concurrent marking phase. These oops point to newly allocated objects
5936 // that are guaranteed to be kept alive. Either by the direct allocation
5937 // code, or when the young collector processes the roots. Hence,
5938 // we don't have to revisit the _handles block during the remark phase.
5939
5940 verify_work_stacks_empty();
5941 // Restore evacuated mark words, if any, used for overflow list links
5942 if (!CMSOverflowEarlyRestoration) {
5943 restore_preserved_marks_if_any();
5944 }
5945 verify_overflow_empty();
5946 }
5947
5948 ////////////////////////////////////////////////////////
5949 // Parallel Reference Processing Task Proxy Class
5950 ////////////////////////////////////////////////////////
5951 class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues {
5952 typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
5953 CMSCollector* _collector;
5954 CMSBitMap* _mark_bit_map;
5955 const MemRegion _span;
5956 ProcessTask& _task;
5957
5958 public:
5959 CMSRefProcTaskProxy(ProcessTask& task,
5960 CMSCollector* collector,
5961 const MemRegion& span,
5962 CMSBitMap* mark_bit_map,
5963 AbstractWorkGang* workers,
5964 OopTaskQueueSet* task_queues):
5965 // XXX Should superclass AGTWOQ also know about AWG since it knows
5966 // about the task_queues used by the AWG? Then it could initialize
5967 // the terminator() object. See 6984287. The set_for_termination()
5968 // below is a temporary band-aid for the regression in 6984287.
5969 AbstractGangTaskWOopQueues("Process referents by policy in parallel",
5970 task_queues),
5971 _task(task),
5972 _collector(collector), _span(span), _mark_bit_map(mark_bit_map)
5973 {
5974 assert(_collector->_span.equals(_span) && !_span.is_empty(),
5975 "Inconsistency in _span");
5976 set_for_termination(workers->active_workers());
5977 }
5978
5979 OopTaskQueueSet* task_queues() { return queues(); }
5980
5981 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5982
5983 void do_work_steal(int i,
5984 CMSParDrainMarkingStackClosure* drain,
5985 CMSParKeepAliveClosure* keep_alive,
5986 int* seed);
5987
5988 virtual void work(uint worker_id);
5989 };
5990
5991 void CMSRefProcTaskProxy::work(uint worker_id) {
5992 ResourceMark rm;
5993 HandleMark hm;
5994 assert(_collector->_span.equals(_span), "Inconsistency in _span");
5995 CMSParKeepAliveClosure par_keep_alive(_collector, _span,
5996 _mark_bit_map,
5997 work_queue(worker_id));
5998 CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
5999 _mark_bit_map,
6000 work_queue(worker_id));
6001 CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
6002 _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack);
6003 if (_task.marks_oops_alive()) {
6004 do_work_steal(worker_id, &par_drain_stack, &par_keep_alive,
6005 _collector->hash_seed(worker_id));
6006 }
6007 assert(work_queue(worker_id)->size() == 0, "work_queue should be empty");
6008 assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
6009 }
6010
6011 class CMSRefEnqueueTaskProxy: public AbstractGangTask {
6012 typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
6013 EnqueueTask& _task;
6014
6015 public:
6016 CMSRefEnqueueTaskProxy(EnqueueTask& task)
6017 : AbstractGangTask("Enqueue reference objects in parallel"),
6018 _task(task)
6019 { }
6020
6021 virtual void work(uint worker_id)
6022 {
6023 _task.work(worker_id);
6024 }
6025 };
6026
6027 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
6028 MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue):
6029 _span(span),
6030 _bit_map(bit_map),
6031 _work_queue(work_queue),
6032 _mark_and_push(collector, span, bit_map, work_queue),
6033 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
6034 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads)))
6035 { }
6036
6037 // . see if we can share work_queues with ParNew? XXX
6038 void CMSRefProcTaskProxy::do_work_steal(int i,
6039 CMSParDrainMarkingStackClosure* drain,
6040 CMSParKeepAliveClosure* keep_alive,
6041 int* seed) {
6042 OopTaskQueue* work_q = work_queue(i);
6043 NOT_PRODUCT(int num_steals = 0;)
6044 oop obj_to_scan;
6045
6046 while (true) {
6047 // Completely finish any left over work from (an) earlier round(s)
6048 drain->trim_queue(0);
6049 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
6050 (size_t)ParGCDesiredObjsFromOverflowList);
6051 // Now check if there's any work in the overflow list
6052 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
6053 // only affects the number of attempts made to get work from the
6054 // overflow list and does not affect the number of workers. Just
6055 // pass ParallelGCThreads so this behavior is unchanged.
6056 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
6057 work_q,
6058 ParallelGCThreads)) {
6059 // Found something in global overflow list;
6060 // not yet ready to go stealing work from others.
6061 // We'd like to assert(work_q->size() != 0, ...)
6062 // because we just took work from the overflow list,
6063 // but of course we can't, since all of that might have
6064 // been already stolen from us.
6065 continue;
6066 }
6067 // Verify that we have no work before we resort to stealing
6068 assert(work_q->size() == 0, "Have work, shouldn't steal");
6069 // Try to steal from other queues that have work
6070 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
6071 NOT_PRODUCT(num_steals++;)
6072 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
6073 assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
6074 // Do scanning work
6075 obj_to_scan->oop_iterate(keep_alive);
6076 // Loop around, finish this work, and try to steal some more
6077 } else if (terminator()->offer_termination()) {
6078 break; // nirvana from the infinite cycle
6079 }
6080 }
6081 NOT_PRODUCT(
6082 if (PrintCMSStatistics != 0) {
6083 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
6084 }
6085 )
6086 }
6087
6088 void CMSRefProcTaskExecutor::execute(ProcessTask& task)
6089 {
6090 GenCollectedHeap* gch = GenCollectedHeap::heap();
6091 FlexibleWorkGang* workers = gch->workers();
6092 assert(workers != NULL, "Need parallel worker threads.");
6093 CMSRefProcTaskProxy rp_task(task, &_collector,
6094 _collector.ref_processor()->span(),
6095 _collector.markBitMap(),
6096 workers, _collector.task_queues());
6097 workers->run_task(&rp_task);
6098 }
6099
6100 void CMSRefProcTaskExecutor::execute(EnqueueTask& task)
6101 {
6102
6103 GenCollectedHeap* gch = GenCollectedHeap::heap();
6104 FlexibleWorkGang* workers = gch->workers();
6105 assert(workers != NULL, "Need parallel worker threads.");
6106 CMSRefEnqueueTaskProxy enq_task(task);
6107 workers->run_task(&enq_task);
6108 }
6109
6110 void CMSCollector::refProcessingWork(bool asynch, bool clear_all_soft_refs) {
6111
6112 ResourceMark rm;
6113 HandleMark hm;
6114
6115 ReferenceProcessor* rp = ref_processor();
6116 assert(rp->span().equals(_span), "Spans should be equal");
6117 assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
6118 // Process weak references.
6119 rp->setup_policy(clear_all_soft_refs);
6120 verify_work_stacks_empty();
6121
6122 CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
6123 &_markStack, false /* !preclean */);
6124 CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
6125 _span, &_markBitMap, &_markStack,
6126 &cmsKeepAliveClosure, false /* !preclean */);
6127 {
6128 GCTraceTime t("weak refs processing", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
6129
6130 ReferenceProcessorStats stats;
6131 if (rp->processing_is_mt()) {
6132 // Set the degree of MT here. If the discovery is done MT, there
6133 // may have been a different number of threads doing the discovery
6134 // and a different number of discovered lists may have Ref objects.
6135 // That is OK as long as the Reference lists are balanced (see
6136 // balance_all_queues() and balance_queues()).
6137 GenCollectedHeap* gch = GenCollectedHeap::heap();
6138 int active_workers = ParallelGCThreads;
6139 FlexibleWorkGang* workers = gch->workers();
6140 if (workers != NULL) {
6141 active_workers = workers->active_workers();
6142 // The expectation is that active_workers will have already
6143 // been set to a reasonable value. If it has not been set,
6144 // investigate.
6145 assert(active_workers > 0, "Should have been set during scavenge");
6146 }
6147 rp->set_active_mt_degree(active_workers);
6148 CMSRefProcTaskExecutor task_executor(*this);
6149 stats = rp->process_discovered_references(&_is_alive_closure,
6150 &cmsKeepAliveClosure,
6151 &cmsDrainMarkingStackClosure,
6152 &task_executor,
6153 _gc_timer_cm,
6154 _gc_tracer_cm->gc_id());
6155 } else {
6156 stats = rp->process_discovered_references(&_is_alive_closure,
6157 &cmsKeepAliveClosure,
6158 &cmsDrainMarkingStackClosure,
6159 NULL,
6160 _gc_timer_cm,
6161 _gc_tracer_cm->gc_id());
6162 }
6163 _gc_tracer_cm->report_gc_reference_stats(stats);
6164
6165 }
6166
6167 // This is the point where the entire marking should have completed.
6168 verify_work_stacks_empty();
6169
6170 if (should_unload_classes()) {
6171 {
6172 GCTraceTime t("class unloading", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
6173
6174 // Unload classes and purge the SystemDictionary.
6175 bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure);
6176
6177 // Unload nmethods.
6178 CodeCache::do_unloading(&_is_alive_closure, purged_class);
6179
6180 // Prune dead klasses from subklass/sibling/implementor lists.
6181 Klass::clean_weak_klass_links(&_is_alive_closure);
6182 }
6183
6184 {
6185 GCTraceTime t("scrub symbol table", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
6186 // Clean up unreferenced symbols in symbol table.
6187 SymbolTable::unlink();
6188 }
6189
6190 {
6191 GCTraceTime t("scrub string table", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
6192 // Delete entries for dead interned strings.
6193 StringTable::unlink(&_is_alive_closure);
6194 }
6195 }
6196
6197
6198 // Restore any preserved marks as a result of mark stack or
6199 // work queue overflow
6200 restore_preserved_marks_if_any(); // done single-threaded for now
6201
6202 rp->set_enqueuing_is_done(true);
6203 if (rp->processing_is_mt()) {
6204 rp->balance_all_queues();
6205 CMSRefProcTaskExecutor task_executor(*this);
6206 rp->enqueue_discovered_references(&task_executor);
6207 } else {
6208 rp->enqueue_discovered_references(NULL);
6209 }
6210 rp->verify_no_references_recorded();
6211 assert(!rp->discovery_enabled(), "should have been disabled");
6212 }
6213
6214 #ifndef PRODUCT
6215 void CMSCollector::check_correct_thread_executing() {
6216 Thread* t = Thread::current();
6217 // Only the VM thread or the CMS thread should be here.
6218 assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
6219 "Unexpected thread type");
6220 // If this is the vm thread, the foreground process
6221 // should not be waiting. Note that _foregroundGCIsActive is
6222 // true while the foreground collector is waiting.
6223 if (_foregroundGCShouldWait) {
6224 // We cannot be the VM thread
6225 assert(t->is_ConcurrentGC_thread(),
6226 "Should be CMS thread");
6227 } else {
6228 // We can be the CMS thread only if we are in a stop-world
6229 // phase of CMS collection.
6230 if (t->is_ConcurrentGC_thread()) {
6231 assert(_collectorState == InitialMarking ||
6232 _collectorState == FinalMarking,
6233 "Should be a stop-world phase");
6234 // The CMS thread should be holding the CMS_token.
6235 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6236 "Potential interference with concurrently "
6237 "executing VM thread");
6238 }
6239 }
6240 }
6241 #endif
6242
6243 void CMSCollector::sweep(bool asynch) {
6244 assert(_collectorState == Sweeping, "just checking");
6245 check_correct_thread_executing();
6246 verify_work_stacks_empty();
6247 verify_overflow_empty();
6248 increment_sweep_count();
6249 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
6250
6251 _inter_sweep_timer.stop();
6252 _inter_sweep_estimate.sample(_inter_sweep_timer.seconds());
6253
6254 assert(!_intra_sweep_timer.is_active(), "Should not be active");
6255 _intra_sweep_timer.reset();
6256 _intra_sweep_timer.start();
6257 if (asynch) {
6258 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6259 CMSPhaseAccounting pa(this, "sweep", _gc_tracer_cm->gc_id(), !PrintGCDetails);
6260 // First sweep the old gen
6261 {
6262 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
6263 bitMapLock());
6264 sweepWork(_cmsGen, asynch);
6265 }
6266
6267 // Update Universe::_heap_*_at_gc figures.
6268 // We need all the free list locks to make the abstract state
6269 // transition from Sweeping to Resetting. See detailed note
6270 // further below.
6271 {
6272 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock());
6273 // Update heap occupancy information which is used as
6274 // input to soft ref clearing policy at the next gc.
6275 Universe::update_heap_info_at_gc();
6276 _collectorState = Resizing;
6277 }
6278 } else {
6279 // already have needed locks
6280 sweepWork(_cmsGen, asynch);
6281 // Update heap occupancy information which is used as
6282 // input to soft ref clearing policy at the next gc.
6283 Universe::update_heap_info_at_gc();
6284 _collectorState = Resizing;
6285 }
6286 verify_work_stacks_empty();
6287 verify_overflow_empty();
6288
6289 if (should_unload_classes()) {
6290 // Delay purge to the beginning of the next safepoint. Metaspace::contains
6291 // requires that the virtual spaces are stable and not deleted.
6292 ClassLoaderDataGraph::set_should_purge(true);
6293 }
6294
6295 _intra_sweep_timer.stop();
6296 _intra_sweep_estimate.sample(_intra_sweep_timer.seconds());
6297
6298 _inter_sweep_timer.reset();
6299 _inter_sweep_timer.start();
6300
6301 // We need to use a monotonically non-decreasing time in ms
6302 // or we will see time-warp warnings and os::javaTimeMillis()
6303 // does not guarantee monotonicity.
6304 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
6305 update_time_of_last_gc(now);
6306
6307 // NOTE on abstract state transitions:
6308 // Mutators allocate-live and/or mark the mod-union table dirty
6309 // based on the state of the collection. The former is done in
6310 // the interval [Marking, Sweeping] and the latter in the interval
6311 // [Marking, Sweeping). Thus the transitions into the Marking state
6312 // and out of the Sweeping state must be synchronously visible
6313 // globally to the mutators.
6314 // The transition into the Marking state happens with the world
6315 // stopped so the mutators will globally see it. Sweeping is
6316 // done asynchronously by the background collector so the transition
6317 // from the Sweeping state to the Resizing state must be done
6318 // under the freelistLock (as is the check for whether to
6319 // allocate-live and whether to dirty the mod-union table).
6320 assert(_collectorState == Resizing, "Change of collector state to"
6321 " Resizing must be done under the freelistLocks (plural)");
6322
6323 // Now that sweeping has been completed, we clear
6324 // the incremental_collection_failed flag,
6325 // thus inviting a younger gen collection to promote into
6326 // this generation. If such a promotion may still fail,
6327 // the flag will be set again when a young collection is
6328 // attempted.
6329 GenCollectedHeap* gch = GenCollectedHeap::heap();
6330 gch->clear_incremental_collection_failed(); // Worth retrying as fresh space may have been freed up
6331 gch->update_full_collections_completed(_collection_count_start);
6332 }
6333
6334 // FIX ME!!! Looks like this belongs in CFLSpace, with
6335 // CMSGen merely delegating to it.
6336 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
6337 double nearLargestPercent = FLSLargestBlockCoalesceProximity;
6338 HeapWord* minAddr = _cmsSpace->bottom();
6339 HeapWord* largestAddr =
6340 (HeapWord*) _cmsSpace->dictionary()->find_largest_dict();
6341 if (largestAddr == NULL) {
6342 // The dictionary appears to be empty. In this case
6343 // try to coalesce at the end of the heap.
6344 largestAddr = _cmsSpace->end();
6345 }
6346 size_t largestOffset = pointer_delta(largestAddr, minAddr);
6347 size_t nearLargestOffset =
6348 (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
6349 if (PrintFLSStatistics != 0) {
6350 gclog_or_tty->print_cr(
6351 "CMS: Large Block: " PTR_FORMAT ";"
6352 " Proximity: " PTR_FORMAT " -> " PTR_FORMAT,
6353 largestAddr,
6354 _cmsSpace->nearLargestChunk(), minAddr + nearLargestOffset);
6355 }
6356 _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
6357 }
6358
6359 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
6360 return addr >= _cmsSpace->nearLargestChunk();
6361 }
6362
6363 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
6364 return _cmsSpace->find_chunk_at_end();
6365 }
6366
6367 void ConcurrentMarkSweepGeneration::update_gc_stats(int current_level,
6368 bool full) {
6369 // The next lower level has been collected. Gather any statistics
6370 // that are of interest at this point.
6371 if (!full && (current_level + 1) == level()) {
6372 // Gather statistics on the young generation collection.
6373 collector()->stats().record_gc0_end(used());
6374 }
6375 }
6376
6377 void ConcurrentMarkSweepGeneration::rotate_debug_collection_type() {
6378 if (PrintGCDetails && Verbose) {
6379 gclog_or_tty->print("Rotate from %d ", _debug_collection_type);
6380 }
6381 _debug_collection_type = (CollectionTypes) (_debug_collection_type + 1);
6382 _debug_collection_type =
6383 (CollectionTypes) (_debug_collection_type % Unknown_collection_type);
6384 if (PrintGCDetails && Verbose) {
6385 gclog_or_tty->print_cr("to %d ", _debug_collection_type);
6386 }
6387 }
6388
6389 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* gen,
6390 bool asynch) {
6391 // We iterate over the space(s) underlying this generation,
6392 // checking the mark bit map to see if the bits corresponding
6393 // to specific blocks are marked or not. Blocks that are
6394 // marked are live and are not swept up. All remaining blocks
6395 // are swept up, with coalescing on-the-fly as we sweep up
6396 // contiguous free and/or garbage blocks:
6397 // We need to ensure that the sweeper synchronizes with allocators
6398 // and stop-the-world collectors. In particular, the following
6399 // locks are used:
6400 // . CMS token: if this is held, a stop the world collection cannot occur
6401 // . freelistLock: if this is held no allocation can occur from this
6402 // generation by another thread
6403 // . bitMapLock: if this is held, no other thread can access or update
6404 //
6405
6406 // Note that we need to hold the freelistLock if we use
6407 // block iterate below; else the iterator might go awry if
6408 // a mutator (or promotion) causes block contents to change
6409 // (for instance if the allocator divvies up a block).
6410 // If we hold the free list lock, for all practical purposes
6411 // young generation GC's can't occur (they'll usually need to
6412 // promote), so we might as well prevent all young generation
6413 // GC's while we do a sweeping step. For the same reason, we might
6414 // as well take the bit map lock for the entire duration
6415
6416 // check that we hold the requisite locks
6417 assert(have_cms_token(), "Should hold cms token");
6418 assert( (asynch && ConcurrentMarkSweepThread::cms_thread_has_cms_token())
6419 || (!asynch && ConcurrentMarkSweepThread::vm_thread_has_cms_token()),
6420 "Should possess CMS token to sweep");
6421 assert_lock_strong(gen->freelistLock());
6422 assert_lock_strong(bitMapLock());
6423
6424 assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context");
6425 assert(_intra_sweep_timer.is_active(), "Was switched on in an outer context");
6426 gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
6427 _inter_sweep_estimate.padded_average(),
6428 _intra_sweep_estimate.padded_average());
6429 gen->setNearLargestChunk();
6430
6431 {
6432 SweepClosure sweepClosure(this, gen, &_markBitMap,
6433 CMSYield && asynch);
6434 gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
6435 // We need to free-up/coalesce garbage/blocks from a
6436 // co-terminal free run. This is done in the SweepClosure
6437 // destructor; so, do not remove this scope, else the
6438 // end-of-sweep-census below will be off by a little bit.
6439 }
6440 gen->cmsSpace()->sweep_completed();
6441 gen->cmsSpace()->endSweepFLCensus(sweep_count());
6442 if (should_unload_classes()) { // unloaded classes this cycle,
6443 _concurrent_cycles_since_last_unload = 0; // ... reset count
6444 } else { // did not unload classes,
6445 _concurrent_cycles_since_last_unload++; // ... increment count
6446 }
6447 }
6448
6449 // Reset CMS data structures (for now just the marking bit map)
6450 // preparatory for the next cycle.
6451 void CMSCollector::reset(bool asynch) {
6452 if (asynch) {
6453 CMSTokenSyncWithLocks ts(true, bitMapLock());
6454
6455 // If the state is not "Resetting", the foreground thread
6456 // has done a collection and the resetting.
6457 if (_collectorState != Resetting) {
6458 assert(_collectorState == Idling, "The state should only change"
6459 " because the foreground collector has finished the collection");
6460 return;
6461 }
6462
6463 // Clear the mark bitmap (no grey objects to start with)
6464 // for the next cycle.
6465 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6466 CMSPhaseAccounting cmspa(this, "reset", _gc_tracer_cm->gc_id(), !PrintGCDetails);
6467
6468 HeapWord* curAddr = _markBitMap.startWord();
6469 while (curAddr < _markBitMap.endWord()) {
6470 size_t remaining = pointer_delta(_markBitMap.endWord(), curAddr);
6471 MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
6472 _markBitMap.clear_large_range(chunk);
6473 if (ConcurrentMarkSweepThread::should_yield() &&
6474 !foregroundGCIsActive() &&
6475 CMSYield) {
6476 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6477 "CMS thread should hold CMS token");
6478 assert_lock_strong(bitMapLock());
6479 bitMapLock()->unlock();
6480 ConcurrentMarkSweepThread::desynchronize(true);
6481 ConcurrentMarkSweepThread::acknowledge_yield_request();
6482 stopTimer();
6483 if (PrintCMSStatistics != 0) {
6484 incrementYields();
6485 }
6486 icms_wait();
6487
6488 // See the comment in coordinator_yield()
6489 for (unsigned i = 0; i < CMSYieldSleepCount &&
6490 ConcurrentMarkSweepThread::should_yield() &&
6491 !CMSCollector::foregroundGCIsActive(); ++i) {
6492 os::sleep(Thread::current(), 1, false);
6493 ConcurrentMarkSweepThread::acknowledge_yield_request();
6494 }
6495
6496 ConcurrentMarkSweepThread::synchronize(true);
6497 bitMapLock()->lock_without_safepoint_check();
6498 startTimer();
6499 }
6500 curAddr = chunk.end();
6501 }
6502 // A successful mostly concurrent collection has been done.
6503 // Because only the full (i.e., concurrent mode failure) collections
6504 // are being measured for gc overhead limits, clean the "near" flag
6505 // and count.
6506 size_policy()->reset_gc_overhead_limit_count();
6507 _collectorState = Idling;
6508 } else {
6509 // already have the lock
6510 assert(_collectorState == Resetting, "just checking");
6511 assert_lock_strong(bitMapLock());
6512 _markBitMap.clear_all();
6513 _collectorState = Idling;
6514 }
6515
6516 // Stop incremental mode after a cycle completes, so that any future cycles
6517 // are triggered by allocation.
6518 stop_icms();
6519
6520 NOT_PRODUCT(
6521 if (RotateCMSCollectionTypes) {
6522 _cmsGen->rotate_debug_collection_type();
6523 }
6524 )
6525
6526 register_gc_end();
6527 }
6528
6529 void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) {
6530 gclog_or_tty->date_stamp(PrintGC && PrintGCDateStamps);
6531 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6532 GCTraceTime t(GCCauseString("GC", gc_cause), PrintGC, !PrintGCDetails, NULL, _gc_tracer_cm->gc_id());
6533 TraceCollectorStats tcs(counters());
6534
6535 switch (op) {
6536 case CMS_op_checkpointRootsInitial: {
6537 SvcGCMarker sgcm(SvcGCMarker::OTHER);
6538 checkpointRootsInitial(true); // asynch
6539 if (PrintGC) {
6540 _cmsGen->printOccupancy("initial-mark");
6541 }
6542 break;
6543 }
6544 case CMS_op_checkpointRootsFinal: {
6545 SvcGCMarker sgcm(SvcGCMarker::OTHER);
6546 checkpointRootsFinal(true, // asynch
6547 false, // !clear_all_soft_refs
6548 false); // !init_mark_was_synchronous
6549 if (PrintGC) {
6550 _cmsGen->printOccupancy("remark");
6551 }
6552 break;
6553 }
6554 default:
6555 fatal("No such CMS_op");
6556 }
6557 }
6558
6559 #ifndef PRODUCT
6560 size_t const CMSCollector::skip_header_HeapWords() {
6561 return FreeChunk::header_size();
6562 }
6563
6564 // Try and collect here conditions that should hold when
6565 // CMS thread is exiting. The idea is that the foreground GC
6566 // thread should not be blocked if it wants to terminate
6567 // the CMS thread and yet continue to run the VM for a while
6568 // after that.
6569 void CMSCollector::verify_ok_to_terminate() const {
6570 assert(Thread::current()->is_ConcurrentGC_thread(),
6571 "should be called by CMS thread");
6572 assert(!_foregroundGCShouldWait, "should be false");
6573 // We could check here that all the various low-level locks
6574 // are not held by the CMS thread, but that is overkill; see
6575 // also CMSThread::verify_ok_to_terminate() where the CGC_lock
6576 // is checked.
6577 }
6578 #endif
6579
6580 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
6581 assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
6582 "missing Printezis mark?");
6583 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
6584 size_t size = pointer_delta(nextOneAddr + 1, addr);
6585 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6586 "alignment problem");
6587 assert(size >= 3, "Necessary for Printezis marks to work");
6588 return size;
6589 }
6590
6591 // A variant of the above (block_size_using_printezis_bits()) except
6592 // that we return 0 if the P-bits are not yet set.
6593 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
6594 if (_markBitMap.isMarked(addr + 1)) {
6595 assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects");
6596 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
6597 size_t size = pointer_delta(nextOneAddr + 1, addr);
6598 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6599 "alignment problem");
6600 assert(size >= 3, "Necessary for Printezis marks to work");
6601 return size;
6602 }
6603 return 0;
6604 }
6605
6606 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
6607 size_t sz = 0;
6608 oop p = (oop)addr;
6609 if (p->klass_or_null() != NULL) {
6610 sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
6611 } else {
6612 sz = block_size_using_printezis_bits(addr);
6613 }
6614 assert(sz > 0, "size must be nonzero");
6615 HeapWord* next_block = addr + sz;
6616 HeapWord* next_card = (HeapWord*)round_to((uintptr_t)next_block,
6617 CardTableModRefBS::card_size);
6618 assert(round_down((uintptr_t)addr, CardTableModRefBS::card_size) <
6619 round_down((uintptr_t)next_card, CardTableModRefBS::card_size),
6620 "must be different cards");
6621 return next_card;
6622 }
6623
6624
6625 // CMS Bit Map Wrapper /////////////////////////////////////////
6626
6627 // Construct a CMS bit map infrastructure, but don't create the
6628 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
6629 // further below.
6630 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
6631 _bm(),
6632 _shifter(shifter),
6633 _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true) : NULL)
6634 {
6635 _bmStartWord = 0;
6636 _bmWordSize = 0;
6637 }
6638
6639 bool CMSBitMap::allocate(MemRegion mr) {
6640 _bmStartWord = mr.start();
6641 _bmWordSize = mr.word_size();
6642 ReservedSpace brs(ReservedSpace::allocation_align_size_up(
6643 (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
6644 if (!brs.is_reserved()) {
6645 warning("CMS bit map allocation failure");
6646 return false;
6647 }
6648 // For now we'll just commit all of the bit map up front.
6649 // Later on we'll try to be more parsimonious with swap.
6650 if (!_virtual_space.initialize(brs, brs.size())) {
6651 warning("CMS bit map backing store failure");
6652 return false;
6653 }
6654 assert(_virtual_space.committed_size() == brs.size(),
6655 "didn't reserve backing store for all of CMS bit map?");
6656 _bm.set_map((BitMap::bm_word_t*)_virtual_space.low());
6657 assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
6658 _bmWordSize, "inconsistency in bit map sizing");
6659 _bm.set_size(_bmWordSize >> _shifter);
6660
6661 // bm.clear(); // can we rely on getting zero'd memory? verify below
6662 assert(isAllClear(),
6663 "Expected zero'd memory from ReservedSpace constructor");
6664 assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
6665 "consistency check");
6666 return true;
6667 }
6668
6669 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
6670 HeapWord *next_addr, *end_addr, *last_addr;
6671 assert_locked();
6672 assert(covers(mr), "out-of-range error");
6673 // XXX assert that start and end are appropriately aligned
6674 for (next_addr = mr.start(), end_addr = mr.end();
6675 next_addr < end_addr; next_addr = last_addr) {
6676 MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
6677 last_addr = dirty_region.end();
6678 if (!dirty_region.is_empty()) {
6679 cl->do_MemRegion(dirty_region);
6680 } else {
6681 assert(last_addr == end_addr, "program logic");
6682 return;
6683 }
6684 }
6685 }
6686
6687 void CMSBitMap::print_on_error(outputStream* st, const char* prefix) const {
6688 _bm.print_on_error(st, prefix);
6689 }
6690
6691 #ifndef PRODUCT
6692 void CMSBitMap::assert_locked() const {
6693 CMSLockVerifier::assert_locked(lock());
6694 }
6695
6696 bool CMSBitMap::covers(MemRegion mr) const {
6697 // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
6698 assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
6699 "size inconsistency");
6700 return (mr.start() >= _bmStartWord) &&
6701 (mr.end() <= endWord());
6702 }
6703
6704 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
6705 return (start >= _bmStartWord && (start + size) <= endWord());
6706 }
6707
6708 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
6709 // verify that there are no 1 bits in the interval [left, right)
6710 FalseBitMapClosure falseBitMapClosure;
6711 iterate(&falseBitMapClosure, left, right);
6712 }
6713
6714 void CMSBitMap::region_invariant(MemRegion mr)
6715 {
6716 assert_locked();
6717 // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
6718 assert(!mr.is_empty(), "unexpected empty region");
6719 assert(covers(mr), "mr should be covered by bit map");
6720 // convert address range into offset range
6721 size_t start_ofs = heapWordToOffset(mr.start());
6722 // Make sure that end() is appropriately aligned
6723 assert(mr.end() == (HeapWord*)round_to((intptr_t)mr.end(),
6724 (1 << (_shifter+LogHeapWordSize))),
6725 "Misaligned mr.end()");
6726 size_t end_ofs = heapWordToOffset(mr.end());
6727 assert(end_ofs > start_ofs, "Should mark at least one bit");
6728 }
6729
6730 #endif
6731
6732 bool CMSMarkStack::allocate(size_t size) {
6733 // allocate a stack of the requisite depth
6734 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6735 size * sizeof(oop)));
6736 if (!rs.is_reserved()) {
6737 warning("CMSMarkStack allocation failure");
6738 return false;
6739 }
6740 if (!_virtual_space.initialize(rs, rs.size())) {
6741 warning("CMSMarkStack backing store failure");
6742 return false;
6743 }
6744 assert(_virtual_space.committed_size() == rs.size(),
6745 "didn't reserve backing store for all of CMS stack?");
6746 _base = (oop*)(_virtual_space.low());
6747 _index = 0;
6748 _capacity = size;
6749 NOT_PRODUCT(_max_depth = 0);
6750 return true;
6751 }
6752
6753 // XXX FIX ME !!! In the MT case we come in here holding a
6754 // leaf lock. For printing we need to take a further lock
6755 // which has lower rank. We need to recalibrate the two
6756 // lock-ranks involved in order to be able to print the
6757 // messages below. (Or defer the printing to the caller.
6758 // For now we take the expedient path of just disabling the
6759 // messages for the problematic case.)
6760 void CMSMarkStack::expand() {
6761 assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted");
6762 if (_capacity == MarkStackSizeMax) {
6763 if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6764 // We print a warning message only once per CMS cycle.
6765 gclog_or_tty->print_cr(" (benign) Hit CMSMarkStack max size limit");
6766 }
6767 return;
6768 }
6769 // Double capacity if possible
6770 size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax);
6771 // Do not give up existing stack until we have managed to
6772 // get the double capacity that we desired.
6773 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6774 new_capacity * sizeof(oop)));
6775 if (rs.is_reserved()) {
6776 // Release the backing store associated with old stack
6777 _virtual_space.release();
6778 // Reinitialize virtual space for new stack
6779 if (!_virtual_space.initialize(rs, rs.size())) {
6780 fatal("Not enough swap for expanded marking stack");
6781 }
6782 _base = (oop*)(_virtual_space.low());
6783 _index = 0;
6784 _capacity = new_capacity;
6785 } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6786 // Failed to double capacity, continue;
6787 // we print a detail message only once per CMS cycle.
6788 gclog_or_tty->print(" (benign) Failed to expand marking stack from "SIZE_FORMAT"K to "
6789 SIZE_FORMAT"K",
6790 _capacity / K, new_capacity / K);
6791 }
6792 }
6793
6794
6795 // Closures
6796 // XXX: there seems to be a lot of code duplication here;
6797 // should refactor and consolidate common code.
6798
6799 // This closure is used to mark refs into the CMS generation in
6800 // the CMS bit map. Called at the first checkpoint. This closure
6801 // assumes that we do not need to re-mark dirty cards; if the CMS
6802 // generation on which this is used is not an oldest
6803 // generation then this will lose younger_gen cards!
6804
6805 MarkRefsIntoClosure::MarkRefsIntoClosure(
6806 MemRegion span, CMSBitMap* bitMap):
6807 _span(span),
6808 _bitMap(bitMap)
6809 {
6810 assert(_ref_processor == NULL, "deliberately left NULL");
6811 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6812 }
6813
6814 void MarkRefsIntoClosure::do_oop(oop obj) {
6815 // if p points into _span, then mark corresponding bit in _markBitMap
6816 assert(obj->is_oop(), "expected an oop");
6817 HeapWord* addr = (HeapWord*)obj;
6818 if (_span.contains(addr)) {
6819 // this should be made more efficient
6820 _bitMap->mark(addr);
6821 }
6822 }
6823
6824 void MarkRefsIntoClosure::do_oop(oop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6825 void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6826
6827 Par_MarkRefsIntoClosure::Par_MarkRefsIntoClosure(
6828 MemRegion span, CMSBitMap* bitMap):
6829 _span(span),
6830 _bitMap(bitMap)
6831 {
6832 assert(_ref_processor == NULL, "deliberately left NULL");
6833 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6834 }
6835
6836 void Par_MarkRefsIntoClosure::do_oop(oop obj) {
6837 // if p points into _span, then mark corresponding bit in _markBitMap
6838 assert(obj->is_oop(), "expected an oop");
6839 HeapWord* addr = (HeapWord*)obj;
6840 if (_span.contains(addr)) {
6841 // this should be made more efficient
6842 _bitMap->par_mark(addr);
6843 }
6844 }
6845
6846 void Par_MarkRefsIntoClosure::do_oop(oop* p) { Par_MarkRefsIntoClosure::do_oop_work(p); }
6847 void Par_MarkRefsIntoClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoClosure::do_oop_work(p); }
6848
6849 // A variant of the above, used for CMS marking verification.
6850 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
6851 MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm):
6852 _span(span),
6853 _verification_bm(verification_bm),
6854 _cms_bm(cms_bm)
6855 {
6856 assert(_ref_processor == NULL, "deliberately left NULL");
6857 assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
6858 }
6859
6860 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
6861 // if p points into _span, then mark corresponding bit in _markBitMap
6862 assert(obj->is_oop(), "expected an oop");
6863 HeapWord* addr = (HeapWord*)obj;
6864 if (_span.contains(addr)) {
6865 _verification_bm->mark(addr);
6866 if (!_cms_bm->isMarked(addr)) {
6867 oop(addr)->print();
6868 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)", addr);
6869 fatal("... aborting");
6870 }
6871 }
6872 }
6873
6874 void MarkRefsIntoVerifyClosure::do_oop(oop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6875 void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6876
6877 //////////////////////////////////////////////////
6878 // MarkRefsIntoAndScanClosure
6879 //////////////////////////////////////////////////
6880
6881 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
6882 ReferenceProcessor* rp,
6883 CMSBitMap* bit_map,
6884 CMSBitMap* mod_union_table,
6885 CMSMarkStack* mark_stack,
6886 CMSCollector* collector,
6887 bool should_yield,
6888 bool concurrent_precleaning):
6889 _collector(collector),
6890 _span(span),
6891 _bit_map(bit_map),
6892 _mark_stack(mark_stack),
6893 _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table,
6894 mark_stack, concurrent_precleaning),
6895 _yield(should_yield),
6896 _concurrent_precleaning(concurrent_precleaning),
6897 _freelistLock(NULL)
6898 {
6899 _ref_processor = rp;
6900 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6901 }
6902
6903 // This closure is used to mark refs into the CMS generation at the
6904 // second (final) checkpoint, and to scan and transitively follow
6905 // the unmarked oops. It is also used during the concurrent precleaning
6906 // phase while scanning objects on dirty cards in the CMS generation.
6907 // The marks are made in the marking bit map and the marking stack is
6908 // used for keeping the (newly) grey objects during the scan.
6909 // The parallel version (Par_...) appears further below.
6910 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6911 if (obj != NULL) {
6912 assert(obj->is_oop(), "expected an oop");
6913 HeapWord* addr = (HeapWord*)obj;
6914 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6915 assert(_collector->overflow_list_is_empty(),
6916 "overflow list should be empty");
6917 if (_span.contains(addr) &&
6918 !_bit_map->isMarked(addr)) {
6919 // mark bit map (object is now grey)
6920 _bit_map->mark(addr);
6921 // push on marking stack (stack should be empty), and drain the
6922 // stack by applying this closure to the oops in the oops popped
6923 // from the stack (i.e. blacken the grey objects)
6924 bool res = _mark_stack->push(obj);
6925 assert(res, "Should have space to push on empty stack");
6926 do {
6927 oop new_oop = _mark_stack->pop();
6928 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6929 assert(_bit_map->isMarked((HeapWord*)new_oop),
6930 "only grey objects on this stack");
6931 // iterate over the oops in this oop, marking and pushing
6932 // the ones in CMS heap (i.e. in _span).
6933 new_oop->oop_iterate(&_pushAndMarkClosure);
6934 // check if it's time to yield
6935 do_yield_check();
6936 } while (!_mark_stack->isEmpty() ||
6937 (!_concurrent_precleaning && take_from_overflow_list()));
6938 // if marking stack is empty, and we are not doing this
6939 // during precleaning, then check the overflow list
6940 }
6941 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6942 assert(_collector->overflow_list_is_empty(),
6943 "overflow list was drained above");
6944 // We could restore evacuated mark words, if any, used for
6945 // overflow list links here because the overflow list is
6946 // provably empty here. That would reduce the maximum
6947 // size requirements for preserved_{oop,mark}_stack.
6948 // But we'll just postpone it until we are all done
6949 // so we can just stream through.
6950 if (!_concurrent_precleaning && CMSOverflowEarlyRestoration) {
6951 _collector->restore_preserved_marks_if_any();
6952 assert(_collector->no_preserved_marks(), "No preserved marks");
6953 }
6954 assert(!CMSOverflowEarlyRestoration || _collector->no_preserved_marks(),
6955 "All preserved marks should have been restored above");
6956 }
6957 }
6958
6959 void MarkRefsIntoAndScanClosure::do_oop(oop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6960 void MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6961
6962 void MarkRefsIntoAndScanClosure::do_yield_work() {
6963 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6964 "CMS thread should hold CMS token");
6965 assert_lock_strong(_freelistLock);
6966 assert_lock_strong(_bit_map->lock());
6967 // relinquish the free_list_lock and bitMaplock()
6968 _bit_map->lock()->unlock();
6969 _freelistLock->unlock();
6970 ConcurrentMarkSweepThread::desynchronize(true);
6971 ConcurrentMarkSweepThread::acknowledge_yield_request();
6972 _collector->stopTimer();
6973 if (PrintCMSStatistics != 0) {
6974 _collector->incrementYields();
6975 }
6976 _collector->icms_wait();
6977
6978 // See the comment in coordinator_yield()
6979 for (unsigned i = 0;
6980 i < CMSYieldSleepCount &&
6981 ConcurrentMarkSweepThread::should_yield() &&
6982 !CMSCollector::foregroundGCIsActive();
6983 ++i) {
6984 os::sleep(Thread::current(), 1, false);
6985 ConcurrentMarkSweepThread::acknowledge_yield_request();
6986 }
6987
6988 ConcurrentMarkSweepThread::synchronize(true);
6989 _freelistLock->lock_without_safepoint_check();
6990 _bit_map->lock()->lock_without_safepoint_check();
6991 _collector->startTimer();
6992 }
6993
6994 ///////////////////////////////////////////////////////////
6995 // Par_MarkRefsIntoAndScanClosure: a parallel version of
6996 // MarkRefsIntoAndScanClosure
6997 ///////////////////////////////////////////////////////////
6998 Par_MarkRefsIntoAndScanClosure::Par_MarkRefsIntoAndScanClosure(
6999 CMSCollector* collector, MemRegion span, ReferenceProcessor* rp,
7000 CMSBitMap* bit_map, OopTaskQueue* work_queue):
7001 _span(span),
7002 _bit_map(bit_map),
7003 _work_queue(work_queue),
7004 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
7005 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads))),
7006 _par_pushAndMarkClosure(collector, span, rp, bit_map, work_queue)
7007 {
7008 _ref_processor = rp;
7009 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7010 }
7011
7012 // This closure is used to mark refs into the CMS generation at the
7013 // second (final) checkpoint, and to scan and transitively follow
7014 // the unmarked oops. The marks are made in the marking bit map and
7015 // the work_queue is used for keeping the (newly) grey objects during
7016 // the scan phase whence they are also available for stealing by parallel
7017 // threads. Since the marking bit map is shared, updates are
7018 // synchronized (via CAS).
7019 void Par_MarkRefsIntoAndScanClosure::do_oop(oop obj) {
7020 if (obj != NULL) {
7021 // Ignore mark word because this could be an already marked oop
7022 // that may be chained at the end of the overflow list.
7023 assert(obj->is_oop(true), "expected an oop");
7024 HeapWord* addr = (HeapWord*)obj;
7025 if (_span.contains(addr) &&
7026 !_bit_map->isMarked(addr)) {
7027 // mark bit map (object will become grey):
7028 // It is possible for several threads to be
7029 // trying to "claim" this object concurrently;
7030 // the unique thread that succeeds in marking the
7031 // object first will do the subsequent push on
7032 // to the work queue (or overflow list).
7033 if (_bit_map->par_mark(addr)) {
7034 // push on work_queue (which may not be empty), and trim the
7035 // queue to an appropriate length by applying this closure to
7036 // the oops in the oops popped from the stack (i.e. blacken the
7037 // grey objects)
7038 bool res = _work_queue->push(obj);
7039 assert(res, "Low water mark should be less than capacity?");
7040 trim_queue(_low_water_mark);
7041 } // Else, another thread claimed the object
7042 }
7043 }
7044 }
7045
7046 void Par_MarkRefsIntoAndScanClosure::do_oop(oop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
7047 void Par_MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
7048
7049 // This closure is used to rescan the marked objects on the dirty cards
7050 // in the mod union table and the card table proper.
7051 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
7052 oop p, MemRegion mr) {
7053
7054 size_t size = 0;
7055 HeapWord* addr = (HeapWord*)p;
7056 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
7057 assert(_span.contains(addr), "we are scanning the CMS generation");
7058 // check if it's time to yield
7059 if (do_yield_check()) {
7060 // We yielded for some foreground stop-world work,
7061 // and we have been asked to abort this ongoing preclean cycle.
7062 return 0;
7063 }
7064 if (_bitMap->isMarked(addr)) {
7065 // it's marked; is it potentially uninitialized?
7066 if (p->klass_or_null() != NULL) {
7067 // an initialized object; ignore mark word in verification below
7068 // since we are running concurrent with mutators
7069 assert(p->is_oop(true), "should be an oop");
7070 if (p->is_objArray()) {
7071 // objArrays are precisely marked; restrict scanning
7072 // to dirty cards only.
7073 size = CompactibleFreeListSpace::adjustObjectSize(
7074 p->oop_iterate(_scanningClosure, mr));
7075 } else {
7076 // A non-array may have been imprecisely marked; we need
7077 // to scan object in its entirety.
7078 size = CompactibleFreeListSpace::adjustObjectSize(
7079 p->oop_iterate(_scanningClosure));
7080 }
7081 #ifdef ASSERT
7082 size_t direct_size =
7083 CompactibleFreeListSpace::adjustObjectSize(p->size());
7084 assert(size == direct_size, "Inconsistency in size");
7085 assert(size >= 3, "Necessary for Printezis marks to work");
7086 if (!_bitMap->isMarked(addr+1)) {
7087 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size);
7088 } else {
7089 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size-1);
7090 assert(_bitMap->isMarked(addr+size-1),
7091 "inconsistent Printezis mark");
7092 }
7093 #endif // ASSERT
7094 } else {
7095 // An uninitialized object.
7096 assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
7097 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
7098 size = pointer_delta(nextOneAddr + 1, addr);
7099 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
7100 "alignment problem");
7101 // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
7102 // will dirty the card when the klass pointer is installed in the
7103 // object (signaling the completion of initialization).
7104 }
7105 } else {
7106 // Either a not yet marked object or an uninitialized object
7107 if (p->klass_or_null() == NULL) {
7108 // An uninitialized object, skip to the next card, since
7109 // we may not be able to read its P-bits yet.
7110 assert(size == 0, "Initial value");
7111 } else {
7112 // An object not (yet) reached by marking: we merely need to
7113 // compute its size so as to go look at the next block.
7114 assert(p->is_oop(true), "should be an oop");
7115 size = CompactibleFreeListSpace::adjustObjectSize(p->size());
7116 }
7117 }
7118 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
7119 return size;
7120 }
7121
7122 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
7123 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7124 "CMS thread should hold CMS token");
7125 assert_lock_strong(_freelistLock);
7126 assert_lock_strong(_bitMap->lock());
7127 // relinquish the free_list_lock and bitMaplock()
7128 _bitMap->lock()->unlock();
7129 _freelistLock->unlock();
7130 ConcurrentMarkSweepThread::desynchronize(true);
7131 ConcurrentMarkSweepThread::acknowledge_yield_request();
7132 _collector->stopTimer();
7133 if (PrintCMSStatistics != 0) {
7134 _collector->incrementYields();
7135 }
7136 _collector->icms_wait();
7137
7138 // See the comment in coordinator_yield()
7139 for (unsigned i = 0; i < CMSYieldSleepCount &&
7140 ConcurrentMarkSweepThread::should_yield() &&
7141 !CMSCollector::foregroundGCIsActive(); ++i) {
7142 os::sleep(Thread::current(), 1, false);
7143 ConcurrentMarkSweepThread::acknowledge_yield_request();
7144 }
7145
7146 ConcurrentMarkSweepThread::synchronize(true);
7147 _freelistLock->lock_without_safepoint_check();
7148 _bitMap->lock()->lock_without_safepoint_check();
7149 _collector->startTimer();
7150 }
7151
7152
7153 //////////////////////////////////////////////////////////////////
7154 // SurvivorSpacePrecleanClosure
7155 //////////////////////////////////////////////////////////////////
7156 // This (single-threaded) closure is used to preclean the oops in
7157 // the survivor spaces.
7158 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
7159
7160 HeapWord* addr = (HeapWord*)p;
7161 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
7162 assert(!_span.contains(addr), "we are scanning the survivor spaces");
7163 assert(p->klass_or_null() != NULL, "object should be initialized");
7164 // an initialized object; ignore mark word in verification below
7165 // since we are running concurrent with mutators
7166 assert(p->is_oop(true), "should be an oop");
7167 // Note that we do not yield while we iterate over
7168 // the interior oops of p, pushing the relevant ones
7169 // on our marking stack.
7170 size_t size = p->oop_iterate(_scanning_closure);
7171 do_yield_check();
7172 // Observe that below, we do not abandon the preclean
7173 // phase as soon as we should; rather we empty the
7174 // marking stack before returning. This is to satisfy
7175 // some existing assertions. In general, it may be a
7176 // good idea to abort immediately and complete the marking
7177 // from the grey objects at a later time.
7178 while (!_mark_stack->isEmpty()) {
7179 oop new_oop = _mark_stack->pop();
7180 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
7181 assert(_bit_map->isMarked((HeapWord*)new_oop),
7182 "only grey objects on this stack");
7183 // iterate over the oops in this oop, marking and pushing
7184 // the ones in CMS heap (i.e. in _span).
7185 new_oop->oop_iterate(_scanning_closure);
7186 // check if it's time to yield
7187 do_yield_check();
7188 }
7189 unsigned int after_count =
7190 GenCollectedHeap::heap()->total_collections();
7191 bool abort = (_before_count != after_count) ||
7192 _collector->should_abort_preclean();
7193 return abort ? 0 : size;
7194 }
7195
7196 void SurvivorSpacePrecleanClosure::do_yield_work() {
7197 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7198 "CMS thread should hold CMS token");
7199 assert_lock_strong(_bit_map->lock());
7200 // Relinquish the bit map lock
7201 _bit_map->lock()->unlock();
7202 ConcurrentMarkSweepThread::desynchronize(true);
7203 ConcurrentMarkSweepThread::acknowledge_yield_request();
7204 _collector->stopTimer();
7205 if (PrintCMSStatistics != 0) {
7206 _collector->incrementYields();
7207 }
7208 _collector->icms_wait();
7209
7210 // See the comment in coordinator_yield()
7211 for (unsigned i = 0; i < CMSYieldSleepCount &&
7212 ConcurrentMarkSweepThread::should_yield() &&
7213 !CMSCollector::foregroundGCIsActive(); ++i) {
7214 os::sleep(Thread::current(), 1, false);
7215 ConcurrentMarkSweepThread::acknowledge_yield_request();
7216 }
7217
7218 ConcurrentMarkSweepThread::synchronize(true);
7219 _bit_map->lock()->lock_without_safepoint_check();
7220 _collector->startTimer();
7221 }
7222
7223 // This closure is used to rescan the marked objects on the dirty cards
7224 // in the mod union table and the card table proper. In the parallel
7225 // case, although the bitMap is shared, we do a single read so the
7226 // isMarked() query is "safe".
7227 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
7228 // Ignore mark word because we are running concurrent with mutators
7229 assert(p->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(p)));
7230 HeapWord* addr = (HeapWord*)p;
7231 assert(_span.contains(addr), "we are scanning the CMS generation");
7232 bool is_obj_array = false;
7233 #ifdef ASSERT
7234 if (!_parallel) {
7235 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
7236 assert(_collector->overflow_list_is_empty(),
7237 "overflow list should be empty");
7238
7239 }
7240 #endif // ASSERT
7241 if (_bit_map->isMarked(addr)) {
7242 // Obj arrays are precisely marked, non-arrays are not;
7243 // so we scan objArrays precisely and non-arrays in their
7244 // entirety.
7245 if (p->is_objArray()) {
7246 is_obj_array = true;
7247 if (_parallel) {
7248 p->oop_iterate(_par_scan_closure, mr);
7249 } else {
7250 p->oop_iterate(_scan_closure, mr);
7251 }
7252 } else {
7253 if (_parallel) {
7254 p->oop_iterate(_par_scan_closure);
7255 } else {
7256 p->oop_iterate(_scan_closure);
7257 }
7258 }
7259 }
7260 #ifdef ASSERT
7261 if (!_parallel) {
7262 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
7263 assert(_collector->overflow_list_is_empty(),
7264 "overflow list should be empty");
7265
7266 }
7267 #endif // ASSERT
7268 return is_obj_array;
7269 }
7270
7271 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
7272 MemRegion span,
7273 CMSBitMap* bitMap, CMSMarkStack* markStack,
7274 bool should_yield, bool verifying):
7275 _collector(collector),
7276 _span(span),
7277 _bitMap(bitMap),
7278 _mut(&collector->_modUnionTable),
7279 _markStack(markStack),
7280 _yield(should_yield),
7281 _skipBits(0)
7282 {
7283 assert(_markStack->isEmpty(), "stack should be empty");
7284 _finger = _bitMap->startWord();
7285 _threshold = _finger;
7286 assert(_collector->_restart_addr == NULL, "Sanity check");
7287 assert(_span.contains(_finger), "Out of bounds _finger?");
7288 DEBUG_ONLY(_verifying = verifying;)
7289 }
7290
7291 void MarkFromRootsClosure::reset(HeapWord* addr) {
7292 assert(_markStack->isEmpty(), "would cause duplicates on stack");
7293 assert(_span.contains(addr), "Out of bounds _finger?");
7294 _finger = addr;
7295 _threshold = (HeapWord*)round_to(
7296 (intptr_t)_finger, CardTableModRefBS::card_size);
7297 }
7298
7299 // Should revisit to see if this should be restructured for
7300 // greater efficiency.
7301 bool MarkFromRootsClosure::do_bit(size_t offset) {
7302 if (_skipBits > 0) {
7303 _skipBits--;
7304 return true;
7305 }
7306 // convert offset into a HeapWord*
7307 HeapWord* addr = _bitMap->startWord() + offset;
7308 assert(_bitMap->endWord() && addr < _bitMap->endWord(),
7309 "address out of range");
7310 assert(_bitMap->isMarked(addr), "tautology");
7311 if (_bitMap->isMarked(addr+1)) {
7312 // this is an allocated but not yet initialized object
7313 assert(_skipBits == 0, "tautology");
7314 _skipBits = 2; // skip next two marked bits ("Printezis-marks")
7315 oop p = oop(addr);
7316 if (p->klass_or_null() == NULL) {
7317 DEBUG_ONLY(if (!_verifying) {)
7318 // We re-dirty the cards on which this object lies and increase
7319 // the _threshold so that we'll come back to scan this object
7320 // during the preclean or remark phase. (CMSCleanOnEnter)
7321 if (CMSCleanOnEnter) {
7322 size_t sz = _collector->block_size_using_printezis_bits(addr);
7323 HeapWord* end_card_addr = (HeapWord*)round_to(
7324 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7325 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7326 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7327 // Bump _threshold to end_card_addr; note that
7328 // _threshold cannot possibly exceed end_card_addr, anyhow.
7329 // This prevents future clearing of the card as the scan proceeds
7330 // to the right.
7331 assert(_threshold <= end_card_addr,
7332 "Because we are just scanning into this object");
7333 if (_threshold < end_card_addr) {
7334 _threshold = end_card_addr;
7335 }
7336 if (p->klass_or_null() != NULL) {
7337 // Redirty the range of cards...
7338 _mut->mark_range(redirty_range);
7339 } // ...else the setting of klass will dirty the card anyway.
7340 }
7341 DEBUG_ONLY(})
7342 return true;
7343 }
7344 }
7345 scanOopsInOop(addr);
7346 return true;
7347 }
7348
7349 // We take a break if we've been at this for a while,
7350 // so as to avoid monopolizing the locks involved.
7351 void MarkFromRootsClosure::do_yield_work() {
7352 // First give up the locks, then yield, then re-lock
7353 // We should probably use a constructor/destructor idiom to
7354 // do this unlock/lock or modify the MutexUnlocker class to
7355 // serve our purpose. XXX
7356 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7357 "CMS thread should hold CMS token");
7358 assert_lock_strong(_bitMap->lock());
7359 _bitMap->lock()->unlock();
7360 ConcurrentMarkSweepThread::desynchronize(true);
7361 ConcurrentMarkSweepThread::acknowledge_yield_request();
7362 _collector->stopTimer();
7363 if (PrintCMSStatistics != 0) {
7364 _collector->incrementYields();
7365 }
7366 _collector->icms_wait();
7367
7368 // See the comment in coordinator_yield()
7369 for (unsigned i = 0; i < CMSYieldSleepCount &&
7370 ConcurrentMarkSweepThread::should_yield() &&
7371 !CMSCollector::foregroundGCIsActive(); ++i) {
7372 os::sleep(Thread::current(), 1, false);
7373 ConcurrentMarkSweepThread::acknowledge_yield_request();
7374 }
7375
7376 ConcurrentMarkSweepThread::synchronize(true);
7377 _bitMap->lock()->lock_without_safepoint_check();
7378 _collector->startTimer();
7379 }
7380
7381 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
7382 assert(_bitMap->isMarked(ptr), "expected bit to be set");
7383 assert(_markStack->isEmpty(),
7384 "should drain stack to limit stack usage");
7385 // convert ptr to an oop preparatory to scanning
7386 oop obj = oop(ptr);
7387 // Ignore mark word in verification below, since we
7388 // may be running concurrent with mutators.
7389 assert(obj->is_oop(true), "should be an oop");
7390 assert(_finger <= ptr, "_finger runneth ahead");
7391 // advance the finger to right end of this object
7392 _finger = ptr + obj->size();
7393 assert(_finger > ptr, "we just incremented it above");
7394 // On large heaps, it may take us some time to get through
7395 // the marking phase (especially if running iCMS). During
7396 // this time it's possible that a lot of mutations have
7397 // accumulated in the card table and the mod union table --
7398 // these mutation records are redundant until we have
7399 // actually traced into the corresponding card.
7400 // Here, we check whether advancing the finger would make
7401 // us cross into a new card, and if so clear corresponding
7402 // cards in the MUT (preclean them in the card-table in the
7403 // future).
7404
7405 DEBUG_ONLY(if (!_verifying) {)
7406 // The clean-on-enter optimization is disabled by default,
7407 // until we fix 6178663.
7408 if (CMSCleanOnEnter && (_finger > _threshold)) {
7409 // [_threshold, _finger) represents the interval
7410 // of cards to be cleared in MUT (or precleaned in card table).
7411 // The set of cards to be cleared is all those that overlap
7412 // with the interval [_threshold, _finger); note that
7413 // _threshold is always kept card-aligned but _finger isn't
7414 // always card-aligned.
7415 HeapWord* old_threshold = _threshold;
7416 assert(old_threshold == (HeapWord*)round_to(
7417 (intptr_t)old_threshold, CardTableModRefBS::card_size),
7418 "_threshold should always be card-aligned");
7419 _threshold = (HeapWord*)round_to(
7420 (intptr_t)_finger, CardTableModRefBS::card_size);
7421 MemRegion mr(old_threshold, _threshold);
7422 assert(!mr.is_empty(), "Control point invariant");
7423 assert(_span.contains(mr), "Should clear within span");
7424 _mut->clear_range(mr);
7425 }
7426 DEBUG_ONLY(})
7427 // Note: the finger doesn't advance while we drain
7428 // the stack below.
7429 PushOrMarkClosure pushOrMarkClosure(_collector,
7430 _span, _bitMap, _markStack,
7431 _finger, this);
7432 bool res = _markStack->push(obj);
7433 assert(res, "Empty non-zero size stack should have space for single push");
7434 while (!_markStack->isEmpty()) {
7435 oop new_oop = _markStack->pop();
7436 // Skip verifying header mark word below because we are
7437 // running concurrent with mutators.
7438 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
7439 // now scan this oop's oops
7440 new_oop->oop_iterate(&pushOrMarkClosure);
7441 do_yield_check();
7442 }
7443 assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
7444 }
7445
7446 Par_MarkFromRootsClosure::Par_MarkFromRootsClosure(CMSConcMarkingTask* task,
7447 CMSCollector* collector, MemRegion span,
7448 CMSBitMap* bit_map,
7449 OopTaskQueue* work_queue,
7450 CMSMarkStack* overflow_stack,
7451 bool should_yield):
7452 _collector(collector),
7453 _whole_span(collector->_span),
7454 _span(span),
7455 _bit_map(bit_map),
7456 _mut(&collector->_modUnionTable),
7457 _work_queue(work_queue),
7458 _overflow_stack(overflow_stack),
7459 _yield(should_yield),
7460 _skip_bits(0),
7461 _task(task)
7462 {
7463 assert(_work_queue->size() == 0, "work_queue should be empty");
7464 _finger = span.start();
7465 _threshold = _finger; // XXX Defer clear-on-enter optimization for now
7466 assert(_span.contains(_finger), "Out of bounds _finger?");
7467 }
7468
7469 // Should revisit to see if this should be restructured for
7470 // greater efficiency.
7471 bool Par_MarkFromRootsClosure::do_bit(size_t offset) {
7472 if (_skip_bits > 0) {
7473 _skip_bits--;
7474 return true;
7475 }
7476 // convert offset into a HeapWord*
7477 HeapWord* addr = _bit_map->startWord() + offset;
7478 assert(_bit_map->endWord() && addr < _bit_map->endWord(),
7479 "address out of range");
7480 assert(_bit_map->isMarked(addr), "tautology");
7481 if (_bit_map->isMarked(addr+1)) {
7482 // this is an allocated object that might not yet be initialized
7483 assert(_skip_bits == 0, "tautology");
7484 _skip_bits = 2; // skip next two marked bits ("Printezis-marks")
7485 oop p = oop(addr);
7486 if (p->klass_or_null() == NULL) {
7487 // in the case of Clean-on-Enter optimization, redirty card
7488 // and avoid clearing card by increasing the threshold.
7489 return true;
7490 }
7491 }
7492 scan_oops_in_oop(addr);
7493 return true;
7494 }
7495
7496 void Par_MarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
7497 assert(_bit_map->isMarked(ptr), "expected bit to be set");
7498 // Should we assert that our work queue is empty or
7499 // below some drain limit?
7500 assert(_work_queue->size() == 0,
7501 "should drain stack to limit stack usage");
7502 // convert ptr to an oop preparatory to scanning
7503 oop obj = oop(ptr);
7504 // Ignore mark word in verification below, since we
7505 // may be running concurrent with mutators.
7506 assert(obj->is_oop(true), "should be an oop");
7507 assert(_finger <= ptr, "_finger runneth ahead");
7508 // advance the finger to right end of this object
7509 _finger = ptr + obj->size();
7510 assert(_finger > ptr, "we just incremented it above");
7511 // On large heaps, it may take us some time to get through
7512 // the marking phase (especially if running iCMS). During
7513 // this time it's possible that a lot of mutations have
7514 // accumulated in the card table and the mod union table --
7515 // these mutation records are redundant until we have
7516 // actually traced into the corresponding card.
7517 // Here, we check whether advancing the finger would make
7518 // us cross into a new card, and if so clear corresponding
7519 // cards in the MUT (preclean them in the card-table in the
7520 // future).
7521
7522 // The clean-on-enter optimization is disabled by default,
7523 // until we fix 6178663.
7524 if (CMSCleanOnEnter && (_finger > _threshold)) {
7525 // [_threshold, _finger) represents the interval
7526 // of cards to be cleared in MUT (or precleaned in card table).
7527 // The set of cards to be cleared is all those that overlap
7528 // with the interval [_threshold, _finger); note that
7529 // _threshold is always kept card-aligned but _finger isn't
7530 // always card-aligned.
7531 HeapWord* old_threshold = _threshold;
7532 assert(old_threshold == (HeapWord*)round_to(
7533 (intptr_t)old_threshold, CardTableModRefBS::card_size),
7534 "_threshold should always be card-aligned");
7535 _threshold = (HeapWord*)round_to(
7536 (intptr_t)_finger, CardTableModRefBS::card_size);
7537 MemRegion mr(old_threshold, _threshold);
7538 assert(!mr.is_empty(), "Control point invariant");
7539 assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
7540 _mut->clear_range(mr);
7541 }
7542
7543 // Note: the local finger doesn't advance while we drain
7544 // the stack below, but the global finger sure can and will.
7545 HeapWord** gfa = _task->global_finger_addr();
7546 Par_PushOrMarkClosure pushOrMarkClosure(_collector,
7547 _span, _bit_map,
7548 _work_queue,
7549 _overflow_stack,
7550 _finger,
7551 gfa, this);
7552 bool res = _work_queue->push(obj); // overflow could occur here
7553 assert(res, "Will hold once we use workqueues");
7554 while (true) {
7555 oop new_oop;
7556 if (!_work_queue->pop_local(new_oop)) {
7557 // We emptied our work_queue; check if there's stuff that can
7558 // be gotten from the overflow stack.
7559 if (CMSConcMarkingTask::get_work_from_overflow_stack(
7560 _overflow_stack, _work_queue)) {
7561 do_yield_check();
7562 continue;
7563 } else { // done
7564 break;
7565 }
7566 }
7567 // Skip verifying header mark word below because we are
7568 // running concurrent with mutators.
7569 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
7570 // now scan this oop's oops
7571 new_oop->oop_iterate(&pushOrMarkClosure);
7572 do_yield_check();
7573 }
7574 assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
7575 }
7576
7577 // Yield in response to a request from VM Thread or
7578 // from mutators.
7579 void Par_MarkFromRootsClosure::do_yield_work() {
7580 assert(_task != NULL, "sanity");
7581 _task->yield();
7582 }
7583
7584 // A variant of the above used for verifying CMS marking work.
7585 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
7586 MemRegion span,
7587 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
7588 CMSMarkStack* mark_stack):
7589 _collector(collector),
7590 _span(span),
7591 _verification_bm(verification_bm),
7592 _cms_bm(cms_bm),
7593 _mark_stack(mark_stack),
7594 _pam_verify_closure(collector, span, verification_bm, cms_bm,
7595 mark_stack)
7596 {
7597 assert(_mark_stack->isEmpty(), "stack should be empty");
7598 _finger = _verification_bm->startWord();
7599 assert(_collector->_restart_addr == NULL, "Sanity check");
7600 assert(_span.contains(_finger), "Out of bounds _finger?");
7601 }
7602
7603 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
7604 assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
7605 assert(_span.contains(addr), "Out of bounds _finger?");
7606 _finger = addr;
7607 }
7608
7609 // Should revisit to see if this should be restructured for
7610 // greater efficiency.
7611 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
7612 // convert offset into a HeapWord*
7613 HeapWord* addr = _verification_bm->startWord() + offset;
7614 assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
7615 "address out of range");
7616 assert(_verification_bm->isMarked(addr), "tautology");
7617 assert(_cms_bm->isMarked(addr), "tautology");
7618
7619 assert(_mark_stack->isEmpty(),
7620 "should drain stack to limit stack usage");
7621 // convert addr to an oop preparatory to scanning
7622 oop obj = oop(addr);
7623 assert(obj->is_oop(), "should be an oop");
7624 assert(_finger <= addr, "_finger runneth ahead");
7625 // advance the finger to right end of this object
7626 _finger = addr + obj->size();
7627 assert(_finger > addr, "we just incremented it above");
7628 // Note: the finger doesn't advance while we drain
7629 // the stack below.
7630 bool res = _mark_stack->push(obj);
7631 assert(res, "Empty non-zero size stack should have space for single push");
7632 while (!_mark_stack->isEmpty()) {
7633 oop new_oop = _mark_stack->pop();
7634 assert(new_oop->is_oop(), "Oops! expected to pop an oop");
7635 // now scan this oop's oops
7636 new_oop->oop_iterate(&_pam_verify_closure);
7637 }
7638 assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
7639 return true;
7640 }
7641
7642 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
7643 CMSCollector* collector, MemRegion span,
7644 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
7645 CMSMarkStack* mark_stack):
7646 MetadataAwareOopClosure(collector->ref_processor()),
7647 _collector(collector),
7648 _span(span),
7649 _verification_bm(verification_bm),
7650 _cms_bm(cms_bm),
7651 _mark_stack(mark_stack)
7652 { }
7653
7654 void PushAndMarkVerifyClosure::do_oop(oop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
7655 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
7656
7657 // Upon stack overflow, we discard (part of) the stack,
7658 // remembering the least address amongst those discarded
7659 // in CMSCollector's _restart_address.
7660 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
7661 // Remember the least grey address discarded
7662 HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
7663 _collector->lower_restart_addr(ra);
7664 _mark_stack->reset(); // discard stack contents
7665 _mark_stack->expand(); // expand the stack if possible
7666 }
7667
7668 void PushAndMarkVerifyClosure::do_oop(oop obj) {
7669 assert(obj->is_oop_or_null(), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7670 HeapWord* addr = (HeapWord*)obj;
7671 if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
7672 // Oop lies in _span and isn't yet grey or black
7673 _verification_bm->mark(addr); // now grey
7674 if (!_cms_bm->isMarked(addr)) {
7675 oop(addr)->print();
7676 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)",
7677 addr);
7678 fatal("... aborting");
7679 }
7680
7681 if (!_mark_stack->push(obj)) { // stack overflow
7682 if (PrintCMSStatistics != 0) {
7683 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7684 SIZE_FORMAT, _mark_stack->capacity());
7685 }
7686 assert(_mark_stack->isFull(), "Else push should have succeeded");
7687 handle_stack_overflow(addr);
7688 }
7689 // anything including and to the right of _finger
7690 // will be scanned as we iterate over the remainder of the
7691 // bit map
7692 }
7693 }
7694
7695 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
7696 MemRegion span,
7697 CMSBitMap* bitMap, CMSMarkStack* markStack,
7698 HeapWord* finger, MarkFromRootsClosure* parent) :
7699 MetadataAwareOopClosure(collector->ref_processor()),
7700 _collector(collector),
7701 _span(span),
7702 _bitMap(bitMap),
7703 _markStack(markStack),
7704 _finger(finger),
7705 _parent(parent)
7706 { }
7707
7708 Par_PushOrMarkClosure::Par_PushOrMarkClosure(CMSCollector* collector,
7709 MemRegion span,
7710 CMSBitMap* bit_map,
7711 OopTaskQueue* work_queue,
7712 CMSMarkStack* overflow_stack,
7713 HeapWord* finger,
7714 HeapWord** global_finger_addr,
7715 Par_MarkFromRootsClosure* parent) :
7716 MetadataAwareOopClosure(collector->ref_processor()),
7717 _collector(collector),
7718 _whole_span(collector->_span),
7719 _span(span),
7720 _bit_map(bit_map),
7721 _work_queue(work_queue),
7722 _overflow_stack(overflow_stack),
7723 _finger(finger),
7724 _global_finger_addr(global_finger_addr),
7725 _parent(parent)
7726 { }
7727
7728 // Assumes thread-safe access by callers, who are
7729 // responsible for mutual exclusion.
7730 void CMSCollector::lower_restart_addr(HeapWord* low) {
7731 assert(_span.contains(low), "Out of bounds addr");
7732 if (_restart_addr == NULL) {
7733 _restart_addr = low;
7734 } else {
7735 _restart_addr = MIN2(_restart_addr, low);
7736 }
7737 }
7738
7739 // Upon stack overflow, we discard (part of) the stack,
7740 // remembering the least address amongst those discarded
7741 // in CMSCollector's _restart_address.
7742 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7743 // Remember the least grey address discarded
7744 HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
7745 _collector->lower_restart_addr(ra);
7746 _markStack->reset(); // discard stack contents
7747 _markStack->expand(); // expand the stack if possible
7748 }
7749
7750 // Upon stack overflow, we discard (part of) the stack,
7751 // remembering the least address amongst those discarded
7752 // in CMSCollector's _restart_address.
7753 void Par_PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7754 // We need to do this under a mutex to prevent other
7755 // workers from interfering with the work done below.
7756 MutexLockerEx ml(_overflow_stack->par_lock(),
7757 Mutex::_no_safepoint_check_flag);
7758 // Remember the least grey address discarded
7759 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
7760 _collector->lower_restart_addr(ra);
7761 _overflow_stack->reset(); // discard stack contents
7762 _overflow_stack->expand(); // expand the stack if possible
7763 }
7764
7765 void PushOrMarkClosure::do_oop(oop obj) {
7766 // Ignore mark word because we are running concurrent with mutators.
7767 assert(obj->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7768 HeapWord* addr = (HeapWord*)obj;
7769 if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
7770 // Oop lies in _span and isn't yet grey or black
7771 _bitMap->mark(addr); // now grey
7772 if (addr < _finger) {
7773 // the bit map iteration has already either passed, or
7774 // sampled, this bit in the bit map; we'll need to
7775 // use the marking stack to scan this oop's oops.
7776 bool simulate_overflow = false;
7777 NOT_PRODUCT(
7778 if (CMSMarkStackOverflowALot &&
7779 _collector->simulate_overflow()) {
7780 // simulate a stack overflow
7781 simulate_overflow = true;
7782 }
7783 )
7784 if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
7785 if (PrintCMSStatistics != 0) {
7786 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7787 SIZE_FORMAT, _markStack->capacity());
7788 }
7789 assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
7790 handle_stack_overflow(addr);
7791 }
7792 }
7793 // anything including and to the right of _finger
7794 // will be scanned as we iterate over the remainder of the
7795 // bit map
7796 do_yield_check();
7797 }
7798 }
7799
7800 void PushOrMarkClosure::do_oop(oop* p) { PushOrMarkClosure::do_oop_work(p); }
7801 void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); }
7802
7803 void Par_PushOrMarkClosure::do_oop(oop obj) {
7804 // Ignore mark word because we are running concurrent with mutators.
7805 assert(obj->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7806 HeapWord* addr = (HeapWord*)obj;
7807 if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
7808 // Oop lies in _span and isn't yet grey or black
7809 // We read the global_finger (volatile read) strictly after marking oop
7810 bool res = _bit_map->par_mark(addr); // now grey
7811 volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
7812 // Should we push this marked oop on our stack?
7813 // -- if someone else marked it, nothing to do
7814 // -- if target oop is above global finger nothing to do
7815 // -- if target oop is in chunk and above local finger
7816 // then nothing to do
7817 // -- else push on work queue
7818 if ( !res // someone else marked it, they will deal with it
7819 || (addr >= *gfa) // will be scanned in a later task
7820 || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
7821 return;
7822 }
7823 // the bit map iteration has already either passed, or
7824 // sampled, this bit in the bit map; we'll need to
7825 // use the marking stack to scan this oop's oops.
7826 bool simulate_overflow = false;
7827 NOT_PRODUCT(
7828 if (CMSMarkStackOverflowALot &&
7829 _collector->simulate_overflow()) {
7830 // simulate a stack overflow
7831 simulate_overflow = true;
7832 }
7833 )
7834 if (simulate_overflow ||
7835 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
7836 // stack overflow
7837 if (PrintCMSStatistics != 0) {
7838 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7839 SIZE_FORMAT, _overflow_stack->capacity());
7840 }
7841 // We cannot assert that the overflow stack is full because
7842 // it may have been emptied since.
7843 assert(simulate_overflow ||
7844 _work_queue->size() == _work_queue->max_elems(),
7845 "Else push should have succeeded");
7846 handle_stack_overflow(addr);
7847 }
7848 do_yield_check();
7849 }
7850 }
7851
7852 void Par_PushOrMarkClosure::do_oop(oop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7853 void Par_PushOrMarkClosure::do_oop(narrowOop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7854
7855 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
7856 MemRegion span,
7857 ReferenceProcessor* rp,
7858 CMSBitMap* bit_map,
7859 CMSBitMap* mod_union_table,
7860 CMSMarkStack* mark_stack,
7861 bool concurrent_precleaning):
7862 MetadataAwareOopClosure(rp),
7863 _collector(collector),
7864 _span(span),
7865 _bit_map(bit_map),
7866 _mod_union_table(mod_union_table),
7867 _mark_stack(mark_stack),
7868 _concurrent_precleaning(concurrent_precleaning)
7869 {
7870 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7871 }
7872
7873 // Grey object rescan during pre-cleaning and second checkpoint phases --
7874 // the non-parallel version (the parallel version appears further below.)
7875 void PushAndMarkClosure::do_oop(oop obj) {
7876 // Ignore mark word verification. If during concurrent precleaning,
7877 // the object monitor may be locked. If during the checkpoint
7878 // phases, the object may already have been reached by a different
7879 // path and may be at the end of the global overflow list (so
7880 // the mark word may be NULL).
7881 assert(obj->is_oop_or_null(true /* ignore mark word */),
7882 err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7883 HeapWord* addr = (HeapWord*)obj;
7884 // Check if oop points into the CMS generation
7885 // and is not marked
7886 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7887 // a white object ...
7888 _bit_map->mark(addr); // ... now grey
7889 // push on the marking stack (grey set)
7890 bool simulate_overflow = false;
7891 NOT_PRODUCT(
7892 if (CMSMarkStackOverflowALot &&
7893 _collector->simulate_overflow()) {
7894 // simulate a stack overflow
7895 simulate_overflow = true;
7896 }
7897 )
7898 if (simulate_overflow || !_mark_stack->push(obj)) {
7899 if (_concurrent_precleaning) {
7900 // During precleaning we can just dirty the appropriate card(s)
7901 // in the mod union table, thus ensuring that the object remains
7902 // in the grey set and continue. In the case of object arrays
7903 // we need to dirty all of the cards that the object spans,
7904 // since the rescan of object arrays will be limited to the
7905 // dirty cards.
7906 // Note that no one can be interfering with us in this action
7907 // of dirtying the mod union table, so no locking or atomics
7908 // are required.
7909 if (obj->is_objArray()) {
7910 size_t sz = obj->size();
7911 HeapWord* end_card_addr = (HeapWord*)round_to(
7912 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7913 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7914 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7915 _mod_union_table->mark_range(redirty_range);
7916 } else {
7917 _mod_union_table->mark(addr);
7918 }
7919 _collector->_ser_pmc_preclean_ovflw++;
7920 } else {
7921 // During the remark phase, we need to remember this oop
7922 // in the overflow list.
7923 _collector->push_on_overflow_list(obj);
7924 _collector->_ser_pmc_remark_ovflw++;
7925 }
7926 }
7927 }
7928 }
7929
7930 Par_PushAndMarkClosure::Par_PushAndMarkClosure(CMSCollector* collector,
7931 MemRegion span,
7932 ReferenceProcessor* rp,
7933 CMSBitMap* bit_map,
7934 OopTaskQueue* work_queue):
7935 MetadataAwareOopClosure(rp),
7936 _collector(collector),
7937 _span(span),
7938 _bit_map(bit_map),
7939 _work_queue(work_queue)
7940 {
7941 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7942 }
7943
7944 void PushAndMarkClosure::do_oop(oop* p) { PushAndMarkClosure::do_oop_work(p); }
7945 void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); }
7946
7947 // Grey object rescan during second checkpoint phase --
7948 // the parallel version.
7949 void Par_PushAndMarkClosure::do_oop(oop obj) {
7950 // In the assert below, we ignore the mark word because
7951 // this oop may point to an already visited object that is
7952 // on the overflow stack (in which case the mark word has
7953 // been hijacked for chaining into the overflow stack --
7954 // if this is the last object in the overflow stack then
7955 // its mark word will be NULL). Because this object may
7956 // have been subsequently popped off the global overflow
7957 // stack, and the mark word possibly restored to the prototypical
7958 // value, by the time we get to examined this failing assert in
7959 // the debugger, is_oop_or_null(false) may subsequently start
7960 // to hold.
7961 assert(obj->is_oop_or_null(true),
7962 err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7963 HeapWord* addr = (HeapWord*)obj;
7964 // Check if oop points into the CMS generation
7965 // and is not marked
7966 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7967 // a white object ...
7968 // If we manage to "claim" the object, by being the
7969 // first thread to mark it, then we push it on our
7970 // marking stack
7971 if (_bit_map->par_mark(addr)) { // ... now grey
7972 // push on work queue (grey set)
7973 bool simulate_overflow = false;
7974 NOT_PRODUCT(
7975 if (CMSMarkStackOverflowALot &&
7976 _collector->par_simulate_overflow()) {
7977 // simulate a stack overflow
7978 simulate_overflow = true;
7979 }
7980 )
7981 if (simulate_overflow || !_work_queue->push(obj)) {
7982 _collector->par_push_on_overflow_list(obj);
7983 _collector->_par_pmc_remark_ovflw++; // imprecise OK: no need to CAS
7984 }
7985 } // Else, some other thread got there first
7986 }
7987 }
7988
7989 void Par_PushAndMarkClosure::do_oop(oop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7990 void Par_PushAndMarkClosure::do_oop(narrowOop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7991
7992 void CMSPrecleanRefsYieldClosure::do_yield_work() {
7993 Mutex* bml = _collector->bitMapLock();
7994 assert_lock_strong(bml);
7995 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7996 "CMS thread should hold CMS token");
7997
7998 bml->unlock();
7999 ConcurrentMarkSweepThread::desynchronize(true);
8000
8001 ConcurrentMarkSweepThread::acknowledge_yield_request();
8002
8003 _collector->stopTimer();
8004 if (PrintCMSStatistics != 0) {
8005 _collector->incrementYields();
8006 }
8007 _collector->icms_wait();
8008
8009 // See the comment in coordinator_yield()
8010 for (unsigned i = 0; i < CMSYieldSleepCount &&
8011 ConcurrentMarkSweepThread::should_yield() &&
8012 !CMSCollector::foregroundGCIsActive(); ++i) {
8013 os::sleep(Thread::current(), 1, false);
8014 ConcurrentMarkSweepThread::acknowledge_yield_request();
8015 }
8016
8017 ConcurrentMarkSweepThread::synchronize(true);
8018 bml->lock();
8019
8020 _collector->startTimer();
8021 }
8022
8023 bool CMSPrecleanRefsYieldClosure::should_return() {
8024 if (ConcurrentMarkSweepThread::should_yield()) {
8025 do_yield_work();
8026 }
8027 return _collector->foregroundGCIsActive();
8028 }
8029
8030 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
8031 assert(((size_t)mr.start())%CardTableModRefBS::card_size_in_words == 0,
8032 "mr should be aligned to start at a card boundary");
8033 // We'd like to assert:
8034 // assert(mr.word_size()%CardTableModRefBS::card_size_in_words == 0,
8035 // "mr should be a range of cards");
8036 // However, that would be too strong in one case -- the last
8037 // partition ends at _unallocated_block which, in general, can be
8038 // an arbitrary boundary, not necessarily card aligned.
8039 if (PrintCMSStatistics != 0) {
8040 _num_dirty_cards +=
8041 mr.word_size()/CardTableModRefBS::card_size_in_words;
8042 }
8043 _space->object_iterate_mem(mr, &_scan_cl);
8044 }
8045
8046 SweepClosure::SweepClosure(CMSCollector* collector,
8047 ConcurrentMarkSweepGeneration* g,
8048 CMSBitMap* bitMap, bool should_yield) :
8049 _collector(collector),
8050 _g(g),
8051 _sp(g->cmsSpace()),
8052 _limit(_sp->sweep_limit()),
8053 _freelistLock(_sp->freelistLock()),
8054 _bitMap(bitMap),
8055 _yield(should_yield),
8056 _inFreeRange(false), // No free range at beginning of sweep
8057 _freeRangeInFreeLists(false), // No free range at beginning of sweep
8058 _lastFreeRangeCoalesced(false),
8059 _freeFinger(g->used_region().start())
8060 {
8061 NOT_PRODUCT(
8062 _numObjectsFreed = 0;
8063 _numWordsFreed = 0;
8064 _numObjectsLive = 0;
8065 _numWordsLive = 0;
8066 _numObjectsAlreadyFree = 0;
8067 _numWordsAlreadyFree = 0;
8068 _last_fc = NULL;
8069
8070 _sp->initializeIndexedFreeListArrayReturnedBytes();
8071 _sp->dictionary()->initialize_dict_returned_bytes();
8072 )
8073 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
8074 "sweep _limit out of bounds");
8075 if (CMSTraceSweeper) {
8076 gclog_or_tty->print_cr("\n====================\nStarting new sweep with limit " PTR_FORMAT,
8077 _limit);
8078 }
8079 }
8080
8081 void SweepClosure::print_on(outputStream* st) const {
8082 tty->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")",
8083 _sp->bottom(), _sp->end());
8084 tty->print_cr("_limit = " PTR_FORMAT, _limit);
8085 tty->print_cr("_freeFinger = " PTR_FORMAT, _freeFinger);
8086 NOT_PRODUCT(tty->print_cr("_last_fc = " PTR_FORMAT, _last_fc);)
8087 tty->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d",
8088 _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced);
8089 }
8090
8091 #ifndef PRODUCT
8092 // Assertion checking only: no useful work in product mode --
8093 // however, if any of the flags below become product flags,
8094 // you may need to review this code to see if it needs to be
8095 // enabled in product mode.
8096 SweepClosure::~SweepClosure() {
8097 assert_lock_strong(_freelistLock);
8098 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
8099 "sweep _limit out of bounds");
8100 if (inFreeRange()) {
8101 warning("inFreeRange() should have been reset; dumping state of SweepClosure");
8102 print();
8103 ShouldNotReachHere();
8104 }
8105 if (Verbose && PrintGC) {
8106 gclog_or_tty->print("Collected "SIZE_FORMAT" objects, " SIZE_FORMAT " bytes",
8107 _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
8108 gclog_or_tty->print_cr("\nLive "SIZE_FORMAT" objects, "
8109 SIZE_FORMAT" bytes "
8110 "Already free "SIZE_FORMAT" objects, "SIZE_FORMAT" bytes",
8111 _numObjectsLive, _numWordsLive*sizeof(HeapWord),
8112 _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
8113 size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree)
8114 * sizeof(HeapWord);
8115 gclog_or_tty->print_cr("Total sweep: "SIZE_FORMAT" bytes", totalBytes);
8116
8117 if (PrintCMSStatistics && CMSVerifyReturnedBytes) {
8118 size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
8119 size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes();
8120 size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes;
8121 gclog_or_tty->print("Returned "SIZE_FORMAT" bytes", returned_bytes);
8122 gclog_or_tty->print(" Indexed List Returned "SIZE_FORMAT" bytes",
8123 indexListReturnedBytes);
8124 gclog_or_tty->print_cr(" Dictionary Returned "SIZE_FORMAT" bytes",
8125 dict_returned_bytes);
8126 }
8127 }
8128 if (CMSTraceSweeper) {
8129 gclog_or_tty->print_cr("end of sweep with _limit = " PTR_FORMAT "\n================",
8130 _limit);
8131 }
8132 }
8133 #endif // PRODUCT
8134
8135 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
8136 bool freeRangeInFreeLists) {
8137 if (CMSTraceSweeper) {
8138 gclog_or_tty->print("---- Start free range at " PTR_FORMAT " with free block (%d)\n",
8139 freeFinger, freeRangeInFreeLists);
8140 }
8141 assert(!inFreeRange(), "Trampling existing free range");
8142 set_inFreeRange(true);
8143 set_lastFreeRangeCoalesced(false);
8144
8145 set_freeFinger(freeFinger);
8146 set_freeRangeInFreeLists(freeRangeInFreeLists);
8147 if (CMSTestInFreeList) {
8148 if (freeRangeInFreeLists) {
8149 FreeChunk* fc = (FreeChunk*) freeFinger;
8150 assert(fc->is_free(), "A chunk on the free list should be free.");
8151 assert(fc->size() > 0, "Free range should have a size");
8152 assert(_sp->verify_chunk_in_free_list(fc), "Chunk is not in free lists");
8153 }
8154 }
8155 }
8156
8157 // Note that the sweeper runs concurrently with mutators. Thus,
8158 // it is possible for direct allocation in this generation to happen
8159 // in the middle of the sweep. Note that the sweeper also coalesces
8160 // contiguous free blocks. Thus, unless the sweeper and the allocator
8161 // synchronize appropriately freshly allocated blocks may get swept up.
8162 // This is accomplished by the sweeper locking the free lists while
8163 // it is sweeping. Thus blocks that are determined to be free are
8164 // indeed free. There is however one additional complication:
8165 // blocks that have been allocated since the final checkpoint and
8166 // mark, will not have been marked and so would be treated as
8167 // unreachable and swept up. To prevent this, the allocator marks
8168 // the bit map when allocating during the sweep phase. This leads,
8169 // however, to a further complication -- objects may have been allocated
8170 // but not yet initialized -- in the sense that the header isn't yet
8171 // installed. The sweeper can not then determine the size of the block
8172 // in order to skip over it. To deal with this case, we use a technique
8173 // (due to Printezis) to encode such uninitialized block sizes in the
8174 // bit map. Since the bit map uses a bit per every HeapWord, but the
8175 // CMS generation has a minimum object size of 3 HeapWords, it follows
8176 // that "normal marks" won't be adjacent in the bit map (there will
8177 // always be at least two 0 bits between successive 1 bits). We make use
8178 // of these "unused" bits to represent uninitialized blocks -- the bit
8179 // corresponding to the start of the uninitialized object and the next
8180 // bit are both set. Finally, a 1 bit marks the end of the object that
8181 // started with the two consecutive 1 bits to indicate its potentially
8182 // uninitialized state.
8183
8184 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
8185 FreeChunk* fc = (FreeChunk*)addr;
8186 size_t res;
8187
8188 // Check if we are done sweeping. Below we check "addr >= _limit" rather
8189 // than "addr == _limit" because although _limit was a block boundary when
8190 // we started the sweep, it may no longer be one because heap expansion
8191 // may have caused us to coalesce the block ending at the address _limit
8192 // with a newly expanded chunk (this happens when _limit was set to the
8193 // previous _end of the space), so we may have stepped past _limit:
8194 // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740.
8195 if (addr >= _limit) { // we have swept up to or past the limit: finish up
8196 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
8197 "sweep _limit out of bounds");
8198 assert(addr < _sp->end(), "addr out of bounds");
8199 // Flush any free range we might be holding as a single
8200 // coalesced chunk to the appropriate free list.
8201 if (inFreeRange()) {
8202 assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit,
8203 err_msg("freeFinger() " PTR_FORMAT" is out-of-bounds", freeFinger()));
8204 flush_cur_free_chunk(freeFinger(),
8205 pointer_delta(addr, freeFinger()));
8206 if (CMSTraceSweeper) {
8207 gclog_or_tty->print("Sweep: last chunk: ");
8208 gclog_or_tty->print("put_free_blk " PTR_FORMAT " ("SIZE_FORMAT") "
8209 "[coalesced:%d]\n",
8210 freeFinger(), pointer_delta(addr, freeFinger()),
8211 lastFreeRangeCoalesced() ? 1 : 0);
8212 }
8213 }
8214
8215 // help the iterator loop finish
8216 return pointer_delta(_sp->end(), addr);
8217 }
8218
8219 assert(addr < _limit, "sweep invariant");
8220 // check if we should yield
8221 do_yield_check(addr);
8222 if (fc->is_free()) {
8223 // Chunk that is already free
8224 res = fc->size();
8225 do_already_free_chunk(fc);
8226 debug_only(_sp->verifyFreeLists());
8227 // If we flush the chunk at hand in lookahead_and_flush()
8228 // and it's coalesced with a preceding chunk, then the
8229 // process of "mangling" the payload of the coalesced block
8230 // will cause erasure of the size information from the
8231 // (erstwhile) header of all the coalesced blocks but the
8232 // first, so the first disjunct in the assert will not hold
8233 // in that specific case (in which case the second disjunct
8234 // will hold).
8235 assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit,
8236 "Otherwise the size info doesn't change at this step");
8237 NOT_PRODUCT(
8238 _numObjectsAlreadyFree++;
8239 _numWordsAlreadyFree += res;
8240 )
8241 NOT_PRODUCT(_last_fc = fc;)
8242 } else if (!_bitMap->isMarked(addr)) {
8243 // Chunk is fresh garbage
8244 res = do_garbage_chunk(fc);
8245 debug_only(_sp->verifyFreeLists());
8246 NOT_PRODUCT(
8247 _numObjectsFreed++;
8248 _numWordsFreed += res;
8249 )
8250 } else {
8251 // Chunk that is alive.
8252 res = do_live_chunk(fc);
8253 debug_only(_sp->verifyFreeLists());
8254 NOT_PRODUCT(
8255 _numObjectsLive++;
8256 _numWordsLive += res;
8257 )
8258 }
8259 return res;
8260 }
8261
8262 // For the smart allocation, record following
8263 // split deaths - a free chunk is removed from its free list because
8264 // it is being split into two or more chunks.
8265 // split birth - a free chunk is being added to its free list because
8266 // a larger free chunk has been split and resulted in this free chunk.
8267 // coal death - a free chunk is being removed from its free list because
8268 // it is being coalesced into a large free chunk.
8269 // coal birth - a free chunk is being added to its free list because
8270 // it was created when two or more free chunks where coalesced into
8271 // this free chunk.
8272 //
8273 // These statistics are used to determine the desired number of free
8274 // chunks of a given size. The desired number is chosen to be relative
8275 // to the end of a CMS sweep. The desired number at the end of a sweep
8276 // is the
8277 // count-at-end-of-previous-sweep (an amount that was enough)
8278 // - count-at-beginning-of-current-sweep (the excess)
8279 // + split-births (gains in this size during interval)
8280 // - split-deaths (demands on this size during interval)
8281 // where the interval is from the end of one sweep to the end of the
8282 // next.
8283 //
8284 // When sweeping the sweeper maintains an accumulated chunk which is
8285 // the chunk that is made up of chunks that have been coalesced. That
8286 // will be termed the left-hand chunk. A new chunk of garbage that
8287 // is being considered for coalescing will be referred to as the
8288 // right-hand chunk.
8289 //
8290 // When making a decision on whether to coalesce a right-hand chunk with
8291 // the current left-hand chunk, the current count vs. the desired count
8292 // of the left-hand chunk is considered. Also if the right-hand chunk
8293 // is near the large chunk at the end of the heap (see
8294 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
8295 // left-hand chunk is coalesced.
8296 //
8297 // When making a decision about whether to split a chunk, the desired count
8298 // vs. the current count of the candidate to be split is also considered.
8299 // If the candidate is underpopulated (currently fewer chunks than desired)
8300 // a chunk of an overpopulated (currently more chunks than desired) size may
8301 // be chosen. The "hint" associated with a free list, if non-null, points
8302 // to a free list which may be overpopulated.
8303 //
8304
8305 void SweepClosure::do_already_free_chunk(FreeChunk* fc) {
8306 const size_t size = fc->size();
8307 // Chunks that cannot be coalesced are not in the
8308 // free lists.
8309 if (CMSTestInFreeList && !fc->cantCoalesce()) {
8310 assert(_sp->verify_chunk_in_free_list(fc),
8311 "free chunk should be in free lists");
8312 }
8313 // a chunk that is already free, should not have been
8314 // marked in the bit map
8315 HeapWord* const addr = (HeapWord*) fc;
8316 assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
8317 // Verify that the bit map has no bits marked between
8318 // addr and purported end of this block.
8319 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8320
8321 // Some chunks cannot be coalesced under any circumstances.
8322 // See the definition of cantCoalesce().
8323 if (!fc->cantCoalesce()) {
8324 // This chunk can potentially be coalesced.
8325 if (_sp->adaptive_freelists()) {
8326 // All the work is done in
8327 do_post_free_or_garbage_chunk(fc, size);
8328 } else { // Not adaptive free lists
8329 // this is a free chunk that can potentially be coalesced by the sweeper;
8330 if (!inFreeRange()) {
8331 // if the next chunk is a free block that can't be coalesced
8332 // it doesn't make sense to remove this chunk from the free lists
8333 FreeChunk* nextChunk = (FreeChunk*)(addr + size);
8334 assert((HeapWord*)nextChunk <= _sp->end(), "Chunk size out of bounds?");
8335 if ((HeapWord*)nextChunk < _sp->end() && // There is another free chunk to the right ...
8336 nextChunk->is_free() && // ... which is free...
8337 nextChunk->cantCoalesce()) { // ... but can't be coalesced
8338 // nothing to do
8339 } else {
8340 // Potentially the start of a new free range:
8341 // Don't eagerly remove it from the free lists.
8342 // No need to remove it if it will just be put
8343 // back again. (Also from a pragmatic point of view
8344 // if it is a free block in a region that is beyond
8345 // any allocated blocks, an assertion will fail)
8346 // Remember the start of a free run.
8347 initialize_free_range(addr, true);
8348 // end - can coalesce with next chunk
8349 }
8350 } else {
8351 // the midst of a free range, we are coalescing
8352 print_free_block_coalesced(fc);
8353 if (CMSTraceSweeper) {
8354 gclog_or_tty->print(" -- pick up free block " PTR_FORMAT " (" SIZE_FORMAT ")\n", fc, size);
8355 }
8356 // remove it from the free lists
8357 _sp->removeFreeChunkFromFreeLists(fc);
8358 set_lastFreeRangeCoalesced(true);
8359 // If the chunk is being coalesced and the current free range is
8360 // in the free lists, remove the current free range so that it
8361 // will be returned to the free lists in its entirety - all
8362 // the coalesced pieces included.
8363 if (freeRangeInFreeLists()) {
8364 FreeChunk* ffc = (FreeChunk*) freeFinger();
8365 assert(ffc->size() == pointer_delta(addr, freeFinger()),
8366 "Size of free range is inconsistent with chunk size.");
8367 if (CMSTestInFreeList) {
8368 assert(_sp->verify_chunk_in_free_list(ffc),
8369 "free range is not in free lists");
8370 }
8371 _sp->removeFreeChunkFromFreeLists(ffc);
8372 set_freeRangeInFreeLists(false);
8373 }
8374 }
8375 }
8376 // Note that if the chunk is not coalescable (the else arm
8377 // below), we unconditionally flush, without needing to do
8378 // a "lookahead," as we do below.
8379 if (inFreeRange()) lookahead_and_flush(fc, size);
8380 } else {
8381 // Code path common to both original and adaptive free lists.
8382
8383 // cant coalesce with previous block; this should be treated
8384 // as the end of a free run if any
8385 if (inFreeRange()) {
8386 // we kicked some butt; time to pick up the garbage
8387 assert(freeFinger() < addr, "freeFinger points too high");
8388 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8389 }
8390 // else, nothing to do, just continue
8391 }
8392 }
8393
8394 size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) {
8395 // This is a chunk of garbage. It is not in any free list.
8396 // Add it to a free list or let it possibly be coalesced into
8397 // a larger chunk.
8398 HeapWord* const addr = (HeapWord*) fc;
8399 const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
8400
8401 if (_sp->adaptive_freelists()) {
8402 // Verify that the bit map has no bits marked between
8403 // addr and purported end of just dead object.
8404 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8405
8406 do_post_free_or_garbage_chunk(fc, size);
8407 } else {
8408 if (!inFreeRange()) {
8409 // start of a new free range
8410 assert(size > 0, "A free range should have a size");
8411 initialize_free_range(addr, false);
8412 } else {
8413 // this will be swept up when we hit the end of the
8414 // free range
8415 if (CMSTraceSweeper) {
8416 gclog_or_tty->print(" -- pick up garbage " PTR_FORMAT " (" SIZE_FORMAT ")\n", fc, size);
8417 }
8418 // If the chunk is being coalesced and the current free range is
8419 // in the free lists, remove the current free range so that it
8420 // will be returned to the free lists in its entirety - all
8421 // the coalesced pieces included.
8422 if (freeRangeInFreeLists()) {
8423 FreeChunk* ffc = (FreeChunk*)freeFinger();
8424 assert(ffc->size() == pointer_delta(addr, freeFinger()),
8425 "Size of free range is inconsistent with chunk size.");
8426 if (CMSTestInFreeList) {
8427 assert(_sp->verify_chunk_in_free_list(ffc),
8428 "free range is not in free lists");
8429 }
8430 _sp->removeFreeChunkFromFreeLists(ffc);
8431 set_freeRangeInFreeLists(false);
8432 }
8433 set_lastFreeRangeCoalesced(true);
8434 }
8435 // this will be swept up when we hit the end of the free range
8436
8437 // Verify that the bit map has no bits marked between
8438 // addr and purported end of just dead object.
8439 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8440 }
8441 assert(_limit >= addr + size,
8442 "A freshly garbage chunk can't possibly straddle over _limit");
8443 if (inFreeRange()) lookahead_and_flush(fc, size);
8444 return size;
8445 }
8446
8447 size_t SweepClosure::do_live_chunk(FreeChunk* fc) {
8448 HeapWord* addr = (HeapWord*) fc;
8449 // The sweeper has just found a live object. Return any accumulated
8450 // left hand chunk to the free lists.
8451 if (inFreeRange()) {
8452 assert(freeFinger() < addr, "freeFinger points too high");
8453 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8454 }
8455
8456 // This object is live: we'd normally expect this to be
8457 // an oop, and like to assert the following:
8458 // assert(oop(addr)->is_oop(), "live block should be an oop");
8459 // However, as we commented above, this may be an object whose
8460 // header hasn't yet been initialized.
8461 size_t size;
8462 assert(_bitMap->isMarked(addr), "Tautology for this control point");
8463 if (_bitMap->isMarked(addr + 1)) {
8464 // Determine the size from the bit map, rather than trying to
8465 // compute it from the object header.
8466 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
8467 size = pointer_delta(nextOneAddr + 1, addr);
8468 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
8469 "alignment problem");
8470
8471 #ifdef ASSERT
8472 if (oop(addr)->klass_or_null() != NULL) {
8473 // Ignore mark word because we are running concurrent with mutators
8474 assert(oop(addr)->is_oop(true), "live block should be an oop");
8475 assert(size ==
8476 CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
8477 "P-mark and computed size do not agree");
8478 }
8479 #endif
8480
8481 } else {
8482 // This should be an initialized object that's alive.
8483 assert(oop(addr)->klass_or_null() != NULL,
8484 "Should be an initialized object");
8485 // Ignore mark word because we are running concurrent with mutators
8486 assert(oop(addr)->is_oop(true), "live block should be an oop");
8487 // Verify that the bit map has no bits marked between
8488 // addr and purported end of this block.
8489 size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
8490 assert(size >= 3, "Necessary for Printezis marks to work");
8491 assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
8492 DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
8493 }
8494 return size;
8495 }
8496
8497 void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc,
8498 size_t chunkSize) {
8499 // do_post_free_or_garbage_chunk() should only be called in the case
8500 // of the adaptive free list allocator.
8501 const bool fcInFreeLists = fc->is_free();
8502 assert(_sp->adaptive_freelists(), "Should only be used in this case.");
8503 assert((HeapWord*)fc <= _limit, "sweep invariant");
8504 if (CMSTestInFreeList && fcInFreeLists) {
8505 assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists");
8506 }
8507
8508 if (CMSTraceSweeper) {
8509 gclog_or_tty->print_cr(" -- pick up another chunk at " PTR_FORMAT " (" SIZE_FORMAT ")", fc, chunkSize);
8510 }
8511
8512 HeapWord* const fc_addr = (HeapWord*) fc;
8513
8514 bool coalesce;
8515 const size_t left = pointer_delta(fc_addr, freeFinger());
8516 const size_t right = chunkSize;
8517 switch (FLSCoalescePolicy) {
8518 // numeric value forms a coalition aggressiveness metric
8519 case 0: { // never coalesce
8520 coalesce = false;
8521 break;
8522 }
8523 case 1: { // coalesce if left & right chunks on overpopulated lists
8524 coalesce = _sp->coalOverPopulated(left) &&
8525 _sp->coalOverPopulated(right);
8526 break;
8527 }
8528 case 2: { // coalesce if left chunk on overpopulated list (default)
8529 coalesce = _sp->coalOverPopulated(left);
8530 break;
8531 }
8532 case 3: { // coalesce if left OR right chunk on overpopulated list
8533 coalesce = _sp->coalOverPopulated(left) ||
8534 _sp->coalOverPopulated(right);
8535 break;
8536 }
8537 case 4: { // always coalesce
8538 coalesce = true;
8539 break;
8540 }
8541 default:
8542 ShouldNotReachHere();
8543 }
8544
8545 // Should the current free range be coalesced?
8546 // If the chunk is in a free range and either we decided to coalesce above
8547 // or the chunk is near the large block at the end of the heap
8548 // (isNearLargestChunk() returns true), then coalesce this chunk.
8549 const bool doCoalesce = inFreeRange()
8550 && (coalesce || _g->isNearLargestChunk(fc_addr));
8551 if (doCoalesce) {
8552 // Coalesce the current free range on the left with the new
8553 // chunk on the right. If either is on a free list,
8554 // it must be removed from the list and stashed in the closure.
8555 if (freeRangeInFreeLists()) {
8556 FreeChunk* const ffc = (FreeChunk*)freeFinger();
8557 assert(ffc->size() == pointer_delta(fc_addr, freeFinger()),
8558 "Size of free range is inconsistent with chunk size.");
8559 if (CMSTestInFreeList) {
8560 assert(_sp->verify_chunk_in_free_list(ffc),
8561 "Chunk is not in free lists");
8562 }
8563 _sp->coalDeath(ffc->size());
8564 _sp->removeFreeChunkFromFreeLists(ffc);
8565 set_freeRangeInFreeLists(false);
8566 }
8567 if (fcInFreeLists) {
8568 _sp->coalDeath(chunkSize);
8569 assert(fc->size() == chunkSize,
8570 "The chunk has the wrong size or is not in the free lists");
8571 _sp->removeFreeChunkFromFreeLists(fc);
8572 }
8573 set_lastFreeRangeCoalesced(true);
8574 print_free_block_coalesced(fc);
8575 } else { // not in a free range and/or should not coalesce
8576 // Return the current free range and start a new one.
8577 if (inFreeRange()) {
8578 // In a free range but cannot coalesce with the right hand chunk.
8579 // Put the current free range into the free lists.
8580 flush_cur_free_chunk(freeFinger(),
8581 pointer_delta(fc_addr, freeFinger()));
8582 }
8583 // Set up for new free range. Pass along whether the right hand
8584 // chunk is in the free lists.
8585 initialize_free_range((HeapWord*)fc, fcInFreeLists);
8586 }
8587 }
8588
8589 // Lookahead flush:
8590 // If we are tracking a free range, and this is the last chunk that
8591 // we'll look at because its end crosses past _limit, we'll preemptively
8592 // flush it along with any free range we may be holding on to. Note that
8593 // this can be the case only for an already free or freshly garbage
8594 // chunk. If this block is an object, it can never straddle
8595 // over _limit. The "straddling" occurs when _limit is set at
8596 // the previous end of the space when this cycle started, and
8597 // a subsequent heap expansion caused the previously co-terminal
8598 // free block to be coalesced with the newly expanded portion,
8599 // thus rendering _limit a non-block-boundary making it dangerous
8600 // for the sweeper to step over and examine.
8601 void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) {
8602 assert(inFreeRange(), "Should only be called if currently in a free range.");
8603 HeapWord* const eob = ((HeapWord*)fc) + chunk_size;
8604 assert(_sp->used_region().contains(eob - 1),
8605 err_msg("eob = " PTR_FORMAT " eob-1 = " PTR_FORMAT " _limit = " PTR_FORMAT
8606 " out of bounds wrt _sp = [" PTR_FORMAT "," PTR_FORMAT ")"
8607 " when examining fc = " PTR_FORMAT "(" SIZE_FORMAT ")",
8608 eob, eob-1, _limit, _sp->bottom(), _sp->end(), fc, chunk_size));
8609 if (eob >= _limit) {
8610 assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit");
8611 if (CMSTraceSweeper) {
8612 gclog_or_tty->print_cr("_limit " PTR_FORMAT " reached or crossed by block "
8613 "[" PTR_FORMAT "," PTR_FORMAT ") in space "
8614 "[" PTR_FORMAT "," PTR_FORMAT ")",
8615 _limit, fc, eob, _sp->bottom(), _sp->end());
8616 }
8617 // Return the storage we are tracking back into the free lists.
8618 if (CMSTraceSweeper) {
8619 gclog_or_tty->print_cr("Flushing ... ");
8620 }
8621 assert(freeFinger() < eob, "Error");
8622 flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger()));
8623 }
8624 }
8625
8626 void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) {
8627 assert(inFreeRange(), "Should only be called if currently in a free range.");
8628 assert(size > 0,
8629 "A zero sized chunk cannot be added to the free lists.");
8630 if (!freeRangeInFreeLists()) {
8631 if (CMSTestInFreeList) {
8632 FreeChunk* fc = (FreeChunk*) chunk;
8633 fc->set_size(size);
8634 assert(!_sp->verify_chunk_in_free_list(fc),
8635 "chunk should not be in free lists yet");
8636 }
8637 if (CMSTraceSweeper) {
8638 gclog_or_tty->print_cr(" -- add free block " PTR_FORMAT " (" SIZE_FORMAT ") to free lists",
8639 chunk, size);
8640 }
8641 // A new free range is going to be starting. The current
8642 // free range has not been added to the free lists yet or
8643 // was removed so add it back.
8644 // If the current free range was coalesced, then the death
8645 // of the free range was recorded. Record a birth now.
8646 if (lastFreeRangeCoalesced()) {
8647 _sp->coalBirth(size);
8648 }
8649 _sp->addChunkAndRepairOffsetTable(chunk, size,
8650 lastFreeRangeCoalesced());
8651 } else if (CMSTraceSweeper) {
8652 gclog_or_tty->print_cr("Already in free list: nothing to flush");
8653 }
8654 set_inFreeRange(false);
8655 set_freeRangeInFreeLists(false);
8656 }
8657
8658 // We take a break if we've been at this for a while,
8659 // so as to avoid monopolizing the locks involved.
8660 void SweepClosure::do_yield_work(HeapWord* addr) {
8661 // Return current free chunk being used for coalescing (if any)
8662 // to the appropriate freelist. After yielding, the next
8663 // free block encountered will start a coalescing range of
8664 // free blocks. If the next free block is adjacent to the
8665 // chunk just flushed, they will need to wait for the next
8666 // sweep to be coalesced.
8667 if (inFreeRange()) {
8668 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8669 }
8670
8671 // First give up the locks, then yield, then re-lock.
8672 // We should probably use a constructor/destructor idiom to
8673 // do this unlock/lock or modify the MutexUnlocker class to
8674 // serve our purpose. XXX
8675 assert_lock_strong(_bitMap->lock());
8676 assert_lock_strong(_freelistLock);
8677 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
8678 "CMS thread should hold CMS token");
8679 _bitMap->lock()->unlock();
8680 _freelistLock->unlock();
8681 ConcurrentMarkSweepThread::desynchronize(true);
8682 ConcurrentMarkSweepThread::acknowledge_yield_request();
8683 _collector->stopTimer();
8684 if (PrintCMSStatistics != 0) {
8685 _collector->incrementYields();
8686 }
8687 _collector->icms_wait();
8688
8689 // See the comment in coordinator_yield()
8690 for (unsigned i = 0; i < CMSYieldSleepCount &&
8691 ConcurrentMarkSweepThread::should_yield() &&
8692 !CMSCollector::foregroundGCIsActive(); ++i) {
8693 os::sleep(Thread::current(), 1, false);
8694 ConcurrentMarkSweepThread::acknowledge_yield_request();
8695 }
8696
8697 ConcurrentMarkSweepThread::synchronize(true);
8698 _freelistLock->lock();
8699 _bitMap->lock()->lock_without_safepoint_check();
8700 _collector->startTimer();
8701 }
8702
8703 #ifndef PRODUCT
8704 // This is actually very useful in a product build if it can
8705 // be called from the debugger. Compile it into the product
8706 // as needed.
8707 bool debug_verify_chunk_in_free_list(FreeChunk* fc) {
8708 return debug_cms_space->verify_chunk_in_free_list(fc);
8709 }
8710 #endif
8711
8712 void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const {
8713 if (CMSTraceSweeper) {
8714 gclog_or_tty->print_cr("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")",
8715 fc, fc->size());
8716 }
8717 }
8718
8719 // CMSIsAliveClosure
8720 bool CMSIsAliveClosure::do_object_b(oop obj) {
8721 HeapWord* addr = (HeapWord*)obj;
8722 return addr != NULL &&
8723 (!_span.contains(addr) || _bit_map->isMarked(addr));
8724 }
8725
8726
8727 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector,
8728 MemRegion span,
8729 CMSBitMap* bit_map, CMSMarkStack* mark_stack,
8730 bool cpc):
8731 _collector(collector),
8732 _span(span),
8733 _bit_map(bit_map),
8734 _mark_stack(mark_stack),
8735 _concurrent_precleaning(cpc) {
8736 assert(!_span.is_empty(), "Empty span could spell trouble");
8737 }
8738
8739
8740 // CMSKeepAliveClosure: the serial version
8741 void CMSKeepAliveClosure::do_oop(oop obj) {
8742 HeapWord* addr = (HeapWord*)obj;
8743 if (_span.contains(addr) &&
8744 !_bit_map->isMarked(addr)) {
8745 _bit_map->mark(addr);
8746 bool simulate_overflow = false;
8747 NOT_PRODUCT(
8748 if (CMSMarkStackOverflowALot &&
8749 _collector->simulate_overflow()) {
8750 // simulate a stack overflow
8751 simulate_overflow = true;
8752 }
8753 )
8754 if (simulate_overflow || !_mark_stack->push(obj)) {
8755 if (_concurrent_precleaning) {
8756 // We dirty the overflown object and let the remark
8757 // phase deal with it.
8758 assert(_collector->overflow_list_is_empty(), "Error");
8759 // In the case of object arrays, we need to dirty all of
8760 // the cards that the object spans. No locking or atomics
8761 // are needed since no one else can be mutating the mod union
8762 // table.
8763 if (obj->is_objArray()) {
8764 size_t sz = obj->size();
8765 HeapWord* end_card_addr =
8766 (HeapWord*)round_to((intptr_t)(addr+sz), CardTableModRefBS::card_size);
8767 MemRegion redirty_range = MemRegion(addr, end_card_addr);
8768 assert(!redirty_range.is_empty(), "Arithmetical tautology");
8769 _collector->_modUnionTable.mark_range(redirty_range);
8770 } else {
8771 _collector->_modUnionTable.mark(addr);
8772 }
8773 _collector->_ser_kac_preclean_ovflw++;
8774 } else {
8775 _collector->push_on_overflow_list(obj);
8776 _collector->_ser_kac_ovflw++;
8777 }
8778 }
8779 }
8780 }
8781
8782 void CMSKeepAliveClosure::do_oop(oop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8783 void CMSKeepAliveClosure::do_oop(narrowOop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8784
8785 // CMSParKeepAliveClosure: a parallel version of the above.
8786 // The work queues are private to each closure (thread),
8787 // but (may be) available for stealing by other threads.
8788 void CMSParKeepAliveClosure::do_oop(oop obj) {
8789 HeapWord* addr = (HeapWord*)obj;
8790 if (_span.contains(addr) &&
8791 !_bit_map->isMarked(addr)) {
8792 // In general, during recursive tracing, several threads
8793 // may be concurrently getting here; the first one to
8794 // "tag" it, claims it.
8795 if (_bit_map->par_mark(addr)) {
8796 bool res = _work_queue->push(obj);
8797 assert(res, "Low water mark should be much less than capacity");
8798 // Do a recursive trim in the hope that this will keep
8799 // stack usage lower, but leave some oops for potential stealers
8800 trim_queue(_low_water_mark);
8801 } // Else, another thread got there first
8802 }
8803 }
8804
8805 void CMSParKeepAliveClosure::do_oop(oop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8806 void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8807
8808 void CMSParKeepAliveClosure::trim_queue(uint max) {
8809 while (_work_queue->size() > max) {
8810 oop new_oop;
8811 if (_work_queue->pop_local(new_oop)) {
8812 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
8813 assert(_bit_map->isMarked((HeapWord*)new_oop),
8814 "no white objects on this stack!");
8815 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8816 // iterate over the oops in this oop, marking and pushing
8817 // the ones in CMS heap (i.e. in _span).
8818 new_oop->oop_iterate(&_mark_and_push);
8819 }
8820 }
8821 }
8822
8823 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
8824 CMSCollector* collector,
8825 MemRegion span, CMSBitMap* bit_map,
8826 OopTaskQueue* work_queue):
8827 _collector(collector),
8828 _span(span),
8829 _bit_map(bit_map),
8830 _work_queue(work_queue) { }
8831
8832 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
8833 HeapWord* addr = (HeapWord*)obj;
8834 if (_span.contains(addr) &&
8835 !_bit_map->isMarked(addr)) {
8836 if (_bit_map->par_mark(addr)) {
8837 bool simulate_overflow = false;
8838 NOT_PRODUCT(
8839 if (CMSMarkStackOverflowALot &&
8840 _collector->par_simulate_overflow()) {
8841 // simulate a stack overflow
8842 simulate_overflow = true;
8843 }
8844 )
8845 if (simulate_overflow || !_work_queue->push(obj)) {
8846 _collector->par_push_on_overflow_list(obj);
8847 _collector->_par_kac_ovflw++;
8848 }
8849 } // Else another thread got there already
8850 }
8851 }
8852
8853 void CMSInnerParMarkAndPushClosure::do_oop(oop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8854 void CMSInnerParMarkAndPushClosure::do_oop(narrowOop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8855
8856 //////////////////////////////////////////////////////////////////
8857 // CMSExpansionCause /////////////////////////////
8858 //////////////////////////////////////////////////////////////////
8859 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
8860 switch (cause) {
8861 case _no_expansion:
8862 return "No expansion";
8863 case _satisfy_free_ratio:
8864 return "Free ratio";
8865 case _satisfy_promotion:
8866 return "Satisfy promotion";
8867 case _satisfy_allocation:
8868 return "allocation";
8869 case _allocate_par_lab:
8870 return "Par LAB";
8871 case _allocate_par_spooling_space:
8872 return "Par Spooling Space";
8873 case _adaptive_size_policy:
8874 return "Ergonomics";
8875 default:
8876 return "unknown";
8877 }
8878 }
8879
8880 void CMSDrainMarkingStackClosure::do_void() {
8881 // the max number to take from overflow list at a time
8882 const size_t num = _mark_stack->capacity()/4;
8883 assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
8884 "Overflow list should be NULL during concurrent phases");
8885 while (!_mark_stack->isEmpty() ||
8886 // if stack is empty, check the overflow list
8887 _collector->take_from_overflow_list(num, _mark_stack)) {
8888 oop obj = _mark_stack->pop();
8889 HeapWord* addr = (HeapWord*)obj;
8890 assert(_span.contains(addr), "Should be within span");
8891 assert(_bit_map->isMarked(addr), "Should be marked");
8892 assert(obj->is_oop(), "Should be an oop");
8893 obj->oop_iterate(_keep_alive);
8894 }
8895 }
8896
8897 void CMSParDrainMarkingStackClosure::do_void() {
8898 // drain queue
8899 trim_queue(0);
8900 }
8901
8902 // Trim our work_queue so its length is below max at return
8903 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
8904 while (_work_queue->size() > max) {
8905 oop new_oop;
8906 if (_work_queue->pop_local(new_oop)) {
8907 assert(new_oop->is_oop(), "Expected an oop");
8908 assert(_bit_map->isMarked((HeapWord*)new_oop),
8909 "no white objects on this stack!");
8910 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8911 // iterate over the oops in this oop, marking and pushing
8912 // the ones in CMS heap (i.e. in _span).
8913 new_oop->oop_iterate(&_mark_and_push);
8914 }
8915 }
8916 }
8917
8918 ////////////////////////////////////////////////////////////////////
8919 // Support for Marking Stack Overflow list handling and related code
8920 ////////////////////////////////////////////////////////////////////
8921 // Much of the following code is similar in shape and spirit to the
8922 // code used in ParNewGC. We should try and share that code
8923 // as much as possible in the future.
8924
8925 #ifndef PRODUCT
8926 // Debugging support for CMSStackOverflowALot
8927
8928 // It's OK to call this multi-threaded; the worst thing
8929 // that can happen is that we'll get a bunch of closely
8930 // spaced simulated overflows, but that's OK, in fact
8931 // probably good as it would exercise the overflow code
8932 // under contention.
8933 bool CMSCollector::simulate_overflow() {
8934 if (_overflow_counter-- <= 0) { // just being defensive
8935 _overflow_counter = CMSMarkStackOverflowInterval;
8936 return true;
8937 } else {
8938 return false;
8939 }
8940 }
8941
8942 bool CMSCollector::par_simulate_overflow() {
8943 return simulate_overflow();
8944 }
8945 #endif
8946
8947 // Single-threaded
8948 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
8949 assert(stack->isEmpty(), "Expected precondition");
8950 assert(stack->capacity() > num, "Shouldn't bite more than can chew");
8951 size_t i = num;
8952 oop cur = _overflow_list;
8953 const markOop proto = markOopDesc::prototype();
8954 NOT_PRODUCT(ssize_t n = 0;)
8955 for (oop next; i > 0 && cur != NULL; cur = next, i--) {
8956 next = oop(cur->mark());
8957 cur->set_mark(proto); // until proven otherwise
8958 assert(cur->is_oop(), "Should be an oop");
8959 bool res = stack->push(cur);
8960 assert(res, "Bit off more than can chew?");
8961 NOT_PRODUCT(n++;)
8962 }
8963 _overflow_list = cur;
8964 #ifndef PRODUCT
8965 assert(_num_par_pushes >= n, "Too many pops?");
8966 _num_par_pushes -=n;
8967 #endif
8968 return !stack->isEmpty();
8969 }
8970
8971 #define BUSY (cast_to_oop<intptr_t>(0x1aff1aff))
8972 // (MT-safe) Get a prefix of at most "num" from the list.
8973 // The overflow list is chained through the mark word of
8974 // each object in the list. We fetch the entire list,
8975 // break off a prefix of the right size and return the
8976 // remainder. If other threads try to take objects from
8977 // the overflow list at that time, they will wait for
8978 // some time to see if data becomes available. If (and
8979 // only if) another thread places one or more object(s)
8980 // on the global list before we have returned the suffix
8981 // to the global list, we will walk down our local list
8982 // to find its end and append the global list to
8983 // our suffix before returning it. This suffix walk can
8984 // prove to be expensive (quadratic in the amount of traffic)
8985 // when there are many objects in the overflow list and
8986 // there is much producer-consumer contention on the list.
8987 // *NOTE*: The overflow list manipulation code here and
8988 // in ParNewGeneration:: are very similar in shape,
8989 // except that in the ParNew case we use the old (from/eden)
8990 // copy of the object to thread the list via its klass word.
8991 // Because of the common code, if you make any changes in
8992 // the code below, please check the ParNew version to see if
8993 // similar changes might be needed.
8994 // CR 6797058 has been filed to consolidate the common code.
8995 bool CMSCollector::par_take_from_overflow_list(size_t num,
8996 OopTaskQueue* work_q,
8997 int no_of_gc_threads) {
8998 assert(work_q->size() == 0, "First empty local work queue");
8999 assert(num < work_q->max_elems(), "Can't bite more than we can chew");
9000 if (_overflow_list == NULL) {
9001 return false;
9002 }
9003 // Grab the entire list; we'll put back a suffix
9004 oop prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
9005 Thread* tid = Thread::current();
9006 // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was
9007 // set to ParallelGCThreads.
9008 size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads;
9009 size_t sleep_time_millis = MAX2((size_t)1, num/100);
9010 // If the list is busy, we spin for a short while,
9011 // sleeping between attempts to get the list.
9012 for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) {
9013 os::sleep(tid, sleep_time_millis, false);
9014 if (_overflow_list == NULL) {
9015 // Nothing left to take
9016 return false;
9017 } else if (_overflow_list != BUSY) {
9018 // Try and grab the prefix
9019 prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
9020 }
9021 }
9022 // If the list was found to be empty, or we spun long
9023 // enough, we give up and return empty-handed. If we leave
9024 // the list in the BUSY state below, it must be the case that
9025 // some other thread holds the overflow list and will set it
9026 // to a non-BUSY state in the future.
9027 if (prefix == NULL || prefix == BUSY) {
9028 // Nothing to take or waited long enough
9029 if (prefix == NULL) {
9030 // Write back the NULL in case we overwrote it with BUSY above
9031 // and it is still the same value.
9032 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
9033 }
9034 return false;
9035 }
9036 assert(prefix != NULL && prefix != BUSY, "Error");
9037 size_t i = num;
9038 oop cur = prefix;
9039 // Walk down the first "num" objects, unless we reach the end.
9040 for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--);
9041 if (cur->mark() == NULL) {
9042 // We have "num" or fewer elements in the list, so there
9043 // is nothing to return to the global list.
9044 // Write back the NULL in lieu of the BUSY we wrote
9045 // above, if it is still the same value.
9046 if (_overflow_list == BUSY) {
9047 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
9048 }
9049 } else {
9050 // Chop off the suffix and return it to the global list.
9051 assert(cur->mark() != BUSY, "Error");
9052 oop suffix_head = cur->mark(); // suffix will be put back on global list
9053 cur->set_mark(NULL); // break off suffix
9054 // It's possible that the list is still in the empty(busy) state
9055 // we left it in a short while ago; in that case we may be
9056 // able to place back the suffix without incurring the cost
9057 // of a walk down the list.
9058 oop observed_overflow_list = _overflow_list;
9059 oop cur_overflow_list = observed_overflow_list;
9060 bool attached = false;
9061 while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
9062 observed_overflow_list =
9063 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
9064 if (cur_overflow_list == observed_overflow_list) {
9065 attached = true;
9066 break;
9067 } else cur_overflow_list = observed_overflow_list;
9068 }
9069 if (!attached) {
9070 // Too bad, someone else sneaked in (at least) an element; we'll need
9071 // to do a splice. Find tail of suffix so we can prepend suffix to global
9072 // list.
9073 for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark()));
9074 oop suffix_tail = cur;
9075 assert(suffix_tail != NULL && suffix_tail->mark() == NULL,
9076 "Tautology");
9077 observed_overflow_list = _overflow_list;
9078 do {
9079 cur_overflow_list = observed_overflow_list;
9080 if (cur_overflow_list != BUSY) {
9081 // Do the splice ...
9082 suffix_tail->set_mark(markOop(cur_overflow_list));
9083 } else { // cur_overflow_list == BUSY
9084 suffix_tail->set_mark(NULL);
9085 }
9086 // ... and try to place spliced list back on overflow_list ...
9087 observed_overflow_list =
9088 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
9089 } while (cur_overflow_list != observed_overflow_list);
9090 // ... until we have succeeded in doing so.
9091 }
9092 }
9093
9094 // Push the prefix elements on work_q
9095 assert(prefix != NULL, "control point invariant");
9096 const markOop proto = markOopDesc::prototype();
9097 oop next;
9098 NOT_PRODUCT(ssize_t n = 0;)
9099 for (cur = prefix; cur != NULL; cur = next) {
9100 next = oop(cur->mark());
9101 cur->set_mark(proto); // until proven otherwise
9102 assert(cur->is_oop(), "Should be an oop");
9103 bool res = work_q->push(cur);
9104 assert(res, "Bit off more than we can chew?");
9105 NOT_PRODUCT(n++;)
9106 }
9107 #ifndef PRODUCT
9108 assert(_num_par_pushes >= n, "Too many pops?");
9109 Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
9110 #endif
9111 return true;
9112 }
9113
9114 // Single-threaded
9115 void CMSCollector::push_on_overflow_list(oop p) {
9116 NOT_PRODUCT(_num_par_pushes++;)
9117 assert(p->is_oop(), "Not an oop");
9118 preserve_mark_if_necessary(p);
9119 p->set_mark((markOop)_overflow_list);
9120 _overflow_list = p;
9121 }
9122
9123 // Multi-threaded; use CAS to prepend to overflow list
9124 void CMSCollector::par_push_on_overflow_list(oop p) {
9125 NOT_PRODUCT(Atomic::inc_ptr(&_num_par_pushes);)
9126 assert(p->is_oop(), "Not an oop");
9127 par_preserve_mark_if_necessary(p);
9128 oop observed_overflow_list = _overflow_list;
9129 oop cur_overflow_list;
9130 do {
9131 cur_overflow_list = observed_overflow_list;
9132 if (cur_overflow_list != BUSY) {
9133 p->set_mark(markOop(cur_overflow_list));
9134 } else {
9135 p->set_mark(NULL);
9136 }
9137 observed_overflow_list =
9138 (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list);
9139 } while (cur_overflow_list != observed_overflow_list);
9140 }
9141 #undef BUSY
9142
9143 // Single threaded
9144 // General Note on GrowableArray: pushes may silently fail
9145 // because we are (temporarily) out of C-heap for expanding
9146 // the stack. The problem is quite ubiquitous and affects
9147 // a lot of code in the JVM. The prudent thing for GrowableArray
9148 // to do (for now) is to exit with an error. However, that may
9149 // be too draconian in some cases because the caller may be
9150 // able to recover without much harm. For such cases, we
9151 // should probably introduce a "soft_push" method which returns
9152 // an indication of success or failure with the assumption that
9153 // the caller may be able to recover from a failure; code in
9154 // the VM can then be changed, incrementally, to deal with such
9155 // failures where possible, thus, incrementally hardening the VM
9156 // in such low resource situations.
9157 void CMSCollector::preserve_mark_work(oop p, markOop m) {
9158 _preserved_oop_stack.push(p);
9159 _preserved_mark_stack.push(m);
9160 assert(m == p->mark(), "Mark word changed");
9161 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
9162 "bijection");
9163 }
9164
9165 // Single threaded
9166 void CMSCollector::preserve_mark_if_necessary(oop p) {
9167 markOop m = p->mark();
9168 if (m->must_be_preserved(p)) {
9169 preserve_mark_work(p, m);
9170 }
9171 }
9172
9173 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
9174 markOop m = p->mark();
9175 if (m->must_be_preserved(p)) {
9176 MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
9177 // Even though we read the mark word without holding
9178 // the lock, we are assured that it will not change
9179 // because we "own" this oop, so no other thread can
9180 // be trying to push it on the overflow list; see
9181 // the assertion in preserve_mark_work() that checks
9182 // that m == p->mark().
9183 preserve_mark_work(p, m);
9184 }
9185 }
9186
9187 // We should be able to do this multi-threaded,
9188 // a chunk of stack being a task (this is
9189 // correct because each oop only ever appears
9190 // once in the overflow list. However, it's
9191 // not very easy to completely overlap this with
9192 // other operations, so will generally not be done
9193 // until all work's been completed. Because we
9194 // expect the preserved oop stack (set) to be small,
9195 // it's probably fine to do this single-threaded.
9196 // We can explore cleverer concurrent/overlapped/parallel
9197 // processing of preserved marks if we feel the
9198 // need for this in the future. Stack overflow should
9199 // be so rare in practice and, when it happens, its
9200 // effect on performance so great that this will
9201 // likely just be in the noise anyway.
9202 void CMSCollector::restore_preserved_marks_if_any() {
9203 assert(SafepointSynchronize::is_at_safepoint(),
9204 "world should be stopped");
9205 assert(Thread::current()->is_ConcurrentGC_thread() ||
9206 Thread::current()->is_VM_thread(),
9207 "should be single-threaded");
9208 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
9209 "bijection");
9210
9211 while (!_preserved_oop_stack.is_empty()) {
9212 oop p = _preserved_oop_stack.pop();
9213 assert(p->is_oop(), "Should be an oop");
9214 assert(_span.contains(p), "oop should be in _span");
9215 assert(p->mark() == markOopDesc::prototype(),
9216 "Set when taken from overflow list");
9217 markOop m = _preserved_mark_stack.pop();
9218 p->set_mark(m);
9219 }
9220 assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(),
9221 "stacks were cleared above");
9222 }
9223
9224 #ifndef PRODUCT
9225 bool CMSCollector::no_preserved_marks() const {
9226 return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty();
9227 }
9228 #endif
9229
9230 // Transfer some number of overflown objects to usual marking
9231 // stack. Return true if some objects were transferred.
9232 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
9233 size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,
9234 (size_t)ParGCDesiredObjsFromOverflowList);
9235
9236 bool res = _collector->take_from_overflow_list(num, _mark_stack);
9237 assert(_collector->overflow_list_is_empty() || res,
9238 "If list is not empty, we should have taken something");
9239 assert(!res || !_mark_stack->isEmpty(),
9240 "If we took something, it should now be on our stack");
9241 return res;
9242 }
9243
9244 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
9245 size_t res = _sp->block_size_no_stall(addr, _collector);
9246 if (_sp->block_is_obj(addr)) {
9247 if (_live_bit_map->isMarked(addr)) {
9248 // It can't have been dead in a previous cycle
9249 guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
9250 } else {
9251 _dead_bit_map->mark(addr); // mark the dead object
9252 }
9253 }
9254 // Could be 0, if the block size could not be computed without stalling.
9255 return res;
9256 }
9257
9258 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() {
9259
9260 switch (phase) {
9261 case CMSCollector::InitialMarking:
9262 initialize(true /* fullGC */ ,
9263 cause /* cause of the GC */,
9264 true /* recordGCBeginTime */,
9265 true /* recordPreGCUsage */,
9266 false /* recordPeakUsage */,
9267 false /* recordPostGCusage */,
9268 true /* recordAccumulatedGCTime */,
9269 false /* recordGCEndTime */,
9270 false /* countCollection */ );
9271 break;
9272
9273 case CMSCollector::FinalMarking:
9274 initialize(true /* fullGC */ ,
9275 cause /* cause of the GC */,
9276 false /* recordGCBeginTime */,
9277 false /* recordPreGCUsage */,
9278 false /* recordPeakUsage */,
9279 false /* recordPostGCusage */,
9280 true /* recordAccumulatedGCTime */,
9281 false /* recordGCEndTime */,
9282 false /* countCollection */ );
9283 break;
9284
9285 case CMSCollector::Sweeping:
9286 initialize(true /* fullGC */ ,
9287 cause /* cause of the GC */,
9288 false /* recordGCBeginTime */,
9289 false /* recordPreGCUsage */,
9290 true /* recordPeakUsage */,
9291 true /* recordPostGCusage */,
9292 false /* recordAccumulatedGCTime */,
9293 true /* recordGCEndTime */,
9294 true /* countCollection */ );
9295 break;
9296
9297 default:
9298 ShouldNotReachHere();
9299 }
9300 }